Composite material, electrode, and battery

Abstract

Provided is a composite material in which the surface of flaked graphite is coated with a coating substance, wherein the full width at half maximum of the 002 diffraction line of the flaked graphite is in the range of 0.15-3.00° in an XRD measurement.

Description

Composite materials, electrodes and batteries

[0001] The present disclosure relates to composite materials, electrodes, and batteries.

[0002] Exfoliated graphite such as graphene obtained by exfoliating graphite, which is a laminated material, has been used as a conductive additive for electrodes of secondary batteries (see, for example, Patent Document 1). Exfoliated graphite has a problem of poor handling due to its low bulk density, etc. Furthermore, when used as a conductive additive for electrodes, exfoliated graphite has a problem of being unable to reduce the volume resistivity of the electrodes, and therefore unable to obtain sufficient electrical conductivity.

[0003] JP 2016-060887 A

[0004] An object of the present disclosure is to provide a material containing exfoliated graphite that has excellent handleability and, when used as a conductive additive for an electrode, can reduce the volume resistivity of the electrode. In the present disclosure, "excellent handleability" refers to the powder being less likely to scatter, being easy to transport at low cost, etc.

[0005] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by a composite material in which the surface of exfoliated graphite, which has a half-width of the 002 diffraction line in X-ray diffraction (XRD) measurement within a predetermined range, is coated with a coating substance.

[0006] That is, the present disclosure provides a composite material in which the surface of exfoliated graphite is coated with a coating substance, and characterized in that, in XRD measurement, the half-width of the 002 diffraction line of the exfoliated graphite is in the range of 0.15° or more and 3.00° or less.

[0007] According to the present disclosure, it is possible to provide a composite material that is easy to handle and, when used as a conductive additive in an electrode, can reduce the volume resistivity of the electrode.

[0008] A. Composite Material The composite material of the present disclosure is a composite material in which the surface of exfoliated graphite is coated with a coating substance, and is characterized in that, in XRD measurement, the half-width of the 002 diffraction line of the exfoliated graphite is in the range of 0.15° to 3.00°. Furthermore, the bulk density of the composite material of the present disclosure is not particularly limited, but from the viewpoint of excellent handleability, it is preferably 0.05 g / ml to 0.50 g / ml, and more preferably 0.05 g / ml to 0.40 g / ml. Each component used in the composite material of the present disclosure is described in detail below. In the present disclosure, the bulk density (g / ml) can be determined by gently placing exfoliated graphite that is not coated with a composite material or a coating substance into a measuring cylinder and measuring the volume and mass of the exfoliated graphite that is not coated with a composite material or a coating substance.

[0009] [A-1. Exfoliated Graphite] The exfoliated graphite used in the present disclosure is characterized in that, in the diffraction pattern obtained by XRD measurement of the exfoliated graphite, the full width at half maximum (FWHM) of the 002 diffraction line is in the range of 0.15° to 3.00°. The full width at half maximum of the 002 diffraction line of the exfoliated graphite used in the present disclosure is preferably 0.15° to 2.00°, more preferably 0.15° to 1.00°, even more preferably 0.15° to 0.70°, and most preferably 0.20° to 0.60°.

[0010] In the present disclosure, the peak of the 002 diffraction line of exfoliated graphite can be seen in the range of diffraction angle 2θ of 24.0° to 26.5°, which corresponds to the (002) plane of exfoliated graphite. The half-width of the 002 diffraction line indicates the width of the diffraction line at a position half the height of the peak from the baseline of the 002 diffraction line in XRD measurement of exfoliated graphite. The baseline of the 002 diffraction line is based on the straight line connecting the intensity value at 2θ = 24° and the intensity value at 2θ = 29°. The unit of the half-width of the 002 diffraction line is the angle (°), which is the unit of 2θ. Generally, the higher the crystallinity of exfoliated graphite, the smaller the half-width of the 002 diffraction line.

[0011] The half-width of the (002) plane can be measured using an X-ray diffractometer (Rigaku Corporation, model: Ultima IV). Specifically, the measurement is performed under the following conditions and procedures. The radiation source is CuKα radiation, with an acceleration voltage and current of 40 kV and 40 mA, respectively. The sampling width is 0.02°, the measurement range is 2θ = 10° to 80°, the scan speed is 1.0° / min, the divergence slit width is 1 / 2°, the receiving slit width is 0.15 mm, and the scattering slit is automatic. The obtained X-ray diffraction data can be automatically analyzed using "PDXL2," the software provided with the X-ray diffractometer, and the half-width output can be used to calculate the half-width. Note that when analyzing the X-ray diffraction data, peaks derived from Kα2 are not removed.

[0012] The average thickness of the exfoliated graphite used in the present disclosure is not particularly limited, but from the viewpoint of excellent handleability and low volume resistivity of the electrode, it is preferably 10 nm to 250 nm, more preferably 12 nm to 200 nm, even more preferably 12 nm to 160 nm, even more preferably 12 nm to 120 nm, even more preferably 12 nm to 90 nm, and most preferably 15 nm to 70 nm. In the present disclosure, the thickness of exfoliated graphite refers to the thickness in the direction perpendicular to the stacking plane of the exfoliated graphite, and the average thickness refers to the average value of the thicknesses of any 30 or more pieces of exfoliated graphite. The thickness of exfoliated graphite can be measured, for example, using an SEM image of the exfoliated graphite taken with a scanning electron microscope. Note that exfoliated graphite consisting of one unit layer is called graphene, and its theoretical thickness is approximately 0.335 nm.

[0013] The specific surface area of ​​the exfoliated graphite used in the present disclosure is not particularly limited, but from the viewpoint of excellent handleability and low volume resistivity of the electrode, it is preferred that the specific surface area be 8 m 2 / g to 40m 2 / g, and 10m 2 / g~35m 2 / g, more preferably 10m 2 / g to 30m 2In the present disclosure, the specific surface area of ​​exfoliated graphite is a value measured by the BET method in accordance with JIS Z8830 (Method for measuring the specific surface area of ​​powder (solid) by gas adsorption).

