WO2018155609A1 - Lithium-ion secondary cell provided with negative electrode for high energy density cell - Google Patents

Lithium-ion secondary cell provided with negative electrode for high energy density cell Download PDF

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WO2018155609A1
WO2018155609A1 PCT/JP2018/006621 JP2018006621W WO2018155609A1 WO 2018155609 A1 WO2018155609 A1 WO 2018155609A1 JP 2018006621 W JP2018006621 W JP 2018006621W WO 2018155609 A1 WO2018155609 A1 WO 2018155609A1
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negative electrode
weight
ion secondary
carbon
lithium ion
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PCT/JP2018/006621
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French (fr)
Japanese (ja)
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丈史 莇
卓 玉井
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日本電気株式会社
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Priority to JP2019501823A priority Critical patent/JP7092109B2/en
Publication of WO2018155609A1 publication Critical patent/WO2018155609A1/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
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • 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
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials

Definitions

  • the present invention relates to a lithium ion secondary battery, a method of manufacturing a lithium ion secondary battery, and a vehicle equipped with the lithium ion secondary battery.
  • a carbon-based material is used for the negative electrode of a lithium ion secondary battery, but in order to increase the energy density of the battery, a silicon oxide having a large amount of occlusion / release of lithium ions per unit volume is used as the negative electrode. It is being considered for use.
  • silicon oxide provides a high capacity, the expansion and contraction of the active material when lithium ions are occluded and released are large, so that the cycle characteristics are degraded due to cutting of the conductive path or peeling of the active material particles. .
  • the silicon oxide is generally used by being mixed with another negative electrode active material such as graphite so that the ratio in the negative electrode active material layer is reduced.
  • Patent Document 1 describes a lithium ion secondary battery containing silicon oxide represented by SiO x (0.3 ⁇ x ⁇ 1.6) and graphite.
  • the lithium ion secondary battery described in Patent Document 1 has room for improvement in energy density because the silicon oxide content is lower than that of graphite. It is desired to further increase the mixing ratio of silicon oxide in the negative electrode active material layer. When the mixing ratio of the silicon oxide is high, it becomes more important to select a binder having a high binding force in order to prevent the deterioration of the negative electrode active material layer due to the large expansion and contraction of the silicon oxide.
  • polyimide Since polyimide has a high binding force, it is generally used as a binder for a negative electrode having a high silicon oxide content ratio. However, in polyimide, an organic solvent having a high environmental load such as N-methylpyrrolidone (NMP) is used. In recent years, an aqueous binder is required from the viewpoint of environmental harmony and industrial applicability. In addition, polyimide also has a problem that heat treatment at a high temperature is required for imidization and that good cycle characteristics cannot be obtained when the negative electrode is densified by pressing.
  • NMP N-methylpyrrolidone
  • rubber-based binders such as styrene butadiene rubber (SBR) and polyacrylic acid are known.
  • SBR styrene butadiene rubber
  • the rubber binder can be used up to a silicon oxide mixing ratio of about 5 to 7% by weight.
  • polyacrylic acid has a higher binding force than rubber-based binders, there is little capacity deterioration.
  • polyacrylic acid has a lower binding force than polyimide, the cycle characteristics are still insufficient.
  • a battery using polyacrylic acid has a problem of high resistance.
  • an object of the present invention is to provide a lithium ion secondary battery that uses polyacrylic acid that is an aqueous binder and has a high energy density and improved cycle characteristics. There is.
  • a first lithium ion secondary battery of the present invention includes a positive electrode including a positive electrode active material layer including a lithium-containing layered nickel composite oxide, composite particles including silicon oxide and carbon, graphite particles, a conductive material, and polyacryl
  • a lithium ion secondary battery including a negative electrode including a negative electrode active material layer including an acid wherein the conductive material has a specific surface area of 40 to 800 m 2 / g, and the amount of the composite particles in the negative electrode active material layer Is 50% by weight or more, the amount of the polyacrylic acid is 3% by weight or more and 8% by weight or less, the total amount of the conductive material and the polyacrylic acid is 4% by weight or more and 13% by weight or less, and the composite In the particles, the amount of carbon is 2% by weight or more.
  • a lithium ion secondary battery using polyacrylic acid which has a high energy density and improved cycle characteristics, can be provided.
  • FIG. 1 It is a disassembled perspective view which shows the basic structure of a film-clad battery. It is sectional drawing which shows the cross section of the battery of FIG. 1 typically. It is an impedance plot of a battery using polyacrylic acid or SBR / CMC and various conductive materials in the negative electrode. It is a SEM image of the negative electrode which uses a carbon nanotube. It is a SEM image of the negative electrode which uses carbon nanohorn.
  • the positive electrode includes a current collector and a positive electrode active material layer that is provided on the current collector and includes a positive electrode active material, a binder, and, if necessary, a conductive material.
  • the positive electrode active material contains a lithium-containing layered nickel composite oxide.
  • a lithium-containing layered nickel composite oxide that is a high-capacity material, the energy density of the battery can be improved.
  • Examples of the lithium-containing layered nickel composite oxide include those represented by the following formula (1).
  • Li y Ni (1-x) M x O 2 (1) (However, 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1.2, and M is at least one element selected from the group consisting of Co, Al, Mn, Fe, Ti, and B.)
  • the Ni content is high, that is, in the formula (1), x is preferably less than 0.5, and more preferably 0.4 or less.
  • x is preferably less than 0.5, and more preferably 0.4 or less.
  • LiNi 0.8 Co 0.05 Mn 0.15 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2, LiNi 0.8 Co 0.1 Al can be preferably used 0.1 O 2 or the like.
  • the Ni content does not exceed 0.5, that is, in the formula (1), x is 0.5 or more. It is also preferred that the number of specific transition metals does not exceed half.
  • LiNi 0.4 Co 0.3 Mn 0.3 O 2 (abbreviated as NCM433), LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 (abbreviated as NCM523), LiNi 0.5 Co 0.3 Mn 0.2 O 2 (abbreviated as NCM532), etc. (however, the content of each transition metal in these compounds varies by about 10%) Can also be included).
  • NCM532 or NCM523 and NCM433 range from 9: 1 to 1: 9 (typically 2 It is also preferable to use a mixture in 1).
  • the material with high Ni content (x is 0.4 or less) and the material with Ni content not exceeding 0.5 (x is 0.5 or more, for example, NCM433) are mixed. As a result, a battery having a high capacity and high thermal stability can be formed.
  • positive electrode active materials may be used together with the lithium-containing layered nickel composite oxide.
  • positive electrode active materials for example, LiMnO 2 , Li x Mn 2 O 4 (0 ⁇ x ⁇ 2), Li 2 MnO 3 , xLi 2 MnO 3 — (1-x) LiMO 2 (x is 0.
  • M is one or more elements selected from the group consisting of Mn, Fe, Co, Ni, Ti, Al and Mg), Li x Mn 1.5 Ni 0.5 Lithium manganate having a layered structure or spinel structure such as O 4 (0 ⁇ x ⁇ 2); LiCoO 2 or a part of these transition metals replaced with another metal; chemistry in these lithium transition metal oxides Those having an excess of Li rather than the stoichiometric composition; and those having an olivine structure such as LiFePO 4 .
  • any of the positive electrode active materials described above can be used alone or in combination of two or more.
  • the content of the lithium-containing layered nickel composite oxide in the total amount of the positive electrode active material is preferably 50% by weight or more, more preferably 80% by weight or more, and may be 100% by weight.
  • the binder used for the positive electrode is not particularly limited, but polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, polypropylene, Polyethylene, polybutadiene, polyacrylic acid, polyacrylic acid ester, polystyrene, polyacrylonitrile, polyimide, polyamideimide and the like can be used.
  • the binder may be a mixture of a plurality of resins, a copolymer, and a crosslinked product thereof, such as styrene butadiene rubber (SBR). Further, when an aqueous binder such as an SBR emulsion is used, a thickener such as carboxymethyl cellulose (CMC) can also be used.
  • SBR styrene butadiene rubber
  • the amount of the binder in the positive electrode is preferably 1 part by weight or more, more preferably 2 parts by weight or more, and preferably 30 parts by weight or less, more preferably 25 parts by weight or less as the upper limit with respect to 100 parts by weight of the positive electrode active material. It is.
  • the positive electrode current collector is not particularly limited, but aluminum, nickel, silver, or an alloy thereof can be used.
  • Examples of the shape of the positive electrode current collector include a foil, a flat plate, and a mesh.
  • a conductive material may be added for the purpose of reducing the impedance.
  • the conductive material include carbonaceous fine particles such as graphite, carbon black, and acetylene black.
  • the positive electrode according to the present embodiment can be produced by preparing a slurry containing a positive electrode active material, a binder and a solvent, and applying the slurry onto a positive electrode current collector to form a positive electrode active material layer.
  • the negative electrode includes a current collector and a negative electrode active material layer provided on the current collector and including a negative electrode active material, a binder, and a conductive material.
  • a negative electrode active material e.g., composite particles and graphite particles containing silicon oxide and carbon are used as the negative electrode active material, and polyacrylic acid is used as the binder.
  • the negative electrode active material of the present embodiment includes composite particles containing silicon oxide and carbon (hereinafter, this composite particle is also simply referred to as silicon oxide particles).
  • Silicon oxide is not particularly limited, for example, expressed by a composition formula SiO x (0 ⁇ x ⁇ 2 ). Further, the silicon oxide may contain Li, and the silicon oxide containing Li is represented by, for example, SiLi y O z (y> 0, 2>z> 0). Further, the silicon oxide may contain a trace amount of a metal element or a nonmetal element. The silicon oxide can contain, for example, 0.1 to 5% by weight of one or more elements selected from nitrogen, boron and sulfur. By containing a trace amount of a metal element or a non-metal element, the electrical conductivity of the silicon oxide can be improved.
  • the silicon oxide may be crystalline or amorphous.
  • Silicon oxide particles contain carbon together with silicon oxide.
  • the carbon coats the entire surface or part of the periphery of the silicon oxide that is the core of the particle.
  • the carbon film can be formed by, for example, a sputtering method or a vapor deposition method using a carbon source.
  • Examples of the vapor deposition method include an arc vapor deposition method and a chemical vapor deposition method.
  • the chemical vapor deposition method which is chemical vapor deposition is preferable because the vapor deposition temperature and vapor deposition atmosphere can be easily controlled.
  • This chemical vapor deposition method can be performed by using silicon oxide particles in an alumina or quartz boat.
  • the chemical vapor deposition method can be performed in a state where the silicon oxide particles are suspended or transported in the gas.
  • the carbon source used in the chemical vapor deposition method can be used without particular limitation as long as it generates carbon by thermal decomposition, and can be appropriately selected according to the conditions.
  • the carbon source include hydrocarbon compounds such as methane, ethane, ethylene, acetylene, and benzene, organic solvents such as methanol, ethanol, toluene, and xylene, or CO.
  • an inert gas such as argon or nitrogen, or a mixed gas of these and hydrogen can be used.
  • the temperature in the chemical vapor deposition method is, for example, in the range of 400 to 1200 ° C.
  • the amount of carbon in the silicon oxide particles is 2% by weight or more, preferably 3% by weight or more, and more preferably 4.5% by weight or more.
  • the amount of carbon in the silicon oxide particles is preferably 8% by weight or less, more preferably 6% by weight or less.
  • the amount of silicon oxide is preferably 60% by weight or more, more preferably 70% by weight or more, and still more preferably 92% by weight or more.
  • the amount of silicon oxide in the silicon oxide particles is preferably 98% by weight or less, more preferably 95.5% by weight or less.
  • the content of silicon oxide particles in the negative electrode active material layer is preferably 50% by weight or more, more preferably 60% by weight or more, and still more preferably 70% by weight or more. By containing many silicon oxide particles in the negative electrode, the energy density of the battery can be improved.
  • the content of silicon oxide particles in the negative electrode active material layer is preferably 95% by weight or less, more preferably 90% by weight or less.
  • the average particle diameter of the silicon oxide particles is preferably 1 ⁇ m or more, more preferably 3 ⁇ m or more as a lower limit.
  • the upper limit of the average particle diameter of the silicon oxide particles is preferably 10 ⁇ m or less, more preferably 7 ⁇ m or less.
  • the average particle size represents a particle size at an integrated volume of 50%.
  • the average particle diameter can be measured by a laser diffraction / scattering particle size distribution measuring apparatus.
  • the specific surface area of the silicon oxide particles is preferably 1 m 2 / g or more, more preferably 3 m 2 / g or more as a lower limit.
  • the specific surface area of the silicon oxide particles is preferably 20 m 2 / g or less, more preferably 12 m 2 / g or less as the upper limit. Specific surface area can be measured using the BET method with nitrogen adsorption.
  • the negative electrode active material of this embodiment further contains graphite particles.
  • the graphite used in this embodiment may be artificial graphite or natural graphite.
  • Artificial graphite is graphitized in a relatively high temperature range of 2200 ° C. to 3000 ° C. using coal coke, pitch, heavy oil and the like as main raw materials.
  • natural graphite uses natural minerals as the main raw material.
  • Artificial graphite is usually not coated on the surface, while natural graphite is usually coated on the surface with carbon. Since this carbon film has a high irreversible capacity and is easily damaged by the expansion and contraction of silicon oxide, it can cause deterioration.
  • the shape of the graphite particles is not particularly limited, and for example, spherical, lump, scale-like particles can be used.
  • the content of the graphite particles in the negative electrode active material layer is preferably 1% by weight or more, more preferably 5% by weight or more, and still more preferably 10% by weight or more. Content of the graphite particle in a negative electrode active material layer becomes like this. Preferably it is 40 weight% or less, More preferably, it is 25 weight% or less.
  • the average particle diameter of the graphite particles is preferably 5 ⁇ m or more, more preferably 8 ⁇ m or more as a lower limit.
  • the average particle diameter of the graphite particles is preferably 30 ⁇ m or less, more preferably 25 ⁇ m or less as the upper limit.
  • the specific surface area of the graphite particles is preferably 1 m 2 / g or more, more preferably 2 m 2 / g or more as a lower limit.
  • the specific surface area of the graphite particles is preferably 10 m 2 / g or less, more preferably 5 m 2 / g or less as the upper limit. Specific surface area can be measured using the BET method with nitrogen adsorption.
  • the binder of this embodiment includes polyacrylic acid.
  • Polyacrylic acid is a polymer containing monomer units derived from (meth) acrylic acid represented by the following formula (2) or a metal salt thereof.
  • the amount of the monomer unit represented by the formula (2) in the polyacrylic acid is not particularly limited, but is, for example, 50% by weight or more, 70% by weight or more, and may be 100% by weight.
  • (meth) acrylic acid means acrylic acid and methacrylic acid.
  • R 1 is a hydrogen atom or a methyl group.
  • the carboxylic acid in the monomer unit represented by the formula (2) may be a carboxylic acid metal salt.
  • the metal is preferably a monovalent metal.
  • the monovalent metal include alkali metals (for example, Na, Li, K, Rb, Cs, Fr, etc.) and noble metals (for example, Ag, Au, Cu, etc.).
  • alkali metals are preferable.
  • Na, Li, and K are preferable, and Na is most preferable.
  • the adhesion with the constituent material of the negative electrode active material layer may be further improved.
  • Polyacrylic acid may contain other monomer units.
  • the polyacrylic acid further includes a monomer unit other than (meth) acrylic acid, the peel strength between the negative electrode active material layer and the current collector may be improved.
  • monomer units include monocarboxylic acid compounds such as crotonic acid and pentenoic acid, dicarboxylic acid compounds such as itaconic acid and maleic acid, sulfonic acid compounds such as vinyl sulfonic acid, and phosphonic acids such as vinyl phosphonic acid.
  • Acids having an ethylenically unsaturated group such as compounds; aromatic olefins having acidic groups such as styrene sulfonic acid and styrene carboxylic acid; (meth) acrylic acid alkyl esters; acrylonitrile; aliphatic olefins such as ethylene, propylene and butadiene; Examples include monomer units derived from monomers such as aromatic olefins such as styrene.
  • the other monomer unit may be a monomer unit constituting a known polymer used as a binder for a secondary battery. In these monomer units, if present, the acid may be a salt.
  • At least one hydrogen atom in the main chain and the side chain may be substituted with halogen (fluorine, chlorine, boron, iodine, etc.) or the like.
  • the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer. Any of a polymer etc. and these combinations may be sufficient.
  • the content of polyacrylic acid in the negative electrode active material layer is preferably 1% by weight or more, more preferably 2% by weight or more, and further preferably 3% by weight or more.
  • the content of polyacrylic acid in the negative electrode active material layer is preferably 8% by weight or less, more preferably 7% by weight or less.
  • the negative electrode active material layer includes a conductive material in order to suppress an increase in resistance due to polyacrylic acid.
  • the conductive material used in the present embodiment has a specific surface area of 40 to 800 m 2 / g.
  • the specific surface area of the conductive material is 50 to 600 m 2 / g. Specific surface area can be measured using the BET method with nitrogen adsorption.
  • a conductive material having such a specific surface area can be present on the surface of silicon oxide particles or graphite particles, which are active materials, by polyacrylic acid used as a binder, thereby forming many conductive paths between the active materials. it can. Therefore, battery resistance can be reduced.
  • the surface of the negative electrode active material particles can be confirmed by an electron microscope such as SEM (scanning electron microscope). Observe the particle surface with an electron microscope image, and consider the ratio (%) of the area where the conductive material is attached to the confirmed particle area as the coverage of the conductive material on the active material particle surface. Can do.
  • the coverage of the conductive material on the surface of the silicon oxide particles is preferably 30% or more, more preferably 50% or more, and may be 100% in terms of the number average of the particles. .
  • Examples of the conductive material having such a specific surface area include carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotube, and carbon nanohorn.
  • Carbon black is carbon fine particles produced by thermal decomposition of hydrocarbons.
  • a plurality of primary particles form a structure.
  • the average primary particle diameter of carbon black is preferably 20 nm or more and 80 nm or less.
  • the specific surface area of carbon black is preferably 40 m 2 / g or more and 80 m 2 / g or less.
  • the amount of carbon black in the negative electrode active material layer is preferably 1% by weight or more and 10% by weight or less.
  • Acetylene black is a kind of carbon black and can be produced by pyrolyzing acetylene.
  • Ketjen black is a kind of carbon black and has high conductivity.
  • the carbon nanotube may be any carbon nanotube having a single-layer or coaxial multilayer structure in which a planar graphene sheet having a six-membered ring of carbon is formed in a cylindrical shape, but is preferably a multilayer. Further, both ends of the cylindrical carbon nanotube may be open, but are preferably closed with a hemispherical fullerene containing a carbon 5-membered ring or 7-membered ring.
  • the diameter of the outermost cylinder of the carbon nanotube is preferably 10 nm or more and 30 nm or less.
  • the specific surface area of the carbon nanotube is preferably 100 m 2 / g or more and 200 m 2 / g or less.
  • the amount of carbon nanotubes in the negative electrode active material layer is preferably 1% by weight or more and 6% by weight or less.
  • a single carbon nanohorn has a shape in which a single graphene sheet is rounded into a cylindrical shape, and the tip of the carbon nanohorn has a conical shape with a tip angle of about 20 °.
  • the carbon nanohorn preferably has a diameter of 80 nm to 160 nm. Further, it is preferable that the specific surface area of the carbon nanohorn or less 200 meters 2 / g or more 400m 2 / g.
  • the amount of carbon nanohorn in the negative electrode active material layer is preferably 1% by weight or more and 6% by weight or less.
  • FIG. 3 shows impedance characteristics of a battery using polyacrylic acid or SBR / CMC and various conductive materials in the negative electrode. It can be seen from FIG. 3 that a battery using no conductive material or a battery using plate-like graphite having a specific surface area of 20 m 2 / g as the negative electrode has a large electronic resistance (Rsol) and charge transfer resistance (Rct). A battery using carbon black, carbon nanotube, or carbon nanohorn having a specific surface area of 40 to 800 m 2 / g has a small Rsol and Rct. It is considered that appropriate conductive paths are formed between these active materials and between the active materials and the current collector foil.
  • Rsol electronic resistance
  • Rct charge transfer resistance
  • the content of the conductive material in the negative electrode active material layer is preferably 1% by weight or more, more preferably 3% by weight or more.
  • the content of the conductive material in the negative electrode active material layer is preferably 10% by weight or less, more preferably 6% by weight or less.
  • the total amount of polyacrylic acid and the conductive material is 13% by weight or less, preferably 10% by weight or less of the negative electrode active material layer. It is. In order to improve the cycle characteristics, the total amount of polyacrylic acid and the conductive material is 4% by weight or more, preferably 5% by weight or more of the negative electrode active material layer.
  • the weight ratio of the conductive material to the polyacrylic acid is preferably 0.12 or more and 2 or less, more preferably 0.3 or more and 1.8 or less, and further preferably 1 or more and 1.7. It is as follows. By controlling the weight ratio of the conductive material to the polyacrylic acid, the cycle characteristics can be further improved.
  • the negative electrode current collector aluminum, nickel, stainless steel, chromium, copper, silver, and alloys thereof can be used because of electrochemical stability.
  • Examples of the shape include foil, flat plate, and mesh.
  • the copper alloy preferably contains one or more elements selected from the group consisting of Zn, Sn, and In in an amount of 0.01 to 1.0% by weight.
