JP2017091859A - Conductive paste for lithium ion battery positive electrode, and mixture material paste for lithium ion battery positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a conductive paste for a lithium ion battery positive electrode, which has a viscosity serving to facilitate its coating even with a relatively small blend volume of a dispersant; and a mixture material paste for a lithium ion battery positive electrode.SOLUTION: A conductive paste for a lithium ion battery positive electrode comprises: a dispersant (A); a conductive carbon (B); and a solvent (C). The dispersant (A) includes a polyvinyl alcohol resin (a1) and an aromatic ring-containing acrylic resin (a2). The polyvinyl alcohol resin (a1) has a repeating unit expressed by the formula, -(CH-CH(OH))- at a rate of 30-100 mass% in a polymer chain. The polyvinyl alcohol resin (a1) and the aromatic ring-containing acrylic resin (a2) are blended in a range of 99.9/0.1 to 80.0/20.0 on a resin solid content proportion basis.SELECTED DRAWING: None

Description

  The present invention relates to a conductive paste for a lithium ion battery positive electrode and a composite paste for a lithium ion battery positive electrode.

  The lithium ion secondary battery is a kind of non-aqueous electrolyte secondary battery, and is a secondary battery in which lithium ions in the electrolyte bear electric conduction. Lithium ion secondary batteries have excellent characteristics such as high energy density, excellent charge energy retention characteristics, and a small so-called memory phenomenon that reduces apparent capacity. Therefore, lithium ion secondary batteries are used in a wide range of fields such as mobile phones, smartphones, personal computers, hybrid vehicles, and electric vehicles.

  Here, the lithium ion secondary battery mainly includes a positive electrode plate, a negative electrode plate, a separator for insulating the positive electrode plate and the negative electrode plate, a non-aqueous electrolyte, and the like. The positive electrode plate is obtained by forming a positive electrode mixture layer on the surface of a positive electrode core material. The positive electrode mixture layer is formed by applying a positive electrode mixture paste obtained by mixing an electrode active material to a conductive paste containing a conductive additive (carbon, etc.), a binder, and a solvent to the surface of the positive electrode core material and drying it. Can be manufactured.

  As described above, since the positive electrode mixture layer is produced by applying the positive electrode mixture paste on the surface of the positive electrode core material, the positive electrode mixture paste and the conductive paste as its constituent material have a low viscosity. It is required to be. Under such circumstances, there is known a method of adding a dispersing agent for dispersing a conductive additive in a conductive paste or dispersion (Patent Documents 1 and 2). In addition, a method using a specific vinyl alcohol polymer as a binder is also known (Patent Document 3). However, if a large amount of a dispersant or the like is blended, battery performance (internal resistance, capacity) is affected. The amount is limited. Therefore, a dispersant capable of reducing the viscosity of the conductive paste with a small amount is desired.

JP2013-89485 JP 2014-193986 JP-A-11-250915

  The problem to be solved by the present invention is to provide a lithium ion battery positive electrode conductive paste and a lithium ion battery positive electrode mixture paste having a viscosity that is easy to apply even if the amount of the dispersant is relatively small.

  Under such circumstances, as a result of intensive studies, the present inventors have used the dispersant (A) containing a certain amount of the polyvinyl alcohol resin (a1) having a specific structure and the aromatic ring-containing acrylic resin (a2) to achieve the above problem. It was found that can be solved. The present invention is based on such novel findings.

Accordingly, the present invention provides the following sections:
Item 1. A conductive paste containing a dispersant (A), a conductive carbon (B), and a solvent (C),
The dispersant (A) includes a polyvinyl alcohol resin (a1) and an aromatic ring-containing acrylic resin (a2),
The polyvinyl alcohol resin (a1) has a repeating unit represented by the following formula at a ratio of 30 to 100% by mass in the polymer chain,

The compounding ratio of the polyvinyl alcohol resin (a1) and the aromatic ring-containing acrylic resin (a2) is in the range of 99.9 / 0.1 to 80.0 / 20.0 in terms of resin solid content, for a lithium ion battery positive electrode Conductive paste.

  Item 2. Item 2. The conductive paste for a lithium ion battery positive electrode according to Item 1, wherein the conductive carbon (B) contains acetylene black.

  Item 3. Item 1 or 2 characterized in that the aromatic ring-containing acrylic resin (a2) is a copolymer of raw material monomers containing 5 to 50% by mass of the aromatic ring-containing monomer, based on the total solid content of the raw material monomers. The electrically conductive paste for lithium ion battery positive electrodes of description.

  Item 4. Item 4. The conductive paste for a lithium ion battery positive electrode according to any one of Items 1 to 3, wherein the conductive carbon (B) further contains graphite.

  Item 5. Item 5. The conductive paste for a lithium ion battery positive electrode according to any one of Items 1 to 4, wherein the solvent (C) contains N-methyl-2-pyrrolidone.

  Item 6. Item 6. A paste for a lithium ion battery positive electrode obtained by further blending an electrode active material with the conductive paste according to any one of items 1 to 5.

Item 7. A method for producing a conductive paste comprising a step of mixing a dispersant (A), a conductive carbon (B), and a solvent (C),
The dispersant (A) includes a polyvinyl alcohol resin (a1) and an aromatic ring-containing acrylic resin (a2),
The polyvinyl alcohol resin (a1) has a repeating unit represented by the following formula at a ratio of 30 to 100% by mass in the polymer chain,

The method whose compounding ratio of a polyvinyl alcohol resin (a1) and an aromatic ring containing acrylic resin (a2) is the range of 99.9 / 0.1-80.0 / 20.0 by resin solid content ratio.

  Item 8. Item 8. The method according to Item 7, wherein the conductive carbon (B) contains acetylene black.

