Binder aqueous solution for lithium-ion battery, electrode slurry for lithium-ion battery, electrode for lithium-ion battery and manufacturing method therefor, and lithium-ion battery and manufacturing method therefor

Abstract

Provided are: a binder aqueous solution for a lithium-ion battery, the binder aqueous solution comprising a water-soluble polymer (A), carbon nanotubes (B), and a compound (C) represented by general formula (1); an electrode slurry for a lithium-ion battery; an electrode for a lithium-ion battery and a manufacturing method therefor; and a lithium-ion battery and a manufacturing method therefor.

Description

Aqueous binder solution for lithium-ion batteries, electrode slurry for lithium-ion batteries, electrode for lithium-ion batteries and method for manufacturing the same, lithium-ion battery and method for manufacturing the same

[0001] The present invention relates to an aqueous binder solution for lithium-ion batteries, an electrode slurry for lithium-ion batteries, an electrode for lithium-ion batteries and a method for manufacturing the same, and a lithium-ion battery and a method for manufacturing the same.

[0002] Lithium-ion batteries are used in electronic devices such as mobile phones and laptop computers, and in recent years, their application to automotive and home energy storage batteries has also been progressing. A lithium-ion battery consists of components such as a positive electrode, a negative electrode, a separator, and an electrolyte. The positive and negative electrodes are manufactured by applying an electrode slurry, which is a mixture of an active material that allows for the insertion and removal of lithium ions, a conductive additive, a binder, and a solvent, onto a current collector and then drying it.

[0003] Conductive additives are primarily used to create conductive pathways by interposing them between active material particles. Carbon black and acetylene black have been widely used as conductive additives, but in recent years, carbon nanotubes (CNTs), which have excellent conductivity, have attracted attention and are being put into practical use as conductive additives for lithium-ion batteries.

[0004] Conductive additives are required to be uniformly dispersed within electrodes in order to form many contact points with the active material. However, carbon nanotubes have a tendency to aggregate in water, making it difficult to uniformly disperse them when used as a conductive additive in aqueous slurries. Therefore, research has been conducted to improve the dispersibility of carbon nanotubes.

[0005] Patent Document 1 discloses a slurry composition for a secondary battery negative electrode, comprising at least carbon nanotubes, a conductive material, an active material for the negative electrode, a dispersant, and a binder component, wherein the dispersant is characterized by being carboxymethylcellulose or a metal salt thereof with a mass average molecular weight of 300,000 or less, and carboxymethylcellulose or a metal salt thereof with a mass average molecular weight of 1,000,000 to 3,000,000.

[0006] Japanese Patent Publication No. 2024-065983

[0007] As described in Patent Document 1, the dispersibility of carbon nanotubes in water can be improved by using a dispersant such as carboxymethylcellulose. However, according to the inventors' studies, even if carbon nanotubes are well dispersed in water in the absence of a binder, it has been confirmed that the carbon nanotubes re-aggregate when a binder is added to create an aqueous binder solution containing both carbon nanotubes and the binder.

[0008] This invention has been made in view of the above circumstances, and aims to provide an aqueous binder solution for lithium-ion batteries with excellent dispersibility of carbon nanotubes, an electrode slurry for lithium-ion batteries, an electrode for lithium-ion batteries and a method for producing the same, as well as a lithium-ion battery and a method for producing the same.

[0009] As a result of diligent research, the present inventors have found that the above problems can be solved by using a specific dispersant, and have completed the present invention as follows. That is, the present invention relates to the following [1] to

[13] . [1] An aqueous binder solution for lithium-ion batteries containing a water-soluble polymer (A), a carbon nanotube (B), and a compound (C) represented by the following general formula (1). (In the formula, X represents a hydrocarbon group having a carboxyl group or a salt thereof, or a hydrocarbon group having a sulfonic acid group or a salt thereof. R １ ~R １０ Each of these independently represents a hydrogen atom or a substituent. In the formula, the number of hydroxyl groups in the structure other than X is 0 to 2.) [2] The aqueous binder solution for lithium-ion batteries described in [1] above, wherein the compound (C) is represented by the following general formula (2). (In the formula, X, R １ , R ３ , R ４ and R ７The explanation is the same as the explanation for general formula (1) above. In the formula, the number of hydroxyl groups in the structure other than X is 0 to 2.) [3] The aqueous binder solution for lithium-ion batteries according to [1] or [2] above, wherein X is a hydrocarbon group having a salt of a carboxyl group or a hydrocarbon group having a salt of a sulfonic acid group. [4] The aqueous binder solution for lithium-ion batteries according to [3] above, wherein the salt of the carboxyl group is a sodium salt or lithium salt of the carboxyl group, and the salt of the sulfonic acid group is a sodium salt or lithium salt of the sulfonic acid group. [5] The aqueous binder solution for lithium-ion batteries according to any one of [1] to [4] above, wherein the water-soluble polymer (A) is one or more selected from the group consisting of a polymer containing structural units derived from vinyl ether (A1), a polymer containing structural units derived from acrylic acid (A2), carboxymethylcellulose or a derivative thereof (A3), a polymer containing structural units derived from alkylene oxide (A4), and a polymer containing structural units derived from vinyl alcohol (A5). [6] An aqueous binder solution for lithium-ion batteries according to any one of [1] to [5] above, wherein the ratio of the mass-based content of compound (C) to the mass-based content of carbon nanotubes (B) [(C) / (B)] is 0.1 to 20. [7] An aqueous binder solution for lithium-ion batteries according to any one of [1] to [6] above, wherein the content of the water-soluble polymer (A) is 1 to 50% by mass. [8] An aqueous binder solution for lithium-ion batteries according to any one of [1] to [7] above, wherein the content of carbon nanotubes (B) is 0.01 to 1.0% by mass. [9] An electrode slurry for lithium-ion batteries containing an aqueous binder solution for lithium-ion batteries and an active material according to any one of [1] to [8] above.

[10] A method for manufacturing an electrode for lithium-ion batteries using an aqueous binder solution for lithium-ion batteries according to any one of [1] to [8] above.

[11] A method for manufacturing a lithium-ion battery using an aqueous binder solution for lithium-ion batteries described in any of [1] to [8] above.

[12] An electrode for a lithium-ion battery containing a water-soluble polymer (A), a carbon nanotube (B), a compound (C) represented by the following general formula (1), and an active material. (In the formula, X represents a hydrocarbon group having a carboxy group or a salt thereof, or a hydrocarbon group having a sulfonic acid group or a salt thereof. R １ ~R １０ each independently represents a hydrogen atom or a substituent. In the formula, the number of hydroxy groups contained in the structure excluding X is 0 to 2.)

[13] A lithium ion battery containing the electrode for a lithium ion battery described in the above

[12] .

[0010] According to the present invention, it is possible to provide an aqueous binder solution for a lithium ion battery excellent in the dispersibility of carbon nanotubes, an electrode slurry for a lithium ion battery, an electrode for a lithium ion battery and a method for producing the same, and a lithium ion battery and a method for producing the same.

[0011] In this specification, for preferable numerical ranges, the lower limit value and the upper limit value described stepwise can be combined independently of each other. For example, from the description "preferably 10 to 90, more preferably 30 to 60", it is also possible to combine the "preferred lower limit value (10)" and the "more preferred upper limit value (60)" to obtain "10 to 60".

[0012] In this specification, for example, "(meth)acrylic acid" means both "acrylic acid" and "methacrylic acid", and the same applies to other similar terms.

[0013] In this specification, the "structural unit" means a unit of the structure based on one molecule of a monomer formed by polymerization of one molecule of the monomer.

[0014] [Aqueous Binder Solution for Lithium Ion Battery] The aqueous binder solution for a lithium ion battery of the present embodiment (hereinafter, also simply referred to as "the binder aqueous solution of the present embodiment") is an aqueous binder solution for a lithium ion battery containing a water-soluble polymer (A), carbon nanotubes (B), and a compound (C) represented by the following general formula (1).

