WO2012032700A1 - 二次電池用非水電解質および非水電解質二次電池 - Google Patents
二次電池用非水電解質および非水電解質二次電池 Download PDFInfo
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- H01M10/05—Accumulators with non-aqueous electrolyte
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- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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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- 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
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- 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
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- 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
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- 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
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- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- 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 for a secondary battery and a non-aqueous electrolyte secondary battery, and more particularly to an improvement in a non-aqueous electrolyte containing propylene carbonate (PC) and diethyl carbonate (DEC).
- PC propylene carbonate
- DEC diethyl carbonate
- a non-aqueous solvent solution of lithium salt is used as the non-aqueous electrolyte.
- the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC) and PC, and chain carbonates such as DEC. In general, a plurality of carbonates are often used in combination.
- Patent Document 1 EC and PC are mixed in an equal volume.
- a carbonate such as vinylene carbonate
- a non-aqueous solvent containing 40% by volume or more of PC is added to a non-aqueous solvent containing 40% by volume or more of PC.
- EC and PC are used in substantially equal volumes.
- Patent Document 3 discloses a non-aqueous electrolyte containing 10 to 60% by volume of PC, 1 to 20% by volume of EC and 30 to 85% by volume of linear carbonate such as DEC, and added with 1,3-propane sultone and vinylene carbonate. Yes.
- the non-aqueous electrolytes of Patent Documents 1 and 2 have a high viscosity because they contain a large amount of EC and do not contain or contain a small amount of DEC.
- the viscosity of the non-aqueous electrolyte is high, not only does the non-aqueous electrolyte not easily penetrate into the electrode plate, but also the ionic conductivity is lowered, so that the rate characteristics, particularly the rate characteristics at low temperatures, are likely to be lowered.
- EC is susceptible to oxidative decomposition and subsequent reductive decomposition, it generates many gases such as CO, CO 2 , methane, and ethane.
- the oxidative decomposition of EC is particularly remarkable when a lithium-containing transition metal oxide containing nickel is used as a positive electrode active material.
- Patent Documents 1 and 2 since the content of EC is large, if the battery is stored in a high temperature environment or is repeatedly charged / discharged, the amount of gas derived from EC becomes very large, and the charge / discharge capacity of the battery Decreases.
- PC is not easily decomposed.
- content of PC is increased by reducing the ratio of EC and DEC, the generation of gas accompanying reductive decomposition at the negative electrode cannot be ignored.
- the decomposition of PC at the negative electrode is suppressed to some extent by using an additive such as vinylene carbonate.
- vinylene carbonate itself is easily oxidized and decomposed at the positive electrode, and gas is generated accordingly.
- One aspect of the present invention includes a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent, and the non-aqueous solvent includes a fluorine-containing cyclic carbonate, propylene carbonate, and diethyl carbonate,
- the fluorine-containing cyclic carbonate content W FCC is 2 to 12% by mass
- the propylene carbonate content W PC is 40 to 70% by mass
- the diethyl carbonate content W DEC is 20 to 50% with respect to the whole solvent. It is related with the nonaqueous electrolyte for secondary batteries which is the mass%.
- Another aspect of the present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte for a secondary battery.
- gas generation can be remarkably suppressed even when the nonaqueous electrolyte secondary battery is stored in a high temperature environment or when charging and discharging are repeated. As a result, a decrease in charge / discharge capacity due to gas generation can be suppressed. Moreover, since it can suppress that the ionic conductivity of a nonaqueous electrolyte falls, the fall of the rate characteristic in low temperature can be suppressed.
- the nonaqueous electrolyte for a secondary battery includes a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent.
- the non-aqueous solvent contains a fluorinated cyclic carbonate, PC, and DEC.
- fluorine-containing cyclic carbonate examples include monofluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,2,3-trifluoropropylene carbonate, 2,3-difluoro-2,3-butylene carbonate, 1,1 And fluorine-containing cyclic carbonates having 1 to 6 fluorine atoms such as 1,4,4,4-hexafluoro-2,3-butylene carbonate.
- the fluorine-containing cyclic carbonate is preferably a 5- to 8-membered fluorine-containing cyclic carbonate, more preferably a 5- to 7-membered fluorine-containing cyclic carbonate.
- the fluorinated cyclic carbonate preferably contains monofluoroethylene carbonate (FEC).
- FEC content in the fluorine-containing cyclic carbonate is, for example, 80% by mass or more, preferably 90% by mass or more.
- the content of each solvent with respect to the whole non-aqueous solvent is as follows.
- the content W FCC of the fluorinated cyclic carbonate is 2 to 12% by mass
- the content W PC of the PC is 40 to 70% by mass
- the content DEC of the DEC is 20 to 50% by mass.
- a fluorine-containing cyclic carbonate is used in place of EC frequently used as a non-aqueous solvent.
- the fluorine-containing cyclic carbonate has higher oxidation resistance than EC. Therefore, by using a fluorine-containing cyclic carbonate, it is possible to prevent gas from being generated due to oxidative decomposition such as EC and subsequent reductive decomposition.
- the non-aqueous solvent may contain EC, but in order to reduce the amount of gas generated, the EC content in the non-aqueous solvent is, for example, 5% by mass or less (0 to 5% by mass), preferably 0. 0.1 to 3% by mass, more preferably 0.5 to 2% by mass.
- Fluorine-containing cyclic carbonate is easier to form a solid electrolyte layer (SEI; Solid Electrolyte Interphase) or a protective film at a higher reduction potential in the negative electrode than EC and vinylene carbonate. Therefore, even if the additive having a film forming ability at the negative electrode, such as vinylene carbonate, is small, it is possible to suppress reductive decomposition of PC at the negative electrode by adding the fluorine-containing cyclic carbonate. Therefore, although the content of PC in the nonaqueous solvent is large as described above, the generation of reductive cracking gas (methane, ethane, propene, propane, etc.) derived from PC can be remarkably suppressed.
- SEI Solid Electrolyte Interphase
- the content of PC can be increased, the content of DEC, which is more easily decomposed than PC, can be relatively reduced. Gases (CO, CO 2 , methane, ethane) accompanying oxidative decomposition and reductive decomposition of DEC can also be achieved. Etc.) can be reduced.