  Item 9. A step of obtaining an aromatic ring-containing acrylic resin (a2) by copolymerizing a raw material monomer containing 5 to 50% by mass of the aromatic ring-containing monomer, based on the total solid content of the raw material monomer, and a polyvinyl alcohol resin (a1) and Item 9. The method according to Item 7 or 8, further comprising a step of blending the aromatic ring-containing acrylic resin (a2) to obtain the dispersant (A).

  Item 10. Item 10. The method according to any one of Items 7 to 9, wherein the conductive carbon (B) further contains graphite.

  Item 11. Item 11. The method according to any one of Items 7 to 10, wherein the solvent (C) contains N-methyl-2-pyrrolidone.

  Item 12. The manufacturing method of the lithium ion battery positive electrode mixture paste including the process of mix | blending an electrode active material with the process of obtaining an electrically conductive paste by the method of any one of claim | item 7 -11, and an electrically conductive paste.

  The dispersant (A) blended in the conductive paste for lithium ion battery positive electrode and the composite paste for lithium ion battery positive electrode of the present invention is a pigment-dispersed resin conventionally used in the conductive paste for lithium ion battery positive electrode and the composite paste. The viscosity of the paste can be sufficiently reduced with a relatively small blending amount.

In the present specification, “(meth) acrylate” means acrylate and / or methacrylate, and “(meth) acrylic acid” means acrylic acid and / or methacrylic acid. “(Meth) acryloyl” means acryloyl and / or methacryloyl. “(Meth) acrylamide” means acrylamide and / or methacrylamide. The “polymerizable unsaturated monomer” means a monomer having a polymerizable unsaturated group capable of radical polymerization, and examples of the polymerizable unsaturated group include (meth) acryloyl group, acrylamide group, vinyl group. , Allyl group, (meth) acryloyloxy group, vinyl ether group and the like.

The present invention is a conductive paste containing a dispersant (A), conductive carbon (B), and a solvent (C),
The dispersant (A) includes a polyvinyl alcohol resin (a1) and an aromatic ring-containing acrylic resin (a2),
The polyvinyl alcohol resin (a1) has a repeating unit represented by the following formula in a proportion of 30 to 95% by mass in the polymer chain,

The compounding ratio of the polyvinyl alcohol resin (a1) and the aromatic ring-containing acrylic resin (a2) is in the range of 99.9 / 0.1 to 80.0 / 20.0 in terms of resin solid content, for a lithium ion battery positive electrode A conductive paste is provided.

Dispersant (A)
The dispersant (A) used for the conductive paste of the present invention contains a polyvinyl alcohol resin (a1) and an aromatic ring-containing acrylic resin (a2).

Polyvinyl alcohol resin (a1)
The polyvinyl alcohol resin (a1) that can be used in the present invention has a repeating unit represented by the following formula in a polymer chain in a proportion of usually 30 to 100% by mass, preferably 30 to 95% by mass. And In addition, the ratio of the repeating unit can be determined by the ratio of the monomer constituting the resin and the saponification ratio.

  The polyvinyl alcohol resin (a1) can be obtained by a polymerization method known per se, for example, by polymerizing and hydrolyzing a fatty acid vinyl ester typified by vinyl acetate.

  Examples of the fatty acid vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate and other linear or branched saturated fatty acid vinyl esters. Is mentioned. Of these, vinyl acetate is preferred.

The polyvinyl alcohol resin can also be obtained by copolymerization with a polymerizable unsaturated monomer other than the fatty acid vinyl ester.
Examples of polymerizable unsaturated monomers copolymerizable with fatty acid vinyl esters include olefins such as ethylene and propylene; alkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate and the like ( (Meth) acryloyl group-containing monomers; allyl ethers such as allyl glycidyl ether; vinyl halide compounds such as vinyl chloride, vinylidene chloride and vinyl fluoride; vinyl ethers such as alkyl vinyl ether and 4-hydroxy vinyl ether. These can be used alone or in combination of two or more.

  In the following, description will be made mainly with reference to vinyl acetate, but the present invention is not limited thereto.

  The polymerization method of the polyvinyl alcohol resin can be manufactured by a polymerization method known per se, for example, a method of producing a polyvinyl acetate by solution polymerization of vinyl acetate in an alcohol-based organic solvent and saponifying it. However, it is not limited to this, and for example, bulk polymerization, emulsion polymerization, suspension polymerization or the like may be used. When solution polymerization is performed, continuous polymerization or batch polymerization may be performed, and the monomers may be charged all at once, may be charged separately, or may be added continuously or intermittently.

  The polymerization initiator used in the solution polymerization is not particularly limited, but azobisisobutyronitrile, azobis-2,4-dimethylpareronitrile, azobis (4-methoxy-2,4-dimethylpareronitrile). ), Etc .; peroxides such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; diisopropylpropyl Percarbonate compounds such as dicarbonate, di-2-ethylhexylperoxydicarbonate, diethoxyethylperoxydicarbonate; t-butylperoxyneodecanate, α-cumylperoxyneodecanate, t-butylperoxyneo Decanate The perester compound; azobisdimethylvaleronitrile can be used a known radical polymerization initiator such as azo-bis-methoxy valeronitrile.

  The polymerization reaction temperature is not particularly limited, but can usually be set in the range of about 30 to 150 ° C.

Saponification conditions for producing the polyvinyl alcohol resin are not particularly limited, and can be saponified by a known method. Generally, it can carry out by hydrolyzing the ester part in a molecule | numerator in presence of an alkali catalyst or an acid catalyst in alcohol solutions, such as methanol.
Examples of the alkali catalyst that can be used include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, and potassium methylate, alcoholates, and the like. As the acid catalyst, for example, an inorganic acid aqueous solution such as hydrochloric acid or sulfuric acid, or an organic acid such as p-toluenesulfonic acid can be used, but sodium hydroxide is preferably used.
The temperature of the saponification reaction is not particularly limited, but is preferably 10 to 70 ° C, more preferably 30 to 40 ° C. Although reaction time is not specifically limited, It is desirable to carry out in 30 minutes-3 hours.

