WO2019244933A1 - Positive electrode material for lithium ion secondary battery, positive electrode active material layer, and lithium ion secondary battery - Google Patents

Positive electrode material for lithium ion secondary battery, positive electrode active material layer, and lithium ion secondary battery Download PDF

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Publication number
WO2019244933A1
WO2019244933A1 PCT/JP2019/024306 JP2019024306W WO2019244933A1 WO 2019244933 A1 WO2019244933 A1 WO 2019244933A1 JP 2019024306 W JP2019024306 W JP 2019024306W WO 2019244933 A1 WO2019244933 A1 WO 2019244933A1
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positive electrode
ion secondary
lithium ion
active material
secondary battery
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PCT/JP2019/024306
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French (fr)
Japanese (ja)
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和徳 小関
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積水化学工業株式会社
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Priority to CN201980041161.6A priority Critical patent/CN112385058B/en
Priority to JP2020525770A priority patent/JP6832474B2/en
Publication of WO2019244933A1 publication Critical patent/WO2019244933A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a positive electrode material for a lithium ion secondary battery, a positive electrode active material layer made of the positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery.
  • Lithium-ion secondary batteries are used as large stationary power supplies for power storage and power supplies for electric vehicles, etc.
  • a lithium ion secondary battery includes both electrodes (positive electrode and negative electrode) each having an electrode active material layer formed on a surface of a metal foil, and a separator disposed between the both electrodes.
  • the separator plays a role in preventing a short circuit between the two electrodes and holding the electrolytic solution.
  • the positive electrode of a lithium ion secondary battery generally includes a positive electrode active material layer including a positive electrode active material, a conductive additive, and a binder (binder). It is known that the types and amounts of these individual components in the positive electrode active material layer affect various performances such as cycle characteristics and output characteristics of the lithium ion secondary battery.
  • Patent Literature 1 discloses a lithium ion secondary battery having a positive electrode active material having an average pore diameter of 10 nm to 300 nm, a binder containing polyvinylidene fluoride having a weight average molecular weight of 500,000 to 1.5 million, and a conductive additive. A positive electrode material is described, which indicates that the cycle characteristics and the like are good.
  • a positive electrode material for a lithium ion secondary battery capable of manufacturing a lithium ion secondary battery having excellent cycle characteristics and output characteristics, and a positive electrode active material comprising the positive electrode material for the lithium ion secondary battery And a lithium ion secondary battery including the positive electrode active material layer.
  • the present inventors have found that a positive electrode material containing a positive electrode active material, a conductive auxiliary, and a binder, the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder, and the conductivity per 1 g of the positive electrode material
  • the inventors have found that the above problems can be solved by setting the total surface area of the auxiliary agent and the BET specific surface area of the positive electrode active material in specific ranges, and completed the present invention described below.
  • the gist of the present invention is the following [1] to [8].
  • [5] The positive electrode material for a lithium ion secondary battery according to any of [1] to [4], wherein the positive electrode active material is a lithium nickel cobalt aluminum-based oxide.
  • a positive electrode active material layer comprising the positive electrode material for a lithium ion secondary battery according to any one of the above [1] to [5].
  • the lithium ion secondary battery according to the above [7] comprising the positive electrode, a negative electrode arranged to face the positive electrode, and a separator arranged between the positive electrode and the negative electrode.
  • a positive electrode material for a lithium ion secondary battery capable of obtaining a lithium ion secondary battery having excellent cycle characteristics and output characteristics, a positive electrode active material layer including the positive electrode material for the lithium ion secondary battery, A lithium ion secondary battery including a positive electrode active material layer can be provided.
  • FIG. 1 is a schematic sectional view showing one embodiment of a lithium ion secondary battery of the present invention.
  • the positive electrode material for a lithium secondary battery of the present invention includes a positive electrode active material, a conductive auxiliary, and a binder, and the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder is 700 m 2. / G or less, the total surface area of the conductive additive per 1 g of the positive electrode material is 16 m 2 / g or more, and the BET specific surface area of the positive electrode active material is 1.2 m 2 / g or less.
  • the positive electrode material of the present invention has a specific range of the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder, the total surface area of the conductive auxiliary per 1 g of the positive electrode material, and the BET specific surface area of the positive electrode active material as described above. Therefore, the lithium ion secondary battery manufactured using the positive electrode material has good cycle characteristics and output characteristics.
  • the positive electrode material of the present invention contains a positive electrode active material having a BET specific surface area of 1.2 m 2 / g or less.
  • the BET specific surface area of the positive electrode active material exceeds 1.2 m 2 / g, the cycle characteristics of the lithium ion secondary battery tend to deteriorate, and the strength of the lithium ion secondary battery tends to decrease.
  • the BET specific surface area of the positive electrode active material is preferably 1.0 m 2 / g or less, more preferably 0.8 m 2 / g or less, and Preferably, it is at least 0.1 m 2 / g.
  • the BET specific surface area can be determined by the BET method, and specifically, can be determined by the BET method using nitrogen gas adsorption.
  • Examples of the positive electrode active material include a lithium metal oxide compound.
  • Examples of the lithium metal oxide compound include lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), and the like. Further, olivine-type lithium iron phosphate (LiFePO 4 ) may be used. Further, a plurality of metals other than lithium may be used, and a lithium nickel cobalt manganese-based oxide (NCM), a lithium nickel cobalt aluminum-based oxide (NCA), or the like may be used. Among them, lithium nickel cobalt aluminum oxide (NCA) is preferable from the viewpoint of improving the charge / discharge capacity of the lithium ion secondary battery.
  • the lithium nickel cobalt aluminum oxide is obtained by substituting a part of nickel of lithium nickel oxide with aluminum and cobalt.
  • Lithium-nickel-cobalt-aluminum-based oxide by the formula Li t Ni 1-x-y Co x Al y O 2 (where, 0.95 ⁇ t ⁇ 1.15,0 ⁇ x ⁇ 0.3,0 ⁇ y ⁇ 0.2, x + y ⁇ 0.5).
  • the average particle diameter of the positive electrode active material is preferably from 0.5 to 50 ⁇ m, more preferably from 1 to 30 ⁇ m, even more preferably from 5 to 15 ⁇ m. From the viewpoint of improving the cycle characteristics of the lithium ion secondary battery, the average particle size of the positive electrode active material is preferably 12 ⁇ m or more, and is preferably 50 ⁇ m or less, more preferably 30 ⁇ m or less, and still more preferably 15 ⁇ m or less. .
  • the average particle diameter means a particle diameter (D50) at a volume integration of 50% in a particle size distribution of the positive electrode active material obtained by a laser diffraction / scattering method.
  • the average particle diameter of the negative electrode active material described later and the average particle diameter of the insulating fine particles can be measured by the same method.
  • the content of the positive electrode active material in the positive electrode material is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the positive electrode material.
  • the positive electrode material of the present invention contains a conductive auxiliary. By containing the conductive auxiliary, the electric conductivity of the positive electrode material can be improved.
  • the total surface area of the conductive additive per 1 g of the positive electrode material is 16 m 2 / g or more. When the total surface area of the conductive additive per 1 g of the positive electrode material is less than 16 m 2 / g, the output characteristics of the lithium ion secondary battery deteriorate.
  • the total surface area of the conductive additive per 1 g of the positive electrode material is preferably 16.3 m 2 / g or more, more preferably 17 m 2 / g or more. Preferably, it is 200 m 2 / g or less, more preferably 50 m 2 / g or less.
  • the total surface area of the positive electrode active material and the conductive auxiliary agent per 1 g of the binder is 700 m 2 / g or less.
  • the total surface area exceeds 700 m 2 / g the cycle characteristics of the lithium ion secondary battery tend to deteriorate, and the strength tends to decrease. This is because, when the total surface area of the positive electrode active material and the conductive additive per 1 g of the binder is large, the binder is consumed on the surface of the positive electrode active material and the conductive additive, thereby reducing the strength of the entire electrode. Conceivable.
  • the total surface area of the positive electrode active material and the conductive auxiliary agent per 1 g of the binder is preferably 697 m 2 / g or less, more preferably 695 m 2 / g or less.
  • the total surface area of the positive electrode active material and the conductive auxiliary agent per 1 g of the binder can be determined by dividing the sum of the following [1] and [2] by the mass ratio (wt%) of the binder in the positive electrode material. . That is, it can be determined by the formula of ([1] + [2]) / (mass ratio (wt%) of binder in positive electrode material).
  • conductive assistant a and conductive assistant b which will be described later, instead of the above [2], the following [2 '] is used, and the positive electrode active material per 1 g of binder and The total surface area of the conductive additive can be determined.
  • the conductive assistant contained in the positive electrode material of the present invention preferably contains a conductive assistant a and a conductive assistant b having different BET specific surface areas.
  • a positive electrode material containing a conductive additive having a different BET specific surface area cycle characteristics and output characteristics of a lithium ion secondary battery can be improved.
  • the BET specific surface area of the conductive additive a is preferably at least 600 m 2 / g, more preferably at least 800 m 2 / g, even more preferably at least 1000 m 2 / g, and 2,000 m 2 / g. Or less, more preferably 1500 m 2 / g or less.
  • the BET specific surface area of the conductive additive b is less than 100 m 2 / g, preferably at 50 m 2 / g or less, still more preferably less 20 m 2 / g, and, 5 m 2 / g or more And more preferably 10 m 2 / g or more.
  • the content of the conductive additive is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass, based on the total amount of the positive electrode material.
  • the content of the conductive assistant means the content when one kind of the conductive assistant is used, and means the total amount of the plurality of conductive assistants when a plurality of the conductive assistants are used.
  • the conductive additive includes the conductive aids a and b having different BET specific surface areas
  • the content of the conductive aid a may be 0.2 to 15% by mass based on the total amount of the positive electrode material. Preferably, it is 0.5 to 10% by mass, more preferably 1 to 5% by mass.
  • the content of the conductive additive b is preferably 0.3 to 15% by mass, more preferably 0.5 to 10% by mass, and more preferably 2 to 7% by mass, based on the total amount of the positive electrode material. Is more preferred. From the viewpoint of improving the cycle characteristics and output characteristics of the lithium ion secondary battery, the content of the conductive auxiliary agent b is more than the content of the conductive auxiliary agent a in the conductive auxiliary agent. It is more preferable that the content of the conductive additive b with respect to the content of the conductive additive a be 1.2 to 3.0, more preferably 1.5 to 2.5.
  • the type of the conductive additive is not particularly limited as long as it is a material having higher conductivity than the positive electrode active material, but it is preferable to use a carbon material.
  • the carbon material include, but are not particularly limited to, chain carbon, fibrous or rod-like carbon, and graphite particles.
  • the conductive assistant contains the conductive assistants a and b having different BET specific surface areas as described above, these types are not particularly limited, but preferably both are carbon materials. More specifically, the conductive additive a is preferably at least one selected from chain carbon and graphite particles.
  • the chain carbon refers to particles in which particles are connected in a chain by fusing or agglomeration, and examples thereof include carbon black such as acetylene black and furnace black. Examples of the acetylene black include “DENKA BLACK” (trade name, manufactured by Denki Kagaku Kogyo Co., Ltd.). Examples of the furnace black include “Super P” (trade name, manufactured by Imerys Corporation). Further, “Ketjen Black” manufactured by Lion Specialty Chemicals Co., Ltd.
  • the graphite particles may be either natural graphite or artificial graphite, and may be graphite particles having a surface layer such as a carbonaceous layer. Specific examples of the graphite particles include “UP-5 ⁇ ” and “SP-5030 ⁇ ” manufactured by Nippon Graphite Co., Ltd., and “KS4” and “KS6” manufactured by Imeris.
  • the conductive particles b are preferably fibrous or rod-like carbon.
  • the fibrous or rod-like carbon include carbon nanofibers, carbon nanotubes, and carbon nanohorns. Among them, carbon nanotubes are preferable, and vapor-grown carbon fibers are more preferable. Examples of the vapor-grown carbon fiber include “VGCF-H” manufactured by Showa Denko KK.
