JP7196597B2 - Carbon nanotube dispersion and its use - Google Patents

Description

The present invention relates to dispersions of carbon nanotubes. More specifically, a carbon nanotube dispersion, a resin composition containing a carbon nanotube dispersion and a binder resin, a mixture slurry containing a carbon nanotube dispersion, a resin and an active material, and an electrode film formed by forming it into a film. , to a lithium ion secondary battery comprising an electrode film and an electrolyte.

With the spread of electric vehicles and the miniaturization, weight reduction and performance enhancement of mobile devices, there is a demand for secondary batteries with high energy density and higher capacity secondary batteries. Under such circumstances, lithium-ion secondary batteries using non-aqueous electrolytes have come to be used in many devices due to their characteristics of high energy density and high voltage.
As a negative electrode material used in these lithium ion secondary batteries, a carbon material typified by graphite, which has a base potential close to that of lithium (Li) and a large charge/discharge capacity per unit mass, is used. However, these electrode materials are used until the charge/discharge capacity per mass is close to the theoretical value, and the energy density per mass as a battery is approaching its limit. Therefore, in order to increase the utilization rate as an electrode, attempts have been made to reduce the amount of conductive aids and binders that do not contribute to the discharge capacity.

Carbon black, ketjen black, fullerene, graphene, fine carbon materials, and the like are used as conductive aids. In particular, carbon nanotubes, which are a kind of fine carbon fibers, are often used. For example, by adding carbon nanotubes to the graphite or silicon negative electrode, the electrode resistance can be reduced, the load resistance of the battery can be improved, the strength of the electrode can be increased, and the expansion/contraction property of the electrode can be increased. It improves the cycle life of secondary batteries. (See, for example, Patent Documents 1, 2, and 3.) Further, studies are being conducted to reduce the electrode resistance by adding carbon nanotubes to the positive electrode. (See, for example, Patent Documents 4 and 5) Among them, multi-walled carbon nanotubes with an outer diameter of 10 nm to several tens of nm are relatively inexpensive and are expected to be put to practical use.

When carbon nanotubes with a small average outer diameter are used, a small amount of carbon nanotubes can efficiently form a conductive network, and the amount of the conductive aid contained in the positive electrode and negative electrode for a lithium ion secondary battery can be reduced. However, since carbon nanotubes with a small average outer diameter have a strong cohesive force and are difficult to disperse, a carbon nanotube dispersion with sufficient dispersibility could not be obtained.

Therefore, methods for stabilizing the dispersion of carbon nanotubes using various dispersants have been proposed. For example, dispersion in water and NMP (N-methyl-2-pyrrolidone) using a polymer-based dispersant such as water-soluble polymer polyvinylpyrrolidone has been proposed (see Patent Documents 4, 5 and 6). However, in Patent Document 4, electrodes fabricated using carbon nanotubes with an outer diameter of 10 to 150 nm are evaluated, but there is a problem of high electrode resistance. Further, Patent Document 5 proposes a dispersion liquid using carbon nanotubes with a small DBP oil absorption, but although the dispersibility is improved, there is a problem that it is difficult to obtain high conductivity. Patent Document 6 discusses dispersion using single-walled carbon nanotubes, but it was difficult to disperse carbon nanotubes in a solvent at a high concentration. In Patent Document 7, dispersion using double-walled carbon nanotubes is studied, but it is necessary to oxidize the carbon nanotubes and disperse them with an ultrasonic homogenizer, and it is necessary to disperse the carbon nanotubes in a solvent at a high concentration. was difficult. Therefore, obtaining a carbon nanotube dispersion in which carbon nanotubes having a small outer diameter are uniformly dispersed in a dispersion medium at a high concentration has been an important issue for expanding applications.

JP-A-4-155776 JP-A-4-237971 JP 2004-178922 A JP 2011-70908 A JP 2014-19619 A JP 2005-162877 A JP 2010-254546 A

The problem to be solved by the present invention is to provide a carbon nanotube dispersion, a carbon nanotube resin composition, and a mixture slurry having high dispersibility in order to obtain an electrode film with high adhesion and conductivity. More specifically, the object is to provide a lithium ion secondary battery with excellent rate characteristics and cycle characteristics.

^The inventors of the present invention have made intensive studies to solve the above problems, and have found that the accumulated The inventors have found that an electrode film having excellent conductivity and adhesion can be obtained by using a carbon nanotube dispersion having a particle size D50 of 200 to 1000 nm, and have completed the present invention.

That is, the present invention provides a carbon nanotube dispersion containing carbon nanotubes (A), a dispersant (B), and a solvent (C) containing water and/or a water-soluble organic solvent, wherein the carbon nanotubes (A) has a specific surface area of 500 to 800 m ² /g, and a cumulative particle diameter D50 of 200 to 1000 nm as measured by a dynamic light scattering method.

The present invention also relates to the carbon nanotube dispersion having a pH of 6 to 11.

The present invention also relates to the above carbon nanotube dispersion, wherein the carbon nanotubes (A) have an average outer diameter of 1 nm or more and less than 10 nm.

The present invention also relates to the above carbon nanotube dispersion, wherein the carbon nanotubes (A) have a volume resistivity of 1.0×10 ⁻³ to 1.5×10 ⁻² Ω·cm.

Further, the present invention provides a carbon nanotube dispersion containing 0.2 to 2.0 parts by mass of carbon nanotubes (A) with respect to 100 parts by mass of the carbon nanotube dispersion, wherein the viscosity of the carbon nanotube dispersion is type B. Using a viscometer, when the viscosity measured at 6 rpm is X and the viscosity measured at 60 rpm is Y, X / Y satisfies 1.5 ≤ X / Y ≤ 5.5, It relates to the above carbon nanotube dispersion.

The present invention also relates to the above carbon nanotube dispersion, characterized in that the dispersant (B) is contained in an amount of 30 to 200 parts by mass based on 100 parts by mass of the carbon nanotubes (A).