- the content W FCC of the fluorinated cyclic carbonate is preferably 5 to 10% by mass, more preferably 7 to 10% by mass.
- the PC content W PC is preferably 50 to 70% by mass, more preferably 50 to 60% by mass.
- the DEC content W DEC is preferably 25 to 45% by mass, more preferably 30 to 40% by mass.
- the content of the fluorine-containing cyclic carbonate is too small, the contents of PC and DEC are relatively increased, and the reductive decomposition of PC cannot be sufficiently suppressed, making it difficult to sufficiently suppress gas generation. If the content of the fluorinated cyclic carbonate is too large, the reduction protective coating derived from the fluorinated cyclic carbonate at the negative electrode becomes thick, and the coating resistance increases to inhibit the lithium ion insertion or desorption reaction. May decrease.
- the viscosity of the nonaqueous electrolyte tends to be high, and it becomes difficult to penetrate into the electrode plate, ion conductivity is lowered, and rate characteristics at low temperature are lowered.
- the viscosity of the non-aqueous electrolyte is, for example, 3 to 6.5 mPa ⁇ s, preferably 4.5 to 6 mPa ⁇ s at 25 ° C.
- the viscosity can be measured, for example, by a rotary viscometer using a cone plate type spindle.
- the non-aqueous solvent may contain a solvent other than the above three types as necessary.
- examples of such other non-aqueous solvents include chain carbonates other than DEC (such as ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC)); ⁇ -butyrolactone (GBL), ⁇ -valerolactone (GVL). And the like, and the like.
- chain carbonates other than DEC such as ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC)
- GBL ⁇ -butyrolactone
- GVL ⁇ -valerolactone
- the content of the other nonaqueous solvent is, for example, 5% by mass or less (0 to 5% by mass), preferably 0.1 to 3% by mass with respect to the entire nonaqueous solvent.
- the non-aqueous electrolyte may contain a known additive, for example, a cyclic carbonate having a C ⁇ C bond, a sultone compound, cyclohexylbenzene, diphenyl ether and the like, if necessary.
- the cyclic carbonate having a C ⁇ C bond and the sultone compound have a film forming ability at the positive electrode and / or the negative electrode.
- SEI and a protective film are formed on the negative electrode, and decomposition of the nonaqueous solvent can be effectively prevented without using such an additive having a film forming ability. This does not preclude the use of such additives.
- Examples of the cyclic carbonate having a C ⁇ C bond include unsaturated cyclic carbonates such as vinylene carbonate; cyclic carbonates having a C 2-4 alkenyl group such as vinyl ethylene carbonate and divinyl ethylene carbonate.
- Examples of sultone compounds include C 3-4 alkane sultones such as 1,3-propane sultone and C 3-4 alkene sultones such as 1,3-propene sultone. You may use an additive individually by 1 type or in combination of 2 or more types. The content of the additive is, for example, 10% by mass or less, preferably 0.1 to 5% by mass with respect to the entire nonaqueous electrolyte.
- lithium salt for example, a lithium salt of a fluorine-containing acid (LiPF 6 , LiBF 4 , LiCF 3 SO 3 and the like), a lithium salt of a fluorine-containing acid imide (LiN (CF 3 SO 2 ) 2 and the like), and the like can be used.
- a lithium salt can be used individually by 1 type or in combination of 2 or more types.
- the concentration of the lithium salt in the nonaqueous electrolyte is, for example, 0.5 to 2 mol / L.
- the nonaqueous electrolyte can be prepared by a conventional method, for example, by mixing a nonaqueous solvent and a lithium salt and dissolving the lithium salt in the nonaqueous solvent.
- the order of mixing each solvent and each component is not particularly limited. For example, after mixing a nonaqueous solvent in advance, a lithium salt may be added and dissolved. Further, the lithium salt may be dissolved in a part of the nonaqueous solvent, and then the remaining nonaqueous solvent may be mixed.
- Such a non-aqueous electrolyte suppresses the reaction between the non-aqueous solvent contained in the non-aqueous electrolyte and the positive electrode and / or the negative electrode, and can remarkably suppress gas generation, thereby preventing a decrease in charge / discharge capacity. it can. Moreover, since it is low-viscosity, high ion conductivity can be ensured even at low temperatures, and deterioration in rate characteristics can be suppressed. Therefore, it is advantageous for use in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.
- the non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode together with the non-aqueous electrolyte.
- the positive electrode includes a positive electrode active material such as a lithium-containing transition metal oxide.
- the positive electrode usually includes a positive electrode current collector and a positive electrode active material layer attached to the surface of the positive electrode current collector.
- the positive electrode current collector may be a non-porous conductive substrate (metal foil, metal sheet, etc.), or a porous conductive substrate (punching sheet, expanded metal, etc.) having a plurality of through holes. Good.
- the metal material used for the positive electrode current collector examples include stainless steel, titanium, aluminum, and an aluminum alloy. From the viewpoint of the strength and light weight of the positive electrode, the thickness of the positive electrode current collector is, for example, 3 to 50 ⁇ m, preferably 5 to 30 ⁇ m.
- the positive electrode active material layer may be formed on one side of the positive electrode current collector or on both sides.
- the positive electrode active material layer contains a positive electrode active material and a binder.
- the positive electrode active material layer may further contain a thickener, a conductive material, and the like as necessary.
- Examples of the positive electrode active material include transition metal oxides commonly used in the field of nonaqueous electrolyte secondary batteries, such as lithium-containing transition metal oxides.
- transition metal elements include Co, Ni, and Mn. These transition metals may be partially substituted with a different element. Examples of the different element include at least one selected from Na, Mg, Sc, Y, Cu, Fe, Zn, Al, Cr, Pb, Sb, and B.
- a positive electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.
- Specific positive electrode active material for example, Li x Ni y M z Me 1- (y + z) O 2 + d, Li x M y Me 1-y O 2 + d, etc. Li x Mn 2 O 4 Is mentioned.
- M is at least one element selected from the group consisting of Co and Mn.
