Resin composition, carbon material dispersion composition, mixture slurry, electrode film, secondary battery, and vehicle

Abstract

Provided is a resin composition containing a copolymer (X) having an alkylene structural unit and a nitrile group-containing structural unit, and an alkali metal. The content of the alkali metal is not less than 50 ppm but less than 10,000 ppm. The resin composition has a resistivity of 5,000-25,000 Ω·cm when the content percentage of non-volatile components in the resin composition is set to 8 mass% by using N-methyl-2 pyrrolidone.

Description

Resin composition, carbon material dispersion composition, composite slurry, electrode film, secondary battery, and vehicle

[0001] The present disclosure relates to a resin composition and a carbon material dispersion composition. More specifically, the present disclosure relates to a carbon material dispersion composition containing the resin composition and a carbon material, a composite slurry containing the carbon material dispersion composition and an active material, an electrode film formed by coating them, a secondary battery including an electrode having the electrode film and an electrolyte, and a vehicle including the secondary battery.

[0002] With the spread of electric vehicles and the miniaturization, weight reduction, and improved performance of portable devices, secondary batteries with high energy density and even higher capacity are required. Against this background, non-aqueous electrolyte secondary batteries using a non-aqueous electrolyte, particularly lithium-ion secondary batteries, are being used in many devices because of their high energy density and high voltage.

[0003] The negative electrode materials used in these lithium-ion secondary batteries are carbon materials, such as graphite, which have a large charge / discharge capacity per unit mass at a base potential close to that of lithium (Li). However, these electrode materials are being used to achieve charge / discharge capacities per mass close to the theoretical value, and the energy density per mass of the battery is approaching its limit. Therefore, in order to increase the electrode utilization rate, studies are being conducted to reduce the conductive additives and binders that do not contribute to the discharge capacity.

[0004] Conductive additives play a role in forming conductive paths within electrodes, and are required to be resistant to breakage due to the expansion and contraction of the electrode film. To maintain conductive paths with a small amount of conductive additive, it is effective to use carbon materials with a large specific surface area, particularly carbon nanotubes (CNTs), a type of nanocarbon. However, carbon materials with a large specific surface area have strong cohesive forces, making it difficult to uniformly disperse them in composite slurries and electrode films.

[0005] In view of this background, many methods have been proposed in which a carbon material dispersion composition is prepared using various dispersants, and a composite slurry is produced via the carbon material dispersion composition.

[0006] For example, Patent Documents 1 and 2 propose carbon material dispersion compositions with improved dispersibility by adding a basic compound together with a polymer dispersant such as polyvinylpyrrolidone, hydrogenated nitrile rubber, etc. However, while these dispersants can produce carbon material dispersion compositions in a well-dispersed state, they can sometimes result in poor dispersion of the carbon material during the process of forming an electrode film, resulting in poor conductivity.

[0007] In addition, in Patent Documents 3 and 4, a predetermined Mooney viscosity (ML １＋４ It has been proposed that the use of an electrode binder composition containing hydrogenated nitrile rubber having a weight-average molecular weight of 190,000 to 210,000 g / mol enables the carbon material to be dispersed well in a composite slurry. Patent Document 5 proposes the use of a dispersant composition containing hydrogenated nitrile rubber having a weight-average molecular weight of 190,000 to 210,000 g / mol. However, these dispersants have low dispersibility, making it difficult to disperse carbon materials with large specific surface areas at high concentrations.

[0008] Therefore, Patent Document 6 proposes a technology in which a copolymer having a specific structural unit and molecular weight is used as a dispersant to disperse a carbon material well in a solvent and maintain a good dispersion state when preparing a composite slurry and when producing an electrode film. However, a large amount of base must be added to obtain the specific structure, which poses a problem of a decrease in electrode strength due to a decrease in the molecular weight of the dispersant and / or deterioration of the binder resin.

[0009] Japanese Patent Publication No. 2014-181140 Korean Patent Registration No. 10-1831562 Patent No. 6848862 Patent No. 6863278 Special Publication No. 2022-536304 Japanese Patent Publication No. 2021-122751

[0010] Therefore, the problem to be solved by the present disclosure is to provide a resin composition and a carbon material dispersion composition that can achieve both good dispersibility and good electrode properties, a composite slurry that can obtain an electrode film with high conductivity and adhesion, and more specifically, a secondary battery that has excellent rate characteristics and cycle characteristics, and a vehicle that has the secondary battery and is therefore highly safe and has improved fuel efficiency.

[0011] The present inventors conducted extensive research to solve the above-mentioned problems and found that the above-mentioned problems can be solved by a resin composition containing a copolymer (X) having a specific structure and an alkali metal in an amount of 50 ppm or more and less than 10,000 ppm, and having a resistivity within a specific range when the nonvolatile content is adjusted to 8% by mass with N-methyl-2-pyrrolidone.

[0012] That is, the present disclosure includes the following embodiments. The embodiments of the present disclosure are not limited to the following. [1] A resin composition containing a copolymer (X) having an alkylene structural unit and a nitrile group-containing structural unit, and an alkali metal, wherein the content of the alkali metal is 50 ppm or more and less than 10,000 ppm, and the resin composition has a resistivity of 5,000 Ω·cm or more and 25,000 Ω·cm or less when the non-volatile content is adjusted to 8% by mass with N-methyl-2-pyrrolidone. [2] The resin composition according to [1], wherein the Z-average molecular weight of the copolymer (X) is 20,000 or more and 200,000 or less. [3] The resin composition according to [1] or [2], wherein the ratio (Mz / Mw) of the Z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the copolymer (X) is 2.0 or less. [4] A carbon material dispersion composition containing the resin composition according to any one of [1] to [3], and a carbon material. [5] A composite slurry containing the carbon material dispersion composition according to [4] and an active material. [6] An electrode film obtained by coating the composite slurry according to [5]. [7] A secondary battery comprising an electrode having the electrode film according to [6] and an electrolyte. [8] A vehicle comprising the secondary battery according to [7].

[0013] The resin composition of the present disclosure has excellent dispersibility of dispersed substances such as carbon materials, and by using a carbon material dispersion composition containing this resin composition, an electrode film with excellent conductivity and adhesion can be obtained. Furthermore, a secondary battery with excellent rate characteristics and cycle characteristics can be obtained. This makes the resin composition suitable for use in vehicles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, where high capacity, high output, and high durability are required for the secondary battery to be installed.

[0014] The resin composition, carbon material dispersion composition, composite slurry, electrode film, and secondary battery of the present disclosure will be described in detail below, but are not limited thereto. Note that the numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples.

[0015] In addition, in this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the range's lower and upper limits.

[0016] In this specification, "N-methyl-2-pyrrolidone" may be referred to as "NMP," "carbon black" as "CB," "carbon nanotubes" as "CNT," and "carbon material dispersion composition" as "dispersion composition." The non-volatile content refers to the solid content excluding the solvent, and is determined by measuring the content of the residue remaining after volatilization or evaporation when the resin composition is heated at a temperature equal to or higher than the boiling point of the contained solvent.

[0017] In the embodiments of the present disclosure, the resin composition refers to a state before the carbon material and electrode active material are added, and the carbon material dispersion composition refers to a state before the electrode active material is added. In this respect, the resin composition and the carbon material dispersion composition are distinguished from a composite slurry containing an electrode active material. This concept excludes a state in which the carbon material and electrode active material are intentionally added to the resin composition. The carbon material and electrode active material may be present in an amount of 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, based on the non-volatile component content of the resin composition (100% by mass). This concept excludes a state in which the electrode active material is intentionally added to the carbon material dispersion composition. The electrode active material may be present in an amount of 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, based on the non-volatile component content of the carbon material dispersion composition (100% by mass). Unless otherwise noted, the various components mentioned in this specification may be used independently, either singly or in combination of two or more. The numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples.

[0018] Resin Composition The resin composition of this embodiment contains a copolymer (X) having at least an alkylene structural unit and a nitrile group-containing structural unit, and an alkali metal. The alkali metal content is 50 ppm or more and less than 10,000 ppm. Furthermore, when this resin composition is dissolved in N-methyl-2-pyrrolidone to a nonvolatile content of 8% by mass, the resistivity is 5,000 Ω cm or more and 25,000 Ω cm or less. This resin composition provides excellent dispersibility of the dispersed material and a stable dispersion composition. In particular, when the dispersed material is a carbon material, a carbon material dispersion composition with excellent dispersibility and oxidation resistance is obtained, and the resulting composition also has excellent conductivity. Therefore, secondary batteries using this composition can have excellent rate characteristics and high-temperature cycle characteristics.

[0019] As the material to be dispersed, any of conventionally known inorganic pigments, organic pigments, etc. can be used in addition to the carbon materials described below, but it is particularly effective for carbon materials.

[0020] Examples of inorganic pigments include metal powders such as gold, silver, copper, silver-plated copper powder, silver-copper composite powder, silver-copper alloy, amorphous copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, and platinum; inorganic powders coated with these metals; powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, and ruthenium oxide; inorganic powders coated with these metal oxides; carbon nanotubes, carbon black, and graphite.

[0021] Examples of organic pigments include various pigments used in inks, etc. Examples of such pigments include soluble azo pigments, insoluble azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, perylene pigments, perinone pigments, dioxazine pigments, anthraquinone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, pyranthrone pigments, and diketopyrrolopyrrole pigments.

[0022] When the resin composition of the present disclosure is adjusted to a non-volatile content of 8% by mass using N-methyl-2-pyrrolidone, the resistivity is 5,000 Ω·cm or more and 25,000 Ω·cm or less. This resin composition can achieve both good dispersibility and good electrode characteristics. Resistivity can be measured by first measuring the non-volatile content of the resin composition, adding N-methyl-2-pyrrolidone so that the non-volatile content is 8% by mass, and mixing to prepare a sample for measuring liquid resistance. Resistivity can be measured by the method described in the examples.

