Binder composition for electrochemical element, binder solution for electrochemical element, composite particles for electrochemical element electrode, electrode for electrochemical element, and electrochemical element

Abstract

The present invention provides a binder composition for an electrochemical element that enables the electrochemical element to exhibit excellent cycle characteristics and can also improve the flexibility of an electrode. This binder composition for an electrochemical element is characterized by including a first polymer and a second polymer, wherein both the first polymer and the second polymer are a block copolymer hydride, the weight average molecular weight of the first polymer is 120,000–550,000, and the ratio (weight average molecular weight of first polymer / weight average molecular weight of second polymer) of the weight average molecular weight of the first polymer and the weight average molecular weight of the second polymer is 1.2–8.

Description

Binder composition for electrochemical elements, binder solution for electrochemical elements, composite particles for electrodes of electrochemical elements, electrodes for electrochemical elements, and electrochemical elements

[0001] The present invention relates to a binder composition for an electrochemical device, a binder solution for an electrochemical device, composite particles for an electrode for an electrochemical device, an electrode for an electrochemical device, and an electrochemical device.

[0002] Electrochemical devices such as nonaqueous secondary batteries (e.g., lithium ion secondary batteries) are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes have been investigated with the aim of further improving the performance of electrochemical devices.

[0003] Here, electrodes of electrochemical elements such as lithium ion secondary batteries typically include a current collector and an electrode mixture layer (positive electrode mixture layer, negative electrode mixture layer) formed on the current collector. Methods under consideration for forming the electrode mixture layer include a method in which a slurry composition containing an electrode active material, a conductive material, a binder, a solvent, etc. is applied to an electrode substrate and dried to form the electrode mixture layer, and a method in which a slurry composition containing an electrode active material, a conductive material, a binder, a solvent, etc. is subjected to spray-drying or the like to obtain composite particles, and the obtained composite particles are pressure-molded onto the electrode substrate to form the electrode mixture layer.

[0004] In recent years, attempts have been made to improve the binder compositions and slurry compositions used in forming the electrode mixture layer in order to achieve further improvements in the performance of electrochemical elements.

[0005] Specifically, for example, Patent Document 1 discloses a binder composition for non-aqueous batteries, which contains a particulate polymer containing a block copolymer represented by a predetermined formula. In Patent Document 1, the use of the binder composition improves the flexibility of electrodes and the cycle characteristics of non-aqueous secondary batteries.

[0006] International Publication No. 2020 / 203371

[0007] However, the binder compositions of the above-mentioned prior art have room for improvement in terms of improving the flexibility of the electrode and the cycle characteristics of the electrochemical device.

[0008] Therefore, an object of the present invention is to provide a binder composition for electrochemical elements that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Another object of the present invention is to provide a binder solution for electrochemical elements that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Another object of the present invention is to provide composite particles for electrochemical element electrodes that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. A further object of the present invention is to provide an electrode for electrochemical elements that has excellent flexibility and is capable of enabling the electrochemical element to exhibit excellent cycle characteristics, and an electrochemical element that has excellent cycle characteristics.

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and have newly discovered that by using a binder composition for electrochemical elements, which comprises a first polymer that is a hydrogenated block copolymer having a predetermined weight-average molecular weight and a second polymer that is a hydrogenated block copolymer, and in which the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer is within a predetermined range, it is possible to improve the flexibility of an electrode for electrochemical elements prepared using the binder composition for electrochemical elements, while allowing an electrochemical element including an electrode prepared using the binder composition for electrochemical elements to exhibit excellent cycle characteristics, thereby completing the present invention.

[0010] The present invention aims to advantageously solve the above-mentioned problems. The present invention provides a binder composition for electrochemical devices, comprising: [1] a first polymer and a second polymer, each of which is a hydrogenated block copolymer; the first polymer has a weight-average molecular weight of 120,000 or more and 550,000 or less; and the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer (weight-average molecular weight of the first polymer / weight-average molecular weight of the second polymer) is 1.2 or more and 8 or less. Thus, in a binder composition comprising a first polymer that is a hydrogenated block copolymer having a predetermined weight-average molecular weight and a second polymer that is a hydrogenated block copolymer, by setting the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer within a predetermined range, the flexibility of an electrode fabricated using the binder composition can be improved, while the electrochemical device can exhibit excellent cycle characteristics. In the present invention, the "weight-average molecular weight of the polymer" can be measured by the method described in the Examples.

[0011] [2] In the binder composition for electrochemical elements according to [1] above, the ratio of the weight average molecular weight of the first polymer to the weight average molecular weight of the second polymer (weight average molecular weight of the first polymer / weight average molecular weight of the second polymer) is preferably 1.2 to 5. As described above, when the ratio of the weight average molecular weight of the first polymer to the weight average molecular weight of the second polymer is within the above range, the flexibility of the obtained electrode can be further improved, and the electrochemical element can exhibit even better cycle characteristics.

[0012] [3] In the binder composition for electrochemical elements according to [1] or [2] above, the mass ratio of the first polymer to the second polymer (first polymer / second polymer) is preferably 10 / 90 or more and 70 / 30 or less. Thus, if the mass ratio of the first polymer to the second polymer is within the above-mentioned range, the flexibility of the resulting electrode can be further improved, while the electrochemical element can exhibit even better cycle characteristics. In the present invention, the mass ratio of the first polymer to the second polymer can be measured by the method described in the Examples.

[0013] [4] In the binder composition for electrochemical elements according to any one of [1] to [3] above, at least one of the first polymer and the second polymer preferably has a triblock structure. If at least one of the first polymer and the second polymer has a triblock structure, the flexibility of the resulting electrode can be further improved, and the electrochemical element can exhibit even better cycle characteristics.

[0014] [5] In the binder composition for electrochemical elements according to [4] above, the first polymer preferably has an asymmetric triblock structure. When the first polymer has such an asymmetric triblock structure, the flexibility of the electrode can be further improved, and the electrochemical element can exhibit even better cycle characteristics.

[0015] [6] In the binder composition for electrochemical elements according to any one of [1] to [5] above, it is preferable that each of the first polymer and the second polymer contains a block A consisting of aromatic vinyl monomer units and a block B consisting of structural units derived from an aliphatic conjugated diene monomer. In this way, if the first polymer and the second polymer contain the predetermined block A and the predetermined block B, respectively, the flexibility of the obtained electrode can be further improved, and the electrochemical element can exhibit even better cycle characteristics.

[0016] [7] In the binder composition for electrochemical elements according to [6] above, the content of the block A in the total of the first polymer and the second polymer is preferably 10% by mass or more and 60% by mass or less. As described above, when the content of the block A in the total of the first polymer and the second polymer is within the above-mentioned range, the flexibility of the obtained electrode can be further improved, and the cycle characteristics of the electrochemical element can be further improved.

[0017] Another object of the present invention is to advantageously solve the above-mentioned problems, and the present invention provides a binder solution for electrochemical elements, comprising [8] a solvent and the binder composition for electrochemical elements according to any one of [1] to [7] above, wherein the first polymer and the second polymer are dissolved in the solvent. Thus, the binder solution for electrochemical element electrodes, comprising a solvent and the binder composition for electrochemical elements, in which the first polymer and the second polymer are dissolved in the solvent, can form an electrode mixture layer that can improve the flexibility of the electrode and enable the electrochemical element to exhibit excellent cycle characteristics.

[0018] [9] In the binder solution for an electrochemical element according to the above [8], the solvent is preferably an organic solvent. In this way, the use of an organic solvent as the solvent can suppress deterioration of the positive electrode active material compared to the use of water as the solvent.

[0019] The present invention also aims to advantageously solve the above-mentioned problems, and provides a composite particle for an electrochemical element electrode, comprising

[10] an electrode active material and any one of the binder compositions for an electrochemical element described above in [1] to [7]. In this way, the composite particle for an electrochemical element electrode, comprising an electrode active material and the binder composition for an electrochemical element, is excellent in strength and can form an electrode mixture layer that can improve the flexibility of the electrode and enable the electrochemical element to exhibit excellent cycle characteristics.

[0020] Another object of the present invention is to advantageously solve the above-mentioned problems, and the present invention provides an electrode for an electrochemical device, comprising an electrode mixture layer containing

[11] an electrode active material and the binder composition for an electrochemical device according to any one of [1] to [7] above. In this way, when an electrode comprises an electrode mixture layer containing an electrode active material and the binder composition for an electrochemical device, the electrode has excellent flexibility and can enable the electrochemical device to exhibit excellent cycle characteristics.

[0021] Another object of the present invention is to advantageously solve the above-mentioned problems, and the present invention provides

[12] an electrochemical element comprising the electrode for electrochemical elements according to the above

[11] . In this way, by using the electrode for electrochemical elements, an electrochemical element having excellent cycle characteristics can be obtained.

[0022] According to the present invention, it is possible to provide a binder composition for electrochemical elements that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a binder solution for electrochemical elements that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide composite particles for electrochemical element electrodes that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide an electrode for electrochemical elements that has excellent flexibility and is capable of enabling the electrochemical element to exhibit excellent cycle characteristics, and an electrochemical element that has excellent cycle characteristics.

