CN113571772A - Lithium secondary battery and nonaqueous electrolyte used therein - Google Patents

Lithium secondary battery and nonaqueous electrolyte used therein Download PDF

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CN113571772A
CN113571772A CN202110646170.7A CN202110646170A CN113571772A CN 113571772 A CN113571772 A CN 113571772A CN 202110646170 A CN202110646170 A CN 202110646170A CN 113571772 A CN113571772 A CN 113571772A
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active material
positive electrode
negative electrode
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electrode active
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宫城秀和
加藤竜一
横沟正和
宇尾野宏之
松本一志
佐藤智洋
古田土稔
中岛孝之
铃木仁
大岛裕之
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Mu Electrolyte Co Ltd
Mitsubishi Chemical Corp
MU Ionic Solutions Corp
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Mitsubishi Chemical Corp
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
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    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
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    • H—ELECTRICITY
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    • H01M10/00—Secondary cells; Manufacture thereof
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    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • H01M2300/004—Three solvents
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Abstract

The invention provides a nonaqueous electrolyte for a secondary battery, which contains at least a nonaqueous solvent and a lithium salt, wherein the nonaqueous electrolyte contains 1, 3-propane sultone and a difluorophosphate, the content of the 1, 3-propane sultone in the whole nonaqueous electrolyte is within the range of 0.001-5 mass%, and the content of the difluorophosphate in the whole nonaqueous electrolyte is 10ppm or more.

Description

Lithium secondary battery and nonaqueous electrolyte used therein
The present application is a divisional application of the application having a filing date of 19/10/2006 and an application number of 201710119547.7, entitled "lithium secondary battery and nonaqueous electrolytic solution used therein".
Technical Field
The present invention relates to a lithium secondary battery and a nonaqueous electrolytic solution used therein, and more particularly, to a lithium secondary battery which has a nonaqueous electrolytic solution for a lithium secondary battery containing a specific component, and a positive electrode and a negative electrode having specific compositions and physical properties and capable of storing and releasing lithium, and which is excellent in low-temperature discharge characteristics, high in capacity, long in life, and high in output, and a nonaqueous electrolytic solution used therein.
Background
In recent years, with the miniaturization of electronic devices, there has been an increasing demand for higher capacity of secondary batteries, and lithium secondary batteries having higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries have been attracting attention.
Lithium secondary batteries are used in various applications because they have a high capacity, but they are mainly used in relatively small batteries such as mobile phones, and are expected to be expanded in applications to large batteries for automobile applications in the future. In particular, in large batteries, there is a demand for output, and simply increasing the size of conventional small batteries is not sufficient in terms of performance. Various methods for improving battery materials for increasing output have been proposed (for example, see patent documents 1 to 25, non-patent document 1, and the like). However, sufficient output is still not obtained, and further improvement is demanded.
Patent document 1: japanese unexamined patent publication No. 2005-071749
Patent document 2: japanese laid-open patent publication No. 2005-123180
Patent document 3: japanese unexamined patent application publication No. 2001-206722
Patent document 4: japanese laid-open patent publication No. 2003-267732
Patent document 5: japanese unexamined patent publication No. 2001-015108
Patent document 6: WO2003/34518
Patent document 7: japanese unexamined patent publication No. 11-067270
Patent document 8: japanese patent laid-open publication No. 61-168512
Patent document 9: japanese unexamined patent publication No. 6-275263
Patent document 10: japanese laid-open patent publication No. 2000-340232
Patent document 11: japanese unexamined patent publication No. 2005-235397
Patent document 12: japanese unexamined patent publication No. 11-031509
Patent document 13: japanese unexamined patent publication Hei 3-055770
Patent document 14: japanese laid-open patent publication No. 2004-071458
Patent document 15: japanese unexamined patent application publication No. 2004-087459
Patent document 16: japanese unexamined patent publication Hei 10-270074
Patent document 17: japanese laid-open patent publication No. 2002-075440
Patent document 18: japanese unexamined patent publication Hei 10-270075
Patent document 19: japanese unexamined patent publication No. 8-045545
Patent document 20: japanese unexamined patent publication No. 2001-006729
Patent document 21: japanese unexamined patent publication Hei 10-050342
Patent document 22: japanese unexamined patent publication No. 9-106835
Patent document 23: japanese laid-open patent publication No. 2000-058116
Patent document 24: japanese laid-open patent publication No. 2001-015158
Patent document 25: japanese unexamined patent publication No. 2005-306619
Non-patent document 1: j.electrochem.soc.,145, L1(1998)
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made in view of the above-mentioned background art, and an object thereof is to provide a lithium secondary battery having a high capacity, a long life, and a high output even when it is made larger.
Means for solving the problems
As a result of intensive studies on the above problems, the present inventors have found that a lithium secondary battery having a high capacity, a long life and a high output can be obtained by using a positive electrode and a negative electrode having specific compositions and physical properties and a non-aqueous electrolyte containing a compound selected from a specific group, and have completed the present invention.
That is, the present invention provides a lithium secondary battery comprising at least: an electrode group comprising a positive electrode and a negative electrode with a microporous membrane separator interposed therebetween, and a nonaqueous electrolyte comprising a nonaqueous solvent and a lithium salt contained therein, wherein the nonaqueous electrolyte is contained in a battery case,
the positive electrode and the negative electrode each have an active material layer containing an active material capable of occluding and releasing lithium ions formed on a current collector;
the nonaqueous electrolytic solution contains at least one compound selected from the group consisting of the following substances, the content of which in the entire nonaqueous electrolytic solution is 10ppm or more, the substances including:
a cyclic siloxane compound represented by the following general formula (1),
[ chemical formula 1]
Figure BDA0003109774980000031
[ in the general formula (1), R1And R2The same or different, and represents an organic group having 1 to 12 carbon atoms, and n represents an integer of 3 to 10. ]
A fluorosilane compound represented by the following general formula (2),
[ chemical formula 2]
SiFxR3 pR4 qR5 r (2)
[ in the general formula (2), R3～R5The same or different organic groups may be used, and each represents an organic group having 1 to 12 carbon atoms, x represents an integer of 1 to 3, p, q and r each represent an integer of 0 to 3, and 1. ltoreq. p + q + r. ltoreq.3.]
A compound represented by the following general formula (3),
[ chemical formula 3]
Figure BDA0003109774980000032
[ in the general formula (3), R6～R8The same or different organic groups may be used, and each A represents a group consisting of H, C, N, O, F, S, Si and/or P.]And an
Compounds having an S-F bond in the molecule, nitrates, nitrites, monofluorophosphates, difluorophosphates, acetates and propionates;
the positive electrode is any one positive electrode selected from the following positive electrodes [1] to [5 ]:
positive electrode [1 ]: a positive electrode containing a positive electrode active material containing manganese;
positive electrode [2 ]: a positive electrode containing a positive electrode active material having a composition represented by the following composition formula (4),
LixNi(1-y-z)CoyMzO2component formula (4)
[ in the composition formula (4), M represents at least one element selected from the group consisting of Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.5, and z represents a number satisfying 0.01. ltoreq. z.ltoreq.0.5. H;
Positive electrode [3 ]: a positive electrode comprising a positive electrode active material selected from any one of the following (a) to (d),
(a) BET specific surface area of 0.4m2/g～2m2Positive electrode active material/g
(b) A positive electrode active material having an average primary particle diameter of 0.1 to 2 μm
(c) Median particle diameter d50A positive electrode active material of 1 to 20 μm
(d) Tap density of 1.3g/cm3～2.7g/cm3The positive electrode active material of (1);
positive electrode [4 ]: a positive electrode satisfying any one of the following conditions (e) to (f),
(e) a positive electrode formed by forming a positive electrode active material layer containing a positive electrode active material, a conductive material and a binder on a current collector, wherein the content of the conductive material in the positive electrode active material layer is in the range of 6-20 mass%
(f) A positive electrode prepared by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector, wherein the density of the positive electrode active material layer is 1.7g/cm3～3.5g/cm3Range of (1)
(g) A positive electrode formed by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector, wherein the ratio of the thicknesses of the positive electrode active material layer and the current collector (the thickness of the active material layer on the side before the nonaqueous electrolyte solution is injected)/(the thickness of the current collector) is 1.6 to 20;
Positive electrode [5 ]: a positive electrode containing 2 or more positive electrode active materials having different compositions.
In addition, the present invention provides a lithium secondary battery comprising at least: an electrode assembly comprising a positive electrode and a negative electrode with a microporous membrane separator interposed therebetween, and a nonaqueous electrolytic solution comprising a nonaqueous solvent and a lithium salt contained therein, wherein the nonaqueous electrolytic solution is contained in a battery case,
the positive electrode and the negative electrode each have an active material layer containing an active material capable of occluding and releasing lithium ions formed on a current collector;
the nonaqueous electrolytic solution contains at least one compound selected from the group consisting of: a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate;
the negative electrode is any one negative electrode selected from the following negative electrodes [1] to [10 ]:
negative electrode [1 ]: a negative electrode containing 2 or more carbonaceous materials having different crystallinity as a negative electrode active material;
Cathode [2 ]]: containing amorphous carbonaceous material asA negative electrode of a negative electrode active material, wherein the amorphous carbon has a (002) plane interplanar spacing (d002) of 0.337nm or more and a crystallite size (Lc) of 80nm or less as measured by wide-angle X-ray diffraction, and has a value of 1360cm as measured by argon ion laser Raman spectroscopy-1Peak intensity of (2) relative to 1580cm-1A Raman R value defined as a ratio of peak intensities of (A) to (B) is 0.2 or more;
negative electrode [3 ]: a negative electrode containing a metal oxide as a negative electrode active material, the metal oxide containing titanium capable of occluding and releasing lithium;
negative electrode [4 ]: a negative electrode containing a carbonaceous material as a negative electrode active material, wherein the carbonaceous material has a circularity of 0.85 or more and a surface functional group amount O/C value of 0 to 0.01;
negative electrode [5 ]: a negative electrode containing a heteroorientation carbon composite as a negative electrode active material, the heteroorientation carbon composite containing 2 or more carbonaceous materials having different orientations;
cathode [6 ]]: a negative electrode comprising, as a negative electrode active material, a graphitic carbon particle having a circularity of 0.85 or more, an interplanar spacing (d002) of (002) plane as measured by wide-angle X-ray diffraction method of less than 0.337nm, and a thickness of 1360cm as measured by argon ion laser Raman spectroscopy -1Relative to 1580cm-1The ratio of the peak intensities defined as a Raman R value of 0.12 to 0.8;
negative electrode [7 ]: a negative electrode containing, as a negative electrode active material, a negative electrode active material (C) containing multiple elements, which contains at least one of a lithium-occluding metal (a) and/or a lithium-occluding alloy (B) selected from Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb, and contains C and/or N as an element Z;
negative electrode [8 ]: a negative electrode containing 2 or more negative electrode active materials having different properties as a negative electrode active material;
cathode [9 ]]: containing a tap density of 0.1g/cm3A negative electrode containing a negative electrode active material having a pore volume of 0.01mL/g or more, measured by a mercury porosimeter, corresponding to particles having a diameter in the range of 0.01 to 1 μm;
negative electrode [10 ]: when the battery is charged to 60% of the nominal capacity of the negative electrode, the reaction resistance of the counter battery of the negative electrode is 500 Ω or less.
In addition, the present invention provides a lithium secondary battery comprising at least: an electrode assembly comprising a positive electrode and a negative electrode with a microporous membrane separator interposed therebetween, and a nonaqueous electrolytic solution comprising a nonaqueous solvent and a lithium salt contained therein, wherein the nonaqueous electrolytic solution is contained in a battery case,
The positive electrode and the negative electrode each have an active material layer containing an active material capable of occluding and releasing lithium ions formed on a current collector;
the nonaqueous electrolytic solution contains at least one compound selected from the group consisting of: a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate;
the nonaqueous electrolytic solution is an electrolytic solution satisfying any one condition selected from the following electrolytic solutions [1] to [9 ]:
electrolyte solution [1 ]: the nonaqueous solvent constituting the electrolyte is a mixed solvent containing at least ethylene carbonate, and the ratio of ethylene carbonate to the total amount of the nonaqueous solvent is 1 to 25% by volume;
electrolyte solution [2 ]: the nonaqueous solvent constituting the electrolyte contains at least one asymmetric chain carbonate, and the content ratio of the asymmetric chain carbonate in the entire nonaqueous solvent is 5 to 90% by volume;
Electrolyte solution [3 ]: the nonaqueous solvent constituting the electrolytic solution contains at least one chain carboxylic ester;
electrolyte solution [4 ]: the nonaqueous solvent constituting the electrolyte contains a solvent having a flash point of 70 ℃ or higher and the content thereof is 60% by volume or more of the entire nonaqueous solvent;
electrolyte [5 ]]: containing LiN (C)nF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate as a lithium salt constituting the electrolyte;
electrolyte solution [6 ]: the lithium salt constituting the electrolyte is a fluorine-containing lithium salt, and the total nonaqueous electrolyte contains 10ppm to 300ppm of Hydrogen Fluoride (HF);
electrolyte [7 ]: the electrolyte contains vinylene carbonate, and the content of the vinylene carbonate is 0.001-3% by mass of the total mass of the electrolyte;
electrolyte [8 ]: the electrolyte solution further contains at least one compound selected from the group consisting of a compound represented by the following general formula (4), a heterocyclic compound containing nitrogen and/or sulfur, a cyclic carboxylic ester, and a fluorine-containing cyclic carbonate, and the content thereof in the entire nonaqueous electrolyte solution is in the range of 0.001 to 5% by mass,
[ chemical formula 4]
Figure BDA0003109774980000061
[ in the general formula (4), R9～R12The same or different groups may be used, and each group is composed of at least one element selected from H, C, N, O, F, S and P. ]；
Electrolyte [9 ]: the electrolyte solution also contains an overcharge inhibitor.
Among the above-mentioned secondary batteries, a secondary battery having any one property selected from the following items (1) to (3) is particularly preferable,
(1) the area ratio of the total electrode area of the positive electrode to the surface area of the case of the secondary battery is 20 times or more;
(2) the DC resistance component of the secondary battery is less than 20 milliohm (m omega);
(3) the capacity of the battery element contained in one battery case of the secondary battery is 3 ampere hours (Ah) or more.
In addition, the present invention provides a lithium secondary battery comprising at least: an electrode assembly comprising a positive electrode and a negative electrode with a microporous membrane separator interposed therebetween, and a nonaqueous electrolytic solution comprising a nonaqueous solvent and a lithium salt contained therein, wherein the nonaqueous electrolytic solution is contained in a battery case,
the positive electrode and the negative electrode each have an active material layer containing an active material capable of occluding and releasing lithium ions formed on a current collector;
the nonaqueous electrolytic solution contains at least one compound selected from the group consisting of: a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate;
The secondary battery has any one property selected from the following structures [1] to [6 ]:
structure [1 ]: an area ratio of a total electrode area of the positive electrode to a surface area of a case of the secondary battery is 20 times or more;
structure [2 ]: a DC resistance component of the secondary battery is 20 milliohms (m Ω) or less;
structure [3 ]: a battery element contained in one battery case of the secondary battery has a capacity of 3 ampere hours (Ah) or more;
structure [4 ]: the current collectors of the positive and negative electrodes of the secondary battery are made of metal materials, respectively, and the metal materials of the current collectors and a conductor for taking out current to the outside are welded by any one of groove welding, high-frequency welding, or ultrasonic welding;
structure [5 ]: the case of the secondary battery is aluminum or an aluminum alloy;
structure [6 ]: the casing material of the secondary battery forming the battery casing is the following casing material: at least a part of the inner surface side of the battery includes a sheet formed using a thermoplastic resin, and the battery pack can be sealed by heat-sealing the thermoplastic resin layers together while accommodating the battery pack.
The present invention also provides a nonaqueous electrolyte for a secondary battery, comprising at least a nonaqueous solvent and a lithium salt,
the nonaqueous electrolytic solution contains at least one compound selected from the group consisting of: a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate;
the nonaqueous electrolytic solution satisfies any one condition selected from the following electrolytic solutions [1] to [9 ]:
electrolyte solution [1 ]: the nonaqueous solvent constituting the electrolyte is a mixed solvent containing at least ethylene carbonate, and the ratio of ethylene carbonate to the total amount of the nonaqueous solvent is 1 to 25% by volume;
electrolyte solution [2 ]: the nonaqueous solvent constituting the electrolyte contains at least one asymmetric chain carbonate, and the content ratio of the asymmetric chain carbonate in the entire nonaqueous solvent is 5 to 90% by volume;
Electrolyte solution [3 ]: the nonaqueous solvent constituting the electrolytic solution contains at least one chain carboxylic ester;
electrolyte solution [4 ]: the nonaqueous solvent constituting the electrolyte contains a solvent having a flash point of 70 ℃ or higher, and the content thereof is 60% by volume or more of the entire nonaqueous solvent;
electrolyte [5 ]]: containing LiN (C)nF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate as a lithium salt constituting the electrolyte;
electrolyte solution [6 ]: the lithium salt constituting the electrolyte is a fluorine-containing lithium salt, and the total nonaqueous electrolyte contains 10ppm to 300ppm of Hydrogen Fluoride (HF);
electrolyte [7 ]: the electrolyte contains vinylene carbonate, and the content of the vinylene carbonate is in the range of 0.001-3% by mass of the total mass of the electrolyte;
electrolyte [8 ]: the electrolyte solution further contains at least one compound selected from the group consisting of a compound represented by the general formula (4), a heterocyclic compound containing nitrogen and/or sulfur, a cyclic carboxylic ester, and a fluorine-containing cyclic carbonate, and the content thereof in the entire nonaqueous electrolyte solution is in the range of 0.001 to 5% by mass;
electrolyte [9 ]: the electrolyte solution also contains an overcharge inhibitor.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a lithium secondary battery having excellent low-temperature discharge characteristics can be provided, and the following effects can be exhibited, for example, by various aspects of the invention described later.
Positive electrode [1 ]:
according to the present invention, since a long life and a high output can be obtained with a cheaper material, a lithium secondary battery particularly suitable for a large-sized battery for automobile use or the like can be provided.
Positive electrode [2 ]:
according to the present invention, a lithium secondary battery having a high capacity, a long life, and a high output can be provided, and a lithium secondary battery particularly suitable for a large-sized battery for use in, for example, automobiles can be provided.
Positive electrode [3 ]:
according to the present invention, since a long-life and high-output lithium secondary battery can be obtained, a lithium secondary battery particularly suitable for a large-sized battery for use in, for example, automobiles can be provided.
Positive electrode [4 ]:
according to the present invention, a high-output lithium secondary battery can be obtained, and therefore, a lithium secondary battery particularly suitable for a large-sized battery for, for example, automobile use can be provided.
Positive electrode [5 ]:
according to the present invention, a lithium secondary battery having a high capacity, a long life, and a high output, and in which a decrease in battery capacity and output due to repeated charging and discharging of the battery (excellent repeated charging and discharging characteristics (cycle characteristics)) is suppressed can be obtained, and therefore, a lithium secondary battery particularly suitable for a large-sized battery for use in, for example, automobiles can be provided.
Negative electrode [1 ]:
according to the present invention, it is possible to provide a lithium secondary battery which is particularly suitable as a large-sized battery, can maintain an effect of improving cycle characteristics, can maintain high output characteristics from the initial stage to the final stage of a cycle, and can maintain output characteristics at a high power even after deterioration after a charge-discharge cycle.
Negative electrode [2 ]:
according to the present invention, a lithium secondary battery having excellent high-current-density charge/discharge characteristics in a short time can be provided.
Negative electrode [3 ]:
according to the present invention, a lithium secondary battery having a small output resistance and capable of effectively utilizing energy can be provided.
Negative electrode [4 ]:
according to the present invention, a lithium secondary battery having improved high-temperature storage resistance at a low charge depth can be provided.
Negative electrode [5 ]:
according to the present invention, a lithium secondary battery that can maintain good performance even when charge and discharge are repeated for a long time at a low charge depth can be provided.
Negative electrode [6 ]:
according to the present invention, a lithium secondary battery that can recover from a low output state at low temperature and has high output can be provided.
Negative electrode [7 ]:
according to the present invention, a lithium secondary battery having a large capacity and good charge acceptance when the battery is made larger can be provided.
Negative electrode [8 ]:
according to the present invention, a lithium secondary battery having excellent cycle characteristics and low-temperature output can be provided.
Negative electrode [9] [10 ]:
according to the present invention, it is possible to provide a lithium secondary battery which has a large cycle retention rate even when the battery is made larger, can achieve a good battery life, can achieve a high output even after a charge-discharge cycle test, or both.
Electrolyte solution [1 ]:
according to the present invention, the low-temperature characteristics of the nonaqueous electrolyte secondary battery can be greatly improved, and more specifically, the low-temperature characteristics can be improved without deteriorating the cycle characteristics and the storage characteristics.
Electrolyte solution [2 ]:
according to the present invention, a nonaqueous electrolyte solution for a secondary battery having both cycle characteristics and low-temperature characteristics greatly improved, and a secondary battery using the nonaqueous electrolyte solution and having excellent performance can be provided.
Electrolyte solution [3 ]:
according to the present invention, a nonaqueous electrolyte solution for a secondary battery and a secondary battery having greatly improved low-temperature output characteristics can be provided.
Electrolyte solution [4 ]:
according to the present invention, there can be provided a nonaqueous electrolyte for a secondary battery and a secondary battery comprising: although the nonaqueous electrolyte for a secondary battery has an electrolyte composition which causes few problems when a large amount of a low-viscosity solvent is contained, such as salt precipitation due to evaporation of a solvent, a decrease in flash point, and an increase in internal pressure at high temperature, high low-temperature characteristics and output characteristics can be maintained.
Electrolyte solution [5 ]:
according to the present invention, a nonaqueous electrolyte solution for a secondary battery and a secondary battery, which have greatly improved output characteristics and are excellent in high-temperature storage characteristics and cycle characteristics, can be provided.
Electrolyte solution [6 ]:
according to the present invention, a nonaqueous electrolyte for a secondary battery which is excellent in high-temperature storage characteristics and cycle characteristics and has greatly improved output characteristics can be provided.
Electrolyte [7 ]:
according to the present invention, a secondary battery having both cycle characteristics and low-temperature characteristics greatly improved can be provided.
Electrolyte [8 ]:
according to the present invention, a nonaqueous electrolyte for a secondary battery and a secondary battery, which are greatly improved in low-temperature discharge characteristics and excellent in high-temperature storage characteristics and cycle characteristics, can be provided.
Electrolyte [9 ]:
according to the present invention, it is possible to provide a secondary battery that satisfies both high rate characteristics and safety upon overcharge.
Structures [1] to [5 ]:
according to the present invention, a lithium secondary battery having a high capacity, a long life, a high output and high safety even when overcharged can be obtained, and therefore, a lithium secondary battery particularly suitable for a large-sized battery for use in, for example, automobiles can be provided.
Structure [6 ]:
according to the present invention, a lithium secondary battery having a high capacity, a long life, a high output, and little generated gas, i.e., having high safety even when overcharged, can be obtained, and therefore, a lithium secondary battery particularly suitable for a large-sized battery for use in, for example, automobiles, can be provided.
Detailed Description
The embodiments of the present invention will be described in detail below, but the description of the constituent elements described below is an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these specific contents as long as the gist thereof is not exceeded.
The lithium secondary battery of the present invention comprises at least: an electrode assembly comprising a positive electrode and a negative electrode with a microporous membrane separator interposed therebetween, and a nonaqueous electrolytic solution comprising a nonaqueous solvent and a lithium salt contained therein, wherein the nonaqueous electrolytic solution is contained in a battery case,
the positive electrode and the negative electrode each have an active material layer containing an active material capable of occluding and releasing lithium ions formed on a current collector;
the nonaqueous electrolytic solution contains at least one compound (hereinafter, these are simply referred to as "specific compound") selected from the following substances, and the content thereof in the entire nonaqueous electrolytic solution is 10ppm or more, the substances including: a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an S — F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate;
And the positive electrode, the negative electrode, the electrolytic solution or the battery structure satisfies specific conditions.
The lithium secondary battery of the present invention will be described in more detail below.
Positive electrode
The positive electrode used in the lithium secondary battery of the present invention will be described below.
The positive electrode used in the present invention is not particularly limited as long as it is a positive electrode in which an active material layer containing an active material capable of occluding and releasing lithium ions is formed, and the positive electrode is preferably any one selected from the following positive electrodes [1] to [5 ]:
positive electrode [1 ]: a positive electrode containing a positive electrode active material containing manganese;
positive electrode [2 ]: a positive electrode containing a positive electrode active material having a composition represented by the following composition formula (4),
LixNi(1-y-z)CoyMzO2component formula (4)
[ in the composition formula (4), M represents at least one element selected from the group consisting of Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, y represents a number satisfying 0.05 < y.ltoreq.0.5, and z represents a number satisfying 0.01. ltoreq. z.ltoreq.0.5. H;
positive electrode [3 ]: a positive electrode comprising a positive electrode active material selected from any one of the following (a) to (d),
(a) BET specific surface area of 0.4m2/g～2m2Positive electrode active material/g
(b) A positive electrode active material having an average primary particle diameter of 0.1 to 2 μm
(c) Median particle diameter d50A positive electrode active material of 1 to 20 μm
(d) Tap density of 1.3g/cm3～2.7g/cm3The positive electrode active material of (1);
positive electrode [4 ]: a positive electrode satisfying any one of the following conditions (e) to (f),
(e) the positive electrode is manufactured by forming a positive electrode active material layer containing a positive electrode active material, a conductive material and a binder on a current collector, wherein the content of the conductive material in the positive electrode active material layer is in the range of 6-20 mass%
(f) The positive electrode is prepared by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector, wherein the density of the positive electrode active material layer is 1.7g/cm3～3.5g/cm3Range of (1)
(g) The positive electrode is manufactured by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector, wherein the value of the ratio of the thicknesses of the positive electrode active material layer and the current collector (the thickness of the active material layer on one side before the nonaqueous electrolyte is injected)/(the thickness of the current collector) is 1.6-20;
positive electrode [5 ]: a positive electrode containing 2 or more positive electrode active materials having different compositions.
Next, a positive electrode generally used for the lithium secondary battery of the present invention will be described.
[ Positive electrode active Material ]
The following describes a positive electrode active material generally used for a positive electrode.
[ [ composition ] ]
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. The material containing lithium and at least one transition metal is preferable, and examples thereof include a lithium-transition metal complex oxide and a lithium-containing transition metal phosphate compound.
As the transition metal of the lithium-transition metal composite oxide, V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable, and specific examples thereof include LiCoO2And the like lithium-cobalt composite oxides; LiNiO2And the like lithium-nickel composite oxides; LiMnO2、LiMn2O4、Li2MnO3And lithium-manganese composite oxides; by substituting a part of transition metal atoms forming the main body of the lithium-transition metal composite oxide with another metal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, or SiSubstances, and the like. As a specific example of the substance obtained as an alternative, for example, LiNi can be mentioned0.5Mn0.5O2、LiNi0.85Co0.10Al0.05O2、LiNi0.33Co0.33Mn0.33O2、LiMn1.8Al0.2O4、 LiMn1.5Ni0.5O4And the like.
The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, or the like, and specific examples thereof include LiFePO 4、Li3Fe2(PO4)3、 LiFeP2O7And the like; LiCoPO4Cobalt phosphates, etc.; and those obtained by substituting a part of the transition metal atoms forming the main body of the lithium-containing transition metal phosphate compound with another metal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, or Si.
[ [ surface coating ] ]
Further, it is preferable that a material having a different composition from that of the positive electrode active material of the core is adhered to the surface of the positive electrode active material. Examples of the substance to be attached to the surface (hereinafter, simply referred to as "surface-attached substance") include oxides such as alumina, silica, titania, zirconia, magnesia, calcia, boria, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.
These surface-adhering substances may be adhered to the surface of the positive electrode active material by a method comprising: for example, a method in which a surface-adhering substance is dissolved or suspended in a solvent, and then impregnated with a positive electrode active material and dried; a method in which a precursor of a surface-adhering substance is dissolved or suspended in a solvent, and then impregnated and added to a positive electrode active material, followed by reaction by heating or the like; a method of adding a surface-adhering substance to the positive electrode active material precursor and sintering the same.
The lower limit of the amount of the surface-adhering substance is preferably 0.1ppm or more, more preferably 1ppm or more, and still more preferably 10ppm or more, by mass, based on the positive electrode active material; the upper limit thereof is preferably 20% or less, more preferably 10% or less, and further preferably 5% or less. The surface-attached substance can suppress the oxidation reaction of the nonaqueous electrolytic solution on the surface of the positive electrode active material, and can improve the battery life, but when the amount of the attached substance is too small, the effect cannot be sufficiently exhibited, and when the amount is too large, the resistance may increase because the introduction and discharge of lithium ions are hindered.
[ [ shape ] ]
The particle shape of the positive electrode active material in the present invention may be a block shape, a polyhedron shape, a spherical shape, an ellipsoid shape, a plate shape, a needle shape, a columnar shape, or the like, which is conventionally used, and among them, it is preferable that primary particles are aggregated to form secondary particles, and the shape of the secondary particles is a spherical shape or an ellipsoid shape. In general, in an electrochemical device, an active material in an electrode expands and contracts with charge and discharge, and thus deterioration such as breakage of the active material or disconnection of a conductive path due to the stress is likely to occur. Therefore, it is preferable that the primary particles are aggregated to form the secondary particles as compared with a single-particle active material of only the primary particles, because the formation of the secondary particles can relax the stress of expansion and contraction, thereby preventing deterioration. In addition, spherical or ellipsoidal particles are preferable to the particles having equiaxed orientation in a plate shape because the spherical or ellipsoidal particles have less orientation during electrode molding, have less expansion and contraction of an electrode during charge and discharge, and are easily mixed uniformly when mixed with a conductive agent during electrode production.
[ [ tap density ] ]
The tap density of the positive electrode active material is usually 1.3g/cm3Above, preferably 1.5g/cm3Above, more preferably 1.6g/cm3Above, most preferably 1.7g/cm3The above. If the tap density of the positive electrode active material is less than the lower limit, the amount of the dispersion medium required for forming the positive electrode active material layer increases, the amount of the conductive material or the binder required increases, and the filling rate of the positive electrode active material in the positive electrode active material layer is restrictedThe battery capacity is sometimes limited. By using the composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. Generally, the tap density is preferably as large as possible, and there is no particular upper limit, but if the tap density is too large, diffusion of lithium ions in the positive electrode active material layer using a nonaqueous electrolyte solution as a medium becomes a factor determining the rate, and the load characteristic is likely to be lowered, so the tap density is usually 2.9g/cm3Hereinafter, it is preferably 2.7g/cm3Hereinafter, more preferably 2.5g/cm3The following.
In the present invention, tap density is defined as follows: the sample was dropped to 20cm through a sieve having an aperture of 300. mu.m3After the container volume was filled in the tapping cell (Tap cell), a powder density measuring instrument (for example, Tap densifier (タップデンサー) manufactured by Seishin (セイシン) corporation) was used to vibrate for 1000 strokes with a length of 10mm, and the Tap density was determined from the volume at that time and the weight of the sample.
[ [ median particle diameter d ]50]]
Median diameter d of particles of positive electrode active material50(secondary particle diameter when the primary particles are aggregated to form secondary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, most preferably 3 μm or more, and its upper limit is usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, most preferably 15 μm or less. If the median particle diameter d50When the amount of the lithium ion battery is less than the lower limit, a product having a high tap density may not be obtained, and when the amount of the lithium ion battery is more than the upper limit, it takes time for lithium in the particles to diffuse, which may cause problems such as deterioration of battery performance, and streaks when a positive electrode for a battery is formed, that is, when an active material, a conductive agent, a binder, or the like is slurried in a solvent and then applied in a film form. Here, 2 or more kinds having different median particle diameters d are mixed50The positive electrode active material of (3) can further improve the filling property in the production of a positive electrode.
Further, the median diameter d in the present invention50The known laser diffraction/scattering particle size division can be utilizedThe cloth was measured by a cloth measuring apparatus. When LA-920 manufactured by HORIBA Inc. was used as a particle size distribution meter, a 0.1 mass% aqueous solution of sodium hexametaphosphate was used as a dispersion medium used for measurement, ultrasonic dispersion was performed for 5 minutes, and then the refractive index was measured with a setting of 1.24.
[ [ average primary particle diameter ] ]
When the primary particles are aggregated to form the secondary particles, the average primary particle diameter of the positive electrode active material is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, most preferably 0.1 μm or more, and usually 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, most preferably 0.6 μm or less. If the average primary particle diameter exceeds the upper limit, spherical secondary particles are difficult to form, adversely affecting the powder filling property, or the specific surface area is greatly reduced, so that the possibility of a reduction in battery performance such as output characteristics may be high. On the other hand, if the average primary particle size is less than the lower limit, the crystal is generally incomplete, and therefore, problems such as poor charge/discharge reversibility may occur.
In addition, the primary particle diameter can be measured by observation using a Scanning Electron Microscope (SEM). Specifically, the following method was used to obtain: in the photographs of 10000 times magnification, the longest value of the slice generated by the left and right boundary lines of the primary particle on the horizontal straight line was obtained for any 50 primary particles, and the average value was taken.
[ [ BET specific surface area ] ]
The BET specific surface area of the positive electrode active material to be provided to a lithium secondary battery of the present invention is usually 0.2m 2A ratio of 0.3m or more per gram2A value of at least one per gram, more preferably 0.4m2A value of at least one member selected from the group consisting of,/g, and an upper limit of usually 4.0m2A ratio of 2.5m or less per gram2A ratio of 1.5m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered, whereas if the BET specific surface area is larger than this range, the tap density tends to be difficult to increase, and there may be a problem in coatability when forming the positive electrode active material.
The BET specific surface area is defined as the following value: a value measured by a nitrogen adsorption BET 1 point method by a gas flow method using a nitrogen helium mixed gas properly adjusted to a relative pressure value of nitrogen to atmospheric pressure of 0.3 after pre-drying a sample at 150 ℃ for 30 minutes under a nitrogen flow using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research).
[ [ manufacturing method ] ]
As the method for producing the positive electrode active material, a general method as a method for producing an inorganic compound is used. In particular, when preparing a spherical or ellipsoidal active material, various methods can be considered, and examples thereof include the following: dissolving or pulverizing transition metal raw material such as transition metal nitrate and transition metal sulfate and other elements used as required, dispersing in solvent such as water, stirring while adjusting pH to obtain spherical precursor, drying as required, adding LiOH and Li 2CO3、LiNO3A method of obtaining an active material by sintering a Li source at a high temperature; dissolving or pulverizing transition metal raw material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, etc. and other elements used as required, dispersing in solvent such as water, drying and molding with spray dryer, etc. to obtain spherical or elliptical precursor, adding LiOH and Li2CO3、LiNO3A method of obtaining an active material by sintering a Li source at a high temperature; and a transition metal raw material such as transition metal nitrate, transition metal sulfate, transition metal hydroxide, transition metal oxide, and LiOH, Li2CO3、LiNO3And a method in which a raw material substance such as an Li source and other elements used as needed is dissolved or pulverized and dispersed in a solvent such as water, and the resultant is dried and molded by a spray dryer or the like to form a spherical or oval-spherical precursor, and then the precursor is sintered at a high temperature to obtain an active material.
[ Structure of Positive electrode ]
Next, the structure of the positive electrode used in the present invention will be described.
[ [ electrode structure and production method ] ]
The positive electrode used in the lithium secondary battery of the present invention is produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be produced by a conventional method. That is, a positive electrode can be obtained by dry-mixing a positive electrode active material, a binder, and, if necessary, a conductive material, a thickener, etc. to prepare a sheet, pressing and bonding the obtained sheet to a positive electrode current collector, or dissolving or dispersing these materials in a liquid medium to prepare a slurry, and applying and drying the slurry on the positive electrode current collector.
In the present invention, the content of the positive electrode active material in the positive electrode active material layer is usually 10 mass% or more, preferably 30 mass% or more, and particularly preferably 50 mass% or more. The upper limit is usually 99.9% by mass or less, preferably 99% by mass or less. If the content of the positive electrode active material powder in the positive electrode active material layer is low, the capacitance may become insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient. The positive electrode active material may be used singly, or 2 or more kinds of positive electrode active materials having different compositions or different powder physical properties may be used in combination in any combination and ratio.
[ [ compaction ] ]
In order to increase the packing density of the positive electrode active material, the positive electrode active material layer obtained by coating and drying is preferably compacted by a manual press, a roll press, or the like. The lower limit of the density of the positive electrode active material layer is preferably 1g/cm3Above, more preferably 1.5g/cm3The above is more preferably 2g/cm3Above, the upper limit is preferably 4g/cm3Hereinafter, more preferably 3.5g/cm3Hereinafter, it is more preferably 3g/cm3The following ranges. If the amount exceeds this range, the permeability of the nonaqueous electrolytic solution into the vicinity of the current collector/active material interface may decrease, and particularly, the charge-discharge characteristics at high current density may decrease. In addition, the first and second substrates are, If the content is less than this range, the conductivity between the active materials decreases, and the battery impedance may increase.
[ [ conductive material ] ]
As the conductive material, a known conductive material can be arbitrarily used. Specific examples thereof include metal materials such as copper and nickel; natural graphite, artificial graphite, and other graphite; carbon black such as acetylene black; and carbon materials such as amorphous carbon such as needle coke. These may be used alone, or 2 or more of them may be used in combination in any combination and ratio.
The proportion of the conductive material used in the positive electrode active material layer is usually 0.01 wt% or more, preferably 0.1 wt% or more, and more preferably 1 wt% or more, and the upper limit thereof is usually 50 wt% or less, preferably 30 wt% or less, and more preferably 15 wt% or less. If the content is less than this range, the conductivity may be insufficient. On the contrary, if the content is higher than the range, the battery capacity may be decreased.
[ [ adhesive ] ]
The binder used in the production of the positive electrode active material layer is not particularly limited, and when a coating method is used, it is sufficient if it is a material that can be dissolved or dispersed in a liquid medium used in the production of the electrode, and specific examples thereof include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or hydrogenated products thereof, EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers or hydrogenated products thereof; flexible resinous polymers such as syndiotactic 1, 2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, propylene- α -olefin copolymers, and the like; fluorine-based polymers such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer; and a polymer composition having ion conductivity of alkali metal ions (particularly, lithium ions). These may be used alone or in combination of 2 or more in any combination and ratio.
The proportion of the binder in the positive electrode active material layer is usually 0.1% by mass or more, preferably 1% by mass or more, and more preferably 3% by mass or more, and the upper limit thereof is usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and most preferably 10% by mass or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained, the mechanical strength of the positive electrode is insufficient, and the battery performance such as cycle characteristics deteriorates. On the other hand, if the proportion of the binder is too high, a decrease in battery capacity or conductivity may sometimes result.
[ [ liquid medium ] ]
The liquid medium used for forming the slurry is not particularly limited as long as it is a solvent capable of dissolving or dispersing the positive electrode active material, the conductive agent, the binder, and the thickener used as needed, and any of an aqueous solvent and an organic solvent can be used.
Examples of the aqueous medium include water and a mixed solvent of alcohol and water. Examples of the organic solvent include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N, N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and Tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethylsulfoxide.
In particular, when an aqueous solvent is used, it is preferable to form a slurry using a thickener and a latex of styrene-butadiene rubber (SBR). Thickeners are commonly used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specifically, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof can be mentioned. These may be used alone, or may be used in combination of 2 or more in any combination and ratio. When the thickener is added, the proportion of the thickener to the active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more, and the upper limit thereof is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. If the content is less than this range, the coatability may be significantly reduced. On the other hand, if the amount exceeds this range, the proportion of the active material in the positive electrode active material layer decreases, which may cause a problem of a decrease in the capacity of the battery or a problem of an increase in the impedance between the positive electrode active materials.
[ [ Current collector ] ]
The material of the positive electrode current collector is not particularly limited, and a known material can be arbitrarily used. Specific examples thereof include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon cloth, carbon paper, and the like. Among them, a metal material is preferable, and aluminum is particularly preferable.
As the shape of the current collector, in the case of a metal material, there are exemplified a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded alloy (エキスパンドメタル), a perforated metal, a foamed metal, and the like; in the case of the carbon material, a carbon plate, a carbon thin film, a carbon cylinder, and the like can be exemplified. Of these, a metal thin film is preferable. In addition, the film may be appropriately formed into a net shape. The thickness of the film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and is usually 1mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the film is thinner than this range, the strength necessary as a current collector may be insufficient. Conversely, if the film thickness is larger than this range, the handling properties may be impaired.
The ratio of the thicknesses of the current collector and the positive electrode active material layer is not particularly limited (thickness of the active material layer on the side before the nonaqueous electrolytic solution is injected)/(thickness of the current collector) is preferably 150 or less, more preferably 20 or less, and most preferably 10 or less, and the lower limit thereof is preferably 0.1 or more, more preferably 0.4 or more, and most preferably 1 or more. If the amount exceeds this range, the current collector may generate heat by joule heat during high current density charge and discharge. If the amount is less than this range, the volume ratio of the current collector to the positive electrode active material may increase, resulting in a decrease in the battery capacity.
[ [ electrode area ] ]
When the nonaqueous electrolytic solution of the present invention is used, the area of the positive electrode active material layer is preferably larger than the outer surface area of the battery case from the viewpoint of high output and improved stability at high temperatures. Specifically, the sum of the electrode areas of the positive electrodes is preferably 15 times or more, and more preferably 40 times or more, in terms of an area ratio with respect to the surface area of the case of the secondary battery. The outer surface area of the case is a total area obtained by calculating the dimensions of the case portion filled with the power generating elements excluding the protruding portion of the terminal from the dimensions of the length, width, and thickness, in the case of a bottomed square shape. In the case of a bottomed cylindrical shape, the geometric surface area is obtained by approximating a case portion filled with the power generating element except for the protruding portion of the terminal to a cylinder. The total electrode area of the positive electrode is the geometric surface area of the positive electrode composite material layer facing the composite material layer (the body frame body) containing the negative electrode active material, and in a configuration in which the positive electrode composite material layers are formed on both sides with the current collector foil interposed therebetween, the total electrode area of each side is calculated.
[ [ discharge capacity ] ])
When the nonaqueous electrolyte solution for a secondary battery of the present invention is used, it is preferable that the capacity of the battery element (the capacity when the battery is discharged from a fully charged state to a discharged state) contained in the battery case of 1 secondary battery is 3 ampere hours (Ah) or more, since the effect of improving the low-temperature discharge characteristics is large.
Therefore, the positive electrode plate is preferably designed to have a discharge capacity of 3 ampere-hours (Ah) or more and less than 20Ah, more preferably 4Ah or more and less than 10Ah at full charge. If the current is less than 3Ah, the voltage drop due to the electrode reaction impedance becomes large when a large current is taken out, and the power efficiency may be deteriorated. When the temperature is 20Ah or more, the electrode reaction impedance becomes small and the power efficiency becomes good, but the temperature distribution caused by the heat generation inside the battery during pulse charge and discharge becomes large, and the durability of repeated charge and discharge is poor, and the heat release efficiency also becomes poor at the time of intense heat generation at the time of abnormality such as overcharge or internal short circuit, and the probability of occurrence of a phenomenon (valve operation) in which the internal pressure rises to operate the purge valve and a phenomenon (rupture) in which the battery contents are vigorously discharged to the outside may increase.
[ [ thickness of positive electrode plate ] ]
The thickness of the positive electrode is not particularly limited, but from the viewpoint of high capacity and high output, the lower limit of the thickness of the multilayer material layer on one surface of the current collector, which is obtained by subtracting the thickness of the metal foil of the core material, is preferably 10 μm or more, more preferably 20 μm, and the upper limit thereof is preferably 200 μm or less, more preferably 100 μm or less.
Positive electrode (1)
Next, the "positive electrode containing a positive electrode active material containing manganese" of the positive electrode [1] used in the lithium secondary battery of the present invention will be described.
[ Positive electrode active Material for Positive electrode [1]
Next, a positive electrode active material used in the positive electrode [1] will be described.
[ [ composition ] ]
The positive electrode active material is a material containing a transition metal capable of electrochemically occluding and releasing lithium ions, and at least a part of the transition metal is a positive electrode active material containing manganese. Preferably, the lithium-containing composite oxide further contains lithium, and more preferably contains lithium and manganese.
The positive electrode active material containing manganese is not particularly limited, but is preferably a positive electrode active material having a composition represented by the following composition formula (5).
LixMn(1-y)M1 yO2Component formula (5)
[ in the compositional formula (5), M1Represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8]。
In the compositional formula (5), M1Particularly, Ni, Co, and Fe are preferable, and x is particularly preferably 0.2. ltoreq. x.ltoreq.1.15, and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.7. Specific examples of the substance having the composition represented by the composition formula (5) include LiMn0.5Ni0.5O2。
In addition, M is particularly preferred1A positive electrode active material which is Ni and has a composition represented by the following composition formula (6).
LixMn(1-y-z)Ni1 yM2 zO2Component formula (6)
[ in the compositional formula (6), M2Represents at least one element selected from the group consisting of Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8, and z represents a number satisfying 0.01. ltoreq. z.ltoreq.0.5]。
In the compositional formula (6), M2Co, Al, Fe, Mg are particularly preferred, x is particularly preferably 0.2. ltoreq. x.ltoreq.1.15, y is particularly preferably 0.1. ltoreq. y.ltoreq.0.7, z is particularly preferably 0.1. ltoreq. z.ltoreq.0.7, and y + z is particularly preferably 0.2. ltoreq. y + z.ltoreq.0.7. Specific examples of the substance having the composition represented by the composition formula (6) include LiMn0.33Ni0.33Co0.33O2And the like.
The positive electrode active material containing manganese is preferably a positive electrode active material having a composition represented by the following composition formula (7).
LixMn(2-y)M3 yO4Component formula (7)
[ in the compositional formula (7), M3Represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8]。
In the compositional formula (7), M3Particularly, Ni, Co, Al and Mg are preferable, and x is particularly preferably 0.05. ltoreq. x.ltoreq.1.15 and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.7. Specific examples of the substance having the composition represented by the composition formula (7) include LiMn1.8Al0.2O4、LiMn1.5Ni0.5O4And the like.
[ [ surface coating ] ]
In addition, it is preferable to use a positive electrode active material in which a material having a different composition from the positive electrode active material containing manganese is attached to the surface of the positive electrode active material. The kind, method and amount of the surface-adhering substance are the same as those described above.
[ [ shape ] ]
The particle shape of the positive electrode active material is the same as described above.
[ [ tap density ] ]
The tap density of the positive electrode active material is the same as described above.
[ [ median particle diameter d ]50]]
The median diameter d of the particles of the positive electrode active material50(secondary particle diameter when the primary particles are aggregated to form secondary particles) is the same as described above.
[ [ average primary particle diameter ] ]
When the primary particles are aggregated to form the secondary particles, the average primary particle diameter of the positive electrode active material is the same as described above.
[ [ BET specific surface area ] ]
The BET specific surface area of the positive electrode active material is the same as described above.
[ [ manufacturing method ] ]
As a method for producing the positive electrode active material, a general method as a method for producing an inorganic compound is used. In particular, when preparing a spherical or ellipsoidal active material, various methods can be considered, and examples thereof include the following: dissolving or pulverizing manganese raw material such as manganese nitrate and manganese sulfate and other elements used as required, dispersing in solvent such as water, stirring while adjusting pH to obtain spherical precursor, drying as required, adding LiOH and Li2CO3、LiNO3A method of obtaining an active material by sintering a Li source at a high temperature; dissolving or pulverizing manganese raw material such as manganese nitrate, manganese sulfate, manganese oxide, and basic manganese hydroxide and other elements as required, dispersing in solvent such as water, and spray drying Drying and shaping to obtain spherical or elliptical precursor, adding LiOH and Li2CO3、LiNO3A method of obtaining an active material by sintering a Li source at a high temperature; and manganese raw material such as manganese nitrate, manganese sulfate, manganese oxide, basic manganese hydroxide and the like, LiOH and Li2CO3、LiNO3And a method in which a raw material substance such as an Li source and other elements used as needed is dissolved or pulverized and dispersed in a solvent such as water, and the resultant is dried and molded by a spray dryer or the like to prepare a spherical or oval-spherical precursor, and then the precursor is sintered at a high temperature to obtain an active material.
The positive electrode active material of the present invention may be used alone or in combination with one or more kinds of positive electrode active materials having a different composition or different powder properties from the positive electrode active material containing manganese at an arbitrary combination and ratio. Preferable combinations for this include a positive electrode active material containing manganese and LiNiO2Or a combination of substances in which part of Ni is replaced by another transition metal; or a positive electrode active material containing manganese and LiCoO2Or a combination of substances in which a part of Co is replaced by another transition metal. Further, particularly preferred combinations include positive electrode active materials represented by composition formulas (5) to (7) and LiNiO 2Or a combination of substances in which part of Ni is replaced by another transition metal; or positive electrode active materials and LiCoO represented by the composition formulas (5) to (7)2Or a combination of substances in which a part of Co is replaced by another transition metal. The positive electrode active material containing manganese, particularly the positive electrode active materials represented by the composition formulas (5) to (7), is preferably 30% by mass or more, more preferably 50% by mass or more of the entire positive electrode active material. If the usage ratio of the positive electrode active material represented by the composition formulas (5) to (7) is small, the cost of the positive electrode may not be reduced.
[ Structure of Positive electrode [1]
Next, the structure of the positive electrode used for the positive electrode [1] will be described.
The electrode structure and the manufacturing method in the positive electrode [1], the compaction of the positive electrode active material layer, the conductive material, the binder used in the production of the positive electrode active material layer, the liquid medium for forming the slurry, the current collector, the electrode area, the discharge capacity, the thickness of the positive electrode plate, and the like are the same as described above.
Positive electrode (2)
Next, a description will be given of "a positive electrode containing a positive electrode active material having a specific composition represented by the composition formula (4)" as the positive electrode [2] used in the lithium secondary battery of the present invention.
[ Positive electrode active Material for Positive electrode [2]
Next, a positive electrode active material used for the positive electrode [2] will be described.
[ [ composition ] ]
As the positive electrode active material, a material containing a transition metal capable of electrochemically occluding and releasing lithium ions (hereinafter, simply referred to as "the positive electrode active material") having a composition represented by the following composition formula (4) is used.
LixNi(1-y-z)CoyMzO2Component formula (4)
[ in the composition formula (4), M represents at least one element selected from the group consisting of Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.5, and z represents a number satisfying 0.01. ltoreq. z.ltoreq.0.5 ].
In the composition formula (4), M is preferably Mn, Al or Mg, and x is preferably 0.2. ltoreq. x.ltoreq.1.15. Further, y is preferably 0.08. ltoreq. y.ltoreq.0.4, particularly preferably 0.1. ltoreq. y.ltoreq.0.3. In addition, z is preferably 0.02. ltoreq. z.ltoreq.0.4, particularly preferably 0.03. ltoreq. z.ltoreq.0.3.
[ [ surface coating ] ]
In addition, it is preferable to use a positive electrode active material in which a material having a different composition from the positive electrode active material is attached to the surface of the positive electrode active material. The kind, method and amount of the surface-adhering substance are the same as those described above.
[ [ shape ] ]
The particle shape of the positive electrode active material is the same as described above.
[ [ tap density ] ]
The tap density of the positive electrode active material is the same as described above.
[ [ median particle diameter d ]50]]
The median diameter d of the particles of the positive electrode active material50(secondary particle diameter when the primary particles are aggregated to form secondary particles) is the same as described above.
[ [ average primary particle diameter ] ]
When the primary particles are aggregated to form the secondary particles, the average primary particle diameter of the positive electrode active material is the same as described above.
[ [ BET specific surface area ] ]
The BET specific surface area of the positive electrode active material is the same as described above.
[ [ manufacturing method ] ]
As a method for producing the positive electrode active material, a general method as a method for producing an inorganic compound can be used. In particular, when preparing a spherical or ellipsoidal active material, various methods can be considered, and examples thereof include the following: dissolving or pulverizing nickel material such as nickel nitrate and nickel sulfate, cobalt material such as cobalt nitrate and cobalt sulfate, and material of M in composition formula (4) in solvent such as water, adjusting pH under stirring to obtain spherical precursor, drying, adding LiOH and Li2CO3、LiNO3A method of obtaining an active material by sintering a Li source at a high temperature; dissolving or pulverizing nickel raw material such as nickel nitrate, nickel sulfate, nickel oxide, nickel hydroxide, and basic nickel hydroxide, cobalt raw material such as cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, and basic cobalt hydroxide, and raw material M in formula (4), dispersing in solvent such as water, drying and molding with spray dryer to obtain spherical or elliptical precursor, adding LiOH, Li, etc 2CO3、LiNO3A method of obtaining an active material by sintering a Li source at a high temperature; and a combination of a nickel raw material such as nickel nitrate, nickel sulfate, nickel oxide, nickel hydroxide, or basic nickel hydroxide and a cobalt raw material such as cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, or basic cobalt hydroxideM in formula (4) with LiOH and Li2CO3、LiNO3And a method in which a Li source is dissolved or pulverized and dispersed in a solvent such as water, and the resultant is dried and molded by a spray dryer or the like to prepare a spherical or oval-spherical precursor, and then the precursor is sintered at a high temperature to obtain an active material.
In order to produce the positive electrode in the present invention, the positive electrode active material (the positive electrode active material represented by the composition formula (4) and/or the positive electrode active material represented by the composition formula (4) coated with the surface-adhering substance) may be used alone, or the positive electrode active material and one or more substances having a composition different from that of the positive electrode active material may be used in combination at an arbitrary combination and ratio. A preferable combination in this case is the positive electrode active material and LiMn2O4Or a combination of substances in which part of Mn is replaced by another transition metal; or the positive electrode active material and LiCoO2Or a combination of substances in which a part of Co is replaced by another transition metal.
Here, the positive electrode active material is preferably 30% by mass or more, more preferably 50% by mass or more of the total positive electrode active material. If the proportion of the positive electrode active material used is reduced, the battery capacity may be reduced. The "positive electrode active material" and the "positive electrode active material other than the positive electrode active material" are collectively referred to as "positive electrode active material".
[ Structure of Positive electrode [2]
The structure of the positive electrode used for the positive electrode [2] will be described below.
The electrode structure and the manufacturing method in the positive electrode [2], the compaction of the positive electrode active material layer, the conductive material, the binder used in the production of the positive electrode active material layer, the liquid medium for forming the slurry, the current collector, the electrode area, the discharge capacity, the thickness of the positive electrode plate, and the like are the same as described above.
Positive electrode (3)
Next, a positive electrode [3] used in the lithium secondary battery of the present invention "a positive electrode containing any one positive electrode active material selected from the following (a) to (d)" will be described.
(a) BET specific surface area of 0.4m2/g～2m2Positive electrode active material/g
(b) A positive electrode active material having an average primary particle diameter of 0.1 to 2 μm
(c) Median particle diameter d50A positive electrode active material of 1 to 20 μm
(d) Tap density of 1.3g/cm3～2.7g/cm3The positive electrode active material of (1).
[ Positive electrode active Material for Positive electrode [3]
Next, the positive electrode active material used for the positive electrode [3] will be described.
[ [ composition ] ]
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. The material containing lithium and at least one transition metal is preferable, and examples thereof include a lithium-transition metal complex oxide and a lithium-containing transition metal phosphate compound. Specifically, a substance having the same composition as described above can be used.
[ [ surface coating ] ]
The positive electrode active material is preferably a positive electrode active material having a composition different from that of the positive electrode active material of the core, adhered to the surface of the positive electrode active material. The kind, method and amount of the surface-adhering substance are the same as those described above.
[ [ shape ] ]
The particle shape of the positive electrode active material is the same as described above.
[ [ BET specific surface area ] ]
The BET specific surface area of the positive electrode active material is preferably 0.4m2A value of at least one per gram, more preferably 0.5m2A value of at least one per gram, more preferably 0.6m2A ratio of 2m or more in terms of upper limit thereof2A ratio of 1.8m or less per gram2A ratio of 1.5m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered, whereas if the BET specific surface area is larger than this range, the tap density tends to be difficult to increase, and there may be a case where a problem tends to occur in coatability when forming the positive electrode active material.
The BET specific surface area is defined as the following value: a value measured by a nitrogen adsorption BET 1 point method by a gas flow method using a nitrogen helium mixed gas properly adjusted to a relative pressure value of nitrogen to atmospheric pressure of 0.3 after pre-drying a sample at 150 ℃ for 30 minutes under a nitrogen flow using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research).
[ [ average primary particle diameter ] ]
When the primary particles are aggregated to form the secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 0.2 μm or more, still more preferably 0.3 μm or more, and most preferably 0.4 μm or more, and the upper limit thereof is preferably 2 μm or less, more preferably 1.6 μm or less, still more preferably 1.3 μm or less, and most preferably 1 μm or less. If the average primary particle diameter exceeds the upper limit, spherical secondary particles are difficult to form, adversely affecting the powder filling property, or the specific surface area is greatly reduced, so that the possibility of a reduction in battery performance such as output characteristics may be high. On the other hand, if the average primary particle size is less than the lower limit, the crystallization is generally incomplete, and therefore, problems such as poor reversibility of charge and discharge may occur.
The primary particle diameter can be measured by observation using a Scanning Electron Microscope (SEM). Specifically, the following method was used to obtain: in the photographs of 10000 times magnification, the longest value of a slice generated by the left and right boundary lines of a primary particle on a horizontal straight line is obtained for any 50 primary particles, and the average value is taken.
[ [ median particle diameter d ]50]]
The median diameter d of the particles of the positive electrode active material50(secondary particle diameter when the primary particles are aggregated to form secondary particles) is preferably 1 μm or more, more preferably 1.2 μm or more, further preferably 1.5 μm or more, and most preferably 2 μm or more, and its upper limit is preferably 20 μm or less, more preferably 18 μm or less, further preferably 16 μm or less, and most preferably 15 μm or less. If the median particle diameter d50When the amount of the catalyst is less than the lower limit, a product having a high tap density may not be obtained, and when the amount of the catalyst exceeds the upper limit, the particles may be dispersedThe diffusion of lithium in the battery takes time, and therefore, there may be problems such as a decrease in battery performance, or streaks when the positive electrode of the battery is produced, that is, when the active material, the conductive agent, the binder, and the like are slurried in a solvent and then coated in a film form. The positive electrode active material of the present invention is a mixture of 2 or more kinds of positive electrode active materials having different median particle diameters d 50The positive electrode active material obtained according to the above process is preferable because the filling property in the production of the positive electrode can be further improved.
Further, the median diameter d in the present invention50The particle size distribution can be measured by a known laser diffraction/scattering particle size distribution measuring apparatus. When LA-920 manufactured by HORIBA Inc. was used as a particle size distribution meter, the measurement was carried out by using a 0.1 mass% aqueous solution of sodium hexametaphosphate as a dispersion medium used for the measurement, carrying out ultrasonic dispersion for 5 minutes, and then setting the measurement refractive index to 1.24.
[ [ tap density ] ]
The tap density of the positive electrode active material is preferably 1.3g/cm3Above, more preferably 1.5g/cm3Above, more preferably 1.6g/cm3Above, most preferably 1.7g/cm3The above. If the tap density of the positive electrode active material is less than the lower limit, the amount of the dispersion medium required for forming the positive electrode active material layer increases, and the necessary amount of the conductive material or the binder increases, so that the filling rate of the positive electrode active material in the positive electrode active material layer is restricted, and the battery capacity may be restricted. By using the composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. Generally, the higher the tap density, the more preferable the tap density is, there is no particular upper limit, but if the tap density is too large, the diffusion of lithium ions in the positive electrode active material layer using the electrolyte as a medium becomes a factor determining the rate, and the load characteristic is liable to be lowered in some cases, so the upper limit of the tap density is preferably 2.7g/cm 3Hereinafter, more preferably 2.5g/cm3The following.
In the present invention, tap density is defined as follows: the sample was dropped to 20cm through a sieve having an aperture of 300. mu.m3In the container, filling the container volumeThen, the vibration was performed 1000 times with a stroke length of 10mm using a powder density measuring instrument (for example, Tap densifier manufactured by seishin corporation), and the bulk density at this time was defined as Tap density.
From the viewpoint of long life and high output, it is particularly preferable that the positive electrode active material in the lithium secondary battery of the present invention satisfies the BET specific surface area, the average primary particle diameter, and the median particle diameter d described above at the same time50And 2 or more physical properties in tap density.
[ [ manufacturing method ] ]
The method for producing the positive electrode active material is the same as described above.
The positive electrode active materials in the lithium secondary battery of the present invention may be used alone, or 2 or more kinds of positive electrode active materials having different compositions or different powder physical properties may be combined at an arbitrary combination and ratio. In addition, the positive electrode of the present invention preferably contains a positive electrode active material having any of the above physical properties (the positive electrode active material) and a positive electrode active material having a different composition from the positive electrode active material, from the viewpoint of improving the lifetime.
[ Structure of Positive electrode [3]
The structure of the positive electrode used for the positive electrode [3] will be described below.
The electrode structure and the manufacturing method in the positive electrode [3], the compaction of the positive electrode active material layer, the conductive material, the binder used in the production of the positive electrode active material layer, the liquid medium for forming the slurry, the current collector, the electrode area, the discharge capacity, the thickness of the positive electrode plate, and the like are the same as described above.
Positive electrode (4)
Next, a positive electrode [4] used in the lithium secondary battery of the present invention "a positive electrode satisfying any one condition selected from the following (e) to (f)" will be described.
(e) A positive electrode produced by forming a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder on a current collector, wherein the content of the conductive material in the positive electrode active material layer is in the range of 6 to 20 mass% (embodiment 1)
(f) Forming a positive electrode active material on a current collectorA positive electrode comprising a positive electrode active material layer of a material and a binder, wherein the positive electrode active material layer has a density of 1.7g/cm3～3.5g/cm3Range of (mode 2)
(g) A positive electrode is produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector, wherein the ratio of the thicknesses of the positive electrode active material layer and the current collector (the thickness of the active material layer on the side before the nonaqueous electrolyte solution is injected)/(the thickness of the current collector) is 1.6 to 20 (embodiment 3).
[ Positive electrode active Material for Positive electrode [4]
Next, the positive electrode active material used in the positive electrode [4] will be described.
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. The material containing lithium and at least one transition metal is preferable, and examples thereof include a lithium-transition metal complex oxide and a lithium-containing transition metal phosphate compound. Specifically, a substance having the same composition as described above can be used.
The surface coating, shape, tap density and median diameter d of the positive electrode active material50The average primary particle diameter, BET specific surface area, production method and the like are the same as those described above.
[ Structure of Positive electrode [4]
The structure of the positive electrode used for the positive electrode [4] will be described below.
[ [ electrode structure and production method ] ]
The positive electrode [4] in the lithium secondary battery of the present invention is produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be produced by a conventional method. That is, at least the positive electrode active material, the binder, the conductive material (the essential component in embodiment 1) used as needed, and the thickener and the like used as needed are dry-mixed to form a sheet, and the sheet is pressed and bonded to the positive electrode current collector, or the sheet is dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried, whereby the positive electrode active material layer can be formed on the current collector, and the positive electrode can be obtained.
The content of the positive electrode active material in the positive electrode active material layer is preferably 80 mass% or more, more preferably 82 mass% or more, and particularly preferably 84 mass% or more. The upper limit thereof is preferably 95% by mass or less, and more preferably 93% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the capacitance may become insufficient. On the contrary, if the content of the positive electrode active material is too high, the strength of the positive electrode may be insufficient.
[ [ conductive material ] ]
As the conductive material, a known conductive material can be arbitrarily used. As a specific example, the same conductive materials as described above can be cited.
The content of the conductive material used in the positive electrode of the lithium secondary battery of the present invention in the positive electrode active material layer is as follows: in embodiment 1, it is necessary to be 6% by mass or more, preferably 7% by mass or more, more preferably 8% by mass or more, and further preferably 9% by mass or more; although not particularly limited in embodiments 2 and 3, the content is preferably 6% by mass or more, more preferably 7% by mass or more, and still more preferably 8% by mass or more. If the content of the conductive material in the positive electrode active material layer is too small, the conductivity may be insufficient, and a high output may not be obtained.
In addition, the upper limit of the content of the conductive material in the positive electrode active material layer is as follows: in embodiment 1, the content is necessarily 20% by mass or less, preferably 18% by mass or less, and particularly preferably 15% by mass or less; in addition, although not particularly limited in the embodiments 2 and 3, the content is preferably 20% by mass or less, more preferably 18% by mass or less, and still more preferably 15% by mass or less. If the content is too large, the battery capacity decreases and a high output may not be obtained.
[ [ adhesive ] ]
The binder used for producing the positive electrode active material layer is not particularly limited, and when the coating method is used, it is sufficient if it is a material that can be dissolved or dispersed in a liquid medium used for producing the electrode, and specific examples thereof include the same ones as described above.
The proportion of the binder in the positive electrode active material layer is usually 0.1% by mass or more, preferably 1% by mass or more, and more preferably 3% by mass or more, and the upper limit thereof is usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and further preferably 10% by mass or less. If the proportion of the binder is too low, the positive electrode active material may not be sufficiently retained, the mechanical strength of the positive electrode may be insufficient, and the battery performance such as cycle characteristics may be deteriorated. On the other hand, if the proportion of the binder is too high, a decrease in battery capacity or conductivity may sometimes result.
[ [ liquid medium for forming a slurry ] ]
The liquid medium used for forming the slurry is not particularly limited as long as it is a solvent capable of dissolving or dispersing the positive electrode active material, the conductive agent, the binder, and the thickener used as needed, and any of an aqueous solvent and an organic solvent can be used. Specific examples thereof include those similar to the above. The kind and amount of the tackifier are the same as those described above.
[ [ compaction ] ]
In order to increase the packing density of the positive electrode active material, the positive electrode active material layer obtained by coating and drying is preferably compacted by a manual press, a roll press, or the like. The lower limit of the density of the positive electrode active material layer in embodiment 2 must be 1.7g/cm3Above, preferably 2.0g/cm3Above, 2.2g/cm is particularly preferable3The above; the ratio of 1.7g/cm is not particularly limited in embodiments 1 and 33Above, more preferably 2.0g/cm3Above, more preferably 2.2g/cm3The above. If the density is less than this range, the conductivity between the active materials decreases, the battery impedance increases, and a high output may not be obtained.
The upper limit of the density of the positive electrode active material layer in embodiment 2 must be 3.5g/cm 3Hereinafter, it is preferably 3.0g/cm3Hereinafter, 2.8g/cm is particularly preferable3The following; in addition, in the embodiments 1 and 3, there is no particular descriptionIs limited, but is preferably 3.5g/cm3Hereinafter, more preferably 3.0g/cm3Hereinafter, more preferably 2.8g/cm3The following. If the density is higher than this range, the permeability of the nonaqueous electrolytic solution into the vicinity of the current collector/active material interface is reduced, and particularly, the charge-discharge characteristics at a high current density are reduced, and thus, a high output may not be obtained.
[ [ Current collector ] ]
The material of the positive electrode current collector is not particularly limited, and is the same as described above. The shape of the current collector and the thickness of the thin film are also the same as described above.
The value of the ratio of the thicknesses of the positive electrode active material layer and the current collector (the thickness of the active material layer on the one side before the nonaqueous electrolyte solution is injected)/(the thickness of the current collector) in embodiment 3 must be 20 or less, preferably 15 or less, and particularly preferably 10 or less; although not particularly limited in embodiments 1 and 2, the content is preferably 20 or less, more preferably 15 or less, and particularly preferably 10 or less. If the amount exceeds this range, the collector may generate heat due to joule heat during high current density charging and discharging, and the positive electrode may be damaged.
The lower limit of the value of (thickness of active material layer on the side before injecting the nonaqueous electrolytic solution)/(thickness of current collector) must be 1.6 or more, preferably 1.8 or more, and particularly preferably 2 or more in embodiment 1; further, although not particularly limited in the embodiments 1 and 2, the number is preferably 1.6 or more, more preferably 1.8 or more, and further preferably 2 or more. If the amount is less than this range, the volume ratio of the current collector to the positive electrode active material increases, and the capacity of the battery decreases, and high output may not be obtained.
If the above-mentioned "content of the conductive material in the positive electrode active material layer", "density of the positive electrode active material layer", "thickness ratio of the positive electrode active material layer to the current collector, that is, the value of (thickness of the active material layer on the side before the nonaqueous electrolytic solution is injected)/(thickness of the current collector)" are combined in the respective preferable ranges, a more preferable high-output lithium secondary battery can be formed.
[ [ electrode area ] ]
In the case of using the nonaqueous electrolytic solution of the present invention, it is preferable that the area of the positive electrode active material layer is larger than the outer surface area of the battery case from the viewpoint of high output and improvement of stability at high temperature, which are the same as described above.
[ [ discharge capacity ] ])
When the nonaqueous electrolyte solution for a secondary battery of the present invention is used, it is preferable that the capacity of the battery element (the capacity when the battery is discharged from a fully charged state to a discharged state) contained in the battery case of 1 secondary battery is 3 ampere hours (Ah) or more, since the effect of improving the output characteristics is large.
Therefore, the design and the like of the positive electrode plate and the like are also the same as described above.
[ [ thickness of positive electrode plate ] ]
The thickness of the positive electrode plate is not particularly limited, and is the same as described above.
Positive electrode (5)
Next, the positive electrode [5] used in the lithium secondary battery of the present invention will be described.
[ Positive electrode active Material for Positive electrode [5]
Next, a positive electrode active material used in the positive electrode [5] will be described.
[ [ composition ] ]
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. The material containing lithium and at least one transition metal is preferable, and examples thereof include a lithium-transition metal complex oxide and a lithium-containing transition metal phosphate compound.
As the transition metal of the lithium-transition metal composite oxide, V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable, and specific examples thereof include LiCoO 2And the like lithium-cobalt composite oxides; LiNiO2And the like lithium-nickel composite oxides; LiMnO2、LiMn2O4、Li2MnO3And lithium-manganese composite oxides; by substituting a part of transition metal atoms forming the main body of the lithium-transition metal composite oxide with another metal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, or SiThe resulting substance, and the like.
The lithium-cobalt composite oxide is not particularly limited, but is preferably a lithium-cobalt composite oxide having a composition represented by the following composition formula (8).
LixCo(1-y)M1 yO2Component formula (8)
[ in the compositional formula (8), M1Represents at least one element selected from the group consisting of Ni, Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8]。
In the compositional formula (8), M1Particularly, Ni, Mn, Al and Fe are preferable, and x is particularly preferably 0.2. ltoreq. x.ltoreq.1.15 and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.5.
The lithium-nickel composite oxide is not particularly limited, but is preferably a lithium-nickel composite oxide having a composition represented by the following composition formula (9).
LixNi(1-y)M2 yO2Component formula (9)
[ in the compositional formula (9), M2Represents at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8 ]。
In the compositional formula (9), M2Co, Mn, Al and Fe are particularly preferable, and x is particularly preferably 0.2. ltoreq. x.ltoreq.1.15 and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.5.
The lithium-manganese composite oxide is not particularly limited, but is preferably a lithium-manganese composite oxide having a composition represented by the following composition formula (10).
LixMn(1-y)M3 yO2Component formula (10)
[ in the compositional formula (10), M3Represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8]。
In the compositional formula (10), M3Particularly, Ni, Co, and Fe are preferable, and x is particularly preferably 0.2. ltoreq. x.ltoreq.1.15, and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.7.
The lithium-manganese composite oxide is preferably a material having a composition represented by the following composition formula (11).
LixMn(2-y)M4 yO4Component formula (11)
[ in the compositional formula (11), M4Represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8]。
In the compositional formula (11), M4Particularly, Ni, Co, Al and Mg are preferable, and x is particularly preferably 0.05. ltoreq. x.ltoreq.1.15 and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.7.
The lithium-manganese composite oxide is preferably a material having a composition represented by the following composition formula (12).
LixMn(1-y)M5 yO3Component formula (12)
[ in the compositional formula (12), M5Represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.2.4, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8]。
In the compositional formula (12), M5Particularly, Ni, Co, Al and Mg are preferable, and x is particularly preferably 0.1. ltoreq. x.ltoreq.2.3 and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.5.
The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, or the like, and specific examples thereof include LiFePO4、Li3Fe2(PO4)3、 LiFeP2O7And the like; LiCoPO4Cobalt phosphates, etc.; and those obtained by substituting a part of the transition metal atoms forming the main body of the lithium-containing transition metal phosphate compound with another metal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, or Si.
The iron phosphate is not particularly limited, but is preferably a substance having a composition represented by the following composition formula (13).
LixFe(1-y)M6 yPO4Component formula (13)
[ in the compositional formula (13), M6Represents at least one element selected from the group consisting of Ni, Co, Mn, Al, Ti, Mg, Cr, Ga, Cu, Zn and Nb, x represents a number satisfying 0 < x.ltoreq.1.2, and y represents a number satisfying 0.05. ltoreq. y.ltoreq.0.8 ]。
In the compositional formula (13), M6Particularly, Ni, Co, Mn and Al are preferable, and x is particularly preferably 0.2. ltoreq. x.ltoreq.1.15 and y is particularly preferably 0.1. ltoreq. y.ltoreq.0.5.
In the present invention, it is preferable to use 2 or more species of the positive electrode active material having different compositions in combination at arbitrary combinations and ratios. Since the respective performances of each positive electrode active material are different, it is preferable that the positive electrode active materials combine required performances according to the intended use of the battery. In general, it is considered that the performance can be averaged by combination, but the effect of the positive electrode active material having a long life can be further obtained unexpectedly in terms of life, and the high-output, large-capacity, and long-life lithium secondary battery of the present invention can be realized by combination of the positive electrode active material having a relatively good life and the positive electrode active material having a relatively poor life but having other good performances.
Examples of preferred combinations include the following combinations:
a positive electrode active material represented by the composition formula (8), a positive electrode active material represented by the composition formula (10),
A positive electrode active material represented by the composition formula (8), a positive electrode active material represented by the composition formula (11),
A positive electrode active material represented by the composition formula (8), a positive electrode active material represented by the composition formula (12),
A positive electrode active material represented by the composition formula (8), a positive electrode active material represented by the composition formula (13),
A positive electrode active material represented by the composition formula (9), a positive electrode active material represented by the composition formula (10),
A positive electrode active material represented by the composition formula (9), a positive electrode active material represented by the composition formula (11),
A positive electrode active material represented by the composition formula (9), a positive electrode active material represented by the composition formula (12),
A positive electrode active material represented by the composition formula (9), a positive electrode active material represented by the composition formula (13),
A positive electrode active material represented by the composition formula (10), a positive electrode active material represented by the composition formula (11),
A positive electrode active material represented by the composition formula (10), a positive electrode active material represented by the composition formula (12),
A positive electrode active material represented by the composition formula (10) and a positive electrode active material represented by the composition formula (13).
It is particularly preferred that the first and second substrates are,
a positive electrode active material represented by the composition formula (9), a positive electrode active material represented by the composition formula (11),
A positive electrode active material represented by the composition formula (10) and a positive electrode active material represented by the composition formula (11).
The combination ratio is not particularly limited, but is preferably 10:90 to 90:10, more preferably 20:80 to 80: 20.
The positive electrode used in the lithium secondary battery of the present invention contains 2 or more positive electrode active materials having different compositions, and preferably at least one of the positive electrode active materials has BET specific surface area, average primary particle diameter, and median particle diameter d 50And/or tap density (hereinafter, abbreviated as "physical properties") is within the following specific range. The positive electrode active material having 2 or more types of positive electrode active materials with different compositions includes a positive electrode active material having certain physical properties out of the following ranges, but preferably all of the positive electrode active materials having 2 or more types of positive electrode active materials have certain physical properties in the following ranges. The content ratio of "all the positive electrode active materials having any of the following physical properties within the following specific ranges" to "all the positive electrode active materials contained in the positive electrode" depends on the physical properties thereof, and is not particularly limited, but is preferably 30% by mass or more, more preferably 50% by mass or more, and particularly preferably all of them. Each of the 2 or more positive electrode active materials contained in the positive electrode preferably has one or more physical properties within the following specific ranges, more preferably has one or more physical properties within the following specific ranges, and particularly preferably has one or more physical properties within the following specific rangesThe 3 or more physical properties fall within the following specific ranges, and most preferably all of the following physical properties fall within the following specific ranges.
[ [ BET specific surface area ] ]
At least one positive electrode active material among the positive electrode active materials preferably has a BET specific surface area of 0.4m 2A value of at least one per gram, more preferably 0.5m2A value of at least one per gram, more preferably 0.6m2More than g, with an upper limit of 2m2A ratio of 1.8m or less per gram2A ratio of 1.5m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the BET specific surface area is smaller than this range, the battery performance tends to be lowered, whereas if the BET specific surface area is larger than this range, the tap density tends to be difficult to increase, and there may be a case where a problem tends to occur in coatability when forming the positive electrode active material.
The BET specific surface area is defined as the following value: a value measured by a nitrogen adsorption BET 1 point method by a gas flow method using a nitrogen helium mixed gas properly adjusted to a relative pressure value of nitrogen to atmospheric pressure of 0.3 after pre-drying a sample at 150 ℃ for 30 minutes under a nitrogen flow using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research).
[ [ average primary particle diameter ] ]
The average primary particle size of at least one of the positive electrode active materials is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and most preferably 0.4 μm or more, and the upper limit thereof is preferably 2 μm or less, more preferably 1.6 μm or less, even more preferably 1.3 μm or less, and most preferably 1 μm or less. If the amount exceeds the upper limit, spherical secondary particles are difficult to form, and the powder filling property is adversely affected, or the specific surface area is greatly reduced, so that the possibility of deterioration in battery performance such as output characteristics may be increased. On the other hand, if the amount is less than the lower limit, the crystallization is generally incomplete, and therefore, problems such as poor reversibility of charge and discharge may occur.
In addition, the primary particle diameter can be measured by observation using a Scanning Electron Microscope (SEM). Specifically, the following method was used to obtain: in the photographs of 10000 times magnification, the longest value of the slice generated by the left and right boundary lines of the primary particle on the horizontal straight line was obtained for any 50 primary particles, and the average value was taken. Although the primary particles may aggregate to form the secondary particles, in this case, only the primary particles are measured.
[ [ median particle diameter d ]50]]
The median diameter d of the particles of at least one positive electrode active material in the positive electrode active material50(secondary particle diameter when the primary particles are aggregated to form secondary particles) is preferably 1 μm or more, more preferably 1.2 μm or more, further preferably 1.5 μm or more, and most preferably 2 μm or more, and its upper limit is preferably 20 μm or less, more preferably 18 μm or less, further preferably 16 μm or less, and most preferably 15 μm or less. If the amount is less than the lower limit, a product having a high tap density may not be obtained, while if the amount exceeds the upper limit, it takes time for lithium in the particles to diffuse, which may result in a decrease in battery performance, or may cause problems such as streaks when a positive electrode for a battery, that is, when an active material, a conductive agent, a binder, or the like is slurried in a solvent and then applied in a film form. Here, 2 or more kinds of particles having different median diameters d are mixed 50The positive electrode active material of (3) can further improve the filling property in the production of a positive electrode.
Median diameter d in the present invention50The particle size distribution can be measured by a known laser diffraction/scattering particle size distribution measuring apparatus. While LA-920 manufactured by HORIBA Inc. was used as a particle size distribution meter, a 0.1 mass% aqueous solution of sodium hexametaphosphate was used as a dispersion medium for measurement, ultrasonic dispersion was performed for 5 minutes, and then the refractive index was measured with a setting of 1.24.
[ [ [ tap density ] ] ]
The tap density of at least one positive electrode active material in the positive electrode active materials is preferably 1.3g/cm3Above, more preferably 1.5g/cm3Above, more preferably 1.6g/cm3Above, most preferably 1.7g/cm3The above. When the tap density of the positive electrode active material is less than the lower limit, the positive electrode active material is formedIn the case of the positive electrode active material layer, the amount of the dispersion medium required is increased, and the amount of the conductive material or the binder required is increased, so that the filling rate of the positive electrode active material in the positive electrode active material layer is limited, and the battery capacity is sometimes limited. By using the composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. Generally, the higher the tap density, the more preferable the tap density is, there is no particular upper limit, but if the tap density is too large, the diffusion of lithium ions in the positive electrode active material layer using the nonaqueous electrolytic solution as a medium becomes a factor determining the rate, and the load characteristic is likely to be lowered in some cases, so the upper limit of the tap density is preferably 2.7g/cm 3Hereinafter, more preferably 2.5g/cm3The following.
In the present invention, tap density is defined as follows: the sample was dropped to 20cm through a sieve having an aperture of 300. mu.m3The container volume of (1) was filled, and then a powder density measuring instrument (for example, Tap densitometer manufactured by seishin corporation) was used to vibrate the container 1000 times with a stroke length of 10mm, and the bulk density at this time was defined as Tap density.
[ [ surface coating ] ]
As at least one of the positive electrode active materials, a material having a composition different from that of the positive electrode active material or the positive electrode active material core constituting the main body of the positive electrode active material (hereinafter, simply referred to as "surface-attached material") attached to the surface thereof is preferably used. The kind, method, amount and the like of the surface-adhering substance are the same as those described above.
[ [ shape ] ]
The particle shape of at least one of the positive electrode active materials can be the same as that described above as conventionally used.
[ [ manufacturing method ] ]
As the method for producing the positive electrode active material, a general method as a method for producing an inorganic compound similar to the above can be used.
[ Structure of Positive electrode [5]
The structure of the positive electrode used for the positive electrode [5] will be described below.
In the present invention, the electrode structure and the manufacturing method, the compaction of the positive electrode active material layer, the conductive material, the binder used in the production of the positive electrode active material layer, the liquid medium for forming the slurry, the current collector, the electrode area, the discharge capacity, the thickness of the positive electrode plate, and the like are the same as those described above. The positive electrode active material may be used by mixing 2 or more kinds thereof in advance when the positive electrode is produced, or may be added and mixed at the same time when the positive electrode is produced.
Negative electrode
The negative electrode used in the lithium secondary battery of the present invention is not particularly limited as long as it is a negative electrode in which an active material layer containing an active material capable of absorbing and desorbing lithium ions is formed on a current collector, and the negative electrode is preferably any one negative electrode selected from the following negative electrodes [1] to [10 ]:
negative electrode [1 ]: a negative electrode containing 2 or more carbonaceous materials having different crystallinity as a negative electrode active material;
cathode [2 ]]: a negative electrode comprising, as a negative electrode active material, an amorphous carbon material having a (002) plane interplanar spacing (d002) of 0.337nm or more and a crystallite size (Lc) of 80nm or less as measured by wide-angle X-ray diffraction, and having a particle size of 1360cm as measured by argon ion laser Raman spectroscopy -1Peak intensity of (2) relative to 1580cm-1A Raman R value defined as a ratio of peak intensities of (A) to (B) is 0.2 or more;
negative electrode [3 ]: a negative electrode containing a metal oxide as a negative electrode active material, the metal oxide containing titanium capable of occluding and releasing lithium ions;
negative electrode [4 ]: a negative electrode containing a carbonaceous material as a negative electrode active material, wherein the carbonaceous material has a circularity of 0.85 or more and a surface functional group amount O/C value of 0 to 0.01;
negative electrode [5 ]: a negative electrode containing a heteroorientation carbon composite as a negative electrode active material, the heteroorientation carbon composite containing 2 or more carbonaceous materials having different orientations;
cathode [6 ]]: a negative electrode comprising, as a negative electrode active material, graphitic carbon particles having a circularity of 0.85 or more and an interplanar spacing of (002) plane as measured by wide-angle X-ray diffractionDistance (d002) is less than 0.337nm, as determined by argon ion laser Raman spectroscopy, and is 1360cm-1Relative to 1580cm-1The ratio of the peak intensities defined as a Raman R value of 0.12 to 0.8;
negative electrode [7 ]: a negative electrode containing, as a negative electrode active material, a negative electrode active material (C) containing multiple elements, which contains at least one of a lithium-occluding metal (a) and/or a lithium-occluding alloy (B) selected from Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb, and contains C and/or N as an element Z;
Negative electrode [8 ]: a negative electrode containing 2 or more negative electrode active materials having different properties as a negative electrode active material;
cathode [9 ]]: containing a tap density of 0.1g/cm3A negative electrode containing a negative electrode active material having a pore volume of 0.01mL/g or more, measured by a mercury porosimeter, corresponding to particles having a diameter in the range of 0.01 to 1 μm;
negative electrode [10 ]: when the battery is charged to 60% of the nominal capacity of the negative electrode, the reaction resistance of the counter battery of the negative electrode is 500 Ω or less.
Next, a negative electrode generally used in the lithium secondary battery of the present invention will be described.
[ negative electrode active Material ]
Next, a negative electrode active material generally used for a negative electrode will be described.
[ [ composition ] ]
The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions, and examples thereof include carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as lithium simple substance and lithium aluminum alloy, and metals such as Sn and Si that can be alloyed with lithium. These may be used alone, or 2 or more kinds may be used in combination in any combination and ratio. Among them, a carbonaceous material or a lithium composite oxide is preferably used from the viewpoint of safety.
The metal composite oxide is not particularly limited as long as it can store and release lithium, but preferably contains titanium and/or lithium as a constituent component in view of high current density charge-discharge characteristics.
As the carbonaceous material, the following carbonaceous materials are preferable from the viewpoint of balance of initial irreversible capacity and high current density charge-discharge characteristics:
(1) natural graphite;
(2) artificial carbonaceous matter and artificial graphite matter; a carbonaceous material [ for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or a material obtained by oxidizing these pitches, needle coke, pitch coke, and a carbon material obtained by partially graphitizing these; examples of the organic material include thermal decomposition products of organic materials such as furnace black, acetylene black and pitch-based carbon fibers, and organic materials that can be carbonized (for example, coal-based heavy oil such as coal tar pitch or retort liquefied oil from soft pitch to hard pitch, straight-run heavy oil such as atmospheric residual oil or vacuum residual oil, decomposed petroleum heavy oil such as ethylene tar that is a by-product of thermal decomposition of crude oil or naphtha, aromatic hydrocarbons such as acenaphthene, decacycloolefin, anthracene and phenanthrene, nitrogen-ring compounds such as phenazine and acridine, sulfur-ring compounds such as thiophene and bithiophene, polyphenyls such as biphenyl and terphenyl, organic high molecules such as polyvinyl chloride, polyvinyl alcohol and polyvinyl butyral, insolubilized products thereof, nitrogen-containing polyacrylonitrile and polypyrrole, organic high molecules such as sulfur-containing polythiophene and polystyrene, natural high molecules such as polysaccharides represented by cellulose, lignin, mannose, polygalacturonic acid, chitosan and sucrose, polyphenylene sulfide, carbon black, and carbon black, Thermoplastic resins such as polyphenylene ether; thermosetting resins such as furfuryl alcohol resin, phenol resin, and imide resin) and carbides thereof; or a carbon material formed by heat-treating a carbonizable organic substance once or more at 400 to 3200 ℃ in a solution obtained by dissolving the organic substance in a low-molecular-weight organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane, or a carbide thereof;
(3) The negative electrode active material layer is composed of at least 2 or more carbonaceous materials having different crystallinities, and/or a carbon material in which carbonaceous materials having different crystallinities have a contact interface;
(4) the negative electrode active material layer is composed of at least 2 or more carbonaceous materials having different orientation properties, and/or a carbonaceous material having different orientation properties and having a contact interface.
[ Structure, Properties and production method of negative electrode ]
With respect to the properties of the carbon material, the negative electrode comprising the carbon material, the method of electric polarization, the current collector, and the lithium secondary battery, it is preferable that any one or more items 1 to 9 shown below are satisfied at the same time.
(1) X-ray parameters
The carbon material preferably has a d value (interlayer distance) of a lattice plane (002) of 0.335nm or more as determined by X-ray diffraction using a vibroseis method, and the upper limit thereof is usually 0.36nm or less, preferably 0.35nm or less, and more preferably 0.345nm or less. The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is preferably 1nm or more, and more preferably 1.5nm or more.
(2) Ash content
The ash content in the carbonaceous material is preferably 1 mass% or less, more preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, and the lower limit is preferably 1ppm or more, based on the total mass of the carbonaceous material. If the amount exceeds the above range, deterioration of battery performance due to reaction with the nonaqueous electrolytic solution during charge and discharge cannot be ignored. If it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost sometimes rises.
(3) Volume-based average particle diameter
The volume-based average particle diameter of the carbonaceous material is a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and particularly preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, an uneven coating surface is likely to be formed when the electrode is produced by coating, and this is not preferable in the battery production process.
In the present invention, the volume-based average particle diameter is defined by a median particle diameter, which is determined by the following method: the carbon powder was dispersed in a 0.2 mass% aqueous solution (about 10mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant, and measured using a laser diffraction/scattering particle size distribution meter (for example, LA-700 manufactured by horiba ltd.).
(4) Raman R value, Raman half value width
The R value of the carbonaceous material measured by the argon ion laser raman spectroscopy is usually 0.01 or more, preferably 0.03 or more, more preferably 0.1 or more, and the upper limit thereof is 1.5 or less, preferably 1.2 or less, more preferably 1.0 or less, and further preferably 0.5 or less. If the value of R is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites (サイト) where Li enters between layers may decrease as charging and discharging progresses. That is, the charge acceptance may be reduced. In addition, when the negative electrode is densified by pressing after being coated on a current collector, crystals tend to be oriented in a direction parallel to an electrode plate, and load characteristics may be degraded. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the nonaqueous electrolytic solution is increased, and the efficiency may be lowered or the amount of generated gas may be increased.
In addition, the carbonaceous material is 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 10cm-1Above, preferably 15cm-1Above, its upper limit is usually 100cm-1Hereinafter, preferably 80cm-1Hereinafter, more preferably 60cm-1Hereinafter, more preferably 40cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites (サイト) where Li enters between layers may decrease with charge and discharge. That is, the charge acceptance may be reduced. In addition, when the negative electrode is densified by pressing after being coated on a current collector, crystals tend to be oriented in a direction parallel to the electrode plate, which may result in a decrease in load characteristics. In addition On the other hand, if it is higher than this range, the crystallinity of the particle surface is lowered, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in generated gas.
The raman spectrum was measured as follows: a sample is naturally dropped and filled in a measurement cell (cell) using a raman spectrometer (for example, a raman spectrometer manufactured by japan spectroscopy), and the surface of the sample in the cell is irradiated with an argon ion laser while the cell is rotated in a plane perpendicular to the laser. For the obtained Raman spectrum, 1580cm was measured-1Nearby peak PAStrength I ofAAnd 1360cm-1Nearby peak PBStrength I ofBCalculating the intensity ratio R (R ═ I)B/IA) It is defined as the raman R value of the carbonaceous material. The Raman spectrum obtained by measurement was 1580cm-1Nearby peak PAIs defined as the raman half-value width of the carbonaceous material.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10-20 cm-1
Measurement range: 1100cm-1～1730cm-1
R-value, half-value width analysis: background (background) treatment
Smoothing (smoothening) process: simple average, convolution 5 points (コンボリュション 5 ポイント)
(5) BET specific surface area
The specific surface area of the carbonaceous material of the present invention measured by the BET method is usually 0.1m2A ratio of 0.7m or more2A value of at least g, more preferably 1.0m2A total of 1.5m or more2More than g. Its upper limit is typically 100m2A ratio of 25m or less per gram2A ratio of 15m or less per gram2A total of 10m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. When the specific surface area is less than the above range, the negative electrode is usedLithium acceptance during charging is poor, and lithium is likely to precipitate on the electrode surface. On the other hand, if it is higher than the above range, the reactivity with the nonaqueous electrolytic solution increases when used as a negative electrode material, and the amount of generated gas tends to increase, and it may be difficult to obtain a preferable battery.
The specific surface area measured by the BET method uses a value determined as follows: the sample was preliminarily dried at 350 ℃ for 15 minutes under a nitrogen gas flow using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research), and then measured by a nitrogen adsorption BET 1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
(6) Micro pore size distribution
The pore size distribution of the carbonaceous material used in the present invention is an amount corresponding to voids in particles having a pore diameter of 0.01 to 1 μm, irregularities due to irregularities on the particle surface, contact surfaces between particles, and the like, which are determined by a mercury porosimeter (mercury intrusion method), of 0.01mL/g or more, preferably 0.05mL/g or more, more preferably 0.1mL/g or more, and an upper limit thereof is 0.6mL/g or less, preferably 0.4mL/g or less, more preferably 0.3mL/g or less. If the amount exceeds this range, a large amount of binder may be required for producing the electrode plate. If the amount is less than this range, the high-current-density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total pore volume corresponding to the pore diameter in the range of 0.01 to 100 μm is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and still more preferably 0.4mL/g or more, and the upper limit thereof is 10mL/g or less, preferably 5mL/g or less, and more preferably 2mL/g or less. If it is higher than this range, a large amount of binder is sometimes required in manufacturing the electrode plate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained in the production of the electrode plate.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. If the amount is less than this range, the high current density charge-discharge characteristics may be deteriorated.
As a device used as a mercury porosimeter, a mercury porosimeter (autopore (オートポア) 9520; manufactured by micromeritics (マイクロメリテックス)) can be used. About 0.2g of the sample was sealed in a powder container, and degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes to carry out pretreatment. Subsequently, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased from 4psia (about 28kPa) to 40000psia (about 280MPa) in a stepwise manner, and then the pressure was reduced to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore diameter distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 degrees. The average pore diameter is the pore diameter at which the cumulative pore volume reaches 50%.
(7) Degree of circularity
The circularity is taken as the degree of sphericity of the carbonaceous material, and the circularity of particles having a particle diameter in the range of 3 to 40 μm is preferably 0.1 or more, particularly preferably 0.5 or more, more preferably 0.8 or more, further preferably 0.85 or more, and most preferably 0.9 or more. A large circularity is preferable because high current density charge/discharge characteristics are improved.
The circularity is defined by the following formula, and a theoretical true sphere is obtained when the circularity is 1.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the value measured as follows was used: for example, particles having a particle size in the range of 3 to 40 μm were measured by dispersing about 0.2g of a sample in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant using a flow-type particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial (シスメックスインダストリアル)), irradiating the sample with ultrasonic waves of 28kHz for 1 minute at an output of 60W, and determining that the ultrasonic waves had a detection range of 0.6 to 400 μm.
The method for increasing the circularity is not particularly limited, but is preferably a method in which the electrode body is formed by performing a spheroidizing treatment (mechanical energy treatment) to make the particles spherical, so that the shape of the voids between the particles can be made uniform when the electrode body is formed. Examples of the spheroidizing treatment include a method of mechanically approximating a spherical shape by applying a shearing force or a compressive force, a mechanical/physical treatment method of granulating a plurality of fine particles by an adhesive or an adhesive force of the particles themselves, and the like.
(8) True density
The carbonaceous material typically has a true density of 1.4g/cm3Above, preferably 1.6g/cm3Above, more preferably 1.8g/cm3Above, more preferably 2.0g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase. In the present invention, the true density is defined as a value measured by a liquid phase substitution method (a gravimetric method) using butanol.
