WO2024063003A1

WO2024063003A1 - Electroconductive pigment paste, mix paste, and electrode for lithium-ion batteries

Info

Publication number: WO2024063003A1
Application number: PCT/JP2023/033509
Authority: WO
Inventors: 敦史塚本; 陸矢鈴木
Original assignee: 関西ペイント株式会社
Priority date: 2022-09-19
Filing date: 2023-09-14
Publication date: 2024-03-28

Abstract

The present invention addresses the problem of providing an electroconductive pigment paste and a mix paste which, even when having a high pigment concentration, are excellent in terms of pigment dispersibility and storage stability, and of providing an electrode for lithium-ion batteries which has various excellent performances. The electroconductive pigment paste comprises a pigment-dispersing resin (A), an electroconductive pigment (B), a solvent (C), a fluororesin (D), and a basic low-molecular-weight component (E), wherein the pigment-dispersing resin (A) has at least one kind of polar functional groups and has a concentration of the polar functional groups of 0.3-23 mmol/g, the electroconductive pigment (B) includes carbon nanotubes (B1), and when the content of the basic low-molecular-weight component (E) per 100 parts by mass of the content of the carbon nanotubes (B1) is expressed by α (parts by mass) and the BET specific surface area of the carbon nanotubes (B1) is expressed by β (m²/g), then X=α/β×300 and the X is 5 or greater.

Description

Conductive pigment paste, composite paste, and electrodes for lithium-ion batteries

The present invention relates to a conductive pigment paste and composite material paste that have excellent pigment dispersibility and storage stability even at high pigment concentrations, and an electrode for lithium ion batteries coated with the composite material paste.

Conventionally, paste-like pigment dispersions in which pigments are dispersed in mixtures of pigment dispersion resins, solvents, etc. have been widely used in various fields. In these fields, improvements in performance such as pigment dispersibility, storage stability, coating properties, conductivity, finishing properties, and solvent resistance are increasingly required. Pigment dispersion resins and pigment pastes are being developed that have excellent storage stability that does not cause re-agglomeration of pigment particles in a pigment dispersion.

When designing a pigment paste, make sure that the pigment dispersion resin does not have a negative effect on the performance of the final product itself, such as an electrode, or reduce the amount of solvent and pigment dispersion resin used, or reduce the energy used during drying. From this point of view, it is important to prepare a highly concentrated and uniformly dispersed pigment paste using a small amount of pigment dispersion resin.
It is also important that the pigment paste can be stored for a long period of time without deterioration.

Under such circumstances, Patent Document 1 includes bundle-shaped carbon nanotubes, a dispersion medium, and a polyvinyl butyral resin having a weight average molecular weight of more than 50,000, and the dispersed particle size of the bundle-shaped carbon nanotubes is 3 to 3 in the particle size distribution D50. Carbon nanotube dispersions that are 10 μm are described.
However, although the electrode slurry containing the carbon nanotube dispersion liquid, electrode active material, and binder resin has good initial dispersibility, viscosity, and other properties, long-term storage performance may not be sufficient.

Special table 2018-535284 publication

The problems to be solved by the present invention are conductive pigment pastes and composite pastes that have excellent pigment dispersibility and appropriate viscosity (low viscosity) even at high pigment concentrations, and excellent storage stability, as well as various performances (battery). The purpose of the present invention is to provide an electrode for a lithium ion battery that has excellent performance (performance, etc.).

As a result of intensive studies to solve the above problems, the inventors have found that
A first aspect is a conductive pigment paste containing a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E), , the pigment dispersion resin (A) has at least one kind of polar functional group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol/g, and the conductive pigment (B) contains carbon nanotubes (B1), the content of the basic low molecular weight component (E) is α (parts by mass) with respect to 100 parts by mass of the carbon nanotubes (B1), and the BET specific surface area of the carbon nanotubes (B1) is In the case of a conductive pigment paste in which the value of X in formula ( ¹ ) shown by X=α/β×300 is 5 or more, and/or
A second embodiment is a conductive pigment paste containing a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E), , the pigment dispersion resin (A) has at least one kind of polar functional group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol/g, and the conductive pigment (B) contains carbon nanotubes (B1), the basic low molecular weight component (E) contains an amine compound (E1), and the basic low molecular weight component (E) is based on 100 parts by mass of the carbon nanotubes (B1). When the content of is α (parts by mass), the BET specific surface area of the carbon nanotube (B1) is β (m ² /g), and the amount of acidic groups of the carbon nanotube (B1) is γ (mmol/g), Y= In the case of a conductive pigment paste in which the value of Y in formula (2) expressed by α/β/γ is 0.01 or more,
The inventors have discovered that the above problems can be solved, and have completed the present invention.

That is, the present invention provides the following conductive pigment paste, composite paste, and electrode for lithium ion batteries.
[Item 1] A conductive pigment paste containing a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E),
The pigment dispersion resin (A) has at least one polar functional group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol/g,
The conductive pigment (B) contains carbon nanotubes (B1),
When the content of the basic low molecular weight component (E) is α (parts by mass) with respect to 100 parts by mass of the carbon nanotube (B1), and the BET specific surface area of the carbon nanotube (B1) is β (m ² /g). , a conductive pigment paste in which the value of X in the following formula (1) is 5 or more.
X=α/β×300...Formula (1)
[Item 2] A conductive pigment paste containing a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E),
The pigment dispersion resin (A) has at least one polar functional group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol/g,
The conductive pigment (B) contains carbon nanotubes (B1),
The content of the basic low molecular weight component (E) with respect to 100 parts by mass of the carbon nanotube (B1) is α (parts by mass), the BET specific surface area of the carbon nanotube (B1) is β (m ² /g), and the carbon nanotube A conductive pigment paste in which the value of Y in the following formula (2) is 0.01 or more, where the amount of acidic groups in (B1) is γ (mmol/g).
Y=α/β/γ...Formula (2)
[Item 3] The conductive pigment paste according to Item 1 or 2, wherein the basic low molecular weight component (E) contains an amine compound (E1).
[Item 4] The conductive pigment paste according to any one of Items 1 to 3, wherein the carbon nanotube (B1) has a volumetric median diameter (D50) of 10 to 250 μm.
[Item 5] Items 1 to 4, wherein the content of the basic low molecular weight component (E) is 12% by mass or more and 500% by mass or less, based on 100% by mass of the solid content of the conductive pigment (B). The conductive pigment paste according to any one of the items.
[Item 6] The conductive pigment paste according to any one of Items 1 to 5, wherein the carbon nanotube (B1) has an acidic group content of 0.01 mmol/g to 0.5 mmol/g.
[Item 7] The BET specific surface area of the carbon nanotube (B1) is 100 m ² /g to 800 m ² /g, and the maximum within the range of 1560 m ⁻¹ to 1600 cm ⁻¹ in the Raman spectrum of the carbon nanotube (B1). As described in any one of items 1 to 6, the G/D ratio is 0.1 to 5, where the peak intensity is G and the maximum peak intensity within the range of 1310 m ^-1 to 1350 ^cm -1 is D. conductive pigment paste.
[Item 8] The conductive pigment paste according to any one of Items 1 to 7, wherein the solvent (C) has a water content of 1% by mass or less and an amine compound content of 1% by mass or less.
[Item 9] The conductive pigment paste according to any one of Items 1 to 8, wherein the basic low molecular weight component (E) has a weight average molecular weight of less than 1000.
[Item 10] The conductive pigment paste according to any one of Items 3 to 9, wherein the amine compound (E1) has an amine value of 105 mgKOH/g to 1000 mgKOH/g.
[Item 11] The conductive pigment paste according to any one of Items 1 to 10, wherein the solvent (C) is N-methyl-2-pyrrolidone.
[Item 12] A composite paste obtained by blending the conductive pigment paste according to any one of Items 1 to 11 and an electrode active material (F).
[Item 13] An electrode for a lithium ion battery obtained using the composite paste according to Item 12.