[0015] (In the formula, X represents a hydrocarbon group having a carboxy group or a salt thereof, or a hydrocarbon group having a sulfonic acid group or a salt thereof. R １ ~R １０Each of these independently represents a hydrogen atom or a substituent. In the formula, the number of hydroxyl groups in the structure excluding X is between 0 and 2.

[0016] The binder aqueous solution of this embodiment exhibits excellent dispersibility of carbon nanotubes (B). The details of the reason for this are not clear, but it is presumed to be as follows. Compound (C) contained in the binder aqueous solution of this embodiment has X, which is a hydrocarbon group having a hydrophilic carboxyl group or a salt thereof, or a hydrocarbon group having a sulfonic acid group or a salt thereof, as represented by the general formula (1) above. Furthermore, compound (C) has an aliphatic condensed ring structure excluding X, and since this aliphatic condensed ring structure has low polarity, it is thought to have good affinity with the surface of carbon nanotubes (B). In other words, since compound (C) has both a hydrophilic group X and an aliphatic condensed ring structure that has good affinity with the surface of carbon nanotubes (B), it is presumed that compound (C) plays a role in increasing the affinity between the surface of carbon nanotubes (B) and water at the interface between the two. Similarly, it is presumed that compound (C), due to its good affinity with carbon nanotubes (B), was able to suppress aggregation that occurs when a water-soluble polymer (A) is added, as the water-soluble polymer (A) is adsorbed onto the carbon nanotubes (B). The following describes, in order, each component that may be contained in the binder aqueous solution of this embodiment.

[0017] <Water-soluble polymer (A)> Water-soluble polymer (A) is a polymer used as a binder in the binder aqueous solution of this embodiment. Water-soluble polymer (A) is not particularly limited as long as it is a polymer that is water-soluble. In this context, "water-soluble" means that the amount that dissolves in 100 parts by mass of water at 23°C is 1 part by mass or more. Water-soluble polymer (A) may be used alone or in combination of two or more types.

[0018] Examples of the water-soluble polymer (A) include one or more selected from the group consisting of polymers containing structural units derived from vinyl ether (A1), polymers containing structural units derived from acrylic acid (A2), carboxymethylcellulose or its derivatives (A3), polymers containing structural units derived from alkylene oxide (A4), and polymers containing structural units derived from vinyl alcohol (A5). Among these, from the viewpoint of more easily exhibiting the effects of the present invention, one or more selected from the group consisting of polymers containing structural units derived from vinyl ether (A1), polymers containing structural units derived from acrylic acid (A2), carboxymethylcellulose or its derivatives (A3), and polymers containing structural units derived from alkylene oxide (A4) are preferred, and polymers containing structural units derived from vinyl ether (A1) are more preferred.

[0019] (Polymer (A1) containing structural units derived from vinyl ether) The polymer containing structural units derived from vinyl ether (hereinafter also referred to as "polymer (A1)") is not particularly limited as long as it is a polymer containing structural units derived from vinyl ether, and may be a homopolymer of vinyl ether or a copolymer of vinyl ether and a monomer other than vinyl ether. In this specification, "vinyl ether" means a compound having a vinyl group and an etheric oxygen atom bonded to the vinyl group.

[0020] [Structural units derived from vinyl ether] Structural units derived from vinyl ether are structural units formed by the addition reaction of vinyl groups present in vinyl ether. The vinyl ether-derived structural units contained in polymer (A1) may be one type alone or two or more types.

[0021] Examples of vinyl ethers from which structural units derived from vinyl ethers are derived include alkyl vinyl ethers and polyoxyalkylene vinyl ethers. The number of carbon atoms in the vinyl ether is preferably 3 to 12, more preferably 4 to 10, and even more preferably 5 to 8. The number of vinyl groups in one molecule of vinyl ether is 1 or more, and from the viewpoint of suppressing gelation during synthesis, it is preferably 3 or less, more preferably 2 or less, and even more preferably 1. The number of carbon atoms in the alkyl group of alkyl vinyl ether is preferably 1 to 10, more preferably 2 to 7, and even more preferably 2 to 5. The number of carbon atoms per oxyalkylene unit of polyoxyalkylene vinyl ether is preferably 1 to 5, more preferably 1 to 4, and even more preferably 2 to 3. The number of oxyalkylene units in polyoxyalkylene vinyl ether is 2 or more, preferably 4 or less, more preferably 3 or less, and even more preferably 2.

[0022] While vinyl ethers are not particularly limited, hydroxyl group-containing vinyl ethers are preferred from the viewpoint of binder water solubility. Hydroxyl group-containing vinyl ethers are not particularly limited as long as they are compounds having a hydroxyl group, a vinyl group, and an etheric oxygen atom bonded to the vinyl group. The number of hydroxyl groups in one molecule of a hydroxyl group-containing vinyl ether is one or more, preferably three or less, more preferably two or less, and even more preferably one.

[0023] From the viewpoint of reactivity, flexibility, etc., the hydroxyl group-containing vinyl ether is preferably a vinyl ether having a hydroxyalkyl group or a vinyl ether having a hydroxypolyoxyalkylene chain containing two or more oxyalkylene units.

[0024] The number of carbon atoms in the hydroxyalkyl group of the vinyl ether having the above-mentioned hydroxyalkyl group is preferably 1 to 10, more preferably 2 to 7, and even more preferably 2 to 5. Examples of vinyl ethers having a hydroxyalkyl group include hydroxymethyl vinyl ether, 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, 7-hydroxypentyl vinyl ether, 8-hydroxyoctyl vinyl ether, 9-hydroxynonyl vinyl ether, and 10-hydroxydecyl vinyl ether. Among these, 4-hydroxybutyl vinyl ether is preferred.

[0025] The number of carbon atoms per oxyalkylene unit in a vinyl ether having a hydroxypolyoxyalkylene chain containing two or more oxyalkylene units is preferably 1 to 5, more preferably 1 to 4, and even more preferably 2 to 3. The number of oxyalkylene units in the hydroxypolyoxyalkylene chain is two or more, preferably four or less, more preferably three or less, and even more preferably two. Examples of vinyl ethers having a hydroxypolyoxyalkylene chain containing two or more oxyalkylene units include diethylene glycol monovinyl ether, triethylene glycol monovinyl ether, dipropylene glycol monovinyl ether, and tripropylene glycol monovinyl ether. Among these, diethylene glycol monovinyl ether is preferred.

[0026] The content of vinyl ether-derived structural units in polymer (A1) is preferably 5 to 80 mol%, more preferably 10 to 70 mol%, even more preferably 20 to 60 mol%, and even more preferably 30 to 50 mol% of the total structural units of polymer (A1). If the content of vinyl ether-derived structural units is above the lower limit, the polymer becomes flexible, and cracking of electrodes can be suppressed when used as a binder. Furthermore, if the content of vinyl ether-derived structural units is below the upper limit, the generation of residual monomers during the synthesis of polymer (A1) can be suppressed.

[0027] The content of structural units derived from hydroxyl group-containing vinyl ether in polymer (A1) is preferably 5 to 80 mol%, more preferably 10 to 70 mol%, even more preferably 20 to 60 mol%, and even more preferably 30 to 50 mol%, of the total structural units of polymer (A1). If the content of structural units derived from hydroxyl group-containing vinyl ether is above the lower limit, the polymer becomes flexible, and cracking of electrodes can be suppressed when used as a binder. Furthermore, if the content of structural units derived from hydroxyl group-containing vinyl ether is below the upper limit, the generation of residual monomers during the synthesis of polymer (A1) can be suppressed.

