WO2014083848A1 - Non-aqueous electrolyte secondary battery - Google Patents

Non-aqueous electrolyte secondary battery Download PDF

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Publication number
WO2014083848A1
WO2014083848A1 PCT/JP2013/006978 JP2013006978W WO2014083848A1 WO 2014083848 A1 WO2014083848 A1 WO 2014083848A1 JP 2013006978 W JP2013006978 W JP 2013006978W WO 2014083848 A1 WO2014083848 A1 WO 2014083848A1
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secondary battery
electrolyte secondary
carbonate
lithium
positive electrode
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PCT/JP2013/006978
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French (fr)
Japanese (ja)
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高橋　康文
明宏 前田
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三洋電機株式会社
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Publication of WO2014083848A1 publication Critical patent/WO2014083848A1/en

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    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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

Definitions

  • the present invention relates to a non-aqueous electrolyte secondary battery.
  • lithium-containing transition metal oxides produced by ion-exchange of sodium-containing transition metal oxides have been studied (see Non-Patent Document 1).
  • One kind of such lithium-containing transition metal oxides is different from a positive electrode active material (such as lithium cobaltate (LiCoO 2) having a crystal structure belonging to space group R-3m) that is currently in practical use, and is a crystal belonging to space group P6 3 mc. It has a structure.
  • the lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc can be charged / discharged even when about 80% of the lithium in the oxide is extracted, and is a promising candidate for the next generation high capacity positive electrode active material. It is.
  • a non-aqueous electrolyte secondary battery using a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc as a positive electrode active material has a problem in charge / discharge cycle characteristics.
  • the non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a negative electrode, and a non-aqueous electrolyte including a non-aqueous solvent.
  • the non-aqueous solvent contains a lithium-containing transition metal oxide having a crystal structure belonging to 3 mc, the non-aqueous solvent being 7% by volume or more and 70% by volume or less of a fluorinated cyclic carbonate and 30% as a chain carbonate And at least one of methyl ethyl carbonate and diethyl carbonate in an amount of not less than volume% and not more than 93 volume%.
  • a nonaqueous electrolyte secondary battery having a high energy density and excellent charge / discharge cycle characteristics can be provided.
  • a nonaqueous electrolyte secondary battery which is an example of an embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode, and a nonaqueous electrolyte including a nonaqueous solvent.
  • a separator between the positive electrode and the negative electrode.
  • the nonaqueous electrolyte secondary battery has, for example, a structure in which an electrode body in which a positive electrode and a negative electrode are wound via a separator and a nonaqueous electrolyte are accommodated in an exterior body.
  • the positive electrode includes, for example, a positive electrode current collector such as a metal foil and a positive electrode active material layer formed on the positive electrode current collector.
  • a positive electrode current collector such as a metal foil and a positive electrode active material layer formed on the positive electrode current collector.
  • the positive electrode active material layer preferably includes a conductive agent and a binder in addition to the positive electrode active material.
  • the positive electrode active material includes a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc.
  • a crystal structure belongs to the space group P6 3 mc and is defined by, for example, an O 2 structure.
  • the O2 structure is a structure in which lithium is present in the center of the oxygen octahedron and two types of overlapping of oxygen and transition metal oxide exist per unit cell.
  • the positive electrode active material may contain other oxides such as LiNi a Co b Mn c O 2 having an O3 structure belonging to the space group C2 / m, C2 / c, or R-3m within a range that does not impair the object of the present invention.
  • the O3 structure is common to the O2 structure in that lithium is present at the center of the oxygen octahedron, but differs from the O2 structure in that there are three types of overlapping of oxygen and transition metal oxide per unit lattice.
  • the lithium-containing transition metal oxide is Li x1 Na y1 Co ⁇ 1 M ⁇ 1 O ⁇ 1 (0.66 ⁇ x1 ⁇ 1.1, 0 ⁇ y1 ⁇ 0.05, 0.75 ⁇ ⁇ 1 ⁇ 1.0, 0 ⁇ Those represented by ⁇ 1 ⁇ 0.25, 1.8 ⁇ ⁇ 1 ⁇ 2.2) are preferable.
  • M is a metal element other than lithium (Li), sodium (Na), and cobalt (Co), and is preferably at least manganese (Mn).
  • x1 is less than the above range (0.66), the amount of lithium that can be involved in charge / discharge decreases, and the theoretical capacity decreases. On the other hand, when x1 is larger than the above range (1.1), lithium enters the transition metal site and the capacity density decreases.
  • y1 is larger than the above range (0.05), the crystal structure is likely to be broken when sodium is inserted and desorbed.
  • y1 is more preferably 0.02 or less, and the crystal structure is further stabilized by satisfying y1 ⁇ 0.02.
  • sodium may not be detected by powder X-ray diffraction measurement.
  • ⁇ 1 When ⁇ 1 is less than the above range (0.75), the discharge potential is lowered. If ⁇ 1 is larger than the above range (1.0), a positive crystal potential is high (eg, 4.6 V (vs. Li / Li + )), and a stable crystal structure cannot be obtained in the charging process. It is more preferable that ⁇ 1 is in the range of 0.80 to 0.95 because the energy density is further increased.
  • M is preferably at least Mn as described above.
  • M is only Mn, when ⁇ 1 is larger than the above range (0.25), the discharge capacity density of 3.2 V or less increases, and as a result, the average discharge potential is lowered.
  • M is a metal element other than Mn, such as magnesium (Mg), nickel (Ni), zirconium (Zr), molybdenum (Mo), tungsten (W), aluminum (Al), chromium (Cr), vanadium (V ), Cerium (Ce), titanium (Ti), iron (Fe), potassium (K), gallium (Ga), indium (In), and the like.
  • Mg magnesium
  • Ni nickel
  • Zr zirconium
  • Mo molybdenum
  • Al aluminum
  • Cr chromium
  • V vanadium
  • Cerium (Ce) Cerium
  • iron (Fe) iron
  • K gallium
  • Ga indium
  • In indium
  • at least one selected from the other metal elements in addition to Mn is added to the lithium-containing transition metal oxide.
  • Ti is particularly preferable.
  • the addition amount of these elements is preferably 10 mol% or less with respect to the total molar amount of Co and M
  • the surface of the lithium-containing transition metal oxide may be covered with fine particles of an oxide such as aluminum oxide (Al 2 O 3 ), an inorganic compound such as a phosphoric acid compound, or a boric acid compound.
  • an oxide such as aluminum oxide (Al 2 O 3 )
  • an inorganic compound such as a phosphoric acid compound, or a boric acid compound.
  • the lithium-containing transition metal oxide is preferably prepared by ion exchange of sodium in the sodium-containing transition metal oxide with lithium.
  • Sodium-containing transition metal oxides include, for example, sodium and lithium that does not exceed the molar amount of sodium. Specifically, Li x2 Na y2 Co ⁇ 2 M ⁇ 2 O ⁇ 2 (0 ⁇ x2 ⁇ 0.1, 0.66 ⁇ y2 ⁇ 0.75, 0.75 ⁇ ⁇ 2 ⁇ 1, 0 ⁇ ⁇ 2 ⁇ 0.25, Those represented by 1.9 ⁇ ⁇ 2 ⁇ 2.1) are preferred.
  • Examples of the method for ion-exchanging sodium to lithium include at least one selected from the group consisting of lithium nitrate, lithium sulfate, lithium chloride, lithium carbonate, lithium hydroxide, lithium iodide, lithium bromide, and lithium chloride.
  • a method of adding a molten salt bed of lithium salt to a sodium-containing transition metal oxide is mentioned.
  • a method of immersing a sodium-containing transition metal oxide in a solution containing at least one lithium salt can be given.
  • the conductive agent is used to increase the electrical conductivity of the positive electrode active material layer.
  • the conductive agent include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more.
  • the above binder is used for maintaining a good contact state between the positive electrode active material and the conductive agent and enhancing the binding property of the positive electrode active material and the like to the surface of the positive electrode current collector.
  • the binder for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or a modified product thereof is used.
  • the binder may be used in combination with a thickener such as carboxymethyl cellulose (CMC) or polyethylene oxide (PEO).
  • the positive electrode potential in a fully charged state of the positive electrode having the above structure can be set to a high potential of 4.0 V (vs. Li / Li + ) or higher.
  • End-of-charge potential of the positive electrode in view of high capacity, preferably 4.5V (vs.Li/Li +) or more, 4.55V (vs.Li/Li +) or more preferred.
  • the upper limit of the charge termination potential of the positive electrode is not particularly limited, but is preferably 5.0 V (vs. Li / Li + ) or less from the viewpoint of suppressing decomposition of the nonaqueous electrolyte.
  • the negative electrode includes, for example, a negative electrode current collector such as a metal foil, and a negative electrode active material layer formed on the negative electrode current collector.
  • a negative electrode current collector such as a metal foil
  • a negative electrode active material layer formed on the negative electrode current collector.
  • a metal foil that is stable in the potential range of the negative electrode such as copper a film in which a metal that is stable in the potential range of the negative electrode such as copper is arranged on the surface layer, or the like can be used.
  • the negative electrode active material layer preferably contains a binder in addition to the negative electrode active material capable of inserting and extracting lithium ions.
  • PTFE styrene-butadiene copolymer
  • the binder may be used in combination with a thickener such as CMC.
  • Examples of the negative electrode active material include natural graphite, artificial graphite, lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, lithium alloy, carbon and silicon in which lithium is previously occluded, and alloys and mixtures thereof. Etc. can be used.
  • the non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.
  • the nonaqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolyte solution), and may be a solid electrolyte using a gel polymer or the like.
  • the non-aqueous solvent contains a fluorinated cyclic carbonate and a specific chain carbonate in a blending ratio described later.
  • a good protective film is formed on the positive electrode. , Approximately 100%), the crystal structure is stable. That is, application of the non-aqueous solvent improves the cycle characteristics of the non-aqueous electrolyte secondary battery.
  • the fluorinated cyclic carbonate is preferably a fluorinated cyclic carbonate having a fluorine atom directly bonded to the carbonate ring.
  • fluoroethylene carbonate examples include 4-fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, 4,4,5,5- Tetrafluoroethylene carbonate is mentioned. Of these, monofluoroethylene carbonate and difluoroethylene carbonate having a relatively low viscosity are preferable from the viewpoint of achieving both storage characteristics and cycle characteristics, among which 4-fluoroethylene carbonate and 4,5-difluoroethylene carbonate are particularly preferable.
  • 4-fluoroethylene carbonate or the like it is assumed that a good protective film is formed not only on the negative electrode but also on the positive electrode, thereby improving cycle characteristics and the like.
  • the content of the fluorinated cyclic carbonate is preferably 7% by volume or more and 70% by volume or less, and 25% by volume or more and 70% by volume or less based on the total volume of the nonaqueous solvent in the nonaqueous electrolyte from the viewpoint of improving cycle characteristics. Is more preferable, and 50 volume% or more and 70 volume% or less are especially preferable.
  • various characteristics such as storage characteristics and load characteristics, and from the viewpoint of optimization of battery design including manufacturing costs, for example, 7% by volume to 50% by volume, or 7% by volume. More than 25 volume% may be suitable.
  • the specific chain carbonates are methyl ethyl carbonate (hereinafter referred to as MEC) and diethyl carbonate (hereinafter referred to as DEC).
  • MEC and DEC may be used in a range of 30 to 90% by volume with respect to the total volume of the nonaqueous solvent. However, from the viewpoint of improving cycle characteristics, it is preferable that the ratio of DEC is higher than that of MEC. More preferably, only DEC is used as the carbonic acid ester.
  • the content of the specific chain carbonate is preferably from 30 to 93% by volume, more preferably from 30% to 75% by volume, based on the total volume of the nonaqueous solvent in the nonaqueous electrolyte, from the viewpoint of improving cycle characteristics. It is preferably 30% by volume or more and 50% by volume or less.
  • various characteristics such as storage characteristics and load characteristics, and from the viewpoint of optimization of battery design including manufacturing cost, for example, 50 volume% or more and 93 volume% or less, or 75 volume% More than 93 volume% may be suitable.