[0023] From the viewpoint of achieving both the dispersibility of the dispersed substance and the electrode resistance, the resistivity is preferably 5,000 Ω cm or more and 20,000 Ω cm or less, more preferably 7,000 Ω cm or more and 15,000 Ω cm or less. The resistivity of the resin composition can be adjusted by modifying the copolymer with a basic compound such as an alkali metal compound, or by applying shear stress to the copolymer, thereby controlling the molecular weight, molecular weight distribution, ion concentration, etc. of the copolymer. In this specification, modification of the copolymer not only refers to modification of a portion of the structural units of the copolymer by hydrolysis, etc., but also includes changes in the viscoelasticity and molecular weight of the copolymer.

[0024] The initial viscosity of the resin composition of this embodiment, measured using a Brookfield viscometer at 100 rpm and 25°C, is preferably 10 mPa·s or more and 2,000 mPa·s or less, more preferably 100 mPa·s or more and 1,000 mPa·s or less, and even more preferably 100 mPa·s or more and 500 mPa·s or less. Within the above ranges, the resin composition can have better stability. Furthermore, when an alkali metal compound is contained in the resin composition, precipitation of the alkali metal compound is suppressed, resulting in better stability.

[0025] (Copolymer (X)) The copolymer (X) is a copolymer having an alkylene structural unit and a nitrile group-containing structural unit. This copolymer may also have other structural units.

[0026] From the viewpoint of dispersibility of the dispersed substance, the total content of the alkylene structural unit and the nitrile group-containing structural unit is preferably 50% by mass or more and 100% by mass or less, more preferably 80% by mass or more, based on 100% by mass of the copolymer (X). When the copolymer (X) is a modified copolymer, from the viewpoint of dispersibility of the dispersed substance, the total content of the alkylene structural unit and the nitrile group-containing structural unit is preferably 50% by mass or more and 100% by mass or less, based on 100% by mass of the copolymer (X). Furthermore, when the nitrile group-containing structural unit is modified by hydrolysis, the total content is preferably 50% by mass or more and 97% by mass or less, more preferably 80% by mass or more and 95% by mass or less. The content of other structural units is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. When the nitrile group-containing structural unit has been modified to have an amide group-containing structural unit, the content of the amide group-containing structural unit is preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the copolymer (X). If the content of the amide group-containing structural unit is high, when the copolymer is dissolved in an electrolyte solution, the viscosity of the electrolyte solution may increase, and the ionic conductivity may be significantly reduced.

[0027] The copolymer (X) is preferably modified by adjusting the amount of a basic compound such as an alkali metal compound added, so as to control only the molecular weight or properties such as viscoelasticity while maintaining the composition.

[0028] A structural unit is a state in which a monomer is incorporated into a polymer after polymerization, and the content of a structural unit formed by polymerizing a monomer usually coincides with the ratio of the monomer to all the monomers used in the polymerization of the polymer (feed ratio), unless otherwise specified. In other words, the content of each monomer based on the total of all the monomers is the content of each structural unit.

[0029] The copolymer (X) may be a copolymer modified by adding a basic compound such as an alkali metal compound. When the nitrile group contained in the nitrile group-containing structural unit of the copolymer is modified by hydrolysis or the like, it is preferable that the content of the alkylene structural unit and the nitrile group-containing structural unit of the modified copolymer (X) is within the above range. The content of the alkylene structural unit and the nitrile group-containing structural unit can be calculated by IR measurement. For example, it can be calculated by the method described in ISO14558:2016. It can also be measured by the ATR method without using the KBr tablet method. By using the above method, the structural unit and its content can be identified even for copolymers (X) modified with a basic compound.

[0030] The number average molecular weight (Mn) of the copolymer (X) of this embodiment is preferably 70,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. It is also preferably 10,000 or more. When the number average molecular weight (Mn) of the copolymer (X) is within the above range, the copolymer is easily adsorbed to the dispersed material, and the dispersed material is easily wetted by the solvent.

[0031] The weight average molecular weight (Mw) of the copolymer (X) of this embodiment is preferably 20,000 or more and 180,000 or less, more preferably 20,000 or more and 150,000 or less, and even more preferably 20,000 or more and 100,000 or less.

[0032] The Z-average molecular weight (Mz) of the copolymer (X) of this embodiment is preferably 20,000 to 250,000, more preferably 20,000 to 200,000, still more preferably 25,000 to 180,000, and particularly preferably 30,000 to 100,000.

[0033] When the weight-average molecular weight (Mw) and Z-average molecular weight (Mz) of the copolymer (X) are within the above ranges, not only is dispersion of a dispersed substance such as a carbon material facilitated when the resin composition contains the dispersed substance, but the viscosity of the resin composition is also reduced. This also improves the efficiency of removing metal foreign particles contained in the resin composition using a filter or magnet. The number-average molecular weight (Mn), weight-average molecular weight (Mw), and Z-average molecular weight (Mz) are values ​​calculated in terms of polystyrene and can be measured by gel permeation chromatography (GPC).

[0034] The Z-average molecular weight is a weighted average using the square of the molecular weight as the weight, and is a value that is easily affected by the high molecular weight. The copolymer (X) has a molecular weight distribution, and the low-molecular-weight component functions to improve the wettability of the dispersed material. The high-molecular-weight component also functions to improve battery properties such as the viscosity stability of the dispersed material, the oxidation resistance of the copolymer, and the electrolyte dissolution resistance. By controlling the Z-average molecular weight of the copolymer (X) within the above range before adding a dispersed material such as a carbon material to the resin composition, the viscosity of the resin composition can be reduced, the dispersed material can be more easily wetted, and dispersion can proceed more easily. Furthermore, because the viscosity of the carbon material dispersion composition described below is reduced, the dispersion media moves more efficiently when using a disperser using media such as a bead mill. The kinetic energy of the dispersion media is proportional to the mass and the square of the speed of the dispersion media. Therefore, by efficiently moving the dispersion media in the carbon material dispersion composition, not only can the desired degree of dispersion be adjusted, but the carbon material dispersion composition can also be homogenized, resulting in a carbon material dispersion composition with excellent stability over time and excellent conductivity.

[0035] The Z-average molecular weight (Mz) of the copolymer (X) can be controlled by the synthesis conditions of the copolymer (X) (composition, amount of blend, catalyst, reaction temperature, reaction time, etc.), modifying the copolymer, applying shear stress to the copolymer, etc. The Z-average molecular weight can be reduced by applying mechanical shear stress using, for example, a roll or a kneader.

[0036] The polydispersity index (Mw / Mn) of the copolymer (X) of this embodiment is preferably 2.2 or less, more preferably 2.0 or less, and even more preferably 1.8 or less. Also, it is preferably 1.2 or more. When the polydispersity index (Mw / Mn) is within the above range, the ratio of low molecular weight components contained in the copolymer (X) is appropriate, and particularly when dispersing a carbon material, wetting of the dispersed material proceeds quickly, so dispersion progresses easily. This makes it possible to obtain a carbon material dispersion composition while maintaining the structure of the carbon material, and it is easy to obtain an electrode film and a secondary battery having high conductivity and adhesion.

[0037] The ratio (Mz / Mw) of the weight average molecular weight (Mw) to the Z average molecular weight (Mz) of the copolymer (X) is preferably 2.2 or less, more preferably 2.0 or less, even more preferably 1.9 or less, and particularly preferably 1.8 or less. Also, it is preferably 1.5 or more, more preferably 1.6 or more. When the ratio (Mz / Mw) of the weight average molecular weight (Mw) to the Z average molecular weight (Mz) is within the above range, the ratio of high molecular weight components contained in the copolymer (X) is appropriate, and a dispersion composition having good dispersion stability of the dispersed material is easily obtained.

[0038] The number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) of the copolymer (X) can be adjusted, for example, by dispersing the copolymer and an amide polar solvent under high pressure. A resin composition containing an amide polar solvent may also be dispersed under high pressure. For high pressure dispersion, a "Starburst" manufactured by Sugino Machine Ltd. or the like can be used. In particular, the number average molecular weight (Mn) is preferably adjusted by dispersing the copolymer and an amide polar solvent under high pressure in the presence of an alkali metal.

[0039] [Alkylene structural unit] The alkylene structural unit is a structural unit containing an alkylene structure, and preferably a structural unit consisting of only an alkylene structure. The alkylene structure is preferably a linear alkylene structure or a branched alkylene structure. However, this does not include structural units having a nitrile group.

[0040] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1A).

[0041] General formula (1A)

[0042] In general formula (1A), 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.

[0043] The alkylene structural unit preferably contains a structural unit represented by the following general formula (1B).

[0044] General formula (1B)

[0045] In general formula (1B), 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.

[0046] The method for introducing the alkylene structural unit into the copolymer is not particularly limited, but examples thereof include the following method (1a) or (1b).

[0047] 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 disclosure, "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 contains units obtained by hydrogenating the conjugated diene monomer units as alkylene structural units.

[0048] 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 also contain a monomer unit that does not have a carbon-carbon double bond and contains 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 containing a branch point, the copolymer prepared above and the copolymer are branched polymers.

[0049] In the method (1b), a copolymer is prepared by a polymerization reaction using a monomer composition containing an α-olefin monomer. The prepared copolymer contains α-olefin monomer units. The finally obtained copolymer contains the α-olefin monomer units as alkylene structural units.

[0050] 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.

[0051] 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.

[0052] 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, rhodium, platinum, and copper.

[0053] 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 preferably 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.

[0054] 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 (1A) and structural units represented by the above formula (1B).

[0055] The content of the alkylene structural unit is preferably 50% by mass or more and 75% by mass or less, more preferably 55% by mass or more and 70% by mass or less, and even more preferably 55% by mass or more and 65% by mass or less, based on 100% by mass of the total content of the alkylene structural unit and the nitrile group-containing structural unit. By setting the content of the alkylene 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 the copolymer to the electrolyte can be controlled, and problems such as the copolymer dissolving in the electrolyte in the battery and increasing the resistance of the electrolyte can be prevented.

[0056] [Nitrile group-containing structural unit] 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.

[0057] The nitrile group-containing structural unit preferably contains a structural unit represented by the following general formula (2A).

[0058] General formula (2A)

[0059] 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.

[0060] The nitrile group-containing structural unit may include a structural unit represented by the following general formula (2B).

