Conductive slurry

Abstract

To provide an electrical conduction material slurry with an excellent dispersibility of a carbon nano-tube.SOLUTION: The present invention discloses, in one aspect, an electrical conduction material slurry containing: an electrical conduction material; a dispersant; and an organic solvent. In the electrical conduction material, 50 mass% or more is a carbon nano-tube. The dispersant is a polymer containing 60 to 99 mass% of vinyl alcohol unit in one molecular. A content amount of the vinyl alcohol unit in the electrical conduction material slurry is 17.0 to 60.0 mass part to 100 mass part of the content amount of the carbon nano-tube. The electrical conduction material slurry preferably further contains a binding agent, and the content amount of the binding agent in the electrical conduction material slurry is preferably 150 to 700 mass part against 100 mass part of the content amount of the vinyl alcohol unit.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a conductive material slurry, a battery positive electrode paste, and a battery positive electrode. [Background technology]

[0002] In recent years, there has been active development of electric vehicles that do not emit carbon dioxide, with a view to curbing global warming. Electric vehicles have the drawback of having a shorter driving range and longer battery charging times than gasoline-powered vehicles. To shorten charging times, it is necessary to increase the speed at which electrons move in the positive electrode. Currently, carbon black is used as a conductive additive (conductive material) in the positive electrodes of non-aqueous electrolyte batteries, but there is a demand for conductive materials with lower electronic resistance than carbon black.

[0003] Carbon nanotubes (hereinafter sometimes referred to as "CNTs") are a conductive material with lower electronic resistance than carbon black, and their physical and chemical properties make them promising for application in a variety of fields. CNTs have a high aspect ratio and can form conductive paths with a small amount. CNTs are essentially nanocarbon materials that have the shape of a single sheet of graphite rolled into a cylindrical shape; those rolled in a single layer are called single-walled CNTs, and those rolled coaxially in multiple layers are called multi-walled CNTs.

[0004] It is necessary to uniformly disperse a carbon material in an organic solvent. Patent Document 1 discloses a carbon material dispersion containing a dispersant copolymer of stearyl methacrylate and polyoxypropylene methacrylate (average number of added moles: 14), a carbon material such as CNT, and an organic solvent. Patent Document 2 discloses a carbon nanotube slurry and a battery positive electrode paste containing carbon nanotubes and a polyvinyl alcohol resin with a saponification degree of 71 mol% (56 mass% converted to the content of vinyl alcohol units) and an average polymerization degree of 1,000 or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-166154 [Patent Document 2] Japanese Patent Application Publication No. 2019-102259 Summary of the Invention [Problem to be solved by the invention]

[0006] To obtain a battery positive electrode paste that can efficiently form a conductive path with a small number of CNTs in the positive electrode composite layer, the CNTs must be highly dispersed, with thick bundles of several tens of CNTs and strong agglomerations of CNTs broken down.To obtain such a positive electrode paste, it is necessary to use a CNT dispersion in which CNTs are highly dispersed in a solvent.

[0007] Therefore, the present disclosure provides a conductive material slurry with good CNT dispersibility, and also provides a battery positive electrode paste prepared using the conductive material slurry. [Means for solving the problem]

[0008] In one aspect, the present disclosure provides a conductive material slurry comprising a conductive material, a dispersant, and an organic solvent, The conductive material is made up of 50 mass % or more of carbon nanotubes, the dispersant is a polymer containing 60 to 99 mass% of vinyl alcohol units in one molecule, The present invention relates to a conductive material slurry, wherein the content of the vinyl alcohol unit in the conductive material slurry is 17.0 to 60.0 parts by mass with respect to 100 parts by mass of the carbon nanotube content.

[0009] In one aspect, the present disclosure provides a positive electrode paste for a battery, the positive electrode paste including a positive electrode active material, a binder, a conductive material, a dispersant, and an organic solvent, the conductive material contains carbon nanotubes in an amount of 50 mass % or more; the dispersant is a polymer containing 60 to 99 mass% of vinyl alcohol units in one molecule, The present invention relates to a battery positive electrode paste, wherein the content of the vinyl alcohol unit in the conductive material slurry is 17.0 to 60.0 parts by mass with respect to 100 parts by mass of the carbon nanotube content.

[0010] The present disclosure provides, in one aspect, a positive electrode for a battery including a positive electrode mixture layer, the positive electrode mixture layer includes a positive electrode active material, a conductive material, a polymer, and a binder, the conductive material contains carbon nanotubes in an amount of 50 mass % or more; the polymer contains 60 to 99 mass% of vinyl alcohol units in one molecule, The present invention relates to a positive electrode for a battery, wherein the content of the vinyl alcohol unit in the positive electrode mixture layer is 17.0 to 60.0 parts by mass per 100 parts by mass of the carbon nanotube content. [Effects of the Invention]

[0011] The conductive material slurry of the present disclosure contains a polymer containing 60 to 99 mass% of vinyl alcohol units in one molecule as a dispersant, and the content of vinyl alcohol units in the conductive material slurry is 17.0 to 60.0 parts by mass per 100 parts by mass of the carbon nanotube content, so that CNTs can be dispersed well in the conductive material slurry. Furthermore, the battery positive electrode paste of the present disclosure is prepared using the conductive material slurry, which enables a reduction in the coating resistance of the positive electrode mixture layer. DETAILED DESCRIPTION OF THE INVENTION

[0012] The conductive material slurry of the present disclosure contains a polymer containing vinyl alcohol units in a specific mass ratio per molecule as a dispersant, and is based on the finding that by setting the amount of vinyl alcohol units to a specific amount per 100 parts by mass of CNTs in the conductive material slurry, the dispersibility of CNTs in the conductive material slurry is improved.

