JP6297121B2 - Conductive paste for lithium ion battery positive electrode and composite paste for lithium ion battery positive electrode - Google Patents

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 found that the dispersant (A) obtained by copolymerizing a monomer mixture containing a certain amount of the monomer (A-1) having a polycyclic aromatic hydrocarbon and the specific It has been found that the above problem can be solved by using a dispersant (B) containing a polyvinyl alcohol resin (b1) having the structure: 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 dispersant (B), a conductive carbon (C), and a solvent (D),
The dispersant (A) is a copolymer of a monomer mixture containing 1 to 70% by mass of the monomer (A-1) having a polycyclic aromatic hydrocarbon based on the total amount of solids,
The dispersant (B) contains a polyvinyl alcohol resin (b1)),
The polyvinyl alcohol resin (b1) has a repeating unit represented by the following formula at a ratio of 30 to 100% by mass in the polymer chain.

Conductive paste for lithium ion battery positive electrode.

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

  Item 3. Item 3. The lithium ion battery according to Item 1 or 2, wherein the monomer (A-1) having a polycyclic aromatic hydrocarbon is a polymerizable unsaturated monomer having a naphthyl group or a derivative (A-2) thereof. Conductive paste for positive electrode.

  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 (C) 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 (D) 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 dispersant (B), a conductive carbon (C), and a solvent (D),
The dispersant (A) is obtained by copolymerizing a monomer mixture containing 1 to 70% by mass of the monomer (A-1) having a polycyclic aromatic hydrocarbon based on the total amount of solids,
The dispersant (B) contains a polyvinyl alcohol resin (b1)),
The polyvinyl alcohol resin (b1) has a repeating unit represented by the following formula at a ratio of 30 to 100% by mass in the polymer chain.

Method.

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

  Item 9. Item 9. The method according to Item 7 or 8, wherein the monomer (A-1) having a polycyclic aromatic hydrocarbon is a polymerizable unsaturated monomer having a naphthyl group or a derivative (A-2) thereof.

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

  Item 11. Item 11. The method according to any one of Items 7 to 10, wherein the solvent (D) 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.

  Item 13. Item 7. A lithium ion battery positive electrode obtained using the lithium ion battery positive electrode composite paste according to Item 6.

  Item 14. Item 14. A lithium ion battery having the electrode for a lithium ion battery positive electrode according to item 13.

  The dispersant (A) and the dispersant (B) blended in the conductive paste for a lithium ion battery positive electrode and the composite paste for a lithium ion battery positive electrode of the present invention are conventionally used for 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 as compared with the pigment dispersion resin that has been used.

The present invention is a conductive paste containing a dispersant (A), a dispersant (B), a conductive carbon (C), and a solvent (D),
The dispersant (A) is 1 to 70% by mass, preferably 5 to 60% by mass, more preferably 10 to 50% by mass of the monomer (A-1) having a polycyclic aromatic hydrocarbon, based on the total amount of solids. It is obtained by copolymerizing a monomer mixture containing mass%,
The dispersant (B) contains a polyvinyl alcohol resin (b1)),
The polyvinyl alcohol resin (b1) has a repeating unit represented by the following formula in a proportion of 30 to 95% by mass in the polymer chain.

Provided is a conductive paste for a lithium ion battery positive electrode.

Dispersant (A)
The dispersant (A) contained in the conductive pace for the lithium ion battery positive electrode of the present invention is 1 to 70 masses of the monomer (A-1) having polycyclic aromatic hydrocarbons based on the total amount of the solid content of the monomer mixture. % Of the monomer mixture is contained by copolymerization. Therefore, in this invention, a dispersing agent (A) is a monomer mixture containing 1-70 mass% of monomer (A-1) which has a polycyclic aromatic hydrocarbon on the basis of the total amount of solid content of a monomer mixture. In other words, it can be called a copolymer.

  Examples of the dispersant (A) include acrylic resins, polyester resins, epoxy resins, polyether resins, alkyd resins, urethane resins, silicone resins, polycarbonate resins, silicate resins, chlorine resins, fluorine resins, and These composite resins and the like can be mentioned, and acrylic resins are particularly preferable.