- Me is the above-mentioned different element, and is preferably at least one selected from the group consisting of Al, Cr, Fe, Mg and Zn.
- x is 0.98 ⁇ x ⁇ 1.2
- y is 0.3 ⁇ y ⁇ 1
- z is 0 ⁇ z ⁇ 0.7.
- y + x is 0.9 ⁇ (y + z) ⁇ 1, preferably 0.93 ⁇ (y + z) ⁇ 0.99.
- d is ⁇ 0.01 ⁇ d ⁇ 0.01.
- x is preferably 0.99 ⁇ x ⁇ 1.1.
- y is 0.7 ⁇ y ⁇ 0.9 (particularly 0.75 ⁇ y ⁇ 0.85), and z is 0.05 ⁇ z ⁇ 0.4 (particularly 0.1 ⁇ z ⁇ 0). .25) is preferred.
- y is 0.25 ⁇ y ⁇ 0.5 (particularly 0.3 ⁇ y ⁇ 0.4), and z is 0.5 ⁇ z ⁇ 0.75 (particularly 0.6 ⁇ z). ⁇ 0.7) is also preferable.
- the element M may be a combination of Co and Mn, and the molar ratio Co / Mn between Co and Mn is 0.2 ⁇ Co / Mn ⁇ 4, preferably 0.5 ⁇ Co / Mn. ⁇ 2, more preferably 0.8 ⁇ Co / Mn ⁇ 1.2.
- the positive electrode active material since EC is not contained or is contained in a small amount, gas generation can be greatly suppressed even when a lithium-containing transition metal oxide containing Ni that easily decomposes EC is used as the positive electrode active material.
- Such lithium-containing transition metal oxide, of the positive electrode active material corresponds to Li x Ni y M z Me 1- (y + z) O 2 + d.
- the lithium-containing transition metal oxide containing Ni is also advantageous in that it has a high capacity.
- binder examples include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and vinylidene fluoride (VDF) -hexafluoropropylene (HFP) copolymer; polyolefin resins such as polyethylene and polypropylene; Polyamide resins such as aramid; Polyimide resins such as polyimide and polyamideimide; Acrylic resins such as polymethyl acrylate and ethylene-methyl methacrylate copolymer; Vinyl resins such as polyvinyl acetate and ethylene-vinyl acetate copolymer; Poly Ether sulfone; polyvinyl pyrrolidone; rubbery materials such as acrylic rubber.
- a binder can be used individually by 1 type or in combination of 2 or more types. The ratio of the binder is, for example, 0.1 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.
- the conductive material examples include carbon black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; natural or artificial graphite.
- a conductive material can be used individually by 1 type or in combination of 2 or more types.
- the proportion of the conductive material is, for example, 0 to 15 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.
- the thickener examples include cellulose derivatives such as carboxymethyl cellulose (CMC); poly C 2-4 alkylene glycol such as polyethylene glycol and ethylene oxide-propylene oxide copolymer; polyvinyl alcohol; solubilized modified rubber and the like. .
- a thickener can be used individually by 1 type or in combination of 2 or more types.
- the ratio of the thickener is not particularly limited, and is, for example, 0 to 10 parts by mass, preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material.
- the positive electrode can be formed by preparing a positive electrode slurry containing a positive electrode active material and a binder and applying it to the surface of the positive electrode current collector.
- the positive electrode slurry usually contains a dispersion medium, and if necessary, a conductive material and further a thickener may be added.
- the dispersion medium is not particularly limited, and examples thereof include water, alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, N-methyl-2-pyrrolidone (NMP), or a mixed solvent thereof. .
- the positive electrode slurry can be prepared by a method using a conventional mixer or kneader.
- the positive electrode slurry can be applied to the surface of the positive electrode current collector by a conventional application method, for example, a coating method using various coaters such as a die coater, a blade coater, a knife coater, and a gravure coater.
- the coating film of the positive electrode slurry formed on the surface of the positive electrode current collector is usually dried and subjected to rolling. Drying may be natural drying, or may be performed under heating or under reduced pressure. When rolling with a roller, the pressure is a linear pressure, for example, 1 to 30 kN / cm.
- the thickness of the positive electrode active material layer (or positive electrode mixture layer) is, for example, 30 to 100 ⁇ m, preferably 50 to 70 ⁇ m.
- the negative electrode includes a negative electrode current collector and a negative electrode active material layer attached to the negative electrode current collector.
- a negative electrode current collector a nonporous or porous conductive substrate exemplified for the positive electrode current collector can be used.
- the metal material forming the negative electrode current collector include stainless steel, nickel, copper, copper alloy, aluminum, and aluminum alloy. Of these, copper or a copper alloy is preferable.
- a copper foil particularly an electrolytic copper foil is preferable.
- the copper foil may contain 0.2 mol% or less of components other than copper.
- the thickness of the negative electrode current collector can be selected from the range of 3 to 50 ⁇ m, for example, and preferably 5 to 30 ⁇ m.
- the negative electrode active material layer includes a negative electrode active material as an essential component, and may include a binder, a conductive material, and / or a thickener as optional components. When the binder is used, the binder adheres the particles of the negative electrode active material in the negative electrode active material layer.
- the negative electrode active material layer may be formed on one side of the negative electrode current collector or on both sides.
- the negative electrode may be a deposited film formed by a vapor phase method, or may be a mixture layer containing a negative electrode active material and a binder, and if necessary, a conductive material and / or a thickener.
- the deposited film can be formed by depositing the negative electrode active material on the surface of the negative electrode current collector by a vapor phase method such as a vacuum evaporation method, a sputtering method, or an ion plating method.
- a vapor phase method such as a vacuum evaporation method, a sputtering method, or an ion plating method.
- the negative electrode active material for example, silicon, a silicon compound, a lithium alloy, and the like described later can be used.
- the mixture layer can be formed by preparing a negative electrode slurry containing a negative electrode active material and a binder, and optionally a conductive material and / or a thickener, and applying it to the surface of the negative electrode current collector.
- the negative electrode slurry usually contains a dispersion medium.
- a thickener and / or a conductive material is usually added to the negative electrode slurry.
