Binder for electrodes, electrode binder, electrode for energy devices, and energy device

Abstract

An electrode binder including structural units containing an acidic functional group, structural units containing an alkyleneoxy group, a copolymer in which the proportion of structural units containing the alkyleneoxy group is at least 5 mass% of the total structural units, and a basic compound capable of forming the acidic functional group and a salt.

Description

Technical Field

[0001] The present invention relates to a binder for electrodes, an electrode mixture, an electrode for an energy device, and an energy device.

Background Art

[0002] As a power source for portable information terminals such as notebook computers, mobile phones, PDAs, etc., and a power source for electric vehicles, a lithium-ion secondary battery, which is a non-aqueous electrolyte energy device having a high energy density, is widely used.

[0003] The electrodes of a lithium-ion secondary battery are manufactured as follows. First, an active material, a binder, and a solvent are kneaded to prepare a slurry-like electrode mixture. This electrode mixture is applied to one or both sides of a metal foil, which is a current collector, using a transfer roll or the like, and the solvent is dried and removed to form a mixture layer. Then, the electrode is manufactured through a process of compression molding the mixture layer using a roll press or the like.

[0004] The binder used here is required to be excellent in characteristics such as adhesion between active materials and between the active material and the current collector, and electrochemical stability. Also, it is required to satisfy these characteristics with a smaller addition amount for increasing the capacity of the lithium-ion secondary battery. Further, from the viewpoint of reducing environmental load, it is preferably to use water as the solvent used for preparing the electrode mixture, and compatibility with an aqueous solvent is also one of the requirements for the binder.

[0005] As a binder used together with an aqueous solvent, Patent Document 1 discloses an aqueous dispersion of a copolymer containing a structural unit derived from (meth)acrylonitrile and a structural unit derived from a compound having two or more ethylenically unsaturated bonds. However, since the resin component is in a particulate state without being dissolved, the contact area with the active material is small, and there is a risk of a decrease in the battery capacity due to side reactions occurring on the surface of the active material.

[0006] As a binder in which a resin component is dissolved in an aqueous solvent, Patent Document 2 discloses a binder containing a copolymer having a structural unit containing a nitrile group and a structural unit containing an acidic functional group, and at least a part of the acidic functional group forming a salt.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Since the resin component is dissolved in the binder described in Patent Document 2, the contact area with the active material can be increased, and an effect of suppressing side reactions occurring on the surface of the active material can be expected. On the other hand, there is room for improvement in the dispersion stability of the electrode mixture prepared using this binder. When the dispersion stability of the electrode mixture is good, separation of components in the coating machine and the liquid feeding pipe can be suppressed, and a uniform electrode can be easily obtained. In addition, it is possible to suppress the deposition of solid components in the coating machine and the liquid feeding pipe and the occurrence of defects in the device.

[0009] In view of the above circumstances, an object of the present invention is to provide an electrode binder having excellent dispersion stability when preparing an electrode mixture. 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 Problems

[0010] Means for solving the above problems include the following embodiments. <1>A copolymer containing a structural unit containing an acidic functional group and a structural unit containing an alkyleneoxy group, wherein the proportion of the structural unit containing an alkyleneoxy group is 5% by mass or more of all the structural units, and a basic compound capable of forming a salt with the acidic functional group. An electrode binder containing the same. <2>The electrode binder according to <1>, wherein the proportion of the structural unit containing an alkyleneoxy group is 50% by mass or less of all the 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 is less than 50% by mass of all the structural units. <4>The electrode binder according to any one of <1> to <3>, wherein the number of alkyleneoxy structures contained in the alkyleneoxy group is 5 or more. <5>The electrode binder according to any one of <1> to <4>, further containing water and being in a state where the copolymer is dissolved in the water. <6>The electrode binder according to any one of <1> to <5>, wherein the acidic functional group contains at least one selected from the group consisting of a carboxy group, a sulfo group, and a phospho group. <7>The electrode binder according to any one of <1> to <6>, wherein the structural unit having the 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 contains a 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 containing the electrode binder according to any one of <1> to <9> and an active material. <11>The electrode binder according to <10>, wherein the active material contains a silicon-containing compound. <12>An electrode for an energy device, comprising a current collector and an electrode binder layer provided on at least one surface of the current collector and containing the electrode binder according to <10> or <11>. <13>An energy device comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode contains the electrode binder and the active material according to any one of <1> to <9>.

Advantages of the Invention

[0011] According to the present invention, there is provided an electrode binder excellent in dispersion stability when preparing an electrode binder. Further, according to the present invention, there are provided an electrode binder obtained by using this electrode binder, an electrode for an energy device, and an energy device.

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present invention. In this specification, the term "step" includes, in addition to steps independent of other steps, also those steps that cannot be clearly distinguished from other steps but whose purpose is achieved. In the numerical range indicated by "~" in this specification, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In this specification, the content ratio of each component in the composition means the total content ratio of the plurality of substances corresponding to each component in the composition, unless otherwise specified, when there are a plurality of substances corresponding to each component in the composition. In this specification, when there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component in the composition means a value for the mixture of the plurality of types of particles present in the composition, unless otherwise specified. In this specification, the terms "layer" or "film" include not only the case where they are formed over the entire region where the layer or film exists, but also the case where they are formed only in a part of the region when observing the region where the layer or film exists. In this specification, the term "lamination" indicates stacking layers, and two or more layers may be bonded, and two or more layers may be detachable. In this specification, "(meth)acryl" 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.

[0014] <Binder for electrode> The binder for an electrode of the present disclosure (hereinafter, also simply referred to as a binder) includes a structural unit containing an acidic functional group and a structural unit containing an alkyleneoxy group, and is a copolymer in which the proportion of the structural unit containing an alkyleneoxy group is 5% by mass or more of all the structural units, and a basic compound capable of forming a salt with the acidic functional group. It is preferable that the acidic functional group of the copolymer contained in the binder and the basic compound form a salt in the binder.

[0015] Since at least a part of the acidic functional groups of the copolymer contained in the binder of the present disclosure can form salts by neutralization reaction with basic compounds, it has excellent solubility in water. Therefore, the electrode can be manufactured without using an organic solvent to dissolve the copolymer, and it is excellent in terms of safety and environmental compatibility. In addition, since the binder of the present disclosure has a higher viscosity than the state in which the copolymer is dispersed in water, it is possible to omit the addition of a thickener such as carboxymethyl cellulose. Therefore, it is possible to avoid a decrease in adhesion, storage stability, etc. caused by the thickener.

[0016] Furthermore, as a result of the studies by the present inventors, it has been found that when the copolymer contains a structural unit containing an alkyleneoxy group at a specific ratio, the dispersion stability of the electrode mixture prepared using the binder is improved.

[0017] (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 ratio of the structural unit containing an alkyleneoxy group is 5% by mass or more of all the structural units.