The conductive pigment paste and composite material paste of the present invention have excellent pigment dispersibility and appropriate viscosity (low viscosity) even at high pigment concentrations, excellent storage stability, and excellent electrical conductivity of the coating film. Furthermore, the lithium ion battery electrode obtained by applying the composite material paste has excellent various performances (battery performance, etc.).

Hereinafter, modes for carrying out the present invention will be described in detail.

It should be noted that the present invention is not limited to the following embodiments, but should be understood to include various modifications that may be implemented without departing from the gist of the present invention.
In the present invention, the "specific surface area" refers to the BET specific surface area determined by the nitrogen adsorption method.
In the present invention, first, a conductive pigment paste having a conductive pigment in an appropriately dispersed state is prepared. Furthermore, in order to obtain an electrode for a lithium ion battery that satisfies various performances, a composite paste is produced by adding components such as an electrode active material to the conductive pigment paste.

[Conductive pigment paste]
The conductive pigment paste of the first aspect of the present invention contains a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E). A conductive pigment paste containing a pigment dispersion resin (A) having at least one polar functional group, and a polar functional group concentration of the pigment dispersion resin (A) of 0.3 mmol/g to 23 mmol/g. The conductive pigment (B) contains carbon nanotubes (B1), and the content of the basic low molecular weight component (E) with respect to 100 parts by mass of the carbon nanotubes (B1) is α (parts by mass), When the BET specific surface area of carbon nanotubes (B1) is β (m ² /g), a conductive pigment paste in which the value of X in the following formula (1) is 5 or more is suitable.
X=α/β×300...Formula (1)
The value of More preferably it is 500 or less, still more preferably 300 or less. Moreover, a suitable range is preferably 5 or more and 2,500 or less, more preferably 10 or more and 1,000 or less, still more preferably 40 or more and 500 or less, particularly preferably 60 or more and 300 or less.
Within this range, the surface of the carbon nanotubes (B1) can be sufficiently wetted with the basic low molecular weight component (E), and the dispersibility (including viscosity) and storage stability (increase) of the carbon nanotubes (B1) can be improved. It has been found that the properties (including viscosity control) can be improved.
If the content of the basic low molecular weight component (E) is excessive with respect to the BET specific surface area of the carbon nanotubes (B1), the odor becomes strong and the cost increases. If the content is insufficient, the basic low molecular weight component (E) content may be insufficient relative to the BET specific surface area of the carbon nanotubes (B1), resulting in poor dispersibility and storage stability (suppression of viscosity increase).

Further, the conductive pigment paste of the second aspect of the present invention includes a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E ), wherein the pigment dispersion resin (A) has at least one kind of polar functional group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol. /g, the conductive pigment (B) contains carbon nanotubes (B1), and the content of the basic low molecular weight component (E) is α (parts by mass) with respect to 100 parts by mass of the carbon nanotubes (B1). ), the BET specific surface area of the carbon nanotube (B1) is β (m ² /g), and the amount of acidic groups of the carbon nanotube (B1) is γ (mmol/g), then the value of Y in the following formula (2) is , 0.01 or more is suitable.
Y=α/β/γ...Formula (2)
The value of Y is preferably 0.01 or more, more preferably 1 or more, even more preferably 2 or more, particularly preferably 3 or more, for example 400 or less, preferably 200 or less. Yes, more preferably 150 or less, still more preferably 100 or less. Moreover, a suitable range is preferably 0.01 or more and 400 or less, more preferably 1 or more and 200 or less, still more preferably 2 or more and 150 or less, and particularly preferably 3 or more and 100 or less.
Within this range, the surface of the carbon nanotube (B1) having a certain amount of acidic groups can be sufficiently wetted with the basic low molecular weight component (E), and the dispersibility (including viscosity) of the carbon nanotube (B1) ) and storage stability (including inhibition of thickening).
If the content of the basic low molecular weight component (E) is excessive with respect to the BET specific surface area of the carbon nanotube (B1) having an acidic group, the odor becomes strong and the cost increases. If the content is insufficient, the basic low molecular weight component (E) content may be insufficient relative to the BET specific surface area of the carbon nanotube (B1) having acidic groups, resulting in poor dispersibility and storage stability (inhibition of thickening). .

Pigment dispersion resin (A)
The pigment dispersion resin (A) 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, a silanol group, a cyano group, a pyrrolidone group, and an ether group. group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol/g. Moreover, the above acid group may be in the form of a salt.

The type of resin is not particularly limited as long as it is a resin other than the fluororesin (D) described below. For example, acrylic resin, polyester resin, epoxy resin, polyether resin, alkyd resin, urethane resin, polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, polyvinyl acetate, silicone resin, polycarbonate resin, chlorine resin, and composite resins thereof, etc. can be mentioned. These resins can be used alone or in combination of two or more.

Among these, from the viewpoints of pigment dispersibility, storage stability, finishing properties, etc., as the pigment dispersion resin (A), a monomer containing a polymerizable unsaturated group-containing monomer of the following formula (1) is polymerized or copolymerized. It is preferable to contain a vinyl (co)polymer (A1) obtained by. In addition, 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.]
The vinyl (co)polymer (A1) preferably contains in its structure a structural unit represented by "-CH ₂ -CH(-X)-" (wherein X is an active hydrogen group or an organic group containing an active hydrogen group). Examples of the vinyl (co)polymer (A1) include hydroxyl group-containing vinyl (co)polymers, carboxyl group-containing vinyl (co)polymers, amide group-containing vinyl (co)polymers, sulfonic acid group-containing vinyl (co)polymers, phosphate group-containing vinyl (co)polymers, and pyrrolidone group-containing vinyl (co)polymers. These (co)polymers may be used alone or in combination of two or more.

Examples of the hydroxyl group-containing vinyl (co)polymer include polyhydroxyalkyl (meth)acrylate (such as polyhydroxyethyl (meth)acrylate), polyvinyl alcohol, vinyl alcohol-fatty acid vinyl copolymer, and vinyl alcohol-ethylene copolymer. , vinyl alcohol-(N-vinylformamide) copolymers, copolymers of hydroxyalkyl (meth)acrylates (such as hydroxyethyl (meth)acrylate) and other polymerizable unsaturated monomers, and the like. The vinyl alcohol units in the (co)polymer may be those obtained by (co)polymerizing fatty acid vinyl units and then hydrolyzing them.

Examples of the carboxyl group-containing vinyl (co)polymer include a polymer of (meth)acrylic acid, a copolymer of (meth)acrylic acid and other polymerizable unsaturated monomers, and the like.

