Carbon nanotube dispersion, resin composition using the same, conductive film, composite slurry, electrode, and non-aqueous electrolyte secondary battery

Abstract

To provide a carbon nanotube dispersion, a carbon nanotube resin composition and a mixture slurry which have good dispersion so as to obtain a conductive film and an electrode film having high conductivity and adhesion, and a nonaqueous electrolyte secondary battery having excellent rate characteristics and cycle characteristics.SOLUTION: A carbon nanotube dispersion contains boron-containing nanotube, and a solvent, in which complex elastic modulus of the carbon nanotube dispersion by dynamic viscoelasticity is less than 200 Pa, and a phase angle at a frequency of 1 Hz is 10° or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a boron-containing carbon nanotube dispersion. More specifically, it relates to a resin composition containing the carbon nanotube dispersion and a resin, a composite slurry containing the carbon nanotube dispersion, a resin, and an active material, a conductive film and an electrode film formed by forming them into a film shape, and a non-aqueous electrolyte secondary battery including the electrode film and an electrolyte.

Background Art

[0002] In recent years, the development of electronics has been remarkable, and for conductive materials used in various electronic devices and batteries, there has been a growing demand for smaller size, lighter weight, lower cost, and longer life under various usage environments of the products. As conductive carbon materials, various conductive materials with low volume resistivity such as various graphites and carbon nanotubes have been studied to date. Also, in the case of carbon nanotubes, research has been reported on improving the conductivity of carbon nanotubes by doping boron into carbon nanotubes through high-temperature heat treatment of carbon nanotubes and boron compounds at a maximum temperature of 3000°C (Patent Document 1). By doping 3% or more of boron into carbon nanotubes, conductivity at the level of 10 -2 Ω·cm has been obtained. However, further improvement in the conductivity of conductive materials remains an issue. On the other hand, when a conductive material is used in various electronic devices and batteries, a dispersion in which the conductive material is dispersed by a solvent or the like is often used, but the most significant problem is that the dispersion causes deterioration of characteristics such as a decrease in conductivity. Therefore, it is very important to prepare a dispersion that provides desired characteristics.

[0003] Taking a lithium-ion secondary battery as an example, as the negative electrode material used in a lithium-ion secondary battery, carbon materials typified by graphite, which has a low potential close to lithium and a large charge-discharge capacity per unit mass, are used. However, these electrode materials are used up to a point where the charge-discharge capacity per mass is close to the theoretical value, and the energy density per mass of the battery is approaching its limit. Therefore, in order to increase the utilization rate as an electrode, attempts have been made to reduce the conductive aids and binders that do not contribute to the discharge capacity.

[0004] As the conductive aid, carbon black, ketjen black, graphene, fine carbon materials, etc. are used, and in particular, carbon nanotubes, which are a type of fine carbon fiber, are widely used. For example, by adding carbon nanotubes to graphite or silicon, which are negative electrode active materials, the resistance of the electrode can be reduced, the internal resistance of the battery can be improved, the strength of the electrode can be increased, and the expansion and contraction properties of the electrode can be increased, thereby improving the cycle life of the lithium-ion secondary battery (Patent Documents 2 to 4). In addition, studies have also been conducted on reducing the electrode resistance by adding carbon nanotubes to the positive electrode (Patent Documents 5 and 6).

[0005] When using carbon nanotubes with a small average outer diameter, a conductive network can be efficiently formed in a small amount, and the amount of conductive aid contained in the positive and negative electrodes for lithium-ion secondary batteries can be reduced. It is also known that the same effect is obtained when using carbon nanotubes with a large fiber length (Patent Document 7). However, because these carbon nanotubes with these characteristics have strong cohesive force and are difficult to disperse, a carbon nanotube dispersion with sufficient dispersibility could not be obtained.

[0006] Therefore, various proposals have been made. For example, there is a method of stabilizing the dispersion of carbon nanotubes using a dispersant, and a dispersion liquid using a polymer-based dispersant such as polyvinylpyrrolidone, a water-soluble polymer, in water and NMP (N-methyl-2-pyrrolidone) has been disclosed (Patent Documents 5, 6, 8). However, in Patent Document 5, although an electrode was fabricated using carbon nanotubes with an outer diameter of 10 to 150 nm, the resistance of the electrode was high, which was a problem. In addition, in Patent Document 6, a dispersion liquid using carbon nanotubes with a small DBP oil absorption amount was disclosed. Although the dispersibility was improved, the improvement in conductivity was insufficient. In Patent Document 8, a dispersion liquid using single-walled carbon nanotubes was disclosed, but it was difficult to disperse carbon nanotubes at a high concentration in a solvent. In Patent Document 9, a dispersion liquid using double-walled carbon nanotubes was disclosed. However, since an oxidation treatment of carbon nanotubes and a dispersion treatment using an ultrasonic homogenizer were performed, not only did the conductivity decrease, but it was also insufficient to disperse carbon nanotubes at a high concentration in a solvent. In Patent Document 10, in order to obtain carbon nanotubes suitable as a conductive aid for a lithium-ion secondary battery, a carbon nanotube dispersion liquid in which carbon nanotubes with an outer diameter of 150 nm were dispersed to a fiber length of about 2 to 7 μm using a ball mill type disperser was disclosed. However, it was necessary to use a large amount of carbon nanotubes to obtain sufficient conductivity. Therefore, obtaining a carbon nanotube dispersion liquid with good conductivity, high concentration, and uniform dispersion was an important issue for expanding applications.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

[0008] An object of the present invention is to provide a carbon nanotube dispersion liquid, a carbon nanotube resin composition, and a composite slurry having good dispersibility in order to obtain a conductive film and an electrode film having high conductivity and adhesion. Further, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent rate characteristics and cycle characteristics. [Means for Solving the Problems]

[0009] The present invention relates to a carbon nanotube dispersion liquid containing boron-containing carbon nanotubes and a solvent, wherein the complex elastic modulus of the carbon nanotube dispersion liquid by dynamic viscoelasticity measurement is less than 200 Pa, and the phase angle at a frequency of 1 Hz is 10° or more.

[0010] The present invention also relates to the carbon nanotube dispersion liquid, characterized in that the boron content of the boron-containing carbon nanotubes is 0.01 to 3 mol%.

[0011] The present invention also relates to the carbon nanotube dispersion characterized in that the content of boron element doped so as to substitute the carbon element on the surface of the boron-containing carbon nanotube is 0.01 to 1 mol%.

[0012] The present invention also relates to the carbon nanotube dispersion further comprising a dispersant.

[0013] The present invention also relates to a carbon nanotube resin composition comprising the carbon nanotube dispersion and a binder.

[0014] The present invention also relates to a conductive film characterized by being a coating film of the carbon nanotube dispersion or the carbon nanotube resin composition.

[0015] The present invention also relates to a composite material slurry comprising the carbon nanotube resin composition and an active material.

[0016] The present invention also relates to an electrode film characterized by being a coating film of the composite material slurry.

[0017] The present invention also relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode contains the electrode film.

Advantages of the Invention

[0018] By using the carbon nanotube dispersion of the present invention, a conductive film excellent in conductivity, a resin composition excellent in conductivity and adhesion, a composite material slurry, and an electrode can be obtained. Further, a non-aqueous electrolyte secondary battery excellent in rate characteristics and cycle characteristics can be obtained. Therefore, it is possible to use the carbon nanotube dispersion of the present invention in various application fields where high conductivity, adhesion, and durability are required.

Brief Description of the Drawings

[0019]

Figure 1

Embodiments for Carrying Out the Invention

[0020] Hereinafter, the carbon nanotube dispersion, resin composition, conductive film, composite slurry, electrode, and non-aqueous electrolyte secondary battery of the present invention will be described in detail. In this specification, boron-containing carbon nanotubes may be described as carbon nanotubes or CNTs.

[0021] <Boron-containing carbon nanotube> First, the shape of the carbon nanotubes of the present invention will be described. Carbon nanotubes have a shape in which planar graphite is wound into a cylindrical shape. Single-walled carbon nanotubes have 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 sidewalls of the carbon nanotubes do not necessarily have to be a graphite structure. For example, carbon nanotubes having sidewalls with an amorphous structure can also be used as carbon nanotubes. Further, these carbon nanotubes may be a mixture of a plurality of carbon nanotubes having a total number.

[0022] The shape of the carbon nanotubes of the present invention is not limited. Such shapes include various shapes including needle-like, cylindrical tube-like, fishbone-like (fishbone or cup stacking type), and coil-like. Also, it may be a secondary aggregate in the form of a plate or platelet obtained by performing a dry process on cylindrical tube-shaped carbon nanotubes. Among them, the shape of the carbon nanotubes in the present invention is preferably needle-like or cylindrical tube-like. The carbon nanotubes may be of a single shape or a combination of two or more shapes.

[0023] The forms of the carbon nanotubes of the present invention include, for example, graphite whiskers, filamentous carbon, graphite fibers, ultra-fine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers, but are not limited thereto. The carbon nanotubes may have these individual forms or a combined form of two or more thereof.

[0024] Next, the boron-containing form of the boron-containing carbon nanotubes of the present invention will be described. The content of boron in the boron-containing carbon nanotubes (the content of boron in the whole material) is preferably 0.005 to 10 mol%, more preferably 0.01 to 3 mol%, and even more preferably 0.1 to 1 mol%. When the boron content is 0.005 mol% or more, the doping effect of boron is easily obtained and the conductivity is improved. Also, when the boron content is less than 10 mol%, a decrease in conductivity due to inhibition of electron movement is less likely to occur. Further, by containing boron, the affinity with organic solvents, dispersants, resins, etc. is increased, and the dispersibility of the dispersion is improved. On the other hand, when the boron content is high, the hardness of the carbon nanotubes tends to increase, and it is possible to improve the durability against external forces such as impact, the coating film strength, and maintain the contact of the conductive aid in the expansion and contraction of the electrode active material accompanying the charge and discharge of the secondary battery. However, when the content exceeds 3 mol%, it tends to be difficult to disperse, and from the viewpoints of the strength and dispersibility of the carbon nanotubes, the boron content is preferably 3 mol% or less, and more preferably 1 mol% or less. The content of boron in the boron-containing carbon nanotubes can be determined by methods such as ICP emission spectrometry and ICP mass spectrometry. As an example, a measurement method conforming to JIS-R7223 can be mentioned. Also, the content of boron in the boron-containing carbon nanotubes indicates the total amount of boron in elemental boron contained on the surface or inside of the carbon material, boron doped so as to substitute for the carbon element in the carbon material, or boron compounds.

[0025] Next, the boron that is doped to replace the carbon element on the surface of the boron-containing carbon nanotube of the present invention will be described. The content of boron that is doped to replace the carbon element on the surface of the boron-containing carbon nanotube can be determined by a method such as X-ray photoelectron spectroscopy (XPS).

[0026] The B1s spectrum of boron obtained by XPS measurement appears in the binding energy range (around 185 - 197 eV) of the B1s electrons of the boron element, and is known to consist of four components roughly classified. The values of the binding energy (peak top) of each component are as follows: for boron clusters, it is 186 - 187 eV; for boron carbide, it is 187 - 188 eV; for boron (BC 3 ) that is doped to replace the carbon element with a hexagonal carbon network as the basic skeleton, it is 188 - 189.3 eV; for various boron oxides BC 2 O, it is 189.5 - 190.5 eV; for BCO 2 , it is 191.5 - 192 eV; for B 2 O 3 , it appears at 192.5 - 193 eV. When these peaks overlap, fitting can be performed by optimizing the peak intensity, peak position, and full width at half maximum of each component as parameters using a Gaussian function to separate the peaks, and the ratio can be determined. Therefore, by separating the peaks of B1s, the state of boron on the surface of the boron-containing carbon nanotube can be analyzed. Therefore, the value of the binding energy of boron that is doped to replace the carbon element on the surface of the boron-containing carbon nanotube of the present invention appears at 188 - 189.3 eV.

[0027] Also, the boron-containing carbon nanotube of the present invention is a carbon material with a hexagonal carbon network as the basic skeleton, and can be confirmed by Raman spectrum measurement and X-ray diffraction measurement.

[0028] In Raman spectrum measurement, for example, the G band (1560 - 1620 cm -1By confirmation of , it can be confirmed that it is a carbon material having a carbon hexagonal network plane as a basic skeleton. Also, when the intensity ratio (G / D ratio) with the D band (1310~1370 cm -1 ) representing the defect of the carbon material is high, the crystallinity of the boron-doped carbon material is high and the conductivity is also high. It is preferably 0.6 or more, more preferably 0.8 or more.

[0029] In the X-ray diffraction (XRD) measurement, in the XRD pattern of the boron-containing carbon nanotube obtained using CuKα ray as the X-ray source, by confirmation of the diffraction peak of the (002) plane appearing in the vicinity of the diffraction angle (2θ) of 24.0~27.0°, it can be confirmed that it is a carbon material having a carbon hexagonal network plane as a basic skeleton.

[0030] The average outer diameter of the boron-containing carbon nanotube of the present invention is preferably 1~250 nm, more preferably 2~50 nm, still more preferably 5~25 nm, and even more preferably 5~15 nm. When the average outer diameter of the carbon nanotube is within the above range, the surface of the electrode active material is easily coated with the carbon nanotube, and the conductivity and adhesion of the electrode film are improved.