  • the thickness of the current collector is not particularly limited, but is preferably 1 to 15 ⁇ m, more preferably 4 to 8 ⁇ m. In these ranges of thicknesses, the current collector can have adequate strength against silicon oxide expansion and contraction.
  • the electrode density is 1.35 g / cm 3 , for example, 10 ⁇ 5 ⁇ ⁇ cm 2 or more and 10 ⁇ 2 ⁇ ⁇ cm 2 or less, or 10 ⁇ 4 ⁇ ⁇ cm 2.
  • the electrode resistance (also referred to as interface resistance) at the negative electrode / electrolyte interface can be reduced within the range of 10 ⁇ 3 ⁇ ⁇ cm 2 or less.
  • this electrode resistance value is particularly small, it is effective to use a positive electrode, electrolyte, separator, etc. to produce a cell and measure the negative electrode itself instead of measuring the AC impedance. The inventor found out.
  • the effect of the conductive material and polyacrylic acid can also be confirmed when measured by the AC impedance method as a cell, but in order to show that the effect of the present invention is remarkable, the influence of the positive electrode, the electrolyte, and the separator Therefore, the value calculated from the electrode resistance measuring instrument was used as the interface resistance value of the negative electrode of the present invention.
  • an electrode resistance measuring device capable of measuring a low resistance value.
  • Step 1 Consider the electrode sheet as a three-layer resistor and assume a three-dimensional resistance matrix model.
  • Step 2 A constant current is passed through the electrode surface, and 100 potentials generated on the surface are measured.
  • Step 3 Current is passed through the three-dimensional resistance matrix model assumed in Step 1 to calculate the potential.
  • Step 4 The measured potential is compared with the computer-simulated potential, and if it matches, the process ends.
  • the value of the three-dimensional resistance matrix model is updated in a timely manner and the recalculation is repeated. That is, while updating the resistance of the electrode layer and the interface resistance in a timely manner, the interface resistance can be obtained by calculating until the measured potential and the potential simulated by the computer match.
  • the negative electrode according to the present embodiment can be produced by preparing a slurry containing a negative electrode active material, a conductive material, polyacrylic acid and a solvent, and applying this to a negative electrode current collector to form a negative electrode active material layer.
  • the negative electrode can be prepared as follows. First, a negative electrode active material such as silicon oxide particles and graphite particles, polyacrylic acid, and a conductive material are dispersed and kneaded in a solvent in a predetermined blending amount to prepare a negative electrode slurry.
  • the solvent is preferably water.
  • the negative electrode can be produced by coating this negative electrode slurry on a negative electrode current collector and drying it.
  • the obtained negative electrode can adjust an electrode density by compressing a negative electrode active material layer by methods, such as a roll press.
  • the electrode density is preferably in the range of 1.0 g / cm 3 or more and 2.0 g / cm 3 or less.
  • the electrode density is 1.0 g / cm 3 or more, the charge / discharge capacity tends to be good.
  • the electrode density is 2.0 g / cm 3 or less, it is easy to impregnate the electrolytic solution, and the charge / discharge capacity tends to be good.
  • polyacrylic acid may be attached to the conductive material in advance, and then the negative electrode active material and the conductive material may be bound.
  • the negative electrode can be prepared as follows. First, polyacrylic acid and a conductive material are mixed in a solvent to attach polyacrylic acid to the conductive material.
  • the solvent is preferably water.
  • negative electrode active materials such as silicon oxide particles and graphite particles are further added to the mixture to prepare a negative electrode slurry.
  • the negative electrode can be produced by coating this negative electrode slurry on a negative electrode current collector and drying it.
  • the conductive material can be bound to the surface of the negative electrode active material particles such as silicon oxide particles with a higher coverage such as 70% or more or 80% or more.
  • the electrolytic solution includes a nonaqueous solvent and a supporting salt.
  • a nonaqueous solvent For example, Cyclic carbonates, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC); Dimethyl carbonate (DMC), Diethyl carbonate (DEC) ), Chain carbonates such as ethyl methyl carbonate (MEC), dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as propylene carbonate derivatives, methyl formate, methyl acetate, ethyl propionate; diethyl ether, ethyl propyl ether Aprotic organic solvents such as ethers such as trimethyl phosphate, triethyl phosphate, tripropyl phosphate, trioctyl phosphate, and triphenyl phosphate, and the number of hydrogen atoms in these compounds
  • Some fluorinated aprotic organic solvent such as propylene carbonate (PC),
  • cyclic such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), dipropyl carbonate (DPC), etc.
  • chain carbonates are included.
  • Non-aqueous solvents can be used alone or in combination of two or more.
  • the supporting salt is not particularly limited except that it contains Li.
  • the supporting salt include LiPF 6 , LiAsF 6 , LiAlCl 4 , LiClO 4 , LiBF 4 , LiSbF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC (CF 3 SO 2 ) 3 , LiN (FSO 2). ) 2 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiB 10 Cl 10 and the like.
  • Other examples of the supporting salt include lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, and the like.
  • a support salt can be used individually by 1 type or in combination of 2 or more types.
  • the concentration of the supporting salt in the electrolytic solution is preferably 0.5 to 1.5 mol / L. By setting the concentration of the supporting salt within this range, it becomes easy to adjust the density, viscosity, electrical conductivity, and the like to an appropriate range.
  • the electrolytic solution can further contain an additive.
  • an additive A halogenated cyclic carbonate, an unsaturated cyclic carbonate, cyclic
  • Any separator may be used as long as it suppresses the conduction between the positive electrode and the negative electrode without impeding the permeation of the charged body and has durability against the electrolytic solution.
  • Specific materials include polyolefins such as polypropylene and polyethylene, polyesters such as cellulose, polyethylene terephthalate and polybutylene terephthalate, polyimide, polyvinylidene fluoride, polymetaphenylene isophthalamide, polyparaphenylene terephthalamide and copolyparaphenylene-3, Aromatic polyamide (aramid) such as 4′-oxydiphenylene terephthalamide can be used. These can be used as porous films, woven fabrics, non-woven fabrics and the like.
  • An insulating layer may be formed on at least one surface of the positive electrode, the negative electrode, and the separator.
  • Examples of the method for forming the insulating layer include a doctor blade method, a dip coating method, a die coater method, a CVD method, and a sputtering method.
  • An insulating layer can be formed simultaneously with the formation of the positive electrode, the negative electrode, and the separator.
  • Examples of the material constituting the insulating layer include a mixture of an insulating filler such as aluminum oxide or barium titanate and a binder such as SBR or PVDF.
  • the lithium ion secondary battery of this embodiment has a structure as shown in FIGS. 1 and 2, for example.
  • This lithium ion secondary battery includes a battery element 20, a film outer package 10 that accommodates the battery element 20 together with an electrolyte, and a positive electrode tab 51 and a negative electrode tab 52 (hereinafter also referred to simply as “electrode tabs”). ing.
  • the battery element 20 is formed by alternately stacking a plurality of positive electrodes 30 and a plurality of negative electrodes 40 with a separator 25 interposed therebetween.
  • the electrode material 32 is applied to both surfaces of the metal foil 31.
  • the electrode material 42 is applied to both surfaces of the metal foil 41. Note that the present embodiment is not necessarily limited to a stacked battery, and can also be applied to a wound battery.
  • the lithium ion secondary battery may have a configuration in which the electrode tab is drawn out on one side of the outer package as shown in FIGS. 1 and 2, but the lithium ion secondary battery has the electrode tab pulled out on both sides of the outer package. It can be a thing. Although detailed illustration is omitted, each of the positive and negative metal foils has an extension on a part of the outer periphery. The extensions of the negative electrode metal foil are collected together and connected to the negative electrode tab 52, and the extensions of the positive electrode metal foil are collected together and connected to the positive electrode tab 51 (see FIG. 2). The portions gathered together in the stacking direction between the extension portions in this way are also called “current collecting portions”.
  • the film outer package 10 is composed of two films 10-1 and 10-2 in this example.
  • the films 10-1 and 10-2 are heat sealed to each other at the periphery of the battery element 20 and sealed.
  • the positive electrode tab 51 and the negative electrode tab 52 are drawn in the same direction from one short side of the film outer package 10 sealed in this way.
  • FIGS. 1 and 2 show examples in which the cup portion is formed on one film 10-1 and the cup portion is not formed on the other film 10-2.
  • a configuration in which a cup portion is formed on both films (not shown) or a configuration in which neither cup portion is formed (not shown) may be employed.
  • the lithium ion secondary battery of this embodiment has a high energy density.
  • the lithium ion secondary battery of the present embodiment can have a high volume energy density such as 540 Wh / L or more and 660 Wh / L or less, 600 Wh / or more and 660 Wh / L or less.
  • the lithium ion secondary battery according to the present embodiment can be produced according to a normal method. Taking a laminated laminate type lithium ion secondary battery as an example, an example of a method for producing a lithium ion secondary battery will be described. First, in a dry air or an inert atmosphere, an electrode element is formed by arranging a positive electrode and a negative electrode to face each other with a separator interposed therebetween. Next, this electrode element is accommodated in an exterior body (container), and an electrolytic solution is injected to impregnate the electrode with the electrolytic solution. Then, the opening part of an exterior body is sealed and a lithium ion secondary battery is completed.
  • a plurality of lithium ion secondary batteries according to this embodiment can be combined to form an assembled battery.
  • the assembled battery may have a configuration in which two or more lithium ion secondary batteries according to the present embodiment are used and connected in series, in parallel, or both. Capacitance and voltage can be freely adjusted by connecting in series and / or in parallel. About the number of the lithium ion secondary batteries with which an assembled battery is provided, it can set suitably according to battery capacity or an output.
  • the lithium ion secondary battery or its assembled battery according to this embodiment can be used in a vehicle.
  • Vehicles according to this embodiment include hybrid vehicles, fuel cell vehicles, and electric vehicles (all include four-wheel vehicles (passenger cars, trucks, buses and other commercial vehicles, light vehicles, etc.), motorcycles (motorcycles), and tricycles. ).
  • vehicle according to the present embodiment is not limited to an automobile, and may be used as various power sources for other vehicles, for example, moving bodies such as trains.
  • ⁇ Negative electrode conductive material carbon black (specific surface area: 45 m 2 / g)> [Example 1] (Production of battery) LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture.
  • a positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 ⁇ m thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
  • Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 ⁇ m as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 ⁇ m was used.
  • Carbon coated SiO particles, artificial graphite particles, carbon black having a BET specific surface area of 45 m 2 / g and an average particle size (primary particles) of 0.045 ⁇ m are dispersed in a mixed solution of polyacrylic acid and water as a binder.
  • the weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 1.
  • the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20.
  • This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 ⁇ m. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
  • the resistance measuring device used was a model XF-057 probe unit manufactured by Hioki Electric. With respect to each negative electrode, the thickness of the active material layer and the thickness of the current collector foil were input, and the probe of the resistance measuring device was pressed to obtain the interface resistance value of each negative electrode.
  • the positive electrode and the negative electrode cut out to 3 cm ⁇ 3 cm were arranged so as to face each other with a separator interposed therebetween.
  • a PET nonwoven fabric with a thickness of 15 ⁇ m was used as the separator.
  • the electrolytic solution was prepared by mixing a solvent and a supporting salt.
  • a solvent ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
  • the above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced.
  • the positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
  • the battery volume (L) was calculated from the basis weight and density of the electrode, the thickness of the current collector, and the thickness of the separator. Energy from specific capacity (mAh / g) of each cell, actual value (%) of aging efficiency when each cell is aged at 45 ° C. for 20 days, and actual value (V) of average operating voltage after aging of each cell The capacity (Wh) was calculated. The value obtained by dividing the energy capacity by the battery volume was defined as the volume energy density (Wh / L). As the aging efficiency, the value of the recovery capacity (mAh) after 45 days at 45 ° C. with respect to the initial charge capacity (mAh) was used.
  • ⁇ Negative electrode conductive material carbon black (specific surface area: 65 m 2 / g)> [Example 9] LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture.
  • a positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 ⁇ m thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
  • Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 ⁇ m as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 ⁇ m was used.
  • Carbon coated SiO particles, artificial graphite particles, carbon black having a BET specific surface area of 65 m 2 / g and an average particle size (primary particles) of 0.065 ⁇ m are dispersed in a mixed solution of polyacrylic acid and water as a binder.
  • the weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 2.
  • the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20.
  • This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 ⁇ m. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
  • the interface resistance was evaluated in the same manner as in Example 1.
  • the positive electrode and the negative electrode cut out to 3 cm ⁇ 3 cm were arranged so as to face each other with a separator interposed therebetween.
  • a PET nonwoven fabric with a thickness of 15 ⁇ m was used as the separator.
  • the electrolytic solution was prepared by mixing a solvent and a supporting salt.
  • a solvent ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
  • the above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced.
  • the positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
  • ⁇ Negative electrode conductive material carbon nanotube (specific surface area: 150 m 2 / g)> [Example 15] LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture.
  • a positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 ⁇ m thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
  • Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 ⁇ m as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 ⁇ m was used.
  • Carbon-coated SiO particles, artificial graphite particles, carbon nanotubes having a specific surface area of 150 m 2 / g and an average particle diameter of 0.02 ⁇ m are dispersed in a mixed solution of polyacrylic acid and water as a binder, and a negative electrode slurry is prepared.
  • the weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 3.
  • the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20.
  • This negative electrode slurry was uniformly applied onto a current collector made of high strength Cu alloy foil having a thickness of 8 ⁇ m. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
  • the interface resistance was evaluated in the same manner as in Example 1.
  • the positive electrode and the negative electrode cut out to 3 cm ⁇ 3 cm were arranged so as to face each other with a separator interposed therebetween.
  • a PET nonwoven fabric with a thickness of 15 ⁇ m was used as the separator.
  • the electrolytic solution was prepared by mixing a solvent and a supporting salt.
  • a solvent ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
  • the above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced.
  • the positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
  • Example 19 The negative electrode produced in Example 19 was observed by SEM before charge / discharge.
  • the SEM image is shown in FIG. From the SEM image, it can be seen that the surface of silicon oxide particles of about 60 to 70% is covered with carbon nanotubes.
  • ⁇ Negative electrode conductive material carbon nanohorn (specific surface area: 300 m 2 / g)>
  • LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture.
  • a positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 ⁇ m thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
  • Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 ⁇ m as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 ⁇ m was used.
  • Carbon-coated SiO particles, artificial graphite particles, carbon nanohorns having a specific surface area of 300 m 2 / g and an average particle size of 0.15 ⁇ m are dispersed in a mixed solution of polyacrylic acid and water as a binder, and a negative electrode slurry is prepared.
  • the weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 4.
  • the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20.
  • This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 ⁇ m. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
  • the interface resistance was evaluated in the same manner as in Example 1.
  • the positive electrode and the negative electrode cut out to 3 cm ⁇ 3 cm were arranged so as to face each other with a separator interposed therebetween.
  • a PET nonwoven fabric with a thickness of 15 ⁇ m was used as the separator.
  • the electrolytic solution was prepared by mixing a solvent and a supporting salt.
  • a solvent ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
  • the above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced.
  • the positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
  • Example 26 The negative electrode produced in Example 26 was observed by SEM before charge / discharge.
  • the SEM image is shown in FIG. From the SEM image, it can be seen that the surface of silicon oxide particles of about 50 to 60% is covered with carbon nanohorns.
  • ⁇ Negative electrode conductive material Ketjen black (specific surface area: 800 m 2 / g)> [Example 29] LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture.
  • a positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 ⁇ m thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
  • Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 ⁇ m as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 ⁇ m was used.
  • Disperse Ketjen Black having carbon-coated SiO particles, artificial graphite particles, a specific surface area of 800 m 2 / g and an average particle size (primary particles) of 0.04 ⁇ m in a mixed solution of polyacrylic acid and water as a binder.
  • the weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 5.
  • the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20.
  • This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 ⁇ m. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
  • the interface resistance was evaluated in the same manner as in Example 1.
  • the positive electrode and the negative electrode cut out to 3 cm ⁇ 3 cm were arranged so as to face each other with a separator interposed therebetween.
  • a PET nonwoven fabric with a thickness of 15 ⁇ m was used as the separator.
  • the electrolytic solution was prepared by mixing a solvent and a supporting salt.
  • a solvent ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
  • the above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced.
  • the positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
  • ⁇ Negative electrode conductive material plate-like graphite (specific surface area 17 m 2 / g)>
  • LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture.
  • a positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 ⁇ m thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
  • Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 ⁇ m as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 ⁇ m was used.
  • Carbon-coated SiO particles, artificial graphite particles, plate graphite having a specific surface area of 17 m 2 / g and an average particle diameter of 10 ⁇ m are dispersed in a mixed solution of polyacrylic acid and water as a binder to produce a negative electrode slurry.
  • the weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 6.
  • the weight ratio of the carbon-coated SiO particles that are the negative electrode active material and the graphite particles is 80:20.
  • This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 ⁇ m. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
  • the interface resistance was evaluated in the same manner as in Example 1.
  • the positive electrode and the negative electrode cut out to 3 cm ⁇ 3 cm were arranged so as to face each other with a separator interposed therebetween.
  • a PET nonwoven fabric with a thickness of 15 ⁇ m was used as the separator.
  • the electrolytic solution was prepared by mixing a solvent and a supporting salt.
  • a solvent ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
  • the above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced.
  • the positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
  • ⁇ Negative electrode conductive material Ketjen black (specific surface area: 1270 m 2 / g)>
  • LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture.
  • a positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 ⁇ m thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
  • Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 ⁇ m as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 ⁇ m was used.
  • Disperse Ketjen Black having carbon-coated SiO particles, artificial graphite particles, a specific surface area of 1270 m 2 / g and an average particle size (primary particles) of 0.035 ⁇ m in a mixed solution of polyacrylic acid and water as a binder.
  • the weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 7.
  • the weight ratio of the carbon-coated SiO particles that are the negative electrode active material and the graphite particles is 80:20.
  • This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 ⁇ m. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
  • the interface resistance was evaluated in the same manner as in Example 1.
  • the positive electrode and the negative electrode cut out to 3 cm ⁇ 3 cm were arranged so as to face each other with a separator interposed therebetween.
  • a PET nonwoven fabric with a thickness of 15 ⁇ m was used as the separator.
  • the electrolytic solution was prepared by mixing a solvent and a supporting salt.
  • a solvent ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
  • the above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced.
  • the positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
  • Example 24 in which the above-described carbon nanohorn was used as the conductive material, a current collector foil made of high strength Cu alloy having a thickness of 8 ⁇ m was used for the negative electrode current collector, but as described in Table 8 below, the stainless steel foil was used. Or changed to electrolytic copper foil. Otherwise, a battery was fabricated in the same manner as in Example 24. Table 8 shows the evaluation results of the fabricated batteries.
  • the capacity deterioration was so large that the capacity retention rate could not be maintained up to 300 cycles.
  • the strength of the electrolytic copper foil is low, and it was suggested that the copper foil cannot withstand the expansion and contraction of SiO present at a high content.
  • the interfacial resistance was higher than that of the high-strength Cu alloy foil, but the capacity retention rate was the same as that of the high-strength Cu alloy foil.
  • the negative electrode produced in Examples 37 and 38 was observed by SEM before charge and discharge. From the SEM image, it was found that about 80% of the silicon oxide particles were coated with carbon nanohorns. It is thought that the coverage of the conductive material on the silicon oxide particles was increased by attaching polyacrylic acid to the carbon nanohorn in advance. As a result, compared with Examples 24 and 26 having the same design specifications, the interface resistance was lowered, the cycle characteristics were increased, and the volume energy density was also high.
  • the conductive material has a specific surface area of 40 to 800 m 2 / g, and in the negative electrode active material layer, the amount of the composite particles is 50% by weight or more, and the polyacrylic acid
  • the amount of the conductive material is 1% by weight or more, the total amount of the conductive material and the polyacrylic acid is 13% by weight or less, and in the composite particle,
  • (Appendix 2) The lithium ion secondary battery according to appendix 1, wherein a weight ratio of the conductive material to the polyacrylic acid is 0.12 or more and 2 or less.
  • (Appendix 3) The lithium ion secondary battery according to appendix 1 or 2, wherein the graphite particles are artificial graphite.
  • (Appendix 4) The graphite particles, the lithium ion secondary battery according to any one of appendices 1 to 3 having the following specific surface area average particle diameter and 2m 2 / g or more 8 ⁇ m above 25 ⁇ m or less 5 m 2 / g.
  • (Appendix 5) The lithium ion secondary battery according to any one of supplementary notes 1 to 4, wherein the composite particles have an average particle diameter of 3 ⁇ m to 7 ⁇ m and a specific surface area of 3 m 2 / g to 12 m 2 / g.
  • (Appendix 6) The lithium ion secondary battery according to any one of appendices 1 to 5, wherein the amount of the silicon oxide in the composite particles is 70% by weight or more.
  • (Appendix 7) The lithium ion secondary battery according to any one of appendices 1 to 6, wherein the conductive material covers 70% or more of the surface of the composite particle.
  • (Appendix 10) The lithium ion secondary battery according to any one of supplementary notes 1 to 9, wherein the negative electrode has an interface resistance of 10 ⁇ 5 ⁇ ⁇ cm 2 or more and 10 ⁇ 2 ⁇ ⁇ cm 2 or less.