The present invention also relates to the above carbon nanotube dispersion, wherein the solvent (C) is water.

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

The present invention also relates to the above carbon nanotube resin composition, wherein the binder resin (D) is one or more selected from carboxymethylcellulose, styrene-butene rubber and polyacrylic acid.

The present invention also relates to a mixture slurry characterized by containing the carbon nanotube resin composition and the active material (E).

The present invention also relates to an electrode film (F) formed by forming the above mixture slurry into a film.

The present invention also provides a lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte in which lithium ions can migrate, wherein at least one of the positive electrode and the negative electrode includes the above electrode film. It relates to a lithium ion secondary battery.

By using the carbon nanotube dispersion of the present invention, it is possible to obtain a resin composition, a mixture slurry, and an electrode film having excellent conductivity and adhesion. Also, a lithium ion secondary battery having excellent rate characteristics and cycle characteristics can be obtained. Therefore, the carbon nanotube dispersion of the present invention can be used in various fields of application where high conductivity, adhesion and durability are required.

Hereinafter, the carbon nanotube dispersion, the resin composition, the mixture slurry, the electrode film formed by forming it into a film, and the lithium ion secondary battery of the present invention will be described in detail.

(1) Carbon nanotube (A)
The carbon nanotube (A) of this embodiment has a shape in which planar graphite is rolled into a cylindrical shape. Carbon nanotubes (A) may be mixed with single-walled carbon nanotubes. A single-walled carbon nanotube has a structure in which a single layer of graphite is wound. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are wound. Also, the side wall of the carbon nanotube (A) may not have a graphite structure. For example, carbon nanotubes with sidewalls having an amorphous structure can also be used as the carbon nanotubes (A).

The shape of the carbon nanotube (A) of this embodiment is not limited. Such shapes include a variety of shapes including needles, cylindrical tubes, fish bones (fish bones or cup stacks), tramp (platelets) and coils. In the present embodiment, the shape of the carbon nanotube (A) is preferably needle-like or cylindrical tube-like. Carbon nanotubes (A) may be of a single shape or a combination of two or more shapes.

Examples of the form of the carbon nanotube (A) of the present embodiment include graphite whisker, filamentous carbon, graphite fiber, ultrafine carbon tube, carbon tube, carbon fibril, carbon microtube and carbon nanofiber. is not limited to The carbon nanotube (A) may have a single form or a form in which two or more of these forms are combined.

The BET specific surface area of the carbon nanotube (A) of the present embodiment is 500-800 m ² /g, more preferably 500-750 m ² /g.

The average outer diameter of the carbon nanotubes (A) of the present embodiment is preferably 1 nm or more and less than 10 nm, more preferably 3 nm or more and less than 10 nm, and even more preferably 3 nm or more and less than 8 nm.

The standard deviation of the outer diameter of the carbon nanotubes (A) of the present embodiment is preferably 0.4 to 5 nm, more preferably 0.4 to 4 nm.

The outer diameter and average outer diameter of the carbon nanotube (A) of this embodiment are obtained as follows. First, the carbon nanotube (A) is observed and imaged by a transmission electron microscope. Next, in the observation photograph, 300 arbitrary carbon nanotubes (A) are selected and the outer diameter of each is measured. Next, the average outer diameter (nm) of the carbon nanotube (A) is calculated as the number average of outer diameters.

The fiber length of the carbon nanotube (A) of the present embodiment before dispersion is preferably 0.1 to 150 μm, more preferably 1 to 10 μm.

The carbon purity of the carbon nanotube (A) of the present embodiment is represented by the carbon atom content (% by mass) in the carbon nanotube (A). The carbon purity is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more with respect to 100% by mass of the carbon nanotubes (A).

The amount of metal contained in the carbon nanotube (A) of the present embodiment is preferably less than 10% by mass, more preferably less than 5% by mass, and even more preferably less than 2% by mass with respect to 100% by mass of the carbon nanotube (A). . Examples of the metal contained in the carbon nanotube (A) include metals and metal oxides used as catalysts when synthesizing the carbon nanotube (A). Specific examples include metals such as cobalt, nickel, aluminum, magnesium, silica, manganese and molybdenum, metal oxides, and composite oxides thereof.

Various conventionally known methods can be used as a purification treatment method for the carbon nanotubes (A) of the present embodiment. Examples thereof include acid treatment, graphitization treatment and chlorination treatment.

The acid used for the acid treatment of the carbon nanotubes (A) of the present embodiment may be any acid as long as it can dissolve the metal and metal oxide contained in the carbon nanotubes (A). Among inorganic acids, hydrochloric acid, sulfuric acid and nitric acid are particularly preferred.

The acid treatment of the carbon nanotubes (A) of the present embodiment is preferably carried out in a liquid phase, and more preferably the carbon nanotubes are dispersed and/or mixed in the liquid phase. The carbon nanotubes after acid treatment are preferably washed with water and dried.

The carbon nanotube (A) of this embodiment can be graphitized by heating the carbon nanotube (A) at 1500° C. to 3500° C. in an inert atmosphere with an oxygen concentration of 0.1% by volume or less.

The chlorination treatment of the carbon nanotubes (A) of the present embodiment is carried out by introducing chlorine gas in an inert atmosphere with an oxygen concentration of 0.1% by volume or less and heating the carbon nanotubes (A) at 800° C. to 2000° C. It can be done by

The carbon nanotubes (A) of this embodiment usually exist as secondary particles. The shape of the secondary particles may be, for example, a state in which carbon nanotubes (A), which are general primary particles, are intricately entangled. It may be an aggregate of linear carbon nanotubes (A). Secondary particles, which are aggregates of straight carbon nanotubes (A), are easier to loosen than tangled particles. In addition, linear ones are better in dispersibility than entangled ones, so they can be suitably used as the carbon nanotube (A).

The carbon nanotube (A) of the present embodiment may be a surface-treated carbon nanotube. The carbon nanotube (A) may also be a carbon nanotube derivative to which a functional group typified by a carboxyl group is added. In addition, carbon nanotubes (A) containing substances represented by organic compounds, metal atoms, or fullerenes can also be used.

