Carbon nanotube dispersion and use thereof

Abstract

The present disclosure provides a carbon nanotube dispersion liquid and use thereof. A carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a solvent, the carbon nanotube dispersion liquid satisfying (1) to (4) below. (1) When a maximum peak intensity in a range of 1560 cm ‑1 - 1600 cm ‑1 in a Raman spectrum of the carbon nanotubes is set as G and a maximum peak intensity in a range of 1310 cm ‑1 - 1350 cm ‑1 is set as D, a G / D ratio of the carbon nanotubes is 5 to 100 (2) 30 parts by mass or more and less than 250 parts by mass of the dispersant are contained per 100 parts by mass of the carbon nanotubes (3) a complex elastic modulus of the carbon nanotube dispersion liquid at 25°C and a frequency of 1 Hz is 5 Pa or more and less than 650 Pa, and a phase angle is 5° or more and less than 50° (4) a BET specific surface area of the carbon nanotubes is 550 m 2 / g to 1200 m 2 / g.

Description

[0001] The disclosures in this case are related to the subject matter described in Japanese Patent Application No. 2020-171017 filed on October 9, 2020 and Japanese Patent Application No. 2021-160281 filed on September 30, 2021, and the entire disclosures of those patents are incorporated herein by reference. 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 binder, a composite slurry comprising a carbon nanotube dispersion, a binder and an active substance, 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, attempts are being made to reduce conductive additives or 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 graphite or silicon anodes 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, for example, Patent Document 1). Furthermore, research has been conducted on reducing electrode resistance by adding carbon nanotubes to the cathode (see, for example, Patent Documents 2 and 3). Multilayer carbon nanotubes with outer diameters of tens of nanometers are relatively inexpensive and are expected to be practically applicable.

[0006] Using carbon nanotubes with a small average outer diameter allows for the efficient formation of a conductive network 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, for example, Patent Document 4).

[0007] In addition, methods for stabilizing the dispersion of carbon nanotubes using various dispersants have been proposed. For example, dispersion in water and N-methyl-2-pyrrolidone (NMP) using polymeric dispersants such as water-soluble polymers has been proposed (see Patent Documents 1, 5, and 6). Furthermore, a method for stabilizing the dispersion of multilayer carbon nanotubes using nitrile rubber as a dispersant has been proposed (see Patent Document 7).

[0008] Existing technical documents

[0009] Patent documents

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

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

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

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

[0014] Patent Document 5: Japanese Patent Application Publication No. 2010-254546

[0015] Patent Document 6: Japanese Patent Application Publication No. 2005-162877

[0016] Patent Document 7: Japanese Patent Publication No. 2018-533175 Summary of the Invention

[0017] The problem that the invention aims to solve

[0018] However, carbon nanotubes, characterized by their small average outer diameter and large fiber length, are difficult to disperse due to their strong cohesion, making it impossible to obtain a sufficiently dispersible carbon nanotube dispersion. In Patent Document 1, for monolayer carbon nanotubes, zirconium oxide beads were used for dispersion in an NMP solvent containing polyvinylpyrrolidone, but this resulted in long dispersion times and smaller dispersed particle sizes of the carbon nanotubes. While the conductivity of the electrode was improved, the electrode strength could not be significantly enhanced. In Patent Document 5, for oxidized bilayer carbon nanotubes, an ultrasonic homogenizer was used for dispersion in a carboxymethyl cellulose aqueous solution, but it was difficult to achieve high-concentration dispersion of carbon nanotubes in the solvent. Furthermore, in Patent Document 6, for monolayer carbon nanotubes, ultrasonic dispersion was used in an NMP solvent containing polyvinylpyrrolidone, but it was also difficult to achieve high-concentration dispersion of carbon nanotubes in the solvent. In Patent Document 7, it was proposed that by preparing a multilayer carbon nanotube dispersion with a specific complex elastic modulus, the output characteristics of the electrode could be improved. However, in multilayer carbon nanotubes with an outer diameter of 10 nm or more, the improvement in electrode strength is insufficient, making it difficult to improve the cycle characteristics of lithium-ion secondary batteries. Therefore, obtaining carbon nanotube dispersions, especially monolayer carbon nanotubes, which can be used as micro-fibers, and uniformly dispersed in a dispersion medium at high concentrations is an important issue for expanding their applications.

[0019] The problem to be solved by this invention is to provide a carbon nanotube dispersion, a carbon nanotube resin composition, and a composite slurry with high dispersibility and elastic modulus, so as to obtain an electrode film with excellent electrode strength and conductivity. More specifically, it provides a non-aqueous electrolyte secondary battery with excellent rate characteristics and cycle characteristics.

[0020] Technical means to solve the problem

[0021] That is, the present invention relates to a carbon nanotube dispersion comprising carbon nanotubes, a dispersant and a solvent, wherein the carbon nanotube dispersion satisfies the following (1) to (4).

[0022] (1) When 1560 cm⁻¹ is used in the Raman spectrum of carbon nanotubes -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 specified range is set as D, the G / D ratio of carbon nanotubes is 5–100.

[0023] (2) Contains 30 to 250 parts by weight of dispersant relative to 100 parts by weight of carbon nanotubes.

[0024] (3) The complex elastic modulus of the carbon nanotube dispersion at 25℃ and 1Hz is greater than 5Pa but less than 650Pa, and the phase angle is greater than 5° but less than 50°.

[0025] (4) The Brunauer-Emmett-Teller (BET) specific surface area of ​​carbon nanotubes is 550 m². 2 / g~1200m 2 / g

[0026] Furthermore, this invention relates to the carbon nanotube dispersion, wherein, when a 1560 cm⁻¹ [element / component] is observed in the Raman spectrum of the carbon nanotubes... -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 of carbon nanotubes is 10–50.

[0027] Furthermore, this invention relates to the carbon nanotube dispersion, wherein, when a rheometer is used at a shear rate of 1 (s) -1 When measuring the carbon nanotube dispersion at 25℃, the value was above 5 Pa·s but less than 40 Pa·s.

[0028] In addition, the present invention relates to the carbon nanotube dispersion wherein the cumulative particle size D10, as determined by dynamic light scattering, is greater than 200 nm and less than 500 nm.

[0029] Furthermore, the present invention relates to the carbon nanotube dispersion, wherein the volume resistivity of the carbon nanotubes is 1.0 × 10⁻⁶. -3 Ω·cm~1.0×10 -2 Ω·cm.

[0030] In addition, the present invention relates to the carbon nanotube dispersion wherein the cumulative particle size D50, as determined by dynamic light scattering, is greater than 500 nm and less than 3000 nm.

[0031] In addition, the present invention relates to the carbon nanotube dispersion, wherein the weight average molecular weight of the dispersant is 10,000 to 100,000.