(9) Tap density
The tap density of the carbonaceous material is usually 0.1g/cm3Above, preferably 0.5g/cm3Above, more preferably 0.7g/cm3Above, 1.0g/cm is particularly preferable3The above. Further, the upper limit thereof is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, the packing density is difficult to increase when the negative electrode is used, and a high-capacity battery may not be obtained. On the other hand, if the amount exceeds this range, the number of voids between particles in the electrode is too small, and it is difficult to ensure conductivity between particles, and it may be difficult to obtain preferable battery characteristics. The tap density is measured by the same method as that described in the positive electrode, and is defined by this method.
(10) Orientation ratio
The orientation ratio of the carbonaceous material is usually 0.005 or more, preferably 0.01 or more, and more preferably 0.015 or more, and the upper limit thereof is in the range of 0.67 or less of the theoretical value. If the amount is less than this range, the high-density charge-discharge characteristics may be degraded.
The orientation ratio was measured by X-ray diffraction after the sample was pressure molded. 0.47g of the sample was charged into a molding machine having a diameter of 17mm at 600kgf/cm2The molded body was obtained by compression, fixed with clay so as to be flush with the surface of the sample holder for measurement, and then measured for X-ray diffraction. From the peak intensities of the (110) diffraction and the (004) diffraction of the obtained carbon, a ratio expressed as (110) diffraction integrated intensity/(004) diffraction integrated intensity is calculated, and the ratio is defined as an orientation ratio of the active material.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit:
divergence slit of 0.5 degree, light acceptance slit of 0.15mm, and scattering slit of 0.5 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 75 degrees is less than or equal to 2 theta and less than or equal to 80 degrees 1 degree/60 seconds
(004) Dough making: 2 theta is more than or equal to 52 degrees and less than or equal to 57 degrees and 1 degree/60 seconds
(11) Aspect ratio (powder)
The aspect ratio is theoretically 1 or more, and the upper limit is 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks may occur during the production of the electrode plate, and a uniform coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the carbonaceous material particles to the shortest diameter B perpendicular thereto in three-dimensional observation. The carbon particles were observed by a scanning electron microscope which allows observation with magnification. Arbitrary 50 graphite particles fixed to the end face of a metal plate having a thickness of 50 μm or less were selected, a stage on which a sample was fixed was rotated and tilted, A, B of each particle was measured, and the average value of a/B was determined.
(12) Mixing of auxiliary materials
The term "mixed with the auxiliary material" means that 2 or more carbonaceous materials having different properties are contained in the negative electrode and/or the negative electrode active material. The properties referred to herein include one or more of X-ray diffraction parameters, median particle diameter, aspect ratio, BET specific surface area, orientation ratio, raman R value, tap density, true density, micropore distribution, circularity, and ash content.
Particularly preferred embodiments include a volume-based particle size distribution which is asymmetric about the median particle diameter, contains 2 or more types of carbonaceous materials having different raman R values, and has different X-ray parameters.
Examples of the effects include the incorporation of graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbonaceous materials such as amorphous carbon, such as needle coke, can be used as a conductive agent to reduce the resistance. These may be used alone, or may be used in combination of 2 or more in any combination and in any ratio. When added as a conductive agent, the content is 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more, and the upper limit thereof is 45% by mass or less, and preferably 40% by mass. If the content is less than this range, the effect of improving the conductivity may be difficult to obtain. If the amount is more than the above range, the initial irreversible capacity may increase.
(13) Electrode fabrication
The electrode can be formed by a conventional method. For example, a binder, a solvent, and, if necessary, a thickener, a conductive material, a filler, etc. are added to the negative electrode active material to prepare a slurry, and the slurry is applied to a current collector, dried, and pressed to form an electrode. The thickness of the negative electrode active material on each surface of the battery at the stage before the nonaqueous electrolyte injection step is usually 15 μm or more, preferably 20 μm or more, and more preferably 30 μm or more, and the upper limit thereof is 150 μm or less, preferably 120 μm or less, and more preferably 100 μm or less. If the amount exceeds this range, the nonaqueous electrolytic solution is less likely to penetrate into the vicinity of the interface of the current collector, and therefore, the high-current-density charge/discharge characteristics are degraded. If the amount is less than this range, the volume ratio of the current collector to the negative electrode active material increases, and the battery capacity may decrease. The negative electrode active material may be roll-molded to form a sheet electrode, or may be compression-molded to form a pellet electrode.
(14) Current collector
As the current collector, a known current collector can be arbitrarily used. As the current collector of the negative electrode, metal materials such as copper, nickel, stainless steel, nickel-plated steel, and the like can be cited, and among them, copper is preferable from the viewpoint of easy processing and cost. When the collector is made of a metal material, examples of the shape of the collector include a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded alloy, a perforated metal, and a foamed metal. Among these, a metal thin film is preferable, a copper foil is more preferable, and a rolled copper foil produced by a rolling method and an electrolytic copper foil produced by an electrolytic method are further preferable, and both can be used as the current collector. When the thickness of the copper foil is thinner than 25 μm, a copper alloy (phosphor bronze, titanium copper, corson alloy, Cu — Cr — Zr alloy, or the like) having a higher strength than pure copper can be used. Further, aluminum foil is preferably used because it has a low specific gravity and can reduce the weight of a battery when used for a current collector.
In the current collector made of the copper foil produced by the rolling method, since copper crystals are aligned in the rolling direction, the current collector is less likely to break even if the negative electrode is bent tightly or bent at an acute angle, and is suitable for a small cylindrical battery. The electrolytic copper foil is prepared as follows: for example, a drum made of a metal is immersed in a nonaqueous electrolytic solution in which copper ions are dissolved, and current is applied while the drum is rotated, whereby copper is deposited on the surface of the drum and then peeled off. Copper may be deposited on the surface of the rolled copper foil by electrolytic method. One or both surfaces of the copper foil may be subjected to roughening treatment or surface treatment (e.g., chromate treatment with a thickness of about several nm to 1 μm, primer treatment with Ti, etc.).
The current collector substrate is required to have the following properties.
(1) Average surface roughness (Ra)
The average surface roughness (Ra) of the active material thin film-formed surface of the current collector substrate defined by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.05 μm or more, preferably 0.1 μm or more, and particularly preferably 0.15 μm or more, and the upper limit thereof is usually 1.5 μm or less, preferably 1.3 μm or less, and particularly preferably 1.0 μm or less. By setting the average surface roughness (Ra) of the current collector substrate within the range between the lower limit and the upper limit, good charge-discharge cycle characteristics can be expected. By setting the lower limit value or more, the interface area with the active material thin film becomes large, and the adhesion with the active material is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, and when the average surface roughness (Ra) exceeds 1.5. mu.m, it is difficult to obtain a foil having a thickness suitable for a battery, and therefore, it is preferably 1.5 μm or less.
(2) Tensile strength
The tensile strength of the current collector substrate is not particularly limited, but is usually 100N/mm2Above, preferably 250N/mm2Above, more preferably 400N/mm2Above, 500N/mm is particularly preferable 2As above. The tensile strength is a value obtained by dividing the maximum tensile force required for the test piece to break by the cross-sectional area of the test piece. The tensile strength in the present invention can be measured by the same apparatus and method as those for measuring the elongation. If the collector substrate has a high tensile strength, cracks in the collector substrate due to expansion and contraction of the active material film during charge and discharge can be suppressed, and good cycle characteristics can be obtained.
(3) 0.2% proof stress
The 0.2% proof stress of the current collector substrate is not particularly limited, but is usually 30N/mm2Above, preferably 150N/mm2Above, 300N/mm is particularly preferable2The above. The 0.2% proof stress is a load required to generate a plastic (permanent) deformation of 0.2%, and after applying the load of this magnitude, the deformation of 0.2 is maintained even when the load is removed. The 0.2% proof stress in the present invention can be measured by the same apparatus and method as the elongation. If the current collector substrate has a high proof stress of 0.2%, plastic deformation of the current collector substrate due to expansion/contraction of the active material film during charge/discharge can be suppressed, and good cycle characteristics can be obtained.
The thickness of the metal thin film is arbitrary, and is usually 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more. The upper limit is usually 1mm or less, preferably 100 μm or less, and more preferably 30 μm or less. When the thickness is smaller than 1 μm, the strength is lowered and the coating may be difficult. Further, if the thickness is larger than 100 μm, the shape of the electrode may be deformed such as curled. In addition, the metal thin film may be a mesh.
(15) Ratio of thicknesses of current collector and active material layer
The ratio of the thicknesses of the current collector and the active material layer (the thickness of the active material layer on the side before the nonaqueous electrolytic solution is injected)/(the thickness of the current collector) is not particularly limited, and is preferably 150 or less, particularly preferably 20 or less, more preferably 10 or less, and the lower limit thereof is preferably 0.1 or more, more preferably 0.4 or less, and further preferably 1 or more. If the amount exceeds this range, the collector may generate heat due to joule heat during high current density charging and discharging. If the amount is less than this range, the volume ratio of the current collector to the negative electrode active material may increase, resulting in a decrease in the battery capacity.
(16) Electrode density
The electrode structure when the negative electrode active material is formed into an electrode is not particularly limited, and the density of the active material existing on the current collector is preferably 1.0g/cm3Above, more preferably 1.2g/cm3Above, more preferably 1.3g/cm3Above, the upper limit is usually 2.0g/cm3Hereinafter, it is preferably 1.9g/cm3Hereinafter, more preferably 1.8g/cm3Hereinafter, more preferably 1.7g/cm3The following ranges. If the amount exceeds this range, the active material is destroyed, leading to an increase in initial irreversible capacity and a decrease in the permeability of the nonaqueous electrolytic solution into the vicinity of the current collector/active material interface, and thus to deterioration of high-current-density charge/discharge characteristics. If the amount is less than this range, the conductivity between the active materials decreases, the battery resistance increases, and the battery capacity per unit volume may decrease.
(17) Adhesive agent
The binder for binding the active material is not particularly limited as long as it is a material that is stable to the nonaqueous electrolytic solution or the solvent used in the production of the electrode. Specific examples thereof include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), styrene-propylene rubber, and the like; a styrene-butadiene-styrene block copolymer or a hydrogenated product thereof; thermoplastic elastomer-like polymers such as EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-styrene copolymer, styrene-isobutylene-styrene block copolymer, or hydrogenated product thereof; soft resinous polymers such as syndiotactic 1,2 polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene- α -olefin copolymer and the like; fluorine polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer; and a polymer composition having ion conductivity of alkali metal ions (particularly lithium ions). These may be used alone, or may be used in combination of 2 or more in any combination and ratio.
The solvent used for forming the slurry is not particularly limited as long as it can dissolve or disperse the active material, the binder, and the thickener and the conductive agent used as needed, and any of an aqueous solvent and an organic solvent can be used. Examples of the aqueous solvent include water, alcohol, and the like; examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N-dimethylaminopropylamine, propylene oxide, Tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphoramide, dimethylsulfide, benzene, xylene, quinoline, pyridine, methylnaphthalene, and hexane. In particular, when an aqueous solvent is used, the thickener, the dispersant and the like are added together, and a latex such as SBR is used for slurrying. These may be used alone, or 2 or more kinds may be used in combination in any combination and ratio.
The proportion of the binder to the active material is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and more preferably 0.6% by mass or more, and the upper limit thereof is usually 20% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 8% by mass or less. If the amount of the binder exceeds this range, the proportion of the binder that does not contribute to the battery capacity increases, and the battery capacity may be reduced. If the content is less than the above range, the strength of the negative electrode may be reduced. In particular, when the main component contains a rubbery polymer represented by SBR, the proportion of the binder to the active material is usually 0.1 mass% or more, preferably 0.5 mass% or more, and more preferably 0.6 mass% or more, and the upper limit thereof is usually 5 mass% or less, preferably 3 mass% or less, and more preferably 2 mass% or less. When a fluorine-based polymer represented by polyvinylidene fluoride is contained as the main component, the proportion of the binder to the active material is usually 1 mass% or more, preferably 2 mass% or more, and more preferably 3 mass% or more, and the upper limit thereof is usually 15 mass% or less, preferably 10 mass% or less, and more preferably 8 mass% or less.
Thickeners are commonly used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specifically, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof, and the like can be mentioned. These may be used alone, or 2 or more kinds may be used in combination in any combination and ratio. When the thickener is added, the proportion of the thickener to the active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit thereof is usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. If the content is less than this range, the coatability may be significantly reduced. If the amount exceeds this range, the proportion of the active material in the negative electrode active material layer decreases, which may cause a problem of a decrease in battery capacity or a problem of an increase in resistance between the negative electrode active materials.
(18) Orientation ratio of polar plate
The plate orientation ratio is preferably 0.001 or more, more preferably 0.005 or more, and particularly preferably 0.01 or more, and the upper limit is 0.67 or less, which is a theoretical value. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
The plate orientation ratio was measured as follows. And measuring the orientation ratio of the active material of the electrode by X-ray diffraction on the cathode electrode pressed into the target density. The specific method is not particularly limited, and as a standard method, peaks of the (110) diffraction and the (004) diffraction of carbon obtained by X-ray diffraction are fitted using asymmetric pearson (ピアソン) VII as a distribution (profile) function to perform peak separation, and integrated intensities of the peaks of the (110) diffraction and the (004) diffraction are calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated. The active material orientation ratio of the electrode calculated by this measurement is defined as a plate orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha line) graphite monochrometer
Slit: divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
Sample preparation: the electrodes were fixed to the glass plate by means of a double-sided adhesive tape having a thickness of 0.1mm
(19) Impedance (L)
The impedance of the negative electrode when charged from a discharged state to 60% of the nominal capacity is preferably 100 Ω or less, more preferably 50 Ω or less, particularly preferably 20 Ω or less, and/or the electric double layer capacity is preferably 1 × 10-6F or more, more preferably 1X 10-5F, particularly preferably 1X 10-4F. This range is preferable because of its good output characteristics.
The negative electrode resistance and the electric double layer capacity were measured by the following methods. The lithium secondary battery to be tested used the following batteries: after charging at a current value capable of charging to a nominal capacity in 5 hours, the battery is maintained for 20 minutes without charging and discharging, and then, the battery is discharged at a current value capable of discharging the nominal capacity in 1 hour, wherein the capacity at that time is 80% or more of the nominal capacity. For the lithium secondary battery in the above-described discharged state, the lithium secondary battery was immediately transferred into a spherical container under an argon atmosphere by being charged to 60% of the nominal capacity at a current value capable of being charged to the nominal capacity in 5 hours. The lithium secondary battery was rapidly disassembled without discharge or short circuit, and the negative electrode was taken out, and if the electrode was a double-coated electrode, the electrode active material on one side was peeled without damaging the electrode active material on the other side, 2 negative electrode electrodes were punched to 12.5mm phi, and the active material surfaces were opposed without a gap by sandwiching a separator. 60. mu.L of nonaqueous electrolyte used in the battery was dropped between the separator and the two negative electrodes, and bonded to each other while keeping the separator in a state of not contacting the outside, and the current collectors of the two negative electrodes were made conductive to carry out an AC impedance method. The measurement was carried out at a temperature of 25 ℃ and at 10 ℃ -2～105The complex impedance is measured in the frequency band of Hz, and the surface resistance (R) and the electric double layer capacity (Cd1) are determined by approximating the arc of the negative electrode resistance component of call, plot determined to be a semicircle.
(20) Area and thickness of the negative plate
The area of the negative electrode plate is not particularly limited, and is generally designed to be slightly larger than the opposing positive electrode plate so that the positive electrode plate is not exposed to the outside of the negative electrode plate. From the viewpoint of cycle life of repeated charge and discharge and suppression of deterioration due to high-temperature storage, it is preferable to further increase the proportion of electrodes that operate uniformly and efficiently and to improve the characteristics if the area is as close as possible to the area equal to the positive electrode. In particular, the design of the electrode area is important when used at high currents.
The thickness of the negative electrode plate is not particularly limited, and is designed according to the positive electrode plate to be used, but the thickness of the clad material layer obtained by subtracting the thickness of the metal foil of the core material is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit thereof is usually 150 μm or less, preferably 120 μm or less, more preferably 100 μm or less.
< negative electrode [1] >
Hereinafter, the negative electrode [1] used in the lithium secondary battery of the present invention, "a negative electrode containing 2 or more carbonaceous materials having different crystallinity as a negative electrode active material" will be described.
[ negative electrode active material for negative electrode [1]
Next, the negative electrode active material used for the negative electrode [1] will be described.
[ [ constitution ] ]
The negative electrode active material used for the negative electrode [1] of the lithium secondary battery of the present invention is characterized by containing 2 or more carbonaceous materials having different crystallinities. Here, "containing 2 or more carbonaceous materials having different crystallinity" means that carbonaceous materials having different crystallinity coexist in the negative electrode, and the coexisting form thereof may be a state in which they are present as single particles and mixed together, or may be contained in one secondary particle, or may be a mixture of both. The negative electrode active material preferably contains a composite carbonaceous material containing 2 or more carbonaceous materials having different crystallinities, and more preferably contains, as a sub-material, one or more carbonaceous materials (carbonaceous materials) different from the composite carbonaceous material in terms of carbonaceous physical properties.
The term "contained in one secondary particle" as used herein means a state in which carbonaceous substances having different crystallinity are bound together, a physically constrained state, a state in which the shape is maintained by electrostatic constraint, and the like. The term "physical constraint" as used herein means a state in which one carbonaceous material having different crystallinity is included in another carbonaceous material and is entangled with each other, and the term "electrostatic constraint" means a state in which one carbonaceous material having different crystallinity is attached to another carbonaceous material by electrostatic energy. The "state of being bound by bonding" means chemical bonds such as hydrogen bond, covalent bond, and ionic bond.
Among these, in a state where at least a part of the surface of the carbonaceous material to be the core has an interface with the coating layer having a different crystallinity formed by bonding, the resistance to movement of lithium between the carbonaceous materials having different crystallinity is advantageously small. The coating layer may be formed by bonding with a material supplied from the outside and/or a modified material thereof, or by modifying a material of the surface portion of the carbonaceous substance. Here, the term "cover" means a state in which at least a part of the interface with the surface of the carbonaceous material has a chemical bond, and shows (1) a state in which the entire surface is covered, (2) a state in which the carbon particles are partially covered, (3) a state in which the surfaces are selectively covered, and (4) a state in which the carbon particles are present in a very small region containing a chemical bond. The crystallinity may be changed continuously or discontinuously at the interface.
The composite carbonaceous material preferably has an interface formed by coating a particulate carbonaceous material with a carbonaceous material having a crystallinity different from that of the particulate carbonaceous material, and/or an interface formed by bonding a carbonaceous material having a crystallinity different from that of the particulate carbonaceous material to the particulate carbonaceous material, and the crystallinity of the interface changes continuously and/or discontinuously. The "particulate carbonaceous material" and the "carbonaceous material having a crystallinity different from that of the particulate carbonaceous material" are not particularly limited in that they have high crystallinity, but the above-described effects of the present invention can be achieved when the particulate carbonaceous material has high crystallinity, which is preferable.
The difference in crystallinity is judged by the difference in (002) plane surface distance (d002), the difference in Lc, and the difference in La as measured by an X-ray wide angle diffractometry, and from the viewpoint of the effect of the present invention, the difference in crystallinity is preferably 0.0002nm or more in terms of (d002), or 1nm or more in terms of La, or 1nm or more in terms of Lc. In the above range, the difference in (d002) is preferably 0.0005nm or more, more preferably 0.001nm or more, and still more preferably 0.003nm or more, and the upper limit thereof is usually 0.03nm or less, preferably 0.02nm or less. If the amount is less than this range, the effect of the difference in crystallinity may be reduced. On the other hand, if it exceeds the above range, the crystallinity of the portion having low crystallinity tends to be low, and the irreversible capacity caused by the low crystallinity may be increased. In the above range, the difference in La or Lc is preferably 2nm or more, more preferably 5nm or more, and still more preferably 10nm or more. In general, graphite is undefined at 100nm or more, and therefore, an upper limit cannot be specified. If the amount is less than this range, the effect of the difference in crystallinity may be reduced.
The composite carbonaceous material is obtained by coating and/or bonding a carbonaceous material having crystallinity different from that of the particulate carbonaceous material onto the particulate carbonaceous material, and it is sufficient that either one of the "particulate carbonaceous material" and the "carbonaceous material having crystallinity different from that of the particulate carbonaceous material" is a graphite-based carbonaceous material and the other is a low-crystalline carbonaceous material, and it is preferable that the "particulate carbonaceous material" is a graphite-based carbonaceous material and the "carbonaceous material having crystallinity different from that of the particulate carbonaceous material" is a low-crystalline carbonaceous material.
[ [ [ particulate carbonaceous material ] ] ]
The particulate carbonaceous material is preferably a graphite-based carbonaceous material containing natural graphite and/or artificial graphite, or a carbonaceous material containing at least one selected from the group consisting of (a), (b) and (c) which have slightly lower crystallinity than the graphite-based carbonaceous material,
(a) thermal decomposition products of organic substances selected from coal-based coke, petroleum-based coke, furnace black, acetylene black and pitch-based carbon fiber;
(b) carbides of organic gases;
(c) a carbonaceous material obtained by graphitizing a part or all of (a) or (b).
[ [ [ [ [ carbonaceous matter of graphite class ] ] ] ]
The particulate carbonaceous material is preferably a graphite-based carbonaceous material containing natural graphite and/or artificial graphite. The graphite-like carbonaceous material is a carbonaceous material having high crystallinity in which the (002) plane interplanar spacing (d002) measured by X-ray wide-angle diffraction is less than 0.340 nm.
As specific examples of the graphite-based carbonaceous material, powders selected from the following are preferable: natural graphite, artificial graphite, or mechanically pulverized products thereof, reheat-treated products of expanded graphite, or highly purified products of these graphites. As a specific example of the artificial graphite, one or more organic substances selected from the group consisting of: coal tar pitch, coal-based heavy oil, atmospheric residual oil, petroleum-based heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polystyrene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol resin, imide resin, and the like.
(physical Properties of graphite-based carbonaceous Material)
The properties of the graphite-based carbonaceous material preferably satisfy one or more of the following (1) to (11) at the same time.
(1) X-ray parameters
The value of d (interlayer distance) of the lattice plane (002) of the graphite-based carbonaceous material, which is determined by X-ray diffraction using a vibroseis method, is preferably 0.335nm or more. The lower limit is less than 0.340nm, preferably 0.337nm or less, from the viewpoint of definition. If the value of d is too large, crystallinity may be reduced, and initial irreversible capacity may be increased. On the other hand, 0.335 is a theoretical value of graphite. The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is usually in the range of 30nm or more, preferably 50nm or more, and more preferably 100nm or more. If the content is less than this range, the crystallinity may be lowered, and the initial irreversible capacity may be increased.
(2) Ash content
The ash content in the graphitic carbonaceous material is preferably 1 mass% or less, more preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, with the lower limit being 1ppm or more, based on the total mass of the graphitic carbonaceous material. If the amount exceeds the above range, deterioration of battery performance due to reaction with the electrolyte during charge and discharge cannot be ignored. If it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost sometimes rises.
(3) Volume-based average particle diameter
The volume-based average particle diameter of the graphite-based carbonaceous material is a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and particularly preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, the resulting electrode plate tends to have an uneven coating surface when produced, which is not preferable in the battery production process.
In the present invention, the volume-based average particle diameter is defined by a median particle diameter, which is determined by the following method: the carbon powder was dispersed in a 0.2 mass% aqueous solution (about 1mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant, and measured using a laser diffraction/scattering particle size distribution meter (for example, LA-700 manufactured by horiba ltd.).
(4) Raman R value, Raman half value width
The R value of the graphite-based carbonaceous material measured by argon ion laser raman spectroscopy is usually 0.01 or more, preferably 0.03 or more, more preferably 0.10 or more, and the upper limit thereof is usually 0.60 or less, preferably 0.40 or less. If the R value is less than this range, the crystallinity of the particle surface becomes too high, and Li may be less likely to enter into the interlayer during charging and discharging. That is, the charge acceptance may be reduced. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the electrolyte solution is increased, and the efficiency may be lowered or the amount of gas generated may be increased.
The graphite-based carbonaceous material is 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 10cm-1Above, preferably 15cm-1Above, the upper limit is usually 60cm-1Hereinafter, preferably 45cm-1Hereinafter, more preferably 40cm-1The following ranges. If the Raman half-value width is below this range, the particleThe crystallinity of the surface is too high, and the number of sites where Li enters the interlayer is sometimes reduced by charge and discharge. That is, the charge acceptance may be reduced. On the other hand, if the amount is more than this range, the crystallinity of the particle surface is lowered, the reactivity with the electrolytic solution is increased, and the efficiency may be lowered or the amount of generated gas may be increased.
The raman spectrum was measured as follows: a sample is allowed to naturally fall down using a raman spectrometer (for example, a raman spectrometer manufactured by japan spectroscopy corporation) and filled in a measurement cell, and the surface of the sample in the cell is irradiated with an argon ion laser while the cell is rotated in a plane perpendicular to the laser. For the obtained Raman spectrum, 1580cm was determined-1Nearby peak PAStrength I ofAAnd 1360cm-1Nearby peak PBStrength I ofBAnd calculating the intensity ratio R (R ═ I)B/IA) It is defined as the raman R value of the carbon material. The Raman spectrum obtained by measurement was 1580cm-1Nearby peak PAIs defined as the raman half-value width of the carbon material.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10-20 cm-1
Measurement range: 1100cm-1～1730cm-1
R-value, half-value width analysis: background processing
Smoothing treatment: simple average, convolution 5 points
(5) BET specific surface area
The specific surface area of the graphite-based carbonaceous material of the present invention measured by the BET method is usually 0.1m2A ratio of 0.7m or more2A value of 1m or more, more preferably 1m2A total of 1.5m or more2The ratio of the water to the water is higher than that of the water to the water. Its upper limit is typically 100m 2A ratio of 25m or less per gram2A ratio of 15m or less per gram2A ratio of 10m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the value of the specific surface area is less thanWhen the lithium ion secondary battery is used as a negative electrode, lithium acceptance during charging is poor, and lithium is likely to precipitate on the electrode surface. On the other hand, if the amount exceeds the above range, the reactivity with the electrolyte increases when the negative electrode material is used, the amount of gas generated increases, and it may be difficult to obtain a preferable battery.
The BET specific surface area is defined as a value determined as follows: the sample was preliminarily dried at 350 ℃ for 15 minutes under flowing of nitrogen gas using a surface area meter (for example, a fully automatic surface area measuring apparatus manufactured by a large warehouse), and then measured by a nitrogen adsorption BET1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
(6) Distribution of micropores
The amount of the graphite-based carbonaceous material corresponding to voids in particles having a diameter of 0.01 to 1 μm and irregularities due to irregularities on the particle surface, as determined by a mercury porosimeter (mercury intrusion method), is usually not less than 0.01mL/g, preferably not less than 0.05mL/g, more preferably not less than 0.1mL/g, and the upper limit is usually not more than 0.6mL/g, preferably not more than 0.4mL/g, more preferably not more than 0.3 mL/g. If this range is exceeded, a large amount of binder is required for manufacturing the plate. On the other hand, if the amount is less than this range, the high-current-density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of adhesive is sometimes required for producing the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. On the other hand, if the amount is less than this range, the high current density charge-discharge characteristics may be degraded.
As a device for the mercury porosimeter, a mercury porosimeter (autopore 9520; manufactured by micromeritics) can be used. About 0.2g of a sample (negative electrode material) was weighed, sealed in a powder container, degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes, and subjected to pretreatment. Subsequently, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased stepwise from 4psia (about 28kPa) to 40000psia (about 280MPa), followed by pressure reduction to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 °. The average pore size is the pore size at which the cumulative pore volume reaches 50%.
(7) Degree of circularity
The circularity is used as the degree of sphericity of the graphite-based carbonaceous material, and the circularity of particles having a particle diameter of 3 to 40 μm of the graphite-based carbonaceous material is preferably 0.1 or more, particularly preferably 0.5 or more, more preferably 0.8 or more, further preferably 0.85 or more, and most preferably 0.9 or more. A large circularity is preferable because high current density charge/discharge characteristics are improved. The circularity is defined by the following equation, and a circularity of 1 is a theoretical true sphere.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the value measured as follows was used: for example, particles having a particle size in the range of 3 to 40 μm were measured by dispersing about 0.2g of a sample in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant using a flow-type particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial Co., Ltd.), irradiating the sample with ultrasonic waves of 28kHz for 1 minute at an output of 60W, and then designating 0.6 to 400 μm as a detection range.
The method for increasing the circularity is not particularly limited, but is preferably a method for increasing the circularity because the shape of the voids between particles can be made uniform when the electrode body is produced by performing the spheroidization treatment to make the particles spherical. Examples of the spheroidizing treatment include a method of mechanically approximating a sphere by applying a shear force or a compression force; a mechanical/physical treatment method of granulating a plurality of fine particles by a binder or adhesion force of the particles themselves, and the like.
(8) True density
The graphite-based carbonaceous material usually has a true density of 2g/cm3Above, preferably 2.1g/cm3Above, more preferably 2.2g/cm3Above, more preferably 2.22g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase. In the present invention, the true density is defined as a value measured by a liquid phase displacement method (densitometry method) using butanol.
(9) Tap density
The tap density of the graphite-based carbonaceous material is usually 0.1g/cm3Above, preferably 0.5g/cm3Above, more preferably 0.7g/cm3Above, particularly preferably 0.9g/cm3The above. Further, the upper limit thereof is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if the amount is more than this range, the number of voids between particles in the electrode is too small, and it is difficult to secure conductivity between particles, and it may be difficult to obtain preferable battery characteristics.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300 μm and dropped to 20cm 3The container (2) is tapped until the upper end face of the container is filled with the sample, and then a powder density measuring instrument (for example, a Tap densitometer manufactured by seishin corporation) is used to vibrate the container 1000 times with a stroke length of 10mm, and the bulk density at this time is defined as Tap density.
(10) Orientation ratio (powder)
The orientation ratio of the graphite-based carbonaceous material is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction of carbon obtained by X-ray diffraction were fitted using asymmetric pearson VII as a distribution function, peak separation was performed, and integrated intensities of the peaks of (110) diffraction and (004) diffraction were calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as an active material orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit:
divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
(11) Aspect ratio (powder)
The aspect ratio of the graphite-based carbonaceous material is theoretically 1 or more, and the upper limit is usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks are generated when the electrode plate is produced, and a uniform coating surface cannot be obtained, and the high-current-density charge/discharge characteristics may be deteriorated.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the carbon material particles to the shortest diameter B perpendicular thereto in three-dimensional observation. The carbon particles were observed by a scanning electron microscope which allows for magnified observation. Arbitrary 50 graphite particles fixed to the end faces of a metal having a thickness of 50 μm or less were selected, a stage on which a sample was fixed was rotated and tilted, A, B of each of these particles was measured, and the average value of a/B was determined.
[ [ [ [ [ low crystalline carbonaceous material ] ] ] ] ] ])
The low-crystalline carbonaceous material is a carbonaceous material having low crystallinity in which the (002) plane interplanar spacing (d002) measured by X-ray wide-angle diffraction method is 0.340nm or more.
(composition of Low-crystalline carbonaceous Material)
The "carbonaceous material different from the particulate carbonaceous material in crystal" is preferably a low-crystalline carbonaceous material having a lower crystallinity than the particulate carbonaceous material. In addition, the following carbide (d) or (e) is particularly preferable.
(d) A carbonizable organic substance selected from the group consisting of coal-based heavy oils, straight-run heavy oils, decomposed petroleum-based heavy oils, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenyls, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins;
(e) a solution obtained by dissolving these organic substances that can be carbonized in a low-molecular organic solvent.
Coal-based heavy oils, preferably coal tar pitch ranging from soft pitch to hard pitch, or gas oil from dry distillation; as the straight-run heavy oil, atmospheric residual oil, vacuum residual oil, and the like are preferable; the decomposed petroleum heavy oil is preferably ethylene tar or the like which is a by-product produced in the thermal decomposition of crude oil, naphtha or the like; as the aromatic hydrocarbon, acenaphthylene, decacycloolefin, anthracene, phenanthrene, and the like are preferable; as the N-ring compound, phenazine, acridine and the like are preferable; as the S ring compound, thiophene, bithiophene, and the like are preferable; as the polyphenylene, biphenyl, terphenyl, and the like are preferable; the organic polymer is preferably polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, an insoluble material thereof, polyacrylonitrile, polypyrrole, polythiophene, polystyrene, or the like; the natural polymer is preferably a polysaccharide such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, or sucrose; as the thermoplastic resin, polyphenylene sulfide, polyphenylene ether, or the like is preferable; as the thermosetting resin, furfuryl alcohol resin, phenol resin, imide resin, and the like are preferable.
The "carbonaceous material having a crystallinity different from that of the particulate carbonaceous material" is preferably a carbide of the above "organic substance capable of carbonization", and is preferably a carbide obtained by dissolving these "organic substance capable of carbonization" in a low-molecular-weight organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane to obtain a solution or the like. The "carbonaceous material having a crystallinity different from that of the particulate carbonaceous material" is preferably a carbide of coal coke or petroleum coke.
The above (d) or (e) is particularly preferably in a liquid state. That is, from the viewpoint of partially forming an interface with the graphite-based carbonaceous material, carbonization in a liquid phase is preferred.
(Properties of Low-crystalline carbonaceous Material)
The physical properties of the low-crystalline carbonaceous material preferably satisfy at the same time any one or more of the following (1) to (5). One kind of low crystalline carbonaceous material exhibiting these physical properties may be used alone, or 2 or more kinds may be used in combination at any combination and ratio.
(1) X-ray parameters
The d value (interlayer distance) of the lattice plane (002 plane) of the low-crystalline carbonaceous substance moiety, which is determined by X-ray diffraction using a vibroseis method, is 0.340nm or more, preferably 0.340nm or more, and particularly preferably 0.341nm or more, by definition. The upper limit is 0.380nm or less, particularly preferably 0.355nm or less, and further preferably 0.350 nm or less. If the value of d is too large, a surface having remarkably low crystallinity is formed, and the irreversible capacity may be increased, whereas if the value of d is too small, the effect of improving the charge acceptance by providing a low-crystalline carbonaceous material on the surface is small, and the effect of the present invention is small. The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is usually 1nm or more, preferably 1.5nm or more. If the content is less than this range, the crystallinity may be lowered, and the initial irreversible capacity may be increased.
(2) Ash content
The ash content in the low-crystalline carbonaceous substance portion is preferably 1 mass% or less, more preferably 0.5 mass% or less, and particularly preferably 0.1 mass% or less, with the lower limit being preferably 1ppm or more, based on the total mass of the composite carbonaceous substance. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the electrolyte during charge and discharge cannot be ignored. If the amount is less than this range, a long time and energy are required for manufacturing and a facility for preventing contamination is required, and the cost may be increased.
(3) Raman R value, Raman half value width
The R value of the low-crystalline carbonaceous substance moiety measured by argon ion laser raman spectroscopy is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and the upper limit thereof is usually 1.5 or less, preferably 1.2 or less. If the R value is less than this range, the crystallinity of the particle surface becomes too high, and Li may be less likely to enter into the interlayer during charging and discharging. That is, the charge acceptance may be reduced. In addition, when the negative electrode is densified by pressing after being applied to a current collector, crystals tend to be oriented in a direction parallel to the electrode plate, which may result in a decrease in load characteristics. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the electrolyte solution is increased, and the efficiency may be lowered or the amount of gas generated may be increased.
The low-crystalline carbonaceous material portion was 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 40cm-1Above, preferably 50cm-1Above, its upper limit is usually 100cm-1Hereinafter, it is preferably 90cm-1Hereinafter, more preferably 80cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters the interlayer is sometimes reduced as Li is charged and discharged. That is, the charge acceptance may be reduced. In addition, when the negative electrode is densified by pressing after being coated on a current collector, crystals tend to be oriented in a direction parallel to the electrode plate, and load characteristics may be reduced. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, and the reactivity with the electrolyte solution is increased, which may result in a decrease in efficiency or an increase in gas generation.
(4) True density
The true density of the low-crystalline carbonaceous substance moiety is usually 1.4g/cm3Above, preferably 1.5g/cm3Above, more preferably 1.6g/cm3Above, more preferably 1.7g/cm3Above, the upper limit is usually 2.1g/cm3Hereinafter, it is preferably 2g/cm3The following. If this range is exceeded, the charge acceptance may be impaired. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
(5) Orientation ratio (powder)
The orientation ratio of the low-crystalline carbonaceous substance portion is usually 0.005 or more, preferably 0.01 or more, and more preferably 0.015 or more, and the upper limit thereof is 0.67 or less of the theoretical value. If the content is less than this range, the high density charge/discharge characteristics may be deteriorated, which is not preferable. The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction obtained by X-ray diffraction from carbon were fitted using asymmetric pearson VII as a distribution function, and peak separation was performed to calculate integrated intensities of the peaks of (110) diffraction and (004) diffraction, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as an active material orientation ratio.
[ [ [ composite carbonaceous material ] ] ]
The composite carbonaceous material used in the negative electrode [1] in the lithium secondary battery of the present invention preferably contains a "particulate carbonaceous material" and a "carbonaceous material having a crystallinity different from that of the particulate carbonaceous material", and in this case, either one of the two is a graphite-based carbonaceous material, and the other is a low-crystalline carbonaceous material. Further, it is preferable that the "particulate carbonaceous material" is a graphite-based carbonaceous material, and the "carbonaceous material having a crystallinity different from that of the particulate carbonaceous material" is a low-crystalline carbonaceous material.
In the composite carbonaceous material, the mass ratio of the graphite-based carbonaceous material to the low-crystalline carbonaceous material is preferably 50/50 or more, more preferably 80/20 or more, and particularly preferably 90/10 or more, and is preferably 99.9/0.1 or less, more preferably 99/1 or less, and particularly preferably 98/2 or less. If the amount exceeds the above range, the effect of the carbonaceous material having 2 types of crystallinity may not be obtained, and if the amount is less than the above range, the initial irreversible capacity tends to increase, which may cause a problem in battery design. The graphite-based carbonaceous material is 50 mass% or more of the total composite carbonaceous material.
(physical Properties of composite carbonaceous Material)
The composite carbonaceous material preferably satisfies any one or more of (1) to (11) shown below. One kind of composite carbonaceous material exhibiting these physical properties may be used alone, or 2 or more kinds may be used in combination in any combination and ratio.
(1) X-ray parameters
The d value (interlayer distance) of the lattice plane (002) of the composite carbonaceous material, which is determined by X-ray diffraction using a vibroseis method, is preferably 0.335nm or more, and is usually 0.350nm or less, preferably 0.345nm or less, and more preferably 0.340nm or less. The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is usually 1.5nm or more, and preferably 3.0nm or more. If the content is less than this range, the crystallinity may be reduced, and the increase in initial irreversible capacity may increase.
(2) Ash content
The ash content in the composite carbonaceous material is preferably 1 mass% or less, more preferably 0.5 mass% or less, and particularly preferably 0.1 mass% or less, with the lower limit thereof being preferably 1ppm or more, based on the total mass of the composite carbonaceous material. If the amount exceeds the above range, deterioration of battery performance due to reaction with the electrolyte during charge and discharge cannot be ignored. If it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost sometimes rises.
(3) Volume-based average particle diameter
The volume-based average particle diameter of the composite carbonaceous material is a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, and particularly preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, an uneven coating surface is likely to be formed when the electrode plate is produced, which is not preferable in the battery production process.
(4) Raman R value, Raman half-value width
The R value of the composite carbonaceous material measured by argon ion laser raman spectroscopy is usually 0.03 or more, preferably 0.10 or more, more preferably 0.15 or more, and the upper limit thereof is usually 0.60 or less, preferably 0.50 or less. If the R value is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters into the interlayer may decrease with charge and discharge. That is, the charge acceptance may be reduced. In addition, when the negative electrode is densified by pressing after being applied to a current collector, crystals tend to be oriented in a direction parallel to the electrode plate, which may result in a decrease in load characteristics. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the electrolyte solution is increased, and the efficiency may be lowered or the amount of gas generated may be increased.
In addition, the composite carbonaceous material is 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 15cm-1Above, preferably 20cm-1Above, its upper limit is usually 70cm-1Hereinafter, preferably 60cm-1Hereinafter, more preferably 50cm-1The following ranges. If the Raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers may decrease with charge and discharge. That is, the charge acceptance may be reduced. In addition, when the negative electrode is densified by pressing after being coated on a current collector, crystals tend to be oriented in a direction parallel to an electrode plate, and load characteristics may be degraded. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, and the reactivity with the electrolyte solution is increased, which may result in a decrease in efficiency or an increase in gas generation.
(5) BET specific surface area
The specific surface area of the composite carbonaceous material of the invention measured by the BET method is usually 0.1m2A ratio of at least 0.7 m/g2A value of 1m or more, more preferably 1m2A total of 1.5m or more2More than g. It is composed ofThe upper limit is usually 100m2A ratio of 25m or less per gram2A ratio of 15m or less per gram2A total of 10m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the specific surface area is less than the above range, the acceptance of lithium during charging is poor and lithium is likely to precipitate on the electrode surface when used as a negative electrode material. On the other hand, if the amount exceeds the above range, the reactivity with the electrolyte increases when the negative electrode material is used, the amount of gas generated increases, and it may be difficult to obtain a preferable battery.
(6) Distribution of micropores
The composite carbonaceous material is obtained by subjecting the voids in the particles having a diameter of 0.01 to 1 μm, which are measured by a mercury porosimeter (mercury intrusion method), to unevenness due to the level of the particle surface, and the amount of the irregularities is usually 0.01mL/g or more, preferably 0.05mL/g or more, and more preferably 0.1mL/g or more, and the upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, and more preferably 0.3mL/g or less. If it exceeds this range, a large amount of binder is required for forming the electrode plate. If the amount is less than this range, the high current density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of the binder may be required. On the other hand, if the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 80 μm or less, preferably 50 μm or less, and more preferably 20 μm or less. If the amount exceeds this range, a large amount of the binder may be required. On the other hand, if the amount is less than this range, the high current density charge/discharge characteristics may be deteriorated.
(7) Degree of circularity
The circularity is used as the degree of sphericity of the composite carbonaceous material, and the circularity of particles having a particle diameter of 3 to 40 μm of the composite carbonaceous material is preferably 0.85 or more, more preferably 0.87 or more, and even more preferably 0.9 or more. A large circularity is preferable because high current density charge/discharge characteristics are improved.
(8) True density
The true density of the composite carbonaceous matter is usually 1.9g/cm 3Above, preferably 2g/cm3Above, more preferably 2.1g/cm3Above, more preferably 2.2g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
(9) Tap density
The tap density of the composite carbonaceous substance is usually 0.1g/cm3Above, preferably 0.5g/cm3Above, more preferably 0.7g/cm3Above, 1g/cm is particularly preferable3The above. Further, the upper limit thereof is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if the amount exceeds this range, the number of voids between particles in the electrode is too small, and it is difficult to ensure conductivity between particles, and it may be difficult to obtain preferable battery characteristics. Tap density is determined by and defined according to the same method as described above.
(10) Orientation ratio (powder)
The orientation ratio of the composite carbonaceous material is usually 0.005 or more, preferably 0.01 or more, and more preferably 0.015 or more, and the upper limit thereof is theoretically 0.67 or less. If the content is less than this range, the high density charge/discharge characteristics may be deteriorated.
(11) Aspect ratio (powder)
The aspect ratio of the composite carbonaceous material is theoretically 1 or more, and the upper limit thereof is usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks may occur in the formation of an electrode plate, and a uniform coating surface cannot be obtained, resulting in a decrease in high-current density charge/discharge characteristics.
(method for producing composite carbonaceous Material)
The method for producing these composite carbonaceous materials is not particularly limited, and the following methods can be mentioned.
The graphite-based carbonaceous material and the low-crystalline carbonaceous material can be combined by the following method: a method of obtaining a composite powder by directly using a carbon precursor for obtaining a low-crystalline carbonaceous material and heat-treating a mixture of the carbon precursor and a graphite-based carbonaceous material powder; a method in which the carbon precursor is partially carbonized to prepare a low-crystalline carbonaceous material powder in advance, and the low-crystalline carbonaceous material powder is mixed with a graphite-based carbonaceous material powder and then subjected to heat treatment to form a composite; a method of preparing the low-crystalline carbonaceous material powder in advance, mixing the graphite-based carbonaceous material powder, the low-crystalline carbonaceous material powder, and the carbon precursor, and heating the mixture to form a composite. In the latter two methods of preparing the low-crystalline carbonaceous material powder in advance, it is preferable to use low-crystalline carbonaceous material particles having an average particle diameter of one tenth or less of the average particle diameter of the graphite-based carbonaceous material. In addition, the following method may also be employed: a method of producing a structure in which one substance is mixed with another substance or a structure in which static electricity is attached by applying mechanical energy such as pulverization to a low-crystalline carbonaceous substance and a graphite-based carbonaceous substance prepared in advance.
Preferably, the intermediate material is obtained by heating a mixture obtained by mixing the graphite-based carbonaceous material particles and the carbon precursor, or the intermediate material is obtained by heating a mixture obtained by mixing the carbon precursor and a mixture of the graphite-based carbonaceous material particles and the low-crystalline carbonaceous material particles, and then the intermediate material is carbonized, sintered, and pulverized, thereby finally obtaining a composite carbonaceous material in which the low-crystalline carbonaceous material is composited with the graphite-based carbonaceous material particles.
The production process for obtaining the composite carbonaceous material is divided into the following 4 steps.
Step 1: the mixture is obtained by mixing (the graphite-based carbonaceous material particles or (the mixed particles of the graphite-based carbonaceous material particles and the low-crystalline carbonaceous material particles)) and the carbon precursor of the low-crystalline carbonaceous material particles with a solvent added as needed using various commercially available mixers or kneaders.
And a 2 nd step: the mixture is heated to obtain an intermediate material from which the solvent and volatile components derived from the carbon precursor are removed. In this case, the reaction can be carried out while stirring the mixture, if necessary. Even if the volatile components remain, they can be removed in the subsequent 3 rd step, and therefore, there is no problem.
And a 3 rd step: the above mixture or intermediate is heated to 400 to 3200 ℃ in an inert gas atmosphere such as nitrogen, carbon dioxide or argon to obtain a graphite/low-crystalline carbonaceous material composite material.
And a 4 th step: the composite material is subjected to powder processing such as pulverization, crushing, classification treatment and the like as required.
In these steps, the 2 nd step and the 4 th step may be omitted as the case may be, and the 4 th step may be performed before the 3 rd step. However, when the 4 th step is performed before the 3 rd step, the composite carbonaceous material is obtained by performing powder processing such as pulverization, crushing, classification, and the like again, if necessary.
In addition, as the heat treatment conditions in the 3 rd step, the thermal history temperature conditions are important. The lower limit of the temperature varies depending on the type of the carbon precursor and the thermal history, but is usually 400 ℃ or higher, preferably 900 ℃ or higher. On the other hand, the upper limit temperature can be set to a temperature at which the crystal structure of the particle core of the carbonaceous material of graphite does not substantially have a structural order exceeding that of the particle core. Therefore, the upper limit temperature of the heat treatment is usually 3200 ℃ or lower, preferably 2000 ℃ or lower, and more preferably 1500 ℃ or lower. Under such heat treatment conditions, the temperature rise rate, cooling rate, heat treatment time, and the like can be arbitrarily set according to the purpose. Further, after the heat treatment is performed in a relatively low temperature range, the temperature may be raised to a predetermined temperature. The reactor used in the present step may be a batch type or a continuous type, or may be one or a plurality of reactors.
[ [ mixture of auxiliary materials ] ]
In addition to the composite carbonaceous material, the negative electrode active material of the lithium secondary battery of the present invention contains one or more carbonaceous materials (carbonaceous materials) different from the composite carbonaceous material in terms of carbonaceous physical properties, and thus can further improve battery performance. The "carbonaceous physical properties" referred to herein mean one or more characteristics of X-ray diffraction parameters, median particle diameter, aspect ratio, BET specific surface area, orientation ratio, raman R value, tap density, true density, micropore distribution, circularity, and ash content. In addition, preferred embodiments include a volume-based particle size distribution that is asymmetric from left to right about a median particle diameter, contains 2 or more carbonaceous materials having different raman R values, and has different X-ray parameters. Examples of the effect include the addition of graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke are used as a sub-material to reduce resistance and the like. These may be used alone, or may be used in combination of 2 or more in any combination and in any ratio. When added as a sub-material, the amount of addition is 0.1 mass% or more, preferably 0.5 mass% or more, more preferably 0.6 mass% or more, and the upper limit thereof is 80 mass% or less, preferably 50 mass% or less, more preferably 40 mass% or less, and still more preferably 30 mass% or less. If the amount is less than this range, the effect of improving the conductivity may be difficult to obtain. If the amount exceeds the above range, the initial irreversible capacity may increase.
[ production of negative electrode [1] electrode ]
The negative electrode [1] can be produced by a usual method, and the negative electrode [1] can be formed in the same manner as described above. The thickness ratio of the current collector, and the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
< negative electrode [2] >
Next, the negative electrode [2] used in the lithium secondary battery of the present invention is described]The negative electrode contains, as an active material, amorphous carbonaceous material having a (002) plane interplanar spacing (d002) of 0.337nm or more as measured by wide-angle X-ray diffraction method and a crystallite size (Lc)) 80nm or less, 1360cm in argon ion laser Raman spectroscopy-1Peak intensity of (2) relative to 1580cm-1The ratio of the peak intensities of (a) is defined as a Raman R value of 0.2 or more.
[ negative electrode active material for negative electrode [2]
Next, a negative electrode active material used in the negative electrode [2] will be described.
The negative electrode active material used for the negative electrode [2] of the lithium secondary battery of the present invention contains at least amorphous carbon that satisfies the following requirements (a), (b), and (c).
(a) The (002) plane surface spacing (d002) measured by wide-angle X-ray diffraction method is more than 0.337 nm;
(b) crystallite size Lc of (002) plane measured by wide-angle X-ray diffraction method is below 80 nm;
(c) In argon ion laser Raman spectroscopy at 1360cm-1Peak intensity of (2) relative to 1580cm-1The ratio of the peak intensities of (a) is defined as a Raman R value (hereinafter, may be simply referred to as "Raman R value") of 0.2 or more.
The negative electrode active material used in the present invention contains at least amorphous carbon materials satisfying (a), (b), and (c), and the content of these amorphous carbon materials in the total negative electrode active material is preferably 10% by mass or more, more preferably 50% by mass or more, and particularly preferably 100% by mass, that is, all the active materials are amorphous carbon. The negative electrode active material used in combination with the amorphous carbon is not particularly limited, and a known negative electrode active material, for example, artificial graphite, natural graphite, or the like can be used.
[ [ inter-planar distances (d002), Lc ] ]
The amorphous carbon used as the negative electrode active material of the negative electrode [2] in the lithium secondary battery of the present invention has a (002) plane interplanar spacing (d002) of 0.337nm or more, preferably 0.34nm or more, as measured by wide-angle X-ray diffractometry. The upper limit is usually 0.39nm or less, preferably 0.38nm or less, more preferably 0.37nm or less, still more preferably 0.36nm or less, and particularly preferably 0.35nm or less. If the amount exceeds this range, the crystallinity is significantly reduced, and the reduction in the conductivity between particles cannot be ignored, and it may be difficult to obtain the effect of improving the charge-discharge characteristics at a high current density in a short time. On the other hand, if the amount is less than this range, the crystallinity becomes too high, and it may be difficult to obtain an effect of improving the charge-discharge characteristics at a high current density in a short time.
The inter-plane distance (d002) of the (002) plane measured by the wide-angle X-ray method as referred to in the present invention means the d value (interlayer distance) of the (002) plane of the lattice plane obtained by X-ray diffraction by the vibroseis method.
The crystallite size (Lc) of the (002) plane of amorphous carbon as determined by X-ray diffraction measured by the vibroseis method is 80nm or less, preferably 35nm or less, more preferably 20nm or less, and still more preferably 10nm or less. The lower limit is usually 0.1nm or more, preferably 1nm or more. If the amount is less than this range, the crystallinity is significantly reduced, the decrease in the conductivity between particles may not be negligible, and the effect of improving the charge and discharge with high current density in a short time may not be obtained. On the other hand, if it exceeds this range, the crystallinity becomes too high, and the effect of improving the charge and discharge with high current density in a short time may be difficult to obtain.
[ [ Raman R value ] ]
The amorphous carbon used as the negative electrode active material of the negative electrode [2] in the lithium secondary battery of the present invention has a raman R value of 0.2 or more, preferably 0.5 or more, particularly preferably 0.7 or more, and more preferably 0.8 or more. The upper limit is usually 1.5 or less, and more preferably 1.2 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the charge acceptance is lowered, and therefore, the effect of improving the charge-discharge characteristics at a high current density in a short time may be difficult to obtain. On the other hand, if it exceeds this range, the crystallinity of the particle surface is significantly reduced, and therefore the contact resistance between particles becomes large, and it may be difficult to obtain the effect of improving the charge and discharge with high current density in a short time.
The raman spectrum was measured as follows: a sample is naturally dropped into a measurement vessel by using a raman spectrometer (for example, a raman spectrometer manufactured by japan spectroscopy corporation) and filled with the sample by irradiating the surface of the sample in the vessel with an argon ion laser and rotating the vessel in a plane perpendicular to the laser.For the obtained Raman spectrum, 1580cm was measured-1Peak P of (1)AStrength I ofAAnd 1360cm-1Peak P of (1)BStrength I ofBAnd calculating the intensity ratio R (R ═ I)B/IA) This is defined as the Raman R value of amorphous carbon. The Raman spectrum obtained by measurement was 1580cm-1Peak P of (1)AIs defined as the Raman half-value width of amorphous carbon.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10-20 cm-1
Measurement range: 1100cm-1～1730cm-1
Raman R value, raman half-value width analysis: background processing
Smoothing treatment: simple average, convolution 5 points
In addition, the lithium secondary battery of the present invention was used as the negative electrode [2 ]]The amorphous carbon used as the negative electrode active material of (3) is 1580cm-1The Raman half-value width of (A) is not particularly limited, but is usually 20cm -1Above, preferably 25cm-1Above, in addition, the upper limit is usually 150cm-1Hereinafter, preferably 140cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the charging receptivity is lowered, and therefore, the effect of improving the short-time high-current-density charging and discharging may be difficult to obtain. On the other hand, if it exceeds the above range, the crystallinity of the particle surface is significantly reduced, and therefore, the contact resistance between particles becomes large, and there is a possibility that the effect of improving the charge and discharge with high current density in a short time is difficult to obtain. However, the raman half-value width may not be determined by the peak shape.
The amorphous carbon used in the present invention satisfies the above-mentioned conditions of the surface-to-surface distance (d002), crystallite size (Lc) and raman R value, but more preferably satisfies one or more of the following conditions from the viewpoint of cell balance. Among these, it is particularly preferable that the conditions of one or more of the true density, H/C value, O/C value, tap density, BET specific surface area, micropore volume in the range of 0.01 to 1 μm, ash content, and volume average particle diameter are satisfied at the same time.
[ [ true density ] ]
The amorphous carbonaceous material generally has a true density of 2.22g/cm 3Hereinafter, it is preferably 2.2g/cm3Hereinafter, more preferably 2.1g/cm3Hereinafter, more preferably 2.0g/cm3The lower limit is usually 1.4g/cm3Above, preferably 1.5g/cm3Above, more preferably 1.6g/cm3Above, more preferably 1.7g/cm3Above, 1.8g/cm is particularly preferable3The above range. If the amount is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase. If the amount exceeds this range, the crystallinity of carbon becomes too high, and the effect of improving charge and discharge with high current density in a short time is difficult to obtain.
In the present invention, the true density is defined as a value measured by a liquid phase displacement method (densitometry method) using butanol.
[ [ O/C value ] ]
The upper limit of the atomic ratio of oxygen to carbon (O/C) value of amorphous carbon is usually 0.15 or less, preferably 0.1 or less, more preferably 0.05 or less, and still more preferably 0.03 or less, and the lower limit thereof is usually 0 or more, preferably 0.01 or more.
The O/C value represents a ratio of a molar concentration of oxygen atoms to a molar concentration of carbon atoms present in the amorphous carbonaceous material, and is an index indicating an amount of functional groups such as carboxyl groups, phenolic hydroxyl groups, carbonyl groups, and the like present. In amorphous carbons having a large O/C value, oxygen-containing functional groups are often bonded to the end faces of carbon crystallites. If the O/C value exceeds the above range, the irreversible capacity may increase.
[ [ H/C value ] ]
The upper limit of the atomic ratio H/C value of the amorphous carbon is usually 0.3 or less, preferably 0.15 or less, more preferably 0.1 or less, and still more preferably 0.08 or less, and the lower limit thereof is usually 0 or more, preferably 0.01 or more.
The H/C value is an index indicating the ratio of the molar concentration of hydrogen atoms to the molar concentration of carbon atoms present in the amorphous carbon and indicates the amount of hydrogen present on the end faces of the crystallites of the amorphous carbon. Amorphous carbon materials having a large H/C value often show a larger amount of carbon than the amount of carbon, such as crystallite end faces of the carbon on the particle surface. If the H/C value exceeds the above range, the irreversible capacity may increase.
The "O/C value" and "H/C value" in the present invention were obtained by the CHN elemental analysis shown below.
[ [ CHN elemental analysis ] ]
The amorphous carbonaceous material to be measured was dried at 120 ℃ under reduced pressure for about 15 hours, and then placed on a hot plate in a drying oven to be dried at 100 ℃ for 1 hour. Next, the sample was placed in an aluminum cup under an argon atmosphere, the carbon content was determined from the weight of carbon dioxide gas generated by combustion, the hydrogen content was determined from the weight of water generated, the nitrogen content was calculated from the weight of nitrogen dioxide generated, and the inorganic content was determined from the weight of residue remaining after combustion. The value of oxygen content is obtained by subtracting the carbon content, hydrogen content, nitrogen content, inorganic content from the total weight. The molar number was calculated from these values, and the O/C value and H/C value were determined by the following equations using the molar numbers of the respective contents obtained.
O/C value (moles oxygen/moles carbon)
H/C value hydrogen/carbon containing mole
[ [ tap density ] ]
In the lithium secondary battery of the invention as a negative electrode [2 ]]The tap density of the amorphous carbon used as the active material of (3) is preferably 0.1g/cm3Above, more preferably 0.2g/cm3Above, more preferably 0.5g/cm3Above, particularly preferably 0.7g/cm3The above. Further, the upper limit thereof is preferably 1.4g/cm3Below, more preferably 1.2g/cm3The concentration is preferably 1.1g/cm or less3The following. If the tap density is less than this range, it is difficult to increase the packing density when used as a negative electrode, and the contact area between particles decreases, so that the impedance between particles increases, and the short-time high-current density charge/discharge characteristics may be degraded. On the other hand, such asIf the amount exceeds this range, the number of voids between particles in the electrode is too small, and the flow path of the nonaqueous electrolytic solution is reduced, and therefore, the high-current-density charge/discharge characteristics may be reduced in a short time.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300. mu.m, and the sample was dropped into a 20cm cell3The Tap density of (1) was determined by vibrating the container 1000 times with a stroke length of 10mm using a powder density measuring instrument (for example, Tap densitometer manufactured by seishin corporation) until the upper end face of the container was filled with the sample, and determining the density from the volume at that time and the weight of the sample.
[ [ BET specific surface area ] ]
In the lithium secondary battery of the invention as a negative electrode [2 ]]The specific surface area of the amorphous carbonaceous material used for the negative electrode active material of (3) is preferably 0.1m as measured by the BET method2A specific ratio of 0.5m to g2A value of at least one per gram, more preferably 0.7m2A total of 1.5m or more2More than g. The upper limit is preferably 100m2A specific ratio of 50m or less per gram2A ratio of 25m or less per gram2A total of 15m or less, preferably2The ratio of the carbon atoms to the carbon atoms is less than g. If the BET specific surface area is less than this range, the acceptance of lithium during charging is likely to deteriorate and lithium may precipitate on the electrode surface when used as a negative electrode material. On the other hand, if the BET specific surface area exceeds this range, the reactivity with the nonaqueous electrolytic solution increases when the negative electrode material is used, and the amount of generated gas increases, and a preferable battery may not be obtained.
The BET specific surface area is defined as the following value: the sample was preliminarily dried at 350 ℃ for 15 minutes under flowing of nitrogen gas using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research), and then measured by a nitrogen adsorption BET1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
[ [ volume average particle diameter ] ]
The volume average particle diameter of the amorphous carbon used as the negative electrode active material of the negative electrode [2] in the lithium secondary battery of the present invention is defined as a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and still more preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, the resulting electrode plate tends to have an uneven coating surface, which is not preferable in the battery production process.
[ [ micropore volume ] ]
The volume of the amorphous carbon micropores used as a negative electrode active material for the negative electrode [2] in the lithium secondary battery of the present invention is in the range of 0.01mL/g or more, preferably 0.05mL/g or more, more preferably 0.1mL/g or more, corresponding to the voids in the particles having a diameter of 0.01 to 1 μm, as determined by a mercury porosimeter (mercury intrusion method), and the amount of irregularities due to the irregularities on the particle surface, and the upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, more preferably 0.3mL/g or less. If this range is exceeded, a large amount of adhesive is required to manufacture the plate. On the other hand, if the amount is less than this range, the high current density charge-discharge characteristics are deteriorated in a short time, and the effect of moderating expansion and contraction of the electrode during charge and discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of the binder may be required. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. On the other hand, if the amount is less than this range, the high current density charge-discharge characteristics may be deteriorated in a short time.
As a device for the mercury porosimeter, a mercury porosimeter (autopore 9520; manufactured by micromeritics) can be used. About 0.2g of a sample (negative electrode material) was weighed, sealed in a powder container, degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes, and subjected to pretreatment. Subsequently, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased from 4psia (about 28kPa) to 40000psia (about 280MPa) in a stepwise manner, and then the pressure was reduced to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 °. The average pore size is the pore size at which the cumulative pore volume reaches 50%.
[ [ ash ] ])
The ash content in the carbonaceous material is preferably 1 mass% or less, more preferably 0.5 mass% or less, and particularly preferably 0.1 mass% or less, with respect to the total mass of the carbonaceous material, and the lower limit is preferably 1ppm or more by mass. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolyte solution during charging and discharging cannot be ignored. On the other hand, if it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination, and the cost sometimes rises.
[ [ circularity ] ]
The circularity of amorphous carbon used as the negative electrode active material of the negative electrode [2] in the lithium secondary battery of the present invention is usually 0.1 or more, preferably 0.8 or more, more preferably 0.85 or more, and still more preferably 0.9 or more. As an upper limit, the circularity reaches a theoretical true sphere at 1. If the amount is less than this range, the filling property of the negative electrode active material decreases, the inter-particle impedance increases, and the high current density charge/discharge characteristics may decrease in a short time.
The circularity of the present invention is defined by the following formula.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the following values are used: for example, about 0.2g of a sample is dispersed in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant by using a flow particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.), and particles having a particle diameter in the range of 3 to 40 μm are measured by irradiating ultrasonic waves of 28kHz for 1 minute at an output of 60W, designating 0.6 to 400 μm as a detection range, and using the average value of the measurement.
[ [ orientation ratio ] ]
The orientation ratio of the amorphous carbon material used as the negative electrode active material of the negative electrode [2] in the lithium secondary battery of the present invention is usually 0.005 or more, preferably 0.01 or more, and more preferably 0.015 or more, and the upper limit thereof is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated in a short period of time.
The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction of carbon obtained by X-ray diffraction were fitted using asymmetric pearson VII as a distribution function, peak separation was performed, and integrated intensities of the peaks of (110) diffraction and (004) diffraction were calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as an active material orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit:
divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
[ [ length-diameter ratio ] ]
The aspect ratio of amorphous carbon used as the negative electrode active material of the negative electrode [2] in the lithium secondary battery of the present invention is theoretically 1 or more, and the upper limit is usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks may occur during the production of the electrode plate, and a uniform coating surface cannot be obtained, resulting in a decrease in the high-current-density charge/discharge characteristics in a short time.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the carbonaceous material particles to the shortest diameter B perpendicular thereto in three-dimensional observation. The carbon particles were observed by a scanning electron microscope which allows observation with magnification. The average value of A/B was determined by selecting arbitrarily 50 particles fixed to the end face of a metal plate having a thickness of 50 μm or less, rotating and tilting a stage on which a sample was fixed, and measuring A, B values of the particles.
The amorphous carbon contained in the negative electrode active material used as the negative electrode active material of the negative electrode [2] in the lithium secondary battery of the present invention is preferably an amorphous carbon selected from the following items (1) to (4).
(1) A substance obtained by further heat-treating a carbide selected from the group consisting of coal-based coke, petroleum-based coke, furnace black, acetylene black and pitch-based carbon fiber;
(2) organic materials selected from asphalt raw materials, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenyls, organic synthetic polymers, natural polymers, thermoplastic resins and thermosetting resins, and/or thermal decomposition products thereof, and/or further heat-treated;
(3) dissolving the organic substance of (2) in a low-molecular-weight organic solvent to obtain a thermal decomposition product of the solution and/or further performing heat treatment to obtain a substance;
(4) carbides of gases containing organic matter.
The component (2) may be any one that can be carbonized, and examples thereof include aromatic hydrocarbons such as a raw material of asphalt, acenaphthylene, decacycloolefin, anthracene, and phenanthrene; n-ring compounds such as phenazine and acridine; s ring compounds such as thiophene and bithiophene; polyphenyl, such as biphenyl and terphenyl; organic polymers such as polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, crosslinked products thereof, insoluble products thereof, nitrogen-containing polyacrylonitrile, and polypyrrole; organic polymers such as sulfur-containing polythiophene and polystyrene; polysaccharides such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, and sucrose; thermoplastic resins such as polyphenylene sulfide and polyphenylene ether; thermosetting resins such as furfuryl alcohol resin, phenol resin, and imide resin; or organic substances such as solutions obtained by dissolving them in low-molecular-weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane; carbonizable gas containing these organic substances, and the like.
Among these, the asphalt raw material is preferred because it has a high char yield (char yield) and can be produced in a high yield. In the present specification, the term "pitch raw material" refers to pitch and substances belonging to pitch, and means substances that can be carbonized or graphitized by an appropriate treatment. As specific examples of the asphalt material, tar, heavy oil, asphalt, or the like can be used. Specific examples of the tar include coal tar, petroleum tar and the like. Specific examples of the heavy oil include a pyrolysis oil, a thermal decomposition oil, an atmospheric residue, a vacuum residue, and the like of a petroleum heavy oil. Specific examples of the pitch include coal tar pitch, petroleum pitch, and synthetic pitch. Among them, coal tar pitch is preferred because of its high aromaticity. These asphalt materials may be used alone or in combination of 2 or more in any combination and ratio.
Preferable examples of (3) include a carbide in which the organic substance of (2) is dissolved in a low-molecular-weight organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane to obtain a solution, and a thermal decomposition product of the solution is used as a precursor.
Examples of (4) include hydrocarbon compounds such as methane, ethane, propane, benzene, acetylene, and ethylene; carbon monoxide, and the like.
The crosslinking treatment is preferably performed. The crosslinking treatment is performed to make a carbonaceous material obtained by heat-treating a crosslinked pitch raw material or the like hard to graphitize, and by performing these treatments, the charge capacity per unit mass can be increased.
Examples of the crosslinking treatment include the following treatment methods: crosslinking treatment using α, α' -Azobisisobutyronitrile (AIBN), Benzoyl Peroxide (BPO), lauroyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, hydrogen peroxide, or the like as a radical polymerization initiator for a vinyl monomer such as divinylbenzene, trivinylbenzene, diallyl phthalate, ethylene glycol dimethacrylate, N-methylenebisacrylamide, or the like; the oxidizing agent treatment is performed using an oxidizing gas such as oxygen, ozone, or nitrogen dioxide, or an oxidizing liquid such as sulfuric acid, nitric acid, or an aqueous hydrogen peroxide solution. An example of the crosslinking treatment is a treatment in which the asphalt material is mixed with a crosslinking agent, an oxidizing agent or the like while the temperature of the asphalt material is controlled to 50 to 400 ℃.
[ [ Li-NMR shift ] ]
In the lithium secondary battery of the present invention, the so-called negative electrode [2 ] is used when the battery is charged to full charge]The negative electrode active material of (3) is prepared by using an amorphous carbon7In the Li-NMR analysis, a main resonance peak shifted by 80 to 200ppm toward the low magnetic field side of the resonance line of LiCl as a reference substance is observed, and it is preferable to use a crosslinked amorphous carbon substance in order to increase the capacity per unit mass of the amorphous carbon substance.
[ [ method for producing amorphous carbon ]
The method for producing amorphous carbon is not particularly limited as long as it is within the scope of the gist of the present invention, and various methods can be exemplified. In the production of amorphous carbon, the heat treatment process must be performed 1 time, but the heat treatment may be divided into 2 or more times, and it is preferable to perform various treatments before and after the heat treatment and/or at an intermediate stage of the heat treatment. The various treatments include pulverization, classification, and the above-mentioned crosslinking treatment, and the pulverization and classification treatment may be carried out before, after, or in an intermediate stage of the heat treatment as long as they are in a solid state. The crosslinking treatment is preferably performed before or at an intermediate stage of the heat treatment. By performing these treatments, the specific surface area of the anode active material can be controlled, and the capacity per unit mass can be increased.
The apparatus used for the pulverization before the heat treatment is not particularly limited, and examples of the coarse pulverizer include a shear mill, a jaw crusher, an impact crusher, a cone crusher, and the like, the intermediate pulverizer includes a roll crusher, a hammer crusher, and the like, and examples of the fine pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, a jet mill, and the like.
The apparatus used for the heat treatment of the raw material is not particularly limited, and examples thereof include a shuttle furnace (シャトル furnace), a tunnel furnace (トンネル furnace), an electric furnace, a coke roasting furnace (リードハンマー furnace), a rotary kiln, a reactor such as an autoclave, a cook (heat treatment vessel manufactured by cooks), and a direct current furnace. When the raw material is treated, stirring may be carried out as necessary.
The temperature conditions for the heat treatment are not particularly limited, but are usually 600 ℃ or higher, preferably 900 ℃ or higher, and the upper limit thereof is usually 2500 ℃ or lower, preferably 1300 ℃ or lower. If the temperature condition is lower than the above range, the crystallinity becomes too low, and the irreversible capacity may increase. On the other hand, if it exceeds the upper limit, the crystallinity becomes too high, and the short-time high-current-density charge-discharge characteristics may be degraded.
The amorphous carbon material after heat treatment may be pulverized or classified according to the size of its lump or particle. The device used for the pulverization is not particularly limited, and examples of the coarse pulverizer include a shear mill, a jaw crusher, an impact crusher, a cone crusher, and the like, examples of the intermediate pulverizer include a roll crusher, a hammer crusher, and the like, and examples of the fine pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, a jet mill, and the like. The apparatus used for the classification treatment is not particularly limited, and for example, in the case of dry sieving, a rotary sieve, a shaker sieve, a rotary sieve (cyclone sieve), a vibrating sieve, or the like can be used, in the case of dry air classification, a gravity classifier, an inertia classifier, a centrifugal classifier (classifier, cyclone) or the like can be used, and in the case of wet sieving, a mechanical wet classifier, a hydraulic classifier, a sedimentation classifier, a centrifugal wet classifier, or the like can be used.
[ electrode for negative electrode [2]
The negative electrode [2] can be produced by a usual method, and the negative electrode [2] can be formed in the same manner as described above. The thickness ratio of the current collector, and the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
Negative electrode (3)
Next, a negative electrode [3] used in the lithium secondary battery of the present invention, which contains a metal oxide containing titanium capable of occluding and releasing lithium as a negative electrode active material, will be described.
[ negative electrode active material for negative electrode [3]
Next, a negative electrode active material used in the negative electrode [3] will be described.
[ [ constitution of negative electrode active material ] ]
A negative electrode active material used in a negative electrode [3] of a lithium secondary battery of the present invention contains a metal oxide containing titanium capable of occluding and releasing lithium. Among the metal oxides, a composite oxide of lithium and titanium (hereinafter, simply referred to as "lithium-titanium composite oxide") is preferable, and the metal oxide is preferably a titanium-containing metal oxide having a spinel structure. In addition, the use of a metal oxide satisfying these conditions simultaneously, that is, the inclusion of a lithium titanium composite oxide having a spinel structure in the negative electrode active material for a lithium secondary battery is particularly preferable because the output impedance can be greatly reduced.
In addition, it is preferable that lithium or titanium in the lithium-titanium composite oxide is substituted with at least one other metal element, for example, at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.
The metal oxide is a lithium-titanium composite oxide represented by the general formula (1), and in the general formula (1), it is preferable that x is 0.7. ltoreq. x.ltoreq.1.5, y is 1.5. ltoreq. y.ltoreq.2.3, and z is 0. ltoreq. z.ltoreq.1.6, from the viewpoint of structural stability at the time of doping/dedoping of lithium ions.
LixTiyMzO4 (1)
[ in the general formula (1), M represents at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb ].
Among the compositions represented by the above general formula (1), the following structures are particularly preferable because of a good balance of battery performance.
In the general formula (1) LixTiyMzO4In (1),
(a)1.2≤x≤1.4、1.5≤y≤1.7、z＝0
(b)0.9≤x≤1.1、1.9≤y≤2.1、z＝0
(c)0.7≤x≤0.9、2.1≤y≤2.3、z＝0
particularly preferred representatives of the abovementioned compounds have the composition: (a) is Li4/3Ti5/3O4And (b) is Li1Ti2O4And (c) is Li4/5Ti11/5O4。
In addition, for the structure of Z ≠ 0, for example, Li is cited4/3Ti4/3Al1/3O4As a preferred composition.
[ [ physical Properties, shape, etc. of negative electrode active Material ]
The negative electrode active material used for the negative electrode [3] of the lithium secondary battery of the present invention preferably satisfies at least one of the following physical properties in addition to the above-mentioned requirements. In addition, it is particularly preferable that at least 2 or more of the following physical properties are satisfied simultaneously in addition to the above requirements.
[ [ [ BET specific surface area ] ] ]
Negative electrode [3] in lithium secondary battery of the invention]The specific surface area of the titanium-containing metal oxide used as the negative electrode active material in (2) is preferably 0.5m as measured by the BET method 2A value of at least one per gram, more preferably 0.7m2A specific ratio of 1.0m or more per g2A total of 1.5m or more2More than g. The upper limit is preferably 200m2A ratio of 100m or less per gram2A specific ratio of 50m or less per gram2A total of 25m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. When the BET specific surface area value is less than this range, the process is carried outWhen the material is used as a negative electrode material, the reaction area in contact with the nonaqueous electrolytic solution decreases, and the output impedance may increase. On the other hand, if the BET specific surface area exceeds this range, the crystal surface or end face portion of the metal oxide containing titanium increases, and thus unevenness (distortion) of the crystal also occurs, so that the irreversible capacity becomes not negligible, and a preferable battery may not be obtained.
The BET specific surface area is defined as the following value: the sample was preliminarily dried at 350 ℃ for 15 minutes under flowing of nitrogen gas using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research), and then measured by a nitrogen adsorption BET1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
[ [ [ volume average particle diameter ] ] ]
The volume average particle diameter (secondary particle diameter when primary particles are aggregated to form secondary particles) of the metal oxide containing titanium used as the negative electrode active material of the negative electrode [3] in the lithium secondary battery of the present invention is defined as a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is preferably 0.1 μm or more, more preferably 0.5 μm or more, and still more preferably 0.7 μm or more. The upper limit is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and further preferably 25 μm or less. If the amount is less than the above range, a large amount of binder is required for the production of the electrode, and as a result, the battery capacity may be reduced. If the amount exceeds the above range, the resulting electrode plate tends to have an uneven coating surface, which is not preferable in the battery production process.
[ [ [ average primary particle diameter ] ] ]
When the primary particles are aggregated to form secondary particles, the average primary particle diameter of the metal oxide containing titanium used as the negative electrode active material of the lithium secondary battery of the present invention is preferably 0.01 μm or more, more preferably 0.05 μm or more, further preferably 0.1 μm or more, most preferably 0.2 μm or more, and the upper limit thereof is preferably 2 μm or less, more preferably 1.6 μm or less, further preferably 1.3 μm or less, most preferably 1 μm or less. If the average primary particle diameter exceeds the upper limit, spherical secondary particles are difficult to form, and the powder filling property is adversely affected, or the specific surface area is greatly reduced, so that the possibility of deterioration in battery performance such as output characteristics may be increased. On the other hand, if the average primary particle size is less than the lower limit, the crystal is generally incomplete, and therefore, problems such as poor charge/discharge reversibility may occur.
The primary particle diameter can be measured by observation using a Scanning Electron Microscope (SEM). Specifically, the following method was used to obtain: in the photographs with magnification of 10000 to 100000 times, the longest value of the slice generated by the left and right boundary lines of the primary particle on the straight line in the horizontal direction is obtained for arbitrary 50 primary particles, and the average value is taken.
[ [ [ shape ] ] ]
The particle shape of the titanium-containing metal oxide used in the negative electrode [3] of the lithium secondary battery of the present invention may be a block shape, a polyhedral shape, a spherical shape, an ellipsoidal shape, a plate shape, a needle shape, a columnar shape, or the like, which has been conventionally used, and among them, it is preferable that primary particles are aggregated to form secondary particles, and the shape of the secondary particles is a spherical shape or an ellipsoidal shape. In general, in an electrochemical device, an active material in an electrode expands and contracts with charge and discharge, and therefore, deterioration such as breakage of the active material or disconnection of a conductive path due to the stress is likely to occur. Therefore, it is preferable that the primary particles are aggregated to form the secondary particles as compared with a single-particle active material of only the primary particles, because the formation of the secondary particles can relax the stress of expansion and contraction, thereby preventing deterioration. In addition, spherical or ellipsoidal particles are preferable to plate-like equiaxed-oriented particles because spherical or ellipsoidal particles have less orientation during electrode molding, have less expansion and contraction of an electrode during charge and discharge, and are easily mixed uniformly when mixed with a conductive agent during electrode production.
[ [ [ tap density ] ] ]
In the lithium secondary battery of the invention as a negative electrode [3 ]The tap density of the titanium-containing metal oxide used as the negative electrode active material of (3) is preferably 0.05g/cm3Above, it is more preferableIs selected to be 0.1g/cm3Above, more preferably 0.2g/cm3Above, particularly preferably 0.4g/cm3The above. Further, the upper limit thereof is preferably 2.8g/cm3Hereinafter, more preferably 2.4g/cm3Hereinafter, 2g/cm is particularly preferable3The following. If the tap density is less than this range, the packing density is difficult to increase when the negative electrode is used, and the contact area between particles decreases, so that the impedance between particles increases, and the output resistance may increase. On the other hand, if it exceeds this range, the number of voids between particles in the electrode is too small, and the flow path of the nonaqueous electrolytic solution is reduced, and therefore the output resistance may be increased.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300. mu.m, and the sample was dropped into a 20cm cell3The Tap density of (1) was determined by vibrating the container 1000 times with a stroke length of 10mm using a powder density measuring instrument (for example, Tap densitometer manufactured by seishin corporation) until the upper end face of the container was filled with the sample, and determining the density from the volume at that time and the weight of the sample.
[ [ [ circularity ] ] ]
The circularity of the metal oxide containing titanium used as the negative electrode active material of the negative electrode [3] in the lithium secondary battery of the present invention is usually 0.10 or more, preferably 0.80 or more, more preferably 0.85 or more, and further preferably 0.90 or more. As an upper limit, a circularity of 1 is a theoretical true sphere. If the content is less than this range, the filling property of the negative electrode active material decreases, the inter-particle impedance increases, and the short-time high-current density charge/discharge characteristics may decrease.
The circularity of the present invention is defined by the following formula.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the following values are used: for example, the value obtained by dispersing about 0.2g of a sample in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant using a flow particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial Co., Ltd.), irradiating the solution with ultrasonic waves of 28kHz for 1 minute at an output of 60W, designating 0.6 to 400 μm as a detection range, and measuring particles having a particle diameter in the range of 3 to 40 μm is obtained.
[ [ [ length-diameter ratio ] ] ]
The aspect ratio of the metal oxide containing titanium used as the negative electrode active material of the negative electrode [3] in the lithium secondary battery of the present invention is theoretically 1 or more, and the upper limit is 5 or less, preferably 4 or less, more preferably 3 or less, and still more preferably 2 or less. If the amount exceeds the upper limit, streaks may occur during the production of the electrode plate, and a uniform coating surface cannot be obtained, resulting in a decrease in the high-current-density charge/discharge characteristics in a short time.
When the longest diameter of the particle in three-dimensional observation is defined as a and the shortest diameter perpendicular to the longest diameter is defined as B, the aspect ratio is represented by a/B. The particles were observed by a scanning electron microscope which can observe the particles under magnification. 50 graphite particles fixed to the end face of a metal plate having a thickness of 50 μm or less were arbitrarily selected, a stage on which a sample was fixed was rotated and tilted, A, B of each of these particles was measured, and the average value of A/B was determined.
[ [ method for producing negative electrode active material ] ]
As a negative electrode [3 ] in the lithium secondary battery of the present invention]The method for producing the negative electrode active material of (3) is not particularly limited insofar as it does not exceed the gist of the present invention, and several methods are mentioned, and a general method for producing an inorganic compound can be used. Examples thereof include titanium raw material such as titanium oxide, raw material of other elements used as needed, and LiOH and Li2CO3、LiNO3And mixing Li source uniformly, and sintering at high temperature to obtain active material. In particular, when a spherical or ellipsoidal active material is produced, various methods can be considered, and examples thereof include the following: dissolving or pulverizing titanium raw material such as titanium oxide and other elements used as required, dispersing in solvent such as water, adjusting pH while stirring to obtain spherical precursor, drying as required, adding LiOH and Li 2CO3、LiNO3isoLi source at high temperatureA method of obtaining an active material by sintering; dissolving or pulverizing titanium raw material such as titanium oxide and other elements used as required in a solvent such as water, drying and molding the resultant by a spray dryer or the like to obtain spherical or elliptical precursor, and adding LiOH and Li2CO3、LiNO3A method of obtaining an active material by sintering a Li source at a high temperature; and titanium raw material such as titanium oxide, LiOH and Li2CO3、LiNO3And a method in which a raw material substance such as an Li source and other elements used as needed is dissolved or pulverized and dispersed in a solvent such as water, and the resultant is dried and molded by a spray dryer or the like to form a spherical or oval-spherical precursor, and then the precursor is sintered at a high temperature to obtain an active material.
In these steps, elements other than Ti, for example, Al, Mn, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, C, Si, Sn, and Ag may be present in the metal oxide structure containing titanium and/or in contact with the oxide containing titanium. By containing these elements, the operating voltage and capacity of the battery can be controlled.
[ electrode for negative electrode [3]
The negative electrode [3] can be produced by a usual method, and the negative electrode [3] can be formed in the same manner as described above. The thickness ratio of the current collector, and the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
Negative pole (4)
The following describes a negative electrode [4] used in the lithium secondary battery of the present invention, which contains a carbonaceous material as a negative electrode active material, wherein the carbonaceous material has a circularity of 0.85 or more and a surface functional group amount O/C value of 0 to 0.01.
[ negative electrode active material for negative electrode [4]
Next, the negative electrode active material used in the negative electrode [4] will be described.
The negative electrode active material used in the negative electrode [4] of the lithium secondary battery of the present invention contains at least a carbonaceous material satisfying the conditions (a) and (b).
(a) The circularity is more than 0.85;
(b) the O/C value of the surface functional group amount is 0 to 0.01.
The carbonaceous material used in the present invention will be described in detail below.
[ [ circularity ] ]
The circularity of the carbonaceous material is usually 0.85 or more, preferably 0.87 or more, more preferably 0.89 or more, and particularly preferably 0.92 or more. As an upper limit, a circularity of 1 is a theoretical true sphere. If the amount is less than this range, the filling property of the negative electrode active material decreases, making it difficult to compact the negative electrode, resulting in breakage of the particles during compaction, and the surface of the inside of the particles, which has poor high-temperature storage resistance at a low depth of charge, may be easily exposed.
The circularity in the present invention is defined by the following formula.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the following values are used: for example, the value obtained by dispersing about 0.2g of a sample in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant using a flow particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial Co., Ltd.), irradiating the solution with ultrasonic waves of 28kHz for 1 minute at an output of 60W, designating 0.6 to 400 μm as a detection range, and measuring particles having a particle diameter in the range of 3 to 40 μm is obtained.
[ [ O/C value ] ]
The carbonaceous material must have an O/C value of 0 to 0.01 in terms of the amount of surface functional groups. The upper limit of the O/C value is preferably 0.005 or less, and is preferably as close to 0 as possible.
The O/C value in the present invention is a ratio of the amount of surface functional groups measured by X-ray photoelectron spectroscopy (XPS), and if the O/C value of the amount of surface functional groups exceeds the above range, the amount of functional groups on the particle surface increases, and when charging is performed in the presence of a specific compound, the stability of the SEI film formed on the surface is insufficient, and the high-temperature storage characteristics at a low charge depth may be degraded.
The surface functional group amount O/C represents a ratio of a molar concentration of oxygen atoms to a molar concentration of carbon atoms present in the surface of the graphite material or the like, and is an index representing an amount of functional groups such as carboxyl groups, phenolic hydroxyl groups, carbonyl groups, and the like present in the surface. In carbon materials having a large surface functional group content O/C value, surface oxygen-containing functional groups are often bonded to the crystallite end faces of the particle-surface carbon. Further, as the O/C value of the surface functional group amount of the graphite material, the following values were used: in the X-ray photoelectron spectroscopy analysis, the peak areas of the spectra of C1s and O1s were obtained, and the atomic concentration ratio of C and O (O atomic concentration/C atomic concentration) was calculated. The specific measurement procedure is not particularly limited, and as an example thereof, the following is mentioned.
That is, the spectra of C1s (280-300 eV) and O1s (525-545 eV) were measured by multiplex measurement using an X-ray photoelectronic spectrometer (for example, ESCA manufactured by Ulvac-phi (アルバック - ファイ)) as an X-ray photoelectronic spectroscopy method, in which the surface of a measurement object (here, a graphite material) is flattened while being placed on a sample stage, and K.alpha.rays of aluminum are used as an X-ray source. The peak top of the obtained C1s was set to 284.3eV for charge compensation, and the peak areas of the spectra of C1s and O1s were obtained, and the surface atomic concentrations of C and O were calculated by multiplying the product by the device sensitivity coefficient. The atomic concentration ratio of O to C (O atomic concentration/C atomic concentration) was calculated and defined as the O/C value of the surface functional group amount of the graphite material.
The carbonaceous material used in the present invention satisfies the above-mentioned conditions of "circularity" and "surface functional group amount O/C value", but from the viewpoint of the balance of the battery, it is more preferable to satisfy one or more of the following conditions at the same time. Of these, it is preferable to satisfy the condition of any one or more of the tap density, the raman R value, and the volume average particle diameter at the same time.
[ [ tap density ] ]
The tap density of the carbonaceous material is usually 0.55g/cm3Above, preferably 0.7g/cm3Above, more preferably 0.8g/cm3Above, particularly preferably 0.9g/cm3The above. Further, the upper limit thereof is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, it is difficult to increase the packing density when used as a negative electrode, and a high capacity battery may not be obtained. On the other hand, if the amount exceeds this range, the number of voids between particles in the electrode is too small, and it is difficult to ensure conductivity between particles, and it may be difficult to obtain preferable battery characteristics.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300. mu.m, and the sample was dropped into a 20cm cell3The Tap density of (1) was determined by calculating the density from the volume and weight of the sample in the Tap container (1) after the sample filled the upper end face of the container and by vibrating the sample 1000 times with a stroke length of 10mm using a powder density measuring instrument (for example, Tap densifier manufactured by seishin corporation).
[ [ Raman R value, half-value Width ] ]
The R value of the carbonaceous material measured by argon ion laser raman spectroscopy is usually 0.001 or more, preferably 0.01 or more, and the upper limit thereof is usually 0.2 or less, preferably 0.18 or less, and more preferably 0.15 or less. If the R value is less than this range, the crystallinity of the particle surface becomes too high, and Li may be less likely to enter into the interlayer during charging and discharging. That is, the charge acceptance is reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, and when charging is performed in the presence of a specific compound, the stability of the SEI film formed on the surface is insufficient, and the high-temperature storage characteristics at a low charge depth may be lowered.
In addition, the carbonaceous material is 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 10cm-1Above, preferably 15cm-1Above, the upper limit is usually 35cm-1Hereinafter, preferably 30cm-1The following ranges. If the Raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters the interlayer may decrease with charge and discharge. That is, the charge acceptance may be reduced. On the other hand, if the amount is more than the above range, the crystallinity of the particle surface is lowered, and a stripe in which a specific compound is present is formed When charging is performed under a material, the stability of the SEI film formed on the surface is insufficient, and the high-temperature storage characteristics at a low charging depth may be degraded.
The raman spectrum was measured as follows: the sample is filled by using raman spectroscopy (for example, a raman spectrometer manufactured by japan spectroscopy corporation) by naturally dropping the sample into a measurement vessel, and the measurement is performed by irradiating the surface of the sample in the vessel with an argon ion laser and rotating the vessel in a plane perpendicular to the laser. For the obtained Raman spectrum, 1580cm was measured-1Nearby peak PAStrength I ofAAnd 1360cm-1Nearby peak PBStrength I ofBAnd calculating the intensity ratio R (R ═ I)B/IA) This is defined as the raman R value of the carbonaceous material. The Raman spectrum obtained by measurement was 1580cm-1Nearby peak PAIs defined as the raman half-value width of the carbonaceous material.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10-20 cm-1
Measurement range: 1100cm-1～1730cm-1
R-value, half-value width analysis: background processing
Smoothing treatment: simple average, convolution 5 points
[ [ volume-based average particle diameter ] ]
The volume-based average particle diameter of the carbonaceous material is a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and still more preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial loss of battery capacity may occur. If the amount exceeds the above range, the resulting electrode plate tends to have an uneven coating surface, which is not preferable in the battery production process.
Further, the ratio (d) of the 90% particle diameter to the 10% particle diameter of the distribution is calculated on the basis of the volume-based particle diameter90/d10) Is 1.2 or more, preferably 1.5 or more, and more preferably 1.7 or more. The upper limit is 8 or less, preferably 5 or less, more preferably 4 or less, and still more preferably 3 or less.
In the present invention, the volume-based average particle diameter is defined by a median particle diameter, which is determined by the following method: the carbon powder was dispersed in a 0.2 mass% aqueous solution (about 1mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant, and measured using a laser diffraction/scattering particle size distribution meter (for example, LA-700 manufactured by horiba ltd.). As the ratio (d) of 90% particle diameter to 10% particle diameter 90/d10) The volume-based 90% particle diameter and 10% particle diameter can be measured in the same manner, and the ratio (d) thereof can be used90/d10)。
[ [ X-ray parameters ] ]
The carbonaceous material preferably has a d value (interlayer distance) of a lattice plane (002) of 0.335nm or more as determined by X-ray diffraction using a vibroseis method. The upper limit is 0.340nm or less, preferably 0.337nm or less. If the value of d is too large, crystallinity may be reduced, and initial irreversible capacity may be increased. On the other hand, 0.335 is the theoretical value of graphite. The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is usually in the range of 30nm or more, preferably 50nm or more, and more preferably 80nm or more. If the content is less than this range, the crystallinity of the particles may be reduced, and the initial irreversible capacity may be increased.
[ [ ash ] ])
The ash content in the carbonaceous material is 1 mass% or less, preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, based on the total mass of the carbonaceous material, and the lower limit thereof is 1ppm or more. If the amount exceeds the above range, deterioration of battery performance due to reaction with the electrolyte during charge and discharge cannot be ignored. If it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost sometimes rises.
[ [ BET specific surface area ] ]
The specific surface area of the carbonaceous material measured by the BET method is usually 0.1m2A ratio of 0.7m or more2A value of 1m or more, more preferably 1m2A total of 1.5m or more2More than g. The upper limit is usually 100m2A ratio of 25m or less per gram2A ratio of 15m or less per gram2A total of 10m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the value of the specific surface area is less than the above range, the acceptance of lithium during charging is deteriorated and lithium is likely to be deposited on the electrode surface when the negative electrode material is used. On the other hand, if the amount exceeds the above range, the reactivity with the electrolyte increases when the negative electrode material is used, the amount of gas generated increases, and it may be difficult to obtain a preferable battery.
The BET specific surface area is defined as a value determined as follows: the sample was preliminarily dried at 350 ℃ for 15 minutes under flowing of nitrogen gas using a surface area meter (for example, a fully automatic surface area measuring apparatus manufactured by a large warehouse), and then measured by a nitrogen adsorption BET1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
[ [ micropore distribution ] ]
The amount of voids in the carbonaceous material corresponding to particles having a diameter of 0.01 to 1 μm, which are measured by a mercury porosimeter (mercury intrusion method), and irregularities due to the surface roughness of the particles is usually 0.01mL/g or more, preferably 0.05mL/g or more, more preferably 0.1mL/g or more, and the upper limit is usually 0.6mL/g or less, preferably 0.4mL/g or less, more preferably 0.3mL/g or less. If the amount exceeds this range, a large amount of binder is sometimes required for manufacturing the electrode plate. On the other hand, if the amount is less than this range, the high-current-density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of adhesive is sometimes required for producing the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. On the other hand, if the amount is less than this range, the high current density charge-discharge characteristics may be degraded.
As a device for the mercury porosimeter, a mercury porosimeter (autopore 9520; manufactured by micromeritics) can be used. About 0.2g of a sample (negative electrode material) was weighed, sealed in a powder container, degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes, and subjected to pretreatment. Subsequently, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased stepwise from 4psia (about 28kPa) to 40000psia (about 280MPa), followed by pressure reduction to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 °. The average pore size is the pore size at which the cumulative pore volume reaches 50%.
[ [ true density ] ]
The carbonaceous matter generally has a true density of 2g/cm3Above, preferably 2.1g/cm3Above, more preferably 2.2g/cm3Above, more preferably 2.22g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase. In the present invention, the true density is defined as a value measured by a liquid phase substitution method (a gravimetric method) using butanol.
[ [ orientation ratio ] ]
The orientation ratio of the carbonaceous material is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be degraded.
The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction of carbon obtained by X-ray diffraction were fitted using asymmetric pearson VII as a distribution function, peak separation was performed, and integrated intensities of the peaks of (110) diffraction and (004) diffraction were calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as an active material orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit: divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
[ [ length-diameter ratio ] ]
The carbonaceous material has an aspect ratio of theoretically 1 or more and an upper limit of 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks are generated when the electrode plate is produced, and a uniform coating surface cannot be obtained, and the high-current-density charge/discharge characteristics may be deteriorated.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the particle and the shortest diameter B perpendicular thereto in three-dimensional observation. The particles are observed by a scanning electron microscope which can observe the particles under magnification. Arbitrary 50 graphite particles fixed to the end faces of a metal having a thickness of 50 μm or less were selected, and a stage on which a sample was fixed was rotated and tilted, and A, B of each of these particles was measured to obtain an average value of a/B.