Examples of the amide group-containing vinyl (co)polymer include a polymer of (meth)acrylamide, a polymer of (meth)acrylamide derivatives (such as 3-(meth)acrylamidopropyltrimethylammonium chloride, or a polymer of (meth)acrylamide and others). Examples include copolymers with polymerizable unsaturated monomers.

Examples of the sulfonic acid group-containing vinyl (co)polymer include polymers of allylsulfonic acid or styrenesulfonic acid, copolymers of allylsulfonic acid and/or styrenesulfonic acid, and other polymerizable unsaturated monomers, etc. can be mentioned.

Examples of the phosphoric acid group-containing vinyl (co)polymer include a polymer of (meth)acryloyloxyalkyl acid phosphate, or a copolymer of (meth)acryloyloxyalkyl acid phosphate and other polymerizable unsaturated monomers. can be mentioned.

The vinyl (co)polymer (A1) contains, in addition to the structural unit represented by "-CH ₂ --CH(-X)-", a polymerizable unsaturated group-containing monomer that can be copolymerized as necessary. may contain structural units derived from Examples of copolymerizable polymerizable unsaturated group-containing monomers include vinyl formate, vinyl acetate, vinyl propionate, isopropenyl acetate, vinyl valerate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl stearate, Carboxylic acid vinyl ester monomers such as vinyl benzoate, vinyl versatate, and vinyl pivalate; Olefins such as ethylene, propylene, and butylene; Aromatic vinyls such as styrene and α-methylstyrene; (meth)acrylic acid Ethylenically unsaturated carboxylic acids such as methyl, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dimethyl fumarate, dimethyl maleate, diethyl maleate, diisopropyl itaconate, etc. Alkyl ester monomer; Vinyl ether monomer such as methyl vinyl ether, n-propyl vinyl ether, isobutyl vinyl ether, dodecyl vinyl ether; Vinyl halide monomer or vinylidene monomer such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc. Allyl compounds such as allyl acetate and allyl chloride; Quaternary ammonium group-containing monomers such as vinyltrimethoxysilane, N-vinylformamide, and N-vinyl-2-pyrrolidone. These monomers can be used alone or in combination of two or more.

The polar functional group concentration of the pigment dispersion resin (A) is usually 0.3 mmol/g to 23 mmol/g, preferably 9 mmol/g from the viewpoint of pigment dispersibility, storage stability, and compatibility with solvents. It is preferable that the amount is 23 mmol/g.

The vinyl (co)polymer (A1) can be produced by a known polymerization method, for example, it is preferable to use solution polymerization, but it is not limited to this, and bulk polymerization or emulsification is preferred. Polymerization, suspension polymerization, etc. may be used. When solution polymerization is carried out, it may be continuous or batch polymerization, and the monomers may be charged all at once, divided into portions, or added continuously or intermittently.

The polymerization initiator used in solution polymerization is not particularly limited, but specifically, for example, azobisisobutyronitrile, azobis-2,4-dimethylparellonitrile, azobis(4-methoxy-2 azo compounds such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, etc. Percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate , perester compounds such as t-butylperoxyneodecanate; known radical polymerization initiators such as azobisdimethylvaleronitrile and azobismethoxyvaleronitrile can be used. These can be used alone or in combination of two or more.

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

The vinyl (co)polymer (A1) that can be obtained 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.

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

The weight average molecular weight is usually in the range of 500 to 50,000, more preferably in the range of 1,000 to 20,000, and more particularly in the range of 1,500 to 20,000, from the viewpoint of finishability, corrosion resistance, etc. Preferably, it is within the range of 000.
In addition, unless otherwise specified, the weight average molecular weight in this specification is based on the retention time (retention capacity) measured using gel permeation chromatography (GPC) of standard polystyrene with a known molecular weight measured under the same conditions. This value is calculated by converting the retention time (retention capacity) into the molecular weight of polystyrene. Specifically, "HLC8120GPC" (trade name, manufactured by Tosoh Corporation) was used as a gel permeation chromatograph, and "TSKgel G-4000HXL", "TSKgel G-3000HXL", and "TSKgel G-2500HXL" were used as columns. and "TSKgel G-2000HXL" (trade names, both manufactured by Tosoh Corporation), and can be measured under the conditions of a mobile phase of tetrahydrofuran, a measurement temperature of 40° C., a flow rate of 1 mL/min, and a detector RI.

The above vinyl (co)polymer (A1) can be made into a solid or a resin solution substituted with an arbitrary solvent by removing the solvent and/or replacing the solvent after completion of the synthesis.

The solvent may be removed by heating at normal pressure or under reduced pressure. As a method of solvent replacement, a replacement solvent may be introduced at any stage before desolvation, during desolvation, or after desolvation.

(Content of pigment dispersion resin (A))
The solid content of the pigment dispersion resin (A) is, for example, 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, based on the total solid content of the conductive pigment paste. For example, it is 40% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less.

The solid content of the pigment dispersion resin (A) is, based on the content of the conductive pigment (B), for example, 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, and for example, 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less.

Conductive pigment (B)
The conductive pigment (B) contains carbon nanotubes (B1).
The conductive pigment (B) may further contain a conductive pigment (B2) other than the carbon nanotubes (B1).
The content of carbon nanotubes (B1) in the conductive pigment (B) is preferably 50% by mass or more, more preferably 75% by mass or more, and 95% by mass, based on 100% by mass of the conductive pigment (B). % or more is more preferable.

(Carbon nanotube (B1))
As the carbon nanotubes (B1), single-walled carbon nanotubes or multi-walled carbon nanotubes can be used alone or in combination. In particular, from the viewpoint of viscosity, conductivity, and cost, it is preferable to use multi-walled carbon nanotubes.

The average outer diameter of the carbon nanotubes (B1) 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 (B1) 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 (B1) is, for example, 100 m ² /g, preferably 130 m ² /g, more preferably 160 m ² /g, for example 800 m ² from the viewpoint of viscosity and conductivity. /g, preferably 600 m ² /g or less, more preferably 400 m ² /g or less.

The amount of acidic groups in the carbon nanotubes (B1) is, for example, 0.01 mmol/g to 0.5 mmol/g, preferably 0.01 mmol/g to 0.2 mmol/g, from the viewpoint of dispersibility and storage stability. and more preferably 0.01 mmol/g to 0.1 mmol/g. If the amount of acidic groups is 0.01 mmol/g or more, the dispersibility will be good, and if the amount is 1.0 mmol/g or less, the storage stability will be good.
The above acidic group can be provided by the following acid treatment of carbon nanotubes.

<Acid treatment method>
The acid treatment method is not particularly limited as long as the acid can be brought into contact with the carbon nanotubes, but a method of immersing the carbon nanotubes in an acid treatment solution (aqueous acid solution) is preferred. Although the acid contained in the acid treatment liquid is not particularly limited, 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 carbon nanotubes can be adjusted by adjusting the concentration, temperature, treatment time, etc. of the acid treatment solution.

After the acid treatment, excess acid components adhering to the surface can be removed by a cleaning method to be described later, and acid-treated carbon nanotubes can be obtained.
The method for washing the acid-treated carbon nanotubes is not particularly limited, but washing with water is preferred. For example, carbon nanotubes are recovered from acid-treated carbon nanotubes by a known method such as filtration, and then the carbon nanotubes are washed with water. After the above washing, water adhering to the surface may be removed by drying, if necessary, to obtain acid-treated carbon nanotubes.

