Carbon nanotube-dispersed paste, method for producing carbon nanotube-dispersed paste, mixture paste for lithium ion secondary battery, electrode layer for non-aqueous electrolyte lithium ion secondary battery, electrode for non-aqueous electrolyte lithium ion secondary battery, and non-aqueous electrolyte lithium ion secondary battery

Abstract

The present invention addresses the problem of providing: a carbon nanotube-dispersed paste which exhibits excellent carbon nanotube dispersibility, has a low initial viscosity at time of production, and exhibits excellent storage stability at high temperatures (for example, 45°C or higher, and especially 50°C or higher); a method for producing said carbon nanotube-dispersed paste; a mixture paste for a lithium ion secondary battery, which contains said carbon nanotube-dispersed paste; an electrode layer for a non-aqueous electrolyte lithium ion secondary battery, in which said mixture paste for a lithium ion secondary battery is used; an electrode for non-aqueous electrolyte lithium ion secondary battery, in which said electrode layer for a non-aqueous electrolyte lithium ion secondary battery is used; and a non-aqueous electrolyte lithium ion secondary battery comprising at least said electrode for non-aqueous electrolyte lithium ion secondary battery. As a solution, the present invention provides a carbon nanotube-dispersed paste which contains a dispersed resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), and N-methyl-2-pyrrolidone (C). When the dispersed resin (A) is dissolved in the N-methyl-2-pyrrolidone and measured using a static light scattering method, the second virial coefficient at a liquid temperature of 50°C is 2.7×10-3 cm3·mol / g2 or less.

Description

Carbon nanotube dispersion paste, method for manufacturing carbon nanotube dispersion paste, composite paste for lithium-ion secondary batteries, electrode layer for non-aqueous electrolyte lithium-ion secondary batteries, electrode for non-aqueous electrolyte lithium-ion secondary batteries, and non-aqueous electrolyte lithium-ion secondary battery

[0001] The present invention relates to a carbon nanotube dispersion paste, a method for producing a carbon nanotube dispersion paste, a composite paste for lithium-ion secondary batteries, an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery, an electrode for a non-aqueous electrolyte lithium-ion secondary battery, and a non-aqueous electrolyte lithium-ion secondary battery. In particular, the present invention relates to a carbon nanotube dispersion paste with excellent dispersibility, initial viscosity, and storage stability at high temperatures, a method for producing the carbon nanotube dispersion paste, a composite paste for lithium-ion secondary batteries containing the carbon nanotube dispersion paste, an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery using the composite paste for lithium-ion secondary batteries, an electrode for a non-aqueous electrolyte lithium-ion secondary battery using the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery, and a non-aqueous electrolyte lithium-ion secondary battery comprising at least the electrode for a non-aqueous electrolyte lithium-ion secondary battery.

[0002] Carbon pigments such as carbon nanotubes and carbon black are widely incorporated into materials such as paints, coatings, sealants, filters, films, sheets, inks, cosmetic materials, magnet modifiers, encapsulants, device components, electronic equipment components, printed circuit boards, battery materials, and resin molded products, providing functions such as electrostatic coating properties, conductivity, electromagnetic shielding properties, and antistatic properties. When forming materials containing such carbon pigments, it is important to disperse the carbon pigment in the solvent at a high concentration and uniformly so that it can be easily applied, in order to streamline the production process. For this reason, there is a demand for carbon pigment dispersion pastes with excellent properties such as pigment dispersibility, storage stability, conductivity, coating properties, and finish. In designing carbon pigment dispersion pastes, it is important that components such as dispersion resins do not adversely affect the conductivity of the final product itself, such as the coating film, that the amount of solvent and dispersion resin used is reduced, that the energy used during drying can be reduced, and that the carbon pigment paste is highly concentrated and uniformly dispersed.

[0003] For example, Patent Documents 1 to 4 describe carbon nanotube dispersions containing a dispersant, carbon nanotubes, and a solvent. However, these carbon nanotube dispersions have shortcomings, such as poor dispersibility and inability to achieve uniform dispersion, high initial viscosity during manufacturing, and poor storage stability at high temperatures, and improvements have been needed.

[0004] Japanese Patent Publication No. 2019-192537, Japanese Patent Publication No. 2023-29200, Japanese Patent Publication No. 2024-000897, Japanese Patent Publication No. 2011-70908

[0005] One of the problems that the present invention aims to solve is a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, a carbon nanotube (B), and N-methyl-2-pyrrolidone (C), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C measured by static light scattering is 2.7 × 10⁻¹⁴. －３ cm ３ mol / g ２The objective is to provide a carbon nanotube dispersion paste, a method for producing the carbon nanotube dispersion paste, a composite paste for lithium-ion secondary batteries containing the carbon nanotube dispersion paste, an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery using the composite paste for lithium-ion secondary batteries, an electrode for a non-aqueous electrolyte lithium-ion secondary battery using the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery, and a non-aqueous electrolyte lithium-ion secondary battery comprising at least the electrode for a non-aqueous electrolyte lithium-ion secondary battery. One of the problems that the present invention aims to solve is to provide a carbon nanotube dispersion paste that has excellent dispersibility of carbon nanotubes, low initial viscosity during manufacturing, and excellent storage stability at high temperatures (e.g., 45°C or higher, particularly 50°C or higher). Furthermore, the invention aims to provide a method for producing the carbon nanotube dispersion paste, a composite paste for lithium-ion secondary batteries containing the carbon nanotube dispersion paste, an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery using the composite paste for lithium-ion secondary batteries, an electrode for a non-aqueous electrolyte lithium-ion secondary battery using the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery, and a non-aqueous electrolyte lithium-ion secondary battery comprising at least the electrode for a non-aqueous electrolyte lithium-ion secondary battery.

[0006] The present inventors, after diligent research to solve the above problems, have found a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, a carbon nanotube (B), and N-methyl-2-pyrrolidone (C), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering, is 2.7 × 10⁻⁶. －３ cm ３ mol / g ２The present inventors have found that the above problems can be solved by a carbon nanotube dispersion paste, a method for producing the carbon nanotube dispersion paste, a composite paste for a lithium ion secondary battery containing the carbon nanotube dispersion paste, an electrode layer for a non-aqueous electrolyte lithium ion secondary battery using the composite paste for a lithium ion secondary battery, an electrode for a non-aqueous electrolyte lithium ion secondary battery using the electrode layer for a non-aqueous electrolyte lithium ion secondary battery, and a non-aqueous electrolyte lithium ion secondary battery including at least the electrode for a non-aqueous electrolyte lithium ion secondary battery, and thus completed the present invention.

[0007] That is, the present invention relates to the following carbon nanotube dispersion paste, method for producing a carbon nanotube dispersion paste, composite paste for a lithium ion secondary battery, electrode layer for a non-aqueous electrolyte lithium ion secondary battery, electrode for a non-aqueous electrolyte lithium ion secondary battery, and non-aqueous electrolyte lithium ion secondary battery.

[0008] [Item 1] A carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), and N-methyl-2-pyrrolidone (C), wherein the second virial coefficient at a liquid temperature of 50 ° C. measured by dissolving the dispersion resin (A) in the N-methyl-2-pyrrolidone (C) and using the static light scattering method is 2.7 × 10 －３ cm ３ ·mol / g ２ or less. The above carbon nanotube dispersion paste. [Item 2] The second virial coefficient at a liquid temperature of 50 ° C. is -2.0 × 10 －３ cm ３ ·mol / g ２The carbon nanotube dispersion paste according to item 1, wherein the dispersion resin (A) has an aromatic ring and / or a heterocycle, according to item 1 or 2. [Item 4] The carbon nanotube dispersion paste according to any one of items 1 to 3, wherein the dispersion resin (A) has at least one polar functional group selected from the group consisting of amide groups, imide groups, hydroxyl groups, carboxyl groups, sulfonic acid groups, phosphate groups, amino groups and cyano groups, and the concentration of the polar functional group is 0.1 mmol / g or more and 8.5 mmol / g or less. [Item 5] The carbon nanotube dispersion paste according to any one of items 1 to 4, wherein the water content of the N-methyl-2-pyrrolidone (C) is 10,000 ppm or less. [Item 6] The carbon nanotube dispersion paste according to any one of items 1 to 5, which contains a polyvinylidene fluoride resin (D). [Item 7] The carbon nanotube dispersion paste according to any one of items 1 to 6, which contains a highly polar, low molecular weight component (E). [Item 8] A carbon nanotube dispersion paste according to any one of items 1 to 7, wherein the water content is 10,000 ppm or less. [Item 9] A method for producing a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group having 15 or more carbon atoms, a carbon nanotube (B), and N-methyl-2-pyrrolidone (C), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C measured by static light scattering is 2.7 × 10 －３ cm ３ mol / g ２ A method for producing the carbon nanotube dispersion paste using the following dispersion resin: [Item 10] A composite paste for lithium-ion secondary batteries containing a dispersion resin (A), carbon nanotubes (B), N-methyl-2-pyrrolidone (C), polyvinylidene fluoride resin (D), and electrode active material (F), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering, is 2.7 × 10 －３ cm ３ mol / g ２The following is the composite paste for lithium-ion secondary batteries: [Item 11] An electrode layer for a non-aqueous electrolyte lithium-ion secondary battery obtained by coating the composite paste for lithium-ion secondary batteries described in Item 10 onto a current collector. [Item 12] An electrode for a non-aqueous electrolyte lithium-ion secondary battery, wherein an electrode insulating portion is provided at the end or upper layer of the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery described in Item 11. [Item 13] A non-aqueous electrolyte lithium-ion secondary battery comprising at least a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, each having the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery described in Item 12.

[0009] The present invention provides a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, a carbon nanotube (B), and N-methyl-2-pyrrolidone (C), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering, is 2.7 × 10⁻⁶. －３ cm ３ mol / g ２ The present invention provides a carbon nanotube dispersion paste, a method for manufacturing the carbon nanotube dispersion paste, an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery using the lithium-ion secondary battery composite paste, an electrode for a non-aqueous electrolyte lithium-ion secondary battery using the non-aqueous electrolyte lithium-ion secondary battery electrode, and a non-aqueous electrolyte lithium-ion secondary battery comprising at least the electrode. The present invention provides a carbon nanotube dispersion paste that exhibits excellent dispersibility of carbon nanotubes, low initial viscosity during manufacturing, and excellent storage stability at high temperatures (e.g., 45°C or higher, particularly 50°C or higher), and further provides a method for manufacturing the carbon nanotube dispersion paste, an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery using the lithium-ion secondary battery composite paste, an electrode for a non-aqueous electrolyte lithium-ion secondary battery using the non-aqueous electrolyte lithium-ion secondary battery electrode, and a non-aqueous electrolyte lithium-ion secondary battery comprising at least the electrode.

[0010] The embodiments for carrying out the present invention will be described in detail below. It should be understood that the present invention is not limited to the following embodiments, but also includes various modifications that do not alter the essence of the invention. In this specification, carbon nanotubes may be referred to as "CNTs".

[0011] [Carbon Nanotube Dispersion Paste] The carbon nanotube dispersion paste of the present invention is a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), and N-methyl-2-pyrrolidone (C), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C measured by static light scattering is 2.7 × 10⁻⁶. －３ cm ３ mol / g ２ The following is a carbon nanotube dispersion paste. The second virial coefficient at a liquid temperature of 50°C is -2.0 × 10⁻⁶. －３ cm ３ mol / g ２ The above is also possible. The dispersion resin (A) may have an aromatic ring and / or a heterocycle. The dispersion resin (A) may have at least one polar functional group selected from the group consisting of an amide group, an imide group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphate group, an amino group, and a cyano group, and the concentration of the polar functional group may be 0.1 mmol / g or more and 8.5 mmol / g or less. The water content of the N-methyl-2-pyrrolidone (C) may be 10,000 ppm or less. The carbon nanotube dispersion paste of the present invention may contain a polyvinylidene fluoride resin (D). The carbon nanotube dispersion paste of the present invention may contain a highly polar, low molecular weight component (E). The carbon nanotube dispersion paste of the present invention may have a water content of 10,000 ppm or less. The following is a detailed explanation.

[0012] <Dispersion resin (A) having an alkyl group with 15 or more carbon atoms> The carbon nanotube dispersion paste of the present invention contains a dispersion resin (A) having an alkyl group with 15 or more carbon atoms. Dispersion resin (A) having an alkyl group with 15 or more carbon atoms is dissolved in N-methyl-2-pyrrolidone (C) and the second virial coefficient at a liquid temperature of 50°C measured by static light scattering method is 2.7 × 10⁻⁶ －３ cm ３ mol / g ２ The following applies: Dispersion resin (A) having an alkyl group with 15 or more carbon atoms has a second virial coefficient of -2.0 × 10 at a liquid temperature of 50°C. －３ cm ３ mol / g ２ The above is also acceptable. The dispersion resin (A) having an alkyl group with 15 or more carbon atoms may have an aromatic ring and / or a heterocycle. The dispersion resin (A) having an alkyl group with 15 or more carbon atoms may have at least one polar functional group selected from the group consisting of an amide group, an imide group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphate group, an amino group, and a cyano group, and the concentration of the polar functional group may be 0.1 mmol / g to 8.5 mmol / g.