  • the non-aqueous solvent preferably does not contain a fluorinated chain ester such as 2,2,2-trifluoroethyl methyl carbonate or methyl 3,3,3-trifluoropropionate. Since the fluorinated chain ester is more expensive than the fluorinated cyclic carbonate and is inferior in mass productivity, it is useful to improve the cycle characteristics without using it.
  • “not containing a fluorinated chain ester” means substantially not containing a fluorinated chain ester. Specifically, it means that 0.5% by volume or more of the fluorinated chain ester is not contained with respect to the total volume of the nonaqueous solvent in the nonaqueous electrolyte.
  • non-aqueous solvent in addition to the fluorinated cyclic carbonate and the specific chain carbonate, a non-fluorine solvent generally used as a non-aqueous solvent can be used in combination.
  • a non-fluorine solvent generally used as a non-aqueous solvent can be used in combination.
  • Specific examples include cyclic carbonates, chain carbonates (excluding MEC and DEC), carboxylic acid esters, cyclic ethers, chain ethers, nitriles, amides, and mixed solvents thereof. .
  • cyclic carbonate examples include ethylene carbonate, propylene carbonate, butylene carbonate and the like.
  • chain carbonate examples include diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate and the like.
  • carboxylic acid esters examples include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and ⁇ -butyrolactone.
  • cyclic ethers examples include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1, 4-Dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineol, crown ether and the like can be mentioned.
  • chain ethers examples include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether.
  • Pentylphenyl ether methoxytoluene, benzylethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, Examples include traethylene glycol dimethyl.
  • nitriles examples include acetonitrile, and examples of the amides include dimethylformamide.
  • a cyclic carbonate and a chain ester are preferably used.
  • the nonaqueous electrolyte does not contain a solvent other than the fluorinated cyclic carbonate and the specific chain carbonate.
  • does not contain a solvent other than the fluorinated cyclic carbonate and the fluorinated chain ester means that it contains substantially no other solvent. Specifically, it means that no other solvent is contained in an amount of 0.5% by volume or more based on the total volume of the nonaqueous solvent in the nonaqueous electrolyte.
  • the electrolyte salt is preferably a lithium salt.
  • the lithium salt those generally used as a supporting salt in a conventional nonaqueous electrolyte secondary battery can be used. Specific examples include LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , LiN (FSO 2 ) 2 , LiN (C 1 F 2l + 1 SO 2 ) (C m F 2m + 1 SO 2 ).
  • These lithium salts may be used alone or in combination of two or more.
  • separator a porous sheet having ion permeability and insulating properties is used.
  • the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric.
  • material of the separator polyolefin such as polyethylene and polypropylene is suitable.
  • Example 1 [Production of positive electrode] To obtain Na 0.8 Co 8/9 Mn 1/9 O 2 (prepared composition), sodium nitrate (NaNO 3 ), cobalt oxide (II III) (Co 3 O 4 ), and manganese (III) oxide (Mn 2 O 3 ) was mixed. Then, the said mixture was hold
  • a molten salt bed in which lithium nitrate (LiNO 3 ) and lithium hydroxide (LiOH) were mixed at a molar ratio of 61:39 was equivalent to 5 times equivalent (5 g) to 5 g of the obtained sodium-containing transition metal oxide. )added. Then, a part of sodium of the sodium-containing transition metal oxide was ion-exchanged into lithium by holding the mixture at 200 ° C. for 10 hours. Further, the ion-exchanged material was washed with water to obtain a lithium-containing transition metal oxide.
  • the obtained lithium-containing transition metal oxide was analyzed by a powder X-ray diffraction method (manufactured by Rigaku Corporation, using a powder XRD measuring device RINT2200 (radiation source Cu-K ⁇ ); the same applies hereinafter) to identify the crystal structure. It was.
  • the obtained crystal structure was assigned to the O2 structure of the space group P6 3 mc.
  • the composition of the lithium-containing transition metal oxide was calculated by ICP emission analysis (Thermo Fisher Scientific, using ICP emission spectroscopic analyzer iCAP6300. The same applies hereinafter).
  • ICP emission analysis Thermo Fisher Scientific, using ICP emission spectroscopic analyzer iCAP6300. The same applies hereinafter).
  • the obtained lithium-containing transition metal oxide is used as a positive electrode active material
  • the positive electrode active material is 95% by mass
  • the conductive agent is 2.5% by mass of acetylene black
  • the binder is 2.5% by mass of polyvinylidene fluoride.
  • non-aqueous electrolyte 4-Fluoroethylene carbonate (hereinafter referred to as FEC) as a fluorinated cyclic carbonate and MEC were mixed at a volume ratio of 25:75 to obtain a nonaqueous solvent.
  • a nonaqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (hereinafter referred to as LiPF 6 ) as an electrolyte salt in the nonaqueous solvent so as to have a concentration of 1.0 mol / l.
  • LiPF 6 lithium hexafluorophosphate
  • test cell A1 which is a 363562-type square nonaqueous electrolyte secondary battery with a rated capacity of 900 mAh was produced.
  • Example 2 In order to obtain Na 0.8 Co 8/9 Mn 2/27 Ti 1/27 O 2 (prepared composition), sodium nitrate (NaNO 3 ), cobalt oxide (II III) (Co 3 O 4 ), manganese oxide (III ) (Mn 2 O 3 ) and titanium dioxide (TiO 2 ). Then, the sodium containing transition metal oxide was obtained by hold
  • a molten salt bed in which lithium nitrate (LiNO 3 ) and lithium hydroxide (LiOH) were mixed at a molar ratio of 61:39 was equivalent to 5 times equivalent (5 g) to 5 g of the obtained sodium-containing transition metal oxide. )added. Then, a part of sodium of the sodium-containing transition metal oxide was ion-exchanged into lithium by holding the mixture at 200 ° C. for 10 hours. Further, the ion-exchanged material was washed with water to obtain a lithium-containing transition metal oxide.
  • the obtained lithium-containing transition metal oxide was analyzed by a powder X-ray diffraction method, and the crystal structure was identified. The obtained crystal structure was assigned to the O2 structure of the space group P6 3 mc. Further, the composition of the lithium-containing transition metal oxides, the result calculated by ICP emission analysis was Li 0.86 Na 0.022 Co 0.89 Mn 0.07 Ti 0.04 O 2. Test cell A2 was produced in the same manner as in Example 1 except that the lithium-containing transition metal oxide thus obtained was used as the positive electrode active material.
  • Example 3 As the nonaqueous solvent for the nonaqueous electrolyte, a nonaqueous solvent in which 4,5-difluoroethylene carbonate (hereinafter referred to as DFEC) and MEC were mixed at a volume ratio of 25:75 was used. Test cell A3 was produced in the same manner as in Example 2.
  • Example 4 A test cell A4 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and DEC were mixed at a volume ratio of 25:75 was used as a nonaqueous solvent for the nonaqueous electrolyte. .
  • Example 5 A test cell A5 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 10:90 was used as the nonaqueous electrolyte nonaqueous solvent. .
  • Test cell A6 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 50:50 was used as the nonaqueous solvent for the nonaqueous electrolyte. .
  • Test cell A7 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 70:30 was used as the nonaqueous solvent for the nonaqueous electrolyte. .
  • Example 8> A test cell A8 was produced in the same manner as in Example 2 except that a nonaqueous solvent in which DFEC and MEC were mixed at a volume ratio of 50:50 was used as a nonaqueous electrolyte nonaqueous electrolyte. .
  • Test cell A9 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 7:93 was used as a nonaqueous electrolyte nonaqueous electrolyte. .
  • the crystal structure was assigned to the O3 structure of the space group R-3m.
  • the composition of the lithium-containing transition metal oxide was calculated by ICP emission analysis, and was Li 1.01 CoO 2 .
  • Comparative Example 2 The same as Comparative Example 1 except that a nonaqueous solvent in which ethylene carbonate (hereinafter referred to as EC) and MEC were mixed at a volume ratio of 25:75 was used as the nonaqueous solvent for the nonaqueous electrolyte. Thus, a test cell X2 was produced.
  • EC ethylene carbonate
  • MEC ethylene carbonate
  • Example 3 A test cell X3 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which EC and MEC were mixed at a volume ratio of 25:75 was used as the nonaqueous electrolyte nonaqueous solvent. .
  • test cell X4 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 5:95 was used as a nonaqueous solvent for the nonaqueous electrolyte. .
  • Test cell X5 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 90:10 was used as the nonaqueous solvent for the nonaqueous electrolyte. .
  • Table 1 shows a summary of the composition and crystal structure (space group) of the positive electrode active material and the composition of the nonaqueous electrolyte in Examples 1 to 9 and Comparative Examples 1 to 5.
  • Table 2 shows capacity retention rates after 15, 30, and 50 cycles for test cells A1 to A9 of Examples 1 to 9 and test cells X1 to X5 of Comparative Examples 1 to 5.
  • test cells A1 to A8 of the example all show excellent cycle characteristics as compared with the test cells X1 to X5 of the comparative example. That is, a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc is used as a positive electrode active material, and mixed in a predetermined volume ratio with a fluorinated cyclic carbonate (FEC, DFEC) and a specific chain carbonate (MEC). , DEC) is applied to the non-aqueous electrolyte, it is considered that capacity reduction due to decomposition of the non-aqueous electrolyte accompanying charge / discharge is suppressed, and good cycle characteristics are obtained.
  • FEC fluorinated cyclic carbonate
  • MEC specific chain carbonate
  • test cells X1 and X2 of Comparative Examples 1 and 2 of Comparative Examples 1 and 2 a fluorinated cyclic carbonate and a specific chain carbonate mixed with a predetermined volume ratio of lithium cobaltate having a crystal structure belonging to space group R-3m as a positive electrode active material.
  • a non-aqueous solvent containing an ester was applied to the non-aqueous electrolyte, but good cycle characteristics were not obtained. That is, with respect to lithium cobaltate having a crystal structure belonging to the space group R-3m that is currently in practical use, the non-aqueous solvent containing a fluorinated cyclic carbonate and a specific chain carbonate did not show an effect of improving cycle characteristics. .
  • the fluorinated cyclic carbonate mixed at a predetermined volume ratio and Good cycle characteristics were obtained by applying a non-aqueous solvent containing a specific chain carbonate. That is, the non-aqueous solvent which has no effect on the positive electrode active material currently in practical use has a large cycle characteristic when the positive electrode active material is a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc. Improve.
  • the active material is easily cleaved with charge and discharge, and a coating that smoothly inserts and desorbs lithium on the newly generated active material surface is provided. Although it is thought that it was formed, the evaluation result was extremely good than expected.
  • the fluorinated cyclic carbonate is 7% by volume or more and 70% by volume or less with respect to the total volume of the nonaqueous solvent, and at least one of the specific chain carbonates MEC and DEC is 30% by volume. It is obtained only when the content is 93% by volume or less, and cannot be obtained when the amount is outside this range.
  • the ratio of the fluorinated cyclic carbonate exceeds 70% by volume, the cycle characteristics are remarkably deteriorated, and charge / discharge cannot be performed with a low number of cycles as in the test cell X5 of Comparative Example 5.
  • the ratio of the fluorinated cyclic carbonate is less than 7% by volume, good cycle characteristics cannot be obtained as in the test cell X4 of Comparative Example 4.
  • cycling characteristics can be improved, so that the ratio of the fluorinated cyclic carbonate in a non-aqueous solvent is made high in the range of 7 volume% or more and 70 volume% or less.
  • the non-aqueous electrolyte is substantially free of fluorinated cyclic carbonate and other solvents other than MEC and DEC, and the volume ratio of the two is 7:93 to 70:30, and 25:75 More preferably, it is ⁇ 70: 30, and particularly preferably 50:50 to 70:30.
  • DEFC fluorinated cyclic ester carbonate
  • FEC fluorinated cyclic ester carbonate
  • specific chain carbonate it is preferable to use a larger amount of DEC than MEC or to use only DEC. Thereby, cycle characteristics can be further improved (see Examples 1 and 4).
  • the positive electrode active material it is preferable to use a lithium-containing transition metal oxide containing Ti in addition to Co and Mn as transition metal elements.
  • the contents of Co, Mn, and Ti are preferably Co>Mn> Ti.
