Method for manufacturing composite for secondary battery electrodes

Abstract

The purpose of the present invention is to provide a composite for secondary battery electrodes that provides composite particles capable of achieving both reduction of drying energy required for removal of a solvent at the time of production of an electrode and homogeneous combination of fibrous carbon having high cohesive force and an active material and that is capable of acquiring high electrical conductivity even in the electrode. The present invention provides a method for manufacturing a composite for secondary battery electrodes that include an electrode active material and fibrous carbon, said method comprising: a step for using a mechanochemical mixing device to combine, in a non-slurry state, an electrode active material and a fibrous carbon dispersion in which fibrous carbon is dispersed in a solvent; and a step for removing and drying the solvent.

Description

Method for manufacturing a composite for secondary battery electrodes

[0001] The present invention relates to a method for producing a composite for a secondary battery electrode.

[0002] With the spread of electric vehicles and the trend toward smaller, lighter, and more powerful portable devices, secondary batteries with high energy density and even higher capacity are required. Against this background, non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, which use a non-aqueous electrolyte solution, are being used in many devices due to their high energy density and high voltage characteristics.

[0003] Furthermore, with the expansion of applications for lithium-ion secondary batteries, there is a demand not only for improved battery performance such as higher capacity, faster charging, and longer life, but also for reduced battery costs and a reduction in the environmental impact of production. ２ There is a growing need to reduce the environmental impact, which will lead to reduced emissions, and reducing the energy consumption involved in manufacturing lithium-ion secondary batteries, which account for a large portion of the costs and energy consumption required to manufacture electric vehicles, is a challenge.

[0004] To address these issues, conventional electrode manufacturing methods using composite slurries require a large amount of drying energy to remove the solvent. Therefore, a method for manufacturing electrodes using powder molding, which does not require composite slurries, has been proposed. In electrode manufacturing using powder molding, improving productivity and uniformity of electrode materials are key issues. Therefore, composite particles of active materials are utilized, which are expected to improve material fluidity and narrow particle size distribution. For example, Patent Document 1 discloses a method for improving thickness accuracy at low basis weight during powder molding by controlling the particle size distribution of composite particles produced by spraying and drying a composite particle slurry containing an electrode active material, a water-soluble polymer, a binder resin, and a dispersion medium. Patent Document 2 also discloses an example of producing composite particles with excellent particle strength by spray granulating a slurry containing a positive electrode active material, carbon black, and cellulose nanofibers. Furthermore, composite particles of active materials are expected to be useful not only in powder molding but also in conventional manufacturing processes using composite slurries. Increasing the capacity of secondary batteries requires increasing the active material ratio in electrodes, which requires minimizing the amount of auxiliary components. Therefore, the use of fibrous carbon, which has a small outer diameter and long fiber length and can form a conductive network with a small amount of addition, is considered promising as a conductive agent. However, the strong cohesive force makes it difficult to distribute it uniformly throughout the electrode. Therefore, a method using composite particles with fibrous carbon pre-adsorbed onto the surface of the active material has been proposed. For example, Patent Document 3 discloses an example in which positive electrode active material particles and fibrous carbon are dispersed in a solvent using an ultrasonic disperser, and the resulting slurry is spray-granulated to produce composite particles in which the materials are uniformly mixed. This composite particle is then used to prepare a composite slurry and form an electrode. Patent Document 4 also discloses an example in which a positive electrode active material and carbon nanotubes are combined by mechanochemical treatment under a nitrogen atmosphere to produce a positive electrode active material with high electronic conductivity and high mechanical strength.

[0005] Japanese Patent No. 6954424 Japanese Patent No. 6380526 Japanese Patent No. 5377946 Japanese Patent Publication No. 2016-201228

[0006] The methods disclosed in Patent Documents 1 to 3 require a spray granulation process when producing composite particles. A slurry containing uniformly dispersed materials is sprayed and instantly dried in a heating tank, producing homogeneous composite particles. However, the viscosity of the slurry must be reduced to allow for spraying, limiting the amount of high solids that can be achieved. This requires a larger amount of solvent than that used in conventional composite slurries, limiting the effect of reducing energy consumption in electrode production. The method disclosed in Patent Document 4 can produce composite particles without using a solvent because the materials are mixed in a powder state. However, it is difficult to disentangle the fibrous, entangled carbon nanotubes during the composite formation process. This prevents uniform adsorption of the carbon nanotubes to the active material surface, resulting in non-uniform composite particles, making it difficult to form a uniform conductive network in the electrode.

[0007] The present invention aims to provide composite particles that can solve the above-mentioned problems, i.e., reduce the drying energy required to remove the solvent during electrode production, while achieving a uniform composite of fibrous carbon with high cohesive strength and active material, and to provide a composite for secondary battery electrodes that can achieve high conductivity even in the electrode.

[0008] Some embodiments of the present invention are exemplified below. The present invention relates to a method for producing a composite for a secondary battery electrode, which comprises an electrode active material and fibrous carbon, and is characterized by comprising the steps of: combining, in a non-slurry state, the electrode active material and a fibrous carbon dispersion in which the fibrous carbon is dispersed in a solvent, using a mechanochemical mixer; and removing the solvent and drying the mixture.

[0009] The present invention relates to a method for producing the composite for a secondary battery electrode, wherein the fibrous carbon dispersion comprises fibrous carbon, a dispersant, and a solvent, and the dispersant comprises a copolymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit.

[0010] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the copolymer contains an aliphatic hydrocarbon structural unit, a nitrile group-containing structural unit, and an alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit, the aliphatic hydrocarbon structural unit contains an alkylene structural unit, the content of the aliphatic hydrocarbon structural unit is 40 mass% or more and less than 85 mass% based on the mass of the copolymer, the content of the nitrile group-containing structural unit is 15 mass% or more and 50 mass% or less based on the mass of the copolymer, and the content of the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is 10 mass% or less based on the mass of the copolymer, the total content of the aliphatic hydrocarbon structural unit, the nitrile group-containing structural unit, and the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is 80 mass% or more based on the mass of the copolymer, and the weight average molecular weight of the copolymer is 5,000 to 400,000.

[0011] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the copolymer further contains less than 1 mass % of a carboxyl group-containing structural unit based on the mass of the copolymer.

[0012] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the fibrous carbon dispersion contains 1% by mass or more and 20% by mass or less of a base based on the mass of the copolymer.

[0013] The present invention also provides the method for producing a composite for a secondary battery electrode, characterized in that the composite for a secondary battery electrode has an exothermic peak temperature of 520°C or less, obtained by simultaneous thermogravimetry-differential thermal analysis under an oxygen atmosphere.

[0014] The present invention relates to a method for producing the composite for a secondary battery electrode, wherein the composite for a secondary battery electrode contains a binder resin.

[0015] The present invention relates to a method for producing an electrode film, which includes producing an electrode composite for a secondary battery according to the above-described method, and forming an electrode film using the electrode composite for a secondary battery.

[0016] The present invention relates to a method for producing a secondary battery, which includes preparing an electrode composite for a secondary battery according to the above-described method, and forming an electrode film using the electrode composite for a secondary battery.

[0017] Some other embodiments of the present invention are exemplified below. The present invention is a method for producing a composite for a secondary battery electrode containing an electrode active material and fibrous carbon, which comprises the steps of: combining, in a non-slurry state, the electrode active material and a fibrous carbon dispersion in which the fibrous carbon is dispersed in a solvent using a mechanochemical mixer; and removing the solvent and drying the mixture, wherein the fibrous carbon dispersion contains fibrous carbon, a dispersant, and a solvent, the dispersant contains a copolymer A containing a nitrile group-containing structural unit and an aliphatic hydrocarbon structural unit, and the Mooney viscosity (ML １＋４ , 100°C) is 10 to 70, and the phase angle of the fibrous carbon dispersion at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement is 19° or more.

[0018] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the complex modulus of elasticity of the fibrous carbon dispersion as determined by dynamic viscoelasticity measurement is less than 20 Pa.

[0019] The present invention relates to the method for producing the composite for a secondary battery electrode, wherein the content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less, and the content of the aliphatic hydrocarbon structural unit is 40% by mass or more and less than 85% by mass, based on the mass of the copolymer A.

[0020] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the composite for a secondary battery electrode has an exothermic peak temperature of 520°C or less, as determined by simultaneous thermogravimetry and differential thermal analysis under an oxygen atmosphere, and a volume resistivity of 100 Ω cm or less under a load of 20 kN.

[0021] Further embodiments of the present invention are exemplified below. The present invention relates to a method for producing a composite for a secondary battery electrode, which comprises an electrode active material and fibrous carbon, the method comprising the steps of: combining, in a non-slurry state, the electrode active material and a fibrous carbon dispersion in which the fibrous carbon is dispersed in a solvent using a mechanochemical mixer; and removing the solvent and drying the mixture, wherein the fibrous carbon dispersion comprises fibrous carbon, a dispersant, and a solvent, and the product (X × Y) of the complex modulus X (Pa) and the phase angle Y (°) of the fibrous carbon dispersion measured by dynamic viscoelasticity measurement is 30 to 3,000, and the phase angle Y (°) of the fibrous carbon dispersion measured by dynamic viscoelasticity measurement is 5 to 80°.

[0022] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the complex modulus of elasticity of the fibrous carbon dispersion as determined by dynamic viscoelasticity measurement is 0.1 Pa or more and 200 Pa or less.

[0023] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the dispersant comprises a copolymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit, the aliphatic hydrocarbon structural unit comprises an alkylene structural unit, the content of the aliphatic hydrocarbon structural unit is 40% by mass or more and less than 85% by mass based on the mass of the polymer, and the content of the nitrile group-containing structural unit is 15% by mass or more and 50% by mass or less based on the mass of the polymer.

[0024] The present invention relates to the method for producing a composite for a secondary battery electrode, wherein the TI value of the fibrous carbon dispersion measured with a Brookfield viscometer is 1.5 to 5.0.

[0025] According to an embodiment of the present invention, by precisely controlling the dispersion state of the fibrous carbon on the active material, a composite for a secondary battery electrode having excellent conductivity can be provided. According to still another embodiment of the present invention, a non-aqueous electrolyte secondary battery having high output and long life and an electrode membrane used therein can be provided.

[0026] Figure 1 shows infrared spectra of Copolymer 1, Dispersant 1, and Dispersant 3 obtained by infrared spectroscopic analysis using total reflectance measurement. Figure 2 shows C-NMR quantitative spectra of Dispersant 1 and Dispersant 3 obtained by a nuclear magnetic resonance spectrometer.

[0027] Hereinafter, a method for producing a composite for a secondary battery electrode according to an embodiment of the present invention will be described in detail. The present invention is not limited to the following embodiment, and the present invention also includes embodiments that are implemented within the scope of the present invention.

[0028] 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 this specification, a carbon nanotube dispersion may be simply referred to as a "CNT dispersion" or "dispersion." Furthermore, a composite for a secondary battery electrode may be referred to as an "electrode composite" or "composite."

[0029] [First embodiment] <Method for manufacturing a composite for secondary battery electrode> The method for manufacturing an electrode composite for secondary battery of the present invention is characterized by including a step of combining an electrode active material and a fibrous carbon dispersion in a non-slurry state, in which fibrous carbon is dispersed in a solvent, using a mechanochemical mixer, and a step of removing the solvent or liquid medium and drying the mixture.

[0030] In the manufacturing process of the secondary battery electrode composite of the present invention, the following (1) to (3) are important factors for producing a composite with good resistance characteristics: (1) Use of a fibrous carbon dispersion; (2) Control of the state of the mixture of the electrode active material and the dispersion in which the fibrous carbon is dispersed; and (3) Compounding using a mechanochemical mixer. The reasons for these are explained below. (1) In order to adsorb the fibrous carbon to the surface of the active material in the form of loose primary particles or bundle particles, the fibrous carbon, which has strong cohesive force, must be disintegrated to the above state, which requires dispersion in a liquid phase (slurry). However, compounding with the active material in a slurry state makes it impossible to reduce the drying energy required for the solvent used in electrode production. Therefore, it is necessary to use a fibrous carbon dispersion in which the primary particles or bundle particles of the fibrous carbon are uniformly dispersed and stabilized in advance. (2) Compounding in a non-slurry state with a high solids concentration makes it possible to reduce the total amount of drying energy required for the solvent compared to conventional electrode production using a composite slurry. Furthermore, when the mixture is in a non-slurry state, it does not have the fluidity of a liquid, and therefore, even if the composition contains less resin than a typical composite slurry, it can suppress component separation during drying and dry aggregation of the fibrous carbon. A non-slurry mixture preferably has a solids concentration of 80% by mass or more. The morphology of the mixture changes as follows depending on the solvent content: from higher solvent content to higher solvent content, it becomes a slurry (with liquid fluidity), a clay-like (without liquid fluidity and viscosity), a crumbly (without liquid fluidity and viscosity), and a powder (absolutely dry). In this invention, a non-slurry state refers to a clay-like or crumbly state. These morphological changes significantly affect not only the appearance but also the mixing state of the mixture. A crumbly state is preferable for the morphology of the mixture in the composite of the present invention, as it can suppress dry aggregation of the fibrous carbon during the solvent removal process. (3) While mixing in a non-slurry state can be expected to suppress dry aggregation, the lack of liquid fluidity makes it difficult for the fibrous carbon dispersion to spread over the active material surface, resulting in uneven wetting and spreading.Therefore, by using a mechanochemical mixer capable of applying shear force to press the fibrous carbon dispersion against the surface of the active material and promoting wetting and spreading, it is expected that the fibrous carbon will be loosened and evenly adsorbed onto the surface of the active material.By using the above (1) to (3), it is possible to reduce the drying energy required during electrode production, the fibrous carbon will be loosened and evenly adsorbed onto the surface of the active material, and separation of the contained components and drying aggregation of the fibrous carbon will be less likely to occur during the solvent concentration and evaporation process, making it possible to obtain a composite and electrode with high conductivity.

[0031] <Combining Process Using a Mechanochemical Mixer> The mechanochemical mixer is not particularly limited as long as it is a device that can apply shear force to a non-slurry mixture to mix it. Examples include high-speed agitators such as Henschel mixers and Supermixers, particle compounding devices "NanoCure," "Nobilta," and "Mechanofusion" manufactured by Hosokawa Micron Corporation, powder surface modification devices "Miraro" manufactured by Nara Machinery Manufacturing Co., Ltd., "Hibismix" and "Hibisdepermix" manufactured by Primix Corporation, mixers "Planetary Mixer" and "Trimix" manufactured by Inoue Manufacturing Co., Ltd., and mixer / granulator "High Speed ​​Mixer" manufactured by EarthTechnica Corporation. Among mechanochemical mixers, planetary mixers, trimix, Mechanofusion, and Nobilta are preferred, as they are capable of shear compounding and uniform mixing of materials.

[0032] <Electrode active material> The electrode active material is a material that causes a battery reaction required to extract electrical energy, and 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 as the positive electrode active material. For example, lithium manganese composite oxides (e.g., Li ｘ Mn ２ O ４ or Li ｘ MnO ２ ), lithium nickel composite oxide (e.g., Li ｘ NiO ２ ), lithium cobalt composite oxide (Li ｘ CoO ２), lithium nickel cobalt composite oxide (e.g., 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 ), lithium phosphate powder having an olivine structure (e.g., Li ｘ FePO ４ , Li ｘ Fe １－ｙ Mn ｙ P.O. ４ , Li ｘ CoPO ４ etc.), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide (e.g., V ２ O ５ , V ６ O １３ ), transition metal oxide powder such as titanium oxide, iron sulfate (Fe ２ (SO ４ ) ３ ), TiS ２and transition metal sulfide powders such as FeS. Here, x, y, and z are numbers, and 0<x<1, 0<y<1, 0<z<1, and 0<y+z<1. These positive electrode active materials can be used singly or in combination. Among these active materials, active materials containing Ni and / or Mn (especially when the total amount of Ni and / or Mn in the transition metals is 50 mol% or more) tend to become highly basic due to the elution of raw material-derived components or metal ions, which can easily cause gelation of the binder resin or deterioration of the dispersion state. Therefore, this embodiment is particularly effective for batteries containing active materials containing Ni and / or Mn.

[0033] Examples of the negative electrode active material include metal Li, or its alloy, tin alloy, silicon-based material (metal Si, Si alloy, SiO ｘ etc.), Li Ｘ TiO ２ , Li Ｘ FeO ３ , Li Ｘ Fe ３ O ４ , Li Ｘ WO ２ Examples of materials that can be used include metal oxides such as those listed above, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, and resin-baked carbon materials. Here, x is a number, 0<x<1. These negative electrode active materials can be used alone or in combination. In particular, when silicon-based materials are used, their theoretical capacity is large but their volume expansion is extremely large. Therefore, it is preferable to use them in combination with artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, resin-baked carbon materials, and the like.

[0034] <Fibrous Carbon> Fibrous carbon is a fibrous carbon material that has a high aspect ratio in the longitudinal direction and, compared to particulate carbon such as carbon black, facilitates the formation of a conductive network. Examples of fibrous carbon include carbon fiber (CNF) and carbon nanotubes (CNT). CNTs have a cylindrical shape formed by rolling planar graphite, and include single-walled CNTs, double-walled CNTs, thin-walled (several-walled) CNTs, and multi-walled CNTs, and these may be mixed. Single-walled CNTs have a structure in which one layer of graphite is rolled. Multi-walled CNTs have a structure in which two or more layers of graphite are rolled. Furthermore, the sidewalls of CNTs do not have to have a graphite structure. Furthermore, for example, CNTs having sidewalls with an amorphous structure are also considered CNTs in this specification.

[0035] The shape of the CNTs is not limited. Examples of such shapes include needle-like, cylindrical tubular, fishbone-like (fishbone or cup stacked), trump-like (platelet), and coil-like. Of these, needle-like or cylindrical tubular shapes are preferred. The CNTs may have a single shape or a combination of two or more shapes.

[0036] Examples of the form of CNT include graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. The carbon nanotubes may have a single form or a combination of two or more of these forms.

[0037] The average outer diameter of the fibrous carbon is preferably 100 nm or less, more preferably 50 nm or less. If the average outer diameter is too large, it may be difficult to uniformly combine with the composite. It is also preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 13 nm or less. It is also preferably 1 nm or more, more preferably 3 nm or more. The average outer diameter of the fibrous carbon can be calculated by observing and photographing the fibrous carbon with a transmission electron microscope, randomly selecting 300 pieces of fibrous carbon from the observation photograph, and measuring the outer diameter of each piece.

[0038] <Dispersant> The dispersant for the fibrous carbon dispersion is preferably one that can stabilize the dispersion of the fibrous carbon in the fibrous carbon dispersion. Either a resin-type dispersant or a surfactant can be used as the dispersant, but a resin-type dispersant is preferred because it has a strong adsorption power to the fibrous carbon and can provide good dispersion stability. Depending on the properties required for dispersing the fibrous carbon, an appropriate type of dispersant can be used in an appropriate blending amount.

[0039] Examples of resin-type dispersants that can be used include (meth)acrylic polymers, polymers derived from ethylenically unsaturated hydrocarbons, cellulose derivatives, and copolymers thereof. Examples of polymers derived from ethylenically unsaturated hydrocarbons include polyvinyl alcohol resins, polyvinylpyrrolidone resins, polyacrylonitrile resins, and nitrile rubbers. Examples of polyvinyl alcohol resins include polyvinyl alcohol, modified polyvinyl alcohols having functional groups other than hydroxyl groups (e.g., acetyl groups, sulfo groups, carboxy groups, carbonyl groups, and amino groups), polyvinyl alcohols modified with various salts, other anion- or cation-modified polyvinyl alcohols, and polyvinyl acetals (polyvinyl acetoacetal, polyvinyl butyral, etc.) modified with aldehydes (acetoacetal-modified, butyral-modified, etc.). The polyacrylonitrile resin may be a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer, or a modified product thereof. Preferred examples include polyacrylonitrile 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 derived from (meth)acrylic acid alkyl esters or α-olefins. For example, the acrylonitrile copolymer described in JP 2020-163362 A can be used. Nitrile rubbers include acrylonitrile butadiene rubber and hydrogenated acrylonitrile butadiene rubber. Cellulose derivatives include cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethylhydroxyethyl cellulose, nitrocellulose, methylcellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and copolymers thereof.In addition, dispersants described in International Publication No. 2008 / 108360, JP 2018-192379 A, ​​JP 2019-087304 A, Japanese Patent No. 6524479 A, ​​and JP 2009-026744 A may be used, but are not limited to these. In particular, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile homopolymers, polyacrylonitrile copolymers, and hydrogenated acrylonitrile butadiene rubber are preferred. Polymers in which other substituents have been introduced into some of these polymers, modified polymers, etc. may also be used. From the viewpoint of the balance of affinity between the dispersed substance and the dispersion medium and resistance to the electrolyte, the weight average molecular weight of the resin-type dispersant is preferably 500,000 or less, more preferably 300,000 or less, and preferably 3,000 or more, and more preferably 5,000 or more. The resin-type dispersants may be used alone or in combination of two or more.

