JP7708236B2 - Carbon nanotube dispersion and its use - Google Patents

Description

The present invention relates to a carbon nanotube dispersion containing an acidic compound. More specifically, the present invention relates to a carbon nanotube dispersion containing an acidic compound, a resin composition containing a carbon nanotube dispersion containing an acidic compound and a resin, a composite slurry containing a carbon nanotube dispersion containing an acidic compound, a resin, and an active material, an electrode film coated with the composite slurry, and a nonaqueous electrolyte secondary battery comprising an electrode film and an electrolyte containing lithium.

In recent years, with the widespread use of mobile phones and notebook personal computers, non-aqueous electrolyte secondary batteries, especially lithium-ion secondary batteries, have been attracting attention. Lithium-ion secondary batteries usually have a negative electrode made of a carbon-based material, a positive electrode containing an active material that allows lithium ions to reversibly enter and exit, and a non-aqueous electrolyte in which they are immersed. The positive electrode is manufactured by applying a composite slurry made of an active material, a conductive material, and a binder to a current collector.

Conductive materials include carbon black, ketjen black, fullerene, graphene, fine carbon materials, etc. In particular, carbon nanotubes (hereinafter also referred to as CNTs), a type of fine carbon fiber, are tubular carbon with a diameter of 1 μm or less, and their use as conductive materials for lithium-ion secondary batteries is being considered due to their high conductivity based on their unique structure (for example, Patent Documents 1 and 2).
Multi-walled CNTs of 1000 nm are relatively inexpensive and are expected to be put to practical use.

By using CNTs with a small average outer diameter, a conductive network can be efficiently formed with a small amount, and the amount of conductive material contained in the positive and negative electrodes of lithium-ion secondary batteries can be reduced. However, CNTs with a small average outer diameter have strong cohesion and are difficult to disperse, making it difficult to obtain a CNT dispersion with sufficient dispersibility.

In addition, there is a demand for higher capacity lithium-ion secondary batteries, and to achieve this, the use of electrode active materials containing high amounts of highly basic elements such as Al, Ni, and Mn is being considered. However, when these active materials are used, bases are eluted into the composite slurry, which reduces the storage stability of the composite slurry and raises concerns about the difficulty of coating the film, the production process, and the uniformity of the coating.

There have been reports of studies on reducing the reaction with alkali and improving the storage stability of the composite slurry by creating a low-temperature, low-humidity atmosphere for the preparation and application of the composite slurry (Patent Documents 3 and 4), but this requires a large initial investment.

In addition, improvements to the storage stability of the composite slurry have been investigated by using additives when the conductive assistant is carbon black (Patent Document 5), but when the conductive assistant is CNT, the composite slurry thickens, raising concerns about the homogeneity of the production process and the coating film. In addition, there is a problem that CNT, a conductive assistant with strong cohesive power, re-aggregates from a dispersed state in the composite slurry, preventing the formation of a conductive network and reducing the performance of the electrode.

CNT dispersions are required to thoroughly disperse CNTs, which have high cohesive strength, so that they can efficiently form a conductive network within the electrode film even at lower additive amounts than conventional carbon black, and to maintain the dispersion state of the CNTs, the composite slurry must also have good storage stability.

JP 2011-70908 A JP 2014-19619 A JP 2013-37955 A JP 2017-188203 A JP 2016-46188 A

The problem that the present invention aims to solve is to solve the above-mentioned conventional problems, and to provide a CNT dispersion liquid and a resin composition for improving the storage stability of the composite slurry and obtaining a highly conductive electrode film. More specifically, the present invention aims to provide a CNT dispersion liquid, a resin composition, and a composite slurry that have high dispersibility and excellent storage stability of the composite slurry. More specifically, the present invention aims to provide a nonaqueous electrolyte secondary battery that has excellent rate characteristics and excellent productivity.

The inventors of the present invention have conducted intensive research to solve the above problems. They have discovered that by using a CNT dispersion liquid containing an acidic compound, a highly conductive electrode film can be obtained, and a CNT dispersion liquid with excellent storage stability of the composite slurry can be obtained. Based on this discovery, the inventors have come up with the present invention.

That is, the present invention relates to a carbon nanotube dispersion liquid containing carbon nanotubes (A), a solvent (B), a dispersant (C) and an acidic compound (D) having a molecular weight of 350 or less, characterized in that the amount of the acidic compound (D) is 1 to 25 parts by mass per 100 parts by mass of the carbon nanotubes (A).

The present invention also relates to the carbon nanotube dispersion liquid, wherein the acidic compound (D) is an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a thiol group.

The present invention also relates to the above CNT dispersion, characterized in that, in the Raman spectrum of the carbon nanotubes (A), the G/D ratio is 0.5 to ^5.0 , where G is the maximum peak intensity in the range of 1560 to 1600 cm-1 and D is the maximum peak intensity in the range of 1310 to 1350 cm ^-1 .

The present invention also relates to the above carbon nanotube dispersion, wherein the carbon nanotubes (A) have a BET specific surface area of 180 to 850 ^{m 2} /g.

The present invention also relates to the carbon nanotube dispersion liquid, in which the carbon nanotubes (A) have a peak at a diffraction angle 2θ = 25° ± 2° in powder X-ray diffraction analysis, and the half-width of the peak is 2° to 6°.

The present invention also relates to the carbon nanotube dispersion liquid, wherein the carbon nanotubes (A) have an outer diameter of 3 to 25 nm.

The present invention also relates to the carbon nanotube dispersion liquid, characterized in that the G/D ratio is 1.8 to 4.5, where G is the maximum peak intensity in the range of 1560 to 1600 cm ^-1 in the Raman spectrum of the carbon nanotubes (A) and D is the maximum peak intensity in the range of 1310 to 1350 cm ^-1 .

The carbon nanotube dispersion liquid is characterized in that, in powder X-ray diffraction analysis, the carbon nanotubes (A) have a peak at a diffraction angle 2θ = 25° ± 2°, and the half-width of the peak is 2° to 3°.

The present invention also relates to a resin composition comprising the carbon nanotube dispersion and a binder (E).

The present invention also relates to a composite slurry comprising the above-mentioned resin composition and an active material (F).

The present invention also relates to an electrode film (G) coated with the composite slurry.

The present invention also relates to a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that at least one of the positive electrode and the negative electrode contains the above-mentioned electrode film (G).

