Carbon nanotube dispersion liquid and use thereof

Abstract

The present disclosure relates to a carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a solvent, the carbon nanotube dispersion liquid satisfying the following (1)-(4). (1) When the maximum peak intensity in the range of 1560 cm-1 to 1600 cm-1 is represented by G and the maximum peak intensity in the range of 1310 cm-1 to 1350 cm-1 is represented by D in the Raman spectrum of the carbon nanotubes, the G / D ratio of the carbon nanotubes is 5 to 100 (2) per 100 parts by mass of the carbon nanotubes, G represents the maximum peak intensity in the range of 1560 cm-1 to 1600 cm-1, and D represents the maximum peak intensity in the range of 1310 cm-1 to 1350 cm-1. (3) the complex elastic modulus of the carbon nanotube dispersion at 25 DEG C and a frequency of 1 Hz is 5 Pa or more and less than 650 Pa, and the phase angle is 5 DEG or more and less than 50 DEG; and (4) the BET specific surface area of the carbon nanotubes is 550 m2 / g to 1200 m2 / g.

Description

[0001] This application is a divisional application of the patent application entitled "Carbon Nanotube Dispersion Liquid and Use Thereof" with International Application No. PCT / JP2021 / 037078 filed on October 7, 2021, and entered a national phase in the People's Republic of China on January 31, 2023, with Chinese Patent Application No. 202180058872.1, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The disclosure of the present application is associated with the subject matter described in Japanese Patent Application No. 2020-171017 filed on October 9, 2020, and Japanese Patent Application No. 2021-160281 filed on September 30, 2021, the entire disclosures of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to a dispersion liquid of carbon nanotubes. More specifically, it relates to a carbon nanotube dispersion liquid, a resin composition containing the carbon nanotube dispersion liquid and a binder, a composite material paste containing the carbon nanotube dispersion liquid, a binder, and an active material, an electrode film formed by forming the composite material paste into a film, and a non-aqueous electrolyte secondary battery containing the electrode film and an electrolyte. BACKGROUND

[0004] With the popularization of electric vehicles or the miniaturization and high performance of portable devices, a secondary battery with high energy density is sought, and further, high capacity of the secondary battery is required. Under such a background, due to the characteristics of high energy density and high voltage, non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, using non-aqueous electrolytes are used in a large number of devices.

[0005] As a negative electrode material used in these lithium ion secondary batteries, a carbon material represented 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 have been used to the extent that the charge-discharge capacity per mass approaches the theoretical value, and the energy density per mass of the battery approaches the limit. Therefore, in order to improve the utilization rate as an electrode, attempts are being made to reduce the conductive aid or binder that does not contribute to the discharge capacity.

[0006] As the conductive aid, carbon black, Ketjen black, fullerene, graphene, fine carbon material, etc. are used. In particular, carbon nanotubes, which are one of fine carbon fibers, are used in large amounts. For example, it is known that by adding carbon nanotubes to graphite or silicon negative electrodes, the electrode strength such as the conductivity, adhesion, or expansion and contraction of the electrode, the rate characteristics and cycle characteristics of lithium ion secondary batteries are improved (for example, refer to Patent Document 1). In addition, research has also been conducted to reduce the electrode resistance by adding carbon nanotubes to the positive electrode (for example, refer to Patent Documents 2 and 3). Among them, multi-walled carbon nanotubes with an outer diameter of ten to several tens of nanometers are relatively inexpensive and are expected to be practical.

[0007] If carbon nanotubes with a small average outer diameter are used, a conductive network can be formed efficiently in a small amount, and the amount of conductive aid contained in the positive electrode and the negative electrode for lithium ion secondary batteries can be reduced. In addition, it is known that the same effect is obtained even when carbon nanotubes with a large fiber length are used (for example, refer to Patent Document 4).

[0008] In addition, methods for stabilizing the dispersion of carbon nanotubes using various dispersants have been proposed. For example, dispersion in water and N-methyl-2-pyrrolidone (NMP) using a polymer dispersant such as a water-soluble polymer has been proposed (refer to Patent Documents 1, 5, and 6). In addition, a method for stabilizing the dispersion of multi-walled carbon nanotubes using a nitrile-based rubber as a dispersant has been proposed (refer to Patent Document 7).

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Laid-Open No. 2020-105316

[0012] Patent Document 2: Japanese Patent Laid-Open No. 2011-70908

[0013] Patent Document 3: Japanese Patent Laid-Open No. 2014-19619

[0014] Patent Document 4: Japanese Patent Laid-Open No. 2012-221672

[0015] Patent Document 5: Japanese Patent Laid-Open No. 2010-254546

[0016] Patent Document 6: Japanese Patent Laid-Open No. 2005-162877

[0017] Patent Document 7: Japanese Patent Laid-Open No. 2018-533175 SUMMARY

[0018] PROBLEMS TO BE SOLVED BY THE INVENTION

[0019] However, carbon nanotubes having a small average outer diameter and a large fiber length are difficult to disperse due to strong cohesive force, and thus a carbon nanotube dispersion liquid having sufficient dispersibility cannot be obtained. In Patent Literature 1, single-walled carbon nanotubes are dispersed in an NMP solvent containing polyvinylpyrrolidone using zirconia beads, but there is a problem that the dispersion time is long and the dispersed particle diameter of the carbon nanotubes becomes small, and although the conductivity of the electrode is improved, the electrode strength cannot be sufficiently improved. In Patent Literature 5, oxidized double-walled carbon nanotubes are dispersed in a carboxymethylcellulose aqueous solution using an ultrasonic homogenizer, but it is difficult to disperse the carbon nanotubes at a high concentration in the solvent. In Patent Literature 6, single-walled carbon nanotubes are dispersed in an NMP solvent containing polyvinylpyrrolidone using ultrasonic waves, but it is difficult to disperse the carbon nanotubes at a high concentration in the solvent. In Patent Literature 7, it is proposed that the output characteristics of an electrode are improved by producing a multi-walled carbon nanotube dispersion liquid having a specific complex elastic modulus. However, in multi-walled carbon nanotubes having an outer diameter of 10 nm or more, the electrode strength is not sufficiently improved, and it is difficult to improve the cycle characteristics of a lithium ion secondary battery. Therefore, obtaining a carbon nanotube dispersion liquid in which carbon nanotubes, particularly single-walled carbon nanotubes, as fine carbon fibers are dispersed at a high concentration and uniformly in a dispersion medium is an important issue for expanding the use.

[0020] The present application has been made to solve the above problems, and an object of the present application is to provide a carbon nanotube dispersion liquid having high dispersibility and an elastic modulus, a carbon nanotube resin composition, and a composite material slurry, to obtain an electrode film excellent in electrode strength and conductivity. More specifically, the present application provides a nonaqueous electrolyte secondary battery excellent in rate characteristics and cycle characteristics.

[0021] Technical means for solving the problem

[0022] That is, the present application relates to a carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a solvent, the carbon nanotube dispersion liquid satisfying (1) to (4) below.

[0023] (1) When the maximum peak intensity in the range of 1560 cm -1 to 1600 cm -1 is set as G and the maximum peak intensity in the range of 1310 cm -1 to 1350 cm -1 is set as D in the Raman spectrum of the carbon nanotubes, the G / D ratio of the carbon nanotubes is 5 to 100

[0024] (2) The dispersant is contained at 30 parts by mass or more and less than 250 parts by mass with respect to 100 parts by mass of the carbon nanotubes

[0025] (3) The complex elastic modulus of the carbon nanotube dispersion liquid at 25°C and a frequency of 1 Hz is 5 Pa or more and less than 650 Pa, and the phase angle is 5° or more and less than 50°

[0026] (4) The Brunauer-Emmett-Teller (BET) specific surface area of the carbon nanotubes is 550 m 2 / g to 1200 m 2 / g

[0027] Further, the present application relates to the carbon nanotube dispersion liquid, wherein, when a maximum peak intensity in a range of 1560 cm -1 to 1600 cm -1 is set as G and a maximum peak intensity in a range of 1310 cm -1 to 1350 cm -1 is set as D, the G / D ratio of the carbon nanotubes is 10 to 50.

[0028] Further, the present application relates to the carbon nanotube dispersion liquid, wherein, when a 25°C carbon nanotube dispersion liquid is measured using a rheometer at a shear rate of 1 (s -1 ) or more and less than 40 Pa s.

[0029] Further, the present application relates to the carbon nanotube dispersion liquid, wherein the cumulative particle diameter D10 measured by a dynamic light scattering method is 200 nm or more and less than 500 nm.

[0030] Further, the present application relates to the carbon nanotube dispersion liquid, wherein the volume resistivity of the carbon nanotubes is 1.0 x 10 -3 Ω cm to 1.0 x 10 -2 Ω cm.

[0031] Further, the present application relates to the carbon nanotube dispersion liquid, wherein the cumulative particle diameter D50 measured by a dynamic light scattering method is 500 nm or more and less than 3000 nm.

[0032] Further, the present application relates to the carbon nanotube dispersion liquid, wherein the weight average molecular weight of the dispersant is 10,000 to 100,000.

[0033] Further, the present application relates to the carbon nanotube dispersion liquid, wherein the solvent contains water.