  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. In this specification, a “derivative” is obtained by changing a small part (or a plurality of parts) in a molecule by introducing a functional group, substituting an atom, or other chemical reaction with respect to a compound. Means a compound. For example, naphthalene has one or more functional groups such as an alkyl group, an alkoxy group, a hydroxyl group, a sulfonic acid group, a carboxyl group, an amino group, a nitro group, a halogen atom, an aryloxy group, an alkylthio group, and an arylthio group. The introduced compound is a naphthalene derivative.

Monomer having polycyclic aromatic hydrocarbon (A-1)
Examples of the polycyclic aromatic hydrocarbon of the monomer (A-1) having a polycyclic aromatic hydrocarbon that can be used in the pigment dispersion resin of the present invention include a naphthalene ring, an anthracene ring, a triphenylene ring, a tetraphen ring, Examples thereof include a hydrocarbon group having a tetracene ring, a chrysene ring, a pyrene ring, a pentacene ring, a hexacene ring, a heptacene ring, a coronene ring and a keklen ring, and derivatives thereof. In a preferred embodiment of the present invention, the monomer (A-1) having a polycyclic aromatic hydrocarbon is a polymerizable unsaturated monomer having a naphthalene ring among the above polycyclic aromatics, that is, a naphthyl group. Or the derivative (A-2) is mentioned. As a polymerizable unsaturated monomer which has a naphthyl group, or its derivative (A-2), for example, the polymerizable unsaturated monomer which has a naphthyl group represented by formula (2) mentioned later, or its derivative (A-1-2) Etc.

  The monomer (A-1) having a polycyclic aromatic hydrocarbon is a polymerizable unsaturated monomer (A-1-1) having a polycyclic aromatic hydrocarbon represented by the following formula (1). It is preferable.

(Wherein R represents a hydrogen atom or a methyl group, A represents a polycyclic aromatic hydrocarbon group, W may or may not be present. When W is present, W is a carbon atom, An organic group having 1 to 20 nitrogen atoms and / or oxygen atoms, and when W is not present, W is directly bonded to A.) “Polymerizable unsaturated monomer” is a polymer capable of radical polymerization. Means a monomer having a polymerizable unsaturated group, 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. .

  Specific examples of the polymerizable unsaturated monomer (A-1-1) having a polycyclic aromatic hydrocarbon include, for example, vinyl naphthalene, naphthyl (meth) acrylate, naphthylalkyl (meth) acrylate, vinylanthracene, Anthracenyl (meth) acrylate, anthracenyl alkyl (meth) acrylate, vinylpyrene, pyrenyl (meth) acrylate, pyrenylalkyl (meth) acrylate, vinyl chrysene, vinyl naphthacene, vinyl pentacene, and derivatives thereof may be mentioned. Also included are those obtained by reacting a polymerizable unsaturated group monomer having a reactive functional group such as a glycidyl group or an isocyanate group with a polycyclic aromatic hydrocarbon having a functional group that reacts with the reactive functional group. . Any combination of functional groups that react with each other can be suitably used, but a combination of a carboxyl group and a glycidyl group, an amino group and a glycidyl group, or a hydroxyl group and an isocyanate group is more preferable. Specifically, for example, glycidyl (meth) acrylate and 1-naphthyl acetic acid, 2- (meth) acryloyloxyethyl isocyanate and 1-naphthol, 2- (meth) acryloyloxyethyl isocyanate and 1- (2-naphthyl) ethanol The combination etc. are mentioned. These can be used alone or in combination of two or more.

  Among these, as the polymerizable unsaturated monomer (A-1-1) having a polycyclic aromatic hydrocarbon, a polymerizable unsaturated monomer having a naphthyl group represented by the following formula (2) or a derivative thereof (A-1 -2).