[0061] General formula (2B)

[0062] In general formula (2B), R represents a methyl group.

[0063] The method for introducing the nitrile group-containing structural unit into the copolymer is not particularly limited, but a method (method (2a)) in which a copolymer is prepared by polymerization using a monomer composition containing a nitrile group-containing monomer is preferably used. The finally obtained copolymer contains the nitrile group-containing structural unit as the nitrile group-containing structural unit. Examples of nitrile group-containing monomers that can form 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, and specific examples include acrylonitrile and methacrylonitrile. In particular, from the viewpoint of increasing the intermolecular forces between copolymers and / or between the copolymer and the dispersed substance (adsorbate), it is preferable that the nitrile group-containing monomer contains acrylonitrile. The nitrile group-containing monomers can be used alone or in combination of two or more.

[0064] The content of the nitrile group-containing structural unit is preferably 25% by mass or more and 50% by mass or less, more preferably 30% by mass or more and 45% by mass or less, and even more preferably 35% by mass or more and 45% by mass or less, based on 100% by mass of the total content of the alkylene structural unit and the nitrile group-containing structural unit. 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 the resin composition to the electrolyte can be controlled, and problems such as the resin composition dissolving in the electrolyte in the battery and increasing the resistance of the electrolyte can be prevented.

[0065] [Other Structural Units] Structural units other than alkylene structural units and nitrile group-containing structural units may be contained as necessary within the scope that does not impair the effects of the present disclosure. Examples of other structural units include amide group-containing structural units and carboxyl group-containing structural units.

[0066] (Alkali Metal) The resin composition of the present disclosure contains an alkali metal. The content of the alkali metal in the resin composition is 50 ppm or more and less than 10,000 ppm. Preferably, it is 500 ppm or more and 8,000 ppm or less, and more preferably, it is 2,000 ppm or more and 5,000 ppm or less. When the alkali metal content is within the above range, when a dispersed material such as a carbon material is dispersed, the adsorption to non-dispersed material and affinity to the dispersion medium are improved, thereby improving dispersibility. Furthermore, when the amount of alkali metal in the resin composition is within the above range, it is easy to control the molecular weight of the copolymer (X) within an appropriate range by modifying it using an alkali metal compound as a basic compound or by applying shear stress to the copolymer, which has the effect of improving the dispersibility of the dispersed material.

[0067] The alkali metal is contained in the resin composition by the monomer used to synthesize the copolymer before modification or the copolymer (X), the alkali metal compound used to modify the copolymer, the alkali metal compound used as an additive for adjusting pH, or the alkali metal contained in a solvent, etc. That is, the alkali metal contained in the resin composition includes not only intentionally added alkali metal compounds but also alkali metals derived from the raw material monomers, catalysts, additives, solvents, etc.

[0068] Examples of alkali metals include lithium, sodium, potassium, etc. The alkali metal content in the resin composition can be determined using an ICP emission spectrophotometer by the method described in the examples.

[0069] (Solvent) The resin composition of this embodiment preferably contains a solvent. Any solvent capable of dissolving the copolymer may be used, but amide-based polar solvents are preferred. Examples of amide-based polar solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam. Among these, it is more preferred to contain at least one solvent selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0070] (Method for Producing Resin Composition) The method for producing the resin composition of this embodiment is not particularly limited, and any method may be used to produce the resin composition. For example, a method may be used in which a copolymer is prepared by polymerization using a monomer composition containing a conjugated diene monomer and a nitrile group-containing monomer, and the conjugated diene monomer units of the copolymer are hydrogenated to obtain a resin composition containing copolymer (X). Alternatively, a copolymer having an alkylene structural unit and a nitrile group-containing structural unit may be modified with a basic compound such as an alkyl metal compound or subjected to shear stress to obtain a resin composition containing copolymer (X).

[0071] Furthermore, as a method for ensuring that the alkali metal content is 50 ppm or more and less than 10,000 ppm and that the resistivity of the resin composition when adjusted to a non-volatile content of 8 mass % with N-methyl-2-pyrrolidone is 5,000 Ω cm or more and 25,000 Ω cm or less, in addition to the raw materials or blending amounts for producing the copolymer, the following methods can be mentioned. Examples of such methods include <1> a method of applying shear stress to a copolymer containing an alkali metal using a pulverizer or the like; <2> a method of adding an alkali metal or an alkali metal compound to a copolymer to form a modified copolymer and then applying shear stress using the above-mentioned pulverizer; and <3> a method of applying shear stress to a copolymer using a pulverizer or the like and then adding an alkali metal or an alkali metal compound. Among these, methods <2> and <3> are preferred, and it is preferable to use an alkali metal compound with a maximum particle size of 150 μm or less, particularly sodium hydroxide. By applying shear stress to the copolymer in the presence of an alkali metal compound with a maximum particle size of 150 μm or less, the finely dispersed alkali metal compound absorbs moisture, comes into contact with the copolymer, promotes the hydrolysis reaction of the copolymer, and controls the structure, molecular weight, and molecular weight distribution suitable for dispersing the substance to be dispersed.

[0072] In <2> or <3>, the alkali metal compound used to modify the copolymer may be, for example, an alkali metal hydroxide or alkoxide, etc. Preferably, it is an alkali metal hydroxide.

[0073] That is, the method for producing a resin composition preferably includes, for example, a step of mixing an alkali metal compound with a copolymer having an alkylene structural unit and a nitrile group-containing structural unit to produce a resin composition containing copolymer (X) and an alkali metal.

[0074] In this case, the copolymer before modification is preferably a copolymer having alkylene structural units and nitrile group-containing structural units in a content of 50% by mass or more and 75% by mass or less of alkylene structural units and 25% by mass or more and 50% by mass or less of nitrile group-containing structural units, which is obtained by mixing an alkali metal compound with a copolymer having alkylene structural units and nitrile group-containing structural units.

[0075] To obtain a resin composition that satisfies the above requirements, the copolymer before modification is preferably dissolved in an amide polar solvent at 60° C. to 100° C. The alkali metal compound is preferably mixed at a temperature of 40° C. to 100° C., more preferably at 60° C. to 80° C.

[0076] Examples of alkali metal compounds include alkali metal hydroxides and alkali metal alkoxides, with alkali metal hydroxides being preferred. Examples of alkali metal hydroxides that can be used include lithium hydroxide, sodium hydroxide, and potassium hydroxide. From the standpoint of processability and handling, such as particle size control, sodium hydroxide is preferred because it provides excellent dispersion stability for the dispersed material. Sodium hydroxide is hygroscopic and can exert excellent effects when modifying a portion of the structural units of a copolymer by hydrolysis or the like. Examples of alkali metal alkoxides that can be used include sodium ethoxide and sodium butoxide.

[0077] The alkali metal compound used to modify the copolymer preferably has a maximum particle size of 150 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Also, 20 μm or more is preferable. When the maximum particle size of the alkali metal compound is within the above range, precipitation of the alkali metal compound in the resin composition is suppressed, resulting in superior stability of the resin composition. The sedimentation rate of the alkali metal compound in the resin composition can be estimated using Stokes' equation, and the viscosity of the resin composition and the density and particle size of the alkali metal compound are important in controlling the dispersion stability of the dispersed material. The maximum particle size of the alkali metal compound can be calculated, for example, by filtering through a filter with a known mesh size.

[0078] The particle size of the alkali metal compound is preferably controlled by dry and / or wet pulverization using a conventionally known pulverizer. A conventionally known pulverizer can be used for the pulverization. By setting the maximum particle size of the alkali metal compound within the above range, it is possible to appropriately control not only the composition and structure of the structural units constituting the copolymer (X), but also changes in the molecular weight of the copolymer (X) due to modification. By controlling the molecular weight and molecular weight distribution of the copolymer (X) in this way, a dispersion composition with lower viscosity can be obtained when the dispersed material is dispersed. If the maximum particle size of the alkali metal compound is large, the alkali metal compound will precipitate in the resin composition, making it impossible to control the molecular weight of the copolymer, and the stability over time of the carbon material dispersion composition and composite slurry described below may be reduced.

[0079] A pulverizer is a device that applies forces such as compression, impact, shear, and friction to a sample to reduce its size. Devices that can be used to control particle size include mortars, pin mills, hammer mills, pulverizers, attritors, jet mills, cutter mills, ball mills, bead mills, colloid mills, conical mills, disc mills, edge mills, wonder crushers, vibration mills, ultrasonic homogenizers, and high-shear mixers.

[0080] In order to control the alkali metal content and the predetermined resistivity of the resin composition, the copolymer before modification is preferably dissolved in a solvent at 60°C to 100°C. Therefore, in a more preferred embodiment, the resin composition containing the solvent contains 1 to 50, 2 to 40, 5 to 30, or 10 to 20 mass% of copolymer (X) relative to the total amount of the resin composition. In a more preferred embodiment, the solvent contains an amide-based polar solvent. Furthermore, in order to obtain a resin composition that satisfies the above requirements, the alkali metal compound is preferably dissolved in a solvent at 40°C to 100°C or 60°C to 80°C. Therefore, in a more preferred embodiment, the resin composition containing the solvent contains 0.1 to 20 mass%, 0.5 to 10 mass%, 1 to 8 mass%, or 2 to 5 mass% of the alkali metal compound relative to the total amount of the resin composition. By ensuring that both the copolymer (X) and the alkali metal compound satisfy these ranges relative to the total amount of the resin composition, the alkali metal content and the predetermined resistivity of the resin composition can be more easily controlled.

[0081] In order to control the alkali metal content and the predetermined resistivity of the resin composition, an alkali metal compound may be added in the manufacturing method of the resin composition. In this case, as one embodiment of the manufacturing method of the resin composition, the copolymer (X) and the alkali metal compound may be mixed in a state of being dissolved in a solvent. In this case, it is more preferable to prepare a solution in which the copolymer (A) is dissolved in a solvent and a solution in which the alkali metal compound is dissolved in a solvent separately, and then mix them. As the solvent, an amide-based polar solvent may be used.