  • (Appendix 11) The lithium ion secondary battery according to any one of supplementary notes 1 to 10, wherein the volume energy density is 540 Wh / L or more and 660 Wh / L or less.
  • (Appendix 12) A vehicle equipped with the lithium ion secondary battery according to any one of appendices 1 to 11.
  • a negative electrode slurry prepared by mixing a conductive material having a specific surface area of 40 to 800 m 2 / g, silicon oxide and carbon, and composite particles and graphite particles containing 2% by weight or more of carbon, and polyacrylic acid in a solvent.
  • the negative electrode slurry is applied to a current collector, the amount of the composite particles is 50% by weight or more, the amount of the polyacrylic acid is 3% by weight or more and 8% by weight or less, and the conductive And a step of forming a negative electrode active material layer in which the total amount of the material and the polyacrylic acid is 4% by weight or more and 13% by weight or less.
  • the lithium ion secondary battery according to the present invention can be used in, for example, all industrial fields that require a power source and industrial fields related to transport, storage, and supply of electrical energy.
  • power sources for mobile devices such as mobile phones and laptop computers
  • power sources for mobile vehicles such as electric vehicles, hybrid cars, electric motorcycles, electric assist bicycles, electric vehicles, trains, satellites, submarines, etc .
  • It can be used for backup power sources such as UPS; power storage facilities for storing power generated by solar power generation, wind power generation, etc.

Abstract

This lithium-ion secondary cell includes a positive electrode provided with: a positive electrode active material layer containing a lithium-containing layered nickel composite oxide; and a negative electrode provided with a negative electrode active material layer containing polyacrylic acid, an electroconductive member, graphite particles, and composite particles containing carbon and a silicon oxide, wherein the lithium-ion secondary cell is characterized in that: the electroconductive member has a specific surface area of 40-800 m2/g; the negative electrode active material layer has a composite particle content of at least 50 wt%, a polyacrylic acid content of 3-8 wt%, and a total electroconductive member/polyacrylic acid content of 4-13 wt%; and the composite particles have a carbon content of at least 2 wt%.

Description

高エネルギー密度セル用負極を備えたリチウムイオン二次電池Lithium ion secondary battery with negative electrode for high energy density cell
　本発明は、リチウムイオン二次電池、リチウムイオン二次電池の製造方法、およびリチウムイオン二次電池を搭載した車両に関する。 The present invention relates to a lithium ion secondary battery, a method of manufacturing a lithium ion secondary battery, and a vehicle equipped with the lithium ion secondary battery.
　リチウムイオン二次電池の負極には炭素系材料を使用するのが一般的であるが、電池の高エネルギー密度化のために、単位体積当たりのリチウムイオンの吸蔵放出量が大きいケイ素酸化物を負極に使用することが検討されている。しかしながら、ケイ素酸化物は、高容量を与える一方で、リチウムイオンが吸蔵放出される際の活物質の膨張収縮が大きいために、導電パスの切断や活物質粒子の剥落などによりサイクル特性が低下する。このため、ケイ素酸化物は、負極活物質層中の比率が少なくなるように、黒鉛などの他の負極活物質と混合して使用されることが一般的であった。特許文献１には、ＳｉＯｘ（０．３≦ｘ≦１．６）で表されるケイ素酸化物と、黒鉛とを含むリチウムイオン二次電池が記載されている。 Generally, a carbon-based material is used for the negative electrode of a lithium ion secondary battery, but in order to increase the energy density of the battery, a silicon oxide having a large amount of occlusion / release of lithium ions per unit volume is used as the negative electrode. It is being considered for use. However, while silicon oxide provides a high capacity, the expansion and contraction of the active material when lithium ions are occluded and released are large, so that the cycle characteristics are degraded due to cutting of the conductive path or peeling of the active material particles. . For this reason, the silicon oxide is generally used by being mixed with another negative electrode active material such as graphite so that the ratio in the negative electrode active material layer is reduced. Patent Document 1 describes a lithium ion secondary battery containing silicon oxide represented by SiO x (0.3 ≦ x ≦ 1.6) and graphite.
特開２０１３－１０１９２０号公報JP 2013-101920 A
　近年では、電子機器の高性能化や、電気自動車等へのリチウムイオン二次電池の利用が進み、エネルギー密度のさらなる改善が強く望まれている。これに対して、特許文献１に記載のリチウムイオン二次電池は、ケイ素酸化物の含有量が黒鉛に対して低いため、エネルギー密度に改善の余地があった。負極活物質層中のケイ素酸化物の混合比率をさらに上げることが望まれている。ケイ素酸化物の混合比率が高い場合、ケイ素酸化物の大きな膨張収縮による負極活物質層の劣化を防止するため、結着力の高いバインダを選択することがより重要となってくる。 In recent years, there has been a strong demand for further improvements in energy density as the performance of electronic devices has increased and the use of lithium ion secondary batteries in electric vehicles has progressed. On the other hand, the lithium ion secondary battery described in Patent Document 1 has room for improvement in energy density because the silicon oxide content is lower than that of graphite. It is desired to further increase the mixing ratio of silicon oxide in the negative electrode active material layer. When the mixing ratio of the silicon oxide is high, it becomes more important to select a binder having a high binding force in order to prevent the deterioration of the negative electrode active material layer due to the large expansion and contraction of the silicon oxide.
　ポリイミドは結着力が高いため、ケイ素酸化物の含有比率が高い負極のバインダとして一般的に用いられている。しかしながら、ポリイミドでは、Ｎ－メチルピロリドン（ＮＭＰ）など、環境負荷の高い有機溶剤が使用されるが、近年では環境調和や産業上の利用性の点から、水系バインダが求められている。また、ポリイミドは、イミド化するために高い温度での熱処理が必要である点やプレスにより負極を高密度化したときに良好なサイクル特性が得られない点も課題である。 Since polyimide has a high binding force, it is generally used as a binder for a negative electrode having a high silicon oxide content ratio. However, in polyimide, an organic solvent having a high environmental load such as N-methylpyrrolidone (NMP) is used. In recent years, an aqueous binder is required from the viewpoint of environmental harmony and industrial applicability. In addition, polyimide also has a problem that heat treatment at a high temperature is required for imidization and that good cycle characteristics cannot be obtained when the negative electrode is densified by pressing.
　水系バインダとしてスチレンブタジエンゴム（ＳＢＲ）などゴム系バインダやポリアクリル酸が知られている。ゴム系バインダは、ケイ素酸化物の混合比率が５～７重量％程度までは使用できる。しかしながら、よりケイ素酸化物の混合比率を上げる場合には、結着性が低いために、膨張収縮による電池の容量劣化が大きくなり、適さない。ポリアクリル酸は、ゴム系バインダに比べて結着力が高いので容量劣化が少ない。しかしながら、ポリアクリル酸は、ポリイミドよりは結着力が劣るため、サイクル特性が依然として不十分であった。また、ポリアクリル酸を使用した電池は、抵抗が高いとういう問題点もあった。 As the water-based binder, rubber-based binders such as styrene butadiene rubber (SBR) and polyacrylic acid are known. The rubber binder can be used up to a silicon oxide mixing ratio of about 5 to 7% by weight. However, when the mixing ratio of the silicon oxide is further increased, since the binding property is low, the capacity deterioration of the battery due to expansion and contraction increases, which is not suitable. Since polyacrylic acid has a higher binding force than rubber-based binders, there is little capacity deterioration. However, since polyacrylic acid has a lower binding force than polyimide, the cycle characteristics are still insufficient. In addition, a battery using polyacrylic acid has a problem of high resistance.
　本発明の目的は、上述した課題を鑑み、水系バインダであるポリアクリル酸を使用するリチウムイオン二次電池であって、高いエネルギー密度および改善されたサイクル特性を有するリチウムイオン二次電池を提供することにある。 In view of the above-described problems, an object of the present invention is to provide a lithium ion secondary battery that uses polyacrylic acid that is an aqueous binder and has a high energy density and improved cycle characteristics. There is.
　本発明の第１のリチウムイオン二次電池は、リチウム含有層状ニッケル複合酸化物を含む正極活物質層を備える正極と、ケイ素酸化物および炭素を含む複合粒子、黒鉛粒子、導電材、およびポリアクリル酸を含む負極活物質層を備える負極を含むリチウムイオン二次電池であって、前記導電材が４０～８００ｍ２／ｇの比表面積を有し、前記負極活物質層において、前記複合粒子の量が５０重量％以上であり、前記ポリアクリル酸の量が３重量％以上８重量％以下であり、前記導電材と前記ポリアクリル酸の総量が４重量％以上１３重量％以下であり、前記複合粒子において、前記炭素の量が２重量％以上であることを特徴とする。 A first lithium ion secondary battery of the present invention includes a positive electrode including a positive electrode active material layer including a lithium-containing layered nickel composite oxide, composite particles including silicon oxide and carbon, graphite particles, a conductive material, and polyacryl A lithium ion secondary battery including a negative electrode including a negative electrode active material layer including an acid, wherein the conductive material has a specific surface area of 40 to 800 m 2 / g, and the amount of the composite particles in the negative electrode active material layer Is 50% by weight or more, the amount of the polyacrylic acid is 3% by weight or more and 8% by weight or less, the total amount of the conductive material and the polyacrylic acid is 4% by weight or more and 13% by weight or less, and the composite In the particles, the amount of carbon is 2% by weight or more.
　本発明の一実施形態によれば、ポリアクリル酸を使用するリチウムイオン二次電池であって、高いエネルギー密度および改善されたサイクル特性を有するリチウムイオン二次電池を提供できる。 According to an embodiment of the present invention, a lithium ion secondary battery using polyacrylic acid, which has a high energy density and improved cycle characteristics, can be provided.
フィルム外装電池の基本的構造を示す分解斜視図である。It is a disassembled perspective view which shows the basic structure of a film-clad battery. 図１の電池の断面を模式的に示す断面図である。It is sectional drawing which shows the cross section of the battery of FIG. 1 typically. 負極においてポリアクリル酸またはＳＢＲ／ＣＭＣと、各種の導電材とを使用した電池のインピーダンスプロットである。It is an impedance plot of a battery using polyacrylic acid or SBR / CMC and various conductive materials in the negative electrode. カーボンナノチューブを使用する負極のＳＥＭ画像である。It is a SEM image of the negative electrode which uses a carbon nanotube. カーボンナノホーンを使用する負極のＳＥＭ画像である。It is a SEM image of the negative electrode which uses carbon nanohorn.
　以下、本実施形態のリチウムイオン二次電池の一例を構成要素ごとに説明する。 Hereinafter, an example of the lithium ion secondary battery of the present embodiment will be described for each component.
　［正極］
　正極は、集電体と、集電体上に設けられた、正極活物質、バインダおよび必要に応じ導電材を含む正極活物質層とを備える。 [Positive electrode]
The positive electrode includes a current collector and a positive electrode active material layer that is provided on the current collector and includes a positive electrode active material, a binder, and, if necessary, a conductive material.
　正極活物質は、リチウム含有層状ニッケル複合酸化物を含む。高容量材料であるリチウム含有層状ニッケル複合酸化物を使用することにより、電池のエネルギー密度を向上できる。リチウム含有層状ニッケル複合酸化物としては、例えば、下式（１）で表されるものが挙げられる。 The positive electrode active material contains a lithium-containing layered nickel composite oxide. By using a lithium-containing layered nickel composite oxide that is a high-capacity material, the energy density of the battery can be improved. Examples of the lithium-containing layered nickel composite oxide include those represented by the following formula (1).
　　　ＬｉｙＮｉ（１－ｘ）ＭｘＯ２　　　（１）
（但し、０≦ｘ＜１、０＜ｙ≦１．２、ＭはＣｏ、Ａｌ、Ｍｎ、Ｆｅ、Ｔｉ及びＢからなる群より選ばれる少なくとも１種の元素である。） Li y Ni (1-x) M x O 2 (1)
(However, 0 ≦ x <1, 0 <y ≦ 1.2, and M is at least one element selected from the group consisting of Co, Al, Mn, Fe, Ti, and B.)
　高容量の観点では、Ｎｉの含有量が高いこと、即ち式（１）において、ｘが０．５未満が好ましく、さらに０．４以下が好ましい。このような化合物としては、例えば、ＬｉαＮｉβＣｏγＭｎδＯ２（０＜α≦１．２好ましくは１≦α≦１．２、β＋γ＋δ＝１、β≧０．７、γ≦０．２）、ＬｉαＮｉβＣｏγＡｌδＯ２（０＜α≦１．２好ましくは１≦α≦１．２、β＋γ＋δ＝１、β≧０．６好ましくはβ≧０．７、γ≦０．２）などが挙げられ、特に、ＬｉＮｉβＣｏγＭｎδＯ２（０．７５≦β≦０．８５、０．０５≦γ≦０．１５、０．１０≦δ≦０．２０）が挙げられる。より具体的には、例えば、ＬｉＮｉ０．８Ｃｏ０．０５Ｍｎ０．１５Ｏ２、ＬｉＮｉ０．８Ｃｏ０．１Ｍｎ０．１Ｏ２、ＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２、ＬｉＮｉ０．８Ｃｏ０．１Ａｌ０．１Ｏ２等を好ましく用いることができる。 From the viewpoint of high capacity, the Ni content is high, that is, in the formula (1), x is preferably less than 0.5, and more preferably 0.4 or less. Examples of such a compound include Li α Ni β Co γ Mn δ O 2 (0 <α ≦ 1.2, preferably 1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.7, γ ≦ 0. .2), Li α Ni β Co γ Al δ O 2 (0 <α ≦ 1.2, preferably 1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.6, preferably β ≧ 0.7, γ ≦ 0.2), etc., especially LiNi β Co γ Mn δ O 2 (0.75 ≦ β ≦ 0.85, 0.05 ≦ γ ≦ 0.15, 0.10 ≦ δ ≦ 0.20). ). More specifically, for example, LiNi 0.8 Co 0.05 Mn 0.15 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2, LiNi 0.8 Co 0.1 Al can be preferably used 0.1 O 2 or the like.
　また、熱安定性の観点では、Ｎｉの含有量が０．５を超えないこと、即ち、式（１）において、ｘが０．５以上であることも好ましい。また特定の遷移金属が半数を超えないことも好ましい。このような化合物としては、ＬｉαＮｉβＣｏγＭｎδＯ２（０＜α≦１．２好ましくは１≦α≦１．２、β＋γ＋δ＝１、０．２≦β≦０．５、０．１≦γ≦０．４、０．１≦δ≦０．４）が挙げられる。より具体的には、ＬｉＮｉ０．４Ｃｏ０．３Ｍｎ０．３Ｏ２（ＮＣＭ４３３と略記）、ＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２、ＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２（ＮＣＭ５２３と略記）、ＬｉＮｉ０．５Ｃｏ０．３Ｍｎ０．２Ｏ２（ＮＣＭ５３２と略記）など（但し、これらの化合物においてそれぞれの遷移金属の含有量が１０％程度変動したものも含む）を挙げることができる。 Further, from the viewpoint of thermal stability, it is also preferable that the Ni content does not exceed 0.5, that is, in the formula (1), x is 0.5 or more. It is also preferred that the number of specific transition metals does not exceed half. Such compounds include Li α Ni β Co γ Mn δ O 2 (0 <α ≦ 1.2, preferably 1 ≦ α ≦ 1.2, β + γ + δ = 1, 0.2 ≦ β ≦ 0.5, 0 0.1 ≦ γ ≦ 0.4, 0.1 ≦ δ ≦ 0.4). More specifically, LiNi 0.4 Co 0.3 Mn 0.3 O 2 (abbreviated as NCM433), LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 (abbreviated as NCM523), LiNi 0.5 Co 0.3 Mn 0.2 O 2 (abbreviated as NCM532), etc. (however, the content of each transition metal in these compounds varies by about 10%) Can also be included).
　また、式（１）で表される化合物を２種以上混合して使用してもよく、例えば、ＮＣＭ５３２またはＮＣＭ５２３とＮＣＭ４３３とを９：１～１：９の範囲（典型的な例として、２：１）で混合して使用することも好ましい。さらに、式（１）においてＮｉの含有量が高い材料（ｘが０．４以下）と、Ｎｉの含有量が０．５を超えない材料（ｘが０．５以上、例えばＮＣＭ４３３）とを混合することで、高容量で熱安定性の高い電池を構成することもできる。 In addition, two or more compounds represented by the formula (1) may be used as a mixture. For example, NCM532 or NCM523 and NCM433 range from 9: 1 to 1: 9 (typically 2 It is also preferable to use a mixture in 1). Furthermore, in Formula (1), the material with high Ni content (x is 0.4 or less) and the material with Ni content not exceeding 0.5 (x is 0.5 or more, for example, NCM433) are mixed. As a result, a battery having a high capacity and high thermal stability can be formed.
　リチウム含有層状ニッケル複合酸化物とともに、その他の正極活物質を使用してもよい。その他の正極活物質としては、例えば、ＬｉＭｎＯ２、ＬｉｘＭｎ２Ｏ４（０＜ｘ＜２）、Ｌｉ２ＭｎＯ３、ｘＬｉ２ＭｎＯ３－（１－ｘ）ＬｉＭＯ２（ｘは、０．１＜ｘ＜０．８、Ｍは、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｔｉ、ＡｌおよびＭｇから成る群より選択される１種以上の元素である）、ＬｉｘＭｎ１．５Ｎｉ０．５Ｏ４（０＜ｘ＜２）等の層状構造またはスピネル構造を有するマンガン酸リチウム；ＬｉＣｏＯ２またはこれらの遷移金属の一部を他の金属で置き換えたもの；これらのリチウム遷移金属酸化物において化学量論組成よりもＬｉを過剰にしたもの；及びＬｉＦｅＰＯ４などのオリビン構造を有するもの等が挙げられる。さらに、これらの金属酸化物をＡｌ、Ｆｅ、Ｐ、Ｔｉ、Ｓｉ、Ｐｂ、Ｓｎ、Ｉｎ、Ｂｉ、Ａｇ、Ｂａ、Ｃａ、Ｈｇ、Ｐｄ、Ｐｔ、Ｔｅ、Ｚｎ、Ｌａ等により一部置換した材料も使用することができる。上記に記載した正極活物質はいずれも、１種を単独で、または２種以上を組合せて用いることができる。 Other positive electrode active materials may be used together with the lithium-containing layered nickel composite oxide. As other positive electrode active materials, for example, LiMnO 2 , Li x Mn 2 O 4 (0 <x <2), Li 2 MnO 3 , xLi 2 MnO 3 — (1-x) LiMO 2 (x is 0. 1 <x <0.8, M is one or more elements selected from the group consisting of Mn, Fe, Co, Ni, Ti, Al and Mg), Li x Mn 1.5 Ni 0.5 Lithium manganate having a layered structure or spinel structure such as O 4 (0 <x <2); LiCoO 2 or a part of these transition metals replaced with another metal; chemistry in these lithium transition metal oxides Those having an excess of Li rather than the stoichiometric composition; and those having an olivine structure such as LiFePO 4 . Furthermore, a material in which these metal oxides are partially substituted with Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, etc. Can also be used. Any of the positive electrode active materials described above can be used alone or in combination of two or more.
　正極活物質の総量におけるリチウム含有層状ニッケル複合酸化物の含有量は、好ましくは５０重量％以上、より好ましくは８０重量％以上であり、１００重量％であってもよい。 The content of the lithium-containing layered nickel composite oxide in the total amount of the positive electrode active material is preferably 50% by weight or more, more preferably 80% by weight or more, and may be 100% by weight.
　正極に用いられるバインダとしては、特に制限されるものではないが、ポリフッ化ビニリデン、ビニリデンフルオライド－ヘキサフルオロプロピレン共重合体、ビニリデンフルオライド－テトラフルオロエチレン共重合体、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレン、ポリブタジエン、ポリアクリル酸、ポリアクリル酸エステル、ポリスチレン、ポリアクリロニトリル、ポリイミド、ポリアミドイミド等を用いることができる。また、バインダは、前記の複数の樹脂の混合物、共重合体およびその架橋体、例えばスチレンブタジエンゴム（ＳＢＲ）等であってもよい。さらに、ＳＢＲ系エマルジョンのような水系バインダを用いる場合、カルボキシメチルセルロース（ＣＭＣ）等の増粘剤を用いることもできる。 The binder used for the positive electrode is not particularly limited, but polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, polypropylene, Polyethylene, polybutadiene, polyacrylic acid, polyacrylic acid ester, polystyrene, polyacrylonitrile, polyimide, polyamideimide and the like can be used. The binder may be a mixture of a plurality of resins, a copolymer, and a crosslinked product thereof, such as styrene butadiene rubber (SBR). Further, when an aqueous binder such as an SBR emulsion is used, a thickener such as carboxymethyl cellulose (CMC) can also be used.
　正極においてバインダの量は、正極活物質１００重量部に対して、下限として好ましくは１重量部以上、より好ましくは２重量部以上、上限として好ましくは３０重量部以下、より好ましくは２５重量部以下である。 The amount of the binder in the positive electrode is preferably 1 part by weight or more, more preferably 2 parts by weight or more, and preferably 30 parts by weight or less, more preferably 25 parts by weight or less as the upper limit with respect to 100 parts by weight of the positive electrode active material. It is.
