Method for manufacturing carbon material

Abstract

To provide a carbon material which exhibits high dispersibility; a carbon material dispersion composition; a mixture slurry that can yield an electrode film having a high electrical conductivity; and, more specifically, a secondary battery having excellent rate characteristics and cycle characteristics; and a vehicle having the secondary battery.SOLUTION: Provided is a carbon material that satisfies (1) and (2) in the following: (1) the BET specific surface area is 400 m2 / g to 650 m2 / g; and (2) in powder X-Ray diffraction analysis, at least two peaks are present within the diffraction angle range 2θ=24.0°-27.0°.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carbon material and a carbon material dispersion composition. More specifically, it relates to a carbon material dispersion composition containing a carbon material, a dispersant, and a dispersion medium, a composite slurry containing the carbon material dispersion composition and an active material, an electrode film formed by coating the composite slurry, a secondary battery including an electrode having the electrode film and an electrolyte, and a vehicle including the secondary battery.

Background Art

[0002] With the popularization of electric vehicles and the miniaturization, light weight, and high performance of portable devices, there is a demand for secondary batteries having a high energy density, and further, an increase in the capacity of such secondary batteries. Under such circumstances, non-aqueous electrolyte secondary batteries using a non-aqueous electrolyte, particularly lithium ion secondary batteries, have come to be used in many devices due to their characteristics of high energy density and high voltage.

[0003] As the negative electrode material used in these lithium ion secondary batteries, a carbon material typified by graphite, which has a low potential close to lithium (Li) and a large charge-discharge capacity per unit mass, is 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 of the electrode, studies are underway to reduce the conductive aids and binders that do not contribute to the discharge capacity.

[0004] As the conductive aid, carbon materials such as carbon black, ketjen black, fullerene, graphene, and fine carbon materials are used. In recent years, in particular, carbon nanotubes having a large specific surface area, which are a type of fine carbon material, are widely used. For example, it is known that an electrode film formed by coating a composite slurry containing a carbon nanotube dispersion composition and an active material has low electrode resistance and improved load resistance and cycle characteristics of the battery (see, for example, Patent Documents 1 and 2).

[0005] However, conventional carbon nanotubes with a large specific surface area have low wettability in solvents, making it difficult to produce a dispersion composition with high concentration and excellent dispersion stability.

[0006] Therefore, there is an urgent need to develop carbon nanotubes with excellent wettability in solvents, a high specific surface area, and excellent electrical conductivity.

[0007] As a method for improving the properties of carbon nanotubes, for example, a method of heat-treating carbon nanotubes at 1000 to 3000 °C in an inert atmosphere has been proposed (see Patent Documents 1 and 3). However, these methods mainly aim to remove metals and metal oxides contained in the obtained carbon nanotubes, and no detailed study has been conducted on the heat treatment of carbon nanotubes with a large specific surface area, and it is not possible to achieve both dispersibility and electrical conductivity.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, the problems to be solved by the present invention are to provide a carbon material having high dispersibility and electrical conductivity, and a carbon material dispersion composition. Further, a composite slurry capable of obtaining an electrode film with high electrical conductivity, and more specifically, a secondary battery having excellent rate characteristics and cycle characteristics, and a vehicle having high safety and improved fuel efficiency by having the secondary battery.

Means for Solving the Problems

[0010] The inventors of the present invention have intensively studied to solve the above problems. The inventors have found that the BET specific surface area of a carbon material containing multi-walled carbon nanotubes is 400 m 2 / g to 650 m 2 / g, and further has at least two peaks at diffraction angles 2θ = 24.0° to 27.0° in powder X-ray diffraction analysis, indicating high dispersibility. Further, by using such a carbon material, it has been found that an electrode film excellent in conductivity can be obtained, and a secondary battery having excellent rate characteristics and cycle characteristics can be obtained. Based on such findings, the inventors have made the present invention.

[0011] That is, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following. [1] A carbon material comprising multi-walled carbon nanotubes and satisfying the following (1) and (2). (1) The BET specific surface area is 400 m 2 / g to 650 m 2 / g. (2) In powder X-ray diffraction analysis, having at least two peaks in the range of diffraction angle 2θ = 24.0° to 27.0°. [2] The carbon material according to [1], wherein when the peak intensity on the low-angle side in the range of diffraction angle 2θ = 24.0° to 27.0° is A and the peak intensity on the high-angle side is B in powder X-ray diffraction analysis, the B / A ratio is 1.0 to 2.5. [3] The carbon material according to [1] or [2], having a purity of 99.9% or more. [4] In the Raman spectrum, when the maximum peak intensity in the range of 1560 cm -1 to 1600 cm -1 is G and the maximum peak intensity in the range of 1310 cm -1 to 1350 cm -1 is D, the carbon material according to any one of [1] to [3], wherein the G / D ratio is 1.0 to 4.5. [5] A carbon material dispersion composition comprising the carbon material according to any one of [1] to [4], a dispersant, and a dispersion medium. 〔6〕The carbon material dispersion composition after being stored at 60°C for one week after the production of the carbon material dispersion composition has a viscosity of 500 mPa·s to 20,000 mPa·s as measured by a B-type viscometer at 25°C and a rotor rotation speed of 6 rpm, which is the carbon material dispersion composition described in 〔5〕. 〔7〕The carbon material dispersion composition according to any one of 〔5〕 to 〔6〕, which contains a fluororesin. 〔8〕A composite material slurry containing the carbon material dispersion composition described in 〔5〕 to 〔7〕 and an active material. 〔9〕An electrode film formed from the composite material slurry described in 〔8〕. 〔10〕A secondary battery including an electrode having the electrode film described in 〔9〕 and an electrolyte. 〔11〕A vehicle equipped with the secondary battery described in 〔10〕. 〔12〕A step of mixing a carbon material dispersion composition (I) containing a carbon material, a dispersant, and a dispersion medium, and a carbon material dispersion composition (II) containing a single-walled carbon nanotube and a fluororesin (however, excluding the case where it is the carbon material dispersion composition (I)). The carbon material contains multi-walled carbon nanotubes and is a carbon material that satisfies the following (1) and (2). A method for producing a carbon material dispersion composition. (1) The BET specific surface area is 400 m 2 / g to 650 m 2 / g. (2) In powder X-ray diffraction analysis, it has at least two peaks within the range of diffraction angle 2θ = 24.0° to 27.0°.

Advantages of the Invention

[0012] The carbon material containing multi-walled carbon nanotubes of the present invention has excellent dispersibility. By using such a carbon material, a carbon material dispersion composition, a composite material slurry, and an electrode film with excellent conductivity can be obtained. In addition, a secondary battery with excellent rate characteristics and cycle characteristics can be obtained. Thereby, even in vehicle applications such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, where high capacity, high output, and high durability are required for the secondary battery to be mounted, it can be suitably used.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] Hereinafter, the carbon material, carbon material dispersion composition, composite slurry, electrode film, and secondary battery of the present invention will be described in detail, but are not limited thereto. The numerical values specified in this specification are values obtained by the methods disclosed in the embodiments or examples. In this specification, carbon nanotubes may be denoted as "CNT".

[0015] Also, in this specification, the numerical range specified using "~" shall include the numerical values described before and after "~" as the range of the lower limit value and the upper limit value. Unless otherwise noted, the various components appearing in this specification may each be used alone or in combination of two or more.

[0016] ≪Carbon Material≫ The carbon material of this embodiment contains multi-walled carbon nanotubes and satisfies the following (1) and (2). (1) The BET specific surface area is 400 m 2 / g to 650 m 2 / g. (2) In powder X-ray diffraction analysis, it has at least two peaks within the range of diffraction angle 2θ = 24.0° to 27.0°.

[0017] A carbon nanotube has a shape in which planar graphite is wound into a cylindrical shape. A single-walled carbon nanotube has a structure in which a single layer of graphite is wound, and a multi-walled carbon nanotube has a structure in which two or more layers of graphite are wound. Also, the side wall of the carbon nanotube does not necessarily have to be a graphite structure. For example, a carbon nanotube having a side wall with an amorphous structure can also be used as the carbon nanotube. The carbon material of the present embodiment preferably has a main component of multi-walled carbon nanotubes, but may contain single-walled carbon nanotubes mixed therein. Note that the main component refers to the component having the highest content among the components constituting the carbon material.