Carbon nanotubes are evaluated by the G/D ratio (peak ratio of G-band and D-band). The G/D ratio of the carbon nanotube (A) of this embodiment is determined by Raman spectroscopy. In the carbon nanotube (A) of the present 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 0.5-50, more preferably 10-50, even more preferably 30-50.

There are various laser wavelengths used in Raman spectroscopy, but 532 nm and 632 nm are used here. The Raman shift seen around 1590 cm ⁻¹ in the Raman spectrum is called the G band derived from graphite, and the Raman shift seen around 1350 cm ⁻¹ is called the D band derived from defects in amorphous carbon and graphite. A carbon nanotube with a higher G/D ratio has a higher degree of graphitization.

The carbon nanotube (A) of the present embodiment preferably has a volume resistivity of 1.0×10 ⁻³ to 1.5×10 ⁻² Ω·cm, and preferably 1.0×10 ⁻³ to 1.0×10 −3 Ω·cm. More preferably, it is 10 ^-2 Ω·cm. The volume resistivity of the carbon nanotube (A) can be measured using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: Lorestar GP powder resistivity measuring system MCP-PD-51)). .

The carbon nanotube (A) of this embodiment may be a carbon nanotube produced by any method. Carbon nanotubes (A) can generally be produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, and a combustion method, but are not limited to these. For example, carbon nanotubes (A) can be produced by contact-reacting a carbon source with a catalyst at 500 to 1000° C. in an atmosphere with an oxygen concentration of 1% by volume or less. The carbon source may be at least one of hydrocarbons and alcohols.

Any conventionally known raw material gas can be used as the carbon source of the carbon nanotubes (A). For example, as a raw material gas containing carbon, hydrocarbons represented by methane, ethylene, propane, butane and acetylene, carbon monoxide, and alcohols can be used, but not limited thereto. Especially from the viewpoint of ease of use, it is desirable to use at least one of hydrocarbon and alcohol as source gas.

(2) Dispersant (B)
The dispersant (B) of the present embodiment is not particularly limited as long as it can stabilize the dispersion of the carbon nanotubes (A), and surfactants and resin-type dispersants can be used. Surfactants are mainly classified as anionic, cationic, nonionic and amphoteric. A suitable type of dispersant can be used in a suitable blending amount depending on the properties required for dispersing the carbon nanotubes (A).

When an anionic surfactant is selected, the type is not particularly limited. Specifically, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylarylsulfonates, alkylnaphthalenesulfonates, dialkylsulfonates, dialkylsulfosuccinates, alkyl phosphates, polyoxy ethylene alkyl ether sulfates, polyoxyethylene alkyl aryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfonates, glycerol borate fatty acid esters and polyoxyethylene glycerol fatty acid esters. is not limited to More specific examples include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and sodium salt of β-naphthalenesulfonic acid formalin condensate. , but not limited to.

Cationic surfactants also include alkylamine salts and quaternary ammonium salts. Specifically, stearylamine acetate, trimethylyac ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyloleyl diethanol chloride, tetramethylammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfate, cetylpyridinium bromide. , 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide and dodecylbenzyltriethylammonium chloride. Amphoteric surfactants also include, but are not limited to, aminocarboxylates.

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 alkylallyl ethers. Specific examples include, but are not limited to, polyoxyethylene lauryl ether, sorbitan fatty acid ester, and polyoxyethylene octylphenyl ether.

The selected surfactant is not limited to a single surfactant. Therefore, it is also possible to use a combination of two or more surfactants. For example, a combination of anionic and nonionic surfactants or a combination of cationic and nonionic surfactants can be used. The blending amount at that time is preferably a blending amount suitable for each surfactant component. As a combination, a combination of an anionic surfactant and a nonionic surfactant is preferred. Preferably, the anionic surfactant is a polycarboxylate. Preferably, the nonionic surfactant is polyoxyethylene phenyl ether.

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 , carboxymethylcellulose, etc.), polyvinyl alcohol, polyvinyl butyral, and polyvinylpyrrolidone. Especially preferred are methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral and polyvinylpyrrolidone.

(3) Solvent (C)
The solvent (C) of the present embodiment is not particularly limited as long as the carbon nanotubes (A) can be dispersed. , more preferably water. When water is included, it is preferably at least 95% by mass, more preferably at least 98% by mass, relative to the entire solvent (C).

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, etc.). 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 monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amines (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine , ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic ring systems (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2 -imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethylsulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), others, tetrahydrofuran, urea, aceto Nitrile or the like can be used.

(4) Carbon nanotube dispersion The carbon nanotube dispersion of the present embodiment contains carbon nanotubes (A), a dispersant (B) and a solvent (C).

The cumulative particle diameter D50 of the carbon nanotube dispersion liquid of the present embodiment is 200 to 1000 nm, preferably 200 to 800 nm. The cumulative particle diameter D50 of the carbon nanotube dispersion can be measured using a particle size distribution meter (Nanotrac UPA, model UPA-EX, manufactured by Microtrack Bell Co., Ltd.).

In order to obtain the carbon nanotube dispersion liquid of the present embodiment, it is preferable to perform a treatment of dispersing the carbon nanotubes (A) in the solvent (C). The dispersing device used for performing such treatment is not particularly limited.

As a dispersing device, a dispersing machine commonly used for dispersing pigments and the like can be used. For example, mixers such as disper, homomixer, and planetary mixer, homogenizers (Advanced Digital Sonifer (registered trademark) manufactured by BRANSON, MODEL 450DA, "Clearmix" manufactured by M Technic, "Filmix" manufactured by PRIMIX, etc., silver Son's "Abramix", etc.), paint conditioner (Red Devil), colloid mills (PUC's "PUC Colloid Mill", IKA's "Colloid Mill MK"), cone mills (IKA's "Cone Mill MKO", etc.), ball mill, sand mill ("Dyno Mill" manufactured by Shinmaru Enterprises, etc.), attritor, pearl mill ("DCP Mill" manufactured by Eirich, etc.), media-type dispersing machines such as coball mills, wet jet mills (Jenus Co., Ltd. "Genus PY" manufactured by Sugino Machine, "Starburst" manufactured by Sugino Machine, "Nanomizer" manufactured by Nanomizer, etc.), "Crea SS-5" manufactured by M Technic, "MICROS" manufactured by Nara Machinery, etc. Other examples include a roll mill and the like, but are not limited to these.