[0032] In addition, the present invention relates to the carbon nanotube dispersion, wherein the solvent comprises water.

[0033] In addition, the present invention relates to a carbon nanotube resin composition comprising the carbon nanotube dispersion and an adhesive.

[0034] In addition, the present invention relates to a composite slurry comprising the aforementioned carbon nanotube resin composition and an active substance.

[0035] In addition, the present invention relates to an electrode film, which is a coating film of the composite material slurry.

[0036] In addition, the present invention relates to a non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode comprises the electrode membrane.

[0037] The effects of the invention

[0038] By using the carbon nanotube dispersion of the present invention, resin compositions, composite slurries, and electrode films with excellent electrode strength and adhesion can be obtained. Furthermore, non-aqueous electrolyte secondary batteries with excellent rate characteristics and cycle characteristics can be obtained. Therefore, the carbon nanotube dispersion of the present invention can be used in various applications requiring high conductivity and durability. Attached Figure Description

[0039] Figure 1 This is a chart showing the Raman spectra of the carbon nanotubes used in the embodiments and comparative examples of the present invention. Detailed Implementation

[0040] The carbon nanotube dispersion, resin composition, composite slurry, electrode film as a coating film of the composite slurry, and non-aqueous electrolyte secondary battery of the present invention will be described in detail below.

[0041] (1) Carbon nanotubes

[0042] The carbon nanotubes used in this embodiment are preferably single-layer carbon nanotubes. Single-layer carbon nanotubes and multi-layer carbon nanotubes may also coexist. Single-layer carbon nanotubes have a structure formed by a single layer of graphite, while multi-layer carbon nanotubes have a structure formed by two or more layers of graphite.

[0043] The average outer diameter of the carbon nanotubes in this embodiment is 0.5 nm to 5 nm, preferably 1 nm to 3 nm, and more preferably 1 nm to 2 nm. The average outer diameter of the carbon nanotubes can be observed using a transmission electron microscope (manufactured by Nippon Electron Ltd.), measuring the length of 100 short axes and calculating it based on their average value.

[0044] The BET specific surface area of ​​the carbon nanotubes in this embodiment is 550 m². 2 / g~1200m 2 / g, preferably 600m 2 / g~1200m 2 / g, more preferably 800m 2 / g~1200m 2 / g, and more preferably 800m 2 / g~1000m 2 / g.

[0045] Regarding the carbon nanotubes of this embodiment, when the 1560 cm⁻¹ nanotube is used 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 5–100, more preferably 10–50, and even more preferably 20–50. Raman spectroscopy can be performed using Raman spectroscopy and a laser beam with a wavelength of 532 nm.

[0046] The volume resistivity of the carbon nanotubes in this embodiment is preferably 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 Ω·cm. The volume resistivity of carbon nanotubes can be measured using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech, Inc.: Loresta GP Powder Resistivity Measuring System MCP-PD-51).

[0047] The carbon purity of the carbon nanotubes in this embodiment is expressed as the percentage (%) of carbon atoms contained in the carbon nanotubes. The carbon purity is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to 100% by mass of the carbon nanotubes.

[0048] The amount of metal contained in the carbon nanotubes of this embodiment 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 used as catalysts in the synthesis of carbon nanotubes, metal oxides, etc. Specifically, examples include: cobalt, nickel, aluminum, magnesium, silicon dioxide, manganese, molybdenum, alloys of these metals, metal oxides of these metals, and composite oxides of these metals.

[0049] The carbon nanotubes in this embodiment can be surface-treated carbon nanotubes. Alternatively, the 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.

[0050] The carbon nanotubes in this embodiment can also be carbon nanotubes that have undergone a pulverization process. Pulverization refers to the process of pulverizing carbon nanotubes using a pulverizer containing pulverizing media such as beads or steel balls, without the substantial introduction of liquid substances; this is also known as dry pulverization. Pulverization utilizes the pulverizing or destructive force generated by the collision of the pulverizing media. Pulverization primarily reduces the size of the secondary particles of the carbon nanotubes, thereby improving their dispersibility. Known methods such as dry mills, ball mills, vibratory mills, and bead mills can be used as the dry pulverization apparatus, and the pulverization time can be arbitrarily set according to the apparatus.

[0051] The carbon nanotubes in this embodiment can also be carbon nanotubes manufactured using 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.

[0052] (2) Dispersant

[0053] The dispersant used in this embodiment is not particularly limited to any range that can stabilize the dispersion of carbon nanotubes; 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.

[0054] 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 are not limited to these. 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 are not limited to these.

[0055] In addition, alkylamine salts and quaternary ammonium salts are examples of cationic surfactants. 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 these are not limited to these. Furthermore, aminocarboxylate salts are examples of amphoteric surfactants, but these are not limited to these.

[0056] In addition, examples of nonionic surfactants include: polyoxyethylene alkyl ethers, polyoxyethylene alkylene derivatives, polyoxyethylene phenyl ethers, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, and alkyl allyl ethers, but are not limited to these. Specifically, examples include: polyoxyethylene lauryl ether, sorbitol fatty acid esters, and polyoxyethylene octylphenyl ether, but are not limited to these.

[0057] 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.

[0058] 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.

[0059] Carboxymethyl cellulose, as a resin-type dispersant, can be used in the form of a sodium salt or other salts of carboxymethyl cellulose, wherein the sodium salt of carboxymethyl cellulose is formed by substituting the hydroxyl groups of carboxymethyl cellulose with sodium carboxymethyl groups. The degree of etherification of the carboxymethyl cellulose as a resin-type dispersant is preferably 0.5 to 1.5, more preferably 0.6 to 1.0. The degree of etherification of carboxymethyl cellulose can be determined according to conventional methods, specifically according to the methods described in the examples.

[0060] The dispersant in this embodiment, based on its pullulan 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 carbon nanotubes and further enhances the stability of the carbon nanotube dispersion. However, when using a dispersant exceeding this 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. Furthermore, resin-type dispersants, in addition to their dispersing ability, sometimes also possess binding ability. The resin-type dispersant described above can also be used as a binder. When using a resin of the same type as the resin-type dispersant as a binder, it is preferable to use a resin with a weight-average molecular weight larger than that of the resin-type dispersant.

[0061] Here, the weight-average molecular weight (Mw) of the dispersant can be determined using gel permeation chromatography (GPC) equipped with a differential refractive index (RI) detector, and is expressed as a Pullulan conversion.

[0062] In addition to the dispersant of this embodiment, the mixture may also contain an inorganic base and / or an inorganic metal salt. Preferably, the inorganic base and inorganic metal salt are compounds having at least one of an alkali metal and an alkaline earth metal. Specifically, examples include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals and alkaline earth metals. Furthermore, among these, chlorides, hydroxides, and carbonates of alkali metals and alkaline earth metals are preferred in terms of readily supplying cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Examples of alkali metal carbonates include lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferred among these.

