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

Abstract

Provided is a resin composition for secondary battery electrodes which contains carbon nanotubes, a dispersing agent, a fluororesin, and a dispersion medium and in which 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 viscoelastic measurement is 30 to 5,000.

Description

Technical Field

[0001] The present invention relates to 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

[0002] With the spread of electric vehicles and the miniaturization, light weight, and high performance of portable devices, there is a demand for secondary batteries having a high energy density, and further, an increase in the capacity of such secondary batteries. Under such circumstances, non-aqueous electrolyte secondary batteries using a non-aqueous electrolyte, particularly lithium-ion secondary batteries, are being used in many devices due to their characteristics of high energy density and high voltage.

[0003] The electrode of a secondary battery is manufactured by coating a current collector with a composite material slurry containing a positive electrode active material or a negative electrode active material, a conductive material, a binder resin, etc. By preparing a conductive material dispersion liquid in which the conductive material is dispersed in a dispersion medium and adding the active material and the binder resin to the conductive material dispersion liquid to prepare a composite material slurry, the conductive material is uniformly dispersed and contained in the electrode film, and the conductivity of the electrode film can be improved. The conductive material dispersion liquid can be commonly used for various composite material slurries, but the composite material slurry is prepared by adjusting the type of the active material, the blending ratio of each component, etc. according to the specifications of the battery or the electrode. Therefore, it is preferable that the dispersibility and fluidity are maintained even during the storage of the conductive material dispersion liquid before adding the active material. Furthermore, if it can be stored in the state of a resin composition in which a binder resin is added to the conductive material dispersion liquid, the operation of preparing the composite material slurry can be simplified.

[0004] As the conductive material, carbon black, fullerene, graphene, fine carbon materials, etc. are used. In particular, carbon nanotubes, which are a type of fine carbon fiber, are widely 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. Also, by adding carbon nanotubes to the 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, and the expansion and contraction properties of the electrode can be enhanced, thereby improving the cycle life of the lithium secondary battery. Among them, multi-walled carbon nanotubes with an outer diameter of several nm to several tens of nm are relatively inexpensive and are in progress of practical application. When using carbon nanotubes with a small average outer diameter and a large fiber length, an efficient conductive network can be formed even with a small amount, and the high capacity of the secondary battery can be achieved. On the other hand, carbon nanotubes having these characteristics have a strong cohesive force, making it more difficult to further enhance the dispersibility of the carbon nanotube dispersion.

[0005] Patent Document 1 discloses a conductive material dispersion liquid containing a bundled carbon nanotube, a dispersant such as hydrogenated nitrile butadiene rubber, and a dispersion medium, and having a phase angle of 3° to 18° at a frequency of 1 Hz during rheometer measurement. In Patent Document 1, a composition obtained by adding an active material and a binder to a conductive material dispersion liquid containing carbon nanotubes has a reduced viscosity and elasticity, exhibits a rapid change over time during coating, and causes cracks in the formation of the electrode active material layer. Therefore, the phase angle of the conductive material dispersion liquid is controlled to 18° or less to provide solid-like properties, thereby preventing the occurrence of cracks in the produced electrode active material layer. Patent Document 2 discloses a conductive material dispersion liquid containing a bundled carbon nanotube, a dispersant containing hydrogenated nitrile rubber, and a dispersion medium, and having a complex elastic modulus (G*|@1Hz) of 20 Pa to 500 Pa at a frequency of 1 Hz during rheometer measurement. According to Patent Document 2, since linear carbon nanotubes have different particle sizes depending on the measurement angle in particle size analysis, it is difficult to evaluate their dispersibility. Therefore, an attempt is made to control the dispersibility and viscosity characteristics of the conductive material dispersion liquid by the complex elastic modulus of the conductive material dispersion liquid. From the evaluation of the examples in Patent Document 2, it has been confirmed that the value of the complex elastic modulus, which is a measure of the elastic modulus, decreases as the dispersion state of the conductive material dispersion liquid improves.

[0006] Patent Document 3 discloses a method for manufacturing a slurry for a secondary battery positive electrode, in which a conductive material such as acetylene black and a first binder are mixed to obtain a conductive material paste 1, 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. According to Patent Document 3, the first binder includes a resin containing at least one monomer unit selected from the group consisting of a conjugated diene monomer unit, a 1-olefin monomer unit, and a (meth)acrylate monomer unit, the second binder includes a fluorine-based polymer such as polyvinylidene fluoride, and by adding and mixing the first binder and the second binder in this order, the conductive material is appropriately dispersed in the resulting slurry, a good conductive network is formed between the conductive materials in the produced positive electrode composite layer, the cycle characteristics of the secondary battery are improved, and the capacity deterioration at low temperatures is suppressed. Patent Document 4 discloses a method for manufacturing a slurry for a secondary battery positive electrode, in which 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 and a positive electrode active material are mixed. According to Patent Document 4, when the solid content of the conductive material paste is within this range, a good conductive network is formed between the conductive materials in the produced positive electrode composite layer, the cycle characteristics of the secondary battery are improved, and the internal resistance is reduced.

[0007] Ideally, the finer the conductive material, the more efficiently it can form an ideal conductive network. However, the finer the conductive material, the larger its specific surface area and the higher its cohesive force, making it difficult to obtain a high-concentration and good resin composition. If the concentration of the conductive material is forced to increase, the resin composition will have a higher viscosity and poorer fluidity. Also, the fine conductive material and the binder resin may become entangled, causing poor dispersion. In a resin composition with poor fluidity, when transporting the resin composition in a tank or the like, or storing and using it for a long time, there may be a problem that it becomes difficult to take it out from the tank or the like. On the other hand, in a resin composition with a low concentration of the conductive material, there are problems such as a lower degree of design freedom when blending materials such as active materials, and a higher transportation cost per solid content of the conductive material. Therefore, it is an urgent task to obtain a resin composition in which fine conductive materials are well dispersed in a highly fluid state.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] The conductive material dispersion liquid disclosed in Patent Document 1 has relatively strong solid-like characteristics, and the conductive material dispersion liquid disclosed in Patent Document 2 has relatively strong elastic behavior. Therefore, both have poor fluidity and are not suitable for transportation by tank or long-term storage. In Patent Document 1, the phase angle is controlled to obtain a conductive material dispersion liquid with high solid-like characteristics, and then an active material and a binder are added to prepare a composition. However, the conductive material dispersion liquid with high solid-like characteristics has a high viscosity, and the miscibility with the subsequently added binder may decrease. In Patent Document 2, a conductive material dispersion liquid with controlled dispersibility and viscosity characteristics is obtained by using the complex elastic modulus, and then an active material and a binder are added to prepare a composition. However, simply controlling the conductive material dispersion liquid by the complex elastic modulus may not sufficiently obtain the miscibility with the subsequently added binder. For example, when a binder resin is added to a carbon nanotube dispersion liquid in which the fiber length of carbon nanotubes is maintained and finely dispersed, the carbon nanotubes may aggregate or the binder resin may gel, resulting in a decrease in the dispersibility and fluidity of the resin composition.

[0010] In Patent Documents 3 and 4, acetylene black is specifically examined as the conductive material, but carbon nanotubes have not been sufficiently examined. When fibrous carbon materials such as carbon nanotubes are broken by 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 may decrease. Also, when the composite material slurry contains carbon nanotubes with a long fiber length, the fibers and resin components are likely to become entangled and aggregate. If the electrode film is formed with the fibers not being separated from each other, the conductive network between the conductive materials in the electrode film may decrease.

[0011] When the inventors compared and examined in detail the minute differences in the dispersion state of the conductive material, they found that when fibrous carbon nanotubes are used as the conductive material, even if the particle size distribution and viscosity, which have often been used as indices of the dispersion degree in the past, have the same measured values, the characteristics may differ when used in a secondary battery, indicating that the dispersion state of the conductive material has not been accurately grasped. For example, in the case of the particle size distribution, since fibrous non-spherical particles are calculated assuming they are spherical, a deviation from the actual state is likely to occur. In the case of viscosity, generally, it is said that the lower the viscosity, the better the dispersion state of the conductive material. However, when 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, its elasticity becomes stronger. Also, when the fibers are broken, the viscosity changes due to two factors: deaggregation and breakage, so it is difficult to accurately represent the state of the conductive material only by viscosity. When the fibers of carbon nanotubes are broken, it becomes difficult to form a developed conductive network in the electrode due to an increase in the contact resistance between the carbon nanotubes. Therefore, it is effective to disperse the fibers uniformly without breaking them as much as possible. In the conventional technology, the minute control of the dispersion state of the resin composition containing carbon nanotubes has not been sufficiently achieved.

[0012] That is, the problem to be solved by the present invention is to finely control the dispersion state of carbon nanotubes as a conductive material, to provide a resin composition for a secondary battery electrode having high dispersibility and fluidity in a state containing a fluororesin, and further to provide a composite slurry for a secondary battery electrode having good dispersibility of carbon nanotubes in a state containing an active material. More specifically, it is to provide a non-aqueous electrolyte secondary battery with high output, high capacity, and long life, and an electrode film used therein.

Means for Solving the Problem

[0013] According to the intensive studies by the present inventors for the purpose of solving the above problems, a composition containing carbon nanotubes, a dispersant, a fluororesin, and a dispersion medium, wherein the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) at 25°C and 1 Hz by dynamic viscoelasticity measurement is 30 or more and 5,000 or less, maintains fluidity even in a state containing carbon nanotubes and a fluororesin, and the long fibers of the carbon nanotubes are dispersed while being appropriately maintained without being broken in the resin composition. By forming an electrode film using this resin composition, it is possible to form a developed conductive network in the electrode film. As a result, it becomes possible to provide a secondary battery with high output, high capacity, and long life.

[0014] That is, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following. <1> A resin composition for a secondary battery electrode, which contains carbon nanotubes, a dispersant, a fluororesin, and a dispersion medium, does not contain an active material, and the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) at 25°C and 1 Hz by dynamic viscoelasticity measurement is 30 or more and 5,000 or less. <2> The resin composition for a secondary battery electrode according to <1>, wherein the complex elastic modulus at 25°C and 1 Hz by dynamic viscoelasticity measurement is 0.1 Pa or more and 300 Pa or less. <3> The resin composition for a secondary battery electrode according to <1> or <2>, wherein the phase angle at 25°C and 1 Hz by dynamic viscoelasticity measurement is 3° or more and 90° or less.

[0015] <4> The resin composition for a secondary battery electrode according to any one of <1> to <3>, wherein the content of the carbon nanotubes is 0.5% by mass or more and 15% by mass or less based on the total amount of the resin composition. <5> The resin composition for a secondary battery electrode according to any one of <1> to <4>, wherein the mass ratio of the dispersant to the carbon nanotubes is 0.01 or more and 2 or less. <6> The resin composition for a secondary battery electrode according to any one of <1> to <5>, wherein the mass ratio of the fluororesin to the carbon nanotubes is 0.1 or more and 10 or less. <7>The carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes, and the resin composition for a secondary battery electrode according to any one of <1> to <6>.

[0016] <8>The resin composition for a secondary battery electrode according to any one of <1> to <7>, further comprising carbon black. <9>A method for producing a composite slurry for a secondary battery electrode, comprising adding an active material to the resin composition for a secondary battery electrode according to any one of <1> to <8>. <10>The method for producing a composite slurry for a secondary battery electrode according to <9>, further comprising adding carbon black before, after, simultaneously with, or in combination of these, to the resin composition for a secondary battery electrode before adding the active material.

[0017] <11>A method for producing an electrode film, comprising adding an active material to the resin composition for a secondary battery electrode according to any one of <1> to <8> to prepare a composite slurry, and coating the composite slurry to form an electrode film. <12>A method for producing a secondary battery including a positive electrode, a negative electrode, and an electrolyte, comprising adding an active material to the resin composition for a secondary battery electrode according to any one of <1> to <8> to prepare a composite slurry, and forming at least one of the positive electrode and the negative electrode by coating the composite slurry on a current collector to form an electrode film.