- a negative electrode slurry can be prepared according to the preparation method of a positive electrode slurry. The negative electrode slurry can be applied by the same method as the application of the positive electrode.
- Examples of the negative electrode active material include carbon materials; silicon, silicon compounds; lithium alloys containing at least one selected from tin, aluminum, zinc, and magnesium.
- Examples of the carbon material include graphite (natural graphite, artificial graphite, graphitized mesophase carbon, etc.), coke, graphitized carbon, graphitized carbon fiber, and amorphous carbon.
- As the amorphous carbon for example, an easily graphitizable carbon material (soft carbon) that is easily graphitized by heat treatment at a high temperature (for example, 2800 ° C.), a non-graphitizable carbon material that hardly graphitizes even by the heat treatment ( Hard carbon).
- Soft carbon has a structure in which microcrystallites such as graphite are arranged in substantially the same direction, and hard carbon has a turbostratic structure.
- Examples of the silicon compound include silicon oxide SiO ⁇ (0.05 ⁇ ⁇ 1.95). ⁇ is preferably 0.1 to 1.8, more preferably 0.15 to 1.6. In the silicon oxide, a part of silicon may be substituted with one or more elements. Examples of such elements include B, Mg, Ni, Co, Ca, Fe, Mn, Zn, C, N, and Sn.
- the negative electrode active materials graphite particles are preferable. From the viewpoint of more effectively suppressing the reductive decomposition of the nonaqueous solvent in the negative electrode, a graphite particle coated with a water-soluble polymer may be used as the negative electrode active material, if necessary.
- the diffraction image of graphite particles measured by the wide-angle X-ray diffraction method has a peak attributed to the (101) plane and a peak attributed to the (100) plane.
- the ratio between the peak intensity I (101) attributed to the (101) plane and the peak intensity I (100) attributed to the (100) plane is preferably 0.01 ⁇ I (101). /I(100) ⁇ 0.25, more preferably 0.08 ⁇ I (101) / I (100) ⁇ 0.20.
- the peak intensity means the peak height.
- the average particle diameter of the graphite particles is, for example, 5 to 25 ⁇ m, preferably 10 to 25 ⁇ m, and more preferably 14 to 23 ⁇ m.
- the average particle diameter means the median diameter (D50) in the volume particle size distribution of the graphite particles.
- the volume particle size distribution of the graphite particles can be measured by, for example, a commercially available laser diffraction type particle size distribution measuring apparatus.
- the average circularity of the graphite particles is preferably 0.90 to 0.95, and more preferably 0.91 to 0.94.
- the average circularity is represented by 4 ⁇ S / L 2 (where S is the area of the orthographic image of graphite particles, and L is the perimeter of the orthographic image).
- S is the area of the orthographic image of graphite particles
- L is the perimeter of the orthographic image.
- the average circularity of 100 arbitrary graphite particles is preferably in the above range.
- the specific surface area S of the graphite particles is preferably 3 to 5 m 2 / g, more preferably 3.5 to 4.5 m 2 / g.
- the specific surface area is included in the above range, the slipperiness of the graphite particles in the negative electrode active material layer is improved, which is advantageous in improving the adhesive strength between the graphite particles.
- the preferred amount of the water-soluble polymer that covers the surface of the graphite particles can be reduced.
- the type of the water-soluble polymer is not particularly limited, and examples thereof include cellulose derivatives; polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone, and derivatives thereof. Of these, cellulose derivatives and polyacrylic acid are particularly preferable. As the cellulose derivative, methyl cellulose, carboxymethyl cellulose, Na salt of carboxymethyl cellulose and the like are preferable.
- the molecular weight of the cellulose derivative is preferably 10,000 to 1,000,000.
- the molecular weight of polyacrylic acid is preferably from 5,000 to 1,000,000.
- the amount of the water-soluble polymer contained in the negative electrode active material layer is, for example, 0.5 to 2.5 parts by mass, preferably 0.5 to 1.5 parts by mass, more preferably 0, per 100 parts by mass of the graphite particles. .5 to 1.0 part by mass.
- the water-soluble polymer can cover the surface of the graphite particles with a high coverage.
- the graphite particle surface is not excessively covered with the water-soluble polymer, and the increase in the internal resistance of the negative electrode is also suppressed.
- the coating of the graphite particles can be performed, for example, by mixing graphite particles, water, and a water-soluble polymer dissolved in water, and drying the obtained mixture.
- a water-soluble polymer dissolved in water
- an aqueous solution is prepared by dissolving a water-soluble polymer in water.
- the obtained aqueous solution and graphite particles are mixed, and then the water is removed and the mixture is dried.
- the water-soluble polymer efficiently adheres to the surface of the graphite particles, and the coverage of the graphite particle surface with the water-soluble polymer is increased.
- the surface of the graphite particles Prior to the preparation of the negative electrode slurry, the surface of the graphite particles may be coated with a water-soluble polymer to coat the surface. Further, in the process of preparing the negative electrode slurry, the surface of the graphite particles may be coated with the water-soluble polymer by adding a water-soluble polymer.
- the viscosity of the aqueous solution of the water-soluble polymer is preferably controlled to 1 to 10 Pa ⁇ s at 25 ° C.
- the viscosity is measured using a B-type viscometer at a peripheral speed of 20 mm / s and using a 5 mm ⁇ spindle.
- the amount of graphite particles mixed with 100 parts by mass of the water-soluble polymer aqueous solution is preferably 50 to 150 parts by mass.
- the drying temperature of the mixture is preferably 80 to 150 ° C., and the drying time is preferably 1 to 8 hours.
- a negative electrode slurry is prepared by mixing a mixture obtained by drying, a binder, and a dispersion medium.
- the binder adheres to the surface of the graphite particles coated with the water-soluble polymer. Since the slipperiness between the graphite particles is good, the binder adhering to the surface of the graphite particles receives a sufficient shearing force and effectively acts on the surface of the graphite particles.
- a solvent similar to the dispersion medium such as NMP
- alcohol water-soluble alcohol such as methanol, ethanol, etc.
- a mixed solvent of a solvent and water may be used.