　正極集電体としては、特に制限されるものではないが、アルミニウム、ニッケル、銀、またはそれらの合金を使用できる。正極集電体の形状としては、例えば、箔、平板状、メッシュ状が挙げられる。 The positive electrode current collector is not particularly limited, but aluminum, nickel, silver, or an alloy thereof can be used. Examples of the shape of the positive electrode current collector include a foil, a flat plate, and a mesh.
　正極の作製に際して、インピーダンスを低下させる目的で、導電材を添加してもよい。導電材としては、例えば、グラファイト、カーボンブラック、アセチレンブラック等の炭素質微粒子が挙げられる。 In producing the positive electrode, a conductive material may be added for the purpose of reducing the impedance. Examples of the conductive material include carbonaceous fine particles such as graphite, carbon black, and acetylene black.
　本実施形態に係る正極は、正極活物質、バインダ及び溶媒を含むスラリーを調製し、これを正極集電体上に塗布し、正極活物質層を形成することにより作製できる。 The positive electrode according to the present embodiment can be produced by preparing a slurry containing a positive electrode active material, a binder and a solvent, and applying the slurry onto a positive electrode current collector to form a positive electrode active material layer.
　［負極］
　負極は、集電体と、集電体上に設けられた、負極活物質、バインダおよび導電材を含む負極活物質層とを備える。本実施形態において、負極活物質にはケイ素酸化物および炭素を含む複合粒子および黒鉛粒子を、バインダにはポリアクリル酸を使用する。 [Negative electrode]
The negative electrode includes a current collector and a negative electrode active material layer provided on the current collector and including a negative electrode active material, a binder, and a conductive material. In the present embodiment, composite particles and graphite particles containing silicon oxide and carbon are used as the negative electrode active material, and polyacrylic acid is used as the binder.
　本実施形態の負極活物質は、ケイ素酸化物および炭素を含む複合粒子（以降、この複合粒子を単にケイ素酸化物粒子とも記載する）を含む。ケイ素酸化物は、特に限定されるものではないが、例えば、組成式ＳｉＯｘ（０＜ｘ≦２）で表される。また、ケイ素酸化物はＬｉを含んでもよく、Ｌｉを含むケイ素酸化物は、例えばＳｉＬｉｙＯｚ（ｙ＞０、２＞ｚ＞０）で表される。また、ケイ素酸化物は微量の金属元素や非金属元素を含んでも良い。ケイ素酸化物は、例えば、窒素、ホウ素およびイオウの中から選ばれる一種または二種以上の元素を、例えば０．１～５重量％含有することができる。微量の金属元素や非金属元素を含有することで、ケイ素酸化物の電気伝導性を向上させることができる。また、ケイ素酸化物は結晶であってもよく、非晶質であってもよい。 The negative electrode active material of the present embodiment includes composite particles containing silicon oxide and carbon (hereinafter, this composite particle is also simply referred to as silicon oxide particles). Silicon oxide is not particularly limited, for example, expressed by a composition formula SiO x (0 <x ≦ 2 ). Further, the silicon oxide may contain Li, and the silicon oxide containing Li is represented by, for example, SiLi y O z (y> 0, 2>z> 0). Further, the silicon oxide may contain a trace amount of a metal element or a nonmetal element. The silicon oxide can contain, for example, 0.1 to 5% by weight of one or more elements selected from nitrogen, boron and sulfur. By containing a trace amount of a metal element or a non-metal element, the electrical conductivity of the silicon oxide can be improved. The silicon oxide may be crystalline or amorphous.
　ケイ素酸化物粒子はケイ素酸化物とともに炭素を含む。炭素は、粒子の核であるケイ素酸化物の周囲の全面または一部を被覆する。炭素被膜の形成方法は、例えば、炭素源を用いたスパッタ法又は蒸着法等により行うことができる。蒸着法としては、例えば、アーク蒸着法、化学蒸着法などが挙げられる。これらのうち、化学蒸着である化学気相堆積法（ＣＶＤ法）が蒸着温度、蒸着雰囲気を制御しやすいため好ましい。この化学気相堆積法は、酸化ケイ素粒子をアルミナや石英のボート等において実施することができる。また、化学気相堆積法は、酸化ケイ素粒子をガス中に浮遊させた状態もしくは搬送している状態で実施することもできる。 Silicon oxide particles contain carbon together with silicon oxide. The carbon coats the entire surface or part of the periphery of the silicon oxide that is the core of the particle. The carbon film can be formed by, for example, a sputtering method or a vapor deposition method using a carbon source. Examples of the vapor deposition method include an arc vapor deposition method and a chemical vapor deposition method. Among these, the chemical vapor deposition method (CVD method) which is chemical vapor deposition is preferable because the vapor deposition temperature and vapor deposition atmosphere can be easily controlled. This chemical vapor deposition method can be performed by using silicon oxide particles in an alumina or quartz boat. In addition, the chemical vapor deposition method can be performed in a state where the silicon oxide particles are suspended or transported in the gas.
　化学気相堆積法に用いる炭素源としては、熱分解により炭素を生成するものであれば、特に制限されずに用いることができ、条件に応じて適宜選択できる。炭素源としては、例えば、メタン、エタン、エチレン、アセチレン若しくはベンゼン等の炭化水素化合物、メタノール、エタノール、トルエン若しくはキシレン等の有機溶媒、又はＣＯ等が挙げられる。また、雰囲気ガスとしては、アルゴン、窒素等の不活性ガス、あるいはこれらと水素との混合ガスを用いることができる。化学気相堆積法における温度は、例えば４００～１２００℃の範囲である。 The carbon source used in the chemical vapor deposition method can be used without particular limitation as long as it generates carbon by thermal decomposition, and can be appropriately selected according to the conditions. Examples of the carbon source include hydrocarbon compounds such as methane, ethane, ethylene, acetylene, and benzene, organic solvents such as methanol, ethanol, toluene, and xylene, or CO. Further, as the atmospheric gas, an inert gas such as argon or nitrogen, or a mixed gas of these and hydrogen can be used. The temperature in the chemical vapor deposition method is, for example, in the range of 400 to 1200 ° C.
　ケイ素酸化物粒子において炭素の量は、２重量％以上、好ましくは３重量％以上、さらに好ましくは４．５重量％以上である。ケイ素酸化物粒子において炭素の量は、好ましくは８重量％以下、より好ましくは６重量％以下である。 The amount of carbon in the silicon oxide particles is 2% by weight or more, preferably 3% by weight or more, and more preferably 4.5% by weight or more. The amount of carbon in the silicon oxide particles is preferably 8% by weight or less, more preferably 6% by weight or less.
　ケイ素酸化物粒子においてケイ素酸化物の量は、好ましくは６０重量％以上、より好ましくは７０重量％以上、さらに好ましくは９２重量％以上である。ケイ素酸化物粒子においてケイ素酸化物の量は、好ましくは９８重量％以下、より好ましくは９５．５重量％以下である。ケイ素酸化物の量を増加することで、負極の容量の増加と目付量の低減が可能となり、６００Ｗｈ／Ｌを超えるエネルギー密度のセルを得ることができる。 In the silicon oxide particles, the amount of silicon oxide is preferably 60% by weight or more, more preferably 70% by weight or more, and still more preferably 92% by weight or more. The amount of silicon oxide in the silicon oxide particles is preferably 98% by weight or less, more preferably 95.5% by weight or less. By increasing the amount of silicon oxide, the capacity of the negative electrode can be increased and the basis weight can be reduced, and a cell having an energy density exceeding 600 Wh / L can be obtained.
　負極活物質層におけるケイ素酸化物粒子の含有量は、好ましくは５０重量％以上、より好ましくは６０重量％以上、さらに好ましくは７０重量％以上である。ケイ素酸化物粒子を多く負極に含有することにより、電池のエネルギー密度を向上させることができる。負極活物質層におけるケイ素酸化物粒子の含有量は、好ましくは９５重量％以下、より好ましくは９０重量％以下である。 The content of silicon oxide particles in the negative electrode active material layer is preferably 50% by weight or more, more preferably 60% by weight or more, and still more preferably 70% by weight or more. By containing many silicon oxide particles in the negative electrode, the energy density of the battery can be improved. The content of silicon oxide particles in the negative electrode active material layer is preferably 95% by weight or less, more preferably 90% by weight or less.
　ケイ素酸化物粒子の平均粒子径は、下限として好ましくは１μｍ以上、より好ましくは３μｍ以上である。ケイ素酸化物粒子の平均粒子径は、上限として好ましくは１０μｍ以下、より好ましくは７μｍ以下である。本明細書において、平均粒子径は、体積基準の積算５０％における粒径を表す。平均粒子径は、レーザー回折・散乱式粒度分布測定装置によって測定できる。 The average particle diameter of the silicon oxide particles is preferably 1 μm or more, more preferably 3 μm or more as a lower limit. The upper limit of the average particle diameter of the silicon oxide particles is preferably 10 μm or less, more preferably 7 μm or less. In the present specification, the average particle size represents a particle size at an integrated volume of 50%. The average particle diameter can be measured by a laser diffraction / scattering particle size distribution measuring apparatus.
　ケイ素酸化物粒子の比表面積は、下限として好ましくは１ｍ２／ｇ以上、より好ましくは３ｍ２／ｇ以上である。ケイ素酸化物粒子の比表面積は、上限として好ましくは２０ｍ２／ｇ以下、より好ましくは１２ｍ２／ｇ以下である。比表面積は、窒素吸着によるＢＥＴ法を用いて測定され得る。 The specific surface area of the silicon oxide particles is preferably 1 m 2 / g or more, more preferably 3 m 2 / g or more as a lower limit. The specific surface area of the silicon oxide particles is preferably 20 m 2 / g or less, more preferably 12 m 2 / g or less as the upper limit. Specific surface area can be measured using the BET method with nitrogen adsorption.
　本実施形態の負極活物質は、さらに黒鉛粒子を含む。黒鉛粒子を含むことにより、ケイ素酸化物の膨張収縮による劣化を抑制することができる。本実施形態で使用する黒鉛は、人造黒鉛であっても天然黒鉛であってもよい。人造黒鉛とは、石炭コークス、ピッチ、重質油などを主原料として、２２００℃～３０００℃という比較的に高い温度領域で黒鉛化処理されたものである。一方で、天然黒鉛は、天然鉱物を主原料とする。人造黒鉛は、通常、表面が被覆されていないが、天然黒鉛は、通常、表面が炭素で被覆されている。この炭素被膜は、不可逆容量が高く、またケイ素酸化物の膨張収縮により、ダメージを受けやすいため、劣化の要因となり得る。サイクル特性の改善のために、人造黒鉛を使用することが好ましい。黒鉛粒子の形状としては、特に限定されるものではないが、例えば、球状、塊状、鱗片状などの粒子を使用できる。 The negative electrode active material of this embodiment further contains graphite particles. By including the graphite particles, deterioration due to expansion and contraction of the silicon oxide can be suppressed. The graphite used in this embodiment may be artificial graphite or natural graphite. Artificial graphite is graphitized in a relatively high temperature range of 2200 ° C. to 3000 ° C. using coal coke, pitch, heavy oil and the like as main raw materials. On the other hand, natural graphite uses natural minerals as the main raw material. Artificial graphite is usually not coated on the surface, while natural graphite is usually coated on the surface with carbon. Since this carbon film has a high irreversible capacity and is easily damaged by the expansion and contraction of silicon oxide, it can cause deterioration. In order to improve the cycle characteristics, it is preferable to use artificial graphite. The shape of the graphite particles is not particularly limited, and for example, spherical, lump, scale-like particles can be used.
　負極活物質層における黒鉛粒子の含有量は、好ましくは１重量％以上、より好ましくは５重量％以上、さらに好ましくは１０重量％以上である。負極活物質層における黒鉛粒子の含有量は、好ましくは４０重量％以下、より好ましくは２５重量％以下である。 The content of the graphite particles in the negative electrode active material layer is preferably 1% by weight or more, more preferably 5% by weight or more, and still more preferably 10% by weight or more. Content of the graphite particle in a negative electrode active material layer becomes like this. Preferably it is 40 weight% or less, More preferably, it is 25 weight% or less.
　黒鉛粒子の平均粒子径は、下限として好ましくは５μｍ以上、より好ましくは８μｍ以上である。黒鉛粒子の平均粒子径は、上限として好ましくは３０μｍ以下、より好ましくは２５μｍ以下である。 The average particle diameter of the graphite particles is preferably 5 μm or more, more preferably 8 μm or more as a lower limit. The average particle diameter of the graphite particles is preferably 30 μm or less, more preferably 25 μm or less as the upper limit.
　黒鉛粒子の比表面積は、下限として好ましくは１ｍ２／ｇ以上、より好ましくは２ｍ２／ｇ以上である。黒鉛粒子の比表面積は、上限として好ましくは１０ｍ２／ｇ以下、より好ましくは５ｍ２／ｇ以下である。比表面積は、窒素吸着によるＢＥＴ法を用いて測定され得る。 The specific surface area of the graphite particles is preferably 1 m 2 / g or more, more preferably 2 m 2 / g or more as a lower limit. The specific surface area of the graphite particles is preferably 10 m 2 / g or less, more preferably 5 m 2 / g or less as the upper limit. Specific surface area can be measured using the BET method with nitrogen adsorption.
　本実施形態のバインダは、ポリアクリル酸を含む。ポリアクリル酸は、下記式（２）で表される（メタ）アクリル酸またはその金属塩に由来する単量体単位を含む重合体である。ポリアクリル酸中の式（２）で表される単量体単位の量は特には限定されないが、例えば５０重量％以上や７０重量％以上であり、１００重量％であってもよい。なお、本明細書において、用語「（メタ）アクリル酸」は、アクリル酸及びメタクリル酸を意味する。 The binder of this embodiment includes polyacrylic acid. Polyacrylic acid is a polymer containing monomer units derived from (meth) acrylic acid represented by the following formula (2) or a metal salt thereof. The amount of the monomer unit represented by the formula (2) in the polyacrylic acid is not particularly limited, but is, for example, 50% by weight or more, 70% by weight or more, and may be 100% by weight. In the present specification, the term “(meth) acrylic acid” means acrylic acid and methacrylic acid.
Figure JPOXMLDOC01-appb-C000001
 （式中、Ｒ１は、水素原子又はメチル基である。）
Figure JPOXMLDOC01-appb-C000001
 (In the formula, R 1 is a hydrogen atom or a methyl group.)
　式（２）で表される単量体単位におけるカルボン酸は、カルボン酸金属塩であってよい。金属は好ましくは一価金属である。一価金属としては、アルカリ金属（例えば、Ｎａ、Ｌｉ、Ｋ、Ｒｂ、Ｃｓ、Ｆｒ等）、及び、貴金属（例えば、Ａｇ、Ａｕ、Ｃｕ等）等が挙げられる。これらの中でも、アルカリ金属が好ましい。アルカリ金属としては、Ｎａ、Ｌｉ、Ｋが好ましく、Ｎａが最も好ましい。ポリアクリル酸が、少なくとも一部にカルボン酸塩を含むことにより、負極活物質層の構成材料との密着性をさらに向上させることができる場合がある。 The carboxylic acid in the monomer unit represented by the formula (2) may be a carboxylic acid metal salt. The metal is preferably a monovalent metal. Examples of the monovalent metal include alkali metals (for example, Na, Li, K, Rb, Cs, Fr, etc.) and noble metals (for example, Ag, Au, Cu, etc.). Among these, alkali metals are preferable. As the alkali metal, Na, Li, and K are preferable, and Na is most preferable. When the polyacrylic acid contains a carboxylate at least partially, the adhesion with the constituent material of the negative electrode active material layer may be further improved.
　ポリアクリル酸は、その他の単量体単位を含んでいてもよい。ポリアクリル酸が、（メタ）アクリル酸以外の単量体単位をさらに含むことで、負極活物質層と集電体との剥離強度を改善できる場合がある。その他の単量体単位としては、例えば、クロトン酸、ペンテン酸等のモノカルボン酸化合物、イタコン酸、マレイン酸等のジカルボン酸化合物、ビニルスルホン酸等のスルホン酸化合物、ビニルホスホン酸等のホスホン酸化合物等のエチレン性不飽和基を有する酸；スチレンスルホン酸、スチレンカルボン酸等の酸性基を有する芳香族オレフィン；（メタ）アクリル酸アルキルエステル；アクリロニトリル；エチレン、プロピレン、ブタジエン等の脂肪族オレフィン；スチレン等の芳香族オレフィン等のモノマーに由来する単量体単位が挙げられる。また、その他の単量体単位は、二次電池のバインダとして使用される公知のポリマーを構成する単量体単位であってもよい。これらの単量体単位においても、存在する場合、酸が塩となっていてもよい。 Polyacrylic acid may contain other monomer units. When the polyacrylic acid further includes a monomer unit other than (meth) acrylic acid, the peel strength between the negative electrode active material layer and the current collector may be improved. Examples of other monomer units include monocarboxylic acid compounds such as crotonic acid and pentenoic acid, dicarboxylic acid compounds such as itaconic acid and maleic acid, sulfonic acid compounds such as vinyl sulfonic acid, and phosphonic acids such as vinyl phosphonic acid. Acids having an ethylenically unsaturated group such as compounds; aromatic olefins having acidic groups such as styrene sulfonic acid and styrene carboxylic acid; (meth) acrylic acid alkyl esters; acrylonitrile; aliphatic olefins such as ethylene, propylene and butadiene; Examples include monomer units derived from monomers such as aromatic olefins such as styrene. The other monomer unit may be a monomer unit constituting a known polymer used as a binder for a secondary battery. In these monomer units, if present, the acid may be a salt.
　さらに、本実施形態に係るポリアクリル酸は、主鎖および側鎖の少なくとも１つの水素原子が、ハロゲン（フッ素、塩素、ホウ素、ヨウ素等）等で置換されていてもよい。 Furthermore, in the polyacrylic acid according to this embodiment, at least one hydrogen atom in the main chain and the side chain may be substituted with halogen (fluorine, chlorine, boron, iodine, etc.) or the like.
　なお、本実施形態に係るポリアクリル酸が２種以上の単量体単位を含む共重合体である場合、共重合体は、ランダム共重合体、交互共重合体、ブロック共重合体、グラフト共重合体等、及びこれらの組合せのいずれであってもよい。 When the polyacrylic acid according to this embodiment is a copolymer containing two or more types of monomer units, the copolymer may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer. Any of a polymer etc. and these combinations may be sufficient.
　負極活物質層におけるポリアクリル酸の含有量は、好ましくは１重量％以上、より好ましくは２重量％以上、さらに好ましくは３重量％以上である。負極活物質層におけるポリアクリル酸の含有量は、好ましくは８重量％以下、より好ましくは７重量％以下である。 The content of polyacrylic acid in the negative electrode active material layer is preferably 1% by weight or more, more preferably 2% by weight or more, and further preferably 3% by weight or more. The content of polyacrylic acid in the negative electrode active material layer is preferably 8% by weight or less, more preferably 7% by weight or less.
　本実施形態において、ポリアクリル酸による抵抗上昇を抑制するために、負極活物質層は、導電材を含む。本実施形態において使用する導電材は、４０～８００ｍ２／ｇの比表面積を有する。好ましくは、導電材の比表面積は５０～６００ｍ２／ｇである。比表面積は、窒素吸着によるＢＥＴ法を用いて測定され得る。このような比表面積を有する導電材は、バインダとして用いるポリアクリル酸により活物質であるケイ素酸化物粒子や黒鉛粒子の表面に多く存在させることができるため、活物質間に多くの導電パスを形成できる。よって、電池抵抗を低減できる。負極活物質粒子の表面は、例えばＳＥＭ（走査型電子顕微鏡）などの電子顕微鏡により確認できる。粒子表面を電子顕微鏡画像にて観察し、確認された粒子の面積に対して導電材の付着している部分の面積の割合（％）を、活物質粒子表面における導電材の被覆率として考えることができる。本発明に係る負極では、ケイ素酸化物粒子表面における導電材の被覆率が、粒子の数平均において、好ましくは３０％以上であり、より好ましくは５０％以上であり、１００％であってもよい。 In the present embodiment, the negative electrode active material layer includes a conductive material in order to suppress an increase in resistance due to polyacrylic acid. The conductive material used in the present embodiment has a specific surface area of 40 to 800 m 2 / g. Preferably, the specific surface area of the conductive material is 50 to 600 m 2 / g. Specific surface area can be measured using the BET method with nitrogen adsorption. A conductive material having such a specific surface area can be present on the surface of silicon oxide particles or graphite particles, which are active materials, by polyacrylic acid used as a binder, thereby forming many conductive paths between the active materials. it can. Therefore, battery resistance can be reduced. The surface of the negative electrode active material particles can be confirmed by an electron microscope such as SEM (scanning electron microscope). Observe the particle surface with an electron microscope image, and consider the ratio (%) of the area where the conductive material is attached to the confirmed particle area as the coverage of the conductive material on the active material particle surface. Can do. In the negative electrode according to the present invention, the coverage of the conductive material on the surface of the silicon oxide particles is preferably 30% or more, more preferably 50% or more, and may be 100% in terms of the number average of the particles. .
　このような比表面積を有する導電材としては、例えば、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、カーボンナノチューブ、カーボンナノホーンなどの炭素材料が挙げられる。 Examples of the conductive material having such a specific surface area include carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotube, and carbon nanohorn.