Further, the volume-converted median diameter (D50) of the carbon nanotube (B1) is, for example, 10 μm or more, preferably 15 μm or more, and more preferably 20 μm or more, when measured by the method described in Examples. , for example, 250 μm or less, preferably 200 μm or less, and more preferably 150 μm or less. Here, the median diameter (D50) can be determined by irradiating carbon nanotube particles 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 aggregates of carbon nanotubes are present, which means that the dispersibility is poor. If the median diameter (D50) is larger than 250 μm, there is a high possibility that aggregates of carbon nanotubes will exist in the electrode, resulting in non-uniform conductivity throughout the electrode. On the other hand, when the median diameter (D50) is smaller than 10 μm, the conductive path is insufficient because the fiber length is short, and the conductivity decreases. When the median diameter (D50) is within the range of 10 to 250 μm, carbon nanotubes can be uniformly dispersed within the electrode while maintaining conductivity.

In addition, in the Raman spectrum of the carbon nanotube (B1), the maximum peak intensity within the range of 1560 cm ^-1 to 1600 cm ^-1 is designated as G, and the maximum peak intensity within the range of 1310 cm ^-1 to 1350 cm ^-1 is designated as D. The G/D ratio is, for example, 0.1 or more, preferably 0.4 or more, more preferably 0.6 or more, for example 5.0 or less, preferably 3.0 or less. Yes, and more preferably 1.0 or less.
Here, it is preferable that the G/D ratio is within the range of 0.1 to 5.0 because there are fewer defects and crystal interfaces on the carbon surface and the conductivity tends to be high.

(Other conductive pigments (B2))
Other conductive pigments (B2) other than carbon nanotubes (B1) are not particularly limited, and include, for example, at least one kind selected from the group consisting of acetylene black, Ketjen black, furnace black, thermal black, graphene, and graphite. Examples include conductive carbon. Preferably, it is one or more selected from the group consisting of acetylene black, Ketjen black, furnace black, and thermal black, more preferably one or more selected from the group consisting of acetylene black, Ketjen black, and Preferably it is one or more types of acetylene black.

The average primary particle diameter of the other conductive pigment (B2) is preferably 10 to 80 nm, more preferably 20 to 70 nm. Here, the average primary particle diameter is determined by observing the conductive carbon (B2) with an electron microscope, determining the projected area of each of 100 particles, and determining the diameter assuming a circle equal to the area. The average diameter of primary particles is determined by simply averaging the diameters of the particles. Note that if the pigment is in an aggregated state, calculations are performed using the primary particles that make up the aggregated particles.

The BET specific surface area of the conductive carbon (B2) is not particularly limited. In terms of viscosity and conductivity, it 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 for example 500 m ² /g or less, preferably 250 m ² /g or less. , more preferably 200 m ² /g or less.

The dibutyl phthalate (DBP) oil absorption amount of the conductive carbon (B2) is not particularly limited. In terms of pigment dispersibility and conductivity, the amount is, for example, 60 ml/100 g or more, preferably 150 ml/100 g or more, and is, for example, 1,000 ml/100 g or less, preferably 800 ml/100 g or less.

(Content of conductive pigment (B))
From the viewpoint of conductivity and pigment dispersibility, the solid content of the conductive pigment (B) is, for example, 10.0% by mass or more, preferably 30.0% by mass, based on the total solid content of the conductive pigment paste. As mentioned above, it is more preferably 40.0% by mass or more, for example, 99.0% by mass or less, preferably 80.0% by mass or less, more preferably 60.0% by mass or less.

Solvent (C)
As the solvent (C), water, various organic solvents, etc. can be suitably used.
Specifically, for example, water; hydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, and cyclobutane; aromatic solvents such as toluene and xylene; n- Ether solvents such as butyl ether, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol; ethyl acetate, n-butyl acetate, isobutyl acetate, ethylene glycol monomethyl ether acetate, butyl carbitol acetate, Ester solvents; Ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; Alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, and isobutanol; Equamide (trade name, Idemitsu Kosan Co., Ltd.) amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide, N-methylacetamide, N-methylpropioamide, N-methyl-2-pyrrolidone, etc. etc. can be mentioned.
Among these, amide solvents are preferred, and N-methyl-2-pyrrolidone is more preferred. These solvents can be used alone or in combination of two or more.

Further, from the viewpoint of pigment dispersibility of the conductive pigment paste and prevention of deterioration or hydrolysis of the resin component, it is preferable that the conductive pigment paste does not substantially contain water. Here, "substantially free of water" means that the water content is usually 1% by mass or less, preferably 0.5% by mass or less, and especially It is preferably 0.1% by mass or less.
In the present invention, the water content of the conductive pigment paste can be measured by Karl Fischer coulometric titration. Specifically, a Karl Fischer moisture content meter (manufactured by Kyoto Denshi Kogyo Co., Ltd., trade name: MKC-610) was used, and the settings of a moisture vaporizer (manufactured by Kyoto Denshi Kogyo Co., Ltd., trade name ADP-611) included in the device were performed. The temperature can be measured as 130°C.

When using an amide compound (solvent) such as N-methyl-2-pyrrolidone, it may contain an amine component as an impurity, and in the conductive pigment paste of the present invention, the viscosity or Thickening trends were sometimes different.
In addition, when the conductive pigment paste of the present invention is made into an electrode layer by the method described below, the solvent etc. will volatilize and will not remain. It is preferable to collect and reuse. That is, it is preferable to use a recycled product as the solvent (C). This recycled solvent (recycled product) also contains the amine compound (E1) originally contained in the conductive pigment paste of the present invention, and the viscosity or thickening tendency of the conductive pigment paste varies from lot to lot. It will be different. Furthermore, amine compounds often have a strong odor.
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% by mass or less, preferably 0.5% by mass. % or less, particularly preferably 0.1% by mass or less.
In addition, the above-mentioned "using a recycled product as the solvent (C)" means that the solvent (C) used in the conductive pigment paste of the present invention contains 10% or more (preferably 20% or more) of a recycled product. It is.

The content of the solvent (C) in the conductive pigment paste is, for example, 40% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, for example 99% by mass, based on the total amount of the conductive pigment paste. % or less, preferably 98% by mass or less, more preferably 97% by mass or less.

In addition, from the viewpoint of resin solubility, it is preferable that the solubility parameter δA of the pigment dispersion resin (A) and the solubility parameter δC of the solvent (C) have a relationship of |δA−δC|<2.0. . The solubility parameter δC of the solvent (C) itself is preferably 10.0 or more, more preferably 10.5 or more, preferably 12.0 or less, and more preferably 11.5 or less.

The solubility parameter of the resin is numerically quantified based on the turbidity measurement method known to those skilled in the art. 2359, 1968).

The solubility parameter of a solvent can be determined according to the method described in "Polymer Handbook VII" edited by J. Brandrup and EHImmergut, Solubility Parameter Values, pp519-559 (John Wiley & Sons, 3rd edition published in 1989).
When two or more solvents (C) are used in combination as a mixed solvent, the solubility parameter of the mixed solvent can be determined experimentally. It can also be determined by the sum of products with solubility parameters.
In the present invention, the unit of solubility parameter is "(cal/cm ³ ) ^1/2 ".