[0082] In order to control the alkali metal content and the predetermined resistivity of the resin composition, as described above, there is a method of controlling the amount and method of adding the alkali metal compound in the production method of the resin composition. This method makes it possible to control the alkali metal content in the resulting resin composition and also to control the predetermined resistivity.

[0083] Another method for controlling the alkali metal content and the predetermined resistivity of the resin composition is to control the molecular weight and molecular weight distribution of the copolymer (X). For example, even when the alkali metal content is low and the predetermined resistivity is high, the increase in the predetermined resistivity can be suppressed by reducing the molecular weight of the copolymer (X). Preferably, the number-average molecular weight Mn of the copolymer (X) is 70,000 or less, 60,000 or less, or 50,000 or less. In another embodiment, the Mw / Mn of the copolymer (X) is preferably 2.60 or less, 2.50 or less, or 2.40 or less. In a more preferred embodiment, when the Mw / Mn of the copolymer (X) is 2.60 or less, 2.50 or less, or 2.40 or less, the Z-average molecular weight Mz is 400,000 or less, 300,000 or less, or 250,000 or less. Some methods for controlling the molecular weight and molecular weight distribution include controlling the time for mixing the copolymer (X) and the alkali metal compound, the amount of the alkali metal compound used, the content of each of the copolymer (X) and the alkali metal compound relative to the total amount of the resin composition, and the number of passes when a pass-type dispersing device is used.

[0084] <Carbon material dispersion composition> The carbon material dispersion composition of the present embodiment includes at least a carbon material and the resin composition of the present embodiment. It is preferable that the carbon material dispersion composition also includes a solvent. By including a solvent in the carbon material dispersion composition, it is easier to obtain a carbon material dispersion composition in a good dispersed state.

[0085] (Carbon Material) As the carbon material, various types of carbon black can be used, such as acetylene black, furnace black, hollow carbon black, channel black, thermal black, and Ketjen black. Also usable are amorphous carbonaceous materials such as oxidation-treated carbon black, graphitized carbon black, and mesophase carbon black; soft carbon and hard carbon; and carbon fibers such as carbon nanotubes or carbon nanofibers, which are fibrous carbon, and vapor-grown carbon fibers. Among these, it is preferable to include at least one selected from the group consisting of carbon black and carbon fiber, and it is particularly preferable to include carbon nanotubes.

[0086] The carbon purity of the carbon material is preferably 95% by mass or more, and more preferably 97% by mass or more, based on the mass of the carbon material (the mass of the carbon material being 100% by mass).

[0087] Carbon nanotubes have a structure in which planar graphite is wound into a cylindrical shape, and include single-walled carbon nanotubes and multi-walled carbon nanotubes, or a mixture of these. Among these, multi-walled carbon nanotubes are preferred. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are wound, and single-walled carbon nanotubes have a structure in which only one layer of graphite is wound. The sidewalls of carbon nanotubes do not have to have a graphite structure. For example, carbon nanotubes with sidewalls having an amorphous structure can also be used as the carbon material.

[0088] The average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 3 nm or more and 20 nm or less, and even more preferably 4 nm or more and 15 nm or less. When the average outer diameter is within the above range, a good conductive network is easily formed within the electrode, and the active material inside the secondary battery is uniformly utilized during charge and discharge, thereby suppressing deterioration of the active material and further improving the cycle characteristics of the secondary battery.

[0089] The BET specific surface area of ​​carbon nanotubes is 100 m ２ / g or more 1000m ２ / g or less, and ２ / g or more 700m ２ / g or less is more preferable. When the BET specific surface area is within the above range, an efficient conductive network can be formed with a small amount, allowing the amount of conductive material in the electrode to be reduced. This increases the degree of freedom in battery design, such as by increasing the amount of active material and binder resin. Furthermore, when preparing the composite slurry, the active material and carbon nanotubes are more likely to be combined, making it easier to obtain an electrode film having a homogeneous conductive network in which the active material surface is coated with carbon nanotubes, thereby suppressing the electrolyte decomposition reaction at the interface between the electrolyte and the active material and improving the battery's cycle characteristics. The BET specific surface area can be measured by the BET method described in JIS Z 8830:2013.

[0090] The G / D ratio of carbon nanotubes (peak ratio between G-band and D-band) is 1560 cm in the Raman spectrum. －１ ~1600cm －１ The maximum peak intensity within the range of G, 1310 cm －１ ~1350cm －１ When the maximum peak intensity within this range is defined as D, the G / D ratio is preferably 0.5 to 10, and more preferably 0.7 to 4.5. When the G / D ratio of the carbon nanotubes is within the above range, it is believed that the contact resistance between the carbon nanotubes is reduced, making it easier to obtain good conductivity. This is also presumably because the amount of functional groups on the multi-walled carbon nanotube surface is appropriate, resulting in good affinity with the solvent and better dispersibility.

[0091] The volume resistivity of carbon nanotubes is 1.0×10 －２ Ω・cm~3.0×10 －２ Preferably, the resistance is Ω cm, and 1.0×10 －２ Ω・cm~2.0×10 －２ It is more preferable that the volume resistivity of the carbon nanotubes is Ω cm. The volume resistivity of the carbon nanotubes can be measured using a powder resistivity measuring device (Loresta GP Powder Resistivity Measuring System MCP-PD-51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). When the volume resistivity is within the above range, the conductivity of the electrode film tends to be good, and a secondary battery with excellent rate characteristics and cycle characteristics tends to be obtained.

[0092] It is preferable that the carbon nanotubes have been subjected to magnetic removal of metal foreign particles using an electromagnet. For example, it is preferable to remove metal foreign particles by passing the carbon nanotubes through an electromagnet during the crushing or filling process of the carbon nanotubes. The higher the carbon purity of the carbon nanotubes, the more preferable it is, and it is preferably 98.0% by mass or more, more preferably 99.5% by mass or more, even more preferably 99.8% by mass or more, and particularly preferably 99.9% by mass or more, based on 100% by mass of the carbon nanotubes. That is, the lower the content of metal foreign particles, the more preferable it is, and it is preferably 2.0% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less, based on 100% by mass of the carbon nanotubes. By using carbon nanotubes produced by a manufacturing method that does not use a metal catalyst as a nucleus, or carbon nanotubes obtained by a conventionally known purification method such as acid treatment, the content of metallic foreign particles can be reduced to 0.5 mass% or less relative to 100 mass% of the carbon nanotubes, thereby reducing the content of metallic foreign particles in the carbon nanotube dispersion composition and improving the characteristics of secondary batteries. The carbon purity of the carbon nanotubes can be determined using an ICP optical emission spectrometer by the method described in the Examples.

[0093] The solvent is not particularly limited as long as it is miscible with the resin composition of the present embodiment, but it is preferably capable of dissolving the resin composition, more 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 high-dielectric-constant solvents. In addition, the high-dielectric-constant solvent may be mixed with one or more other solvents.

[0094] 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), and others, such as tetrahydrofuran, urea, and acetonitrile. The dispersion medium preferably contains an amide-based polar solvent, and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone. The relative dielectric constant of the high-dielectric-constant solvent can be a value described in a solvent handbook or the like, and is preferably 2.5 or more at 20°C. By using a high-dielectric-constant solvent as the solvent, it is possible to enhance the interaction between the nitrile group contained in the resin composition of this embodiment, the carbon material, and the solvent.

[0095] The water content of the solvent is preferably 100 ppm or more and 1500 ppm or less, and more preferably 100 ppm or more and 1000 ppm or less. When the water content is within the above range, the alkali metal contained in the resin composition of the present embodiment dissolves in the carbon material dispersion composition, and the dispersion stability of the carbon material dispersion composition tends to be good.

[0096] The content of the solvent in this embodiment is preferably 90% by mass to 99% by mass, and more preferably 92% by mass to 98% by mass, based on the mass of the carbon material dispersion composition (the mass of the carbon material dispersion composition being 100% by mass). When the content is within the above range, a carbon material dispersion composition with good flowability and excellent dispersion stability is easily obtained. By using a carbon material dispersion composition with excellent dispersion stability, an electrode film with stable conductivity is obtained, and the quality of the secondary battery is likely to be stable.

[0097] To obtain the carbon material dispersion composition of this embodiment, it is preferable to carry out a treatment of dispersing the carbon material in a solvent. The dispersing device used for this treatment is not particularly limited.

[0098] The dispersing device can be a disperser commonly used for pigment dispersion, etc. For example, either a media-less disperser or a media-type disperser may be used. Examples of media-less dispersers include mixers such as a Disper, a Homomixer, and a planetary mixer; homogenizers (such as Advanced Digital Sonifer (registered trademark) Model 450DA manufactured by BRANSON, "Clearmix" manufactured by M Technique, "Filmix" manufactured by PRIMIX, and "Abramix" manufactured by Silverson); paint conditioners (manufactured by Red Devil), colloid mills (such as "PUC Colloid Mill" manufactured by PUC and "Colloid Mill MK" manufactured by IKA), and cone mills (such as "Cone Mill MKO" manufactured by IKA). Examples of media-type dispersers include ball mills, sand mills (such as "Dynomill" manufactured by Shinmaru Enterprises), attritors, pearl mills (such as "DCP Mill" manufactured by Eirich), coball mills, bead mills (Mugen Flow (registered trademark) manufactured by Ashizawa Finetech Co., Ltd.), and media-type paint conditioners. Further examples include high-pressure homogenizers (such as "Genus PY" manufactured by Genus, "Starburst" manufactured by Sugino Machine Ltd., and "Nanomizer" manufactured by Nanomizer Co., Ltd.), media-less dispersers such as "Claire SS-5" manufactured by M Technique Co., Ltd. and "MICROS" manufactured by Nara Kikai Co., Ltd., and other roll mills. Dispersers are not limited to these.

[0099] The content of the carbon material contained in the carbon material dispersion composition is preferably 1 mass % or more and 20 mass % or less, more preferably 2 mass % or more and 15 mass % or less, and even more preferably 3 mass % or more and 10 mass % or less, based on the mass of the carbon material dispersion composition (the mass of the carbon material dispersion composition being 100 mass %).