[0014] The exfoliated graphite used in the present disclosure can be produced by exfoliating graphite. The graphite used as a raw material may be either natural graphite or artificial graphite. The method for producing the exfoliated graphite used in the present disclosure is not particularly limited, and can be achieved by applying shear force, ultrasonic vibration, cavitation, microwaves, or the like to graphite using a known device to exfoliate the graphite until the half-width of the 002 diffraction line falls within the above-mentioned range. For example, the half-width of the 002 diffraction line can be increased by increasing the microwave energy or shear force applied to the graphite, and the half-width of the 002 diffraction line can be reduced by decreasing the microwave energy or shear force applied to the graphite. Examples of devices used to exfoliate graphite include media-agitating mills such as sand mills, attritors, and bead mills; container-driven mills using balls or rods as media, such as rotary mills, vibration mills, and planetary mills; jet mills, roll mills, hammer mills, pin mills, high-pressure emulsifiers, ultrasonic emulsifiers, and microwave ovens. Examples of high-pressure emulsifiers include penetration-type high-pressure emulsifiers and collision-type high-pressure emulsifiers. Penetration types of penetration-type high-pressure emulsifiers include single-nozzle types and slit-nozzle types. Collision types of collision-type high-pressure emulsifiers include a type in which a liquid containing raw materials is collided with a flat surface such as a valve or a spherical surface such as a ball, and a type in which liquids containing raw materials are collided with each other.

[0015] The method for exfoliating graphite may be either a wet exfoliation method using a solvent or a dry exfoliation method not using a solvent, and may be selected depending on the type of device used for exfoliation.

[0016] Preferred solvents for use in the wet exfoliation method include alcohol-based solvents such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, and methoxyethanol; ketone-based solvents such as acetone and methyl ethyl ketone; heterocyclic solvents such as pyridine, piperidine, morpholine, tetrahydrofuran, and dioxane; ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and water.

[0017] When graphite is exfoliated by a wet exfoliation method, polyethylene glycol, diol-type polypropylene glycol, triol-type polypropylene glycol, polyvinyl alcohol, polyoxyethylene polyoxypropylene glycol, a propylene oxide adduct of bisphenol A, or the like may be used in combination to adjust the viscosity of the solvent and promote the exfoliation of the graphite.

[0018] When graphite is exfoliated by a wet exfoliation method, a surfactant may be used in combination. The surfactant disperses the graphite in a solvent, promoting exfoliation, and also facilitates penetration of the solvent between the graphite layers, promoting exfoliation. After exfoliation, the surfactant may be removed by washing with a solvent, if necessary. Preferred surfactants include nonionic surfactants such as glycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and alkyl glycosides.

[0019] When graphite is exfoliated by a wet exfoliation method, an acid may be used in combination. Examples of the acid include mineral acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as acetic acid, lactic acid, and citric acid; and sulfonic acids such as methanesulfonic acid and benzenesulfonic acid.

[0020] [A-2. Coating substance] The surface of the composite material of the present disclosure is coated with a coating substance. The coating substance used in the present disclosure is not particularly limited as long as it is an organic compound that can be dissolved in a solvent such as water and can form a stable coating on the surface of exfoliated graphite.

[0021] Examples of coating materials used in the present disclosure include polyvinyl compounds such as polyacrylate, polymethacrylate, polystyrene, polyacrylonitrile, polyacrylamide, polyvinyl acetate, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, ethylene vinyl acetate copolymer, polyvinyl ether, polyvinyl pyrrolidone, and polyvinyl acetamide; polymer compounds such as olefin-maleic acid copolymer, olefin-fumaric acid copolymer, methyl cellulose, ethyl cellulose, acetyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polysiloxane, polyacrylic acid, polytetrafluoroethylene, polyetherimide, and sodium polyacrylate; diglycidyl ethers of bisphenols such as bisphenol A diglycidyl ether and bisphenol F diglycidyl ether; phenol novolac epoxy resins; cresol novolac epoxy resins; 3,4-epoxycyclohexylmethyl-3,4-epoxy Epoxy compounds such as cyclohexane carboxylate; oxetane compounds such as 3-ethyl-3-[(phenoxy)methyl]oxetane and 3,7-bis(3-oxetanyl)-5-oxa-nonane; isocyanate compounds such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate and 1,6-hexamethylene diisocyanate; methyl acrylate, ethyl acrylate, butyl acrylate acrylate compounds such as methyl methacrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, ethylene glycol diacrylate, and propylene glycol diacrylate; methacrylate compounds such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and dodecyl methacrylate; vinyl ether compounds such as butyl vinyl ether, cyclohexyl vinyl ether, and hydroxyethyl vinyl ether; vinyl ester compounds such as vinyl hexanoate, vinyl neodecanoate, and vinyl benzoate;Alkoxysilane compounds such as methyltrimethoxysilane, butyltrimethoxysilane, and phenyltrimethoxysilane; antioxidants such as dibutylhydroxytoluene, butylhydroxyanisole, stearyl (3,5-di-t-butyl-4-hydroxyphenyl) propionate, tridecyl phosphite, dilauryl thiodipropionate, ditridecyl thiodipropionate, phenylnaphthylamine, and 4,4'-bis(dialkyl)diphenylamine; ultraviolet absorbers such as benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers; hindered amine-based light stabilizers such as 2,2,6,6-tetramethyl-4-piperidinol fatty acid esters; tetrabromobisphenol A, tetrachlorophthalic anhydride, tricresin, and the like. Examples of suitable surfactants include flame retardants such as diyl phosphate; plasticizers such as diheptyl phthalate, dioctyl phthalate, dioctyl adipate, diisodecyl adipate, dioctyl sebacate, trioctyl trimellitate, and tetraoctyl pyromellitate; lubricants such as fatty acid amides, ethylene bisfatty acid amides, metal soaps, polyethylene wax, montan wax, and hydrogenated castor oil; surfactants such as anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants; hydrocarbons such as paraffinic mineral oil, naphthenic mineral oil, aromatic mineral oil, polybutene, and poly-α-olefin; and ionic liquids such as 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-butyl-3-methylimidazolium dicyanimide.