[0040] Commercially available polyvinyl alcohol resins include various grades under trade names such as Kuraray Poval (polyvinyl alcohol resin manufactured by Kuraray), Gohsenol, and Gohsenex (polyvinyl alcohol resin manufactured by Nippon Synthetic Chemical Industry). Modified polyvinyl alcohols having various functional groups are also available. Commercially available polyvinylpyrrolidone resins include Polyvinylpyrrolidone K30, K90 (manufactured by Fujifilm Wako), and K120 (manufactured by DSP Gokei Food & Chemical). Commercially available nitrile rubbers include Therban (hydrogenated nitrile rubber manufactured by Arlanseo), Baymod (nitrile rubber manufactured by Arlanseo), Zetpole (hydrogenated nitrile rubber manufactured by Nippon Zeon), and Nipole NBR (nitrile rubber manufactured by Nippon Zeon). Various grades with different nitrile ratios, hydrogenation rates, molecular weights, etc. are available. Dispersants synthesized by known synthesis methods may also be used. Surfactants may be used in place of or in addition to the resin-type dispersants described above. Surfactants are classified into anionic, cationic, amphoteric ionic surfactants and nonionic surfactants.

[0041] The resin-type dispersant may be a polymer containing at least an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit. The aliphatic hydrocarbon structural unit of the polymer may contain an alkylene structural unit. The polymer may be hydrogenated.

[0042] The dispersant preferably contains a copolymer containing the following aliphatic hydrocarbon structural units, nitrile group-containing units, and carbamoyl group-containing structural units, because this inhibits aggregation of the fibrous carbon during drying of the composite. The aliphatic hydrocarbon structural units contain at least alkylene structural units. The content of the aliphatic hydrocarbon structural units is 40% by mass or more and less than 85% by mass, based on the mass of the copolymer; the content of the nitrile group-containing units is 15% by mass or more and 50% by mass or less, based on the mass of the copolymer; and the content of the carbamoyl group-containing structural units is 10% by mass or less, based on the mass of the copolymer. It is more preferable for the weight-average molecular weight of the copolymer to be 5,000 or more and 400,000 or less, because this effectively inhibits the aggregation force of the fibrous carbon, leading to the production of a homogeneous composite.

[0043] In this specification, this copolymer may be referred to as "Copolymer I." In addition, in this specification, a "substituted or unsubstituted carbamoyl group" (-CO-NR'2 (each R' is independently a hydrogen atom or a substituent)) may be referred to as an "amide group."

[0044] The aliphatic hydrocarbon structural unit is a structural unit containing an aliphatic hydrocarbon structure, and preferably a structural unit consisting solely of an aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure contains at least a saturated aliphatic hydrocarbon structure and may further contain an unsaturated aliphatic hydrocarbon structure. The aliphatic hydrocarbon structure preferably contains at least a linear aliphatic hydrocarbon structure and may further contain a branched aliphatic hydrocarbon structure.

[0045] 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. The aliphatic hydrocarbon structural unit contains at least an alkylene structural unit.

[0046] The alkylene structural unit is a structural unit containing an alkylene structure, and is preferably a structural unit consisting of only an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure.

[0047] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1A).

[0048] General formula (1A)

[0049] 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, and more preferably an integer of 5 or less. In particular, n is preferably 4. In this specification, "*" represents a bonding site to another structure.

[0050] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1B).

[0051] General formula (1B)

[0052] In general formula (1B), n represents an integer of 1 or more. n is preferably an integer of 2 or more, and more preferably an integer of 3 or more. n is preferably an integer of 5 or less, and more preferably an integer of 4 or less. In particular, n is preferably 3.

[0053] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1C):

[0054] General formula (1C)

[0055] 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 even more preferably an integer of 2 or less. In particular, n is preferably 2.

[0056] The method for introducing the alkylene structural unit into Copolymer I is not particularly limited, but examples thereof include the following method (1a) or (1b).

[0057] In method (1a), a copolymer is prepared by polymerization using a monomer composition containing a conjugated diene monomer. The prepared copolymer contains monomer units derived from the conjugated diene monomer. In the present invention, "monomer units derived from a conjugated diene monomer" may be referred to as "conjugated diene monomer units," and the same may be abbreviated for monomer units derived from other monomers. Next, the conjugated diene monomer units are hydrogenated to convert at least a portion of the conjugated diene monomer units into alkylene structural units. Hereinafter, "hydrogenation" may be referred to as "hydrogenation." The finally obtained copolymer I contains units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0058] The conjugated diene monomer unit contains at least a monomer unit having one carbon-carbon double bond. For example, the 1,3-butadiene monomer unit, which is a conjugated diene monomer unit, contains at least one monomer unit selected from the group consisting of a monomer unit having a cis-1,4 structure, a monomer unit having a trans-1,4 structure, and a monomer unit having a 1,2 structure, and may contain two or more types of monomer units. The conjugated diene monomer unit may further contain a monomer unit having no carbon-carbon double bond and including a branch point. In this specification, the term "branch point" refers to a branch point in a branched polymer, and when the conjugated diene monomer unit contains a monomer unit having a branch point, the copolymer prepared above and copolymer I are branched polymers.

[0059] In the method (1b), a copolymer is prepared by polymerization using a monomer composition containing an α-olefin monomer. The prepared copolymer contains α-olefin monomer units. The finally obtained copolymer I contains the α-olefin monomer units as alkylene structural units.

[0060] Among these, method (1a) is preferred because it allows for easy production of the copolymer. The conjugated diene monomer has 4 or more carbon atoms, preferably 4 to 6. Examples of conjugated diene monomers include conjugated diene compounds such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Of these, 1,3-butadiene is preferred. The alkylene structural unit preferably contains a structural unit obtained by hydrogenating a conjugated diene monomer unit (hydrogenated conjugated diene monomer unit), and more preferably contains a structural unit obtained by hydrogenating a 1,3-butadiene monomer unit (hydrogenated 1,3-butadiene monomer unit). The conjugated diene monomers can be used alone or in combination of two or more.

[0061] The hydrogenation is preferably carried out by a method capable of selectively hydrogenating the conjugated diene monomer units. Examples of the hydrogenation method include known methods such as oil phase hydrogenation and aqueous phase hydrogenation.

[0062] The hydrogenation can be carried out by a conventional method. For example, the hydrogenation can be carried out by treating a copolymer having conjugated diene monomer units dissolved in a suitable solvent with hydrogen gas in the presence of a hydrogenation catalyst. Examples of the hydrogenation catalyst include nickel, palladium, platinum, and copper.

[0063] In the method (1b), the α-olefin monomer has 2 or more carbon atoms, preferably 3 or more carbon atoms, and more preferably 4 or more carbon atoms. The α-olefin monomer has 6 or less carbon atoms, and more preferably 5 or less carbon atoms. Examples of the α-olefin monomer include α-olefin compounds such as ethylene, propylene, 1-butene, and 1-hexene. The α-olefin monomers can be used alone or in combination of two or more.

[0064] The alkylene structural unit preferably includes at least one selected from the group consisting of structural units containing a linear alkylene structure and structural units containing a branched alkylene structure, more preferably includes at least one selected from the group consisting of structural units consisting only of linear alkylene structures and structural units consisting only of branched alkylene structures, and further preferably includes at least one selected from the group consisting of structural units represented by the above formula (1B) and structural units represented by the above formula (1C).

[0065] The alkylene structural unit may include a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure. When the alkylene structural unit includes a structural unit containing a linear alkylene structure and a structural unit containing a branched alkylene structure, 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 (i.e., 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 even more preferably 15% by mass or less. When the copolymer I includes 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, 5% by mass or more, or even 10% by mass or more, based on the mass of the alkylene structural unit (i.e., when the mass of the alkylene structural unit is 100% by mass).

[0066] In the aliphatic hydrocarbon structural units, the content of the alkylene structural units is preferably 60% by mass or more, more preferably 70% by mass or more, even 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 (i.e., when the mass of the aliphatic hydrocarbon structural units is 100% by mass). The content of the alkylene structural units is, based on the total mass of the aliphatic hydrocarbon structural units (i.e., 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 units may be 100% by mass.

[0067] The content of the aliphatic hydrocarbon structural unit is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, based on the mass of copolymer I (i.e., when the mass of copolymer I 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 even more preferably 70% by mass or less, based on the mass of copolymer I (i.e., when the mass of copolymer I is 100% by mass).

[0068] The nitrile group-containing structural unit is a structural unit containing a nitrile group, preferably a structural unit containing an alkylene structure substituted with a nitrile group, more preferably a structural unit consisting of only an alkylene structure substituted with a nitrile group. The alkylene structure is preferably a linear or branched alkylene structure. The nitrile group-containing structural unit may further contain a structural unit containing (or consisting of) an alkyl structure substituted with a nitrile group. The number of nitrile groups contained in the nitrile group-containing structural unit is preferably one.

[0069] The nitrile group-containing structural unit preferably contains a structural unit represented by the following general formula (2A).

[0070] General formula (2A)

[0071] In general formula (2A), n represents an integer of 2 or more. n is preferably an integer of 6 or less, more preferably an integer of 4 or less, and even more preferably an integer of 3 or less. In particular, n is preferably 2.

[0072] The nitrile group-containing structural unit preferably contains a structural unit represented by the following general formula (2B).

[0073] General formula (2B)

[0074] In formula (2B), R represents a hydrogen atom or a methyl group, and R is preferably a hydrogen atom.

[0075] The method for introducing the nitrile group-containing structural unit into copolymer I is not particularly limited, but a method (method (2a)) of preparing a copolymer by polymerization reaction using a monomer composition containing a nitrile group-containing monomer can be preferably used. The finally obtained copolymer I contains the nitrile group-containing monomer unit as the nitrile group-containing structural unit. Examples of nitrile group-containing monomers capable of forming the nitrile group-containing structural unit include monomers containing a polymerizable carbon-carbon double bond and a nitrile group. Examples include α,β-ethylenically unsaturated group-containing compounds having a nitrile group, such as acrylonitrile and methacrylonitrile. In particular, from the viewpoint of increasing the intermolecular forces between copolymers I and / or between copolymer I and the dispersed substance (adsorbate), it is preferable that the nitrile group-containing monomer contains acrylonitrile. The nitrile group-containing monomer can be used alone or in combination of two or more.

[0076] The content of the nitrile group-containing structural unit is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the mass of copolymer I (i.e., when the mass of copolymer I 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 even more preferably 40% by mass or less, based on the mass of copolymer I (i.e., when the mass of copolymer I is 100% by mass). By setting the content of the nitrile group-containing structural unit within the above range, it is possible to control the adsorption to the dispersed substance and the affinity to the dispersion medium, and the dispersed substance can be stably present in the dispersion medium. In addition, the affinity of copolymer I to the electrolyte can be controlled, and problems such as copolymer I dissolving in the electrolyte in the battery and increasing the resistance of the electrolyte can be prevented.

[0077] The amide group-containing structural unit is a structural unit containing an amide group, preferably a structural unit containing an alkylene structure substituted with an amide group, and more preferably a structural unit consisting solely of an alkylene structure substituted with an amide group. The alkylene structure is preferably a linear or branched alkylene structure. The amide group-containing structural unit may further contain a structural unit containing (or consisting solely of) an alkyl structure substituted with an amide group. The number of amide groups contained in the amide group-containing structural unit is preferably one. The amide group is a substituted or unsubstituted carbamoyl group, and examples of the substituent include an alkyl group and a hydroxyalkyl group. By incorporating the amide group-containing structural unit into Copolymer I, the adsorption force to the dispersed substance can be significantly improved, thereby improving dispersibility and robustness. Furthermore, since the amide group can form strong hydrogen bonds, incorporating the amide group-containing structural unit into Copolymer I may introduce a crosslinked structure due to hydrogen bonding into the molecule of Copolymer I. Copolymer I with the introduced crosslinked structure can be three-dimensionally adsorbed to the dispersed substance, thereby further improving dispersibility and robustness.

[0078] The amide group-containing structural unit preferably contains a structural unit represented by the following general formula (3A).

[0079] General formula (3A)

[0080] In general formula (3A), 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 even more preferably an integer of 3 or less. In particular, n is preferably 2. R' each independently represents a hydrogen atom or a substituent. The substituent is preferably an alkyl group or a hydroxyalkyl group. It is preferable that at least one R' is a hydrogen atom, and more preferably two R' are hydrogen atoms.

[0081] The amide group-containing structural unit preferably contains a structural unit represented by the following general formula (3B).

[0082] General formula (3B)

[0083] In general formula (3B), R represents a hydrogen atom or a methyl group. R is preferably a hydrogen atom. R' each independently represents a hydrogen atom or a substituent. The substituent is preferably an alkyl group or a hydroxyalkyl group. It is preferable that at least one R' is a hydrogen atom, and more preferably two R's are hydrogen atoms.

[0084] The method for introducing the amide group-containing structural unit into Copolymer I is not particularly limited, but examples thereof include the following method (3a) or (3b).

[0085] In the method (3a), a copolymer is prepared by polymerization using a monomer composition containing an amide group-containing monomer. The prepared copolymer contains amide group-containing monomer units. The finally obtained copolymer I contains the amide group-containing monomer units as amide group-containing structural units.

[0086] In the method (3b), a copolymer containing a nitrile group-containing structural unit is prepared. Next, the nitrile groups contained in the nitrile group-containing structural unit are hydrolyzed under a basic atmosphere to convert at least a portion of the nitrile group-containing structural unit into an amide group-containing structural unit. The copolymer containing the nitrile group-containing structural unit can be obtained, for example, by the above method (2a). The finally obtained copolymer I contains, as an amide group-containing structural unit, a unit obtained by modifying the nitrile group contained in the nitrile group-containing structural unit by hydrolysis.

[0087] When copolymer I is prepared via method (3b), the introduction of amide groups into copolymer I can be confirmed by NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurements. Alternatively, this can be confirmed simply by the change in weight-average molecular weight and / or viscosity (solution viscosity) between the copolymer before hydrolysis and copolymer I. The weight-average molecular weight of copolymer I tends to be smaller than the weight-average molecular weight of the copolymer before hydrolysis (e.g., 0.05 to 0.6 times). Furthermore, for example, the viscosity of a solution of copolymer I at a shear stress of 1,000 / s tends to be smaller than the viscosity of a solution of copolymer before hydrolysis at a shear stress of 1,000 / s (e.g., 0.05 to 0.6 times). Regardless of the preparation method of copolymer I, the introduction of amide groups into copolymer I can be confirmed by NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurements.

[0088] In method (3a), examples of the amide group-containing monomer include monoalkyl(meth)acrylamides such as (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, and N-isopropyl(meth)acrylamide; dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; N-(hydroxyalkyl)(meth)acrylamides such as N-(2-hydroxyethyl)(meth)acrylamide, N-(2-hydroxypropyl)(meth)acrylamide, and N-(2-hydroxybutyl)(meth)acrylamide; diacetone(meth)acrylamide; and acryloylmorpholine. In this specification, "(meth)acryl" refers to either acrylic or methacrylic. In particular, the amide group-containing monomer preferably includes at least one selected from the group consisting of acrylamide, methacrylamide, and N,N-dimethylacrylamide. The amide group-containing monomers can be used alone or in combination of two or more.

[0089] In the method (3b), at least one base selected from the group consisting of inorganic bases and organic hydroxides (organic bases) can be used to create a basic atmosphere.

[0090] Examples of inorganic bases include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, or borates of alkali metals or alkaline earth metals; and ammonium hydroxide. Among these, alkali metal or alkaline earth metal hydroxides are preferred from the viewpoint of easy supply of cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. The metal contained in the inorganic base may be a transition metal.

[0091] The organic hydroxide is a salt containing an organic cation and a hydroxide ion. Examples of the organic hydroxide include trimethyl-2-hydroxyethylammonium hydroxide, tetramethylammonium hydroxide, cetyltrimethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, trimethylphenylammonium hydroxide, 3-trifluoromethyl-phenyltrimethylammonium hydroxide, and benzyltrimethylammonium hydroxide. Among these, it is particularly preferable to use at least one selected from the group consisting of trimethyl-2-hydroxyethylammonium hydroxide and tetramethylammonium hydroxide.

[0092] The amount of base used is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on the mass of the copolymer. The amount of 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 copolymer. If the amount used is too small, modification of the nitrile group by hydrolysis tends to be difficult. If the amount used is too large, it may cause corrosion of the dispersion device and / or the inside of the battery.

[0093] In method (3b), hydrolysis can be carried out by mixing a copolymer containing alkylene structural units and nitrile group-containing monomer units with a base and a solvent. Any other components may be mixed. The order of adding the copolymer, base, and solvent to a container and the mixing method are not limited. They may be added to the container simultaneously; the copolymer, base, and solvent may be added separately to a container; or one or both of the copolymer and the base may be mixed with a solvent to prepare a copolymer-containing liquid and / or a base-containing liquid, and the copolymer-containing liquid and / or the base-containing liquid may then be added to the container. In particular, a method in which a base dispersion in a solvent is added to a copolymer solution in which the copolymer is dissolved in a solvent while stirring is preferred, since this method can efficiently modify nitrile groups. A disperser (disperser) or a homogenizer can be used for stirring. The solvents listed in the description of the dispersant composition described below can be used as the solvent.

[0094] Although there are no limitations on the temperature during mixing, heating to 30°C or higher can accelerate the denaturation. Furthermore, to promote the denaturation, a small amount of water and / or alcohol may be added to the container. The water and / or alcohol may be added to the container while mixing the copolymer and the base, before adding the copolymer and the base to the container, or simultaneously with or subsequent to the copolymer and the base. Furthermore, if the copolymer, the base, and any optional components used as needed are highly hygroscopic, water may be contained as absorbed water. The amount of water and / or alcohol is preferably 0.05 to 20% by mass, more preferably 0.05 to 5% by mass, and even more preferably 0.05 to 1% by mass, based on the mass of the copolymer.

[0095] Examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, and thiodiglycol. The alcohols may be used alone or in combination of two or more. The hydrolysis is preferably carried out in the presence of at least one selected from the group consisting of methanol, ethanol, and water, and is particularly preferably carried out in the presence of water.

[0096] The content of the amide group-containing structural unit is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less, based on the mass of copolymer I (i.e., when the mass of copolymer I is 100% by mass). When the content of the amide group-containing structural unit is below the above range, the problem of gelation of the fibrous carbon dispersion during storage, which may occur due to excessively strong hydrogen bonds between copolymers I, can be prevented. The content of the amide group-containing structural unit is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and particularly preferably 0.7% by mass or more, based on the mass of copolymer I (i.e., when the mass of copolymer I is 100% by mass). When the content of the amide group-containing structural unit is above the above range, the adsorption force to the dispersed material can be sufficiently improved, and a favorable effect of improving dispersibility and robustness can be obtained.

[0097] Copolymer I may contain any structural unit. Examples of the structural unit include a carboxyl group-containing structural unit, an alkenylene structural unit, an alkyl structural unit, and a structural unit containing a branch point such as an alkanetriyl structural unit or an alkanetetrayl structural unit. The structural unit containing a branch point is a structural unit different from a structural unit containing a branched alkylene structure and a structural unit containing a branched alkyl structure.

[0098] The carboxyl group-containing structural unit is a structural unit containing a carboxyl group, preferably a structural unit containing an alkylene structure substituted with a carboxyl group, and more preferably a structural unit consisting solely of an alkylene structure substituted with a carboxyl group. The alkylene structure is preferably a linear or branched alkylene structure. The carboxyl group-containing structural unit may further contain a structural unit containing (or consisting solely of) an alkyl structure substituted with a carboxyl group. The number of carboxyl groups contained in the carboxyl group-containing structural unit is preferably one or two. By including a carboxyl group-containing structural unit in copolymer I, the adsorption force to the dispersed material can be significantly improved, the viscosity of the fibrous carbon dispersion can be reduced, and the dispersion efficiency can be improved.

[0099] The carboxyl group-containing structural unit preferably contains a structural unit represented by the following general formula (4A).

[0100] General formula (4A)

[0101] In general formula (4A), 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 even more preferably an integer of 3 or less. In particular, n is preferably 2.

[0102] The carboxyl group-containing structural unit preferably contains a structural unit represented by the following general formula (4B).