[0018] From the viewpoint of the dispersion stability of the electrode mixture, the ratio of the structural unit containing an alkyleneoxy group is preferably 10% by mass or more, more preferably 15% by mass or more of all the structural units. From the viewpoint of the balance with other properties, the ratio of the structural unit 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 all the structural units. Regarding the measurement of the mass ratio of the structural unit containing an alkyleneoxy group, although not particularly limited, for example, it can be measured by 1H-NMR.

[0019] The ratio of the structural unit containing an alkyleneoxy group in the copolymer can be adjusted, for example, by the molecular weight of the monomer containing an alkyleneoxy group used in the synthesis of the copolymer, the amount of the monomer, etc. When the monomer used for the synthesis of the copolymer has both an alkyleneoxy group and an acidic functional group, the above ratio is calculated in a state where the structural unit derived from this monomer is also included in the "structural unit containing an alkyleneoxy group".

[0020] The number of alkyleneoxy structures contained in the alkyleneoxy group is preferably 5 or more, more preferably 9 or more. Increasing the content of the alkyleneoxy group in the copolymer on a molar basis may be difficult in synthesis. Therefore, by increasing the number of alkyleneoxy structures contained in the alkyleneoxy group, the content of the alkyleneoxy group in the copolymer on a mass basis can be easily increased. From the viewpoints of handleability 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, tetramethylene oxide, etc., and among them, ethylene oxide is preferable.

[0021] From the viewpoint of improving solubility in water, the ratio of the structural unit containing an acidic functional group 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 all the structural units. From the viewpoint of balance with other properties, the ratio of the structural unit containing an acidic functional group is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less of all the structural units.

[0022] The ratio of the structural unit containing an acidic functional group in the copolymer can be adjusted, for example, by the molecular weight of the monomer containing an acidic functional group used for the synthesis of the copolymer, the amount of the monomer, etc. When the monomer used for the synthesis of the copolymer has both an alkyleneoxy group and an acidic functional group, the above ratio is calculated in a state where the structural unit derived from this monomer is also included in the "structural unit containing an acidic functional group".

[0023] The total proportion of the structural unit containing an acidic functional group and the structural unit 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 the structural units.

[0024] Some or all of the acidic functional groups in the copolymer may form a salt with a basic compound. For example, 50 mol% or more, 80 mol% or more, or 90 mol% or more of the acidic functional groups in the copolymer may form a salt. The proportion of the acidic functional groups that form a salt can be adjusted by the amount of the basic compound reacted with the copolymer and the like.

[0025] From the viewpoint of suppressing swelling in the electrolyte, it is preferable that the copolymer does not contain a structural unit containing a nitrile group or the proportion of the structural unit containing a nitrile group is less than 50% by mass of all the structural units. More preferably, the copolymer does not contain a structural unit containing a nitrile group or the proportion of the structural unit containing a nitrile group is less than 30% by mass of all the structural units. Even more preferably, the proportion of the structural unit containing a nitrile group in all the structural units is less than 15% by mass.

[0026] 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. When 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 when 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 the polymerization initiator, the addition of a chain transfer agent, and the like.

[0027] In the present disclosure, the weight average molecular weight of the copolymer is a value measured as follows. Dissolve the measurement target in N-methyl-2-pyrrolidone, and remove the insoluble matter through a PTFE (polytetrafluoroethylene) filter [Kurashiki Boseki Co., Ltd., for HPLC (high performance liquid chromatography) pretreatment, chromatographic disk, model number: 13N, pore size: 0.45 μm]. Measure the weight average molecular weight using GPC [pump: L6200 Pump (Hitachi, Ltd.), detector: differential refractive index detector L3300 RI Monitor (Hitachi, Ltd.), column: TSKgel-G5000HXL and TSKgel-G2000HXL (2 columns in total) (both Tosoh Corporation) connected in series, column temperature: 30 °C, eluent: N-methyl-2-pyrrolidone, flow rate: 1.0 mL / min, standard substance: polystyrene].

[0028] The acid value of the copolymer is preferably 0 mgKOH / g to 70 mgKOH / g, more preferably 0 mgKOH / g to 20 mgKOH / g, and even more preferably 0 mgKOH / g to 5 mgKOH / g.

[0029] The acid value of the copolymer can be adjusted, for example, by the amount of monomers used in the synthesis of the copolymer, the ratio of acidic functional groups neutralized with basic compounds, etc.

[0030] In the present disclosure, the acid value of the copolymer is a value measured as follows. First, accurately weigh 1 g of the measurement target, then add 30 g of acetone to the measurement target to dissolve it. Next, add an appropriate amount of phenolphthalein, which is an indicator, to the solution of the measurement target, and titrate it with a 0.1N aqueous KOH solution. Then, calculate the acid value according to the following formula (A) from the titration result (where Vf represents the titration volume (mL) of phenolphthalein, Wp represents the mass (g) of the solution of the measurement target, and I represents the proportion (mass%) of the non-volatile matter in the solution of the measurement target). Acid value (mgKOH / g) = 10 × Vf × 56.1 / (Wp × I) (A) The non-volatile matter in the solution of the measurement target is calculated from the residue weight by measuring approximately 1 mL of the solution of the measurement target into an aluminum pan and drying it on a hot plate heated to 160 °C for 15 minutes.

[0031] 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, if necessary, other monomers. Hereinafter, examples of the monomers used in the synthesis of the copolymer are shown.

[0032] - Acidic functional group-containing monomer - Examples of the acidic functional group-containing monomer include compounds having an ethylenically unsaturated double bond and an acidic functional group, and compounds capable of introducing an acidic functional group into the side chain of the copolymer. Examples of the acidic functional group include a carboxy group, a sulfo group, a phospho group, etc., and among them, a carboxy group is preferable.

[0033] Examples of the monomer containing a carboxy group as the 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, vinylbenzoic acid, etc. Further, monomers containing a hydrocarbon group having 5 or less carbon atoms, preferably 3 or less carbon atoms, more preferably 2 or less carbon atoms (which may be a combination with an oxygen atom) and a carboxy group (for example, monomers represented by the following general formulas (V) and (VI)) are included.

[0034]

Chemical formula

[0035] In the formula, R5 is H or CH3. R6 is an alkylene group or an alkyleneoxy group having 1 to 5 carbon atoms, preferably an alkylene group or an alkyleneoxy group having 1 or 2 carbon atoms, more preferably a methylene group.

[0036]

Chemical formula

[0037] Here, R7 is H or CH3. R8 is an alkylene chain or an alkyleneoxy chain having 1 to 5 carbon atoms, preferably an alkylene group or an alkyleneoxy group having 1 or 2 carbon atoms, more preferably a methylene group.

[0038] Examples of the monomer containing a sulfo group as an acidic functional group include vinylbenzenesulfonic acid, (meth)allylsulfonic acid, (meth)allyloxybenzenesulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof (sodium salt, lithium salt, etc.).