By using the CNT dispersion of the present invention, a CNT dispersion, a resin composition, a composite slurry, and an electrode film having excellent electrical conductivity and storage stability of the composite slurry can be obtained. In addition, a non-aqueous electrolyte secondary battery having excellent rate characteristics can be obtained. Therefore, the CNT dispersion of the present invention can be used in various fields of application where high electrical conductivity is required.

The CNT dispersion, acidic compound, resin composition, composite slurry, and the electrode film and nonaqueous electrolyte secondary battery coated with the same according to the present invention will be described in detail below.

(1) Carbon nanotubes (A)
The carbon nanotube (A) (CNT(A)) of this embodiment has a shape in which planar graphite is wound into a cylindrical shape. The CNT(A) may also include single-walled CNTs. Single-walled CNTs have a structure in which a single layer of graphite is wound. Multi-walled CNTs have a structure in which two or more layers of graphite are wound. In addition, the sidewall of the CNT(A) does not have to have a graphite structure. For example, a CNT having a sidewall with an amorphous structure can also be used as the CNT(A).

The shape of the CNT (A) in this embodiment is not limited. Examples of such shapes include various shapes including needle-like, cylindrical tube-like, fishbone-like (fishbone or cup stack type), trump-like (platelet) and coil-like. In this embodiment, the shape of the CNT (A) is preferably needle-like or cylindrical tube-like. The CNT (A) may be a single shape or a combination of two or more shapes.

The form of the CNT (A) in this embodiment may be, for example, graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers, but is not limited to these. The CNT (A) may have any one of these forms or a combination of two or more of them.

The CNT(A) of this embodiment is usually present as a secondary particle. The shape of this secondary particle may be, for example, a state in which CNT(A), which is a general primary particle, is intricately entangled.
It may be an aggregate of linear CNT(A). The secondary particles, which are an aggregate of linear CNT(A), are easier to disintegrate than those in which the CNT(A) are entangled. In addition, linear CNT(A) has better dispersibility than entangled CNT(A), and therefore can be suitably used as CNT(A).

The CNT (A) of this embodiment may be a CNT that has been subjected to a surface treatment. The CNT (A) may also be a CNT derivative to which a functional group, such as a carboxyl group, has been added. Carbon nanotubes (A) that encapsulate organic compounds, metal atoms, or substances, such as fullerenes, may also be used.

The manufacturing method of the CNT (A) in this embodiment is not particularly limited, and the CNT may be manufactured by any method.

The G/D ratio of the CNT (A) of this embodiment is determined by Raman spectroscopy. In the CNT (A) of this embodiment, when the maximum peak intensity in the range of 1560 to 1600 cm ⁻¹ in the Raman spectrum is G and the maximum peak intensity in the range of 1310 to 1350 cm ⁻¹ is D, the G/D ratio is preferably 0.5 to 5.0. It is preferably 1.0 to 4.5, more preferably 1.8 to 4.5, and even more preferably 1.8 to 3.0.

There are various laser wavelengths used in Raman spectroscopy, but here we use 532 nm and 632 nm. The Raman shift observed in the vicinity of 1590 cm ⁻¹ in the Raman spectrum is called the G band derived from graphite, and the Raman shift observed in the vicinity of 1350 cm ⁻¹ is called the D band derived from defects in amorphous carbon and graphite. The higher the G/D ratio of CNT, the higher the degree of graphitization.

The BET specific surface area of the CNT (A) of this embodiment is preferably 180 to 850 ^{m 2} /g, and more preferably 200 to 550 m ² /g.

The layer structure of CNT(A) can be analyzed by powder X-ray diffraction analysis using the following method.

First, CNT(A) is packed in a specified sample holder so that the surface is flat, and set in a powder X-ray diffraction analyzer. The irradiation angle of the X-ray source is changed from 15° to 35° and measurement is performed. For example, CuKα radiation is used as the X-ray source. CNT(A) can be evaluated by reading the diffraction angle 2θ at which a peak appears. In graphite, a peak is usually detected at 2θ around 26°, which is known to be a peak due to interlayer diffraction. Since CNT(A) also has a graphite structure, a peak due to graphite interlayer diffraction is detected in this vicinity. However, since CNT has a cylindrical structure, the value differs from that of graphite. The appearance of a peak at the value 2θ of 25°±2° indicates that the composition contains a multilayer structure rather than a single layer. Since the peak that appears at this position is a peak due to interlayer diffraction of a multilayer structure, it is possible to determine the number of layers of CNT(A). Since single-walled CNTs only have one layer, no peak appears at 25°±2° with single-walled CNTs alone. However, even single-walled CNTs are not 100% single-walled CNTs, and if multi-walled CNTs or the like are mixed in, a peak may appear at 2θ of 25°±2°.

In other words, the smaller the half-width of this peak, the more layers the multi-walled CNT (A) has. Conversely, the larger the half-width of this peak, the fewer layers the CNT has.

The CNT (A) of this embodiment has a diffraction angle 2θ = 25° ± 2° when subjected to powder X-ray diffraction analysis.
The half width of the peak is preferably 2° to 6°, more preferably 2° to 5°, and even more preferably 2° to 3°.

In this embodiment, the outer diameter of the CNT (A) is preferably 3 nm to 25 nm, more preferably 3 nm to 20 nm, and even more preferably 3 nm to 16 nm.

The outer diameter and average outer diameter of the CNT (A) in this embodiment are determined as follows. First, the CNT (A) is observed and photographed using a transmission electron microscope. Next, 300 CNT (A) are randomly selected from the observation photograph, and the outer diameter of each is measured. Next, the average outer diameter (nm) of the CNT (A) is calculated as the number average of the outer diameters.

(2) Solvent (B)
The solvent (B) in this embodiment is not particularly limited as long as it is capable of dispersing the CNTs (A), but is preferably water and/or a mixed solvent consisting of one or more water-soluble organic solvents.

Water-soluble organic solvents include alcohols (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, etc.), polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ethers (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monoethyl ether, monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amine-based (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amide-based (N-methyl-2-pyrrolidone (NMP), N- Ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethyl sulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), and others such as tetrahydrofuran, urea, and acetonitrile can be used. Among these, water or an amide-based organic solvent is more preferable, and among the amide-based organic solvents, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone are particularly preferable.

When only an amide-based organic solvent is used as the solvent (B) in this embodiment, the water content in the solvent (B) is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

(3) Dispersant (C)
The dispersant (C) of this embodiment is not particularly limited as long as it can disperse and stabilize the CNT (A), and triazine derivatives, resin-type dispersants, surfactants, etc. can be used, and a suitable type of dispersant can be used in a suitable amount depending on the characteristics required for dispersing the CNT (A). However, the dispersant (C) does not include those that satisfy the conditions of the acidic compound (D) below.