Advantages of the Invention

[0018] According to an embodiment of the present invention, it is possible to provide a resin composition for a secondary battery electrode having high fluidity and dispersibility. According to another embodiment of the present invention, it is possible to provide a composite slurry for a secondary battery electrode having good dispersibility of carbon nanotubes. According to still another embodiment of the present invention, it is possible to provide a non-aqueous electrolyte secondary battery with high output, high capacity, and long life, and an electrode film used therefor.

Modes for Carrying Out the Invention

[0019] Hereinafter, the resin composition for secondary battery electrodes, the method for manufacturing the composite slurry for secondary battery electrodes, the method for manufacturing the electrode film, and the method for manufacturing 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 of the present invention.

[0020] In this specification, carbon nanotubes may be referred to as "CNT". Hydrogenated nitrile rubber may be referred to as "H-NBR", and N-methyl-2-pyrrolidone may be referred to as "NMP". In addition, in this specification, the carbon nanotube dispersion may be simply referred to as "CNT dispersion" or "dispersion", and the resin composition for secondary battery electrodes may be simply referred to as "resin composition".

[0021] <Carbon nanotubes> The resin composition for secondary battery electrodes contains carbon nanotubes, a dispersant, a fluororesin, and a dispersion medium, and may further contain optional components. The carbon nanotubes (CNT) function as a conductive material. The resin composition may contain a conductive material other than carbon nanotubes. Examples of other conductive materials include carbon materials such as carbon black, fullerene, graphene, multi-layer graphene, and graphite. When using a conductive material other than CNT, carbon black is preferable from the viewpoint of the adsorption performance of the dispersant, and examples of carbon black include acetylene black, furnace black, hollow carbon black, and ketjen black. These carbon blacks may be neutral, acidic, or basic, and oxidized carbon black or graphitized carbon black may be used. Other conductive materials may be used alone or in combination of two or more.

[0022] The CNTs to be added to the resin composition preferably have the following physical properties. The CNTs have a shape in which planar graphite is wound into a cylindrical shape, including single-walled CNTs and multi-walled CNTs, and these may be mixed. The single-walled CNTs have a structure in which a single layer of graphite is wound. The multi-walled CNTs have a structure in which two or more layers of graphite are wound. Also, the side walls of the CNTs do not have to be a graphite structure. Also, for example, CNTs having side walls with an amorphous structure are also CNTs in this specification.

[0023] The shape of the CNTs is not limited. Such shapes include various shapes including needle-like, cylindrical tube-like, fishbone-like (fishbone or cup stacking type), trump-like (platelet), and coil-like. Among them, the shape of the CNTs is preferably needle-like or cylindrical tube-like. The CNTs may be of a single shape or a combination of two or more shapes.

[0024] The form of the CNTs includes, for example, graphite whiskers, filamentous carbon, graphite fibers, ultra-fine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. The carbon nanotubes may have these single forms or a combination of two or more.

[0025] The average outer diameter of the CNTs is preferably 1 nm or more, more preferably 3 nm or more. Also, it is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 15 nm or less. The average outer diameter of the CNTs can be calculated by first observing and imaging the CNTs with a transmission electron microscope, selecting any 300 CNTs in the observation photograph, and measuring their respective outer diameters.

[0026] The resin composition may be prepared by separately preparing two or more types of CNTs having different average outer diameters and adding them to a dispersion medium. When using two or more types of CNTs having different average outer diameters 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 even more preferably 20 nm or less. When using two or more types of CNTs having different average outer diameters 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, even more preferably 1:10 to 1:100, and still more preferably 1:10 to 1:50.

[0027] Here, when using single-walled carbon nanotubes as the first CNT and multi-walled carbon nanotubes as the second CNT, the average outer diameter of the single-walled carbon nanotubes 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 even more preferably 1.5 nm or more and 2.0 nm or less. The average outer diameter of the multi-walled carbon nanotubes is preferably more than 3 nm and 30 nm or less, more preferably 3 nm or more and 20 nm or less, and even more preferably 5 nm or more and 15 nm or less. In the resin composition, a combination of single-walled carbon nanotubes and multi-walled carbon nanotubes may be included as the carbon nanotubes. In this case, the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is preferably 1:1 to 1:100, more preferably 1:2 to 1:50, and even more preferably 1:3 to 1:10. Since the outer diameter and fiber length are different between single-walled carbon nanotubes and multi-walled carbon nanotubes, the state of forming a good conductive network and dispersion stabilization is different. By setting the mass ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes within the above range, the entanglement between the carbon nanotubes can be suppressed, and a dispersion liquid with excellent fluidity can be obtained.

[0028] The average fiber length of the CNT is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.0 μm or more. Also, it is preferably 20 μm or less, more preferably 10 μm or less. The average fiber length of the CNT can be calculated by first observing and imaging the CNT with a scanning electron microscope, and then selecting any 300 CNTs in the observation photograph and measuring their respective fiber lengths.

[0029] The value obtained by dividing the fiber length of the CNT by the 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 obtained. The higher the aspect ratio of the conductive material, the higher the conductivity can be obtained when forming the electrode. The aspect ratio of the CNT is preferably 30 or more, more preferably 50 or more, and even more preferably 80 or more. Also, it is preferably 10,000 or less, more preferably 3,000 or less, and even more preferably 1,000 or less.

[0030] The specific surface area of the CNT is preferably 100 m 2 / g or more, more preferably 150 m 2 / g or more, and even more preferably 200 m 2 / g or more. Also, it is preferably 1200 m 2 / g or less, more preferably 1000 m 2 / g or less. The specific surface area of the CNT is calculated by the BET method using nitrogen adsorption measurement. When the average outer diameter, average fiber length, aspect ratio, and specific surface area of the CNT are within the above ranges, it becomes easier to form a developed conductive path in the electrode.

[0031] The carbon purity of CNTs is represented by the content rate (mass%) of carbon atoms in the CNTs. 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 with respect to 100 mass% of the CNTs. By setting the carbon purity within the above range, it is possible to prevent problems such as dendrites being formed due to impurities such as metal catalysts and short circuits occurring.

[0032] For the purpose of removing or reducing impurities such as metal catalysts and increasing the carbon purity, CNTs that have been subjected to a purification treatment may be used. The method of the purification treatment is not particularly limited, and known methods can be used. For example, a method of evaporating impurities by treating at a high temperature (for example, 3000°C) in an inert atmosphere may be used. This method is preferable in that it can be treated under conditions with relatively little risk of explosion or the like. Further, a method of mixing a gas containing a halogen (such as chlorine gas, fluorine gas, carbon tetrachloride gas, carbon tetrafluoride gas, etc.) into an inert gas and performing heat treatment to evaporate the halogenated impurities may be used. Since the boiling point of the impurities is lowered by halogenation, they can be removed at a lower temperature (for example, 1600°C) compared to the case without halogenation, and the carbon purity can be increased without changing the physical properties such as the crystallinity, density, and conductivity of the CNTs, which is preferable. Furthermore, when the CNTs are densified and then heat-treated, the scattering of the CNTs can be suppressed, and the processing amount can be increased to efficiently purify them. Also, a method of impregnating the CNTs in an acidic or basic solution to dissolve and remove the impurities may be used. When treated with an acidic or basic solution, functional groups may be introduced to the surface or ends of the CNTs. If the amount of functional groups is small, the dispersibility is likely to be improved. If the amount of functional groups is large, the conductivity may be likely to decrease.

[0033] When the CNTs are dispersed by a disperser through collision with media such as a bead mill, or when a process is performed in which the disperser is repeatedly passed through over a long period of time, the CNTs may be damaged to produce short carbonaceous materials. When short carbonaceous materials are produced, the viscosity of the resin composition decreases, and the gloss of the coating film obtained by coating and drying the resin composition increases. Therefore, judging only from these evaluation results, the dispersion state seems to be good. However, since the short carbonaceous materials have a high contact resistance and it is difficult to form a conductive network, the resin composition produced through such a dispersion treatment may deteriorate the resistance of the electrode. The degree of generation of short carbonaceous materials can be confirmed by methods such as diluting the dispersion liquid, dropping it onto a substrate with a smooth surface and good affinity with the dispersion medium, drying the sample, and observing it with a scanning electron microscope. By adjusting the dispersion conditions and the formulation of the dispersion liquid so that carbonaceous materials of 0.1 μm or less are not produced, an electrode with high conductivity can be obtained.

[0034] The carbon nanotubes may be carbon nanotubes subjected to surface treatment. The carbon nanotubes may be carbon nanotube derivatives to which a functional group typified by a carboxy group is imparted. Also, carbon nanotubes encapsulating an organic compound, a metal atom, or a substance typified by fullerene can also be used.

[0035] The carbon nanotubes may be carbon nanotubes produced by any method. Carbon nanotubes can generally be produced by laser ablation method, arc discharge method, thermal CVD method, plasma CVD method, and combustion method, but are not limited thereto. For example, carbon nanotubes can be produced by bringing a carbon source into catalytic contact reaction at 500 to 1000 °C in an atmosphere with an oxygen concentration of 1% by volume or less. The carbon source may be at least one of hydrocarbons and alcohols.

[0036] As the source gas for carbon nanotubes, any conventionally known one can be used. For example, hydrocarbons typified by methane, ethylene, propane, butane and acetylene, carbon monoxide, and alcohols can be used as the source gas containing carbon, but are not limited thereto. From the viewpoint of ease of use, it is desirable to use at least one of hydrocarbons and alcohols as the source gas.

[0037] <Dispersant> The resin composition contains a dispersant. The dispersant is preferably one that can disperse and stabilize CNTs in the resin composition. As the dispersant, either a resin-type dispersant or a surfactant can be used, but a resin-type dispersant is preferred because it has a strong adsorption force to CNTs and good dispersion stability. A suitable type of dispersant can be used in a suitable blending amount according to the properties required for the dispersion of carbon nanotubes.

[0038] As the resin-type dispersant, (meth)acrylic polymers, polymers derived from ethylenically unsaturated hydrocarbons, cellulose derivatives, copolymers thereof, etc. can be used.

[0039] Examples of polymers derived from ethylenically unsaturated hydrocarbons include polyvinyl alcohol-based resins, polyvinyl pyrrolidone-based resins, polyacrylonitrile-based resins, nitrile rubbers, etc. Examples of polyvinyl alcohol-based resins include polyvinyl alcohol, modified polyvinyl alcohol having a functional group other than a hydroxyl group (for example, an acetyl group, a sulfo group, a carboxy group, a carbonyl group, an amino group), polyvinyl alcohol modified with various salts, other anionically or cationically modified polyvinyl alcohols, and polyvinyl acetals (such as polyvinyl acetoacetal and polyvinyl butyral) acetal-modified (such as acetoacetal modification or butyral modification) with aldehydes. Examples of polyacrylonitrile-based resins may include homopolymers of polyacrylonitrile, copolymers of polyacrylonitrile, and modified products thereof, and polyacrylonitrile-based resins having at least one selected from the group consisting of active hydrogen groups such as hydroxyl groups, carboxy groups, primary amino groups, secondary amino groups, and mercapto groups, basic groups, and alkyl groups introduced from (meth)acrylic acid alkyl esters or α-olefins, etc. are preferred. For example, the acrylonitrile copolymer described in JP-A-2020-163362 can be used. Examples of polyacrylonitrile-based resins may include homopolymers of polyacrylonitrile, copolymers of polyacrylonitrile, and modified products thereof, and polyacrylonitrile-based resins having at least one selected from the group consisting of active hydrogen groups such as hydroxyl groups, carboxy groups, primary amino groups, secondary amino groups, and mercapto groups, basic groups, and alkyl groups introduced from (meth)acrylic acid alkyl esters, etc. are preferred. For example, the acrylonitrile copolymer described in JP-A-2020-163362 can be used. Examples of nitrile rubbers include acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber, etc.Examples of the cellulose derivative 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. Further, a dispersant described in International Publication No. 2008 / 108360 pamphlet, JP-A No. 2018-192379, JP-A No. 2019-087304, Patent No. 6524479, and JP-A No. 2009-026744 may be used, but are not limited thereto. In particular, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, a homopolymer of polyacrylonitrile, a copolymer of polyacrylonitrile, and hydrogenated acrylonitrile butadiene rubber are preferable. Polymers in which other substituents are introduced into a part of these polymers, modified polymers, etc. may also be used. From the viewpoints of the affinity balance between the object to be dispersed and the dispersion medium and the resistance to the electrolytic solution, the weight average molecular weight of the resin type dispersant is preferably 500,000 or less, more preferably 300,000 or less, preferably 3,000 or more, and more preferably 5,000 or more. The resin type dispersant may be used alone or in combination of two or more kinds.