  • the positive electrode material of the present invention contains a binder.
  • the positive electrode material is configured by binding the above-described positive electrode active material and conductive assistant to the binder.
  • the binder include fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), polymethyl acrylate (PMA), and polymethyl acrylate (PMA).
  • Acrylic resin such as methyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene-butadiene rubber, poly (meth) acrylic acid, carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol and the like.
  • binders may be used alone or in combination of two or more.
  • carboxymethylcellulose and the like may be used in the form of a salt such as a sodium salt.
  • a fluorine-containing resin is preferable, and among the fluorine-containing resins, polyvinylidene fluoride (PVDF) is preferably used.
  • the content of the binder in the positive electrode material is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and further preferably 2 to 4% by mass, based on the total amount of the positive electrode material. .
  • the positive electrode material for a lithium secondary battery of the present invention can be used as a positive electrode active material layer of a lithium ion secondary battery.
  • a lithium ion secondary battery provided with a positive electrode having the positive electrode active material layer has good cycle characteristics and output characteristics.
  • FIG. 1 is a schematic sectional view showing one embodiment of the lithium ion secondary battery of the present invention.
  • the lithium ion secondary battery 10 includes a positive electrode 12, a negative electrode 11 disposed to face the positive electrode 12, and a separator 13 disposed between the positive electrode 12 and the negative electrode 11.
  • the negative electrode 11 includes a negative electrode current collector 11a and a negative electrode active material layer 11b laminated on the negative electrode current collector 11a.
  • the positive electrode 12 has a positive electrode current collector 12a and a positive electrode current collector 12a. And a positive electrode active material layer 12b made of the positive electrode material of the present invention laminated thereon.
  • the positive electrode active material layer 12b composed of the positive electrode material of the present invention has a total surface area of the positive electrode active material and 1 g of the conductive auxiliary per 1 g of the binder, a total surface area of the conductive auxiliary per 1 g of the positive electrode material, and The BET specific surface area is defined as a specific range.
  • an insulating layer (not shown) may be provided between the negative electrode active material layer 11b and the separator 13 or between the positive electrode active material layer 12b and the separator 13. By providing the insulating layer, a short circuit between the positive electrode 12 and the negative electrode 11 can be effectively prevented.
  • the positive electrode in the lithium ion secondary battery of the present invention has a positive electrode active material layer made of the positive electrode material of the present invention, and preferably includes a positive electrode current collector and a positive electrode active material layer stacked on the positive electrode current collector.
  • the thickness of the positive electrode active material layer is not particularly limited, but is preferably from 10 to 200 ⁇ m, and more preferably from 50 to 150 ⁇ m.
  • Examples of a material constituting the positive electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Preferably, aluminum or copper, and more preferably, aluminum is used.
  • the positive electrode current collector is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 ⁇ m.
  • the positive electrode material is preferably formed from a positive electrode material composition.
  • the composition for a positive electrode material is a composition containing the above-described positive electrode active material, a conductive additive, and a binder.
  • the composition for a positive electrode material preferably further contains a solvent.
  • the composition for the positive electrode material is generally a slurry.
  • the content of each component in the positive electrode material composition may be adjusted so that the content of each component excluding the solvent becomes the content described in the positive electrode material described above.
  • the positive electrode in which the positive electrode active material layer made of the positive electrode material is formed on the positive electrode current collector can be obtained by applying and drying the composition for the positive electrode material on the positive electrode current collector.
  • the negative electrode in the lithium ion secondary battery of the present invention has a negative electrode active material layer made of a negative electrode material, and preferably has a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector.
  • the negative electrode active material layer typically contains a negative electrode active material and a negative electrode binder.
  • Examples of the negative electrode active material used for the negative electrode active material layer include graphite, carbon materials such as hard carbon, a composite of a tin compound and silicon and carbon, and lithium. Among these, carbon materials are preferable, and graphite is preferable. More preferred.
  • the negative electrode active material is not particularly limited, but preferably has an average particle size of 0.5 to 50 ⁇ m, more preferably 1 to 30 ⁇ m.
  • the content of the negative electrode active material in the negative electrode active material layer is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the negative electrode active material layer.
  • the negative electrode active material layer may contain a conductive auxiliary.
  • a conductive additive a material having higher conductivity than the above-described negative electrode active material is used, and specific examples thereof include carbon materials such as carbon black, carbon nanofiber, carbon nanotube, and graphite particles.
  • the content of the conductive auxiliary is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, based on the total amount of the negative electrode active material layer. Is more preferred.
  • the negative electrode binder contained in the negative electrode active material layer the same kind of binder as used in the above-described positive electrode material can be used.
  • the content of the negative electrode binder in the negative electrode active material layer is preferably 1.5 to 40% by mass, more preferably 2.0 to 25% by mass, based on the total amount of the negative electrode active material layer.
  • the thickness of the negative electrode active material layer is not particularly limited, but is preferably from 10 to 200 ⁇ m, and more preferably from 50 to 150 ⁇ m.
  • Examples of a material constituting the negative electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum or copper is preferable, and copper is more preferable.
  • the negative electrode current collector is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 ⁇ m.
  • a negative electrode active material, a negative electrode binder, a conductive auxiliary, and a negative electrode material composition containing a solvent to be blended as necessary are coated on a negative electrode current collector and dried. Thereby, a negative electrode in which the negative electrode active material layer is formed on the negative electrode current collector can be obtained.
  • the lithium ion secondary battery of the present invention includes a separator disposed between a negative electrode and a positive electrode.
  • the separator effectively prevents a short circuit between the positive electrode and the negative electrode. Further, the separator may hold an electrolyte described later.
  • the separator include a porous polymer film, a nonwoven fabric, and a glass fiber. Among these, a porous polymer film is preferable.
  • the porous polymer film include an olefin-based porous film such as an ethylene-based porous film.
  • the lithium ion secondary battery of the present invention may have an insulating layer on the negative electrode active material layer or the positive electrode active material layer. A short circuit between the positive electrode and the negative electrode is effectively prevented by the insulating layer.
  • the insulating layer preferably includes an insulating fine particle and a binder for the insulating layer, and is a layer having a porous structure formed by binding the insulating fine particle with the binder for the insulating layer.
  • the insulating fine particles are not particularly limited as long as they are insulating, and may be organic particles or inorganic particles.
  • Specific organic particles include, for example, cross-linked polymethyl methacrylate, cross-linked styrene-acrylic acid copolymer, cross-linked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamido-2-methylpropanesulfonate), Examples include particles composed of an organic compound such as a polyacetal resin, an epoxy resin, a polyester resin, a phenol resin, and a melamine resin.
  • Silicon dioxide as inorganic particles, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb 2 O 5), tantalum oxide (Ta 2 O 5), potassium fluoride,
  • examples include particles composed of inorganic compounds such as lithium chloride, clay, zeolite, and calcium carbonate.
  • the inorganic particles may be particles composed of a known composite oxide such as a niobium-tantalum composite oxide or a magnesium-tantalum composite oxide.
  • One kind of the insulating fine particles may be used alone, or a plurality of kinds may be used in combination.
  • the average particle diameter of the insulating fine particles is not particularly limited as long as it is smaller than the thickness of the insulating layer, and is, for example, 0.001 to 1 ⁇ m, preferably 0.05 to 0.8 ⁇ m, and more preferably 0.1 to 0.6 ⁇ m. is there.
  • the content of the insulating fine particles contained in the insulating layer is preferably 15 to 95% by mass, more preferably 40 to 90% by mass, and still more preferably 60 to 85% by mass, based on the total amount of the insulating layer. When the content of the insulating fine particles is within the above range, the insulating layer can form a uniform porous structure, and is provided with appropriate insulating properties.
  • the binder for the insulating layer the same binder as that used in the above-described positive electrode material can be used.
  • the content of the binder for the insulating layer in the insulating layer is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and still more preferably 15 to 40% by mass, based on the total amount of the insulating layer.
  • the thickness of the insulating layer is preferably 1 to 10 ⁇ m, more preferably 2 to 8 ⁇ m, and still more preferably 3 to 7 ⁇ m.
  • the lithium ion secondary battery of the present invention includes an electrolyte.
  • the electrolyte is not particularly limited, and a known electrolyte used in a lithium ion secondary battery may be used.
  • an electrolyte is used as the electrolyte.
  • the electrolyte include an electrolyte containing an organic solvent and an electrolyte salt.
  • the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, ⁇ -butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, and tetrohydra.
  • Examples thereof include polar solvents such as furan, 2-methyltetrahydrofuran, dioxolan, and methyl acetate, or a mixture of two or more of these solvents.
  • polar solvents such as furan, 2-methyltetrahydrofuran, dioxolan, and methyl acetate, or a mixture of two or more of these solvents.
  • electrolyte salt LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiCF 3 CO 2 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 CF 2 CF 3 ) 2 , LiN (COCF 3 )
  • lithium-containing salts such as LiN (COCF 2 CF 3 ) 2 and lithium bisoxalate borate (LiB (C 2 O 4 ) 2.
  • the electrolyte may be a gel electrolyte further containing a polymer compound in the above-mentioned electrolytic solution.
  • the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacryl-based polymer such as poly (methyl) methacrylate.
  • the gel electrolyte may be used as a separator.
  • the electrolyte may be disposed between the negative electrode and the positive electrode.
  • the electrolyte solution is filled in the battery cell in which the above-described negative electrode, positive electrode, and separator are housed.
  • the electrolyte may be, for example, applied on the negative electrode or the positive electrode and disposed between the negative electrode and the positive electrode.
  • the lithium ion secondary battery may have a multilayer structure in which a plurality of negative electrodes and a plurality of positive electrodes are stacked.
  • the negative electrode and the positive electrode may be provided alternately along the laminating direction.
  • the separator may be provided between each negative electrode and each positive electrode. When an insulating layer is provided, it may be provided between the negative electrode and the separator or between the positive electrode and the separator.
  • the obtained lithium ion secondary battery was evaluated by the following evaluation method.
  • the coating amounts of the composition for the positive electrode material and the composition for the negative electrode material were adjusted so that the capacity of the manufactured battery was 3 mA / cm 2 , and lithium ion secondary batteries of Examples and Comparative Examples were obtained as described later.
  • the voltage range was set such that the lower limit voltage of the terminal voltage was 2.5 V and the upper limit voltage of the discharge was 4.2 V. Charge and discharge were repeated under the following conditions.
  • Electrode strength The electrode strength of each of the positive electrodes (electrodes) manufactured in each of Examples and Comparative Examples was measured as follows. The positive electrode was cut into 30 mm x 100 mm, and the positive electrode active material layer was bent inward and sandwiched from above and below with a 10 mm thick acrylic plate. After being sandwiched, a 500 g weight was placed and held for 5 seconds. Thereafter, the folded surface was opened with the bent surface facing upward, the appearance was inspected, and the evaluation was made according to the following criteria. A: The positive electrode active material layer did not crack. B: Part of the positive electrode active material layer was powdered. C: The positive electrode active material layer was powdered and the current collector foil was visible.
  • Example 1 (Preparation of positive electrode) A slurry-type positive electrode material in which the positive electrode materials shown in Table 1 (positive electrode active material, conductive auxiliary agent, and positive electrode binder) were mixed with N-methylpyrrolidone (NMP) as a solvent and the solid content concentration was adjusted to 60% by mass. A composition for use was prepared. This composition for a positive electrode material was applied to both sides of a 15 ⁇ m-thick aluminum foil as a positive electrode current collector, preliminarily dried, and then vacuum dried at 120 ° C.
  • NMP N-methylpyrrolidone
  • the positive electrode current collector coated with the composition for a positive electrode material on both sides is pressed with a roller at a linear pressure of 400 kN / m by a roller, and further punched into a 100 mm ⁇ 200 mm square of the electrode dimensions to form a positive electrode active material layer on both sides.
  • the area where the positive electrode active material was applied was 100 mm ⁇ 180 mm.