[0023] Hereinafter, embodiments of the present invention will be described in detail. Herein, the binder composition for electrochemical elements of the present invention (hereinafter also simply referred to as the "binder composition") can be used, for example, as a material for preparing the conductive material dispersion for electrochemical elements of the present invention (hereinafter also simply referred to as the "conductive material dispersion"), the binder solution for electrochemical elements of the present invention (hereinafter also simply referred to as the "binder solution"), the composite particles for electrochemical element electrodes of the present invention (hereinafter also simply referred to as the "composite particles"), and the electrode mixture layer of the electrode for electrochemical elements of the present invention (hereinafter also simply referred to as the "electrode of the present invention"). Furthermore, the conductive material dispersion of the present invention can be used as a material for preparing the composite particles of the present invention and the electrode mixture layer of the electrode for electrochemical elements of the present invention (hereinafter also simply referred to as the "electrode"). Furthermore, the composite particles of the present invention can be used as a material for preparing the electrode mixture layer of the electrode for electrochemical elements of the present invention (hereinafter also simply referred to as the "electrode of the present invention"). The electrochemical element of the present invention comprises the electrode for electrochemical elements of the present invention.

[0024] (Binder Composition for Electrochemical Elements) The binder composition for electrochemical elements of the present invention comprises a first polymer and a second polymer, each of which is a hydrogenated block copolymer. The binder composition of the present invention is also characterized in that the weight-average molecular weight of the first polymer is 120,000 or more and 550,000 or less, and the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer (weight-average molecular weight of the first polymer / weight-average molecular weight of the second polymer) is 1.2 or more and 8 or less. The binder composition of the present invention may further contain, as an optional component, a component used in the field of electrochemical elements in addition to the components described above. The binder composition of the present invention may contain a solvent, but is preferably substantially solvent-free. Here, "substantially solvent-free" means that the binder composition does not contain any solvent other than that inevitably mixed in during the preparation process of the binder composition. Furthermore, since the binder composition of the present invention contains two types of polymers (a first polymer and a second polymer) having different weight-average molecular weights, the molecular weight distribution measured by gel permeation chromatography has at least two peaks, one derived from the first polymer and the other derived from the second polymer.

[0025] Furthermore, the binder composition of the present invention can improve the flexibility of an electrode produced using the binder composition, while allowing an electrochemical device including an electrode having an electrode mixture layer produced using the binder composition to exhibit excellent cycle characteristics.

[0026] <First Polymer> The first polymer contained in the binder composition is a component that can hold components contained in an electrode mixture layer so that they do not detach from the electrode mixture layer in an electrode having the electrode mixture layer produced using the binder composition (i.e., can function as a binder). The first polymer is a polymer obtained by hydrogenating a block copolymer.

[0027] [Properties] The weight-average molecular weight of the first polymer needs to be 120,000 or more and 550,000 or less. If the weight-average molecular weight of the first polymer is outside this range, the flexibility of the electrode and the cycle characteristics of the electrical device will deteriorate. Furthermore, from the viewpoint of further improving the flexibility of the electrode and achieving even better cycle characteristics in the electrochemical device, the weight-average molecular weight of the first polymer is preferably 150,000 or more, more preferably 195,000 or more, and even more preferably 200,000 or more, and is preferably 500,000 or less, more preferably 480,000 or less, and even more preferably 450,000 or less.

[0028] [Composition] The first polymer is not particularly limited as long as it is a polymer obtained by hydrogenating a block copolymer as a precursor, but it preferably contains, as repeating units constituting the blocks, aromatic vinyl monomer units and structural units derived from an aliphatic conjugated diene monomer, and may optionally further contain repeating units other than aromatic vinyl monomer units and structural units derived from an aliphatic conjugated diene monomer (hereinafter also referred to as "other repeating units"). Note that "containing monomer units" means that "structural units derived from the monomer are contained in a polymer obtained using that monomer."

[0029] -Aromatic vinyl monomer unit- Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include, but are not limited to, styrene, styrene sulfonic acid and its salts, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. These may be used alone or in combination of two or more in any ratio. Among these, styrene is preferred from the viewpoints of further improving the flexibility of the resulting electrode and further improving the cycle characteristics of the electrochemical element.

[0030] The proportion of aromatic vinyl monomer units in the first polymer is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 55% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less, when the amount of all repeating units (monomer units and structural units) in the first polymer is taken as 100% by mass. The content of aromatic vinyl monomer units within the above ranges can further improve the flexibility of the electrode and the cycle characteristics of the electrical device. When the first polymer has a block A (described below) composed of aromatic vinyl monomer units, the proportion of the aromatic vinyl monomer units in the first polymer typically coincides with the proportion of the block A in the first polymer.

[0031] —Structural Units Derived from Aliphatic Conjugated Diene Monomers— Examples of aliphatic conjugated diene monomers that can form structural units derived from aliphatic conjugated diene monomers include aliphatic conjugated diene compounds having 4 or more carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. These may be used alone, or two or more may be used in combination in any ratio. Among these, 1,3-butadiene and isoprene are preferred from the viewpoint of further improving the flexibility of the electrode. Note that the term “structural unit derived from an aliphatic conjugated diene monomer” refers to an aliphatic conjugated diene monomer unit and / or a structural unit obtained by hydrogenating an aliphatic conjugated diene monomer unit (a hydrogenated aliphatic conjugated diene monomer unit).

[0032] Here, the structural unit (hydrogenated aliphatic conjugated diene monomer unit) obtained by hydrogenating the aliphatic conjugated diene monomer unit is usually represented by the general formula: -C ｎ H ２ｎ- [where n is an integer of 2 or greater]. The alkylene structural unit may be linear or branched, but the alkylene structural unit is preferably linear, i.e., a linear alkylene structural unit. The alkylene structural unit preferably has 4 or more carbon atoms (i.e., n in the above general formula is an integer of 4 or greater).

[0033] The proportion of structural units derived from aliphatic conjugated diene monomers in the first polymer (the total proportion of aliphatic conjugated diene monomer units and structural units obtained by hydrogenating the aliphatic conjugated diene monomer units) is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 45% by mass or less, when the amount of all repeating units (monomer units and structural units) in the first polymer is taken as 100% by mass. When the content of structural units derived from aliphatic conjugated diene monomers is within the above range, the flexibility of the electrode can be further improved, while the cycle characteristics of the electrochemical device can be further improved. Note that when the first polymer has a block B described below consisting of structural units derived from an aliphatic conjugated diene monomer, the proportion of structural units derived from the aliphatic conjugated diene monomers in the first polymer usually matches the proportion of the block B in the polymer.

[0034] -Other repeating units- Monomers that can form other repeating units (hereinafter also referred to as "other monomers") are not particularly limited, and examples thereof include (meth)acrylic acid ester monomers and polymerizable monomers having a hydrophilic group. These monomers can be used alone or in combination of two or more. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic.

[0035] Here, examples of the (meth)acrylic acid ester monomer include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; and alkyl methacrylates such as ethyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. Among these, preferred (meth)acrylic acid ester monomers are ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, with n-butyl acrylate being more preferred.

[0036] Examples of polymerizable monomers having a hydrophilic group include monomers having a carboxylic acid group, monomers having a sulfonic acid group, monomers having a phosphoric acid group, and monomers having a hydroxyl group. From the viewpoint of increasing the binding strength of the polymer, the hydrophilic group is preferably a carboxylic acid group or a sulfonic acid group, and more preferably a carboxylic acid group.

[0037] Examples of monomers having a carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid esters such as methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride. Further, as the monomer having a carboxylic acid group, an acid anhydride that generates a carboxyl group upon hydrolysis can also be used.Other examples include monoesters and diesters of α,β-ethylenically unsaturated polycarboxylic acids such as monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate.

[0038] Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0039] Examples of the monomer having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, etc. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0040] Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; and compounds of the general formula: CH ２ =CR １ -COO-(C ｎ H ２ｎ O) ｍ -H (wherein m is an integer from 2 to 9, n is an integer from 2 to 4, R １represents hydrogen or a methyl group) and (meth)acrylic acid esters; mono(meth)acrylic acid esters of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; alkyl ethers such as (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; mono(meth)allyl ethers of ethylene glycol; polyoxyalkylene glycol mono(meth)allyl ethers such as diethylene glycol mono(meth)allyl ether and dipropylene glycol mono(meth)allyl ether; mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol, and halogen-substituted products thereof; (meth)allyl thioethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and the like.

[0041] The proportion of the other repeating units in the first polymer is preferably 10% by mass or less, and more preferably 5% by mass or less, when the amount of all repeating units (structural units and monomer units) in the first polymer is taken as 100% by mass. If the proportion of the other repeating units is equal to or less than the upper limit, the effects of the present invention are easily obtained, which is preferable.

[0042] [Structure] From the viewpoint of further improving the flexibility of the electrode and the cycle characteristics of the electrochemical device, the first polymer is preferably a hydrogenated block copolymer containing one or more blocks A composed of first repeating units and one or more blocks B composed of second repeating units. Here, the number of blocks A in the first polymer is usually three or less, preferably two. The number of blocks B in the first polymer is usually two or less, preferably one. The first polymer may further contain a block or random region composed of the above-mentioned other repeating units.

[0043] The block structure of the first polymer is not particularly limited and may be a chain block or a radial block. However, a chain block is preferred, and a linear block is more preferred. From the viewpoint of further improving the flexibility of the electrode and the cycle characteristics of the electrochemical device, the first polymer preferably has a diblock structure having one of each of two types of blocks (e.g., a structure consisting of block A and block B) or a triblock structure consisting of three blocks. Among these, a structure in which block A is bonded to both ends of block B is more preferred. Examples of such a structure in which block A is bonded to both ends of block B include a triblock structure represented by [A]-[B]-[A] and a pentablock structure represented by [A]-[B]-[A]-[B]-[A], and a triblock structure represented by [A]-[B]-[A] is more preferred. From the same viewpoint, the first polymer preferably has a triblock structure, and more preferably a triblock structure represented by [A]-[B]-[A]. The triblock structure or pentablock structure may be a symmetric block structure or an asymmetric block structure. For example, the triblock structure represented by [A]-[B]-[A] may be a symmetric triblock structure in which the two blocks A have the same degree of polymerization and / or the same type of structural unit, or an asymmetric triblock structure in which the two blocks A have different degrees of polymerization and / or the same type of structural unit. Among these, it is preferable that the first polymer has an asymmetric triblock structure.