　カーボンブラックは、炭化水素の熱分解により製造される炭素微粒子である。カーボンブラックは、一次粒子が複数連なってストラクチャーを形成する。カーボンブラックの平均一次粒子径は、好ましくは２０ｎｍ以上８０ｎｍ以下である。カーボンブラックの比表面積は、好ましくは４０ｍ２／ｇ以上８０ｍ２／ｇ以下である。負極活物質層におけるカーボンブラックの量は、好ましくは１重量％以上１０重量％以下である。 Carbon black is carbon fine particles produced by thermal decomposition of hydrocarbons. In carbon black, a plurality of primary particles form a structure. The average primary particle diameter of carbon black is preferably 20 nm or more and 80 nm or less. The specific surface area of carbon black is preferably 40 m 2 / g or more and 80 m 2 / g or less. The amount of carbon black in the negative electrode active material layer is preferably 1% by weight or more and 10% by weight or less.
　アセチレンブラックは、カーボンブラックの１種であり、アセチレンを熱分解して製造され得る。ケッチェンブラックは、カーボンブラックの１種であり、高い導電性を有する。 Acetylene black is a kind of carbon black and can be produced by pyrolyzing acetylene. Ketjen black is a kind of carbon black and has high conductivity.
　カーボンナノチューブは、炭素の６員環を有する平面状のグラフェンシートを円筒状に形成した単層又は同軸状の多層構造を有するものであれば良いが、多層のものが好ましい。また、円筒状のカーボンナノチュ－ブの両端は、開放されていてもよいが、炭素の５員環又は７員環を含む半球状のフラーレン等で閉じられたものが好ましい。カーボンナノチューブの最外円筒の直径は、好ましくは１０ｎｍ以上３０ｎｍ以下である。カーボンナノチューブの比表面積は、好ましくは１００ｍ２／ｇ以上２００ｍ２／ｇ以下である。負極活物質層におけるカーボンナノチューブの量は、好ましくは１重量％以上６重量％以下である。 The carbon nanotube may be any carbon nanotube having a single-layer or coaxial multilayer structure in which a planar graphene sheet having a six-membered ring of carbon is formed in a cylindrical shape, but is preferably a multilayer. Further, both ends of the cylindrical carbon nanotube may be open, but are preferably closed with a hemispherical fullerene containing a carbon 5-membered ring or 7-membered ring. The diameter of the outermost cylinder of the carbon nanotube is preferably 10 nm or more and 30 nm or less. The specific surface area of the carbon nanotube is preferably 100 m 2 / g or more and 200 m 2 / g or less. The amount of carbon nanotubes in the negative electrode active material layer is preferably 1% by weight or more and 6% by weight or less.
　カーボンナノホーンは、単一では一枚のグラフェンシートが円筒状に丸まり、その先端部が先端角約２０°の円錐状となった形状を有している。カーボンナノホーンは８０ｎｍ以上１６０ｎｍ以下の直径を有するものが好ましい。また、カーボンナノホーンの比表面積は２００ｍ２／ｇ以上４００ｍ２／ｇ以下であることが好ましい。負極活物質層におけるカーボンナノホーンの量は、好ましくは１重量％以上６重量％以下である。 A single carbon nanohorn has a shape in which a single graphene sheet is rounded into a cylindrical shape, and the tip of the carbon nanohorn has a conical shape with a tip angle of about 20 °. The carbon nanohorn preferably has a diameter of 80 nm to 160 nm. Further, it is preferable that the specific surface area of the carbon nanohorn or less 200 meters 2 / g or more 400m 2 / g. The amount of carbon nanohorn in the negative electrode active material layer is preferably 1% by weight or more and 6% by weight or less.
　これらの導電材を含む負極では、ポリアクリル酸を使用しても抵抗上昇を抑制できる。このことは、電池のインピーダンス特性からも確認できる。図３に、負極においてポリアクリル酸またはＳＢＲ／ＣＭＣと、各種の導電材とを使用した電池のインピーダンス特性を示す。導電材を使用していない電池や比表面積２０ｍ２／ｇの板状黒鉛を負極に使用した電池は、電子抵抗（Ｒｓｏｌ）や電荷移動抵抗（Ｒｃｔ）が大きいことが図３から分かる。比表面積４０～８００ｍ２／ｇのカーボンブラック、カーボンナノチューブ、またはカーボンナノホーンを使用した電池は、ＲｓｏｌおよびＲｃｔが小さい。これらの導電材により、活物質間および活物質－集電箔間に適切な導電パスが形成されていると考えられる。 In the negative electrode containing these conductive materials, even if polyacrylic acid is used, an increase in resistance can be suppressed. This can also be confirmed from the impedance characteristics of the battery. FIG. 3 shows impedance characteristics of a battery using polyacrylic acid or SBR / CMC and various conductive materials in the negative electrode. It can be seen from FIG. 3 that a battery using no conductive material or a battery using plate-like graphite having a specific surface area of 20 m 2 / g as the negative electrode has a large electronic resistance (Rsol) and charge transfer resistance (Rct). A battery using carbon black, carbon nanotube, or carbon nanohorn having a specific surface area of 40 to 800 m 2 / g has a small Rsol and Rct. It is considered that appropriate conductive paths are formed between these active materials and between the active materials and the current collector foil.
　負極活物質層における導電材の含有量は、好ましくは１重量％以上、より好ましくは３重量％以上である。負極活物質層における導電材の含有量は、好ましくは１０重量％以下、より好ましくは６重量％以下である。 The content of the conductive material in the negative electrode active material layer is preferably 1% by weight or more, more preferably 3% by weight or more. The content of the conductive material in the negative electrode active material layer is preferably 10% by weight or less, more preferably 6% by weight or less.
　高い含有量でケイ素酸化物を使用することにより得られるエネルギー密度を損なわないために、ポリアクリル酸と導電材の総量は、負極活物質層の１３重量％以下であり、好ましくは１０重量％以下である。サイクル特性を改善するために、ポリアクリル酸と導電材の総量は、負極活物質層の４重量％以上であり、好ましくは５重量％以上である。 In order not to impair the energy density obtained by using silicon oxide with a high content, the total amount of polyacrylic acid and the conductive material is 13% by weight or less, preferably 10% by weight or less of the negative electrode active material layer. It is. In order to improve the cycle characteristics, the total amount of polyacrylic acid and the conductive material is 4% by weight or more, preferably 5% by weight or more of the negative electrode active material layer.
　ポリアクリル酸に対する導電材の重量比率（導電材重量／ポリアクリル酸重量）は、好ましくは０．１２以上２以下、より好ましくは０．３以上１．８以下、さらに好ましくは１以上１．７以下である。ポリアクリル酸に対する導電材の重量比率を制御することにより、サイクル特性をさらに改善することができる。 The weight ratio of the conductive material to the polyacrylic acid (conductive material weight / polyacrylic acid weight) is preferably 0.12 or more and 2 or less, more preferably 0.3 or more and 1.8 or less, and further preferably 1 or more and 1.7. It is as follows. By controlling the weight ratio of the conductive material to the polyacrylic acid, the cycle characteristics can be further improved.
　負極集電体としては、電気化学的な安定性から、アルミニウム、ニッケル、ステンレス、クロム、銅、銀、およびそれらの合金を使用できる。その形状としては、箔、平板状、メッシュ状が挙げられる。高強度および高導電性集電体である銅合金製またはステンレス製の集電箔を使用してもよい。銅合金は、好ましくはＺｎ、Ｓｎ、およびＩｎから成る群より選択される１種以上の元素を０．０１～１．０重量％の量で含む。集電体の厚さは、特に限定されるものではないが、好ましくは１～１５μｍであり、より好ましくは４～８μｍである。これらの範囲の厚さにおいて、集電体はケイ素酸化物の膨張収縮に対する適切な強度を有し得る。 As the negative electrode current collector, aluminum, nickel, stainless steel, chromium, copper, silver, and alloys thereof can be used because of electrochemical stability. Examples of the shape include foil, flat plate, and mesh. A current collector foil made of copper alloy or stainless steel, which is a high strength and highly conductive current collector, may be used. The copper alloy preferably contains one or more elements selected from the group consisting of Zn, Sn, and In in an amount of 0.01 to 1.0% by weight. The thickness of the current collector is not particularly limited, but is preferably 1 to 15 μm, more preferably 4 to 8 μm. In these ranges of thicknesses, the current collector can have adequate strength against silicon oxide expansion and contraction.
　本実施形態の構成を採用することにより、電極密度を１．３５ｇ／ｃｍ３としたとき、例えば、１０－５Ω・ｃｍ２以上１０－２Ω・ｃｍ２以下や１０－４Ω・ｃｍ２以上１０－３Ω・ｃｍ２以下などの範囲内に負極／電解質界面での電極抵抗（界面抵抗とも呼ぶ）が低減され得る。この電極抵抗の値が特に小さい場合、正極、電解液、セパレータなどを用いてセルを作製し、これを交流インピーダンス測定するのではなく、負極自体を直接測定する評価方法が有効であることを本案発明者は見出した。なお、セルとして交流インピーダンス法により測定した場合にも、導電材やポリアクリル酸の効果を確認できるが、本発明の効果が顕著であることを示すためには、正極、電解液、セパレータの影響を排除できる方法が有効であることから、本発明の負極の界面抵抗の値は、電極抵抗測定器から算出された値を用いた。 By adopting the configuration of the present embodiment, when the electrode density is 1.35 g / cm 3 , for example, 10 −5 Ω · cm 2 or more and 10 −2 Ω · cm 2 or less, or 10 −4 Ω · cm 2. The electrode resistance (also referred to as interface resistance) at the negative electrode / electrolyte interface can be reduced within the range of 10 −3 Ω · cm 2 or less. When this electrode resistance value is particularly small, it is effective to use a positive electrode, electrolyte, separator, etc. to produce a cell and measure the negative electrode itself instead of measuring the AC impedance. The inventor found out. Note that the effect of the conductive material and polyacrylic acid can also be confirmed when measured by the AC impedance method as a cell, but in order to show that the effect of the present invention is remarkable, the influence of the positive electrode, the electrolyte, and the separator Therefore, the value calculated from the electrode resistance measuring instrument was used as the interface resistance value of the negative electrode of the present invention.
　一般には、抵抗Ｒに電流Ｉが流れたとき、抵抗の両端には電圧Ｖが発生する。この時、Ｒ，Ｉ，Ｖの間にはオームの法則によりＶ＝Ｉ×Ｒという関係が成り立つ。従って、Ｒが未知であってもＩとＶが分かれば、Ｒを知ることができる。この原理を用いた電極測定の方法として、一般には２端子法と４探針法がある。２端子法は、配線抵抗や接触抵抗が大きいという課題、４探針法は複雑なリチウムイオン二次電池の電極には再現性のある抵抗値が得られないという課題がある。本発明の一実施形態においては、活物質層よりも抵抗の低い集電箔を有する負極を用いることから、低い抵抗値を測定可能な電極抵抗測定装置を用いることが好ましい。低抵抗電極に適した電極抵抗測定装置の測定原理を以下に述べる。ステップ１：電極シートを３層の抵抗体とみなし、３次元の抵抗マトリックスモデルを仮定する。ステップ２：電極表面に定電流を流し、表面に発生する電位を１００点計測する。ステップ３：ステップ１で仮定した３次元の抵抗マトリックスモデルに対して、電流を流し、電位を計算する。ステップ４：実測した電位を、計算機シミュレーションした電位と比較して一致している場合には終了し、不一致の場合には適時３次元の抵抗マトリックスモデルの値を更新して、再計算を繰り返す。すなわち、電極層の抵抗と界面抵抗を適時更新しながら、実測電位と計算機シミュレーションされた電位が一致するまで演算して、界面抵抗を得ることができる。 Generally, when a current I flows through the resistor R, a voltage V is generated across the resistor. At this time, a relationship of V = I × R is established between R, I, and V according to Ohm's law. Therefore, even if R is unknown, if I and V are known, R can be known. In general, there are a two-terminal method and a four-probe method as electrode measurement methods using this principle. The two-terminal method has a problem that wiring resistance and contact resistance are large, and the four-probe method has a problem that a reproducible resistance value cannot be obtained for an electrode of a complicated lithium ion secondary battery. In one embodiment of the present invention, since a negative electrode having a current collector foil having a lower resistance than that of the active material layer is used, it is preferable to use an electrode resistance measuring device capable of measuring a low resistance value. The measurement principle of an electrode resistance measuring device suitable for a low resistance electrode will be described below. Step 1: Consider the electrode sheet as a three-layer resistor and assume a three-dimensional resistance matrix model. Step 2: A constant current is passed through the electrode surface, and 100 potentials generated on the surface are measured. Step 3: Current is passed through the three-dimensional resistance matrix model assumed in Step 1 to calculate the potential. Step 4: The measured potential is compared with the computer-simulated potential, and if it matches, the process ends. If not, the value of the three-dimensional resistance matrix model is updated in a timely manner and the recalculation is repeated. That is, while updating the resistance of the electrode layer and the interface resistance in a timely manner, the interface resistance can be obtained by calculating until the measured potential and the potential simulated by the computer match.
　本実施形態に係る負極は、負極活物質、導電材、ポリアクリル酸及び溶媒を含むスラリーを調製し、これを負極集電体上に塗布し、負極活物質層を形成することにより作製できる。例えば、以下のように負極を調製できる。まずケイ素酸化物粒子および黒鉛粒子などの負極活物質と、ポリアクリル酸と、導電材とを所定の配合量で溶媒中に分散混練し、負極スラリーを調製する。溶媒は、好ましくは水である。この負極スラリーを負極集電体に塗工、乾燥することで負極を製造することができる。得られた負極はロールプレス等の方法により負極活物質層を圧縮して電極密度を調整することができる。 The negative electrode according to the present embodiment can be produced by preparing a slurry containing a negative electrode active material, a conductive material, polyacrylic acid and a solvent, and applying this to a negative electrode current collector to form a negative electrode active material layer. For example, the negative electrode can be prepared as follows. First, a negative electrode active material such as silicon oxide particles and graphite particles, polyacrylic acid, and a conductive material are dispersed and kneaded in a solvent in a predetermined blending amount to prepare a negative electrode slurry. The solvent is preferably water. The negative electrode can be produced by coating this negative electrode slurry on a negative electrode current collector and drying it. The obtained negative electrode can adjust an electrode density by compressing a negative electrode active material layer by methods, such as a roll press.
　電極密度は、１．０ｇ／ｃｍ３以上２．０ｇ／ｃｍ３以下の範囲であることが好ましい。電極密度が１．０ｇ／ｃｍ３以上の場合、充放電容量が良好となる傾向がある。電極密度が２．０ｇ／ｃｍ３以下の場合、電解液を含浸させることが容易となり、充放電容量が良好となる傾向がある。 The electrode density is preferably in the range of 1.0 g / cm 3 or more and 2.0 g / cm 3 or less. When the electrode density is 1.0 g / cm 3 or more, the charge / discharge capacity tends to be good. When the electrode density is 2.0 g / cm 3 or less, it is easy to impregnate the electrolytic solution, and the charge / discharge capacity tends to be good.
　導電材を負極活物質の表面に被覆させるために、事前にポリアクリル酸を導電材に付着させ、その後に負極活物質と導電材を結着させてもよい。例えば、以下のように負極を調製できる。まず、ポリアクリル酸と導電材とを溶媒中で混合して、導電材にポリアクリル酸を付着させる。溶媒は、好ましくは水である。次いで、この混合物にさらにケイ素酸化物粒子および黒鉛粒子などの負極活物質を加えて負極スラリーを調製する。この負極スラリーを負極集電体に塗工、乾燥することで負極を製造することができる。この結果、例えば７０％以上や８０％以上などのより高い被覆率でケイ素酸化物粒子など負極活物質粒子の表面に導電材を結着できる。 In order to coat the surface of the negative electrode active material with the conductive material, polyacrylic acid may be attached to the conductive material in advance, and then the negative electrode active material and the conductive material may be bound. For example, the negative electrode can be prepared as follows. First, polyacrylic acid and a conductive material are mixed in a solvent to attach polyacrylic acid to the conductive material. The solvent is preferably water. Next, negative electrode active materials such as silicon oxide particles and graphite particles are further added to the mixture to prepare a negative electrode slurry. The negative electrode can be produced by coating this negative electrode slurry on a negative electrode current collector and drying it. As a result, the conductive material can be bound to the surface of the negative electrode active material particles such as silicon oxide particles with a higher coverage such as 70% or more or 80% or more.
　［電解液］
　電解液は、非水溶媒と、支持塩を含む。非水溶媒としては、特に限定されるものではないが、例えば、プロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ブチレンカーボネート（ＢＣ）等の環状カーボネート類；ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＭＥＣ）、ジプロピルカーボネート（ＤＰＣ）等の鎖状カーボネート類；プロピレンカーボネート誘導体、ギ酸メチル、酢酸メチル、プロピオン酸エチル等の脂肪族カルボン酸エステル類；ジエチルエーテル、エチルプロピルエーテル等のエーテル類、リン酸トリメチル、リン酸トリエチル、リン酸トリプロピル、リン酸トリオクチル、リン酸トリフェニル等のリン酸エステル類等の非プロトン性有機溶媒、及び、これらの化合物の水素原子の少なくとも一部をフッ素原子で置換したフッ素化非プロトン性有機溶媒等が挙げられる。 [Electrolyte]
The electrolytic solution includes a nonaqueous solvent and a supporting salt. Although it does not specifically limit as a nonaqueous solvent, For example, Cyclic carbonates, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC); Dimethyl carbonate (DMC), Diethyl carbonate (DEC) ), Chain carbonates such as ethyl methyl carbonate (MEC), dipropyl carbonate (DPC); aliphatic carboxylic acid esters such as propylene carbonate derivatives, methyl formate, methyl acetate, ethyl propionate; diethyl ether, ethyl propyl ether Aprotic organic solvents such as ethers such as trimethyl phosphate, triethyl phosphate, tripropyl phosphate, trioctyl phosphate, and triphenyl phosphate, and the number of hydrogen atoms in these compounds When Some fluorinated aprotic organic solvents such as substituted with a fluorine atom a.
　これらの中でも、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＭＥＣ）、ジプロピルカーボネート（ＤＰＣ）等の環状または鎖状カーボネート類を含むことが好ましい。 Among these, cyclic such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), dipropyl carbonate (DPC), etc. Or it is preferable that chain carbonates are included.
　非水溶媒は、１種を単独で、または２種以上を組み合わせて使用することができる。 Non-aqueous solvents can be used alone or in combination of two or more.
　支持塩は、Ｌｉを含有すること以外は特に限定されない。支持塩としては、例えば、ＬｉＰＦ６、ＬｉＡｓＦ６、ＬｉＡｌＣｌ４、ＬｉＣｌＯ４、ＬｉＢＦ４、ＬｉＳｂＦ６、ＬｉＣＦ３ＳＯ３、ＬｉＣ４Ｆ９ＳＯ３、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＮ（ＦＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２、ＬｉＢ１０Ｃｌ１０等が挙げられる。また、支持塩としては、他にも、低級脂肪族カルボン酸リチウム、クロロボランリチウム、四フェニルホウ酸リチウム、ＬｉＢｒ、ＬｉＩ、ＬｉＳＣＮ、ＬｉＣｌ等が挙げられる。支持塩は、１種を単独で、又は２種以上を組み合わせて使用することができる。 The supporting salt is not particularly limited except that it contains Li. Examples of the supporting salt include LiPF 6 , LiAsF 6 , LiAlCl 4 , LiClO 4 , LiBF 4 , LiSbF 6 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiC (CF 3 SO 2 ) 3 , LiN (FSO 2). ) 2 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiB 10 Cl 10 and the like. Other examples of the supporting salt include lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, and the like. A support salt can be used individually by 1 type or in combination of 2 or more types.
　支持塩の電解液中の濃度は、０．５～１．５ｍｏｌ／Ｌであることが好ましい。支持塩の濃度をこの範囲とすることにより、密度や粘度、電気伝導率等を適切な範囲に調整し易くなる。 The concentration of the supporting salt in the electrolytic solution is preferably 0.5 to 1.5 mol / L. By setting the concentration of the supporting salt within this range, it becomes easy to adjust the density, viscosity, electrical conductivity, and the like to an appropriate range.
　電解液は、さらに添加剤を含むことができる。添加剤としては特に限定されるものではないが、ハロゲン化環状カーボネート、不飽和環状カーボネート、及び、環状または鎖状ジスルホン酸エステル等が挙げられる。これらの化合物を添加することにより、サイクル特性等の電池特性を改善することができる。これは、これらの添加剤がリチウムイオン二次電池の充放電時に分解して電極活物質の表面に皮膜を形成し、電解液や支持塩の分解を抑制するためと推定される。 The electrolytic solution can further contain an additive. Although it does not specifically limit as an additive, A halogenated cyclic carbonate, an unsaturated cyclic carbonate, cyclic | annular or chain | strand-shaped disulfonic acid ester, etc. are mentioned. By adding these compounds, battery characteristics such as cycle characteristics can be improved. This is presumed to be because these additives decompose during charging / discharging of the lithium ion secondary battery to form a film on the surface of the electrode active material and suppress decomposition of the electrolytic solution and the supporting salt.