Fluororesin (D)
The fluororesin (D) is a resin intended for forming an electrode layer.

As the fluororesin (D), polyvinylidene fluoride (PVDF) is particularly preferred, and one type can be used alone or two or more types can be used in combination.

The fluororesin (D) may be contained during pigment dispersion, or may be added and contained after pigment dispersion. The weight average molecular weight of the fluororesin (D) is preferably 100,000 or more, more preferably 500,000, and more preferably 650,000 or more from the viewpoints of adhesion to the base material, reinforcement of film physical properties, and solvent resistance. is more preferable, preferably 3 million or less, and more preferably 2 million or less.

The content of the fluororesin (D) is, for example, 10.0% by mass or more, preferably 30.0% by mass or more, more preferably 40.0% by mass or more, based on the solid content of the conductive pigment paste, For example, it is 99.0% by mass or less, preferably 80.0% by mass or less, more preferably 60.0% by mass or less.

Basic low molecular weight component (E)
The basic low molecular weight component (E) may be either an inorganic base compound or an organic base compound. For example, hydroxides such as lithium hydroxide, barium hydroxide, sodium hydroxide, potassium hydroxide; metal hydrides such as sodium hydride, potassium hydride; lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, Carbonates such as potassium carbonate, potassium hydrogen carbonate, and cesium carbonate; Phosphates such as trisodium phosphate and tripotassium phosphate; Acetate salts such as lithium acetate, sodium acetate, and potassium acetate; Sodium methoxide, sodium ethoxide, Examples include alkoxide compounds such as potassium tertiary butoxide; amine compounds such as ammonia, primary amines, secondary amines, and tertiary amines; and the like.
These basic low molecular weight components (E) can be used alone or in combination of two or more.
The molecular weight of the basic low molecular weight component (E) is, for example, less than 1000, preferably 500 or less, more preferably 350 or less, still more preferably 250 or less, particularly preferably 120 or less.

The basic low molecular weight component (E) preferably contains an amine compound (E1) from the viewpoint of improving the wettability and/or storage stability of the conductive pigment.
The content of the amine compound (E1) in the basic low molecular weight component (E) is preferably 50% by mass or more, more preferably 75% by mass or more, based on 100% by mass of the basic low molecular weight component (E). It is preferably 95% by mass or more, and more preferably 95% by mass or more.
Examples of the amine compound (E1) include ammonia, primary amines, secondary amines, tertiary amines, and the like.

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, Primary monoamines such as α-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-bis Aminopropylcyclohexane, 1,4-bisaminopropylcyclohexane, hydrogenated 4,4'-diaminodiphenylmethane, 2-aminopiperidine, 4-aminopiperidine, 2-aminomethylpiperidine, 4-aminomethylpiperidine, 2-aminoethylpiperidine, 4-aminoethylpiperidine, N-aminoethylpiperidine, N-aminopropylpiperidine, N-aminoethylmorpholine, N-aminopropylmorpholine, isophoronediamine, menthanediamine, 1,4-bisaminopropylpiperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 2,4-tolylenediamine, 2,6-tolylenediamine, 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, benzylamine, 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 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.

Examples of secondary amines include diethylamine, dipropylamine, di-n-butylamine, di-sec-butylamine, diisobutylamine, di-n-pentylamine, di-3-pentylamine, dihexylamine, dioctylamine, di- (2-ethylhexyl)amine, methylhexylamine, diallylamine, pyrrolidine, piperidine, 2,4-lupetidine, 2,6-lupetidine, 3,5-lupetidine, diphenylamine, N-methylaniline, N-ethylaniline, dibenzylamine , methylbenzylamine, dinaphthylamine, pyrrole, indoline, indole, morpholine and other secondary monoamines; N,N'-dimethylethylenediamine, N,N'-dimethyl-1,2-diaminopropane, N,N'-dimethyl- 1,3-diaminopropane, N,N'-dimethyl-1,2-diaminobutane, N,N'-dimethyl-1,3-diaminobutane, N,N'-dimethyl-1,4-diaminobutane, N , N'-dimethyl-1,5-diaminopentane, N,N'-dimethyl-1,6-diaminohexane, N,N'-dimethyl-1,7-diaminoheptane, N,N'-diethylethylenediamine, N , N'-diethyl-1,2-diaminopropane, N,N'-diethyl-1,3-diaminopropane, N,N'-diethyl-1,2-diaminobutane, N,N'-diethyl-1, 3-diaminobutane, 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, 1,4- Examples include secondary polyamines such as di-(4-piperidyl)butane.

Examples of the tertiary amine 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-diethylethanol Amine, N,N-dimethylethanolamine, N-ethyldiethanolamine, triethanolamine, tribenzylamine, N,N-dimethylbenzylamine, diethylbenzylamine, 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, Tertiary monoamines such as 2-(2-dimethylaminoethoxy)-4-methyl-1,3,2-dioxabornane, 2-, 3-, 4-picoline; tetramethylethylenediamine, pyrazine, N,N'-dimethylpiperazine , N,N'-bis((2-hydroxy)propyl)piperazine, hexamethylenetetramine, N,N,N',N'-tetramethyl-1,3-butanamine, 2-dimethylamino-2-hydroxypropane, Examples include tertiary polyamines such as 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.
Among these, it is preferable that it does not contain other functional groups such as acid groups and hydroxyl groups, primary amine compounds are preferable, and monovalent amine compounds (monoamines) are preferable.
Examples of the amine compound (E1) include aliphatic amines, alicyclic amines, aromatic amines, etc., and any of them can be preferably used, but aromatic amines, primary aliphatic amine compounds having a hydroxyl group, A secondary aliphatic amine compound having the following is preferable, and a primary aromatic amine compound is more preferable.
Further, it is preferable that the nitrogen atoms in the amine compound (E1) are only nitrogen atoms constituting an amino group.
Further, the amine compound (E1) preferably has 3 or less nitrogen atoms, more preferably 2 or less, and even more preferably 1 nitrogen atom.

Further, the amine compound (E1) is preferably not an amine compound having a triazine ring in the molecule.
When an aliphatic amine compound and an amine compound having a triazine ring in the molecule are used together, the aliphatic amine compound should be mixed in an amount exceeding 1 molar equivalent per 1 molar equivalent of the amine compound having a triazine ring. is preferred. In this case, when the aliphatic amine compound is a primary monovalent aliphatic amine compound, it is preferable that the molecular weight thereof is less than 116.

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 1000, more preferably 500 or less, and even more preferably 350 or less. It is preferably 250 or less, particularly preferably 120 or less, and even more preferably 120 or less. Note that the primary aliphatic amine compound having a hydroxyl group is preferably a primary aliphatic amine compound having a hydroxyl group and having a weight average molecular weight of 89 or more.
For the same reason, the boiling point of the amine compound is preferably 400°C or lower, more preferably 300°C or lower, and even more preferably 200°C or lower.
Further, the amine value of the amine compound (E1) is, for example, 5 mgKOH/g or more, preferably 105 mgKOH/g or more, more preferably 250 mgKOH/g or more, still more preferably 400 mgKOH/g or more, and, for example, 1000 mgKOH/g or less. Preferably, it is within this range.

