Carbon nanotube dispersion, resin composition, composite material slurry and preparation method thereof, electrode film and non-aqueous electrolyte secondary battery

Abstract

The present invention provides a carbon nanotube dispersion, a resin composition, a composite material slurry, a method for preparing the same, an electrode film, and a non-aqueous electrolyte secondary battery. The carbon nanotube dispersion comprises carbon nanotubes, a dispersant, and a solvent. The carbon nanotubes in the carbon nanotube dispersion include first carbon nanotubes having an average outer diameter of 0.5 nm to 5 nm and second carbon nanotubes having an average outer diameter of 5 nm to 20 nm. The mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:10 to 1:100.

Description

Technical Field

[0001] The present invention relates to a carbon nanotube dispersion. More specifically, it relates to a carbon nanotube dispersion, a resin composition comprising the carbon nanotube dispersion and a resin, a composite slurry comprising the carbon nanotube dispersion, a resin, and an active material, a method for preparing the same, an electrode film formed by forming the composite slurry into a film, and a non-aqueous electrolyte secondary battery comprising the electrode film and an electrolyte. Background Art

[0002] With the increasing popularity of electric vehicles and the miniaturization, lightness, and performance of portable devices, there is a growing demand for secondary batteries with high energy density, and consequently, for higher capacity. Against this backdrop, non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, using non-aqueous electrolytes are being used in a wide range of devices due to their high energy density and high voltage.

[0003] As negative electrode materials for these lithium-ion secondary batteries, carbon materials, typified by graphite, are used, due to their low potential, close to that of lithium (Li), and their high charge-discharge capacity per unit mass. However, these electrode materials have been used until their charge-discharge capacity per unit mass approaches their theoretical value, reaching their energy density per unit mass as batteries. Therefore, efforts are underway to increase their utilization as electrodes by reducing conductive additives and binders, which do not contribute to discharge capacity.

[0004] As conductive additives, carbon black, Ketjen black, fullerene, graphene, fine carbon materials, etc. are used. In particular, carbon nanotubes, which are a type of fine carbon fiber, are used in large quantities. For example, it is known that by adding carbon nanotubes to a negative electrode comprising graphite or silicon, the electrode strength such as the conductivity, adhesion, and expansion and contraction of the electrode, as well as the rate characteristics and cycle characteristics of the lithium ion secondary battery are improved (see patent document 1). In addition, research on reducing electrode resistance by adding carbon nanotubes to the positive electrode has also been carried out (see patent document 2 and patent document 3). Among them, multi-layer carbon nanotubes with an outer diameter of ten nanometers to tens of nanometers are relatively cheap and can be expected to be practical.

[0005] 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 the conductive aid contained in the positive pole and the negative pole of the lithium ion secondary battery can be reduced. In addition, it is known that the same effect is also achieved when using carbon nanotubes with large fiber lengths (with reference to patent documentation 4). However, the cohesive force of the carbon nanotubes with these characteristics is strong and difficult to disperse, and therefore, it is impossible to obtain a carbon nanotube dispersion with sufficient dispersibility.

[0006] Therefore, a method for stabilizing the dispersion of carbon nanotubes using various dispersants has been proposed. For example, a dispersion in water and N-methyl-2-pyrrolidone (NMP) using a polymer dispersant such as a water-soluble polymer has been proposed (see Patent Document 1 and Patent Document 5). In Patent Document 1, zirconium oxide beads are used to disperse in an NMP solvent containing polyvinyl pyrrolidone for single-layer carbon nanotubes, thereby improving the conductivity of the electrode and the cycle characteristics of the battery. However, there are problems such as a long dispersion time and a smaller dispersed particle size of the carbon nanotubes, and the specific surface area of ​​the carbon nanotubes becomes larger. Due to the influence of the solid electrolyte interface (SEI) film generated on the surface, the output characteristics are not sufficient. In addition, in Patent Document 5, ultrasonic waves are used to disperse in an NMP solvent containing polyvinyl pyrrolidone for single-layer carbon nanotubes, but it is difficult to disperse the carbon nanotubes in a high concentration in the solvent. In addition, a method has been proposed for stabilizing the dispersion of multilayered carbon nanotubes using nitrile rubber as a dispersant (see Patent Document 6). Patent Document 6 proposes improving the output characteristics of an electrode by preparing a dispersion of multilayered carbon nanotubes with an outer diameter of 10 nm to 30 nm. However, due to the shape and strength of multilayered carbon nanotubes, it is difficult to form conductive pathways like single-walled carbon nanotubes, resulting in insufficient cycling characteristics for lithium-ion secondary batteries.

[0007] Therefore, obtaining a carbon nanotube dispersion with both good cycle and output properties is an important issue facing the expansion of its applications.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-105316

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2011-70908

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2014-19619

[0013] Patent Document 4: Japanese Patent Application Laid-Open No. 2012-221672

[0014] Patent Document 5: Japanese Patent Application Laid-Open No. 2005-162877

[0015] Patent Document 6: Japanese Patent Application No. 2018-533175 Summary of the Invention

[0016] Problems to be solved by the invention

[0017] The present invention aims to provide a highly dispersible carbon nanotube dispersion, carbon nanotube resin composition, and composite slurry to produce an electrode film with excellent conductivity. More specifically, it aims to provide a non-aqueous electrolyte secondary battery with excellent rate and cycle characteristics.

[0018] Technical means to solve the problem

[0019] The inventors of the present invention have conducted extensive research to address the aforementioned issues. They have discovered that by using a carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a solvent, and containing at least two types of carbon nanotubes having different average outer diameters at a specific mass ratio, the properties of the two types of carbon nanotubes can be maximized, resulting in an electrode film with excellent conductivity and a non-aqueous electrolyte secondary battery with good conductive pathways and excellent rate and cycle characteristics.

[0020] That is, one embodiment of the present invention relates to a carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a solvent, wherein the carbon nanotubes in the carbon nanotube dispersion comprise first carbon nanotubes having an average outer diameter of 0.5 nm to 5 nm and second carbon nanotubes having an average outer diameter of 5 nm to 20 nm, and the mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:10 to 1:100.

[0021] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the total Brunauer-Emmett-Teller (BET) specific surface area of ​​the first carbon nanotubes and the second carbon nanotubes contained in the carbon nanotube dispersion is 240 m 2 / g~750m 2 / g.

[0022] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the aspect ratio of the first carbon nanotubes is 2,000 to 10,000, and the aspect ratio of the second carbon nanotubes is 50 to 200.

[0023] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein when the 1560 cm -1 ~1600cm -1 The maximum peak intensity within the range is defined as G, and the peak intensity at 1310 cm -1 ~1350cm -1 When the maximum peak intensity in the range of is defined as D, the G / D ratio is 10-100.

[0024] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the BET specific surface area of ​​the first carbon nanotube is 600 m2 / g~1200m 2 / g.

[0025] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the volume resistivity of the first carbon nanotube is 1.0×10 -3 Ω·cm~3.0×10 -2 Ω·cm.

[0026] Furthermore, another embodiment of the present invention relates to the carbon nanotube dispersion liquid, wherein the complex elastic modulus is 5 Pa or more and less than 650 Pa.

[0027] Furthermore, another embodiment of the present invention relates to the carbon nanotube dispersion liquid, wherein the phase angle is 5° or more and less than 50°.

[0028] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, which is a dispersion containing 0.3 parts by mass or more and 5.0 parts by mass or less of carbon nanotubes in 100 parts by mass of the carbon nanotube dispersion, and has a viscosity of 10 mPa·s or more and less than 2000 mPa·s as measured at 25° C. with a rotor rotation speed of 60 rpm using a Brookfield viscometer.

[0029] Furthermore, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the cumulative particle size D50 measured by a dynamic light scattering method is 400 nm to 4000 nm.

[0030] In addition, another embodiment of the present invention relates to a carbon nanotube resin composition comprising the carbon nanotube dispersion and a binder.

[0031] In addition, another embodiment of the present invention relates to a composite material slurry comprising the carbon nanotube resin composition and an active substance.

[0032] In addition, another embodiment of the present invention relates to a method for producing the composite material slurry, which includes the following steps (1) and (2).

[0033] (1) A step of dispersing a mixed solution containing the first carbon nanotubes, the second carbon nanotubes, a dispersant, and a solvent to obtain a carbon nanotube dispersion.

[0034] (2) A step of mixing the carbon nanotube dispersion obtained in (1), a binder, and an active material.

[0035] In addition, another embodiment of the present invention relates to a method for producing the composite material slurry, which includes the following steps (1) to (3).

[0036] (1) A step of dispersing a mixed solution containing first carbon nanotubes, a dispersant, and a solvent to obtain a first carbon nanotube dispersion.

[0037] (2) A step of dispersing a mixed solution containing the second carbon nanotubes, a dispersant, and a solvent to obtain a second carbon nanotube dispersion.

[0038] (3) A step of mixing the first carbon nanotube dispersion, the second carbon nanotube dispersion, a binder, and an active material.

[0039] Furthermore, another embodiment of the present invention relates to an electrode film obtained by forming the composite material slurry into a film shape.

[0040] Another embodiment of the present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode or the negative electrode of the non-aqueous electrolyte secondary battery includes the electrode film.

