JP7700780B2 - Electrode binders, electrode mixtures, electrodes for energy devices, and energy devices - Google Patents

Description

The present invention relates to an electrode binder, an electrode mixture, an electrode for an energy device, and an energy device.

Lithium-ion secondary batteries, which are non-aqueous electrolyte energy devices with high energy density, are widely used as power sources for portable information terminals such as notebook computers, mobile phones, and PDAs, as well as for electric vehicles.

Electrodes for lithium-ion secondary batteries are manufactured as follows. First, an active material, binder, and solvent are mixed together to prepare a slurry-like electrode mixture. This electrode mixture is applied to one or both sides of a metal foil current collector using a transfer roll or similar, and the solvent is then dried and removed to form a mixture layer. The mixture layer is then compression molded using a roll press or similar to produce the electrode.

The binder used here is required to have excellent properties such as adhesion between active materials and between the active materials and the current collector, as well as electrochemical stability. Furthermore, in order to increase the capacity of lithium-ion secondary batteries, it is required that these properties be satisfied with a smaller amount of additive. Furthermore, from the perspective of reducing the environmental load, it is considered preferable to use water as the solvent used in preparing the electrode mixture, and compatibility with aqueous solvents is also one of the requirements for the binder.

As a binder to be used with an aqueous solvent, Patent Document 1 discloses an aqueous dispersion of a copolymer containing structural units derived from (meth)acrylonitrile and structural units derived from a compound having two or more ethylenically unsaturated bonds. However, since the resin component is not dissolved and is particulate, the contact area with the active material is small, and there is a risk of a decrease in battery capacity due to side reactions occurring on the surface of the active material.

As an example of a binder in which a resin component is dissolved in an aqueous solvent, Patent Document 2 discloses a binder that contains a copolymer having structural units containing nitrile groups and structural units containing acidic functional groups, in which at least a portion of the acidic functional groups form a salt.

International Publication No. 2014/098233 JP 2019-160691 A

The binder described in Patent Document 2 is expected to have an effect of suppressing side reactions occurring on the surface of the active material because the binder has a dissolved resin component and can increase the contact area with the active material. On the other hand, the electrode mixture prepared using this binder has room for improvement in terms of dispersion stability.
When the electrode mixture has good dispersion stability, separation of the components in the coater or liquid delivery pipe can be suppressed, making it easier to obtain a uniform electrode. In addition, the accumulation of solids in the coater or liquid delivery pipe, which causes equipment failure, can be suppressed.

In view of the above circumstances, an object of the present invention is to provide an electrode binder that has excellent dispersion stability when an electrode mixture is prepared. Another object of the present invention is to provide an electrode mixture, an electrode for an energy device, and an energy device obtained using this electrode binder.

Means for solving the above problems include the following embodiments.
<1> An electrode binder comprising: a copolymer containing a structural unit containing an acidic functional group and a structural unit containing an alkyleneoxy group, wherein a ratio of the structural unit containing the alkyleneoxy group is 5 mass% or more of all structural units; and a basic compound capable of forming a salt with the acidic functional group.
<2> The electrode binder according to <1>, wherein the proportion of the structural units containing an alkyleneoxy group is 50 mass % or less of all structural units.
<3> The electrode binder according to <1> or <2>, wherein the copolymer does not contain a structural unit containing a nitrile group, or the proportion of the structural unit containing a nitrile group in the total structural units is less than 50 mass %.
<4> The electrode binder according to any one of <1> to <3>, wherein the alkyleneoxy group contains 5 or more alkyleneoxy structures.
<5> The electrode binder according to any one of <1> to <4>, further comprising water, wherein the copolymer is dissolved in the water.
<6> The electrode binder according to any one of <1> to <5>, wherein the acidic functional group includes at least one selected from the group consisting of a carboxy group, a sulfo group, and a phospho group.
<7> The binder for electrodes according to any one of <1> to <6>, wherein the structural unit having an acidic functional group is derived from at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, crotonic acid, itaconic acid, citraconic acid, vinylbenzoic acid, and vinylbenzenesulfonic acid.
<8> The electrode binder according to any one of <1> to <7>, wherein the basic compound includes one compound selected from the group consisting of hydroxides of alkali metals and alkaline earth metals, carbonates of alkali metals and alkaline earth metals, ammonia, amines having 1 to 50 carbon atoms, pyridines having 5 to 20 carbon atoms, and azoles having 2 to 20 carbon atoms.
<9> The electrode binder according to any one of <1> to <8>, for forming an electrode containing a silicon-containing compound as an active material.
<10> An electrode mixture comprising the electrode binder according to any one of <1> to <9> and an active material.
<11> The electrode mixture according to <10>, wherein the active material contains a compound containing silicon.
<12> An electrode for an energy device, comprising: a current collector; and an electrode mixture layer provided on at least one surface of the current collector, the electrode mixture layer comprising the electrode mixture according to <10> or <11>.
<13> An energy device comprising a positive electrode and a negative electrode, at least one of the positive electrode and the negative electrode containing the electrode binder according to any one of <1> to <9> and an active material.

According to the present invention, an electrode binder is provided that has excellent dispersion stability when an electrode mixture is prepared. In addition, according to the present invention, an electrode mixture, an electrode for an energy device, and an energy device obtained using the electrode binder are provided.

1 is a cross-sectional view showing an example of the configuration of a lithium ion secondary battery, which is an example of an energy device.

Hereinafter, the embodiment for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiment. In the following embodiment, the components (including element steps, etc.) are not essential unless specifically stated. The same applies to the numerical values and their ranges, and they do not limit the present invention.
In this specification, the term "step" includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.
In the present specification, the numerical range indicated using "to" includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.
In this specification, the content of each component in a composition means, when multiple substances corresponding to each component are present in the composition, the total content of those multiple substances present in the composition, unless otherwise specified.
In this specification, when multiple types of particles corresponding to each component are present in a composition, the particle size of each component in the composition means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
In this specification, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.
As used herein, the term "lamination" refers to stacking layers, and two or more layers may be bonded together, or two or more layers may be detachable.
In this specification, "(meth)acrylic" means at least one of acrylic and methacrylic, "(meth)acrylate" means at least one of acrylate and methacrylate, and "(meth)allyl" means at least one of allyl and methallyl.

<Electrode binder>
The binder for electrodes (hereinafter also simply referred to as the binder) of the present disclosure is a binder comprising: a copolymer containing a structural unit containing an acidic functional group and a structural unit containing an alkyleneoxy group, in which the proportion of the structural unit containing an alkyleneoxy group is 5 mass% or more of all structural units; and a basic compound capable of forming a salt with the acidic functional group.
The acidic functional group of the copolymer contained in the binder and the basic compound preferably form a salt in the binder.

The copolymer contained in the binder of the present disclosure has excellent solubility in water because at least a portion of the acidic functional groups can form a salt by neutralization reaction with a basic compound. Therefore, electrodes can be manufactured without using an organic solvent to dissolve the copolymer, and are excellent in terms of safety and environmental compatibility. In addition, since the binder of the present disclosure has a higher viscosity than the copolymer dispersed in water, the addition of a thickener such as carboxymethyl cellulose can be omitted. Therefore, it is possible to avoid the deterioration of adhesion, storage stability, etc. caused by the thickener.

Furthermore, as a result of the inventors' investigations, it was found that when the copolymer contains structural units containing alkyleneoxy groups in a specific ratio, the dispersion stability of the electrode mixture prepared using the binder is improved.

(copolymer)
The copolymer is not particularly limited as long as it contains a structural unit containing an acidic functional group and a structural unit containing an alkyleneoxy group, and the proportion of the structural unit containing an alkyleneoxy group is 5 mass% or more of the total structural units.