[0044] The first polymer may be a mixture of two or more types selected from the group consisting of a block copolymer having a pentablock structure, a block copolymer having a triblock structure, and a block copolymer having a diblock structure. Preferably, the first polymer comprises 90% by mass or more, more preferably 95% by mass or more, of a block copolymer having a triblock structure, and even more preferably comprises a block copolymer having a triblock structure.

[0045] —Block A— From the viewpoint of further improving the flexibility of the electrode and providing the electrochemical device with even better cycle characteristics, the first repeating unit constituting block A is preferably an aromatic vinyl monomer unit. That is, block A preferably consists of an aromatic vinyl monomer unit. If block A consists of an aromatic vinyl monomer unit, it functions as an adsorption moiety for a conductive carbon material such as carbon black, which will be described later, and can effectively disperse the conductive carbon material, for example, in a slurry composition containing an electrode active material, a binder composition, a conductive carbon material, a solvent, etc., or in composite particles containing an electrode active material, a binder composition, a conductive carbon material, etc. Here, block A may be composed of only one type of aromatic vinyl monomer unit or multiple types of aromatic vinyl monomer units, but is preferably composed of only one type of aromatic vinyl monomer unit. Furthermore, when the first polymer has multiple blocks A, the types and proportions of the aromatic vinyl monomer units constituting these multiple blocks A may be the same or different, but are preferably the same.

[0046] The weight-average molecular weight of block A in the first polymer is not particularly limited, but is preferably at least 8,000, more preferably at least 10,000, and is preferably at most 300,000, more preferably at most 250,000. In the present invention, the weight-average molecular weight of block A in the polymer can be measured by the method described in the examples.

[0047] When the first polymer has multiple blocks A, the weight-average molecular weights of the multiple blocks A (A1, A2, ...) may be the same or different, but are preferably different. Specifically, for example, when the first polymer includes two blocks A1 and A2 (e.g., when the first polymer has a structure represented by [A1]-[B]-[A2] in which blocks A1 and A2 are bonded to both ends of block B), from the viewpoint of further improving the flexibility of the electrode and further improving the cycle characteristics of the electrochemical device, the weight-average molecular weight of block A1 is preferably 8,000 or more, more preferably 10,000 or more, and preferably 30,000 or less, more preferably 15,000 or less; on the other hand, the weight-average molecular weight of block A2 is preferably 100,000 or more, more preferably 200,000 or more, and preferably 300,000 or less, more preferably 250,000 or less.

[0048] From the viewpoint of further improving the flexibility of the electrode and improving the cycle characteristics of the electrical element, the ratio of the weight-average molecular weight of the block A2 to the weight-average molecular weight of the block A1 (weight-average molecular weight of block A2 / weight-average molecular weight of block A1) is preferably 8 or more, more preferably 14 or more, and is preferably 30 or less, more preferably 25 or less.

[0049] -Block B- From the viewpoint of enabling an electrochemical device to exhibit even better cycle characteristics, the second repeating unit constituting block B is preferably a structural unit derived from an aliphatic conjugated diene monomer. That is, block B is preferably composed of structural units derived from an aliphatic conjugated diene monomer. Here, block B may be composed of only one type of structural unit derived from an aliphatic conjugated diene monomer, or may be composed of multiple types of structural units. Furthermore, when the first polymer has multiple blocks B, the types and proportions of the structural units derived from the aliphatic conjugated diene monomer constituting these multiple blocks B may be the same or different, but are preferably the same.

[0050] The weight-average molecular weight of block B in the first polymer is preferably 50,000 or more, more preferably 70,000 or more, and even more preferably 100,000 or more, and is preferably 250,000 or less, and more preferably 200,000 or less. When the weight-average molecular weight of block B is equal to or greater than the above-mentioned lower limit, the flexibility of the electrode can be further improved. When the weight-average molecular weight of block B is equal to or less than the above-mentioned upper limit, a decrease in the strength of the polymer can be suppressed. In the present invention, the weight-average molecular weight of block B in the polymer can be easily determined by the method described in the Examples. When the polymer contains multiple blocks B, the weight-average molecular weights of the multiple blocks B may be the same or different, but are preferably the same.

[0051] —Ratio of Blocks A and B— The ratio of block A in the first polymer (the total ratio when there are multiple blocks A) is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 55% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. When the ratio of block A in the first polymer is within the above range, the flexibility of the electrode can be further improved, and the cycle characteristics of the electrical device can be further improved.

[0052] Furthermore, the content of block B in the first polymer (the total content when there are multiple blocks B) is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 45% by mass or less. When the content of block B in the first polymer is within the above range, the flexibility of the electrode can be further improved, and the cycle characteristics of the electrochemical device can be further improved.

[0053] —Ratio of Blocks A and B— The mass ratio of block A to block B (block A / block B) in the first polymer is preferably 0.8 or more, more preferably 1.5 or more, and is preferably 3.5 or less, more preferably 2.5 or less. When the mass ratio of block A to block B in the first polymer is within the above range, the flexibility of the electrode can be further improved, and the cycle characteristics of the electrochemical device can be further improved.

[0054] <Second Polymer> The second polymer contained in the binder composition is, like the first polymer, a component that can hold components contained in an electrode mixture layer so that they do not detach from the electrode mixture layer in an electrode having the electrode mixture layer produced using the binder composition (i.e., can function as a binder). The second polymer is a polymer obtained by hydrogenating a block copolymer.

[0055] [Properties] The weight-average molecular weight of the second polymer is not particularly limited as long as the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer (weight-average molecular weight of first polymer / weight-average molecular weight of second polymer), which will be described later, is 1.2 or more and 8 or less. However, from the viewpoint of further improving the flexibility of the electrode and enabling the electrochemical device to exhibit even better cycle characteristics, the weight-average molecular weight is preferably 70,000 or more, more preferably 90,000 or more, and even more preferably 100,000 or more, and is preferably 300,000 or less, and more preferably 250,000 or less.

[0056] [Composition] The second polymer is not particularly limited as long as it is a polymer obtained by hydrogenating a block copolymer, and can have the same composition as the first polymer described above. That is, the second polymer preferably contains aromatic vinyl monomer units and structural units derived from an aliphatic conjugated diene monomer, and may optionally further contain other repeating units.

[0057] -Aromatic vinyl monomer units- Preferred types of aromatic vinyl monomer units in the second polymer are the same as those in the first polymer. Furthermore, the proportion of aromatic vinyl monomer units in the second polymer is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 14% by mass or more, and is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 25% by mass or less, when the amount of all repeating units (monomer units and structural units) in the second polymer is taken as 100% by mass. When the proportion of aromatic vinyl monomer units in the second polymer is within the above range, the flexibility of the electrode can be further improved, while the cycle characteristics of the electrochemical device can be further improved.

[0058] -Structural Units Derived from Aliphatic Conjugated Diene Monomer- The preferred types and proportions of structural units derived from aliphatic conjugated diene monomers in the second polymer are the same as those in the first polymer.

[0059] [Structure] The second polymer is not particularly limited and can have the same structure as the first polymer described above. That is, the second polymer is preferably a hydrogenated block copolymer containing one or more blocks A consisting of the first repeating unit and one or more blocks B consisting of the second repeating unit, and optionally further containing blocks or random regions consisting of other repeating units. Here, the preferred numbers of blocks A and B in the second polymer and the preferred block configurations are the same as those of the first polymer. In particular, the second polymer preferably has a symmetric triblock structure.

[0060] -Block A- Preferred types of the first repeating units constituting the block A in the second polymer are the same as those in the first polymer described above. The weight-average molecular weight of the block A in the second polymer is not particularly limited, but is preferably 8,000 or more, more preferably 10,000 or more, and is preferably 30,000 or less, more preferably 20,000 or less. When the weight-average molecular weight of the block A in the second polymer is equal to or greater than the above-mentioned lower limit, the flexibility of the electrode can be further improved. When the weight-average molecular weight of the block A in the second polymer is equal to or less than the above-mentioned upper limit, the flexibility of the electrode can be further improved. Here, when the second polymer has multiple blocks A, the weight-average molecular weights of the multiple blocks A (A1, A2, ...) may be the same or different, but are preferably the same.

[0061] -Block B- The preferred type of the second repeating unit constituting the block B in the second polymer, the preferred weight average molecular weight of the block B, etc. are the same as those of the first polymer.

[0062] —Ratio of Blocks A and B— The ratio of block A in the second polymer (the total ratio when there are multiple blocks A) is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 14% by mass or more, and is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 25% by mass or less. When the ratio of block A in the second polymer is within the above range, the flexibility of the electrode can be further improved, and the cycle characteristics of the electrochemical device can be further improved.

[0063] Furthermore, the content of block B in the second polymer (the total content when there are multiple blocks B) is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 45% by mass or less. When the content of block B in the second polymer is within the above range, the flexibility of the electrode can be further improved, and the cycle characteristics of the electrical device can be further improved.

[0064] <Ratio of Weight-Average Molecular Weight of First Polymer to Weight-Average Molecular Weight of Second Polymer> The ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer (weight-average molecular weight of first polymer / weight-average molecular weight of second polymer) needs to be 1.2 or more and 8 or less. If the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer is outside the above range, the flexibility of the electrode and the cycle characteristics of the electrochemical device will deteriorate. From the viewpoint of further improving the flexibility of the electrode and the cycle characteristics of the electrochemical device, the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer is preferably 1.5 or more, more preferably 2 or more, and preferably 4 or less, more preferably 3 or less.

