Binder suitable for a storage device electrode, binder solution, storage device electrode slurry, storage device electrode, and storage device

Abstract

The present invention provides a binder for electricity storage device electrodes, said binder being not susceptible to the formation of gel-like lumps when dissolved, while enabling the formation of a suitably uniform electrode that has a low resistance and a high discharge capacity if used for an electricity storage device electrode.　The present invention discloses a binder which contains a water-soluble resin powder that is composed of particles having an average particle diameter of from 100 to 2,000 μm. With respect to 50 particles randomly selected from the particles contained in the water-soluble resin powder and having a diameter of from 100 to 1,000 μm, the average value PA of the roundness P represented by formula (1) of each particle is from 0.1 to 0.8. (In formula (1), ri represents the radius of curvature of each corner of each particle; R represents the radius of the maximum inscribed circle of each particle; and N represents the number of corners of each particle, provided that if the number of corners of a particle is 9 or more, the radii of curvature of 8 corners are selected in ascending order of the radii of curvature, and N is set to 8.)

Description

Technical Field

[0001] This patent application claims priority under the Paris Convention with respect to Japanese Patent Application No. 2020-044897 (filing date: March 16, 2020), the entire disclosure of which is hereby incorporated herein by reference in its entirety. The present invention relates to a binder suitable for a power storage device electrode, a binder solution, a power storage device electrode slurry, a power storage device electrode, and a power storage device.

Background Art

[0002] In recent years, the spread of mobile terminals such as mobile phones, notebook personal computers, and tablet information terminal devices has been remarkable. As mobile terminals are required to have more comfortable portability and are rapidly miniaturized, thinned, lightened, and enhanced in performance, the batteries used in mobile terminals are also required to be miniaturized, thinned, lightened, and enhanced in performance. As a power storage device used as a power source for such mobile terminals, lithium-ion secondary batteries are widely used. A non-aqueous electrolyte battery such as a lithium-ion secondary battery has a structure in which a positive electrode and a negative electrode are provided via a separator, and an electrolytic solution in which a lithium salt such as LiPF6, LiBF4, LiTFSI (lithium (bis(trifluoromethylsulfonyl)imide)), or LiFSI (lithium (bis(fluorosulfonyl)imide)) is dissolved in an organic liquid such as ethylene carbonate, and these electrodes are housed in a container.

[0003] The negative electrode and the positive electrode constituting the power storage device are usually formed by applying an electrode slurry obtained by dissolving or dispersing a binder and a thickener in water or a solvent and mixing an active material, a conductive auxiliary agent (conductive imparting agent), etc. thereto onto a current collector, and then drying the water or the solvent to bind them as a mixed layer.

[0004] From the perspective of reducing the environmental load and improving the simplicity of manufacturing equipment, especially in the production of negative electrodes, the trend of using an aqueous medium in electrode slurries is rapidly advancing. As binders for such electrode slurries using an aqueous medium, vinyl alcohol-based polymers (hereinafter also referred to as "PVA"), acrylic polymers such as acrylic acid, and binders of amide / imide-based polymers are known (for example, Patent Documents 1 and 2).

[0005] On the other hand, in the production of positive electrodes, generally, electrode slurries using solvents are used. Examples of such solvents include organic solvents such as N-methyl-2-pyrrolidone, dimethylformamide, N,N-dimethylacetamide, N,N-dimethylmethanesulfonamide, and hexamethylphosphoric triamide. As binders for such electrode slurries using organic solvents, vinylidene fluoride-based polymers, tetrafluoroethylene-based polymers, fluororubbers, etc. are known (for example, Patent Documents 3 and 4).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the production of both the negative electrode and the positive electrode described in Patent Documents 1 to 4, the slurry (electrode slurry) obtained by mixing a binder, a solvent (water or a solvent), an active material, a conductive assistant (conductive agent), etc. has various conditions in the form of materials such as the binder in the slurry and in the slurry preparation when this is applied to a current collector to form an electrode. For example, many problems as shown below have occurred.

[0008] When using resin powder as a binder, it is necessary to dissolve the resin powder in water or a solvent (such as N-methyl-2-pyrrolidone (NMP)) in advance. However, in the case of water-soluble resin powder, the particles constituting the powder may fuse in pipes or silos to form aggregates, and gel-like lumps may occur during dissolution. When preparing a slurry using a binder solution containing many gel-like lumps, it becomes difficult for the active material, etc. in the slurry to disperse, resulting in difficulty in forming a uniform electrode, and sufficient performance, particularly low resistance and high discharge capacity, cannot be obtained. Due to properties such as water solubility and hygroscopicity of the water-soluble resin powder, there is a problem that such aggregates are likely to occur and gel-like lumps are likely to occur during dissolution, particularly in an environment with high humidity.

[0009] Therefore, an object of the present invention is to provide a binder that hardly forms gel-like lumps during the dissolution of water-soluble resin powder, and particularly, when used for an electrode of an electric storage device, can preferably form a uniform electrode (an electrode with a small variation in the film thickness of the coated electrode), and moreover, provides an electric storage device electrode having a low resistance and a high discharge capacity.

Means for Solving the Problems

[0010] The above object is achieved by the present invention including the following preferred embodiments. [1] A binder containing water-soluble resin powder, the water-soluble resin powder is composed of particles having an average particle diameter of 100 to 2,000 μm, Regarding 50 particles arbitrarily extracted from the particles having a particle diameter of 100 to 1,000 μm contained in the water-soluble resin powder, for each particle, the following formula (1) [Number] [In formula (1), r i is the radius of curvature for each angle of the particle, R is the radius of the maximum inscribed circle of the particle, N is the number of angles the particle has, However, when the number of angles of the particle is 9 or more, the radii of curvature of 8 angles are adopted in ascending order of the radius of curvature, and N is taken as 8] The binder in which the average value PA of the circularity P represented by is 0.1 to 0.8. [2] The binder according to [1], wherein the water-soluble resin is a vinyl alcohol-based polymer. [3] The binder according to [1] or [2], wherein the viscosity average degree of polymerization of the vinyl alcohol-based polymer is 200 to 5,000, and the degree of saponification is 35 to 99.99 mol%. [4] The following formula (2) PA × S ≧ 18 (2) [In formula (2), PA is the same as defined above, and S is the degree of saponification (mol%) of the vinyl alcohol-based polymer] The binder according to any one of claims 1 to 3, which satisfies the following and the average particle diameter of the water-soluble resin powder is 100 to 1,000 μm. [5] The binder according to any one of [1] to [4], wherein the content of particles having a particle diameter of 100 to 1,000 μm in the water-soluble resin powder is 50% by mass or more. [6] A storage device electrode containing the binder according to any one of [1] to [5]. [7] A binder solution for a storage device electrode containing the binder according to any one of [1] to [5] and water. [8] The binder solution for a storage device electrode according to [7], which contains N-methyl-2-pyrrolidone. [9] A storage device electrode slurry containing the binder solution for a storage device electrode according to [7] or [8] and an active material.