(In the formula, R represents a hydrogen atom or a methyl group, X and Y may be the same or different, and a hydrogen atom, alkyl group, alkoxy group, alkoxycarbonyloxy group, phosphoryloxy group, hydroxyl group, sulfone) An acid group, a carboxyl group, an amino group, a nitro group, a halogen atom, an aryloxy group, an alkylthio group or an arylthio group, and when W is present, W is the number of carbon atoms, nitrogen atoms and / or oxygen atoms. Is an organic group of 1 to 20 or a single bond.)
Examples of the polymerizable unsaturated monomer having a naphthyl group or a derivative (A-1-2) thereof include vinyl naphthalene, naphthyl (meth) acrylate, naphthylalkyl (meth) acrylate, and derivatives thereof. These can be used alone or in combination of two or more.

  Especially, it is preferable that naphthyl (meth) acrylate or its derivative (A-1-2) is naphthyl (meth) acrylate or its derivative (A-1-3) represented by following formula (3).

(In the formula, R represents a hydrogen atom or a methyl group, X and Y may be the same or different, and a hydrogen atom, alkyl group, alkoxy group, hydroxyl group, sulfonic acid group, carboxyl group, alkoxycarbonyloxy group) Group, phosphoryloxy group, amino group, nitro group, halogen atom, aryloxy group, alkylthio group or arylthio group.)
As said naphthyl (meth) acrylate or its derivative (A-1-3), 1-naphthyl (meth) acrylate, 2-naphthyl (meth) acrylate, these derivatives, etc. are mentioned, for example, These are 1 type. Can be used alone or in combination of two or more.

  Among these, naphthyl (meth) acrylate or a derivative thereof (A-1-3) is a 4-substituted-1-naphthyl (meth) acrylate (A-1-4) represented by the following formula (4). preferable.

(In the formula, R represents a hydrogen atom or a methyl group, and Z represents a hydroxyl group or an alkoxy group having 1 to 8 carbon atoms.)
When Z which is a substituent in the formula (4) is an alkoxy group, the number of carbon atoms of the alkoxy group is usually 1 to 8, preferably 1 to 4, more preferably 1 to 2, Particularly preferred is 1.

  Examples of the 4-substituted-1-naphthyl (meth) acrylate (A-1-4) include 4-methyl-1-naphthyl (meth) acrylate, 4-ethyl-1-naphthyl (meth) acrylate, 4- Methoxy-1-naphthyl (meth) acrylate, 4-ethoxy-1-naphthyl (meth) acrylate, 4-hydroxy-1-naphthyl (meth) acrylate, 2-methoxy-4-hydroxy-1-naphthyl (meth) acrylate, 2-ethoxy-4-hydroxy-1-naphthyl (meth) acrylate, 2-hydroxy-4-methoxy-1-naphthyl (meth) acrylate, 2-hydroxy-4-ethoxy-1-naphthyl (meth) acrylate, 4- Methoxycarbonyloxy-1-naphthyl (meth) acrylate, 4-phenoxycarbonyloxy 1-naphthyl (meth) acrylate, and 4-phosphoryloxy-1-naphthyl (meth) acrylate, or a derivative thereof and the like, which can be used in combination alone, or two or more kinds.

  The reason why the pigment dispersion resin having the polycyclic aromatic hydrocarbon of the present invention is effective in the dispersibility and stability of the pigment is not known in detail, but for example, the pigment has an aromatic ring. In this case, it is considered to be stabilized by the π-π interaction between the pigment and the pigment dispersion resin. The π-π interaction is a dispersion force acting between the aromatic rings and is also called a stacking interaction because it tends to be stabilized in an arrangement in which two aromatic rings are stacked with coins.

  Further, the reason why the substituent of the 4-substituted-1-naphthyl (meth) acrylate (A-1-4) is effective in the dispersibility and stability of the pigment is not known in detail. It is speculated that by having a substituent, the electrostatic potential of the aromatic ring is increased and the affinity with the pigment is increased.