[0031] The outer diameter and average outer diameter of the boron-containing carbon nanotube of the present invention are determined as follows. First, the carbon nanotube is observed and imaged by a transmission electron microscope. Next, in the observation photograph, 300 arbitrary carbon nanotubes are selected and the outer diameter of each is measured. Next, the average outer diameter (nm) of the carbon nanotube is calculated as the number average of the outer diameters.

[0032] The boron-containing carbon nanotube of the present invention preferably has 3 or more and 30 or less layers of carbon nanotubes, more preferably 3 or more and 20 or less layers, and still more preferably 3 or more and 10 or less layers.

[0033] The BET specific surface area of the boron-containing carbon nanotube of the present invention is preferably 10~1500 m 2 / g, more preferably 150~800 m 2Those with a value of 200 to 700 m / g are more preferable, and those with a value of / g are even more preferable. 2 Those with a value of / g are even more preferable.

[0034] The volume resistivity of the boron-containing carbon nanotubes of the present invention is preferably 1.0×10 -2 Ω·cm or less, more preferably 5.0×10 -3 Ω·cm or less, and even more preferably 3.0×10 -3 Ω·cm or less. The volume resistivity of the carbon nanotubes can be measured using a powder resistivity measuring device (manufactured by Nitto Seiko Analytic Co., Ltd.: Loresta GP - Powder Resistivity Measuring System MCP - PD - 51)).

[0035] The carbon purity of the boron-containing carbon nanotubes of the present invention is represented by the content rate (%) of carbon atoms in the carbon nanotubes. 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 based on 100% by mass of the carbon nanotubes.

[0036] The amount of metal contained in the boron-containing carbon nanotubes of the present invention is preferably less than 10% by mass, more preferably less than 5% by mass, and even more preferably less than 2% by mass based on 100% by mass of the carbon nanotubes. Examples of the metal contained in the carbon nanotubes include metals and metal oxides used as catalysts when synthesizing the carbon nanotubes. Specifically, metals such as cobalt, nickel, aluminum, magnesium, silica, manganese, and molybdenum, metal oxides, and composite oxides thereof can be mentioned.

[0037] The boron-containing carbon nanotubes of the present invention usually exist as secondary particles. The shape of these secondary particles may be, for example, a state in which carbon nanotubes, which are common primary particles, are intricately intertwined. It may also be an aggregate of linear carbon nanotubes. The secondary particles that are aggregates of linear carbon nanotubes are more likely to unravel compared to those that are intertwined. Also, linear ones have better dispersibility compared to those that are intertwined, so they can be suitably used as carbon nanotubes.

[0038] The boron-containing carbon nanotubes of the present invention may be carbon nanotubes that have been surface-treated. Also, the carbon nanotubes may be carbon nanotube derivatives to which a functional group typified by a carboxyl group has been imparted. Further, carbon nanotubes encapsulating a substance typified by an organic compound, a metal atom, or fullerene can also be used.

[0039] The boron-containing carbon nanotubes of the present invention can be carbon nanotubes produced by any method. Carbon nanotubes can generally be produced by laser ablation method, arc discharge method, thermal CVD method, plasma CVD method, and combustion method, but are not limited thereto. For example, carbon nanotubes can be produced by causing a carbon source to undergo a catalytic reaction 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.

[0040] As the raw material gas serving as the carbon source for the boron-containing carbon nanotubes of the present invention, any conventionally known one can be used. For example, hydrocarbons typified by methane, ethylene, propane, butane, and acetylene, carbon monoxide, and alcohols can be used as the raw material gas containing carbon, but are not limited thereto. Particularly from the viewpoint of ease of use, it is desirable to use at least one of hydrocarbons and alcohols as the raw material gas.

[0041] <Manufacturing method of boron-containing carbon nanotubes> As a method for producing boron-containing carbon nanotubes in the present invention, although not particularly limited, a carbon source and a boron source can be heat-treated and synthesized. Specifically, a method of mixing a carbon source, carbon nanotubes, and a boron source such as a boron compound (boron carbide, etc.) and heat-treating to produce boron-containing carbon nanotubes, a method of heat-treating a carbon source such as an aromatic hydrocarbon gas and a boron source such as boron gas on a metal catalyst supported on a substrate to cause chemical vapor deposition (CVD), a method of heat-treating a carbon source such as a hydrocarbon gas and a boron source such as boron gas on a metal catalyst suspended by spraying or the like to cause catalytic chemical vapor deposition (CCVD), a method of synthesizing by ion implantation treatment of boron into a carbon source, etc. can be used.

[0042] Next, the boron source used for the production of boron-containing carbon nanotubes will be described. The boron source is not particularly limited, and examples thereof include boron carbide, boron oxide, boron nitride, metal borides, boric oxo acids, boranes, boron-containing organic compounds, and the like. Specifically, in the case of boron carbide, B 4 C (B 12 C 3 ), B 12 C 2 (B 6 C), etc. In the case of boron oxide, BC 2 O, BCO 2 , B 2 O 2 , B 2 O 3 , B 4 O 3 , B 4 O 5 , etc. In the case of boron nitride, BN, etc. In the case of metal borides, AlB 2 , CoB, FeB, MgB 2 , NiB, TiB 2 , etc. In the case of boric oxo acids, orthoboric acid, metaboric acid, tetraboric acid, etc. In the case of boranes, monoborane, diborane, decaborane, etc. Examples of boron-containing organic compounds include boric acid esters such as trimethyl borate and triethyl borate, substituted boranes such as triethyl borane and triphenyl borane, and boronic acids such as phenylboronic acid and phenylboronic acid ester.

[0043] The raw material composition ratio of the carbon source and the boron source for producing boron-containing carbon nanotubes is not particularly limited, but the ratio of the boron source is 0.01 to 300 parts by mass, preferably 0.05 to 100 parts by mass, and more preferably 0.1 to 50 parts by mass with respect to 100 parts by mass of the carbon source.

[0044] The mixing method of the carbon source and the boron source is not particularly limited, but dry mixing and wet mixing are preferred. As the mixing device, the following dry mixing devices and wet mixing devices can be used.

[0045] Examples of the dry mixing device include roll mills such as two-roll mills and three-roll mills, high-speed stirrers such as Henschel mixers and super mixers, fluid energy pulverizers such as micronizers and jet mills, attritors, particle compounding devices "Nano Cure", "Novilta", "Mechano Fusion" manufactured by Hosokawa Micron Corporation, and powder surface modification devices "Hybridization System", "Mekano Micros", "Mirrorlo" manufactured by Nara Machinery Co., Ltd. When using a dry mixing device, other raw materials may be directly added to the raw material powder as the matrix in powder form. However, in order to produce a more uniform mixture, other raw materials may be dissolved or dispersed in a small amount of solvent in advance and added while dissociating the aggregated particles of the raw material powder as the matrix. Further, in order to improve the efficiency of the treatment, it may be heated.

[0046] Examples of wet mixing devices include mixers such as disper, homomixer, or planetary mixer, homogenizers such as "Clear Mix" manufactured by M Technique Co., Ltd. or "Fill Mix" manufactured by PRIMIX Corporation, paint conditioner manufactured by Red Devil, sand mills such as "Dyno Mill" manufactured by Simar Enterprises, media type dispersers such as attritor or coball mill, wet jet mills such as "Genus PY" manufactured by Genus Co., Ltd., "Starburst" manufactured by Sugino Machine Limited, "Nanomizer" manufactured by Nanomizer Co., Ltd., media-less dispersers such as "Clear SS-5" manufactured by M Technique Co., Ltd. or "Micro S" manufactured by Nara Machinery Co., Ltd., or other roll mills, kneaders, etc., but are not limited thereto. Further, as the wet mixing device, it may be preferable to use one that has been subjected to a process for preventing metal contamination from the device. For example, when using a media type disperser, it is preferable to use a disperser in which the agitator and the vessel are made of ceramic or resin, or a disperser in which the surface of the metal agitator and the vessel is treated by tungsten carbide spraying or resin coating. As the media, it is preferable to use glass beads, or ceramic beads such as zirconia beads or alumina beads. Also, when using a roll mill, it is preferable to use a ceramic roll. The dispersing device may use only one type or a combination of multiple types of devices.

[0047] Also, when the raw materials are not uniformly dissolved or dispersed, a dispersant may be added as necessary to improve the wettability and dispersibility of each raw material in the solvent, and then dispersed and mixed.

[0048] The conditions for heat-treating the mixture of the carbon source and the boron source vary depending on the types and amounts of the carbon source and boron source used as raw materials and are not particularly limited. However, the heating temperature is 1000 to 3000 °C, preferably 1100 to 2500 °C, more preferably 1200 to 2000 °C. Also, the heating time is not particularly limited, but it is 10 minutes to 72 hours, preferably 30 minutes to 10 hours. For the atmosphere in the heat-treatment step, an inert gas such as nitrogen or argon, or an atmosphere under vacuum is preferable in order to prevent side reactions such as oxidation of the raw materials. Also, the heat-treatment step may be not only a treatment step performed in one stage with respect to a certain atmosphere, temperature, and time, but also a treatment step performed in multiple stages with respect to the atmosphere, temperature, and temperature.

[0049] <Solvent> Next, the solvent used in the carbon nanotube dispersion of the present invention will be described. The solvent is not particularly limited as long as it can disperse carbon nanotubes, but it is preferably water, or a mixed solvent composed of any one or two or more of organic solvents, and more preferably a solvent composed of any one of water or a water-soluble organic solvent, or a mixed solvent composed of any two or more of water-soluble organic solvents. Also, when using a dispersant described later, it is preferable that the dispersant can be partially or completely dissolved in the solvent, and the solvent is not particularly limited, but preferably contains water or a water-soluble organic solvent.

[0050] Examples of organic solvents that can be used include alcohol-based (such as methanol), polyhydric alcohol-based (such as ethylene glycol), polyhydric alcohol ether-based (such as ethylene glycol monomethyl ether), amine-based (such as ethanolamine), amide-based (such as N-methyl-2-pyrrolidone (NMP)), heterocyclic-based (such as γ-butyrolactone), sulfoxide-based (such as dimethyl sulfoxide), sulfone-based (such as sulfolane), aromatic-based (such as toluene, xylene), hydrocarbon-based (such as hexane), lower ketone-based (such as acetone), ester-based (such as ethyl acetate), and the like. Preferred water-soluble organic solvents include 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-based (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxide-based (dimethyl sulfoxide, etc.), sulfone-based (hexamethylphosphoramide, sulfolane, etc.), alcohol-based (methanol, ethanol, etc.), polyhydric alcohol-based (ethylene glycol, diethylene glycol, etc.), lower ketone-based (acetone, methyl ethyl ketone, etc.), and others such as tetrahydrofuran, urea, acetonitrile, etc. can be used.

[0051] <Dispersant> The dispersant in the present invention is not particularly limited as long as it can disperse and stabilize carbon nanotubes, and surfactants and resin-type dispersants can be used. Surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric. Depending on the properties required for the dispersion of carbon nanotubes, appropriate types of dispersants can be used in appropriate blending amounts.

[0052] When selecting an anionic surfactant, its type is not particularly limited. Specifically, fatty acid salts, polysulfonate salts, polycarboxylate salts, alkyl sulfate esters, alkylaryl sulfonate salts, alkylnaphthalene sulfonate salts, dialkyl sulfonate salts, dialkyl sulfosuccinate salts, alkyl phosphate salts, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfonate salts, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters can be mentioned, but are not limited thereto. Further specifically, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate ester salt, and sodium salt of β-naphthalene sulfonic acid formalin condensate can be mentioned, but are not limited thereto.

[0053] Also, as cationic surfactants, there are alkylamine salts and quaternary ammonium salts. Specifically, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethylammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercaptopyridine, poly(vinyl pyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride can be mentioned, but are not limited thereto.

[0054] Examples of 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. Specifically, examples include, but are not limited to, polyoxyethylene lauryl ether, sorbitan fatty acid ester, and polyoxyethylene octyl phenyl ether. Examples of amphoteric surfactants include, but are not limited to, aminocarboxylates.

[0055] Surfactants can be used alone or in 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. The blending amount at that time is preferably a suitable blending amount for each surfactant component. As the combination, a combination of an anionic surfactant and a nonionic surfactant is preferred. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably a polyoxyethylene phenyl ether.

[0056] Specific examples of resin-type dispersants include cellulose derivatives (such as cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyacrylonitrile-based polymers, various rubbers, etc. Particularly, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyacrylonitrile-based polymers, various rubbers (such as partially hydrogenated nitrile rubber) are preferred.

[0057] The resin-based dispersant is particularly preferably prepared by using, as a structural unit, a polymer containing at least one selected from the group consisting of a nitrile group-containing structural unit, a carboxyl group-containing structural unit, a hydroxyl group-containing structural unit, and a heterocyclic ring-containing structural unit. This enhances the adsorptivity to the boron-containing carbon nanotubes and the affinity to the medium. The polymer preferably contains an alkylene structure in the main chain, and has a structure of any one of a nitrile group, a carboxyl group, a hydroxyl group, and a heterocyclic ring having strong polarization, thereby enhancing the adsorptivity to the carbon nanotubes and the affinity to the medium, and enabling the carbon nanotubes to stably exist in the medium. Further, it is more preferable that the polymer contains two or more selected from the group consisting of a nitrile group-containing structural unit, a carboxyl group-containing structural unit, a hydroxyl group-containing structural unit, and a heterocyclic ring-containing structural unit, as this further enhances the adsorptivity to the carbon nanotubes and the affinity to the medium.

