WO2024204168A1

WO2024204168A1 - Carbon nanotube dispersion paste, composite paste, and lithium ion secondary battery electrode layer production method

Info

Publication number: WO2024204168A1
Application number: PCT/JP2024/011901
Authority: WO
Inventors: 凌我宮村; 誠也柴田
Original assignee: 関西ペイント株式会社
Priority date: 2023-03-27
Filing date: 2024-03-26
Publication date: 2024-10-03

Abstract

The present invention addresses the problem of providing: production methods for a composite paste and a carbon nanotube dispersion paste that have excellent pigment dispersibility and storage stability even at high pigment concentrations; and a lithium ion secondary battery electrode layer that has excellent performance (electric conductivity, battery characteristics, etc.). Provided as a solution is a production method for a carbon nanotube dispersion paste, said production method comprising a step for mixing and dispersing a component containing a dispersion resin (A) that has a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) that has a moisture content of less than 10000 ppm, and a polyvinylidene fluoride (D) that can be included as necessary, said production method being characterized in that the moisture content of the carbon nanotube dispersion paste is less than 10000 ppm.

Description

Carbon nanotube dispersion paste, composite paste, and method for manufacturing electrode layer for lithium ion secondary battery

The present invention relates to a carbon nanotube dispersion paste (also referred to as a conductive pigment paste in the present invention) that has excellent electrical conductivity, pigment dispersibility, and storage stability even at a high pigment concentration, a composite paste, a method for producing an electrode layer for a lithium ion secondary battery, and a method for producing an electrode layer for a battery that has excellent battery performance.

　Traditionally, paste-like pigment dispersions, in which pigments are dispersed in a mixture of pigment dispersion resins and solvents, have been widely used in fields such as paints, battery electrodes, coating materials, electromagnetic shielding, display panels, touch screen panels, colored films, colored sheets, decorative materials, protective materials, magnet modifiers, printing inks, device components, electronic equipment components, printed wiring boards, solar cells, functional rubber components, and resin molding films. Furthermore, conductive pigments and conductive polymers are added to these materials to impart functions such as electrostatic paintability, conductivity, electromagnetic shielding, and antistatic properties.

In these fields, there is an increasing demand for improved pigment dispersibility, storage stability, electrical conductivity, coatability, finish, and other performance features. As a result, pigment dispersion resins and pigment pastes are being developed that have excellent pigment dispersion capabilities and excellent pigment dispersion stability that prevents re-agglomeration of pigment particles in the formed pigment dispersion.

When designing a pigment paste, it is important to create a highly concentrated, uniformly dispersed pigment paste using a small amount of pigment dispersion resin so that the pigment dispersion resin does not adversely affect the conductive properties of the final product itself, such as the coating film, and from the perspective of reducing the amount of solvent and pigment dispersion resin used and reducing the energy used during drying.

For example, Patent Document 1 discloses a method for producing a slurry for electrodes of lithium secondary batteries, which is characterized by dispersing a solvent containing fibrous carbon with a media (hereinafter sometimes written as "media") type disperser to obtain a slurry, and kneading the slurry with an electrode active material to obtain a slurry to be applied to a current collector. However, in the case of a paste with a high pigment concentration and/or high viscosity, uniform dispersion cannot be achieved and storage stability is sometimes poor. In particular, if the slurry contains a large amount of water, high viscosity and gelation can occur.

JP 2014-182892 A

The object of the present invention is to provide a method for producing a carbon nanotube-dispersed paste and a method for producing a composite paste that are excellent in pigment dispersibility and storage stability even in a paste with a high pigment concentration and/or high viscosity, and further to provide an electrode layer for a lithium-ion secondary battery that is excellent in finish quality, conductivity, etc.

As a result of intensive research into solving the above problems, the inventors have discovered that the above problems can be solved by a method for producing a carbon nanotube dispersion paste, which includes a step of mixing and dispersing components containing a dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) having a moisture content of less than 10,000 ppm, and polyvinylidene fluoride (D), which can be included as necessary, and in which the moisture content of the carbon nanotube dispersion paste is less than 10,000 ppm, and thus has completed the present invention.

That is, the present invention provides the following carbon nanotube dispersion paste, composite paste, and method for producing an electrode layer for a lithium ion secondary battery.
Item 1.
A method for producing a carbon nanotube dispersion paste, comprising a step of mixing and dispersing components containing a dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) having a moisture content of less than 10,000 ppm, and polyvinylidene fluoride (D) which may be included as necessary, wherein the moisture content of the carbon nanotube dispersion paste is less than 10,000 ppm.
Item 2.
2. A method for producing a carbon nanotube dispersion paste according to item 1, characterized in that the mixing and/or dispersion is carried out in an atmosphere with a dew point of 10° C. or less.
Item 3.
Item 3. The method for producing a carbon nanotube dispersion paste according to item 1 or 2, characterized in that the dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms has 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 phosphoric acid group, an amino group and a cyano group, and has a polar functional group concentration of 0.1 mmol/g to 8.5 mmol/g.
Item 4.
Item 4. The method for producing a carbon nanotube dispersion paste according to any one of items 1 to 3, characterized in that the solvent (C) contains a recycled product of N-methyl-2-pyrrolidone, and the water content in N-methyl-2-pyrrolidone is controlled to less than 10,000 ppm.
Item 5.
5. The method for producing a carbon nanotube dispersion paste according to any one of items 1 to 4, wherein the carbon nanotube dispersion paste contains the polyvinylidene fluoride (D).
Item 6.
6. The method for producing a carbon nanotube dispersion paste according to item 5, wherein the step of mixing the polyvinylidene fluoride (D) includes a step of mixing and dissolving the polyvinylidene fluoride (D) with a solvent having a liquid temperature of 40° C. or higher in advance, or a step of mixing the polyvinylidene fluoride (D) with a solvent and then heating the mixture to a temperature of 40° C. or higher.
Item 7.
7. The method for producing a carbon nanotube-dispersed paste according to any one of items 1 to 6, wherein the carbon nanotube-dispersed paste further contains a highly polar, low-molecular-weight component (E).
Item 8.
8. The method for producing a carbon nanotube-dispersed paste according to any one of items 1 to 7, wherein the carbon nanotube-dispersed paste further contains a dehydrating agent (F).
Item 9.
9. The method for producing a carbon nanotube-dispersed paste according to any one of items 1 to 8, wherein the carbon nanotubes (B) are previously dry-dispersed using a media-type grinder.
Item 10.
The mixing and dispersing step comprises:
Step 1: adding a component containing carbon nanotubes (B) in an amount of 70% by mass or less based on 100% by mass of the total amount of carbon nanotubes (B) contained in the carbon nanotube dispersion paste obtained after dispersion to a dispersing machine and performing a dispersing process; and Step 2: adding carbon nanotubes (B) to a dispersing machine until a desired concentration is reached, and performing a dispersing process.
10. The method for producing a carbon nanotube dispersion paste according to any one of items 1 to 9, comprising the steps of:
Item 11.
When the moisture absorption amount of the carbon nanotube (B) is Y (mass%) and the BET specific surface area is Z (m ² /g), the following formula:
X = Y x Z
The value of X obtained by the above is in the range of X≦500,
The moisture absorption amount Y is measured under the following conditions: the mass of carbon nanotubes obtained by drying at 140° C. for 3 hours is Y1, and the mass of carbon nanotubes obtained by leaving at 20° C. for 24 hours under conditions of a relative humidity of 65% is Y2. The moisture absorption amount Y is calculated by the following formula: Y=(Y2-Y1)/Y1×100.
Item 11. The method for producing a carbon nanotube dispersion paste according to any one of items 1 to 10, wherein the value of Y (% by mass) obtained in step (a) is defined as the moisture absorption amount Y.
Item 12.
Item 12. A method for producing a composite paste for a lithium ion secondary battery, comprising mixing the carbon nanotube-dispersed paste obtained by the carbon nanotube-dispersed paste production method according to any one of Items 1 to 11 with an electrode active material (G).
Item 13.
The following steps:
A process for producing a carbon nanotube dispersion paste, the process comprising a process for mixing and dispersing components containing a dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) having a water content of less than 10,000 ppm, and polyvinylidene fluoride (D) which may be included as necessary, the carbon nanotube dispersion paste having a water content of less than 10,000 ppm; and
A step of producing a composite paste for a lithium ion secondary battery, the step including a step of mixing the carbon nanotube dispersion paste with an electrode active material (G), the composite paste having a moisture content of less than 10,000 ppm, and the electrode active material (G) being an electrode active material composite (G-1) having at least a part of its surface covered with carbon nanotubes;
A method for producing a composite paste for a lithium ion secondary battery comprising the steps of:
Item 14.
Item 13. A method for producing an electrode layer for a lithium ion secondary battery, comprising the step of applying the composite paste obtained by the method for producing the electrode layer for a lithium ion secondary battery to a current collector.
Item 15.
Item 15. A method for producing an electrode for a lithium ion secondary battery, comprising the step of applying an electrode insulating part to an end or an upper layer of the electrode layer obtained by the production method according to item 14.
Item 16.
Item 15. A method for producing a lithium ion secondary battery using a positive electrode having an electrode layer obtained by the production method according to item 14, a negative electrode, a non-aqueous electrolyte, and a separator.

The method for producing a carbon nanotube dispersion paste of the present invention is excellent in pigment dispersibility and storage stability even at high pigment concentrations and/or high viscosities, and can sufficiently reduce the viscosity of the paste with a relatively small amount of dispersion resin. In addition, the electrode layer for lithium ion secondary batteries produced by this method is excellent in finish, conductivity, battery performance, etc.

The following provides a detailed explanation of how to implement the present invention.

It should be understood that the present invention is not limited to the following embodiments, but includes various modified examples that are implemented within the scope that does not deviate from the gist of the present invention.
In the present invention, the paste containing carbon nanotubes is called a "carbon nanotube dispersion paste", but it can also be called an "conductive pigment paste".
The paste prepared by further mixing at least one electrode active material and, optionally, other various components in order to coat the carbon nanotube dispersion paste is called a "composite paste." The composite paste that is coated on a substrate and dried is called a "coating film" or a "composite layer."
It can be said that the carbon nanotube dispersion paste is a paste that does not substantially contain an electrode active material.
The carbon nanotubes can also be abbreviated as "CNT."
When the coating film is used as an electrode for a battery, it can also be called an "electrode layer."

In the present invention, by making the moisture content of the carbon nanotube dispersion paste less than 10,000 ppm (and further making the moisture content of the solvent (C) less than 10,000 ppm), it is possible to suppress high viscosity and gelation during storage.

