Carbon nanotube dispersion liquid, resin composition, composite material slurry and method for producing same, electrode film, and non

Abstract

The invention provides a carbon nanotube dispersion liquid, a resin composition, a composite material slurry, a preparation method of the composite material slurry, an electrode film and a non-aqueous electrolyte secondary battery. The carbon nanotube dispersion liquid contains carbon nanotubes, a dispersant, and a solvent, in the carbon nanotube dispersion liquid, the carbon nanotubes 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, and the mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1: 10 to 1: 100.

Description

[0001] This invention is a divisional application of the invention patent application filed on November 11, 2021, with application number 202180054066.7 and invention title "Carbon nanotube dispersion, resin composition, composite slurry and its preparation method, electrode film and non-aqueous electrolyte secondary battery". Technical Field

[0002] This invention relates to a dispersion of carbon nanotubes. More specifically, it relates to a carbon nanotube dispersion, a resin composition comprising a carbon nanotube dispersion and a resin, a composite slurry comprising a carbon nanotube dispersion, a resin and an active substance, and 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 Technology

[0003] With the increasing popularity of electric vehicles and the miniaturization, lightweighting, and high performance of portable devices, there is a demand for secondary batteries with high energy density, which in turn requires high capacity. Against this backdrop, due to their high energy density and high voltage characteristics, non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, especially lithium-ion secondary batteries, are widely used in various devices.

[0004] As the negative electrode material used in these lithium-ion secondary batteries, carbon materials, represented by graphite, are used because they have a low potential close to that of lithium (Li) and a high charge / discharge capacity per unit mass. However, these electrode materials have been used until the charge / discharge capacity per mass is close to the theoretical value, and the energy density per mass of the battery is approaching its limit. Therefore, in order to improve the utilization rate of the electrode, efforts are being made to reduce conductive additives and binders that do not contribute to the discharge capacity.

[0005] Carbon black, Ketjenblack, fullerenes, graphene, and micro-fine carbon materials are used as conductive additives. Carbon nanotubes, in particular, are widely used as a type of micro-fine carbon fiber. For example, it is known that adding carbon nanotubes to a negative electrode containing graphite or silicon improves electrode strength, such as conductivity, adhesion, and expansion / contraction properties, as well as the rate characteristics and cycle characteristics of lithium-ion secondary batteries (see Patent Document 1). Furthermore, research has been conducted on reducing electrode resistance by adding carbon nanotubes to the positive electrode (see Patent Documents 2 and 3). Multilayer carbon nanotubes with an outer diameter of ten to tens of nanometers are relatively inexpensive and are expected to be practically applicable.

[0006] Using carbon nanotubes with small average outer diameters allows for the efficient formation of conductive networks in small quantities, reducing the amount of conductive additives required in the positive and negative electrodes of lithium-ion secondary batteries. Furthermore, it is known that using carbon nanotubes with large fiber lengths also achieves the same effect (see Patent Document 4). However, carbon nanotubes with these characteristics exhibit strong cohesion and are difficult to disperse, thus making it impossible to obtain a carbon nanotube dispersion with sufficient dispersibility.

[0007] Therefore, methods for stabilizing carbon nanotube dispersion using various dispersants have been proposed. For example, dispersion in water and N-methyl-2-pyrrolidone (NMP) using water-soluble polymeric dispersants has been proposed (see Patent Documents 1 and 5). In Patent Document 1, for monolayer carbon nanotubes, zirconium oxide beads were dispersed in an NMP solvent containing polyvinylpyrrolidone, improving the conductivity of the electrode and the cycle characteristics of the battery. However, this method suffers from problems such as long dispersion time, smaller dispersed particle size of carbon nanotubes, and larger specific surface area of ​​carbon nanotubes. Due to the influence of the solid electrolyte interphase (SEI) film formed on the surface, the output characteristics are not sufficient. In addition, in Patent Document 5, for monolayer carbon nanotubes, ultrasonic waves were used to disperse them in an NMP solvent containing polyvinylpyrrolidone, but it was difficult to achieve high-concentration dispersion of carbon nanotubes in the solvent. In addition, a method for stabilizing the dispersion of multilayer carbon nanotubes using nitrile rubber as a dispersant has been proposed (see Patent Document 6). Patent Document 6 describes improving the output characteristics of an electrode by fabricating a multilayer carbon nanotube dispersion with an outer diameter of 10 nm to 30 nm. However, from the viewpoint of shape and strength, it is difficult to form conductive pathways in multilayer carbon nanotubes like in single-layer carbon nanotubes, resulting in insufficient cycle characteristics for lithium-ion secondary batteries.

[0008] Therefore, obtaining carbon nanotube dispersions that combine both recycling and output characteristics is an important issue to address in order to expand their applications.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2020-105316

[0012] Patent Document 2: Japanese Patent Application Publication No. 2011-70908

[0013] Patent Document 3: Japanese Patent Application Publication No. 2014-19619

[0014] Patent Document 4: Japanese Patent Application Publication No. 2012-221672

[0015] Patent Document 5: Japanese Patent Application Publication No. 2005-162877

[0016] Patent Document 6: Japanese Patent Publication No. 2018-533175 Summary of the Invention

[0017] The problem that the invention aims to solve

[0018] The problem to be solved by this invention is to provide a highly dispersible carbon nanotube dispersion, a carbon nanotube resin composition, and a composite slurry to obtain an electrode film with excellent conductivity. More specifically, it provides a non-aqueous electrolyte secondary battery with excellent rate characteristics and cycle characteristics.

[0019] Technical means to solve the problem

[0020] The inventors of this invention have conducted intensive research to solve the aforementioned problem. They discovered that by using a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a solvent, and comprising at least two types of carbon nanotubes with different average outer diameters in a specific mass ratio, the characteristics of each type of carbon nanotube can be maximized, resulting in an electrode film with excellent conductivity. Furthermore, a non-aqueous electrolyte secondary battery with well-formed conductive pathways and excellent rate and cycle characteristics can be obtained.

[0021] 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 a first carbon nanotube with an average outer diameter of 0.5 nm to 5 nm and a second carbon nanotube with an average outer diameter of 5 nm to 20 nm, and the mass ratio of the first carbon nanotube to the second carbon nanotube is 1:10 to 1:100.

[0022] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the total Brunauer-Emmett-Teller (BET) surface area of ​​the first and second carbon nanotubes contained in the carbon nanotube dispersion is 240 m². 2 / g~750m 2 / g.

[0023] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the aspect ratio of the first carbon nanotube is 2000 to 10000, and the aspect ratio of the second carbon nanotube is 50 to 200.

[0024] Furthermore, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein, when a 1560 cm⁻¹ [amount of material] is observed in the Raman spectrum of the first carbon nanotube, [the following is a description of the process]. -1~1600cm -1 The maximum peak intensity within the range is set as G, and 1310 cm⁻¹ is used. -1 ~1350cm -1 When the maximum peak intensity within the range is set to D, the G / D ratio is 10 to 100.

[0025] 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. 2 / g~1200m 2 / g.

[0026] Furthermore, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the volume resistivity of the first carbon nanotube is 1.0 × 10⁻⁶. -3 Ω·cm~3.0×10 -2 Ω·cm.

[0027] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the complex elastic modulus is 5 Pa or more but less than 650 Pa.

[0028] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the phase angle is 5° or more but less than 50°.

[0029] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, which is a dispersion in which 100 parts by mass contain 0.3 parts by mass and 5.0 parts by mass of carbon nanotubes, and the viscosity measured at 25°C with a rotor rotation speed of 60 rpm of a type B viscometer is 10 mPa·s or more and less than 2000 mPa·s.

[0030] In addition, another embodiment of the present invention relates to the carbon nanotube dispersion, wherein the cumulative particle size D50, determined by dynamic light scattering, is 400 nm to 4000 nm.

[0031] In addition, another embodiment of the present invention relates to a carbon nanotube resin composition comprising the carbon nanotube dispersion and a binder.

[0032] Another embodiment of the present invention relates to a composite slurry comprising the carbon nanotube resin composition and an active substance.

[0033] In addition, another embodiment of the present invention relates to a method for manufacturing the composite slurry, the method comprising the steps of (1) and (2) below.

[0034] (1) A process of dispersing a mixture containing a first carbon nanotube, a second carbon nanotube, a dispersant, and a solvent to obtain a carbon nanotube dispersion.

[0035] (2) The process of mixing the carbon nanotube dispersion, binder and active substance obtained in (1).

[0036] In addition, another embodiment of the present invention relates to a method for manufacturing the composite slurry, the method comprising the steps (1) to (3) below.

[0037] (1) A process of dispersing a mixture containing a first carbon nanotube, a dispersant, and a solvent to obtain a first carbon nanotube dispersion.

[0038] (2) A process of dispersing a mixture containing second carbon nanotubes, a dispersant, and a solvent to obtain a second carbon nanotube dispersion.