[0065] <Content of aromatic vinyl monomer units> The proportion of aromatic vinyl monomer units in the total of the first polymer and the second polymer in the binder composition is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less, when the total proportion of repeating units (monomer units and structural units) in the first polymer and the second polymer is taken as 100% by mass. If the content of aromatic vinyl monomer units is within the above range, the flexibility of the electrode can be further improved and the cycle characteristics of the electrochemical device can be further improved.

[0066] <Mass Ratio of First Polymer to Second Polymer> From the viewpoint of further improving the flexibility of the electrode and enabling the electrochemical element to exhibit even better cycle characteristics, the mass ratio of the first polymer to the second polymer (first polymer / second polymer) in the binder composition is preferably 10 / 90 or more, more preferably 20 / 80 or more, and is preferably 70 / 30 or less, more preferably 60 / 40 or less.

[0067] <Other Components> In addition to the above components, the binder composition may contain components such as a reinforcing material, a leveling agent, a viscosity modifier, and an electrolyte additive. These are not particularly limited as long as they do not affect the electrochemical reaction, and known components, such as those described in WO 2012 / 115096, can be used. Furthermore, these components may be used alone or in combination of two or more types in any ratio.

[0068] <Method of Preparing Binder Composition> The binder composition is not particularly limited and can be prepared, for example, by preparing a solution containing two types of block copolymers as precursors of a first polymer and a second polymer, hydrogenating each block copolymer, and then removing the solvent used in preparing the polymers. Here, the solution containing the two types of block copolymers may be prepared by preparing a solution containing a block copolymer as a precursor of the first polymer and a solution containing a block copolymer as a precursor of the second polymer and then mixing the two solutions, or by sequentially synthesizing the two types of block copolymers in one solvent. Alternatively, the binder composition may be prepared by preparing a solution containing a first polymer and a solution containing a second polymer, mixing the two solutions to obtain a mixed solution, and then removing the solvent from the mixed solution. If other components are to be added, they may be mixed using a known method before or after removing the solvent.

[0069] [Preparation of block copolymer] The method for preparing the block copolymer is not particularly limited, and for example, a solution obtained by polymerizing a first monomer component is polymerized with a second monomer component different from the first monomer component, and the polymerization is optionally repeated to prepare a block copolymer. Specifically, examples of methods for producing block copolymers include those described in WO 2003 / 018656, WO 2011 / 096389, WO 2021 / 065623, etc.

[0070] [Hydrogenation] A hydrogenated block copolymer can be obtained by hydrogenating at least the carbon-carbon unsaturated bonds derived from the aliphatic conjugated diene monomer units of the above-described block copolymer. Here, each hydrogenated block copolymer may be a polymer in which only the non-aromatic carbon-carbon unsaturated bonds in the main chain and side chain derived from the aliphatic conjugated diene monomer units of the block copolymer are selectively hydrogenated, or may be a polymer in which the non-aromatic carbon-carbon unsaturated bonds in the main chain and side chain derived from the aliphatic conjugated diene monomer units of the block copolymer and the aromatic carbon-carbon unsaturated bonds in the aromatic ring derived from the aromatic vinyl monomer units of the block copolymer are hydrogenated. However, a polymer in which only the non-aromatic carbon-carbon unsaturated bonds in the main chain and side chain derived from the aliphatic conjugated diene monomer units of the block copolymer are selectively hydrogenated is preferred.

[0071] Specifically, during hydrogenation, the hydrogenation rate of the aromatic carbon-carbon unsaturated bonds in each block copolymer (i.e., the proportion of hydrogenated carbon-carbon unsaturated bonds in the aromatic rings of the aromatic vinyl monomer units, etc.) is preferably 50% or less, more preferably 30% or less, even more preferably 15% or less, even more preferably 3% or less, and particularly preferably 0%. When the hydrogenation rate of the aromatic carbon-carbon unsaturated bonds in the aromatic vinyl monomer units is equal to or less than the upper limit described above, the cycle characteristics of the electrochemical device can be further improved. When each hydrogenated block copolymer is composed of a block A consisting of aromatic vinyl monomer units and a block B consisting of structural units derived from an aliphatic conjugated diene compound, the hydrogenation rate of the aromatic carbon-carbon unsaturated bonds usually matches the hydrogenation rate of the aromatic carbon-carbon unsaturated bonds in block A.

[0072] Furthermore, during hydrogenation, the hydrogenation rate of non-aromatic carbon-carbon unsaturated bonds in the main chain and side chain derived from the aliphatic conjugated diene monomer units, etc. of each block copolymer (i.e., the proportion of hydrogenated carbon-carbon unsaturated bonds in the main chain and side chain derived from the aliphatic conjugated diene monomer units, etc.) is preferably 50% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 95% or more. When the hydrogenation rate of non-aromatic carbon-carbon unsaturated bonds is equal to or greater than the above-mentioned lower limit, the flexibility of the electrode can be further improved while the cycle characteristics of the electrochemical device can be further improved. When each hydrogenated block copolymer is composed of a block A composed of aromatic vinyl monomer units and a block B composed of structural units derived from an aliphatic conjugated diene monomer, the hydrogenation rate of the non-aromatic carbon-carbon unsaturated bonds usually matches the hydrogenation rate of the non-aromatic carbon-carbon unsaturated bonds of block B.

[0073] The hydrogenation rate is １ The H-NMR spectrum is measured, and the amount of change can be calculated based on the decrease in the integrated values ​​of the signals corresponding to the unsaturated bonds in the main chain and side chain portions and the unsaturated bonds in the aromatic ring before and after the hydrogenation reaction.

[0074] The hydrogenation method and reaction form of the unsaturated bonds in the block copolymer are not particularly limited, and may be carried out according to known methods. Examples of methods for selectively hydrogenating the non-aromatic carbon-carbon unsaturated bonds in the main chain and side chain derived from the aliphatic conjugated diene monomer of the block copolymer include known hydrogenation methods such as those described in JP 2015-78090 A. Furthermore, any known selective hydrogenation catalyst can be used without limitation, and palladium-based catalysts and rhodium-based catalysts can be used. Furthermore, nickel-based catalysts such as Ni(AcAc)2-TIBAL and nickel(II) acetylacetonate, and aluminum-based catalysts such as triisobutylaluminum can also be used. Two or more of these hydrogenation catalysts may be used in combination.

[0075] The reaction liquid after the hydrogenation reaction may then be optionally subjected to a catalyst removal (demineralization) treatment by a conventionally known method, and the resulting polymer may be filtered, washed, dried, etc. to recover the binder composition. The binder composition may be a dispersion in which the first polymer and the second polymer are dispersed in a solvent, but as will be described later, it is preferable to use a binder solution in which the first polymer and the second polymer are dissolved in a solvent.

[0076] (Binder solution for electrochemical elements) The binder solution for electrochemical elements of the present invention contains a solvent and the binder composition for electrochemical elements of the present invention described above, and may further contain other components used in the field of electrochemical elements. The binder solution of the present invention is characterized in that a first polymer and a second polymer are dissolved in the solvent. Note that the binder solution of the present invention does not contain a conductive carbon material or a conductive material, which will be described later.

[0077] Since the binder solution of the present invention contains the binder composition of the present invention, electrodes produced using the binder solution have excellent flexibility, and electrochemical devices equipped with the electrodes can exhibit excellent cycle characteristics. Here, by using a binder solution, the strength of the composite particles, the flexibility of the electrodes, and the cycle characteristics of the electrochemical devices can be further improved. The reason for this is not entirely clear, but it is presumed that the solution provides better coverage of the first polymer and the second polymer on the electrode active material and conductive carbon materials such as carbon black, as described below, compared to a dispersion in which particulate first and second polymers are dispersed in a solvent (dispersion medium). As a result, the binding strength between the electrode active material and the conductive carbon material is enhanced.

[0078] <Binder Composition for Electrochemical Devices> The binder composition for electrochemical devices can be any of those described above. That is, the binder solution contains the first polymer and second polymer described above. Here, the binder solution preferably has a solids concentration of 30% by mass or less, more preferably 20% by mass or less, preferably 1% by mass or more, and more preferably 5% by mass or more. When the solids concentration of the binder solution is within the above range, the strength of the resulting composite particles can be further increased. Furthermore, of the total solids contained in the binder solution, the proportion of the first polymer and the second polymer is preferably 90% by mass or more, more preferably 95% by mass or more, and may even be 100% by mass. When the proportion of the binder is equal to or greater than the above lower limit, the strength of the resulting composite particles can be further increased.

[0079] <Solvent> The solvent is a component (compound) capable of dissolving the first polymer and the second polymer. Here, "the first polymer and the second polymer are dissolved in the solvent" means that no peaks of particle size of the first polymer and the second polymer are detected when measured using a laser diffraction / scattering particle size distribution analyzer capable of detecting measurement targets down to the nm order (e.g., a measurable range of 0.01 μm to 3000 μm). Specifically, "the state in which the first polymer and the second polymer are dissolved in the solvent" can be confirmed by the following method. [Method for Confirming That the First Polymer and the Second Polymer are Dissolved in the Solvent in the Binder Solution] The binder solution is diluted with cyclohexane to adjust the total solids concentration to 0.1% by mass to obtain a test solution. 10 mL of the obtained test solution is placed in a plastic bottle and subjected to ultrasonic dispersion for 10 minutes using an ultrasonic cleaner (manufactured by SND Corporation, "US-105N"). 1 mL of the sample is dropped into the sample inlet of the measuring device, and measurement is carried out to confirm whether a peak in the particle size distribution is detected.