From the viewpoint of dispersion stability of the electrode mixture, the ratio of the structural units containing an alkyleneoxy group is preferably 10% by mass or more, more preferably 15% by mass or more, of the total structural units. From the viewpoint of balance with other properties, the ratio of the structural units containing an alkyleneoxy group is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, of the total structural units.
The mass ratio of the structural unit containing an alkyleneoxy group is not particularly limited, but may be determined as follows:
For example, it can be measured by 1H-NMR.

The proportion of structural units containing an alkyleneoxy group in the copolymer can be adjusted, for example, by adjusting the molecular weight of the monomer containing an alkyleneoxy group used in the synthesis of the copolymer, the amount of the monomer, and the like.
When a monomer used in the synthesis of the copolymer has both an alkyleneoxy group and an acidic functional group, the above ratio is calculated by including the structural unit derived from this monomer in the "structural unit containing an alkyleneoxy group."

The number of alkyleneoxy structures contained in the alkyleneoxy group is preferably 5 or more, more preferably 9 or more. It may be difficult to synthesize the content of alkyleneoxy groups in the copolymer on a molar basis. Therefore, by increasing the number of alkyleneoxy structures contained in the alkyleneoxy group, the content of alkyleneoxy groups in the copolymer on a mass basis can be easily increased. From the viewpoint of handling and polymerizability, the number of alkyleneoxy structures contained in the alkyleneoxy group is preferably 50 or less, more preferably 30 or less, and even more preferably 20 or less.
Examples of the alkyleneoxy structure contained in the alkyleneoxy group include ethylene oxide, propylene oxide, and tetramethylene oxide, and among these, ethylene oxide is preferable.

From the viewpoint of improving solubility in water, the proportion of structural units containing acidic functional groups in the copolymer is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more of the total structural units. From the viewpoint of balance with other properties, the proportion of structural units containing acidic functional groups is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less of the total structural units.

The proportion of structural units containing an acidic functional group in the copolymer can be adjusted, for example, by adjusting the molecular weight of the monomer containing an acidic functional group used in the synthesis of the copolymer, the amount of the monomer, etc.
When a monomer used in the synthesis of the copolymer has both an alkyleneoxy group and an acidic functional group, the above ratio is calculated by including the structural unit derived from this monomer in the "structural unit containing an acidic functional group."

The total ratio of the structural units containing an acidic functional group and the structural units containing an alkyleneoxy group in the copolymer is not particularly limited. For example, it can be selected from the range of 70% by mass to 100% by mass of all structural units.

Some or all of the acidic functional groups in the copolymer may form salts with basic compounds. For example, 50 mol% or more of the acidic functional groups in the copolymer may form salts, 80 mol% or more of the acidic functional groups may form salts, or 90 mol% or more of the acidic functional groups may form salts. The proportion of the acidic functional groups that form salts can be adjusted by the amount of the basic compound reacted with the copolymer, etc.

From the viewpoint of suppressing swelling in the electrolyte, it is preferable that the proportion of structural units containing nitrile groups or structural units containing nitrile groups is less than 50 mass% of the total structural units, it is more preferable that the proportion of structural units containing nitrile groups or structural units containing nitrile groups is less than 30 mass% of the total structural units, and it is even more preferable that the proportion of structural units containing nitrile groups or structural units containing nitrile groups is less than 15 mass% of the total structural units.

The weight average molecular weight of the copolymer is preferably 50,000 to 3,000,000, and more preferably 100,000 to 1,500,000. If the weight average molecular weight of the copolymer is 50,000 or more, the stability of the film formed on the surface of the active material tends to be excellent, and if it is 3,000,000 or less, the handleability of the aqueous solution containing the copolymer tends to be excellent. The weight average molecular weight of the copolymer can be adjusted by the temperature during the polymerization reaction (the higher the temperature, the smaller the molecular weight tends to be), the type of polymerization initiator, the addition of a chain transfer agent, etc.

In the present disclosure, the weight average molecular weight of the copolymer is a value measured as follows.
The measurement object is dissolved in N-methyl-2-pyrrolidone, and insoluble matter is removed through a PTFE (polytetrafluoroethylene) filter [Kurashiki Boseki Co., Ltd., for HPLC (high performance liquid chromatography) pretreatment, chromatodisk, model number: 13N, pore size: 0.45 μm]. The weight average molecular weight is measured using GPC [pump: L6200 Pump (Hitachi, Ltd.), detector: differential refractive index detector L3300 RI Monitor (Hitachi, Ltd.), column: TSKgel-G5000HXL and TSKgel-G2000HXL (total of 2 columns) (both Tosoh Corporation) connected in series, column temperature: 30° C., eluent: N-methyl-2-pyrrolidone, flow rate: 1.0 mL/min, standard substance: polystyrene].

The acid value of the copolymer is preferably 0 mg KOH/g to 70 mg KOH/g, more preferably 0 mg KOH/g to 20 mg KOH/g, and even more preferably 0 mg KOH/g to 5 mg KOH/g.

The acid value of the copolymer can be adjusted, for example, by the amount of monomers used in synthesizing the copolymer and the proportion of acidic functional groups that are neutralized with basic compounds.

In the present disclosure, the acid value of the copolymer is a value measured as follows.
First, 1 g of the object to be measured is weighed out, and then 30 g of acetone is added to the object to dissolve it. Next, an appropriate amount of phenolphthalein, which is an indicator, is added to the solution of the object to be measured, and titration is performed using a 0.1 N KOH aqueous solution. Then, the acid value is calculated from the titration results using the following formula (A) (wherein Vf represents the titration amount (mL) of phenolphthalein, Wp represents the mass (g) of the solution of the object to be measured, and I represents the proportion (mass%) of the non-volatile content of the solution of the object to be measured).
Acid value (mgKOH/g) = 10 x Vf x 56.1/(Wp x I) (A)
The non-volatile content of the solution to be measured is calculated from the weight of the residue after measuring about 1 mL of the solution to be measured into an aluminum pan and drying for 15 minutes on a hot plate heated to 160°C.

The copolymer may be obtained, for example, by copolymerizing a monomer containing an acidic functional group (acidic functional group-containing monomer), a monomer containing an alkyleneoxy group (alkyleneoxy group-containing monomer), and other monomers as necessary. Examples of monomers used in the synthesis of the copolymer are shown below.

- Monomer containing an acidic functional group -
The acidic functional group-containing monomer is a compound having an ethylenically unsaturated double bond and an acidic functional group, and can introduce an acidic functional group into the side chain of the copolymer. The acidic functional group can be a carboxy group, a sulfo group, a phospho group, etc., and among them, a carboxy group is preferable.

Examples of monomers containing a carboxy group as an acidic functional group include acrylic carboxy group-containing monomers such as acrylic acid and methacrylic acid, crotonic carboxy group-containing monomers such as crotonic acid, maleic carboxy group-containing monomers such as maleic acid and its anhydride, itaconic carboxy group-containing monomers such as itaconic acid and its anhydride, citraconic carboxy group-containing monomers such as citraconic acid and its anhydride, vinyl benzoic acid, etc. Furthermore, monomers containing a hydrocarbon group (which may be in combination with an oxygen atom) having 5 or less carbon atoms, preferably 3 or less carbon atoms, more preferably 2 or less carbon atoms, and a carboxy group (for example, monomers represented by the following general formulas (V) and (VI)) can be mentioned.