The content of the basic low molecular weight component (E) is, for example, 1% by mass or more, preferably 10% by mass or more, more preferably 40% by mass or more, based on 100% by mass of the solid content of the conductive pigment paste. For example, it is preferably 300% by mass or less, preferably 200% by mass or less, more preferably 150% by mass or less.
Furthermore, the lower limit is, for example, 1% by mass or more, preferably 12% by mass or more, more preferably 40% by mass or more, still more preferably 80% by mass or more, based on 100% by mass of the solid content of the conductive pigment (B). It is. The upper limit is, for example, 1000% by mass or less, preferably 500% by mass or less, more preferably 350% by mass or less, still more preferably 300% by mass or less. Since the basic low molecular weight component (E) [especially the amine compound (E1)] often has a strong odor, the working environment may deteriorate during the blending or drying process. Furthermore, since they are generally expensive, the cost may increase. Therefore, it is necessary to keep the content to the minimum necessary.
In addition, the content ratio of the solvent (C) and the basic low molecular weight component (E) is usually 100/0.1 to 100/10 in mass ratio of the solvent (C) and the basic low molecular weight component (E). within the range, preferably within the range of 100/0.5 to 100/8, more preferably within the range of 100/1 to 100/6, and more preferably 100/1.5 to 100/4. It is preferable that it be within the range of .

Other components In addition to the above components (A), (B), (C), (D), and (E), the conductive pigment paste of the present invention may contain other components as necessary. can do.

Other components include, for example, resins other than pigment dispersion resin (A) and fluororesin (D), neutralizers, antifoaming agents, preservatives, rust preventives, plasticizers, and conductive pigments other than (B). Examples include pigments.

Pigments other than the conductive pigment (B) include, for example, white pigments such as titanium white and zinc white; blue pigments such as cyanine blue and industhrene blue; green pigments such as cyanine green and verdigris; azo-based and quinacridone-based pigments, etc. Red pigments such as organic red pigments and red pigments; organic yellow pigments such as benzimidazolone series, isoindolinone series, isoindoline series, and quinophthalone series; yellow pigments such as titanium yellow and yellow lead; These pigments can be used alone or in combination of two or more. Pigments other than these conductive pigments (B) can be used for purposes such as color adjustment and reinforcing the physical properties of the film within a range that does not significantly impair conductivity. It may be dispersed simultaneously with B), or it may be mixed as a pigment or a pigment paste after a paste is prepared by dispersing the pigment dispersion resin (A) and the conductive pigment (B).

The content of pigments other than the conductive pigment (B) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, based on the total pigments in the conductive pigment paste. It is particularly preferable that it does not substantially contain it.
Moreover, it is preferable that the conductive pigment paste of the present invention does not contain a pigment derivative. In particular, it is preferable not to contain a triazine-based pigment derivative containing a triazine ring in the molecule.

From the viewpoint of pigment dispersibility and storage stability, the viscosity of the conductive pigment paste at a shear rate of 2 s ^-1 is less than 5000 mPa·s, preferably less than 2500 mPa·s, and 1000 mPa·s. s, and 10 mPa·s or more, preferably 50 mPa·s or more, and more preferably 100 mPa·s or more. For example, it is preferably 10 mPa·s or more and less than 5000 mPa·s, more preferably 50 mPa·s or more and less than 2500 mPa·s, and particularly preferably 100 mPa·s or more and less than 1000 mPa·s.

The viscosity can be measured using, for example, a cone and plate viscometer (manufactured by HAAKE, trade name: Mars2, diameter 35 mm, 2° inclination cone and plate).

The conductive pigment paste of the present invention can be prepared using a paint shaker, a sand mill, a ball mill, a pebble mill, a LMZ mill, a DCP pearl mill, a planetary ball mill, a homogenizer, a twin-screw kneader, a thin film rotating high-speed mixer ( It can be prepared by uniformly mixing and dispersing using a conventionally known dispersing machine such as (trade name: CLEAR MIX, FIL MIX, etc.).

[Mixture paste]
The present invention provides a composite paste formed by further blending an electrode active material (F) with the above conductive pigment paste. The composite paste is suitable for use as a positive electrode or a negative electrode for a lithium ion battery electrode, and preferably as a positive electrode.
In addition, the second aspect of the composite material paste of the present invention includes a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), a basic low molecular weight component (E), and Contains an electrode active material (F), and the pigment dispersion resin (A) consists of an amide group, an imide group, a hydroxyl group, a carboxyl group, a sulfonic acid group, a phosphoric acid group, a silanol group, a cyano group, a pyrrolidone group, and an ether group. The conductive pigment (B) has at least one polar functional group selected from the group consisting of carbon nanotubes ( The manufacturing method (order of mixing the components) is not limited as long as it contains B1).

Electrode active material (F)
Examples of the electrode active material (F) include lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium cobalt oxide (LiCoO ₂ ), and LiNi _1/3 Co _1/3 Mn _1/3 O. Lithium composite oxides such as No. ₂ ; lithium iron phosphate (LiFePO ₄ ); sodium composite oxides; potassium composite oxides, and the like. These electrode active materials (F) 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, so it can be suitably used.
The particle size of the electrode active material is, for example, 0.5 μm or more, preferably 10.5 μm or more, and, for example, 30 μm or less, preferably 20 μm or less.

The solid content of the electrode active material (F) in the solid content of the composite paste of the present invention is usually 70% by mass or more and less than 100% by mass, preferably 80% by mass or more and less than 100% by mass. is preferable from the viewpoint of battery capacity, battery resistance, etc.

When the composite paste contains the electrode active material (F), it may thicken during storage. The reason for this is that the electrode active material (F) 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 conductive pigment (B) having an acidic surface. Therefore, by containing a certain amount or more of a basic low molecular weight component (E) [particularly an amine compound (E1)], it is possible to suppress the thickening of the composite paste during storage.

Method for Producing Composite Material Paste The composite material paste of the present invention can be obtained by first preparing the above-mentioned conductive pigment paste, and then blending at least one type of electrode active material (F) into the paste.
Further, the composite material paste of the present invention may be prepared by mixing the aforementioned components (A), (B), (C), (D), (E), and the electrode active material (F).

The solid content of the pigment dispersion resin (A) in the solid content of the composite material paste of the present invention is, for example, 0.01% by mass or more, preferably 0.02% by mass or more, and, for example, 20% by mass or less, preferably The content is preferably 10% by mass or less in terms of battery performance, paste viscosity, etc.

The composite paste of the present invention contains a basic low molecular weight component (E) from the viewpoint of storage stability (suppression of thickening) in the composite paste.
By bringing the basic low molecular weight component (E) into contact with (wetting) the conductive pigment (B) and then mixing the electrode active material (F), the conductive pigment (B) and the electrode active material (F) are combined. From the viewpoint of alleviating aggregation, it is preferable to first include the order of mixing the conductive pigment (B) and the basic low molecular weight component (E).

In the composite paste of the present invention, the lower limit of the content of the basic low molecular weight component (E) based on the solid content of the conductive pigment (B) is 100% by mass. From the viewpoint of (viscosity suppression), the content is usually 1% by mass or more, preferably 10% by mass or more, more preferably 40% by mass or more, and still more preferably 80% by mass or more. The upper limit is usually 500% by mass or less, preferably 400% by mass or less, more preferably 350% by mass or less, still more preferably 300% by mass or less, from the viewpoint of the amount of component (E) remaining in the electrode film.