  • cycle characteristics can be further improved (see Examples 1 and 2).
  • the effect of improving cycle characteristics due to the addition of Ti is remarkable, and the capacity retention ratio after 50 cycles of test cell A1 (Example 1) using Li 0.84 Na 0.028 Co 0.89 Mn 0.11 O 2 as the positive electrode active material is 79.9%.
  • the same capacity retention rate of Test Cell A2 (Example 2) using Li 0.86 Na 0.022 Co 0.89 Mn 0.07 Ti 0.04 O 2 as the positive electrode active material was 96.6%.
  • Example 10 A three-electrode cell B1 was produced using the positive electrode produced in Example 1 as a working electrode and metal lithium as a counter electrode and a reference electrode. The battery was charged at a constant current rate of 0.2 C until the positive electrode potential reached 4.6 V, and further charged at a constant potential of 4.6 V until the current value reached 1/20 C. Then, the charge / discharge capacity (mAh) of the battery was measured by discharging until the positive electrode potential reached 3.2 V at a constant current of 0.2 C. This charge / discharge was repeated, and the charge / discharge efficiency was evaluated by multiplying the value obtained by dividing the discharge capacity at the 10th cycle by the charge capacity.
  • mAh charge / discharge capacity
  • Example 6 A test cell Y1 was prepared in the same manner as in Example 10 except that a nonaqueous solvent in which EC and MEC were mixed at a volume ratio of 25:75 was used as the nonaqueous electrolyte nonaqueous electrolyte. The charge / discharge efficiency at the 10th cycle was evaluated.
  • Table 3 shows a summary of the composition of the positive electrode active material, the composition of the nonaqueous electrolyte, and the charge / discharge efficiency at the 10th cycle in Example 10 and Comparative Example 6.
  • the test cell B1 of Example 10 exhibits excellent charge / discharge efficiency as compared to the test cell Y1 of Comparative Example 6, and is considered to have good cycle characteristics.
  • a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc is used as a positive electrode active material, and a non-aqueous solvent containing a fluorinated cyclic carbonate and a chain carbonate mixed in a predetermined volume ratio is applied to a non-aqueous electrolyte. By doing so, a charge / discharge cycle involving charging to a high potential of 4.55V, 4.6V becomes possible.

Abstract

A non-aqueous electrolyte secondary battery is provided with a positive electrode including a positive electrode active material, a negative electrode, and a non-aqueous electrolyte containing a non-aqueous solvent, the positive electrode active material including a lithium-containing transition metal oxide having a crystal structure belonging to a space group P63mc, and the non-aqueous solvent containing, with respect to the total volume, 7-70%, inclusive, by volume of fluorinated cyclic carbonate esters and 30-93%, inclusive, by volume of at least one of methylethyl carbonate and diethyl carbonate as chain carbonate esters.

Description

非水電解質二次電池Nonaqueous electrolyte secondary battery
　本発明は、非水電解質二次電池に関する。 The present invention relates to a non-aqueous electrolyte secondary battery.
　次世代の高容量正極活物質の一つとして、ナトリウム含有遷移金属酸化物をイオン交換して作製されるリチウム含有遷移金属酸化物が研究されている（非特許文献１参照）。かかるリチウム含有遷移金属酸化物の一種は、現在実用化されている正極活物質（空間群Ｒ－３ｍに属する結晶構造のコバルト酸リチウム（ＬｉＣｏＯ２）等）と異なり、空間群Ｐ６3ｍｃに属する結晶構造を有する。空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物は、酸化物中のリチウムが約８０％引き抜かれても充放電が可能であり、次世代の高容量正極活物質の有力な候補である。 As one of the next generation high-capacity positive electrode active materials, lithium-containing transition metal oxides produced by ion-exchange of sodium-containing transition metal oxides have been studied (see Non-Patent Document 1). One kind of such lithium-containing transition metal oxides is different from a positive electrode active material (such as lithium cobaltate (LiCoO 2) having a crystal structure belonging to space group R-3m) that is currently in practical use, and is a crystal belonging to space group P6 3 mc. It has a structure. The lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc can be charged / discharged even when about 80% of the lithium in the oxide is extracted, and is a promising candidate for the next generation high capacity positive electrode active material. It is.
　しかしながら、空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物を正極活物質に用いた非水電解質二次電池は、充放電サイクル特性に問題がある。 However, a non-aqueous electrolyte secondary battery using a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc as a positive electrode active material has a problem in charge / discharge cycle characteristics.
　本発明に係る非水電解質二次電池は、正極活物質を含む正極と、負極と、非水溶媒を含む非水電解質とを備える非水電解質二次電池において、正極活物質は、空間群Ｐ６3ｍｃに属する結晶構造を有するリチウム含有遷移金属酸化物を含み、非水溶媒は、その総体積に対して７体積％以上７０体積％以下のフッ素化環状炭酸エステルと、鎖状炭酸エステルとして３０体積％以上９３体積％以下のメチルエチルカーボネート及びジエチルカーボネートの少なくとも一方とを含む。 The non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a negative electrode, and a non-aqueous electrolyte including a non-aqueous solvent. The non-aqueous solvent contains a lithium-containing transition metal oxide having a crystal structure belonging to 3 mc, the non-aqueous solvent being 7% by volume or more and 70% by volume or less of a fluorinated cyclic carbonate and 30% as a chain carbonate And at least one of methyl ethyl carbonate and diethyl carbonate in an amount of not less than volume% and not more than 93 volume%.
　本発明によれば、エネルギー密度が高く、かつ充放電サイクル特性に優れた非水電解質二次電池を提供することができる。 According to the present invention, a nonaqueous electrolyte secondary battery having a high energy density and excellent charge / discharge cycle characteristics can be provided.
　以下、本発明に係る実施の形態につき、詳細に説明する。本発明の実施形態の一例である非水電解質二次電池は、正極活物質を含む正極と、負極と、非水溶媒を含む非水電解質とを備える。また、正極と負極との間には、セパレータを設けることが好適である。非水電解質二次電池は、例えば、正極及び負極がセパレータを介して巻回されてなる電極体と、非水電解質とが外装体に収容された構造を有する。 Hereinafter, embodiments according to the present invention will be described in detail. A nonaqueous electrolyte secondary battery which is an example of an embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode, and a nonaqueous electrolyte including a nonaqueous solvent. In addition, it is preferable to provide a separator between the positive electrode and the negative electrode. The nonaqueous electrolyte secondary battery has, for example, a structure in which an electrode body in which a positive electrode and a negative electrode are wound via a separator and a nonaqueous electrolyte are accommodated in an exterior body.
　〔正極〕
　正極は、例えば、金属箔等の正極集電体と、正極集電体上に形成された正極活物質層とで構成される。正極集電体には、アルミニウムなどの正極の電位範囲で安定な金属の箔、アルミニウムなどの正極の電位範囲で安定な金属を表層に配置したフィルム等が用いられる。正極活物質層は、正極活物質の他に、導電剤及び結着剤を含むことが好適である。 [Positive electrode]
The positive electrode includes, for example, a positive electrode current collector such as a metal foil and a positive electrode active material layer formed on the positive electrode current collector. As the positive electrode current collector, a metal foil that is stable in the potential range of the positive electrode such as aluminum, a film in which a metal that is stable in the potential range of the positive electrode such as aluminum is disposed on the surface layer, or the like is used. The positive electrode active material layer preferably includes a conductive agent and a binder in addition to the positive electrode active material.
　上記正極活物質は、空間群Ｐ６3ｍｃに属する結晶構造を有するリチウム含有遷移金属酸化物を含む。かかる結晶構造は、空間群Ｐ６3ｍｃに属し、例えばＯ２構造で規定される。Ｏ２構造とは、リチウムが酸素八面体の中心に存在し、かつ酸素と遷移金属酸化物との重なり方が単位格子あたり２種類存在する構造である。なお、上記正極活物質は、本発明の目的を損なわない範囲で他の酸化物、例えば空間群Ｃ２／ｍ、Ｃ２／ｃ、又はＲ－３ｍに属するＯ３構造のＬｉＮｉaＣｏbＭｎcＯ2（０＜ａ＜１、０＜ｂ＜１、０＜ｃ＜１）等を含んでいてもよい。Ｏ３構造は、リチウムが酸素八面体の中心に存在する点でＯ２構造と共通するが、酸素と遷移金属酸化物との重なり方が単位格子あたり３種類存在する点でＯ２構造と異なる。 The positive electrode active material includes a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc. Such a crystal structure belongs to the space group P6 3 mc and is defined by, for example, an O 2 structure. The O2 structure is a structure in which lithium is present in the center of the oxygen octahedron and two types of overlapping of oxygen and transition metal oxide exist per unit cell. Note that the positive electrode active material may contain other oxides such as LiNi a Co b Mn c O 2 having an O3 structure belonging to the space group C2 / m, C2 / c, or R-3m within a range that does not impair the object of the present invention. (0 <a <1, 0 <b <1, 0 <c <1) may be included. The O3 structure is common to the O2 structure in that lithium is present at the center of the oxygen octahedron, but differs from the O2 structure in that there are three types of overlapping of oxygen and transition metal oxide per unit lattice.
　上記リチウム含有遷移金属酸化物は、Ｌｉx1Ｎａy1Ｃｏα1Ｍβ1Ｏγ1（０．６６＜ｘ１＜１.１、０＜ｙ１≦０．０５、０．７５≦α１＜１.０、０≦β１≦０．２５、１．８≦γ１≦２．２）で表されるものが好ましい。Ｍは、リチウム（Ｌｉ）、ナトリウム（Ｎａ）、コバルト（Ｃｏ）以外の金属元素であり、少なくともマンガン（Ｍｎ）であることが好ましい。 The lithium-containing transition metal oxide is Li x1 Na y1 Coα 1 Mβ 1 Oγ 1 (0.66 <x1 <1.1, 0 <y1 ≦ 0.05, 0.75 ≦ α1 <1.0, 0 ≦ Those represented by β1 ≦ 0.25, 1.8 ≦ γ1 ≦ 2.2) are preferable. M is a metal element other than lithium (Li), sodium (Na), and cobalt (Co), and is preferably at least manganese (Mn).
　ｘ１が上記範囲（０．６６）より少ないと充放電に関与できるリチウムが少なくなるため、理論容量が減少する。また、ｘ１が上記範囲（１．１）より多いと遷移金属サイトにリチウムが入り、容量密度が減少する。 If x1 is less than the above range (0.66), the amount of lithium that can be involved in charge / discharge decreases, and the theoretical capacity decreases. On the other hand, when x1 is larger than the above range (1.1), lithium enters the transition metal site and the capacity density decreases.
　ｙ１が上記範囲（０．０５）より多いと、ナトリウムが挿入・脱離するときに結晶構造の破壊が起こりやすくなる。ｙ１は、０．０２以下がより好ましく、ｙ１≦０．０２とすることで結晶構造がさらに安定化する。ｙ１≦０．０２の場合、粉末Ｘ線回折測定でナトリウムを検出できない場合がある。 When y1 is larger than the above range (0.05), the crystal structure is likely to be broken when sodium is inserted and desorbed. y1 is more preferably 0.02 or less, and the crystal structure is further stabilized by satisfying y1 ≦ 0.02. When y1 ≦ 0.02, sodium may not be detected by powder X-ray diffraction measurement.
　α１が上記範囲（０．７５）より少ないと放電電位が低くなる。また、α１が上記範囲（１.０）より多いと正極電位が高い（例えば、４．６Ｖ（ｖｓ．Ｌｉ／Ｌｉ+））充電過程で安定な結晶構造が得られない。なお、α１が０．８０～０．９５の範囲であると、エネルギー密度がさらに高くなるため、より好ましい。 When α1 is less than the above range (0.75), the discharge potential is lowered. If α1 is larger than the above range (1.0), a positive crystal potential is high (eg, 4.6 V (vs. Li / Li + )), and a stable crystal structure cannot be obtained in the charging process. It is more preferable that α1 is in the range of 0.80 to 0.95 because the energy density is further increased.