Polymerizable unsaturated monomer other than polymerizable unsaturated monomer (A-1) having a polycyclic aromatic hydrocarbon The dispersant (A) of the present invention is a polymerizable unsaturated monomer having a polycyclic aromatic hydrocarbon (A -1) and a polymerizable unsaturated monomer other than (A-1) can be obtained by copolymerization. As the polymerizable unsaturated monomer other than the polymerizable unsaturated monomer (A-1) having a polycyclic aromatic hydrocarbon, any polymerizable unsaturated monomer usually used in the synthesis of an acrylic resin can be used without any particular limitation. For example, alkyl (meth) acrylates having 3 or less carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and 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 ( ) Acrylate, isostearyl (meth) acrylate, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tricyclodecanyl (meth) acrylate, etc. Alkyl or cycloalkyl (meth) acrylate; polymerizable unsaturated compound having an isobornyl group such as isobornyl (meth) acrylate; polymerizable unsaturated compound having an adamantyl group such as adamantyl (meth) acrylate; benzyl (meth) acrylate, styrene , Α-methylstyrene, vinyltoluene and other aromatic ring-containing polymerizable unsaturated monomers; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxy Monoesterified product of (meth) acrylic acid such as droxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate and a dihydric alcohol having 2 to 8 carbon atoms, the (meth) acrylic acid and 2 to 2 carbon atoms Hydroxyl-containing polymerization such as ε-caprolactone modified product of monoesterified with dihydric alcohol of No. 8, N-hydroxymethyl (meth) acrylamide, allyl alcohol, (meth) acrylate having a polyoxyalkylene chain having a molecular terminal hydroxyl group Unsaturated monomer; carboxyl group-containing polymerizable unsaturated monomer such as (meth) acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate; (meth) acrylonitrile, (meth) acrylamide, N, N-dimethylaminoethyl (Meth) acrylate, N, N-diethylaminoethyl Nitrogen-containing polymerizable unsaturated monomer containing no urethane bond such as ru (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, adduct of glycidyl (meth) acrylate and amines; isocyanate group-containing polymerizability Polymerizable unsaturated monomer having a urethane bond such as a reaction product of an unsaturated monomer and a hydroxyl group-containing compound or a reaction product of a hydroxyl group-containing polymerizable unsaturated monomer and an isocyanate group-containing compound; glycidyl (meth) acrylate, β- Epoxy groups such as methyl glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate, 3,4-epoxycyclohexylpropyl (meth) acrylate, and allyl glycidyl ether Including Polymerizable unsaturated monomer; (meth) acrylate having polyoxyethylene chain whose molecular terminal is an alkoxy group; 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth) acrylate, allylsulfonic acid, 4-styrene Polymerizable unsaturated monomers having a sulfonic acid group such as sodium salt and ammonium salt of these sulfonic acids; 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate, Polymerizable unsaturated monomers having a phosphate group such as 2-methacryloyloxypropyl acid phosphate; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) sila , Polymerizable unsaturated monomers having an alkoxysilyl group such as γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane; perfluorobutylethyl (meth) acrylate, perfluorooctyl Perfluoroalkyl (meth) acrylate such as ethyl (meth) acrylate; polymerizable unsaturated monomer having a fluorinated alkyl group such as fluoroolefin; polymerizable unsaturated monomer having a photopolymerizable functional group such as maleimide group; (Meth) acrylate having a polyoxyethylene chain in which is an alkoxy group; allyl (meth) 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-trishydroxymethylethanedi (meth) acrylate, 1,1,1 -Polymerizable unsaturated groups such as trishydroxymethylethane tri (meth) acrylate, 1,1,1-trishydroxymethylpropane tri (meth) acrylate, triallyl isocyanurate, diallyl terephthalate, divinylbenzene, etc. Such polymerizable unsaturated monomer having two or more in the molecule. These can be used alone or in combination of two or more.

  Especially, it is preferable to contain at least 1 sort (s) of styrene, and it is more preferable to contain 5-65 mass% of styrene on the basis of the total amount of a polymerizable unsaturated monomer component.

  Furthermore, from the viewpoint of forming a resin steric repulsion layer and ensuring the stability of the pigment dispersion paste, it preferably contains at least one polyalkylene glycol macromonomer, based on the total amount of polymerizable unsaturated monomer components. It is more preferable to contain 1-30 mass% of polyalkylene glycol macromonomer.