[0018] Specifically, the content of the multi-walled carbon nanotubes contained in the carbon material of the present embodiment is preferably 50% by mass or more and 99.9% by mass or less in 100% by mass of the carbon material, and more preferably 60% by mass or more and 98% by mass or less. The content of the multi-walled carbon nanotubes can be determined, for example, by using TG-DTA, heating to 25°C to 600°C in a nitrogen atmosphere, then lowering the heating temperature to 400°C, and switching the atmosphere gas from nitrogen to air and heating to 400°C to 1000°C. At this time, the weight loss amount when heated to 600°C in a nitrogen atmosphere can be regarded as the weight of amorphous carbon, the weight loss amount when heated to 800°C after switching to an air atmosphere can be regarded as the weight of multi-walled carbon nanotubes, and the weight loss amount when heated to 800°C to 1000°C can be regarded as the weight of crystalline carbon. By including multi-walled carbon nanotubes, when used as a conductive material for a secondary battery, the load resistance and cycle characteristics of the secondary battery can be improved.

[0019] The carbon material of the present embodiment has a BET specific surface area of 400 m 2 / g to 650 m 2 / g, preferably 450 m 2 / g to 600 m 2 / g, and more preferably 450 m 2 / g to 550 m 2It is more preferably g. In addition to (2), the BET specific surface area is 400 m of (1) 2 / g to 650 m 2 Within the range of / g, an efficient conductive network can be formed with a small amount, and the amount of the conductive material in the electrode can be reduced. Thereby, the degree of freedom in battery design such as increasing the amount of the active material and the binder resin is increased. Furthermore, during the preparation of the composite slurry, since the composite of the active material and the carbon nanotube easily proceeds, an electrode film having a homogeneous conductive network in which the surface of the active material is covered with the carbon nanotube can be easily obtained, suppressing the electrolyte decomposition reaction at the interface between the electrolyte and the active material, and improving the cycle characteristics of the battery. The BET specific surface area can be measured by the BET method described in JIS Z 8833.

[0020] The carbon material of the present embodiment has at least two peaks in the range of diffraction angle 2θ = 24.0° to 27.0° in powder X-ray diffraction analysis. Preferably, it has two peaks. Of the two peaks, the peak on the low angle side is presumed to be derived from multi-walled carbon nanotubes, and the peak mainly on the high angle side is a peak derived from graphite. By being such a carbon material, excellent dispersibility and conductivity can be achieved. The reason for the excellent dispersibility is considered that the amorphous carbon component existing in the defective part of the multi-walled carbon nanotubes is selectively graphitized, so that multi-walled carbon nanotubes with uniform shapes are easily obtained during the preparation of the dispersion composition. Also, the reason for the excellent conductivity is considered that the defective parts of the multi-walled carbon nanotubes are graphitized and the crystallinity is improved, the conductivity of the multi-walled carbon nanotubes which are the main component of the carbon material is improved, and the contact resistance between the multi-walled carbon nanotubes is reduced.

[0021] When the peak intensity on the low angle side is A and the peak intensity on the high angle side is B, the B / A ratio is preferably 1.0 to 2.5, and more preferably less than 1.5. By being such a carbon material, the dispersibility and conductivity become more excellent. In addition, when there are two or more peaks, it is preferable that the two peaks with the highest peak intensities satisfy the above requirements.

[0022] The carbon material of the present embodiment preferably has an interplanar spacing d002 calculated by powder X-ray diffraction analysis of 3.45 Å to 3.80 Å.

[0023] For powder X-ray diffraction analysis, the carbon material and high-purity silicon are thoroughly mixed using an agate mortar, then packed into a predetermined sample holder so that the surface is flat, set in a powder X-ray diffractometer, and measured by changing the irradiation angle of the X-ray source from 5° to 80°. For example, CuKα rays are used as the X-ray source.

[0024] The carbon material of the present embodiment preferably has a sulfur content of 500 ppm or less, and more preferably 100 ppm or less. If the sulfur content is below the above content, it is preferable because it can suppress a decrease in dispersibility.

[0025] The carbon material of the present embodiment preferably has a purity of 95% or more, more preferably 99% or more, and even more preferably 99.9% or more. When the purity of the carbon material is higher than the above, there are fewer conductive foreign substances other than the carbon material, so the storage stability of the secondary battery can be improved. more

[0026] The purity of the carbon material can be determined by subtracting the total weight of iron, cobalt, magnesium, aluminum, copper, nickel, zirconia, and molybdenum contained in the carbon material from the weight of the carbon material. The total content of iron, cobalt, magnesium, aluminum, copper, nickel, zirconia, and molybdenum is preferably 300 ppm or less, and more preferably 100 ppm or less.

[0027] The contents of the above-mentioned metal and sulfur can be analyzed using a multi-type ICP emission spectrometer (Agilent, 720-ES) after drying the carbon material, decomposing it by acid using a microwave sample pretreatment device (manufactured by Milestone General, ETHOS1), and extracting the metal contained in the carbon material.

[0028] The G / D ratio (peak ratio of G-band and D-band) of the carbon material of this embodiment is 1560 cm in the Raman spectrum -1 ~1600 cm -1 When the maximum peak intensity within the range is G, and the maximum peak intensity within the range of 1310 cm -1 ~1350 cm -1 is D, the G / D ratio is preferably 1.0 to 5.0, and more preferably 1.0 to 4.5. When the G / D ratio of the carbon material is within the above range, the defects of the multi-walled carbon nanotubes are graphitized, the contact resistance between the multi-walled carbon nanotubes becomes small, and it is considered that good conductivity is easily obtained. In addition, it is presumed that the amount of functional groups on the surface of the multi-walled carbon nanotubes is appropriate, the affinity with the solvent is good, and the dispersibility is better.

[0029] The carbon material of this embodiment preferably has an average outer diameter of 4 nm to 25 nm, and more preferably 4 nm to 9 nm. When the average outer diameter is within the above range, it is easy to form a good conductive network in the electrode, and during charge and discharge, the active material inside the secondary battery is uniformly utilized, so the deterioration of the active material is suppressed and the cycle characteristics of the secondary battery are further improved.

[0030] The outer diameter and average outer diameter of the carbon material of this embodiment are determined as follows. First, observe and image the carbon material with a transmission electron microscope. Next, in the observation photograph, select any 300 carbon materials and measure their respective outer diameters. Next, calculate the average outer diameter (nm) of the carbon material as the number average of the outer diameters.

[0031] The volume resistivity of the carbon material of this embodiment is 1.0×10 -2 Ω·cm to 3.0×10-2 It is preferably Ω·cm, and 1.0×10 -2 Ω·cm~2.0×10 -2 It is more preferably Ω·cm. The volume resistivity of the carbon material can be measured using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: Loresta GP Powder Resistivity Measuring System MCP-PD-51). When the volume resistivity of the carbon material is within the above range, the conductivity of the electrode film tends to be good, and a secondary battery having excellent rate characteristics and cycle characteristics can be easily obtained.

[0032] The ash content of the carbon material of this embodiment is preferably 500 ppm or less, and more preferably 300 ppm or less.

[0033] <Manufacturing method of carbon material> The carbon material of this embodiment may be a carbon material manufactured by any method as long as it contains multi-walled carbon nanotubes and satisfies the characteristics of (1) and (2). Carbon materials can generally be manufactured by laser ablation method, arc discharge method, thermal CVD method, plasma CVD method and combustion method, but are not limited thereto. For example, in an atmosphere with an oxygen concentration of 1% by volume or less, at 500°C to 1000°C, a carbon material can be manufactured by bringing a carbon source into catalytic contact reaction. And the carbon source may be at least one of hydrocarbons and alcohols.

[0034] The carbon material of this embodiment has a maximum peak intensity in the range of 1560 cm -1 ~1600 cm -1 in the Raman spectrum as G, and when the maximum peak intensity in the range of 1310 cm -1 ~1350 cm -1 is D, it is more preferable to further heat-treat a carbon material with a G / D ratio of less than 1.0. The heat treatment temperature is preferably 1000°C to 2000°C, more preferably 1400°C to 1800°C, and even more preferably 1400°C to 1600°C.