[ [ method for producing carbonaceous Material and raw Material ]
The carbonaceous material used in the present invention may be a naturally occurring material or an artificially produced material, but is preferably a material derived from natural graphite. In addition, naturally occurring substances or artificially manufactured substances may also be subjected to specific treatments. The production method (including the sorting method) is not particularly limited, and for example, a material obtained by sorting a carbonaceous material having the above-described characteristics by a classification method such as sieving or air classification may be used.
Among these, carbonaceous materials obtained by heat-treating naturally occurring carbon materials (natural graphite materials) are preferred because they are easily available and easily processed in the previous step. From the viewpoint of improving the filling property, etc., a carbonaceous material obtained by: a carbon material produced naturally (natural graphite material) or an artificially produced carbon material is subjected to mechanical energy treatment to be modified and spheroidized, and the obtained spheroidized carbon is subjected to heat treatment. In addition, from the viewpoint of the balance of the performance of the lithium secondary battery, and the like, the carbonaceous material prepared as follows is particularly preferable: and (3) applying mechanical energy to the natural graphite raw material for treatment, and carrying out heat treatment on the obtained spheroidized natural graphite. Hereinafter, the carbon material (raw material) before heat treatment such as the natural graphite raw material may be referred to simply as "raw material before heat treatment".
[ [ Natural graphite raw Material ] ]
As described above, natural graphite is particularly preferable as the raw material of the carbonaceous material.
Natural GRAPHITEs are classified according to their properties as Flake Graphite (Flake Graphite), Flake Graphite (vessel) Graphite, AND soil Graphite (Amorphous Graphite) (see "integration OF powder technology" (Co., Ltd.) in the center OF Industrial AND technology, as Graphite published in Showa 49, AND "HAND BOOK CARBON, GRAPHITE, DIAMOND FULLERENES", published by Noyes Publications). The graphitization degree was highest with flaky graphite, 100%, followed by flaky graphite, 99.9%, and soil graphite as low as 28%. The quality of natural graphite is determined mainly according to the place of production and the vein. The flaky graphite is mainly produced from Madagascar, China, Brazil, Ukrainian, Canada and the like; the scale graphite is mainly produced from srilanca, and the main production sites of soil graphite are korean, china, mexico, and the like. Among these natural graphites, scaly graphite and scaly graphite are preferable as a raw material for carbonaceous materials because they have advantages such as high graphitization degree and small impurity amount.
[ [ [ mechanical energy treatment, spheroidization ] ] ]
The mechanical energy treatment is performed so that the volume average particle diameter before and after the treatment is 1 or less. The "volume average particle diameter ratio before and after treatment" is a value obtained by dividing the volume average particle diameter after treatment by the volume average particle diameter before treatment. In the present invention, the mechanical energy treatment performed to produce the raw material before the heat treatment is preferably such that the average particle size ratio before and after the treatment is 1 or less.
The mechanical energy treatment is a treatment in which the particle size is reduced so that the average particle diameter ratio before and after the powder particle treatment is 1 or less, and the particle shape is controlled. The mechanical energy treatment belongs to the pulverization treatment in the engineering unit operations that can be effectively utilized in particle design, such as pulverization, classification, mixing, granulation, surface modification, reaction, and the like.
The term "pulverization" means that a force is applied to a substance to reduce its size and thereby to adjust the particle size, particle size distribution, and filling properties of the substance. The pulverization treatment is classified according to the kind of force applied to the material and the treatment form. The forces applied to a substance are roughly classified into 4 types as follows: (1) knocking force (impact force), (2) crushing force (compression force), (3) grinding force (grinding force), and (4) scraping force (shear force). On the other hand, the treatment forms are roughly classified into the following 2 types: volume pulverization in which cracks are generated in the particles and propagated, and surface pulverization in which the surfaces of the particles are cut. The volume crushing can be carried out by adopting impact force, compression force and shearing force; the surface pulverization can be carried out by using a grinding force or a shearing force. Pulverization is a process in which the kinds and treatment forms of the force applied to these substances are combined in various ways. The combination thereof may be appropriately determined depending on the purpose of the processing.
The pulverization may be carried out by using a chemical reaction such as blasting or volume expansion, but is usually carried out by using a mechanical device such as a pulverizer. The pulverization treatment used in the production of the spheroidized carbonaceous material as the raw material of the present invention is preferably a treatment in which the ratio of the final surface treatment is increased, regardless of the presence or absence of volume pulverization. This is because it is important to remove the corners of the particle surface pulverization to introduce circularity to the particle shape. Specifically, the surface treatment may be performed after the volume pulverization to some extent, or only the surface treatment may be performed without performing the volume pulverization at all, or the volume pulverization and the surface treatment may be performed at the same time. Preferably, the surface pulverization is performed finally, and the pulverization treatment is performed by removing corners from the surface of the particles.
The device for performing the kinetic energy treatment is selected from devices capable of performing the above-described preferred treatments. The mechanical energy treatment can be achieved by using one or more of the 4 types of forces applied to the substance, but it is preferable to apply an impact force to the particles by repeating mechanical actions such as compression, friction, and shearing force including interactions of the particles to the host. Thus, in particular, the following devices are preferred: the apparatus has a rotor having a plurality of blades inside a casing, and performs surface treatment while performing volume pulverization by applying mechanical actions such as impact compression, friction, and shearing force to a carbon material introduced into the casing by rotating the rotor at a high speed. Further, an apparatus having a mechanism for repeatedly imparting a mechanical action to carbonaceous materials by circulating or convecting the carbonaceous materials is more preferable.
Preferred examples of the apparatus include a mixing system (manufactured by Nara machinery manufacturing Co., Ltd.), a krypton (クリプトロン) (manufactured by Earth technical (アーステクニカ)) a CF mill (manufactured by Yu Ming Co., Ltd.), a mechanofusion system (manufactured by hosokawamicon (ホソカワミクロン)) and the like. Of these, a mixing system manufactured by Nara machine manufacturing company is preferable. When the apparatus is used for treatment, the peripheral speed of the rotating rotor is preferably set to 30 to 100 m/sec, more preferably 40 to 100 m/sec, and still more preferably 50 to 100 m/sec. The treatment may be carried out by passing only the carbonaceous material, but is preferably carried out by circulating or retaining in the apparatus for 30 seconds or more, and more preferably carried out by circulating or retaining in the apparatus for 1 minute or more.
By performing the mechanical energy treatment in this way, the carbon particles become particles as follows: the crystallinity is maintained high as a whole, but the vicinity of the surface of the particle is roughened, and the edge surface is inclined and exposed. Thus, the area on which lithium ions can be taken in and out increases, and the capacity is high even at a high current density.
Generally, the smaller the particle size of the scale-like, scaly or plate-like carbon material is, the more the filling property tends to deteriorate. This is considered to be due to the following reasons: the particles are more amorphized by pulverization, or protrusions such as "burrs", "peeling" and "bending" formed on the particle surface are increased, or fine amorphous particles are adhered to the particle surface with a certain degree of strength, so that the resistance between adjacent particles is increased, and the filling property is deteriorated.
If the amorphousness of these particles is reduced and the particle shape is close to spherical, the filling property is rarely reduced even if the particle size is reduced, and theoretically, both the large-particle-size carbon powder and the small-particle-size carbon powder should exhibit the same tap density.
[ [ [ Properties of raw Material before Heat treatment ] ] ]
The physical properties of the raw materials before heat treatment preferably satisfy at the same time one or more of (1) to (11) shown below. The intangible measurement method and definition are the same as those of the carbonaceous material.
(1) X-ray parameters
The d value (interlayer distance) of the lattice plane (002) of the raw material before heat treatment, which is determined by X-ray diffraction using the vibro-optic method, is preferably 0.335nm or more. The lower limit is less than 0.340nm, preferably 0.337nm or less. If the value of d is too large, crystallinity may be reduced, and initial irreversible capacity may be increased. On the other hand, 0.335 is a theoretical value of graphite. The crystallite size (Lc) of the carbon material obtained by X-ray diffraction using a vibroseis method is usually in the range of 30nm or more, preferably 50nm or more, and more preferably 80nm or more. If the content is less than this range, the crystallinity may be lowered, and the initial irreversible capacity may be increased.
(2) Ash content
The ash content in the raw material before heat treatment is usually 1 mass% or less, preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, based on the total mass of the raw material before heat treatment, and the lower limit thereof is usually 1ppm or more. If the amount exceeds the above range, deterioration of battery performance due to reaction with the electrolyte during charge and discharge cannot be ignored. If the amount is less than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost may be increased.
(3) Volume-based average particle diameter
The volume-based average particle diameter of the raw material before heat treatment is a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and still more preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, an uneven coating surface is likely to be formed when the electrode plate is produced, which is not preferable in the battery production process.
(4) Raman R value, Raman half value width
The R value of the raw material before heat treatment as measured by argon ion laser raman spectroscopy is usually 0.10 or more, preferably 0.15 or more, more preferably 0.17 or more, and still more preferably 0.2 or more, and the upper limit thereof is usually 0.8 or less, preferably 0.6 or less, and more preferably 0.4 or less. If the R value is less than this range, the particles may not be spheroidized, and the effect of improving the filling property may not be obtained. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, and the reactivity with the electrolyte solution is increased, which may result in a decrease in efficiency or an increase in gas generation.
The raw material before heat treatment was 1580cm in length-1The near-Raman half-value width is not particularly limited, but is usually 10cm-1Above, preferably 15cm-1Above, the upper limit is usually 80cm-1The following are excellentIs selected to be 60cm-1Hereinafter, more preferably 45cm-1Hereinafter, more preferably 40cm-1The following ranges. If the raman half-value width is less than this range, the particles may not be spheroidized, and the effect of improving the filling property may not be obtained. On the other hand, if the amount is more than this range, the crystallinity of the particle surface is lowered, the reactivity with the electrolyte solution is increased, and the efficiency may be lowered or the amount of generated gas may be increased.
(5) BET specific surface area
The specific surface area of the raw material before heat treatment, measured by the BET method, is usually 0.1m2More than g, preferably 0.7m2A value of 1m or more, more preferably 1m2A total of 1.5m or more2More than g. Its upper limit is typically 100m2A ratio of 50m or less per gram2A ratio of 15m or less per gram2A concentration of 10m or less is further preferable2The ratio of the carbon atoms to the carbon atoms is less than g. If the value of the specific surface area is less than the above range, the acceptance of lithium during charging is poor when the negative electrode material is used, and lithium is likely to precipitate on the electrode surface. On the other hand, if the amount exceeds the above range, the specific surface area is reduced by heat treatment, and a reaction with the electrolyte solution is generated more than necessary, and the amount of generated gas increases, and it is sometimes difficult to obtain a preferable battery.
(6) Distribution of micropores
The amount of voids in the particles corresponding to the diameters of 0.01 to 1 μm and irregularities due to the irregularities on the particle surfaces of the raw material before the heat treatment, which are determined by a mercury porosimeter (mercury intrusion method), is usually 0.01mL/g or more, preferably 0.05mL/g or more, and more preferably 0.1mL/g or more, and the upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, and more preferably 0.3mL/g or less. If this range is exceeded, a large amount of binder is required for manufacturing the plate. On the other hand, if the amount is less than this range, the high current density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of adhesive is sometimes required for producing the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. On the other hand, if the amount is less than this range, the high current density charge-discharge characteristics may be degraded.
(7) Degree of circularity
The circularity is used as the degree of sphericity of the raw material before heat treatment, and the circularity of particles having a particle diameter of 3 to 40 μm of the raw material before heat treatment is preferably 0.85 or more, more preferably 0.87 or more, particularly preferably 0.90 or more, and further preferably 0.92 or more. A large circularity is preferable because high current density charge/discharge characteristics are improved.
The method for increasing the circularity is not particularly limited, but the sphericization treatment by the mechanical energy described above is preferably performed to form a sphere, because the shape of the inter-particle voids is uniform when the electrode body is formed.
(8) True density
The true density of the raw material before heat treatment is usually 2g/cm3Above, preferably 2.1g/cm3Above, more preferably 2.2g/cm3Above, more preferably 2.22g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
(9) Tap density
The tap density of the raw material before heat treatment is usually 0.55g/cm3Above, preferably 0.7g/cm3More preferably 0.8g/cm or more3Above, particularly preferably 0.9g/cm3The above. Further, the upper limit thereof is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if the amount is more than this range, the number of voids between particles in the electrode is too small, and it is difficult to secure conductivity between particles, and it may be difficult to obtain preferable battery characteristics.
(10) Orientation ratio
The orientation ratio of the raw material before heat treatment is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
(11) Aspect ratio
The aspect ratio of the raw material before heat treatment is theoretically 1 or more, and the upper limit is usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks are generated when the electrode plate is produced, and a uniform coating surface cannot be obtained, and the high-current-density charge/discharge characteristics may be deteriorated.
[ [ [ Heat treatment temperature ] ] ]
The heat treatment temperature of the raw material before heat treatment is usually 600 ℃ or higher, preferably 1200 ℃ or higher, more preferably 2000 ℃ or higher, still more preferably 2500 ℃ or higher, and particularly preferably 2800 ℃ or higher. The upper limit is usually 3200 ℃ or lower, preferably 3100 ℃ or lower. If the temperature condition is less than this range, the crystal repair of the surface of the graphite particles which are scattered by spheroidizing treatment or the like may be insufficient, and the raman R value and BET specific surface area may not be reduced. On the other hand, if the amount exceeds the above range, the sublimation amount of graphite tends to increase.
[ [ Heat treatment method ] ] ]
The heat treatment may be carried out by passing through the above-mentioned temperature range once. The holding time for holding the temperature condition in the above range is not particularly limited, but is usually longer than 10 seconds and 168 hours or less.
The heat treatment is usually performed in an inert gas atmosphere such as nitrogen or in a non-oxidizing atmosphere obtained from a gas generated from the raw material graphite. However, in a furnace of the type embedded in coke powder (fine pitch sintered carbon), air is sometimes mixed at the beginning. In such a case, it is not necessary to use a completely inert gas atmosphere.
The apparatus used for the heat treatment is not particularly limited, and for example, a shuttle furnace, a tunnel furnace, an electric furnace, a coke baking furnace, a rotary furnace, a direct electric furnace, an attorney electric furnace, a resistance heating furnace, an induction heating furnace, or the like can be used.
In addition to the above-described respective processes, various processes such as a classification process may be performed. The classification treatment is a treatment for obtaining a target particle diameter and removing coarse powder and fine powder. The apparatus used for the classification treatment is not particularly limited, and for example, in the case of dry screening, a rotary screen, a shaker screen, a rotary screen, a vibrating screen, or the like; in the case of dry air classification, a gravity classifier, an inertia classifier, a centrifugal classifier (classifier, cyclone), or the like; in the case of wet screening, a mechanical wet classifier, a hydraulic classifier, a sedimentation classifier, a centrifugal wet classifier, or the like may be used. The classification treatment may be performed before the heat treatment, or may be performed at another time, for example, after the heat treatment. Further, the classification processing itself may also be omitted. However, from the viewpoint of productivity of the graphite powder negative electrode material, it is preferable to perform the classification treatment immediately after the spheroidization treatment and before the heat treatment.
[ [ mixture of auxiliary materials ] ]
In addition to the carbonaceous material, the negative electrode active material used in the present invention contains one or more carbonaceous materials (carbonaceous materials) different from the carbonaceous material in terms of carbonaceous physical properties, and thus can further improve battery performance. The "carbonaceous physical properties" referred to herein mean one or more characteristics of X-ray diffraction parameters, median particle diameter, aspect ratio, BET specific surface area, orientation ratio, raman R value, tap density, micropore distribution, circularity, and ash content. Further, preferred embodiments include a volume-based particle size distribution which is asymmetric about the median diameter, contains 2 or more carbon materials having different raman R values, and has different X-ray parameters. Examples of the effect include the addition of graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke are used as a sub-material to reduce electrical resistance and the like. These may be used alone, or may be used in combination of 2 or more in any combination and in any ratio. When added as a subcomponent, the amount of addition is usually 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more, and the upper limit thereof is usually 80% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less, and particularly preferably 30% by mass or less. If the amount is less than this range, the effect of improving the conductivity may be difficult to obtain. If the content exceeds the above range, the initial irreversible capacity may increase.
[ electrode for negative electrode [4]
The negative electrode [4] can be produced by a usual method, and the negative electrode [4] can be formed in the same manner as described above. The thickness ratio of the current collector, and the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
< negative electrode [5] >
Next, a negative electrode [5] used in the lithium secondary battery of the present invention, which contains a heteroorientation carbon composite containing 2 or more carbonaceous materials having different orientations as an active material, will be described.
[ negative electrode active material for negative electrode [5]
Next, a negative electrode active material used for the negative electrode [5] will be described.
[ [ constitution of heteroleptic carbon composite ] ]
The negative electrode active material used in the negative electrode [5] of the lithium secondary battery of the present invention contains a heteroorientation carbon composite containing 2 or more carbonaceous materials having different orientations.
The term "different orientation" as used herein means that at least one of the size, direction, number, and the like of the anisotropic units of the optically anisotropic structure is different when the powder is observed with a polarization microscope, i.e., when the size, direction, number, and the like of the anisotropic units are visually compared. For example, there may be mentioned a case where one of the carbons 1 and 2 has a crystal orientation in one direction and the other has a random crystal orientation; or the carbonaceous materials 1 and 2 may have crystal orientations in a certain direction, but the directions are different from each other. In addition, in the case where one or both of the carbon 1 and carbon 2 are not a single crystal but an aggregate of a plurality of crystals, the unit of the aggregate is regarded as 1 region, and the aggregate pattern of the anisotropic unit of the optically anisotropic structure is compared.
In addition, the form in which the carbonaceous particles 1 and 2 coexist in the anisotropic carbon composite is preferably contained in 1 secondary particle. The term "contained in 1 secondary particle" as used herein means a state in which carbonaceous materials having different orientation are physically bound and adhered; a state in which the shape is maintained by electrostatic confinement or adhesion; a state of being bound by bonding, and the like. The term "physically bound and attached" as used herein means a state in which one carbonaceous material is included in another carbonaceous material and is connected to the other carbonaceous material; the term "electrostatically bound and attached" refers to a state in which one carbonaceous material is attached to another carbonaceous material by electrostatic energy. In the bound and adhered state, the above-described orientation may be different, or the original carbonaceous material may be the same. The "state of being bound by bonding" refers to chemical bonding such as hydrogen bond, covalent bond, ionic bond, and the like.
Among these, it is preferable that at least a part of the surface of one carbonaceous material is attached and/or bonded to cause another carbonaceous material to have an interface having a different orientation. In comparison with the case where the interface is not present, it is preferable that the particles having the same shape have a larger area in expansion due to inclusion of lithium ions during charging, and thus the battery can be prevented from being deteriorated.
The portion having different orientation may be formed by bonding with an externally supplied material and/or a modified substance thereof, or may be formed by modifying a material of a surface portion of the carbonaceous substance. Among them, the coating means that the coating has a chemical bond in at least a part of the interface with the surface of the carbonaceous material, and shows: (1) a state in which the entire surface is covered, (2) a state in which the carbonaceous material is partially covered, (3) a state in which the surface is selectively covered, and (4) a state in which the carbonaceous material is present in a very small region including a chemical bond.
In addition, the orientation of the carbonaceous material may be continuously changed or may be discontinuously changed in the vicinity of the interface. That is, the heteroorientable carbon composite preferably has an interface formed by attaching and/or bonding carbonaceous materials having different orientations, and the orientation of the carbonaceous materials in the interface changes discontinuously and/or continuously.
The structural component of the hetero-oriented carbonaceous composite (a) is not particularly limited as long as it has crystallinity, but it is preferable that at least one of the carbonaceous materials having different orientations is a graphite-based carbonaceous material (B) derived from natural graphite (D) (hereinafter, simply referred to as "natural graphite-based carbonaceous material (B)") in view of high charge capacity per unit mass.
The proportion of the natural graphite-based carbonaceous material (B) contained in the anisotropic carbon composite to the anisotropic carbon composite is usually 5 mass% or more, preferably 20 mass% or more, more preferably 30 mass% or more, still more preferably 40 mass% or more, and particularly preferably 50 mass% or more. The upper limit is usually 99.9 mass% or less, preferably 99 mass% or less, more preferably 95 mass% or less, and still more preferably 90 mass% or less. If the amount is less than this range, the load of the electrode during rolling may be significantly increased, which may cause peeling of the electrode. On the other hand, if the molecular weight exceeds this range, the adhesion at the interface of the composite of particles having different orientation properties may be weakened.
In addition, as another constituent component of the heteroorientation carbon composite, it is preferable that the carbonaceous material (C) selected from the following (1) to (5) is one or more carbonaceous materials having different orientations from the viewpoint of interfacial formation and improvement of interfacial adhesion during the production of the heteroorientation carbon composite.
(1) A carbide selected from coal-based coke, petroleum-based coke, furnace black, acetylene black, and pitch-based carbon fiber;
(2) A carbide having as a precursor an organic substance selected from the group consisting of asphalt raw materials, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenyls, organic synthetic polymers, natural polymers, thermoplastic resins and thermosetting resins, and/or a thermal decomposition product thereof;
(3) a carbide in which a thermal decomposition product of the solution is a precursor, which is obtained by dissolving the organic substance of (2) in a low-molecular-weight organic solvent;
(4) carbides of organic matter-containing gases;
(5) the graphited products of (1) to (4).
The component (2) is not particularly limited as long as it is a substance that can be carbonized, and examples thereof include aromatic hydrocarbons such as raw materials for asphalt, acenaphthylene, decacycloolefin, anthracene, and phenanthrene; n-ring compounds such as phenazine and acridine; s ring compounds such as thiophene and bithiophene; polyphenyl, such as biphenyl and terphenyl; organic high molecules such as polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insoluble products thereof, nitrogen-containing polyacrylonitrile, and polypyrrole; organic polymers such as sulfur-containing polythiophene and polystyrene; polysaccharides such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, and sucrose; thermoplastic resins such as polyphenylene sulfide and polyphenylene ether; thermosetting resins such as furfuryl alcohol resin, phenol resin, and imide resin; or organic substances such as solutions obtained by dissolving them in low-molecular-weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane; carbonizable gases, and the like.
Among these, the asphalt raw material is preferred because it has a high char yield and can be produced in a high yield. In the present specification, the term "pitch raw material" refers to pitch and substances belonging to pitch, and means substances that can be carbonized and/or graphitized by appropriate treatment. As specific examples of the asphalt material, tar, heavy oil, asphalt, or the like can be used. Specific examples of the tar include coal tar and petroleum tar. Specific examples of the heavy oil include a contact decomposed oil of a petroleum heavy oil, a thermal decomposed oil, an atmospheric residue, a vacuum residue, and the like. Specific examples of the pitch include coal tar pitch, petroleum pitch, and synthetic pitch. Among them, coal tar pitch is preferred because of its high aromaticity. These draining materials may be used singly or in combination of 2 or more in any combination and ratio.
Preferable examples of (3) include a carbide in which the organic substance of (2) is dissolved in a low-molecular-weight organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane to obtain a solution, and a thermal decomposition product of the solution is used as a precursor.
Examples of (4) include hydrocarbon compounds such as methane, ethane, propane, benzene, acetylene, and ethylene; carbon monoxide, and the like.
The proportion of the carbonaceous material (C) contained in the heterooriented carbon composite is usually in the range of 0.1 mass% or more, preferably 1 mass% or more, more preferably 5 mass% or more, and still more preferably 10 mass% or more. The upper limit is not particularly limited as long as the interface has different orientation. If the content is less than this range, the adhesion of the interface in the heteroleptic carbon composite may be weakened. If the amount exceeds this range, the effect of suppressing deformation of the particles during pressing due to the carbonaceous material (C) is reduced, and the cycle characteristics are degraded.
As a more preferable configuration of the negative electrode active material used in the lithium secondary battery of the present invention, it is preferable that the anisotropic carbon composite contains at least one natural graphite-based carbonaceous material (B) and at least one carbonaceous material (C) in combination from the viewpoint of a compressive load during electrode pressure and a balance of adhesiveness as an interface of the composite.
For the same reason as described above, the mass ratio of the natural graphite-based carbonaceous material (B) to the carbonaceous material (C) (natural graphite-based carbonaceous material (B)/carbonaceous material (C)) in the anisotropic carbon composite is usually 20/80 or more, preferably 40/60 or more, more preferably 60/40 or more, and still more preferably 70/30 or more. The upper limit is 99.9/0.1 or less, preferably 99/1 or less, and more preferably 95/5 or less. If the ratio exceeds this range (if the ratio of the natural graphite-based carbonaceous material (B) is too large), the interfacial adhesiveness by the carbonaceous material (C) may be reduced. On the other hand, if the ratio is less than this range (if the ratio of the natural graphite-based carbonaceous material (B) is too small), the load applied during electrode rolling becomes significantly large, and delamination may occur during rolling.
The heterooriented carbon composite containing the natural graphite-based carbonaceous material (B) and the carbonaceous material (C) may take any form as long as it does not depart from the scope of the present invention, and an example thereof will be described below.
(1) A form in which the carbonaceous material (C) is attached to and/or covered and/or bonded to the entire surface or a part of the surface of the natural graphite-based carbonaceous material (B);
(2) a form in which the carbonaceous material (C) is bonded to the entire surface or a part of the surface of the natural graphite-based carbonaceous material (B) and 2 or more natural graphite-based carbonaceous materials (B) and/or carbonaceous materials (C) are combined;
(3) the above (1) and (2) are mixed at an arbitrary ratio.
In addition, the natural graphite-based carbonaceous material (B) may be replaced with the carbonaceous material (C), and specific composite forms of the heteroorientation carbon composite include a form in which a carbonaceous material is attached to and/or covered and/or bonded on the surface of particles as a core; a form in which the surfaces of a plurality of particles as cores are attached and/or covered and/or bonded; or a state in which the particles as the core are granulated in a non-parallel manner. The non-parallel granulation state referred to herein means a state in which particles having a certain crystallinity are fixed by another carbonaceous material in a random direction, and are bonded so as to exhibit a different orientation.
[ [ preparation of heteroleptic carbon composite ] ]
The preparation of the heteroepitaxial carbon composite is described below in "methods 1 and 2 for producing a heteroepitaxial carbon composite", and the heteroepitaxial carbon composite can be prepared by applying heat treatment to improve crystallinity and increase the capacity per unit weight. The heat treatment temperature is usually 400 ℃ or higher, preferably 1000 ℃ or higher, more preferably 2000 ℃ or higher, still more preferably 2400 ℃ or higher, and particularly preferably 2800 ℃ or higher. The upper limit is usually 3400 ℃ or lower, preferably 3200 ℃ or lower. If the content is less than this range, the crystallinity may not be sufficiently improved, and the effect of increasing the capacity per unit weight may not be obtained. On the other hand, if the amount exceeds this range, the loss due to sublimation of carbon cannot be ignored, and the yield may be reduced.
[ [ Properties of heteroleptic carbon composite ] ]
The properties of the heteroepitaxial carbon composite preferably satisfy one or more of the following items (1) to (5) at the same time.
(1) Degree of circularity
The degree of circularity is used as the degree of sphericity of the heteroorientation carbon composite, and the degree of circularity of particles having a particle diameter of 3 to 40 μm of the heteroorientation carbon composite is usually 0.1 or more, preferably 0.5 or more, more preferably 0.8 or more, further preferably 0.85 or more, and most preferably 0.9 or more. A large circularity is preferable because high current density charge/discharge characteristics are improved. The circularity is defined by the following formula, and a theoretical true sphere is obtained when the circularity is 1.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the value measured as follows was used: for example, particles having a particle size in the range of 3 to 40 μm were measured by dispersing about 0.2g of a sample in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant using a flow-type particle image analyzer (e.g., FPIA manufactured by Sysmex Industrial Co., Ltd.), irradiating the sample with ultrasonic waves of 28kHz for 1 minute at an output of 60W, and then designating 0.6 to 400 μm as a detection range.
The method for increasing the circularity is not particularly limited, but is preferably a method in which the electrode body is formed into a spherical shape by performing a spheroidizing treatment so that the shape of voids between particles can be made uniform when the electrode body is manufactured. Examples of the spheroidizing treatment include a method of mechanically approximating a spherical shape by applying a shearing force or a compressive force, a mechanical/physical treatment method of granulating a plurality of fine particles by a binder or an adhesive force of the particles themselves, and the like.
(2) Raman R value, Raman half value width
The raman R value of the heteroepitaxial carbon composite measured by argon ion laser raman spectroscopy is usually 0.01 or more, preferably 0.02 or more, and more preferably 0.04 or more, and the upper limit thereof is usually 0.35 or less, preferably 0.30 or less, and more preferably 0.25 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers is sometimes reduced as charging and discharging are performed. That is, the charge acceptance may be reduced. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in generated gas.
The carbon material of the present invention was 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 5cm-1Above, preferably 10cm-1Above, in addition, the upper limit is usually 40cm-1Hereinafter, preferably 35cm-1Hereinafter, more preferably 30cm-1The following ranges. If the Raman half width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters the interlayer may decrease as charging and discharging are performed. That is, the charge acceptance may be reduced. On the other hand, if it is higher than this range, the crystallinity of the particle surface is lowered, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in generated gas.
The raman spectrum was measured as follows: a sample is allowed to naturally fall down using a raman spectrometer (for example, a raman spectrometer manufactured by japan spectroscopy corporation) and filled in a measurement cell, and the surface of the sample in the cell is irradiated with an argon ion laser while the cell is rotated in a plane perpendicular to the laser. For the obtained Raman spectrum, 1580cm was determined-1Nearby peakPAStrength I ofAAnd 1360cm-1Nearby peak PBStrength I ofBAnd calculating the intensity ratio R (R ═ I)B/IA) It is defined as the raman R value of the carbon material. The Raman spectrum obtained by measurement was 1580cm -1Nearby peak PAIs defined as the raman half-value width of the carbon material.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10-20 cm-1
Measurement range: 1100cm-1～1730cm-1
Raman R value, raman half-value width analysis: background processing
Smoothing treatment: simple average, convolution 5 points
(3) Tap density
The tap density of the heteroleptic carbon composite is usually 0.55g/cm3Above, preferably 0.70g/cm3Above, more preferably 0.9g/cm3Above, 1g/cm is particularly preferable3The above. Further, it is preferably 2.0g/cm3Hereinafter, more preferably 1.8g/cm3Hereinafter, more preferably 1.7g/cm3The concentration is preferably 1.5g/cm3The following. If the tap density is less than this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if the amount is more than this range, the number of voids between particles in the electrode is too small, and it may be difficult to secure conductivity between particles, and it may be difficult to obtain preferable battery characteristics.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300 μm and dropped to 20cm 3The container (2) is tapped until the upper end face of the container is filled with the sample, and then vibrated for 1000 strokes of 10mm in length by a powder density measuring instrument (for example, Tap densifier manufactured by seishin corporation), and the density obtained from the volume and the weight of the sample at that time is defined asTap density.
(4) BET specific surface area
The specific surface area of the heteroorientation carbon composite measured by the BET method is usually 0.1m2A ratio of 0.7m or more2A value of at least g, more preferably 1.0m2A total of 1.2m or more2More than g. Its upper limit is typically 100m2A ratio of 25m or less per gram2A ratio of 15m or less per gram2A total of 10m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the specific surface area is less than this range, lithium acceptance during charging is likely to deteriorate and lithium is likely to precipitate on the electrode surface when used as a negative electrode material. On the other hand, if it is higher than the above range, the reactivity with the nonaqueous electrolytic solution increases when used as a negative electrode material, and the amount of generated gas tends to increase, and it may be difficult to obtain a preferable battery.
The BET specific surface area is defined as a value determined as follows: the sample was preliminarily dried at 350 ℃ for 15 minutes under a nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring apparatus manufactured by large-scale commercial research), and then measured by a nitrogen adsorption BET 1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
(5) Volume-based average particle diameter
The volume-based average particle diameter of the heterooriented carbon composite is a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 100 μm or less, preferably 50 μm or less, more preferably 40 μm or less, still more preferably 30 μm or less, and particularly preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, the resulting electrode plate tends to have an uneven coating surface when produced, which is not preferable in the battery production process.
In the present invention, the volume-based average particle diameter is defined by a median particle diameter, which is determined by the following method: the carbon powder is dispersed in a 0.2 mass% aqueous solution (about 1mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant, and measured using a laser diffraction particle size distribution meter (for example, LA-700 manufactured by horiba ltd.).
From the viewpoint of the balance of battery characteristics, it is preferable that one or more of the following items (6) to (11) be satisfied in addition to the items (1) to (5).
(6) X-ray parameters
The d value (interlayer distance) of the lattice plane (002) of the heteroorientation carbon composite, which is determined by X-ray diffraction using a vibro-optic method, is preferably 0.335nm or more, and is usually 0.340nm or less, preferably 0.337nm or less. If the content is less than this range, the crystallinity may be reduced, and the initial irreversible capacity may be increased. The lower limit of 0.335 is a theoretical value of graphite. The crystallite size (Lc) of the carbon material obtained by X-ray diffraction using a vibroseis method is usually in the range of 30nm or more, preferably 50nm or more, and more preferably 80nm or more. If the content is less than this range, the crystallinity may be lowered, and the initial irreversible capacity may be increased.
(7) Ash content
The ash content in the heteroepitaxial carbon composite is usually 1 mass% or less, preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, based on the total mass of the heteroepitaxial carbon composite, and the lower limit thereof is usually 1ppm or more. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolytic solution during charging and discharging cannot be ignored. If the amount is less than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost may be increased.
(8) Distribution of micropores
The amount of voids in the heteroorientation carbon composite corresponding to particles having a diameter of 0.01 to 1 μm and irregularities due to the surface roughness of the particles, which are determined by a mercury porosimeter (mercury intrusion method), is usually 0.001mL/g or more, preferably 0.002mL/g or more, and the upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, more preferably 0.3mL/g or less. If this range is exceeded, a large amount of binder is sometimes required for manufacturing the plate. On the other hand, if the amount is less than this range, the high current density charge-discharge characteristics are degraded, and the effect of moderating expansion and contraction of the electrode during charge and discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of adhesive is sometimes required for producing the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. On the other hand, if the amount is less than this range, the high current density charge-discharge characteristics may be degraded.
As a device for the mercury porosimeter, a mercury porosimeter (autopore 9520; manufactured by micromeritics) can be used. About 0.2g of a sample (negative electrode material) was weighed, sealed in a powder container, degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes, and subjected to pretreatment. Subsequently, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased stepwise from 4psia (about 28kPa) to 40000psia (about 280MPa), followed by pressure reduction to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 °. The average pore size is the pore size at which the cumulative pore volume reaches 50%.
(9) True density
The true density of the heteroepitaxial carbon composite is usually 2.0g/cm3Above, preferably 2.1g/cm3Above, more preferably 2.2g/cm3The above, further advantagesIs selected to be 2.22g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the amount is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase. In the present invention, the true density is defined as a value measured by a liquid phase displacement method (densitometry method) using butanol.
(10) Orientation ratio (powder)
The orientation ratio of the heteroepitaxial carbon composite is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction of carbon obtained by X-ray diffraction were fitted using asymmetric pearson VII as a distribution function, peak separation was performed, and integrated intensities of the peaks of (110) diffraction and (004) diffraction were calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as an active material orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit: divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
(11) Aspect ratio (powder)
The aspect ratio of the heteroepitaxial carbon composite is theoretically 1 or more, and the upper limit is 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks are generated when the electrode plate is produced, and a uniform coating surface cannot be obtained, and the high-current-density charge/discharge characteristics may be deteriorated.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the carbon material particles to the shortest diameter B perpendicular thereto in three-dimensional observation. The particles are observed by a scanning electron microscope which can observe the particles under magnification. Arbitrary 50 graphite particles fixed to the end face of a metal having a thickness of 50 μm or less were selected, and a stage on which a sample was fixed was rotated and tilted, A, B of each of these particles was measured, and the average value of a/B was determined.
[ [ raw Material of Natural graphite-based carbonaceous Material (B) ] ]
As a raw material of the natural graphite-based carbonaceous material (B) contained in the heteroleptic carbon composite, there is generally mentioned a material obtained by using, as a raw material, natural graphite having high crystallinity in which the interplanar spacing (d002) of the (002) plane measured by an X-ray wide angle diffraction method is 0.340nm or less. Specifically, powders selected from the following materials are preferred: natural graphite, a product obtained by adding a mechanically pulverized material thereto to increase the circularity, a product obtained by heat-treating the natural graphite or the mechanically pulverized material at 100 ℃ or higher, a heat-treated product of expanded graphite, or a high-purity purified product of these graphites.
The natural Graphite (D) which is a precursor OF the natural Graphite-based carbonaceous material (B) is classified into Flake Graphite (Flake Graphite), Flake Graphite (crystal Graphite), soil Graphite (Amorphous Graphite) (see the Graphite OF integration OF powder AND granular technology, published by the center OF Industrial technology, Showa 49 years), AND "HAND BOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES", issued by Noyes Publications) according to its properties. The graphitization degree was highest with flake graphite at 100%, followed by flake graphite at 99.9%, and soil graphite as low as 28%. Flake graphite as natural graphite is produced from madagascar, china, brazil, ukraina, canada, and the like; the graphite flakes are produced primarily from srilanca. The main producing areas of soil graphite are korea, china, mexico, and the like. Among these natural graphites, soil graphites are generally not only small in particle size but also low in purity. In contrast, flaky graphite and flaky graphite are preferably used in the present invention because they have advantages such as low graphitization degree or impurity amount.
[ [ preparation of Natural graphite-based carbonaceous Material (B) ] ]
The preparation of the natural graphite-based carbonaceous material (B) will be described later in "production method 1 and production method 2 of a heterooriented carbon composite".
[ [ Properties of Natural graphite-based carbonaceous Material (B) ] ]
The natural graphite-based carbonaceous material (B) preferably satisfies any one or more of the following items (1) to (11) at the same time. The definition and the measurement method of each are the same as those described in the section of the heteroorientation carbon composite.
(1) X-ray parameters
The natural graphite-based carbonaceous material has a d value (interlayer distance) of a lattice plane (002) determined by X-ray diffraction using a vibroseis method of preferably 0.335nm or more, and usually 0.340nm or less, preferably 0.337nm or less. If the content is less than this range, the crystallinity may be reduced, and the initial irreversible capacity may be increased. In addition, 0.335nm is the theoretical value for graphite. The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is usually in the range of 30nm or more, preferably 50nm or more, and more preferably 90nm or more. If the content is less than this range, the crystallinity may be reduced, and the increase in initial irreversible capacity may increase.
(2) Ash content
The ash content in the natural graphite-based carbonaceous material is usually 1 mass% or less, preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, based on the total mass of the natural graphite-based carbonaceous material, and the lower limit thereof is usually 1ppm or more. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolytic solution during charging and discharging may not be negligible. If it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost sometimes rises.
(3) Volume-based average particle diameter
The volume-based average particle diameter of the natural graphite-based carbonaceous material is a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and still more preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, an uneven coating surface is likely to be formed when the electrode plate is produced, which is not preferable in the battery production process.
(4) Raman R value, Raman half value width
The natural graphite-based carbonaceous material has a raman R value, as measured by argon ion laser raman spectroscopy, of usually 0.01 or more, preferably 0.02 or more, and more preferably 0.04 or more, and the upper limit thereof is usually 0.35 or less, preferably 0.30 or less, and more preferably 0.25 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers is sometimes reduced as charging and discharging are performed. That is, the charge acceptance may be reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface is reduced, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a reduction in efficiency or an increase in generated gas.
The carbon material of the present invention was 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 5cm-1Above, preferably 10cm-1Above, in addition, the upper limit is usually 40cm-1Hereinafter, preferably 35cm-1Hereinafter, more preferably 30cm-1The following ranges. If the Raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters the interlayer is sometimes reduced by charge and discharge. That is, the charge acceptance may be reduced. On the other hand, if it is higher than this range, the crystallinity of the particle surface is lowered, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in generated gas.
(5) BET specific surface area
The specific surface area of the natural graphite-based carbon measured by the BET method is usually 0.1m2More than g, preferably 0.7m2A value of at least g, more preferably 1.0m2A total of 1.5m or more2More than g. The upper limit is usually 100m2A ratio of 25m or less per gram2A ratio of 15m or less per gram2A total of 10m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the specific surface area is less than this range, lithium acceptance during charging is poor when the material is used as a negative electrode material, and lithium is likely to precipitate on the electrode surface. On the other hand, if the amount is more than the above range, the reactivity with the nonaqueous electrolytic solution increases when the negative electrode material is used, and the amount of generated gas tends to increase, and it may be difficult to obtain a preferable battery.
(6) Distribution of micropores
The amount of voids in particles corresponding to a particle diameter of 0.01 to 1 μm and irregularities due to surface irregularities of the particles in the natural graphite-based carbonaceous material, as determined by a mercury porosimeter (mercury intrusion method), is usually 0.01mL/g or more, preferably 0.05mL/g or more, and more preferably 0.1mL/g or more, and the upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, and more preferably 0.3mL/g or less. If this range is exceeded, a large amount of binder is sometimes required for manufacturing the plate. If the amount is less than this range, the high-current-density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of adhesive is sometimes required for producing the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, particularly preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. If the amount is less than this range, the high current density charge-discharge characteristics may be deteriorated.
(7) Degree of circularity
The degree of circularity is defined as the degree of sphericity of the natural graphite-based carbon material, and the degree of circularity of particles having a particle diameter of 3 to 40 μm of the natural graphite-based carbon material is usually 0.1 or more, preferably 0.5 or more, more preferably 0.8 or more, still more preferably 0.85 or more, and most preferably 0.9 or more. A large circularity is preferable because high current density charge/discharge characteristics are improved.
(8) True density
The natural graphite-based carbon generally has a true density of 2.0g/cm3Above, preferably 2.1g/cm3Above, more preferably 2.2g/cm3Above, more preferably 2.22g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the amount is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
(9) Tap density
The tap density of natural graphite-based carbons is usually 0.1g/cm3Above, preferably 0.5g/cm3Above, more preferably 0.7g/cm3Above, particularly preferably 0.9g/cm3The above. Further, it is preferably 2.0g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, the packing density is difficult to increase when used as a negative electrode, and a high-capacity battery may not be obtained. On the other hand, if the amount is more than this range, the number of voids between particles in the electrode is too small, and it is difficult to secure conductivity between particles, and it may be difficult to obtain preferable battery characteristics.
(10) Orientation ratio (powder)
The orientation ratio of the natural graphite-based carbon is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
(11) Aspect ratio (powder)
The aspect ratio of the natural graphite-based carbon is theoretically 1 or more, and the upper limit is usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks are generated when the electrode plate is produced, and a uniform coating surface cannot be obtained, and the high-current-density charge/discharge characteristics may be deteriorated.
[ [ raw material of carbonaceous Material (C) ] ]
The raw material of the carbonaceous material (C) contained in the heteroorientation carbon composite of the present invention is not particularly limited as long as it is a material that can be carbonized, and examples thereof include pitch raw materials, aromatic hydrocarbons such as acenaphthylene, decacycloolefin, anthracene, phenanthrene, and the like; n-ring compounds such as phenazine and acridine; s-ring compounds such as thiophene and bithiophene; polyphenyl, such as biphenyl and terphenyl; organic polymers such as polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insoluble products thereof, nitrogen-containing polyacrylonitrile, and polypyrrole; organic polymers such as sulfur-containing polythiophene and polystyrene; polysaccharides such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, and sucrose; thermoplastic resins such as polyphenylene sulfide and polyphenylene ether; thermosetting resins such as furfuryl alcohol resin, phenol resin, and imide resin; or organic substances such as solutions obtained by dissolving them in low-molecular-weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane; carbonizable gases, and the like.
Among these, the asphalt raw material is preferred because it has a high char yield and can be produced in a high yield. In the present specification, the term "pitch raw material" refers to pitch and substances belonging to pitch, and means substances that can be carbonized and/or graphitized by appropriate treatment. As specific examples of the asphalt material, tar, heavy oil, asphalt, or the like can be used. Specific examples of the tar include coal tar and petroleum tar. Specific examples of the heavy oil include a contact decomposed oil of a petroleum heavy oil, a thermal decomposed oil, an atmospheric residue, a vacuum residue, and the like. Specific examples of the pitch include coal tar pitch, petroleum pitch, and synthetic pitch. Among them, coal tar pitch is preferred because of its high aromaticity. These draining materials may be used singly or in combination of 2 or more in any combination and ratio.
The content of the above-mentioned quinoline-insoluble component in the asphalt material is not particularly limited, but generally an asphalt material in the range of 30 or less is used. The quinoline insoluble component is ultrafine carbon particles or ultrafine sludge contained in coal tar in a trace amount, and if these are contained in a large amount, the improvement of crystallinity is significantly inhibited during graphitization, and the discharge capacity after graphitization is significantly reduced. As a method for measuring the quinoline insoluble component, for example, a method specified in JIS K2425 can be used.
In addition, various thermosetting resins, thermoplastic resins, and the like may be used in combination with the asphalt raw material as a raw material as long as the effects of the present invention are not impaired.
[ [ preparation of carbonaceous Material (C) ] ]
The preparation of the carbonaceous material (C) will be described later in "production method 1 and production method 2 of a heterooriented carbon composite".
[ [ Properties of carbonaceous Material (C) ] ]
The carbonaceous material (C) preferably satisfies one or more of the following items (1) to (4) at the same time. The definition, measurement method, and the like of these are the same as those described in the section of the heteroorientation carbon composite.
(1) X-ray parameters
The d value (interlayer distance) of the lattice plane (002) of the carbonaceous material (C) as determined by X-ray diffraction using a vibroseis method is preferably 0.335nm or more, and is usually 0.345nm or less, preferably 0.340nm or less, and more preferably 0.337nm or less. The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is usually in the range of 5nm or more, preferably 10nm or more, more preferably 50nm or more, and still more preferably 80nm or more. If the content is less than this range, the crystallinity may be reduced, and the increase in initial irreversible capacity may increase.
(2) Ash content
The ash content in the carbonaceous material (C) is usually 1 mass% or less, preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, based on the total mass of the heteroorientable carbon composite, and the lower limit thereof is usually 1ppm or more. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolytic solution during charging and discharging may not be negligible. If it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost sometimes rises.
(3) Raman R value, Raman half value width
The raman R value of the carbonaceous material (C) measured by argon ion laser raman spectroscopy is usually 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, and the upper limit thereof is usually 0.60 or less, preferably 0.30 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers is sometimes reduced as charging and discharging are performed. That is, the charge acceptance may be reduced. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, the reactivity with the nonaqueous electrolytic solution is increased, and the efficiency may be lowered or the amount of generated gas may be increased.
The carbonaceous material (C) of the present invention is 1580cm-1The near-Raman half-value width is not particularly limited, but is usually 5cm-1Above, preferably 10cm-1Above, in addition, the upper limit is usually 60cm-1Hereinafter, preferably 45cm-1Hereinafter, more preferably 30cm-1The following ranges. If the Raman half width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters the interlayer may decrease as charging and discharging are performed. On the other hand, if the amount is more than this range, the crystallinity of the particle surface is lowered, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in gas generation.
(4) True density
The carbonaceous matter (C) has a true density of usually 2.0g/cm3Above, preferably 2.2g/cm3Above, more preferably 2.22g/cm3The upper limit is 2.26g/cm, which is the theoretical upper limit of graphite3The following. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
[ method for producing heteroleptic carbon composite for negative electrode [5]
The production method is not particularly limited, and any method may be used as long as it does not exceed the scope of the gist of the present invention, and the outline of preferred examples is as follows (1) and (2).
(1) The starting material of the carbonaceous material (C) is entirely or partially in a liquid state in any one step, and is mixed and/or kneaded with the natural graphite (D) in the liquid state;
(2) the composite obtained in this step is subjected to devolatilization/sintering, graphitization, and then to pulverization and classification to adjust the particle size. More than one pulverizing/classifying step may be performed between these steps.
Specific examples of the above outline are shown below.
[ [ method for producing heteroleptic carbon composite 1] ]
The hetero-oriented carbon composite of the present invention is preferably obtained by compounding a natural graphite-based carbonaceous material (B) and a carbonaceous material (C) having a different orientation from the natural graphite-based carbonaceous material (B), and examples thereof include the following methods: and a method in which a pitch raw material that is a precursor of the carbonaceous material (C), a material obtained by heat-treating and pulverizing a pitch raw material or the like (hereinafter, simply referred to as "heat-treated graphite crystal precursor"), a natural polymer, and the like are mixed at a predetermined ratio with the natural graphite (D), and the mixture is subjected to a heat treatment a, then pulverized, and then subjected to a heat treatment B (sintering and graphitization). In addition, if it is not necessary to sufficiently reduce the median particle diameter, the above-mentioned pulverization may not be carried out.
[ [ [ production of Heat-treated graphite Crystal precursor ] ] ]
The pitch raw material is heat-treated in advance to obtain a heat-treated graphite crystal precursor. This prior heat treatment is referred to as pitch heat treatment. The heat-treated graphite crystal precursor is pulverized, mixed with natural graphite (D), and then subjected to heat treatment a, in which a part or all of the graphite is melted, and the molten state can be appropriately controlled by adjusting the content of volatile components by a previous heat treatment (pitch heat treatment). Further, as the volatile component contained in the heat-treated graphite crystal precursor, hydrogen, benzene, naphthalene, anthracene, pyrene and the like are generally cited.
The temperature conditions for the heat treatment of the asphalt are not particularly limited, and are usually in the range of 300 ℃ to 550 ℃. If the temperature of the heat treatment is lower than this range, volatile components increase, and therefore, it may be difficult to safely pulverize in air. On the other hand, if the amount exceeds the upper limit, part or all of the heat-treated graphite crystal precursor is not melted during the heat treatment a, and it may be difficult to obtain particles (heterograin carbon composite) in which the natural graphite-based carbonaceous material (B) and the heat-treated graphite crystal precursor are combined. The asphalt heat treatment is performed in an inert gas atmosphere such as nitrogen or in a volatile component atmosphere generated from the asphalt raw material.
The apparatus used for the heat treatment of the asphalt is not particularly limited, and examples thereof include a reactor such as a shuttle furnace, a tunnel furnace, an electric furnace, and an autoclave, and a coka (コーカー) (heat treatment tank manufactured by cokes (コークス)). When the asphalt heat treatment is performed, stirring may be performed as necessary.
Further, as the heat-treated graphite crystal precursor, a material having a volatile content of usually 5 mass% or more is preferably used. By using a graphite crystal precursor having a volatile content in this range and heat-treating a, a natural graphite-based carbonaceous material (B) and a carbonaceous material (C) are combined, and a heterooriented carbon composite having the above-described predetermined physical properties can be obtained.
First, a method of producing a bulk mesophase (バルクメソフェーズ, bulk mesophase) which is a precursor of a graphite crystal (a precursor of a graphite crystal which is heat-treated in advance, hereinafter, abbreviated as "heat-treated graphite crystal precursor") by heat-treating a pitch raw material in advance will be described.
(volatile component of graphite Crystal precursor Heat treatment)
The volatile content of the graphite crystal precursor obtained by the pitch heat treatment is not particularly limited, but is usually 5% by mass or more, preferably 6% by mass or more, and is usually 20% by mass or less, preferably 15% by mass or less. If the volatile content is less than the above range, it may be difficult to safely pulverize the graphite in air because of a large amount of volatile content, and if the volatile content exceeds the upper limit, part or all of the graphite crystal precursor may not melt during the heat treatment a, and it may be difficult to obtain particles (heterograin carbon composite) in which the natural graphite-based carbonaceous material (B) and the heat-treated graphite crystal precursor are combined. The volatile component is measured, for example, by a method specified in JIS M8812.
(softening Point of graphite Crystal precursor Heat treatment)
The softening point of the graphite crystal precursor obtained by the pitch heat treatment is not particularly limited, but is usually 250 ℃ or higher, preferably 300 ℃ or higher, more preferably 370 ℃ or higher, and is usually 470 ℃ or lower, preferably 450 ℃ or lower, more preferably 430 ℃ or lower. If the content is less than the lower limit, the carbonization yield of the graphite crystal precursor after the heat treatment is low, and it is difficult to obtain a uniform mixture with the natural graphite-based carbonaceous material (B), and if the content exceeds the upper limit, part or all of the graphite crystal precursor is not melted during the heat treatment a, and it may be difficult to obtain particles (heteroleptic carbon composite) in which the natural graphite-based carbonaceous material (B) and the heat-treated graphite crystal precursor are composited.
As the softening point, the following values were used: a sample molded into a thickness of 1mm with a tablet molding machine was measured by a penetration method (ペネトレーション method) under a nitrogen flow at a temperature rise rate of 10 ℃/min, a tip shape of 1 mm. phi., and a weight of 20gf using a thermomechanical analyzer (for example, TMA4000 manufactured by Bruke-axs (ブルカー. エイエックス).
(pulverization of graphite Crystal precursor for Heat treatment)
Next, the heat-treated graphite crystal precursor obtained by the pitch heat treatment is pulverized. This is because the heat treatment reduces the size of the crystals of the heat-treated graphite crystal precursor having large units and arranged in the same direction, and/or uniformly mixes and composites the natural graphite (D) and the heat-treated graphite crystal precursor.
The graphite crystal precursor obtained by the pitch heat treatment is not particularly limited, but the particle size of the heat-treated graphite crystal precursor after the pulverization is usually 1 μm or more, preferably 5 μm or more, and usually 10mm or less, preferably 5mm or less, more preferably 500 μm or less, particularly preferably 200 μm or less, and further preferably 50 μm or less. When the particle size is less than 1 μm, the surface of the heat-treated graphite crystal precursor after heat treatment during or after pulverization is oxidized by contact with air, which may inhibit improvement of crystallinity during graphitization, and may cause a decrease in discharge capacity after graphitization. On the other hand, if the particle size exceeds 10mm, the effect of refining by grinding is reduced, the crystals are easily oriented, the carbonaceous material (C) is easily oriented, the orientation ratio of the active material of the electrode using the heteroorientation carbonaceous composite (a) is low, and it is difficult to suppress swelling of the electrode during charging of the electrode. And/or the natural graphite (D) and the heat-treated graphite crystal precursor are difficult to mix homogeneously because of a large difference in particle size, and the composite formation is likely to become nonuniform.
The device for pulverization is not particularly limited, and as the coarse pulverizer, for example, a shear mill, a jaw crusher, an impact crusher, a cone crusher, etc.; as the intermediate crusher, a roll crusher, a hammer crusher, and the like can be mentioned; examples of the micro-pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, a jet mill, a turbine mill (turbomill), and the like.
[ [ [ Heat treatment of Natural graphite (D) and Heat-treated graphite Crystal precursor ] ]
Natural graphite (D) and a heat-treated graphite crystal precursor (a raw material of the carbonaceous material (C)) are mixed at a predetermined ratio, and heat treatment a, pulverization, and heat treatment B (sintering and graphitization) are performed to produce an anisotropic carbon composite.
(mixing of Natural graphite (D) and Heat-treated graphite Crystal precursor)
The mixing ratio of the natural graphite (D) and the heat-treated graphite crystal precursor before the heat treatment a is not particularly limited, and the ratio of the natural graphite (D) to the mixture is usually 20 mass% or more, preferably 30 mass% or more, more preferably 40 mass% or more, and usually 95 mass% or less, preferably 90 mass% or less. If the content is less than the lower limit, the proportion of the carbonaceous material (C) in the heterooriented carbon composite (a) increases, and therefore, it becomes difficult to increase the packing density in the production of an electrode, and an excessive pressing load is required, and the effect of compounding the natural graphite-based carbonaceous material (B) may not be obtained. If the amount exceeds the upper limit, the surface of the natural graphite-based carbonaceous material (B) in the anisotropic carbon composite (a) may be exposed more, and the specific surface area of the anisotropic carbon composite (a) may become large, which is sometimes not preferable in terms of powder properties.
When the natural graphite (D) and the heat-treated graphite crystal precursor adjusted to a predetermined particle size are mixed, the apparatus used is not particularly limited, and examples thereof include a V-type mixer, a W-type mixer, a container-variable type mixer, a kneader, a roll mixer, and a shear mixer.
(Heat treatment A)
Next, heat treatment a is performed on the mixture of the natural graphite (D) and the heat-treated graphite crystal precursor. This is because the natural graphite (D) and the finely divided heat-treated graphite crystal precursor particles are fixed by bringing them into contact in a non-oriented state by re-melting or fusing the heat-treated graphite crystal precursor after pulverization. Thus, the mixture of the natural graphite (D) and the heat-treated graphite crystal precursor can be a more uniform composite mixture (hereinafter, appropriately referred to as "graphite composite mixture") rather than merely a mixture of particles.
The temperature conditions for the heat treatment a are not particularly limited, but are usually 300 ℃ or more, preferably 400 ℃ or more, more preferably 450 ℃ or more, and usually 650 ℃ or less, preferably 600 ℃ or less. If the temperature of the heat treatment a is lower than the above range, a large amount of volatile components remain in the material after the heat treatment a, and therefore, fusion between the powders may occur in the sintering or graphitization step, and it may be necessary to perform re-pulverization. On the other hand, if it exceeds the above range, the remelted component may be separated into needle-like forms during pulverization, resulting in a decrease in tap density. The heat treatment a is performed in an inert gas atmosphere such as nitrogen or in a volatile component atmosphere generated by the heat-treated graphite crystal precursor pulverized and refined.
The apparatus used for the heat treatment A is not particularly limited, and for example, a shuttle furnace, a tunnel furnace, an electric furnace or the like can be used.
(pulverization of Heat-treated graphite Crystal precursor and substitution treatment of Heat treatment A)
However, as an alternative to the pulverization and the heat treatment a, a treatment capable of making the structure of the heat-treated graphite crystal precursor finer and non-oriented may be used, and for example, the heat treatment may be performed by mixing with the natural graphite (D) while performing a treatment for imparting mechanical energy in a temperature range in which the heat-treated graphite crystal precursor is melted or softened.
The heat treatment as the alternative treatment is not particularly limited, but is usually carried out at 200 ℃ or higher, preferably 250 ℃ or higher, and usually 450 ℃ or lower, preferably 400 ℃ or lower. If the temperature condition is lower than the above range, the melting and softening of the graphite crystal precursor in the substitution treatment may be insufficient, and it may be difficult to form a composite with the natural graphite (D). If the amount exceeds the above range, the heat treatment tends to proceed rapidly, and particles of the carbonaceous heat-treated graphite crystal precursor or the like tend to separate into needle-like particles during pulverization, which may easily cause a decrease in tap density.
The substitution treatment is usually performed in an inert atmosphere such as nitrogen or in an oxidizing atmosphere such as air. However, when the treatment is performed in an oxidizing atmosphere, it is sometimes difficult to obtain high crystallinity after graphitization, and therefore, it is necessary to prevent excessive progress of oxygen-induced meltdown. Specifically, the amount of oxygen in the graphite crystal precursor after the substitution treatment is usually 8% by mass or less, and preferably 5% by mass or less.
Further, the apparatus used in the alternative treatment is not particularly limited, and for example, a mixer, a kneader, or the like can be used.
(crushing)
Next, the graphite composite mixture subjected to the heat treatment a is pulverized. This is because the graphite composite mixture block which is made to composite with the natural graphite (D) by the heat treatment a and melted or fused in a state of refining the structure and making it non-oriented is pulverized to have a target particle diameter.
The particle size of the graphite composite mixture after pulverization is not particularly limited, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, further preferably 7 μm or more, and further usually 50 μm or less, preferably 35 or less, more preferably 30 μm or less. If the particle size is less than the above range, the tap density of the anisotropic carbonaceous composite (a) becomes small, and therefore, it is difficult to increase the packing density of the active material when forming an electrode, and it is difficult to obtain a high-capacity battery. On the other hand, if the amount exceeds the above range, coating unevenness may easily occur when an electrode is produced by coating the composite in the form of the anisotropic carbonaceous composite (a).
The device for pulverization is not particularly limited, and for example, as the coarse pulverizer, a jaw crusher, an impact crusher, a cone crusher, etc.; examples of the intermediate mill include a roll mill, a hammer mill, and the like; examples of the micro-pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, a jet mill, and the like.
(Heat treatment B: sintering)
Heat treatment B refers to sintering and graphitization. Next, the sintering is started. However, sintering may also be omitted. The graphite composite mixture pulverized by pulverization is sintered. This is because the fusion of the graphite composite mixture at the time of graphitization is suppressed and the volatile components of the graphite composite mixture are removed by sintering.
The temperature condition at the time of sintering is not particularly limited, but is usually 600 ℃ or higher, preferably 1000 ℃ or higher, and the upper limit is usually 2400 ℃ or lower, preferably 1300 ℃ or lower. If the temperature condition is lower than the above range, fusion of the graphite composite powder may easily occur at the time of graphitization. On the other hand, if the temperature exceeds the above range, the sintering equipment is expensive, and therefore, the sintering is usually performed within the above temperature range.
The sintering is performed in an inert atmosphere such as nitrogen or in a non-oxidizing atmosphere formed by a gas generated from the re-pulverized graphite composite mixture. Further, in order to simplify the production process, the graphitization may be performed without performing a sintering process.
The apparatus for sintering is not particularly limited, and for example, a shuttle furnace, a tunnel furnace, an electric furnace, a coke baking furnace, a rotary kiln, or the like can be used.
(Heat treatment B: graphitization)
Subsequently, the graphite composite mixture subjected to the sintering is graphitized. This is because the discharge capacity in the battery evaluation was increased and the crystallinity was improved. By graphitization, the heteroorientation carbonaceous composite (a) can be obtained.
The temperature condition for carrying out graphitization is not particularly limited, but is usually 2800 ℃ or higher, preferably 2900 ℃ or higher, more preferably 3000 ℃ or higher, and usually 3400 ℃ or lower, preferably 3200 ℃ or lower. If the amount exceeds the above range, the reversible capacity of the battery may be reduced, and it may be difficult to produce a high-capacity battery. If the amount exceeds the above range, the amount of sublimation of graphite tends to increase.
Graphitization is performed in an inert atmosphere such as argon or in a non-oxidizing atmosphere formed by a gas generated from a sintered graphite composite mixture. The apparatus used for graphitization is not particularly limited, and examples thereof include a direct electric furnace, an attorney electric furnace, a resistance heating furnace as an indirect electric furnace, and an induction heating furnace.
In addition, at the time of graphitization treatment or in the previous steps, that is, the steps from heat treatment to sintering, a graphitization catalyst such as Si or B may be added to or on the surface of the material (natural graphite (D), pitch raw material, or graphite crystal precursor).
(other treatment)
In addition to the above-described respective processes, various processes such as a classification process may be performed as long as the effects of the present invention are not impaired. The classification treatment is performed to remove coarse powder and fine powder while setting the particle size after the graphitization treatment to a target particle size.
As the apparatus used for the classification treatment, there is no particular limitation, and for example, in the case of dry screening, a rotary screen, a shaker screen, a rotary screen, a vibrating screen, or the like can be used; in the case of dry air classification, a gravity classifier, an inertial classifier, a centrifugal classifier (classifier, cyclone), or the like; as the wet screening, a mechanical wet classifier, a hydraulic classifier, a sedimentation classifier, a centrifugal wet classifier, or the like can be used.
The classification treatment may be continued immediately after the pulverization after the heat treatment a, or may be performed at other times, for example, after the sintering after the pulverization, or after the graphitization. In addition, the hierarchical processing itself may also be omitted. However, from the viewpoint of reducing the BET specific surface area of the heterogeneous carbonaceous composite (a) and from the viewpoint of productivity, it is preferable to continue the pulverization immediately after the heat treatment a.
(treatment after production of the heterogeneous carbon composite (A))
In order to control the BET specific surface area of the negative electrode material, improve the electrode compactibility, improve the discharge capacity, reduce the cost, and the like, artificial graphite powder or natural graphite powder separately produced may be added to and mixed with the heterooriented carbonaceous composite (a) produced in the above-described order.
[ method 2 for producing a heteroleptic carbon composite for negative electrode [5]
The heteroepitaxial carbon composite can be produced by the following method. The heterooriented carbon composite of the present invention is preferably obtained by combining a natural graphite-based carbonaceous material (B) with a carbonaceous material (C) having a different orientation from the natural graphite-based carbonaceous material (B), and examples thereof include the following methods: the natural graphite (D) is produced by subjecting a pitch raw material, which is a precursor of the carbonaceous material (C), to steps such as "kneading (mixing)", "molding", "sintering", "graphitization", and "pulverization". However, in these steps, "molding", "sintering" and "pulverizing" may be omitted and/or performed simultaneously with other steps. Specifically, it can be obtained by the following production methods and the like.
[ [ kneading (mixing) ] ]
The natural graphite (D), the pitch raw material, and optionally, a graphitization catalyst are mixed. In this case, heating is preferably performed for uniform mixing. This makes it possible to add the liquid pitch raw material to the raw material which is not melted at the kneading temperature of the natural graphite (D). In this case, all the raw materials may be fed into the kneader while kneading and raising the temperature, or the components other than the asphalt raw material may be fed into the kneader and heated while stirring, and after the temperature is raised to the kneading temperature, the asphalt raw material in a normal temperature or a vulcanized molten state may be fed.
The heating temperature is usually not lower than the softening point of the asphalt material, preferably not lower than 10 ℃ higher than the softening point, and more preferably not lower than 20 ℃ higher than the softening point. The upper limit is usually 300 ℃ or lower, preferably 250 ℃ or lower. If the amount is less than this range, the viscosity of the asphalt material may be increased, which may make mixing difficult. On the other hand, if it exceeds this range, the viscosity of the mixed system may become too high due to volatilization and polycondensation.
The mixer is preferably of a type having a stirring blade, and a general stirring blade such as a Z-type or マチスケータ -type stirring blade can be used as the stirring blade. The amount of the raw material charged into the mixer is usually 10 vol% or more, preferably 15 vol% or more, and 50 vol% or less, preferably 30 vol% or less of the volume of the mixer. The mixing time is required to be 5 minutes or more, and the time until a significant change in viscosity is caused by volatilization of volatile components is at most, and is usually 30 to 120 minutes. The mixer is preferably preheated to the kneading temperature before mixing.
[ [ Molding ] ]
The resulting mixture may be directly supplied to a devolatilization/sintering process for devolatilization and carbonization, but is preferably supplied to the devolatilization/sintering process after molding for ease of handling.
The molding method is not particularly limited as long as the shape can be maintained, and extrusion molding, die molding, hydrostatic molding, or the like can be employed. Among them, extrusion molding and die molding are preferable because the particles are easily oriented in the molded body, and die molding is easier to handle than hydrostatic molding in view of productivity although the particle orientation is maintained random, and a molded body is obtained without breaking the randomly oriented structure at the time of mixing.
The molding temperature may be either room temperature (low temperature) or under heating (high temperature, temperature equal to or higher than the softening point of the asphalt material). In the case of molding at a low temperature, it is desirable to coarsely pulverize the mixture cooled after kneading in advance to a maximum size of 1mm or less in order to improve moldability and obtain uniformity of the molded article. The shape and size of the molded article are not particularly limited, but in the case of thermoforming, if the molded article is too large, it takes time to uniformly preheat before molding, and therefore, a maximum size of about 150cm or less is generally preferable.
If the pressure of the molding pressure is too high, it becomes difficult to remove volatile components passing through micropores of the molded article, and the natural graphite (D) which is not perfectly round is oriented, and it becomes difficult to pulverize in the subsequent step, so that the upper limit of the molding pressure is usually 3000kgf/cm2(294MPa) or less, preferably 500kgf/cm2(49MPa) or less, more preferably 10kgf/cm2(0.98MPa) or less. The lower limit of the pressure is not particularly limited, but is preferably set to such an extent that the shape of the molded body can be maintained in the devolatilization/sintering step.
[ [ devolatilization/sintering ] ]
The molded article obtained is devolatilized/sintered in order to remove volatile components of the natural graphite (D) and the pitch raw material, and to prevent contamination of the filler during graphitization and adhesion of the filler to the molded article. Devolatilization/sintering is typically carried out at temperatures above 600 ℃, preferably above 650 ℃, and typically below 1300 ℃, preferably below 1100 ℃ for 0.1 to 10 hours. In order to prevent oxidation, heating is generally performed in a non-oxidizing atmosphere in which an inert gas such as nitrogen or argon is circulated or a granular carbon material such as coke breeze (breeze) or coke (Packing coke) is filled in the gap.
The equipment used for devolatilization/sintering is not particularly limited as long as it is an equipment capable of sintering in a non-oxidizing atmosphere, such as an electric furnace, a gas furnace, and a coke baking furnace for electrode materials. The rate of temperature rise during heating is preferably low for removing volatile components, and is usually from about 200 ℃ at which the low boiling point component begins to volatilize at 3 to 100 ℃/hr to about 700 ℃ at which only hydrogen is produced.
[ [ graphitization ] ]
The carbide shaped bodies obtained by devolatilization/sintering are then graphitized by heating at high temperatures. The conditions for graphitization are the same as those described in production method 1.
In order to prevent oxidation, graphitization is performed under a non-oxidizing atmosphere in which an inert gas such as nitrogen or argon is circulated or a granular carbon material such as coke slag or coke is filled in the gap. The equipment used for graphitization is not particularly limited as long as it is an electric furnace, a gas furnace, an attritor furnace for electrode materials, or the like that can achieve the above object, and the temperature rise rate, cooling rate, heat treatment time, and the like can be arbitrarily set within the allowable range of the equipment used.
[ [ pulverize ] ]
The graphitized material thus obtained is usually in a lump form and is difficult to use as a negative electrode active material, and therefore, pulverization and/or removal of large-particle-size substances and small-particle-size substances are performed. The method for pulverizing the graphitized product is not particularly limited, and examples of the pulverizing device include a ball mill, a hammer mill, a CF mill, a fine mill, a pulverizer (pulverze), and a pulverizing device utilizing wind power, such as a jet mill. For the coarse pulverization and the intermediate pulverization, pulverization methods using impact force such as a jaw crusher, a hammer mill, and a roll mill may be used. Here, the pulverization time may be before graphitization or after graphitization.
[ mixing of auxiliary Material for negative electrode [5]
In addition to the above-described heteroepitaxial carbon composite, the negative electrode active material of the lithium secondary battery of the present invention contains one or more carbon materials (carbonaceous materials) different from the above-described heteroepitaxial carbon composite in terms of carbonaceous physical properties, thereby further improving the battery performance. The term "carbonaceous material" as used herein means one or more of X-ray diffraction parameters, median particle diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, micropore distribution, circularity, and ash content. In addition, preferred embodiments include a volume-based particle size distribution that is asymmetric about the median particle diameter, contains 2 or more carbon materials having different raman R values, and has different X-ray parameters. Examples of the effect include the addition of graphite such as natural graphite and artificial graphite; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke are used as a sub-material to reduce resistance and the like. These may be used alone, or may be used in combination of 2 or more in any combination and in any ratio. When added as a subcomponent, the amount of addition is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit thereof is usually 80% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less. If the amount is less than this range, the effect of improving the conductivity may be difficult to obtain. If the amount exceeds the above range, the initial irreversible capacity may increase.
[ electrode for negative electrode [5]
The negative electrode [5] can be formed by a common method in the same manner as described above. The current collector, the ratio of the thicknesses of the current collector and the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
< negative electrode [6] >
Next, the negative electrode [6] used in the lithium secondary battery of the present invention is described]The negative electrode contains, as a negative electrode active material, a graphitic carbon particle having a circularity of 0.85 or more, a (002) plane interplanar spacing (d002) of less than 0.337nm as measured by wide-angle X-ray diffraction, and a thickness of 1360cm as measured by argon ion laser Raman spectroscopy-1Peak intensity of (2) relative to 1580cm-1The ratio of the peak intensities defined as a Raman R value of 0.12 to 0.8.
[ negative electrode active material for negative electrode [6]
Next, a negative electrode active material used for the negative electrode [6] will be described.
The negative electrode active material used for the negative electrode [6] of the lithium secondary battery of the present invention contains at least graphitic carbon particles satisfying the following (a), (b), and (c).
(a) The circularity is more than 0.85;
(b) the (002) plane interplanar spacing (d002) as measured by wide-angle X-ray diffraction method is less than 0.337 nm;
(c) determined by argon ion laser Raman spectroscopy at 1360cm -1Peak intensity of (2) relative to 1580cm-1The Raman R value (hereinafter, sometimes simply referred to as "Raman R value") defined as the ratio of the peak intensities of (A) is 0.12 to 0.8.
[ [ circularity ] ]
The circularity of the graphitic carbon particle used as the negative electrode active material of the lithium secondary battery of the present invention is usually 0.85 or more, preferably 0.87 or more, more preferably 0.89 or more, and particularly preferably 0.92 or more. As an upper limit, when the circularity is 1, it is a theoretical true sphere. If the circularity is less than this range, the filling property of the negative electrode active material decreases, and the thermal conductivity decreases, and therefore early output recovery may be hindered, and particularly, output recovery from a low output state at low temperatures may be slow.
The circularity in the present invention is defined by the following formula.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the value measured as follows was used: about 0.2g of a sample was dispersed in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant by using a flow particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.), and particles having a particle diameter in the range of 3 to 40 μm were measured by irradiating the sample with ultrasonic waves of 28kHz for 1 minute at an output of 60W while specifying 0.6 to 400 μm as a detection range.
[ [ interplanar spacing (d002) ] ]
The graphite carbon particles used as the negative electrode active material of the negative electrode [6] in the lithium secondary battery of the present invention have a (002) plane interplanar spacing (d002) of less than 0.337nm, preferably 0.336nm or less, as measured by wide-angle X-ray diffraction. The lower limit is 0.335, which is the theoretical value of graphite. If the amount exceeds this range, the crystallinity is lowered, the thermal conductivity due to electrons is lowered, and the early output recovery characteristic is lowered, and particularly, the recovery of the output from a low output state at low temperature is slowed in some cases.
The inter-plane distance (d002) of the (002) plane measured by the wide-angle X-ray diffraction method in the present invention is a d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the vibroseis method.
The crystallite size (Lc) of the graphitic carbon material determined by X-ray diffraction using a vibroseis method is not particularly limited, but is usually in the range of 10nm or more, preferably 30nm or more, and more preferably 80nm or more. If the amount is less than this range, the crystallinity may be reduced, the thermal conductivity due to electrons may be reduced, and the early output recovery characteristics may be reduced.
[ [ Raman R value ] ]
The raman R value of the graphite carbon particles used as the negative electrode active material of the negative electrode [6] in the lithium secondary battery of the present invention is necessarily 0.12 or more, preferably 0.15 or more, more preferably 0.17 or more, and particularly preferably 0.2 or more. The upper limit thereof is preferably 0.8 or less, more preferably 0.6 or less, and particularly preferably 0.45 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the output may decrease as the charge/discharge potential point decreases. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, the heat conduction by electrons is lowered, and the recovery characteristic of the output may be lowered.
The raman spectrum was measured as follows: a sample is allowed to naturally fall down using a raman spectrometer (for example, a raman spectrometer manufactured by japan spectroscopy corporation) and filled in a measurement cell, and the surface of the sample in the cell is irradiated with an argon ion laser while the cell is rotated in a plane perpendicular to the laser. For the obtained Raman spectrum, 1580cm was determined-1Nearby peak PAStrength I ofAAnd 1360cm-1Nearby peak PBStrength I ofBAnd calculating the intensity ratio R (R ═ I)B/IA) It is defined as the raman R value of the graphitic carbon material. The Raman spectrum obtained by measurement was 1580cm-1Nearby peak PADefined as the raman half-value width of the graphitic carbon material.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10-20 cm-1
Measurement range: 1100cm-1～1730cm-1
Raman R-value, half-value width analysis: background processing
Smoothing treatment: simple average, convolution 5 points
As the negative electrode [6 ] in the lithium secondary battery of the present invention]The negative electrode active material of (3) is obtained by using graphite carbon particles of 1580cm in diameter-1The near-Raman half-value width is not particularly limited, but is usually 10cm-1Above, preferably 15cm -1Above, in addition, the upper limit is usually 60cm-1Hereinafter, preferably 50cm-1Hereinafter, more preferably 45cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the output may decrease as the number of charge/discharge sites decreases. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, the heat conduction by electrons is lowered, and the recovery characteristic of the output may be lowered.
[ [ tap density ] ]
As the negative electrode [6 ] in the lithium secondary battery of the present invention]The tap density of the graphite carbon particles used in the negative electrode active material of (3) is usually 0.55g/cm3Above, preferably 0.7g/cm3Above, more preferably 0.8g/cm3Above, 1g/cm is particularly preferable3The above. Further, the upper limit is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, the packing density is difficult to increase when used as a negative electrode, and the contact area between particles decreases, so that the thermal conductivity may decrease. On the other hand, if it exceeds this range, the number of voids between particles in the electrode is too small, and the flow path of the nonaqueous electrolytic solution is reduced, so that the output itself may be reduced.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300 μm and dropped to 20cm3The container (2) is vibrated until the sample fills the upper end face of the container, and then vibrated for 1000 strokes of 10mm in length by a powder density measuring instrument (for example, Tap densifier manufactured by seishin corporation), and the density obtained from the volume and the weight of the sample at that time is defined as Tap density.
[ [ BET specific surface area ] ]
Negative electrode [6 ] as measured by BET method in lithium Secondary Battery of the present invention]The specific surface area of the graphitic carbon particles used for the negative electrode active material of (3) is preferably 0.1m2A value of at least one per gram, more preferably 0.7m2A total of 1m or more, particularly 1m2A total of 1.5m or more2More than g. The upper limit is preferably 100m2A ratio of 50m or less per gram2A specific ratio of 25m or less per gram2A total of 15m or less, preferably2The ratio of the carbon atoms to the carbon atoms is less than g. When the BET specific surface area is less than this range, lithium acceptance during charging tends to be poor when used as a negative electrode material, and lithium tends to precipitate on the electrode surface in some cases. On the other hand, if it is higher than the above range, the reactivity with the nonaqueous electrolytic solution increases when used as a negative electrode material, and the amount of generated gas tends to increase, and it may be difficult to obtain a preferable battery.
The BET specific surface area is defined as a value determined as follows: the sample was preliminarily dried at 350 ℃ for 15 minutes under a nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring apparatus manufactured by large-scale commercial research), and then measured by a nitrogen adsorption BET 1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
[ [ volume average particle diameter ] ]
The volume average particle diameter of the graphite carbon particles used as the negative electrode active material of the negative electrode [6] in the lithium secondary battery of the present invention is defined as a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is preferably 1 μm or more, more preferably 3 μm or more, particularly preferably 5 μm or more, and further preferably 7 μm or more. The upper limit is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and particularly preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, an uneven coating surface is likely to be formed when the electrode plate is produced, which is not preferable in the battery production process.
[ [ micropore volume ] ]
The volume of pores of graphite carbon particles used as a negative electrode active material for a negative electrode [6] in a lithium secondary battery of the present invention is usually 0.01mL/g or more, preferably 0.05mL/g or more, more preferably 0.1mL/g or more, corresponding to voids in particles having a diameter of 0.01 to 1 μm as determined by a mercury porosimeter (mercury intrusion method), and the amount of irregularities due to the surface roughness of the particles, and the upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, more preferably 0.3mL/g or less. If this range is exceeded, a large amount of binder is sometimes required for manufacturing the plate. If the amount is less than this range, the high current density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of adhesive is sometimes required for producing the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. If the amount is less than this range, the high current density charge/discharge characteristics may be deteriorated.
As a device for the mercury porosimeter, a mercury porosimeter (autopore 9520; manufactured by micromeritics) can be used. About 0.2g of a sample (negative electrode material) was weighed, sealed in a powder container, degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes, and subjected to pretreatment. Subsequently, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased stepwise from 4psia (about 28kPa) to 40000psia (about 280MPa), followed by pressure reduction to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 °. The average pore size is the pore size at which the cumulative pore volume reaches 50%.
[ [ ash ] ])
The ash content of the graphite carbon particles used as the negative electrode active material of the negative electrode [6] in the lithium secondary battery of the present invention is preferably 1 mass% or less, particularly preferably 0.5 mass% or less, and more preferably 0.1 mass% or less, based on the total mass of the graphite carbon particles. The lower limit is preferably 1ppm or more. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolytic solution during charge and discharge may not be negligible. On the other hand, if it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost may be increased.
The graphitic carbon particles typically have a true density of 2.0g/cm3Above, preferably 2.1g/cm3Above, more preferably 2.2g/cm3Above, more preferably 2.22g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase. In the present invention, the true density is defined as a value measured by a liquid phase displacement method (densitometry method) using butanol.
[ [ orientation ratio ] ]
The orientation ratio of the graphite carbon particles used as the negative electrode active material of the negative electrode [6] in the lithium secondary battery of the present invention is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction of carbon obtained by X-ray diffraction were fitted using asymmetric pearson VII as a distribution function, peak separation was performed, and integrated intensities of the peaks of (110) diffraction and (004) diffraction were calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as an active material orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit: divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
[ [ length-diameter ratio ] ]
The aspect ratio of the graphite carbon particles used as the negative electrode active material of the negative electrode [6] in the lithium secondary battery of the present invention is theoretically 1 or more, and the upper limit thereof is 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, streaks are generated when the electrode plate is produced, and a uniform coating surface cannot be obtained, and the high-current-density charge/discharge characteristics may be deteriorated.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the particle and the shortest diameter B perpendicular thereto in three-dimensional observation. The particles are observed by a scanning electron microscope which can observe the particles under magnification. Arbitrary 50 graphite particles fixed to the end faces of a metal having a thickness of 50 μm or less were selected, and a stage on which a sample was fixed was rotated and tilted, and A, B of each of these particles was measured to obtain an average value of a/B.
The graphite carbon particles used as the negative electrode active material of the negative electrode [6] in the lithium secondary battery of the present invention may be produced naturally or artificially, but preferably the graphite carbon particles contain natural graphite. In addition, naturally occurring substances or artificially manufactured substances may also be subjected to specific treatments. The production method (including a sorting method) is not particularly limited, and for example, graphite carbon particles having the above-described characteristics can be obtained by sorting the particles by a classification method such as sieving or air classification.
Among these, particularly preferred graphitic carbon particles are those produced by modifying naturally occurring carbonaceous particles or artificially produced carbonaceous particles by applying mechanical energy treatment. More preferably, the carbonaceous particles as the raw material for mechanical energy treatment contain natural graphite.
[ [ mechanical energy treatment ] ]
The mechanical energy treatment will be described below. The carbonaceous particles as the raw material to be subjected to the mechanical energy treatment are not particularly limited, and natural or artificial graphite-based carbonaceous particles, carbonaceous particles as a graphite precursor, and the like are used. The properties of these materials are shown below.
[ [ [ graphite-based carbonaceous particles as a raw material for mechanical energy treatment ] ]
The properties of the raw material graphite-based carbonaceous particles preferably satisfy at the same time any one or more of (1) to (11) shown below. The physical property measurement method and definition are the same as those of the graphite carbon particles.
(1) X-ray parameters
The d value (interlayer distance) of the lattice plane (002) of the graphite-based carbon particle as a raw material, which is determined by X-ray diffraction using a vibroseis method, is preferably 0.335nm or more, and the upper limit thereof is usually 0.340nm or less, preferably 0.337nm or less. The crystallite size (Lc) of the graphitic carbon particle determined by X-ray diffraction using a vibroseis method is usually in the range of 30nm or more, preferably 50nm or more, and more preferably 100nm or more. If the content is less than this range, the crystallinity may be reduced, and the increase in initial irreversible capacity may increase.
(2) Ash content
The ash content in the graphite-based carbonaceous particles as the raw material is 1 mass% or less, preferably 0.5 mass% or less, particularly preferably 0.1 mass% or less, based on the total mass of the graphite-based carbonaceous particles, and the lower limit thereof is usually 1ppm or more. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolytic solution during charge and discharge may not be negligible. If the amount is less than this range, a long time and energy are required for manufacturing and equipment for preventing contamination is required, and the cost may be increased.
(3) Volume-based average particle diameter
The volume-based average particle diameter of the raw graphite-based carbonaceous particles is defined as a volume-based average particle diameter (median diameter) determined by a laser diffraction/scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is not particularly limited, but is usually 10mm or less, preferably 1mm or less, more preferably 500 μm or less, still more preferably 100 μm or less, and particularly preferably 50 μm or less. If the content is less than the above range, the particle size may be too small by applying an optical energy treatment, resulting in an increase in irreversible capacity. If the amount exceeds the above range, the device to which the mechanical energy treatment is applied may be difficult to operate effectively, resulting in a loss of time.
(4) Raman R value, Raman half value width
The raw graphite-based carbonaceous particles have a raman R value, as measured by argon ion laser raman spectroscopy, of usually 0.01 or more, preferably 0.03 or more, more preferably 0.1 or more, and the upper limit thereof is usually 0.6 or less, preferably 0.4 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, the raman value increases due to the application of mechanical energy treatment, and the sites where Li enters into the interlayer are sometimes decreased with charge and discharge due to the decrease in crystallinity, that is, the charge acceptance is sometimes decreased. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is further reduced by the mechanical energy treatment, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a reduction in efficiency or an increase in generated gas.
In addition, 1580cm-1The Raman half-value width of (A) is not particularly limited, but is usually 10cm-1In the above-mentioned manner,preferably 15cm-1Above, in addition, the upper limit is usually 50cm-1Hereinafter, preferably 45cm-1Hereinafter, more preferably 40cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface is too high, the raman value increases due to the application of mechanical energy treatment, and the sites where Li enters into the interlayer are sometimes decreased with charge and discharge due to the decrease in crystallinity, that is, the charge acceptance is sometimes decreased. On the other hand, if the amount is more than this range, the crystallinity of the particle surface is further decreased by the mechanical energy treatment, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in generated gas.
(5) BET specific surface area
The specific surface area of the raw material graphite-based carbonaceous particles measured by the BET method is usually 0.05m2More than g, preferably 0.2m2A value of at least one per gram, more preferably 0.5m2A total of 1m or more, particularly 1m2More than g. Its upper limit is typically 50m2A ratio of 25m or less per gram2A ratio of 15m or less per gram2A specific preferable range is 10m or less per gram2The ratio of the carbon atoms to the carbon atoms is less than g. If the BET specific surface area value is less than this range, the BET specific surface area increases by applying the mechanical energy treatment, so that the acceptance of lithium during charging is likely to deteriorate, and lithium is likely to precipitate on the electrode surface. On the other hand, if it is more than the above range, the BET specific surface area further increases by the mechanical energy treatment, and when used as a negative electrode active material, the reactivity with the nonaqueous electrolytic solution increases, the amount of generated gas tends to increase, and it may be difficult to obtain a preferable battery.
(7) Degree of circularity
The circularity is used as the degree of sphericity of the raw material graphite-based carbonaceous particles, and the circularity of particles having a particle diameter of 3 to 40 μm of the raw material graphite-based carbonaceous particles is preferably 0.1 or more, more preferably 0.2 or more, particularly preferably 0.4 or more, further preferably 0.5 or more, and most preferably 0.6 or more. If the amount is less than this range, the spherical shape may not be sufficiently formed even if the mechanical energy treatment is applied, and the high-current density charge/discharge characteristics may be deteriorated.
(8) True density
The raw material graphite-based carbonaceous particles usually have a true density of 2g/cm3Above, preferably 2.1g/cm3More preferably 2.2g/cm or more3Above, more preferably 2.22g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the amount is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
(9) Tap density
The tap density of the graphite-based carbonaceous particles as a raw material is usually 0.05g/cm3Above, preferably 0.1g/cm3Above, more preferably 0.2g/cm3Above, particularly preferably 0.5g/cm3The above. Further, it is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is less than this range, the tap density will not be sufficiently increased even if the treatment with mechanical energy is applied, and when the negative electrode active material is used, the packing density will be difficult to increase, and a high capacity battery may not be obtained. On the other hand, if the amount is more than this range, the tap density further increases upon the application of mechanical energy treatment, and the voids between particles in the electrode after the electrode is formed are too small, which may result in a decrease in high-current-density charge/discharge characteristics due to insufficient flow channels of the nonaqueous electrolytic solution. The tap density of the graphite-based carbonaceous particles is also measured and defined by the same method as described above.
(10) Orientation ratio (powder)
The orientation ratio of the raw material graphite-based carbonaceous particles is usually 0.001 or more, and preferably 0.005 or more. The upper limit is theoretically 0.67 or less. If the amount is less than this range, the orientation ratio may not be sufficiently improved even if the mechanical energy treatment is applied, and the high-density charge/discharge characteristics may be deteriorated.
(11) Aspect ratio (powder)
The aspect ratio of the graphite-based carbonaceous particles is theoretically 1 or more, and the upper limit is usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the ratio exceeds the upper limit, the aspect ratio may not be sufficiently reduced even by the mechanical energy treatment, and when the electrode plate is produced, streaks may occur, and a uniform coating surface may not be obtained, resulting in a decrease in high-current density charge/discharge characteristics.
Among the raw material graphite-based carbonaceous particles, examples of the highly crystalline carbon material having a developed carbon hexagonal network structure include highly oriented graphite in which hexagonal network surfaces are grown in a planar orientation, and isotropic high-density graphite in which highly oriented graphite particles are aggregated in an isotropic direction. Preferred highly oriented graphite includes natural graphite produced by srilanka or magagassia, so-called kish graphite precipitated as supersaturated carbon from molten iron, artificial graphite having a partially high graphitization degree, and the like.
Natural GRAPHITEs are classified according to their properties as Flake GRAPHITEs, soil GRAPHITEs (Amorphous GRAPHITEs) (see "integration OF powder technology, ((Co., Ltd.) center for Industrial technology, Showa 49) as GRAPHITEs; AND" HAND BOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES ", (distributed by Noyes Publications)). The graphitization degree was highest with flaky graphite, 100%, followed by flaky graphite, 99.9%, and soil graphite as low as 28%. Flake graphite as natural graphite is produced from motor gaska, china, brazil, ukraina, canada, and the like; the graphite flakes are produced primarily from srilanca. The main producing areas of the soil graphite are korea, china, mexico and the like. Among these natural graphites, soil graphite generally has a small particle size and a low purity. On the contrary, the flaky graphite or the scaly graphite has advantages such as high graphitization degree and small impurity amount, and thus can be preferably used in the present invention.
The artificial graphite can be produced by heating petroleum heavy oil, coal heavy oil, petroleum coke, or coal coke at 1500 to 3000 ℃ or higher in a non-oxidizing atmosphere.
In the present invention, any artificial graphite may be used as a raw material as long as it shows high orientation and high capacity after being subjected to mechanical energy treatment and heat treatment. In the artificial graphite, even a material which is not completely graphitized, for example, a graphite precursor, can be used as a raw material for the mechanical energy treatment of the present invention as long as it can be converted into graphitic carbon particles satisfying the above physical properties by the mechanical energy treatment.
[ [ [ contents of mechanical energy treatment ] ] ]
The mechanical energy treatment of these graphite-based carbonaceous particles as a raw material can reduce the particle size to 1 or less in the ratio of the volume average particle size after the treatment to that before the treatment, and can increase the tap density by the treatment, and the raman R value can be 1.1 times or more by the treatment.
By performing such mechanical energy treatment, the carbonaceous particles such as graphite-based carbonaceous particles as a raw material become particles as follows: the crystallinity is maintained high as a whole, but the vicinity of the surface of the particles is roughened, and the edge surface is inclined and exposed. Thus, the area on which lithium ions can enter and exit is increased, and the capacity is high even at a high current density.
The "mechanical energy treatment" in the present invention is classified as "pulverization treatment" among the engineering elementary operations that can be effectively utilized in particle design such as pulverization, classification, mixing, granulation, surface modification, reaction, and the like, but also includes surface treatment in which a fine structure defect is generated by impact, friction, compression, or the like on a surface structure.
Generally, the pulverization treatment is a treatment of applying a force to a substance to reduce its size to adjust the particle size, particle size distribution, and filling property of the substance. The pulverization treatment is classified according to the kind of force applied to the material and the treatment form. The forces applied to a substance are roughly classified into 4 types as follows: (1) knocking force (impact force), (2) crushing force (compression force), (3) grinding force (grinding force), and scraping force (shear force). On the other hand, the treatment forms are roughly classified into the following 2 types: volume pulverization in which cracks are generated in the particles and propagated, and surface pulverization in which the surfaces of the particles are cut. The volume crushing can be carried out by adopting impact force, compression force and shearing force; the surface pulverization can be carried out by using a grinding force or a shearing force. The pulverization treatment is a treatment in which the kinds and treatment forms of the forces applied to these substances are combined in various ways. The combination thereof may be appropriately determined depending on the purpose of the treatment. The pulverization treatment may be performed by using a chemical reaction such as blasting or volume expansion, but is generally performed by using a mechanical device such as a pulverizer.
The mechanical energy treatment preferably used for producing the graphite carbonaceous particles of the present invention preferably includes a treatment for increasing the proportion of the surface-treated particle surface portion in the final product (surface pulverization), regardless of the presence or absence of volume pulverization. This is because the pulverization of the particle surface is important for removing corners of the carbonaceous particles such as graphite carbonaceous particles to make the particle shape into a circular shape. Specifically, the mechanical energy treatment may be performed by performing the volume pulverization to some extent and then performing the surface pulverization, or may be performed by performing only the surface pulverization without performing the volume pulverization. The mechanical energy treatment may be performed by performing the volume pulverization and the surface pulverization at the same time. Preferably, the mechanical energy treatment is performed by pulverizing the surface of the particles and removing the corners from the surface of the particles.
The mechanical energy treatment of the present invention can reduce the particle size to a ratio of the volume average particle size after the treatment to that before the treatment of 1 or less, and can increase the tap density by the treatment, and can also increase the raman R value by 1.1 times or more by the treatment.
The "ratio of the volume average particle diameter before and after the treatment" is a value obtained by dividing the volume average particle diameter after the treatment by the volume average particle diameter before the treatment. The value of (volume average particle diameter after treatment)/(volume average particle diameter before treatment) is 1 or less, preferably 0.95 or less. If the number is substantially 1, the effect of improving the filling property by improving the circularity by the mechanical energy treatment may be small. Further, the particle shape can be controlled by reducing the particle size so that the ratio of the average particle diameter after the treatment to that before the treatment is 1 or less.
The tap density can be improved by the mechanical energy treatment in the invention. The increase in tap density means an increase in the degree of sphericity represented by circularity as described later. Therefore, the mechanical energy treatment must be such a treatment. The value of (tap density after treatment)/(tap density before treatment) is 1 or more, preferably 1.1 or more. If the amount is less than 1, the effect of improving the filling property by improving the circularity may be small.
The raman R value can be 1.1 times or more by the mechanical energy treatment in the present invention. The improvement of the raman R value means that crystallinity in the vicinity of the particle surface is reduced as described later, and the mechanical energy treatment is required to be such a treatment. The value of (raman R value after treatment)/(raman R value before treatment) is 1.1 or more, preferably 1.4 or more. If the value is less than 1.1, the effect of improving the charge acceptance due to the change in the raman R value may be small.