[0022] In the present disclosure, from the viewpoint of excellent handleability and the ability to reduce the volume resistivity of the electrode, the coating substance is preferably a polymer compound or an epoxy compound, and more preferably a polymer compound. Among polymer compounds, those containing one or more selected from the group consisting of polyvinyl compounds, polyethylene glycol, and polyacrylic acid are preferred, those containing one or more selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid, and polyethylene glycol are more preferred, and polyvinylpyrrolidone is even more preferred. From the viewpoint of excellent handleability and the ability to reduce the volume resistivity of the electrode, the weight-average molecular weight (Mw) of polyvinylpyrrolidone is preferably 100,000 to 700,000.

[0023] In the composite material of the present disclosure, the surface of exfoliated graphite is coated with a coating material. In the present disclosure, the coating material may cover at least a portion of the surface of the exfoliated graphite, or may cover the entire surface, but preferably covers the majority of the surface. Furthermore, the coating material may cover the surface of the exfoliated graphite continuously or discontinuously.

[0024] From the viewpoint of achieving excellent handleability and a low volume resistivity of the electrode, the coating amount of the coating substance in the composite material of the present disclosure is preferably 0.1 parts by mass to 100 parts by mass, more preferably 0.1 parts by mass to 70 parts by mass, even more preferably 0.1 parts by mass to 40 parts by mass, even more preferably 0.1 parts by mass to 10 parts by mass, even more preferably 0.1 parts by mass to 5 parts by mass, and most preferably 0.1 parts by mass to 3 parts by mass, relative to 100 parts by mass of the total of exfoliated graphite and coating substance. Note that in the present disclosure, the coating amount of the coating substance is a theoretical value calculated from the charged amounts of exfoliated graphite and coating substance used when producing the composite material.

[0025] [A-3. Method for Producing Composite Material] Examples of methods for coating the surface of exfoliated graphite with a coating substance include a method of dropping the coating substance or a solution in which the coating substance is dissolved while stirring the exfoliated graphite, a method of spraying vapor or mist of the coating substance onto the exfoliated graphite, and a method of immersing the exfoliated graphite in a solution in which the coating substance is dissolved. After coating the surface of the exfoliated graphite with the coating substance by the above-mentioned method or the like, the composite material of the present disclosure can be obtained by heat drying or natural drying as necessary. Because exfoliated graphite tends to agglomerate, it is preferable to coat the surface of the exfoliated graphite with the coating substance while crushing the secondary particles formed by agglomeration of exfoliated graphite particles. From the viewpoint of facilitating coating the exfoliated graphite with the coating substance while crushing it, a preferred method for producing the composite material of the present disclosure is to immerse the exfoliated graphite in a solution in which the coating substance is dissolved, followed by heat drying or natural drying.

[0026] [A-4. Uses] The composite material of the present disclosure is suitable for use as a conductive additive for the positive and negative electrodes of various secondary batteries, as a general conductive paint, etc. In particular, when the composite material of the present disclosure is used as a conductive additive for the positive and negative electrodes of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, a non-aqueous electrolyte secondary battery having excellent battery characteristics can be obtained.

[0027] B. Electrodes The electrodes of the present disclosure have an electrode layer comprising the composite material described above in the section "A. Composite Material."

[0028] By using the electrode of the present disclosure in a battery, the discharge capacity can be increased and the cycle characteristics can be improved.

[0029] [B-1. Electrode Layer] In the present disclosure, the term "electrode layer" refers to a layer containing the composite material. In addition, in this specification, when the electrode is a positive electrode, the electrode layer may be referred to as a "positive electrode active material layer," and when the electrode is a negative electrode, the electrode layer may be referred to as a "negative electrode active material layer." The thickness of the electrode layer can usually be 1 μm to 1000 μm.

[0030] In the present disclosure, from the viewpoint of effectively functioning as a conductive additive and increasing discharge capacity, the content of the composite material is preferably 0.9 parts by mass to 28 parts by mass, more preferably 0.12 parts by mass to 9 parts by mass, and even more preferably 0.18 parts by mass to 2.8 parts by mass, per 100 parts by mass of the electrode layer. In this specification, the "composite material" in the "content of the composite material" means one that includes exfoliated graphite and a coating material.

[0031] The electrode layer contains a composite material, but may contain other components as needed. When the electrode layer is used as a positive electrode active material layer or a negative electrode active material layer, the other components include a binder and an active material, and may contain, as needed, a conductive aid, a viscosity adjuster, a reinforcing material, an antioxidant, etc., other than the composite material of the present disclosure.

[0032] As the binder, a binder known for use as a binder for an electrode layer can be used. Examples of binders include styrene-butadiene rubber, butadiene rubber, polyethylene, polypropylene, polyamide, polyamideimide, polyimide, polyacrylonitrile, polyurethane, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-propylene-diene rubber, fluororubber, styrene-acrylic acid ester copolymer, ethylene-vinyl alcohol copolymer, acrylonitrile-butadiene rubber, styrene-isoprene rubber, polymethyl methacrylate, polyacrylate, polyvinyl alcohol, polyvinyl ether, carboxymethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose, cellulose nanofiber, polyethylene oxide, starch, polyvinylpyrrolidone, polyvinyl chloride, polyacrylic acid, and the like. Only one binder may be used, or two or more binders may be used in combination. Among these, aqueous binders are preferred from the viewpoint of low environmental impact and excellent binding properties, and one or more selected from the group consisting of styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid are more preferred.