[0013] (Resin) The resin constituting the dispersion resin (A) having an alkyl group with 15 or more carbon atoms is not particularly limited as long as it is a resin other than the polyvinylidene fluoride resin (D) described later. For example, one or more can be selected from the group consisting of acrylic resins, polyester resins, epoxy resins, polyether resins, alkyd resins, polyurethane resins, polyvinyl alcohol resins, polyvinyl acetal resins, polyvinylpyrrolidone resins, polyvinyl acetate resins, silicone resins, polycarbonate resins, chlorine resins, and composite resins thereof. In this invention, the acrylic resin includes methacrylic resin. In this invention, "(poly)X resin" means that in addition resins, the main monomer is X, and in condensation resins, the bond produced by the main condensation reaction is X.

[0014] The alkyl group having 15 or more carbon atoms in the dispersion resin (A) is not particularly limited. Preferably, it can be an alkyl group having 16 or more carbon atoms, more preferably an alkyl group having 18 or more carbon atoms, and even more preferably an alkyl group having 19 or more carbon atoms. The upper limit of the number of carbon atoms in the alkyl group is, for example, 30 or less, preferably 26 or less, more preferably 24 or less, and even more preferably 23 or less. The alkyl group having 15 or more carbon atoms may be a linear alkyl group or a branched alkyl group. A linear alkyl group is preferred. The dispersion resin (A) having an alkyl group having 15 or more carbon atoms becomes a resin with relatively bulky side chains, and it is presumed that the carbon nanotube dispersibility and storage stability will be improved due to steric repulsion.

[0015] The method for preparing a dispersion resin (A) having an alkyl group having 15 or more carbon atoms (a method for introducing an alkyl group having 15 or more carbon atoms into the dispersion resin) is not particularly limited. Examples include (co)polymerization reactions of monomers containing an alkyl group having 15 or more carbon atoms, modification reactions of polymers (resins), and / or addition reactions. Examples of polymerizable monomers containing an alkyl group having 15 or more carbon atoms include one or more selected from the group consisting of pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, eicosyl (meth)acrylate, behenyl (meth)acrylate, stearyl (meth)acrylamide, behenyl (meth)acrylamide, vinyl stearate, etc.

[0016] In a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, the content of the alkyl group with 15 or more carbon atoms is not particularly limited. Based on 100% by mass of all monomers constituting the dispersion resin (A) having an alkyl group with 15 or more carbon atoms, the content of polymerizable monomers containing an alkyl group with 15 or more carbon atoms can be, for example, 1% by mass or more, preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, 100% by mass or less, preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 60% by mass or less, for example, 1% by mass or more and 100% by mass or less, for example, 1% by mass or more and 90% by mass or less, for example, 1% by mass or more and 80% by mass or less. The following can be, for example, 1% by mass or more and 60% by mass or less, for example, 10% by mass or more and 100% by mass or less, for example, 10% by mass or more and 90% by mass or less, for example, 10% by mass or more and 80% by mass or less, for example, 10% by mass or more and 60% by mass or less, for example, 20% by mass or more and 100% by mass or less, for example, 20% by mass or more and 90% by mass or less, for example, 20% by mass or more and 80% by mass or less, for example, 20% by mass or more and 60% by mass or less, for example, 30% by mass or more and 100% by mass or less, for example, 30% by mass or more and 90% by mass or less, for example, 30% by mass or more and 80% by mass or less, for example, 30% by mass or more and 60% by mass or less.Furthermore, when reacting a resin with a compound having an alkyl group with 15 or more carbon atoms, the mass ratio of the compound to the total mass of the resin and the compound can be, for example, 1% by mass or more, preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, less than 100% by mass, preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 60% by mass or less, for example 1% by mass or more and less than 100% by mass, for example 1% by mass or more and 90% by mass or less, for example 1% by mass or more and 80% by mass It can be less than or equal to a certain mass, for example, 1% by mass or more and 60% by mass or less, for example, 10% by mass or more and less than 100% by mass, for example, 10% by mass or more and 90% by mass or less, for example, 10% by mass or more and 80% by mass or less, for example, 10% by mass or more and 60% by mass or less, for example, 20% by mass or more and less than 100% by mass, for example, 20% by mass or more and 90% by mass or less, for example, 20% by mass or more and 80% by mass or less, for example, 20% by mass or more and 60% by mass or less, for example, 30% by mass or more and less than 100% by mass, for example, 30% by mass or more and 90% by mass or less, for example, 30% by mass or more and 80% by mass or less, for example, 30% by mass or more and 60% by mass or less.

[0017] A dispersion resin (A) having an alkyl group with 15 or more carbon atoms may further contain an aromatic ring and / or a heterocycle. Examples of aromatic rings that may be included in the dispersion resin (A) having an alkyl group with 15 or more carbon atoms include a phenyl ring, a naphthalene ring, and an anthracene ring. These aromatic rings may have substituents such as alkyl groups, hydroxyl groups, carboxyl groups, sulfonic acid groups, phosphate groups, amino groups, and cyano groups. It is preferable to have an aromatic ring that does not contain a polycyclic aromatic ring. Examples of heterocycles that may be included in the dispersion resin (A) having an alkyl group with 15 or more carbon atoms include a ring in which, in addition to carbon atoms, one or more atoms other than carbon, such as oxygen, nitrogen, and sulfur, constitute the cyclic structure. The number of cyclic structures included in the heterocycle is preferably one or two, and more preferably one. As atoms other than carbon that constitute the ring, oxygen and / or nitrogen are preferred, and nitrogen is more preferred. If the dispersion resin (A) having an alkyl group with 15 or more carbon atoms is a resin with a heterocyclic ring, it is presumed that polarization will easily occur within the heterocyclic ring due to atoms other than carbon atoms, thereby causing the dispersion resin (A) having an alkyl group with 15 or more carbon atoms to strongly interact with carbon nanotubes. Furthermore, it is thought that the resin will have relatively bulky side chains, and that steric repulsion will improve carbon nanotube dispersibility and storage stability.

[0018] The method for introducing aromatic rings and / or heterocycles into a dispersion resin (A) having an alkyl group with 15 or more carbon atoms is not particularly limited. Examples include (co)polymerization reactions of monomers containing aromatic rings and / or monomers containing heterocycles, modification reactions and / or addition reactions of polymers (resins). Examples of polymerizable monomers containing aromatic rings include one or more selected from the group consisting of styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, vinylanthracene, benzyl (meth)acrylate, phenyl (meth)acrylate, vinyl benzoate, hydroxystyrene, etc. Polymerizable monomers that do not contain two or more aromatic rings are particularly preferred, and styrene is more preferred. Examples of polymerizable monomers containing heterocycles include one or more selected from the group consisting of 2- or 4-vinylpyridine, N-vinylimidazole, N-vinylpyrrole, N-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactam, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholindione, glycidyl (meth)acrylate, maleic anhydride, itaconic anhydride, and the like.

[0019] The content of aromatic rings and / or heterocycles in the dispersion resin (A) having an alkyl group with 15 or more carbon atoms is not particularly limited. Based on 100% by mass of all monomers constituting the dispersed resin (A) having alkyl groups with 15 or more carbon atoms, polymerizable monomers including aromatic rings and / or heterocycles can be, for example, 1% by mass or more, preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, less than 100% by mass, preferably 99% by mass or less, more preferably 95% by mass or less, for example 1% by mass or more and less than 100% by mass, for example 1% by mass or more and 99% by mass or less, for example 1% by mass or more and 95% by mass or less, for example 10% by mass or more and less than 100% by mass, for example 10% by mass or more and 99% by mass or less, for example 10% by mass or more and 95% by mass or less, for example 30% by mass or more and less than 100% by mass, for example 30% by mass or more and 99% by mass or less, for example 30% by mass or more and 95% by mass or less, for example 50% by mass or more and less than 100% by mass, for example 50% by mass or more and 99% by mass or less, for example 50% by mass or more and 95% by mass or less. Furthermore, when reacting a resin with a compound having an aromatic ring and / or a heterocycle, the mass ratio of the compound to the total mass of the resin and the compound can be, for example, 1% by mass or more, preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, less than 100% by mass, preferably 99% by mass or less, more preferably 95% by mass or less, for example 1% by mass or more and less than 100% by mass, for example 1% by mass or more and 99% by mass or less, for example 1% by mass or more and 95% by mass or less, for example 10% by mass or more and less than 100% by mass, for example 10% by mass or more and 99% by mass or less, for example 10% by mass or more and 95% by mass or less, for example 30% by mass or more and less than 100% by mass, for example 30% by mass or more and 99% by mass or less, for example 30% by mass or more and 95% by mass or less, for example 50% by mass or more and less than 100% by mass, for example 50% by mass or more and 99% by mass or less, for example 50% by mass or more and 95% by mass or less.

[0020] As a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, the following formula (1): CR is used, from the viewpoint of carbon nanotube dispersibility, initial viscosity, high-temperature storage stability, and finish quality. １ R２ =CR ３ R ４ ...(1) (In formula (1), R １ ~R ４ These may be the same or different, and are either a hydrogen atom or a monovalent organic group. Also, R １ and R ２ They may be bonded to each other to form a ring, R １ or R ２ And, R ３ or R ４ It is preferable to contain a vinyl (co)polymer (A1) obtained by polymerizing or copolymerizing a monomer component containing a polymerizable unsaturated group-containing monomer represented by ). In this invention, the (co)polymer includes both polymers obtained by polymerizing one type of monomer and copolymers obtained by copolymerizing two or more types of monomers.

[0021] The vinyl (co)polymer (A1) contains the following in its structure: formula (2): -CH ２ -CR ５ (-X)-...(2) (In formula (2), R ５ It is preferable that the structure unit represented by ) is a hydrogen or methyl group, and X is a functional group or a functional group-containing group. Examples of vinyl (co)polymer (A1) include one or more selected from the group consisting of hydroxyl group-containing vinyl (co)polymer, carboxyl group-containing vinyl (co)polymer, amide group-containing vinyl (co)polymer, sulfonic acid group-containing vinyl (co)polymer, phosphate group-containing vinyl (co)polymer, pyrrolidone group-containing vinyl (co)polymer, etc.

[0022] Examples of hydroxyl group-containing vinyl (co)polymers include one or more selected from the group consisting of polyhydroxyalkyl (meth)acrylate (such as polyhydroxyethyl (meth)acrylate), polyvinyl alcohol, vinyl alcohol-fatty acid vinyl copolymer, vinyl alcohol-ethylene copolymer, vinyl alcohol-(N-vinylformamide) copolymer, and copolymers of hydroxyalkyl (meth)acrylate and other polymerizable unsaturated monomers. The vinyl alcohol structural units in the (co)polymer can be obtained by polymerizing the monomer component containing fatty acid vinyl and then hydrolyzing it.

[0023] Examples of carboxyl group-containing vinyl (co)polymers include one or more selected from the group consisting of (meth)acrylic acid polymers, copolymers of (meth)acrylic acid and other polymerizable unsaturated monomers, vinyl benzoate polymers, and copolymers of vinyl benzoate and other polymerizable unsaturated monomers.

[0024] Examples of amide group-containing vinyl (co)polymers include one or more selected from the group consisting of (meth)acrylamide polymers and (meth)acrylamide derivatives (polymers such as 3-(meth)acrylamidopropyltrimethylammonium chloride, copolymers of (meth)acrylamide and other polymerizable unsaturated monomers, etc.).

[0025] Examples of sulfonic acid group-containing vinyl (co)polymers include one or more selected from the group consisting of polymers such as allyl sulfonic acid or styrene sulfonic acid, and copolymers of allyl sulfonic acid and / or styrene sulfonic acid with other polymerizable unsaturated monomers.

[0026] Examples of phosphate-containing vinyl (co)polymers include one or more selected from the group consisting of polymers of (meth)acryloyloxyalkyl acid phosphates, copolymers of (meth)acryloyloxyalkyl acid phosphates and other polymerizable unsaturated monomers, etc.