　Ｍは、上記のように、少なくともＭｎであることが好ましい。ＭがＭｎのみである場合、β１が上記範囲（０．２５）より多くなると、３．２Ｖ以下の放電容量密度が増し、結果的に平均放電電位の低下を招く。 M is preferably at least Mn as described above. When M is only Mn, when β1 is larger than the above range (0.25), the discharge capacity density of 3.2 V or less increases, and as a result, the average discharge potential is lowered.
　Ｍは、Ｍｎ以外の他の金属元素、例えばマグネシウム（Ｍｇ）、ニッケル（Ｎｉ）、ジルコニウム（Ｚｒ）、モリブデン（Ｍｏ）、タングステン（Ｗ）、アルミニウム（Ａｌ）、クロム（Ｃｒ）、バナジウム（Ｖ）、セリウム（Ｃｅ）、チタン（Ｔｉ）、鉄（Ｆｅ）、カリウム（Ｋ）、ガリウム（Ｇａ）、インジウム（Ｉｎ）等であってもよい。好ましくは、Ｍｎに加えて当該他の金属元素から選ばれる少なくとも一種が上記リチウム含有遷移金属酸化物に添加される。当該他の金属元素としては、Ｔｉが特に好ましい。これら元素の添加量は、ＣｏとＭｎの総モル量に対して１０ｍｏｌ％以下であることが好ましい。 M is a metal element other than Mn, such as magnesium (Mg), nickel (Ni), zirconium (Zr), molybdenum (Mo), tungsten (W), aluminum (Al), chromium (Cr), vanadium (V ), Cerium (Ce), titanium (Ti), iron (Fe), potassium (K), gallium (Ga), indium (In), and the like. Preferably, at least one selected from the other metal elements in addition to Mn is added to the lithium-containing transition metal oxide. As the other metal element, Ti is particularly preferable. The addition amount of these elements is preferably 10 mol% or less with respect to the total molar amount of Co and Mn.
　上記リチウム含有遷移金属酸化物の表面は、酸化アルミニウム（Ａｌ2Ｏ3）等の酸化物、リン酸化合物、ホウ酸化合物等の無機化合物の微粒子で覆われていてもよい。 The surface of the lithium-containing transition metal oxide may be covered with fine particles of an oxide such as aluminum oxide (Al 2 O 3 ), an inorganic compound such as a phosphoric acid compound, or a boric acid compound.
　上記リチウム含有遷移金属酸化物は、ナトリウム含有遷移金属酸化物のナトリウムをリチウムにイオン交換することによって作製することが好適である。ナトリウム含有遷移金属酸化物は、例えば、ナトリウム及びナトリウムのモル量を超えないリチウムを含む。具体的には、Ｌｉx2Ｎａy2Ｃｏα2Ｍβ2Ｏγ2（０＜ｘ２≦０.１、０．６６＜ｙ２＜０．７５、０．７５≦α２＜１、０≦β２≦０．２５、１．９≦γ２≦２．１）で表されるものが好ましい。 The lithium-containing transition metal oxide is preferably prepared by ion exchange of sodium in the sodium-containing transition metal oxide with lithium. Sodium-containing transition metal oxides include, for example, sodium and lithium that does not exceed the molar amount of sodium. Specifically, Li x2 Na y2 Coα 2 Mβ 2 Oγ 2 (0 <x2 ≦ 0.1, 0.66 <y2 <0.75, 0.75 ≦ α2 <1, 0 ≦ β2 ≦ 0.25, Those represented by 1.9 ≦ γ2 ≦ 2.1) are preferred.
　コバルト量α２が増加するにつれて、イオン交換後のリチウム量ｘ１が増加する。これは、イオン交換前のＬｉx2Ｎａy2Ｃｏα2Ｍβ2Ｏγ2中では、コバルトは３価以上の状態でも安定であるのに対し、イオン交換時にコバルトが還元され、イオン交換後のＬｉx1Ｎａy1Ｃｏα1Ｍβ1Ｏγ1中では、コバルトは３価の状態で安定となり、リチウムイオンが構造中に吸蔵されるためと推測される。 As the amount of cobalt α2 increases, the amount of lithium after ion exchange x1 increases. In Li x2 Na y2 Coα 2 Mβ 2 Oγ 2 before ion exchange, cobalt is stable even in a trivalent or higher state, whereas cobalt is reduced during ion exchange, and Li x1 Na after ion exchange. In y1 Coα 1 Mβ 1 Oγ 1 , it is presumed that cobalt is stable in a trivalent state, and lithium ions are occluded in the structure.
　ナトリウムをリチウムにイオン交換する方法としては、例えば、硝酸リチウム、硫酸リチウム、塩化リチウム、炭酸リチウム、水酸化リチウム、ヨウ化リチウム、臭化リチウム、及び塩化リチウムからなる群より選ばれた少なくとも一種のリチウム塩の溶融塩床をナトリウム含有遷移金属酸化物に加える方法が挙げられる。他にも、これら少なくとも一種のリチウム塩を含む溶液中にナトリウム含有遷移金属酸化物を浸漬する方法が挙げられる。 Examples of the method for ion-exchanging sodium to lithium include at least one selected from the group consisting of lithium nitrate, lithium sulfate, lithium chloride, lithium carbonate, lithium hydroxide, lithium iodide, lithium bromide, and lithium chloride. A method of adding a molten salt bed of lithium salt to a sodium-containing transition metal oxide is mentioned. In addition, a method of immersing a sodium-containing transition metal oxide in a solution containing at least one lithium salt can be given.
　上記導電剤は、正極活物質層の電気伝導性を高めるために用いられる。導電剤には、カーボンブラック、アセチレンブラック、ケッチェンブラック、黒鉛等の炭素材料が挙げられる。これらを単独で用いてもよく、２種類以上を組み合わせて用いてもよい。 The conductive agent is used to increase the electrical conductivity of the positive electrode active material layer. Examples of the conductive agent include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more.
　上記結着剤は、正極活物質及び導電剤間の良好な接触状態を維持し、かつ正極集電体表面に対する正極活物質等の結着性を高めるために用いられる。結着剤には、例えば、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶｄＦ）、又はこれらの変性体等が用いられる。結着剤は、カルボキシメチルセルロース（ＣＭＣ）、ポリエチレンオキシド（ＰＥＯ）等の増粘剤と併用されてもよい。 The above binder is used for maintaining a good contact state between the positive electrode active material and the conductive agent and enhancing the binding property of the positive electrode active material and the like to the surface of the positive electrode current collector. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or a modified product thereof is used. The binder may be used in combination with a thickener such as carboxymethyl cellulose (CMC) or polyethylene oxide (PEO).
　上記構成を備えた正極の満充電状態での正極電位は、４.０Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以上の高電位とすることができる。正極の充電終止電位は、高容量化の観点から、４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以上が好ましく、４．５５Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以上がより好ましい。正極の充電終止電位の上限は、特に限定されないが、非水電解質の分解抑制等の観点から、５．０Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）以下が好ましい。 The positive electrode potential in a fully charged state of the positive electrode having the above structure can be set to a high potential of 4.0 V (vs. Li / Li + ) or higher. End-of-charge potential of the positive electrode, in view of high capacity, preferably 4.5V (vs.Li/Li +) or more, 4.55V (vs.Li/Li +) or more preferred. The upper limit of the charge termination potential of the positive electrode is not particularly limited, but is preferably 5.0 V (vs. Li / Li + ) or less from the viewpoint of suppressing decomposition of the nonaqueous electrolyte.
　〔負極〕
　負極は、例えば、金属箔等の負極集電体と、負極集電体上に形成された負極活物質層とを備える。負極集電体には、銅などの負極の電位範囲で安定な金属の箔、銅などの負極の電位範囲で安定な金属を表層に配置したフィルム等を用いることができる。負極活物質層は、リチウムイオンを吸蔵・脱離可能な負極活物質の他に、結着剤を含むことが好適である。結着剤としては、正極の場合と同様にＰＴＦＥ等を用いることもできるが、スチレン－ブタジエン共重合体（ＳＢＲ）又はこの変性体等を用いることが好ましい。結着剤は、ＣＭＣ等の増粘剤と併用されてもよい。 [Negative electrode]
The negative electrode includes, for example, a negative electrode current collector such as a metal foil, and a negative electrode active material layer formed on the negative electrode current collector. As the negative electrode current collector, a metal foil that is stable in the potential range of the negative electrode such as copper, a film in which a metal that is stable in the potential range of the negative electrode such as copper is arranged on the surface layer, or the like can be used. The negative electrode active material layer preferably contains a binder in addition to the negative electrode active material capable of inserting and extracting lithium ions. As the binder, PTFE or the like can be used as in the case of the positive electrode, but it is preferable to use a styrene-butadiene copolymer (SBR) or a modified product thereof. The binder may be used in combination with a thickener such as CMC.
　上記負極活物質には、天然黒鉛、人造黒鉛、リチウム、珪素、炭素、錫、ゲルマニウム、アルミニウム、鉛、インジウム、ガリウム、リチウム合金、予めリチウムを吸蔵させた炭素並びに珪素、及びこれらの合金並びに混合物等を用いることができる。 Examples of the negative electrode active material include natural graphite, artificial graphite, lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, lithium alloy, carbon and silicon in which lithium is previously occluded, and alloys and mixtures thereof. Etc. can be used.
　〔非水電解質〕
　非水電解質は、非水溶媒と、非水溶媒に溶解した電解質塩とを含む。非水電解質は、液体電解質（非水電解液）に限定されず、ゲル状ポリマー等を用いた固体電解質であってもよい。 [Non-aqueous electrolyte]
The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolyte solution), and may be a solid electrolyte using a gel polymer or the like.
　上記非水溶媒は、フッ素化環状炭酸エステルと、特定の鎖状炭酸エステルとを後述の配合比で含有する。上記リチウム含有遷移金属酸化物を正極活物質として用いる場合に、当該非水溶媒を適用することにより、正極上にも良好な保護被膜が形成され、リチウム含有遷移金属酸化物から多くのリチウム（例えば、略１００％）を引き抜いた状態でも結晶構造が安定する。即ち、当該非水溶媒の適用により、本非水電解質二次電池のサイクル特性が向上する。 The non-aqueous solvent contains a fluorinated cyclic carbonate and a specific chain carbonate in a blending ratio described later. When the lithium-containing transition metal oxide is used as a positive electrode active material, by applying the non-aqueous solvent, a good protective film is formed on the positive electrode. , Approximately 100%), the crystal structure is stable. That is, application of the non-aqueous solvent improves the cycle characteristics of the non-aqueous electrolyte secondary battery.
　上記フッ素化環状炭酸エステルは、カーボネート環にフッ素原子が直接結合したフッ素化環状炭酸エステルであることが好ましい。 The fluorinated cyclic carbonate is preferably a fluorinated cyclic carbonate having a fluorine atom directly bonded to the carbonate ring.
　上記フルオロエチレンカーボネートの例としては、４－フルオロエチレンカーボネート、４，５－ジフルオロエチレンカーボネート、４，４－ジフルオロエチレンカーボネート、４，４，５－トリフルオロエチレンカーボネート、４，４，５，５－テトラフルオロエチレンカーボネートが挙げられる。これらのうち、保存特性、サイクル特性の両立等の観点から、比較的粘度が低いモノフルオロエチレンカーボネート、ジフルオロエチレンカーボネートが好ましく、中でも４－フルオロエチレンカーボネート、４，５－ジフルオロエチレンカーボネートが特に好ましい。４－フルオロエチレンカーボネート等を用いることにより、負極はもとより正極においても良好な保護被膜が形成されてサイクル特性等が向上するものと想定される。 Examples of the fluoroethylene carbonate include 4-fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, 4,4,5,5- Tetrafluoroethylene carbonate is mentioned. Of these, monofluoroethylene carbonate and difluoroethylene carbonate having a relatively low viscosity are preferable from the viewpoint of achieving both storage characteristics and cycle characteristics, among which 4-fluoroethylene carbonate and 4,5-difluoroethylene carbonate are particularly preferable. By using 4-fluoroethylene carbonate or the like, it is assumed that a good protective film is formed not only on the negative electrode but also on the positive electrode, thereby improving cycle characteristics and the like.