[0063] In addition to the dispersant of this embodiment, an acid may also be included. By adding an acid, the charge state or the hydrophilic / hydrophobic balance in the dispersion system changes, sometimes improving dispersibility. The type of acid is not particularly limited; one type or a combination of several can be used. Examples include: oxalic acid, lactic acid, citric acid, polyacrylic acid, polystyrene sulfonic acid, acetic acid, malonic acid, hydrochloric acid, nitric acid, sulfuric acid, boric acid, phosphoric acid, etc.

[0064] In addition to the dispersant of this embodiment, an antifoaming agent may also be included. Any commercially available antifoaming agent, wetting agent, hydrophilic organic solvent, water-soluble organic solvent, or other substance with antifoaming effect may be used; one type may be used, or multiple types may be used in combination.

[0065] 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.

[0066] Fatty acid esters; diethylene glycol laurate, glyceryl monoricinoleate, alkenyl succinic acid derivatives, sorbitol monolaurate, sorbitol trioleate, polyoxyethylene monolaurate, polyoxyethylene sorbitol monolaurate, natural waxes, etc.

[0067] Amide compounds; polyoxyalkylene amides, acrylate polyamines, etc.

[0068] Phosphate esters; tributyl phosphate, sodium octyl phosphate, etc.

[0069] Metallic soaps; aluminum stearate, calcium oleate, etc.

[0070] Oils and fats; animal and vegetable oils, sesame oil, castor oil, etc.

[0071] Mineral oil series: kerosene, paraffin, etc.

[0072] Silicone-based products; dimethyl silicone oil, silicone paste, silicone emulsion, organically modified polysiloxane, fluorosilicone oil, etc.

[0073] (3) Solvent

[0074] The solvent used in this embodiment is not particularly limited as long as it falls within the range where carbon nanotubes can disperse. Preferably, it is selected from any one of the groups consisting of water and water-soluble organic solvents, or a mixed solvent containing two or more of these groups, more preferably containing water. When water is included, it is preferably 95% by mass or more, and more preferably 98% by mass or more, relative to 100% by mass of the solvent. It may also be a single solvent of water.

[0075] 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, hexanediol, thiodiglycol, etc.), and polyol ethers (ethylene glycol monomethyl ether, ethylene glycol monomethyl ether, etc.). Ethers, 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.; amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.); heterocyclics (cyclohexylpyrrolidone, 2-oxazolidinone, 1,3-dimethyl-2-imidazolium, γ-butyrolactone, etc.); sulfoxides (dimethyl sulfoxide, etc.); sulfones (hexamethylphosphotriamide, sulfolane, etc.); lower ketones (acetone, methyl ethyl ketone, etc.); and tetrahydrofuran, urea, acetonitrile, etc. Preferably, the solvent is an amide-based water-soluble organic solvent, and more preferably, it is N-methyl-2-pyrrolidone (NMP).

[0076] (4) Carbon nanotube dispersion

[0077] The carbon nanotube dispersion of this embodiment includes carbon nanotubes, a dispersant, and a solvent.

[0078] The carbon nanotube dispersion of this embodiment has a complex elastic modulus of 5 Pa or more and less than 650 Pa at 25°C and a frequency of 1 Hz, preferably 5 Pa or more and less than 400 Pa, and more preferably 10 Pa or more and less than 400 Pa. The complex elastic modulus of the carbon nanotube dispersion reflects its hardness, 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, when the fiber length of the carbon nanotubes is large, the complex elastic modulus can sometimes be high due to the inherent structural viscosity of the carbon nanotubes.

[0079] The carbon nanotube dispersion of this embodiment has a phase angle of 5° or more and less than 50° at 25°C and a frequency of 1Hz, more preferably 10° or more and less than 50°. The phase angle refers to the phase shift of a stress wave when the strain applied to the carbon nanotube dispersion is set as a sine wave. If it is 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, if it is a purely viscous body, it becomes a stress wave that has advanced 90°. Carbon nanotube dispersions with a complex elastic modulus and phase angle within the aforementioned range exhibit good dispersion particle size and dispersion state of the carbon nanotubes, making them suitable as carbon nanotube dispersions for improving electrode strength and conductivity.

[0080] The complex elastic modulus and phase angle of the carbon nanotube dispersion can be determined as follows: using a rheometer with a diameter of 35 mm and a 2° cone, dynamic viscoelasticity is measured at 25°C and a frequency of 1 Hz, with a strain rate ranging from 0.01% to 5%. When the measured value includes a decimal point, it is rounded to the nearest integer according to Rule B of Japanese Industrial Standards (JIS) Z8401:1999. Furthermore, when the measured value has one decimal place, the complex elastic modulus of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz is preferably 4.5 Pa or more and less than 650.4 Pa, and the phase angle of the carbon nanotube dispersion at 25°C and a frequency of 1 Hz is preferably 4.5° or more and less than 50.4°.

[0081] By ensuring that the fiber length of carbon nanotubes does not decrease due to breakage, and by maintaining a certain length, they can be uniformly and well dispersed, thereby forming a well-developed conductive network. Therefore, it is not sufficient for the conductive material dispersion to merely have low viscosity and (apparently) good dispersibility; it is particularly effective to combine the complex elastic modulus and / or phase angle with previous indicators such as viscosity to determine the dispersion state. By setting the complex elastic modulus and / or phase angle to the aforementioned range, a conductive material dispersion with good conductivity and electrode strength can be obtained.

[0082] Regarding the viscosity of the carbon nanotube dispersion in this embodiment, a rheometer was used at 25°C with a shear rate of 1 (s). -1 When performing the measurement, it is preferable to have a pressure of 5 Pa·s or more but less than 60 Pa·s, more preferably 10 Pa·s or more but less than 40 Pa·s, and even more preferably 20 Pa·s or more but less than 40 Pa·s. Additionally, when using a rheometer at 25°C with a shear rate of 10 (s⁻¹)... -1 When performing the measurement, it is preferable to have a shear rate of 1 Pa·s or higher but less than 10 Pa·s. The shear rate is measured by... -1 The shear viscosity at a certain range can be used to determine the dispersibility of carbon nanotube dispersions. Carbon nanotube dispersions within the specified range have good dispersed particle size and dispersion state, making them suitable as carbon nanotube dispersions for improving electrode strength and conductivity.