[0035] The carbon material of this embodiment is preferably produced by further heat-treating a carbon material containing iron, cobalt, and / or nickel, and more preferably by further heat-treating carbon nanotubes containing 1000 ppm to 10000 ppm of iron and / or cobalt. Iron, cobalt, and nickel have the effect of promoting graphitization, and by optimizing the amounts of iron, cobalt, and nickel contained in the carbon nanotubes, graphitization can be achieved at a low temperature. Therefore, it is considered that the defective portions of the carbon nanotubes can be selectively graphitized, and the conductivity can be improved without losing the characteristics of the carbon nanotubes themselves.

[0036] ≪Carbon material dispersion composition≫ The carbon material dispersion composition contains at least the carbon material of the present invention, a dispersant, and a dispersion medium. Moreover, it is preferable that the carbon material dispersion composition contains a fluororesin. By including a fluororesin in the carbon material dispersion composition, due to the steric hindrance of the fluororesin, aggregation of the carbon material is less likely to occur, and a carbon material dispersion composition with a good dispersion state is easily obtained. Also, when a fluororesin is used as the dispersant, it has excellent compatibility with the binder resin during the production of the composite material slurry described later. Moreover, when a fluororesin is used as the binder resin, it is preferable from the viewpoint of electrochemical oxidation-reduction resistance. In this specification, when it contains an active material, it is defined as a composite material slurry.

[0037] <Dispersant> The dispersant of this embodiment is not particularly limited as long as it can disperse and stabilize the carbon material, and surfactants, resin-type dispersants, fluororesins, etc. can be used. Surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric types. Appropriate types of dispersants can be used in appropriate blending amounts according to the characteristics required for the dispersion of the carbon material.

[0038] The content of the dispersant is preferably 1 to 100 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 20 to 50 parts by mass with respect to 100 parts by mass of the carbon material. When the amount of the dispersant is within the above range, the amount of the dispersant adsorbed on the surface of the carbon material is appropriate, and a carbon material dispersion composition excellent in conductivity and dispersion stability can be easily obtained.

[0039] 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, sodium polyoxyethylene nonylphenyl ether sulfate ester, and sodium salts of β-naphthalene sulfonic acid formalin condensates can be mentioned, but are not limited thereto.

[0040] Moreover, as the cationic surfactant, alkylamine salts and quaternary ammonium salts There are. Specifically, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercapto pyridine, poly(vinyl pyridine)-dodecyl bromide and dodecyl benzyl triethyl ammonium chloride can be mentioned, but are not limited thereto. Also, as amphoteric surfactants, aminocarboxylates can be mentioned, but are not limited thereto.

[0041] Also, as nonionic surfactants, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters and alkyl allyl ethers can be mentioned, but are not limited thereto. Specifically, polyoxyethylene lauryl ether, sorbitan fatty acid ester and polyoxyethylene octyl phenyl ether can be mentioned, but are not limited thereto.

[0042] The surfactant selected is not limited to a single surfactant. Therefore, it is also possible to use a combination of two or more surfactants. For example, a combination of 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 preferable. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0043] Specific examples of the resin-type dispersant 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, hydrogenated nitrile butadiene rubber, polyacrylonitrile-based polymers, etc. In particular, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, hydrogenated nitrile butadiene rubber, and polyacrylonitrile-based polymers are preferred, and polyvinyl pyrrolidone, polyvinyl butyral, and hydrogenated nitrile butadiene rubber are more preferred. The molecular weight of the resin-type dispersant is preferably from 10,000 to 300,000, and more preferably from 10,000 to 150,000.

[0044] Fluororesin is a high molecular compound having fluorine atoms in the molecule. Specific examples include polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc.

[0045] When using a fluororesin as the dispersant, it is more preferably used in combination with a dispersant other than the fluororesin, such as a surfactant or a resin-type dispersant. When a surfactant or a resin-type dispersant and a fluororesin are used as the dispersant, the surfactant or the resin-type dispersant is likely to adsorb on the surface of the carbon material, and the wettability and dispersibility are likely to be improved.

[0046] The weight average molecular weight of the fluororesin of this embodiment is preferably from 10,000 to 2,000,000, more preferably from 100,000 to 1,000,000, and particularly preferably from 200,000 to 1,000,000.

[0047] The content of the fluororesin in this embodiment is preferably 1 to 100 parts by mass, more preferably 10 to 70 parts by mass, based on 100 parts by mass of the carbon material in the carbon material dispersion composition. When the content of the fluororesin is within the above range, a carbon material dispersion composition with good fluidity is easily obtained.

[0048] In addition to the dispersant, it is preferable to add an amine compound or an inorganic base. As the amine compound, primary amines, secondary amines, and tertiary amines are used, and ammonia and quaternary ammonium compounds are not included. In addition to monoamines, amine compounds having a plurality of amino groups in the molecule, such as diamines, triamines, and tetraamines, can be used as the amine-based compound. Specifically, for example, aliphatic primary amines such as methylamine, ethylamine, butylamine, and octylamine, aliphatic secondary amines such as dimethylamine, diethylamine, and dibutylamine, aliphatic tertiary amines such as trimethylamine, triethylamine, and dimethyloctylamine, amino acids such as alanine, methionine, proline, serine, asparagine, glutamine, lysine, arginine, histidine, aspartic acid, glutamic acid, and cysteine, alkanolamines such as dimethylaminoethanol, monoethanolamine, diethanolamine, methylethanolamine, and triethanolamine, alicyclic nitrogen-containing heterocyclic compounds such as hexamethylenetetramine, morpholine, and piperidine, etc. can be mentioned, but it is not limited thereto. Examples of the inorganic base include hydroxides of alkali metals, hydroxides of alkaline earth metals, carbonates of alkali metals, carbonates of alkaline earth metals, phosphates of alkali metals, and phosphates of alkaline earth metals.

[0049] The usage amount of the amine compound and the inorganic base is preferably 0.01 part by mass or more, more preferably 0.1 part by mass or more, based on 100 parts by mass of the dispersant. The usage amount of the amine compound and the inorganic base is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, based on 100 parts by mass of the dispersant.

[0050] <Dispersion medium> The solvent, which is the dispersion medium of this embodiment, is not limited as long as the carbon material can be dispersed therein, but water or an amide-based organic solvent is preferred. Examples of the amide-based organic solvent include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, and the like. In particular, it is more preferable to contain at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0051] When an amide-based organic solvent is used as the dispersion medium, the water content is preferably 1000 ppm or less, and more preferably 500 ppm or less.

[0052] The content of the dispersion medium of this embodiment is preferably 90% by mass to 99% by mass, and more preferably 95% by mass to 99% by mass, based on the carbon material dispersion composition (100% by mass). When within the above range, a fluid carbon material dispersion composition is easily obtained, and a carbon material dispersion composition excellent in dispersion stability is easily obtained. By using a carbon material composition excellent in dispersion stability, an electrode film having stable conductivity can be obtained, and the quality of the secondary battery is easily stabilized.

[0053] <Binder resin> The carbon material dispersion composition of this embodiment may contain a binder resin. The binder resin is a resin used to bind between the substances of the carbon material. The binder resin is not particularly limited. For example, polymers or copolymers containing, as constituent units, fluororesin, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc.; polyurethane resin, polyester resin, phenol resin, epoxy resin, etc. Phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; Cellulose resins such as carboxymethyl cellulose - Resins; Rubbers such as styrene-butadiene rubber; Conductive resins such as polyaniline and polyacetylene, etc. may be mentioned. Among them, from the viewpoint of electrochemical oxidation-reduction resistance, it is preferable to use a fluororesin as the binder resin. As the fluororesin, the same fluororesin as that described in the dispersant can be used.

[0054] As the fluororesin of this embodiment, for example, polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene are preferable.

[0055] The weight average molecular weight of the fluororesin of this embodiment is preferably from 10,000 to 2,000,000, more preferably from 100,000 to 1,000,000, and particularly preferably from 200,000 to 1,000,000.

[0056] The content of the binder resin in this embodiment is preferably from 1 part by mass to 100 parts by mass, and more preferably from 10 parts by mass to 70 parts by mass, based on 100 parts by mass of the carbon material in the carbon material dispersion composition. When the content of the binder resin is within the above range, a carbon material dispersion composition with good fluidity is easily obtained.

[0057] <Method for producing carbon material dispersion composition> To obtain the carbon material dispersion composition of this embodiment, it is preferable to perform a treatment of dispersing the carbon material in a dispersion medium. The dispersion device used for performing such a treatment is not particularly limited.