　上記フッ素化環状炭酸エステルの含有量は、サイクル特性向上の観点から、非水電解質における非水溶媒の総体積に対して７体積％以上７０体積％以下が好ましく、２５体積％以上７０体積％以下がより好ましく、５０体積％以上７０体積％以下が特に好ましい。なお、サイクル特性に加えて、保存特性、負荷特性等の種々の特性、また製造コストを含めた電池設計の最適化の観点からは、例えば、７体積％以上５０体積％以下、又は７体積％以上２５体積％以下が好適な場合がある。 The content of the fluorinated cyclic carbonate is preferably 7% by volume or more and 70% by volume or less, and 25% by volume or more and 70% by volume or less based on the total volume of the nonaqueous solvent in the nonaqueous electrolyte from the viewpoint of improving cycle characteristics. Is more preferable, and 50 volume% or more and 70 volume% or less are especially preferable. In addition to cycle characteristics, various characteristics such as storage characteristics and load characteristics, and from the viewpoint of optimization of battery design including manufacturing costs, for example, 7% by volume to 50% by volume, or 7% by volume. More than 25 volume% may be suitable.
　上記特定の鎖状炭酸エステルは、メチルエチルカーボネート（以下、ＭＥＣとする）及びジエチルカーボネート（以下、ＤＥＣとする）である。上記非水溶媒は、鎖状炭酸エステルとして、ＭＥＣ及びＤＥＣの少なくとも一方を含む。ＭＥＣ及びＤＥＣは、非水溶媒の総体積に対して３０～９０体積％の範囲で併用されてもよいが、サイクル特性向上の観点からは、ＭＥＣよりもＤＥＣの割合が多い方が好ましく、鎖状炭酸エステルとしてＤＥＣのみを用いることがより好ましい。 The specific chain carbonates are methyl ethyl carbonate (hereinafter referred to as MEC) and diethyl carbonate (hereinafter referred to as DEC). The non-aqueous solvent contains at least one of MEC and DEC as a chain carbonate. MEC and DEC may be used in a range of 30 to 90% by volume with respect to the total volume of the nonaqueous solvent. However, from the viewpoint of improving cycle characteristics, it is preferable that the ratio of DEC is higher than that of MEC. More preferably, only DEC is used as the carbonic acid ester.
　上記特定の鎖状炭酸エステルの含有量は、サイクル特性向上の観点から、非水電解質における非水溶媒の総体積に対して３０～９３体積％が好ましく、３０体積％以上７５体積％以下がより好ましく、３０体積％以上５０体積％以下が特に好ましい。なお、サイクル特性に加えて、保存特性、負荷特性等の種々の特性、また製造コストを含めた電池設計の最適化の観点からは、例えば、５０体積％以上９３体積％以下、又は７５体積％以上９３体積％以下が好適な場合がある。 The content of the specific chain carbonate is preferably from 30 to 93% by volume, more preferably from 30% to 75% by volume, based on the total volume of the nonaqueous solvent in the nonaqueous electrolyte, from the viewpoint of improving cycle characteristics. It is preferably 30% by volume or more and 50% by volume or less. In addition to cycle characteristics, various characteristics such as storage characteristics and load characteristics, and from the viewpoint of optimization of battery design including manufacturing cost, for example, 50 volume% or more and 93 volume% or less, or 75 volume% More than 93 volume% may be suitable.
　なお、上記非水溶媒は、２，２，２－トリフルオロエチルメチルカーボネートや３，３，３－トリフルオロプロピオン酸メチル等のフッ素化鎖状エステルを含まないことが好適である。フッ素化鎖状エステルは、上記フッ素化環状炭酸エステルよりも高価で、かつ量産性に劣ることから、これを用いることなくサイクル特性を向上させることは有用である。ここで、「フッ素化鎖状エステルを含まない」とは、実質的にフッ素化鎖状エステルを含まないことを意味する。具体的には、フッ素化鎖状エステルを非水電解質における非水溶媒の総体積に対して０．５体積％以上含まないことを意味する。 The non-aqueous solvent preferably does not contain a fluorinated chain ester such as 2,2,2-trifluoroethyl methyl carbonate or methyl 3,3,3-trifluoropropionate. Since the fluorinated chain ester is more expensive than the fluorinated cyclic carbonate and is inferior in mass productivity, it is useful to improve the cycle characteristics without using it. Here, “not containing a fluorinated chain ester” means substantially not containing a fluorinated chain ester. Specifically, it means that 0.5% by volume or more of the fluorinated chain ester is not contained with respect to the total volume of the nonaqueous solvent in the nonaqueous electrolyte.
　上記非水溶媒は、上記フッ素化環状炭酸エステル及び上記特定の鎖状炭酸エステル以外にも、非水溶媒として一般的に用いられている非フッ素系溶媒を併用することも可能である。具体的には、環状炭酸エステル、鎖状炭酸エステル（ＭＥＣ、ＤＥＣを除く）、カルボン酸エステル類、環状エーテル類、鎖状エーテル類、ニトリル類、アミド類、及びこれらの混合溶媒等が挙げられる。 As the non-aqueous solvent, in addition to the fluorinated cyclic carbonate and the specific chain carbonate, a non-fluorine solvent generally used as a non-aqueous solvent can be used in combination. Specific examples include cyclic carbonates, chain carbonates (excluding MEC and DEC), carboxylic acid esters, cyclic ethers, chain ethers, nitriles, amides, and mixed solvents thereof. .
　上記環状炭酸エステルの例としては、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート等が挙げられる。 Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate and the like.
　上記鎖状炭酸エステルの例としては、ジエチルカーボネート、メチルプロピルカーボネート、エチルプロピルカーボネート、メチルイソプロピルカーボネート等が挙げられる。 Examples of the chain carbonate include diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate and the like.
　上記カルボン酸エステル類の例としては、酢酸メチル、酢酸エチル、酢酸プロピル、プロピオン酸メチル、プロピオン酸エチル、γ－ブチロラクトン等が挙げられる。 Examples of the carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone.
　上記環状エーテル類の例としては、１，３－ジオキソラン、４－メチル－１，３－ジオキソラン、テトラヒドロフラン、２－メチルテトラヒドロフラン、プロピレンオキシド、１，２－ブチレンオキシド、１，３－ジオキサン、１，４－ジオキサン、１，３，５－トリオキサン、フラン、２－メチルフラン、１，８－シネオール、クラウンエーテル等が挙げられる。 Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1, 4-Dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineol, crown ether and the like can be mentioned.
　上記鎖状エーテル類の例としては、１，２－ジメトキシエタン、ジエチルエーテル、ジプロピルエーテル、ジイソプロピルエーテル、ジブチルエーテル、ジヘキシルエーテル、エチルビニルエーテル、ブチルビニルエーテル、メチルフェニルエーテル、エチルフェニルエーテル、ブチルフェニルエーテル、ペンチルフェニルエーテル、メトキシトルエン、ベンジルエチルエーテル、ジフェニルエーテル、ジベンジルエーテル、o－ジメトキシベンゼン、１，２－ジエトキシエタン、１，２－ジブトキシエタン、ジエチレングリコールジメチルエーテル、ジエチレングリコールジエチルエーテル、ジエチレングリコールジブチルエーテル、１，１－ジメトキシメタン、１，１－ジエトキシエタン、トリエチレングリコールジメチルエーテル、テトラエチレングリコールジメチル等が挙げられる。 Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether. , Pentylphenyl ether, methoxytoluene, benzylethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, Examples include traethylene glycol dimethyl.
　上記ニトリル類の例としては、アセトニトリル等、上記アミド類としては、ジメチルホルムアミド等が挙げられる。 Examples of the nitriles include acetonitrile, and examples of the amides include dimethylformamide.
　上記非フッ素系溶媒を併用する場合、環状炭酸エステル、鎖状エステル（ＭＥＣ、ＤＥＣを除く）の併用が好ましい。但し、サイクル特性向上の観点からは、非水溶媒として上記フッ素化環状炭酸エステル及び上記特定の鎖状炭酸エステル（ＭＥＣ及びＤＥＣの少なくとも一方）のみを用いることが好適である。即ち、サイクル特性を向上させるためには、非水電解質が上記フッ素化環状炭酸エステル及び上記特定の鎖状炭酸エステル以外の溶媒を含まないことが好適である。ここで、「上記フッ素化環状炭酸エステル及び上記フッ素化鎖状エステル以外の溶媒を含まない」とは、実質的にこれら以外の他の溶媒を含まないことを意味する。具体的には、他の溶媒を非水電解質における非水溶媒の総体積に対して０．５体積％以上含まないことを意味する。 When the non-fluorinated solvent is used in combination, a cyclic carbonate and a chain ester (excluding MEC and DEC) are preferably used. However, from the viewpoint of improving cycle characteristics, it is preferable to use only the fluorinated cyclic carbonate and the specific chain carbonate (at least one of MEC and DEC) as the non-aqueous solvent. That is, in order to improve cycle characteristics, it is preferable that the nonaqueous electrolyte does not contain a solvent other than the fluorinated cyclic carbonate and the specific chain carbonate. Here, “does not contain a solvent other than the fluorinated cyclic carbonate and the fluorinated chain ester” means that it contains substantially no other solvent. Specifically, it means that no other solvent is contained in an amount of 0.5% by volume or more based on the total volume of the nonaqueous solvent in the nonaqueous electrolyte.
　上記電解質塩は、リチウム塩であることが好ましい。リチウム塩には、従来の非水電解質二次電池において支持塩として一般に使用されているものを用いることができる。具体例としては、ＬｉＰＦ6、ＬｉＢＦ4、ＬｉＡｓＦ6、ＬｉＣｌＯ4、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＦＳＯ2）2、ＬｉＮ（Ｃ1Ｆ2l+1ＳＯ2）（ＣmＦ2m+1ＳＯ2）（ｌ，ｍは１以上の整数）、ＬｉＣ（ＣPＦ2p+1ＳＯ2）（ＣqＦ2q+1ＳＯ2）（ＣrＦ2r+1ＳＯ2）（p，q，rは１以上の整数）、Ｌｉ[Ｂ(Ｃ2Ｏ4)2]（ビス（オキサレート）ホウ酸リチウム(ＬｉＢＯＢ)）、Ｌｉ[Ｂ(Ｃ2Ｏ4)Ｆ2] 、Ｌｉ[Ｐ(Ｃ2Ｏ4)Ｆ4]、Ｌｉ[Ｐ(Ｃ2Ｏ4)2Ｆ2]等が挙げられる。これらのリチウム塩は、１種類で使用してもよく、また２種類以上組み合わせて使用してもよい。 The electrolyte salt is preferably a lithium salt. As the lithium salt, those generally used as a supporting salt in a conventional nonaqueous electrolyte secondary battery can be used. Specific examples include LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , LiN (FSO 2 ) 2 , LiN (C 1 F 2l + 1 SO 2 ) (C m F 2m + 1 SO 2 ). (l, m is an integer of 1 or more), LiC (C P F 2p + 1 SO 2) (C q F 2q + 1 SO 2) (C r F 2r + 1 SO 2) (p, q, r are 1 Integers above), Li [B (C 2 O 4 ) 2 ] (bis (oxalate) lithium borate (LiBOB)), Li [B (C 2 O 4 ) F 2 ], Li [P (C 2 O 4) ) F 4 ], Li [P (C 2 O 4 ) 2 F 2 ] and the like. These lithium salts may be used alone or in combination of two or more.
　〔セパレータ〕
　セパレータには、イオン透過性及び絶縁性を有する多孔性シートが用いられる。多孔性シートの具体例としては、微多孔薄膜、織布、不織布等が挙げられる。セパレータの材質としては、ポリエチレン、ポリプロピレン等のポリオレフィンが好適である。 [Separator]
As the separator, a porous sheet having ion permeability and insulating properties is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. As the material of the separator, polyolefin such as polyethylene and polypropylene is suitable.
　以下、実施例により本発明をさらに説明するが、本発明はこれらの実施例に限定されるものではない。 Hereinafter, the present invention will be further described with reference to examples, but the present invention is not limited to these examples.