[0083] The viscosity of the carbon nanotube dispersion can be determined as follows: After the carbon nanotube dispersion has been allowed to stand in a constant temperature bath at 25°C for more than 1 hour, it is thoroughly stirred. Then, using a rheometer with a diameter of 35 mm and a 2° cone, the viscosity is measured at 25°C and a shear rate of 1 s. -1 and shearing speed 10s -1 The shear viscosity at the specified value. If the measured value contains a decimal point, it is rounded to the nearest integer according to Rule B of JIS Z 8401:1999.

[0084] The cumulative particle size D10 of the carbon nanotube dispersion in this embodiment, as measured by dynamic light scattering, is preferably 200 nm or more and less than 500 nm, more preferably 200 nm or more and less than 400 nm, and even more preferably 300 nm or more and less than 400 nm. Furthermore, the cumulative particle size D50 of the carbon nanotube dispersion, as measured by dynamic light scattering, is preferably 500 nm or more and less than 3000 nm, more preferably 500 nm or more and less than 2000 nm, and even more preferably 500 nm or more and less than 1500 nm. The cumulative particle size D10 and 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). The particle size determined by dynamic light scattering is related to the fiber length of carbon nanotubes. In carbon nanotube dispersions with a cumulative particle size D10 within the specified range, the carbon nanotubes are well dispersed in the dispersion.

[0085] 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 performing this treatment is not particularly limited.

[0086] 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 mixers; homogenizers (such as the Advanced Digital Sonifer (registered trademark) 450DA manufactured by BRANSON, Clearmix manufactured by M-technique, Filmix manufactured by PRIMIX, and Abramix manufactured by Silverson); paint conditioners (manufactured by Red Devil); colloid mills (such as the PUC colloid mill manufactured by PUC and the MK colloid mill manufactured by IKA); cone mills (such as the MKO cone mill manufactured by IKA); ball mills; and sand mills (such as Shinmaru Corporation). This includes media dispersers such as the "Dyno-mill" manufactured by ENTERPRISES, grinding mills, pearl mills (such as the "DCP mill" manufactured by Eirich), and ball mills; media-free dispersers such as wet jet mills (such as the "Jenius PY" manufactured by Jenius, the "Starburst" manufactured by SUGINO Machine, and the "nanomizer" manufactured by Nanomizer), the "clear SS-5" manufactured by M-technique, and the "MICROS" manufactured by Nara Machinery; and other roller mills, but is not limited to these.

[0087] The amount of carbon nanotubes in the carbon nanotube dispersion of this embodiment is preferably 0.2 to 1.5 parts by mass relative to 100 parts by mass of the carbon nanotube dispersion, more preferably 0.4 to 1.2 parts by mass, and even more preferably 0.4 to 1.0 parts by mass.

[0088] In this embodiment, the amount of dispersant in the carbon nanotube dispersion is preferably 30 to 250 parts by mass relative to 100 parts by mass of carbon nanotubes, more preferably 50 to 150 parts by mass, and even more preferably 50 to 100 parts by mass.

[0089] The pH of the carbon nanotube dispersion in this embodiment is preferably 6 to 11, more preferably 7 to 11, even more preferably 8 to 11, and particularly preferably 9 to 11. The pH of the carbon nanotube dispersion can be measured using a pH meter (Horiba Manufacturing Co., Ltd., pH Meter F-52).

[0090] (5) Adhesive

[0091] Adhesives are resins used to bond materials such as carbon nanotubes together.

[0092] Examples of adhesives used in this embodiment include: polymers or copolymers comprising ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, methacrylic acid, methacrylate, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc.; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluoropolymers; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified forms or mixtures of these resins, and copolymers, may also be used. Polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid are preferred.

[0093] The carboxymethyl cellulose used as a binder is preferably of high viscosity; for example, the viscosity of a 1% aqueous solution is preferably 500 mPa·s to 6000 mPa·s, and more preferably 1000 mPa·s to 3000 mPa·s. The viscosity of a 1% aqueous solution of carboxymethyl cellulose can be measured at 25°C using a type B viscometer with a rotor speed of 60 rpm.

[0094] The carboxymethyl cellulose used as an adhesive is preferably highly etherified. For example, the degree of etherification is preferably 0.6 to 1.5, more preferably 0.6 to 1.2, and even more preferably 0.8 to 1.2.

[0095] Regarding the amount of binder in the composite slurry of this embodiment, when the mass of the active material is set to 100% by mass, it is preferably 0.5% to 30% by mass, more preferably 1% to 25% by mass, and particularly preferably 2% to 20% by mass. Furthermore, the type or proportion of 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 as a binder in the composite slurry, 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, more preferably 1.0% to 2.0% by mass.

[0096] If the styrene-butadiene rubber is an oil-in-water emulsion, then a material commonly used as a binder for electrodes can be used. In the composite slurry, regarding the amount of styrene-butadiene rubber used as a binder, 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.

[0097] In the composite slurry, regarding the amount of polyacrylic acid used as a binder, when the mass of the active material 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.

[0098] In the composite slurry, regarding the amount of polyvinylidene fluoride used as a binder, when the mass of the active material is set to 100% by mass, the proportion of polyvinylidene fluoride is preferably 1% to 10% by mass, and more preferably 1% to 5% by mass.

[0099] (6) Carbon nanotube resin composition

[0100] The carbon nanotube resin composition of this embodiment includes carbon nanotubes, a dispersant, a solvent, and a binder.

[0101] 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.

[0102] (7) Composite material slurry

[0103] The composite slurry of this embodiment is a substance containing carbon nanotubes, dispersants, solvents, binders, and active substances.

[0104] <Active Substances>

[0105] The active material in this embodiment is the material that forms the basis of the battery reaction. In terms of electromotive force, the active material is divided into positive electrode active material and negative electrode active material.

[0106] There are no particular limitations on the active material used as the positive electrode; metal compounds such as metal oxides and metal sulfides, as well as conductive polymers, that can be doped or intercalated with lithium ions can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, examples include MnO, V₂O₅, and V₆O. 13 Transition metal oxide powders such as TiO2, lithium-transition metal composite oxide powders such as layered lithium nickelate, lithium cobalt oxide, lithium manganese oxide, and spinel-structured lithium manganese oxide, lithium iron phosphate materials as olivine-structured phosphate compounds, and transition metal sulfide powders such as TiS2 and FeS, etc. Additionally, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Furthermore, the aforementioned inorganic or organic compounds can be mixed and used.

[0107] As a negative electrode active material, there are no particular limitations as long as it can be doped or intercalated with lithium ions. Examples include: metallic Li, alloys such as tin alloys, silicon alloys, and lead alloys, etc. x Fe2O3, Li x Fe3O4, Li x WO2 (where x is a number where 0 < x < 1), lithium titanate, lithium vanadate, lithium silicate and other metal oxides, conductive polymers such as polyacetylene and poly(p-phenylene oxide), amorphous carbonaceous materials such as soft carbon or hard carbon, artificial graphite or natural graphite powders, carbon black, mesophase carbon black, resin-sintered carbon materials, air-grown carbon fibers, carbon fibers and other carbon-based materials. These negative electrode active materials can be used individually or in combination.