[0034] Further, the present application relates to a carbon nanotube resin composition comprising the carbon nanotube dispersion liquid and a binder.

[0035] Further, the present application relates to a composite material slurry comprising the carbon nanotube resin composition and an active material.

[0036] In addition, the present application relates to an electrode film, which is a coated film of the composite material slurry.

[0037] In addition, the present application relates to a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode includes the electrode film.

[0038] Effects of the Invention

[0039] By using the carbon nanotube dispersion liquid of the present application, a resin composition, a composite material slurry, and an electrode film, each of which has excellent electrode strength and adhesion, can be obtained. In addition, a nonaqueous electrolyte secondary battery, which has excellent rate characteristics and cycle characteristics, can be obtained. Therefore, the carbon nanotube dispersion liquid of the present application can be used in various fields where high conductivity and durability are required. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a graph showing Raman spectra of carbon nanotubes used in Examples and Comparative Examples of the present application. DETAILED DESCRIPTION

[0041] Hereinafter, the carbon nanotube dispersion liquid, the resin composition, the composite material slurry, the electrode film as a coated film of the composite material slurry, and the nonaqueous electrolyte secondary battery of the present application will be described in detail.

[0042] (1) Carbon Nanotube

[0043] The carbon nanotube of the present embodiment is preferably a single-layer carbon nanotube. The single-layer carbon nanotube and the multi-layer carbon nanotube can be present in mixture. The single-layer carbon nanotube has a structure in which one layer of graphite is wound, and the multi-layer carbon nanotube has a structure in which two or more layers of graphite are wound.

[0044] The average outer diameter of the carbon nanotube of the present embodiment is 0.5 nm to 5 nm, preferably 1 nm to 3 nm, and more preferably 1 nm to 2 nm. As for the average outer diameter of the carbon nanotube, the morphology of the carbon nanotube can be observed using a transmission electron microscope (manufactured by JEOL Ltd.), the length of 100 short axes can be measured, and the average value can be calculated based on the number.

[0045] The BET specific surface area of the carbon nanotube of the present embodiment is 550 m 2 / g to 1200 m 2 / g, preferably 600 m 2 / g to 1200 m 2 / g, and more preferably 800 m 2 / g to 1200 m 2 / g, and further preferably 800 m2 / g ~ 1000 m 2 / g.

[0046] Regarding the carbon nanotube of the present embodiment, when a maximum peak intensity in the range of 1560 cm -1 ~ 1600 cm -1 is set as G, and a maximum peak intensity in the range of 1310 cm -1 ~ 1350 cm -1 is set as D, the G / D ratio is 5 ~ 100, more preferably 10 ~ 50, and further preferably 20 ~ 50. The Raman spectrum can be measured in accordance with Raman spectroscopy using laser light of wavelength 532 nm.

[0047] The volume resistivity of the carbon nanotube of the present embodiment is preferably 1.0 x 10 -3 Ω·cm ~ 3.0 x 10 -2 Ω·cm, more preferably 1.0 x 10 -3 Ω·cm ~ 1.0 x 10 -2 Ω·cm. The volume resistivity of the carbon nanotube 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).

[0048] The carbon purity of the carbon nanotube of the present embodiment is represented by the content (%) of carbon atoms in the carbon nanotube. The carbon purity is preferably 80 mass% or more, more preferably 90 mass% or more, and further preferably 95 mass% or more, with respect to 100 mass% of the carbon nanotube.

[0049] The amount of metal contained in the carbon nanotube of the present embodiment is preferably 20 mass% or less, more preferably 10 mass% or less, and further preferably 5 mass% or less, with respect to 100 mass% of the carbon nanotube. As the metal contained in the carbon nanotube, metals such as cobalt, nickel, aluminum, magnesium, silicon dioxide, manganese, and molybdenum, alloys of these metals, metal oxides of these metals, and composite oxides of these metals can be exemplified.

[0050] The carbon nanotube of the present embodiment can be a carbon nanotube that has been subjected to surface treatment. Alternatively, the carbon nanotube can be a carbon nanotube derivative to which a functional group represented by a carboxyl group has been imparted. Alternatively, a carbon nanotube that has encapsulated therein an organic compound, a metal atom, or a substance represented by a fullerene can be used.

[0051] The carbon nanotubes of the present embodiment can also be carbon nanotubes that have been subjected to a pulverization treatment. The so-called pulverization treatment is a treatment in which a pulverizer having a pulverizing medium such as a bead or a steel ball is used to pulverize the carbon nanotubes without substantially intervening a liquid substance, and is also referred to as dry pulverization. The pulverization is performed using a pulverizing force or a destructive force generated by the collision of the pulverizing medium with each other. The pulverization has an effect of making secondary particles of the carbon nanotubes smaller, and can improve the dispersibility of the carbon nanotubes. As the dry pulverization device, a known method such as a dry grinder, a ball mill, a vibration mill, a bead mill, or the like can be used, and the pulverization time can be arbitrarily set according to the device.

[0052] The carbon nanotubes of the present embodiment can also be carbon nanotubes that have been manufactured by any method. The carbon nanotubes can generally be manufactured by a laser ablation method, an arc discharge method, a thermal chemical vapor deposition (CVD) method, a plasma CVD method, and a combustion method, but are not limited thereto.

[0053] (2) Dispersant

[0054] The dispersant of the present embodiment is not particularly limited in a range in which the carbon nanotubes can be stably dispersed, and a surfactant, a resin-type dispersant can be used. The surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric. The dispersant of a preferred kind can be used in a preferred blending amount as appropriate in accordance with the characteristics required for the dispersion of the carbon nanotubes.

[0055] In the case of selecting an anionic surfactant, the kind thereof is not particularly limited. Specifically, a fatty acid salt, a polysulfonic acid salt, a polycarboxylic acid salt, an alkyl sulfate salt, an alkyl aryl sulfonic acid salt, an alkyl naphthalene sulfonic acid salt, a dialkyl sulfonic acid salt, a dialkyl sulfosuccinic acid salt, an alkyl phosphate salt, a polyoxyethylene alkyl ether sulfate salt, a polyoxyethylene alkyl aryl ether sulfate salt, a naphthalene sulfonic acid formalin condensate, a polyoxyethylene alkyl phosphoric acid sulfonic acid salt, a glycerol borate ester fatty acid ester, and a polyoxyethylene glycerol fatty acid ester can be listed, but are not limited thereto. Further, specifically, sodium dodecylbenzenesulfonate, sodium laurate sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonyl phenyl ether sulfate, and a sodium salt of a β-naphthalene sulfonic acid formalin condensate can be listed, but are not limited thereto.

[0056] In addition, as the cationic surfactant, there are alkylamine salts and quaternary ammonium salts. Specifically, there are, for example, stearylamine acetate, trimethylcocoamine chloride, trimethyltallowamine chloride, dimethyldioleylamine chloride, methyloleylamine diethanol chloride, tetramethylammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfate, cetylpyridinium bromide, 4-alkylmercapto pyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride, but not limited to these. In addition, as the amphoteric surfactant, there are amino carboxylic acid salts, but not limited to these.

[0057] In addition, as the nonionic surfactant, there are, for example, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkylallyl ethers, but not limited to these. Specifically, there are, for example, polyoxyethylene lauryl ether, sorbitan fatty acid ester, and polyoxyethylene octylphenyl ether, but not limited to these.

[0058] The selected surfactant is not limited to a single surfactant. Therefore, two or more surfactants can be combined and used. 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 this time is preferably set to the preferable 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 polycarboxylic acid salt. The nonionic surfactant is preferably a polyoxyethylene phenyl ether.

[0059] In addition, as the resin-type dispersant, there are, for example, cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethylhydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, and the like), polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyacrylonitrile polymers, and the like. Methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and polyacrylonitrile polymers are particularly preferable.

[0060] The carboxymethyl cellulose as the resin-type dispersant can be used in the form of a salt such as a sodium salt of carboxymethyl cellulose, which is obtained by substituting sodium carboxymethyl groups for the hydroxyl groups of carboxymethyl cellulose. The etherification degree of the carboxymethyl cellulose as the resin-type dispersant is preferably 0.5 to 1.5, more preferably 0.6 to 1.0. The etherification degree of the carboxymethyl cellulose can be measured according to a conventional method, specifically according to the method described in the Examples.

[0061] The dispersant of the present embodiment preferably has a weight average molecular weight of 5,000 or more and 300,000 or less, more preferably 10,000 or more and 100,000 or less, and further preferably 10,000 or more and 50,000 or less in terms of pullulan. If a dispersant having a moderate weight average molecular weight is used, the adsorptivity to carbon nanotubes is improved, and the stability of the carbon nanotube dispersion liquid is further improved. In addition, in the case where a dispersant exceeding the range is used, the viscosity of the carbon nanotube dispersion liquid becomes high, and when a dispersing machine such as a high-pressure homogenizer of a nozzle type is passed through a narrow flow path by the dispersed liquid, there is a case where the dispersing efficiency is reduced. Furthermore, the resin-type dispersant sometimes has a binding ability in addition to the dispersing ability, and the resin-type dispersant as described above can be used as an adhesive, and the same kind of resin as the resin-type dispersant can be used as the adhesive. In the case where the same kind of resin as the resin-type dispersant is used as the adhesive, a resin having a weight average molecular weight larger than that of the resin-type dispersant is preferably used.