[0103] General formula (4B)

[0104] In general formula (4B), R represents a hydrogen atom or a methyl group, and R is preferably a hydrogen atom.

[0105] The method for introducing the carboxyl group-containing structural unit is not particularly limited, but examples thereof include the following method (4a) or (4b).

[0106] In the method (4a), a copolymer is prepared by polymerization using a composition containing a carboxyl group-containing monomer. The prepared copolymer contains carboxyl group-containing monomer units. The finally obtained copolymer I contains the carboxyl group-containing monomer units as carboxyl group-containing structural units.

[0107] In the method (4b), a copolymer containing an amide group-containing structural unit is prepared. Next, the amide group contained in the amide group-containing structural unit is hydrolyzed under an acidic atmosphere to convert the amide group-containing structural unit into a carboxyl group-containing structural unit. The copolymer containing the amide group-containing structural unit can be obtained, for example, by the above method (3a) or (3b). The finally obtained copolymer I contains, as a carboxyl group-containing structural unit, a unit obtained by modifying the amide group contained in the amide group-containing structural unit by hydrolysis.

[0108] In the method (4a), examples of the carboxyl group-containing monomer include unsaturated monocarboxylic acids such as (meth)acrylic acid, crotonic acid, and isocrotonic acid; and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, and itaconic acid. In particular, the carboxyl group-containing monomer preferably contains at least one selected from the group consisting of acrylic acid and maleic acid. The carboxyl group-containing monomer may be used alone or in combination of two or more.

[0109] In the method (4b), at least one acid selected from the group consisting of inorganic acids and organic acids can be used to create an acidic atmosphere.

[0110] Examples of inorganic acids include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid, etc. Examples of organic acids include formic acid, acetic acid, citric acid, oxalic acid, succinic acid, malic acid, benzoic acid, benzenesulfonic acid, etc. Among these, succinic acid and citric acid are preferred.

[0111] The amount of acid used 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 mass of the copolymer. The amount of acid used is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on the mass of the copolymer. If the amount used is too small, modification of the amide group by hydrolysis tends to be difficult. If the amount used is too large, it may cause corrosion of the dispersion device and / or the inside of the battery.

[0112] The content of the carboxyl group-containing structural unit is preferably less than 1% by mass, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, based on the mass of copolymer I (i.e., when the mass of copolymer I is 100% by mass). If the content of the carboxyl group-containing structural unit is less than (or less than) the above range, the problem of gelation of the fibrous carbon dispersion during storage, which may occur due to excessively strong hydrogen bonds between copolymers I, as described below, can be prevented. The content of the carboxyl group-containing structural unit is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, based on the mass of copolymer I (i.e., when the mass of copolymer I is 100% by mass). If the content of the carboxyl group-containing structural unit is greater than or equal to the above range, the adsorption force to the dispersed material can be sufficiently improved, and the viscosity of the fibrous carbon dispersion can be reduced, thereby improving the dispersion efficiency.

[0113] The alkenylene structural unit is a structural unit containing an alkenylene structure, and is preferably a structural unit consisting of only an alkenylene structure. The alkenylene structure is preferably a linear alkenylene structure or a branched alkenylene structure.

[0114] The alkenylene structural unit preferably includes at least one selected from the group consisting of structural units containing a linear alkenylene structure and structural units containing a branched alkenylene structure, and more preferably includes at least one selected from the group consisting of structural units consisting only of a linear alkenylene structure and structural units consisting only of a branched alkenylene structure.

[0115] For example, when copolymer I is obtained via the above method (1a), a conjugated diene monomer unit having a carbon-carbon double bond therein may remain in the molecule without being hydrogenated in copolymer I. The finally obtained copolymer I may contain a conjugated diene monomer unit having a carbon-carbon double bond therein as an alkenylene structural unit.

[0116] The alkyl structural unit is a structural unit containing an alkyl structure (however, it is a structural unit that does not fall under other aliphatic hydrocarbon structural units such as branched alkylene structural units, nitrile group-containing structural units, amide group-containing structural units, or carboxyl group-containing structural units), and is preferably a structural unit consisting only of an alkyl structure. The alkyl structure is preferably a linear alkyl structure or a branched alkyl structure.

[0117] The alkyl structural unit preferably includes at least one selected from the group consisting of structural units containing a linear alkyl structure and structural units containing a branched alkyl structure, and more preferably includes at least one selected from the group consisting of structural units consisting only of a linear alkyl structure and structural units consisting only of a branched alkyl structure.

[0118] For example, when copolymer I is obtained via the above method (1a) or (1b), it is preferred that at least a hydrogenated conjugated diene monomer unit or an α-olefin monomer unit is introduced into copolymer I as a terminal group of copolymer I. The finally obtained copolymer I may contain these monomer units as alkyl structural units.

[0119] The alkanetriyl structural unit is a structural unit containing an alkanetriyl structure, preferably a structural unit consisting solely of an alkanetriyl structure. The alkanetetrayl structural unit is a structural unit containing an alkanetetrayl structure, preferably a structural unit consisting solely of an alkanetetrayl structure.

[0120] For example, when copolymer I is obtained via the above method (1a), the conjugated diene monomer unit may be introduced into the molecule of copolymer I as a monomer unit containing a branch point and not containing a carbon-carbon double bond. In this case, the finally obtained copolymer I is a branched polymer, and may contain the conjugated diene monomer unit as an aliphatic hydrocarbon structural unit containing a branch point, such as an alkanetriyl structural unit or an alkanetetrayl structural unit. When the aliphatic hydrocarbon structural unit contains a structural unit containing a branch point, copolymer I is a branched polymer. The branched polymer may be a network polymer. Copolymer I containing a structural unit containing a branch point can be three-dimensionally adsorbed to the dispersed material, thereby further improving dispersibility and robustness.

[0121] Preferred embodiments of copolymer I include the following. - Copolymer I in which the total content of aliphatic hydrocarbon structural units, nitrile group-containing structural units, and carbamoyl group-containing structural units contained in copolymer I is 80% by mass or more and 100% by mass or less, based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. - Copolymer I in which the total content of aliphatic hydrocarbon structural units, nitrile group-containing structural units, carbamoyl group-containing structural units, and carboxyl group-containing structural units contained in copolymer I is 80% by mass or more and 100% by mass or less, based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. Copolymer I comprising a structural unit represented by general formula (1A), a structural unit represented by general formula (2A), and a structural unit represented by general formula (3A), and optionally comprising a structural unit represented by general formula (4A) as an optional structural unit, wherein the total content of the structural units is 80% by mass or more and 100% by mass or less, based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. Copolymer I comprising a structural unit represented by general formula (1B), a structural unit represented by general formula (2B), and a structural unit represented by general formula (3B), and optionally comprising a structural unit represented by general formula (4B) as an optional structural unit, wherein the total content of the structural units is 80% by mass or more and 100% by mass or less, based on the mass of copolymer I. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.

[0122] In this specification, the content of the structural unit can be determined by utilizing the amount of the monomer used, NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurement.

[0123] Preferred embodiments of the method for producing copolymer I include the following: - A method for producing copolymer I, comprising: preparing a copolymer by polymerization using a monomer composition containing a conjugated diene monomer and a nitrile group-containing monomer (methods (1a) and (2a)); hydrogenating the conjugated diene monomer units contained in the copolymer (method (1a)); and modifying the nitrile group-containing structural units contained in the copolymer by hydrolysis (method (3b)). In this method, some or all of the conjugated diene monomer units are hydrogenated. Also, some (but not all) of the nitrile group-containing structural units are modified by hydrolysis so that copolymer I contains nitrile group-containing structural units. - A method for producing copolymer I, comprising: preparing a copolymer by polymerization using a monomer composition containing a conjugated diene monomer, a nitrile group-containing monomer, and an amide group-containing monomer (methods (1a), (2a), and (3a)); and hydrogenating the conjugated diene monomer units contained in the copolymer (method (1a)). In this method, some or all of the conjugated diene monomer units are hydrogenated.

[0124] In the production method of the above aspect, the monomer composition may further contain a carboxyl group-containing monomer, or the production method of the above aspect may further include modifying the amide group-containing structural unit by hydrolysis (method (4b)), in which part (but not all) of the amide group-containing structural unit is modified by hydrolysis.

[0125] The copolymer I produced by the method (3b) can be used as a dispersant in the state of a mixture (dispersant-containing liquid) containing the copolymer I, a base, and a solvent after hydrolysis. Alternatively, the copolymer I produced by the method (3b) can be used as a dispersant in the state of a mixture (dispersant-containing liquid) containing the copolymer I and a solvent after extracting and removing the base from the mixture (dispersant-containing liquid) containing the copolymer I, a base, and a solvent after hydrolysis. The method for extracting and removing the base is not particularly limited, but an example is a method in which the mixture (dispersant-containing liquid) is dropped into a washing solvent that is a good solvent for the base and a poor solvent for the copolymer I, and the precipitated copolymer I is recovered. The more washing solvent used, the higher the removal efficiency. In addition, the removal efficiency can be increased by redissolving the precipitated copolymer I and repeatedly washing the copolymer I. The mixture (dispersant-containing liquid) may be thoroughly mixed with a solvent that is a good solvent for the base and a good solvent for the copolymer I, and then washed in the same manner.

[0126] The polymerization reaction used to prepare the copolymer is preferably an emulsion polymerization reaction, and a conventional emulsion polymerization method can be used. The polymerization agents used in emulsion polymerization, such as emulsifiers (surfactants), polymerization initiators, chelating agents, oxygen scavengers, and molecular weight modifiers, can be any conventionally known agent, and are not particularly limited. For example, anionic emulsifiers or anionic and nonionic emulsifiers are usually used.

[0127] Examples of anionic emulsifiers include fatty acid salts such as potassium tallow fatty acid, partially hydrogenated potassium tallow fatty acid, potassium oleate, and sodium oleate; resin acid salts such as potassium rosinate, sodium rosinate, hydrogenated potassium rosinate, and hydrogenated sodium rosinate; and alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate. Examples of nonionic emulsifiers include emulsifiers such as polyethylene glycol ester type, polypropylene glycol ester type, and Pluronic (registered trademark) type emulsifiers such as block copolymers of ethylene oxide and propylene oxide.

[0128] Examples of the polymerization initiator include thermal decomposition initiators such as persulfates, e.g., potassium persulfate and ammonium persulfate; organic peroxides, e.g., t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, octanoyl peroxide, and 3,5,5-trimethylhexanoyl peroxide; azo compounds, e.g., azobisisobutyronitrile; and redox initiators formed from these and a reducing agent, e.g., divalent iron ions. Among these, redox initiators are preferred. The amount of the initiator used is, for example, in the range of 0.01 to 10% by mass based on the total amount of monomers.

[0129] The emulsion polymerization reaction may be either continuous or batchwise. The polymerization temperature may be either low-temperature or high-temperature polymerization, but is preferably 0 to 50°C, more preferably 0 to 35°C. The method of adding the monomers (such as all-at-once addition or divided addition), the polymerization time, the polymerization conversion rate, etc. are not particularly limited. The conversion rate is preferably 85% by mass or more, more preferably 90% by mass or more.

[0130] The weight average molecular weight of copolymer I is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 50,000 or more. The weight average molecular weight of copolymer I is preferably 400,000 or less, more preferably 350,000 or less, and even more preferably 300,000 or less. When the weight average molecular weight of copolymer I is 5,000 or more and 400,000 or less, the adsorption to the dispersed substance and the affinity to the dispersion medium are improved, and the stability of the dispersion tends to be improved. The weight average molecular weight is the weight average molecular weight in terms of polystyrene and can be measured by gel permeation chromatography (GPC). Specifically, it may be measured by the method described in the examples.

[0131] The dispersant contains at least copolymer I. The dispersant may further contain any polymer, any copolymer, etc. The content of copolymer I in the dispersant is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The content of copolymer I in the dispersant may be 100% by mass, in which case the dispersant consists solely of copolymer I.

[0132] <Dispersant Composition> The dispersant composition contains a dispersant, 1% by mass or more and 20% by mass or less of a base based on the mass of copolymer I, and a solvent. That is, the dispersant composition contains copolymer I, 1% by mass or more and 20% by mass or less of a base based on the mass of copolymer I, and a solvent. When copolymer I is obtained via the above-mentioned method (3b), the dispersant composition may contain the base used in method (3b). The content of the base is 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more, based on the mass of copolymer I. From the viewpoint of preventing gelation, thickening over time, and corrosion of the dispersing device and / or the inside of the battery, the content of the base is 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less, based on the mass of copolymer I. The dispersant composition may contain an optional component such as an acid.

[0133] The dispersant composition contains a solvent. The solvent is preferably a solvent capable of dissolving Copolymer I, and is preferably a solvent consisting of any one of water-soluble organic solvents or a mixed solvent consisting of two or more of water-soluble organic solvents.

[0134] Examples of water-soluble organic solvents that can be used include amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclics (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethyl sulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), and others such as tetrahydrofuran, urea, and acetonitrile. The water-soluble organic solvent preferably contains an amide organic solvent, and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0135] The content of copolymer I in the dispersant composition is preferably 2% by mass or more, and more preferably 5% by mass or more, based on the mass of the dispersant composition, from the viewpoint of ensuring a sufficient concentration of the conductive material and / or electrode active material in the fibrous carbon dispersion, the binder resin-containing fibrous carbon dispersion, and the slurry for an electrode film. When the concentration of the conductive material and / or electrode active material is sufficient, good coatability is obtained and an increase in production costs due to increased drying time and transportation costs can be prevented. From the viewpoint of preventing the generation of insoluble matter, the content of copolymer I is preferably 15% by mass or less, and more preferably 10% by mass or less, based on the mass of the dispersant composition.

[0136] The mixture (dispersant-containing liquid) containing copolymer I, a base, and a solvent obtained via the above-mentioned method (3b) may be used as a dispersant composition. Also, the mixture (dispersant-containing liquid) containing copolymer I, a base, an acid, and a solvent obtained via the above-mentioned methods (3b) and (4b) may be used as a dispersant composition.

[0137] <Solvent> The solvent (dispersion medium) for the fibrous carbon dispersion is not particularly limited, but is preferably a high-dielectric-constant solvent, and preferably contains a solvent consisting of any one of high-dielectric-constant solvents or a mixed solvent consisting of two or more of them. In addition, the high-dielectric-constant solvent may be mixed with one or more other solvents.

[0138] Examples of high-dielectric-constant solvents that can be used include amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclics (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethyl sulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), carbonates (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate), water, and others, such as tetrahydrofuran, urea, and acetonitrile. The dispersion medium preferably contains an amide organic solvent or water, and the amide organic solvent more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. The dielectric constant of the high-dielectric solvent can be a value listed in a solvent handbook or the like, and is preferably 2.5 or more at 20°C.

[0139] <Fibrous Carbon Dispersion> The fibrous carbon dispersion contains fibrous carbon and a solvent (dispersion medium), and optionally contains a dispersant. The fibrous carbon dispersion may contain optional components such as other additives such as wetting agents, surfactants, pH adjusters, wetting and penetrating agents, and leveling agents, other conductive materials, and other polymer components, as needed, within a range that does not impair the object of the present invention. The optional components can be added at any timing, such as before preparing the dispersion, during dispersion, after dispersion, or a combination thereof.

[0140] The dispersibility of the fibrous carbon in the fibrous carbon dispersion can also be evaluated by the median diameter (μm) determined using a laser diffraction / scattering particle size distribution analyzer. The median diameter (μm) determined using a laser diffraction / scattering particle size distribution analyzer allows the particle size of the fibrous carbon aggregate particles to be estimated from the scattered light intensity distribution by the particles. The median diameter (μm) is preferably 0.4 μm or more, and preferably 5.0 μm or less, and more preferably 2.0 μm or less. By setting the median diameter within the above range, a fibrous carbon dispersion in an appropriately dispersed state can be obtained. If the median diameter is below the above range, the fibrous carbon will be in an aggregated state, and if the median diameter is above the above range, a large amount of finely cut fibrous carbon will be generated, making it difficult to form an efficient conductive network. The median diameter can be measured by the method described in the examples.

[0141] The viscosity of the fibrous carbon dispersion, measured using a Brookfield viscometer at 25°C and 60 rpm, is preferably 10 mPa·s or more and less than 10,000 mPa·s, more preferably 10 mPa·s or more and less than 2,000 mPa·s, and even more preferably 10 mPa·s or more and less than 1,000 mPa·s.

[0142] The TI value of the fibrous carbon dispersion can be calculated by dividing the viscosity (mPa s) at 6 rpm measured at 25°C with a Brookfield viscometer by the viscosity (mPa s) at 60 rpm. The TI value is preferably 1.0 or more and less than 10.0, more preferably 1.0 or more and less than 5.0, and even more preferably 1.0 or more and less than 3.0. The higher the TI value, the greater the structural viscosity due to entanglement of the fibrous carbon, dispersant, and other resin components, or their intermolecular forces, etc., 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 entanglement of the fibrous carbon, dispersant, and other resin components while allowing these intermolecular forces to act appropriately.

[0143] The average fiber length of the fibrous carbon in the fibrous carbon dispersion 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 the fibrous carbon in the fibrous carbon dispersion can be calculated by diluting the fibrous carbon dispersion 50 times with a nonaqueous solvent such as NMP, dropping the diluted fibrous carbon dispersion onto a substrate, drying the resulting sample, observing the sample with a scanning electron microscope, and randomly selecting 300 pieces of fibrous carbon from the observation photograph and measuring the fiber length of each piece.

[0144] The content of the fibrous carbon 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, relative to the total amount of the fibrous carbon dispersion. It is also preferably 20% by mass or less, and more preferably 10% by mass or less. By adjusting the content within the above range, the fibrous carbon can be maintained in a good and stable state without causing sedimentation or gelation. It is more preferably 0.1 to 20% by mass, and even more preferably 0.5 to 10% by mass. It is also preferable to appropriately adjust the content of the fibrous carbon so as to obtain a fibrous carbon dispersion with appropriate fluidity or viscosity, depending on the specific surface area of ​​the fibrous carbon, its affinity for the dispersion medium, the dispersibility of the dispersant, and the like.

[0145] 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, relative to 100 parts by mass of the fibrous carbon. The content of the dispersant is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, relative to the total amount of the fibrous carbon dispersion.

[0146] The solid content of the fibrous carbon dispersion is preferably 0.2 to 40 mass %, more preferably 0.5 to 20 mass %, and even more preferably 1 to 10 mass %.

[0147] The fibrous carbon dispersion may be prepared by separately preparing two or more types of fibrous carbon different in average outer diameter and adding them to a dispersion medium. When two or more types of fibrous carbon different in average outer diameter are used as the fibrous carbon, the average outer diameter of the first fibrous carbon is preferably 1 nm or more and less than 5 nm. The average outer diameter of the second fibrous carbon is preferably 5 nm or more and 30 nm or less, and more preferably 20 nm or less. When two or more types of fibrous carbon different in average outer diameter are used as the fibrous carbon, the mass ratio of the first fibrous carbon to the second fibrous carbon is preferably 1:10 to 1:100, and more preferably 1:10 to 1:50.

[0148] The average fiber length of the fibrous carbon 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, and more preferably 10 μm or less. The average fiber length of the fibrous carbon can be calculated by first observing and photographing the fibrous carbon with a scanning electron microscope, randomly selecting 300 pieces of fibrous carbon from the photograph, and measuring the fiber length of each piece.

[0149] The aspect ratio is the value obtained by dividing the fiber length of fibrous carbon by the outer diameter. A typical aspect ratio can be calculated using the average fiber length and the average outer diameter. A conductive material with a higher aspect ratio can obtain higher conductivity when formed into an electrode. The aspect ratio of fibrous carbon is preferably 30 or more, more preferably 50 or more, and even more preferably 80 or more. It is also preferably 10,000 or less, more preferably 3,000 or less, and even more preferably 1,000 or less.

[0150] The specific surface area of ​​fibrous carbon is 100m ２ / g or more, and ２ / g or more is more preferable, and 200m ２ / g or more is more preferable. ２ / g or less, and ２ / g or less is more preferable. The specific surface area of ​​the fibrous carbon 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 fibrous carbon are within the above ranges, a well-developed conductive path is easily formed in the electrode.

[0151] The carbon purity of the fibrous carbon is expressed as the content (mass%) of carbon atoms in the fibrous carbon, and is preferably 80 mass% or more relative to 100 mass% of the fibrous carbon.

[0152] For the purpose of removing or reducing impurities such as metal catalysts and increasing the carbon purity, fibrous carbon that has been subjected to a high-purification treatment may be used.

