Resin composition for secondary battery electrode, composite material slurry for secondary battery electrode, electrode film, and method for manufacturing secondary battery

Abstract

A manufacturing method of a resin composition for a secondary battery electrode, a composite material slurry for a secondary battery electrode, an electrode film, and a secondary battery, comprising adding an adhesive resin to a carbon nanotube dispersion liquid, the carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a non-aqueous dispersion medium, and the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement is 30 or more and 1,700 or less, and the phase angle is 3° or more and 90° or less.

Description

[0001] The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2021-116727 filed with the Japan Patent Office on July 14, 2021, and the entire disclosure content thereof is incorporated herein by reference. Technical Field

[0002] The present invention relates to a method for manufacturing a resin composition for a secondary battery electrode, a method for manufacturing a composite material slurry for a secondary battery electrode, a method for manufacturing an electrode film, and a method for manufacturing a secondary battery. Background Art

[0003] With the popularization of electric vehicles, the miniaturization, light weight, and high performance of portable devices, secondary batteries with high energy density are required, and further, high capacity of the secondary batteries is required. Under such a background, non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, particularly lithium ion secondary batteries, have started to be used in a large number of devices due to their characteristics of high energy density and high voltage.

[0004] The electrodes of secondary batteries are produced by coating a composite material slurry containing a positive electrode active material or a negative electrode active material, a conductive material, an adhesive resin, etc. on a current collector. By preparing a conductive material dispersion liquid in which a conductive material is dispersed in a dispersion medium in advance, and adding an active material and an adhesive resin to the conductive material dispersion liquid to produce a composite material slurry, the conductive material can be uniformly dispersed in the electrode film, thereby improving the conductivity of the electrode film. The conductive material dispersion liquid can be commonly used for various composite material slurries, but the composite material slurry is adjusted according to the specifications of the battery or the electrode in terms of the type of the active material, the blending ratio of each component, etc. Therefore, it is preferable to maintain the dispersibility and fluidity during the storage period of the conductive material dispersion liquid before adding the active material. Further, if it can be stored in the state of a resin composition in which an adhesive resin is added to the conductive material dispersion liquid, the operation of producing the composite material slurry can be simplified.

[0005] As the conductive material, carbon black, fullerene, graphene, fine carbon materials, etc. can be used. In particular, carbon nanotubes, which are a type of fine carbon fiber, are often used. For example, by adding carbon nanotubes to the positive electrode, the conductivity of the electrode film can be improved and the electrode resistance can be reduced. In addition, by adding carbon nanotubes to a graphite or silicon negative electrode, the electrode resistance can be reduced, the load resistance of the battery can be improved, the strength of the electrode can be increased, or the expansion and contraction properties of the electrode can be improved, thereby improving the cycle life of the lithium secondary battery. Among them, multi-walled carbon nanotubes with an outer diameter of several nanometers to dozens of nanometers have a lower price and are being promoted for practical use. If carbon nanotubes with a small average outer diameter and a large fiber length are used, a conductive network can be efficiently formed even with a small amount, enabling high capacity of the secondary battery. On the other hand, the cohesion of carbon nanotubes with these characteristics is strong, and it is difficult to further improve the dispersibility of the carbon nanotube dispersion.

[0006] A conductive material dispersion is disclosed in Patent Document 1, which contains a conductive material containing bundle-type carbon nanotubes, a dispersant such as hydrogenated nitrile-butadiene rubber, and a dispersion medium, and when measured with a rheometer, the phase angle at a frequency of 1 Hz is 3° to 18°. In Patent Document 1, in the conductive material dispersion containing carbon nanotubes, the viscosity and elasticity of the composition obtained by adding an active material and a binder are reduced, and the change over time during coating is fast, which causes cracks in the formation of the electrode active material layer. Therefore, the phase angle of the conductive material dispersion is controlled to be below 18° to make it have solid-like characteristics, thereby preventing cracks in the fabricated electrode active material layer. A conductive material dispersion is disclosed in Patent Document 2, which contains a conductive material containing bundle-type carbon nanotubes, a dispersant containing hydrogenated nitrile rubber, and a dispersion medium, and when measured with a rheometer, the complex elastic modulus (G*|@1Hz) at a frequency of 1 Hz is 20 Pa to 500 Pa. According to Patent Document 2, the particle size of linear carbon nanotubes varies depending on the measurement angle in particle size analysis, so it is difficult to evaluate the dispersibility. Therefore, it is set to control the dispersibility and viscosity characteristics of the conductive material dispersion by the complex elastic modulus of the conductive material dispersion. According to the evaluation of the examples in Patent Document 2, it is confirmed that the better the dispersion state of the conductive material dispersion, the lower the value of the complex elastic modulus as a measure of the elastic modulus.

[0007] The following method is disclosed in Patent Document 3: A conductive material paste 1 is obtained by mixing a conductive material such as acetylene black with a first binder, a second binder is added to the conductive material paste 1 to obtain a conductive material paste 2, and the conductive material paste 2 is mixed with a positive electrode active material to manufacture a slurry for a secondary battery positive electrode. According to Patent Document 3, the first binder contains a resin containing at least one monomer unit selected from the group consisting of conjugated diene monomer units, 1-olefin monomer units, and (meth)acrylate monomer units, and the second binder contains a fluorine-based polymer such as polyvinylidene fluoride. By adding and mixing in the order of the first binder and the second binder, the conductive material is moderately dispersed in the obtained slurry, and a good conductive network is formed between the conductive materials in the manufactured positive electrode composite material layer, the cycle characteristics of the secondary battery are improved, and the capacity deterioration at low temperatures is suppressed. The following method is disclosed in Patent Document 4: A conductive material paste containing a conductive material such as acetylene black, a binder, and a fluorine-based polymer such as polyvinylidene fluoride and having a solid content concentration of 5% by mass or more and 15% by mass or less is prepared, and the conductive material paste is mixed with a positive electrode active material to manufacture a slurry for a secondary battery positive electrode. According to Patent Document 4, by the solid content amount of the conductive material paste being in the above range, a good conductive network is formed between the conductive materials in the manufactured positive electrode composite material layer, the cycle characteristics of the secondary battery are improved, and the internal resistance is reduced.

[0008] The finer the conductive material, the more efficiently an ideal conductive network can be formed. However, the finer the conductive material, the larger the specific surface area and the higher the cohesive force, and it becomes more difficult to obtain a resin composition with a high concentration and good properties. If the concentration of the conductive material is forcibly increased, the resin composition will become highly viscous and its fluidity will deteriorate. In addition, sometimes the fine conductive material and the binder resin will be entangled with each other, resulting in poor dispersion. In a resin composition with poor fluidity, when the resin composition is transported using a tank or the like, or used after long-term storage, there may be a problem that it is difficult to take out from the tank or the like. On the other hand, in a resin composition with a low concentration of the conductive material, there will be problems such as a lower degree of freedom in designing when formulating materials such as the active material, or a higher transportation cost per unit solid content of the conductive material. Therefore, the urgent task is to obtain a resin composition in which fine conductive materials are well dispersed in a state of high fluidity.

[0009] [Prior Art Documents]

[0010] [Patent Documents]

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-534731

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-533175

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 2015-133302

[0014] Patent Document 4: Japanese Patent Laid-Open No. 2015-128012 Summary of the Invention

[0015] [Problems to be Solved by the Invention]

[0016] The solid-like characteristics of the conductive material dispersion disclosed in Patent Document 1 are strong, and the elastic behavior of the conductive material dispersion disclosed in Patent Document 2 is strong. Therefore, both have problems of poor fluidity and being unsuitable for transportation or long-term storage using a tank. In Patent Document 1, the phase angle was controlled to obtain a conductive material dispersion with high solid-like characteristics, and then an active substance and a binder were added to prepare a composition. However, the viscosity of the conductive material dispersion with high solid-like characteristics becomes high, and the miscibility with the subsequently added binder sometimes decreases. In Patent Document 2, a conductive material dispersion in which the dispersibility and viscosity characteristics were controlled using the complex elastic modulus was obtained, and then an active substance and a binder were added to prepare a composition. However, sometimes the miscibility with the subsequently added binder cannot be sufficiently obtained only by controlling the conductive material dispersion using the complex elastic modulus. For example, when a binder resin is added to a carbon nanotube dispersion in which the fiber length of the carbon nanotubes is maintained and they are finely dispersed, sometimes the carbon nanotubes aggregate or the binder resin gels, resulting in a decrease in the dispersibility and fluidity of the resin composition.

[0017] In Patent Documents 3 and 4, acetylene black was specifically studied as the conductive material, but carbon nanotubes were not sufficiently studied. Regarding fibrous carbon materials such as carbon nanotubes, if the fibers break due to dispersion treatment or stirring treatment during the manufacturing process of the composite material slurry, the conductive network between the conductive materials in the electrode film sometimes weakens. In addition, when the composite material slurry contains carbon nanotubes with long fiber lengths, the fibers and the resin component are likely to entangle and aggregate. If the electrode film is made in a state where the fibers are not untangled from each other, the conductive network between the conductive materials in the electrode film sometimes weakens.

[0018] The inventors of the present invention have conducted a detailed comparative study on minute differences in the dispersion state of conductive materials, and as a result, it has been found that when fibrous carbon nanotubes are used as conductive materials, even if the measured values are the same in the particle size distribution or viscosity, which have often been used as indices of dispersion degree in the past, the characteristics when used in secondary batteries may sometimes be different, and the dispersion state of the conductive material has not been accurately grasped. For example, in the case of particle size distribution, since fibrous non-spherical particles are assumed to be spherical and calculated, it is likely to deviate from the actual situation. In the case of viscosity, generally, the better the dispersion state of the conductive material, the lower the viscosity. However, in the case where the conductive material is fibrous and easily entangled, even if the conductive material is uniformly and stably dispersed in the dispersion medium, due to the structural viscosity of the conductive material itself, the elasticity becomes stronger. In addition, in the case of fiber breakage, the viscosity changes according to two factors, namely, deaggregation and breakage. Therefore, it is difficult to accurately represent the state of the conductive material only by viscosity. When the fibers of carbon nanotubes are broken, it is difficult to form a developed conductive network in the electrode due to the increase in the contact resistance between carbon nanotubes. Therefore, it is effective to keep the fibers unbroken and uniformly dispersed as much as possible. In the prior art, the fine control of the dispersion state of a conductive material dispersion liquid containing carbon nanotubes is insufficient, and when a binder resin is added to the conductive material dispersion liquid, the dispersibility and fluidity sometimes decrease.

[0019] That is, the problem to be solved by the present invention is to provide a resin composition for a secondary battery electrode that finely controls the dispersion state of carbon nanotubes as a conductive material and has high dispersibility and fluidity in a state containing a binder resin, and a composite material slurry for a secondary battery electrode having good dispersibility of carbon nanotubes in a state containing an active material. More specifically, a non-aqueous electrolyte secondary battery with high output power, high capacity, and long life, and an electrode film for use therein are provided.

[0020] [Means for Solving the Problem]

[0021] The inventors of the present invention have made intensive studies for the purpose of solving the above problems, and as a result, it has been found that by adding a binder resin to the following carbon nanotube dispersion liquid, that is, a carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a non-aqueous dispersion medium and dispersed in such a manner that the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) obtained by dynamic viscoelasticity measurement is 30 or more and 1,700 or less, even in a state where a binder resin is added to the carbon nanotube dispersion liquid, the fluidity can be maintained, and in the resin composition, the long fibers of carbon nanotubes are dispersed in a state where they are moderately maintained without breakage. By forming an electrode film using the resin composition, a developed conductive network can be formed in the electrode film. Thereby, a secondary battery with high output power, high capacity, and long life can be provided.

[0022] That is, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following embodiments.

[0023] <1> A method for manufacturing a resin composition for a secondary battery electrode, comprising adding a binder resin to a carbon nanotube dispersion liquid and not including adding an active material, the carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a non-aqueous dispersion medium, the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement being 30 or more and 1,700 or less, and the phase angle being 3° or more and 90° or less.

[0024] <2> The method for manufacturing a resin composition for a secondary battery electrode according to <1>, wherein the complex elastic modulus of the carbon nanotube dispersion liquid at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement is 0.1 Pa or more and 200 Pa or less.

[0025] <3> The method for manufacturing a resin composition for a secondary battery electrode according to <1> or <2>, wherein the complex elastic modulus of the resin composition for a secondary battery electrode at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement is 0.1 Pa or more and 300 Pa or less.

[0026] <4> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <3>, wherein the phase angle of the resin composition for a secondary battery electrode at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement is 3° or more and 90° or less.

[0027] <5> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <4>, wherein the binder resin is added to the carbon nanotube dispersion liquid in powder form.

[0028] <6> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <5>, wherein the content of the carbon nanotubes contained in the carbon nanotube dispersion liquid is 0.5% by mass or more and 10% by mass or less based on the total amount of the carbon nanotube dispersion liquid.

[0029] <7> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <6>, wherein the carbon nanotubes contained in the carbon nanotube dispersion liquid include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0030] <8> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <7>, wherein the binder resin is 10% by mass or more and 300% by mass or less based on the mass ratio with respect to the carbon nanotubes contained in the carbon nanotube dispersion liquid.

[0031] <9> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <6>, wherein the carbon nanotubes contained in the carbon nanotube dispersion liquid include one of single-walled carbon nanotubes and multi-walled carbon nanotubes, and the method for manufacturing the resin composition for a secondary battery electrode includes: in a state where one of single-walled carbon nanotubes and multi-walled carbon nanotubes is dispersed in the carbon nanotube dispersion liquid, before adding the binder resin to the carbon nanotube dispersion liquid, after the addition, at the same time as the addition, or a combination of these, further adding the other of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0032] <10> The method for manufacturing a resin composition for a secondary battery electrode according to <9>, wherein the binder resin is 10% by mass or more and 300% by mass or less based on the mass ratio with respect to the total amount of the carbon nanotubes contained in the resin composition.

[0033] <11> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <10>, wherein the carbon nanotube dispersion liquid further contains carbon black.

[0034] <12> The method for manufacturing a resin composition for a secondary battery electrode according to any one of <1> to <11>, including: before adding the binder resin to the carbon nanotube dispersion liquid, after the addition, at the same time as the addition, or a combination of these, further adding carbon black.

[0035] <13> A method for manufacturing a composite material slurry for a secondary battery electrode, including: producing a resin composition for a secondary battery electrode according to the method described in any one of <1> to <12>; and adding an active material to the resin composition.

[0036] <14> The method for manufacturing a composite material slurry for a secondary battery electrode according to <13>, including: before adding the active material to the resin composition, after the addition, at the same time as the addition, or a combination of these, further adding carbon black.

[0037] <15> A method for manufacturing an electrode film, including: producing a composite material slurry for a secondary battery electrode according to the method described in <13> or <14>, and coating the composite material slurry to form an electrode film.

[0038] <16>A method for manufacturing a secondary battery, comprising: preparing a composite material slurry for a secondary battery electrode according to the method described in <13> or <14>, and applying the composite material slurry to a current collector to form an electrode film.

[0039] [Advantages of the Invention]

[0040] Through the embodiments of the present invention, a resin composition for a secondary battery electrode having high fluidity and dispersibility can be provided. Through another embodiment of the present invention, a composite material slurry for a secondary battery electrode with good dispersibility of carbon nanotubes can be provided. Through yet another embodiment of the present invention, a non-aqueous electrolyte secondary battery with high output power, high capacity, and high lifespan, and an electrode film therefor can be provided. Detailed Embodiments

[0041] Hereinafter, the manufacturing method of the resin composition for a secondary battery electrode, the manufacturing method of the composite material slurry for a secondary battery electrode, the manufacturing method of the electrode film, and the manufacturing method of the secondary battery according to the embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and the present invention also includes embodiments implemented within the scope of not changing the gist.