  • the negative electrode current collector coated with the composition for a negative electrode material on both surfaces is pressed with a roller at a linear pressure of 300 kN / m, and further punched out into 110 mm ⁇ 210 mm square of the electrode dimensions to form a negative electrode active material layer on both surfaces.
  • the area where the negative electrode active material was applied was 110 mm ⁇ 190 mm.
  • LiPF 6 as an electrolyte salt was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 (EC: DEC) so as to have a concentration of 1 mol / liter, and the electrolytic solution was dissolved.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • the laminated body was sandwiched between aluminum laminated films, the terminal tabs were projected outside, and three sides were sealed by lamination.
  • the electrolyte solution obtained above was injected from one side left without sealing, and vacuum sealing was performed to produce a laminate type cell.
  • Table 1 shows the evaluation results of the obtained lithium ion secondary batteries.
  • Example 2 Comparative Examples 1 to 5
  • a lithium ion secondary battery was obtained in the same manner as in Example 1, except that the cathode material was changed as shown in Table 1.
  • Table 1 shows the evaluation results.
  • the positive electrode active material, the conductive auxiliary agent, and the binder for electrodes used in the preparation of the positive electrode are as follows.
  • (Positive electrode active material) NCA1: lithium nickel cobalt aluminum oxide (average particle diameter: 13.3 ⁇ m, BET specific surface area 0.66 m 2 / g)
  • NCA2 lithium nickel cobalt aluminum oxide (average particle size: 11.1 ⁇ m, BET specific surface area 1.3 m 2 / g)
  • NCA3 lithium nickel cobalt aluminum oxide (average particle diameter: 10.5 ⁇ m, BET specific surface area 1.7 m 2 / g)
  • NCA4 lithium nickel cobalt aluminum oxide (average particle size: 7.7 ⁇ m, BET specific surface area 2.0 m 2 / g)

Abstract

The present invention is a positive electrode material for a lithium ion secondary battery, the positive electrode material comprising a positive electrode active material, a conductive additive, and a binder, wherein the total surface area of the positive electrode active material and the conductive additive per 1 g of the binder is 700 m2/g or less, the total surface area of the conductive additive per 1 g of the positive electrode material is 16 m2/g or more, and the BET specific surface area of the positive electrode active material is 1.2 m2/g or less. Thus, the present invention is capable of providing: the positive electrode material for a lithium ion secondary battery with which a lithium ion secondary battery that has good cycle characteristics and output characteristics can be manufactured; a positive electrode active material layer that comprises the positive electrode material for a lithium ion secondary battery; and a lithium ion secondary battery that includes the positive electrode active material layer.

Description

リチウムイオン二次電池用正極材料、正極活物質層、及びリチウムイオン二次電池Positive electrode material for lithium ion secondary battery, positive electrode active material layer, and lithium ion secondary battery
　本発明は、リチウムイオン二次電池用正極材料、該リチウムイオン二次電池用正極材料からなる正極活物質層、及びリチウムイオン二次電池に関する。 The present invention relates to a positive electrode material for a lithium ion secondary battery, a positive electrode active material layer made of the positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery.
　リチウムイオン二次電池は、電力貯蔵用の大型定置用電源、電気自動車用等の電源として利用されており、近年では電池の小型化及び薄型化の研究が進展している。リチウムイオン二次電池は、金属箔の表面に電極活物質層を形成した両電極（正極及び負極）と、両電極の間に配置されるセパレータを備えるものが一般的である。セパレータは、両電極間の短絡防止や電解液を保持する役割を果たす。 (4) Lithium-ion secondary batteries are used as large stationary power supplies for power storage and power supplies for electric vehicles, etc. In recent years, research into battery miniaturization and thinning has been advanced. Generally, a lithium ion secondary battery includes both electrodes (positive electrode and negative electrode) each having an electrode active material layer formed on a surface of a metal foil, and a separator disposed between the both electrodes. The separator plays a role in preventing a short circuit between the two electrodes and holding the electrolytic solution.
　リチウムイオン二次電池の正極は、一般には、正極活物質と、導電助剤と、バインダー（結着剤）とを含む正極活物質層を備えている。正極活物質層中のこれらの個々の成分の種類及び量は、リチウムイオン二次電池のサイクル特性、出力特性などの各種性能に影響を及ぼすことが知られている。
　例えば、特許文献１では、平均細孔径が１０ｎｍ～３００ｎｍである正極活物質と、重量平均分子量５０万～１５０万のポリフッ化ビニリデンを含むバインダーと、導電助剤とを有するリチウムイオン二次電池用正極材料が記載されており、サイクル特性などが良好であることが示されている。 The positive electrode of a lithium ion secondary battery generally includes a positive electrode active material layer including a positive electrode active material, a conductive additive, and a binder (binder). It is known that the types and amounts of these individual components in the positive electrode active material layer affect various performances such as cycle characteristics and output characteristics of the lithium ion secondary battery.
For example, Patent Literature 1 discloses a lithium ion secondary battery having a positive electrode active material having an average pore diameter of 10 nm to 300 nm, a binder containing polyvinylidene fluoride having a weight average molecular weight of 500,000 to 1.5 million, and a conductive additive. A positive electrode material is described, which indicates that the cycle characteristics and the like are good.
特開２０１５－０６９８２２号公報JP 2015-069822 A
　近年、より高性能なリチウムイオン二次電池が求められているが、リチウムイオン二次電池のサイクル特性、及び出力特性を共に良好とすることは難しい。例えば、正極活物質剤中の導電助剤の量を多くすると、抵抗が下がるため出力特性は向上するものの、電極が脆くなったり、サイクル特性の低下などが生じてしまう。
　このような背景より、本発明では、サイクル特性及び出力特性が共に良好なリチウムイオン二次電池を製造できるリチウムイオン二次電池用正極材料、該リチウムイオン二次電池用正極材料からなる正極活物質層、及び該正極活物質層を備えるリチウムイオン二次電池を提供することを目的とする。 In recent years, higher performance lithium ion secondary batteries have been demanded, but it is difficult to improve both the cycle characteristics and the output characteristics of the lithium ion secondary batteries. For example, when the amount of the conductive auxiliary agent in the positive electrode active material agent is increased, the output characteristics are improved because the resistance is reduced, but the electrodes become brittle or the cycle characteristics are reduced.
From such a background, in the present invention, a positive electrode material for a lithium ion secondary battery capable of manufacturing a lithium ion secondary battery having excellent cycle characteristics and output characteristics, and a positive electrode active material comprising the positive electrode material for the lithium ion secondary battery And a lithium ion secondary battery including the positive electrode active material layer.
　本発明者らは、鋭意検討の結果、正極活物質、導電助剤、及びバインダーを含む正極材料であって、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積、正極材料１ｇあたりの導電助剤の総表面積、及び正極活物質のＢＥＴ比表面積を特定範囲とすることにより、上記課題を解決できることを見出し、以下の本発明を完成させた。本発明の要旨は、以下の［１］～［８］である。
［１］正極活物質、導電助剤、及びバインダーを含む正極材料であって、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積が７００ｍ２／ｇ以下であり、正極材料１ｇあたりの導電助剤の総表面積が１６ｍ２／ｇ以上であり、正極活物質のＢＥＴ比表面積が１．２ｍ２／ｇ以下である、リチウムイオン二次電池用正極材料。
［２］前記導電助剤が、ＢＥＴ比表面積の異なる導電助剤ａ及び導電助剤ｂを含有する、上記［１］に記載のリチウムイオン二次電池用正極材料。
［３］前記導電助剤ａのＢＥＴ比表面積が６００ｍ２／ｇ以上であり、前記導電助剤ｂのＢＥＴ比表面積が１００ｍ２／ｇ未満である、上記［２］に記載のリチウムイオン二次電池用正極材料。
［４］前記導電助剤ａが鎖状のカーボン及び黒鉛粒子から選択される少なくとも１種であり、前記導電助剤ｂが繊維状又は棒状のカーボンである、上記［２］又は［３］に記載のリチウムイオン二次電池用正極材料。
［５］前記正極活物質がリチウムニッケルコバルトアルミニウム系酸化物である、上記［１］～［４］のいずれかに記載のリチウムイオン二次電池用正極材料。
［６］上記［１］～［５］のいずれかに記載のリチウムイオン二次電池用正極材料からなる正極活物質層。
［７］上記［６］に記載の正極活物質層を有する正極を備える、リチウムイオン二次電池。
［８］前記正極と、正極と対向するように配置される負極と、正極と負極の間に配置されるセパレータとを備える、上記［７］に記載のリチウムイオン二次電池。 As a result of intensive studies, the present inventors have found that a positive electrode material containing a positive electrode active material, a conductive auxiliary, and a binder, the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder, and the conductivity per 1 g of the positive electrode material The inventors have found that the above problems can be solved by setting the total surface area of the auxiliary agent and the BET specific surface area of the positive electrode active material in specific ranges, and completed the present invention described below. The gist of the present invention is the following [1] to [8].
[1] A positive electrode material containing a positive electrode active material, a conductive auxiliary, and a binder, wherein the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder is 700 m 2 / g or less, and the conductive property per 1 g of the positive electrode material is A positive electrode material for a lithium ion secondary battery, wherein the total surface area of the auxiliary agent is 16 m 2 / g or more, and the BET specific surface area of the positive electrode active material is 1.2 m 2 / g or less.
[2] The positive electrode material for a lithium ion secondary battery according to the above [1], wherein the conductive auxiliary contains a conductive auxiliary a and a conductive auxiliary b having different BET specific surface areas.
[3] The lithium ion secondary according to the above [2], wherein the BET specific surface area of the conductive auxiliary agent a is 600 m 2 / g or more and the BET specific surface area of the conductive auxiliary agent b is less than 100 m 2 / g. Cathode material for battery.
[4] The method according to [2] or [3], wherein the conductive auxiliary agent a is at least one selected from chain carbon and graphite particles, and the conductive auxiliary agent b is fibrous or rod-shaped carbon. The positive electrode material for a lithium ion secondary battery according to the above.
[5] The positive electrode material for a lithium ion secondary battery according to any of [1] to [4], wherein the positive electrode active material is a lithium nickel cobalt aluminum-based oxide.
[6] A positive electrode active material layer comprising the positive electrode material for a lithium ion secondary battery according to any one of the above [1] to [5].
[7] A lithium ion secondary battery including a positive electrode having the positive electrode active material layer according to [6].
[8] The lithium ion secondary battery according to the above [7], comprising the positive electrode, a negative electrode arranged to face the positive electrode, and a separator arranged between the positive electrode and the negative electrode.
　本発明によれば、サイクル特性及び出力特性が共に良好なリチウムイオン二次電池を得られるリチウムイオン二次電池用正極材料、該リチウムイオン二次電池用正極材料からなる正極活物質層、及び該正極活物質層を備えたリチウムイオン二次電池を提供することができる。 According to the present invention, a positive electrode material for a lithium ion secondary battery capable of obtaining a lithium ion secondary battery having excellent cycle characteristics and output characteristics, a positive electrode active material layer including the positive electrode material for the lithium ion secondary battery, A lithium ion secondary battery including a positive electrode active material layer can be provided.
本発明のリチウムイオン二次電池の一実施形態を示す概略断面図である。FIG. 1 is a schematic sectional view showing one embodiment of a lithium ion secondary battery of the present invention.
＜リチウムイオン二次電池用正極材料＞
　本発明のリチウム二次電池用正極材料（以下、正極材料ともいう）は、正極活物質、導電助剤、及びバインダーを含み、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積が７００ｍ２／ｇ以下であり、正極材料１ｇあたりの導電助剤の総表面積が１６ｍ２／ｇ以上であり、正極活物質のＢＥＴ比表面積が１．２ｍ２／ｇ以下である。
　本発明の正極材料は、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積、正極材料１ｇあたりの導電助剤の総表面積、及び正極活物質のＢＥＴ比表面積を上記のとおりと特定範囲としているため、該正極材料を用いて製造したリチウムイオン二次電池は、サイクル特性及び出力特性が良好となる。 <Positive electrode material for lithium ion secondary batteries>
The positive electrode material for a lithium secondary battery of the present invention (hereinafter also referred to as a positive electrode material) includes a positive electrode active material, a conductive auxiliary, and a binder, and the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder is 700 m 2. / G or less, the total surface area of the conductive additive per 1 g of the positive electrode material is 16 m 2 / g or more, and the BET specific surface area of the positive electrode active material is 1.2 m 2 / g or less.