[0041] Effects of the Invention

[0042] The embodiments of the present invention can provide a carbon nanotube dispersion liquid, a carbon nanotube resin composition, and a composite material slurry with high dispersibility, and further provide a non-aqueous electrolyte secondary battery with excellent rate characteristics and cycle characteristics. DETAILED DESCRIPTION

[0043] The following describes in detail a carbon nanotube dispersion, resin composition, composite slurry, electrode film as a coating film thereof, and non-aqueous electrolyte secondary battery according to one embodiment of the present invention. Furthermore, in this specification, a numerical range represented by "to" indicates a range that includes the numerical values ​​described before and after the "to" as the minimum and maximum values, respectively. In numerical ranges described in stages throughout this specification, the upper or lower limit of a numerical range in one stage may be arbitrarily combined with the upper or lower limit of a numerical range in another stage.

[0044] Carbon Nanotube Dispersion

[0045] A carbon nanotube dispersion liquid (hereinafter also referred to simply as a dispersion liquid) according to one embodiment of the present invention contains at least carbon nanotubes, a dispersant, and a solvent. Hereinafter, the carbon nanotubes, the dispersant, and the solvent will be described in detail.

[0046] (Carbon Nanotubes)

[0047] The carbon nanotubes (hereinafter also referred to as CNTs) in this embodiment include two or more types of carbon nanotubes having different average outer diameters, and specifically include at least a first carbon nanotube and a second carbon nanotube.

[0048] The average outer diameter of the first carbon nanotube is 0.5 nm or more and less than 5 nm, preferably 1 nm or more and 3 nm or less, more preferably 1 nm or more and 2 nm or less. The average outer diameter of the second carbon nanotube is 5 nm or more and 20 nm or less, more preferably 5 nm or more and 15 nm or less. Regarding the average outer diameter of the carbon nanotubes, the morphology of the carbon nanotubes can be observed using a transmission electron microscope, the length of the minor axis can be measured, and the average value of 300 carbon nanotubes can be calculated. Specifically, regarding the average outer diameter of the carbon nanotubes, for example, a film can be formed using a dilution of the carbon nanotubes, and a direct transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.) can be used for observation at a magnification of 50,000 times, and the outer diameters of 300 randomly extracted carbon nanotubes can be measured, and the average value can be calculated.

[0049] The first carbon nanotube is preferably a single-walled carbon nanotube, and the second carbon nanotube is preferably a multi-walled carbon nanotube. A single-walled carbon nanotube has a structure formed by winding one layer of graphite, and a multi-walled carbon nanotube has a structure formed by winding two or more layers of graphite.

[0050] The first carbon nanotubes are a carbon material with strong cohesion, poor dispersion, and high linearity. Therefore, they are thought to facilitate electrical conduction between active materials that are relatively far apart in the electrode layer, but their probability of contact with the active materials is relatively low. On the other hand, the second carbon nanotubes are a carbon material with weak cohesion, good dispersion, and low linearity. Therefore, they are thought to facilitate electrical conduction between active materials that are relatively close together, and their probability of contact with the active materials is relatively high.

[0051] The mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:10 to 1:100, preferably 1:12 to 1:70, and more preferably 1:15 to 1:40. Within this range, a carbon nanotube dispersion can be obtained that exhibits good dispersibility, excellent conductivity between active materials, a high probability of contact with the active materials, and excellent peel strength (adhesion) for forming an electrode layer.

[0052] Regarding the first carbon nanotube, when the 1560 cm -1 ~1600cm -1 The maximum peak intensity within the range is defined as G, and the peak intensity at 1310 cm -1 ~1350cm -1 When the maximum peak intensity in the range of is defined as D, the G / D ratio is 10 to 100, preferably 10 to 50, and more preferably 20 to 50. The G / D ratio of the second carbon nanotubes is 0.5 or more and less than 10, preferably 0.5 to 4.5, and more preferably 1.0 to 4.0.

[0053] The BET (Brunauer Emmett Teller) specific surface area of ​​the first carbon nanotube is 600 m 2 / g~1200m 2 / g, preferably 600m 2 / g~1000m 2 / g, more preferably 800m 2 / g~1000m 2 / g. The BET specific surface area of ​​the second carbon nanotube is 150m 2 / g~750m 2 / g, preferably 200m 2 / g~750m 2 / g, more preferably 230m 2 / g~750m 2 / g.

[0054] The total BET specific surface area of ​​the carbon nanotubes is preferably 240 m 2 / g~750m 2 / g, more preferably 240m 2 / g~650m 2 / g, more preferably 250m 2 / g~650m 2 / g. The total BET specific surface area can be calculated based on the BET specific surface areas of the first and second carbon nanotubes and the mass ratio of the respective carbon nanotubes. By staying within this range, electrical conductivity between the active materials in the electrode layer is ensured, while the amount of SEI formed on the CNT surface during charge and discharge can be suppressed, thereby improving the battery's output performance.

[0055] The volume resistivity of the first carbon nanotube is preferably 1.0×10 -3 Ω·cm~3.0×10 -2 Ω·cm, more preferably 1.0×10 -3 Ω·cm~1.0×10 -2 Ω·cm. The volume resistivity of the second carbon nanotube is preferably 1.0×10 -2 Ω·cm~3.0×10 -2 Ω·cm, more preferably 1.0×10 -2 Ω·cm~2.0×10 -2 Ω·cm. The volume resistivity of carbon nanotubes can be measured using, for example, a powder resistivity measuring device (Loresta GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0056] The carbon purity of carbon nanotubes is represented by the carbon atom content (mass %) in the carbon nanotubes. The carbon purity is preferably 90 mass % or higher, more preferably 95 mass % or higher, and even more preferably 98 mass % or higher, relative to 100 mass % of the carbon nanotubes.

[0057] The amount of metal contained in the carbon nanotubes is preferably less than 20% by mass, more preferably less than 10% by mass, and even more preferably less than 5% by mass relative to 100% by mass of the carbon nanotubes. Examples of the metal contained in the carbon nanotubes include metals and metal oxides used as catalysts in the synthesis of carbon nanotubes. Specifically, examples include metals such as cobalt, nickel, aluminum, magnesium, silicon dioxide, manganese, and molybdenum, metal oxides, and composite oxides thereof.

[0058] The carbon nanotubes may be surface-treated carbon nanotubes. Alternatively, the carbon nanotubes may be carbon nanotube derivatives endowed with functional groups such as carboxyl groups. Furthermore, carbon nanotubes containing organic compounds, metal atoms, or substances such as fullerenes may also be used.

[0059] The carbon nanotubes in this embodiment may be produced by any method. Carbon nanotubes can generally be produced by laser ablation, arc discharge, thermal chemical vapor deposition (CVD), plasma CVD, and combustion, but are not limited to these methods.

[0060] (Dispersant)

[0061] The dispersant in this embodiment is not particularly limited as long as it can stabilize the dispersion of the carbon nanotubes. For example, surfactants and resin-type dispersants can be used. Surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric surfactants. Depending on the desired properties of the carbon nanotube dispersion, a preferred type of dispersant can be used in a preferred amount.

[0062] When anionic surfactants are selected, their types are not particularly limited. Specifically, for example, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfate salts, alkyl aryl sulfonates, alkyl naphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl aryl ether sulfates, naphthalenesulfonic acid formalin condensates, polyoxyethylene alkyl phosphoric acid sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters can be mentioned, but are not limited to these. Furthermore, specifically, for example, sodium dodecylbenzenesulfonate, sodium laurate sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate salts, and sodium salts of β-naphthalenesulfonic acid formalin condensates can be mentioned, but are not limited to these.

[0063] Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Specific examples include, but are not limited to, stearylamine acetate, trimethyl cocoyl ammonium chloride, trimethyl tallow ammonium chloride, dimethyl dioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride.

[0064] Examples of nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers. Specific examples include, but are not limited to, polyoxyethylene lauryl ether, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ether. Examples of amphoteric surfactants include, but are not limited to, aminocarboxylates.

[0065] 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 anionic and nonionic surfactants, or a combination of cationic and nonionic surfactants, can be used. In this case, the blending amount is preferably set to the optimal blending amount relative to each surfactant component. As a combination, a combination of anionic and nonionic surfactants is preferred. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0066] Specific examples of resin-type dispersants include 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, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and polyacrylonitrile-based polymers. Particularly preferred are methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and polyacrylonitrile-based polymers.

[0067] Carboxymethyl cellulose can be used in the form of a salt such as sodium salt of carboxymethyl cellulose, wherein the sodium salt of carboxymethyl cellulose is obtained by substituting a sodium carboxymethyl group for a hydroxyl group of the carboxymethyl cellulose.

[0068] Dispersant is in the weight average molecular weight that pullulan (pullulan) converts, preferably more than 5000 and less than 300,000, more preferably more than 10,000 and less than 100,000, and then preferably more than 10,000 and less than 50,000.If using the dispersant with appropriate weight average molecular weight, then the adsorptivity to CNT is improved, and the stability of carbon nanotube dispersion liquid is further improved.In addition, in the case of using the dispersant exceeding the scope, the viscosity of carbon nanotube dispersion liquid uplifts, when using the high pressure homogenizer of nozzle type etc. in narrow flow path by the disperser of dispersed liquid, there is the situation that dispersion efficiency reduces.

[0069] In addition to the dispersant, inorganic bases and inorganic metal salts may also be included. The inorganic bases and inorganic metal salts are preferably compounds containing 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. Among these, chlorides, hydroxides, and carbonates of alkali metals and alkaline earth metals are preferred because they can easily supply 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. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred.

[0070] In addition to the dispersant, a defoaming agent may also be included. Any commercially available defoaming agent, such as a wetting agent, a hydrophilic organic solvent, or a water-soluble organic solvent, having a defoaming effect may be used. One type of defoaming agent may be used alone, or a combination of multiple types may be used.