[0062] Here, the weight average molecular weight (Mw) of the dispersant can be measured using a gel permeation chromatography (GPC) equipped with a differential refractive index (RI) detector, and is a value in terms of pullulan.

[0063] In addition to the dispersant of this embodiment, the mixture may also contain an inorganic base and / or an inorganic metal salt. Preferably, the inorganic base and inorganic metal salt are compounds having at least one of an alkali metal and an alkaline earth metal. Specifically, examples include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals and alkaline earth metals. Furthermore, among these, chlorides, hydroxides, and carbonates of alkali metals and alkaline earth metals are preferred in terms of readily supplying cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred among these.

[0064] In addition to the dispersant of this embodiment, an acid may also be included. By adding an acid, the charge state or the hydrophilic / hydrophobic balance in the dispersion system changes, sometimes improving dispersibility. The type of acid is not particularly limited; one type or a combination of several can be used. Examples include: oxalic acid, lactic acid, citric acid, polyacrylic acid, polystyrene sulfonic acid, acetic acid, malonic acid, hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, etc.

[0065] In addition to the dispersant of this embodiment, an antifoaming agent may also be included. Any commercially available antifoaming agent, wetting agent, hydrophilic organic solvent, water-soluble organic solvent, or other substance with antifoaming effect may be used; one type may be used, or multiple types may be used in combination.

[0066] Examples include: alcohols; ethanol, propanol, isopropanol, butanol, octyl alcohol, hexadecyl alcohol, ethynyl alcohol, ethylene glycol monobutyl ether, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, ethynyl ethylene glycol, polyoxyalkylene glycol, propylene glycol, and other glycols, etc.

[0067] Fatty acid esters; diethylene glycol laurate, glyceryl monoricinoleate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trioleate, polyoxyethylene monolaurate, polyoxyethylene sorbitol monolaurate, natural waxes, etc.

[0068] Amide compounds; polyoxyalkylene amides, acrylate polyamines, etc.

[0069] Phosphate esters; tributyl phosphate, sodium octyl phosphate, etc.

[0070] Metallic soaps; aluminum stearate, calcium oleate, etc.

[0071] Oils and fats; animal and vegetable oils, sesame oil, castor oil, etc.

[0072] Mineral oils: kerosene, paraffin, etc.

[0073] Silicone oils: dimethyl silicone oil, silicone cream, silicone emulsion, organically modified polysiloxane, fluorosilicone oil, etc.

[0074] (3) Solvent

[0075] The solvent of the present embodiment is not particularly limited as long as the carbon nanotubes can be dispersed therein, and is preferably any one selected from the group consisting of water and water-soluble organic solvents, or a mixed solvent containing two or more selected from the group, more preferably contains water. In the case of containing water, it is preferably 95% by mass or more, and further preferably 98% by mass or more, relative to 100% by mass of the solvent, and can also be a single solvent of water.

[0076] As the water-soluble organic solvent, the following can be used: alcohol-based (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol, benzyl alcohol, etc.), polyhydric alcohol-based (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexylene glycol, pentylene glycol, glycerol, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ether-based (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amine-based (ethanolamine, diethanolamine, triethanolamine, N-methyl diethanolamine, N-ethyl diethanolamine, morpholine, N-ethyl morpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethyltriamine, tetramethylpropylenediamine, etc.), amide-based (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl caprolactam, etc.), heterocyclic-based (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidone, gamma-butyrolactone, etc.), sulfoxide-based (dimethyl sulfoxide, etc.), sulfone-based (hexamethylphosphoramide, sulfolane, etc.), lower ketone-based (acetone, methyl ethyl ketone, etc.), and tetrahydrofuran, urea, acetonitrile, etc. Among these, the amide-based water-soluble organic solvent is preferable, and N-methyl-2-pyrrolidone (NMP) is more preferable.

[0077] (4) Carbon nanotube dispersion liquid

[0078] The carbon nanotube dispersion of this embodiment includes carbon nanotubes, a dispersant, and a solvent.

[0079] The carbon nanotube dispersion of this embodiment has a complex elastic modulus of 5 Pa or more and less than 650 Pa at 25°C and a frequency of 1 Hz, preferably 5 Pa or more and less than 400 Pa, and more preferably 10 Pa or more and less than 400 Pa. The complex elastic modulus of the carbon nanotube dispersion reflects the hardness of the dispersion, and there is a tendency for a smaller complex elastic modulus to be associated with better dispersion of carbon nanotubes and lower viscosity of the dispersion. On the other hand, when the fiber length of the carbon nanotubes is large, even with good dispersion, the complex elastic modulus can sometimes be high due to the inherent structural viscosity of the carbon nanotubes.

[0080] The carbon nanotube dispersion of this embodiment has a phase angle of 5° or more and less than 50° at 25°C and a frequency of 1 Hz, more preferably 10° or more and less than 50°. The phase angle refers to the phase shift of a stress wave when the strain applied to the carbon nanotube dispersion is set as a sine wave. In a purely elastic body, it becomes a sine wave with the same phase as the applied strain, and therefore the phase angle is 0°. On the other hand, in a purely viscous body, it becomes a stress wave that has advanced 90°. Carbon nanotube dispersions with a complex elastic modulus and phase angle within the aforementioned range exhibit good dispersion particle size and dispersion state of the carbon nanotubes, making them suitable as carbon nanotube dispersions for improving electrode strength and conductivity.

[0081] The complex elastic modulus and phase angle of the carbon nanotube dispersion can be determined as follows: using a rheometer with a diameter of 35 mm and a 2° cone, dynamic viscoelasticity is measured at 25°C and a frequency of 1 Hz, with a strain rate ranging from 0.01% to 5%. When the measured value includes a decimal point, it is rounded to the nearest integer according to Rule B of Japanese Industrial Standards (JIS) Z8401:1999. Furthermore, when the measured value has one decimal place, the complex elastic modulus of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz is preferably 4.5 Pa or more and less than 650.4 Pa, and the phase angle of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz is preferably 4.5° or more and less than 50.4°.

[0082] In a manner that the fiber length of the carbon nanotubes does not become shorter due to breakage, the carbon nanotubes are uniformly and favorably dispersed in a state that maintains a certain length, and thus a developed conductive network can be formed. Therefore, it is not sufficient that only the viscosity of the conductive material dispersion is low and the dispersibility (apparent) is good, and it is particularly effective to combine the complex modulus and / or the phase angle with the previous indexes such as the viscosity to judge the dispersion state. By setting the complex modulus and / or the phase angle to the range, a conductive material dispersion having good conductivity and electrode strength can be obtained.

[0083] Regarding the viscosity of the carbon nanotube dispersion liquid of the present embodiment, when measured at 25°C using a rheometer at a shear rate of 1 (s -1 ) is preferably 5 Pa-s or more and less than 60 Pa-s, more preferably 10 Pa-s or more and less than 40 Pa-s, and further preferably 20 Pa-s or more and less than 40 Pa-s. In addition, when measured at 25°C using a rheometer at a shear rate of 10 (s -1 ) is preferably 1 Pa-s or more and less than 10 Pa-s. By measuring the shear viscosity at a shear rate of 1 (s -1 ), the dispersibility of the carbon nanotube dispersion liquid can be judged, and in the carbon nanotube dispersion liquid of the range, the dispersed particle diameter and the dispersion state of the carbon nanotubes are good, and it is suitable as a carbon nanotube dispersion liquid for improving the electrode strength and the conductivity.

[0084] The viscosity of the carbon nanotube dispersion liquid can be obtained in the following manner: after the carbon nanotube dispersion liquid is left to stand in a thermostat at 25°C for 1 hour or more, the carbon nanotube dispersion liquid is sufficiently stirred, and then using a cone of 35 mm in diameter and 2°, using a rheometer, the shear viscosity at 25°C, a shear rate of 1 s -1 , and a shear rate of 10 s -1 is measured. In the case where the measured value includes a decimal point, it is rounded to an integer according to the rule B of JIS Z8401:1999.

[0085] The cumulative particle diameter D10 of the carbon nanotube dispersion liquid of the present embodiment measured by the dynamic light scattering method is preferably 200 nm or greater but less than 500 nm, more preferably 200 nm or greater but less than 400 nm, and further preferably 300 nm or greater but less than 400 nm. In addition, the cumulative particle diameter D50 of the carbon nanotube dispersion liquid measured by the dynamic light scattering method is preferably 500 nm or greater but less than 3000 nm, more preferably 500 nm or greater but less than 2000 nm, and further preferably 500 nm or greater but less than 1500 nm. The cumulative particle diameter D10 and the cumulative particle diameter D50 of the carbon nanotube dispersion liquid can be measured using a particle size distribution meter (manufactured by Microtrac-BEL Corporation, Nanotrac UPA, model UPA-EX). The particle diameter measured by the dynamic light scattering method is correlated with the fiber length of the carbon nanotube, and in the carbon nanotube dispersion liquid in which the cumulative particle diameter D10 is in the range, the dispersion state of the carbon nanotube in the dispersion liquid is good.