[10] The content of the binder is 0.1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the active material, and the electrode slurry for a power storage device according to [9].

[11] A power storage device electrode including a cured body of the electrode slurry for a power storage device according to [9] or

[10] and a current collector.

[12] A power storage device including the power storage device electrode according to

[11] .

[13] A step of obtaining a coarse powder of the water-soluble resin by pulverizing a resin solid content containing the water-soluble resin, and A step of processing the surface of the particles constituting the coarse powder A method for producing the binder according to any one of [1] to [5], including the above steps.

Advantages of the Invention

[0011] According to the present invention, gel-like lumps are less likely to occur during the dissolution of the water-soluble resin powder, and when used for a power storage device electrode, a suitable uniform electrode (an electrode with a small variation in the film thickness of the coated electrode) can be formed. Moreover, a binder for a power storage device electrode having a low resistance and providing a high discharge capacity can be provided.

Embodiments for Carrying Out the Invention

[0012] <Resin Powder>[[]] The binder of the present invention contains a water-soluble resin powder. This powder is composed of particles having an average particle diameter of 100 to 2,000 μm. For 50 particles arbitrarily extracted from the particles having a particle diameter of 100 to 1,000 μm contained in the water-soluble resin powder, the formula (1) of each particle

Number

[0013] The water-soluble resin powder contained in the binder of the present invention has an average circularity PA of 0.1 to 0.8 as described above, preferably 0.12 to 0.7, more preferably 0.14 to 0.65, and still more preferably 0.16 to 0.6.

[0014] When the average circularity is within the above specific range, compared with a binder made of a conventional water-soluble resin powder, it is difficult for aggregates to occur due to the fusion of the resin powder in pipes and silos. The reason for this is not necessarily clear, but it is presumed that since the corners of each particle are rounded, the contact area between the particles is small, and as a result, it is difficult for the particles to fuse.

[0015] The water-soluble resin is not particularly limited as long as it has a solubility of 1 g or more of the resin with respect to 100 g of water. For example, such water-soluble resins include vinyl alcohol-based polymers and their derivatives, acrylic-based polymers such as (meth)acrylic acid and their derivatives, cellulose derivatives such as carboxymethyl cellulose, alginic acid and its neutralized products, polyvinylpyrrolidone, and the like.

[0016] Among these, vinyl alcohol-based polymers and their derivatives are preferably used as the water-soluble resin because they have good affinity for active materials used in power storage devices such as carbon materials, metals, and metal oxides.

[0017] When using PVA as the water-soluble resin, it is usually the main component of the water-soluble resin powder. The main component refers to the component with the highest content on a mass basis. The content of PVA in the non-volatile matter of the water-soluble resin powder is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and in some cases, even more preferably 99% by mass or more. The upper limit of the content of PVA in the non-volatile matter of the water-soluble resin powder may be 100% by mass. Examples of non-volatile matters other than PVA that may be contained in the water-soluble resin powder include resins other than PVA, surfactants, plasticizers, defoamers, additives such as viscosity modifiers, and various compounds used during production. Also, the content of volatile matter in the water-soluble resin powder is usually 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. Examples of volatile matters that may be contained in the water-soluble resin powder include alcohol, water, and the like.

[0018] A vinyl alcohol-based polymer (also referred to as "polyvinyl alcohol" or simply "PVA") is a polymer having vinyl alcohol units as monomer units (i.e., constituent units). PVA is usually obtained by saponifying polyvinyl ester. The ratio of vinyl alcohol units in all monomer units of PVA is preferably 35 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol% or more, and in some cases, even more preferably 80 mol% or more or 90 mol% or more. By setting the ratio of vinyl alcohol units to be not less than the above lower limit value, the permeability in an environment with particularly high humidity is increased, and it becomes easier to efficiently produce the water-soluble resin powder in the present invention by a production method involving crushing and surface processing. On the other hand, the ratio of the above vinyl alcohol units may be 100 mol%, but is preferably 99.99 mol% or less, and more preferably 99 mol% or less.

[0019] The degree of saponification of PVA is preferably 35 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol% or more, and may be even more preferably 80 mol% or more or 90 mol% or more. By setting the degree of saponification to the above lower limit or more, the adhesiveness to various members is improved, battery performance such as discharge capacity is likely to be improved, and the water-soluble resin powder in the present invention can be efficiently produced by a manufacturing method including crushing and surface processing. On the other hand, the above degree of saponification may be 100 mol% or less, preferably 99.99 mol% or less, and more preferably 99 mol% or less. The degree of saponification can be measured by the method described in JIS K6726:1994.

[0020] PVA may have other monomer units (constituent units) in addition to vinyl alcohol units and vinyl ester units. Examples of monomers that provide the above other monomer units include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylic acid and methacrylic acid; acrylic esters such as methyl acrylate and ethyl acrylate; methacrylic esters such as methyl methacrylate and ethyl methacrylate; acrylamide derivatives such as N-methylacrylamide and N-ethylacrylamide; methacrylamide derivatives such as N-methylmethacrylamide and N-ethylmethacrylamide; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, and n-butyl vinyl ether; hydroxy group-containing vinyl ethers such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether, and 1,4-butanediol vinyl ether; allyl acetate; allyl ethers such as propyl allyl ether, butyl allyl ether, and hexyl allyl ether; monomers having an oxyalkylene group; isopropenyl acetate; hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decen-1-ol, and 3-methyl-3-buten-1-ol; monomers having a silyl group such as vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, 3-(meth)acrylamidopropyltrimethoxysilane, and 3-(meth)acrylamidopropyltriethoxysilane. Among these, α-olefins, acrylic acid, methacrylic acid, acrylic esters, and methacrylic esters are preferred.

[0021] The proportion of the above other monomer units in all monomer units in PVA may preferably be 20 mol% or less, and more preferably 10 mol% or less. On the other hand, the proportion of the above other monomer units may be, for example, 0.1 mol% or more, or 1 mol% or more.