　［セパレータ］
　セパレータは、荷電体の透過を阻害せずに正極および負極の導通を抑制し、電解液に対して耐久性を有するものであれば、いずれであってもよい。具体的な材質としては、ポリプロピレンおよびポリエチレン等のポリオレフィン、セルロース、ポリエチレンテレフタレートおよびポリブチレンテレフタレートなどのポリエステル、ポリイミド、ポリフッ化ビニリデンならびにポリメタフェニレンイソフタルアミド、ポリパラフェニレンテレフタルアミドおよびコポリパラフェニレン－３，４’－オキシジフェニレンテレフタルアミド等の芳香族ポリアミド（アラミド）等が挙げられる。これらは、多孔質フィルム、織物、不織布等として用いることができる。 [Separator]
Any separator may be used as long as it suppresses the conduction between the positive electrode and the negative electrode without impeding the permeation of the charged body and has durability against the electrolytic solution. Specific materials include polyolefins such as polypropylene and polyethylene, polyesters such as cellulose, polyethylene terephthalate and polybutylene terephthalate, polyimide, polyvinylidene fluoride, polymetaphenylene isophthalamide, polyparaphenylene terephthalamide and copolyparaphenylene-3, Aromatic polyamide (aramid) such as 4′-oxydiphenylene terephthalamide can be used. These can be used as porous films, woven fabrics, non-woven fabrics and the like.
　［絶縁層］
　正極、負極、およびセパレータの少なくとも１つの表面に絶縁層を形成してもよい。絶縁層の形成方法としては、ドクターブレード法、ディップコーティング法、ダイコーター法、ＣＶＤ法、スパッタリング法等が挙げられる。正極、負極、セパレータの形成と同時に絶縁層を形成することもできる。絶縁層を構成する物質としては、酸化アルミニウムやチタン酸バリウムなどの絶縁性フィラーとＳＢＲやＰＶＤＦなどの結着剤との混合物などが挙げられる。 [Insulation layer]
An insulating layer may be formed on at least one surface of the positive electrode, the negative electrode, and the separator. Examples of the method for forming the insulating layer include a doctor blade method, a dip coating method, a die coater method, a CVD method, and a sputtering method. An insulating layer can be formed simultaneously with the formation of the positive electrode, the negative electrode, and the separator. Examples of the material constituting the insulating layer include a mixture of an insulating filler such as aluminum oxide or barium titanate and a binder such as SBR or PVDF.
　［リチウムイオン二次電池の構造］
　本実施形態のリチウムイオン二次電池は、例えば、図１および図２のような構造を有する。このリチウムイオン二次電池は、電池要素２０と、それを電解質と一緒に収容するフィルム外装体１０と、正極タブ５１および負極タブ５２（以下、これらを単に「電極タブ」ともいう）とを備えている。 [Structure of lithium ion secondary battery]
The lithium ion secondary battery of this embodiment has a structure as shown in FIGS. 1 and 2, for example. This lithium ion secondary battery includes a battery element 20, a film outer package 10 that accommodates the battery element 20 together with an electrolyte, and a positive electrode tab 51 and a negative electrode tab 52 (hereinafter also referred to simply as “electrode tabs”). ing.
　電池要素２０は、図２に示すように、複数の正極３０と複数の負極４０とがセパレータ２５を間に挟んで交互に積層されたものである。正極３０は、金属箔３１の両面に電極材料３２が塗布されており、負極４０も、同様に、金属箔４１の両面に電極材料４２が塗布されている。なお、本実施形態は、必ずしも積層型の電池に限らず捲回型などの電池にも適用しうる。 As shown in FIG. 2, the battery element 20 is formed by alternately stacking a plurality of positive electrodes 30 and a plurality of negative electrodes 40 with a separator 25 interposed therebetween. In the positive electrode 30, the electrode material 32 is applied to both surfaces of the metal foil 31. Similarly, in the negative electrode 40, the electrode material 42 is applied to both surfaces of the metal foil 41. Note that the present embodiment is not necessarily limited to a stacked battery, and can also be applied to a wound battery.
　リチウムイオン二次電池は図１および図２のように電極タブが外装体の片側に引き出された構成であってもよいが、リチウムイオン二次電池は電極タブが外装体の両側に引き出されたものであってもいい。詳細な図示は省略するが、正極および負極の金属箔は、それぞれ、外周の一部に延長部を有している。負極金属箔の延長部は一つに集められて負極タブ５２と接続され、正極金属箔の延長部は一つに集められて正極タブ５１と接続される（図２参照）。このように延長部どうし積層方向に１つに集めた部分は「集電部」などとも呼ばれる。 The lithium ion secondary battery may have a configuration in which the electrode tab is drawn out on one side of the outer package as shown in FIGS. 1 and 2, but the lithium ion secondary battery has the electrode tab pulled out on both sides of the outer package. It can be a thing. Although detailed illustration is omitted, each of the positive and negative metal foils has an extension on a part of the outer periphery. The extensions of the negative electrode metal foil are collected together and connected to the negative electrode tab 52, and the extensions of the positive electrode metal foil are collected together and connected to the positive electrode tab 51 (see FIG. 2). The portions gathered together in the stacking direction between the extension portions in this way are also called “current collecting portions”.
　フィルム外装体１０は、この例では、２枚のフィルム１０－１、１０－２で構成されている。フィルム１０－１、１０－２どうしは電池要素２０の周辺部で互いに熱融着されて密閉される。図１では、このように密閉されたフィルム外装体１０の１つの短辺から、正極タブ５１および負極タブ５２が同じ方向に引き出されている。 The film outer package 10 is composed of two films 10-1 and 10-2 in this example. The films 10-1 and 10-2 are heat sealed to each other at the periphery of the battery element 20 and sealed. In FIG. 1, the positive electrode tab 51 and the negative electrode tab 52 are drawn in the same direction from one short side of the film outer package 10 sealed in this way.
　当然ながら、異なる２辺から電極タブがそれぞれ引き出されていてもよい。また、フィルムの構成に関し、図１、図２では、一方のフィルム１０－１にカップ部が形成されるとともに他方のフィルム１０－２にはカップ部が形成されていない例が示されているが、この他にも、両方のフィルムにカップ部を形成する構成（不図示）や、両方ともカップ部を形成しない構成（不図示）なども採用しうる。 Of course, electrode tabs may be drawn from two different sides. As for the structure of the film, FIGS. 1 and 2 show examples in which the cup portion is formed on one film 10-1 and the cup portion is not formed on the other film 10-2. In addition, a configuration in which a cup portion is formed on both films (not shown) or a configuration in which neither cup portion is formed (not shown) may be employed.
　本実施形態のリチウムイオン二次電池は、高いエネルギー密度を有する。パウチ型の構造としたとき、本実施形態のリチウムイオン二次電池は、例えば、５４０Ｗｈ／Ｌ以上６６０Ｗｈ／Ｌ以下、６００Ｗｈ／以上６６０Ｗｈ／以下などの高い体積エネルギー密度を有し得る。 The lithium ion secondary battery of this embodiment has a high energy density. When the pouch-type structure is adopted, the lithium ion secondary battery of the present embodiment can have a high volume energy density such as 540 Wh / L or more and 660 Wh / L or less, 600 Wh / or more and 660 Wh / L or less.
　［リチウムイオン二次電池の製造方法］
　本実施形態によるリチウムイオン二次電池は、通常の方法に従って作製することができる。積層ラミネート型のリチウムイオン二次電池を例に、リチウムイオン二次電池の製造方法の一例を説明する。まず、乾燥空気または不活性雰囲気において、正極および負極を、セパレータを介して対向配置して、電極素子を形成する。次に、この電極素子を外装体（容器）に収容し、電解液を注入して電極に電解液を含浸させる。その後、外装体の開口部を封止してリチウムイオン二次電池を完成する。 [Method for producing lithium ion secondary battery]
The lithium ion secondary battery according to the present embodiment can be produced according to a normal method. Taking a laminated laminate type lithium ion secondary battery as an example, an example of a method for producing a lithium ion secondary battery will be described. First, in a dry air or an inert atmosphere, an electrode element is formed by arranging a positive electrode and a negative electrode to face each other with a separator interposed therebetween. Next, this electrode element is accommodated in an exterior body (container), and an electrolytic solution is injected to impregnate the electrode with the electrolytic solution. Then, the opening part of an exterior body is sealed and a lithium ion secondary battery is completed.
　［組電池］
　本実施形態に係るリチウムイオン二次電池を複数組み合わせて組電池とすることができる。組電池は、例えば、本実施形態に係るリチウムイオン二次電池を２つ以上用い、直列、並列又はその両方で接続した構成とすることができる。直列および／または並列接続することで容量および電圧を自由に調節することが可能になる。組電池が備えるリチウムイオン二次電池の個数については、電池容量や出力に応じて適宜設定することができる。 [Battery]
A plurality of lithium ion secondary batteries according to this embodiment can be combined to form an assembled battery. For example, the assembled battery may have a configuration in which two or more lithium ion secondary batteries according to the present embodiment are used and connected in series, in parallel, or both. Capacitance and voltage can be freely adjusted by connecting in series and / or in parallel. About the number of the lithium ion secondary batteries with which an assembled battery is provided, it can set suitably according to battery capacity or an output.
　［車両］
　本実施形態に係るリチウムイオン二次電池またはその組電池は、車両に用いることができる。本実施形態に係る車両としては、ハイブリッド車、燃料電池車、電気自動車（いずれも四輪車（乗用車、トラック、バス等の商用車、軽自動車等）のほか、二輪車（バイク）や三輪車を含む）が挙げられる。なお、本実施形態に係る車両は自動車に限定されるわけではなく、他の車両、例えば電車等の移動体の各種電源として用いることもできる。 [vehicle]
The lithium ion secondary battery or its assembled battery according to this embodiment can be used in a vehicle. Vehicles according to this embodiment include hybrid vehicles, fuel cell vehicles, and electric vehicles (all include four-wheel vehicles (passenger cars, trucks, buses and other commercial vehicles, light vehicles, etc.), motorcycles (motorcycles), and tricycles. ). Note that the vehicle according to the present embodiment is not limited to an automobile, and may be used as various power sources for other vehicles, for example, moving bodies such as trains.
　＜負極導電材：カーボンブラック（比表面積：４５ｍ２／ｇ）＞
　［実施例１］
　（電池の作製）
　正極活物質としてのＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２（９４重量％）に、バインダとしてのポリフッ化ビニリデン（３重量％）と、導電材としてカーボンブラック（３重量％）とを混合して正極合剤とした。該正極合剤をＮ－メチル－２－ピロリドンに分散させることにより、正極スラリーを調製した。この正極スラリーを厚さ１２μｍのアルミニウム製集電箔の片面に、均一に塗布した。乾燥させた後、ロールプレスで圧縮成型することにより正極を作製した。 <Negative electrode conductive material: carbon black (specific surface area: 45 m 2 / g)>
[Example 1]
(Production of battery)
LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture. A positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 μm thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
　負極活物質として４．６ｍ２／ｇのＢＥＴ比表面積および５．０μｍの平均粒子径を有する炭素被覆ＳｉＯ粒子および２．８ｍ２／ｇのＢＥＴ比表面積および１２μｍの平均粒子径を有する人造黒鉛粒子を用いた。ここで使用したＳｉＯは、ＳｉとＳｉＯ２を複合化した粒子であり、粒子の表面には炭素を被覆させた（重量比：ケイ素酸化物／炭素＝９５／５）。炭素被覆ＳｉＯ粒子と、人造黒鉛粒子と、４５ｍ２／ｇのＢＥＴ比表面積および０．０４５μｍの平均粒子径（一次粒子）を有するカーボンブラックを、バインダであるポリアクリル酸と水の混合溶液に分散させ、負極スラリーを作製した。負極スラリー中のそれぞれの負極材料の重量比率は、表１に記載した通りとした。本実施例では、負極活物質である炭素被覆ＳｉＯ粒子と黒鉛粒子の重量比率は、８０：２０である。この負極スラリーを厚さ８μｍの高強度Ｃｕ合金製集電箔上に均一に塗布した。乾燥後、電極をプレスし、負極密度を１．３５ｇ／ｃｍ３とした。 Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 μm as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 μm Was used. The SiO used here is a particle in which Si and SiO 2 are combined, and the surface of the particle is coated with carbon (weight ratio: silicon oxide / carbon = 95/5). Carbon coated SiO particles, artificial graphite particles, carbon black having a BET specific surface area of 45 m 2 / g and an average particle size (primary particles) of 0.045 μm are dispersed in a mixed solution of polyacrylic acid and water as a binder. To produce a negative electrode slurry. The weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 1. In this example, the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20. This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 μm. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 .
　（界面抵抗の測定）
　抵抗測定装置は、日置電機製の型式ＸＦ－０５７プローブユニットを用いた。各負極に関して活物質層の厚さ、集電箔の厚さを入力し、抵抗測定装置のプローブを押し当て、各負極の界面抵抗値を得た。 (Measurement of interface resistance)
The resistance measuring device used was a model XF-057 probe unit manufactured by Hioki Electric. With respect to each negative electrode, the thickness of the active material layer and the thickness of the current collector foil were input, and the probe of the resistance measuring device was pressed to obtain the interface resistance value of each negative electrode.
　３ｃｍ×３ｃｍに切り出した正極と負極をセパレータを介して対向するように配置させた。セパレータには、厚さ１５μｍのＰＥＴ不織布を用いた。 The positive electrode and the negative electrode cut out to 3 cm × 3 cm were arranged so as to face each other with a separator interposed therebetween. A PET nonwoven fabric with a thickness of 15 μm was used as the separator.
　電解液は、溶媒と支持塩を混合することによって作製した。溶媒には、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）を体積比３０／６０／１０として使用し、支持塩には、０．９ｍｏｌ／Ｌの支持塩濃度のＬｉＰＦ６を使用した。 The electrolytic solution was prepared by mixing a solvent and a supporting salt. As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
　上記の正極、負極、セパレータ、及び電解液を、ラミネート外装体の中に配置し、ラミネートを封止し、リチウムイオン二次電池を作製した。正極と負極は、タブが接続され、ラミネートの外部から電気的に接続された状態とした。 The above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced. The positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
　（サイクル特性評価）
　４５℃の恒温槽中で３００回の充放電サイクル試験を行い、その容量維持率を測定し、寿命を評価した。充電は、０．５Ｃの定電流充電を上限電圧４．１５Ｖまで行い、続いて４．１５Ｖで定電圧充電を行い、総充電時間２．５時間で行った。放電は、０．５Ｃで定電流放電を３．０Ｖまで行った。充放電サイクル試験後の容量を測定し、充放電サイクル試験前の容量に対する割合（百分率）を算出した。 (Cycle characteristic evaluation)
A charge / discharge cycle test was performed 300 times in a 45 ° C. thermostat, the capacity retention rate was measured, and the life was evaluated. Charging was performed by constant current charging at 0.5 C up to the upper limit voltage of 4.15 V, followed by constant voltage charging at 4.15 V and a total charging time of 2.5 hours. The discharge was performed at a constant current of 0.5C up to 3.0V. The capacity after the charge / discharge cycle test was measured, and the ratio (percentage) to the capacity before the charge / discharge cycle test was calculated.
　（体積エネルギー密度の測定）
　リチウムイオン二次電池の体積エネルギー密度は、電極の目付量と密度、集電体の厚さ、およびセパレータの厚さから電池体積（Ｌ）を計算した。各セルの比容量（ｍＡｈ／ｇ）、各セルの４５℃２０日でエージングしたときのエージング効率の実測値（％）、および各セルのエージング後の平均動作電圧の実測値（Ｖ）からエネルギー容量（Ｗｈ）を計算した。エネルギー容量を電池体積で除した値を体積エネルギー密度（Ｗｈ／Ｌ）とした。なお、エージング効率は、初回充電容量（ｍＡｈ）に対する、４５℃２０日後の回復容量（ｍＡｈ）の値を用いた。 (Measurement of volumetric energy density)
As the volume energy density of the lithium ion secondary battery, the battery volume (L) was calculated from the basis weight and density of the electrode, the thickness of the current collector, and the thickness of the separator. Energy from specific capacity (mAh / g) of each cell, actual value (%) of aging efficiency when each cell is aged at 45 ° C. for 20 days, and actual value (V) of average operating voltage after aging of each cell The capacity (Wh) was calculated. The value obtained by dividing the energy capacity by the battery volume was defined as the volume energy density (Wh / L). As the aging efficiency, the value of the recovery capacity (mAh) after 45 days at 45 ° C. with respect to the initial charge capacity (mAh) was used.
　［その他の例］
　表１に記載される通り、負極材料および負極材料の重量比率を変更して、同様に電池を作製して、評価した。結果を表１に示す。 [Other examples]
As shown in Table 1, batteries were similarly prepared and evaluated by changing the weight ratio of the negative electrode material and the negative electrode material. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　＜負極導電材：カーボンブラック（比表面積：６５ｍ２／ｇ）＞
　［実施例９］
　正極活物質としてのＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２（９４重量％）に、バインダとしてのポリフッ化ビニリデン（３重量％）と、導電材としてカーボンブラック（３重量％）とを混合して正極合剤とした。該正極合剤をＮ－メチル－２－ピロリドンに分散させることにより、正極スラリーを調製した。この正極スラリーを厚さ１２μｍのアルミニウム製集電箔の片面に、均一に塗布した。乾燥させた後、ロールプレスで圧縮成型することにより正極を作製した。 <Negative electrode conductive material: carbon black (specific surface area: 65 m 2 / g)>
[Example 9]
LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture. A positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 μm thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
　負極活物質として４．６ｍ２／ｇのＢＥＴ比表面積および５．０μｍの平均粒子径を有する炭素被覆ＳｉＯ粒子および２．８ｍ２／ｇのＢＥＴ比表面積および１２μｍの平均粒子径を有する人造黒鉛粒子を用いた。ここで使用したＳｉＯは、ＳｉとＳｉＯ２を複合化した粒子であり、粒子の表面には炭素を被覆させた（重量比：ケイ素酸化物／炭素＝９５／５）。炭素被覆ＳｉＯ粒子と、人造黒鉛粒子と、６５ｍ２／ｇのＢＥＴ比表面積および０．０６５μｍの平均粒子径（一次粒子）を有するカーボンブラックを、バインダであるポリアクリル酸と水の混合溶液に分散させ、負極スラリーを作製した。負極スラリー中のそれぞれの負極材料の重量比率は、表２に記載した通りとした。本実施例では、負極活物質である炭素被覆ＳｉＯ粒子と黒鉛粒子の重量比率は、８０：２０である。この負極スラリーを厚さ８μｍの高強度Ｃｕ合金製集電箔上に均一に塗布した。乾燥後、電極をプレスし、負極密度を１．３５ｇ／ｃｍ３とした。実施例１と同様に界面抵抗を評価した。 Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 μm as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 μm Was used. The SiO used here is a particle in which Si and SiO 2 are combined, and the surface of the particle is coated with carbon (weight ratio: silicon oxide / carbon = 95/5). Carbon coated SiO particles, artificial graphite particles, carbon black having a BET specific surface area of 65 m 2 / g and an average particle size (primary particles) of 0.065 μm are dispersed in a mixed solution of polyacrylic acid and water as a binder. To produce a negative electrode slurry. The weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 2. In this example, the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20. This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 μm. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 . The interface resistance was evaluated in the same manner as in Example 1.
　３ｃｍ×３ｃｍに切り出した正極と負極をセパレータを介して対向するように配置させた。セパレータには、厚さ１５μｍのＰＥＴ不織布を用いた。 The positive electrode and the negative electrode cut out to 3 cm × 3 cm were arranged so as to face each other with a separator interposed therebetween. A PET nonwoven fabric with a thickness of 15 μm was used as the separator.
　電解液は、溶媒と支持塩を混合することによって作製した。溶媒には、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）を体積比３０／６０／１０として使用し、支持塩には、０．９ｍｏｌ／Ｌの支持塩濃度のＬｉＰＦ６を使用した。 The electrolytic solution was prepared by mixing a solvent and a supporting salt. As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
　上記の正極、負極、セパレータ、及び電解液を、ラミネート外装体の中に配置し、ラミネートを封止し、リチウムイオン二次電池を作製した。正極と負極は、タブが接続され、ラミネートの外部から電気的に接続された状態とした。 The above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced. The positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
　実施例１と同様に、作製した電池のサイクル特性、体積エネルギー密度を評価した。結果を表２に示す。 In the same manner as in Example 1, the cycle characteristics and volume energy density of the produced batteries were evaluated. The results are shown in Table 2.