[0153] When fibrous carbon is dispersed using a disperser that involves collision with media such as a bead mill, or when the fibrous carbon is repeatedly passed through a disperser over a long period of time, the fibrous carbon may be broken, resulting in the formation of short flakes. The formation of short flakes reduces the viscosity of the fibrous carbon dispersion and increases the gloss of the coating film obtained by coating and drying the fibrous carbon dispersion. Judging from these evaluation results alone, the dispersion state may appear to be good. However, the short flakes have high contact resistance and make it difficult to form a conductive network, which may worsen the resistance of the electrode. The extent of the formation of short flakes can be confirmed by diluting the dispersion, dropping it onto a substrate with a smooth surface and good affinity with the dispersion medium, and then observing the dried sample with a scanning electron microscope. By adjusting the dispersion conditions and the formulation of the dispersion to prevent the formation of carbonaceous particles of 0.1 μm or less, a highly conductive electrode can be obtained.

[0154] The fibrous carbon may be produced by any method. Generally, the fibrous carbon can be produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, or a combustion method, but is not limited to these. For example, the fibrous carbon can be produced by catalytically reacting a carbon source with a catalyst 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 a hydrocarbon and an alcohol.

[0155] <Drying Step> The method for removing the solvent and drying is not particularly limited as long as it can remove the solvent from the non-slurry mixture, and examples thereof include drying methods such as hot air drying, vacuum drying, freeze drying, etc. Among these, hot air drying and vacuum drying are preferred from the viewpoint of productivity.

[0156] <Composite for Secondary Battery Electrode> The composite for secondary battery electrode contains an electrode active material, fibrous carbon, and may further contain an optional binder resin. The composite for electrode may further contain optional components.

[0157] The fibrous carbon contained in the electrode composite of the present invention is at least partially crushed and adheres to the surface of the active material.

[0158] The presence of crushed fibrous carbon on the surface of an active material allows for efficient supply of electrons required for the battery reaction to the active material. It also contributes to reducing contact resistance between active materials when an electrode is fabricated. Therefore, when crushed fibrous carbon is uniformly adsorbed on the surface of an active material and contains aggregates of fibrous carbon with an appropriate particle size and number, the electrode resistance is reduced when used as an electrode for a secondary battery. This not only facilitates the formation of an electron conduction path to the active material during the battery reaction, but also improves the battery rate characteristics and cycle characteristics. Furthermore, because an efficient conductive path can be formed with a small amount of conductive additive, the amount of conductive additive in the electrode can be reduced, allowing for improved battery capacity.

[0159] The crushed form of fibrous carbon refers to a form in which secondary particles (aggregates) of fibrous carbon are broken down into primary particles or a bundle state in which multiple primary particles are bundled together. The state in which fibrous carbon is crushed and adsorbed onto the surface of an active material includes a state in which the primary particles and / or bundles are isolated, and a state in which the primary particles and / or bundles are overlapped. From the viewpoint of electron supply to the active material and conductive paths between composites, a state in which the primary particles and / or bundles are overlapped and adsorbed in a network-like form is preferred.

[0160] In the present invention, the state in which the fibrous carbon is adsorbed on the surface of the active material in a crushed form means that the area occupied by the fibrous carbon adsorbed on the active material in a crushed fiber state is 10% or more of the entire surface of the active material, preferably 20% or more, and more preferably 50% or more.

[0161] The area occupied by the fibrous carbon adsorbed on the active material in a state in which the above-mentioned fibers were crushed can be measured from the contrast difference between the active material and the fibrous carbon in an observation image taken at a magnification of 5,000 to 50,000 times using a scanning electron microscope (SEM) or a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), and the average value of the above-mentioned areas calculated from 20 pieces of active material in the composite was used.

[0162] When the combustion temperature of the fibrous carbon in an oxygen-containing atmosphere is 520° C. or less, the electrode composite of the present invention becomes a composite in a homogeneous state in which the fibrous carbon adsorbed on the surface of the active material is loosened.

[0163] The exothermic peak temperature of the present invention can be determined by TG-DTA (Thermogravimetry-Differential Thermal Analysis) measurement. Specifically, a TG curve and a DTA curve are obtained by performing TG-DTA measurement under air or oxygen flow conditions. The top of the maximum exothermic peak resulting from the combustion of the fibrous carbon, which is located around 400 to 700°C, in the obtained DTA curve is read and defined as the exothermic peak temperature of the fibrous carbon. This represents the combustion temperature of the fibrous carbon. Fibrous carbon generally has thick bundles in which primary particles are strongly aggregated by van der Waals forces, and large secondary aggregates in which bundles aggregate together. Differences in these aggregation states result in different physical properties, such as thermal stability. Therefore, even for the same type of fibrous carbon, the combustion temperature varies depending on the aggregation state, and the stronger the aggregation, the higher the combustion temperature.

[0164] The combustion temperature of the fibrous carbon in the secondary battery electrode composite in an oxygen-containing atmosphere is preferably 520°C or less, since the fibrous carbon on the active material is adsorbed in a more loosened state, which favors the formation of an electron conduction path from the fibrous carbon to the active material and improves battery characteristics. It is more preferably 480°C or less, and even more preferably 450°C or less.

[0165] When the volume resistivity of the electrode composite for secondary batteries under a load of 20 kN is 500 Ω cm or less, the fibrous carbon in the composite is not unevenly distributed and is adsorbed on the active material in a more uniform state, thereby reducing the electrode resistance when used as a secondary battery electrode. A volume resistivity of 100 Ω cm or less is preferable, and 50 Ω cm or less is more preferable.

[0166] The volume resistivity of a secondary battery electrode composite can be determined by performing resistivity measurements based on the four-terminal four-probe method. Specifically, four needle-shaped probes (electrodes) are brought into contact with the secondary battery electrode composite to be measured, and the resistance of the test piece is determined from the current passed between the two outer probes and the potential difference generated between the two inner probes. The volume resistivity of the CNT can then be calculated from the measured resistance and the thickness of the test piece. Measurements are performed using a volume resistivity measuring device (e.g., Nitto Seiko Analytech Automatic Powder Resistivity Measurement System, Low Resistance Version, MCP-PD600) under a load of 20 kN.

[0167] The secondary battery electrode composite is preferably in the form of particles, and the average particle size is preferably from 0.5 μm to 500 μm, more preferably from 1 μm to 200 μm.

[0168] As described above, when the combustion temperature is 520°C or lower and the volume resistivity is 100 Ω cm or lower, the fibrous carbon in the composite is crushed and uniformly adsorbed onto the active material, which is preferable because, when used as an electrode for a secondary battery, it reduces the electrode resistance and favors the formation of an electron conduction path to the active material during the battery reaction, thereby improving the battery rate characteristics and cycle characteristics. In addition, because an efficient conductive path can be formed with a small amount of conductive additive, the amount of conductive additive in the electrode can be reduced, allowing for an improvement in battery capacity.

[0169] The content of fibrous carbon in the composite is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the composite for secondary battery electrodes. It is also preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. If it exceeds the above range, the amount of active material filled in the electrode decreases, resulting in a decrease in battery capacity. For high-capacity batteries in particular, 10% by mass or less is preferable. If it is below the above range, the conductivity of the electrode and battery may be insufficient.

[0170] The composite may contain a conductive material other than fibrous carbon. Examples of the other conductive material include carbon materials such as carbon black, fullerene, graphene, multilayer graphene, and graphite. The carbon black may be neutral, acidic, or basic, and oxidation-treated carbon black or graphitized carbon black may be used. The other conductive materials may be used alone or in combination of two or more.

[0171] <Binder Resin> The composite of the present invention may contain a binder resin as needed. There are no particular limitations on the binder resin, so long as it is typically used as a binder resin, and it can be appropriately selected depending on the purpose. The binder resin used in the composite is preferably a resin capable of bonding materials such as active materials and fibrous carbon. Examples of binder resins used in the composite include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, or the like as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose-based resins such as carboxymethyl cellulose; elastomers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified products, mixtures, and copolymers of these resins are also acceptable. Fluorine resins are particularly preferred, and examples thereof include polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), and modified products thereof. These may be used alone or in combination of two or more. Among these, from the viewpoint of durability, polymers or copolymers having fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, resins having these structural units, and modified products thereof are preferred.

[0172] The content of the binder resin in the composite is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, based on the mass of the active material (the mass of the active material being 100% by mass), and is preferably 20% by mass or less, more preferably 10% by mass or less.

[0173] <Secondary Battery Electrode> The secondary battery electrode of the present invention includes a composite for a secondary battery electrode. The electrode may further include optional components such as a binder and a dispersant. Generally, the electrode is formed by powder compression molding or by applying a composite slurry onto a current collector and removing volatile components.

[0174] The material and shape of the current collector are not particularly limited and can be appropriately selected from those suitable for various secondary batteries. Examples of current collector materials include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. While flat foils are generally used, current collectors with roughened surfaces, perforated foils, and mesh-shaped current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0175] <Method for manufacturing secondary battery electrode> A secondary battery electrode can be formed by adding a binder or the like to a composite for a secondary battery electrode, forming each component into a sheet by pressing or the like under dry conditions without using a solvent, and then powder pressure molding the sheet, or by preparing a composite slurry, applying it to a current collector, and removing volatile components. The powder pressure molding method without using a composite slurry is preferred because it can reduce energy consumption required to dry the solvent.

[0176] The method of powder pressure molding is not particularly limited, and known methods can be used. When an electrode is produced by powder pressure molding without using a composite slurry, a dry mixture in which an electrode composite and a binder, etc. are mixed in advance, or a dried product after wet mixing may be used. The method of adding a binder, etc. to a secondary battery electrode composite and dry mixing or wet mixing the components is not particularly limited, and various dispersers, mixers, granulators, etc. can be appropriately selected.

[0177] When forming an electrode by powder pressure molding by adding a binder or the like to a composite for a secondary battery electrode and forming each component into a sheet by pressing or the like, the components obtained by adding the binder or the like to the composite for a secondary battery electrode, or a dried product of the dry mixture or wet mixture, may be directly supplied to a current collector and pressure molded, or a free-standing film made of the components obtained by adding the binder or the like to the composite for a secondary battery electrode, or the dried product of the dry mixture or wet mixture, may be prepared in advance and then laminated on a current collector. Also, a current collector on which a resin thin film serving as a binder component has already been formed may be used or prepared.

[0178] Examples of methods for powder pressure molding include a planographic press, a calendar roll, etc. Among these, the use of a calendar roll is preferred in terms of productivity and uniform molding.

[0179] The method for producing an electrode using the composite slurry is not particularly limited, and known methods can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic coating. Drying methods after coating include, but are not limited to, standing, air drying, hot air drying, infrared heating, and far-infrared heating.

[0180] After the composite slurry is applied, it may be rolled using a lithographic press, a calender roll, etc. The thickness of the electrode film is, for example, 1 μm or more and 500 μm or less, and preferably 10 μm or more and 300 μm or less.

[0181] <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 an electrode film made from the composite of the present invention.

[0182] The positive electrode may be formed by forming an electrode film containing a positive electrode active material on a current collector, and the negative electrode may be formed by forming an electrode film containing a negative electrode active material on a current collector.

[0183] 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. As the electrolyte salt, various conventionally known electrolytes capable of transferring ions may 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, LiC４ F ９ SO ３ , Li(CF ３ SO ２ ) ３ C, LiI, LiBr, LiCl, LiAlCl, LiHF ２ , LiSCN, or LiBPh ４ (wherein Ph is a phenyl group), etc. The electrolyte salt is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0184] The non-aqueous solvent is not particularly limited, but examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-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. These solvents may be used alone or in combination of two or more.

[0185] The secondary battery preferably includes a separator, such as, but not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by subjecting these to hydrophilic treatment.

[0186] The structure of the secondary battery is not particularly limited, but it usually comprises a positive electrode, a negative electrode, and a separator that is provided as needed, and can be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type.

[0187] The composite for secondary battery electrodes of the present invention is an ideal composite of active material and fibrous carbon, and therefore can be suitably used not only for electrodes made from composite slurries but also for electrodes made by solid or semi-solid processes. These electrodes made by solid processes can be applied not only to lithium ion secondary batteries using conventional electrolyte solutions, but also to all-solid batteries, semi-solid batteries, and the like.

[0188] The secondary battery of the present invention can be suitably used as a battery for vehicles such as automobiles, and portable electronic devices such as personal computers and smartphones.

[0189] Second Embodiment A second embodiment will now be described.

[0190] The copolymer in the second embodiment is referred to as "Copolymer A."

[0191] Copolymer A in the second embodiment is characterized by having a Mooney viscosity (ML1+4,100°C) of 10 to 70. When copolymer A, which contains nitrile group-containing monomer units and aliphatic hydrocarbon structural units and has a Mooney viscosity (ML1+4,100°C) of 10 to 70, is used as a dispersant, carbon fibers can be well dispersed when preparing a dispersion containing carbon fibers as a conductive material. The "Mooney viscosity (ML1+4,100°C)" in the second embodiment can be measured at a temperature of 100°C in accordance with JIS K6300-1.

[0192] In the second embodiment, preferred aspects of copolymer A include the following. - Copolymer A in which the total content of aliphatic hydrocarbon structural units and nitrile group-containing structural units contained in copolymer A is 80% by mass or more and 100% by mass or less, based on the mass of copolymer A. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. - Copolymer A in which the total content of aliphatic hydrocarbon structural units, nitrile group-containing structural units, and amide group-containing structural units contained in copolymer A is 80% by mass or more and 100% by mass or less, based on the mass of copolymer A. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. - Copolymer A in which the total content of aliphatic hydrocarbon structural units, nitrile group-containing structural units, amide group-containing structural units, and carboxyl group-containing structural units contained in copolymer A is 80% by mass or more and 100% by mass or less, based on the mass of copolymer A. The total content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.

[0193] The Mooney viscosity of copolymer A must be 10 or more and 70 or less, preferably 60 or less, more preferably 55 or less, and even more preferably 50 or less. If the Mooney viscosity of copolymer A exceeds the above upper limit, the adsorptive power of copolymer A to the carbon fiber surface is low, making it impossible to disperse carbon fibers with strong cohesive power, and it is difficult to prepare a uniform conductive material dispersion. In addition, since the obtained conductive material dispersion has a high viscosity, metallic foreign matter contained in the raw materials cannot be efficiently removed by methods such as iron removal with a magnet, filtration, and centrifugation, and there is a risk that the remaining metallic foreign matter will deteriorate the battery performance.

[0194] The method for adjusting the Mooney viscosity of copolymer A is not particularly limited. For example, the Mooney viscosity can be adjusted by changing the composition (e.g., structural unit type and content, hydrogenation rate), structure (e.g., linearity), molecular weight, preparation conditions (e.g., polymerization temperature, amount of molecular weight modifier) ​​of copolymer A. Specifically, the Mooney viscosity of copolymer A can be adjusted by the following methods. In method (5a), the Mooney viscosity is reduced by increasing the amount of molecular weight modifier used in preparing copolymer A. In method (5b), the Mooney viscosity of copolymer A is reduced by adding a base to hydrolyze the nitrile groups contained in the nitrile group-containing structural units of copolymer A. In method (5c), the Mooney viscosity is reduced by applying a mechanical shear force to copolymer A or a dispersant containing copolymer A using a disperser that applies a larger shear force.

[0195] Examples of molecular weight modifiers that can be used in the above method (5a) include alkyl mercaptans such as octyl mercaptan, nonyl mercaptan, decyl mercaptan, dodecyl mercaptan, and 3-mercapto-1,2-propanediol; thioglycolic acid esters such as octyl thioglycolate, nonyl thioglycolate, and 2-ethylhexyl thioglycolate; 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, α-pinene, and β-pinene.

[0196] In the above method (5b), a base may be added when preparing copolymer A containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units, or a base may be added after dissolving an already prepared copolymer containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units in a solvent that can dissolve the copolymer. The base to be added may be at least one selected from the group consisting of inorganic bases and organic hydroxides (organic bases).

[0197] In the method (5b), the modification of the nitrile groups by hydrolysis can be carried out by mixing a copolymer A containing an aliphatic hydrocarbon structural unit and a nitrile group-containing monomer unit with a base and a solvent. The order of adding the copolymer A, the base, and the solvent to a container and the mixing method are not limited. They may be added to the container simultaneously; the copolymer A, the base, and the solvent may be added separately to the container; or one or both of the copolymer A and the base may be mixed with a solvent to prepare a copolymer-containing liquid and / or a base-containing liquid, which may then be added to the container. In particular, a method in which a base dispersion in a solvent is added to a copolymer solution in which the copolymer A is dissolved in a solvent while stirring is preferred, as this method can efficiently modify the nitrile groups. A disperser (disperser) or a homogenizer can be used for stirring. The solvents described below can be used as the solvent.

[0198] Although there is no limitation on the temperature during mixing, heating to 30°C or higher can accelerate the denaturation. Furthermore, to promote the denaturation of copolymer A, a small amount of water and / or alcohol may be added to the container. Water and / or alcohol may be added to the container while mixing copolymer A and the base, before adding copolymer A and the base to the container, or simultaneously with or subsequent to copolymer A and the base. Furthermore, when copolymer A, the base, and any optional components used as needed are highly hygroscopic, water may be contained as absorbed water. The amount of water and / or alcohol is preferably 0.05 to 20% by mass, more preferably 0.05 to 5% by mass, and even more preferably 0.05 to 1% by mass, based on the mass of copolymer A.

[0199] In the above method (5c), the Mooney viscosity may be adjusted by applying a mechanical shearing force when preparing copolymer A containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units, or by dissolving an already prepared copolymer containing nitrile group-containing monomer units and aliphatic hydrocarbon structural units in a solvent that can dissolve the copolymer and then applying a mechanical shearing force. The Mooney viscosity can also be reduced by applying a mechanical shearing force to copolymer A before dissolution using a roll or kneader, but since copolymer A is used as a dispersant in a state where it is dissolved in a solvent that can dissolve it, it is more preferable to apply a shearing force to the copolymer solution.

[0200] Examples of methods for applying shear force to copolymer A in a solution state include methods using dispersing means such as a homogenizer or a Silverson mixer. Although shear force can be applied using a disperser or the like, it is preferable to use dispersing means capable of applying higher shear force, such as a homogenizer or a Silverson mixer. Examples of methods for applying mechanical shear force to copolymer A before dissolution include methods using dispersing means such as a kneader or a two-roll mill.

[0201] In the second embodiment, the dispersibility of fibrous carbon in the fibrous carbon dispersion can be evaluated by the phase angle and complex modulus obtained by dynamic viscoelasticity measurement. The phase angle means the phase shift of the stress wave when the strain applied to the fibrous carbon dispersion is a sine wave. In a purely elastic body, the sine wave is in phase with the applied strain, so the phase angle is 0°. On the other hand, in a purely viscous body, the stress wave is advanced by 90°. In a typical viscoelasticity measurement sample, the phase angle is a sine wave greater than 0° and less than 90°, and if the dispersibility of fibrous carbon in the fibrous carbon dispersion is good, the phase angle approaches 90°, which is the case for a pure viscous body. Furthermore, the complex modulus of the fibrous carbon dispersion becomes smaller as the dispersibility of fibrous carbon improves and the viscosity of the fibrous carbon dispersion decreases.

[0202] The phase angle and complex modulus measured by dynamic viscoelasticity measurement depend on the concentration of fibrous carbon in the dispersion. When carbon fibers (such as CNTs) with a high specific surface area are used as the fibrous carbon, the lower the content of fibrous carbon containing carbon fibers, the closer the resulting dispersion becomes to a pure viscous body, and the phase angle approaches 90°. Conversely, it is difficult to uniformly disperse a dispersion containing a high concentration of fibrous carbon containing carbon fibers, and the phase angle of the resulting dispersion is less than 19°. In the present invention, since copolymer A can achieve both good dispersibility and stability, a fibrous carbon dispersion having a phase angle of 19° or more at a frequency of 1 Hz can be obtained even when the concentration of fibrous carbon is high.

[0203] In the second embodiment, the fibrous carbon dispersion has a phase angle of 19° or more at a frequency of 1 Hz measured by dynamic viscoelasticity measurement, more preferably 30° or more, and even more preferably 45° or more. The phase angle at a frequency of 1 Hz is preferably 90° or less, more preferably 85° or less, and even more preferably 80° or less. Furthermore, the complex modulus of the fibrous carbon dispersion of the present invention measured by dynamic viscoelasticity measurement is preferably less than 20 Pa, more preferably 10 Pa or less, and even more preferably 5 Pa or less. The complex modulus of the fibrous carbon dispersion is preferably 0.01 Pa or more, more preferably 0.05 Pa or more, and even more preferably 0.1 Pa or more. The complex modulus and phase angle can be measured by the methods described in the examples.