[0013] In the present disclosure, the details of the mechanism by which the dispersibility of CNTs in the conductive material slurry is improved are not clear, but are presumed to be as follows. In the present disclosure, a polymer containing 60 to 99% by mass of vinyl alcohol units in one molecule is used as a dispersant for CNTs, and the content of vinyl alcohol units in the conductive material slurry is within the range of 17.0 to 60.0 parts by mass per 100 parts by mass of CNTs. Therefore, it is presumed that the vinyl alcohol units adsorbed to the CNTs hold the CNTs, and the vinyl structure that forms the main chain spreads over the CNT surface, causing a strong steric repulsion between the CNTs due to this steric repulsion, making the CNTs highly dispersible in the solvent. When the vinyl alcohol unit content in one molecule of the polymer is 60% by mass or more, the solubility of the polymer in organic solvents such as N-methyl-2-pyrrolidone (NMP) is suppressed, and the polymer's adsorption to CNTs is increased, which is thought to contribute to improved dispersibility. Furthermore, when the content of vinyl alcohol units is 17.0 parts by mass or more relative to 100 parts by mass of CNTs, dispersibility is increased, CNT aggregation is suppressed, and the stability of the conductive material slurry is maintained.On the other hand, when the content of vinyl alcohol units is 60.0 parts by mass or less relative to 100 parts by mass of CNTs, aggregation between vinyl alcohol units during solvent drying is suppressed, and contact between the CNTs is maintained, which is thought to result in low coating film resistance of the positive electrode coating film. However, the present invention is not limited to these mechanisms. The dispersibility of CNTs in the conductive material slurry can be evaluated by the viscosity of the conductive material slurry. The lower the viscosity, the better the dispersibility of CNTs.

[0014] <Conductive slurry> In one aspect, the present disclosure relates to a conductive material slurry comprising a conductive material, a dispersant, and an organic solvent, wherein the conductive material is composed of 50 mass % or more of CNTs, the dispersant is a polymer containing 60 to 99 mass % of vinyl alcohol units, and the content of the vinyl alcohol units in the conductive material slurry is 17.0 to 60.0 mass parts per 100 mass parts of CNTs. The conductive material slurry of the present disclosure allows for good dispersion of CNTs in the conductive material slurry.

[0015] [Conductive material] In the conductive material slurry of the present disclosure, the conductive material is composed of 50 mass % or more of CNT. The conductive material is preferably 80 mass % or more, more preferably 90 mass % or more, even more preferably 95 mass % or more, still more preferably 98 mass % or more, still more preferably substantially 100 mass %, and still more preferably 100 mass % CNT. Examples of conductive materials other than CNT contained in the conductive material slurry of the present disclosure include carbon materials such as acetylene black, ketjen black, and graphite, and these can be used alone or in combination of two or more types.

[0016] In the present disclosure, CNT refers to a whole including multiple CNTs. The form of the CNTs used in preparing the conductive material slurry of the present disclosure is not particularly limited, and may be, for example, multiple CNTs that are independent of each other, multiple CNTs that are bundled or entangled, or a mixture of these forms. The CNTs may have various numbers of walls or diameters. The CNTs may contain impurities (e.g., catalysts and amorphous carbon) derived from the CNT manufacturing process.

[0017] In one or more embodiments, the CNT has a cylindrical shape formed by rolling one surface of graphite. Those wound into one layer are called single-walled CNTs (SWCNTs), those wound into two layers are called double-walled CNTs (DWCNTs), and those wound into three or more layers are called multi-walled CNTs (MWCNTs). Depending on the properties required for the positive electrode composite layer obtained using a battery positive electrode paste (hereinafter sometimes abbreviated as "positive electrode paste") containing the conductive material slurry of the present disclosure, single-walled, double-walled, or multi-walled CNTs, or a mixture thereof, can be used. Multi-walled CNTs are preferably used to obtain a positive electrode composite layer with good CNT dispersion and low resistance.

[0018] The average diameter of CNTs is measured using a scanning electron microscope (SEM) or an atomic force microscope (AFM). In the present disclosure, the average diameter is not particularly limited, but from the viewpoint of improving CNT dispersibility, it is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 8 nm or more. From the viewpoint of improving conductivity, it is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, still more preferably 20 nm or less, and even more preferably 15 nm or less. Specifically, the average diameter of CNTs is preferably 3 to 100 nm, more preferably 3 to 50 nm, even more preferably 3 to 30 nm, still more preferably 5 to 20 nm, still more preferably 8 to 20 nm, and even more preferably 8 to 15 nm.

[0019] The average length of the CNTs is measured using a scanning electron microscope (SEM) or an atomic force microscope (AFM). In the present disclosure, the average length is not particularly limited, but from the viewpoint of improving electrical conductivity, it is preferably 2 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 30 μm or more. From the viewpoint of improving dispersibility, it is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and even more preferably 120 μm or less. Specifically, the average length of the CNTs is preferably 2 to 500 μm, more preferably 5 to 300 μm, even more preferably 10 to 200 μm, and even more preferably 30 to 120 μm.

[0020] The impurity content in CNTs is measured by methods such as thermogravimetric analysis, and in the present disclosure, the lower the better. From the viewpoint of achieving a high concentration of useful CNT content, the impurity content in CNTs is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably substantially 0% by mass.

[0021] The content of the conductive material in the conductive material slurry of the present disclosure is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of improving the convenience of adjusting the concentration of the positive electrode paste, and is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of imparting a viscosity to the conductive material slurry that is easy to handle. Specifically, the content of the conductive material in the conductive material slurry of the present disclosure is preferably 0.5 to 10% by mass, more preferably 1 to 5% by mass, and even more preferably 1.5 to 3% by mass.

[0022] [Dispersant] The dispersant contained in the conductive material slurry of the present disclosure is a polymer containing 60 to 99% by mass of vinyl alcohol units per molecule. When the vinyl alcohol units per molecule of the polymer are less than 60% by mass, the polymer is highly soluble in organic solvents such as N-methyl-2-pyrrolidone (NMP), resulting in poor adsorption of the polymer to CNTs and is therefore not considered effective in improving CNT dispersibility. On the other hand, when the vinyl alcohol units per molecule are more than 99% by mass, the polymer is less soluble in organic solvents such as NMP, which makes it extremely time-consuming to prepare the conductive material slurry or positive electrode paste, resulting in poor productivity and insufficient stability of the conductive material slurry. Furthermore, when the vinyl alcohol units per molecule of the polymer are less than 60% by mass, even if the vinyl alcohol units are adsorbed to the CNTs, the vinyl structure of the main chain cannot be maintained on the CNT surface. As a result, it is presumed that effective steric repulsion by the polymer does not occur, resulting in poor dispersibility. In contrast, polymers containing 60 to 99% by mass of vinyl alcohol units are thought to function particularly effectively as dispersants because they can achieve a favorable balance between the polymer's moderate solubility in organic solvents such as NMP, its adsorption to CNTs, and the steric repulsion effect after adsorption.