The polyvinyl alcohol resin thus obtained preferably has a degree of polymerization of 100 to 4,000, and more preferably 100 to 3,000.
Moreover, it is preferable that saponification degree is 50-100 mol%, It is more preferable that it is 60-95 mol%, It is further more preferable that it is 70-90 mol%. In the present invention, the degree of saponification of the polyvinyl alcohol resin means the proportion (mol%) of the ester unit derived from the fatty acid vinyl ester contained in the polyvinyl alcohol resin in which the ester bond is hydrolyzed. In the present invention, the saponification degree can be measured by completely saponifying the polyvinyl alcohol resin with an alkaline substance such as sodium hydroxide and measuring the amount of the obtained fatty acid salt (for example, acetate). (Complete saponification can be confirmed by infrared absorption analysis.)
The polyvinyl alcohol resin may be a commercially available product.

The said polyvinyl alcohol resin (a1) can be made into the resin solution substituted by solid or arbitrary solvent by carrying out solvent removal and / or solvent substitution after completion | finish of a synthesis | combination. As the substitution solvent, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, propylene glycol monomethyl ether, methanol, water and the like are preferable.
As a method for removing the solvent, it may be carried out by heating at normal pressure or may be removed under reduced pressure. As a solvent replacement method, the replacement solvent may be added at any stage before, during or after the solvent removal.

Aromatic ring-containing acrylic resin (a2)
The aromatic ring-containing acrylic resin (a2) that can be used in the present invention is a resin other than the polyvinyl alcohol resin (a1), and contains an aromatic ring-containing monomer in the raw material monomer of the acrylic resin. Features. The aromatic ring-containing monomer is preferably a compound containing an aromatic group and a polymerizable unsaturated group in the structure. Specifically, phenyl acrylate, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, Examples include monomers having monocyclic aromatic hydrocarbons such as phenoxydiethylene glycol (meth) acrylate, ethylene oxide-modified nonylphenol (meth) acrylate, styrene, vinyltoluene, and α-methylstyrene, and these may be used alone or in combination of two. The above can be used in combination. In particular, it is preferable to use styrene.

  The content of the aromatic ring-containing monomer contained in the raw material monomer of the aromatic ring-containing acrylic resin (a2) is preferably 5 to 50% by mass of the aromatic ring-containing monomer based on the total solid content of the raw material monomer. 7 to 45% by mass is more preferable.

The aromatic ring-containing acrylic resin (a2) that can be used in the present invention can be obtained by copolymerizing the compound containing the aromatic group and polymerizable unsaturation with another polymerizable unsaturated monomer. Therefore, in the present invention, the aromatic ring-containing acrylic resin (a2) can be rephrased as a polymer or copolymer of raw material monomers containing an aromatic ring-containing monomer. As the other polymerizable unsaturated monomer, it can be used without particular limitation as long as it is a polymerizable unsaturated monomer usually used in the synthesis of an acrylic resin. For example, (meth) acrylic acid, methyl (meth) acrylate, Alkyl (meth) acrylates having 3 or less carbon atoms such as ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t- Butyl (meth) acrylate, n-hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) Acrylate, isostearyl Alkyl or cycloalkyl (meth) such as (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tricyclodecanyl (meth) acrylate Polymerizable unsaturated compounds having an isobornyl group such as isobornyl (meth) acrylate; Polymerizable unsaturated compounds having an adamantyl group such as adamantyl (meth) acrylate; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl ( Monoe of (meth) acrylic acid such as (meth) acrylate, 3-hydroxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate and a dihydric alcohol having 2 to 8 carbon atoms. Telluride, ε-caprolactone modified product of monoesterified product of (meth) acrylic acid and dihydric alcohol having 2 to 8 carbon atoms, N-hydroxymethyl (meth) acrylamide, allyl alcohol, molecular terminal is hydroxyl group Hydroxyl-containing polymerizable unsaturated monomers such as (meth) acrylate having a polyoxyalkylene chain; polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate, etc. A polyalkylene glycol macromonomer; carboxyl group-containing polymerizable unsaturated monomers such as (meth) acrylic acid, crotonic acid, β-carboxyethyl acrylate; (meth) acrylonitrile, (meth) acrylic N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, N-isopropylacrylamide, acryloylmorpholine, glycidyl (meth) acrylate -Containing polymerizable unsaturated monomers not containing urethane bonds such as adducts of amines and amines; reaction products of isocyanate group-containing polymerizable unsaturated monomers and hydroxyl group-containing compounds or hydroxyl group-containing polymerizable unsaturated monomers and isocyanate groups Polymerizable unsaturated monomer having a urethane bond such as a reaction product with a containing compound; glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4- Epoxy cyclo Epoxy group-containing polymerizable unsaturated monomers such as xylethyl (meth) acrylate, 3,4-epoxycyclohexylpropyl (meth) acrylate, and allyl glycidyl ether; (meth) acrylate having a polyoxyethylene chain whose molecular terminal is an alkoxy group; 2-acrylamido-2-methylpropane sulfonic acid, 2-sulfoethyl (meth) acrylate, allyl sulfonic acid, 4-styrene sulfonic acid, etc., polymerizable unsaturated groups having sulfonic acid groups such as sodium salt and ammonium salt of these sulfonic acids Monomer; 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate, 2-methacryloyloxypropyl acid phosphate Polymerizable unsaturated monomers having a phosphoric acid group such as vinyl trimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) Polymerizable unsaturated monomers having an alkoxysilyl group such as acryloyloxypropyltriethoxysilane; perfluoroalkyl (meth) acrylates such as perfluorobutylethyl (meth) acrylate and perfluorooctylethyl (meth) acrylate; fluoroolefins and the like Polymerizable unsaturated monomer having a fluorinated alkyl group; Polymerizable unsaturated monomer having a photopolymerizable functional group such as a maleimide group; (meth) acrylate having a polyoxyethylene chain whose molecular terminal is an alkoxy group; Acrylate, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1 , 4-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol di (Meth) acrylate, 1,1,1-trishydroxymethylethane di (meth) acrylate, 1,1,1-trishydroxymethylethane tri (meth) acrylate, 1,1,1-trishi Examples thereof include polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule such as droxymethylpropane tri (meth) acrylate, triallyl isocyanurate, diallyl terephthalate and divinylbenzene. These can be used alone or in combination of two or more.
Especially, it is preferable to contain a polyalkylene glycol macromonomer.
The polyalkylene glycol macromonomer is a nonionic polymerizable unsaturated monomer represented by the following formula (1), and polyethylene glycol (meth) acrylate and polypropylene glycol (meth) acrylate are particularly preferable.
^{_{CH 2 = C (R 1)}} COO (C n H 2n O) m -R 2 ··· Equation (1)
[Wherein, R ¹ represents a hydrogen atom or a methyl group, R ² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m is an integer of 4 to 60, particularly 4 to 55, and n is 2 Is an integer of ˜3, where the m oxyalkylene units (C _n H _2n O) may be the same or different from each other. ].