[0042] In this specification, carbon nanotubes are sometimes referred to as "CNT". Hydrogenated nitrile rubber is sometimes referred to as "H-NBR", and N-methyl-2-pyrrolidone is sometimes referred to as "NMP". In addition, in this specification, the carbon nanotube dispersion is sometimes simply referred to as "CNT dispersion" or "dispersion", and the resin composition for a secondary battery electrode is sometimes simply referred to as "resin composition".

[0043] <Manufacturing Method of Resin Composition for Secondary Battery Electrode>

[0044] The resin composition for a secondary battery electrode contains carbon nanotubes, a dispersant, a binder resin, and a non-aqueous dispersion medium, and may further contain optional components. The manufacturing method of the resin composition for a secondary battery electrode includes adding a binder resin to a carbon nanotube dispersion containing carbon nanotubes, a dispersant, and a non-aqueous dispersion medium, and having a product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) obtained by dynamic viscoelasticity measurement of 30 or more and 1,700 or less.

[0045] <Carbon Nanotubes>

[0046] The carbon nanotube dispersion contains carbon nanotubes (CNTs), a dispersant, and a non-aqueous dispersion medium. The CNTs function as a conductive material. The CNT dispersion may also contain a conductive material other than the carbon nanotubes. As other conductive materials, for example, carbon materials such as carbon black, fullerenes, graphene, multi-layer graphene, and graphite can be cited. In the case of using a conductive material other than CNTs, from the viewpoint of the adsorption performance of the dispersant, carbon black is preferred, and examples thereof include carbon blacks such as acetylene black, furnace black, hollow carbon black, and Ketjen black. These carbon blacks can be any of neutral, acidic, and basic, and oxidized carbon black or graphitized carbon black can also be used. One or two or more of the other conductive materials can be used in combination.

[0047] CNTs are formed by winding planar graphite into a cylindrical shape, and include single-walled CNTs and multi-walled CNTs, which can be mixed. The single-walled CNTs have a structure formed by winding one layer of graphite. The multi-walled CNTs have a structure formed by winding two or more layers of graphite. In addition, the sidewalls of the CNTs may not be a graphite structure. In addition, for example, CNTs including sidewalls with an amorphous structure are also CNTs in this specification.

[0048] The shape of the CNTs is not limited. As the shape, various shapes including needle-like, cylindrical tubular, herringbone (fishbone type or cup stack type), playing card-like (platelet), and coil-like can be cited. Among them, the shape of the CNTs is preferably needle-like or cylindrical tubular. The CNTs can be in a single shape or a combination of two or more shapes.

[0049] Examples of the morphology of the CNTs include graphite whisker, filamentous carbon, graphite fiber, ultra-fine carbon tube, carbon tube, carbon fibril, carbon microtube, and carbon nanofiber. The carbon nanotubes can have a single morphology of these or a morphology formed by combining two or more of them.

[0050] The average outer diameter of the CNTs is preferably 1 nm or more, more preferably 3 nm or more. In addition, it is preferably 30 nm or less, more preferably 20 nm or less, and further preferably 13 nm or less. In addition, the average outer diameter of the CNTs can be calculated as follows: First, observe and photograph the CNTs using a transmission electron microscope, and in the observation photograph, select any 300 CNTs and measure their respective outer diameters.

[0051] Two or more types of CNTs having different average outer diameters may be separately prepared and added to a non-aqueous dispersion medium to prepare a CNT dispersion. When two or more types of CNTs having different average outer diameters are used as the CNTs, the average outer diameter of the first CNT is preferably 1 nm or more and less than 5 nm. The average outer diameter of the second CNT is preferably 3 nm or more and 30 nm or less, more preferably 5 nm or more and 30 nm or less, and further preferably 20 nm or less. When two or more types of CNTs having different average outer diameters are used as the CNTs, the mass ratio of the first CNT to the second CNT is preferably 1:1 to 1:100, more preferably 1:3 to 1:100, further preferably 1:10 to 1:100, and still further preferably 1:10 to 1:50.

[0052] Here, when a single-walled carbon nanotube is used as the first CNT and a multi-walled carbon nanotube is used as the second CNT, the average outer diameter of the single-walled carbon nanotube is preferably 1 nm or more and 3 nm or less, more preferably 1.3 nm or more and 2.5 nm or less, and further preferably 1.5 nm or more and 2.0 nm or less. The average outer diameter of the multi-walled carbon nanotube is preferably more than 3 nm and 30 nm or less, more preferably 3 nm or more and 20 nm or less, and further preferably 5 nm or more and 15 nm or less. In the resin composition, a combination of a single-walled carbon nanotube and a multi-walled carbon nanotube may also be included as the carbon nanotube. In this case, the mass ratio of the single-walled carbon nanotube to the multi-walled carbon nanotube is preferably 1:1 to 1:100, more preferably 1:2 to 1:50, and further preferably 1:3 to 1:10. In the single-walled carbon nanotube and the multi-walled carbon nanotube, since the outer diameter and the fiber length are different, the state of forming a good conductive network or stabilizing dispersion is different. By setting the mass ratio of the single-walled carbon nanotube to the multi-walled carbon nanotube within the above range, entanglement between the carbon nanotubes is suppressed, and a dispersion having excellent fluidity can be obtained.

[0053] The average fiber length of the CNT is preferably 0.5 μm or more, more preferably 0.8 μm or more, and further preferably 1.0 μm or more. In addition, it is preferably 20 μm or less, more preferably 10 μm or less. Further, the average fiber length of the CNT can be calculated as follows: First, the CNT is observed and photographed using a scanning electron microscope. In the observation photograph, any 300 CNTs are selected and the fiber length of each is measured.

[0054] The value obtained by dividing the fiber length of CNT by its outer diameter is the aspect ratio. Using the values of the average fiber length and the average outer diameter, a representative aspect ratio can be determined. The higher the aspect ratio of the conductive material, the higher the conductivity that can be obtained when forming an electrode. The aspect ratio of CNT is preferably 30 or more, more preferably 50 or more, and still more preferably 80 or more. Additionally, it is preferably 10,000 or less, more preferably 3,000 or less, and still more preferably 1,000 or less.

[0055] The specific surface area of CNT is preferably 100 m 2 / g or more, more preferably 150 m 2 / g or more, and still more preferably 200 m 2 / g or more. Additionally, it is preferably 1200 m 2 / g or less, more preferably 1000 m 2 / g or less. The specific surface area of CNT is calculated by the Brunauer - Emmett - Teller (BET) method based on nitrogen adsorption measurement. If the average outer diameter, average fiber length, aspect ratio, and specific surface area of CNT are within the above ranges, it is easy to form a well - developed conductive path in the electrode.

[0056] The carbon purity of CNT is represented by the content rate (mass%) of carbon atoms in CNT. Relative to 100 mass% of CNT, the carbon purity is preferably 80 mass% or more, more preferably 90 mass% or more, still more preferably 95 mass% or more, and particularly preferably 98 mass% or more. By setting the carbon purity within the above range, it is possible to prevent adverse conditions such as short - circuits caused by the formation of dendrites due to impurities.

[0057] CNTs that have been purified to a high purity for the purpose of removing or reducing impurities such as metal catalysts to improve carbon purity can also be used. The method of high-purity purification is not particularly limited, and known methods can be used. For example, a method of evaporating impurities by treating at a high temperature (e.g., 3000 °C) in an inert atmosphere can be used. In this method, the treatment can be carried out under conditions with relatively little risk of explosion, and thus it is preferred in this regard. Additionally, a method of heat-treating by mixing a gas containing a halogen (such as chlorine gas, fluorine gas, carbon tetrachloride gas, carbon tetrafluoride gas, etc.) in an inert gas and evaporating the halogenated impurities can also be used. Since the boiling point of the impurities decreases due to halogenation, they can be removed at a lower temperature (e.g., 1600 °C) compared to the case without halogenation, and the carbon purity can be improved without changing the physical properties such as the crystallinity, density, and conductivity of the CNTs, and thus it is preferred in this regard. Furthermore, if the CNTs are heat-treated after being densified, the amount of treatment can be increased while suppressing the scattering of the CNTs, thereby efficiently purifying them. Additionally, a method of dissolving and removing impurities by impregnating the CNTs in an acidic or alkaline solution can also be used. When treating with an acidic or alkaline solution, functional groups may sometimes be introduced on the surface or ends of the CNTs. If the amount of functional groups is small, the dispersibility is easily improved. On the other hand, if the amount of functional groups is large, the conductivity sometimes easily decreases.

[0058] In the case of dispersing CNTs using a disperser based on collision with a medium such as a bead mill, or in the case of repeatedly performing the process of passing CNTs through a disperser for a long time, the CNTs may sometimes be damaged and short strip-like carbonaceous substances may be generated. If short strip-like carbonaceous substances are generated, the viscosity of the CNT dispersion decreases, and the gloss of the coating film obtained by coating the CNT dispersion and drying it becomes high. Therefore, if judged only based on these evaluation results, it would be considered that the dispersion state is good. However, the contact resistance of the short strip-like carbonaceous substances is high, and it is difficult to form an electric conduction network, so sometimes the resistance of the electrode deteriorates. The degree of generation of short strip-like carbonaceous substances can be confirmed by methods such as diluting the dispersion, dropping it onto a substrate with a smooth surface and good affinity with the dispersion medium, drying to obtain a sample, and observing the sample using a scanning electron microscope. If the dispersion conditions or the formulation of the dispersion are adjusted so that carbonaceous substances with a size of less than 0.1 μm are not generated, an electrode with high conductivity can be obtained.

[0059] The carbon nanotubes can be surface-treated carbon nanotubes. The carbon nanotubes can also be carbon nanotube derivatives to which functional groups represented by carboxyl groups are imparted. Additionally, carbon nanotubes encapsulating organic compounds, metal atoms, or substances represented by fullerenes can also be used.

[0060] The carbon nanotubes can be carbon nanotubes manufactured by any method. The carbon nanotubes can generally be manufactured by methods such as laser ablation, arc discharge, thermal chemical vapor deposition (CVD), plasma CVD, and combustion method, but are not limited to these methods. For example, carbon nanotubes can be manufactured by bringing a carbon source into contact reaction with a catalyst in an atmosphere with an oxygen concentration of 1% by volume or less at 500°C to 1000°C. The carbon source can be at least any one of hydrocarbons and alcohols.

[0061] As the raw material gas for the carbon source of the carbon nanotubes, any known gas can be used. For example, as the raw material gas containing carbon, hydrocarbons represented by methane, ethylene, propane, butane, and acetylene, carbon monoxide, and alcohols can be used, but are not limited to these gases. In particular, from the viewpoint of ease of use, it is desirable to use at least any one of hydrocarbons and alcohols as the raw material gas.

[0062] <Dispersant>

[0063] The resin composition contains a dispersant. The dispersant is preferably a substance that can stably disperse CNTs in the resin composition. Either a resin-type dispersant or a surfactant can be used as the dispersant, but a resin-type dispersant is preferred in terms of having a strong adsorption force to CNTs and obtaining good dispersion stability. Preferred types of dispersants can be appropriately used in a preferred blending amount according to the characteristics required for the dispersion of carbon nanotubes.

[0064] As the resin-type dispersant, (meth)acrylic polymers, polymers derived from ethylenically unsaturated hydrocarbons, cellulose derivatives, copolymers thereof, etc. can be used.

[0065] Examples of polymers derived from ethylenically unsaturated hydrocarbons include polyvinyl alcohol resins, polyvinylpyrrolidone resins, polyacrylonitrile resins, nitrile rubbers, etc. Examples of polyvinyl alcohol resins include polyvinyl alcohol, modified polyvinyl alcohol having functional groups other than hydroxyl groups (e.g., acetyl group, sulfo group, carboxyl group, carbonyl group, amino group), polyvinyl alcohol modified with various salts, polyvinyl alcohol modified by other anionic or cationic modifications, polyvinyl acetals (polyvinylacetoacetal, polyvinyl butyral, etc.) obtained by acetal modification (e.g., acetyl acetal modification or butyral acetal modification) with aldehydes, etc. Examples of polyacrylonitrile resins include homopolymers of polyacrylonitrile, copolymers of polyacrylonitrile, modified products thereof, etc., and preferably polyacrylonitrile resins having at least one selected from the group consisting of active hydrogen groups such as hydroxyl group, carboxyl group, primary amino group, secondary amino group, and mercapto group, basic groups, and alkyl groups introduced from (meth)acrylic acid alkyl esters or α-olefins, etc. For example, the acrylonitrile copolymer described in Japanese Patent Application Laid-Open No. 2020-163362 can be used. Examples of nitrile rubbers include acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber, etc. Examples of cellulose derivatives include 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., or copolymers thereof. In addition, the dispersants described in International Publication No. 2008 / 108360, Japanese Patent Application Laid-Open No. 2018-192379, Japanese Patent Application Laid-Open No. 2019-087304, Japanese Patent No. 6524479, and Japanese Patent Application Laid-Open No. 2009-026744 can be used, but the dispersants are not limited thereto. Particularly preferred are methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, homopolymers of polyacrylonitrile, copolymers of polyacrylonitrile, and hydrogenated acrylonitrile-butadiene rubber. Polymers in which other substituents are introduced into a part of these polymers, modified polymers, etc. can also be used. From the viewpoints of the affinity balance between the dispersed substance and the dispersion medium and the resistance to the electrolyte, the weight average molecular weight of the resin-type dispersant is preferably 500,000 or less, more preferably 300,000 or less, and preferably 3,000 or more, more preferably 5,000 or more. The resin-type dispersant can be used alone or in combination of two or more.

[0066] As commercially available polyvinyl alcohol-based resins, for example, various grades can be obtained under trade names such as Kuraray Poval (polyvinyl alcohol resin manufactured by Kuraray), Gohsenol, Gohsenex (polyvinyl alcohol resins manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), Denka Poval (polyvinyl alcohol resin manufactured by Denka), J-Poval (polyvinyl alcohol resin manufactured by Japan Vam & Poval), etc. In addition, modified polyvinyl alcohols having various functional groups can be obtained in the same manner. Further, polyvinyl alcohol-based resins synthesized by known synthesis methods can also be used. As commercially available polyvinylpyrrolidone-based resins, specifically, examples include Luvitec K17 (K value: 15.0 to 19.0, low molecular weight), K30 (K value 27.0 to 33.0), K80 (K value 74.0 to 82.0), K85 (K value 84.0 to 88.0), K90 (K value 88.0 to 92.0), K90HM (K value 92.0 to 96.0, high molecular weight) (manufactured by BASF Japan), K15, K30, K90, K120 (manufactured by ISP), polyvinylpyrrolidone K30 (K value 27.0 to 33.0), K85 (K value 84.0 to 88.0), K90 (K value 88.0 to 96.0) (manufactured by Nippon Catalyst), PVP K12 (K value 10 to 14), K15 (K value 13 to 19), K30 (K26 to K35), K60 (K value 50 to 62), K90 (K value 88 to 100), K120 (K value 114 to 130) (manufactured by DSP Gokyo Food & Chemical), etc. From the viewpoint of preventing an increase in viscosity, polyvinylpyrrolidone preferably has a K value of 150 or less, more preferably a K value of 100 or less, and still more preferably a K value of 85 or less. As commercially available nitrile rubbers, various grades having different nitrile ratios, hydrogenation ratios, and molecular weights can be obtained under trade names such as Therban (hydrogenated nitrile rubber manufactured by Arlanxeo), Baymod (nitrile rubber manufactured by Arlanxeo), Zetpole (hydrogenated nitrile rubber manufactured by Zeon Corporation), Nipole NBR (nitrile rubber manufactured by Zeon Corporation), etc. In addition, nitrile rubbers synthesized by known synthesis methods can also be used.