[0022] The viscosity average degree of polymerization of PVA is not particularly limited, but is preferably 200 or more, more preferably 250 or more, still more preferably 400 or more, and particularly preferably 600 or more. The above viscosity average degree of polymerization is preferably 5,000 or less, more preferably 4,500 or less, and still more preferably 3,500 or less. By setting the viscosity average degree of polymerization within the above range, the industrial production of the resin particles having the above average circularity becomes easy. The viscosity average degree of polymerization can be measured according to JIS K6726:1994. That is, after saponifying PVA to a saponification degree of 99.5 mol% or more and purifying it, it can be obtained from the intrinsic viscosity [η] (unit: liter / g) measured in water at 30°C by the following formula. Viscosity average degree of polymerization = ([η] × 10000 / 8.29) ^ (1 / 0.62)

[0023] The average particle diameter of the water-soluble resin powder (that is, the particles constituting the water-soluble resin powder) in the present invention is 100 μm or more, preferably 150 μm or more, and more preferably 300 μm or more. When the average particle diameter is 100 μm or more, dust explosion is less likely to occur, and safety can be enhanced. The above average particle diameter is 2,000 μm or less, preferably 1,500 μm or less, more preferably 1,000 μm or less, and still more preferably 850 μm or less. When the average particle diameter is 2000 μm or less, it becomes easier to dissolve in a solvent, the generation of gel-like lumps can be suppressed, and a uniform electrode can be produced.

[0024] The average particle diameter of the water-soluble resin powder (that is, the particles constituting the water-soluble resin powder) can be measured in accordance with the method described in JIS K7369:2009.

[0025] The average circularity (the average value PA of the circularity P of 50 particles arbitrarily extracted from particles with a particle size of 100 to 1,000 μm) of the water-soluble resin powder (i.e., the particles constituting the water-soluble resin powder) in the present invention is importantly 0.1 or more, preferably 0.2 or more, more preferably 0.25 or more, still more preferably 0.3 or more, particularly preferably 0.33 or more, and extremely preferably 0.35 or more in some cases. By setting the average circularity to 0.1 or more, dissolution in a solvent becomes easier, generation of gel-like lumps is suppressed, and a uniform electrode can be produced. On the other hand, it is important that the above average circularity is 0.8 or less, and preferably 0.7 or less. By setting the average circularity to 0.8 or less, the productivity of the water-soluble resin powder in the present invention can be increased. Further, the water-soluble resin powder having an average circularity below the above upper limit can be effectively produced by a production method that performs crushing and surface processing.

[0026] The average circularity of the water-soluble resin powder (i.e., the particles constituting the water-soluble resin powder) can be determined by the following method. Arbitrarily extract 50 particles from particles with a particle size of 100 to 1,000 μm (or a particle size of 106 to 1,000 μm based on the sieve mesh) in the water-soluble resin powder. The particles with a particle size of 100 to 1,000 μm can be selected as the particles that passed through a sieve mesh with a nominal mesh opening of 1,000 μm (16 mesh) and did not pass through a sieve mesh with a nominal mesh opening of 106 μm (150 mesh) in sieving. The above mechanical sieving can be performed, for example, by the method described in JIS K7369:2009. For one extracted particle, for the projection view with the largest apparent area, eight corners (if the number of corners is less than 8, i.e., 7 or less, then all of its corners) are extracted in ascending order of the radius of curvature r i and the radius of curvature r i of each corner is measured. Also, based on the projection view with the largest apparent area, the radius R of the maximum inscribed circle of the particle is measured. Let the number of corners of the particle be N (when the number of corners of the particle is 9 or more, N is 8), and the measured r iBased on R and [parameters not specified], the circularity P of one particle is determined by the following formula (1). When the circularity P is low, it indicates that the particle has many angular corners, and when the circularity is high, it indicates that the particle is rounded.

[0027] [Number] [In formula (1), r i is the radius of curvature for each corner of the particle, R is the radius of the maximum inscribed circle of the particle, N is the number of corners the particle has, However, when the number of corners of the particle is 9 or more, the radii of curvature of 8 corners are adopted in ascending order of the radius of curvature, and N is taken as 8.

[0028] The above circularity P is measured for the 50 extracted particles, and the average value PA of the circularity P of these 50 particles is determined. This average value PA is the average circularity.

[0029] In the water-soluble resin powder of the present invention, the content of particles having a particle size of 100 to 1,000 μm (or a particle size based on the sieve mesh of 106 to 1,000 μm) is not particularly limited, but it is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more. On the other hand, the upper limit of the content of particles having a particle size of 100 to 1,000 μm may be 100% by mass. When the content of particles having a particle size of 100 to 1,000 μm is within the above range, it becomes difficult for the particles to fuse with each other in pipes and silos, and it becomes difficult for gel-like lumps to form during the dissolution of the resin powder. Accordingly, when used as a binder solution for electrode production, the uniformity (homogeneity) of the electrode is enhanced. The content of particles having a particle size of 100 to 1,000 μm in the resin powder can be determined using a sieve mesh with a nominal mesh opening of 1,000 μm (16 mesh) and a sieve mesh with a nominal mesh opening of 106 μm (150 mesh) in accordance with the method described in JIS K7369:2009.

[0030] The water-soluble resin powder in the present invention (i.e., the particles constituting the water-soluble resin powder) preferably satisfies the following formula (2), and more preferably satisfies the following formula (2) and has an average particle diameter of 100 to 1,000 μm. In such a case, it is possible to particularly suppress the fusion of particles and the generation of aggregates under high humidity. According to the study by the present inventor, the higher the average circularity, the less likely the particles are to fuse. On the other hand, particularly under high humidity, the water-soluble resin powder containing PVA with a low saponification degree is likely to cause particle fusion due to the influence of its hygroscopicity, etc. Therefore, by making the product (PA × S) of the average value PA (average circularity) of the circularity P and the saponification degree S of PVA be a predetermined value or more, it is possible to suppress the fusion of particles even under high humidity. PA × S ≥ 18 (2) In formula (2), PA is the average value of the circularity P. S is the saponification degree (mol%) of PVA.

[0031] The product (PA × S) of the average value PA (average circularity) of the circularity P and the saponification degree S of PVA is more preferably 19 or more, and even more preferably 20 or more. On the other hand, the upper limit of this product (PA × S) is not particularly limited, and may be, for example, 80 or less, or may be 60 or less.