  A conventionally known method can be used as the method for polymerizing the acrylic resin. For example, it can be produced by solution polymerization of a polymerizable unsaturated monomer in an organic solvent, but is not limited thereto, and for example, bulk polymerization, emulsion polymerization, suspension polymerization, or the like may be used. When performing solution polymerization, it may be continuous polymerization or batch polymerization, and the polymerizable unsaturated monomer may be charged all at once, may be charged separately, or may be added continuously or intermittently. Good.

  As a radical polymerization initiator used for polymerization, a conventionally known method can be used. For example, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis ( tert-butylperoxy) cyclohexane, n-butyl-4,4-bis (tert-butylperoxy) valerate, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 1,3 -Bis (tert-butylperoxy-m-isopropyl) benzene, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, diisopropylbenzene peroxide, tert-butylcumyl peroxide, decanoylper Oxide, Lauroyl peroxide, Ben Ile peroxide, 2,4-dichlorobenzoyl peroxide, di-tert-amyl peroxide, bis (tert-butylcyclohexyl) peroxydicarbonate, tert-butyl peroxybenzoate, 2,5-dimethyl-2,5- Peroxide-based polymerization initiators such as di (benzoylperoxy) hexane and tert-butylperoxy-2-ethylhexanoate; 2,2′-azobis (isobutyronitrile), 1,1-azobis (cyclohexane -1-carbonitrile), azocumene, 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobisdimethylvaleronitrile, 4,4'-azobis (4-cyanovaleric acid), 2 -(T-butylazo) -2-cyanopropane, 2,2'-azobis (2,4,4-trimethylpentane), 2,2'- Zobisu (2-methylpropane), dimethyl 2,2'-azobis (2-methylpropionate) may be mentioned azo-based polymerization initiators such as. These can be used alone or in combination of two or more.

  There is no restriction | limiting in particular as a solvent used for said superposition | polymerization or dilution, Water, an organic solvent, or its mixture etc. can be mentioned. Examples of the organic solvent include hydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane and cyclobutane; aromatic solvents such as toluene and xylene; methyl isobutyl ketone and the like Ketone solvents; ether solvents such as n-butyl ether, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol; ethyl acetate, n-butyl acetate, isobutyl acetate, Ester solvents such as ethylene glycol monomethyl ether acetate and butyl carbitol acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone; Alcohol solvents such as butanol, isopropanol, n-butanol, sec-butanol, isobutanol, etc .; Examide (trade name, manufactured by Idemitsu Kosan Co., Ltd.), N, N-dimethylformamide, N, N-dimethylacetamide, N- Conventionally known solvents such as amide solvents such as methylformamide, N-methylacetamide, N-methylpropioamide and N-methyl-2-pyrrolidone can be exemplified. These can be used alone or in combination of two or more.

  In solution polymerization in an organic solvent, a method in which a polymerization initiator, a polymerizable unsaturated monomer component, and an organic solvent are mixed and heated while stirring, and the organic solvent is used as a reaction tank in order to suppress the temperature rise of the system due to reaction heat. The polymerizable unsaturated monomer component and the polymerization initiator are mixed and dropped or separated over a predetermined time while blowing an inert gas such as nitrogen or argon as necessary while stirring at a temperature of 60 ° C. to 200 ° C. A dripping method or the like is used.

  The polymerization can be generally performed for about 1 to 10 hours. You may provide the additional catalyst process which heats a reaction tank, dripping a polymerization initiator as needed after superposition | polymerization of each step.

  The pigment-dispersed resin of the present invention obtained as described above preferably has a weight average molecular weight of 1,000 to 10,000, more preferably 3,000 to 50,000.

  In the present specification, the number average molecular weight and the weight average molecular weight are the retention time (retention capacity) measured using a gel permeation chromatograph (GPC) and the retention time of a standard polystyrene having a known molecular weight measured under the same conditions. (Retention capacity) is a value obtained by converting to the molecular weight of polystyrene. Specifically, “HLC8120GPC” (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph, and “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, “TSKgel G-2500HXL” are used as columns. ”And“ TSKgel G-2000HXL ”(trade names, all manufactured by Tosoh Corporation), and can be measured under the conditions of mobile phase tetrahydrofuran, measurement temperature 40 ° C., flow rate 1 mL / min, and detector RI. it can.

The aromatic ring-containing acrylic resin (a2) can be made into a resin solution substituted with a solid or an arbitrary solvent by removing the solvent and / or replacing the solvent after completion of the synthesis. As the substitution solvent, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, propylene glycol monomethyl ether, methanol, water and the like are preferable.
As a method for removing the solvent, it may be carried out by heating at normal pressure or may be removed under reduced pressure. As a solvent replacement method, the replacement solvent may be added at any stage before, during or after the solvent removal.