[0033] From the viewpoint of further increasing the discharge capacity, the content of the binder in the electrode layer is preferably 0.1 parts by mass to 30 parts by mass, and more preferably 1 part by mass to 20 parts by mass, relative to 100 parts by mass of the active material in the electrode layer.

[0034] The positive electrode active material layer may contain at least a known active material (hereinafter, sometimes referred to as "positive electrode active material"). Examples of the positive electrode active material include lithium transition metal composite oxides, lithium-containing transition metal phosphate compounds, and lithium-containing silicate compounds. Only one type of positive electrode active material may be used, or two or more types may be used in combination.

[0035] Examples of the transition metal in the lithium transition metal composite oxide include vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, etc. Specific examples of the lithium transition metal composite oxide include lithium cobalt composite oxides such as LiCoO2, lithium nickel composite oxides such as LiNiO2, lithium manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO3, and lithium transition metal composite oxides in which a portion of the main transition metal atoms of these lithium transition metal composite oxides has been substituted with other metals such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, and zirconium. Specific examples of the lithium transition metal composite oxide in which a portion of the main transition metal atoms has been substituted with other metals include Li, 1.1 Mn 1.8 Mg 0.1 O4, Li 1.1 Mn 1.85 Al 0.05 O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Mn 0.5 O2, LiNi 0.80 Co 0.17 Al 0.03 O2, LiNi 0.80 Co 0.15 Al 0.05O2, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 ) O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiMn 1.8 Al 0.2 O4, LiNi 0.5 Mn 1.5 O4, Li2MnO3-LiMO2 (M=Co, Ni, Mn), etc.

[0036] Examples of the transition metal in the lithium-containing transition metal phosphate compound include vanadium, titanium, manganese, iron, cobalt, and nickel. Specific examples of the lithium-containing transition metal phosphate compound include LiFePO4, LiMn x Fe 1-x Examples of such lithium transition metal phosphate compounds include iron phosphate compounds such as PO4 (0<x<1), iron sulfate compounds such as LiFeSO4F, cobalt phosphate compounds such as LiCoPO4, lithium transition metal phosphate compounds in which some of the main transition metal atoms are substituted with other metals such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, and niobium, and vanadium phosphate compounds such as Li3V2(PO4)3.

[0037] The lithium-containing silicate compound may be Li2FeSiO4 or the like.

[0038] The negative electrode active material layer may contain at least a known active material (hereinafter, sometimes referred to as "negative electrode active material").

[0039] In the case of lithium ion secondary batteries, examples of negative electrode active materials include natural graphite, artificial graphite, non-graphitizable carbon, easily graphitizable carbon, lithium, lithium alloys, silicon, silicon alloys, silicon oxide, silicon carbide, tin, tin alloys, tin oxide, phosphorus, germanium, indium, copper oxide, antimony sulfide, titanium oxide, iron oxide, manganese oxide, cobalt oxide, nickel oxide, lead oxide, ruthenium oxide, tungsten oxide, zinc oxide, as well as LiVO2, Li2VO4, Li4Ti5O 12The negative electrode active material may be used alone or in combination of two or more.

[0040] In the case of a sodium-ion secondary battery, among the negative electrode active materials used in the lithium-ion secondary battery described above, a negative electrode active material that does not contain lithium atoms and a negative electrode active material in which lithium atoms are replaced with sodium atoms can be used. Note that when the negative electrode active material is lithium or a lithium alloy, or sodium or a sodium alloy, it may be used as an electrode without using a current collector. In addition, other negative electrode active materials such as potassium, magnesium, calcium, aluminum, and zinc can be used.

[0041] As a conductive additive other than the composite material of the present disclosure (hereinafter, sometimes referred to as "other conductive additives"), a conductive additive known as a conductive additive for an electrode layer can be used. Examples of other conductive additives include carbon materials such as natural graphite, artificial graphite, carbon black, ketjen black, acetylene black, channel black, furnace black, lamp black, thermal black, carbon nanotubes, vapor-grown carbon fiber (VGCF), graphene, fullerene, and needle coke; metal powders such as aluminum powder, nickel powder, and titanium powder; conductive metal oxides such as zinc oxide and titanium oxide; and sulfides such as LaS, SmS, CeS, and TiS. Only one type of other conductive additive may be used, or two or more types may be used in combination.

[0042] From the viewpoint of increasing discharge capacity, the average particle diameter of the other conductive additive is preferably 0.01 μm to 100 μm, and more preferably 0.01 μm to 50 μm. In the present disclosure, "average particle diameter" refers to the 50% particle diameter measured by a laser diffraction light scattering method. In the laser diffraction light scattering method, the particle diameter is a volume-based diameter, and the secondary particle diameter of the object to be measured is measured. When measuring the average particle diameter by the laser diffraction light scattering method, the object to be measured is dispersed in a dispersion medium such as water and then measured.

[0043] When the composite material of the present disclosure is used in combination with another conductive additive, the ratio of the composite material of the present disclosure to the other conductive additive is preferably 25 parts by mass to 1,500 parts by mass, more preferably 50 parts by mass to 600 parts by mass, and even more preferably 100 parts by mass to 300 parts by mass, relative to 100 parts by mass of the composite material of the present disclosure, from the viewpoint of obtaining excellent rate characteristics even when the content of the positive electrode active material is high.