The amount of carbon nanotubes (A) in the present embodiment is preferably 0.2 to 20 parts by mass, preferably 0.2 to 10 parts by mass, and 0.5 to 5 parts by mass with respect to 100 parts by mass of the carbon nanotube dispersion. % is more preferred.

The amount of the dispersant (B) in the carbon nanotube dispersion liquid of the present embodiment is preferably 30 to 200 parts by mass, preferably 30 to 100 parts by mass, with respect to 100 parts by mass of the carbon nanotubes (A). is more preferable, and it is even more preferable to use 30 to 80 parts by mass.

The fiber length of the carbon nanotubes (A) in the carbon nanotube dispersion of this embodiment is preferably 0.1 to 10 μm, preferably 0.2 to 5 μm, particularly preferably 0.3 to 2 μm.

The pH of the carbon nanotube dispersion of the present embodiment is preferably 6 to 11, more preferably 7 to 11, even more preferably 7 to 10, particularly 7.5 to 10. preferable. The pH of the carbon nanotube dispersion can be measured using a pH meter (pH METER F-52, manufactured by Horiba, Ltd.).

The viscosity of the carbon nanotube dispersion liquid of the present embodiment is determined using a Brookfield viscometer, where X is the viscosity measured at 25° C. at 6 rpm, and Y is the viscosity measured at 60 rpm, where X/Y is 1.5. ≤X/Y≤5.5, and more preferably 1.5≤X/Y≤4.0.

(5) Binder resin (D)
The binder resin (D) is a resin that binds substances such as carbon nanotubes.

Examples of the binder resin (D) of the present embodiment include ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, and vinyl butyral. , vinyl acetal, vinyl pyrrolidone, etc. as structural units; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicon resins, fluororesins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubbers and fluororubbers; conductive resins such as polyaniline and polyacetylene; Modified products, mixtures, and copolymers of these resins may also be used. Among these, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid are preferred.

The type and amount ratio of the binder are appropriately selected according to the properties of coexisting substances such as carbon nanotubes and active materials. For example, regarding the amount of carboxymethylcellulose used in the negative electrode, when the mass of the negative electrode active material is 100% by mass, the ratio of carboxymethylcellulose is preferably 0.5 to 3.0% by mass, and 1.0 to 2.0% by mass. % by mass is more preferred.

Styrene-butadiene rubber that is generally used as a binder for graphite-based negative electrodes can be used as long as it is an oil-in-water emulsion. Regarding the amount of styrene-butadiene rubber used in the negative electrode, the ratio of styrene-butadiene rubber is preferably 0.5 to 3.0% by mass, preferably 1.0 to 2.0%, when the mass of the negative electrode active material is 100% by mass. % by mass is more preferred.

Regarding the amount of polyacrylic acid used in the negative electrode, the proportion of polyacrylic acid is preferably 1 to 20% by mass, more preferably 5 to 15% by mass, when the mass of the negative electrode active material is 100% by mass.

(5) Carbon nanotube resin composition The carbon nanotube resin composition of the present embodiment contains carbon nanotubes (A), dispersant (B), solvent (C) and binder resin (D).

In order to obtain the carbon nanotube resin composition of the present embodiment, it is preferable to mix the carbon nanotube dispersion (C) and the binder resin (D) and homogenize them. As a mixing method, conventionally known various methods can be used. The carbon nanotube resin composition can be prepared using the dispersing apparatus described for the carbon nanotube dispersion.

(6) Compound Slurry The compound slurry of the present embodiment contains carbon nanotubes (A), dispersant (B), solvent (C), binder resin (D), and active material (E).
<Active material (E)>
The active material (E) of the present embodiment is a material that serves as a basis for battery reaction. Active materials are classified into positive electrode active materials and negative electrode active materials according to the electromotive force.

The positive electrode active material is not particularly limited, but metal oxides capable of doping or intercalating lithium ions, metal compounds such as metal sulfides, conductive polymers, and the like can be used. Examples thereof include transition metal oxides such as Fe, Co, Ni and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ , layered structure lithium nickel oxide, lithium cobalt oxide, lithium manganate, spinel structure lithium manganate, and the like. Composite oxide powders of lithium and transition metals, lithium iron phosphate-based materials that are phosphoric acid compounds having an olivine structure, transition metal sulfide powders such as TiS ₂ and FeS, and the like. Conductive polymers such as polyaniline, polyacetylene, polypyrrole and polythiophene can also be used. Further, the above 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, tin alloys thereof, silicon alloys, alloys such as lead alloys, Li _x Fe ₂ O ₃ , Li _x Fe ₃ O ₄ , Li _x WO ₂ (where x is a number of 0<x<1 ), metal oxides such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymers such as polyacetylene and poly-p-phenylene, and amorphous carbonaceous materials such as soft carbon and hard carbon. , carbonaceous materials such as 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, and carbon fibers. These negative electrode active materials can also be used singly or in combination.

As the negative electrode active material of the present embodiment, it is preferable to use a graphite-based negative electrode active material in addition to the silicon-based negative electrode active material.

Examples of silicon-based negative electrode active materials include so-called metallurgical grade silicon produced by reducing silicon dioxide with carbon, industrial grade silicon obtained by reducing impurities by acid treatment or unidirectional solidification of metallurgical grade silicon, and silicon. High-purity silicon with different crystal states such as high-purity single crystal, polycrystal, and amorphous made from silane obtained by reaction, and industrial-grade silicon with high purity by sputtering method or EB vapor deposition (electron beam vapor deposition) method. At the same time, silicon whose crystalline state and precipitation state are adjusted can be mentioned.