- the binder, the dispersion medium, the conductive material, and the thickener the same materials as those exemplified in the section of the positive electrode slurry can be used.
- the components exemplified as the conductive material those other than graphite are often used for the negative electrode slurry.
- binder particles having rubber elasticity are preferable.
- a binder a polymer containing a styrene unit and a butadiene unit is preferable. Such a polymer is excellent in elasticity and stable at the negative electrode potential.
- the average particle diameter of the particulate binder is, for example, 0.1 ⁇ m to 0.3 ⁇ m, preferably 0.1 to 0.25 ⁇ m, and more preferably 0.1 to 0.15 ⁇ m.
- the average particle diameter of the binder is, for example, an SEM photograph of 10 binder particles taken with a transmission electron microscope (manufactured by JEOL Ltd., acceleration voltage 200 kV), and the average of these maximum diameters. It can be obtained as a value.
- the ratio of the binder can be selected from the range of, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material (graphite particles and the like).
- the ratio of the binder is, for example, 0.4 to 1.5 parts by mass, preferably 0.4 to 1 part by mass with respect to 100 parts by mass of the graphite particles. Part.
- the surface of the graphite particles is coated with a water-soluble polymer, the slipping between the graphite particles is improved, so that the binder adhering to the surface of the graphite particles receives sufficient shearing force and effectively acts on the surface of the graphite particles.
- a particulate binder having a small average particle size has a high probability of contacting the surface of the graphite particles. Therefore, sufficient binding properties are exhibited even with a small amount of the binder.
- the negative electrode can be produced according to the production method of the positive electrode. Specifically, for example, it can be formed by applying the negative electrode slurry prepared as described above to the surface of the negative electrode current collector.
- the coating film formed on the surface of the negative electrode current collector is usually dried and further rolled. The method of drying the coating film, rolling conditions (linear pressure, etc.) are the same as in the case of the positive electrode.
- the proportion of the conductive material is not particularly limited, and is, for example, 0 to 5 parts by mass, preferably 0.01 to 3 parts by mass with respect to 100 parts by mass of the negative electrode active material.
- the ratio of the thickener is not particularly limited, and is, for example, 0 to 10 parts by mass, preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the negative electrode active material.
- the thickness of the negative electrode active material layer (or negative electrode mixture layer) is, for example, 30 to 110 ⁇ m, preferably 50 to 90 ⁇ m.
- separator examples include a resin porous membrane (porous film) or a nonwoven fabric.
- resin constituting the separator include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer.
- the porous film may contain inorganic oxide particles as necessary.
- the thickness of the separator is, for example, 5 to 100 ⁇ m, preferably 7 to 50 ⁇ m.
- the shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be a cylindrical shape, a flat shape, a coin shape, a square shape, or the like.
- the nonaqueous electrolyte secondary battery can be manufactured by a conventional method depending on the shape of the battery.
- a positive electrode, a negative electrode, and a separator that separates the positive electrode and the negative electrode are wound to form an electrode group, and the electrode group and the nonaqueous electrolyte are accommodated in a battery case. it can.
- the electrode group is not limited to a wound one, but may be a laminated one or a folded one.
- the shape of the electrode group may be a cylindrical shape and a flat shape having an oval end surface perpendicular to the winding axis, depending on the shape of the battery or battery case.
- the battery case may be made of a laminate film, but is usually made of metal from the viewpoint of pressure strength.
- a material for the battery case aluminum, an aluminum alloy (such as an alloy containing a trace amount of a metal such as manganese or copper), a steel plate, or the like can be used.
- Example 1 Production of negative electrode Step (i) A sodium salt of carboxymethyl cellulose (hereinafter referred to as CMC-Na salt, molecular weight 400,000) as a water-soluble polymer was dissolved in water to obtain an aqueous solution having a CMC-Na salt concentration of 1.0% by mass. 100 parts by mass of natural graphite particles (average particle size 20 ⁇ m, average circularity 0.92, specific surface area 4.2 m 2 / g) and 100 parts by mass of CMC-Na salt aqueous solution are mixed, and the temperature of the mixture is adjusted to 25 ° C. Stir with control. Thereafter, the mixture was dried at 120 ° C. for 5 hours to obtain a dry mixture. In the dry mixture, the amount of CMC-Na salt per 100 parts by mass of graphite particles was 1.0 part by mass.
- CMC-Na salt carboxymethyl cellulose
- Step (ii) 101 parts by mass of the obtained dry mixture, 0.6 parts by mass of a binder (hereinafter referred to as SBR) having a rubber elasticity, which is in the form of particles having an average particle size of 0.12 ⁇ m, includes styrene units and butadiene units, and 0 .9 parts by mass of CMC-Na salt and an appropriate amount of water were mixed to prepare a negative electrode slurry.
- SBR was mixed with other components in the state of an emulsion using water as a dispersion medium (BM-400B (trade name) manufactured by Nippon Zeon Co., Ltd., SBR mass ratio: 40 mass%).
- Step (iii) The obtained negative electrode slurry was applied to both surfaces of an electrolytic copper foil (thickness 12 ⁇ m) as a negative electrode core material using a die coater, and the coating film was dried at 120 ° C. Thereafter, the dried coating film was rolled with a rolling roller at a linear pressure of 0.25 ton / cm to form a negative electrode active material layer having a graphite density of 1.5 g / cm 3 . The total thickness of the negative electrode was 140 ⁇ m.
- a negative electrode was obtained by cutting the negative electrode active material layer into a predetermined shape together with the negative electrode core material.
- (D) Battery assembly A square lithium ion secondary battery as shown in FIG. 1 was produced.
- the negative electrode and the positive electrode are wound with a separator (A089 (trade name) manufactured by Celgard Co., Ltd.) made of a polyethylene microporous film having a thickness of 20 ⁇ m interposed therebetween, and the cross section is substantially elliptical.
- the electrode group 21 was configured.
- the electrode group 21 was housed in an aluminum square battery can 20.
- the battery can 20 has a bottom portion 20a and a side wall 20b, an upper portion is opened, and the shape thereof is substantially rectangular.
- the thickness of the main flat part of the side wall was 80 ⁇ m.