[0044] As the viscosity modifier, a known viscosity modifier for the electrode layer can be used. Examples of viscosity modifiers include cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; (modified) poly(meth)acrylic acid and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohols such as copolymers of acrylic acid or acrylic acid salts with vinyl alcohol, and copolymers of maleic anhydride or maleic acid or fumaric acid with vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, oxidized starch, starch phosphate, casein, various modified starches, cellulose nanofibers, and hydrogenated acrylonitrile-butadiene copolymers. These may also be used as dispersants.

[0045] The reinforcing material may be any known material for reinforcing electrode layers, including various inorganic and organic spherical, plate-like, rod-like, or fibrous fillers.

[0046] As the antioxidant, any known antioxidant for an electrode layer can be used, including phenol compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds, and polymeric phenol compounds.

[0047] The method for forming the electrode layer may be any method that can form the electrode layer, and examples thereof include a method in which an electrode layer-forming composition containing the composite material of the present disclosure, an active material, other components that are contained as necessary, and a solvent is applied to a current collector or the like, and then the solvent is dried and removed from the coating film.

[0048] Examples of solvents used in the electrode layer-forming composition include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, nitromethane, N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, polyethylene oxide, tetrahydrofuran, dimethyl sulfoxide, sulfolane, γ-butyrolactone, water, alcohol, etc. The amount of solvent used can be adjusted depending on the application method. For example, in the case of the doctor blade method, from the viewpoint of ease of production, the amount of solvent used is preferably 20 parts by mass to 300 parts by mass, and more preferably 30 parts by mass to 200 parts by mass, relative to 100 parts by mass of the total amount of the composite material of the present disclosure, the active material, the binder used as needed, and other conductive additives.

[0049] The method for preparing the electrode layer-forming composition is not particularly limited, and examples thereof include a method of mixing the composite material of the present disclosure, the active material, other components contained as necessary, and a solvent using a conventional ball mill, sand mill, bead mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, rotation-revolution mixer, planetary mixer, Filmix, Disper, jet paster, or the like.

[0050] The coating method is not particularly limited, and various methods can be used, such as a die coater method, a comma coater method, a curtain coater method, a spray coater method, a gravure coater method, a flexo coater method, a knife coater method, a doctor blade method, a reverse roll method, a brush coating method, a dipping method, etc. Among the coating methods, the die coater method, the doctor blade method, the knife coater method, and the comma coater method are preferred from the viewpoint of being able to obtain a good surface condition of a coating film in accordance with the physical properties such as viscosity and drying properties of the electrode layer-forming composition.

[0051] The method for drying and removing the solvent is not particularly limited, and may be heating, reducing pressure, or a combination of these. The heating temperature may be 40° C. to 200° C. The heating and reducing pressure device may be a heating furnace, an infrared heating furnace, a vacuum oven, or the like.

[0052] This drying volatilizes volatile components such as the solvent, forming an electrode layer. Thereafter, the electrode layer may be pressed, if necessary. Examples of pressing methods include die pressing and roll pressing.

[0053] [B-2. Other Components] The electrode of the present disclosure has the electrode layer described above, but may have other components as necessary. Examples of other components include a current collector.

[0054] The current collector may be made of a conductive material such as titanium, a titanium alloy, aluminum, an aluminum alloy, copper, nickel, stainless steel, nickel-plated steel, or a conductive resin. The surface of these conductive materials may be coated with carbon. The current collector may be in the form of a foil, plate, mesh, or porous. Among these, aluminum is preferred, and aluminum foil is more preferred, from the viewpoints of conductivity and cost. When the current collector is in the form of a foil, its thickness is preferably 1 μm to 100 μm, from the viewpoints of further increasing the discharge capacity and ease of manufacture.

[0055] [B-3. Uses] The use of the electrode of the present disclosure is not particularly limited, but can include batteries. Examples of batteries include primary batteries and secondary batteries. Examples of secondary batteries include lithium ion secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, magnesium ion secondary batteries, calcium ion secondary batteries, and aluminum ion secondary batteries. That is, lithium sulfur secondary batteries, sodium sulfur secondary batteries, potassium sulfur secondary batteries, magnesium sulfur secondary batteries, calcium sulfur secondary batteries, and aluminum sulfur secondary batteries are also possible.

[0056] From the viewpoint of practicality, the electrode of the present disclosure is preferably used as an electrode for a secondary battery, and more preferably as an electrode for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. The electrode of the present disclosure can be used as either a positive electrode or a negative electrode, but is preferably used as a positive electrode from the viewpoint of further increasing the discharge capacity and ease of production.

[0057] In the present disclosure, the electrode may be subjected to a pressing process, if necessary. Examples of the pressing process include a mold pressing method and a roll pressing method.

[0058] C. Battery The battery of the present disclosure has the electrodes described above in the section "B. Electrodes."

[0059] The battery of the present disclosure has a large discharge capacity and excellent cycle characteristics. In the battery of the present disclosure, the electrode may be either a positive electrode or a negative electrode, but from the viewpoints of further increasing the discharge capacity and ease of production, it is preferable that the electrode be a positive electrode.

[0060] The battery of the present disclosure may have other components as needed, such as a counter electrode paired with the electrode, an electrolyte, a separator, and an exterior member.

[0061] [C-1. Counter electrode] A counter electrode is an electrode used in combination with an electrode of the present disclosure. When the electrode of the present disclosure is a positive electrode, the counter electrode is a negative electrode. When the electrode of the present disclosure is a negative electrode, the counter electrode is a positive electrode. Hereinafter, the positive electrode and negative electrode used as a counter electrode for the electrode of the present disclosure will be described.

[0062] (1) Negative electrode The negative electrode used as the counter electrode may have a negative electrode active material layer. The negative electrode active material layer may contain at least a known active material, for example, the negative electrode active material described in the section "B. Electrode" above.

[0063] The negative electrode active material layer contains a negative electrode active material, and may contain, as necessary, for example, a binder, other conductive additives, etc. The binder and other conductive additives used in the negative electrode active material layer may be the same as those described in the section "B. Electrode" above, and therefore will not be described here.