[0028] [Structural units derived from (meth)acrylamide group-containing compounds] It is preferable that polymer (A1) further contains structural units derived from (meth)acrylamide group-containing compounds. Structural units derived from (meth)acrylamide group-containing compounds are structural units formed by an addition reaction of the carbon-carbon double bond contained in the (meth)acryloyl group of the (meth)acrylamide group-containing compound. By polymer (A1) containing structural units derived from (meth)acrylamide group-containing compounds, the reactivity of monomers during the synthesis of polymer (A1) is improved, and the generation of residual monomers tends to be further suppressed. In this specification, "(meth)acrylamide group" refers to the group represented by the following general formula (b-1).

[0029] (In the formula, R ｂ１ (* indicates a hydrogen atom or a methyl group. * indicates a bonding site.)

[0030] However, in the present invention, compounds containing a (meth)acrylamide group having a sulfonic acid group or a salt thereof shall be classified as "ethylenically unsaturated monomers having a sulfonic acid group or a salt thereof" as described later.

[0031] The structural units derived from the (meth)acrylamide group-containing compound contained in polymer (A1) may be one type alone or two or more types.

[0032] The (meth)acrylamide group-containing compound is not particularly limited as long as it contains the above-mentioned (meth)acrylamide group, but examples include the compound represented by the following general formula (b-2).

[0033] (In the formula, R ｂ１ R represents a hydrogen atom or a methyl group. ｂ２ and R ｂ３ Each independently represents a hydrogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms, R ｂ２ and R ｂ３ (They may be joined together to form a ring.)

[0034] In the above general formula (b-2), R ｂ２ and R ｂ３ Examples of substituted or unsubstituted C1-C20 hydrocarbon groups represented by include substituted or unsubstituted C1-C20 alkyl groups, substituted or unsubstituted C2-C20 alkenyl groups, substituted or unsubstituted C2-C20 alkynyl groups, substituted or unsubstituted C6-C20 aromatic hydrocarbon groups, etc. ｂ２ and R ｂ３ The ring formed by the bonding of these is R ｂ２ and R ｂ３ A heterocycle formed from a nitrogen atom bonded to it and 2 to 20 carbon atoms, R ｂ２ and R ｂ３Examples include heterocycles formed from a nitrogen atom bonded to a carbon atom, one or more oxygen atoms, and 2 to 20 carbon atoms. The number of carbon atoms in a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms may be 1 to 10 or 1 to 5. The number of carbon atoms in substituents is not included in this calculation. Examples of substituents that a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms may have include hydroxyl groups, halogen atoms, cyano groups, nitro groups, carboxyl groups, amino groups, alkoxy groups, aryloxy groups, acyloxy groups, etc. The number of carbon atoms in substituents may be 1 to 5 or 1 to 3.

[0035] Among the above options, R ｂ２ and R ｂ３ From the viewpoint of reactivity, it is preferable that it be a hydrogen atom.

[0036] Examples of compounds containing a (meth)acrylamide group include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide, N-t-butyl(meth)acrylamide, and N-hexyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; (meth)acrylamides having a hydroxyalkyl group such as N-hydroxymethyl(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, and N-(2-hydroxypropyl)(meth)acrylamide; and (meth)acrylamides having a ring structure such as N-acryloylpyrrolidine, 3-acryloyl-2-oxazolidinone, 4-acryloylmorpholine, N-acryloylpiperidine, and N-methacryloylpiperidine. Among these, N,N-dimethyl(meth)acrylamide and (meth)acrylamide are preferred from the viewpoint of reactivity.

[0037] When polymer (A1) contains structural units derived from a (meth)acrylamide group-containing compound, the content of structural units derived from the (meth)acrylamide group-containing compound in polymer (A1) is preferably 5 to 95 mol%, more preferably 10 to 90 mol%, even more preferably 20 to 80 mol%, and even more preferably 30 to 70 mol%, of the total structural units of polymer (A1). When the content of structural units derived from the (meth)acrylamide group-containing compound is above the lower limit, the generation of residual monomers during the synthesis of polymer (A1) tends to be further suppressed. Also, when the content of structural units derived from the (meth)acrylamide group-containing compound is below the upper limit, curl during electrode drying tends to be further suppressed.

[0038] [Structural units derived from ethylenically unsaturated monomers having sulfonic acid groups or salts thereof] Polymer (A1) may further contain structural units derived from ethylenically unsaturated monomers having sulfonic acid groups or salts thereof. Structural units derived from ethylenically unsaturated monomers having sulfonic acid groups or salts thereof are structural units formed by an addition reaction of the ethylenically unsaturated group possessed by the ethylenically unsaturated monomer having sulfonic acid groups or salts thereof. In this specification, "ethylenically unsaturated group" means a functional group containing an ethylenically unsaturated bond. The structural units derived from ethylenically unsaturated monomers having sulfonic acid groups or salts thereof may be one type alone or two or more types.

[0039] Ethylene-unsaturated monomers having a sulfonic acid group or a salt thereof have a sulfonic acid group or a salt thereof and an ethylenically unsaturated group. Examples of ethylenically unsaturated groups in ethylenically unsaturated monomers having a sulfonic acid group or a salt thereof include a vinyl group, an allyl group, and a (meth)acryloyl group. Among these, the (meth)acryloyl group is preferred. That is, ethylenically unsaturated monomers having a sulfonic acid group or a salt thereof are preferably compounds having a sulfonic acid group or a salt thereof and a (meth)acryloyl group.

[0040] A salt of a sulfonic acid group is a salt of a sulfonic acid group (-S (=O) ２This refers to a structure in which an OH group forms a salt, for example, the sodium salt of a sulfonic acid group (-S (=O) ２ ONa), lithium salt of sulfonic acid group (-S (=O) ２ OLi), potassium salt of sulfonic acid group (-S (=O) ２ OK), ammonium salt of sulfonic acid group (-S (=O) ２ ONH ４ Examples include:

[0041] Compounds having a sulfonic acid group or a salt thereof and a (meth)acryloyl group include (meth)acrylamides having a sulfonic acid group or a salt thereof, and specifically, 2-acrylamido-2-methyl-1-propanesulfonic acid or its sodium salt is preferred.

[0042] The content of structural units derived from ethylenically unsaturated monomers having sulfonic acid groups or salts thereof in polymer (A1) is preferably 1 to 30 mol%, more preferably 2 to 20 mol%, even more preferably 3 to 10 mol%, and even more preferably 4 to 6 mol%, of the total structural units of polymer (A1). When the content of structural units derived from ethylenically unsaturated monomers having sulfonic acid groups or salts thereof is above the lower limit, the dispersibility of the active material is improved, and the generation of residual monomers during the synthesis of polymer (A1) can be suppressed. When the content of structural units derived from ethylenically unsaturated monomers having sulfonic acid groups or salts thereof is below the upper limit, the water absorption rate of the water-soluble polymer (A) can be suppressed.

[0043] [Structural units derived from vinyl cyanide compounds] Polymer (A1) may further contain structural units derived from vinyl cyanide compounds. Structural units derived from vinyl cyanide compounds are structural units formed by the addition reaction of vinyl groups of vinyl cyanide compounds. Examples of vinyl cyanide compounds include acrylonitrile and methacrylonitrile. The content of structural units derived from vinyl cyanide compounds in polymer (A1) is preferably 1 to 40 mol%, more preferably 5 to 30 mol%, even more preferably 10 to 25 mol%, and even more preferably 15 to 20 mol%, of the total structural units of polymer (A1).

[0044] [Other Structural Units] Polymer (A1) may or may not contain structural units derived from other monomers other than vinyl ethers, (meth)acrylamide group-containing compounds, ethylenically unsaturated monomers having a sulfonic acid group or a salt thereof, and vinyl cyanide compounds (hereinafter also referred to as "other structural units"). Examples of the above other monomers include α-olefin compounds such as ethylene, propylene, n-butene, and isobutylene; (meth)acrylic acid ester compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate; unsaturated carboxylic acid compounds such as (meth)acrylic acid and sodium (meth)acrylate or salts thereof; and so on. The other structural units contained in polymer (A1) may be one type alone or two or more types. If polymer (A1) contains other structural units, the content of other structural units in polymer (A1) is preferably 60 mol% or less, more preferably 40 mol% or less, and even more preferably 20 mol% or less, of the total structural units of polymer (A1).