[0039] Examples of the commercially available monomer containing a phospho group as an acidic functional group include acid phosphoxyethyl methacrylate (Uni-Chemical Co., Ltd., trade name: Phosmer M), acid phosphoxypolyoxyethylene glycol monomethacrylate (Uni-Chemical Co., Ltd., trade name: Phosmer PE), 3-chloro-2-acid phosphoxypropyl methacrylate (Uni-Chemical Co., Ltd., trade name: Phosmer CL), acid phosphoxypolyoxypropylene glycol monomethacrylate (Uni-Chemical Co., Ltd., trade name: Phosmer PP), etc.

[0040] Among these, a monomer containing a carboxy group as an acidic functional group is preferable, acrylic acid or methacrylic acid is more preferable, and acrylic acid is even more preferable.

[0041] (Monomer containing an alkyleneoxy group) Examples of the monomer containing an alkyleneoxy group include compounds having an ethylenically unsaturated double bond and an alkyleneoxy group, and compounds capable of introducing an alkyleneoxy group into the side chain of the copolymer. In addition, the structure in which the carbon atom adjacent to the oxygen atom in the ester bond of the monomer is bonded (-O-R in -C(=O)-O-C-R, where R represents a substituent) is not included in the "alkyleneoxy group".

[0042] Examples of the alkyleneoxy structure contained in the alkyleneoxy group include ethylene oxide, propylene oxide, tetramethylene oxide, etc., and among them, ethylene oxide is preferred. Examples of the alkyleneoxy group-containing monomer containing ethylene oxide include compounds represented by the following general formula (I).

[0043]

Chemical formula

[0044] 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 of 1 to 50, preferably an integer of 5 to 30, more preferably an integer of 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, an aromatic ring, a cycloalkane having 3 to 10 carbon atoms, etc. The alkyl group may be linear, branched, or cyclic.

[0045] Specific examples of the commercially available compounds represented by the general formula (I) include ethoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Acrylate EC-A), methoxytriethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Acrylate MTG-A, manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester AM-30G), methoxypoly(n = 9)ethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Acrylate 130-A, manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester AM-90G), methoxypoly(n = 13)ethylene glycol acrylate (trade name: NK Ester AM-130G), methoxypoly(n = 23)ethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester AM-230G), octoxypoly(n = 18)ethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester A-OC-18E), phenoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Acrylate P-200A, manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester AMP-20GY), phenoxypoly(n = 6)ethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester AMP-60G), nonylphenol EO adduct (n = 4) acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Acrylate NP-4EA), nonylphenol EO adduct (n = 8) acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Acrylate NP-8EA), methoxydiethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Ester MC,Manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester M-20G), methoxytriethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Ester MTG), methoxypoly(n=9)ethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Ester 130MA, manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester M-90G), methoxypoly(n=23)ethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., trade name: NK Ester M-230G), methoxypoly(n=30)ethylene glycol methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name: Light Ester 041MA), etc. can be mentioned.,

[0046] Among the alkyleneoxy group-containing monomers, those having 5 or more alkyleneoxy structures contained in the alkyleneoxy group are preferred, and those having 9 or more are more preferred. From the viewpoints of handleability and polymerizability, those having 50 or less alkyleneoxy structures contained in the alkyleneoxy group are preferred, those having 30 or less are more preferred, and those having 20 or less are even more preferred.

[0047] -Other monomers- The copolymer may be used with monomers other than the acidic group-containing monomer and the alkyleneoxy group-containing monomer (other monomers) as copolymerization components as necessary. Examples of other monomers include monomers containing a nitrile group (nitrile group-containing monomers), monomers containing an alkyl group (alkyl group-containing monomers), vinyl halides such as vinyl chloride, vinyl bromide, and vinylidene chloride, maleimide, phenylmaleimide, (meth)acrylamide, styrene, α-methylstyrene, vinyl acetate, etc. Other monomers may be used alone or in combination of two or more.

[0048] Examples of the nitrile group-containing monomer include compounds having an ethylenically unsaturated double bond and a nitrile group, and compounds capable of introducing a nitrile group into the side chain of the copolymer. For example, acrylic nitrile group-containing monomers such as acrylonitrile and methacrylonitrile, cyanide nitrile group-containing monomers such as α-cyanoacrylate and dicyanovinylidene, and fumaric nitrile group-containing monomers such as fumaronitrile can be mentioned.

[0049] Examples of the alkyl group-containing monomer include alkyl (meth)acrylic acid esters having an alkyl group with 1 to 60 carbon atoms. From the viewpoint of obtaining sufficient swelling resistance against the electrolytic solution, 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, an aromatic ring, and cycloalkanes having 3 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic.

[0050] Specific examples of the alkyl group-containing monomer 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, isobornyl (meth)acrylate, and the like.

[0051] -Basic Compound- 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.

[0052] Specific examples of the basic compound derived from a metal 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 hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, magnesium hydrogen carbonate, calcium hydrogen carbonate, barium hydrogen carbonate, etc., and metal alcoholates such as lithium methoxide, sodium methoxide, lithium tert-butoxide, potassium tert-butoxide, etc.

[0053] Examples of the basic compound not derived from a metal include ammonia, amine compounds, pyridine compounds, azole compounds, etc.

[0054] The amine compound preferably has 1 to 50 carbon atoms, more preferably 3 to 25 carbon atoms. Also, a tertiary amine compound is preferred. Specific examples of the amine compound include the following compounds. Ph represents a phenyl group.

[0055]

Chemical formula

[0056] The pyridine compound preferably has 5 to 20 carbon atoms, more preferably 5 to 10 carbon atoms. For example, pyridine derivatives such as pyridine and picoline can be mentioned. The azole compound preferably has 2 to 20 carbon atoms, more preferably 2 to 10 carbon atoms. For example, triazole and its derivatives can be mentioned. Specific examples of the pyridine compound and the azole compound include the following compounds.

[0057] [Chemical formula]

[0058] -Synthesis method of copolymer- The method for synthesizing the copolymer is not particularly limited. Polymerization methods such as precipitation polymerization in water, bulk polymerization, suspension polymerization, emulsion polymerization, and solution polymerization can be applied. In terms of ease of resin synthesis, ease of post-treatment such as recovery and purification, precipitation polymerization in water and emulsion polymerization are preferred, and precipitation polymerization in water is more preferred.

[0059] As the polymerization initiator used when 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 redox-type polymerization initiators obtained by combining oxidizing agents such as persulfates with reducing agents such as sodium bisulfite, ammonium bisulfite, sodium thiosulfate, and hydrosulfite and polymerization accelerators such as sulfuric acid, iron sulfate, and copper sulfate. Among these, persulfates (more preferably ammonium persulfate) and water-soluble azo compounds are preferred in terms of ease of resin synthesis and the like. The polymerization initiator is preferably used in the range of, for example, 0.001 mol% to 5 mol% with respect to the total amount of the monomers used in the synthesis of the copolymer, and more preferably in the range of 0.01 mol% to 2 mol%.