[0040] Examples of commercially available polyvinyl alcohol resins include various grades available under trade names such as Kuraray Poval (polyvinyl alcohol resin manufactured by Kuraray), Gohsenol, Gohsenex (polyvinyl alcohol resin manufactured by Nippon Gohsei Chemical Industry Co., Ltd.), Denka Poval (polyvinyl alcohol resin manufactured by Denka Co., Ltd.), J-Poval (polyvinyl alcohol resin manufactured by Nippon Vinyl Acetate - Poval Co., Ltd.). Modified polyvinyl alcohols having various functional groups can also be obtained in the same manner. Also, those synthesized by known synthesis methods may be used. Specific examples of commercially available polyvinylpyrrolidone resins include Luvitec K17 (K value: 15.0 - 19.0, low molecular weight), K30 (K value 27.0 - 33.0), K80 (K value 74.0 - 82.0), K85 (K value 84.0 - 88.0), K90 (K value 88.0 - 92.0), K90HM (K value 92.0 - 96.0, high molecular weight) (manufactured by BASF Japan), K15, K30, K90, K120 (manufactured by ISP), polyvinylpyrrolidone K30 (K value 27.0 - 33.0), K85 (K value 84.0 - 88.0), K90 (K value 88.0 - 96.0) (manufactured by Nippon Shokubai Co., Ltd.), PVP K12 (K value 10 - 14), K15 (K value 13 - 19), K30 (K26 - K35), K60 (K value 50 - 62), K90 (K value 88 - 100), K120 (K value 114 - 130) (manufactured by DSP Fine Chemicals Co., Ltd.). From the viewpoint of preventing viscosity increase, the K value of polyvinylpyrrolidone is preferably 150 or less, more preferably 100 or less, and even more preferably 85 or less. Examples of commercially available nitrile rubbers include various grades with different nitrile ratios, hydrogenation rates, molecular weights, etc. available under trade names such as Therban (hydrogenated nitrile rubber manufactured by LANXESS), Baymod (nitrile rubber manufactured by LANXESS), Zetpole (hydrogenated nitrile rubber manufactured by Nippon Zeon Co., Ltd.), Nipole NBR (nitrile rubber manufactured by Nippon Zeon Co., Ltd.). Also, those synthesized by known synthesis methods may be used.

[0041] Instead of or in addition to the above-described resin-type dispersant, a surfactant may be used. Surfactants are classified into anionic, cationic, amphoteric ionic surfactants, and nonionic surfactants.

[0042] As the resin-type dispersant, a polymer containing at least an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit may be used. The aliphatic hydrocarbon structural unit of the polymer may include an alkylene structural unit. This polymer may be hydrogenated.

[0043] The aliphatic hydrocarbon structural unit is a structural unit containing an aliphatic hydrocarbon structure, preferably a structural unit consisting only of an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure includes at least a saturated aliphatic hydrocarbon structure and may further include an unsaturated aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure preferably includes at least a linear aliphatic hydrocarbon structure and may further include a branched aliphatic hydrocarbon structure.

[0044] Examples of the aliphatic hydrocarbon structural unit include an alkylene structural unit, an alkenylene structural unit, an alkyl structural unit, an alkanetriyl structural unit, an alkanetetrayl structural unit, etc. Structural units containing a branching point such as an alkanetriyl structural unit and an alkanetetrayl structural unit are different structural units from the structural units containing a branched alkylene structure and the structural units containing a branched alkyl structure described below. The aliphatic hydrocarbon structural unit preferably includes at least an alkylene structural unit.

[0045] The alkylene structural unit is a structural unit containing an alkylene structure, preferably a structural unit consisting only of an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

[0046] The alkylene structural unit preferably includes a structural unit represented by the following general formula (1A).

[0047] General formula (1A)

Chemical formula

[0048] In 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. In particular, n is preferably 4. In this specification, "*" represents a joint part with other structures.

[0049] The alkylene structural unit preferably includes a structural unit represented by the following general formula (1B).

[0050] General formula (1B)

Chemical formula

[0051] 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. In particular, n is preferably 3.

[0052] The alkylene structural unit preferably includes a structural unit represented by the following general formula (1C).

[0053] General formula (1C)

Chemical formula

[0054] 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, and still more preferably an integer of 2 or less. In particular, n is preferably 2.

[0055] The method for introducing an alkylene structural unit into a polymer is not particularly limited, and examples thereof include the following methods (1a) or (1b).

[0056] In the method of (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, the "monomer units derived from the conjugated diene monomer" may be referred to as "conjugated diene monomer units", and the same may be omitted for monomer units derived from other monomers. Next, by hydrogenating the conjugated diene monomer units, at least a part of the conjugated diene monomer units is converted into alkylene structural units. In this specification, "hydrogenation" may be referred to as "hydrogen addition". The finally obtained polymer contains units obtained by hydrogenating conjugated diene monomer units as alkylene structural units.

[0057] Note that the conjugated diene monomer units at least include monomer units having one carbon-carbon double bond. For example, the 1,3-butadiene monomer units, which are conjugated diene monomer units, include 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 include two or more types of monomer units. Further, the conjugated diene monomer units may be monomer units having no carbon-carbon double bond and further include monomer units containing a branch point. In this specification, the "branch point" refers to the branch point in a branched polymer. When the conjugated diene monomer units include monomer units containing a branch point, the above-prepared polymer is a branched polymer.

[0058] 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.

[0059] Among these, the method of (1a) is preferred because the polymer can be easily produced. The number of carbon atoms in the conjugated diene monomer is 4 or more, preferably 4 or more and 6 or less. 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 includes a structural unit obtained by hydrogenating a conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and more preferably includes 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.

[0060] 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.

[0061] The hydrogenation can be carried out by a usual method. For example, the hydrogenation can be carried out by treating a polymer having a conjugated diene monomer unit with hydrogen gas in the presence of a hydrogenation catalyst in a state where it is dissolved in an appropriate solvent. Examples of the hydrogenation catalyst include iron, nickel, palladium, platinum, copper, etc.

[0062] In the method of (1b), the number of carbon atoms in the α-olefin monomer is 2 or more, preferably 3 or more, and more preferably 4 or more. The number of carbon atoms in the α-olefin monomer is preferably 6 or less, and more preferably 5 or less. 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.

[0063] 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 consisting only of a linear alkylene structure and a structural unit consisting only of a branched alkylene structure, and still more preferably contains at least one selected from the group consisting of the structural unit represented by the above formula (1B) and the structural unit represented by the above formula (1C).

[0064] The alkylene structural unit may contain a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure. When the alkylene structural unit contains a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, the content of the branched alkylene structure is preferably 70% by mass or less, more preferably 65% by mass or less, based on the mass of the alkylene structural unit (that is, when the mass of the alkylene structural unit is 100% by mass). In particular, it is preferably 20% by mass or less, more preferably 18% by mass or less, and still more preferably 15% by mass or less. When the polymer contains a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, the content of the branched alkylene structure is, for example, 1% by mass or more, may be 5% by mass or more, and may further be 10% by mass or more, based on the mass of the alkylene structural unit (that is, when the mass of the alkylene structural unit is 100% by mass).

[0065] In the aliphatic hydrocarbon structural unit, 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 units (that is, when the mass of the aliphatic hydrocarbon structural units is 100% by mass). The content of the alkylene structural unit is, based on the total mass of the aliphatic hydrocarbon structural units (that is, when the mass of the aliphatic hydrocarbon structural units is 100% by mass), 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.

[0066] 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 (that is, when the mass of the polymer is 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, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass).

[0067] The nitrile group-containing structural unit is a structural unit containing a nitrile group, preferably contains a structural unit containing an alkylene structure substituted by a nitrile group, and more preferably contains a structural unit consisting only of an alkylene structure substituted by a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The nitrile group-containing structural unit may further contain (or consist only of) a structural unit containing an alkyl structure substituted by a nitrile group. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably 1.

[0068] The nitrile group-containing structural unit preferably contains a structural unit represented by the following general formula (2A).

[0069] General formula (2A) [Chemical formula]

[0070] In the 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. In particular, n is preferably 2.

[0071] The nitrile group-containing structural unit preferably includes a structural unit represented by the following general formula (2B).

[0072] General formula (2B) [Chemical formula]

[0073] In the general formula (2B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom.

[0074] The method for introducing the nitrile group-containing structural unit into the polymer is not particularly limited, but a method of preparing a polymer by a polymerization reaction using a monomer composition containing a nitrile group-containing monomer (method (2a)) can be preferably used. The finally obtained polymer contains a nitrile group-containing monomer unit as a nitrile group-containing structural unit. Examples of the nitrile group-containing monomer capable of forming a nitrile group-containing structural unit include monomers containing a polymerizable carbon-carbon double bond and a nitrile group. For example, α,β-ethylenically unsaturated group-containing compounds having a nitrile group can be mentioned, and specifically, acrylonitrile, methacrylonitrile, etc. can be mentioned. In particular, from the viewpoint of enhancing the intermolecular force between polymers and / or between a polymer and a dispersed substance (adsorbed substance), the nitrile group-containing monomer preferably contains acrylonitrile. The nitrile group-containing monomer can be used alone or in combination of two or more.

[0075] 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 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, based on the mass of the polymer (that is, when the mass of the polymer is 100% by mass). By setting 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. Also, the affinity of the polymer to the electrolyte can be controlled, and problems such as the polymer dissolving in the electrolyte and increasing the resistance of the electrolyte in the battery can be prevented.

[0076] The polymer may contain any structural unit. Examples of the arbitrary structural unit include an amide group-containing structural unit and a carboxy group-containing structural unit.

[0077] As a preferred embodiment of the polymer, there is a polymer in which the total content of the aliphatic hydrocarbon structural unit and the nitrile group-containing structural unit contained in the polymer is 80% by mass or more and 100% by mass or less based on the mass of the polymer. 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.

[0078] In this specification, the content of the structural unit can be determined using the amount of the monomer used, NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurements.

[0079] 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. Also, it is 80 or less, preferably 70 or less. In this specification, "Mooney viscosity (ML 1+4, "(at 100 °C)" can be measured at a temperature of 100 °C in accordance with JIS K6300-1. By setting the Mooney viscosity within the above range, it is considered that an appropriate repulsive force can be provided in the state adsorbed to the conductive material, and the dispersion stability can be enhanced. If it is below the above range, there is a concern that the solubility in the solvent increases and the balance between the conductive material and the dispersion medium deteriorates. Also, 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 the energy transfer efficiency of the dispersing machine decreases, or metal foreign substances mixed in from the raw materials cannot be efficiently removed by methods such as iron removal with a magnet, filtration, or centrifugation, and the battery performance may decrease due to the remaining metal foreign substances.

[0080] 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 and content of structural units, hydrogenation rate, etc.), structure (linearity, etc.), molecular weight, preparation conditions (polymerization temperature, amount of molecular weight regulator, etc.), etc. Specifically, the Mooney viscosity of the polymer can be adjusted by the following methods. In the method of (2a), the Mooney viscosity is decreased by increasing the amount of the molecular weight regulator used in the preparation of the polymer. In the method of (2b), the Mooney viscosity of the polymer is decreased by adding a base and modifying it by hydrolyzing the nitrile groups contained in the nitrile group-containing structural units of the polymer. In the method of (2c), the Mooney viscosity is decreased by applying a mechanical shear force to the polymer.