[0027] The vinyl (co)polymer (A1) may, in addition to the structural unit represented by formula (2), optionally contain structural units derived from copolymerizable polymerizable unsaturated group-containing monomers. Examples of copolymerizable polymerizable unsaturated group-containing monomers include vinyl carboxylate monomers such as vinyl formate, vinyl acetate, vinyl propionate, isopropenyl acetate, vinyl valerate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl versaticate, and vinyl pivalate; olefins such as ethylene, propylene, and butylene; methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dimethyl fumarate, dimethyl maleate, and maleate. One or more monomers selected from the group consisting of: ethylenically unsaturated carboxylate alkyl monomers such as diethyl acid and diisopropyl itaconate; vinyl ether monomers such as methyl vinyl ether, n-propyl vinyl ether, isobutyl vinyl ether, and dodecyl vinyl ether; vinyl halogenated monomers or vinylidene monomers such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; quaternary ammonium group-containing monomers; and vinyltrimethoxysilane and N-vinylformamide.

[0028] (Degree of Polymerization and Weight-Average Molecular Weight) The weight-average molecular weight of the dispersion resin (A) having alkyl groups with 15 or more carbon atoms is not particularly limited. For example, it can be 500 or more, preferably 1,000 or more, more preferably 2,000 or more, even more preferably 7,000 or more, and even more preferably 20,000 or more. For example, it can be 2,000,000 or less, preferably 1,000,000 or less, more preferably 500,000 or less, and even more preferably 100,000 or less. For example, 500 to 2,000,000, for example 500 to 1,000,000, for example 500 to 500,000, for example 500 to 100,000, for example 1,000 to 2,000. It can be expressed as ,000 or less, for example 1,000 or more and 1,000,000 or less, for example 1,000 or more and 500,000 or less, for example 1,000 or more and 100,000 or less, for example 2,000 or more and 2,000,000 or less, for example 2,000 or more and 1,000,000 or less, for example 2,000 or more and 500,000 or less, for example 2,000 or more and 100,000 or less, for example 7,000 or more and 2,000,000 or less, for example 7,000 or more and 1,000,000 or less, for example 7,000 or more and 500,000 or less, for example 7,000 or more and 100,000 or less.

[0029] Unless otherwise specified, the weight-average molecular weight can be obtained by converting the retention time (retention volume) measured using gel permulation chromatography (GPC) to the molecular weight of polystyrene using the retention time (retention volume) of standard polystyrene with a known molecular weight measured under the same conditions. Specifically, the weight-average molecular weight can be obtained by using "HLC8120GPC" (product name, manufactured by Tosoh Corporation) as the gel permulation chromatograph, and four columns: "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (product names, all manufactured by Tosoh Corporation), under the conditions of tetrahydrofuran mobile phase, measurement temperature of 40°C, flow rate of 1 mL / min, and detector RI.

[0030] (Polymerization Method) The method for synthesizing the dispersion resin (A) having an alkyl group with 15 or more carbon atoms is not particularly limited. In the case of addition resins, it can be polymerized and synthesized by a known addition polymerization reaction, and in the case of condensation resins, it can be polymerized and synthesized by a known condensation polymerization reaction. Among these, when a vinyl (co)polymer (A1) is used as the dispersion resin (A) having an alkyl group with 15 or more carbon atoms, the method for synthesizing the vinyl (co)polymer (A1) (polymerization method) is not particularly limited. A method known in itself can be used as the polymerization method for the vinyl (co)polymer. For example, solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc. can be used. In the present invention, solution polymerization is preferred. Solution polymerization may be continuous polymerization or batch polymerization. The monomer components may be charged all at once, charged in parts, or added continuously or intermittently. The polymerization reaction temperature is not particularly limited, but for example, it can be in the range of 30°C to 200°C.

[0031] The polymerization initiator used in the solution polymerization of vinyl (co)polymer (A1) is not particularly limited. For example, one or more selected from the group consisting of azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), and azobis-4-methoxyvaleronitrile; peroxides such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; peroxycarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; and perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and t-butyl peroxyneodecanate.

[0032] A dispersion resin (A) having an alkyl group with 15 or more carbon atoms can be converted into a solid or a resin solution in any solvent by desolvation and / or solvent substitution after the synthesis is complete. Desolvation can be carried out by heating under atmospheric pressure, or by desolvation under reduced pressure. Solvent substitution can be carried out by adding a substitution solvent before, during, or after desolvation. In the present invention, it is preferable to dissolve the dispersion resin (A) having an alkyl group with 15 or more carbon atoms in a resin solution and then mix and disperse it with other components.

[0033] When a dispersion resin (A) having an alkyl group with 15 or more carbon atoms has an aromatic ring and / or a heterocycle, if the resin is to be dissolved from a solid state, it is preferable to dissolve it by mixing it with a solvent whose liquid temperature is 40°C or higher, preferably 50°C or higher, and for example, 100°C or lower, preferably 80°C or lower, from the viewpoint of solubility in the solvent. Here, the liquid temperature refers to the temperature of the solvent or resin solution at the time of dissolution. When dissolving the resin, the solid dispersion resin (A) having an alkyl group with 15 or more carbon atoms may be mixed with a solvent whose liquid temperature is 40°C or higher and dissolved, or the solid dispersion resin (A) having an alkyl group with 15 or more carbon atoms may be mixed with a solvent and then heated to a temperature of 60°C or higher. When dissolving the resin, components other than the dispersion resin (A) having an alkyl group with 15 or more carbon atoms and the solvent may be included. The solvent used for dissolving the resin is not particularly limited. One or more solvents can be used as appropriate. Of these, N-methyl-2-pyrrolidone (C), which will be described later, is preferred. It is preferable to cool the resin solution, which has been dissolved in resin, to a predetermined temperature in the range of 10°C to 40°C. From the viewpoint of preventing precipitation, it is preferable that the cooling rate, defined by the following formula: Cooling rate = (Solution temperature at the start of cooling - Solution temperature at the end of cooling) / Cooling time, be 0.5°C / min or more, preferably 1°C / min or more.

[0034] (Second Virial Coefficient) In the present invention, the dispersion resin (A) having an alkyl group with 15 or more carbon atoms is dissolved in N-methyl-2-pyrrolidone (C), and the second virial coefficient measured by static light scattering at a liquid temperature of 50°C is 2.7 × 10⁻¹⁰. －３ cm ３ mol / g ２ The following is preferred: Preferably 1.0 × 10 －３ cm ３ mol / g ２ More preferably, 0.0 × 10 －３ cm ３ mol / g ２ The following is possible. In the present invention, the lower limit of the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering in a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, is not particularly limited. Preferably, -2.0 × 10 －３ cm ３ mol / g ２ , more preferably -1.0 × 10 －３ cm ３ mol / g ２ This can be achieved. In the present invention, a dispersion resin (A) having an alkyl group with 15 or more carbon atoms is dissolved in N-methyl-2-pyrrolidone (C), and the range of the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering, is, for example, -2.0 × 10 －３ cm ３ mol / g ２ The above 2.7 x 10 －３ cm ３ mol / g ２ For example, -2.0 × 10 －３ cm ３ mol / g ２ The above 1.0 x 10 －３ cm ３ mol / g ２ For example, -2.0 × 10 －３ cm ３ mol / g ２ The above 0.0 × 10 －３ cm ３ mol / g ２ For example, -1.0 × 10 －３ cm ３ mol / g２ Above 2.7×10 －３ cm ３ ·mol / g ２ Hereinafter, for example, -1.0×10 －３ cm ３ ·mol / g ２ Above 1.0×10 －３ cm ３ ·mol / g ２ Hereinafter, for example, -1.0×10 －３ cm ３ ·mol / g ２ Above 0.0×10 －３ cm ３ ·mol / g ２ It can be set as follows.

[0035] In the present invention, the second virial coefficient can be obtained, for example, by dissolving a dispersion resin (A) having an alkyl group with 15 or more carbon atoms in N-methyl-2-pyrrolidone (C) as a solvent and performing static light scattering measurement at a temperature of 50°C. Details include the methods shown in the examples described later.

[0036] The second virial coefficient is a parameter indicating the degree of affinity between the dispersion resin (A) having an alkyl group with 15 or more carbon atoms and N-methyl-2-pyrrolidone (C) (solvent). The larger the numerical value, the better the affinity (compatibility). In the present invention, the second virial coefficient at a liquid temperature of 50°C obtained by dissolving the dispersion resin (A) having an alkyl group with 15 or more carbon atoms in N-methyl-2-pyrrolidone (C) and measuring by the static light scattering method is usually 2.7×10 －３ cm ３ ·mol / g ２ Hereinafter (preferably 1.0×10 －３ cm ３ ·mol / g ２ Hereinafter, more preferably 0.0×10 －３ cm ３ ·mol / g ２By setting the range to the following, the affinity between the dispersion resin and the solvent at high temperatures (50°C) is reduced, allowing the dispersion resin to adsorb onto carbon nanotubes, thereby improving the stability of the dispersion paste. Therefore, the dispersibility of the carbon nanotube dispersion paste (dispersion causes the paste temperature to rise) or the storage stability at high temperatures is improved. Furthermore, dispersion resins with excellent various properties tend to have poor solubility in solvents, especially at room temperature (e.g., 20°C) (resin solution is cloudy), which indicates a tendency to adsorb onto carbon nanotubes without dissolving in the solvent. Also, if the second virial coefficient becomes too low, the affinity (compatibility) between the dispersion resin and the solvent becomes too poor, so for example, preferably -2.0 × 10 －３ cm ３ mol / g ２ More preferably -1.0 × 10 －３ cm ３ mol / g ２ The above is preferable. For example, -2.0 × 10 －３ cm ３ mol / g ２ The above is 2.7 x 10 －３ cm ３ mol / g ２ By setting the following range, the carbon nanotube dispersion paste of the present invention can be made to have excellent carbon nanotube dispersibility, low initial viscosity during manufacturing, and excellent storage stability at high temperatures (e.g., 45°C or higher, especially 50°C or higher).

[0037] (Polar functional group) The dispersion resin (A) having an alkyl group with 15 or more carbon atoms may have at least one polar functional group selected from the group consisting of amide group, imide group, hydroxyl group, carboxyl group, sulfonic acid group, phosphate group, amino group and cyano group, and the concentration of the polar functional group may be 0.1 mmol / g or more and 8.5 mmol / g or less.

[0038] The amide group is, for example, usually a primary amide group or a secondary amide group, with a secondary amide group being preferred. The amino group is, for example, usually a secondary amino group or a tertiary amino group, with a tertiary amino group being preferred. In the present invention, the carboxyl group may be a carboxylate salt, the sulfonic acid group may be a sulfonate salt, the phosphate group may be a phosphate salt, and the amino group may be an amine salt. The polar functional group is preferably at least one of an amide group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphate group, an amino group, and a cyano group, more preferably at least one of an amide group, a carboxyl group, a hydroxyl group, an amino group, and a cyano group, even more preferably at least one of an amide group, an amino group, and a cyano group, and particularly preferably at least one of a secondary amide group, a tertiary amino group, and a cyano group.

[0039] The concentration of polar functional groups is 0.1 mmol / g or more and 8.5 mmol / g or less. Preferably it can be 0.2 mmol / g or more, more preferably 0.3 mmol / g or more, even more preferably 0.4 mmol / g or more, preferably 6.0 mmol / g or less, more preferably 4.0 mmol / g or less, even more preferably 2.0 mmol / g or less, for example 0.1 mmol / g or more and 6.0 mmol / g or less, for example 0.1 mmol / g or more and 4.0 mmol / g or less, for example 0.1 mmol / g or more and 2.0 mmol / g or less, for example 0.2 mmol / g or more and 8.5 mmol / g or less, for example 0.2 mmol / g or more and 8.5 mmol / g or less, for example 0.1 mmol / g or more and 8.5 mmol / g or less, for example 0.1 mmol / g or more and 8.5 mmol / g or less.

[0040] (Content of dispersion resin (A) having alkyl groups with 15 or more carbon atoms) The content of dispersion resin (A) having alkyl groups with 15 or more carbon atoms in the carbon nanotube dispersion paste is not particularly limited. Based on 100% by mass of the total amount of the carbon nanotube dispersion paste, it can be, for example, 0.1% by mass or more, preferably 0.4% by mass or more, more preferably 0.7% by mass or more, and can be, for example, 10% by mass or less, preferably 5% by mass or less, and more preferably 2% by mass or less. Also, based on 100% by mass of the total amount of solids in the carbon nanotube dispersion paste, it can be, for example, 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and can be, for example, 40% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less.

[0041] Furthermore, the content of the dispersion resin (A) having an alkyl group with 15 or more carbon atoms in the carbon nanotube dispersion paste can be, for example, 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, based on the carbon nanotube (B) content of 100% by mass, and can be, for example, 150% by mass or less, preferably 120% by mass or less, more preferably 80% by mass or less.

[0042] <Carbon Nanotubes (B)> The carbon nanotube dispersion paste of the present invention contains carbon nanotubes (B). Carbon nanotubes (B) are not particularly limited. One or more single-walled carbon nanotubes and multi-walled carbon nanotubes can be used. In particular, multi-walled carbon nanotubes are preferred due to their viscosity, conductivity, and cost.