[0058] The nitrile group-containing structural unit is a structural unit containing a nitrile group, and preferably includes a structural unit containing an alkylene structure substituted by a substituent containing a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably one or two, and more preferably one. The method for introducing the nitrile group-containing structural unit into the polymer is not particularly limited, but for example, a method of preparing the polymer by a polymerization reaction of a monomer containing a nitrile group can be preferably used.

[0059] Examples of the monomer containing a nitrile group include acrylonitrile, methacrylonitrile, fumaronitrile, etc., and one kind can be used alone or two or more kinds can be used in combination. In particular, from the viewpoints of enhancing the intermolecular force between polymers and / or between the polymer and the dispersed substance (adsorbed substance), easy availability of raw materials, and reactivity, the monomer containing a nitrile group is preferably acrylonitrile. The content of the nitrile group-containing structural unit is preferably 15% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass). Also, it is preferably 100% by mass or less, more preferably 90% by mass or less, and still more preferably 85% by mass or less. By setting the content of the nitrile group-containing structural unit within the above range, it is considered that the adsorptivity to the dispersed substance and the affinity to the dispersion medium can be controlled, and the dispersed substance can be stably present in the dispersion medium. Also, the affinity of the polymer to the electrolyte can be controlled, and it is considered that problems such as the polymer dissolving in the electrolyte and increasing the resistance of the electrolyte in the battery can be prevented.

[0060] The carboxyl group-containing structural unit is a structural unit containing a carboxyl group, and preferably includes a structural unit containing an alkylene structure substituted by a substituent containing a carboxyl group. The alkylene structure is preferably a linear or branched alkylene structure. The number of carboxyl groups contained in the carboxyl group-containing structural unit is preferably one or two, and more preferably one. The method for introducing the carboxyl group-containing structural unit into the polymer is not particularly limited, and examples include a method of preparing a polymer by a polymerization reaction of a monomer containing a carboxyl group, or a method of preparing a polymer by a polymerization reaction of a monomer containing a functional group other than a carboxyl group and modifying it to a carboxyl group.

[0061] Examples of the monomer containing a carboxyl group include unsaturated fatty acids such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, and the like. Further, a monomer containing a carboxyl group may be obtained by hydrolyzing the carbamoyl group of a polymer obtained by a polymerization reaction of a monomer containing a carbamoyl group such as (meth)acrylamide. The carboxyl group-containing monomer is preferably an unsaturated fatty acid, more preferably (meth)acrylic acid, and even more preferably acrylic acid.

[0062] From the viewpoint of giving an appropriate affinity with the solvent, the content of the carboxyl group-containing structural unit is preferably 60% by mass or more, more preferably 80% by mass or more, preferably 98% by mass or less, and may be 100% by mass, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass). Further, it is more preferable to further contain one or more selected from the group consisting of a nitrile group-containing structural unit, a hydroxyl group-containing structural unit, and a heterocyclic ring-containing structural unit, since the affinity between the carbon nanotube and the medium is increased. When further containing one or more selected from the group consisting of a nitrile group-containing structural unit, a hydroxyl group-containing structural unit, and a heterocyclic ring-containing structural unit, the content of the carboxyl group-containing structural unit is preferably 3% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass). Further, from the viewpoint of electrolyte resistance, it is preferably 50% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0063] The hydroxyl group-containing structural unit is a structural unit containing a hydroxyl group, and preferably includes a structural unit containing an alkylene structure substituted by a substituent containing a hydroxyl group. The alkylene structure is preferably a linear or branched alkylene structure. The number of hydroxyl groups contained in the hydroxyl group-containing structural unit is preferably one or two, and more preferably one. The method for introducing the hydroxyl group-containing structural unit into the polymer is not particularly limited. For example, a method of preparing a polymer by a polymerization reaction of a monomer containing a hydroxyl group, or a method of preparing a polymer by a polymerization reaction of a monomer containing a functional group other than a hydroxyl group and modifying it to a hydroxyl group can be mentioned.

[0064] Examples of the monomer containing a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono (meth)acrylate, 4-hydroxyvinylbenzene, 2-hydroxy-3-phenoxypropyl acrylate, or a caprolactone adduct of these monomers (the number of added moles is 1 to 5). The monomer containing a hydroxyl group is preferably a hydroxyalkyl (meth)acrylate, more preferably 2-hydroxyethyl (meth)acrylate, and even more preferably 2-hydroxyethyl acrylate.

[0065] As a method of preparing a polymer by a polymerization reaction of a monomer containing a functional group other than a hydroxyl group and modifying it to a hydroxyl group, for example, a method of saponifying the acetyl group of polyvinyl acetate obtained by polymerizing vinyl acetate with an alkali such as sodium hydroxide to form a hydroxyl group can be mentioned (saponification reaction). By changing the concentration of sodium hydroxide and the treatment time, the reaction rate (degree of saponification) of saponification can be arbitrarily controlled.

[0066] Also, for the purpose of enhancing the affinity between the carbon nanotube and the medium, the hydroxyl groups in the polymer may be reacted with an aldehyde compound and modified to acetal groups for use (acetalization). As the aldehyde compound used in the acetalization reaction, for example, compounds such as linear, branched, cyclic saturated, unsaturated, or aromatic aldehydes having 1 to 15 carbon atoms can be used, but are not limited thereto. Specifically, formaldehyde, acetaldehyde, propionaldehyde, n-butylaldehyde, isobutylaldehyde, tert-butylaldehyde, benzaldehyde, etc. can be mentioned. These aldehyde compounds may be used alone or in combination of two or more. From the viewpoint of versatility, compounds such as linear, branched, cyclic saturated, unsaturated, or aromatic aldehydes having 1 to 10 carbon atoms are preferable, and linear aldehyde compounds having 1 to 4 carbon atoms are more preferable. By changing the aldehyde compound and the treatment time, the reaction rate (degree of acetalization) of acetalization can be arbitrarily controlled.

[0067] The content of the hydroxyl group-containing structural unit is preferably 80% by mass or more, more preferably 85% by mass or more, and preferably 99.8% by mass or less based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass). However, when further containing one or more selected from the group consisting of a nitrile group-containing structural unit, a hydroxyl group-containing structural unit, and a heterocyclic ring-containing structural unit, it is preferably 5% by mass or more, preferably 95% by mass or less, and more preferably 85% by mass or less. By setting it within the above range, polarization can be enhanced and the affinity for the carbon nanotube and the medium can be increased. Also, it is preferable from the viewpoint of electrolyte resistance. The content of the acetal group is preferably within the preferable range of the content of the hydroxyl group-containing structural unit for the same reason as the content of the hydroxyl group-containing structural unit.

[0068] The heterocyclic ring-containing structural unit is a structural unit containing a heterocyclic ring, and a structural unit containing an alkylene structure substituted by a substituent containing a heterocyclic ring is more preferable. The alkylene structure is preferably a linear or branched alkylene structure. The heterocyclic ring contained in the heterocyclic ring-containing structural unit may be a monocyclic structure or a condensed ring structure, but a monocyclic structure is preferable. Also, the number of heterocyclic rings contained in the heterocyclic ring-containing structural unit is preferably one or two, and more preferably one. The heterocyclic ring contains atoms other than carbon in the atoms constituting the ring, for example, contains one or two or more nitrogen, oxygen, sulfur atoms, etc. As the atom other than carbon in the atoms constituting the ring, nitrogen or oxygen is preferable, and nitrogen is more preferable. When the atoms constituting the ring contain atoms other than carbon, polarization occurs in the heterocyclic ring, and it can strongly act on the carbon nanotube. Also, the method for introducing the heterocyclic ring into the polymer is not particularly limited, but for example, a method of preparing a polymer by a polymerization reaction of a monomer containing a heterocyclic ring can be used.

[0069] As the monomer containing a heterocyclic ring, an N-vinyl cyclic amide structural unit is preferable, and examples thereof include N-vinyl-2-pyrrolidone, N-vinyl-ε-caprolactam, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, etc. In particular, N-vinyl-2-pyrrolidone is preferable from the viewpoint of improving battery characteristics. These can be used alone or in combination of two or more.

[0070] The content of the heterocyclic ring-containing structural unit is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 100% by mass, from the viewpoint of enhancing the action on the carbon nanotube, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass).

[0071] The polymer may further contain, as other structural units, one or more structural units selected from the group consisting of active hydrogen group-containing structural units (excluding carboxyl groups and hydroxyl groups), basic group-containing structural units, and ester group-containing structural units. By selecting and incorporating the above structural units according to the properties such as hydrophilicity, hydrophobicity, acidity, and basicity of the substrate to which the conductive material dispersion of the present invention is applied or the material to be mixed, it can be applied to various uses.

[0072] The active hydrogen group-containing structural unit is a structural unit having, as an active hydrogen group, for example, a primary amino group, a secondary amino group, a mercapto group, or the like. Here, the "primary amino group" means -NH2 (amino group), and the "secondary amino group" means a group in which one hydrogen atom on the primary amino group is substituted with an organic residue such as an alkyl group. However, the primary amino group and the secondary amino group in the acid amide are not included in the active hydrogen group in this specification.

[0073] The basic group-containing structural unit is a structural unit having a basic group. Examples of the basic group include a tertiary amino group, an amide group, and the like. Note that a structural unit having a primary amino group and a structural unit having a secondary amino group may be included in the basic group-containing structural unit, but in the present invention, they are treated as the active hydrogen group-containing structural units and are not included in the basic group-containing structural units.

[0074] The ester group-containing structural unit is (R1) 2 a structural unit having a structure represented by C=CH-CO-O-R2 (wherein R1 is a hydrogen atom or a methyl group, at least one of which is a hydrogen atom, and R2 is an alkyl group which may have a substituent). Note that an alkyl group having the active hydrogen group or the basic group as a substituent is treated as the active hydrogen group-containing structural unit or the basic group-containing structural unit and is not included in the ester group-containing structural unit.

[0075] The method for producing the polymer is not particularly limited, and examples thereof include solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method, precipitation polymerization, etc., among which solution polymerization or precipitation polymerization method is preferred. The polymerization reaction system includes, for example, addition polymerization such as ionic polymerization, free radical polymerization, living radical polymerization, etc., among which free radical polymerization or living radical polymerization is preferred. Further, examples of the radical polymerization initiator include peroxides, azo initiators, etc. When polymerizing the polymer, a molecular weight regulator such as a chain transfer agent can be used.

[0076] As the polymerization initiator, when radical polymerization is carried out, although not limited to the following, for example, organic peroxides such as di-t-butyl peroxide, lauroyl peroxide, stearyl peroxide, benzoyl peroxide, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, dilauroyl peroxide, dicumyl peroxide, t-butyl peroxy-2-ethylhexanoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and general radical polymerization initiators of azo type such as azobisisobutyronitrile, azobisisovaleronitrile, 1,1-azobis(1-cyclohexanecarbonitrile), 2,2'-azobis-4-methoxy-2,4-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis-2-methylbutyronitrile can be mentioned. These may be used alone only one kind, or two or more kinds may be used in combination. These polymerization initiators are generally used at 1% by mass or less based on the total mass of all monomers used (that is, when the total mass of all monomers is 100% by mass), and can be appropriately selected in consideration of the polymerization temperature and the half-life of the initiator.

[0077] In the production process of the polymer, within the range that does not impair the object of the present invention, the molecular weight of the polymer produced using a chain transfer agent or the like can be controlled. Examples of the chain transfer agent include alkyl mercaptans such as octyl mercaptan, nonyl mercaptan, decyl mercaptan, dodecyl mercaptan, 3-mercapto-1,2-propanediol, thio glycolic acid esters such as octyl thio glycolate, nonyl thio glycolate, 2-ethylhexyl thio glycolate, 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, -pinene, β-pinene, and the like. From the viewpoints of handleability and stability, particularly, 3-mercapto-1,2-propanediol, thio glycolic acid esters, 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, -pinene, β-pinene, and the like are preferable. These can be appropriately added according to the required molecular weight. Specifically, the amount of the chain transfer agent used is preferably 0.01 to 4% by mass, more preferably 0.1 to 2% by mass, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass).

[0078] Further, as other methods for controlling the molecular weight, there are mentioned a method of changing the polymerization method, a method of adjusting the amount of the polymerization initiator, a method of changing the polymerization temperature, and the like. These methods for controlling the molecular weight may be used alone or in combination of two or more kinds.

[0079] When a polymer is used as a dispersant in the carbon nanotube dispersion, the content of the polymer is preferably determined according to the specific surface area and wettability of the carbon nanotubes, and is preferably 2% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and preferably 250% by mass or less, more preferably 150% by mass or less, further preferably 100% by mass or less, based on the mass of the conductive material (that is, when the mass of the carbon nanotubes is 100% by mass).

[0080] The dispersant preferably contains at least a polymer. The dispersant may further contain any polymer, any copolymer, etc. The content of the polymer in the dispersant is preferably 50% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more. The content of the polymer in the dispersant may be 100% by mass. In this case, the dispersant consists only of the polymer.