In the formula, _R5 is H or _CH3 . _R6 is an alkylene group or alkyleneoxy group having 1 to 5 carbon atoms, preferably an alkylene group or alkyleneoxy group having 1 or 2 carbon atoms, and more preferably a methylene group.

Here, _R7 is H or _CH3 . _R8 is an alkylene chain or alkyleneoxy chain having 1 to 5 carbon atoms, preferably an alkylene group or alkyleneoxy group having 1 or 2 carbon atoms, and more preferably a methylene group.

Examples of monomers containing a sulfo group as an acidic functional group include vinylbenzenesulfonic acid, (meth)allyl sulfonic acid, (meth)allyloxybenzenesulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof (sodium salts, lithium salts, etc.).

Commercially available monomers containing a phospho group as an acidic functional group include acid phosphooxyethyl methacrylate (Unichemical Co., Ltd., product name: Phosmer M), acid phosphooxy polyoxyethylene glycol monomethacrylate (Unichemical Co., Ltd., product name: Phosmer PE), 3-chloro-2-acid phosphooxypropyl methacrylate (Unichemical Co., Ltd., product name: Phosmer CL), acid phosphooxy polyoxypropylene glycol monomethacrylate (Unichemical Co., Ltd., product name: Phosmer PP), etc.

Among these, monomers containing a carboxy group as an acidic functional group are preferred, acrylic acid or methacrylic acid are more preferred, and acrylic acid is even more preferred.

(Alkyleneoxy Group-Containing Monomer)
The alkyleneoxy group-containing monomer includes a compound having an ethylenically unsaturated double bond and an alkyleneoxy group, and capable of introducing an alkyleneoxy group into the side chain of a copolymer.
Note that a structure in which an oxygen atom in an ester bond of a monomer is bonded to an adjacent carbon atom (-C(=O)-O-C-R, where -O-R, R represents a substituent) is not included in the "alkyleneoxy group".

Examples of the alkyleneoxy structure contained in the alkyleneoxy group include ethylene oxide, propylene oxide, tetramethylene oxide, etc., and among these, ethylene oxide is preferred. Examples of alkyleneoxy group-containing monomers containing ethylene oxide include compounds represented by the following general formula (I).

In the formula, _R1 is H or _CH3 . _R2 is H, an alkyl group having 1 to 12 carbon atoms, or a phenyl group. n is an integer from 1 to 50, preferably an integer from 5 to 30, and more preferably an integer from 9 to 20.
The alkyl group having 1 to 12 carbon atoms or the phenyl group represented by _R2 may be unsubstituted or may have a substituent. Examples of the substituent include halogen atoms such as fluorine, chlorine, bromine, and iodine, nitrogen, phosphorus, aromatic rings, and cycloalkanes having 3 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic.

Specific examples of commercially available compounds represented by general formula (I) include ethoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Acrylate EC-A), methoxytriethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Acrylate MTG-A, manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester AM-30G), methoxypoly(n=9) ethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Acrylate 130-A, manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester AM-90G), methoxypoly(n=13) ethylene glycol acrylate (product name: NK Ester AM-130G), methoxypoly(n=23) ethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester AM-230G), Octoxypoly(n=18) ethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester A-OC-18E), phenoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Acrylate P-200A, manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester AMP-20GY), phenoxypoly(n=6) ethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester AMP-60G), nonylphenol EO adduct (n=4) Acrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Acrylate NP-4EA), nonylphenol EO adduct (n=8) Acrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Acrylate NP-8EA), methoxydiethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Ester MC, manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester M-20G), methoxytriethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Ester MC), Examples of such methoxypoly(n=9) ethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Ester 130MA, manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester M-90G), methoxypoly(n=23) ethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product name: NK Ester M-230G), and methoxypoly(n=30) ethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name: Light Ester 041MA).

Among the alkyleneoxy group-containing monomers, those in which the number of alkyleneoxy structures contained in the alkyleneoxy group is 5 or more are preferred, and those in which the number is 9 or more are more preferred. From the viewpoints of handleability and polymerizability, those in which the number of alkyleneoxy structures contained in the alkyleneoxy group is 50 or less are preferred, those in which the number is 30 or less are more preferred, and those in which the number is 20 or less are even more preferred.

-Other monomers-
The copolymer may contain, as necessary, a monomer (other monomer) other than the acidic group-containing monomer and the alkyleneoxy group-containing monomer as a copolymerization component. Examples of the other monomer include a monomer containing a nitrile group (nitrile group-containing monomer), a monomer containing an alkyl group (alkyl group-containing monomer), vinyl halides such as vinyl chloride, vinyl bromide, and vinylidene chloride, maleimide, phenylmaleimide, (meth)acrylamide, styrene, α-methylstyrene, and vinyl acetate. The other monomers may be used alone or in combination of two or more.

Nitrile group-containing monomers include compounds that have an ethylenically unsaturated double bond and a nitrile group, and that can introduce a nitrile group into the side chain of a copolymer. Examples include acrylic nitrile group-containing monomers such as acrylonitrile and methacrylonitrile, cyanide nitrile group-containing monomers such as α-cyanoacrylate and dicyanovinylidene, and fumaronitrile nitrile group-containing monomers.

Examples of the alkyl group-containing monomer include alkyl (meth)acrylate esters having an alkyl group with a carbon number of 1 to 60. From the viewpoint of obtaining sufficient resistance to swelling in the electrolyte, the alkyl group preferably has 6 or more carbon atoms.
The alkyl group of the alkyl group-containing monomer may be unsubstituted or may have a substituent. Examples of the substituent include halogen atoms such as fluorine, chlorine, bromine, and iodine, nitrogen, phosphorus, aromatic rings, and cycloalkanes having 3 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic.

Specific examples of alkyl group-containing monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, hexadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.

- Basic compounds -
The basic compound contained in the binder is not particularly limited as long as it can form a salt with the acidic functional group of the copolymer. For example, it may be a basic compound derived from a metal or a basic compound not derived from a metal. The basic compound may be used alone or in combination of two or more kinds.

Specific examples of basic compounds derived from metals include inorganic basic substances such as lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, calcium bicarbonate, and barium bicarbonate, and metal alcoholates such as lithium methoxide, sodium methoxide, lithium tert-butoxide, and potassium tert-butoxide.

Examples of basic compounds not derived from metals include ammonia, amine compounds, pyridine compounds, and azole compounds.

The amine compound preferably has 1 to 50 carbon atoms, more preferably 3 to 25 carbon atoms. Tertiary amine compounds are also preferred. Specific examples of amine compounds include the following compounds. Ph represents a phenyl group.

The pyridine compound preferably has a carbon number of 5 to 20, and more preferably has a carbon number of 5 to 10. Examples include pyridine and pyridine derivatives such as picoline.
The azole compound preferably has 2 to 20 carbon atoms, and more preferably has 2 to 10 carbon atoms. Examples include triazole and its derivatives.
Specific examples of the pyridine compound and the azole compound include the following compounds.

- Copolymer synthesis method -
The method for synthesizing the copolymer is not particularly limited. Polymerization methods such as underwater precipitation polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization can be applied. In terms of ease of resin synthesis and ease of post-treatment such as recovery and purification, underwater precipitation polymerization and emulsion polymerization are preferred, and underwater precipitation polymerization is more preferred.