The positive electrode material of the present invention has a specific range of the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder, the total surface area of the conductive auxiliary per 1 g of the positive electrode material, and the BET specific surface area of the positive electrode active material as described above. Therefore, the lithium ion secondary battery manufactured using the positive electrode material has good cycle characteristics and output characteristics.
（正極活物質）
　本発明の正極材料は、ＢＥＴ比表面積が１．２ｍ２／ｇ以下である正極活物質を含有する。正極活物質のＢＥＴ比表面積が１．２ｍ２／ｇを超える場合は、リチウムイオン二次電池のサイクル特性が悪くなりやすく、リチウムイオン二次電池の強度も低下しやすい。リチウムイオン二次電池のサイクル特性を良好とする観点から、正極活物質のＢＥＴ比表面積は、好ましくは１．０ｍ２／ｇ以下であり、より好ましくは０．８ｍ２／ｇ以下であり、そして好ましくは０．１ｍ２／ｇ以上である。
　ＢＥＴ比表面積はＢＥＴ法により求めることができ、具体的には、窒素ガス吸着によるＢＥＴ法により求めることができる。 (Positive electrode active material)
The positive electrode material of the present invention contains a positive electrode active material having a BET specific surface area of 1.2 m 2 / g or less. When the BET specific surface area of the positive electrode active material exceeds 1.2 m 2 / g, the cycle characteristics of the lithium ion secondary battery tend to deteriorate, and the strength of the lithium ion secondary battery tends to decrease. From the viewpoint of improving the cycle characteristics of the lithium ion secondary battery, the BET specific surface area of the positive electrode active material is preferably 1.0 m 2 / g or less, more preferably 0.8 m 2 / g or less, and Preferably, it is at least 0.1 m 2 / g.
The BET specific surface area can be determined by the BET method, and specifically, can be determined by the BET method using nitrogen gas adsorption.
　正極活物質としては、金属酸リチウム化合物が挙げられる。金属酸リチウム化合物としては、コバルト酸リチウム（ＬｉＣｏＯ２）、ニッケル酸リチウム（ＬｉＮｉＯ２）、マンガン酸リチウム（ＬｉＭｎ２Ｏ４）等が例示できる。また、オリビン型リン酸鉄リチウム（ＬｉＦｅＰＯ４）などであってもよい。さらに、リチウム以外の金属を複数使用したものでもよく、リチウムニッケルコバルトマンガン系酸化物（ＮＣＭ）、リチウムニッケルコバルトアルミニウム系酸化物（ＮＣＡ）などを使用してもよい。これらの中でも、リチウムイオン二次電池の充放電容量を向上させる観点から、リチウムニッケルコバルトアルミニウム系酸化物（ＮＣＡ）が好ましい。 Examples of the positive electrode active material include a lithium metal oxide compound. Examples of the lithium metal oxide compound include lithium cobaltate (LiCoO 2 ), lithium nickelate (LiNiO 2 ), lithium manganate (LiMn 2 O 4 ), and the like. Further, olivine-type lithium iron phosphate (LiFePO 4 ) may be used. Further, a plurality of metals other than lithium may be used, and a lithium nickel cobalt manganese-based oxide (NCM), a lithium nickel cobalt aluminum-based oxide (NCA), or the like may be used. Among them, lithium nickel cobalt aluminum oxide (NCA) is preferable from the viewpoint of improving the charge / discharge capacity of the lithium ion secondary battery.
　リチウムニッケルコバルトアルミニウム系酸化物は、ニッケル酸リチウムのニッケルの一部をアルミニウム及びコバルトで置換したものである。リチウムニッケルコバルトアルミニウム系酸化物は、一般式ではＬｉtＮｉ１－ｘ－ｙＣｏｘＡｌｙＯ２（但し、０．９５≦ｔ≦１．１５、０＜ｘ≦０．３、０＜ｙ≦０．２、ｘ＋ｙ≦０．５を満たす。）と表される。 The lithium nickel cobalt aluminum oxide is obtained by substituting a part of nickel of lithium nickel oxide with aluminum and cobalt. Lithium-nickel-cobalt-aluminum-based oxide, by the formula Li t Ni 1-x-y Co x Al y O 2 ( where, 0.95 ≦ t ≦ 1.15,0 <x ≦ 0.3,0 <y ≦ 0.2, x + y ≦ 0.5).
　正極活物質の平均粒子径は０．５～５０μｍであることが好ましく、１～３０μｍであることがより好ましく、５～１５μｍであることが更に好ましい。リチウムイオン二次電池のサイクル特性を良好とする観点から、正極活物質の平均粒子径は１２μｍ以上であることが好ましく、そして好ましくは５０μｍ以下、より好ましくは３０μｍ以下、さらに好ましくは１５μｍ以下である。
　なお、平均粒子径は、レーザー回折・散乱法によって求めた正極活物質の粒度分布において、体積積算が５０％での粒径（Ｄ５０）を意味する。後述する負極活物質の平均粒子径、及び絶縁性微粒子の平均粒子径も同様の方法で測定できる。
　正極材料における正極活物質の含有量は、正極材料全量基準で５０～９８．５質量％が好ましく、６０～９８質量％がより好ましい。 The average particle diameter of the positive electrode active material is preferably from 0.5 to 50 μm, more preferably from 1 to 30 μm, even more preferably from 5 to 15 μm. From the viewpoint of improving the cycle characteristics of the lithium ion secondary battery, the average particle size of the positive electrode active material is preferably 12 μm or more, and is preferably 50 μm or less, more preferably 30 μm or less, and still more preferably 15 μm or less. .
The average particle diameter means a particle diameter (D50) at a volume integration of 50% in a particle size distribution of the positive electrode active material obtained by a laser diffraction / scattering method. The average particle diameter of the negative electrode active material described later and the average particle diameter of the insulating fine particles can be measured by the same method.
The content of the positive electrode active material in the positive electrode material is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the positive electrode material.
（導電助剤）
　本発明の正極材料は、導電助剤を含有する。導電助剤を含有することにより、正極材料の電気伝導性を向上させることができる。
　本発明の正極材料において、正極材料１ｇあたりの導電助剤の総表面積は１６ｍ２／ｇ以上である。正極材料１ｇあたりの導電助剤の総表面積が１６ｍ２／ｇ未満であると、リチウムイオン二次電池の出力特性が悪くなる。リチウムイオン二次電池の出力特性を良好とする観点から、正極材料１ｇあたりの導電助剤の総表面積は１６．３ｍ２／ｇ以上であることが好ましく、１７ｍ２／ｇ以上であることがより好ましく、そして２００ｍ２／ｇ以下であることが好ましく、５０ｍ２／ｇ以下であることがより好ましい。 (Conduction aid)
The positive electrode material of the present invention contains a conductive auxiliary. By containing the conductive auxiliary, the electric conductivity of the positive electrode material can be improved.
In the positive electrode material of the present invention, the total surface area of the conductive additive per 1 g of the positive electrode material is 16 m 2 / g or more. When the total surface area of the conductive additive per 1 g of the positive electrode material is less than 16 m 2 / g, the output characteristics of the lithium ion secondary battery deteriorate. From the viewpoint of improving the output characteristics of the lithium ion secondary battery, the total surface area of the conductive additive per 1 g of the positive electrode material is preferably 16.3 m 2 / g or more, more preferably 17 m 2 / g or more. Preferably, it is 200 m 2 / g or less, more preferably 50 m 2 / g or less.
　本発明の正極材料においては、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積が７００ｍ２／ｇ以下である。該総表面積が７００ｍ２／ｇを超える場合は、リチウムイオン二次電池のサイクル特性が悪くなりやすく、また強度も低下しやすい。これは、バインダー１ｇあたりの正極活物質及び導電助剤の該総表面積が大きい場合は、正極活物質及び導電助剤の表面にバインダーが消費されてしまうことによって電極全体の強度が低下するためと考えられる。
　サイクル特性を向上させる観点から、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積は６９７ｍ２／ｇ以下であることが好ましく、６９５ｍ２／ｇ以下であることがより好ましい。
　バインダー１ｇあたりの正極活物質及び導電助剤の総表面積は、以下の［１］と［２］との合計を正極材料中のバインダーの質量割合（ｗｔ％）で除することで求めることができる。すなわち、（［１］＋［２］）／（正極材料中のバインダーの質量割合（ｗｔ％））の式で求めることができる。
［１］：正極材料中の正極活物質の質量割合（ｗｔ％）×正極活物質のＢＥＴ比表面積（ｍ２／ｇ）
［２］：正極材料中の導電助剤の質量割合（ｗｔ％）×導電助剤のＢＥＴ比表面積（ｍ２／ｇ）
　また、導電助剤を２種以上用いる場合は、個々の導電助剤の正極材料中の質量割合とＢＥＴ比表面積の積を総和すればよい。例えば、導電助剤を後述する導電助剤ａと導電助剤ｂの２種類を用いる場合は、上記［２］に代えて、下記［２’］を用いて、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積を求めることができる。
［２’］：正極材料中の導電助剤ａの質量割合（ｗｔ％）×導電助剤ａのＢＥＴ比表面積（ｍ２／ｇ）＋正極材料中の導電助剤ｂの質量割合（ｗｔ％）×導電助剤ｂのＢＥＴ比表面積（ｍ２／ｇ）
　なお、正極活物質を２種以上用いる場合も、導電助剤を２種以上用いる場合と同様に計算することができる。 In the positive electrode material of the present invention, the total surface area of the positive electrode active material and the conductive auxiliary agent per 1 g of the binder is 700 m 2 / g or less. When the total surface area exceeds 700 m 2 / g, the cycle characteristics of the lithium ion secondary battery tend to deteriorate, and the strength tends to decrease. This is because, when the total surface area of the positive electrode active material and the conductive additive per 1 g of the binder is large, the binder is consumed on the surface of the positive electrode active material and the conductive additive, thereby reducing the strength of the entire electrode. Conceivable.
From the viewpoint of improving the cycle characteristics, the total surface area of the positive electrode active material and the conductive auxiliary agent per 1 g of the binder is preferably 697 m 2 / g or less, more preferably 695 m 2 / g or less.
The total surface area of the positive electrode active material and the conductive auxiliary agent per 1 g of the binder can be determined by dividing the sum of the following [1] and [2] by the mass ratio (wt%) of the binder in the positive electrode material. . That is, it can be determined by the formula of ([1] + [2]) / (mass ratio (wt%) of binder in positive electrode material).
[1]: Mass ratio of cathode active material in cathode material (wt%) × BET specific surface area of cathode active material (m 2 / g)
[2]: mass ratio (wt%) of conductive additive in positive electrode material × BET specific surface area of conductive additive (m 2 / g)
When two or more conductive additives are used, the product of the mass ratio of each conductive additive in the positive electrode material and the BET specific surface area may be summed up. For example, in the case of using two types of conductive assistants, conductive assistant a and conductive assistant b, which will be described later, instead of the above [2], the following [2 '] is used, and the positive electrode active material per 1 g of binder and The total surface area of the conductive additive can be determined.
[2 ′]: mass ratio of conductive auxiliary agent a in positive electrode material (wt%) × BET specific surface area of conductive auxiliary agent a (m 2 / g) + mass ratio of conductive auxiliary agent b in positive electrode material (wt%) ) × BET specific surface area of conductive assistant b (m 2 / g)
Note that when two or more kinds of the positive electrode active materials are used, the calculation can be performed in the same manner as when two or more kinds of the conductive auxiliary agents are used.