[0023] The content of vinyl alcohol units in one molecule of the polymer is 60% by mass or more, preferably 75% by mass or more, more preferably 83% by mass or more, even more preferably 84% by mass or more, and even more preferably 85% by mass or more, from the viewpoint of improving CNT dispersibility, and is 99% by mass or less, preferably 95% by mass or less, more preferably 92% by mass or less, even more preferably 90% by mass or less, even more preferably 88% by mass or less, and even more preferably 87% by mass or less, from the viewpoint of productivity and the stability of the conductive material slurry. In the present disclosure, the content of vinyl alcohol units in one molecule of the polymer is specifically preferably 75 to 95% by mass, more preferably 83 to 92% by mass, even more preferably 83 to 90% by mass, even more preferably 84 to 88% by mass, and even more preferably 85 to 87% by mass.

[0024] As long as the mass ratio of vinyl alcohol units in one molecule of the polymer is within the above range, the polymer may contain, as structural units other than vinyl alcohol units, one or more structural units selected from vinyl ester units, vinyl butyral units, polyalkylene glycol (meth)acrylate units, styrene units, ethylene units, and butadiene units. The vinyl ester units are derived from vinyl ester monomers used as raw material monomers for the polymer. Examples of vinyl ester monomers include vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl laurate.

[0025] As long as the mass ratio of vinyl alcohol units in one molecule of the polymer is within the above range, the polymer also includes polyvinyl alcohol into which one or more functional groups other than hydroxyl, acetyl, acetal, or formal groups, such as acetoacetyl, sulfonic acid, carboxyl, carbonyl, or amino groups, have been introduced, or these functional groups have been modified with various salts, or have been anion- or cation-modified, or have an ether, ester, or other structure. The polymer may contain one or more of these modified polyvinyl alcohols, or may contain both modified and unmodified polyvinyl alcohols.

[0026] The content of vinyl alcohol units in the conductive material slurry of the present disclosure is 17.0 to 60.0 parts by mass per 100 parts by mass of CNTs. If the content of vinyl alcohol units is less than 17.0 parts by mass per 100 parts by mass of CNTs, the CNTs will aggregate, making it difficult to maintain the stability of the conductive material slurry. If the content of vinyl alcohol units exceeds 60.0 parts by mass per 100 parts by mass of CNTs, the aggregation effect of vinyl alcohol units during solvent drying will hinder contact between CNTs, resulting in increased coating resistance of the positive electrode coating film. Here, the "content of vinyl alcohol units in the conductive material slurry" refers to the total amount of vinyl alcohol units contained in the conductive material slurry.

[0027] The content of vinyl alcohol units in the conductive material slurry of the present disclosure is preferably 23.0 parts by mass or more, more preferably 25.0 parts by mass or more, relative to 100 parts by mass of CNTs, from the viewpoint of high dispersibility of CNTs and stability of the conductive material slurry, and is preferably 55.0 parts by mass or less, more preferably 40.0 parts by mass or less, and even more preferably 30.0 parts by mass or less, relative to 100 parts by mass of CNTs, from the viewpoint of coating film resistance. Specifically, the content of vinyl alcohol units in the conductive material slurry of the present disclosure is preferably 23.0 to 55.0 parts by mass, more preferably 23.0 to 40.0 parts by mass, and even more preferably 25.0 to 30.0 parts by mass, relative to 100 parts by mass of CNTs.

[0028] From the viewpoint of improving the dispersibility of CNTs by favorably covering the CNTs with the vinyl structure, the degree of polymerization of the polymer is preferably 20 or more, more preferably 50 or more, even more preferably 200 or more, and even more preferably 300 or more, and from the viewpoint of improving the dispersibility of CNTs by improving the dispersibility of the polymer itself, the degree of polymerization is preferably 5000 or less, more preferably 3000 or less, even more preferably 2000 or less, and even more preferably 1000 or less. In the present disclosure, the degree of polymerization of the polymer is specifically preferably 20 to 5000, more preferably 50 to 3000, even more preferably 200 to 2000 mass%, and even more preferably 300 to 1000.

[0029] [Polymer manufacturing method] The method for synthesizing the polymer is not particularly limited, and the polymer can be obtained by a known method. For example, the polymer can be obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate.

[0030] [Organic solvents] The solvent contained in the conductive material slurry of the present disclosure is preferably an organic solvent capable of dissolving the binder contained in the battery positive electrode paste. Examples of the organic solvent include amide polar organic solvents such as dimethylformamide (DMF), diethylformamide, dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP); alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 2-methyl-1-propanol (isobutanol), 2-butanol (sec-butanol), 1-methyl-2-propanol (tert-butanol), pentanol, hexanol, heptanol, and octanol; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, and hexylene glycol; glycerin, trimethylolpropane, pentanol, and hexylene glycol. Examples of suitable organic solvents include polyhydric alcohols such as taerythritol or sorbitol; glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol monobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, and cyclopentanone; and esters such as ethyl acetate, γ-butyl lactone, and ε-propiolactone. The organic solvent contained in the conductive material slurry may be one type or a combination of two or more types. When the binder is PVDF (polyvinylidene fluoride resin), which is contained in conventional battery positive electrode pastes, the organic solvent is generally N-methyl-2-pyrrolidone (NMP). NMP is particularly preferred as the organic solvent from the viewpoint of improving the dispersibility of CNTs.

[0031] [Binder] The binder contained in the positive electrode paste of the present disclosure, which will be described later, may be added to the conductive material slurry or the positive electrode active material of the present disclosure when preparing the positive electrode paste. In one embodiment, the binder may be contained in the conductive material slurry of the present disclosure in advance.

[0032] The binder is not particularly limited, and known binders used in the production of battery electrodes can be used. For example, vinylidene fluoride polymers such as polyvinylidene fluoride (PVDF), vinylidene fluoride copolymers with hexafluoropropylene or monochlorotrifluoroethylene, and modified vinylidene fluoride with carboxylic acid can be used. There are no particular limitations on the weight-average molecular weight of these vinylidene fluoride polymers, but vinylidene fluoride polymers with a molecular weight of 100,000 to 1,500,000 are generally used. The vinylidene fluoride polymer may be mixed with styrene-butadiene rubber, polyacrylonitrile, or the like.

[0033] The amount of binder contained in the conductive material slurry or positive electrode paste is preferably 150 parts by mass or more, more preferably 300 parts by mass or more, and even more preferably 350 parts by mass or more, relative to 100 parts by mass of vinyl alcohol units in the conductive material slurry or positive electrode paste, from the viewpoints of ensuring the integrity of the positive electrode mixture layer and the adhesion between the positive electrode mixture layer and the current collector; and from the viewpoints of preventing a loss of dispersion stability of the conductive material slurry or positive electrode paste due to the dispersibility of CNTs and an increase in the viscosity of the conductive material slurry or positive electrode paste accompanying the addition of the binder, the amount of binder is preferably 700 parts by mass or less, more preferably 650 parts by mass or less, and even more preferably 620 parts by mass or less, relative to 100 parts by mass of vinyl alcohol units in the conductive material slurry or positive electrode paste. Specifically, the amount of binder contained in the conductive material slurry or positive electrode paste is preferably 150 to 700 parts by mass, more preferably 300 to 650 parts by mass, and even more preferably 350 to 620 parts by mass, per 100 parts of vinyl alcohol units in the conductive material slurry or positive electrode paste.