[0108] The anode active material used in this embodiment is preferably a silicon-based anode active material, and more specifically, a silicon-containing anode active material such as silicon alloy or lithium silicate is preferred.

[0109] Examples of silicon-based anode active materials include: so-called metallurgical-grade silicon produced by reducing silicon dioxide with carbon; industrial-grade silicon that reduces impurities by acid treatment or unidirectional solidification of metallurgical-grade silicon; high-purity silicon with different crystal states such as single crystal, polycrystalline, and amorphous produced by reacting silicon to obtain silane; and silicon that adjusts the crystal state or precipitation state while making industrial-grade silicon high-purity through sputtering or electron beam evaporation (EB) methods.

[0110] Alternatively, silicon oxide, a compound of silicon and oxygen, or silicon, as well as various alloys and silicon compounds whose crystallinity is adjusted by methods such as rapid cooling, can be cited as examples. 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.

[0111] 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, artificial graphite such as highly graphitized carbon materials, or carbonaceous powder such as natural graphite. Among these, the use of carbonaceous powder such as artificial graphite or natural graphite is preferred.

[0112] 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.

[0113] 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.

[0114] The average particle size of the active material in this embodiment is preferably in the range of 0.5 μm to 50 μm, and 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.

[0115] (8) Method for manufacturing composite material slurry

[0116] The composite slurry of this embodiment can be prepared by various methods known in the art. Examples include: methods of preparing the slurry by adding an active substance to a carbon nanotube resin composition, or methods of preparing the slurry by adding an active substance to a carbon nanotube dispersion and then adding a binder.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] (9) Electrode film

[0122] 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.

[0123] The material or shape of the current collector used in the electrode film of this embodiment is 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 such as aluminum, copper, nickel, titanium, or stainless steel, and alloys of these metals. 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.

[0124] There are no particular limitations on the method of applying 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, methods such as placement drying, forced air drying, warm air drying, infrared heating machine, and far-infrared heating machine can be used, but they are not particularly limited to these.

[0125] 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.

[0126] (10) Non-aqueous electrolyte secondary battery

[0127] The non-aqueous electrolyte secondary battery of this embodiment includes a positive electrode, a negative electrode, and an electrolyte. Preferably, at least one of the positive and negative electrodes contains the electrode film of this embodiment.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] Example

[0135] 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".

[0136] <Methods for Determining Physical Properties>

[0137] The physical properties of the CNTs used in the embodiments and comparative examples described below were determined using the following methods.

[0138] <CNT's G / D ratio>

[0139] 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.

[0140] <BET specific surface area of ​​CNT>

[0141] 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).

[0142] <Average outer diameter of CNT>

[0143] 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.

[0144] <Volume resistivity of CNTs>

[0145] 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.

[0146] <Particle size distribution of CNT dispersion>

[0147] 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 D10 and cumulative particle size D50 of the CNT dispersion were measured using a particle size analyzer (Manufactured by Microtrac-BEL Co., Ltd., Nanotrac UPA, model UPA-EX). Permeability was set to absorption, CNT density was set to 1.8, and 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 ranging from 0.8 to 1.2.

[0148] <Complex elastic modulus and phase angle of CNT dispersion>

[0149] 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%.

[0150] <Viscosity of CNT dispersion>

[0151] After the CNT dispersion was allowed to stand in a constant temperature bath at 25°C for more than 1 hour, the CNT dispersion was thoroughly stirred. Then, using a 35mm diameter, 2° cone rheometer (RheoStress 1 rotary rheometer manufactured by Thermo Fisher Scientific), the stress at 25°C and a shear rate of 1s was measured. -1 and shearing speed 10s -1 The shear viscosity at the specified value is used for evaluation.

[0152] <Peel strength of electrode film for negative electrode>

[0153] 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 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. 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 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.

[0154] <Peel strength of positive electrode film>

[0155] 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.

[0156] <Making a Standard Positive Electrode>

[0157] 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 Material Japan, Kureha KF polymer W#1300) were added to a volume of 150 cm⁻¹. 3 After filling the plastic container, mix the powder with a spatula until it is uniform. Then, add 20.5 parts by weight of NMP and stir at 2000 rpm for 30 seconds using a rotary mixer (Thinky ARE-310). Next, mix the mixture in the plastic container with a spatula until uniform and stir at 2000 rpm for 30 seconds using the same rotary mixer. Then, add 14.6 parts by weight of NMP and stir at 2000 rpm for 30 seconds using the same rotary mixer. Finally, stir at 3000 rpm for 10 minutes using a high-speed mixer to obtain a composite slurry for the positive electrode. Then, apply the composite slurry for the positive electrode onto a 20 μm thick aluminum foil as a current collector using a coating applicator, and dry 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.

[0158] <Making a Standard Negative Electrode>

[0159] In a 150ml plastic container, add 0.5 parts by weight of acetylene black (DENKA BLACK (registered trademark) HS-100, manufactured by DENKA), 1 part by weight of MAC500LC (Sunrose special type MAC500L sodium carboxymethyl cellulose, manufactured by Nippon Paper Corporation, 100% non-volatile components), and 98.4 parts by weight of water. Then, using a rotary mixer (Thinky Corporation, Defoaming Rentarō, ARE-310), stir at 2000 rpm for 30 seconds. Next, add 87 parts by weight of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries) and 10 parts by weight of silicon as active materials, and stir at 3000 rpm for 10 minutes using a high-speed mixer. 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 the aforementioned rotary mixer to obtain a composite slurry for the negative electrode. Then, a coating apparatus was used to apply the slurry at a unit area weight of 8 mg / cm² for each electrode unit. 2 The negative electrode 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.

[0160] <Evaluation of the rate characteristics of lithium-ion secondary batteries>

[0161] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 25°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric Co., Ltd., SM-8). Constant current and constant voltage charging (cutoff current 1.1mA (0.02C)) was performed at a charging current of 11mA (0.2C) and a charging termination voltage of 4.2V, followed by constant current discharging at a discharging current of 11mA (0.2C) and a discharging termination voltage of 2.5V. This operation was repeated three times. Then, constant current and constant voltage charging (cutoff current 1.1mA and 0.02C) was performed at a charging current of 11mA (0.2C) and a charging termination voltage of 4.2V, followed by constant current discharging at discharging currents of 0.2C and 3C until the discharging termination voltage of 2.5V was reached. The discharge capacity was calculated for each discharge. The rate characteristic is the ratio of the 0.2C discharge capacity to the 3C discharge capacity, which can be expressed by Equation 1 below.