As the polymerization initiator used in synthesizing the copolymer, it is preferable to use a water-soluble polymerization initiator in terms of polymerization initiation efficiency and the like.
Examples of the water-soluble polymerization initiator include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; water-soluble peroxides such as hydrogen peroxide; water-soluble azo compounds such as 2,2'-azobis(2-methylpropionamidine hydrochloride); and oxidation-reduction type (redox type) polymerization initiators obtained by combining an oxidizing agent such as a persulfate with a reducing agent such as sodium hydrogen sulfite, ammonium hydrogen sulfite, sodium thiosulfate, and hydrosulfite and a polymerization accelerator such as sulfuric acid, iron sulfate, and copper sulfate.
Among these, persulfates (more preferably ammonium persulfate) and water-soluble azo compounds are preferred from the standpoint of ease of resin synthesis.
The polymerization initiator is preferably used in an amount of, for example, 0.001 mol % to 5 mol %, and more preferably 0.01 mol % to 2 mol %, based on the total amount of monomers used in the synthesis of the copolymer.

When synthesizing the copolymer, a chain transfer agent may be used for the purpose of adjusting the molecular weight, etc. Examples of chain transfer agents include mercaptan compounds such as thioglycol, carbon tetrachloride, and α-methylstyrene dimer. Among these, α-methylstyrene dimer is preferred because it has less odor.

When synthesizing the copolymer, a solvent may be used. Examples of the solvent include water and an organic solvent. When synthesizing the copolymer by underwater precipitation polymerization, water and an organic solvent may be used in combination in order to adjust the particle size of the precipitated copolymer.
Examples of the solvent other than water include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; ureas such as N,N-dimethylethyleneurea, N,N-dimethylpropyleneurea, and tetramethylurea; lactones such as γ-butyrolactone and γ-caprolactone; carbonates such as propylene carbonate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, ethyl cellosolve acetate, and ethyl carbitol acetate; glymes such as diglyme, triglyme, and tetraglyme; hydrocarbons such as toluene, xylene, and cyclohexane; sulfoxides such as dimethyl sulfoxide; sulfones such as sulfolane; and alcohols such as methanol, isopropanol, and n-butanol. These solvents may be used alone or in combination of two or more.

The synthesis conditions for the copolymer are not particularly limited. For example, the synthesis is carried out by introducing the monomers into a solvent, maintaining the polymerization temperature at preferably 0° C. to 100° C., more preferably 30° C. to 90° C., and holding the temperature for preferably 1 hour to 50 hours, more preferably 2 hours to 12 hours.
If the polymerization temperature is 0° C. or higher, the polymerization reaction tends to be accelerated. Also, if the polymerization temperature is 100° C. or lower, even when water is used as a solvent, water is less likely to evaporate, making it difficult to polymerize.

By reacting the acidic functional groups of the synthesized copolymer with a basic compound, at least a portion of the acidic functional groups can be made to form a salt.

The method of reacting the copolymer with the basic compound is not particularly limited and can be carried out by known methods. The amount of the basic compound used in the reaction with the copolymer can be set according to the amount of acidic functional groups contained in the copolymer, the proportion of the acidic functional groups to be reacted with the base, etc.

The amount of the basic compound is, for example, preferably 0.01 to 1.5 molar equivalents relative to the acidic functional groups contained in the copolymer, more preferably 0.3 to 1.1 molar equivalents, and even more preferably 0.5 to 1.0 molar equivalents.

-Binder uses-
The binder of the present disclosure is preferably used as an electrode material (particularly, as a binder for active materials) for energy devices, particularly non-aqueous electrolyte energy devices. A non-aqueous electrolyte energy device refers to an electricity storage or power generation device (apparatus) that uses an electrolyte other than water. Examples of energy devices include lithium ion secondary batteries, electric double layer capacitors, solar cells, and fuel cells. Among these, the binder is preferably used as an electrode material that contains a silicon-containing compound as an active material, which has a large expansion and contraction due to charging and discharging.

<Electrode mixture>
The electrode mixture of the present disclosure includes the above-mentioned binder and an active material. The type of active material contained in the electrode mixture is not particularly limited and can be selected from those commonly used as materials for electrodes of energy devices. Since the binder contained in the electrode mixture of the present disclosure has excellent coverage of the active material, an electrode having excellent cycle characteristics can be formed even when the electrode mixture includes an active material that expands and contracts greatly during charging and discharging.

The active material contained in the electrode mixture may contain a compound containing silicon. When a silicon-containing compound is used as an active material for the negative electrode of an energy device (negative electrode active material), a higher capacity can be achieved compared to negative electrode active materials such as graphite. On the other hand, the active material has a tendency to deteriorate due to its large expansion and contraction during charging and discharging, and the cycle characteristics are difficult to maintain. The binder of the present disclosure has excellent coating properties for the active material, so that even if the active material contains silicon, it is difficult to deteriorate and good cycle characteristics are easily maintained.

Examples of compounds containing silicon include silicon oxides, such as silicon monoxide, silicon dioxide, and silicon suboxide. These may be used alone or in combination of two or more.

Silicon monoxide can be obtained, for example, by the known sublimation method of heating a mixture of silicon dioxide and silicon metal to produce silicon monoxide gas, which is then cooled and precipitated. Silicon monoxide can also be obtained from the market as silicon oxide, silicon monoxide, etc.

The silicon oxide may have a structure in which silicon crystallites are dispersed in silicon oxide (preferably a structure in which silicon crystallites are dispersed in silicon dioxide). The presence of silicon crystallites in silicon oxide makes it easier to obtain a high initial discharge capacity and good initial charge/discharge efficiency.

When the silicon oxide is particulate, its average particle size is not particularly limited. For example, it is preferably 0.1 μm to 20 μm, and more preferably 0.5 μm to 10 μm.

In the present disclosure, the average particle size of the active material is defined as the value (median diameter (D50)) at which the cumulative total from the small diameter side is 50% in the volume-based particle size distribution measured by dispersing a sample in purified water containing a surfactant and measuring the particle size distribution using a laser diffraction particle size distribution measuring device (e.g., SALD-3000J, manufactured by Shimadzu Corporation).
The BET specific surface area can be measured from the nitrogen adsorption capacity in accordance with, for example, JIS Z 8830: 2013. As an evaluation device, for example, AUTOSORB-1 (product name) manufactured by QUANTACROME Inc. can be used. Since moisture adsorbed on the sample surface and in the structure is considered to affect the gas adsorption capacity, it is preferable to first perform a pretreatment for removing moisture by heating when measuring the BET specific surface area.
In the pretreatment, a measurement cell containing 0.05 g of a measurement sample is depressurized to 10 Pa or less using a vacuum pump, heated to 110° C., and held for 3 hours or more, and then naturally cooled to room temperature (25° C.) while maintaining the depressurized state. After this pretreatment, the evaluation temperature is set to 77 K, and the evaluation pressure range is set to less than 1 in terms of relative pressure (equilibrium pressure with respect to the saturated vapor pressure).

Silicon oxide particles can be produced, for example, by crushing and classifying lump silicon oxide. More specifically, a preferred method is to first crush the lump silicon oxide to a size that can be fed into a fine grinding mill, followed by classification, and then to subject the crushed material to secondary crushing (classification) in the fine grinding mill.

The electrode mixture of the present disclosure may contain a compound containing silicon as an active material and other active materials. The other active materials may be selected from those commonly used as negative electrode active materials for lithium ion secondary batteries. Specific examples include carbon materials, metallic lithium, lithium alloys, intermetallic compounds, metal complexes, organic polymer compounds, and the like. Among these, carbon materials are preferred. Examples of carbon materials include graphite such as natural graphite (e.g., flake graphite) and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon fibers.