[0034] [Nitrogen-containing organic compounds] In one embodiment, the positive electrode paste of the present disclosure, which will be described later, may further contain a nitrogen-containing organic compound. The nitrogen-containing organic compound may be added to the conductive material slurry of the present disclosure or other components when preparing the positive electrode paste. In one embodiment, the nitrogen-containing organic compound may be pre-contained in the conductive material slurry of the present disclosure. The addition of the nitrogen-containing organic compound allows the preparation of a conductive material slurry and a positive electrode paste that have low viscosity and good handleability.

[0035] Although the details of the mechanism by which the addition of a nitrogen-containing organic compound reduces viscosity are unclear, it is believed that a polymer containing 60 to 99% by mass of vinyl alcohol units does not cover the entire surface of the carbonaceous conductive material, leaving some exposed portions on the surface. Therefore, adjacent carbonaceous conductive materials aggregate in an organic solvent due to π-π interactions and hydrogen bonding between polar groups present on the surface of the carbonaceous conductive material. However, when a nitrogen-containing organic compound is added, the nitrogen-containing organic compound interacts with the polar groups (neutralization reaction or dipole-dipole interaction) to suppress hydrogen bonding between the carbonaceous conductive materials. Furthermore, the amine (cation) interacts with the π electrons on the carbonaceous conductive material to suppress π-π interactions between the carbonaceous conductive materials. It is presumed that the suppression of hydrogen bonding and the suppression of π-π interactions improves the dispersibility of the carbonaceous conductive material, resulting in a lower viscosity compared to when a nitrogen-containing organic compound is not added. However, the present disclosure should not be interpreted as being limited to these mechanisms.

[0036] The nitrogen-containing organic compound is preferably a compound having at least one primary, secondary, or tertiary amino group in the molecule (hereinafter referred to as a primary, secondary, or tertiary amine). In the present application, a primary, secondary, or tertiary amino group refers to a structure in which all three bonds to the central nitrogen atom are single bonds. As long as the nitrogen-containing organic compound has one such primary, secondary, or tertiary amino group, it may have other nitrogen atoms in the molecule, and the other nitrogen atoms may be primary, secondary, or tertiary amino groups or may constitute an imino group having a double bond. When other nitrogen atoms are present in the molecule, it is preferable that they are not adjacent to the nitrogen atom of the amino group.

[0037] The primary to tertiary amines are preferably aliphatic amines, and may be linear (branched or linear) or cyclic. In the case of cyclic amines, saturated rings are preferred. Non-cyclic amines may have an unsaturated group such as an imino group along with an amino group. The hydrocarbon group portion of the aliphatic amine may be substituted with OH, an amino group, COOH, or the like. In addition, -CH2- in the aliphatic group may be replaced with O (oxygen atom), and in this case, it is preferable that the O (oxygen atom) is not adjacent to the nitrogen atom of the amino group. Examples of the primary to tertiary amines include alkylamines, amino group-containing alcohols, carboxyl-substituted alkylamines, imidazoles, piperazines, guanidines, piperidines, and pyrrolidines.

[0038] As the alkylamines, primary to tertiary amines in which the alkyl groups present are each independently a branched or linear alkyl group are preferred, and more preferably have alkyl groups such that the total number of carbon atoms in the molecule is 15 or less. Specific examples include hexylamine, octylamine, diethylamine, dibutylamine, trimethylamine, triethylamine, tributylamine, N-propylethylamine, N-butylethylamine, and N,N-dimethylcyclohexylamine. Furthermore, the alkyl group may be substituted with an amino group, in which case the amine contains two or more primary, secondary, or tertiary amino groups, and examples thereof include di- or triamines such as ethylenediamine and diethylenediaminetriamine.

[0039] As the amino group-containing alcohol, compounds in which hydrogen of the alkyl group in the above-mentioned alkylamine is substituted with OH are preferred, and examples thereof include monoethanolamine, diethanolamine, triethanolamine, N-butyldiethanolamine, N,N-dimethylaminoethanol, Nn-butylethanolamine, 2-(methylamino)ethanol, N-methylethanolamine, N-ethylethanolamine, 2-amino-1-propanol, 2-amino-2-methyl-1-propanol, 1-amino-2-propanol, 2-amino-1,3-propanediol, etc. Among them, 2-amino-1,3-propanediol is preferred.

[0040] Carboxyl-substituted alkylamines include compounds in which hydrogen atoms in the alkyl group of the above-mentioned alkylamines are substituted with COOH, such as ethylenediaminetetraacetic acid, 1,3-propanediaminetetraacetic acid, 1,2-propanediaminetetraacetic acid, 1,3-diamino-2-hydroxypropanetetraacetic acid, glycol ether diaminetetraacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, hexamethylenediaminetetraacetic acid, dicarboxymethylglutamic acid, dicarboxymethylaspartic acid, S,S-ethylenediaminedisuccinic acid, ethylenediaminedi(o-hydroxyphenyl)acetic acid, hydroxyethyliminodiacetic acid, ethylenediaminediacetic acid, iminodiacetic acid, ethylenediaminedipropionic acid, nitrilotriacetic acid, hydroxyethylenediaminetriacetic acid, nitrilotripropionic acid, methylglycinediacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid. Furthermore, some or all of the carboxyl groups may form a salt with an alkali metal such as sodium.

[0041] Specific examples of imidazoles include 1,2-dimethylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 4-ethyl-2-methylimidazole, and 1-methyl-4-ethylimidazole.

[0042] Preferred piperazines are unsubstituted or alkyl-substituted piperazines, where the alkyl group may further have an amino group. The alkyl group may be substituted at any position on the piperazine ring, either on a nitrogen atom or on a carbon atom. Specific examples include piperazine, 1-methylpiperazine, 1-ethylpiperazine, 1-propylpiperazine, 1,4-dimethylpiperazine, 1,4-diethylpiperazine, 1,4-dipropylpiperazine, 2-methylpiperazine, 2-ethylpiperazine, 3-propylpiperazine, 2,6-dimethylpiperazine, 2,6-diethylpiperazine, 2,6-dipropylpiperazine, 2,5-dimethylpiperazine, 2,5-diethylpiperazine, and 2,5-dipropylpiperazine. Also preferred are piperazines substituted with an aminoalkyl group, such as 1-aminoethylpiperazine.