[0067] A surfactant may also be used in place of the resinous dispersant or in combination therewith. Surfactants can be classified into anionic, cationic, zwitterionic, and nonionic surfactants.

[0068] As the resinous dispersant, a polymer containing at least an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit may also be used. The aliphatic hydrocarbon structural unit of the polymer may contain an alkylene structural unit. The polymer may be hydrogenated.

[0069] An aliphatic hydrocarbon structural unit is a structural unit containing an aliphatic hydrocarbon structure, preferably a structural unit composed only of an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure contains at least a saturated aliphatic hydrocarbon structure and may also contain an unsaturated aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure preferably contains at least a linear aliphatic hydrocarbon structure and may also contain a branched aliphatic hydrocarbon structure.

[0070] Examples of the aliphatic hydrocarbon structural unit include an alkylene structural unit, an alkenylene structural unit, an alkyl structural unit, an alkane triyl structural unit, an alkane tetrayl structural unit, etc. Structural units containing a branching point such as an alkane triyl structural unit and an alkane tetrayl structural unit are different from the structural units containing a branched alkylene structure and the structural units containing a branched alkyl structure described later. The aliphatic hydrocarbon structural unit preferably contains at least an alkylene structural unit.

[0071] An alkylene structural unit is a structural unit containing an alkylene structure, preferably a structural unit composed only of an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

[0072] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1A).

[0073] General formula (1A)

[0074] [Chemical formula 1]

[0075]

[0076] In the general formula (1A), n represents an integer of 1 or more. n is preferably an integer of 2 or more, more preferably an integer of 3 or more, and particularly preferably an integer of 4 or more. n is preferably an integer of 6 or less, more preferably an integer of 5 or less. Particularly preferably, n is 4. In this specification, "*" represents a bonding portion with other structures.

[0077] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1B).

[0078] General formula (1B)

[0079] [Chemical formula 2]

[0080]

[0081] In general formula (1B), n represents an integer of 1 or more. n is preferably an integer of 2 or more, more preferably an integer of 3 or more. n is preferably an integer of 5 or less, more preferably an integer of 4 or less. Particularly preferably, n is 3.

[0082] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1C).

[0083] General formula (1C)

[0084] [Chemical formula 3]

[0085]

[0086] In general formula (1C), n represents an integer of 1 or more. n is preferably an integer of 4 or less, more preferably an integer of 3 or less, still more preferably an integer of 2 or less. Particularly preferably, n is 2.

[0087] The method for introducing the alkylene structural unit into the polymer is not particularly limited, and for example, the following methods (1a) or (1b) can be mentioned.

[0088] In the method (1a), a polymer is prepared by a polymerization reaction using a monomer composition containing a conjugated diene monomer. The prepared polymer contains monomer units derived from the conjugated diene monomer. In this specification, "monomer units derived from the conjugated diene monomer" are sometimes referred to as "conjugated diene monomer units", and monomer units derived from other monomers are sometimes omitted in the same way. Then, at least a part of the conjugated diene monomer units is converted into alkylene structural units by hydrogenating the conjugated diene monomer units. In this specification, "hydrogenation" is sometimes referred to as "hydrogenation". The finally obtained polymer contains units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0089] In addition, the conjugated diene monomer units at least contain monomer units having one carbon-carbon double bond. For example, the 1,3-butadiene monomer units as the conjugated diene monomer units contain at least one monomer unit selected from the group consisting of monomer units having a cis-1,4 structure, monomer units having a trans-1,4 structure, and monomer units having a 1,2 structure, and may also contain two or more monomer units. In addition, the conjugated diene monomer units may further contain monomer units that do not have a carbon-carbon double bond and contain a branching point. In this specification, a "branching point" refers to a branching point in a branched polymer. When the conjugated diene monomer units contain monomer units containing a branching point, the polymer prepared above is a branched polymer.

[0090] In the method of (1b), a polymer is prepared by a polymerization reaction using a monomer composition containing an α-olefin monomer. The prepared polymer contains α-olefin monomer units. The finally obtained polymer contains α-olefin monomer units as alkylene structural units.

[0091] Among these methods, in terms of ease of polymer production, the method of (1a) is preferred. The conjugated diene monomer has 4 or more carbon atoms, preferably 4 or more and 6 or less carbon atoms. Examples of the conjugated diene monomer include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Among them, 1,3-butadiene is preferred. The alkylene structural unit preferably contains a structural unit obtained by hydrogenating a conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), more preferably contains a structural unit obtained by hydrogenating a 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomer can be used alone or in combination of two or more.

[0092] The hydrogenation is preferably a method capable of selectively hydrogenating the conjugated diene monomer unit. Examples of the hydrogenation method include known methods such as an oil-phase hydrogenation method or an aqueous-phase hydrogenation method.

[0093] The hydrogenation can be carried out by a usual method. The hydrogenation can be carried out, for example, by subjecting a polymer having a conjugated diene monomer unit to a hydrogen treatment in the presence of a hydrogenation catalyst in a state where the polymer is dissolved in an appropriate solvent. Examples of the hydrogenation catalyst include iron, nickel, palladium, platinum, copper, etc.

[0094] In the method of (1b), the α-olefin monomer has 2 or more carbon atoms, preferably 3 or more carbon atoms, more preferably 4 or more carbon atoms. The α-olefin monomer preferably has 6 or less carbon atoms, more preferably 5 or less carbon atoms. Examples of the α-olefin monomer include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomer can be used alone or in combination of two or more.

[0095] The alkylene structural unit preferably contains at least one selected from the group consisting of a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, more preferably contains at least one selected from the group consisting of a structural unit composed only of a linear alkylene structure and a structural unit composed only of a branched alkylene structure, and further preferably contains at least one selected from the group consisting of the structural unit represented by the formula (1B) and the structural unit represented by the formula (1C).

[0096] The alkylene structural unit may also include a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure. When the alkylene structural unit includes a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, based on the mass of the alkylene structural unit (i.e., when the mass of the alkylene structural unit is set to 100% by mass), the content of the branched alkylene structure is preferably 70% by mass or less, more preferably 65% by mass or less. Particularly preferably, it is 20% by mass or less, more preferably 18% by mass or less, and still more preferably 15% by mass or less. When the polymer includes a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, based on the mass of the alkylene structural unit (i.e., when the mass of the alkylene structural unit is set to 100% by mass), the content of the branched alkylene structure is, for example, 1% by mass or more, may also be 5% by mass or more, and may further be 10% by mass or more.

[0097] In the aliphatic hydrocarbon structural unit, based on the total mass of the aliphatic hydrocarbon structural unit (i.e., when the mass of the aliphatic hydrocarbon structural unit is set to 100% by mass), the content of the alkylene structural unit is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Based on the total mass of the aliphatic hydrocarbon structural unit (i.e., when the mass of the aliphatic hydrocarbon structural unit is set to 100% by mass), the content of the alkylene structural unit is, for example, less than 100% by mass, and may be 99.5% by mass or less, 99% by mass or less, or 98% by mass or less. The content of the alkylene structural unit may be 100% by mass.

[0098] Based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass), the content of the aliphatic hydrocarbon structural unit is preferably 40% by mass or more, more preferably 50% by mass or more, and still more preferably 60% by mass or more. Based on the mass of the polymer (i.e., when the mass of the polymer is set to 100% by mass), the content of the aliphatic hydrocarbon structural unit is preferably less than 85% by mass, more preferably 75% by mass or less, and still more preferably 70% by mass or less.

[0099] The nitrile group-containing structural unit is a structural unit containing a nitrile group, preferably a structural unit containing an alkylene structure substituted with a nitrile group, and more preferably a structural unit composed only of an alkylene structure substituted with a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The nitrile group-containing structural unit may further include a structural unit containing an alkyl structure substituted with a nitrile group (or composed only of it). The number of nitrile groups contained in the nitrile group-containing structural unit is preferably 1.

[0100] The nitrile group-containing structural unit is preferably a structural unit represented by the following general formula (2A).

[0101] General formula (2A)

[0102] [Chemical formula 4]

[0103]

[0104] In general formula (2A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and still more preferably an integer of 3 or less. Particularly preferably, n is 2.

[0105] The nitrile group-containing structural unit is preferably a structural unit represented by the following general formula (2B).

[0106] General formula (2B)

[0107] [Chemical formula 5]

[0108]

[0109] In general formula (2B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom.

[0110] The method for introducing the nitrile group-containing structural unit into the polymer is not particularly limited, and a method of preparing a polymer by a polymerization reaction using a monomer composition containing a nitrile group-containing monomer ((2a) method) can be preferably used. The finally obtained polymer contains a nitrile group-containing monomer unit as the nitrile group-containing structural unit. Examples of the nitrile group-containing monomer that can form the nitrile group-containing structural unit include monomers containing a polymerizable carbon-carbon double bond and a nitrile group. For example, compounds having a nitrile group and an α,β-ethylenically unsaturated group can be cited, and specifically, acrylonitrile, methacrylonitrile, etc. can be cited. In particular, from the viewpoint of improving the intermolecular force between polymers and / or between the polymer and the dispersed substance (adsorbed substance), the nitrile group-containing monomer is preferably acrylonitrile-containing. The nitrile group-containing monomer can be used alone or in combination of two or more.

[0111] Based on the mass of the polymer (that is, when the mass of the polymer is set to 100% by mass), the content of the nitrile group-containing structural unit is preferably 15% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more. Based on the mass of the polymer (that is, when the mass of the polymer is set to 100% by mass), the content of the nitrile group-containing structural unit is preferably 50% by mass or less, more preferably 46% by mass or less, and still more preferably 40% by mass or less. By making the content of the nitrile group-containing structural unit within the above range, the adsorptivity to the dispersed substance and the affinity to the dispersion medium can be controlled, and the dispersed substance can be stably present in the dispersion medium. In addition, the affinity of the polymer to the electrolyte can also be controlled, and adverse conditions such as the dissolution of the polymer in the electrolyte in the battery and the increase in the resistance of the electrolyte can be prevented.

[0112] The polymer may contain arbitrary structural units. As the arbitrary structural units, structural units containing an amide group, structural units containing a carboxyl group, etc. may be mentioned.

[0113] As a preferred form of the polymer, a polymer in which the total content of aliphatic hydrocarbon structural units and nitrile group-containing structural units contained in the polymer is 80% by mass or more and 100% by mass or less based on the mass of the polymer may be mentioned. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and still more preferably 98% by mass or more.

[0114] In this specification, the content of the structural unit can be determined by using the amount of the monomer used, nuclear magnetic resonance (NMR) and / or infrared spectroscopy (IR) measurement.

[0115] The polymer preferably has a Mooney viscosity (ML 1+4 , 100 °C) of 20 or more and 80 or less. The Mooney viscosity of the polymer is 20 or more, preferably 30 or more, and more preferably 40 or more. In addition, it is 80 or less, preferably 70 or less. In this specification, "Mooney viscosity (ML 1+4 , 100 °C)" can be measured at a temperature of 100 °C according to Japanese Industrial Standards (JIS) K6300-1. It is considered that by setting the Mooney viscosity within the above range, it is possible to have an appropriate resilience in the state of being adsorbed to the conductive material and improve the dispersion stability. If it is lower than the above range, the solubility in the solvent increases, and there is a concern that the balance between the conductive material and the dispersion medium deteriorates. In addition, when the Mooney viscosity exceeds the above range, the viscosity of the CNT dispersion liquid and the resin composition containing the same becomes too high, and sometimes the energy transfer efficiency of the dispersing machine decreases, or metal foreign matters mixed from the raw materials cannot be efficiently removed by methods such as iron removal using a magnet, filtration, or centrifugation, resulting in a decrease in battery performance due to the remaining metal foreign matters.

[0116] The method for adjusting the Mooney viscosity of the polymer is not particularly limited. For example, the Mooney viscosity can be adjusted by changing the composition of the polymer (type or content of structural units, hydrogenation rate, etc.), structure (linearity rate, etc.), molecular weight, preparation conditions (polymerization temperature, molecular weight regulator dosage, etc.), etc. Specifically, the Mooney viscosity of the polymer can be adjusted by the following methods.

[0117] In the method of (2a), the Mooney viscosity is reduced by increasing the amount of the molecular weight regulator used in the preparation of the polymer.

[0118] In the method of (2b), an alkali is added to modify the nitrile groups contained in the nitrile group-containing structural units of the polymer by hydrolysis or the like, thereby reducing the Mooney viscosity of the polymer.

[0119] In the method of (2c), the Mooney viscosity is reduced by applying mechanical shear force to the polymer.

[0120] In the method of (2b), the reduction of the Mooney viscosity can be carried out by mixing a polymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing monomer unit, an alkali, and a solvent. Any component can be further mixed. The order of addition of the polymer, alkali, and solvent to the container and the mixing method are not limited, and these can be added to the container simultaneously; the polymer, alkali, and solvent can also be added to the container separately; or, either one or both of the polymer and the alkali can be mixed with the solvent to prepare a polymer-containing liquid and / or an alkali-containing liquid, and the polymer-containing liquid and / or the alkali-containing liquid can be added to the container. Particularly in terms of enabling efficient modification of the nitrile groups, the following method is preferred: while stirring, an alkali dispersion obtained by dispersing an alkali in a solvent is added to a polymer solution obtained by dissolving the polymer in a solvent. A disperser (dispersing machine) or a homogenizer can be used for stirring. As the solvent, the solvents described later can be used.

[0121] In addition to being used in the method of (2b), if an alkali is contained in the resin composition, the wettability of the CNT to the dispersion medium is improved and the dispersibility or the dispersion stability is improved, and in this regard, it is also preferred. As the added alkali, at least one selected from the group consisting of inorganic bases, inorganic metal salts, organic bases, and organic metal salts can be used.

[0122] Examples of the inorganic base and the inorganic metal salt include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates of alkali metals or alkaline earth metals; and ammonium hydroxide, etc. Among these, from the viewpoint of easily supplying cations, hydroxides or alkoxides of alkali metals or alkaline earth metals are preferred. Examples of the hydroxides of alkali metals include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. Examples of the hydroxides of alkaline earth metals include calcium hydroxide, magnesium hydroxide, etc. Among these, it is more preferred to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. In addition, the metal of the inorganic base can also be a transition metal.

[0123] Examples of the organic base include primary amine compounds, secondary amine compounds, tertiary amine compounds (alkylamines, amino alcohols, etc.), or organic hydroxides having 1 to 40 carbon atoms that may have substituents.

[0124] Examples of the primary alkylamine having 1 to 40 carbon atoms which may have a substituent include alkylamines such as propylamine, butylamine, isobutylamine, octylamine, 2-ethylhexylamine, laurylamine, stearylamine, oleylamine; amino alcohols such as 2-aminoethanol, 3-aminopropanol; 3-ethoxypropylamine, 3-lauryl-oxypropylamine, etc.