The mechanical energy treatment of the present invention is to increase the tap density of particles by rounding the particles. To increase the tap density of the powder particles, it is known that smaller particles that fill in the voids that can enter into the particles and form between the particles are preferred. Therefore, it is considered that the tap density can be increased if the particle diameter is reduced by pulverizing carbon particles such as graphite-based carbonaceous particles, but the tap density is generally reduced by reducing the particle diameter by such a method. The reason for this is considered to be that the particle shape becomes more amorphous by pulverization.
On the other hand, the larger the number of particles (coordination number n) in contact with one particle (particle of interest) in the powder particle group is, the lower the proportion of voids in the filler layer is. That is, as a factor affecting the tap density, the ratio of the sizes of the particles and the composition ratio, that is, the particle size distribution are important. However, this study was made only on the basis of spherical particle groups of a model, and carbonaceous particles such as graphite-based carbonaceous particles before treatment used in the present invention are scaly, and plate-like, and attempts have been made to improve tap density by controlling particle size distribution only by ordinary pulverization, classification, and the like, but such a high filling state cannot be produced.
Generally, the tap density tends to decrease as the particle diameter of carbonaceous particles such as flaky, scaly, and tabular graphite-based carbonaceous particles decreases. This is considered to be due to the following reasons: the particles are more amorphized by pulverization, and protrusions such as "burrs", "peeling" and "bending" formed on the particle surface are increased, and finer amorphous particles are adhered to the particle surface with a certain degree of strength, so that the resistance between adjacent particles is increased, and the filling property is deteriorated.
If the amorphousness of these particles is reduced and the particle shape is close to spherical, the filling property is reduced even if the particle diameter is reduced, and theoretically, both the large particle diameter particles and the small particle diameter particles should exhibit the same tap density.
The inventors of the present invention confirmed the following by their studies: carbonaceous or graphitic particles having substantially the same true density and substantially the same average particle diameter exhibit a higher tap density as the shape becomes spherical. That is, it is important to make the particle shape band circular, and to approach a sphere. If the particle shape is close to spherical, the filling properties of the powder are also significantly improved. In the present invention, for the above reasons, the tap density of the powder is used as an index when the mechanical energy is applied. When the filling ratio of the treated powder or granule is increased before the treatment, it is considered that the result is that the particles are spherical by the treatment method used. In the method of the present invention, when the tap density of the carbon material obtained by performing the treatment so that the particle diameter is significantly reduced is higher than the tap density of the carbon material having the same particle diameter obtained by ordinary pulverization, the result of spheroidization is considered to be obtained.
As an index of crystallinity of the particles and roughness of the particle surface, that is, the amount of edge face of the crystal, the interplanar spacing (d002) of the (002) face, the crystallite size (Lc) and the raman R value measured by a wide-angle X-ray diffraction method can be used. In general, the smaller the value of the interplanar spacing (d002) of the (002) plane and the larger the crystallite size (Lc), the smaller the raman R value of the carbon material. That is, all the carbon particles such as graphite-based carbonaceous particles exhibit almost the same crystal state. On the contrary, the graphitic carbon particles of the present invention have a large raman R value, although the value of the interplanar spacing (d002) at the (002) plane is small and the crystallite size (Lc) is large. That is, the graphite carbon particles have high crystallinity in the lump but are near the surface (distant from the particle surface)
Figure BDA0003109774980001281
Level) and the exposure of the edge face becomes large.
From the viewpoint of improving the filling property, the circularity is more preferably 1.02 times, particularly preferably 1.04 times by the mechanical energy treatment in the present invention.
[ [ [ device for mechanical energy treatment ] ] ]
The apparatus for performing the kinetic energy treatment is selected from apparatuses capable of performing the above-described preferred treatments. The present inventors have found, when conducting research, that the above-described application of 4 kinds of forces to a substance can be achieved by using one or more of the following means: mainly impact force, and repeatedly apply mechanical actions such as compression, friction, and shearing force to the particles including the interaction of the particles. Specifically, the following devices are preferred: the apparatus has a rotor having a plurality of blades inside a casing, and performs surface pulverization while performing volume pulverization by applying mechanical actions such as impact compression, friction, and shearing force to carbonaceous particles introduced inside by rotating the rotor at a high speed. Further, an apparatus having a mechanism for repeatedly imparting a mechanical action by circulating or convecting carbonaceous particles is more preferable. The number of blades in the tank is preferably 3 or more, and particularly preferably 5 or more.
An example of a preferred apparatus satisfying such requirements is a mixing system manufactured by Nara machinery manufacturing company. When the apparatus is used for treatment, the circumferential speed of the rotating rotor is preferably set to 30 to 100 m/sec, more preferably 40 to 100 m/sec, and still more preferably 50 to 100 m/sec. The treatment may be carried out by passing only the carbonaceous particles, but is preferably carried out by circulating or staying in the apparatus for 30 seconds or more, and more preferably carried out by circulating or staying in the apparatus for 1 minute or more.
When the true density of the graphite-based carbonaceous particles as the raw material is less than 2.25 and the crystallinity is not so high, it is preferable to further perform a heat treatment for improving the crystallinity after the mechanical energy treatment. Such heat treatment is preferably performed at 2000 ℃ or higher, more preferably at 2500 ℃ or higher, and still more preferably at 2800 ℃ or higher.
[ electrode for negative electrode [6]
The negative electrode [6] can be formed by a common method in the same manner as described above. The current collector, the ratio of the thicknesses of the current collector and the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
< negative electrode [7] >
Next, a negative electrode [7] used In the lithium secondary battery of the present invention, which contains, as a negative electrode active material, a negative electrode active material (C) containing a plurality of elements, the negative electrode active material (C) containing at least one of a lithium-occluding metal (a) and/or a lithium-occluding alloy (B) selected from Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb, and containing C and/or N as an element Z, will be described.
[ negative electrode active material for negative electrode [7]
Next, a negative electrode active material used for the negative electrode [7] will be described.
[ [ composition ] ]
A negative electrode active material used for a negative electrode [7] of a lithium secondary battery of the present invention is characterized by containing at least a metal capable of occluding lithium (lithium-occluding metal (A)) and/or an alloy (lithium-occluding alloy (B)), and by containing C and/or N as an element Z.
The lithium-occluding metal (a) is at least one selected from the group consisting of Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb. Among these, Al, Si, Sn, or Pb is preferable, Si or Sn is more preferable, and Si is further preferable. The reason why Si is preferred is that the capacity per unit mass is large.
The lithium-absorbing alloy (B) is an alloy containing 2 or more of the above-mentioned lithium-absorbing metals (a), or an alloy containing "the lithium-absorbing metal (a) and an element other than C, N". The "element other than the lithium-absorbing metals (a) and C, N" is preferably one or more elements selected from groups 4, 5, 6, 8, 9, 10, 11, 13, and 16 of the periodic table, more preferably Ti, Zr, V, Cr, W, B, O, and Co, and even more preferably Ti, Zr, W, O, and Co. These elements are preferably used in view of controlling reactivity because they easily form a high melting point compound. From the viewpoint of capacity, the content of the "elements other than the lithium-occluding metals (a) and C, N" forming the alloy is preferably 50 mol% or less with respect to the lithium-occluding alloy (B).
Examples of the form in which C and/or N of the element Z is contained in the negative electrode active material (C) containing a plurality of elements include the following:
1. a state contained in the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) (a lithium-occluding substance (D) containing an element Z);
2. a state existing around the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) (the lithium-occluding substance (F) other than the element Z);
3. The states 1 and 2 described above are combined.
As a preferable mode of the lithium-occluding substance (D) containing the element Z, it is preferable that the element Z (C and/or N) exists in a non-equilibrium state in the lithium-occluding metal (a) and/or the lithium-occluding alloy (B), and it is particularly preferable that the lithium-occluding metal (a) is Si.
As a preferable mode of the lithium-occluding substance (F) other than the element Z, a state in which the element Z is C and C can exhibit electrical conductivity is preferable.
The negative electrode active material (C) containing a plurality of elements used in the present invention contains a lithium-absorbing metal (a) and/or a lithium-absorbing alloy (B), contains C and/or N as an essential component, and preferably further contains one or more elements selected from groups 4, 5, 6, 8, 9, 10, 11, 13, and 16 of the periodic table. Such an element is more preferably a Ti, Zr, V, Cr, W, B, O, or Co element, and still more preferably a Ti, Zr, W, O, or Co element.
1. Lithium occlusion material (D) containing element Z
In the lithium-absorbing metal (a) of the present invention, Si is easy to obtain an effect, and therefore, it is used as an inclusion elementThe lithium-absorbing material (D) of Z is preferably a compound having a phase in which the element Z is present in Si in an unbalanced manner, and having a general formula SiZ as a main component xMy(wherein Z, M, x and y are as shown in the following conditions (1) to (4)).
(1) Element Z is an element comprising C and/or N;
(2) the element M is one or 2 or more elements selected from Si and elements other than the element Z;
(3) x is a value that allows a Z concentration ratio q (Z) to be 0.10 to 0.95, the Z concentration ratio q (Z) being calculated from a formula q (Z) ([ x/(1+ x) ]/[ p/(a + p) ] with respect to a Z concentration (p/(a + p)) of a compound SiaZp (wherein a and p are integers) present in a composition equilibrium closest to Si;
(4) y is a number within the range of 0-0.50.
(with respect to SiZxMy)
((element Z))
SiZxMyThe element Z in (A) is an element including C and/or N. The reason why C and/or N is preferably used as the element Z included is as follows:
(1) a compound having a melting point higher than that of Si can be formed;
(2) the covalent bond radius is smaller than that of Si;
(3) the diffusion coefficient in Si is small;
(4) and even if it reacts with lithium, its volume change is small, etc.
In particular, element C, N may form SiC, Si3N4A compound having an equilibrious melting point higher than that of Si. Further, since a high-melting-point compound is a very stable compound having a negative free energy of formation in general, C and/or N is preferable as the element Z from the viewpoint that the activity of Si can be effectively reduced and the reactivity with the nonaqueous electrolytic solution can be suppressed.
Further, since the atomic radius of the covalent bond of element C, N is smaller than that of Si, it is considered that it is difficult to form it in SiZxMyThe compound existing in equilibrium among the compounds is effective for more uniform distribution of the element Z at a high concentration, and details thereof are not clear, but effective for reducing the activity of Si and suppressing the reaction with the nonaqueous electrolytic solutionFrom the viewpoint of the compatibility, it is preferable.
Since the element C, N has a small diffusion coefficient in Si, when the element C, N is dispersed in Si, aggregation and crystallization of Si due to charge and discharge are suppressed, and it is preferable from the viewpoint of suppressing the Si from being micronized or reacting with the nonaqueous electrolytic solution. Element C, N is preferable because it has a small volume change even when it reacts with lithium, and therefore does not easily affect the interruption of the conduction path of Si.
In addition, Cu is an element such as Cu or Ni3Si、Ni2When a compound capable of being present in equilibrium, such as Si, has a lower melting point than Si, the activity of Si cannot be effectively reduced, and it is difficult to suppress the reaction with the nonaqueous electrolytic solution, and the diffusion coefficient of Cu and Ni elements in Si is large, so Si is likely to be finely pulverized due to aggregation or crystallization of Si during charge and discharge, and the cycle characteristics are not improved in some cases. In addition, in SiZ xMyWhen a compound existing in equilibrium in the compound is a main component, the activity of Si cannot be reduced, and the reactivity with the nonaqueous electrolytic solution cannot be suppressed, so that the cycle characteristics may be deteriorated.
((element M))
SiZxMyThe element M in (B) is one or 2 or more elements selected from elements other than Si and the element Z, preferably one or 2 or more elements selected from groups 4, 5, 6, 8, 9, 10, 11, 13 and 16 of the periodic table, and is more preferably Ti, Zr, V, Cr, W, B and O elements, and even more preferably Ti, Zr, W and O elements, from the viewpoint of suppressing reactivity, because a high-melting-point compound is easily formed.
At SiZxMyIn the composition of (1), SiZxMyX of (b) is a value which brings the concentration ratio of Z, Q (Z), into the following range: usually 0.10 or more, preferably 0.15 or more, more preferably 0.30 or more, particularly preferably 0.40 or more, and the upper limit is usually 0.95 or less, preferably 0.85 or less, more preferably 0.75 or less, further preferably 0.65 or less; the concentration ratio of Z, Q (Z), is relative to the compound existing in the composition equilibrium closest to SiThe Z concentration (p/(a + p)) of the compound SiaZp (wherein a and p are integers) is represented by the formula q (Z) ([ x/(1+ x)) ]/[p/(a+p)]And then calculated. The term "compound existing in a composition equilibrium closest to Si" means a compound SiaZp in which p/(a + p) is the lowest value among siazps and exists in equilibrium.
In the present invention, a Phase diagram of Si and an element Z (for example, "Desk handbook Phase diagnostics for Binary Alloys" published by ASM International corporation) describes a compound SiaZp existing in the closest compositional equilibrium to Si, and in the present invention, the Z concentration ratio q (Z) is set with respect to the Z concentration (p/(a + p)) of the SiaZp, and the range of x is defined by using the numerical range of the Z concentration ratio q (Z).
The compound in equilibrium here is a compound Si which is described as the top of the diagram in the phase diagram or the likeaZpIn the present invention, SiC is known as a stable compound when Z is C, and the compound is present in equilibrium. Therefore, when Z is C, SiC corresponds to Si of the present inventionaZp. In addition, when Z is N, for example, Si is known3N4Is the most stable compound, but Si is also known2N3SiN is also present as a fixed ratio compound, and in the present invention, all of these compounds are present as a balance compound. Thus, SiN corresponds to Si in the present invention when Z is N aZp。
On the other hand, the compounds of the phases that are not present in equilibrium refer to compounds other than the compounds that are present in equilibrium. In the case of a compound existing in non-equilibrium, a specific fixed ratio compound is not formed, and the Si atom and the Z atom are uniformly dispersed in macroscopical view.
If the concentration ratio of Z is less than this range, the effect of reducing the activity of Si is small, the reactivity with the nonaqueous electrolytic solution cannot be suppressed, the electrode expansion becomes large, and the preferable cycle characteristics may not be obtained. On the other hand, if this range is exceeded, a stable compound Si in equilibrium is formedaZpEtc. even if the element Z is increased, the activity of Si is not reducedLow, reactivity with the nonaqueous electrolytic solution may not be suppressed. In addition, due to SiaZpAnd the like, and therefore, when such a compound is formed, the conductivity of the active material is deteriorated, and doping and dedoping of lithium are difficult, and charging and discharging may not be performed.
Here, the concentration ratio of Z, Q (Z), of 1 means that Si forms a stable compound SiaZpIt is not preferred. If the content of Si is significantly larger than this range, it is difficult to obtain the effect of increasing the capacity due to the Si content, and preferable battery characteristics may not be obtained.
Further, when C and N are used together as the element Z, Si is obtained for each of 2 elements aZpThe Z concentration ratio q (Z) of the reference Z concentration of the element is regarded as the Z concentration ratio q (Z).
SiZxMyY in (b) is a real number satisfying 0. ltoreq. y.ltoreq.0.5. Compound SiZxMyContaining the element M, and when y is not equal to 0, the compound SiZxMyThe ratio y of the element M in (A) is usually 0.08 or more, preferably 0.10 or more, and its upper limit is usually 0.50 or less, preferably 0.40 or less, more preferably 0.30 or less. If y exceeds this range, the Si content decreases, and it may be difficult to obtain a high capacity. When the element M is substantially not contained, the ratio y of the element M is 0 or y is approximately equal to 0. In the present invention, y ≈ 0 means a case where the element M is inevitably contained (substantially not containing M) in a production process of the negative electrode active material according to the present invention or the like, for example, a case where y is less than 0.08.
The composition of the negative electrode active material (C) containing a plurality of elements can be determined by a usual method, for example, by placing the side containing the negative electrode compound on a sample stage with the surface thereof facing upward using an X-ray photoelectron spectrometer (for example, "ESCA" manufactured by ulvac-phi corporation), and performing depth profile (デ プ ス プ ロ ファイ ル, depth profile) measurement while Ar sputtering is performed using K α rays of aluminum as an X-ray source to calculate the atomic concentrations of Si, element Z, element M, and the like.
(SiCxOyComposition of (2)
When the element Z is C and the element M is O, in the general formula SiCxOyIn (b), x is usually 0.053 or more, preferably 0.08 or more, more preferably 0.15 or more, and particularly preferably 0.25 or more, and its upper limit is usually 0.90 or less, preferably 0.75 or less, more preferably 0.60 or less, and particularly preferably 0.45 or less. Y is usually 0 or more, preferably a value larger than 0, particularly preferably 0.08 or more, and more preferably 0.10 or more, and its upper limit is usually 0.50 or less, preferably 0.40 or less, and particularly preferably 0.30 or less.
(existence state of element Z in Si in the lithium-occluding material (D) containing element Z)
In the negative electrode compound SiZ of the inventionxMyThe value of XIsz measured by X-ray diffraction of the presence of the element Z in Si is not particularly limited, and when the element Z is C, it is preferably 1.2 or less, and more preferably 0.7 or less. When the element Z is N, it is preferably 1.1 or less, more preferably 1.0 or less. The XIsz value being less than the above range means that Si is a main component of a phase in which the element Z is present in non-equilibrium in SiaZpThe compound having an equilibria is not a main component, and the following problem that the XIsz value exceeds the above range does not occur, and therefore, it is preferable. When the value of XIsz exceeds the above range, i.e., Si aZpWhen the phase of the compound existing in equilibrium is a main component (silicon carbide when the element Z is C, and silicon nitride when the element Z is N), the following may occur: the reactivity with a nonaqueous electrolytic solution cannot be suppressed without lowering the activity of Si, and the cycle characteristics are deteriorated; due to SiaZpAnd the like, and the active material thin film has poor conductivity, and doping and dedoping of lithium are difficult, and charging and discharging cannot be performed; or the discharge capacity per unit mass of the active material becomes small. The lower limit of the XIsz value is usually 0.00 or more.
((X-ray diffraction measuring method))
The XIsz value measured by X-ray diffraction can be measured, for example, by using an X-ray diffraction apparatus (for example, an "X-ray diffraction apparatus" manufactured by japan (リガク)) with the negative electrode active material of the present invention set as an irradiation surface, and the measurement conditions are as shown in the examples described later.
The XIsz value is defined as follows.
((XIsz value when element Z is C)))
The peak intensity Isz of 35.7 degrees 2 θ and the peak intensity Is of 28.4 degrees 2 θ were measured, and the intensity ratio XIsz ═ Isz/Is calculated and defined as the XIsz of the active material film. Here, a peak at 35.7 degrees 2 θ is considered to be derived from SiC, a peak at 28.4 degrees is derived from silicon, and an XIsz value of 1.2 or less means that SiC is hardly detected.
((XIsz value when element Z is N)))
The peak intensity Isz of 70.2 degrees 2 θ and the peak intensity Is of 28.4 degrees 2 θ were measured, and the intensity ratio XIsz ═ Isz/Is calculated and defined as the XIsz of the active material film. Here, the peak at 27.1 degrees 2. theta. is considered to be derived from Si3N4A peak of 28.4 degrees is a peak derived from silicon, and an XIsz value of 1.1 or less means that Si is hardly detected3N4。
(distribution state of element Z in lithium-occluding material (D) containing element Z)
SiZ of the inventionxMyThe element Z in (2) is present in a size of 1 μm or less, for example, an atom, a molecule, or a cluster (cluster), and the distribution of the element Z is preferably SiZxMyIs uniformly distributed, more preferably from SiZxMyThe concentration gradient of the element Z is inclined to be higher in the surface direction at the center (in the case of a thin-film negative electrode material to be described later, the concentration gradient is inclined to be higher from the contact portion with the current collector toward the film surface, and in the case of a powdery negative electrode material, the concentration gradient is inclined to be higher from the particle center toward the film surface). In the negative electrode active material, when the distribution of the element Z is unevenly localized, expansion and contraction accompanying charge and discharge of Si are concentrated in the Si portion where the element Z is not present, and therefore, the conductivity may be deteriorated as the cycle progresses. The dispersion state of the element Z can be confirmed by EPMA or the like, as described later.
(distribution status of element M)
SiZ of the inventionxMyThe distribution state of the element M in (b) is not particularly limited, and may be uniformly distributed or non-uniformly distributed.
(Raman RC value, Raman RSC value, Raman RS value)
The raman RC value of the lithium-absorbing material (D) containing the element Z in the present invention measured by raman spectroscopy is usually 0.0 or more, and the upper limit thereof is preferably 2.0 or less. If the raman RC value exceeds this range, it is difficult to obtain the effect of high capacity due to Si content, and it is difficult to obtain preferable battery characteristics. In particular, when the element Z contains C, the negative electrode active material SiZ of the present inventionxMyThe raman RC value of (a) is preferably 2.0 or less, more preferably 1.0 or less, and particularly preferably 0.5 or less. For reasons of measurement, the lower limit of the raman RC value is usually 0.0 or more.
The raman RSC value of the lithium-absorbing material (D) containing the element Z in the present invention, as measured by raman spectroscopy, is usually 0.0 or more, and the upper limit thereof is preferably 0.25 or less. If the raman RSC value exceeds this range, the conductivity is deteriorated, and doping and dedoping of lithium are difficult, and charging and discharging may be impossible. In particular, when the element Z contains C, the RSC value is preferably 0.25 or less, and more preferably 0.20 or less. For measurement reasons, the lower limit of the raman RSC value is usually 0.0 or more.
The raman RS value of the lithium-absorbing material (D) containing the element Z in the present invention measured by raman spectroscopy is preferably 0.40 or more, more preferably 0.50 or more, and the upper limit thereof is preferably 1.00 or less, more preferably 0.90 or less. If the raman RS value is below this range, the cycle characteristics may deteriorate. On the other hand, if the amount exceeds this range, charging and discharging may not be performed, which is not preferable. In particular, when the element Z contains C, the RS value is preferably 0.40 or more, more preferably 0.50 or more; the upper limit thereof is preferably 0.75 or less, and preferably 0.65 or less. In particular, when the element Z contains N, the RS value is preferably 0.40 or more, more preferably 0.50 or more; the upper limit is preferably 1.00 or less, and preferably 0.90 or less.
The raman RC value, raman RSC value, and raman RS value measured by raman spectroscopy in the present invention are obtained by raman spectroscopy using the following raman measurement method, and are defined as follows.
((Raman measurement method))
The negative electrode for a nonaqueous electrolyte secondary battery of the present invention is mounted in a measuring cell using a raman spectrometer (for example, "raman spectrometer" manufactured by japan spectrochemical corporation), and the surface of a sample in the cell is irradiated with an argon ion laser to perform measurement. And performing background compensation on the measured Raman spectrum to obtain a Raman RC value, a Raman RSC value and a Raman RS value. In addition, background compensation is performed as follows: the end points of the peaks are connected by a straight line, the background is calculated, and the value is subtracted from the peak intensity.
Under the raman measurement conditions, smoothing is a simple average of 15 points of convolution.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-40 mW
Resolution: 10-20 cm-1
Measurement range: 200cm-1～1900cm-1
((Raman RC value)))
Measurement of 1300cm-1～1600cm-1Peak intensity Ic of the peak c appearing in the vicinity, 300cm-1～500cm-1The peak intensity Ias of the peak as appearing in the vicinity was calculated as the intensity ratio RC (RC ═ Ic/Ias), and this was defined as the raman RC value of the negative electrode. Here, since the peak c and the peak as are derived from carbon and silicon, respectively, the raman RC value reflects the amount of carbon, and a raman RC value of 2.0 or less means that carbon is hardly detected.
(((Raman RSC value)))
Measuring 650cm-1～850cm-1Peak intensity Isc of nearby peak sc, 300cm-1～500cm-1The peak intensity Ias of the peak as appearing in the vicinity was calculated as the intensity ratio RSC (RSC ═ Isc/Ias), and this was defined as the negative raman RSC value.
Here, since the peak sc and the peak as are derived from SiC and silicon, respectively, the raman RSC value reflects the amount of SiC, and a raman RSC value of 0.25 or less means that SiC is hardly detected.
((Raman RS value)))
Measurement of 520cm-1Intensity Is of (1), 300cm-1～500cm-1The peak intensity Ias of the peak as appearing in the vicinity was calculated as the intensity ratio RS (RS ═ Is/Ias), and this was defined as the negative raman RS value. The raman RS value reflects the state of Si.
(IRsc value)
The negative electrode having a negative electrode active material used in the present invention after charging and discharging is preferably 0.90 or more, more preferably 1.1 or more, and particularly preferably 1.2 or more in IRsc value measured by infrared reflection spectroscopy. If IRsc is less than this range, the negative electrode containing Si reacts with the nonaqueous electrolytic solution during cycling, and the amount of active material that can substantially be charged and discharged gradually decreases, and it may be difficult to obtain preferable cycle characteristics. The upper limit of the IRsc value is about 3.0. The IRsc value of the negative electrode measured by infrared reflected light analysis in the present invention is obtained by the following infrared reflected light measurement using an infrared spectrophotometer, and is defined as follows.
(method of measuring Infrared reflectance analysis Using Infrared Spectrophotometer)
The active material surface of the negative electrode of the lithium secondary battery after charging and discharging was attached to a measuring cell using an infrared spectrophotometer (for example, "Magna 560" manufactured by thermionic electron (サーモエレクトロン) corporation), and measured by a reflection method. The measurement was performed in an inert atmosphere using a sample holder (フォルダー) for reflection measurement made of diamond as a window material. The IRsc value was obtained by performing background compensation of the measured infrared absorption spectrum. In addition, background compensation is performed as follows: the connection is 2000-4000 cm -1The minimum value of the range, and the line is extended to find the background, and the value is subtracted from each intensity. Measurement at 1600cm-1Reflected light intensity Isc of lower intensity, 1650cm-1The reflected light intensity Iaco below was calculated as an intensity ratio IRsc (IRsc ═ Isc/Iaco), and defined as an IRsc value after charge and discharge.
Although not specifically defined, since Isc is a film derived from Si and Iaco is a film derived from alkyl lithium carbonate, IRsc reflects the state and amount ratio of the film (solid electrolyte interface: SEI) of the negative electrode, and a value of IRsc of 0.9 or more means that the film derived from alkyl lithium carbonate and the film derived from Si constitute the negative electrode.
Action and principle
First, the activity will be explained. Generally, the so-called activity is a thermodynamic concentration. For the inclusion of substance n1、n2…ni… in the multi-component system, if the chemical potential of the component i is set to μiSetting the chemical potential of the pure substance to mui 0Then the following formula will be described
μi－μi 0＝RTlogai
A of definitioniReferred to as activity.
In addition, activity aiAnd concentration ciRatio of gammaiReferred to as the activity coefficient.
ai/ci＝γi
For example, when a certain system including a solvent and a solute is considered as a thermodynamic solution, the activity coefficient is an amount corresponding to the difference between the chemical potential of a certain component when the system is considered as an ideal solution and the true chemical potential of a certain component when the system is considered as a true solution. (1) In the case where a component i is an actual solution of a solute, if the concentration of the solute becomes low, the system approaches an ideal solution in which the component i is a solute, and the activity coefficient approaches 1. On the contrary, (2) in the case where a component i is an actual solution of a solvent, if the concentration of the solvent becomes high, the system approaches an ideal solution in which the component i is a solvent, and the activity coefficient approaches 1. In addition, when the real solution is more stable than the ideal solution, the chemical potential of the component i is gamma i＜1。
In the present invention, if Si showing good characteristics is exemplified, the component i is Si, and Si as a solvent contains an element Z as a solute, so that the activity a of Si as a solventiThe process is reduced and the time required for the preparation, γi< 1, the Si compound (solid solution: regarded as a true solution) containing the element Z is more stable than Si (regarded as an ideal solution), and as a result, the reactivity with the nonaqueous electrolytic solution can be suppressed.
However, if a compound Si is formed in which Si and the element Z exist in equilibriumaZpFor example, the activity of Si cannot be effectively reduced, and therefore it is important that the element Z exist in Si in an unbalanced manner.
[ form of negative electrode [7]
In the present invention, the form of the negative electrode active material used in the negative electrode [7] is generally a film or a powder. In the present invention, as described in the production method described later, the negative electrode using the thin film active material can be obtained by vapor-phase deposition of the active material layer on the current collector, and the negative electrode using the powdery active material can be formed by, for example, coating the powdery active material, the binder, and the like on the current collector to form the active material layer.
[ [ film-like active material ] ]
[ [ [ structure ] ] ]
Examples of the structure of the thin film-like active material formed on the current collector include a columnar structure and a layered structure.
[ [ [ film thickness ] ] ]
The thickness of the thin film-like active material corresponds to the thickness of the active material layer in which the thin film-like active material is used, and is usually 1 μm or more, preferably 3 μm or more, and the upper limit thereof is usually 30 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. If the film thickness of the film-like active material is less than this range, the negative electrode of the present invention using the film-like active material (hereinafter, the negative electrode using the film-like active material may be referred to as "film negative electrode") has a small capacity per one sheet, and a large number of negative electrodes are required to obtain a large-capacity battery. On the other hand, if the amount exceeds this range, the film-like active material layer may be peeled off from the current collector substrate due to expansion and contraction caused by charge and discharge, and the cycle characteristics may be deteriorated.
[ [ powdered active material ] ]
[ [ [ shape ] ] ]
Examples of the shape of the powdery active material include a spherical shape, a polyhedral shape, and an amorphous shape.
[ [ [ volume-based average particle diameter ] ] ]
The volume-based average particle diameter of the powdery active material is not particularly limited, but is usually 0.1 μm or more, preferably 1 μm or more, and more preferably 3 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 30 μm or less, and more preferably 25 μm or less. If the volume-based average particle diameter of the powdery active material is less than the above range, it is difficult to obtain a conductive path between the powdery active materials or a conductive path between the powdery active material and a conductive agent described later because the particle diameter is too small, and the cycle characteristics sometimes deteriorate. On the other hand, if the amount exceeds the above range, unevenness may occur when the negative electrode active material layer is produced on a current collector by coating as described later.
As the volume-based average particle diameter of the powdery active material, the following values were used: a 2 vol% aqueous solution (about 1mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant was mixed with a measurement target, and a volume-based average particle diameter (median particle diameter) was measured using a laser diffraction/scattering type particle size distribution meter (for example, "LA-920" manufactured by horiba ltd.) with ion-exchanged water as a dispersion medium. In examples described later, the volume-based average particle diameter was determined by this method.
[ [ [ BET specific surface area ] ] ]
The BET specific surface area of the powdery active material is not particularly limited, but is usually 0.1m2A ratio of 0.5m or more per gram2A value of at least g, more preferably 1.0m2A total of 100m or more per g2A ratio of 30m or less in terms of/g2A ratio of 15m or less per gram2(ii) a range of,/g or less. If the BET specific surface area value is less than the lower limit of the above range, in the case of using in a negative electrode, inWhen the battery is charged, lithium acceptance is liable to deteriorate, and lithium is liable to precipitate on the electrode surface, which is not preferable from the viewpoint of safety. On the other hand, if the BET specific surface area value exceeds the upper limit of the above range, the reactivity with the nonaqueous electrolytic solution increases and the amount of generated gas increases when the negative electrode is produced, and it may be difficult to obtain a preferable battery.
In addition, the BET specific surface area of the powdery active material uses a value determined as follows: the powdery active material was preliminarily dried at 350 ℃ for 15 minutes under flowing of nitrogen gas using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research), and then measured by a nitrogen adsorption BET1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
[ [ [ tap density ] ] ]
The tap density of the active substance in powder form is not particularly limited, but is usually 0.2g/cm3Above, preferably 0.3g/cm3Above, more preferably 0.5g/cm3Above, in addition, it is usually 3.5g/cm3Hereinafter, it is preferably 2.5g/cm3The following ranges. If the tap density is less than this range, it may be difficult to increase the packing density of the negative electrode active material layer, and a high-capacity battery may not be obtained. On the other hand, if it exceeds this range, the amount of pores in the negative electrode active material may be reduced, and it may be difficult to obtain preferable battery characteristics.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300 μm and dropped to 20cm3The container (2) is vibrated until the upper end surface of the container is filled with the powdery active material, and then vibrated for 1000 strokes of 10mm in length by a powder density measuring instrument (for example, Tap densifier manufactured by seishin corporation), and the density is determined from the volume at that time and the weight of the sample, and defined as the tapped density.
2. Lithium occlusion material (F) external to element Z
The lithium-absorbing material (F) other than the element Z is a material obtained by combining a lithium-absorbing metal (a) and/or a lithium-absorbing alloy (B) with C (carbon) as the element Z (carbonaceous material (E)) in the negative electrode. The term "composite" as used herein means a state in which the lithium-absorbing metal (a) and/or the lithium-absorbing alloy (B) and the carbonaceous material (E) are bound by bonding, a state in which they are physically bound, a state in which they are held in shape by electrostatic binding, and the like. The "physical constraint" referred to herein means a state in which the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) are occluded in the carbonaceous material (E) and are linked together; the term "electrostatic confinement" refers to a state in which the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) are attached to the carbonaceous material (E) by electrostatic energy. The "state of being bound by bonding" refers to chemical bonding such as hydrogen bonding, covalent bonding, and ionic bonding.
Among these, from the viewpoint of reducing the resistance, a state in which at least a part of the surface of the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) has an interface with the layer of the carbonaceous substance (E) by bonding is advantageous. The coating here means a state in which a chemical bond is present in at least a part of the interface with the surface of the carbonaceous material (E), and shows (1) a state in which the entire surface is coated, (2) a state in which the carbonaceous particles are partially coated, (3) a state in which the surface is selectively coated, and (4) a state in which the surface is present in an extremely fine region containing a chemical bond.
The crystallinity may be changed continuously or discontinuously at the interface. That is, the element Z has an interface formed by covering and/or bonding the lithium-absorbing metal (a) and/or the lithium-absorbing alloy (B) with the carbonaceous material (E) in the lithium-absorbing material (F), and the crystallinity of the interface preferably changes discontinuously and/or continuously.
[ Properties of carbonaceous Material (E) of negative electrode [7]
[ [ composition of carbonaceous Material (E) ] ]
The carbonaceous material (E) is particularly preferably a carbide of (a) or (b) shown below, and may contain a graphite material (G) such as natural graphite or artificial graphite. Since the graphite (G) has very high crystallinity, it generally has higher conductivity than the graphite (E), and has a higher conductivity improving effect than the graphite (E), and therefore, it is preferable to be present together with the graphite (E) from the viewpoint of improving conductivity.
(a) A carbonizable organic substance selected from the group consisting of coal-based heavy oils, straight-run heavy oils, decomposed petroleum-based heavy oils, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenyls, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins;
(b) a solution obtained by dissolving these organic substances that can be carbonized in a low-molecular organic solvent.
Here, as the coal-based heavy oil, coal tar pitch ranging from soft pitch to hard pitch, or dry distillation liquefied oil, etc. are preferable; as the straight-run heavy oil, atmospheric residual oil, vacuum residual oil, and the like are preferable; the decomposed heavy petroleum oils are preferably ethylene tar and the like which are by-produced during thermal decomposition of crude oil, naphtha and the like; as the aromatic hydrocarbon, acenaphthylene, decacycloolefin, anthracene, phenanthrene, and the like are preferable; as the N-ring compound, phenazine, acridine and the like are preferable; as the S ring compound, thiophene, bithiophene, and the like are preferable; as the polyphenylene, biphenyl, terphenyl, and the like are preferable; as the organic polymer, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insoluble treatment thereof, polyacrylonitrile, polypyrrole, polythiophene, polystyrene, and the like are preferable; the natural polymer is preferably a polysaccharide such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, or sucrose; as the thermoplastic resin, polyphenylene sulfide, polyphenylene ether, or the like is preferable; as the thermosetting resin, furfuryl alcohol resin, phenol resin, imide resin, and the like are preferable.
The carbonaceous material (E) is preferably a carbide of the above-mentioned "organic substance capable of carbonization", and is also preferably a carbide of a solution obtained by dissolving such "organic substance capable of carbonization" in a low-molecular-weight organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane.
As the above (a) and (b), liquid ones are particularly preferable. That is, from the viewpoint of forming an interface with the occlusion metal (a) and/or the lithium occlusion alloy (B), carbonization is preferably performed in a liquid phase.
[ [ physical Properties of carbonaceous Material (E) ] ]
The physical properties of the carbonaceous material (E) preferably satisfy one or more of the following items (1) to (3) at the same time. One kind of carbonaceous material (E) exhibiting such physical properties may be used alone, or 2 or more kinds may be used in combination at any combination and ratio.
(1) X-ray parameters
The physical properties of the carbonaceous material (E) are preferably 0.38nm or less, particularly preferably 0.36nm or less, and further preferably 0.35nm or less, in the d value (interlayer distance) (hereinafter, abbreviated as "d 002") of the lattice plane (002 plane) determined by X-ray diffraction using a vibroseis method. If the value of d is too large, a surface having remarkably low crystallinity is formed, and the impedance is increased, so that the effect of improving the charge acceptance is small, and the effect of the present invention is small. The lower limit is 0.335nm or more of the theoretical value of graphite.
The crystallite size (Lc) of the carbon material determined by X-ray diffraction using a vibroseis method is usually 1nm or more, preferably 1.5nm or more. If the amount is less than this range, the impedance increases, and the effect of improving the charge acceptance may be reduced.
(2) Raman R value, Raman half value width
The raman R value of the carbonaceous material (E) portion measured by argon ion laser raman spectroscopy is usually 0.2 or more, preferably 0.3 or more, more preferably 0.4 or more, and the upper limit thereof is usually 1.5 or less, preferably 1.2 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers is sometimes reduced as charging and discharging are performed. That is, the charge acceptance may be reduced. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface decreases, and the reactivity with the nonaqueous electrolytic solution increases, which may result in a decrease in efficiency or an increase in generated gas.
The carbonaceous material (E) was found to be 1580cm in part-1The near-Raman half-value width is not particularly limited, but is usually 20cm-1Above, preferably 30cm-1Above, in addition, the upper limit is usually 140cm-1Hereinafter, preferably 100cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers is sometimes reduced as charging and discharging are performed. That is, the charge acceptance may be reduced. On the other hand, if the range is exceeded On the other hand, the crystallinity of the particle surface is decreased, and the reactivity with the nonaqueous electrolytic solution is increased, which may cause a decrease in efficiency or an increase in generated gas.
(3) True density
The true density of the carbonaceous matter (E) portion is usually 1.4g/cm3Above, preferably 1.5g/cm3Above, more preferably 1.6g/cm3Above, more preferably 1.7g/cm3Above, the upper limit is 2.26g/cm of the theoretical value of graphite3The following. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
The negative electrode active material (C) containing a plurality of elements used for the negative electrode active material of the negative electrode [7] of the lithium secondary battery of the present invention is preferably an element Z other than the lithium-absorbing material (F) obtained by combining the carbonaceous material (E) with the absorbing metal (a) and/or the lithium-absorbing alloy (B), and is preferably carbon (C) further containing a graphitic material (G) other than the carbonaceous material (E) as the element Z.
[ [ composition and physical Properties of graphite Material (G) ]
Examples of the composition of the graphite material (G) include natural graphite, artificial graphite, and those obtained by subjecting these to a treatment such as pulverization, and it is preferable that the physical properties of the graphite material (G) satisfy one or more of the following items (1) to (3). One kind of the graphite substance (G) exhibiting such properties may be used alone, or 2 or more kinds may be used in combination at an arbitrary combination and ratio.
(1) X-ray parameters
The d value (interlayer distance) of the lattice plane (002 plane) of the graphite substance (G) portion, which is obtained by X-ray diffraction using a vibroseis method, is 0.335nm or more, which is the theoretical value of graphite. The upper limit is preferably 0.340nm or less, more preferably 0.338nm or less, and particularly preferably 0.337nm or less. If the value of d is too large, a surface having remarkably low crystallinity is formed, and the impedance is increased, so that the effect of improving the charge acceptance is small, and the effect of the present invention is small.
The crystallite size (Lc) of the graphitic material (G) determined by X-ray diffraction using a vibroseis method is generally in the range of 10nm or more, preferably 50nm or more, and more preferably 80nm or more. If the amount is less than this range, the impedance increases, and therefore the effect of improving the charge acceptance may be small.
(2) Raman R value, Raman half value width
The raman R value of the graphite substance (G) portion measured by argon ion laser raman spectroscopy is usually 0.01 or more, preferably 0.10 or more, and the upper limit thereof is usually 0.40 or less, preferably 0.35 or less, and more preferably 0.25 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers is sometimes reduced as charging and discharging are performed. That is, the charge acceptance may be reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in generated gas.
The graphite material (G) was found to be 1580cm in length-1The near-Raman half-value width is not particularly limited, but is usually 10cm-1Above, preferably 15cm-1Above, in addition, the upper limit is usually 50cm-1Hereinafter, preferably 40cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the number of sites where Li enters between layers is sometimes reduced as Li is charged and discharged. That is, the charge acceptance may be reduced. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, and the reactivity with the nonaqueous electrolytic solution is increased, which may result in a decrease in efficiency or an increase in generated gas.
(3) True density
The true density of the graphite substance (G) portion is usually 2.0G/cm3Above, preferably 2.1g/cm3More preferably 2.2g/cm or more3Above, more preferably 2.22g/cm3Above, the upper limit is 2.26g/cm of the theoretical value of graphite3The following. If the content is less than this range, the crystallinity of carbon is too low, and the initial irreversible capacity may increase.
In the lithium-absorbing material (F), the mass ratio of the absorbing metal (a) and/or the lithium-absorbing alloy (B) to the carbonaceous material (E) in the lithium-absorbing material (F) is usually 20/80 or more, preferably 50/50 or more, more preferably 80/20 or more, particularly preferably 90/10 or more, and preferably 99.9/0.1 or less, more preferably 99/1 or less, and particularly preferably 98/2 or less. If the content exceeds the above range, the effect of having the carbonaceous material (E) may not be obtained, while if the content is below the above range, the effect of increasing the capacity per unit mass may be small. The content of the occlusion metal (a) and/or the lithium occlusion alloy (B) is preferably 20% by mass or more of the lithium occlusion material (F) with respect to the total element Z.
When the graphite substance (G) is contained, the graphite substance (G) is preferably 5 mass% or more, more preferably 20 mass% or more, and further preferably 50 mass% or more with respect to the total amount of the carbonaceous substance (E) and the graphite substance (G). The upper limit thereof is preferably 99 mass% or less, and more preferably 95 mass% or less. If the amount of the graphite substance (G) is too large, the bonding at the interface is weakened, and the effect of improving the conductivity may not be obtained, whereas if the amount of the graphite substance (G) is too small, the effect of improving the conductivity due to the graphite substance (G) being contained may not be obtained.
In the present invention, the form of the lithium-occluding material (F) other than the element Z is generally a film or a powder. In the present invention, the negative electrode using the thin film active material can be obtained by vapor-phase deposition of the active material layer on the current collector as described later in the manufacturing method, and the negative electrode using the powdery active material can be formed by, for example, applying the powdery active material, a binder, and the like on the current collector to form the active material layer.
The preferable ranges of the powder physical properties of the lithium-absorbing material (F) containing the element Z in the outside thereof are the same as the preferable ranges of the powder physical properties of the lithium-absorbing material (D) containing the element Z therein.
[ Current collector of negative electrode [7]
(Material quality)
As the material of the current collector, copper, nickel, stainless steel, and the like are cited, and among them, copper which is easily processed into a thin film and is inexpensive is preferable. The copper foil includes a rolled copper foil produced by a rolling method and an electrolytic copper foil produced by an electrolytic method, and both can be used as the current collector. When the thickness of the copper foil is smaller than 25 μm, a copper alloy (phosphor bronze, titanium copper, corson alloy, Cu — Cr — Zr alloy, or the like) having higher strength than pure copper can be used.
In the current collector made of the copper foil produced by the rolling method, since copper crystals are aligned in the rolling direction, the current collector is less likely to break even if the negative electrode is bent tightly or bent at an acute angle, and is suitable for a small cylindrical battery. The electrolytic copper foil is prepared as follows: for example, a drum made of a metal is immersed in a nonaqueous electrolytic solution in which copper ions are dissolved, and current is applied while the drum is rotated, whereby copper is deposited on the surface of the drum and then peeled off. Copper may be deposited on the surface of the rolled copper foil by electrolytic method. One or both surfaces of the copper foil may be subjected to roughening treatment or surface treatment (e.g., chromate treatment with a thickness of about several nm to 1 μm, primer treatment with Ti, etc.).
(thickness)
In the current collector substrate made of copper foil or the like, a thin film negative electrode can be produced, and a thin film negative electrode having a larger surface area can be preferably incorporated in a battery container having the same storage volume, but if it is too thin, the strength is insufficient, and the copper foil may be cut when winding or the like in the production of a battery, and therefore, the thickness is preferably 10 to 70 μm. In the case of forming the active material layer on both surfaces of the copper foil, the copper foil is preferably thinner, but in this case, the copper foil is more preferably 8 to 35 μm thick in view of avoiding the occurrence of cracks due to expansion/contraction of the active material film caused by charge and discharge. When a metal foil other than the copper foil is used as the current collector, a preferable thickness can be used for each metal foil, but the thickness is generally within a range of about 10 to 70 μm.
(Properties)
The current collector substrate is also desired to have the following properties.
(1) Average surface roughness (Ra)
The average surface roughness (Ra) of the active material thin film-formed surface of the current collector substrate defined by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.01 μm or more, preferably 0.03 μm or more, and is usually 1.5 μm or less, preferably 1.3 μm or less, and particularly preferably 1.0 μm or less.
By setting the average surface roughness (Ra) of the current collector substrate within the range between the lower limit and the upper limit, good charge-discharge cycle characteristics can be expected. That is, by setting the above lower limit or more, the interface area with the active material film becomes large, and the adhesion with the active material film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, and when the average surface roughness (Ra) exceeds 1.5 μm, it is difficult to obtain a foil having a suitable thickness for a battery, and therefore, it is preferably 1.5 μm or less.
(2) Tensile strength
The tensile strength of the current collector substrate is not particularly limited, and is usually 50N/mm2Above, preferably 100N/mm2Above, more preferably 150N/mm2The above. The tensile strength is a value obtained by dividing the maximum tensile force required for the test piece to break by the cross-sectional area of the test piece. The tensile strength in the present invention can be measured by the same apparatus and method as those for measuring the elongation. When the collector substrate has a high tensile strength, cracks in the collector substrate due to expansion and contraction of the active material film during charge and discharge can be suppressed, and good cycle characteristics can be obtained.
(3) 0.2% proof stress
The 0.2% proof stress of the current collector substrate is not particularly limited, but is usually 30N/mm2Above, preferably 100N/mm2Above, it is particularly preferably 150N/mm2The above. The 0.2% proof stress is a load required to generate a plastic (permanent) deformation of 0.2%, and after applying the load of this magnitude, the deformation of 0.2% is maintained even when the load is removed. The 0.2% proof stress in the present invention can be measured by the same apparatus and method as the elongation measurement. If the current collector has a high proof stress of 0.2%, plastic deformation of the current collector substrate due to expansion/contraction of the active material film during charge/discharge can be suppressed, and good cycle characteristics can be obtained.
[ method for producing negative electrode active material (C) containing multiple elements for negative electrode [7]
The method for producing the negative electrode active material (C) containing a plurality of elements (the lithium-absorbing material (D) containing the element Z and the lithium-absorbing material (F) other than the element Z) of the present invention is not particularly limited, and for example, the negative electrode active material can be produced by the following production method.
1. Method for producing lithium-absorbing material (D) containing element Z
Production method 1
The evaporation source, sputtering source or sputtering source uses any one of the following substances:
(i) a combination of Si, an element Z and an element M (wherein, when y is 0 or y is approximately equal to 0, the combination of Si and the element Z);
(ii) A mixture of Si, an element Z and an element M (wherein, when y ═ 0 or y ≈ 0, the mixture of Si and the element Z);
(iii) si, the element Z, and the element M (each simple substance may be a gas containing each element) (wherein y is 0 or y is approximately equal to 0, and is a simple substance of Si and the element Z);
(iv) a combination or mixture of Si and Z with the simple substance of the element M (which may be a gas containing M);
(v) a gas containing Si, an element Z, and an element M (wherein y ═ 0 or y ≈ 0 is a gas containing Si and an element Z);
(vi) a composition or mixture of elemental Si, element Z, and element M;
(vii) a combination or mixture of Si and element M with the simple substance of element Z (which may also be a gas containing M),
and simultaneously forming Si, an element Z and an element M (wherein, Si and the element Z are present when y is 0 or y is approximately equal to 0) on the current collector substrate by a vapor deposition method, a sputtering method and a thermal spraying method, wherein the thickness of the active material thin film is 1 to 30 μ M, preferably the thickness of the active material thin film is described in one item of the film thickness.
(raw materials)
As the Si simple substance raw material of the vapor deposition source, the sputtering source, or the sputtering (sputtering) source (hereinafter, sometimes referred to as "raw material") there may be used, for example, crystalline Si, amorphous Si, or the like. As the Z raw material, C, N element can be used. The element Z may be any element satisfying the above items, and 2 or more kinds of elements may be used simultaneously.
In the raw material, (i) a combination of Si, the element Z and the element M (wherein y is 0 or a combination of Si and the element Z is about 0), a single compound obtained by combining Si, the element Z and the element M, or by combining Si and the element Z may be used, or a plurality of compounds may be prepared and used. The Si, Z and M materials may be used in the form of powder, granule, pellet, block, plate, or the like.
In the general formula SiZxMyIn the case where y ≠ 0 and the element M is contained, the element M may be one or 2 or more elements selected from the group consisting of elements of groups 2, 4, 8, 9, 10, 11, 13, 14, 15 and 16 of the periodic table other than Si and the element Z, preferably Ti, Zr, W, O and Co elements, and more preferably O element.
(film formation method)
The method for forming the active material thin film includes a vapor phase film forming method, and specifically, a vapor deposition method (vacuum deposition method, CVD method, ion plating method), a sputtering method, a thermal spraying method (flame spraying method, plasma spraying method), and the like. The film can be formed by a combination of a sputtering method and a vapor deposition method, and a sputtering method and a thermal spraying method.
Next, a method for forming the negative electrode active material thin film will be described.
A. Sputtering method
The sputtering method is a method in which an active material emitted from a target containing the above-mentioned raw material is collided with a current collector substrate by plasma under reduced pressure to deposit a thin film. When the sputtering method is used, the interface state between the active material thin film and the current collector substrate is good, and the adhesion of the active material thin film to the current collector is also high.
As a method of applying the sputtering voltage to the target, either a direct current voltage or an alternating current voltage can be used, and in this case, a substantially negative bias voltage is applied to the current collector substrate, and the collision energy of ions derived from plasma can be controlled. The ultimate degree of vacuum in the chamber before the film formation is started is usually 0.1Pa or less to prevent impurities from being mixed.
As the sputtering gas, an inert gas such as Ne, Ar, Kr, Xe, or the like is used. Among them, argon gas is preferably used in view of sputtering efficiency and the like. Furthermore, the compound SiZxMyWhen the element Z in (b) is N, it is preferable in terms of production that a trace amount of nitrogen gas is present together in the inert gas. The pressure of the sputtering gas is usually about 0.05 to 70 Pa. The temperature of the current collector substrate when the active material thin film is formed by the sputtering method can be controlled by water cooling, a heater, or the like. The temperature range of the current collector substrate is usually from room temperature to 900 ℃, but is preferably 150 ℃ or lower. The film forming speed when forming the active material thin film by the sputtering method is usually 0.01 to 0.5 μm/min.
Before the active material thin film is formed, the surface of the current collector substrate may be etched by a pretreatment such as reverse sputtering or other plasma treatment. Such pretreatment is effective for removing contaminants or oxide films on the surface of the copper foil serving as the current collector substrate and improving the adhesion of the active material thin film.
B. Vacuum evaporation method
The vacuum deposition method is a method of melting and evaporating the above raw materials as the active material to deposit the active material on the collector substrate, and generally has an advantage that a thin film can be formed at a higher film formation rate than the sputtering method. In view of shortening the time required for forming an active material thin film having a predetermined thickness, the vacuum deposition method can be advantageously applied to the manufacturing cost more flexibly than the sputtering method. Specific examples thereof include an induction heating method, a resistance heating method, an electron beam heating vapor deposition method, and the like. The induction heating method is a method in which a deposition material is heated and melted by induction current in a deposition crucible of graphite or the like and evaporated to form a film; the resistance heating method is a method in which a deposition material is heated and melted in a deposition boat or the like by an energized heating current and is evaporated to form a film; the electron beam heating evaporation is a film formed by heating and melting an evaporation material by an electron beam and evaporating the evaporation material.
As atmosphere gas for vacuum evaporationTypically, a vacuum is used. Furthermore, the compound SiZxMyWhen Z is N, a trace amount of nitrogen gas may be introduced together with an inert gas and the pressure may be reduced to simultaneously form SiZ under vacuumxMy. The ultimate vacuum degree in the chamber before the film formation is started is usually 0.1Pa or less to prevent impurities from being mixed.
The temperature of the current collector substrate when the active material thin film is formed by the vacuum deposition method can be controlled by a heater or the like. The temperature range of the current collector substrate is usually room temperature to 900 ℃, but is preferably 150 ℃ or lower. The film forming speed when forming the negative electrode active material thin film by the vacuum evaporation method is usually 0.1 to 50 μm/min.
In addition, as in the case of the sputtering method, before depositing the active material thin film on the current collector substrate, the surface of the current collector substrate may be subjected to an etching treatment by ion irradiation with an ion gun or the like. By such etching treatment, the adhesion between the substrate and the active material thin film can be further improved. In addition, when a thin film is formed, by causing ions to collide with the current collector substrate, the adhesion of the active material thin film to the current collector substrate can be further improved.
C. CVD method
The CVD method is a method in which the above-described raw materials as the active material are deposited on the current collector substrate by a vapor phase chemical reaction. Generally, the CVD method has the following features: since the compound gas in the reaction chamber is controlled by the gas inflow, various materials can be synthesized with high purity, and specific examples thereof include a thermal CVD method, a plasma CVD method, a photo CVD method, a cat-CVD method, and the like. In the thermal CVD method, a raw material gas of a halogen compound having a high vapor pressure is introduced into a heated reaction vessel together with a carrier gas or a reaction gas at about 1000 ℃ to cause a thermochemical reaction, thereby forming a thin film. The plasma CVD method is a method using plasma instead of heat energy; photo CVD is a method of using light energy instead of heat energy. The cat-CVD method is a catalytic chemical vapor deposition method, and forms a thin film by applying a contact decomposition reaction of a raw material gas and a heating catalyst.
In the raw material gas used in the CVD methodSiH as elemental Si source4、SiCl4Etc.; as source of element Z NH3、N2、BCl3、CH4、C2H6、C3H8And the like.
D. Ion plating method
The ion plating method is a method in which the above raw materials as active materials are melted and evaporated, and the evaporated particles are ionized and excited under plasma, thereby forming a firm film on the current collector substrate. Specifically, examples of the method for melting and evaporating the raw material include an induction heating method, a resistance heating method, an electron beam heating and evaporation method, and the like; examples of the ionization and excitation method include an activation reaction vapor deposition method, a multi-cathode thermal electron irradiation method, a high-frequency excitation method, an HCD method, an ion beam method (クラスターイオンビーム method), and a multi-arc method. Further, the method of evaporating the above-mentioned raw materials and the method of ionizing and exciting may be carried out in an appropriate combination.
E. Spraying method
The thermal spraying method is a method in which the above-mentioned raw materials as the active material are melted or softened by heating to be formed into fine particles and accelerated, thereby solidifying and depositing the particles on the current collector substrate. Specific examples of the method include a flame spraying method, an arc spraying method, a direct current plasma spraying method, an RF plasma spraying method, and a laser spraying method.
F. Combination of sputtering and evaporation
By utilizing the advantage of the high film formation rate of the vapor deposition method and the advantage of the strong film formation adhesion to the current collector substrate of the sputtering method, for example, by forming the 1 st thin film layer by the sputtering method and then forming the 2 nd thin film layer by the vapor deposition method at a high speed, it is possible to form an interface region excellent in adhesion to the current collector substrate and also form an active material thin film at a high film formation rate. By using such a mixed combination method of film forming methods, a thin film negative electrode having a high charge/discharge capacity and excellent charge/discharge cycle characteristics can be efficiently produced.
The sputtering method and the vapor deposition method are combined to form the active material thin film, preferably continuously while maintaining a reduced pressure atmosphere. This is because the 1 st thin film layer and the 2 nd thin film layer are formed continuously without being exposed to the atmosphere, and thus impurities can be prevented from being mixed. For example, the following film forming apparatus is preferably used: in the same vacuum environment, the current collector substrate is moved, and sputtering and vapor deposition are performed sequentially.
In the present invention, when the active material thin film is formed on both surfaces of the current collector substrate by such a film formation method, it is preferable to form the active material thin film layer (the combination of the 1 st thin film layer and the 2 nd thin film layer) on one surface of the current collector substrate and the active material thin film layer (the combination of the 1 st thin film layer and the 2 nd thin film layer) on the other surface of the current collector substrate, and to continuously perform the formation while maintaining the reduced pressure atmosphere.
< production method 2>
The following general formula SiZxMyThe production method in the case where the element Z is C will be described.
The evaporation source, sputtering source or sputtering source uses any one of the following substances:
(i) a combination of Si, C and an element M (wherein, when y is 0 or y is approximately equal to 0, the combination of Si and C);
(ii) a mixture of Si, C and an element M (wherein, when y ═ 0 or y ≈ 0, the mixture of Si and C);
(iii) simple substances of Si, C and the element M (wherein the simple substances of Si and C are when y is 0 or y is approximately equal to 0);
(iv) a combination or mixture of Si and C with the simple substance of the element M (which may also be a gas containing M);
(v) a gas containing Si, C and an element M (wherein y ≈ 0 or a gas containing Si and C when y ≈ 0);
(vi) a combination or mixture of elemental Si with C and an element M;
(vii) And a composition or mixture of Si and an element M, and a simple substance C, wherein Si, C and the element M (wherein Si and C are present when y is 0 or y is about 0) are simultaneously deposited on the current collector substrate by a vapor deposition method, a sputtering method and a thermal spraying method to form a film having a thickness of 1 to 30 μ M, preferably a thickness described in the section of the thickness of the active material thin film.
(raw materials)
As the Si material of the vapor deposition source or the sputtering source (hereinafter, sometimes referred to as "material") there may be used, for example, crystalline Si, amorphous Si, or the like. As the C raw material, for example, a carbon material such as natural graphite or artificial graphite can be used. The M raw material is usually Si and elements of groups 2, 4, 8, 9, 10, 11, 13, 14, 15 and 16 of the periodic table other than the element Z, and preferably Ti, Zr, W, O and Co, and particularly preferably O.
In the raw materials, (i) the composition of Si, C and the element M may be a single compound formed by combining Si, C and the element M, or may be a plurality of compounds. The form of the raw materials of Si, C and M may be, for example, powder, granule, pellet, block, plate, etc. Further, the element M may be used as a nitride of Si or C or an oxide of Si or C, and it is preferable in terms of production that O or the like existing as a gas at normal temperature coexist as a raw material gas O or the like in the Si or C film formation.
(film formation method)
The same film formation method as that of the above-mentioned production method 1 is used.
A. Sputtering method
As the sputtering gas, an inert gas such as Ne, Ar, Kr, Xe, or the like is used. Among them, argon gas is preferably used in view of sputtering efficiency and the like. Furthermore, of the formula SiCxMyWhen the element M in (A) is O, it is preferable to coexist a small amount of oxygen in the inert gas in production. The pressure of the sputtering gas is usually about 0.05 to 70 Pa.
B. Vacuum evaporation method
As the atmosphere of the vacuum deposition method, vacuum is generally used. Furthermore, of the formula SiCxMyWhen the element M in (1) is O, Si/C/M can be formed simultaneously under vacuum by introducing a small amount of oxygen together with an inert gas and reducing the pressure.
C. CVD method
SiH is used as the source of Si in the source gas used in the CVD method4、SiCl4Etc.; as source of element C is CH4、C2H6、C3H8And the like.
< production method 3>
The following general formula SiZxMyA production method in which the element Z is C and the element M is O will be described.
The evaporation source, sputtering source or sputtering source uses any one of the following substances:
(I) a combination of Si and C;
(II) a mixture of Si and C;
(III) the simple substances of Si and C,
or
(IV) a gas containing Si and C,
si and C are simultaneously formed on the collector substrate by a vapor deposition method, a sputtering method, and a thermal spraying method in an atmosphere having an oxygen concentration of 0.0001 to 0.125% in a film forming gas (in a residual gas during film formation in vacuum) to have a thickness of 1 to 30 μm, preferably a thickness described in the section of the thickness of the active material thin film.
(raw materials)
As the Si material of the vapor deposition source, sputtering source, or sputtering source of the material, for example, crystalline Si, amorphous Si, or the like can be used. As the C raw material, for example, a carbon material such as natural graphite or artificial graphite can be used. As oxygen in the film forming gas, a gas containing an O element such as oxygen gas is used alone or in combination with an inert gas. The form of the raw materials of Si and C can be, for example, powder, granule, pellet, block, plate, etc. Further, oxygen gas is preferable as a raw material gas in the production of Si and C films in coexistence.
(film formation method)
The same film formation method as that of the above-mentioned production method 1 is used.
(oxygen concentration at film formation)
The oxygen concentration in the film forming gas during deposition and/or sputtering and thermal spraying (in the residual gas during film formation in vacuum) is usually 0.0001% or more, and usually 0.125% or less, preferably 0.100% or less, and more preferably 0.020% or less. If the oxygen concentration in the film-forming gas exceeds this range, the amount of elemental O in the Si/C/O thin film increases, the reactivity with the nonaqueous electrolytic solution increases, and the charge-discharge efficiency may decrease. If the oxygen concentration is too low, the Si/C/O thin film may not be formed.
Further, the oxygen concentration in the film forming gas can be obtained by analyzing the mass spectrum of the film forming gas using a quadrupole mass filter (quadra monitor フィルタ), for example. When argon gas in which oxygen gas is coexistent is used as the film forming gas, the oxygen gas can be measured by an oxygen analyzer.
< production method 4>
The following general formula SiZxMyThe process for producing the intermediate element wherein Z is N and y is 0 or y is about 0 is explained.
The evaporation source, sputtering source or sputtering source uses any one of the following substances:
(I) a simple substance of Si;
(II) a Si-containing composition;
(III) a mixture containing Si,
or
(IV) a gas containing Si,
si and N are simultaneously formed on the current collector substrate by a vapor deposition method, a sputtering method, and a thermal spraying method in an atmosphere in which the nitrogen concentration in a film forming gas (in a residual gas during film formation in vacuum) is 1 to 22%, to a thickness of 1 to 30 μm, preferably a thickness described in the section of the thickness of the active material thin film.
(raw materials)
As the Si raw material of the vapor deposition source, the sputtering source, or the sputtering source of the raw material, for example, crystalline Si, amorphous Si, or the like can be used. As N in the film forming gas, an N-containing gas such as nitrogen gas is used alone or in combination with an inert gas. The form of Si or the like may be, for example, powder, granule, pellet, block, plate, or the like. Nitrogen gas is preferable as a source gas in the production of Si film by coexistence.
(film formation method)
The same film formation method as that of the above-mentioned production method 1 is used.
(Nitrogen concentration at film formation)
The nitrogen concentration in the film forming gas during vapor deposition and/or sputtering, and thermal spraying (in the residual gas during film formation in vacuum) is usually 1% or more, and usually 22% or less, preferably 15% or less, and more preferably 10% or less. SiN when the concentration of nitrogen contained in the film-forming gas exceeds this rangexThe amount of element N in the thin film is increased, and silicon nitride which does not participate in charge and discharge is generated, which may cause a decrease in discharge capacity. If the nitrogen concentration is too low, SiN containing N may not be formedxThin film and results in a reduction in cycle characteristics. The nitrogen concentration in the film-forming gas can be obtained by analyzing the mass spectrum of the film-forming gas using a quadrupole mass filter, for example.
2. Process for producing lithium-occluding substance (F) having element Z outside
< production method 5>
The lithium-absorbing metal (a) and/or the lithium-absorbing alloy (B) is mixed with the organic substance that can be carbonized as described in the composition of the carbonaceous substance (E), and the organic substance is heated and decomposed, and carbonized through a solid phase and/or a liquid phase and/or a gas phase to form the carbonaceous substance (E), thereby obtaining a composite. The particles are then pulverized and classified so that the volume-based average particle diameter is an appropriate value.
(raw materials)
The volume-based average particle diameter of the lithium-absorbing metal (a) and/or the lithium-absorbing alloy (B) as the raw material is usually 100 μm or less, preferably 10 μm or less, more preferably 1 μm or less, and the lower limit thereof is in the range of 1nm or more. If the amount exceeds the upper limit, the swelling during charging is difficult to be alleviated, and the cycle retention rate may decrease. If the content is less than the lower limit, the pulverization is difficult, and a time-consuming and economical loss may be caused. The carbonaceous material (E) is preferably a material that passes through a liquid phase during carbonization, although the material is as described above.
< production method 6>
The composite is obtained by mixing the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) with the graphite material (G), mixing the organic material which can be carbonized as described in the composition of the carbonaceous material (E), heating and decomposing the organic material, and carbonizing the organic material in a liquid phase to form the carbonaceous material (E). The particles are then pulverized and classified so that the volume-based average particle diameter is an appropriate value.
(raw materials)
The raw materials were the same as in < production method 5 >.
< production method 7>
The composite is obtained by mixing the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) with the graphite material (G), mixing the organic material which can be carbonized as described in the composition of the carbonaceous material (E), heating and decomposing the organic material to carbonize the organic material in a solid phase, and passing the organic material through the phase to form the carbonaceous material (E). The particles are further pulverized and classified so that the volume-based average particle diameter is an appropriate value.
(raw materials)
The raw materials were the same as in < production method 5 >.
< production method 8>
The composite is obtained by mixing the lithium-occluding metal (a) and/or the lithium-occluding alloy (B) with the graphite material (G), mixing the organic material which can be carbonized as described in the composition of the carbonaceous material (E), heating and decomposing the organic material to carbonize the organic material in a gas phase, and passing the carbonized organic material through the phase. The particles are further pulverized and classified so that the volume-based average particle diameter is an appropriate value.
(raw materials)
The raw materials were the same as in < production method 5 >.
[ electric polarization of powdery active material of negative electrode [7]
The negative electrode can be produced by a conventional method, and for example, as described above, the negative electrode can be formed by adding a binder and a solvent to the negative electrode active material, adding a thickener, a conductive material, a filler, and the like as needed to prepare a slurry, coating the slurry on a current collector, drying the dried current collector, and then pressing the dried current collector. The thickness of the negative electrode active material layer on each surface in the stage before the electrolyte injection step of the battery is usually 5 μm or more, preferably 10 μm or more, and more preferably 15 μm or more, and the upper limit thereof is 150 μm or less, preferably 120 μm or less, and more preferably 100 μm or less. If the amount exceeds this range, the nonaqueous electrolyte hardly penetrates into the vicinity of the interface of the current collector, and therefore, the high-current-density charge/discharge characteristics may be deteriorated. If the amount is less than this range, the volume ratio of the current collector to the negative electrode active material increases, and the capacity of the battery may decrease. Further, the negative electrode active material may be roll-molded to form a sheet electrode, or compression-molded to form a particulate electrode.
The binders, thickeners, and the like which can be used are the same as described above.
< negative electrode [8] >
The following describes a negative electrode [8] used in the lithium secondary battery of the present invention, wherein the negative electrode [8] contains 2 or more negative electrode active materials having different properties as a negative electrode active material.
[ negative electrode active material for negative electrode [8]
The negative electrode active material used in the negative electrode [8] will be described below.
The negative electrode active material used for the negative electrode [8] of the lithium secondary battery of the present invention is characterized by containing 2 or more negative electrode active materials having different properties.
The term "different properties" as used herein includes not only differences in powder shape and powder physical properties represented by X-ray diffraction parameters, median particle diameter, aspect ratio, BET specific surface area, orientation ratio, raman R value, tap density, true density, micropore distribution, circularity, ash content, and the like, but also differences in the composition of materials such as "composite carbonaceous material containing 2 or more carbonaceous materials having different crystallinities", "heteroorientation carbon composite containing 2 or more carbonaceous materials having different orientations", and the like, or differences in processing such as "heat treatment of negative electrode active material", "mechanical energy treatment of negative electrode active material", and the like.
[ differences in shape, physical Properties, etc. ]
The negative electrode active material used for the negative electrode [8] of the lithium secondary battery of the present invention contains 2 or more types of negative electrode active materials having different volume-based average particle diameters (median particle diameters), and thus can improve cycle characteristics while maintaining low-temperature output. The difference in volume-based average particle diameter (median particle diameter) is usually 1 μm or more, preferably 2 μm or more, and more preferably 5 μm or more. The upper limit is usually 30 μm or less, preferably 25 μm or less. If the average particle diameter exceeds this range, the particle diameter having a large median diameter tends to be too large, and therefore, there is a possibility that problems such as stringing of the coated surface may occur during electrode production. On the other hand, if the content is less than this range, the effect of mixing 2 types of negative electrode active materials may be difficult to be exhibited.
The negative electrode active material used for the negative electrode [8] of the lithium secondary battery of the present invention can exhibit good characteristics even for the material having an uneven volume-based particle size distribution for the same reason as described above. The "volume-based particle size distribution unevenness" means a volume-based particle size distribution in which the horizontal axis is a logarithmic scale, and to the extent that it is not bilaterally symmetrical, the Z value represented by the following formula (1) is usually 0.3 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more, without forming bilateral symmetry around a volume-based average particle diameter (median diameter). If Z is less than this value, the effect of improving the cycle characteristics due to the particle size distribution may be difficult to obtain.
Z | (mode diameter) - (median diameter) | (1)
In formula (1), the unit of both the mode diameter and the median diameter is "μm", and "|" represents an absolute value.
In the present invention, the volume-based average particle diameter (median particle diameter) and the mode diameter are defined as the following values: the negative electrode active material was dispersed in a 0.2 mass% aqueous solution (about 1mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant, and the dispersion was measured using a laser diffraction particle size distribution meter (LA-700 manufactured by horiba ltd.). "median particle diameter" is also commonly referred to as d50The term "mode diameter" refers to a particle diameter in which the larger side and the smaller side are equal when the powder is divided into two parts from a certain particle diameter on a volume basis, and the particle diameter indicates the maximum value of the distribution in the particle size distribution on a volume basis, and any of them is only a value called "median particle diameter" and "mode diameter" in LA-700 manufactured by horiba ltd.
It is preferable to use at least one kind of negative electrode active material having a median particle diameter of 10 μm or less, because the effect of improving the cycle characteristics can be obtained while maintaining the low-temperature output. Particularly preferably 8 μm or less. The negative electrode active material having a median particle diameter of 10 μm or less is particularly preferably used in a range of 0.5 to 10% by mass based on the entire negative electrode active material.
In addition, the negative electrode active material used in the negative electrode [8] of the lithium secondary battery of the present invention contains 2 or more types of negative electrode active materials having different Raman R values measured by argon ion laser Raman spectroscopy, and thus can improve low-temperature output while maintaining cycle characteristics. The difference in raman R value is usually 0.1 or more, preferably 0.2 or more, more preferably 0.3 or more, and the upper limit is usually 1.4 or less, preferably 1.3 or less, more preferably 1.2 or less. If the amount is less than this range, it may be difficult to obtain the effect of the difference in Raman R value. On the other hand, if the raman value exceeds this range, the irreversible capacity may increase due to a portion having a high raman R value.
In the present invention, the raman spectrum is measured as follows: the sample is filled by naturally dropping the sample into a measurement vessel using a raman spectrometer (for example, a raman spectrometer manufactured by japan spectroscopy corporation) in which the surface of the sample in the vessel is irradiated with an argon ion laser and the vessel is rotated in a plane perpendicular to the laser. For the obtained Raman spectrum, 1580cm was measured-1Peak P of (1)AStrength I ofAAnd 1360cm -1Peak P of (1)BStrength I ofBAnd calculating the intensity ratio R (R ═ I)B/IA) This is defined as the raman R value of the graphitic carbon particles. The Raman spectrum obtained by measurement was 1580cm-1Peak P of (1)ADefined as the raman half-value width of the graphitic carbon particles.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10 to 20cm-1
Measurement range: 1100cm-1～1730cm-1
Raman R-value, half-value width analysis: background processing
Smoothing treatment: simple average, convolution 5 points
Further, the negative electrode [8] of the lithium secondary battery of the present invention]1580cm of the negative electrode active material used for the negative electrode active material used in (1)-1The Raman half-value width of (A) is not particularly limited, but is usually 10cm-1Above, preferably 15cm-1Above, in addition, the upper limit is usually 150cm-1Below, preferably 140cm-1The following ranges. If the Raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the low-temperature output power sometimes decreases. On the other hand, if it exceeds this range, the crystallinity of the particle surface is lowered, and the irreversible capacity may be increased.
In addition, even if the negative electrode active material used as the negative electrode active material used in the negative electrode [8] of the lithium secondary battery of the present invention contains 2 or more types of negative electrode active materials having different crystallinities, the low-temperature output can be improved while maintaining the cycle characteristics. The term "crystallinity" as used herein refers to a laminated structure such as a thickness and a pitch of a repeating structure of a carbon hexagonal-mesh laminated body. Specific physical property values indicating different crystallinity are not particularly limited, and include, for example, an inter-plane distance, a crystallite size, and the like, and preferably they differ among 2 or more types of negative electrode active materials used in the lithium secondary battery of the present invention. If the difference in crystallinity is too small, it may be difficult to obtain the effect of mixing.
The negative electrode active material used for the negative electrode [8] of the lithium secondary battery of the present invention contains 2 or more types of negative electrode active materials having different (002) plane surface pitches (d002) measured by a wide-angle X-ray diffraction method, and thus can improve the low-temperature output while maintaining the cycle characteristics. The difference in the inter-plane distance (d002) is usually 0.0005nm or more, preferably 0.001nm or more, more preferably 0.003nm or more, and further preferably 0.004nm or more, and the upper limit thereof is usually 0.05nm or less, preferably 0.04nm or less, more preferably 0.03nm or less, and further preferably 0.02nm or less. If the amount is less than this range, the effect of the difference in crystallinity may be difficult to obtain. On the other hand, if it exceeds this range, the irreversible capacity may increase due to a portion having low crystallinity. The inter-plane distance (d002) of the (002) plane measured by the wide-angle X-ray diffraction method in the present invention means the d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the vibroseis method.
The negative electrode active material used for the negative electrode [8] of the lithium secondary battery of the present invention contains 2 or more types of negative electrode active materials having different crystallite sizes (Lc) determined by X-ray diffraction using a chemical vibration method, and thus can improve low-temperature output while maintaining cycle characteristics. The difference in crystallite size (Lc) as determined by X-ray diffraction using a vibroseis method is usually 1nm or more, preferably 10nm or more, and more preferably 50nm or more. If the amount is less than this range, the effect of the crystallite size may be difficult to obtain.
Further, the negative electrode [8 ] of the lithium secondary battery of the present invention]The negative electrode active material used in (1) can improve low-temperature output while maintaining cycle characteristics by containing 2 or more negative electrode active materials having different true densities. As the difference in true density, it is usually 0.03g/cm3Above, preferably 0.05g/cm3Above, more preferably 0.1g/cm3More preferably 0.2g/cm or more3Above, the upper limit is usually 0.7g/cm3Below, preferably 0.5g/cm3Less than, more preferably 0.4g/cm3The following ranges. If the density is less than this range, the effect due to the difference in the true density may be difficult to obtain. On the other hand, if the value exceeds this range, the irreversible capacity may increase due to a portion having a low true density.
The true density referred to in the present invention is defined as a value measured by a liquid phase displacement method (densitometer method) using butanol.
In addition, the negative electrode active material used in the present invention can maintain low-temperature output and improve cycle characteristics by containing 2 or more types of negative electrode active materials having different circularities. The difference in circularity is usually 0.01 or more, preferably 0.02 or more, and more preferably 0.03 or more, and the upper limit thereof is usually 0.3 or less, preferably 0.2 or less, and more preferably 0.1 or less. If the amount is less than this range, it may be difficult to obtain the effect of the difference in circularity. On the other hand, if the amount exceeds this range, problems such as stringing may occur when the electrode is polarized electrically due to the portion with low circularity.
The circularity in the present invention is defined by the following formula.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the value measured as follows was used: about 0.2g of a sample was dispersed in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant by using a flow particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.), and particles having a particle diameter in the range of 3 to 40 μm were measured by irradiating the sample with ultrasonic waves of 28kHz for 1 minute at an output of 60W while specifying 0.6 to 400 μm as a detection range.
Further, the negative electrode [8 ] of the lithium secondary battery of the present invention]The negative electrode active material used in (1) can maintain low-temperature output and improve cycle characteristics by containing 2 or more types of negative electrode active materials having different tap densities. As the difference in tap density, it is usually 0.1g/cm3Above, preferably 0.2g/cm3Above, more preferably 0.3g/cm3The above. If the content is less than this range, it may be difficult to obtain the effect of mixing materials having different tap densities.
In the present invention, tap density is defined as follows: the sample was passed through a sieve having an aperture of 300. mu.m, and the sample was dropped into a 20cm cell 3The Tap density of (1) was determined by vibrating the container 1000 times with a 10mm stroke length using a powder density measuring instrument (for example, Tap densitometer manufactured by seishin corporation) until the sample filled the upper end face of the container, and calculating the density from the volume at that time and the weight of the sample.
Further, the negative electrode [8 ] of the lithium secondary battery of the present invention]In useThe negative electrode active material contains 2 or more types of negative electrode active materials having different BET specific surface areas, and thus the low-temperature output can be improved while maintaining the cycle characteristics. The BET specific surface area difference is usually 0.1m2A ratio of 0.5m or more2A value of 1m or more, more preferably 1 g or more2More than g, with an upper limit of usually 20m2A ratio of 15m or less in terms of/g2A ratio of 12m or less, more preferably2(ii) a range of,/g or less. If the amount is less than this range, it may be difficult to obtain the effect of mixing materials having different BET specific surface areas. On the other hand, if it exceeds this range, the irreversible capacity may increase due to the large BET specific surface area.
In the present invention, the BET specific surface area is defined as a value as follows: the sample was preliminarily dried at 350 ℃ for 15 minutes under nitrogen flow using a surface area meter (a full-automatic surface area measuring apparatus manufactured by large-scale laboratory research), and then measured by a nitrogen adsorption BET 1 point method using a gas flow method using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure value of nitrogen to atmospheric pressure was 0.3.
The mixing ratio of 2 or more different negative electrode active materials used in the negative electrode [8] of the lithium secondary battery of the present invention is a ratio of one negative electrode active material to the total amount of usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 10% by mass or more, and still more preferably 20% by mass or more, and the upper limit thereof is usually 99.9% by mass or less, preferably 99% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less. If the amount is outside this range, it may be difficult to obtain the effect of containing 2 or more different types of negative electrode active materials.
Among them, natural graphite and/or a processed product of natural graphite is contained in at least one of the 2 different types of negative electrode active materials, and is preferable in terms of cost performance.
Natural GRAPHITEs are classified according to their properties as Flake GRAPHITEs, soil GRAPHITEs (Amorphous GRAPHITEs) (see "integration OF powder technology, ((Co., Ltd.) center for Industrial technology, Showa 49) as GRAPHITEs; AND" HAND BOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES ", (distributed by Noyes Publications)). The graphitization degree was highest with flaky graphite, 100%, followed by flaky graphite, 99.9%, and soil graphite as low as 28%. Flake graphite as natural graphite is produced from motor gaska, china, brazil, ukraina, canada, and the like; the graphite flakes are produced primarily from srilanca. The main producing areas of the soil graphite are korea, china, mexico and the like. Among these natural graphites, soil graphite generally has a small particle size and a low purity. On the contrary, flaky graphite and scaly graphite are preferably used in the present invention because they have advantages such as high graphitization degree and low impurity content.
[ differences in treatment of negative electrode [8]
The negative electrode active material used in the present invention contains 2 or more types of negative electrode active materials processed differently, and thus can improve low-temperature output while maintaining cycle characteristics. Examples of the method of processing natural graphite include a method of applying heat treatment and a method of applying mechanical energy treatment. An example of the heat treatment is as follows.
[ [ Heat treatment temperature ] ]
The heat treatment temperature of the negative electrode active material is usually 600 ℃ or higher, preferably 1200 ℃ or higher, more preferably 2000 ℃ or higher, further preferably 2500 ℃ or higher, and particularly preferably 2800 ℃ or higher. The upper limit is usually 3200 ℃ or lower, preferably 3100 ℃ or lower. If the temperature condition is less than this range, the crystal restoration of the surface of the natural graphite particles may be insufficient. On the other hand, if the amount exceeds the above range, the sublimation amount of graphite tends to increase. The negative electrode active material used in the present invention preferably contains 2 or more types of negative electrode active materials having different heat treatment temperatures.
[ [ Heat treatment method ] ]
The heat treatment is carried out by passing through the above temperature range once. The holding time for holding the temperature condition in the above range is not particularly limited, but is usually longer than 10 seconds and 168 hours or less.
The heat treatment is usually performed in an inert gas atmosphere such as nitrogen or in a non-oxidizing atmosphere formed by a gas generated from the raw material natural graphite. However, in the case of a furnace of the type embedded in pulverized coal (fine pitch sintered carbon), air is sometimes mixed in at first. In this case, it may not be necessary to completely perform the inert gas atmosphere. The apparatus used for the heat treatment is not particularly limited, and for example, a shuttle furnace, a tunnel furnace, an electric furnace, a coke baking furnace, a rotary kiln, a direct electric furnace, an attorney electric furnace, a resistance heating furnace, an induction heating furnace, or the like can be used. The negative electrode active material used in the present invention preferably contains 2 or more types of negative electrode active materials different in heat treatment method.
In addition to the above-described respective processes, various processes such as a classification process may be performed. The classification treatment is a treatment for obtaining a target particle diameter and removing coarse powder and fine powder. The apparatus used for the classification treatment is not particularly limited, and for example, in the case of dry screening, a rotary screen, a shaker screen, a rotary screen, a vibrating screen, or the like; in the case of dry air classification, a gravity classifier, an inertia classifier, a centrifugal classifier (classifier, cyclone), or the like; in the case of wet screening, a mechanical wet classifier, a hydraulic classifier, a sedimentation classifier, a centrifugal wet classifier, or the like may be used. The classification treatment may be performed before the heat treatment, or may be performed at another time, for example, after the heat treatment. Further, the classification processing itself may also be omitted. The negative electrode active material used in the present invention preferably contains 2 or more types of negative electrode active materials having different classification conditions.
The negative electrode active material used in the present invention contains 2 or more types of negative electrode active materials different in mechanical energy treatment described later, and thus can improve low-temperature output while maintaining cycle characteristics. An example of mechanical energy treatment is as follows.
[ [ mechanical energy treatment ] ]
The mechanical energy treatment is performed so that the volume-average particle diameter ratio before and after the treatment is 1 or less. The "volume average particle diameter ratio before and after treatment" is a value obtained by dividing the volume average particle diameter after treatment by the volume average particle diameter before treatment. In the present invention, the mechanical energy treatment performed to produce the raw material before the heat treatment is preferably such that the average particle size ratio before and after the treatment is 1 or less. The mechanical energy treatment is a treatment in which the particle size is reduced so that the average particle diameter ratio before and after the powder particle treatment is 1 or less, and the particle shape is controlled. The mechanical energy treatment belongs to the pulverization treatment in the engineering unit operations that can be effectively utilized in particle design, such as pulverization, classification, mixing, granulation, surface modification, reaction, and the like.
The term "pulverization" means that a force is applied to a substance to reduce its size and thereby to adjust the particle size, particle size distribution, and filling properties of the substance. The pulverization treatment is classified according to the kind of force applied to the material and the treatment form. The forces applied to a substance are roughly classified into 4 types as follows: (1) knocking force (impact force), (2) crushing force (compression force), (3) grinding force (grinding force), and (4) scraping force (shear force). On the other hand, the treatment forms are roughly classified into the following 2 types: volume pulverization in which cracks are generated in the particles and propagated, and surface pulverization in which the surfaces of the particles are cut. The volume crushing can be carried out by adopting impact force, compression force and shearing force; the surface pulverization can be carried out by using a grinding force or a shearing force. Pulverization is a process in which the kinds and treatment forms of the force applied to these substances are combined in various ways. The combination thereof may be appropriately determined depending on the purpose of the processing.
The pulverization may be carried out by using a chemical reaction such as blasting or volume expansion, but is usually carried out by using a mechanical device such as a pulverizer. The pulverization treatment used in the production of the spheroidized carbonaceous material as the raw material of the present invention is preferably a treatment in which the proportion of the final surface treatment is high, regardless of the presence or absence of volume pulverization. This is because it is important to remove the corners of the particle surface where the particles are crushed so that the particle shape becomes circular. Specifically, the surface treatment may be performed after the volume pulverization is performed to some extent, or only the surface treatment may be performed without performing the volume pulverization at all, or the volume pulverization and the surface treatment may be performed at the same time. It is preferable to perform a surface pulverization treatment for removing corners from the surface of the particles. The negative electrode active material used in the present invention contains 2 or more types of negative electrode active materials having different degrees of surface treatment, and thus can improve low-temperature output while maintaining cycle characteristics.
The device for performing the kinetic energy treatment is selected from devices capable of performing the above-described preferred treatments. The mechanical energy treatment can be achieved by using one or more of the 4 types of forces applied to the substance, but it is preferable to apply mechanical actions such as compression, friction, and shear force including interaction of particles to the particles repeatedly, mainly with impact force. Thus, in particular, the following devices are preferred: the apparatus has a rotor having a plurality of blades inside a casing, and performs surface treatment while performing volume pulverization by applying mechanical actions such as impact compression, friction, and shearing force to a carbon material introduced into the casing by rotating the rotor at a high speed. Further, an apparatus having a mechanism for repeatedly imparting a mechanical action by circulating or convecting a carbonaceous material is more preferable.
Preferred examples of the apparatus include a mixing system (manufactured by Nara machinery Co., Ltd.), a krypton (manufactured by Earth technical Co., Ltd.), a CF mill (manufactured by Yu Yongji Co., Ltd.), a mechanofusion system (manufactured by Hosokawamicon Co., Ltd.), and the like. Of these, a mixing system manufactured by Nara machine manufacturing company is preferable. When the apparatus is used for treatment, the peripheral speed of the rotating rotor is preferably set to 30 to 100 m/sec, more preferably 40 to 100 m/sec, and still more preferably 50 to 100 m/sec. The treatment may be carried out by passing only the carbonaceous material, but is preferably carried out by circulating or retaining the carbonaceous material in the apparatus for 30 seconds or longer, and more preferably carried out by circulating or retaining the carbonaceous material in the apparatus for 1 minute or longer.
By performing the mechanical energy treatment in this way, the carbon particles become particles as follows: the crystallinity is maintained high as a whole, but the vicinity of the surface of the particle is roughened, and the edge surface is inclined and exposed. Thus, the area on which lithium ions can be taken in and out increases, and the capacity is high even at a high current density.
Generally, the smaller the particle size of the scale-like, scaly or plate-like carbon material is, the more the filling property tends to deteriorate. This is considered to be due to the following reasons: the particles are more amorphized by pulverization, or protrusions such as "burrs", "peeling" and "bending" formed on the particle surface are increased, or fine amorphous particles are adhered to the particle surface with a certain degree of strength, so that the resistance between adjacent particles is increased, and the filling property is deteriorated. If the amorphousness of these particles is reduced and the particle shape is close to spherical, the filling property is rarely reduced even if the particle size is reduced, and theoretically, both the large-particle-size carbon powder and the small-particle-size carbon powder should exhibit the same tap density.
The ratio of these natural graphite and/or processed natural graphite is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 10% by mass or more, and still more preferably 20% by mass or more, and the upper limit thereof is usually 99.9% by mass or less, preferably 99% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less. If the amount is less than this range, it may be difficult to improve the cost performance by adding natural graphite and/or a processed product of natural graphite. On the other hand, if the amount exceeds this range, it may be difficult to improve the effects of different negative electrode active materials.
[ [ micropore volume, etc. ]
The pore volume of the negative electrode active material used as the negative electrode active material for a lithium secondary battery of the present invention is an amount of irregularities (hereinafter, simply referred to as "micropore volume") corresponding to voids in particles having a diameter of 0.01 to 1 μm or level of the particle surface, as determined by a mercury porosimeter (mercury intrusion method), of usually 0.01mL/g or more, preferably 0.05mL/g or more, more preferably 0.1mL/g or more, and an upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, more preferably 0.3mL/g or less. If this range is exceeded, a large amount of binder is required for manufacturing the plate. If the amount is less than this range, the high-current-density charge/discharge characteristics are degraded, and the effect of alleviating expansion and contraction of the electrode during charge/discharge may not be obtained.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, more preferably 2mL/g or less. If the amount exceeds this range, a large amount of adhesive is sometimes required for producing the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. If the amount is less than this range, the high current density charge/discharge characteristics may be deteriorated.
As a device for the mercury porosimeter, a mercury porosimeter (autopore 9520; manufactured by micromeritics) can be used. About 0.2g of a sample (negative electrode material) was weighed, sealed in a powder container, degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes, and subjected to pretreatment. Next, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased stepwise from 4psia (about 28kPa) to 40000psia (about 280MPa), and then reduced to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 °. The average pore size is the pore size at which the cumulative pore volume reaches 50%.
[ [ ash ] ])
The ash content of the negative electrode active material of the lithium secondary battery of the present invention is preferably 1 mass% or less, more preferably 0.5 mass% or less, and particularly preferably 0.1 mass% or less, based on the total mass of the graphite carbon particles. The lower limit is preferably 1ppm or more. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolytic solution during charge and discharge cannot be ignored. On the other hand, if it is lower than this range, a long time and energy are required for manufacturing and equipment for preventing contamination, and the cost sometimes rises.
[ [ orientation ratio ] ]
The orientation ratio of the graphitic carbon particles used as the negative electrode active material of the lithium secondary battery of the present invention is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction of carbon obtained by X-ray diffraction were fitted using asymmetric pearson VII as a distribution function, peak separation was performed, and integrated intensities of the peaks of (110) diffraction and (004) diffraction were calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as an active material orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit: divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
[ [ length-diameter ratio ] ]
The length-diameter ratio of the graphitic carbon particles used as the negative electrode active material of the lithium secondary battery of the present invention is theoretically 1 or more, and the upper limit thereof is 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, the resultant plate may be drawn or a uniform coating surface may not be obtained, resulting in a decrease in high-current density charge/discharge characteristics.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the particle and the shortest diameter B perpendicular thereto in three-dimensional observation. The particles are observed by a scanning electron microscope which can observe the particles under magnification. Arbitrary 50 graphite particles fixed to the end faces of a metal having a thickness of 50 μm or less were selected, and a stage on which a sample was fixed was rotated and tilted, and A, B of each of these particles was measured to obtain an average value of a/B.
The lithium secondary battery having the negative electrode [8] of the present invention may contain 2 or more types of negative electrode active materials having different properties, and the type of the negative electrode active material is not particularly limited. However, properties measured by X-ray diffraction, such as the surface pitch (d002), crystallite size (Lc), orientation ratio, and plate orientation ratio; properties related to Raman spectrum such as Raman R value, Raman half-value width and the like; and ash, the difference between the above values applies to carbonaceous materials, since the above values are premised on carbonaceous materials. On the other hand, with respect to the properties relating to the particle size distribution, such as median particle diameter, mode diameter, and Z; BET specific surface area; properties of the pore volume, total pore volume, average pore diameter and the like measured by a mercury porosimeter; the true density; circularity; tap density; and an aspect ratio, the above-mentioned values are not limited to carbonaceous materials, and are applicable to all materials that can be used as a negative electrode active material, and the difference between the above-mentioned values is also applicable to all materials. However, the substance having the above 2 properties is preferably a carbonaceous substance. In this case, the above numerical values are regarded as values representing properties of the carbonaceous material, and it is preferable to use 2 or more carbonaceous materials having different properties as the negative electrode active material.
[ method for mixing 2 or more negative electrode active materials for negative electrode [8]
When 2 or more types of negative electrode active materials are mixed, the apparatus used is not particularly limited, and examples thereof include a V-type mixer, a W-type mixer, a container-variable type mixer, a kneader, a drum mixer, a shear mixer, and the like.
[ production of negative electrode [8]
The negative electrode [8] can be produced by a conventional method, and the negative electrode [8] can be formed in the same manner as described above. The current collector, the thickness ratio of the current collector to the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
< negative electrodes [9] and [10]
Next, the negative electrode [9] used in the lithium secondary battery of the present invention](mode A) and a negative electrode [10](mode B) carrying outTo explain, the negative electrode [9]]Containing a tap density of 0.1g/cm3A negative electrode active material having a pore volume of 0.01mL/g or more in terms of the volume of pores corresponding to particles having a diameter in the range of 0.01 to 1 μm as measured by a mercury porosimeter; the negative electrode [10]When the battery is charged to 60% of the nominal capacity of the negative electrode, the reaction resistance of the counter battery of the negative electrode is 500 Ω or less.
< negative electrode [9] (embodiment A) >
Embodiment a of the present invention relates to a lithium secondary battery in which the physical properties of a negative electrode active material contained in the negative electrode active material for use in the present invention are defined, and which includes a nonaqueous electrolytic solution containing the above-described specific compound and a negative electrode containing a negative electrode active material having the following specific physical properties. Mode a of the present invention will be explained below.
[ negative electrode active material for negative electrode [9]
The negative electrode active material in the embodiment a of the present invention can electrochemically occlude and release lithium ions, and also satisfies at least the following requirements (a) and (b).
(a) The tap density is 0.1g/cm3The above;
(b) the volume of micropores in the range of 0.01 to 1 μm as measured by a mercury porosimeter is 0.01mL/g or more.
[ [ tap density ] ]
Negative electrode [9] of lithium secondary electrode of the present invention]The tap density of the negative electrode active material contained in (1) is preferably 0.1g/cm3Above, more preferably 0.5g/cm3Above, more preferably 0.7g/cm3Above, particularly preferably 0.9g/cm3The above. Further, the upper limit thereof is preferably 2g/cm3Hereinafter, more preferably 1.8g/cm3The concentration is preferably 1.6g/cm3The following. If the tap density is below this range, the effect of high output power cannot be achieved in particular. On the other hand, if the amount exceeds this range, the number of voids between particles in the electrode is too small, the number of flow channels in the nonaqueous electrolytic solution is reduced, and the output itself may be reduced.
In the present invention, tappingThe density is defined as follows: the sample was passed through a sieve having an aperture of 300. mu.m, and the sample was dropped into a 20cm cell3The Tap density of (1) was determined by calculating the density from the volume and weight of the sample in the Tap container (1) after the sample filled the upper end face of the container and by vibrating the sample 1000 times with a stroke length of 10mm using a powder density measuring instrument (for example, Tap densifier manufactured by seishin corporation).