Among carbon materials, from the viewpoint of improving the characteristics of energy devices, a carbon material (graphite) having a carbon hexagonal plane spacing (d ₀₀₂ ) of 3.35 Å to 3.40 Å in wide-angle X-ray diffraction and a crystallite (Lc) in the c-axis direction of 100 Å or more is preferred.
On the other hand, from the viewpoint of improving the cycle characteristics and safety of energy devices, a carbon material (amorphous carbon) in which the spacing (d ₀₀₂ ) between hexagonal carbon planes is 3.50 Å to 3.95 Å as measured by wide-angle X-ray diffraction is preferred.
The carbon material preferably has an average particle size of 0.1 μm to 60 μm, more preferably 0.5 μm to 30 μm, and more preferably has a BET specific surface area of 1 m ² /g to 10 m ² /g.

The electrode mixture of the present disclosure is suitable as an electrode mixture for negative electrodes that are manufactured using aqueous solvents because the binder contained therein has excellent compatibility with aqueous solvents, but it may also be an electrode mixture for positive electrodes.

When the electrode mixture is for a positive electrode and contains a positive electrode active material, the type of the positive electrode active material is not particularly limited. For example, it may be selected from those commonly used as positive electrode active materials for lithium ion secondary batteries. Specific examples include lithium-containing metal composite oxides, olivine-type lithium salts, chalcogen compounds, manganese dioxide, and the like. The lithium-containing metal composite oxide is a metal oxide containing lithium and a transition metal, or a metal oxide in which a part of the transition metal in the metal oxide is replaced by a different element. Examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, B, and the like, and among them, Mn, Al, Co, Ni, Mg, and the like are preferable. The different element may be used alone or in combination of two or more kinds.

The positive electrode active material preferably has an average particle size of 0.1 μm to 60 μm, more preferably 0.5 μm to 30 μm, and more preferably has a BET specific surface area of 1 m ² /g to 10 m ² /g.

When the electrode mixture contains a silicon-containing compound and another active material as the active material, the ratio is not particularly limited. For example, the mass ratio (A:B) of the silicon-containing compound A to the other active material B may be 0.5:9.5 to 5:5.

The ratio of the binder and the active material contained in the electrode mixture is not particularly limited. For example, the mass ratio of the binder A to the active material B (A:B) may be 20:80 to 0.1:99.9.

The electrode mixture may contain a liquid medium. In particular, from the viewpoint of workability, it is preferable that the binder contains a liquid medium when used (when mixed with the active material). The liquid medium contained in the electrode mixture is preferably water, but an organic solvent may be contained together with water as necessary.

The viscosity of the electrode mixture during use is, for example, preferably 500 mPa·s to 50,000 mPa·s at 25° C., more preferably 1,000 mPa·s to 20,000 mPa·s, and even more preferably 2,000 mPa·s to 10,000 mPa·s. The viscosity is measured using a rotational shear viscometer at 25° C. and a shear rate of 1.0 s ^-1 .

The electrode mixture may contain components other than the binder, active material, and liquid medium as necessary. For example, it may contain various additives such as a cross-linking component to complement swelling resistance to the electrolyte, a rubber component to complement the flexibility and pliability of the electrode, a thickener to improve the coatability of the electrode mixture, an anti-settling agent, an antifoaming agent, and a leveling agent. The state of the electrode mixture is not particularly limited and can be selected according to the storage method, the electrode formation method, etc. For example, it may be in a slurry state.

<Electrodes for energy devices>
The energy device electrode of the present disclosure comprises a current collector and an electrode mixture layer provided on at least one surface of the current collector and containing the above-mentioned electrode mixture.
The energy device electrode of the present disclosure can be used as an electrode for lithium ion secondary batteries, electric double layer capacitors, solar cells, fuel cells, and the like.
The application of the energy device electrode of the present disclosure to an electrode of a lithium ion secondary battery will be described in detail below, but the energy device electrode of the present disclosure is not limited to the following.

The type of the current collector is not particularly limited, and may be selected from those commonly used in the field of lithium ion secondary batteries.
Examples of the current collector (negative electrode current collector) used in the negative electrode of a lithium ion secondary battery include sheets and foils containing stainless steel, nickel, copper, etc. Among these, sheets or foils containing copper are preferred. The thickness of the sheet or foil is not particularly limited, and from the viewpoint of ensuring the strength and processability required as a current collector, it is preferably, for example, 1 μm to 500 μm, more preferably 2 μm to 100 μm, and even more preferably 5 μm to 50 μm.
Examples of the current collector (positive electrode current collector) used in the positive electrode of a lithium ion secondary battery include sheets and foils containing stainless steel, aluminum, titanium, etc. Among these, sheets or foils containing aluminum are preferred. The thickness of the sheet or foil is not particularly limited, and from the viewpoint of ensuring the strength and processability required as a current collector, it is preferably, for example, 1 μm to 500 μm, more preferably 2 μm to 80 μm, and even more preferably 5 μm to 50 μm.

The electrode mixture layer can be formed using the electrode mixture described above. Specifically, for example, the electrode mixture in a slurry form is applied onto at least one surface of the current collector, the solvent is then removed by drying, and the electrode mixture layer can be formed by rolling as necessary.
The application of the electrode mixture in a slurry form can be carried out, for example, using a comma coater or the like. The application is suitably carried out so that the ratio of the positive electrode capacity to the negative electrode capacity (negative electrode capacity/positive electrode capacity) of the opposing electrodes is equal to or greater than 1. The application amount of the electrode mixture in a slurry form is, for example, preferably 5 g/m ² to 500 g/m ² , and more preferably 50 g/m ² to 300 g/m ² , in terms of the dry mass per side of the electrode mixture layer.
The solvent is removed, for example, by drying at 50° C. to 150° C., preferably 80° C. to 120° C., for 1 to 20 minutes, preferably 3 to 10 minutes.
The rolling is carried out, for example, using a roll press machine, so that the density of the mixture layer becomes, for example, 1 g/cm ³ to 2 g/cm ³ , preferably 1.2 g/cm ³ to 1.8 g/cm ³ in the case of a negative electrode mixture layer, and, for example, 2 g/cm ³ to 5 g/cm ³ , preferably 2 g/cm ³ to 4 g/cm ³ in the case of a positive electrode mixture layer.
Furthermore, in order to remove residual solvent and adsorbed water in the electrode, the electrode may be vacuum dried at 100° C. to 150° C. for 1 to 20 hours.

<Energy Devices>
The energy device of the present disclosure includes a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode contains the above-mentioned binder and active material.
In the energy device electrode of the present disclosure, at least one of the positive electrode and negative electrode contains the above-mentioned binder and active material, and therefore has excellent cycle characteristics even when the active material contains a material that expands and contracts greatly.

In one embodiment, the energy device has at least a negative electrode that includes the binder and active material described above. In another embodiment, the energy device has at least a negative electrode that includes the binder and active material described above, and includes a silicon-containing compound as the active material.

Examples of energy devices disclosed herein include lithium ion secondary batteries, electric double layer capacitors, solar cells, fuel cells, etc. Below, we will explain in detail the case where the energy device is a lithium ion secondary battery, but the energy devices disclosed herein are not limited to the following content.

A lithium ion secondary battery, for example, comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. For details of the positive electrode and the negative electrode, please refer to the description of the electrodes for energy devices mentioned above.

There are no particular limitations on the separator, so long as it provides electronic insulation between the positive and negative electrodes while being ion-permeable, and is resistant to oxidation on the positive electrode side and reduction on the negative electrode side. Resins, inorganic substances, etc. are used as separator materials that satisfy these characteristics.

Examples of the resin that can be used include olefin polymers, fluorine polymers, cellulose polymers, polyimides, nylons, etc. Specifically, it is preferable to select a material that is stable against the electrolyte and has excellent electrolyte retention, and it is preferable to use a porous sheet or nonwoven fabric made from polyolefins such as polyethylene or polypropylene.