[0032] The angle of repose measured after conditioning the water-soluble resin powder in the present invention for 1 week in an atmosphere of 20°C and 30% humidity is preferably less than 38°, and more preferably less than 35°. Also, the angle of repose measured after conditioning the water-soluble resin powder in the present invention for 1 week in an atmosphere of 20°C and 65% humidity is preferably less than 40°, and more preferably less than 38°. When the angle of repose of the water-soluble resin powder is this low, it is possible to suppress the fusion of particles even in a high-humidity environment. The lower limit of these angles of repose is not particularly limited, and may be, for example, 25° or more, or may be 30° or more. The angle of repose of the water-soluble resin powder can be controlled within the above range by controlling the average circularity and the average particle diameter. Also, the angle of repose of the water-soluble resin powder can be measured according to the method described in JIS 9301-2-2:1999.

[0033] <Method for Producing Water-Soluble Resin Powder> The method for producing the water-soluble resin powder in the present invention is not particularly limited, but for example, the following method is preferably used. That is, in one embodiment of the present invention, the method for producing the water-soluble resin powder is a step (step B) of obtaining a coarse powder of the water-soluble resin by pulverizing a resin solid containing the water-soluble resin, and a step (step C) of processing the surface of the particles contained in the coarse powder are included.

[0034] When PVA is used as the water-soluble resin in the water-soluble resin powder in the present invention, a step (step A) of synthesizing PVA and obtaining a resin solid containing PVA may be further included.

[0035] (Step A) Step A can include, for example, a polymerization step, a saponification step, and the like.

[0036] In the polymerization step, a vinyl ester monomer is polymerized to obtain a vinyl ester polymer. Examples of the method for polymerizing the vinyl ester monomer include known methods such as bulk polymerization method, solution polymerization method, suspension polymerization method, and emulsion polymerization method. Among these methods, the bulk polymerization method performed without a solvent and the solution polymerization method performed using a solvent such as alcohol are preferred, and the solution polymerization method performed in the presence of a lower alcohol is more preferred. As the above lower alcohol, an alcohol having 3 or less carbon atoms is preferred, methanol, ethanol, n-propanol, and isopropanol are more preferred, and methanol is even more preferred. When performing the polymerization reaction by the bulk polymerization method or the solution polymerization method, either a batch system or a continuous system can be adopted as the reaction method.

[0037] Examples of the above vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Among them, vinyl acetate is preferred.

[0038] Examples of the initiator used in the polymerization reaction include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); and known initiators such as organic peroxide initiators like benzoyl peroxide and n-propyl peroxycarbonate. There is no particular limitation on the polymerization temperature during the polymerization reaction, but a range of 5°C or higher and 200°C or lower is appropriate.

[0039] When polymerizing the vinyl ester monomer, a comonomer that can be copolymerized can be further copolymerized within a range that does not impair the gist of the present invention. When polymerizing the vinyl ester monomer, a chain transfer agent may be allowed to coexist for the purpose of adjusting the degree of polymerization of the obtained PVA, etc. Examples of the chain transfer agent include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptans such as 2-hydroxyethanethiol; thiocarboxylic acids such as thioacetic acid; and halogenated hydrocarbons such as trichloroethylene and perchloroethylene. Among them, aldehydes and ketones are preferably used. The addition amount of the chain transfer agent is determined according to the chain transfer constant of the chain transfer agent to be added and the target degree of polymerization of PVA, but generally, 0.1 to 10% by mass is preferable with respect to the vinyl ester used.

[0040] In the saponification step, the vinyl ester polymer is saponified in an alcohol solution using an alkali catalyst or an acid catalyst to obtain PVA. For the saponification reaction of the vinyl ester polymer, an alcoholysis or hydrolysis reaction using a conventionally known basic catalyst such as sodium hydroxide, potassium hydroxide, sodium methoxide, etc., or an acidic catalyst such as p-toluenesulfonic acid can be applied. As the solvent used in the saponification reaction, alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene, etc. can be mentioned. These can be used alone or in combination of two or more. Among these, it is simple and preferable to use methanol or a mixed solution of methanol and methyl acetate as the solvent and carry out the saponification reaction in the presence of sodium hydroxide which is a basic catalyst.

[0041] The saponification step can be carried out by a belt type reactor, a kneader type reactor, a tower type reactor, etc. By passing through the saponification step, a resin solid containing PVA is obtained. The content ratio of PVA in the non-volatile matter in the resin solid is, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more in some cases. The non-volatile matter in this resin solid may substantially contain PVA as the main component, but may contain impurities such as sodium acetate and by-products.

[0042] (Step B) In Process B, a resin solid containing a water-soluble resin such as PVA is pulverized. Thereby, a coarse powder containing the water-soluble resin is obtained. The above pulverization can be performed by a known pulverizer. As the pulverizer, an apparatus capable of controlling the degree of pulverization such as the pulverization intensity is preferable in order to adjust the average particle diameter of the particles constituting the obtained coarse powder and ultimately the resin powder. In addition to adjusting the pulverization intensity, the average particle diameter of the particles constituting the obtained coarse powder can also be controlled by the treatment time or the like. The average particle diameter of the particles constituting the coarse powder is not limited, but when performing the surface treatment in Process C described later, it is preferable to set it to be equal to or larger than the average particle diameter of the resin powder finally obtained in consideration of the particle size reduction by this process. For example, by setting the average particle diameter of the particles constituting the coarse powder to 100 to 3000 μm, a resin powder having a desired average particle diameter can be finally obtained. Note that the obtained coarse powder may be saponified again. Further, the obtained coarse powder may be subjected to a washing treatment for reducing impurities such as sodium acetate and by-products, and a drying treatment for reducing volatile components. The resin solid before pulverization may be subjected to a washing treatment or a drying treatment.

[0043] (Process C) In Process C, the surface of the particles constituting the coarse powder is processed. When a resin solid containing a water-soluble resin such as PVA is crushed, usually, the obtained coarse powder has a very sharp shape. Therefore, by Process C, it is possible to efficiently obtain a water-soluble powder with rounded corners and an average roundness within a predetermined range.

[0044] The apparatus used in Process C is not particularly limited as long as it can polish the surface of the coarse powder. For example, a rotary kiln in which a powder filling container rotates and surface polishing progresses due to contact between powders, a planetary mixer capable of imparting three-dimensional motion to the contents by a screw blade that rotates and revolves within the container, a mixer in which paddles or screws within the container rotate and the internal powder is polished by the rotation, and the like can be mentioned. Examples of the mixer include a high-speed mixer, a Henschel mixer, a turbulizer, a Lodige mixer, and the like. Among these, from the viewpoint of processing efficiency, a mixer is preferable, and a turbulizer and a Lodige mixer are more preferable. Further, in Process C, the surface processing of the coarse powder may be performed while heating.