[0080] The solvent contained in the binder solution of the present invention is not particularly limited as long as it can dissolve the first polymer and the second polymer, and either water or an organic solvent can be used, but from the viewpoint of suppressing deterioration of the positive electrode active material, an organic solvent is preferable. The organic solvent is not particularly limited, and organic solvents such as cyclohexane, N-methylpyrrolidone (NMP), N,N-dimethylformamide, and acetone can be used. Among these, cyclohexane is preferred.

[0081] <Other Components> Other components that can be blended into the binder solution of the present invention are not particularly limited, and include the same components as the other components that can be blended into the binder composition of the present invention. These components may be used alone or in combination of two or more at any ratio.

[0082] <Method for preparing binder solution> The binder solution is not particularly limited, and can be obtained, for example, by preparing the first polymer and the second polymer according to the above-mentioned method for preparing the first polymer and the second polymer, and then adding additives as necessary and mixing them by a known method. At this time, a necessary amount of the above-mentioned solvent may be added to adjust the binder solution to a desired solid content concentration.

[0083] (Conductive material dispersion for electrochemical elements) The conductive material dispersion for electrochemical elements of the present invention contains the binder composition for electrochemical elements of the present invention described above, a conductive carbon material, and a solvent, and may optionally further contain other components used in the field of electrochemical elements and conductive materials other than the conductive carbon material. Note that the conductive material dispersion of the present invention does not contain an electrode active material. In the conductive material dispersion of the present invention, it is preferable that the first polymer and the second polymer are dissolved in the solvent. That is, the conductive material dispersion for electrochemical elements of the present invention contains the binder composition for electrochemical elements of the present invention described above and a conductive carbon material, and preferably further contains other components used in the field of electrochemical elements and conductive materials other than the conductive carbon material. Furthermore, since the conductive material dispersion of the present invention contains the binder composition of the present invention, an electrode produced using the conductive material dispersion has excellent flexibility, and an electrochemical element including the electrode can exhibit excellent cycle characteristics.

[0084] <Binder Composition for Electrochemical Elements> The binder composition for electrochemical elements may be any of those described above. The amount of the binder composition for electrochemical elements, calculated as solid content, is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less, per 100 parts by mass of the conductive carbon material. When the amount of the binder composition is equal to or greater than the lower limit, the dispersion stability of the conductive carbon material can be further improved. When the amount of the binder composition is equal to or less than the upper limit, the flexibility of the electrode and the cycle characteristics of the electrochemical element can be further improved.

[0085] <Conductive Carbon Material> Examples of conductive carbon materials that function as conductive materials that ensure electrical contact between electrode active materials in the electrode mixture layer include carbon black (e.g., acetylene black, Ketjen Black (registered trademark), furnace black, etc.), graphite (graphene), carbon fiber (carbon nanofiber), carbon flakes, and ultrashort carbon fibers (e.g., carbon nanotubes (CNT) and vapor-grown carbon fibers). Among these, from the viewpoint of conductivity and output characteristics, carbon black, carbon fiber (carbon nanofiber), graphite (graphene), and carbon nanotubes (CNT) are preferred, carbon black and carbon nanotubes (CNT) are more preferred, and carbon black is particularly preferred. These materials can be used alone or in combination of two or more.

[0086] <Solvent> The solvent is not particularly limited, and examples thereof include the same solvents as those that can be added to the binder solution of the present invention. Among these, cyclohexane is preferred from the viewpoint of dispersion stability of the conductive carbon material.

[0087] <Other Components> Other components that can be blended into the conductive material dispersion liquid are not particularly limited, and include the same components as the other components that can be blended into the binder composition of the present invention. These components may be used alone or in combination of two or more types in any ratio.

[0088] <Other Conductive Materials> Conductive materials other than conductive carbon materials (other conductive materials) are not particularly limited, and fibers, foils, etc. of various metals can be used.

[0089] <Method for preparing conductive material dispersion> The conductive material dispersion can be prepared by mixing the above-mentioned components by a known mixing method. Among them, from the viewpoint of dispersing the conductive carbon material well, it is preferable to prepare the conductive material dispersion by adding and mixing the conductive carbon material and optionally additional solvent into a mixture (e.g., a binder solution) obtained by mixing a binder composition, a solvent, and optionally other components. The mixing can be performed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.

[0090] (Composite particles for electrochemical element electrodes) The composite particles for electrochemical element electrodes of the present invention comprise an electrode active material and the binder composition for electrochemical elements of the present invention described above, and may optionally further comprise a conductive carbon material, a solvent, other components used in the field of electrochemical elements, conductive materials other than conductive carbon materials, etc. The composite particles of the present invention contain the binder composition of the present invention, which improves the flexibility of the electrode while allowing the electrochemical element to exhibit excellent cycle characteristics. Furthermore, the composite particles of the present invention contain the binder composition of the present invention, which results in excellent strength. Note that, below, an example will be described in which the composite particles are composite particles for lithium ion secondary battery positive electrodes, but the present invention is not limited to the following example.

[0091] <Electrode active material> The electrode active material is a material that transfers electrons at the electrode of an electrochemical element. For example, as a positive electrode active material for a lithium ion secondary battery, a material that can absorb and release lithium is usually used. Hereinafter, a positive electrode active material for a lithium ion secondary battery will be described as an example, but the present invention is not limited to the following example.

[0092] The positive electrode active material for lithium ion secondary batteries can be a compound containing a transition metal, such as a transition metal oxide, a transition metal sulfide, or a composite metal oxide of lithium and a transition metal, including Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

[0093] As the transition metal oxide, transition metal sulfide, and composite metal oxide of lithium and transition metal, for example, those described in JP-A-2020-198315 can be used.

[0094] <Binder composition for electrochemical element> The binder composition for electrochemical element may be any of those described above. The amount of the binder composition, calculated as solid content, is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 6 parts by mass or less, and more preferably 3 parts by mass or less, per 100 parts by mass of the electrode active material. When the amount of the binder composition is equal to or greater than the lower limit, an electrode mixture layer can be formed satisfactorily. When the amount of the binder composition is equal to or less than the upper limit, the cycle characteristics of the electrochemical element can be further improved.

[0095] <Conductive Carbon Material> The conductive carbon material that can be arbitrarily blended into the composite particles is not particularly limited, and examples thereof include the same conductive carbon materials that can be blended into the conductive material dispersion of the present invention.

[0096] The amount of the conductive carbon material is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 3 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the electrode active material. If the amount of the conductive carbon material is equal to or greater than the above-mentioned lower limit, the output characteristics of the electrochemical element can be further improved. If the amount of the conductive carbon material is equal to or less than the above-mentioned upper limit, the dispersion stability of the conductive carbon material can be further improved.

[0097] <Solvent> The solvent that can be optionally blended into the composite particles is not particularly limited, and examples thereof include the same solvents that can be blended into the binder solution of the present invention.

[0098] <Other Components> Other components that can be blended into the composite particles are not particularly limited, and include the same components as those that can be blended into the conductive material dispersion of the present invention. These components may be used alone or in combination of two or more in any ratio.

[0099] <Other Conductive Materials> Other components that can be blended into the composite particles are not particularly limited, and include the same components as those that can be blended into the conductive material dispersion of the present invention.

[0100] <Method for producing composite particles> The composite particles can be produced by, but are not particularly limited to, a spray-drying granulation method, a tumbling bed granulation method, a compression granulation method, an agitation granulation method, an extrusion granulation method, a crushing granulation method, a fluidized bed granulation method, a multifunctional fluidized bed granulation method, a melt granulation method, etc. Among these, the agitation granulation method is preferred from the viewpoint of increasing the strength of the composite particles.

[0101] The production of composite particles by the stirring granulation method is not particularly limited, but the composite particles are preferably produced through a step of stirring an electrode active material (pre-stirring step), a step of adding a liquid containing the binder composition of the present invention and a solvent and optionally further containing a conductive carbon material (for example, a liquid containing the binder solution of the present invention and optionally a conductive carbon material) or a conductive material dispersion of the present invention to the electrode active material while stirring the electrode active material to obtain a granulated product (granulation step), and a step of further stirring and sizing the granulated product (sizing step). The production apparatus for composite particles by the stirring granulation method is not particularly limited, and known stirring granulators such as batch-type stirring granulators and continuous stirring granulators can be used.

[0102] (Electrode for electrochemical device) The electrode for electrochemical device of the present invention comprises, for example, a current collector and an electrode mixture layer formed on the current collector, the electrode mixture layer comprising at least an electrode active material and the binder composition of the present invention. That is, the electrode mixture layer contains at least an electrode active material and a binder composition (first polymer, second polymer), and may optionally further contain a conductive carbon material, other components used in the field of electrochemical devices, a conductive material other than the conductive carbon material, etc.

[0103] The electrode of the present invention contains the binder composition of the present invention, and therefore has excellent flexibility. Furthermore, by using this electrode, an electrochemical device having excellent cycle characteristics can be obtained.

[0104] <Current Collector> Examples of materials that can be used for the current collector include metals, carbon, and conductive polymers, with metals being preferred. Metals that are typically used include copper, aluminum, platinum, nickel, tantalum, titanium, stainless steel, and other alloys. Among these, copper, aluminum, or aluminum alloys are preferred in terms of electrical conductivity and voltage resistance.

[0105] <Electrode mixture layer> [Binder composition for electrochemical element] The binder composition for electrochemical element to be blended in the electrode mixture layer can be any of those described above. The blending amount of the binder composition is not particularly limited, and can be the blending amount described above in the section "Composite particles for electrochemical element electrode."

[0106] [Electrode Active Material] The electrode active material to be blended in the electrode mixture layer is not particularly limited, and examples thereof include the same electrode active materials as those to be blended in the composite particles of the present invention.