[0162] (Equation 1) Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%)

[0163] <Evaluation of Cycle Characteristics of Lithium-ion Secondary Batteries>

[0164] The laminated lithium-ion secondary battery was placed in a constant temperature chamber at 25°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric Co., Ltd., SM-8). Constant current and constant voltage charging (cutoff current 1.38mA (0.025C)) was performed at a charging current of 55mA (1C) and a charging termination voltage of 4.2V, followed by constant current discharging at a discharging current of 55mA (1C) and a discharging termination voltage of 2.5V. This operation was repeated 200 times. 1C is defined as the current value that discharges the theoretical capacity of the positive electrode in 1 hour. The cycle characteristic, the ratio of the 1C discharge capacity at the third cycle to the 1C discharge capacity at the 200th cycle at 25°C, can be expressed by the following Equation 2.

[0165] (Equation 2) Cyclic characteristics = 1C discharge capacity at the 200th cycle / 1C discharge capacity at the 3rd cycle × 100 (%)

[0166] <Synthesis of Dispersant (A)>

[0167] 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.

[0168] (Method for determining weight-average molecular weight (Mw))

[0169] 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.

[0170] Test sample: 0.1% by mass aqueous solution

[0171] Device: HLC-8320GPC (manufactured by Tosoh)

[0172] Eluent: 0.1M NaCl aqueous solution

[0173] Column: TSKgel SuperMultiporePW-M (manufactured by Tosoh)

[0174] Flow rate: 1.0 mL / min

[0175] Temperature: 25℃

[0176] Injection volume: 100 μl

[0177] (Method for determining the degree of etherification)

[0178] Add 2.0 g of sodium carboxymethyl cellulose and 100 mL of nitric acid methanol to a 300 mL Erlenmeyer flask with a stopper, and shake for 2 hours to replace the sodium carboxymethyl cellulose with carboxymethyl cellulose. Then, filter the carboxymethyl cellulose through a glass filter by suction, and wash with 200 mL of 80% methanol. Then, replace with 50 mL of anhydrous methanol, filter by suction, and dry at 105 °C for 2 hours. Weigh 1.0 g to 1.5 g of the dried carboxymethyl cellulose and place it in a 300 mL Erlenmeyer flask with a stopper, add 15 mL of 80% methanol to moisten it, and add 50 mL of 1 / 10 N sodium hydroxide, and shake for 2 hours. Then, using phenolphthalein as an indicator, perform a reverse titration of the excess sodium hydroxide with 1 / 10 N sulfuric acid, and calculate the degree of etherification according to equations (3) and (4).

[0179] (Equation 3) A=(50×F1-X×F2) / (Y×10)

[0180] X: Amount of sulfuric acid added; Y: Weight of dried carboxymethyl cellulose.

[0181] F1: Factor of sulfuric acid, F2: Factor of sodium hydroxide

[0182] (Equation 4) Degree of etherification = 0.162A / (1-0.058A)

[0183] Table 1 shows the CNTs used in the embodiments and comparative examples, their outer diameter, specific surface area, G / D ratio, and volume resistivity. Figure 1 The Raman spectra of the CNTs used in the examples and comparative examples are shown in the figure.

[0184] [Table 1]

[0185] Table 1

[0186]

[0187] Table 2 shows the dispersants used in the examples, comparative examples, and reference examples.

[0188] [Table 2]

[0189] Table 2

[0190]

[0191] (Example 1)

[0192] 98.25 parts of ion-exchanged water were added to a stainless steel container, and 0.75 parts of dispersant (A) were added while stirring with a disperser until homogeneous. Then, 1 part of CNT (A) was 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 batch dispersion was performed 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 SUGINOMACHINE) via piping, and batch dispersion was performed 5 times to obtain a CNT dispersion (WA1). The dispersion was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0193] (Examples 2-15), (Examples 19-20), (Comparative Examples 1-2)

[0194] The CNT types, CNT addition amounts, dispersant types, dispersant addition amounts, ion exchange water addition amounts, and number of passes were changed to those recorded in Table 3. Otherwise, the CNT dispersions (WA2 to WF4) were obtained using the same method as in Example 1.

[0195] (Example 16)

[0196] Weigh out 4 parts by weight of the CNT dispersion (WA1) prepared in Example 1 and 6 parts by weight of ion-exchanged water to a volume of 150 cm³. 3 The mixture was placed in a plastic container. Then, using a rotary / revolutionary mixer (Thinky Corporation, Defoaming Rentaro, ARE-310), it was stirred at 2000 rpm for 30 seconds to obtain a CNT dispersion (WA13).

[0197] (Example 17)

[0198] The CNT dispersion (WA3) prepared in Example 3 was used, except that the CNT dispersion (WA14) was obtained by the same method as in Example 16.

[0199] (Example 18)

[0200] The CNT dispersion (WA11) prepared in Example 11 was used, except that the CNT dispersion (WA15) was obtained by the same method as in Example 16.

[0201] (Example 21)

[0202] In a polypropylene bottle, 20 parts of CNT(C) and 480 parts of 8mm diameter zirconia beads were added as a grinding medium and ground for 40 minutes using a paint conditioner manufactured by Red Devil. The zirconia beads were then separated to recover CNT(C). Next, 98.38 parts of deionized water were added to a stainless steel container, and 1.13 parts of dispersant (C) were added while stirring with a disperser until homogeneous. Then, 1.5 parts of the recovered CNT(C) were weighed out and added while stirring with a disperser. The mixture was then batch-dispersed 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 a stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE) via piping, and subjected to 20 batch dispersion processes to obtain a CNT dispersion (WC27). 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.

[0203] (Example 22)

[0204] 98.40 parts of ion-exchanged water were added to a stainless steel container. While stirring with a disperser, 0.50 parts of dispersant (C) and 0.10 parts of polyacrylic acid (manufactured by Fujifilm and Hikari Pure Chemical Industries, Ltd., molecular weight 25000) were added until homogeneous. Then, 1.0 part of CNT (A) was 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 batch dispersion was performed 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 20 batch dispersion processes were performed to obtain a CNT dispersion (WA28). The dispersion was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0205] (Comparative Example 3)

[0206] One part of CNT(A), 0.75 parts of dispersant(A), 98.25 parts of ion-exchanged water, and 120 parts of zirconia beads (bead diameter 1.25mmφ) were placed in a glass bottle (M-140, manufactured by Kashiwa Glass Co., Ltd.). The mixture was dispersed for 8 hours using a paint conditioner manufactured by Red Devil Co., Ltd. Then, an attempt was made to separate the zirconia beads, but the viscosity was too high and a CNT dispersion could not be obtained.