[0045] [Method for producing polymer (A1)] Polymer (A1) can be produced by polymerizing raw material monomers containing vinyl ether and, if necessary, a (meth)acrylamide group-containing compound, an ethylenically unsaturated monomer having a sulfonic acid group or a salt thereof, a vinyl cyanide compound, or other monomers in a solvent. The polymerization method is not particularly limited and may be any method such as solution polymerization or bulk polymerization, but from the viewpoint of productivity, solution polymerization is preferred, and solution polymerization using water as the solvent is more preferred.

[0046] When carrying out a polymerization reaction, it is preferable to use a polymerization initiator. Examples of polymerization initiators include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 2,2'-azobis(2-hydroxymethylpropionitrile); organic peroxides such as lauryl peroxide, tert-butyl hydroperoxide, benzoyl peroxide, tert-butyl peroxybenzoate, and (3,5,5-trimethylhexanoyl) peroxide; and inorganic peroxides such as potassium persulfate, ammonium persulfate, and hydrogen peroxide. Among these, azo compounds are preferred, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride is more preferred. A single polymerization initiator may be used, or two or more may be used in combination.

[0047] The amount of polymerization initiator used is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, relative to the total amount of monomer (100 parts by mass).

[0048] The polymerization reaction is preferably carried out while heating. The reaction temperature is, for example, 50 to 95°C, and the reaction time is, for example, 2 to 8 hours. The monomers may be added all at once or sequentially. The polymerization reaction is preferably carried out under an inert atmosphere such as nitrogen, with stirring.

[0049] (Polymer (A2) containing structural units derived from (meth)acrylic acid) A polymer containing structural units derived from (meth)acrylic acid (hereinafter also referred to as "polymer (A2)") is not particularly limited as long as it is a polymer containing structural units derived from (meth)acrylic acid, and may be a polymer containing only structural units derived from (meth)acrylic acid, or a polymer containing structural units derived from (meth)acrylic acid and structural units derived from monomers other than (meth)acrylic acid.

[0050] The structural units derived from (meth)acrylic acid contained in polymer (A2) are preferably structural units formed by the addition polymerization of acrylic acid or methacrylic acid, and have a structure in which a carboxyl group derived from acrylic acid or methacrylic acid forms a salt. Examples of carboxyl group salts include sodium salt of the carboxyl group (-C(=O)ONa), lithium salt of the carboxyl group (-C(=O)OLi), potassium salt of the carboxyl group (-C(=O)OK), and ammonium salt of the carboxyl group (-C(=O)ONH). ４ Examples include the following. Among these, sodium salts of carboxyl groups are preferred. The content of structural units derived from (meth)acrylic acid in polymer (A2) is preferably 5 to 80 mol%, more preferably 10 to 60 mol%, and even more preferably 20 to 40 mol%, of the total structural units of polymer (A2).

[0051] The polymer (A2) preferably further contains structural units derived from (meth)acrylic acid esters. Examples of (meth)acrylic acid esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, and hydroxyethyl (meth)acrylate. Among these, hydroxyethyl (meth)acrylate is preferred. When polymer (A2) contains structural units derived from (meth)acrylic acid esters, the content is preferably 5 to 80 mol%, more preferably 10 to 60 mol%, and even more preferably 20 to 40 mol%, of the total structural units of polymer (A2).

[0052] The polymer (A2) preferably further contains structural units derived from a (meth)acrylamide group-containing compound. The description of the structural units derived from the (meth)acrylamide group-containing compound is the same as the description for polymer (A1), and the preferred embodiments are also the same. When polymer (A2) contains structural units derived from a (meth)acrylamide group-containing compound, the content thereof is preferably 5 to 80 mol%, more preferably 10 to 60 mol%, and even more preferably 20 to 40 mol%, of the total structural units of polymer (A2).

[0053] The total content of structural units derived from (meth)acrylic acid, structural units derived from (meth)acrylic acid esters, and structural units derived from (meth)acrylamide group-containing compounds in polymer (A2) is preferably 60 to 100 mol%, more preferably 80 to 100 mol%, and even more preferably 90 to 100 mol% of the total structural units of polymer (A2).

[0054] (Carboxymethylcellulose or its derivatives (A3)) Carboxymethylcellulose is a compound having a structure in which some or all of the hydroxyl groups in the glucose residues constituting cellulose are replaced with carboxymethyl ether groups. Examples of carboxymethylcellulose or its derivatives (A3) (hereinafter also referred to as "polymer (A3)") include carboxymethylcellulose, carboxymethylcellulose sodium salt, carboxymethylcellulose ammonium salt, and the like.

[0055] Polymer (A3) may be used in combination with styrene-butadiene rubber (hereinafter also referred to as "SBR"). When polymer (A3) and SBR are used in combination, the content ratio [polymer (A3) / SBR] is preferably 0.2 to 3.0, more preferably 0.4 to 2.0, and even more preferably 0.6 to 1.0 by mass. Note that styrene-butadiene rubber is not included in the concept of water-soluble polymer (A) in this embodiment.

[0056] (Polymer (A4) containing structural units derived from alkylene oxide) Polymer (A4) containing structural units derived from alkylene oxide (hereinafter also referred to as "polymer (A4)") is not particularly limited as long as it is a polymer containing structural units derived from alkylene oxide, and may be a polymer containing only structural units derived from alkylene oxide, or a polymer containing structural units derived from alkylene oxide and structural units derived from monomers other than alkylene oxide. Examples of alkylene oxides include ethylene oxide and propylene oxide. Among these, ethylene oxide is preferred. The content of structural units derived from ethylene oxide in polymer (A4) is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, and even more preferably 90 to 100 mol%, of the total structural units of polymer (A4).

[0057] (Polymer (A5) containing structural units derived from vinyl alcohol) Polymer (A5) containing structural units derived from vinyl alcohol (hereinafter also referred to as "polymer (A5)") is not particularly limited as long as it is a polymer containing structural units derived from vinyl alcohol, and may be a polymer containing only structural units derived from vinyl alcohol, or a polymer containing structural units derived from vinyl alcohol and structural units derived from monomers other than vinyl alcohol. The content of structural units derived from vinyl alcohol in polymer (A5) is preferably 50 to 100 mol%, more preferably 70 to 100 mol%, and even more preferably 90 to 100 mol%, of the total structural units of polymer (A5).

[0058] (Content of water-soluble polymer (A)) From the viewpoint of handling the binder aqueous solution of this embodiment, the content of water-soluble polymer (A) is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, even more preferably 4 to 20% by mass, and even more preferably 5 to 15% by mass.

[0059] <Carbon Nanotube (B)> The binder aqueous solution of this embodiment contains carbon nanotube (B). One type of carbon nanotube (B) may be used alone, or two or more types may be used in combination.

[0060] The carbon nanotube (B) may be a single-walled carbon nanotube (SWCNT) having a structure in which one layer of graphite forms a cylinder, or a multi-walled carbon nanotube (MWCNT) having a structure in which two or more layers of graphite each form a cylinder, and these cylinders are stacked.

[0061] The average length of carbon nanotubes (B) is preferably 1 to 20 μm, more preferably 2 to 10 μm, and even more preferably 3 to 5 μm, from the viewpoint of easily forming good conductive paths. The average diameter of carbon nanotubes (B) is preferably 1 to 20 nm, more preferably 5 to 15 nm, and even more preferably 8 to 11 nm, from the viewpoint of easily forming good conductive paths. The average length and average diameter of carbon nanotubes (B) can be determined by measuring the short axis length and long axis length of any 10 carbon nanotubes (B) in an image taken of the carbon nanotubes (B) using a transmission electron microscope, and taking the arithmetic mean of the short axis lengths as the average diameter and the arithmetic mean of the long axis lengths as the average length.