[0071] For example, alcohols; ethanol, propanol, isopropanol, butanol, octyl alcohol, hexadecyl alcohol, acetylene alcohol, ethylene glycol monobutyl ether, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, acetylene glycol, polyoxyalkylene glycol, propylene glycol, other glycols, etc.

[0072] Fatty acid esters; diethylene glycol laurate, glyceryl monoricinoleate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trioleate, polyoxyethylene monolaurate, polyoxyethylene sorbitan monolaurate, natural wax, etc.

[0073] Amide series; polyoxyalkylene amide, acrylate polyamine, etc.

[0074] Phosphate ester series; tributyl phosphate, sodium octyl phosphate, etc.

[0075] Metal soap series; aluminum stearate, calcium oleate, etc.

[0076] Oils and fats: animal and vegetable oils, sesame oil, castor oil, etc.

[0077] Mineral oil: kerosene, paraffin, etc.

[0078] Silicone series: dimethyl silicone oil, silicone paste, silicone emulsion, organic modified polysiloxane, fluorosilicone oil, etc.

[0079] (solvent)

[0080] The solvent in this embodiment is not particularly limited as long as it can disperse the carbon nanotubes, and is preferably any one of water and / or a water-soluble organic solvent, or a mixed solvent containing two or more thereof, more preferably water. When water is included, it is preferably 95% by mass or more, and more preferably 98% by mass or more, relative to the total solvent.

[0081] As water-soluble organic solvents, the following can be used: alcohols (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, tert-butanol, benzyl alcohol, etc.), polyols (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butanediol, hexanediol, pentanediol, glycerol, hexanetriol, thiodiglycol, etc.); polyol ethers (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether); , ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.); amines (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N- Ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.); amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.); heterocyclics (cyclohexylpyrrolidone, 2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.); sulfoxides (dimethyl sulfoxide, etc.); sulfones (hexamethylphosphoric triamide, cyclopentane, etc.); lower ketones (acetone, methyl ethyl ketone, etc.); in addition, tetrahydrofuran, urea, acetonitrile, etc.

[0082] The carbon nanotube dispersion of the present embodiment comprises the carbon nanotubes, a dispersant, and a solvent. Regarding the aspect ratio of the carbon nanotubes in the carbon nanotube dispersion (i.e., the aspect ratio after the dispersion is prepared), the aspect ratio (average fiber length / average outer diameter) of the first carbon nanotube is preferably 2000 to 10000, more preferably 2500 to 7000, and further preferably 3000 to 6000. The aspect ratio of the second carbon nanotube is preferably 50 to 200, more preferably 50 to 150, and further preferably 55 to 120. The aspect ratio of the carbon nanotube can be calculated as follows: the diluted dispersion is dropped onto a mica substrate, and the deposited carbon nanotubes are observed using a scanning electron microscope (SEM) and image analysis is performed. Specifically, the aspect ratio of the carbon nanotube can be calculated, for example, as follows.

[0083] The CNT dispersion was diluted with the solvent in the CNT dispersion to a CNT concentration of 0.01% by mass. A film was formed using the diluted solution and the film was observed by SEM at a magnification of 50,000 times. CNTs with an outer diameter of less than 5 nm were designated as first CNTs, and CNTs with an outer diameter of 5 nm or greater were designated as second CNTs. The average outer diameter of 100 randomly selected CNTs from each of the first and second CNTs was designated as the average outer diameter of the CNTs.

[0084] The film was observed by SEM at a magnification of 5000 to 20,000 times, and the average value of the lengths of 100 randomly selected fibers of each of the first and second CNTs was taken as the average fiber length of the CNTs in the CNT dispersion.

[0085] The value obtained by dividing the average fiber length of CNTs in the CNT dispersion by the average outer diameter of CNTs in the CNT dispersion was defined as the aspect ratio of CNTs in the CNT dispersion.

[0086] The larger the fiber length of carbon nanotubes, the easier it is to ensure the conduction between active materials, and the smaller the outer diameter, the softer it is, and the easier it is to follow the expansion / contraction of the active material with charge and discharge. In addition, although the outer diameter does not change due to dispersion treatment, sometimes the fiber length will be cut off and change. Therefore, it is believed that in the dispersion (that is, after making the dispersion) the high aspect ratio CNT helps to maintain the conductive network, and the low aspect ratio CNT helps to form a uniform conductive network.

[0087] The complex elastic modulus of the carbon nanotube dispersion is preferably 5Pa or more and less than 650Pa, more preferably 5Pa or more and less than 400Pa, and further preferably 10Pa or more and less than 400Pa. The complex elastic modulus of the carbon nanotube dispersion shows the hardness of the carbon nanotube dispersion, and the better the dispersibility of the carbon nanotubes and the lower the viscosity of the carbon nanotube dispersion, the smaller the complex elastic modulus. On the other hand, when the fiber length of the carbon nanotubes is large, even if the dispersion is good, the complex elastic modulus sometimes becomes a high value due to the structural viscosity of the carbon nanotubes themselves. As described later, the complex elastic modulus of the carbon nanotube dispersion can be measured using a rheometer (RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.).

[0088] The phase angle of the carbon nanotube dispersion is preferably 5 ° or more and less than 50 °, more preferably 10 ° or more and less than 50 °. Phase angle refers to the phase offset of stress wave when the strain imparted to the carbon nanotube dispersion is set to a sine wave. If it is a pure elastomer, it becomes a sine wave with the same phase as the imparted strain, so the phase angle is 0 °. On the other hand, if it is a pure viscous body, it becomes a stress wave that has advanced 90 °. In the carbon nanotube dispersion of the range of the value of the complex elastic modulus and the phase angle, the dispersed particle size and the dispersion state of the carbon nanotube are good, and it is suitable as a carbon nanotube dispersion for improving electrode strength and conductivity. As described later, the phase angle of the carbon nanotube dispersion can be measured using a rheometer (rheological stress (RheoStress) 1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.).

[0089] The viscosity of the carbon nanotube dispersion, measured at 60 rpm using a Brookfield viscometer (manufactured by TOKI SANGYO Co., Ltd., VISCOMETER, MODEL: BL), is preferably 10 mPa·s or more and less than 10,000 mPa·s, more preferably 10 mPa·s or more and less than 2,000 mPa·s.

[0090] The cumulative particle size D50 of the carbon nanotube dispersion measured by dynamic light scattering is preferably 400 nm to 4000 nm, more preferably 1000 nm to 3000 nm. The cumulative particle size D50 of the carbon nanotube dispersion can be measured using a particle size distribution analyzer (Nanotrac UPA, model UPA-EX, manufactured by Microtrac-BEL Co., Ltd.).

[0091] To obtain the carbon nanotube dispersion of this embodiment, it is preferred to disperse the carbon nanotubes in a solvent. The dispersing apparatus used for this process is not particularly limited. Furthermore, the order and timing of adding the carbon nanotubes are not particularly limited. Furthermore, the first and second carbon nanotubes may be dispersed simultaneously, or they may be prepared by mixing the obtained dispersions after each dispersion has been obtained.

[0092] As a dispersing device, a disperser commonly used for pigment dispersion, etc. can be used. For example, a disperser, a homomixer, a planetary mixer, and other mixers; homogenizers (Advanced Digital Sonifer (registered trademark), Model 450DA manufactured by Branson, "Clearmix" manufactured by M-technique, "Filmix" manufactured by PRIMIX, "Abramix" manufactured by Silverson, etc.); paint conditioners (manufactured by Red Devil), colloid mills ("PUC Colloid Mill" manufactured by PUC, "Colloid Mill MK" manufactured by IKA); cone mills ("Cone Mill MKO" manufactured by IKA, etc.), ball mills, sand mills (Shinmaru Enterprise Co., Ltd. The present invention also includes media dispersers such as the "Dyno-mill" manufactured by Eirich Enterprises, a grinder, a pearl mill (such as the "DCP mill" manufactured by Eirich), and a co-ball mill, wet jet mills (such as the "Jenius PY" manufactured by Jenius, the "Starburst" manufactured by Sugino Machine, and the "nanomizer" manufactured by Nanomizer), media-free dispersers such as the "Clear SS-5" manufactured by M-technique and the "MICROS" manufactured by Nara Machinery, and other roller mills, but is not limited to these.

[0093] The amount of carbon nanotubes in the carbon nanotube dispersion is preferably 0.3 to 5.0 parts by mass, more preferably 0.5 to 3.0 parts by mass, and still more preferably 0.8 to 1.5 parts by mass, relative to 100 parts by mass of the carbon nanotube dispersion.

[0094] The dispersion preferably contains 0.3 to 5.0 parts by mass of carbon nanotubes per 100 parts by mass of the carbon nanotube dispersion, and has a viscosity of 10 to 2000 mPa·s as measured at 25° C. with a Brookfield viscometer at a rotor rotation speed of 60 rpm.

[0095] The amount of the dispersant in the carbon nanotube dispersion relative to the carbon nanotubes is preferably 20 to 150 parts by mass, more preferably 25 to 100 parts by mass, and even more preferably 30 to 80 parts by mass, per 100 parts by mass of the carbon nanotubes.

[0096] The amount of the dispersant in the carbon nanotube dispersion relative to the first carbon nanotubes is preferably 50 to 250 parts by mass, more preferably 75 to 200 parts by mass, and even more preferably 75 to 150 parts by mass, per 100 parts by mass of the first carbon nanotubes.

[0097] The amount of the dispersant in the carbon nanotube dispersion relative to the second carbon nanotubes is preferably 20 to 150 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 20 to 60 parts by mass, per 100 parts by mass of the second carbon nanotubes.