  Although the solid content of the polyvinyl alcohol resin (a1) in the dispersant (A) is not particularly limited, for example, it is appropriately set in the range of 20 to 99.9% by mass, preferably 50 to 99.5% by mass. Can do. The solid content of the aromatic ring-containing acrylic resin (a1) in the resin solid content of the dispersant (A) is not particularly limited. Can be set as appropriate. The compounding ratio of the polyvinyl alcohol resin (a1) and the aromatic ring-containing acrylic resin (a2) is in the range of 99.9 / 0.1 to 80.0 / 20.0 in terms of the resin solid content ratio.

Resins other than polyvinyl alcohol resin (a1) and aromatic ring-containing acrylic resin (a2) As resins other than polyvinyl alcohol resin (a1) and aromatic ring-containing acrylic resin (a2), for example, polyvinyl alcohol resin (a1) and aromatic ring Acrylic resins other than the containing acrylic resin (a2), polyester resins, epoxy resins, polyether resins, alkyd resins, urethane resins, silicone resins, polycarbonate resins, silicate resins, chlorine resins, fluorine resins, polyvinyl pyrrolidone resins, polyvinyl alcohol Examples thereof include resins, polyvinyl acetal resins, and composite resins thereof. These resins can be used alone or in combination of two or more. Especially, it is preferable to use together and use at least 1 sort (s) of resin chosen from polyvinyl acetal resin, polyvinyl pyrrolidone resin, polyvinyl alcohol resin, and fluororesin, and it is more preferable to use polyvinylidene fluoride (PVDF) together. These resins can be blended in the conductive paste as a pigment dispersion resin or as an additive resin after pigment dispersion.

Conductive carbon (B)
Examples of the conductive carbon (B) include acetylene black, furnace black, thermal black, channel black, ketjen black, vulcan, carbon nanotube, graphene, vapor grown carbon fiber (VGCF), and graphite. Preferably, acetylene black, graphite, etc. are mentioned, More preferably, acetylene black etc. are mentioned. In a preferred embodiment of the present invention, the conductive carbon (B) may contain both acetylene black and graphite. These conductive carbons can be used alone or in combination of two or more.

Solvent (C)
As a solvent (C), the solvent used for superposition | polymerization or dilution of the aromatic ring containing acrylic resin (a2) mentioned above can be used suitably, for example. Specific examples of the preferred solvent (C) include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, propylene glycol monomethyl ether, methanol, water and the like, preferably N-methyl-2-pyrrolidone and the like Is mentioned. These solvent can be used individually by 1 type or in mixture of 2 or more types.

Other Additives Components other than the above components (A), (B) and (C) (sometimes referred to as other additives) may be blended in the conductive paste for the lithium ion battery positive electrode. Examples of other additives include neutralizers, pigment dispersants, antifoaming agents, antiseptics, rust inhibitors, plasticizers, and binders (binders).

  Examples of the pigment dispersant and / or binder include acrylic resins other than the dispersant (A), polyester resins, epoxy resins, polyether resins, alkyd resins, urethane resins, silicone resins, polycarbonate resins, silicate resins, Examples include chlorine-based resins, fluorine-based resins, polyvinyl pyrrolidone resins, polyvinyl alcohol resins, polyvinyl acetal resins, and composite resins thereof. These resins can be used alone or in combination of two or more. Among these, it is preferable to use polyvinylidene fluoride (PVDF).

Production Method of Conductive Paste for Lithium Ion Battery Positive Electrode of the Present Invention The solid content of the dispersant (A) in the solid content of the conductive paste for lithium ion battery positive electrode of the present invention is usually 30% by mass or less, preferably 20% by mass or less. It is preferable from the viewpoints of viscosity at the time of pigment dispersion, pigment dispersibility, dispersion stability, production efficiency, and the like. Moreover, in preferable embodiment of this invention, content of the dispersing agent (A) in the electrically conductive paste solid content for lithium ion battery positive electrodes of this invention is 20 mass% or less normally from a conductive viewpoint of a coating film. The content is preferably 0.1 to 15% by mass, more preferably 1.0 to 10% by mass.

  The solid content of the conductive carbon (B) in the solid content of the conductive paste for a lithium ion battery positive electrode of the present invention is usually 50% by mass or more and less than 100% by mass, preferably 60% by mass or more and 100% by mass. Less than, more preferably 70% by mass or more and less than 100% by mass is suitable from the viewpoint of battery performance. The content of the solvent (C) in the conductive paste for a lithium ion battery positive electrode of the present invention is usually 50% by mass or more and less than 100% by mass, preferably 70% by mass or more and less than 100% by mass. Preferably 80 mass% or more and less than 100 mass% are suitable from the point of drying efficiency and paste viscosity.

  The conductive paste for a lithium ion battery positive electrode of the present invention comprises the components described above, for example, paint shaker, sand mill, ball mill, pebble mill, LMZ mill, DCP pearl mill, planetary ball mill, homogenizer, biaxial kneader, thin film swirl type It can prepare by mixing and disperse | distributing uniformly using conventionally well-known dispersers, such as a high-speed mixer.

  As will be described later, the conductive paste for a lithium ion battery positive electrode of the present invention can be mixed with an electrode active material and used to produce a lithium ion battery positive electrode mixture paste.

Lithium-ion battery positive electrode composite paste The present invention provides a lithium-ion battery positive electrode composite paste obtained by further blending an electrode active material with the conductive paste.

As an electrode active material , for example, lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium cobaltate (LiCoO ₂ ), LiNi _1/3 Co _1/3 Mn _1/3 O _And lithium composite oxide such as ₂ . These electrode active materials can be used individually by 1 type or in mixture of 2 or more types. The solid content of the electrode active material in the solid paste solid content of the lithium ion battery positive electrode of the present invention is usually 70% by mass or more and less than 100% by mass, preferably 80% by mass or more and less than 100% by mass. It is preferable in terms of battery capacity, battery resistance, and the like.