　本発明の正極材料に含まれる導電助剤は、ＢＥＴ比表面積の異なる導電助剤ａ及び導電助剤ｂを含有することが好ましい。ＢＥＴ比表面積の異なる導電助剤を含有する正極材料を用いることにより、リチウムイオン二次電池のサイクル特性及び出力特性を向上させることができる。
　導電助剤ａのＢＥＴ比表面積は６００ｍ２／ｇ以上であることが好ましく、８００ｍ２／ｇ以上であることがより好ましく、１０００ｍ２／ｇ以上であることが更に好ましく、そして、２０００ｍ２／ｇ以下であることが好ましく、１５００ｍ２／ｇ以下であることがより好ましい。
　導電助剤ｂのＢＥＴ比表面積は１００ｍ２／ｇ未満であることが好ましく、５０ｍ２／ｇ以下であることが好ましく、２０ｍ２／ｇ以下であることが更に好ましく、そして、５ｍ２／ｇ以上であることが好ましく、１０ｍ２／ｇ以上であることがより好ましい。 The conductive assistant contained in the positive electrode material of the present invention preferably contains a conductive assistant a and a conductive assistant b having different BET specific surface areas. By using a positive electrode material containing a conductive additive having a different BET specific surface area, cycle characteristics and output characteristics of a lithium ion secondary battery can be improved.
The BET specific surface area of the conductive additive a is preferably at least 600 m 2 / g, more preferably at least 800 m 2 / g, even more preferably at least 1000 m 2 / g, and 2,000 m 2 / g. Or less, more preferably 1500 m 2 / g or less.
Preferably the BET specific surface area of the conductive additive b is less than 100 m 2 / g, preferably at 50 m 2 / g or less, still more preferably less 20 m 2 / g, and, 5 m 2 / g or more And more preferably 10 m 2 / g or more.
　導電助剤の含有量は、正極材料全量基準で、０．５～３０質量％であることが好ましく、１～２０質量％であることがより好ましい。なお、導電助剤の含有量は、導電助剤が１種類の場合はその含有量を意味し、導電助剤を複数用いる場合は、複数の導電助剤の総量を意味する。
　また、導電助剤が上記したＢＥＴ比表面積の異なる導電助剤ａ及びｂを含む場合は、導電助剤ａの含有量は、正極材料全量基準で、０．２～１５質量％であることが好ましく、０．５～１０質量％であることがより好ましく、１～５質量％であることが更に好ましい。導電助剤ｂの含有量は、正極材料全量基準で、０．３～１５質量％であることが好ましく、０．５～１０質量％であることがより好ましく、２～７質量％であることが更に好ましい。
　導電助剤における導電助剤ａ及びｂの含有量は、リチウムイオン二次電池のサイクル特性及び出力特性を向上させる観点から、導電助剤ａの含有量よりも導電助剤ｂの含有量の方が多いことが好ましく、導電助剤ａの含有量に対する導電助剤ｂの含有量を１．２～３．０とすることがより好ましく、１．５～２．５とすることが更に好ましい。 The content of the conductive additive is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass, based on the total amount of the positive electrode material. In addition, the content of the conductive assistant means the content when one kind of the conductive assistant is used, and means the total amount of the plurality of conductive assistants when a plurality of the conductive assistants are used.
When the conductive additive includes the conductive aids a and b having different BET specific surface areas, the content of the conductive aid a may be 0.2 to 15% by mass based on the total amount of the positive electrode material. Preferably, it is 0.5 to 10% by mass, more preferably 1 to 5% by mass. The content of the conductive additive b is preferably 0.3 to 15% by mass, more preferably 0.5 to 10% by mass, and more preferably 2 to 7% by mass, based on the total amount of the positive electrode material. Is more preferred.
From the viewpoint of improving the cycle characteristics and output characteristics of the lithium ion secondary battery, the content of the conductive auxiliary agent b is more than the content of the conductive auxiliary agent a in the conductive auxiliary agent. It is more preferable that the content of the conductive additive b with respect to the content of the conductive additive a be 1.2 to 3.0, more preferably 1.5 to 2.5.
　導電助剤の種類としては、正極活物質よりも導電性の高い材料であれば特に限定されないが、炭素材料を用いることが好ましい。
　炭素材料としては、特に限定されないが、鎖状のカーボン、繊維状又は棒状のカーボン、黒鉛粒子等が挙げられる。 The type of the conductive additive is not particularly limited as long as it is a material having higher conductivity than the positive electrode active material, but it is preferable to use a carbon material.
Examples of the carbon material include, but are not particularly limited to, chain carbon, fibrous or rod-like carbon, and graphite particles.
　導電助剤が上記したＢＥＴ比表面積の異なる導電助剤ａ及びｂを含む場合は、これらの種類は特に限定されないが、好ましくは、両者共に炭素材料であることが好ましい。
　より詳細には、導電助剤ａは、鎖状のカーボン及び黒鉛粒子から選択される少なくとも１種であることが好ましい。上記鎖状のカーボンとは、粒子同士が融着ないし凝集等により鎖状につながったものをいい、例えば、アセチレンブラック、ファーネスブラックなどのカーボンブラックが挙げられる。上記アセチレンブラックとしては、例えば、電気化学工業社製の商品名「デンカブラック」が挙げられる。上記ファーネスブラックとしては、例えば、イメリス社製の商品名「Ｓｕｐｅｒ　Ｐ」が挙げられる。さらに、ライオン・スペシャリティ・ケミカルズ株式会社製の「ケッチェンブラック」も鎖状のカーボンとして用いることができる。
　上記黒鉛粒子としては、天然黒鉛、人造黒鉛の何れでもよく、炭素質層などの表面層を有する黒鉛粒子であってもよい。黒鉛粒子としては、具体的には、日本黒鉛社製の「ＵＰ－５α」、「ＳＰ－５０３０α」、イメリス社製「ＫＳ４」、「ＫＳ６」などが挙げられる。 When the conductive assistant contains the conductive assistants a and b having different BET specific surface areas as described above, these types are not particularly limited, but preferably both are carbon materials.
More specifically, the conductive additive a is preferably at least one selected from chain carbon and graphite particles. The chain carbon refers to particles in which particles are connected in a chain by fusing or agglomeration, and examples thereof include carbon black such as acetylene black and furnace black. Examples of the acetylene black include “DENKA BLACK” (trade name, manufactured by Denki Kagaku Kogyo Co., Ltd.). Examples of the furnace black include “Super P” (trade name, manufactured by Imerys Corporation). Further, “Ketjen Black” manufactured by Lion Specialty Chemicals Co., Ltd. can also be used as chain carbon.
The graphite particles may be either natural graphite or artificial graphite, and may be graphite particles having a surface layer such as a carbonaceous layer. Specific examples of the graphite particles include “UP-5α” and “SP-5030α” manufactured by Nippon Graphite Co., Ltd., and “KS4” and “KS6” manufactured by Imeris.
　導電粒子ｂは、繊維状又は棒状のカーボンであることが好ましい。繊維状又は棒状のカーボンとしては、例えば、カーボンナノファイバー、カーボンナノチューブ、カーボンナノホーン等が挙げられ、中でも、カーボンナノチューブが好ましく、気相成長カーボンファイバーがより好ましい。気相成長カーボンファイバーとしては、例えば、昭和電工株式会社製、商品名「ＶＧＣＦ－Ｈ」が挙げられる。 The conductive particles b are preferably fibrous or rod-like carbon. Examples of the fibrous or rod-like carbon include carbon nanofibers, carbon nanotubes, and carbon nanohorns. Among them, carbon nanotubes are preferable, and vapor-grown carbon fibers are more preferable. Examples of the vapor-grown carbon fiber include “VGCF-H” manufactured by Showa Denko KK.
（バインダー）
　本発明の正極材料は、バインダーを含有する。これにより正極材料は、上記した正極活物質及び導電助剤がバインダーに結着されて構成される。
　バインダーとしては、例えば、ポリフッ化ビニリデン（ＰＶＤＦ）、ポリフッ化ビニリデン－ヘキサフルオロプロピレン共重合体（ＰＶＤＦ－ＨＦＰ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等のフッ素含有樹脂、ポリメチルアクリレート（ＰＭＡ）、ポリメチルメタクリレート（ＰＭＭＡ）などのアクリル樹脂、ポリ酢酸ビニル、ポリイミド（ＰＩ）、ポリアミド（ＰＡ）、ポリ塩化ビニル（ＰＶＣ）、ポリエーテルニトリル（ＰＥＮ）、ポリエチレン（ＰＥ）、ポリプロピレン（ＰＰ）、ポリアクリロニトリル（ＰＡＮ）、アクリロニトリル・ブタジエンゴム、スチレンブタジエンゴム、ポリ（メタ）アクリル酸、カルボキシメチルセルロース、ヒドロキシエチルセルロース、及びポリビニルアルコール等が挙げられる。これらバインダーは、１種単独で使用されてもよいし、２種以上が併用されてもよい。また、カルボキシメチルセルロースなどは、ナトリウム塩などの塩の態様にて使用されていてもよい。これらの中でも、フッ素含有樹脂であることが好ましく、フッ素含有樹脂の中でもポリフッ化ビニリデン（ＰＶＤＦ）を使用することが好ましい。
　正極材料におけるバインダーの含有量は、正極材料全量基準で、０．１～１０質量％であることが好ましく、０．５～５質量％がより好ましく、２～４質量％であることが更に好ましい。 (binder)
The positive electrode material of the present invention contains a binder. Thus, the positive electrode material is configured by binding the above-described positive electrode active material and conductive assistant to the binder.
Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), polymethyl acrylate (PMA), and polymethyl acrylate (PMA). Acrylic resin such as methyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene-butadiene rubber, poly (meth) acrylic acid, carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol and the like. These binders may be used alone or in combination of two or more. Further, carboxymethylcellulose and the like may be used in the form of a salt such as a sodium salt. Among them, a fluorine-containing resin is preferable, and among the fluorine-containing resins, polyvinylidene fluoride (PVDF) is preferably used.
The content of the binder in the positive electrode material is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, and further preferably 2 to 4% by mass, based on the total amount of the positive electrode material. .
＜リチウムイオン二次電池＞
　本発明のリチウム二次電池用正極材料は、リチウムイオン二次電池の正極活物質層として使用することができる。該正極活物質層を有する正極を備えるリチウムイオン二次電池は、サイクル特性及び出力特性が共に良好となる。
　図１は、本発明のリチウムイオン二次電池の一実施形態を示す概略断面図である。リチウムイオン二次電池１０は、正極１２と、正極１２と対向するように配置される負極１１と、正極１２と負極１１との間に配置されるセパレータ１３とを備えている。
　負極１１は負極集電体１１ａと、負極集電体１１ａの上に積層された負極活物質層１１ｂとを備えており、正極１２も同様に、正極集電体１２ａと、正極集電体１２ａの上に積層された本発明の正極材料からなる正極活物質層１２ｂとを備えている。
　本発明の正極材料からなる正極活物質層１２ｂは、上記したとおり、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積、正極材料１ｇあたりの導電助剤の総表面積、及び正極活物質のＢＥＴ比表面積を特定範囲としている。これにより、リチウムイオン二次電池１０は、サイクル特性及び出力特性が共に良好となる。
　なお、負極活物質層１１ｂとセパレータ１３との間、又は正極活物質層１２ｂとセパレータ１３との間に図示しない絶縁層を設けてもよい。絶縁層を設けることにより、正極１２と負極１１との間の短絡が有効に防止できるようになる。 <Lithium ion secondary battery>
The positive electrode material for a lithium secondary battery of the present invention can be used as a positive electrode active material layer of a lithium ion secondary battery. A lithium ion secondary battery provided with a positive electrode having the positive electrode active material layer has good cycle characteristics and output characteristics.
FIG. 1 is a schematic sectional view showing one embodiment of the lithium ion secondary battery of the present invention. The lithium ion secondary battery 10 includes a positive electrode 12, a negative electrode 11 disposed to face the positive electrode 12, and a separator 13 disposed between the positive electrode 12 and the negative electrode 11.