[0081] The pH of the carbon nanotube dispersion of the present invention is preferably 7.0 or more, more preferably 8.0 or more, and still more preferably 9.0 or more. Also, it is preferably 12.0 or less, and more preferably 11.0 or less. By adjusting the pH within the above range, it is considered that the wettability of the carbon nanotubes can be improved, and furthermore, the action of the polymer as a dispersant can be enhanced. If the pH is outside the above range, the dispersibility of the carbon nanotubes may decrease or gelation of the binder may occur. Also, when used for battery applications, there is a risk that problems such as corrosion of various raw materials and exterior materials in the battery may easily occur. When the carbon nanotube dispersion contains water as a solvent, the pH can be measured using a general pH meter. On the other hand, when the solvent does not substantially contain water, for example, when only NMP is selected as the solvent, by adding water to the carbon nanotube dispersion, when the solid content concentration before adding water is 100%, it is adjusted so that the solid content concentration after adding water becomes 50%, and it refers to the value measured using a general pH meter. For example, it can be measured by the following method. While stirring a carbon nanotube dispersion with a solid content concentration of 5% using a disper or the like, water is added so that the solid content concentration of the carbon nanotube dispersion becomes 2.5%. After uniformly stirring, at 25 °C, the pH of the carbon nanotube dispersion can be measured by using a desktop pH meter (SevenCompact S220Expert Pro, manufactured by Mettler Toledo). In the present invention, "substantially free of water" means that water is not intentionally added. Based on the mass of the solvent, it is preferably less than 5% by mass, more preferably less than 1% by mass, and even more preferably less than 0.5% by mass.

[0082] The pH of the carbon nanotube dispersion is not particularly limited, but can be adjusted by (1) the amount of metal hydroxide contained in the carbon nanotubes, (2) the type and amount of functional groups on the surface of the carbon nanotubes, and (3) the type and amount of base added. By comprehensively adjusting the pH by factors such as the above (1) to (3), it is possible to obtain a carbon nanotube dispersion that not only improves the wettability of the carbon nanotubes but also has excellent dispersibility and stability.

[0083] As described above, in the manufacturing process of carbon nanotubes, metals, metal oxides, and metal hydroxides used as catalysts remain in the system. Among the amount of metal remaining in the carbon nanotubes, the pH can be adjusted by appropriately adjusting the content of the metal hydroxide in particular (1) above. The carbon nanotubes can be adjusted in terms of the amount of residual metal, carbon purity, and the pH of the carbon nanotube dispersion containing the same by a conventionally known purification treatment method.

[0084] The functional groups on the surface of the carbon nanotubes in the above (2) are not particularly limited, and examples thereof include carboxyl groups, sulfo groups, and hydroxyl groups. The method for introducing functional groups into the carbon nanotubes is not particularly limited. For example, to introduce a carboxyl group into the carbon nanotubes, heating with an acid having an oxidizing action may be performed. This operation is relatively easy, and since a carboxyl group rich in reactivity can be added, it is preferable. Examples of the acid having an oxidizing action include concentrated nitric acid, hydrogen peroxide water, a mixed solution of sulfuric acid and nitric acid, aqua regia, and the like. In particular, when concentrated nitric acid is used, its concentration is preferably 5% by mass or more, and more preferably 60% by mass or more. The heating may be performed by a conventional method, and the temperature is preferably below the boiling point of the acid used. For example, in the case of concentrated nitric acid, the range of 50 to 130°C is preferable. Further, the heating time is preferably in the range of 30 minutes to 20 hours, and more preferably in the range of 1 hour to 8 hours. It is preferable that the carbon nanotubes do not have acidic functional groups such as carboxyl groups and sulfo groups. If a large amount of acidic functional groups are contained, the carbon nanotube dispersion may gel during storage.

[0085] The base added for pH adjustment in the above (3) is not particularly limited, and specifically, at least one base selected from the group consisting of inorganic bases, inorganic metal salts, organic hydroxides, and other organic bases can be used.

[0086] Examples of the inorganic base and the inorganic metal salt include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, or borates of an alkali metal or an alkaline earth metal; and ammonium hydroxide and the like. Among these, chlorides, hydroxides, carbonates, and alkoxides of an alkali metal or an alkaline earth metal are preferable from the viewpoint of easily supplying cations. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like. Examples of the alkaline earth metal hydroxide include calcium hydroxide, magnesium hydroxide, and the like. Examples of the alkali metal carbonate include lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, and the like. Examples of the alkali metal alkoxide include lithium methoxide, lithium ethoxide, lithium - n - butoxide, lithium - t - butoxide, potassium methoxide, potassium ethoxide, potassium - n - butoxide, potassium - t - butoxide, sodium methoxide, sodium ethoxide, sodium - n - butoxide, sodium - t - butoxide, and the like. The carbon number of the alkoxide may be 5 or more. Examples of the alkaline earth metal alkoxide include magnesium methoxide, magnesium ethoxide, magnesium - n - butoxide, magnesium - t - butoxide, and the like. The carbon number of the alkoxide may be 5 or more. Among these, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, lithium - t - butoxide, potassium - t - butoxide, and sodium - t - butoxide are more preferable. The metal contained in the inorganic base and the inorganic metal salt of the present invention may be a transition metal.

[0087] An organic hydroxide is a salt containing an organic cation and a hydroxide ion. Examples of the organic hydroxide include trimethyl-2-hydroxyethylammonium hydroxide, tetramethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, trimethylphenylammonium hydroxide, 3-trifluoromethyl-phenyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, and the like. Among these, trimethyl-2-hydroxyethylammonium hydroxide and tetramethylammonium hydroxide are particularly preferred.

[0088] Other organic bases include methylamine, ethylamine, propylamine, butylamine, hexylamine, octylamine, dioctylamine, trioctylamine, aminoethanol, aminopropanol, aminobutanol, 2-methoxyethylamine, and the like. Since these organic bases have high solubility in the electrolyte, if the usage amount is too large, there is a risk of degrading the battery performance. In addition, since these compounds are easily decomposed, decomposition products may remain in the coating film, and if present in the battery, there is a risk of reducing the initial capacity.

[0089] The usage amount of the base is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 3% by mass or more based on the mass of the polymer. The usage amount of the base is preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less based on the mass of the polymer. If the usage amount is too large, the stability of the obtained carbon nanotube dispersion may be poor. Furthermore, it may cause corrosion of the dispersion device and / or inside the battery.

[0090] The reason why the dispersibility is improved by adjusting the pH to a predetermined value is not clear, but the following factors and the like can be considered. Note that the reason for the improved dispersibility is not limited to the factors listed in (1) to (3) below. (1) Enhance the dispersibility of the polymer. By adjusting the pH to a predetermined value, the adsorptive power of a polymer containing one or more selected from the group consisting of a nitrile group-containing structural unit, a carboxyl group-containing structural unit, a hydroxyl group-containing structural unit, and a heterocyclic group-containing structural unit to the dispersoid can be enhanced. Further, since the functional groups of the structural units can form hydrogen bonds, a crosslinked structure due to hydrogen bonds is introduced into the polymer molecule, and it can adsorb three-dimensionally to the dispersoid, and it is considered that a dispersion excellent not only in dispersibility but also in stability can be obtained. (2) Reduce the solution viscosity of the polymer. When the polymer is dissolved in a solvent and used, if the viscosity of the polymer solution is low, it is considered that the dispersant can easily enter into the carbon nanotubes with strong cohesive force, and a uniform dispersion can be obtained. (3) Improve the wettability of the carbon nanotubes. When dispersing carbon nanotubes, by wetting the carbon nanotubes with a solvent, the cohesive force between the carbon nanotubes can be reduced, and then it can be crushed and stabilized to exist as a dispersion. Since the wettability of carbon nanotubes is significantly lower than that of other conductive materials, pretreatment such as chemical treatment or mechanical crushing of carbon nanotubes is required to improve the wettability, but there is a risk that the conductivity may be reduced by these treatments. By adjusting the pH to a predetermined value, it is considered that the wettability can be dramatically improved without impairing the conductivity of the carbon nanotubes.

[0091] Further, the carbon nanotube dispersion of the present invention may contain an antifoaming agent in addition to the dispersant. The antifoaming agent can be arbitrarily used as long as it has an antifoaming effect, such as a commercially available antifoaming agent, a wetting agent, a hydrophilic organic solvent, a water-soluble organic solvent, etc., and one kind or a combination of plural kinds can be used. For example, alcohol-based; ethanol, propanol, isopropanol, butanol, octyl alcohol, hexadecyl alcohol, acetylene alcohol, ethylene glycol monobutyl ether, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, acetylene glycol, polyoxyalkylene glycol, propylene glycol, other glycols, etc., Fatty acid ester-based; diethylene glycol laurate, glycerin monolinoleate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trioleate, polyoxyethylene monolaurate, polyoxyethylene sorbitol monolaurate, natural wax, etc., Amide-based; polyoxyalkylene amide, acrylate polyamine, etc., Phosphate ester-based; tributyl phosphate, sodium octyl phosphate, etc., Metal soap-based; aluminum stearate, calcium oleate, etc., Oil and fat-based; animal and vegetable oils, sesame oil, castor oil, etc., Mineral oil-based: kerosene, paraffin, etc., Silicone-based; dimethyl silicone oil, silicone paste, silicone emulsion, organically modified polysiloxane, fluorosilicone oil, etc. can be mentioned.

[0092] <Other conductive materials> In the carbon nanotube dispersion of the present invention, other conductive materials may optionally be included in addition to the carbon nanotubes. Examples of other conductive materials include metal powders such as gold, silver, copper, silver-plated copper powder, silver-copper composite powder, silver-copper alloy, amorphous copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, platinum, etc., inorganic powder coated with these metals, powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, ruthenium oxide, etc., inorganic powder coated with these metal oxides, and carbon materials such as carbon black and graphite. Other conductive materials may be used alone or in combination of two or more. When using other conductive materials, carbon black is preferred from the viewpoint of the adsorption performance of the dispersant. Other conductive materials are substances (materials) different from the electrode active material described later.

[0093] Examples of carbon black include acetylene black, furnace black, hollow carbon black, channel black, thermal black, ketjen black, etc. Also, carbon black may be neutral, acidic, or basic, and oxidized carbon black or graphitized carbon black may be used.

[0094] <Carbon nanotube dispersion> The carbon nanotube dispersion of the present invention contains boron-containing carbon nanotubes and a solvent, and preferably further contains a dispersant.

[0095] To obtain the carbon nanotube dispersion of the present invention, it is preferable to perform a treatment of dispersing boron-containing carbon nanotubes in a solvent. The dispersion device used for performing such treatment is not particularly limited.

[0096] As the dispersion device, a disperser commonly used for pigment dispersion or the like can be used. For example, mixers such as a disper, a homomixer, a planetary mixer, homogenizers (Advanced Digital Sonifer (registered trademark), MODEL 450DA manufactured by BRANSON, "Claremix" manufactured by M. TECHNIK, "Filmix" of PRIMIX, etc., "Abramix" of SILVERSON, etc.), paint conditioners (manufactured by Red Devil), colloid mills ("PUC colloid mill" manufactured by PUC, "Colloid mill MK" manufactured by IKA), cone mills ("Cone mill MKO" manufactured by IKA, etc.), ball mills, sand mills ("Dynomill" manufactured by Shinmaru Enterprises, etc.), attritors, pearl mills ("DCP mill" manufactured by Ehrlich, etc.), media type dispersers such as coball mills, wet jet mills ("Genus PY" manufactured by Genus, "Starburst" manufactured by Sugino Machine, "Nanomizer" manufactured by Nanomizer, etc.), media - less dispersers such as "Clare SS - 5" manufactured by M. TECHNIK, "MICROS" manufactured by Nara Machinery, and other roll mills, etc. can be mentioned, but it is not limited thereto.

[0097] The amount of the boron - containing carbon nanotubes in the carbon nanotube dispersion liquid of the present invention is preferably 0.2 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 0.5 to 3.0 parts by mass with respect to 100 parts by mass of the carbon nanotube dispersion liquid.

[0098] The amount of the dispersant in the carbon nanotube dispersion liquid of the present invention is preferably 0.1 to 100 parts by mass, more preferably 5 to 80 parts by mass, and even more preferably 20 to 50 parts by mass with respect to 100 parts by mass of the boron - containing carbon nanotubes.

[0099] The dispersibility of carbon nanotubes in a carbon nanotube dispersion can be evaluated by the complex elastic modulus and phase angle obtained from dynamic viscoelasticity measurement. The complex elastic modulus indicates the hardness of the carbon nanotube dispersion, and tends to be smaller as the dispersibility of the carbon nanotubes is better and the viscosity is lower. However, when the fiber length of the carbon nanotubes is large or the structure length of the carbon black is large, even if the carbon nanotubes are uniformly and stably dispersed in the medium, the complex elastic modulus may be a high value because of the structural viscosity of the carbon nanotubes themselves. The carbon nanotube dispersion of the present invention has a complex elastic modulus of less than 200 Pa, preferably less than 50 Pa, and more preferably less than 20 Pa as obtained from dynamic viscoelasticity measurement. Also, it is preferably 1 Pa or more, and more preferably 5 Pa or more.