[0039] (3) The process of mixing the first carbon nanotube dispersion, the second carbon nanotube dispersion, the binder, and the active substance.

[0040] Another embodiment of the present invention relates to an electrode film formed by forming the composite slurry into a film.

[0041] In addition, 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 comprises the electrode membrane.

[0042] The effects of the invention

[0043] The embodiments of the present invention provide a highly dispersible carbon nanotube dispersion, a carbon nanotube resin composition, and a composite slurry. Furthermore, they provide a non-aqueous electrolyte secondary battery with excellent rate characteristics and cycle performance. Detailed Implementation

[0044] The following provides a detailed description of a carbon nanotube dispersion, a resin composition, a composite slurry, an electrode film as a coating film thereof, and a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. Furthermore, in this specification, the numerical range indicated by "~" represents the range in which the values ​​described before and after "~" are respectively the minimum and maximum values. In the numerical ranges described in stages in this specification, the upper or lower limit of a certain stage's numerical range can be arbitrarily combined with the upper or lower limit of another stage's numerical range.

[0045] <Carbon Nanotube Dispersion>

[0046] A carbon nanotube dispersion (hereinafter also simply referred to as dispersion) according to one embodiment of the present invention comprises at least carbon nanotubes, a dispersant, and a solvent. The carbon nanotubes, dispersant, and solvent will be described in detail below.

[0047] (Carbon nanotubes)

[0048] The carbon nanotube (hereinafter also referred to as CNT) in this embodiment comprises two or more types of carbon nanotubes with different average outer diameters, specifically, it comprises at least a first carbon nanotube and a second carbon nanotube.

[0049] 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 less than 3 nm, and more preferably 1 nm or more and less than 2 nm. The average outer diameter of the second carbon nanotube is 5 nm or more and less than 20 nm, and more preferably 5 nm or more and less than 15 nm. The average outer diameter of the carbon nanotubes can be observed using a transmission electron microscope to measure the length of the minor axis and calculate it based on the average value of 300 carbon nanotubes. Specifically, regarding the average outer diameter of the carbon nanotubes, for example, a film can be formed using a diluted solution of carbon nanotubes, observed using a direct transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.) at a magnification of 50,000x, the outer diameter of 300 randomly selected carbon nanotubes can be measured, and the average value can be calculated.

[0050] The first carbon nanotube is preferably a single-layer carbon nanotube, and the second carbon nanotube is preferably a multi-layer carbon nanotube. The single-layer carbon nanotube has a structure formed by a single layer of graphite, and the multi-layer carbon nanotube has a structure formed by two or more layers of graphite.

[0051] The first type of carbon nanotube is a carbon material with strong cohesion, poor dispersibility, and high linearity. Therefore, it is believed to facilitate the conduction between relatively far-distance active materials in the electrode layer, but the probability of contact with the active materials is relatively low. On the other hand, the second type of carbon nanotube is a carbon material with weak cohesion, good dispersibility, and low linearity. Therefore, it is believed to facilitate the conduction between relatively close-distance active materials, and the probability of contact with the active materials is relatively high.

[0052] The mass ratio of the first carbon nanotube to the second carbon nanotube 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 with good dispersibility, excellent conductivity between active substances, high contact probability with active substances, and the ability to form an electrode layer with excellent peel strength (adhesion) can be obtained.

[0053] Regarding the first carbon nanotube, when the 1560 cm⁻¹ is viewed in Raman spectroscopy... -1 ~1600cm-1 The maximum peak intensity within the range is set as G, and 1310 cm⁻¹ is used. -1 ~1350cm -1 When the maximum peak intensity within the range is set 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 nanotube is 0.5 or more but less than 10, preferably 0.5 to 4.5, and more preferably 1.0 to 4.0.

[0054] The first carbon nanotube, BET (Brunauer Emmett Teller), has a specific surface area of ​​600 m². 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 150m². 2 / g~750m 2 / g, preferably 200m 2 / g~750m 2 / g, more preferably 230m 2 / g~750m 2 / g.

[0055] The preferred total BET specific surface area of ​​carbon nanotubes is 240 m². 2 / g~750m 2 / g, more preferably 240m 2 / g~650m 2 / g, and more preferably 250m 2 / g~650m 2 / g. The total BET specific surface area can be calculated based on the BET specific surface area of ​​the first carbon nanotube and the second carbon nanotube and the mass ratio of each carbon nanotube. By defining the range, conductivity between active materials in the electrode layer is ensured, while the amount of SEI generated on the CNT surface can be suppressed during charge and discharge, thereby improving the battery's output characteristics.

[0056] The preferred volume resistivity of the first carbon nanotube is 1.0 × 10⁻⁶. -3 Ω·cm~3.0×10 -2 Ω·cm, more preferably 1.0×10 -3 Ω·cm~1.0×10 -2 The volume resistivity of the second carbon nanotube is preferably 1.0 × 10⁻⁶ Ω·cm. -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, for example, using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech, Inc.: Loresta GP Powder Resistivity Measuring System MCP-PD-51).

[0057] The carbon purity of carbon nanotubes is expressed as the percentage (by mass) of carbon atoms contained in the carbon nanotubes. The carbon purity is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more, relative to 100% by mass of the carbon nanotubes.

[0058] The amount of metal contained in the carbon nanotubes is preferably less than 20% by mass relative to 100% by mass of the carbon nanotubes, more preferably less than 10% by mass, and even more preferably less than 5% by mass. Examples of metals 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.

[0059] Carbon nanotubes can be surface-treated carbon nanotubes. Alternatively, carbon nanotubes can be carbon nanotube derivatives endowed with functional groups represented by carboxyl groups. Furthermore, carbon nanotubes containing organic compounds, metal atoms, or substances represented by fullerenes can also be used.

[0060] The carbon nanotubes in this embodiment can also be carbon nanotubes manufactured by any method. Carbon nanotubes can generally be manufactured by laser ablation, arc discharge, thermochemical vapor deposition (CVD), plasma CVD, and combustion, but are not limited to these methods.

[0061] (Dispersant)

[0062] In this embodiment, the dispersant is not particularly limited as long as it can stabilize the dispersion of carbon nanotubes; for example, surfactants and resin-based dispersants can be used. Surfactants are mainly classified as anionic, cationic, nonionic, and amphoteric. A preferred type of dispersant can be used in a suitable formulation amount according to the characteristics required for the dispersion of carbon nanotubes.

[0063] When choosing anionic surfactants, there is no particular limitation on their type. Specifically, examples include: fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkyl aryl sulfonates, alkyl naphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl aryl ether sulfates, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl phosphate sulfonates, glyceryl borate fatty acid esters, and polyoxyethylene glyceryl fatty acid esters, but these are not limited to. Furthermore, examples include: sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and sodium salts of β-naphthalene sulfonic acid formalin condensate, but these are not limited to.

[0064] Examples of cationic surfactants include, for example, alkylamine salts and quaternary ammonium salts. Specifically, examples include: stearamine acetate, trimethylcocoylammonium chloride, trimethyltallowylammonium chloride, dimethyldioleenylammonium chloride, methyloleenyl diethanol chloride, tetramethylammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfate, cetylpyridinium bromide, 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride, but are not limited to these.

[0065] Examples of nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyethylene alkylene derivatives, polyoxyethylene phenyl ethers, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, and alkyl allyl ethers. Specifically, examples include, but are not limited to, polyoxyethylene lauryl ethers, sorbitol fatty acid esters, and polyoxyethylene octylphenyl ethers. Additionally, examples of amphoteric surfactants include, but are not limited to, aminocarboxylates.

[0066] The selected surfactant is not limited to a single surfactant. Therefore, it is also possible to use a combination of two or more surfactants. For example, a combination of anionic and nonionic surfactants, or a combination of cationic and nonionic surfactants, can be used. In this case, the formulation amount is preferably set to an optimal 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 a polyoxyethylene phenyl ether.

[0067] In addition, as resin-type dispersants, examples include: cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyacrylonitrile polymers. Particularly preferred are methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyacrylonitrile polymers.

[0068] Carboxymethyl cellulose can be used in the form of sodium carboxymethyl cellulose or other salts, wherein the sodium carboxymethyl cellulose is formed by substituting the hydroxyl groups of carboxymethyl cellulose with sodium carboxymethyl groups.

[0069] The dispersant, measured by its pullullan weight-average molecular weight, is preferably 5,000 or more and 300,000 or less, more preferably 10,000 or more and 100,000 or less, and even more preferably 10,000 or more and 50,000 or less. Using a dispersant with a suitable weight-average molecular weight improves the adsorption of CNTs and further enhances the stability of the carbon nanotube dispersion. However, when using a dispersant exceeding the aforementioned range, the viscosity of the carbon nanotube dispersion increases, leading to a decrease in dispersion efficiency when using a nozzle-type high-pressure homogenizer or similar disperser that passes the dispersed liquid through a narrow flow path.