[0064] (2) Positive Electrode The positive electrode used as the counter electrode may have a positive electrode active material layer. The positive electrode active material layer may contain at least a known active material, for example, a positive electrode active material described in the section "B. Electrode" above.

[0065] The positive electrode active material layer contains a positive electrode active material, and may contain, as necessary, for example, a binder, other conductive additives, etc. The binder and other conductive additives used in the positive electrode active material layer may be the same as those described in the section "B. Electrode" above, and therefore will not be described here.

[0066] [C-2. Electrolyte] The electrolyte is not particularly limited, and known electrolytes can be used. Examples of the electrolyte include a liquid electrolyte obtained by dissolving a supporting electrolyte in an organic solvent, a polymer gel electrolyte in which a supporting electrolyte is dissolved in an organic solvent and gelled with a polymer, a polymer electrolyte in which a supporting electrolyte is dispersed in a polymer without containing an organic solvent, and an inorganic solid electrolyte. Two or more of the above electrolytes may also be used in combination. In the present disclosure, from the viewpoints of further increasing the discharge capacity and ease of production, the electrolyte is preferably a liquid electrolyte, a polymer electrolyte, or an inorganic solid electrolyte, and more preferably a liquid electrolyte.

[0067] In the present disclosure, the supporting electrolyte used in the liquid electrolyte and polymer gel electrolyte for lithium-ion secondary batteries is a conventionally known lithium salt, examples of which include LiPF, LiBF, LiAsF, LiCFSO, LiCFCO, LiN(CFSO), LiN(CFSO), LiN(SOF), LiC(CFSO), LiB(CFSO), LiB(CO), LiBF(CO), LiSbF, LiSiF, LiSCN, LiClO, LiCl, LiF, LiBr, LiI, LiAlF, LiAlCl, LiPOF, and derivatives thereof. Among these, from the viewpoint of further increasing the discharge capacity, it is preferable to use one or more selected from the group consisting of LiPF, LiBF, LiClO, LiAsF, LiCFSO, LiN(CFSO), LiN(CFS0), LiN(SOF), and LiC(CFSO), as well as derivatives of LiCFSO and derivatives of LiC(CFSO).

[0068] The content of the supporting electrolyte in the liquid electrolyte or polymer gel electrolyte is preferably 0.5 mol / L to 7 mol / L, and more preferably 0.8 mol / L to 1.8 mol / L, from the viewpoint of further increasing the discharge capacity.

[0069] In the case of a lithium ion secondary battery, examples of the supporting electrolyte used for the polymer electrolyte include LiN(CFSO), LiN(CFSO), LiN(SOF), LiC(CFSO), LiB(CFSO), and LiB(C0).

[0070] In the present disclosure, the inorganic solid electrolyte is, for example, Li 1+x A x B 2-x Phosphate-based materials such as (PO4)3 (A = Al, Ge, Sn, Hf, Zr, Sc, Y, B = Ti, Ge, Zn, 0 < x < 0.5), LiMPO4 (M = Mn, Fe, Co, Ni), Li3PO4; Li3XO4 (X = As, V), Li 3+x A x B 1-x O4 (A=Si, Ge, Ti, B=P, As, V, 0<x<0.6), Li 4+x A x Si 1-x O4 (when A=B, Al, Ga, Cr, Fe, 0<x<0.4; when A=Ni, Co, 0<x<0.1), Li 4-3y Al y SiO4 (0<y<0.06), Li 4-2y Zn y GeO4 (0<y<0.25), LiAlO2, Li2BO4, Li4XO4 (X=Si, Ge, Ti), lithium titanate (LiTiO2, LiTi2O4, Li4TiO4, Li2TiO3, Li2Ti3O7, Li4Ti5O 12 Lithium composite oxides such as LiBr, LiF, LiCl, LiPF, and LiBF; compounds containing lithium and halogen such as LiPON, LiN(SOCF), LiN(SOCF), LiN(SON), and LiN(SOCF); 0.55 Li 0.35 Crystals having a perovskite structure with lithium ion conductivity, such as TiO3; Li7-La3Zr2O 13 Crystals having a garnet structure such as 50Li4SiO4.50Li3BO 33, 90Li3BO3.10Li2SO4 glasses, etc.; 70Li2S.30P2S5, 75Li2S.25P2S5, Li6PS5Cl, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li6PS5P 1.44 C l3 , Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 Lithium phosphorus sulfide crystals such as 30LiS.26BS.44LiI, 50LiS.17P.sub.2S.33LiBH, 50LiS.50GeS.63LiS.36SiS.1Li.sub.3PO.5, 57LiS.38SiS.5Li.sub.4SiO.5, 70LiS.50GeS.Lithium phosphorus sulfide glasses such as Li.sub.7P.sub.3S 11 , Li 3.25 P 0.95 S4, Li 10 GeP2S 12 , Li 9.6 P3S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Examples of the inorganic solid electrolyte include glass ceramics such as those mentioned above. The inorganic solid electrolyte may be coated with a polymer gel electrolyte. When an inorganic solid electrolyte is used, a polymer gel electrolyte layer may be provided between the inorganic solid electrolyte layer and the electrode.

[0071] Examples of polymers used in the polymer gel electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, etc. There are no particular limitations on the blending ratio of the polymers in the polymer gel electrolyte or the gelling method, and blending ratios and gelling methods known in the art may be used.

[0072] In the case of a sodium ion secondary battery, a supporting electrolyte in which the lithium atoms in the above-mentioned lithium ion secondary battery are replaced with sodium atoms may be used.