[0043] Other examples of the nitrogen-containing organic compound include guanidines, piperidines, and pyrrolidines. Specific examples include guanidine and guanidine salts, piperidine, 1-methylpiperidine, 1-ethylpiperidine, 1-propylpiperidine, 2, 3, or 4-methylpiperidine, 2, 3, or 4-ethylpiperidine, 2,6-dimethylpiperidine, 2,6-diethylpiperidine, 2,6-dipropylpiperidine, 2,4-dimethylpiperidine, 2,4-diethylpiperidine, 1-aminoethylpiperidine, morpholine, pyrrolidine, 1-methylpyrrolidine, 1-ethylpyrrolidine, 1-propylpyrrolidine, 2 or 3-methylpyrrolidine, 2 or 3-ethylpyrrolidine, 2,5-dimethylpyrrolidine, 2,5-diethylpyrrolidine, 2,5-dipropylpyrrolidine, 2,4-dimethylpiperidine, 2,4-diethylpiperidine, and 1-aminoethylpyrrolidine.

[0044] The content of the nitrogen-containing organic compound contained in the conductive material slurry or positive electrode paste is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the conductive material, from the viewpoint of improving the dispersibility of the conductive material, and is preferably 2000 parts by mass or less, more preferably 1000 parts by mass or less, and even more preferably 500 parts by mass or less, from the viewpoint of high conductivity. From the same viewpoint, the content of the nitrogen-containing organic compound contained in the conductive material slurry or positive electrode paste is specifically preferably 0.5 to 2000 parts by mass, more preferably 1 to 1000 parts by mass, and even more preferably 5 to 500 parts by mass, relative to 100 parts by mass of the conductive material.

[0045] The conductive material slurries of the present disclosure may further contain other components, such as antioxidants, neutralizing agents, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, plasticizers, etc. (hereinafter also referred to as additives), to the extent that the effects of the present disclosure are not impaired.

[0046] [Method for producing conductive slurry] In one or more embodiments, the conductive material slurry of the present disclosure can be prepared by mixing components such as a conductive material, a dispersant, an organic solvent, and, as necessary, a binder, a nitrogen-containing organic compound, or an additive using a mixer / disperser, and performing a dispersion treatment until a uniform composition is achieved. In one aspect, a method for producing a conductive material slurry of the present disclosure includes the steps of: dissolving a dispersant in an organic solvent to obtain a dispersant solution; adding a conductive material to the dispersant solution; and performing a dispersion treatment using a mixer / disperser on the dispersant solution to which the conductive material has been added.

[0047] The mixer / disperser may be at least one selected from an ultrasonic homogenizer, a vibration mill, a jet mill, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, a high-pressure homogenizer, an ultrasonic device, an attritor, a dissolver, and a paint shaker.

[0048] The dispersion treatment is preferably carried out while circulating the crude dispersion by, for example, discharging it from the mixer-disperser and then injecting it back into the mixer-disperser, and the circulation is preferably carried out 2 to 40 times, and the discharging and injecting rate of the dispersion is preferably 10 to 60 g / min.

[0049] In the method for producing a conductive material slurry of the present disclosure, some of the components constituting the conductive material slurry may be mixed and then mixed with the remainder, or each component may be added in multiple batches rather than all at once. The conductive material may be mixed with the other components in a dry state, or may be mixed with a solvent and then mixed with the other components. Examples of the solvent include the same organic solvents as described above. It is preferable that the binder is dissolved in a solvent, i.e., the binder solution is mixed with the other components. Examples of the solvent include the same organic solvents as described above.

[0050] When preparing the conductive material slurry of the present disclosure containing a binder, it is preferable to mix a binder solution with a crude dispersion containing a conductive material, a dispersant, an organic solvent, and, as necessary, a nitrogen-containing organic compound or an additive, etc., and it is preferable to agitate the mixture containing the crude dispersion and the binder solution with a mixer or the like, and then supply the mixture to a mixer / disperser.

[0051] The viscosity of the conductive material slurry of the present disclosure at 25°C is preferably low, and from the viewpoint of improving handleability during preparation of the positive electrode paste, it is preferably 90 Pa·s or less, more preferably 70 Pa·s or less, and even more preferably 60 Pa·s or less.

[0052] <Battery cathode paste> In one aspect, the present disclosure relates to a positive electrode paste for a battery, comprising a conductive material slurry of the present disclosure and a positive electrode active material. The use of the positive electrode paste for a battery prepared using the conductive material slurry of the present disclosure improves the dispersibility of CNTs in the positive electrode mixture layer, thereby reducing the coating resistance of the positive electrode mixture layer.

[0053] In one aspect, the present disclosure relates to a positive electrode paste for a battery, comprising a positive electrode active material, a binder, a conductive material, a dispersant, and an organic solvent, wherein 50 mass % or more of the conductive material is carbon nanotubes, the dispersant is a polymer containing 60 to 99 mass % of vinyl alcohol units in one molecule, and the content of the vinyl alcohol units in the conductive material slurry is 17.0 to 60.0 parts by mass per 100 parts by mass of the carbon nanotubes. The battery positive electrode paste of the present disclosure contains a polymer containing 60 to 99 mass% vinyl alcohol units in one molecule as a dispersant, and the content of vinyl alcohol units in the battery positive electrode paste is 17.0 to 60.0 parts by mass per 100 parts by mass of carbon nanotubes, thereby enabling good dispersion of CNTs in the battery positive electrode paste and reducing the coating resistance of the positive electrode composite layer.

[0054] [Cathode active material] The positive electrode active material may be any active material capable of absorbing and releasing lithium and capable of undergoing charge-discharge reactions, such as LiCoO2, LiNiO2, LiMn2O4, ternary (NMC) LiNi x Mn y Co z O2, Li-rich (Li(Li x Me 1-x )O2 (Me=Co, Ni, Mn, etc.), Ni-rich type (LiNi x Co y Al z Examples of the positive electrode active material include lithium metal composite oxides such as SiO2. The positive electrode active material is used in the form of particles. The average particle size can be, for example, 1 μm or more and 40 μm or less.