[0058] Further, after performing a treatment of dispersing the carbon material and the dispersant in a dispersion medium, it is preferable to mix and homogenize the binder resin in the obtained dispersion composition and use it. As the mixing method, various conventionally known methods can be performed. As the binder resin, it is preferable to use a fluororesin.

[0059] In addition to the carbon material of the present invention, the carbon material dispersion composition of this embodiment may contain single-walled carbon nanotubes other than the carbon material of the present invention. At this time, the carbon material dispersion composition can be produced by various conventionally known methods. Specifically, a carbon material dispersion composition may be prepared and used by dispersing a mixed liquid containing the carbon material of the present invention, single-walled carbon nanotubes, a dispersant, a dispersion medium, and optional components as required. Alternatively, a carbon material dispersion composition (I) containing the carbon material of the present invention and a carbon material dispersion composition (II) containing single-walled carbon nanotubes (except when it is the carbon material dispersion composition (I)) may be prepared and then used. Among them, it is preferable from the viewpoints of stability and battery characteristics that the carbon material dispersion composition (I) contains a carbon material, a dispersant, and a dispersion medium, and the carbon material dispersion composition (II) is a carbon material dispersion composition containing single-walled carbon nanotubes and a fluororesin.

[0060] The order of mixing the carbon material of the present invention, single-walled carbon nanotubes, a dispersant, and a dispersion medium is not particularly limited, and each may be added sequentially, or any two or more of them may be added simultaneously.

[0061] Among them, it is preferable from the viewpoint of suppressing aggregation of the carbon material and gelation of the fluororesin that the production method (I) is a method including the step of (I-1) below, or the production method (II) is a method including the steps of (II-1) to (II-3) below. The production method (II) including the steps of (II-1) to (II-3) below is more preferable. · Production method (I) (I-1) A step of dispersing a mixed liquid containing the carbon material of the present invention, single-walled carbon nanotubes, a fluororesin, and a dispersion medium. · Production method (II) (II-1) A step of dispersing a mixed liquid containing the carbon material of the present invention, a dispersant, and a dispersion medium to produce a carbon material dispersion composition (I). (II-2) A step of producing a carbon material dispersion composition (II) by dispersing a mixed solution containing single-walled carbon nanotubes, a fluororesin, and a dispersion medium. (II-3) A step of mixing the carbon material dispersion composition (I) and the carbon material dispersion composition (II).

[0062] 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-Technique, "Filmix" manufactured by PRIMI X company "Filmix", etc., "Abramix" manufactured by Silverson, etc.), paint conditioner (manufactured by Red Devil), colloid mills ("PUC colloid mill" manufactured by PUC, "Colloid mill MK" manufactured by IKA), corn mills ("Corn mill MKO" manufactured by IKA, etc.), ball mills, sand mills ("Dynomill" manufactured by Shinmaru Enterprises, etc.), attritors, pearl mills ("DCP mill" manufactured by Erie, etc.), media type dispersers such as coball mills, high-pressure homogenizers ("Genius PY" manufactured by Genius, "Starburst" manufactured by Sugino Machine, "Nanomizer" manufactured by Nanomizer, etc.), media-less dispersers such as "Clare SS-5" manufactured by M-Technique, "MICROS" manufactured by Nara Machinery, and other roll mills, etc. can be mentioned, but it is not limited thereto.

[0063] The carbon material dispersion composition of this embodiment preferably has a moisture content of 100 ppm to 1500 ppm, and more preferably 200 ppm to 1000 ppm. When the moisture content of the carbon material dispersion composition is within the above range, gelation of the composite slurry described later is suppressed, and a composite slurry and an electrode film with stable quality are easily obtained.

[0064] The amount of the dispersant in the carbon material dispersion composition of the present embodiment is preferably 10 parts by mass to 100 parts by mass, more preferably 20 parts by mass to 50 parts by mass, based on 100 parts by mass of the carbon material. When the amount of the dispersant in the carbon material dispersion composition is within the above range, the amount of the dispersant adsorbed on the surface of the carbon material is appropriate, and a carbon material dispersion composition excellent in conductivity and dispersion stability can be easily obtained.

[0065] The content of the carbon material in the carbon material dispersion composition of the present embodiment is preferably 0.5% by mass to 5.0% by mass, more preferably 1.0% by mass to 3.5% by mass, still more preferably 1.5% by mass to 3.0% by mass, based on 100% by mass of the carbon material dispersion composition. When the amount of the carbon material in the carbon material dispersion composition is within the above range, when the carbon material dispersion composition is prepared, multi-walled carbon nanotubes are appropriately dispersed, and a carbon material dispersion composition excellent in conductivity and dispersion stability can be easily obtained.

[0066] The initial viscosity of the carbon material dispersion composition of the present embodiment is preferably such that the viscosity measured at 6 rpm using a B-type viscometer is 100 mPa·s or more and less than 10,000 mPa·s, more preferably 500 mPa·s or more and less than 5,000 mPa·s. When the initial viscosity of the carbon material dispersion composition is within the above range, it is considered that the dispersion state of the multi-walled carbon nanotubes contained in the carbon material composition is appropriate and it is easy to form a conductive network.

[0067] The liquidity of the carbon material dispersion composition can be determined by evaluating the thixotropy (TI value) of the carbon material composition as follows. After the carbon material composition is allowed to stand in a thermostatic bath at 25°C for 24 hours, the viscosity is measured at 6 rpm with the B-type viscometer rotor rotation speed, and then the viscosity is measured at 60 rpm. At this time, when the viscosity measured at 6 rpm is S and the viscosity measured at 60 rpm is T, the S / T ratio becomes the TI value. The TI value of the carbon material composition is preferably 2 or more and less than 7, more preferably 3 or more and 5 or less. When the TI value is within the above range, the aspect ratio of the multi-walled carbon nanotubes contained in the carbon material composition is appropriate, and a carbon material composition excellent in conductivity and stability over time can be easily obtained.

[0068] After manufacturing the carbon material dispersion composition of the present embodiment, the viscosity after storage at 60°C for one week, after cooling to 25°C, is preferably 500 mPa·s to 20,000 mPa·s, and more preferably 2,000 mPa·s to 10,000 mPa·s as measured by a B-type viscometer at 25°C with a rotor rotation speed of 6 rpm. It is considered that the carbon material dispersion composition with viscosity within the above range has an appropriate composition ratio and dispersion process of the carbon material, dispersant, and dispersion medium, and good dispersion stability. Since the adsorption reaction of the dispersant contained in the carbon material dispersion composition to the surface of the carbon material is an endothermic reaction, by evaluating the viscosity of the carbon material dispersion composition after storage under high-temperature conditions, it is possible to determine the necessary and sufficient amount of the dispersant in order to obtain a carbon material dispersion composition with excellent dispersion stability.

[0069] ≪Composite Material Slurry≫ The composite material slurry of the present embodiment contains a carbon material dispersion composition and an active material. That is, it contains at least the carbon material, dispersant, dispersion medium, and active material of the present invention, and preferably contains a fluororesin as the dispersant or binder resin.

[0070] <Active Material> The active material of the present embodiment refers to the material that serves as the basis for 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. In this specification, the positive electrode active material and the negative electrode active material may be simply referred to as "active material". The active material refers to the material that serves as the basis for 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.

[0071] The positive electrode active material is not particularly limited, and metal oxides, metal sulfides and other metal compounds capable of doping or intercalating lithium ions, and conductive polymers can be used. For example, oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides can be mentioned. Specifically, MnO, V2O5, V6O 13, transition metal oxide powders such as TiO2, lithium-transition metal composite oxide powders such as layered lithium nickelate, lithium cobaltate, lithium manganate, spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphate compounds, transition metal sulfide powders such as TiS2 and FeS, etc. can be mentioned. Further, conductive polymers such as polyaniline, polyacetylene, polypyrrole, polythiophene, etc. can also be used. Further, the above inorganic compounds and organic compounds may be mixed and used.

[0072] The negative electrode active material is not particularly limited as long as it can dope or intercalate lithium ions. For example, metal Li, alloy systems such as its alloys tin alloy, silicon alloy, lead alloy, etc., metal oxide systems such as LiXFe2O3, LiXFe3O4, LiXWO2 (x is a number where 0 < x < 1), lithium titanate, lithium vanadate, lithium silicate, etc., conductive polymer systems such as polyacetylene, poly-p-phenylene, etc., soft 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, etc. can be mentioned. These negative electrode active materials can also be used alone or in combination of two or more.