[0204] The complex modulus of the fibrous carbon dispersion in the second embodiment is reduced because the agglomerations of the carbon fibers are loosened by the effect of the dispersant containing copolymer A. In the fibrous carbon dispersion of this embodiment, it is preferable that the carbon fiber concentration x (mass%) in the fibrous carbon dispersion and the complex modulus y (Pa) of the fibrous carbon dispersion measured by dynamic viscoelasticity measurement satisfy the relationships of the following formulas (1), (2), and (3): y<8x (1) y<20 (2) 0.1≦x≦10 (3)

[0205] That is, from the above formulas (1) and (2), it is preferable that the complex modulus y of the fibrous carbon dispersion measured by dynamic viscoelasticity measurement is less than 20 Pa and that y<8x is satisfied. Furthermore, from the above formula (3), it is preferable that the carbon fiber concentration x (mass%) is in the range of 0.1≦x≦10.

[0206] As described above, the dispersibility of fibrous carbon can be determined by the complex modulus and phase angle, and therefore, a preferred embodiment of the method for producing a conductive dispersion includes the following steps I and II. This production method makes it possible to obtain a fibrous carbon dispersion that achieves both good dispersibility and stability. (Step I) A step of mixing fibrous carbon containing carbon fibers, a dispersant containing copolymer A, and a dispersion medium. (Step II) A step of performing a dispersion treatment after step I to obtain a dispersion whose rheometer measurement results show a phase angle of 19° or more at a frequency of 1 Hz and a complex modulus of less than 20 Pa.

[0207] In the second embodiment, other configurations of the secondary battery electrode, the secondary battery, the vehicle or device, and the method for manufacturing a composite for a secondary battery electrode are common to those of the first embodiment described above, and therefore description thereof will be omitted.

[0208] Third Embodiment A third embodiment will now be described.

[0209] In the third embodiment, the dispersibility of the fibrous carbon in the fibrous carbon dispersion can be evaluated by the complex modulus and phase angle measured by dynamic viscoelasticity measurement. The complex modulus and phase angle can be measured by the method described in the Examples. The complex modulus of the fibrous carbon dispersion indicates the hardness of the fibrous carbon dispersion and tends to decrease as the dispersibility of the fibrous carbon improves and the viscosity of the fibrous carbon dispersion decreases. However, when the fiber length of the fibrous carbon is long, even if the fibrous carbon is uniformly and stably dissolved in the medium, the structural viscosity of the fibrous carbon itself may result in a high complex modulus. In addition to the dispersion state of the fibrous carbon, the complex modulus also varies depending on the entanglement of the fibrous carbon, polymer, and other resin components, or the influence of their intermolecular forces. The complex modulus of the fibrous carbon dispersion of the present invention measured by dynamic viscoelasticity measurement is preferably 0.1 Pa or more, more preferably 0.3 Pa or more, and even more preferably 0.5 Pa or more. Furthermore, the pressure is preferably 200 Pa or less, more preferably 100 Pa or less, even more preferably 50 Pa or less, and even more preferably 30 Pa or less.

[0210] The phase angle means the phase shift of the stress wave when the strain applied to the fibrous carbon dispersion is a sine wave. In the case of a purely elastic body, the sine wave is in phase with the applied strain, and the phase angle is 0°. On the other hand, in the case of a purely viscous body, the stress wave is advanced by 90°. In a typical viscoelasticity measurement sample, the phase angle is a sine wave greater than 0° and less than 90°, and if the dispersibility of the fibrous carbon in the fibrous carbon dispersion is good, the phase angle approaches 90°, which is the phase angle of a purely viscous body.

[0211] However, as with the complex modulus, when the fibrous carbon itself has structural viscosity, the phase angle may be low even if the fibrous carbon is uniformly and stably dissolved in the dispersion medium. Furthermore, as with the complex modulus, the phase angle varies depending on the dispersion state of the fibrous carbon, the entanglement of the fibrous carbon, the polymer, and other resin components, or the influence of their intermolecular forces, as well as the dispersion state of the fibrous carbon. The phase angle measured by dynamic viscoelasticity measurement of the fibrous carbon dispersion in the third embodiment is 5° or more, preferably 10° or more, more preferably 15° or more, even more preferably 20° or more, and particularly preferably 30° or more. Furthermore, the phase angle is 80° or less, preferably 70° or less, more preferably 60° or less, and even more preferably 50° or less.

[0212] By uniformly and well dispersing the fibrous carbon while maintaining a certain fiber length or more, a well-developed conductive network is formed. Therefore, it is not enough for the fibrous carbon dispersion to simply have a low viscosity and good (apparent) dispersibility; it is particularly effective to judge the dispersion state by combining the complex modulus and phase angle with conventional indicators such as viscosity. By setting the complex modulus and phase angle within the above ranges, a fibrous carbon dispersion with good conductivity and electrode strength can be obtained.

[0213] Furthermore, in the fibrous carbon dispersion of the third embodiment, the product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is 30 or more and 3,000 or less. By setting it in this range, an electrode film having high concentration, high fluidity, and very good conductivity can be obtained. The product (X × Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) is preferably 40 or more, more preferably 50 or more. Moreover, it is preferably 2,000 or less, more preferably 1,300 or less, and even more preferably 1,000 or less.

[0214] In the third embodiment, the TI value of the fibrous carbon dispersion can be calculated by dividing the viscosity (mPa·s) at 6 rpm measured at 25°C with a Brookfield viscometer by the viscosity (mPa·s) at 60 rpm. The TI value is preferably 1.5 or more and less than 5.0, more preferably 1.5 or more and less than 4.0, and even more preferably 1.5 or more and less than 3.0. The higher the TI value, the greater the structural viscosity due to the entanglement of the fibrous carbon, dispersant, and other resin components, or their intermolecular forces, etc., 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 the fibrous carbon, dispersant, and other resin components while allowing these intermolecular forces to act appropriately.

[0215] In the third embodiment, the dispersion medium of the fibrous carbon dispersion is not particularly limited, but is preferably a high-dielectric solvent, and preferably contains a solvent consisting of any one of high-dielectric solvents or a mixed solvent consisting of two or more of high-dielectric solvents. In addition, the high-dielectric solvent may be mixed with one or more other solvents.

[0216] Examples of high-dielectric-constant solvents that can be used include amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclics (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethyl sulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), carbonates (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate), water, and others, such as tetrahydrofuran, urea, and acetonitrile. The dispersion medium preferably contains an amide organic solvent or water, and the amide organic solvent more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. The dielectric constant of the high-dielectric solvent can be a value listed in a solvent handbook or the like, and is preferably 2.5 or more at 20°C.

[0217] In the third embodiment, the fibrous carbon dispersion of the present invention is preferably produced by, for example, dispersing CNT and / or AB, a polymer, and a dispersion medium using a dispersing device to finely disperse them. Note that the dispersion treatment can be a multi-stage treatment of two or more steps by arbitrarily adjusting the addition timing of the materials to be used.

[0218] Examples of dispersing devices include kneaders, two-roll mills, three-roll mills, planetary mixers, ball mills, horizontal sand mills, vertical sand mills, annular bead mills, attritors, high-shear mixers, high-pressure homogenizers, and ultrasonic homogenizers. In particular, from the viewpoint of promoting wetting of the conductive material and dissolving coarse particles, it is most preferable to use a high-shear mixer in the initial dispersion step, followed by a high-pressure homogenizer from the viewpoint of dispersing the conductive material while maintaining its aspect ratio. Furthermore, by further dispersing the conductive material using a high-pressure homogenizer after dispersing it using a bead mill, it is possible to homogenize the dispersion state while maintaining the fiber length. The pressure when using a high-pressure homogenizer is preferably 60 to 150 MPa, more preferably 60 to 120 MPa.

[0219] Dispersion methods using a dispersing device include batch dispersion, pass dispersion, and circulation dispersion. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method in which dispersion is performed using only the dispersing device itself, without using piping or the like. Because handling is simple, it is preferred for small-scale production. Pass dispersion is a dispersion method in which the dispersing device itself is equipped with a tank that supplies the dispersion liquid via piping and a tank that receives the dispersion liquid, and the dispersion passes through the dispersing device itself. Furthermore, circulation dispersion is a method in which the dispersion liquid that has passed through the dispersing device itself is returned to the tank that supplies the dispersion liquid, and dispersion is performed while circulating. In both methods, the longer the processing time, the more the dispersion progresses; therefore, the pass or circulation can be repeated until the desired dispersion state is achieved, and the processing volume can be increased by changing the tank size or processing time. Pass dispersion is preferred over circulation dispersion because it is easier to achieve a uniform dispersion state. Circulation dispersion is preferred over pass dispersion because the operation and production equipment are simpler. In the dispersion step, the disintegration of aggregated particles, the loosening, wetting, stabilization, etc. of the conductive material proceed sequentially or simultaneously, and the final dispersion state differs depending on how these steps proceed, so it is preferable to control the dispersion state in each dispersion step by using various evaluation methods. For example, it can be controlled by the methods described in the Examples.

[0220] In the third embodiment, other configurations of the secondary battery electrode, the secondary battery, the vehicle or device, and the method for manufacturing a composite for a secondary battery electrode are common to those of the first embodiment described above, and therefore description thereof will be omitted.

[0221] [Experimental Example A] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass". In the examples, a "dispersant-containing liquid" containing a "dispersant" and a solvent may be referred to as a "dispersant solution".

[0222] <Preparation of Sample for Measuring Weight Average Molecular Weight (Mw)> The copolymer was separated and recovered from a dispersant-containing liquid (dispersant composition) containing a copolymer, a base, and a solvent by the following method, and used as a measurement sample. The dispersant-containing liquid was added dropwise to purified water to precipitate the copolymer, and the precipitate was collected by filtration using a Buchner funnel. The precipitate was then rinsed directly on the Buchner funnel with purified water and dissolved in tetrahydrofuran (THF) to obtain a solution. The resulting solution was added dropwise to purified water again, and the filtration and washing steps using purified water were performed. The precipitate was then redissolved in THF to obtain a measurement sample. In addition, the conductive material was separated from a fibrous carbon dispersion containing a copolymer, a base, a solvent, and a conductive material by centrifugation, and the supernatant was subjected to the same steps as above to prepare a measurement sample.

[0223] <Measurement of Weight-Average Molecular Weight (Mw)> The weight-average molecular weight (Mw) of the copolymer was measured by gel permeation chromatography (GPC) equipped with an RI detector. An HLC-8320GPC (manufactured by Tosoh Corporation) was used as the apparatus, and three separation columns were connected in series. The packings were "TSK-GELSUPERAW-4000," "AW-3000," and "AW-2500," all manufactured by Tosoh Corporation, respectively. The oven temperature was 40°C, and an N,N-dimethylformamide solution of 30 mM triethylamine and 10 mM LiBr was used as the eluent. Measurements were performed at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a 1% concentration using a solvent consisting of the eluent, and 20 microliters was injected. The weight-average molecular weight is a polystyrene-equivalent value.

[0224] <Measurement of Viscosity of Copolymer Solution and Dispersant-Containing Liquid> The copolymer was dissolved in NMP as a solvent to form an 8% solution, and the resulting solution was used as a viscosity measurement sample. The dispersant-containing liquid (dispersant composition) was diluted with NMP to form an 8% solution to form a viscosity measurement sample. The viscosity measurement sample was set on a sample stage, and the viscosity was measured continuously from a shear stress of 1 / s to 1,000 / s using a rheometer (RheoStress 1 rotational rheometer manufactured by ThermoFisher Scientific Co., Ltd.) at 25°C with a 60 mm diameter and a 2° cone.

[0225] <Infrared spectroscopic analysis by total reflection measurement method> The solid copolymer was used for measurement as it was. The dispersant-containing liquid (dispersant composition) was treated with hot air at 100°C for 10 hours to thoroughly dry it, and the resulting solid copolymer was used as a measurement sample. The measurement sample was subjected to IR measurement using an infrared spectrophotometer (Nicoleti S5FT-IR spectrometer manufactured by ThermoFisher Scientific Co., Ltd.).

[0226] <Measurement of Hydrogenation Ratio of Copolymer> The hydrogenation ratio was determined by IR measurement using the same method as the above-mentioned infrared spectroscopic analysis using total reflection measurement. The double bond derived from the conjugated diene monomer unit appears as a peak at 970 cm-1, and the hydrogenated single bond appears as a peak at 723 cm-1, so the hydrogenation ratio was calculated from the ratio of the heights of these two peaks.

[0227] <Measurement of the content of amide group-containing structural units> When an amide group-containing structural unit was introduced into a copolymer via a method of hydrolyzing a nitrile group-containing structural unit, the content of the amide group-containing structural unit was determined by calculating the modification rate (molar ratio) of the nitrile group from a C-NMR quantitative spectrum obtained by a nuclear magnetic resonance apparatus (ADVANCE400Nanobay: manufactured by Bruker Japan, using a measurement solvent CDCl3 and a 10 mm NMR tube) using the formula [A] / ([A]+[B]), and converting this into a composition ratio (% by mass) in the entire copolymer. In the tables described below, "amide group amount" means "the content (% by mass) of the amide group-containing structural unit." [A]: Peak area at chemical shift values ​​of 180.5 to 183.5 ppm [B]: Peak area at chemical shift values ​​of 121.5 to 123.0 ppm However, due to the low quantitative sensitivity of C-NMR measurement, the content of amide group-containing structural units cannot be detected unless the content is 1% or more. Therefore, for copolymers in which peaks at approximately 1570 cm-1 and approximately 1650 cm-1 attributable to amide groups were detected by IR measurement using a method similar to the infrared spectroscopic analysis using the total reflectance measurement method described above, the copolymer was determined to contain amide group-containing structural units, and the content of amide group-containing structural units was determined to be less than 1%. Note that, since peaks were detected by IR measurement similar to that described above, the content of amide group-containing structural units was determined to be 0.3% or more. Furthermore, when amide group-containing structural units are introduced via a method of preparing a copolymer using a monomer composition containing an amide group-containing monomer, the content of the amide group-containing structural units was also determined to be less than 1%, because quantification was not possible if the content was less than 1%. When the content of the amide group-containing structural unit was 1% or more, the ratio of the nitrile group-containing structural unit to the amide group-containing structural unit was confirmed by C-NMR quantitative spectroscopy, and it was confirmed that the content of the amide group-containing structural unit in the copolymer, which was 1% or more, matched the content calculated from the amount of the monomer charged during synthesis.

[0228] <Measurement of the Content of Carboxyl Group-Containing Structural Units> The content of carboxyl group-containing structural units can generally be determined from a C-NMR quantitative spectrum using a nuclear magnetic resonance spectrometer, similar to the measurement of the content of amide group-containing structural units. However, quantification is difficult when the content of carboxyl group-containing structural units is less than 1%. Therefore, in IR measurement using a method similar to the infrared spectroscopy analysis using the total reflection method described above, a peak at approximately 1710 cm-1 due to C=O stretching vibration was detected, and the peak at approximately 1570 cm-1 due to amide groups was reduced. Based on this, it was determined that some of the amide groups had been hydrolyzed to introduce carboxyl groups into the copolymer, and that the copolymer contained carboxyl group-containing structural units. Note that, since a peak was detected in the same IR measurement as above, the content of carboxyl group-containing structural units was determined to be 0.3% or more.

[0229] <Preparation of Copolymer 1> 30 parts of acrylonitrile, 70 parts of 1,3-butadiene, 3 parts of potassium soap oleate, 0.3 parts of azobisisobutyronitrile, 0.6 parts of t-dodecyl mercaptan, and 200 parts of ion-exchanged water were added to a stainless steel polymerization reactor. 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 monomer was removed by vacuum stripping to obtain an acrylonitrile-conjugated diene rubber latex with a solids concentration of approximately 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the mixture was placed in a 1 L autoclave equipped with a stirrer. Nitrogen gas was passed through the mixture for 10 minutes to remove dissolved oxygen from the contents. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to the palladium was added to an autoclave. The atmosphere inside the autoclave was purged twice with hydrogen gas, and the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. The contents were then returned to room temperature, a nitrogen atmosphere was created inside the autoclave, and the solids were dried to recover Copolymer 1. The hydrogenation rate of Copolymer 1 was 99.5%, and the weight-average molecular weight (Mw) was 200,000. In the acrylonitrile-conjugated diene rubber, the content of conjugated diene monomer units was 70%, and the content of nitrile group-containing monomer units was 30%, based on the mass of the acrylonitrile-conjugated diene rubber. In addition, the content of aliphatic hydrocarbon structural units including alkylene structural units was 70% and the content of nitrile group-containing monomer units was 30% based on the mass of Copolymer 1. The contents of these monomer units and structural units were determined from the amounts of the monomers used (the same applies hereinafter).

[0230] Synthesis Example 1: Preparation of Dispersant 1 In a stainless steel container 1, 16 parts of NaOH and 84 parts of NMP were placed and stirred with a homogenizer for 1 hour to prepare a NaOH suspension. In a stainless steel container 2, 9 parts of Copolymer 1 obtained in Synthesis Example 1 and 91 parts of NMP were placed and stirred with a homogenizer for 1 hour to prepare a solution of Copolymer 1. Subsequently, the NaOH suspension and the solution of Copolymer 1 were placed in a stainless steel container 3 so that the NaOH and Copolymer 1 had the compositions shown in Table 1, and NMP was further added to adjust the concentration to obtain a mixture. The water content of the mixture was 0.1%. The mixture was stirred with a homogenizer for 2 hours to modify some of the nitrile groups of Copolymer 1 to amide groups, thereby obtaining a Dispersant 1-containing liquid (dispersant composition) containing a copolymer as Dispersant 1 (in the examples, the modified Copolymer 1 may be referred to as "Dispersant 1"), NMP, and NaOH. The content of the amide group-containing structural unit and the weight-average molecular weight (Mw) of Dispersant 1 were as shown in Table 1. In Dispersant 1, the content of aliphatic hydrocarbon structural units including alkylene structural units was 70%, the content of nitrile group-containing monomer units was more than 29% but less than 30%, and the content of amide group-containing structural units was less than 1%, based on the mass of Dispersant 1. The contents of these structural units were determined using the amount of monomer used, NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurement (the same applies hereinafter).

[0231] <Preparation of Copolymer 2> Copolymer 2 was obtained in the same manner as in Synthesis Example 1, except that the monomers used were changed to 20 parts of acrylonitrile, 40 parts of 1,3-butadiene, and 40 parts of 2-methyl-1,3-butadiene. The hydrogenation rate of Copolymer 2 was 99.0%, and the weight average molecular weight (Mw) was 300,000. In Copolymer 2, the content of aliphatic hydrocarbon structural units including alkylene structural units was 80%, the content of nitrile group-containing monomer units was more than 19% and less than 20%, and the content of amide group-containing structural units was less than 1%, based on the mass of Copolymer 2.

[0232] Synthesis Example 2: Preparation of Dispersant 2 A dispersant 2-containing liquid was obtained in the same manner as in Synthesis Example 1, except that the copolymer used was changed to copolymer 2. The water content of the mixture of the NaOH suspension and copolymer 2-containing liquid was 1.0%. The content of amide group-containing structural units and weight average molecular weight (Mw) of dispersant 2 were as shown in Table 1. In copolymer 2 (dispersant 2), the content of aliphatic hydrocarbon structural units including alkylene structural units was 65%, the content of nitrile group-containing monomer units was 34.5%, and the content of amide group-containing monomer units was 0.5%, based on the mass of the copolymer.

[0233] The abbreviations shown in the columns for monomer and base in Table 1 and Table 2 below have the following meanings: BD: 1,3-butadiene MBD: 2-methyl-1,3-butadiene AN: acrylonitrile AAm: acrylamide

[0234] Synthesis Examples 3 and 4: Preparation of Dispersants 3 and 4 Liquids containing Dispersants 3 and 4 were obtained in the same manner as in Synthesis Example 1, except that the type and / or amount of the base used was changed according to Table 1. The content of the amide group-containing structural unit and the weight average molecular weight (Mw) of each dispersant were as shown in Table 1.

[0235] Synthesis Example 5: Preparation of Dispersant 5 Citric acid was further added to the Dispersant 1-containing solution prepared in Synthesis Example 1 in an amount of 5% based on Dispersant 1 (Copolymer 1) to modify some of the amide groups to carboxyl groups, thereby obtaining Dispersant 5. The presence of carboxyl groups was confirmed by infrared spectroscopic analysis using total reflectance measurement. It was determined that Dispersant 5 contained a carboxyl group-containing structural unit.