- an insulator 24 for preventing a short circuit between the battery can 20 and the positive electrode lead 22 or the negative electrode lead 23 was disposed on the upper part of the electrode group 21.
- a rectangular sealing plate 25 having a negative electrode terminal 27 surrounded by an insulating gasket 26 in the center was disposed in the opening of the battery can 20.
- the negative electrode lead 23 was connected to the negative electrode terminal 27.
- the positive electrode lead 22 was connected to the lower surface of the sealing plate 25.
- the end of the opening and the sealing plate 25 were welded with a laser to seal the opening of the battery can 20.
- 2.5 g of nonaqueous electrolyte was injected into the battery can 20 from the injection hole of the sealing plate 25.
- liquid injection hole was closed with a plug 29 by welding to complete a prismatic lithium ion secondary battery 1 having a height of 50 mm, a width of 34 mm, an inner space thickness of about 5.2 mm, and a design capacity of 850 mAh.
- Example 2 A nonaqueous electrolyte was prepared in the same manner as in Example 1 except that the ratio of W FEC : W PC : W DEC was changed as shown in Table 1. Batteries 2 to 17 were produced in the same manner as in Example 1 except that the obtained nonaqueous electrolyte was used. Further, a nonaqueous electrolyte was prepared in the same manner as in Example 1 except that the ratio of W FEC : W PC : W DEC was changed as shown in Table 1 and 5% by mass of EC was added. A battery 18 was produced in the same manner as in Example 1 using a water electrolyte. The batteries 14 to 17 are all comparative batteries. The batteries 2 to 18 were evaluated in the same manner as in Example 1. The results of batteries 1 to 18 are shown in Table 1.
- the batteries using the non-aqueous electrolyte containing FEC, PC and DEC at a specific content all had good cycle capacity retention rates and low-temperature discharge capacity retention rates. Further, it was found that the battery swelling after the cycle was small and the gas generation amount was small. It was found that the batteries 14 to 17 of the comparative example had large battery swelling and a large amount of gas was generated. Further, the cycle capacity maintenance rate was lowered.
- Example 3 Batteries 36 to 39 were produced in the same manner as in Example 1 except that the water-soluble polymer shown in Table 2 was used. As the water-soluble polymers, those having a molecular weight of about 400,000 were used. The batteries 19 to 22 were evaluated in the same manner as in Example 1. The results are shown in Table 2.
- Example 4 Batteries 23 to 37 were produced in the same manner as in Example 1 except that the positive electrode active material shown in Table 3 was used. The batteries 23 to 37 were evaluated in the same manner as in Example 1. The results are shown in Table 3.
- a battery using a non-aqueous electrolyte containing FEC, PC and DEC at a specific content has a good cycle capacity maintenance rate and low temperature discharge capacity maintenance rate when any positive electrode active material is used. there were. Further, it was found that the battery swelling after the cycle was small and the gas generation amount was small.