The mechanism by which the carbon nanotube dispersion paste and the composite paste (for lithium ion secondary batteries) become viscous and gelate has not been clarified, but the following mechanism is presumed.
For example, in a composite paste containing polyvinylidene fluoride, the acidity of the proton adjacent to the fluorine group in polyvinylidene fluoride is very high due to the electron-attracting property of the fluorine group, and therefore, this proton desorption proceeds easily, especially under basic conditions. It is speculated that such proton desorption is particularly likely to proceed when moisture is present in the carbon nanotube dispersion paste and the composite paste. After proton desorption, anions are generated on the carbon, which promotes the desorption of the fluorine group, and double bonds are generated in the main chain of the polyvinylidene fluoride molecule. It is speculated that the multiple polyvinylidene fluoride molecules that have double bonds are polymerized and further polymerized, leading to an increase in viscosity and gelation. In particular, since the electrode active material in the composite paste may contain lithium hydroxide, which is a relatively strong base, the increase in viscosity and gelation are remarkable in the composite paste.

In the present invention, it is believed that by using raw materials with a specified moisture content and by specifying the moisture content of the carbon nanotube dispersion paste and composite paste, polymerization of the polymer component (polyvinylidene fluoride) is suppressed, and the viscosity increase and gelation of the carbon nanotube dispersion paste or composite paste (for lithium ion secondary batteries) can be suppressed.
Furthermore, since the moisture is brought in from various raw materials (particularly solvents) and is mixed in from water vapor contained in the air during the manufacturing process, it is practically impossible to reduce the moisture to zero.
Therefore, the water content of the carbon nanotube dispersion paste that can be used in the present invention is preferably 100 ppm or more, more preferably 200 ppm or more, and even more preferably 500 ppm or more. The water content of the solvent (C) is preferably 100 ppm or more, more preferably 200 ppm or more, and even more preferably 500 ppm or more.
If it is within the above lower limit, production can be performed without excessive moisture content control of the raw materials (reduction of moisture content) or excessive moisture content control in the production process (reduction of moisture contamination).
In addition, in producing the paste of the present invention, it is preferable to carry out mixing and/or pigment dispersion in an atmosphere having a dew point of 10° C. or less, more preferably a dew point of 7° C. or less, and even more preferably a dew point of 5° C. or less, from the viewpoints of reducing moisture contamination and storage stability.

[Method of manufacturing carbon nanotube dispersion paste]
The present invention provides a method for producing a carbon nanotube dispersion paste, comprising a step of mixing and dispersing components containing a dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) having a water content of less than 10,000 ppm, and polyvinylidene fluoride (D) which may be included as necessary, wherein the water content of the carbon nanotube dispersion paste is less than 10,000 ppm.
The water content of the carbon nanotube dispersion paste is preferably less than 7500 ppm, more preferably less than 5000 ppm, further preferably less than 2500 ppm, and particularly preferably less than 1000 ppm.
The carbon nanotube dispersion paste in the present invention can be said to be a substantially non-aqueous paste.

In the present invention, the moisture content can be measured by Karl Fischer coulometric titration. Specifically, a Karl Fischer moisture meter (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name "MKC-610") is used, and the moisture vaporizer (manufactured by Kyoto Electronics Co., Ltd., product name "ADP-611") attached to the device is set at a temperature of 130°C.

Dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms
As the dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, any resin having a heterocycle and/or an alkyl group having 12 or more carbon atoms in the resin can be suitably used.
The heterocycle includes other atoms in addition to carbon atoms in its ring structure, and the other atoms are, for example, oxygen, nitrogen, sulfur, etc. The number of ring structures included in the heterocycle is preferably one or two, and more preferably one. The atoms other than carbon constituting the ring are preferably oxygen and/or nitrogen, and more preferably oxygen. It is believed that when the atoms constituting the ring include atoms other than carbon atoms, polarization occurs in the heterocycle, and the carbon-based conductive pigment (carbon nanotubes in the present invention) can be strongly affected. It is also believed that when the dispersion resin has a relatively bulky side chain such as a heterocycle or an alkyl group having 12 or more carbon atoms, the pigment dispersibility and storage stability are improved due to steric repulsion.

The method of introducing a heterocycle into the dispersion resin (A) is not particularly limited, and examples thereof include (co)polymerization reaction of a monomer containing a heterocycle, modification reaction of a polymer (resin), and/or addition reaction. Examples of polymerizable monomers containing a heterocycle include 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-morpholinedione, glycidyl (meth)acrylate, maleic anhydride, itaconic anhydride, and the like. These may be used alone or in combination of two or more.
The alkyl group having 12 or more carbon atoms can be any known alkyl group (hydrocarbon group) without any particular limitation. A straight-chain or branched alkyl group is preferable, and a straight-chain alkyl group is more preferable.
The alkyl group having 12 or more carbon atoms is preferably an alkyl group having 12 or more and less than 30 carbon atoms, more preferably an alkyl group having 15 or more and less than 26 carbon atoms, and even more preferably an alkyl group having 19 or more and less than 24 carbon atoms.
The method of introducing an alkyl group having 12 or more carbon atoms into the dispersion resin (A) is not particularly limited, and examples thereof include (co)polymerization reaction of a monomer containing an alkyl group having 12 or more carbon atoms, modification reaction of a polymer (resin), and/or addition reaction. Examples of polymerizable monomers containing an alkyl group having 12 or more carbon atoms include lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, behenyl (meth)acrylate, lauryl (meth)acrylamide, stearyl (meth)acrylamide, behenyl (meth)acrylamide, etc. These can be used alone or in combination of two or more.

The type of resin that serves as the skeleton is not particularly limited as long as it is a resin other than polyvinylidene fluoride (D) described below. Examples include acrylic resins, polyester resins, epoxy resins, polyether resins, alkyd resins, urethane resins, polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, polyvinyl acetate, silicone resins, polycarbonate resins, chlorine-based resins, and composite resins thereof. These resins contain heterocycles and/or alkyl groups having 12 or more carbon atoms, or these resins are synthesized and then added or modified to introduce heterocycles and/or alkyl groups having 12 or more carbon atoms, thereby producing resins having heterocycles and/or alkyl groups having 12 or more carbon atoms. These resins can be used alone or in combination of two or more.

Among these, from the viewpoints of pigment dispersibility, storage stability, finish quality, etc., the dispersing resin (A) preferably contains a vinyl (co)polymer (A1) obtained by polymerizing or copolymerizing a monomer containing a polymerizable unsaturated group-containing monomer of the following formula (1), and in particular, an acrylic resin (co)polymerized with at least one polymerizable unsaturated group-containing monomer containing a (meth)acryloyl group is preferred.
Incidentally, the "(co)polymer" of the present invention includes both a polymer obtained by polymerizing one type of monomer and a copolymer obtained by copolymerizing two or more types of monomers.

C(-R) ₂ =C(-R) ₂ ...Formula (1)
[In the above formula, R may be the same or different and is a hydrogen atom or an organic group. R may be linked to each other to form a ring.]
The vinyl (co)polymer (A1) can be produced by a polymerization method known per se. For example, it is preferable to use solution polymerization, but this is not limited thereto. For example, bulk polymerization or emulsion polymerization can be used. When solution polymerization is carried out, it may be continuous polymerization or batch polymerization, and the monomers may be charged all at once or in portions, or may be charged continuously or It may be added intermittently.

The polymerization initiator used in the solution polymerization is not particularly limited, but specific examples include azo compounds such as azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), azobis-2,4-dimethylparabennitrile, and azobis(4-methoxy-2,4-dimethylparabennitrile); acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, and 2,4,4-trimethylpentyl-2,4-dimethylparabennitrile. -Peroxides such as peroxyphenoxyacetate; percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and t-butyl peroxyneodecanate; and known radical polymerization initiators such as azobisdimethylvaleronitrile and azobismethoxyvaleronitrile can be used.

The polymerization reaction temperature is not particularly limited, but can usually be set in the range of 30°C or higher and 200°C or lower.

The vinyl (co)polymer (A1) obtainable as described above has a degree of polymerization of, for example, 100 or more, preferably 150 or more, and, for example, 4,000 or less, preferably 3,000 or less, more preferably 700 or less.

The weight average molecular weight is, for example, 1,000 or more, preferably 2,000 or more, more preferably 7,000 or more, and, for example, 2,000,000 or less, preferably 1,000,000 or less, more preferably 500,000 or less.

In this specification, unless otherwise specified, the weight average molecular weight is a value obtained by converting the retention time (retention volume) measured using a gel permeation chromatograph (GPC) into the molecular weight of polystyrene using the retention time (retention volume) of a standard polystyrene of known molecular weight measured under the same conditions. Specifically, the gel permeation chromatograph is "HLC8120GPC" (product name, manufactured by Tosoh Corporation), and the four columns are "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and "TSKgel G-2000HXL" (all product names, manufactured by Tosoh Corporation), and the measurements can be performed under the following conditions: mobile phase tetrahydrofuran, measurement temperature 40°C, flow rate 1mL/min, and detector RI.

After completion of the synthesis, the vinyl (co)polymer (A1) can be converted into a solid or into a resin solution in which any solvent has been replaced by removing the solvent and/or replacing the solvent.

The method for removing the solvent may be performed by heating at normal pressure or under reduced pressure. The method for replacing the solvent may be performed by adding a replacement solvent at any stage before, during, or after the removal of the solvent.
In addition, the content of the heterocycle in the dispersion resin (A), in the case of the vinyl (co)polymer (A1), is preferably 1 to 100 mass%, more preferably 10 to 100 mass%, further preferably 30 to 99 mass%, and particularly preferably 50 to 95 mass%, in terms of the mass ratio of the polymerizable monomer containing the heterocycle when the total amount of the monomers is taken as 100 mass%.
In the case of the vinyl (co)polymer (A1), the content of the alkyl group having 12 or more carbon atoms in the dispersion resin (A) is preferably 1 to 100 mass%, more preferably 10 to 90 mass%, still more preferably 20 to 80 mass%, and particularly preferably 30 to 60 mass%, expressed as the mass ratio of the polymerizable monomer containing an alkyl group having 12 or more carbon atoms when all monomers are taken as 100 mass%.
In addition, the content of the heterocycle and the alkyl group having 12 or more carbon atoms is calculated based on the mass ratio of the reactive compound (a compound having a heterocycle or an alkyl group having 12 or more carbon atoms) added to the resin later.