[0100] In addition, the phase angle means the phase shift of the stress wave when the strain applied to the CNT dispersion is a sine wave, and indicates the ease of flow. For a pure elastic body, the stress wave is a sine wave in phase with the applied strain, so the phase angle is 0°. On the other hand, for a pure viscous body, the stress wave is advanced by 90°. In a general sample for viscoelasticity measurement, the phase angle is a sine wave greater than 0° and less than 90°. If the dispersibility of the CNTs in the CNT dispersion is good, the phase angle approaches 90°, which is that of a pure viscous body. However, similar to the complex elastic modulus, when the conductive material itself has structural viscosity, even if the conductive material is uniformly and stably dispersed in the medium, the phase angle may be a low value. The phase angle at a frequency of 1 Hz obtained from the dynamic viscoelasticity measurement of the CNT dispersion of the present invention is 10° or more, preferably 20° or more. Also, it is preferably less than 75°, and more preferably less than 65°.

[0101] By uniformly and favorably dispersing a conductive material with a large fiber length of carbon nanotubes or a structure length of carbon black while maintaining the length above a certain level, a developed conductive network is formed. Therefore, it is not simply sufficient that the viscosity of the conductive material dispersion is low (apparent good dispersibility), but it is particularly effective to judge the dispersion state by combining the complex elastic modulus and the phase angle with conventional indices such as viscosity. By setting the complex elastic modulus and the phase angle within the above ranges, a conductive material dispersion with good conductivity and electrode strength can be obtained. The complex elastic modulus and the phase angle of the conductive material dispersion can be measured by the method described in the examples.

[0102] The fiber length of the carbon nanotubes in the carbon nanotube dispersion liquid of the present invention is preferably 0.1 to 5 μm, more preferably 0.2 to 3.5 μm, and even more preferably 0.3 to 2.5 μm.

[0103] The cumulative particle size D50 of the carbon nanotube dispersion liquid of the present invention is preferably 100 to 5000 nm, and more preferably 300 to 3000 nm. The cumulative particle size D50 of the carbon nanotube dispersion liquid can be measured using a particle size distribution meter (manufactured by Microtrac Bell Corporation, Nanotrac UPA, model UPA-EX).

[0104] The viscosity of the carbon nanotube dispersion liquid of the present embodiment is a dispersion liquid containing 0.5 parts by mass or more and 3.0 parts by mass or less of carbon nanotubes in 100 parts by mass of the carbon nanotube dispersion liquid. Using a B-type viscometer, the viscosity measured at 60 rpm is preferably 10 mPa·s or more and less than 10000 mPa·s, more preferably 10 mPa·s or more and less than 5000 mPa·s, and even more preferably 10 mPa·s or more and less than 2000 mPa·s.

[0105] The carbon nanotube dispersion of the present invention not only achieves excellent dispersibility and conductivity, but also improves durability against external forces such as impact and coating film strength. Therefore, it can be suitably used for dispersions for forming conductive wirings and transparent conductive films, and dispersions for forming electrochemical devices such as secondary batteries, capacitors, and sensors.

[0106] <Carbon nanotube resin composition> The carbon nanotube resin composition of the present invention contains carbon nanotubes, a solvent, and a binder.

[0107] To obtain the carbon nanotube resin composition of the present invention, it is preferable to mix and homogenize the carbon nanotube dispersion and the binder. As the mixing method, various conventionally known methods can be used. The carbon nanotube resin composition can be produced using the dispersion device described for the carbon nanotube dispersion.

[0108] <Binder> The binder of the present invention is a resin for binding substances such as carbon nanotubes.

[0109] The binder of the present invention is not particularly limited and can be appropriately selected according to the desired physical properties. For example, polymers or copolymers containing as constituent units ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic esters, methacrylic acid, methacrylic esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc.; polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluorine resins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber and fluorine rubber; conductive resins such as polyaniline and polyacetylene, etc. Also, modified products, mixtures, and copolymers of these resins may be used. Among these, when used as a binder resin for the positive electrode film, polymers or copolymers having fluorine atoms in the molecule are preferred from the perspective of resistance, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. Also, when used as a binder resin for the negative electrode film, carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, etc. with good adhesion are preferred.

[0110] The weight average molecular weight of the binder resin is preferably from 10,000 to 2,000,000, more preferably from 100,000 to 1,000,000, and even more preferably from 200,000 to 1,000,000.

[0111] Carboxymethyl cellulose as a binder resin is preferably of high viscosity. For example, when preparing a 1% aqueous solution, the viscosity is preferably from 500 to 6000 mPa·s, and more preferably from 1000 to 3000 mPa·s. The viscosity of a 1% aqueous solution of carboxymethyl cellulose can be measured at 25°C with a B-type viscometer rotor rotation speed of 60 rpm.

[0112] As the binder resin, carboxymethyl cellulose preferably has a high degree of etherification. For example, the degree of etherification is preferably 0.6 to 1.5, and more preferably 0.8 to 1.2.

[0113] The type and ratio of the binder are appropriately selected according to the properties of substances coexisting such as carbon nanotubes and active materials. For example, regarding the amount of carboxymethyl cellulose used, when the mass of the active material is 100% by mass, the ratio of carboxymethyl cellulose is preferably 0.5 to 3.0% by mass, and more preferably 1.0 to 2.0% by mass.

[0114] For styrene-butadiene rubber, if it is an oil-in-water emulsion, generally those commonly used as the binder of the electrode can be used. Regarding the amount of styrene-butadiene rubber used, when the mass of the active material is 100% by mass, the ratio of styrene-butadiene rubber is preferably 0.5 to 3.0% by mass, and more preferably 1.0 to 2.0% by mass.

[0115] Regarding the amount of polyacrylic acid used, when the mass of the active material is 100% by mass, the ratio of polyacrylic acid is preferably 1 to 25% by mass, and more preferably 5 to 20% by mass.

[0116] <Composite material slurry> The composite material slurry of the present invention contains carbon nanotubes, a solvent, a binder, and an active material.

[0117] <Active material> The active material of the present invention refers to the material that serves as the basis of the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material based on the electromotive force.

[0118] As the positive electrode active material, there is no particular limitation, but metal compounds such as metal oxides and metal sulfides capable of doping or intercalating lithium ions, and conductive polymers can be used. For example, oxides of transition metals such as Fe, Co, Ni, Mn, composite oxides with lithium, inorganic compounds such as transition metal sulfides, etc. can be mentioned. Specifically, transition metal oxide powders such as MnO, V 2 O 5 、V 6 O 13 、TiO 2 and other transition metal oxide powders, composite oxide powders of lithium and transition metals such as layered lithium nickelate, lithium cobaltate, lithium manganate, spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphate compounds, TiS 2 、FeS and other transition metal sulfide powders, etc. can be mentioned. Also, conductive polymers such as polyaniline, polyacetylene, polypyrrole, polythiophene can be used. Further, the above inorganic compounds and organic compounds may be mixed and used.

[0119] As the negative electrode active material, there is no particular limitation as long as it can dope or intercalate lithium ions. For example, metal Li, alloy systems such as its alloys like tin alloy, silicon alloy, lead alloy, etc., Li X Fe 2 O 3 、Li X Fe 3 O 4 、Li X WO 2 (x is a number where 0 < x < 1.), metal oxide systems such as lithium titanate, lithium vanadate, lithium silicate, conductive polymer systems such as polyacetylene, poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon materials, gas-phase grown carbon fibers, carbon fibers and other carbon-based materials can be mentioned. These negative electrode active materials can also be used alone or in combination of two or more.

[0120] As the negative electrode active material of the present invention, a silicon-based negative electrode active material which is a negative electrode active material containing silicon such as a silicon alloy or lithium silicate is preferable.

[0121] Examples of the silicon-based negative electrode active material include so-called metallurgical grade silicon produced by reducing silicon dioxide with carbon, industrial grade silicon obtained by reducing impurities in metallurgical grade silicon by acid treatment or unidirectional solidification, and high-purity single crystals, polycrystals, amorphous, etc. of different crystal states of high-purity silicon produced from silane obtained by reacting silicon, and silicon obtained by making industrial grade silicon highly pure by sputtering or EB evaporation (electron beam evaporation) methods and at the same time adjusting the crystal state and deposition state.

[0122] In addition, silicon dioxide which is a compound of silicon and oxygen, and silicon compounds obtained by adjusting the crystal states of silicon and various alloys by a rapid cooling method or the like are also included. Among them, a silicon-based negative electrode active material having a structure in which silicon nanoparticles are dispersed in silicon dioxide and the outer side is coated with a carbon film is preferable.

[0123] In addition to the silicon-based negative electrode active material, the negative electrode active material of the present invention preferably uses amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite. Among them, it is preferable to use carbonaceous powders such as artificial graphite and natural graphite.

[0124] When the amount of the carbonaceous powder such as artificial graphite or natural graphite is 100% by mass, the amount of the silicon-based negative electrode active material is preferably 3 to 50% by mass, and more preferably 5 to 25% by mass.

[0125] The BET specific surface area of the active material of the present invention is preferably 0.1 to 10 m 2 / g, more preferably 0.2 to 5 m 2 / g, and even more preferably 0.3 to 3 m 2 / g.

[0126] The average particle diameter of the active material of the present invention is preferably in the range of 0.5 to 50 μm, more preferably 2 to 20 μm. The average particle diameter of the active material as referred to in this specification is the average value of the particle diameters measured by an electron microscope for the active material.

[0127] <Method for manufacturing composite material slurry> The composite material slurry of the present invention can be produced by various conventionally known methods. For example, there can be mentioned a method of producing by adding an active material to a carbon nanotube resin composition, and a method of producing by adding an active material to a carbon nanotube dispersion liquid and then adding a binder.

[0128] To obtain the composite material slurry of the present invention, after adding an active material to a carbon nanotube resin composition, it is preferable to perform a dispersion treatment. The dispersion device used for performing such treatment is not particularly limited. The composite material slurry can be obtained using the dispersion device described for the carbon nanotube dispersion liquid.

[0129] The amount of the active material in the composite material slurry of the present invention is preferably 20 to 85 parts by mass, more preferably 30 to 75 parts by mass, and even more preferably 40 to 70 parts by mass with respect to 100 parts by mass of the composite material slurry.

[0130] The amount of the carbon nanotubes in the composite material slurry of the present invention is preferably 0.01 to 10 parts by mass, preferably 0.02 to 5 parts by mass, and preferably 0.03 to 1 part by mass with respect to 100 parts by mass of the active material.

[0131] The amount of the binder in the composite material slurry of the present invention is preferably 0.5 to 30% by mass, more preferably 1 to 25% by mass, and particularly preferably 2 to 20% by mass with respect to 100% by mass of the active material.

[0132] The amount of the solid content of the composite material slurry of the present invention is preferably 30 to 90% by mass, more preferably 30 to 80% by mass, and preferably 40 to 75% by mass with respect to 100% by mass of the composite material slurry.

[0133] <Conductive film and electrode film> The conductive film of the present invention is formed by forming a carbon nanotube dispersion or a carbon nanotube resin composition into a film shape. For example, it is a coating film formed by coating and drying a carbon nanotube dispersion or a carbon nanotube resin composition on a sheet-like substrate. The sheet-like substrate is not particularly limited, and a conductive or non-conductive substrate can be used. As the conductive substrate, the following current collectors and the like can be used. In addition, the electrode film of the present invention is formed by forming a composite material slurry into a film shape. For example, it is a coating film in which an electrode composite material layer is formed by coating and drying a composite material slurry on a current collector.

[0134] The material and shape of the current collector used for the electrode film of the present invention are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, or stainless steel. In addition, as the shape, generally, a foil on a flat plate is used, but those with a roughened surface, perforated foil-like ones, and mesh-shaped current collectors can also be used.

[0135] The method of coating the composite material slurry on the current collector is not particularly limited, and known methods can be used. Specifically, 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 the drying method, air drying, a hot air dryer, a warm air dryer, an infrared heater, a far-infrared heater, etc. can be used, but it is not particularly limited to these.

[0136] Further, a rolling treatment may be performed by a lithographic press, a calendar roll, or the like after coating. The thickness of the electrode composite material layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0137] <Non-aqueous electrolyte secondary battery> The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolyte.

[0138] As the positive electrode, one obtained by coating and drying a composite material slurry containing a positive electrode active material on a current collector to form an electrode film can be used.

[0139] As the negative electrode, one obtained by coating and drying a composite material slurry containing a negative electrode active material on a current collector to form an electrode film can be used.

[0140] As the electrolyte, various conventionally known materials in which ions can move can be used. For example, LiBF 4 , LiClO 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiCF 3 SO 3 , Li(CF 3 SO 2 ) 2 , LiC 4 F 9 SO 3 , Li(CF 3 SO 2 ) 3 , LiI, LiBr, LiCl, LiAlCl, LiHF 2 , LiSCN, or LiBPh 4 (where Ph is a phenyl group), etc., including lithium salts, but not limited to these, and those containing sodium salts or calcium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0141] The non-aqueous solvent is not particularly limited. For example, 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, etc. These solvents may be used alone or in combination of two or more.

[0142] The non-aqueous electrolyte secondary battery of the present invention preferably includes a separator. Examples of the separator include, but are not particularly limited to, polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and those subjected to hydrophilic treatment.