[ [ micropore volume ] ]
The pore volume of the negative electrode active material contained in the negative electrode [9] of the lithium secondary battery of the present invention is in a range of 0.01mL/g or more, preferably 0.05mL/g or more, more preferably 0.1mL/g or more, and the upper limit thereof is usually 0.6mL/g or less, preferably 0.4mL/g or less, more preferably 0.3mL/g or less, in terms of the amount of irregularities (hereinafter, abbreviated as "pore volume") due to voids in particles having a diameter of 0.01 to 1 μm or irregularities on the particle surface, as determined by a mercury porosimeter (mercury intrusion method). If this range is exceeded, a large amount of binder is required for manufacturing the plate. On the other hand, if it is lower than this range, a long life and high output cannot be achieved.
The total micropore volume is preferably 0.1mL/g or more, more preferably 0.25mL/g or more, and still more preferably 0.4mL/g or more, and the upper limit thereof is usually 10mL/g or less, preferably 5mL/g or less, and more preferably 2mL/g or less. If the amount exceeds this range, a large amount of the adhesive is sometimes required for the production of the substrate. If the amount is less than this range, the effect of dispersing the thickener or binder may not be obtained when the electrode plate is produced. The "total pore volume" as used herein means the sum of pore volumes measured under all the following measurement conditions.
The average pore diameter is preferably 0.05 μm or more, more preferably 0.1 μm or more, and still more preferably 0.5 μm or more, and the upper limit thereof is usually 50 μm or less, preferably 20 μm or less, and more preferably 10 μm or less. If the amount exceeds this range, a large amount of the binder may be required. If the amount is less than this range, the high current density charge/discharge characteristics may be deteriorated.
As a device for the mercury porosimeter, a mercury porosimeter (autopore 9520; manufactured by micromeritics) can be used. About 0.2g of a sample (negative electrode material) was weighed, sealed in a powder container, degassed under vacuum (50. mu. mHg or less) at room temperature for 10 minutes, and subjected to pretreatment. Next, the pressure was reduced to 4psia (about 28kPa), mercury was introduced, and the pressure was increased stepwise from 4psia (about 28kPa) to 40000psia (about 280MPa), and then reduced to 25psia (about 170 kPa). The number of stages at the time of pressure increase was 80 or more, and the mercury intrusion amount was measured after 10 seconds of the equilibrium time in each stage. The micropore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn formula. The surface tension (. gamma.) of mercury was 485dyne/cm, and the contact angle (. phi.) was 140 °. The average pore size is the pore size at which the cumulative pore volume reaches 50%.
The lithium secondary battery of embodiment a of the present invention can exhibit the effects of the present invention described above and can sufficiently exhibit the performance as long as the requirements (a) and (b) are satisfied for the negative electrode active material, and further, it is preferable that any one or more of the following physical properties are satisfied for the negative electrode active material at the same time. In addition, it is particularly preferable for the negative electrode to satisfy at the same time one or more of the physical properties and the structure of the negative electrode in the embodiment B described later.
[ [ BET specific surface area ] ]
Negative electrode of lithium secondary battery of the present invention measured by BET method [9 ]]The specific surface area of the negative electrode active material contained in (1) is preferably 0.1m2A value of at least 0.7 m/g, particularly preferably2A value of 1m or more, more preferably 1m2A total of 1.5m or more2More than g. The upper limit is preferably 100m2A specific ratio of 50m or less per gram2A ratio of 25m or less per gram2A total of 15m or less, preferably2The ratio of the carbon atoms to the carbon atoms is less than g. If the BET specific surface area value is less than the above range, the acceptance of lithium during charging is poor, lithium is likely to precipitate on the electrode surface, and high output may not be obtained when the material is used as a negative electrode material. On the other hand, if the amount exceeds the above range, the reactivity with the electrolyte increases when the negative electrode material is used, the amount of gas generated increases, and it may be difficult to obtain a preferable battery.
The BET specific surface area is defined as a value determined as follows: the sample was preliminarily dried at 350 ℃ for 15 minutes under flowing of nitrogen gas using a surface area meter (for example, a fully automatic surface area measuring apparatus manufactured by a large warehouse), and then measured by a nitrogen adsorption BET1 point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen gas to atmospheric pressure was accurately adjusted to 0.3.
[ [ volume average particle diameter ] ]
The volume average particle diameter of the negative electrode active material contained in the negative electrode [9] of the lithium secondary battery of the present invention is defined as a volume-based average particle diameter (median particle diameter) determined by a laser diffraction/scattering method, and is preferably 1 μm or more, particularly preferably 3 μm or more, more preferably 5 μm or more, and still more preferably 7 μm or more. The upper limit is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less, and still more preferably 25 μm or less. If the amount is less than the above range, the irreversible capacity increases, and the initial battery capacity may be lost. If the amount exceeds the above range, an uneven coating surface is likely to be formed when the electrode plate is produced, which is not preferable in the battery production process.
In the present invention, the volume-based average particle diameter is defined by a median particle diameter, which is determined by the following method: the carbon powder was dispersed in a 0.2 mass% aqueous solution (about 1mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant, and measured using a laser diffraction/scattering particle size distribution meter (for example, LA-700 manufactured by horiba ltd.).
[ [ circularity ] ]
The circularity of the negative electrode active material contained in the negative electrode [9] of the lithium secondary electrode of the present invention is usually 0.1 or more, preferably 0.5 or more, more preferably 0.8 or more, particularly preferably 0.85 or more, and further preferably 0.9 or more. As an upper limit, a true sphere is theoretically formed when the circularity is 1. If the circularity is less than this range, problems such as stringing may occur during electric polarization.
The circularity in the present invention is defined by the following formula.
Circularity (perimeter of equivalent circle having the same area as the projected shape of particle)/(actual perimeter of projected shape of particle)
As the value of circularity, the value measured as follows was used: about 0.2g of a sample was dispersed in a 0.2 mass% aqueous solution (about 50mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant by using a flow particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.), and particles having a particle diameter in the range of 3 to 40 μm were measured by irradiating the sample with ultrasonic waves of 28kHz for 1 minute at an output of 60W while specifying 0.6 to 400 μm as a detection range.
[ [ interplanar spacing (d002) ] ]
The (002) plane pitch (d002) of the negative electrode active material contained in the negative electrode [9] of the lithium secondary battery of the present invention measured by wide-angle X-ray diffraction method is usually 0.38nm or less, preferably 0.36nm or less, more preferably 0.35nm or less, further preferably 0.345nm or less, and the lower limit thereof is 0.335nm or more, which is the theoretical value of graphite. If the amount exceeds this range, the crystallinity is significantly reduced, and the irreversible capacity may be increased.
The inter-plane distance (d002) of the (002) plane measured by the wide-angle X-ray diffraction method in the present invention means the d value (interlayer distance) of the (002) plane of the lattice plane obtained by X-ray diffraction by the vibroseis method.
[ [ crystallite size (Lc) ] ]
The crystallite size (Lc) of the negative electrode active material determined by X-ray diffraction using a chemical vibration method is not particularly limited, and is usually in the range of 0.1nm or more, preferably 0.5nm or more, and more preferably 1nm or more. If the content is less than this range, the crystallinity may be significantly reduced, and the irreversible capacity may be increased.
[ [ true density ] ]
Negative electrode [9] of lithium secondary battery of the invention]The true density of the negative electrode active material contained in (1) is usually 1.5g/cm3Above, preferably 1.7g/cm3Above, more preferably 1.8g/cm 3Above, more preferably 1.85g/cm3Above, the upper limit is 2.26g/cm3The following. The upper limit is the theoretical value of graphite. If the amount is less than this range, the crystallinity of carbon is too low,irreversible capacity sometimes increases. In the present invention, the true density is defined as a value measured by a liquid phase displacement method (densitometry method) using butanol.
[ [ Raman R value ] ]
The raman R value of the negative electrode active material contained in the negative electrode [9] of the lithium secondary battery of the present invention is usually 0.01 or more, preferably 0.03 or more, and more preferably 0.1 or more. The upper limit is preferably 1.5 or less, more preferably 1.2 or less, and particularly preferably 0.5 or less. If the raman R value is less than this range, the crystallinity of the particle surface becomes too high, and the output may decrease as the number of charge/discharge sites decreases. On the other hand, if the amount exceeds this range, the crystallinity of the particle surface is lowered, and the irreversible capacity may be increased.
The raman spectrum was measured as follows: a sample is allowed to naturally fall down using a raman spectrometer (for example, a raman spectrometer manufactured by japan spectroscopy corporation) and filled in a measurement cell, and the surface of the sample in the cell is irradiated with an argon ion laser while the cell is rotated in a plane perpendicular to the laser. For the obtained Raman spectrum, 1580cm was determined -1Peak P of (1)AStrength I ofAAnd 1360cm-1Peak P of (1)BStrength I ofBAnd calculating the intensity ratio R (R ═ I)B/IA) This is defined as a raman R value of the negative electrode active material. The Raman spectrum obtained by measurement was 1580cm-1Nearby peak PAIs defined as the raman half-value width of the negative electrode active material.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-25 mW
Resolution: 10-20 cm-1
Measurement range: 1100cm-1～1730cm-1
Raman R value, raman half-value width analysis: background processing
Smoothing treatment: simple average, convolution 5 points
In addition, the negative electrode of the lithium secondary battery of the inventionPole [9 ]]The negative electrode active material contained in (1) is 1580cm-1The Raman half-value width of (A) is not particularly limited, but is usually 10cm-1Above, preferably 15cm-1Above, in addition, the upper limit is usually 150cm-1Hereinafter, preferably 100cm-1Hereinafter, more preferably 60cm-1The following ranges. If the raman half-value width is less than this range, the crystallinity of the particle surface becomes too high, and the output may decrease with decrease in the charge/discharge sites. On the other hand, if the content is more than this range, the crystallinity of the particle surface is lowered, and the irreversible capacity may be increased.
[ [ ash ] ])
The ash content of the negative electrode active material contained in the negative electrode [9] of the lithium secondary battery of the present invention is preferably 1 mass% or less, more preferably 0.5 mass% or less, and particularly preferably 0.1 mass% or less. The lower limit is preferably 1ppm or more. If the amount exceeds the above range, the deterioration of the battery performance due to the reaction with the nonaqueous electrolyte solution during charge and discharge cannot be ignored, and the cycle retention rate may be lowered. On the other hand, if the temperature is lower than this range, a long time and energy are required for manufacturing and a device for preventing contamination is required, and the cost may be increased.
[ [ length-diameter ratio ] ]
The aspect ratio of the negative electrode active material contained in the negative electrode [9] of the lithium secondary battery of the present invention is theoretically 1 or more, and the upper limit is usually 10 or less, preferably 8 or less, and more preferably 5 or less. If the amount exceeds the upper limit, the active material may be drawn or a uniform coating surface may not be obtained during production of the negative electrode, and the high-current density charge/discharge characteristics may be degraded.
The aspect ratio is represented by the ratio a/B of the longest diameter a of the particle and the shortest diameter B perpendicular thereto in three-dimensional observation. The particles are observed by a scanning electron microscope which can observe the particles under magnification. Arbitrary 50 graphite particles fixed to the end faces of a metal having a thickness of 50 μm or less were selected, and a stage on which a sample was fixed was rotated and tilted, and A, B of each of these particles was measured to obtain an average value of a/B.
[ [ orientation ratio ] ]
The orientation ratio of the negative electrode active material contained in the negative electrode [9] of the lithium secondary battery of the present invention is usually 0.005 or more, preferably 0.01 or more, more preferably 0.015 or more, and the upper limit is theoretically 0.67 or less. If the amount is less than this range, the high-density charge-discharge characteristics may be deteriorated.
The orientation ratio was determined by X-ray diffraction. Peaks of (110) diffraction and (004) diffraction of carbon obtained by X-ray diffraction were fitted using asymmetric pearson VII as a distribution function, peak separation was performed, and integrated intensities of the peaks of (110) diffraction and (004) diffraction were calculated, respectively. From the obtained integrated intensities, a ratio represented by (110) diffraction integrated intensity/(004) diffraction integrated intensity was calculated, and this ratio was defined as a negative electrode active material orientation ratio.
The X-ray diffraction measurement conditions herein are as follows. In addition, "2 θ" represents a diffraction angle.
Target: cu (K alpha ray) graphite monochrometer
Slit: divergence slit of 1 degree, light acceptance slit of 0.1mm, and scattering slit of 1 degree
Measurement Range and step Angle/measurement time
(110) Dough making: 76.5 degrees or less and 2 theta or less and 78.5 degrees or less and 0.01 degrees/3 seconds
(004) Dough making: 2 theta is more than or equal to 53.5 degrees and less than or equal to 56.0 degrees and 0.01 degrees/3 seconds
[ electrode for producing negative electrode [9]
The negative electrode [9] can be formed in the same manner as described above. The current collector, the thickness ratio of the current collector to the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
< negative electrode [10] (embodiment B) >
The negative electrode [10] (embodiment B) of the present invention relates to a lithium secondary battery having specified physical properties and/or a structure of the negative electrode for a negative electrode used in the present invention, and the lithium secondary battery comprises a nonaqueous electrolytic solution containing the above-mentioned specific compound and a negative electrode having the following specific physical properties and/or a structure. The negative electrode [10] of the present invention (embodiment B) will be explained below.
[ physical Properties and Structure of negative electrode [10]
The physical properties and structure of the negative electrode used in the lithium secondary battery of embodiment B will be described below. The negative electrode has a negative electrode active material layer on a current collector.
[ [ reaction resistance ] ]
The reaction resistance obtained in the measurement of the opposing impedance (toward インピーダンス) of the negative electrode used in embodiment B of the present invention must be 500 Ω or less, preferably 100 Ω or less, and more preferably 50 Ω or less. The lower limit is not particularly limited. If the amount exceeds this range, the output characteristics before and after the cycle test are degraded when the lithium secondary battery is produced. In addition, the cycle retention may be lowered due to high resistance.
The method for measuring the opposing impedance will be described below. In general, in impedance measurement of a lithium secondary battery, ac impedance measurement is performed between a positive electrode terminal and a negative electrode terminal of the battery, but when this method is used, the impedance of the mixture of the positive electrode and the negative electrode is finally expressed, and it is not possible to clearly determine which of the positive and negative electrode resistances occurs. Therefore, in the present invention, the reaction resistance generated only by the counter cell of the negative electrode was measured. The method for measuring the reaction resistance in the present invention will be described below.
The lithium secondary battery used for the measurement was as follows: after charging at a current value at which the nominal capacity can be charged for 5 hours, the battery is maintained in a state of not being charged and discharged for 20 minutes, and then discharged at a current value at which the nominal capacity can be discharged for 1 hour, wherein the capacity at that time is 80% or more of the nominal capacity. For the lithium secondary battery in the above-described discharged state, the lithium secondary battery was charged to 60% of the nominal capacity at a current value at which the nominal capacity can be charged for 5 hours, and immediately transferred into a glove box under an argon atmosphere. The lithium secondary battery was quickly removed in a state where the negative electrode was not discharged or short-circuited, and if the electrodes were coated on both sides, the electrode active material on one side was peeled off without damaging the electrode active material on the other side, 2 negative electrodes were punched out to 12.5mm phi, and the active material sides were opposed to each other with a separator without being deviated. Dropping non-aqueous electricity used in battery between separator and two negative electrodesThe electrolytic solution was sealed at 60. mu.L, and the current collectors of both negative electrodes were electrically connected to each other while keeping them in a state of not contacting the outside, thereby conducting electricity. The measurement is carried out at a temperature of 25 ℃ and 10 DEG C-2～105Complex impedance measurement is performed in the Hz frequency band, and the arc of the negative electrode resistance component of the obtained coriolis-coriolis curve (コール, コール, プロット) is approximated to a semicircle, thereby obtaining the reaction resistance (Rct) and the double layer capacity (Cdl).
In the lithium secondary battery according to aspect B of the present invention, the effect of the present invention can be exhibited as long as the reaction resistance generated by the facing battery (facing towards セル) of the negative electrode satisfies the above-described requirements, thereby sufficiently exhibiting the performance, and further preferably, one or more of the physical properties and the structure of the negative electrode described below are satisfied at the same time. In addition, the negative electrode active material particularly preferably satisfies one or more of the physical properties of the negative electrode active material described in the embodiment a.
[ [ bilayer capacity (Cdl) ] ]
The double layer capacity (Cdl) obtained in the measurement of the negative electrode opposing impedance used in the present invention is preferably 1 × 10-6F or more, particularly preferably 1X 10-5F or more, more preferably 3X 10-5F or more. If the ratio is less than this range, the area available for reaction decreases, and as a result, the output power may decrease.
[ [ adhesive ] ]
The binder for binding the negative electrode active material and the current collector is not particularly limited as long as it is a material stable to the nonaqueous electrolytic solution or the solvent used in the production of the electrode, and the ratio of the usable material, binder, and the like to the entire negative electrode active material layer are the same as described above.
[ negative electrode [10] electrode production ]
The negative electrode [10] can be produced by a conventional method, and the negative electrode [10] can be formed in the same manner as described above. The current collector, the thickness ratio of the current collector to the active material layer, the electrode density, the binder, the electrode plate orientation ratio, the impedance, and the like are also the same as described above.
< nonaqueous electrolyte solution >
The nonaqueous electrolytic solution used in the present invention is not particularly limited as long as it contains an electrolyte (lithium salt), a nonaqueous solvent dissolving the electrolyte, and a specific compound, and it is preferable that the nonaqueous electrolytic solution satisfies any condition selected from the following electrolytic solutions [1] to [9 ]:
electrolyte solution [1 ]: the nonaqueous solvent constituting the electrolyte is a mixed solvent containing at least ethylene carbonate, and the ratio of ethylene carbonate to the total amount of the nonaqueous solvent is 1 to 25% by volume;
electrolyte solution [2 ]: the nonaqueous solvent constituting the electrolyte contains at least one asymmetric chain carbonate, and the content ratio of the asymmetric chain carbonate in the entire nonaqueous solvent is 5 to 90% by volume;
electrolyte solution [3 ]: the nonaqueous solvent constituting the electrolytic solution contains at least one chain carboxylic ester;
electrolyte solution [4 ]: the nonaqueous solvent constituting the electrolyte contains a solvent having a flash point of 70 ℃ or higher and the content thereof is 60% by volume or more of the entire nonaqueous solvent;
Electrolyte [5 ]]: containing LiN (C)nF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate as a lithium salt constituting the electrolyte;
electrolyte solution [6 ]: the lithium salt constituting the electrolyte is a fluorine-containing lithium salt, and the total nonaqueous electrolyte contains 10ppm to 300ppm of Hydrogen Fluoride (HF);
electrolyte [7 ]: the electrolyte contains vinylene carbonate, and the content of the vinylene carbonate is 0.001-3% by mass of the total mass of the electrolyte;
electrolyte [8 ]: the electrolyte solution further contains at least one compound selected from the group consisting of a compound represented by the general formula (4), a heterocyclic compound containing nitrogen and/or sulfur, a cyclic carboxylic ester, and a fluorine-containing cyclic carbonate, and the content thereof in the entire nonaqueous electrolyte solution is in the range of 0.001 to 5% by mass;
electrolyte [9 ]: the electrolyte solution also contains an overcharge inhibitor.
Hereinafter, a nonaqueous electrolytic solution generally used in the lithium secondary battery of the present invention will be described.
[ lithium salt ]
The electrolyte is not particularly limited as long as it is a known lithium salt that can be used as an electrolyte of a nonaqueous electrolyte solution for a lithium secondary battery, and examples thereof include the following lithium salts.
Inorganic lithium salt: LiPF 6、LiBF4、LiAsF6、LiSbF6Inorganic fluoride salts; LiClO4、 LiBrO4、LiIO4A salt of a halogen acid of equal height; LiAlCl4And inorganic chloride salts, and the like.
Fluorine-containing organic lithium salt: LiCF3SO3Isoperfluoroalkane sulfonates; LiN (CF)3SO2)2、LiN(CF3CF2SO2)2、LiN(CF3SO2)(C4F9SO2) Isoperfluoroalkanesulfonylimide salts; LiC (CF)3SO2)3Isoperfluoroalkanesulfonyl methide salt, Li [ PF ]5(CF2CF2CF3)]、 Li[PF4(CF2CF2CF3)2]、Li[PF3(CF2CF2CF3)3]、Li[PF5(CF2CF2CF2CF3)]、 Li[PF4(CF2CF2CF2CF3)2]、Li[PF3(CF2CF2CF2CF3)3]And fluoroalkyl fluorophosphate.
Oxalato borate salt: lithium bis (oxalato) borate, lithium difluorooxalato borate, and the like.
These may be used alone, or may be used in combination of 2 or more in any combination and ratio. Among them, if the solubility in a nonaqueous solvent, the charge/discharge characteristics when a secondary battery is produced, the output characteristics, the cycle characteristics, and the like are comprehensively judged, LiPF is preferable6。
One preferable example of the case where 2 or more kinds of substances are used in combination is the case where LiPF is used in combination6And LiBF4At this time, LiBF4The ratio of the two components is preferably 0.01 to 20% by mass, and particularly preferably 0.1 to 5% by mass.
In another example, in which an inorganic fluoride salt and a perfluoroalkanesulfonylimide salt are used in combination, the ratio of the inorganic fluoride salt to the total of the both is preferably 70 to 99% by mass, and more preferably 80 to 98% by mass. The combined use of the two has an effect of suppressing deterioration due to high-temperature storage.
The concentration of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is usually 0.5mol/L or more, preferably 0.6mol/L or more, and more preferably 0.7mol/L or more. The upper limit is usually not more than 2mol/L, preferably not more than 1.8mol/L, and more preferably not more than 1.7 mol/L. If the concentration is too low, the conductivity of the nonaqueous electrolytic solution may be insufficient, while if the concentration is too high, the conductivity may be lowered due to an increase in viscosity, and the performance of the lithium secondary battery may be lowered.
[ non-aqueous solvent ]
The nonaqueous solvent can be selected and used from among solvents conventionally proposed as solvents for nonaqueous electrolytic solutions. Examples thereof include the following nonaqueous solvents.
1) Cyclic carbonate ester:
the number of carbon atoms of the alkylene group constituting the cyclic carbonate is preferably 2 to 6, and particularly preferably 2 to 4. Specific examples thereof include ethylene carbonate, propylene carbonate, and butylene carbonate. Among them, ethylene carbonate and propylene carbonate are preferable.
2) Chain carbonate
The chain carbonate is preferably a dialkyl carbonate, and the number of carbon atoms in the alkyl group constituting the dialkyl carbonate is preferably 1 to 5, and particularly preferably 1 to 4. Specific examples thereof include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, methylethyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Among them, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are preferable.
3) Cyclic ester:
specific examples thereof include γ -butyrolactone and γ -valerolactone.
4) Chain ester:
specific examples thereof include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.
5) Cyclic ethers
Specific examples thereof include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like.
6) Chain ether:
specific examples thereof include dimethoxyethane and dimethoxymethane.
7) Sulfur-containing organic solvent:
specific examples thereof include sulfolane and diethylsulfone.
These compounds may be used alone, or 2 or more compounds may be used in combination, and preferably 2 or more compounds are used in combination. For example, a solvent having a high dielectric constant such as a cyclic carbonate or a cyclic ester is preferably used in combination with a low-viscosity solvent such as a chain carbonate or a chain ester.
One of the preferable combinations of the nonaqueous solvents is a combination mainly composed of cyclic carbonates and chain carbonates. Among these, the total amount of the cyclic carbonates and the chain carbonates accounts for 80% by volume or more, preferably 85% by volume or more, and more preferably 90% by volume or more in the nonaqueous solvent. The content of the cyclic carbonate is 5% or more, preferably 10% or more, more preferably 15% or more, and usually 50% or less, preferably 35% or less, more preferably 30% or less, based on the total amount of the cyclic carbonate and the chain carbonate. In particular, it is preferable to combine the above-mentioned preferable capacity range of the total amount of carbonates in the nonaqueous solvent with the above-mentioned preferable capacity range of the cyclic carbonates with respect to the cyclic and chain carbonates. The use of such a combination of nonaqueous solvents is preferable because the balance between the cycle characteristics and the high-temperature storage characteristics (particularly, residual capacity after high-temperature storage and high-load discharge capacity) of a battery produced using the combination is excellent.
The nonaqueous electrolytic solution containing at least one compound selected from the group consisting of a lithium salt, a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an S — F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate and a propionate in the mixed solvent is preferable because the balance of cycle characteristics and high-temperature storage characteristics (particularly, residual capacity and high-load discharge capacity after high-temperature storage) and suppression of gas generation of the battery produced using the nonaqueous electrolytic solution is excellent.
Specific examples of preferable combinations of the cyclic carbonates and the chain carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and the like. A combination in which propylene carbonate is further added to the combination of ethylene carbonate and chain carbonate is cited as a preferable combination. When the propylene carbonate is contained, the volume ratio of ethylene carbonate to propylene carbonate is usually 99:1 to 40:60, preferably 95:5 to 50: 50.
Further, if the amount of the propylene carbonate in the entire nonaqueous solvent is 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, and is usually 10% by volume or less, preferably 8% by volume or less, more preferably 5% by volume or less, the low-temperature characteristics can be more excellent while maintaining the characteristics of the combination of ethylene carbonate and chain carbonates, and therefore, it is preferable.
Among them, it is more preferable to contain an asymmetric chain carbonate, and particularly, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, ethylene carbonates such as ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and symmetric chain carbonates and asymmetric chain carbonates are preferable because the balance between the cycle characteristics and the large current discharge characteristics is excellent. Among them, the asymmetric chain carbonate is preferably ethyl methyl carbonate, and the number of carbon atoms of the alkyl group constituting the dialkyl carbonate is preferably 1 to 2.
Another example of the preferable nonaqueous solvent is a nonaqueous solvent containing a chain ester. The chain ester is particularly preferably methyl acetate, ethyl acetate or the like. The content of the chain ester in the nonaqueous solvent is usually 5% or more, preferably 8% or more, more preferably 15% or more, and usually 50% or less, preferably 35% or less, more preferably 30% or less, and still more preferably 25% or less. In particular, it is preferable that the chain ester is contained in the mixed solvent of the cyclic carbonate and the chain carbonate in order to improve the low-temperature characteristics of the battery.
Examples of other preferable nonaqueous solvents include one organic solvent selected from ethylene carbonate, propylene carbonate, γ -butyrolactone, and γ -valerolactone, and a mixed solvent containing 2 or more organic solvents selected from this group, which accounts for 60% by volume or more of the total solvent. Such a mixed solvent preferably has a flash point of 50 ℃ or higher, and particularly preferably has a flash point of 70 ℃ or higher. The nonaqueous electrolyte using the solvent is reduced in evaporation or leakage of the solvent even when used at high temperatures. Among them, if a solvent in which γ -butyrolactone accounts for 60% by volume or more in the nonaqueous solvent, a solvent in which the total amount of ethylene carbonate and γ -butyrolactone accounts for 80% by volume or more, preferably 90% by volume or more in the nonaqueous solvent and the capacity ratio of ethylene carbonate to γ -butyrolactone is 5:95 to 45:55, or a solvent in which the total amount of ethylene carbonate and propylene carbonate accounts for 80% by volume or more, preferably 90% by volume or more in the nonaqueous solvent and the capacity ratio of ethylene carbonate to propylene carbonate is 30:70 to 60:40 is used, the balance of the general cycle characteristics, the large current discharge characteristics, and the like is excellent.
[ specific Compound ]
As described above, the nonaqueous electrolytic solution of the present invention is characterized by containing or adding at least one compound (which may be simply referred to as "specific compound") selected from the group consisting of a cyclic siloxane compound represented by the general formula (1), a fluorosilane compound represented by the general formula (2), a compound represented by the general formula (3), a compound having an S — F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate.
[ [ Cyclic siloxane Compound represented by the general formula (1) ]
R in the cyclic siloxane compound represented by the general formula (1)1And R2Are organic groups having 1 to 12 carbon atoms which may be the same or different from each other as R1And R2Examples thereof include chain alkyl groups such as methyl, ethyl, n-propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl; cyclic alkyl groups such as cyclohexyl and norbornyl; alkenyl groups such as vinyl, 1-propenyl, allyl, butenyl and 1, 3-butadienyl; alkynyl groups such as ethynyl, propynyl and butynyl; halogenated alkyl groups such as trifluoromethyl; an alkyl group having a saturated heterocyclic group such as 3-pyrrolidinopropyl group; an aryl group such as a phenyl group which may have an alkyl substituent; aralkyl groups such as phenylmethyl and phenylethyl; trialkylsilyl groups such as trimethylsilyl; trialkylsilyloxy groups such as trimethylsiloxy groups, and the like.
Among them, a group having a small carbon number is preferable because it is easy to exhibit characteristics, and an organic group having 1 to 6 carbon atoms is preferable. The alkenyl group is preferably one which acts on the nonaqueous electrolytic solution or the coating film on the surface of the electrode to improve the output power characteristics, and the aryl group is preferably one which functions to capture radicals generated in the battery during charge and discharge to improve the overall performance of the battery. Thus, as R 1And R2Particularly preferred is a methyl group, a vinyl group or a phenyl group.
In the general formula (1), n represents an integer of 3 to 10, preferably an integer of 3 to 6, and particularly preferably 3 or 4.
Examples of the cyclic siloxane compound represented by the general formula (1) include cyclotrisiloxanes such as hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane, hexaphenylcyclotrisiloxane and 1,3, 5-trimethyl-1, 3, 5-triethylenecyclotrisiloxane; cyclotetrasiloxane such as octamethylcyclotetrasiloxane; cyclopentasiloxane such as decamethylcyclopentasiloxane, and the like. Among them, cyclotrisiloxanes are particularly preferable.
[ [ fluorosilane compound represented by the general formula (2) ]
R in the fluorosilane compound represented by the general formula (2)3～R5An organic group having 1 to 12 carbon atoms which may be the same or different from each other except for R in the general formula (1)1And R2Examples of the alkyl group include a chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, a halogenated alkyl group, an alkyl group having a saturated heterocyclic group, an aryl group such as a phenyl group which may have an alkyl group, an aralkyl group, a trialkylsilyl group and a trialkylsiloxy group, and further include a carbonyl group such as an ethoxycarbonylethyl group; carboxyl groups such as acetoxy, acetoxymethyl, trifluoroacetoxy, etc.; an oxy group such as methoxy, ethoxy, propoxy, butoxy, phenoxy, allyloxy, etc.; an amino group such as an allylamino group; benzyl, and the like.
In the general formula (2), x represents an integer of 1 to 3, p, q and r each represent an integer of 0 to 3, and 1. ltoreq. p + q + r. ltoreq.3. Further, inevitably, x + p + q + r becomes 4.
Examples of the fluorosilane compound represented by the general formula (2) include monofluorosilanes such as trimethylfluorosilane, triethylfluorosilane, tripropylfluorosilane, phenyldimethylfluorosilane, triphenylfluorosilane, vinyldimethylfluorosilane, vinyldiethylfluorosilane, vinyldiphenylfluorosilane, trimethoxyfluorosilane and triethoxyfluorosilane, and difluorosilanes such as dimethyldifluorosilane, diethyldifluorosilane, divinyldifluorosilane and ethylvinyldifluorosilane; trifluorosilanes such as methyltrifluorosilane and ethyltrifluorosilane.
If the fluorosilane compound represented by the general formula (2) has a low boiling point, it may be difficult to contain a predetermined amount in the nonaqueous electrolytic solution due to volatilization. When the nonaqueous electrolyte is contained, the nonaqueous electrolyte may volatilize under conditions such as heat generation of the battery due to charge and discharge or high temperature of the external environment. Therefore, compounds having a boiling point of 50 ℃ or higher at 1 atmosphere are preferable, and among them, compounds having a boiling point of 60 ℃ or higher are particularly preferable.
Further, similarly to the compound of the general formula (1), as the organic group, a group having a small carbon number is likely to exhibit an effect, and an alkenyl group having 1 to 6 carbon atoms acts on the nonaqueous electrolytic solution or a coating film on the surface of an electrode to improve the output characteristics, and an aryl group has an effect of trapping radicals generated in the battery during charge and discharge to improve the overall performance of the battery. From this viewpoint, the organic group is preferably a methyl group, a vinyl group or a phenyl group, and examples of the compound are particularly preferably trimethylfluorosilane, vinyldimethylfluorosilane, phenyldimethylfluorosilane, vinyldiphenylfluorosilane and the like.
[ [ Compound represented by the general formula (3) ] ]
R in the compound represented by the general formula (3)6～R8Are organic groups having 1 to 12 carbon atoms which may be the same or different from each other, and examples thereof are similarly given as R in the general formula (2)3～R5Examples thereof include a chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, a halogenated alkyl group, an alkyl group having a saturated heterocyclic group, an aryl group such as a phenyl group which may have an alkyl group, an aralkyl group, a trialkylsilyl group, a trialkylsilyloxy group, a carbonyl group, a carboxyl group, an oxy group, an amino group, and a benzyl group.
A in the compound represented by the general formula (3) is not particularly limited as long as it is a group composed of H, C, N, O, F, S, Si and/or P, and C, S, Si or P is preferable as the element directly bonded to an oxygen atom in the general formula (3). The form of existence of these atoms is preferably, for example, in a chain alkyl group, a cyclic alkyl group, an alkenyl group, an alkynyl group, a haloalkyl group, a carbonyl group, a sulfonyl group, a trialkylsilyl group, a phosphoryl group, a phosphinyl group or the like.
The molecular weight of the compound represented by the general formula (3) is preferably 1000 or less, particularly preferably 800 or less, and more preferably 500 or less. Examples of the compound represented by the general formula (3) include siloxane compounds such as hexamethyldisiloxane, 1, 3-diethyltetramethyldisiloxane, hexaethyldisiloxane, octamethyltrisiloxane, and the like; alkoxysilanes such as methoxytrimethylsilane and ethoxytrimethylsilane; peroxides such as bis (trimethylsilyl) peroxide; carboxylic acid esters such as trimethylsilyl acetate, triethylsilyl acetate, trimethylsilyl propionate, trimethylsilyl methacrylate, and trimethylsilyl trifluoroacetate; sulfonic acid esters such as trimethylsilyl methanesulfonate, trimethylsilyl ethanesulfonate, triethylsilyl methanesulfonate, and trimethylsilyl fluoromethanesulfonate; sulfuric acid esters such as bis (trimethylsilyl) sulfate; boric acid esters such as tris (trimethylsiloxy) boron; phosphoric acids such as tris (trimethylsilyl) phosphate and tris (trimethylsilyl) phosphite, and phosphites.
Among them, silicone compounds, sulfonic acid esters, and sulfuric acid esters are preferable, and sulfonic acid esters are particularly preferable. As the siloxane compound, hexamethyldisiloxane is preferable; as the sulfonic acid esters, trimethyl silyl methanesulfonate is preferable; as the sulfuric acid ester, bis (trimethylsilyl) sulfate is preferable.
[ [ Compound having S-F bond in molecule ] ]
The compound having an S — F bond in the molecule is not particularly limited, but sulfonyl fluorides and fluorosulfonate esters are preferable.
Examples thereof include methanesulfonyl fluoride, ethanesulfonyl fluoride, methanebis (sulfonyl fluoride), ethane-1, 2-bis (sulfonyl fluoride), propane-1, 3-bis (sulfonyl fluoride), butane-1, 4-bis (sulfonyl fluoride), difluoromethanebis (sulfonyl fluoride), 1,2, 2-tetrafluoroethane-1, 2-bis (sulfonyl fluoride), 1,2,2,3, 3-hexafluoropropane-1, 3-bis (sulfonyl fluoride), methyl fluorosulfonate, and ethyl fluorosulfonate. Among them, methanesulfonyl fluoride, methanebis (sulfonyl fluoride) or methanesulfonic acid methyl ester is preferable.
[ [ nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate ] ]
The counter cation of nitrate, nitrite, monofluorophosphate, difluorophosphate, acetate, propionate is not particularly limited, and may be NR in addition to metal elements such as Li, Na, K, Mg, Ca, Fe, Cu and the like 9R10R11R12(in the formula, R9～R12Each independently represents a hydrogen atom or a carbon atom having 1 to 12 carbon atomsOrganic group), quaternary ammonium. Wherein, as R9～R12Examples of the organic group having 1 to 12 carbon atoms include an alkyl group which may be substituted with a halogen atom, a cycloalkyl group which may be substituted with a halogen atom, an aryl group which may be substituted with a halogen atom, and a heterocyclic group containing a nitrogen atom. As R9～ R12Each of them is preferably a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group containing a nitrogen atom, or the like. Among these counter cations, lithium, sodium, potassium, magnesium, calcium, or NR are preferable from the viewpoint of battery characteristics when used in a lithium secondary battery9R10R11R12Lithium is particularly preferred. Among these, from the viewpoint of the output power improvement rate and the cycle characteristics, a nitrate or difluorophosphate is preferable, and lithium difluorophosphate is particularly preferable. These compounds may be synthesized in a nonaqueous solvent as they are, or may be added to a nonaqueous solvent as they are, or may be separately synthesized and substantially separated.
The specific compound, that is, the cyclic siloxane compound represented by the general formula (1), the fluorosilicone compound represented by the general formula (2), the compound represented by the general formula (3), the compound having an S — F bond in the molecule, the nitrate, the nitrite, the monofluorophosphate, the difluorophosphate, the acetate, or the propionate may be used alone, or 2 or more compounds may be used in combination in any combination and ratio. In addition, among the specific compounds, even among the above-mentioned compounds classified individually, one kind may be used alone, or 2 or more kinds may be used in combination in an arbitrary combination and ratio.
The ratio of these specific compounds in the nonaqueous electrolytic solution is necessarily 10ppm or more (0.001 mass% or more), preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and still more preferably 0.1 mass% or more, based on the total amount of the nonaqueous electrolytic solution. The upper limit is preferably 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less. If the concentration of the specific compound is too low, the effect of improving the output of the battery or the effect of extending the life of the battery may be difficult to obtain, while if the concentration is too high, the charge-discharge efficiency may be reduced.
Further, if these specific compounds are actually supplied to the production of a secondary battery as a nonaqueous electrolytic solution, the nonaqueous electrolytic solution is taken out again after the battery is disassembled, and the content thereof is often significantly reduced. Therefore, it is also within the scope of the present invention that at least the specific compound described above can be detected from the nonaqueous electrolytic solution drawn out from the battery. The nonaqueous electrolytic solution according to the present invention can be prepared by dissolving an electrolyte lithium salt, a specific compound, and other compounds as needed in a nonaqueous solvent. In the production of the nonaqueous electrolytic solution, it is preferable to dehydrate each raw material in advance so that the water content is usually 50ppm or less, preferably 30ppm or less, and particularly preferably 10ppm or less.
[ other Compounds ]
The nonaqueous electrolytic solution in the present invention contains a lithium salt as an electrolyte and a specific compound as essential components in a nonaqueous solvent, and may contain other compounds in an arbitrary amount as necessary within a range not impairing the effects of the present invention. Specific examples of the other compounds include the following compounds:
(1) aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partial hydride of terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-pentylbenzene, diphenyl ether, dibenzofuran, and the like; partial fluorides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, etc.; overcharge inhibitors such as fluorine-containing anisole compounds including 2, 4-difluoroanisole, 2, 5-difluoroanisole, 2, 6-difluoroanisole and 3, 5-difluoroanisole;
(2) negative electrode coating film-forming agents such as vinylene carbonate, vinyl ethylene carbonate, ethylene fluorocarbon, propylene trifluorocarbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride;
(3) and positive electrode protecting agents such as ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, butane sultone, methyl methanesulfonate, butyl methanesulfonate, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, and dipyridyl disulfide.
As the overcharge inhibitor, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partial hydrogenated product of terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, dibenzofuran, and the like are preferable. These may be used in combination of 2 or more. When 2 or more kinds are used in combination, the combination of cyclohexylbenzene or terphenyl (or partial hydride thereof) and tert-butylbenzene or tert-pentylbenzene is particularly preferable.
As the negative electrode coating film forming agent, vinylene carbonate, vinyl ethylene carbonate, ethylene fluorocarbon acid, succinic anhydride, and maleic anhydride are preferable. These may be used in combination of 2 or more. When 2 or more species are used in combination, vinylene carbonate and vinyl ethylene carbonate, fluoro ethylene carbonate, succinic anhydride, or maleic anhydride are preferable. The positive electrode protecting agent is preferably ethylene sulfite, propylene sulfite, propane sultone, butane sultone, methyl methanesulfonate, or butyl methanesulfonate. These may be used in combination of 2 or more. In addition, it is particularly preferable to use the negative electrode coating forming agent and the positive electrode protecting agent in combination, and to use the overcharge inhibitor, the negative electrode coating forming agent, and the positive electrode protecting agent in combination.
The content ratio of these other compounds in the nonaqueous electrolytic solution is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass, and still more preferably 0.2% by mass, with respect to the entire nonaqueous electrolytic solution, and the upper limit thereof is preferably 5% by mass or less, more preferably 3% by mass, and still more preferably 2% by mass or less. By adding these compounds, it is possible to suppress the rupture/ignition of the battery when abnormality is caused by overcharge, or to improve the capacity retention characteristics and cycle characteristics after high-temperature storage.
The method for producing the nonaqueous electrolytic solution for a secondary battery of the present invention is not particularly limited, and a lithium salt, a specific compound, and other compounds as needed may be dissolved in a nonaqueous solvent according to a conventional method.
< electrolyte solution [1] >
In the above-mentioned nonaqueous electrolytic solution, the nonaqueous solvent constituting the electrolytic solution is preferably a mixed solvent containing at least "ethylene carbonate", and the ratio of ethylene carbonate to the total amount of the nonaqueous solvent is preferably 1 to 25% by volume (electrolytic solution [1 ]).
The types and contents of the "lithium salt", "nonaqueous solvent other than Ethylene Carbonate (EC)", "specific compound", "other compound" in the electrolyte solution [1] of the present invention, the conditions for use, the method for producing the nonaqueous electrolyte solution, and the like are the same as described above.
< electrolyte solution [2]
In the above-mentioned nonaqueous electrolytic solution, it is preferable that the nonaqueous solvent constituting the electrolytic solution contains "at least one asymmetric chain carbonate" and the content ratio of the asymmetric chain carbonate in the entire nonaqueous solvent is 5 to 90% by volume (electrolytic solution [2 ]).
The types and contents of the "lithium salt", "nonaqueous solvent other than asymmetric chain carbonate", "specific compound" and "other compound" in the electrolyte solution [2] of the present invention, the conditions for use, the method for producing a nonaqueous electrolyte solution, and the like are the same as described above.
In the present invention (electrolyte solution [2]), at least one asymmetric chain carbonate is contained in an amount of 5 to 90 vol% based on the total nonaqueous solvent. Further, the content of the non-asymmetric chain carbonate in at least one of the total non-aqueous solvents is preferably 8% by volume or more, more preferably 10% by volume or more, further preferably 15% by volume or more, and particularly preferably 20% by volume or more, and the upper limit is preferably 85% by volume or less, more preferably 70% by volume or less, further preferably 60% by volume or less, and particularly preferably 45% by volume or less, because of having both the high low-temperature characteristics and the cycle characteristics of the present invention.
The asymmetric chain carbonate is not particularly limited, but is preferably an asymmetric alkyl carbonate, and the number of carbon atoms in the alkyl group is preferably 1 to 4. Specific examples of such asymmetric alkyl carbonates include ethyl methyl carbonate, n-propyl ethyl carbonate, isopropyl methyl carbonate, isopropyl ethyl carbonate, n-butyl methyl carbonate, and n-butyl ethyl carbonate. Among them, methyl ethyl carbonate, methyl n-propyl carbonate, ethyl n-propyl carbonate, methyl n-butyl carbonate, and ethyl n-butyl carbonate are preferable, methyl ethyl carbonate, methyl n-propyl carbonate, and methyl n-butyl carbonate are more preferable, and methyl ethyl carbonate is particularly preferable. These asymmetric chain carbonates may be used in a mixture of 2 or more.
As described above, 2 or more kinds of nonaqueous solvents can be used in combination. In particular, from the viewpoint of improvement in cycle characteristics and storage characteristics of the secondary battery, it is preferable that the asymmetric chain carbonate further contains at least one cyclic carbonate. When the cyclic carbonate is contained, the proportion of the cyclic carbonate in the whole nonaqueous solvent is usually 5% by volume or more, preferably 10% by volume or more, and more preferably 15% by volume or more, and the upper limit is usually 50% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less, and further preferably 25% by volume or less. If the proportion of the cyclic carbonate in the total nonaqueous solvent is too small, the cycle characteristics or storage characteristics of the secondary battery may not be improved, while if too large, the low-temperature discharge characteristics may be degraded.
In addition, from the viewpoint of improving the balance between the cycle characteristics and the storage characteristics of the secondary battery and the low-temperature discharge characteristics, it is preferable that the asymmetric chain carbonate further contains at least one of the asymmetric chain carbonates. When the symmetrical chain carbonate is contained, the ratio of the symmetrical chain carbonate in the entire nonaqueous solvent is usually 5% by volume or more, preferably 10% by volume or more, and more preferably 15% by volume or more, and the upper limit is usually 80% by volume or less, preferably 70% by volume or less, more preferably 50% by volume or less, and further preferably 40% by volume or less. If the proportion of the symmetrical chain carbonate in the whole nonaqueous solvent is too small, the cycle characteristics or the balance between the storage characteristics and the low-temperature discharge characteristics may not be improved, while if too large, excellent cycle characteristics may not be obtained.
Further, a mixed solvent of the asymmetric chain carbonate and other 2 or more kinds of nonaqueous solvents is preferable. That is, a mixed solvent containing 3 or more components of the asymmetric chain carbonate is preferable. As a mixed solvent of 2 or more kinds of nonaqueous solvents other than the asymmetric chain carbonate, since all battery performances such as charge-discharge characteristics and battery life can be improved, it is preferable to use a high dielectric constant solvent such as a cyclic carbonate or a cyclic ester in combination with a low viscosity solvent such as a symmetric chain carbonate or a chain ester, and it is particularly preferable to use a combination of a cyclic carbonate and a symmetric chain carbonate. The mixing ratio in this case is not particularly limited, but it is preferable that the amount of the high dielectric constant solvent such as a cyclic carbonate or a cyclic ester is 10 to 400 parts by volume and the amount of the low viscosity solvent such as a symmetrical chain carbonate or a chain ester is 10 to 800 parts by volume per 100 parts by volume of the asymmetrical chain carbonate in view of improvement of cycle characteristics, storage characteristics, and the like.
One of the preferable combinations of 2 or more nonaqueous solvents other than the asymmetric chain carbonate is a combination mainly composed of a cyclic carbonate and a symmetric chain carbonate. Specific examples of preferable combinations of the cyclic carbonate and the symmetrical chain carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate, and diethyl carbonate. The content ratio of the water-insoluble agent in the whole water-insoluble agent is not particularly limited, but preferably 8 to 80 vol% for the asymmetric chain carbonate, 10 to 35 vol% for the cyclic carbonate, and 10 to 70 vol% for the symmetric chain carbonate.
A preferred combination is a combination of ethylene carbonate and a symmetrical chain carbonate, and propylene carbonate is further added to the combination. When propylene carbonate is contained, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99:1 to 40:60, and particularly preferably 95:5 to 50: 50.
Another preferable combination of 2 or more kinds of nonaqueous solvents other than the asymmetric chain carbonate is a combination containing a chain ester. In particular, from the viewpoint of improvement in low-temperature characteristics of the battery, the combination containing the cyclic carbonate and the chain ester is preferable, and the chain ester is particularly preferably methyl acetate, ethyl acetate, or the like. The ratio of the chain ester in the entire nonaqueous solvent is preferably 5% by volume or more, more preferably 8% by volume or more, and particularly preferably 15% by volume or more, and the upper limit thereof is preferably 50% by volume or less, more preferably 35% by volume or less, further preferably 30% by volume or less, and particularly preferably 25% by volume or less. Therefore, the content ratio in the entire nonaqueous solvent at this time is preferably as follows: 8 to 85 vol% of the asymmetric chain carbonate, 10 to 35 vol% of the cyclic carbonate, and 5 to 50 vol% of the chain carbonate.
A preferred combination is a combination of a symmetrical chain carbonate and a chain ester. When the symmetrical chain carbonate is contained, the content ratio of the symmetrical chain carbonate in the entire nonaqueous solvent is preferably 10 to 60% by volume.
Specific examples of a preferable combination of the nonaqueous solvents of the nonaqueous electrolytic solution for a secondary battery of the present invention include: combinations of asymmetric chain carbonates and cyclic carbonates such as ethyl methyl carbonate and ethylene carbonate, methyl n-propyl carbonate and ethylene carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate, methyl n-propyl carbonate, ethylene carbonate and propylene carbonate; a combination of asymmetric chain carbonates, cyclic carbonates, and symmetric chain carbonates such as ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, and dimethyl carbonate, methyl n-propyl carbonate, ethylene carbonate, and diethyl carbonate, methyl n-propyl carbonate, ethylene carbonate, diethyl carbonate, and dimethyl carbonate; combinations of asymmetric chain carbonates, cyclic carbonates, and chain esters such as ethyl methyl carbonate, ethylene carbonate, and methyl acetate; and combinations of asymmetric chain carbonates such as ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, and methyl acetate, cyclic carbonates, symmetric chain carbonates, and chain esters.
The nonaqueous electrolytic solution containing a lithium salt and the specific compound, for example, a difluorophosphate, in an amount of 10ppm or more based on the total mass of the electrolytic solution in the mixed solvent, wherein the content of the asymmetric chain carbonate in the entire nonaqueous solvent is 5 to 90 vol% is preferable because the balance of cycle characteristics, low-temperature discharge characteristics, high-temperature storage characteristics (particularly, residual capacity after high-temperature storage and high-load discharge capacity) and suppression of gas generation of a secondary battery produced using the nonaqueous electrolytic solution is excellent.
< electrolyte solution [3]
In the above-mentioned nonaqueous electrolytic solution, the nonaqueous solvent constituting the electrolytic solution preferably contains at least "one or more chain carboxylic acid esters" (electrolytic solution [3 ]).
The kind and content of the "lithium salt", "the nonaqueous solvent other than the chain carboxylate", "the" specific compound "and" the "other compound" in the electrolyte solution [3] of the present invention, the conditions for use, the method for producing the nonaqueous electrolyte solution, and the like are the same as those described above.
The chain carboxylate used in the present invention (electrolyte [3]) is not particularly limited, but is preferably an alkyl ester having 1 to 4 carbon atoms of a carboxylic acid having 1 to 5 carbon atoms including the carbon of the carboxyl group. The number of the carboxylic acid is not particularly limited, and a monocarboxylic acid or a dicarboxylic acid is preferable.
Among them, fatty acid esters such as formate, acetate, propionate, and butyrate are preferable; various dicarboxylic acid esters and the like, and particularly preferred are acetate esters and propionate esters.
Specifically, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, or ethyl propionate is preferable, and methyl acetate, ethyl acetate, or methyl propionate is particularly preferable.
These chain carboxylates may be used in combination of 2 or more. The combination of the mixture is not particularly limited, and preferable combinations include methyl acetate and ethyl acetate, methyl acetate and methyl propionate, ethyl acetate and methyl propionate, methyl acetate, ethyl acetate and methyl propionate, and the like. This makes it possible to adjust the balance between the output characteristics and the high-temperature storage characteristics according to the purpose.
When a mixed solvent of the chain carboxylic ester and the non-aqueous solvent other than the chain carboxylic ester is used, the content ratio of the chain carboxylic ester to the entire non-aqueous solvent is preferably 3% by volume or more, more preferably 5% by volume or more, further preferably 8% by volume or more, and particularly preferably 10% by volume or more, and the upper limit thereof is preferably 50% by volume or less, more preferably 35% by volume or less, further preferably 30% by volume or less, and particularly preferably 25% by volume or less, and is preferable because of having both the high low-temperature characteristics and the cycle characteristics of the present invention.
Although the reason why the low-temperature output characteristics are greatly improved by using the chain carboxylic acid ester and the specific compound in combination is not clear, the specific compound may have a certain degree of low-temperature characteristic improving effect even when the specific compound does not contain the chain carboxylic acid ester, and it is considered that the specific compound permeates into the electrode plate without exerting an effect wastefully by having a certain effect on the electrode and the chain carboxylic acid ester accelerates the effect, in other words, by having the chain carboxylic acid ester having high fluidity at low temperature, or the chain carboxylic acid ester propagates the interaction between the specific compound and the electrode.
< electrolyte solution [4] >
In the nonaqueous electrolytic solution, the nonaqueous solvent constituting the electrolytic solution preferably contains a solvent (electrolytic solution [4]) having a flash point of 70 ℃ or higher, which is 60% by volume or more of the entire nonaqueous solvent.
The types and contents of the "lithium salt", "nonaqueous solvent other than solvent having a flash point of 70 ℃ or higher", "specific compound", "other compound" in the electrolyte solution [4] of the present invention, the conditions for use, the method for producing the nonaqueous electrolyte solution, and the like are the same as described above.
In the present invention, the nonaqueous solvent must contain a solvent having a flash point of 70 ℃ or higher, which is 60% by volume or more of the entire nonaqueous solvent, based on the total amount. Further, it is preferable that the total amount of the solvent contains 60% by volume or more of the total amount of the nonaqueous solvent and a flash point of 80 ℃ or more, and it is particularly preferable that the total amount of the solvent contains 60% by volume or more of the total amount of the nonaqueous solvent and a flash point of 90 ℃ or more.
The solvent having a flash point of 70 ℃ or higher is not particularly limited, and examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, γ -butyrolactone, γ -valerolactone, and the like as preferable solvents, and among these, ethylene carbonate, propylene carbonate, and γ -butyrolactone are particularly preferable. One or more kinds of these solvents may be used in combination, and the combination is not particularly limited.
In addition, from the viewpoint of improvement of cycle characteristics, a composition containing 10% by volume or more of ethylene carbonate or propylene carbonate with respect to the entire nonaqueous solvent is preferable. On the other hand, if a large amount of ethylene carbonate is contained, the low-temperature characteristics are degraded, and the content of ethylene carbonate is preferably 70% by volume or less, particularly preferably 60% by volume or less, of the entire nonaqueous solvent.
Preferred examples of the nonaqueous solvent containing a solvent having a flash point of 70 ℃ or higher of 60% by volume or more of the total nonaqueous solvents are:
(1) a nonaqueous solvent in which gamma-butyrolactone accounts for 60% by volume or more of the total nonaqueous solvent;
(2) a nonaqueous solvent in which the total amount of ethylene carbonate and γ -butyrolactone accounts for 80% by volume or more, preferably 85% by volume or more of the entire nonaqueous solvent, and the volume ratio of ethylene carbonate to γ -butyrolactone is 5:95 to 45: 55;
(3) And a nonaqueous solvent in which the total of ethylene carbonate and propylene carbonate accounts for 80% by volume or more, preferably 85% by volume or more of the entire nonaqueous solvent and the volume ratio of ethylene carbonate to propylene carbonate is 30:70 to 60: 40.
When these nonaqueous solvents are used, the balance between the cycle characteristics and the large current discharge characteristics is particularly excellent.
The nonaqueous electrolytic solution preferably has a flash point of 40 ℃ or higher, more preferably 50 ℃ or higher, still more preferably 60 ℃ or higher, and particularly preferably 70 ℃ or higher. If the flash point of the nonaqueous electrolyte is too low, the battery may be exposed to high temperatures, which may cause ignition of the electrolyte.
The nonaqueous solvent used in the nonaqueous electrolyte for a secondary battery of the present invention may further contain a nonaqueous solvent component having a flash point of less than 70 ℃ (hereinafter simply referred to as "other nonaqueous solvent component") in a solvent having a flash point of 70 ℃. Such other nonaqueous solvent component can be appropriately selected from solvents proposed as solvents for conventional nonaqueous electrolytic solutions. Examples thereof include the following nonaqueous solvents.
(1) Chain carbonate
The chain carbonate is preferably a dialkyl carbonate, and the number of carbon atoms in the alkyl group constituting the dialkyl carbonate is preferably 1 to 5, and particularly preferably 1 to 4. Specific examples thereof include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, methylethyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Among them, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are preferable.
(2) Chain ester
Specific examples thereof include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.
(3) Cyclic ethers
Specific examples thereof include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like.
(4) Chain ether
Specific examples thereof include dimethoxyethane and dimethoxymethane.
The other nonaqueous solvent component may be used in combination with one kind of "solvent having a flash point of 70 ℃ or higher", or may be used in combination with 2 or more kinds of other nonaqueous solvent components. In this case, it is preferable to use a chain carbonate and/or a chain ester in combination with the "solvent having a flash point of 70 ℃ or higher" from the viewpoints of, in particular, cycle characteristics and large current discharge characteristics.
The content of the solvent having a flash point of 70 ℃ or higher in the entire nonaqueous solvent is necessarily 60% by volume or higher, preferably 70% by volume or higher, more preferably 75% by volume or higher, still more preferably 80% by volume or higher, and particularly preferably 85% by volume or higher. The upper limit thereof is preferably 100% by volume or less, and particularly preferably 90% by volume or less. If the content of the solvent having a flash point of 70 ℃ or higher is too small, the desired effect such as a tendency to increase the internal pressure may not be obtained when the battery is stored at high temperature, while if too large, the conductivity may decrease due to an increase in viscosity, and the performance of the lithium secondary battery may decrease.
The reason why the nonaqueous electrolyte secondary battery using the nonaqueous electrolyte solution (electrolyte solution [4]) of the present invention is excellent in output characteristics when a solvent having a flash point higher than a certain amount is used is not clear, but the present invention is not limited to the following reason. That is, it is considered that the specific compound acts on the electrode to reduce the reaction resistance associated with the entrance and exit of lithium ions, thereby improving the output characteristics. It is also considered that solvents having high flash points such as ethylene carbonate, propylene carbonate, butylene carbonate, γ -butyrolactone, and γ -valerolactone have a higher dielectric constant than chain carbonates, and that the effect thereof is remarkable when a solvent having a dielectric constant higher than a certain level is present. It is further considered that when the battery element housed in 1 battery case of the secondary battery has a battery capacity of 3 ampere hours (Ah) or more and/or when the dc resistance component of the secondary battery is 10 milliohms (Ω) or less, the contribution of the dc resistance component is reduced, and the effect of the nonaqueous electrolytic solution is more likely to be exhibited than a battery having a large contribution of the dc resistance component.
< electrolyte solution [5]
Preferably, the nonaqueous electrolytic solution contains LiN (C) nF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate as an electrolyte (electrolyte [5]) as a "lithium salt" constituting the electrolyte])。
The types and contents of the "nonaqueous solvent", "specific compound" and "other compound" in the electrolyte solution [5] of the present invention, the conditions for use, the method for producing the nonaqueous electrolyte solution, and the like are the same as those described above.
The nonaqueous electrolyte solution (electrolyte solution [5]) for secondary batteries of the present invention]) At least a lithium salt is dissolved in a nonaqueous solventContains a lithium salt selected from LiN (C)nF2n+1SO2)2(wherein n is an integer of 1 to 4) and lithium bis (oxalato) borate. These may be used alone, or may be used in combination of 2 or more in any combination and ratio.
The nonaqueous electrolyte for a secondary battery, which is obtained by using 10ppm or more of the above-mentioned "specific compound" in combination with the following (a), can provide a nonaqueous electrolyte for a secondary battery that is greatly improved in output characteristics and excellent in high-temperature storage characteristics and cycle characteristics.
(a)LiN(CnF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate
The (a) is not particularly limited, and LiN (CF)3SO2)2Or lithium bis (oxalato) borate is particularly preferable because the above effects can be exerted.
The nonaqueous electrolyte solution for a secondary battery of the present invention contains LiN (C) as a lithium salt as described abovenF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate as essential components, but other conventionally known lithium salts (hereinafter, simply referred to as "other lithium salts") may be used in combination.
The other lithium salt is not particularly limited, and examples thereof include the following lithium salts.
Inorganic lithium salt: LiPF6、LiBF4、LiAsF6、LiSbF6Inorganic fluoride salts; LiClO4、 LiBrO4、LiIO4A salt of a halogen acid of equal height; LiAlCl4And inorganic chloride salts, and the like.
Fluorine-containing organic lithium salt: LiCF3SO3Isoperfluoroalkane sulfonates; LiC (CF)3SO2)3Isoperfluoroalkanesulfonyl methide salts; li [ PF ]5(CF2CF2CF3)]、Li[PF4(CF2CF2CF3)2]、 Li[PF3(CF2CF2CF3)3]、Li[PF5(CF2CF2CF2CF3)]、Li[PF4(CF2CF2CF2CF3)2]、Li[PF3(CF2CF2CF2CF3)3]And fluoroalkyl fluorophosphate.
Other lithium oxalato borates: lithium difluorooxalato borate, and the like.
These may be used alone, or may be used in combination of 2 or more in any combination and ratio. Among these "other lithium salts", LiPF is preferable if the solubility in a nonaqueous solvent, the charge/discharge characteristics when used as a secondary battery, the output characteristics, the cycle characteristics, and the like are comprehensively judged6、LiBF4Particularly preferred is LiPF6。
LiN (C) in nonaqueous electrolytenF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate, when these salts are used as the main salts, the concentration thereof is usually 0.3mol/L or more, preferably 0.5mol/L or more, more preferably 0.7mol/L or more, and the upper limit thereof is usually 2mol/L or less, preferably 1.8mol/L or less, more preferably 1mol/L or less. Further, LiPF is added 6、LiBF4When other lithium salts are used as the main salt, LiN (C)nF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate, and the concentration is 0.001mol/L or more, preferably 0.01mol/L or more, more preferably 0.03mol/L or more, and the upper limit thereof is usually 0.3mol/L or less, preferably 0.2mol/L or less, more preferably 0.1mol/L or less. The main salt here means a lithium salt having the highest concentration in the nonaqueous electrolytic solution.
The total concentration of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is usually 0.5mol/L or more, preferably 0.6mol/L or more, and more preferably 0.7mol/L or more. The upper limit is usually 2mol/L or less, preferably 1.8mol/L or less, and more preferably 1.7mol/L or less. If the concentration is too low, the conductivity of the nonaqueous electrolytic solution may be insufficient, while if the concentration is too high, the conductivity may be lowered due to an increase in viscosity, and the performance of the lithium secondary battery may be lowered.
A preferable example of the case where 2 or more lithium salts are used in combination is a lithium salt selected from LiN (C)nF2n+1SO2)2LiPF and at least one lithium salt selected from the group consisting of lithium (wherein n is an integer of 1 to 4) and lithium bis (oxalato) borate6Are used in combination. By using the combination, the output power characteristic and the storage characteristic can be improved. In this case, it is selected from LiN (C) nF2n+1SO2)2(wherein n is an integer of 1 to 4) and lithium bis (oxalato) borate, wherein the concentration of at least one lithium salt in the nonaqueous electrolytic solution is as follows: when these lithium salts are used as the main salts, they are preferably 0.4mol/L or more, more preferably 0.5mol/L or more, and particularly preferably 0.6mol/L or more. The upper limit is preferably 1.8mol/L or less, more preferably 1.5mol/L or less, and particularly preferably 1.2mol/L or less. LiPF in this case6The concentration of (B) is preferably 0.001mol/L or more, more preferably 0.01mol/L or more, and particularly preferably 0.1mol/L or more. Further, the upper limit is LiPF6The ratio is selected from LiN (C)nF2n+1SO2)2In the formula, n is an integer of 1 to 4, and the concentration of at least one lithium salt of lithium bis (oxalato) borate is low, and is preferably 1mol/L or less, more preferably 0.8mol/L or less, and particularly preferably 0.3mol/L or less.
Mixing LiPF6When used as the main salt, is selected from LiN (C)nF2n+1SO2)2The concentration of at least one lithium salt selected from the group consisting of (wherein n is an integer of 1 to 4) and lithium bis (oxalato) borate is preferably 0.001mol/L or more, more preferably 0.01mol/L or more, and particularly preferably 0.03mol/L or more. The upper limit is preferably 0.3mol/L or less, more preferably 0.2mol/L or less, and particularly preferably 0.1mol/L or less. LiPF in this case 6The concentration of (B) is preferably 0.5mol/L or more, more preferably 0.6mol/L or more, particularly preferably 0.7mol/L or more. The upper limit is preferably 1.8mol/L or less, more preferably 1.7mol/L or less, and particularly preferably 1.5mol/L or less.
In addition, if the compound is selected from LiN (C)nF2n+1SO2)2LiPF and at least one lithium salt selected from the group consisting of lithium (wherein n is an integer of 1 to 4) and lithium bis (oxalato) borate6In combination with LiBF4It is preferable to have an effect of suppressing deterioration due to high-temperature storage. At this time, LiBF4The concentration of (B) is usually 0.001mol/L or more, preferably 0.01mol/L or more, more preferably 0.03mol/L or more, and the upper limit thereof is usually 0.4mol/L or less, preferably 0.15mol/L or less, more preferably 0.1mol/L or less.
Containing LiN (C)nF2n+1SO2)2A nonaqueous electrolytic solution containing lithium bis (oxalato) borate and at least one compound selected from the group consisting of a cyclic compound represented by the general formula (1), a compound represented by the general formula (2), a chain compound having a structure represented by the general formula (3) in the molecule, a compound having an S — F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate, is preferable because the balance between cycle characteristics and high-temperature storage characteristics (particularly, residual capacity after high-temperature storage and high-load discharge capacity) of a battery produced using the nonaqueous electrolytic solution is excellent.
The reason why the nonaqueous electrolyte secondary battery using the nonaqueous electrolytic solution of the present invention is excellent in output characteristics and high-temperature storage stability and cycle characteristics is not clear, but it is considered that the specific compound acts on the electrode to reduce the reaction resistance associated with the entry and exit of lithium ions, thereby improving the output characteristics. It is presumed that LiN (C) is usednF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or lithium bis (oxalato) borate as a lithium salt, and these lithium salts react appropriately on the surfaces of the negative electrode and the positive electrode to form a stable composite protective coating film having excellent lithium ion permeability derived from the lithium salt with other nonaqueous electrolyte components, and the composite coating film suppresses excessive side reactions of the highly active electrode and the nonaqueous electrolyte, thereby improving the output characteristics and also improving the high-temperature storage characteristics and cycle characteristics.
< electrolyte solution [6] >
In the above-mentioned nonaqueous electrolytic solution, the lithium salt constituting the electrolytic solution is preferably a fluorine-containing lithium salt, and 10ppm to 300ppm of Hydrogen Fluoride (HF) (electrolytic solution [6]) is contained in the entire nonaqueous electrolytic solution.
The invention (electrolyte [6]]) The types and contents of the "nonaqueous solvent", "specific compound" and "other compound" in (1) and (3), the conditions for use, the method for producing the nonaqueous electrolytic solution, and the like are the same as those described above. The invention (electrolyte [6] ]) The "fluorine-containing lithium salt" is not particularly limited as long as it is a known fluorine-containing lithium salt that can be used as an electrolyte of a nonaqueous electrolyte solution for a lithium secondary battery, and for example, the above-mentioned lithium salt can be used. These may be used alone, or may be used in combination of 2 or more in any combination and ratio. Among them, LiPF is preferable from the viewpoint of easy generation of Hydrogen Fluoride (HF) in the presence of the alcohol described later6、LiBF4And the like. Further, if the solubility in a nonaqueous solvent, the charge-discharge characteristics when a secondary battery is produced, the output characteristics, the cycle characteristics, and the like are comprehensively judged, LiPF is preferable6。
In addition, a fluorine-free lithium salt may be used in combination with the fluorine-containing lithium salt in the electrolyte solution, and the following lithium salts may be mentioned as examples.
Inorganic lithium salt: LiClO4、LiBrO4、LiIO4A salt of a halogen acid of equal height; LiAlCl4And inorganic chloride salts, and the like.
Oxalato borate salt: lithium bis (oxalato) borate, and the like.
The concentration of the lithium salt in the nonaqueous electrolytic solution is not particularly limited, and is usually 0.5mol/L or more, preferably 0.6mol/L or more, and more preferably 0.7mol/L or more. The upper limit is usually 2mol/L or less, preferably 1.8mol/L or less, and more preferably 1.7mol/L or less. If the concentration is too low, the conductivity of the nonaqueous electrolytic solution may be insufficient, while if the concentration is too high, the conductivity may be reduced due to an increase in viscosity, and the performance of the lithium secondary battery may be reduced.
The concentration of the fluorine-containing lithium salt in the nonaqueous electrolytic solution is not particularly limited, but is usually 0.5mol/L or more, preferably 0.6mol/L or more, and more preferably 0.7mol/L or more. The upper limit is usually 2mol/L or less, preferably 1.8mol/L or less, and more preferably 1.7mol/L or less. If the concentration is too low, the conductivity of the nonaqueous electrolytic solution may be insufficient or the generation of Hydrogen Fluoride (HF) may be insufficient, while if the concentration is too high, the viscosity may be increased, the conductivity may be decreased or the generation of Hydrogen Fluoride (HF) may be excessively advanced, and the performance of the lithium secondary battery may be lowered.
The ratio of the fluorine-containing lithium salt to the entire lithium salt in the nonaqueous electrolytic solution is preferably 50 mass% or more, particularly preferably 70 mass% or more, of the fluorine-containing lithium salt to the entire lithium salt. In addition, it is particularly preferable that the lithium salt to be mixed is a fluorine-containing lithium salt. If the ratio of the fluorine-containing lithium salt is too low, the generation of hydrogen fluoride may be insufficient.
One kind of lithium salt may be used alone, or 2 or more kinds of lithium salts may be used in combination in any combination and ratio, and LiPF is a preferable example when 2 or more kinds of lithium salts are used in combination6And LiBF4In this case, LiBF 4The ratio of the two components in total is preferably 0.01 to 20% by mass, more preferably 0.1 to 5% by mass. In another preferable example, the inorganic fluoride salt and the perfluoroalkanesulfonylimide salt are used in combination, and in this case, the ratio of the inorganic fluoride salt to the total of the both is preferably 70 to 99% by mass, and more preferably 80 to 98% by mass. The combined use of the two has an effect of suppressing deterioration due to high-temperature storage.
LiPF is dissolved in the non-aqueous solvent6The nonaqueous electrolytic solution obtained by using a fluorine-containing lithium salt contains Hydrogen Fluoride (HF) in a large amount. The reason why Hydrogen Fluoride (HF) is contained is that hydrogen fluoride derived from impurities in the fluorine-containing lithium salt, as well as hydrogen fluoride generated by the reaction between a slight amount of water or alcohol in the nonaqueous solvent and the fluorine-containing lithium salt exist. In patent document 16, it is necessary to remove Hydrogen Fluoride (HF) in the nonaqueous electrolytic solution as much as possible, and it is particularly preferable that the Hydrogen Fluoride (HF) is 15ppm or less, and the cycle characteristics of the nonaqueous electrolytic solution of 9ppm in examples are the most excellentAnd (5) fruit.
In the case of the electrolyte [6] of the present invention, the content of Hydrogen Fluoride (HF) is usually 10ppm or more, preferably 12ppm or more, more preferably 15ppm or more, and particularly preferably 20ppm or more, and is usually 300ppm or less, preferably 250ppm or less, more preferably 200ppm or less, and particularly preferably 150ppm or less. If the content is too low, the effect of improving the output may be insufficient, and if the content exceeds the range, the output and the cycle characteristics may be adversely affected.
In order to contain Hydrogen Fluoride (HF), water or an alcohol may be added to the nonaqueous electrolytic solution or the nonaqueous solvent of the raw material as it is, or may be generated inside the nonaqueous electrolytic solution by a reaction between water or an alcohol and a fluorine-containing lithium salt. In this case, a certain time may be required until the reaction is completed. In other words, in the case of preparing an electrolyte solution containing a specific compound by dissolving a fluorine-containing lithium salt in a nonaqueous solvent containing water or an alcohol, it takes time before the reaction between water or an alcohol and the fluorine-containing lithium salt is completed, but when the electrolyte solution is used for manufacturing a battery, it is not necessary to wait for the completion of the reaction. In the present invention, when functioning as a battery, Hydrogen Fluoride (HF) may be present in a specific concentration range, or may be generated in the battery. When Hydrogen Fluoride (HF) is generated in the nonaqueous solvent of the raw material, Hydrogen Fluoride (HF) may be generated in a part of the nonaqueous solvent used as the raw material and mixed with a nonaqueous solvent not containing water or alcohols.
When water or an alcohol is previously contained in the nonaqueous solvent, water or an alcohol may be contained in an amount larger than necessary from the beginning depending on the purity of the solvent used. In this case, it is preferable to use the nonaqueous solvent by purifying it by adsorption treatment, distillation, crystallization or the like, and removing water or alcohols. The nonaqueous solvent from which water or alcohols are removed as they are and a predetermined amount of water or alcohols remains may be used as it is, or water or alcohols may be added to the purified nonaqueous solvent so as to be a predetermined amount.
The adsorption treatment may be performed in a liquid state, and may be performed by dissolving in a non-aqueous solvent such as alumina, activated carbon, silica gel, molecular sieve (trade name) 4A and/or molecular sieve 5A, or by purifying with an adsorbent that does not react with the non-aqueous solvent. In this case, a raw material that is liquid at ordinary temperature, such as dimethyl carbonate, may be purified separately, and a raw material that is solid at ordinary temperature, such as ethylene carbonate, may be mixed with another raw material to form a liquid, and the liquid may be purified together. Examples of the contact method include a method of continuously immersing the nonaqueous solvent (hereinafter referred to as a continuous method), and a method of adding an adsorbent to the nonaqueous solvent, and standing or stirring the mixture (hereinafter referred to as a batch method). In the case of the continuous process, the contact time is preferably 0.1 to 5/hr in terms of Liquid Hourly Space Velocity (LHSV). In addition, the contact temperature is preferably 10 to 60 ℃. In the case of the batch method, it is preferable to add 0.1 to 30 mass% of the adsorbent to the nonaqueous solvent and treat the mixture for 0.25 to 24 hours.
Further, a raw material which is solid at room temperature such as ethylene carbonate may be subjected to crystallization treatment. Crystallization can be carried out using solvents such as acetonitrile, acetone, toluene, and the like.
The purification conditions are preferably adjusted as appropriate depending on the kind or purity of the raw material used and the content of the target water or alcohol.
When the nonaqueous electrolytic solution of the present invention (the electrolytic solution [6]) is prepared without adding Hydrogen Fluoride (HF), water or an alcohol is contained in the nonaqueous solvent used for the nonaqueous electrolytic solution. That is, water or alcohol is added and then used or water or alcohol is not removed and used. Preferably containing alcohols, especially mono-or diols. The alcohol is not particularly limited, and the kind of the alkyl group or the number of the alcohol is not particularly limited, and specific examples thereof include monohydric alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol; glycols such as ethylene glycol and propylene glycol; trihydric alcohols such as glycerin are preferred alcohols. Examples of the "water or alcohol" particularly preferable in the case of addition include methanol, ethanol, ethylene glycol, propylene glycol, and the like.
In the nonaqueous solvent for the electrolyte solution to be used, it is industrially preferable to use an alcohol mixed in due to the production process thereof or the like in view of productivity, cost, and the like. Particularly preferred nonaqueous solvents to be used contain methanol, ethanol, ethylene glycol or propylene glycol.
The nonaqueous solvent used for the nonaqueous electrolytic solution (electrolytic solution [6]) of the present invention preferably has a water or alcohol content of 3ppm or more, preferably 10ppm or more, more preferably 20ppm or more, and still more preferably 30ppm or more, and has an upper limit of 150ppm or less, preferably 130ppm or less, more preferably 120ppm or less, and still more preferably 100ppm or less. If the content of water or alcohol in the nonaqueous solvent is too small, the high power characteristics which are the features of the present invention may not be sufficiently obtained, and if too large, the cycle characteristics or high-temperature storage characteristics may be deteriorated.
Among these, the monohydric alcohols are preferably 5ppm or more, more preferably 10ppm or more, and still more preferably 15ppm or more, and preferably 100ppm or less, more preferably 80ppm or less, and still more preferably 50ppm or less in the nonaqueous solvent. The glycol is preferably 3ppm or more, preferably 10ppm or more, more preferably 15ppm or more, further preferably 20ppm or more, and preferably 100ppm or less, more preferably 90ppm or less, further preferably 80ppm or less, and particularly preferably 70ppm or less in the nonaqueous solvent. The amount of water in the nonaqueous solvent is 3ppm or more, preferably 5ppm or more, more preferably 10ppm or more, and preferably 100ppm or less, more preferably 80ppm or less, and still more preferably 70ppm or less.
If the above-mentioned specific amount of Hydrogen Fluoride (HF) and the above-mentioned specific compound coexist in the nonaqueous electrolytic solution, the output of the lithium secondary battery can be improved without adversely affecting the cycle characteristics.
The reason why the output can be improved without adversely affecting the cycle characteristics by coexistence of a certain amount of Hydrogen Fluoride (HF) and a specific compound in the nonaqueous electrolytic solution of the present invention is not clear, but is considered to be as follows. In addition, the present invention is not limited to the following operation principle. That is, the above-mentioned specific compound is likely to have a certain degree of output improvement effect regardless of the content of Hydrogen Fluoride (HF). This is considered to be because the specific compound has some effect on the electrode of the battery, and the reaction resistance associated with the entrance and exit of lithium ions is reduced. Among them, Hydrogen Fluoride (HF) may function to enhance or transfer the effect. For example, the specific compound acts on the electrode together with Hydrogen Fluoride (HF) or Hydrogen Fluoride (HF) functions as a mediator when the specific compound acts on the electrode. It is considered that Hydrogen Fluoride (HF) having such a function can be stably present in the battery, and thus adverse effects such as reduction in cycle characteristics are not likely to be caused.
< electrolyte solution [7]
In the nonaqueous electrolytic solution, vinylene carbonate is preferably contained in the electrolytic solution, and the content of the vinylene carbonate is preferably in the range of 0.001 to 3 mass% of the total mass of the electrolytic solution (electrolytic solution [7 ]).
The types and contents of the "lithium salt", "nonaqueous solvent", "specific compound" and "other compound" in the electrolyte solution [7] of the present invention, the conditions for use, the method for producing the nonaqueous electrolyte solution, and the like are the same as those described above.
The nonaqueous electrolytic solution of the present invention is characterized by containing vinylene carbonate, as described above. In the present invention, the ratio of vinylene carbonate in the entire nonaqueous electrolytic solution is usually 0.001 mass% or more, preferably 0.01 mass% or more, and more preferably 0.1 mass% or more. The content is usually 3% by mass or less, preferably 2.8% by mass or less, and more preferably 2.5% by mass or less. If the concentration of vinylene carbonate is too low, the effect of improving the cycle characteristics may be difficult to obtain, while if the concentration is too high, the low-temperature characteristics of the battery may be deteriorated.
The content of vinylene carbonate in the nonaqueous electrolytic solution is not particularly limited, but is preferably 0.01 or more, more preferably 0.1 or more, and particularly preferably 0.3 or more in terms of a mass ratio, and the upper limit thereof is preferably 300 or less, more preferably 100 or less, and particularly preferably 30 or less. If the amount is significantly outside this range, the object of excellent cycle characteristics and low temperature characteristics may not be achieved at the same time.
The reason why the cycle characteristics are improved by using vinylene carbonate in combination with the above-mentioned specific compound such as difluorophosphate, that is, by using a small amount of vinylene carbonate, is not clear, but it is considered that the reason is: specific compounds such as difluorophosphate salts suppress the amount of vinylene carbonate consumed at the positive electrode due to charge and discharge of the battery, and vinylene carbonate can form a coating film at the negative electrode without waste; and a coating film formed on the negative electrode changes in quality by mixing a specific compound such as difluorophosphate with vinylene carbonate, and a thin, low-resistance coating film having a high quality capable of further greatly suppressing decomposition of the electrolyte lithium salt is formed. It is thus considered that improvement of low-temperature characteristics can also be achieved.
< electrolyte solution [8] >
In the nonaqueous electrolytic solution, it is preferable that the electrolytic solution further contains at least one compound selected from the group consisting of the compound represented by the general formula (4), a heterocyclic compound containing nitrogen and/or sulfur, a cyclic carboxylic ester, and a fluorine-containing cyclic carbonate, and the content thereof in the entire nonaqueous electrolytic solution is in the range of 0.001 to 5% by mass (electrolytic solution [8 ]).
The types and contents of the "lithium salt", "nonaqueous solvent", "specific compound" and "other compound" in the electrolyte solution [8] of the present invention, the conditions for use, the method for producing the nonaqueous electrolyte solution, and the like are the same as those described above.
The nonaqueous electrolytic solution of the present invention (electrolytic solution [8]) further contains at least one compound selected from the group consisting of the compounds represented by the above general formula (4), heterocyclic compounds containing nitrogen and/or sulfur, cyclic carboxylic acid esters, and fluorine-containing cyclic carbonates (hereinafter, these may be abbreviated as "specific compound B"), and the content thereof in the whole nonaqueous electrolytic solution is in the range of 0.001 to 5% by mass.
[ [ Compound represented by the general formula (4) ] ]
In the above general formula (4), R9～R12Represent groups composed of more than one element selected from H, C, N, O, F, S and P, which may be the same or different from each other.
Specifically, the atoms are preferably present in a hydrogen atom, a fluorine atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, a haloalkyl group, an alkoxy group, a carbonyl group, a carbonyloxy group, an oxycarbonyl group, an oxycarbonyloxy group, a sulfonyl group, an oxysulfonyl group, a sulfonyloxy group, a phosphoryl group, a phosphinyl group, or the like. The molecular weight of the compound represented by the general formula (4) is preferably 500 or less, more preferably 300 or less, and still more preferably 200 or less.
Specific examples of the compound represented by the general formula (4) include carbonates such as vinyl ethylene carbonate, divinyl ethylene carbonate, methyl vinyl carbonate, ethyl vinyl carbonate, propyl vinyl carbonate, divinyl carbonate, allyl methyl carbonate, allyl ethyl carbonate, allyl propyl carbonate, and diallyl carbonate; esters such as vinyl acetate, vinyl propionate, vinyl acrylate, vinyl crotonate, vinyl methacrylate, allyl acetate, allyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate, and propyl methacrylate; sulfones such as divinyl sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, propyl vinyl sulfone, diallyl sulfone, allyl methyl sulfone, allyl ethyl sulfone, and allyl propyl sulfone; sulfites such as divinyl sulfite, methyl vinyl sulfite, ethyl vinyl sulfite, and diallyl sulfite; sulfonates such as vinyl methanesulfonate, vinyl ethanesulfonate, allyl methanesulfonate, allyl ethanesulfonate, methyl vinylsulfonate, and ethyl vinylsulfonate; sulfuric acid esters such as divinyl sulfate, methyl vinyl sulfate, ethyl vinyl sulfate, and diallyl sulfate. Among them, vinyl ethylene carbonate, divinyl ethylene carbonate, vinyl acetate, vinyl propionate, vinyl acrylate, divinyl sulfone, vinyl methane sulfonate, and the like are particularly preferable.
[ [ heterocyclic compound containing nitrogen and/or sulfur ] ]
The heterocyclic compound containing nitrogen and/or sulfur is not particularly limited, and examples thereof include 1-methyl-2-pyrrolidone, 1, 3-dimethyl-2-pyrrolidone, 1, 5-dimethyl-2-pyrrolidone, and 1-ethyl-2-pyrrolidinePyrrolidones such as ketone and 1-cyclohexyl-2-pyrrolidone; 3-methyl-2-
Figure BDA0003109774980001951
Oxazolidinone, 3-ethyl-2-
Figure BDA0003109774980001952
Oxazolidinone, 3-cyclohexyl-2-
Figure BDA0003109774980001953
Oxazolidinones and the like
Figure BDA0003109774980001954
Oxazolidinones; piperidones such as 1-methyl-2-piperidone and 1-ethyl-2-piperidone; imidazolones such as 1, 3-dimethyl-2-imidazolidinone and 1, 3-diethyl-2-imidazolidinone; sulfolanes such as sulfolane, 2-methylsulfolane and 3-methylsulfolane; sulfolene; sulfurous acid esters such as ethylene sulfite and propylene sulfite; and sultones such as 1, 3-propane sultone, 1-methyl-1, 3-propane sultone, 3-methyl-1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propene sultone, and 1, 4-butene sultone. Among them, 1-methyl-2-pyrrolidone, 1-methyl-2-piperidone, 1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propene sultone, 1, 4-butene sultone and the like are particularly preferable.
[ [ Cyclic carboxylic acid ester ] ]
The cyclic carboxylic acid ester is not particularly limited, and examples thereof include γ -butyrolactone, γ -valerolactone, γ -caprolactone, γ -heptalactone, γ -octalactone, γ -nonalactone, γ -decalactone, γ -undecanolactone, γ -dodecalactone, α -methyl- γ -butyrolactone, α -ethyl- γ -butyrolactone, α -propyl- γ -butyrolactone, α -methyl- γ -valerolactone, α -ethyl- γ -valerolactone, α -dimethyl- γ -butyrolactone, α -dimethyl- γ -valerolactone, δ -caprolactone, δ -octalactone, δ -nonalactone, δ -decalactone, γ -valerolactone, γ -decalactone, γ -valerolactone, α -methyl- γ -butyrolactone, α -dimethyl- γ -butyrolactone, α - γ -valerolactone, δ -caprolactone, γ -valerolactone, γ -butyrolactone, α -methyl-gamma-butyrolactone, α -methyl-gamma-butyrolactone, α -gamma-butyrolactone, α -gamma-caprolactone, α -caprolactone, δ -caprolactone, α -caprolactone, or the like-lactone of a-lactone, or the like, Delta-undecanolactone, delta-dodecanolactone, and the like. Among them, gamma-butyrolactone, gamma-valerolactone and the like are particularly preferable.
[ [ fluorinated cyclic carbonate ] ]
The fluorinated cyclic carbonate is not particularly limited, and examples thereof include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, and trifluoropropylene carbonate. Among them, ethylene fluorocarbonate and the like are particularly preferable.
The specific compound B, that is, at least one compound selected from the group consisting of the compound represented by the general formula (4), a nitrogen-and/or sulfur-containing heterocyclic compound, a cyclic carboxylic acid ester, and a fluorine-containing cyclic carbonate may be used alone or 2 or more compounds may be used in combination in any combination and ratio. In addition, in the specific compound B, even if the above-mentioned compounds classified individually can be used singly or 2 or more compounds can be used in combination in an arbitrary combination and ratio.
The content ratio of the specific compound B in the nonaqueous electrolytic solution to the entire nonaqueous electrolytic solution is usually 0.001% by mass or more, more preferably 0.05% by mass or more, and still more preferably 0.1% by mass or more in total. The upper limit is usually 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less, based on the total amount. If the concentration of the specific compound B is too low, the effect of improving the cycle characteristics and the storage characteristics may be difficult to obtain, while if the concentration is too high, the charge-discharge efficiency may be reduced.
The reason why the nonaqueous electrolyte secondary battery using the nonaqueous electrolyte solution of the present invention is excellent in low-temperature discharge characteristics and high-temperature storage characteristics or cycle characteristics is not clear, but the present invention is not limited to the following operation principle. Namely, the reason is presumed to be as follows: the specific compound B is reductively decomposed on the negative electrode at the initial charging, and a stable coating derived from the specific compound B is formed on the surface of the negative electrode, whereby the storage characteristics and the cycle characteristics can be improved. However, this coating film has a problem that the resistance increases significantly at low temperature, and the low-temperature discharge characteristics deteriorate. The coexistence of the specific compound A suppresses an excessive reaction of the specific compound B, and forms a stable composite protective coating film having excellent lithium ion permeability even at low temperatures, thereby improving low-temperature discharge characteristics and high-temperature storage characteristics or cycle characteristics.
It is further considered that when the battery element contained in 1 battery case of the secondary battery has a battery capacity of 3 ampere hours (Ah) or more and/or when the dc resistance component of the secondary battery is 10 milliohms (Ω) or less, the contribution of the dc resistance component is reduced, and the effect of the non-aqueous electrolyte is more likely to be exhibited than a battery in which the contribution of the dc resistance component is large.
< electrolyte solution [9]
In the nonaqueous electrolytic solution, it is preferable that an overcharge inhibitor (electrolyte solution [9]) is further contained in the electrolytic solution.
The types and contents of the "lithium salt", "nonaqueous solvent", "specific compound" and "other compound" in the electrolyte solution [9] of the present invention, the conditions for use, the method for producing the nonaqueous electrolyte solution, and the like are the same as those described above.
The nonaqueous electrolyte solution for a secondary battery of the present invention (electrolyte solution [9]) is characterized by containing an overcharge inhibitor. The overcharge inhibitor is not particularly limited, but is preferably a compound represented by the following (1), (2) or (3).
(1) Biphenyl, terphenyl, diphenyl ether or dibenzofuran which may be substituted by alkyl and/or fluorine atoms;
(2) partial hydrides of terphenyl;
(3) benzene substituted with a tertiary alkyl group, a cycloalkyl group, a fluorine atom and/or a methoxy group.
The compound (1) is not particularly limited, and examples thereof include benzene ring-linked compounds such as biphenyl, alkylbiphenyl, and terphenyl; fluorine-containing benzene ring-linking compounds such as 2-fluorobiphenyl; aromatic ethers such as diphenyl ether; and aromatic heterocyclic compounds such as dibenzofuran.
The compound (3) is not particularly limited, and examples thereof include (cyclo) alkylbenzenes such as cyclohexylbenzene, tert-butylbenzene, and tert-pentylbenzene; fluorine atom-substituted benzenes such as o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; fluorine-containing anisoles such as 2, 4-difluoroanisole, 2, 5-difluoroanisole, 2, 6-difluoroanisole and 3, 5-difluoroanisole.
Preferable specific examples thereof include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partial hydride of terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, and dibenzofuran. These compounds are particularly preferable because the rate characteristic improving effect after high-temperature storage in the present invention is increased.
Two or more overcharge preventing agents may be used in combination. When two or more kinds are used in combination, cyclohexylbenzene or terphenyl (or a partial hydride thereof) and tert-butylbenzene or tert-pentylbenzene are particularly preferably used in combination.
The partial hydride of terphenyl as used herein means a hydride obtained by partially adding hydrogen to the double bond of the benzene ring of terphenyl. The partial hydride of terphenyl may be a single compound or a mixture containing a plurality of compounds. For example, the partial hydride may be a mixture of partial hydrides of 2 or more terphenyls having different partial hydrogenation ratios, or a partial hydride of a terphenyl having an equal partial hydrogenation ratio. Further, it may be a mixture of hydrides having different positions of hydrogenated benzene rings, a mixture having different positions of double bonds, or a mixture containing structural isomers.
The partial hydrogenation ratio of terphenyl is a value obtained by calculating the partial hydrogenation ratio of 0% where hydrogen is not added to the double bonds of the benzene ring of terphenyl and the partial hydrogenation ratio of 100% where hydrogen is added to all double bonds, that is, the total hydrogenation ratio of terphenyl (where 18 moles of hydrogen atoms are added to 1 mole of terphenyl), and the average value per mole is obtained in the case of a mixture. For example, when 2 moles of hydrogen atoms were added to 1 mole of terphenyl, the partial hydrogenation ratio was 11.1% (═ 2/18).
When the partial hydrogenation ratio defined above is used, the partial hydrogenation ratio of the partial hydride of terphenyl used in the present invention may take a value exceeding 0% and less than 100%. The partial hydride of terphenyl may contain terphenyl (partial hydrogenation rate 0%), a complete hydride of m-terphenyl (partial hydrogenation rate 100%), and the molar average partial hydrogenation rate of the mixture preferably takes a value exceeding 0% and less than 100%. The partial hydrogenation rate of terphenyl is preferably 30 to 70%, more preferably 35 to 60%, from the viewpoint of the storage characteristics of the battery and the solubility in the electrolyte solution. The partial hydride of terphenyl or terphenyl is not particularly limited, but is particularly preferably m-terphenyl or m-terphenyl.
The proportion of each of these overcharge inhibitors in the nonaqueous electrolytic solution is usually 0.01% by mass or more, preferably 0.1% by mass or more, and particularly preferably 0.2% by mass or more, and the upper limit thereof is usually 5% by mass or less, preferably 3% by mass or less, and particularly preferably 2% by mass or less. If the content is less than the lower limit, the safety during overcharge may not be sufficiently ensured, and if the content exceeds the upper limit, a battery having excellent storage characteristics may not be obtained even when the battery is mixed with a specific compound described below.
The reason why the deterioration of the rate characteristics after storage due to the overcharge additive is less likely to occur in the presence of the specific compound is not clear, but is presumed to be as follows. In general, an overcharge inhibitor can form a polymer coating film on the surface of a positive electrode during overcharge to greatly improve the internal resistance of a battery, or can improve the safety of a secondary battery by operating a current interrupting device inside a battery can by gas generated during the polymerization, but the polymer coating film is partially formed even during high-temperature storage of a battery in a charged state, which causes a reduction in the discharge capacity or a deterioration in rate characteristics of the battery. If the specific compound specified in the present invention is present therein, the compound acts on the surface of the positive electrode to inhibit the reaction of the overcharge inhibitor and the positive electrode active material in the usual state of charge by forming a weak barrier. However, when the battery is overcharged and the positive electrode becomes excessively active, the weak barrier is broken or the reaction between the positive electrode and the overcharge inhibitor is accelerated beyond the barrier formed by the barrier, and the polymerization reaction proceeds, whereby the intended safety at overcharge can be secured.
< design of Battery (Battery construction) >
The structure (battery structure) of the lithium secondary battery of the present invention will be described in detail below.
The rechargeable lithium secondary battery of the present invention comprises at least a positive electrode and a negative electrode capable of occluding and releasing lithium ions, the nonaqueous electrolytic solution, a microporous membrane separator disposed between the positive electrode and the negative electrode, a current collecting terminal, and a case. Protective elements may also be installed inside the battery and/or outside the battery as needed. In the present specification, the characteristic parts of the structure (battery structure) of the lithium secondary battery according to the present invention are sometimes referred to as structures [1] to [6 ].
[ discharge Capacity ] (Structure [3])
In the lithium secondary battery of the present invention, it is preferable that the effect of improving the output characteristics is increased if the capacity of the battery element (the capacity when the battery is discharged from a fully charged state to a discharged state) (which may be simply referred to as "battery capacity") contained in 1 battery case of the secondary battery is 3 ampere hours (Ah) or more. Therefore, the positive electrode plate is preferably designed to have a discharge capacity of 3 ampere-hours (Ah) to 20Ah, more preferably 4Ah to 10Ah (structure [3]) at full charge. When the current is less than 3Ah, the voltage drop due to the electrode reaction resistance is increased when a large current is discharged, and the power utilization factor may be deteriorated. On the other hand, if the value is more than 20Ah, the electrode reaction resistance is decreased and the power utilization coefficient is improved, but the temperature distribution due to the internal heat generation of the battery during pulse charge and discharge is large, the durability of repeated charge and discharge is poor, the heat release efficiency against rapid heat generation during abnormality such as overcharge or internal short circuit is also poor, the internal pressure is increased, the gas release valve operation phenomenon (valve operation) is not stopped, and the possibility that the phenomenon (rupture) in which the battery content is rapidly discharged to the outside may be increased
[ Current collecting Structure ] (Structure [2], Structure [4])
The current collecting structure is not particularly limited, but in order to more effectively improve the output power characteristics of the lithium secondary battery of the present invention, it is necessary to form a structure that reduces the resistance of the wiring portion or the junction portion. When the internal resistance is low, the effect of using the nonaqueous electrolytic solution is particularly excellent.