Silicon oxide, which is a compound of silicon and oxygen, silicon and various alloys, and silicon compounds obtained by adjusting the crystalline state thereof by a quenching method, etc., can also be used. Among them, a silicon-based negative electrode active material having a structure in which silicon nanoparticles are dispersed in silicon oxide and whose outer surface is coated with a carbon film is preferable.

The amount of the silicon-based negative electrode active material is preferably 3 to 50% by mass, more preferably 5 to 25% by mass, based on 100% by mass of the graphite-based negative electrode active material.

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

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

(7) Method for producing composite material slurry

The mixture slurry of the present embodiment can be produced by various conventionally known methods. For example, there is a method of adding the active material (E) to the carbon nanotube resin composition, and a method of adding the binder resin (D) after adding the active material (E) to the carbon nanotube dispersion. mentioned.

In order to obtain the mixture slurry of the present embodiment, it is preferable to perform a dispersing treatment after adding the active material to the carbon nanotube resin composition. The dispersing device used for performing such treatment is not particularly limited. The mixture slurry can be obtained by using the dispersing device described in the carbon nanotube dispersion.

The amount of the active material (E) in the mixture slurry of the present embodiment is preferably 20 to 85% by mass, more preferably 30 to 75% by mass, with respect to 100% by mass of the mixture slurry. It is more preferably 40 to 70% by mass.

The amount of carbon nanotubes (A) in the mixture slurry of the present embodiment is preferably 0.01 to 10% by mass, preferably 0.02 to 2% by mass, with respect to 100% by mass of the active material. It is preferably 0.03 to 1% by mass.

The amount of the binder resin (D) in the mixture slurry of the present embodiment is preferably 0.5 to 30% by mass, more preferably 1 to 25% by mass, with respect to 100% by mass of the active material. , 2 to 20% by weight.

The solid content of the composite material slurry of the present embodiment is preferably 30 to 90% by mass, more preferably 30 to 80% by mass, relative to 100% by mass of the composite material slurry, and 40 to 75% by mass. % by mass is preferred.

(8) Electrode film The electrode film of the present embodiment is formed by forming a mixture slurry into a film. For example, it is a coating film in which an electrode mixture layer is formed by coating and drying a mixture slurry on a current collector.

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

There are no particular restrictions on the method of applying the mixture slurry onto the current collector, and known methods can be used. Specific examples include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method or an electrostatic coating method. As a method, drying by standing, a blow dryer, a hot air dryer, an infrared heater, a far-infrared heater, etc. can be used, but the method is not particularly limited to these.

Further, after application, a rolling treatment using a lithographic press, calendar rolls, or the like may be performed. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

(8) Lithium Ion Secondary Battery The lithium ion secondary battery of the present embodiment comprises a positive electrode, a negative electrode, and an electrolyte, and at least one of the positive electrode and the negative electrode contains the electrode film of the present invention.

As the positive electrode, an electrode film can be prepared by coating slurry containing a positive electrode active material on a current collector and drying it.

As the negative electrode, an electrode film can be prepared by coating slurry containing a negative electrode active material on a current collector and drying it.

As the electrolyte, various conventionally known substances in which ions can move can be used. For example, _LiBF4 , LiClO4, _LiPF6 , _LiAsF6 , _{LiSbF6 , LiCF3SO3 ,} Li _{( CF3SO2} ) _2N , _LiC4F9SO3 , Li _{( CF3SO2} ) _{3C , LiI} , LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh ₄ (where Ph is a phenyl group) containing lithium salts. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

Examples of non-aqueous solvents include, but are not limited to, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate; γ-butyrolactone, γ-valerolactone, and γ - lactones such as octanoic lactone; tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1, glymes such as 2-dibutoxyethane; esters such as methylformate, methylacetate and methylpropionate; sulfoxides such as dimethylsulfoxide and sulfolane; and nitriles such as acetonitrile. Each of these solvents may be used alone, or two or more of them may be mixed and used.

It is preferable that the lithium ion secondary battery of the present embodiment contain a separator. Examples of separators include polyethylene nonwoven fabrics, polypropylene nonwoven fabrics, polyamide nonwoven fabrics, and those subjected to hydrophilic treatment, but are not particularly limited to these.

Although the structure of the lithium ion secondary battery of the present embodiment is not particularly limited, it usually consists of a positive electrode and a negative electrode and a separator provided as necessary, and can be used in a paper type, cylindrical type, button type, laminated type, etc. It can have various shapes depending on the purpose of use.

EXAMPLES The present invention will be described more specifically with reference to examples below. The present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples, "carbon nanotube" may be abbreviated as "CNT". In addition, unless otherwise indicated, "part" represents "mass part" and "%" represents "mass%."

<Method for measuring physical properties>
The physical properties of CNTs used in Examples and Comparative Examples described later were measured by the following methods.

<Raman spectroscopic analysis of CNT>
The CNTs were placed in a Raman microscope (XploRA, manufactured by Horiba, Ltd.) and measured using a laser wavelength of 532 nm. Measurement conditions were as follows: acquisition time 60 seconds, integration times 2, neutral density filter 10%, objective lens magnification 20, confocus hole 500, slit width 100 μm, measurement wavelength 100 to 3000 cm ⁻¹ . CNTs for measurement were dispensed onto a slide glass and flattened using a spatula. Among the obtained peaks, the maximum peak intensity in the range of 1560 to 1600 cm ^-1 in the spectrum is G, the maximum peak intensity in the range of 1310 to 1350 cm ^-1 is D, and the ratio of G / D is G of CNT. D ratio.