[0143] The structure of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited. Usually, it is composed of a positive electrode, a negative electrode, and a separator provided as needed, and can have various shapes such as a paper type, a cylindrical type, a button type, a laminated type, etc., according to the purpose of use.

Examples

[0144] Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples unless it exceeds the gist thereof. In the examples, "carbon nanotube" may be abbreviated as "CNT". Unless otherwise specified, "part" represents "part by mass".

[0145] <cnt> The CNTs used in the following Examples and Comparative Examples and their physical properties are shown.

[0146] (Boron-containing CNT) The production examples of CNTs will be described below.

[0147] [Production Example (A)] According to the method described in paragraph

[0117] of JP-A-2018-150218, a catalyst for CNT synthesis was prepared. Thereafter, a heat-resistant dish made of quartz glass, which was pressurizable and heatable with an external heater and had an internal volume of 10 L, was placed at the center of a horizontal reaction tube, and 1.0 g of the catalyst for CNT synthesis was sprayed on it. While injecting nitrogen gas, evacuation was carried out to replace the air in the reaction tube with nitrogen gas, and the atmosphere in the horizontal reaction tube was made to have an oxygen concentration of 1% by volume or less. Next, heating was carried out 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 at a flow rate of 2 L per minute as a carbon source, and a contact 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 temperature of the reaction tube was cooled to 100°C or less and taken out to obtain CNT (A).

[0148] [Production Example (B)] According to the methods described in paragraphs

[0147] and

[0148] of JP-A-2019-108256, a catalyst for CNT synthesis was prepared. Thereafter, a heat-resistant dish made of quartz glass, which was pressurizable and heatable with an external heater and had an internal volume of 10 L, was placed at the center of a horizontal reaction tube, and 1 g of the catalyst for CNT synthesis was sprayed on it. While injecting nitrogen gas, evacuation was carried out to replace the air in the reaction tube with nitrogen gas, and heating was carried out until the ambient temperature in the horizontal reaction tube reached 700°C. After reaching 700°C, ethylene gas was introduced into the reaction tube at a flow rate of 2 L per minute as a hydrocarbon, and a contact reaction was carried out for 15 minutes. After the reaction was completed, the gas in the reaction tube was replaced with nitrogen gas, and the temperature of the reaction tube was cooled to 100°C or less and taken out to obtain CNT (B).

[0149] [Production Example (1)] 95 parts of CNT(A) as the carbon source, 5 parts of boric acid as the boron source, and 9900 parts of toluene / ethanol (=1 / 1, weight ratio) as the solvent were mixed, and wet mixing was performed by ultrasonic treatment. Then, the mixture was heated and dried at 65 °C to remove the solvent, and precursor (1) was prepared. Next, the precursor (1) was filled into a graphite crucible and heated in a firing furnace under an argon atmosphere at a heating rate of 10 °C / min until the furnace temperature reached 1700 °C. Then, heat treatment was performed at 1700 °C for 2 hours to obtain boron-containing CNT(1).

[0150] [Production Example (2)] 92.5 parts of 100P (carbon nanotube from KUMHO PETROCHEMICAL) as the carbon source and 7.5 parts of boric acid as the boron source were mixed, and dry treatment was performed by mechanofusion (manufactured by Hosokawa Micron Corporation) to prepare precursor (2). Next, the precursor (2) was filled into a graphite crucible and heated in a firing furnace under an argon atmosphere at a heating rate of 10 °C / min until the furnace temperature reached 1650 °C. Then, heat treatment was performed at 1650 °C for 2 hours to obtain boron-containing CNT(2).

[0151] [Production Examples (3), (5), (8), (9)] Boron-containing CNT(3), (5), (8), (9) were obtained in the same manner as in Production Example 2, except that the carbon source, boron source, and firing temperature were changed as shown in Table 1.

[0152] [Production Examples (4), (6), (7)] Boron-containing CNT(4), (6), (7) were obtained in the same manner as in Production Example 1, except that the carbon source, boron source, solvent, and firing temperature were changed as shown in Table 1.

[0153]

Table 1

[0154] (Content of boron element in CNT) The content of boron element in CNT was measured using ICP emission spectrometry (SPECTRO ARCOS FHS12 manufactured by SPECTRO). The obtained value indicates the amount (mol%) of boron element contained in the entire CNT material.

[0155] (Amount of substituted boron element in CNT) XPS (K-Alpha manufactured by Thermo Fisher scientific) was used to measure the amount (mol%) of substituted boron on the surface of CNT. Since the spectrum of boron 1s electrons appears at a binding energy of 185 - 194 eV, the state of boron on the surface can be evaluated by obtaining the peak area. Specifically, boron clusters are at 186 - 187 eV, boron carbide is at 187 - 188 eV, boron element (substituted boron on the surface) doped to substitute carbon element with a hexagonal network plane as the basic skeleton is at 188 - 189.3 eV, various boron oxides such as BC2O are at 189.5 - 190.5 eV, BCO2 is at 191.5 - 192 eV, and B2O3 is at 192.5 - 193 eV. Therefore, the peak separation of boron 1s can be performed to analyze the doping state of boron on the surface of CNT, and thus the amount of substituted boron in CNT can be measured.

[0156] (Average outer diameter of CNT) Using an electronic balance, 0.2 g of CNT was weighed into a sample bottle, 200 mL of toluene was added, and then a dispersion treatment was performed under ice cooling for 5 minutes at an amplitude of 50% using an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, manufactured by BRANSON) to prepare a CNT dispersion. Then, the CNT dispersion was appropriately diluted, several μL was dropped in the form of a collodion film, dried at room temperature, and then observed directly using a transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.). The observation was carried out at a magnification of 50,000 times. A plurality of photos containing 10 or more CNTs in the field of view were taken, and the outer diameters of 300 arbitrarily extracted CNTs were measured, and the average value was taken as the average outer diameter (nm) of CNT.

[0157] (BET specific surface area of CNT) Using an electronic balance, 0.03 g of CNT was weighed, and then dried at 110 °C for 15 minutes while degassing. Subsequently, the BET specific surface area of CNT was measured using a fully automatic specific surface area measurement device (HM-model1208, manufactured by MOUNTECH).

[0158] (G / D ratio of CNT) CNT was placed on a Raman microscope (XploRA, manufactured by Horiba, Ltd.), and measurement was performed using a laser wavelength of 532 nm. The measurement conditions were an acquisition time of 60 seconds, an integration number of 2 times, a neutral density filter of 10%, an objective lens magnification of 20 times, a confocal hole of 500, a slit width of 100 μm, and a measurement wavelength of 100 to 3000 cm -1 . The CNT for measurement was collected on a slide glass and flattened using a spatula. Among the obtained peaks, the maximum peak intensity in the spectrum within the range of 1560 to 1600 cm -1 was defined as G, and the maximum peak intensity within the range of 1310 to 1350 cm -1 was defined as D, and the ratio of G / D was defined as the G / D ratio of CNT.

[0159] (Volume resistivity of CNT) Using a powder resistance measurement system (MCP-PD51 type, manufactured by Nitto Seiko Analytic Co., Ltd.), the volume resistivity of CNT was measured. The volume resistivity was measured while applying a load after adding CNT to the measurement cell, and the value of the volume resistivity of CNT at a density of 1 g / cm 3 was evaluated.

[0160]

Table 2

[0161] <Dispersant> The dispersants used in the following examples and comparative examples are shown.

[0162] Dispersant (1): Acrylonitrile-conjugated diene rubber (hereinafter, Synthesis Example 1) Dispersant (2): Polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., K-30) Dispersant (3): Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., Kuraray POVAL PVA-403) Dispersant (4): Therban (registered trademark) 3406, (manufactured by ARLANXEO) Dispersant (5): Zetpole (registered trademark) 2000L (manufactured by Nippon Zeon Co., Ltd.) Dispersant (6): Polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., Esrec BL-10) Dispersant (7): Acrylonitrile-acrylic acid copolymer (described below, Synthesis Example 2) Dispersant (8): Carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., APP-084) Dispersant (9): Ammonium carboxymethyl cellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Metholose (registered trademark) SM-4) Dispersant (10): Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., Kuraray POVAL SD1000) Dispersant (11): Sodium carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., Sunrose (registered trademark) F01MC)

[0163] [Synthesis Example (1)] To a stainless steel polymerization reactor, 35 parts of acrylonitrile, 65 parts of 1,3-butadiene, 3 parts of potassium oleate soap, 0.3 part of azobisisobutyronitrile, 0.55 part of t-dodecyl mercaptan, and 200 parts of ion-exchanged water were added. Under a nitrogen atmosphere, while stirring, polymerization was carried out at 45 °C for 20 hours, and the polymerization was terminated at a conversion rate of 90%. Unreacted monomers were removed by vacuum stripping to obtain an acrylonitrile-conjugated diene rubber latex with a solid content concentration of about 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solid content concentration to 12%, and it was charged into an autoclave equipped with a stirrer with a volume of 1 L. Nitrogen gas was flowed for 10 minutes to remove dissolved oxygen in the contents. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water to which nitric acid four times the molar amount of palladium was added was added to the autoclave. After replacing the inside of the autoclave twice with hydrogen gas, the contents of the autoclave were heated to 50 °C under a pressure of hydrogen gas up to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. Then, the contents were returned to room temperature, and after making the atmosphere inside the autoclave a nitrogen atmosphere, the solid content was dried to recover dispersant (1). The hydrogenation rate of dispersant (1) was 99.6%, and the weight average molecular weight (Mw) was 150,000.

[0164] [Synthesis Example (2)] 100 parts of acetonitrile was charged into a reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer, and replaced with nitrogen gas. The inside of the reaction vessel was heated to 75 °C, and a mixture of 90.0 parts of acrylonitrile, 10.0 parts of acrylic acid, and 5.0 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by NOF Corporation; V-65) was added dropwise over 3 hours to carry out a polymerization reaction. After completion of the dropwise addition, the reaction was further carried out at 75 °C for 1 hour, then 0.5 part of perbutyl O was added, and the reaction was continued at 75 °C for 1 hour. Then, it was confirmed by non-volatile content measurement that the conversion rate exceeded 98%, and it was concentrated under reduced pressure to completely remove the dispersion medium to obtain dispersant (7). The weight average molecular weight (Mw) of dispersant (7) was 45,000.

[0165] <CNT Dispersion Liquid> Next, the preparation of the CNT dispersion and the evaluation method of the dispersion are shown.

[0166] [Example 1-N1] 0.9 part of dispersant (1), 94.064 parts of NMP (N-methylpyrrolidone) as a solvent, and 0.036 part of NaOH as an additive were added to a stainless steel container and stirred with a disper until uniform. Then, 5 parts of boron-containing CNT (1) were added while stirring with a disper. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was carried out at a speed of 8,500 rpm until the whole became uniform and the dispersion particle size became 250 μm or less as measured by a grind gauge. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Turbo HJP-17007, manufactured by Sugino Machine) through a pipe, and 20-pass dispersion treatment was performed. The dispersion treatment was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain a CNT dispersion (N1).

[0167] [Examples 1-N2 to N15] According to the compositions shown in Table 3, each CNT dispersion (N2) to (N15) was obtained in the same manner as in Example 1-N1.

[0168] [Comparative Example 1-N1] According to the compositions shown in Table 3, CNT, NMP, a dispersant, and 140 parts of zirconia beads (bead diameter: 0.3 mm φ) were charged into a glass bottle, and after performing dispersion treatment for 8 hours using a paint conditioner manufactured by Red Devil, the zirconia beads were separated to obtain a CNT dispersion (N16).

[0169] [Comparative Example 1-N2] According to the composition shown in Table 3, a dispersant and NMP were added to a stainless-steel container, and after adding NMP and adjusting the concentration, it was stirred with a disper until it became uniform. Then, boron-containing CNT(6) was added while stirring with a disper, a square-hole high-shear screen was attached to a high-shear mixer, and batch dispersion was carried out at a speed of 8,500 rpm until the whole became uniform and the dispersion particle size became 250 μm or less as measured by a grind gauge. Subsequently, the liquid to be dispersed was supplied from the stainless-steel container to a high-pressure homogenizer through a pipe, and 5-pass dispersion treatment was carried out. The dispersion treatment was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain a CNT dispersion (N17).

[0170] [Comparative Example 1-N3] According to the composition shown in Table 3, 140 parts of boron-containing CNT, NMP, a dispersant, and zirconia beads (bead diameter 0.3 mmφ) were charged into a glass bottle, and after carrying out dispersion treatment for 2 hours using a paint conditioner manufactured by Red Devil Co., Ltd., the zirconia beads were separated to obtain a CNT dispersion (N18).

[0171] [Example 1-W1] 97.7 parts of ion-exchanged water, 0.45 parts of a dispersant (2), and 0.05 parts of an antifoaming agent (A) (SN Deformer 1312 manufactured by San Nopco Ltd.) were added to a stainless-steel container and stirred with a disper until it became uniform. Then, while stirring with a disper, 1.8 parts of boron-containing CNT(1) were added and further stirred with a disper until it became uniform. After that, dispersion treatment was carried out using a high-pressure homogenizer (manufactured by Sugino Machine, Starburst 10). The dispersion treatment was carried out using a single-nozzle chamber at a nozzle diameter of 0.17 mm and a pressure of 100 MPa for 5 passes to obtain a CNT dispersion (W1).