[0081] In the method of (2b), the decrease in Mooney viscosity can be achieved by mixing a polymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing monomer unit, a base, and a solvent. Further, optional components may be mixed. There is no limitation on the order of addition of the polymer, base, and solvent to the container and the mixing method, and these may be added to the container simultaneously; the polymer, base, and solvent may be added to the container separately; or either one or both of the polymer and the base may be mixed with the solvent to prepare a polymer-containing liquid and / or a base-containing liquid, and the polymer-containing liquid and / or the base-containing liquid may be added to the container. In particular, since the nitrile group can be efficiently modified, a method of adding a base dispersion in which the base is dispersed in the solvent to a polymer solution in which the polymer is dissolved in the solvent while stirring is preferred. For stirring, a disper (dispersion machine) or a homogenizer can be used. As the solvent, the solvents described later can be used.

[0082] In addition to being used in the method of (2b), it is preferable to contain a base in the resin composition because it can improve the wettability of CNT to the dispersion medium and improve the dispersibility, or improve the dispersion stability. As the base to be added, at least one selected from the group consisting of inorganic bases, inorganic metal salts, organic bases, and organic metal salts can be used.

[0083] Examples of the inorganic base and the inorganic metal salt include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates of an alkali metal or an alkaline earth metal; and ammonium hydroxide and the like. Among these, from the viewpoint of easily supplying cations, hydroxides or alkoxides of an alkali metal or an alkaline earth metal are preferred. Examples of the hydroxide of an alkali metal include lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Examples of the hydroxide of an alkaline earth metal include calcium hydroxide, magnesium hydroxide and the like. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. Note that the metal contained in the inorganic base may be a transition metal.

[0084] Examples of the organic base include primary, secondary, and tertiary amine compounds (such as alkylamines and aminoalcohols) having 1 to 40 carbon atoms which may have substituents, or organic hydroxides.

[0085] Examples of the primary alkylamine having 1 to 40 carbon atoms which may have substituents include alkylamines such as propylamine, butylamine, isobutylamine, octylamine, 2-ethylhexylamine, laurylamine, stearylamine, oleylamine; aminoalcohols such as 2-aminoethanol and 3-aminopropanol; and 3-ethoxypropylamine, 3-lauryloxypropylamine, etc.

[0086] Examples of the secondary alkylamine having 1 to 40 carbon atoms which may have substituents include alkylamines such as dibutylamine, diisobutylamine, N-methylhexylamine, dioctylamine, distearylamine; and aminoalcohols such as 2-methylaminoethanol.

[0087] Examples of the tertiary alkylamine having 1 to 40 carbon atoms which may have substituents include alkylamines such as triethylamine, tributylamine, N,N-dimethylbutylamine, N,N-diisopropylethylamine, dimethyloctylamine, trioctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dilaurylmonomethylamine; and triethanolamine, 2-(dimethylamino)ethanol, etc.

[0088] An 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, and the like. Among these, it is particularly preferable to use at least one selected from the group consisting of trimethyl-2-hydroxyethylammonium hydroxide and tetramethylammonium hydroxide. 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.

[0089] Examples of the organometallic salt include alkoxides of alkali metals and acetates of alkali metals. Examples of the alkoxide of an alkali metal include lithium methoxide, lithium ethoxide, lithium propoxide, lithium-t-butoxide, lithium-n-butoxide, sodium methoxide, sodium ethoxide, sodium propoxide, sodium-t-butoxide, sodium-n-butoxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium-t-butoxide, potassium-n-butoxide, and the like. Among these, sodium-t-butoxide is preferable from the viewpoint of easily supplying a cation. Note that the metal contained in the inorganic base may be a transition metal.

[0090] 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 even more preferably 10% by mass or less, based on the mass of the polymer. If the amount used is too small, the Mooney viscosity tends not to decrease easily. If the amount used is too large, it may cause corrosion of the dispersing device and / or inside the battery.

[0091] The method of (2c) above may be adjusted by applying mechanical shear force when preparing a polymer containing a nitrile group-containing monomer unit and an aliphatic hydrocarbon structural unit, or a polymer already prepared containing a nitrile group-containing monomer unit and an aliphatic hydrocarbon structural unit may be dissolved in a solvent capable of dissolving it, and then adjusted by applying mechanical shear force. The Mooney viscosity can also be reduced by applying mechanical shear force to the polymer before dissolution using a roll, kneader, etc., but since the polymer is used more efficiently as a dispersant in a state dissolved in a solvent capable of dissolving it, it is more preferable to apply shear force in the polymer solution state.

[0092] Examples of the method of applying shear force in the polymer solution state include methods using dispersing means such as a homogenizer and a Silverson mixer. Shear force can also be applied using a disper, etc., but it is preferable to use dispersing means such as a homogenizer and a Silverson mixer that can apply a higher shear force. Examples of the method of applying mechanical shear force to the polymer before dissolution include methods using dispersing means such as a kneader and a two-roll mill.

[0093] In addition to the dispersant described above, 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 by the method (2b) of the polymer described above. These are preferably in a total amount of 0.001 to 0.1% by mass, more preferably 0.005 to 0.05% by mass, based on the total amount of the resin composition.

[0094] <Dispersion medium> The resin composition contains a dispersion medium. The dispersion medium is not particularly limited, but is preferably a high dielectric constant solvent, and preferably contains a solvent composed of any one of high dielectric constant solvents or a mixed solvent composed of two or more kinds. Further, one or two or more other solvents may be mixed with the high dielectric constant solvent and used.

[0095] Examples of the high dielectric constant solvent include amide-based (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic-based (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxide-based (dimethyl sulfoxide, etc.), sulfone-based (hexamethylphosphoramide, sulfolane, etc.), lower ketone-based (acetone, methyl ethyl ketone, etc.), carbonate-based (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate), and others such as tetrahydrofuran, urea, and acetonitrile can be used. As the dispersion medium, it is preferably an amide-based organic solvent, and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. The relative dielectric constant of the high dielectric constant solvent can be the value described in a solvent handbook or the like, and is preferably 2.5 or more at 20°C.

[0096] <Fluororesin> The resin composition contains a fluororesin. The fluororesin is a resin containing fluorine, is excellent in heat resistance, chemical resistance, and adhesiveness, and functions as a binder resin. The fluororesin preferably has a structure in which the hydrogen of polyethylene is substituted with fluorine or trifluoromethyl. Examples of the fluororesin include homopolymers such as polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVdF), polychlorotrifluoroethylene (PCTFE), etc.; copolymers such as perfluoroalkoxyalkane (PFA), perfluoroethylene propene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), tetrafluoroethylene-perfluorodioxole copolymer (TPE / PDD), etc. These may be used alone or in combination of two or more. Among the fluororesins, polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVdF), resins having these structural units, modified products thereof, or combinations thereof are preferable from the viewpoint of resistance. Among them, polyvinylidene fluoride-based resins are preferable, and examples include homopolymers of polyvinylidene fluoride; copolymers of vinylidene fluoride and hexafluoropropylene, tetrafluoroethylene, etc. The polyvinylidene fluoride-based resin may be modified, and for example, an acidic group such as a carboxy group may be introduced. The fluororesin may be used alone or in combination of two or more.

[0097] The weight average molecular weight (Mw) of the fluororesin is preferably from 1,000,000 to 5,000,000, more preferably from 200,000 to 3,000,000, and even more preferably from 500,000 to 1,500,000 in order to maintain a good balance between resistance and adhesion and resin viscosity. The glass transition point of the fluororesin is preferably 20°C or lower, more preferably 10°C or lower, and even more preferably 0°C or lower from the viewpoint of the film-forming property of the electrode film.

[0098] Examples of commercially available polyvinylidene fluoride and its modified products include, for example, 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 Kuraray Co., Ltd., 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).

[0099] The resin composition may contain a binder resin other than the fluororesin and the resin-type dispersant. Other binder resins are not particularly limited as long as they are usually used as the binder resin for paints, and can be appropriately selected according to the purpose. The binder resin used in the resin composition is preferably a resin that can bind between active substances, substances such as CNT, etc. Examples of the binder resin used in the resin composition include polymers or copolymers containing, as structural units, ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, etc.; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins; elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Also, modified products, mixtures, and copolymers of these resins may be used, and they may be used alone or in combination of two or more.

[0100] <Resin Composition> The resin composition contains carbon nanotubes, a dispersant, a fluororesin, and a dispersion medium. The resin composition may, as necessary, appropriately contain optional components such as wetting agents, surfactants, pH adjusters, wetting and penetrating agents, leveling agents, and other additives, other conductive materials, resin components such as other binder resins, etc., within a range that does not inhibit 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 resin composition for a secondary battery electrode means the one in the state before the active material is added. In this regard, the resin composition for a secondary battery electrode is distinguished from the composite slurry containing the active material. That is, the resin composition for a secondary battery electrode substantially does not contain the active material. This is a concept excluding the state where the active material is intentionally added to the resin composition for a secondary battery electrode. The active material may be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, or 0% by mass, based on the total mass of the resin composition for a secondary battery electrode. The active material will be described later.

[0101] The dispersibility of CNTs in the resin composition can be evaluated by the complex elastic modulus and phase angle measured by dynamic viscoelasticity measurement. In this specification, the complex elastic modulus and phase angle of the resin composition 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 resin composition indicates the hardness of the resin composition, and tends to be smaller as the dispersibility of CNTs is better and as the resin composition has a lower viscosity. However, when the fiber length of CNTs is large, even if the CNTs are in a state of being uniformly and stably unraveled in the medium, due to the structural viscosity of the CNTs themselves, the complex elastic modulus may be a high value. Also, in addition to the dispersion state of CNTs, it also changes due to the entanglement of CNTs, the dispersant, the fluororesin, and other resin components, or the influence of intermolecular forces between them.

[0102] Also, the phase angle means the phase shift of the stress wave when the strain applied to the resin composition is a sine wave. In the case of a pure elastic body, it becomes a sine wave in phase with the applied strain, so the phase angle is 0°. On the other hand, in the case of a pure viscous body, it becomes a stress wave advanced by 90°. In a general sample for viscoelastic measurement, it becomes a sine wave with a phase angle greater than 0° and less than 90°. If the dispersion of CNTs in the resin composition is good, the phase angle approaches 90°, which is that of a pure viscous body. However, similar to the complex elastic modulus, when CNT itself has structural viscosity, even if the CNTs are uniformly and stably dispersed in the dispersion medium, the phase angle may be a low value. Also, similar to the complex elastic modulus, it changes due to the entanglement of CNTs, dispersants, fluororesins, and other resin components, or the influence of intermolecular forces between these, in addition to the dispersion state of CNTs.

[0103] In the resin composition, when the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is 30 or more and 5,000 or less, an electrode film can be obtained in which the resin composition has high concentration and high fluidity and has very good conductivity. The product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is preferably 30 or more, more preferably 50 or more, still more preferably 100 or more, and even more preferably 500 or more. Also, it is preferably 5,000 or less, more preferably 3,000 or less, still more preferably 1,500 or less, and even more preferably 1,000 or less. Preferably, the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is 50 or more and 3,000 or less, more preferably 100 or more and 1,500 or less, and still more preferably 500 or more and 1,000 or less.

[0104] The complex elastic modulus by dynamic viscoelasticity measurement of the resin composition is preferably 0.1 Pa or more, more preferably 0.3 Pa or more, still more preferably 0.4 Pa or more, even more preferably 0.5 Pa or more, and even more preferably 1 Pa or more. Further, it is preferably 300 Pa or less, more preferably 200 Pa or less, still more preferably 100 Pa or less, even more preferably 50 Pa or less, and even more preferably 30 Pa or less. More preferably, it is 0.1 Pa or more and 300 Pa or less.

[0105] The phase angle by dynamic viscoelasticity measurement of the resin composition is preferably 3° or more, more preferably 5° or more, still more preferably 10° or more, and particularly preferably 30° or more. Further, it may be 90° or less, preferably 88° or less, and more preferably 85° or less. More preferably, it is 3° or more and 90° or less, and still more preferably 5° or more and 88° or less. Further, it is preferable that the resin composition satisfies the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) within the above preferable range, and the complex elastic modulus and the phase angle by dynamic viscoelasticity measurement satisfy the above preferable ranges respectively.