<Volume resistivity of CNT>
Using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: Lorestar GP powder resistivity measuring system MCP-PD-51), the sample mass was 1.2 g, and a powder probe unit (four probes Using a ring electrode, electrode spacing of 5.0 mm, electrode radius of 1.0 mm, sample radius of 12.5 mm), the applied voltage limiter is set to 90 V, and the volume resistivity [Ω cm] of the conductive powder under various pressures is measured. did. The value of volume resistivity of CNT at a density of 1 g/cm ³ was evaluated.

<Measurement of CNT purity>
CNTs were acid-decomposed using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General Co.) to extract metals contained in the CNTs. After that, analysis was performed using a multi-type ICP emission spectrometer (manufactured by Agilent, 720-ES) to calculate the amount of metal contained in the extract. The CNT purity was calculated as follows.
(Formula 1) CNT purity (%) = ((CNT mass - metal mass in CNT) / CNT mass) x 100
<Specific surface area of CNT>
After weighing 0.03 g of CNT using an electronic balance (manufactured by Sartorius, MSA225S100DI), the CNT was dried at 110° C. for 15 minutes while degassing. After that, the specific surface area of CNT was measured using a fully automatic specific surface area measuring device (HM-model 1208 manufactured by MOUNTECH).

<Measurement of viscosity of CNT dispersion>
After allowing the CNT dispersion to stand in a constant temperature bath at 25° C. for 1 hour or longer, the CNT dispersion was sufficiently stirred, and then stirred at a stirring speed of 6 rpm using a viscometer (TOKISANGYO CO. LTD, VISCOMETER, MODEL BL). Viscosity was measured at 60 rpm.

<Particle size distribution measurement of CNT dispersion>
After allowing the CNT dispersion to stand in a constant temperature bath at 25° C. for 1 hour or more, the CNT dispersion was sufficiently stirred and diluted, and then measured with a particle size distribution meter (manufactured by Microtrack Bell Co., Ltd., Nanotrac UPA, model UPA-EX ) was used to measure the cumulative particle size D50 of the CNT dispersion. The CNT particles had a refractive index of 1.8 and were aspherical in shape. The refractive index of the solvent was 1.333. The measurement was performed by diluting the concentration of the CNT dispersion so that the numerical value of the loading index was in the range of 0.8 to 1.2.

<pH measurement of CNT dispersion>
After allowing the CNT dispersion to stand in a constant temperature bath at 25°C for 1 hour or longer, the CNT dispersion was sufficiently stirred and then measured using a pH meter (pH METER F-52, manufactured by Horiba, Ltd.). .

<Volume resistivity of electrode film for negative electrode>
After coating the negative electrode mixture slurry on a copper foil using an applicator so that the weight per unit of the electrode is 8 mg/cm ² , it is placed in an electric oven at 120°C ± 5°C for 25 minutes. The coating was allowed to dry. Thereafter, the surface resistivity (Ω/□) of the dried coating film was measured using Loresta GP, MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd. After the measurement, the volume resistivity (Ω·cm) of the electrode film for the negative electrode was obtained by multiplying the thickness of the electrode mixture layer formed on the copper foil. The thickness of the electrode mixture layer is obtained by subtracting the thickness of the copper foil from the average value obtained by measuring three points in the electrode film using a film thickness gauge (DIGIMICRO MH-15M manufactured by NIKON). It was taken as volume resistivity (Ω·cm).

<Peel strength of electrode film for negative electrode>
Using an applicator, the mixture slurry was applied onto a copper foil so that the unit weight of the electrode was 8 mg/cm ² , and then the coating was applied in an electric oven at 120°C ± 5°C for 25 minutes. was dried. After that, two rectangular pieces of 90 mm×20 mm were cut with the major axis in the coating direction. A desktop tensile tester (Strograph E3, manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used to measure the peel strength, and the peel strength was evaluated by the 180 degree peel test method. Specifically, a 100 mm × 30 mm double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) is pasted on a stainless steel plate, and the prepared battery electrode mixture layer is adhered to the other side of the double-sided tape. The film was peeled off while being pulled upward at a constant speed (50 mm/min), and the average value of the stress at this time was taken as the peel strength.

<Evaluation of rate characteristics of lithium ion secondary battery>
The laminated lithium ion secondary battery was placed in a constant temperature room at 25° C., and charge/discharge measurements were performed using a charge/discharge device (SM-8, manufactured by Hokuto Denko Co., Ltd.). After performing constant current constant voltage charging (cutoff current 1 mA (0.02 C)) at a charging current of 10 mA (0.2 C) and a charging end voltage of 4.3 V, discharge at a discharging current of 10 mA (0.2 C). Constant current discharge was performed at a final voltage of 3V. After repeating this operation three times, constant current constant voltage charge (cutoff current (1 mA 0.02 C)) was performed at a charge current of 10 mA (0.2 C) and a charge cut-off voltage of 4.3 V, and a discharge current of 0.2 C and Constant current discharge was carried out at 3 C until the final discharge voltage of 3.0 V was reached, and the discharge capacity was determined for each. The rate characteristic can be expressed by the ratio of the 0.2C discharge capacity and the 3C discharge capacity, which is the following formula 1.
(Formula 1) Rate characteristics = 3C discharge capacity/3rd 0.2C discharge capacity x 100 (%)

<Evaluation of cycle characteristics of lithium ion secondary battery>
The laminated lithium ion secondary battery was placed in a constant temperature room at 25° C., and charge/discharge measurements were performed using a charge/discharge device (SM-8, manufactured by Hokuto Denko Co., Ltd.). After performing constant current constant voltage charging (cutoff current 2.5 mA (0.05 C)) at a charging current of 25 mA (0.5 C) and a charging end voltage of 4.3 V, discharge current is 25 mA (0.5 C) , constant-current discharge was performed at a discharge final voltage of 3V. This operation was repeated 50 times. 1C was the current value for discharging the theoretical capacity of the positive electrode in 1 hour. Cycle characteristics can be expressed by the following formula 2, which is the ratio of the 3rd 0.5C discharge capacity to the 50th 0.5C discharge capacity at 25°C.
(Formula 2) Cycle characteristics = 3rd 0.5C discharge capacity/50th 0.5C discharge capacity x 100 (%)

<Preparation of positive electrode mixture slurry and positive electrode>
A positive electrode mixture slurry and a positive electrode used in Examples and Comparative Examples described later were prepared by the following method.