　＜実施例１＞
　［正極の作製］
　Ｎａ0.8Ｃｏ8/9Ｍｎ1/9Ｏ2（仕込み組成）が得られるように、硝酸ナトリウム（ＮａＮＯ3）、酸化コバルト（II III）（Ｃｏ3Ｏ4）、及び酸化マンガン（III）（Ｍｎ2Ｏ3）を混合した。その後、当該混合物を９００℃で１０時間保持することによって、ナトリウム含有遷移金属酸化物を得た。 <Example 1>
[Production of positive electrode]
To obtain Na 0.8 Co 8/9 Mn 1/9 O 2 (prepared composition), sodium nitrate (NaNO 3 ), cobalt oxide (II III) (Co 3 O 4 ), and manganese (III) oxide (Mn 2 O 3 ) was mixed. Then, the said mixture was hold | maintained at 900 degreeC for 10 hours, and the sodium containing transition metal oxide was obtained.
　硝酸リチウム（ＬｉＮＯ3）と水酸化リチウム（ＬｉＯＨ）をｍｏｌ％で６１：３９の割合になるように混合した溶融塩床を、得られたナトリウム含有遷移金属酸化物５ｇに対し５倍当量（２５ｇ）加えた。その後、当該混合物を２００℃で１０時間保持させることによって、ナトリウム含有遷移金属酸化物のナトリウムの一部をリチウムにイオン交換した。さらに、イオン交換後の物質を水洗して、リチウム含有遷移金属酸化物を得た。 A molten salt bed in which lithium nitrate (LiNO 3 ) and lithium hydroxide (LiOH) were mixed at a molar ratio of 61:39 was equivalent to 5 times equivalent (5 g) to 5 g of the obtained sodium-containing transition metal oxide. )added. Then, a part of sodium of the sodium-containing transition metal oxide was ion-exchanged into lithium by holding the mixture at 200 ° C. for 10 hours. Further, the ion-exchanged material was washed with water to obtain a lithium-containing transition metal oxide.
　得られたリチウム含有遷移金属酸化物について、粉末Ｘ線回折法（リガク社製、粉末ＸＲＤ測定装置ＲＩＮＴ２２００（線源Ｃｕ－Ｋα）を使用。以下同様。）により解析し、結晶構造の同定を行った。得られた結晶構造は、空間群Ｐ６3ｍｃのＯ２構造と帰属された。また、このリチウム含有遷移金属酸化物の組成を、ＩＣＰ発光分析（Ｔｈｅｒｍｏ　Ｆｉｓｈｅｒ　Ｓｃｉｅｎｔｉｆｉｃ社製、ＩＣＰ発光分光分析装置ｉＣＡＰ６３００を使用。以下同様。）により算出した結果、Ｌｉ0.84Ｎａ0.028Ｃｏ0.89Ｍｎ0.11Ｏ2であった。 The obtained lithium-containing transition metal oxide was analyzed by a powder X-ray diffraction method (manufactured by Rigaku Corporation, using a powder XRD measuring device RINT2200 (radiation source Cu-Kα); the same applies hereinafter) to identify the crystal structure. It was. The obtained crystal structure was assigned to the O2 structure of the space group P6 3 mc. The composition of the lithium-containing transition metal oxide was calculated by ICP emission analysis (Thermo Fisher Scientific, using ICP emission spectroscopic analyzer iCAP6300. The same applies hereinafter). As a result, Li 0.84 Na 0.028 Co 0.89 Mn 0.11 O 2
　得られたリチウム含有遷移金属酸化物を正極活物質とし、正極活物質が９５質量％、導電剤としてアセチレンブラックが２．５質量％、結着剤としてポリフッ化ビニリデンが２．５質量％となるように混合し、Ｎ－メチル－２－ピロリドンを用いてスラリー化した。その後、正極集電体であるアルミニウム箔集電体上に当該スラリーを塗布し、１１０℃で真空乾燥して正極を作製した。 The obtained lithium-containing transition metal oxide is used as a positive electrode active material, the positive electrode active material is 95% by mass, the conductive agent is 2.5% by mass of acetylene black, and the binder is 2.5% by mass of polyvinylidene fluoride. And slurried with N-methyl-2-pyrrolidone. Thereafter, the slurry was applied onto an aluminum foil current collector, which was a positive electrode current collector, and vacuum dried at 110 ° C. to produce a positive electrode.
　［負極の作製］
　人造黒鉛を負極活物質とし、負極活物質が９８質量％、増粘剤としてカルボキシメチルセルロースのナトリウム塩が１質量％、結着剤としてスチレンーブタジエン共重合体が１質量％となるように混合し、水を用いてスラリー化した。その後、負極集電体である銅箔集電体上に当該スラリーを塗布し、１２０℃で真空乾燥して負極を作製した。 [Production of negative electrode]
Artificial graphite is used as a negative electrode active material, and mixed so that the negative electrode active material is 98% by mass, the sodium salt of carboxymethyl cellulose is 1% by mass as a thickener, and the styrene-butadiene copolymer is 1% by mass as a binder. And slurried with water. Thereafter, the slurry was applied on a copper foil current collector as a negative electrode current collector, and vacuum dried at 120 ° C. to prepare a negative electrode.
　［非水電解質の作製］
　フッ素化環状炭酸エステルとして４－フルオロエチレンカーボネート（以下、ＦＥＣとする）と、ＭＥＣとを体積比で２５：７５の割合になるように混合して非水溶媒を得た。当該非水溶媒に、電解質塩として六フッ化リン酸リチウム（以下、ＬｉＰＦ6とする）を１．０ｍｏｌ／ｌの濃度になるように溶解させて非水電解質を作製した。 [Production of non-aqueous electrolyte]
4-Fluoroethylene carbonate (hereinafter referred to as FEC) as a fluorinated cyclic carbonate and MEC were mixed at a volume ratio of 25:75 to obtain a nonaqueous solvent. A nonaqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (hereinafter referred to as LiPF 6 ) as an electrolyte salt in the nonaqueous solvent so as to have a concentration of 1.0 mol / l.
　作製された正極及び負極を、ポリエチレン製のセパレータを介して対向するように巻回して電極体を作製し、ドライボックス中にて、電極体を非水電解質とともにラミネート外装体に封入した。こうして、定格容量９００ｍＡｈで３６３５６２形角形の非水電解質二次電池である試験セルＡ１を作製した。 The produced positive electrode and negative electrode were wound so as to face each other through a polyethylene separator, and an electrode body was produced. The electrode body was enclosed in a laminate outer package together with a nonaqueous electrolyte in a dry box. Thus, a test cell A1 which is a 363562-type square nonaqueous electrolyte secondary battery with a rated capacity of 900 mAh was produced.
　＜実施例２＞
　Ｎａ0.8Ｃｏ8/9Ｍｎ2/27Ｔｉ1/27Ｏ2（仕込み組成）が得られるように、硝酸ナトリウム（ＮａＮＯ3）、酸化コバルト（II III）（Ｃｏ3Ｏ4）、酸化マンガン（III）（Ｍｎ2Ｏ3）、及び二酸化チタン（ＴｉＯ2）を混合した。その後、９００℃で１０時間保持することによって、ナトリウム含有遷移金属酸化物を得た。 <Example 2>
In order to obtain Na 0.8 Co 8/9 Mn 2/27 Ti 1/27 O 2 (prepared composition), sodium nitrate (NaNO 3 ), cobalt oxide (II III) (Co 3 O 4 ), manganese oxide (III ) (Mn 2 O 3 ) and titanium dioxide (TiO 2 ). Then, the sodium containing transition metal oxide was obtained by hold | maintaining at 900 degreeC for 10 hours.
　硝酸リチウム（ＬｉＮＯ3）と水酸化リチウム（ＬｉＯＨ）をｍｏｌ％で６１：３９の割合になるように混合した溶融塩床を、得られたナトリウム含有遷移金属酸化物５ｇに対し５倍当量（２５ｇ）加えた。その後、当該混合物を２００℃で１０時間保持させることによって、ナトリウム含有遷移金属酸化物のナトリウムの一部をリチウムにイオン交換した。さらに、イオン交換後の物質を水洗して、リチウム含有遷移金属酸化物を得た。 A molten salt bed in which lithium nitrate (LiNO 3 ) and lithium hydroxide (LiOH) were mixed at a molar ratio of 61:39 was equivalent to 5 times equivalent (5 g) to 5 g of the obtained sodium-containing transition metal oxide. )added. Then, a part of sodium of the sodium-containing transition metal oxide was ion-exchanged into lithium by holding the mixture at 200 ° C. for 10 hours. Further, the ion-exchanged material was washed with water to obtain a lithium-containing transition metal oxide.
　得られたリチウム含有遷移金属酸化物について、粉末Ｘ線回折法により解析し、結晶構造の同定を行った。得られた結晶構造は、空間群Ｐ６3ｍｃのＯ２構造と帰属された。また、このリチウム含有遷移金属酸化物の組成を、ＩＣＰ発光分析により算出した結果、Ｌｉ0.86Ｎａ0.022Ｃｏ0.89Ｍｎ0.07Ｔｉ0.04Ｏ2であった。このようにして得られたリチウム含有遷移金属酸化物を正極活物質に用いた以外は、実施例１と同様にして試験セルＡ２を作製した。 The obtained lithium-containing transition metal oxide was analyzed by a powder X-ray diffraction method, and the crystal structure was identified. The obtained crystal structure was assigned to the O2 structure of the space group P6 3 mc. Further, the composition of the lithium-containing transition metal oxides, the result calculated by ICP emission analysis was Li 0.86 Na 0.022 Co 0.89 Mn 0.07 Ti 0.04 O 2. Test cell A2 was produced in the same manner as in Example 1 except that the lithium-containing transition metal oxide thus obtained was used as the positive electrode active material.
　＜実施例３＞
　非水電解質の非水溶媒として、４，５－ジフルオロエチレンカーボネート（以下、ＤＦＥＣとする）とＭＥＣとを体積比で２５：７５の割合になるように混合した非水溶媒を用いた以外は、実施例２と同様にして試験セルＡ３を作製した。 <Example 3>
As the nonaqueous solvent for the nonaqueous electrolyte, a nonaqueous solvent in which 4,5-difluoroethylene carbonate (hereinafter referred to as DFEC) and MEC were mixed at a volume ratio of 25:75 was used. Test cell A3 was produced in the same manner as in Example 2.
　＜実施例４＞
　非水電解質の非水溶媒として、ＦＥＣとＤＥＣとを体積比で２５：７５の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＡ４を作製した。 <Example 4>
A test cell A4 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and DEC were mixed at a volume ratio of 25:75 was used as a nonaqueous solvent for the nonaqueous electrolyte. .
　＜実施例５＞
　非水電解質の非水溶媒として、ＦＥＣとＭＥＣとを体積比で１０：９０の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＡ５を作製した。 <Example 5>
A test cell A5 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 10:90 was used as the nonaqueous electrolyte nonaqueous solvent. .
　＜実施例６＞
　非水電解質の非水溶媒として、ＦＥＣとＭＥＣとを体積比で５０：５０の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＡ６を作製した。 <Example 6>
Test cell A6 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 50:50 was used as the nonaqueous solvent for the nonaqueous electrolyte. .
　＜実施例７＞
　非水電解質の非水溶媒として、ＦＥＣとＭＥＣとを体積比で７０：３０の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＡ７を作製した。 <Example 7>
Test cell A7 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 70:30 was used as the nonaqueous solvent for the nonaqueous electrolyte. .
　＜実施例８＞
　非水電解質の非水溶媒として、ＤＦＥＣとＭＥＣとを体積比で５０：５０の割合になるように混合した非水溶媒を用いた以外は、実施例２と同様にして試験セルＡ８を作製した。 <Example 8>
A test cell A8 was produced in the same manner as in Example 2 except that a nonaqueous solvent in which DFEC and MEC were mixed at a volume ratio of 50:50 was used as a nonaqueous electrolyte nonaqueous electrolyte. .
　＜実施例９＞
　非水電解質の非水溶媒として、ＦＥＣとＭＥＣとを体積比で７：９３の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＡ９を作製した。 <Example 9>
Test cell A9 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 7:93 was used as a nonaqueous electrolyte nonaqueous electrolyte. .