- the present invention even when stored in a high temperature environment or when charging and discharging are repeated, it is possible to suppress a decrease in charge / discharge capacity and rate characteristics at low temperatures. Therefore, it is useful as a nonaqueous electrolyte for secondary batteries used in electronic devices such as mobile phones, personal computers, digital still cameras, game devices, and portable audio devices.
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Abstract
Description
特許文献3は、PC10~60体積%、EC1~20体積%およびDECなどの鎖状カーボネート30~85体積%を含み、1,3-プロパンスルトンおよびビニレンカーボネートを添加した非水電解質を開示している。
本発明の他の目的は、ガス発生に伴う充放電容量および低温でのレート特性の低下を抑制できる二次電池用非水電解質および非水電解質二次電池を提供することにある。
二次電池用非水電解質は、非水溶媒、および前記非水溶媒に溶解したリチウム塩を含む。本発明では、非水溶媒が、含フッ素環状カーボネートと、PCと、DECとを含有する。含フッ素環状カーボネートとしては、モノフルオロエチレンカーボネート(FEC)、1,2-ジフルオロエチレンカーボネート、1,2,3-トリフルオロプロピレンカーボネート、2,3-ジフルオロ-2,3-ブチレンカーボネート、1,1,1,4,4,4-ヘキサフルオロ-2,3-ブチレンカーボネートなどの1~6個のフッ素原子を有する含フッ素環状カーボネートが例示できる。含フッ素環状カーボネートは、好ましくは5~8員、さらに好ましくは5~7員の含フッ素環状カーボネートである。
非水溶媒は、ECを含んでいてもよいが、ガスの発生量を低減するため、非水溶媒中のEC含有量は、例えば、5質量%以下(0~5質量%)、好ましくは0.1~3質量%、さらに好ましくは0.5~2質量%である。
低温でのレート特性を維持する観点から、非水電解質の粘度は、25℃において、例えば、3~6.5mPa・s、好ましくは4.5~6mPa・sである。粘度は、例えば、コーンプレートタイプのスピンドルを用いて回転型粘度計により測定できる。
添加剤は、一種を単独で又は二種以上組み合わせて用いてもよい。添加剤の含有量は、非水電解質全体に対して、例えば、10質量%以下、好ましくは0.1~5質量%である。
本発明の非水電解質二次電池は、上記非水電解質とともに、正極、負極、正極と負極との間に介在するセパレータを具備する。
(正極)
正極は、リチウム含有遷移金属酸化物などの正極活物質を含む。正極は、通常、正極集電体と、正極集電体の表面に付着した正極活物質層とを含む。正極集電体は、無孔の導電性基板(金属箔、金属シートなど)であってもよく、複数の貫通孔を有する多孔性の導電性基板(パンチングシート、エキスパンドメタルなど)であってもよい。
正極の強度および軽量性などの点から、正極集電体の厚みは、例えば、3~50μm、好ましくは5~30μmである。
正極活物質としては、非水電解質二次電池の分野で常用される遷移金属酸化物、例えば、リチウム含有遷移金属酸化物などが例示できる。
Mは、CoおよびMnからなる群より選択された少なくとも一種の元素である。Meは、上記異種元素であり、好ましくは、Al、Cr、Fe、MgおよびZnからなる群より選択された少なくとも一種である。
ただし、y+xは、0.9≦(y+z)≦1、好ましくは0.93≦(y+z)≦0.99である。dは、-0.01≦d≦0.01である。
結着剤の割合は、正極活物質100質量部に対して、例えば、0.1~20質量部、好ましくは1~10質量部である。
導電材の割合は、例えば、正極活物質100質量部に対して0~15質量部、好ましくは1~10質量部である。
増粘剤の割合は、特に制限されず、例えば、正極活物質100質量部に対して0~10質量部、好ましくは0.01~5質量部である。
分散媒としては、特に制限されないが、例えば、水、エタノールなどのアルコール、テトラヒドロフランなどのエーテル、ジメチルホルムアミドなどのアミド、N-メチル-2-ピロリドン(NMP)、またはこれらの混合溶媒などが例示できる。
正極活物質層(または正極合剤層)の厚みは、例えば、30~100μm、好ましくは50~70μmである。
負極は、負極集電体と、負極集電体に付着した負極活物質層を含む。負極集電体としては、正極集電体で例示の無孔または多孔性の導電性基板などが使用できる。負極集電体を形成する金属材料としては、例えば、ステンレス鋼、ニッケル、銅、銅合金、アルミニウム、アルミニウム合金などが例示できる。なかでも、銅または銅合金などが好ましい。
負極集電体としては、銅箔、特に電解銅箔が好ましい。銅箔は、0.2モル%以下の銅以外の成分を含んでいてもよい。
負極集電体の厚みは、例えば、3~50μmの範囲から選択でき、好ましくは5~30μmである。
堆積膜は、負極活物質を、真空蒸着法、スパッタリング法、イオンプレーティング法などの気相法により、負極集電体の表面に堆積させることにより形成できる。この場合、負極活物質としては、例えば、後述するケイ素、ケイ素化合物、リチウム合金などが利用できる。
炭素材料としては、例えば、黒鉛(天然黒鉛、人造黒鉛、黒鉛化メソフェーズカーボンなど)、コークス、黒鉛化途上炭素、黒鉛化炭素繊維、非晶質炭素などが挙げられる。非晶質炭素としては、例えば、高温(例えば、2800℃)の熱処理によって容易に黒鉛化する易黒鉛化性炭素材料(ソフトカーボン)、前記熱処理によってもほとんど黒鉛化しない難黒鉛化性炭素材料(ハードカーボン)などが含まれる。ソフトカーボンは、黒鉛のような微小結晶子がほぼ同一方向に配列した構造を有し、ハードカーボンは乱層構造を有する。
混合物の乾燥温度は80~150℃が好ましく、乾燥時間は1~8時間が好適である。
結着剤、分散媒、導電材および増粘剤としては、正極スラリーの項で例示したものと同様のものが使用できる。なお、負極スラリーには、前記導電材として例示した成分のうち、グラファイト以外のものを用いる場合が多い。
塗膜の乾燥方法、圧延の条件(線圧など)などは、正極の場合と同様である。
負極活物質層(または負極合剤層)の厚みは、例えば、30~110μm、好ましくは50~90μmである。
セパレータとしては、樹脂多孔膜(多孔性フィルム)または不織布などが例示できる。セパレータを構成する樹脂としては、例えば、ポリエチレン、ポリプロピレン、エチレン-プロピレン共重合体などのポリオレフィン樹脂が挙げられる。多孔性フィルムは、必要により、無機酸化物粒子を含有してもよい。
セパレータの厚みは、例えば、5~100μm、好ましくは7~50μmである。
非水電解質二次電池の形状は、特に制限されず、円筒型、扁平型、コイン型、角型などであってもよい。
非水電解質二次電池は、電池の形状などに応じて、慣用の方法により製造できる。円筒型電池または角型電池では、例えば、正極と、負極と、正極および負極を隔離するセパレータとを捲回して電極群を形成し、電極群および非水電解質を電池ケースに収容することにより製造できる。
《実施例1》
(a)負極の作製
工程(i)
水溶性高分子としてのカルボキシメチルセルロースのナトリウム塩(以下、CMC-Na塩、分子量40万)を水に溶解し、CMC-Na塩濃度1.0質量%の水溶液を得た。天然黒鉛粒子(平均粒径20μm、平均円形度0.92、比表面積4.2m2/g)100質量部と、CMC-Na塩水溶液100質量部とを混合し、混合物の温度を25℃に制御しながら攪拌した。その後、混合物を120℃で5時間乾燥させ、乾燥混合物を得た。乾燥混合物において、黒鉛粒子100質量部あたりのCMC-Na塩の量は1.0質量部であった。