[0207] (Comparative Examples 4 to 6)

[0208] The CNT addition amount, dispersion time, and bead size were changed to those recorded in Table 3. Otherwise, the CNT dispersion (WA17~WA19) was obtained by separating the zirconia beads after dispersion treatment in the same way as in Comparative Example 3.

[0209] [Table 3]

[0210]

[0211] (Example 23)

[0212] 99.3 parts NMP were added to a stainless steel container, and 0.3 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 batch dispersion was performed at 8,600 rpm until the mixture became 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 20 batch dispersion processes were performed to obtain a CNT dispersion (A20). 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.

[0213] (Examples 24 to 26)

[0214] The number of passes was changed to those recorded in Table 4, and the CNT dispersions (A21 to A23) were obtained by the same method as in Example 23.

[0215] (Comparative Example 7)

[0216] 0.4 parts of CNT(A), 0.3 parts of dispersant(E), 99.3 parts of NMP and 120 parts of zirconia beads (bead diameter 1.25mmφ) were packed into a glass bottle (M-140, manufactured by Kashiwa Glass Co., Ltd.). The mixture was dispersed for 8 hours using a paint conditioner manufactured by Red Devil Co., Ltd., and then the zirconia beads were separated to obtain the CNT dispersion (A24).

[0217] [Table 4]

[0218] Table 4

[0219]

[0220] Table 5 shows the evaluation results of the CNT dispersions prepared in Examples 1 to 26 and Comparative Examples 1 to 7. Regarding the evaluation of the phase angle of the CNT dispersion at 25°C and 1Hz, a value of 10 or more but less than 50 was designated as ○ (Good), 5 or more but less than 10 as △ (Acceptable), and less than 5 or more as × (Unacceptable). Regarding the evaluation of the complex elastic modulus of the CNT dispersion at 25°C and 1Hz, a value of 5 or more but less than 400 was designated as ○ (Good), 400 or more but less than 650 as △ (Acceptable), and less than 5 as × (Unacceptable). Regarding the evaluation of the viscosity of the CNT dispersion, a shear viscosity of 20 or more but less than 40 at a shear rate of 1 was designated as ◎ (Excellent), a value of 10 or more but less than 20, or 40 or more but less than 60 as ○ (Good), 5 or more but less than 10 as △ (Acceptable), and less than 5 as × (Unacceptable). Regarding the particle size evaluation of CNT dispersions, a particle size distribution of 200 or more but less than 300 at particle size distribution D10 is ◎ (excellent), a particle size distribution of 300 or more but less than 500 is ○ (good), and a particle size distribution of less than 200 is × (unacceptable).

[0221] [Table 5]

[0222]

[0223] (Example 28)

[0224] Weigh out 0.63 parts by weight of CNT dispersion (WA1), 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 13.8 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 (WA1). Next, 2.92 parts by weight of silica (Osaka Titanium Technologies Corporation, SILICON MONOOXIDE, SiO 1.3C 5μm) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the same rotary / revolutionary mixer. Then, 21.44 parts by weight of artificial graphite (Nippon Graphite Industry Co., Ltd., CGB-20) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the same rotary / revolutionary mixer. Next, 0.78 parts by weight of styrene-butadiene rubber (manufactured by JSR Corporation, TRD2001) are added, and the mixture is stirred at 2000 rpm for 30 seconds using the aforementioned rotary / revolutionary mixer to obtain a composite slurry for the negative electrode (WA1).

[0225] (Examples 29 to 49), (Comparative Examples 8 to 12)

[0226] The CNT dispersion was changed to the one described in Table 6, and the amount of CNT dispersion and ion-exchange water added was adjusted so that the CNT content in 100 parts by weight of the composite slurry was 0.025 parts by weight. Otherwise, the CNT resin composition (WA2-WA19) and the negative electrode composite slurry (WA2-WA19) were obtained by the same method as in Example 28. The non-volatile component of the negative electrode composite slurry was set to 48% by weight.

[0227] (Example 50)

[0228] Weigh 7.0 parts by weight of NMP containing 8% by weight of PVDF (Solvay, Solef #5130) to a volume of 150 cm³. 3 The mixture was placed in a plastic container. Then, 0.19 parts by weight of CNT dispersion (A20) 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 (A20). Next, 36.9 parts of positive electrode active material (manufactured by BASF Toda 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 the aforementioned spin / revolution mixer to obtain the positive electrode composite slurry (A20).

[0229] (Examples 51-53), (Comparative Example 13)

[0230] The CNT dispersion was changed to the one described in Table 6. Otherwise, the CNT resin composition (A21-A24) and the positive electrode composite slurry (A21-A24) were obtained by the same method as in Example 50.

[0231] [Table 6]

[0232] Table 6

[0233] Composite slurry for negative electrode CNT resin composition CNT dispersion Example 28 WA1 WA1 WA1 Example 29 WA2 WA2 WA2 Example 30 WA3 WA3 WA3 Example 31 WA4 WA4 WA4 Example 32 WA5 WA5 WA5 Example 33 WA6 WA6 WA6 Example 34 WA7 WA7 WA7 Example 35 WA8 WA8 WA8 Example 36 WA9 WA9 WA9 Example 37 WA10 WA10 WA10 Example 38 WA11 WA11 WA11 Example 39 WA12 WA12 WA12 Example 40 WB4 WB4 WB4 Example 41 WC4 WC4 WC4 Example 42 WD4 WD4 WD4 Example 43 WA13 WA13 WA13 Example 44 WA14 WA14 WA14 Example 45 WA15 WA15 WA15 Example 46 WA25 WA25 WA25 Example 47 WA26 WA26 WA26 Example 48 WC27 WC27 WC27 Example 49 WA28 WA28 WA28 Comparative Example 8 WE4 WE4 WE4 Comparative Example 9 WF4 WF4 WF4 Comparative Example 10 WA17 WA17 WA17 Comparative Example 11 WA18 WA18 WA18 Comparative Example 12 WA19 WA19 WA19 Positive electrode composite slurry CNT resin composition CNT dispersion Example 50 A20 A20 A20 Example 51 A21 A21 A21 Example 52 A22 A22 A22 Example 53 A23 A23 A23 Comparative Example 13 A24 A24 A24

[0234] (Example 54)

[0235] Using a dressing applicator, the weight per unit area of ​​the electrode is 8 mg / cm². 2 The negative electrode composite slurry (WA1) is coated onto the copper foil and then dried in an electric oven at 120℃±5℃ for 25 minutes to obtain the electrode film (WA1).

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

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

[0238] (Example 76)

[0239] Using a dressing applicator, the weight per unit area of ​​the electrode is 20 mg / cm². 2 The positive electrode composite slurry (A20) was coated onto the copper foil and then dried in an electric oven at 120℃±5℃ for 25 minutes to obtain the electrode film (A20).