[0070] In addition to the dispersant, the mixture may also contain inorganic bases and inorganic metal salts. Preferably, the inorganic bases and inorganic metal salts are compounds containing at least one of alkali metals and alkaline earth metals. Specifically, examples include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals and alkaline earth metals. Furthermore, among these, chlorides, hydroxides, and carbonates of alkali metals and alkaline earth metals are preferred in terms of readily providing cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred among these.

[0071] In addition to dispersants, defoamers may also be included. Any commercially available defoamer, wetting agent, hydrophilic organic solvent, water-soluble organic solvent, or other substance with defoaming properties can be used; one type or a combination of multiple types can be used.

[0072] Examples include: alcohols; ethanol, propanol, isopropanol, butanol, octyl alcohol, hexadecyl alcohol, ethynyl alcohol, ethylene glycol monobutyl ether, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, ethynyl ethylene glycol, polyoxyalkylene glycol, propylene glycol, and other glycols, etc.

[0073] Fatty acid esters; diethylene glycol laurate, glyceryl monoricinoleate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trioleate, polyoxyethylene monolaurate, polyoxyethylene sorbitol monolaurate, natural waxes, etc.

[0074] Amide compounds; polyoxyalkylene amides, acrylate polyamines, etc.

[0075] Phosphate esters; tributyl phosphate, sodium octyl phosphate, etc.

[0076] Metallic soaps; aluminum stearate, calcium oleate, etc.

[0077] Oils and fats; animal and vegetable oils, sesame oil, castor oil, etc.

[0078] Mineral oil series: kerosene, paraffin, etc.

[0079] Silicone-based products; dimethyl silicone oil, silicone paste, silicone emulsion, organically modified polysiloxane, fluorosilicone oil, etc.

[0080] (solvent)

[0081] In this embodiment, the solvent is not particularly limited as long as it can disperse carbon nanotubes. It is preferably any one of water and / or water-soluble organic solvents, or a mixed solvent containing two or more of them, and more preferably contains 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.

[0082] As a water-soluble organic solvent, it can be used with: 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, glycerol, thiodiglycol, etc.); and 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-... Ethyl diethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.; amide systems (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.); heterocyclic systems (cyclohexylpyrrolidone, 2-oxazolidinone, 1,3-dimethyl-2-imidazolium, γ-butyrolactone, etc.); sulfoxide systems (dimethyl sulfoxide, etc.); sulfone systems (hexamethylphosphotriamide, sulfolane, etc.); lower ketone systems (acetone, methyl ethyl ketone, etc.); and other substances such as tetrahydrofuran, urea, and acetonitrile.

[0083] The carbon nanotube dispersion of this embodiment includes the carbon nanotubes, a dispersant, and a solvent. Regarding the aspect ratio of the carbon nanotubes in the 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 2000-10000, more preferably 2500-7000, and even more preferably 3000-6000. The aspect ratio of the second carbon nanotube is preferably 50-200, more preferably 50-150, and even more preferably 55-120. The aspect ratio of the carbon nanotubes can be calculated by dropping the diluted dispersion onto a mica substrate and observing and analyzing the deposited carbon nanotubes using a scanning electron microscope (SEM). Specifically, the aspect ratio of the carbon nanotubes can be calculated, for example, as follows.

[0084] The CNT dispersion was diluted with the solvent in the CNT dispersion to a 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 the first CNT, and CNTs with an outer diameter of more than 5 nm were designated as the second CNT. The average outer diameter of 100 randomly selected CNTs from the first and second CNTs was taken as the average outer diameter of the CNT.

[0085] In addition, the membrane was observed by SEM at a magnification of 5,000 to 20,000 times, and the average length of 100 randomly selected fibers in the first CNT and the second CNT was taken as the average fiber length of CNT in the CNT dispersion.

[0086] The aspect ratio of CNTs in the CNT dispersion is obtained by dividing the average fiber length of CNTs in the CNT dispersion by the average outer diameter of CNTs in the CNT dispersion.

[0087] The longer the carbon nanotube fibers, the easier it is to ensure conductivity between active materials, and the smaller the outer diameter, the more flexible they are, and the easier they are to follow the expansion / contraction of the active materials during charging and discharging. Furthermore, although the outer diameter does not change due to dispersion processing, the fiber length can sometimes be altered by cutting. Therefore, it is believed that CNTs with high aspect ratios in the dispersion (i.e., after dispersion preparation) help maintain a conductive network, while CNTs with low aspect ratios help form a uniform conductive network.

[0088] The complex elastic modulus of the carbon nanotube dispersion is preferably 5 Pa or more and less than 650 Pa, more preferably 5 Pa or more and less than 400 Pa, and even more preferably 10 Pa or more and less than 400 Pa. The complex elastic modulus of the carbon nanotube dispersion reflects the hardness of the dispersion, and there is a tendency for a smaller complex elastic modulus to be associated with better dispersion of carbon nanotubes and lower viscosity of the dispersion. On the other hand, even with good dispersion, the complex elastic modulus can sometimes be high due to the inherent structural viscosity of the carbon nanotubes when the fiber length is large. As will be described later, the complex elastic modulus of the carbon nanotube dispersion can be measured using a rheometer (a RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific).

[0089] 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°. The phase angle refers to the phase shift of the stress wave when the strain applied to the carbon nanotube dispersion is considered a sine wave. In the case of a purely elastic body, it becomes a sine wave with the same phase as the applied strain, and therefore the phase angle is 0°. On the other hand, in the case of a purely viscous body, it becomes a stress wave that has advanced 90°. Carbon nanotube dispersions with a complex elastic modulus and phase angle within the aforementioned range exhibit good particle size and dispersion state of the carbon nanotubes, making them suitable as carbon nanotube dispersions for improving electrode strength and conductivity. As described later, the phase angle of the carbon nanotube dispersion can be measured using a rheometer (a RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific).

[0090] Regarding the viscosity of the carbon nanotube dispersion, the viscosity measured at 60 rpm using a Type B viscometer (manufactured by TOKI SANGYO, model: BL) is preferably 10 mPa·s or more and less than 10,000 mPa·s, and more preferably 10 mPa·s or more and less than 2,000 mPa·s.

[0091] The cumulative particle size D50 of the carbon nanotube dispersion, determined 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 analyzer (manufactured by Microtrac-BEL Co., Ltd., Nanotrac UPA, model UPA-EX).

[0092] To obtain the carbon nanotube dispersion of this embodiment, it is preferable to perform a treatment that disperses the carbon nanotubes in a solvent. The dispersion apparatus used for this treatment is not particularly limited. Furthermore, the order and timing of adding the carbon nanotubes are not particularly limited. Alternatively, the first and second carbon nanotubes can be dispersed simultaneously, or they can be mixed after obtaining their respective dispersions.

[0093] As a dispersion device, a disperser commonly used in pigment dispersion and other applications can be used. Examples include: dispersers, homogenizers, planetary mixers, and other similar mixers; homogenizers (e.g., BRANSON Advanced Digital Sonifer (registered trademark), Model 450DA; M-technique Clearmix; PRIMIX Filmix; Silverson Abramix); paint conditioners (Red Devil); colloid mills (PUC colloid mill; IKA MK colloid mill); cone mills (IKA MKO cone mill); ball mills; and sand mills (Shinmaru). This includes media dispersers such as the "Dyno-mill" manufactured by ENTERPRISES, grinding mills, pearl mills (such as the "DCPmill" manufactured by Eirich), and ball mills; media-free dispersers such as wet jet mills ("Jenius PY" manufactured by Jenius, "Starburst" manufactured by SUGINO Machine, "nanomizer" manufactured by Nanomizer, etc.), "clear SS-5" manufactured by M-technique, and "MICROS" manufactured by Nara Machinery; and other roller mills, but is not limited to these.

[0094] The amount of carbon nanotubes in the carbon nanotube dispersion is preferably 0.3 to 5.0 parts by mass relative to 100 parts by mass of the carbon nanotube dispersion, more preferably 0.5 to 3.0 parts by mass, and even more preferably 0.8 to 1.5 parts by mass.

[0095] Furthermore, it is preferable to have a dispersion in which 100 parts by mass contain 0.3 parts by mass and 5.0 parts by mass of carbon nanotubes, and the viscosity measured at 25°C with a rotor speed of 60 rpm on a type B viscometer is 10 mPa·s or more and less than 2000 mPa·s.

[0096] Regarding the amount of dispersant in the carbon nanotube dispersion relative to the carbon nanotubes, it is preferable to use 20 to 150 parts by mass relative to 100 parts by mass of carbon nanotubes, more preferably 25 to 100 parts by mass, and even more preferably 30 to 80 parts by mass.

[0097] Regarding the amount of dispersant in the carbon nanotube dispersion relative to the first carbon nanotube, it is preferably 50 to 250 parts by mass relative to 100 parts by mass of the first carbon nanotube, more preferably 75 to 200 parts by mass, and even more preferably 75 to 150 parts by mass.