[0055] (Positive electrode active material content in positive electrode paste) The content of the positive electrode active material in the positive electrode paste of the present disclosure is, in terms of solid content, preferably 80% by mass or more, more preferably 90% by mass or more, from the viewpoint of increasing energy density and capacity, and is preferably 99.5% by mass or less, more preferably 99% by mass or less, from the viewpoint of improving the binding strength of the positive electrode mixture layer to the current collector. Note that, in this application, the contents of the positive electrode active material, binder, dispersant (polymer), and conductive material, in terms of solid content, are values ​​calculated assuming that the total solid content of the positive electrode active material, binder, dispersant, and conductive material is 100% by mass.

[0056] From the viewpoints of suppressing aggregation of the positive electrode active material particles and stabilizing the positive electrode paste, the content of the positive electrode active material in the positive electrode paste, expressed as a mass ratio (positive electrode active material / vinyl alcohol unit) to the vinyl alcohol units in the positive electrode paste, is preferably 350 or more, more preferably 400 or more, and even more preferably 450 or more. Furthermore, from the viewpoints of suppressing aggregation of the positive electrode active material particles in the positive electrode mixture layer after solvent removal due to the positive electrode active material being covered with an excess amount of dispersant, and suppressing an increase in the coating resistance of the positive electrode mixture layer, the content of the positive electrode active material in the positive electrode paste, expressed as the mass ratio (positive electrode active material / vinyl alcohol unit), is preferably 900 or less, more preferably 800 or less, and even more preferably 700 or less. Specifically, the content of the positive electrode active material in the positive electrode paste, expressed as the mass ratio (positive electrode active material / vinyl alcohol unit), is preferably 350 to 900, more preferably 400 to 800, and even more preferably 450 to 700.

[0057] (Dispersant content in positive electrode paste) The content of the dispersant (polymer) in the positive electrode paste of the present disclosure is, in terms of solid content, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, from the viewpoint of reducing the resistance of the positive electrode mixture layer, and preferably 1% by mass or less, more preferably 0.5% by mass or less, from the viewpoint of maintaining a high energy density of the battery. Specifically, the content of the dispersant (polymer) in the positive electrode paste of the present disclosure is preferably 0.05 to 1% by mass, more preferably 0.10 to 0.5% by mass.

[0058] (Conductive material content in positive electrode paste) The content of the conductive material in the positive electrode paste of the present disclosure is preferably 0.3 mass% or more, more preferably 0.5 mass% or more, calculated as solid content, from the viewpoint of the conductivity of the positive electrode mixture layer, and is preferably 2 mass% or less, more preferably 1 mass% or less, from the viewpoint of maintaining a high energy density of the battery. Specifically, the content of the conductive material in the positive electrode paste of the present disclosure is preferably 0.3 to 2 mass%, more preferably 0.5 to 1 mass%.

[0059] (Binder content in positive electrode paste) The content of the binder in the positive electrode paste of the present disclosure is preferably 0.5 mass% or more, more preferably 0.8 mass% or more, calculated as solid content, from the viewpoints of the coating properties of the positive electrode mixture layer and the binding strength with the current collector, and is preferably 1.5 mass% or less, more preferably 1.2 mass% or less, from the viewpoint of maintaining a high energy density of the battery. Specifically, the content of the binder in the positive electrode paste of the present disclosure is preferably 0.5 to 1.5 mass%, more preferably 0.8 to 1.2 mass%.

[0060] The positive electrode pastes of the present disclosure may further contain other components, such as antioxidants, neutralizing agents, antifoaming agents, preservatives, dehydrating agents, rust inhibitors, and plasticizers, as long as the effects of the present disclosure are not impaired.

[0061] (Positive electrode paste manufacturing method) In one or more embodiments, the positive electrode paste of the present disclosure can be produced by mixing and stirring a positive electrode active material, the conductive material slurry of the present disclosure, a solvent (additional solvent) for adjusting the solid content, etc., and, if necessary, a binder, etc. The components may be mixed in any order. Examples of the solvent (additional solvent) include the same organic solvents as those described above, with NMP being preferred. A planetary mixer, a bead mill, a jet mill, etc. can be used for mixing and stirring, or these can be used in combination.

[0062] The positive electrode paste of the present disclosure may be prepared by premixing some of the components used in the preparation of the positive electrode paste and then mixing the premixed components with the remaining components. Alternatively, each component may be added in multiple batches rather than all at once. This reduces the mechanical load on the stirring device. The solids concentration of the positive electrode paste of the present disclosure may be adjusted according to the viscosity suitable for applying the positive electrode paste to the current collector. Alternatively, components other than the positive electrode active material may be mixed and dispersed until homogeneous, after which the positive electrode active material may be added and stirred until further homogeneous. In one aspect, the method for producing a positive electrode paste of the present disclosure includes a step of adding and dispersing a positive electrode active material into the conductive slurry of the present disclosure. In another aspect, the method for producing a positive electrode paste of the present disclosure includes adding a binder solution prepared by dissolving a binder in an organic solvent to the conductive slurry of the present disclosure, mixing the two, and then adding and dispersing the positive electrode active material.

[0063] <Battery cathode> In one aspect, the present disclosure relates to a battery positive electrode formed using the positive electrode paste of the present disclosure. The battery positive electrode of the present disclosure includes a current collector and a positive electrode composite layer bonded to the current collector, and the positive electrode composite layer is formed using the positive electrode paste of the present disclosure. In the battery positive electrode formed using the positive electrode paste of the present disclosure, the CNTs have good dispersibility in the positive electrode composite layer, so the coating resistance of the positive electrode composite layer is low.

[0064] The positive electrode paste of the present disclosure is applied to a current collector such as aluminum foil, and then dried to form a positive electrode composite layer. To increase the density of the positive electrode, compaction can be performed using a press. A die head, a cone reverse roll, a direct roll, a gravure roll, or the like can be used to apply the positive electrode paste. Drying after application can be performed using heating, airflow, infrared irradiation, or a combination thereof. The positive electrode can be pressed using a roll press or the like.

[0065] In one aspect, the present disclosure relates to a battery positive electrode including a positive electrode mixture layer, the positive electrode mixture layer including a positive electrode active material, a conductive material, a polymer, and a binder, wherein 50% or more by mass of the conductive material is carbon nanotubes, the polymer contains 60 to 99% by mass of vinyl alcohol units per molecule, and the content of the vinyl alcohol units in the positive electrode mixture layer is 17.0 to 60.0 parts by mass per 100 parts by mass of the carbon nanotubes. In the battery positive electrode of the present disclosure, the positive electrode mixture layer is formed using a positive electrode paste containing the polymer as a dispersant, so that the dispersibility of CNTs in the positive electrode mixture layer is good and therefore the coating resistance of the positive electrode mixture layer is low. [Example]

[0066] The present invention will be described in more detail below with reference to Production Examples, Examples and Comparative Examples.