The triazine derivative is preferably a triazine derivative represented by the following general formula (1).

In general formula (1), R ¹ represents a group represented by -X ¹ -Y ^1. X ¹ represents an arylene group which may have a substituent, and Y ¹ represents a sulfo group, a carboxyl group or a phosphate group.

The "substituents" of the arylene group which may have a substituent of X ¹ may be the same or different,
Specific examples of such substituents include a hydroxyl group, a halogen group such as fluorine, chlorine, or bromine, a nitro group, an alkyl group, an aryl group, a cycloalkyl group, an alkoxyl group, an aryloxy group, an alkylthio group, an arylthio group, etc. Furthermore, a plurality of these substituents may be present.

The "arylene group" of the arylene group which may have a substituent includes a phenylene group, a naphthylene group, etc.

^Q1 represents -OH or -NH- ^R2 . ^Q2 represents -OH or -NH- ^R3 . ^R2 and ^R3 each independently represent an aryl group which may have a substituent, a heterocyclic group which may have a substituent, or a group represented by ^-X1 - ^Y1 . However, ^R2 and ^R3 are not ^-X1 - ^Y1 at the same time.

The "substituents" of the optionally substituted aryl group and optionally substituted heterocyclic group of ^R2 and ^R3 have the same meaning as the substituent of ^X1 .

The "aryl group" of the aryl group which may have a substituent of ^R2 and ^R3 includes a phenyl group, a naphthyl group, and the like.

^R and R The "heterocyclic group" of the heterocyclic group which may have ³ substituents includes, for example, an aromatic or aliphatic heterocycle containing a nitrogen atom, an oxygen atom, a sulfur atom, or a phosphorus atom, and specifically includes a thienyl group, a benzo[b]thienyl group, a naphtho[2,3-b]thienyl group, a pyrrolyl group, a thianthrenyl group, a furyl group, a pyranyl group, an isobenzofuranyl group, a chromenyl group, a xanthenyl group, a phenoxathiinyl group, a 2H-pyrrolyl group, an imidazolyl group, a pyrazolyl group, a pyridyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolizinyl group, an isoindolyl group, a 3H-indolyl group, an indolyl group, a 1H-indazolyl group, a purinyl group, a 4H-quinolizinyl group, an isoquinolyl group, a quinolyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolin ... Examples of such groups include an aryl group, a cinnolinyl group, a pteridinyl group, a 4aH-carbazolyl group, a carbazolyl group, a β-carbolinyl group, a phenanthridinyl group, an acridinyl group, a perimidinyl group, a phenanthrolinyl group, a phenazinyl group, a phenarsazinyl group, an isothiazolyl group, a phenothiazinyl group, an isoxazolyl group, a furazanyl group, a phenoxazinyl group, an isochromanyl group, a chromanyl group, a pyrrolidinyl group, a pyrrolinyl group, an imidazolidinyl group, an imidazolinyl group, a pyrazolidinyl group, a pyrazolinyl group, a piperidyl group, a piperazinyl group, an indolinyl group, an isoindolinyl group, a quinuclidinyl group, a morpholinyl group, a thioxanthryl group, a benzofuryl group, a benzothiazolyl group, a benzoxazolyl group, a benzimidazolyl group, and a benzotriazolyl group. In particular, heterocyclic groups containing at least either a nitrogen atom or an oxygen atom are preferred due to their excellent dispersibility, and among these, a carbazolyl group and a benzimidazolyl group are more preferred.

The structure of a triazine derivative is exemplified below. The method for producing a triazine derivative is not particularly limited, and any well-known method can be applied. For example, the method described in JP-A-2004-217842 can be applied. The disclosure of the above publication is incorporated by reference into this specification.

Specific examples of resin-type dispersants include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, etc.), polyvinyl alcohol, vinyl alcohol resins such as polyvinyl butyral, and polyvinyl pyrrolidone. In particular, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and polyvinyl pyrrolidone are preferred.

Examples of surfactants include anionic, cationic, nonionic and amphoteric surfactants. The surfactant to be selected is not limited to a single surfactant. For this reason, it is also possible to use a combination of two or more surfactants. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. In this case, it is preferable to use an appropriate amount for each surfactant component.

Cationic surfactants include alkylamine salts and quaternary ammonium salts. Specific examples include, but are not limited to, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyl triethyl ammonium chloride. Amphoteric surfactants include, but are not limited to, amino carboxylates.

Nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers. Specific examples include, but are not limited to, polyoxyethylene lauryl ethers, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ethers.

(4) Acidic compound (D)
The acidic compound (D) of the present embodiment is a compound having a molecular weight of 350 or less, and represents a compound that behaves as an acid relative to the electrode active material used. Regardless of whether it is a commercially available product or a synthetic product, it can be used alone or in combination of two or more types.

The acid dissociation constant (pKa) of the acidic compound is preferably -5 to 10, more preferably -3 to 9, even more preferably -3 to 7, even more preferably -3 to 5, even more preferably -3 to 3, and particularly preferably 1 to 3. The value of the acid dissociation constant can be obtained from a chemical handbook or the like as a value in an aqueous solution at 25°C. If the acid dissociation constant is too large, the expected effect may not be obtained, whereas if it is too small, corrosion of the production line or care in handling may be required.

Specific examples of acidic compounds used in the present invention include saturated fatty acids such as acetic acid, propionic acid, caprylic acid, and stearic acid, unsaturated carboxylic acids such as oleic acid and sorbic acid, hydroxy acids such as tartaric acid, citric acid, and glyceric acid, aromatic carboxylic acids such as benzoic acid, salicylic acid, and phthalic acid, dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, and maleic acid, carboxylic anhydrides such as acetic anhydride, benzoic anhydride, phthalic anhydride, and maleic anhydride, sulfonic acids such as benzenesulfonic acid and toluenesulfonic acid, 1,3-diketones such as acetylacetone, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, other oxoacid compounds, compounds having a thiol group, compounds having a phosphoric acid group, phenols, enols, and derivatives and polymers of these compounds, but are not limited to these.

The acidic compound used in the present invention is preferably an organic acid or 1,3-diketone having a molecular weight of 350 or less, more preferably an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of carboxyl groups, sulfonic acid groups, phosphoric acid groups, and thiol groups, more preferably an organic acid or 1,3-diketone having one or more acidic functional groups selected from the group consisting of carboxyl groups and sulfonic acid groups, even more preferably an organic acid having a carboxyl group or a sulfonic acid group, and particularly preferably an organic acid having a carboxylic acid group. It is also preferable that the compound has an aromatic ring.