[0172] [Examples 1-W3, W4, W6, W7, W9, W11, W12, W15] CNT dispersions (W3), (W4), (W6), (W7), (W9), (W11), (W12), and (W15) were obtained in the same manner as in Example 1-W1, except that the CNT type, CNT addition amount, ion-exchanged water addition amount, dispersant type, dispersant addition amount, antifoaming agent addition amount, and number of passes were changed as shown in Table 5.

[0173] [Example 1-W2] Into a glass bottle, 2 parts of boron-containing CNT (1), 0.5 part of dispersant (7), 0.05 part of antifoaming agent (A) (SN Deformer 1312 manufactured by San Nopco Ltd.), 97.45 parts of ion-exchanged water, and 140 parts of zirconia beads (bead diameter: 0.3 mmφ) were charged, and after performing a dispersion treatment for 4 hours using a paint conditioner manufactured by Red Devil, the zirconia beads were separated to obtain a CNT dispersion (W2).

[0174] [Examples 1-W5, W8, W10, W13, W14] CNT dispersions (W5), (W8), (W10), (W13), and (W14) were obtained in the same manner as in Example 1-W2, except that the CNT type, CNT addition amount, ion-exchanged water addition amount, dispersant type, dispersant addition amount, antifoaming agent addition amount, and dispersion time were changed as listed in Table 5.

[0175] [Comparative Example 1-W1] According to the composition shown in Table 5, into a glass bottle, CNT, ion-exchanged water, a dispersant, an antifoaming agent, and 140 parts of zirconia beads (bead diameter: 0.3 mmφ) were charged, and after performing a dispersion treatment for 4 hours using a paint conditioner manufactured by Red Devil, the zirconia beads were separated to obtain a CNT dispersion (W16).

[0176] [Comparative Example 1-W2] To 97.85 parts of ion-exchanged water, 0.1 part of dispersant (8), and 0.05 part of antifoaming agent (A) (SN Deformer 1312 manufactured by San Nopco Ltd.) were added to a stainless steel container, and the mixture was stirred with a disperser until it became uniform. Then, while stirring with a disperser, 2 parts of boron-containing CNT (9) were added and further stirred with a disperser until it became uniform. After that, dispersion treatment was performed using a high-pressure homogenizer. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.17 mm and a pressure of 100 MPa, and a one-pass treatment was performed to obtain a CNT dispersion (W17).

[0177] [Comparative Example 1-W3] According to the composition shown in Table 5, 140 parts of boron-containing CNT, ion-exchanged water, dispersant, antifoaming agent, and zirconia beads (bead diameter 0.3 mmφ) were charged into a glass bottle, and after performing dispersion treatment for 0.5 hours using a paint conditioner manufactured by Red Devil Co., the zirconia beads were separated to obtain a CNT dispersion (W18).

[0178] [Table 3]

[0179] [Table 4]

[0180] [Table 5]

[0181] [Table 6]

[0182] (Measurement of Complex Elastic Modulus and Phase Angle of CNT Dispersion) The complex elastic modulus and phase angle of the CNT dispersion were evaluated by performing dynamic viscoelasticity measurements at 25 °C and a frequency of 1 Hz in the range of strain rates from 0.01% to 5% using a rheometer (RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) with a cone having a diameter of 60 mm and an angle of 2°. The smaller the obtained complex elastic modulus, the better the dispersibility, and the larger the obtained complex elastic modulus, the worse the dispersibility. Also, the larger the obtained phase angle, the better the dispersibility, and the smaller the obtained phase angle, the worse the dispersibility. Judgment Criteria (Complex Elastic Modulus) ◎: Less than 20 Pa (Extremely Excellent) ○: 20 Pa or more and less than 50 Pa (Excellent) ○△: 50 Pa or more and less than 100 Pa (Good) △: 100 Pa or more and less than 200 Pa (Fair) ×: 200 Pa or more (Poor) Judgment Criteria (Phase Angle) ◎: 30° or more (Excellent) ○: 20° or more and less than 30° (Good) △: 10° or more and less than 20° (Fair) ×: Less than 10° (Poor)

[0183] (Viscosity of Dispersion) After leaving the CNT dispersion to stand in a thermostatic bath at 25 °C for 1 hour or more, the CNT dispersion was sufficiently stirred and then immediately measured at a B-type viscometer rotor rotation speed of 60 rpm. The rotor used for the measurement was No. 1 when the viscosity value was less than 100 mPa·s, No. 2 when it was 100 or more and less than 500 mPa·s, No. 3 when it was 500 or more and less than 2000 mPa·s, and No. 4 when it was 2000 or more and less than 10000 mPa·s. Judgment Criteria ◎: Less than 2000 mPa·s (Excellent) ○: 2000 mPa·s or more and less than 5,000 mPa·s (Good) △: 5,000 mPa·s or more and less than 10,000 mPa·s (Fair) ×: 10,000 mPa·s or more, sedimentation or separation (Poor)

[0184] (Evaluation of the Stability of the Dispersion) The evaluation of storage stability was carried out based on the change in the liquid properties after allowing the conductive material dispersion to stand at 50 °C for 7 days. The change in the liquid properties was judged from the ease of stirring when stirred with a spatula. Criteria for Judgment ○: No problem (good) △: Viscosity has increased but no gelation has occurred (acceptable) ×: Gelation has occurred (extremely poor)

[0185] (Length of CNT Fibers in the Dispersion) The CNT dispersion was diluted with the solvent used when preparing the CNT dispersion so that the CNT concentration became 0.01 mass%. After dropping several μL onto a mica substrate, it was dried in an electric oven at 120 °C to prepare a substrate for observing the CNT fiber length. Then, the surface of the prepared substrate for observing the CNT fiber length was sputtered with platinum. Further, SEM was used for observation. The observation was carried out at magnifications of 5000 times or 20000 times according to the fiber length of the CNTs. A plurality of photos containing 10 or more CNTs in the field of view were taken, and the fiber lengths of 100 arbitrarily extracted CNTs were measured, and the average value was taken as the CNT fiber length (μm) in the CNT dispersion.

[0186] (Measurement of the Particle Size Distribution of the Dispersion) After allowing the CNT dispersion to stand in a thermostatic bath at 25 °C for 1 hour or more, the CNT dispersion was sufficiently stirred and diluted, and then the cumulative particle size D50 of the CNT dispersion was measured using a particle size distribution meter (manufactured by Microtrac BEL Corporation, Nanotrac UPA, model UPA-EX).

[0187] (Volume Resistivity of the CNT Coating Film) The CNT dispersion was coated on a PET substrate using an applicator and then dried in an oven at 120 °C for 30 minutes to obtain a CNT coating film (film thickness: 3 μm). Subsequently, the surface resistivity (Ω / sq) of the dried coating film was measured using Loresta GP and MCP-T610 manufactured by Nitto Seiko Analytic Co., Ltd. After the measurement, the thickness of the CNT coating film formed on the PET substrate was multiplied to obtain the volume resistivity (Ω·cm) of the coating film. The thickness of the coating film was calculated by subtracting the film thickness of the PET substrate from the average value measured at five points in the film using a film thickness gauge, and the volume resistivity (Ω·cm) of the coating film was calculated. The judgment criteria are shown below. Judgment Criteria ◎: The volume resistivity (Ω·cm) of the CNT coating film is less than 7×10 -3 (Excellent) 〇: The volume resistivity (Ω·cm) of the CNT coating film is 7×10 -3 or more and less than 1×10 -2 (Good) △: The volume resistivity (Ω·cm) of the CNT coating film is 1×10 -2 or more and less than 2×10 -2 (Fair) ×: The volume resistivity (Ω·cm) of the CNT coating film is 2×10 -2 or more (Poor)

[0188] From the results of the above examples, it was revealed that by using a carbon nanotube dispersion in which the complex elastic modulus and phase angle are within the scope of the present invention, the conductivity is superior compared to the comparative examples. In the carbon nanotube dispersion of the present invention, it is considered that the carbon nanotubes in the coating film could efficiently form a conductive network with respect to Comparative Examples 1-N2, 1-N3, 1-W2, and 1-W3. However, in Comparative Examples 1-N1 and 1-W1, even though the dispersibility of the carbon nanotubes in the dispersion is good, the conductivity is low. Here, when Example 1-W2 is compared with Comparative Example 1-W1, a carbon nanotube dispersion is prepared under the same conditions except for the carbon nanotubes, and it was revealed that Example 1-W2 has a longer carbon nanotube fiber length and a smaller particle size distribution in the dispersion. This is because the boron-containing carbon nanotubes of Example 1-W2 are harder than the boron-free carbon nanotubes of the comparative examples and have high durability against energy such as impact applied during the dispersion of the carbon nanotubes, making the carbon nanotubes less likely to break and allowing them to be dispersed while maintaining the fiber length of the carbon nanotubes. As a result, it is considered that the carbon nanotube dispersion of the present invention enabled the carbon nanotubes in the coating film to form a good conductive network. On the other hand, when Examples 1-N1, 1-N5, and 1-N10 are compared, it was also found that the difference in the boron content of the carbon nanotubes greatly affects the dispersion state of the carbon nanotube dispersion and also affects the conductivity of the coating film. Although the details of these are not clear, it is considered that in the case of carbon nanotubes with a high boron content, it becomes difficult to disperse the carbon nanotubes separately because they are too hard, and sufficient dispersibility cannot be obtained, which also affects the conductivity of the coating film.

[0189] <Composite Material Slurry, Fabrication and Evaluation of Electrodes> Next, the fabrication and evaluation methods of the composite material slurry, electrodes, and batteries are shown.

[0190] [Example 2-N1] CNT dispersion (1) and NMP containing 8% by mass of PVDF (Solef#5130, Solvey Co., Ltd.) were added so that the composition (mass ratio) of CNT, PVDF, and active material was 0.25 / 1.5 / 98.25, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Then, electrode active material NCM523 (Nippon Chemical Industry Co., Ltd., composition: LiNi 0.5 Co 0.2 Mn 0.3 O 2 ) was added and stirred for 20 minutes at 2000 rpm using a planetary centrifugal mixer. Further, NMP was added so that the solid content of the positive electrode composite slurry was 75 mass%, and the mixture was stirred for 30 seconds at 2000 rpm using a planetary centrifugal mixer to obtain a positive electrode composite slurry (1).

[0191] [Examples 2-N2 to N15, Comparative Examples 2-N1 to N3] Positive electrode composite slurries (N2) to (N18) were obtained in the same manner as in Example 2-1, except that the materials shown in Table 7 were used.

[0192] [Example 2-W1] 7.5 parts by mass of CNT dispersion (W1), 12.5 parts by mass of an aqueous solution in which 2% by mass of CMC (manufactured by Daicel FineChem Co., Ltd., #1190) was dissolved, and 4.9 parts by mass of ion-exchanged water were weighed. Then, the mixture was stirred for 30 seconds at 2000 rpm using a planetary centrifugal mixer to obtain a CNT resin composition (W1). Then, 2.4 parts by mass of silicon monoxide (manufactured by Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5 μm) was added, and the mixture was stirred for 30 seconds at 2000 rpm using a planetary centrifugal mixer. Furthermore, 21.9 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added, and the mixture was stirred for 30 seconds at 2000 rpm using a planetary centrifugal mixer. Thereafter, 0.78 parts by mass of styrene-butadiene emulsion (TRD2001, manufactured by JSR Corporation) was further added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer to obtain a negative electrode mixture slurry (W1).

[0193] [Example 2-W2 to W15, Comparative Example 2-W1 to W3] The materials shown in Table 7 were changed, and anode composite slurries (W2) to (W18) were obtained in the same manner as in Example 2-W1, except that the addition amounts of the CNT resin composition and the CNT dispersion liquid were adjusted so that the amount of CNT in 100 parts by mass of the composite slurry was 0.27 parts by mass.