[0067] <Production of dispersants> (Dispersant a1) A copolymerization reaction was carried out at 60°C using 100 parts of vinyl acetate as a polymerizable monomer, methanol as a solvent, and azobisisobutyronitrile as a polymerization initiator in a reaction vessel equipped with a thermometer, reflux condenser, nitrogen gas inlet tube, and stirrer. Unreacted monomers were then removed under reduced pressure to obtain a resin solution. A methanol solution of sodium hydroxide was then added to the resin solution to carry out a saponification reaction. The mixture was thoroughly washed and then dried in a hot air dryer. Finally, dispersant a1, a polyvinyl alcohol resin with a degree of polymerization of 200 and a degree of saponification of 99 mol% (vinyl alcohol units; PV-OH 98.1% by mass), was obtained. 6 parts of the resulting dispersant a1 (6 parts solids) were added to 962 parts of N-methyl-2-pyrrolidone (NMP) heated to 80°C and mixed to completely dissolve dispersant a1, yielding an NMP solution of dispersant a1. It took 6 hours for complete dissolution. The time required for complete dissolution was measured by mixing 6 parts of dispersant a1 with 962 parts of N-methyl-2-pyrrolidone (NMP) and heating the mixture to 80°C, and measuring the time required for the presence of undissolved aggregates to disappear when visually inspected.

[0068] By controlling the time of the copolymerization reaction and the saponification reaction described in the above (dispersant a1), dispersants a2 to a9 described in Table 1 were prepared. The time required for complete dissolution of the obtained dispersant in NMP is shown in Table 2.

[0069]

Table 1

[0070] <Preparation of CNT Slurry> As an example of the conductive material slurry, the following CNT slurries A1 to A13 were prepared by the following method.

[0071] (CNT Slurry A1) To 100 g (solid content 0.624 g) of an NMP solution of dispersant a1 (vinyl alcohol unit 98.1% by mass), 2 g of multi-walled carbon nanotubes (MWCNT, average diameter 12 nm, average length 40 μm) as a fibrous carbon nanostructure were added to obtain a crude dispersion. Then, the crude dispersion containing MWCNT and dispersant a1 was filled into a high-pressure homogenizer (manufactured by Birei Co., Ltd., product name "BERYU MINI") having a multi-stage pressure control device (multi-stage pressure reducer) that applies back pressure during dispersion, and the crude dispersion was dispersed at a pressure of 100 MPa. Specifically, while applying back pressure, a shear force was applied to the crude dispersion to disperse MWCNT, and CNT slurry A1 as a fibrous carbon nanostructure dispersion was obtained. The dispersion treatment was performed while circulating the dispersion by discharging it from the high-pressure homogenizer and injecting it back into the high-pressure homogenizer. This circulation was performed 20 times, and the discharge and injection speed of the dispersion was 30 g / min. The content of the vinyl alcohol unit in CNT slurry A1 was 30.6 parts with respect to 100 parts of the CNT content.

[0072] (CNT Slurries A2 to A5, A7, A8, A11, A12) CNT slurries A2 to A5, A7, A8, A11, and A12 were each prepared by the same operation as the preparation of CNT slurry A1 so as to have the compositions described in Table 2.

[0073] (CNT slurry A6) CNT slurry A6 was prepared in the same manner as CNT slurry A1, except that dispersant a5 was used as the dispersant and the amount of multi-walled carbon nanotubes MWCNTs (average diameter 12 nm, average length 40 μm) added was changed to 1 g.

[0074] (CNT slurry A9) To 100 g (solid content 0.624 g) of an NMP solution of dispersant a3 (vinyl alcohol unit 87.0 mass%), 2 g of multi-walled carbon nanotubes (MWCNT) (average diameter 12 nm, average length 40 μm) as fibrous carbon nanostructures and 0.3 g of 2-amino-1,3-propanediol, a nitrogen-containing organic compound, were added to obtain a crude dispersion. The crude dispersion containing MWCNT, dispersant a3, and the nitrogen-containing organic compound was then subjected to a dispersion treatment under the same conditions as for the preparation of (CNT slurry A1), to prepare CNT slurry A9.

[0075] (CNT slurry A10) 0.64 g of dispersant a3 (87.0 wt % vinyl alcohol units) was added to 94.3 g of N-methyl-2-pyrrolidone heated to 80°C and mixed until dispersant a3 was completely dissolved. After cooling to room temperature, 3.4 g of PVDF powder (KF Polymer L#7200, manufactured by Kureha Corporation) was added, and the mixture was then stirred for 5 minutes using a planetary centrifugal mixer (AR-100, manufactured by Thinky Corporation). 2.1 g of multi-walled carbon nanotubes (MWCNTs) (average diameter 12 nm, average length 40 μm) as fibrous carbon nanostructures was then added to obtain a crude dispersion. This was then dispersed under the same conditions as for the preparation of CNT Slurry A1, to prepare CNT Slurry A10. The content of PVDF (binder) in CNT Slurry A10 per 100 parts by weight of vinyl alcohol units was 611 parts by weight.

[0076] (CNT slurry A13) A crude dispersion was obtained by adding 10 g of MWCNTs (average diameter 12 nm, average length 40 μm) as fibrous carbon nanostructures to 190 g of an NMP solution of dispersant a6 (solid content 2 g).The crude dispersion containing MWCNTs and dispersant a6 was then subjected to a dispersion treatment under the same conditions as for the preparation of (CNT slurry A1), to prepare CNT slurry A13.

[0077] [Viscosity measurement] The viscosities of the CNT slurries A1 to A13 (25°C) prepared as described above were measured. Specifically, an Anton Paar MCR302 rheometer equipped with a parallel plate PP50 was used, and the shear rate was set in the range of 0.1 to 1000 (1 / s). The viscosities of the CNT slurries at a shear rate of 1 (1 / s) are shown in Table 2.

[0078] [Particle size measurement] The CNT slurries A1 to A13 prepared as described above were each diluted 500 times with NMP. Each was placed in a glass cell as the measurement target, and the cell was attached to a ZETASIZER Nano-S manufactured by Malvern Panalytical to measure the particle size of the CNTs when the temperature of the measurement target was 20°C.