[0125] Examples of the secondary alkylamine having 1 to 40 carbon atoms which may have a substituent include alkylamines such as dibutylamine, diisobutylamine, N-methylhexylamine, dioctylamine, distearylamine; amino alcohols such as 2-methylaminoethanol, etc.

[0126] Examples of the tertiary alkylamine having 1 to 40 carbon atoms which may have a substituent include alkylamines such as triethylamine, tributylamine, N,N-dimethylbutylamine, N,N-diisopropylethylamine, dimethyloctylamine, trioctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dilaurylmonomethylamine; triethanolamine, 2-(dimethylamino)ethanol, etc.

[0127] The organic hydroxide is a salt containing an organic cation and a hydroxide ion. Examples of the organic hydroxide include trimethyl-2-hydroxyethylammonium hydroxide, tetramethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, trimethylphenylammonium hydroxide, 3-trifluoromethyl-phenyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, etc. Among these, it is particularly preferable to use at least one selected from the group consisting of trimethyl-2-hydroxyethylammonium hydroxide and tetramethylammonium hydroxide.

[0128] Among these, from the viewpoint of the action on CNT, it is more preferable to use at least one selected from the group consisting of 2-aminoethanol, 3-aminopropanol, triethanolamine, and trimethyl-2-hydroxyethylammonium hydroxide.

[0129] Examples of the organic metal salt include alcoholates of alkali metals, acetates of alkali metals, etc. Examples of the alcoholates of alkali metals include lithium methoxide, lithium ethoxide, lithium propoxide, lithium tert-butoxide, lithium n-butoxide, sodium methoxide, sodium ethoxide, sodium propoxide, sodium tert-butoxide, sodium n-butoxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium tert-butoxide, potassium n-butoxide, etc. Among these, from the viewpoint of easily supplying a cation, sodium tert-butoxide is preferable. In addition, the metal of the organic metal salt may also be a transition metal.

[0130] Based on the mass of the polymer, the amount of the base used is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. Based on the mass of the polymer, the amount of the base used is preferably 20% by mass or less, more preferably 15% by mass or less, and still more preferably 10% by mass or less. If the amount used is too small, there is a tendency that it is difficult to cause a decrease in Mooney viscosity. If the amount used is too large, it may cause corrosion of the dispersion device and / or inside the battery.

[0131] In the method of (2c) above, when preparing a polymer containing a nitrile group-containing monomer unit and an aliphatic hydrocarbon structural unit, it can be adjusted by applying mechanical shear force. Alternatively, after dissolving the prepared polymer containing a nitrile group-containing monomer unit and an aliphatic hydrocarbon structural unit in a solvent capable of dissolving it, it can be adjusted by applying mechanical shear force. Although the Mooney viscosity can be reduced by applying mechanical shear force to the polymer before dissolution using a roll or a kneader, etc., it is more efficient to use the polymer as a dispersant in a state where it is dissolved in a solvent capable of dissolving it. Therefore, it is more preferable to apply shear force in the polymer solution state.

[0132] As a method of applying shear force in the polymer solution state, methods using dispersion members such as a homogenizer and a Silverson mixer can be cited. Although shear force can also be applied using a disperser, etc., it is preferable to use dispersion members such as a homogenizer and a Silverson mixer that can apply higher shear force. As a method of applying mechanical shear force to the polymer before dissolution, methods using dispersion members such as a kneader and a two-roll mill can be cited.

[0133] In addition to the above-mentioned dispersant, the resin composition may further contain an inorganic base, an inorganic metal salt, an organic base, an organic metal salt, or a combination thereof. Specifically, it may contain the inorganic base, inorganic metal salt, organic base, organic metal salt, or a combination thereof described in the method of (2b) of the above-mentioned polymer. Relative to the total amount of the resin composition, these are preferably 0.001% by mass to 0.1% by mass in total, more preferably 0.005% by mass to 0.05% by mass.

[0134] <Non-aqueous dispersion medium>

[0135] The carbon nanotube dispersion contains a non-aqueous dispersion medium. The non-aqueous dispersion medium is not particularly limited, and is preferably a high dielectric constant solvent, and preferably a solvent containing any one high dielectric constant solvent or a mixed solvent containing two or more high dielectric constant solvents. In addition, one or two or more other solvents can be mixed and used in the high dielectric constant solvent.

[0136] As the high-dielectric constant solvent, amide solvents (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic solvents (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxide solvents (dimethyl sulfoxide, etc.), sulfone solvents (hexamethylphosphoric triamide, sulfolane, etc.), lower ketone solvents (acetone, methyl ethyl ketone, etc.), carbonate solvents (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate), tetrahydrofuran, urea, acetonitrile, etc.) can be used. As the non-aqueous dispersion medium, an amide organic solvent is preferably included, and more preferably at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone is included. The relative dielectric constant of the high-dielectric constant solvent can be set to the value described in a solvent manual or the like, and is preferably 2.5 or more at 20°C.

[0137] <Carbon nanotube dispersion>

[0138] The carbon nanotube dispersion contains carbon nanotubes, a dispersant, and a non-aqueous dispersion medium. The CNT dispersion can appropriately contain optional components such as a wetting agent, a surfactant, a pH adjuster, a wetting penetrant, a leveling agent, other additives, other conductive materials, other polymer components, etc. within the range that does not hinder the object of the present invention as needed. The optional components can be added at any timing such as before the preparation of the dispersion, during dispersion, after dispersion, or a combination thereof. The carbon nanotube dispersion refers to the substance in the state before the addition of the active substance. In this regard, the carbon nanotube dispersion is distinguished from the composite material slurry containing the active substance. That is, the carbon nanotube dispersion substantially does not contain the active substance. It is a concept excluding the state where the active substance is intentionally added to the carbon nanotube dispersion, and the active substance may be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, or may be 0% by mass, relative to the total mass of the carbon nanotube dispersion. The active substance will be described later.

[0139] The dispersibility of CNTs in the CNT dispersion can be evaluated using the complex elastic modulus and phase angle obtained by dynamic viscoelasticity measurement. In this specification, the complex elastic modulus and phase angle of the CNT dispersion are the measured values at 25°C and a frequency of 1 Hz. Specifically, they can be measured by the method described in the examples. The complex elastic modulus of the CNT dispersion indicates the hardness of the CNT dispersion, and there is a tendency that the better the dispersibility of CNTs and the lower the viscosity of the CNT dispersion, the smaller the complex elastic modulus. However, when the fiber length of CNTs is large, even in a state where CNTs are uniformly and stably dispersed in the medium, due to the structural viscosity of CNTs themselves, the complex elastic modulus may sometimes be a high value. In addition, in addition to the influence of the dispersion state of CNTs, the complex elastic modulus also varies due to the entanglement of CNTs, dispersants, and other resin components, or the intermolecular forces between them, etc.

[0140] In addition, the phase angle refers to the phase shift of the stress wave when the strain applied to the CNT dispersion is a sine wave. For a purely elastic body, it becomes a sine wave with the same phase as the applied strain, so the phase angle becomes 0°. On the other hand, for a purely viscous body, it becomes a stress wave advanced by 90°. In a general viscoelasticity measurement sample, it becomes a sine wave with a phase angle greater than 0° and less than 90°. If the dispersibility of CNTs in the CNT dispersion is good, the phase angle approaches 90°, which is a purely viscous body. However, similar to the complex elastic modulus, when there is the structural viscosity of CNTs themselves, even in a state where CNTs are uniformly and stably dispersed in the dispersion medium, the phase angle may sometimes be a low value. In addition, similar to the complex elastic modulus, in addition to the influence of the dispersion state of CNTs, the phase angle also varies due to the entanglement of CNTs, dispersants, and other resin components, or the intermolecular forces between them, etc.

[0141] In the CNT dispersion liquid, when the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is 30 or more and 1,700 or less, the CNT dispersion liquid is of high concentration and has high fluidity, and an electrode film with very good conductivity can be obtained. The product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is 30 or more, preferably 35 or more, more preferably 45 or more. In addition, the product (X × Y) is 1,700 or less, preferably 1,500 or less, more preferably 1,000 or less. Further, the product (X × Y) is preferably 800 or less, more preferably 500 or less, and further preferably 100 or less. Thereby, the dispersibility and fluidity can be further improved in the state where a binder resin is added to the CNT dispersion liquid. The product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is preferably 30 or more and 1,500 or less, 35 or more and 1,000 or less, 45 or more and 800 or less, 45 or more and 500 or less, or 45 or more and 100 or less.

[0142] The complex elastic modulus obtained by dynamic viscoelasticity measurement of the CNT dispersion liquid is preferably 0.1 Pa or more, more preferably 0.4 Pa or more, further preferably 0.5 Pa or more, and further more preferably 1 Pa or more. In addition, it is preferably 200 Pa or less, more preferably 100 Pa or less, more preferably 50 Pa or less, and further preferably 30 Pa or less. More preferably, it is 0.1 Pa or more and 200 Pa or less, further preferably 0.4 Pa or more and 50 Pa or less, and further more preferably 0.5 Pa or more and 30 Pa or less.

[0143] The phase angle obtained by dynamic viscoelasticity measurement of the CNT dispersion liquid is preferably 3° or more, more preferably 5° or more, further preferably 10° or more, and particularly preferably 30° or more. In addition, it can be 90° or less, preferably 88° or less, more preferably 80° or less. More preferably, it is 3° or more and 90° or less, further preferably 10° or more and 90° or less, and further more preferably 30° or more and 88° or less.

[0144] By uniformly and favorably dispersing CNTs with a large fiber length of CNTs while maintaining the length at a certain level or more, a developed conductive network can be formed. Therefore, it is not sufficient that the viscosity of the CNT dispersion liquid is low and the (apparent) dispersibility is good. It is particularly effective to combine the complex elastic modulus and the phase angle with previous indices such as viscosity to judge the dispersion state. By setting the complex elastic modulus and the phase angle within the above ranges, a CNT dispersion liquid with good conductivity and electrode strength can be obtained. For example, the CNT dispersion liquid preferably satisfies 0.1 Pa or more and 200 Pa or less and 3° or more and 90° or less for the complex elastic modulus and the phase angle obtained by dynamic viscoelasticity measurement, respectively. Further, the CNT dispersion liquid preferably satisfies the above preferred range for the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°), and the complex elastic modulus and the phase angle obtained by dynamic viscoelasticity measurement satisfy the above preferred ranges, respectively.

[0145] The dispersibility of CNTs in the CNT dispersion liquid can also be evaluated by the median particle diameter (μm) obtained using a laser diffraction / scattering type particle size distribution meter. When it is the median particle diameter (μm) obtained using a laser diffraction / scattering type particle size distribution meter, the particle diameter of CNT agglomerated particles can be estimated based on the scattered light intensity distribution of the particles. The median particle diameter (μm) of the CNT dispersion liquid is preferably 40 μm or less, more preferably 35 μm or less. Further, the median particle diameter (μm) of the CNT dispersion liquid is preferably 0.4 μm or more, and preferably 5.0 μm or less, more preferably 2.0 μm or less. By setting it within the above ranges, a CNT dispersion liquid with an appropriate dispersion state can be obtained. If it is below the above range, there are CNTs in an agglomerated state. In addition, if it is above the above range, a large amount of finely cut CNTs are generated, so it is difficult to efficiently form a conductive network. The median particle diameter can be measured by the method described in the examples.

[0146] The dispersibility of CNTs in the CNT dispersion can also be evaluated by the gloss measured at 60° (i.e., the intensity of the reflected light at 60° with respect to the incident angle) of a coating film obtained by coating on a smooth glass substrate and then baking and drying. Regarding the light incident on the coating film, since the better the dispersibility, the smoother the surface of the coating film, the higher the gloss. On the contrary, since the worse the dispersibility, the more light scattering will be caused by the unevenness of the coating film surface, the lower the gloss. The gloss at 60° can be measured by the method described in the examples. The gloss at 60° is preferably 10 or more, more preferably 20 or more. In addition, it is preferably 120 or less, and still more preferably 110 or less. By setting it within the above range, a CNT dispersion with an appropriate dispersion state can be obtained. If it is lower than the above range, there are aggregated CNTs. In addition, if it is higher than the above range, a large amount of finely cut CNTs are generated, so it is difficult to efficiently form a conductive network. In addition, the gloss of the coating film is affected not only by the dispersibility of CNTs but also by the crystallinity or smoothness of the dispersant, so it is advisable to make a relative judgment.

[0147] Regarding the viscosity of the CNT dispersion, the viscosity measured at 25 °C and 60 rpm using a B-type viscometer is preferably 10 mPa·s or more and less than 10000 mPa·s, more preferably 10 mPa·s or more and less than 2000 mPa·s, and still more preferably 10 mPa·s or more and less than 1000 mPa·s.

[0148] The thixotropy index (TI) value of the CNT dispersion can be calculated by dividing the viscosity (mPa·s) at 6 rpm measured at 25 °C using a B-type viscometer by the viscosity (mPa·s) at 60 rpm. The TI value is preferably 1.0 or more and less than 10.0, more preferably 1.0 or more and less than 5.0, and still more preferably 1.0 or more and less than 3.0. The higher the TI value, the greater the structural viscosity due to the entanglement of CNTs, dispersants, other resin components, or the intermolecular forces between these. The lower the TI value, the smaller the structural viscosity. By setting the TI value within the above range, while suppressing the entanglement of CNTs, dispersants, and other resin components, the intermolecular forces between these can act moderately.

[0149] The average fiber length of CNTs in the CNT dispersion is preferably 0.1 μm or more, more preferably 0.2 μm or more, and still more preferably 0.3 μm or more. In addition, it is preferably 20 μm or less, more preferably 10 μm or less. Furthermore, the average fiber length of CNTs in the CNT dispersion can be calculated as follows: A substance obtained by diluting the CNT dispersion 50 times with a non-aqueous solvent such as NMP is dropped onto a substrate and dried to obtain a specimen. The specimen is observed with a scanning electron microscope. Any 300 CNTs are selected in the observation photograph, and their fiber lengths are measured and averaged.

[0150] Here, when the resin composition contains single-walled carbon nanotubes and multi-walled carbon nanotubes, the average fiber length of CNTs in the resin composition is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 40 μm. The fiber lengths of single-walled carbon nanotubes and multi-walled carbon nanotubes before the dispersion treatment are different, and the fiber lengths capable of forming a good conductive network are also different. By setting the average fiber length of CNTs in the resin composition within the above range, the carbon nanotubes can exist in a more uniform and stable dispersed state with as little breakage as possible, and a good conductive network can be formed. In addition, when the resin composition contains single-walled carbon nanotubes and multi-walled carbon nanotubes, the average fiber length of CNTs in the resin composition is the average value obtained by measuring the total fiber lengths of the carbon nanotubes contained in the resin composition.

[0151] Relative to the total amount of the CNT dispersion, the content of CNTs is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 0.8% by mass or more. In addition, it is preferably 20% by mass or less, more preferably 10% by mass or less. By being within the above range, sedimentation or gelation does not occur, and CNTs can exist well and stably. More preferably, it is 0.1% by mass to 20% by mass, and still more preferably 0.5% by mass to 10% by mass. In addition, it is preferably adjusted appropriately according to the specific surface area of CNTs, the affinity for the dispersion medium, the dispersion ability of the dispersant, etc. to obtain a carbon nanotube dispersion with appropriate fluidity or viscosity.