[0060] When synthesizing the copolymer, a chain transfer agent may be used for purposes such as molecular weight regulation. Examples of the chain transfer agent include mercaptan compounds such as thioglycol, carbon tetrachloride, α-methylstyrene dimer, and the like. Among these, α-methylstyrene dimer is preferred in terms of having less odor and the like.

[0061] When synthesizing the copolymer, a solvent may be used. Examples of the solvent include water and organic solvents. When synthesizing the copolymer by precipitation polymerization in water, water and an organic solvent may be used in combination for purposes such as adjusting the particle diameter of the precipitated copolymer. Examples of solvents other than water include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide; ureas such as N,N-dimethylethyleneurea, N,N-dimethylpropyleneurea, tetramethylurea; lactones such as γ-butyrolactone, γ-caprolactone; carbonates such as propylene carbonate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; esters such as methyl acetate, ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, ethyl cellosolve acetate, ethyl carbitol acetate; glymes such as diglyme, triglyme, tetraglyme; hydrocarbons such as toluene, xylene, cyclohexane; sulfoxides such as dimethyl sulfoxide; sulfones such as sulfolane; alcohols such as methanol, isopropanol, n-butanol, and the like. These solvents may be used alone or in combination of two or more.

[0062] The synthesis conditions of the copolymer are not particularly limited. For example, the monomer is introduced into a solvent, and the polymerization temperature is preferably 0°C to 100°C, more preferably 30°C to 90°C, and is preferably maintained for 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 promoted. Also, if the polymerization temperature is 100°C or lower, even when water is used as the solvent, water is less likely to evaporate and prevent the polymerization.

[0063] By reacting the acidic functional groups of the synthesized copolymer with a basic compound, at least a part of the acidic functional groups can be in a state of forming a salt.

[0064] 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 ratio of acidic functional groups to be reacted with the base, etc.

[0065] The amount of the basic compound is preferably, for example, 0.01 molar equivalent to 1.5 molar equivalents, more preferably 0.3 molar equivalent to 1.1 molar equivalents, and even more preferably 0.5 molar equivalent to 1.0 molar equivalent based on the acidic functional groups contained in the copolymer.

[0066] -Use of the binder- The binder of the present disclosure is suitably used as a material for an electrode (particularly, a binder for an active material) of an energy device, particularly an energy device using a non-aqueous electrolyte system. The non-aqueous electrolyte system energy device refers to a power storage or power generation device (apparatus) using an electrolyte other than water. Examples of the energy device include a lithium ion secondary battery, an electric double layer capacitor, a solar cell, a fuel cell, etc. Among them, it is suitably used as a material for an electrode containing a compound containing silicon, which has a large expansion and contraction due to charge and discharge, as an active material.

[0067] <Electrode binder> The electrode binder of the present disclosure contains the above-mentioned binder and an active material. The type of the active material contained in the electrode binder is not particularly limited and can be selected from those generally used as materials for electrodes of energy devices. Since the binder contained in the electrode binder of the present disclosure has excellent coating properties for the active material, an electrode excellent in cycle characteristics can be formed even when the active material has a large expansion and contraction accompanying charge and discharge.

[0068] The active material contained in the electrode mixture may contain a silicon-containing compound. When a silicon-containing compound is used as the active material (negative electrode active material) for the negative electrode of an energy device, a higher capacity can be achieved compared to negative electrode active materials such as graphite. On the other hand, it has the property that the active material is likely to deteriorate due to large expansion and contraction accompanying charge and discharge, and it is difficult to maintain good cycle characteristics. Since the binder of the present disclosure is excellent in the coating property of the active material, even if the active material contains silicon, it is difficult to deteriorate, and good cycle characteristics are likely to be maintained.

[0069] Examples of the silicon-containing compound include silicon oxides, and examples of the silicon oxides include silicon monoxide, silicon dioxide, silicon suboxide, etc. These may be used alone or in combination of two or more.

[0070] Silicon monoxide can be obtained, for example, by a known sublimation method in which a gas of silicon monoxide generated by heating a mixture of silicon dioxide and metallic silicon is cooled and deposited. Also, it can be obtained from the market as silicon oxide, silicon monoxide, etc.

[0071] The silicon oxide may have a structure in which silicon crystallites are dispersed in the silicon oxide (preferably, a structure in which silicon crystallites are dispersed in silicon dioxide). When silicon crystallites are present in the silicon oxide, it is easy to obtain a higher initial discharge capacity and good initial charge-discharge efficiency.

[0072] When the silicon oxide is in a particulate form, 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.

[0073] In the present disclosure, the average particle size of the active material is the value (median diameter (D50)) when the cumulative from the small diameter side becomes 50% in the volume-based particle size distribution measured by a laser diffraction particle size distribution measuring device (for example, Shimadzu Corporation, SALD-3000J) in which the sample is dispersed in purified water containing a surfactant. The BET specific surface area can be measured from the nitrogen adsorption capacity, for example, in accordance with JIS Z 8830:2013. As an evaluation apparatus, for example, AUTOSORB-1 (trade name) manufactured by QUANTACHROME can be used. Since it is considered that the moisture adsorbed on the sample surface and in the structure affects 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 into which 0.05 g of the measurement sample is introduced is depressurized to 10 Pa or less with a vacuum pump, then heated at 110 °C, held for 3 hours or more, and then naturally cooled to room temperature (25 °C) while maintaining the depressurized state. After performing this pretreatment, the evaluation temperature is set to 77 K, and the measurement is performed with the evaluation pressure range being less than 1 in terms of relative pressure (equilibrium pressure with respect to the saturated vapor pressure).

[0074] The silicon oxide particles can be produced, for example, by pulverizing and classifying massive silicon oxide. Specifically, first, primary pulverization and classification are performed to pulverize the massive silicon oxide to a size that can be introduced into a fine pulverizer, and then the pulverized material is secondarily pulverized (classified) by a fine pulverizer. This method is preferable.

[0075] The electrode binder of the present disclosure may contain a silicon-containing compound as an active material and another active material. The other active material may be selected, for example, from those commonly used as the negative electrode active material of a lithium-ion secondary battery. Specifically, carbon materials, metallic lithium, lithium alloys, intermetallic compounds, metal complexes, organic polymer compounds, etc. can be mentioned. Among these, carbon materials are preferable. Examples of the carbon materials include graphite such as natural graphite (scaly graphite, etc.) and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, thermal black, lamp black, and carbon fibers.