Further, the polyalkylene glycol macromonomer is a nonionic polymerizable unsaturated monomer represented by the following formula (5). Specific examples of such a monomer include, for example, polyethylene glycol (meth) acrylate, polypropylene glycol (Meth) acrylate, methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate and the like can be mentioned. Of these, 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 (5)
[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. ]
Further, it preferably contains at least one (meth) acrylamide compound. As the (meth) acrylamide compound, those known per se can be used without particular limitation. Specific examples include acrylamide, methacrylamide, 2-acrylamide-2-methylpropanesulfonic acid, N-methylacrylamide. N-methylmethacrylamide, N-methylolacrylamide butyl ether, N-methylol methacrylamide butyl ether, N-ethylacrylamide, N-ethylmethacrylamide, Nn-propylacrylamide, Nn-propylmethacrylamide, N-isopropylacrylamide N-isopropylmethacrylamide, N-cyclopropylacrylamide, N-cyclopropylmethacrylamide, diacetone acrylamide, diacetone methacrylamide, N-hydroxy Methylacrylamide, N-hydroxymethylmethacrylamide, N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, N-hydroxybutylacrylamide, N-hydroxypentylacrylamide, N-hydroxymethyl-N-ethylacrylamide, N-methyl-N- Hydroxyethyl acrylamide, N, N-dihydroxymethyl acrylamide, N, N-dihydroxyethyl acrylamide, N, N-dihydroxypropyl acrylamide, N, N-dihydroxybutyl acrylamide, N, N-dihydroxypentyl acrylamide, N-hydroxymethyl methacrylamide N-hydroxyethyl methacrylamide, N-hydroxypropyl methacrylamide, N-hydroxybutyl methacryl N-hydroxypentyl methacrylamide, N-hydroxymethyl-N-ethyl methacrylamide, N-methyl-N-hydroxyethyl methacrylamide, N, N-dihydroxymethyl methacrylamide, N, N-dihydroxyethyl methacrylamide, N , N-dihydroxypropyl methacrylamide, N, N-dihydroxybutyl methacrylamide, N, N-dihydroxypentyl methacrylamide, N, N-dihydroxybutyl (meth) acrylamide, N- [tris (hydroxymethyl) methyl] acrylamide, N N-dimethylacrylamide, N, N-dimethylmethacrylamide, N, N-diethylacrylamide, N, N-diethylmethacrylamide, N-methyl-N-ethylacrylamide, N-methyl-N-ethyl Methacrylamide, N-methylol acrylamide methyl ether, N-methylol methacrylamide methyl ether, N-methylol acrylamide ethyl ether, N-methylol methacrylamide ethyl ether, N-methylol acrylamide propyl ether, N-methylol methacrylamide propyl ether, N -Methylolacrylamide butyl ether, N-methylol methacrylamide butyl ether, N, N-dimethylaminoethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N, N-diethylaminoethyl (meth) acrylamide, N, N -Amino group-containing (meth) acrylamide compounds such as dipropylaminoethyl (meth) acrylamide, methacryloyloxyethyl Trimethyl ammonium chloride (ACRYESTER DMC, tradename, manufactured by Mitsubishi Rayon Co., Ltd.) Quaternary ammonium salt group-containing acrylamide compounds such as, and the like acryloyl morpholine. These can be used alone or in combination of two or more.
Especially, it is preferable that it is a (meth) acrylamide compound represented by following formula (6).
CH ₂ = C (—R ¹ ) —C (═O) —N (—R ² ) —R ³ (6)
R ¹ in the formula (6) is a hydrogen atom or a methyl group, and R ² and R ³ may be different or the same, and are at least one selected from a hydrogen atom, an organic group having a hydroxyl group, and an alkyl group. Preferably there is. Further, it is more preferable that both or one of R ² and R ³ is an organic group having a hydroxyl group. Specifically, for example, N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N- Hydroxypropyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide, N-hydroxymethyl-N-ethyl (meth) acrylamide, N-methyl-N-hydroxyethyl (meth) acrylamide, N-ethyl-N-hydroxyethyl (Meth) acrylamide, N-hydroxyethyl-N-butyl (meth) acrylamide, N-hydroxybutyl-N-butyl (meth) acrylamide, N, N-dihydroxymethyl (meth) acrylamide, N, N-dihydroxyethyl (meta) ) Acrylamide, N, N Dihydroxypropyl (meth) acrylamide, N, and particularly preferably at least one selected from N- dihydroxy-butyl (meth) acrylamide, and N- [tris (hydroxymethyl) methyl] acrylamide.