　＜比較例１＞
　仕込み組成がＬｉＣｏＯ2となるように、炭酸リチウム（Ｌｉ2ＣＯ3）、及び酸化コバルト（II，III）（Ｃｏ3Ｏ4）を混合した。その後、当該混合物を９００℃で１０時間保持することによってリチウム含有遷移金属酸化物を得た。このリチウム含有遷移金属酸化物を正極活物質に用いた以外は、実施例１と同様にして試験セルＸ１を作製した。 <Comparative Example 1>
Lithium carbonate (Li 2 CO 3 ) and cobalt oxide (II, III) (Co 3 O 4 ) were mixed so that the charged composition was LiCoO 2 . Then, the lithium containing transition metal oxide was obtained by hold | maintaining the said mixture at 900 degreeC for 10 hours. Test cell X1 was produced in the same manner as in Example 1 except that this lithium-containing transition metal oxide was used as the positive electrode active material.
　なお、粉末Ｘ線回折法により得られたリチウム含有遷移金属酸化物の結晶構造を同定した結果、結晶構造は、空間群Ｒ－３ｍのＯ３構造と帰属された。また、このリチウム含有遷移金属酸化物の組成を、ＩＣＰ発光分析により算出した結果、Ｌｉ1.01ＣｏＯ2であった。 As a result of identifying the crystal structure of the lithium-containing transition metal oxide obtained by the powder X-ray diffraction method, the crystal structure was assigned to the O3 structure of the space group R-3m. The composition of the lithium-containing transition metal oxide was calculated by ICP emission analysis, and was Li 1.01 CoO 2 .
　＜比較例２＞
　非水電解質の非水溶媒として、エチレンカーボネート（以下、ＥＣとする）とＭＥＣとを体積比で２５：７５の割合になるように混合した非水溶媒を用いた以外は、比較例１と同様にして試験セルＸ２を作製した。 <Comparative Example 2>
The same as Comparative Example 1 except that a nonaqueous solvent in which ethylene carbonate (hereinafter referred to as EC) and MEC were mixed at a volume ratio of 25:75 was used as the nonaqueous solvent for the nonaqueous electrolyte. Thus, a test cell X2 was produced.
　＜比較例３＞
　非水電解質の非水溶媒として、ＥＣとＭＥＣとを体積比で２５：７５の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＸ３を作製した。 <Comparative Example 3>
A test cell X3 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which EC and MEC were mixed at a volume ratio of 25:75 was used as the nonaqueous electrolyte nonaqueous solvent. .
　＜比較例４＞
　非水電解質の非水溶媒として、ＦＥＣとＭＥＣとを体積比で５：９５の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＸ４を作製した。 <Comparative example 4>
A test cell X4 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 5:95 was used as a nonaqueous solvent for the nonaqueous electrolyte. .
　＜比較例５＞
　非水電解質の非水溶媒として、ＦＥＣとＭＥＣとを体積比で９０：１０の割合になるように混合した非水溶媒を用いた以外は、実施例１と同様にして試験セルＸ５を作製した。 <Comparative Example 5>
Test cell X5 was produced in the same manner as in Example 1 except that a nonaqueous solvent in which FEC and MEC were mixed at a volume ratio of 90:10 was used as the nonaqueous solvent for the nonaqueous electrolyte. .
　表１に、実施例１～９、比較例１～５における正極活物質の組成・結晶構造（空間群）、及び非水電解質の組成をまとめたものを示す。 Table 1 shows a summary of the composition and crystal structure (space group) of the positive electrode active material and the composition of the nonaqueous electrolyte in Examples 1 to 9 and Comparative Examples 1 to 5.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　[サイクル特性の評価]
　作製した非水電解質二次電池を、４５０ｍＡの定電流で、電池電圧が４．４５Ｖに達するまで充電し、さらに、４．４５Ｖの定電圧で電流値が１８ｍＡになるまで充電した後、４５０ｍＡの定電流で、電池電圧が３．０Ｖに達するまで放電することにより、電池の充放電容量(ｍＡｈ)を測定した。なお、電池電圧４．４５Ｖは、正極電位４．５５Ｖ（ｖｓ．Ｌｉ／Ｌｉ+）に相当する。その後、上記充放電を繰り返し行い、充放電を繰り返すサイクル特性として、１５，３０，５０サイクル後の放電容量を、１サイクル目の放電容量で除した値に１００をかけて、容量維持率を評価した。 [Evaluation of cycle characteristics]
The produced non-aqueous electrolyte secondary battery was charged at a constant current of 450 mA until the battery voltage reached 4.45 V, and further charged at a constant voltage of 4.45 V until the current value reached 18 mA. By discharging at a constant current until the battery voltage reached 3.0V, the charge / discharge capacity (mAh) of the battery was measured. A battery voltage of 4.45 V corresponds to a positive electrode potential of 4.55 V (vs. Li / Li + ). Thereafter, the above charge / discharge is repeated, and the charge retention is repeated, and the capacity retention rate is evaluated by multiplying the value obtained by dividing the discharge capacity after 15, 30, 50 cycles by the discharge capacity at the first cycle by 100. did.
　表２に、実施例１～９の試験セルＡ１～Ａ９、比較例１～５の試験セルＸ１～Ｘ５について、１５，３０，５０サイクル後の容量維持率を示す。 Table 2 shows capacity retention rates after 15, 30, and 50 cycles for test cells A1 to A9 of Examples 1 to 9 and test cells X1 to X5 of Comparative Examples 1 to 5.
Figure JPOXMLDOC01-appb-T000002
 ※電池の放電容量維持率が５０％以下、もしくは放電容量が５００ｍＡｈ未満となったセル及び充放電不可となったセルは試験中止とした。
※比較例５において充放電できなかったのは、フッ素化環状炭酸エステルの組成を高くしために電解液の粘度が高くなりすぎたためと考えられる。
Figure JPOXMLDOC01-appb-T000002
 * Tests were discontinued for cells with a discharge capacity maintenance rate of 50% or less, or cells with a discharge capacity of less than 500 mAh and cells with no charge / discharge capability.
* The reason why charging / discharging was not possible in Comparative Example 5 is considered to be because the viscosity of the electrolyte solution was too high due to the high composition of the fluorinated cyclic carbonate.
　表２より、実施例の試験セルＡ１～Ａ８は、比較例の試験セルＸ１～Ｘ５と比べて、いずれも優れたサイクル特性を示すことがわかる。即ち、空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物を正極活物質とし、所定の体積比で混合したフッ素化環状炭酸エステル（ＦＥＣ、ＤＦＥＣ）及び特定の鎖状炭酸エステル（ＭＥＣ、ＤＥＣ）を含む非水溶媒を非水電解質に適用することで、充放電に伴う非水電解質の分解による容量減少が抑制されて良好なサイクル特性が得られたと考えられる。この効果は、正極活物質として空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物を用いた場合であっても、非水電解質にフッ素化環状炭酸エステルが含まれない場合には発現しない（比較例３，６参照）。 From Table 2, it can be seen that the test cells A1 to A8 of the example all show excellent cycle characteristics as compared with the test cells X1 to X5 of the comparative example. That is, a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc is used as a positive electrode active material, and mixed in a predetermined volume ratio with a fluorinated cyclic carbonate (FEC, DFEC) and a specific chain carbonate (MEC). , DEC) is applied to the non-aqueous electrolyte, it is considered that capacity reduction due to decomposition of the non-aqueous electrolyte accompanying charge / discharge is suppressed, and good cycle characteristics are obtained. This effect is manifested when the non-aqueous electrolyte does not contain a fluorinated cyclic carbonate even when a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc is used as the positive electrode active material. No (see Comparative Examples 3 and 6).
　比較例１，２の試験セルＸ１，Ｘ２では、空間群Ｒ－３ｍに属する結晶構造のコバルト酸リチウムを正極活物質とし、所定の体積比で混合したフッ素化環状炭酸エステル及び特定の鎖状炭酸エステルを含む非水溶媒を非水電解質に適用したが、良好なサイクル特性は得られなかった。即ち、現在実用化されている空間群Ｒ－３ｍに属する結晶構造のコバルト酸リチウムについて、フッ素化環状炭酸エステル及び特定の鎖状炭酸エステルを含む非水溶媒はサイクル特性の向上効果を示さなかった。 In test cells X1 and X2 of Comparative Examples 1 and 2, a fluorinated cyclic carbonate and a specific chain carbonate mixed with a predetermined volume ratio of lithium cobaltate having a crystal structure belonging to space group R-3m as a positive electrode active material. A non-aqueous solvent containing an ester was applied to the non-aqueous electrolyte, but good cycle characteristics were not obtained. That is, with respect to lithium cobaltate having a crystal structure belonging to the space group R-3m that is currently in practical use, the non-aqueous solvent containing a fluorinated cyclic carbonate and a specific chain carbonate did not show an effect of improving cycle characteristics. .
　これに対して、空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物を正極活物質とする実施例の試験セルＡ１～Ａ９では、所定の体積比で混合したフッ素化環状炭酸エステル及び特定の鎖状炭酸エステルを含む非水溶媒を適用することで良好なサイクル特性が得られた。即ち、現在実用化されている正極活物質では全く効果のない当該非水溶媒は、正極活物質が空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物である場合にサイクル特性を大きく向上させる。本構造を持つ正極活物質を用いた試験セルＡ１～Ａ９の場合は、充放電に伴い活物質がへき開しやすく、新たに生じた活物質表面にリチウムの挿入及び脱離を円滑にする被膜が形成されたためと考えられるが、評価結果は想定を超える極めて良好なものであった。 On the other hand, in the test cells A1 to A9 in which the lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc is used as the positive electrode active material, the fluorinated cyclic carbonate mixed at a predetermined volume ratio and Good cycle characteristics were obtained by applying a non-aqueous solvent containing a specific chain carbonate. That is, the non-aqueous solvent which has no effect on the positive electrode active material currently in practical use has a large cycle characteristic when the positive electrode active material is a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc. Improve. In the case of the test cells A1 to A9 using the positive electrode active material having this structure, the active material is easily cleaved with charge and discharge, and a coating that smoothly inserts and desorbs lithium on the newly generated active material surface is provided. Although it is thought that it was formed, the evaluation result was extremely good than expected.
　一方、従来の正極活物質を用いた比較例の試験セルＸ１ないしＸ２の場合は上記の効果が表れず、また空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物を用いた場合においても、フッ素化環状炭酸エステルを適量使用しなかった試験セルＸ３～Ｘ５の場合では、上記のサイクル特性の向上効果が表れなかったと想定される。 On the other hand, in the case of the test cells X1 and X2 of the comparative example using the conventional positive electrode active material, the above effect does not appear, and in the case of using a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc However, in the case of test cells X3 to X5 in which an appropriate amount of the fluorinated cyclic carbonate was not used, it is assumed that the effect of improving the cycle characteristics was not exhibited.
　実施例の顕著な効果は、非水溶媒の総体積に対してフッ素化環状炭酸エステルが７体積％以上７０体積％以下、特定の鎖状炭酸エステルであるＭＥＣ及びＤＥＣの少なくとも一方が３０体積％以上９３体積％以下である場合にのみ得られ、この範囲を逸脱する場合には得られない。具体的には、フッ素化環状炭酸エステルの割合が７０体積％を超えると、サイクル特性の低下が著しく、比較例５の試験セルＸ５のように低いサイクル数で充放電ができなくなる。また、フッ素化環状炭酸エステルの割合が７体積％を下回る場合も、比較例４の試験セルＸ４のように良好なサイクル特性は得られない。 The remarkable effects of the examples are that the fluorinated cyclic carbonate is 7% by volume or more and 70% by volume or less with respect to the total volume of the nonaqueous solvent, and at least one of the specific chain carbonates MEC and DEC is 30% by volume. It is obtained only when the content is 93% by volume or less, and cannot be obtained when the amount is outside this range. Specifically, when the ratio of the fluorinated cyclic carbonate exceeds 70% by volume, the cycle characteristics are remarkably deteriorated, and charge / discharge cannot be performed with a low number of cycles as in the test cell X5 of Comparative Example 5. In addition, when the ratio of the fluorinated cyclic carbonate is less than 7% by volume, good cycle characteristics cannot be obtained as in the test cell X4 of Comparative Example 4.