[0073] The positive electrode active material is preferably a composite oxide of lithium containing transition metals such as Al, Fe, Co, Ni, Mn, more preferably a composite oxide of lithium containing any one of Al, Co, Ni, Mn, and particularly preferably a composite oxide of lithium containing Ni and / or Mn. When these active materials are used, particularly good effects can be obtained.

[0074] The BET specific surface area of the active material is preferably 0.1 m 2 / g to 10 m 2 / g, more preferably 0.2 m 2 / g to 5 m 2 / g, and even more preferably 0.3 m2 / g to 3 m 2 Those of / g are more preferable.

[0075] The average particle diameter of the active material is preferably in the range of 0.05 μm to 100 μm, more preferably in the range of 0.1 μm to 50 μm. The average particle diameter of the active material as used herein refers to the average value of the particle diameters measured by an electron microscope for the active material.

[0076] <Method for manufacturing composite slurry> To obtain the composite slurry of the present embodiment, it is preferable to perform a dispersion treatment after adding the active material to the carbon material dispersion composition. The dispersion device used for performing such treatment is not particularly limited. The composite slurry can be obtained by using the dispersion device described for the carbon material dispersion composition.

[0077] The content of the active material in the composite slurry is preferably 20% by mass to 85% by mass, particularly preferably 40% by mass to 85% by mass, based on 100% by mass of the composite slurry.

[0078] The content of the carbon material in the composite slurry is preferably 0.05% by mass to 10% by mass, preferably 0.1% by mass to 5% by mass, preferably 0.1% by mass to 3% by mass, based on 100% by mass of the active material.

[0079] The content of the fluororesin in the composite slurry is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, particularly preferably 1% by mass to 5% by mass, based on 100% by mass of the active material.

[0080] The solid content concentration of the composite slurry is preferably 30% by mass to 90% by mass, preferably 40% by mass to 85% by mass, based on 100% by mass of the composite slurry.

[0081] The water content in the composite slurry is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

[0082] <<Electrode>> The electrode film of this embodiment includes a current collector and an electrode film formed from a composite slurry. The electrode film is a coating film of the composite slurry. For example, by coating and drying the composite slurry on the current collector, it is a coating film in which an electrode composite layer is formed.

[0083] The material and shape of the current collector used for the electrode film of this embodiment are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, as the material of the current collector, metals and alloys such as aluminum , copper, nickel, titanium, or stainless steel can be mentioned. Also, 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.

[0084] As a method of coating the composite slurry on the current collector to form the electrode film, there is no particular limitation, and known methods can be used. Specifically, die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method, gravure coating method, screen printing method, or electrostatic coating method, etc. can be mentioned. As the drying method, air drying, hot air dryer, warm air dryer, infrared heater, far-infrared heater, etc. can be used, but it is not particularly limited to these.

[0085] Also, rolling treatment by a flat plate press, calendar roll, etc. may be performed after coating. The thickness of the electrode composite layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0086] <<Secondary Battery>> The secondary battery of this embodiment includes an electrode having the electrode film of the present invention and an electrolyte. The carbon material of the present invention has excellent rate characteristics in order to form a good conductive network in the secondary battery electrode. During charge and discharge, since the active material is uniformly utilized, the deterioration of the active material is less likely to progress. Furthermore, overcharge and over-discharge during charge and discharge are suppressed. Therefore, deterioration of battery characteristics due to electrolyte decomposition or metal precipitation is unlikely to occur, and the cycle characteristics are excellent.

[0087] As the positive electrode, one obtained by coating and drying a composite slurry containing a positive electrode active material on a current collector to produce an electrode film can be used.

[0088] As the negative electrode, one obtained by coating and drying a composite slurry containing a negative electrode active material on a current collector to produce an electrode film can be used.

[0089] As the electrolyte, various conventionally known ones in which ions can move can be used. For example, those containing lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is a phenyl group) can be mentioned, but it is not limited to these, and those containing sodium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0090] 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.

[0091] The secondary battery of this embodiment 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 obtained by subjecting these to hydrophilic treatment.

[0092] The structure of the secondary battery of this embodiment is not particularly limited. Usually, it is composed of a positive electrode and a negative electrode, and a separator provided as needed, and can have various shapes according to the purpose of use, such as a paper type, a cylindrical type, a button type, a laminated type, etc.

[0093] The application of the secondary battery of this embodiment is not particularly restricted. Specifically, it can be used as a power source for consumer devices such as mobile phones, notebook computers, digital cameras, etc., as an emergency power source for hospitals, factories, buildings, etc., and for vehicles such as hybrid vehicles, plug-in hybrid vehicles, electric vehicles, assist bicycles, railway vehicles, etc. The secondary battery, for example, recovers the regenerative energy of the vehicle's power.

[0094] Among them, since it is a secondary battery having high charge and discharge performance and excellent cycle characteristics, it can be suitably used for vehicles, and a vehicle with high safety and expected fuel consumption improvement can be obtained. Furthermore, excellent effects can be exhibited even in the case of vehicle applications where charge and discharge at a large current are desired.

[0095] The mounting position of the secondary battery in the vehicle of the present embodiment is not particularly limited. For example, when mounting the secondary battery in an automobile, the secondary battery can be mounted in the engine room of the vehicle, behind the vehicle body, or under the seat.

Examples

[0096] The present invention will be described more specifically with reference to the following examples. The present invention is not limited to the following examples as long as the gist thereof is not exceeded. Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass". In addition, the compounding amounts in the table are in parts by mass, and except for the solvent, they are values in terms of non-volatile content. Note that the blanks in the table indicate that they are not compounded.

[0097] The materials used in the examples and comparative examples are shown below. <Dispersant> · Polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., K-30, weight average molecular weight 40,000) was hereinafter used as dispersant (A). · Polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., BL-10, weight average molecular weight 15,000) was hereinafter used as dispersant (B). · Hydrogenated nitrile butadiene rubber (dispersant 6 manufactured according to Japanese Patent No. 6933285) was hereinafter used as dispersant (C).

[0098] <Measurement of weight average molecular weight (Mw) of dispersant> The weight average molecular weight (Mw) of the dispersant was measured by gel permeation chromatography (GPC) equipped with an RI detector. HLC-8320GPC (manufactured by Tosoh Corporation) was used as the apparatus, and three separation columns were connected in series. As the packing material, "T" manufactured by Tosoh Corporation was used in order. Using "SK-GEL SUPER AW-4000", "AW-3000", and "AW-2500", the measurement was carried out at an oven temperature of 40 °C using a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide as the eluent at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a concentration of 1% using the solvent consisting of the above eluent and 20 microliters were injected. The weight average molecular weight is a polystyrene equivalent value.

[0099] <Fabrication of Standard Negative Electrode> To a plastic container with a volume of 150 ml, 0.5 parts by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka), 1 part by mass of MAC500LC (sodium carboxymethyl cellulose salt, Sanroze special type MAC500L, manufactured by Nippon Paper Industries Co., Ltd., non-volatile content 100%), and 98.4 parts by mass of water were added, and then using a rotation-revolution mixer (Sinkee's Awatori Rentaro, ARE-310), it was stirred at 2000 rpm for 30 seconds. Furthermore, 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries, CGB-20) and 5 parts by mass of silicon (manufactured by Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5μm, non-volatile content 100%) were added as active materials, and using a high-speed stirrer, it was stirred at 3000 rpm for 10 minutes. Subsequently, 3.1 parts by mass of SBR (TRD2001, manufactured by JSR Corporation) was added, and using the above rotation-revolution mixer, it was stirred at 2000 rpm for 30 seconds to obtain a composite slurry for the negative electrode. Then, the composite slurry for the negative electrode was coated on a copper foil using an applicator so that the basis weight per unit of the electrode was 8 mg / cm 2 After that, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes. Furthermore, rolling treatment was performed using a roll press (manufactured by Sank Metal Co., Ltd., 3t hydraulic roll press) so that the density of the composite layer was 1.6 g / cm 3 A standard negative electrode was fabricated.