[0098] Regarding the amount of dispersant in the carbon nanotube dispersion relative to the second carbon nanotube, it is preferably 20 to 150 parts by mass relative to 100 parts by mass of the second carbon nanotube, more preferably 20 to 100 parts by mass, and even more preferably 20 to 60 parts by mass.

[0099] The pH of the carbon nanotube dispersion is preferably 6 to 11, more preferably 7 to 11, even more preferably 8 to 11, and particularly preferably 9 to 11. The pH of the carbon nanotube dispersion can be measured using a pH meter (Horiba Manufacturing Co., Ltd., pH meter F-52).

[0100] <Adhesive>

[0101] Adhesives are resins used to bond materials such as carbon nanotubes together.

[0102] Examples of adhesives used in this embodiment include: polymers or copolymers comprising ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, methacrylic acid, methacrylate, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc.; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluoropolymers; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified forms or mixtures of these resins, and copolymers, may also be used. Carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid are preferred.

[0103] The type and proportion of the binder can be appropriately selected according to the properties of the 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% by mass, the proportion of carboxymethyl cellulose is preferably 0.5% to 3.0% by mass, and more preferably 1.0% to 2.0% by mass.

[0104] Carboxymethyl cellulose is preferably a sodium salt of carboxymethyl cellulose obtained by substituting the hydroxyl groups of carboxymethyl cellulose with sodium carboxymethyl groups.

[0105] The viscosity of a 1% aqueous solution of carboxymethyl cellulose is preferably 500 mPa·s to 6000 mPa·s, and more preferably 1000 mPa·s to 3000 mPa·s. The viscosity of the 1% aqueous solution of carboxymethyl cellulose can be measured at 25°C using a type B viscometer with a rotor speed of 60 rpm.

[0106] The degree of etherification of carboxymethyl cellulose is preferably 0.6 to 1.5, and more preferably 0.8 to 1.2.

[0107] If the styrene-butadiene rubber is an oil-in-water emulsion, then a material commonly used as a binder for electrodes can be used. Regarding the amount of styrene-butadiene rubber used, with the mass of the active material set at 100% by mass, 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.

[0108] Regarding the amount of polyacrylic acid used, when the mass of the active substance is set to 100% by mass, the proportion of polyacrylic acid is preferably 1% to 25% by mass, and more preferably 5% to 20% by mass.

[0109] [Carbon nanotube resin composition]

[0110] The carbon nanotube resin composition of this embodiment includes carbon nanotubes, a dispersant, a solvent, and a binder.

[0111] To obtain the carbon nanotube resin composition of this embodiment, it is preferable to mix and homogenize the carbon nanotube dispersion with a binder. Various methods known in the art can be used as mixing methods. The carbon nanotube resin composition can be prepared using the dispersion apparatus described in the carbon nanotube dispersion.

[0112] [Composite slurry]

[0113] The composite slurry of this embodiment is a substance containing carbon nanotubes, dispersants, solvents, binders, and active substances.

[0114] <Active Substances>

[0115] The active material in this embodiment refers to the material that forms the basis of the battery reaction. In terms of electromotive force, the active material is divided into positive electrode active material and negative electrode active material.

[0116] There are no particular limitations on the active material used as the positive electrode; metal compounds such as metal oxides and metal sulfides, as well as conductive polymers, that can be doped or intercalated with lithium ions can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, examples include MnO, V₂O₅, and V₆O. 13 Transition metal oxide powders such as TiO2; composite oxide powders of lithium and transition metals such as layered lithium nickelate, lithium cobalt oxide, lithium manganese oxide, and spinel-structured lithium manganese oxide; transition metal sulfide powders such as lithium iron phosphate materials with olivine structure, TiS2, and FeS, etc. Additionally, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Furthermore, the aforementioned inorganic and organic compounds can be mixed and used.

[0117] As a negative electrode active material, there are no particular limitations as long as it can be doped or intercalated with lithium ions. Examples include: metallic Li, and alloys such as tin alloys, silicon alloys, and lead alloys; Li x Fe2O3, Li x Fe3O4, Li x Metal oxides such as WO2 (where x is a number where 0 < x < 1), lithium titanate, lithium vanadate, and lithium silicate; conductive polymers such as polyacetylene and poly(p-phenylene); amorphous carbon materials such as soft carbon or hard carbon, or highly graphitized carbon materials such as artificial graphite or natural graphite powders; carbon black, mesophase carbon black, resin-sintered carbon materials, vapor-grown carbon fibers, and carbon fibers. These negative electrode active materials can be used individually or in combination.

[0118] The preferred anode active material in this embodiment is a silicon-based anode active material, which is a silicon alloy or lithium silicate, or other silicon-containing anode active material.

[0119] Examples of silicon-based anode active materials include: so-called metallurgical-grade silicon produced by reducing silicon dioxide with carbon; industrial-grade silicon that reduces impurities by acid treatment or unidirectional solidification of metallurgical-grade silicon; high-purity silicon with different crystal states such as single crystal, polycrystalline, and amorphous produced by reacting silicon to obtain silane; and silicon that achieves high purity by adjusting the crystal state and precipitation state of industrial-grade silicon through sputtering or electron beam evaporation (EB) methods.

[0120] Additionally, silicon oxide, a compound of silicon and oxygen, can also be listed; silicon and various alloys, as well as silicon compounds whose crystallinity is adjusted by methods such as rapid cooling. Among these, silicon-based anode active materials with a structure in which silicon nanoparticles are dispersed in silicon oxide and are coated with a carbon film on the outside are preferred.

[0121] In this embodiment, the negative electrode active material, in addition to using silicon-based negative electrode active materials, is preferably made of amorphous carbonaceous materials such as soft carbon or hard carbon, or carbonaceous powders such as artificial graphite or natural graphite, which are highly graphitized carbon materials. Among these, the use of carbonaceous powders such as artificial graphite and natural graphite is preferred.

[0122] When the carbonaceous powder, such as artificial graphite or natural graphite, is set to 100% by mass, the amount of silicon-based negative electrode active material is preferably 3% to 50% by mass, more preferably 5% to 25% by mass.

[0123] In this embodiment, the BET specific surface area of ​​the active material is preferably 0.1 m². 2 / g~10m 2 / g, more preferably 0.2m 2 / g~5m 2 / g, and more preferably 0.3m 2 / g~3m 2 / g.

[0124] In this embodiment, the average particle size of the active material is preferably 0.5 μm to 50 μm, more preferably 2 μm to 20 μm. The average particle size of the active material mentioned in this specification is the average particle size obtained by measuring the active material using an electron microscope.

[0125] [Manufacturing method of composite material slurry]

[0126] The composite slurry of this embodiment can be prepared by various methods known in the past. A carbon nanotube dispersion can be prepared by dispersing a mixture containing a first carbon nanotube, a second carbon nanotube, a dispersant, and a solvent, or a dispersion of the first carbon nanotube and a dispersion of the second carbon nanotube can be prepared separately and then mixed for use.

[0127] The mixing order of the carbon nanotube dispersion, binder, and active material is not particularly limited; they can be added sequentially or simultaneously. For example, the active material can be added to the carbon nanotube resin composition, or the active material can be added to the carbon nanotube dispersion followed by the binder. Alternatively, a carbon nanotube resin composition containing a dispersion of one carbon nanotube can be prepared, and then the active material and a dispersion of another carbon nanotube can be added simultaneously or sequentially to prepare a composite slurry. In particular, the method of separately preparing dispersions of the first and second carbon nanotubes, and then mixing the binder and active material, allows for the equal distribution of the first and second carbon nanotubes among the active materials, thus forming a good conductive network, which is preferable from this perspective.

[0128] To obtain the composite slurry of this embodiment, it is preferable to perform a treatment in which an active substance is added to the carbon nanotube resin composition and then dispersed therein. The dispersion apparatus used for performing this treatment is not particularly limited. Regarding the composite slurry, the dispersion apparatus described in the carbon nanotube dispersion can be used to obtain the composite slurry.

[0129] The amount of active substance in the composite slurry of this embodiment is preferably 20 to 85 parts by mass relative to 100 parts by mass of the composite slurry, more preferably 30 to 75 parts by mass, and even more preferably 40 to 70 parts by mass.

[0130] The amount of carbon nanotubes in the composite slurry of this embodiment is preferably 0.01 to 10 parts by mass relative to 100 parts by mass of the active material, more preferably 0.02 to 5 parts by mass, and even more preferably 0.03 to 1 part by mass.

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

[0132] The amount of solids in the composite slurry of this embodiment is preferably 30% to 90% by mass relative to 100% by mass of the composite slurry, more preferably 30% to 80% by mass, and even more preferably 40% to 75% by mass.

[0133] [Electrode film]

[0134] The electrode film of this embodiment is formed by molding a composite material slurry. For example, it is a coating film formed by coating a composite material slurry onto a current collector and then drying it.