The molecular weight of the acidic compound is 350 or less. Among them, those having a molecular weight of 30 to 350 are preferred, those having a molecular weight of 100 to 350 are more preferred, and those having a molecular weight of 100 to 200 are particularly preferred.

The number of acidic groups in each molecule of the acidic compound is preferably 1 to 3, and more preferably 1 to 2.

The acidic compound is preferably soluble in the CNT dispersion, and more preferably dissolves in an amount of 0.1 part by mass or more per 100 parts by mass of N-methyl-2-pyrrolidone at atmospheric pressure and at 0°C to 40°C.

(5) Carbon Nanotube Dispersion The CNT dispersion of the present embodiment contains CNTs (A), a solvent (B), a dispersant (C), and an acidic compound (D).

To obtain the CNT dispersion of this embodiment, it is preferable to carry out a process to disperse the CNTs (A) in the solvent (B). There are no particular limitations on the dispersing device used to carry out such a process.

As the dispersing device, a dispersing machine that is generally used for dispersing pigments, etc., can be used. For example, mixers such as a disperser, a homomixer, and a planetary mixer, homogenizers (Advanced Digital Sonifer (registered trademark), Model 450DA, manufactured by BRANSON, "Clearmix", PRIMI, manufactured by M Technique, etc.)
Examples of media-type dispersers include media-type dispersers such as "Filmix" manufactured by X Co., "Abramix" manufactured by Silverson Co., Ltd., paint conditioners (manufactured by Red Devil Co., Ltd.), colloid mills ("PUC Colloid Mill" manufactured by PUC Co., Ltd., "Colloid Mill MK" manufactured by IKA Co., Ltd.), cone mills ("Cone Mill MKO" manufactured by IKA Co., Ltd., etc.), ball mills, sand mills ("Dyno Mill" manufactured by Shinmaru Enterprises Co., Ltd., etc.), attritors, pearl mills ("DCP Mill" manufactured by Eirich Co., Ltd., etc.), and Coball mills; wet jet mills ("Genus PY" manufactured by Genus Co., Ltd., "Starburst" manufactured by Sugino Machine Co., Ltd., "Nanomizer" manufactured by Nanomizer Co., Ltd., etc.); media-less dispersers such as "Claire SS-5" manufactured by M Technique Co., Ltd. and "MICROS" manufactured by Nara Kikai Co., Ltd.; and other roll mills, but are not limited thereto.

The amount of solids in the CNT dispersion of this embodiment is preferably 0.1 to 30% by mass, more preferably 0.5 to 25% by mass, more preferably 1 to 10% by mass, and particularly preferably 2 to 10% by mass, relative to 100% by mass of the CNT dispersion.

In this embodiment, the amount of dispersant (C) in the CNT dispersion is preferably 3 to 300% by mass relative to 100% by mass of CNT (A). From the viewpoint of electrical conductivity, it is preferable to use 5 to 100% by mass, and it is particularly preferable to use 10 to 50% by mass.

In this embodiment, the amount of acidic compound (D) in the CNT dispersion is preferably 1 to 25 mass% relative to 100 mass% of CNT in the CNT dispersion, and it is particularly preferable to use 5 to 20 mass%.

(6) Binder (E)
The binder (E) means a resin that bonds substances together.

Examples of the binder (E) in this embodiment include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. as constituent units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluororesins; cellulose resins such as carboxymethylcellulose; rubbers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Modified bodies, mixtures, and copolymers of these resins are also acceptable. In particular, from the standpoint of resistance, it is preferable to use polymer compounds having fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene.

The weight average molecular weight of these resins as the binder (E) of this embodiment is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and particularly preferably 200,000 to 1,000,000. If the molecular weight is small, the resistance and adhesion of the binder may decrease. If the molecular weight is large, the resistance and adhesion of the binder improves, but the viscosity of the binder itself increases, reducing workability, and the binder may act as an aggregating agent, causing significant aggregation of dispersed particles.

In view of the anticipated industrial applicability of the present invention, the binder (E) preferably contains a polymeric compound having fluorine atoms, is preferably a polymeric compound having fluorine atoms, is more preferably a vinylidene fluoride copolymer, and is particularly preferably polyvinylidene fluoride.

(7) Resin Composition The resin composition of the present embodiment contains CNTs (A), a solvent (B), a dispersant (C), an acidic compound (D), and a binder (E).

To obtain the resin composition of this embodiment, it is preferable to mix and homogenize the CNT dispersion liquid and the binder (E). As a mixing method, various conventionally known methods can be used. The resin composition can be prepared using the dispersion device described above for the CNT dispersion liquid.

(8) Active material (F)
The active material (F) in this embodiment is a material that is the basis of the battery reaction. The active materials are classified into positive electrode active materials and negative electrode active materials based on the electromotive force.

The positive electrode active material is not particularly limited, but may be a metal compound such as a metal oxide or metal sulfide capable of doping or intercalating lithium ions, and a conductive polymer. For example, an oxide of a transition metal such as Fe, Co, Ni, or Mn, a composite oxide with lithium, or an inorganic compound such as a transition metal sulfide may be used. Specifically, a transition metal oxide powder such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , or TiO ₂ , a composite oxide powder of lithium and a transition metal such as lithium nickel oxide having a layered structure, lithium cobalt oxide, lithium manganate, or lithium manganate having a spinel structure, a lithium iron phosphate material which is a phosphoric acid compound having an olivine structure, or a transition metal sulfide powder such as TiS ₂ or FeS may be used. In addition, a conductive polymer such as polyaniline, polyacetylene, polypyrrole, or polythiophene may be used. In addition, the above-mentioned inorganic compounds and organic compounds may be mixed and used.

The negative electrode active material is not particularly limited as long as it can dope or intercalate lithium _{ions. For example, metal Li, its alloys such as tin alloys, silicon alloys, and lead alloys, LixFe2O3 , LixFe3O4 , and LixWO2 ( x} is 0<
x is a number < 1.), metal oxides such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymers such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-baked carbon materials, vapor-grown carbon fibers, carbon fibers, and other carbonaceous materials. These negative electrode active materials can be used alone or in combination.

The positive electrode active material is preferably a composite oxide of lithium containing a transition metal such as Al, Fe, Co, Ni, or Mn, more preferably a composite oxide of lithium containing any of Al, Co, Ni, or Mn, and particularly preferably a composite oxide of lithium containing Ni and/or Mn. When these active materials are used, particularly good effects can be obtained.