[0076] Among the carbon materials, from the viewpoint of improving the characteristics of the energy device, a carbon material (graphite) in which the distance (d 002 ) between the carbon hexagonal planes in the wide-angle X-ray diffraction method is 3.35 Å to 3.40 Å and the crystallite (Lc) in the c-axis direction is 100 Å or more is preferable. On the other hand, from the viewpoint of improving the cycle characteristics and safety of the energy device, a carbon material (amorphous carbon) in which the distance (d 002 ) between the carbon hexagonal planes in the wide-angle X-ray diffraction method is 3.50 Å to 3.95 Å is preferable. The average particle diameter of the carbon material is preferably 0.1 μm to 60 μm, and more preferably 0.5 μm to 30 μm. Further, the BET specific surface area of the carbon material is 1 m 2 / g to 10 m 2 / g is preferable.

[0077] Since the binder contained in the electrode binder of the present disclosure is excellent in compatibility with an aqueous solvent, it is suitable as an electrode binder for a negative electrode in which a manufacturing method using an aqueous solvent is adopted, but it may also be an electrode binder for a positive electrode.

[0078] When the electrode binder 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 the positive electrode active material of a lithium ion secondary battery. Specifically, lithium-containing metal composite oxides, olivine-type lithium salts, chalcogen compounds, manganese dioxide, and the like can be mentioned. 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 substituted with 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, etc., and among them, Mn, Al, Co, Ni, Mg, etc. are preferable. The different elements may be used alone or in combination of two or more.

[0079] The average particle diameter of the positive electrode active material is preferably 0.1 μm to 60 μm, and more preferably 0.5 μm to 30 μm. Further, the BET specific surface area of the positive electrode active material is 1 m 2 / g to 10 m 2 / g is preferable.

[0080] When the electrode mixture contains a silicon-containing compound as an active material and other active materials, 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.

[0081] The ratio of the binder to the active material contained in the electrode mixture is not particularly limited. For example, the mass ratio (A:B) of the binder A to the active material B may be 20:80 to 0.1:99.9.

[0082] The electrode mixture may contain a liquid medium. In particular, from the viewpoint of workability, it is preferable to contain a liquid medium when using the binder (when mixing with the active material). Water is preferable as the liquid medium contained in the electrode mixture, but an organic solvent may be contained together with water as necessary.

[0083] The viscosity of the electrode mixture during use is preferably, for example, 500 mPa·s to 50000 mPa·s at 25°C, more preferably 1000 mPa·s to 20000 mPa·s, and even more preferably 2000 mPa·s to 10000 mPa·s. The viscosity is measured using a rotational shear viscometer at 25°C and a shear rate of 1.0 s -1 and measured.

[0084] The electrode mixture may contain components other than the binder, active material, and liquid medium as necessary. For example, a cross-linking component for complementing the swelling resistance to the electrolyte, a rubber component for complementing the flexibility and ductility of the electrode, a thickening agent for improving the coating property of the electrode mixture, various additives such as an anti-settling agent, an anti-foaming agent, and a leveling agent may be contained. 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.

[0085] <Electrode for Energy Device> The electrode for an energy device of the present disclosure has a current collector and an electrode mixture layer provided on at least one surface of the current collector and containing the above-described electrode mixture. The electrode for an energy device of the present disclosure can be used as an electrode for a lithium-ion secondary battery, an electric double layer capacitor, a solar cell, a fuel cell, or the like. Hereinafter, the case where the electrode for an energy device of the present disclosure is applied to an electrode of a lithium-ion secondary battery will be described in detail, but the electrode for an energy device of the present disclosure is not limited to the following content.

[0086] The type of the current collector is not particularly limited. For example, it 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 for the negative electrode of a lithium-ion secondary battery include sheets and foils containing stainless steel, nickel, copper, etc. Among these, a sheet or foil containing copper is preferable. The thickness of the sheet and the foil is not particularly limited, and from the viewpoint of ensuring the strength and workability required for the current collector, for example, it is preferably 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 for the positive electrode of a lithium-ion secondary battery include sheets and foils containing stainless steel, aluminum, titanium, etc. Among these, a sheet or foil containing aluminum is preferable. The thickness of the sheet and the foil is not particularly limited, and from the viewpoint of ensuring the strength and workability required for the current collector, for example, it is preferably 1 μm to 500 μm, more preferably 2 μm to 80 μm, and even more preferably 5 μm to 50 μm.

[0087] The electrode binder layer can be formed using the above-described electrode binder. Specifically, for example, a slurry-like electrode binder can be applied onto at least one surface of the current collector, and then the solvent is dried and removed, and if necessary, it can be formed by rolling. The application of the slurry-like electrode binder can be performed using, for example, a comma coater or the like. The application is preferably carried out such that the ratio of the negative electrode capacity to the positive electrode capacity (negative electrode capacity / positive electrode capacity) is 1 or more in the opposing electrodes. The application amount of the slurry-like electrode binder is, for example, such that the dry mass per side of the electrode binder layer is 5 g / m 2 ~500 g / m 2 and preferably 50 g / m 2 ~300 g / m 2 . The removal of the solvent is carried out, for example, by drying at 50°C to 150°C, preferably 80°C to 120°C, for 1 minute to 20 minutes, preferably 3 minutes to 10 minutes. Rolling is carried out using, for example, a roll press machine, and the density of the binder layer is, for example, 1 g / cm 3 ~2 g / cm 3 for the negative electrode binder layer, preferably 1.2 g / cm 3 ~1.8 g / cm 3 and for the positive electrode binder layer, for example, 2 g / cm 3 ~5 g / cm 3 and is preferably pressed to be 2 g / cm 3 ~4 g / cm 3 . Furthermore, for the removal of residual solvents and adsorbed water in the electrode, etc., vacuum drying may be carried out at 100°C to 150°C for 1 to 20 hours.

[0088] <Energy Device> 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 binder and the active material described above. Since at least one of the positive and negative electrodes of the electrode for an energy device of the present disclosure contains the binder and the active material described above, even when a material with large expansion and contraction is included as the active material, the cycle characteristics are excellent.

[0089] In one embodiment, the energy device includes at least a negative electrode containing the binder and the active material described above. In another embodiment, the energy device includes at least a negative electrode containing the binder and the active material described above, and contains a compound containing silicon as the active material.

[0090] Examples of the energy device of the present disclosure include lithium ion secondary batteries, electric double layer capacitors, solar cells, fuel cells, etc. Hereinafter, the case where the energy device is a lithium ion secondary battery will be described in detail, but the energy device of the present disclosure is not limited to the following content.

[0091] The lithium ion secondary battery includes, for example, a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolytic solution. For details of the positive electrode and the negative electrode, reference can be made to those described in the electrode for an energy device described above.

[0092] The separator is not particularly limited as long as it has ion permeability while electronically insulating between the positive electrode and the negative electrode, and has resistance to oxidizing properties on the positive electrode side and reducing properties on the negative electrode side. As materials (materials) of such a separator satisfying such characteristics, resins, inorganic substances, etc. are used.

[0093] Examples of the above resin include olefin polymers, fluorine polymers, cellulose polymers, polyimides, nylons, etc. Specifically, it is preferably selected from materials that are stable to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use porous sheets, non-woven fabrics, etc. made of polyolefins such as polyethylene and polypropylene as raw materials.