　［その他の例］
　表２に記載される通り、負極材料の重量比率を変更して、同様に電池を作製、評価した。結果を表２に示す。 [Other examples]
As described in Table 2, batteries were similarly prepared and evaluated by changing the weight ratio of the negative electrode material. The results are shown in Table 2.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　＜負極導電材：カーボンナノチューブ（比表面積：１５０ｍ２／ｇ）＞
　［実施例１５］
　正極活物質としてのＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２（９４重量％）に、バインダとしてのポリフッ化ビニリデン（３重量％）と、導電材としてカーボンブラック（３重量％）とを混合して正極合剤とした。該正極合剤をＮ－メチル－２－ピロリドンに分散させることにより、正極スラリーを調製した。この正極スラリーを厚さ１２μｍのアルミニウム製集電箔の片面に、均一に塗布した。乾燥させた後、ロールプレスで圧縮成型することにより正極を作製した。 <Negative electrode conductive material: carbon nanotube (specific surface area: 150 m 2 / g)>
[Example 15]
LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture. A positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 μm thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
　負極活物質として４．６ｍ２／ｇのＢＥＴ比表面積および５．０μｍの平均粒子径を有する炭素被覆ＳｉＯ粒子および２．８ｍ２／ｇのＢＥＴ比表面積および１２μｍの平均粒子径を有する人造黒鉛粒子を用いた。ここで使用したＳｉＯは、ＳｉとＳｉＯ２を複合化した粒子であり、粒子の表面には炭素を被覆させた（重量比：ケイ素酸化物／炭素＝９５／５）。炭素被覆ＳｉＯ粒子と、人造黒鉛粒子と、１５０ｍ２／ｇの比表面積および０．０２μｍの平均粒子径を有するカーボンナノチューブを、バインダであるポリアクリル酸と水の混合溶液に分散させ、負極スラリーを作製した。負極スラリー中のそれぞれの負極材料の重量比率は、表３に記載した通りとした。本実施例では、負極活物質である炭素被覆ＳｉＯ粒子と黒鉛粒子の重量比率は、８０：２０である。この負極スラリーを厚さ８μｍの高強度Ｃｕ合金箔製集電体上に均一に塗布した。乾燥後、電極をプレスし、負極密度を１．３５ｇ／ｃｍ３とした。実施例１と同様に界面抵抗を評価した。 Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 μm as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 μm Was used. The SiO used here is a particle in which Si and SiO 2 are combined, and the surface of the particle is coated with carbon (weight ratio: silicon oxide / carbon = 95/5). Carbon-coated SiO particles, artificial graphite particles, carbon nanotubes having a specific surface area of 150 m 2 / g and an average particle diameter of 0.02 μm are dispersed in a mixed solution of polyacrylic acid and water as a binder, and a negative electrode slurry is prepared. Produced. The weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 3. In this example, the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20. This negative electrode slurry was uniformly applied onto a current collector made of high strength Cu alloy foil having a thickness of 8 μm. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 . The interface resistance was evaluated in the same manner as in Example 1.
　３ｃｍ×３ｃｍに切り出した正極と負極をセパレータを介して対向するように配置させた。セパレータには、厚さ１５μｍのＰＥＴ不織布を用いた。 The positive electrode and the negative electrode cut out to 3 cm × 3 cm were arranged so as to face each other with a separator interposed therebetween. A PET nonwoven fabric with a thickness of 15 μm was used as the separator.
　電解液は、溶媒と支持塩を混合することによって作製した。溶媒には、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）を体積比３０／６０／１０として使用し、支持塩には、０．９ｍｏｌ／Ｌの支持塩濃度のＬｉＰＦ６を使用した。 The electrolytic solution was prepared by mixing a solvent and a supporting salt. As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
　上記の正極、負極、セパレータ、及び電解液を、ラミネート外装体の中に配置し、ラミネートを封止し、リチウムイオン二次電池を作製した。正極と負極は、タブが接続され、ラミネートの外部から電気的に接続された状態とした。 The above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced. The positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
　実施例１と同様に、作製した電池のサイクル特性、体積エネルギー密度を評価した。結果を表３に示す。 In the same manner as in Example 1, the cycle characteristics and volume energy density of the produced batteries were evaluated. The results are shown in Table 3.
　［その他の例］
　表３に記載される通り、負極材料および負極材料の重量比率を変更して、同様に電池を作製、評価した。結果を表３に示す。 [Other examples]
As described in Table 3, batteries were similarly prepared and evaluated by changing the weight ratio of the negative electrode material and the negative electrode material. The results are shown in Table 3.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　実施例１９において作製した負極を充放電前にＳＥＭにより観察した。ＳＥＭ画像を図４に示す。ＳＥＭ画像より、６０～７０％程度のケイ素酸化物粒子表面に、カーボンナノチューブが被覆していることが分かる。 The negative electrode produced in Example 19 was observed by SEM before charge / discharge. The SEM image is shown in FIG. From the SEM image, it can be seen that the surface of silicon oxide particles of about 60 to 70% is covered with carbon nanotubes.
　＜負極導電材：カーボンナノホーン（比表面積：３００ｍ２／ｇ）＞
　［実施例２３］
　正極活物質としてのＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２（９４重量％）に、バインダとしてのポリフッ化ビニリデン（３重量％）と、導電材としてカーボンブラック（３重量％）とを混合して正極合剤とした。該正極合剤をＮ－メチル－２－ピロリドンに分散させることにより、正極スラリーを調製した。この正極スラリーを厚さ１２μｍのアルミニウム製集電箔の片面に、均一に塗布した。乾燥させた後、ロールプレスで圧縮成型することにより正極を作製した。 <Negative electrode conductive material: carbon nanohorn (specific surface area: 300 m 2 / g)>
[Example 23]
LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture. A positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 μm thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
　負極活物質として４．６ｍ２／ｇのＢＥＴ比表面積および５．０μｍの平均粒子径を有する炭素被覆ＳｉＯ粒子および２．８ｍ２／ｇのＢＥＴ比表面積および１２μｍの平均粒子径を有する人造黒鉛粒子を用いた。ここで使用したＳｉＯは、ＳｉとＳｉＯ２を複合化した粒子であり、粒子の表面には炭素を被覆させた（重量比：ケイ素酸化物／炭素＝９５／５）。炭素被覆ＳｉＯ粒子と、人造黒鉛粒子と、３００ｍ２／ｇの比表面積および０．１５μｍの平均粒子径を有するカーボンナノホーンを、バインダであるポリアクリル酸と水の混合溶液に分散させ、負極スラリーを作製した。負極スラリー中のそれぞれの負極材料の重量比率は、表４に記載した通りとした。本実施例では、負極活物質である炭素被覆ＳｉＯ粒子と黒鉛粒子の重量比率は、８０：２０である。この負極スラリーを厚さ８μｍの高強度Ｃｕ合金製集電箔上に均一に塗布した。乾燥後、電極をプレスし、負極密度を１．３５ｇ／ｃｍ３とした。実施例１と同様に界面抵抗を評価した。 Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 μm as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 μm Was used. The SiO used here is a particle in which Si and SiO 2 are combined, and the surface of the particle is coated with carbon (weight ratio: silicon oxide / carbon = 95/5). Carbon-coated SiO particles, artificial graphite particles, carbon nanohorns having a specific surface area of 300 m 2 / g and an average particle size of 0.15 μm are dispersed in a mixed solution of polyacrylic acid and water as a binder, and a negative electrode slurry is prepared. Produced. The weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 4. In this example, the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20. This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 μm. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 . The interface resistance was evaluated in the same manner as in Example 1.
　３ｃｍ×３ｃｍに切り出した正極と負極をセパレータを介して対向するように配置させた。セパレータには、厚さ１５μｍのＰＥＴ不織布を用いた。 The positive electrode and the negative electrode cut out to 3 cm × 3 cm were arranged so as to face each other with a separator interposed therebetween. A PET nonwoven fabric with a thickness of 15 μm was used as the separator.
　電解液は、溶媒と支持塩を混合することによって作製した。溶媒には、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）を体積比３０／６０／１０として使用し、支持塩には、０．９ｍｏｌ／Ｌの支持塩濃度のＬｉＰＦ６を使用した。 The electrolytic solution was prepared by mixing a solvent and a supporting salt. As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
　上記の正極、負極、セパレータ、及び電解液を、ラミネート外装体の中に配置し、ラミネートを封止し、リチウムイオン二次電池を作製した。正極と負極は、タブが接続され、ラミネートの外部から電気的に接続された状態とした。 The above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced. The positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
　実施例１と同様に、作製した電池のサイクル特性、体積エネルギー密度を評価した。結果を表４に示す。 In the same manner as in Example 1, the cycle characteristics and volume energy density of the produced batteries were evaluated. The results are shown in Table 4.
　［その他の例］
　表４に記載される通り、負極材料の重量比率を変更して、同様に電池を作製、評価した。結果を表４に示す。 [Other examples]
As described in Table 4, batteries were similarly prepared and evaluated by changing the weight ratio of the negative electrode material. The results are shown in Table 4.
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
　実施例２６において作製した負極を充放電前にＳＥＭにより観察した。ＳＥＭ画像を図５に示す。ＳＥＭ画像より、５０～６０％程度のケイ素酸化物粒子表面に、カーボンナノホーンが被覆していることが分かる。 The negative electrode produced in Example 26 was observed by SEM before charge / discharge. The SEM image is shown in FIG. From the SEM image, it can be seen that the surface of silicon oxide particles of about 50 to 60% is covered with carbon nanohorns.
　＜負極導電材：ケッチェンブラック（比表面積：８００ｍ２／ｇ）＞
　［実施例２９］
　正極活物質としてのＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２（９４重量％）に、バインダとしてのポリフッ化ビニリデン（３重量％）と、導電材としてカーボンブラック（３重量％）とを混合して正極合剤とした。該正極合剤をＮ－メチル－２－ピロリドンに分散させることにより、正極スラリーを調製した。この正極スラリーを厚さ１２μｍのアルミニウム製集電箔の片面に、均一に塗布した。乾燥させた後、ロールプレスで圧縮成型することにより正極を作製した。 <Negative electrode conductive material: Ketjen black (specific surface area: 800 m 2 / g)>
[Example 29]
LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture. A positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 μm thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
　負極活物質として４．６ｍ２／ｇのＢＥＴ比表面積および５．０μｍの平均粒子径を有する炭素被覆ＳｉＯ粒子および２．８ｍ２／ｇのＢＥＴ比表面積および１２μｍの平均粒子径を有する人造黒鉛粒子を用いた。ここで使用したＳｉＯは、ＳｉとＳｉＯ２を複合化した粒子であり、粒子の表面には炭素を被覆させた（重量比：ケイ素酸化物／炭素＝９５／５）。炭素被覆ＳｉＯ粒子と、人造黒鉛粒子と、８００ｍ２／ｇの比表面積および０．０４μｍの平均粒子径（一次粒子）を有するケッチェンブラックを、バインダであるポリアクリル酸と水の混合溶液に分散させ、負極スラリーを作製した。負極スラリー中のそれぞれの負極材料の重量比率は、表５に記載した通りとした。本実施例では、負極活物質である炭素被覆ＳｉＯ粒子と黒鉛粒子の重量比率は、８０：２０である。この負極スラリーを厚さ８μｍの高強度Ｃｕ合金製集電箔上に均一に塗布した。乾燥後、電極をプレスし、負極密度を１．３５ｇ／ｃｍ３とした。実施例１と同様に界面抵抗を評価した。 Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 μm as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 μm Was used. The SiO used here is a particle in which Si and SiO 2 are combined, and the surface of the particle is coated with carbon (weight ratio: silicon oxide / carbon = 95/5). Disperse Ketjen Black having carbon-coated SiO particles, artificial graphite particles, a specific surface area of 800 m 2 / g and an average particle size (primary particles) of 0.04 μm in a mixed solution of polyacrylic acid and water as a binder. To produce a negative electrode slurry. The weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 5. In this example, the weight ratio of the carbon-coated SiO particles, which are the negative electrode active material, and the graphite particles is 80:20. This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 μm. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 . The interface resistance was evaluated in the same manner as in Example 1.
　３ｃｍ×３ｃｍに切り出した正極と負極をセパレータを介して対向するように配置させた。セパレータには、厚さ１５μｍのＰＥＴ不織布を用いた。 The positive electrode and the negative electrode cut out to 3 cm × 3 cm were arranged so as to face each other with a separator interposed therebetween. A PET nonwoven fabric with a thickness of 15 μm was used as the separator.
　電解液は、溶媒と支持塩を混合することによって作製した。溶媒には、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）を体積比３０／６０／１０として使用し、支持塩には、０．９ｍｏｌ／Ｌの支持塩濃度のＬｉＰＦ６を使用した。 The electrolytic solution was prepared by mixing a solvent and a supporting salt. As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
　上記の正極、負極、セパレータ、及び電解液を、ラミネート外装体の中に配置し、ラミネートを封止し、リチウムイオン二次電池を作製した。正極と負極は、タブが接続され、ラミネートの外部から電気的に接続された状態とした。 The above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced. The positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
　実施例１と同様に、作製した電池のサイクル特性、体積エネルギー密度を評価した。結果を表５に示す。 In the same manner as in Example 1, the cycle characteristics and volume energy density of the produced batteries were evaluated. The results are shown in Table 5.
　［その他の例］
　表５に記載される通り、負極材料の重量比率を変更して、同様に電池を作製、評価した。結果を表５に示す。 [Other examples]
As described in Table 5, batteries were similarly prepared and evaluated by changing the weight ratio of the negative electrode material. The results are shown in Table 5.
Figure JPOXMLDOC01-appb-T000006
Figure JPOXMLDOC01-appb-T000006
　＜負極導電材：板状黒鉛（比表面積１７ｍ２／ｇ）＞
　［比較例２４］
　正極活物質としてのＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２（９４重量％）に、バインダとしてのポリフッ化ビニリデン（３重量％）と、導電材としてカーボンブラック（３重量％）とを混合して正極合剤とした。該正極合剤をＮ－メチル－２－ピロリドンに分散させることにより、正極スラリーを調製した。この正極スラリーを厚さ１２μｍのアルミニウム製集電箔の片面に、均一に塗布した。乾燥させた後、ロールプレスで圧縮成型することにより正極を作製した。 <Negative electrode conductive material: plate-like graphite (specific surface area 17 m 2 / g)>
[Comparative Example 24]
LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture. A positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 μm thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
　負極活物質として４．６ｍ２／ｇのＢＥＴ比表面積および５．０μｍの平均粒子径を有する炭素被覆ＳｉＯ粒子および２．８ｍ２／ｇのＢＥＴ比表面積および１２μｍの平均粒子径を有する人造黒鉛粒子を用いた。ここで使用したＳｉＯは、ＳｉとＳｉＯ２を複合化した粒子であり、粒子の表面には炭素を被覆させた（重量比：ケイ素酸化物／炭素＝９５／５）。炭素被覆ＳｉＯ粒子と、人造黒鉛粒子と、１７ｍ２／ｇの比表面積および１０μｍの平均粒子径を有する板状黒鉛を、バインダであるポリアクリル酸と水の混合溶液に分散させ、負極スラリーを作製した。負極スラリー中のそれぞれの負極材料の重量比率は、表６に記載した通りとした。本比較例では、負極活物質である炭素被覆ＳｉＯ粒子と黒鉛粒子の重量比率は、８０：２０である。この負極スラリーを厚さ８μｍの高強度Ｃｕ合金製集電箔上に均一に塗布した。乾燥後、電極をプレスし、負極密度を１．３５ｇ／ｃｍ３とした。実施例１と同様に界面抵抗を評価した。 Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 μm as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 μm Was used. The SiO used here is a particle in which Si and SiO 2 are combined, and the surface of the particle is coated with carbon (weight ratio: silicon oxide / carbon = 95/5). Carbon-coated SiO particles, artificial graphite particles, plate graphite having a specific surface area of 17 m 2 / g and an average particle diameter of 10 μm are dispersed in a mixed solution of polyacrylic acid and water as a binder to produce a negative electrode slurry. did. The weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 6. In this comparative example, the weight ratio of the carbon-coated SiO particles that are the negative electrode active material and the graphite particles is 80:20. This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 μm. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 . The interface resistance was evaluated in the same manner as in Example 1.
　３ｃｍ×３ｃｍに切り出した正極と負極をセパレータを介して対向するように配置させた。セパレータには、厚さ１５μｍのＰＥＴ不織布を用いた。 The positive electrode and the negative electrode cut out to 3 cm × 3 cm were arranged so as to face each other with a separator interposed therebetween. A PET nonwoven fabric with a thickness of 15 μm was used as the separator.
　電解液は、溶媒と支持塩を混合することによって作製した。溶媒には、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）を体積比３０／６０／１０として使用し、支持塩には、０．９ｍｏｌ／Ｌの支持塩濃度のＬｉＰＦ６を使用した。 The electrolytic solution was prepared by mixing a solvent and a supporting salt. As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
　上記の正極、負極、セパレータ、及び電解液を、ラミネート外装体の中に配置し、ラミネートを封止し、リチウムイオン二次電池を作製した。正極と負極は、タブが接続され、ラミネートの外部から電気的に接続された状態とした。 The above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced. The positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
　実施例１と同様に、作製した電池のサイクル特性、体積エネルギー密度を評価した。結果を表６に示す。 In the same manner as in Example 1, the cycle characteristics and volume energy density of the produced batteries were evaluated. The results are shown in Table 6.
　［その他の例］
　表６に記載される通り、負極材料の重量比率を変更して、同様に電池を作製、評価した。結果を表６に示す。 [Other examples]
As shown in Table 6, batteries were similarly prepared and evaluated by changing the weight ratio of the negative electrode material. The results are shown in Table 6.
Figure JPOXMLDOC01-appb-T000007
Figure JPOXMLDOC01-appb-T000007
　＜負極導電材：ケッチェンブラック（比表面積：１２７０ｍ２／ｇ）＞
　［比較例３４］
　正極活物質としてのＬｉＮｉ０．８Ｃｏ０．１５Ａｌ０．０５Ｏ２（９４重量％）に、バインダとしてのポリフッ化ビニリデン（３重量％）と、導電材としてカーボンブラック（３重量％）とを混合して正極合剤とした。該正極合剤をＮ－メチル－２－ピロリドンに分散させることにより、正極スラリーを調製した。この正極スラリーを厚さ１２μｍのアルミニウム製集電箔の片面に、均一に塗布した。乾燥させた後、ロールプレスで圧縮成型することにより正極を作製した。 <Negative electrode conductive material: Ketjen black (specific surface area: 1270 m 2 / g)>
[Comparative Example 34]
LiNi 0.8 Co 0.15 Al 0.05 O 2 (94 wt%) as the positive electrode active material, polyvinylidene fluoride (3 wt%) as the binder, and carbon black (3 wt%) as the conductive material Were mixed to obtain a positive electrode mixture. A positive electrode slurry was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone. This positive electrode slurry was uniformly applied to one side of a 12 μm thick aluminum current collector foil. After drying, a positive electrode was produced by compression molding with a roll press.
　負極活物質として４．６ｍ２／ｇのＢＥＴ比表面積および５．０μｍの平均粒子径を有する炭素被覆ＳｉＯ粒子および２．８ｍ２／ｇのＢＥＴ比表面積および１２μｍの平均粒子径を有する人造黒鉛粒子を用いた。ここで使用したＳｉＯは、ＳｉとＳｉＯ２を複合化した粒子であり、粒子の表面には炭素を被覆させた（重量比：ケイ素酸化物／炭素＝９５／５）。炭素被覆ＳｉＯ粒子と、人造黒鉛粒子と、１２７０ｍ２／ｇの比表面積および０．０３５μｍの平均粒子径（一次粒子）を有するケッチェンブラックを、バインダであるポリアクリル酸と水の混合溶液に分散させ、負極スラリーを作製した。負極スラリー中のそれぞれの負極材料の重量比率は、表７に記載した通りとした。本比較例では、負極活物質である炭素被覆ＳｉＯ粒子と黒鉛粒子の重量比率は、８０：２０である。この負極スラリーを厚さ８μｍの高強度Ｃｕ合金製集電箔上に均一に塗布した。乾燥後、電極をプレスし、負極密度を１．３５ｇ／ｃｍ３とした。実施例１と同様に界面抵抗を評価した。 Carbon-coated SiO particles having a BET specific surface area of 4.6 m 2 / g and an average particle diameter of 5.0 μm as the negative electrode active material, and artificial graphite particles having a BET specific surface area of 2.8 m 2 / g and an average particle diameter of 12 μm Was used. The SiO used here is a particle in which Si and SiO 2 are combined, and the surface of the particle is coated with carbon (weight ratio: silicon oxide / carbon = 95/5). Disperse Ketjen Black having carbon-coated SiO particles, artificial graphite particles, a specific surface area of 1270 m 2 / g and an average particle size (primary particles) of 0.035 μm in a mixed solution of polyacrylic acid and water as a binder. To produce a negative electrode slurry. The weight ratio of each negative electrode material in the negative electrode slurry was as shown in Table 7. In this comparative example, the weight ratio of the carbon-coated SiO particles that are the negative electrode active material and the graphite particles is 80:20. This negative electrode slurry was uniformly applied onto a high strength Cu alloy current collector foil having a thickness of 8 μm. After drying, the electrode was pressed to make the negative electrode density 1.35 g / cm 3 . The interface resistance was evaluated in the same manner as in Example 1.
　３ｃｍ×３ｃｍに切り出した正極と負極をセパレータを介して対向するように配置させた。セパレータには、厚さ１５μｍのＰＥＴ不織布を用いた。 The positive electrode and the negative electrode cut out to 3 cm × 3 cm were arranged so as to face each other with a separator interposed therebetween. A PET nonwoven fabric with a thickness of 15 μm was used as the separator.