[0236] Synthesis Example 6: Preparation of Dispersant 6 A stainless steel polymerization reactor was charged with 34.5 parts of acrylonitrile, 65 parts of 1,3-butadiene, 0.5 parts of acrylamide, 3 parts of potassium soap oleate, 0.3 parts of azobisisobutyronitrile, 0.6 parts of t-dodecyl mercaptan, and 200 parts of ion-exchanged water. 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, yielding an amide group-containing acrylonitrile-conjugated diene rubber latex with a solids concentration of approximately 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the mixture was placed in a 1 L autoclave equipped with a stirrer. Dissolved oxygen in the contents was removed by flowing nitrogen gas for 10 minutes. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to the palladium was added to an autoclave. The autoclave was purged twice with hydrogen gas, and the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. The contents were then returned to room temperature, a nitrogen atmosphere was created inside the autoclave, and the solids were dried to recover Dispersant 6. The hydrogenation rate of Dispersant 6 was 99.5%, and the weight-average molecular weight (Mw) was 200,000. In Copolymer 6 (Dispersant 6), the content of aliphatic hydrocarbon structural units containing alkylene structural units was 65%, the content of nitrile group-containing monomer units was 34.5%, and the content of amide group-containing monomer units was 0.5%, based on the mass of Copolymer 6.

[0237] Figure 1 shows the IR spectra of Copolymer 1, Dispersant 1, and Dispersant 3. Comparing the IR spectra of Copolymer 1, Dispersant 1, and Dispersant 3, Dispersant 3 has sharp peaks at approximately 1570 cm-1 and 1650 cm-1 attributable to amide groups, and it can be confirmed that Dispersant 1 also has peaks attributable to amide groups, although the intensity is lower. On the other hand, since Copolymer 1 does not have amide groups, this peak is absent. The peak observed at approximately 1690 cm-1 nearby is attributable to the solvent NMP. From this, it was confirmed that amide groups had indeed been introduced into Dispersant 1 and Dispersant 3. It was determined that Dispersant 1 and Dispersant 3 contain amide group-containing structural units. Similar confirmation was also performed for other dispersants.

[0238] 2 shows the C-NMR spectra of Dispersant 1 and Dispersant 3. The content of the amide group-containing structural unit calculated from the C-NMR spectrum was less than 1% for Dispersant 1 and 3.0% for Dispersant 3.

[0239]

[0240] <Preparation of Fibrous Carbon Dispersion> (Production Example 1) A fibrous carbon dispersion was prepared as follows according to the materials and composition shown in Table 2. First, NMP was placed in a stainless steel container and heated to 50°C. A dispersant was added while stirring with a disperser, and then the mixture was stirred for 1 hour to dissolve the dispersant. Next, fibrous carbon was added while stirring with a disperser, and a square-hole high-shear screen was attached to a high-shear mixer (L5M-A, manufactured by SILVERSON). Batch dispersion was performed at a speed of 8,000 rpm until the entire mixture became uniform and the dispersion particle size was 250 μm or less as measured by a grind gauge with a maximum groove depth of 300 μm. Next, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and 50-pass dispersion treatment was performed with the high-pressure homogenizer. Fibrous carbon dispersion 1 was obtained. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0241] (Production Examples 2 to 9) Fibrous carbon dispersions 2 to 9 were obtained in the same manner as in Production Example 1, except that the materials and compositions were changed according to Table 2 and the number of passes through the high-pressure homogenizer was changed.

[0242]

[0243] The abbreviations used in Table 2 mean the following: BT1003: LUCAN BT1003M (manufactured by LG Chem Ltd., multi-walled CNT, fiber diameter 13 nm) 8S: JENOTUBE8S (manufactured by JEIO Corporation, multi-walled CNT, fiber diameter 6.8 nm) H-NBR1: Therban® 3406 (manufactured by LANXESS Corporation, hydrogenated acrylonitrile-butadiene rubber, acrylonitrile content 34%) PVP: Polyvinylpyrrolidone K30 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) NaOH: Sodium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd., purity >98.0%, granular) KOH: Potassium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd.) NMP: N-methylpyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0244] <Secondary Battery Electrode Composite> (Example 1-1) An electrode composite for a secondary battery was prepared as follows according to the composition shown in Table 3. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser, followed by stirring for 30 minutes. Next, NMC and the above dispersion were placed in the container of a planetary mixer (Hibismix® 2P-1 model, manufactured by Primix Corporation), and a mixture was prepared by stirring for 60 minutes at a rotation speed (revolution) of 60 rpm. The temperature was controlled at 25°C using a temperature-controlled chiller during stirring. The resulting mixture was then transferred to a stainless steel tray and vacuum-dried at 100°C for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 1.

[0245] Examples 1-2 to 1-8 Composites 2 to 8 were obtained in the same manner as in Example 1-1 according to the compositions shown in Table 3.

[0246] (Examples 1-9) Secondary battery electrode composites were prepared as follows according to the compositions shown in Table 3. First, fibrous carbon dispersion 9 was placed in a stainless steel container, and NMP was added while stirring with a disperser. The mixture was stirred for 30 minutes. Next, NMC and the above dispersion were placed in a Nobilta (NOB-MINI, manufactured by Hosokawa Micron Corporation) container, and the mixture was stirred for 10 minutes at a rotation speed of 5,000 rpm to prepare a mixture. The temperature was controlled at 25°C using a temperature-controlled chiller during stirring. The resulting mixture was then transferred to a stainless steel tray and vacuum-dried at 100°C for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 9.

[0247] Example 1-10 Composite 10 was obtained in accordance with the composition shown in Table 3 in the same manner as in Example 1-1, except that the rotation speed (revolution) of the planetary mixer was changed to 100 rpm.

[0248] (Examples 1-11) Secondary battery electrode composites were prepared as follows according to the compositions shown in Table 3. First, fibrous carbon dispersion 2 was placed in a stainless steel container, and NMP was added while stirring with a disperser, followed by stirring for 30 minutes. Next, NMC and the above dispersion were placed in a Mechanofusion (AMS-MINI, manufactured by Hosokawa Micron Corporation) container, and a mixture was prepared by stirring at 3000 rpm for 10 minutes. During stirring, the temperature was controlled at 25°C using a temperature-controlled chiller. The resulting mixture was then transferred to a stainless steel tray and vacuum-dried at 100°C for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 11.

[0249] (Examples 1-12) Secondary battery electrode composites were prepared as follows according to the compositions shown in Table 3. First, fibrous carbon dispersion 2 was placed in a stainless steel container, and NMP was added while stirring with a disperser, followed by stirring for 30 minutes. Next, NMC and the above dispersion were placed in a Trimmix (TX-2L, manufactured by Inoue Seisakusho Co., Ltd.) container, and the mixture was stirred for 30 minutes at a rotation speed (revolution) of 50 rpm. The temperature was controlled at 25°C using a temperature-controlled chiller during stirring. The resulting mixture was then removed from a stainless steel tray and vacuum-dried at 100°C for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 12.

[0250] (Examples 1-13) Secondary battery electrode composites were prepared as follows according to the compositions shown in Table 3. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser, followed by stirring for 30 minutes. Next, NMC and the above dispersion were placed in the container of a planetary mixer (Hibismix® 2P-1 model, manufactured by Primix Corporation), and a mixture was prepared by stirring for 60 minutes at a rotation speed (revolution) of 60 rpm. The temperature was controlled at 25°C using a temperature-controlled chiller during stirring. The resulting mixture was then transferred to a stainless steel tray and vacuum-dried at 100°C for 2.5 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 13.

[0251] (Examples 1-14) Secondary battery electrode composites were prepared as follows according to the compositions shown in Table 3. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser. The mixture was stirred for 30 minutes. Next, NMC and the dispersion were charged into the container of a planetary mixer (Hibismix® 2P-1 model, manufactured by Primix Corporation). After stirring for 60 minutes at a rotation speed (revolution) of 60 rpm, a 10% binder solution (polyvinylidene fluoride resin: KF polymer #1300) previously dissolved in NMP was added, and the mixture was stirred for 45 minutes at a rotation speed (revolution) of 60 rpm to prepare a mixture. The temperature was controlled at 25°C using a temperature-controlled chiller during stirring. Thereafter, the temperature inside the container was maintained at 80°C using a hot water chiller, and the mixture was dried for 3 hours under reduced pressure using a vacuum pump to completely remove the solvent. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 14.

[0252] (Examples 1-15) Secondary battery electrode composites were prepared as follows according to the compositions shown in Table 3. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser. The mixture was stirred for 30 minutes. Next, NMC and the above dispersion were placed in a high-speed mixer container, and the mixture was stirred for 45 minutes at an agitator rotation speed of 500 rpm and a chopper rotation speed of 1500 rpm. After that, a 10% binder solution (polyvinylidene fluoride resin: KF polymer #1300) previously dissolved in NM was added, and the mixture was stirred for 30 minutes at the same rotation speed to prepare a mixture. The temperature was controlled at 25°C using a temperature-controlled chiller during stirring. Then, the mixture was dried for 3 hours under reduced pressure using a vacuum pump while maintaining the temperature inside the container at 80°C using a hot water chiller to completely remove the solvent. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 15.

[0253] (Comparative Example 1-1) An electrode composite for a secondary battery was produced as follows according to the composition shown in Table 3. NMC and fibrous carbon were charged into a container of a Mechanofusion (AMS-MINI, manufactured by Hosokawa Micron Corporation) and stirred at a rotation speed of 5000 rpm for 10 minutes to obtain an electrode composite for a secondary battery 16. During stirring, the temperature was controlled at 25°C using a temperature-controlled chiller.

[0254] (Comparative Example 1-2) According to the composition shown in Table 3, NMC and fibrous carbon dispersion 2 were weighed out and placed in a container, and the mixture was stirred with a medicine spoon for 10 minutes to prepare a mixture. The mixture obtained was then transferred to a stainless steel tray and vacuum dried at 100°C for 2 hours using a vacuum dryer to completely remove the liquid component. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 17.

[0255] Comparative Examples 1-3 and 1-4 Composites 18 and 19 were obtained in the same manner as in Example 1-1, except that the drying temperature and drying time were changed to 120° C. and 4 hours, according to the compositions shown in Table 3.

[0256] <Evaluation of the State of Fibrous Carbon in Composite> The dispersion state of the fibrous carbon in the composite was evaluated using a scanning electron microscope JSM-7800F manufactured by JEOL Ltd.

[0257] - Criteria for determining fibrous carbon agglomerates: ◎: Contains or does not contain fibrous carbon agglomerates of 5 μm or less. ○: Contains fibrous carbon agglomerates of more than 5 μm and 10 μm or less. △: Contains fibrous carbon agglomerates of more than 10 μm and 50 μm or less. ×: Contains fibrous carbon agglomerates of more than 50 μm.

[0258] Criteria for determining the state of disintegration of fibrous carbon on the surface of an active material: ◎: The area occupied by fibrous carbon adsorbed to the active material in a state where the fibers are disintegrated is 50% or more of the entire surface of the active material. ○: The area occupied by fibrous carbon adsorbed to the active material in a state where the fibers are disintegrated is 20% or more and less than 50% of the entire surface of the active material. △: The area occupied by fibrous carbon adsorbed to the active material in a state where the fibers are disintegrated is 10% or more and less than 20% of the entire surface of the active material. ×: The fiber is not adsorbed to the active material in a state where the fibers are disintegrated.

[0259] <Exothermic Peak Temperature of Fibrous Carbon> The exothermic peak temperature of the fibrous carbon was evaluated using a differential thermobalance Thermoplus EV02TG8121 manufactured by Rigaku Corporation. Compressed air was flowed at 200 mL / min, and the exothermic peak temperature obtained when the temperature was increased from 40°C to 800°C at 10°C / min was used as an index. The exothermic peak temperature was calculated by reading the peak top temperature of the exothermic peak due to the combustion of the fibrous carbon in the range of 400 to 700°C in the DTA curve obtained by measurement.

[0260]

[0261]

[0262] The abbreviations used in Table 3 have the following meanings: NMC: NCM523 (manufactured by Nippon Chemical Industry Co., Ltd., composition: LiNi ０．５ Co ０．２ Mn ０．３ O ２ )

[0263] As shown in Table 3, from the exothermic peak temperatures of SEM and TG-DTA, it can be seen that in the Examples, the fibrous carbon in the composite was in a state of being moderately disintegrated and adsorbed on the surface of the active material without excessive aggregation. On the other hand, in the Comparative Examples, the disintegration of the aggregates of the fibrous carbon and the adsorption of the disintegrated material on the surface of the active material were insufficient.

[0264] <Preparation of Electrode Film for Positive Electrode> An electrode film for positive electrode was prepared using the electrode composite prepared in the example. 1.5 parts of polyvinylidene fluoride resin (KF polymer #1300) as a binder and 98.5 parts of electrode composite 1 were weighed into a plastic container and stirred at 2,000 rpm for 15 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310). The obtained powder mixture was calendered onto a 20 μm thick aluminum foil current collector using a powder feeder and a calender roll (roll temperature 200° C.), thereby obtaining an electrode film for positive electrode 1. The density of the electrode film for positive electrode was 3.0 g / cm ３ It was.

[0265] Positive electrode films 2 to 13 and 16 to 19 were obtained in the same manner as in the positive electrode film 1 using the composites 2 to 13 and 16 to 19.

[0266] 0.75 parts of polyvinylidene fluoride resin (KF polymer #1300) as a binder and 99.25 parts of electrode composite 14 were weighed into a plastic container and stirred at 2,000 rpm for 15 seconds using a planetary centrifugal mixer (Thinky Awatori Rentaro, ARE-310). The resulting powder mixture was calendered onto a 20 μm thick aluminum foil current collector using a powder feeder and a calender roll (roll temperature 200°C), to obtain a positive electrode film 14. The density of the positive electrode film was 3.0 g / cm. ３ It was.

[0267] The composite 15 was used to obtain a positive electrode film 15 in the same manner as the positive electrode film 14 .

[0268] (Resistance of Positive Electrode Film) The volume resistivities of electrode films 1 to 19 were measured by a four-probe method using a Loresta GP (manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS-K7194. Note that for the resistance measurement, a measurement electrode was used in which the coating substrate used in the preparation of each electrode was changed from aluminum foil to a PET substrate. A relative value (%) based on the volume resistivity of the electrode film of Comparative Examples 1 to 3 was determined and evaluated according to the following criteria.

[0269] Electrode resistance characteristic evaluation criteria ◎: 200% or more (very good) ○: 150% or more and less than 200% (excellent) ○△: 100% or more and less than 150% (good) △: 50% or more and less than 100% (poor) ×: Less than 50% (very bad)

[0270] <Assembly of a cell for evaluating the positive electrode of a lithium-ion secondary battery> The previously prepared electrode films 1 to 19 were punched out to a diameter of 16 mm to serve as the working electrode, and metallic lithium foil (thickness: 0.15 mm) was used as the counter electrode. A separator (porous polypropylene film) was inserted and laminated between the working electrode and the counter electrode, and the cell was filled with an electrolyte (a nonaqueous electrolyte prepared by dissolving LiPF6 at a concentration of 1 M in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) to assemble a bipolar sealed metal cell (HS Flat Cell manufactured by Hosen Co., Ltd.). The cell was assembled in a glove box purged with argon gas.

[0271] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Battery Positive Electrode> The prepared lithium-ion secondary battery positive electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C current) was performed at a charge rate of 0.2C with a charge cut-off voltage of 4.2V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cut-off voltage of 2.5V. This operation was repeated three times, followed by constant-current, constant-voltage charging (cut-off current: 0.02C current) at a charge rate of 0.2C with a charge cut-off voltage of 4.2V, followed by constant-current discharging at a discharge rate of 3C with a discharge cut-off voltage of 2.5V. 1C was the current value required to charge or discharge the theoretical capacity of the positive electrode in one hour. The rate characteristics can be expressed by the ratio of the 0.2C discharge capacity to the 3C discharge capacity, as shown in Equation 1 below. (Formula 1) Rate characteristic=3C discharge capacity / 0.2C discharge capacity×100(%) Relative values ​​(%) based on the rate characteristic of Comparative Example 1-3 were determined and evaluated according to the following criteria.

[0272] Rate characteristic evaluation criteria ◎: 150% or more (very good) ○: 130% or more and less than 150% (excellent) ○△: 100% or more and less than 130% (good) ×: Less than 100% (bad)

[0273] <Evaluation of Cycle Characteristics of Lithium-Ion Secondary Battery Positive Electrode> The prepared lithium-ion secondary battery positive electrode evaluation cell was placed in a thermostatic chamber at 25°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current: 0.02C) was performed at a charge rate of 0.2C with a charge cutoff voltage of 4.2V, followed by constant-current discharging at a discharge rate of 0.2C with a discharge cutoff voltage of 2.5V. This procedure was repeated 200 times. 1C was defined as the current value required to charge or discharge the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed as the ratio of the 3rd 0.2C discharge capacity to the 60th 0.2C discharge capacity, as shown in Equation 2 below: (Equation 2) Cycle Characteristics = 60th 0.2C Discharge Capacity / 3rd 0.2C Discharge Capacity × 100 (%). The relative values ​​(%) based on the cycle characteristics of Comparative Examples 1-3 were calculated and evaluated according to the following criteria.

[0274] Cycle characteristic evaluation criteria ◎: 180% or more (very good) ○: 150% or more and less than 180% (excellent) 〇△: 100% or more and less than 150% (good) ×: Less than 100% (poor)

[0275] As shown in Table 4, the Examples exhibited superior battery characteristics compared to the Comparative Examples. The fibrous carbon in the composites of the Examples was disintegrated and adsorbed onto the surface of the active material without excessive aggregation. Therefore, it is believed that uniform formation of conductive paths within the electrode led to reduced electrode resistance and improved rate and cycle characteristics. Among these, those with favorable adsorption of fibrous carbon exhibited particularly good performance. On the other hand, in the Comparative Examples, insufficient disintegration of the fibrous carbon during the composite manufacturing process and excessive drying and aggregation during the drying process resulted in a reduced amount of adsorption onto the active material surface and uneven distribution of the material, resulting in non-uniform formation of conductive paths within the electrode, which is believed to have led to increased electrode resistance and deterioration of rate and cycle characteristics. From the above, it was demonstrated that the electrode composites produced by the manufacturing method of the present invention can exhibit excellent battery characteristics.

[0276] [Experimental Example B]

[0277] <Measurement of Weight-Average Molecular Weight (Mw) of Copolymer> The weight-average molecular weight (Mw) of the copolymer was measured by gel permeation chromatography (GPC) equipped with an RI detector. An HLC-8320GPC (manufactured by Tosoh Corporation) was used as the apparatus, and three separation columns were connected in series. The packings were "TSK-GELSUPERAW-4000," "AW-3000," and "AW-2500," all manufactured by Tosoh Corporation, respectively. The oven temperature was 40°C, and an N,N-dimethylformamide solution of 30 mM triethylamine and 10 mM LiBr was used as the eluent. Measurements were performed at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a 1% concentration using a solvent consisting of the eluent, and 20 microliters was injected. The weight-average molecular weight is a polystyrene-equivalent value.

[0278] <Measurement of Hydrogenation Ratio of Copolymer> The hydrogenation ratio was determined by IR measurement using the same method as the above-mentioned infrared spectroscopic analysis using total reflection measurement. The double bond derived from the conjugated diene monomer unit appears as a peak at 970 cm-1, and the hydrogenated single bond appears as a peak at 723 cm-1, so the hydrogenation ratio was calculated from the ratio of the heights of these two peaks.

[0279] <Mooney viscosity of copolymer (ML １＋４ Measurement of Mooney viscosity (ML) of a copolymer is measured by preparing a measurement sample from a copolymer solution containing a solvent capable of dissolving the copolymer. When the copolymer is dissolved in NMP, the NMP solution of the copolymer is coagulated with water, washed with methanol, and vacuum dried at 60°C for 12 hours to obtain a measurement sample. The Mooney viscosity (ML) of 40 g of the measurement sample is measured at 100°C using an L-type rotor in accordance with Japanese Industrial Standard JIS K6300-1. １＋４ , 100°C) was measured.

[0280] <Measurement of Initial Viscosity of Fibrous Carbon Dispersion> The viscosity value was measured using a Brookfield viscometer ("BL" manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25°C. The fibrous carbon dispersion was thoroughly stirred with a spatula, and then immediately measured at a Brookfield viscometer rotor rotation speed of 60 rpm. The rotors used for the measurement were No. 1 when the viscosity value was less than 100 mPa·s, No. 2 when the viscosity value was 100 or more but less than 500 mPa·s, No. 3 when the viscosity value was 500 or more but less than 2,000 mPa·s, and No. 4 when the viscosity value was 2,000 or more but less than 10,000 mPa·s. The lower the viscosity, the better the dispersibility, and the higher the viscosity, the poorer the dispersibility. The obtained fibrous carbon dispersion, which clearly separated or settled, was judged to have poor dispersibility.