[0043] The average outer diameter of the carbon nanotubes (B) is, for example, 1 nm or more, preferably 3 nm or more, more preferably 5 nm or more, and for example, 30 nm or less, preferably 28 nm or less, more preferably 25 nm or less.

[0044] The average length of the carbon nanotubes (B) is, for example, 0.1 μm or more, preferably 1 μm or more, more preferably 5 μm or more, and for example, 100 μm or less, preferably 80 μm or less, more preferably 60 μm or less.

[0045] Carbon nanotubes (B) showed a Raman spectrum of 1560 cm⁻¹. －１ More than 1600cm －１ The maximum peak intensity within the following range is G, 1310 cm. －１ 1350cm or more －１ The G / D ratio, where D is the maximum peak intensity within the following range, is, for example, 0.1 or more, preferably 0.4 or more, more preferably 0.6 or more, and for example, 5.0 or less, preferably 3.0 or less, more preferably 1.0 or less. A G / D ratio within the range of 0.1 to 5.0 is preferable because it tends to have high conductivity due to fewer defects and crystal interfaces on the carbon surface. The Raman spectrum of carbon nanotube (B) can be obtained, for example, by placing the carbon nanotube in a Raman microscope (manufactured by Horiba, Ltd., product name "XploRA") and measuring it using a laser wavelength of 532 nm.

[0046] The BET specific surface area of ​​carbon nanotubes (B) is typically 100 m² due to the relationship between viscosity and conductivity. ２ / g or more, preferably 130m ２ / g or more, more preferably 160m ２ It is 1 / g or more, and usually 800m ２ / g or less, preferably 600m ２ / g or less, more preferably 400m ２ It is less than / g. The BET specific surface area of ​​carbon nanotubes (B) can be calculated by the BET method using nitrogen adsorption measurement. Specifically, for example, in accordance with JIS Z8830:2013, the BET specific surface area (m²) can be calculated using a specific surface area measuring device (BERSORP-MAX (Microtrac-Bell Co., Ltd.)). ２ It can measure ( / g).

[0047] The amount of acidic groups in the carbon nanotube (B) described above is usually 0.01 mmol / g or more, preferably 0.02 mmol / g or more, and usually 1.0 mmol / g or less, preferably 0.5 mmol / g or less, more preferably 0.2 mmol / g or less, and even more preferably 0.1 mmol / g or less, from the viewpoint of dispersibility and storability. If the amount of acidic groups is 0.01 mmol / g or more, dispersibility is good, and if it is 1.0 mmol / g or less, storability is good.

[0048] The above-mentioned acidic groups can be imparted to carbon nanotubes by acid treatment as described below.

[0049] (Acid Treatment Method) The acid treatment method is not particularly limited as long as the carbon nanotubes can be brought into contact with an acid, but a method of immersing the carbon nanotubes in an acid treatment solution (an aqueous solution of acid) is preferred. The acid contained in the acid treatment solution is not particularly limited, but for example, one or more selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, etc. Among these, nitric acid and / or sulfuric acid are preferred. The amount of acidic groups in the carbon nanotubes can be adjusted by the concentration of the acid treatment solution, temperature, treatment time, etc.

[0050] After acid treatment, excess acid components adhering to the surface can be removed by the washing method described later to obtain acid-treated carbon nanotubes. There are no particular limitations on the method for washing the acid-treated carbon nanotubes, but washing with water is preferred. For example, carbon nanotubes can be recovered from the acid-treated carbon nanotubes by a known method such as filtration, and then the carbon nanotubes can be washed with water. After the above washing, if necessary, the water adhering to the surface can be removed by drying to obtain the acid-treated carbon nanotubes.

[0051] The carbon nanotube (B) content in the carbon nanotube dispersion paste is not particularly limited. Based on 100% by mass of the total amount of the carbon nanotube dispersion paste, it can be, for example, 0.05% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and can be, for example, 10% by mass or less, preferably 7% by mass or less, and more preferably 5% by mass or less. Also, based on 100% by mass of the total amount of solids in the carbon nanotube dispersion paste, it can be, for example, 30% by mass or more, preferably 40% by mass or more, more preferably 50% by mass or more, and can be, for example, 90% by mass or less, preferably 85% by mass or less, and more preferably 80% by mass or less.

[0052] <N-methyl-2-pyrrolidone (C)> The carbon nanotube dispersion paste of the present invention contains N-methyl-2-pyrrolidone (C). The N-methyl-2-pyrrolidone (C) is not particularly limited. A commercially available N-methyl-2-pyrrolidone reagent (solvent) can be used, and recycled N-methyl-2-pyrrolidone can also be used. Recycled N-methyl-2-pyrrolidone is obtained by recovering a used product and purifying it as necessary. For example, N-methyl-2-pyrrolidone recovered during heating and drying when forming a composite layer on a current collector to create battery electrodes using a composite paste for lithium-ion secondary batteries containing the carbon nanotube dispersion paste of the present invention can be used. Furthermore, the term "using recycled products" refers to the fact that the carbon nanotube dispersion paste according to the present invention contains, for example, 5% by mass or more, preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more of recycled N-methyl-2-pyrrolidone (C). In the present invention, using recycled N-methyl-2-pyrrolidone is advantageous in terms of waste reduction, environmental compliance, and / or raw material cost reduction.

[0053] The water content of N-methyl-2-pyrrolidone (C) is preferably less than 10,000 ppm, more preferably less than 7,500 ppm, even more preferably less than 5,000 ppm, particularly preferably less than 2,500 ppm, most preferably less than 1,000 ppm, and can be, for example, 100 ppm or more, preferably 200 ppm or more, and more preferably 500 ppm or more. If the water content of N-methyl-2-pyrrolidone (C) is 10,000 ppm or more, the carbon nanotube dispersion paste and the lithium-ion secondary battery composite paste containing the carbon nanotube dispersion paste may become highly viscous (thickened) or gel. The water content of N-methyl-2-pyrrolidone (C) can be measured by Karl Fischer coulometric titration. For example, a Karl Fischer moisture meter (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name "MKC-610") can be used to measure moisture content by setting the moisture vaporizer (manufactured by Kyoto Electronics Co., Ltd., product name "ADP-611") equipped in the device to a temperature of 130°C.

[0054] The amine component content of N-methyl-2-pyrrolidone (C) is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less. The amine component of N-methyl-2-pyrrolidone (C) originates from amine components contained as impurities, and also from amine components contained in the lithium-ion secondary battery composite paste in the recycled N-methyl-2-pyrrolidone. Examples of amine components contained in N-methyl-2-pyrrolidone (C) include one or more of the amine components in the high-polarity low-molecular-weight component (E) described later. The amine component content of N-methyl-2-pyrrolidone (C) can be quantified by general analysis such as ion chromatography-mass spectrometry (IC-MS). The content can be quantified by creating a calibration curve in advance for the peaks of amine species that are expected to be present. By limiting the amine component content of N-methyl-2-pyrrolidone (C) to 1% by mass or less, it becomes possible to maintain a consistent viscosity and thickening tendency of the carbon nanotube dispersion paste, which can be affected by differences in manufacturing lots of N-methyl-2-pyrrolidone, and also solve the problem of odor caused by amine compounds.

[0055] When recycled N-methyl-2-pyrrolidone (C) is used, and the carbon nanotube dispersion paste of the present invention contains a highly polar, low molecular weight component (E) described later, it is necessary to remove the highly polar, low molecular weight component (E) when reusing N-methyl-2-pyrrolidone (C) as a recycled product. Therefore, when the boiling point of N-methyl-2-pyrrolidone (C) is (Xc)°C and the boiling point of the highly polar, low molecular weight component (E) is (Xe)°C, it is preferable that (Xc)-10 > (Xe), and (Xc)-15 > (Xe) from the viewpoint of distillation (removal of the highly polar, low molecular weight component (E)). Furthermore, it is preferable that the highly polar, low molecular weight component (E) includes an amine compound (E1).

[0056] The content of N-methyl-2-pyrrolidone (C) in the carbon nanotube dispersion paste is not particularly limited. Based on 100% by mass of the total amount of the carbon nanotube dispersion paste, it can be, for example, 40% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and can be, for example, 99% by mass or less, preferably 98% by mass or less, and more preferably 97% by mass or less. Furthermore, the content of N-methyl-2-pyrrolidone (C) in the carbon nanotube dispersion paste can be such that the solid content of the carbon nanotube dispersion paste is, for example, 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and can be such that the solid content is 60% by mass or less, preferably 40% by mass or less, and more preferably 20% by mass or less.

[0057] <Polyvinylidene fluoride resin (D)> The carbon nanotube dispersion paste of the present invention may contain polyvinylidene fluoride resin (D). Polyvinylidene fluoride resin is a resin intended for forming electrode layers and can be included in the carbon nanotube dispersion paste of the present invention as needed. Polyvinylidene fluoride resin (D) is an essential component in the composite paste for lithium-ion secondary batteries described later.

[0058] As the polyvinylidene fluoride resin (D), polyvinylidene fluoride (a homopolymer of vinylidene fluoride) can be used. Modified polyvinylidene fluoride (D1), which has undergone various modifications, can also be suitably used, and it is preferable that it has polar functional groups from the viewpoint of adhesion to the substrate. Examples of polar functional groups include one or more selected from the group consisting of carboxyl groups, carboxylic acid bases, sulfonic acid groups, sulfonic acid bases, hydroxyl groups, amino groups, phosphate groups, phosphate bases, silanol groups, cyano groups, pyrrolidone groups, etc. The polyvinylidene fluoride resin (D) may consist of only one type, or it may be composed of two or more types of polyvinylidene fluoride resins.

[0059] The weight-average molecular weight of the polyvinylidene fluoride resin (D) is, from the viewpoint of adhesion to the substrate, reinforcement of film properties, and solvent resistance, for example, 100,000 or more, preferably 500,000 or more, more preferably 650,000 or more, and for example, 3 million or less, preferably 2 million or less.

[0060] The polyvinylidene fluoride resin (D) described above can be used in the form of a resin solution. The step of converting the polyvinylidene fluoride resin (D) from a solid state into a resin solution preferably includes a step of mixing and dissolving it in a solvent with a liquid temperature of 40°C or higher (preferably 60°C or higher, more preferably 80°C or higher, for example 200°C or lower, preferably 100°C or lower) in advance, from the viewpoint of solubility in the solvent. Here, the liquid temperature refers to the temperature of the solvent or resin solution at the time of dissolution. As a method for preparing a resin solution of polyvinylidene fluoride resin (D), for example, solid polyvinylidene fluoride resin (D) may be mixed and dissolved in a solvent with a liquid temperature of 40°C or higher in advance, or solid polyvinylidene (E) may be mixed with a solvent and then heated to a temperature of 40°C or higher. One type of solvent may be used alone or two or more types may be used in combination. Furthermore, when preparing a resin solution of polyvinylidene fluoride (D), it is preferable to heat the resin solution to a temperature of 40°C or higher and then cool it to a predetermined temperature of 10°C or higher but less than 40°C. When cooling, it is preferable from the viewpoint of preventing the precipitation of polyvinylidene fluoride (D) that the cooling rate, defined by the following formula: Cooling rate (°C / min) = (Solution temperature at the start of cooling - Solution temperature at the end of cooling) / Cooling time, be 0.5°C / min or higher (preferably 1°C / min or higher).

[0061] As the solvent, the aforementioned N-methyl-2-pyrrolidone can be used, and other solvents listed in the section on other components described later can also be used. Furthermore, the resin solution of polyvinylidene fluoride resin (D) may contain components other than polyvinylidene fluoride resin (D) and the solvent.

[0062] When the carbon nanotube dispersion paste contains polyvinylidene fluoride resin (D), the content is, for example, 10.0% by mass or more, preferably 30.0% by mass or more, more preferably 40.0% by mass or more, based on 100% by mass of the solid content of the carbon nanotube dispersion paste, for example, 99.0% by mass or less, preferably 80.0% by mass or less, more preferably 60.0% by mass or less. Also, based on 100% by mass of the total amount of the carbon nanotube dispersion paste, the content is, for example, 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1% by mass or more, for example, 10% by mass or less, preferably 7% by mass or less, more preferably 5% by mass or less.

[0063] <High-Polarity Low-Molecular-Weight Component (E)> The carbon nanotube dispersion paste of the present invention may contain a high-polarity low-molecular-weight component (E). The high-polarity low-molecular-weight component (E) is a component that improves the wettability of carbon nanotubes and / or the storage stability of the carbon nanotube dispersion paste. Examples of the high-polarity low-molecular-weight component (E) include one or more selected from organic base components, inorganic base components, organic acid components, and inorganic acid components. The molecular weight of the high-polarity low-molecular-weight component (E) is less than 1200, preferably 1000 or less, more preferably 800 or less, even more preferably 500 or less, even more preferably 350 or less, and particularly preferably 250 or less.