　電解液は、溶媒と支持塩を混合することによって作製した。溶媒には、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、メチルエチルカーボネート（ＭＥＣ）を体積比３０／６０／１０として使用し、支持塩には、０．９ｍｏｌ／Ｌの支持塩濃度のＬｉＰＦ６を使用した。 The electrolytic solution was prepared by mixing a solvent and a supporting salt. As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC) were used at a volume ratio of 30/60/10, and the supporting salt was LiPF having a supporting salt concentration of 0.9 mol / L. 6 was used.
　上記の正極、負極、セパレータ、及び電解液を、ラミネート外装体の中に配置し、ラミネートを封止し、リチウムイオン二次電池を作製した。正極と負極は、タブが接続され、ラミネートの外部から電気的に接続された状態とした。 The above positive electrode, negative electrode, separator, and electrolytic solution were placed in a laminate outer package, the laminate was sealed, and a lithium ion secondary battery was produced. The positive electrode and the negative electrode were connected to a tab and electrically connected from the outside of the laminate.
　実施例１と同様に、作製した電池のサイクル特性、体積エネルギー密度を評価した。結果を表７に示す。 In the same manner as in Example 1, the cycle characteristics and volume energy density of the produced batteries were evaluated. The results are shown in Table 7.
　［その他の例］
　表７に記載される通り、負極材料の重量比率を変更して、同様に電池を作製、評価した。結果を表７に示す。 [Other examples]
As described in Table 7, batteries were similarly prepared and evaluated by changing the weight ratio of the negative electrode material. The results are shown in Table 7.
Figure JPOXMLDOC01-appb-T000008
Figure JPOXMLDOC01-appb-T000008
　＜集電箔の種類と厚さの影響＞
　集電箔の種類および厚さの影響を確認した。上述したカーボンナノホーンを導電材に使用する実施例２４では、負極集電体に厚さ８μｍ高強度Ｃｕ合金製集電箔を使用していたが、以下の表８に記載される通り、ステンレス箔または電解銅箔に変更した。その他は実施例２４と同様に電池を作製した。作製した電池の評価結果を表８に記載する。 <Effects of current collector foil type and thickness>
The effect of the type and thickness of the current collector foil was confirmed. In Example 24 in which the above-described carbon nanohorn was used as the conductive material, a current collector foil made of high strength Cu alloy having a thickness of 8 μm was used for the negative electrode current collector, but as described in Table 8 below, the stainless steel foil was used. Or changed to electrolytic copper foil. Otherwise, a battery was fabricated in the same manner as in Example 24. Table 8 shows the evaluation results of the fabricated batteries.
Figure JPOXMLDOC01-appb-T000009
 　集電箔に、電解銅箔を用いた場合には、３００サイクルまで容量維持率が維持できないほど容量劣化が大きい傾向を示した。劣化要因としては、電解銅箔の強度が低いことが考えられ、高含有量で存在するＳiＯの膨張収縮に耐えられないことが示唆された。一方、ステンレス製の箔の場合には、高強度Ｃｕ合金箔に比べて、界面抵抗の値は高くなるが、高強度Ｃｕ合金箔と同等な容量維持率を示した。
Figure JPOXMLDOC01-appb-T000009
 When the electrolytic copper foil was used as the current collector foil, the capacity deterioration was so large that the capacity retention rate could not be maintained up to 300 cycles. As a deterioration factor, it is considered that the strength of the electrolytic copper foil is low, and it was suggested that the copper foil cannot withstand the expansion and contraction of SiO present at a high content. On the other hand, in the case of the stainless steel foil, the interfacial resistance was higher than that of the high-strength Cu alloy foil, but the capacity retention rate was the same as that of the high-strength Cu alloy foil.
　＜負極活物質層の作製方法の影響＞
　上述したカーボンナノホーンを導電材に使用する実施例２４および２６では、負極活物質と導電材を同時にポリアクリル酸と水の混合溶液に混合する混合方式１を採用したが、導電材を最初にポリアクリル酸と水の混合溶液に混合し、次いで、その混合溶液に負極活物質を混合する混合方式２に変更した。その他は実施例２４または２６と同様に電池を作製した。作製した電池の評価結果を表９に記載する。 <Influence of production method of negative electrode active material layer>
In Examples 24 and 26 in which the carbon nanohorn described above is used as a conductive material, the mixing method 1 in which the negative electrode active material and the conductive material are simultaneously mixed in a mixed solution of polyacrylic acid and water is employed. It mixed into the mixed solution of acrylic acid and water, and it changed into the mixing system 2 which mixes a negative electrode active material with the mixed solution then. Otherwise, a battery was fabricated in the same manner as in Example 24 or 26. Table 9 shows the evaluation results of the fabricated batteries.
Figure JPOXMLDOC01-appb-T000010
Figure JPOXMLDOC01-appb-T000010
　実施例３７および３８において作製した負極を充放電前にＳＥＭにより観察した。ＳＥＭ画像より８０％程度のケイ素酸化物粒子表面に、カーボンナノホーンが被覆していることが分かった。事前にポリアクリル酸をカーボンナノホーンに付着させることにより、導電材のケイ素酸化物粒子への被覆率が高くなったと考えられる。この結果として、同じ設計仕様の実施例２４および２６と比べて、界面抵抗が低くなり、サイクル特性が高くなり、体積エネルギー密度も高い値を示した。 The negative electrode produced in Examples 37 and 38 was observed by SEM before charge and discharge. From the SEM image, it was found that about 80% of the silicon oxide particles were coated with carbon nanohorns. It is thought that the coverage of the conductive material on the silicon oxide particles was increased by attaching polyacrylic acid to the carbon nanohorn in advance. As a result, compared with Examples 24 and 26 having the same design specifications, the interface resistance was lowered, the cycle characteristics were increased, and the volume energy density was also high.
　上記の実施形態の一部または全部は、以下の付記のようにも記載されうるが、本出願の開示事項は以下の付記に限定されない。
（付記１）
　リチウム含有層状ニッケル複合酸化物を含む正極活物質層を備える正極と、ケイ素酸化物および炭素を含む複合粒子、黒鉛粒子、導電材、およびポリアクリル酸を含む負極活物質層を備える負極を含むリチウムイオン二次電池であって、前記導電材が４０～８００ｍ２／ｇの比表面積を有し、前記負極活物質層において、前記複合粒子の量が５０重量％以上であり、前記ポリアクリル酸の量が３重量％以上８重量％以下であり、前記導電材の量が１重量％以上であり、前記導電材と前記ポリアクリル酸の総量が１３重量％以下であり、前記複合粒子において、前記炭素の量が２重量％以上である、リチウムイオン二次電池。
（付記２）
　前記ポリアクリル酸に対する前記導電材の重量比が、０．１２以上２以下である、付記１に記載のリチウムイオン二次電池。
（付記３）
　前記黒鉛粒子が人造黒鉛である、付記１または２に記載のリチウムイオン二次電池。
（付記４）
　前記黒鉛粒子が、８μｍ以上２５μｍ以下の平均粒子径および２ｍ２／ｇ以上５ｍ２／ｇ以下の比表面積を有する付記１～３のいずれかに記載のリチウムイオン二次電池。
（付記５）
　前記複合粒子が、３μｍ以上７μｍ以下の平均粒子径および３ｍ２／ｇ以上１２ｍ２／ｇ以下の比表面積を有する付記１～４のいずれかに記載のリチウムイオン二次電池。
（付記６）
　前記複合粒子において、前記ケイ素酸化物の量が７０重量％以上である、付記１～５のいずれかに記載のリチウムイオン二次電池。
（付記７）
　前記導電材が、前記複合粒子の表面の７０％以上を被覆している、付記１～６のいずれかに記載のリチウムイオン二次電池。
（付記８）
　前記負極が銅合金製またはステンレス製の集電箔を有する、付記１～７のいずれかに記載のリチウムイオン二次電池。
（付記９）
　前記導電材が、２０ｎｍ以上８０ｎｍ以下の平均粒子径および４０ｍ２／ｇ以上８０ｍ２／ｇ以下の比表面積を有するカーボンブラック、１０ｎｍ以上３０ｎｍ以下の直径および１００ｍ２／ｇ以上２００ｍ２／ｇの比表面積を有するカーボンナノチューブ、ならびに８０ｎｍ以上１６０ｎｍ以下の直径および２００ｍ２／ｇ以上４００ｍ２／ｇ以下の比表面積を有するカーボンナノホーンから選択される、付記１～８のいずれかに記載のリチウムイオン二次電池。
（付記１０）
　前記負極の界面抵抗が１０－５Ω・ｃｍ２以上１０－２Ω・ｃｍ２以下である、付記１～９のいずれかに記載のリチウムイオン二次電池。
（付記１１）
　体積エネルギー密度が５４０Ｗｈ／Ｌ以上６６０Ｗｈ／Ｌ以下である、付記１～１０のいずれかに記載のリチウムイオン二次電池。
（付記１２）
　付記１～１１のいずれかに記載のリチウムイオン二次電池を搭載した車両。
（付記１３）
　４０～８００ｍ２／ｇの比表面積を有する導電材、ケイ素酸化物および炭素を含み前記炭素の量が２重量％以上である複合粒子および黒鉛粒子、ならびにポリアクリル酸を溶媒に混合して負極スラリーを調製する工程と、前記負極スラリーを集電体に塗布し、前記複合粒子の量が５０重量％以上であり、前記ポリアクリル酸の量が３重量％以上８重量％以下であり、前記導電材と前記ポリアクリル酸の総量が４重量％以上１３重量％以下である負極活物質層を形成する工程と、を含む負極の製造方法。
（付記１４）
　４０～８００ｍ２／ｇの比表面積を有する導電材、およびポリアクリル酸を溶媒に混合してスラリーを調製する工程と、前記スラリーに、ケイ素酸化物および炭素を含み前記炭素の量が２重量％以上である複合粒子および黒鉛粒子をさらに混合し、負極スラリーを調製する工程と、前記負極スラリーを集電体に塗布し、前記複合粒子の量が５０重量％以上であり、前記ポリアクリル酸の量が３重量％以上８重量％以下であり、前記導電材と前記ポリアクリル酸の総量が４重量％以上１３重量％以下である負極活物質層を形成する工程と、を含む負極の製造方法。 A part or all of the above embodiment can be described as the following supplementary notes, but the disclosure of the present application is not limited to the following supplementary notes.
(Appendix 1)
Lithium including a positive electrode including a positive electrode active material layer including a lithium-containing layered nickel composite oxide, and a negative electrode including a composite particle including silicon oxide and carbon, graphite particles, a conductive material, and a negative electrode active material layer including polyacrylic acid In the ion secondary battery, the conductive material has a specific surface area of 40 to 800 m 2 / g, and in the negative electrode active material layer, the amount of the composite particles is 50% by weight or more, and the polyacrylic acid The amount of the conductive material is 1% by weight or more, the total amount of the conductive material and the polyacrylic acid is 13% by weight or less, and in the composite particle, A lithium ion secondary battery in which the amount of carbon is 2% by weight or more.
(Appendix 2)
The lithium ion secondary battery according to appendix 1, wherein a weight ratio of the conductive material to the polyacrylic acid is 0.12 or more and 2 or less.
(Appendix 3)
The lithium ion secondary battery according to appendix 1 or 2, wherein the graphite particles are artificial graphite.
(Appendix 4)
The graphite particles, the lithium ion secondary battery according to any one of appendices 1 to 3 having the following specific surface area average particle diameter and 2m 2 / g or more 8μm above 25μm or less 5 m 2 / g.
(Appendix 5)
The lithium ion secondary battery according to any one of supplementary notes 1 to 4, wherein the composite particles have an average particle diameter of 3 μm to 7 μm and a specific surface area of 3 m 2 / g to 12 m 2 / g.
(Appendix 6)
The lithium ion secondary battery according to any one of appendices 1 to 5, wherein the amount of the silicon oxide in the composite particles is 70% by weight or more.
(Appendix 7)
The lithium ion secondary battery according to any one of appendices 1 to 6, wherein the conductive material covers 70% or more of the surface of the composite particle.
(Appendix 8)
The lithium ion secondary battery according to any one of appendices 1 to 7, wherein the negative electrode has a current collector foil made of copper alloy or stainless steel.
(Appendix 9)
The ratio of the conductive material, 80 nm or less of the average particle diameter of more than 20nm and 40 m 2 / g or more 80 m 2 / g carbon black having the following specific surface area, 10 nm or more 30nm or less in diameter and 100 m 2 / g or more 200 meters 2 / g The lithium ion secondary according to any one of appendices 1 to 8, selected from carbon nanotubes having a surface area, and carbon nanohorns having a diameter of 80 nm to 160 nm and a specific surface area of 200 m 2 / g to 400 m 2 / g battery.
(Appendix 10)
The lithium ion secondary battery according to any one of supplementary notes 1 to 9, wherein the negative electrode has an interface resistance of 10 −5 Ω · cm 2 or more and 10 −2 Ω · cm 2 or less.
(Appendix 11)
The lithium ion secondary battery according to any one of supplementary notes 1 to 10, wherein the volume energy density is 540 Wh / L or more and 660 Wh / L or less.
(Appendix 12)
A vehicle equipped with the lithium ion secondary battery according to any one of appendices 1 to 11.
(Appendix 13)
A negative electrode slurry prepared by mixing a conductive material having a specific surface area of 40 to 800 m 2 / g, silicon oxide and carbon, and composite particles and graphite particles containing 2% by weight or more of carbon, and polyacrylic acid in a solvent. The negative electrode slurry is applied to a current collector, the amount of the composite particles is 50% by weight or more, the amount of the polyacrylic acid is 3% by weight or more and 8% by weight or less, and the conductive And a step of forming a negative electrode active material layer in which the total amount of the material and the polyacrylic acid is 4% by weight or more and 13% by weight or less.
(Appendix 14)
A step of preparing a slurry by mixing a conductive material having a specific surface area of 40 to 800 m 2 / g, and polyacrylic acid in a solvent; and the amount of the carbon containing silicon oxide and carbon in the slurry is 2% by weight The step of further mixing the composite particles and the graphite particles as described above to prepare a negative electrode slurry, applying the negative electrode slurry to a current collector, the amount of the composite particles is 50% by weight or more, and the polyacrylic acid Forming a negative electrode active material layer in which the amount is 3 wt% or more and 8 wt% or less, and the total amount of the conductive material and the polyacrylic acid is 4 wt% or more and 13 wt% or less. .
　この出願は、２０１７年２月２３日に出願された日本出願特願２０１７－３２１４３を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2017-32143 filed on Feb. 23, 2017, the entire disclosure of which is incorporated herein.
　以上、実施形態及び実施例を参照して本願発明を説明したが、本願発明は上記実施形態及び実施例に限定されるものではない。本願発明の構成や詳細には、本願発明のスコープ内で当業者が理解し得る様々な変更をすることができる。 As mentioned above, although this invention was demonstrated with reference to embodiment and an Example, this invention is not limited to the said embodiment and Example. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.
　本発明によるリチウムイオン二次電池は、例えば、電源を必要とするあらゆる産業分野、ならびに電気的エネルギーの輸送、貯蔵および供給に関する産業分野において利用することができる。具体的には、携帯電話、ノートパソコン等のモバイル機器の電源；電気自動車、ハイブリッドカー、電動バイク、電動アシスト自転車等を含む電動車両、電車、衛星、潜水艦等の移動・輸送用媒体の電源；ＵＰＳ等のバックアップ電源；太陽光発電、風力発電等で発電した電力を貯める蓄電設備；等に、利用することができる。 The lithium ion secondary battery according to the present invention can be used in, for example, all industrial fields that require a power source and industrial fields related to transport, storage, and supply of electrical energy. Specifically, power sources for mobile devices such as mobile phones and laptop computers; power sources for mobile vehicles such as electric vehicles, hybrid cars, electric motorcycles, electric assist bicycles, electric vehicles, trains, satellites, submarines, etc .; It can be used for backup power sources such as UPS; power storage facilities for storing power generated by solar power generation, wind power generation, etc.
１０　フィルム外装体
２０　電池要素
２５　セパレータ
３０　正極
４０　負極 DESCRIPTION OF SYMBOLS 10 Film exterior 20 Battery element 25 Separator 30 Positive electrode 40 Negative electrode

Claims (10)

  1. 　リチウム含有層状ニッケル複合酸化物を含む正極活物質層を備える正極と、
    　ケイ素酸化物および炭素を含む複合粒子、黒鉛粒子、導電材、およびポリアクリル酸を含む負極活物質層を備える負極を含むリチウムイオン二次電池であって、
    　前記導電材が４０～８００ｍ２／ｇの比表面積を有し、
    　前記負極活物質層において、前記複合粒子の量が５０重量％以上であり、前記ポリアクリル酸の量が３重量％以上８重量％以下であり、前記導電材と前記ポリアクリル酸の総量が４重量％以上１３重量％以下であり、
    　前記複合粒子において、前記炭素の量が２重量％以上である、リチウムイオン二次電池。     A positive electrode comprising a positive electrode active material layer comprising a lithium-containing layered nickel composite oxide;
    A lithium ion secondary battery including a negative electrode including a composite particle including silicon oxide and carbon, a graphite particle, a conductive material, and a negative electrode active material layer including polyacrylic acid,
    The conductive material has a specific surface area of 40 to 800 m 2 / g;
    In the negative electrode active material layer, the amount of the composite particles is 50% by weight or more, the amount of the polyacrylic acid is 3% by weight or more and 8% by weight or less, and the total amount of the conductive material and the polyacrylic acid is 4%. % By weight to 13% by weight,
    The lithium ion secondary battery in which the amount of the carbon is 2% by weight or more in the composite particle.
  2. 　前記ポリアクリル酸に対する前記導電材の重量比が、０．１２以上２以下である、請求項１に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1, wherein a weight ratio of the conductive material to the polyacrylic acid is 0.12 or more and 2 or less.
  3. 　前記黒鉛粒子が人造黒鉛である、請求項１または２に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 1 or 2, wherein the graphite particles are artificial graphite.
  4. 　前記複合粒子において、前記ケイ素酸化物の量が７０重量％以上である、請求項１～３のいずれか１項に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 3, wherein the amount of the silicon oxide in the composite particles is 70 wt% or more.
  5. 　前記導電材が、前記複合粒子の表面の７０％以上を被覆している、請求項１～４のいずれか１項に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 4, wherein the conductive material covers 70% or more of the surface of the composite particles.
  6. 　前記負極が銅合金製またはステンレス製の集電箔を有する、請求項１～５のいずれか１項に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 5, wherein the negative electrode has a current collector foil made of copper alloy or stainless steel.
  7. 　前記導電材が、２０ｎｍ以上８０ｎｍ以下の平均粒子径および４０ｍ２／ｇ以上８０ｍ２／ｇ以下の比表面積を有するカーボンブラック、１０ｎｍ以上３０ｎｍ以下の直径および１００ｍ２／ｇ以上２００ｍ２／ｇ以下の比表面積を有するカーボンナノチューブ、ならびに８０ｎｍ以上１６０ｎｍ以下の直径および２００ｍ２／ｇ以上４００ｍ２／ｇ以下の比表面積を有するカーボンナノホーンから選択される、請求項１～６のいずれか１項に記載のリチウムイオン二次電池。 The conductive material is carbon black having an average particle diameter of 20 nm to 80 nm and a specific surface area of 40 m 2 / g to 80 m 2 / g, a diameter of 10 nm to 30 nm, and a diameter of 100 m 2 / g to 200 m 2 / g. The carbon nanotube having a specific surface area, and carbon nanohorns having a diameter of 80 nm or more and 160 nm or less and a specific surface area of 200 m 2 / g or more and 400 m 2 / g or less, according to any one of claims 1 to 6. Lithium ion secondary battery.
  8. 　体積エネルギー密度が５４０Ｗｈ／Ｌ以上６６０Ｗｈ／Ｌ以下である、請求項１～７のいずれか１項に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to any one of claims 1 to 7, wherein the volume energy density is 540 Wh / L or more and 660 Wh / L or less.
  9. 　請求項１～８のいずれか１項に記載のリチウムイオン二次電池を搭載した車両。 A vehicle equipped with the lithium ion secondary battery according to any one of claims 1 to 8.
  10. 　４０～８００ｍ２／ｇの比表面積を有する導電材、およびポリアクリル酸を溶媒に混合してスラリーを調製する工程と、
    　前記スラリーに、ケイ素酸化物および炭素を含み前記炭素の量が２重量％以上である複合粒子および黒鉛粒子をさらに混合し、負極スラリーを調製する工程と、
    　前記負極スラリーを集電体に塗布し、前記複合粒子の量が５０重量％以上であり、前記ポリアクリル酸の量が３重量％以上８重量％以下であり、前記導電材と前記ポリアクリル酸の総量が４重量％以上１３重量％以下である負極活物質層を形成する工程と、を含む負極の製造方法。     A step of preparing a slurry by mixing a conductive material having a specific surface area of 40 to 800 m 2 / g and polyacrylic acid in a solvent;
    A step of preparing a negative electrode slurry by further mixing composite particles and graphite particles containing silicon oxide and carbon and the amount of the carbon is 2% by weight or more into the slurry;
    The negative electrode slurry is applied to a current collector, the amount of the composite particles is 50% by weight or more, the amount of the polyacrylic acid is 3% by weight or more and 8% by weight or less, the conductive material and the polyacrylic acid Forming a negative electrode active material layer having a total amount of 4% by weight or more and 13% by weight or less.
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