[0107] [Conductive carbon material] The conductive carbon material that can be arbitrarily blended into the electrode mixture layer is not particularly limited, and examples thereof include the same conductive carbon materials that can be blended into the conductive material dispersion of the present invention. The blending amount of the conductive carbon material is not particularly limited, and can be the blending amount described above in the section "Composite particles for electrochemical element electrodes."

[0108] [Other Components] Other components that can be optionally blended into the electrode mixture layer are not particularly limited, and include the same components as those that can be blended into the composite particles of the present invention.

[0109] [Other Conductive Materials] Other conductive materials that can be blended into the electrode mixture layer are not particularly limited, and examples thereof include the same conductive materials as those that can be blended into the composite particles of the present invention.

[0110] In the following, an example will be described in which the electrode of the present invention is an electrode for a lithium ion secondary battery, but the present invention is not limited to the following example.

[0111] <Method for Manufacturing Electrodes for Lithium Ion Secondary Batteries> Electrodes for lithium ion secondary batteries are manufactured, for example, by a method of forming an electrode mixture layer on a current collector using the composite particles of the present invention described above. Specifically, for example, electrodes for lithium ion secondary batteries are manufactured by a method of forming the composite particles of the present invention described above into a sheet and then laminating them on a current collector, or by a method of directly pressurizing the composite particles on the current collector. Among these, a method of directly pressurizing the composite particles on the current collector is preferred. Examples of pressurizing methods include a roll pressurizing method using a roll pressurizing device equipped with a pair of rolls, in which the current collector is fed by the rolls while the composite particles are fed into the roll pressurizing device with a feeder such as a vibration feeder or a screw feeder to form an electrode active material layer on the current collector; a method in which the composite particles are sprayed on a current collector, smoothed with a blade or the like to adjust the thickness, and then molded with a pressure device; and a method in which the composite particles are filled into a mold and pressurized to mold the mold. Among these, the roll pressurizing method is preferred.

[0112] Furthermore, to eliminate variations in thickness of the formed lithium-ion secondary battery electrode and increase the density of the electrode active material layer to achieve high capacity, post-pressing may be performed as needed. A preferred method of post-pressing is a roll pressing process. In the roll pressing process, two cylindrical rolls are arranged parallel to each other with a small gap between them, rotated in opposite directions, and pressed by clamping the electrode between them. In this process, the temperature of the rolls may be adjusted, for example, by heating or cooling.

[0113] Alternatively, an electrode for a lithium ion secondary battery can also be produced by a method including a step of applying a slurry composition containing the above-described components onto a current collector (application step), and a step of drying the slurry composition applied onto the current collector to form an electrode mixture layer on the current collector (drying step).

[0114] Here, the method for applying the slurry composition to the current collector and the method for drying the slurry composition on the current collector are not particularly limited, and for example, known methods described in JP 2022-041228 A can be used. The slurry composition can also be prepared by mixing the above-mentioned components using a known mixing method. For example, the slurry composition can be prepared by preparing in advance a liquid containing the binder composition of the present invention and a solvent, and optionally further containing a conductive carbon material, or the above-mentioned conductive material dispersion of the present invention, and adding an electrode active material to the liquid or conductive material dispersion and mixing them. When a conductive carbon material is added, from the viewpoint of dispersing the conductive carbon material well, it is preferable to prepare the slurry composition by adding the electrode active material and optional components (such as additional solvents, other components, other conductive materials, etc.) to the conductive material dispersion of the present invention and mixing them. The amount of each of the above components in the slurry composition is not particularly limited, and can be the same as the amount described above in the "Composite Particles for Electrochemical Element Electrodes" section. The mixing can be carried out using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.

[0115] (Electrochemical element) The electrochemical element of the present invention includes, for example, a positive electrode, a negative electrode, an electrolyte, and a separator, and uses the electrode of the present invention as at least one of the positive electrode and the negative electrode, preferably as the positive electrode. Since the electrochemical element of the present invention includes the electrode of the present invention, it has excellent cycle characteristics. Hereinafter, a description will be given of a case where the electrochemical element is a lithium ion secondary battery as an example, but the present invention is not limited to the following example.

[0116] <Electrode> Known electrodes can be used as electrodes other than the electrode of the present invention. Specifically, the electrode can be, for example, a negative electrode made of a thin plate of metallic lithium, or an electrode formed by forming an electrode mixture layer on a current collector. The current collector can be made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum. The electrode mixture layer can be a layer containing an electrode active material and a binder. Furthermore, the binder is not particularly limited, and any known material can be used.

[0117] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt is used. As the lithium salt, for example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is particularly preferred because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred, and LiPF ６ is particularly preferred. Note that one type of electrolyte may be used alone, or two or more types may be used in combination in any ratio. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0118] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (EMC) are preferred. Other suitable solvents include esters such as γ-butyrolactone and methyl formate, ethers such as 1,2-dimethoxyethane and tetrahydrofuran, and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents may also be used. Among these, carbonates are preferred because of their high dielectric constant and wide stable potential range, and a mixture of ethylene carbonate and ethyl methyl carbonate is even more preferred. The concentration of the electrolyte in the electrolyte can be adjusted as appropriate. For example, it is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and even more preferably 5 to 10% by mass.

[0119] <Separator> The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the thickness of the entire separator to be thin, thereby increasing the proportion of electrode active material in the electrochemical device and increasing the capacity per volume.

[0120] The electrochemical element is assembled by, for example, stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary according to the shape of the electrochemical element, placing the stack in a container, injecting an electrolyte into the container, and sealing the container. To prevent internal pressure buildup, overcharging and overdischarging, and the like, a fuse, an overcurrent protection element such as a PTC element, expanded metal, lead plates, and the like may be provided as necessary. The shape of the assembled electrochemical element may be any of, for example, a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like.

[0121] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, the terms "%" and "parts" used to represent amounts are based on mass unless otherwise specified. Furthermore, in a polymer produced by copolymerizing multiple types of monomers, the proportion of a structural unit formed by polymerizing a certain monomer in the polymer usually corresponds to the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the weight-average molecular weights of the first polymer and the second polymer, the weight-average molecular weight of each block, the mass ratio of the first polymer to the second polymer, the flexibility of the electrode, and the cycle characteristics of the lithium-ion secondary battery were measured, calculated, or evaluated using the following methods.

[0122] <Weight-Average Molecular Weight of Polymers> The weight-average molecular weights of the first polymer and second polymer prepared in the examples and comparative examples were determined as polystyrene-equivalent molecular weights by high-performance liquid chromatography using tetrahydrofuran as a carrier at a flow rate of 0.35 ml / min. The analyzer used was a Tosoh HLC8320, the column consisted of three connected Shodex (registered trademark) KF-404HQ columns manufactured by Showa Denko K.K. (column temperature: 40°C), and the detectors used were a differential refractometer and an ultraviolet detector. Molecular weight calibration was performed using 12 standard polystyrene points (5,000,000 to 3,000,000) manufactured by Polymer Laboratory Co., Ltd. <Mass Ratio of First Polymer to Second Polymer> The mass ratio of the first polymer to the second polymer (first polymer / second polymer) was determined from the area ratio of the peaks corresponding to the first polymer and the second polymer in the chart obtained by the above-mentioned high-performance liquid chromatography. <Weight-Average Molecular Weight of Block Composed of Aromatic Vinyl Monomer Units (Block A)> Rubber Chem. Technol., 45, 1295 (1972), the first polymer and the second polymer (hydrogenated block copolymer) were each reacted with ozone and reduced with lithium aluminum hydride to decompose the block (Block B) consisting of structural units derived from aliphatic conjugated diene monomers in each polymer. Specifically, the procedure was as follows: 300 mg of sample was dissolved in a reaction vessel containing 100 ml of dichloromethane treated with molecular sieves. The reaction vessel was then placed in a cooling bath and cooled to −25°C. Ozone generated by an ozone generator was then introduced into the reaction vessel while oxygen was flowing into the reaction vessel at a flow rate of 170 ml / min. Thirty minutes after the start of the reaction, the completion of the reaction was confirmed by introducing the gas flowing out of the reaction vessel into an aqueous potassium iodide solution. Next, 50 ml of diethyl ether and 470 mg of lithium aluminum hydride were placed in another reaction vessel purged with nitrogen, and the solution reacted with ozone was slowly added dropwise to the reaction vessel while the reaction vessel was cooled with ice water. The reaction vessel was then placed in a water bath, gradually heated, and refluxed at 40°C for 30 minutes. Thereafter, dilute hydrochloric acid was added dropwise to the reaction vessel while stirring the solution, and the addition was continued until almost no hydrogen generation was observed.After the reaction, the solid product formed in the solution was filtered and extracted with 100 ml of diethyl ether for 10 minutes. This extract and the filtrate were combined, and the solvent was removed by distillation to obtain a solid sample. The weight-average molecular weight of the sample thus obtained was measured according to the above-described method for measuring weight-average molecular weight, and the resulting value was used as the weight-average molecular weight of the block composed of aromatic vinyl monomer units. <Weight-Average Molecular Weight of Block (Block B) Composed of Structural Units Derived from Aliphatic Conjugated Diene Monomer> The weight-average molecular weight of the block composed of structural units derived from an aliphatic conjugated diene monomer was determined by subtracting the weight-average molecular weight of the block composed of aromatic vinyl monomer units from the weight-average molecular weights of the first polymer and the second polymer obtained as described above. <Strength of Composite Particles> The strength of the composite particles produced in the examples and comparative examples was calculated using the following formula based on the particle diameter D50 of the composite particles measured by the method described below. Strength of composite particle: Sp = D50B / D50A In the formula, D50A represents D50 automatically calculated from the particle size distribution at an air dispersion pressure of 0.10 MPa by a dry measurement method using a particle size distribution analyzer MT3000 manufactured by Microtrac, and D50B represents D50 automatically calculated from the particle size distribution at an air dispersion pressure of 0.25 MPa by a dry measurement method using a particle size distribution analyzer MT3000 manufactured by Microtrac. A: Composite particle strength of 0.6 or more B: Composite particle strength of 0.4 or more and less than 0.6 C: Composite particle strength of 0.2 or more and less than 0.4 D: Composite particle strength of less than 0.2 <Electrode flexibility> The positive electrodes for lithium ion secondary batteries produced in the examples and comparative examples were wrapped around rods of different diameters to evaluate whether the positive electrode composite layer cracked. The smaller the diameter of the rod on which the positive electrode composite layer does not crack when wound around the rod, the more flexible the electrode is and the better the winding ability. The flexibility of the electrode was evaluated according to the diameter of the thinnest rod on which the positive electrode composite layer did not crack, using the following criteria: A: No crack when wound around a rod with a diameter of 1.50 mm. B: No crack when wound around a rod with a diameter of 1.80 mm. C: No crack when wound around a rod with a diameter of 2.10 mm. D: No crack when wound around a rod with a diameter of 3.00 mm.<Cycle Characteristics> After injecting the electrolyte, the lithium ion secondary batteries as electrochemical elements prepared in the Examples and Comparative Examples were left standing at 25°C for 5 hours. Next, they were charged to a cell voltage of 3.65 V at 25°C using a constant current method at 0.2 C, and then aged for 12 hours at 60°C. Then, they were discharged to a cell voltage of 3.00 V using a constant current method at 25°C and 0.2 C. Thereafter, they were subjected to CC-CV charging (upper limit cell voltage 4.20 V) using a constant current method at 0.2 C, and CC discharging to 3.00 V using a constant current method at 0.2 C. This 0.2 C charge-discharge cycle was repeated three times to prepare an evaluation cell. Next, the evaluation cell was subjected to 100 cycles of charge-discharge at a cell voltage of 4.20-3.00 V and a charge-discharge rate of 0.5 C under a temperature of 45°C. The discharge capacity at the first cycle was defined as X1, and the discharge capacity at the 100th cycle as X2. Using the discharge capacities X1 and X2, the capacity retention rate = (X2 / X1) x 100 (%) was calculated and evaluated according to the following criteria. A larger capacity retention rate indicates that the lithium ion secondary battery has better cycle characteristics. A: Capacity retention rate is 90% or more B: Capacity retention rate is 85% or more but less than 90% C: Capacity retention rate is 80% or more but less than 85% D: Capacity retention rate is less than 80%.