When the electrode group has a laminated structure as described below, it is preferable to use a structure in which a collector tab (collector タブ) of each electrode layer is bundled and connected to a terminal. Since the internal resistance increases when the area of one electrode increases, it is preferable to provide a plurality of current collecting plates in the electrode to reduce the resistance. When the electrode group has a winding structure described later, a plurality of current collecting tabs are provided on the positive electrode and the negative electrode, respectively, and are bundled together at the terminals, whereby internal resistance can be reduced.
By optimizing the current collecting structure, the internal resistance can be reduced as much as possible. In a battery used at a high current, the impedance measured by the 10kHz ac method (hereinafter simply referred to as "dc resistance component") is preferably 20 milliohms (m Ω) or less, more preferably 10 milliohms (m Ω) or less, and still more preferably 5 milliohms (m Ω) or less (structure [2 ]). On the other hand, when the dc resistance component is less than 0.1 milliohm, although the high output power characteristics are improved, the ratio of the current collecting structural material used is increased, and the battery capacity may be decreased.
For the measurement of the impedance, the resistance when an alternating current of 10kHz was applied under a bias of 5mV was measured as a direct current resistance component using a battery measuring device 1470 manufactured by SOLAR (ソーラートロン) and a frequency response analyzer 1255B manufactured by SOLAR as measuring devices.
The nonaqueous electrolytic solution of the present invention is effective for reducing the reaction resistance associated with the entry and exit of lithium into and out of the electrode active material, and is considered to be a main factor that can realize excellent output characteristics. However, in a battery having a large dc resistance component, the effect of reducing the reaction resistance is not reflected 100% in the output characteristics due to the inhibition of the dc resistance component. This problem can be solved by using a battery having a small direct current resistance component, and the effects of the present invention can be fully exerted.
From the viewpoint of producing a battery exhibiting the effect of the nonaqueous electrolytic solution and having high output characteristics, it is particularly preferable to satisfy both the above-described condition and the condition that the capacity of the battery element (the capacity when the battery is discharged from a fully charged state to a discharged state) (the battery capacity) contained in 1 battery case of the secondary battery is 3 ampere hours (Ah) or more.
The connection of the current collecting tab and the terminal is preferably joined by any one of spot welding, high-frequency welding, and ultrasonic welding (structure [4 ]). These welding methods have been conventionally simple welding methods having low electric resistance, but when used for a long time, the welded portion is deteriorated by reaction with impurities, by-products, and the like in the non-aqueous electrolyte, and the dc resistance component is increased. However, when the nonaqueous electrolytic solution containing the specific compound is used, a stable coating film can be formed at the welded portion, and the secondary reaction of the nonaqueous electrolytic solution in the positive electrode can be suppressed, so that deterioration of the welded portion is not easily performed even when the nonaqueous electrolytic solution is used for a long time, and high output can be maintained without increasing the dc resistance component.
[ Battery case 1] (Structure 5)
The material of the battery case is not particularly limited as long as it is stable to the nonaqueous electrolytic solution used. Specifically, a metal such as nickel-plated steel sheet, stainless steel, aluminum, an aluminum alloy, or a magnesium alloy, or a laminated film (laminated film) of a resin and an aluminum foil can be used as a preferable material. From the viewpoint of weight reduction, it is particularly preferable to use a metal or laminated film of aluminum or aluminum alloy.
In the present invention, when the nonaqueous electrolytic solution is used, a metal (structure [5]) of aluminum or an aluminum alloy is particularly preferably used. Aluminum or an aluminum alloy is a material having light weight and high moldability, but when used as a battery case for a long time, it is deteriorated by reaction with impurities, by-products, and the like in the nonaqueous electrolytic solution, and if deteriorated, the strength of the case and the opening may be reduced. When the nonaqueous electrolytic solution containing the specific compound is used, a stable coating film can be formed on the surface of aluminum or the surface of aluminum alloy, and a side reaction of the nonaqueous electrolytic solution on the positive electrode can be suppressed, so that deterioration of the case is less likely to proceed even after long-term use.
The case using the metal base includes a case having a hermetically sealed structure formed by welding metal by laser welding, resistance welding, or ultrasonic welding, and a case having a caulking structure formed by using the metal base through a resin gasket. The case using the laminate film includes a case having a hermetically sealed structure formed by thermally fusing resin layers to each other. In order to improve the sealing property, a resin different from the resin used in the laminate film may be present between the above resin layers. In particular, when the resin layers are thermally fused together through the current collecting terminal to form a sealed structure, since the metal and the resin are bonded to each other, it is preferable to use a resin having a polar group or a modified resin into which a polar group is introduced as the resin existing between the resin layers.
[ Battery case 2] (Structure 6)
In the present invention, it is preferable that at least a part of the inner surface side of the battery, of the case material forming the battery case, contains a sheet formed using a thermoplastic resin, and the battery pack is sealed by incorporating the electrode assembly therein and heat-sealing the thermoplastic resin layer (structure [6 ]).
In order to achieve weight reduction of the battery, the material of the battery case in the configuration [6] is light and stable to the nonaqueous electrolytic solution to be used, and the electrode group must be easily and reliably sealed, so that at least a part of the inner surface side of the battery must contain a sheet formed using a thermoplastic resin.
In the structure [6], the electrode group is sealed by heat-sealing the thermoplastic resin layers, wherein the term "heat-sealing" means that the thermoplastic resin layers are bonded to each other by setting a temperature equal to or higher than the melting point of the thermoplastic resin. A sealing machine having a band-shaped heat generating part and capable of heating while pressurizing is preferably used. In addition, a thermoplastic resin is used for at least a part of the inner surface side of the battery, wherein "at least a part" refers to a region including a portion capable of sealing only the electrode group in the outer peripheral portion of the sheet, and a thermoplastic resin may be used only in the heat-sealed portion. From the viewpoint of efficiency of the sheet production process, it is preferable that the entire sheet surface on the inner surface side of the battery is covered with the thermoplastic resin layer.
In the structure [6], when the microporous membrane separator described later has a property of plugging the pores by heating, it is preferable that the casing material contains a sheet formed using a thermoplastic resin having a melting point higher than the plugging start temperature of the pores of the microporous membrane separator at least a part of the inner surface side of the battery from the viewpoint of safety in an abnormal state such as overcharge. That is, when abnormal heat generation occurs during overcharge or the like, the battery temperature rises, and if it exceeds the melting point of the thermoplastic resin of the casing material, the battery casing may be broken or the electrolyte may leak to cause ignition, but if the microporous membrane separator has a property of blocking the pores by heating, the pores of the microporous membrane separator are blocked before the electrolyte leaks from the casing material, and therefore, the generation of heat can be suppressed more, and therefore, the rupture and ignition are not caused, which is preferable. The melting point is a melting temperature measured according to JIS K7121.
The thermoplastic resin in the structure [6] is not particularly limited, and preferable examples thereof include polyolefins such as polyethylene, polypropylene, modified polyolefin, and polyolefin copolymer; polyesters such as polyethylene terephthalate; polyamides such as nylon. One or more than 2 kinds of thermoplastic resins may be used.
As the "at least a part of the housing material" in the structure [6], only a thermoplastic resin may be used, but a composite material of a thermoplastic resin and a thermosetting resin, an elastomer, a metal material, a glass fiber, a carbon fiber, or the like is preferably used. Further, a filler such as a filler may be contained. As the composite material, a laminate sheet of a thermoplastic resin layer and an alloy such as a simple metal such as aluminum, iron, copper, nickel, titanium, molybdenum, or gold, or an alloy such as stainless steel or hastelloy, and a laminate sheet of an aluminum metal having excellent workability is particularly preferable. That is, the housing material further preferably includes at least a laminate sheet including a laminate layer of an aluminum layer and a thermoplastic resin layer. These metals or alloys may be used in the form of a foil of a metal or the like, or may be used in the form of a metal vapor deposition film.
In the structure [6], examples of the case using the case material include a case having a hermetically sealed structure formed by heat-fusing a resin layer. In order to improve the sealing property, a resin different from the resin used for the housing material may be present between the resin layers. In particular, when the resin layers are thermally fused together through the current collecting terminal to form a sealed structure, since the metal and the resin are bonded to each other, it is preferable to use a resin having a polar group or a modified resin into which a polar group is introduced as the resin existing between the resin layers.
In the structure [6], the thickness of the casing material is not particularly limited, but is preferably 0.03mm or more, more preferably 0.04mm or more, and further preferably 0.05mm or more. The upper limit is preferably 0.5mm or less, more preferably 0.3mm or less, and still more preferably 0.2mm or less. If the shell material is thinner than this range, the strength is reduced, and the shell material may be easily deformed or broken. On the other hand, if the outer covering material is thicker than this range, the weight of the battery may not be reduced due to the increase in the mass of the case.
The battery having the structure [6] using the casing material has advantages of light weight and high degree of freedom in shape, and on the other hand, when gas is generated inside the battery, the internal pressure increases and the casing material is likely to be deformed. In the lithium secondary battery of the present invention, since the specific compound in the nonaqueous electrolytic solution is adsorbed on the surface of the positive electrode active material, the side reaction of the positive electrode can be suppressed, and the generation of the gas component can be suppressed, the above-mentioned disadvantage is not exhibited even if the casing material is used, and only the above-mentioned advantage of the casing material is exhibited, and therefore, the lithium secondary battery is preferable.
[ microporous membrane separator ]
The microporous membrane separator used in the present invention is not particularly limited as long as it has a predetermined mechanical strength for electrically insulating the both electrodes, has a large ion permeability, and has both resistance to oxidation on the side in contact with the positive electrode and resistance to reduction on the negative electrode side. As a material of the microporous membrane separator having such characteristics, a resin, an inorganic material, a glass fiber, or the like is used.
The resin is not particularly limited, and examples thereof include olefin polymers, fluorine polymers, cellulose polymers, polyimides, and nylons. Specifically, it is preferable to select from materials which are stable to the nonaqueous electrolytic solution and have excellent liquid retention properties, and porous sheets or nonwoven fabrics made of polyolefins such as polyethylene and polypropylene are preferably used. The inorganic substance is not particularly limited, and for example, oxides such as alumina and silica; nitrides such as aluminum nitride and silicon nitride; and sulfates such as barium sulfate and calcium sulfate. For the shape, a particle-like or fiber-like shape may be used.
The form is preferably a film form such as a nonwoven fabric, woven fabric, microporous film, or the like. Among the thin film shapes, a thin film having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above-described independent film shape, a form in which a composite porous layer containing the above-described inorganic particles is formed on the surface layer of the positive electrode and/or the negative electrode with a binder made of resin may be used. Such an embodiment includes, for example, a porous layer formed by forming 90% of alumina particles having a particle diameter of 1 μm or less on both surfaces of the positive electrode using a fluororesin as a binder.
The microporous membrane separator used in the present invention is preferably a separator having a property of plugging pores by heating. If the microporous membrane separator is used in combination with a casing material formed of a thermoplastic resin having a melting point higher than the pore-clogging initiation temperature of the microporous membrane separator as at least a part of the inner surface side of the battery, the casing material can stop heat generation before the battery casing is broken or the electrolyte leaks when abnormal heat generation such as overcharge occurs. The "property of blocking pores by heating" referred to herein means that the porous layer forming the electrolyte solution movable between the positive and negative electrodes contains a thermoplastic resin, and when the porous layer is heated to a temperature near the melting point of the thermoplastic resin, the porous layer blocks, and the electrolyte solution cannot move between the positive and negative electrodes.
[ shape of Battery ]
The shape of the battery is not particularly limited, and examples thereof include a bottomed cylindrical shape, a bottomed square shape, a thin shape, a sheet shape, and a paper shape. When incorporated into a system or a device, in order to improve the capacity efficiency and the storage property, it is also possible to take into consideration the shape of a peripheral system arranged around the battery, such as a horseshoe shape or a comb shape. From the viewpoint of efficiently releasing heat from the inside of the battery to the outside, a square shape having at least one relatively smooth large-area face is preferable.
In the battery having a bottomed cylindrical shape, since the outer surface area of the battery element is reduced with respect to the filled power generating element, it is preferable to provide a design that efficiently releases joule heat generated by internal resistance at the time of charge or discharge to the outside. It is preferable to increase the filling ratio of the substance having high thermal conductivity and to reduce the internal temperature distribution.
In the bottomed square shape, the area S of the largest surface is preferable1(the product of the width and height of the external dimension of the terminal portion was removed, unit cm2) Ratio of 2 times of (2 × S) to thickness T (unit cm) of the outer shape of the battery1The value of/T) is 100 or more, more preferably 200 or more. By increasing the maximum surface area, even in the case of a high-output and large-capacity battery, the cycle performance, high-temperature storage, and other characteristics can be improved, and the heat release efficiency during abnormal heat generation can be improved, thereby suppressing the occurrence of a "crack" or "fire" dangerous state.
[ electrode group ]
The electrode group may be any of a laminate-structured electrode group formed by sandwiching a microporous membrane separator described later between a positive electrode plate and a negative electrode plate described later, and a wound-structured electrode group spirally wound by sandwiching a microporous membrane separator described later between a positive electrode plate and a negative electrode plate described later. The ratio of the volume of the electrode group to the volume of the protrusion not including the battery case (hereinafter simply referred to as "electrode group occupancy") is preferably 0.3 to 0.7, and more preferably 0.4 to 0.6. If the electrode group occupancy is less than 0.3, the battery capacity decreases, and if it exceeds 0.7, the void space decreases, and the volume necessary for the current collecting structure described later cannot be sufficiently secured, and there is a possibility that the battery resistance increases, and the battery becomes high in temperature, and the components swell, or the vapor pressure of the liquid component of the electrolyte increases, and the internal pressure increases, and there is a case where various characteristics as the repeated charge and discharge performance of the battery, high-temperature storage, and the like decrease, or the gas release valve operates to release the internal pressure to the outside.
In addition, when the electrode group has a laminated structure, the positive electrodeThe sum L (unit cm) of the lengths around the electrodes and the negative electrode and the electrode area S are preferably selected2(unit cm)2) 2 times (L/(2 XS)2) ) is 1 or less, more preferably 0.5 or less, and still more preferably 0.3 or less. The lower limit thereof is preferably 0.02 or more, more preferably 0.03 or more, and still more preferably 0.05 or more. In the case of the stacked structure, since there is a possibility that the adhesion of the electrode film is deteriorated by a shock due to residual stress or cutting at a portion close to the periphery of the electrode, L/(2 × S)2) When the amount exceeds the above range, the output characteristics may be degraded. Furthermore, if L/(2 XS)2) If the amount is less than the above range, the battery area becomes too large, which may not be practical.
When the electrode group has a wound structure, the ratio of the length of the positive electrode in the longitudinal direction to the length of the positive electrode in the width direction is preferably 15 to 200. If the ratio is less than the above range, the bottomed cylindrical shape of the battery case may become too large in height relative to the bottom area, making the balance less practical, or the positive electrode active material layer may become thick, making it impossible to obtain high output. If the ratio is lower than the above range, the height of the bottomed cylindrical shape of the battery case is too small with respect to the bottom area, and the balance may be deteriorated, which may not be practical, or the ratio of the current collector may be increased, which may decrease the battery capacity.
[ area of Positive electrode ] (Structure [1])
In the present invention, when the nonaqueous electrolytic solution is used, the area of the positive electrode active material layer is preferably larger than the outer surface area of the battery case in terms of high output and improvement in stability at high temperatures. Specifically, from the viewpoint of improvement in output and effective discharge of heat generated by charge and discharge by the current collector, the total electrode area of the positive electrode is preferably 15 times or more, more preferably 20 times or more, in terms of an area ratio to the surface area of the case of the secondary battery (structure [1 ]). The outer surface area of the case is a total area obtained by calculating the dimensions of the case portion filled with the power generating element excluding the protruding portion of the terminal from the dimensions of the length, width and thickness in the case of a bottomed square shape. In the case of the bottomed cylindrical shape, the case portion filled with the power generating element excluding the protruding portion of the terminal is approximately the geometric surface area of a cylinder. The total electrode area of the positive electrode means a geometric surface area of the positive electrode composite layer facing the composite layer containing the negative electrode active material, and in a structure in which the positive electrode composite layer is formed on both surfaces by the current collector foil, the total area of the respective surfaces is calculated.
[ protective element ]
Examples of the protective element include a PTC (positive temperature coefficient) whose resistance increases when abnormal heat generation or an excessive current flows, a temperature fuse, a thermistor, and a valve (current blocking valve) that blocks a current flowing through a circuit due to a rapid increase in the internal pressure or the internal temperature of the battery during abnormal heat generation. The protective element is preferably selected so as not to be in an operating condition during normal use of a high current, and is more preferably designed so as not to cause abnormal heat generation or thermal runaway even without the protective element, from the viewpoint of high output.
[ assembled Battery ]
When the lithium secondary battery of the present invention is actually used as a power supply, the voltage required for the power supply is often equal to or higher than the cell voltage, and a booster device or the like in which cells are connected in series must be used correspondingly. Therefore, the lithium secondary battery of the present invention is preferably used as a battery pack in which a plurality of lithium secondary batteries are connected in series. By forming the battery pack, the resistance of the connection portion is reduced, so that a decrease in output power as the battery pack can be suppressed. In view of the power supply voltage, it is preferable that 5 or more batteries be connected in series.
In addition, when a plurality of batteries are connected to form a battery pack, the influence of heat generation due to charge and discharge is increased, and therefore, it is preferable to provide a cooling mechanism for keeping the batteries at a constant temperature or lower. The battery temperature is preferably 10 to 40 ℃, and is preferably cooled by water cooling or air cooling using outside air.
[ use ]
The lithium secondary battery of the present invention and the assembled battery formed by connecting a plurality of lithium secondary batteries of the present invention have high output, long life, high safety, and the like, and therefore are preferably used for applications to be mounted on a vehicle and to supply at least power to a drive system of the vehicle.
Further, it is considered that the specific compound is adsorbed on the surface of the positive electrode active material or the surface of the metal material, thereby suppressing a side reaction with the electrolyte solution or the like. This suppression of the side reaction on the surface of the positive electrode active material is preferable because gas generation is small and deformation of the battery or increase in internal pressure is unlikely to occur even if a sheet-like casing material is used. Further, it is considered that the suppression of the side reaction on the surface of the positive electrode active material improves the life, output and safety of the battery upon overcharge, and this is advantageous for application to large-sized batteries. Further, it is considered that, by suppressing the side reaction on the surface of the metal material, even when a simple welding method with a small resistance is used for connecting the current collecting plate and the terminal, the increase of the direct current resistance component is suppressed in long-term use, and therefore, the application to a large-sized battery is facilitated. In addition, it is considered that reducing the reaction resistance of the positive electrode is effective for further increasing the output in a battery designed to have a high output such as a battery shape or a positive electrode area, and therefore, is preferable.
Examples
The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.
Positive electrode [1] [ Positive electrode active Material ]
The types and physical properties of the positive electrode active materials used in the following examples and comparative examples are as follows.
Positive electrode [1] Table 1
[ Table 1]
Figure BDA0003109774980002061
Positive electrode [1]]In table 1, BET specific surface area, average primary particle diameter (measured by SEM), and median particle diameter d were measured as physical properties of the positive electrode active material in accordance with the methods described above50And measuring tap density.
[ Positive electrode active Material A ]
The positive electrode active material a was a lithium transition metal composite oxide synthesized by the method shown below, using LiMn as a composition formula0.33Ni0.33Co0.33O2And (4) showing. Mn as a manganese raw material was weighed in a molar ratio of Mn to Ni to Co of 1 to 13O4NiO as a raw material of nickel and Co (OH) as a raw material of cobalt2And pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.2 μm by a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 5 μm, which contained only the manganese raw material, the nickel raw material, and the cobalt raw material. To the obtained granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Mn, Ni and Co was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of granulated particles of a nickel raw material, a cobalt raw material and a manganese raw material and a lithium raw material. The mixed powder was sintered at 950 ℃ for 12 hours (5 ℃/min. ramp-down rate) under air flow, and then pulverized, and passed through a sieve having a mesh size of 45 μm, to obtain a positive electrode active material a.
[ Positive electrode active Material B ]
The positive electrode active material B is a lithium transition metal complex oxide synthesized in the same manner as the positive electrode active material A, and uses a composition formula LiMn0.33Ni0.33Co0.33O2It is shown, with the following differences: the spray drying conditions were changed to prepare granulated particles having a particle size of about 1 μm, and the sintering temperature was 930 ℃.
[ Positive electrode active Material C ]
The positive electrode active material C was synthesized by the method shown below, and a sulfur compound and an antimony compound were attached to the surface of the positive electrode active material a. That is, 96.7 parts by weight of the positive electrode active material a was stirred in a flow cell while spraying 1.3 parts by weight of lithium sulfate (Li) thereto2SO4H2O) is sprayed. In the best ofTo the mixture was added 2.0 parts by weight of antimony trioxide (Sb)2O3Particle median diameter of 0.8 μm) were thoroughly mixed. The mixture was transferred to an alumina container and sintered at 680 ℃ for 2 hours in an air atmosphere to obtain a positive electrode active material C.
[ Positive electrode active Material D ]
The positive electrode active material D is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula Li1.04Mn1.84Al0.12O4And (4) showing. LiOH as a lithium raw material and Mn as a manganese raw material were weighed in a molar ratio of Li, Mn and Al of 1.04:1.84:0.12 2O3And AlOOH as an aluminum raw material, and pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.5 μm using a circulating medium-stirring type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 10 μm, which contained only the lithium material, the manganese material, and the aluminum material. The granulated particles were sintered at 900 ℃ for 3 hours (at a temperature rise rate of 5 ℃/min) while flowing nitrogen, then the flowing gas was changed from nitrogen to air, and further sintered at 900 ℃ for 2 hours (at a temperature fall rate of 1 ℃/min). After cooling to room temperature, the resultant was taken out and pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material D.
[ Positive electrode active Material E ]
The positive electrode active material E is a commercially available product (lithium cobaltate manufactured by Nippon chemical industries Co., Ltd.) and is a lithium secondary battery using a composition formula Li1.03CoO2Lithium cobalt oxide as shown.
Positive electrode [1] example 1
Preparation of Positive electrode
A slurry was prepared by mixing 90 mass% of a positive electrode active material a as a positive electrode active material, 5 mass% of acetylene black as a conductive material, and 5 mass% of polyvinylidene fluoride (PVdF) as a binder in an N-methylpyrrolidone solvent. The obtained slurry was coated on both sides of an aluminum foil having a thickness of 15 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 100mm, The positive electrode was formed of a positive electrode active material layer having a length of 100mm and an uncoated portion having a width of 30 mm. The density of the positive electrode active material was 2.35g/cm3The value of (the thickness of the positive electrode active material layer on one surface)/(the thickness of the current collector) was 2.2.
Production of negative electrode
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timcal (ティムカル)) was added 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
Preparation of electrolyte
In a mixed solvent of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) at a volume ratio of 3:3:4, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L in a dry argon atmosphere 6). Further, hexamethylcyclotrisiloxane was contained in an amount of 0.3 mass%.
Production of Battery
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of an electrolyte was injected into the battery can with the electrode group attached, and the electrode was sufficiently impregnated and sealed to prepare a battery. The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 20.6.
Evaluation of Battery
(method of measuring Battery Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) at a voltage range of 4.1V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle at this time was taken as the initial capacity. The results of the battery evaluation are shown in table 2 of the positive electrode [1 ].
(method of measuring initial output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage line and a lower limit voltage (3V) is used as the output power (W). The results of the battery evaluation are shown in table 2 of the positive electrode [1 ].
(cycle test (method of measuring Battery Capacity after Endurance and output Power after Endurance))
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.1V by the constant current-constant voltage method of 2C, discharging to the end-of-discharge voltage of 3.0V by the constant current of 2C as one charge-discharge cycle, and the cycle was repeated up to 500 cycles. After the end of the cycle test, the battery was charged and discharged at a current value of 0.2C for 3 cycles in an environment of 25 ℃, and the 0.2C discharge capacity at the 3 rd cycle was defined as the after-endurance battery capacity. The output of the battery after the end of the cycle test was measured and used as the output after endurance. The results of the battery evaluation are shown in table 2 of the positive electrode [1 ].
Positive electrode [1] example 2
The same procedure as in example 1 of positive electrode [1] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [1 ].
Positive electrode [1] example 3
The same procedure as in example 1 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [1 ].
Positive electrode [1] example 4
The same procedure as in example 1 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [1 ].
Positive electrode [1] comparative example 1
The same procedure as in example 1 of positive electrode [1] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 2 of the positive electrode [1 ].
Positive electrode [1] Table 2
[ Table 2]
Figure BDA0003109774980002101
Positive electrode [1] example 5
Except that a positive electrode active material obtained by sufficiently mixing a positive electrode active material A and a positive electrode active material B at a mass ratio of 2:1 was used as a positive electrode active material to prepare a positive electrode, the positive electrode active material was mixed with a positive electrode [1]]Example 1 was performed in the same manner. The BET specific surface area of the mixed positive electrode active material was 1.8m 2A mean primary particle diameter of 0.22 μm and a median particle diameter d503.2 μm, tap density 1.5g/cm2. The results of the battery evaluation are shown in the positive electrode [1]]Table 3.
Positive electrode [1] example 6
The same procedure as in example 5 of positive electrode [1] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [1 ].
Positive electrode [1] example 7
The same procedure as in example 5 of positive electrode [1] was repeated, except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [1 ].
Positive electrode [1] example 8
The same procedure as in example 5 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [1 ].
Positive electrode [1] comparative example 2
The same procedure as in example 5 of positive electrode [1] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 3 of the positive electrode [1 ].
Positive electrode [1] Table 3
[ Table 3]
Figure BDA0003109774980002111
Positive electrode [1] example 9
The same procedure as in example 1 of positive electrode [1] was carried out except that a positive electrode was prepared using the positive electrode active material C as a positive electrode active material. The results of the battery evaluation are shown in table 4 of the positive electrode [1 ].
Positive electrode [1] example 10
The same procedure as in example 9 of positive electrode [1] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [1 ].
Positive electrode [1] example 11
The same procedure as in example 9 of positive electrode [1] was repeated, except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [1 ].
Positive electrode [1] example 12
The same procedure as in example 9 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [1 ].
Positive electrode [1] comparative example 3
The same procedure as in example 9 of positive electrode [1] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 4 of the positive electrode [1 ].
Positive electrode [1] Table 4
[ Table 4]
Figure BDA0003109774980002121
Positive electrode [1] example 13
A battery was produced in the same manner as in example 1 of positive electrode [1], except that a positive electrode was produced using positive electrode active material D as a positive electrode active material, the positive electrode was rolled to a thickness of 108 μm using a press, and 28 sheets of the positive electrode and 29 sheets of the negative electrode were used. (thickness of positive electrode active material layer on one surface of positive electrode/thickness of positive electrode current collector) was 3.1, and the ratio of the total electrode area of the positive electrode to the total surface area of the case of the battery was 18.1. The battery was evaluated in the same manner as in example 1 of the positive electrode [1] except that the voltage range for capacity measurement was 3.0 to 4.2V and the upper limit voltage in the cycle test was 4.2V. The results of the battery evaluation are shown in table 5 of the positive electrode [1 ].
Positive electrode [1] example 14
The same procedure as in example 13 of positive electrode [1] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [1 ].
Positive electrode [1] example 15
The same procedure as in example 13 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [1 ].
Positive electrode [1] example 16
The same procedure as in example 13 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [1 ].
Positive electrode [1] comparative example 4
The same procedure as in example 13 of positive electrode [1] was carried out, except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 5 of the positive electrode [1 ].
Positive electrode [1] Table 5
[ Table 5]
Figure BDA0003109774980002131
Positive electrode [1] example 17
A positive electrode was prepared by using a positive electrode active material obtained by sufficiently mixing a positive electrode active material D and a positive electrode active material E at a mass ratio of 2:1 as a positive electrode active material, and was rolled to a thickness of 94 μm by a press, 29 pieces of the positive electrode and 30 pieces of the negative electrode were used, and in addition, the positive electrode was used in combination with a positive electrode [1] ]Example 1 was performed in the same manner. (thickness of positive electrode active material layer on one surface of positive electrode/thickness of positive electrode current collector) was 2.6, and the ratio of the total electrode area of the positive electrode to the total surface area of the case of the battery was 18.7. The BET specific surface area of the mixed positive electrode active material was 0.8m2A median particle diameter d of 0.50 μm/g508.3 μm, tap density 2.5g/cm3. The results of the battery evaluation are shown in the positive electrode [1]]Table 6.
Positive electrode [1] example 18
The same procedure as in example 17 of positive electrode [1] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [1 ].
Positive electrode [1] example 19
The same procedure as in example 17 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [1 ].
Positive electrode [1] example 20
The same procedure as in example 17 of positive electrode [1] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [1 ].
Positive electrode [1] comparative example 5
The same procedure as in example 17 of positive electrode [1] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 6 of the positive electrode [1 ].
Positive electrode [1] Table 6
[ Table 6]
Figure BDA0003109774980002141
As is clear from the results of the positive electrodes [1] table 2 to [1] table 6, in any of the positive electrodes, since the specific compound is contained in the electrolytic solution, the output and the capacity retention rate are improved, and the battery capacity and the output can be sufficiently maintained even after the cycle test.
Positive electrode [2] [ Positive electrode active Material ]
The types and physical properties of the positive electrode active materials used in the following examples and comparative examples are as follows.
Positive electrode [2] Table 1
[ Table 7]
Figure BDA0003109774980002142
Positive electrode [2]]In table 1, BET specific surface area, average primary particle diameter (measured by SEM), and median particle diameter d were measured as physical properties of the positive electrode active material in accordance with the methods described above50And measuring tap density.
[ Positive electrode active Material A ]
The positive electrode active material A is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula Li1.05Ni0.80Co0.15Al0.05O2And (4) showing. NiO as a nickel raw material and Co (OH) as a cobalt raw material were weighed so that the molar ratio of Ni, Co and Al was 80:15:52And AlOOH as an Al raw material, and pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.25 μm using a circulating medium-stirring type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 10 μm, which contained only the nickel material, the cobalt material, and the aluminum material. To the obtained granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Ni, Co and Al was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of the granulated particles of the nickel raw material, the cobalt raw material and the aluminum raw material and the lithium raw material. The mixed powder was sintered at 740 ℃ for 6 hours (the rising/falling temperature rate was 5 ℃/min) under oxygen flow, and then pulverized, and passed through a sieve having a mesh size of 45 μm, to obtain a positive electrode active material a.
[ Positive electrode active Material B ]
The positive electrode active material B is a lithium transition metal complex oxide synthesized in the same manner as the positive electrode active material A, and is represented by the composition formula Li1.05Ni0.80Co0.15Al0.05O2It is shown, with the following differences: the spray drying conditions were changed to prepare granulated particles having a particle size of about 1 μm, and the sintering temperature was 720 ℃.
[ Positive electrode active Material C ]
The positive electrode active material C was synthesized by the method shown below, and a sulfur compound and an antimony compound were attached to the surface of the positive electrode active material a. That is, 96.7 parts by weight of the positive electrode active material a was stirred in a flow cell while spraying 1.3 parts by weight of lithium sulfate (Li) thereto 2SO4H2O) is sprayed. To the resulting mixture was added 2.0 parts by weight of antimony trioxide (Sb)2O3Particle median diameter of 0.8 μm) were thoroughly mixed. The mixture was transferred to an alumina container and sintered at 680 ℃ for 2 hours in an air atmosphere to obtain a positive electrode active material C.
[ Positive electrode active Material D ]
The positive electrode active material D is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula Li1.03Ni0.65Co0.20Mn0.15O2And (4) showing. Ni (OH) was weighed as a nickel raw material in a molar ratio of Li to Co to Mn of 65 to 20 to 152Co (OH) as a raw material for cobalt2And Mn as a raw material of manganese2O3And adding theretoPure water was made into a slurry, and the solid content in the slurry was wet-pulverized into a median particle diameter of 0.2 μm using a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 12 μm, which contained only the nickel material, the cobalt material, and the manganese material. To the obtained granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Ni, Co and Mn was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of granulated particles of a nickel raw material, a cobalt raw material and a manganese raw material and a lithium raw material. The mixed powder was sintered at 950 ℃ for 12 hours (5 ℃/min. rate of temperature rise and decrease) under air flow, and then pulverized, and passed through a sieve having a mesh size of 45 μm, to obtain a positive electrode active material D.
[ Positive electrode active Material E ]
The positive electrode active material E is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula Li1.04Mn1.84Al0.12O4And (4) showing. LiOH as a lithium raw material and Mn as a manganese raw material were weighed in a molar ratio of Li, Mn and Al of 1.04:1.84:0.122O3And AlOOH as an aluminum raw material, and pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.5 μm using a circulating medium-stirring type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 10 μm, which contained only the lithium material, the manganese material, and the aluminum material. The granulated particles were sintered at 900 ℃ for 3 hours (at a temperature rise rate of 5 ℃/min) while flowing nitrogen, then the flowing gas was changed from nitrogen to air, and further sintered at 900 ℃ for 2 hours (at a temperature fall rate of 1 ℃/min). After cooling to room temperature, the resultant was taken out and pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material E.
Positive electrode [2] example 1
Preparation of Positive electrode
A positive electrode active material as a positive electrode active material was mixed in an N-methylpyrrolidone solvent in an amount of 90 mass%A. 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 66 μm by a press, and cut into a shape having a positive electrode active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the positive electrode active material was 2.35g/cm 3The value of (the thickness of the positive electrode active material layer on one surface)/(the thickness of the current collector) was 1.7.
Production of negative electrode
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
Preparation of electrolyte
In a mixed solvent of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) at a volume ratio of 3:3:4, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L in a dry argon atmosphere6). Further, hexamethylcyclotrisiloxane was contained in an amount of 0.3 mass%.
Production of Battery
34 positive electrodes and 35 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of an electrolyte was injected into the battery can with the electrode group attached, and the electrode was sufficiently impregnated and sealed to prepare a battery. The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 21.9.
Evaluation of Battery
(method of measuring Battery Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) at a voltage range of 4.1V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle at this time was taken as the initial capacity. The results of the battery evaluation are shown in table 2 of the positive electrode [2 ].
(method of measuring initial output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage line and a lower limit voltage (3V) is used as the output power (W). The results of the battery evaluation are shown in table 2 of the positive electrode [2 ].
(cycle test (method of measuring Battery Capacity after Endurance and output Power after Endurance))
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.1V by the constant current-constant voltage method of 2C, discharging to the end-of-discharge voltage of 3.0V by the constant current of 2C as one charge-discharge cycle, and the cycle was repeated up to 500 cycles. After the end of the cycle test, the battery was charged and discharged at a current value of 0.2C for 3 cycles in an environment of 25 ℃, and the 0.2C discharge capacity at the 3 rd cycle was defined as the after-endurance battery capacity. The output of the battery after the end of the cycle test was measured and used as the output after endurance. The results of the battery evaluation are shown in table 2 of the positive electrode [2 ].
Positive electrode [2] example 2
The same procedure as in example 1 of positive electrode [2] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [2 ].
Positive electrode [2] example 3
The same procedure as in example 1 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [2 ].
Positive electrode [2] example 4
The same procedure as in example 1 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [2 ].
Positive electrode [2] comparative example 1
The same procedure as in example 1 of positive electrode [2] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 2 of the positive electrode [2 ].
Positive electrode [2] Table 2
[ Table 8]
Figure BDA0003109774980002181
Positive electrode [2] example 5
Except that a positive electrode was prepared using a positive electrode active material obtained by sufficiently mixing a positive electrode active material A and a positive electrode active material B at a mass ratio of 2:1 as a positive electrode active material, the positive electrode active material was mixed with a positive electrode [2]]Example 1 was performed in the same manner. The BET specific surface area of the mixed positive electrode active material was 1.4m 2A mean primary particle diameter of 0.2 μm and a median particle diameter d506.3 μm, tap density 1.9g/cm2. The results of the battery evaluation are shown in the positive electrode [2]]Table 3.
Positive electrode [2] example 6
The same procedure as in example 5 of positive electrode [2] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [2 ].
Positive electrode [2] example 7
The same procedure as in example 5 of positive electrode [2] was repeated, except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [2 ].
Positive electrode [2] example 8
The same procedure as in example 5 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [2 ].
Positive electrode [2] comparative example 2
The same procedure as in example 5 of positive electrode [2] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 3 of the positive electrode [2 ].
Positive electrode [2] table 3
[ Table 9]
Figure BDA0003109774980002191
Positive electrode [2] example 9
The same procedure as in example 1 of positive electrode [2] was carried out except that a positive electrode was prepared using the positive electrode active material C as a positive electrode active material. The results of the battery evaluation are shown in table 4 of the positive electrode [2 ].
Positive electrode [2] example 10
The same procedure as in example 9 of positive electrode [2] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [2 ].
Positive electrode [2] example 11
The same procedure as in example 9 of positive electrode [2] was repeated, except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [2 ].
Positive electrode [2] example 12
The same procedure as in example 9 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [2 ].
Positive electrode [2] comparative example 3
The same procedure as in example 9 of positive electrode [2] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 4 of the positive electrode [2 ].
Positive electrode [2] Table 4
[ Table 10]
Figure BDA0003109774980002201
Positive electrode [2] example 13
A battery was produced in the same manner as in example 1 of positive electrode [2], except that a positive electrode was produced using positive electrode active material D as a positive electrode active material, the positive electrode was rolled to a thickness of 68 μm using a press, and 34 sheets of the positive electrode and 35 sheets of the negative electrode were used. (thickness of positive electrode active material layer on one surface of positive electrode/thickness of positive electrode current collector) was 1.8, and the ratio of the total electrode area of the positive electrode to the total surface area of the case of the battery was 21.9. The battery was evaluated in the same manner as in example 1 of positive electrode [2] except that the voltage range for capacity measurement was 3.0 to 4.2V and the upper limit voltage in the cycle test was 4.2V. The results of the battery evaluation are shown in table 5 of the positive electrode [2 ].
Positive electrode [2] example 14
The same procedure as in example 13 of positive electrode [2] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [2 ].
Positive electrode [2] example 15
The same procedure as in example 13 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [2 ].
Positive electrode [2] example 16
The same procedure as in example 13 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [2 ].
Positive electrode [2] comparative example 4
The same procedure as in example 13 of positive electrode [2] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 5 of the positive electrode [2 ].
Positive electrode [2] Table 5
[ Table 11]
Figure BDA0003109774980002211
Positive electrode [2] example 17
A positive electrode was prepared by using a positive electrode active material obtained by sufficiently mixing a positive electrode active material A and a positive electrode active material E at a mass ratio of 2:1 as a positive electrode active material, and was rolled to a thickness of 76 μm by a press, and 32 sheets of the positive electrode and 33 sheets of the negative electrode were used, except that the positive electrode was used, and a positive electrode [2] ]Example 1 was performed in the same manner. (thickness of positive electrode active material layer on one surface of positive electrode/thickness of positive electrode current collector) was 2.0, and the ratio of the total electrode area of the positive electrode to the total surface area of the case of the battery was 20.6. The BET specific surface area of the mixed positive electrode active material was 0.7m2A mean primary particle diameter of 0.6 μm and a median particle diameter d508.7 μm, tap density 2.2g/cm3. The results of the battery evaluation are shown in the positive electrode [2]]Table 6.
Positive electrode [2] example 18
The same procedure as in example 17 of positive electrode [2] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [2 ].
Positive electrode [2] example 19
The same procedure as in example 17 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [2 ].
Positive electrode [2] example 20
The same procedure as in example 17 of positive electrode [2] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [2 ].
Positive electrode [2] comparative example 5
The same procedure as in example 17 of positive electrode [2] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 6 of the positive electrode [2 ].
Positive electrode [2] Table 6
[ Table 12]
Figure BDA0003109774980002221
As is clear from the results of the positive electrodes [2] table 2 to [2] table 6, in any of the positive electrodes, since the specific compound is contained in the electrolytic solution, the output and the capacity retention rate are improved, and the battery capacity and the output can be sufficiently maintained even after the cycle test.
Positive electrode [3] [ Positive electrode active Material ]
The types and physical properties of the positive electrode active materials used in the following examples and comparative examples are as follows.
Positive electrode [3] Table 1
[ Table 13]
Figure BDA0003109774980002231
Positive electrode [3]In table 1, BET specific surface area, average primary particle diameter (measured by SEM), and median particle diameter d were measured as physical properties of the positive electrode active material in accordance with the methods described above50And measuring tap density.
[ Positive electrode active Material A ]
The positive electrode active material A is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula Li1.05Ni0.8Co0.2O2And (4) showing. NiO as a nickel raw material and Co (OH) as a cobalt raw material were weighed so that the molar ratio of Ni to Co was 80:202Adding pure water to the mixture to prepare slurry, and stirring the slurry while using a circulating medium The wet bead mill wet-pulverized the solid content in the slurry to a median particle diameter of 0.25. mu.m.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 8 μm, which contained only the nickel material and the cobalt material. To the obtained granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Ni and Co was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of the nickel raw material, granulated particles of the cobalt raw material, and the lithium raw material. The mixed powder was sintered at 740 ℃ for 6 hours (the temperature increase/decrease rate was 5 ℃/min) under oxygen flow, and then pulverized, and passed through a sieve having a mesh size of 45 μm, to obtain a positive electrode active material a.
[ Positive electrode active Material B ]
The positive electrode active material B is a lithium transition metal complex oxide synthesized in the same manner as the positive electrode active material A, and is represented by the composition formula Li1.05Ni0.8Co0.2O2It is shown, with the following differences: the spray drying conditions were changed to prepare granulated particles having a particle size of about 1 μm, and the sintering temperature was 720 ℃.
[ Positive electrode active Material C ]
The positive electrode active material C was synthesized by the method shown below, and a sulfur compound and an antimony compound were attached to the surface of the positive electrode active material a. That is, 96.7 parts by weight of the positive electrode active material a was stirred in a flow cell while spraying 1.3 parts by weight of lithium sulfate (Li) thereto 2SO4H2O) is sprayed. To the resulting mixture was added 2.0 parts by weight of antimony trioxide (Sb)2O3Particle median diameter of 0.8 μm) were thoroughly mixed. The mixture was transferred to an alumina container and sintered at 680 ℃ for 2 hours in an air atmosphere to obtain a positive electrode active material C.
[ Positive electrode active Material D ]
The positive electrode active material D is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula Li1.04Mn1.84Al0.12O4And (4) showing. Li, Mn and Al were weighed in a molar ratio of 1.04:1.84:0.12 as lithium atomsLiOH as raw material, Mn as manganese raw material2O3And AlOOH as an aluminum raw material, and pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.5 μm using a circulating medium-stirring type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 10 μm, which contained only the lithium material, the manganese material, and the aluminum material. The granulated particles were sintered at 900 ℃ for 3 hours (at a temperature rise rate of 5 ℃/min) while flowing nitrogen, then the flowing gas was changed from nitrogen to air, and further sintered at 900 ℃ for 2 hours (at a temperature fall rate of 1 ℃/min). After cooling to room temperature, the resultant was taken out and pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material D.
Positive electrode [3] example 1
Preparation of Positive electrode
A slurry was prepared by mixing 90 mass% of a positive electrode active material a as a positive electrode active material, 5 mass% of acetylene black as a conductive material, and 5 mass% of polyvinylidene fluoride (PVdF) as a binder in an N-methylpyrrolidone solvent. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 65 μm by a press, and cut into a shape having a positive electrode active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to prepare a positive electrode. The density of the positive electrode active material was 2.35g/cm3The value of (the thickness of the positive electrode active material layer on one surface)/(the thickness of the current collector) was 1.7.
Production of negative electrode
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
Preparation of electrolyte
In a mixed solvent of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) at a volume ratio of 3:3:4, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L in a dry argon atmosphere6). Further, hexamethylcyclotrisiloxane was contained in an amount of 0.3 mass%.
Production of Battery
34 positive electrodes and 35 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of an electrolyte was injected into the battery can with the electrode group attached, and the electrode was sufficiently impregnated and sealed to prepare a battery. The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 21.9.
Evaluation of Battery
(method of measuring Battery Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) at a voltage range of 4.1V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle at this time was taken as the initial capacity. The results of the battery evaluation are shown in table 2 of the positive electrode [3 ].
(method of measuring initial output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage line and a lower limit voltage (3V) is used as the output power (W). The results of the battery evaluation are shown in table 2 of the positive electrode [3 ].
(cycle test (method of measuring Battery Capacity after Endurance and output Power after Endurance))
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.1V by the constant current-constant voltage method of 2C, discharging to the end-of-discharge voltage of 3.0V by the constant current of 2C as one charge-discharge cycle, and the cycle was repeated up to 500 cycles. After the end of the cycle test, the battery was charged and discharged at a current value of 0.2C for 3 cycles in an environment of 25 ℃, and the 0.2C discharge capacity at the 3 rd cycle was defined as the after-endurance battery capacity. The output of the battery after the end of the cycle test was measured and used as the output after endurance. The results of the battery evaluation are shown in table 2 of the positive electrode [3 ].
Positive electrode [3] example 2
The same procedure as in example 1 of positive electrode [3] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [3 ].
Positive electrode [3] example 3
The same procedure as in example 1 of positive electrode [3] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [3 ].
Positive electrode [3] example 4
The same procedure as in example 1 of positive electrode [3] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [3 ].
Positive electrode [3] comparative example 1
The same procedure as in example 1 of positive electrode [3] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 2 of the positive electrode [3 ].
Positive electrode [3] table 2
[ Table 14]
Figure BDA0003109774980002261
Positive electrode [3] example 5
Except that a positive electrode active material obtained by sufficiently mixing a positive electrode active material A and a positive electrode active material B at a mass ratio of 2:1 was used as a positive electrode active material, the positive electrode active material was mixed with a positive electrode [3]]Example 1 was performed in the same manner. The BET specific surface area of the mixed positive electrode active material was 1.8m 2A mean primary particle diameter of 0.2 μm and a median particle diameter d504.3 μm, tap density of 1.8g/cm2. The results of the battery evaluation are shown in the positive electrode [3]]Table 3.
Positive electrode [3] example 6
The same procedure as in example 5 of positive electrode [3] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [3 ].
Positive electrode [3] example 7
The same procedure as in example 5 of positive electrode [3] was repeated, except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [3 ].
Positive electrode [3] example 8
The same procedure as in example 5 of positive electrode [3] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [3 ].
Positive electrode [3] comparative example 2
The same procedure as in example 5 of positive electrode [3] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 3 of the positive electrode [3 ].
Positive electrode [3] Table 3
[ Table 15]
Figure BDA0003109774980002271
Positive electrode [3] example 9
The same procedure as in example 1 of positive electrode [3] was carried out except that a positive electrode was prepared using the positive electrode active material C as a positive electrode active material. The results of the battery evaluation are shown in table 4 of the positive electrode [3 ].
Positive electrode [3] example 10
The same procedure as in example 9 of positive electrode [3] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [3 ].
Positive electrode [3] example 11
The same procedure as in example 9 of positive electrode [3] was repeated, except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [3 ].
Positive electrode [3] example 12
The same procedure as in example 9 of positive electrode [3] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [3 ].
Positive electrode [3] comparative example 3
The same procedure as in example 9 of positive electrode [3] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 4 of the positive electrode [3 ].
Positive electrode [3] Table 4
[ Table 16]
Figure BDA0003109774980002281
Positive electrode [3] example 13
A positive electrode was prepared by using a positive electrode active material obtained by sufficiently mixing a positive electrode active material A and a positive electrode active material D at a mass ratio of 2:1 as a positive electrode active material, and was rolled to a thickness of 74 μm by a press, and 32 sheets of the positive electrode and 33 sheets of the negative electrode were used, except that the positive electrode was used, and a positive electrode [3] ]Example 1 was performed in the same manner. (thickness of positive electrode active material layer on one surface of positive electrode/thickness of positive electrode collector) was 2.0, and the total of electrode areas of positive electrodes and the surface of battery caseThe ratio of the sum of the products is 20.6. The BET specific surface area of the mixed positive electrode active material was 1.2m2A mean primary particle diameter of 0.6 μm and a median particle diameter d506.7 μm, tap density 2.2g/cm2. The results of the battery evaluation are shown in the positive electrode [3]]Table 5.
Positive electrode [3] example 14
The same procedure as in example 13 of positive electrode [3] was repeated except that the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [3 ].
Positive electrode [3] example 15
The same procedure as in example 13 of positive electrode [3] was carried out except that the electrolyte solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [3 ].
Positive electrode [3] example 16
The same procedure as in example 13 of positive electrode [3] was carried out except that the electrolyte solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [3 ].
Positive electrode [3] comparative example 4
The same procedure as in example 13 of positive electrode [3] was carried out except that hexamethylcyclotrisiloxane was not contained in the electrolyte solution. The results of the battery evaluation are shown in table 5 of the positive electrode [3 ].
Positive electrode [3] Table 5
[ Table 17]
Figure BDA0003109774980002291
As is clear from the results of the positive electrodes [3] table 2 to [3] table 5, in any of the positive electrodes, since the specific compound is contained in the electrolytic solution, the output and the capacity retention rate are improved, and the battery capacity and the output can be sufficiently maintained even after the cycle test.
Positive electrode [4] [ Positive electrode active Material ]
The types and physical properties of the positive electrode active materials used in the following examples and comparative examples are as follows.
Positive electrode [4] Table 1
[ Table 18]
Figure BDA0003109774980002301
Positive electrode [4]]In table 1, BET specific surface area, average primary particle diameter (measured by SEM), and median particle diameter d were measured as physical properties of the positive electrode active material in accordance with the methods described above50And measuring tap density.
[ Positive electrode active Material A ]
The positive electrode active material a was a lithium cobalt composite oxide synthesized by the method shown below, using a compositional formula LiCoO2And (4) showing. LiOH as a lithium raw material and Co (OH) as a cobalt raw material were weighed in a molar ratio of Li to Co of 1:12And pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.2 μm by a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 9 μm, which contained only the lithium material and the cobalt material. The granulated particles were sintered at 880 ℃ for 6 hours under air ventilation (the temperature increase/decrease rate was 5 ℃/min). After cooling to room temperature, the resultant was taken out and pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material a.
[ Positive electrode active Material B ]
The positive electrode active material B is a lithium transition metal complex oxide synthesized in the same manner as the positive electrode active material A, and is a compound of the compositional formula LiCoO2It is shown, with the following differences: the spray drying conditions were changed to prepare granulated particles having a particle size of about 1 μm, and the sintering temperature was 860 ℃.
[ Positive electrode active Material C ]
The positive electrode active material C was synthesized by the method shown below, and a sulfur compound and an antimony compound were attached to the surface of the positive electrode active material a. That is, 96.7 parts by weight of the positive electrode active material A was flowedWhile stirring in the tank, 1.3 parts by weight of lithium sulfate (Li) was sprayed thereto2SO4H2O) is sprayed. To the resulting mixture was added 2.0 parts by weight of antimony trioxide (Sb)2O3Particle median diameter of 0.8 μm) were thoroughly mixed. The mixture was transferred to an alumina container and sintered at 680 ℃ for 2 hours in an air atmosphere to obtain a positive electrode active material C.
[ Positive electrode active Material D ]
The positive electrode active material D is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula Li1.04Mn1.84Al0.12O4And (4) showing. LiOH as a lithium raw material and Mn as a manganese raw material were weighed in a molar ratio of Li, Mn and Al of 1.04:1.84:0.122O3And AlOOH as an aluminum raw material, and pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.5 μm using a circulating medium-stirring type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 10 μm, which contained only the lithium material, the manganese material, and the aluminum material. The granulated particles were sintered at 900 ℃ for 3 hours (at a temperature rise rate of 5 ℃/min) while flowing nitrogen, then the flowing gas was changed from nitrogen to air, and further sintered at 900 ℃ for 2 hours (at a temperature fall rate of 1 ℃/min). After cooling to room temperature, the resultant was taken out and pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material D.
Positive electrode [4] example 1
Preparation of Positive electrode
A slurry was prepared by mixing 85 mass% of a positive electrode active material a as a positive electrode active material, 10 mass% of acetylene black as a conductive material, and 5 mass% of polyvinylidene fluoride (PVdF) as a binder in an N-methylpyrrolidone solvent. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to 85 μm in thickness by a press, and cut into a shape having a positive electrode active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to prepare a positive electrode. Positive electrode active material The mass density was 2.35g/cm3The value of (the thickness of the positive electrode active material layer on one surface)/(the thickness of the current collector) was 2.3.
Production of negative electrode
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
Preparation of non-aqueous electrolyte
In a mixed solvent of 3:3:4 (volume ratio) of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC), well-dried lithium hexafluorophosphate (LiPF) was dissolved at a concentration of 1mol/L in a dry argon atmosphere6). Further, hexamethylcyclotrisiloxane was contained in an amount of 0.3 mass%.
Production of Battery
31 positive electrodes and 32 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the battery was sealed. The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 20.0.
Evaluation of Battery
(method of measuring Battery Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) at a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle at this time was taken as the initial capacity. The results of the battery evaluation are shown in table 2 of the positive electrode [4 ].
(method of measuring initial output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage line and a lower limit voltage (3V) is used as the output power (W). The results of the battery evaluation are shown in table 2 of the positive electrode [4 ].
(cycle test (method of measuring Battery Capacity after Endurance and output Power after Endurance))
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.2V by the constant current-constant voltage method of 2C, discharging to the end-of-discharge voltage of 3.0V by the constant current of 2C as one charge-discharge cycle, and the cycle was repeated up to 500 cycles. After the end of the cycle test, the battery was charged and discharged at a current value of 0.2C for 3 cycles in an environment of 25 ℃, and the 0.2C discharge capacity at the 3 rd cycle was defined as the after-endurance battery capacity. The output of the battery after the end of the cycle test was measured and used as the output after endurance. The results of the battery evaluation are shown in table 2 of the positive electrode [4 ].
Positive electrode [4] example 2
The same procedure as in example 1 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [4 ].
Positive electrode [4] example 3
The same procedure as in example 1 of positive electrode [4] was carried out except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [4 ].
Positive electrode [4] example 4
The same procedure as in example 1 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [4 ].
Positive electrode [4] comparative example 1
The same procedure as in example 1 of positive electrode [4] was carried out except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 2 of the positive electrode [4 ].
Positive electrode [4] Table 2
[ Table 19]
Figure BDA0003109774980002331
Positive electrode [4] example 5
The same procedure as in example 1 of positive electrode [4] was carried out except that a positive electrode was prepared using positive electrode active material B as a positive electrode active material. The results of the battery evaluation are shown in table 3 of the positive electrode [4 ].
Positive electrode [4] example 6
The same procedure as in example 5 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [4 ].
Positive electrode [4] example 7
The same procedure as in example 5 of positive electrode [4] was carried out except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [4 ].
Positive electrode [4] example 8
The same procedure as in example 5 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [4 ].
Positive electrode [4] comparative example 2
The same procedure as in example 5 of positive electrode [4] was carried out, except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 3 of the positive electrode [4 ].
Positive electrode [4] Table 3
[ Table 20]
Figure BDA0003109774980002341
Positive electrode [4] example 9
A positive electrode was prepared using a positive electrode active material obtained by sufficiently mixing a positive electrode active material A and a positive electrode active material B at a mass ratio of 2:1 as a positive electrode active material, and in addition to this, a positive electrode [4] was prepared]Example 1 was performed in the same manner. The BET specific surface area of the mixed positive electrode active material was 1.8m 2A mean primary particle diameter of 0.2 μm and a median particle diameter d504.9 μm, tap density 1.8g/cm3. The results of evaluation of the battery are shown in the positive electrode [4]]Table 4.
Positive electrode [4] example 10
The same procedure as in example 9 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [4 ].
Positive electrode [4] example 11
The same procedure as in example 9 of positive electrode [4] was carried out except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [4 ].
Positive electrode [4] example 12
The same procedure as in example 9 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [4 ].
Positive electrode [4] comparative example 3
The same procedure as in example 9 of positive electrode [4] was carried out except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 4 of the positive electrode [4 ].
Positive electrode [4] Table 4
[ Table 21]
Figure BDA0003109774980002351
Positive electrode [4] example 13
The same procedure as in example 1 of positive electrode [4] was carried out except that a positive electrode was prepared using the positive electrode active material C as a positive electrode active material. The results of the battery evaluation are shown in table 5 of the positive electrode [4 ].
Positive electrode [4] example 14
The same procedure as in example 13 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of positive electrode [4 ].
Positive electrode [4] example 15
The same procedure as in example 13 of positive electrode [4] was carried out, except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [4 ].
Positive electrode [4] example 16
The same procedure as in example 13 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [4 ].
Positive electrode [4] comparative example 4
The same procedure as in example 13 of positive electrode [4] was carried out except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 5 of the positive electrode [4 ].
Positive electrode [4] Table 5
[ Table 22]
Figure BDA0003109774980002361
Positive electrode [4] example 17
Using a positive electrode active material A and a positive electrode active materialA positive electrode was prepared by using a positive electrode active material obtained by thoroughly mixing the active materials D at a mass ratio of 2:1 as a positive electrode active material, and the mixture was rolled to a thickness of 92 μm by a press, and 30 sheets of the positive electrode and 31 sheets of the negative electrode were used, except that the positive electrode and the negative electrode were used, and a positive electrode [4] was used ]Example 1 was performed in the same manner. The ratio of (thickness of positive electrode active material layer on the positive electrode side)/(thickness of positive electrode current collector) was 2.6, and the total electrode area of the positive electrode to the total surface area of the battery case was 19.4. The BET specific surface area of the mixed positive electrode active material was 1.1m2A mean primary particle diameter of 0.6 μm and a median particle diameter d507.3 μm, tap density 2.2g/cm3. The battery evaluation results are shown in the positive electrode [4]]Table 6.
Positive electrode [4] example 18
The same procedure as in example 17 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 for positive electrode [4 ].
Positive electrode [4] example 19
The same procedure as in example 17 of positive electrode [4] was carried out, except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [4 ].
Positive electrode [4] example 20
The same procedure as in example 17 of positive electrode [4] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [4 ].
Positive electrode [4] comparative example 5
The same procedure as in example 17 of positive electrode [4] was carried out except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 6 of the positive electrode [4 ].
Positive electrode [4] Table 6
[ Table 23]
Figure BDA0003109774980002371
From the results of the positive electrodes [4] table 2 to [4] table 6, it is understood that in any of the positive electrodes, since the specific compound is contained in the nonaqueous electrolytic solution, the initial output is improved. In addition, the capacity retention rate is improved, and the battery capacity and the output power can be sufficiently maintained even after the cycle test.
Positive electrode [5] [ Positive electrode active Material ]
The types and physical properties of the positive electrode active materials used in the following examples and comparative examples are as follows.
Positive electrode [5] Table 1
[ Table 24]
Figure BDA0003109774980002381
Positive electrode [5]]In table 1, BET specific surface area, average primary particle diameter (measured by SEM), and median particle diameter d were measured as physical properties of the positive electrode active material in accordance with the methods described above50And measuring tap density.
[ Positive electrode active Material A ]
The positive electrode active material a was a lithium cobalt composite oxide synthesized by the method shown below, using a compositional formula LiCoO2And (4) showing. LiOH as a lithium raw material and Co (OH) as a cobalt raw material were weighed in a molar ratio of Li to Co of 1:12And pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.2 μm by a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 9 μm, which contained only the lithium material and the cobalt material. The granulated particles were sintered at 880 ℃ for 6 hours under air ventilation (the temperature increase/decrease rate was 5 ℃/min). After cooling to room temperature, the resultant was taken out and pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material a.
[ Positive electrode active Material B ]
The positive electrode active material B is a lithium transition metal composite oxide synthesized by the following method and has a composition formula Li1.05Ni0.80Co0.2O2And (4) showing. NiO as a nickel raw material and Co (OH) as a cobalt raw material were weighed so that the molar ratio of Ni to Co was 80:202And pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.25 μm by a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 8 μm, which contained only the nickel material and the cobalt material. To the resulting granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Ni and Co was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of granulated particles of a nickel raw material, a cobalt raw material, and a lithium raw material. The mixed powder was sintered at 740 ℃ for 6 hours under oxygen flow (the temperature increase/decrease rate was 5 ℃/min), and then pulverized, and passed through a sieve having a mesh size of 45 μm, to obtain a positive electrode active material B.
[ Positive electrode active Material C ]
The positive electrode active material C is a lithium transition metal composite oxide synthesized by the following method to form a composition formula Li1.05Ni0.80Co0.15Al0.05O2And (4) showing. NiO as a nickel raw material and Co (OH) as a cobalt raw material were weighed so that the molar ratio of Ni, Co and Al was 80:15:52And AlOOH as an aluminum raw material, pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.25 μm using a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 10 μm, which contained only the nickel material, the cobalt material, and the aluminum material. To the obtained granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Ni, Co and Al was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of granulated particles of a nickel raw material, a cobalt raw material and an aluminum raw material and a lithium raw material. The mixed powder was sintered at 740 ℃ for 6 hours under oxygen flow (the rising/falling temperature rate was 5 ℃/min), and then pulverized, and passed through a sieve having a mesh size of 45 μm, to obtain a positive electrode active material C.
[ Positive electrode active Material D ]
The positive electrode active material C was synthesized by the method shown below, and a sulfur compound and an antimony compound were attached to the surface of the positive electrode active material C. That is, 96.7 parts by weight of the positive electrode active material C was stirred in the flow tank, and 1.3 parts by weight of lithium sulfate (Li) was sprayed thereto while stirring 2SO4H2O) is sprayed. To the resulting mixture was added 2.0 parts by weight of antimony trioxide (Sb)2O3Particle median diameter of 0.8 μm) were thoroughly mixed. The mixture was transferred to an alumina container and sintered at 680 ℃ for 2 hours in an air atmosphere to obtain a positive electrode active material D.
[ Positive electrode active Material E ]
The positive electrode active material E is a lithium transition metal composite oxide synthesized by the following method to have a compositional formula of LiMn0.33Ni0.33Co0.33O2And (4) showing. Mn as a manganese raw material was weighed in a molar ratio of Mn to Ni to Co of 1 to 13O4NiO as a raw material of nickel and Co (OH) as a raw material of cobalt2Pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.2 μm by a circulating medium-stirring type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 5 μm, which contained only the manganese raw material, the nickel raw material, and the cobalt raw material. To the resulting granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Mn, Ni, and Co was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of granulated particles of a manganese raw material, a nickel raw material, and a cobalt raw material, and a lithium raw material. The mixed powder was sintered at 950 ℃ for 12 hours under oxygen flow (the rising/falling temperature rate was 5 ℃/min), and then pulverized, and passed through a sieve having a mesh size of 45 μm, to obtain a positive electrode active material E.
[ Positive electrode active Material F ]
The positive electrode active material F is a lithium transition metal complex synthesized by the following methodOxide of the formula Li1.04Mn1.84Al0.12O4And (4) showing. LiOH as a lithium raw material and Mn as a manganese raw material were weighed in a molar ratio of Li, Mn and Al of 1.04:1.84:0.122O3And AlOOH as an aluminum raw material, pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.5 μm using a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 10 μm, which contained only the lithium material, the manganese material, and the aluminum material. The resulting granulated particles were sintered at 900 ℃ for 3 hours under a nitrogen flow (cooling/heating rate of 5 ℃/min), then the flow gas was changed from nitrogen to air, and the sintered particles were sintered at 900 ℃ for 2 hours (cooling rate of 1 ℃/min). After cooling to room temperature, the resultant was taken out and pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material F.
Positive electrode [5] example 1
Preparation of Positive electrode
The positive electrode active material a and the negative electrode active material B were sufficiently mixed at a mass ratio of 1:1, and the obtained positive electrode active material was used to produce a positive electrode. The BET specific surface area of the mixed positive electrode active material was 1.2m 2A median particle diameter d of 0.8 μm/g506.5 μm, tap density 2.1g/cm3。
The mixed positive electrode active material a was mixed with 90 mass% of the above-described positive electrode active material a, 5 mass% of acetylene black as a conductive material, and 5 mass% of polyvinylidene fluoride (PVdF) as a binder in an N-methylpyrrolidone solvent to prepare a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 70 μm by a press, and cut into a shape having a positive electrode active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to prepare a positive electrode. The density of the positive electrode active material was 2.35g/cm3The value of (thickness of positive electrode active material layer on one side)/(thickness of current collector) was 1.8.
Production of negative electrode
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
Preparation of non-aqueous electrolyte
In a mixed solvent of 3:3:4 (volume ratio) of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC), well-dried lithium hexafluorophosphate (LiPF) was dissolved at a concentration of 1mol/L in a dry argon atmosphere6). Further, hexamethylcyclotrisiloxane was contained in an amount of 0.3 mass%.
Production of Battery
33 positive electrodes and 34 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the battery was sealed. The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 21.3.
Evaluation of Battery
(method of measuring Battery Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) at a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle at this time was taken as the initial capacity. The results of the battery evaluation are shown in table 2 of the positive electrode [5 ].
(method of measuring initial output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage line and a lower limit voltage (3V) is used as the output power (W). The results of the battery evaluation are shown in table 2 of the positive electrode [5 ].
(cycle test (method of measuring Battery Capacity after Endurance and output Power after Endurance))
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.2V by the constant current-constant voltage method of 2C, discharging to the end-of-discharge voltage of 3.0V by the constant current of 2C as one charge-discharge cycle, and the cycle was repeated up to 500 cycles. After the end of the cycle test, the battery was charged and discharged at a current value of 0.2C for 3 cycles in an environment of 25 ℃, and the 0.2C discharge capacity at the 3 rd cycle was defined as the after-endurance battery capacity. The output of the battery after the end of the cycle test was measured and used as the output after endurance. The results of the battery evaluation are shown in table 2 of the positive electrode [5 ].
Positive electrode [5] example 2
The same procedure as in example 1 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [5 ].
Positive electrode [5] example 3
The same procedure as in example 1 of positive electrode [5] was carried out except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [5 ].
Positive electrode [5] example 4
The same procedure as in example 1 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 2 of the positive electrode [5 ].
Positive electrode [5] comparative example 1
The same procedure as in example 1 of positive electrode [5] was carried out except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 2 of the positive electrode [5 ].
Positive electrode [5] Table 2
[ Table 25]
Figure BDA0003109774980002421
Positive electrode [5] example 5
A positive electrode was prepared using a positive electrode active material obtained by thoroughly mixing a positive electrode active material A and a positive electrode active material E at a mass ratio of 1:1 as a positive electrode active material, and was rolled to a thickness of 78 μm using a press, and a positive electrode [5] was used in addition to 32 sheets of the positive electrode and 33 sheets of the negative electrode ]Example 1 was performed in the same manner. The ratio of (thickness of positive electrode active material layer on one surface of positive electrode)/(thickness of positive electrode current collector) was 2.1, and the sum of electrode areas of positive electrodes to the sum of surface areas of outer cases of batteries was 20.6. The BET specific surface area of the mixed positive electrode active material was 1.2m2A median particle diameter d of 0.8 μm/g505.7 μm and a tap density of 2.0g/cm3. The battery evaluation results are shown in the positive electrode [5]]Table 3.
Positive electrode [5] example 6
The same procedure as in example 5 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [5 ].
Positive electrode [5] example 7
The same procedure as in example 5 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [5 ].
Positive electrode [5] example 8
The same procedure as in example 5 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 3 of the positive electrode [5 ].
Positive electrode [5] comparative example 2
The same procedure as in example 5 of positive electrode [5] was carried out except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 3 of the positive electrode [5 ].
Positive electrode [5] Table 3
[ Table 26]
Figure BDA0003109774980002431
Positive electrode [5] example 9
A positive electrode was prepared using a positive electrode active material obtained by thoroughly mixing a positive electrode active material A and a positive electrode active material F at a mass ratio of 1:1 as a positive electrode active material, and was rolled to a thickness of 91 μm using a press, and 30 sheets of the positive electrode and 31 sheets of the negative electrode were used, except that a positive electrode [5] was used]Example 1 was performed in the same manner. The ratio of (thickness of positive electrode active material layer on one surface of positive electrode)/(thickness of positive electrode current collector) was 2.5, and the total electrode area of the positive electrode to the total surface area of the outer case of the battery was 19.4. The BET specific surface area of the mixed positive electrode active material was 1.0m2A mean primary particle diameter of 0.6 μm and a median particle diameter d507.5 μm, tap density 2.2g/cm3. The battery evaluation results are shown in the positive electrode [5]]Table 4.
Positive electrode [5] example 10
The same procedure as in example 9 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [5 ].
Positive electrode [5] example 11
The same procedure as in example 9 of positive electrode [5] was carried out except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [5 ].
Positive electrode [5] example 12
The same procedure as in example 9 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 4 of the positive electrode [5 ].
Positive electrode [5] comparative example 3
The same procedure as in example 9 of positive electrode [5] was carried out except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 4 of the positive electrode [5 ].
Positive electrode [5] Table 4
[ Table 27]
Figure BDA0003109774980002451
Positive electrode [5] example 13
A positive electrode was prepared using a positive electrode active material obtained by thoroughly mixing a positive electrode active material C and a positive electrode active material E at a mass ratio of 1:1 as a positive electrode active material, and the mixture was rolled to a thickness of 72 μm using a press, and 33 sheets of the positive electrode and 34 sheets of the negative electrode were used, except that the positive electrode was used in combination with a positive electrode [5]]Example 1 was performed in the same manner. The BET specific surface area of the mixed positive electrode active material was 0.9m2A median particle diameter d of 0.7 μm/g506.7 μm, tap density 2.0g/cm 3. The ratio of (thickness of positive electrode active material layer on one surface of positive electrode)/(thickness of positive electrode current collector) was 1.9, and the total electrode area of the positive electrode to the total surface area of the case of the battery was 21.3. A positive electrode [5] except that the voltage range in the capacity measurement is 3.0-4.1V and the upper limit voltage in the cycle test is 4.1V]Example 1 the battery was evaluated in the same manner. The battery evaluation results are shown in the positive electrode [5]]Table 5.
Positive electrode [5] example 14
The same procedure as in example 13 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 for positive electrode [5 ].
Positive electrode [5] example 15
The same procedure as in example 13 of positive electrode [5] was carried out except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [5 ].
Positive electrode [5] example 16
The same procedure as in example 13 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 5 of the positive electrode [5 ].
Positive electrode [5] comparative example 4
The procedure was carried out in the same manner as in example 13 of positive electrode [5] except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 5 of the positive electrode [5 ].
Positive electrode [5] Table 5
[ Table 28]
Figure BDA0003109774980002461
Positive electrode [5] example 17
A positive electrode was prepared using a positive electrode active material obtained by thoroughly mixing a positive electrode active material C and a positive electrode active material F at a mass ratio of 1:1 as a positive electrode active material, and was rolled to a thickness of 78 μm using a press, and a positive electrode [5] was used in addition to 32 sheets of the positive electrode and 33 sheets of the negative electrode]Example 1 was performed in the same manner. The ratio of (thickness of positive electrode active material layer on the positive electrode side)/(thickness of positive electrode current collector) was 2.1, and the total electrode area of the positive electrode to the total surface area of the outer case of the battery was 20.6. The BET specific surface area of the mixed positive electrode active material was 0.8m2A mean primary particle diameter of 0.6 μm and a median particle diameter d508.5 μm, tap density 2.2g/cm3. The battery evaluation results are shown in the positive electrode [5]]Table 6.
Positive electrode [5] example 18
The same procedure as in example 17 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [5 ].
Positive electrode [5] example 19
The same procedure as in example 17 of positive electrode [5] was carried out, except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [5 ].
Positive electrode [5] example 20
The same procedure as in example 17 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 6 of the positive electrode [5 ].
Positive electrode [5] comparative example 5
The procedure was carried out in the same manner as in example 17 of positive electrode [5] except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 6 of the positive electrode [5 ].
Positive electrode [5] Table 6
[ Table 29]
Figure BDA0003109774980002471
Positive electrode [5] example 21
A positive electrode was prepared using a positive electrode active material obtained by thoroughly mixing a positive electrode active material D and a positive electrode active material E at a mass ratio of 1:1 as a positive electrode active material, and the mixture was rolled to a thickness of 72 μm using a press, and 33 sheets of the positive electrode and 34 sheets of the negative electrode were used, except that the positive electrode was used in combination with a positive electrode [5]]Example 1 was performed in the same manner. The BET specific surface area of the mixed positive electrode active material was 0.9m2A median particle diameter d of 0.7 μm/g506.7 μm, tap density 2.0g/cm3. The ratio of (thickness of positive electrode active material layer on one surface of positive electrode)/(thickness of positive electrode current collector) was 1.9, and the total electrode area of the positive electrode to the total surface area of the case of the battery was 21.3. A positive electrode [5] except that the voltage range in the capacity measurement is 3.0-4.1V and the upper limit voltage in the cycle test is 4.1V ]Example 1 the battery was evaluated in the same manner. The battery evaluation results are shown in the positive electrode [5]]Table 7.
Positive electrode [5] example 22
The same procedure as in example 17 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in the positive electrode [5] Table 7.
Positive electrode [5] example 23
The same procedure as in example 17 of positive electrode [5] was carried out, except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 7 of the positive electrode [5 ].
Positive electrode [5] example 24
The same procedure as in example 17 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 7 of the positive electrode [5 ].
Positive electrode [5] comparative example 6
The procedure was carried out in the same manner as in example 17 of positive electrode [5] except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 7 of the positive electrode [5 ].
Positive electrode [5] Table 7
[ Table 30]
Figure BDA0003109774980002481
Positive electrode [5] example 25
A positive electrode was prepared using a positive electrode active material obtained by thoroughly mixing a positive electrode active material E and a positive electrode active material F at a mass ratio of 1:1 as a positive electrode active material, and was rolled to a thickness of 86 μm using a press, and a positive electrode [5] was used in addition to 31 sheets of the positive electrode and 32 sheets of the negative electrode ]Example 1 was performed in the same manner. The ratio of (thickness of positive electrode active material layer on the positive electrode side)/(thickness of positive electrode current collector) was 2.4, and the total electrode area of the positive electrode to the total surface area of the outer case of the battery was 20.0. The BET specific surface area of the mixed positive electrode active material was 1.1m2A mean primary particle diameter of 0.6 μm and a median particle diameter d506.2 μm and a tap density of 2.0g/cm3. Electric powerThe cell evaluation results are shown in the positive electrode [5]]Table 8.
Positive electrode [5] example 26
The same procedure as in example 17 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in the positive electrode [5] Table 8.
Positive electrode [5] example 27
The same procedure as in example 17 of positive electrode [5] was carried out, except that the nonaqueous electrolytic solution contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 8 of the positive electrode [5 ].
Positive electrode [5] example 28
The same procedure as in example 17 of positive electrode [5] was repeated except that the nonaqueous electrolytic solution contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane. The results of the battery evaluation are shown in table 8 of the positive electrode [5 ].
Positive electrode [5] comparative example 7
The procedure was carried out in the same manner as in example 17 of positive electrode [5] except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolytic solution. The results of the battery evaluation are shown in table 8 of the positive electrode [5 ].
Positive electrode [5] Table 8
[ Table 31]
Figure BDA0003109774980002491
As is clear from the results of the positive electrodes [5] table 2 to [5] table 8, in any of the positive electrodes, since the specific compound is contained in the nonaqueous electrolytic solution, the output and the capacity retention ratio are improved, and the battery capacity and the output can be sufficiently maintained even after the cycle test.
Negative electrode [1] [ preparation of negative electrode active Material ]
(preparation of negative electrode active Material 1)
In order to prevent coarse particles from being mixed into a commercially available natural graphite powder as a particulate carbonaceous material, the sieving was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode material thus obtained was used as the carbonaceous material (a).
(preparation of negative electrode active Material 2)
Petroleum heavy oil obtained by pyrolysis of naphtha is carbonized at 1300 ℃ in an inert gas, and then a burned product is classified to obtain a carbonaceous material (B). In the classification treatment, the sieve was repeatedly sieved 5 times using a sieve of ASTM400 mesh in order to prevent the mixing of coarse particles.
(preparation of negative electrode active Material 3)
The carbonaceous material (a) in an amount of 95 mass% and the carbonaceous material (B) in an amount of 5 mass% were uniformly mixed, and the mixture was defined as 2 kinds of crystalline carbonaceous material mixtures (C).
(preparation of negative electrode active Material 4)
Petroleum heavy oil obtained by pyrolysis of naphtha is mixed with a carbonaceous material (a), carbonization treatment is performed at 1300 ℃ in an inert gas, and then a burned product is subjected to classification treatment to obtain a carbonaceous material (D) in which carbonaceous materials having different crystallinities are coated on the surfaces of particles of the carbonaceous material (a). In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed in. From the carbon residue ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite.
(preparation of negative electrode active Material 5)
In addition to reducing and mixing the petroleum-based heavy oil obtained in the naphtha pyrolysis in production 4 of the negative electrode active material, a composite carbonaceous material (E) coated with 1 weight of a low-crystalline carbonaceous material relative to 99 parts by weight of graphite was obtained in the same manner as in production 4 of the negative electrode active material.
(preparation of negative electrode active Material 6)
In the same manner as in production 4 of the negative electrode active material, except that the petroleum-based heavy oil obtained in the pyrolysis of naphtha in production 4 of the negative electrode active material was increased and mixed, the composite carbonaceous material (F) coated with 10 parts by weight of the low-crystalline carbonaceous material relative to 90 parts by weight of graphite was obtained.
(preparation of negative electrode active Material 7)
In addition to increasing the amount of the petroleum-based heavy oil obtained in the pyrolysis of naphtha in preparation 4 of the negative electrode active material and mixing, a composite carbonaceous material (G) coated with 30 parts by weight of a low-crystalline carbonaceous material relative to 70 parts by weight of graphite was obtained in the same manner as in preparation 4 of the negative electrode active material.
(preparation of negative electrode active Material 8)
A composite carbonaceous material (I) coated with 5 parts by weight of a low-crystalline carbonaceous material relative to 95 parts by weight of graphite was obtained in the same manner as in preparation 4 of the negative electrode active material, except that graphitization treatment at 3000 ℃ was performed in an inert gas in preparation 4 of the negative electrode active material.
(preparation of negative electrode active Material 9)
A phenol-formaldehyde solution is mixed with a carbonaceous material (A), a carbonization treatment is performed at 1300 ℃ in an inert gas, and then a calcined product is subjected to a classification treatment to obtain a composite carbonaceous material powder in which carbonaceous materials having different crystallinities are coated on the surfaces of graphite particles. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent the mixing of coarse particles, thereby obtaining a composite carbonaceous material (J). From the carbon residue ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite.
(preparation of negative electrode active Material 10)
Coal tar pitch having a quinoline insoluble content of 0.05 mass% or less was heat-treated in a reaction furnace at 460 ℃ for 10 hours, the obtained bulk carbonaceous material was pulverized with a pulverizer (origin mill (オリエントミル) manufactured by seishin corporation), and the pulverized material was finely pulverized with a micro-pulverizer (turbo mill manufactured by matsubo (マツボー)) to a median particle diameter of 17 μm. The pellets were charged into a metal container and heat-treated at 540 ℃ for 2 hours in a box-shaped electric furnace under a nitrogen flow. The obtained cake was pulverized by a coarse pulverizer (roll crusher (ロールジョークラッシャー) manufactured by yota corporation), then finely pulverized by a fine pulverizer (turbo mill manufactured by matsubo corporation), and the obtained powder was charged in a container and sintered at 1300 ℃ for 1 hour in an electric furnace under a nitrogen atmosphere. Then, the obtained sintered product is subjected to classification treatment, thereby obtaining a carbonaceous material (K). In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed in.
(preparation of negative electrode active Material 11)
A phenol-formaldehyde solution is mixed with a carbonaceous material (K), a carbonization treatment is performed at 1300 ℃ in an inert gas, and then a calcined product is subjected to a classification treatment to obtain a composite carbonaceous material powder in which carbonaceous materials having different crystallinities are coated on the surfaces of graphite particles. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent the mixing of coarse particles, thereby obtaining a composite carbonaceous material (L). From the carbon residue ratio, it was confirmed that the obtained negative electrode active material powder was coated with 40 parts by weight of a low-crystalline carbonaceous material with respect to 60 parts by weight of graphite.
(preparation of negative electrode active Material 12)
Petroleum heavy oil obtained by pyrolysis of naphtha is mixed with a carbonaceous material (K), and the mixture is carbonized at 1300 ℃ in an inert gas, and then the sintered product is classified to obtain composite carbonaceous material powder in which carbonaceous materials having different crystallinities are coated on the surfaces of graphite particles. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent the mixing of coarse particles, thereby obtaining a composite carbonaceous material (M). From the carbon residue ratio, the obtained negative electrode active material powder was coated with 5 parts by weight of a low-crystalline carbonaceous material with respect to 95 parts by weight of graphite.
(preparation of negative electrode active Material 13)
Coal tar pitch having a quinoline insoluble content of 0.05 mass% or less was heat-treated at 460 ℃ for 10 hours in a reaction furnace, the obtained bulk carbonaceous material was pulverized with a pulverizer (origin mill manufactured by senshin corporation), and the pulverized material was finely pulverized with a micro pulverizer (turbo mill manufactured by matsubo corporation) to a median particle diameter of 17 μm. The particles were placed in a metal container and heat-treated at 540 ℃ for 2 hours in a box-shaped electric furnace under a nitrogen gas flow. The obtained cake was pulverized by a coarse pulverizer (roll crusher, manufactured by yota), and then finely pulverized by a fine pulverizer (turbine mill, manufactured by matsubo corporation), and the obtained powder was charged into a container and sintered at 1000 ℃ for 1 hour in an electric furnace under a nitrogen atmosphere. Then, the sintered powder was transferred to a graphite crucible, and graphitized in a direct electric furnace at 3000 ℃ for 5 hours in an inert gas atmosphere to obtain a carbonaceous material (N). Petroleum heavy oil obtained by pyrolysis of naphtha is mixed with a carbonaceous material (N), and the mixture is subjected to carbonization treatment at 900 ℃ in an inert gas, and then the sintered product is subjected to classification treatment to obtain a carbonaceous material (O) in which the surfaces of graphite particles are coated with carbonaceous materials having different crystallinities. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed in. From the carbon residue ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite.
(preparation of negative electrode active Material 14)
In the same manner as in production 4 of the negative electrode active material except that scaly natural graphite was used instead of the carbonaceous material (a) in production 4 of the negative electrode active material, a composite carbonaceous material (P) coated with 5 parts by weight of a low-crystalline carbonaceous material relative to 95 parts by weight of graphite was obtained.
(preparation of negative electrode active Material 15)
The same procedure as in production 4 of the negative electrode active material was followed except that the petroleum-based heavy oil obtained in the pyrolysis of naphtha in production 14 of the negative electrode active material was reduced and mixed, and then the obtained powder was transferred to a graphite crucible and graphitized in a direct electric furnace at 3000 ℃ for 5 hours in an inert gas atmosphere. Then, the sintered product is subjected to a classification treatment to obtain a carbonaceous material (Q), and the composite carbonaceous material (Q) is obtained by coating carbonaceous materials having different crystallinities on the surfaces of graphite particles. In the classification treatment, the sieve was repeatedly sieved 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed. From the carbon residue ratio, it was confirmed that the obtained negative electrode active material powder was coated with 1 weight of the low crystalline carbonaceous material with respect to 99 weight parts of graphite.
(preparation of negative electrode active Material 16)
In the same manner as in preparation 4 of the negative electrode active material except that natural graphite having a volume average particle diameter of 48 μm was used instead of the carbonaceous material (a) in preparation 4 of the negative electrode active material, a composite carbonaceous material (R) coated with 5 parts by weight of a low-crystalline carbonaceous material relative to 95 parts by weight of graphite was obtained.
(preparation of negative electrode active Material 17)
A composite carbonaceous material (S) coated with 5 parts by weight of a low-crystallinity carbonaceous material relative to 95 parts by weight of graphite was obtained in the same manner as in production 4 of the negative electrode active material, except that natural graphite having a low degree of purification and 1% ash content remained was used instead of carbonaceous material (a) in production 4 of the negative electrode active material.
The physical properties of the obtained negative electrode active material are shown in Table 1 of negative electrode [1 ]. The method for measuring the physical properties is the same as described above.
Negative electrode [1] Table 1
[ Table 32]
Figure BDA0003109774980002531
Negative electrode [1] [ preparation of Battery ]
Preparation of Positive electrode 1
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an N-methylpyrrolidone solvent in an amount of 90 mass%2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having a positive electrode active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the positive electrode active material at this time was 2.35g/cm3。
Preparation of Positive electrode 2
A positive electrode was produced in the same manner as in production 1 of the positive electrode, except that the mass of the active material applied to each surface was 2 times that of production 1 of the positive electrode.
Preparation of Positive electrode 3
LiNi as a positive electrode active material was mixed in an N-methylpyrrolidone solvent in an amount of 90 mass%0.80Co0.15Al0.05O25 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 65 μm by a press, and cut into a shape having a positive electrode active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the positive electrode active material at this time was 2.35g/cm3。
Production of negative electrode 1
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration: 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (styrene-butadiene rubber concentration: 50 mass%) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the negative electrode active material at this time was 1.35g/cm 3。
Production of negative electrode 2
A negative electrode was produced in the same manner as in production 1 of the negative electrode, except that the mass of the active material applied to each surface was 2 times or more the amount used in production 1 of the negative electrode.
Preparation of negative electrode 3
Except that the density of the active material on the negative electrode side in production 1 was 1.70g/cm3Except for this, the negative electrode was produced in the same manner as in production 1 of the negative electrode.
Preparation of negative electrode 4
To 95 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration: 1 mass%) as a thickener and 8 parts by weight of an aqueous dispersion of styrene-butadiene rubber (styrene-butadiene rubber concentration: 50 mass%) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode. The active material density at this time was 1.35g/cm3。
Preparation of electrolyte solution 1
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of electrolyte solution 3
In a mixture of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a concentration of 1mol/L under a dry argon atmosphere (volume ratio 3:3:4)Dissolve well dried lithium hexafluorophosphate (LiPF)6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6)。
Production of Battery 1
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω).
Production of Battery 2
16 positive electrodes and 17 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 7 milliohms (m Ω).
Negative electrode [1] example 1
A battery was produced by the method in item "production of battery 1" using a negative electrode produced using the negative electrode active material in item "production of negative electrode 1" as a mixture (C) of two crystalline carbonaceous materials, a positive electrode produced in item "production of positive electrode 1" and an electrolyte produced in item "production of electrolyte 1". The measurement of the battery was carried out by the method described in the section "evaluation of battery" below and the above-mentioned measurement method.
Negative electrode [1] example 2
A battery was produced in the same manner as in example 1, except that the composite carbon material (D) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the evaluation of the battery described in item "evaluation of battery" was performed.
Negative electrode [1] example 3
A battery was produced in the same manner as in example 1, except that the composite carbon material (E) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 4
A battery was produced in the same manner as in example 1, except that the composite carbon material (F) was used as the negative electrode active material in item 1 of production of negative electrode, and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 5
A battery was produced in the same manner as in example 1, except that the composite carbon material (G) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the evaluation of the battery described in item "evaluation of battery" was performed.
Negative electrode [1] example 6
A battery was produced in the same manner as in example 1, except that the composite carbon material (J) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 7
A battery was produced in the same manner as in example 1, except that the composite carbon material (I) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 8
A battery was produced in the same manner as in example 1, except that the composite carbon material (M) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the evaluation of the battery described in item "evaluation of battery" was performed.
Negative electrode [1] example 9
A battery was produced in the same manner as in example 1, except that the composite carbon material (R) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the evaluation of the battery described in item "evaluation of battery" was performed.
Negative electrode [1] example 10
A battery was produced in the same manner as in example 1, except that the composite carbon material (L) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 11
A battery was produced in the same manner as in example 1, except that the composite carbon material (S) was used as the negative electrode active material in item 1 of production of negative electrode, and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 12
A battery was produced in the same manner as in example 1, except that the composite carbon material (O) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the evaluation of the battery described in item "evaluation of battery" was performed.
Negative electrode [1] example 13
A battery was produced in the same manner as in example 1, except that the composite carbon material (P) was used as the negative electrode active material in item 1 of production of negative electrode, and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 14
A battery was produced in the same manner as in example 1, except that the composite carbon material (Q) was used as the negative electrode active material in item "production of negative electrode 1" of negative electrode [1], and the evaluation of the battery described in item "evaluation of battery" was performed.
Negative electrode [1] example 15
A battery was produced by the method in item 2 for production of battery, using a negative electrode produced using the negative electrode active material in item 2 for production of negative electrode as the composite carbonaceous material (D), a positive electrode produced in item 2 for production of positive electrode, and an electrolyte produced in item 1 for production of electrolyte. Further, evaluation of the battery was performed in the same manner as in example 1 of the negative electrode [1 ].
Negative electrode [1] example 16
A battery was produced by the method in item "production of battery 1" using a negative electrode produced using the negative electrode active material in item "production of negative electrode 3" as the composite carbonaceous material (D), a positive electrode produced in item "production of positive electrode 1", and an electrolyte produced in item "production of electrolyte 1". Further, evaluation of the battery was performed in the same manner as in example 1 of the negative electrode [1 ].
Negative electrode [1] example 17
A battery was produced by the method in item "production of battery 1" using a negative electrode produced using the negative electrode active material in item "production of negative electrode 4" as the composite carbonaceous material (D), a positive electrode produced in item "production of positive electrode 1", and an electrolyte produced in item "production of electrolyte 1". Further, evaluation of the battery was performed in the same manner as in example 1 of the negative electrode [1 ].
Negative electrode [1] example 1 to negative electrode [1] the evaluation results of example 17 are shown in negative electrode [1] table 2.
Examples 18 to 34 of negative electrode [1]
Evaluation of the battery was carried out in the same manner as described above except that the electrolytes of examples 1 to 17 of negative electrode [1] were replaced with the electrolyte prepared in section "preparation of electrolyte 2". Negative electrode [1] example 18 to negative electrode [1] example 34 evaluation results are shown in negative electrode [1] table 3.
Examples 35 to 51 of negative electrodes [1]
Evaluation of the battery was carried out in the same manner as described above except that the electrolytes of examples 1 to 17 of negative electrode [1] were replaced with the electrolyte prepared in section "preparation of electrolyte 3". Negative electrode [1] example 35 to negative electrode [1] example 51 evaluation results are shown in negative electrode [1] table 4.
Negative electrode [1] comparative example 1
A battery was produced in the same manner as in negative electrode [1] example 1, except that the carbonaceous material (a) was used as the negative electrode active material in negative electrode production 1, and the battery evaluation described in battery evaluation was performed.
Negative electrode [1] comparative example 2
Batteries were produced in the same manner as in the negative electrode [1] comparative example 1 except that the electrolyte solution produced in section "production of electrolyte solution 4" was used, and the battery evaluation described in section "evaluation of battery" was performed.
Negative electrode [1] comparative example 3
A battery was produced in the same manner as in negative electrode [1] example 1, except that the carbonaceous material (B) was used as the negative electrode active material in negative electrode production 1, and the battery evaluation described in battery evaluation was performed.
Negative electrode [1] comparative example 4
A battery was produced in the same manner as in negative electrode [1] comparative example 3, except that the electrolyte solution produced in "production of electrolyte solution 4" was used as the electrolyte solution of negative electrode [1] comparative example 3, and the battery evaluation described in "evaluation of battery" was performed.
Negative electrode [1] comparative example 5
A battery was produced in the same manner as in example 1 of negative electrode [1], except that the electrolyte solution produced in example 1 of negative electrode [1] was the electrolyte solution produced in item "production of electrolyte solution 4", and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] comparative example 6
A battery was produced in the same manner as in negative electrode [1] example 2 except that the electrolyte solution produced in item "production of electrolyte solution 4" was used, and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] comparative example 7
A battery was produced in the same manner as in example 1, except that the carbonaceous material (K) was used as the negative electrode active material in item 1 of production of negative electrode, and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] comparative example 8
Batteries were produced in the same manner as in the negative electrode [1] comparative example 7 except that the electrolyte solution produced in section "production of electrolyte solution 4" was used, and the battery evaluation described in section "evaluation of battery" was performed.
Negative electrode [1] comparative examples 9 to 11
Batteries were evaluated in the same manner as in comparative examples 1, 3 and 7 except that the electrolyte solutions of the negative electrode [1] were changed to the electrolyte solution prepared in item "preparation of electrolyte solution 2".
Negative electrode [1] comparative examples 12 to 14
Batteries were evaluated in the same manner as in comparative examples 1, 3 and 7 except that the electrolyte solutions of the negative electrode [1] were changed to the electrolyte solution prepared in item "preparation of electrolyte solution 3".
The evaluation results of comparative example 1 of negative electrode [1] to comparative example 14 of negative electrode [1] are shown in Table 5 of negative electrode [1 ].
Negative electrode [1] example 52
A battery was produced by the method in item "production of battery 1" using a negative electrode produced using the negative electrode active material in item "production of negative electrode 1" as the composite carbonaceous material (D), a positive electrode produced in item "production of positive electrode 1", and an electrolyte produced in item "production of electrolyte 1", and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [1] example 53
A battery was produced in the same manner as in example 52, except that the electrolyte solution produced in section "production of electrolyte solution 2" was used, and the battery evaluation described in section "evaluation of battery" was performed.
Negative electrode [1] example 54
A battery was produced in the same manner as in example 52, except that the electrolyte solution prepared in section "preparation of electrolyte solution 3" was used, and the battery evaluation described in section "evaluation of battery" was performed.
Negative electrode [1] comparative example 15
A battery was produced in the same manner as in example 52, except that the electrolyte solution prepared in section "preparation of electrolyte solution 4" was used, and the battery evaluation described in section "evaluation of battery" was performed.
The evaluation results of examples 52 to 54 and comparative example 15 are shown in the negative electrode [1] Table 6.
Negative electrode [1] evaluation of Battery
(Capacity measurement)
For a battery not subjected to charge/discharge cycles, initial charge/discharge was carried out for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle in this case was set as the initial capacity. The output power measurements shown below were then performed.
(measurement of output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage line and a lower limit voltage (3V) is used as the output power (W).
(cycle test)
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.2V by the constant current-constant voltage method of 2C, discharging to the end-of-discharge voltage of 3.0V by the constant current of 2C as one charge-discharge cycle, and the cycle was repeated up to 500 cycles. The battery after the end of the cycle test was charged and discharged for 3 cycles in an environment at 25 ℃, and the 0.2C discharge capacity of the 3 rd cycle was taken as the capacity after the cycle. The cycle retention rate was determined from the initial capacity measured before the cycle and the capacity after the cycle measured after the end of the cycle test by the following calculation formula.
Cycle retention (%) > 100 × capacity after cycle/initial capacity
The output measurement described in the item (output measurement) was performed on the battery after the end of the cycle test. At this time, the output power retention ratio shown in the following equation was calculated using the output power before the cycle test and the output power performed after the cycle test was completed.