Synthesis of Dispersant (A) Dispersant (A) blended in the conductive paste for a lithium ion battery positive electrode of the present invention is a method of solution polymerization in an organic solvent in the presence of a radical polymerization initiator, or in an aqueous medium. It can be obtained by a radical polymerization method known per se, such as a method of emulsion polymerization in

  Examples of the radical polymerization initiator used for polymerization include 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-butyl cumyl peroxide, decanoyl Oxide, lauroyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-tert-amyl peroxide, bis (tert-butylcyclohexyl) peroxydicarbonate, tert-butylperoxybenzoate, 2,5- Peroxide-based polymerization initiators such as dimethyl-2,5-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'-azobis (2-methylpropane), dimethyl 2,2'-azobis (2-methylpropionate), and the like. . 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 tanol, isopropanol, n-butanol, sec-butanol, isobutanol, etc .; Examide (trade name, manufactured by Idemitsu Kosan Co., Ltd., amide solvent), N, N-dimethylformamide, N, N-dimethyl Conventionally known solvents such as amide solvents such as acetamide, N-methylformamide, N-methylacetamide, N-methylpropioamide and N-methyl-2-pyrrolidone can be listed. These can be used alone or in combination of two or more.

  In solution polymerization in an organic solvent, a polymerization initiator, a polymerizable unsaturated monomer component, and an organic solvent are mixed and heated while stirring. While being stirred at a temperature of 60 ° C. to 200 ° C. while introducing an inert gas such as nitrogen or argon as necessary, the polymerizable unsaturated monomer component and the polymerization initiator are mixed or dropped over a predetermined time. The method to do 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 in the range of 1,000 to 100,000, more preferably 3,000 to 50,000.

The pigment dispersant (A) 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.

  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.

Dispersant (B)
The dispersing agent (B) used for the electrically conductive paste of this invention contains polyvinyl alcohol resin (b1) other than the said dispersing agent (A).

Polyvinyl alcohol resin (b1)
The polyvinyl alcohol resin (b1) 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 (b1) 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-dimethylvaleronitrile, azobis (4-methoxy-2,4-dimethylvaleronitrile), etc. Azo compounds such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, etc .; diisopropyl peroxydicarbonate, di Percarbonate compounds such as 2-ethylhexyl peroxydicarbonate and diethoxyethyl peroxydicarbonate; t-butylperoxyneodecanate, α-cumylperoxyneodecanate, t-butylperoxyneodecanate 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 polyvinyl alcohol resin (b1) can be made into a resin solution replaced 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 (b1) in the resin solid content of the dispersant (B) is not particularly limited, for example, it is appropriately set in the range of 0.1 to 100% by mass, preferably 50 to 100% by mass. be able to.

A resin other than the dispersant (A) and the polyvinyl alcohol resin (b1) may optionally be blended in the resin dispersant (B ) other than the dispersant (A) and the polyvinyl alcohol resin (b1). Examples of resins other than the polyvinyl alcohol resin (b1) include acrylic resins other than the polyvinyl alcohol resin (b1), 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. Especially, it is preferable to use together and use together at least 1 sort (s) of resin chosen from polyvinyl acetal resin, polyvinyl pyrrolidone resin, polyvinyl alcohol resin, and a 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 (C)
Examples of the conductive carbon (C) 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 (C) may contain both acetylene black and graphite. These conductive carbons can be used alone or in combination of two or more.

Solvent (D)
As a solvent (D), the solvent used for superposition | polymerization or dilution of the dispersing agent (A) mentioned above can be used suitably. Specific examples of the preferred solvent (D) include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, propylene glycol monomethyl ether, methanol, water and the like, preferably N-methyl-2- Examples include pyrrolidone and the like. These solvent can be used individually by 1 type or in mixture of 2 or more types.