The BET specific surface area of the active material is preferably from 0.1 to 10 m ² /g, more preferably from 0.2 to 5 m ² /g, and even more preferably from 0.3 to 3 m ² /g.

The average particle size of the active material is preferably within the range of 0.05 to 100 μm, and more preferably within the range of 0.1 to 50 μm. In this specification, the average particle size of the active material is the average value of the particle size of the active material measured with an electron microscope.

(9) Composite Slurry The composite slurry of the present embodiment contains CNTs (A), a solvent (B), a dispersant (C), an acidic compound (D), a binder (E), and an active material (F).

In order to obtain the composite slurry of this embodiment, it is preferable to add an active material to the CNT resin composition and then perform a dispersion process. The dispersion device used for such a process is not particularly limited. The composite slurry can be obtained using the dispersion device described above for the CNT dispersion liquid.

The amount of active material (F) in the composite slurry is preferably 20 to 85% by mass, and particularly preferably 40 to 85% by mass, relative to 100% by mass of the composite slurry.

The amount of CNT (A) in the composite slurry is preferably 0.05 to 10 mass%, more preferably 0.1 to 5 mass%, and even more preferably 0.1 to 3 mass%, relative to 100 mass% of the active material.

The amount of binder (E) in the composite slurry is preferably 0.5 to 20% by mass, more preferably 1 to 10% by mass, and particularly preferably 1 to 5% by mass, relative to 100% by mass of the active material.

The amount of solids in the composite slurry is preferably 30 to 90% by mass, and more preferably 40 to 85% by mass, relative to 100% by mass of the composite slurry.

The moisture content in the composite slurry is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

(10) Electrode Film The electrode film of the present embodiment is a coating film formed by applying a mixture slurry onto a current collector and drying the mixture slurry to form an electrode mixture layer.

The material and shape of the current collector used in the electrode film of this embodiment are not particularly limited, and can be appropriately selected from those suitable for various secondary batteries. For example, the material of the current collector can be metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. In addition, the shape of the current collector is generally a flat foil, but current collectors with a roughened surface, perforated foils, and mesh-shaped current collectors can also be used.

There are no particular limitations on the method for applying the composite slurry onto the current collector, and any known method can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. Drying methods that can be used include, but are not limited to, leaving to dry, using a blower dryer, a hot air dryer, an infrared heater, or a far-infrared heater.

After coating, a rolling process using a lithographic press or a calendar roll may be performed. The thickness of the electrode mixture layer is generally 1 to 500 μm, and preferably 10 to 300 μm.

(11) Nonaqueous Electrolyte Secondary Battery The nonaqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, and an electrolyte, and uses an electrolytic solution in which the electrolyte is dissolved in a nonaqueous solvent. The nonaqueous electrolyte secondary battery of the present embodiment is not particularly limited, and examples thereof include a lithium ion secondary battery, a lead storage battery, and a nickel metal hydride battery.

As the positive electrode, an electrode film can be used that is made by coating and drying a composite slurry containing a positive electrode active material.

As the negative electrode, an electrode film can be used that is made by applying and drying a composite slurry containing a negative electrode active material.

As the electrolyte, various conventionally known electrolytes can be used, such as, but _{not limited} to, _LiBF4 , LiClO4, _LiPF6 , _LiAsF6 , _LiSbF6 , _LiCF3SO3 , Li( _{CF3SO2 ) 2N , LiC4F9SO3} , Li( _CF3SO2 ) _{3C ,} LiI, LiBr, LiCl, LiAlCl, _LiHF2 , LiSCN, or _LiBPh4 (wherein _Ph is a phenyl group).

Non-aqueous solvents include, but are not limited to, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

The nonaqueous electrolyte secondary battery of this embodiment preferably includes a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and those that have been subjected to a hydrophilic treatment, but are not limited to these.

The structure of the nonaqueous electrolyte secondary battery of this embodiment is not particularly limited, but is usually composed of a positive electrode, a negative electrode, and a separator that is provided as necessary, and can be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type.

The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

<Method of measuring physical properties>
The physical properties of the CNTs used in the examples and comparative examples described below were measured by the following methods.

<Raman Spectroscopic Analysis of CNTs>
CNT was placed on a Raman microscope (XploRA, manufactured by Horiba, Ltd.) and measured using a laser wavelength of 532 nm. The measurement conditions were: capture time 60 seconds, number of integrations 3 times, neutral density filter 10%, objective lens magnification 20 times, confocus hole 500, slit width 100 μm, measurement wavelength 100 to 3000 cm ⁻¹ . The CNT for measurement was separated onto a slide glass and flattened using a spatula. Of the peaks obtained, the maximum peak intensity in the range of 1560 to 1600 cm ⁻¹ in the spectrum was taken as G, the maximum peak intensity in the range of 1310 to 1350 cm ⁻¹ was taken as D, and the ratio of G/D was taken as the G/D ratio of the CNT.

<Specific surface area of CNT>
0.03 g of CNT was weighed out using an electronic balance (MSA225S100DI, manufactured by Sartorius), and then dried for 20 minutes at 110° C. while degassing. Thereafter, the specific surface area of the CNT was measured using a fully automatic specific surface area measuring device (HM-model 1208, manufactured by MOUNTECH).

<X-ray powder diffraction analysis of CNT>
The CNT was placed on the central recess of an aluminum sample plate (outer diameter φ46 mm, thickness 3 mm, sample part φ26.5 mm, thickness 2 mm) and flattened using a slide glass. Then, a medicine paper was placed on the surface on which the sample was placed, and a load of 1 ton was applied to the surface on which the aluminum high sheet packing was placed to flatten it. Then, the medicine paper and the aluminum high sheet packing were removed to obtain a sample for powder X-ray diffraction analysis of CNT. Then, the sample for powder X-ray diffraction analysis of CNT was placed on an X-ray diffractometer (Ultima 2100, manufactured by Rigaku Corporation), and the analysis was performed by operating from 15° to 35°. Sampling was performed every 0.02°, and the scan speed was 2°/min. The voltage was 40 kV, the current was 40 mA, and the X-ray source was CuKα radiation. The plots appearing at the diffraction angle 2θ = 25° ± 2° were averaged by a simple moving average of 11 points, and the half width of the peak was taken as the half width of the CNT. The baseline was taken as a line connecting the plots at 2θ = 15° and 2θ = 34°.

<Outer diameter of CNT>
The CNTs were observed and photographed using a transmission electron microscope. Next, 300 CNTs were randomly selected from the photograph, and the outer diameters of each were measured. The average outer diameter (nm) of the CNTs was calculated as the number average of the outer diameters.