The dispersion resin (A) having the heterocycle and/or an alkyl group having 12 or more carbon atoms has 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 phosphoric acid group, an amino group, and a cyano group, in addition to the heterocycle and/or the alkyl group having 12 or more carbon atoms, and the polar functional group concentration is preferably 0.1 mmol/g to 8.5 mmol/g, more preferably 0.2 mmol/g to 6.0 mmol/g, even more preferably 0.3 mmol/g to 4.0 mmol/g, and particularly preferably 0.4 mmol/g to 2.0 mmol/g. The acid group and amino group may be in the form of a salt.
Among these, the polar functional group preferably has a hydroxyl group, an acid group and/or an amino group, more preferably has a hydroxyl group and/or an amino group, and further preferably has an amino group.
The amino group is usually a secondary or tertiary amino group, with a tertiary amino group being preferred.

When the dispersion resin (A) having the above-mentioned heterocycle and/or an alkyl group having 12 or more carbon atoms is converted from a solid state into a resin solution, from the viewpoint of solubility in the solvent, it is preferable to first mix and dissolve the resin in a solvent having a liquid temperature of 60°C or higher (preferably 80°C or higher) (upper limit is 200°C or lower, preferably 100°C or lower) to convert it into a resin solution, and after converting it into a resin solution, it is preferable to mix it with other components (components (B), (C), (D), etc.).
The "liquid temperature" refers to the temperature of the solvent or resin solution at the time of dissolution.
The solid dispersion resin (A) may be mixed and dissolved in a solvent at 60° C. or higher in advance, or the solid dispersion resin (A) may be mixed with a solvent and then heated to a temperature of 60° C. or higher.
Furthermore, the dispersion may contain components other than the dispersion resin (A) and the solvent.
The solvent may be used alone or in combination of two or more kinds, and as the type, those exemplified as the solvent (C) described later can be suitably used.
In addition, it is preferable to cool the resin solution that has been hot-dissolved as described above to a predetermined temperature of 10° C. to 40° C., and the cooling step is carried out by the following reaction:
From the viewpoint of preventing precipitation, it is preferable that the cooling rate, defined as cooling rate=(solution temperature at the start of cooling−solution temperature at the end of cooling)/cooling time, is 0.5° C./min or more (preferably 1° C./min or more).

The solid content of the dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms is, based on 100% by mass of the total solid content of the carbon nanotube dispersion paste, for example, 0.1% by mass or more, preferably 1% by mass or more, and more preferably 3% by mass or more, and for example, 40% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less.
In addition, the solid content of the dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms is, based on the total amount of the carbon nanotube dispersion paste as 100 mass%, for example, 0.1 mass% or more, preferably 0.4 mass% or more, and more preferably 0.7 mass% or more, and for example, 10 mass% or less, preferably 5 mass% or less, and more preferably 2 mass% or less.

The solid content of the dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms is, based on the content of the carbon nanotubes (B) of 100% by mass, for example, 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, and for example, 150% by mass or less, preferably 120% by mass or less, more preferably 80% by mass or less.

Carbon nanotubes (B)
As the carbon nanotubes (B), single-walled carbon nanotubes or multi-walled carbon nanotubes can be used alone or in combination. In particular, in terms of viscosity, electrical conductivity, and cost, it is preferable to use multi-walled carbon nanotubes.
The content of carbon nanotubes (B) is, based on 100 mass% of the total amount of the carbon nanotube dispersion paste, for example, 0.5 mass% or more, preferably 1 mass% or more, and more preferably 2 mass% or more, and for example, 10 mass% or less, preferably 7 mass% or less, and more preferably 6 mass% or less.
Furthermore, based on 100% by mass of the total solid content of the carbon nanotube dispersion paste, it is, for example, 5% by mass or more, preferably 10% by mass or more, and more preferably 20% by mass or more, and for example, 90% by mass or less, preferably 70% by mass or less, and more preferably 50% by mass or less.

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 is, for example, 30 nm or less, preferably 28 nm or less, more preferably 25 nm or less.

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 is, for example, 100 μm or less, preferably 80 μm or less, more preferably 60 μm or less.

The BET specific surface area of the carbon nanotubes (B) is, in consideration of the relationship between viscosity and electrical conductivity, usually 100 m ² /g or more, preferably 130 m ² /g or more, more preferably 160 m ² /g or more, and usually 800 m ² /g or less, preferably 600 m ² /g or less, more preferably 400 m ² /g or less.
The BET specific surface area of the present invention can be calculated by the BET method using nitrogen adsorption measurement. Specifically, for example, the BET specific surface area (m ² /g) can be measured using a specific surface area measuring device (BERSORP-MAX (Microtrac-Bell Co., Ltd.)) in accordance with JIS Z8830:2013.

The amount of acidic groups in the carbon nanotubes (B) is usually 0.01 mmol/g or more, preferably 0.01 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 viewpoints of dispersibility and storage property. If the amount of acidic groups is 0.01 mmol/g or more, the dispersibility will be good, and if it is 1.0 mmol/g or less, the storage property will be good.

The above acidic groups can be imparted to carbon nanotubes by acid treatment as described below.

(Acid Treatment Method)
The acid treatment method is not particularly limited as long as it can bring the carbon nanotubes into contact with the acid, but a method of immersing the carbon nanotubes in an acid treatment solution (aqueous solution of acid) is preferred. The acid contained in the acid treatment solution is not particularly limited, but examples thereof include nitric acid, sulfuric acid, and hydrochloric acid. These can be used alone or in combination of two or more. Among these, nitric acid and sulfuric acid are preferred.
The amount of acidic groups in the carbon nanotubes can be adjusted by the concentration of the acid treatment solution, the temperature, the treatment time, and the like.

After the acid treatment, the excess acid component adhering to the surface is removed by a washing method described below, thereby obtaining acid-treated carbon nanotubes.
The method for washing the acid-treated carbon nanotubes is not particularly limited, but washing with water is preferred. For example, the carbon nanotubes are collected from the acid-treated carbon nanotubes by a known method such as filtration, and then washed with water. After the above washing, the water adhering to the surface can be removed by drying, etc., as necessary, to obtain the acid-treated carbon nanotubes.

The volume-equivalent median diameter (D50) of the carbon nanotubes (B) is usually 10 μm or more, preferably 15 μm or more, more preferably 20 μm or more, and usually 250 μm or less, preferably 200 μm or less, more preferably 150 μm or less, when measured by the method described in the examples below. Here, the median diameter (D50) can be obtained by irradiating a carbon nanotube particle with a laser beam and converting the diameter of the carbon nanotube into a sphere from the scattered light. The larger the median diameter (D50), the more carbon nanotube agglomerates there are, which means that the dispersibility is poor. If the median diameter (D50) is larger than 250 μm, there is a high possibility that carbon nanotube agglomerates exist in the electrode, and the conductivity of the entire electrode becomes non-uniform. On the other hand, if the median diameter (D50) is smaller than 10 μm, the fiber length is short, so the conductive path is insufficient, and the conductivity decreases. When the median diameter (D50) is within the range of 10 μm or more and 250 μm or less, the carbon nanotubes can be uniformly dispersed within the electrode while maintaining their electrical conductivity.

In the Raman spectrum of the carbon nanotube (B), the G/D ratio, where G is the maximum peak intensity in the range of 1560 cm ^-1 to 1600 cm ^-1 and D is the maximum peak intensity in the range of 1310 cm ^-1 to 1350 cm ^-1 , is usually 0.1 or more, preferably 0.4 or more, more preferably 0.6 or more, and is usually 5.0 or less, preferably 3.0 or less, more preferably 1.0 or less.

Here, a G/D ratio in 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.

(Dry Dispersion of Carbon Nanotubes)
The carbon nanotubes (B) can be previously dry-dispersed in a media-type grinder before producing the carbon nanotube dispersion paste.
The "dry dispersion" of the present invention refers to pulverization (including disintegration) by a pulverizer at a solid content concentration in the pulverized component of 80% by mass or more (preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more). Although it is possible to pulverize together with components other than the carbon nanotubes (B), it is suitable that the content of the carbon nanotubes (B) contained in the solid content of the pulverized component is usually 80% by mass or more, preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably only the carbon nanotubes (B).
As the components other than the carbon nanotubes (B) in the ground component, solvents, resins, pigments other than the carbon nanotubes (B), etc. can be suitably used, but it is preferable that the ground component contains substantially only the carbon nanotubes (B).
The above "solid content concentration" refers to the proportion of solid content (mass %) when 1 g of a sample is dried by heating at 130° C. for 3 hours.

The above-mentioned dry dispersion is a method of grinding pigments without the inclusion of any liquid components, and since energy can be applied directly to the pigment, it is possible to perform highly efficient and powerful grinding (disintegration). In addition, since the ground surface is activated and interacts with the surrounding substances, good dispersibility and storage stability can be obtained in the paste dispersion process described below, and the coating film can have excellent conductivity and finish.

In the above-mentioned dry dispersion, grinding is carried out using a grinding machine equipped with grinding media such as glass beads, zirconia beads, steel balls, etc. Grinding is carried out by utilizing the crushing force or destructive force caused by collisions between the grinding media and/or between the grinding machine and the grinding media. As the grinding device, known grinding devices such as a high-speed rotation impact mill, jet mill, roll mill, attritor, ball mill, vibration mill, bead mill, etc. can be used.

In addition, various steam or gases can be blown into the grinder during grinding to further activate the surface of the carbon nanotubes (B) or adjust the activity. As the steam, acidic or basic compounds are suitable, and as the gas, oxygen, nitrogen, etc. are suitable.

The outer diameter of the grinding media is preferably 0.1 mm to 5 mm, and more preferably 0.5 mm to 3 mm. Within the above range, the desired grinding force can be obtained, and the pigment can be efficiently ground and crushed without excessively destroying the fiber shape of the carbon nanotubes.

(Moisture absorption of carbon nanotubes)
It is known that the carbon nanotubes (B) adsorb moisture from the air during the processes of producing and storing the carbon nanotubes and producing and storing various pastes, but in the present invention, it is desirable that the carbon nanotubes do not adsorb moisture during each process. The amount of water (moisture absorption) of the carbon nanotubes (B) absorbed by the humidity of the air depends on the humidity, the surface area of the carbon nanotubes, and the surface properties (hydrophilicity) of the carbon nanotubes.

When the moisture absorption amount of carbon nanotubes (B) under certain conditions is Y (mass%) and the BET specific surface area is Z ( ^m2 /g), the upper limit of the moisture absorption rate X obtained by X = Y x Z is usually 1,000 or less, preferably 500 or less, and more preferably 300 or less, and the lower limit is usually 10 or more, preferably 50 or more, and more preferably 100 or more.
The inventors have discovered that by keeping the content within the above range, the amount of moisture adsorption by the carbon nanotubes (B) can be reduced, thereby suppressing thickening and gelling of the paste while also achieving dispersibility (adsorption with a dispersant).