Method for Producing Lithium Ion Battery Positive Electrode Paste The lithium ion battery positive electrode composite paste of the present invention is prepared by first preparing the above-described lithium ion battery positive electrode conductive paste, and applying the lithium ion battery positive electrode conductive paste to the conductive paste. It can be obtained by blending an active material. Moreover, the composite paste for a lithium ion battery positive electrode of the present invention may be prepared by mixing the component (A), the component (B), the component (C) and the electrode active material.

  The solid content of the dispersant (A) in the solid paste solid content for the lithium ion battery positive electrode of the present invention is usually 0.001 to 20% by mass, preferably 0.005 to 10% by mass, It is suitable from the aspects of battery performance and paste viscosity.

  The solid content of the conductive carbon (B) in the solid paste for lithium ion battery positive electrode of the present invention is usually 0.01 to 30% by mass, preferably 0.05 to 20% by mass, more preferably. 0.1-15 mass% is suitable from the point of battery performance. Moreover, content of the solvent (C) in the composite paste for lithium ion battery positive electrodes of this invention is 0.1-60 mass% normally, Preferably it is 0.5-50 mass%, More preferably, it is 1-45. Mass% is preferable from the viewpoint of electrode drying efficiency and paste viscosity.

As described above, the positive electrode mixture layer of the lithium ion secondary battery can be manufactured by applying the lithium ion battery positive electrode mixture paste to the surface of the positive electrode core material and drying it. Moreover, as a use of the paste of this invention, it can be used also as a primer layer between a positive electrode core material and a synthetic layer besides using it as a paste of a compound material layer.
The method of applying the lithium ion battery positive electrode composite paste can be performed by a method known per se using a die coater or the like. The coating amount of the lithium ion battery positive electrode mixture paste is not particularly limited. For example, the thickness of the positive electrode mixture layer after drying is in the range of 0.04 to 0.30 mm, preferably 0.06 to 0.24 mm. Can be set as follows. As temperature of a drying process, it can set suitably in 80-200 degreeC, for example, Preferably in the range of 100-180 degreeC. As time of a drying process, it can set suitably within the range of 5 to 120 second, for example, Preferably it is 5 to 60 second.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these specific embodiments.

  Hereinafter, the present invention will be described in more detail with reference to Production Examples, Examples, and Comparative Examples, but the present invention is not limited thereto. In each example, “parts” indicates mass parts, and “%” indicates mass%.

Production and Production Example 1 of Acrylic Resin Production of Aromatic Ring-Containing Acrylic Resin 250 parts of propylene glycol monomethyl ether was charged into a reaction vessel equipped with a stirring and heating device and a cooling tube, and maintained at 110 ° C. after nitrogen substitution. In this, the following monomer mixture and MPEG2000 (trade name, manufactured by Nippon Oil & Fats Co., Ltd., polyoxyethylene glycol monomethyl ether, number average molecular weight of about 2000, active ingredient 50%, separated and dropped because it does not dissolve with other monomers) 200 Was added dropwise over 3 hours.
<Monomer mixture>
Styrene 200 parts methyl methacrylate 200 parts n-butyl methacrylate 300 parts 2-ethylhexyl acrylate 100 parts 2-hydroxyethyl methacrylate 100 parts 2,2′-azobis (2-methylbutyronitrile) 40 parts 1 hour after the end of dropping A solution prepared by dissolving 5 parts of 2,2′-azobis (2-methylbutyronitrile) in 100 parts of propylene glycol monomethyl ether was added dropwise over 1 hour. After completion of dropping, this was further maintained at 110 ° C. for 1 hour, and then adjusted with methyl isobutyl ketone to obtain an acrylic resin AK-1 solution having a solid content of 70%. The acrylic resin AK-1 had a weight average molecular weight of 11,000.

Production Example 2 Production of Aromatic Ring-Containing Acrylic Resin 250 parts of propylene glycol monomethyl ether was charged into a reaction vessel equipped with a stirring and heating device and a cooling tube, and kept at 110 ° C. after nitrogen substitution. In this, the following monomer mixture and MPEG2000 (trade name, manufactured by Nippon Oil & Fats Co., Ltd., polyoxyethylene glycol monomethyl ether, number average molecular weight of about 2000, active ingredient 50%, separated and dropped because it does not dissolve with other monomers) 200 Was added dropwise over 3 hours.
<Monomer mixture>
Styrene 100 parts methyl methacrylate 300 parts n-butyl methacrylate 300 parts 2-ethylhexyl acrylate 100 parts 2-hydroxyethyl methacrylate 100 parts 2,2′-azobis (2-methylbutyronitrile) 40 parts 1 hour after the end of dropping A solution prepared by dissolving 5 parts of 2,2′-azobis (2-methylbutyronitrile) in 100 parts of propylene glycol monomethyl ether was added dropwise over 1 hour. After completion of dropping, this was further maintained at 110 ° C. for 1 hour, and then adjusted with methyl isobutyl ketone to obtain an acrylic resin AK-2 solution having a solid content of 70%. The acrylic resin AK-2 had a weight average molecular weight of 10,000.

Production Example 3 Production of Aromatic Ring-Containing Acrylic Resin 250 parts of propylene glycol monomethyl ether was charged into a reaction vessel equipped with a stirring and heating device and a cooling tube, and maintained at 110 ° C. after nitrogen substitution. In this, the following monomer mixture and MPEG2000 (trade name, manufactured by Nippon Oil & Fats Co., Ltd., polyoxyethylene glycol monomethyl ether, number average molecular weight of about 2000, active ingredient 50%, separated and dropped because it does not dissolve with other monomers) 200 Was added dropwise over 3 hours.
<Monomer mixture>
Styrene 30 parts Methyl methacrylate 370 parts n-Butyl methacrylate 300 parts 2-Ethylhexyl acrylate 100 parts 2-Hydroxyethyl methacrylate 100 parts 2,2'-azobis (2-methylbutyronitrile) 40 parts 1 hour after the end of dropping A solution prepared by dissolving 5 parts of 2,2′-azobis (2-methylbutyronitrile) in 100 parts of propylene glycol monomethyl ether was added dropwise over 1 hour. After completion of the dropwise addition, this was further maintained at 110 ° C. for 1 hour and then adjusted with methyl isobutyl ketone to obtain an acrylic resin AK-3 solution having a solid content of 70%. The acrylic resin AK-3 had a weight average molecular weight of 9,500.