The solid content of the conductive pigment (B) in the solid content of the composite material paste of the present invention 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. For example, from the viewpoint of battery performance, the content is preferably 30% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less. Further, the content of the solvent (C) in the composite material paste of the present invention is, for example, 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and, for example, 70% by mass or less, preferably From the viewpoint of electrode drying efficiency and paste viscosity, the content is preferably 60% by mass or less, more preferably 50% by mass or less.

[Lithium ion battery electrode]
Manufacturing method for lithium ion battery electrodes As mentioned above, the electrode composite material layer (also called electrode layer or composite material layer) of a lithium ion secondary battery is made by applying composite material paste for lithium ion battery electrodes to the surface of the core material of the positive or negative electrode. It can be manufactured by coating and drying, and the obtained electrode mixture layer of a lithium ion secondary battery is particularly preferably used as a positive electrode.
Further, the conductive pigment paste of the present invention can be used not only as a paste for a composite layer but also as a primer layer between an electrode core material and a composite layer.
The method for applying the composite material paste for lithium ion battery electrodes can be performed by a method known per se using a die coater or the like. The coating amount of the composite material paste for lithium ion battery electrodes is not particularly limited, but for example, the thickness of the composite material layer after drying is 0.04 mm or more, preferably 0.06 mm or more, and, for example, 0.30 mm or less, 0.04 mm or more. It can be set within a range of 24 mm or less. The temperature of the drying step can be appropriately set within the range of, for example, 80 to 200°C, preferably 100 to 180°C. The time for the drying step can be appropriately set, for example, within the range of 5 to 120 seconds, preferably 5 to 60 seconds.

All or part of the solvent (C) and the basic low molecular weight component (E) are volatilized in the above drying process, but as mentioned above, the volatilized components are It is preferable to collect and reuse component (C) and component (E).

The present invention will be described below in more detail with reference to Examples, but the present invention is not limited to these specific embodiments.

[Production of pigment dispersion resin]
Production Example 1 Sulfonic acid modified polyvinyl alcohol resin In a reaction vessel equipped with a thermometer, a reflux condenser, a nitrogen gas inlet tube and a stirrer, 97 parts by mass of vinyl acetate and 3.0 parts by mass of sodium allylsulfonate as polymerizable monomers, methanol as a solvent, and azobisisobutyronitrile as a polymerization initiator were used to carry out a copolymerization reaction at a temperature of about 60 ° C., and unreacted monomers were removed under reduced pressure to obtain a resin solution. Next, a methanol solution of sodium hydroxide was added to carry out a saponification reaction, and the mixture was thoroughly washed and then dried with a hot air dryer. Finally, a sulfonic acid modified polyvinyl alcohol resin with a weight average molecular weight of 17000, a polar functional group concentration of 18.1 mmol / g, and a saponification degree of 90 mol% was obtained.

[Manufacture of conductive pigment paste and composite material paste]
Example 1A
40 parts of sulfonic acid-modified polyvinyl alcohol resin (solid content: 40 parts) obtained in Production Example 1, 200 parts of carbon nanotubes (CNT1), KF Polymer W#7300 (trade name, polyvinylidene fluoride, weight average molecular weight 1 million, Kureha Co., Ltd.) 180 parts of N-methyl-2-pyrrolidone (NMP1), and 200 parts of benzylamine were mixed and dispersed in a ball mill for 5 hours to produce a conductive pigment paste (A-1).

Example 1B
100 parts of the conductive pigment paste (A-1) was mixed with 900 parts of active material particles (lithium nickel manganese oxide particles having a spinel structure represented by the composition formula _{LiNi0.5Mn1.5O4} , average particle size ₆ _μm , BET specific surface area 0.7 ^m2 /g) using a disperser to produce a composite paste (B-1).

Examples 2A to 21A, Comparative Examples 1A to 2A
Conductive pigment pastes (A-2) to (A-23) were obtained in the same manner as in Example 1A except for using the formulations shown in Table 1 below.

Examples 2B to 21B, Comparative Examples 1B to 2B
Mixed material pastes (B-2) to (B-23) were obtained in the same manner as in Example 1B, except for using the formulations shown in Table 1 below.

The details of each component in Table 1 above are as follows.

CNT1 to CNT6 are all multi-walled carbon nanotubes.
In addition, the median diameter (D50), G/D ratio, and acidic group amount in the above table were measured by the following method.

<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, Ltd.) according to the following procedure.

[Preparation of water dispersion medium]
Add 0.10 g of F10MC (trade name, manufactured by Nippon Paper Industries Co., Ltd., carboxymethyl cellulose sodium (hereinafter also referred to as CMCNa)) solid content to 100 mL of distilled water, stir at room temperature for 24 hours or more to dissolve, and dissolve CMCNa0.1% by mass in water. A dispersion medium was prepared.

[Preparation of CMCNa aqueous solution]
A solid content of 2.0 g of F10MC (trade name, manufactured by Nippon Paper Industries, Ltd., sodium carboxymethylcellulose) was added to 100 mL of distilled water, and the mixture was stirred and dissolved at room temperature for 24 hours or more to prepare an aqueous solution containing 2.0% by mass of CMCNa.

[Measurement pre-processing]
6.0 mg of carbon nanotubes were weighed into a vial, and 6.0 g of the aqueous dispersion medium was added thereto. An ultrasonic homogenizer "SmurtNR-50" (trade name, manufactured by Microtech Nichion Co., Ltd.) was used for measurement pretreatment. It was confirmed that there was no deterioration of the chip, and the chip was adjusted so that it was 10 mm or more above the surface of the treated sample liquid. The time set (irradiation time) was set to 40 seconds, the POW SET was set to 50%, and the START POW was set to 50% (output 50%), and the carbon nanotube water was homogenized by ultrasonic irradiation using auto power operation with a constant output power. A dispersion liquid was prepared.

[measurement]
Using the carbon nanotube aqueous dispersion, the ratio of dispersed particles of carbon nanotubes 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 have carbon nanotubes with a refractive index of 1.520 and water with a refractive index of 1.333, and approximately 1.0 mL of a CMCNa aqueous solution is filled after the module has been cleaned. After performing offset measurements, optical alignment, and background measurements at a pump speed of 50%, the prepared aqueous carbon nanotube dispersion was measured using a particle size analyzer with relative concentration, which indicates the percentage of light scattered outside the beam by the particles. 8 to 12% or PIDS to 40% to 55%, irradiated with ultrasonic waves at 78W for 2 minutes using the particle size distribution analyzer attachment (measurement pretreatment), and circulated for 30 seconds to remove air bubbles. Particle size distribution measurements were performed. A graph of volume % versus particle size (particle diameter) was obtained, and the abundance ratio of dispersed particles of 1 μm or less and the median diameter (D50) were determined.
For each sample of carbon nanotubes, three measurement samples were taken from different collection locations, and the particle size distribution was measured, and the proportion of dispersed particles of 1 μm or less and the median diameter (D50) were determined as the average value.

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

<Amount of acidic groups in carbon nanotubes (CNTs)>
2g of CNTs were accurately weighed, immersed in 50ml of 0.01M benzylamine/N-methyl-2-pyrrolidone solution, and dispersed for 1 hour using an ultrasonic irradiator. Thereafter, centrifugation was performed, 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 CNTs was determined.