[0086] In order to obtain the carbon nanotube dispersion liquid of the present embodiment, it is preferable to perform a process of dispersing carbon nanotubes in a solvent. The dispersing device used to perform the process is not particularly limited.

[0087] As the dispersing device, a disperser generally used in pigment dispersion and the like can be used. For example, there can be mentioned: a mixing device such as a disperser, a homomixer, a planetary mixer, and the like, a homogenizer (Advanced Digital Sonifer (registered trademark) MODEL 450DA manufactured by BRANSON Co., Ltd., "clearmix" manufactured by M-technique Co., Ltd., "filmix" manufactured by PRIMIX Co., Ltd., and the like, "abramix" manufactured by Silverson Co., Ltd., and the like), a paint conditioner (manufactured by Red Devil Co.), a colloid mill (PUC colloid mill manufactured by PUC Co., Ltd., "colloid mill MK" manufactured by IKA Co., Ltd.), a cone mill ("cone mill MKO" manufactured by IKA Co., Ltd., and the like), a ball mill, a sand mill ("Dyno-mill" manufactured by SHINMARU ENTERPRISES Co., Ltd., and the like), a grinder, a pearl mill ("DCP mill" manufactured by Eirich Co., Ltd., and the like), a co-ball mill, and the like medium-type disperser, a wet-type jet mill ("Jenius PY" manufactured by Jenius Co., Ltd., "Starburst" manufactured by SUGINO Machine, "nanomizer" manufactured by Nanomizer Co., and the like), "clear SS-5" manufactured by M-technique Co., Ltd., "MICROS" manufactured by Nara Machine Co., and the like mediumless disperser, and other roll mills, but are not limited to these.

[0088] The amount of the carbon nanotubes in the carbon nanotube dispersion liquid of the present embodiment is preferably 0.2 to 1.5 parts by mass, and more preferably 0.4 to 1.2 parts by mass, and even more preferably 0.4 to 1.0 parts by mass, relative to 100 parts by mass of the carbon nanotube dispersion liquid.

[0089] The amount of the dispersant in the carbon nanotube dispersion liquid of the present embodiment is preferably 30 to 250 parts by mass, and more preferably 50 to 150 parts by mass, and even more preferably 50 to 100 parts by mass, relative to 100 parts by mass of the carbon nanotubes.

[0090] The pH of the carbon nanotube dispersion in this embodiment is preferably 6 to 11, more preferably 7 to 11, even more preferably 8 to 11, and particularly preferably 9 to 11. The pH of the carbon nanotube dispersion can be measured using a pH meter (Horiba Manufacturing Co., Ltd., pH Meter F-52).

[0091] (5) Adhesive

[0092] Adhesives are resins used to bond materials such as carbon nanotubes together.

[0093] Examples of adhesives used in this embodiment include: polymers or copolymers comprising ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, methacrylic acid, methacrylate, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc.; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluoropolymers; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified forms or mixtures of these resins, and copolymers, may also be used. Polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid are preferred.

[0094] Carboxymethyl cellulose, used as a binder resin, is preferably of high viscosity; for example, the viscosity of a 1% aqueous solution is preferably 500 mPa·s to 6000 mPa·s, and more preferably 1000 mPa·s to 3000 mPa·s. The viscosity of a 1% aqueous solution of carboxymethyl cellulose can be measured at 25°C using a type B viscometer with a rotor speed of 60 rpm.

[0095] The carboxymethyl cellulose used as an adhesive resin is preferably highly etherified. For example, the degree of etherification is preferably 0.6 to 1.5, more preferably 0.6 to 1.2, and even more preferably 0.8 to 1.2.

[0096] The amount of the binder in the composite material slurry of the present embodiment is preferably 0.5 to 30 mass%, more preferably 1 to 25 mass%, and particularly preferably 2 to 20 mass%, based on 100 mass% of the active material. The kind or amount of the binder is appropriately selected in consideration of the properties of the substances that coexist with the carbon nanotubes, the active material, and the like. For example, in the composite material slurry, the proportion of the carboxymethyl cellulose is preferably 0.5 to 3.0 mass%, more preferably 1.0 to 2.0 mass%, based on 100 mass% of the active material, when the carboxymethyl cellulose is used as the binder.

[0097] The styrene butadiene rubber can be used as a substance generally used as a binder for electrodes, when it is an oil-in-water emulsion. In the composite material slurry, the proportion of the styrene butadiene rubber is preferably 0.5 to 3.0 mass%, more preferably 1.0 to 2.0 mass%, based on 100 mass% of the active material, when the styrene butadiene rubber is used as the binder.

[0098] In the composite material slurry, the proportion of the polyacrylic acid is preferably 1 to 25 mass%, more preferably 5 to 20 mass%, based on 100 mass% of the active material, when the polyacrylic acid is used as the binder.

[0099] In the composite material slurry, the proportion of the polyvinylidene fluoride is preferably 1 to 10 mass%, more preferably 1 to 5 mass%, based on 100 mass% of the active material, when the polyvinylidene fluoride is used as the binder.

[0100] (6) Carbon nanotube resin composition

[0101] The carbon nanotube resin composition of the present embodiment contains carbon nanotubes, a dispersant, a solvent, and a binder.

[0102] To obtain the carbon nanotube resin composition of the present embodiment, it is preferable to mix and homogenize the carbon nanotube dispersion liquid and the binder. As the mixing method, various methods known in the art can be performed. The carbon nanotube resin composition can be produced using the dispersing device described in the carbon nanotube dispersion liquid.

[0103] (7) Composite material slurry

[0104] The composite material slurry of the present embodiment is a substance containing carbon nanotubes, a dispersant, a solvent, a binder, and an active material.

[0105] <Active material>

[0106] The active material in this embodiment is the material that forms the basis of the battery reaction. In terms of electromotive force, the active material is divided into positive electrode active material and negative electrode active material.

[0107] There are no particular limitations on the active material used as the positive electrode; metal compounds such as metal oxides and metal sulfides, as well as conductive polymers, that can be doped or intercalated with lithium ions can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, examples include MnO, V₂O₅, and V₆O. 13 Transition metal oxide powders such as TiO2, lithium-transition metal composite oxide powders such as layered lithium nickelate, lithium cobalt oxide, lithium manganese oxide, and spinel-structured lithium manganese oxide, lithium iron phosphate materials as olivine-structured phosphate compounds, and transition metal sulfide powders such as TiS2 and FeS, etc. Additionally, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Furthermore, the aforementioned inorganic or organic compounds can be mixed and used.

[0108] As a negative electrode active material, there are no particular limitations as long as it can be doped or intercalated with lithium ions. Examples include: metallic Li, alloys such as tin alloys, silicon alloys, and lead alloys, etc. x Fe2O3, Li x Fe3O4, Li x WO2 (where x is a number where 0 < x < 1), lithium titanate, lithium vanadate, lithium silicate and other metal oxides, conductive polymers such as polyacetylene and poly(p-phenylene oxide), amorphous carbonaceous materials such as soft carbon or hard carbon, artificial graphite or natural graphite powders, carbon black, mesophase carbon black, resin-sintered carbon materials, gas-grown carbon fibers, carbon fibers and other carbon-based materials. These negative electrode active materials can be used individually or in combination.

[0109] The anode active material used in this embodiment is preferably a silicon-based anode active material, and more specifically, a silicon-containing anode active material such as silicon alloy or lithium silicate is preferred.

[0110] Examples of silicon-based anode active materials include: so-called metallurgical-grade silicon produced by reducing silicon dioxide with carbon; industrial-grade silicon that reduces impurities by acid treatment or unidirectional solidification of metallurgical-grade silicon; high-purity silicon with different crystal states such as single crystal, polycrystalline, and amorphous produced by reacting silicon to obtain silane; and silicon that adjusts the crystal state or precipitation state while making industrial-grade silicon high-purity through sputtering or electron beam evaporation (EB) methods.

[0111] In addition, as a compound of silicon and oxygen, silicon oxide, or silicon and various alloys, and silicon compounds in which the crystal state of these is adjusted by a quenching method or the like can be exemplified. Among these, a silicon-based negative electrode active material having a structure in which silicon nanoparticles are dispersed in silicon oxide, which is coated with a carbon film on the outside, is preferable.

[0112] The negative electrode active material of the present embodiment is preferably a non-crystalline carbonaceous material such as soft carbon or hard carbon, a synthetic graphite such as a highly graphitized carbon material, or a carbonaceous powder such as natural graphite, in addition to a silicon-based negative electrode active material.

[0113] In the case where the carbonaceous powder such as synthetic graphite or natural graphite is 100 mass%, the amount of the silicon-based negative electrode active material is preferably 3 to 50 mass%, more preferably 5 to 25 mass%.

[0114] The BET specific surface area of the active material of the present embodiment 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 further preferably 0.3 m 2 / g to 3 m 2 / g.

[0115] The average particle diameter of the active material of the present embodiment is preferably in the range of 0.5 μm to 50 μm, more preferably 2 μm to 20 μm. The average particle diameter of the active material referred to in the present specification is an average value of particle diameters measured by electron microscopy on the active material.