Production Example 4 Production of Acrylic Resin 250 parts of propylene glycol monomethyl ether was charged into a reaction vessel equipped with a stirring and heating device and a cooling pipe, and kept at 110 ° C. after nitrogen substitution. In this, the following monomer mixture and MPEG2000 (trade name, manufactured by Nippon Oil & Fats Co., Ltd., polyoxyethylene glycol monomethyl ether, number average molecular weight of about 2000, active ingredient 50%, separated and dropped because it does not dissolve with other monomers) 200 Was added dropwise over 3 hours.
<Monomer mixture>
Methyl methacrylate 400 parts n-butyl methacrylate 300 parts 2-ethylhexyl acrylate 100 parts 2-hydroxyethyl methacrylate 100 parts 2,2′-azobis (2-methylbutyronitrile) 40 parts A solution prepared by dissolving 5 parts of 2,2′-azobis (2-methylbutyronitrile) in 100 parts of propylene glycol monomethyl ether was added dropwise over 1 hour. After completion of the dropwise addition, this was further maintained at 110 ° C. for 1 hour and then adjusted with methyl isobutyl ketone to obtain an acrylic resin AK-4 solution having a solid content of 70%. The acrylic resin AK-4 had a weight average molecular weight of 9,500.

Production Example 1 of Conductive Paste
28.5 parts of PVA-1 (Note 1), 3 parts of acrylic resin AK-1 obtained in Production Example 1 (1.5 parts of solid content), 1200 parts of acetylene black, KF polymer W # 7300 (trade name, polyfluoride) 220 parts of vinylidene chloride (manufactured by Kureha) and 8500 parts of N-methyl-2-pyrrolidone were mixed and dispersed in a ball mill for 5 hours to obtain a conductive paste X-1.

Examples 2-8, Comparative Examples 1-6
Conductive pastes X-2 to X-14 were produced in the same manner as in Example 1 except that the conductive paste composition was changed to Table 1 below. In addition, the compounding quantity in a table | surface is a value of solid content.

(Note 1) PVA-1: polyvinyl alcohol resin, saponification degree 100 mol%, average polymerization degree about 500. Repeating unit _{- (CH 2 -CH (OH)} ) - ratio of about 100% by weight.
(Note 2) PVA-2: polyvinyl alcohol resin, saponification degree 80 mol%, average polymerization degree about 500. Repeating unit _{- (CH 2 -CH (OH)} ) - ratio of about 67 weight percent.
(Note 3) PVA-3: polyvinyl alcohol resin, saponification degree 50 mol%, average polymerization degree about 100. Repeating unit _{- (CH 2 -CH (OH)} ) - ratio of about 33 weight percent.
(Note 4) PVA-4: polyvinyl alcohol resin, saponification degree 35 mol%, average polymerization degree about 1500. Repeating unit _{- (CH 2 -CH (OH)} ) - ratio of about 22 weight percent.

Production Example 9 of Compound Paste
8 parts of the conductive paste X-1 obtained in Example 1, active material particles (lithium nickel manganese oxide particles having a spinel structure represented by the composition formula LiNi _0.5 Mn _1.5 O _4. Average particle diameter 6 μm, 90 parts of a BET specific surface area of 0.7 m ² / g) and 57 parts of N-methyl-2-pyrrolidone were mixed to produce a composite paste Y-1.

Examples 10-16, Comparative Examples 7-12
Compound pastes Y-2 to Y-14 were produced in the same manner as in Example 9 except that the conductive paste was of the type shown in Table 2 below.

  Table 2 below shows the results of evaluation tests described later [viscosity of conductive paste, battery performance (IV resistance increase rate)]. If at least one of the two evaluation tests results in a failure, the conductive paste and the composite paste are rejected.

Evaluation test <viscosity>
Using the cone and plate type viscometer “Mars2” (trade name, manufactured by HAAKE), the viscosity of the conductive paste obtained in Examples and Comparative Examples was measured at a shear rate of 1.0 sec ⁻¹ and evaluated according to the following criteria. . As evaluation, A, B, and C are acceptable, and D is unacceptable.
A: The viscosity is less than 5 Pa · s.
B: The viscosity is 5 Pa · s or more and less than 30 Pa · s.
C: The viscosity is 30 Pa · s or more and less than 100 Pa · s.
D: The viscosity is 100 Pa · s or more.

<Battery performance (IV resistance increase rate)>
Battery performance (IV resistance increase rate) was evaluated using the composite pastes Y-1 to 14 obtained in Examples 9 to 16 and Comparative Examples 7 to 12. The evaluation method was performed according to the following procedure.
(1) A conductive paste and a composite paste to be a blank are manufactured by the method shown in [Manufacture of a conductive paste to be a blank and a composite paste] below, and [Preparation of a positive electrode], [Preparation of a negative electrode] and [ A lithium ion secondary battery in which a positive electrode and a negative electrode were installed was constructed by the method shown in [Construction of Lithium Ion Secondary Battery]. Next, using the obtained lithium ion secondary battery, IV resistance was measured according to [Method of measuring IV resistance] described later.
(2) Lithium ions in which a positive electrode and a negative electrode were installed in the same manner as in (1) above, except that the composite pastes Y-1 to Y-14 obtained in Examples and Comparative Examples were used instead of the blank composite paste. A secondary battery was constructed and the IV resistance was measured. Subsequently, the IV resistance increase rate (%) relative to the blank was calculated and evaluated.
In addition, since there are three kinds of conductive carbon (acetylene black alone, acetylene black and graphite combined use, graphite alone), each was compared with a blank of the same kind of pigment. (The evaluation of the composite paste Y-7 is a blank of 600 parts of acetylene black and 600 parts of graphite, the evaluation of the composite paste Y-8 is a blank of 1200 parts of graphite, and the other composite paste is a blank of 1200 parts of acetylene black)
The battery performance (IV resistance increase rate) was evaluated according to the following criteria. A and B are acceptable and C is unacceptable.
A: The IV resistance increase rate is less than + 5% compared to the blank.
B: The IV resistance increase rate is + 5% or more and less than + 8% as compared with the blank.
C: IV resistance increase rate is + 8% or more compared to blank.