[0106] 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 is formed. Therefore, it is not simply sufficient that the viscosity of the resin composition is low (apparent) and the dispersibility is good, but it is particularly effective to judge the dispersion state in combination with the complex elastic modulus and the phase angle and conventional indexes such as viscosity. By setting the complex elastic modulus and the phase angle within the above ranges, a resin composition with good conductivity and electrode strength can be obtained. For example, it is preferable that the resin composition satisfies the complex elastic modulus and the phase angle by dynamic viscoelasticity measurement of 0.1 Pa or more and 300 Pa or less and 3° or more and 90° or less respectively.

[0107] The median diameter (μm) of the resin composition is preferably 40 μm or less, more preferably 35 μm or less. Further, the median diameter (μm) of the resin composition is preferably 0.4 μm or more, preferably 5.0 μm or less, and 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, CNTs in an aggregated state exist, and if it exceeds the above range, a large number of finely cut CNTs are generated, making it difficult to efficiently form a conductive network.

[0108] The median diameter of the resin composition is measured using a particle size distribution measuring device. Specific measurement conditions are as follows: under the device conditions of "Partical LA-960V2" (trade name) manufactured by HORIBA, the operating conditions of circulation / ultrasound are set as follows: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 1, stirring mode: continuous. Also, during air evacuation, ultrasonic operation is performed at an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds. The refractive index of NMP is 1.470, and the refractive index of the carbon material is 1.92. The measurement is carried out after diluting the measurement sample so that the transmittance of the red laser diode is 60 - 80%, and the particle size standard is volume. More specifically, the median diameter can be measured by the method described in the examples.

[0109] The dispersibility of CNTs in the resin composition can also be evaluated by the gloss measured at 60° of the coating film obtained by coating on a smooth glass substrate and baking and drying (that is, the intensity of the reflected light at 60° with respect to the incident angle). The light incident on the coating film becomes smoother on the surface of the coating film as the dispersibility is better, so the gloss becomes higher. Conversely, as the dispersibility is worse, light scattering occurs due to the unevenness of the coating film surface, so the gloss becomes lower. 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. Also, it is preferably 120 or less, and more preferably 110 or less. By setting it within the above range, a resin composition in an appropriate dispersed state can be obtained. If it is below the above range, CNTs in an aggregated state exist, and if it exceeds the above range, a large number of finely cut CNTs are generated, making it difficult to form an efficient conductive network. In addition, the gloss of the coating film is also affected by the crystallinity or smoothness of the dispersant in addition to the dispersibility of CNTs, so it is better to judge relatively.

[0110] The viscosity of the resin composition 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 even more preferably 10 mPa·s or more and less than 2000 mPa·s, measured at 25°C and 60 rpm using a B-type viscometer.

[0111] 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 with 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 even more preferably 1.0 or more and less than 5.0. The higher the TI value, the greater the structural viscosity caused by the entanglement of CNTs, dispersants, fluororesins, and other resin components, or the intermolecular forces between them, and the lower the TI value, the smaller the structural viscosity. By setting the TI value within the above range, it is possible to suppress the entanglement of CNTs, dispersants, fluororesins, and other resin components while allowing the intermolecular forces between them to act appropriately.

[0112] The average fiber length of CNTs in the resin composition is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. Also, it is preferably 20 μm or less, more preferably 10 μm or less. The average fiber length of CNTs in the resin composition can be calculated by observing a sample obtained by dropping a 50-fold dilution of the resin composition with a non-aqueous solvent such as NMP onto a substrate and drying it with a scanning electron microscope, selecting any 300 CNTs in the observation photograph, measuring the fiber length of each, and averaging them.

[0113] 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 to 50 μm, more preferably 0.5 to 40 μm, and even more preferably 1 to 40 μm. When the average fiber length of CNTs in the resin composition containing single-walled carbon nanotubes is within the above range, a good conductive network can be formed. 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 fiber lengths of all the carbon nanotubes contained in the resin composition.

[0114] The content of CNTs in the resin composition is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the total amount of the resin composition. Also, it is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and most preferably 5% by mass or less. By setting it within the above range, the occurrence of sedimentation and gelation can be suppressed, and on the other hand, CNTs can be present well and stably. More preferably, it is 0.1 to 20% by mass, and even more preferably 0.5% by mass or more and 15% by mass or less.

[0115] In the resin composition, the mass ratio of the dispersant to the carbon nanotube is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.1 or more. Also, it is preferably 2 or less, more preferably 1 or less, and even more preferably 0.5 or less. By setting it within the above range, the dispersion stability of CNT can be further enhanced. More preferably, it is 0.01 or more and 2 or less, and even more preferably 0.1 or more and 1 or less. The content of the dispersant in the resin composition is preferably 0.1 to 5% by mass, more preferably 0.4 to 1% by mass, based on the total amount of the resin composition.

[0116] In the resin composition, the mass ratio of the fluororesin to the carbon nanotube is preferably 0.1 or more, more preferably 0.5 or more. Also, it is preferably 10 or less, more preferably 5 or less. By setting it within the above range, the occurrence of sedimentation and gelation can be suppressed, and on the other hand, the resistance and adhesion of the electrode film can be sufficiently obtained. More preferably, it is 0.1 or more and 10 or less, and even more preferably 0.5 to 5. The content of the fluororesin in the resin composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and even more preferably 1 to 10% by mass, based on the total amount of the resin composition. When the resin composition contains other binder resins, the other binder resin is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, based on the total amount of the fluororesin and the other binder resins.

[0117] The resin composition preferably has a carbon nanotube content of 0.5% by mass or more and 15% by mass or less based on the total amount of the resin composition, a mass ratio of the dispersant to the carbon nanotube of 0.01 or more and 0.2 or less, and a mass ratio of the fluororesin to the carbon nanotube of 0.1 or more and 10 or less. In this range, by having the product of the complex elastic modulus and the phase angle measured by the dynamic viscoelasticity measurement of the resin composition be 30 or more and 5,000 or less, the dispersibility and fluidity of the resin composition can be further improved.

[0118] The solid content of the resin composition is preferably 0.2 to 40% by mass, more preferably 0.5 to 20% by mass, and even more preferably 1 to 10% by mass.

[0119] The manufacturing method of the resin composition is not particularly limited and can be obtained by mixing carbon nanotubes, a dispersant, a fluororesin, and a dispersion medium. For example, a method of producing by mixing and dispersing CNT, a dispersant, a fluororesin, and a dispersion medium all at once or in portions; a method of producing a CNT dispersion liquid containing CNT, a dispersant, and a dispersion medium, and then adding and mixing a fluororesin; a method of producing a dispersant solution containing a dispersant, a fluororesin, and a dispersion medium, and then adding and dispersing CNT, etc. can be mentioned. In any method, the dispersion treatment of CNT is not particularly limited, but various dispersion devices may be used. The dispersion treatment can arbitrarily adjust the addition timing of the materials used and can be a multi-stage treatment of two or more times. The fluororesin may be added in the form of powder or varnish.

[0120] From the viewpoint of the dispersion efficiency of CNT, it is advisable to mix and disperse CNT, a dispersant, and a dispersion medium to produce a CNT dispersion liquid, and then mix the CNT dispersion liquid and a fluororesin. The method of adding a fluororesin to the CNT dispersion liquid is not particularly limited. For example, a powdery fluororesin may be added to the CNT dispersion liquid and mixed. As another method, a varnish in which a fluororesin is dissolved in a non-aqueous solvent may be added to the CNT dispersion liquid and mixed. The non-aqueous solvent for the varnish is not particularly limited, and those that can be used in the resin composition may be used. The mixture obtained by adding a fluororesin to the CNT dispersion liquid may be stirred. For the stirring device, a disper, a homogenizer, etc. can be used. Also, the mixture may be heated during stirring to promote the dissolution of the fluororesin. The heating temperature may be 30 to 80°C. By adding a powdery fluororesin to the CNT dispersion liquid, the amount of the non-aqueous solvent does not increase during the addition of the fluororesin, so a resin composition with a higher concentration can be provided. By sufficiently enhancing the dispersibility of the CNT dispersion liquid before adding the fluororesin, even when adding a powdery fluororesin, a decrease in the fluidity and dispersibility of the resin composition can be prevented.

[0121] When using CNTs with different outer diameters in combination, since the wettability and dispersibility of the combined CNTs are different, it is preferable to separately prepare CNT dispersions obtained by mixing and dispersing CNTs, a dispersant, and a dispersion medium, and then mix the two previously prepared CNT dispersions with a fluororesin. As another method, a fluororesin solution in which one type of CNT is mixed into a varnish obtained by dissolving a fluororesin in a non-aqueous solvent may be added to and mixed with a CNT dispersion prepared using the other type of CNT. More specifically, when using single-walled carbon nanotubes and multi-walled carbon nanotubes in combination, a fluororesin solution in which single-walled carbon nanotubes are mixed into a varnish obtained by dissolving a fluororesin in a non-aqueous solvent may be added to and mixed with a CNT dispersion prepared using multi-walled carbon nanotubes. In the step of mixing carbon nanotubes, a dispersant, a fluororesin, and a dispersion medium, the mixing of single-walled carbon nanotubes and multi-walled carbon nanotubes with other components may be simultaneous.

[0122] <Dispersion method> Examples of the dispersion device include a kneader, a two-roll mill, a three-roll mill, a planetary mixer, a ball mill, a horizontal sand mill, a vertical sand mill, an annular bead mill, an attritor, a high-shear mixer, a high-pressure homogenizer, an ultrasonic homogenizer, etc. Among these, in order to finely disperse CNTs in a CNT dispersion or a resin composition and obtain suitable 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 perspective of promoting the wetting of CNTs and dissociating coarse particles, it is preferable to use a high-shear mixer in the initial stage of dispersion, and then, from the perspective of dispersing while maintaining the aspect ratio of CNTs, it is preferable to use a high-pressure homogenizer. The high-pressure homogenizer can enhance the dispersibility of CNTs by performing multi-stage circulation dispersion. Further, after dispersion with a high-pressure homogenizer, dispersion with a bead mill can homogenize the dispersion state while maintaining the fiber length. The pressure when using a high-pressure homogenizer is preferably 60 to 150 MPa, and more preferably 60 to 120 MPa.

[0123] Dispersion methods using a dispersion device include batch dispersion, pass-through dispersion, circulation dispersion, etc. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method of performing dispersion using only the main body of the dispersion device without using piping or the like. Since it is easy to handle, it is preferable when manufacturing in small quantities. Pass-through dispersion is a dispersion method in which the main body of the dispersion device is provided with a tank for supplying the liquid to be dispersed via a pipe and a tank for receiving the liquid to be dispersed, and the liquid to be dispersed is passed through the main body of the dispersion device. Circulation dispersion is a method in which the liquid to be dispersed that has passed through the main body of the dispersion device is returned to the tank for supplying the liquid to be dispersed and dispersed while being circulated. In all of these methods, the dispersion progresses as the processing time is lengthened. Therefore, it is only necessary to repeat the pass or circulation until the desired dispersion state is achieved, and the throughput can be increased by changing the size of the tank or the processing time. Pass-through dispersion is preferable in that it is easier to make the dispersion state uniform compared to circulation dispersion. Circulation dispersion is preferable in that the work and manufacturing equipment are simpler compared to pass-through dispersion. In the dispersion process, the crushing of agglomerated particles, the unraveling of the conductive material, wetting, stabilization, etc. proceed sequentially or simultaneously, and the final dispersion state differs depending on the manner of progress. Therefore, it is preferable 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.

[0124] Further, the resin composition can further contain carbon black, and the carbon black functions as a conductive material. The carbon black is preferably contained in the resin composition within 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 to 80% by mass, more preferably 1 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 a state containing a fluororesin. Furthermore, the carbon black is preferably 20% by mass or less, more preferably 15% by mass or less, based on the total mass of the resin composition.