[0116] (8) Method for producing composite material slurry

[0117] The composite material slurry of the present embodiment can be produced by various methods known in the art. For example, a method in which an active material is added to a carbon nanotube resin composition to produce a composite material slurry, or a method in which an active material is added to a carbon nanotube dispersion liquid and then a binder is added to produce a composite material slurry can be exemplified.

[0118] In order to obtain the composite material slurry of the present embodiment, a process in which an active material is added to a carbon nanotube resin composition and then dispersed is preferably performed. The dispersing device used for the process is not particularly limited. With respect to the composite material slurry, the dispersing device described in the carbon nanotube dispersion liquid can be used to obtain a composite material slurry.

[0119] The amount of the active material in the composite material slurry of the present embodiment is preferably 20 to 85 parts by mass, more preferably 30 to 75 parts by mass, and further preferably 40 to 70 parts by mass, with respect to 100 parts by mass of the composite material slurry.

[0120] The amount of the carbon nanotube in the composite material slurry of the present embodiment is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 5 parts by mass, and even more preferably 0.03 to 1 part by mass, relative to 100 parts by mass of the active material.

[0121] The amount of the solid component in the composite material slurry of the present embodiment is preferably 30 to 90 mass%, more preferably 30 to 80 mass%, and even more preferably 40 to 75 mass%, relative to 100 mass% of the composite material slurry.

[0122] (9) Electrode film

[0123] The electrode film of the present embodiment is formed by forming a composite material slurry. For example, it is a coating film formed by coating a composite material slurry on a current collector and drying to form an electrode composite layer.

[0124] The material or shape of the current collector used in the electrode film of the present embodiment is not particularly limited, and a material and shape suitable for various secondary batteries can be appropriately selected. For example, as the material of the current collector, metals such as aluminum, copper, nickel, titanium, or stainless steel, alloys of these metals, and the like can be listed. In addition, as the shape, a foil on a flat plate can be generally used, but a current collector in which the surface is roughened, a current collector in a punched foil shape, and a current collector in a mesh shape can also be used.

[0125] The method of coating the composite material slurry on the current collector is not particularly limited, and known methods can be used. Specifically, die coater method, dip coater method, roll coater method, blade coater method, knife coater method, spray coater method, gravure coater method, screen printing method, or electrostatic coating method, and the like can be listed, and as the drying method, standing drying, air blowing dryer, warm air dryer, infrared heater, far infrared heater, and the like can be used, but are not particularly limited to these.

[0126] In addition, calendering treatment using a lithographic press or a calender roll, or the like can also be performed after coating. The thickness of the electrode composite layer is generally 1 μm or more and 500 μm or less, and is preferably 10 μm or more and 300 μm or less.

[0127] (10) Non-aqueous electrolyte secondary battery

[0128] The non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, and an electrolyte. It is preferable that at least one of the positive electrode and the negative electrode include the electrode film of the present embodiment.

[0129] As the positive electrode, a material formed by coating a composite material slurry including a positive electrode active material on a current collector, drying, and producing an electrode film can be used.

[0130] As the negative electrode, a material obtained by coating a collector with a slurry of a composite material containing a negative electrode active material, drying it, and forming an electrode film can be used.

[0131] As the electrolyte, various electrolytes known in the past in which ions can move can be used. For example, electrolytes 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 used, but the application is not limited to these, and electrolytes containing sodium salts or calcium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent to be used as an electrolytic solution.

[0132] As the non-aqueous solvent, there is no particular limitation, and 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-octanolactone; glyme 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 can be used. These solvents can be used individually or two or more of them can be mixed and used.

[0133] The non-aqueous electrolyte secondary battery of the present embodiment preferably contains a separator. As the separator, for example, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabric to which a hydrophilic treatment has been applied can be used, but the application is not limited to these.

[0134] The structure of the non-aqueous electrolyte secondary battery of the present embodiment is not particularly limited, and generally includes a positive electrode and a negative electrode, and a separator provided as necessary, and can be produced in various shapes corresponding to the purpose of use such as a paper type, a cylindrical type, a button type, and a stacked type.

[0135] Example

[0136] Hereinafter, the present application will be described more specifically by citing examples. The present application is not limited to the following examples as long as the gist of the present application is not exceeded. In the examples, "carbon nanotube" is sometimes abbreviated as "CNT". Furthermore, "parts" means "mass parts" and "%" means "mass %" unless otherwise specified.

[0137] <Method for measuring physical properties>

[0138] The physical properties of the CNTs used in each of the examples and comparative examples described later were measured using the following methods.

[0139] G / D ratio of CNT

[0140] The CNTs were set on a Raman microscope (XploRA, manufactured by HORIBA Ltd.) and measured using a laser wavelength of 532 nm. The measurement conditions were set to a taking-in time of 60 seconds, a cumulative number of 2, a light reduction filter of 10%, a magnification of the objective lens 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 CNTs for measurement were separated and taken out onto a glass slide, and a spatula was used to flatten them. Among the peaks obtained, the maximum peak intensity in the range of 1560 cm -1 ~ 1600 cm -1 was set as G, and the maximum peak intensity in the range of 1310 cm -1 ~ 1350 cm -1 was set as D, and the G / D ratio was taken as the G / D ratio of the CNTs.

[0141] BET specific surface area of CNT

[0142] After 0.03 g of the CNTs were weighed using an electronic balance (manufactured by Sartorius, MSA225S100DI), they were dried at 110°C while being degassed for 15 minutes. Then, the BET specific surface area of the CNTs was measured using a full-automatic specific surface area measuring device (manufactured by MOUNTECH, model 1208).

[0143] Average outer diameter of CNT

[0144] A CNT dispersion liquid was prepared by weighing 0.2 g of CNT in a 450 mL SM sample bottle (manufactured by Sanmaru Co., Ltd.), adding 200 mL of toluene, and performing dispersion treatment for 5 minutes at an amplitude of 50% under ice cooling using an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, manufactured by BRANSON Co.). Then, the CNT dispersion liquid was diluted as appropriate, and several μL of the liquid was dropped in the form of a collodion film, which was dried at room temperature and then directly observed using a transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.). The observation was performed at a magnification of 50,000 times, and a photograph containing more than 10 CNTs in the field of view was taken. The outer diameter of 300 CNTs arbitrarily extracted from the photograph was measured, and the average value thereof was taken as the average outer diameter (nm) of the CNTs.

[0145] <Volume resistivity of CNT>

[0146] A powder resistivity measuring device (Loresta GP powder resistivity measuring system MCP-PD-51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used to measure the volume resistivity [Ω-cm] of the conductive powder under various pressures by setting the sample mass to 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), and setting the applied voltage limiter to 90 V. The value of the volume resistivity of the CNTs at a density of 1 g / cm 3 was evaluated.

[0147] <Particle size distribution of CNT dispersion liquid>

[0148] After the CNT dispersion liquid was left to stand in a thermostat at 25°C for 1 hour or more, the CNT dispersion liquid was sufficiently stirred and diluted, and then the cumulative particle diameter D10 and the cumulative particle diameter D50 of the CNT dispersion liquid were measured using a particle size distribution meter (Nanotrac UPA, model UPA-EX, manufactured by Microtrac-BEL Co., Ltd.). The permeability was set to absorption, the density of the CNTs was set to 1.8, and the shape was set to non-spherical. The refractive index of the solvent was set to 1.333. The measurement was performed by diluting the concentration of the CNT dispersion liquid so that the value of the loading index would be in the range of 0.8 to 1.2.

[0149] <Complex elastic modulus and phase angle of CNT dispersion liquid>

[0150] The complex modulus and phase angle of the CNT dispersion liquid were evaluated by performing dynamic viscoelasticity measurement at a frequency of 1 Hz at 25°C in a range of a strain rate of 0.01% to 5% using a rheometer (RheoStress 1 rotary rheometer, manufactured by Thermo Fisher Scientific, Inc.) with a cone of 35 mm in diameter and 2°.

[0151] <Viscosity of CNT dispersion liquid>

[0152] After the CNT dispersion liquid was left to stand in a thermostat at 25°C for 1 hour or more, the CNT dispersion liquid was sufficiently stirred, and then the shear viscosity at 25°C at a shear rate of 1 s -1 and 10 s -1 was measured using a rheometer (RheoStress 1 rotary rheometer, manufactured by Thermo Fisher Scientific, Inc.) with a cone of 35 mm in diameter and 2°, whereby the evaluation was performed.

[0153] <Peeling strength of negative electrode film>

[0154] After the negative electrode composite material paste was applied to a copper foil using an applicator in a manner such that the unit area weight per unit of the electrode was 8 mg / cm 2 , the coated film was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, the coated film was cut into two rectangles of 90 mm x 20 mm with the application direction as the long axis. The peeling strength was evaluated using a table tensile tester (strograph E3, manufactured by Toyo Tekko Seizo Co., Ltd.) by a 180-degree peeling test method. Specifically, a double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) of 100 mm x 30 mm was attached to a stainless steel plate so that the battery electrode composite material layer produced was tightly attached to the other side of the double-sided tape, and the stress at the time of peeling while stretching at a certain speed (50 mm / minute) from the lower side to the upper side was taken as the average value, whereby the peeling strength was evaluated.