[0062] Carbon nanotubes (B) can be manufactured by methods such as arc discharge, chemical vapor deposition (CVD), and laser ablation. Commercially available carbon nanotubes (B) may also be used.

[0063] (Carbon nanotube (B) content) The carbon nanotube (B) content in the binder aqueous solution of this embodiment is preferably 0.01 to 1.0% by mass, more preferably 0.05 to 0.80% by mass, even more preferably 0.10 to 0.50% by mass, and even more preferably 0.15 to 0.30% by mass, from the viewpoint of obtaining good dispersibility of carbon nanotube (B) and ease of handling of the binder aqueous solution.

[0064] <Compound (C)> The binder aqueous solution of this embodiment contains compound (C) represented by the following general formula (1). Compound (C) may be used alone or in combination of two or more types.

[0065] (In the formula, X represents a hydrocarbon group having a carboxyl group or a salt thereof, or a hydrocarbon group having a sulfonic acid group or a salt thereof. R １ ~R １０ Each of these independently represents a hydrogen atom or a substituent. In the formula, the number of hydroxyl groups in the structure excluding X is between 0 and 2.

[0066] In the general formula (1) above, the number of carbon atoms in the hydrocarbon group having a carboxyl group or a salt thereof represented by X is preferably 1 to 15, more preferably 2 to 10, and even more preferably 4 to 8. Examples of hydrocarbon groups having a carboxyl group or a salt thereof include aliphatic hydrocarbon groups having a carboxyl group or a salt thereof, and aromatic hydrocarbon groups having a carboxyl group or a salt thereof. Among these, aliphatic hydrocarbon groups having a carboxyl group or a salt thereof are preferred. The aliphatic hydrocarbon group may be linear or branched. The aliphatic hydrocarbon group having a carboxyl group or a salt thereof is preferably an alkyl group having a carboxyl group or a salt thereof.

[0067] From the viewpoint of improving the dispersibility of carbon nanotubes (B), hydrocarbon groups having a carboxyl group or a salt thereof are preferably hydrocarbon groups having a salt of a carboxyl group. Examples of carboxyl group salts include sodium salt of carboxyl group (-C(=O)ONa), lithium salt of carboxyl group (-C(=O)OLi), potassium salt of carboxyl group (-C(=O)OK), and ammonium salt of carboxyl group (-C(=O)ONH). ４ Examples include the following, and among these, from the viewpoint of improving the dispersibility of carbon nanotubes (B), sodium salts or lithium salts of the carboxyl group are preferred, and sodium salts of the carboxyl group are more preferred.

[0068] In the general formula (1) above, the number of carbon atoms in the hydrocarbon group having a sulfonic acid group or a salt thereof represented by X is preferably 1 to 15, more preferably 2 to 10, and even more preferably 4 to 8. Examples of hydrocarbon groups having a sulfonic acid group or a salt thereof include aliphatic hydrocarbon groups having a sulfonic acid group or a salt thereof, and aromatic hydrocarbon groups having a sulfonic acid group or a salt thereof. Among these, aliphatic hydrocarbon groups having a sulfonic acid group or a salt thereof are preferred. The aliphatic hydrocarbon group may be linear or branched. As an aliphatic hydrocarbon group having a sulfonic acid group or a salt thereof, an alkyl group having a sulfonic acid group or a salt thereof is preferred.

[0069] From the viewpoint of improving the dispersibility of carbon nanotubes (B), hydrocarbon groups having a sulfonic acid group or a salt thereof are preferably hydrocarbon groups having a salt of a sulfonic acid group. Examples of salts of sulfonic acid groups include sodium salts of sulfonic acid groups (-S(=O)). ２ ONa), lithium salt of sulfonic acid group (-S (=O) ２ OLi), potassium salt of sulfonic acid group (-S (=O) ２ OK), ammonium salt of sulfonic acid group (-S (=O) ２ ONH ４Examples include the following, and among these, from the viewpoint of improving the dispersibility of carbon nanotubes (B), sodium salts or lithium salts of sulfonic acid groups are preferred, and sodium salts of sulfonic acid groups are more preferred.

[0070] Among the above options, X is preferably a group represented by the following formula (1-1) or formula (1-2) from the viewpoint of improving the dispersibility of carbon nanotubes (B).

[0071] (In the formula, Y is a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof, and Z is a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof. * indicates a bonding site.)

[0072] In the above general formula (1-1), Y is a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof, but it is preferably a carboxyl group or a salt thereof, and more preferably a salt of a carboxyl group. In the above general formula (1-2), Z is a carboxyl group or a salt thereof, or a sulfonic acid group or a salt thereof, but it is preferably a sulfonic acid group or a salt thereof, and more preferably a salt of a sulfonic acid group.

[0073] In the above general formula (1), R １ ~R １０ Each of these independently represents a hydrogen atom or a substituent. １ ~R １０ Examples of substituents represented by include alkyl groups having 1 to 20 carbon atoms, alkenyl groups having 2 to 20 carbon atoms, alkynyl groups having 2 to 20 carbon atoms, aromatic hydrocarbon groups having 6 to 20 carbon atoms, hydroxyl groups, halogen atoms, cyano groups, nitro groups, carboxyl groups, amino groups, alkoxy groups having 1 to 20 carbon atoms, and aryloxy groups having 6 to 20 carbon atoms. Among the above options, R １ ~R １０ R is preferably a methyl group, a hydrogen atom, or a hydroxyl group, and more preferably a hydrogen atom or a hydroxyl group. However, as stated above, in the general formula (1) above, the number of hydroxyl groups included in the structure other than X is 0 to 2, so R １ ~R １０In a configuration where is a hydrogen atom or a hydroxyl group, R １ ~R １０ A configuration in which all are hydrogen atoms, R １ ~R １０ One of them is a hydroxyl group and the remaining nine are hydrogen atoms, or R １ ~R １０ In one of these configurations, two of the atoms are hydroxyl groups and the remaining eight are hydrogen atoms.

[0074] From the viewpoint of improving the dispersibility of carbon nanotubes (B), compound (C) is preferably a compound represented by the following general formula (2).

[0075] (In the formula, X, R １ , R ３ , R ４ and R ７ The explanation is the same as the explanation for general formula (1) above. In the formula, the number of hydroxyl groups in the structure excluding X is 0 to 2.

[0076] In the above general formula (2), X, R １ , R ３ , R ４ and R ７ A preferred embodiment is as described above for general formula (1). Examples of compounds represented by general formula (2) include R １ and R ３ is a hydroxyl group, R ４ and R ７ Compounds in which the atom is a hydrogen atom, R １ and R ７ is a hydroxyl group, R ３ and R ４ Compounds in which the atom is a hydrogen atom, R １ and R ４ is a hydroxyl group, R ３ and R ７ Examples include compounds in which the atom is a hydrogen atom. Among these, R １ and R ７ is a hydroxyl group, R ３ and R ４ Compounds in which the atom is a hydrogen atom are preferred.

[0077] Specific examples of compound (C) include deoxycholic acid (compound represented by formula (1-a1) below), sodium deoxycholate (compound represented by formula (1-a2) below), taurodeoxycholic acid (compound represented by formula (1-b1) below), sodium taurodeoxycholate (compound represented by formula (1-b2) below), hyodeoxycholic acid (compound represented by formula (1-c1) below), sodium hyodeoxycholate (compound represented by formula (1-c2) below), ursodeoxycholic acid (compound represented by formula (1-d1) below), sodium ursodeoxycholate (compound represented by formula (1-d2) below), glycohyodeoxycholic acid (compound represented by formula (1-e1) below), sodium glycohyodeoxycholate (compound represented by formula (1-e2) below), and the like.

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] Among the above, sodium deoxycholate and sodium taurodeoxycholate are preferred as compound (C) from the viewpoint of improving the dispersibility of carbon nanotubes (B).