The negative electrode 11 includes a negative electrode current collector 11a and a negative electrode active material layer 11b laminated on the negative electrode current collector 11a. Similarly, the positive electrode 12 has a positive electrode current collector 12a and a positive electrode current collector 12a. And a positive electrode active material layer 12b made of the positive electrode material of the present invention laminated thereon.
As described above, the positive electrode active material layer 12b composed of the positive electrode material of the present invention has a total surface area of the positive electrode active material and 1 g of the conductive auxiliary per 1 g of the binder, a total surface area of the conductive auxiliary per 1 g of the positive electrode material, and The BET specific surface area is defined as a specific range. Thereby, both the cycle characteristics and the output characteristics of the lithium ion secondary battery 10 are improved.
Note that an insulating layer (not shown) may be provided between the negative electrode active material layer 11b and the separator 13 or between the positive electrode active material layer 12b and the separator 13. By providing the insulating layer, a short circuit between the positive electrode 12 and the negative electrode 11 can be effectively prevented.
（正極）
　本発明のリチウムイオン二次電池における正極は、本発明の正極材料からなる正極活物質層を有し、好ましくは正極集電体と、正極集電体上に積層された正極活物質層とを有する。正極活物質層の厚みは特に限定されないが、１０～２００μｍであることが好ましく、５０～１５０μｍであることがより好ましい。
　正極集電体を構成する材料としては、例えば、銅、アルミニウム、チタン、ニッケル、ステンレス鋼等の導電性を有する金属が挙げられ、好ましくはアルミニウム又は銅、より好ましくはアルミニウムが使用される。正極集電体は、一般的に金属箔からなり、その厚さは、特に限定されないが、１～５０μｍが好ましい。
　正極材料は、正極材料用組成物から形成されることが好ましい。正極材料用組成物は、上記した正極活物質、導電助剤、及びバインダーを含む組成物である。正極材料用組成物は、さらに溶剤を含有することが好ましい。正極材料用組成物は一般的にスラリーになる。正極材料用組成物中の各成分の含有量は、溶剤を除いた各成分の含有量が、上記した正極材料において説明した含有量となるように調整すればよい。
　正極材料用組成物を、正極集電体上に塗布し乾燥することにより、正極集電体上に正極材料からなる正極活物質層が形成された正極を得ることができる。 (Positive electrode)
The positive electrode in the lithium ion secondary battery of the present invention has a positive electrode active material layer made of the positive electrode material of the present invention, and preferably includes a positive electrode current collector and a positive electrode active material layer stacked on the positive electrode current collector. Have. The thickness of the positive electrode active material layer is not particularly limited, but is preferably from 10 to 200 μm, and more preferably from 50 to 150 μm.
Examples of a material constituting the positive electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Preferably, aluminum or copper, and more preferably, aluminum is used. The positive electrode current collector is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 μm.
The positive electrode material is preferably formed from a positive electrode material composition. The composition for a positive electrode material is a composition containing the above-described positive electrode active material, a conductive additive, and a binder. The composition for a positive electrode material preferably further contains a solvent. The composition for the positive electrode material is generally a slurry. The content of each component in the positive electrode material composition may be adjusted so that the content of each component excluding the solvent becomes the content described in the positive electrode material described above.
The positive electrode in which the positive electrode active material layer made of the positive electrode material is formed on the positive electrode current collector can be obtained by applying and drying the composition for the positive electrode material on the positive electrode current collector.
（負極）
　本発明のリチウムイオン二次電池における負極は、負極材料からなる負極活物質層を有し、好ましくは負極集電体と、負極集電体上に積層された負極活物質層とを有する。負極活物質層は、典型的には、負極活物質と、負極用バインダーとを含む。
　負極活物質層に使用される負極活物質としては、グラファイト、ハードカーボンなどの炭素材料、スズ化合物とシリコンと炭素の複合体、リチウムなどが挙げられるが、これら中では炭素材料が好ましく、グラファイトがより好ましい。
　負極活物質は、特に限定されないが、その平均粒子径が０．５～５０μｍであることが好ましく、１～３０μｍであることがより好ましい。
　負極活物質層における負極活物質の含有量は、負極活物質層全量基準で、５０～９８．５質量％が好ましく、６０～９８質量％がより好ましい。 (Negative electrode)
The negative electrode in the lithium ion secondary battery of the present invention has a negative electrode active material layer made of a negative electrode material, and preferably has a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector. The negative electrode active material layer typically contains a negative electrode active material and a negative electrode binder.
Examples of the negative electrode active material used for the negative electrode active material layer include graphite, carbon materials such as hard carbon, a composite of a tin compound and silicon and carbon, and lithium. Among these, carbon materials are preferable, and graphite is preferable. More preferred.
The negative electrode active material is not particularly limited, but preferably has an average particle size of 0.5 to 50 μm, more preferably 1 to 30 μm.
The content of the negative electrode active material in the negative electrode active material layer is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the negative electrode active material layer.
　負極活物質層は、導電助剤を含有してもよい。導電助剤は、上記負極活物質よりも導電性が高い材料が使用され、具体的には、カーボンブラック、カーボンナノファーバー、カーボンナノチューブ、黒鉛粒子などの炭素材料が挙げられる。
　負極活物質層において、導電助剤が含有される場合、導電助剤の含有量は、負極活物質層全量基準で、１～３０質量％であることが好ましく、２～２５質量％であることがより好ましい。 The negative electrode active material layer may contain a conductive auxiliary. As the conductive additive, a material having higher conductivity than the above-described negative electrode active material is used, and specific examples thereof include carbon materials such as carbon black, carbon nanofiber, carbon nanotube, and graphite particles.
When a conductive auxiliary is contained in the negative electrode active material layer, the content of the conductive auxiliary is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, based on the total amount of the negative electrode active material layer. Is more preferred.
　負極活物質層に含有される負極用バインダーとしては、上記した正極材料にて使用されるバインダーと同種のものが使用できる。
　負極活物質層における負極用バインダーの含有量は、負極活物質層全量基準で、１．５～４０質量％であることが好ましく、２．０～２５質量％がより好ましい。
　負極活物質層の厚みは、特に限定されないが、１０～２００μｍであることが好ましく、５０～１５０μｍであることがより好ましい。 As the negative electrode binder contained in the negative electrode active material layer, the same kind of binder as used in the above-described positive electrode material can be used.
The content of the negative electrode binder in the negative electrode active material layer is preferably 1.5 to 40% by mass, more preferably 2.0 to 25% by mass, based on the total amount of the negative electrode active material layer.
The thickness of the negative electrode active material layer is not particularly limited, but is preferably from 10 to 200 μm, and more preferably from 50 to 150 μm.
　負極集電体を構成する材料としては、例えば、銅、アルミニウム、チタン、ニッケル、ステンレス鋼等の導電性を有する金属が挙げられ、これらの中ではアルミニウム又は銅が好ましく、銅がより好ましい。負極集電体は、一般的に金属箔からなり、その厚さは、特に限定されないが、１～５０μｍが好ましい。 材料 Examples of a material constituting the negative electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum or copper is preferable, and copper is more preferable. The negative electrode current collector is generally made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 μm.
　上記した正極の場合と同様に、負極活物質、負極用バインダー、導電助剤、及び必要に応じて配合される溶媒を含有する負極材料用組成物を、負極集電体上に塗布し乾燥することにより、負極集電体上に負極活物質層が形成された負極を得ることができる。 As in the case of the above-described positive electrode, a negative electrode active material, a negative electrode binder, a conductive auxiliary, and a negative electrode material composition containing a solvent to be blended as necessary are coated on a negative electrode current collector and dried. Thereby, a negative electrode in which the negative electrode active material layer is formed on the negative electrode current collector can be obtained.
　（セパレータ）
　本発明のリチウムイオン二次電池は、負極と正極との間に配置されるセパレータを備える。セパレータにより、正極及び負極の間の短絡が効果的に防止される。また、セパレータは、後述する電解質を保持してもよい。
　セパレータとしては、多孔性の高分子膜、不織布、ガラスファイバー等が挙げられ、これらの中では多孔性の高分子膜が好ましい。多孔性の高分子膜としては、エチレン系多孔質フィルムなどのオレフィン系多孔質フィルムが例示される。 (Separator)
The lithium ion secondary battery of the present invention includes a separator disposed between a negative electrode and a positive electrode. The separator effectively prevents a short circuit between the positive electrode and the negative electrode. Further, the separator may hold an electrolyte described later.
Examples of the separator include a porous polymer film, a nonwoven fabric, and a glass fiber. Among these, a porous polymer film is preferable. Examples of the porous polymer film include an olefin-based porous film such as an ethylene-based porous film.
　（絶縁層）
　本発明のリチウムイオン二次電池は、負極活物質層上又は正極活物質層上に絶縁層を備えるものであってもよい。絶縁層により正極及び負極の間の短絡が効果的に防止される。絶縁層は、好ましくは、絶縁性微粒子と絶縁層用バインダーとを含み、絶縁性微粒子が絶縁層用バインダーによって結着されて構成された多孔質構造を有する層である。 (Insulating layer)
The lithium ion secondary battery of the present invention may have an insulating layer on the negative electrode active material layer or the positive electrode active material layer. A short circuit between the positive electrode and the negative electrode is effectively prevented by the insulating layer. The insulating layer preferably includes an insulating fine particle and a binder for the insulating layer, and is a layer having a porous structure formed by binding the insulating fine particle with the binder for the insulating layer.
　絶縁性微粒子は、絶縁性であれば特に限定されず、有機粒子、無機粒子の何れであってもよい。具体的な有機粒子としては、例えば、架橋ポリメタクリル酸メチル、架橋スチレン－アクリル酸共重合体、架橋アクリロニトリル樹脂、ポリアミド樹脂、ポリイミド樹脂、ポリ（２－アクリルアミド－２－メチルプロパンスルホン酸リチウム）、ポリアセタール樹脂、エポキシ樹脂、ポリエステル樹脂、フェノール樹脂、メラミン樹脂等の有機化合物から構成される粒子が挙げられる。無機粒子としては二酸化ケイ素、窒化ケイ素、アルミナ、ベーマイト、チタニア、ジルコニア、窒化ホウ素、酸化亜鉛、二酸化スズ、酸化ニオブ（Ｎｂ２Ｏ５）、酸化タンタル（Ｔａ２Ｏ５）、フッ化カリウム、フッ化リチウム、クレイ、ゼオライト、炭酸カルシウム等の無機化合物から構成される粒子が挙げられる。また、無機粒子は、ニオブ－タンタル複合酸化物、マグネシウム－タンタル複合酸化物等の公知の複合酸化物から構成される粒子であってもよい。絶縁性微粒子は１種を単独で用いてもよいし、複数種を併用してもよい。
　絶縁性微粒子の平均粒子径は、絶縁層の厚さよりも小さければ特に限定されず、例えば０．００１～１μｍ、好ましくは０．０５～０．８μｍ、より好ましくは０．１～０．６μｍである。
　絶縁層に含有される絶縁性微粒子の含有量は、絶縁層全量基準で、好ましくは１５～９５質量％、より好ましくは４０～９０質量％、更に好ましくは６０～８５質量％である。絶縁性微粒子の含有量が上記範囲内であると、絶縁層は、均一な多孔質構造が形成でき、かつ適切な絶縁性が付与される。 The insulating fine particles are not particularly limited as long as they are insulating, and may be organic particles or inorganic particles. Specific organic particles include, for example, cross-linked polymethyl methacrylate, cross-linked styrene-acrylic acid copolymer, cross-linked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamido-2-methylpropanesulfonate), Examples include particles composed of an organic compound such as a polyacetal resin, an epoxy resin, a polyester resin, a phenol resin, and a melamine resin. Silicon dioxide as inorganic particles, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb 2 O 5), tantalum oxide (Ta 2 O 5), potassium fluoride, Examples include particles composed of inorganic compounds such as lithium chloride, clay, zeolite, and calcium carbonate. Further, the inorganic particles may be particles composed of a known composite oxide such as a niobium-tantalum composite oxide or a magnesium-tantalum composite oxide. One kind of the insulating fine particles may be used alone, or a plurality of kinds may be used in combination.