[0098] The pH of the carbon nanotube dispersion is preferably 6 to 11, more preferably 7 to 11, further preferably 8 to 11, and particularly preferably 9 to 11. The pH of the carbon nanotube dispersion can be measured using a pH meter (pH meter F-52, manufactured by Horiba, Ltd.).

[0099] Adhesives

[0100] The so-called binder is a resin used to bond substances such as carbon nanotubes.

[0101] Examples of the binder in this embodiment include: polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic esters, methacrylic acid, methacrylate, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, and the like as constituent units; polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified products, mixtures, and copolymers of these resins are also possible. Among these, carboxymethyl cellulose, styrene butadiene rubber, and polyacrylic acid are preferred.

[0102] The type and amount ratio of the binder can be appropriately selected in accordance with the properties of coexisting substances such as carbon nanotubes and active materials. For example, regarding the amount of carboxymethyl cellulose used, when the mass of the active material is set to 100 mass%, the proportion of carboxymethyl cellulose is preferably 0.5 mass% to 3.0 mass%, and more preferably 1.0 mass% to 2.0 mass%.

[0103] The carboxymethyl cellulose is preferably a sodium salt of carboxymethyl cellulose in which the hydroxyl groups of the carboxymethyl cellulose are substituted with a carboxymethyl sodium group.

[0104] The viscosity of a 1% aqueous solution of carboxymethyl cellulose is preferably 500 to 6000 mPa·s, more preferably 1000 to 3000 mPa·s. The viscosity of a 1% aqueous solution of carboxymethyl cellulose can be measured at 25°C with a Brookfield viscometer at a rotor speed of 60 rpm.

[0105] The degree of etherification of carboxymethyl cellulose is preferably 0.6 to 1.5, more preferably 0.8 to 1.2.

[0106] If the styrene butadiene rubber is in the form of an oil-in-water emulsion, materials commonly used as electrode binders can be used. Regarding the amount of styrene butadiene rubber used, the proportion of styrene butadiene rubber is preferably 0.5% to 3.0% by mass, and more preferably 1.0% to 2.0% by mass, based on 100% by mass of the active material.

[0107] Regarding the amount of polyacrylic acid used, when the mass of the active material is 100 mass %, the ratio of polyacrylic acid is preferably 1 to 25 mass %, more preferably 5 to 20 mass %.

[0108] [Carbon nanotube resin composition]

[0109] The carbon nanotube resin composition of this embodiment includes carbon nanotubes, a dispersant, a solvent, and a binder.

[0110] To obtain the carbon nanotube resin composition of this embodiment, it is preferred to mix and homogenize the carbon nanotube dispersion with the binder. Various known mixing methods can be used. The carbon nanotube resin composition can be prepared using the dispersing apparatus described above for the carbon nanotube dispersion.

[0111] [Composite material slurry]

[0112] The composite material slurry of this embodiment includes carbon nanotubes, a dispersant, a solvent, a binder, and an active material.

[0113] Active substances

[0114] The active material in this embodiment is a material that serves as the basis for the battery reaction. In terms of electromotive force, active materials are divided into positive electrode active materials and negative electrode active materials.

[0115] There are no particular limitations on the positive electrode active material, and metal compounds such as metal oxides and metal sulfides that can be doped or intercalated with lithium ions, and conductive polymers can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, inorganic compounds such as transition metal sulfides, and the like. Specifically, MnO, V2O5, V6O 13 Transition metal oxide powders such as TiO2; composite oxide powders of lithium and transition metals such as layered lithium nickelate, lithium cobaltate, lithium manganate, and spinel lithium manganate; lithium iron phosphate-based materials such as olivine-structured phosphate compounds; and transition metal sulfide powders such as TiS2 and FeS. Conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene may also be used. Furthermore, a mixture of the aforementioned inorganic and organic compounds may be used.

[0116] There are no particular limitations on the negative electrode active material as long as it can be doped or embedded with lithium ions. Examples include metal Li, and alloys thereof such as tin alloys, silicon alloys, and lead alloys; Li x Fe2O3、Li x Fe3O4、Li x WO2 (x is a number where 0<x<1), metal oxides such as lithium titanate, lithium vanadate, and lithium silicate; conductive polymers such as polyacetylene and polyparaphenylene; amorphous carbonaceous materials such as soft carbon or hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite; carbon materials such as carbon black, mesophase carbon black, resin-fired carbon materials, vapor-grown carbon fibers, and carbon fibers. These negative electrode active materials may be used alone or in combination.

[0117] As the negative electrode active material in this embodiment, a silicon-based negative electrode active material is preferably a negative electrode active material containing silicon, such as a silicon alloy or lithium silicate.

[0118] As silicon-based negative electrode active materials, for example, there are: so-called metallurgical-grade silicon produced by reducing silicon dioxide with carbon; industrial-grade silicon obtained by reducing impurities in metallurgical-grade silicon through acid treatment or unidirectional solidification; and high-purity silicon in different crystalline states such as single crystal, polycrystalline, and amorphous, produced by reacting silane with silicon; and silicon obtained by making industrial-grade silicon of high purity by sputtering or electron beam evaporation (EB (electron beam) evaporation) and adjusting the crystalline state and precipitation state.

[0119] Other examples include silicon oxide, a compound of silicon and oxygen; silicon and various alloys; and silicon compounds obtained by adjusting the crystal state of these by a quenching method. Among these, a silicon-based negative electrode active material having a structure in which silicon nanoparticles are dispersed in silicon oxide and coated with a carbon film is preferred.

[0120] In addition to using a silicon-based negative electrode active material, the negative electrode active material in this embodiment is preferably amorphous carbonaceous materials such as soft carbon or hard carbon, or carbonaceous powders such as artificial graphite or natural graphite, such as highly graphitizable carbon materials. Among them, carbonaceous powders such as artificial graphite and natural graphite are preferably used.

[0121] When the carbonaceous powder such as artificial graphite or natural graphite is taken as 100% by mass, the amount of the silicon-based negative electrode active material is preferably 3% by mass to 50% by mass, and more preferably 5% by mass to 25% by mass.

[0122] The BET specific surface area of ​​the active material in this embodiment is preferably 0.1 m 2 / g~10m 2 / g, more preferably 0.2m 2 / g~5m 2 / g, more preferably 0.3m 2 / g~3m 2 / g.

[0123] The average particle size of the active material in this embodiment is preferably 0.5 μm to 50 μm, more preferably 2 μm to 20 μm. The average particle size of the active material referred to in this specification is the average value of the particle sizes measured using an electron microscope.

[0124] [Method for producing composite material slurry]

[0125] The composite material slurry of this embodiment can be prepared by various conventional methods. A mixture containing the first carbon nanotubes, the second carbon nanotubes, a dispersant, and a solvent can be dispersed to prepare a carbon nanotube dispersion for use, or the first carbon nanotube dispersion and the second carbon nanotube dispersion can be prepared separately and mixed for use.

[0126] The order in which the carbon nanotube dispersion, the binder, and the active material are mixed is not particularly limited, and they can be added separately in sequence, or any two or more can be added simultaneously. For example, the active material can be added to the carbon nanotube resin composition, or the binder can be added to the carbon nanotube dispersion before the active material is added to produce the composite material. Alternatively, a carbon nanotube resin composition comprising a dispersion of one of the carbon nanotubes can be produced, and then the active material and the dispersion of another carbon nanotube can be added simultaneously or sequentially to produce the composite material slurry. In particular, the method of separately producing a dispersion of the first carbon nanotube and a dispersion of the second carbon nanotube, and then mixing the binder and the active material to produce the composite material slurry can evenly arrange the first carbon nanotube and the second carbon nanotube between the active materials, thereby forming a good conductive network, which is preferred from this point of view.

[0127] To obtain the composite slurry of this embodiment, it is preferred to add an active material to the carbon nanotube resin composition and then disperse it. The dispersing device used for this treatment is not particularly limited. The composite slurry can be obtained using the dispersing device described in the carbon nanotube dispersion.

[0128] The amount of the active material in the composite material slurry of this embodiment is preferably 20 to 85 parts by mass, more preferably 30 to 75 parts by mass, and even more preferably 40 to 70 parts by mass, relative to 100 parts by mass of the composite material slurry.

[0129] The amount of carbon nanotubes 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.

[0130] 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 %, relative to 100 mass % of the active material.

[0131] The amount of solid content in the composite material slurry of the present embodiment is preferably 30% to 90% by mass, more preferably 30% to 80% by mass, and even more preferably 40% to 75% by mass, relative to 100% by mass of the composite material slurry.

[0132] 〔Electrode membrane〕

[0133] The electrode film of this embodiment is formed by shaping the composite material slurry. For example, it is a coating film formed by applying the composite material slurry on a current collector and drying it to form an electrode composite material layer.

[0134] The material and shape of the current collector used in the electrode film of this embodiment are not particularly limited, and can be selected from materials and shapes suitable for various secondary batteries. For example, the material of the current collector includes metals and alloys such as aluminum, copper, nickel, titanium, or stainless steel. Furthermore, while a flat foil is generally used, a roughened surface, a perforated foil, or a mesh-shaped current collector can also be used.

[0135] The method for applying the composite material slurry to the current collector is not particularly limited, and known methods can be used. Specifically, for example, die coating, dip coating, roll coating, blade coating, spray coating, gravure coating, screen printing, or electrostatic coating can be mentioned. As a drying method, standing drying, air drying, warm air drying, infrared heating, far-infrared heating, etc. can be used, but it is not particularly limited to these.

[0136] Alternatively, after coating, a rolling treatment using a flat plate press or a calender roll may be performed. The thickness of the electrode composite material layer is generally 1 μm to 500 μm, preferably 10 μm to 300 μm.