[0084] (Content of compound (C)) The content of compound (C) in the binder aqueous solution of this embodiment is preferably 0.01 to 5.00% by mass, more preferably 0.05 to 3.00% by mass, even more preferably 0.10 to 2.00% by mass, and even more preferably 0.15 to 1.00% by mass, from the viewpoint of improving the dispersibility of carbon nanotubes (B) and the handling of the binder aqueous solution.

[0085] In the binder aqueous solution of this embodiment, the ratio of the mass-based content of compound (C) to the mass-based content of carbon nanotubes (B) [(C) / (B)] is preferably 0.1 to 20, more preferably 0.3 to 15, even more preferably 0.6 to 10, and even more preferably 0.8 to 6.0, from the viewpoint of improving the dispersibility of carbon nanotubes (B) and the handling of the binder aqueous solution.

[0086] <Other Aqueous Solution Components> The binder aqueous solution of this embodiment may or may not contain components other than water, water-soluble polymer (A), carbon nanotube (B), and compound (C) as needed (hereinafter also referred to as "other aqueous solution components"). Examples of other aqueous solution components include solvents other than water, polymers other than water-soluble polymer (A), conductive additives other than carbon nanotube (B), dispersants other than compound (C), thickeners, wetting agents, pH adjusters, stabilizers, surfactants, antioxidants, preservatives, etc. Each of these may be used individually or in combination of two or more. The total content of water, water-soluble polymer (A), carbon nanotube (B), and compound (C) in the binder aqueous solution of this embodiment is preferably 60 to 100% by mass, more preferably 80 to 100% by mass, even more preferably 90 to 100% by mass, and even more preferably 95 to 100% by mass.

[0087] <Method for Producing Binder Aqueous Solution> The method for producing the binder aqueous solution in this embodiment is not particularly limited, and water, a water-soluble polymer (A), carbon nanotubes (B), a compound (C), and other aqueous solution components used as needed may be mixed by known methods. As a mixing device, for example, an ultrasonic disperser, ball mill, sand mill, planetary mixer, paint shaker, homomixer, homodisper, homogenizer, and the like can be used.

[0088] [Electrode Slurry for Lithium-Ion Battery] The electrode slurry for a lithium-ion battery of this embodiment (hereinafter, also simply referred to as "the electrode slurry of this embodiment") is an electrode slurry for a lithium-ion battery containing an aqueous binder solution and an active material for a lithium-ion battery of this embodiment. After being applied on a current collector and dried, the electrode slurry of this embodiment is used to form an active material layer containing an active material and the binder of this embodiment on the current collector. The electrode formed using the electrode slurry of this embodiment may be a positive electrode or a negative electrode. The active material may be used alone or in combination of two or more kinds.

[0089] Examples of the active material for a positive electrode include lithium cobalt composite oxides such as LiCoO ２ ; lithium manganese composite oxides such as LiMnO ２ O ４ , LiMnO ２ ; lithium nickel composite oxides such as LiNiO ２ ; lithium transition metal composite phosphate compounds such as LiFePO ４ , LiMnPO ４ ; LiNi １／３ Co １／３ Mn １／３ O ２ , LiNi ０．５ Co ０．３ Mn ０．２ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , LiNi ０．８ Co ０．１ Mn ０．１ O ２ and the like, LiNi ｘ Co ｙ Mn ｚ O ２ (0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1) represented by nickel-cobalt-manganese ternary cathode material (NCM); LiNi ０．８ Co ０．１５ Al ０．０５O ２ LiNi etc. ｘ Co ｙ Al ｚ O ２ Examples include nickel-cobalt-aluminum ternary cathode materials (NCAs) represented by (0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1).

[0090] Examples of active materials for the negative electrode include graphite, hard carbon, silicon, SiO, lithium-doped SiO, and lithium titanate.

[0091] The shape of the active material is not particularly limited and may be, for example, in the form of fragments, spheres, flattened surfaces, fibers, etc.

[0092] The active material content in the total amount (100% by mass) of the electrode slurry of this embodiment is preferably 20 to 90% by mass, more preferably 30 to 80% by mass, and even more preferably 45 to 60% by mass. When the active material content in the electrode slurry is within the above range, better coating properties tend to be obtained.

[0093] In the electrode slurry of this embodiment, the content of water-soluble polymer (A) per 100 parts by mass of active material is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and even more preferably 1 to 5 parts by mass. When the content of water-soluble polymer (A) in the electrode slurry is above the lower limit, the strength of the active material layer can be further improved. Also, when the content of water-soluble polymer (A) in the electrode slurry is below the upper limit, the increase in electrode resistance tends to be suppressed.

[0094] In the electrode slurry of this embodiment, the content of carbon nanotubes (B) per 100 parts by mass of active material is preferably 0.001 to 0.1 parts by mass, more preferably 0.005 to 0.05 parts by mass, and even more preferably 0.01 to 0.03 parts by mass. When the content of carbon nanotubes (B) is above the lower limit, the conductivity of the electrode can be further improved. Also, when the content of carbon nanotubes (B) is below the upper limit, it tends to be easier to increase the proportion of active material.

[0095] The solid content concentration of the electrode slurry in this embodiment is preferably 20 to 90% by mass, more preferably 25 to 85% by mass, and even more preferably 40 to 60% by mass, from the viewpoint of coating properties. In this specification, the solid content of the electrode slurry refers to components other than the liquid medium.

[0096] The electrode slurry of this embodiment may or may not contain components other than the binder aqueous solution and active material of this embodiment (hereinafter also referred to as "other slurry components"). Examples of other slurry components are the same as those listed above as other aqueous solution components.

[0097] The method for producing the electrode slurry of this embodiment is not particularly limited, and for example, it can be produced by mixing the binder aqueous solution, active material, and other slurry components used as needed by known methods. The mixing apparatus can be the same as the mixing apparatus used in the method for producing the binder aqueous solution described above.

[0098] [Electrode for Lithium-ion Battery and Method for Manufacturing the Same] The electrode for lithium-ion battery of this embodiment (hereinafter also simply referred to as "the electrode of this embodiment") is an electrode for lithium-ion battery that contains a water-soluble polymer (A), a carbon nanotube (B), a compound (C) represented by the following general formula (1), and an active material.

[0099] (In the formula, X represents a hydrocarbon group having a carboxyl group or a salt thereof, or a hydrocarbon group having a sulfonic acid group or a salt thereof. R １ ~R １０ Each of these independently represents a hydrogen atom or a substituent. In the formula, the number of hydroxyl groups in the structure excluding X is between 0 and 2.

[0100] The electrode in this embodiment may be a positive electrode or a negative electrode. Preferably, the electrode in this embodiment has an active material layer on a current collector containing an active material, a water-soluble polymer (A), carbon nanotubes (B), and a compound (C). In the electrode of this embodiment, the thickness of the active material layer is not particularly limited and may be, for example, 25 to 500 μm, 50 to 300 μm, or 80 to 200 μm.

[0101] The description of the water-soluble polymer (A), carbon nanotube (B), compound (C), and active material contained in the electrode of this embodiment is the same as the description of the binder aqueous solution and the electrode slurry of this embodiment. In the electrode of this embodiment, the content of the water-soluble polymer (A) and carbon nanotube (B) per 100 parts by mass of active material is the same as the preferred range described in the description of the electrode slurry of this embodiment. Furthermore, the electrode of this embodiment may contain the other aqueous solution components and other slurry components described above.

[0102] The current collector is preferably made of a sheet of metal. Examples of metals that can be used for the current collector include iron, copper, aluminum, nickel, and stainless steel. Among these, aluminum foil is preferred as the positive electrode current collector, and copper foil is preferred as the negative electrode current collector. The thickness of the current collector is, for example, 5 to 20 μm.