<Preparation of positive electrode mixture slurry>
Positive electrode active material (manufactured by BASF Toda Battery Materials LLC, HED (registered trademark) NCM-111 1100) 93 parts by mass, acetylene black (manufactured by Denka Co., Ltd., Denka Black (registered trademark) HS100) 4 parts by mass, PVDF (stock After adding 3 parts by mass of Kureha KF Polymer W#1300 (manufactured by Kureha Battery Materials Japan Co., Ltd.) to a plastic container with a capacity of 150 cm ³ , the mixture was mixed with a spatula until the powder was uniform. After that, 20.5 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Mixer, ARE-310, manufactured by THINKY Co., Ltd.). Thereafter, the mixture in the plastic container was mixed with a spatula until uniform, and stirred at 2000 rpm for 30 seconds using the rotation/revolution mixer. After that, 14.6 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using the rotation/revolution mixer. Finally, using a high-speed stirrer, the mixture was stirred at 3000 rpm for 10 minutes to obtain a positive electrode mixture slurry.

<Preparation of positive electrode>
After applying the above-described positive electrode mixture slurry on an aluminum foil having a thickness of 20 μm as a current collector using an applicator, it is dried in an electric oven at 120 ° C. ± 5 ° C. for 25 minutes. was adjusted to have a basis weight of 20 mg/cm ² . Further, a rolling process was performed by a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to produce a positive electrode having a composite material layer with a density of 3.1 g/cm ³ .

Table 1 shows the CNTs used in the examples and comparative examples, the average outer diameter of the CNTs, the specific surface area of the CNTs, the G/D ratio, the volume resistivity, the carbon purity, the CB, and the particle size of the CB.
The average outer diameter of commercially available CNTs is the catalog value.

Table 2 shows dispersants used in Examples, Comparative Examples and Reference Examples.

(Example 1)
Glass bottle (M-140, manufactured by Kashiwayo Glass Co., Ltd.), 0.8 parts of CNT (JENOTUBE 8S manufactured by JEIO), 0.32 parts of dispersant (A), antifoaming agent (SN Deformer 1312 manufactured by San Nopco Co., Ltd.) ), 78.85 parts of ion-exchanged water, and 140 parts of zirconia beads (bead diameter 0.5 mmφ) were charged, and dispersed for 10 hours using a paint conditioner manufactured by Red Devil. After separation, a CNT dispersion (A1) was obtained.

(Examples 2 to 18), (Comparative Examples 1 to 9)
CNT dispersion liquid (A2) to (H3) was obtained.

Table 4 shows the evaluation results of the CNT dispersions prepared in Examples 1-18 and Comparative Examples 1-9. The TI value was obtained by dividing the viscosity of the CNT dispersion at 6 rpm by the viscosity of the CNT dispersion at 60 rpm.

(Example 19)
2.5 parts by mass of CNT dispersion (A1), 12.5 parts by mass of an aqueous solution of 2% by mass of CMC (carboxymethyl cellulose, #1190, manufactured by Daicel Finechem Co., Ltd.) dissolved in a plastic container with a capacity of 150 cm ³ , ion-exchanged water. 9.9 parts by weight were weighed. Thereafter, the mixture was stirred at 2000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Mixer, ARE-310, manufactured by THINKY CORPORATION) to obtain a CNT resin composition (A1). After that, 1.2 parts by mass of silicon monoxide (SILICON MONOOXIDE, SiO 1.3C 5 μm, manufactured by Osaka Titanium Technology Co., Ltd.) was added and stirred at 2000 rpm for 30 seconds using the rotation/revolution mixer. Further, 23.1 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industry Co., Ltd.) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the rotation/revolution mixer. After that, 0.78 part by mass of a styrene-butadiene emulsion (TRD2001, manufactured by JSR Corporation) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the rotation/revolution mixer to obtain a mixture slurry (A1).

(Examples 20-36), (Comparative Examples 10-18)
It was changed to the CNT dispersion listed in Table 5. When the CNT concentration of the CNT dispersion used is 1.5%, the amount of the CNT dispersion added is 1.7 parts by mass, and when the concentration of the CNT dispersion is 2%, the amount of the CNT dispersion added is 0. When the concentration of the CNT dispersion was 0.8 parts by mass and the concentration of the CNT dispersion was 3%, the mixture slurry (A2) to ( H3) was obtained.

(Comparative Example 19)
Instead of 2.5 parts by mass of the CNT dispersion (A1), 0.025 parts by mass of CB (Ketjenblack EC300J, manufactured by Lion Specialty Chemicals Co., Ltd.) and 2.475 parts by mass of ion-exchanged water were added. A CB resin composition (I1) and a mixture slurry (I1) were obtained in the same manner as in Example 19.

(Example 37)
Instead of 9.9 parts by mass of ion-exchanged water, 0.8 parts by mass of an aqueous solution in which 30% of polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 250,000) is dissolved, and 9.1 parts by mass of ion-exchanged water. A CNT resin composition (AP1) and a mixture slurry (AP1) were obtained in the same manner as in Example 19, except that parts by mass were added.

(Example 38)
Instead of 9.9 parts by mass of ion-exchanged water, 4.2 parts by mass of an aqueous solution in which 30% polyacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., weight average molecular weight 250,000) is dissolved, and 5.7 parts by mass of ion-exchanged water. A CNT resin composition (AP5) and a mixture slurry (AP5) were obtained in the same manner as in Example 19, except that parts by mass were added.

(Example 39)
After applying the mixture slurry (A1) on the copper foil using an applicator so that the basis weight per unit of the electrode is 8 mg / cm ² , in an electric oven at 120 ° C. ± 5 ° C. for 25 minutes. , the coating film was dried to obtain an electrode film (A1).