Examples of inorganic substances that can be used include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, sulfates such as barium sulfate and calcium sulfate, glass, etc. For example, the above-mentioned inorganic substances in a fiber or particle form can be attached to a thin-film substrate such as a nonwoven fabric, a woven fabric, or a microporous film, and the like, and used as the separator.
As the thin-film-shaped substrate, a substrate having a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm is preferably used. In addition, for example, the above-mentioned inorganic substance in a fiber shape or particle shape can be used as a separator by forming a composite porous layer using a binder such as a resin. Furthermore, this composite porous layer may be formed on the surface of a positive electrode or a negative electrode to form a separator. Alternatively, this composite porous layer may be formed on the surface of another separator to form a multi-layer separator. For example, a composite porous layer in which alumina particles having a 90% particle size (D90) of less than 1 μm are bound with a fluororesin as a binder may be formed on the surface of a positive electrode.

The electrolyte contains a solute (supporting salt) and a non-aqueous solvent, and may further contain various additives as necessary. The solute is usually dissolved in the non-aqueous solvent. The electrolyte is impregnated into, for example, a separator.

As the solute, a solute commonly used in this field can be used, specifically, _LiClO4 , LiBF4, _LiPF6 , _LiAlCl4 , _LiSbF6 , _LiSCN , _LiCF3SO3 , _LiCF3CO2 , _LiAsF6 , _{LiB10Cl10 ,} lithium lower aliphatic carboxylates, LiCl, LiBr, _LiI , lithium _chloroborane , borates, imide salts, etc. can be mentioned. Examples of the borate salts include lithium bis(1,2-benzenediolate(2-)-O,O')borate, lithium bis(2,3-naphthalenediolate(2-)-O,O')borate, lithium bis(2,2'-biphenyldiolate(2-)-O,O')borate, and lithium bis(5-fluoro-2-oleate-1-benzenesulfonic acid-O,O')borate. Examples of the imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide ((CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ )NLi), and lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi). The amount of the solute dissolved in the non-aqueous solvent is preferably 0.5 mol/L to 2 mol/L.

As the non-aqueous solvent, those commonly used in this field can be used. Specific examples include cyclic carbonate esters, chain carbonate esters, cyclic carboxylate esters, etc. Examples of cyclic carbonate esters include propylene carbonate (PC) and ethylene carbonate (EC). Examples of chain carbonate esters include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. Examples of cyclic carboxylate esters include gamma-butyrolactone (GBL), gamma-valerolactone (GVL), etc. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

In addition, from the viewpoint of further improving the battery characteristics, it is preferable that the non-aqueous solvent contains vinylene carbonate (VC). When the non-aqueous solvent contains vinylene carbonate (VC), the content is preferably 0.1% by mass to 2% by mass, and more preferably 0.2% by mass to 1.5% by mass, based on the total amount of the non-aqueous solvent.

As an example of the configuration of the lithium ion secondary battery, the configuration of a laminate type lithium ion secondary battery will be described below.
A laminated lithium ion secondary battery can be produced, for example, as follows. First, the positive electrode and the negative electrode are cut into a rectangular shape, and tabs are welded to each electrode to produce a positive electrode terminal and a negative electrode terminal. An electrode laminate is produced by stacking the positive electrode and the negative electrode with a separator interposed between them, and in this state, the laminate is housed in an aluminum laminate pack, and the positive electrode terminal and the negative electrode terminal are taken out of the aluminum laminate pack and sealed. Next, an electrolyte is poured into the aluminum laminate pack, and the opening of the aluminum laminate pack is sealed. This produces a lithium ion secondary battery.

As an example of the configuration of a lithium ion secondary battery, the configuration of a cylindrical lithium ion secondary battery will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of a cylindrical lithium ion secondary battery. As shown in FIG. 1, the lithium ion secondary battery 1 has a cylindrical battery container 6 made of nickel-plated steel and having a bottom. The battery container 6 contains an electrode group 5 in which a strip-shaped positive electrode plate 2 and a negative electrode plate 3 are wound in a spiral shape in cross section via a separator 4. The separator 4 is set to, for example, a width of 58 mm and a thickness of 30 μm. A ribbon-shaped positive electrode tab terminal made of aluminum and fixed at one end to the positive electrode plate 2 is led out from the upper end surface of the electrode group 5. The other end of the positive electrode tab terminal is disposed on the upper side of the electrode group 5 and joined by ultrasonic welding to the lower surface of a disk-shaped battery cover that serves as a positive electrode external terminal. On the other hand, a ribbon-shaped negative electrode tab terminal made of copper and fixed at one end to the negative electrode plate 3 is led out from the lower end surface of the electrode group 5. The other end of the negative electrode tab terminal is joined to the inner bottom of the battery container 6 by resistance welding. Therefore, the positive electrode tab terminal and the negative electrode tab terminal are respectively led out to opposite ends of both end faces of the electrode group 5. An insulating coating (not shown) is applied to the entire outer periphery of the electrode group 5. The battery lid is fixed to the upper part of the battery container 6 by crimping via an insulating resin gasket. Therefore, the inside of the lithium ion secondary battery 1 is sealed. An electrolyte (not shown) is poured into the battery container 6.

The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1
<Synthesis of Copolymer A>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 25.5 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 88.47 mL of a 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 25.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 1.5 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) in which R ₁ is a hydrogen atom, R ₂ is methyl, and n is 9 in the general formula (I) were added to the system, and the system was replaced with nitrogen and heated to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution in which 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer A. The obtained aqueous solution containing copolymer A was dried for 1 hour with a blower type dryer set at 150 ° C. The polymerization rate was calculated from the non-volatile content concentration after drying, and was 99.8%.

Example 2
<Synthesis of Copolymer B>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 30.7 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 83.26 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 24.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 3.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system, and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0°C. After confirming that the temperature in the system was 90.0°C, a solution in which 0.03g of ammonium persulfate as a polymerization initiator was dissolved in 2.0g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer B. The aqueous solution containing copolymer B obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.7%.

Example 3
<Synthesis of Copolymer C>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 41.1 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 72.86 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 21.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 6.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., a solution of 0.03 g of ammonium persulfate as a polymerization initiator dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer C. The aqueous solution containing copolymer C obtained was dried for 1 hour in a blower dryer set at 150 ° C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 100.1%.

Example 4
<Synthesis of Copolymer D>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 35.9 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 78.06 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 22.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 1.5 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system, and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0°C. After confirming that the temperature in the system was 90.0°C, a solution in which 0.03g of ammonium persulfate as a polymerization initiator was dissolved in 2.0g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer D. The aqueous solution containing copolymer D obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.6%.

Example 5
<Synthesis of Copolymer E>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 41.1 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 72.86 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 21.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 3.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system, and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer E. The aqueous solution containing copolymer E obtained was dried for 1 hour in a blower dryer set at 150 ° C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.9%.

Example 6
<Synthesis of Copolymer F>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 51.6 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 62.45 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 18.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 6.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0°C. After confirming that the temperature in the system was 90.0°C, a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer F. The aqueous solution containing copolymer F obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.7%.

(Example 7)
<Synthesis of Copolymer G>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 41.1 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 72.86 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 21.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 1.5 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system, and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer G. The aqueous solution containing copolymer G obtained was dried for 1 hour in a blower type dryer set at 150 ° C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.6%.

(Example 8)
<Synthesis of Copolymer H>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 46.3 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 67.65 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 19.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 3.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer H. The aqueous solution containing copolymer H obtained was dried for 1 hour in a blower type dryer set at 150 ° C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.7%.