[0045] The method for producing the water-soluble resin powder in the present invention may further include a sieving step or the like for adjusting the average particle diameter. Further, after Process C, a washing treatment or a drying treatment may be performed.

[0046] <Binder solution for power storage device electrode> The binder of the present invention may further contain a material for adjusting the viscosity of the binder in a solution state. Examples of the material for adjusting the viscosity include polybasic acids such as citric acid, tartaric acid, and aspartic acid and their salts, condensates thereof, and inorganic substances such as fumed silica and alumina. The addition amounts thereof are not particularly limited, but usually, with respect to 100 parts by mass of PVA, preferably 0.01 part by mass or more and 10 parts by mass or less, more preferably 0.02 part by mass or more and 8 parts by mass or less, still more preferably 0.05 part by mass or more and 5 parts by mass or less. The more such a material for adjusting the viscosity is contained, the more the viscosity of the binder of the present invention in a solution state can be increased. The smaller the particle size of the inorganic substance is, the easier it is to increase the viscosity of the binder in a solution state.

[0047] The binder of the present invention or the binder solution for the electrodes of the power storage device of the present invention described below can further contain compounding agents as long as the effects of the present invention are not impaired. Examples of the compounding agents include light stabilizers, ultraviolet absorbers, freeze stabilizers, thickeners, leveling agents, rheology stabilizers, thixotropic agents, defoaming agents, plasticizers, lubricants, antiseptics, rust preventives, antistatic agents, charge control agents, anti-yellowing agents, pH adjusters, film-forming aids, curing catalysts, crosslinking reaction catalysts, crosslinking agents (such as glyoxal, urea resin, melamine resin, polyvalent metal salts, polyvalent isocyanates, polyamide epichlorohydrin, etc.), and dispersants. They can be selected, combined, and compounded according to each purpose. The content of the compounding agent is, based on the total amount of the binder or the binder solution for the electrodes of the power storage device, for example, 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less.

[0048] The binder of the present invention may be obtained by dissolving a water-soluble resin, particularly PVA, and components other than the water-soluble resin contained as necessary in a solvent (such as water or NMP) to form a solution and then removing the solvent. Further, the solution may be used as it is for the preparation of the subsequent slurry as the binder solution for the electrodes of the power storage device of the present invention described below. In that case, the composition of the components other than the solvent in the binder solution is the binder of the present invention. The binder of the present invention is contained in a state of being mixed with components such as the active material in the cured body of the slurry composition of the present invention.

[0049] The binder solution as one embodiment of the present invention contains the binder of the present invention and at least one solvent. The solvent is preferably water or NMP. When the solvent is water, it is suitable from the viewpoints of reducing environmental impact and simplicity of equipment. On the other hand, when the solvent is NMP, it is suitable especially when applied as a slurry for the positive electrode because it does not deteriorate the active material in the slurry.

[0050] The binder solution can contain, in addition to the binder of the present invention described above, an additive (referred to as additive A) that can be dissolved in a solvent, as long as the effects of the present invention are not impaired. Examples of additive A include polyethylene glycol, polyethylene glycol dimethyl ether, polyethylene glycol diglycidyl ether, polyethyleneimine, and the like. The content of additive A is, based on the total amount of the binder solution, for example, 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less. In particular, it is preferable not to contain additive A.

[0051] The binder solution is obtained by mixing a water-soluble resin such as PVA, a solvent (e.g., water or NMP), and components other than the aqueous resin described above that are contained as necessary, by a known method, for example, a method such as stirring. The mixing temperature and mixing time can be appropriately adjusted according to the type of solvent. Note that the binder solution refers to a solution in which the water-soluble resin described above is dissolved in the solvent. The dissolved state means that the mass of the water-soluble resin, particularly PVA, that is completely dissolved in the solvent is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, even more preferably 99% by mass or more, and still more preferably 100% by mass with respect to the total mass (100% by mass) of the water-soluble resin used when preparing the binder solution.

[0052] The content of the water-soluble resin, particularly PVA, in the binder solution of the present invention is, based on the total amount of the binder solution, preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, particularly preferably 5% by mass or more and 15% by mass or less. When the content of the water-soluble resin is 1% by mass or more, it is easy to improve the adhesion of the active material to the current collector when forming the electrode. When the content of the water-soluble resin is 30% by mass or less, it is possible to suppress the rapid aggregation of the active material when forming the electrode.

[0053] <Electrode slurry for energy storage device> The electrode slurry for an energy storage device according to one embodiment of the present invention contains the binder solution and the active material described above.

[0054] The slurry may be used for either the positive electrode or the negative electrode, or for both the positive and negative electrodes. The active material may be either a positive electrode active material or a negative electrode active material. Also, the type of solvent is not particularly limited, but preferably, water or an NMP solvent can be used, either alone or in combination of two or more kinds.

[0055] As the negative electrode active material, for example, materials conventionally used as the negative electrode active material of a power storage device can be used. Examples thereof include carbonaceous materials such as amorphous carbon, artificial graphite, natural graphite (graphite), mesocarbon microbeads (MCMB), pitch-based carbon fiber, carbon black, activated carbon, carbon fiber, hard carbon, soft carbon, mesoporous carbon, and conductive polymers such as polyacene, Si, SiO x and other silicon-based compounds such as SnO x and composite metal oxides represented by LiTiO x and other metal oxides, lithium-based metals such as lithium metal and lithium alloys, metal compounds such as TiS2 and LiTiS2, and composite materials of metal oxides and carbonaceous materials, hydrogen storage alloys, etc. These negative electrode active materials can be used alone or in combination of two or more kinds.

[0056] As the positive electrode active material, for example, materials conventionally used as the positive electrode active material of a power storage device can be used. Examples thereof include transition metal oxides such as TiS2, TiS3, amorphous MoS3, Cu2V2O3, amorphous V2O-P2O5, MoO3, V2O5, and V6O 13 and lithium-containing composite metal oxides such as LiCoO2, LiNiO2, LiMnO2, LiMn2O4, manganese dioxide, nickel hydroxide, nickel oxyhydroxide, etc. These positive electrode active materials can be used alone or in combination of two or more kinds.

[0057] The slurry may contain a conductive aid. The conductive aid is used to increase the output of the power storage device and can be appropriately selected according to whether it is used for the positive electrode or the negative electrode. Examples thereof include, for example, graphite, acetylene black, carbon black, ketjen black, vapor-grown carbon fiber, and the like. From the viewpoint that the obtained power storage device is likely to have a high output, among these, acetylene black is preferably used.