[0073] In the present disclosure, the organic solvent used in the liquid electrolyte and polymer gel electrolyte may be any organic solvent commonly used in liquid electrolytes. Specific examples of the organic solvent include saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, amide compounds, saturated chain carbonate compounds, chain ether compounds, cyclic ether compounds, saturated chain ester compounds, etc. Among these, saturated cyclic carbonate compounds and saturated chain carbonate compounds are more preferred.

[0074] Examples of the saturated cyclic carbonate compound include ethylene carbonate, fluoroethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, and 1,1-dimethylethylene carbonate.

[0075] Examples of the saturated cyclic ester compound include γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-hexanolactone, and δ-octanolactone.

[0076] Examples of the sulfoxide compound include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, and thiophene.

[0077] Examples of the sulfone compound include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also called tetramethylene sulfone), 3-methyl sulfolane, 3,4-dimethyl sulfolane, 3,4-diphenylmethyl sulfolane, sulfolene, 3-methyl sulfolene, 3-ethyl sulfolene, 3-bromomethyl sulfolene, etc. Among these, sulfolane and tetramethyl sulfolane are preferred from the viewpoint of further increasing the discharge capacity.

[0078] Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

[0079] Examples of the saturated chain carbonate compound include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl butyl carbonate, methyl t-butyl carbonate, diisopropyl carbonate, and t-butyl propyl carbonate.

[0080] Examples of the chain ether compound and cyclic ether compound include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolane, dioxane, 1,2-bis(methoxycarbonyloxy)ethane, 1,2-bis(ethoxycarbonyloxy)ethane, 1,2-bis(ethoxycarbonyloxy)propane, ethylene glycol bis(trifluoroethyl)ether, propylene glycol bis(trifluoroethyl)ether, ethylene glycol bis(trifluoromethyl)ether, diethylene glycol bis(trifluoroethyl)ether, glymes, etc. Among these, dioxolane is preferred from the viewpoint of further increasing discharge capacity.

[0081] Examples of the saturated chain ester compound include monoester compounds and diester compounds having a total carbon number of 2 to 8 in the molecule. Specific examples of the saturated chain ester compound include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, propylene glycol diacetyl, etc. Among these, from the viewpoint of further increasing the discharge capacity, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, and ethyl propionate are preferred.

[0082] Other organic solvents that can be used to prepare the electrolyte include, for example, acetonitrile, propionitrile, nitromethane, and derivatives thereof, and various ionic liquids.

[0083] The electrolyte may contain other known additives, such as an electrode film-forming agent, an antioxidant, a flame retardant, an overcharge inhibitor, etc., in order to improve the battery life, safety, etc. From the viewpoint of further increasing the discharge capacity, the content of the other additives is usually 0.01 parts by mass to 10 parts by mass, and preferably 0.1 parts by mass to 5 parts by mass, per 100 parts by mass of the electrolyte.

[0084] [C-3. Separator] The separator may be any material that allows lithium ions to pass through and prevents contact between the positive electrode and the negative electrode, and is not particularly limited. For example, a polymeric microporous film or nonwoven fabric can be used. Examples of the film include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethers such as polyethylene oxide and polypropylene oxide, various celluloses such as carboxymethyl cellulose and hydroxypropyl cellulose, compounds mainly composed of poly(meth)acrylic acid and various esters thereof, derivatives thereof, copolymers or mixtures thereof, etc. These films may be coated with ceramic materials such as alumina and silica, magnesium oxide, aramid resin, or polyvinylidene fluoride.

[0085] These films may be used alone or may be laminated to form a multilayer film. Furthermore, various additives may be used in these films, and the type and content of the additives are not particularly limited. Among these films, films made of polyethylene, polypropylene, polyvinylidene fluoride, or polysulfone are preferred from the viewpoint of further increasing the discharge capacity of the secondary battery. Note that when the electrolyte is a polymer electrolyte or an inorganic solid electrolyte, a separator may not be included.

[0086] [C-4. Battery Shape and Exterior Material] In the present disclosure, the shape of the battery is not particularly limited, and various shapes such as coin type, cylindrical type, square type, laminate type, etc. may be used.

[0087] The exterior member used in the battery of the present disclosure can be a laminate film or a metal container. The thickness of the exterior member is usually 0.5 mm or less, preferably 0.3 mm or less. The shape of the exterior member can be flat (thin), rectangular, cylindrical, coin-shaped, button-shaped, or the like.

[0088] The laminate film may also be a multilayer film having a metal layer between resin films. The metal layer is preferably aluminum foil or aluminum alloy foil for weight reduction. Polymeric materials such as polypropylene, polyethylene, nylon, and polyethylene terephthalate can be used for the resin film. The laminate film can be sealed by heat fusion to form it into the shape of the exterior component. The metal container can be made of, for example, stainless steel, aluminum, or an aluminum alloy. Aluminum alloys containing elements such as magnesium, zinc, and silicon are preferred. By limiting the content of transition metals such as iron, copper, nickel, and chromium in aluminum or aluminum alloys to 1% by mass or less, long-term reliability and heat dissipation in high-temperature environments can be dramatically improved.

[0089] [C-5. Battery Type] The battery of the present disclosure may be either a primary battery or a secondary battery, but is preferably a secondary battery, and more preferably a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, because it is useful as an in-vehicle battery.

[0090] D. Other aspects of the present disclosure include the following. [1] A composite material in which the surface of exfoliated graphite is coated with a coating substance, characterized in that, in an XRD measurement, the half-width of the 002 diffraction line of the exfoliated graphite is in the range of 0.15° to 3.00°. [2] The composite material according to [1], characterized in that the coating substance is a polymer compound. [3] The composite material according to [2], characterized in that the polymer compound includes one or more selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid, and polyethylene glycol. [4] An electrode having an electrode layer including the composite material according to any one of [1] to [3]. [5] A battery in which the electrode according to [4] is a positive electrode.

[0091] The present disclosure will be described in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples. In the examples, "parts" and "%" are by mass unless otherwise specified.