(Examples 40-58), (Comparative Examples 19-28)
Electrode films (A2) to (I1) were obtained in the same manner as in Example 39, except that the mixture slurry listed in Table 6 was used.

Table 7 shows the evaluation results of the electrode films produced in Examples 39-58 and Comparative Examples 19-28. Conductivity evaluation is +++ (excellent) when the volume resistivity (Ω cm) of the electrode film is less than 0.30, ++ (good) when 0.30 or more and less than 0.40, and 0.40 or more and less than 0.70. + (acceptable), 0.70 or more was indicated as - (impossible). Evaluation of adhesion (N/cm) is ++++ (best) when 1.00 or more, ++ (excellent) when 0.50 or more and less than 1.00, ++ (good) when 0.30 or more and less than 0.50, 0.50 or more and less than 1.00. A score of 20 or more and less than 0.30 was rated as + (acceptable), and a score of less than 0.20 was scored as - (impossible).

(Example 59)
The electrode film (A1) was rolled by a roll press (manufactured by Thank Metal Co., Ltd., 3t hydraulic roll press) to prepare a negative electrode having a composite material layer with a density of 1.6 g/cm ³ .

(Examples 60-78), (Comparative Examples 29-38)
A negative electrode was produced in the same manner as in Example 59, except that the electrode film shown in Table 8 was used.

(Example 79)
The negative electrode (A1) and the positive electrode were punched into 50 mm × 45 mm and 45 mm × 40 mm pieces, respectively. . After that, in a glove box filled with argon gas, an electrolytic solution (ethylene carbonate, dimethyl carbonate, and diethyl carbonate were mixed at a ratio of 1:1:1 (volume ratio) to prepare a mixed solvent, and the electrolytic solution 100 VC (vinylene carbonate) and FEC (fluoroethylene carbonate) were added as additives to each part by mass, and then LiPF ₆ was dissolved to a concentration of 1M. After the injection, the aluminum laminate was sealed to produce a laminate type lithium ion secondary battery (A1).

(Examples 80-98), (Comparative Examples 39-48)
Laminated lithium ion secondary batteries (A2) to (I1) were produced in the same manner except that the negative electrodes listed in Table 9 were used.

Table 10 shows the evaluation results of the laminated lithium ion secondary batteries produced in Examples 79-98 and Comparative Examples 39-48. Rate characteristics are +++ (excellent) when rate characteristics are 80% or more, ++ (good) when 70% or more and less than 80%, + (acceptable) when 60% or more and less than 70%, and less than 60%. - (impossible). Cycle characteristics were evaluated as +++ (excellent) when 96% or more, ++ (good) when 95% or more and less than 96%, + (acceptable) when 93% or more and less than 95%, and - (improper) when less than 93%. .

Table 11 summarizes again in order to clarify the effect of the present invention. Evaluation results of laminated lithium ion secondary batteries produced using CNTs and CNT dispersions used in Examples 1, 6, 12 and 13 and Comparative Examples 1 to 4 and 7 are shown.

In the above examples, a carbon nanotube dispersion containing carbon nanotubes having a specific surface area of 500 to 800 m ² /g and a cumulative particle diameter D50 of 200 to 1000 nm as measured by the dynamic light scattering method was used. In the example, a lithium secondary battery having better cycle characteristics than in the comparative example was obtained. Therefore, it has been clarified that the present invention can provide a lithium secondary battery having electrical conductivity that is difficult to achieve with conventional carbon nanotube dispersions.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

Claims (11)

A carbon nanotube dispersion containing carbon nanotubes (A), a dispersant (B), and a solvent (C) containing water and/or a water-soluble organic solvent,
The cumulative particle diameter _D50 measured by the dynamic light scattering method is 200 to 1000 nm ,
The carbon nanotube (A) has a specific surface area of 500 to 800 m ² /g and an average outer diameter of 1 nm or more and less than 10 nm .
Carbon nanotube dispersion for lithium ion secondary batteries . 2. The carbon nanotube dispersion for a lithium ion secondary battery according to claim 1, wherein the pH of the dispersion is 6-11. 3. The carbon for lithium ion secondary battery according to claim 1 or 2 , wherein the carbon nanotube (A) has a volume resistivity of 1.0×10 ⁻³ to 1.5×10 ⁻² Ω·cm. Nanotube dispersion. A carbon nanotube dispersion containing 0.2 to 2.0 parts by mass of carbon nanotubes (A) with respect to 100 parts by mass of the carbon nanotube dispersion, and the viscosity of the carbon nanotube dispersion is measured using a B-type viscometer, Any one of claims 1 to 3 , wherein X/Y satisfies 1.5≦X/Y≦5.5, where X is the viscosity measured at 6 rpm and Y is the viscosity measured at 60 rpm. Carbon nanotube dispersion liquid for lithium ion secondary batteries according to claim 1. The carbon nanotube dispersion for a lithium ion secondary battery according to any one of claims 1 to 4 , wherein the dispersant (B) is contained in an amount of 30 to 200 parts by mass with respect to 100 parts by mass of the carbon nanotubes (A). . The carbon nanotube dispersion for lithium ion secondary batteries according to any one of claims 1 to 5 , wherein the solvent (C) is water. A carbon nanotube resin composition for lithium ion secondary batteries , comprising the carbon nanotube dispersion for lithium ion secondary batteries according to any one of claims 1 to 6 and a binder resin (D). 8. The carbon nanotube resin composition for a lithium ion secondary battery according to claim 7 , wherein the binder resin (D) is one or more selected from carboxymethylcellulose, styrene-butene rubber and polyacrylic acid. A mixture slurry comprising the carbon nanotube resin composition for a lithium ion secondary battery according to claim 8 and an active material (E). An electrode film (F) formed by forming the mixture slurry according to claim 9 into a film. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte in which lithium ions can move, wherein at least one of the positive electrode and the negative electrode comprises the electrode film according to claim 10 . Lithium-ion secondary battery.