Other additives The conductive paste for a lithium ion battery positive electrode may contain components other than the above components (A), (B), (C) and (D) (sometimes referred to as other additives). Good. 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 dispersants (A) and (B), polyester resins, epoxy resins, polyether resins, alkyd resins, urethane resins, silicone resins, and polycarbonate resins. Silicate resin, chlorine resin, fluorine resin, polyvinyl pyrrolidone resin, polyvinyl alcohol resin, polyvinyl acetal resin, 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).

  Moreover, the conductive paste for lithium ion battery positive electrodes can optionally contain an acidic compound. It does not specifically limit as an acidic compound, Either an inorganic acid and an organic acid can also be used. Examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and the like. Examples of the organic acid include carboxylic acid compounds and sulfonic acid compounds. Carboxylic acid compounds include formic acid, acetic acid, propionic acid, butyric acid, tartaric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, (meth) acrylic acid, crotonic acid, fumaric acid, Examples include maleic acid, itaconic acid, citraconic acid, and fluoroacetic acid. Examples of the sulfonic acid compound include methanesulfonic acid, paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. Further, anhydrides, hydrates, or acidic compounds in which a part of the acidic compound is a salt can also be used. These can be used alone or in combination of two or more.

Production method of conductive paste for lithium ion battery positive electrode of the present invention The total amount of the solid content of the dispersants (A) and (B) 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. It is preferably 20% by mass or less from the viewpoint of viscosity at the time of pigment dispersion, pigment dispersibility, dispersion stability, production efficiency, and the like. Moreover, in preferable embodiment of this invention, solid content of the dispersing agent (A) and dispersing agent (B) in the electrically conductive paste solid content for lithium ion battery positive electrodes of this invention from the electroconductive viewpoint of a coating film. The total amount of is usually 20% by mass or less, preferably 0.1 to 15% by mass, and more preferably 1.0 to 10% by mass. In the conductive paste for a lithium ion battery positive electrode of the present invention, the blending ratio of the dispersant (A) and the dispersant (B) is a resin solid content ratio and is usually 99.9 / 0.1 to 10.0 / 90. 0.0, preferably 95.0 / 5.0 to 40.0 / 60.0.

  The solid content of the conductive carbon (C) in the solid paste for the 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 (D) 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.

Production Method of Lithium Ion Battery Positive Electrode Mixture 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 electrode active material to the lithium ion battery positive electrode conductive paste. It can be obtained by blending. Moreover, you may prepare the compound paste for lithium ion battery positive electrodes of this invention by mixing the above-mentioned component (A), component (B), component (C), component (D), and electrode active material.

  The total amount of the solid content of the dispersant (A) and the dispersant (B) in the solid paste solid content of the lithium ion battery positive electrode of the present invention is usually 0.001 to 20% by mass, preferably 0.005. It is suitable from the aspects of battery performance, paste viscosity, and the like. In the composite paste for a lithium ion battery positive electrode of the present invention, the blending ratio of the dispersant (A) and the dispersant (B) is a resin solid content ratio and is usually 99.9 / 0.1 to 10.0 /. The range is 90.0, preferably 95.0 / 5.0 to 40.0 / 60.0.

  The solid content of the conductive carbon (C) in the solid content of the lithium ion battery positive electrode paste 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. The content of the solvent (D) in the lithium ion battery positive electrode mixture paste of the present invention is usually 0.1 to 60% by mass, preferably 0.5 to 50% by mass, more preferably 1 to 45%. Mass% is preferable from the viewpoint of electrode drying efficiency and paste viscosity.

Method for Producing Lithium Ion Battery Positive Electrode As described above, the positive electrode mixture layer of the lithium ion secondary battery is coated with the lithium ion battery positive electrode mixture paste on the surface of the positive electrode core material and dried. Can be manufactured. 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.

  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 Pigment Dispersing Resin Manufacture of Pigment Dispersing Resin 300 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>
9-anthracenylmethyl methacrylate 300 parts styrene 200 parts n-butyl methacrylate 200 parts 2-ethylhexyl acrylate 100 parts 2-hydroxyethyl methacrylate 100 parts 2,2'-azobis (2-methylbutyronitrile) 40 parts 1 hour later, a solution prepared by dissolving 5 parts of 2,2′-azobis (2-methylbutyronitrile) in 100 parts of propylene glycol monomethyl ether was added dropwise thereto 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 a pigment dispersion resin A-1 solution having a solid content of 70%. Pigment dispersion resin A-1 had a weight average molecular weight of 10,000.