[0094] Examples of the inorganic substance 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, a separator can be used which is obtained by attaching the above inorganic substance in a fibrous shape or a particle shape to a thin film-shaped substrate such as a non-woven fabric, a woven fabric, or a microporous film. As the base material in the form of a thin film, those with a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm are preferably used. Further, for example, a composite porous layer formed by using the above-mentioned inorganic substance in the form of fibers or particles and a binder such as a resin can be used as a separator. Furthermore, this composite porous layer can be formed on the surface of the positive electrode or the negative electrode and used as a separator. Alternatively, this composite porous layer can be formed on the surface of another separator to form a multilayer separator. For example, a composite porous layer in which alumina particles with a 90% particle diameter (D90) of less than 1 μm are bound using a fluororesin as a binder may be formed on the surface of the positive electrode.

[0095] The electrolytic solution contains a solute (supporting salt) and a non-aqueous solvent, and further contains various additives as required. The solute is usually in a dissolved state in the non-aqueous solvent. The electrolytic solution is impregnated into the separator, for example.

[0096] As the solute, those commonly used in this field can be used. Specifically, LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, LiB 10 Cl 10, lithium salts of lower aliphatic carboxylic acids, LiCl, LiBr, LiI, lithium chloroborane, borate salts, imide salts, etc. can be mentioned. Examples of borate salts include lithium bis(1,2-benzenediolate(2-)-O,O’), lithium bis(2,3-naphthalenediolate(2-)-O,O’), lithium bis(2,2’-biphenyldiolate(2-)-O,O’), lithium bis(5-fluoro-2-olate-1-benzenesulfonate-O,O’), etc. Examples of imide salts include lithium bis(trifluoromethanesulfonyl)imide ((CF3SO2)2NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonylimide ((CF3SO2)(C4F9SO2)NLi), lithium bis(pentafluoroethanesulfonyl)imide ((C2F5SO2)2NLi), etc. The solute may be used alone or in combination of two or more. The dissolution amount of the solute in the non-aqueous solvent is preferably 0.5 mol / L to 2 mol / L.

[0097] As the non-aqueous solvent, those commonly used in this field can be used. Specifically, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, etc. can be mentioned. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), etc. Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. The non-aqueous solvent may be used alone or in combination of two or more.

[0098] Also, from the viewpoint of further improving battery characteristics, the non-aqueous solvent preferably 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, more preferably 0.2% by mass to 1.5% by mass, based on the total amount of the non-aqueous solvent.

[0099] As an example of the configuration of a lithium-ion secondary battery, the configuration of a laminated lithium-ion secondary battery will be described below. A laminated lithium-ion secondary battery can be manufactured, for example, as follows. First, the positive electrode and the negative electrode are cut into rectangular shapes, and tabs are welded to the respective electrodes to produce a positive electrode terminal and a negative electrode terminal. An electrode laminate is produced by interposing a separator between the positive electrode and the negative electrode and laminating them. In this state, the electrode 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 electrolytic solution is poured into the aluminum laminate pack, and the opening of the aluminum laminate pack is sealed. Thereby, a lithium-ion secondary battery is obtained.

[0100] 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 bottomed cylindrical battery container 6 made of steel with nickel plating. The battery container 6 houses an electrode group 5 in which a strip-shaped positive electrode plate 2 and a negative electrode plate 3 are wound in a cross-sectional spiral shape with a separator 4 interposed therebetween. The separator 4 is set, for example, to have a width of 58 mm and a thickness of 30 μm. An aluminum ribbon-shaped positive electrode tab terminal with one end fixed 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 above the electrode group 5 and joined to the lower surface of a disk-shaped battery lid serving as a positive electrode external terminal by ultrasonic welding. On the other hand, a copper ribbon-shaped negative electrode tab terminal with one end fixed 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 led out to opposite sides of both end faces of the electrode group 5, respectively. Note that an insulating coating (not shown) is provided on the entire outer peripheral surface of the electrode group 5. The battery lid is caulked and fixed to the upper part of the battery container 6 via an insulating resin gasket. For this reason, the inside of the lithium-ion secondary battery 1 is sealed. Further, an electrolytic solution (not shown) is poured into the battery container 6.

Example

[0101] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0102] (Example 1) (Synthesis of copolymer A) Into a 0.5-liter separable flask equipped with a stirrer, a thermometer and a condenser, 25.5 g of purified water (manufactured by Fujifilm Wako Pure Chemical Corporation), 88.47 mL of 4N lithium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Corporation), and 25.5 g of acrylic acid (manufactured by Fujifilm Wako Pure Chemical Corporation) were added and stirred at 200 revolutions per minute for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by Fujifilm Wako Pure Chemical Corporation) and 1.5 g of methoxypolyethylene glycol acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., AM-90G) in which R1 is a hydrogen atom, R2 is methyl, and n is 9 in the general formula (I) were added to the system, the system was purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by Fujifilm Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer A. The obtained aqueous solution containing copolymer A was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.8%.

[0103] (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 Corporation), 83.26 mL of 4N lithium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Corporation), and 24.0 g of acrylic acid (manufactured by Fujifilm Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by Fujifilm Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by Fujifilm Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer B. The obtained aqueous solution containing copolymer B was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.7%.

[0104] (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 Corporation), 72.86 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 21.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer C. The obtained aqueous solution containing copolymer C was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 100.1%.

[0105] (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 Corporation), 78.06 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 22.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system had reached 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system had reached 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer D. The obtained aqueous solution containing copolymer D was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.6%.

[0106] (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 Corporation), 72.86 mL of 4N lithium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Corporation), and 21.0 g of acrylic acid (manufactured by Fujifilm Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by Fujifilm Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0°C. After confirming that the temperature inside the system was 65.0°C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by Fujifilm Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0°C. After confirming that the temperature inside the system was 90.0°C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer E. The obtained aqueous solution containing copolymer E was dried in a forced-air dryer set at 150°C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.9%.

[0107] (Example 6) (Synthesis of copolymer F) Into 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 Corporation), 62.45 mL of 4N lithium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Corporation), and 18.0 g of acrylic acid (manufactured by Fujifilm Wako Pure Chemical Corporation) were added and stirred at 200 revolutions per minute for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by Fujifilm Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by Fujifilm Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer F. The obtained aqueous solution containing copolymer F was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.7%.

[0108] (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 Corporation), 72.86 mL of a 4N aqueous lithium hydroxide solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 21.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system had reached 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system had reached 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer G. The obtained aqueous solution containing copolymer G was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.6%.

[0109] (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 Corporation), 67.65 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 19.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Then, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer H. The obtained aqueous solution containing copolymer H was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.7%.

[0110] (Example 9) (Synthesis of Copolymer I) Into 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 Corporation), 57.24 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 16.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer I. The obtained aqueous solution containing copolymer I was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.5%.