[0152] Regarding the content of the dispersant, relative to 100 parts by mass of CNTs, it is preferably 5 parts by mass to 200 parts by mass, more preferably 10 parts by mass to 100 parts by mass, and still more preferably 15 parts by mass to 80 parts by mass. Relative to the total amount of the CNT dispersion, the content of the dispersant is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 5% by mass.

[0153] The solid content of the CNT dispersion is preferably 0.2% by mass to 40% by mass, more preferably 0.5% by mass to 20% by mass, and still more preferably 1% by mass to 10% by mass.

[0154] <Dispersion method>

[0155] Hereinafter, as an example of a method for producing a CNT dispersion, a method for dispersing CNTs in a non-aqueous dispersion medium will be described. In addition, in the method for producing a resin composition, a carbon nanotube dispersion can be used regardless of the production method, using a substance having the above-described components and properties. The CNT dispersion is preferably produced, for example, by dispersing CNTs, a dispersant, and a non-aqueous dispersion medium using a dispersion device to finely disperse these. In addition, in the dispersion treatment, the addition timing of the materials used can be arbitrarily adjusted, and a multi-stage treatment of two or more times can be performed.

[0156] Examples of the dispersion device include: kneader, two-roll mill, three-roll mill, planetary mixer, ball mill, horizontal sand mill, vertical sand mill, annular bead mill, grinder, high-shear mixer, high-pressure homogenizer, ultrasonic homogenizer, etc. Among these, in order to finely disperse CNTs in the CNT dispersion to obtain preferable dispersibility, it is preferable to use a high-shear mixer, a high-pressure homogenizer, an ultrasonic homogenizer, or a combination thereof. In particular, from the viewpoint of promoting wetting of CNTs and dispersing coarse particles, it is preferable to use a high-shear mixer in the initial stage of dispersion, and then, from the viewpoint of dispersing while maintaining the aspect ratio of CNTs, it is preferable to use a high-pressure homogenizer. In addition, by dispersing using a bead mill after dispersing using a high-pressure homogenizer, the dispersion state can be made uniform while maintaining the fiber length. The pressure when using a high-pressure homogenizer is preferably 60 MPa to 150 MPa, more preferably 60 MPa to 120 MPa.

[0157] In the dispersion methods using a dispersion device, there are batch dispersion, through dispersion, circulation dispersion, etc. Any of these methods can be used, or two or more methods can be combined. The so-called batch dispersion refers to a method of performing dispersion only in the main body of the dispersion device without using piping or the like. Since the operation is simple, it is preferred in the case of small-scale production. The so-called through dispersion refers to a dispersion method in which the dispersion device main body includes a tank for supplying the liquid to be dispersed via piping and a tank for receiving the liquid to be dispersed, and the liquid to be dispersed passes through the dispersion device main body. In addition, the so-called circulation dispersion refers to a method in which the liquid to be dispersed after passing through the dispersion device main body is returned to the tank for supplying the liquid to be dispersed, and dispersion is performed while circulating it. In the above methods, the longer the processing time, the more the dispersion progresses. Therefore, it is only necessary to repeat the passage or circulation until the target dispersion state is achieved. By changing the size of the tank or the processing time, the throughput can be increased. Compared with circulation dispersion, through dispersion is more likely to homogenize the dispersion state, and is preferred in this regard. Compared with through dispersion, the operation or manufacturing equipment of circulation dispersion is simpler, and is preferred in this regard. In the dispersion process, the fragmentation of agglomerated particles, the dispersion of conductive materials, wetting, stabilization, etc. are carried out sequentially or simultaneously, and depending on the method of implementation, the final dispersion state is different. Therefore, it is preferred to manage the dispersion state in each dispersion process by using various evaluation methods. For example, it can be managed by the method described in the examples.

[0158] <Binder resin>

[0159] The binder resin is not particularly limited as long as it is a resin commonly used as a binder resin for coatings, and can be appropriately selected according to the purpose. The binder resin used in the resin composition is preferably a resin that can bond substances such as active substances and CNTs. Examples of the binder resin used in the resin composition include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylate, methacrylic acid, methacrylate, styrene, etc. as structural units; polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluororesins; elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. In addition, it can also be a modified body, mixture, or copolymer of these resins. Particularly preferred is a fluororesin, and examples thereof include polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), and modified bodies thereof. These can be used alone or in combination of two or more. Among these, in terms of resistance, polymers or copolymers having fluorine atoms in the molecule are preferred, and for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc., resins having these structural units, and modified bodies thereof are preferred.

[0160] Examples of commercially available products of polyvinylidene fluoride and its modified bodies include the KF Polymer Series "W#7300, W#7200, W#1700, W#1300, W#1100, W#9700, W#9300, W#9100, L#7305, L#7208, L#1710, L#1320, L#1120", etc. manufactured by Kureha Corporation, and the solef series "6008, 6010, 6012, 1015, 6020, 5130, 9007, 460, 41308, 11010, 21510, 31508, 60512", etc. manufactured by Solvay (all are trade names).

[0161] The method of adding the binder resin to the CNT dispersion is not particularly limited. It is advisable to add the binder resin to the CNT dispersion including the range of the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) obtained by the dynamic viscoelasticity measurement described above. For example, a powdery binder resin can be added to the CNT dispersion and mixed. As another method, a varnish obtained by dissolving the binder resin in a non-aqueous solvent can also be added to the CNT dispersion and mixed. The non-aqueous solvent for the varnish is preferably a non-aqueous solvent that can be used for the CNT dispersion. It is advisable to stir the mixture in which the binder resin is added to the CNT dispersion. As the stirring device, a disperser, a homogenizer, etc. can be used. In addition, the mixture can be heated during the stirring to promote the dissolution of the binder resin. The heating temperature can be 30°C to 80°C. By adding the powdery binder resin to the CNT dispersion, the amount of the non-aqueous solvent does not increase during the addition of the binder resin, so a resin composition with a higher concentration can be provided. Since the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) of the CNT dispersion is within a specified range, even when the powdery binder resin is added, a decrease in the fluidity and dispersibility of the resin composition can be prevented.

[0162] The resin composition can appropriately contain other optional components as needed within the range that does not hinder the object of the present invention. The optional components can be added at any timing such as before the production of the resin composition, during mixing, after mixing, or a combination thereof. The optional components can be the components described in the CNT dispersion above. The resin composition refers to the substance in the state before adding the active substance. In this regard, the resin composition is distinguished from the composite material slurry containing the active substance. That is, the resin composition substantially does not contain the active substance. It is a concept excluding the state where the active substance is intentionally added to the resin composition, and as long as the active substance is 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, or can also be 0% by mass with respect to the total mass of the resin composition. Regarding the active substance, it will be described later.

[0163] In addition, the resin composition may contain a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes. In this case, as an example of a method for manufacturing the resin composition, there is a method of adding a binder resin to a CNT dispersion containing a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes. As another example, there is a method in which, to a CNT dispersion containing one or both of single-walled carbon nanotubes and multi-walled carbon nanotubes, while the carbon nanotubes are dispersed in the CNT dispersion, the other or both of single-walled carbon nanotubes and multi-walled carbon nanotubes are further added. In this other method, in order to obtain a dispersion in which the single-walled carbon nanotubes and the multi-walled carbon nanotubes are uniformly dispersed without forming entangled aggregates, it is preferable to further add the other of single-walled carbon nanotubes and multi-walled carbon nanotubes to a CNT dispersion containing one of single-walled carbon nanotubes and multi-walled carbon nanotubes, and more preferably to further add single-walled carbon nanotubes to a CNT dispersion containing multi-walled carbon nanotubes. The stage of adding single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof to the CNT dispersion may be before adding the binder resin, after adding, simultaneously with adding, or a combination of these.

[0164] In addition, the resin composition may further contain carbon black, which functions as a conductive material. The carbon black is preferably contained in the resin composition in a range that does not impair the effects of the present invention. With respect to the total mass of the carbon black and the carbon nanotubes, the carbon nanotubes are preferably 1% by mass to 80% by mass, more preferably 1% by mass to 50% by mass. Within these ranges, the dispersion state of the carbon nanotubes can be controlled, and high dispersibility and fluidity can be maintained better in the state containing the binder resin. Furthermore, with respect to the total mass of the resin composition, the carbon black is preferably 20% by mass or less, more preferably 15% by mass or less.

[0165] As an example of a method for manufacturing a resin composition containing carbon black, there is a method of adding a binder resin to a CNT dispersion containing carbon black. In the method for manufacturing the CNT dispersion, the stage of adding carbon black is not particularly limited and may be before adding the carbon nanotubes, after adding, simultaneously with adding, or a combination of these. As another example of a method for manufacturing a resin composition containing carbon black, there is a method of adding carbon black before adding the binder resin to the CNT dispersion, after adding, simultaneously with adding, or a combination of these. In this method, it is preferable to add the carbon black in a state where the carbon nanotubes are dispersed in the CNT dispersion. Alternatively, it may also be a combination of these methods. That is, carbon black may be further added before adding the binder resin to the CNT dispersion containing carbon black, after adding, simultaneously with adding, or a combination of these.

[0166] The median particle size (μm) of the resin composition is preferably 40 μm or less, more preferably 35 μm or less. Further, the median particle size (μm) of the resin composition is preferably 0.4 μm or more, and preferably 5.0 μm or less, more preferably 2.0 μm or less. By setting it within the above range, a resin composition with an appropriate dispersion state can be obtained. If it is below the above range, there will be CNTs in an aggregated state. In addition, if it is above the above range, a large amount of finely cut CNTs will be generated, so it is difficult to efficiently form an electrically conductive network. The median particle size can be measured by the method described in the examples.

[0167] Regarding the viscosity of the resin composition, the viscosity measured at 25 °C and 60 rpm using a B-type viscometer is preferably 10 mPa·s or more and less than 10000 mPa·s, more preferably 10 mPa·s or more and less than 5000 mPa·s, and further preferably 10 mPa·s or more and less than 2000 mPa·s.

[0168] The TI value of the resin composition can be calculated from the value obtained by dividing the viscosity (mPa·s) at 6 rpm measured at 25 °C using a B-type viscometer by the viscosity (mPa·s) at 60 rpm. The TI value is preferably 1.0 or more and less than 10.0, more preferably 1.0 or more and less than 7.0, and further preferably 1.0 or more and less than 5.0. The higher the TI value, the greater the structural viscosity due to the entanglement of CNTs, dispersants, binder resins, other resin components, or the intermolecular forces between these. The lower the TI value, the smaller the structural viscosity. By setting the TI value within the above range, the entanglement of CNTs, dispersants, binder resins, and other resin components can be suppressed while allowing the intermolecular forces between these to act moderately.

[0169] The complex elastic modulus of the resin composition obtained by dynamic viscoelasticity measurement is preferably 0.1 Pa or more, more preferably 0.3 Pa or more, and further preferably 0.5 Pa or more. In addition, it can be 300 Pa or less, preferably 200 Pa or less, more preferably 100 Pa or less, more preferably 50 Pa or less, and further preferably 30 Pa or less. More preferably, it is 0.1 Pa or more and 200 Pa or less.

[0170] The phase angle of the resin composition obtained by dynamic viscoelasticity measurement is preferably 3° or more, more preferably 5° or more, and further preferably 10° or more, particularly preferably 30° or more. In addition, it is preferably 90° or less, more preferably 88° or less, and further preferably 80° or less. More preferably, it is 3° or more and 90° or less.

[0171] For example, the resin composition preferably satisfies 0.1 Pa or more and 200 Pa or less and 3° or more and 90° or less for the complex elastic modulus and phase angle obtained by dynamic viscoelasticity measurement, respectively.

[0172] In this specification, the complex elastic modulus and phase angle of the resin composition are measured values at 25°C and a frequency of 1 Hz. Specifically, they can be measured by the method described in the examples.

[0173] In the resin composition, the binder resin is preferably 10% by mass or more and 10,000% by mass or less based on the mass ratio with respect to CNT. The mass ratio is preferably 10% by mass or more, more preferably 50% by mass or more. Within this range, the adhesion of the conductive film can be further obtained. Since the CNT dispersion has the above physical properties, even when the binder resin is contained at a higher concentration, gelation and aggregation of the resin composition can be prevented. The mass ratio is preferably 1,000% by mass or less, more preferably 500% by mass or less, and further preferably 300% by mass or less. Within this range, the active material concentration of the conductive film can be increased to achieve high capacity. The binder resin is preferably 10% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 300% by mass or less, and further preferably 50% by mass or more and 300% by mass or less based on the mass ratio with respect to CNT. In the said mass ratio, CNT is calculated based on the content of CNT contained in the CNT dispersion. In addition, in the case of manufacturing a resin composition by further adding additional CNT to the CNT dispersion in a state where CNT is dispersed, from the same viewpoint, the mass ratio of the binder resin with respect to the total amount of CNT contained in the resin composition is preferably 10% by mass or more and 1,000% by mass or less, more preferably 10% by mass or more and 500% by mass or less, further preferably 10% by mass or more and 300% by mass or less, and still more preferably 50% by mass or more and 300% by mass or less.

[0174] The content of the binder resin in the resin composition is preferably 0.1% by mass to 20% by mass, more preferably 0.5% by mass to 10% by mass, and further preferably 1% by mass to 6% by mass with respect to the total amount of the resin composition.

[0175] The content of CNT in the resin composition is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more with respect to the total amount of the resin composition. In addition, it is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less. By being in the said range, sedimentation or gelation does not occur, and CNT can exist well and stably. It is more preferably 0.5% by mass to 15% by mass.

[0176] Regarding the content of the dispersant in the resin composition, relative to 100 parts by mass of CNT, it is preferably 10 to 200 parts by mass, more preferably 10 to 100 parts by mass, and still more preferably 10 to 80 parts by mass. Relative to the total amount of the resin composition, the content of the dispersant in the resin composition is preferably 0.1% to 10% by mass, more preferably 0.5% to 5% by mass.

[0177] In the method for manufacturing the resin composition, it is preferable that the content of CNT contained in the CNT dispersion liquid is 0.5% to 10% by mass, and the mass ratio of the binder resin to the carbon nanotubes is 10% to 1000% by mass. The solid content amount of the resin composition is preferably 0.2% to 40% by mass, more preferably 0.5% to 20% by mass, and still more preferably 1% to 10% by mass.

[0178] <Method for manufacturing a composite material slurry for a secondary battery electrode>

[0179] In the case of producing the resin composition according to the above method, the composite material slurry for a secondary battery electrode can be obtained by adding an active material to the CNT dispersion liquid, the resin composition, or both of them. The composite material slurry can also appropriately contain any other components as needed within the range not hindering the object of the present invention. The any component can be added at any timing such as before the production of the composite material slurry, during mixing, after mixing, or a combination of these. The any component can be the components described in the above CNT dispersion liquid.

[0180] The active material can be a positive electrode active material or a negative electrode active material. In this specification, the positive electrode active material and the negative electrode active material are sometimes simply referred to as "active material". The so-called active material is a material that forms the basis of the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material according to the electromotive force. In order to improve the uniformity and processability, the composite material slurry is preferably in a slurry form.