[0100] ≪Physical Property Measurement and Evaluation Method≫ The physical property measurement and evaluation methods of the carbon materials, carbon material dispersion compositions, electrode films, and secondary batteries used in the following examples and comparative examples are as follows.

[0101] <BET specific surface area of carbon material> Using an electronic balance (MSA225S100DI, manufactured by Sartorius), 0.03 g of the carbon material was weighed, and then dried while degassing at 110 °C for 15 minutes. Thereafter, using a fully automatic specific surface area measuring device (HM-model1208, manufactured by MOUNTECH), the BET specific surface area of the carbon material was measured.

[0102] <Graphitization degree (B / A ratio) of carbon material> The carbon material was placed in the recess of a glass sample plate (outer diameter 5.0 cm × 3.5 cm, thickness 3 mm, sample part 2.0 cm × 2.0 cm, thickness 2 mm) and flattened using a slide glass. Thereafter, a powder X-ray diffraction analysis sample of the carbon material was placed in a fully automatic multi-purpose X-ray diffractometer (SmartLab, manufactured by Rigaku), and the operation was performed from 15° to 35° for analysis. Sampling was performed every 0.01°, and the scan speed was 1° / min. The voltage was 40 kV, the current was 40 mA, and the X-ray source was CuKα ray. The ratio of the intensities of the two peaks observed at diffraction angle 2θ = 15° to 35° obtained at this time was calculated as follows: The plots appearing at diffraction angle 2θ = 15° to 35° were each subjected to a simple moving average of 11 points, and in the range of diffraction angle 2θ = 20° to 30°, the peak intensity on the low-angle side was designated as A and the peak intensity on the high-angle side was designated as B. At this time, the baseline was the line connecting the plots at 2θ = 16° and 2θ = 34°. The graphitization degree of the carbon material was calculated by the following formula 1. (Formula 1) Graphitization degree of carbon material = B / A The graphitization degree (B / A ratio) of the carbon material is α; 1.0 or more and less than 1.5 β; 1.5 or more and 2.5 or less γ; exceeding 2.5 -: less than 1.0 or having one peak

[0103] <Carbon purity of carbon material> The carbon material was acid-digested using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General) to extract the metals contained in the carbon material. Subsequently, analysis was performed using a multi-type ICP emission spectrometer (720-ES, manufactured by Agilent), and the amount of metals (total amount of iron, cobalt, magnesium, aluminum, copper, nickel, zirconia, molybdenum) contained in the extract was calculated. The carbon purity of the carbon material was calculated as follows. Carbon purity (%) of carbon material = ((carbon material mass - metal amount) ÷ carbon material mass) × 100

[0104] <G / D ratio of carbon material> The carbon material 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 cm -1 ~3000 cm -1 The carbon material for measurement was aliquoted onto a slide glass and flattened using a spatula. Among the obtained peaks, the maximum peak intensity in the spectrum within the range of 1560 cm -1 ~1600 cm -1 was defined as G, and the maximum peak intensity within the range of 1310 cm -1 ~1350 cm -1 was defined as D, and the ratio of G / D was defined as the G / D ratio of the carbon material.

[0105] <Average outer diameter of carbon material> Using an electronic balance (MSA225S100DI, manufactured by Sartorius), 0.2 g of the carbon material was weighed into a 450 mL SM sample bottle (manufactured by Sansho Co., Ltd.), 200 mL of toluene was added, and an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, manufactured by BRANSON) was used , dispersion treatment was carried out under ice-cooling at 30% amplitude for 5 minutes to adjust the carbon material dispersion composition. Then, the carbon material dispersion composition was appropriately diluted, several μL was dropped in the form of a collodion film, and after drying at room temperature, observation was carried out directly using a transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.). Observation was carried out at a magnification of 50,000 times, and a plurality of photos containing 10 or more multi-walled CNTs in the field of view were taken, and the outer diameters of 300 arbitrarily extracted multi-walled CNTs were measured, and the average value was taken as the average outer diameter (nm) of the carbon material.

[0106] <Volume resistivity of carbon material> Using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: Loresta GP powder resistivity measuring system MCP-PD-51), with a sample mass of 1.2 g, using a powder probe unit (four-probe · ring electrode, electrode interval 5.0 mm, electrode radius 1.0 mm, sample radius 12.5 mm), with the applied voltage limiter set to 90 V, the volume resistivity [Ω·cm] of the carbon material under various pressures was measured. At a density of 1 g / cm 3 The value of the volume resistivity of the carbon material was calculated. The evaluation of the conductivity of the carbon material was based on 1.0×10 ―2 Ω·cm or more and less than 2.0×10 ―2 Ω·cm: ++ (excellent), 2.0×10 ―2 Ω·cm or more and less than 3.0×10 ―2 Ω·cm: + (good), 3.0×10 ―2 Ω·cm or more: - (poor).

[0107] <Initial viscosity of carbon material dispersion composition> After leaving the carbon material dispersion composition in a constant temperature bath at 25°C for 1 hour or more, the carbon material dispersion composition was immediately measured at a B-type viscometer rotor rotation speed of 6 rpm. For the measurement, a No. 3 rotor was used. When the initial viscosity was less than 200 mPa·s, a No. 2 rotor was used. The evaluation criteria for the initial viscosity were 500 mPa·s or more and less than 5,000 mPa·s: ++ (excellent), 100 mPa·s or more and less than 500 mPa·s or 5,000 mPa·s or more and less than 10,000 mPa·s: + (good), less than 100 mPa·s or 10,000 mPa·s or more: - (poor)

[0108] <Thixotropy (TI value) of carbon material dispersion composition> After leaving the carbon material dispersion composition to stand in a thermostat at 25°C for 24 hours, the carbon material dispersion composition was sufficiently stirred and then immediately measured at a B-type viscometer rotor rotation speed of 6 rpm. Then, it was immediately measured at a B-type viscometer rotor rotation speed of 60 rpm. When the viscosity measured at 6 rpm was designated as S and the viscosity measured at 60 rpm was designated as T, S / T was defined as the TI value. The evaluation criteria for the TI value were as follows: 3 or more and less than 5: ++ (excellent), 2 or more and less than 3 or 5 or more and less than 7: + (good), less than 2 or 7 or more: - (poor).

[0109] <Storage stability of carbon material dispersion composition> After leaving the carbon material dispersion composition to stand in a thermostat at 60°C for 7 days, it was transferred to a thermostat at 25°C, and the C NT dispersion composition was left to stand until it reached 25°C. Then, measurements were taken at a B-type viscometer rotor rotation speed of 6 rpm. For the measurements, a No. 3 rotor was used. The evaluation criteria for storage stability were as follows: 2,000 mPa·s or more and 10,000 mPa·s or less: ++ (excellent), 500 mPa·s or more and less than 2,000 mPa·s or exceeding 10,000 mPa·s and less than 20,000 mPa·s: + (good), less than 500 mPa·s or exceeding 20,000 mPa·s: - (poor).

[0110] <Volume resistivity of electrode film> The composite material slurry was applied using an applicator so that the weight per unit area of the electrode was 20 mg / cm 2After coating on the aluminum foil so as to achieve [the desired condition], the coating film was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, using Loresta GP, MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd., the surface resistivity (Ω / sq) of the dried coating film was measured. After the measurement, it was multiplied by the thickness of the electrode composite layer formed on the aluminum foil to obtain the volume resistivity (Ω·cm) of the electrode film. The thickness of the electrode composite layer was obtained by subtracting the film thickness of the aluminum foil from the average value measured at three points in the electrode film using a film thickness gauge (DIGIMICRO MH-15M manufactured by NIKON Corporation), and used as the volume resistivity (Ω·cm) of the electrode film. The evaluation criteria for the volume resistivity were set as follows: less than 4 Ω·cm: ++ (excellent), 4 Ω·cm or more and less than 8 Ω·cm: + (good), 8 Ω·cm or more: - (poor).

[0111] <Peeling Strength of Electrode Film> The composite slurry was coated on the aluminum foil using an applicator so that the weight per unit area of the electrode was 20 mg / cm 2 After coating on the aluminum foil so as to achieve [the desired condition], the coating film was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, it was cut into two rectangles of 90 mm × 20 mm with the coating direction as the major axis. For the measurement of the peeling strength, a tabletop tensile tester (Strograph E3 manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used and evaluated by the 180-degree peeling test method. Specifically, a double-sided tape (No. 5000NS, manufactured by Nitto Denko Corporation) with a size of 100 mm × 30 mm was attached to a stainless steel plate, and the fabricated battery electrode composite layer was adhered to the other side of the double-sided tape. It was peeled while pulling upward from below at a constant speed (50 mm / min), and the average value of the stress at this time was taken as the peeling strength. The evaluation criteria for the peeling strength were set as follows: 0.7 N / cm or more: ++ (excellent), 0.5 N / cm or more and less than 0.7 N / cm: + (good), less than 0.5 N / cm: - (poor).