The moisture absorption amount Y is determined under the following measurement conditions.
[Conditions for measuring moisture absorption amount Y]
The mass of the carbon nanotubes obtained by drying at 140°C for 3 hours is defined as Y1, and the mass of the conductive carbon obtained by leaving it for 24 hours under conditions of a temperature of 20°C and a relative humidity of 65% is defined as Y2. The value of Y (mass%) obtained by the following formula is defined as the moisture absorption amount Y.
Moisture absorption amount Y=(Y2-Y1)/Y1×100

Other conductive pigments (B1)
The carbon nanotube dispersion paste used in the present invention can also use other conductive pigments (B1) other than the carbon nanotubes (B). Examples of other conductive pigments (B1) include at least one conductive carbon selected from the group consisting of acetylene black, ketjen black, furnace black, thermal black, graphene, and graphite. Preferably, it is at least one selected from the group consisting of acetylene black, ketjen black, furnace black, and thermal black, more preferably at least one selected from the group consisting of acetylene black and ketjen black, and even more preferably it is acetylene black.

The average primary particle diameter of the other conductive pigment (B1) is, for example, 10 nm or more, preferably 20 nm or more, and more preferably, for example, 80 nm or less, and more preferably, 70 nm or less. Here, the average primary particle diameter refers to the average particle diameter of the primary particles obtained by observing the conductive pigment (B1) under an electron microscope, calculating the projected area of each of 100 particles, calculating the diameter of a circle assuming an area equal to that area, and then averaging the diameters of the 100 particles. Note that if the pigment is in an aggregated state, the calculation is performed using the primary particles that make up the aggregated particles.

The BET specific surface area of the other conductive pigment (B1) is not particularly limited and is, for example, 1 m ² /g or more, preferably 10 m ² /g or more, more preferably 20 m ² /g or more, and is, for example, 500 m ² /g or less, preferably 250 m ² /g or less, more preferably 200 m ² /g or less, depending on the relationship between viscosity and conductivity.

The dibutyl phthalate (DBP) oil absorption of the other conductive pigment (B1) is not particularly limited. In relation to pigment dispersibility and conductivity, it is, 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.

Solvent (C)
The solvent (C) has a water content of less than 10,000 ppm, and an organic solvent can be suitably used. Specific examples of the solvent include hydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, and cyclobutane; aromatic solvents such as toluene and xylene; 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, and ethylene glycol mono. Examples of the solvent include ester-based solvents such as methyl ether acetate and butyl carbitol acetate; ketone-based solvents such as methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone; alcohol-based solvents such as ethanol, isopropanol, n-butanol, sec-butanol and isobutanol; and amide-based solvents such as Equamide (an amide-based solvent, product name, manufactured by Idemitsu Kosan Co., Ltd.), N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide, N-methylacetamide, N-methylpropioamide and N-methyl-2-pyrrolidone.

Among these, amide-based solvents are preferred, and N-methyl-2-pyrrolidone is more preferred. These solvents can be used alone or in combination of two or more.

The water content of the solvent (C) is usually 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.

When using amide compounds (solvents) such as N-methyl-2-pyrrolidone, amine components may be contained as impurities, and in the carbon nanotube dispersion paste of the present invention, the viscosity or tendency to thicken may vary from lot to lot depending on the amine components as impurities.

In addition, when the carbon nanotube dispersion paste of the present invention is applied to an electrode layer by the method described below, the solvent and the like volatilize and do not remain, but it is preferable to recover and reuse the volatilized solvent in order to reduce waste, be environmentally friendly, and/or reduce raw material costs. That is, it is preferable to use a recycled product as the solvent (C). In the case where the carbon nanotube dispersion paste of the present invention contains an amine compound (E1), this recycled solvent (recycled product) will also contain the amine compound originally contained therein, and similarly, the viscosity or thickening tendency of the paste will differ from lot to lot. Furthermore, amine compounds often have a strong odor.

In this case, therefore, it is preferable to control and adjust the amine compound content in the recycled solvent (C) to a certain amount or less, and the amine compound content is usually 1 mass% or less, preferably 0.5 mass% or less, and particularly preferably 0.1 mass% or less.
The content of the amine compound can be quantified by a general analysis such as ion chromatography-mass spectrometry (IC-MS). The content can be quantified by preparing a calibration curve in advance for the peaks of amine species that are expected to be mixed in.

The above phrase "use of a recycled product as the solvent (C)" means that the solvent (C) used in the present invention contains 5% by mass or more (preferably 10% by mass or more) of a recycled product.
As the above-mentioned recycled product, it is preferable to use the solvent recovered in the process of producing an electrode layer by heating and drying a composite paste, which will be described later.

In addition, when a recycled product is used as the solvent (C) and the carbon nanotube dispersion paste of the present invention contains the highly polar low molecular weight component (E) described later, it is necessary to remove the highly polar low molecular weight component (E) in the solvent (C). Therefore, when the boiling point of the solvent (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 it is preferable that (Xc)-15>(Xe) from the viewpoint of distillation (removal of the highly polar low molecular weight component (E)).
The solvent (C) preferably contains N-methyl-2-pyrrolidone. When N-methyl-2-pyrrolidone is contained, it is preferable to use a recycled product of N-methyl-2-pyrrolidone. Furthermore, it is suitable to control the water content in N-methyl-2-pyrrolidone to 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).
The highly polar, low-molecular-weight component (E) preferably contains an amine compound (E1).

The content of the solvent (C) in the carbon nanotube dispersion paste is, based on 100 mass% of the total amount of the carbon nanotube dispersion paste, for example, 40 mass% or more, preferably 60 mass% or more, and more preferably 80 mass% or more, and for example, 99 mass% or less, preferably 98 mass% or less, and more preferably 97 mass% or less.
The solid content of the carbon nanotube dispersion paste is, based on 100% by mass of the total amount of the carbon nanotube dispersion paste, for example, 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more, and is, for example, 60% by mass or less, preferably 40% by mass or less, and more preferably 20% by mass or less.

Polyvinylidene fluoride (D)
The polyvinylidene fluoride (D) is a resin intended for forming a film of an electrode layer, and can be contained in the carbon nanotube dispersion paste of the present invention as necessary, and is preferably contained. Also, it is an essential component of the composite paste described later.
Also, variously modified modified polyvinylidene fluoride (D1) can be suitably used, and it is preferable that the modified polyvinylidene fluoride has a polar functional group from the viewpoint of adhesion to the substrate.

The weight average molecular weight of polyvinylidene fluoride (D) is, from the viewpoints of adhesion to the substrate, reinforcement of the 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.

When polyvinylidene fluoride (D) is contained, the content is, based on 100% by mass of the solid content of the carbon nanotube dispersion paste, for example, 10.0% by mass or more, preferably 30.0% by mass or more, more preferably 40.0% by mass or more, and 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, and for example, 10% by mass or less, preferably 7% by mass or less, more preferably 5% by mass or less.

The step of converting the polyvinylidene fluoride (D) from a solid state into a resin solution preferably includes a step of mixing and dissolving the polyvinylidene fluoride (D) in a solvent having a liquid temperature of 40° C. or higher (preferably 60° C. or higher, more preferably 80° C. or higher) (upper limit is 200° C. or lower, preferably 100° C. or lower) in advance to convert the polyvinylidene fluoride (D) into a resin solution, from the viewpoint of solubility in the solvent. After conversion into a resin solution, the polyvinylidene fluoride (D) is preferably mixed with other components [components (A), (B), (C), etc.].
The "liquid temperature" refers to the temperature of the solvent or resin solution at the time of dissolution.
Solid polyvinylidene fluoride (D) may be mixed in advance into a solvent at 40° C. or higher and dissolved therein, or solid polyvinylidene fluoride (D) may be mixed with a solvent and then heated to a temperature of 40° C. or higher.
In addition, the composition may contain components other than the polyvinylidene fluoride (D) and the solvent.
The solvent may be used alone or in combination of two or more kinds, and as the type, those exemplified above as the solvent (C) can be suitably used.
In addition, it is preferable to cool the resin solution that has been hot dissolved as described above to a predetermined temperature of 10° C. or more and less than 40° C., and the cooling step is carried out by reacting the resin solution with ... by the following reaction:
From the viewpoint of preventing precipitation, it is preferable that the cooling rate, defined as cooling rate=(solution temperature at the start of cooling−solution temperature at the end of cooling)/cooling time, is 0.5° C./min or more (preferably 1° C./min or more).

Mixing and Dispersing In the manufacturing method of the present invention, the mixing and dispersing step is a step of mixing and further dispersing components containing a dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) having a water content of less than 10,000 ppm, and polyvinylidene fluoride (D) which can be included as necessary, and obtaining a liquid carbon nanotube dispersion paste.

The upper limit of the solids concentration of the carbon nanotube dispersion paste is usually less than 80% by mass, preferably less than 50% by mass, more preferably less than 20% by mass, and even more preferably less than 10% by mass. The lower limit is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more.

In the mixing and dispersing step, the components can be uniformly mixed and dispersed using a conventionally known dispersing machine such as a paint shaker, a sand mill, a ball mill, a pebble mill, an LMZ mill, a DCP pearl mill, a planetary ball mill, a homogenizer, a twin-screw kneader, a thin film rotary high-speed mixer (manufactured by Filmix, product name "Clearmix", etc.), etc. The order in which the components are mixed is not particularly limited.
The mixing and dispersing step further comprises:
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 100% by mass of the total amount of carbon nanotubes (B) contained in the carbon nanotube dispersion paste obtained after dispersion to a dispersing machine and performing a dispersing process; and Step 2: adding carbon nanotubes (B) to a dispersing machine until a desired concentration is reached, and performing a dispersing process.
It is preferable that the method includes the steps of sequentially carrying out the steps.
The dispersion treatment time in step 1 is preferably at least 30 seconds or more (preferably 1 minute or more).
By carrying out the above-mentioned mixing and dispersion, the aggregation of the carbon nanotubes (B) is alleviated, and a homogeneous paste with good dispersibility is obtained even in a high-concentration paste, and the resulting battery electrode layer (coating film) has excellent finish, conductivity, battery performance, etc.

High polar low molecular weight component (E)
The carbon nanotube dispersion paste may further contain a high-polarity, low-molecular-weight component (E). The high-polarity, low-molecular-weight component (E) is a component that increases the wettability and/or storage stability of the conductive pigment. Examples of the compound include basic components and acidic components known per se, and among these, it is preferable to contain an amine compound (E1).