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

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

[0242] Table 7 shows the evaluation results of the electrode films prepared in Examples 54 to 79 and Comparative Examples 14 to 19. Regarding the adhesion evaluation, a peel strength (Ω·cm) of 0.5 or more was set as ◎ (excellent), 0.3 or more but less than 0.5 was set as 〇 (good), 0.1 or more but less than 0.3 was set as △ (acceptable), and less than 0.1 was set as × (unacceptable).

[0243] [Table 7]

[0244] Table 7

[0245] Electrode film Close contact assessment Example 54 WA1 ○ Example 55 WA2 ◎ Example 56 WA3 ◎ Example 57 WA4 ◎ Example 58 WA5 ○ Example 59 WA6 △ Example 60 WA7 ◎ Example 61 WA8 ◎ Example 62 WA9 ○ Example 63 WA10 ◎ Example 64 WA11 ◎ Example 65 WA12 ○ Example 66 WB4 ◎ Example 67 WC4 ○ Example 68 WD4 ○ Example 69 WA13 ◎ Example 70 WA14 ◎ Example 71 WA15 ◎ Example 72 WA25 ◎ Example 73 WA26 ◎ Example 74 WC27 ○ Example 75 WA28 ○ Comparative Example 14 WE4 △ Comparative Example 15 WF4 △ Comparative Example 16 WA17 ○ Comparative Example 17 WA18 △ Comparative Example 18 WA19 △ Example 76 A20 ◎ Example 77 A21 ◎ Example 78 A22 ○ Example 79 A23 ○ Comparative Example 19 A24 △

[0246] (Examples 80 to 101), (Comparative Examples 20 to 24)

[0247] The electrode films (WA1~WA19) were rolled using a roller press (manufactured by Thank-Metal, a 3t hydraulic roller press) to produce a composite layer with a density of 1.7 g / cm³. 3 The negative electrode.

[0248] (Examples 102-105), (Comparative Example 25)

[0249] The electrode films (A20–A24) were rolled using a roller press (manufactured by Thank-Metal, a 3t hydraulic roller press) to produce a composite layer with a density of 3.2 g / cm³. 3 The positive pole.

[0250] Table 8 shows the negative and positive electrodes prepared in Examples 80 to 105 and Comparative Examples 20 to 25.

[0251] [Table 8]

[0252] Table 8

[0253]

[0254] (Example 106)

[0255] The negative electrode (WA1) 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 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 (WA1).

[0256] (Examples 107-127), (Comparative Examples 26-30)

[0257] The negative electrode was changed to the one listed in Table 9. Otherwise, laminated lithium-ion secondary batteries (WA2~WA19) were manufactured using the same method.

[0258] (Example 128)

[0259] The standard negative and positive electrodes (A20) 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 (A20).

[0260] (Examples 129–131), (Comparative Example 31)

[0261] The positive electrode is changed to the one listed in Table 9. Otherwise, laminated lithium-ion secondary batteries (A21 to A24) are manufactured using the same method.

[0262] [Table 9]

[0263] Table 9

[0264]

[0265]

[0266] Table 10 shows the evaluation results of the laminated lithium-ion secondary batteries prepared in Examples 106 to 131 and Comparative Examples 26 to 31. Regarding rate characteristics, a rate characteristic of 80% or more was designated as ◎ (Excellent), 70% or more but less than 80% as 〇 (Good), 60% or more but less than 70% as △ (Acceptable), and less than 60% as × (Unacceptable). Regarding cycle characteristics, a cycle characteristic of 90% or more was designated as ◎ (Excellent), 85% or more but less than 90% as 〇 (Good), 80% or more but less than 85% as △ (Acceptable), and less than 80% as × (Unacceptable).

[0267] [Table 10]

[0268] Table 10

[0269]

[0270] In the above embodiments, the following carbon nanotube dispersion was used: the carbon nanotube dispersion comprises carbon nanotubes, a dispersant, and a solvent, and the G / D ratio of the carbon nanotubes is 5 to 100. Relative to 100 parts by mass of carbon nanotubes, it contains 30 to 250 parts by mass of dispersant. The carbon nanotube dispersion has a complex elastic modulus of 5 Pa or more but less than 650 Pa at 25°C and a frequency of 1 Hz, and a phase angle of 5° or more but less than 50°. In these embodiments, compared to comparative examples, the electrode adhesion tends to be improved. Furthermore, conductivity and electrode strength are improved, thereby obtaining a lithium-ion secondary battery with excellent rate characteristics and cycle characteristics. Therefore, the present invention provides a lithium-ion secondary battery with high capacity, high output power, and high durability that is difficult to achieve using existing carbon nanotube dispersions.

[0271] The present invention has been described above with reference to 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 or details of the present invention within the scope of the invention.

Claims

1. A carbon nanotube dispersion comprising carbon nanotubes, a dispersant, and a solvent, wherein the carbon nanotube dispersion satisfies the following (1) to (4): (1) When 1560 cm⁻¹ is used in the Raman spectrum of carbon nanotubes -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 of carbon nanotubes is 5 to 100. (2) Relative to 100 parts by weight of carbon nanotubes, it contains 30 parts by weight or more but less than 250 parts by weight of dispersant; (3) The complex elastic modulus of the carbon nanotube dispersion at 25°C and 1Hz is greater than 5Pa and less than 650Pa, and the phase angle is greater than 5° and less than 50°. (4) The Buerger specific surface area of ​​carbon nanotubes is 550 m². 2 / g~1200m 2 / g, The cumulative particle size D10, determined by dynamic light scattering, is greater than 200 nm but less than 500 nm.

2. The carbon nanotube dispersion according to claim 1, wherein, When 1560 cm⁻¹ is observed in the Raman spectrum of carbon nanotubes... -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 of carbon nanotubes is 10–50.

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

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

5. The carbon nanotube dispersion according to claim 1 or 2, wherein, The cumulative particle size D50, determined by dynamic light scattering, is greater than 500 nm but less than 3000 nm.

6. The carbon nanotube dispersion according to claim 1 or 2, wherein, The weight-average molecular weight of the dispersant is 10,000 to 100,000.

7. The carbon nanotube dispersion according to claim 1 or 2, wherein, The solvent contains water.

8. A carbon nanotube resin composition comprising a carbon nanotube dispersion according to any one of claims 1 to 7, and a binder.

9. A composite slurry comprising the carbon nanotube resin composition as described in claim 8, and an active substance.

10. An electrode film, which is a coating film of the composite slurry as described in claim 9.

11. A non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode comprises the electrode membrane as described in claim 10.

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