Production Examples 2 to 23 Production of Pigment Dispersion Resin Pigment Dispersion Resin A-2 to A-25 with the same composition and production method as Production Example 1 except that the monomer composition of Production Example 1 is the type and blending amount shown in Table 1 below. A solution was prepared.

Production Example 1 of Conductive Paste
21 parts of pigment dispersion resin A-1 obtained in Production Example 1 (15 parts of solid content), 15 parts of PVA-1 (Note 1), 1200 parts of acetylene black, KF polymer W # 7300 (trade name, polyvinylidene fluoride, 220 parts of Kureha Co., Ltd.) 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 2-30, Comparative Examples 1-4
Conductive pastes X-2 to X-34 were produced in the same manner as in Example 1 except that the conductive paste composition was changed to Table 2 below. In addition, the resin compounding quantity in a table | surface is a value of solid content.

(Note 1) PVA-1: polyvinyl alcohol resin, saponification degree 80 mol%, average polymerization degree about 500. Ratio of repeating unit-(CH2-CH (OH))-is about 67% by mass.
(Note 2) PVA-2: polyvinyl alcohol resin, saponification degree 35 mol%, average polymerization degree about 1500. Ratio of repeating unit-(CH2-CH (OH))-is about 22% by mass.

Compound paste production example 31
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 32 to 60, Comparative Examples 5 to 8
Compound pastes Y-2 to Y-34 were produced in the same manner as in Example 31 except that the conductive paste was of the type shown in Table 3 below.

  Table 3 below lists the results of evaluation tests (viscosity of conductive paste, battery performance) described later. 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 viscometer “Mars2” (trade name, manufactured by HAAKE), the viscosity of the conductive paste obtained in the examples was measured at a shear rate of 1.0 sec ⁻¹ and evaluated according to the following criteria. As evaluation, S, A, B, and C are acceptable, and D is unacceptable.
S: The viscosity is less than 1 Pa · s.
A: The viscosity is 1 Pa · s or more and 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 Y34 obtained in Examples 31 to 60 and Comparative Examples 5 to 8. 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 Y34 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-22 is a blank of 600 parts of acetylene black and 600 parts of graphite, the evaluation of the composite paste Y-23 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. S, A, and B are acceptable and C is unacceptable.
S: IV resistance increase rate is less than + 3% compared to blank.
A: The IV resistance increase rate is + 3% or more and 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 (8)

A conductive paste containing a dispersant (A), a dispersant (B), a conductive carbon (C), and a solvent (D),
The dispersant (A) is a copolymer of a monomer mixture containing 1 to 70% by mass of the monomer (A-1) having a polycyclic aromatic hydrocarbon based on the total amount of solids,
The dispersant (B) contains a polyvinyl alcohol resin (b1)),
The polyvinyl alcohol resin (b1) has a repeating unit represented by the following formula at a ratio of 30 to 100% by mass in the polymer chain.
Conductive paste for lithium ion battery positive electrode. The conductive paste for a lithium ion battery positive electrode according to claim 1, wherein the conductive carbon (C) contains acetylene black. The lithium ion according to claim 1 or 2, wherein the monomer (A-1) having a polycyclic aromatic hydrocarbon is a polymerizable unsaturated monomer having a naphthyl group or a derivative (A-2) thereof. Conductive paste for battery positive electrode. The conductive paste for a lithium ion battery positive electrode according to any one of claims 1 to 3, wherein the conductive carbon (C) further contains graphite. The conductive paste for a lithium ion battery positive electrode according to any one of claims 1 to 4, wherein the solvent (D) 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. A lithium ion battery positive electrode obtained by using the lithium ion battery positive electrode composite paste according to claim 6. The lithium ion battery which has an electrode for lithium ion battery positive electrodes of Claim 7.