[0064] Examples of organic base components include one or more amine compounds (E1). Examples of amine compounds (E1) include ammonia, primary amines, secondary amines, tertiary amines, etc.

[0065] Examples of primary amines include ethylamine, n-propylamine, sec-propylamine, n-butylamine, sec-butylamine, i-butylamine, tert-butylamine, pentylamine, hexylamine, heptylamine, octylamine, decylamine, laurylamine, mystyrylamine, 1,2-dimethylhexylamine, 3-pentylamine, 2-ethylhexylamine, allylamine, aminoethanol, 1-aminopropanol, 2-aminopropanol, aminobutanol, aminopentanol, aminohexanol, 3-ethoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, 3-butoxypropylamine, 3-isobutoxypropylamine, 3-(2-ethylhexyloxy)propylamine, aminocyclopentane, aminocyclohexane, aminonorbornene, aminomethylcyclohexane, aminobenzene, benzylamine, phenethylamine, α-phenylethylamine, naphthylamine, Primary monoamines such as furfurylamine; ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,2-diaminobutane, 1,3-diaminobutane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, dimethylaminopropylamine, diethylaminopropylamine, bis-(3-aminopropyl) ether, 1,2-bis-(3-aminopropoxy)ethane, 1,3-bis -(3-aminopropoxy)-2,2'-dimethylpropane, aminoethylethanolamine, 1,2-bisaminocyclohexane, 1,3-bisaminocyclohexane, 1,4-bisaminocyclohexane, 1,3-bisaminomethylcyclohexane, 1,4-bisaminomethylcyclohexane, 1,3-bisaminoethylcyclohexane, 1,4-bisaminoethylcyclohexane, 1,3-bisaminopropylcyclohexane, 1,4-bisaminopropylcyclohexane, hydrogenated 4,4'-Diaminodiphenylmethane, 2-Aminopiperidine, 4-Aminopiperidine, 2-Aminomethylpiperidine, 4-Aminomethylpiperidine, 2-Aminoethylpiperidine, 4-Aminoethylpiperidine, N-Aminoethylpiperidine, N-Aminopropylpiperidine, N-Aminoethylmorpholine, N-Aminopropylmorpholine, Isophoronediamine, Menthanediamine, 1,4-Bisaminopropylpiperazine, o-Phenylenediamine, m-Phenylenediamine, p-Phenylenediamine, 2,4-Tolylenediamine, 2,6-Tolylenediamine, 2,4-Toluenediamine, m-Aminobenzylamine, 4-Chloro-o-Phenylenediamine, Tetrachloro-p-Xylylenediamine, 4-Methoxy-6-methyl-m-Phenylenediamine, m-Xylylenediamine, p-Xylylenediamine, 1,5-Naphthalenediamine, 2,6-Naphthalenediamine, Benzidine, 4,4'-Bi Su(o-toluidine), dianisidine, 4,4'-diaminodiphenylmethane, 2,2-(4,4'-diaminodiphenyl)propane, 4,4'-diaminodiphenyl ether, 4,4'-thiodianiline, 4,4'-diaminodiphenylsulfone, 4,4'-diaminoditolylsulfone, methylenebis(o-chloroaniline), 3,9-bis(3-aminopropyl)2,4,8,10-tetraoxaspiro[5,5]undecane, diethylenetri One or more examples include mine, iminobispropylamine, methyliminobispropylamine, bis(hexamethylene)triamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, N-aminoethylpiperazine, N-aminopropylpiperazine, 1,4-bis(aminoethylpiperazine), 1,4-bis(aminopropylpiperazine), 2,6-diaminopyridine, and bis(3,4-diaminophenyl)sulfone.

[0066] Examples of secondary amines include secondary monoamines such as diethylamine, dipropylamine, di-n-butylamine, di-sec-butylamine, diisobutylamine, di-n-pentylamine, di-3-pentylamine, dihexylamine, dioctylamine, di(2-ethylhexyl)amine, methylhexylamine, diallylamine, pyrrolidine, piperidine, 2,4-lupetidine, 2,6-lupetidine, 3,5-lupetidine, diphenylamine, N-methylaniline, N-ethylaniline, dibenzylamine, methylbenzylamine, dinaphthylamine, pyrrole, indoline, indole, morpholine, etc.; N,N'-dimethylethylenediamine, N,N'-dimethyl-1,2-diaminopropane, N,N'-dimethyl-1,3-diaminopropane, N,N'-dimethyl-1,2-diaminobutane, N,N'-dimethyl-1,3-diaminobutane, N N'-dimethyl-1,4-diaminobutane, N,N'-dimethyl-1,5-diaminopentane, N,N'-dimethyl-1,6-diaminohexane, N,N'-dimethyl-1,7-diaminoheptane, N,N'-diethylethylenediamine, N,N'-diethyl-1,2-diaminopropane, N,N'-diethyl-1,3-diaminopropane, N,N'-diethyl-1,2-diaminobutane, N,N'-diethyl-1,3-diaminobutane One or more examples include minobutane, N,N'-diethyl-1,4-diaminobutane, N,N'-diethyl-1,6-diaminohexane, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, homopiperazine, 1,1-di-(4-piperidyl)methane, 1,2-di-(4-piperidyl)ethane, 1,3-di-(4-piperidyl)propane, and 1,4-di-(4-piperidyl)butane.

[0067] Examples of tertiary amines include trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, tri-1,2-dimethylpropylamine, tri-3-methoxypropylamine, tri-n-butylamine, tri-iso-butylamine, tri-sec-butylamine, tri-pentylamine, tri-3-pentylamine, tri-n-hexylamine, tri-n-octylamine, tri-2-ethylhexylamine, tri-dodecylamine, tri-laurylamine, dicyclohexylethylamine, cyclohexyldiethylamine, tricyclohexylamine, N,N-dimethylhexylamine, N-methyldihexylamine, N,N-dimethylcyclohexylamine, N-methyldicyclohexylamine, N,N-diethylethanolamine, N,N-dimethylethanolamine, N-ethyldiethanolamine, triethanolamine, tribenzylamine, N,N-dimethylbenzylamine, diethyl Tertiary monoamines such as benzylamine, triphenylamine, N,N-dimethylamino-p-cresol, N,N-dimethylaminomethylphenol, 2-(N,N-dimethylaminomethyl)phenol, N,N-dimethylaniline, N,N-diethylaniline, pyridine, quinoline, N-methylmorpholine, N-methylpiperidine, 2-(2-dimethylaminoethoxy)-4-methyl-1,3,2-dioxabornane, 2-,3-,4-picoline; tetramethylethylenedi One or more examples include amines, pyrazines, N,N'-dimethylpiperazine, N,N'-bis((2-hydroxy)propyl)piperazine, hexamethylenetetramine, N,N,N',N'-tetramethyl-1,3-butanamine, 2-dimethylamino-2-hydroxypropane, diethylaminoethanol, N,N,N-tris(3-dimethylaminopropyl)amine, 2,4,6-tris(N,N-dimethylaminomethyl)phenol, and heptamethylisobiguanide.

[0068] Examples of inorganic bases include one or more metal hydroxides (such as sodium hydroxide and potassium hydroxide).

[0069] Examples of organic acids include organic carboxylic acids (formic acid, acetic acid, propionic acid, benzoic acid, phthalic acid, etc.), organic sulfonic acids (benzenesulfonic acid, etc.), organic phosphonic acids, and one or more of their anhydrides.

[0070] Examples of inorganic acids include one or more such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0071] As the highly polar, low molecular weight component (E), an amine compound (E1) can be used in combination with one or more acidic, highly polar, low molecular weight components, such as organic acid components and / or inorganic acid components. Alternatively, an amine compound (E1) can be used in combination with one or more organic bases and / or inorganic bases.

[0072] In the present invention, it is preferable to include an amine compound (E1) as the highly polar, low molecular weight component (E). Among these, primary amine compounds are preferred, and monovalent amine compounds (monoamines) are preferred.

[0073] Examples of the above-mentioned amine compound (E1) include aliphatic amines, alicyclic amines, aromatic amines, alkanolamines, etc., all of which can be suitably used, but aromatic amines are preferred.

[0074] It is preferable that no amine compound remains in the mixture layer and / or electrode layer after drying. For this reason, the weight-average molecular weight of the amine compound (E1) is preferably less than 1,000, more preferably 800 or less, even more preferably 500 or less, particularly preferably 350 or less, and even more preferably 250 or less. For the same reason, the boiling point of the amine compound is preferably 400°C or less, more preferably 300°C or less, and even more preferably 200°C or less. If the boiling point is low, there is a possibility of volatilization during manufacturing or storage, and furthermore, from the viewpoint of odor, the lower limit of the boiling point is preferably 50°C or higher, and more preferably 100°C or higher.

[0075] The amine value of the amine compound (E1) is usually 5 mg KOH / g or more, preferably 50 mg KOH / g or more, more preferably 105 mg KOH / g or more, and is usually within the range of 1,000 mg KOH / g or less.

[0076] The content of the highly polar, low molecular weight component (E) in the carbon nanotube dispersion paste is 0% by mass or more, based on 100% by mass of the total amount of the carbon nanotube dispersion paste. For example, it can be 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and for example, 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less.

[0077] The content of the highly polar, low molecular weight component (E) relative to 100% by mass of the solid content of the carbon nanotube dispersion paste is 0% by mass or more, for example, 1% by mass or more, preferably 1.5% by mass or more, more preferably 2% by mass or more, for example, 600% by mass or less, preferably 300% by mass or less, more preferably 50% by mass or less.

[0078] The content of the highly polar, low molecular weight component (E) relative to 100% by mass of the solid content of carbon nanotubes (B) is 0% by mass or more, for example, 1% by mass or more, preferably 2% by mass or more, more preferably 5% by mass or more, for example, 1,000% by mass or less, preferably 500% by mass or less, more preferably 50% by mass or less.

[0079] Furthermore, if the carbon nanotube dispersion paste used in the manufacturing method of the present invention contains a highly polar, low molecular weight component (E), the content of the highly polar, low molecular weight component (E) per 100 parts by mass of carbon nanotube (B) is α (parts by mass), and the BET specific surface area of ​​carbon nanotube (B) is β (m²). ２ The value of X in the following formula (I), where ( / g), is usually 1 or more, preferably 5 or more, more preferably 10 or more, and usually within the range of 2,500 or less, preferably 1,000 or less, more preferably 300 or less, and even more preferably 100 or less. X = α / β × 300 ... Formula (I) Within this range, it is possible to sufficiently wet the surface of the carbon nanotube (B) with the highly polar, low molecular weight component (E), and it has been found that the dispersibility (including viscosity) and storage stability (including suppression of thickening) of the carbon nanotube (B) can be improved.

[0080] If the above upper limit is exceeded, the content of high-polarity, low-molecular-weight components (E) relative to the surface area of ​​carbon nanotubes (B) is excessive (resulting in odor and increased costs), and if the above lower limit is exceeded, the content of high-polarity, low-molecular-weight components (E) relative to the surface area of ​​carbon nanotubes (B) is insufficient.

[0081] In the carbon nanotube dispersion paste, the mass-based content ratio of N-methyl-2-pyrrolidone (C) to the highly polar, low molecular weight component (E) is in the range of 100 / 0 to 100 / 10, for example, in the range of 100 / 0.01 to 100 / 10, preferably in the range of 100 / 0.02 to 100 / 7, more preferably in the range of 100 / 0.05 to 100 / 5, and even more preferably in the range of 100 / 0.1 to 100 / 4.

[0082] The content of the amine compound (E1) in the highly polar, low molecular weight component (E) is, for example, 50% by mass or more, preferably 75% by mass or more, and more preferably 95% by mass or more, based on 100% by mass of the highly polar, low molecular weight component (E).

[0083] High-polarity, low-molecular-weight components (E), especially amine compounds (E1), often have strong odors, which can worsen the working environment during compounding and drying. Furthermore, they are generally expensive, potentially increasing costs. Therefore, the content of high-molecular-weight, low-molecular-weight components (E), particularly amine compounds (E1), should be kept to the minimum necessary.

[0084] <Other Components> In addition to components (A) to (C) and components (D) and (E) which may be included as needed, the carbon nanotube dispersion paste of the present invention may further contain other components. Examples of other components include one or more selected from the group consisting of pigments other than carbon nanotubes (B), solvents other than N-methyl-2-pyrrolidone (C), dispersion resins other than dispersion resins (A) having alkyl groups with 15 or more carbon atoms and polyvinylidene fluoride (D), dehydrating agents, neutralizing agents, defoaming agents, preservatives, rust inhibitors, plasticizers, etc.