<Solvent (C)>
The water content and amine content of the solvents used were measured.
The water content and amine content were measured using a Karl Fischer moisture meter "MKC-610" (trade name, manufactured by Kyoto Electronics Industry Co., Ltd.) and ion chromatography.
NMP1: N-methyl-2-pyrrolidone, SP value 11.1, water content 0.1% by mass, amine content 0% by mass
NMP2: N-methyl-2-pyrrolidone, SP value 11.1, water content 1.2% by mass, amine content 0% by mass
Propylene glycol monomethyl ether: SP value 10.4, water content 0.1% by mass, amine content 0% by mass.

[Evaluation test]
Evaluation tests were conducted on the conductive pigment pastes and composite material pastes obtained in the above Examples and Comparative Examples. As for the evaluation, D is a failure. If even one evaluation result is a failure, the evaluation of the conductive pigment paste is a failure. The evaluation results are shown in Table 1.

<Dispersibility>
The dispersibility of the obtained conductive pigment paste was evaluated according to the following criteria using a tube gauge according to the dispersion test of JIS K-5600-2-5.
A: Pigment is dispersed to a particle size of less than 10 μm. Dispersibility is very good.
B: Pigment is dispersed in a thickness of 10 μm or more and less than 20 μm. The dispersibility is rather good.
C: The pigment is dispersed to a thickness of 20 μm or more, but no aggregates are visually observed. Dispersibility is slightly inferior.
D: Aggregates are visually confirmed. Dispersibility is very poor.

<Initial viscosity>
The viscosity of the resulting composite paste was measured using a cone-and-plate viscometer "Mars 2" (trade name, manufactured by HAAKE) at a shear rate of 2.0 sec ^-1 , 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 was compared with the viscosity after storage. 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 with a 2° inclination). 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).

<Volume resistivity (conductivity)>
The conductive pigment pastes obtained in Examples 1A, 7A, 8A, and 9A were further measured for volume resistivity. In the measurement of volume resistivity, a 5% by mass solution of polyvinylidene fluoride (manufactured by Kureha Co., Ltd., trade name "KF Polymer W#7300", solvent: N-methyl-2-pyrrolidone) was used as a binder.
The ratio of the mass of the conductive pigment (B) in the obtained conductive pigment paste to the total mass of the solid content of the pigment dispersion resin (A) and the solid content of KF Polymer W#7300 in the conductive pigment paste is 5:100. The conductive pigment paste and KF Polymer W#7300 solution were weighed out and mixed for 2 minutes using an ultrasonic homogenizer to obtain a measurement sample.

A measurement sample was coated on a glass plate (2 mm x 100 mm x 150 mm) using a doctor blade method, and 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, a resistivity meter "Loresta-GP MCP-T610" (trade name) was measured using an ASP probe "MCP-TP03P" (trade name, manufactured by Mitsubishi Chemical Analytech). , manufactured by Mitsubishi Chemical Analytech, Inc.), and the volume resistivity was calculated by multiplying the obtained resistance value by a resistivity correction factor (RCF) of 4.532 and the film thickness of the coating film. Volume resistivity was evaluated according to the following criteria.
A: The volume resistivity is less than 7 Ω·cm, and the conductivity is good.
B: Volume resistivity is 7 Ω·cm or more and less than 15 Ω·cm, and conductivity is normal.
D: Volume resistivity is 15 Ω·cm or more, and conductivity is poor.
As the evaluation results, the conductive pigment pastes obtained in Examples 1A and 7A were rated "A", and the conductive pigment pastes obtained in Examples 8A and 9A were rated "B".

[Manufacture of battery electrode layer]
Application examples 1 to 21
The composite paste obtained in Examples 1B to 21B was applied to both sides of a long aluminum foil (positive electrode current collector) with an average thickness of 15 μm so that the basis weight per side was 10 mg/cm ² (based on solid content). A positive electrode active material layer was formed by applying the material in a strip using a roller coating method and drying (drying temperature: 180° C., 10 minutes). The positive electrode active material layer (positive electrode layer) supported on this positive electrode current collector was rolled using a roll press machine to form an electrode layer, and its properties were adjusted.
The resulting electrode layer had a residual solvent amount of less than 1%, and had good finishing properties.

Claims

A conductive pigment paste containing a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E),
The pigment dispersion resin (A) has at least one polar functional group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol/g,
The conductive pigment (B) contains carbon nanotubes (B1),
When the content of the basic low molecular weight component (E) is α (parts by mass) with respect to 100 parts by mass of the carbon nanotube (B1), and the BET specific surface area of the carbon nanotube (B1) is β (m 2 /g). , a conductive pigment paste in which the value of X in the following formula (1) is 5 or more.
X=α/β×300...Formula (1)
A conductive pigment paste containing a pigment dispersion resin (A), a conductive pigment (B), a solvent (C), a fluororesin (D), and a basic low molecular weight component (E),
The pigment dispersion resin (A) has at least one polar functional group, and the polar functional group concentration of the pigment dispersion resin (A) is 0.3 mmol/g to 23 mmol/g,
The conductive pigment (B) contains carbon nanotubes (B1),
The content of the basic low molecular weight component (E) with respect to 100 parts by mass of the carbon nanotube (B1) is α (parts by mass), the BET specific surface area of the carbon nanotube (B1) is β (m 2 /g), and the carbon nanotube A conductive pigment paste in which the value of Y in the following formula (2) is 0.01 or more, where the amount of acidic groups in (B1) is γ (mmol/g).
Y=α/β/γ...Formula (2)
The conductive pigment paste according to claim 1 or 2, wherein the basic low molecular weight component (E) contains an amine compound (E1).
The conductive pigment paste according to claim 1 or 2, wherein the carbon nanotube (B1) has a volume-based median diameter (D50) of 10 to 250 μm.
The conductive material according to claim 1 or 2, wherein the content of the basic low molecular weight component (E) is 12% by mass or more and 500% by mass or less based on 100% by mass of the solid content of the conductive pigment (B). color pigment paste.
The conductive pigment paste according to claim 1 or 2, wherein the carbon nanotubes (B1) have an acidic group content of 0.01 mmol/g to 0.5 mmol/g.
The BET specific surface area of the carbon nanotube (B1) is 100 m 2 /g to 800 m 2 /g, and the maximum peak intensity within the range of 1560 m −1 to 1600 cm −1 in the Raman spectrum of the carbon nanotube (B1) is G The conductive pigment paste according to claim 1 or 2, wherein the conductive pigment paste has a G/D ratio of 0.1 to 5, where D is the maximum peak intensity within the range of 1310 m -1 to 1350 cm -1 .
The conductive pigment paste according to claim 3, wherein the solvent (C) has a water content of 1% by mass or less and an amine compound content of 1% by mass or less.
The conductive pigment paste according to claim 1 or 2, wherein the weight average molecular weight of the basic low molecular weight component (E) is less than 1,000.
The conductive pigment paste according to claim 3, wherein the amine compound (E1) has an amine value of 105 mgKOH/g to 1000 mgKOH/g.
The conductive pigment paste according to claim 1 or 2, wherein the solvent (C) is N-methyl-2-pyrrolidone.
A composite paste comprising the conductive pigment paste according to claim 1 or 2 and an electrode active material (F).
An electrode for a lithium ion battery obtained using the composite paste according to claim 12.