[0135] The material and shape of the current collector used in the electrode film of this embodiment are not particularly limited, and materials and shapes suitable for various secondary batteries can be appropriately selected. For example, the materials for the current collector include metals and alloys such as aluminum, copper, nickel, titanium, or stainless steel. In addition, as for the shape, foil on a flat plate can generally be used, but current collectors with roughened surfaces, perforated foil-shaped current collectors, and mesh-shaped current collectors can also be used.

[0136] There are no particular limitations on the method of applying the composite material slurry to the current collector, and known methods can be used. Specifically, examples include: molding coating, dip coating, roller coating, blade coating, spray coating, gravure coating, screen printing, or electrostatic coating. As for drying methods, placement drying, forced air drying, warm air drying, infrared heating machine, far-infrared heating machine, etc. can be used, but they are not particularly limited to these.

[0137] Alternatively, the coating can be followed by rolling using a flatbed press or calendering roller. The thickness of the electrode composite layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0138] Non-aqueous electrolyte secondary batteries

[0139] The non-aqueous electrolyte secondary battery of this embodiment includes a positive electrode, a negative electrode, and an electrolyte.

[0140] As a positive electrode, it can be a material made by coating a current collector with a composite slurry containing a positive electrode active material, drying it, and then forming an electrode film.

[0141] As a negative electrode, it can be a material made by coating a current collector with a composite slurry containing a negative electrode active material, drying it, and then forming an electrode film.

[0142] As the electrolyte, various known electrolytes capable of ion mobility can be used. Examples include lithium salt-containing electrolytes such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is phenyl), but these are not limited to these; electrolytes containing sodium or calcium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent before being used as the electrolyte solution.

[0143] As a non-aqueous solvent, there are no particular limitations. Examples include: carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octyl lactone; ethylene glycol dimethyl ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxacyclopentane, 4-methyl-1,3-dioxacyclopentane, 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 can be used individually or in mixtures of two or more.

[0144] The non-aqueous electrolyte secondary battery of this embodiment preferably includes a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics that have undergone hydrophilic treatment, but are not particularly limited to these.

[0145] The structure of the non-aqueous electrolyte secondary battery in this embodiment is not particularly limited. It typically includes a positive electrode and a negative electrode, as well as a separator as needed. It can be made into various shapes, such as paper type, cylindrical type, button type, and stacked type, depending on the intended use.

[0146] This 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, the entire disclosure of which is incorporated herein by reference.

[0147] [Example]

[0148] The present invention is described in more detail below with examples. The invention is not limited to the following examples as long as it does not depart from its spirit. In the examples, "carbon nanotubes" are sometimes abbreviated as "CNT". Furthermore, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0149] <Methods for Determining Physical Properties>

[0150] The physical properties of the CNTs used in the embodiments and comparative examples described below were determined using the following methods.

[0151] <CNT's G / D ratio>

[0152] CNTs were set on a Raman microscope (XploRA, manufactured by Horiba Manufacturing Co., Ltd.), and measurements were performed using a 532 nm laser wavelength. Measurement conditions were set as follows: acquisition time 60 seconds, number of measurements 2, neutral density filter 10%, objective lens magnification 20x, confocal aperture 500, slit width 100 μm, and measurement wavelength 100 cm⁻¹. -1 ~3000cm -1 The CNTs used for measurement were separated and transferred onto a glass slide, and flattened using a spatula. The obtained peaks, within the spectrum at 1560 cm⁻¹, are... -1 ~1600cm -1 The maximum peak intensity is set to G within the range of 1310 cm⁻¹. -1 ~1350cm -1 Within the range, the maximum peak intensity is set as D, and the ratio of G / D is used as the G / D ratio of CNT.

[0153] <BET specific surface area of ​​CNT>

[0154] 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 specific surface area of ​​the CNTs was then measured using a fully automated specific surface area measuring device (Mountech, HM-model 1208).

[0155] <Total BET specific surface area of ​​CNT>

[0156] The total BET surface area of ​​the CNTs is calculated using the BET specific surface area of ​​the CNTs determined by the method described above, the mass ratio of each CNT in the CNT dispersion prepared in the examples and comparative examples described later, and the following formula.

[0157] (Total surface area of ​​CNT) = (A + B)

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

[0159] B = (BET specific surface area of ​​the second CNT) × (mass ratio of the second CNT in the dispersion)

[0160] <Outer diameter and average outer diameter of CNT>

[0161] Using an electronic balance (Sartorius MSA225S100DI), 0.2 g of CNTs were weighed into a 450 mL SM sample vial (Sanshang Co., Ltd.), and 200 mL of toluene was added. The CNTs were then dispersed for 5 minutes at 50% amplitude in an ice bath using an Advanced Digital Sonifer (registered trademark), model 450DA (Branson). The CNT dispersion was then appropriately diluted by adding several μL 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.). Observation involved taking multiple photographs at 50,000x magnification, each containing more than 10 CNTs within the field of view. The outer diameter of 300 randomly selected CNTs from the photographs was measured, and the average value was taken as the average outer diameter (nm) of the CNTs.

[0162] <CNT aspect ratio in CNT dispersion>

[0163] The CNT dispersion prepared in the following examples was diluted using the solvent used in preparing the CNT dispersion to achieve a CNT concentration of 0.01% by mass. Several microliters (μL) of this solution were then added dropwise to a mica substrate and dried in an electric oven at 120°C to create a substrate for observing CNT fiber length. Platinum was then used to sputter the surface of the substrate for observing CNT fiber length. SEM was then used for observation. During observation, a photograph for outer diameter measurement was taken at 50,000x magnification within a field of view containing 10 or more CNTs. The magnification was then reduced to 5,000x to 20,000x to reveal the entire shape of the CNTs, thus taking photographs for fiber length measurement. Multiple photographs for outer diameter and fiber length measurement were taken by changing the field of view. Then, the outer diameter of the CNTs was determined based on photographs used for outer diameter measurement. CNTs with an outer diameter of less than 5 nm were designated as the first CNTs, and CNTs with an outer diameter of 5 nm or more were designated as the second CNTs. The average outer diameter of 100 randomly selected CNTs from both the first and second CNTs was taken as the average outer diameter of the CNTs. Additionally, the fiber length of the CNTs after outer diameter measurement was determined based on photographs used for fiber length measurement. The average length of the CNTs from both the first and second CNTs was taken as the fiber length of the CNTs in the CNT dispersion. The aspect ratio of the CNTs in the CNT dispersion was 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.

[0164] <Volume resistivity of CNTs>

[0165] Using a powder resistivity measuring apparatus (manufactured by Mitsubishi Chemical Analytech, Inc.: Loresta GP Powder Resistivity Measurement System MCP-PD-51), with a sample mass of 1.2 g, and employing a powder probe unit (four probes - ring electrode, electrode spacing 5.0 mm, electrode radius 1.0 mm, sample radius 12.5 mm), with the applied voltage limiter set to 90 V, the volume resistivity [Ω·cm] of conductive powders under various applied pressures was measured. For 1 g / cm... 3 The volume resistivity of CNTs at a given density was evaluated.

[0166] <Cumulative particle size of CNT dispersion>

[0167] After the CNT dispersion was allowed to stand in a constant temperature bath at 25°C for more than 1 hour, it was thoroughly stirred and diluted. Then, the cumulative particle size D50 of the CNT dispersion was measured using a particle size analyzer 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 to a loading index range of 0.8 to 1.2.

[0168] <Complex elastic modulus and phase angle of CNT dispersion>

[0169] The complex elastic modulus and phase angle of the CNT dispersion were evaluated by using a rheometer (RheoStress 1 rotary rheometer manufactured by Thermo Fisher Scientific) with a diameter of 35 mm and a 2° cone, at 25°C and a frequency of 1 Hz, with a strain rate ranging from 0.01% to 5%.

[0170] <Viscosity of CNT dispersion>

[0171] After allowing the CNT dispersion to stand in a constant temperature bath at 25°C for at least 1 hour, thoroughly stir the CNT dispersion, and then immediately perform the test using a Type B viscometer (manufactured by Toki Sanyo Co., Ltd., model: BL) with a rotor rotation speed of 60 rpm. Regarding the type of rotor used in the test, use 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.

[0172] <Peel strength of electrode film for negative electrode>

[0173] Using a dressing applicator, the weight per unit area of ​​the electrode is 8 mg / cm². 2 The negative electrode composite slurry was coated onto copper foil and then dried in an electric oven at 120℃±5℃ for 25 minutes. Then, using the coating direction as the long axis, it was cut into two 90mm×20mm rectangles. The peel strength was measured using a benchtop tensile testing machine (Toyo Seiki Co., Ltd., strograph E3) using the 180-degree peel test method. Specifically, a 100mm×30mm double-sided tape (No. 5000NS, Nitoms Co., Ltd.) was attached to a stainless steel plate, with the fabricated battery electrode composite layer in close contact with the other side of the tape. The tape was then stretched and peeled from bottom to top at a certain speed (50mm / min), and the average stress at this point was taken as the peel strength.