[0137] Non-aqueous electrolyte secondary batteries

[0138] The nonaqueous electrolyte secondary battery of this embodiment includes a positive electrode, a negative electrode, and an electrolyte.

[0139] As the positive electrode, a composite material slurry containing a positive electrode active material is applied to a current collector and dried to form an electrode film.

[0140] As the negative electrode, a composite material slurry containing a negative electrode active material is applied to a current collector and dried to form an electrode film.

[0141] As an electrolyte, various electrolytes known in the past in which ions can move can be used. For example, LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (wherein Ph is a phenyl group) etc. include electrolytes containing lithium salts, but are not limited to these, and electrolytes containing sodium salts or calcium salts can also be used. The electrolyte is preferably used as an electrolyte after being dissolved in a non-aqueous solvent.

[0142] The non-aqueous solvent is not particularly limited, and examples thereof include 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-octalactone; glycol dimethyl ethers (glymes) such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

[0143] The non-aqueous electrolyte secondary battery of this embodiment preferably includes a separator. Examples of the separator include polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and non-woven fabrics subjected to hydrophilic treatment, but are not particularly limited to these.

[0144] The structure of the non-aqueous electrolyte secondary battery of this embodiment is not particularly limited, and generally includes a positive electrode, a negative electrode, and a separator provided as needed, and can be made into various shapes corresponding to the purpose of use, such as paper type, cylindrical type, button type, and stacked type.

[0145] The present invention is related to the subject matter of Japanese Patent Application No. 2020-190250 filed on November 16, 2020 and Japanese Patent Application No. 2021-111681 filed on July 5, 2021, and all disclosed contents thereof are incorporated into this specification by reference.

[0146] [Example]

[0147] The present invention is further described below with reference to the following examples. The present invention is not limited to the following examples unless the scope of the present invention is exceeded. In the examples, "carbon nanotubes" may be referred to simply as "CNTs." Unless otherwise specified, "parts" means "parts by mass," and "%" means "mass %."

[0148] <Measurement methods of physical properties>

[0149] The physical properties of the CNTs used in the examples and comparative examples described below were measured by the following methods.

[0150] CNT G / D ratio

[0151] CNTs were placed on a Raman microscope (XploRA, manufactured by Horiba, Ltd.) and measured using a laser wavelength of 532 nm. The measurement conditions were an acquisition time of 60 seconds, a cumulative count of 2 times, a 10% neutral density filter, a 20x objective lens magnification, a confocal aperture of 500, a slit width of 100 μm, and a measurement wavelength of 100 cm. -1 ~3000cm -1 The CNTs used for measurement were separated and taken out onto a glass slide and flattened using a spatula. The peaks obtained were at 1560 cm -1 ~1600cm -1 The maximum peak intensity is set as G in the range of 1310 cm -1 ~1350cm -1 The maximum peak intensity within the range of is defined as D, and the ratio of G / D is defined as the G / D ratio of CNT.

[0152] <BET specific surface area of ​​CNT>

[0153] 0.03 g of CNTs were weighed using an electronic balance (Sartorius, MSA225S100DI) and dried at 110°C for 15 minutes while degassing. The BET surface area of ​​the CNTs was then measured using a fully automatic surface area analyzer (Mountech, HM model 1208).

[0154] Total BET surface area of ​​CNTs

[0155] The total BET specific surface area of ​​CNTs was calculated using the BET specific surface area of ​​CNTs measured by the above method and the mass ratio of each CNT in the CNT dispersion prepared in Examples and Comparative Examples described below using the following formula.

[0156] (Total BET specific surface area of ​​CNT) = (A + B)

[0157] A=(BET specific surface area of ​​the first CNT)×(mass ratio of the first CNT in the dispersion)

[0158] B = (BET specific surface area of ​​the second CNT) × (mass ratio of the second CNT in the dispersion)

[0159] <Outer diameter and average outer diameter of CNT>

[0160] Using an electronic balance (Sartorius, MSA225S100DI), 0.2 g of CNTs were weighed in a 450 mL SM sample bottle (Sansho Co., Ltd.), 200 mL of toluene was added, and an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), Model 450DA, Branson) was used to disperse the CNTs for 5 minutes at an amplitude of 50% under ice cooling to prepare a CNT dispersion. The CNT dispersion was then appropriately diluted, and a few μL was added dropwise in the form of a collodion film. After drying at room temperature, the dispersion was directly observed using a transmission electron microscope (H-7650, Hitachi, Ltd.). The observation was performed at a magnification of 50,000 times, with multiple photographs containing 10 or more CNTs within the field of view. The outer diameters of 300 CNTs randomly selected from the photographs were measured, and the average value was used as the average outer diameter (nm) of the CNTs.

[0161] <CNT aspect ratio in CNT dispersion>

[0162] The CNT dispersion prepared in the examples described below was diluted with the solvent used to prepare the CNT dispersion so that the CNT concentration became 0.01% by mass. After a few microliters (μL) were dripped onto a mica substrate, it was dried in an electric oven at 120°C to prepare a substrate for observing the length of the CNT fibers. The surface of the substrate prepared for observing the length of the CNT fibers was then sputtered with platinum. Then, an SEM was used for observation. During observation, a photograph for measuring the outer diameter was taken at a magnification of 50,000 times within a field of view containing more than 10 CNTs. Subsequently, the magnification was reduced to 5,000 to 20,000 times to reveal the entire shape of the photographed CNTs, thereby taking photographs for measuring the fiber length. The field of view was changed to take multiple photographs for measuring the outer diameter and the fiber length. Next, the outer diameter of the CNTs was measured from the outer diameter measurement photograph. CNTs with an outer diameter of less than 5 nm were designated as the first CNT, and CNTs with an outer diameter of 5 nm or greater were designated as the second CNT. The average outer diameter of 100 randomly selected CNTs from each of the first and second CNTs was taken as the average outer diameter of the CNTs. Furthermore, the fiber length of the CNTs after the outer diameter measurement was measured from the fiber length measurement photograph. The average value of the first and second CNTs was taken as the fiber length of the CNTs in the CNT dispersion. The value obtained by dividing the fiber length of the CNTs in the CNT dispersion by the average outer diameter of the CNTs in the CNT dispersion was taken as the aspect ratio of the CNTs in the CNT dispersion.

[0163] Volume Resistivity of CNTs

[0164] Using a powder resistivity measuring device (Mitsubishi Chemical Analytech Co., Ltd.: Loresta GP Powder Resistivity Measuring System MCP-PD-51), the sample mass was set to 1.2 g, and a powder probe unit (four-probe ring electrode, electrode spacing 5.0 mm, electrode radius 1.0 mm, sample radius 12.5 mm) was used. The applied voltage limiter was set to 90 V, and the volume resistivity [Ω·cm] of the conductive powder under various pressures was measured. For 1 g / cm 3 The volume resistivity of CNTs at a density of 100 nm was evaluated.

[0165] Cumulative particle size of CNT dispersion

[0166] After the CNT dispersion was allowed to stand in a thermostatic bath at 25°C for more than one hour, the CNT dispersion was thoroughly stirred and diluted, and the cumulative particle size D50 of the CNT dispersion was measured using a particle size distribution meter utilizing dynamic light scattering (manufactured by Microtrac-BEL Co., Ltd., Nanotrac UPA, model UPA-EX). The refractive index of the CNT particles was set to 1.8, and the shape was set to non-spherical. The refractive index of the solvent was set to 1.333. During the measurement, the concentration of the CNT dispersion was diluted so that the load index value was in the range of 0.8 to 1.2.

[0167] Complex elastic modulus and phase angle of CNT dispersion

[0168] The complex elastic modulus and phase angle of the CNT dispersion were evaluated by performing dynamic viscoelasticity measurements at 25°C and a frequency of 1 Hz using a rheometer (RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific) with a 35 mm diameter, 2° cone and a strain rate range of 0.01% to 5%.

[0169] Viscosity of CNT Dispersion

[0170] After the CNT dispersion was allowed to stand in a thermostatic bath at 25°C for at least 1 hour, the CNT dispersion was thoroughly stirred and immediately measured using a B-type viscometer (manufactured by TOKI SANGYO Co., Ltd., VISCOMETER, MODEL: BL) with a rotor rotation speed of 60 rpm. The rotor used in the measurement was No. 1 for viscosity values ​​less than 100 mPa·s, No. 2 for viscosity values ​​between 100 and 500 mPa·s, No. 3 for viscosity values ​​between 500 and 2000 mPa·s, and No. 4 for viscosity values ​​between 2000 and 10000 mPa·s.

[0171] <Peel strength of negative electrode film>

[0172] Use the applicator to apply the electrode at a weight per unit area of ​​8 mg / cm 2 In this way, after applying the negative electrode composite material slurry to the copper foil, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, with the coating direction as the major axis, it was cut into two 90mm×20mm rectangles. In the determination of peel strength, a desktop tensile testing machine (manufactured by Toyo Seiki Co., Ltd., Strograph E3) was used to evaluate it using a 180-degree peel test method. Specifically, a 100mm×30mm double-sided tape (No.5000NS, manufactured by Nitoms) was attached to a stainless steel plate so that the prepared battery electrode composite material layer was closely attached to the other side of the double-sided tape. It was peeled off while being stretched from bottom to top at a certain speed (50mm / min), and the average value of the stress at this time was used as the peel strength.