[0112] <Rate Performance Evaluation of Lithium-Ion Secondary Battery> The laminated lithium-ion secondary battery was placed in a thermostatic chamber at 25°C, and charge and discharge measurements were carried out using a charge and discharge device (manufactured by Hokuto Denko Corporation, SM-8). After performing constant current and constant voltage charging (cut-off current 1.0 mA (0.02C)) at a charging current of 10 mA (0.2C) and a charging cut-off voltage of 4.2V, constant current discharge was carried out at a discharge current of 10 mA (0.2C) and a discharge cut-off voltage of 2.5V. After repeating this operation 3 times, constant current and constant voltage charging (cut-off current (1.0 mA 0.02C)) was carried out at a charging current of 10 mA (0.2C) and a charging cut-off voltage of 4.2V, and constant current discharge was carried out at discharge currents of 0.2C and 3C until the discharge cut-off voltage of 2.5V was reached, and the discharge capacities were determined 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 2 below. (Equation 2) Rate performance = 3C discharge capacity / 0.2C discharge capacity at the third cycle × 100 (%) For the rate performance evaluation, those with a rate performance of 80% or more were rated +++ (excellent), those with a rate performance of 70% or more but less than 80% were rated ++ (good), those with a rate performance of 60% or more but less than 70% were rated + (acceptable), and those with a rate performance of less than 60% were rated - (poor). For the cycle performance, those with a cycle performance of 90% or more were rated +++ (excellent), those with a cycle performance of 85% or more but less than 90% were rated ++ (good), those with a cycle performance of 80% or more but less than 85% were rated + (acceptable), and those with a cycle performance of less than 80% were rated - (poor).

[0113] <Evaluation of the cycle performance of lithium-ion secondary batteries> The laminated lithium-ion secondary battery was placed in a thermostatic chamber at 25°C, and charge and discharge measurements were carried out using a charge and discharge device (manufactured by Hokuto Denko Corporation, SM-8). After performing constant current and constant voltage charging (cut-off current 1.25 mA (0.025C)) at a charging current of 50 mA (1C) and a charging cut-off voltage of 4.2V, constant current discharge was carried out at a discharge current of 50 mA (1C) and a discharge cut-off voltage of 2.5V. This operation was repeated 200 times. 1C was defined as the current value that discharges the theoretical capacity of the positive electrode in 1 hour. The cycle performance can be expressed by the ratio of the 1C discharge capacity at the third cycle to the 1C discharge capacity at the 200th cycle at 25°C, as shown in Equation 3 below. (Equation 3) Cycle performance = 1C discharge capacity at the third cycle / 1C discharge capacity at the 200th cycle × 100 (%) The cycle characteristics evaluation was carried out with the cycle characteristics being defined as follows: 90% or more was rated as +++ (excellent), 85% or more but less than 90% was rated as ++ (good), 80% or more but less than 85% was rated as + (acceptable), and less than 80% was rated as - (poor).

[0114] (Example 1-1) 10 kg of a carbon material (multi-walled CNT, manufactured by JEIO Co., Ltd., JENOTUBE6A) was weighed into a 120 L heat-resistant container, and the heat-resistant container containing the carbon material was placed in a furnace. Then, nitrogen gas was introduced into the furnace, and while maintaining a positive pressure, the air in the furnace was discharged. After the oxygen concentration in the furnace reached 0.1% or less, it was heated to 1400 °C over 30 hours. While maintaining the furnace temperature at 1400 °C, chlorine gas was introduced at a rate of 50 L / min for 100 hours. Then, nitrogen gas was introduced at 50 L / min and cooled while maintaining a positive pressure to obtain a carbon material (A) containing multi-walled carbon nanotubes.

[0115] (Examples 1-2 to 1-4), (Comparative Examples 1-1 to 1-2) Carbon materials (B) to (F) containing multi-walled carbon nanotubes were obtained in the same manner as in Example 1-1, except that the furnace temperature was changed to the temperature shown in Table 1. However, Examples 1-3 and Example 1-4 are reference examples.

[0116] (Comparative Examples 1-3 to 1-5) The carbon material (multi-walled CNT, manufactured by KUMHO PETROCHEMICAL Co., Ltd., 100T) was designated as carbon material (G), the carbon material (multi-walled CNT, manufactured by Nanocyl SA, NC7000) was designated as carbon material (H), and the carbon material (multi-walled CNT, manufactured by JEIO Co., Ltd., JENOTUBE6A) was designated as carbon material (I). Carbon material (G) contained 3000 ppm of iron and 1500 ppm of cobalt, carbon material (H) contained 11000 ppm of iron and 3000 ppm of cobalt, and carbon material (I) contained 4000 ppm of iron and 2000 ppm of cobalt.

[0117] (Comparative Examples 1-6 to 1-9) The purified CNT (C) of Japanese Patent Publication No. 6586197 was used as the carbon material (J), the CNT (F) of Japanese Patent Publication No. 6590034 was used as the carbon material (K), the CNT (G) of Japanese Patent Publication No. 6590034 was used as the carbon material (L), and the CNT (D) of Japanese Patent Publication No. 6801806 was used as the carbon material (M).

[0118] (Comparative Examples 1-10) CNT (N) was obtained in the same manner as in Example 1-1, except that the carbon material (CNT, manufactured by JEIO Co., Ltd., JENOTUBE6A) was changed to CNT (manufactured by Nanocyl, NC7000).

[0119] Table 1 shows the evaluation results of the CNTs prepared in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-10. All the carbon materials in the examples had two peaks in the range of diffraction angle 2θ = 24.0° to 27.0°, and Comparative Examples 1-3 to 1-5, 1-7, and 1-9 had one peak.

[0120]

Table 1

[0121] (Example 2-1) To a stainless steel container, 95.5 parts of N-methyl-2-pyrrolidone (NMP) and 1.5 parts by mass of dispersant (A) (polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., K-30, weight average molecular weight 40,000)) were added, and the mixture was stirred with a disper until it became uniform. Then, 3.0 parts by mass of carbon material (A) was taken and 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 8,600 rpm until the whole became uniform and the dispersion particle size became 250 μm or less as measured by a grind gauge. Next, the content of the stainless steel container was fed, and a circulation-type dispersion treatment with a residence time of 10 minutes was carried out using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mmφ. Subsequently, the liquid to be dispersed was supplied to a high-pressure homogenizer through a pipe, and a 15-pass type 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. After that, it was passed through a nylon mesh with an opening of 20 μm through a magnetic filter with a surface magnetic flux density of 17,000 gauss to obtain a carbon material dispersion composition (A1) containing 3.0 parts by mass of carbon material (A).

[0122] (Examples 2-2 to 2-12), (Comparative Examples 2-1 to 2-10) Carbon material dispersion compositions (A2) to (N1) of (Examples 2-2) to (Comparative Examples 2-12) were obtained by the same method except that the carbon material, dispersant, and dispersion conditions listed in Table 2 were changed. However, Examples 2-11 and Example 2-12 are reference examples.

[0123] Table 2 shows the evaluation results of the dispersion compositions prepared in (Examples 2-1 to 2-12) and (Comparative Examples 2-1 to 2-10).

[0124]

Table 2

[0125] (Example 2-13) ><Manufacture of single-walled carbon nanotube dispersion composition (S1)> 97.6 parts of NMP was added to a stainless steel container, and while stirring with a disper, 2.0 parts of polyvinylidene fluoride resin (manufactured by Solvay, Solef 5130) was added, and stirred with a disper until Solef 5130 was dissolved. Then, 0.4 parts of single-walled carbon nanotubes (TUBALL: manufactured by OCSiAl, carbon purity 93%) was weighed and 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 performed at a speed of 8,600 rpm until the whole became uniform. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) through a pipe, and the pass-type dispersion treatment was performed 5 times to obtain a single-walled carbon nanotube dispersion composition (S1). The dispersion treatment was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 60 MPa. The BET specific surface area of the single-walled carbon nanotubes (TUBALL: manufactured by OCSiAl, carbon purity 93%) was 975 m 2 / g.