[0155] <Peeling strength of positive electrode film>

[0156] After the positive electrode composite material paste was applied to a copper foil using an applicator in a manner such that the unit area weight per unit of the electrode was 20 mg / cm 2The positive electrode composite material slurry was applied to the aluminum foil in the same manner as in Example 1, and the coated film was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, the coated film was cut into two 90 mm x 20 mm rectangles with the application direction as the long axis. The peel strength was measured using a tensile testing machine (manufactured by Orient Tech Co., Ltd., strograph E3) by the 180-degree peel test method. Specifically, a 100 mm x 30 mm double-sided tape (No. 5000NS, manufactured by Nitoms) was attached to a stainless steel plate, and the prepared battery electrode composite material layer was attached to the other side of the double-sided tape. The stress at the time of peeling was measured by pulling the double-sided tape from the bottom to the top at a certain speed (50 mm / min), and the average value of the stress was taken as the peel strength.

[0157] <Production of standard positive electrode>

[0158] First, 93 parts by mass of a positive electrode active material (manufactured by BASF TODA Battery Materials, 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 polyvinylidene fluoride (PVDF) (manufactured by Kureha Battery Material Japan, Kureha KF Polymer W#1300) were added to a plastic container having a capacity of 150 cm 3 Then, 20.5 parts by mass of NMP was added, and the mixture was stirred for 30 seconds at 2000 rpm using a self-rotation / revolution mixer (THINKY Co., Ltd., ARE-310). Then, the mixture in the plastic container was mixed to be uniform using a spatula, and stirred for 30 seconds at 2000 rpm using the self-rotation / revolution mixer. Then, 14.6 parts by mass of NMP was added, and stirred for 30 seconds at 2000 rpm using the self-rotation / revolution mixer. Finally, the mixture was stirred for 10 minutes at 3000 rpm using a high-speed stirrer, and a positive electrode composite material slurry was obtained. Then, the positive electrode composite material slurry was applied to an aluminum foil having a thickness of 20 μm as a current collector using an applicator, and dried in an electric oven at 120°C ± 5°C for 25 minutes, so that the weight per unit area of the electrode was adjusted to 20 mg / cm 2The composite layer was then rolled using a roller press (a 3t hydraulic roller press manufactured by Thank-Metal Co., Ltd.) to achieve a density of 3.1 g / cm³. 3 The standard positive electrode.

[0159] <Making a Standard Negative Electrode>

[0160] In a 150 ml plastic container, add 0.5 parts by weight of acetylene black (DENKA BLACK (registered trademark) HS-100, manufactured by DENKA), 1 part by weight of MAC500LC (Sunrose special type MAC500L sodium carboxymethyl cellulose, manufactured by Nippon Paper Corporation, 100% non-volatile components), and 98.4 parts by weight of water. Then, using a rotary mixer (Thinky Corporation, Defoaming Rentarō, ARE-310), stir at 2000 rpm for 30 seconds. Next, add 87 parts by weight of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries) and 10 parts by weight of silicon as active materials, and stir at 3000 rpm for 10 minutes using a high-speed mixer. Subsequently, 3.1 parts by weight of SBR (TRD2001, manufactured by JSR Corporation) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the aforementioned rotary mixer to obtain a composite slurry for the negative electrode. Then, a coating apparatus was used to apply the slurry at a unit area weight of 8 mg / cm² for each electrode unit. 2 The negative electrode was coated onto copper foil using a composite slurry, and then dried in an electric oven at 120℃±5℃ for 25 minutes. Subsequently, the coating was rolled using a roller press (a 3t hydraulic roller press manufactured by Thank-Metal Co., Ltd.) to produce a composite layer with a density of 1.7 g / cm³. 3 The standard negative electrode.

[0161] <Evaluation of the rate characteristics of lithium-ion secondary batteries>

[0162] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 25°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric Co., Ltd., SM-8). Constant current and constant voltage charging was performed at a charging current of 11 mA (0.2 C) with a charging termination voltage of 4.2 V (cutoff current 1.1 mA (0.02 C)). Then, constant current discharging was performed at a discharging current of 11 mA (0.2 C) with a discharging termination voltage of 2.5 V. This operation was repeated three times. Then, constant current and constant voltage charging was performed at a charging current of 11 mA (0.2 C) with a charging termination voltage of 4.2 V (cutoff current 1.1 mA and 0.02 C), followed by constant current discharging at discharging currents of 0.2 C and 3 C until the discharging termination voltage of 2.5 V was reached. The discharge capacity was calculated for each discharge. The rate characteristic is the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, which can be expressed by Equation 1 below.

[0163] (Equation 1) Rate characteristic = 3 C discharge capacity / 0.2 C discharge capacity of the third discharge × 100 (%)

[0164] <Evaluation of Cycle Characteristics of Lithium-ion Secondary Batteries>

[0165] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 25°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric Co., Ltd., SM-8). After constant current and constant voltage charging at a charging current of 55 mA (1 C) and a charging termination voltage of 4.2 V (cutoff current 1.38 mA (0.025 C)), constant current discharging was performed at a discharging current of 55 mA (1 C) and a discharging termination voltage of 2.5 V. This operation was repeated 200 times. 1 C is defined as the current value that discharges the theoretical capacity of the positive electrode in 1 hour. The cycle characteristic, the ratio of the 1 C discharge capacity at the third cycle to the 1 C discharge capacity at the 200th cycle at 25°C, can be expressed by the following Equation 2.

[0166] (Equation 2) Cyclic characteristic = (1C discharge capacity at the third cycle / 1C discharge capacity at the 200th cycle) × 100 (%)

[0167] <Synthesis of Dispersant (A)>

[0168] Into a reaction vessel including a gas introduction tube, a thermometer, a condenser, and a stirrer, 100 parts of acetonitrile was charged, and substitution was performed with nitrogen. The reaction vessel was heated to 70°C, and a mixture of 85.0 parts of acrylonitrile, 15.0 parts of acrylic acid, and 5.0 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.; V-65) was added dropwise over 2 hours to perform a polymerization reaction. After the dropwise addition, 0.5 parts of perbutyl O was further added, and the reaction was continued at 70°C for 1 hour. Then, the conversion was confirmed to be over 98% by nonvolatile component measurement, and the dispersion medium was completely removed by concentration under reduced pressure to obtain a dispersant (A). The weight average molecular weight (Mw) of the dispersant (A) was 38,000.

[0169] (Measurement method of weight average molecular weight (Mw))

[0170] The weight average molecular weight (Mw) of the manufactured dispersant (A) was measured using a gel permeation chromatograph (GPC) equipped with an RI detector under the following conditions. The molecular weight was a pullulan conversion value.

[0171] Measurement sample: 0.1 mass% aqueous solution

[0172] Apparatus: HLC-8320 GPC (manufactured by Tosoh)

[0173] Eluent: 0.1 M NaCl aqueous solution

[0174] Column: TSKgel SuperMultipore PW-M (manufactured by Tosoh)

[0175] Flow rate: 1.0 mL / min

[0176] Temperature: 25°C

[0177] Injection amount: 100 μl

[0178] (Measurement method of etherification degree)

[0179] In a 300 mL jointed triangular flask, sodium carboxymethyl cellulose 2.0 g, nitric acid methanol 100 mL were added, and shaken for 2 hours, thereby replacing sodium carboxymethyl cellulose with carboxymethyl cellulose. Then, the carboxymethyl cellulose was suction filtered using a glass filter, and washed with 80% methanol 200 mL. Then, it was replaced with anhydrous methanol 50 mL, suction filtered, and dried at 105°C for 2 hours. 1.0 g to 1.5 g of the dried carboxymethyl cellulose was weighed and put into a 300 mL jointed triangular flask, 80% methanol 15 mL was added to wet it, and 1 / 10 N sodium hydroxide 50 mL was added, and shaken for 2 hours. Then, using phenothalin as an indicator, the excess sodium hydroxide was back-titrated with 1 / 10 N sulfuric acid, and the etherification degree was calculated according to (Formula 3), (Formula 4).

[0180] (Formula 3) A = (50 x F1 - X x F2) / (Y x 10)

[0181] X: sulfuric acid addition amount, Y: weight of dried carboxymethyl cellulose

[0182] F1: factor of sulfuric acid, F2: factor of sodium hydroxide

[0183] (Formula 4) Etherification degree = 0.162A / (1 - 0.058A)

[0184] In Table 1, the CNT used in the examples and comparative examples, the outer diameter of the CNT, the specific surface area of the CNT, the G / D ratio, and the volume resistivity are shown.

[0185] [Table 1]

[0186]

[0187] In Table 2, the dispersants used in the examples, comparative examples, and reference examples are shown.