[0058] When the slurry contains a conductive aid, the content of the conductive aid is preferably 0.1 part by mass or more and 15 parts by mass or less, more preferably 1 part by mass or more and 10 parts by mass or less, and still more preferably 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the active material. When the content of the conductive aid is within this range, a sufficient conductive assistance effect can be obtained without reducing the battery capacity to which the slurry is applied.

[0059] Preferably, the content of the binder in the slurry is 0.1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the active material. When the content is 0.1 part by mass or more, the adhesion of the active material to the current collector is improved, which is advantageous from the viewpoint of maintaining the durability of the applied battery. Further, when the content is 20 parts by mass or less, the discharge capacity is likely to be improved. The range of the content is more preferably 0.2 part by mass or more and 18 parts by mass or less, still more preferably 0.5 part by mass or more and 16 parts by mass or less, and even more preferably 1 part by mass or more and 12 parts by mass or less.

[0060] In addition to the binder, the active material, the conductive aid, and the solvent, the slurry can also contain additives such as a flame retardant aid, a thickener, an antifoaming agent, a leveling agent, and an adhesion-imparting agent as required. When these additives are contained, the content of the additives is preferably about 0.1% by mass or more and 10% by mass or less based on the total amount of the slurry.

[0061] The slurry can be obtained by mixing a binder, an active material, and, if necessary, a conductive aid, a solvent, and additives by a conventional method, for example, using a mixer such as a ball mill, a blender mill, or a three-roll mill.

[0062] <Electrode of energy storage device> The electrode of the energy storage device according to an embodiment of the present invention includes the cured body of the aforementioned slurry and the current collector. The cured body of the slurry is a cured product obtained by removing the solvent in the slurry by drying or the like.

[0063] The electrode can be obtained by applying the slurry of the present invention to the current collector and removing the solvent by drying or the like. Further, the electrode may be rolled after drying.

[0064] The current collector is not particularly limited as long as it is made of a conductive material. For example, metal materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum can be mentioned. These current collectors can be used alone or in combination of two or more. Among these current collectors, from the viewpoints of the adhesiveness of the active material and the discharge capacity, copper is preferable as the negative electrode current collector, and aluminum is preferable as the positive electrode current collector.

[0065] The method for applying the slurry to the current collector is not particularly limited, and examples thereof include an extrusion coater, a reverse roller, a doctor blade, and an applicator. The coating amount of the slurry is appropriately selected according to the desired thickness of the cured body derived from the slurry composition.

[0066] Examples of the rolling method of the electrode include methods such as die pressing and roll pressing. From the viewpoint of easily increasing the battery capacity, the pressing pressure is preferably 1 MPa or more and 40 MPa or less.

[0067] In the electrode of the present invention, the thickness of the current collector is preferably 1 μm or more and 200 μm or less, more preferably 2 μm or more and 150 μm or less. The thickness of the cured body is preferably 10 μm or more and 800 μm, more preferably 20 μm or more and 600 μm or less. The thickness of the electrode is preferably 20 μm or more and 300 μm or less.

[0068] <Energy storage device> The power storage device according to an embodiment of the present invention includes the above-described power storage device electrode as a negative electrode and / or a positive electrode.

[0069] Examples of the power storage device include a lithium-ion secondary battery, a sodium-ion battery, a lithium-sulfur battery, an all-solid-state battery, a lithium-ion capacitor, a lithium battery, a nickel-metal hydride battery, an alkaline dry battery, and the like.

[0070] The power storage device of the present invention is excellent in electrode uniformity and has low electrical resistance and high discharge capacity.

[0071] Note that the discharge capacity of the power storage device can be calculated, for example, by using a method of performing a charge-discharge test using a commercially available charge-discharge tester as shown in the examples described later.

[0072] The electrolytic solution contained in the power storage device is a solution in which an electrolyte is dissolved in a solvent. The electrolyte may be liquid or gel as long as it is used in a normal battery, and those that exhibit the function as a battery according to the types of the negative electrode active material and the positive electrode active material may be appropriately selected. Specific examples of the electrolyte include, for example, known lithium salts that can be preferably used in non-aqueous electrolyte batteries, such as LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, lithium lower aliphatic carboxylate, and the like. In a battery using an aqueous electrolyte, for example, an alkaline aqueous solution containing potassium hydroxide, sodium hydroxide, or lithium hydroxide as a solute can be mentioned.

[0073] The solvent contained in the electrolyte is not particularly limited. Specific examples thereof include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and vinylene carbonate; lactones such as γ-butyrolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane; nitrogen-containing compounds such as acetonitrile and nitromethane; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate; inorganic acid esters such as triethyl phosphate, dimethyl carbonate and diethyl carbonate; diglymes; triglymes; sulfolanes; oxazolidinones such as 3-methyl-2-oxazolidinone; 1,3-propane sultone; and sultones such as 1,4-butane sultone and naphthalene sultone; water and the like. These can be used alone or in combination of two or more. When using a gel-like electrolyte, a nitrile-based polymer, an acrylic-based polymer, a fluorine-based polymer, an alkylene oxide-based polymer or the like can be added as a gelling agent.

[0074] When the electrode of the present invention is used as either the positive electrode or the negative electrode, a conventional electrode can be used for the electrode that does not use the electrode of the present invention.

[0075] In one preferred embodiment, the power storage device of the present invention includes the electrode of the present invention as the negative electrode and a conventional electrode as the positive electrode. The positive electrode is not particularly limited as long as it is a positive electrode commonly used in power storage devices.

[0076] Alternatively, in another preferred embodiment, the power storage device of the present invention includes the electrode of the present invention as the positive electrode and a conventional electrode as the negative electrode. The negative electrode is not particularly limited as long as it is a negative electrode commonly used in power storage devices.

[0077] Further, both the positive electrode and the negative electrode may be electrodes containing the binder of the present invention.

[0078] The method for manufacturing the power storage device of the present invention is not particularly limited. For example, it can be manufactured as follows. That is, the negative electrode and the positive electrode are stacked via a separator such as a polypropylene porous membrane, wound and / or folded according to the battery shape, placed in a battery container, and an electrolytic solution is injected and sealed. The shape of the battery may be any of known coin type, button type, sheet type, cylindrical type, square type, flat type, etc.