[0085] (Pigments other than carbon nanotubes (B)) Examples of pigments other than carbon nanotubes (B) include one or more selected from the group consisting of conductive pigments other than carbon nanotubes (B1) (B1); white pigments such as titanium white and zinc oxide; blue pigments such as cyanine blue and induthlene blue; green pigments such as cyanine green and verdigris; organic red pigments such as azo and quinacridone, red pigments such as red iron oxide; organic yellow pigments such as benzimimidazolone, isoindolinone, isoindoline and quinophthalone, yellow pigments such as titanium yellow and lead yellow, etc.

[0086] Examples of conductive pigments (B1) include at least one conductive carbon selected from the group consisting of acetylene black, Ketjen black, furnace black, thermal black, graphene, graphite, carbon nanofiber, etc. Preferably, it is one or more selected from the group consisting of acetylene black, Ketjen black, furnace black, and thermal black, more preferably one or more selected from the group consisting of acetylene black and Ketjen black, and even more preferably acetylene black.

[0087] The average primary particle diameter of the conductive pigment (B1) is, for example, 10 nm or more, preferably 20 nm or more, and for example, 80 nm or less, preferably 70 nm or less. Here, the average primary particle diameter is the average particle diameter of the primary particles obtained by observing the conductive pigment (B1) with an electron microscope, determining the projected area of ​​100 particles, calculating the diameter when assuming a circle equal to that area, and then simply averaging the diameters of the 100 particles. If the pigment is in an aggregated state, the calculation is performed using the primary particles that constitute the aggregated particles.

[0088] The BET specific surface area of ​​the conductive pigment (B1) is not particularly limited. Based on the relationship between viscosity and conductivity, for example, 1 m ２ / g or more, preferably 10m ２ / g or more, more preferably 20m ２ It can be set to 500m or more, for example, 500m ２ Less than or equal to 250 mg / g, preferably 250 mg / g ２ / g or less, more preferably 200m ２It can be less than or equal to / g.

[0089] The amount of dibutyl phthalate (DBP) absorbed by the conductive pigment (B1) is not particularly limited. Depending on the relationship between pigment dispersibility and conductivity, it can be, for example, 60 ml / 100 g or more, preferably 150 ml / 100 g or more, and for example, 1,000 ml / 100 g or less, preferably 800 ml / 100 g or less.

[0090] Pigments other than carbon nanotubes (B) can be used for purposes such as color adjustment, conductivity adjustment, and coating film property adjustment, as long as they do not significantly impair the conductivity of the carbon nanotube dispersion paste. Pigments other than carbon nanotubes (B) may be dispersed simultaneously with the dispersion resin (A) having an alkyl group with 15 or more carbon atoms and the carbon nanotubes (B), or they may be mixed as a pigment or pigment paste after a paste has been prepared by dispersing the dispersion resin (A) having an alkyl group with 15 or more carbon atoms and the carbon nanotubes (B).

[0091] The content of pigments other than the carbon nanotube (B) described above is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent, based on 100% by mass of all pigments in the carbon nanotube dispersion paste.

[0092] (Solvents other than N-methyl-2-pyrrolidone (C)) Solvents other than N-methyl-2-pyrrolidone (C) are not particularly limited. Organic solvents are preferred. Examples of organic solvents include hydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, and cyclobutane; aromatic solvents such as toluene and xylene; ketone solvents such as methyl isobutyl ketone; ether solvents such as n-butyl ether, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol; ethyl acetate, n-butyl acetate, isobutyl acetate, ethyl acetate Examples of solvents include ester solvents such as methyl 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 ethanol, isopropanol, n-butanol, sec-butanol, and isobutanol; and amide solvents such as equamide (amide solvent, manufactured by Idemitsu Kosan Co., Ltd., trade name), N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide, N-methylacetamide, and N-methylpropioamide. For solvents other than N-methyl-2-pyrrolidone (C), a water content of less than 10,000 ppm is preferred.

[0093] (Dehydrating agent) The above dehydrating agent (F) can be any known agent that has a dehydrating effect without particular limitation. It may be a solid dehydrating agent that does not dissolve in the solvent (C) of the paste, or a dehydrating agent that dissolves in the solvent (C). Specifically, for example, solid dehydrating agents such as zeolite, silica gel, calcium oxide, molecular sieve, activated alumina, barium oxide, calcium hydride, sodium sulfate, etc.; phosphate esters such as trimethyl phosphate, tri-2-propyl phosphate, tributyl phosphate, tetraisopropylethylene phosphonate, etc.; phosphine oxides such as tributylphosphine oxide, trioctylphosphine oxide, triphenylphosphine oxide, etc.; methyl orthoformate, etc. One or more selected from the group consisting of: ethyl orthoesters such as ethyl orthoacetate, methyl orthoacetate, ethyl orthoacetate, and ethyl orthobenzoate; acid anhydrides such as oxalic acid anhydride, acetic anhydride, propionic anhydride, butyric acid anhydride, benzoic acid anhydride, trifluoroacetic acid anhydride, disulfuric acid, dinitrogen pentoxide, diphosphoric acid, diphosphorus pentoxide, diphosphorus trioxide, arsenic pentoxide, arsenic trioxide, methanesulfonic acid anhydride, trifluoromethanesulfonic acid anhydride, and sulfobenzoic acid anhydride; etc.

[0094] <Moisture Content of Carbon Nanotube Dispersion Paste> The moisture content of the carbon nanotube dispersion paste of the present invention is not particularly limited. The moisture content of the carbon nanotube dispersion paste can be, for example, 10,000 ppm or less, preferably less than 7,500 ppm, more preferably less than 5,000 ppm, and even more preferably less than 2,500 ppm.

[0095] In the carbon nanotube dispersion paste of the present invention, by keeping the water content below 10,000 ppm, it is possible to suppress viscosity increase and gelation during storage at high temperatures (e.g., 45°C or higher, particularly 50°C or higher), resulting in a carbon nanotube dispersion paste with excellent storage stability at high temperatures. The water content of the carbon nanotube dispersion paste can be measured using the same method as for measuring the water content of N-methyl-2-pyrrolidone (C).

[0096] <Viscosity of Carbon Nanotube Dispersion Paste> The viscosity of the carbon nanotube dispersion paste of the present invention is not particularly limited. From the viewpoint of pigment dispersibility and storage stability, the viscosity of the carbon nanotube dispersion paste can be, for example, less than 500 mPa·s, preferably less than 200 mPa·s, more preferably less than 50 mPa·s, and can be, for example, 0.1 mPa·s or more, preferably 0.5 mPa·s or more, more preferably 1.0 mPa·s or more. Viscosity can be measured, for example, using a Brookfield viscometer (Type B viscometer) under measurement conditions of 6 revolutions per minute (6 rpm) at 20°C.

[0097] [Method for producing carbon nanotube dispersion paste] The present invention relates to a method for producing carbon nanotube dispersion paste comprising a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), and N-methyl-2-pyrrolidone (C), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C measured by static light scattering is 2.7 × 10 －３ cm ３ mol / g ２ The present invention provides a method for producing a carbon nanotube dispersion paste using the following dispersion resin. The present invention provides a method for producing a carbon nanotube dispersion paste that has excellent dispersibility of carbon nanotubes, low initial viscosity during production, and excellent storage stability at high temperatures (e.g., 45°C or higher, especially 50°C or higher), by using a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, wherein the dispersion resin (A) is dissolved in N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering, falls within a specific range.

[0098] In the method for producing the carbon nanotube dispersion paste of the present invention, the dispersion resin (A) having an alkyl group with 15 or more carbon atoms, the carbon nanotube (B), and the N-methyl-2-pyrrolidone (C) used are the same as those described in the [Carbon Nanotube Dispersion Paste] section above: the dispersion resin (A) having an alkyl group with 15 or more carbon atoms, the carbon nanotube (B), the N-methyl-2-pyrrolidone (C), and the polyvinylidene fluoride resin (D).

[0099] The present invention provides a method for producing a carbon nanotube dispersion paste, which involves mixing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), and N-methyl-2-pyrrolidone (C), and optionally including a polyvinylidene fluoride resin (D), a highly polar, low molecular weight component (E), and other components, and then further dispersing the mixture.

[0100] For mixing and dispersion, uniform mixing and dispersion can be achieved using dispersers such as paint shakers, sand mills, ball mills, pebble mills, LMZ mills, DCP pearl mills, planetary ball mills, homogenizers, twin-shaft kneaders, and thin-film rotary high-speed mixers (such as M-Technique's "Creamix"). The order in which each component is mixed and dispersed is not particularly limited. For example, all components can be mixed and dispersed at once, or, for example, some components can be mixed and dispersed first, and then the remaining components can be mixed and dispersed.

[0101] In the present invention, it is preferable to sequentially perform the following steps: Step 1: Adding a component containing carbon nanotubes (B) in an amount of 70% by mass or less (preferably 50% by mass or less) based on the total amount of carbon nanotubes (B) contained in the carbon nanotube dispersion paste obtained after dispersion, a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, and N-methyl-2-pyrrolidone (C) to a disperser and mixing and performing a dispersion treatment; and Step 2: Then, adding carbon nanotubes (B) to the disperser until the desired concentration is reached and performing a dispersion treatment. In this case, it is preferable that the dispersion treatment time in Step 1 be at least 30 seconds or more (preferably 1 minute or more). By mixing and dispersing in Steps 1 and 2, aggregation of carbon nanotubes (B) is mitigated, and even in carbon nanotube dispersion pastes with a high concentration of carbon nanotubes (B), a paste with good dispersibility and homogeneity can be obtained. Furthermore, the composite layer (coated layer) obtained from the composite paste for lithium-ion secondary batteries containing carbon nanotube dispersion paste exhibits superior finish, conductivity, and battery performance.

[0102] [Compound Paste for Lithium-Ion Secondary Batteries] The composite paste for lithium-ion secondary batteries of the present invention contains a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), N-methyl-2-pyrrolidone (C), polyvinylidene fluoride resin (D), and electrode active material (F), wherein the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering, is 2.7 × 10⁻⁶. －３ cm ３ mol / g ２ The following applies:

[0103] The dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), N-methyl-2-pyrrolidone (C), and polyvinylidene fluoride resin (D) contained in the composite paste for lithium-ion secondary batteries can be the same as those described in the [Carbon Nanotube Dispersion Paste] section, which include the dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), N-methyl-2-pyrrolidone (C), and polyvinylidene fluoride resin (D).

[0104] The lithium-ion secondary battery composite paste of the present invention may contain a highly polar, low molecular weight component (E) from the viewpoint of storage stability at high temperatures and suppression of thickening. The highly polar, low molecular weight component (E) may be the same as the highly polar, low molecular weight component (E) described in the [carbon nanotube dispersion paste] above. The lithium-ion secondary battery composite paste of the present invention preferably contains at least one amine compound (E1) as the highly polar, low molecular weight component (E). The highly polar, low molecular weight component (E) can wet the surface of the carbon nanotubes (B) when brought into contact with the carbon nanotubes (B), thereby mitigating aggregation between the carbon nanotubes (B) and the electrode active material (G) when mixed with the electrode active material (F). For this reason, when the lithium-ion secondary battery composite paste contains a highly polar, low molecular weight component (E), it is preferable to pre-mix the carbon nanotubes (B) and the highly polar, low molecular weight component (E).

[0105] The composite material base of the present invention contains an electrode active material (F). Examples of the electrode active material (F) include alkali metal composite oxides and alkali metal composite phosphates. For example, lithium nickelate (LiNiO) ２ ), lithium manganese (LiMn ２ O ４ ), lithium cobalt oxide (LiCoO ２ ), LiNi ０．５ Mn １．５ O ４ LiNi １／３ Co １／３ Mn １／３ O ２Lithium composite oxides such as lithium iron phosphate (LiFePO) ４ One or more selected from the group consisting of ); sodium complex oxide; potassium complex oxide, etc. In particular, the electrode active material (F) contains nickel and one or more other transition metals, and the nickel content is preferably 15 mol% or more, and more preferably 30 mol% or more, based on the total number of moles of transition metals. The volume average particle diameter of the electrode active material (F) is not particularly limited. For example, it is 0.5 μm or more, preferably 10 μm or more, and usually 30 μm or less, preferably 20 μm or less.

[0106] Composite pastes for lithium-ion secondary batteries containing electrode active material (F) may thicken during storage. The reason for this thickening during storage is unknown, but it is presumed that alkali metal hydroxides (e.g., LiOH, KOH, NaOH, etc.) derived from the raw materials are present on the particle surface of the electrode active material (F), and that this thickening occurs due to aggregation with carbon nanotubes (B) having an acidic surface. On the other hand, if the composite paste for lithium-ion secondary batteries contains a highly polar, low molecular weight component (E), preferably a basic highly polar, low molecular weight component, and more preferably an amine compound (E1), thickening during storage can be suppressed.