[0281] Judgment criteria ◎: Less than 500 mPa·s (Excellent) ○: 500 mPa·s or more but less than 2,000 mPa·s (Good) △: 2,000 mPa·s or more but less than 10,000 mPa·s (Fair) ×: 10,000 mPa·s or more, settling or separation (Poor)

[0282] <Measurement of Complex Elastic Modulus and Phase Angle of Fibrous Carbon Dispersion> The complex elastic modulus and phase angle of the fibrous carbon dispersion were evaluated by performing dynamic viscoelasticity measurement using a rheometer (RheoStress1 rotational rheometer manufactured by ThermoFisherScientific Co., Ltd.) with a 60 mm diameter, 2° cone, at 25°C, a frequency of 1 Hz, and a strain rate in the range of 0.01% to 5%. The larger the obtained phase angle, the better the dispersibility, and the smaller the phase angle, the worse the dispersibility. Furthermore, the smaller the obtained complex elastic modulus, the better the dispersibility, and the larger the complex elastic modulus, the worse the dispersibility.

[0283] Phase angle judgment criteria ◎: 45° or more (excellent) ○: 30° or more and less than 45° (good) △: 19° or more and less than 30° (passable) ×: Less than 19° (poor)

[0284] Complex elastic modulus evaluation criteria: ◎: Less than 5 Pa (excellent) ○: 5 Pa or more and less than 20 Pa (acceptable) ×: 20 Pa or more and less than 100 Pa (poor) xx: 100 Pa or more (very poor)

[0285] <Preparation of Copolymer 1> 30 parts of acrylonitrile, 70 parts of 1,3-butadiene, 3 parts of potassium soap oleate, 0.3 parts of azobisisobutyronitrile, 0.55 parts of t-dodecyl mercaptan, and 200 parts of ion-exchanged water were added to a stainless steel polymerization reactor. 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 solids concentration of approximately 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the mixture was placed in a 1 L autoclave equipped with a stirrer. Nitrogen gas was passed through the mixture for 10 minutes to remove dissolved oxygen from the contents. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to the palladium was added to an autoclave. The atmosphere inside the autoclave was purged twice with hydrogen gas, and the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. The contents were then returned to room temperature, a nitrogen atmosphere was created inside the autoclave, and the solids were dried to recover Copolymer 1. The hydrogenation rate of Copolymer 1 was 99.5%, and the weight-average molecular weight (Mw) was 150,000. In the acrylonitrile-conjugated diene rubber, the content of conjugated diene monomer units was 70%, and the content of nitrile group-containing monomer units was 30%, based on the mass of the acrylonitrile-conjugated diene rubber. In addition, the content of aliphatic hydrocarbon structural units including alkylene structural units was 70% and the content of nitrile group-containing monomer units was 30% based on the mass of Copolymer 1. The contents of these monomer units and structural units were determined from the amounts of the monomers used (the same applies hereinafter).

[0286] Synthesis Example 1: Preparation of Dispersant 1 9 parts of Copolymer 1 and 91 parts of NMP were placed in a stainless steel container 1 and stirred for 1 hour using a disperser to obtain a dispersant 1-containing liquid containing Copolymer 1 and NMP as dispersant 1. The Mooney viscosity (ML １＋４, 100°C) was measured and found to be 50. In Dispersant 1, the content of aliphatic hydrocarbon structural units was 70%, and the content of nitrile group-containing monomer units was 30%, based on the mass of Dispersant 1. The contents of these structural units were determined using the amounts of monomers used, NMR (nuclear magnetic resonance) and / or IR (infrared spectroscopy) measurements (the same applies hereinafter).

[0287] <Preparation of Copolymer 2> Copolymer 2 was obtained in the same manner as Copolymer 1, except that the content of t-dodecyl mercaptan, a molecular weight modifier, was changed to 0.35 parts. The hydrogenation rate of Copolymer 2 was 99.2%, and the weight average molecular weight (Mw) was 180,000. In Copolymer 2, the content of aliphatic hydrocarbon structural units including alkylene structural units was 70%, and the content of nitrile group-containing monomer units was 30%, based on the mass of Copolymer 2.

[0288] Synthesis Example 2 Preparation of Dispersant 2 16 parts of NaOH and 84 parts of NMP were placed in a stainless steel container 1 and stirred for 1 hour using a disperser to prepare a NaOH suspension. 9 parts of copolymer 2 and 91 parts of NMP were placed in a stainless steel container 2 and stirred for 1 hour using a disperser to prepare a solution of copolymer 2. Subsequently, the NaOH suspension and the solution of copolymer 2 were placed in a stainless steel container 3 so that the NaOH and copolymer 2 had the compositions shown in Table B1, and NMP was further added to adjust the concentration. Stirring was continued for 2 hours using a disperser to obtain a dispersant 2-containing solution containing copolymer 2, dispersant 2 containing NaOH, and NMP. The Mooney viscosity (ML) of dispersant 2 was 1000 kJ / ml. １＋４ , 100°C) was measured and found to be 42.

[0289] <Preparation of Copolymer 3> Copolymer 3 was obtained in the same manner as Copolymer 1, except that the content of t-dodecyl mercaptan, a molecular weight modifier, was changed to 0.25 parts. The hydrogenation rate of Copolymer 3 was 99.1%, and the weight average molecular weight (Mw) was 230,000. In Copolymer 3, the content of aliphatic hydrocarbon structural units including alkylene structural units was 70%, and the content of nitrile group-containing monomer units was 30%, based on the mass of Copolymer 3.

[0290] Synthesis Example 3: Preparation of Dispersant 3 A dispersant 3-containing solution containing Copolymer 3 and NMP as Dispersant 3 was obtained in the same manner as in Synthesis Example 1, except that the dispersing machine used was changed to a homogenizer and a shear force was applied to the solution. The Mooney viscosity (ML １＋４ , 100°C) was measured and found to be 55.

[0291] The abbreviations shown in the columns for monomer and molecular weight modifier in Table B1 have the following meanings: BD: 1,3-butadiene, MBD: 2-methyl-1,3-butadiene, AN: acrylonitrile, AAm: acrylamide, BA: butyl acrylate, TDM: t-dodecyl mercaptan.

[0292] <Preparation of Copolymers 4 to 9, Synthesis Examples 4 to 9, and Dispersants 4 to 9> The monomer composition used, the amount of base, and whether or not shearing treatment was performed during preparation were changed according to Table B1, and Copolymers 4 to 9 were prepared with reference to Copolymers 1 to 3, respectively, and Dispersant-containing solutions 4 to 9 were obtained with reference to Synthesis Examples 1 to 3. The Mooney viscosity of each dispersant was as shown in Table B1.

[0293] Synthesis Example 10: Preparation of Dispersant 10 H-NBR1 (H-NBR (hydrogenated acrylonitrile-butadiene rubber) Therban® 3406 manufactured by ARLANXEO, acrylonitrile content 34%) and NMP were added to a stainless steel container 1 and dissolved using a disperser. A high shear force was then applied to the H-NBR1 solution using a homogenizer to obtain a liquid containing Dispersant 10. The Mooney viscosity (ML １＋４ , 100°C) was measured and found to be 50.

[0294] Synthesis Example 12: Preparation of Dispersant 12 A NaOH suspension and a solution of H-NBR2 prepared in the same manner as in Production Example 2 were placed in a stainless steel container 1 so that the composition of NaOH and H-NBR2 (H-NBR (hydrogenated acrylonitrile-butadiene rubber) Zetpol® 2000L manufactured by Zeon Corporation, acrylonitrile content 36.2%) was as shown in Table B1, and NMP was further added to adjust the concentration. The solution was stirred with a homogenizer for 2 hours to apply a high shear force, thereby obtaining a dispersant 12 containing H-NBR2 and NaOH, and a dispersant 12-containing liquid containing NMP. The Mooney viscosity (ML １＋４ , 100°C) was measured and found to be 48.

[0295] Synthesis Examples 11 and 13: Preparation of Dispersants 11 and 13 The type and amount of base used were changed according to Table B1, and dispersant-containing solutions 11 and 13 were obtained with reference to Synthesis Examples 10 and 12, respectively. The Mooney viscosities of the dispersants were as shown in Table B1.

[0296]

[0297] Although the order and method of mixing the base and copolymer are not limited to those described in the examples, dispersing (or dissolving) the base in a solvent in advance and adding it to the copolymer solution increases the contact efficiency between the base and the copolymer, making hydrolysis more likely to proceed, which is also effective in stabilizing quality control and shortening production time.

[0298] <Preparation of Fibrous Carbon Dispersion> <Production Example 1> According to the composition shown in Table B2, a dispersant-containing solution containing a dispersant, NMP, and, if specified, a base, or a dispersant was added to a stainless steel container. NMP was added to adjust the concentration, and the mixture was stirred with a disperser until uniform. Subsequently, the conductive material was added while stirring with a disperser. A high-shear mixer (L5M-A, manufactured by Silverson) equipped with a square-hole high-shear screen was used, and batch dispersion was carried out at a speed of 8,500 rpm until the mixture was uniform throughout and the dispersion particle size measured by a grind gauge was 250 μm or less. Subsequently, the dispersion liquid was supplied from the stainless steel container via piping to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine), and a 25-pass dispersion process was carried out. The dispersion process was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The mixture was then passed through a nylon mesh with 48 μm openings three times, and then filtered through a magnetic filter (manufactured by Toc Engineering) at room temperature and a magnetic flux density of 12,000 gauss to obtain a conductive material dispersion (Dispersion 1). After filtration, magnetic granular metal pieces were found to adhere to the magnetic filter.

[0299] (Production Examples 2 to 13) According to the compositions shown in Table B2, each dispersion (Dispersions 2 to 13) was obtained in the same manner as in Production Example 1. All of the fibrous carbon dispersions of Production Examples 2 to 13 (Dispersions 2 to 13) had low viscosity and good stability.

[0300] The abbreviations in Table B2 have the following meanings: NTP3003: NTP3003 (manufactured by Shenzhen Nanotech Port Co. Ltd., multi-walled CNT, outer diameter 7 to 15 nm)

[0301]

[0302] As shown in Table B2, all of the fibrous carbon dispersions of Production Examples 1 to 13 (Dispersions 1 to 13) had low viscosity and good dispersion. In particular, the Mooney viscosity (ML １＋４ Dispersions with a measured value of 40 or more and 50 or less at 100°C (at 100°C) had extremely low viscosity. Similarly, the complex modulus and phase angle of Dispersions 1 to 13 were all good.

[0303] The dispersants (copolymer A) of Production Examples 1 to 13 have a Mooney viscosity of 70 or less, which is higher than that of ordinary nitrile rubbers having a high Mooney viscosity, and are therefore thought to have improved adsorption to fibrous carbon, making it easier to obtain fibrous carbon dispersions with good dispersibility. Furthermore, if the Mooney viscosity of the nitrile rubber were less than 10, it would be considered that the copolymer would have low adsorption stability to the conductive material and would be unable to disperse carbon fibers with strong cohesive strength at high concentrations. In other words, by including a copolymer having a Mooney viscosity of 10 or more and 70 or less as a dispersant, it is possible not only to suppress the aggregation of carbon fibers and achieve a good dispersion state, but also to achieve both dispersibility and stability even when dispersed at high concentrations.

[0304] <Secondary Battery Electrode Composite> (Example B1-1) An electrode composite for a secondary battery was prepared as follows according to the composition shown in Table 3. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser. The mixture was stirred for 30 minutes. Next, NMC and the dispersion were placed in the container of a planetary mixer (Hibismix® 2P-1, manufactured by Primix Corporation), and the mixture was stirred for 120 minutes at a rotation speed (revolution) of 20 rpm to prepare a mixture. The mixture was not in a slurry state during stirring. The temperature was controlled at 25°C during stirring using a temperature-controlled chiller. The resulting mixture was then transferred to a stainless steel tray and dried at 120°C for 2 hours using a hot air dryer to completely remove the liquid component. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 1.

[0305] Examples B1-2 to B1-13 Composites 2 to 13 were obtained in the same manner as in Example B1-1 according to the compositions shown in Table B3.

[0306] (Comparative Example B1-1) An electrode composite for a secondary battery was prepared as follows according to the composition shown in Table B3. NMC and fibrous carbon were charged into a container of a Mechanofusion (AMS-MINI, manufactured by Hosokawa Micron Corporation) and stirred at a rotation speed of 7,000 rpm for 10 minutes to obtain an electrode composite for a secondary battery 14. The temperature was controlled to 25°C during stirring using a temperature-controlled chiller. (Comparative Example B1-2) An electrode composite for a secondary battery was prepared as follows according to the composition shown in Table B3. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser, followed by stirring at 5,000 rpm for 30 minutes. Next, NMC and the above dispersion were charged into the container of a planetary mixer (Hibismix® 2P-1, manufactured by Primix Corporation) and stirred at a rotation speed (revolution) of 30 rpm for 90 minutes to prepare a slurry-like mixture. The temperature was controlled to 25°C during stirring using a temperature-controlled chiller. The resulting mixture was then transferred to a stainless steel tray and vacuum dried at 110° C. for 3 hours using a vacuum dryer to completely remove the solvent. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 15.

[0307] <Exothermic Peak Temperature of Fibrous Carbon> The exothermic peak temperature of the fibrous carbon was evaluated using a differential thermobalance Thermoplus EV02TG8121 manufactured by Rigaku Corporation. Compressed air was flowed at 200 mL / min, and the exothermic peak temperature obtained when the temperature was increased from 40°C to 800°C at 10°C / min was used as an index. The exothermic peak temperature was calculated by reading the peak top temperature of the exothermic peak of the fibrous carbon in the range of 400 to 700°C in the DTA curve obtained by measurement.

[0308] <Powder Resistivity of Composite> The powder resistivity of the composite was evaluated using a powder resistivity measurement system MCP-PD600 manufactured by Nitto Seiko Analytech Co., Ltd. Measurement was performed using a four-point probe method with a low-resistivity powder probe, and the volume resistivity when a load of 20 kN was applied to each sample was used as an index.

[0309] <Evaluation of the State of Fibrous Carbon in Composite> The dispersion state of the fibrous carbon in the composite was evaluated using a scanning electron microscope JSM-7800F manufactured by JEOL Ltd.

[0310] Criteria for determining the crushed state of the fibrous carbon on the active material surface: ◎: The area occupied by the fibrous carbon adsorbed on the active material in a crushed fiber state is 50% or more of the entire surface of the active material. ○: The area occupied by the fibrous carbon adsorbed on the active material in a crushed fiber state is 10% or more and less than 50% of the entire surface of the active material. ×: The area occupied by the fibrous carbon adsorbed on the active material in a crushed fiber state is less than 10% of the entire surface of the active material.

[0311]

[0312]

[0313] The abbreviations used in Table B3 have the following meanings: NMC: S800 (LiNi ０．８ Mn ０．１ Co ０．１ O ２ , manufactured by Ningbo Ronbay New Energy Technology Co., Ltd.)

[0314] As shown in Table B3, the Examples exhibited superior composite state and powder resistance of the fibrous carbon compared to the Comparative Examples. The fibrous carbon in the composites of the Examples was disintegrated and adsorbed to the surface of the active material without excessive aggregation, allowing for uniform formation of conductive paths within the composite. This is believed to be because the fibrous carbon dispersion, in which the electrode active material and the fibrous carbon were dispersed in a solvent, was compounded in a non-slurry state using a mechanochemical mixer, improving the adsorption strength of the fibrous carbon and suppressing aggregation of the fibrous carbon during the composite mixing process and the solvent drying process. On the other hand, in the Comparative Examples, insufficient disintegration of the fibrous carbon during the composite manufacturing process and excessive drying and aggregation during the drying process resulted in a reduced amount of adsorption to the active material surface and uneven distribution of the material, presumably resulting in non-uniform formation of conductive paths within the composite. Based on the above, the composites of the Examples can be expected to reduce electrode resistance and improve the rate and cycle characteristics of batteries when used as electrode composites.

[0315] [Experimental Example C]

[0316] <Polymer Mooney viscosity (ML １＋４Measurement of Mooney viscosity (ML)> The Mooney viscosity of a polymer is measured by preparing a measurement sample from a copolymer solution containing a solvent capable of dissolving the polymer. When the polymer is dissolved in NMP, the NMP solution of the polymer is coagulated with water, washed with methanol, and vacuum dried at 60°C for 12 hours to obtain a measurement sample. The Mooney viscosity (ML) of 40 g of the measurement sample is measured at 100°C using an L-type rotor in accordance with Japanese Industrial Standard JIS K6300-1. １＋４ , 100°C) was measured.

[0317] <Measurement of Hydrogenation Ratio of Polymer> The hydrogenation ratio was determined by IR measurement using the same method as the above-mentioned infrared spectroscopic analysis using the total reflection measurement method. Since the double bond derived from the conjugated diene monomer unit appears as a peak at 970 cm-1 and the hydrogenated single bond appears as a peak at 723 cm-1, the hydrogenation ratio was calculated from the ratio of the heights of these two peaks.

[0318] <Measurement of Initial Viscosity and TI Value of Fibrous Carbon Dispersion> The viscosity value was measured using a Brookfield viscometer ("BL" manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25°C. The fibrous carbon dispersion was thoroughly stirred with a spatula, and then immediately measured at a Brookfield viscometer rotor rotation speed of 60 rpm. The rotors used for the measurement were No. 1 when the viscosity value was less than 100 mPa·s, No. 2 when the viscosity value was 100 or more but less than 500 mPa·s, No. 3 when the viscosity value was 500 or more but less than 2,000 mPa·s, and No. 4 when the viscosity value was 2,000 or more but less than 10,000 mPa·s. The lower the viscosity, the better the dispersibility, and the higher the viscosity, the poorer the dispersibility. The obtained fibrous carbon dispersion, which clearly separated or settled, was judged to have poor dispersibility.

[0319] Initial viscosity Judgment criteria ◎: Less than 500 mPa·s (Excellent) ○: 500 mPa·s or more but less than 2,000 mPa·s (Good) △: 2,000 mPa·s or more but less than 10,000 mPa·s (Acceptable) ×: 10,000 mPa·s or more, settling or separation (Poor)

[0320] TI value Judgment criteria ◎: 1.5 or more and less than 3.0 (excellent) ○: 3.0 or more and less than 5.0 (good) △: 5.0 or more and less than 7.0 (poor) ×: 7.0 or more, sedimentation or separation (unacceptable)

[0321] <Measurement of Complex Elastic Modulus and Phase Angle of Fibrous Carbon Dispersion> The complex elastic modulus X and phase angle Y of the fibrous carbon dispersion were evaluated by performing dynamic viscoelasticity measurement using a rheometer (RheoStress1 rotational rheometer manufactured by ThermoFisherScientific Co., Ltd.) with a diameter of 60 mm and a 2° cone at 25°C, a frequency of 1 Hz, and a strain rate in the range of 0.01% to 5%. The smaller the obtained complex elastic modulus, the better the dispersibility, and the larger the obtained phase angle, the worse the dispersibility. Furthermore, the product (X × Y) of the obtained complex elastic modulus X (Pa) and the phase angle Y (°) was calculated.

[0322] (Calculation of the average fiber length of CNT and the average structure length of AB) NMP was added dropwise to the fibrous carbon dispersion while stirring with a disperser, and the resulting solution was diluted 50 times. A small amount of this solution was added dropwise to a substrate with a smooth surface and dried to prepare a sample for observation. The obtained sample for observation was observed and photographed with a scanning electron microscope. When the conductive material was CNT, 300 CNTs were randomly selected from the observation photograph, and the fiber length of each was measured, and the average value was calculated to obtain the average fiber length. When the conductive material was AB, 100 A and B were randomly selected from the observation photograph, and the structure length of each was measured, and the average value was calculated to obtain the average structure length.