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).

Examples of the amine compound (E1) include ammonia, primary amines, secondary amines, and tertiary amines.

Primary amines include, for example, ethylamine, n-propylamine, sec-propylamine, n-butylamine, sec-butylamine, i-butylamine, tert-butylamine, pentylamine, hexylamine, heptylamine, octylamine, decylamine, laurylamine, myristyrylamine, 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-furan, primary monoamines such as phenylethylamine, naphthylamine, and 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-bisa Aminopropylpiperazine, 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'-bis(o-toluidine), dianisidine, 4,4'-diaminodiphenylmethane, 2,2-(4,4'-diaminodiphenyl)propane, 4,4'-diaminodiphenyl ether, 4,4'-thiodianiline, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminoditolyl sulfone, methylenebis(o-chloroaniline), 3,9-bis(3-aminopropyl)2,4,8,10-tetraoxaspiro[5,5]undecane, diethylene Examples of primary polyamines include bis(hexamethylene)triamine, 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.

Secondary amines include, for example, 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-leupetidine, 2,6-leupetidine, 3,5-leupetidine, diphenylamine, secondary monoamines such as 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 ... '-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 Examples of secondary polyamines include hexane, 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.

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, tri-cyclohexylamine, N,N-dimethylhexylamine, N-methyldihexylamine, N,N-dimethylcyclohexylamine, N-methyldicyclohexylamine, N,N-diethylethanolamine, N,N-dimethylethanolamine, N-ethyldiethanolamine, triethanolamine, tribenzylamine, N,N-dimethylbenzylamine, diethylbenzylamine, tertiary monoamines such as diphenylamine, 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, and 2-, 3-, and 4-picoline; tetramethylethylenediamine, Examples of tertiary polyamines include pyrazine, 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.

These can be used alone or in combination of two or more types.

Among these, primary amine compounds are preferred, and monovalent amine compounds (monoamines) are more preferred.

The above amine compound (E1) may be an aliphatic amine, an alicyclic amine, an aromatic amine, an alkanolamine, etc., any of which may be suitably used, but aromatic amines are preferred.

Since it is preferable that no amine compound remains in the electrode layer after drying, 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 particularly 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.
Furthermore, if the boiling point is low, there is a possibility that the liquid will volatilize during production or storage, and furthermore, from the viewpoint of odor, the lower limit is preferably 50° C. or higher, and more preferably 100° C. or higher.

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

As other highly polar, low molecular weight components, for example, an acidic highly polar, low molecular weight component selected from organic acids and inorganic acids can be used alone or in combination with two or more of them in combination with the amine compound (E1). Also, a basic highly polar, low molecular weight component selected from organic bases and inorganic bases can be used alone or in combination with two or more of them.

Examples of organic acids include organic carboxylic acids (formic acid, acetic acid, propionic acid, benzoic acid, phthalic acid, etc.) and organic sulfonic acids (benzenesulfonic acid, etc.), while examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc., and their acid anhydrides can also be used.

Examples of organic bases include base components other than amine compounds, and examples of inorganic bases include metal hydroxides (sodium hydroxide, potassium hydroxide, etc.).

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

Based on 100% by mass of the solid content of the carbon nanotubes (B), the lower limit is, for example, 1% by mass or more, preferably 2% by mass or more, and more preferably 5% by mass or more, and the upper limit is, for example, 1,000% by mass or less, preferably 500% by mass or less, and more preferably 50% by mass or less.
Based on 100% by mass of the total amount of the carbon nanotube dispersion paste, the lower limit is, for example, 0.01% by mass or more, preferably 0.05% by mass or more, and more preferably 0.1% by mass or more, and the upper limit is, for example, 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less.

Many highly polar, low molecular weight components (E) [especially amine compounds (E1)] have a strong odor, which can lead to poor working conditions during mixing and drying. In addition, they are generally expensive, which can lead to increased costs. Therefore, it is necessary to keep the content at the minimum necessary.

The content ratio of the solvent (C) to the highly polar, low molecular weight component (E) is usually within the range of 100/0.01 to 100/10, preferably within the range of 100/0.02 to 100/7, more preferably within the range of 100/0.05 to 100/5, and more preferably within the range of 100/0.1 to 100/4, in terms of the mass ratio of the solvent (C) to the highly polar, low molecular weight component (E).

Furthermore, when the carbon nanotube dispersion paste used in the manufacturing method of the present invention contains a highly polar, low molecular weight component (E), the value of X in the following formula (2), where α (parts by mass) is the content of the highly polar, low molecular weight component (E) per 100 parts by mass of the carbon nanotubes (B) and β ( ^m2 /g) is the BET specific surface area of the carbon nanotubes (B), is usually 1 or more, preferably 5 or more, and more preferably 10 or more, and is usually 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 (2)
It has been found that within this range, the highly polar, low molecular weight component (E) can be wetted to the surface of the carbon nanotubes (B) in a necessary and sufficient manner, thereby improving the dispersibility (including viscosity) and storage stability (including inhibition of thickening) of the carbon nanotubes (B).

If the content exceeds the upper limit range, the content of the highly polar, low molecular weight component (E) relative to the surface area of the carbon nanotube (B) is excessive (increased odor and cost), and if the content falls below the lower limit range, the content of the highly polar, low molecular weight component (E) relative to the surface area of the carbon nanotube (B) is insufficient.

In addition, when the carbon nanotube dispersion paste used in the manufacturing method of the present invention contains carbon nanotubes (B) and an amine compound (E1), the value of Y in the following formula (3), where α (parts by mass) is the content of the amine compound (E1) relative to 100 parts by mass of the carbon nanotubes (B), β (m ² /g) is the BET specific surface area of the carbon nanotubes (B), and γ (mmol/g) is the amount of acidic groups in the carbon nanotubes (B), is preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and particularly preferably 1 or more. In addition, the suitable range is preferably 0.01 or more and 400 or less, more preferably 0.05 or more and 100 or less, even more preferably 0.1 or more and 75 or less, and particularly preferably 1 or more and 50 or less.
Y=α/β/γ...Formula (3)
It has been found that within this range, the amine compound (E1) can be sufficiently wetted onto the surface of the carbon nanotube (B) having a certain amount of acidic groups, and the dispersibility (including viscosity) and storage stability (including inhibition of thickening) of the carbon nanotube (B) can be improved.
If the content of the amine compound (E1) is excessive relative to the surface area of the carbon nanotubes (B) having acidic groups, the odor becomes strong and the cost increases, whereas if the content is insufficient, the content of the amine compound (E1) relative to the surface area of the carbon nanotubes (B) having acidic groups is insufficient, and dispersibility and storage stability (suppression of thickening) may be deteriorated.

Other Components The carbon nanotube dispersion paste may further contain other components in addition to the above-mentioned components (A), (B), and (C), and the components (D) and (E) which may be contained as necessary.

Other components include, for example, resins other than the dispersion resin (A) and polyvinylidene fluoride (D), neutralizing agents, defoamers, preservatives, rust inhibitors, plasticizers, pigments other than carbon nanotubes (B), dehydrating agents (F), etc.

Examples of pigments other than carbon nanotubes (B) include the other conductive pigments (B1) described above; white pigments such as titanium white and zinc oxide; blue pigments such as cyanine blue and indanthrene 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 benzimidazolone, isoindolinone, isoindoline and quinophthalone, yellow pigments such as titanium yellow and yellow lead. These pigments can be used alone or in combination of two or more.
These pigments other than the carbon nanotubes (B) can be used for purposes such as color adjustment and reinforcement of the physical properties of the film, as long as the electrical conductivity is not significantly impaired. They may be dispersed simultaneously with the dispersing resin (A) and the carbon nanotubes (B), or they may be mixed as a pigment or pigment paste after dispersing the dispersing resin (A) and the carbon nanotubes (B) to prepare a paste.

The content of pigments other than the carbon nanotubes (B) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of all pigments in the carbon nanotube dispersion paste, and it is particularly preferable that they are substantially not contained.

From the viewpoint of pigment dispersibility and storage stability, the viscosity of the carbon nanotube dispersion paste at a shear rate of 2 s ⁻¹ is, for example, less than 5,000 mPa·s, preferably less than 2,500 mPa·s, more preferably less than 1,000 mPa·s, and is, for example, 10 mPa·s or more, preferably 50 mPa·s or more, more preferably 100 mPa·s or more. The viscosity can be measured, for example, using a cone and plate type viscometer (manufactured by HAAKE, trade name "Mars2", diameter 35 mm, 2° inclined cone and plate).

As the dehydrating agent (F), any known agent having a dehydrating effect can be used without any particular restrictions. 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, and sodium sulfate; phosphate esters such as trimethyl phosphate, tri-2-propyl phosphate, tributyl phosphate, and tetraisopropylethylene phosphonate; phosphine oxides such as tributyl phosphine oxide, trioctyl phosphine oxide, and triphenyl phosphine oxide; orthoformic acid methyl ester, orthoformic acid ethyl ester. orthoesters such as methyl orthoacetate, ethyl orthoacetate, and ethyl orthobenzoate; and acid anhydrides such as oxalic anhydride, acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, trifluoroacetic anhydride, disulfuric acid, dinitrogen pentoxide, diphosphoric acid, diphosphorus pentoxide, diphosphorus trioxide, diarsenic pentoxide, diarsenic trioxide, methanesulfonic anhydride, trifluoromethanesulfonic anhydride, and sulfobenzoic anhydride, which may be used alone or in combination of two or more.

[Method for producing composite paste (for lithium ion secondary batteries)]
In the manufacturing method of the present invention, first, a carbon nanotube dispersion paste having carbon nanotubes (B) is prepared by the above-mentioned method. The carbon nanotube dispersion paste and at least one electrode active material (G) are mixed to produce a composite paste for a lithium ion secondary battery.
The solid content of the electrode active material (G) is usually 10% by mass or more, preferably 20% by mass or more, based on 100% by mass of the total amount of the composite paste, and is usually 99% by mass or less, preferably 95% by mass or less, which is suitable in terms of battery performance.
In addition, polyvinylidene fluoride (D), which was an optional component in the carbon nanotube dispersion paste, is an essential component in the composite paste and is always contained.
The solid content of polyvinylidene fluoride (D) is usually 0.05 mass% or more, preferably 0.1 mass% or more, based on 100 mass% of the total amount of the composite paste, and is usually 10 mass% or less, preferably 2 mass% or less, which is suitable in terms of battery performance, paste viscosity, etc.

In the above-mentioned mixing step of the electrode active material (G), the composite paste can be mixed uniformly using a conventionally known mixer and disperser.