[0100] The content of the dispersant contained in the carbon material dispersion composition is preferably 5% by mass or more and 100% by mass or less, more preferably 10% by mass or more and 75% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less, based on the mass of the carbon material (the mass of the carbon material being 100% by mass). When the amount of the dispersant is within the above range, the dispersion stability of the carbon material in the carbon material dispersion composition tends to be good. In addition, the peel strength of the electrode for the secondary battery is good.

[0101] The carbon material dispersion composition preferably has a water content of 100 ppm to 1500 ppm, and more preferably 200 ppm to 1000 ppm. When the water content of the carbon material dispersion composition is within the above range, gelation of the composite slurry described below is suppressed, and a composite slurry and an electrode film of stable quality are likely to be obtained.

[0102] The initial viscosity of the carbon material dispersion composition of this embodiment, measured using a Brookfield viscometer at 25°C and 100 rpm, is preferably 100 mPa·s or more and 2,000 mPa·s or less, and more preferably 200 mPa·s or more and 1,000 mPa·s or less. When the initial viscosity of the carbon material dispersion composition is within the above range, it is considered that the dispersion state of the carbon material contained in the carbon material dispersion composition is appropriate, and a conductive network is easily formed.

[0103] The viscosity of the carbon material dispersion composition of this embodiment after storage at 60°C for one week, measured after cooling to 25°C with a Brookfield viscometer at 25°C and a rotor rotation speed of 100 rpm, is preferably 500 mPa·s or more and 6,000 mPa·s or less, more preferably 500 mPa·s or more and 3,000 mPa·s or less, and even more preferably 500 mPa·s or more and 2,000 mPa·s or less.

[0104] A carbon material dispersion composition having a viscosity within the above range is considered to have an appropriate composition ratio of the carbon material, resin composition, and solvent, and an appropriate dispersion process, and therefore has good dispersion stability. Because the adsorption reaction of the resin composition contained in the carbon material dispersion composition onto the surface of the carbon material is an endothermic reaction, by evaluating the viscosity of the carbon material dispersion composition after storage under high-temperature conditions, it is possible to determine the amount of resin composition that is necessary and sufficient to obtain a carbon material dispersion composition with excellent dispersion stability.

[0105] The carbon material dispersion composition of the present embodiment is preferably used after removing metallic foreign matter with a filter or a magnet.

[0106] [Step of Removing Metallic Foreign Particles] The method for removing metallic foreign particles is not particularly limited, and examples thereof include a filtration step in which metallic foreign particles are filtered out using a filter, and a magnetic separation step such as magnetic separation treatment using an electromagnet. It is preferable to provide both the filtration step and the magnetic separation step, because the magnetic separation step can remove metallic foreign particles contained in the carbon material, and the filtration step can recover metallic foreign particles that cannot be removed by the magnet. It is also more preferable to perform the magnetic separation step after the filtration step. By performing the filtration step at the end before shipping the carbon material dispersion composition, metallic foreign particles can also be removed from piping, etc.

[0107] (Magnetic Separation Step) As a method for removing metallic foreign matter particles using a magnetic force in the magnetic separation step, various conventionally known methods can be used. In particular, it is preferable to use a method in which, during the production step of the carbon material dispersion composition, an electromagnet is set and the carbon material dispersion composition is passed through to remove the metallic foreign matter particles.

[0108] The magnetic flux density of the electromagnet is preferably 5,000 to 20,000 gauss, more preferably 10,000 to 20,000 gauss. By using an electromagnet within this range, not only can metallic foreign particles contained in the carbon material be removed, but also metallic foreign particles generated during the manufacturing process can be removed.

[0109] Specifically, for example, CS-150HHH, CS-250HHH, CS-300HHH manufactured by Nippon Magnetics Co., Ltd., DVF-50-6, DVF-50-9, DVF-50-12 manufactured by Nippon Eriez Magnetics Co., Ltd., EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Taiho Magnetic Co., Ltd., and the like can be used.

[0110] The flow rate of the carbon material dispersion composition when it comes into contact with the electromagnet is preferably 1 L / min or more and 300 L / min or less, and more preferably 30 L / min or more and 200 L / min or less.

[0111] The carbon material dispersion composition is preferably passed through the electromagnet three or more times. If the number of passes is too small, there is a possibility that metal foreign particles will not be removed. When the carbon material dispersion composition is passed through the electromagnet in a circulating manner, it is preferable to pass the composition through the electromagnet more times in consideration of the uniformity inside the tank used in the production process.

[0112] (Filtering step) The filter for filtering out the foreign metal particles may be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferred. Since foreign metal particles are often not spherical but have an orientation, the use of a depth filter makes it possible to efficiently remove the foreign metal particles from the carbon material dispersion composition.

[0113] Unlike surface filters (filters that capture particulate matter in a fluid mainly on the filter surface), depth filters capture particulate matter in a fluid mainly inside the filter medium and are characterized by high particle retention performance and resistance to clogging. By using a depth filter, it is possible to more selectively remove metal foreign particles from a carbon material dispersion composition.

[0114] As the depth filter, for example, a nonwoven fabric depth cartridge NT-T series manufactured by 3M™ PP can be used.

[0115] The filtration accuracy of the filter is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. If a filter with a small pore size is used to increase the metal foreign particle removal rate in the carbon material dispersion composition, the efficiency of removing metal foreign particles may decrease due to clogging of the carbon material. On the other hand, when a carbon material dispersion composition is filtered through a filter in the above range, the efficiency of removing metal foreign particles is high when the filter is used, so a carbon material dispersion composition with few metal foreign particles is likely to be obtained.

[0116] <<Composite Slurry>> The composite slurry of the present embodiment contains a carbon material dispersion composition and an active material. That is, it contains at least the resin composition of the present disclosure, a carbon material, and an active material, and preferably further contains a binder resin.

[0117] The binder resin is a resin used to bond carbon materials together. The binder resin is not particularly limited, but examples thereof include polymers or copolymers containing fluororesin, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, or the like as structural units; polyurethane resin, polyester resin, phenolic resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, and fluororesin; cellulose resin such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber; and conductive resins such as polyaniline and polyacetylene. Among these, the use of fluororesin as the binder resin is preferred from the viewpoint of electrochemical oxidation-reduction resistance.

[0118] As the fluororesin of this embodiment, for example, polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene are preferable.

[0119] The weight average molecular weight of the fluororesin is preferably 10,000 or more and 2,000,000 or less, more preferably 100,000 or more and 1,000,000 or less, and particularly preferably 200,000 or more and 1,000,000 or less.

[0120] Active materials are materials that are the basis of battery reactions. Active materials are divided into positive electrode active materials and negative electrode active materials based on their electromotive force. In this specification, positive electrode active materials and negative electrode active materials may be simply referred to as "active materials."

[0121] The positive electrode active material is not particularly limited, but may be a metal oxide capable of doping or intercalating lithium ions or sodium ions, a metal compound such as a metal sulfide, or a conductive polymer. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium or sodium, inorganic compounds such as transition metal sulfides, polyanion compounds, and Prussian blue. Specific examples include MnO, V ２ O ５ , V ６ O １３ , TiO ２ transition metal oxide powders such as lithium nickel oxide, lithium cobalt oxide, lithium manganate, and lithium manganate with a spinel structure; lithium iron phosphate-based materials, which are phosphate compounds with an olivine structure; TiS ２ Examples of suitable materials include transition metal sulfide powders such as FeS, layered sodium ferrate, sodium manganate, sodium chromate, sodium nickelate, and sodium iron phosphate-based materials, which are phosphate compounds with an olivine structure. Conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Mixtures of the above inorganic and organic compounds may also be used.

[0122] The positive electrode active material is preferably a composite oxide of lithium containing a transition metal such as Al, Fe, Co, Ni, or Mn, more preferably a composite oxide of lithium containing any of Al, Co, Ni, or Mn, and particularly preferably a composite oxide of lithium containing Ni and / or Mn. When these active materials are used, particularly good effects can be obtained.

[0123] The negative electrode active material is not particularly limited as long as it can be doped or intercalated with lithium or sodium ions. For example, metal Li, its alloys such as tin alloys, silicon alloys, and lead alloys, LiXFe ２ O ３ , LiXFe ３ O ４ , LiXWO ２ (x is a number in the range of 0<x<1), metal oxides such as lithium titanate, lithium vanadate, and lithium silicate, conductive polymers such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-baked carbon materials, vapor-grown carbon fibers, and carbonaceous fibers. These negative electrode active materials can be used singly or in combination.

[0124] The BET specific surface area of ​​the active material is 0.1 m ２ / g or more 10m ２ / g or less is preferable, and 0.2m ２ / g or more 5m ２ / g or less is more preferable, and 0.3m ２ / g or more 3m ２ / g or less is more preferable.

[0125] The average particle size of the active material is preferably in the range of 0.05 μm to 100 μm, and more preferably in the range of 0.1 μm to 50 μm. The average particle size of the active material as used herein refers to the average value of particle sizes measured by an electron microscope.

[0126] To obtain the composite slurry of this embodiment, it is preferable to add an active material to a carbon material dispersion composition and then perform a dispersion treatment. The dispersion device used for such treatment is not particularly limited. The composite slurry can be obtained using the dispersion device described above for the carbon material dispersion composition.

[0127] The content of the active material in the composite slurry is preferably 20% by mass to 85% by mass, and particularly preferably 40% by mass to 85% by mass, based on 100% by mass of the composite slurry.

[0128] The content of the carbon material in the composite slurry is preferably 0.05% by mass to 10% by mass, more preferably 0.1% by mass to 5% by mass, and even more preferably 0.1% by mass to 3% by mass, based on 100% by mass of the active material.

[0129] The content of the binder resin in the composite slurry is preferably 0.5% by mass to 20% by mass, more preferably 1% by mass to 10% by mass, and particularly preferably 1% by mass to 5% by mass, based on 100% by mass of the active material.

[0130] The solid content concentration of the composite slurry is preferably 30% by mass to 90% by mass, and more preferably 40% by mass to 85% by mass, based on 100% by mass of the composite slurry.