[0173] <Peel strength of positive electrode film>

[0174] Use the applicator to apply the electrode at a weight per unit area of ​​20 mg / cm 2In this way, after applying the composite material slurry for the positive electrode to the aluminum foil, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Then, with the coating direction as the major axis, it was cut into two rectangles of 90mm×20mm. In the determination of peel strength, a desktop tensile testing machine (manufactured by Toyo Seiki Co., Ltd., Strograph E3) was used to evaluate it using a 180-degree peel test method. Specifically, a double-sided tape of 100mm×30mm in size (No.5000NS, manufactured by Nitoms) was attached to a stainless steel plate so that the prepared battery electrode composite material layer was closely attached to the other side of the double-sided tape. It was peeled off while being stretched from bottom to top at a certain speed (50mm / min), and the average value of the stress at this time was used as the peel strength.

[0175] <Production of Standard Positive Electrode>

[0176] First, 93 parts by mass of a positive electrode active material (BASF TODA Battery Materials, HED (registered trademark) NCM-111 1100), 4 parts by mass of acetylene black (DENKA BLACK (registered trademark) HS100, manufactured by DENKA Co., Ltd.), and 3 parts by mass of polyvinylidene fluoride (PVDF) (Kureha Battery Materials Japan, Kureha KF polymer W#1300) were added to a 150 cm3 container. 3 After adding 20.5 parts by mass of NMP into the plastic container, use a spatula to mix until the powder is uniform. Then, add 20.5 parts by mass of NMP and stir at 2000 rpm for 30 seconds using a rotation / revolution mixer (Degassing Rentaro, ARE-310 manufactured by Thinky). Then, use a spatula to mix the mixture in the plastic container until it is uniform, and use a rotation / revolution mixer to stir at 2000 rpm for 30 seconds. Then, add 14.6 parts by mass of NMP and use a rotation / revolution mixer to stir at 2000 rpm for 30 seconds. Finally, use a high-speed stirrer to stir at 3000 rpm for 10 minutes to obtain a composite material slurry for the positive electrode. Then, use an applicator to apply the composite material slurry for the positive electrode onto an aluminum foil with a thickness of 20 μm as a current collector, and then dry it in an electric oven at 120°C ± 5°C for 25 minutes, and adjust the unit area weight per unit area of ​​the electrode to 20 mg / cm 2The composite material layer was then rolled using a roller press (manufactured by Thank-Metal Co., Ltd., a 3t hydraulic roller press) to obtain a density of 3.1g / cm 3 The standard positive electrode.

[0177] <Production of Standard Negative Electrode>

[0178] In the capacity of 150cm 3 0.5 parts by mass of acetylene black (DENKA BLACK (registered trademark) HS-100, manufactured by DENKA), 1 part by mass of MAC500LC (carboxymethylcellulose sodium salt Sunrose Special MAC500L, manufactured by Nippon Paper Industries, 100% nonvolatile content), and 98.4 parts by mass of water were added to a plastic container. The mixture was then stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer (Thinky Degassing Rentaro, ARE-310). Furthermore, 87 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries) and 10 parts by mass of silicon were added as active materials, and the mixture was stirred at 3000 rpm for 10 minutes using a high-speed stirrer. Then, 3.1 parts by mass of SBR (TRD2001, manufactured by JSR) was added and stirred at 2000 rpm for 30 seconds using a rotary / revolution mixer (Thinky Degassing Rentaro, ARE-310) to obtain a negative electrode composite slurry. Then, a coating was applied using a coating applicator with a unit area weight of 8 mg / cm2 per unit of electrode. 2 The negative electrode composite material slurry was applied to the copper foil and then dried in an electric oven at 120°C ± 5°C for 25 minutes. The composite material layer was then rolled using a roller press (3 ton hydraulic roller press manufactured by Thank-Metal Co., Ltd.) to obtain a composite material layer with a density of 1.7 g / cm 3 The standard negative electrode.

[0179] <Synthesis of Dispersant (A)>

[0180] 100 parts of acetonitrile were placed in a reaction vessel including a gas inlet pipe, a thermometer, a condenser, and a stirrer, and the mixture was replaced 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 NOF Corporation; V-65) was added dropwise over 2 hours to carry out a polymerization reaction. After the addition was completed, the reaction was continued at 70°C for 1 hour, and then 0.5 parts of perbutyl O were added, and the reaction was continued at 70°C for 1 hour. Then, the conversion rate was confirmed to be over 98% by determination of the non-volatile component, and the dispersion medium was completely removed by vacuum concentration to obtain a dispersant (A). The weight average molecular weight (Mw) of the dispersant (A) was 38,000.

[0181] (Method for measuring weight average molecular weight (Mw))

[0182] The weight average molecular weight (Mw) of the produced dispersant (A) was measured by gel permeation chromatography (GPC) equipped with an RI detector under the following conditions. The molecular weight is a pullulan-equivalent value.

[0183] Measurement sample: 0.1 mass% aqueous solution

[0184] Apparatus: HLC-8320GPC (manufactured by Tosoh Corporation)

[0185] Eluent: 0.1M NaCl aqueous solution

[0186] Column: TSKgel SuperMultiporePW-M (manufactured by Tosoh)

[0187] Flow rate: 1.0 mL / min

[0188] Temperature: 25℃

[0189] Injection volume: 100 μl

[0190] Table 1 shows the CNTs used in Examples, Comparative Examples, and Production Examples, as well as their outer diameters, average outer diameters, specific surface areas, G / D ratios, and powder resistivities (volume resistivities).

[0191] [Table 1]

[0192] Table 1

[0193]

[0194] Table 2 shows the dispersants used in Examples, Comparative Examples, and Production Examples.

[0195] [Table 2]

[0196] Table 2

[0197]

[0198] (Production Example 1)

[0199] 99 parts of ion exchange water were added to a stainless steel container, 0.6 parts of dispersant (A) were added while stirring with a disperser, and the mixture was stirred until uniform. Then, 0.4 parts of CNT (A) were weighed out, 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 dispersed in batches at a speed of 8,600 rpm until the whole became uniform. Then, the dispersed liquid was supplied from the stainless steel container via a pipe to a high pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINOMACHINE), and 10 passes through the dispersion process to obtain a CNT dispersion (WA1). The dispersion process was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0200] (Manufacturing Examples 2 to 17)

[0201] CNT dispersions (WA2 to WA10, WB1, WC1, WD1, WE1, WF1 to WF3) were obtained by the same method as in Production Example 1, except that the CNT type, CNT addition amount, dispersant type, dispersant addition amount, ion exchange water addition amount, and number of passes were changed to those shown in Table 3.

[0202] Table 3 shows the type of CNTs, the amount of CNTs added, the type of dispersant, the amount of dispersant added, the amount of ion-exchanged water added, the number of passes, and the dispersion pressure of the production examples.

[0203] [Table 3]

[0204]

[0205] (Example 1)

[0206] The CNT dispersion (WA1) containing the first CNT and the CNT dispersion (WE1) containing the second CNT, prepared in Production Example 1, were weighed into a stainless steel container to achieve a CNT mass ratio of 1:30. The mixture was then stirred in a disperser until uniform, yielding a CNT dispersion (WAE1) containing the first and second CNTs.

[0207] (Example 2 to Example 19)

[0208] CNT dispersions containing first and second CNTs (WAE2 to WAE13, WBE1, WCE1, WDE1, and WAF1 to WAF3) were obtained by the same method as in Example 1 except that the type of CNT dispersion and the CNT mass ratio described in Table 4 were changed.

[0209] (Comparative Examples 1 to 3)

[0210] CNT dispersions (WAE14, WBE2 to WBE3) containing the first CNT and the second CNT were obtained by the same method as in Example 1 except that the CNT mass ratio was changed to that described in Table 4.

[0211] Table 4 shows the mass ratio of the CNT dispersions used in Examples and Comparative Examples, the CNT mass ratio, the total BET specific surface area (m 2 / g), and the aspect ratio of each of the first CNT and the second CNT in the dispersion.

[0212] [Table 4]

[0213]

[0214] (Production Example 18)

[0215] 99 parts of NMP were added to a stainless steel container, and 0.6 parts of dispersant (E) were added while stirring with a disperser, and the dispersant (E) was dissolved by the disperser. Then, 0.4 parts of CNT (A) were weighed out, 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 dispersed in batches at a speed of 8,600 rpm until the whole became uniform. Then, the dispersed liquid was supplied from the stainless steel container via a pipe to a high pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE), and 10 passes through the dispersion process to obtain a CNT dispersion (A11). The dispersion process was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0216] (Production Examples 19 and 20)

[0217] CNT dispersions (B2, E2) were obtained by the same method as in Preparation Example 18 except that the CNT type, CNT addition amount, dispersant type, dispersant addition amount, NMP addition amount, and number of passes were changed to those shown in Table 5.

[0218] [Table 5]

[0219]

[0220] (Example 20)

[0221] The first CNT dispersion (A11) and the second CNT dispersion (E2) prepared in Preparation Example 18 were weighed into a stainless steel container to achieve a CNT mass ratio of 1:30. The mixture was then stirred in a disperser until uniform, yielding a CNT dispersion (AE15) containing a mixture of the two CNTs.

[0222] (Example 21-Example 22)

[0223] CNT dispersions (AE16 to AE17) containing a mixture of two types of CNTs were obtained by the same method as in Example 20 except that the CNT mass ratio was changed to that described in Table 6.

[0224] (Comparative Examples 4 to 6)

[0225] CNT dispersions (AE18, BE4 to BE5) containing a mixture of two types of CNTs were obtained by the same method as in Example 20 except that the CNT mass ratio was changed to that described in Table 6.