(Example 9)
<Synthesis of Copolymer I>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 56.8 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 57.24 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 16.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 6.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer I. The aqueous solution containing copolymer I obtained was dried for 1 hour in a blower dryer set at 150 ° C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.5%.

(Example 10)
<Synthesis of Copolymer J>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 56.8 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 57.24 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 16.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 1.5 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system, and stirred at 200 rpm for 5 hours. The temperature in the system was then raised to 90.0°C. After confirming that the temperature in the system was 90.0°C, a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer J. The aqueous solution containing copolymer J obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was found to be 99.9%.

Example 11
<Synthesis of Copolymer K>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 62.0 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 52.04 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 15.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 3.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system and stirred at 200 rpm for 5 hours. Then, the temperature in the system was raised to 90.0°C. After confirming that the temperature in the system was 90.0°C, a solution in which 0.03 g of ammonium persulfate as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer K. The aqueous solution containing copolymer K obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.7%.

Example 12
<Synthesis of Copolymer L>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 72.4 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 41.63 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 12.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 6.0 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) were added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution of 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water and added to the system and stirred at 200 rpm for 5 hours. The temperature in the system was then raised to 90.0°C. After confirming that the temperature in the system was 90.0°C, a solution of 0.03g of ammonium persulfate as a polymerization initiator dissolved in 2.0g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer L. The aqueous solution containing copolymer L obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was found to be 100.0%.

(Comparative Example 1)
<Synthesis of Copolymer M>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 20.3 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 93.67 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 27.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution in which 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 5 hours. Next, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0°C, a solution of 0.03g of ammonium persulfate as a polymerization initiator dissolved in 2.0g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer M. The aqueous solution containing copolymer M obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was found to be 100.0%.

(Comparative Example 2)
<Synthesis of Copolymer N>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 30.7 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 83.26 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 24.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution in which 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 5 hours. Next, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0°C, a solution of 0.03g of ammonium persulfate as a polymerization initiator dissolved in 2.0g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer N. The aqueous solution containing copolymer N obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.6%.

(Comparative Example 3)
<Synthesis of Copolymer O>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 35.9 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 78.06 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 22.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution in which 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 5 hours. Next, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., a solution of 0.03 g of ammonium persulfate as a polymerization initiator dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer O. The aqueous solution containing copolymer O obtained was dried for 1 hour in a blower dryer set at 150 ° C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.7%.

(Comparative Example 4)
<Synthesis of Copolymer P>
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, and a cooling tube, 51.6 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 62.45 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 18.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) were added and stirred at 200 rpm for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added to the system, the system was replaced with nitrogen, and the temperature was raised to 65.0 ° C. After confirming that the temperature in the system was 65.0 ° C., a solution in which 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 2.0 g of purified water was added to the system and stirred at 200 rpm for 5 hours. Next, the temperature in the system was raised to 90.0 ° C. After confirming that the temperature in the system was 90.0°C, a solution of 0.03g of ammonium persulfate as a polymerization initiator dissolved in 2.0g of purified water was added to the system and stirred at 200 rpm for 2 hours to synthesize an aqueous solution containing copolymer P. The aqueous solution containing copolymer P obtained was dried for 1 hour in a blower dryer set at 150°C. The polymerization rate was calculated from the non-volatile content concentration after drying and was 99.8%.

(Reference example 1)
98.0 g of purified water was added to a 1 L plastic container with a lid (I-Boy, manufactured by AS ONE Corporation), and then 2.0 g of sodium salt of carboxymethylcellulose (CMC#2200, manufactured by Daicel FineChem Corporation, hereinafter sometimes referred to as CMC) was added and stirred to obtain an aqueous solution of CMC.
In a 0.5-liter separable flask equipped with a stirrer, a thermometer, a cooling tube, and a liquid pump, 335.0 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 21.46 g of a 2.0 mass% aqueous solution of sodium carboxymethylcellulose (manufactured by Daicel FineChem Corporation, CMC # 2200) as an emulsifier were added, the system was replaced with nitrogen, and the temperature was raised to 60.0 ° C. After confirming that the temperature in the system was 60.0 ° C., a solution in which 0.26 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was dissolved in 8.0 g of purified water was added to the system. Immediately after adding ammonium persulfate, while stirring the inside of the system at 250 rpm, a mixture of 16.98 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Industries Co., Ltd.), 68.26 g of butyl methacrylate (manufactured by FUJIFILM Wako Pure Chemical Industries Co., Ltd.), and 0.34 g of ethoxylated pentaerythritol tetraacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., ATM-4E) was dropped over 2 hours using a liquid pump. After the entire mixture was dropped, stirring was continued for 4 hours. Next, the inside of the system was heated to 90.0 ° C. After confirming that the temperature in the system was 90.0 ° C., stirring was continued for 2 hours at 250 rpm to obtain a dispersion of acrylic fine particles.

<Preparation of electrode mixture>
Graphite and SiO, which are negative electrode active materials, and the copolymers synthesized in Examples 1 to 12 and Comparative Examples 1 to 4 were mixed so that the solid content ratio was 92.15% by mass (graphite): 4.85% by mass (SiO): 3.0% by mass (copolymer), and purified water was added to adjust the viscosity to obtain a slurry-like electrode mixture. The purified water was added in an amount such that the viscosity measured under conditions of 25.0 ° C. and 0.5 rpm was 7500 to 10000 mPa · s using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., VISCOMETER TPE-100). Note that, for Reference Example 1, the negative electrode active materials graphite and SiO, the CMC aqueous solution, and the acrylic fine particles synthesized in Reference Example 1 were mixed so that the solid content ratio was 92.15% by mass: 4.85% by mass: 1.5% by mass: 1.5% by mass.

<Evaluation of Dispersion Stability of Electrode Mixture>
20.0 g of the prepared electrode mixture was added to a 50 ml plastic container with a lid (I-Boy, manufactured by AS ONE Corporation), and then allowed to stand for 72 hours in an environment of 25.0° C. Thereafter, the appearance was observed, and the dispersion stability of the electrode mixture was evaluated according to the following criteria.
In the following criteria, A indicates the best dispersion stability of the electrode mixture, and D indicates the worst. The results are shown in Tables 1 to 3. In the tables, AA indicates acrylic acid, AN indicates acrylonitrile, and AM-90G indicates methoxypolyethylene glycol acrylate.

Judgment criteria for dispersion stability of electrode mixture A: No visual separation or less than 1 mm B: Visual separation of 1 mm or more and less than 5 mm C: Visual separation of 5 mm or more and less than 10 mm D: Visual separation of 10 mm or more

From the results shown in Tables 1 to 3, it can be seen that Examples 1 to 12, which used copolymers containing structural units derived from monomers containing alkyleneoxy groups, had excellent dispersion stability of the electrode mixture, whereas Comparative Examples 1 to 4, which used copolymers not containing structural units derived from monomers containing alkyleneoxy groups, had poor dispersion stability of the electrode mixture. These results suggest that a copolymer containing structural units derived from an acidic functional group-containing monomer and structural units derived from a monomer containing an alkyleneoxy group serves as a binder with excellent dispersion stability of the electrode mixture.

Example 13
<Preparation of negative electrode>
The electrode mixture prepared in Example 1 was evenly and homogeneously applied to one side of a Cu foil (current collector) having a thickness of 10 μm so that the coating amount after drying was 78.0 g/m ^2. Thereafter, a drying treatment was performed, and the negative electrode was obtained by rolling the negative electrode by pressing so that the density became 1.6 g/cm ³ .