[0125] 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. The stage of adding carbon black in the method for manufacturing this CNT dispersion is not particularly limited, and may be before, after, simultaneously with, or a combination of these in relation to the addition of carbon nanotubes. As another example of a method for manufacturing a resin composition containing carbon black, there is a method of adding carbon black before, after, simultaneously with, or a combination of these in relation to adding a binder resin to a CNT dispersion. In this method, it is preferable that carbon black is added in a state where carbon nanotubes are dispersed in the CNT dispersion. Alternatively, a combination of these methods may be used. That is, carbon black may be further added before, after, simultaneously with, or a combination of these in relation to adding a binder resin to a CNT dispersion containing carbon black.

[0126] <Carbon nanotube dispersion> Hereinafter, an example of a carbon nanotube dispersion prepared when manufacturing a resin composition will be described. Note that the resin composition having the above-described components and physical properties is not limited to those manufactured using the following CNT dispersion. The carbon nanotube dispersion contains carbon nanotubes, a dispersant, and a dispersion medium, and may appropriately contain optional components as long as the object of the present invention is not inhibited. The optional components can be added at any timing, such as before preparing the dispersion, during dispersion, after dispersion, or a combination of these. As the optional components, those described for the above resin composition can be used.

[0127] The CNT dispersion can be obtained by mixing and dispersing a composition containing CNT, a dispersant, and a dispersion medium. The method described above for the resin composition can be used for the dispersion treatment. The dispersion treatment of the CNT dispersion is preferably carried out until the particle size of the CNT dispersion becomes sufficiently small. For example, for the CNT dispersion after the dispersion treatment, the volume-based median diameter (μm) determined by a laser diffraction / scattering particle size distribution analyzer is preferably 40 μm or less, more preferably 35 μm or less. Further, the median diameter (μm) of the CNT dispersion is preferably 0.4 or more, preferably 5.0 or less, and more preferably 2.0 or less.

[0128] The dispersion treatment of the CNT dispersion is preferably carried out until the viscosity of the CNT dispersion is sufficiently reduced. For example, for the CNT dispersion after 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 5000 mPa·s, further preferably 10 mPa·s or more and less than 2000 mPa·s, and even more preferably 10 mPa·s or more and less than 1000 mPa·s.

[0129] The content of CNT is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, based on the total amount of the CNT dispersion. Also, it is preferably 20% by mass or less, more preferably 10% by mass or less. By setting it within the above range, CNT can be present well and stably. More preferably, it is 0.5 to 10% by mass. Also, the content of CNT is preferably adjusted appropriately so that a carbon nanotube dispersion with appropriate fluidity or viscosity can be obtained, depending on the specific surface area of CNT, the affinity for the dispersion medium, the dispersing ability of the dispersant, etc.

[0130] The content of the dispersant is preferably 5 to 200 parts by mass, more preferably 10 to 100 parts by mass, and even more preferably 15 to 80 parts by mass with respect to 100 parts by mass of CNT. The content of the dispersant is preferably 0.1 to 10% by mass, more preferably 0.5 to 6% by mass with respect to the total amount of the CNT dispersion. The solid content of the CNT dispersion is preferably 0.2 to 40% by mass, more preferably 0.5 to 20% by mass, and even more preferably 1 to 10% by mass.

[0131] <Method for manufacturing a composite slurry for a secondary battery electrode> The composite slurry for a secondary battery electrode can be obtained by adding an active material to the above-described resin composition. The composite slurry may appropriately contain other optional components within a range that does not inhibit the object of the present invention, if necessary. The optional components can be added at any timing, such as before the preparation of the composite slurry, during mixing, after mixing, or a combination thereof. The optional components may be those described in the above resin composition.

[0132] The active material may 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 may be simply referred to as "active material". The active material is a material that serves as the basis of the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material based on the electromotive force. The composite slurry is preferably in a slurry form in order to improve uniformity and processability.

[0133] <Positive electrode active material> The positive electrode active material is not particularly limited. For example, for 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, lithium manganese composite oxide (e.g., Li x Mn 2 O 4 or LixMnO 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., Li x Ni 1-y Co y O 2 ), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O 2 ), lithium nickel manganese cobalt composite oxide (e.g., Li x Ni y Co z Mn 1-y-z O 2 ), spinel-type lithium manganese nickel composite oxide (e.g., Li x Mn 2-y Ni y O 4 ), etc., composite oxide powders of lithium and transition metals, lithium phosphate powders having an olivine structure (e.g., Li x FePO 4 , Li x Fe 1-y Mn y PO 4 , Li x CoPO 4 etc.), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxides (e.g., V 2 O 5 , V 6 O 13 ), transition metal oxide powders such as titanium oxide, iron sulfate (Fe 2 (SO 4 ) 3 ), TiS 2, and transition metal sulfide powders such as FeS, etc. However, x, y, and z are numbers, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and 0 < y + z < 1. These positive electrode active materials can also be used alone 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 become highly basic due to components derived from raw materials or elution of metal ions, and as a result, gelation of the binder resin and deterioration of the dispersion state are likely to occur. Therefore, in the case of a battery containing an active material containing Ni and / or Mn, this embodiment is particularly effective.

[0134] <Negative electrode active material> The negative electrode active material is not particularly limited. For example, it can be metal Li that can reversibly dope or intercalate lithium ions, or its alloy, tin alloy, silicon alloy negative electrode, Li X TiO 2 , Li X 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 poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials can be used. However, x is a number, where 0 < x < 1. These negative electrode active materials can also be used alone or in combination of two or more. In particular, when using a silicon alloy negative electrode, although the theoretical capacity is large, 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-fired carbon materials.

[0135] 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 even more preferably 0.05% or more, based on the mass of the active material (assuming the mass of the active material is 100% by mass). Also, it is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. If it exceeds the above range, the filling amount of the active material in the electrode will decrease, leading to a decrease in the battery capacity. On the other hand, if it is below the above range, the conductivity of the electrode and the battery may be insufficient.

[0136] 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). Also, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[0137] 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). Also, it is preferably 20% by mass or less, more preferably 10% by mass or less.

[0138] 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). Also, it is preferably 90% by mass or less, more preferably 85% by mass or less.

[0139] As a method for preparing the composite material slurry, a method in which a binder resin is added to a CNT dispersion liquid to prepare a resin composition, and then an active material is further added to the resin composition and stirred is preferred. The stirring device used for stirring is not particularly limited. For the stirring device, a disper, a homogenizer, etc. can be used.

[0140] In addition, the composite material slurry can 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. With respect to the total mass of the carbon black and the carbon nanotubes, the carbon nanotubes are preferably 1 to 80% by mass, more preferably 1 to 50% by mass. Within these ranges, the dispersion state of the carbon nanotubes can be controlled, and high dispersibility and fluidity can be better maintained in a state containing the fluororesin. Furthermore, the carbon black is preferably 10% by mass or less, more preferably 5% by mass or less, based on the total mass of the composite material slurry. The method for producing the composite material slurry includes adding an active material to the resin composition for a secondary battery electrode, and can include further adding carbon black before, after, simultaneously with, or in combination of these, to the resin composition before adding the active material. Alternatively, an active material may be added to the resin composition for a secondary battery electrode that precontains carbon black, or an active material and carbon black may be further added to the resin composition for a secondary battery electrode that precontains carbon black.

[0141] <Electrode film> The electrode film is formed by forming the composite material slurry into a film shape and contains CNT, a dispersant, a fluororesin, and an active material. The electrode film may further contain optional components. The electrode film can be obtained by adding an active material to the above-described resin composition to prepare a composite material slurry 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.

[0142] The material and shape of the current collector are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, or stainless steel. Also, as the shape, generally, a foil on a flat plate is used, but those with a roughened surface, perforated foil-shaped ones, and mesh-shaped current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0143] As a method for applying the composite material slurry onto the current collector, there is no particular limitation, and known methods can be used. Specifically, methods such as die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method, gravure coating method, screen printing method, or electrostatic coating method can be mentioned. As the 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.

[0144] After applying the composite material slurry, rolling treatment may be performed using a lithographic press, calendar roll, or the like. 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.

[0145] <Secondary battery> 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 above-described electrode film. In the manufacturing method of the secondary battery, for example, at least one of the positive electrode and the negative electrode is produced by applying a composite material slurry containing an active material onto a current collector to form an electrode film, and the composite material slurry is produced by adding an active material to the above-described resin composition for a secondary battery electrode.

[0146] As the positive electrode, one obtained by applying and drying a composite material slurry containing a positive electrode active material on a current collector to form an electrode film can be used. As the negative electrode, one obtained by applying and drying a composite material slurry containing a negative electrode active material on a current collector to form an electrode film can be used. The above-described materials can be used for the positive electrode active material and the negative electrode active material. The composite material slurry can be produced according to the above-described method.

[0147] The electrolyte may be any 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.

[0148] As the electrolyte salt, various conventionally known ones 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 N, LiC 4 F 9 SO 3 , Li(CF 3 SO 2 ) 3 C, LiI, LiBr, LiCl, LiAlCl, LiHF 2 , LiSCN, or LiBPh 4 (where Ph is a phenyl group), etc. Lithium salts are exemplified, but not limited thereto. The electrolyte salt is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0149] The non-aqueous solvent is not particularly limited. For example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile, etc. These solvents may be used alone or in combination of two or more.

[0150] The secondary battery preferably includes a separator. Examples of the separator include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics subjected to hydrophilic treatment thereof.

[0151] The structure of the secondary battery is not particularly limited. Usually, it includes a positive electrode and a negative electrode, and a separator provided as needed, and can have various shapes according to the purpose of use, such as a paper type, a cylindrical type, a button type, a laminated type, etc.

Examples

[0152] The present invention will be described more specifically with reference to the following examples. The present invention is not limited to the following examples as long as the gist thereof is not exceeded. Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass".

[0153] <Manufacture of Dispersant> (Production Example 1 Production of H-NBR1) Into a stainless steel polymerization reactor, 32 parts of acrylonitrile, 68 parts of 1,3-butadiene, 3 parts of potassium oleate soapstone, 0.3 part of azobisisobutyronitrile, 0.48 part of t-dodecyl mercaptan, and 200 parts of ion-exchanged water were added. Under a nitrogen atmosphere, polymerization was carried out at 45 °C for 20 hours with stirring, and the 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 an autoclave equipped with a stirrer with a volume of 1 L, and nitrogen gas was flowed for 10 minutes to remove dissolved oxygen in the content. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water to which nitric acid four times the molar amount of palladium was added was added to the autoclave. After replacing the inside of the autoclave with hydrogen gas twice, the content of the autoclave was heated to 50 °C under a pressure of up to 3 MPa with hydrogen gas, and a hydrogenation reaction was carried out for 6 hours. Then, the content was returned to room temperature, the inside of the autoclave was made into a nitrogen atmosphere, and the solid content was dried to obtain a dispersant (H-NBR1). The Mooney viscosity (ML 1+4 , 100 °C) (measured using an L-shaped rotor at a temperature of 100 °C in accordance with Japanese Industrial Standard JIS K6300-1) was 44. Also, the hydrogenation rate (calculated from infrared spectroscopic analysis by the total reflection measurement method) was 0.7%.1 The structural unit derived from acrylonitrile determined from the H-NMR quantitative spectrum was 32%.

[0154] (Production Example 2 Production of PAN) The dispersant (A-6: acrylonitrile / hydroxyethyl acrylate = 90 / 10, weight average molecular weight 15,000) described in paragraph (0078) of JP 2020-163362 A was produced. The obtained dispersant is hereinafter referred to as PAN.