[0079] The power storage device of the present invention is useful for various applications. For example, it is very useful as a battery used in portable terminals that require miniaturization, thinning, weight reduction, and high performance. It can also be suitably used for batteries of devices that require flexibility, such as wound dry batteries and laminated batteries.

Examples

[0080] The present invention will be specifically described by the following examples, but the present invention is not limited by these examples in any way. Regarding the physical property values of each PVA used in each of the following examples and comparative examples, the evaluation of the aqueous binder solution and NMP solution containing each PVA, the evaluation in electrode application, and the evaluation in battery application, they were measured according to the following methods.

[0081] [Viscosity average degree of polymerization of PVA] The viscosity average degree of polymerization of PVA was measured according to JIS K6726:1994. Specifically, when the saponification degree of PVA is less than 99.5 mol%, it is saponified until the saponification degree becomes 99.5 mol% or more, and for the obtained PVA, the viscosity average degree of polymerization was determined by the following formula using the limiting viscosity [η] (liter / g) measured in water at 30°C. Viscosity average degree of polymerization = ([η] × 10000 / 8.29)^(1 / 0.62)

[0082] [Saponification degree of PVA] The saponification degree of PVA (including modified PVA) was determined by the method described in JIS K6726:1994.

[0083] [(Water-soluble) average particle diameter of the particles constituting the resin powder, and content of particles having a particle diameter of 100 to 1,000 μm] Using a JIS standard sieve, the average particle diameter of the resin powder and the content of particles having a particle diameter of 100 to 1,000 μm (or particle diameter of 106 to 1,000 μm based on the sieve mesh) were determined by the method described in JIS K7369:2009.

[0084] [(Water-soluble) average circularity of the resin powder] By the above sieving, particles having a particle diameter of 100 to 1,000 μm (or particle diameter of 106 to 1,000 μm based on the sieve mesh) were selected, and 50 arbitrary particles were extracted from these particles. For these particles, based on an image with a magnification of 100 times using a Keyence Corporation digital microscope VHX-900, the radius of curvature r i and the radius R of the maximum inscribed circle were determined, and the circularity P of each particle was determined. The average value PA of the circularity P of the 50 particles was determined and taken as the average circularity.

[0085] [(Water-soluble) angle of repose of the resin powder] The resin powder was conditioned for 1 week in an atmosphere of 20°C and 30% humidity or 20°C and 65% humidity. Then, using a Multi Tester MT-1001 manufactured by Seishin Enterprise Co., Ltd., the angle of repose of the resin powder was measured. The angle of repose was measured in accordance with the method described in JIS 9301-2-2:1999. The inventors have confirmed that the smaller the angle of repose of the resin powder, the less likely the particles are to fuse and agglomerates are to form in pipes and silos.

[0086] [(Water-soluble) evaluation of the solubility of the resin powder] To confirm the solubility of the resin powder in a solvent (water or NMP), 95 parts by mass of water or NMP was added to 5 parts by mass of PVA, and the temperature was raised to 95°C with stirring. Heating and stirring were carried out for 4 hours, and the dissolution state of PVA was visually observed. After cooling, it was passed through a wire mesh with an opening size of 3 mm, and the solubility was evaluated according to the following criteria. For those with an evaluation of A, when used as a binder, the uniformity of the electrode can be improved. A: No residue was confirmed on the wire mesh. B: Transparent gel-like lumps were confirmed on the wire mesh. C: Opaque gel-like lumps were confirmed on the wire mesh.

[0087] [Evaluation of the uniformity (homogeneity) of the electrode in the application of the negative electrode and the positive electrode] To evaluate the uniformity (homogeneity) of the negative electrodes and positive electrodes fabricated in the respective examples and comparative examples described below, the film thickness variation of the coated electrodes for batteries was used as an index, and four electrodes were measured at three points each. Judgments of ⊚, ○, Δ, and × were made according to the following criteria. For those with evaluations of ⊚ and ○, the discharge capacity and DC resistance are excellent, and those with an evaluation of ⊚ are particularly excellent. ⊚: The variation is 1 μm or less with respect to the average film thickness ○: The variation is greater than 1 μm and 2 μm or less with respect to the average film thickness Δ: The variation is greater than 2 μm and 3 μm or less with respect to the average film thickness ×: The variation is greater than 3 μm with respect to the average film thickness

[0088] [Discharge capacity and DC resistance of the lithium-ion secondary battery in the application of the negative electrode] Regarding the coin cells fabricated in the respective examples and comparative examples described below, tests were carried out using a commercially available charge-discharge tester (TOSCAT3100, manufactured by Toyo System). The resistance value when a current of 0.1 mA was passed for 3 seconds after the initial charge was defined as the DC resistance. In charging, constant current charging at 0.2C (about 1 mA / cm 2 ) was carried out up to 0.01 V with respect to the lithium potential, and further constant voltage charging at 0.01 V with respect to the lithium potential was carried out until the current reached 0.02 mA. In discharging, discharging was carried out at 0.2C (about 0.5 mA / cm 2Constant current discharge was performed. The coin cell was placed in a thermostatic bath at 25°C, and initial charge and discharge were carried out under the above conditions, and the discharge capacity and DC resistance were measured.

[0089] [Discharge Capacity and DC Resistance of Lithium-Ion Secondary Battery in Positive Electrode Application] For the coin cells fabricated in each of the following Examples and Comparative Examples, tests were carried out using a commercially available charge-discharge tester (TOSCAT3100, manufactured by Toyo System Co., Ltd.). The resistance value when a current of 0.1 mA was passed for 3 seconds after initial charging was defined as the DC resistance. In charging, constant current charging at 0.2C (about 1 mA / cm 2 ) was carried out up to 4.2 V with respect to the lithium potential. In discharging, constant current discharge at 0.2C (about 0.5 mA / cm 2 ) was carried out until 3 V with respect to the lithium potential. The coin cell was placed in a thermostatic bath at 25°C, and initial charge and discharge were carried out under the above conditions, and the discharge capacity and DC resistance were measured.

[0090] [Discharge Capacity and DC Resistance of Manganese Dioxide Lithium Battery in Positive Electrode Application] For the coin cells fabricated in each of the following Examples and Comparative Examples, tests were carried out using a commercially available charge-discharge tester (TOSCAT3100, manufactured by Toyo System Co., Ltd.). The resistance value when a current of 0.1 mA was passed for 3 seconds before discharging was defined as the DC resistance value. The battery was pre-discharged so that the battery voltage became 3.2 V, and then constant resistance discharge (15 kΩ) was carried out, and the discharge capacity up to 2.0 V was measured.