[Manufacture of conductive paste and composite paste used as blank]
1200 parts of acetylene black, 220 parts of KF polymer W # 7300 (trade name, polyvinylidene fluoride, manufactured by Kureha) and 8500 parts of N-methyl-2-pyrrolidone were mixed and dispersed in a ball mill for 5 hours, without a dispersant. An additive conductive paste was obtained.

8 parts of the conductive paste, active material particles (lithium nickel manganese oxide particles having a spinel structure represented by the composition formula LiNi _0.5 Mn _1.5 O _4. Average particle diameter 6 μm, BET specific surface area 0.7 m ² / g ) 90 parts and 57 parts of N-methyl-2-pyrrolidone were mixed to produce a mixture paste without addition of a dispersant, which was used as a blank. Further, instead of 1200 parts of acetylene black, a blank of 600 parts of acetylene black and 600 parts of graphite and 1200 parts of graphite was also produced. (Manufacturing three types of blanks: acetylene black alone, acetylene black and graphite combined, and graphite alone)
[Preparation of positive electrode]
The composite paste is formed into a belt shape by a roller coating method so that the basis weight per side is 10 mg / cm ² (solid content basis) on both sides of a long aluminum foil (positive electrode current collector) having an average thickness of about 15 μm. The positive electrode active material layer was formed by applying and drying (drying temperature 80 ° C., 1 minute). The positive electrode active material layer supported on the positive electrode current collector was rolled with a roll press to adjust the properties.

[Preparation of negative electrode]
Natural graphite powder (C, average particle size: 5 μm, specific surface area: 3 m ² / g) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener The negative electrode active material layer forming slurry is mixed with ion-exchanged water so that the mass ratio of these materials is C: SBR: CMC = 98: 1: 1 and the solid content concentration is about 45 mass%. Prepared. This slurry was applied in a belt-like manner on both sides of a long copper foil (negative electrode current collector) having an average thickness of about 10 μm by a roller coating method so that the basis weight per side is 7 mg / cm ² (solid content basis). Then, the negative electrode active material layer was formed by drying (drying temperature 120 ° C., 1 minute). This was rolled by a roll press to adjust the properties.

[Construction of lithium ion secondary battery]
The positive electrode sheet and the negative electrode sheet produced above were used as separator sheets (here, a three-layer structure in which polypropylene (PP) was laminated on both sides of polyethylene (PE) and having a thickness of 20 μm). The wound electrode body was produced by placing the electrodes facing each other and winding them in an elliptical shape. The produced electrode body is placed in a cylindrical battery case, and a non-aqueous electrolyte (here, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) is EC: DMC: EMC). = LiPF ₆ as a supporting salt was dissolved at a concentration of 1.0 mol / L in a mixed solvent containing a volume ratio of 3: 4: 3. And after welding a positive electrode terminal and a negative electrode terminal to the positive electrode collector and negative electrode collector which were exposed in the edge part of an electrode body, the battery case was sealed and the 18650 type lithium ion secondary battery was constructed.

[Method for measuring IV resistance]
The IV resistance of the cell for evaluation in an SOC of 60% state (SOC) was measured under an environment of −30 ° C. Here, the IV resistance is a constant current discharge at a predetermined current value (I) for 10 seconds, and the voltage (V) after the discharge is measured. Then, based on the predetermined current value (I) and the voltage (V) after the discharge, I plotted on the X axis and V on the Y axis, and based on the plot obtained by each discharge, An approximate straight line is drawn and the slope is taken as IV resistance. Here, the IV resistance (mΩ) was calculated based on the voltage (V) after each discharge obtained by performing constant current discharge at current values of 0.3C, 1C, and 3C.

Claims (6)

A conductive paste containing a dispersant (A), a conductive carbon (B), and a solvent (C),
The dispersant (A) includes a polyvinyl alcohol resin (a1) and an aromatic ring-containing acrylic resin (a2),
The polyvinyl alcohol resin (a1) has a repeating unit represented by the following formula at a ratio of 30 to 100% by mass in the polymer chain,

The compounding ratio of the polyvinyl alcohol resin (a1) and the aromatic ring-containing acrylic resin (a2) is in the range of 99.9 / 0.1 to 80.0 / 20.0 in terms of resin solid content, for a lithium ion battery positive electrode Conductive paste.   The conductive paste for a lithium ion battery positive electrode according to claim 1, wherein the conductive carbon (B) contains acetylene black. The aromatic ring-containing acrylic resin (a2) is a copolymer of raw material monomers containing 5 to 50% by mass of aromatic ring-containing monomers based on the total solid content of the raw material monomers. The conductive paste for a lithium ion battery positive electrode according to 1. Conductive carbon (B) contains graphite further, The electrically conductive paste for lithium ion battery positive electrodes of any one of Claims 1-3 characterized by the above-mentioned. 5. The conductive paste for a lithium ion battery positive electrode according to claim 1, wherein the solvent (C) contains N-methyl-2-pyrrolidone. A mixture paste for a lithium ion battery positive electrode, which is obtained by further blending an electrode active material with the conductive paste according to any one of claims 1 to 5.