[0188] [Table 2]

[0189]

[0190] (Example 1)

[0191] In a stainless steel container, 98.25 parts of ion exchange water was added while stirring with a disperser, and 0.75 parts of dispersant (A) was added while stirring with a disperser until it became uniform. Then, 1 part of CNT (A) was weighed out, and was added while stirring with a disperser, and a square hole high shear screen was installed on a high shear mixer (L5M-A, manufactured by SILVERSON), and was dispersed in batches at a speed of 8,600 rpm until the whole became uniform. Subsequently, the dispersed liquid was supplied from the stainless steel container to a high pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINOMACHINE) via a pipe, and was subjected to 5 times of batchwise dispersion treatment, and a CNT dispersion liquid (WA1) was obtained. The dispersion treatment was performed using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0192] (Examples 2 to 15), (Examples 19 to 20), (Comparative Examples 1 to 2)

[0193] The CNT type, CNT addition amount, dispersant type, dispersant addition amount, ion exchange water addition amount, and number of passes described in Table 3 were changed, and a CNT dispersion liquid (WA2 to WF4) was obtained by the same method as Example 1 except for this.

[0194] (Example 16)

[0195] 4 parts by mass of the CNT dispersion liquid (WA1) produced in Example 1, and 6 parts by mass of ion exchange water were weighed out into a plastic container with a capacity of 150 cm 3 . Then, using a self-rotation / revolution mixer (defoaming practice taro manufactured by Thinky Corporation, ARE-310), it was stirred at 2000 rpm for 30 seconds, and a CNT dispersion liquid (WA13) was obtained.

[0196] (Example 17)

[0197] Using the CNT dispersion liquid (WA3) produced in Example 3, a CNT dispersion liquid (WA14) was obtained by the same method as Example 16 except for this.

[0198] (Example 18)

[0199] Using the CNT dispersion liquid (WA11) produced in Example 11, a CNT dispersion liquid (WA15) was obtained by the same method as Example 16 except for this.

[0200] (Example 21)

[0201] In a polypropylene-made bottle container, 20 parts of CNT (C) and 480 parts of zirconia beads having a diameter of 8 mm as a pulverizing medium were charged, and a paint conditioner made by Red Devil Co. was used to perform a pulverizing treatment for 40 minutes. Then, the zirconia beads were separated to recover the CNT (C). Subsequently, 98.38 parts of ion exchange water was added to a stainless steel container, and 1.13 parts of dispersant (C) was added while stirring with a disperser, and the stirring was performed with the disperser until it became uniform. Then, 1.5 parts of the recovered CNT (C) was weighed and added while stirring with a disperser, and a square-hole high-shear screen was installed on a high-shear mixer (L5M-A, made by SILVERSON), and batchwise dispersion was performed at a speed of 8,600 rpm until the whole became uniform. Subsequently, the dispersed liquid was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, made by SUGINO MACHINE) via a pipe, and batchwise dispersion treatment was performed 20 times, and a CNT dispersion liquid (WC27) was obtained. The dispersion treatment was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0202] (Example 22)

[0203] In a stainless steel container, 98.40 parts of ion exchange water was added, and 0.50 parts of dispersant (C) and 0.10 parts of polyacrylic acid (made by FUJIFILM and LIGHT PURE CO., LTD., molecular weight 25000) were added while stirring with a disperser, and the stirring was performed with the disperser until it became uniform. Then, 1.0 parts of CNT (A) was weighed and added while stirring with a disperser, and a square-hole high-shear screen was installed on a high-shear mixer (L5M-A, made by SILVERSON), and batchwise dispersion was performed at a speed of 8,600 rpm until the whole became uniform. Subsequently, the dispersed liquid was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, made by SUGINO MACHINE) via a pipe, and batchwise dispersion treatment was performed 20 times, and a CNT dispersion liquid (WA28) was obtained. The dispersion treatment was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0204] (Comparative Example 3)

[0205] A glass bottle (M-140, made by Pyrex Glass Co., Ltd.) was charged with 1 part of CNT (A), 0.75 parts of dispersant (A), 98.25 parts of ion-exchanged water, and 120 parts of zirconia beads (bead diameter 1.25 mmφ), and a paint conditioner made by Red Devil Co. was used to perform dispersion treatment for 8 hours, after which separation of the zirconia beads was attempted, but the viscosity was high and a CNT dispersion liquid could not be obtained.

[0206] (Comparative Examples 4 to 6)

[0207] The CNT addition amount, dispersion time, and bead diameter described in Table 3 were changed, and after dispersion treatment by the same method as Comparative Example 3, a CNT dispersion liquid (WA17 to WA19) was obtained by separating the zirconia beads.

[0208] [Table 3]

[0209]

[0210]

[0211]

[0212] (Example 23)

[0213] A stainless steel container was charged with 99.3 parts of NMP, and 0.3 parts of dispersant (E) was added while stirring with a disperser, and stirring was performed with the disperser until the dispersant (E) was dissolved. Then, 0.4 parts of CNT (A) was weighed out, and was added while stirring with the disperser, and a square-hole high-shear screen was installed on a high-shear mixer (L5M-A, made by SILVERSON), and batchwise dispersion was performed at a speed of 8,600 rpm until the entire contents became uniform. Subsequently, the dispersed liquid was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, made by SUGINO MACHINE) via a pipe, and batchwise dispersion treatment was performed 20 times, and a CNT dispersion liquid (A20) was obtained. The dispersion treatment was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0214] (Examples 24 to 26)

[0215] The number of passes described in Table 4 was changed, and a CNT dispersion liquid (A21 to A23) was obtained by the same method as Example 23.

[0216] (Comparative Example 7)

[0217] A glass bottle (M-140, made by Pyrex Glass Co., Ltd.) was charged with 0.4 parts of CNT (A), 0.3 parts of dispersant (E), 99.3 parts of NMP, and 120 parts of zirconia beads (bead diameter 1.25 mmφ), and a paint shaker made by Red Devil Co. was used to perform dispersion treatment for 8 hours, followed by separation of the zirconia beads, to obtain a CNT dispersion liquid (A24).

[0218] [Table 4]

[0219]

[0220] The evaluation results of the CNT dispersion liquids produced in Examples 1 to 26 and Comparative Examples 1 to 7 are shown in Table 5. Regarding the evaluation of the phase angle of the CNT dispersion liquid at 25°C at a frequency of 1 Hz, 10 or more and less than 50 was set to O (good), 5 or more and less than 10 was set to Δ (fair), and less than 5 or 50 or more was set to X (not good). Regarding the evaluation of the complex elastic modulus of the CNT dispersion liquid at 25°C at a frequency of 1 Hz, 5 or more and less than 400 was set to O (good), 400 or more and less than 650 was set to Δ (fair), and less than 5 was set to X (not good). Regarding the viscosity evaluation of the CNT dispersion liquid, the shear viscosity at a shear rate of 1 of 20 or more and less than 40 was set to O (excellent), 10 or more and less than 20 or 40 or more and less than 60 was set to O (good), 5 or more and less than 10 was set to Δ (fair), and less than 5 was set to X (not good). Regarding the particle size evaluation of the CNT dispersion liquid, the particle size distribution at a particle size distribution D10 of 200 or more and less than 300 was set to O (excellent), 300 or more and less than 500 was set to O (good), and less than 200 was set to X (not good).

[0221] [Table 5]

[0222]

[0223]

[0224] (Example 28)

[0225] A CNT dispersion liquid (WA1) was weighed out at 0.63 parts by mass, a 2% by mass aqueous solution of carboxymethyl cellulose (CMC) (made by Daicel Finechem Ltd., #1190) was weighed out at 12.5 parts by mass, ion exchange water was weighed out at 13.8 parts by mass, and the volume was made 150 cm 3The CNT dispersion liquid (A20) was weighed into a plastic container. Then, 0.19 parts by mass of the CNT dispersion liquid (A20) was added, and a self-rotation / revolution mixer (defoaming jōtarō, ARE-310) was used to stir for 30 seconds at 2000 rpm, thereby obtaining a CNT resin composition (A20). Then, 36.9 parts of a positive electrode active material (HED (registered trademark) NCM-111 1100, manufactured by BASF TODA Battery Materials Corporation) was added, and the self-rotation / revolution mixer was used to stir for 2.5 minutes at 2000 rpm, thereby obtaining a positive electrode composite material slurry (A20).

[0226] (Examples 29 to 49), (Comparative Examples 8 to 12)

[0227] The CNT dispersion liquid described in Table 6 was changed, and the amount of the CNT dispersion liquid and ion-exchanged water was adjusted so that the CNT was 0.025 parts by mass in 100 parts by mass of the composite material slurry, and otherwise, a CNT resin composition (WA2 to WA19), a negative electrode composite material slurry (WA2 to WA19) were obtained by the same method as Example 28. The nonvolatile content of the negative electrode composite material slurry was set to 48% by mass.

[0228] (Example 50)

[0229] NMP in which 8% by mass of PVDF (Solvey Corporation, Solef #5130) was dissolved was weighed into a plastic container with a capacity of 150 cm 3 The CNT dispersion liquid (A20) was weighed into a plastic container. Then, 0.19 parts by mass of the CNT dispersion liquid (A20) was added, and a self-rotation / revolution mixer (defoaming jōtarō, ARE-310) was used to stir for 30 seconds at 2000 rpm, thereby obtaining a CNT resin composition (A20). Then, 36.9 parts of a positive electrode active material (HED (registered trademark) NCM-111 1100, manufactured by BASF TODA Battery Materials Corporation) was added, and the self-rotation / revolution mixer was used to stir for 2.5 minutes at 2000 rpm, thereby obtaining a positive electrode composite material slurry (A20).