<Preparation of Positive Electrode Slurry>
A positive electrode active material, lithium nickel cobalt manganese oxide (NMC), a conductive material, carbon black (Li400, manufactured by Denka Co., Ltd.), and a positive electrode binder, polyvinylidene fluoride, were mixed so that the solid content ratio was 92.00% by mass: 4.00% by mass: 4.0% by mass, and NMP was added to adjust the viscosity to obtain a positive electrode slurry. NMP was added in an amount such that the viscosity measured at 25.0°C and 0.5 rpm using an E-type viscometer (VISCOMETER TPE-100, manufactured by Toki Sangyo Co., Ltd.) was 7500 mPa·s to 10000 mPa·s.

<Preparation of Positive Electrode>
The prepared positive electrode slurry was evenly and homogeneously applied to one side of an Al foil (current collector) having a thickness of 15 μm so that the coating amount after drying was 200.0 g/m ^2. Thereafter, a drying treatment was performed, and the positive electrode was obtained by rolling the positive electrode by pressing so that the density became 2.8 g/cm ³ .

<Preparation of Laminated Cell>
The prepared negative electrode was cut into a rectangle of 4.6 cm in length and 6.2 cm in width, and then a Ni wire for current collection was welded. The prepared positive electrode was cut into a rectangle of 4.5 cm in length and 6.0 cm in width, and then an Al wire for current collection was welded. The negative electrode and the positive electrode were stacked so that the coated surfaces faced each other through a separator, and then placed in a laminate on a bag, 1000 μL of electrolyte was poured, and vacuum sealed to obtain a laminated cell. A polyethylene microporous sheet was used as the separator, and the electrolyte was a 1.0 M LiPF ₆ -containing ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate = 1/1/1 mixed solution (volume ratio) to which 1.0 mass% vinylene carbonate and 1.0 mass% fluoroethylene carbonate were added with respect to the total amount of the mixed solution.

(Examples 14 to 24, Reference Example 2)
Laminate type cells were produced in the same manner as in Example 13, except that the electrode mixtures prepared in Examples 2 to 12 and Reference Example 1 were used, respectively.

<Evaluation of Initial Efficiency and Initial Discharge Capacity of Laminated Cell>
The laminated cell thus prepared was placed in a thermostatic chamber at 25.0°C and connected to a charge/discharge device (TOSCAT-3200, manufactured by Toyo Systems Co., Ltd.). After constant current charging at a constant current of 0.10 CA up to 4.2 V, constant voltage charging at 4.2 V until the current value reached 0.01 CA was performed, and the charge capacity was measured. Next, constant current discharging was performed at a current value of 0.10 CA up to 2.7 V, and the discharge capacity (initial discharge capacity) was measured. The initial efficiency was calculated using the following formula.
Initial efficiency (%) = discharge capacity (mAh) × 100 / charge capacity (mAh)

The obtained initial efficiency and initial discharge capacity were evaluated according to the following criteria. For both initial efficiency and initial discharge capacity, A was judged to be the best and D was judged to be the worst. The results are shown in Tables 4 and 5.

Criteria for initial efficiency A: Initial efficiency is 88.5% or more B: Initial efficiency is 88.0% or more and less than 88.5% C: Initial efficiency is 87.5% or more and less than 88.0% D: Initial efficiency is less than 87.5%

Criteria for initial discharge capacity A: Discharge capacity is 83.2 mAh or more B: Discharge capacity is 82.7 mAh or more but less than 83.2 mAh C: Discharge capacity is 82.3 mAh or more but less than 82.7 mAh D: Discharge capacity is less than 82.7 mAh

<Evaluation of cycle characteristics>
The laminated cell for which the initial efficiency and initial discharge capacity were measured was placed in a thermostatic chamber at 25.0 ° C. and connected to a charger/discharger (TOSCAT-3200, manufactured by Toyo Systems Co., Ltd.). After constant current charging at a constant current of 0.10 CA to 4.2 V, constant voltage charging was performed until the current value at 4.2 V was 0.01 CA. Then, constant current discharging was performed at a current value of 0.10 CA to 2.7 V. This charge/discharge was repeated twice. Next, the laminated cell was placed in a thermostatic chamber at 50.0 ° C. and connected to a charger/discharger (TOSCAT-3200, manufactured by Toyo Systems Co., Ltd.). After constant current charging at a constant current of 0.10 CA to 4.2 V, constant voltage charging was performed until the current value at 4.2 V was 0.01 CA. Then, constant current discharging was performed at a current value of 0.10 CA to 2.7 V. The laminated cell was then placed in a thermostatic chamber at 25.0°C and connected to a charge/discharge device (TOSCAT-3200, manufactured by Toyo Systems Co., Ltd.). After constant current charging at a constant current of 0.50 CA to 4.2 V, it was charged at a constant voltage of 4.2 V until the current value reached 0.01 CA. It was then discharged at a constant current of 1.00 CA to 2.7 V. This charge/discharge was continued 100 times, and the cycle characteristics were evaluated according to the following criteria using the discharge capacity of the 100th charge/discharge. Note that A indicates the best cycle characteristics, and D indicates the worst cycle characteristics. The results are shown in Tables 4 and 5.

Criteria for cycle characteristics: A: 75.0mAh or more B: 74.0mAh or more, less than 75.0mAh C: 73.0mAh or more, less than 74.0mAh D: Less than 73.0mAh

The above results suggest that the binder of the present disclosure, which corresponds to the examples, has excellent dispersion stability of the electrode mixture and can improve the initial efficiency, initial discharge efficiency, and cycle characteristics of the energy device.

The disclosure of Japanese Patent Application No. 2020-34789 is incorporated herein by reference in its entirety.
All publications, patent applications, and standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or standard was specifically and individually indicated to be incorporated by reference.

Claims (8)

An electrode binder comprising: a copolymer containing structural units derived from acrylic acid or methacrylic acid, structural units derived from acrylonitrile or methacrylonitrile, and structural units derived from a compound represented by the following general formula (I), in which the proportion of the structural units derived from acrylic acid or methacrylic acid is 40% by mass to 85% by mass of all structural units, the proportion of the structural units derived from acrylonitrile or methacrylonitrile is 10% by mass to 40% by mass of all structural units, and the proportion of the structural units derived from the compound represented by general formula (I) is 5% by mass to 20% by mass of all structural units; and a basic compound capable of forming a salt with a carboxy group.

In the formula, R ₁ is H or CH ₃ , R ₂ is H, an alkyl group having 1 to 12 carbon atoms or a phenyl group, and n is an integer from 1 to 50. The electrode binder according to claim 1, further comprising water, the copolymer being dissolved in the water. 3. The electrode binder according to claim 1 or 2, wherein the basic compound comprises one compound selected from the group consisting of hydroxides of alkali metals and alkaline earth metals, carbonates of alkali metals and alkaline earth metals, ammonia, amines having 1 to 50 carbon atoms, pyridines having 5 to 20 carbon atoms, and azoles having 2 to 20 carbon atoms. The electrode binder according to any one of claims 1 to 3 , for forming an electrode containing a silicon-containing compound as an active material. An electrode mixture comprising the electrode binder according to any one of claims 1 to 4 and an active material. The electrode mixture according to claim 5 , wherein the active material comprises a compound containing silicon. 7. An electrode for an energy device, comprising: a current collector; and an electrode mixture layer provided on at least one surface of the current collector, the electrode mixture layer comprising the electrode mixture according to claim 5 . 5. An energy device comprising a positive electrode and a negative electrode, at least one of the positive electrode and the negative electrode comprising the electrode binder according to claim 1 and an active material.