[0103] The electrodes of this embodiment can be manufactured using the binder aqueous solution of this embodiment. Specifically, the electrodes can be manufactured by manufacturing the electrode slurry of this embodiment using the binder aqueous solution of this embodiment by the method described above, applying the electrode slurry onto a current collector, and then drying it. Examples of methods for applying the electrode slurry of this embodiment onto a current collector include the reverse roll method, doctor blade method, direct roll method, knife method, extrusion method, curtain method, gravure method, bar method, dip method, squeeze method, etc.

[0104] The electrode slurry in this embodiment may be applied to only one side of the current collector or to both sides. When applying the electrode slurry to both sides of the current collector, it may be applied to one side at a time or to both sides simultaneously. Furthermore, the electrode slurry may be applied continuously to the entire surface of the current collector or intermittently. The amount and area of ​​application of the electrode slurry should be appropriately determined according to the size of the battery, etc.

[0105] Methods for drying the electrode slurry applied to the current collector include, for example, applying hot air, vacuum drying, and using electromagnetic waves such as infrared, far-infrared, and near-infrared heaters. The drying temperature of the electrode slurry is, for example, 80 to 150°C, and the drying time is, for example, 1 to 30 minutes.

[0106] The resulting electrodes may be shaped by cutting or other methods as needed.

[0107] [Lithium-ion battery and method for manufacturing the same] The lithium-ion battery of this embodiment is a lithium-ion battery that includes the electrodes for the lithium-ion battery of this embodiment. An example of the lithium-ion battery of this embodiment is a lithium-ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator. In the lithium-ion battery of this embodiment, at least one of the positive electrode and the negative electrode includes the electrodes of this embodiment, and to that extent, electrodes other than the electrodes of this embodiment may also be included. The electrodes other than the electrodes of this embodiment, the electrolyte, and the separator can be appropriately selected from known ones depending on the application. The shape of the lithium-ion battery of this embodiment is not particularly limited and may be any shape such as coin-type, button-type, sheet-type, cylindrical, rectangular, or flat.

[0108] The lithium-ion battery of this embodiment can be manufactured using the binder aqueous solution of this embodiment. Specifically, the electrode of this embodiment can be manufactured using the binder aqueous solution of this embodiment by the method described above, and the electrode can be used as at least one of the positive electrode and the negative electrode to manufacture a lithium-ion battery by a known method.

[0109] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0110] [Production of water-soluble polymer (A)] Production example 1 (Synthesis of PVE1) In a reaction apparatus equipped with a stirrer, thermometer, reflux condenser and nitrogen gas inlet tube, 944.40 g of purified water and 400.00 g of hydroxybutyl vinyl ether were added, and the temperature was raised to 55°C. Oxygen in the reaction system was removed by passing nitrogen gas through the apparatus. Then, a solution prepared by mixing 160.00 g of N,N-dimethylacrylamide, 160.00 g of 50% by mass aqueous solution of acrylamide, 160.00 g of 50% by mass aqueous solution of 2-acrylamide-2-methyl-1-propanesulfonate sodium salt, 80 g of acrylonitrile, 4.00 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 40.00 g of purified water was added, and the temperature was raised to 70°C and the reaction was carried out for 4 hours. Subsequently, 3.60 g of purified water was added to obtain an aqueous solution of PVE1, which is a water-soluble polymer (A), with a content of 40% by mass of water-soluble polymer (A).

[0111] Manufacturing Example 2 (Synthesis of PVE2) In a reaction apparatus equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 1968.00 g of purified water, 200.00 g of diethylene glycol monovinyl ether, and 398.40 g of a 50% by mass aqueous solution of acrylamide were added, and the temperature was raised to 55°C. Oxygen in the reaction system was removed by passing nitrogen gas through the apparatus. A solution of 2.40 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 24.00 g of purified water was added, and the temperature was raised to 80°C and the reaction was carried out for 4 hours. After that, 1176.36 g of purified water was added to obtain an aqueous solution of PVE2, which is a water-soluble polymer (A) (containing 13% by mass of water-soluble polymer (A)).

[0112] Manufacturing Example 3 (Synthesis of PVE3) In a reaction apparatus equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet, 677.04 g of purified water and 240.00 g of hydroxybutyl vinyl ether were added, and the temperature was raised to 55°C. Oxygen in the reaction system was removed by passing nitrogen gas through the apparatus. A solution of 160.00 g of N,N-dimethylacrylamide, 3.36 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and 33.60 g of purified water was added, and the temperature was raised to 80°C and the reaction was carried out for 4 hours. After that, 2.16 g of purified water was added to obtain an aqueous solution of PVE3, which is a water-soluble polymer (A) (containing 40% by mass of water-soluble polymer (A)).

[0113] Production Example 4 (Synthesis of PAA) In a reaction apparatus equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 2334.20 g of purified water, 147.35 g of hydroxyethyl acrylate, 219.10 g of 50% by mass aqueous acrylamide solution, 91.70 g of acrylic acid, and 1.40 g of sodium methallyl sulfonate were added, and the temperature was raised to 55°C. Oxygen in the reaction system was removed by passing nitrogen gas through the reaction apparatus. A solution of 2.81 g of 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 28.00 g of purified water was added, and the temperature was raised to 80°C and the reaction was carried out for 4 hours. After that, 133.23 g of 10% by mass aqueous sodium hydroxide solution was added to neutralize the mixture and obtain an aqueous solution of PAA, which is a water-soluble polymer (A) (containing 13% by mass of water-soluble polymer (A)).

[0114] [Manufacturing of Lithium-ion Battery Binder Aqueous Solution] The following raw materials were used in the manufacturing of the lithium-ion battery binder aqueous solution.

[0115] <Binder> ・PVE1: Water-soluble polymer produced in Production Example 1 (corresponding to Polymer (A1)) ・PVE2: Water-soluble polymer produced in Production Example 2 (corresponding to Polymer (A1)) ・PVE3: Water-soluble polymer produced in Production Example 3 (corresponding to Polymer (A1)) ・PAA: Water-soluble polymer produced in Production Example 4 (corresponding to Polymer (A2)) ・SBR / CMC2: SBR is styrene-butadiene rubber (manufactured by Nippon A&L Co., Ltd., product name "AL-2001"), and CMC2 is carboxymethylcellulose sodium salt (manufactured by Tokyo Chemical Industry Co., Ltd., product name "Carboxymethyl Cellulose Sodium Salt (n=approx. 500)") (corresponding to Polymer (A3)). The content ratio of CMC2 to SBR [CMC2 / SBR] is 0.75 by mass. Note that the amounts listed in Table 1 represent the total amounts of SBR and CMC2. • PEO: Polyethylene oxide (manufactured by Aldrich, trade name "Poly (ethylene glycol)") (corresponds to polymer (A4))

[0116] <CNT> Single-walled carbon nanotubes (SWCNTs): Manufactured by OCSiAl, product name: TUBALL 01RW03), average diameter 10 nm, average length 4 μm

[0117] <Dispersant> (corresponding to compound (C)) ・Sodium deoxycholate: A compound represented by the following formula (1-a2)

[0118] • Sodium taurodeoxycholate: A compound represented by the following formula (1-b2)

[0119] (Compounds that do not fall under compound (C)) ・CMC1: Carboxymethylcellulose sodium salt (manufactured by Tokyo Chemical Industry Co., Ltd., trade name "Carboxymethyl Cellulose Sodium Salt (n=approx. 500)") ・CMC2: Carboxymethylcellulose sodium salt (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name "BSH-6") ・Sodium cholate: Compound represented by the following formula (1')

[0120] Examples 1-9, Comparative Examples 3-8: In a plastic container (capacity: 200 mL), CNTs, a dispersant, and water were added in the amounts shown in Table 1. Using an ultrasonic disperser manufactured by Sonic Technology Co., Ltd., the mixture was ultrasonically treated at a frequency of 19.5 ± 0.5 kHz for 3 to 20 minutes to prepare a CNT dispersion before binder mixing. Next, the binders of the type and amount shown in Table 1 were added to the CNT dispersion before binder mixing to the amount shown in Table 1. The mixture was stirred with a disperser for 30 minutes to obtain an aqueous binder solution for lithium-ion batteries. Note that the binder amounts shown in Table 1 are for solid content. When the binder is added in aqueous solution form, the amounts of water and binder aqueous solution were adjusted so that the water content and the amount of solid binder were as shown in Table 1.