<Viscosity measurement of CNT dispersion>
The CNT dispersion was allowed to stand in a thermostatic chamber at 25° C. for at least 1 hour, and then thoroughly stirred. The viscosity was then measured at a stirring speed of 60 rpm using a viscometer (TOKISANGYO CO. LTD., VISCOMETER, MODEL BL).

<Storage stability of CNT dispersion>
The storage stability of the CNT dispersion was evaluated from the change in viscosity after storing the CNT dispersion at rest for 7 days at 50° C. The viscosity was measured by leaving the CNT dispersion at rest in a thermostatic chamber at 25° C. for 1 hour or more, thoroughly stirring the CNT dispersion, and then measuring the viscosity at a stirring speed of 60 rpm using a viscometer (TOKISANGYO CO. LTD, VISCOMETER, MODEL BL).
Based on the degree of change in viscosity compared to before the storage stability test, the rating was: +++: up to 120% (excellent), ++: up to 150% (good), +: up to 200% (fair), -: 200% (unfair).

<Viscosity Measurement and Storage Stability of CNT Resin Composition>
The CNT resin composition was measured in the same manner as the CNT dispersion.

<Viscosity measurement and storage stability of composite slurry>
The composite slurry was measured in the same manner as the CNT dispersion.

<Volume resistivity of electrode film>
The composite slurry was applied to an aluminum foil using an applicator so that the weight per unit of the electrode was 20 mg/ ^cm2 , and the coating was dried in an electric oven at 140°C ± 5°C for 25 minutes. Thereafter, the surface resistivity (Ω/□) of the coating film after drying was measured using Mitsubishi Chemical Analytech Co., Ltd.'s Loresta GP, MCP-T610. After the measurement, the volume resistivity (Ω cm) of the electrode film was determined by multiplying the thickness of the electrode composite layer formed on the aluminum foil. The thickness of the electrode composite layer was determined by subtracting the thickness of the aluminum foil from the average value measured at three points in the electrode film using a film thickness meter (NIKON, DIGIMICRO MH-15M), and the thickness of the electrode film was determined.

<Rate characteristics of lithium-ion secondary batteries>
The laminated lithium secondary battery was placed in a thermostatic chamber at 25°C, and charge/discharge measurements were performed using a charge/discharge device (Hokuto Denko Corporation, SM-8). After constant current/constant voltage charging (cutoff current 0.6mA) was performed at a charge current of 12mA (0.2C) and a charge end voltage of 4.3V, constant current discharging was performed at a discharge current of 12mA and a discharge end voltage of 3V. After repeating this operation three times, constant current/constant voltage charging (cutoff current 0.6mA) was performed at a charge current of 12mA (0.2C) and a charge end voltage of 4.3V, and constant current discharging was performed at discharge currents of 12mA (0.2C) and 120mA (2C) until the discharge end voltage reached 3.0V, and the discharge capacity was determined. The rate characteristic can be expressed by the ratio of the 0.2C discharge capacity to the 2C discharge capacity, as shown in the following formula 1.
(Formula 2) Rate characteristic = 2C discharge capacity / 0.2C discharge capacity × 100 (%)

<Catalyst for CNT synthesis and CNT production example>
The CNTs used in the examples described below were produced by the following method.

<Synthesis of CNT-A>
10 kg of multi-walled CNT (JENOTUBE 8S, manufactured by JEIO) was weighed into a 120 L heat-resistant container, and the heat-resistant container containing the CNT was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace became 0.1% or less, it was heated to 1600°C over 30 hours. While maintaining the temperature in the furnace at 1600°C, chlorine gas was introduced at a rate of 50 L/min for 50 hours. Nitrogen gas was then introduced at 50 L/min to cool the furnace while maintaining positive pressure, and CNT-A was obtained.

<CNT synthesis catalyst B>
60 parts by mass of cobalt hydroxide, 138 parts by mass of magnesium acetate tetrahydrate, and 16.2 parts by mass of manganese acetate were weighed into a heat-resistant container, and dried at a temperature of 170±5°C for 1 hour using an electric oven to evaporate moisture, and then the SPEED dial was adjusted to 3 using a grinder (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.) and ground for 1 minute. Then, the ground powders were adjusted to 2 using a grinder (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.) and mixed for 30 seconds to produce a catalyst precursor B for CNT synthesis. Then, the catalyst precursor B for CNT synthesis was transferred to a heat-resistant container and calcined for 30 minutes in an air atmosphere at 450±5°C using a muffle furnace (FO510, manufactured by Yamato Scientific Co., Ltd.), and then ground in a mortar to obtain a catalyst B for CNT synthesis.

<Synthesis of CNT-B>
A quartz glass heat-resistant dish on which 2 g of the CNT synthesis catalyst B was sprayed was placed in the center of a horizontal reaction tube with an internal volume of 10 L, which can be pressurized and heated by an external heater. The air in the reaction tube was replaced with nitrogen gas while nitrogen gas was injected, and the atmosphere in the horizontal reaction tube had an oxygen concentration of 1% by volume or less. The horizontal reaction tube was then heated with an external heater until the central temperature in the horizontal reaction tube reached 680° C. After reaching 680° C., propane gas was introduced into the reaction tube as a carbon source at a flow rate of 2 L per minute, and contact reaction was carried out for 1 hour. After the reaction was completed, the gas in the reaction tube was replaced with nitrogen gas, and the gas in the reaction tube was replaced with nitrogen gas, and the reaction tube was cooled to a temperature of 100° C. or less and taken out, thereby obtaining CNT-B.

<CNT synthesis catalyst C>
40 parts by mass of cobalt hydroxide, 138 parts by mass of magnesium acetate tetrahydrate, and 26.2 parts by mass of manganese acetate were weighed into a heat-resistant container, and dried at a temperature of 170±5°C for 1 hour using an electric oven to evaporate moisture, and then the SPEED dial was adjusted to 3 using a grinder (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.) and ground for 5 minutes. Then, the ground powders were mixed for 5 minutes using a grinder (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.) with the SPEED dial adjusted to 3 to produce a catalyst precursor C for CNT synthesis. Then, the catalyst precursor C for CNT synthesis was transferred to a heat-resistant container and calcined for 30 minutes in an air atmosphere at 800±5°C using a muffle furnace (FO510, manufactured by Yamato Scientific Co., Ltd.), and then ground in a mortar to obtain a catalyst C for CNT synthesis.