[0079] [Preparation of positive electrode paste] (Preparation of positive electrode pastes B1 to B9, B11, and B12) 7.5 g of CNT slurries A1 to A9, A11, and A12, 4.3 g of NMP, and 3.0 g of PVDF (8%) NMP solution (KF Polymer L#7208, manufactured by Kureha Corporation) were weighed into a 50 ml sample bottle and mixed uniformly with a spatula. Then, 24.0 g of LCO (lithium cobalt oxide, manufactured by Nippon Chemical Industry Co., Ltd., CellSeed C-8hV) was added as the positive electrode active material, and the mixture was stirred again with a spatula until uniform. The mixture was further stirred for 5 minutes using a planetary centrifugal mixer (AR-100, manufactured by Thinky Corporation) to obtain positive electrode pastes B1 to B9, B11, and B12, respectively.

[0080] (Preparation of Positive Electrode Paste B10) 7.5 g of CNT slurry A10 and 4.3 g of NMP were weighed into a 50 ml sample bottle and mixed uniformly with a spatula. 24.0 g of LCO (lithium cobalt oxide, manufactured by Nippon Chemical Industry Co., Ltd., CellSeed C-8hV) was then added as the positive electrode active material, and the mixture was again mixed with a spatula until uniform. The mixture was further stirred for 5 minutes using a planetary centrifugal mixer (AR-100, manufactured by Thinky Corporation) to obtain positive electrode paste B10.

[0081] (Preparation of Positive Electrode Paste B13) 1.24 g of CNT slurry A13, 5 g of NMP, and 3.8 g of PVDF (8%) NMP solution (KF Polymer L#7208, manufactured by Kureha Corporation) were weighed into a 50 ml sample bottle and mixed uniformly with a spatula. 24.0 g of LCO (lithium cobalt oxide, manufactured by Nippon Chemical Industry Co., Ltd., CellSeed C-8hV) was then added as the positive electrode active material, and the mixture was stirred again with a spatula until uniform. The mixture was further stirred for 5 minutes using a planetary centrifugal mixer (AR-100, manufactured by Thinky Corporation) to obtain positive electrode paste B13.

[0082] In the positive electrode pastes B1 to B13, the contents (mass %) of the positive electrode active material, binder (PVDF), dispersant (polymer), and conductive material (CNT) are as follows, converted into solid content.

[0083] (mass ratio) Positive electrode pastes B1 to B5, B7 to B9, B11, and B12 (solid content: 63% by mass) Positive electrode active material: binder: dispersant: conductive material = 98.23:0.98:0.19:0.60 Positive electrode paste B6 (solid content: 63% by mass) Positive electrode active material: binder: dispersant: conductive material = 98.52:0.99:0.19:0.30 Positive electrode paste B10 (solid content: 68% by mass) Positive electrode active material: binder: dispersant: conductive material = 98.21:0.99:0.19:0.61 Positive electrode paste B13 (solid content: 72% by mass) Positive electrode active material: binder: dispersant: conductive material = 98.45:1.25:0.05:0.25

[0084] [Measurement of the coating resistance value of the positive electrode composite layer] The positive electrode paste prepared according to the above [Preparation of Positive Electrode Paste] was dropped onto a polyester film and uniformly coated with a 100 μm applicator. This coated polyester film was dried at 100 °C for 1 hour to obtain a positive electrode composite layer with a thickness of 40 μm. The coating resistance was measured at a limit voltage of 10 V using a Loresta-GP (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) equipped with a PSP probe. The results are shown in Table 2.

[0085] [Table 2]

[0086] As shown in Table 2, when the conductive material slurry contained a polymer with 60 to 99 mass% of vinyl alcohol units per molecule as a dispersant and the content of vinyl alcohol units in the conductive material slurry was 17.0 to 60.0 parts by mass per 100 parts by mass of CNT, the viscosity of the conductive material slurry was significantly low and the dispersibility of CNT was good. Furthermore, as can be seen from a comparison between Example 3 and Example 9 in Table 2, when the conductive material slurry contained a nitrogen-containing organic compound, the viscosity of the conductive material slurry was further reduced and the dispersibility of CNT was further improved.

[0087] As shown in Table 2, Examples 2 to 4, in which the content of vinyl alcohol units per molecule in the polymer is 83 to 92 mass %, are preferable compared to Examples 1 and 5 to 8 in terms of the balance between productivity, CNT dispersibility, and coating film resistance. [Industrial Applicability]

[0088] The conductive material slurry of the present disclosure has good dispersibility of CNTs, which results in a low viscosity of the conductive material slurry. When the conductive material slurry of the present disclosure is used to prepare a positive electrode paste, the viscosity of the positive electrode paste is also low, which can contribute to a low resistance of the positive electrode coating film.

Claims

1. A conductive material slurry containing a conductive material, a dispersant, and an amide-based polar organic solvent, the conductive material contains carbon nanotubes in an amount of 50 mass % or more; the dispersant is a polymer containing 75 to 99 mass % of vinyl alcohol units in one molecule, The conductive material slurry has a content of the vinyl alcohol unit of 17.0 to 60.0 parts by mass relative to 100 parts by mass of the carbon nanotubes.

2. Further containing a binder, 2. The conductive material slurry according to claim 1, wherein the content of the binder in the conductive material slurry is 150 to 700 parts by mass per 100 parts by mass of the content of the vinyl alcohol unit.

3. 3. The conductive material slurry according to claim 1, further comprising a compound having at least one primary, secondary or tertiary amino group in the molecule.

4. A battery positive electrode paste containing a positive electrode active material, a binder, a conductive material, a dispersant, and an amide-based polar organic solvent, the conductive material contains carbon nanotubes in an amount of 50 mass % or more; the dispersant is a polymer containing 75 to 99 mass % of vinyl alcohol units in one molecule, The content of the vinyl alcohol unit in the conductive material slurry is 17.0 to 60.0 parts by mass per 100 parts by mass of the carbon nanotubes.

5. The battery positive electrode paste according to claim 4, wherein the content of the binder in the battery positive electrode paste is 150 to 700 parts by mass per 100 parts by mass of the vinyl alcohol unit.

6. The battery positive electrode paste according to claim 4 or 5, wherein the mass ratio of the positive electrode active material to the vinyl alcohol unit in the battery positive electrode (the positive electrode active material / vinyl alcohol unit) is 350 to 900.

7. The battery positive electrode paste according to any one of claims 4 to 6, further comprising a compound having at least one primary, secondary, secondary, or tertiary amino group in the molecule.

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