[0181] <Positive electrode active material>

[0182] The positive electrode active material is not particularly limited. For example, in the case of secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used. For example, it can be cited: lithium manganese composite oxide (e.g., Li x Mn 2 O 4 or Li x MnO 2 ), lithium nickel composite oxide (e.g., Li x NiO 2 ), lithium cobalt composite oxide (Li x CoO 2 ), lithium nickel cobalt composite oxide (e.g., Lix Ni 1-y Co y O 2 ) lithium-manganese-cobalt composite oxides (such as Li x Mn y Co 1-y O 2 ), lithium-nickel-manganese-cobalt composite oxides (such as Li x Ni y Co z Mn 1-y-z O 2 ), spinel-type lithium-manganese-nickel composite oxides (such as Li x Mn 2-y Ni y O 4 ), etc., composite oxide powders of lithium and transition metals, lithium-phosphorus oxide powders having an olivine structure (such as Li x FePO 4 , Li x Fe 1-y Mn y PO 4 , Li x CoPO 4 , etc.), transition metal oxide powders such as manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxides (such as V 2 O 5 , V 6 O 13 ), titanium oxide, etc., transition metal sulfide powders such as iron sulfate (Fe 2 (SO 4 ) 3 ), TiS 2 , and FeS, etc. Among them, x, y, and z are numbers, and 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < y + z < 1. These positive electrode active materials can also be used singly or in combination of two or more. Among these active materials, in particular, active materials containing Ni and / or Mn (especially when the total amount of Ni and / or Mn in the transition metal is 50 mol% or more) tend to have a higher alkalinity due to the dissolution of components or metal ions derived from the raw materials, and as a result, gelation of the binder resin or deterioration of the dispersion state is likely to occur. Therefore, in the case of a battery containing an active material containing Ni and / or Mn, this embodiment is particularly effective.

[0183] <Negative electrode active material>

[0184] The negative electrode active material is not particularly limited. For example, metallic Li that can reversibly dope or intercalate lithium ions, or its alloy, tin alloy, or silicon alloy negative electrode can be used. Li X TiO 2 , LiX Fe 2 O 3 、Li X Fe 3 O 4 、Li X WO 2 and other metal oxide systems, conductive polymers such as polyacetylene and polyphenylene, carbonaceous powders such as highly graphitized carbon materials, artificial graphite or natural graphite, and resin-calcined carbon materials. Among them, X is a number, and 0 < X < 1. These negative electrode active materials can also be used alone or in combination of two or more. In particular, in the case of using a silicon alloy negative electrode, the theoretical capacity is large, and on the contrary, the volume expansion is extremely large. Therefore, it is preferably used in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-calcined carbon materials.

[0185] The content of CNT in the composite material slurry is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass or more based on the mass of the active material (assuming the mass of the active material is 100% by mass). In addition, it is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 3% by mass or less. If it exceeds the above range, the filling amount of the active material in the electrode decreases, resulting in a decrease in the capacity of the battery. In addition, if it is less than the above range, the conductivity of the electrode and the battery may become insufficient.

[0186] The content of the dispersant in the composite material slurry is preferably 0.01% by mass or more, more preferably 0.02% by mass or more based on the mass of the active material (assuming the mass of the active material is 100% by mass). In addition, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[0187] The content of the binder resin in the composite material slurry is preferably 0.1% by mass or more, more preferably 0.3% by mass or more based on the mass of the active material (assuming the mass of the active material is 100% by mass). In addition, it is preferably 20% by mass or less, more preferably 10% by mass or less.

[0188] The solid content in the composite material slurry is preferably 30% by mass or more, more preferably 40% by mass or more based on the mass of the composite material slurry (assuming the mass of the composite material slurry is 100% by mass). In addition, it is preferably 90% by mass or less, more preferably 85% by mass or less.

[0189] In the method of producing a composite material slurry, the order of adding a binder resin and an active material to the CNT dispersion is not particularly limited. For example, there may be mentioned: a method of adding a binder resin to the CNT dispersion to produce a resin composition, and then adding an active material to the resin composition for production; a method of adding an active material to the CNT dispersion, and then adding a binder resin for production; a method of adding a binder resin and an active material to the CNT dispersion simultaneously for production, etc. As the method of producing a composite material slurry, a method of adding a binder resin to the CNT dispersion to produce a resin composition, and further adding an active material to the resin composition and stirring is preferred. The stirring device used in the stirring is not particularly limited. A disperser, a homogenizer, etc. can be used as the stirring device.

[0190] In addition, the composite material slurry may further contain carbon black, and the carbon black functions as a conductive material. The carbon black is preferably contained in the composite material slurry within a range that does not impair the effects of the present invention. Relative to the total mass of the carbon black and the carbon nanotubes, the carbon nanotubes are preferably 1% by mass to 80% by mass, more preferably 1% by mass to 50% by mass. Within these ranges, the dispersion state of the carbon nanotubes can be controlled, and high dispersibility and fluidity can be maintained better in the state containing the binder resin. Furthermore, relative to the total mass of the composite material slurry, the carbon black is preferably 10% by mass or less, more preferably 5% by mass or less. In addition, the manufacturing method of the composite material slurry includes adding an active material to the resin composition for a secondary battery electrode, but may include further adding carbon black before, after, simultaneously with, or in combination of these when adding the active material to the resin composition. Alternatively, an active material may be added to the resin composition for a secondary battery electrode that pre-contains carbon black, or an active material and carbon black may be further added to the resin composition for a secondary battery electrode that pre-contains carbon black.

[0191] <Electrode film>

[0192] The electrode film is formed by forming the composite material slurry into a film shape, and contains CNTs, a dispersant, a binder resin, and an active material. The electrode film may further contain optional components. The electrode film can be formed by producing a composite material slurry according to the above method and coating the composite material slurry. For example, the electrode film can be formed by coating the composite material slurry on a current collector and removing the volatile components.

[0193] The material or shape of the current collector is not particularly limited, and a material or shape suitable for various secondary batteries can be appropriately selected. For example, as the material of the current collector, there may be mentioned metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. In addition, as the shape, a flat foil is generally used, and a current collector with a roughened surface, a perforated foil-shaped current collector, or a mesh-shaped current collector can also be used. The thickness of the current collector is preferably about 0.5 μm to 30 μm.

[0194] As a method for coating the composite material slurry on the current collector, there is no particular limitation, and known methods can be used. Specifically, examples include: die coating method, dip coating method, roll coating method, knife coating method, blade coating method, spray coating method, gravure coating method, screen printing method, electrostatic coating method, etc. As a drying method after coating, air drying, hot air dryer, warm air dryer, infrared heater, far infrared heater, etc. can be used, but it is not particularly limited to these.

[0195] After coating the composite material slurry, rolling treatment can also be performed using a flat press, calender roll, etc. The thickness of the electrode film is, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0196] <Secondary battery>

[0197] The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and at least one selected from the group consisting of the positive electrode and the negative electrode includes the electrode film. The manufacturing method of the secondary battery includes forming the electrode film according to the above method. That is, a secondary battery can be manufactured by preparing a CNT dispersion, adding a binder resin and an active material to the CNT dispersion, and coating the obtained composite material slurry on the current collector to form an electrode film.

[0198] As the positive electrode, a member in which a composite material slurry containing a positive electrode active material is coated on a current collector and dried to form an electrode film can be used. As the negative electrode, a member in which a composite material slurry containing a negative electrode active material is coated on a current collector and dried to form an electrode film can be used. The positive electrode active material and the negative electrode active material can use the above substances. The composite material slurry can be prepared according to the above method.

[0199] The electrolyte can be any one of a liquid electrolyte, a gel electrolyte, and a solid electrolyte. For example, the liquid electrolyte may contain an electrolyte salt such as a lithium salt and a non-aqueous solvent.

[0200] As the electrolyte salt, various known electrolyte salts in which ions can move can be used. For example, LiBF 4 , LiClO 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiCF 3 SO 3 , Li(CF 3 SO 2 ) 2 , LiC 4 F 9 SO 3 , Li(CF 3 SO2 ) 3 C, LiI, LiBr, LiCl, LiAlCl, LiHF 2 , LiSCN, or LiBPh 4 (wherein, Ph is phenyl) and other lithium salts, but not limited to these. The electrolyte salt is preferably dissolved in a non-aqueous solvent and used in the form of an electrolyte solution.

[0201] The non-aqueous solvent is not particularly limited, and examples thereof include: carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanolactone; glycol dimethyl ethers (glyme) such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents can be used alone, or two or more of them can be mixed and used.

[0202] The secondary battery preferably includes a separator. Examples of the separator include, but are not limited to, polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and non-woven fabrics subjected to hydrophilic treatment thereof.

[0203] The structure of the secondary battery is not particularly limited, and generally includes a positive electrode, a negative electrode, and a separator provided as needed, and can be formed into various shapes corresponding to the use purpose, such as a paper type, a cylindrical type, a button type, a laminated type, etc.

[0204] [Examples]

[0205] Examples are listed below to more specifically illustrate the present invention. The present invention is not limited to the following examples as long as it does not exceed its gist. In addition, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0206] <Manufacture of Dispersant>

[0207] (Manufacturing Example 1: Manufacture of H-NBR1)

[0208] Into a stainless-steel polymerization reactor, 32 parts of acrylonitrile, 68 parts of 1,3-butadiene, 3 parts of potassium oleate soap, 0.3 part of azobisisobutyronitrile, 0.48 part of tert-dodecyl mercaptan, and 200 parts of ion-exchanged water were added. Under a nitrogen atmosphere, while stirring, polymerization was carried out at 45 °C for 20 hours, and polymerization was terminated at a conversion rate of 90%. Unreacted monomers were removed by vacuum stripping to obtain an acrylonitrile-conjugated diene rubber latex with a solid content concentration of about 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solid content concentration to 12%, and it was put into a 1-L autoclave equipped with a stirrer. Nitrogen was introduced for 10 minutes to remove dissolved oxygen in the contents. 75 mg of palladium acetate as a hydrogenation catalyst was dissolved in 180 mL of ion-exchanged water with 4 times the molar amount of nitric acid added relative to palladium to prepare a catalyst solution, and the prepared catalyst solution was added to the autoclave. After the autoclave was purged twice with hydrogen, while pressurizing with hydrogen to 3 MPa, the contents of the autoclave were heated to 50 °C and a hydrogenation reaction was carried out for 6 hours. Then, the contents were returned to room temperature, and after making the autoclave atmosphere a nitrogen atmosphere, the solid components were dried to obtain a dispersant (H-NBR1). The Mooney viscosity (ML 1+4 , 100 °C) (measured at a temperature of 100 °C using an L-shaped rotor according to Japanese Industrial Standard JIS K6300-1) of H-NBR1 was 44. In addition, the hydrogenation rate (calculated by infrared spectroscopic analysis based on the total reflection measurement method) was 0.7%. The structural unit derived from acrylonitrile determined by quantitative spectroscopy of hydrogen nuclear magnetic resonance ( 1 H-NMR) was 32%.

[0209] (Production Example 2 Production of PAN)

[0210] In a reaction vessel including a gas inlet tube, a thermometer, a condenser, and a stirrer, 100 parts of acetonitrile were charged and purged with nitrogen. The inside of the reaction vessel was heated to 70 °C, and a mixture of 100 parts of acrylonitrile, 2 parts of 3-mercapto-1,2-propanediol, and 0.5 part of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by NOF Corporation; V-65) was added dropwise over 3 hours to carry out a polymerization reaction. After the dropwise addition was completed, the reaction was further carried out at 70 °C for 1 hour, then 0.5 part of V-65 was added, and the reaction was further continued at 70 °C for 1 hour to obtain a precipitate as the target product. Then, it was confirmed by non-volatile component measurement that the conversion rate exceeded 95%. The product was separated by filtration through vacuum filtration, washed with 100 parts of acetonitrile, and then the solvent was completely removed by vacuum drying to obtain a dispersant (PAN). The weight average molecular weight (Mw) of PAN was 53,000.

[0211] <High-purity treatment of carbon nanotubes>

[0212] (Production Example 3: Production of 100T-P)

[0213] To 1 g of carbon nanotubes (K-Nanos 100T, manufactured by Kumho Petrochemical), 5 g of water was added, and stirring was carried out using a Henschel mixer to obtain granular carbon nanotubes (particle size of about 7 mm). The granular carbon nanotubes were spread out on a tray and dried in a reduced-pressure hot air oven at 100 °C for 7 hours to obtain compressed CNT. The obtained compressed CNT was placed in a ceramic crucible and arranged in a calcination furnace. After evacuating the inside of the furnace to below 1 Torr, the temperature was raised to 1000 °C. Carbon tetrachloride gas was introduced at a rate of 0.3 L per minute until the pressure inside the furnace reached 90 Torr, and then the temperature inside the furnace was raised to 1600 °C and maintained for 1 hour. Subsequently, after stopping the heater, the pressure was slowly reduced to 1 Torr and cooled to room temperature. The pressure inside the furnace was released, and the highly purified carbon nanotubes (100T-P) were recovered from the crucible.

[0214] <Manufacture of Single-Layer CNT Resin Composition>

[0215] (Production Example 4: Production of TUBALL-F)

[0216] To a stainless-steel container, 97.6 parts of N-methyl-2-pyrrolidone (NMP) was added, and while stirring using a disperser, 2.0 parts of polyvinylidene fluoride resin (Solef 5130, manufactured by Solvay) was added, and stirring was carried out using the disperser until the polyvinylidene fluoride resin was dissolved. Then, 0.4 parts of single-layer carbon nanotubes (TUBALL, manufactured by OCSiAl, carbon purity 93%) was weighed out and added while stirring using the disperser. A square-hole high-shear wire mesh was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON), and batchwise dispersion was carried out at a speed of 8,600 rpm until the whole became uniform. Subsequently, the dispersed liquid was supplied from the stainless-steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by Sugino Machine) via a pipe, and five pass-through dispersion treatments were carried out to obtain an adhesive solution containing single-layer carbon nanotubes (TUBALL-F). The dispersion treatment was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 60 MPa.

[0217] In the examples and comparative examples, in addition to the dispersants manufactured in Production Example 1 and Production Example 2, the following dispersants were also used.

[0218] · H-NBR2: Therban(R) 3406 (manufactured by ARLANXEO, hydrogenated acrylonitrile-butadiene rubber)

[0219] · H-NBR3: Therban(R) AT 3404 (manufactured by ARLANXEO, hydrogenated acrylonitrile-butadiene rubber)

[0220] · H-NBR4: Zetpole 2000L (manufactured by Zeon, hydrogenated acrylonitrile-butadiene rubber)

[0221] · PVP: Polyvinylpyrrolidone K-30 (manufactured by Nippon Catalyst)

[0222] · PVA: Kuraray Poval 3-88 (manufactured by Kuraray, polyvinyl alcohol)

[0223] In the examples and comparative examples, in addition to the carbon nanotubes produced in Production Example 3, the following carbon nanotubes were also used.

[0224] · 100T: K-Nanos 100T (manufactured by Kumho Petrochemical, multi-walled CNT, average outer diameter 13 nm, specific surface area 210 m 2 / g)

[0225] · BT1001M: LUCAN BT1001M (manufactured by LG chem Ltd, multi-walled CNT, average outer diameter 13 nm, specific surface area 250 m 2 / g)

[0226] · 10B: JENOTUBE 10B (manufactured by JEIO, multi-walled CNT, average outer diameter 10 nm, specific surface area 230 m 2 / g)

[0227] · 8B: JENOTUBE 8B (manufactured by JEIO, multi-walled CNT, average outer diameter 8 nm, specific surface area 300 m 2 / g)

[0228] · 6A: JENOTUBE 6A (manufactured by JEIO, multi-walled CNT, average outer diameter 6 nm, specific surface area 700 m 2 / g)

[0229] · TUBALL: Single-walled carbon nanotubes (manufactured by OCSiAl, average outer diameter 1.6 nm, carbon purity 93%, specific surface area 975 m 2 / g)

[0230] In the examples and comparative examples, in addition to carbon nanotubes, the following conductive materials were also used.