<Synthesis of CNT-C>
A quartz glass heat-resistant dish on which 2 g of the CNT synthesis catalyst C was sprayed was placed in the center of a horizontal reaction tube with an internal volume of 10 L, which can be pressurized and heated by an external heater. The air in the reaction tube was replaced with nitrogen gas while nitrogen gas was injected, and the atmosphere in the horizontal reaction tube had an oxygen concentration of 0.5 vol% or less. The horizontal reaction tube was then heated with an external heater until the central temperature in the horizontal reaction tube reached 800°C. After reaching 800°C, acetylene gas was introduced into the reaction tube as a carbon source at a flow rate of 3 L per minute, and the reaction was carried out for 2 hours. After the reaction was completed, the gas in the reaction tube was replaced with nitrogen gas, and the gas in the reaction tube was replaced with nitrogen gas, and the reaction tube was cooled to a temperature of 100°C or less and taken out, thereby obtaining CNT-C.

<Synthesis of CNT-D>
10 kg of CNT (KUMHO PETROCHEMICAL, 100T) was weighed into a 120 L heat-resistant container, and the heat-resistant container containing the CNT was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace became 0.1% or less, it was heated to 1600°C over 30 hours. While maintaining the furnace temperature at 1600°C, chlorine gas was introduced at a rate of 50 L/min for 50 hours. Nitrogen gas was then introduced at 50 L/min to cool while maintaining positive pressure, and CNT-D was obtained.

<Preparation of standard negative electrode composite slurry and standard negative electrode>
The negative electrode mixture slurries and negative electrodes used in the examples and comparative examples described below were prepared by the following methods.

<Preparation of standard negative electrode composite slurry>
As the negative electrode active material, 49 parts by mass of artificial graphite (manufactured by Nippon Graphite Co., Ltd., CGB-20) and 25 parts by mass (0.5 parts by mass as solid content) of an aqueous composition in which 2% by mass of carboxymethyl cellulose (manufactured by Daicel Chemical Industries, Ltd., #1190) was dissolved were placed in a planetary mixer and kneaded, and then 22 parts by mass of ion-exchanged water and 1 part by mass (0.5 parts by mass as solid content) of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD2001) were mixed to obtain a negative electrode composite slurry.
<Preparation of standard negative electrode>
The above-mentioned negative electrode composite slurry was applied to a copper foil having a thickness of 20 μm as a current collector using an applicator, and then dried in an electric oven at 120° C.±5° C. for 25 minutes to adjust the weight per unit area of the electrode to 12 mg/cm ^2. Further, a rolling process was performed using a roll press (3 t hydraulic roll press, manufactured by Thank Metal Co., Ltd.) to prepare a negative electrode with a composite layer density of 1.5 g/cm ³ .

<Dispersant>
The structures of triazine derivatives A, B, and C, which are dispersants A, E, and G used in the examples described below, are shown in Chemical Formula 4. The method for producing triazine derivative A is not particularly limited, and a well-known method can be applied. For example, the method described in JP-A-2004-217842 can be applied. The disclosure of the above publication is incorporated by reference into this specification.

Table 1 shows the G/D ratio, specific surface area (m ² /g), half width (°), outer diameter (nm) of the CNTs and the specific surface area of the carbon black used in the examples and comparative examples.

Table 2 shows the dispersants used in the examples and comparative examples.

Table 3 shows the acidic compounds used in the examples and comparative examples.

Example 1
A glass bottle (M-225, manufactured by Kashiwa Glass Co., Ltd.) was charged with 2,400 parts of CNT-D, 0.720 parts of dispersant A (triazine derivative A), 0.024 parts of acidic compound A (benzoic acid), 76.856 parts of NMP, and 80,000 zirconia beads (bead diameter 0.5 mmφ), and a dispersion treatment was carried out for 8 hours using a paint conditioner manufactured by Red Devil Co., Ltd., and then the zirconia beads were separated to obtain a CNT dispersion liquid (A1).

(Examples 2 to 32), (Comparative Examples 1 to 5)
A CNT dispersion was obtained in the same manner as in Example 1, except that the CNT, CNT concentration, dispersant type, acidic compound type, and acidic compound amount listed in the table were changed. When Denka Black was used instead of CNT, the dispersion treatment was carried out for 2 hours.

Table 5 shows the evaluation results of the CNT dispersions prepared in Examples 1 to 32 and Comparative Examples 1 to 5.

(Example 33)
10.6 parts by mass of NMP in which 8% by mass of PVDF (Solvey, Solef #5130) was dissolved was weighed into a plastic container with a capacity of 150 ^cm3 . Then, 0.5 parts by mass of CNT dispersion (A1) was added, and the mixture was stirred for 30 seconds at 2000 rpm using a rotation/revolution mixer (Thinky, Awatori Rentaro, ARE-310). Further, 6.5 parts by mass of CNT dispersion (A1) was added, and the mixture was stirred for 30 seconds at 2000 rpm using the mixer to obtain a CNT resin composition (A1). Further, 55.1 parts by mass of a positive electrode active material (Toda Kogyo, NAC7150) was added, and the mixture was stirred for 2.5 minutes at 2000 rpm using the mixer. Finally, 2.3 parts by mass of NMP was added, and the mixture was stirred for 30 seconds at 2000 rpm using the mixer.
The mixture was stirred at 1000rpm for 2.5 minutes to obtain a composite slurry (A1).

(Examples 34 to 64), (Comparative Examples 6 to 10)
A composite slurry was obtained in the same manner as in Example 33, except that the CNT dispersion liquid was changed to that shown in Table 6.

Table 6 shows the evaluation results of the CNT resin compositions and composite slurries prepared in Examples 34 to 64 and Comparative Examples 6 to 10.

(Example 65)
The composite slurry (A1) was applied onto an aluminum foil using an applicator so that the weight per unit area of the electrode was 20 mg/ ^cm2 , and the coating was then dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (A1).

(Examples 66 to 96), (Comparative Examples 11 to 15)
An electrode film was obtained in the same manner as in Example 65, except that the composite slurry was changed to that shown in Table 6.

Table 7 shows the evaluation results of the electrode films produced. The conductivity was evaluated as follows: if the volume resistivity (Ω·cm) of the electrode film was less than 5, it was ++++ (excellent); if it was 5 or more and less than 10, it was +++ (excellent); if it was 10 or more and less than 20, it was ++ (good); if it was 20 or more and less than 100, it was + (fair); if it was 100 or more, it was - (bad).