[0226] [Table 6]

[0227]

[0228] (Example 23)

[0229] 8.9 parts of ion exchange water were added to a stainless steel container, and 0.06 parts of dispersant (A) were added while stirring with a disperser, and stirred until uniform. Then, 0.04 parts of CNT (A) were weighed out, 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). The mixture was dispersed in batches at a speed of 8,600 rpm until the whole mixture became uniform, thereby obtaining a premix (A). Subsequently, 89.26 parts of ion exchange water were added to a stainless steel container, and 0.54 parts of dispersant (A) were added while stirring with a disperser, and stirred until uniform. Then, 1.2 parts of CNT (E) were weighed out, added while stirring with a disperser, and a square hole high shear screen was installed on a high shear mixer. The mixture was dispersed in batches at a speed of 8,600 rpm until the whole mixture became uniform, thereby obtaining a premix (B). The premix (B) was then supplied from the stainless steel container via a pipe to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE) for 30 passes. The premix (A) was then supplied via a pipe to the high-pressure homogenizer for a further 10 passes, yielding a CNT dispersion (WAE19). The dispersion was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0230] Table 7 shows the amount of CNT added, the amount of dispersant added, the amount of ion exchange water added, the total number of passes, the dispersion pressure (MPa), the total specific surface area (m 2 / g), aspect ratio.

[0231] [Table 7]

[0232]

[0233] Table 8 shows the evaluation results of the CNT dispersions prepared in Examples 1 to 23 and Comparative Examples 1 to 6. Regarding the phase angle evaluation of the CNT dispersions, a value of 10 or greater and less than 50 was designated as A (good), a value of 5 or greater and less than 10 was designated as B (acceptable), and a value of less than 5 or 50 or greater was designated as C (unacceptable). Regarding the complex elastic modulus evaluation of the CNT dispersions, a value of 5 or greater and less than 400 was designated as A (good), a value of 400 or greater and less than 650 was designated as B (acceptable), and a value of less than 5 was designated as C (unacceptable). Regarding the viscosity evaluation of the CNT dispersions, a value of less than 500 mPa·s was designated as AA (excellent), a value of 500 mPa·s or greater and less than 2000 mPa·s was designated as A (good), a value of 2000 mPa·s or greater and less than 10000 mPa·s was designated as B (acceptable), and a value of 10000 mPa·s or greater with sedimentation or separation was designated as C (unacceptable). Regarding the particle size evaluation of the CNT dispersion, a particle size distribution of 900 nm or more and less than 4000 nm at the cumulative particle size D50 was rated A (good), a particle size distribution of 400 nm or more and less than 900 nm was rated B (acceptable), and a particle size distribution of less than 400 nm or 4000 nm or more was rated C (unacceptable).

[0234] [Table 8]

[0235] Table 8

[0236]

[0237] (Example 24)

[0238] 6.9 parts by mass of CNT dispersion (WAE1), 12.5 parts by mass of an aqueous solution containing 2% by mass of carboxymethyl cellulose (CMC) (manufactured by Daicel Finechem Co., Ltd., #1190), and 7.7 parts by mass of ion-exchanged water were weighed to a volume of 150 cm 3) in a plastic container. Then, a rotation / revolution mixer (a degassing Rentaro, ARE-310 manufactured by Thinky) was used to stir at 2000 rpm for 30 seconds to obtain a CNT resin composition (WAE1). Then, 2.4 parts by mass of silicon monoxide (manufactured by Osaka Titanium Technologies Co., Ltd., silicon nanooxide (SILICON MONOOXIDE, SiO1.3C 5μm) was added and stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer. Furthermore, 21.9 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries, Ltd., CGB-20) was added and stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer. Then, 0.78 parts by mass of styrene butadiene emulsion (TRD2001 manufactured by JSR Corporation) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the aforementioned rotation / revolution mixer to obtain a negative electrode composite material slurry (WAE1).

[0239] (Example 25 to Example 44), (Comparative Example 7 to Comparative Example 11)

[0240] The CNT dispersion liquid described in Table 9 was changed, and the addition amounts of the CNT dispersion liquid and ion exchange water were adjusted so that the CNT addition amount in 100 parts by mass of the composite material slurry became the value described in Table 9. CNT resin compositions (WAE2-WAE3, WAE4-1-WAE4-2, WAE5-WAE14, WBE1-WBE3, WCE1, WDE1, WAF1-WAF3, WAE19, WA1, WE1) and negative electrode composite material slurries (WAE2-WAE3, WAE4-1-WAE4-2, WAE5-WAE14, WBE1-WBE3, WCE1, WDE1, WAF1-WAF3, WAE19, WA1, WE1) were obtained by the same method as in Example 24. The non-volatile content of the negative electrode composite material slurry was set to 48% by mass.

[0241] (Example 45)

[0242] 7.0 parts by mass of NMP in which 8% by mass of PVDF (Solef #5130 manufactured by Solvay) was dissolved was weighed out to a volume of 150 cm 3. Then, 15.6 parts by mass of the CNT dispersion (AE15) was added and stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer (Degassing Rentaro, ARE-310) to obtain a CNT resin composition (AE15). Then, 36.9 parts of a positive electrode active material (manufactured by BASF TODA Battery Materials, HED (registered trademark) NCM-111 1100) was added and stirred at 2000 rpm for 2.5 minutes using a rotation / revolution mixer to obtain a positive electrode composite material slurry (AE15).

[0243] (Example 46 to Example 47), (Comparative Example 12 to Comparative Example 14)

[0244] The CNT dispersion liquid was changed to the one described in Table 9, and the amount of the CNT dispersion liquid added was adjusted so that the amount of CNT added in 100 parts by mass of the composite slurry became the value described in Table 9. In addition, the CNT resin composition (AE16~AE18, BE4~BE5) and the composite slurry for the positive electrode (AE16~AE18, BE4~BE5) were obtained by the same method as in Example 45.

[0245] (Example 48)

[0246] 0.6 parts by mass of the CNT dispersion (WA1), 12.5 parts by mass of an aqueous solution containing 2% by mass of CMC (Daicel Finechem Co., Ltd., #1190), and 7.7 parts by mass of ion-exchanged water were weighed to a volume of 150 cm 3plastic container. Then, using a rotation / revolution mixer (degassing Rentaro, ARE-310 manufactured by Xinji (Thinky) Co., Ltd.), stirring at 2000rpm for 30 seconds to obtain a CNT resin composition (WA1). Then, 2.4 parts by mass of silicon monoxide (manufactured by Osaka Titanium Technologies Co., Ltd., silicon nanooxide (SILICON MONOOXIDE), SiO 1.3C 5μm) were added and stirred at 2000rpm for 30 seconds using a rotation / revolution mixer. Furthermore, 21.9 parts by mass of artificial graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-20) were added and stirred at 2000rpm for 30 seconds using a rotation / revolution mixer. Furthermore, 0.63 parts by mass of a CNT dispersion (WE1) was added and stirred at 2000rpm for 30 seconds using a rotation / revolution mixer. Then, 0.78 parts by mass of styrene butadiene emulsion (TRD2001 manufactured by JSR Corporation) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer to obtain a negative electrode composite material slurry (WAE20).

[0247] [Table 9]

[0248] Table 9

[0249]

[0250]

[0251] (Example 49)

[0252] Use the applicator to apply the electrode at a weight per unit area of ​​8 mg / cm 2 After applying the negative electrode composite material slurry (WAE1) onto a copper foil in a manner, the coating was dried in an electric oven at 120°C±5°C for 25 minutes to obtain an electrode film (WAE1).

[0253] (Example 50 to Example 70), (Comparative Example 15 to Comparative Example 19)

[0254] Except for changing to the composite material slurry for negative electrode described in Table 10, the electrode membrane (WAE2~WAE3, WAE4-1~WAE4-2, WAE5~WAE14, WAE19~WAE20, WBE1~WBE3, WCE1, WDE1, WAF1~WAF3, WA1, WE1) was obtained by the same method as Example 49.

[0255] (Example 71)

[0256] Use the applicator to apply the electrode at a weight per unit area of ​​20 mg / cm 2 After applying the positive electrode composite material slurry (AE15) onto a copper foil in a manner, the coating was dried in an electric oven at 120°C±5°C for 25 minutes to obtain an electrode film (AE15).

[0257] (Example 72 to Example 73), (Comparative Example 20 to Comparative Example 22)

[0258] Electrode films (AE16 to AE18, BE4, and BE5) were obtained by the same method as in Example 71 except that the positive electrode composite material slurry described in Table 10 was used.

[0259] Table 10 shows the evaluation results of the electrode films produced in Examples 49 to 73 and Comparative Examples 15 to 22. Regarding the adhesion evaluation, a peel strength (N / cm) of 0.5 or greater was rated AA (excellent), 0.3 or greater and less than 0.5 was rated A (good), 0.1 or greater and less than 0.3 was rated B (acceptable), and less than 0.1 was rated C (unacceptable).