The solid content of the dispersed resin (A) in the composite paste solids is usually 0.01% by mass or more, preferably 0.05% by mass or more, based on 100% by mass of the total amount of the composite paste, and is usually 10% by mass or less, preferably 1% by mass or less, which is suitable in terms of battery performance, paste viscosity, etc.

In the composite paste of the present invention, from the viewpoint of storage stability (suppression of thickening) in the composite paste, it contains a highly polar, low molecular weight component (E), and it is preferable that the highly polar, low molecular weight component (E) contains at least one type of amine compound (E1).
From the viewpoint of alleviating aggregation between the carbon nanotubes (B) and the electrode active material (G) by contacting (wetting) the high-polarity, low-molecular-weight component (E) with the carbon nanotubes (B) and then mixing the electrode active material (G), it is preferable to include a sequence of first mixing the carbon nanotubes (B) and the high-polarity, low-molecular-weight component (E).

The solid content of carbon nanotubes (B) in the composite paste solids of the present invention is typically 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, based on 100% by mass of the total composite paste, and is typically 30% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, which is preferred in terms of battery performance. The content of solvent (C) in the composite paste of the present invention is typically 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 composite paste, and is typically 90% by mass or less, preferably 70% by mass or less, more preferably 50% by mass or less, which is preferred in terms of electrode drying efficiency and paste viscosity.

The above composite paste is suitable for use as a positive or negative electrode for lithium ion secondary batteries, and is preferably used as a positive electrode.

In addition, the moisture content of the composite paste is usually 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 the increase in viscosity or gelation of the composite paste described above.
The composite paste used in the present invention can be said to be a substantially non-aqueous composite paste.
Furthermore, for the reasons described above (moisture carried over from raw materials and moisture mixed in during the manufacturing process), the moisture content of the composite paste is preferably 100 ppm or more, more preferably 200 ppm or more, and even more preferably 500 ppm or more.

Electrode active material (G)
Examples of the electrode active material (G) include lithium composite oxides such as lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium cobalt oxide (LiCoO ₂ ), and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ; lithium iron phosphate (LiFePO ₄ ); sodium composite oxide; and potassium composite oxide. These electrode active materials (G) can be used alone or in combination of two or more. The electrode active material containing lithium iron phosphate is inexpensive and has relatively good cycle characteristics and energy density, and can therefore be used preferably.

The particle diameter of the electrode active material (G) is usually 0.5 μm or more, preferably 10.5 μm or more, and usually 30 μm or less, preferably 20 μm or less.

The solid content of the electrode active material (G) in the 100% by mass solids of the composite paste for lithium ion secondary battery electrodes of the present invention is usually 50% by mass or more, preferably 60% by mass or more, and is preferably less than 100% by mass in terms of battery capacity, battery resistance, etc.

When the composite paste contains the electrode active material (G), it may thicken during storage. The reason for this is that the electrode active material (G) has alkali metal hydroxides (e.g., LiOH, KOH, NaOH, etc.) derived from the raw materials on the particle surface, and is thought to aggregate (thicken) due to the carbon nanotubes (B) that have an acidic surface. Therefore, by containing a certain amount or more of a highly polar low molecular weight component (E) [particularly an amine compound (E1)], it is possible to suppress the thickening of the composite paste during storage.

The amount of water contained in the electrode active material (G) is usually 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 the increase in viscosity or gelation of the composite paste described above.

As the electrode active material (G) of the present invention, an electrode active material composite (G-1) having at least a part of its surface covered with carbon nanotubes can be suitably used.
The composite (G-1) can be obtained in advance by mixing the electrode active material (G), the carbon nanotubes, and, if necessary, other components (e.g., a solvent or a dispersion resin). If necessary, a drying step can be added after mixing, so that the carbon nanotubes can be more uniformly adsorbed and/or fixed to the electrode active material (G).
Furthermore, the electrode active material composite (G-1) produced as described above can form a uniform conductive network around the electrode active material by adsorbing and/or fixing the carbon nanotubes to the surface of the electrode active material.
As the carbon nanotubes that can be used in the electrode active material composite (G-1), any known carbon nanotubes can be used without particular limitation, but the carbon nanotubes exemplified as the carbon nanotubes (B) can be preferably used.

As described above, an electrode layer for a lithium ion secondary battery (also referred to as an electrode mixture layer or a mixture layer) can be produced by applying a mixture paste for a lithium ion secondary battery to a core surface (current collector) of a positive electrode or a negative electrode and drying the applied paste, and is particularly preferably used for a positive electrode.

In addition, the carbon nanotube dispersion paste obtained by the manufacturing method of the present invention can be used not only as a paste for a composite layer (electrode layer), but also as a primer layer (also called a functional layer or adhesive layer) between the electrode core material and the composite layer (electrode layer).
The method of applying the composite paste for lithium ion secondary batteries can be carried out by a method known per se using a die coater or the like. The amount of application of the composite paste for lithium ion secondary batteries is not particularly limited, but can be set so that the thickness of the composite layer after drying is, for example, 0.04 mm or more, preferably 0.06 mm or more, and, for example, 0.30 mm or less, preferably 0.24 mm or less. The temperature of the drying step can be appropriately set, for example, 80° C. or more, preferably 100° C. or more, and, for example, 250° C. or less, preferably 200° C. or less. The time of the drying step can be appropriately set, for example, 5 seconds or more, and, for example, 120 minutes or less, preferably 60 minutes or less.

In the drying step, all or a part of the solvent (C) and the highly polar, low molecular weight component (E) that may be contained as necessary volatilize. As described above, in order to reduce waste, be environmentally friendly, and/or reduce costs, it is preferable to recover and reuse the volatilized components (C) and (E).
In addition, in lithium ion secondary batteries, there is a problem that the cycle life is reduced when impurities such as moisture are present in the electrode layer. That is, if the carbon nanotube dispersion paste or the composite paste contains moisture above a specified level, or if the electrode layer is not dried sufficiently in the manufacturing process, moisture remains in the electrode layer, which causes deterioration of the cycle characteristics of the battery. The moisture content in the electrode layer is usually 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.

As described above, when the composite paste is applied to a current collector and dried by heating, the vapor containing the solvent (C) (and, if necessary, the highly polar, low molecular weight component (E)) can be recovered, and then impurities other than the solvent (C) can be removed by distillation to produce a recycled version of the solvent (C).

In addition, after the above-mentioned composite paste is applied in a band shape onto a current collector to form an electrode layer, an insulating paste can be applied to form an electrode insulating portion for the purpose of insulating the ends or upper layer of the electrode layer.
As the insulating paste, any material capable of providing insulation can be suitably used, but a paste containing an inorganic filler, a binder, a dispersant, and a solvent is preferred, and in particular, a paste containing boehmite as the inorganic filler, polyvinylidene fluoride as the binder, and N-methyl-2-pyrrolidone as the solvent is suitable.
The insulating paste described in International Publication No. 2021/193286 can be suitably used as the insulating paste.

The carbon nanotube dispersion paste, composite paste, and electrode layer of the present invention can be particularly suitably used in lithium ion secondary batteries that include a non-aqueous electrolyte solution.
The lithium ion secondary battery having the non-aqueous electrolyte is a battery having at least a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and is a non-aqueous electrolyte type lithium ion secondary battery.

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 % by mass.

[Production of Dispersion Resin]
Production Example 1
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator was charged with 75 parts of N-methyl-2-pyrrolidone (note 1) and heated to 120°C in a nitrogen stream. When the temperature reached 120°C, a mixture of the monomer species (total 100 parts) shown in Table 1 below and 2 parts of 2,2'-azobis(2-methylbutyronitrile) was added dropwise over 3 hours. After the addition was completed, 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 an acrylic resin (A1) with a solid content of 50%. The polar functional group concentration was 1.3 (mmol/g).
(Note 1) N-methyl-2-pyrrolidone: A solvent for the recycled product, made by mixing new material and the recycled product produced in Application Example 1 in a 1:1 ratio. The water content is 500 ppm (Note 2) and the amine content is 500 ppm (Note 2).
(Note 2) The water content and the amine content were measured using a Karl Fischer moisture meter (Kyoto Electronics Manufacturing Co., Ltd., product name "MKC-610") and ion chromatography (Shimadzu Corporation, product name "Prominence HIC-NS").

Production Examples 2 to 5
Acrylic resins (A2) to (A5) each having a solid content of 50% were obtained in the same manner as in Production Example 1, except that the monomer types shown in Table 1 below were used.
The weight average molecular weights of the resins obtained are shown in Table 1. In the table, "Resin A1" to "Resin A5" mean "Acrylic Resin (A1)" to "Acrylic Resin (A5)," respectively.

The abbreviations for the monomer species in Table 1 above are as follows.
iBA: i-butyl acrylate (having a hydrocarbon group with 4 carbon atoms)
SLMA: Lauryl methacrylate (having a hydrocarbon group with 12 carbon atoms)
SMA: Stearyl methacrylate (having a hydrocarbon group with 18 carbon atoms)
BEMA: Behenyl methacrylate (having a hydrocarbon group with 22 carbon atoms)
St: styrene; DMAEMA: N,N-dimethylaminoethyl methacrylate; AN: acrylonitrile.

[Production of electrode active material composite]
Production Example 6
One part of carbon nanotubes (CNT-C) shown in Table 2 below, 0.2 parts of acrylic resin (A1) (solid content 0.1 part), and 98.8 parts of N-methyl-2-pyrrolidone (Note 1) were mixed with stirring, and then mixed with 900 parts of electrode active material particles (lithium _nickel manganese oxide particles with _a spinel structure represented by the composition formula _{LiNi0.5Mn1.5O4} , average particle size 6 μm, BET specific surface area 0.7 ^m2 /g) to prepare an electrode active material composite (G1) of CNT and electrode active material.