[0111] (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 Corporation), 57.24 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 16.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Then, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer J. The obtained aqueous solution containing copolymer J was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.9%.

[0112] (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 Corporation), 52.04 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 15.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system had reached 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system had reached 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer K. The obtained aqueous solution containing copolymer K was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.7%.

[0113] (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 Corporation), 41.63 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 12.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) 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 purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system had reached 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system had reached 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer L. The obtained aqueous solution containing copolymer L was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 100.0%.

[0114] (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 Corporation), 93.67 mL of 4N lithium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Corporation), and 27.0 g of acrylic acid (manufactured by Fujifilm Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 3.0 g of acrylonitrile (manufactured by Fujifilm Wako Pure Chemical Corporation) was added to the system, the system was purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system had reached 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by Fujifilm Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system had reached 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer M. The obtained aqueous solution containing copolymer M was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 100.0%.

[0115] (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 Corporation), 83.26 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 24.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 6.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) was added to the system, the system was purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system had reached 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Then, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system had reached 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer N. The obtained aqueous solution containing copolymer N was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.6%.

[0116] (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 Corporation), 78.06 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 22.5 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 7.5 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) was added to the system, the system was purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), which is a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, which is a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer O. The obtained aqueous solution containing copolymer O was dried in a forced-air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.7%.

[0117] (Comparative Example 4) (Synthesis of Copolymer P) Into 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 Corporation), 62.45 mL of 4N lithium hydroxide aqueous solution (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 18.0 g of acrylic acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) were added, and the mixture was stirred at 200 revolutions per minute for 1 hour. Next, 12.0 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation) was added to the system, the system was purged with nitrogen, and the temperature was raised to 65.0 °C. After confirming that the temperature inside the system was 65.0 °C, a solution prepared by dissolving 0.15 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 5 hours. Then, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, a solution prepared by dissolving 0.03 g of ammonium persulfate, a polymerization initiator, in 2.0 g of purified water was added to the system, and the mixture was stirred at 200 revolutions per minute for 2 hours to synthesize an aqueous solution containing copolymer P. The obtained aqueous solution containing copolymer P was dried in a hot air dryer set at 150 °C for 1 hour. As a result of calculating the polymerization rate from the non-volatile content concentration after drying, it was 99.8%.

[0118] (Reference Example 1) After adding 98.0 g of purified water to a 1-L covered plastic container (manufactured by AS ONE Corporation, I-BOY), 2.0 g of sodium carboxymethyl cellulose (manufactured by Daicel Finechem Ltd., CMC#2200, hereinafter sometimes referred to as CMC) was added and stirred to obtain an aqueous solution of CMC. Into a 0.5-liter separable flask equipped with a stirrer, a thermometer, a cooling tube, and a liquid delivery pump, 335.0 g of purified water (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 21.46 g of a 2.0 mass% aqueous solution of sodium carboxymethyl cellulose (manufactured by Daicel Finechem Ltd., CMC#2200) as an emulsifier were added. The system was purged with nitrogen and heated to 60.0 °C. After confirming that the temperature inside the system was 60.0 °C, a solution prepared by dissolving 0.26 g of ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation), a polymerization initiator, in 8.0 g of purified water was added to the system. Immediately after adding ammonium persulfate, while stirring the system at 250 revolutions per minute, a mixture of 16.98 g of acrylonitrile (manufactured by FUJIFILM Wako Pure Chemical Corporation), 68.26 g of butyl methacrylate (manufactured by FUJIFILM Wako Pure Chemical Corporation), and 0.34 g of ethoxylated pentaerythritol tetraacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., ATM-4E) was dropped into the system over 2 hours using a liquid delivery pump. After dropping the entire amount of the mixture, stirring was continued for 4 hours. Next, the temperature inside the system was raised to 90.0 °C. After confirming that the temperature inside the system was 90.0 °C, stirring was carried out at 250 revolutions per minute for 2 hours to obtain a dispersion of acrylic fine particles.

[0119] <Preparation of Electrode Paste> 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 mass% (graphite): 4.85 mass% (SiO): 3.0 mass% (copolymer). Further, purified water was added for viscosity adjustment to obtain a slurry-like electrode paste. The purified water was added in an amount such that the viscosity measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., VISCOMETER TPE-100) under the conditions of 25.0 °C and 0.5 revolutions per minute was 7500 to 10000 mPa·s. For Reference Example 1, graphite and SiO, which are negative electrode active materials, an aqueous CMC solution, and the acrylic fine particles synthesized in Reference Example 1 were mixed so that the solid content ratio was 92.15 mass%: 4.85 mass%: 1.5 mass%: 1.5 mass%.

[0120] <Evaluation of Dispersion Stability of Electrode Paste> After adding 20.0 g of the prepared electrode binder to a 50-ml capped plastic container (manufactured by AS ONE Corporation, I-BOY), it was allowed to stand for 72 hours in an environment at 25.0°C. Thereafter, the appearance was observed, and the dispersion stability of the electrode binder was evaluated according to the following criteria. In the following criteria, it is shown that A is the most excellent in the dispersion stability of the electrode binder, and D is the most inferior. The results are shown in Tables 1 to 3. AA in the table represents acrylic acid, AN represents acrylonitrile, and AM-90G represents methoxypolyethylene glycol acrylate, respectively.

[0121] Judgment criteria for the dispersion stability of the electrode binder A: No separation visually, or less than 1 mm B: Visual separation is 1 mm or more and less than 5 mm C: Visual separation is 5 mm or more and less than 10 mm D: Visual separation is 10 mm or more

[0122]

Table 1

[0123]

Table 2

[0124]

Table 3

[0125] From the results shown in Tables 1 to 3, it can be seen that Examples 1 to 12 using a copolymer containing a structural unit derived from a monomer containing an alkyleneoxy group are excellent in the dispersion stability of the electrode binder, while Comparative Examples 1 to 4 using a copolymer not containing a structural unit derived from a monomer containing an alkyleneoxy group have low dispersion stability of the electrode binder. From this result, it is suggested that a copolymer containing a structural unit derived from an acidic functional group-containing monomer and a structural unit derived from a monomer containing an alkyleneoxy group becomes a binder excellent in the dispersion stability of the electrode binder.

[0126] (Example 13) <Fabrication of Negative Electrode> The electrode mixture prepared in Example 1 was uniformly and homogeneously applied to one side of a Cu foil (current collector) with a thickness of 10 μm such that the coating amount after drying was 78.0 g / m 2 Thereafter, a drying treatment was performed, and rolling was carried out by pressing so that the density became 1.6 g / cm 3 to obtain a negative electrode.