[0131] The water content in the composite slurry is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

[0132] The electrode film of the present embodiment includes a current collector and an electrode film formed from a composite slurry. The electrode film is a coating film of the composite slurry. For example, the electrode film is a coating film formed by coating the composite slurry on a current collector and drying the coating film to form an electrode composite layer.

[0133] The material and shape of the current collector used in the electrode film of this embodiment are not particularly limited, and can be appropriately selected from those suitable for various secondary batteries. For example, the current collector material can be metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. Furthermore, while flat foils are generally used, current collectors with roughened surfaces, perforated foils, and mesh-shaped current collectors can also be used.

[0134] The method for applying the composite slurry onto the current collector to form the electrode film is not particularly limited, and any known method can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. Drying methods that can be used include, but are not limited to, standing to dry, a blower dryer, a hot air dryer, an infrared heater, and a far-infrared heater.

[0135] After coating, the electrode mixture layer may be rolled using a lithographic press, a calendar roll, etc. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, and preferably 10 μm or more and 300 μm or less.

[0136] <Secondary Battery> The secondary battery of this embodiment includes an electrode having the electrode film of the present disclosure and an electrolyte. The carbon material dispersion composition using the resin composition of this embodiment forms a good conductive network in the secondary battery electrode, resulting in excellent rate characteristics. Since the active material is uniformly utilized during charge and discharge, deterioration of the active material is unlikely to proceed. Furthermore, overcharge and overdischarge during charge and discharge are suppressed. Therefore, deterioration of battery characteristics due to electrolyte decomposition and metal deposition is unlikely to occur, resulting in excellent cycle characteristics.

[0137] The positive electrode may be prepared by coating a composite slurry containing a positive electrode active material on a current collector and drying the coated composite slurry.

[0138] The negative electrode may be prepared by coating a current collector with a composite slurry containing a negative electrode active material and drying the coated slurry to form an electrode film.

[0139] As the electrolyte, various known materials in which ions can move can be used. For example, LiBF ４ , LiClO ４ , LiPF ６ , LiAsF ６ , LiSbF ６ , LiCF ３ SO ３ , Li(CF ３ SO ２ ) ２ N, LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ３ C, LiI, LiBr, LiCl, LiAlCl, LiHF ２ , LiSCN, or LiBPh ４ (where Ph is a phenyl group), but is not limited thereto, and a material containing a sodium salt can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0140] 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.

[0141] The secondary battery of this embodiment preferably includes a separator, such as, but not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and those that have been subjected to a hydrophilic treatment.

[0142] The structure of the secondary battery of the present embodiment is not particularly limited, but is usually composed of 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.

[0143] The applications of the secondary battery of this embodiment are not particularly limited, and specifically, it can be used as a power source for consumer devices such as mobile phones, laptop computers, and digital cameras, as an emergency power source for hospitals, factories, buildings, etc., and for vehicles such as hybrid automobiles, plug-in hybrid automobiles, electric automobiles, assisted bicycles, and railroad cars. The secondary battery is used to recover regenerative energy for powering vehicles, for example.

[0144] In particular, since the secondary battery has high charge / discharge performance and excellent cycle characteristics, it can be suitably used in vehicles, and vehicles that are highly safe and can be expected to have improved fuel efficiency can be obtained. Furthermore, it can also exhibit excellent effects in vehicle applications where large current charge / discharge is desired.

[0145] The mounting position of the secondary battery in the vehicle of this embodiment is not particularly limited. For example, when the secondary battery is mounted in an automobile, the secondary battery can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

[0146] The present disclosure will be explained in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass". The blending amounts in the tables are parts by mass. Blank spaces in the tables indicate that no blending is performed.

[0147] The materials used in the examples and comparative examples are as follows: Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, liquid hydrogenated nitrile butadiene rubber, number average molecular weight 20,000, weight average molecular weight 35,000, Z average molecular weight 60,000, alkylene structural units 66% by mass, nitrile group-containing structural unit content 34% by mass), hereinafter referred to as HNBR1; Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35052, Mooney viscosity 20, number average molecular weight 48,000, weight average molecular weight 110,000, Z average molecular weight 210,000, alkylene structural units 66% by mass, nitrile group-containing structural unit content 34% by mass), hereinafter referred to as HNBR2. Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35053, Mooney viscosity 35, number average molecular weight 53,000, weight average molecular weight 133,000, Z average molecular weight 270,000, alkylene structural units 64% by mass, nitrile group-containing structural unit content 36% by mass), hereinafter referred to as HNBR3. Hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35056, Mooney viscosity 65, number average molecular weight 75,000, weight average molecular weight 183,000, Z average molecular weight 364,000, alkylene structural units 64% by mass, nitrile group-containing structural unit content 36% by mass), hereinafter referred to as HNBR4. Hydrogenated nitrile butadiene rubber (manufactured by ARLANXEO, Therban® 3406, Mooney viscosity 63, number average molecular weight 78,000, weight average molecular weight 209,000, Z-average molecular weight 434,000, alkylene structural units 66% by mass, content of nitrile group-containing structural units 34% by mass), hereinafter referred to as HNBR5. Carbon nanotubes (manufactured by JEIO, JENOTUBE 6A, average outer diameter 6 nm, BET specific surface area 650 m ２ / g), hereinafter referred to as CNT1. Carbon nanotubes (manufactured by JEIO, JENOTUBE10B, average outer diameter 10 nm, BET specific surface area 230 m ２ / g), hereinafter referred to as CNT2. HS-100: Denka Black HS-100 (manufactured by Denka Company, acetylene black, average primary particle diameter 48 nm, BET specific surface area 39 m ２ / g) or less is referred to as CB1.

[0148] The methods for measuring the physical properties of the materials used in each of the examples and comparative examples are as follows.

[0149] <Specific Surface Area> The BET specific surface area of ​​carbon nanotubes and carbon black can be measured by the BET method using nitrogen adsorption measurement in accordance with JIS Z 8830:2013.

[0150] <Average Outer Diameter> The average outer diameter of carbon nanotubes can be calculated by observing and photographing carbon nanotubes with a transmission electron microscope, then randomly selecting 300 carbon nanotubes from the photograph and measuring the outer diameter of each. The average primary particle diameter of carbon black can be calculated by first observing and photographing carbon black with a transmission electron microscope, then randomly selecting 100 spherical-like carbon black primary particles from the photograph and measuring the outer diameter of each.

[0151] <Mooney Viscosity> The Mooney viscosity of the hydrogenated nitrile butadiene rubber was measured as the Mooney viscosity (ML1+4, 100°C) at a temperature of 100°C using an L-type rotor in accordance with Japanese Industrial Standard JIS K6300-1.

[0152] <Preparation of standard negative electrode> 0.5 parts by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka) and 1 part by mass of MAC500LC (carboxymethylcellulose sodium salt Sunrose special type MAC500L, manufactured by Nippon Paper Industries Co., Ltd., non-volatile content 100%) and 98.4 parts by mass of water were added to a 150 ml plastic container, and then stirred at 2000 rpm for 30 seconds using a centrifugal mixer (Thinky Awatori Rentaro, ARE-310). Further, 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industries, CGB-20) and 5 parts by mass of silicon oxide (manufactured by Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5 μm, non-volatile content 100%) were added as active materials, and the mixture was stirred at 3000 rpm for 10 minutes using a high-speed stirrer. Next, 3.1 parts by mass of styrene butadiene rubber (SBR, TRD2001, manufactured by JSR Corporation) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the rotation / revolution mixer to obtain a negative electrode composite slurry. Thereafter, the negative electrode composite slurry was applied using an applicator to an electrode with a weight per unit area of ​​8 mg / cm. ２ After coating on copper foil so that the density of the composite layer became 1.6 g / cm, the coating film was dried in an electric oven at 120°C ± 5°C for 25 minutes. Further, rolling treatment was carried out using a roll press (3 ton hydraulic roll press, manufactured by Thank Metal Co., Ltd.) to obtain a composite layer having a density of 1.6 g / cm. ３ A standard negative electrode was fabricated.

[0153] <Preparation of alkali metal compound dispersion> Volume: 2000 cm ３ 950 parts by mass of NMP and 50 parts by mass of NaOH (sodium hydroxide, manufactured by Tosoh Corporation, Toso Pearl) were added to a plastic container, and a fine emulsion screen was attached to a high-shear mixer (L5M-A, manufactured by Silverson) and the mixture was dispersed at a speed of 9000 rpm until the mixture was uniform.The mixture was then passed through a nylon filter with a mesh size of 150 μm using a filter bell to prepare a NaOH dispersion (NaOH concentration 5% by mass).The maximum particle size of the sodium hydroxide was 150 μm or less.

[0154] <<Methods for Measuring and Evaluating Physical Properties>> The methods for measuring and evaluating the physical properties of the resin compositions, carbon material dispersion compositions, electrode films, and secondary batteries used in the examples and comparative examples described below are as follows.

[0155] <Measurement of Number Average Molecular Weight, Weight Average Molecular Weight, and Z-Average Molecular Weight of Copolymer> (Preparation of Sample for Molecular Weight Measurement) To measure the number average molecular weight (Mn), weight average molecular weight (Mw), and Z-average molecular weight (Mz) of the copolymer, a sample for molecular weight measurement was prepared by the following method. The resin composition was added dropwise to purified water to precipitate the copolymer, and the precipitate was collected by filtration using a Buchner funnel. The precipitate was rinsed directly on the Buchner funnel with purified water and then dissolved in tetrahydrofuran (THF) to obtain a solution. The obtained solution was added dropwise again to purified water, and the above-mentioned filtration and washing steps using purified water were repeated. The precipitate was then redissolved in THF to obtain a sample for molecular weight measurement.

[0156] (Measurement of molecular weight) Using a sample for molecular weight measurement, measurement was performed 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-GEL SUPER AW-4000", "AW-3000", and "AW-2500" 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. Measurement was performed at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a concentration of 1% using a solvent consisting of the above eluent, and 20 microliters was injected. The average molecular weight is a polystyrene equivalent value.