[0174] <Peel strength of positive electrode film>

[0175] Using a dressing applicator, the weight per unit area of ​​the electrode is 20 mg / cm². 2The positive electrode composite slurry was coated onto aluminum foil and dried in an electric oven at 120℃±5℃ for 25 minutes. Then, using the coating direction as the long axis, it was cut into two 90mm×20mm rectangles. The peel strength was measured using a benchtop tensile testing machine (Toyo Seiki Co., Ltd., strograph E3) using the 180-degree peel test method. Specifically, a 100mm×30mm double-sided tape (No. 5000NS, Nitoms Co., Ltd.) was attached to a stainless steel plate, with the prepared battery electrode composite layer in close contact with the other side of the tape. The tape was then stretched and peeled from bottom to top at a certain speed (50mm / min), and the average stress at this point was taken as the peel strength.

[0176] <Making a Standard Positive Electrode>

[0177] First, 93 parts by weight of the positive electrode active material (manufactured by BASF Toda Battery Materials, HED (registered trademark) NCM-111 1100), 4 parts by weight of acetylene black (manufactured by DENKA Corporation, DENKA BLACK (registered trademark) HS100), and 3 parts by weight of polyvinylidene fluoride (PVDF) (manufactured by Kureha Battery Materials Japan, Kureha KF polymer W#1300) were added to a volume of 150 cm⁻¹. 3 After placing the mixture in a plastic container, use a spatula to mix until the powder is uniform. Then, add 20.5 parts by weight of NMP and stir at 2000 rpm for 30 seconds using a spin / revolution mixer (Thinky ARE-310). Next, use a spatula to mix the mixture in the plastic container until uniform, and stir at 2000 rpm for 30 seconds using a spin / revolution mixer. Then, add 14.6 parts by weight of NMP and stir at 2000 rpm for 30 seconds using a spin / revolution mixer. Finally, stir at 3000 rpm for 10 minutes using a high-speed mixer to obtain a composite slurry for the positive electrode. Then, use a coating applicator to coat the composite slurry for the positive electrode onto a 20 μm thick aluminum foil as the current collector, and dry it in an electric oven at 120℃±5℃ for 25 minutes, adjusting the weight per unit area of ​​the electrode to 20 mg / cm². 2The composite layer was then rolled using a roller press (a 3t hydraulic roller press manufactured by Thank-Metal Co., Ltd.) to achieve a density of 3.1 g / cm³. 3 The standard positive electrode.

[0178] <Making a Standard Negative Electrode>

[0179] With a capacity of 150cm 3 In a plastic container, 0.5 parts by weight of acetylene black (DENKA BLACK (registered trademark) HS-100, manufactured by DENKA, Japan), 1 part by weight of MAC500LC (Sunrose special type MAC500L sodium carboxymethyl cellulose, manufactured by Nippon Paper Corporation, 100% non-volatile components), and 98.4 parts by weight of water were added. The mixture was then stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer (Thinky defoaming Rentarō, ARE-310). Next, 87 parts by weight of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries) and 10 parts by weight of silicon were added as active materials, and the mixture was stirred at 3000 rpm for 10 minutes using a high-speed mixer. Next, 3.1 parts by weight of SBR (TRD2001, manufactured by JSR Corporation) were added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer (Thinky Defoaming Rentarō, ARE-310) to obtain a composite slurry for the negative electrode. Then, a coating apparatus was used to measure the electrode at a unit area weight of 8 mg / cm². 2 The negative electrode composite slurry was coated onto copper foil and then dried in an electric oven at 120℃±5℃ for 25 minutes. Subsequently, it was rolled using a roller press (a 3t hydraulic roller press manufactured by Thank-Metal Co., Ltd.) to produce a composite layer with a density of 1.7 g / cm³. 3 The standard negative electrode.

[0180] <Synthesis of Dispersant (A)>

[0181] 100 parts of acetonitrile were charged into a reaction vessel including a gas inlet pipe, thermometer, condenser, and stirrer, and the vessel was purged 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-dimethylpentanonitrile) (manufactured by Nippon Oil Co., Ltd.; V-65) was added dropwise over 2 hours to carry out the polymerization reaction. After the dropwise addition was completed, the reaction was carried out 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 non-volatile component determination, and the dispersion medium was completely removed under reduced pressure to obtain dispersant (A). The weight average molecular weight (Mw) of dispersant (A) was 38,000.

[0182] (Method for determining weight-average molecular weight (Mw))

[0183] The weight-average molecular weight (Mw) of the manufactured dispersant (A) was determined by gel permeation chromatography (GPC) equipped with an RI detector under the following conditions. Molecular weight is expressed as pullulan.

[0184] Test sample: 0.1% by mass aqueous solution

[0185] Device: HLC-8320GPC (manufactured by Tosoh Corporation)

[0186] Eluent: 0.1M NaCl aqueous solution

[0187] Column: TSKgel SuperMultiporePW-M (manufactured by Tosoh)

[0188] Flow rate: 1.0 mL / min

[0189] Temperature: 25℃

[0190] Injection volume: 100 μl

[0191] Table 1 shows the CNTs used in the Examples, Comparative Examples, and Manufacturing Examples, along with their outer diameter, average outer diameter, specific surface area, G / D ratio, and powder resistivity (volume resistivity).

[0192] [Table 1]

[0193] Table 1

[0194]

[0195] Table 2 shows the dispersants used in the examples, comparative examples, and manufacturing examples.

[0196] [Table 2]

[0197] Table 2

[0198]

[0199] (Manufacturing Example 1)

[0200] 99 parts of ion-exchanged water were added to a stainless steel container, and 0.6 parts of dispersant (A) were added while stirring with a disperser until homogeneous. Then, 0.4 parts of CNT (A) were weighed out and added while stirring with a disperser. The mixture was then dispersed in batches at 8,600 rpm using a square-hole high-shear screen on a high-shear mixer (L5M-A, manufactured by SILVERSON) until homogeneous. Subsequently, the dispersion was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINOMACHINE) via piping for 10 pass-through dispersion treatments to obtain a CNT dispersion (WA1). The dispersion treatment was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0201] (Manufacturing Examples 2 to 17)

[0202] The CNT types, CNT addition amounts, dispersant types, dispersant addition amounts, ion exchange water addition amounts, and number of passes were changed to those listed in Table 3. Otherwise, CNT dispersions (WA2~WA10, WB1, WC1, WD1, WE1, WF1~WF3) were obtained by the same method as in Manufacturing Example 1.

[0203] Table 3 shows the CNT type, CNT addition amount, dispersant type, dispersant addition amount, ion exchange water addition amount, number of passes, and dispersion pressure for the manufacturing examples.

[0204] [Table 3]

[0205]

[0206] (Example 1)

[0207] The CNT dispersion (WA1) containing the first CNT and the CNT dispersion (WE1) containing the second CNT prepared in Manufacturing Example 1 were weighed into a stainless steel container at a CNT mass ratio of 1:30. Then, the mixture was stirred using a disperser until homogeneous to obtain a CNT dispersion (WAE1) containing the first CNT and the second CNT.

[0208] (Examples 2 to 19)

[0209] The CNT dispersion types and CNT mass ratios were changed to those listed in Table 4. Otherwise, CNT dispersions (WAE2~WAE13, WBE1, WCE1, WDE1, WAF1~WAF3) containing the first CNT and the second CNT were obtained by the same method as in Example 1.

[0210] (Comparative Examples 1 to 3)

[0211] The CNT mass ratio was changed to that shown in Table 4. Otherwise, a CNT dispersion (WAE14, WBE2 to WBE3) containing the first CNT and the second CNT was obtained by the same method as in Example 1.

[0212] Table 4 shows the mass ratio of CNT dispersions, the CNT mass ratio, and the total BET specific surface area (m²) of CNTs in the dispersions used in the examples and comparative examples. 2 (g), and the aspect ratios of the first CNT and the second CNT in the dispersion.

[0213] [Table 4]

[0214]

[0215] (Manufacturing Example 18)

[0216] 99 parts NMP were added to a stainless steel container, and 0.6 parts dispersant (E) were added while stirring with a disperser until the dispersant (E) dissolved. Then, 0.4 parts CNT (A) were weighed out and added while stirring with a disperser. A high-shear mixer (L5M-A, manufactured by SILVERSON) with a square-hole high-shear screen was installed, and the mixture was dispersed in batches at 8,600 rpm until homogeneous. Subsequently, the dispersion was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE) via piping, and subjected to 10 pass-through dispersion processes to obtain a CNT dispersion (A11). The dispersion process was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0217] (Manufacturing Examples 19 to 20)

[0218] The CNT type, CNT addition amount, dispersant type, dispersant addition amount, NMP addition amount, and number of passes were changed to those listed in Table 5. Otherwise, the CNT dispersion (B2, E2) was obtained by the same method as in Manufacturing Example 18.