[0127] <Fabrication of Positive Electrode Slurry> Lithium nickel cobalt manganese oxide (NMC) as a positive electrode active material, carbon black (manufactured by Denka Co., Ltd., Li400) as a conductive agent, and polyvinylidene fluoride as a binder for the positive electrode were mixed so that the ratio of the solid content was 92.00% by mass: 4.00% by mass: 4.0% by mass. Further, NMP was added for viscosity adjustment to obtain a positive electrode slurry. The amount of NMP added was such that the viscosity measured using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., VISCOMETER TPE-100) under the conditions of 25.0 °C and 0.5 rotation / min was 7500 mPa·s to 10000 mPa·s.

[0128] <Fabrication of Positive Electrode> The prepared positive electrode slurry was uniformly and homogeneously applied to one side of an Al foil (current collector) with a thickness of 15 μm such that the coating amount after drying was 200.0 g / m 2 Thereafter, a drying treatment was performed, and rolling was carried out by pressing so that the density became 2.8 g / cm 3 to obtain a positive electrode.

[0129] <Fabrication of Laminate-Type Cell> After cutting the fabricated negative electrode into a rectangle with a length of 4.6 cm and a width of 6.2 cm, a Ni wire for current collection was welded. After cutting the fabricated positive electrode into a rectangle with a length of 4.5 cm and a width of 6.0 cm, an Al wire for current collection was welded. After overlapping the negative electrode and the positive electrode so that the coating surfaces faced each other through a separator, they were placed in a laminate on the bag, 1000 μL of electrolyte was injected, vacuum sealed, and a laminate-type cell was obtained. A polyethylene microporous sheet was used as the separator, and as the electrolyte, a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 1 / 1 / 1 (volume ratio) containing 1.0 M of LiPF6 with 1.0 mass% of vinylene carbonate and 1.0 mass% of fluoroethylene carbonate added to the total amount of the mixed solution was used.

[0130] (Examples 14 to 24, Reference Example 2) A laminate-type cell was fabricated in the same manner as in Example 13, except that the electrode binders prepared in Examples 2 to 12 and Reference Example 1 were used respectively.

[0131] <Evaluation of the initial efficiency and initial discharge capacity of the laminate-type cell> The fabricated laminate-type cell was placed in a thermostat at 25.0 °C and connected to a charge-discharge device (manufactured by Toyo System Co., Ltd., TOSCAT-3200). After constant-current charging to 4.2 V at a constant current of 0.10 CA, constant-voltage charging was performed at 4.2 V until the current value reached 0.01 CA, and the charging capacity was measured. Next, constant-current discharging was performed at a current value of 0.10 CA 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 / Charging capacity (mAh)

[0132] The obtained initial efficiency and initial discharge capacity were evaluated according to the following criteria. It was judged that A was the most excellent and D was the most inferior both in terms of the initial efficiency and the initial discharge capacity. The results are shown in Tables 4 and 5.

[0133] Judgment criteria for the initial efficiency A: The initial efficiency is 88.5% or more B: The 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%

[0134] Judgment criteria for initial discharge capacity A: Discharge capacity is 83.2 mAh or more B: Discharge capacity is 82.7 mAh or more and less than 83.2 mAh C: Discharge capacity is 82.3 mAh or more and less than 82.7 mAh D: Discharge capacity is less than 82.7 mAh

[0135] <Evaluation of cycle characteristics> The laminated cell for which the initial efficiency and initial discharge capacity were measured was placed in a thermostat at 25.0°C and connected to a charge-discharge device (manufactured by Toyo System Co., Ltd., TOSCAT-3200). After constant current charging up to 4.2 V at a constant current of 0.10 CA, constant voltage charging was performed until the current value reached 0.01 CA at 4.2 V. Next, constant current discharge was performed at a current value of 0.10 CA until 2.7 V. This charge-discharge was repeated twice. Next, the laminated cell was placed in a thermostat at 50.0°C and connected to a charge-discharge device (manufactured by Toyo System Co., Ltd., TOSCAT-3200). After constant current charging up to 4.2 V at a constant current of 0.10 CA, constant voltage charging was performed until the current value reached 0.01 CA at 4.2 V. Next, constant current discharge was performed at a current value of 0.10 CA until 2.7 V. Next, the laminated cell was placed in a thermostat at 25.0°C and connected to a charge-discharge device (manufactured by Toyo System Co., Ltd., TOSCAT-3200). After constant current charging up to 4.2 V at a constant current of 0.50 CA, constant voltage charging was performed until the current value reached 0.01 CA at 4.2 V. Next, constant current discharge was performed at a current value of 1.00 CA until 2.7 V. This charge-discharge was continued 100 times, and using the discharge capacity at the 100th time, the cycle characteristics were evaluated according to the following criteria. Note that for cycle characteristics, A is the best and D is the worst. The results are shown in Tables 4 and 5.

[0136] Judgment criteria for cycle characteristics A: 75.0 mAh or more B: 74.0 mAh or more and less than 75.0 mAh C: 73.0 mAh or more and less than 74.0 mAh D: Less than 73.0 mAh

[0137]

Table 4

[0138]

Table 5

[0139] From the above results, it is suggested that the binder of the present disclosure corresponding to the examples is excellent in the dispersion stability of the electrode binder, and can improve the initial efficiency, initial discharge efficiency, and cycle characteristics of the energy device.

[0140] The disclosure of Japanese Patent Application No. 2020-34789 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

Claim 1: A binder for an electrode, comprising a structural unit derived from acrylic acid or methacrylic acid, a structural unit derived from acrylonitrile or methacrylonitrile, and a structural unit derived from a compound represented by the following general formula (I), wherein the proportion of the structural unit derived from acrylic acid or methacrylic acid is 40% to 85% by mass of all the structural units, the proportion of the structural unit derived from acrylonitrile or methacrylonitrile is 10% to 40% by mass of all the structural units, and the proportion of the structural unit derived from the compound represented by the general formula (I) is 5% to 20% by mass of all the structural units, and a basic compound capable of forming a salt with a carboxy group. In the formula, R1 is H or CH3, R2 is H, an alkyl group having 1 to 12 carbon atoms, or a phenyl group, and n is an integer of 1 to 50. Claim 2 The binder for an electrode according to claim 1, further comprising water and being in a state where the copolymer is dissolved in the water. Claim 3 The binder for an electrode according to claim 1 or 2, wherein the basic compound contains a 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. Claim 4 The binder for an electrode according to any one of claims 1 to 3, for forming an electrode containing a silicon-containing compound as an active material. Claim 5 An electrode mixture, comprising the binder for an electrode according to any one of claims 1 to 4 and an active material. Claim 6 The electrode mixture according to claim 5, wherein the active material contains a silicon-containing compound. Claim 7 An electrode for an energy device, having a current collector and an electrode mixture layer provided on at least one surface of the current collector and containing the electrode mixture according to claim 5 or 6. Claim 8 An energy device, comprising a positive electrode and a negative electrode, wherein at least one of the positive electrode and the negative electrode contains the binder for an electrode according to any one of claims 1 to 4 and an active material.

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