[0231] · Super-P (manufactured by IMERYS Graphite&Carbon, conductive carbon black, BET specific surface area 62 m 2 / g)

[0232] <Preparation of carbon nanotube dispersion>

[0233] (Example 1-1)

[0234] A carbon nanotube dispersion (CNT dispersion 1) was prepared as follows according to the materials and composition shown in Table 1. NMP was placed in a stainless steel container and heated to 50°C. While stirring with a disperser, a dispersant and an additive were added, and then stirred for 1 hour to dissolve the dispersant. Subsequently, while stirring with a disperser, CNTs were added, a square-hole high-shear wire mesh was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was carried out at a speed of 8,000 rpm until the whole became uniform and the dispersion particle size measured by a grind gauge with a maximum depth of 300 μm of the tank became 250 μm or less. At this time, the dispersion particle size confirmed by the particle size meter was 180 μm. The charging amounts were set to the amounts described in Charging 1 respectively. Subsequently, the dispersion was supplied from the stainless steel container to a high-pressure homogenizer (HJP-17007, manufactured by Sugino Machine, Star BurstLabo) via a pipe, and a cyclic dispersion treatment was carried out. The dispersion treatment was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Dispersion was carried out until the viscosity at 60 rpm of the dispersion measured by a B-type viscometer (manufactured by TOKI SANGYO, VISCOMETER, MODEL: BL) became 3,000 mPa·s or less. Then, while stirring with a disperser, CNTs, a dispersant, and an additive in the amounts described in Charging 2 / Charging 3 of Table 1 were further added to the stainless steel container, and the cyclic dispersion treatment was carried out again using the high-pressure homogenizer. After the cyclic dispersion using the high-pressure homogenizer until the viscosity became 3,000 mPa·s or less, the operation of adding CNTs, a dispersant, and an additive in the amounts described in Charging 2 / Charging 3 of Table 1 to the stainless steel container while stirring with a disperser was repeated again (the total added amount of CNTs was 6.0 mass parts). According to the number of passes after charging the total amount shown in Table 1, a through-type dispersion treatment was carried out using the high-pressure homogenizer to obtain CNT dispersion 1 containing 6.0 mass parts of CNTs.

[0235] (Examples 1-2 to 1-18)

[0236] Except for changing the materials, composition, and the number of passes after charging the total amount shown in Table 1, CNT dispersions 2 to 18 were obtained in the same manner as in Example 1-1.

[0237] (Examples 1-19 and 1-20)

[0238] According to the materials and compositions shown in Table 1-2 and the number of passes after total charging, the following process was changed. Except for this, CNT dispersions 19 and 20 were obtained in the same manner as in Example 1-1. In the production of CNT dispersion 19, when adding CNTs, 6A and TUBALL were added simultaneously (the total addition amount of CNTs was set to 2.5 parts by mass of 6A and 0.5 parts by mass of TUBALL). In the production of CNT dispersion 20, when adding CNTs, 6A, TUBALL, and Super-P (as another conductive material) were added together simultaneously (the total addition amount of CNTs was set to 2.5 parts by mass of 6A and 0.5 parts by mass of TUBALL, and Super-P was set to 15 parts by mass).

[0239] (Comparative Example 1-1)

[0240] According to the materials and compositions shown in Table 1, and changing the number of passes through the high-pressure homogenizer to 10 times, except for this, comparative CNT dispersion 1 was obtained in the same manner as in Example 1-1.

[0241] (Comparative Example 1-2)

[0242] According to the materials and compositions shown in Table 1, and changing the number of passes through the high-pressure homogenizer to 15 times, except for this, comparative CNT dispersion 2 was obtained in the same manner as in Example 1-12.

[0243] (Comparative Example 1-3)

[0244] In Example 1-1, instead of using a high-pressure homogenizer for dispersion, a bead mill (manufactured by Ashizawa, Star Mill LMZ06, bead diameter 1.0 mm, bead filling rate 80%) was used for dispersion to obtain comparative CNT dispersion 3. In addition, the number of passes was set to 25 times.

[0245]

[0246]

[0247] In addition, the additives described in Table 1 are as follows.

[0248] · NaOH: Sodium hydroxide (manufactured by Tokyo Chemical Industry, purity > 98.0%, granular)

[0249] · Aminoethanol: 2-Aminoethanol (manufactured by Tokyo Chemical Industry, purity > 99.0%)

[0250] · t-BuONa: Sodium tert-butoxide (manufactured by Tokyo Chemical Industry, purity > 98.0%)

[0251] <Evaluation of Carbon Nanotube Dispersion Liquid>

[0252] (Method for Measuring Dispersion Particle Size)

[0253] The dispersion particle size of the carbon nanotube dispersion liquid is determined using a particle size analyzer with a maximum cell depth of 100 μm and by the judgment method based on JIS K5600-2-5.

[0254] Particle Size Judgment Criteria

[0255] ◎: Less than 20 μm

[0256] ○: 20 μm or more and less than 50 μm

[0257] △: 50 μm or more and less than 90 μm

[0258] ×: 90 μm or more

[0259] (Method for Measuring Viscosity of Carbon Nanotube Dispersion Liquid)

[0260] Regarding the viscosity of the carbon nanotube dispersion liquid, use a B-type viscometer ("BL" manufactured by Toki Sangyo). After thoroughly stirring the dispersion liquid with a spatula at a dispersion liquid temperature of 25°C, immediately measure it at a rotor rotation speed of 6 rpm with the B-type viscometer, and then measure it at 60 rpm. The viscosity measured at 60 rpm is taken as the initial viscosity. The lower the viscosity, the better the dispersibility; the higher the viscosity, the worse the dispersibility. A resin composition in which the obtained dispersion liquid is significantly separated or settled is regarded as having poor dispersibility. In addition, calculate the TI value by dividing the viscosity (mPa·s) at 60 rpm by the viscosity (mPa·s) at 6 rpm.

[0261] Initial Viscosity Judgment Criteria

[0262] ◎: Less than 1,000 mPa·s

[0263] ○: 1,000 mPa·s or more and less than 2,000 mPa·s

[0264] △: 2,000 mPa·s or more and less than 10,000 mPa·s

[0265] ×: 10,000 mPa·s or more, with sedimentation or separation

[0266] TI Value Judgment Criteria

[0267] ◎: Less than 3.0

[0268] ○: 3.0 or more and less than 5.0

[0269] △: 5.0 or more and less than 10.0

[0270] ×: Above 10.0, sedimentation or separation occurs

[0271] (Method for measuring gloss)

[0272] The sample for gloss measurement is obtained as follows: 1 mL of the carbon nanotube dispersion is dropped onto a smooth glass substrate and coated at 2 cm / second using a bar coater No. 7, then baked in a hot air oven at 140 °C for 10 minutes and allowed to cool. The coating area is set to approximately 10 cm × 10 cm. Using a gloss meter (micro-gloss 60° manufactured by BYK Gardner), three points are randomly selected within the coating surface excluding the ends, and each is measured once, and the average value is taken as the gloss at 60°.

[0273] Gloss judgment criteria

[0274] ◎: 30 or above

[0275] ○: 20 or above and less than 30

[0276] △: 10 or above and less than 20

[0277] ×: Less than 10

[0278] (Method for measuring the median particle size of the carbon nanotube dispersion)

[0279] The median particle size is measured using a particle size distribution measuring device (Partical LA-960V2, manufactured by HORIBA). The operating conditions for circulation / ultrasound are set as follows: circulation speed: 3, ultrasound intensity: 7, ultrasound time: 1 minute, stirring speed: 1, stirring mode: continuous. In addition, during the degassing process, ultrasound was applied at an ultrasound intensity of 7 and an ultrasound time of 5 seconds. The refractive index of NMP is set to 1.470, and the refractive index of the carbon material is set to 1.92. The measurement is carried out after diluting the measurement sample so that the transmittance of the red laser diode becomes 60% - 80%, and the particle size standard is set to volume.

[0280] Median particle size judgment criteria

[0281] ○: 0.4 μm or above and less than 2.0 μm

[0282] △: 2.0 μm or above and less than 5.0 μm

[0283] ×: Less than 0.4 μm or 5.0 μm or above

[0284] (Measurement of the complex elastic modulus and phase angle of the carbon nanotube dispersion)

[0285] The complex elastic modulus X and phase angle Y of the carbon nanotube dispersion are evaluated as follows: Using a cone with a diameter of 60 mm and an angle of 2°, a rheometer (RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) is used to perform dynamic viscoelasticity measurement at 25°C and a frequency of 1 Hz within a strain rate range of 0.01% to 5%. The smaller the obtained complex elastic modulus, the better the dispersibility; the larger it is, the worse the dispersibility. In addition, the larger the obtained phase angle, the better the dispersibility; the smaller it is, the worse the dispersibility. Furthermore, the product (X × Y) of the obtained complex elastic modulus X (Pa) and phase angle Y (°) is calculated.

[0286] (Calculation of the average fiber length of CNTs)

[0287] While stirring with a disperser, NMP is gradually added dropwise in small amounts to the carbon nanotube dispersion, and it is diluted 50 times. A small amount of the obtained product is dropped onto a substrate with a smooth surface and dried to prepare an observation sample. The obtained observation sample is observed and photographed using a scanning electron microscope. In the observation photograph, any 300 CNTs are selected and their respective fiber lengths are measured, and the average value is calculated as the average fiber length.

[0288] The evaluation results of the CNT dispersions prepared in Examples 1-1 to 1-20 and Comparative Examples 1-1 to 1-3 are shown in Table 2.

[0289]

[0290] <Production of resin composition>

[0291] (Examples 2-1 to 2-24, Comparative Examples 2-1 to 2-3)

[0292] According to the combinations shown in Table 3, an adhesive is added to the carbon nanotube dispersion (CNT dispersions 1 to 20, Comparative CNT dispersions 1 to 3) to prepare resin compositions (resin compositions 1 to 24, Comparative resin compositions 1 to 3) as follows. The concentration of the solid component of the adhesive in the resin composition is all set to 3.0 parts by mass. The carbon nanotube dispersion is placed in a stainless steel container and heated to 50°C, and the adhesive is gradually added dropwise in small amounts while stirring with a disperser. Stir for 2 hours in a state heated to 50°C to dissolve the adhesive and obtain the resin composition.

[0293] (Example 2-25)

[0294] According to the combination shown in Table 3, an adhesive was added to the carbon nanotube dispersion (CNT dispersion 1) to prepare a resin composition (resin composition 25) as follows. The concentration of the solid component of the adhesive in the resin composition was set to 3.0 parts by mass. The carbon nanotube dispersion was placed in a stainless steel container, and the adhesive solution was added little by little while stirring with a disperser, and then stirred for 30 minutes to obtain the resin composition.

[0295] (Example 2-26)

[0296] According to the combination shown in Table 3, the adhesive solution containing single-walled carbon nanotubes (TUBALL-F) prepared in Production Example 4 was added to the carbon nanotube dispersion (CNT dispersion 17) to prepare a resin composition (resin composition 26) as follows. The concentration of the solid component of the adhesive in the resin composition was set to 3.0 parts by mass. CNT dispersion 17 was placed in a stainless steel container, and the adhesive solution (TUBALL-F) was added little by little while stirring with a disperser, and then stirred for 30 minutes to obtain resin composition 26. In resin composition 26, the total addition amount of CNT was set to 1.33 parts by mass for 6A and 0.27 parts by mass for TUBALL.

[0297] (Comparative Example 2-4)

[0298] The comparative resin composition 4 was prepared as follows. The types and solid component concentrations of the respective raw materials used in the comparative resin composition 4 were set as follows: CNT: 100T, 3.0 parts; dispersant: H-NBR1, 0.6 part; additive: NaOH, 0.006 part; binder: L#7305, 3.0 parts. NMP was placed in a stainless steel container and heated to 50°C. While stirring with a disperser, the dispersant and additive were added, and then stirred for 1 hour to dissolve the dispersant. Next, while stirring with a disperser, the binder solution was slowly added and mixed. Subsequently, the CNT was added to the solution while stirring with a disperser. A square-hole high-shear wire mesh was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON), and batchwise dispersion was performed at a speed of 8,000 rpm until the whole became uniform and the dispersion particle size measured with a particle size meter having a maximum depth of the tank of 300 μm became 250 μm or less. At this time, the dispersion particle size confirmed with the particle size meter was 210 μm. The filling amount was set to 2 / 3 with respect to the total filling amount. Subsequently, the dispersed liquid was supplied from the stainless steel container to a high-pressure homogenizer (HJP-17007, manufactured by Sugino Machine, Star Burst Labo) via a pipe, and cyclic dispersion treatment was performed. The dispersion treatment was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Dispersion was performed until the viscosity at 60 rpm measured with a B-type viscometer (manufactured by TOKI SANGYO, VISCOMETER, MODEL: BL) of the dispersed liquid became 3,000 mPa·s or less. Then, while stirring with a disperser, CNT, dispersant, additive, and binder in an amount of 1 / 2 of the remaining filling amount were further added to the stainless steel container, and cyclic dispersion treatment was performed again using the high-pressure homogenizer. After cyclic dispersion using the high-pressure homogenizer until the viscosity became 3,000 mPa·s or less, the operation of further adding the remaining CNT, dispersant, additive, and binder to the stainless steel container while stirring with a disperser was repeated again (the total added amount of CNT was 3.0 mass parts). Immediately thereafter, 15 passes of dispersion treatment were performed using the high-pressure homogenizer to obtain the comparative resin composition 4 containing 3.0 mass parts of CNT.

[0299] In the examples and comparative examples, the following binders were used.

[0300] ·W#7300: KF polymer W#7300 (manufactured by Kureha, polyvinylidene fluoride resin)

[0301] ·W#7200: KF Polymer W#7200 (manufactured by Kureha, polyvinylidene fluoride resin)

[0302] ·W#1300: KF Polymer W#1300 (manufactured by Kureha, polyvinylidene fluoride resin)

[0303] ·W#9300: KF Polymer W#9300 (manufactured by Kureha, polyvinylidene fluoride resin)

[0304] ·S-5130: Solef 5130 (manufactured by Solvay, polyvinylidene fluoride resin)

[0305] ·L#7305: KF Polymer L#7305 (manufactured by Kureha, polyvinylidene fluoride resin varnish, 5% solution of W#7300 / N-methyl-2-pyrrolidone)

[0306] <Evaluation of resin composition>

[0307] (Method for measuring particle size)

[0308] Regarding the presence or absence and particle size of coarse particles in the resin composition, a particle size meter with a maximum groove depth of 100 μm is used, and the values are obtained by the determination method based on JIS K5600-2-5.

[0309] Particle size determination criteria

[0310] ◎: Less than 20 μm

[0311] ○: 20 μm or more and less than 50 μm

[0312] △: 50 μm or more and less than 90 μm

[0313] ×: 90 μm or more

[0314] (Method for measuring viscosity of resin composition)

[0315] Similar to the carbon nanotube dispersion, the initial viscosity and TI value are obtained.