[0219] [Table 5]

[0220]

[0221] (Example 20)

[0222] The first CNT dispersion (A11) and the second CNT dispersion (E2) prepared in Manufacturing Example 18 were weighed into a stainless steel container at a CNT mass ratio of 1:30. Then, the mixture was stirred using a disperser until homogeneous to obtain a CNT dispersion (AE15) in which the two CNTs are mixed.

[0223] (Examples 21-22)

[0224] The CNT mass ratio was changed to that shown in Table 6. Otherwise, a CNT dispersion (AE16-AE17) containing two CNTs was obtained by the same method as in Example 20.

[0225] (Comparative Examples 4 to 6)

[0226] The CNT mass ratio was changed to that shown in Table 6. Otherwise, a CNT dispersion (AE18, BE4-BE5) containing two CNTs was obtained by the same method as in Example 20.

[0227] [Table 6]

[0228]

[0229] (Example 23)

[0230] Add 8.9 parts of ion-exchanged water to a stainless steel container, and while stirring with a disperser, add 0.06 parts of dispersant (A) until homogeneous. Then, weigh out 0.04 parts of CNT (A) and add it while stirring with a disperser. Disperse in batches at 8,600 rpm using a square-hole high-shear screen on a high-shear mixer (L5M-A, manufactured by SILVERSON) until homogeneous, obtaining premix (A). Next, add 89.26 parts of ion-exchanged water to a stainless steel container, and while stirring with a disperser, add 0.54 parts of dispersant (A) until homogeneous. Then, weigh out 1.2 parts of CNT (E) and add it while stirring with a disperser. Disperse in batches at 8,600 rpm using a square-hole high-shear screen on a high-shear mixer until homogeneous, obtaining premix (B). Then, premixed liquid (B) was supplied from a stainless steel container via piping to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE) for 30 pass-through dispersion treatments. Next, premixed liquid (A) was supplied to the high-pressure homogenizer via piping for a further 10 pass-through dispersion treatments, thereby obtaining the CNT dispersion (WAE19). The dispersion treatment was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0231] Table 7 shows the CNT addition amount, dispersant addition amount, ion exchange water addition amount, total number of passes, dispersion pressure (MPa), and total specific surface area (m²) of the CNT dispersion prepared in Example 23. 2 / g), aspect ratio.

[0232] [Table 7]

[0233]

[0234] Table 8 shows the evaluation results of the CNT dispersions prepared in Examples 1 to 23 and Comparative Examples 1 to 6. Regarding the evaluation of the phase angle of the CNT dispersion, a value of 10 or more but less than 50° was designated as A (Good), a value of 5 or more but less than 10° was designated as B (Acceptable), and a value less than 5° or more than 5° was designated as C (Unacceptable). Regarding the evaluation of the complex elastic modulus of the CNT dispersion, a value of 5 or more but less than 400° was designated as A (Good), a value of 400 or more but less than 650° was designated as B (Acceptable), and a value less than 5° was designated as C (Unacceptable). Regarding the evaluation of the viscosity of the CNT dispersion, a value less than 500 mPa·s was designated as AA (Excellent), a value of 500 mPa·s or more but less than 2000 mPa·s was designated as A (Good), a value of 2000 mPa·s or more but less than 10000 mPa·s was designated as B (Acceptable), and a value of 10000 mPa·s or more, or sedimentation or separation, was designated as C (Unacceptable). Regarding the particle size evaluation of CNT dispersions, a particle size distribution with a cumulative particle size D50 of 900 nm or more but less than 4000 nm is designated as A (Good), a particle size distribution with a cumulative particle size D50 of 400 nm or more but less than 900 nm is designated as B (Acceptable), and a particle size distribution with a cumulative particle size D50 of less than 400 nm or more than 4000 nm is designated as C (Unacceptable).

[0235] [Table 8]

[0236] Table 8

[0237]

[0238] (Example 24)

[0239] Weigh out 6.9 parts by weight of CNT dispersion (WAE1), 12.5 parts by weight of an aqueous solution containing 2% by weight of carboxymethyl cellulose (CMC) (manufactured by Daicel Finechem Co., Ltd., #1190), and 7.7 parts by weight of deionized water to a volume of 150 cm³. 3The mixture was placed in a plastic container. Then, using a rotary / revolutionary mixer (Thinky Corporation, Defoaming Rentarō, ARE-310), it was stirred at 2000 rpm for 30 seconds to obtain a CNT resin composition (WAE1). Next, 2.4 parts by weight of silica (manufactured by Osaka Titanium Technologies Co., Ltd., SILICON MONOOXIDE, SiO1.3C 5μm) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer. Then, 21.9 parts by weight of artificial graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-20) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer. Next, 0.78 parts by weight of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD2001) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the aforementioned rotary / revolutionary mixer to obtain a composite slurry for the negative electrode (WAE1).

[0240] (Examples 25 to 44), (Comparative Examples 7 to 11)

[0241] The CNT dispersion was changed to the one described in Table 9, and the amount of CNT dispersion and ion-exchange water added was adjusted so that the amount of CNT added in 100 parts by mass of the composite slurry was the value described in Table 9. Otherwise, CNT resin compositions (WAE2-WAE3, WAE4-1-WAE4-2, WAE5-WAE14, WBE1-WBE3, WCE1, WDE1, WAF1-WAF3, WAE19, WA1, WE1) and negative electrode composite 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 component of the negative electrode composite slurry was set to 48% by mass.

[0242] (Example 45)

[0243] Weigh out 7.0 parts by weight of NMP containing 8% by weight of PVDF (Solvay, Solef #5130) to a volume of 150 cm³. 3The mixture was placed in a plastic container. Then, 15.6 parts by weight of CNT dispersion (AE15) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a spin / revolution mixer (Defoaming Rentarō, ARE-310) to obtain the CNT resin composition (AE15). Next, 36.9 parts of positive electrode active material (manufactured by BASFTODA Battery Materials Contract Company, HED (registered trademark) NCM-111 1100) was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a spin / revolution mixer to obtain the positive electrode composite slurry (AE15).

[0244] (Examples 46-47), (Comparative Examples 12-14)

[0245] The CNT dispersion was changed to the one described in Table 9, and the amount of CNT dispersion added was adjusted so that the amount of CNT added in 100 parts by mass of composite material slurry was the value described in Table 9. Otherwise, CNT resin composition (AE16-AE18, BE4-BE5) and positive electrode composite material slurry (AE16-AE18, BE4-BE5) were obtained by the same method as in Example 45.

[0246] (Example 48)

[0247] Weigh out 0.6 parts by weight of CNT dispersion (WA1), 12.5 parts by weight of an aqueous solution containing 2% by weight of CMC (manufactured by Daicel Finechem, Inc., #1190), and 7.7 parts by weight of ion-exchanged water to a volume of 150 cm³. 3The mixture was placed in a plastic container. Then, using a rotary / revolutionary mixer (Thinky Corporation, Defoaming Rentarō, ARE-310), it was stirred at 2000 rpm for 30 seconds to obtain a CNT resin composition (WA1). Next, 2.4 parts by weight of silica (manufactured by Osaka Titanium Technologies Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5μm) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer. Then, 21.9 parts by weight of artificial graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-20) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer. Finally, 0.63 parts by weight of the CNT dispersion (WE1) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer. Next, 0.78 parts by weight of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD2001) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary / revolutionary mixer to obtain a composite slurry for the negative electrode (WAE20).

[0248] [Table 9]

[0249] Table 9

[0250]

[0251] (Example 49)

[0252] Using a dressing applicator, the weight per unit area of ​​the electrode is 8 mg / cm². 2 The negative electrode composite slurry (WAE1) is coated onto the copper foil and then dried in an electric oven at 120℃±5℃ for 25 minutes to obtain the electrode film (WAE1).

[0253] (Examples 50-70), (Comparative Examples 15-19)

[0254] The negative electrode composite slurry was changed to the one listed in Table 10. Otherwise, the electrode film (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 in Example 49.

[0255] (Example 71)

[0256] Using a dressing applicator, the weight per unit area of ​​the electrode is 20 mg / cm². 2The positive electrode composite slurry (AE15) was coated onto the copper foil and then dried in an electric oven at 120℃±5℃ for 25 minutes to obtain the electrode film (AE15).

[0257] (Examples 72-73), (Comparative Examples 20-22)

[0258] The positive electrode composite slurry was changed to the one listed in Table 10. Otherwise, the electrode films (AE16-AE18, BE4, BE5) were obtained by the same method as in Example 71.

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

[0260] [Table 10]

[0261] Table 10

[0262] Electrode film Close contact assessment 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] (Examples 74-95), (Comparative Examples 23-27)

[0264] The electrode films (WAE1~WAE3, WAE4-1~WAE4-2, WAE5~WAE14, WAE19~WAE20, WBE1~WBE3, WCE1, WDE1, WAF1~WAF3, WA1, WE1) were rolled using a roller press (a 3t hydraulic roller press manufactured by Thank-Metal Co., Ltd.) to produce a composite layer with a density of 1.7 g / cm³. 3 The negative electrode.