[0107] The lithium-ion secondary battery composite paste of the present invention can use an electrode active material composite (F-1) in which at least a portion of the surface of the electrode active material (F) is coated with carbon nanotubes. The electrode active material composite (F-1) can be obtained by mixing the electrode active material (F), carbon nanotubes, and other components such as solvents and dispersion resins as needed. After mixing, it can be dried as needed, thereby allowing the carbon nanotubes to be more uniformly adsorbed and / or fixed to at least a portion of the surface of the electrode active material (F). Furthermore, in the electrode active material composite (G-1), a uniform conductive network can be formed around the electrode active material because the carbon nanotubes are adsorbed and / or fixed to the surface of the electrode active material. The carbon nanotubes that can be used in forming the electrode active material composite (G-1) are not particularly limited, and for example, the same as the carbon nanotubes (B) described in the [carbon nanotube dispersion paste] above can be used.

[0108] The water content of the electrode active material (F) can be, for example, less than 10,000 ppm, preferably less than 7,500 ppm, more preferably less than 5,000 ppm, even more preferably less than 2,500 ppm, and particularly preferably less than 1,000 ppm, from the viewpoint of suppressing viscosity increase or gelation of the composite paste for lithium-ion secondary batteries.

[0109] The content of the dispersion resin (A) having an alkyl group with 15 or more carbon atoms in the lithium-ion secondary battery composite paste is not particularly limited. From the viewpoint of battery performance and paste viscosity, etc., it can be, for example, 0.01% by mass or more, preferably 0.05% by mass or more, and for example, 10% by mass or less, preferably 1% by mass or less, based on 100% by mass of the total solid content of the lithium-ion secondary battery composite paste.

[0110] The carbon nanotube (B) content in the lithium-ion secondary battery composite paste is not particularly limited. From the viewpoint of battery performance, etc., based on 100% by mass of the total solid content of the lithium-ion secondary battery composite paste, it can be, for example, 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and for example, 30% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less.

[0111] The content of N-methyl-2-pyrrolidone (C) in the composite paste for lithium-ion secondary batteries is not particularly limited. From the viewpoint of drying efficiency during composite layer preparation and paste viscosity, etc., the content can be, for example, 1% by mass or more, preferably 4% by mass or more, more preferably 7% by mass or more, based on 100% by mass of the total amount of the composite paste for lithium-ion secondary batteries, and can be, for example, 90% by mass or less, preferably 70% by mass or less, more preferably 50% by mass or less.

[0112] The content of polyvinylidene fluoride resin (D) in the lithium-ion secondary battery composite paste is not particularly limited. From the viewpoint of battery performance and paste viscosity, etc., it can be, for example, 0.05% by mass or more, preferably 0.1% by mass or more, and for example, 10% by mass or less, preferably 2% by mass or less, based on 100% by mass of the total solid content of the lithium-ion secondary battery composite paste.

[0113] The content of electrode active material (F) in the composite paste for lithium-ion secondary batteries is not particularly limited. From the viewpoint of battery capacity, battery resistance, battery performance, etc., the content can be, for example, 20% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, based on 100% by mass of the total solid content of the composite paste for lithium-ion secondary batteries, and can be, for example, 99.85% by mass or less.

[0114] From the viewpoint of suppressing viscosity increase or gelation, the moisture content of the lithium-ion secondary battery composite paste can be, for example, less than 10,000 ppm, preferably less than 7,500 ppm, more preferably less than 5,000 ppm, even more preferably less than 2,500 ppm, and particularly preferably less than 1,000 ppm. Furthermore, due to moisture introduced from the constituent components of the lithium-ion secondary battery composite paste and moisture contamination during the manufacturing process, the moisture content of the lithium-ion secondary battery composite paste can be, for example, 100 ppm or more, preferably 200 ppm or more, and more preferably 500 ppm or more. The lithium-ion secondary battery composite paste of the present invention is preferably substantially aqueous.

[0115] The method for producing the composite paste for lithium-ion secondary batteries is not particularly limited. For example, a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group having 15 or more carbon atoms, carbon nanotubes (B), N-methyl-2-pyrrolidone (C), and a polyvinylidene fluoride-based resin (D) can be prepared, and then one or more electrode active materials (G) can be mixed and dispersed to produce the composite paste for lithium-ion secondary batteries. Alternatively, for example, a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group having 15 or more carbon atoms, carbon nanotubes (B), and N-methyl-2-pyrrolidone (C) can be prepared, and then one or more polyvinylidene fluoride-based resins (D) and one or more electrode active materials (G) can be mixed and dispersed to produce the composite paste for lithium-ion secondary batteries.

[0116] When mixing and dispersing a carbon nanotube dispersion paste with one or more electrode active materials (G), or when mixing and dispersing a carbon nanotube dispersion paste with one or more polyvinylidene fluoride-based resins (D) and one or more electrode active materials (G), known mixers and / or dispersers can be used to uniformly mix the composite paste for lithium-ion secondary batteries. For example, a disperser used for mixing and dispersing each component in the production of a carbon nanotube dispersion paste can be used.

[0117] The lithium-ion secondary battery composite paste of the present invention can be used in the manufacture of the positive or negative electrode of a battery, for example, by applying it to a current collector and drying it to form a composite layer. Preferably, it can be used in the manufacture of the positive electrode of a lithium-ion secondary battery.

[0118] [Electrode layer for non-aqueous electrolyte lithium-ion secondary battery] The electrode layer for a non-aqueous electrolyte lithium-ion secondary battery of the present invention is obtained by coating the [composite paste for lithium-ion secondary battery] onto a current collector.

[0119] The current collector is not particularly limited as long as it is made of a conductive material used in battery electrodes. Examples include metals such as aluminum, copper, titanium, and alloys of two or more of these, carbon materials, and composites thereof. The current collector can be in the form of foil, plate, etc., and is preferably foil. In the present invention, either aluminum foil or copper foil is preferably used.

[0120] The thickness of the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery is not particularly limited. The thickness of the portion of the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery obtained by coating the lithium-ion secondary battery composite paste onto a current collector and drying it can be, for example, 0.04 mm or more, preferably 0.06 mm or more, and can be, for example, 0.30 mm or less, preferably 0.24 mm or less. The method of coating the lithium-ion secondary battery composite paste onto the current collector is not particularly limited. Examples include roller coating and coating methods using a die coater. The temperature and time for drying the lithium-ion secondary battery composite paste coated onto the current collector are not particularly limited. The temperature can be, for example, 80°C or more, preferably 100°C or more, and can be, for example, 250°C or less, preferably 200°C or less. The drying time can be, for example, 5 seconds or more, and can be, for example, 120 minutes or less, preferably 60 minutes or less.

[0121] In this invention, when applying a lithium-ion secondary battery composite paste to a current collector, a primer layer can be formed on the current collector beforehand. The primer layer corresponds to a functional layer or adhesive layer. As a material for forming the primer layer, for example, the aforementioned [carbon nanotube dispersion paste] can be used.

[0122] When a lithium-ion secondary battery composite paste is applied to a current collector and dried to form an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery, all or part of the N-methyl-2-pyrrolidone (C) and, if necessary, the high-polarity, low-molecular-weight component (E) contained in the lithium-ion secondary battery composite paste will volatilize. In the present invention, in order to reduce waste, address environmental concerns, and reduce costs, it is preferable to recover the volatilized N-methyl-2-pyrrolidone (C) and high-polarity, low-molecular-weight component (E), purify them by means of distillation or other means, and reuse them as a recycled N-methyl-2-pyrrolidone product.

[0123] When forming a battery electrode from the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery of the present invention and using it as an electrode for a lithium-ion secondary battery, the presence of impurities such as water in the battery electrode, particularly in the electrode layer for the non-aqueous electrolyte lithium-ion secondary battery, may reduce the cycle life. For example, if the carbon nanotube dispersion paste or the composite paste for lithium-ion secondary batteries contains more water than specified, or if the drying process in the manufacturing process of the electrode layer for the non-aqueous electrolyte lithium-ion secondary battery is insufficient, impurities such as water may remain in the electrode layer for the non-aqueous electrolyte lithium-ion secondary battery, which can cause deterioration of the battery's cycle characteristics. For this reason, the amount of water in the composite paste layer for lithium-ion secondary batteries used in forming the electrode layer for the non-aqueous electrolyte lithium-ion secondary battery can be, for example, less than 1000 ppm, preferably less than 750 ppm, more preferably less than 500 ppm, even more preferably less than 250 ppm, and particularly preferably less than 100 ppm.

[0124] [Electrodes for Non-Aqueous Electrolyte Lithium-Ion Secondary Batteries] The electrode for a non-aqueous electrolyte lithium-ion secondary battery of the present invention has an electrode insulating portion provided at the end or upper layer of the [Electrode Layer for Non-Aqueous Electrolyte Lithium-Ion Secondary Battery]. The electrode insulating portion can be provided, for example, by coating with an insulating paste. The insulating paste is not particularly limited as long as it can form an insulating film. For example, a paste containing an inorganic filler, a binder, a dispersant, and a solvent is preferred. Of these, an insulating paste containing boehmite as the inorganic filler, polyvinylidene fluoride as the binder, and N-methyl-2-pyrrolidone as the solvent is preferred. As an insulating paste, for example, the insulating paste described in International Publication No. 2021 / 193286 can also be used.

[0125] [Non-aqueous electrolyte lithium-ion secondary battery] The non-aqueous electrolyte lithium-ion secondary battery of the present invention comprises at least a positive electrode having an electrode layer for non-aqueous electrolyte lithium-ion secondary batteries, a negative electrode, a non-aqueous electrolyte, and a separator.

[0126] The electrode layer for a non-aqueous electrolyte lithium-ion secondary battery in the positive electrode can be the same as that described above in [Electrode Layer for Non-Aqueous Electrolyte Lithium-ion Secondary Battery].

[0127] Examples of negative electrodes include carbon, metal, and composite materials in which a negative electrode composite layer containing a negative electrode active material is formed on a current collector.

[0128] As a non-aqueous electrolyte, for example, a solution containing a salt in an organic solvent that is a non-aqueous solvent can be used. Examples of non-aqueous solvents include one or more organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. Examples of salts include LiPF ６ LiBF ４ LiClO ４ One or more lithium salts such as the following are examples. The concentration of the salt is not particularly limited, but for example it can be 0.7 mol / L or more and 1.3 mol / L or less.

[0129] Examples of separators include resin sheets. The resin sheet is preferably composed of one or more materials such as polyethylene, polypropylene, polyester, cellulose, and polyamide, and is preferably a porous resin sheet. The porous resin sheet may have a single-layer structure or a laminated structure of two or more layers. The resin sheet may also have a heat-resistant layer as needed. Examples of heat-resistant layers include those formed from a heat-resistant layer-forming material containing an inorganic filler such as alumina, magnesia, or boehmite, a resin binder, and a thickener.

[0130] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these specific embodiments. In each example, "parts" refers to parts by mass, and "%" refers to mass percent. Carbon nanotubes may be abbreviated as "CNT". In the examples, the water content was measured using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name "MKC-610").

[0131] [Production of Dispersion Resin] <Production Example 1> 75 parts of N-methyl-2-pyrrolidone (water content 8000 ppm) were added to a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and water separator, and heated to 120°C under a nitrogen atmosphere. Once 120°C was reached, a mixture of the monomer species shown in Table 1 below (total 100 parts) and 2 parts of 2,2'-azobis(2-methylbutyronitrile) was added dropwise over 3 hours. After the addition was complete, the mixture was aged at 120°C for 30 minutes, and a mixture of 1 part of 2,2'-azobis(2-methylbutyronitrile) and 20 parts of N-methyl-2-pyrrolidone (Note 1) was added dropwise over 1 hour. After further aging at 120°C for 1 hour, the mixture was cooled, and N-methyl-2-pyrrolidone (Note 1) was added to obtain a dispersion resin (A-1) with a solid content of 50%. The polar functional group concentration was 1.4 (mol / g).