[Production of carbon nanotube dispersion paste and composite paste]
Example 1A
Using a continuous dry bead mill "Drystar SDA1" (manufactured by Ashizawa Finetech Co., Ltd.), carbon nanotubes (CNT-C) shown in Table 2 below were pulverized (dry dispersed) at a supply rate of 0.5 kg/hr using zirconia beads (diameter 3.0 mm), a filling rate of 70%, and a mill peripheral speed of 5.0 m/s.
Next, 5,000 parts of N-methyl-2-pyrrolidone (Note 1), 80 parts of polyvinylpyrrolidone (40 parts solids) as a dispersion resin (Note 3), 1,800 parts of resin solution of KF polymer W#7300 (Kureha Corporation, trade name, polyvinylidene fluoride, weight average molecular weight 1,000,000) (180 parts solids) (Note 4), 25 parts of benzylamine as an amine, and 200 parts of the above-mentioned crushed carbon nanotubes were mixed with a disperser while stirring, and finally N-methyl-2-pyrrolidone (Note 1) was used to adjust the total mass to 10,000 parts. Then, the mixture was dispersed in a ball mill for 4 hours to produce a carbon nanotube dispersion paste (A-1). The water content of the carbon nanotube dispersion paste (A-1) was 800 ppm (Note 2).
The above manufacturing steps were all carried out in an atmosphere with a dew point of 10° C. or less.
In addition, to disperse carbon nanotubes (200 parts) in a disperser, the other components were first thoroughly mixed, and then half the amount (100 parts) of the CNTs was added and mixed in the disperser while stirring. After confirming that the CNTs were thoroughly mixed, the remainder was gradually added and dispersed.
(Note 3) Polyvinylpyrrolidone: heterocycle-containing resin, weight average molecular weight (Mw) 12,000, functional group concentration 9 (mmol/g)
(Note 4) The polyvinylidene fluoride resin solution was prepared by mixing and dissolving polyvinylidene fluoride and N-methyl-2-pyrrolidone (Note 1) at a temperature of 80° C. Then, the solution was cooled to 30° C. at a cooling rate of about 1° C./min.

The above carbon nanotubes are all multi-walled carbon nanotubes.
The median diameter (D50), G/D ratio, specific surface area (BET specific surface area), and amount of acidic groups in Table 2 were measured by the methods described below.

Examples 2A to 10A, 13A, Comparative Examples 1A to 3A
Carbon nanotube dispersion pastes (A-2) to (A-10) and (A-13) to (A-16) were obtained in the same manner as in Example 1A except that the compositions were as shown in Table 3 below.
In Example 8A (carbon nanotube dispersion paste (A-8)), unpulverized carbon nanotubes (CNT-C) were used.

Examples 11A to 12A, Comparative Example 4A
Water was added to the carbon nanotube dispersion paste (A-3) (moisture content 800 ppm) obtained in Example 3A so as to have the following moisture content (Note 2), and the mixture was thoroughly stirred to obtain the following carbon nanotube dispersion pastes (A-11), (A-12), and (A-17).
Example 12A: Carbon nanotube dispersion paste (A-11), water content 4000 ppm
Example 13A: Carbon nanotube dispersion paste (A-12), water content 8000 ppm
Comparative Example 4A: Carbon nanotube dispersion paste (A-17), moisture content 12,000 ppm
The water content of the carbon nanotube dispersion paste (Note 2) and the results of the evaluation test described below are shown in Table 3 below.

The resin amounts in Table 3 above are values based on solid content.
The compositions of the dispersing resins in Table 3 above are as follows:
Polyvinyl butyral: average degree of polymerization 600, amount of hydroxyl groups 12 mol%, amount of butyral groups 87 mol%, amount of acetyl groups 1 mol%, concentration of polar functional groups 1.0 (mmol/g)
Polyvinyl alcohol: average degree of polymerization 600, degree of saponification 80 mol%, polar functional group concentration 16.1 (mmol/g)
Polymethyl methacrylate: weight average molecular weight 20,000, homopolymer of methyl methacrylate, polar functional group concentration 0 (mmol/g)
The boiling points and molecular weights of the amines in Table 3 above are as follows:
Benzylamine: boiling point 185°C, molecular weight 107
Aminomethylpropanol: boiling point 166°C, molecular weight 89.

Example 1B
100 parts of the carbon nanotube dispersion paste (A-1) was mixed with 900 parts of electrode active material particles (lithium nickel _manganese oxide particles having a spinel structure represented _by the composition formula _{LiNi0.5Mn1.5O4} , average particle diameter 6 μm, BET specific surface area 0.7 ^m2 /g, moisture content 100 ppm) using a disperser to produce a composite paste (B-1).
The moisture content of the composite paste (B-1) was 800 ppm (Note 2).
The above manufacturing steps were all carried out in an atmosphere with a dew point of 10° C. or less.

Examples 2B to 9B, 11B to 12B, Comparative Examples 1B to 4B
Except for the formulations shown in Table 4 below, the same procedures as in Example 1B were carried out to obtain composite pastes (B-2) to (B-9), (B-11) to (B-12), and (B-14) to (B-17).

Example 10B
100 parts of the carbon nanotube dispersion paste (A-10) was mixed with 1000 parts of the electrode active material composite (G1) obtained in Production Example 6 (900 parts of electrode active material particles) using a disper to produce a composite paste (B-10).
The moisture content of the composite paste (B-10) was 800 ppm (Note 2).

Example 13B
A composite paste (B-13) was produced by mixing 100 parts of the carbon nanotube dispersion paste (A-13) with 16 parts (solid content 1.6 parts) (Note 4 ₎ of a resin solution of KF Polymer W# ₇₃₀₀ (manufactured by Kureha Corporation, product name, polyvinylidene fluoride, weight average molecular weight 1,000,000) and 900 parts of electrode active material particles (lithium nickel manganese oxide particles having a spinel structure represented by the composition formula _{LiNi0.5Mn1.5O4} , average particle diameter 6 μm, BET specific surface area 0.7 ^m2 /g, moisture content 100 ppm) using a disper.
The moisture content of the composite paste (B-13) was 800 ppm (Note 2).
The results of the evaluation test of the composite paste described below are shown in Table 3 above.

Examples (2-1A) to (2-5A)
Carbon nanotube dispersion pastes (2-A-1) to (2-A-5) were obtained in the same manner as in Example 3A, except that the CNT species shown in Table 5 below were used (the CNTs were pulverized (dry dispersed) in the same manner as in Example 1A).
The moisture absorption (X) of the carbon nanotubes and the results of the evaluation test of the carbon nanotube dispersion paste described below are shown in Table 5 below.
The moisture absorption (X) was calculated by the following method.
[Measurement of Hygroscopicity (X)]
Approximately 5 g of carbon nanotubes (CNTs) are weighed out and dried at 140°C for 3 hours to obtain a mass of CNTs of Y1. The mass of CNTs obtained by leaving the CNTs for 24 hours under conditions of a temperature of 20°C and a relative humidity of 65% is then Y2. The value of Y obtained by the following formula is defined as the moisture absorption amount Y.
Moisture absorption amount Y=(Y2-Y1)/Y1×100
Furthermore, when the moisture absorption amount is Y (mass %) and the BET specific surface area measured by the method described later is Z (m ² /g), the value X obtained by "X = Y × Z" is defined as the moisture absorption rate X.

The carbon nanotubes (CNT-A) to (CNT-E) in Table 5 above are as described in Table 2.

Examples (2-1B) to (2-5B)
Composite pastes (2-B-1) to (2-B-5) were obtained in the same manner as in Example 1B except that the compositions were as shown in Table 6 below.
The results of the evaluation test of the composite paste described below are shown in Table 5 above.

<Median diameter (D50)>
The median diameter (D50) was measured using a laser diffraction/scattering type particle size distribution measuring device "LA-960" (trade name, manufactured by HORIBA Co., Ltd.) according to the following procedure.

(Preparation of aqueous dispersion medium)
0.10 g of F10MC (trade name, carboxymethylcellulose sodium (hereinafter also referred to as CMCNa), manufactured by Nippon Paper Industries Co., Ltd.) was added to 100 mL of distilled water and dissolved by stirring at room temperature for 24 hours or more to prepare an aqueous dispersion medium containing 0.1% by mass of CMCNa.

(Preparation of CMCNa aqueous solution)
2.0 g of F10MC (trade name, sodium carboxymethylcellulose, manufactured by Nippon Paper Industries Co., Ltd.) was added to 100 mL of distilled water and dissolved by stirring at room temperature for 24 hours or more to prepare an aqueous solution of 2.0 mass % CMCNa.

(Pre-measurement processing)
6.0 mg of carbon nanotubes were weighed into a vial, and 6.0 g of the aqueous dispersion medium was added. An ultrasonic homogenizer (Microtec Nithion, "SmurtNR-50") was used for pre-measurement treatment. The tip was confirmed to be free of deterioration, and was adjusted so that the tip was immersed 10 mm or more below the surface of the sample to be treated. The time set (irradiation time) was 40 seconds, the power set was 50%, the start power was 50% (output 50%), and the carbon nanotube aqueous dispersion was homogenized by ultrasonic irradiation using auto power operation with a constant output power.

[measurement]
<Proportion of Dispersed Carbon Nanotube Particles of 1 μm or Less and Median Diameter (D50)> Using the carbon nanotube aqueous dispersion, the proportion of dispersed carbon nanotube particles of 1 μm or less and the median diameter (D50) were measured according to the following method.
The optical model of the LS 13 320 universal liquid module is set to a refractive index of 1.520 for carbon nanotubes and 1.333 for water, and after the module has been washed, it is filled with approximately 1.0 mL of a CMCNa aqueous solution.
After performing offset measurement, optical axis adjustment, and background measurement under the condition of 50% pump speed, the prepared carbon nanotube aqueous dispersion was added to the particle size distribution meter so that the relative concentration, which indicates the percentage of light scattered outside the beam by the particles, was 8 to 12%, or the PIDS was 40 to 55%, and ultrasonic irradiation was performed for 2 minutes at 78 W using the particle size distribution meter attachment (measurement pretreatment), and after circulating for 30 seconds to remove air bubbles, the particle size distribution was measured. A graph of particle size (particle diameter) versus volume % was obtained, and the presence ratio and median diameter (D50) of dispersed particles of 1 μm or less were determined.
For each carbon nanotube sample, three measurement samples were taken from different locations and particle size distribution was measured. The proportion of dispersed particles of 1 μm or less and the median diameter (D50) were calculated as the average value.

<G/D ratio of carbon nanotubes>
The Raman spectrum of the carbon nanotube was measured by placing the carbon nanotube in a Raman microscope (manufactured by Horiba, Ltd., product name "XploRA") and using a laser wavelength of 532 nm. The G/D ratio of the carbon nanotube was determined by taking the maximum peak intensity G within the range of 1560 cm ^-1 to 1600 cm ^-1 in the spectrum and the maximum peak intensity D within the range of 1310 cm ^-1 to 1350 cm ^-1 .

<Specific surface area (BET specific surface area)>
The BET specific surface area of the carbon nanotubes was measured as a BET specific surface area (m ² /g) in accordance with JIS Z8830:2013 using a specific surface area measuring device (BERSORP-MAX (Microtrac-Bell Corporation)).