[0260] [Table 10]

[0261] Table 10

[0262] electrode membrane Adhesion evaluation Example 49 WAE1 AA Example 50 WAE2 AA Example 51 WAE3 A Example 52 WAE4-1 AA Example 53 WAE4-2 B Example 54 WAE5 AA Example 55 WAE6 A Example 56 WAE7 A Example 57 WAE8 AA Example 58 WAE9 A Example 59 WAE10 A Example 60 WAE11 AA Example 61 WAE12 A Example 62 WAE13 A Example 63 WBE1 AA Example 64 WCE1 AA Example 65 WDE1 AA Example 66 WAF1 AA Example 67 WAF2 AA Example 68 WAF3 AA Example 69 WAE19 AA Example 70 WAE20 AA Comparative Example 15 WAE14 B Comparative Example 16 WBE2 C Comparative Example 17 WBE3 A Comparative Example 18 WA1 A Comparative Example 19 WE1 B Example 71 AE15 AA Example 72 AE16 A Example 73 AE17 AA Comparative Example 20 AE18 B Comparative Example 21 BE4 C Comparative Example 22 BE5 A

[0263] (Example 74 to Example 95), (Comparative Example 23 to Comparative Example 27)

[0264] The electrode membranes (WAE1-WAE3, WAE4-1-WAE4-2, WAE5-WAE14, WAE19-WAE20, WBE1-WBE3, WCE1, WDE1, WAF1-WAF3, WA1, WE1) were rolled using a roller press (manufactured by Thank-Metal Co., Ltd., a 3-ton hydraulic roller press) to produce a composite material layer with a density of 1.7 g / cm 3 of the negative electrode.

[0265] (Example 96 to Example 98), (Comparative Example 28 to Comparative Example 30)

[0266] The electrode membranes (AE15-AE18, BE4, BE5) were rolled using a roller press (manufactured by Thank-Metal Co., Ltd., a 3-ton hydraulic roller press) to produce a composite material layer with a density of 3.2 g / cm 3 positive electrode.

[0267] Table 11 shows the negative electrodes and positive electrodes produced in Examples 74 to 98 and Comparative Examples 23 to 30.

[0268] [Table 11]

[0269] Table 11

[0270]

[0271]

[0272] (Example 99)

[0273] The negative electrode (WAE1) and the standard positive electrode were punched into 50 mm × 45 mm and 45 mm × 40 mm, respectively. They were placed in an aluminum laminate bag along with a separator (porous polypropylene film) and dried in an electric oven at 60°C for 1 hour. Then, 2 mL of an electrolyte solution (a non-aqueous electrolyte prepared by dissolving LiPF6 at a concentration of 1 M in a mixed solvent consisting of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 3:5:2 (volume ratio) and, as additives, 1 part each of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) per 100 parts by mass) was injected into an argon-filled glove box. The aluminum laminate bag was then sealed to produce a laminated lithium-ion secondary battery (WAE1).

[0274] (Example 100 to Example 120), (Comparative Example 31 to Comparative Example 35)

[0275] Laminated lithium-ion secondary batteries (WAE2 to WAE3, WAE4-1 to WAE4-2, WAE5 to WAE14, WAE19 to WAE20, WBE1 to WBE3, WCE1, WDE1, WAF1 to WAF3, WA1, WE1) were produced by the same method except that the negative electrode was changed to the one described in Table 12.

[0276] (Example 121)

[0277] The standard negative electrode and positive electrode (AE15) were punched into 50 mm × 45 mm and 45 mm × 40 mm, respectively, and inserted into an aluminum laminate bag along with a separator (porous polypropylene film) interposed therebetween. The bags were then dried in an electric oven at 60°C for 1 hour. Then, 2 mL of an electrolyte solution (a non-aqueous electrolyte prepared by dissolving LiPF6 at a concentration of 1 M in a mixed solvent comprising ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 3:5:2 (volume ratio), and further additives of 1 part each of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) per 100 parts by mass) was injected into an argon-filled glove box. The aluminum laminate bag was then sealed to produce a laminated lithium-ion secondary battery (AE15).

[0278] (Example 122 to Example 123), (Comparative Example 36 to Comparative Example 38)

[0279] Laminated lithium ion secondary batteries (AE15 to AE18, BE4 to BE5) were produced by the same method except that the positive electrode described in Table 12 was used.

[0280] [Table 12]

[0281] Table 12

[0282]

[0283]

[0284] Table 13 shows the evaluation results of the laminated lithium-ion secondary batteries produced in Examples 124 to 148 and Comparative Examples 39 to 46. Regarding rate characteristics, a rate characteristic of 80% or more was designated as AA (excellent), 70% or more and less than 80% was designated as A (good), 60% or more and less than 70% was designated as B (acceptable), and less than 60% was designated as C (unacceptable). Regarding cycle characteristics, a rate characteristic of 97% or more was designated as AA (excellent), 93% or more and less than 97% was designated as A (good), 90% or more and less than 93% was designated as B (acceptable), and less than 90% was designated as C (unacceptable).

[0285] [Table 13]

[0286] Table 13

[0287]

[0288]

[0289] In the above-described embodiment, a carbon nanotube dispersion containing at least two different carbon nanotubes, wherein the first CNT has an average outer diameter of 0.5 nm to less than 5 nm, the second CNT has an average outer diameter of 5 nm to less than 20 nm, and the mass ratio of the first CNT to the second CNT is between 1:10 and 1:100, was used. A lithium-ion secondary battery exhibiting superior rate and cycle characteristics compared to the comparative example was obtained. When the mass ratio exceeds 1:100, it is believed that the conductive network is not sufficiently constructed, resulting in reduced cycle characteristics. When the mass ratio is less than 1:10, the specific surface area occupied by the carbon nanotubes in the system becomes excessive, which is believed to increase the proportion of the irreversible resistance component (SEI) formed on the carbon nanotube surface, resulting in reduced rate characteristics. Thus, it is clarified that within the mass ratio range of 1:10 to 1:100, the advantages of each carbon nanotube can be utilized while compensating for its disadvantages, thereby providing a lithium-ion secondary battery with high output and a long life.

[0290] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the invention.

Claims

1. A carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a solvent, wherein: The carbon nanotubes include first carbon nanotubes having an average outer diameter of 0.5 nm or more and less than 5 nm, and second carbon nanotubes having an average outer diameter of 5 nm or more and 20 nm or less. The mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:10 to 1:

100. When the 1560 cm -1 ~1600cm -1 The maximum peak intensity within the range is defined as G, and the peak intensity at 1310 cm -1 ~1350cm -1 When the maximum peak intensity within the range is set as D, The G / D ratio of the first carbon nanotubes is 10 to 100, and The G / D ratio of the second carbon nanotubes is 0.5 or more and less than 10.

2. The carbon nanotube dispersion according to claim 1, wherein The total Buerter specific surface area of ​​the first carbon nanotube and the second carbon nanotube is 240 m 2 / g~750m 2 / g.

3. The carbon nanotube dispersion according to claim 1, wherein The aspect ratio of the first carbon nanotube is 2000 to 10000, The aspect ratio of the second carbon nanotubes is 50-200.

4. The carbon nanotube dispersion according to claim 2, wherein The aspect ratio of the first carbon nanotube is 2000 to 10000, The aspect ratio of the second carbon nanotube is 50 to 200, The first carbon nanotubes are single-walled carbon nanotubes, and the second carbon nanotubes are multi-walled carbon nanotubes.

5. The carbon nanotube dispersion according to any one of claims 1 to 4, wherein The mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:30 to 1:

100.

6. The carbon nanotube dispersion according to any one of claims 1 to 4, wherein The Buerter specific surface area of ​​the first carbon nanotube is 600 m 2 / g~1200m 2 / g.

7. The carbon nanotube dispersion according to any one of claims 1 to 4, wherein The volume resistivity of the first carbon nanotube is 1.0×10 -3 Ω·cm~3.0×10 -2 Ω·cm.

8. The carbon nanotube dispersion according to claim 5, wherein The volume resistivity of the first carbon nanotube is 1.0×10 -3 Ω·cm~3.0×10 -2 Ω·cm, and the average outer diameter of the first carbon nanotubes is greater than or equal to 0.5 nm and less than or equal to 2 nm.

9. The carbon nanotube dispersion according to any one of claims 1 to 4, wherein The complex elastic modulus is 5 Pa or more and less than 650 Pa.

10. The carbon nanotube dispersion according to any one of claims 1 to 4, wherein The phase angle is greater than or equal to 5° and less than 50°.

11. The carbon nanotube dispersion according to any one of claims 1 to 4, comprising 0.3 parts by mass or more and 5.0 parts by mass or less of the carbon nanotubes per 100 parts by mass of the carbon nanotube dispersion, and having a viscosity of 10 mPa·s or more and less than 2000 mPa·s as measured at 25°C with a Brookfield viscometer at a rotor rotation speed of 60 rpm.

12. The carbon nanotube dispersion according to any one of claims 1 to 4, wherein The cumulative particle size D50 measured by a dynamic light scattering method is 400 nm to 4000 nm. 13 . A carbon nanotube resin composition comprising the carbon nanotube dispersion according to claim 1 and a binder. 14 . A composite material slurry comprising the carbon nanotube resin composition according to claim 13 and an active substance.

15. A method for producing a composite material slurry, which is the method for producing a composite material slurry according to claim 14, comprising the following steps (1) and (2): (1) dispersing a mixed solution containing the first carbon nanotubes, the second carbon nanotubes, the dispersant, and the solvent to obtain the carbon nanotube dispersion; (2) A step of mixing the carbon nanotube dispersion obtained in (1), a binder, and an active material.

16. A method for producing a composite material slurry, which is the method for producing a composite material slurry according to claim 14, comprising the following steps (1) to (3): (1) dispersing a mixed solution containing the first carbon nanotubes, the dispersant, and the solvent to obtain a first carbon nanotube dispersion; (2) dispersing a mixed solution containing the second carbon nanotubes, the dispersant, and the solvent to obtain a second carbon nanotube dispersion; (3) A step of mixing the first carbon nanotube dispersion, the second carbon nanotube dispersion, a binder, and an active material.

17. An electrode film, which is obtained by forming the composite material slurry according to claim 14 into a film shape.

18. 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 includes the electrode film according to claim 17 .

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