[0092] 1. Exfoliated Graphite [Production Example 1: Exfoliated Graphite A-1] 74 parts by mass of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 26 parts by mass of polyethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, product name: Polyethylene Glycol 20000) were mixed and dissolved by heating, and 10 parts by mass of natural graphite (manufactured by Fujifilm Wako Pure Chemical Industries) were dispersed in the mixture. 0.6 g of this dispersion was poured into a 0.5 cm 3 The dispersion was collected in a vial and capped, and then irradiated with microwaves of 2450 MHz at 180° C. for 30 minutes using a microwave synthesis apparatus (Initiator+ manufactured by Biotage Japan). Thereafter, the dispersion was washed with acetone, filtered, and then heated and dried in an oven to obtain exfoliated graphite A-1.

[0093] [Production Example 2: Exfoliated graphite A-2] Except for changing the microwave irradiation time from 30 minutes at 180°C to 30 minutes at 200°C in Production Example 1, the same operation as in Production Example 1 was performed to obtain exfoliated graphite A-2.

[0094] [Exfoliated Graphite B-1] Highly purified flake graphite-199, manufactured by Teda Tianrun Carbon Materials Co., Ltd., was used as exfoliated graphite B-1.

[0095] [Exfoliated Graphite B-2] Graphene Nanoplatelets-Grade C (C750), manufactured by XG Sciences, was used as exfoliated graphite B-2.

[0096] The half-width, average thickness, and specific surface area of ​​the 002 diffraction line of each exfoliated graphite were measured. The results are shown in Table 1.

[0097]

[0098] 2. Regarding Composite Materials [Production of Composite Materials] Exfoliated graphite, coating material, and water were mixed in the formulations shown in Tables 2 to 5, and a bead mill (manufactured by Kotobuki Industries, product name: UAM-015) was used to impregnate the exfoliated graphite into the water containing the coating material and to disperse the secondary particles of the exfoliated graphite for 30 minutes, followed by heating and drying under reduced pressure to remove the water, thereby producing the composite materials of Examples 1 to 14 and Comparative Examples 1 and 2. [Coating materials] Coating material B1: Polyvinylpyrrolidone (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., product name: Pitzcol K-90, Mw: 360,000) Coating material B2: Polyacrylic acid (manufactured by Aldrich, Mw: 250,000) Coating material B3: Polyethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: Polyethylene glycol 20000) Coating material B4: Carboxymethyl cellulose (manufactured by Daicel FineChem, product name: CMC Daicel 2200) Coating material B5: Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., product name: PVA-217) Coating material B6: Polyethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: Polyethylene glycol 6000) Coating material B7: Methylcellulose (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: Methylcellulose 400) Coating material B8: Polytetrafluoroethylene (manufactured by Daikin Corporation, product name: Polyflon PTFE D-210C) Coating material B9: Polyetherimide (manufactured by Fujifilm Wako Pure Chemical Industries, trade name: Polyethyleneimine (average molecular weight: approximately 10,000)) Coating material B10: Sodium polyacrylate (manufactured by Fujifilm Wako Pure Chemical Industries, trade name: Sodium polyacrylate (degree of polymerization: 2,700 to 7,500))

[0099]

[0100]

[0101]

[0102]

[0103] [Bulk Density] The bulk density (g / ml) was determined by gently placing exfoliated graphite that was not coated with a composite material or a coating substance into a 10 ml measuring cylinder and measuring the volume and mass of the exfoliated graphite that was not coated with a composite material or a coating substance. The results are shown in Tables 6 to 9.

[0104] [Production of Positive Electrode] 0.75 parts by mass of exfoliated graphite not coated with the composite material or coating material shown in Tables 6 to 9 as a conductive additive and LiNi as a positive electrode active material. 0.6 Co 0.2 Mn 0.2 96.2 parts by mass of O2 (NCM622), 3.0 parts by mass of styrene-butadiene rubber (aqueous dispersion, manufactured by Zeon Corporation) as a binder, and 120 parts by mass of water as a solvent were charged together and dispersed for 60 minutes using a rotation / revolution mixer, thereby preparing a composition for forming a positive electrode active material layer. This composition for forming a positive electrode active material layer was applied to a current collector made of aluminum foil (thickness 20 μm) by a doctor blade method, and left to dry at 90 ° C. for 1 hour to prepare a positive electrode consisting of a positive electrode active material layer and a current collector. Thereafter, this positive electrode was cut to a predetermined size and further vacuum dried at 130 ° C. for 6 hours immediately before use to prepare the lithium ion secondary battery positive electrodes (basis weight: 25 g / cm 2 , Density: 2.4g / cm 3 ) was prepared.

[0105] <Volume Resistivity> The volume resistivity (Ω cm) of the positive electrodes for lithium ion secondary batteries produced in each Example and Comparative Example was measured using an electrode resistance measurement system (RM2610 manufactured by HIOKI) in an environment of 25° C. The results are shown in Tables 6 to 9.

[0106]

[0107]

[0108]

[0109]

[0110] From the above results, it can be said that the composite material of the present disclosure has excellent handleability due to its high bulk density, and that the electrode containing the composite material of the present disclosure has low volume resistivity, making it useful as a conductive additive for electrodes.

Claims

1. A composite material in which the surface of exfoliated graphite is coated with a coating substance, characterized in that in XRD measurement, the half-width of the 002 diffraction line of the exfoliated graphite is in the range of 0.15° to 3.00°.

2. The composite material according to claim 1, characterized in that the coating substance is a polymer compound.

3. The composite material according to claim 2, wherein the polymer compound comprises at least one selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid, and polyethylene glycol.

4. An electrode having an electrode layer comprising the composite material according to any one of claims 1 to 3.

5. A battery in which the electrode according to claim 4 is a positive electrode.

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