<Amount of Acidic Groups in Carbon Nanotubes (CNTs)>
2 g of CNT was weighed out, immersed in 50 ml of 0.01 M benzylamine/n-methylpyrrolidone solution, and dispersed for 1 hour using an ultrasonic irradiator. Then, the mixture was centrifuged and the supernatant was filtered through a filter. The benzylamine remaining in the obtained filtrate was quantitatively analyzed by potentiometric titration with 0.1 M hydrochloric acid, and the amount of acidic groups (mmol/g) per 1 g of the obtained CNT was identified.

Evaluation test: The carbon nanotube dispersion paste and composite paste obtained in the above examples and comparative examples were subjected to an evaluation test. Evaluation D is a failure. If there is even one failure evaluation result, the evaluation of the carbon nanotube dispersion paste or composite paste is a failure.

<Dispersibility>
The resulting carbon nanotube dispersion paste was evaluated for dispersibility according to the dispersion degree test of JIS K-5600-2-5 using a grain gauge and the following criteria.
A: The pigment is dispersed at a particle size of less than 10 μm. The dispersibility is very good.
B: The pigment is dispersed at a size of 10 μm or more and less than 20 μm. The dispersibility is somewhat good.
C: The pigment is dispersed at a particle size of 20 μm or more, but no aggregates are visible. Dispersibility is somewhat poor.
D: Aggregates are visually observed. Dispersibility is very poor.

<Volume resistivity (conductivity)>
The volume resistivity of the resulting carbon nanotube dispersion paste was further measured using a 5% by mass solution of polyvinylidene fluoride (manufactured by Kureha Corporation, product name "KF Polymer W#7300", solvent: N-methyl-2-pyrrolidone) as a binder.
The carbon nanotube-dispersed paste and the KF Polymer W#7300 solution were weighed out so that the ratio of the mass of the carbon nanotubes (B) in the obtained carbon nanotube-dispersed paste to the combined mass of the dispersed resin (A) solid content and the KF Polymer W#7300 solid content in the carbon nanotube-dispersed paste was 5:100, and the mixture was mixed for 2 minutes with an ultrasonic homogenizer to obtain a measurement sample.
A sample for measurement was applied to a glass plate (2 mm x 100 mm x 150 mm) by the doctor blade method, and then dried by heating at 80 ° C. for 60 minutes to form a coating film on the glass plate. After measuring the film thickness of the obtained coating film, the resistance value was measured with an ASP probe (manufactured by Mitsubishi Chemical Analytech Co., Ltd., product name "MCP-TP03P") and a resistivity meter (manufactured by Mitsubishi Chemical Analytech Co., Ltd., product name "Loresta-GP MCP-T610"), and the obtained resistance value was multiplied by a resistivity correction factor (RCF) of 4.532 and the film thickness of the coating film to calculate the volume resistivity. The volume resistivity was evaluated according to the following criteria.
A: The volume resistivity is less than 5 Ω·cm and the electrical conductivity is good.
B: The volume resistivity is 5 Ω·cm or more and less than 15 Ω·cm, and the electrical conductivity is normal.
D: The volume resistivity is 15 Ω·cm or more, and the electrical conductivity is poor.

<Initial viscosity>
The viscosity of the obtained composite paste was measured at a shear rate of 2.0 sec ^-1 using a cone and plate viscometer (manufactured by HAAKE Corporation, trade name "Mars2", diameter 35 mm, 2° inclined cone and plate) and evaluated according to the following criteria.
A: The viscosity is less than 10 Pa·s.
B: Viscosity is 10 Pa·s or more and less than 20 Pa·s.
C: Viscosity is 20 Pa·s or more and less than 50 Pa·s.
D: Viscosity is 50 Pa·s or more.

<Storage stability>
The obtained composite paste was stored at 50° C. for 2 weeks, and the initial viscosity and the viscosity after storage were compared. The viscosity was measured at a shear rate of 2.0 s ^-1 using a cone and plate viscometer (manufactured by HAAKE, product name "Mars2", diameter 35 mm, cone and plate inclined at 2°). The viscosity increase rate was calculated using the following formula, and the storage stability was evaluated according to the following criteria.
Viscosity increase rate (%) = viscosity after storage (mPa·s) / initial viscosity (mPa·s) × 100 - 100
S: The viscosity increase rate (%) after storage is less than 10%.
A: The viscosity increase rate (%) after storage is 10% or more and less than 20%.
B: The viscosity increase rate (%) after storage is 20% or more and less than 50%.
C: The viscosity increase rate (%) after storage is 50% or more and less than 200%.
D: The viscosity increase rate (%) after storage is 200% or more (or gelation makes it impossible to measure).

[Production of battery electrode layer]
Application example 1C
The composite paste obtained in Example 3B was applied in strips by roller coating to both sides of a long aluminum foil (positive electrode current collector) having an average thickness of 15 μm so that the basis weight per side was 10 mg/cm ² (based on solid content), and then dried (drying temperature 180° C., 30 minutes) to form a positive electrode layer. The positive electrode active material layer (positive electrode layer) supported on this positive electrode current collector was rolled by a roll press machine to adjust the properties.
The resulting electrode layer had a residual solvent amount of less than 1% and was an electrode layer with good finish and other properties.
In addition, the vapor evaporated during the heating and drying in the above step was recovered to obtain a recovered solution (mixed solution).
The mixed solution was then placed in a flask equipped with a condenser, and the flask was heated to 185°C or higher to distill off the amine (benzylamine). This was continued until the amine content reached 1000 ppm (note 2), producing a regenerated N-methyl-2-pyrrolidone. The water content of the regenerated N-methyl-2-pyrrolidone was 1000 ppm (note 2).

Application example 2C
As in Application Example 1, the composite paste was applied in a strip shape on an aluminum foil (positive electrode current collector), and then the insulating paste of Example 5A described in International Publication No. 2021/193286 was applied to both ends of the composite paste on the aluminum foil (positive electrode current collector) to install an electrode insulating part. Then, the electrode was dried (drying temperature 180 ° C., 30 minutes) to form a positive electrode layer and an insulating part. The positive electrode active material layer (positive electrode layer) supported on this positive electrode current collector was rolled with a roll press machine to adjust the properties.

Claims

A method for producing a carbon nanotube dispersion paste, comprising a step of mixing and dispersing components containing a dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) having a water content of less than 10,000 ppm, and polyvinylidene fluoride (D) which may be included as necessary, wherein the water content of the carbon nanotube dispersion paste is less than 10,000 ppm.
The method for producing the carbon nanotube dispersion paste according to claim 1, characterized in that the mixing and/or dispersion is carried out in an atmosphere with a dew point of 10°C or less.
The method for producing a carbon nanotube dispersion paste according to claim 1, characterized in that the dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms has 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 polar functional group concentration is 0.1 mmol/g to 8.5 mmol/g.
The method for producing a carbon nanotube dispersion paste according to claim 1, characterized in that the solvent (C) contains recycled N-methyl-2-pyrrolidone, and the moisture content in the N-methyl-2-pyrrolidone is controlled to less than 10,000 ppm.
The method for producing a carbon nanotube dispersion paste according to claim 1, characterized in that the carbon nanotube dispersion paste contains the polyvinylidene fluoride (D).
The method for producing a carbon nanotube dispersion paste according to claim 5, characterized in that the step of mixing the polyvinylidene fluoride (D) includes a step of mixing and dissolving it in a solvent having a liquid temperature of 40°C or higher in advance, or a step of mixing the polyvinylidene fluoride (D) with a solvent and then heating the mixture to a temperature of 40°C or higher.
The method for producing a carbon nanotube dispersion paste according to claim 1, characterized in that the carbon nanotube dispersion paste further contains a highly polar, low molecular weight component (E).
The method for producing a carbon nanotube dispersion paste according to claim 1, characterized in that the carbon nanotube dispersion paste further contains a dehydrating agent (F).
The method for producing a carbon nanotube dispersion paste according to claim 1, characterized in that the carbon nanotubes (B) are previously dry-dispersed using a media-type grinder.
The mixing and dispersing step comprises:
Step 1: adding a component containing carbon nanotubes (B) in an amount of 70% by mass or less based on 100% by mass of the total amount of carbon nanotubes (B) contained in the carbon nanotube dispersion paste obtained after dispersion to a dispersing machine and performing a dispersing process; and Step 2: adding carbon nanotubes (B) to a dispersing machine until a desired concentration is reached, and performing a dispersing process.
2. The method for producing a carbon nanotube dispersion paste according to claim 1, further comprising the steps of:
When the moisture absorption amount of the carbon nanotube (B) is Y (mass%) and the BET specific surface area is Z (m 2 /g), the following formula:
X = Y x Z
The value of X obtained by the above is in the range of X≦500,
The moisture absorption amount Y is measured under the following conditions: the mass of carbon nanotubes obtained by drying at 140° C. for 3 hours is Y1, and the mass of carbon nanotubes obtained by leaving at 20° C. for 24 hours under conditions of a relative humidity of 65% is Y2. The moisture absorption amount Y is calculated by the following formula: Y=(Y2-Y1)/Y1×100.
2. The method for producing a carbon nanotube dispersion paste according to claim 1, wherein the value of Y (mass %) obtained in step (a) is defined as the moisture absorption amount Y.
A method for producing a composite paste for a lithium ion secondary battery, comprising a step of mixing a carbon nanotube dispersion paste obtained by the method for producing a carbon nanotube dispersion paste according to any one of claims 1 to 11 with an electrode active material (G).
The following steps:
A process for producing a carbon nanotube dispersion paste, the process including a process for mixing and dispersing components containing a dispersion resin (A) having a heterocycle and/or an alkyl group having 12 or more carbon atoms, carbon nanotubes (B), a solvent (C) having a water content of less than 10,000 ppm, and polyvinylidene fluoride (D) which may be included as necessary, the carbon nanotube dispersion paste having a water content of less than 10,000 ppm; and
A step of producing a composite paste for a lithium ion secondary battery, the step including a step of mixing the carbon nanotube dispersion paste with an electrode active material (G), the composite paste having a moisture content of less than 10,000 ppm, and the electrode active material (G) being an electrode active material composite (G-1) having at least a part of its surface covered with carbon nanotubes;
A method for producing a composite paste for a lithium ion secondary battery comprising the steps of:
A method for producing an electrode layer for a lithium ion secondary battery, comprising the step of applying the composite paste obtained by the method of claim 12 to a current collector.
A method for manufacturing an electrode for a lithium ion secondary battery, comprising a step of applying an electrode insulating part to the end or upper layer of the electrode layer obtained by the manufacturing method described in claim 14.
A method for producing a lithium ion secondary battery using a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator having an electrode layer obtained by the method of claim 14.