(Example 97)
The electrode film (A1) was subjected to a rolling treatment using a roll press (3 t hydraulic roll press, manufactured by Thank Metal Co., Ltd.) to prepare a positive electrode having a mixture layer density of 3.2 g/cm ³ .

(Examples 98 to 128), (Comparative Examples 16 to 20)
A positive electrode was prepared in the same manner as in Example 97, except that the electrode film was changed to that shown in Table 8.

(Example 129)
The positive electrode (A1) and the negative electrode were punched out to 45 mm x 40 mm and 50 mm x 45 mm, respectively, and the separator (porous polypropylene film) inserted between them was inserted into an aluminum laminate bag and dried in an electric oven at 60 ° C. for 1 hour. After that, in a glove box filled with argon gas, 2 mL of an electrolytic composition (a nonaqueous electrolytic composition in which LiPF ₆ was dissolved at a concentration of 1 M in a mixed solvent in which ethylene carbonate, dimethyl carbonate, and diethyl carbonate were mixed in a ratio of 1:1:1 (volume ratio)) was injected, and then the aluminum laminate was sealed to prepare a laminate-type lithium ion secondary battery (A1).

(Examples 130 to 160), (Comparative Examples 21 to 25)
A laminate type lithium ion secondary battery was produced in the same manner except that the positive electrode was changed to one shown in Table 8.

Table 9 shows the evaluation results of the laminated lithium secondary batteries. The rate characteristics were 90% or more: ++++ (excellent), 80% or more but less than 90%: +++ (excellent), 70% or more but less than 80%: ++ (good), 60% or more but less than 70%: + (passable), and less than 60%: - (unacceptable).

In the above examples, a CNT dispersion liquid containing CNTs, a dispersant, and an acidic compound was used. In the examples, a lithium ion secondary battery was obtained that had superior storage stability of the composite material and superior rate characteristics compared to the comparative examples. Therefore, it has become clear that the present invention can provide a lithium secondary battery that has productivity and conductivity that are difficult to achieve with conventional CNT dispersion liquids.

The present invention has been described above with reference to the embodiment, but the present invention is not limited to the above. Various modifications that can be understood by a person skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

Claims (9)

A resin composition comprising carbon nanotubes (A), a solvent (B), a dispersant (C), an acidic compound (D) having a molecular weight of 350 or less, and a binder (E) ,
The carbon nanotube (A) has an outer diameter of 3 to 25 nm;
The solvent (B) contains N-methyl-2-pyrrolidone,
The binder (E) contains polyvinylidene fluoride,
The acidic compound (D) includes at least one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid , and acetylacetone;
A resin composition for use in a positive electrode mixture slurry, characterized in that the acidic compound (D) is contained in an amount of 1 to 25 parts by mass per 100 parts by mass of carbon nanotubes (A). The resin composition used in the positive electrode composite slurry according to claim 1, characterized in that the G/D ratio is 0.5 to 5.0, where G is the maximum peak intensity in the range of 1560 to 1600 cm ^-1 in the Raman spectrum of the carbon nanotube (A) and D is the maximum peak intensity in the range of 1310 to 1350 cm ^- 1. 3. The resin composition according to claim 1, wherein the carbon nanotubes (A) have a BET specific surface area of 180 to 850 ^{m 2} /g. The carbon nanotubes (A) have a peak at a diffraction angle 2θ = 25 ° ± 2 ° in a powder X-ray diffraction analysis, and the half width of the peak is 2 ° to 6 °. The resin composition used for the positive electrode composite slurry according to any one of claims 1 to 3. A method for producing a resin composition comprising carbon nanotubes (A), a solvent (B), a dispersant (C), an acidic compound (D) having a molecular weight of 350 or less, and a binder resin (E), comprising the steps of:
The method includes a step of dispersing carbon nanotubes (A) in a solvent (B),
The carbon nanotube (A) has an outer diameter of 3 to 25 nm;
The solvent (B) contains N-methyl-2-pyrrolidone,
The binder (E) contains polyvinylidene fluoride,
the acidic compound (D) includes at least one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid, and acetylacetone , and the amount of the acidic compound (D) is 1 to 25 parts by mass per 100 parts by mass of the carbon nanotubes (A);
A method for producing a resin composition used in a positive electrode composite slurry. A method for producing a positive electrode composite slurry, comprising: carbon nanotubes (A); a solvent (B); a dispersant (C); an acidic compound (D) having a molecular weight of 350 or less; a binder resin (E); and a positive electrode active material , the method comprising the steps of:
The method includes a step of dispersing carbon nanotubes (A) in a solvent (B),
The carbon nanotube (A) has an outer diameter of 3 to 25 nm;
The solvent (B) contains N-methyl-2-pyrrolidone,
The binder (E) contains polyvinylidene fluoride,
The acidic compound (D) includes at least one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid , and acetylacetone;
The amount of the acidic compound (D) is 1 to 25 parts by mass relative to 100 parts by mass of the carbon nanotubes (A);
A method for producing a positive electrode composite slurry. A method for producing a positive electrode composite slurry, comprising: carbon nanotubes (A); a solvent (B); a dispersant (C); an acidic compound (D) having a molecular weight of 350 or less; a binder resin (E); and a positive electrode active material, the method comprising the steps of:
The method includes a step of producing a carbon nanotube dispersion liquid containing carbon nanotubes (A), a solvent (B), a dispersant (C), and an acidic compound (D) having a molecular weight of 350 or less,
The carbon nanotube (A) has an outer diameter of 3 to 25 nm;
The solvent (B) contains N-methyl-2-pyrrolidone,
The binder (E) contains polyvinylidene fluoride,
The acidic compound (D) includes at least one selected from the group consisting of acetic acid, propionic acid, caprylic acid, stearic acid, oleic acid, sorbic acid, tartaric acid, citric acid, glyceric acid, benzoic acid, salicylic acid, phthalic acid, oxalic acid, succinic acid, adipic acid, maleic acid, acetic anhydride, benzoic anhydride, phthalic anhydride, maleic anhydride, benzenesulfonic acid, toluenesulfonic acid, and acetylacetone;
The amount of the acidic compound (D) is 1 to 25 parts by mass relative to 100 parts by mass of the carbon nanotubes (A);
A method for producing a positive electrode mixture slurry. 8. The method for producing a positive electrode composite slurry according to claim 7, wherein the positive electrode active material is a composite oxide of lithium and one or more transition metals selected from the group consisting of Al, Fe, Co, Ni, and Mn. A carbon nanotube dispersion liquid used in the method for producing a positive electrode mixture slurry according to claim 7 or 8.