[0126] <Manufacture of Carbon Material Dispersion Composition> Subsequently, to 66.7 parts of the single-walled carbon nanotube dispersion composition (S1), 33.3 parts of the dispersion composition (A1) prepared in Example 2-1 and 24 parts of NMP were added, and stirred with a disper until it became uniform to obtain a dispersion composition (A1S1-1). The solid content of the dispersion composition (A1S1-1) was 2.5%.

[0127] (Example 2-14) A carbon material dispersion composition (A1S1-2) was obtained in the same manner as in Example 2-13, except that 50 parts of the single-walled carbon nanotube dispersion composition (S1) was used instead of 66.7 parts of the single-walled carbon nanotube dispersion composition (S1), 50 parts of the carbon material dispersion composition (A1) was used instead of 33.3 parts of the carbon material dispersion composition (A1), and 18 parts of NMP was used instead of 24 parts of NMP. The solid content of the carbon material dispersion composition (A1S1-2) was 2.5%.

[0128] (Example 2-15) Instead of using 66.7 parts of single-walled carbon nanotube dispersion composition (S1), 33.3 parts of single-walled carbon nanotube dispersion composition (S1) were used. Instead of using 33.3 parts of carbon material dispersion composition (A1), 66.7 parts of carbon material dispersion composition (A1) were used. Instead of using 24 parts of NMP, 52 parts of NMP were used. Carbon material dispersion composition (A1S1-3) was obtained in the same manner as in Example 2-13. The solid content of the carbon material dispersion composition (A1S1-3) was 2.5%.

[0129] (Example 2-16) Instead of using 66.7 parts of single-walled carbon nanotube dispersion composition (S1), 20 parts of single-walled carbon nanotube dispersion composition (S1) were used. Instead of using 33.3 parts of carbon material dispersion composition (A1), 80 parts of carbon material dispersion composition (A1) were used. Instead of using 24 parts of NMP, 63 parts of NMP were used. Carbon material dispersion composition (A1S1-4) was obtained in the same manner as in Example 2-13. The solid content of the carbon material dispersion composition (A1S1-4) was 2.5%.

[0130] Table 3 shows the evaluation results of the dispersion compositions prepared in Examples 2-13 to 2-16.

[0131]

Table 3

[0132] (Example 3-1) In a plastic container with a volume of 150 cm 3 , 6.3 parts by mass of an NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, manufactured by Solvey, Solef#5130) was dissolved and 20 parts by mass of NMP were weighed. Then, 8.3 parts by mass of the carbon material dispersion composition (A1) were added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation-revolution mixer (Avatomizer, ARE-310). Thereafter, 98.7 parts by mass of the positive electrode active material (manufactured by BASF Toda Battery Materials Co., Ltd., HED (registered trademark) NCM-111 1100) were added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotation-revolution mixer (Avatomizer, ARE-310) to obtain a composite slurry (A1).

[0133] Subsequently, the composite material slurry (A1) was applied onto the aluminum foil using an applicator so that the basis weight per unit of the electrode was 20 mg / cm 2 . After that, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes to obtain the electrode film (A1). Then, the electrode film (A1) was subjected to rolling treatment using a roll press (manufactured by Sanku Metal, 3t hydraulic roll press) to obtain the positive electrode (A1). The basis weight per unit of the composite material layer was 20 mg / cm 2 , and the density of the composite material layer after the rolling treatment was 3.1 g / cc.

[0134] (Examples 3-2 to 3-16), (Comparative Examples 3-1 to 3-10) As described in Table 4, composite material slurries (A2) to (N1) were obtained in the same manner as the production of the composite material slurry (A1), except that the dispersion compositions (A2) to (N1) were used instead of the dispersion composition (A1). Subsequently, as described in Table 4, electrode films (A2) to (N1) and positive electrodes (A2) to (N1) were produced in the same manner as the production of the positive electrode (A1), except that the composite material slurry (A1) was changed to the composite material slurries (A2) to (N1). However, Examples 3-11 and Example 3-12 are reference examples.

[0135] Table 4 shows the evaluation results of the electrode films produced in (Examples 3-1 to 3-16) and (Comparative Examples 3-1 to 3-10).

Table 4

[0136] (Example 4-1) The positive electrode (A1) and the standard negative electrode were each punched out to 45 mm × 40 mm and 50 mm × 45 mm, and a separator (porous polypropylene film) inserted therebetween was inserted into an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Thereafter, in a glove box filled with argon gas, an electrolytic solution (a mixed solvent prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate at a ratio of 1:1:1 (volume ratio), and further, as an additive, 2 parts by mass of VC (vinylene carbonate) was added to 100 parts by mass of the mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M non-aqueous electrolytic solution) was injected in an amount of 2 mL, and then the aluminum laminate was sealed to fabricate a laminate type lithium ion secondary battery (A1).

[0137] (Examples 4-2 to 4-16), (Comparative Examples 4-1 to 4-10) Laminate type lithium ion secondary batteries (A2) to (N1) were fabricated in the same manner as the fabrication of the laminate type lithium ion secondary battery (A1), except that the positive electrodes listed in Table 5 were changed. However, Examples 4-11 and Example 4-12 are reference examples.

[0138] Table 5 shows the evaluation results of the lithium ion secondary batteries fabricated in (Examples 4-1 to 4-16), (Comparative Examples 4-1 to 4-10).

[0139]

Table 5

[0140] In the above examples, the BET specific surface area of the carbon material was 400 m 2 / g to 650 m 2 / g, and a carbon material having two peaks in the range of diffraction angle 2θ = 24.0° to 27.0° was used in the powder X-ray diffraction analysis. In the examples, compared with the comparative examples, the carbon material dispersion composition was excellent in stability over time, and the electrode film using the same had excellent volume resistivity and peel strength, and a lithium-ion secondary battery with excellent rate characteristics and cycle characteristics was obtained. Therefore, it has become clear that the present invention can provide a lithium-ion secondary battery having high capacity, high output, and high durability, which is difficult to achieve with conventional carbon material dispersion compositions. It was confirmed that a vehicle having the lithium-ion secondary battery of the present invention has high charge and discharge performance and excellent cycle characteristics, so that a vehicle with high safety and improved fuel efficiency can be obtained.

[0141] As described above, the present invention of the application has been described with reference to the embodiments, but the present invention of the application is not limited by the above. Various changes that can be understood by those skilled in the art within the scope of the invention can be made to the configuration and details of the present invention of the application.

Claims

Claim 1 A method for producing a carbon material, comprising: the following step <1> and / or step <2>, wherein the carbon material contains multi-walled carbon nanotubes and satisfies the following (1) and (2): A method for producing a carbon material. (1) In the Raman spectrum, when the maximum peak intensity within the range of 1560 cm -1 to 1600 cm -1 is defined as G, and the maximum peak intensity within the range of 1310 cm -1 to 1350 cm -1 is defined as D, the G / D ratio is 1.0 to 2.

2. (2) In powder X-ray diffraction analysis, having at least two peaks in the range of diffraction angle 2θ = 24.0° to 27.0°. Step <1>: A step of heat-treating a carbon material containing 1000 ppm to 10000 ppm of iron and / or cobalt at 1400°C to 1500°C In the Raman spectrum of Engineering <2>, the maximum peak intensity within the range of 1560 cm -1 to 1600 cm -1 is defined as G, and when the maximum peak intensity within the range of 1310 cm -1 to 1350 cm -1 is defined as D, a step of heat-treating a carbon material with a G / D ratio of less than 1.0 at 1400°C to 1500°C Claim 2 The method for producing a carbon material according to Claim 1, wherein the carbon purity of the carbon material is 99.9% or more. Claim 3 The method for producing a carbon material according to Claim 1 or 2, wherein the average outer diameter of the carbon material is 4 nm to 25 nm. Claim 4 The volume resistivity of the carbon material is 2.0×10 -2 Ω·cm or less, and the method for producing the carbon material according to claim 1 or 2. Claim 5 The BET specific surface area of the carbon material is 400 m 2 / g to 650 m 2 / g, and the method for producing the carbon material according to claim 1 or 2.

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