Output power holding ratio (%) (100 × output power after completion of cycle test/output power before cycle test)
The impedance Rct and the double layer capacity Cdl in the negative electrode [1] table 2 are one of parameters contributing to the output power, and the smaller the value of the impedance Rct is, or the larger the value of the double layer capacity Cdl is, the more the output power tends to be improved. The "impedance Rct" and the "double-layer capacitance Cdl" are obtained by the methods described in the section describing the impedance.
Negative electrode [1] Table 2
[ Table 33]
Figure BDA0003109774980002611
Cathode [1]]In Table 2, the electrolyte contained 0.3 mass% of lithium difluorophosphate (LiPO) prepared in "preparation of electrolyte 12F2)。
Negative electrode [1] Table 3
[ Table 34]
Figure BDA0003109774980002621
Negative electrode [1] in Table 3, the electrolyte solution contained 0.3 mass% of trimethylsilyl methanesulfonate prepared in "preparation of electrolyte solution 2".
Negative electrode [1] Table 4
[ Table 35]
Figure BDA0003109774980002631
Negative electrode [1] in Table 4, the electrolyte solution contained 0.3 mass% of hexamethylcyclotrisiloxane produced in "production of electrolyte solution 3".
Negative electrode [1] Table 5
[ Table 36]
Figure BDA0003109774980002641
Negative electrode [1] Table 6
Watch [36]
Figure BDA0003109774980002642
From the results of tables 2 to 6 of the negative electrode [1], it was found that the output retention rate after the cycle can be dramatically improved by combining the case of containing lithium difluorophosphate, trimethylsilyl methanesulfonate, and hexamethylcyclotrisiloxane and the case of containing 2 or more carbonaceous materials having different crystallinities as the negative electrode active material.
Negative electrode [2] [ preparation of negative electrode active Material ]
(preparation of negative electrode active Material 1)
Coal tar pitch having a quinoline insoluble content of 0.05 mass% or less was heat-treated at 460 ℃ for 10 hours in a reaction furnace, the obtained bulk carbonaceous material was pulverized with a pulverizer (origin mill manufactured by seishin corporation), and the pulverized material was finely pulverized with a micro-pulverizer (turbo mill manufactured by matsubo corporation) to a median particle diameter of 18 μm. The particles were charged into a metal container and heat-treated at 540 ℃ for 2 hours in a box-shaped electric furnace under a nitrogen flow. The obtained cake was pulverized by a coarse pulverizer (roll crusher, manufactured by yota corporation), then finely pulverized by a fine pulverizer (turbine mill, manufactured by matsubo corporation), and the obtained powder was charged into a container and fired in an electric furnace at 1000 ℃ for 1 hour under a nitrogen atmosphere. Then, the obtained sintered product is subjected to classification treatment, thereby obtaining amorphous carbonaceous material (a). In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed in.
(preparation of negative electrode active Material 2)
The coal tar pitch having a quinoline-insoluble content of 0.05 mass% or less was subjected to a heat treatment in a reaction furnace at 460 ℃ for 10 hours, and the obtained cake was placed in a container and subjected to a heat treatment in a box-shaped electric furnace at 1000 ℃ for 2 hours under a nitrogen atmosphere. Then, the obtained sintered product is subjected to classification treatment, thereby obtaining amorphous carbonaceous material (a). The obtained amorphous bulk material was pulverized by a coarse pulverizer (roll crusher manufactured by yota corporation), and then finely pulverized by a fine pulverizer (turbine mill manufactured by matsubo corporation) to obtain an amorphous powder. In order to prevent the resultant powder from being mixed with coarse particles, the sieve was repeatedly sieved 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as the amorphous carbon material (B).
(preparation of negative electrode active Material 3)
The amorphous bulk material obtained in (preparation 2 of negative electrode active material) was transferred to a graphite crucible, and heat-treated at 2200 ℃ for 5 hours in an inert gas atmosphere using a direct electric furnace, the obtained bulk material was pulverized with a coarse pulverizer (roll crusher, manufactured by yota corporation), and then finely pulverized with a fine pulverizer (turbine mill, manufactured by matsubo corporation), and the obtained powder was repeatedly sieved 5 times with a sieve of ASTM400 mesh to prevent coarse particles from being mixed. The negative electrode active material thus obtained was used as amorphous carbon material (C).
(preparation of negative electrode active Material 4)
The amorphous bulk material obtained in (preparation 2 of negative electrode active material) was transferred to a graphite crucible, graphitized at 3000 ℃ for 5 hours in an inert gas atmosphere using a direct electric furnace, the obtained bulk material was pulverized with a coarse pulverizer (roll crusher, manufactured by yota corporation), and then finely pulverized with a fine pulverizer (turbo mill, manufactured by matsubo corporation), and the obtained powder was repeatedly sieved 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed therein. The negative electrode active material thus obtained was used as an amorphous carbonaceous material (D).
(preparation of negative electrode active Material 5)
In order to prevent coarse particles from being mixed into the commercially available flaky natural graphite powder, the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as an amorphous carbon material (E).
The properties, shapes, and the like of the negative electrode active materials obtained in production 1 to 5 of the negative electrode active material were measured by the methods described above. The results are shown in the negative electrode [2] Table 1.
Negative electrode [2] Table 1
[ Table 37]
Figure BDA0003109774980002661
Negative electrode [2] [ preparation of Battery ]
Preparation of Positive electrode 1
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an N-methylpyrrolidone solvent in an amount of 90 mass%2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the positive electrode active material at this time was 2.35g/cm3。
Production of negative electrode 1
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration: 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (styrene-butadiene rubber concentration: 50 mass%) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the negative electrode active material at this time was 1.35g/cm 3。
Production of nonaqueous electrolyte solution 1
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of nonaqueous electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of nonaqueous electrolyte solution 3
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of nonaqueous electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6)。
Production of Battery 1
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω). The ratio of the sum of the electrode areas of the positive electrode to the sum of the surface areas of the battery case was 20.6.
Negative electrode [2] example 1
A battery was produced by the method in item "production of battery 1" using the negative electrode active material in item "production of negative electrode 1" as the negative electrode produced from amorphous carbon material (a), the positive electrode produced in item "production of positive electrode 1" and the electrolyte produced in item "production of electrolyte 1". The battery was evaluated by the method described in the following item "evaluation of battery". The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] example 2
A battery was produced in the same manner as in example 1 of negative electrode [2] except that amorphous carbon (B) was used as the negative electrode active material in item "production of negative electrode 1", and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] example 3
A battery was produced in the same manner as in example 1 of negative electrode [2] except that amorphous carbon (C) was used as the negative electrode active material in item "production of negative electrode 1", and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] examples 4 to 6
Batteries were produced and evaluated in the same manner as in the production of nonaqueous electrolyte solution 2 except that the nonaqueous electrolyte solution of examples 1 to 2 of negative electrode [2] was replaced with the nonaqueous electrolyte solution produced in the production of nonaqueous electrolyte solution 2. The results are shown in the negative electrode [2] Table 2.
Examples 7 to 9 of the negative electrode [2]
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 3 except that the nonaqueous electrolyte solutions of examples 1 to 3 of negative electrode [2] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] comparative examples 1 to 3
Batteries were produced and evaluated in the same manner as in production 4 of nonaqueous electrolyte solution except that the nonaqueous electrolyte solutions of comparative examples 1 to 3 of negative electrode [2] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] comparative example 4
A battery was produced in the same manner as in example 1 of negative electrode [2] except that graphite carbonaceous (D) was used as the negative electrode active material in item "production of negative electrode 1", and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] comparative example 5
A battery was produced in the same manner as in example 1 of negative electrode [2] except that the graphite carbonaceous material (E) was used as the negative electrode active material in item "production of negative electrode 1", and the evaluation of the battery described in item "evaluation of battery" was performed. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] comparative examples 6 to 7
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 2 except that the nonaqueous electrolyte solutions of comparative examples 4 to 5 in the negative electrode [2] were replaced with the nonaqueous electrolyte solutions produced in production of nonaqueous electrolyte solutions. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] comparative examples 8 to 9
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 3 except that the nonaqueous electrolyte solutions of comparative examples 4 to 5 of negative electrode [2] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] comparative examples 10 to 11
Batteries were produced and evaluated in the same manner as in production 4 of nonaqueous electrolyte solution except that the nonaqueous electrolyte solutions of comparative examples 4 to 5 of negative electrodes [2] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [2] Table 2.
Negative electrode [2] evaluation of Battery
(Capacity measurement)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles (voltage range 4.1V to 3.0V) at 25 ℃ in a voltage range of 4.1V to 3.0V. At this time, 0.2 (the current value of the 1-hour discharge rated capacity, which is determined by the discharge capacity of the 1-hour rate (one-hour-rate), hereinafter the same) C discharge capacity of the 5 th cycle was used as the initial capacity.
(short-time high-current density charge-discharge characteristics test)
The battery after the capacity measurement was charged with a constant current of 0.2C for 150 minutes at 25 ℃ in a room temperature environment. The test was continuously repeated for one cycle of 35 seconds including the rest time by applying a high load current of 10C for about 10 seconds in both the charging direction and the discharging direction, with the voltage at this time as the center. At the time of 10 ten thousand cycles, the battery was taken out, discharged to 3V at a current of 0.2C, and subjected to 1 cycle as a capacity after the cycle in the same manner as in the item (capacity measurement). The short-time high-current-density charge/discharge characteristics were calculated by the following equation.
[ short-time high-current density charge-discharge characteristics ] × [ capacity after cycle ]/[ initial capacity ]
Negative electrode [2] Table 2
[ Table 38]
Figure BDA0003109774980002701
From the results of table 2 of the negative electrode [2], it is understood that the short-time high-current density charge/discharge characteristics can be dramatically improved by containing lithium difluorophosphate, trimethylsilyl methanesulfonate, and hexamethylcyclotrisiloxane, and by containing, as a negative electrode active material, amorphous carbonaceous material having a (002) plane surface pitch (d002) of 0.337 or more, an Lc of 80nm or less, and a raman R value of 0.2 or more as measured by a wide-angle X-ray diffraction method.
Negative electrode [3] [ preparation of negative electrode active Material ]
(preparation of negative electrode active Material 1)
In order to prevent the coarse particles from being mixed, commercially available Li having a volume average particle diameter of 23 μm was sieved using a sieve of ASTM400 mesh1.33Ti1.66O4And repeating the sieving for 5 times to obtain the lithium-titanium composite oxide (A).
(preparation of negative electrode active Material 2)
In order to prevent the coarse particles from being mixed, commercially available Li having a volume average particle diameter of 1.0 μm was sieved using an ASTM400 mesh sieve1.33Ti1.66O4And repeating the sieving for 5 times to obtain the lithium-titanium composite oxide (B).
(preparation of negative electrode active Material 3)
In order to prevent the coarse particles from being mixed, commercially available Li having a volume average particle diameter of 0.1 μm was sieved using an ASTM400 mesh sieve1.33Ti1.66O4Repetition ofAnd sieving for 5 times to obtain the lithium-titanium composite oxide (C).
(preparation of negative electrode active Material 4)
In order to prevent coarse particles from being mixed into the commercially available flaky natural graphite powder, the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as the graphite carbonaceous material (D).
The composition, structure, shape, physical properties and the like of the negative electrode active material are summarized in Table 1 of negative electrode [3 ].
Negative electrode [3] Table 1
[ Table 39]
Figure BDA0003109774980002711
Negative electrode [3] [ preparation of Battery ]
Preparation of Positive electrode 1
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an N-methylpyrrolidone solvent in an amount of 90 mass%2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the active material of the positive electrode at this time was 2.35g/cm3。
Production of negative electrode 1
A slurry was prepared by mixing 90 mass% of a negative electrode active material, 5 mass% of acetylene black as a conductive material, and 5 mass% of polyvinylidene fluoride (PVdF) as a binder in an N-methylpyrrolidone solvent. The obtained slurry was applied to one surface of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 90 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode.
Production of nonaqueous electrolyte solution 1
Under dry argon atmosphere, in carbonIn a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC), lithium hexafluorophosphate (LiPF) which was sufficiently dried was dissolved at a concentration of 1mol/L6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of nonaqueous electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of nonaqueous electrolyte solution 3
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of nonaqueous electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6)。
(production of Battery 1)
The negative electrode and the positive electrode were punched out to 12.5mm phi, vacuum-dried at 110 ℃, and then transferred to a glove box, and the positive electrode and the negative electrode were placed in opposition to each other with a polyethylene separator punched out to 14mm phi under argon atmosphere, and the nonaqueous electrolytic solution described in the section of the production of the nonaqueous electrolytic solution was added to produce a 2032 type coin battery (lithium secondary battery).
Negative electrode [3] example 1
A battery was produced by the method described in section 1 of production of battery, using a negative electrode produced by using the lithium-titanium composite oxide (a) as the negative electrode active material described in section 1 of production of negative electrode, a positive electrode produced in section 1 of production of positive electrode, and an electrolyte produced in section 1 of production of nonaqueous electrolyte. The battery was evaluated as described in the following item "evaluation of battery". The results are shown in the negative electrode [3] Table 2.
Negative electrode [3] example 2
A battery was produced in the same manner as in example 1 of negative electrode [3], except that the lithium titanium composite oxide (B) was used as the negative electrode active material in example 1 of negative electrode [3] and example 1, and the evaluation of the battery described in evaluation of battery. The results are shown in the negative electrode [3] Table 2.
Negative electrode [3] embodiment 3
A battery was produced in the same manner as in example 1 of negative electrode [3], except that the lithium titanium composite oxide (C) was used as the negative electrode active material in example 1 of negative electrode [3] and example 1, and the evaluation of the battery described in evaluation of battery. The results are shown in the negative electrode [3] Table 2.
Negative electrode [3] examples 4 to 6
Batteries were produced and evaluated in the same manner as in the production of nonaqueous electrolyte solution 2 except that the nonaqueous electrolyte solutions of examples 1 to 3 of negative electrode [3] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [3] Table 2.
Examples 7 to 9 of the negative electrode [3]
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 3 except that the nonaqueous electrolyte solutions of examples 1 to 3 of negative electrode [3] were replaced with the nonaqueous electrolyte solutions produced in the above. The results are shown in the negative electrode [3] Table 2.
Negative electrode [3] comparative examples 1 to 3
Batteries were produced and evaluated in the same manner as in production 4 of nonaqueous electrolyte solution except that the nonaqueous electrolyte solutions of examples 1 to 3 of negative electrode [3] were replaced with the nonaqueous electrolyte solutions produced in the above. The results are shown in the negative electrode [3] Table 2.
Negative electrode [3] comparative example 4
A battery was produced in the same manner as in example 1 of negative electrode [3], except that graphite carbonaceous (D) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [3], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [3] Table 2.
Negative electrode [3] comparative example 5
Batteries were produced and evaluated in the same manner as in item 2 "production of nonaqueous electrolyte solution" except that the nonaqueous electrolyte solution of comparative example 4 was replaced with the nonaqueous electrolyte solution of negative electrode [3 ]. The results are shown in negative [3] Table 2.
Negative electrode [3] comparative example 6
Batteries were produced and evaluated in the same manner as in item 3 "production of nonaqueous electrolyte solution" except that the nonaqueous electrolyte solution of comparative example 4 was replaced with the nonaqueous electrolyte solution of negative electrode [3 ]. The results are shown in negative [3] Table 2.
Negative electrode [3] comparative example 7
Batteries were produced and evaluated in the same manner as in item 4 "production of nonaqueous electrolyte solution" except that the nonaqueous electrolyte solution of comparative example 4 in the negative electrode [3] was replaced with the nonaqueous electrolyte solution. The results are shown in negative [3] Table 2.
Negative electrode [3] evaluation of Battery
(measurement of Capacity)
The capacity of the new battery which was not subjected to charge-discharge cycles was calculated from the amount of the active material present on the copper foil in terms of 175mAh/g of the lithium-titanium composite oxide and 350mAh/g of the graphite carbon. And, based on the battery capacity, the lithium titanium composite oxide was initially charged and discharged for 5 cycles at a voltage range of 2.7V to 1.9V at 25 ℃. Similarly, the graphite carbon is subjected to initial charge and discharge at 25 ℃ and a voltage ranging from 4.1V to 3.0V. The 0.2C discharge capacity at the 5 th cycle at this time was set as the initial capacity.
(measurement of output resistance)
The charging was carried out at 25 ℃ for 150 minutes by a constant current of 0.2C, and the discharge was carried out at-30 ℃ for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C and 10.0C, respectively, to measure the voltage at 10 th second. The slope of the current-voltage line was taken as the output resistance (Ω), and the results are shown in table 2 for the negative electrode [3 ].
Negative electrode [3] Table 2
[ Table 40]
Figure BDA0003109774980002751
In the negative electrode [3] table 2, the "output resistance reduction rate" is a reduction rate (%) of the output resistance compared with the output resistance of a corresponding battery containing no specific compound.
As is clear from the results of the negative electrode [3] table 2, the use of a negative electrode active material containing lithium difluorophosphate, trimethylsilyl methanesulfonate, hexamethylcyclotrisiloxane, and a metal oxide containing titanium capable of occluding and releasing lithium can dramatically reduce the output resistance.
Negative electrode [4] [ preparation of negative electrode active Material ]
(preparation of negative electrode active Material 1)
High-purity flaky natural graphite (ash content 0.05 wt%) having a median particle size of about 150 μm was spheroidized at 6500rpm for 5 minutes using a spheroidizing apparatus (mixing system manufactured by Nara machinery Co., Ltd.), and 45 wt% of fine powder was removed using an air classifier (OMC-100 manufactured by Seishin Ltd.) to obtain spheroidized natural graphite (C).
(preparation of negative electrode active Material 2)
The classified powder of the spheroidized natural graphite (C) was charged into a graphite crucible, and heat-treated at 3000 ℃ for 5 hours in an inert atmosphere using a direct electric furnace to obtain a carbonaceous material (D).
(preparation of negative electrode active Material 3)
A carbonaceous material (E) was obtained in the same manner except that the heat treatment temperature in (preparation of negative electrode active material 2) was set to 2000 ℃.
(preparation of negative electrode active Material 4)
A carbonaceous material (F) was obtained in the same manner except that the heat treatment temperature in (preparation of negative electrode active material 2) was set to 1600 ℃.
(preparation of negative electrode active Material 5)
A carbonaceous material (G) was obtained in the same manner except that the heat treatment temperature in (preparation of negative electrode active material 2) was set to 1200 ℃.
(preparation of negative electrode active Material 5)
The high-purity treated medium particle diameter is 17 μm, and the tap density is 0.5g/cm3BET specific surface area 6m2The flaky natural graphite (ash content 0.1 wt%) was heat-treated in the same manner as in (preparation of negative electrode active material 2) without spheroidizing to obtain heat-treated natural graphite (H).
(preparation of negative electrode active Material 6)
The high-purity treated medium particle diameter is 20 μm, and the tap density is 0.75g/cm 3BET specific surface area 3m2The natural graphite (ash content 0.5 wt%) was subjected to heat treatment without spheroidization as it is (preparation of negative electrode active material 2) to obtain carbonaceous material (I).
The shapes and physical properties of the prepared spheroidized natural graphite (C), carbonaceous material (D), carbonaceous material (E), carbonaceous material (F), carbonaceous material (G), heat-treated natural graphite (H), and carbonaceous material (I) were measured by the above-described methods. The results are shown in the negative electrode [4] Table 1.
Negative electrode [4] Table 1
Figure BDA0003109774980002771
Negative electrode [4] [ preparation of Battery ]
Preparation of Positive electrode 1
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an N-methylpyrrolidone solvent in an amount of 90 mass%2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width,as the positive electrode. The density of the active material of the positive electrode at this time was 2.35g/cm3。
Production of negative electrode 1
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration: 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (styrene-butadiene rubber concentration: 50 mass%) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the active material of the negative electrode at this time was 1.35g/cm 3。
Production of nonaqueous electrolyte solution 1
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of nonaqueous electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of nonaqueous electrolyte solution 3
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of nonaqueous electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6)。
(production of Battery 1)
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω). The ratio of the sum of the electrode areas of the positive electrode to the sum of the surface areas of the battery case was 20.6.
Negative electrode [4] example 1
A battery was produced by the method in item 1 for production of a battery, using a negative electrode produced using the negative electrode active material in item 1 for production of a negative electrode as a carbonaceous material (D), a positive electrode produced in item 1 for production of a positive electrode, and a nonaqueous electrolytic solution produced in item 1 for production of a nonaqueous electrolytic solution. The measurement of the battery was carried out by the method described in the section "evaluation of battery" below and the above-mentioned measurement method. The results are shown in Table 2 for negative electrode [4 ].
Negative electrode [4] example 2
A battery was produced in the same manner as in example 1 of negative electrode [4], except that carbonaceous material (E) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [4], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] example 3
A battery was produced in the same manner as in example 1 of negative electrode [4], except that the carbonaceous material (F) was used as the negative electrode active material in example 1 of negative electrode [4] and evaluation of the battery was performed as described in evaluation of battery. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] example 4
A battery was produced in the same manner as in example 1 of negative electrode [4], except that carbonaceous material (G) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [4], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] example 5
A battery was produced in the same manner as in example 1 of negative electrode [4], except that carbonaceous material (I) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [4], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [4] Table 2.
Examples 6 to 10 of negative electrode [4]
Batteries were produced and evaluated in the same manner as in preparation of nonaqueous electrolyte solution 2 except that the nonaqueous electrolyte solutions of examples 1 to 5 in negative electrode [4] were each replaced with a nonaqueous electrolyte solution. The results are shown in Table 2 (negative electrode [4] Table 2).
Examples 11 to 15 of negative electrode [4]
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 3 except that the nonaqueous electrolyte solutions of examples 1 to 5 in negative electrode [4] were each replaced with a nonaqueous electrolyte solution. The results are shown in negative [4] Table 2.
Negative electrode [4] comparative example 1
A battery was produced in the same manner as in example 1 of negative electrode [4], except that spheroidized natural graphite (C) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [4], and the evaluation of the battery described in item "evaluation of battery" was performed. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] comparative example 2
A battery was produced in the same manner as in comparative example 1 of negative electrode [4], except that the nonaqueous electrolytic solution produced in comparative example 1 of negative electrode [4] was the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] comparative example 3
A battery was produced in the same manner as in example 1 of negative electrode [4], except that heat-treated natural graphite (H) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [4], and evaluation of the battery described in item "evaluation of battery" was performed. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] comparative example 4
A battery was produced in the same manner as in comparative example 3 of negative electrode [4], except that the nonaqueous electrolytic solution produced in comparative example 3 of negative electrode [4] was the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] comparative example 5
A battery was produced in the same manner as in example 5 of negative electrode [4] except that the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4" was used as the nonaqueous electrolytic solution of example 5 of negative electrode [4], and the battery evaluation described in item "evaluation of Battery" was carried out. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] comparative example 6
A battery was produced in the same manner as in example 1 of negative electrode [4], except that the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4" was used as the nonaqueous electrolytic solution of example 1 of negative electrode [4], and the battery evaluation described in item "evaluation of Battery" was carried out. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] comparative examples 7 and 8
Batteries were produced and evaluated in the same manner as in comparative examples 1 and 3 of negative electrode [4] except that the nonaqueous electrolytic solutions prepared in section "production of nonaqueous electrolytic solution 2" were used. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] comparative examples 9 and 10
Batteries were produced and evaluated in the same manner as in comparative examples 1 and 3 of negative electrode [4] except that the nonaqueous electrolytic solutions prepared in section "production of nonaqueous electrolytic solution 3" were used. The results are shown in the negative electrode [4] Table 2.
Negative electrode [4] Table 2
Figure BDA0003109774980002821
Negative electrode [4] evaluation of Battery
(Capacity measurement)
For a battery not subjected to charge/discharge cycles, initial charge/discharge was carried out for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle in this case was set as the initial capacity.
(preservation test)
The storage is performed under a high temperature environment of 60 ℃ which is regarded as the practical use upper limit temperature of the lithium secondary battery. The cells were charged by a constant current and constant voltage method of 0.2C until the capacity reached 20% of the initial capacity measured at the time of capacity measurement and reached an upper charge limit voltage of 4.2V, and then stored at a high temperature of 60 ℃ for 1 week. The battery after storage was discharged to 3V at 0.2C in an environment of 25 ℃, and further, charge and discharge were performed for 3 cycles under the same conditions as (capacity measurement), and the 0.2C discharge capacity of the 3 rd cycle was taken as the low charge depth storage capacity. The cycle retention rate was calculated from the initial capacity measured before the storage test and the low charge depth after storage capacity measured after the storage test according to the following calculation formula.
Recovery after low-charge deep storage (%) (100 × capacity after low-charge deep storage/initial capacity)
From the above results, it was found that by using a negative electrode containing a carbonaceous material containing a lithium difluorophosphate, trimethylsilyl methanesulfonate, and hexamethylcyclotrisiloxane and having a circularity of 0.85 or more and a surface functional group amount O/C of 0 to 0.01 as a negative electrode active material, the recovery rate after storage at a low charge depth after a storage test at a low charge depth can be dramatically improved.
Negative electrode [5] [ preparation of negative electrode Material ]
[ production of negative electrode Material 1]
A coal tar pitch having a quinoline insoluble content of 0.05 mass% or less is subjected to a heat treatment at 460 ℃ for 10 hours in a reaction furnace to obtain a massive heat-treated graphite crystal precursor having a softening point of 385 ℃ and a melting property. The obtained block-shaped heat-treated graphite crystal precursor was pulverized by an intermediate pulverizer (origin mill manufactured by seishin corporation), and then finely pulverized by a micro-pulverizer (turbine mill manufactured by matsubo corporation), thereby obtaining a finely pulverized graphite crystal precursor powder (E) having a median particle diameter of 17 μm.
In the finely divided graphite crystal precursor powder (E), a median particle diameter of 17 μm, a major axis ratio of 1.4 and a tap density of 1.0g/cm were mixed in a proportion of 50% by mass based on the total weight of the finely divided graphite crystal precursor powder and natural graphite 3The BET specific surface area was 6.5g/cm3And natural graphite having a circularity of 0.92 to obtain a mixed powder.
The mixed powder of the heat-treated graphite crystal precursor was charged into a metal container, and heat treatment A was carried out in a box-shaped electric furnace at 540 ℃ for 2 hours under a nitrogen flow. In the heat treatment a, the finely divided graphite crystal precursor powder is melted to form a mass of a mixture of heat-treated graphite crystal precursors which is uniformly combined with natural graphite.
The solidified heat-treated graphite crystal precursor mixture was pulverized by a coarse pulverizer (roll crusher, manufactured by yota corporation), and then finely pulverized by a fine pulverizer (turbine mill, manufactured by matsubo corporation), to obtain a powder having a median particle diameter of 18.5 μm.
The obtained powder was charged into a container and fired at 1000 ℃ for 1 hour in an electric furnace under a nitrogen atmosphere. After firing, the obtained powder (precursor mixture (F) before heat treatment B) was still in the form of powder, and melting and fusion were hardly observed.
The fired powder was transferred to a graphite crucible, graphitized at 3000 ℃ for 5 hours in an inert atmosphere using a direct electric furnace, and the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed, thereby obtaining a heterograin carbon composite (G).
[ production of negative electrode Material 2]
The natural graphite used in [ production 1 of negative electrode material ] and binder pitch having a softening point of 88 ℃ as a graphitizable binder were mixed at a weight ratio of 100:30, and put into a kneader having a kneader type stirring blade heated to 128 ℃ in advance, and mixed for 20 minutes.
Filling the well kneaded mixture into a mold of a molding press preheated to 108 ℃ in advance, standing for 5 minutes, pressing a plunger while the temperature of the mixture is stabilized, and applying 2kfg/cm2Molding was carried out under a pressure of (0.20 MPa). After the pressure was maintained for 1 minute, the driving was stopped, and after the pressure reduction was completed, the molded body obtained by compounding the natural graphite and the graphite crystal precursor powder was taken out.
The obtained molded body was charged into a refractory metal box as a heat-resistant container, and the gap was filled with graphite coke powder. Heating from room temperature to 1000 deg.C for 48 hr, holding at 1000 deg.C for 3 hr, devolatilizing, and firing. Next, the molded body was placed in a graphite crucible, and the gap was filled with graphite coke powder, and the molded body was heated at 3000 ℃ for 4 hours in an inert atmosphere using a direct electric furnace to be graphitized.
The obtained graphite molded article was coarsely pulverized by a jaw crusher and then finely pulverized by a mill having a pulverizing blade rotation speed of 4000 rpm. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed, and the heterograin carbon composite (H) was obtained.
[ production of negative electrode Material 3]
A heteroepitaxial carbon composite (I) was obtained in the same manner as in [ preparation of negative electrode material 2] except that the heat treatment using a direct electric furnace of [ preparation of negative electrode material 2] was performed at 2200 ℃.
[ production of negative electrode Material 4]
Except that [ preparation of negative electrode Material 2]]The natural graphite has a median particle diameter of 10 μm, a length-diameter ratio of 2.3, and a tap density of 0.64g/cm3A BET specific surface area of 9.5m2(ii) coke having a circularity of 0.83 other than thatAnd preparation of cathode Material 2]Similarly, a heteroepitaxial carbon composite (J) was obtained.
[ production of negative electrode Material 5]
A heterograin carbon composite (K) was obtained in the same manner as in [ preparation of negative electrode material 2] except that coke used in [ preparation of negative electrode material 4], silicon carbide as a graphitization catalyst, and binder pitch having a softening point of 88 ℃ as a graphitizable binder were mixed at a mass ratio of 100:10: 30.
[ production of negative electrode Material 6]
Except that [ preparation of negative electrode Material 2]]The natural graphite has a median particle diameter of 19.8 μm, a length-diameter ratio of 3.2, and a tap density of 0.47g/cm3A BET specific surface area of 5.9m2(ii) preparation of negative electrode Material 2 except for flaky Natural graphite having circularity of 0.81 ]Similarly, a heteroepitaxial carbon composite (L) was obtained.
[ production of negative electrode Material 7]
Except that [ preparation of negative electrode Material 2]]The natural graphite has a median particle diameter of 35 μm, a length-diameter ratio of 1.4, and a tap density of 1.02g/cm3A BET specific surface area of 3.9m2(g) natural graphite having a circularity of 0.90 and [ preparation of negative electrode Material 2]]Similarly, a heteroepitaxial carbon composite (M) was obtained.
[ production of negative electrode Material 8]
A heterograin carbon composite (N) was obtained in the same manner as in [ preparation of negative electrode material 2] except that the number of rotation of the pulverizing blade in [ preparation of negative electrode material 2] was set to 1500 rpm.
[ production of negative electrode Material 9]
Except that [ preparation of negative electrode Material 2]]The natural graphite has a median particle diameter of 6 μm, a length-diameter ratio of 1.5, and a tap density of 0.15g/cm3In addition to the natural graphite (2) and [ preparation of negative electrode Material]Similarly, a heteroepitaxial carbon composite (O) was obtained.
[ production of negative electrode Material 10]
The graphite crystal precursor powder (E) obtained in [ production of negative electrode material 1] was charged into a metal container, and heat treatment a was performed at 540 ℃ for 2 hours in a box-shaped electric furnace under nitrogen flow. In the heat treatment a, the graphite crystal precursor powder (E) is melted to be a bulk.
The solidified heat-treated graphite crystal precursor block was pulverized by a coarse pulverizer (roll crusher, manufactured by yota), and then finely pulverized by a fine pulverizer (turbine mill, manufactured by matsubo) to obtain a powder having a median particle diameter of 18.5 μm.
The obtained powder was placed in a container and fired at 1000 ℃ for 1 hour in an electric furnace under a nitrogen atmosphere. After firing, the obtained powder was in the form of powder, and melting and fusion were hardly observed.
The fired powder was transferred to a graphite crucible, graphitized at 3000 ℃ for 5 hours in an inert atmosphere using a direct electric furnace, and sieved 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed, to obtain carbonaceous material (P).
[ production of negative electrode Material 11]
The natural graphite used in [ production 1 of negative electrode material ] was charged into a metal container, and heat treatment A was performed at 540 ℃ for 2 hours in a box-shaped electric furnace under nitrogen flow. After heat treatment a, almost no melting, fusion of the natural graphite was found. The obtained powder was placed in a container and fired at 1000 ℃ for 1 hour in an electric furnace under a nitrogen atmosphere. After firing, the obtained powder was in the form of powder, and melting and fusion were hardly observed.
Further, the fired powder was transferred to a graphite crucible, graphitized for 5 hours at 3000 ℃ in an inert atmosphere using a direct electric furnace, and the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent the incorporation of coarse particles, to obtain a carbonaceous material (Q).
[ production of negative electrode Material 12]
The carbonaceous material (P) and the carbonaceous material (Q) were mixed by 50 mass% each, and uniformly mixed to obtain a carbonaceous material mixture (R).
Negative electrode [5] [ preparation of Battery ]
Preparation of Positive electrode 1
90 mass% of a positive electrode active material is mixed in an N-methylpyrrolidone solventLithium cobaltate (LiCoO)2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the active material of the positive electrode at this time was 2.35g/cm3。
Production of negative electrode 1
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration: 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (styrene-butadiene rubber concentration: 50 mass%) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the active material of the negative electrode at this time was 1.35g/cm 3。
Production of nonaqueous electrolyte solution 1
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of nonaqueous electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of nonaqueous electrolyte solution 3
Under dry argon atmosphereIn a mixture of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) (volume ratio 3:3:4), lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of nonaqueous electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6)。
(production of Battery 1)
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the direct current resistance measured by the 10kHz alternating current method was about 5 milliohms (m Ω).
Negative electrode [5] example 1
A battery was produced by the method described in section 1 of production of batteries, using a negative electrode produced by using the heterooriented carbon composite (G) as the negative electrode active material in section 1 of production of negative electrode, a positive electrode produced in section 1 of production of positive electrode, and a nonaqueous electrolytic solution produced in section 1 of production of nonaqueous electrolytic solution. The measurement of the battery was carried out by the method described in the section "evaluation of battery" below and the above-mentioned measurement method.
Negative electrode [5] example 2
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (H) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [5], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [5] embodiment 3
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (I) was used as the negative electrode active material in example 1 of negative electrode [5] and evaluation of the battery was performed as described in evaluation of battery.
Negative electrode [5] example 4
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (J) was used as the negative electrode active material in example 1 of negative electrode [5] and evaluation of the battery was performed as described in evaluation of battery.
Negative electrode [5] example 5
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (K) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [5], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [5] example 6
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (L) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [5], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [5] example 7
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (M) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [5], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [5] example 8
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (N) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [5], and the battery evaluation described in item "evaluation of battery" was performed.
Negative electrode [5] example 9
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the hetero-oriented carbon composite (O) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [5], and the battery evaluation described in item "evaluation of battery" was performed.
Examples 10 to 18 of negative electrode [5]
Batteries were produced in the same manner as in example 1 to example 9 of negative electrode [5] except that the nonaqueous electrolytic solution was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 2", and evaluation of batteries was carried out in the same manner.
Negative electrode [5] examples 19 to 27
Batteries were produced in the same manner as in example 1 to example 9 of negative electrode [5] except that the nonaqueous electrolytic solution was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 3", and evaluation of batteries was carried out in the same manner.
Negative electrode [5] comparative example 1
A battery was produced in the same manner as in example 1 of negative electrode [5], except that carbonaceous material (P) was used as the negative electrode active material in example 1 of negative electrode [5] and evaluation of the battery was performed as described in evaluation of battery.
Negative electrode [5] comparative example 2
A battery was produced in the same manner as in comparative example 1 of negative electrode [5], except that the nonaqueous electrolytic solution of comparative example 1 of negative electrode [5] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed.
Negative electrode [5] comparative example 3
A battery was produced in the same manner as in example 1 of negative electrode [5], except that carbonaceous material (Q) was used as the negative electrode active material in example 1 of negative electrode [5], and the battery evaluation described in "evaluation of battery" was performed.
Negative electrode [5] comparative example 4
A battery was produced in the same manner as in comparative example 3 of negative electrode [5], except that the nonaqueous electrolytic solution of comparative example 3 of negative electrode [5] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed.
Negative electrode [5] comparative example 5
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the carbonaceous material mixture (R) was used as the negative electrode active material in example 1 of negative electrode [5] and evaluation of the battery was performed as described in evaluation of battery.
Negative electrode [5] comparative example 6
A battery was produced in the same manner as in comparative example 5 of negative electrode [5], except that the nonaqueous electrolytic solution of comparative example 5 of negative electrode [5] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed.
Negative electrode [5] comparative example 7
A battery was produced in the same manner as in example 1 of negative electrode [5], except that the nonaqueous electrolytic solution of example 1 of negative electrode [5] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was carried out.
Negative electrode [5] comparative example 8
A battery was produced in the same manner as in example 2 of negative electrode [5], except that the nonaqueous electrolytic solution of example 2 of negative electrode [5] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was carried out.
Negative electrode [5] comparative example 9
A battery was produced in the same manner as in example 4 of negative electrode [5] except that the nonaqueous electrolytic solution of example 4 of negative electrode [5] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was carried out.
Negative electrode [5] comparative example 10
A battery was produced in the same manner as in example 5 of negative electrode [5], except that the nonaqueous electrolytic solution of example 5 of negative electrode [5] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was carried out.
Negative electrode [5] comparative examples 11 to 13
Batteries were produced in the same manner as in comparative examples 1, 3 and 5 of negative electrode [5] except that the nonaqueous electrolytic solution was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 2", and evaluation of batteries was carried out in the same manner.
Negative electrode [5] comparative examples 14 to 16
Batteries were produced in the same manner as in comparative examples 1, 3 and 5 of negative electrode [5] except that the nonaqueous electrolytic solution was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 3", and evaluation of batteries was carried out in the same manner.
Negative electrode [5] evaluation of Battery
(Capacity measurement)
For a battery not subjected to charge/discharge cycles, initial charge/discharge was carried out for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle in this case was set as the initial capacity. The following output power measurement was performed.
(Low Charge deep cycle test)
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. The charge and discharge were performed in 1 cycle by charging the battery to a capacity of 20% of the initial capacity measured in the capacity measurement and 4.2V as the upper limit charge voltage by a constant current and constant voltage method of 2C, and then discharging the battery to a discharge end voltage of 3.0V by a constant current and repeating the cycle up to 500 cycles.
After the end of the cycle test, the battery was charged and discharged at 25 ℃ for 3 cycles, and the 0.2C discharge capacity of the 3 rd cycle was defined as the capacity after the low-depth charge cycle. The cycle retention ratio was calculated from the initial capacity measured before the cycle test and the capacity after the low-charge-depth cycle measured after the cycle test according to the following calculation formula.
Cycle retention (%) > 100 × capacity after low charge depth cycle/initial capacity
The list of negative electrode active materials used in the negative electrode [5] examples and the negative electrode [5] comparative examples is shown in the negative electrode [5] Table 1, and the results of battery evaluation are shown in the negative electrode [5] Table 2 and the negative electrode [5] Table 3. As is clear from the results of the negative electrode [5] table 2 and the negative electrode [5] table 3, it was found that the capacity retention rate (cycle retention rate) after a cycle test at a low charge depth can be dramatically improved by containing lithium difluorophosphate, trimethylsilyl methanesulfonate, and hexamethylcyclotrisiloxane in combination with the heteroepitaxial carbon composite as the negative electrode active material.
Negative electrode [5] Table 1
Figure BDA0003109774980002921
Negative electrode [5] Table 2
[ Table 44]
Figure BDA0003109774980002931
Negative electrode [5] Table 3
[ Table 45]
Figure BDA0003109774980002941
Negative electrode [6] [ preparation of negative electrode active Material ]
(preparation of negative electrode active Material 1)
In order to prevent coarse particles from being mixed into the commercially available natural graphite powder (a), the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as the carbonaceous material (B).
(preparation of negative electrode active Material 2)
A commercially available natural graphite powder (C) (d 002: 0.336nm, Lc: 100nm or more, Raman R value: 0.11, tap density: 0.46 g/cm) was subjected to a micro-mill (turbo mill manufactured by matsubo Co., Ltd.)3And true density: 2.27g/cm3Volume average particle diameter: 28.7 μm) and the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent the mixing of coarse particles, thereby preparing a carbonaceous material (D).
(preparation of negative electrode active Material 3)
The natural graphite powder (C) was treated with a mixing system (NHS-1 type mixing system manufactured by Nara machine Co., Ltd.) at a treatment amount of 90g, a peripheral speed of the rotor of 60m/s and a treatment time of 3 minutes to spheroidize the powder, and the sieving was repeated 5 times using a sieve of ASTM400 mesh to prevent the coarse particles from being mixed. The negative electrode active material thus obtained was used as a carbonaceous material (E). By repeating this operation, the amount necessary for battery production is ensured.
(preparation of negative electrode active Material 4)
A commercially available natural graphite powder (F) (d 002: 0.336nm, Lc: 100nm or more, Raman R value: 0.09, tap density: 0.57 g/cm) was treated with a mixing system at a treatment amount of 90g, a peripheral speed of the rotor of 30m/s and a treatment time of 1 minute 3And true density: 2.26g/cm3Volume average particle diameter: 85.4 μm) and, in order to prevent the coarse particles from being mixed in, the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as the carbonaceous material (G). By repeating this operation, the amount necessary for battery production is ensured.
(preparation of negative electrode active Material 5)
A coal tar pitch having a quinoline insoluble content of 0.05 mass% or less is subjected to heat treatment at 460 ℃ for 10 hours in a reaction furnace to obtain a massive carbonization precursor having a softening point of 385 ℃ and a melting property. The obtained bulk carbonization precursor was charged into a metal container, and heat-treated in a box-shaped electric furnace at 1000 ℃ for 2 hours under nitrogen flow. The obtained amorphous cake was pulverized by a coarse pulverizer (roll crusher, manufactured by yota corporation), and then finely pulverized by a fine pulverizer (turbine mill, manufactured by matsubo corporation), to obtain an amorphous powder having a volume-based average particle diameter of 18 μm. In order to prevent the resulting powder from being mixed with coarse particles, the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as the carbonaceous material (H).
(preparation of negative electrode active Material 6)
The carbonaceous material (H) obtained in (preparation of negative electrode active material 5) was transferred again to a graphite crucible, graphitized at 3000 ℃ for 5 hours in an inert atmosphere using a direct electric furnace, and the sieving was repeated 5 times using a sieve of ASTM400 mesh in order to prevent the resulting powder from being mixed with coarse particles. The negative electrode active material obtained here was used as the carbonaceous material (I).
(preparation of negative electrode active Material 7)
The carbonaceous material (I) obtained in (preparation 6 of negative electrode active material) was spheroidized using a mixing system under the conditions of a treatment amount of 90g, a rotor peripheral speed of 30m/s, and a treatment time of 1 minute, and the sieving was repeated 5 times using a sieve of ASTM400 mesh in order to prevent the mixing of coarse particles. The negative electrode active material thus obtained was used as a carbonaceous material (J). By repeating this operation, the amount necessary for battery production is ensured.
(preparation of negative electrode active Material 8)
The natural graphite powder (K) with the purity lower than that of the natural graphite powder (A) (d 002: 0.336nm, Lc: more than 100nm, Raman R value: 0.10, tap density: 0.49 g/cm)3And true density: 2.27g/cm3Volume average particle diameter: 27.3 μm and 0.5 mass% ash) were spheroidized and sieved under the same conditions as in (preparation of negative electrode active material 3) to prepare a carbonaceous material (L). By repeating this operation, the amount necessary for battery production is ensured.
(preparation of negative electrode active Material 9)
In order to prevent coarse particles from being mixed into the commercially available flaky natural graphite powder (M), the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as a carbonaceous material (N).
The shapes and physical properties of the carbonaceous materials (B), (D), (E), (G), (H), (I), (J), (L) and (N) were measured by the methods described above. The results are shown in Table 1 for negative electrode [6 ].
Negative electrode [6] Table 1
Figure BDA0003109774980002971
Negative electrode [6] [ preparation of Battery ]
Preparation of Positive electrode 1
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the active material of the positive electrode at this time was 2.35g/cm3。
Production of negative electrode 1
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration: 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (styrene-butadiene rubber concentration: 50 mass%) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the active material of the negative electrode at this time was 1.35g/cm 3。
Production of nonaqueous electrolyte solution 1
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of nonaqueous electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of nonaqueous electrolyte solution 3
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of nonaqueous electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6)。
Production of Battery 1
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω). The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 20.6.
Negative electrode [6] example 1
A battery was produced by the method in item 1 for production of a battery, using a negative electrode produced using the negative electrode active material in item 1 for production of a negative electrode as a carbonaceous material (D), a positive electrode produced in item 1 for production of a positive electrode, and a nonaqueous electrolytic solution produced in item 1 for production of a nonaqueous electrolytic solution. The measurement of the battery was carried out by the method described in the section "evaluation of battery" below and the above-mentioned measurement method. The results are shown in Table 2 (negative electrode [6] Table 2).
Negative electrode [6] example 2
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (E) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] example 3
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (G) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] example 4
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (J) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] example 5
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (L) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Examples 6 to 10 of negative electrode [6]
Batteries were produced and evaluated in the same manner as in the production of nonaqueous electrolyte solution 2 except that the nonaqueous electrolyte solutions of examples 1 to 5 of negative electrode [6] were replaced with the nonaqueous electrolyte solutions. The results are shown in Table 2 for negative electrode [6 ].
Examples 11 to 15 of negative electrode [6]
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 3 except that the nonaqueous electrolyte solutions of examples 1 to 5 of negative electrode [6] were replaced with the nonaqueous electrolyte solutions. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 1
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (B) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 2
A battery was produced in the same manner as in comparative example 1 of negative electrode [6], except that the nonaqueous electrolytic solution of comparative example 1 of negative electrode [6] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 3
A battery was produced in the same manner as in example 2 of negative electrode [6], except that the nonaqueous electrolytic solution of example 2 of negative electrode [6] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was carried out. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 4
A battery was produced in the same manner as in example 1 of negative electrode [6], except that the nonaqueous electrolytic solution of example 1 of negative electrode [6] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 5
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (H) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 6
A battery was produced in the same manner as in comparative example 5 of negative electrode [6], except that the nonaqueous electrolytic solution of comparative example 5 of negative electrode [6] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 7
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (N) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 8
A battery was produced in the same manner as in comparative example 7 of negative electrode [6], except that the nonaqueous electrolytic solution of comparative example 7 of negative electrode [6] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 9
A battery was produced in the same manner as in example 1 of negative electrode [6], except that carbonaceous material (I) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [6], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative example 10
A battery was produced in the same manner as in comparative example 9 of negative electrode [6], except that the nonaqueous electrolytic solution of comparative example 9 of negative electrode [6] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was performed. The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative examples 11 to 14
Batteries were produced and evaluated in the same manner as in comparative examples 1, 5, 7 and 9 except that the nonaqueous electrolytic solution of negative electrode [6] was changed to the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 2". The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] comparative examples 15 to 18
Batteries were produced and evaluated in the same manner as in comparative examples 1, 5, 7 and 9 except that the nonaqueous electrolytic solution of negative electrode [6] was changed to the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 3". The results are shown in Table 2 for negative electrode [6 ].
Negative electrode [6] evaluation of Battery
(Capacity measurement)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles (voltage range 4.1V to 3.0V) at 25 ℃ in a voltage range of 4.1V to 3.0V. The initial capacity was determined as 0.2C (1C is a current value of a 1-hour discharge rated capacity determined by a discharge capacity at a 1-hour rate (one-hour-rate), which is the same below) discharge capacity at the 5 th cycle.
(output Power measurement 1)
The voltage at 10 seconds was measured by charging the sample at 25 ℃ for 150 minutes with a constant current of 0.2C, leaving the sample at-30 ℃ for 3 hours, and then discharging the sample at 0.1C, 0.3C, 1.0C, 3.0C, and 5.0C for 10 seconds. The area of a triangle surrounded by a current-voltage line and the lower limit voltage (3V) is defined as the initial low-temperature output power (W).
(output Power measurement 2)
After the output power measurement 1, the battery was charged at a low voltage of 4.1V for 1 hour, and then transferred to an environment at 25 ℃, and after 15 minutes, the battery was discharged at 0.1C, 0.3C, 1.0C, 3.0C, and 5.0C for 10 seconds, and the voltage at 10 seconds was measured. The output power (W) at the time of temperature rise was determined as the area of a triangle surrounded by a current-voltage line and a lower limit voltage (3V).
The temperature-adaptive output power increase rate (%) was calculated from the results of the output power measurement 1 and the output power measurement 2 by the following calculation formula.
Rate of increase in output Power (%)
(output power at temperature rise (W)/initial low-temperature output power (W)) -1 ] × 100 ═ temperature rise (r) ((r) ("output power at temperature rise (W)/initial low-temperature output power (W)))
The impedance Rct and the double layer capacity Cdl in the negative electrode [6] table 2 are one of parameters contributing to the output power, and the smaller the value of the impedance Rct is, or the larger the value of the double layer capacity Cdl is, the more the output power tends to be improved. The "impedance Rct" and the "double-layer capacitance Cdl" are obtained by the methods described in the section describing the impedance.
Negative electrode [6] Table 2
[ Table 47]
Figure BDA0003109774980003031
From the results of table 2 of the negative electrode [6], it was found that the recovery of the output in a low temperature state of-30 ℃ with the temperature rise can be dramatically accelerated by containing lithium difluorophosphate, trimethylsilyl methanesulfonate, hexamethylcyclotrisiloxane, and, as the negative electrode active material, graphite carbon particles having a circularity of 0.85 or more, a wide-angle X-ray diffraction method of measuring the (002) plane interplanar spacing (d002) of less than 0.337, and a raman R value of 0.12 to 0.8.
Negative pole [7] (manufacture of negative pole)
(preparation of negative electrode 1)
A mixture of Si and C (a disc having an area ratio of Si to C of approximately 100 to 9) was used as a target material, and the target material had an average surface roughness (Ra) of 0.2 μm and a tensile strength of 280N/mm20.2% proof stress of 220N/mm2An electrolytic copper foil having a thickness of 18 μm was used as a current collector substrate, and an active material thin film was formed for 45 minutes by using a direct current sputtering apparatus ("HSM-52" manufactured by Shimadzu corporation), thereby obtaining a thin film negative electrode (1).
At this time, the current collector substrate was mounted on a water-cooled jig, maintained at about 25 ℃, and the container was previously vacuum-sucked to 4 × 10-4Pa, flowing high-purity argon gas of 40sccm into the container, adjusting the opening degree of the main valve to 1.6Pa, and then adjusting the power density to 4.7W/cm2The deposition rate (film formation rate) was about 1.8 nm/sec (0.108 μm/min). The oxygen concentration of the sputtering gas was 0.0010%. In addition, in order to remove the oxide film on the surface of the electrolytic copper foil, reverse sputtering is performed before forming a thin film, and the surface of the substrate is etched.
When the cross section of the obtained thin film of the thin film negative electrode (1) was observed by a Scanning Electron Microscope (SEM), the thickness of the thin film after film formation was 6 μm (see fig. 1 (a)). When the composition of the thin film was analyzed by XPS according to the following method, the content of the element C in the thin film was 24 atomic%, and the concentration ratio q (C) of C to the concentration of the element C in SiC corresponded to 0.49. In addition, if expressed by an atomic concentration ratio, Si/C/O is 1.00/0.33/0.04. When the raman value of the film was obtained by raman measurement according to the following method, RC was 0.05, a peak with RSC not detected, and RS was 0.55. When the thin film was measured by X-ray diffraction according to the following method, a clear SiC peak was not detected, and XIsz was 0.38. The results are shown in negative [7] Table 1.
When the mass concentration distribution of Si in the thin film in the film thickness direction is measured by an Electron Probe Microanalyzer (EPMA) according to the following method, the difference (absolute value) between the maximum value or minimum value of Si and the average value is 25% or less, and Si is substantially continuously formed on the current collector, as shown in fig. 1 (b). When the distribution of the element C in the thin film is measured, the element C is uniformly distributed in the Si thin film in a size of 1 μm or less as shown in fig. 1 (C).
(preparation of negative electrode 2)
An active material thin film was formed in the same manner as in (production 1 of negative electrode) except that Si was used as a target material, to produce a thin-film negative electrode (2).
When the cross section of the obtained thin film of the thin film negative electrode (2) was observed by a Scanning Electron Microscope (SEM), the film thickness of the thin film after film formation was 6 μm. When the composition of the thin film was analyzed, the element C, N was not contained in the thin film, and when the element was represented by an atomic concentration ratio, Si/O was 1.00/0.02. When the raman value of the film was obtained, a peak having RC ═ c, a peak having RSC ═ sc, and RS ═ 0.30 were not detected. The results are shown in negative [7] Table 1.
XPS assay
As the X-ray photoelectron spectroscopy measurement, a depth profile measurement was performed by placing a thin film negative electrode on a sample table with the surface thereof flat and Ar sputtering with K α rays of aluminum as an X-ray source using an X-ray photoelectron spectrometer (for example, "ESCA" manufactured by ulvac-phi corporation). Obtaining the spectra of Si2p (90-110 eV), C1s (280-300 eV) and O1s (525-545 eV) at a certain depth (e.g. 200nm) to a certain concentration. The peak top of the obtained C1s was set to 284.5eV for charge compensation, and the peak areas of the spectra of Si2p, C1s, and O1s were obtained, and the atomic concentrations of Si, C, and O were calculated by multiplying the device sensitivity coefficient. From the obtained atomic concentrations of Si, O and C, an atomic concentration ratio Si/C/O (Si atomic concentration/C atomic concentration/O atomic concentration) was calculated, and defined as a composition value Si/C/O of the thin film.
Raman measurement
As the raman measurement, a raman spectrometer (for example, "raman spectrometer" manufactured by japan spectrochemical) is used, and the thin film negative electrode is attached to a measurement cell, and the surface of a sample in the cell is irradiated with an argon ion laser for measurement.
The raman measurement conditions herein are as follows.
Argon ion laser wavelength: 514.5nm
Laser power on the sample: 15-40 mW
Resolution: 10-20 cm-1
Measurement range: 200cm-1～1900cm-1
Smoothing treatment: simple average, convolution 15 points
X-ray diffraction measurement
As the X-ray diffraction measurement, "RINT 2000 PC" manufactured by science corporation was used, and the thin film negative electrode was attached to a measuring cell, and measurement was performed in a range of 2 θ of 10 to 70 degrees by an out-of-plane method. The background compensation is performed by connecting the 2 theta of 15-20 degrees and 40-45 degrees by straight lines.
EPMA measurement
As the mass concentration distribution in the film thickness direction and the distribution analysis of the thin film cross section measured by EPMA, elemental analysis from the current collector to the thin film surface was performed on the thin film negative electrode having a cross section formed by a microtome without resin embedding using an electron probe microanalyzer ("JXA-8100" manufactured by JEOL corporation). When the mass concentration distribution in the film thickness direction is obtained, the mass concentration distribution of Si in the film thickness direction is obtained using a value obtained by converting the total of the measured elements to 100%.
Negative electrode [7] Table 1
[ Table 48]
Figure BDA0003109774980003061
Negative electrode [7] in Table 1, (Si) does not correspond to the element Z.
Production of negative pole (7) < positive pole >
(preparation of Positive electrode 1)
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The resulting slurry was coated on one side of an aluminum foil having a thickness of 15 μm, dried, and rolled to a thickness of 80 μm with a press.
Production of negative electrode [7] nonaqueous electrolyte
(preparation of nonaqueous electrolyte solution 1)
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
(preparation of nonaqueous electrolyte solution 2)
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
(preparation of nonaqueous electrolyte solution 3)
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
(preparation of nonaqueous electrolyte solution 4)
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6)。
Negative electrode [7] manufacture of lithium secondary battery
The thin film negative and positive electrodes were punched out to 10mm phi, vacuum-dried at 110 ℃, then transferred to a glove work box, and the positive and negative electrodes were opposed by a polyethylene separator punched out to 14mm phi in an argon atmosphere, and a nonaqueous electrolyte was added to prepare a 2032 type coin battery (lithium secondary battery).
Negative electrode [7] example 1
A coin cell was produced by the method described in "production of lithium Secondary Battery" using the negative electrode produced in (production of negative electrode 1), the positive electrode produced in (production of positive electrode), and the nonaqueous electrolytic solution produced in (production of nonaqueous electrolytic solution 1). The battery characteristics of the secondary battery were obtained by the method described in the following "battery evaluation".
Negative electrode [7] example 2
A battery was produced in the same manner as in example 1 of negative electrode [7], except that the nonaqueous electrolytic solution of example 1 of negative electrode [7] was replaced with the nonaqueous electrolytic solution produced in (production of nonaqueous electrolytic solution 2), and the battery was evaluated by the method described in (evaluation of battery). The results are shown in Table 2 for negative electrode [7 ].
Negative electrode [7] example 3
A battery was produced in the same manner as in example 1 of negative electrode [7], except that the nonaqueous electrolytic solution of example 1 of negative electrode [7] was replaced with the nonaqueous electrolytic solution produced in (production of nonaqueous electrolytic solution 3), and the battery was evaluated by the method described in (evaluation of battery). The results are shown in Table 2 for negative electrode [7 ].
Negative electrode [7] comparative example 1
A battery was produced in the same manner as in example 1 of negative electrode [7], except that the nonaqueous electrolytic solution of example 1 of negative electrode [7] was replaced with the nonaqueous electrolytic solution produced in (production of nonaqueous electrolytic solution 4), and the battery was evaluated by the method described in (evaluation of battery). The results are shown in Table 2 for negative electrode [7 ].
Negative electrode [7] comparative example 2
A battery was produced in the same manner as in example 1 of negative electrode [7], except that the negative electrode of example 1 of negative electrode [7] was changed to the electrode produced in (production of negative electrode 2), and the battery was evaluated by the method described in (evaluation of battery). The results are shown in Table 2 for negative electrode [7 ].
Negative electrode [7] comparative example 3
A battery was produced in the same manner as in comparative example 2 of negative electrode [7], except that the nonaqueous electrolytic solution of comparative example 2 of negative electrode [7] was replaced with the nonaqueous electrolytic solution produced in item (production of nonaqueous electrolytic solution 2), and the battery was evaluated by the method described in < evaluation of battery >. The results are shown in Table 2 for negative electrode [7 ].
Negative electrode [7] comparative example 4
A battery was produced in the same manner as in comparative example 2 of negative electrode [7], except that the nonaqueous electrolytic solution of comparative example 2 of negative electrode [7] was replaced with the nonaqueous electrolytic solution produced in item (production of nonaqueous electrolytic solution 3), and the battery was evaluated by the method described in < evaluation of battery >. The results are shown in Table 2 for negative electrode [7 ].
Negative electrode [7] comparative example 5
A battery was produced in the same manner as in comparative example 2 of negative electrode [7], except that the nonaqueous electrolytic solution of comparative example 2 of negative electrode [7] was replaced with the nonaqueous electrolytic solution produced in item (production of nonaqueous electrolytic solution 4), and the battery was evaluated by the method described in "evaluation of Battery". The results are shown in Table 2 for negative electrode [7 ].
Evaluation of negative electrode [7] Battery
The coin batteries produced in the item "production of lithium secondary batteries" were evaluated for discharge capacity and measured for charge acceptance by the following methods.
Evaluation of discharge Capacity
At 1.23mA/cm2The current density of (2) was set to 4.2V, and then charged at a constant voltage of 4.2V until the current reached 0.123mA, and after doping lithium in the negative electrode, 1.23mA/cm2The lithium counter electrode was discharged to 2.5V at the current density of (2), and this charge-discharge cycle was repeated 5 times, and the average value of the discharge in the 3 rd to 5 th cycles was defined as the discharge capacity. In the case of the discharge capacity per unit mass, the mass of the active material can be calculated by subtracting the mass of the copper foil punched out to have the same area from the mass of the negative electrode, and the mass is calculated by the following equation.
Discharge capacity (mAh/g)
[ average discharge capacity (mAh) at cycles 3 to 5 ]/[ active material mass (g) ]
Mass of active material (g) ═ mass of negative electrode (g) — mass of copper foil of the same area (g)
Measurement of Charge acceptance
In an environment of 25 ℃, a capacity when charged to 4.2V at 0.2C (a current value of a 1-hour discharge rated capacity depending on a discharge capacity of a 1-hour rate (hereinafter the same) is taken as 1C) is taken as a 0.2C charge capacity, and then discharged to 2.5V at 0.2C, and then charged to 4.2V at 1C, and the capacity at this time is taken as a 1C charge capacity. From the obtained results, the charge acceptance was determined by the following equation.
Charge acceptance (%) < 100 × [1C charge capacity ]/[0.2C charge capacity ]
Negative electrode [7] Table 2
[ Table 49]
Figure BDA0003109774980003091
As is clear from the results of table 2 of the negative electrode [7], a lithium secondary battery containing a lithium difluorophosphate salt, trimethylsilyl methanesulfonate, or hexamethylcyclotrisiloxane in a nonaqueous electrolytic solution and using, as a negative electrode active material, (C) containing at least one lithium-occluding metal (a) and/or lithium-occluding alloy (B) and containing at least one element (element Z) selected from C and N, the negative electrode active material containing multiple elements, which contains at least one lithium-occluding metal (a) and/or lithium-occluding alloy (B), can dramatically improve charge acceptance.
Negative electrode [8] [ preparation of negative electrode active Material ]
(preparation of negative electrode active Material 1)
Natural graphite powder (d 002: 0.336nm, Lc: 100nm or more, Raman R value: 0.11, tap density: 0.46 g/cm) was treated with a mixing system (type NHS-1 mixing System manufactured by Nara machine Co., Ltd.) at a treatment amount of 90g, a peripheral rotor speed of 60m/s and a treatment time of 3 minutes3And the true density: 2.27g/cm3Volume-based average particle diameter: 35.4 mum) to be spheroidized, and the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed. The negative electrode active material thus obtained was used as the carbonaceous material (a). By repeating this operation, the amount necessary for cell fabrication is ensured.
(preparation of negative electrode active Material 2)
The fine powder of a commercially available flaky natural graphite powder was removed by an air classifier, and the obtained powder was repeatedly sieved 5 times with a sieve of ASTM400 mesh to prevent coarse particles from being mixed therein. The negative electrode active material thus obtained was used as the carbonaceous material (B).
(preparation of negative electrode active Material 3)
A coal tar pitch having a quinoline insoluble content of 0.05 mass% or less is subjected to heat treatment at 460 ℃ for 10 hours in a reaction furnace to obtain a bulk carbonized precursor having a softening point of 385 ℃ and a meltability. The obtained bulk carbonization precursor was charged into a metal container and heat-treated in a box-shaped electric furnace at 1000 ℃ for 2 hours under a nitrogen flow. The obtained amorphous mass was pulverized by a coarse pulverizer (roll crusher manufactured by yota corporation), and then finely pulverized by a fine pulverizer (turbine mill manufactured by matsubo corporation), and then the fine powder was removed by a pneumatic classifier, and the obtained powder was repeatedly sieved 5 times with a sieve of ASTM400 mesh to obtain amorphous powder having a volume-based particle size of 9 μm, in order to prevent coarse particles from being mixed in the powder. The negative electrode active material thus obtained was used as the carbonaceous material (C).
(preparation of negative electrode active Material 4)
Petroleum heavy oil obtained by pyrolysis of naphtha is mixed with carbonaceous material (a) obtained by coating surfaces of particles of carbonaceous material (a) with carbonaceous materials having different crystallinities, carbonizing the resulting mixture at 1300 ℃ in an inert gas, and then classifying the sintered product. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent the mixing of coarse particles, thereby obtaining a carbonaceous material (D). From the carbon residue ratio, the obtained negative electrode active material powder was coated with 5 parts by weight of carbonaceous material derived from petroleum heavy oil with respect to 95 parts by weight of graphite.
(preparation of negative electrode active Material 5)
The carbonaceous material (a) in an amount of 80 mass% and the carbonaceous material (B) in an amount of 20 mass% were mixed until uniform to prepare a mixed carbonaceous material (E).
(preparation of negative electrode active Material 6)
The 95 mass% carbonaceous material (a) and the 5 mass% carbonaceous material (C) were mixed until uniform to prepare a mixed carbonaceous material (F).
(preparation of negative electrode active Material 7)
The carbonaceous material (D) in an amount of 80 mass% and the carbonaceous material (a) in an amount of 20 mass% were mixed until uniform to prepare a mixed carbonaceous material (G).
The physical properties, shapes, and the like of the carbonaceous materials (a), (B), and (C) and the mixed carbonaceous materials (E), (F), and (G) prepared in preparation 1 to 7 of the negative electrode active material were determined by the methods described above. The results are summarized in Table 1 for negative electrode [8 ].
Negative electrode [8] Table 1
Figure BDA0003109774980003111
Negative electrode [8] [ preparation of Battery ]
Preparation of Positive electrode 1
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the active material of the positive electrode at this time was 2.35g/cm3。
Production of negative electrode 1
To 98 parts by weight of the negative electrode active material were added 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50 mass%) as a binder
%) were mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the active material of the negative electrode at this time was 1.35g/cm3。
Production of nonaqueous electrolyte solution 1
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of nonaqueous electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of nonaqueous electrolyte solution 3
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of nonaqueous electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6)。
Production of Battery 1
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω). The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 20.6.
Negative electrode [8] embodiment 1
A battery was produced by the method described in section 1 of production of battery, using a negative electrode produced by mixing a carbonaceous material (E) with the negative electrode active material described in section 1 of production of negative electrode, a positive electrode produced in section 1 of production of positive electrode, and a nonaqueous electrolytic solution produced in section 1 of production of nonaqueous electrolytic solution. The battery was evaluated as described in the following item "evaluation of battery". The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] embodiment 2
A battery was produced in the same manner as in example 1 of negative electrode [8], except that the mixed carbon material (F) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [8], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] embodiment 3
A battery was produced in the same manner as in example 1 of negative electrode [8], except that the mixed carbon material (G) was used as the negative electrode active material in item "production of negative electrode 1" of example 1 of negative electrode [8], and the battery evaluation described in item "evaluation of battery" was performed. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] examples 4 to 6
Batteries were produced and evaluated in the same manner as in the production of nonaqueous electrolyte solution 2 except that the nonaqueous electrolyte solution of examples 1 to 3 of negative electrode [8] was replaced with the nonaqueous electrolyte solution. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] examples 7 to 9
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 3 except that the nonaqueous electrolyte solutions of examples 1 to 3 of negative electrode [8] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative example 1
A battery was produced in the same manner as in example 1 of negative electrode [8], except that the nonaqueous electrolytic solution of example 1 of negative electrode [8] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was carried out. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative example 2
A battery was produced in the same manner as in example 2 of negative electrode [8], except that the nonaqueous electrolytic solution of example 2 of negative electrode [8] was replaced with the nonaqueous electrolytic solution produced in item "production of nonaqueous electrolytic solution 4", and the battery evaluation described in item "evaluation of Battery" was carried out. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative example 3
A battery was produced in the same manner as in comparative example 1 of negative electrode [8], except that the carbonaceous material (a) was used as the negative electrode active material in comparative example 1 of negative electrode [8], and the battery evaluation described in evaluation of battery was performed. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative example 4
A battery was produced in the same manner as in comparative example 1 of negative electrode [8], except that the carbonaceous material (B) was used as the negative electrode active material in comparative example 1 of negative electrode [8], and the battery evaluation described in evaluation of battery was performed. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative example 5
A battery was produced in the same manner as in comparative example 1 of negative electrode [8], except that the carbonaceous material (C) was used as the negative electrode active material in comparative example 1 of negative electrode [8], and the battery evaluation described in evaluation of battery was performed. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative examples 6 to 8
Batteries were produced and evaluated in the same manner as in production 1 of nonaqueous electrolyte solution except that the nonaqueous electrolyte solutions of comparative examples 3 to 5 in the negative electrode [8] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative examples 9 to 11
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 2 except that the nonaqueous electrolyte solutions of comparative examples 3 to 5 in the negative electrode [8] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] comparative examples 12 to 14
Batteries were produced and evaluated in the same manner as in production of nonaqueous electrolyte solution 3 except that the nonaqueous electrolyte solutions of comparative examples 3 to 5 in the negative electrode [8] were replaced with the nonaqueous electrolyte solutions. The results are shown in the negative electrode [8] Table 2.
Negative electrode [8] evaluation of Battery
(Capacity measurement)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles (voltage range 4.1V to 3.0V) at 25 ℃ in a voltage range of 4.1V to 3.0V. The initial capacity was determined as 0.2C (1C is a current value of a 1-hour discharge rated capacity determined by a discharge capacity at a 1-hour rate (one-hour-rate), which is the same below) discharge capacity at the 5 th cycle.
(output Power measurement 1)
The voltage at 10 seconds was measured by charging the sample at 25 ℃ for 150 minutes with a constant current of 0.2C, leaving the sample at-30 ℃ for 3 hours, and then discharging the sample at 0.1C, 0.3C, 1.0C, 3.0C, and 5.0C for 10 seconds. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the low-temperature output power (W).
(cycle test)
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. Charging to a charging upper limit voltage of 4.2V by a constant current constant voltage method of 2C, then discharging to a discharging end voltage of 3.0V by a constant current of 2C, taking the charging and discharging cycle as 1 cycle, and repeating the cycle up to 500 cycles. The battery after the end of the cycle test was charged and discharged at 25 ℃ for 3 cycles, and the 0.2C discharge capacity of the 3 rd cycle was defined as the capacity after the cycle. The cycle retention rate was calculated from the initial capacity measured before the cycle test and the capacity after the cycle measured after the cycle test according to the following calculation formula.
Cycle retention (%) > 100 × capacity after cycle/initial capacity
Negative electrode [8] Table 2
[ Table 51]
Figure BDA0003109774980003161
As is clear from the results of table 2 of the negative electrode [8], the cycle characteristics and the low-temperature output were both good by using a negative electrode containing 2 or more negative electrode active materials having different properties, and containing lithium difluorophosphate, trimethylsilyl methanesulfonate, and hexamethylcyclotrisiloxane.
Negative electrode [9] [10] [ preparation of negative electrode active Material ]
(preparation of negative electrode active Material 1)
High-purity flaky natural graphite (d 002: 0.336nm, Lc: 100nm or more, Raman R: 0.11, true density: 2.27 g/cm) having a median particle diameter of about 150 μm was treated at 6500rpm using a spheroidizing apparatus (mixing system manufactured by Nara machine)3Ash content: 0.05 mass%) was subjected to spheroidization for 5 minutes, and 45 mass% of fine powder was removed by an air classifier (OMC-100 manufactured by Seishin corporation) to obtain a carbonaceous material (A).
(preparation of negative electrode active Material 2)
The carbonaceous material (a) prepared in (preparation of negative electrode active material 1) was charged into a graphite crucible, and heat-treated at 3000 ℃ for 5 hours in an inert atmosphere using a direct electric furnace to obtain a carbonaceous material (B).
(preparation of negative electrode active Material 3)
Petroleum heavy oil obtained by pyrolysis of naphtha was mixed with carbonaceous material (a) prepared (preparation of negative electrode active material 1), carbonized at 1300 ℃ in an inert gas, and then the sintered product was subjected to classification treatment to obtain carbonaceous material in which carbonaceous materials having different crystallinities were coated on the surfaces of carbonaceous material (a) particles. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent the mixing of coarse particles, thereby obtaining a carbonaceous material (C). From the carbon residue ratio, the obtained negative electrode active material powder was coated with 5 parts by weight of carbonaceous material derived from petroleum heavy oil with respect to 95 parts by weight of graphite.
(preparation of negative electrode active Material 4)
A coal tar pitch having a quinoline insoluble content of 0.05 mass% or less is subjected to heat treatment at 460 ℃ for 10 hours in a reaction furnace to obtain a bulk carbonized precursor having a softening point of 385 ℃ and a meltability. The obtained bulk carbonization precursor was charged into a metal container and heat-treated in a box-shaped electric furnace at 1000 ℃ for 2 hours under a nitrogen flow. The obtained amorphous cake was pulverized by a coarse pulverizer (roll crusher, manufactured by yota corporation), and then finely pulverized by a fine pulverizer (turbine mill, manufactured by matsubo corporation), to obtain an amorphous powder having a volume-based average particle diameter of 17 μm. In order to prevent the resulting powder from being mixed with coarse particles, the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode active material thus obtained was used as the carbonaceous material (D).
The shapes and physical properties of the produced carbonaceous materials (a), (B), (C), and (D) were measured by the methods described above. The results are shown in negative [9] [10] Table 1.
Negative electrode [9] [10] Table 1
[ Table 52]
Figure BDA0003109774980003181
Negative electrode [9] [10] [ preparation of Battery ]
Preparation of Positive electrode 1
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having a positive electrode active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the positive electrode active material layer of the positive electrode at this time was 2.35g/cm3。
Production of negative electrode 1
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (sodium carboxymethyl cellulose concentration: 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (styrene-butadiene rubber concentration: 50 mass%) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The slurry thus obtained was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having a negative electrode active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
The density of the negative electrode active material layer of the negative electrode is 1.33 to 1.36g/cm3Range of (shown in cathode [9 ], respectively)][10]The right-most column of table 2). As can be seen from the above, the content of the styrene-butadiene rubber as a binder in the negative electrode active material layer was 1 mass% with respect to the entire negative electrode active material layer. In addition, [ (thickness of negative electrode active material layer of one side)/(thickness of current collector)]The value of (2) is 75 μm/10 μm-7.5.
Production of nonaqueous electrolyte solution 1
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, fully dried hexa-ethanol was dissolved at a concentration of 1mol/LLithium fluorophosphate (LiPF)6). Further, 0.3 mass% of lithium difluorophosphate (LiPO) was contained2F2)。
Preparation of nonaqueous electrolyte solution 2
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6). Further, 0.3 mass% of trimethylsilyl methanesulfonate was contained.
Preparation of nonaqueous electrolyte solution 3
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried 6). Further, 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of nonaqueous electrolyte solution 4
In a mixture (volume ratio 3:3:4) of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a dry argon atmosphere, lithium hexafluorophosphate (LiPF) was dissolved in a concentration of 1mol/L, which was sufficiently dried6)。
Production of Battery 1
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω). The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 20.6.
Negative electrode [9] [10] example 1
A battery was produced by the method in item 1 of production of battery, using a negative electrode produced by using the negative electrode active material in item 1 of production of negative electrode as a carbonaceous material (A), a positive electrode produced in item 1 of production of positive electrode, and a nonaqueous electrolytic solution produced in item 1 of production of nonaqueous electrolytic solution. The battery was measured by the method described in the section "evaluation of battery" below. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 2
A battery was produced in the same manner as in negative electrode [9] [10] example 1 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 1 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 2", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 3
A battery was produced in the same manner as in negative electrode [9] [10] example 1 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 1 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 3", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] comparative example 1
A battery was produced in the same manner as in negative electrode [9] [10] example 1 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 1 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 4", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 4
A battery was produced in the same manner as in negative electrode [9] [10] example 1, except that the carbonaceous material (B) was used as the negative electrode active material in negative electrode [9] [10] example 1 "production of negative electrode 1", and was evaluated in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 5
A battery was produced in the same manner as in negative electrode [9] [10] example 4 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 4 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 2", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 6
A battery was produced in the same manner as in negative electrode [9] [10] example 4 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 4 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 3", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] comparative example 2
A battery was produced in the same manner as in negative electrode [9] [10] example 4 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 4 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 4", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 7
A battery was produced in the same manner as in negative electrode [9] [10] example 1, except that the carbonaceous material (C) was used as the negative electrode active material in negative electrode [9] [10] example 1 "production of negative electrode 1", and was evaluated in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 8
A battery was produced in the same manner as in negative electrode [9] [10] example 7 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 7 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 2", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 9
A battery was produced in the same manner as in negative electrode [9] [10] example 7 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 7 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 3", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] comparative example 3
A battery was produced in the same manner as in negative electrode [9] [10] example 7 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 7 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 4", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 10
A battery was produced in the same manner as in negative electrode [9] [10] example 1, except that the carbonaceous material (D) was used as the negative electrode active material in negative electrode [9] [10] example 1 "production of negative electrode 1", and was evaluated in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 11
A battery was produced in the same manner as in negative electrode [9] [10] example 10 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 10 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 2", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] example 12
A battery was produced in the same manner as in negative electrode [9] [10] example 10 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 10 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 3", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] comparative example 4
A battery was produced in the same manner as in negative electrode [9] [10] example 10 except that the nonaqueous electrolytic solution of negative electrode [9] [10] example 10 was replaced with the nonaqueous electrolytic solution produced in section "production of nonaqueous electrolytic solution 4", and the evaluation was performed in the same manner. The results are shown in negative [9] [10] Table 2.
Negative electrode [9] [10] evaluation of Battery
(Capacity measurement)
For a battery not subjected to charge/discharge cycles, initial charge/discharge was carried out for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle in this case was set as the initial capacity. The following output power measurement was performed.
(measurement of output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the output power (W). The output power before the cycle test was defined as "initial output power".
(cycle test)
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. Charging to a charging upper limit voltage of 4.2V by a constant current constant voltage method of 2C, then discharging to a discharging end voltage of 3.0V by a constant current of 2C, taking the charging and discharging cycle as 1 cycle, and repeating the cycle up to 500 cycles. The battery after the end of the cycle test was charged and discharged at 25 ℃ for 3 cycles, and the 0.2C discharge capacity of the 3 rd cycle was defined as the capacity after the cycle. The cycle retention rate was calculated from the initial capacity measured before the cycle test and the capacity after the cycle measured after the cycle test according to the following calculation formula.
Cycle retention (%) > 100 × capacity after cycle/initial capacity
The impedance Rct and the double-layer capacitance Cdl in the negative electrode [9] [10] table 2 are one of parameters contributing to the output power, and the smaller the value of the impedance Rct is, or the larger the value of the double-layer capacitance Cdl is, the more the output power tends to be improved. The "impedance Rct" and the "double-layer capacitance Cdl" are obtained by the methods described in the section describing the impedance.
The output measurement described in the above (output measurement) item was performed on the battery after the end of the cycle test, and the obtained value was taken as "post-cycle test output". The results of measuring the output power, the capacity measurement results, the cycle retention ratio, and the reaction resistance and the double-layer capacity obtained by the above-described measurement of the opposing impedance of the lithium secondary batteries of the negative electrode [9] [10] example and the negative electrode [9] [10] comparative example are shown in Table 2 of the negative electrode [9] [10 ].
Cathode [9] [10] TABLE 2
[ Table 53]
Figure BDA0003109774980003231
From the results of table 2 of the negative electrode [9] [10], it is understood that by containing a specific compound such as lithium difluorophosphate, trimethylsilyl methanesulfonate, hexamethylcyclotrisiloxane and the like in the nonaqueous electrolytic solution, and by containing a negative electrode active material having a tap density of 0.1 or more and a pore volume of 0.01mL/g or more in the range of 0.01 μm to 1 μm as measured by a mercury porosimeter in the negative electrode, it is possible to realize a high output after cycling and a high cycle retention rate even for a large-sized battery, and thus to provide a lithium secondary battery having both a high output and a long life.
Further, by containing the specific compound in the nonaqueous electrolytic solution and making the reaction resistance of the counter battery of the negative electrode 500 Ω or less, it is possible to realize a high output after the cycle and a high cycle retention rate even for a large-sized battery, and to achieve both a high output and a good life.
Electrolyte solution [1] manufacture of secondary battery
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the DC resistance component measured by the 10kHz AC method was about 5 milliohms.
[ evaluation of Battery ]
(method of measuring initial Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles (voltage range 4.1V to 3.0V) at 25 ℃ in a voltage range of 4.1V to 3.0V. The initial capacity was determined as 0.2C (1C is a current value of a 1-hour discharge rated capacity determined by a discharge capacity at a 1-hour rate (one-hour-rate), which is the same below) discharge capacity at the 5 th cycle.
(method of measuring Low temperature output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at-30 ℃ at 0.1C, 0.3C, 1.0C, 3.0C, and 5.0C, respectively, and the voltage at the 10 th second was measured. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the output power (W).
Electrolyte [1] example 1
In a dry argon atmosphere, 1 mol/ml are added to a mixture of Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) (volume ratio 15:85)L lithium hexafluorophosphate (LiPF) was added6) And dissolved, and the mixed solution was mixed with hexamethylcyclotrisiloxane in an amount of 0.3 mass% to prepare a nonaqueous electrolytic solution. A battery was produced using the nonaqueous electrolyte solution in accordance with the above method, and the low-temperature output was measured. As a result, an electrolyte [1]]Shown in table 1.
Electrolyte [1] example 2
Electrolyte [1] the nonaqueous electrolyte prepared in example 1 with a volume ratio of EC to EMC of 20:80 was used to fabricate a battery, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 3
Electrolyte [1] a nonaqueous electrolyte prepared by changing the nonaqueous solvent in example 1 to a mixture of EC, dimethyl carbonate (DMC) and EMC (volume ratio 15:40:45) was used to prepare a battery, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 4
A battery was produced using a nonaqueous electrolytic solution prepared by mixing phenyldimethylsiloxane instead of hexamethylcyclotrisiloxane in electrolyte [1] example 1, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 5
A battery was produced using a nonaqueous electrolytic solution prepared by mixing hexamethyldisiloxane in place of hexamethylcyclotrisiloxane in the electrolytic solution [1] example 1, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 6
Using a nonaqueous electrolytic solution prepared by mixing trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane in electrolyte [1] example 1, a battery was produced, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [1 ].
Electrolyte [1] example 7
A battery was produced using a nonaqueous electrolytic solution prepared by mixing methyl fluorosulfonate instead of hexamethylcyclotrisiloxane in the electrolytic solution [1] in example 1, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 8
A battery was produced using a nonaqueous electrolytic solution obtained by storing lithium nitrate mixed in place of hexamethylcyclotrisiloxane in the electrolytic solution [1] in example 1 for 3 days, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 9
A battery was produced using, as a nonaqueous electrolyte solution, a nonaqueous electrolyte solution prepared by mixing lithium difluorophosphate prepared according to the method described in Inorganic Nuclear Chemistry Letters (1969),5, (7) on pages 581 to 582 in place of hexamethylcyclotrisiloxane as the electrolyte solution [1] in example 1, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 10
Electrolyte [1] in example 9, a battery was produced using a nonaqueous electrolyte obtained by changing the mixing amount of lithium difluorophosphate to 0.08 mass% with respect to the mixed solution of a nonaqueous solvent and lithium hexafluorophosphate, and the low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 11
A battery was prepared using a nonaqueous electrolytic solution obtained by storing lithium acetate mixed in place of hexamethylcyclotrisiloxane in the electrolytic solution [1] in example 1 for 3 days, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] example 12
Production of secondary battery-2
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent 2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Wherein the front and back surfaces are all in lengthThe uncoated portion was set to 50mm in the direction, and the length of the active material layer was 780 mm.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ preparation of electrolyte ]
A nonaqueous electrolytic solution similar to the electrolytic solution [1] in example 1 was prepared.
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are mounted in the battery case so as to be exposed to the outside.
Then, 5mL of an electrolyte solution described later was injected thereinto, followed by caulking, thereby producing a 18650 type cylindrical battery. The rated discharge capacity of the battery was about 0.7 ampere-hour (Ah), and the direct current resistance measured by the 10kHz alternating current method was about 35 milliohms (m Ω). The area ratio of the total electrode area of the positive electrode to the surface area of the case of the secondary battery was 19.4 times. The low-temperature output of the above-mentioned battery was measured in the same manner as in example 1 of electrolyte [1 ]. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 1
Electrolyte solution [1] a battery was produced using a nonaqueous electrolyte solution prepared without mixing hexamethylcyclotrisiloxane in example 1, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 2
A battery was produced using the nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane as the electrolyte [1] in example 2, and the low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 3
A battery was produced using the nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane as the electrolyte [1] in example 3, and the low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 4
To a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 4:6) was added lithium hexafluorophosphate (LiPF) at 1mol/L under an atmosphere of dry argon6) And dissolved, and then hexamethylcyclotrisiloxane was mixed in an amount of 0.3 mass% with respect to the mixed solution to prepare a nonaqueous electrolytic solution.
A battery was produced using this nonaqueous electrolyte, and the low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 5
A battery was produced using a nonaqueous electrolytic solution prepared by mixing phenyldimethylsiloxane in place of hexamethylcyclotrisiloxane in comparative example 4 of electrolytic solution [1], and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 6
A battery was produced using a nonaqueous electrolytic solution prepared by mixing hexamethyldisiloxane in place of hexamethylcyclotrisiloxane in the electrolytic solution [1] comparative example 4, and the low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 7
A battery was produced using a nonaqueous electrolytic solution prepared by mixing trimethylsilyl methanesulfonate instead of the hexamethylcyclotrisiloxane in comparative example 4 of electrolytic solution [1], and low-temperature output was measured. The results are shown in Table 1 for electrolyte [1 ].
Electrolyte [1] comparative example 8
A battery was produced using a nonaqueous electrolytic solution prepared by mixing methyl fluorosulfonate instead of hexamethylcyclotrisiloxane in the electrolytic solution [1] comparative example 4, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 9
A battery was produced using a nonaqueous electrolytic solution obtained by storing lithium nitrate mixed in place of hexamethylcyclotrisiloxane in the electrolytic solution [1] comparative example 4 for 3 days, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 10
A battery was produced using a nonaqueous electrolytic solution prepared by mixing lithium difluorophosphate instead of hexamethylcyclotrisiloxane as in comparative example 4 of electrolytic solution [1], and the low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 11
A battery was prepared using a nonaqueous electrolytic solution obtained by storing lithium acetate mixed in place of hexamethylcyclotrisiloxane in the electrolytic solution [1] comparative example 4 for 3 days, and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 12
A battery was produced using the nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane as the electrolyte [1] comparative example 4, and the low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] comparative example 13
Electrolyte [1] in example 12, a battery was produced using the same nonaqueous electrolyte as in comparative example 1 of electrolyte [1], and low-temperature output was measured. The results are shown in Table 1 for the electrolyte [1 ].
Electrolyte [1] Table 1
[ Table 54]
Figure BDA0003109774980003291
As is clear from table 1 of the electrolyte solutions [1] below, the lithium secondary batteries of examples 1 to 11, which contained specific amounts of EC and a specific compound in a nonaqueous electrolyte solution, exhibited improved low-temperature output characteristics not only as compared with the lithium secondary battery of comparative example 12, which contained an excessive amount of EC and did not contain a specific compound, but also as compared with the lithium secondary batteries of comparative examples 1 to 3, which contained no specific compound despite the EC amount being within a specific range, and comparative examples 4 to 11, which contained an excessive amount of EC despite the specific compound. Further, the lithium secondary battery of example 12, which is the electrolyte solution [1] containing a specific amount of EC and a specific compound in a nonaqueous electrolyte solution, is improved in low-temperature output characteristics as compared with the lithium secondary battery of comparative example 13, which is the electrolyte solution [1] containing no specific compound although the EC amount is within a specific range.
In addition, the effect is not the simple superposition of the two, and the effect is obviously enhanced by meeting the two conditions. The electrolyte [1] table 1 shows that the rate of increase in low-temperature output when a nonaqueous electrolyte solution containing a specific compound (except the same composition) is used is larger in the electrolyte [1] examples 1 to 12 than in the electrolyte [1] comparative examples 4 to 11 in which the EC amount is excessive, and the effect of the present invention is large.
It is understood that the output increase rate of the electrolytic solution [1] in example 12 was 20.8% relative to the electrolytic solution [1] in comparative example 13, and the output increase rate of the electrolytic solution [1] in example 1, which is different in the battery structure from the electrolytic solution [1] in comparative example 1, was 26.4% although the same material was used, and the battery structure had a large influence on the effect of the nonaqueous electrolytic solution of the present invention. That is, the effect of the present invention is particularly great for a high-capacity battery or a battery with a small direct current resistance.
Further, although not shown in the table, when an electrolyte solution having an EC content of less than 1% by volume was used, the initial capacity was slightly decreased as compared with the electrolyte solution [1] example 1, and the output characteristics and cycle characteristics at room temperature were deteriorated.
As described above, the nonaqueous electrolyte solution for a secondary battery according to the present invention, that is, the nonaqueous electrolyte solution for a secondary battery having the following characteristics, can exhibit very large low-temperature output characteristics: the nonaqueous electrolyte solution is a mixed solvent containing at least ethylene carbonate, wherein the proportion of the ethylene carbonate to the total amount of the nonaqueous solvent is 1 to 25% by volume, and the nonaqueous electrolyte solution further contains at least one compound selected from the following substances, and the content of the compound in the whole nonaqueous electrolyte solution is 10ppm or more, wherein the substances include: a cyclic siloxane compound represented by general formula (1), a fluorosilane compound represented by general formula (2), a compound represented by general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate.
In addition, this effect can be more remarkably exhibited in the battery structure of the electrolyte solution [1] of example 1, that is, in the battery having a high capacity and the battery having a small direct current resistance, than in the battery structure of the electrolyte solution [1] of example 12.
Electrolyte solution 2 (manufacture of secondary battery-1)
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent 2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Both the front and back surfaces were provided with 50mm uncoated portions in the longitudinal direction, and the length of the active material layer was 780 mm.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are mounted in the battery case so as to be exposed to the outside. Then, 5mL of an electrolyte solution described later was injected thereinto, followed by caulking, thereby producing a 18650 type cylindrical battery. The capacity of the battery element housed in 1 battery case of the secondary battery, that is, the rated discharge capacity of the secondary battery is about 0.7 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method is about 35 milliohms (m Ω).
[ evaluation of Battery ]
(initial Charge and discharge)
The manufactured battery was charged to 4.2V at 25 ℃ by a constant current constant voltage charging method of 0.2C, and then discharged to 3.0V at a constant current of 0.2C. This was subjected to 5 cycles to stabilize the cell. The discharge capacity at the 5 th cycle at this time was defined as an initial capacity. Further, a current value of a 1-hour discharge rated capacity depending on a discharge capacity of a 1-hour rate (one-hour-rate) was taken as 1C.
(cycle test)
The battery subjected to initial charge and discharge was charged at 60 ℃ to 4.2V at a constant current and constant voltage of 1C, and then discharged at a constant current of 1C to 3.0V for 500 cycles of charge and discharge. The ratio of the 500 th-cycle discharge capacity to the 1 st-cycle discharge capacity at this time was defined as the cycle retention rate.
(Low temperature test)
The batteries subjected to initial charge and discharge were charged to 4.2V by a constant current constant voltage charging method of 0.2C at 25 ℃ and then subjected to constant current discharge of 0.2C at-30 ℃. The discharge capacity at this time was defined as an initial low-temperature capacity, and the ratio of the initial low-temperature capacity to the initial capacity was defined as an initial low-temperature discharge rate.
Further, the battery after the cycle test was charged to 4.2V at 25 ℃ by a constant current constant voltage charging method of 0.2C, and then discharged to 3.0V at a constant current of 0.2C. This was subjected to 3 cycles, and the discharge capacity at the 3 rd cycle was defined as the capacity after the cycle. Then, the same battery was charged to 4.2V by a constant current constant voltage charging method at 25 ℃ and 0.2C, and then constant current discharge was performed at-30 ℃. The discharge capacity at this time was taken as the low-temperature capacity after the cycle, and the ratio of the low-temperature capacity after the cycle to the capacity after the cycle was taken as the low-temperature discharge rate after the cycle.
Electrolyte [2] example 1
To a mixture of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) (volume ratio 2:4:4) was added lithium hexafluorophosphate (LiPF) at 0.9mol/L under dry argon atmosphere6) The resultant mixture was dissolved to contain 0.3 mass% of lithium difluorophosphate prepared by the method described in Inorganic Nuclear Chemistry Letters (1969),5(7), pages 581 to 582, to prepare a nonaqueous electrolytic solution. A 18650 type cylindrical battery was produced using this nonaqueous electrolyte, and the cycle retention rate and the low-temperature discharge rate were measured. As a result, for example, an electrolyte [2] ]Shown in table 1. Then, the electrolyte solution was recovered from the battery after the low-temperature capacity measurement after the cycle by a centrifugal separator, and the amount of dimethyl carbonate (DMC) produced in the transesterification reaction was 0.5 mass% in the electrolyte solution when the amount was analyzed by Gas Chromatography (GC).
Electrolyte [2] comparative example 1
A 18650 type cylindrical battery was produced in the same manner as in electrolyte [2] example 1 except that lithium difluorophosphate was not contained, and the cycle retention rate and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [2 ]. Then, the electrolyte solution was recovered from the battery after the low-temperature capacity measurement after the cycle by a centrifugal separator, and the amount of dimethyl carbonate (DMC) produced in the transesterification reaction was 9.7% by mass in the electrolyte solution when the amount was analyzed by Gas Chromatography (GC).
Electrolyte [2] comparative example 2
To a mixture of Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio 2:8) was added lithium hexafluorophosphate (LiPF) at 0.9mol/L under dry argon atmosphere6) And dissolving the mixtureThe liquid contained 0.3 mass% of lithium difluorophosphate to prepare a nonaqueous electrolytic solution. A 18650 type cylindrical battery was produced using this nonaqueous electrolyte, and the cycle retention rate and the low-temperature discharge rate were measured. As a result, for example, an electrolyte [2] ]Shown in table 1.
Electrolyte [2] example 2
A 18650 type cylindrical battery was produced in the same manner as in example 1 of electrolyte [2] except that methyl-n-propyl carbonate was used instead of ethyl methyl carbonate, and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [2 ].
Electrolyte [2] comparative example 3
A 18650 type cylindrical battery was produced in the same manner as in electrolyte [2] example 2 except that lithium difluorophosphate was not contained, and the cycle retention rate and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [2 ].
Electrolyte 2 (manufacture of secondary battery-2)
Manufacture of positive electrode
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode.
Manufacture of negative electrode
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
Assembly of Battery
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently impregnate the electrodes, and the electrode was sealed to prepare a rectangular battery. The capacity of the battery element housed in 1 battery case of the secondary battery, that is, the rated discharge capacity of the secondary battery, was about 6 ampere hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω).
Electrolyte [2] example 3
A rectangular battery was produced using the electrolyte used in example 1 of electrolyte [2], and a cycle test and a low-temperature test were carried out in the same manner as in example 1 of electrolyte [2], and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [2 ].
Electrolyte [2] comparative example 4
A rectangular battery was produced using the electrolyte used in comparative example 1 of electrolyte [2], and a cycle test and a low-temperature test were performed to measure the cycle retention and the low-temperature discharge rate. The results are shown in Table 1 for electrolyte [2 ].
Electrolyte [2] comparative example 5
A rectangular battery was produced using the electrolyte used in comparative example 2 of electrolyte [2], and a cycle test and a low-temperature test were performed to measure the cycle retention and the low-temperature discharge rate. The results are shown in Table 1 for electrolyte [2 ].
Electrolyte [2] Table 1
[ Table 55]
Figure BDA0003109774980003341
As is clear from table 1 of the electrolyte solution [2], when cylindrical batteries (electrolyte solution [2] examples 1 and 2, electrolyte solution [2] comparative examples 1 to 3) and rectangular batteries (electrolyte solution [2] example 3, electrolyte solution [2] comparative examples 4 and 5) are compared with each other, the lithium secondary battery of the electrolyte solution [2] example containing both an asymmetric chain carbonate and a difluorophosphate in a nonaqueous electrolyte solution is improved in both cycle retention and low-temperature discharge rate as compared with the lithium secondary battery of the electrolyte solution [2] comparative example not containing any of these.