[0155] (Purification treatment of carbon nanotubes) (Production Example 3 Production of 100T-P) To 1 g of carbon nanotubes (K-Nanos 100T: manufactured by Kumho Petrochemical), 5 g of water was added, and then stirred with a Henschel mixer to obtain granular carbon nanotubes (particle size of about 7 mm). The granular carbon nanotubes were spread out in a vat and dried in a vacuum hot air oven at 100 °C for 7 hours to obtain compressed CNT. The obtained compressed CNT was placed in a ceramic crucible and placed in a firing furnace. The inside of the furnace was evacuated to 1 Torr or less and then heated to 1000 °C. Carbon tetrachloride gas at 0.3 L per minute was introduced until the pressure inside the furnace reached 90 Torr, and then the temperature inside the furnace was raised to 1600 °C and held for 1 hour. Subsequently, after stopping the heater, the pressure was slowly reduced to 1 Torr and allowed to cool to room temperature. The vacuum inside the furnace was released, and the purified carbon nanotubes (100T-P) were recovered from the crucible.

[0156] (Production of single-layer CNT resin composition) (Production Example 4 Production of TUBALL-F) Add 97.6 parts of N-methyl-2-pyrrolidone (NMP) to a stainless steel container, and while stirring with a disper, add 2.0 parts of polyvinylidene fluoride resin (Solef 5130, manufactured by Solvay), and stir with a disper until the polyvinylidene fluoride resin dissolves. Then, weigh 0.4 part of single-walled carbon nanotubes (TUBALL: manufactured by OCSiAl, carbon purity 93%), add while stirring with a disper, attach a square-hole high-shear screen to a high-shear mixer (L5M-A, manufactured by SILVERSON), and perform batch dispersion at a speed of 8,600 rpm until the whole becomes uniform. Subsequently, supply the dispersion liquid from the stainless steel container to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) through a pipe, and perform the pass-type dispersion treatment 5 times to obtain a single-walled carbon nanotube resin composition (TUBALL-F). The dispersion treatment was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 60 MPa.

[0157] In the examples and comparative examples, in addition to the dispersants produced in Production Examples 1 and 2, the following dispersants were used. · H-NBR2: Therban(R) 3406 (manufactured by ARLANXEO, hydrogenated acrylonitrile-butadiene rubber) · H-NBR3: Therban(R) AT 3404 (manufactured by ARLANXEO, hydrogenated acrylonitrile-butadiene rubber) · H-NBR4: Zetpole 2000L (manufactured by Nippon Zeon, hydrogenated acrylonitrile-butadiene rubber) · PVP: Polyvinylpyrrolidone K-15 (manufactured by ISP) · PVA: Kuraray POVAL 3-86SD (manufactured by Kuraray, modified polyvinyl alcohol)

[0158] In the examples and comparative examples, in addition to the carbon nanotubes produced in Production Example 3, the following carbon nanotubes were used. · 100T: K-Nanos 100T (manufactured by Kumho Petrochemical, multi-walled CNT, average outer diameter 13 nm, specific surface area 210 m 2 / g) · BT1001M: LUCAN BT1001M (manufactured by LG Chem Ltd, multi-walled CNT, average outer diameter 13 nm, specific surface area 250 m 2 / g) · 10B: JENOTUBE10B (manufactured by JEIO, multi-walled CNT, average outer diameter 10 nm, specific surface area 230 m 2 / g) · 8B: JENOTUBE8B (manufactured by JEIO, multi-walled CNT, average outer diameter 8 nm, specific surface area 300 m 2 / g) · 6A: JENOTUBE6A (manufactured by JEIO, multi-walled CNT, average outer diameter 6 nm, specific surface area 700 m 2 / g) · TUBALL: single-walled carbon nanotube (manufactured by OCSiAl, average outer diameter 1.6 nm, carbon purity 93%, specific surface area 975 m 2 / g)

[0159] In the examples and comparative examples, the following conductive materials were used in addition to the carbon nanotubes. · Super-P (manufactured by IMERYS Graphite & Carbon, conductive carbon black, BET specific surface area 62 m 2 / g)

[0160] In the examples and comparative examples, the following binders were used. · S-5130: solef5130 (manufactured by solvay, polyvinylidene fluoride resin) · W#7300: KF polymer W#7300 (manufactured by Kureha, polyvinylidene fluoride resin) · W#7200: KF polymer W#7200 (manufactured by Kureha, polyvinylidene fluoride resin) · W#1300: KF polymer W#1300 (manufactured by Kureha, polyvinylidene fluoride resin) · W#9300: KF polymer W#9300 (manufactured by Kureha, polyvinylidene fluoride resin)

[0161] <Preparation of resin composition> (Example 1-1) According to the materials and compositions shown in Table 1, the materials excluding the binder were sequentially added to prepare a carbon nanotube dispersion as follows. First, NMP was placed in a stainless steel container and heated to 50°C. While stirring with a disper, a dispersant and an additive were added, and then stirred for 1 hour to dissolve the dispersant. Subsequently, CNT was added while stirring with a disper, a square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,000 rpm until the whole became uniform and the dispersion particle size became 250 μm or less as measured by a grind gauge with a maximum groove depth of 300 μm. At this time, the dispersion particle size confirmed by the grind gauge was 180 μm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) through a pipe, and a circulation-type 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. After dispersing until the viscosity at 60 rpm measured with a B-type viscometer (manufactured by TOKI SANGYO, VISCOMETER, MODEL: BL) of the dispersion liquid became 3,000 mPa·s or less, a pass-type dispersion treatment was performed with the high-pressure homogenizer according to the number of passes shown in Table 1 to obtain a carbon nanotube dispersion liquid. Subsequently, it was heated to 50°C, and the binder was added in small portions in full while stirring with a disper. It was stirred for 2 hours to dissolve the whole amount of the binder, and Resin Composition 1 was obtained.

[0162] (Examples 1-2 to 1-25) Resin Compositions 2 to 25 were obtained in the same manner as in Example 1-1 except that they were changed according to the materials, compositions, and number of passes shown in Table 1. In the preparation of Resin Composition 24, 6A and TUBALL were added simultaneously when adding CNT. In the preparation of Resin Composition 25, Super-P of other conductive materials was added simultaneously with 6A and TUBALL when adding CNT.

[0163] (Example 1-26) A resin composition 26 was obtained in the same manner as in Example 1-1, except that the binder was previously dissolved in NMP and used as an 8% solution. When preparing the carbon nanotube dispersion, the NMP used for dissolving the binder was set aside to adjust the final composition.

[0164] (Example 1-27) A carbon nanotube dispersion was prepared in the same manner as in Example 1-18, except that no binder was added. Then, 100 parts of the carbon nanotube dispersion was placed in a stainless steel container, and 80 parts of the single-walled CNT resin composition (TUBALL-F) prepared in Production Example 4 was added to 100 parts of the carbon nanotube dispersion, and stirred with a disper until uniform to obtain a resin composition 27.

[0165] (Example 1-28) A resin composition 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 disper, a dispersant and an additive were added, and then stirred for 1 hour to dissolve the dispersant. The CNT and the binder were tumbled in a powder state and then added to the dispersant solution while stirring with a disper. A square-hole high-shear screen was attached to 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 became 250 μm or less as measured by a grind gauge with a maximum groove depth of 300 μm. Subsequently, in the same manner as the preparation process of the carbon nanotube dispersion in Example 1-1, a pass-type dispersion treatment was performed with a high-pressure homogenizer to obtain a resin composition 28.

[0166] (Examples 1-29 to 1-31) Resin compositions 29 to 31 were obtained in the same manner as in Example 1-28, except that the dispersants shown in Table 1 were used.

[0167] (Example 1-32) According to the materials and compositions shown in Table 1, a resin composition was prepared as follows. NMP was placed in a stainless-steel container and heated to 50 °C. While stirring with a disper, a dispersant, an additive, and a binder were added, and then stirred for 1 hour to dissolve. CNT was added to the dispersant solution while stirring with a disper. A square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 8,000 rpm until the whole became uniform and the dispersion particle size became 250 μm or less as measured by a grind gauge with a maximum groove depth of 300 μm. Hereinafter, in the same manner as the production process of the carbon nanotube dispersion liquid of Example 1-1, a pass-type dispersion treatment was performed with a high-pressure homogenizer to obtain a resin composition 32.

[0168] (Comparative Example 1-1) According to the materials and compositions shown in Table 1, a comparative resin composition 1 was obtained in the same manner as in Example 1-1, except that the number of passes of the high-pressure homogenizer was changed to 10 times.

[0169] (Comparative Example 1-2) According to the materials and compositions shown in Table 1, a comparative resin composition 2 was obtained in the same manner as in Example 1-13, except that the number of passes of the high-pressure homogenizer was changed to 15 times.

[0170] (Comparative Example 1-3) In Example 1-1, instead of using a high-pressure homogenizer for dispersion, a bead mill (manufactured by Asizawa, Star Mill LMZ06, bead diameter 1.0 mm, bead filling rate 80%) was used for dispersion to obtain a comparative resin composition 3. The number of passes was set to 25 times.

[0171]

Table 1

[0172] The additives described in Table 1 are as follows. · NaOH: Sodium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd., purity > 98.0%, granular) · Aminoethanol: 2-Aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd., purity > 99.0%) · t-BuONa: Sodium t-butoxide (manufactured by Tokyo Chemical Industry Co., Ltd., purity > 98.0%)

[0173] <Evaluation of resin composition> (Method for measuring particle size) The presence or absence and particle size of coarse particles in the resin composition were determined by a determination method in accordance with JIS K5600-2-5 using a grind gauge with a maximum groove depth of 100 μm. Particle size judgment criteria ◎: Less than 20 μm 〇: 20 μm or more and less than 50 μm △: 50 μm or more and less than 90 μm ×: 90 μm or more

[0174] (Method for measuring viscosity of resin composition) The viscosity of the resin composition was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., "BL") at a temperature of 25°C. After thoroughly stirring with a spatula, the measurement was immediately carried out at a B-type viscometer rotor rotation speed of 6 rpm, and then at 60 rpm. The viscosity measured at 60 rpm was taken as the initial viscosity. The lower the viscosity, the better the dispersibility, and the higher the viscosity, the worse the dispersibility. Those in which the obtained dispersion clearly separated or sedimented were regarded as having poor dispersibility. Also, the TI value was obtained from the value obtained by dividing the viscosity (mPa·s) at 60 rpm by the viscosity (mPa·s) at 6 rpm. Initial viscosity judgment criteria ◎: Less than 1,000 mPa·s ○: 1,000 mPa·s or more and less than 2,000 mPa·s △: 2,000 mPa·s or more and less than 10,000 mPa·s ×: 10,000 mPa·s or more, sedimentation or separation TI value judgment criteria ◎: Less than 3.0 ○: 3.0 or more and less than 5.0 △: 5.0 or more and less than 10.0 ×: 10.0 or more, sedimentation or separation

[0175] (Method for measuring gloss of resin composition) For the sample for gloss measurement, 1 mL of the resin composition was dropped onto a smooth glass substrate and coated at 2 cm / second using a No. 7 bar coater. Then, it was baked in a hot air oven at 140 °C for 10 minutes and allowed to cool to obtain the sample. The coating area was about 10 cm × 10 cm. Using a gloss meter (BYK Gardner micro - gross60° gloss meter), three locations randomly selected within the coating film surface excluding the edges were measured once each, and the average value was taken as the gloss at 60°. Gloss Judgment Criteria ◎: 30 or more ○: 20 or more and less than 30 △: 10 or more and less than 20 ×: Less than 10

[0176] (Method for Measuring the Median Diameter of the Resin Composition) The median diameter was measured using a particle size distribution measuring device (Partical LA - 960V2, manufactured by HORIBA). The operating conditions for circulation / ultrasonic were as follows: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 1, stirring mode: continuous. Also, during air venting, ultrasonic operation was performed at an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds. The refractive index of NMP was 1.470, and the refractive index of the carbon material was 1.92. The measurement was carried out after diluting the measurement sample so that the transmittance of the red laser diode was 60 - 80%, and the particle size standard was volume. Median Diameter Judgment Criteria ○: 0.4 μm or more and less than 2.0 μm △: 2.0 μm or more and less than 5.0 μm ×: Less than 0.4 μm or 5.0 μm or more

[0177] (Measurement of Complex Elastic Modulus and Phase Angle of the Resin Composition) The complex elastic modulus X and phase angle Y of the resin composition were evaluated by performing dynamic viscoelasticity measurement at 25°C and a frequency of 1 Hz in the range of strain rate from 0.01% to 5% using a rheometer (RheoStress 1 rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) with a cone having a diameter of 60 mm and an angle of 2°. The smaller the obtained complex elastic modulus, the better the dispersibility, and the larger the obtained complex elastic modulus, the worse the dispersibility. Also, the larger the obtained phase angle, the better the dispersibility, and the smaller the obtained phase angle, the worse the dispersibility. Furthermore, the product (X × Y) of the obtained complex elastic modulus X (Pa) and phase angle Y (°) was calculated.