[0123] Example 1 Preparation of Binder Solution A reactor equipped with a stirrer and thoroughly purged with nitrogen was charged with 120 parts of dehydrated cyclohexane, 0.2 parts of dibutyl ether, and 5.2 parts of dehydrated styrene as an aromatic vinyl monomer. 0.05 parts of n-butyllithium (15% cyclohexane solution) as a polymerization initiator was then added. The entire mixture was then stirred at 50°C for 30 minutes (first-stage polymerization). Gas chromatography of the reaction solution revealed a polymerization conversion of 99.5% at this point. Next, 21.4 parts of dehydrated isoprene as an aliphatic conjugated diene monomer was continuously added to the reaction solution over 30 minutes, and after the addition was completed, the entire mixture was stirred for 30 minutes (second-stage polymerization). The polymerization conversion at this point was 99.5%. Subsequently, 5.2 parts of dehydrated styrene as an aromatic vinyl monomer was added and stirred for 30 minutes (third-stage polymerization). The polymerization conversion at this point was 99.7%. At this point, 0.1 parts of ethanol was added to the reaction solution to partially terminate the reaction. This resulted in a polymer solution containing a block copolymer having a styrene-isoprene-styrene triblock structure as a precursor of the second polymer. Subsequently, 9 parts of dehydrated styrene as an aromatic vinyl monomer was added to the polymer solution and stirred for 30 minutes (fourth polymerization stage). At this point, the polymerization conversion rate was nearly 100%. At this point, 0.2 parts of ethanol was added to the reaction solution to terminate the reaction. This resulted in a polymer solution further containing a block copolymer having a styrene-isoprene-styrene triblock structure as a precursor of the first polymer. Next, the polymer solution was transferred to a pressure-resistant reactor equipped with a stirrer, and a Ni(AcAc)2-TIBAL catalyst was added as a hydrogenation catalyst in a ratio of 0.5% relative to the block copolymer composition before hydrogenation. The hydrogenation reaction was carried out at a temperature of 80°C and a pressure of 0.9 MPa for 6 hours. Next, in order to remove metal components derived from the hydrogenation catalyst, 1.1 parts of malic acid and 0.2 parts of a nonionic surfactant block copolymer of ethylene oxide and propylene oxide (manufactured by ADEKA Corporation, product name "L-64") were dissolved in 500 parts of ion-exchanged water in the polymer solution, and the solution was then added to the reactor and stirred for 5 hours.Thereafter, 1 part of a xylene solution containing 0.1 parts of the phenolic antioxidant pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (manufactured by Koyo Chemical Laboratory, product name "Songnox 1010") was added and dissolved. Cyclohexane was further added to prepare a binder solution of a predetermined concentration containing a first polymer and a second polymer (binder composition). Then, using a portion of the binder solution, the weight-average molecular weights of the first polymer and the second polymer, the mass ratio between the first polymer and the second polymer, and the weight-average molecular weight of each block contained in the first polymer and the second polymer were determined. The results are shown in Table 1.

[0124] <Preparation of Conductive Material Dispersion> Carbon black (BET specific surface area: 62 m) was used as a conductive carbon material. ２ / g, bulk density 0.16 g / cm ３ ) and 2 parts of the binder solution (solid content equivalent), and cyclohexane was further added as a solvent to obtain a mixture of a conductive carbon material, a binder composition, and a solvent (solid content concentration 10%, total amount 1 kg). Next, the obtained mixture was dispersed for 1 hour using a bead mill (LMZ015, manufactured by Ashizawa Fine Tech) using zirconia beads with a diameter of 0.5 mm at a peripheral speed of 12 m / s, thereby preparing a conductive material dispersion containing a conductive carbon material, a binder composition, and a solvent.

[0125] <Production of Composite Particles> A composite particle production apparatus was prepared. The apparatus consisted of a cylindrical vessel with an inner diameter of 180 mm and a capacity of 2 L, and two agitating blades, one vertical and one horizontal, with the axis of the cylindrical vessel being the vertical direction (the main agitating blade was the vertical axis and the auxiliary agitating blade was the horizontal axis). The main agitating blade was an inclined paddle with three main blades each 170 mm in diameter, and the auxiliary agitating blade had a V-shaped anchor blade with a diameter of 30 mm. The main and auxiliary agitating blades were sealed by ventilating air to prevent raw materials from being mixed into their drive mechanisms. Using the composite particle production apparatus, composite particles were produced by performing (i) a preliminary agitation operation, (ii) a granulation operation, and (iii) a sizing operation in this order. Specifically, in (i) the preliminary agitation operation, 96 parts by mass (1,344 g) of NMC532 (average particle diameter 6 μm), a positive electrode active material for lithium-ion secondary batteries, was first added to the granulation vessel. Next, room-temperature air (hereinafter also referred to as "sealing air") for sealing the drive parts of the main and auxiliary stirring blades was circulated at 20 L / min (airflow rate 10 / min), and stirring was performed for 15 minutes under operating conditions of a main stirring blade peripheral speed of 5 m / s and a auxiliary stirring blade peripheral speed of 6 m / s. The solids concentration of the powder material after stirring was measured and found to be 99% by mass or more. Next, (ii) as a granulation operation, room-temperature sealing air was circulated at 20 L / min (airflow rate 10 / min), and the main stirring blade peripheral speed was 5 m / s and the auxiliary stirring blade peripheral speed was 6 m / s. 4 parts (560) g of the conductive material dispersion obtained above (solids concentration: 10% by mass, solvent: cyclohexane) was continuously added to the pre-stirred positive electrode active material over 15 minutes using a dropping funnel. Finally, (iii) as a particle size adjustment operation, room temperature sealing air was circulated at 20 L / min (airflow rate 10 / min), and the mixture was operated for 10 minutes under the conditions of a main stirring impeller peripheral speed of 2 m / s and a sub-stirring impeller peripheral speed of 2 m / s, to produce composite particles. The maximum temperature in the system throughout steps (i) to (iii) was 38°C. The strength of the composite particles was then measured. The results are shown in Table 1.

[0126] <Preparation of a positive electrode for a lithium-ion secondary battery> The composite particles prepared above were supplied to a press roll (roll temperature 100°C, press linear pressure 500 kN / m) of a roll press machine ("Oshikuri Rough Surface Hot Roll" manufactured by Hirano Giken Kogyo Co., Ltd.) using a quantitative feeder ("Nikka Spray K-V" manufactured by Nikka Corporation). An aluminum foil having a thickness of 20 μm was inserted between the press rolls, and the composite particles supplied from the quantitative feeder were attached to the aluminum foil as a current collector, followed by pressure molding at a molding speed of 1.5 m / min to obtain a positive electrode having a basis weight of 30 mg / cm. ２ This positive electrode raw sheet was rolled with a roll press to a density of 3.5 g / cm. ３ A sheet-shaped positive electrode for a lithium ion secondary battery was fabricated, which consisted of the positive electrode mixture layer and aluminum foil. The flexibility of the resulting positive electrode for a lithium ion secondary battery was evaluated. The results are shown in Table 1.