得られた乾燥混合物101質量部と、平均粒径0.12μmの粒子状であり、スチレン単位およびブタジエン単位を含み、ゴム弾性を有する結着剤(以下、SBR)0.6質量部と、0.9質量部のCMC-Na塩と、適量の水とを混合し、負極スラリーを調製した。なお、SBRは水を分散媒とするエマルジョン(日本ゼオン(株)製のBM-400B(商品名)、SBR質量割合40質量%)の状態で他の成分と混合した。
得られた負極スラリーを、負極芯材である電解銅箔(厚さ12μm)の両面にダイコーターを用いて塗布し、塗膜を120℃で乾燥させた。その後、乾燥塗膜を圧延ローラで線圧0.25トン/cmで圧延して、黒鉛密度1.5g/cm3の負極活物質層を形成した。負極全体の厚みは、140μmであった。負極活物質層を負極芯材とともに所定形状に裁断することにより、負極を得た。
正極活物質である100質量部のLiNi0.80Co0.15Al0.05O2に対し、結着剤であるPVDFを4質量部添加し、適量のNMPとともに混合し、正極スラリーを調製した。得られた正極スラリーを、正極芯材である厚さ20μmのアルミニウム箔の両面に、ダイコーターを用いて塗布し、塗膜を乾燥させ、更に、圧延して、正極活物質層を形成した。正極活物質層を正極芯材とともに所定形状に裁断することにより、正極を得た。
FECと、PCと、DECとを、質量比WFEC:WPC:WDEC=1:5:4で含む混合溶媒に、1mol/Lの濃度でLiPF6を溶解させて非水電解質を調製した。回転粘度計によって測定したところ、25℃における非水電解質の粘度は、5.4mPa・sであった。
図1に示すような角型リチウムイオン二次電池を作製した。
負極と正極とを、これらの間に厚さ20μmのポリエチレン製の微多孔質フィルムからなるセパレータ(セルガード(株)製のA089(商品名))を介在させて捲回し、横断面が略楕円形の電極群21を構成した。電極群21はアルミニウム製の角型の電池缶20に収容した。電池缶20は、底部20aと、側壁20bとを有し、上部は開口しており、その形状は略矩形である。側壁の主要平坦部の厚みは80μmとした。
(i)サイクル容量維持率の評価
電池1に対し、充放電サイクルを45℃で繰り返した。充放電サイクルにおいて、充電処理では、600mAの電流で充電電圧が4.2Vになるまで定電流充電し、次いで4.2Vの電圧で、電流が43mAになるまで、定電圧充電を行った。充電後の休止時間は、10分間とした。一方、放電処理では、850mAの電流で、放電電圧が2.5Vになるまで、定電流放電を行った。放電後の休止時間は、10分間とした。
3サイクル目の放電容量を100%とし、この放電容量を基準として、500サイクルを経過したときの放電容量の比を百分率で表し、これをサイクル容量維持率[%]とした。
また、3サイクル目の充電後における状態と、501サイクル目の充電後における状態とで、電池1の最大平面(縦50mm、横34mm)に垂直な中央部の厚みを測定した。その電池厚みの差から、45℃での充放電サイクル経過後における電池膨れの量[mm]を求めた。
電池1に対し、充放電サイクルを25℃で3サイクル繰り返した。次に、4サイクル目の充電処理を25℃で行った後、0℃で3時間放置後、そのまま0℃で放電処理を行った。3サイクル目(25℃)の放電容量を100%とし、この放電容量を基準として、4サイクル目(0℃)の放電容量の比を百分率で表し、これを低温放電容量維持率[%]とした。なお、充放電条件は、温度および充電後の休止時間以外は評価(i)と同様にした。
WFEC:WPC:WDECの比を、表1のように変化させたこと以外、実施例1と同様にして、非水電解質を調製した。得られた非水電解質を用いたこと以外、実施例1と同様にして、電池2~17を作製した。
また、WFEC:WPC:WDECの比を、表1のように変化させ、5質量%のECを追加したこと以外、実施例1と同様にして、非水電解質を調製し、この非水電解質を用いて、実施例1と同様に電池18を作製した。
なお、電池14~17は、いずれも比較例の電池である。
電池2~18について、実施例1と同様に評価を行った。
電池1~18の結果を表1に示す。
比較例の電池14~17は、電池膨れが大きく、多量のガスが発生しているのがわかった。また、サイクル容量維持率が低下していた。
水溶性高分子として表2に示すものを用いたこと以外、実施例1と同様にして、電池36~39を作製した。水溶性高分子は、いずれも分子量約40万のものを用いた。
電池19~22について、実施例1と同様に評価を行った。結果を表2に示す。
正極活物質として表3に示すものを用いたこと以外、実施例1と同様にして、電池23~電池37を作製した。
電池23~37について、実施例1と同様に評価を行った。結果を表3に示す。
21 電極群
22 正極リード
23 負極リード
24 絶縁体
25 封口板
26 絶縁ガスケット
29 封栓
Claims (8)
- 非水溶媒と、前記非水溶媒に溶解したリチウム塩とを含み、
前記非水溶媒が、含フッ素環状カーボネートと、プロピレンカーボネートと、ジエチルカーボネートとを含み、
前記非水溶媒全体に対して、前記含フッ素環状カーボネートの含有量WFCCが2~12質量%、前記プロピレンカーボネートの含有量WPCが40~70質量%、前記ジエチルカーボネートの含有量WDECが20~50質量%である、二次電池用非水電解質。 - 前記非水溶媒全体に対して、前記含フッ素環状カーボネートの含有量WFCCが5~10質量%、前記プロピレンカーボネートの含有量WPCが50~70質量%、前記ジエチルカーボネートの含有量WDECが25~45質量%である、請求項1に記載の二次電池用非水電解質。
- 前記非水溶媒が、5質量%以下のエチレンカーボネートをさらに含む、請求項1または2に記載の二次電池用非水電解質。
- 前記含フッ素環状カーボネートが、フルオロエチレンカーボネートを含む、請求項1~3のいずれか1項に記載の二次電池用非水電解質。
- 正極、負極、前記正極と前記負極との間に介在するセパレータ、および請求項1~4のいずれか1項に記載の二次電池用非水電解質を含む、非水電解質二次電池。
- 前記正極が、LixNiyMzMe1-(y+z)O2+d(Mは、CoおよびMnからなる群より選択された少なくとも一種、Meは、Al、Cr、Fe、MgおよびZnからなる群より選択された少なくとも一種、0.98≦x≦1.2、0.3≦y≦1、0≦z≦0.7、0.9≦(y+z)≦1、および-0.01≦d≦0.01である)で表されるリチウム含有遷移金属酸化物を含む、請求項5に記載の非水電解質二次電池。
- 前記負極が、負極集電体および前記負極集電体に付着した負極活物質層を含み、
前記負極活物質層が、黒鉛粒子と、前記黒鉛粒子間を接着する結着剤とを含む、請求項5または6に記載の非水電解質二次電池。 - 前記黒鉛粒子の表面が、セルロース誘導体およびポリアクリル酸から選択された少なくとも一種の水溶性高分子で被覆されている、請求項7に記載の非水電解質二次電池。
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KR20150032743A (ko) | 2012-07-20 | 2015-03-27 | 쓰리엠 이노베이티브 프로퍼티즈 컴파니 | 리튬 이온 배터리용 고 전압 캐소드 조성물 |
KR20140106292A (ko) * | 2013-02-26 | 2014-09-03 | 삼성에스디아이 주식회사 | 리튬 이차전지용 음극 및 이를 채용한 리튬 이차전지 |
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