[0178] (Calculation of average fiber length of CNT) While stirring in a disper, NMP was gradually dropped into the resin composition, and a small amount of the diluted 50-fold solution was dropped onto a substrate with a smooth surface and dried to obtain a sample for observation. The obtained sample for observation was observed and imaged with a scanning electron microscope. In the observation photograph, 300 arbitrary CNTs were selected, the fiber length of each was measured, and the average value was calculated and taken as the average fiber length.

[0179] (Method for evaluating storage stability of resin composition) For the evaluation of storage stability, the viscosity was measured after the dispersion liquid was allowed to stand and stored at 50°C for 7 days. The measurement method was the same as the method for the initial viscosity. Storage stability judgment criteria ◎: Equivalent to the initial ○: The viscosity changed slightly △: The viscosity increased but did not gel ×: Gelled

[0180]

Table 2

[0181] (Preparation of positive electrode composite slurry and positive electrode) (Examples 2-1 to 2-37, Comparative Examples 3-1 to 3-3) According to the combinations and composition ratios shown in Table 3, a positive electrode composite slurry and a positive electrode were prepared as follows. With a capacity of 150 cm3 A resin composition and a positive electrode active material were added to a plastic container, and the mixture was stirred at 2,000 rpm for 150 seconds using a rotating and revolving mixer (Sumiki Seisakusho's Awatori Rentaro, ARE-310) to obtain a positive electrode composite slurry. The non-volatile content of the positive electrode composite slurry was 68.17% by mass. In Example 2-36, according to the composition ratios shown in the table, in a plastic container with a volume of 150 cm 3 A composite slurry for positive electrode 36 was prepared according to the above method, except that a resin composition, a positive electrode active material, and further a binder (S-5130: solef5130 (manufactured by Solvay)) were added to a plastic container with a volume of 150 cm 3 A composite slurry for positive electrode 37 was prepared according to the above method, except that a resin composition, a positive electrode active material, and further another conductive material (Super-P (manufactured by IMERYS Graphite & Carbon, conductive carbon black)) were added to a plastic container with a volume of 150 cm

[0182] The positive electrode composite slurry was coated on an aluminum foil with a thickness of 20 μm using an applicator, and then dried in an electric oven at 120 °C ± 5 °C for 25 minutes to produce an electrode film. Thereafter, the electrode film was subjected to rolling treatment using a roll press (manufactured by Sanku Metal, 3t hydraulic roll press) to obtain positive electrodes (positive electrodes 1 to 37, comparative positive electrodes 1 to 3). The basis weight per unit of the composite layer was 20 mg / cm 2 and the density of the composite layer after rolling treatment was 3.2 g / cc.

[0183] In the examples and comparative examples, the following positive electrode active materials were used. · NMC1: Celsiode NMC (LiNi 0.6 Co 0.2 Mn 0.2 O 2 , manufactured by Nippon Chemical Industry Co., Ltd.) · NMC2: S800 (LiNi 0.8 Mn 0.1 Co 0.1 O 2 , manufactured by Kimwa Co., Ltd.) · NCA: NAT-7050 (LiNi 0.8 Co 0.15 Al0.05 O 2 (manufactured by BASF Toda Battery Materials) ·LFP: HED (trademark) LFP-400 (lithium iron phosphate, manufactured by BASF)

[0184] <Positive Electrode Evaluation> (Method for Evaluating Conductivity of Positive Electrode) The obtained positive electrode was used with Loresta GP, MCP-T610 manufactured by Mitsubishi Chemical Analytech to measure the surface resistivity (Ω / □) of the composite layer. After the measurement, it was multiplied by the thickness of the composite layer to obtain the volume resistivity (Ω·cm) of the positive electrode. The thickness of the composite layer was measured at three points in the electrode using a film thickness gauge (DIGIMICRO MH-15M, manufactured by NIKON), and the film thickness of the aluminum foil was subtracted from the average value to obtain the volume resistivity (Ω·cm) of the positive electrode. Conductivity Judgment Criteria ◎: Less than 10 Ω·cm 〇: 10 Ω·cm or more and less than 20 Ω·cm △: 20 Ω·cm or more and less than 30 Ω·cm ×: 30 Ω·cm or more

[0185] (Method for Evaluating Adhesion of Positive Electrode) The obtained positive electrode was cut into two rectangles of 90 mm × 20 mm with the coating direction as the major axis. For the measurement of the peel strength, a desktop tensile testing machine (Strograph E3, manufactured by Toyo Seiki Seisakusho) was used and evaluated 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 layer side of the prepared positive electrode was adhered to the other side of the double-sided tape to form a test sample. Then, the test sample was vertically fixed with the short side of the rectangle at the top and bottom, and the end of the aluminum foil was peeled while being pulled upward from the bottom at a constant speed (50 mm / min), and the average value of the stress at this time was taken as the peel strength. Adhesion Judgment Criteria ◎: 0.8 N / cm or more ○: 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

[0186]

Table 3

[0187] <Fabrication and Evaluation of Secondary Battery> (Fabrication of Standard Negative Electrode) To a plastic container with a capacity of 150 ml, 0.5 part of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka), 1 part of MAC500LC (sodium carboxymethyl cellulose salt, Sanrose special type MAC500L, manufactured by Nippon Paper Industries, non-volatile content 100%), and 98.4 parts of water were added. Then, using a rotation-revolution mixer (Sinkei's Awatori Rentaro, ARE-310), it was stirred at 2,000 rpm for 30 seconds. Further, 97 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industry Co., Ltd.) was added as an active material, and using a rotation-revolution mixer (Sinkei's Awatori Rentaro, ARE-310), it was stirred at 2,000 rpm for 150 seconds. Subsequently, 3.1 parts of SBR (styrene-butadiene rubber, TRD2001, non-volatile content 48%, manufactured by JSR) was added, and using a rotation-revolution mixer (Sinkei's Awatori Rentaro, ARE-310), it was stirred at 2,000 rpm for 30 seconds to obtain a standard negative electrode composite slurry. The non-volatile content of the standard negative electrode composite slurry was set to 50% by mass.

[0188] After applying the above-mentioned standard negative electrode composite slurry onto a copper foil with a thickness of 20 μm serving as a current collector using an applicator, it was dried in an electric oven at 80 °C ± 5 °C for 25 minutes so that the coating weight per unit area of the electrode was 10 mg / cm 2 and adjusted. Further, rolling treatment was performed using a roll press (manufactured by Sanku Metal, 3t hydraulic roll press) to fabricate a standard negative electrode with a density of the composite layer of 1.6 g / cm 3 .

[0189] (Examples 3-1 to 3-37, Comparative Examples 3-1 to 3-3) (Fabrication of Secondary Battery) Using the positive electrode and the standard negative electrode described in Table 4, they were punched out to 50 mm × 45 mm and 45 mm × 40 mm, respectively. The punched positive electrode, the standard negative electrode, and the separator (porous polypropylene film) inserted therebetween were inserted into an aluminum laminate bag and dried in an electric oven at 70 °C for 1 hour. Then, in a glove box filled with argon gas, an electrolytic solution (a mixed solvent prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a volume ratio of 1:1:1, and further adding 1 part by mass of vinylene carbonate to 100 parts by mass, and then dissolving LiPF 6 at a concentration of 1 M) was injected with 2 mL, and then the aluminum laminate was sealed to fabricate secondary batteries, respectively.

[0190] (Method for evaluating rate characteristics of secondary battery) The obtained secondary batteries were placed in a constant temperature chamber at 25 °C, and charge and discharge measurements were performed using a charge and discharge device (manufactured by Beidou Electric Works, SM-8). After performing constant current constant voltage charging (cutoff current 1 mA (0.02C)) at a charging termination voltage of 4.3 V with a charging current of 10 mA (0.2C), constant current discharge was performed at a discharge current of 10 mA (0.2C) and a discharge termination voltage of 3 V. After repeating this operation 3 times, constant current constant voltage charging (cutoff current (1 mA 0.02C)) was performed at a charging termination voltage of 4.3 V with a charging current of 10 mA (0.2C), and constant current discharge was performed at discharge currents of 0.2C and 3C until the discharge termination voltage of 3.0 V was reached, and the discharge capacities were determined respectively. The rate characteristics can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in the following formula 1. (Formula 1) Rate characteristics = 3C discharge capacity / 0.2C discharge capacity of the third time × 100 (%) Rate characteristics judgment criteria ◎: 80% or more ○: 60% or more and less than 80% △: 40% or more and less than 60% ×: Less than 40%

[0191] (Method for evaluating cycle characteristics of secondary battery) The obtained secondary battery was placed in a constant temperature chamber at 25°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Hokuto Denko, SM-8). After performing constant current-constant voltage charging (cut-off current 2.5 mA (0.05C)) at a charging current of 25 mA (0.5C) and a charging end voltage of 4.3V, constant current discharge was performed at a discharge current of 25 mA (0.5C) and a discharge end voltage of 3V. This operation was repeated 200 times. The cycle characteristics can be represented by the ratio of the 3rd 0.5C discharge capacity to the 200th 0.5C discharge capacity at 25°C, as shown in the following mathematical formula 2. (Mathematical formula 2) Cycle characteristics = 3rd 0.5C discharge capacity / 200th 0.5C discharge capacity × 100 (%) Cycle characteristics judgment criteria ◎: 85% or more ○: 80% or more and less than 85% △: 50% or more and less than 80% ×: Less than 50%

[0192]

Table 4

[0193] As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited thereto. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0194] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2021-116718 filed with the Japan Patent Office on July 14, 2021, and all the disclosure contents thereof are incorporated herein by reference.

Claims

Claim 1: A resin composition comprising carbon nanotubes, a dispersant, a fluororesin, and a dispersion medium, and not containing an active material, wherein the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes, the content of the carbon nanotubes is 0.1% by mass or more and 20% by mass or less based on the total amount of the resin composition, the mass ratio of the dispersant to the carbon nanotubes is 0.01 or more and 2 or less, the mass ratio of the fluororesin to the carbon nanotubes is 0.1 or more and 10 or less, the solid content of the resin composition is 0.2% by mass or more and 40% by mass or less, A resin composition for a secondary battery electrode, wherein the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) at 25°C and 1 Hz by dynamic viscoelasticity measurement is 30 or more and 5,000 or less.

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

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

4. The resin composition for a secondary battery electrode according to claim 1, wherein the content of the carbon nanotubes is 0.5% by mass or more and 15% by mass or less based on the total amount of the resin composition.

5. The resin composition for a secondary battery electrode according to claim 1, further comprising carbon black.

6. A method for producing a composite material slurry for a secondary battery electrode, comprising adding an active material to the resin composition for a secondary battery electrode according to any one of claims 1 to 5.

7. A method for producing a composite material slurry for a secondary battery electrode, comprising adding an active material to the resin composition for a secondary battery electrode according to any one of claims 1 to 5, and further adding carbon black before, after, simultaneously with, or in combination of these when adding the active material to the resin composition for a secondary battery electrode.

8. A method for producing an electrode film, comprising adding an active material to the resin composition for a secondary battery electrode according to any one of claims 1 to 5 to prepare a composite material slurry, and coating the composite material slurry to prepare an electrode film.

9. A method for manufacturing a secondary battery including a positive electrode, a negative electrode, and an electrolyte, the method comprising: adding an active material to the resin composition for a secondary battery electrode according to any one of claims 1 to 5 to prepare a composite material slurry; and manufacturing at least one of the positive electrode and the negative electrode by coating the composite material slurry on a current collector to form an electrode film.

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