The average particle diameter of the insulating fine particles is not particularly limited as long as it is smaller than the thickness of the insulating layer, and is, for example, 0.001 to 1 μm, preferably 0.05 to 0.8 μm, and more preferably 0.1 to 0.6 μm. is there.
The content of the insulating fine particles contained in the insulating layer is preferably 15 to 95% by mass, more preferably 40 to 90% by mass, and still more preferably 60 to 85% by mass, based on the total amount of the insulating layer. When the content of the insulating fine particles is within the above range, the insulating layer can form a uniform porous structure, and is provided with appropriate insulating properties.
　絶縁層用バインダーとしては、上記した正極材料にて使用されるバインダーと同種のものが使用できる。絶縁層における絶縁層用バインダーの含有量は、絶縁層全量基準で、５～５０質量％であることが好ましく、１０～４５質量％がより好ましく、１５～４０質量％が更に好ましい。
　絶縁層の厚さは、１～１０μｍが好ましく、２～８μｍがより好ましく、３～７μｍが更に好ましい。 As the binder for the insulating layer, the same binder as that used in the above-described positive electrode material can be used. The content of the binder for the insulating layer in the insulating layer is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and still more preferably 15 to 40% by mass, based on the total amount of the insulating layer.
The thickness of the insulating layer is preferably 1 to 10 μm, more preferably 2 to 8 μm, and still more preferably 3 to 7 μm.
　（電解質）
　本発明のリチウムイオン二次電池は、電解質を備える。電解質は特に限定されず、リチウムイオン二次電池で使用される公知の電解質を使用すればよい。電解質としては例えば電解液を使用する。
　電解液としては、有機溶媒と、電解質塩を含む電解液が例示できる。有機溶媒としては、例えば、エチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート、γ－ブチロラクトン、スルホラン、ジメチルスルホキシド、アセトニトリル、ジメチルホルムアミド、ジメチルアセトアミド、１，２－ジメトキシエタン、１，２－ジエトキシエタン、テトロヒドラフラン、２－メチルテトラヒドロフラン、ジオキソラン、メチルアセテートなどの極性溶媒、又はこれら溶媒の２種類以上の混合物が挙げられる。電解質塩としては、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＳｂＦ６、ＬｉＣＦ３ＣＯ２、ＬｉＮ（ＳＯ２ＣＦ３）２、ＬｉＮ（ＳＯ２ＣＦ２ＣＦ３）２、ＬｉＮ（ＣＯＣＦ３）２及びＬｉＮ（ＣＯＣＦ２ＣＦ３）２、リチウムビスオキサレートボラート（ＬｉＢ（Ｃ２Ｏ４）２等のリチウムを含む塩が挙げられる。また、有機酸リチウム塩－三フッ化ホウ素錯体、ＬｉＢＨ４等の錯体水素化物等の錯体が挙げられる。これらの塩又は錯体は、１種単独で使用してもよいが、２種以上の混合物であってもよい。
　また、電解質は、上記電解液に更に高分子化合物を含むゲル状電解質であってもよい。高分子化合物としては、例えば、ポリフッ化ビニリデン等のフッ素系ポリマー、ポリ（メタ）アクリル酸メチル等のポリアクリル系ポリマーが挙げられる。なお、ゲル状電解質は、セパレータとして使用されてもよい。
　電解質は、負極及び正極間に配置されればよく、例えば、電解質液は、上記した負極、正極、及びセパレータが内部に収納されたバッテリーセル内に充填される。また、電解質は、例えば、負極又は正極上に塗布されて負極及び正極間に配置されてもよい。 (Electrolytes)
The lithium ion secondary battery of the present invention includes an electrolyte. The electrolyte is not particularly limited, and a known electrolyte used in a lithium ion secondary battery may be used. For example, an electrolyte is used as the electrolyte.
Examples of the electrolyte include an electrolyte containing an organic solvent and an electrolyte salt. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, and tetrohydra. Examples thereof include polar solvents such as furan, 2-methyltetrahydrofuran, dioxolan, and methyl acetate, or a mixture of two or more of these solvents. As the electrolyte salt, LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiCF 3 CO 2 , LiN (SO 2 CF 3 ) 2 , LiN (SO 2 CF 2 CF 3 ) 2 , LiN (COCF 3 ) And lithium-containing salts such as LiN (COCF 2 CF 3 ) 2 and lithium bisoxalate borate (LiB (C 2 O 4 ) 2. Also, lithium organic acid salt-boron trifluoride complex, LiBH And complexes such as complex hydrides such as 4. These salts or complexes may be used alone or in a mixture of two or more.
Further, the electrolyte may be a gel electrolyte further containing a polymer compound in the above-mentioned electrolytic solution. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacryl-based polymer such as poly (methyl) methacrylate. Note that the gel electrolyte may be used as a separator.
The electrolyte may be disposed between the negative electrode and the positive electrode. For example, the electrolyte solution is filled in the battery cell in which the above-described negative electrode, positive electrode, and separator are housed. Further, the electrolyte may be, for example, applied on the negative electrode or the positive electrode and disposed between the negative electrode and the positive electrode.
　リチウムイオン二次電池は、負極、正極がそれぞれ複数積層された多層構造であってもよい。この場合、負極及び正極は、積層方向に沿って交互に設けられればよい。また、セパレータは各負極と各正極の間に配置されればよく、絶縁層を設ける場合は、負極－セパレータ間又は正極－セパレータ間に設ければよい。 The lithium ion secondary battery may have a multilayer structure in which a plurality of negative electrodes and a plurality of positive electrodes are stacked. In this case, the negative electrode and the positive electrode may be provided alternately along the laminating direction. The separator may be provided between each negative electrode and each positive electrode. When an insulating layer is provided, it may be provided between the negative electrode and the separator or between the positive electrode and the separator.
　以下に実施例を用いて本発明をさらに詳しく説明するが、本発明はこれら実施例に限定されるものではない。 The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
　得られたリチウムイオン二次電池は、以下の評価方法により評価した。 The obtained lithium ion secondary battery was evaluated by the following evaluation method.
（サイクル特性の評価）
　作製した電池の容量が３ｍＡ／ｃｍ２になるように正極材料用組成物及び負極材料用組成物の塗工量を調整し、後述するように実施例、比較例のリチウムイオン二次電池を得た。２５℃の恒温下、端子電圧の充電下限電圧を２．５Ｖ、放電の上限電圧を４．２Ｖとした電圧範囲とした。以下の条件で充放電を繰り返した。
充電：６ｍＡ／ｃｍ２、４．２Ｖの定電流後、０．３ｍＡ／ｃｍ２の電流値となるまで低電圧充電
放電：６ｍＡ／ｃｍ２の定電流、２．５Ｖの終始条件で放電
繰り返し数：１０００回
　１０００回の充放電の後の放電容量を１回目の放電容量の値で除した割合を容量維持率とし、以下のように評価した。
　Ａ：８０％≦容量維持率
　Ｂ：６０％≦容量維持率＜８０％
　Ｃ：容量維持率＜６０％ (Evaluation of cycle characteristics)
The coating amounts of the composition for the positive electrode material and the composition for the negative electrode material were adjusted so that the capacity of the manufactured battery was 3 mA / cm 2 , and lithium ion secondary batteries of Examples and Comparative Examples were obtained as described later. Was. At a constant temperature of 25 ° C., the voltage range was set such that the lower limit voltage of the terminal voltage was 2.5 V and the upper limit voltage of the discharge was 4.2 V. Charge and discharge were repeated under the following conditions.
Charging: 6 mA / cm 2, after 4.2V constant current, low voltage charge-discharge until the current value of 0.3mA / cm 2: 6mA / cm 2 constant current, the number of repetitions of electric discharge in throughout the conditions of 2.5V : 1000 times The rate obtained by dividing the discharge capacity after 1000 times of charge / discharge by the value of the first discharge capacity was defined as the capacity retention ratio, and evaluated as follows.
A: 80% ≦ capacity maintenance ratio B: 60% ≦ capacity maintenance ratio <80%
C: Capacity maintenance rate <60%
（出力特性評価）
　作製した電池の容量が３ｍＡ／ｃｍ２になるように正極材料用組成物及び負極材料用組成物の塗工量を調整し、後述するように実施例、比較例のリチウムイオン二次電池を得た。２５℃の恒温下、端子電圧の充電下限電圧を２．５Ｖ、放電の上限電圧を４．２Ｖとした電圧範囲で３ｍＡ／ｃｍ２の定電流放電と１５ｍＡ／ｃｍ２の定電流放電を実施した際の比を出力特性評価とした。なお以下のように判定した。
Ａ：６０％以上
Ｂ：５０％以上６０％未満
Ｃ：５０％未満 (Output characteristic evaluation)
The coating amounts of the composition for the positive electrode material and the composition for the negative electrode material were adjusted so that the capacity of the manufactured battery was 3 mA / cm 2 , and lithium ion secondary batteries of Examples and Comparative Examples were obtained as described later. Was. At a constant temperature of 25 ° C., constant current discharge of 3 mA / cm 2 and constant current discharge of 15 mA / cm 2 were performed in a voltage range in which the lower limit voltage of the terminal voltage was 2.5 V and the upper limit voltage of the discharge was 4.2 V. The ratio at this time was evaluated as output characteristics. The determination was made as follows.
A: 60% or more B: 50% or more and less than 60% C: less than 50%
（電極強度）
　各実施例、比較例で作製した正極（電極）について、以下のように電極強度を測定した。
　正極を３０ｍｍ×１００ｍｍにカットし、正極活物質層を内側に折り曲げ１０ｍｍ厚のアクリル板で上下から挟み込んだ。挟み込んだのち、５００ｇの錘を載せて５秒間保持した。その後、折り曲げ面を上にして開き、外観を検査し、以下の基準で評価した。
Ａ：正極活物質層が亀裂を生じなかった。
Ｂ：正極活物質層が一部粉落ちした。
Ｃ：正極活物質層が粉落ちし、集電箔が見えた。 (Electrode strength)
The electrode strength of each of the positive electrodes (electrodes) manufactured in each of Examples and Comparative Examples was measured as follows.
The positive electrode was cut into 30 mm x 100 mm, and the positive electrode active material layer was bent inward and sandwiched from above and below with a 10 mm thick acrylic plate. After being sandwiched, a 500 g weight was placed and held for 5 seconds. Thereafter, the folded surface was opened with the bent surface facing upward, the appearance was inspected, and the evaluation was made according to the following criteria.
A: The positive electrode active material layer did not crack.
B: Part of the positive electrode active material layer was powdered.
C: The positive electrode active material layer was powdered and the current collector foil was visible.
［実施例１］
（正極の作製）
　表１に示す正極材料（正極活物質、導電助剤、及び正極用バインダー）を、溶媒としてのＮ－メチルピロリドン(ＮＭＰ)と混合し、固形分濃度６０質量％に調整したスラリー状の正極材料用組成物を作製した。この正極材料用組成物を、正極集電体としての厚さ１５μｍのアルミニウム箔の両面に塗布し、予備乾燥後、１２０℃で真空乾燥した。その後、両面に正極材料用組成物を塗布した正極集電体を、４００ｋＮ／ｍの線圧でローラにより加圧プレスし、更に電極寸法の１００ｍｍ×２００ｍｍ角に打ち抜いて、両面に正極活物質層を有する正極を作製した。該寸法のうち、正極活物質が塗布された面積は１００ｍｍ×１８０ｍｍであった。 [Example 1]
(Preparation of positive electrode)
A slurry-type positive electrode material in which the positive electrode materials shown in Table 1 (positive electrode active material, conductive auxiliary agent, and positive electrode binder) were mixed with N-methylpyrrolidone (NMP) as a solvent and the solid content concentration was adjusted to 60% by mass. A composition for use was prepared. This composition for a positive electrode material was applied to both sides of a 15 μm-thick aluminum foil as a positive electrode current collector, preliminarily dried, and then vacuum dried at 120 ° C. Thereafter, the positive electrode current collector coated with the composition for a positive electrode material on both sides is pressed with a roller at a linear pressure of 400 kN / m by a roller, and further punched into a 100 mm × 200 mm square of the electrode dimensions to form a positive electrode active material layer on both sides. Was produced. Among these dimensions, the area where the positive electrode active material was applied was 100 mm × 180 mm.