[0265] (Examples 96-98), (Comparative Examples 28-30)

[0266] The electrode films (AE15-AE18, BE4, BE5) were rolled using a roller press (manufactured by Thank-Metal Co., Ltd., a 3t hydraulic roller press) to produce a composite layer with a density of 3.2 g / cm³. 3 The positive pole.

[0267] Table 11 shows the negative and positive electrodes prepared 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 respectively cut into 50mm×45mm and 45mm×40mm pieces, and inserted together with the separator (porous polypropylene membrane) inserted between them into an aluminum laminated bag. They were then dried in an electric oven at 60°C for 1 hour. Then, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a 3:5:2 (volume ratio) mixture as an additive, and then adding 1 part by mass of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) to each of 100 parts by mass of the mixed solvent, and then dissolving LiPF6 at a concentration of 1M) was injected into an argon-filled glove box. The aluminum laminated bag was then sealed to produce a laminated lithium-ion secondary battery (WAE1).

[0274] (Examples 100-120), (Comparative Examples 31-35)

[0275] The negative electrode is changed to the one listed in Table 12. Otherwise, laminated lithium-ion secondary batteries (WAE2~WAE3, WAE4-1~WAE4-2, WAE5~WAE14, WAE19~WAE20, WBE1~WBE3, WCE1, WDE1, WAF1~WAF3, WA1, WE1) are manufactured using the same method.

[0276] (Example 121)

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

[0278] (Examples 122-123), (Comparative Examples 36-38)

[0279] The positive electrode was changed to the one listed in Table 12. Otherwise, laminated lithium-ion secondary batteries (AE15~AE18, BE4~BE5) were manufactured using the same method.

[0280] [Table 12]

[0281] Table 12

[0282]

[0283] Table 13 shows the evaluation results of the laminated lithium-ion secondary batteries prepared in Examples 124 to 148 and Comparative Examples 39 to 46. Regarding rate characteristics, a rate characteristic of 80% or more was designated AA (Excellent), 70% or more but less than 80% was designated A (Good), 60% or more but less than 70% was designated B (Acceptable), and less than 60% was designated C (Unacceptable). Regarding cycle characteristics, a cycle characteristic of 97% or more was designated AA (Excellent), 93% or more but less than 97% was designated A (Good), 90% or more but less than 93% was designated B (Acceptable), and less than 90% was designated C (Unacceptable).

[0284] [Table 13]

[0285] Table 13

[0286]

[0287] In the above embodiments, in examples using a carbon nanotube dispersion containing at least two different types of carbon nanotubes, where the average outer diameter of the first CNT is 0.5 nm or more but less than 5 nm, the average outer diameter of the second CNT is 5 nm or more but less than 20 nm, and the mass ratio of the first CNT to the second CNT is 1:10 to 1:100, a lithium-ion secondary battery with superior rate characteristics and cycle characteristics compared to the comparative example can be obtained. When the mass ratio exceeds 1:100, the construction of the conductive network is considered insufficient, 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 too large, thus increasing the proportion of the irreversible resistive component (SEI) formed on the surface of the carbon nanotubes, leading to reduced rate characteristics. Therefore, it is clear that within a mass ratio range of 1:10 to 1:100, the advantages of each carbon nanotube can be utilized while compensating for its disadvantages, providing a lithium-ion secondary battery with high output power and long lifespan.

[0288] The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above description. 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 liquid comprising carbon nanotubes, a resin-type dispersant, and a solvent, wherein the carbon nanotube dispersion liquid contains the carbon nanotubes, the resin-type dispersant, and the solvent, the carbon nanotubes contain 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, a mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:10 to 1:100, a G / D ratio of the first carbon nanotubes is 10 to 100, and a G / D ratio of the second carbon nanotubes is 0.5 or more and less than 10. The first carbon nanotubes are single-walled carbon nanotubes, and the second carbon nanotubes are multi-walled carbon nanotubes. The mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:12 to 1:

70. When the maximum peak intensity in the range of 1560 cm -1 ~ 1600 cm -1 in the Raman spectrum of the carbon nanotube is set as G, and the maximum peak intensity in the range of 1310 cm -1 ~ 1350 cm -1 is set as D, The mass ratio of the first carbon nanotubes to the second carbon nanotubes is 1:15 to 1:

90. The average outer diameter of the first carbon nanotubes is 0.5 nm or more and 2 nm or less, and the average outer diameter of the second carbon nanotubes is 5 nm or more and 15 nm or less.

2. The carbon nanotube dispersion of claim 1, wherein, The aspect ratio of the first carbon nanotubes is 2000 to 10000.

3. The carbon nanotube dispersion of claim 2, wherein, The aspect ratio of the second carbon nanotubes is 50 to 200.

4. The carbon nanotube dispersion of claim 2, wherein, The aspect ratio of the first carbon nanotubes is 2100 to 6100.

5. The carbon nanotube dispersion of claim 3, wherein, The aspect ratio of the second carbon nanotubes is 50 to 150.

6. The carbon nanotube dispersion liquid according to any one of claims 1 to 5, wherein, The total Brunauer-Emmett-Teller surface area of the first carbon nanotubes and the second carbon nanotubes is 240 m 2 / g ~ 750 m 2 / g.

7. The carbon nanotube dispersion liquid according to any one of claims 1 to 5, wherein, 9. The carbon nanotube dispersion liquid according to any one of claims 1 to 3, wherein the G / D ratio of the first carbon nanotubes is 20 to 50, and the G / D ratio of the second carbon nanotubes is 0.5 to 4.

5. The solvent is a mixed solvent containing water and a water-soluble organic solvent, and the water-soluble organic solvent contains an amide-based solvent.

8. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, The resin-type dispersant contains at least one selected from the group consisting of a cellulose derivative, a polyvinyl alcohol, a polyvinyl butyral, a polyvinyl pyrrolidone, and a polyacrylonitrile-based polymer. The solvent contains water, and the content of water in the solvent is preferably 95% by mass or more. The resin-type dispersant contains at least one selected from the group consisting of a cellulose derivative, a polyvinyl alcohol, a polyvinyl butyral, and a polyvinyl pyrrolidone. The solvent contains a water-soluble organic solvent, and the water-soluble organic solvent contains an amide-based solvent. The resin-type dispersant contains a polyacrylonitrile-based polymer.

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

11. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, The phase angle is 5° or more and less than 50°.

12. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, 19. The carbon nanotube dispersion liquid according to any one of claims 1 to 5, which is a dispersion liquid containing 0.3 parts by mass or more and 5.0 parts by mass or less of the carbon nanotubes in 100 parts by mass of the carbon nanotube dispersion liquid, and has a viscosity of 10 mPa-s or more and less than 2000 mPa-s as measured at 25°C at a rotational speed of 60 rpm of a B-type viscometer.

13. The carbon nanotube dispersion of claim 12, wherein, The cumulative particle size D50 measured by a dynamic light scattering method is 400 nm to 4000 nm.

14. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, ​ 15. The carbon nanotube dispersion of claim 14, wherein, ​ 16. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, the first carbon nanotubes have a Brunauer-Emmett-Teller specific surface area of 600 m 2 / g to 1000 m 2 / g, and the second carbon nanotubes have a Brunauer-Emmett-Teller specific surface area of 230 m 2 / g to 720 m 2 / g.

17. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, ​ 18. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, ​ ​ 20. The carbon nanotube dispersion of any one of claims 1 to 5, wherein, ​ 21. A composite material slurry comprising a carbon nanotube resin composition and an active material, the carbon nanotube resin composition comprising the carbon nanotube dispersion liquid according to any one of claims 1 to 20 and a binder.

22. A method for producing a composite material slurry, the method for producing a composite material slurry according to claim 21, the method for producing a composite material slurry comprising the following (1) and (2), (1) a step of dispersing a mixed solution containing the first carbon nanotube, the second carbon nanotube, the dispersant, and the solvent to obtain the carbon nanotube dispersion liquid; (2) a step of mixing the carbon nanotube dispersion liquid obtained in (1), a binder, and an active material.

23. A method for producing a composite material slurry, the method for producing a composite material slurry according to claim 21, the method for producing a composite material slurry comprising the following (1) to (3), (1) a step of dispersing a mixed solution containing the first carbon nanotube, the dispersant, and the solvent to obtain a first carbon nanotube dispersion liquid; (2) a step of dispersing a mixed solution containing the second carbon nanotube, the dispersant, and the solvent to obtain a second carbon nanotube dispersion liquid; (3) a step of mixing the first carbon nanotube dispersion liquid, the second carbon nanotube dispersion liquid, a binder, and an active material.

24. An electrode film formed by forming the composite material slurry according to claim 21 into a film shape.

25. A nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and an electrolyte, in the nonaqueous electrolyte secondary battery, at least one of the positive electrode or the negative electrode includes the electrode film according to claim 24.

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