[0127] <Preparation of Negative Electrode> 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as an acidic group-containing monomer, 63.5 parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50 ° C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to terminate the polymerization reaction, and a mixture containing a particulate binder (styrene-butadiene copolymer) was obtained. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust the pH to 8, and unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to 30 ° C or below to obtain an aqueous dispersion containing a binder for the negative electrode. Next, 48.75 parts of artificial graphite as a negative electrode active material, 48.75 parts of natural graphite, and 1 part of carboxymethyl cellulose as a thickener were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solids concentration of 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the aqueous dispersion containing the negative electrode binder obtained as described above, equivalent to the solids content, was added, and the mixture was kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to obtain a viscosity of 3000±500 mPa·s (measured with a Brookfield viscometer at 25°C and 60 rpm), thereby preparing a negative electrode composite layer slurry. Next, a 15 μm thick copper foil was prepared as a current collector. The negative electrode composite layer slurry was applied to the copper foil in a coating amount of 15 mg / cm after drying. ２ The coating was dried at 60°C for 20 minutes and at 120°C for 20 minutes. Thereafter, the coating was heated at 150°C for 2 hours to obtain a negative electrode blank. This negative electrode blank was rolled using a roll press to a density of 1.6 g / cm. ３ A sheet-shaped negative electrode was prepared, which consisted of the negative electrode mixture layers (on both sides) of the above and copper foil.

[0128] <Preparation of Lithium-ion Secondary Battery> A single-layer laminate cell (discharge capacity equivalent to 250 mAh) was prepared using the positive and negative electrodes prepared above and a separator (made of polyethylene, thickness 12 μm) and placed in an aluminum package. Then, a 1.0 M LiPF 6 electrolyte was placed in the aluminum package. ６A solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 volume % vinylene carbonate (solvent ratio)) was filled. Furthermore, in order to seal the opening of the aluminum packaging, the aluminum packaging was closed by heat sealing at a temperature of 150°C, and a lithium ion secondary battery was produced. The cycle characteristics were evaluated using this lithium ion secondary battery. The results are shown in Table 1.

[0129] Example 2 In the preparation of the binder solution, the amount of dehydrated styrene as an aromatic vinyl monomer added in the first polymerization stage was changed from 5.2 parts to 2.4 parts, the amount of dehydrated isoprene as an aliphatic conjugated diene monomer added in the second polymerization stage was changed from 21.4 parts to 20.6 parts, the amount of dehydrated styrene as an aromatic vinyl monomer added in the third polymerization stage was changed from 5.2 parts to 2.4 parts, and the amount of dehydrated styrene as an aromatic vinyl monomer added in the fourth polymerization stage was changed from 9 parts to 15.4 parts. A binder solution, a conductive material dispersion, composite particles, a positive electrode and a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were prepared or manufactured in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0130] Example 3 In the preparation of the binder solution, the amount of dehydrated styrene as an aromatic vinyl monomer added in the first polymerization stage was changed from 5.2 parts to 5.9 parts, the amount of dehydrated isoprene as an aliphatic conjugated diene monomer added in the second polymerization stage was changed from 21.4 parts to 25.5 parts, the amount of dehydrated styrene as an aromatic vinyl monomer added in the third polymerization stage was changed from 5.2 parts to 5.9 parts, and the amount of dehydrated styrene as an aromatic vinyl monomer added in the fourth polymerization stage was changed from 9 parts to 3.5 parts. The binder solution, the conductive material dispersion, the composite particles, the positive and negative electrodes for a lithium ion secondary battery, and the lithium ion secondary battery were prepared or manufactured in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0131] Example 4 In the preparation of the binder solution, the amount of dehydrated styrene as the aromatic vinyl monomer added in the first polymerization stage was changed from 5.2 parts to 5.5 parts, the amount of dehydrated isoprene as the aliphatic conjugated diene monomer added in the second polymerization stage was changed from 21.4 parts to 28.6 parts, the amount of dehydrated styrene as the aromatic vinyl monomer added in the third polymerization stage was changed from 5.2 parts to 5.5 parts, and the amount of dehydrated styrene as the aromatic vinyl monomer added in the fourth polymerization stage was changed from 9 parts to 1.1 parts. Except for this, binder solutions, conductive material dispersions, composite particles, positive and negative electrodes for lithium ion secondary batteries, and lithium ion secondary batteries were prepared or manufactured in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0132] (Example 5) In preparing the binder solution, except that isoprene was changed to 1,3-butadiene as the aliphatic conjugated diene monomer, a binder solution, a conductive material dispersion, composite particles, a positive electrode and a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were prepared or manufactured in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0133] Example 6 In the preparation of the binder solution, the amount of dehydrated styrene as an aromatic vinyl monomer added in the first polymerization stage was changed from 5.2 parts to 3.2 parts, the amount of dehydrated isoprene as an aliphatic conjugated diene monomer added in the second polymerization stage was changed from 21.4 parts to 25.9 parts, the amount of dehydrated styrene as an aromatic vinyl monomer added in the third polymerization stage was changed from 5.2 parts to 3.2 parts, and the amount of dehydrated styrene as an aromatic vinyl monomer added in the fourth polymerization stage was changed from 9 parts to 8.5 parts. The binder solution, the conductive material dispersion, the composite particles, the positive and negative electrodes for a lithium ion secondary battery, and the lithium ion secondary battery were prepared or manufactured in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 1.

[0134] Comparative Example 1 A binder solution, a conductive material dispersion, composite particles, a positive electrode and a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were prepared or manufactured in the same manner as in Example 2, except that the fourth polymerization stage was not carried out and the first polymer was not synthesized in the preparation of the binder solution, and various measurements and evaluations were carried out. The results are shown in Table 1.

[0135] Comparative Example 2 In the preparation of the binder solution, the amount of dehydrated styrene as the aromatic vinyl monomer added in the first polymerization stage was changed from 5.2 parts to 3.9 parts, the amount of dehydrated isoprene as the aliphatic conjugated diene monomer added in the second polymerization stage was changed from 21.4 parts to 17.7 parts, the amount of dehydrated styrene as the aromatic vinyl monomer added in the third polymerization stage was changed from 5.2 parts to 19.2 parts, and the fourth polymerization stage was not performed, thereby not including the second polymer. In the same manner as in Example 1, except for this, a binder solution, a conductive material dispersion, composite particles, a positive electrode and a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery were prepared or manufactured, and various measurements and evaluations were performed. The results are shown in Table 1.

[0136] The results shown in Table 1 show that in Examples 1 to 6, which used binder compositions containing a first polymer and a second polymer, each of which was a hydrogenated block copolymer, in which the weight-average molecular weight of the first polymer was 120,000 or more and 550,000 or less, and in which the ratio of the weight-average molecular weight of the first polymer to the weight-average molecular weight of the second polymer (weight-average molecular weight of the first polymer / weight-average molecular weight of the second polymer) was 1.2 or more and 8 or less, the resulting electrodes had excellent flexibility and the electrochemical elements were able to exhibit excellent cycle characteristics.

[0137] According to the present invention, it is possible to provide a binder composition for electrochemical elements that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a binder solution for electrochemical elements that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide composite particles for electrochemical element electrodes that can improve the flexibility of an electrode and enable the electrochemical element to exhibit excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide an electrode for electrochemical elements that has excellent flexibility and is capable of enabling the electrochemical element to exhibit excellent cycle characteristics, and an electrochemical element that has excellent cycle characteristics.

Claims

1. A binder composition for electrochemical elements comprising a first polymer and a second polymer, wherein the first polymer and the second polymer are each a hydrogenated block copolymer, the weight average molecular weight of the first polymer is 120,000 or more and 550,000 or less, and the ratio of the weight average molecular weight of the first polymer to the weight average molecular weight of the second polymer (weight average molecular weight of the first polymer / weight average molecular weight of the second polymer) is 1.2 or more and 8 or less.

2. The binder composition for electrochemical elements according to claim 1, wherein the ratio of the weight average molecular weight of the first polymer to the weight average molecular weight of the second polymer (weight average molecular weight of the first polymer / weight average molecular weight of the second polymer) is 1.2 or more and 5 or less.

3. The binder composition for electrochemical elements according to claim 1, wherein the mass ratio of the first polymer to the second polymer (first polymer / second polymer) is 10 / 90 or more and 70 / 30 or less.

4. The binder composition for an electrochemical element according to claim 1, wherein at least one of the first polymer and the second polymer has a triblock structure.

5. The binder composition for an electrochemical element according to claim 4, wherein the first polymer has an asymmetric triblock structure.

6. The binder composition for electrochemical elements according to claim 1, wherein each of the first polymer and the second polymer comprises a block A consisting of aromatic vinyl monomer units and a block B consisting of structural units derived from an aliphatic conjugated diene monomer.

7. The binder composition for electrochemical elements according to claim 6, wherein the content of said block A in the total of said first polymer and said second polymer is 10 mass % or more and 60 mass % or less.

8. A binder solution for electrochemical elements comprising a solvent and the binder composition for electrochemical elements according to any one of claims 1 to 7, in which the first polymer and the second polymer are dissolved in the solvent.

9. The binder solution for an electrochemical element according to claim 8, wherein the solvent is an organic solvent.

10. Composite particles for an electrochemical element electrode, comprising an electrode active material and the binder composition for an electrochemical element according to any one of claims 1 to 7.

11. An electrode for an electrochemical element, comprising an electrode mixture layer containing an electrode active material and the binder composition for an electrochemical element according to any one of claims 1 to 7.

12. An electrochemical element comprising the electrode for an electrochemical element according to claim 11.

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