[0157] <Contents of alkylene structural units and nitrile group-containing structural units of the copolymer> (Preparation of sample for IR measurement) The resin composition was dropped into purified water to precipitate the copolymer, and the precipitate was collected by filtration using a Buchner funnel. The precipitate was rinsed directly on the Buchner funnel with purified water, and then dried at 140°C for 1 hour using a hot air oven to prepare a sample for IR measurement. (IR measurement) The sample for IR measurement was measured using a Fourier transform infrared spectrometer (Nicleti S5, manufactured by ThermoFisher Scientific), and the contents of alkylene structural units and nitrile group-containing structural units of the copolymer in the resin composition were calculated.

[0158] <Measurement of Resistivity of Resin Composition> (Preparation of Sample for Resistivity Measurement) Capacity: 250 cm ３ The resin composition and N-methyl-2-pyrrolidone were weighed out and placed in a plastic container to prepare 200 parts by mass of a sample for measuring liquid resistance with a non-volatile content of 8% by mass. (Measurement of Resistivity) Using the sample for measuring liquid resistance, measurement was performed with a resistivity meter (IEST Genneng Technology (registered trademark), Battery Slurry Resistivity BSR2300), and the resistivity at 25°C was calculated. The resistivity value was measured using the measurement result of the middle channel.

[0159] <Measurement of alkali metal content in resin composition> The resin composition was dried using a hot air oven, and then subjected to acid decomposition using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General Co., Ltd.), and the alkali metals (lithium, sodium, potassium) contained in the resin composition were calculated. The alkali metal content was taken as the sum of the contents of lithium, sodium, and potassium.

[0160] <Initial Viscosity of Carbon Material Dispersion Composition> After leaving the carbon material dispersion composition to stand in a thermostatic bath at 25°C for one hour or more, the carbon material dispersion composition was immediately subjected to measurement using a Brookfield viscometer at a rotor rotation speed of 100 rpm. The evaluation criteria for the initial viscosity were as follows: 100 mPa·s or more and less than 500 mPa·s: ⊚ (excellent), 500 mPa·s or more and less than 1000 mPa·s: ◯ (good), 1000 mPa·s or more and less than 2000 mPa·s: Δ (fair), and more than 2000 mPa·s: × (poor).

[0161] <Temporal Viscosity of Carbon Material Dispersion Composition> The carbon material dispersion composition was left to stand in a thermostatic chamber at 60°C for one week, and then cooled to 25°C. Immediately thereafter, the carbon material dispersion composition was measured using a Brookfield viscometer at a rotor rotation speed of 100 rpm. The evaluation criteria for temporal viscosity were as follows: 500 mPa·s or more and 2000 mPa·s or less: ⊚ (excellent), more than 2000 mPa·s and 3000 mPa·s or less: ◯ (good), more than 3000 mPa·s and 6000 mPa·s or less: Δ (fair), and more than 6000 mPa: × (poor).

[0162] <60° Specular Gloss of Carbon Material Dispersion Composition> The surface smoothness of the coating film was evaluated based on the gloss value, which represents the degree of dispersion of the dispersed material. The carbon material dispersion composition was applied to a PET (polyethylene terephthalate) film using a bar coater No. 7, and then dried in a hot air oven at 120°C for 5 minutes. The 60° specular gloss was measured from the surface coated with the carbon material dispersion composition using a glossmeter (VG7000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS Z8741. The evaluation criteria for 60° specular gloss were as follows: ⊚ (excellent): 50° or more and less than 80°; ◯ (good): 40° or more and less than 50°, or 80° or more and less than 90°; Δ (fair): 30° or more and less than 40°, or 90° or more; and × (poor): less than 30°.

[0163] <Volume Resistivity of Electrode Film> The composite slurry was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm ２After coating on aluminum foil so that the coating was as follows, the coating was dried in an electric oven at 120 ° C. ± 5 ° C. for 25 minutes. Thereafter, the surface resistivity (Ω / □) of the dried coating film was measured using a Loresta GP (MCP-T610, probe: AP2 probe (RMH333)) manufactured by Mitsubishi Chemical Analytech Co., Ltd. After measurement, the surface resistivity was multiplied by the thickness of the electrode mixture layer formed on the aluminum foil to obtain the volume resistivity (Ω cm) of the electrode film. The thickness of the electrode mixture layer was determined by subtracting the film thickness of the aluminum foil from the average value measured at three points in the electrode film using a film thickness meter (DIGIMICRO MH-15M manufactured by NIKON Corporation), and the volume resistivity (Ω cm) of the electrode film was obtained. The evaluation criteria for volume resistivity were as follows: less than 8 Ω·cm: ⊚ (excellent); 8 Ω·cm or more and less than 12 Ω·cm: ◯ (good); 12 Ω·cm or more and less than 15 Ω·cm: △ (fair); and 15 Ω·cm or more: × (poor).

[0164] <Peel Strength of Electrode Film> The composite slurry was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm. ２ After coating on aluminum foil so that the coating was formed, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes. Two 90mm x 20mm rectangles were then cut with the coating direction as the long axis. Peel strength was measured using a tabletop tensile tester (Strograph E3, manufactured by Toyo Seiki Seisakusho Co., Ltd.) and evaluated using a 180-degree peel test method. Specifically, a 100mm x 30mm double-sided tape (No. 5000NS, manufactured by Nitoms Inc.) was attached to a stainless steel plate, and the prepared battery electrode composite layer was adhered to the other side of the double-sided tape. The layer was peeled off while being pulled from below to above at a constant speed (50mm / min). The average stress value at this time was taken as the peel strength. The evaluation criteria for peel strength were as follows: 1.0 N / cm or more: ⊚ (excellent); 0.7 N / cm or more and less than 1.0 N / cm: ◯ (good); 0.5 N / cm or more and less than 0.7 N / cm: △ (passable); and less than 0.5 N / cm: × (poor).

[0165] <Evaluation of Rate Characteristics of Lithium-Ion Secondary Battery> A laminated lithium-ion secondary battery 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). A constant-current, constant-voltage charge (cutoff current 1.0 mA (0.02 C)) was performed at a charge current of 10 mA (0.2 C) with a charge end voltage of 4.2 V, followed by a constant-current discharge at a discharge current of 10 mA (0.2 C) with a discharge end voltage of 2.5 V. This operation was repeated three times, and then a constant-current, constant-voltage charge (cutoff current (1.0 mA 0.02 C)) was performed at a charge current of 10 mA (0.2 C) with a charge end voltage of 4.2 V, followed by a constant-current discharge at discharge currents of 0.2 C and 3 C until the discharge end voltage reached 2.5 V, and the discharge capacity was determined for each. The rate characteristics can be expressed as the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, using the following equation 2: (Formula 2) Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%) The evaluation criteria for rate characteristic were as follows: ⊚ (excellent) for a rate characteristic of 80% or more, ◯ (good) for a rate characteristic of 70% or more and less than 80%, △ (fair) for a rate characteristic of 60% or more and less than 70%, and × (poor) for a rate characteristic of less than 60%.

[0166] <Evaluation of High-Temperature Cycle Characteristics of Lithium-Ion Secondary Battery> A laminated lithium-ion secondary battery was placed in a thermostatic chamber at 45°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). A constant-current, constant-voltage charge (cutoff current 1.25 mA (0.025 C)) was performed at a charge current of 50 mA (1 C) with a charge cut-off voltage of 4.2 V, followed by a constant-current discharge at a discharge current of 50 mA (1 C) with a discharge cut-off voltage of 2.5 V. This operation was repeated 100 times. 1 C was the current value required to discharge the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed as the ratio of the 100th 1 C discharge capacity at 45°C to the third 1 C discharge capacity, as shown in Equation 3 below. (Equation 3) High-temperature cycle characteristic=100th 1C discharge capacity / 3rd 1C discharge capacity×100(%) The evaluation criteria for the high-temperature cycle characteristic were as follows: ⊚ (excellent) for cycle characteristic of 90% or more, ◯ (good) for cycle characteristic of 85% or more and less than 90%, △ (fair) for cycle characteristic of 80% or more and less than 85%, and × (poor) for cycle characteristic of less than 80%.

[0167] (Example 1-1) A reaction vessel equipped with a gas inlet tube, thermometer, condenser, and stirrer was charged with 780 parts by mass of NMP and purged with nitrogen gas. Thereafter, the reaction vessel was heated to 80°C, 200 parts of HNBR1 was added, and the mixture was stirred until the hydrogenated nitrile-butadiene rubber was completely dissolved. Thereafter, 20 parts by mass of NaOH dispersion was added, and the mixture was stirred while adding air. The reaction vessel was heated while maintaining the temperature at 80°C for 12 hours, to obtain a resin composition (R-1) containing copolymer (A1) as copolymer (X) and an alkali metal. Based on a total content of alkylene structural units and nitrile group-containing structural units of copolymer (A1) of 100% by mass, the alkylene structural units were 66% by mass, the nitrile group-containing structural units were 34% by mass, the number average molecular weight (Mn) was 18,000, the weight average molecular weight (Mw) was 30,000, and the Z average molecular weight (Mz) was 49,000. The content of other structural units constituting the copolymer (A1) was 3% by mass or less based on 100% by mass of the copolymer (A1).The alkali metal content in the resin composition was 700 ppm.

[0168] (Examples 1-2 to 1-9), (Comparative Examples 1-1 to 1-5, 1-7 to 1-9) Resin compositions (R-2 to R-9) containing copolymer (X) and the like shown in Table 1 and comparative resin compositions (RC-1 to RC-5, RC-7 to RC-9) were obtained in the same manner as in Example 1-1, except that the conditions were changed to those shown in Table 1.

[0169] (Example 1-10) Resin composition 9 prepared in Example 1-9 was subjected to a three-pass dispersion treatment using a high-pressure homogenizer (Starburst Lab, manufactured by Sugino Machine Ltd.) The dispersion treatment was performed using a nozzle diameter of 0.17 mm and a pressure of 150 MPa, to obtain a resin composition (R-10) containing copolymer (E2).

[0170] (Example 1-11) Resin composition 9 prepared in Example 1-9 was subjected to a five-pass dispersion treatment using a high-pressure homogenizer (Starburst Lab, manufactured by Sugino Machine Ltd.) The dispersion treatment was performed using a nozzle diameter of 0.17 mm and a pressure of 150 MPa, to obtain a resin composition (R-11) containing copolymer (E3).