As described above, the cylindrical batteries of the present example and the comparative example had a rated discharge capacity of less than 3 ampere-hours (Ah) and a dc resistance component of more than 10 milliohms (m Ω). On the other hand, the square batteries of the present example and the comparative example had a rated discharge capacity of 3 ampere-hours (Ah) or more and a dc resistance component of 10 milliohms (m Ω) or less. That is, the prismatic battery of the present example and the present comparative example has a smaller resistance and a larger capacitance than the cylindrical battery. Further, in the electrolyte solution [2] example 3, the low-temperature characteristics are improved to a greater extent than in the electrolyte solution [2] comparative example 4 than in the electrolyte solution [2] comparative example 1, and the effect of the present invention is greater in the secondary battery with a large capacitance or the secondary battery with a small direct current resistance.
Electrolyte [3] manufacture of secondary battery-1
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm).
Then, 20mL of the nonaqueous electrolytic solutions of the following electrolyte solution [3] examples and electrolyte solution [3] comparative examples were poured into a battery can equipped with an electrode group, and the electrodes were sufficiently impregnated and sealed to prepare a rectangular battery. The rated discharge capacity of the battery was about 6 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω). The area ratio of the total electrode area of the positive electrode to the surface area of the case of the secondary battery was 20.65 times.
[ evaluation of Battery ]
(Capacity measurement)
A fresh battery that has not been charged and discharged is initially charged and discharged for 5 cycles (voltage range 4.1V to 3.0V) at 25 ℃ in a voltage range of 4.1V to 3.0V. The initial capacity was determined as 0.2C (1C is a current value of a 1-hour discharge rated capacity determined by a discharge capacity at a 1-hour rate (one-hour-rate), which is the same below) discharge capacity at the 5 th cycle.
(measurement of output Power)
The charge was carried out at a constant current of 0.2C for 150 minutes in an environment of 25 ℃ and the discharge was carried out at 0.1C, 0.3C, 1.0C, 3.0C and 5.0C for 10 seconds in an environment of-30 ℃ to measure the voltage at 10 th second. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the output power (W).
Electrolyte [3] example 1
To a mixture (volume ratio 3:6:1) of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and Methyl Propionate (MP) was added lithium hexafluorophosphate (LiPF) at 1mol/L under a dry argon atmosphere6) And dissolved, and then mixed with hexamethylcyclotrisiloxane in an amount of 0.3 mass% to prepare a nonaqueous electrolyte solution. A battery was produced using this nonaqueous electrolyte solution by the above-described method, and the low-temperature output was measured. As a result, for example, an electrolyte [3]]Shown in table 1.
Electrolyte [3] example 2
A battery was produced using a nonaqueous electrolytic solution prepared by replacing methyl propionate in the electrolytic solution [3] example 1 with an equal amount of Ethyl Acetate (EA), and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 3
A battery was produced using a nonaqueous electrolytic solution prepared by replacing methyl propionate in example 1 of electrolyte [3] with an equal amount of Methyl Acetate (MA), and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 4
To a mixture of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC), Methyl Propionate (MP) and Methyl Acetate (MA) (volume ratio 30:60:5:5) was added lithium hexafluorophosphate (LiPF) at 1mol/L under dry argon atmosphere6) And dissolved, and then mixed with hexamethylcyclotrisiloxane in an amount of 0.3 mass% to prepare a nonaqueous electrolytic solution. A battery was produced using this nonaqueous electrolyte solution by the above-described method, and the low-temperature output was measured. As a result, for example, an electrolyte [3]]Shown in table 1.
Electrolyte [3] example 5
Using the nonaqueous electrolytic solution prepared by changing the volume ratio of the mixture of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and Methyl Propionate (MP) to 3:4:3 in the electrolytic solution [3] example 1, a battery was produced in accordance with the above-described method, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 6
To a mixture of Ethylene Carbonate (EC) and Methyl Propionate (MP) (volume ratio 3:7) was added lithium hexafluorophosphate (LiPF) at 1mol/L under dry argon atmosphere6) And dissolved, and then mixed with the mixed solution in an amount of 0.3 mass% to prepare a nonaqueous electrolytic solution. A battery was produced using the nonaqueous electrolyte solution by the above-described method, and the low-temperature output was measured. As a result, for example, an electrolyte [3] ]Shown in table 1.
Electrolyte [3] example 7
A battery was produced using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of phenyldimethylsiloxane instead of the hexamethylcyclotrisiloxane in the electrolytic solution [3] example 1, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 8
A battery was produced using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of hexamethylcyclodisiloxane in place of the hexamethylcyclotrisiloxane in the electrolytic solution [3] example 1, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 9
A battery was produced using, as a nonaqueous electrolyte solution, a nonaqueous electrolyte solution obtained by mixing an equal amount of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane in electrolyte solution [3] example 1, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 10
A battery was produced using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of methyl fluorosulfonate in place of hexamethylcyclotrisiloxane in the electrolytic solution [3] example 1, and low-temperature output power was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 11
A battery was produced using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of lithium nitrate in place of hexamethylcyclotrisiloxane in the electrolytic solution [3] in example 1 and storing for 3 days, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 12
A battery was produced using, as a nonaqueous electrolytic solution, an equivalent amount (an amount of 0.3 mass% relative to a mixed solution of a nonaqueous solvent and lithium hexafluorophosphate) of lithium difluorophosphate prepared by the method described in organic Nuclear Chemistry Letters (1969), page 581 to page 582 of 5(7) in place of hexamethylcyclotrisiloxane in the electrolytic solution [3] in example 1, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 13
A battery was produced using a nonaqueous electrolytic solution prepared by changing the mixing amount of lithium difluorophosphate in the electrolytic solution [3] in example 12 to 0.08 mass% with respect to the mixing solution of the nonaqueous solvent and lithium hexafluorophosphate, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] example 14
Production of secondary battery-2
Manufacture of positive electrode
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Both the front and back surfaces were provided with 50mm uncoated portions in the longitudinal direction, and the length of the active material layer was 780 mm.
Manufacture of negative electrode
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ preparation of electrolyte ]
The same nonaqueous electrolytic solution as in example 1 of electrolyte [3] was prepared.
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are housed in the battery case so as to be exposed to the outside. Then, 5mL of an electrolyte solution described later was injected thereinto, followed by caulking and molding to manufacture a 18650 type cylindrical battery. The rated discharge capacity of the battery was about 0.7Ah, and the direct current resistance measured by the 10kHz alternating current method was about 35 milliohms (m.OMEGA.). The area ratio of the total electrode area of the positive electrode to the surface area of the case of the secondary battery was 19.4 times. In the above battery, the low-temperature output was measured in the same manner as in example 1 of the electrolyte [3 ]. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 1
The nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane was used as the electrolyte [3] in example 1, and a battery was produced by the above method, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 2
The nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane was used as the electrolyte [3] in example 2, and a battery was produced by the above method, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 3
Electrolyte solution [3] the nonaqueous electrolyte solution prepared without mixing hexamethylcyclotrisiloxane in example 3 was used to prepare a battery by the above-described method, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 4
The nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane was used as the electrolyte [3] in example 4, and a battery was produced by the above method, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 5
The nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane was used as the electrolyte [3] in example 5, and a battery was produced by the above method, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 6
To a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) was added lithium hexafluorophosphate (LiPF) at 1mol/L under a dry argon atmosphere6) And dissolved to prepare a nonaqueous electrolytic solution. A battery was produced using this nonaqueous electrolyte solution by the above-described method, and the low-temperature output was measured. As a result, for example, an electrolyte [3]]Shown in table 1.
Electrolyte [3] comparative example 7
To a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3:7) was added lithium hexafluorophosphate (LiPF) at 1mol/L under a dry argon atmosphere 6) And dissolved, and then mixed with hexamethylcyclotrisiloxane in an amount of 0.3 mass% to prepare a nonaqueous electrolytic solution. A battery was produced using this nonaqueous electrolyte solution by the above-described method, and the low-temperature output was measured. As a result, for example, an electrolyte [3]]Shown in table 1.
Electrolyte [3] comparative example 8
A battery was produced by the above-described method using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of phenyldimethylsiloxane instead of hexamethylcyclotrisiloxane as in the electrolytic solution [3] comparative example 7, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 9
A battery was produced by the above-described method using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of hexamethylcyclodisiloxane in place of hexamethylcyclotrisiloxane as electrolytic solution [3] comparative example 7, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 10
A battery was produced by the above-described method using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane in electrolyte [3] comparative example 7, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 11
A battery was produced by the above-described method using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of methyl fluorosulfonate in place of hexamethylcyclotrisiloxane in the electrolytic solution [3] comparative example 7, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 12
A battery was produced by the above-described method using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of lithium nitrate in place of hexamethylcyclotrisiloxane in the electrolytic solution [3] comparative example 7 and storing for 3 days, and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 13
A battery was produced by the above-described method using, as a nonaqueous electrolytic solution, a nonaqueous electrolytic solution obtained by mixing an equal amount of lithium difluorophosphate instead of hexamethylcyclotrisiloxane in the electrolytic solution [3] comparative example 7, and the low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] comparative example 14
Electrolyte [3] in example 14, a battery was produced by the above-described method using a nonaqueous electrolyte prepared in the same manner as in comparative example 1 of electrolyte [3], and low-temperature output was measured. The results are shown in Table 1 for electrolyte [3 ].
Electrolyte [3] Table 1
[ Table 56]
Figure BDA0003109774980003411
As is clear from Table 1 of the electrolyte [3], the lithium secondary batteries of examples 1 to 13, which contain a chain carboxylate and a specific compound in a nonaqueous electrolyte, have improved low-temperature output characteristics not only compared with the lithium secondary battery of comparative example 6, which does not contain any of the above electrolyte [3], but also compared with the lithium secondary batteries of comparative examples 1 to 5, which do not contain any specific compound, and comparative examples 7 to 13, which do not contain any chain carboxylate, of the electrolyte [3 ]. In addition, the effect is not a mere superposition of the two, and the effect is obviously enhanced by using the two.
While the output increase rate of the electrolytic solution [3] in example 14 was about 21% relative to the electrolytic solution [3] in comparative example 14, the output increase rate of the electrolytic solution [3] in example 1 using the same material and having a different battery structure was about 29% relative to the electrolytic solution [3] in comparative example 1, and it was found that the battery structure had an influence on the effect of the nonaqueous electrolytic solution of the present invention.
As described above, the nonaqueous electrolyte solution for a secondary battery according to the present invention, that is, the nonaqueous electrolyte solution for a secondary battery having the following characteristics, can exhibit very large low-temperature output characteristics: contains at least one chain carboxylic ester and at least one compound selected from the following substances, and the content of the compound in the whole nonaqueous electrolyte is more than 10ppm, wherein the substances comprise: a cyclic siloxane compound represented by general formula (1), a fluorosilane compound represented by general formula (2), a compound represented by general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate.
Production of electrolyte [4] < Secondary Battery-1 (production of Square Battery)
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was coated to a thickness of 1Both sides of 5 μm aluminum foil were dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer with a width of 100mm, a length of 100mm and a non-coated portion with a width of 30mm, to obtain a positive electrode.
[ production of negative electrode ]
2kg of artificial graphite powder KS-44 (trade name, manufactured by timecal Co., Ltd.) and 1kg of petroleum pitch were mixed, and the resulting slurry mixture was heated in a batch type heating furnace in an inert atmosphere for 2 hours up to 1100 ℃ and held at that temperature for 2 hours.
The resulting material is pulverized, and the particle size is adjusted to 18 to 22 μm by a vibrating sieve, thereby finally obtaining an "amorphous-coated graphite-based carbonaceous material" having a graphite surface coated with 7 mass% of amorphous carbon. This "amorphous coated graphite-based carbonaceous material" was used as a negative electrode active material, and 98 parts by weight of the "amorphous coated graphite-based carbonaceous material" were mixed with 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (the concentration of sodium carboxymethylcellulose being 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (the concentration of styrene-butadiene rubber being 50 mass%) as a binder, and the resulting mixture was made into a slurry by a disperser. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10mm) equipped with a discharge valve. Then, 20mL of a nonaqueous electrolyte solution described later was injected into the battery can with the electrode group attached, and the electrodes were sufficiently impregnated and sealed to prepare a rectangular battery. The capacity of the battery element contained in 1 battery case of the secondary battery, that is, the rated discharge capacity of the battery was about 6Ah, and the dc resistance component measured by the 10kHz ac method was about 5 milliohms.
Evaluation of Battery
(Capacity measurement)
For a battery not subjected to charge/discharge cycles, initial charge/discharge was carried out for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle in this case was set as the initial capacity.
(measurement of output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the output power (W).
Electrolyte [4] example 1
To a mixture (volume ratio 2:7:1) of ethylene carbonate (EC: flash point 143 ℃ C.), gamma-butyrolactone (GBL: flash point 101 ℃ C.) and diethyl carbonate (DEC: flash point 25 ℃ C.) was added 0.3mol/L of LiPF under a dry argon atmosphere6And 0.7mol/L of LiBF4And dissolved to make the mixed solution contain 1 mass% of vinylene carbonate and 0.3 mass% of hexamethylcyclotrisiloxane, thereby preparing a nonaqueous electrolytic solution. The flash point of the nonaqueous electrolyte was 61 ℃. A rectangular battery was produced using this nonaqueous electrolyte solution by the above-described method, and the output was measured. As a result, for example, an electrolyte [4]]Shown in table 1.
Electrolyte [4] example 2
A rectangular battery was produced in the same manner as in example 1 of electrolyte [4] except that a nonaqueous electrolyte was prepared using phenyldimethylsiloxane instead of hexamethylcyclotrisiloxane, and the output was measured. The results are shown in Table 1 for electrolyte [4 ].
Electrolyte [4] example 3
A rectangular battery was produced in the same manner as in example 1 of electrolyte [4], except that a nonaqueous electrolyte was prepared using methyl fluorosulfonate instead of hexamethylcyclotrisiloxane, and the output was measured. The results are shown in Table 1 for electrolyte [4 ].
Electrolyte [4] example 4
A rectangular battery was produced in the same manner as in example 1 of electrolyte [4], except that a nonaqueous electrolyte was prepared using lithium difluorophosphate prepared by the method described in Inorganic Nuclear Chemistry Letters (1969),5, (7) on pages 581 to 582 in place of hexamethylcyclotrisiloxane, and the output power was measured. The results are shown in Table 1 for electrolyte [4 ].
Electrolyte [4] comparative example 1
A rectangular battery was produced in the same manner as in example 1 of electrolyte [4] except that the nonaqueous electrolyte solution contained no hexamethylcyclotrisiloxane, and the output was measured. The results are shown in Table 1 for electrolyte [4 ].
Electrolyte [4] < manufacture of Secondary Battery-2 (manufacture of cylindrical Battery) ]
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Both the front and back surfaces were provided with 50mm uncoated portions in the longitudinal direction, and the length of the active material layer was 780 mm.
[ production of negative electrode ]
2kg of artificial graphite powder KS-44 (trade name, manufactured by timecal Co., Ltd.) and 1kg of petroleum pitch were mixed, and the resulting slurry mixture was heated in a batch type heating furnace in an inert atmosphere for 2 hours up to 1100 ℃ and held at that temperature for 2 hours.
The resulting material is pulverized, and the particle size is adjusted to 18 to 22 μm by a vibrating sieve, thereby finally obtaining an "amorphous-coated graphite-based carbonaceous material" having a graphite surface coated with 7 mass% of amorphous carbon. This "amorphous coated graphite-based carbonaceous material" was used as a negative electrode active material, and 98 parts by weight of the "amorphous coated graphite-based carbonaceous material" were mixed with 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (the concentration of sodium carboxymethylcellulose being 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (the concentration of styrene-butadiene rubber being 50 mass%) as a binder, and the resulting mixture was made into a slurry by a disperser. The slurry thus obtained was applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are housed in the battery case so as to be exposed to the outside. Then, 5mL of a nonaqueous electrolytic solution described later was injected thereinto, followed by caulking and molding to produce a 18650 type cylindrical battery. The capacity of the battery element housed in 1 battery case of the secondary battery, that is, the rated discharge capacity of the battery is about 0.7 ampere-hour (Ah), and the direct-current resistance component measured by the 10kHz alternating-current method is about 35 milliohms (m Ω).
Electrolyte [4] example 5
A cylindrical battery was produced using the nonaqueous electrolyte used in electrolyte [4] example 1 as a nonaqueous electrolyte, and the output was measured. The results are shown in Table 1 for electrolyte [4 ].
Electrolyte [4] comparative example 2
A cylindrical battery was produced in the same manner as in example 5 using the electrolyte solution [4], except that the nonaqueous electrolyte solution used in comparative example 1 using the electrolyte solution [4] was used as the nonaqueous electrolyte solution, and the output was measured. The results are shown in Table 1 for electrolyte [4 ].
Electrolyte [4] Table 1
[ Table 57]
No. Specific compound Output power (W)
Example 1 Hexamethylcyclotrisiloxane 500
Example 2 Phenyl dimethyl fluorosilane 510
Example 3 Fluorosulfonic acid methyl ester 510
Example 4 Lithium difluorophosphate 525
Example 5 Hexamethylcyclotrisiloxane 45
Comparative example 1 ――― 390
Comparative example 2 ――― 37
As is clear from Table 1 of the electrolyte [4], the output of the lithium secondary battery of the present example was improved by comparing the respective prismatic batteries (examples 1 to 4 of the electrolyte [4], comparative example 1 of the electrolyte [4 ]) and the cylindrical batteries (example 5 of the electrolyte [4], comparative example 2 of the electrolyte [4 ]).
As described above, the square batteries of the present example and the present comparative example had a rated discharge capacity of 3 ampere hours (Ah) or more and a dc resistance component of 10 milliohms (m Ω) or less. On the other hand, the cylindrical batteries of the present example and the comparative example had a rated discharge capacity of less than 3 ampere-hours (Ah) and a dc resistance component of more than 10 milliohms (m Ω). That is, the prismatic battery of the present example and the present comparative example has a smaller resistance and a larger capacitance than the cylindrical battery. Further, the effect of the present invention is greater in the case of the electrolytic solution [4] example 1, in which the output power is improved to a greater extent than in the case of the electrolytic solution [4] example 5, in which the output power is improved to a greater extent than in the case of the electrolytic solution [4] comparative example 2, and in the case of the secondary battery having a large capacitance or the secondary battery having a small direct current resistance.
Electrolyte [5] manufacture of secondary battery
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10mm) equipped with a discharge valve. Then, 20mL of a nonaqueous electrolyte solution described later was injected into the battery can with the electrode group attached, and the electrodes were sufficiently impregnated and sealed to prepare a rectangular battery. The capacity of the battery element accommodated in 1 battery case of the secondary battery, that is, the rated discharge capacity of the battery was about 6Ah, and the dc resistance component measured by the 10kHz ac method was about 5 milliohms (m Ω).
[ evaluation of Battery ]
(Capacity measurement)
For a battery not subjected to charge/discharge cycles, initial charge/discharge was carried out for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle in this case was set as the initial capacity.
(measurement of output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the output power (W).
(cycle test)
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.2V by constant current constant voltage method of 2C, discharging to the end discharge voltage of 3.0V by constant current of 2C, taking the charge-discharge cycle as 1 cycle, and repeating the cycle up to 500 times.
(preservation test)
The storage test was conducted in a high temperature environment of 60 ℃. The battery previously charged to a charging upper limit voltage of 4.2V by a constant current constant voltage method under an environment of 25 ℃ was stored at 60 ℃ for 1 month.
The output power of the battery after the capacity measurement, the battery after the cycle test, and the battery after the storage test was measured and used as the initial output power, the output power after the cycle, and the output power after the storage, respectively.
Electrolyte [5] example 1
To a mixture of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) (volume ratio 2:5:3) was added 1mol/L LiPF under dry argon atmosphere 6And 0.01mol/L of LiN (CF)3SO2)2And dissolved to contain 0.3 mass% of hexamethylcyclotrisiloxane to prepare a nonaqueous electrolytic solution. A battery was produced using this nonaqueous electrolyte solution by the above-described method, and the initial output, the output after cycling, and the output after storage were measured. Results as electrolyte [5]]Shown in table 1.
Electrolyte [5] example 2
A battery was produced in the same manner as in example 1 of electrolyte [5] except that a nonaqueous electrolyte was prepared using phenyldimethylsiloxane instead of hexamethylcyclotrisiloxane, and the initial output, the output after cycling, and the output after storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 3
A battery was produced in the same manner as in example 1 of electrolyte [5] except that a nonaqueous electrolyte solution was prepared using methyl fluorosulfonate instead of hexamethylcyclotrisiloxane, and the initial output, the output after cycling, and the output after storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 4
Batteries were produced in the same manner as in example 1 of electrolyte [5], except that lithium difluorophosphate prepared by the method described in Inorganic Nuclear Chemistry Letters (1969),5, (7) on pages 581 to 582 was used in place of hexamethylcyclotrisiloxane to prepare a nonaqueous electrolyte, and the initial output, the output after circulation, and the output after storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 5
Except that lithium bis (oxalato) borate (LiBOB) was used instead of LiN (CF)3SO2)2Prepared into a non-aqueous electrolyte, and an electrolyte [5]]In example 1, a battery was produced in the same manner as in example 1, and the initial output, the post-cycle output, and the post-storage output were measured. Results as electrolyte [5]]Shown in table 1.
Electrolyte [5] example 6
Except that lithium bis (oxalato) borate (LiBOB) was used instead of LiN (CF)3SO2)2Prepared into a non-aqueous electrolyte, and an electrolyte [5]]In example 4, a battery was produced in the same manner as in example 4, and the initial output, the post-cycle output, and the post-storage output were measured. Results as electrolyte [5]]Shown in table 1.
Electrolyte [5] comparative example 1
Except that LiN (CF) is not dissolved in the nonaqueous electrolytic solution3SO2)2Except for this, a battery was produced in the same manner as in example 1, and the initial output, the output after cycling, and the output after storage were measured. Results as electrolytic solutions [5]]Shown in table 1.
Electrolyte [5] comparative example 2
A battery was produced in the same manner as in example 1 of electrolyte [5] except that hexamethylcyclotrisiloxane was not contained in the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] comparative example 3
Except that the nonaqueous electrolyte does not contain LiN (CF)3SO2)2And sixWith electrolytes other than methylcyclotrisiloxane [5]]In example 1, a battery was produced in the same manner as in example 1, and the initial output, the output after cycling, and the output after storage were measured. Results as electrolyte [5]]Shown in table 1.
Electrolyte [5] example 7
Production of Secondary Battery-2
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Both the front and back surfaces were provided with 50mm uncoated portions in the longitudinal direction, and the length of the active material layer was 780 mm.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are housed in the battery case so as to be exposed to the outside. Then, 5mL of a nonaqueous electrolytic solution described later was injected thereinto, followed by caulking and molding to produce a 18650 type cylindrical battery. The capacity of a battery element housed outside 1 battery of the secondary battery, that is, the rated discharge capacity of the secondary battery is about 0.7 ampere-hours (Ah), and the dc resistance component measured by the 10kHz ac method is about 35 milliohms (m Ω).
A cylindrical battery was produced using the nonaqueous electrolytic solution used in the electrolytic solution [5] example 1 as a nonaqueous electrolytic solution, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 8
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in example 2 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 9
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in example 3 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 10
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in example 4 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 11
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in example 5 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] example 12
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in example 6 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] comparative example 4
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in comparative example 1 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] comparative example 5
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in comparative example 2 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] comparative example 6
A cylindrical battery was produced in the same manner as in example 7 of electrolyte [5] except that the nonaqueous electrolyte used in comparative example 3 of electrolyte [5] was used as the nonaqueous electrolyte, and the initial output, the output after the cycle and the output after the storage were measured. The results are shown in Table 1 for electrolyte [5 ].
Electrolyte [5] Table 1
[ Table 58]
Figure BDA0003109774980003511
From an electrolyte [5]]As can be seen from Table 1, for each prismatic cell (electrolyte solution [5]]Examples 1 to 6, electrolyte [5]]Comparative examples 1 to 3), cylindrical battery (electrolyte [5]]Examples 7 to 12, electrolyte solution [5] ]Comparative examples 4 to 6) revealed that LiN (C) was contained in the nonaqueous electrolytic solution together with the nonaqueous electrolytic solutionnF2n+1SO2)2(wherein n is an integer of 1 to 4) and/or an electrolyte solution of lithium bis (oxalato) borate and a specific compound [5]]Lithium secondary batteries of examples, and electrolyte not containing any of these [5]]The output power was obtained in comparison with the lithium secondary battery of the comparative exampleAnd (5) improving.
As described above, the square batteries of the present example and the present comparative example had a rated discharge capacity of 3 ampere hours (Ah) or more and a dc resistance component of 10 milliohms (m Ω) or less. On the other hand, the cylindrical batteries of the present example and the comparative example had a rated discharge capacity of less than 3 ampere-hours (Ah) and a dc resistance component of more than 10 milliohms (m Ω). That is, the prismatic battery of the present example and the present comparative example has a smaller resistance and a larger capacitance than the cylindrical battery. The degree of improvement in output power of the electrolyte [5] of example 1 over the electrolyte [5] of comparative example 1 was greater than that of the electrolyte [5] of example 7 over the electrolyte [5] of comparative example 4. In particular, there is a large difference between the degree of output power increase after cycling and the degree of output power increase after storage. From this, it is understood that the effect of the present invention is greater in a secondary battery with a large capacitance or a secondary battery with a small direct current resistance.
Preparation of electrolyte [6] non-aqueous solvent
Commercially available Ethylene Carbonate (EC) was subjected to adsorption treatment with molecular sieve 4A (50 ℃ C., LHSV, l/hr). On the other hand, after dimethyl carbonate and ethyl methyl carbonate were sufficiently rectified at a reflux ratio of 1 and a theoretical plate number of 30, respectively, adsorption treatment was carried out using molecular sieves 4A (25 ℃ C., LHSV, l/hr). Then, they were mixed with EC: DMC: EMC (volume ratio 3:3:4), and further subjected to adsorption treatment with molecular sieve 4A (25 ℃, LHSV, l/hr) to prepare a mixed nonaqueous solvent. At this time, water or alcohols were not detected in the nonaqueous solvent.
Electrolyte (6) manufacture of secondary battery
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10mm) provided with a vent valve. Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently permeate the electrodes, and the electrode was sealed to prepare a prismatic battery. The rated discharge capacity of the battery was high, about 6Ah, and the DC resistance component measured by the 10kHz AC method was about 5 mOhm.
[ evaluation of Battery ]
(Capacity measurement)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) at a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle in this case was set as the initial capacity.
(measurement of output Power)
Under an environment of 25 ℃, charging was carried out for 150 minutes by a constant current of 0.2C, and discharging was carried out for 10 seconds at 0.1C, 0.3C, 1.0C, 3.0C, and 10.0C, respectively, and the voltage at 10 th second was measured. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the output power (W).
(cycle test)
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.2V by constant current constant voltage method of 2C, discharging to the end discharge voltage of 3.0V by constant current of 2C, taking the charge-discharge cycle as 1 cycle, and repeating the cycle up to 500 times. After the end of the cycle test, the battery was charged and discharged at 25 ℃ for 3 cycles, and the 0.2C discharge capacity of the 3 rd cycle was defined as the capacity after the cycle, and the ratio of the capacity after the cycle to the initial capacity was defined as the capacity retention ratio.
Electrolyte [6] example 1
Methanol was mixed with the above mixed nonaqueous solvent in an amount of 10ppm under a dry argon atmosphere, and lithium hexafluorophosphate (LiPF) was added at 0.8mol/L6) And dissolution is carried out. The amount of Hydrogen Fluoride (HF) in the solution was 12ppm after 1 day and 14ppm again after 2 weeks. To the mixed solution (after 2 weeks of mixing) was mixed hexamethylcyclotrisiloxane in an amount of 0.3 mass% to prepare a nonaqueous electrolytic solution. A battery was produced using the nonaqueous electrolyte solution by the above-described method, and the output and capacity retention rate were measured. Results as electrolyte [6]]Shown in table 1.
Electrolyte [6] example 2
Except in the electrolyte [6]]In example 1, the amount of methanol was changed to 20ppm based on the amount of the nonaqueous solvent and the electrolyte solution [6]]In example 1, a nonaqueous electrolytic solution was prepared in the same manner, a battery was produced using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. Results as electrolyte [6]]Shown in table 1. Further, LiPF is mixed6The amount of Hydrogen Fluoride (HF) in the mixed solution after 1 day was 16ppm, and when measured again after 2 weeks, it was 19 ppm.
Electrolyte [6] example 3
Except in the electrolyte [6]]In example 1, the mixing amount of methanol was changed relative to the mixing of non-water Solvent in an amount of not more than 35ppm, and electrolyte [6]]In example 1, a nonaqueous electrolytic solution was prepared in the same manner, a battery was produced using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. Results as electrolyte [6]]Shown in table 1. Further, LiPF is mixed6The amount of Hydrogen Fluoride (HF) in the mixed solution after 1 day was 22ppm, and when measured again after 2 weeks, it was 27 ppm.
Electrolyte [6] example 4
Except in the electrolyte [6]]In example 1, Ethylene Glycol (EG) was mixed in an amount of 15ppm based on the mixed nonaqueous solvent in place of methanol with an electrolyte solution [6]]In example 1, a nonaqueous electrolytic solution was prepared in the same manner, a battery was produced using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. Results as electrolyte [6]]Shown in table 1. Further, LiPF is mixed6The amount of Hydrogen Fluoride (HF) in the mixed solution after 1 day was 14ppm, and when measured again after 2 weeks, it was 16 ppm.
Electrolyte [6] example 5
Except in the electrolyte [6]]In example 1, an electrolytic solution [6] was mixed with ethylene glycol in an amount of 35ppm based on the mixed nonaqueous solvent in place of methanol]In example 1, a nonaqueous electrolytic solution was prepared in the same manner, a battery was produced using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. Results as electrolyte [6] ]Shown in table 1. Further, LiPF is mixed6The amount of Hydrogen Fluoride (HF) in the mixed solution after 1 day was 23ppm, and when measured again after 2 weeks, it was 27 ppm.
Electrolyte [6] example 6
Except in the electrolyte [6]]In example 1, an electrolyte solution [6] was mixed with 25ppm of methanol and 25ppm of ethylene glycol with respect to a mixed nonaqueous solvent]In example 1, a nonaqueous electrolytic solution was prepared in the same manner, a battery was produced using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. Results as electrolyte [6]]Shown in table 1. Further, LiPF is mixed6The amount of Hydrogen Fluoride (HF) in the mixed solution after 1 day was 31ppm, and was 36ppm when measured again after 2 weeks.
Electrolyte [6] example 7
A nonaqueous electrolytic solution was prepared in the same manner as in example 1 of electrolytic solution [6], except that lithium difluorophosphate (prepared by the method described in Inorganic Nuclear Chemistry Letters (1969), page 581 to page 582 of 5 (7)) was mixed in an amount of 0.3 mass% with respect to the mixed solution in example 1 of electrolytic solution [6] in place of hexamethylcyclotrisiloxane, and a battery was produced using the nonaqueous electrolytic solution, and the output and capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] example 8
A nonaqueous electrolytic solution was prepared in the same manner as in example 3 of electrolytic solution [6], except that lithium difluorophosphate was mixed in an amount of 0.3 mass% with respect to the mixed solution in example 3 of electrolytic solution [6] instead of hexamethylcyclotrisiloxane, and a battery was fabricated using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] example 9
A nonaqueous electrolytic solution was prepared in the same manner as in electrolytic solution [6] example 4 except that lithium difluorophosphate was mixed in an amount of 0.3 mass% with respect to the mixed solution in electrolytic solution [6] example 4 instead of hexamethylcyclotrisiloxane, and a battery was fabricated using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] example 10
A nonaqueous electrolytic solution was prepared in the same manner as in electrolytic solution [6] example 6 except that lithium difluorophosphate was mixed in an amount of 0.3 mass% with respect to the mixed solution in electrolytic solution [6] example 6 instead of hexamethylcyclotrisiloxane, and a battery was fabricated using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] example 11
A nonaqueous electrolytic solution was prepared in the same manner as in example 6 of electrolytic solution [6] except that trimethylsilyl methanesulfonate was mixed in an amount of 0.3 mass% with respect to the mixed solution in example 6 of electrolytic solution [6] instead of hexamethylcyclotrisiloxane, and a battery was produced using this nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] example 12
Production of secondary battery-2
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Both the front and back surfaces were provided with 50mm uncoated portions in the longitudinal direction, and the length of the active material layer was 780 mm.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ preparation of nonaqueous electrolyte solution ]
A nonaqueous electrolytic solution similar to the electrolytic solution [6] in example 6 was prepared.
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are housed in the battery case so as to be exposed to the outside. Then, 5mL of a nonaqueous electrolytic solution described later was injected thereinto, followed by caulking and molding to produce a 18650 type cylindrical battery. The rated discharge capacity of the battery was about 0.7 ampere-hour (Ah), and the direct current resistance measured by the 10kHz alternating current method was about 35 milliohms (m Ω). The output and capacity retention of the above-mentioned battery were measured in the same manner as in example 6 of electrolyte [6 ]. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] comparative example 1
Electrolyte [6] in example 3, a battery was produced using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and output and capacity retention rates were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] comparative example 2
Electrolyte [6] in example 5, a battery was produced using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and output and capacity retention rates were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] comparative example 3
Electrolyte [6] in example 6, a battery was produced using a non-aqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane, and output and capacity retention rates were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] comparative example 4
Electrolyte [6]]In example 1, a battery was produced using a nonaqueous electrolytic solution prepared without mixing methanol with a mixed nonaqueous solvent, and the output and the capacity retention rate were measured. Results as electrolyte [6]]Shown in table 1. Further, LiPF is mixed6The amount of Hydrogen Fluoride (HF) in the solution was 9ppm after 1 day and was still 9ppm when measured again after 2 weeks.
Electrolyte [6] comparative example 5
Electrolyte [6] in comparative example 4, a battery was produced using a nonaqueous electrolyte prepared by mixing 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane, and the output and capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] comparative example 6
Electrolyte [6] in comparative example 4, a nonaqueous electrolyte prepared by mixing 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane was used to prepare a battery, and output and capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] comparative example 7
Electrolyte [6]]In example 1, the nonaqueous electrolyte solution was mixed with an electrolytic solution [6] except that the amount of methanol was changed to 700ppm based on the amount of the mixed nonaqueous solvent]In example 1, a nonaqueous electrolytic solution was prepared in the same manner, a battery was produced using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. Results as electrolyte [6]]Shown in table 1. Further, LiPF is mixed6The amount of Hydrogen Fluoride (HF) in the solution after 1 day was 321ppm and after 2 weeks, 403ppm when measured again.
Electrolyte [6] comparative example 8
Electrolyte [6] in example 1, a battery was produced using a nonaqueous electrolyte prepared without mixing methanol and hexamethylcyclotrisiloxane in a mixed nonaqueous solvent, and the output and capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] comparative example 9
A nonaqueous electrolytic solution was prepared in the same manner as in example 12 of electrolyte solution [6], except that hexamethylcyclotrisiloxane was not mixed in example 12 of electrolyte solution [6], and a battery was produced using the nonaqueous electrolytic solution, and the output and the capacity retention rate were measured. The results are shown in Table 1 for electrolyte [6 ].
Electrolyte [6] Table 1
[ Table 59]
Figure BDA0003109774980003581
As is clear from the electrolyte [6] Table 1, the lithium secondary batteries of comparative examples 1 to 3, which contain a larger amount of Hydrogen Fluoride (HF), are inferior to the lithium secondary batteries of comparative example 8, which is the electrolyte [6], in both the output characteristics and the cycle characteristics, but the lithium secondary batteries of examples 1 to 11, which are the electrolytes [6] containing a specific compound, are improved in both the output characteristics and the cycle characteristics. Further, the lithium secondary batteries of examples 1 to 11 of the electrolyte solution [6] had higher performance in terms of output than the lithium secondary batteries of comparative examples 4 to 6 of the electrolyte solution [6] containing a small amount of Hydrogen Fluoride (HF) although containing a specific compound, and the presence of hydrogen fluoride gave a surprising result of enhancing the output improvement effect by the specific compound. However, the electrolyte solution [6] containing excessive Hydrogen Fluoride (HF) gave a result that the lithium secondary battery of comparative example 7 was inferior in cycle characteristics in particular.
Further, the increase in output of the electrolyte [6] of example 12 having a battery configuration with a low capacity and a high direct current resistance was only about 19% with respect to the electrolyte [6] of comparative example 9, while the increase in output of the electrolyte [6] of example 6 having a battery configuration with a high capacity and a low direct current resistance was about 29% with respect to the electrolyte [6] of comparative example 3 (both containing 25ppm of methanol and 25ppm of ethylene glycol), the increase in output of the electrolyte [6] of example 5 was about 26% with respect to the electrolyte [6] of comparative example 2 (both containing 35ppm of ethylene glycol), and the increase in output of the electrolyte [6] of example 3 was about 26% with respect to the electrolyte [6] of comparative example 1 (both containing 35ppm of methanol). From this, it is found that the effect of the present invention is particularly great in a battery structure having a high capacity and a low direct current resistance.
As described above, by using the nonaqueous electrolytic solution of the present invention, that is, the nonaqueous electrolytic solution for a secondary battery obtained by mixing a fluorine-containing lithium salt with a nonaqueous solvent, the nonaqueous electrolytic solution for a secondary battery can obtain a large output characteristic without deteriorating the cycle characteristics, and is characterized in that: the nonaqueous electrolyte contains 10ppm to 300ppm of Hydrogen Fluoride (HF), and further contains at least one compound selected from the following substances, and the content of the compound in the whole nonaqueous electrolyte is 10ppm or more, wherein the substances include: a cyclic siloxane compound represented by general formula (1), a fluorosilane compound represented by general formula (2), a compound represented by general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate.
In the present example, although the effect is exhibited by adding an alcohol to the purified nonaqueous solvent, when an alcohol or water is originally contained in the nonaqueous solvent, the same effect can be obtained without adding an alcohol to the nonaqueous solvent by adjusting the purification conditions of the nonaqueous solvent. In general, purification of a nonaqueous solvent requires time and effort, and increases the cost industrially, but in the present invention, a high-performance nonaqueous electrolytic solution can be produced without requiring excessive purification, and the value thereof is very high.
Electrolyte [7] battery production-1
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Both the front and back surfaces were provided with 50mm uncoated portions in the longitudinal direction, and the length of the active material layer was 780 mm.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ preparation of electrolyte ]
In a mixed solvent of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a volume ratio of 3:3:4 under a dry argon atmosphere, sufficiently dried lithium hexafluorophosphate (LiPF) was dissolved at a concentration of 1mol/L6) A nonaqueous electrolytic solution (1) was prepared. Further, this nonaqueous electrolyte solution (1) was made to contain 0.5 mass% of lithium difluorophosphate prepared by the method described in Inorganic Nuclear Chemistry Letters (1969),5(7) on pages 581 to 582And an electrolyte (2).
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are housed in the battery case so as to be exposed to the outside. Then, 5mL of a nonaqueous electrolytic solution described later was injected thereinto, followed by caulking and molding to produce a 18650 type cylindrical battery.
[ evaluation of Battery ]
(initial Charge and discharge)
The manufactured cylindrical battery was charged to 4.2V at 25 ℃ by a constant current constant voltage charging method of 0.2C, and then discharged to 3.0V at a constant current of 0.2C. This was subjected to 5 cycles to stabilize the cell. The discharge capacity at the 5 th cycle at this time was defined as an initial capacity. In addition, a current value of a discharge rated capacity at 1 hour, which is determined by a discharge capacity at a 1-hour rate (one-hour-rate), was set as 1C.
(cycle test)
The battery subjected to initial charge and discharge was charged at 60 ℃ to 4.2V at a constant current and constant voltage of 1C, and then discharged at a constant current of 1C to 3.0V, and such charge and discharge was performed for 500 cycles. The ratio of the 500 th-cycle discharge capacity to the 1 st-cycle discharge capacity at this time was taken as a cycle retention rate.
(Low temperature test)
The batteries subjected to initial charge and discharge were charged to 4.2V by a constant current constant voltage charging method of 0.2C at 25 ℃ and then subjected to constant current discharge of 0.2C at-30 ℃. The discharge capacity at this time was defined as an initial low-temperature capacity, and the ratio of the initial low-temperature capacity to the initial capacity was defined as an initial low-temperature discharge rate.
Further, the battery after the cycle test was charged to 4.2V at 25 ℃ by a constant current constant voltage charging method of 0.2C, and then discharged to 3.0V at a constant current of 0.2C. This was subjected to 3 cycles, and the discharge capacity at the 3 rd cycle was defined as the capacity after the cycle. Then, the same battery was charged to 4.2V by a constant current constant voltage charging method at 25 ℃ and 0.2C, and then constant current discharge was performed at-30 ℃. The discharge capacity at this time was taken as the low-temperature capacity after the cycle, and the ratio of the low-temperature capacity after the cycle to the capacity after the cycle was taken as the low-temperature discharge rate after the cycle.
Electrolyte [7] example 1
In the nonaqueous electrolytic solution (2), vinylene carbonate (hereinafter, abbreviated as "VC") was mixed in an amount of 1 mass% with respect to the total electrolyte mass to prepare a nonaqueous electrolytic solution (3). Using this nonaqueous electrolyte (3), a 18650 type battery was produced, and the cycle retention rate and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ]. The electrolyte was collected from the cell after completion of the initial charge and discharge by a centrifuge, and the measured VC amount was 0.40 mass%.
Electrolyte [7] comparative example 1
A 18650 type battery was produced using the nonaqueous electrolyte (1) in the same manner as in example 1 of electrolyte [7], and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ].
Electrolyte [7] comparative example 2
In the nonaqueous electrolytic solution (1), VC was mixed in an amount of 1 mass% relative to the total electrolyte mass to prepare a nonaqueous electrolytic solution (4). Using this nonaqueous electrolyte (4), a 18650 type battery was produced in the same manner as in example 1 of electrolyte [7], and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ]. The electrolyte was collected from the cell after completion of the initial charge and discharge by a centrifuge, and the measured VC amount was 0.22 mass%.
Electrolyte [7] comparative example 3
A 18650 type battery was produced in the same manner as in example 1 of electrolyte [7] except that the nonaqueous electrolyte (2) was used and VC was not mixed, and the cycle retention rate and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ].
Electrolyte [7] comparative example 4
In the nonaqueous electrolytic solution (2), VC was mixed in an amount of 5 mass% with respect to the total electrolyte mass to prepare a nonaqueous electrolytic solution (5). Electrolyte [7] in example 1, a 18650 type battery was produced using this nonaqueous electrolyte (5), and the cycle retention and low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ].
Electrolyte [7] example 2
Production of battery-2
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10 mm). Then, 20mL of nonaqueous electrolyte (3) was injected into the battery can containing the electrode group to sufficiently permeate the electrodes, and the resultant was sealed to prepare a prismatic battery.
The prismatic battery thus fabricated was subjected to a cycle test and a low-temperature test in the same manner as in example 1 of the electrolyte [7], and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ].
Electrolyte [7] comparative example 5
Electrolyte [7] in example 2, a rectangular battery was produced using the nonaqueous electrolyte (1) instead of the nonaqueous electrolyte (3), and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ].
Electrolyte [7] comparative example 6
Electrolyte [7] in example 2, a rectangular battery was produced using a nonaqueous electrolyte (4) instead of the nonaqueous electrolyte (3), and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ].
Electrolyte [7] comparative example 7
Electrolyte [7] in example 2, a rectangular battery was produced using the nonaqueous electrolyte (2) instead of the nonaqueous electrolyte (3), and the cycle retention and the low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [7 ].
Electrolyte [7] Table 1
[ Table 60]
Figure BDA0003109774980003631
As is clear from table 1 of the electrolytic solution [7], the electrolytic solution [7] containing vinylene carbonate and difluorophosphate in the nonaqueous electrolytic solution improves both the cycle retention rate and the low-temperature discharge rate of the lithium secondary battery of example 1, compared with the lithium secondary battery of comparative example 1, which has the same structure as the electrolytic solution [7] except that it does not contain any of them in the nonaqueous electrolytic solution.
Furthermore, it was found that the cycle retention rate and the low-temperature discharge rate were improved even in comparison with the lithium secondary battery of comparative example 2, which had the same structure except that VC alone was contained in the nonaqueous electrolytic solution [7 ]. The cycle retention rate significantly varies depending on the presence or absence of VC, and its effect is increased by adding difluorophosphate thereto. There was a difference of about 2 times in the amount of VC detected from the battery after initial charge and discharge, and it is considered that the remaining VC suppressed the battery degradation in the cycle test.
As is clear from the electrolyte [7] example 1 and the electrolyte [7] comparative example 3, the cycle retention rate cannot be sufficiently improved by the difluorophosphate alone. Electrolyte [7] the lithium secondary battery of example 1 had the same initial low-temperature discharge rate as the lithium secondary battery of comparative example 3 of electrolyte [7], but not only was the cycle retention rate greatly improved, but also the low-temperature discharge efficiency after the cycle was improved. The increase in the internal resistance of the battery due to the cycle test was suppressed by the synergistic effect of VC and difluorophosphate.
The same applies to the electrolyte [7] in example 2 and the electrolyte [7] in comparative examples 5 to 7.
When the lithium secondary battery of the electrolyte [7] of example 1 was compared with the lithium secondary battery of the electrolyte [7] of comparative example 4 containing a large amount of VC, it was found that the electrolyte [7] of comparative example 4 was remarkably inferior in low-temperature discharge characteristics and could not withstand use in a low-temperature environment, although the cycle retention rate was considerably excellent.
The values of the direct current resistance measured by the 10kHz alternating current method are shown in the table. Compared with a cylindrical battery, the square battery in the experiment has small resistance and large capacitance. As compared with the degree of improvement in low-temperature characteristics of the electrolyte solution [7] in example 1 relative to the electrolyte solution [7] in comparative example 1, the degree of improvement in low-temperature characteristics of the electrolyte solution [7] in example 2 relative to the electrolyte solution [7] in comparative example 5 is large, and it is found that a secondary battery having a high capacitance or a secondary battery having a small direct current resistance is particularly suitable as an object of the nonaqueous electrolyte solution of the present invention.
Electrolyte (8) manufacture of secondary battery
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was coated on both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into an active material layer 100mm in width and 100mm in length and an uncoated layer 30mm in widthPartially shaped as a positive electrode.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10mm) provided with a vent valve. Then, 20mL of a nonaqueous electrolyte solution described later was injected into the battery can with the electrode group attached, and the electrodes were sufficiently impregnated and sealed to prepare a rectangular battery.
The capacity of the battery element housed in 1 battery case of the secondary battery, that is, the rated discharge capacity of the secondary battery is about 6 ampere hours (Ah), and the dc resistance component measured by the 10kHz ac method is about 5 milliohms (m Ω).
Electrolyte [8] < evaluation of Battery >
[ cycle Retention ratio ]
[ initial Charge/discharge ]
After being charged to 4.2V at 25 ℃ by a constant current constant voltage charging method of 0.2C, it was discharged to 3.0V at a constant current of 0.2C. This was subjected to 5 cycles to stabilize the cell. The discharge capacity in the 5 th cycle at this time was defined as an initial capacity. The current value at the discharge rated capacity of 1 hour was defined as 1C.
(cycle test)
The battery subjected to initial charge and discharge was charged to 4.2V by a constant current constant voltage method of 1C at 60C, and then discharged to 3.0V by a constant current of 1C, and the charge and discharge were performed for 500 cycles. The ratio of the 500 th-cycle discharge capacity to the 1 st-cycle discharge capacity at this time was taken as a cycle retention rate.
[ initial Low-temperature discharge Rate ]
(Low temperature test)
The batteries subjected to initial charge and discharge were charged to 4.2V by a constant current constant voltage charging method of 0.2C at 25 ℃ and then subjected to constant current discharge of 0.2C at-30 ℃. The discharge capacity at this time was defined as an initial low-temperature capacity, and the ratio of the initial low-temperature capacity to the initial capacity was defined as an initial low-temperature discharge rate.
[ Low temperature discharge Rate after circulation ]
Further, the battery after the cycle test was charged to 4.2V at 25 ℃ by a constant current constant voltage charging method of 0.2C, and then discharged to 3.0V at a constant current of 0.2C. This was subjected to 3 cycles, and the discharge capacity at the 3 rd cycle was defined as the capacity after the cycle. Then, the same cell was charged to 4.2V at 25 ℃ by a constant current constant voltage charging method of 0.2C, and then constant current discharge of 0.2C was carried out at-30 ℃. The discharge capacity at this time was taken as the low-temperature capacity after the cycle, and the ratio of the low-temperature capacity after the cycle to the capacity after the cycle was taken as the low-temperature discharge rate after the cycle.
Electrolyte [8] example 1
Under dry argon atmosphere, 1mol/L LiPF is added to a mixture of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) (volume ratio 2:5:3)6Then, the mixture was dissolved to prepare a nonaqueous electrolytic solution containing 0.3 mass% of hexamethylcyclotrisiloxane and 1 mass% of vinyl ethylene carbonate. Batteries were produced using this nonaqueous electrolyte solution by the above-described method, and the cycle retention, initial low-temperature discharge rate, and low-temperature discharge rate after cycling were measured. Results as electrolyte [8]]Shown in table 1.
Electrolyte [8] example 2
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that a nonaqueous electrolyte was prepared using phenyldimethylsiloxane instead of hexamethylcyclotrisiloxane, and the cycle retention rate, the initial low-temperature discharge rate, and the post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 3
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that a nonaqueous electrolyte was prepared using methyl fluorosulfonate instead of hexamethylcyclotrisiloxane, and the cycle retention, initial low-temperature discharge rate, and post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 4
Batteries were produced in the same manner as in example 1 of electrolyte [8], except that lithium difluorophosphate prepared by the method described in Inorganic Nuclear Chemistry Letters (1969),5, (7) on pages 581 to 582 was used in place of hexamethylcyclotrisiloxane to prepare a nonaqueous electrolyte, and the cycle retention, the initial low-temperature discharge rate, and the post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 5
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that a nonaqueous electrolyte was prepared using 1, 3-propanesultone instead of vinyl ethylene carbonate, and the cycle retention, initial low-temperature discharge rate, and post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 6
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that a nonaqueous electrolyte was prepared using γ -butyrolactone instead of vinyl ethylene carbonate, and the cycle retention, initial low-temperature discharge rate, and post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 7
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that a nonaqueous electrolyte was prepared using fluoroethylene carbonate instead of vinyl ethylene carbonate, and the cycle retention, initial low-temperature discharge rate, and post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 8
Batteries were produced in the same manner as in example 4 of electrolyte [8] except that a nonaqueous electrolyte was prepared using 1, 3-propanesultone instead of vinyl ethylene carbonate, and the cycle retention, initial low-temperature discharge rate, and post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 9
Batteries were produced in the same manner as in example 4 of electrolyte [8] except that a nonaqueous electrolyte was prepared using γ -butyrolactone instead of vinyl ethylene carbonate, and the cycle retention, initial low-temperature discharge rate, and post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 10
Batteries were produced in the same manner as in example 4 of electrolyte [8] except that a nonaqueous electrolyte was prepared using fluoroethylene carbonate instead of vinyl ethylene carbonate, and the cycle retention, the initial low-temperature discharge rate, and the post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] comparative example 1
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that the nonaqueous electrolyte solution contained no hexamethylcyclotrisiloxane, and the cycle retention rate, the initial low-temperature discharge rate, and the low-temperature discharge rate after the cycle were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] comparative example 2
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that the nonaqueous electrolyte solution contained no vinyl ethylene carbonate, and the cycle retention, the initial low-temperature discharge rate, and the low-temperature discharge rate after the cycle were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] comparative example 3
Batteries were produced in the same manner as in example 1 of electrolyte [8] except that the nonaqueous electrolyte solution contained no hexamethylcyclotrisiloxane and no vinyl ethylene carbonate, and the cycle retention, the initial low-temperature discharge rate, and the low-temperature discharge rate after the cycle were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 11
Production of secondary battery-2
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, rolled to a thickness of 80 μm by a press, and cut into pieces having a width of 52mm and a length of 830mm to obtain positive electrodes. Both the front and back surfaces were provided with 50mm uncoated portions in the longitudinal direction, and the length of the active material layer was 780 mm.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was uniformly applied to both sides of a copper foil having a thickness of 18 μm as a negative electrode current collector, dried, rolled to a thickness of 85 μm by a press, and cut into a size of 56mm in width and 850mm in length to obtain a negative electrode. Wherein the front and back surfaces are provided with 30mm uncoated portions in the longitudinal direction.
[ Assembly of Battery ]
The positive electrode and the negative electrode were wound together with a polyethylene separator so as not to directly contact the positive electrode and the negative electrode, thereby producing an electrode body. The positive and negative terminals are housed in the battery case so as to be exposed to the outside. Then, 5mL of a nonaqueous electrolytic solution described later was injected thereinto, followed by caulking and molding to produce a 18650 type cylindrical battery. The capacity of the battery element housed in 1 battery case of the secondary battery, that is, the rated discharge capacity of the battery is about 0.7 ampere-hour (Ah), and the direct-current resistance component measured by the 10kHz alternating-current method is about 35 milliohms (m Ω).
Electrolyte [8] the nonaqueous electrolyte used in example 1 was used as a nonaqueous electrolyte to prepare a cylindrical battery, and the cycle retention, the initial low-temperature discharge rate, and the post-cycle low-temperature discharge rate were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] example 12
A cylindrical battery was produced in the same manner as in example 11 of electrolyte [8] except that the nonaqueous electrolyte used in example 4 of electrolyte [8] was used as the nonaqueous electrolyte, and the cycle retention, the initial low-temperature discharge rate, and the low-temperature discharge rate after the cycle were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] comparative example 4
Cylindrical batteries were produced in the same manner as in example 11 of electrolyte [8] except that the nonaqueous electrolyte used in comparative example 1 of electrolyte [8] was used as the nonaqueous electrolyte, and the cycle retention, initial low-temperature discharge rate, and low-temperature discharge rate after the cycle were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] comparative example 5
Cylindrical batteries were produced in the same manner as in example 11 of electrolyte [8] except that the nonaqueous electrolyte used in comparative example 2 of electrolyte [8] was used as the nonaqueous electrolyte, and the cycle retention, initial low-temperature discharge rate, and low-temperature discharge rate after the cycle were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] comparative example 6
Cylindrical batteries were produced in the same manner as in example 11 of electrolyte [8] except that the nonaqueous electrolyte used in comparative example 3 of electrolyte [8] was used as the nonaqueous electrolyte, and the cycle retention, initial low-temperature discharge rate, and low-temperature discharge rate after the cycle were measured. The results are shown in Table 1 for electrolyte [8 ].
Electrolyte [8] Table 1
[ Table 61]
Figure BDA0003109774980003691
As is clear from Table 1 of the electrolyte [8], when square batteries (used in examples 1 to 10 of the electrolyte [8], comparative examples 1 to 3 of the electrolyte [8 ]) and cylindrical batteries (used in examples 11 and 12 of the electrolyte [8], comparative examples 4 to 6 of the electrolyte [8 ]) are compared with each other, the lithium secondary battery of the electrolyte [8] example containing at least one specific compound A and at least one specific compound B in the nonaqueous electrolyte is improved in cycle retention, initial low-temperature discharge rate and post-cycle low-temperature discharge rate as compared with the lithium secondary battery of the comparative example containing no electrolyte [8] of any of these.
As described above, the square batteries of the present example and the present comparative example had a rated discharge capacity of 3 ampere hours (Ah) or more and a dc resistance component of 10 milliohms (m Ω) or less. On the other hand, the cylindrical batteries of the present example and the comparative example had a rated discharge capacity of less than 3 ampere-hours (Ah) and a dc resistance component of more than 10 milliohms (m Ω). That is, the prismatic battery of the present example and the present comparative example has a smaller resistance and a larger capacitance than the cylindrical battery. The effect of the present invention is greater in a secondary battery having a large capacity or a secondary battery having a small direct current resistance, because the degree of increase in output power of the electrolytic solution [8] in example 1 relative to the electrolytic solution [8] in comparative example 1 is greater than the degree of increase in output power of the electrolytic solution [8] in example 11 relative to the electrolytic solution [8] in comparative example 4.
Electrolyte (9) manufacture of secondary battery
[ production of Positive electrode ]
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 80 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode.
[ production of negative electrode ]
To 98 parts by weight of artificial graphite powder KS-44 (trade name, manufactured by timecal corporation), 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1% by mass) as a thickener, and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50% by mass) as a binder were added, and the mixture was mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a width of 104mm and a length of 104mm and an uncoated portion having a width of 30mm, to obtain a negative electrode.
[ Assembly of Battery ]
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were welded together to prepare a current collecting tab, and the electrode assembly was sealed in a battery can (outer dimensions: 120X 110X 10mm) provided with a vent valve. Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently permeate the electrodes, and the electrode was sealed to prepare a prismatic battery.
[ capacitance and DC resistance component ]
The rated discharge capacity (the capacity of the battery element housed in 1 battery case) of this battery was high, about 6Ah, and the dc resistance component measured by the 10kHz ac method was about 5 milliohms.
[ evaluation of Battery ]
(method of measuring Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) at a voltage range of 4.2V to 3.0V at 25 ℃. The 0.2C discharge capacity of the 5 th cycle at this time was taken as a capacity.
(5C discharge capacity after storage)
The storage test was conducted in a high temperature environment of 60 ℃. The battery previously charged to a charging upper limit voltage of 4.2V by a constant current constant voltage method under an environment of 25 ℃ was stored at 60 ℃ for 1 month. For the battery after storage, a speed test was performed in an environment of 25 ℃. That is, a battery previously charged to a charging upper limit voltage of 4.2V by a constant current constant voltage method in an environment of 25 ℃ was discharged at a constant current value corresponding to 5C, and the discharge capacity after storage was determined to be 5C.
(overcharge test)
The overcharge test was conducted in an environment of 25 ℃. The charge was carried out from the discharged state (3V) at a constant current of 3C, and the behavior was observed. Here, "valve operation" indicates a phenomenon in which the vent valve operates to release the electrolyte component, and "rupture" indicates a phenomenon in which the battery container is ruptured by a strong force and the contents are forcibly released.
Electrolyte [9] example 1
Lithium hexafluorophosphate (LiPF) was added to a mixture of Ethylene Carbonate (EC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC) (volume ratio 3:3:4) at 1mol/L under dry argon atmosphere6) And dissolved, and Cyclohexylbenzene (CHB) in an amount of 1 mass% and hexamethylcyclotrisiloxane in an amount of 0.3 mass% were mixed in the mixed solution to prepare a nonaqueous electrolytic solution. Using this nonaqueous electrolyte, a battery was produced by the above-described method, and the 5C discharge capacity after storage was measured. Results as electrolyte [9] ]Shown in table 1.
Electrolyte [9] example 2
A battery was produced using a nonaqueous electrolytic solution prepared by mixing phenyldimethylsiloxane in place of hexamethylcyclotrisiloxane in electrolyte [9] example 1, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 3
Using a nonaqueous electrolytic solution prepared by mixing trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane in the electrolytic solution [9] example 1, a battery was produced, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 4
A battery was prepared by using a nonaqueous electrolytic solution prepared by mixing lithium difluorophosphate prepared by the method described in Inorganic Nuclear Chemistry Letters (1969),5(7) on pages 581 to 582 in place of hexamethylcyclotrisiloxane as used in the electrolytic solution [9] example 1, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 5
A battery was produced using a nonaqueous electrolyte prepared by mixing biphenyl instead of cyclohexylbenzene in the electrolyte [9] example 1, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 6
A battery was produced using a nonaqueous electrolytic solution prepared by mixing phenyldimethylsiloxane in place of hexamethylcyclotrisiloxane in electrolyte [9] example 5, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 7
A battery was produced using a nonaqueous electrolytic solution prepared by mixing trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane in the electrolytic solution [9] example 5, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 8
A battery was prepared by using a nonaqueous electrolytic solution prepared by mixing lithium difluorophosphate prepared by the method described in Inorganic Nuclear Chemistry Letters (1969),5, (7) on pages 581 to 582 in place of hexamethylcyclotrisiloxane as used in the electrolytic solution [9] in example 5, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 9
A battery was produced using a nonaqueous electrolytic solution prepared by mixing tert-amylbenzene instead of cyclohexylbenzene in the electrolytic solution [9] example 1, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] example 10
A nonaqueous electrolyte prepared by mixing 3.7 mass% m-terphenyl and 42% partial hydride of m-terphenyl instead of cyclohexylbenzene in the electrolyte [9] example 1 was used to prepare a battery, and the 5C discharge capacity after storage was measured. The results are shown in Table 1 for electrolyte [9 ]. Further, as the partial hydride of m-terphenyl used in the example of the electrolyte solution [9], a substance obtained by reacting m-terphenyl as a raw material with hydrogen under high temperature and pressure conditions in the coexistence of a platinum, palladium or nickel catalyst was used. The partial hydrogenation ratio is determined by averaging the composition ratios of the constituent components of the partially hydrogenated m-terphenyl obtained by gas chromatography. The content of m-terphenyl was also determined from the gas chromatography value.
Electrolyte [9] comparative example 1
A battery was produced using the nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane as the electrolyte [9] in example 1, and the 5C discharge capacity was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] comparative example 2
A battery was produced using the nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane as the electrolyte [9] in example 5, and the 5C discharge capacity was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] comparative example 3
A battery was produced using the nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane as the electrolyte [9] in example 9, and the 5C discharge capacity was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] comparative example 4
A battery was produced using the nonaqueous electrolyte prepared without mixing hexamethylcyclotrisiloxane in the electrolyte [9] in example 10, and the 5C discharge capacity was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] comparative example 5
A battery was produced using the nonaqueous electrolytic solution prepared without mixing any of hexamethylcyclotrisiloxane and CHB in the electrolytic solution [9] in example 1, and the 5C discharge capacity was measured. The results are shown in Table 1 for electrolyte [9 ].
Electrolyte [9] Table 1
[ Table 62]
Figure BDA0003109774980003741
As is apparent from Table 1 of the electrolyte [9], the lithium secondary batteries of examples 1 to 10 of the electrolyte [9] containing an overcharge inhibitor and a specific compound in a nonaqueous electrolyte solution can avoid battery rupture during overcharge test, and exhibit more excellent characteristics than the lithium secondary batteries of comparative examples 1 to 4 of the electrolyte solution [9] even in a large current (5C) discharge test after storage. This characteristic is close to that of the lithium secondary battery of comparative example 5 of electrolyte [9] containing no overcharge inhibitor, and it is understood that the practical value is very high while the overcharge safety is improved.
As described above, by using a nonaqueous electrolyte for a secondary battery formed by mixing a lithium salt in a nonaqueous solvent, which has the following characteristics: contains an overcharge inhibitor and at least one compound selected from the following substances in an amount of 10ppm or more in the entire nonaqueous electrolytic solution, the substances including: a cyclic siloxane compound represented by general formula (1), a fluorosilane compound represented by general formula (2), a compound represented by general formula (3), a compound having an S-F bond in the molecule, a nitrate, a nitrite, a monofluorophosphate, a difluorophosphate, an acetate, and a propionate. In particular, it is possible to provide a battery having a high practicality in which the capacity of the battery element housed in 1 battery case is 3 ampere hours (Ah) or more, which has been difficult to satisfy these 2 elements at the same time.
Structures [1] to [5] example 1
Preparation of non-aqueous electrolyte
Well-dried lithium hexafluorophosphate (LiPF) was dissolved in a mixed solvent of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a volume ratio of 3:3:4 at a concentration of 1mol/L under a dry argon atmosphere 6). Further, hexamethylcyclotrisiloxane was contained in an amount of 0.3 mass%.
Preparation of Positive electrode
The positive electrode active material is a lithium transition metal composite oxide synthesized by the following method and has a composition formula of LiMn0.33Ni0.33Co0.33O2And (4) showing. Mn as a manganese raw material was weighed in a molar ratio of Mn to Ni to Co of 1 to 13O4NiO as a raw material of nickel and Co (OH) as a raw material of cobalt2Pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.2 μm using a circulating medium agitation type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 5 μm, which contained only the manganese raw material, the nickel raw material, and the cobalt raw material. To the obtained granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Mn, Ni and Co was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of granulated particles of a nickel raw material, a cobalt raw material and a manganese raw material and a lithium raw material. The mixed powder was fired at 950 ℃ for 12 hours (5 ℃/min) under air flow, and then pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material. The BET specific surface area of the positive electrode active material was 1.2m 2A median particle diameter d of 0.8 μm/g504.4 μm, tap density 1.6g/cm3。
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 81 μm by a press, and cut into a shape having an active material layer 100mm in width and 100mm in length and an uncoated portion 30mm in width to obtain a positive electrode. The density of the positive electrode active material layer was 2.35g/cm3The (thickness of the positive electrode active material layer on one side)/(thickness of the current collector) was 2.2, and L/(2 × S)2) Is 0.2.
Production of negative electrode
In order to prevent coarse particles from being mixed into a commercially available natural graphite powder as a granular carbonaceous material, the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode material thus obtained was used as the carbonaceous material (a).
Petroleum heavy oil obtained by pyrolysis of naphtha is mixed with a carbonaceous material (a), and the mixture is carbonized at 1300 ℃ in an inert gas, and then the sintered product is classified to obtain a composite carbonaceous material as a negative electrode active material, wherein carbonaceous materials having different crystallinities are coated on the surfaces of carbonaceous material (a) particles. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed in. From the carbon residue ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite. The physical properties of the negative electrode active material are shown in Table 1 with structures [1] to [5 ].
Structures [1] to [5] Table 1
[ Table 63]
Figure BDA0003109774980003761
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50 mass%) as a binder were added and mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into a shape having an active material layer having a size of 104mm in width and 104mm in length and an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the negative electrode active material at this time was 1.35g/cm3，L/(2×S2) Is 0.19.
Production of Battery
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness: 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. The uncoated portions of the positive electrode and the negative electrode were bundled and spot welded to prepare a current collecting tab, and the electrode assembly was sealed in an aluminum battery can (outer dimensions: 120X 110X 10 mm). As the battery can, one having a collector terminal of a positive electrode and a collector terminal of a negative electrode, a pressure relief valve, and an inlet for a nonaqueous electrolytic solution in a lid portion is used. The collector plate and the collector terminal are connected by spot welding. Then, 20mL of nonaqueous electrolyte was injected into the battery can containing the electrode group to sufficiently permeate the electrodes, and the injection port was sealed to prepare a battery. The ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas of the battery was 20.5, 2 × S 1The value of/T was 264, and the electrode group occupancy was 0.54.
Evaluation of Battery
(method of measuring Battery Capacity)
An initial charge and discharge was performed for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.1V to 3.0V at 25 ℃. The 0.2C discharge capacity at the 5 th cycle at this time was set as the initial capacity. The results of the battery evaluation are shown in Table 2 with the structures [1] to [5 ].
(method of measuring initial output Power)
The charge was carried out at 25 ℃ for 150 minutes by a constant current of 0.2C, and the discharge was carried out at 0.1C, 0.3C, 1.0C, 3.0C and 10.0C for 10 seconds, respectively, to measure the voltage at 10 seconds. The area of a triangle surrounded by a current-voltage straight line and the lower limit voltage (3V) is used as the output power (W). The results of the battery evaluation are shown in Table 2 with the structures [1] to [5 ].
(method of measuring initial series resistance)
The charging was carried out at 25 ℃ for 150 minutes by a constant current of 0.2C, and an AC current of 10kHz was applied to measure the impedance as a DC resistance. The results of the battery evaluation are shown in Table 2 with the structures [1] to [5 ].
(cycle test (method of measuring Battery Capacity after Endurance and output Power after Endurance))
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.1V by a constant current and constant voltage method of 2C, the charge and discharge were performed to the end discharge voltage of 3.0V by a constant current and constant voltage method of 2C, and the cycle was repeated up to 500 cycles with the charge and discharge cycle set to 1 cycle. After the end of the cycle test, the battery was charged and discharged at 25 ℃ for 3 cycles at a current value of 0.2C, and the 0.2C discharge capacity at the 3 rd cycle was defined as the durable battery capacity. Further, the output was measured for the battery after the end of the cycle test, and the series resistance was measured as the output after endurance, and the series resistance was measured as the series resistance after endurance. The results of the battery evaluation are shown in Table 2 with the structures [1] to [5 ].
(overcharge test)
The overcharge test was conducted in an environment of 25 ℃. The charge was carried out from the discharged state (3V) at a constant current of 3C, and the behavior was observed. Here, "valve operation" indicates a phenomenon in which the vent valve operates to release the electrolyte component, and "rupture" indicates a phenomenon in which the battery container is ruptured by a strong force and the contents are forcibly released. The results of the battery evaluation are shown in Table 2 with the structures [1] to [5 ].
Structures [1] to [5] example 2
Batteries were produced in the same manner as in example 1 of structures [1] to [5] except that 0.3 mass% of trimethylsilyl methanesulfonate was contained in the nonaqueous electrolytic solution instead of hexamethylcyclotrisiloxane in example 1 of structures [1] to [5], and battery evaluation was performed in the same manner. The results are shown in Table 2 with the structures [1] to [5 ].
Structures [1] to [5] example 3
Batteries were produced in the same manner as in structure [1] to [5] example 1 except that 0.3 mass% of phenyldimethylfluorosilane was contained in the nonaqueous electrolytic solution instead of hexamethylcyclotrisiloxane in structure [1] to [5] example 1, and the battery evaluation was performed in the same manner. The results are shown in Table 2 with the structures [1] to [5 ].
Structures [1] to [5] example 4
Batteries were produced in the same manner as in example 1 of structures [1] to [5] except that lithium difluorophosphate was contained in an amount of 0.3 mass% in the nonaqueous electrolytic solution instead of hexamethylcyclotrisiloxane in example 1 of structures [1] to [5], and evaluation of the batteries was carried out in the same manner. The results are shown in Table 2 with the structures [1] to [5 ].
Structures [1] to [5] comparative example 1
Batteries were produced in the same manner as in example 1 of structures [1] to [5] except that the nonaqueous electrolytic solution of example 1 of structures [1] to [5] did not contain hexamethylcyclotrisiloxane, and evaluation of the batteries was performed in the same manner. The results are shown in Table 2 with the structures [1] to [5 ].
Structures [1] to [5] Table 2
[ Table 64]
Figure BDA0003109774980003781
Structures [1] to [5] example 5
Preparation of Positive electrode
Use and Structure [1]～[5]Example 1 same positive electrode active material, structure [1]]～[5]Example 1 a slurry was prepared in the same manner. The obtained slurry was applied to both sides of an aluminum foil 15 μm in thickness, dried, rolled to a thickness of 81 μm by a press, and cut into positive electrode active material layers 100mm in width and 3200mm in length, and had a shape having uncoated portions 6mm in width at intervals of 20mm in the longitudinal direction, to obtain a positive electrode. The density of the positive electrode active material layer was 2.35g/cm3The (thickness of the positive electrode active material layer on one surface)/(thickness of the current collector) was 2.2. The ratio of the length of the positive electrode in the width direction to the length of the positive electrode in the longitudinal direction was 32.
Production of negative electrode
Use and Structure [1]～[5]Negative electrode active material similar to that of example 1, and Structure [1]～[5]Example 1 a slurry was prepared in the same manner. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into active material layers having a width of 104mm and a length of 3300mm, each in the longitudinal directionThe space of 20mm had a shape of an uncoated portion having a width of 6mm as a negative electrode. The density of the negative electrode active material at this time was 1.35g/cm 3。
Production of Battery
The electrode body was prepared by stacking and winding a microporous membrane separator (thickness 25 μm) of a porous polyethylene sheet between the electrodes so that the positive electrode and the negative electrode were not in direct contact with each other, and the positive electrode and the negative electrode were wound in a circular shape with the uncoated portion on the opposite side. The positive electrode and the negative electrode were spot-welded to each other on a central axis of the bundle winding to prepare current collecting tabs, and the battery assembly was mounted in a battery can (outer dimensions: 36. phi. times.120 mm) made of aluminum with the negative electrode current collecting tab as a base. The negative collector plate is spot welded to the bottom of the can to form a negative collector terminal of the battery can. A battery can lid having a positive electrode collector terminal and a pressure relief valve was prepared, and the positive electrode collector tab and the positive electrode collector terminal were connected by spot welding. Then, 20mL of nonaqueous electrolyte was injected into the battery can with the electrode group attached, the electrode was sufficiently impregnated, and the battery can lid was sealed by caulking molding to produce a cylindrical battery. The ratio of the total electrode area of the positive electrode to the total surface area of the outer case of the battery was 41.0, and the electrode group occupancy was 0.58.
Evaluation of Battery
Battery evaluation was performed in the same manner as in example 1 of constitutions [1] to [5] except that the cylindrical battery was used. The structure of the battery evaluation is shown in Table 3 with structures [1] to [5 ].
Structures [1] to [5] example 6
Batteries were produced in the same manner as in examples 5 of structures [1] to [5] and evaluated in the same manner except that the nonaqueous electrolytic solution contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane in example 5 of structures [1] to [5 ]. The results are shown in Table 3 for structures [1] to [5 ].
Structures [1] to [5] example 7
Batteries were produced in the same manner as in the examples 5 of the structures [1] to [5] except that the nonaqueous electrolytic solution in the example 5 of the structures [1] to [5] contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane, and the battery evaluations were performed in the same manner. The results are shown in Table 3 for structures [1] to [5 ].
Structures [1] to [5] example 8
Batteries were produced in the same manner as in the examples 5 of the structures [1] to [5] except that the nonaqueous electrolytic solution in the example 5 of the structures [1] to [5] contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane, and the battery evaluations were performed in the same manner. The results are shown in Table 3 for structures [1] to [5 ].
Structures [1] to [5] comparative example 2
Batteries were produced in the same manner as in the structures [1] to [5] examples 5 except that the nonaqueous electrolytic solution contained no hexamethylcyclotrisiloxane in the structures [1] to [5] examples 5, and the battery evaluations were performed in the same manner. The results are shown in Table 3 for structures [1] to [5 ].
Structures [1] to [5] Table 3
[ Table 65]
Figure BDA0003109774980003801
As is clear from the results of structures [1] to [5] table 2 and structures [1] to [5] table 3, in any of the batteries, the output, capacity retention rate, and safety were improved by containing the specific compound in the nonaqueous electrolytic solution, and the increase in the direct current resistance component was small even after the cycle test, and the battery capacity and output were sufficiently maintained.
Structure [6] example 1
Preparation of non-aqueous electrolyte
Well-dried lithium hexafluorophosphate (LiPF) was dissolved in a mixed solvent of purified Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC) in a volume ratio of 3:3:4 at a concentration of 1mol/L under a dry argon atmosphere6). And 0.3 mass% of hexamethylcyclotrisiloxane was contained.
Preparation of Positive electrode
The positive electrode active material is a lithium transition metal composite oxide synthesized by the following method and has a composition formula of LiMn0.33Ni0.33Co0.33O2And (4) showing. Mn as a manganese raw material was weighed in a molar ratio of Mn to Ni to Co of 1 to 13O4NiO as a raw material of nickel and Co (OH) as a raw material of cobalt2Pure water was added thereto to prepare a slurry, and the solid content in the slurry was wet-pulverized to a median particle diameter of 0.2 μm by a circulating medium-stirring type wet bead mill while stirring.
The slurry was spray-dried by a spray dryer to obtain substantially spherical granulated particles having a particle diameter of about 5 μm, which contained only the manganese raw material, the nickel raw material, and the cobalt raw material. To the obtained granulated particles, LiOH powder having a median particle diameter of 3 μm was added so that the ratio of the number of moles of Li to the total number of moles of Mn, Ni and Co was 1.05, and the mixture was mixed by a high-speed mixer to obtain a mixed powder of granulated particles of a nickel raw material, a cobalt raw material and a manganese raw material and a lithium raw material. The mixed powder was fired at 950 ℃ for 12 hours (5 ℃/min) under air flow, and then pulverized, and passed through a sieve having a mesh size of 45 μm to obtain a positive electrode active material. The BET specific surface area of the positive electrode active material was 1.2m2A median particle diameter d of 0.8 μm/g504.4 μm, tap density 1.6g/cm3。
Lithium cobaltate (LiCoO) as a positive electrode active material was mixed in an amount of 90 mass% in an N-methylpyrrolidone solvent2) 5 mass% of acetylene black as a conductive material and 5 mass% of polyvinylidene fluoride (PVdF) as a binder were made into a slurry. The obtained slurry was applied to both sides of an aluminum foil 15 μm thick, dried, rolled to a thickness of 81 μm by a press, and cut into a positive electrode active material layer having a width of 100mm and a length of 100mm, and having a shape of an uncoated portion 30mm wide, to obtain a positive electrode. The density of the positive electrode active material layer was 2.35g/cm 3The ratio of (thickness of positive electrode active material layer on one side)/(thickness of current collector) was 2.2, L/(2 XS)2) Is 0.2.
Production of negative electrode
In order to prevent coarse particles from being mixed into a commercially available natural graphite powder as a granular carbonaceous material, the sieve was repeated 5 times using a sieve of ASTM400 mesh. The negative electrode material thus obtained was used as the carbonaceous material (a).
Petroleum heavy oil obtained by pyrolysis of naphtha is mixed with a carbonaceous material (a), and the mixture is carbonized at 1300 ℃ in an inert gas, and then the sintered product is classified to obtain a composite carbonaceous material as a negative electrode active material, wherein carbonaceous materials having different crystallinities are coated on the surfaces of carbonaceous material (a) particles. In the classification treatment, the sieve was repeated 5 times using a sieve of ASTM400 mesh to prevent coarse particles from being mixed in. From the carbon residue ratio, it was confirmed that the obtained negative electrode active material powder was coated with 5 parts by weight of a low crystalline carbonaceous material with respect to 95 parts by weight of graphite. The physical properties of the negative electrode active material are shown in Table 1 of the following Structure [6 ].
Structure [6] Table 1
[ Table 66]
Figure BDA0003109774980003811
To 98 parts by weight of the negative electrode active material, 100 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose is 1 mass%) as a thickener and 2 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber is 50 mass%) as a binder were added and mixed with a disperser to prepare a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm, dried, rolled to a thickness of 75 μm by a press, and cut into an active material layer having a width of 104mm and a length of 104mm and having a shape of an uncoated portion having a width of 30mm, to obtain a negative electrode. The density of the negative electrode active material at this time was 1.35g/cm 3，L/(2×S2) Is 0.19.
Production of Battery
32 positive electrodes and 33 negative electrodes were alternately arranged, and a porous polyethylene sheet separator (thickness 25 μm) was interposed between the electrodes to laminate them. In this case, the positive electrode active material surface and the negative electrode active material surface are opposed to each other, and the negative electrode active material surface is not exposed. Bundling the respective uncoated portions of the positive and negative electrodes with each otherThe bundle was connected to a metal piece as a current collecting terminal by spot welding to prepare a current collecting piece, and an electrode group was prepared. Above, the porous polyethylene sheet blocks pores at a temperature above 135 ℃. As a case material of the battery, a sheet (total thickness of 0.1mm) obtained by laminating a polypropylene film, an aluminum foil having a thickness of 0.04mm, and a nylon film in this order was used, and a rectangular cup was molded with the polypropylene film on the inner surface side to form a case. The melting point of the polypropylene film was 165 ℃. The electrode group was sealed in a case, the current collecting terminal was exposed to the outside from the unsealed portion at the upper end of the cup, and 20mL of nonaqueous electrolytic solution was injected to sufficiently permeate the electrode. The upper end of the cup was heat-sealed under reduced pressure to seal it, thereby producing a battery. The cell was substantially square, and the ratio of the sum of the electrode areas of the positive electrode to the sum of the case surface areas (the case material surface area excluding the heat-sealed portion) of the cell was 22.6, (2 XS) 1and/T) is 411.
Evaluation of Battery
(method of measuring Battery Capacity)
A fresh battery which has not undergone charge-discharge cycles is initially charged and discharged for 5 cycles at a current value of 0.2C (a current value of 1-hour discharge rated capacity depending on the discharge capacity of 1-hour rate (the same applies hereinafter) in a voltage range of 4.1V to 3.0V at 25 ℃. The 5 th cycle 0.2C discharge capacity at this time was defined as "battery capacity" (Ah). The results of the battery evaluation are shown in Table 3 of Structure [6 ].
(method of measuring DC resistance component)
The resultant was charged at 25 ℃ for 150 minutes by a constant current of 0.2C, and an AC current of 10kHz was applied to measure the impedance as a "DC resistance component" (m.OMEGA.). The results of the battery evaluation are shown in Table 3 of Structure [6 ].
(method of measuring initial output Power)
The charge was carried out at 25 ℃ for 150 minutes by a constant current of 0.2C, and the discharge was carried out at 0.1C, 0.3C, 1.0C, 3.0C and 10.0C for 10 seconds, respectively, to measure the voltage at 10 seconds. The area of a triangle surrounded by a current-voltage line and the lower limit voltage (3V) is defined as "initial output power" (W). The results of the battery evaluation are shown in Table 3 of the structure [6 ].
(cycle test)
(method of measuring Battery Capacity after Endurance, DC resistance component after Endurance, and output Power after Endurance)
The cycle test was performed under a high temperature environment of 60 c, which is regarded as the practical use upper limit temperature of the lithium secondary battery. After charging to the upper limit charging voltage of 4.1V by a constant current constant voltage method of 2C, the charge/discharge was discharged to the end discharge voltage of 3.0V by a constant current method of 2C, and the cycle was repeated up to 500 cycles with the charge/discharge cycle set to 1 cycle. After the end of the cycle test, the battery was charged and discharged at 25 ℃ for 3 cycles at a current value of 0.2C, and the 0.2C discharge capacity at the 3 rd cycle was defined as "durable battery capacity". Further, the dc resistance component of the battery after the end of the cycle test was measured and used as the "dc resistance component after endurance", and the output was measured and used as the "output after endurance". The results of the battery evaluation are shown in Table 3 of Structure [6 ].
(overcharge test)
The overcharge test was conducted in an environment of 25 ℃. The charge was carried out from the discharged state (3V) at a constant current of 3C, and the behavior was observed. Here, "valve operation" indicates a phenomenon in which the nonaqueous electrolyte solution component is released by the operation of the vent valve, and "rupture" indicates a phenomenon in which the battery container is ruptured with a strong force and the contents are forcibly released. The results of the battery evaluation are shown in Table 3 of Structure [6 ].
(method of measuring volume Change Rate)
The volume of the cell in the discharged state (3V) was measured in an environment at 25 ℃. The volume was determined by adding ethanol to a graduated container and submerging the cell in ethanol. The ratio of the volume after the cycle test to the volume before the cycle test was defined as "volume change rate". The evaluation results are shown in Table 3 of Structure [6 ].
Structure [6] example 2
A battery was produced in the same manner as in example 1 except that the nonaqueous electrolytic solution in structure [6] in example 1 contained 0.3 mass% of trimethylsilyl methanesulfonate instead of hexamethylcyclotrisiloxane, and the battery was evaluated in the same manner. The results are shown in Table 3 for Structure [6 ].
Structure [6] example 3
Batteries were produced in the same manner as in structure [6] example 1 except that the nonaqueous electrolytic solution in structure [6] example 1 contained 0.3 mass% of phenyldimethylfluorosilane instead of hexamethylcyclotrisiloxane, and the battery evaluations were performed in the same manner. The results are shown in Table 3 for Structure [6 ].
Structure [6] example 4
A battery was produced in the same manner as in structure [6] example 1 except that the nonaqueous electrolytic solution in structure [6] example 1 contained 0.3 mass% of lithium difluorophosphate instead of hexamethylcyclotrisiloxane, and the battery was evaluated in the same manner. The results are shown in Table 3 for Structure [6 ].
Structure [6] comparative example 1
A battery was produced in the same manner as in structure [6] example 1 except that the nonaqueous electrolytic solution in structure [6] example 1 did not contain hexamethylcyclotrisiloxane, and the battery evaluation was performed in the same manner. The results are shown in Table 3 for Structure [6 ].
Structure [6] Table 2
[ Table 67]
No. Specific compound in nonaqueous electrolytic solution
Example 1 Hexamethylcyclotrisiloxane
Example 2 Methanesulfonic acid trimethylsilyl ester
Example 3 Phenyl dimethyl fluoro siliconAlkane (I) and its preparation method
Example 4 Lithium difluorophosphate
Comparative example 1 Is free of
Structure [6] Table 3
[ Table 68]
Figure BDA0003109774980003841
As is clear from the results of structure [6] table 3, by containing a specific compound in the nonaqueous electrolytic solution, the initial output, the capacity retention rate, and the safety were improved, the battery capacity and the output could be sufficiently maintained even after the cycle test, and the change in the battery volume was small.
Industrial applicability
The application of the lithium secondary battery of the present invention is not particularly limited, and the lithium secondary battery can be used in various known applications. Specific examples thereof include a notebook personal computer, a pen-input personal computer, a mobile personal computer, an Electronic book player (Electronic book player), a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a camcorder, a liquid crystal television, a handy cleaner, a portable CD, a mini disc player, a radio transceiver, an Electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a bicycle with a motor, a bicycle, a lighting apparatus, a toy, a game machine, a clock, an electric tool, a strobe, a camera, and the like. The lithium secondary battery of the present invention has a large capacity, an excellent life and a high output, generates little gas, and has high safety even when overcharged, and therefore, the lithium secondary battery can be suitably and widely used particularly in a field where a large capacity is required.
While the foregoing has been particularly described using the present invention and specific forms thereof, it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention. Further, the present application is based on the following japanese patent applications, all of which are incorporated by reference.
Japanese Special application 2005-331255 (application date: 11/16/2005)
Japanese Special application 2005-331362 (application date: 11/16/2005)
Japanese Special application 2005-331391 (application date: 11/16/2005)
Japanese Special application 2005-331477 (application date: 11/16/2005)
Japanese Special application 2005-331513 (application date: 11/16/2005)
Japanese Special application 2005-339794 (application date: 11/25/2005)
Japanese Special application 2006-019863 (application date: 2006, 1 and 27)
Japanese Special application 2006-005622 (application date: 1/13/2005)
Japanese Special application 2005-367747 (application date: 2005-12 and 21)
Japanese Special application 2005-377366 (application date: 2005-12 and 28)
Japanese Special application 2005-349052 (application date: 2005-12-2)
Japanese Special application 2005-359061 (application date: 2005-12-13)
Japanese Special application 2006-019879 (application date: 2006, 1 and 27)
Japanese Special application 2006-013664 (application date: 1/23/2005)
Japanese Special application 2005-314043 (application date: 2005-28/10)
Japanese Special application 2005-331585 (application date: 11/16/2005)
Japanese Special application 2005-305368 (application date: 10/20/2005)
Japanese Special application 2005-344732 (application date: 11/29/2005)
Japanese Special application 2005-343629 (application date: 11/29 in 2005)
Japanese Special application 2005-332173 (application date: 11/16/2005)
Japanese Special application 2005-305300 (application date: 10/20/2005)
Japanese Special application 2005-353005 (application date: 2005, 12 and 7)
Japanese Special application 2005-314260 (application date: 2005, 10 and 28)
Japanese Special application 2005-369824 (application date: 2005-12-22)
Japanese Special application 2005-370024 (application date: 2005-12-22)
Drawings
[ FIG. 1] (a) is a cross-sectional Scanning Electron Microscope (SEM) photograph of the thin film negative electrode (1) used in examples 1 to 3 and comparative example 1, which is the negative electrode [7 ]. (b) Is a photograph showing the mass concentration distribution of the element Si in the film thickness direction obtained by an Electron Probe Microanalyzer (EPMA) of the thin film negative electrode (1) of the negative electrode [7 ]. And (C) is a photograph showing the mass concentration distribution of the element C in the film thickness direction obtained by an Electron Probe Microanalyzer (EPMA) with respect to the thin film negative electrode (1) of the negative electrode [7 ].

Claims (22)

1. A nonaqueous electrolyte for a secondary battery, comprising at least a nonaqueous solvent and a lithium salt, wherein the nonaqueous electrolyte contains 1, 3-propanesultone and a difluorophosphate, the content of the 1, 3-propanesultone in the entire nonaqueous electrolyte is in the range of 0.001 to 5% by mass, and the content of the difluorophosphate in the entire nonaqueous electrolyte is 10ppm or more.
2. The nonaqueous electrolyte solution for a secondary battery according to claim 1, wherein the nonaqueous electrolyte solution contains 0.01 to 5 mass% of a difluorophosphate.
3. The nonaqueous electrolytic solution for a secondary battery according to claim 1, wherein the difluorophosphate is lithium difluorophosphate.
4. The nonaqueous electrolytic solution for a secondary battery according to claim 2, wherein the difluorophosphate is lithium difluorophosphate.
5. The nonaqueous electrolytic solution for a secondary battery according to claim 1, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
6. The nonaqueous electrolytic solution for a secondary battery according to claim 2, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
7. The nonaqueous electrolytic solution for a secondary battery according to claim 3, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
8. The nonaqueous electrolyte for a secondary battery according to claim 4, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
9. The nonaqueous electrolyte for a secondary battery according to any one of claims 1 to 8, wherein the nonaqueous solvent is a mixed solvent containing at least ethylene carbonate, and a ratio of ethylene carbonate to a total amount of the nonaqueous solvent is 1 to 25% by volume.
10. A lithium secondary battery comprising at least: an electrode assembly comprising a positive electrode and a negative electrode with a microporous membrane separator interposed therebetween, and a nonaqueous electrolytic solution comprising a nonaqueous solvent and a lithium salt contained therein, wherein the nonaqueous electrolytic solution is contained in a battery case,
the positive electrode and the negative electrode each have an active material layer containing an active material capable of occluding and releasing lithium ions formed on a current collector;
the nonaqueous electrolyte contains 1, 3-propanesultone and difluorophosphate, wherein the content of the 1, 3-propanesultone in the whole nonaqueous electrolyte is in the range of 0.001-5% by mass, and the content of the difluorophosphate in the whole nonaqueous electrolyte is 10ppm or more.
11. The lithium secondary battery according to claim 10, wherein the nonaqueous electrolytic solution contains 0.01 to 5 mass% of a difluorophosphate.
12. The lithium secondary battery according to claim 10, wherein the difluorophosphate is lithium difluorophosphate.
13. The lithium secondary battery according to claim 11, wherein the difluorophosphate is lithium difluorophosphate.
14. The lithium secondary battery according to claim 10, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
15. The lithium secondary battery according to claim 11, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
16. The lithium secondary battery according to claim 12, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
17. The lithium secondary battery according to claim 13, wherein the nonaqueous solvent contains at least ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
18. The lithium secondary battery according to any one of claims 10 to 17, wherein the nonaqueous solvent is a mixed solvent containing at least ethylene carbonate, and a ratio of ethylene carbonate to a total amount of the nonaqueous solvent is 1 to 25% by volume.
19. The lithium secondary battery according to any one of claims 10 to 17, wherein the secondary battery has any one property selected from the following (1) to (3):
(1) the area ratio of the total electrode area of the positive electrode to the surface area of the case of the secondary battery is 20 times or more;
(2) the DC resistance component of the secondary battery is 20 milliohm or less;
(3) the capacity of the battery element contained in one battery case of the secondary battery is 3 ampere hours or more.
20. The lithium secondary battery according to claim 18, wherein the secondary battery has any one property selected from the following (1) to (3):
(1) the area ratio of the total electrode area of the positive electrode to the surface area of the case of the secondary battery is 20 times or more;
(2) the DC resistance component of the secondary battery is 20 milliohm or less;
(3) the capacity of the battery element contained in one battery case of the secondary battery is 3 ampere hours or more.
21. A lithium secondary battery comprising at least: an electrode assembly comprising a positive electrode and a negative electrode with a microporous membrane separator interposed therebetween, and a nonaqueous electrolytic solution comprising a nonaqueous solvent and a lithium salt contained therein, wherein the nonaqueous electrolytic solution is contained in a battery case,
The positive electrode and the negative electrode each have an active material layer containing an active material capable of occluding and releasing lithium ions formed on a current collector;
the non-aqueous electrolyte contains at least one compound selected from nitrates and difluorophosphates, and the content thereof in the entire non-aqueous electrolyte is 10ppm or more;
the negative electrode is any one negative electrode selected from the following negative electrodes [1] to [10 ]:
negative electrode [1 ]: a negative electrode containing 2 or more carbonaceous materials having different crystallinity as a negative electrode active material;
cathode [2 ]]: an anode containing amorphous carbon as an anode active material, and a method for producing the sameThe amorphous carbon has a (002) plane interplanar spacing (d002) of 0.337nm or more and a crystallite size (Lc) of 80nm or less as measured by wide-angle X-ray diffraction, and has a value of 1360cm as measured by argon ion laser Raman spectroscopy-1Peak intensity of (2) relative to 1580cm-1A Raman R value defined as a ratio of peak intensities of (A) to (B) is 0.2 or more;
negative electrode [3 ]: a negative electrode containing a metal oxide as a negative electrode active material, the metal oxide containing titanium capable of occluding and releasing lithium;
negative electrode [4 ]: a negative electrode containing a carbonaceous material as a negative electrode active material, wherein the carbonaceous material has a circularity of 0.85 or more and a surface functional group amount O/C value of 0 to 0.01;
Negative electrode [5 ]: a negative electrode containing a heteroorientation carbon composite as a negative electrode active material, wherein the heteroorientation carbon composite contains at least 2 kinds of carbonaceous materials with different orientation;
cathode [6 ]]: a negative electrode comprising, as a negative electrode active material, a graphitic carbon particle having a circularity of 0.85 or more, an interplanar spacing (d002) of (002) plane as measured by wide-angle X-ray diffraction method of less than 0.337nm, and a thickness of 1360cm as measured by argon ion laser Raman spectroscopy-1Peak intensity of (2) relative to 1580cm-1The ratio of the peak intensities defined as a Raman R value of 0.12 to 0.8;
negative electrode [7 ]: a negative electrode containing, as a negative electrode active material, a negative electrode active material C containing multiple elements, which contains at least one of a lithium-occluding metal a and/or a lithium-occluding alloy B selected from Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb, and contains an element Z, which is C and/or N;
negative electrode [8 ]: a negative electrode containing 2 or more negative electrode active materials having different properties as a negative electrode active material;
cathode [9 ]]: containing a tap density of 0.1g/cm3A negative electrode containing a negative electrode active material having a pore volume of 0.01mL/g or more in terms of the volume of pores corresponding to particles having a diameter in the range of 0.01 to 1 μm as measured by a mercury porosimeter;
Negative electrode [10 ]: when the battery is charged to 60% of the nominal capacity of the negative electrode, the reaction resistance of the counter battery of the negative electrode is 500 Ω or less.
22. The lithium secondary battery according to claim 21, wherein the nonaqueous electrolytic solution contains at least one compound selected from the group consisting of a nitrate and a difluorophosphate in an amount of 0.01 to 5% by mass.
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