[0323] <Polymer Production> (Synthesis Example 1: Preparation of Polymer 1 Solution) 30 parts of acrylonitrile, 70 parts of 1,3-butadiene, 3 parts of potassium soap oleate, 0.3 parts of azobisisobutyronitrile, 0.48 parts of t-dodecyl mercaptan, and 200 parts of ion-exchanged water were added to a stainless steel polymerization reactor. 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, yielding an acrylonitrile-conjugated diene rubber latex with a solids concentration of approximately 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the mixture was placed in a 1 L autoclave equipped with a stirrer. Dissolved oxygen in the contents was removed by flowing nitrogen gas for 10 minutes. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to the palladium was added to an autoclave. The atmosphere inside the autoclave was purged twice with hydrogen gas, and the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. The contents were then returned to room temperature, a nitrogen atmosphere was created inside the autoclave, and the solids were dried to recover the polymer product. The resulting polymer product was dissolved in NMP to prepare a 7% solution. A high-shear mixer (L5M-A, manufactured by Silverson) equipped with a square-hole high-shear screen was used, and shear force was applied at a speed of 8,600 rpm for 1 hour to obtain a 7% solution of Polymer 1.

[0324] Synthesis Example 2: Preparation of Polymer 2 Solution A 7% solution of Polymer 2 was obtained in the same manner as in Synthesis Example 1, except that the content of t-dodecyl mercaptan, a molecular weight modifier, was changed to 0.6 parts.

[0325] Synthesis Example 3 Preparation of Polymer 3 Solution A 7% solution of Polymer 3 was obtained in the same manner as in Production Example 1, except that the content of t-dodecyl mercaptan, the molecular weight modifier, used was changed to 0.65 parts and the treatment with a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) was used instead of the high-shear mixer. The treatment with the high-pressure homogenizer was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0326] Synthesis Example 4 Preparation of Polymer 4 Solution Hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene rubber, Therban® 3406, manufactured by ARLANXEO) was dissolved in NMP to prepare a 7% solution. A high shear mixer (L5M-A, manufactured by SILVERSON) equipped with a square-hole high shear screen was then used to apply shear force at a speed of 8,600 rpm for 1 hour to obtain a 7% solution of Polymer 4.

[0327] Synthesis Example 5 Preparation of Polymer 5 Solution A 7% solution of polymer 5 was obtained in the same manner as in Synthesis Example 4, except that hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene rubber, Therban® AT3404, manufactured by ARLANXEO) was used.

[0328] Synthesis Example 6 Preparation of Polymer 6 Solution A 7% solution of Polymer 6 was obtained in the same manner as in Synthesis Example 4, except that hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene rubber, Zetpol® 2000L, manufactured by Zeon Corporation) was used.

[0329] Synthesis Example 7: Preparation of Polymer 7 Solution To a stainless steel polymerization reactor, 30 parts of acrylonitrile, 70 parts of 1,3-butadiene, 3 parts of potassium soap oleate, 0.3 parts of azobisisobutyronitrile, 0.6 parts 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, yielding an acrylonitrile-conjugated diene rubber latex with a solids concentration of approximately 30%. Subsequently, ion-exchanged water was added to the latex to adjust the total solids concentration to 12%, and the mixture was placed in a 1 L autoclave equipped with a stirrer. Nitrogen gas was passed through the mixture for 10 minutes to remove dissolved oxygen from the contents. A catalyst solution prepared by dissolving 75 mg of palladium acetate as a hydrogenation catalyst in 180 mL of ion-exchanged water containing 4 times the molar amount of nitric acid relative to the palladium was added to an autoclave. The atmosphere inside the autoclave was purged twice with hydrogen gas, and the contents of the autoclave were heated to 50°C while pressurized with hydrogen gas to 3 MPa, and a hydrogenation reaction was carried out for 6 hours. The contents were then returned to room temperature, and a nitrogen atmosphere was created inside the autoclave. The solids were then dried and the polymer product was recovered. The obtained polymer product was dissolved in NMP to obtain a 7% solution of Polymer 7.

[0330] Synthesis Example 8 Preparation of Polymer 8 Solution Hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene rubber, Therban® 3407, manufactured by ARLANXEO) was dissolved in NMP to obtain a 7% solution of polymer 8.

[0331] Synthesis Example 9 Preparation of Polymer 9 Solution Hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene rubber, Therban® 3629, manufactured by ARLANXEO) was dissolved in NMP to obtain a 7% solution of Polymer 9.

[0332] The Mooney viscosity, hydrogenation rate, and ratio of aliphatic hydrocarbon structural units and nitrile group-containing structural units in the polymers of polymers 1 to 9 are shown in Table C1.

[0333]

[0334] <Preparation of Fibrous Carbon Dispersion> (Production Example 1) A 7% concentration polymer 1 solution and NMP were added to a stainless steel container so that the polymer was 0.6 parts by mass and the total amount of NMP was 91.1 parts by mass. 3.0 parts by mass of 10B (CNT) were taken and added while stirring with a disperser. A high shear mixer (L5M-A, manufactured by SILVERSON) equipped with a square-hole high shear screen was used, and batch dispersion was carried out at a speed of 8,600 rpm until the entire mixture became uniform and the dispersion particle size measured by the grind gauge was 250 μm or less. At this time, the dispersion particle size measured by the grind gauge was 180 μm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a circulation dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The viscosity of the dispersion liquid measured with a Brookfield viscometer (TOKISANGYO, VISCOMETER, MODEL: BL) at 60 rpm was 3,000 mPa s or less, and then the polymer 1 solution was further added to the stainless steel container so that 1.0 part by mass of 10B and 0.2 parts by mass of polymer 1 were added while stirring with a disperser, and a circulation dispersion treatment was again carried out with a high-pressure homogenizer. After circulation dispersion with a high-pressure homogenizer until the viscosity was 3,000 mPa s or less, the operation of adding 10B and polymer 1 solution to the stainless steel container while stirring with a disperser was repeated again (the total amount of 10B added was 5.0 parts by mass). Subsequently, a 25-pass dispersion treatment was carried out with a high-pressure homogenizer to obtain a fibrous carbon dispersion (dispersion 1) containing 5.0 parts by mass of CNT.

[0335] (Production Examples 2 to 6) Fibrous carbon dispersions (dispersions 2 to 6) were obtained in the same manner as in Production Example 1, except that the polymer 1 solution was changed to the polymer solutions shown in Table C2.

[0336] (Production Examples 7 to 9) In Production Example 2, except that a part of the NMP initially added to the stainless steel container was replaced with the additives listed in Table C2, fibrous carbon dispersions (dispersions 7 to 9) were obtained in the same manner as in Production Example 2.

[0337] (Production Example 10) A 7% PVP / NMP solution was prepared, and a fibrous carbon dispersion (dispersion 10) was obtained in the same manner as in Production Example 2, except that 40% of the polymer 2 solution used in Production Example 2 was replaced with the 7% PVP / NMP solution.

[0338] (Production Example 11) A fibrous carbon dispersion (dispersion 11) was obtained in the same manner as in Production Example 1, except that the polymer 1 solution added in Production Example 1 was changed to a PVP solution and the number of passes of the high-pressure homogenizer was changed to 10.

[0339]

[0340] The abbreviations used in Table C2 have the following meanings: 10B: JENOTUBE10B (manufactured by JEIO Corporation, multi-walled CNT, average outer diameter 10 nm) PVP: Polyvinylpyrrolidone K30 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Aminoethanol: 2-aminoethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) NaOH: Sodium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd., purity >98.0%, granular) BuONa: Sodium t-butoxide (manufactured by Tokyo Chemical Industry Co., Ltd.) NMP: N-methylpyrrolidone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0341] The evaluation results of each fibrous carbon dispersion are shown in Table C3.

[0342]

[0343] <Electrode Composite for Secondary Battery> (Example C1-1) An electrode composite for secondary battery was prepared as follows according to the composition shown in Table C4. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser, followed by stirring for 30 minutes. Next, NCA and the above dispersion were placed in a Nobilta (NOB-MINI, manufactured by Hosokawa Micron Corporation) container, and stirred at a rotation speed of 5,000 rpm for 20 minutes to prepare a non-slurry mixture. During stirring, the temperature was controlled at 25°C using a temperature-controlled chiller. Thereafter, the obtained mixture was taken out into a stainless steel tray and vacuum-dried at 100°C for 1 hour using a vacuum dryer to completely remove the solvent. The dried product was coarsely pulverized in a mortar to obtain electrode composite for secondary battery 1.

[0344] Examples C1-2 to C1-12 Composites 2 to 12 were obtained in the same manner as in Example C1 according to the compositions shown in Table C4.

[0345] Comparative Example C1-1 An electrode composite for a secondary battery was produced as follows according to the composition shown in Table C4: NCA and fibrous carbon 10B were weighed out, placed in a Nobilta (NOB-MINI, manufactured by Hosokawa Micron Corporation) container, and stirred at 5000 rpm for 20 minutes to obtain electrode composite 13 for a secondary battery.

[0346] (Comparative Example C1-2) A secondary battery electrode composite was prepared as follows according to the composition shown in Table C4. First, fibrous carbon dispersion 1 was placed in a stainless steel container, and NMP was added while stirring with a disperser. The mixture was stirred at 5,000 rpm for 30 minutes. Next, NMC and the dispersion were placed in the container of a planetary mixer (Hibismix® 2P-1 model, manufactured by Primix Corporation), and the mixture was stirred at a rotation speed (revolution) of 20 rpm for 90 minutes to prepare a slurry-like mixture. The temperature was controlled at 25°C using a temperature-controlled chiller during stirring. The resulting mixture was then transferred to a stainless steel tray and vacuum-dried at 110°C for 3 hours using a vacuum dryer to completely remove the solvent. The dried product was coarsely pulverized in a mortar to obtain secondary battery electrode composite 14.

[0347] <Evaluation of the State of Fibrous Carbon in Composite> The dispersion state of the fibrous carbon in the composite was evaluated using a scanning electron microscope JSM-7800F manufactured by JEOL Ltd.

[0348] Criteria for determining the crushed state of fibrous carbon on the surface of an active material: ◎: The area occupied by fibrous carbon adsorbed to the active material in a crushed fiber state is 50% or more of the entire surface of the active material. ○: The area occupied by fibrous carbon adsorbed to the active material in a crushed fiber state is 10% or more and less than 50% of the entire surface of the active material. △: The area occupied by fibrous carbon adsorbed to the active material in a crushed fiber state is less than 10% of the entire surface of the active material. ×: The fibrous carbon fibers are not adsorbed to the active material in a crushed state.

[0349] <Exothermic Peak Temperature of Fibrous Carbon> The exothermic peak temperature of the fibrous carbon was evaluated using a differential thermobalance Thermoplus EV02TG8121 manufactured by Rigaku Corporation. Compressed air was flowed at 200 mL / min, and the exothermic peak temperature obtained when the temperature was increased from 40°C to 800°C at 10°C / min was used as an index. The exothermic peak temperature was calculated by reading the peak top of the exothermic peak of the fibrous carbon due to combustion in the range of 400 to 700°C in the DTA curve obtained by measurement.

[0350]

[0351]

[0352] The abbreviations used in Table C4 have the following meanings: NCA: HED (registered trademark) NAT-7050 (manufactured by BASF Toda Battery Materials LLC, composition: LiNi ０．８ Co ０．１５ Al ０．０５ O ２ )

[0353] As shown in Table C4, from the exothermic peak temperatures of SEM and TG-DTA, it can be seen that in the Examples, the fibrous carbon in the composite was in a state of being moderately loosened and adsorbed on the surface of the active material without excessive aggregation. On the other hand, in the Comparative Examples, the loosening of the agglomerates of the fibrous carbon and the adsorption of the loosened material on the surface of the active material were insufficient.

[0354] <Preparation of Positive Electrode Film> (Example C2-1) 2 parts of polyvinylidene fluoride resin (KF polymer #1300) as a binder and 98 parts of electrode composite 1 were weighed into a plastic container and stirred at 2,000 rpm for 15 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310). The obtained powder mixture was calendered onto a 20 μm-thick aluminum foil current collector using a powder feeder and a calender roll (roll temperature 200° C.) to form an electrode film, thereby obtaining a positive electrode film 1.

[0355] Examples C2-2 to C2-12, Comparative Examples C2-1 and 2-2 Positive electrode films 2 to 14 were obtained in the same manner as for the positive electrode film 1 using the composites 2 to 14.

[0356] <Evaluation of Resistance of Positive Electrode Film> The volume resistivities of electrode films 1 to 14 were measured by the four-probe method using a Loresta GP (manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS-K7194. For the resistance measurements, a measurement electrode was used in which the coating substrate used in the preparation of each electrode was changed from aluminum foil to a PET substrate. The relative value (%) based on the volume resistivity of the electrode film of Comparative Example 2-2 was determined and evaluated according to the following criteria.

[0357] Electrode resistance characteristic evaluation criteria ◎: 200% or more (very good) ○: 150% or more and less than 200% (excellent) ○△: 100% or more and less than 150% (good) △: 50% or more and less than 100% (poor) ×: Less than 50% (very bad)

[0358] <Evaluation of strength variation of electrode film for positive electrode> The indentation elastic modulus of the composite layer portion of the electrode film was determined using a microhardness tester (Fischer Instruments, FISCHERSCOPE H100). The electrode film was fixed to a base with the composite layer side facing up, and an indentation test was performed on the composite layer. A round indenter (diameter 400 μm) was used as the indenter, and measurements were taken at 100 locations under a load of 1 mN, a loading rate of 0.2 mN / s, and a creep time of 5 s. The strength variation of the electrode film was evaluated from the relative standard deviation of the obtained indentation elastic modulus.

[0359] Criteria for variability in electrode film strength ◎: Less than 10% (very good) ○: 10% or more and less than 20% (excellent) ○△: 20% or more and less than 40% (good) △: 40% or more and less than 50% (poor) ×: 50% or more (very bad)

[0360]

[0361] As shown in Table C5, the Examples exhibited superior electrode resistance and smaller variations in indentation strength compared to the Comparative Examples. The fibrous carbon in the composite in the Examples was disintegrated and adsorbed onto the active material surface without excessive agglomeration. Therefore, it is presumed that the conductive paths within the electrode were uniformly formed, leading to reduced electrode resistance. Furthermore, because the composite was homogeneous, a homogeneous electrode was formed even when mixed with a binder, and variations in electrode strength were also suppressed. Among these, those in which the product (X × Y) of the complex modulus X (Pa) and the phase angle Y (°) of the fibrous carbon dispersion was within a preferred range exhibited particularly good electrode resistance and small variations in electrode strength. On the other hand, in the Comparative Examples, insufficient disintegration of the fibrous carbon during the composite manufacturing process and excessive drying and agglomeration during the drying process resulted in a reduced amount of adsorption to the active material surface and uneven distribution of the material, resulting in non-uniform formation of the conductive paths within the electrode. Additionally, it is presumed that a non-homogeneous composite would result in non-uniform material composition within the fabricated electrode, resulting in greater variations in electrode strength. If the conductive path, composition, and strength of the electrode become non-uniform, this will cause a decrease in capacity when repeated charge / discharge tests are performed. From the above, it has been demonstrated that the electrode composite produced by the production method of the present invention has homogeneous and excellent electrode properties, and it can be expected to exhibit excellent battery properties.

[0362] Although the present invention has been described with reference to the above-mentioned several embodiments, the present invention is not limited to these several embodiments. Various modifications can be made to the configuration and details of the present invention within the scope of the present invention.

[0363] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-108281 filed on June 30, 2023, the subject matter described in Japanese Patent Application No. 2023-108282 filed on June 30, 2023, and the subject matter described in Japanese Patent Application No. 2023-108389 filed on June 30, 2023, the entire disclosures of which are incorporated herein by reference.

Claims

1. A method for producing a composite for a secondary battery electrode, comprising an electrode active material and fibrous carbon, the method comprising the steps of: combining the electrode active material and a fibrous carbon dispersion, in which the fibrous carbon is dispersed in a solvent, in a non-slurry state using a mechanochemical mixer; and removing the solvent and drying the composite.

2. The method for producing a composite for a secondary battery electrode according to claim 1, wherein the fibrous carbon dispersion comprises fibrous carbon, a dispersant, and a solvent, and the dispersant comprises a copolymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit.

3. The method for producing a composite for a secondary battery electrode according to claim 1 or 2, wherein the copolymer contains an aliphatic hydrocarbon structural unit, a nitrile group-containing structural unit, and an alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit, the aliphatic hydrocarbon structural unit contains an alkylene structural unit, the content of the aliphatic hydrocarbon structural unit is 40 mass% or more and less than 85 mass% based on the mass of the copolymer, the content of the nitrile group-containing structural unit is 15 mass% or more and 50 mass% or less based on the mass of the copolymer, and the content of the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is 10 mass% or less based on the mass of the copolymer, the total content of the aliphatic hydrocarbon structural unit, the nitrile group-containing structural unit, and the alkyl group-substituted or unsubstituted carbamoyl group-containing structural unit is 80 mass% or more based on the mass of the copolymer, and the weight average molecular weight of the copolymer is 5,000 to 400,000.

4. A method for producing a composite for a secondary battery electrode according to any one of claims 1 to 3, wherein the copolymer further contains less than 1 mass % of a carboxyl group-containing structural unit based on the mass of the copolymer.

5. A method for producing a composite for a secondary battery electrode according to any one of claims 1 to 4, wherein the fibrous carbon dispersion contains 1 mass % or more and 20 mass % or less of a base based on the mass of the copolymer.

6. A method for producing a composite for a secondary battery electrode according to any one of claims 1 to 5, characterized in that the composite for a secondary battery electrode has an exothermic peak temperature of 520°C or less of the fibrous carbon obtained by simultaneous thermogravimetry and differential thermal analysis under an oxygen atmosphere.

7. The fibrous carbon dispersion comprises fibrous carbon, a dispersant, and a solvent, the dispersant comprises a copolymer A containing a nitrile group-containing structural unit and an aliphatic hydrocarbon structural unit, and the Mooney viscosity (ML １＋４ 2. The method for producing a composite for a secondary battery electrode according to claim 1, wherein the fibrous carbon dispersion has a phase angle of 19° or more at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement.

8. The method for producing a composite for a secondary battery electrode according to claim 7, wherein the complex modulus of elasticity of the fibrous carbon dispersion as determined by dynamic viscoelasticity measurement is less than 20 Pa.

9. The method for producing a composite for a secondary battery electrode according to claim 7 or 8, wherein the content of the nitrile group-containing structural unit is 15 mass% or more and 50 mass% or less, and the content of the aliphatic hydrocarbon structural unit is 40 mass% or more and less than 85 mass%, based on the mass of the copolymer A.

10. The method for producing a composite for a secondary battery electrode according to any one of claims 7 to 9, wherein the composite for a secondary battery electrode has an exothermic peak temperature of 520°C or less, as determined by simultaneous thermogravimetry and differential thermal analysis in an oxygen atmosphere, and a volume resistivity of 100 Ω cm or less under a load of 20 kN.

11. The method for producing a composite for a secondary battery electrode according to claim 1, wherein the fibrous carbon dispersion comprises fibrous carbon, a dispersant, and a solvent, the product (X×Y) of the complex modulus X (Pa) and the phase angle Y (°) measured by dynamic viscoelasticity measurement of the fibrous carbon dispersion is 30 or more and 3,000 or less, and the phase angle Y (°) measured by dynamic viscoelasticity measurement of the fibrous carbon dispersion is 5° or more and 80° or less.

12. The method for producing a composite for a secondary battery electrode according to claim 11, wherein the complex modulus X of the fibrous carbon dispersion as determined by dynamic viscoelasticity measurement is 0.1 Pa or more and 200 Pa or less.

13. A method for producing a composite for a secondary battery electrode according to claim 11 or 12, wherein the dispersant comprises a copolymer containing an aliphatic hydrocarbon structural unit and a nitrile group-containing structural unit, the aliphatic hydrocarbon structural unit comprises an alkylene structural unit, the content of the aliphatic hydrocarbon structural unit is 40 mass% or more and less than 85 mass% based on the mass of the polymer, and the content of the nitrile group-containing structural unit is 15 mass% or more and 50 mass% or less based on the mass of the polymer.

14. The method for producing a composite for a secondary battery electrode according to any one of claims 11 to 13, wherein the TI value of the fibrous carbon dispersion measured with a Brookfield viscometer is 1.5 to 5.

0.

15. The method for producing a composite for a secondary battery electrode according to any one of claims 11 to 14, wherein the exothermic peak temperature of the fibrous carbon obtained by simultaneous thermogravimetry and differential thermal analysis in an oxygen atmosphere is 520°C or less.

16. A method for producing a composite for a secondary battery electrode according to any one of claims 1 to 15, wherein the composite for a secondary battery electrode contains a binder resin.

17. A method for producing an electrode film, comprising: preparing an electrode composite for a secondary battery according to the method of any one of claims 1 to 15; and forming an electrode film using the electrode composite for a secondary battery.

18. A method for producing a secondary battery, comprising: preparing an electrode composite for a secondary battery according to the method of any one of claims 1 to 15; and forming an electrode film using the electrode composite for a secondary battery.

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