　なお、非水溶媒中のフッ素化環状炭酸エステルの割合を７体積％以上７０体積％以下の範囲において高くするほど、サイクル特性を向上させることができる。特に優れたサイクル特性を得るためには、フッ素化環状炭酸エステルの割合を５０体積％以上７０体積％以下に調整することが好適である。また、非水電解質中にフッ素化環状炭酸エステル及びＭＥＣ、ＤＥＣ以外の他の溶媒が実質的に含まれず、かつ両者の体積比が７：９３～７０：３０であることが好ましく、２５：７５～７０：３０であることがより好ましく、５０：５０～７０：３０であることが特に好ましい。 In addition, cycling characteristics can be improved, so that the ratio of the fluorinated cyclic carbonate in a non-aqueous solvent is made high in the range of 7 volume% or more and 70 volume% or less. In order to obtain particularly excellent cycle characteristics, it is preferable to adjust the ratio of the fluorinated cyclic carbonate to 50% by volume or more and 70% by volume or less. In addition, it is preferable that the non-aqueous electrolyte is substantially free of fluorinated cyclic carbonate and other solvents other than MEC and DEC, and the volume ratio of the two is 7:93 to 70:30, and 25:75 More preferably, it is ˜70: 30, and particularly preferably 50:50 to 70:30.
　さらに、フッ素化環状炭酸エステルとしては、フッ素の１置換体であるＦＥＣよりも２置換体であるＤＥＦＣの方がサイクル特性の向上に寄与する（実施例２，３参照）。特定の鎖状炭酸エステルとしては、ＭＥＣよりもＤＥＣの使用量を多くする、又はＤＥＣのみを使用することが好ましい。これにより、サイクル特性をさらに向上させることができる（実施例１，４参照）。 Furthermore, as a fluorinated cyclic ester carbonate, DEFC, which is a 2-substitution, contributes to improvement of cycle characteristics rather than FEC, which is a mono-substitution of fluorine (see Examples 2 and 3). As the specific chain carbonate, it is preferable to use a larger amount of DEC than MEC or to use only DEC. Thereby, cycle characteristics can be further improved (see Examples 1 and 4).
　正極活物質としては、遷移金属元素としてＣｏ、Ｍｎに加えて、Ｔｉを含有するリチウム含有遷移金属酸化物を用いることが好ましい。なお、Ｃｏ、Ｍｎ、Ｔｉの含有量は、Ｃｏ＞Ｍｎ＞Ｔｉとすることが好ましい。これにより、サイクル特性をさらに向上させることができる（実施例１，２参照）。Ｔｉの添加によるサイクル特性の向上効果は著しく、Ｌｉ0.84Ｎａ0.028Ｃｏ0.89Ｍｎ0.11Ｏ2を正極活物質として用いた試験セルＡ１（実施例１）の５０サイクル後の容量維持率が７９．９％であるのに対し、Ｌｉ0.86Ｎａ0.022Ｃｏ0.89Ｍｎ0.07Ｔｉ0.04Ｏ2を正極活物質として用いた試験セルＡ２（実施例２）の同容量維持率は９６．６％であった。 As the positive electrode active material, it is preferable to use a lithium-containing transition metal oxide containing Ti in addition to Co and Mn as transition metal elements. Note that the contents of Co, Mn, and Ti are preferably Co>Mn> Ti. Thereby, cycle characteristics can be further improved (see Examples 1 and 2). The effect of improving cycle characteristics due to the addition of Ti is remarkable, and the capacity retention ratio after 50 cycles of test cell A1 (Example 1) using Li 0.84 Na 0.028 Co 0.89 Mn 0.11 O 2 as the positive electrode active material is 79.9%. On the other hand, the same capacity retention rate of Test Cell A2 (Example 2) using Li 0.86 Na 0.022 Co 0.89 Mn 0.07 Ti 0.04 O 2 as the positive electrode active material was 96.6%.
　＜実施例１０＞
　実施例１で作製した正極を作用極、金属リチウムを対極及び参照極として、３電極式セルＢ１を作製した。そして、電流レート０．２Ｃの定電流で、正極電位が４．６Ｖに達するまで充電し、さらに４．６Ｖの定電位で電流値が１／２０Ｃになるまで充電した。その後、０．２Ｃの定電流で、正極電位が３．２Ｖに達するまで放電することにより、電池の充放電容量(ｍＡｈ)を測定した。この充放電を繰り返し、１０サイクル目の放電容量を充電容量で除した値に１００をかけて充放電効率を評価した。 <Example 10>
A three-electrode cell B1 was produced using the positive electrode produced in Example 1 as a working electrode and metal lithium as a counter electrode and a reference electrode. The battery was charged at a constant current rate of 0.2 C until the positive electrode potential reached 4.6 V, and further charged at a constant potential of 4.6 V until the current value reached 1/20 C. Then, the charge / discharge capacity (mAh) of the battery was measured by discharging until the positive electrode potential reached 3.2 V at a constant current of 0.2 C. This charge / discharge was repeated, and the charge / discharge efficiency was evaluated by multiplying the value obtained by dividing the discharge capacity at the 10th cycle by the charge capacity.
　＜比較例６＞
　非水電解質の非水溶媒として、ＥＣとＭＥＣとを体積比で２５：７５の割合になるように混合した非水溶媒を用いた以外は、実施例１０と同様にして試験セルＹ１を作製し、１０サイクル目の充放電効率を評価した。 <Comparative Example 6>
A test cell Y1 was prepared in the same manner as in Example 10 except that a nonaqueous solvent in which EC and MEC were mixed at a volume ratio of 25:75 was used as the nonaqueous electrolyte nonaqueous electrolyte. The charge / discharge efficiency at the 10th cycle was evaluated.
　表３に、実施例１０、比較例６における正極活物質の組成、非水電解質の組成、及び１０サイクル目の充放電効率をまとめたものを示す。 Table 3 shows a summary of the composition of the positive electrode active material, the composition of the nonaqueous electrolyte, and the charge / discharge efficiency at the 10th cycle in Example 10 and Comparative Example 6.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表３に示すように、実施例１０の試験セルＢ１は、比較例６の試験セルＹ１に比べて優れた充放電効率を示し、良好なサイクル特性を有すると考えられる。空間群Ｐ６3ｍｃに属する結晶構造のリチウム含有遷移金属酸化物を正極活物質とし、所定の体積比で混合したフッ素化環状炭酸エステル及び鎖状炭酸エステルを含む非水溶媒を非水電解質に適用することで、４．５５Ｖ、４．６Ｖといった高電位までの充電を伴う充放電サイクルが可能となる。 As shown in Table 3, the test cell B1 of Example 10 exhibits excellent charge / discharge efficiency as compared to the test cell Y1 of Comparative Example 6, and is considered to have good cycle characteristics. A lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc is used as a positive electrode active material, and a non-aqueous solvent containing a fluorinated cyclic carbonate and a chain carbonate mixed in a predetermined volume ratio is applied to a non-aqueous electrolyte. By doing so, a charge / discharge cycle involving charging to a high potential of 4.55V, 4.6V becomes possible.

Claims (9)

  1. 　正極活物質を含む正極と、負極と、非水溶媒を含む非水電解質とを備える非水電解質二次電池において、
    　前記正極活物質は、空間群Ｐ６3ｍｃに属する結晶構造を有するリチウム含有遷移金属酸化物を含み、
    　前記非水溶媒は、その総体積に対して７体積％以上７０体積％以下のフッ素化環状炭酸エステルと、鎖状炭酸エステルとして３０体積％以上９３体積％以下のメチルエチルカーボネート及びジエチルカーボネートの少なくとも一方とを含む非水電解質二次電池。     In a non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode, and a non-aqueous electrolyte including a non-aqueous solvent,
    The positive electrode active material includes a lithium-containing transition metal oxide having a crystal structure belonging to the space group P6 3 mc,
    The non-aqueous solvent comprises at least 7% by volume to 70% by volume of fluorinated cyclic carbonate and 30% by volume to 93% by volume of methyl ethyl carbonate and diethyl carbonate as a chain carbonate based on the total volume. And a non-aqueous electrolyte secondary battery.
  2. 　請求項１に記載の非水電解質二次電池において、
    　前記フッ素化環状炭酸エステルは、カーボネート環にフッ素原子が直接結合したフルオロエチレンカーボネートである非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to claim 1,
    The non-aqueous electrolyte secondary battery in which the fluorinated cyclic carbonate is fluoroethylene carbonate in which a fluorine atom is directly bonded to a carbonate ring.
  3. 　請求項２に記載の非水電解質二次電池において、
    　前記フルオロエチレンカーボネートは、４－フッ化エチレンカーボネート及び４、５－ジフルオロエチレンカーボネートの少なくとも一方である非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to claim 2,
    The non-aqueous electrolyte secondary battery, wherein the fluoroethylene carbonate is at least one of 4-fluorinated ethylene carbonate and 4,5-difluoroethylene carbonate.
  4. 　請求項１から３のいずれか１項に記載の非水電解質二次電池において、
    　前記リチウム含有遷移金属酸化物は、Ｌｉx1Ｎａy1Ｃｏα1Ｍβ1Ｏγ1（０．６６＜ｘ１＜１.１、０＜ｙ１≦０．０５、０．７５≦α１＜１、ＭはＭｎを含む1つ以上の金属元素、０≦β１≦０．２５、１．８≦γ１≦２．２）で表される非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3,
    The lithium-containing transition metal oxide is Li x1 Na y1 Coα 1 Mβ 1 Oγ 1 (0.66 <x1 <1.1, 0 <y1 ≦ 0.05, 0.75 ≦ α1 <1, M represents Mn 1 or more metal elements to be included, 0 ≦ β1 ≦ 0.25, 1.8 ≦ γ1 ≦ 2.2).
  5. 　請求項１から４のいずれか１項に記載の非水電解質二次電池において、
    　前記リチウム含有遷移金属酸化物は、Ｌｉx2Ｎａy2Ｃｏα2Ｍβ2Ｏγ2（０≦ｘ２≦０.１、０．６６＜ｙ２＜０．７５、ＭはＭｎを含む1つ以上の金属元素、０．７５≦α２＜１、 ０≦β２≦０．２５、１．９≦γ２≦２．１）で表されるナトリウム含有酸化物に含まれるナトリウムの一部をリチウムでイオン交換することによって得られる非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4,
    The lithium-containing transition metal oxide is Li x2 Na y2 Coα 2 Mβ 2 Oγ 2 (0 ≦ x2 ≦ 0.1, 0.66 <y2 <0.75, where M is one or more metal elements including Mn, 0.75 ≦ α2 <1, 0 ≦ β2 ≦ 0.25, 1.9 ≦ γ2 ≦ 2.1), obtained by ion exchange of a part of sodium contained in the sodium-containing oxide represented by lithium Non-aqueous electrolyte secondary battery.
  6. 　請求項４又は５に記載の非水電解質二次電池において、
    　前記リチウム含有遷移金属酸化物は、チタンを含有する非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to claim 4 or 5,
    The lithium-containing transition metal oxide is a non-aqueous electrolyte secondary battery containing titanium.
  7. 　請求項１から６のいずれか１項に記載の非水電解質二次電池において、
    　前記非水溶媒は、フッ素化鎖状エステルを含まない非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6,
    The non-aqueous solvent is a non-aqueous electrolyte secondary battery containing no fluorinated chain ester.
  8. 　請求項１から７のいずれか１項に記載の非水電解質二次電池において、
    　前記非水溶媒は、前記鎖状炭酸エステルとして前記ジエチルカーボネートのみを含む非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7,
    The non-aqueous solvent is a non-aqueous electrolyte secondary battery containing only the diethyl carbonate as the chain carbonate.
  9. 　請求項１から８のいずれか１項に記載の非水電解質二次電池において、
    　前記正極の充電終止電位は、４．５Ｖ以上５．０Ｖ以下（ｖｓ．Ｌｉ／Ｌｉ+）である非水電解質二次電池。     The nonaqueous electrolyte secondary battery according to any one of claims 1 to 8,
    The non-aqueous electrolyte secondary battery in which a charge end potential of the positive electrode is 4.5 V or more and 5.0 V or less (vs. Li / Li + ).
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