[0194] (Volume resistivity of the anode composite layer) The anode composite slurry was applied onto a PET substrate using an applicator so that the coating weight of the electrode was 20 mg / cm 2 Then, it was dried in an electric oven at 120 °C for 30 minutes to obtain an anode. Thereafter, the surface resistivity (Ω / square) of the dried coating film was measured using Loresta GP and MCP-T610 manufactured by Nitto Seiko Analytic Co., Ltd. After the measurement, the thickness of the electrode composite layer formed on the PET substrate was multiplied to obtain the volume resistivity (Ω·cm) of the electrode film for the anode. The thickness of the electrode composite layer was calculated by subtracting the film thickness of the PET substrate from the average value measured at 5 points in the electrode film using a film thickness gauge, and the volume resistivity (Ω·cm) of the composite layer was calculated. The judgment criteria are shown below, and the results are shown in Table 7. Judgment criteria ◎: Volume resistivity (Ω·cm) of the anode composite layer is less than 8 (excellent) 〇: Volume resistivity (Ω·cm) of the anode composite layer is 8 or more and less than 12 (good) △: Volume resistivity (Ω·cm) of the anode composite layer is 12 or more and less than 16 (fair) ×: Volume resistivity (Ω·cm) of the anode composite layer is 16 or more (poor)

[0195] (Peel strength of the anode composite layer) The anode composite slurry was applied onto a PET substrate using an applicator so that the coating weight of the electrode was 20 mg / cm 2 After coating on the aluminum foil so as to achieve the following, the coating film was dried in an oven at 120 °C for 30 minutes. Thereafter, it was cut into two rectangles of 90 mm × 20 mm with the coating direction as the major axis. A tensile tester was used to measure the peel strength, and it was evaluated by the 180-degree peel test method. Specifically, a double-sided tape with a size of 100 mm × 30 mm was attached onto a stainless steel plate, and the prepared battery electrode composite material layer was adhered to the other surface of the double-sided tape. While pulling it upward from below at a constant speed (50 mm / min), the average value of the stress at this time was taken as the peel strength. The judgment criteria are shown below, and the results are shown in Table 87. ◎: The peel strength (N / cm) of the positive electrode composite material layer is 0.3 or more (excellent) 〇: The peel strength (N / cm) of the positive electrode composite material layer is 0.25 or more and less than 0.3 (good) △: The peel strength (N / cm) of the positive electrode composite material layer is 0.2 or more and less than 0.25 (fair) ×: The peel strength (N / cm) of the positive electrode composite material layer is less than 0.2 (poor)

[0196] (Volume resistivity of the composite material layer for the negative electrode) Using the composite material slurry for the negative electrode, the volume resistivity (Ω·cm) of the composite material layer was measured in the same manner as the composite material layer for the positive electrode, except that the coating weight of the electrode was made 8 mg / cm 2 . The judgment criteria are shown below, and the results are shown in Table 7. Judgment criteria ◎: The volume resistivity (Ω·cm) of the negative electrode composite material layer is less than 0.12 (excellent) 〇: The volume resistivity (Ω·cm) of the negative electrode composite material layer is 0.12 or more and less than 0.15 (good) △: The volume resistivity (Ω·cm) of the negative electrode composite material layer is 0.15 or more and less than 0.25 (fair) ×: The volume resistivity (Ω·cm) of the negative electrode composite material layer is 0.25 or more (poor)

[0197] (Peel strength of the composite material layer for the negative electrode) Using the composite material slurry for the negative electrode, the peel strength of the composite material layer for the negative electrode was measured in the same manner as the peel strength of the composite material layer for the positive electrode, except that it was coated on the copper foil so that the coating weight of the electrode was 8 mg / cm 2 . The judgment criteria are shown below, and the results are shown in Table 7. Judgment criteria ◎: The peel strength (N / cm) of the negative electrode composite material layer is 0.5 or more (excellent). 〇: The peel strength (N / cm) of the negative electrode composite material layer is 0.4 or more and less than 0.5 (good). △: The peel strength (N / cm) of the negative electrode composite material layer is 0.3 or more and less than 0.4 (fair). ×: The peel strength (N / cm) of the negative electrode composite material layer is less than 0.3 (poor).

[0198] <Fabrication and Characterization of Non-aqueous Electrolyte Secondary Batteries> [Examples 3-N1 to N15, 3-W1 to W15, Comparative Examples 3-N1 to N3, 3-W1 to W3] The positive and negative electrodes for evaluation were fabricated by the following method. After applying the positive electrode composite slurry onto an aluminum foil with a thickness of 20 μm serving as a current collector using an applicator, it was dried in an oven at 120 °C for 30 minutes so that the electrode coating weight became 20 mg / cm 2 and then further subjected to a rolling process by roll pressing to fabricate a positive electrode with a density of the positive electrode composite material layer of 3.1 g / cm 3 Also, after applying the negative electrode composite slurry onto a copper foil with a thickness of 20 μm serving as a current collector using an applicator, it was dried in an oven at 80 °C for 30 minutes so that the electrode coating weight became 10 mg / cm 2 and then further subjected to a rolling process by roll pressing to fabricate a negative electrode with a density of the negative electrode composite material layer of 1.6 g / cm 3 was fabricated. The positive electrodes shown in Table 7 and the following standard negative electrode, or the negative electrodes shown in Table 7 and the following standard positive electrode were each punched out to 50 mm × 45 mm and 45 mm × 40 mm, and a separator (porous polypropylene film) to be inserted between them was inserted into an aluminum laminate bag and dried in an electric oven at 70 °C for 1 hour. Subsequently, in a glove box filled with argon gas, 2 mL of an electrolytic solution was injected, and the aluminum laminate bag was sealed to fabricate non-aqueous electrolyte secondary batteries (N1) to (N18), (W1) to (W18). The electrolytic solution was prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, and further, as an additive, 1 part of VC (vinylene carbonate) was added to 100 parts of the electrolytic solution, and then LiPF 6 It is a non-aqueous electrolyte solution dissolved at a concentration of 1 M.

[0199] [Fabrication of Standard Negative Electrode] Acetylene black (manufactured by Denka Co., Ltd., Denka Black (registered trademark) HS-100), CMC (manufactured by Daicel Finechem Co., Ltd., Carboxymethylcellulose #1190), and water were added to a plastic container with a capacity of 150 mL. Then, using a rotation and revolution mixer, it was stirred at 2,000 rpm for 30 seconds. Further, artificial graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) was added as a negative electrode active material, and using a rotation and revolution mixer, it was stirred at 2,000 rpm for 150 seconds. Subsequently, SBR (manufactured by JSR Corporation, TRD2001, solid content 48% dispersion) was added, and using a rotation and revolution mixer, it was stirred at 2,000 rpm for 30 seconds to obtain a composite slurry for the standard negative electrode. The solid content of the composite slurry for the standard negative electrode was 48 mass%. The solid content ratio of the negative electrode active material: conductive material: CMC: SBR in the composite slurry for the standard negative electrode was 97:0.5:1:1.5. Next, the composite slurry for the standard negative electrode was coated on a copper foil with a thickness of 20 μm serving as a current collector using an applicator, and then dried in an electric oven at 80 °C for 30 minutes so that the coating weight per unit area of the electrode was 10 mg / cm 2 It was adjusted to be. Further, rolling treatment was performed by a roll press to fabricate a standard negative electrode (SA) with a density of the negative electrode composite layer of 1.6 g / cm 3

[0200] [Fabrication of Standard Positive Electrode] A capacity of 150 cm 3 ​In a plastic container, 93 parts by mass of a positive electrode active material (manufactured by BASF Toda Battery Materials Co., Ltd., HED (registered trademark) NCM-111 1100), 4 parts by mass of acetylene black (manufactured by Denka Co., Ltd., Denka Black (registered trademark) HS100), and 3 parts by mass of PVDF (manufactured by Kuraray Battery Materials Japan Co., Ltd., Kuraray KF Polymer W#1300) were added, and then mixed with a spatula until the powder became uniform. Then, 20.5 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary mixer. Then, the mixture in the plastic container was mixed with a spatula until it became uniform, and then stirred at 2000 rpm for 30 seconds using the planetary mixer. Further, 14.6 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using the planetary mixer. Finally, the mixture was stirred at 3000 rpm for 10 minutes using a high-speed stirrer to obtain a composite slurry for a standard positive electrode. Then, the composite slurry for a standard positive electrode was coated on an aluminum foil with a thickness of 20 μm serving as a current collector using an applicator, and then dried in an electric oven at 120 °C for 30 minutes so that the areal density per unit area of the electrode was 20 mg / cm 2 was adjusted. Further, rolling treatment was performed by a roll press to produce a standard positive electrode (SC) having a density of the composite layer of 3.1 g / cm 3 .

[0201] (Rate characteristics evaluation of non-aqueous electrolyte secondary battery) A non-aqueous electrolyte secondary battery was installed in a thermostatic chamber at 25°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Hokuto Denko Corporation, SM-8). After performing constant current and constant voltage charging (cut-off current 1 mA (0.02C)) at a charging current of 10 mA (0.2C) and a charging end voltage of 4.3V, constant current discharge was performed at a discharge current of 10 mA (0.2C) and a discharge end voltage of 3V. After repeating this operation 3 times, constant current and constant voltage charging (cut-off current 1 mA (0.02C)) was performed at a charging current of 10 mA (0.2C) and a charging end voltage of 4.3V, and constant current discharge was performed at discharge currents of 0.2C and 3C until the discharge end voltage reached 3.0V, and the discharge capacities were obtained respectively. The rate performance can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 1 below. Also, the judgment criteria are shown below, and the results are shown in Table 7. (Equation 1) Rate performance = 3C discharge capacity / 0.2C discharge capacity at the third cycle × 100 (%) Judgment criteria ◎: Rate performance is 80% or more (extremely excellent) 〇: Rate performance is 70% or more and less than 80% (excellent) 〇△: Rate performance is 60% or more and less than 70% (good) △: Rate performance is 50% or more and less than 60% (fair) ×: Rate performance is less than 50% (poor)

[0202] (Method for evaluating cycle performance of non-aqueous electrolyte secondary battery) A non-aqueous electrolyte secondary battery was installed in a thermostatic chamber at 40°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Hokuto Denko Corporation, SM-8). After performing constant current and constant voltage charging (cut-off current 2.5 mA (0.05C)) at a charging current of 25 mA (0.5C) and a charging end voltage of 4.3V, constant current discharge was performed at a discharge current of 25 mA (0.5C) and a discharge end voltage of 3V. This operation was repeated 200 times. The cycle performance can be expressed by the ratio of the 0.5C discharge capacity at the third cycle at 25°C to the 0.5C discharge capacity at the 200th cycle, as shown in Equation 2 below. Also, the judgment criteria are shown below, and the results are shown in Table 7. (Equation 2) Cycle performance = 0.5C discharge capacity at the third cycle / 0.5C discharge capacity at the 200th cycle × 100 (%) Judgment Criteria ◎: Cycle characteristics are 80% or more (extremely excellent) 〇: Cycle characteristics are 70% or more and less than 80% (excellent) 〇△: Cycle characteristics are 60% or more and less than 70% (good) △: Cycle characteristics are 60% or more and less than 70% (fair) ×: Cycle characteristics are less than 60% (poor)

[0203]

Table 7

[0204] From the results of the above examples, it was found that by using a carbon nanotube dispersion in which the complex elastic modulus and phase angle are within the scope of the present invention, a lithium ion secondary battery excellent in rate characteristics and cycle characteristics can be obtained as compared with the comparative examples. The carbon nanotube dispersion of the present invention has a low viscosity, good dispersibility, and good dispersion stability. Therefore, it is considered that the carbon nanotubes in the electrode efficiently formed a conductive network, resulting in good cycle characteristics. However, in Comparative Examples 3-N1 and 3-W1, even though the dispersibility of the carbon nanotube dispersion was good, the conductivity was insufficient, so sufficient rate characteristics could not be obtained. Also, in Comparative Examples 3-N1 and 3-W1, even though a conductive network in the electrode could be formed, the cycle characteristics were worse than those of the examples. These results are considered to be because the boron-containing carbon nanotubes of the present invention are harder than the carbon nanotubes not containing boron, so the conductive network of the carbon nanotubes can be maintained without collapsing against the repeated expansion and contraction of the active material in the electrode during charging and discharging of the battery, thus improving the cycle characteristics. On the other hand, when comparing Examples 2-N1, 2-N5, 2-N10, or Examples 3-N1, 3-N5, 3-N10, it was also found that the difference in the boron content of the carbon nanotubes affects the conductivity, peel strength of the electrode (composite layer), and battery characteristics (rate characteristics, cycle characteristics). From the above, it has become clear that the present invention can provide a lithium-ion secondary battery having high capacity, high output, and high durability, which are difficult to achieve with conventional carbon nanotube dispersions.

Explanation of symbols

[0205] 1: Peak of boron cluster (186 - 187 eV) 2: Peak of boron carbide (187 - 188 eV) 3: Peak of boron (188.2 - 189.3 eV) doped so as to substitute for carbon element having a hexagonal network plane as a basic skeleton 4: Boron oxide BC 2 Peak of O (189.5 - 190.5 eV) 5: Boron oxide BCO 2 (191.5 - 192 eV) peak 6: Boron oxide B 2 O 3 (192.5 - 193 eV) peak< / cnt>

Claims

1. A carbon nanotube dispersion containing a boron-containing carbon nanotube (provided that it has a cylindrical hollow structure, a fiber outer diameter of 0.5 μm or less, an aspect ratio of 10 or more, and a compression resistivity of 0.02 Ω·cm or less, and is a branched vapor-phase carbon fiber excluding single-walled carbon nanotubes) and a solvent, wherein the complex elastic modulus of the carbon nanotube dispersion measured by dynamic viscoelasticity is less than 200 Pa, the phase angle at a frequency of 1 Hz is 10° or more, the boron content of the boron-containing carbon nanotube is 0.01 to 3 mol%, and the content of the boron element doped so as to replace the carbon element on the surface of the boron-containing carbon nanotube is 0.01 to 1 mol%. A carbon nanotube dispersion characterized by the above.

2. The carbon nanotube dispersion according to claim 1, further comprising a dispersant.

3. A carbon nanotube resin composition comprising the carbon nanotube dispersion according to claim 1 or 2 and a binder.

4. A conductive film characterized by being a coating film of the carbon nanotube dispersion according to claim 1 or 2 or the carbon nanotube resin composition according to claim 3.

5. A composite material slurry comprising the carbon nanotube resin composition according to claim 3 and an active material.

6. An electrode film characterized by being a coating film of the composite material slurry according to claim 5.

7. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode contains the electrode film according to claim 6.

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