（負極の作製）
　負極活物質としてグラファイト（平均粒子径１０μｍ）１００質量部と、負極用バインダーとしてカルボキシメチルセルロース（ＣＭＣ）のナトリウム塩を１．５質量部と、その他のバインダーとしてスチレンブタジエンゴム（ＳＢＲ）１．５質量部と、溶媒として水とを混合し、固形分５０質量％に調整したスラリー状の負極材料用組成物を得た。この負極材料用組成物を、負極集電体としての厚さ１２μｍの銅箔の両面に塗布して１００℃で真空乾燥した。その後、両面に負極材料用組成物を塗布した負極集電体を、３００ｋＮ／ｍの線圧でローラにより加圧プレスし、更に電極寸法の１１０ｍｍ×２１０ｍｍ角に打ち抜いて、両面に負極活物質層を有する負極を作製した。該寸法のうち、負極活物質が塗布された面積は１１０ｍｍ×１９０ｍｍであった。 (Preparation of negative electrode)
100 parts by mass of graphite (average particle diameter: 10 μm) as a negative electrode active material, 1.5 parts by mass of a sodium salt of carboxymethyl cellulose (CMC) as a binder for a negative electrode, and 1.5 parts by mass of styrene butadiene rubber (SBR) as another binder Parts and water as a solvent were mixed to obtain a slurry-like negative electrode material composition adjusted to a solid content of 50% by mass. This composition for a negative electrode material was applied on both sides of a copper foil having a thickness of 12 μm as a negative electrode current collector, and dried at 100 ° C. under vacuum. Thereafter, the negative electrode current collector coated with the composition for a negative electrode material on both surfaces is pressed with a roller at a linear pressure of 300 kN / m, and further punched out into 110 mm × 210 mm square of the electrode dimensions to form a negative electrode active material layer on both surfaces. Was produced. Of the dimensions, the area where the negative electrode active material was applied was 110 mm × 190 mm.
（電解液の調製）
　エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）を３：７の体積比（ＥＣ：ＤＥＣ）で混合した溶媒に、電解質塩としてＬｉＰＦ６を１モル／リットルとなるように溶解して、電解液を調製した。 (Preparation of electrolyte solution)
LiPF 6 as an electrolyte salt was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 (EC: DEC) so as to have a concentration of 1 mol / liter, and the electrolytic solution was dissolved. Prepared.
（リチウムイオン二次電池の製造）
　上記で得た負極１０枚と、正極９枚と、セパレータ１８枚を積層し仮積層体を得た。ここで、負極と正極は交互に配置して、各負極と正極の間にセパレータを配置した。また、セパレータとしては、ポリエチレン製多孔質フィルムを用いた。
　各正極の正極集電体の露出部の端部を纏めて超音波融着で接合するとともに、外部に突出する端子用タブを接合した。同様に、各負極の負極集電体の露出部の端部を纏めて超音波融着で接合するとともに、外部に突出する端子用タブを接合した。
　次いで、アルミラミネートフィルムで上記積層体を挟み、端子用タブを外部に突出させ、三辺をラミネート加工によって封止した。封止せずに残した一辺から、上記で得た電解液を注入し、真空封止することによってラミネート型のセルを製造した。
　得られたリチウムイオン二次電池の評価結果を表１に示す。 (Manufacture of lithium ion secondary batteries)
Ten pieces of the negative electrode, nine pieces of the positive electrode, and 18 pieces of the separator obtained above were laminated to obtain a temporary laminate. Here, the negative electrode and the positive electrode were alternately arranged, and a separator was arranged between each negative electrode and the positive electrode. In addition, a polyethylene porous film was used as the separator.
The ends of the exposed portions of the positive electrode current collector of each positive electrode were joined together by ultrasonic fusion, and a terminal tab projecting to the outside was joined. Similarly, the ends of the exposed portions of the negative electrode current collectors of the respective negative electrodes were joined together by ultrasonic fusion, and terminal tabs projecting to the outside were joined.
Next, the laminated body was sandwiched between aluminum laminated films, the terminal tabs were projected outside, and three sides were sealed by lamination. The electrolyte solution obtained above was injected from one side left without sealing, and vacuum sealing was performed to produce a laminate type cell.
Table 1 shows the evaluation results of the obtained lithium ion secondary batteries.
［実施例２、比較例１～５］
　正極材料を表１に記載のとおりに変更した以外は、実施例１と同様にしてリチウムイオン二次電池を得た。評価結果を表１に示す。 [Example 2, Comparative Examples 1 to 5]
A lithium ion secondary battery was obtained in the same manner as in Example 1, except that the cathode material was changed as shown in Table 1. Table 1 shows the evaluation results.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　なお、正極の作製に用いた正極活物質、導電助剤及び電極用バインダーは以下のとおりである。
（正極活物質）
・ＮＣＡ１：リチウムニッケルコバルトアルミニウム系酸化物（平均粒子径：１３．３μｍ、ＢＥＴ比表面積０．６６ｍ２／ｇ）
・ＮＣＡ２：リチウムニッケルコバルトアルミニウム系酸化物（平均粒子径：１１．１μｍ、ＢＥＴ比表面積１．３ｍ２／ｇ）
・ＮＣＡ３：リチウムニッケルコバルトアルミニウム系酸化物（平均粒子径：１０．５μｍ、ＢＥＴ比表面積１．７ｍ２／ｇ）
・ＮＣＡ４：リチウムニッケルコバルトアルミニウム系酸化物（平均粒子径：７．７μｍ、ＢＥＴ比表面積２．０ｍ２／ｇ） In addition, the positive electrode active material, the conductive auxiliary agent, and the binder for electrodes used in the preparation of the positive electrode are as follows.
(Positive electrode active material)
NCA1: lithium nickel cobalt aluminum oxide (average particle diameter: 13.3 μm, BET specific surface area 0.66 m 2 / g)
NCA2: lithium nickel cobalt aluminum oxide (average particle size: 11.1 μm, BET specific surface area 1.3 m 2 / g)
NCA3: lithium nickel cobalt aluminum oxide (average particle diameter: 10.5 μm, BET specific surface area 1.7 m 2 / g)
NCA4: lithium nickel cobalt aluminum oxide (average particle size: 7.7 μm, BET specific surface area 2.0 m 2 / g)
（導電助剤）
・鎖状のカーボン：ライオン・スペシャリティ・ケミカルズ株式会社製（「ケッチェンブラック６００」）、ＢＥＴ比表面積１２７５ｍ２／ｇ
・棒状のカーボン：気相成長カーボンファイバー、昭和電工株式会社製（「ＶＧＣＦ－Ｈ」）、
ＢＥＴ比表面積１３ｍ２／ｇ
（正極用バインダー）
・ＰＶＤＦ：ポリフッ化ビニリデン (Conductive agent)
· Chain of carbon: The Lion Specialty Chemicals Co., Ltd. ( "Ketchen black 600"), BET specific surface area of 1275m 2 / g
-Rod-like carbon: vapor-grown carbon fiber, manufactured by Showa Denko KK ("VGCF-H"),
BET specific surface area 13m 2 / g
(Binder for positive electrode)
・ PVDF: Polyvinylidene fluoride
　本発明のリチウムイオン二次電池用正極材料を用いた実施例１～２のリチウムイオン二次電池は、サイクル特性及び出力特性のいずれも良好になることが分かった。
　一方、本発明のリチウムイオン二次電池用電極を用いない比較例１～５のリチウムイオン二次電池は、いずれもサイクル特性及び出力特性の両方を良好とすることができなかった。 It was found that both the cycle characteristics and the output characteristics of the lithium ion secondary batteries of Examples 1 and 2 using the positive electrode material for a lithium ion secondary battery of the present invention were improved.
On the other hand, none of the lithium ion secondary batteries of Comparative Examples 1 to 5 using the electrode for a lithium ion secondary battery of the present invention could have good cycle characteristics and output characteristics.
　１０　　リチウムイオン二次電池
　１１　　負極
　１１ａ　負極集電体
　１１ｂ　負極活物質層
　１２　　正極
　１２ａ　正極集電体
　１２ｂ　正極活物質層
　１３　　セパレータ Reference Signs List 10 lithium ion secondary battery 11 negative electrode 11a negative electrode current collector 11b negative electrode active material layer 12 positive electrode 12a positive electrode current collector 12b positive electrode active material layer 13 separator

Claims (8)

  1. 　正極活物質、導電助剤、及びバインダーを含む正極材料であって、バインダー１ｇあたりの正極活物質及び導電助剤の総表面積が７００ｍ２／ｇ以下であり、正極材料１ｇあたりの導電助剤の総表面積が１６ｍ２／ｇ以上であり、正極活物質のＢＥＴ比表面積が１．２ｍ２／ｇ以下である、リチウムイオン二次電池用正極材料。 A positive electrode material including a positive electrode active material, a conductive auxiliary, and a binder, wherein the total surface area of the positive electrode active material and the conductive auxiliary per 1 g of the binder is 700 m 2 / g or less, and the amount of the conductive auxiliary per 1 g of the positive electrode material is A positive electrode material for a lithium ion secondary battery, wherein the total surface area is 16 m 2 / g or more, and the BET specific surface area of the positive electrode active material is 1.2 m 2 / g or less.
  2. 　前記導電助剤が、ＢＥＴ比表面積の異なる導電助剤ａ及び導電助剤ｂを含有する、請求項１に記載のリチウムイオン二次電池用正極材料。 The positive electrode material for a lithium ion secondary battery according to claim 1, wherein the conductive auxiliary contains a conductive auxiliary a and a conductive auxiliary b having different BET specific surface areas.
  3. 　前記導電助剤ａのＢＥＴ比表面積が６００ｍ２／ｇ以上であり、前記導電助剤ｂのＢＥＴ比表面積が１００ｍ２／ｇ未満である、請求項２に記載のリチウムイオン二次電池用正極材料。 The BET specific surface area of the conductive additive a is not less 600 meters 2 / g or more, the BET specific surface area of the conductive additive b is less than 100 m 2 / g, the positive electrode material for a lithium ion secondary battery according to claim 2 .
  4. 　前記導電助剤ａが鎖状のカーボン及び黒鉛粒子から選択される少なくとも１種であり、前記導電助剤ｂが繊維状又は棒状のカーボンである、請求項２又は３に記載のリチウムイオン二次電池用正極材料。 The lithium ion secondary according to claim 2, wherein the conductive assistant a is at least one selected from chain carbon and graphite particles, and the conductive assistant b is fibrous or rod-shaped carbon. Cathode material for battery.
  5. 　前記正極活物質がリチウムニッケルコバルトアルミニウム系酸化物である、請求項１～４のいずれかに記載のリチウムイオン二次電池用正極材料。 The positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the positive electrode active material is a lithium nickel cobalt aluminum-based oxide.
  6. 　請求項１～５のいずれかに記載のリチウムイオン二次電池用正極材料からなる正極活物質層。 A positive electrode active material layer comprising the positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 5.
  7. 　請求項６に記載の正極活物質層を有する正極を備える、リチウムイオン二次電池。 A lithium ion secondary battery comprising a positive electrode having the positive electrode active material layer according to claim 6.
  8. 　前記正極と、正極と対向するように配置される負極と、正極と負極の間に配置されるセパレータとを備える、請求項７に記載のリチウムイオン二次電池。 The lithium ion secondary battery according to claim 7, further comprising: the positive electrode, a negative electrode disposed to face the positive electrode, and a separator disposed between the positive electrode and the negative electrode.
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