[0121] Comparative Examples 1 and 2: Except for not using a dispersant, aqueous binder solutions for lithium-ion batteries were obtained using the same procedure as in Examples 1 to 9, with the compositions shown in Table 1.

[0122] [Evaluation] The lithium-ion battery binder aqueous solution obtained above was evaluated as follows. The results are shown in Table 1.

[0123] (Method for Evaluating the Dispersibility of CNTs) In each example, the appearance of the CNT dispersion before binder mixing (indicated as "Before Binder Mixing" in Table 1) and the appearance of the lithium-ion battery binder aqueous solution obtained by mixing the binder with the CNT dispersion (indicated as "After Binder Mixing" in Table 1) were observed visually and under 200x magnification using an optical microscope (manufactured by Keyence Corporation, product name "VHX-S500"), and the CNT dispersibility was evaluated based on the following criteria. Note that in Comparative Examples 1 and 2, aggregation of CNTs was confirmed by visual observation before binder mixing, so evaluation after binder mixing was not performed. <Evaluation Criteria> A: No aggregates are visible to the naked eye, and no aggregates are visible under an optical microscope, or only very few are present. B: No aggregates are visible to the naked eye, and only a small amount of aggregates are visible under an optical microscope. C: There are aggregates visible to the naked eye, but fewer than in D. D: There are a very large number of aggregates visible to the naked eye.

[0124] (Method for measuring electrode resistance) (1) Electrode preparation Add the binder of the type listed in Table 1, purified water, and the CNT dispersion prepared in each example to a glass container (capacity: 140 mL), and stir at 2,000 rpm for 10 minutes using a disperser (Primix Corporation, product name "Labo-Solution", stirring section: Homodisper 2.5 type). Then add 35.00 g of graphite (Shanghai Shanshan New Materials Co., Ltd., product name "FSN-1") as the active material, and stir at 2,000 rpm using a rotation-orbit stirrer (Thinky Corporation, model number "AR-100") By stirring and defoaming for 10 minutes, a lithium-ion battery electrode slurry was obtained with a solid content of 50% by mass, a binder content of 2.5 parts by mass (Examples 1-7, 9, Comparative Examples 1-2, 4-8) or 3.5 parts by mass (Example 8 and Comparative Example 3) per 100 parts by mass of active material, and a CNT content of 0.02 parts by mass per 100 parts by mass of active material. In Comparative Examples 1 and 2, it was not possible to prepare a lithium-ion battery electrode slurry due to the aggregation of CNTs, so the subsequent operations were not performed. The prepared lithium-ion battery electrode slurry was applied onto copper foil (manufactured by UACJ Corporation, 10 μm thick) using an applicator with a 140 μm gap, and then dried in an oven at 120°C for 10 minutes to obtain a lithium-ion battery electrode having a 100 μm thick active material layer on the current collector (copper foil). The obtained lithium-ion battery electrode was punched out into a disc shape with a diameter of 16 mm and used as the negative electrode.

[0125] (2) Fabrication of a Negative Electrode Half Cell The negative electrode, separator, and counter electrode (lithium metal foil) obtained above were placed in a coin-type battery container in that order, and an electrolyte was injected to fabricate a coin-type negative electrode half cell. As the electrolyte, a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (the volume ratio of EC to DMC was 1:1) was used, in which LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) was dissolved to a concentration of 1 mol / L. As the counter electrode (lithium metal foil), metallic lithium punched into a disc shape with a diameter of 16 mm was used. As the separator, a polyolefin microporous membrane with a thickness of 7 μm was used.

[0126] (3) DCR Measurement The negative electrode half cell obtained above was subjected to constant current discharge at a discharge rate of 0.1C in an environment of 25°C until the voltage reached 0.1V. Then, constant current charging was performed at 25°C with a current of 0.1C to bring the SOC to 50%, and then discharged at 25°C with a current of 0.2C for 30 seconds. After that, constant current charging was performed at 0.2C for 30 seconds, followed by a 10-minute rest period. Next, it was discharged at 0.5C for 30 seconds, then charged at 0.2C for 75 seconds, followed by a 10-minute rest period. Finally, it was discharged at 1.0C for 30 seconds. The relationship between the current at each discharge current and the voltage at 10 seconds after the start of discharge was plotted, and the internal resistance was determined from the slope of the straight line obtained from the three plots.

[0127]

[0128] Table 1 shows that the binder aqueous solution of this embodiment exhibits excellent dispersibility of carbon nanotubes.

Claims

1. An aqueous binder solution for a lithium-ion battery, containing a water-soluble polymer (A), a carbon nanotube (B), and a compound (C) represented by the following general formula (1). (In the formula, X represents a hydrocarbon group having a carboxy group or its salt, or a hydrocarbon group having a sulfonic acid group or its salt. R １ ~R １０ each independently represents a hydrogen atom or a substituent. The number of hydroxy groups contained in the structure excluding X in the formula is 0 to 2.) 2. The aqueous binder solution for lithium-ion batteries according to claim 1, wherein the compound (C) is represented by the following general formula (2). (In the formula, X, R １ , R ３ , R ４ and R ７ The explanation is the same as the explanation for general formula (1) above. In the formula, the number of hydroxyl groups in the structure excluding X is 0 to 2.

3. The aqueous binder solution for lithium-ion batteries according to claim 1 or 2, wherein X is a hydrocarbon group having a salt of a carboxyl group or a hydrocarbon group having a salt of a sulfonic acid group.

4. The aqueous binder solution for lithium-ion batteries according to claim 3, wherein the salt of the carboxyl group is a sodium salt or lithium salt of the carboxyl group, and the salt of the sulfonic acid group is a sodium salt or lithium salt of the sulfonic acid group.

5. The aqueous binder aqueous solution for lithium-ion batteries according to claim 1 or 2, wherein the water-soluble polymer (A) is one or more selected from the group consisting of a polymer containing structural units derived from vinyl ether (A1), a polymer containing structural units derived from acrylic acid (A2), carboxymethylcellulose or a derivative thereof (A3), a polymer containing structural units derived from alkylene oxide (A4), and a polymer containing structural units derived from vinyl alcohol (A5).

6. The aqueous binder solution for lithium-ion batteries according to claim 1 or 2, wherein the ratio of the mass-based content of compound (C) to the mass-based content of carbon nanotubes (B) [(C) / (B)] is 0.1 to 20.

7. The aqueous binder solution for lithium-ion batteries according to claim 1 or 2, wherein the content of the water-soluble polymer (A) is 1 to 50% by mass.

8. The aqueous binder solution for lithium-ion batteries according to claim 1 or 2, wherein the carbon nanotube (B) content is 0.01 to 1.0% by mass.

9. An electrode slurry for a lithium-ion battery containing the lithium-ion battery binder aqueous solution and active material according to claim 1 or 2.

10. A method for manufacturing an electrode for a lithium-ion battery, using an aqueous solution of the lithium-ion battery binder described in claim 1 or 2.

11. A method for manufacturing a lithium-ion battery, using an aqueous binder solution for lithium-ion batteries according to claim 1 or 2.

12. An electrode for a lithium-ion battery containing a water-soluble polymer (A), carbon nanotubes (B), a compound (C) represented by the following general formula (1), and an active material. (In the formula, X represents a hydrocarbon group having a carboxyl group or a salt thereof, or a hydrocarbon group having a sulfonic acid group or a salt thereof. R １ ~R １０ Each of these independently represents a hydrogen atom or a substituent. In the formula, the number of hydroxyl groups in the structure excluding X is between 0 and 2.

13. A lithium-ion battery comprising the lithium-ion battery electrode described in claim 12.

Images