[0132] <Production Examples 2-9> Dispersed resins (A-2) to (A-9) with a solid content of 50% were obtained in the same manner as in Production Example 1, except that the monomer species were as shown in Table 1 below. Dispersed resins (A-2) to (A-9) are all acrylic resins. The values ​​of the second virial coefficient and the weight-average molecular weight of the obtained resins are shown in Table 1 below. The abbreviations for monomer species in Table 1 above are as follows: • St: Styrene • iBA: i-butyl acrylate (has a hydrocarbon group with 4 carbon atoms) • SLMA: Lauryl methacrylate (has a hydrocarbon group with 12 carbon atoms) • SMA: Stearyl methacrylate (has a hydrocarbon group with 18 carbon atoms) • BEMA: Behenyl methacrylate (has a hydrocarbon group with 22 carbon atoms) • AN: Acrylonitrile • DMAEMA: N,N-dimethylaminoethyl methacrylate • DAAm: Diacetone acrylamide • MAAc: Methacrylic acid

[0133] The second virial coefficient of the obtained resin was determined as follows: [Static Light Scattering Measurement] The obtained dispersed resin (A) was dissolved in N-methyl-2-pyrrolidone (C) to prepare three levels of measurement solutions with concentrations of 1 mg / mL, 3 mg / mL, and 5 mg / mL. Then, each measurement solution was filtered through a hydrophilic PTFE membrane filter with a pore size of 0.45 μm, and then filtered again through a hydrophilic PTFE membrane filter with a pore size of 0.20 μm. Subsequently, static light scattering measurements of the filtrates were performed using a static light scattering photometer (ELSZ-2000, manufactured by Otsuka Electronics Co., Ltd.). Filtration and measurement were performed at 50°C. Toluene was used for calibration of the instrument. Furthermore, when determining the second virial coefficient, the refractive index concentration increment (dn / dc) of the resin composition required was measured using a refractometer (NAR-2T, Atago Corporation) with dispersant solutions adjusted to three levels of approximately 0.01 to 0.1 g / mL. The measurements were performed at 50°C. A Debye plot was created from the scattering intensity obtained by static light scattering measurement, and the second virial coefficient of the resin composition was determined according to the conventional method.

[0134] [Production of Carbon Nanotube Dispersion Paste] <Example (X1)> 900 parts of N-methyl-2-pyrrolidone (water content 8000 ppm), 24 parts of dispersion resin (A-1) (solid content 12 parts), 5 parts of benzylamine (boiling point 185°C, molecular weight 107), and 40 parts of CNT (CNT1) were mixed in a disperser for 10 minutes with stirring in sequence, and finally, N-methyl-2-pyrrolidone (water content 8000 ppm) was added to adjust the total mass to 1000 parts. Subsequently, rotor R2 and screen S2.0-24 were attached to a high-speed homogenizer: Creamix CLM-0.8S (trade name, manufactured by M-Technique), and the mixture was stirred at a speed of 8000 rpm for 1 minute, and then stirred at a speed of 12000 rpm for 2 minutes to perform the dispersion treatment. Next, a batch-type dispersion process was performed 10 times using a high-pressure homogenizer: NanoVator NVL-ES008A-D10 (product name, manufactured by Yoshida Machinery Co., Ltd.) to obtain a carbon nanotube dispersion paste (X-1). The dispersion process in the high-pressure homogenizer was performed using a straight nozzle NVGL-IT230 (nozzle diameter 230 μm) at a pressure of 100 MPa. All of the above manufacturing processes were carried out in an atmosphere with a dew point of 10°C or lower. After the production of the carbon nanotube dispersion paste, the paste was quickly adjusted to 20°C. The moisture content of the obtained carbon nanotube dispersion paste (X-1) was 8000 ppm. Table 3 shows the results of the evaluation test of the carbon nanotube dispersion paste described later. The CNTs used (CNT1) were multi-walled carbon nanotubes, and their average outer diameter, average length, and specific surface area are as shown in Table 2. The specific surface area (BET specific surface area) in Table 2 was obtained by the following method.

[0135] <Specific surface area of ​​CNT (BET specific surface area)> Using a specific surface area measuring device (BERSORP-MAX (Microtrac Bell Co., Ltd.)), the BET specific surface area of ​​CNT (m²) was calculated in accordance with JIS Z8830:2013. ２ The specific surface area (per g) was measured and defined as the specific surface area of ​​the carbon nanotube (CNT).

[0136] <Examples (X2) to (X7), Comparative Examples (X8) to (X12)> Carbon nanotube dispersion pastes were obtained in the same manner as in Example (X1), except that the dispersion resin was as described in Table 3 below. The water content of the carbon nanotube dispersion pastes in each example and comparative example was approximately the same as that of the carbon nanotube dispersion paste in Example (X1). The results of the evaluation tests of the carbon nanotube dispersion pastes, described later, are shown in Table 3.

[0137] The names of the dispersion resins in Table 3 are as follows. Each dispersion resin was blended into the carbon nanotube dispersion paste to a solid content of 12 parts. • Dispersion resins A-1 to A-9: Dispersion resins (A-1) to (A-9) obtained in Production Examples 1 to 9 • PVB: Polyvinyl butyral (weight-average molecular weight 45000, hydroxyl group content 12 mol%, butyral group content 87 mol%, acetyl group content 1 mol%, polar functional group concentration 1.0 mmol / g, second virial coefficient 1.15 × 10) －３ cm ３ mol / g ２ ) ・PVA: Polyvinyl alcohol (weight-average molecular weight 26000, degree of saponification 99.9 mol%, polar functional group concentration 22.7 (mol / g), second virial coefficient 7.82 × 10) －３ cm ３ mol / g ２ (Polar functional group type: hydroxyl group) ・PVP: Polyvinylpyrrolidone (weight-average molecular weight 67000, polar functional group concentration 9.0 (mol / g), second virial coefficient 4.59 × 10⁻⁶) －３ cm ３ mol / g ２ , polar functional group type: amide group)

[0138] [Manufacturing of composite paste for lithium-ion secondary batteries] <Example (Z1)> While stirring with a disperser, 10 parts of polyvinylidene fluoride resin solution are mixed with 90 parts of the above carbon nanotube dispersion paste (X-1) and electrode active material particles (composition formula LiNi ０．５ Mn １．５ O ４ Lithium nickel manganese oxide particles with a spinel structure, represented by [formula], average particle size 6 μm, BET specific surface area 0.7 m². ２A lithium-ion secondary battery composite paste (Z-1) was manufactured by sequentially mixing 900 parts of ( / g) with the other ingredients. The water content of the lithium-ion secondary battery composite paste (Z-1) was 1500 ppm. The polyvinylidene fluoride resin solution used was a resin solution prepared by mixing 5 parts of KF Polymer #9700 (trade name, manufactured by Kureha Corporation, polar group modified polyvinylidene fluoride, molecular weight 800,000 to 900,000) and 95 parts of N-methyl-2-pyrrolidone (water content 8000 ppm) at a temperature of 50°C.

[0139] <Examples (Z2) to (Z7), Comparative Examples (Z8) to (Z12)> Composite pastes for lithium-ion secondary batteries were obtained in the same manner as in Example (Z1), except that the carbon nanotube dispersion paste was as described in Table 4. The water content of the lithium-ion secondary battery composite pastes in each example and comparative example was approximately the same as that of the lithium-ion secondary battery composite paste in Example (Z1).

[0140] [Evaluation] The carbon nanotube dispersion pastes obtained in Examples (X1) to (X7) and Comparative Examples (X8) to (X12) were evaluated as follows. The results are shown in Table 3. In the evaluation tests, a D rating and an E rating are considered failures. If even one evaluation result is a failure, the carbon nanotube dispersion paste is considered unsuccessful. Note that storage stability evaluation tests were not performed on carbon nanotube dispersion pastes that received a D or E rating for initial viscosity.

[0141] <Dispersibility> The dispersibility of the obtained carbon nanotube dispersion paste was evaluated using a particle gauge according to the dispersibility test of JIS K-5600-2-5, based on the following criteria. A: Pigment is dispersed at less than 15 μm. Dispersibility is good. B: Pigment is dispersed at 15 μm or more and less than 30 μm. Dispersibility is moderately good. D: Pigment is dispersed at 30 μm or more, or aggregates are visible to the naked eye. Dispersibility is poor.

[0142] <Initial Viscosity> The viscosity of carbon nanotube dispersion paste immediately after manufacturing was measured using a Brookfield viscometer (Type B viscometer) at 20°C and a rotation speed of 6 revolutions per minute (6 rpm), and evaluated according to the following criteria. A: Viscosity is less than 8 Pa·s. Initial viscosity is very good. B: Viscosity is 8 Pa·s or more and less than 15 Pa·s. Initial viscosity is good. C: Viscosity is 15 Pa·s or more and less than 40 Pa·s. Initial viscosity is somewhat good. D: Viscosity is 40 Pa·s or more and less than 70 Pa·s. Initial viscosity is poor. E: Viscosity is 70 Pa·s or more. Initial viscosity is very poor.

[0143] <Storage Stability> The obtained carbon nanotube dispersion paste was stored at 50°C for two weeks, and the initial viscosity and the viscosity after storage were compared. Viscosity was measured using a Brookfield viscometer (Type B viscometer) under measurement conditions of 20°C and a rotation speed of 6 revolutions / minute (6 rpm). The viscosity increase rate was calculated using the following formula: Viscosity increase rate (%) = Viscosity after storage (mPa·s) / Initial viscosity (mPa·s) × 100 - 100, and the storage stability was evaluated according to the following criteria. S: Viscosity increase rate (%) after storage is less than 10%. Storage stability is very good. A: Viscosity increase rate (%) after storage is 10% or more and less than 20%. Storage stability is good. B: Viscosity increase rate (%) after storage is 20% or more and less than 50%. Storage stability is moderately good. C: Viscosity increase rate (%) after storage is 50% or more and less than 200%. Storage stability is average. D: Viscosity increase rate (%) after storage is 200% or more (or gelled and unmeasurable). Storage stability is poor.

[0144] [Manufacturing of electrode layers for non-aqueous electrolyte lithium-ion secondary batteries] <Application Example 1Y> The lithium-ion secondary battery composite paste obtained in Example Z4 was applied to both sides of a long aluminum foil (positive electrode current collector) with an average thickness of 15 μm, with a basis weight of 10 mg / cm² per side. ２A positive electrode layer was formed by applying a strip of material using a roller coating method to a certain level (based on solid content) and drying it (drying temperature 180°C, 30 minutes). This positive electrode layer (positive electrode active material layer) supported on the positive electrode current collector was rolled using a roll press to obtain an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery. The obtained electrode layer for a non-aqueous electrolyte lithium-ion secondary battery had good finish and other properties.

Claims

A carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, carbon nanotubes (B), and N-methyl-2-pyrrolidone (C), The dispersion resin (A) was dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C, measured by static light scattering, was 2.7 × 10⁻⁶. －３ cm ３ mol / g ２ The following is: The carbon nanotube dispersion paste. 　 The second virial coefficient at the aforementioned liquid temperature of 50°C is -2.0 × 10⁻⁶ －３ cm ３ mol / g ２ The carbon nanotube dispersion paste according to claim 1 is as described above. 　 The carbon nanotube dispersion paste according to claim 1 or 2, wherein the dispersion resin (A) has an aromatic ring and / or a heterocycle. 　 The carbon nanotube dispersion paste according to claim 1 or 2, wherein the dispersion resin (A) has at least one polar functional group selected from the group consisting of amide groups, imide groups, hydroxyl groups, carboxyl groups, sulfonic acid groups, phosphate groups, amino groups, and cyano groups, and the concentration of the polar functional group is 0.1 mmol / g or more and 8.5 mmol / g or less. 　 The carbon nanotube dispersion paste according to claim 1 or 2, wherein the water content of N-methyl-2-pyrrolidone (C) is 10,000 ppm or less. 　 A carbon nanotube dispersion paste according to claim 1 or 2, comprising a polyvinylidene fluoride resin (D). 　 A carbon nanotube dispersion paste according to claim 1 or 2, comprising a highly polar, low molecular weight component (E). 　 A carbon nanotube dispersion paste according to claim 1 or 2, wherein the water content is 10,000 ppm or less. A method for producing a carbon nanotube dispersion paste containing a dispersion resin (A) having an alkyl group with 15 or more carbon atoms, a carbon nanotube (B), and N-methyl-2-pyrrolidone (C), As the dispersion resin (A), a dispersion resin is used in which the second virial coefficient at a liquid temperature of 50°C measured by the static light scattering method when the dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C) is 2.7×10 －３ cm ３ ·mol / g ２ or less A method for producing the carbon nanotube dispersion paste. 　 A composite paste for lithium-ion secondary batteries containing a dispersed resin (A), carbon nanotubes (B), N-methyl-2-pyrrolidone (C), polyvinylidene fluoride resin (D), and electrode active material (F), The dispersion resin (A) is dissolved in the N-methyl-2-pyrrolidone (C), and the second virial coefficient at a liquid temperature of 50°C is measured by static light scattering, and is 2.7 × 10⁻⁶. －３ cm ３ mol / g ２ The following is: The aforementioned composite paste for lithium-ion secondary batteries. 　 An electrode layer for a non-aqueous electrolyte lithium-ion secondary battery, obtained by coating a lithium-ion secondary battery composite paste according to claim 10 onto a current collector. 　 An electrode for a non-aqueous electrolyte lithium-ion secondary battery, wherein an electrode insulating portion is provided at the end or upper layer of the electrode layer for a non-aqueous electrolyte lithium-ion secondary battery according to claim 11. 　 A non-aqueous electrolyte lithium-ion secondary battery comprising at least a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, each having an electrode layer for a non-aqueous electrolyte lithium-ion secondary battery as described in claim 12.

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