[0316] Initial viscosity determination criteria

[0317] ◎: Less than 1,000 mPa·s

[0318] ○: 1,000 mPa·s or more and less than 2,000 mPa·s

[0319] △: 2,000 mPa·s or more and less than 10,000 mPa·s

[0320] ×: Above 10,000 mPa·s, sedimentation or separation occurs

[0321] TI value determination criteria

[0322] ◎: Less than 3.0

[0323] ○: 3.0 or more and less than 5.0

[0324] △: 5.0 or more and less than 7.0

[0325] ×: 7.0 or more, sedimentation or separation occurs

[0326] (Method for measuring the median particle size of the resin composition)

[0327] Measure the median particle size in the same manner as the carbon nanotube dispersion.

[0328] Median particle size determination criteria

[0329] ○: 0.4 μm or more and less than 2.0 μm

[0330] △: 2.0 μm or more and less than 5.0 μm

[0331] ×: Less than 0.4 μm or 5.0 μm or more

[0332] (Measurement of the complex elastic modulus and phase angle of the resin composition)

[0333] Measure the complex elastic modulus X and phase angle Y in the same manner as the carbon nanotube dispersion. In addition, calculate the product (X × Y) of the obtained complex elastic modulus X (Pa) and phase angle Y (°).

[0334] (Method for evaluating the storage stability of the resin composition)

[0335] In the evaluation of storage stability, measure the viscosity of the dispersion after standing at 50 °C for 7 days. Regarding the measurement method, measure it by the same method as the initial viscosity.

[0336] Storage stability determination criteria

[0337] ◎: Equivalent to the initial stage

[0338] ○: Slight change in viscosity

[0339] △: Viscosity increases but gelation does not occur

[0340] ×: Gelation has occurred

[0341]

[0342] <Fabrication of the positive electrode composite paste and the positive electrode>

[0343] (Examples 3-1 to 3-30, Comparative Examples 3-1 to 3-4)

[0344] According to the combinations and composition ratios shown in Table 4, the positive electrode composite material slurry and the positive electrode were produced as follows. Add the resin composition and the positive electrode active material to a plastic container with a capacity of 150 cm 3 , and use a rotation / revolution mixer (De-bubbling Stirring Taro manufactured by Thinky, ARE-310) to stir at 2,000 rpm for 150 seconds to obtain the positive electrode composite material slurry. The non-volatile component of the positive electrode composite material slurry was set to 68.17% by mass. In addition, in Example 2-30, according to the composition ratio shown in the table, add the resin composition (Resin Composition 19), the positive electrode active material, and other conductive materials (Super-P (manufactured by IMERYS Graphite & Carbon, conductive carbon black)) to a plastic container with a capacity of 150 cm 3 . Except for this, the composite material slurry for Positive Electrode 30 was produced according to the above method.

[0345] After applying the positive electrode composite material slurry onto an aluminum foil with a thickness of 20 μm using an applicator, it was dried in an electric oven at 120°C ± 5°C for 25 minutes to produce an electrode film. Then, the electrode film was rolled using a roll press (3t hydraulic roll press manufactured by Thank-Metal) to obtain the positive electrode (Positive Electrodes 1 to 30, Comparative Positive Electrodes 1 to 4). In addition, the unit area weight per unit of the composite material layer was 20 mg / cm 2 , and the density of the composite material layer after the rolling process was 3.2 g / cc.

[0346] In the examples and comparative examples, the following positive electrode active materials were used.

[0347] · NMC1: Cellseed NMC (LiNi 0.6 Co 0.2 Mn 0.2 O 2 , manufactured by Nippon Chemical Industry Co., Ltd.)

[0348] · NMC2: S800 (LiNi 0.8 Mn 0.1 Co 0.1 O 2 , manufactured by Jinhe Co., Ltd.)

[0349] · NCA: NAT-7050 (LiNi 0.8 Co 0.15 Al 0.05 O 2, BASF (BASF's Toda battery material manufacturing)

[0350] ·LFP: HED (trademark) LFP-400 (lithium iron phosphate, manufactured by BASF)

[0351] <Positive electrode evaluation>

[0352] (Method for evaluating the conductivity of the positive electrode)

[0353] For the obtained positive electrode, the surface resistivity (Ω / γ) of the composite material layer was measured using Loresta GP and MCP-T610 manufactured by Mitsubishi Chemical Analytech. After the measurement, it was multiplied by the thickness of the composite material layer to obtain the volume resistivity (Ω·cm) of the positive electrode. The thickness of the composite material layer was calculated by subtracting the film thickness of the aluminum foil from the average value measured at three points in the counter electrode using a film thickness gauge (manufactured by NIKON, DIGIMICRO MH-15M) to calculate the volume resistivity (Ω·cm) of the positive electrode.

[0354] Conductivity determination criteria

[0355] ◎: Less than 10 Ω·cm

[0356] ○: 10 Ω·cm or more and less than 20 Ω·cm

[0357] △: 20 Ω·cm or more and less than 30 Ω·cm

[0358] ×: 30 Ω·cm or more

[0359] (Method for evaluating the adhesion of the positive electrode)

[0360] The obtained positive electrode was cut into two rectangles of 90 mm × 20 mm with the coating direction as the long axis. A bench-top tensile testing machine (manufactured by Toyo Seiki Seisakusho, Strograph E3) was used for the measurement of the peel strength, and the evaluation was carried out by the 180-degree peel test method. Specifically, a double-sided tape (No. 5000NS, manufactured by Nitoms) with a size of 100 mm × 30 mm was attached to a stainless steel plate, and the composite material layer side of the fabricated positive electrode was made to adhere closely to the other side of the double-sided tape to prepare a test specimen. Subsequently, the test specimen was vertically fixed with the short side of the rectangle facing up and down, and while pulling the end of the aluminum foil upward from the bottom at a constant speed (50 mm / minute) to peel it off, the average value of the stress at this time was taken as the peel strength.

[0361] Adhesion determination criteria

[0362] ◎: 0.8 N / cm or more

[0363] ○: 0.5 N / cm or more and less than 0.8 N / cm △: 0.3 N / cm or more and less than 0.5 N / cm ×: less than 0.3 N / cm

[0364]

[0365] <Fabrication and Evaluation of Secondary Battery>

[0366] (Fabrication of Standard Negative Electrode)

[0367] To a plastic container with a capacity of 150 ml, add 0.5 parts of acetylene black (Denka Black (registered trademark) HS - 100, manufactured by Denka), 1 part of MAC500LC (sodium carboxymethyl cellulose Sunrose special type MAC500L, manufactured by Nippon Paper Industries, non - volatile content 100%), and 98.4 parts of water. Then, using a rotation / revolution mixer (Thinky's defoaming and stirring Taichiro, ARE - 310), stir at 2,000 rpm for 30 seconds. Further add 97 mass parts of artificial graphite (CGB - 20, manufactured by Nippon Graphite Industry Co., Ltd.) as the active material, and using a rotation / revolution mixer (Thinky's defoaming and stirring Taichiro, ARE - 310), stir at 2,000 rpm for 150 seconds. Subsequently, add 3.1 parts of styrene - butadiene rubber (SBR (styrene - butadiene rubber), TRD2001, non - volatile content 48%, manufactured by JSR), and using a rotation / revolution mixer (Thinky's defoaming and stirring Taichiro, ARE - 310), stir at 2,000 rpm for 30 seconds to obtain a standard negative electrode composite material slurry. The non - volatile content of the standard negative electrode composite material slurry is set to 50 mass%.

[0368] Using a coater, apply the standard negative electrode composite material slurry onto a 20 - μm - thick copper foil as the current collector, and then dry it in an electric oven at 80 °C ± 5 °C for 25 minutes to adjust the weight per unit area of the electrode to 10 mg / cm 2 ³. Furthermore, perform rolling treatment using a roll press (manufactured by Thank - Metal, 3t hydraulic roll press) to make the density of the composite material layer reach 1.6 g / cm 3 ³ of the standard negative electrode.

[0369] (Examples 4 - 1 to 4 - 30, Comparative Examples 4 - 1 to 4 - 4)

[0370] (Fabrication of Secondary Battery)

[0371] Using the positive electrode and the standard negative electrode described in Table 5, they were respectively punched into sizes of 50 mm × 45 mm and 45 mm × 40 mm. The punched positive electrode, standard negative electrode, and the separator (porous polypropylene film) inserted therebetween were inserted into an aluminum laminated bag and dried in an electric oven at 70°C for 1 hour. Then, 2 mL of an electrolytic solution (a mixed solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, and further adding 1 part by mass of vinylene carbonate as an additive per 100 parts by mass and dissolving LiPF 6 to form a non-aqueous electrolytic solution) was injected into a glove box filled with argon, and the aluminum laminated bag was sealed to fabricate secondary batteries (Batteries 1 to 30, Comparative Batteries 1 to 4) respectively.

[0372] (Evaluation method for rate characteristics of secondary batteries)

[0373] The obtained secondary batteries were placed in a constant temperature chamber at 25°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Beidou Electric Works, SM-8). After constant current constant voltage charging at a charging current of 10 mA (0.2C) with a charging cut-off voltage of 4.3V (cut-off current 1 mA (0.02C)), constant current discharge was performed at a discharge current of 10 mA (0.2C) with a discharge cut-off voltage of 3V. After repeating the above operation 3 times, constant current constant voltage charging was performed at a charging current of 10 mA (0.2C) with a charging cut-off voltage of 4.3V (cut-off current (1 mA (0.02C))), and constant current discharge was performed at discharge currents of 0.2C and 3C until the discharge cut-off voltage of 3.0V was reached, and the discharge capacities were respectively obtained. The rate characteristics can be represented by the ratio of the 0.2C discharge capacity to the 3C discharge capacity and the following Equation 1.

[0374] (Equation 1) Rate characteristics = 3C discharge capacity / 0.2C discharge capacity of the third cycle × 100 (%)

[0375] Rate characteristic determination criteria

[0376] ◎: 80% or more

[0377] ○: 60% or more and less than 80%

[0378] △: 40% or more and less than 60%

[0379] ×: Less than 40%

[0380] (Evaluation method for cycle characteristics of secondary batteries)

[0381] The obtained secondary battery was placed in a thermostatic chamber at 25°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Beidou Electric Works, SM-8). After constant current and constant voltage charging at a charging current of 25 mA (0.5C) with a charging cut-off voltage of 4.3 V (cut-off current 2.5 mA (0.05C)), constant current discharge was performed at a discharge current of 25 mA (0.5C) with a discharge cut-off voltage of 3 V. The above operation was repeated 200 times. The cycle characteristics can be represented by the ratio of the 0.5C discharge capacity at the 3rd cycle to the 0.5C discharge capacity at the 200th cycle at 25°C, and the following formula 2.

[0382] (Formula 2) Cycle characteristics = 0.5C discharge capacity at the 3rd cycle / 0.5C discharge capacity at the 200th cycle × 100 (%)

[0383] Cycle characteristics judgment criteria

[0384] ◎: 85% or more

[0385] ○: 80% or more and less than 85%

[0386] △: 50% or more and less than 80%

[0387] ×: less than 50%

[0388] [Table 5]

[0389] Table 5

[0390]

[0391] As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited to the above embodiments. Various modifications understandable 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 method for manufacturing a resin composition for a secondary battery electrode, comprising adding a binder resin to a carbon nanotube dispersion liquid without adding an active material, the carbon nanotube dispersion liquid containing carbon nanotubes, a dispersant, and a non-aqueous dispersion medium, and the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement being 30 or more and 1,700 or less, and the phase angle being 3° or more and 90° or less. The resin composition is for a positive electrode. The binder resin is added to the carbon nanotube dispersion liquid in powder form, and the binder resin is polyvinylidene fluoride. The dispersant is selected from at least one of the group consisting of hydrogenated acrylonitrile-butadiene rubber, polyacrylonitrile, polyvinylpyrrolidone, and polyvinyl alcohol. The non-aqueous dispersion medium is selected from at least one of the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. Relative to the total amount of the resin composition, the content of the binder resin is 1% by mass to 6% by mass, the content of the carbon nanotubes is 0.5% by mass to 15% by mass, and the content of the dispersant is 0.5% by mass to 5% by mass. The dispersion of the carbon nanotube dispersion liquid includes performing a dispersion treatment using a high-pressure homogenizer, and the pressure of using the high-pressure homogenizer is 60 MPa to 150 MPa.

2. The method for manufacturing a resin composition for a secondary battery electrode according to claim 1. Wherein, The complex elastic modulus of the carbon nanotube dispersion liquid at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement is 0.1 Pa or more and 200 Pa or less.

3. The method for manufacturing a resin composition for a secondary battery electrode according to claim 1 or 2. Wherein, The complex elastic modulus of the resin composition for a secondary battery electrode at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement is 0.1 Pa or more and 300 Pa or less.

4. The method for manufacturing a resin composition for a secondary battery electrode according to claim 1 or 2. Wherein, The phase angle of the resin composition for a secondary battery electrode at 25°C and 1 Hz obtained by dynamic viscoelasticity measurement is 3° or more and 90° or less.

5. The method for manufacturing a resin composition for a secondary battery electrode according to claim 1 or 2. Wherein, Relative to the total amount of the carbon nanotube dispersion liquid, the content of the carbon nanotubes contained in the carbon nanotube dispersion liquid is 0.5% by mass or more and 10% by mass or less.

6. The method for manufacturing a resin composition for a secondary battery electrode according to claim 1 or 2. Wherein, The carbon nanotubes contained in the carbon nanotube dispersion liquid include single-walled carbon nanotubes and multi-walled carbon nanotubes.

7. The method for manufacturing a resin composition for a secondary battery electrode according to claim 1 or 2. Wherein, Relative to the carbon nanotubes contained in the carbon nanotube dispersion liquid, the binder resin is 10% by mass or more and 300% by mass or less in terms of mass ratio.

8. The method for manufacturing a resin composition for a secondary battery electrode according to claim 1 or 2. Wherein, The carbon nanotubes contained in the carbon nanotube dispersion include either single-walled carbon nanotubes or multi-walled carbon nanotubes. The method for manufacturing the resin composition for a secondary battery electrode includes: in a state where either single-walled carbon nanotubes or multi-walled carbon nanotubes are dispersed in the carbon nanotube dispersion, before, after, simultaneously with, or in a combination of these when adding a binder resin to the carbon nanotube dispersion, further adding the other of single-walled carbon nanotubes and multi-walled carbon nanotubes.

9. The method for manufacturing the resin composition for a secondary battery electrode according to claim 8, wherein, Relative to the total amount of the carbon nanotubes contained in the resin composition, the binder resin is 10% by mass or more and 300% by mass or less in terms of mass ratio.

10. The method for manufacturing the resin composition for a secondary battery electrode according to claim 1 or 2, wherein, The carbon nanotube dispersion further contains carbon black.

11. The method for manufacturing the resin composition for a secondary battery electrode according to claim 1 or 2, including: Before, after, simultaneously with, or in a combination of these when adding a binder resin to the carbon nanotube dispersion, further adding carbon black.

12. A method for manufacturing a composite material slurry for a secondary battery electrode, including: Manufacturing a resin composition for a secondary battery electrode according to any one of claims 1 to 11; And adding an active material to the resin composition.

13. The method for manufacturing the composite material slurry for a secondary battery electrode according to claim 12, including: Before, after, simultaneously with, or in a combination of these when adding an active material to the resin composition, further adding carbon black.

14. A method for manufacturing an electrode film, including: Manufacturing a composite material slurry for a secondary battery electrode according to claim 12 or 13 and coating the composite material slurry to form an electrode film.

15. A method for manufacturing a secondary battery, including: Manufacturing a composite material slurry for a secondary battery electrode according to claim 12 or 13 and coating the composite material slurry on a current collector to form an electrode film.

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