[0171] (Example 1-12) HNBR1 was subjected to a five-pass dispersion treatment using a high-pressure homogenizer (Starburst Lab, manufactured by Sugino Machine Ltd.) The dispersion treatment was carried out at a nozzle diameter of 0.17 mm and a pressure of 150 MPa, to obtain a resin composition (R-12) containing copolymer (A4).

[0172] Comparative Example 1-6 Comparative resin composition 5 prepared in Comparative Example 1-5 was subjected to a five-pass dispersion treatment using a high-pressure homogenizer (Starburst Lab, manufactured by Sugino Machine Ltd.) with a nozzle diameter of 0.17 mm and a pressure of 150 MPa, to obtain a resin composition (RC-6) containing copolymer (E5).

[0173] The respective contents of alkylene structural units and nitrile group-containing structural units, based on 100% by mass of the total content of alkylene structural units and nitrile group-containing structural units, are shown in Table 2. In all copolymers, the other structural units constituting the copolymer were 3% by mass or less, based on 100% by mass of the copolymer.

[0174]

[0175] Table 2 shows the evaluation results of the resin compositions prepared in Example 1-1 to Comparative Example 1-9.

[0176]

[0177] (Example 2-1) 87.75 parts of N-methyl-2-pyrrolidone (NMP) and 8.75 parts of resin composition (R-1) were added to a stainless steel container and stirred using a disperser. Then, 3.5 parts of carbon nanotubes (JEIO, JENOTUBE6A) were weighed out and added while stirring with a disperser. A fine emulsion screen was attached to a high shear mixer (L5M-A, SILVERSON), and the mixture was dispersed in a batch system at a speed of 9000 rpm until the entire mixture became uniform and the dispersion particle size measured with a grind gauge was 200 μm or less. After that, the mixture was passed through a high magnetic force mag filter (Eishin, surface magnetic flux density 17000 Gauss) to prepare a carbon material pre-dispersion composition. Thereafter, the carbon material pre-dispersion composition was sent to a bead mill (Mugen Flow (registered trademark), manufactured by Ashizawa Finetech Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mm, and a circulation dispersion treatment (bead filling rate 80%, peripheral speed 13 m / s) was carried out for a residence time of 10 minutes. The number of circulations was 50. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Lab, manufactured by Sugino Machine Co., Ltd.), and a 15-pass 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, and then the liquid to be dispersed was supplied to an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 gauss, spatial volume 1.7 L, electromagnet equipped with 31 grid screens, each 10 cm in diameter and 1.3 cm in thickness), and after three-pass treatment, the liquid was passed through two depth filters (manufactured by 3M, PP nonwoven fabric depth cartridge NT-T series, filtration accuracy 20 μm) installed in series, to obtain a carbon material dispersion composition 1.

[0178] (Examples 2-2 to 2-16), (Comparative Examples 2-1 to 2-9) Carbon material dispersion compositions 2 to 16 and comparative carbon material dispersion compositions 1 to 9 were obtained in the same manner as in Example 2-1, except that the dispersion conditions, carbon material, resin composition, amount of resin composition added, and NMP listed in Table 3 were changed.

[0179]

[0180] Table 4 shows the evaluation results of the carbon material dispersion compositions prepared in Examples 2-1 to 2-16 and Comparative Examples 2-1 to 2-9.

[0181]

[0182] (Example 3-1) Capacity 150 cm ３ Into a plastic container, 18.8 parts by mass of an NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, Solvay, Solef #5130) was dissolved, and 14.5 parts by mass of NMP were weighed. Thereafter, 11.4 parts by mass of a carbon material dispersion composition (carbon material dispersion composition 1) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinner Mixer, ARE-310). Further, 98.1 parts by mass of a positive electrode active material (BASF Toda Battery Materials, LLC, HED (registered trademark) NCM-111 1100) was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a planetary centrifugal mixer (Thinner Mixer, ARE-310) to obtain a composite slurry (composite slurry 1).

[0183] Next, the composite slurry (composite slurry 1) was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm. ２ After that, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (electrode film 1). The electrode film (electrode film 1) was then rolled using a roll press (Thank Metal, 3 ton hydraulic roll press) to obtain a positive electrode (positive electrode 1). The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 3.1 g / cc.

[0184] (Example 3-2 to Example 3-5, Example 3-8 to Example 3-16), (Comparative Examples 3-1 to 3-9) As shown in Table 5, except that carbon material dispersion compositions 2 to 16 and comparative carbon material dispersion compositions 1 to 9 were used instead of carbon material dispersion composition 1, composite slurries 2 to 5, 8 to 16, comparative composite slurries 1 to 9, electrode films 2 to 5, 8 to 16, comparative electrode films 1 to 9, positive electrodes 2 to 16, and comparative positive electrodes 1 to 9 were obtained in the same manner as in Example 3-1.

[0185] (Example 3-6) Capacity 150 cm ３Into a plastic container, 18.8 parts by mass of an NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, Solvay, Solef #5130) was dissolved, and 18.9 parts by mass of NMP were weighed. Thereafter, 7.1 parts by mass of a carbon material dispersion composition (carbon material dispersion composition 1) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinner Mixer, ARE-310). Further, 98.1 parts by mass of a positive electrode active material (BASF Toda Battery Materials, LLC, HED (registered trademark) NCM-111 1100) was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a planetary centrifugal mixer (Thinner Mixer, ARE-310) to obtain a composite slurry (composite slurry 6).

[0186] Next, the composite slurry (composite slurry 6) was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm ２ After coating on aluminum foil so that the coating was as follows: the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (electrode film 6). The electrode film (electrode film 1) was then rolled using a roll press (a 3-ton hydraulic roll press manufactured by Thank Metals) to obtain a positive electrode (positive electrode 6). The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 3.1 g / cc.

[0187] (Example 3-7) Capacity 150 cm ３ Into a plastic container, 18.8 parts by mass of an NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, Solvay, Solef #5130) was dissolved, and 21.6 parts by mass of NMP were weighed. Thereafter, 5.0 parts by mass of a carbon material dispersion composition (carbon material dispersion composition 1) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinner Mixer, ARE-310). Further, 97.5 parts by mass of a positive electrode active material (BASF Toda Battery Materials, LLC, HED (registered trademark) NCM-111 1100) was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a planetary centrifugal mixer (Thinner Mixer, ARE-310) to obtain a composite slurry (composite slurry 7).

[0188] Next, the composite slurry (composite slurry 7) was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm ２ The mixture was applied to aluminum foil so that the coating was as follows: After that, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film (electrode film 7). The electrode film (electrode film 1) was then rolled using a roll press (a 3-ton hydraulic roll press manufactured by Thank Metals) to obtain a positive electrode (positive electrode 6). The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 3.1 g / cc.

[0189] Table 5 shows the evaluation results of the electrode films produced in Examples 3-1 to 3-16 and Comparative Examples 3-1 to 3-9.

[0190]

[0191] (Example 4-1) A positive electrode (positive electrode 1) and a standard negative electrode were punched out to 45 mm x 40 mm and 50 mm x 45 mm, respectively, and the separator (porous polypropylene film) inserted therebetween was inserted into an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Thereafter, in a glove box filled with argon gas, an electrolyte solution (a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1) was prepared, and 2 parts by mass of VC (vinylene carbonate) was added as an additive to 100 parts by mass of the mixed solvent, and then LiPF ６ After 2 mL of a non-aqueous electrolyte solution prepared by dissolving 1M of ethylenediaminetetraacetic acid in the aluminum laminated bag was poured into the bag, the bag was sealed to prepare a laminated lithium ion secondary battery (secondary battery 1).

[0192] Examples 4-2 to 4-16, Comparative Examples 4-1 to 4-9 Laminated lithium ion secondary batteries (secondary battery 2) to (comparative secondary battery 9) were produced by the same method as for producing the laminated lithium ion secondary battery (secondary battery 1), except that the positive electrode was changed to that shown in Table 6.

[0193]

[0194] In the above examples, a resin composition containing copolymer (X) and 50 ppm or more but less than 10,000 ppm of an alkali metal was used, and the resin composition had a resistivity of 5,000 Ω·cm or more and 25,000 Ω·cm or less when the copolymer content was adjusted to 8 mass% with N-methyl-2-pyrrolidone. In the examples, the carbon material dispersion composition had superior viscosity stability over time compared to the comparative examples, and lithium ion secondary batteries were obtained with excellent secondary battery characteristics, particularly high-temperature cycle characteristics. Therefore, it has become clear that the present disclosure can provide a lithium ion secondary battery with high capacity, high output, and high durability that are difficult to achieve with conventional carbon material dispersion compositions. Vehicles equipped with the lithium ion secondary batteries of the present disclosure have high charge / discharge performance and excellent high-temperature cycle characteristics, resulting in vehicles with high safety and improved fuel economy.

[0195] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0196] 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.

[0197] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-221779, filed December 27, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

1. A resin composition comprising a copolymer (X) having an alkylene structural unit and a nitrile group-containing structural unit, and an alkali metal, wherein the content of the alkali metal is 50 ppm or more and less than 10,000 ppm, and the resistivity of the resin composition when the non-volatile content is adjusted to 8% by mass with N-methyl-2-pyrrolidone is 5,000 Ω·cm or more and 25,000 Ω·cm or less.

2. The resin composition according to claim 1, wherein the Z-average molecular weight of the copolymer (X) is 20,000 or more and 200,000 or less.

3. The resin composition according to claim 1, wherein the ratio (Mz / Mw) of the Z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the copolymer (X) is 2.0 or less.

4. A carbon material dispersion composition comprising the resin composition according to any one of claims 1 to 3 and a carbon material.

5. A composite material slurry comprising the carbon material dispersion composition according to claim 4 and an active material.

6. An electrode film formed by coating the composite material slurry according to claim 5.

7. A secondary battery comprising the electrode film according to claim 6 and an electrolyte.

8. A vehicle comprising the secondary battery according to claim 7.

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