[0230] (Examples 51 to 53), (Comparative Example 13)

[0231] The CNT dispersion liquid described in Table 6 was changed, and otherwise, the CNT resin composition (A21 to A24), the positive electrode composite material slurry (A21 to A24) were obtained by the same method as in Example 50.

[0232] [Table 6]

[0233]

[0234] (Example 54)

[0235] The positive electrode composite material slurry (A20) was applied to a copper foil in a manner that the unit area weight per unit of the electrode was 20 mg / cm 2 in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (A20).

[0236] (Examples 55 to 75), (Comparative Examples 14 to 18)

[0237] The negative electrode composite material slurry described in Table 7 was changed, and otherwise, the electrode film (WA2) to the electrode film (WA19) were obtained by the same method as in Example 54.

[0238] (Example 76)

[0239] The positive electrode composite material slurry (A20) was applied to a copper foil in a manner that the unit area weight per unit of the electrode was 20 mg / cm 2 in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (A20).

[0240] (Examples 77 to 79), (Comparative Example 19)

[0241] The positive electrode composite material slurry described in Table 7 was changed, and otherwise, the electrode film (A21) to the electrode film (A24) were obtained by the same method as in Example 76.

[0242] The evaluation results of the electrode films produced in Examples 54 to 79, Comparative Examples 14 to 19 are shown in Table 7. Regarding the adhesion evaluation, the peeling strength (Ω·cm) of 0.5 or more was set to (excellent), 0.3 or more and less than 0.5 was set to (good), 0.1 or more and less than 0.3 was set to (possible), and less than 0.1 was set to (impossible).

[0243] [Table 7]

[0244]

[0245] (Examples 80 to 101), (Comparative Examples 20 to 24)

[0246] The electrode film (WA1 to WA19) was subjected to rolling treatment using a roll press machine (manufactured by Thank-Metal, 3t oil pressure type roll press machine), and a negative electrode was produced in which the density of the composite material layer was 1.7 g / cm 3

[0247] (Examples 102 to 105), (Comparative Example 25)

[0248] The electrode film (A20 to A24) was subjected to rolling treatment using a roll press machine (manufactured by Thank-Metal, 3t oil pressure type roll press machine), and a positive electrode was produced in which the density of the composite material layer was 3.2 g / cm 3

[0249] The negative and positive electrodes produced in Examples 80 to 105 and Comparative Examples 20 to 25 are shown in Table 8.

[0250] [Table 8]

[0251]

[0252] (Example 106)

[0253] The negative electrode (WA1) and the standard positive electrode were punched out to 50 mm x 45 mm and 45 mm x 40 mm, respectively, and inserted into an aluminum laminated bag together with a separator (porous polypropylene film) interposed therebetween, and dried in an electric oven at 60°C for 1 hour. Then, after injecting 2 mL of an electrolyte solution (a nonaqueous electrolyte solution in which a mixed solvent produced by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate at a ratio of 3:5:2 (volume ratio) was dissolved with LiPF6 at a concentration of 1 M, and 1 part by mass of each of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) was added as an additive with respect to 100 parts by mass of the mixed solvent) in an argon-filled glove box, the aluminum laminated seal was produced to produce a laminated lithium ion secondary battery (WA1).

[0254] (Examples 107 to 127), (Comparative Examples 26 to 30)

[0255] The negative electrode described in Table 9 was changed, and otherwise, a laminated lithium ion secondary battery (WA2 to WA19) was produced by the same method.

[0256] (Example 128)

[0257] ​​The standard negative electrode and the positive electrode (A20) were punched out to 50 mm x 45 mm, 45 mm x 40 mm, respectively, and inserted into an aluminum laminated bag together with a separator (porous polypropylene film) interposed therebetween, and dried in an electric oven at 60°C for 1 hour. Then, after injecting 2 mL of an electrolyte solution (a nonaqueous electrolyte solution prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate at a ratio of 3:5:2 (volume ratio), and further dissolving LiPF6 at a concentration of 1 M after adding 1 mass part of vinylene carbonate (VC) and fluorine ethylene carbonate (FEC) as additives, each 1 mass part, with respect to 100 mass parts of the mixed solvent) in an argon-filled glove box, the aluminum laminated seal was made to produce a laminated lithium ion secondary battery (A20).

[0258] (Examples 129 to 131), (Comparative Example 31)

[0259] The laminated lithium ion secondary batteries (A21 to A24) were produced by the same method except that the positive electrode described in Table 9 was changed.

[0260] [Table 9]

[0261]

[0262]

[0263] The evaluation results of the laminated lithium ion secondary batteries produced in Examples 106 to 131 and Comparative Examples 26 to 31 are shown in Table 10. As for the rate characteristics, the rate characteristics of 80% or more were set to (good), 70% or more and less than 80% were set to (fair), 60% or more and less than 70% were set to (acceptable), and less than 60% were set to (unacceptable). As for the cycle characteristics, the cycle characteristics of 90% or more were set to (good), 85% or more and less than 90% were set to (fair), 80% or more and less than 85% were set to (acceptable), and less than 80% were set to (unacceptable).

[0264] [Table 10]

[0265]

[0266] In the above embodiment, a carbon nanotube dispersion liquid was used, which contains carbon nanotubes, a dispersant, and a solvent, and has a G / D ratio of the carbon nanotubes of 5 to 100, contains 30 parts by mass or more and less than 250 parts by mass of the dispersant with respect to 100 parts by mass of the carbon nanotubes, a complex elastic modulus of the carbon nanotube dispersion liquid at 25°C and a frequency of 1 Hz of 5 Pa or more and less than 650 Pa, and a phase angle of 5° or more and less than 50°. In the embodiment, the adhesiveness of the electrode has a tendency to improve compared to the comparative example. In addition to this, the conductivity and the electrode strength are improved, and thus a lithium ion secondary battery excellent in rate characteristics and cycle characteristics can be obtained. As a result of this, it is clear that the present application can provide a lithium ion secondary battery high in capacity, high in output power, and high in durability, which is difficult to achieve with an existing carbon nanotube dispersion liquid.

[0267] The present application has been described above with reference to the embodiments, but the present application is not limited to the above. Various modifications can be made to the configuration or details of the present application within the scope of the present application, which can be understood by those skilled in the art.

Claims

1. A carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a solvent, wherein the carbon nanotube dispersion satisfies the following (1) to (4). (1) When 1560 cm⁻¹ is used in the Raman spectrum of carbon nanotubes -1 ~1600 cm -1 The maximum peak intensity within the range is set as G, and 1310 cm⁻¹ is used. -1 ~1350 cm -1 When the maximum peak intensity within the specified range is set as D, the G / D ratio of carbon nanotubes is 5–100. (2) The dispersant contains 30 parts by weight or more but less than 250 parts by weight relative to 100 parts by weight of carbon nanotubes. (3) The complex elastic modulus of the carbon nanotube dispersion at 25℃ and 1 Hz is greater than 5 Pa and less than 650 Pa, and the phase angle is greater than 5° and less than 50°. (4) The Buerger specific surface area of ​​carbon nanotubes is 550 m². 2 / g~1200 m 2 / g.

2. The carbon nanotube dispersion according to claim 1, wherein, When 1560 cm⁻¹ is observed in the Raman spectrum of carbon nanotubes... -1 ~1600 cm -1 The maximum peak intensity within the range is set as G, and 1310 cm⁻¹ is used. -1 ~1350 cm -1 When the maximum peak intensity within the range is set to D, the G / D ratio of carbon nanotubes is 10–50.

3. The carbon nanotube dispersion according to claim 1 or 2, wherein, When using a rheometer at a shear rate of 1 (s) -1 When measuring the carbon nanotube dispersion at 25℃, the value was above 5 Pa·s but less than 40 Pa·s.

4. The carbon nanotube dispersion according to any one of claims 1 to 3, wherein, The cumulative particle size D10, determined by dynamic light scattering, is greater than 200 nm but less than 500 nm.

5. The carbon nanotube dispersion according to any one of claims 1 to 4, wherein, The volume resistivity of carbon nanotubes is 1.0 × 10⁻⁶. -3 Ω·cm~1.0×10 -2 Ω·cm.

6. The carbon nanotube dispersion according to any one of claims 1 to 5, wherein, The cumulative particle size D50, determined by dynamic light scattering, is greater than 500 nm but less than 3000 nm.

7. The carbon nanotube dispersion according to any one of claims 1 to 6, wherein, The weight-average molecular weight of the dispersant is 10,000 to 100,000.

8. The carbon nanotube dispersion according to any one of claims 1 to 7, wherein, The solvent contains water.

9. A carbon nanotube resin composition comprising a carbon nanotube dispersion as described in any one of claims 1 to 8, and a binder.

10. A composite slurry comprising the carbon nanotube resin composition as described in claim 9, and an active substance.

11. An electrode film, which is a coating film of the composite slurry as described in claim 10.

12. 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 comprises the electrode membrane as described in claim 11.

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