[0091] [Discharge Capacity and DC Resistance of Nickel-Metal Hydride Battery in Positive and Negative Electrode Applications] For the coin cells fabricated in each of the following Examples and Comparative Examples, tests were carried out using a commercially available charge-discharge tester (TOSCAT3100, manufactured by Toyo System Co., Ltd.). The coin cell was placed in a thermostatic bath at 25°C, and after charging at 0.2C, the charge-discharge operation of discharging at 0.4C until the battery voltage reached 1.0 V was repeated 5 times for initial activation. The resistance value when a current of 0.1 mA was passed for 3 seconds after initial activation was defined as the DC resistance value. The coin cell after initial activation was charged at 0.1C, and the capacity when discharged at 0.2C until the battery voltage reached 1.0 V was measured and defined as the discharge capacity.

[0092] - Preparation of slurry for negative electrodes of lithium-ion secondary batteries The above-mentioned binder aqueous solution with a solid content concentration of 5% by mass, artificial graphite (FSN-1, made by Shanshan, China) as the negative electrode active material, and Super-P (made by Timcal) as the conductive assistant (conductivity imparting agent) were put into a dedicated container and kneaded using a planetary mixer (ARE-250, made by Thinky Corporation) to prepare a negative electrode slurry. When putting them in, the solid content in the binder aqueous solution was 3 parts by mass, the solid content of the artificial graphite was 96 parts by mass, and the solid content of Super-P was 1 part by mass. That is, the composition ratio of the active material, conductive assistant, and binder in the negative electrode slurry was graphite powder:conductive assistant:binder = 96:1:3 (mass ratio) in terms of solid content.

[0093] - Preparation of negative electrodes for lithium-ion secondary batteries The negative electrode slurry obtained as described above was applied onto a current collector of copper foil (CST8G, manufactured by Fukuda Metal Foil and Powder Co., Ltd.) using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). After primary drying in a hot air dryer at 80°C for 30 minutes, rolling treatment was performed using a roll press (manufactured by Hosen Co., Ltd.). After that, it was punched out as a battery electrode (φ14 mm), and then secondary drying was performed under reduced pressure conditions at 140°C for 3 hours to prepare a negative electrode for a coin battery. The uniformity of the electrode was evaluated for the negative electrode for a coin battery prepared by the method described above. The results are summarized in Table 3 below.

[0094] - Fabrication of lithium-ion secondary batteries The negative electrode for the battery obtained as described above was transferred to a glove box (manufactured by Miwa Seisakusho Co., Ltd.) under an argon gas atmosphere. A metallic lithium foil (thickness 0.2 mm, φ16 mm) was used as the positive electrode, a polypropylene-based separator (Celgard #2400, manufactured by Polypore) was used as the separator, and a mixed solvent system (1M-LiPF6, EC / EMC = 3 / 7 vol%, 2 mass% VC) in which vinylene carbonate (VC) was added to ethylene carbonate (EC) and ethyl methyl carbonate (EMC) for lithium hexafluorophosphate (LiPF6) was used as the electrolyte solution and injected. With such a configuration, a coin battery (2032 type) was fabricated. For the fabricated coin battery, the discharge capacity and the DC resistance value were measured by the method described above. The results are summarized in Table 3 below.

[0095] · Preparation of Slurry for Positive Electrode of Lithium-Ion Secondary Battery Furthermore, the binder NMP solution with a solid content concentration of about 5 mass% described above, NCM (manufactured by Nippon Chemical Industry Co., Ltd., "Cellseed C-5H") as the positive electrode active material, and Super-P (manufactured by Timcal) as the conductive assistant (conductivity-imparting agent) were put into a dedicated container and kneaded using a planetary stirrer (ARE-250, manufactured by Shin Kiki Co., Ltd.) to prepare a slurry for the positive electrode. At the time of input, the solid content in the binder NMP solution was 3 parts by mass, NCM was 95 parts by mass, and the solid content of Super-P was 2 parts by mass. That is, the composition ratio of the active material, conductive assistant, and binder in the slurry for the positive electrode was, as solid content, NCM powder: conductive assistant: binder = 95:2:3 (mass ratio).

[0096] · Fabrication of Positive Electrode for Lithium-Ion Secondary Battery The positive electrode slurry obtained as described above was coated onto a current collector of aluminum foil (CST8G, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). After primary drying with a hot air dryer at 80°C for 30 minutes, rolling treatment was performed using a roll press (manufactured by Hosen Co., Ltd.). Thereafter, after punching out as an electrode for a battery (φ14 mm), a positive electrode for a coin battery was produced by secondary drying under reduced pressure conditions at 140°C for 3 hours. The uniformity of the electrode of the produced positive electrode for a coin battery was evaluated by the method described above. The results are summarized in Table 3 below.

[0097] · Fabrication of Lithium-Ion Secondary Battery The positive electrode for a battery obtained as described above was transferred to a glove box (manufactured by Miwa Seisakusho Co., Ltd.) under an argon gas atmosphere. A metal lithium foil (thickness 0.2 mm, φ16 mm) was used for the negative electrode, a polypropylene-based separator (Celgard #2400, manufactured by Polypore) was used, and an electrolytic solution was injected using a mixed solvent system (1M-LiPF6, EC / EMC = 3 / 7 vol%, 2 mass% VC) in which vinylene carbonate (VC) was added to ethylene carbonate (EC) and ethyl methyl carbonate (EMC) for lithium hexafluorophosphate (LiPF6). With such a configuration, a coin battery (2032 type) was fabricated. The discharge capacity and DC resistance value of the fabricated coin battery were measured by the method described above. The results are summarized in Table 3 below.

[0098] · Preparation of Slurry for Positive Electrode of Manganese Dioxide Lithium Battery The foregoing binder aqueous solution with a solid content of 5% by mass, manganese dioxide as a positive electrode active material, and Super-P (manufactured by Timcal) as a conductive assistant (conductive agent) were put into a dedicated container and kneaded using a planetary mixer (ARE-250, manufactured by Shin Kikai Co., Ltd.) to prepare a positive electrode slurry. At the time of input, the solid content in the binder aqueous solution was 3 parts by mass, the solid content of manganese dioxide was 95 parts by mass, and the solid content of Super-P was 2 parts by mass. That is, the composition ratio of the active material, conductive assistant, and binder in the positive electrode slurry was, as solid content, manganese dioxide powder: conductive assistant: binder = 95:2:3 (mass ratio). Note that the obtained slurry can be used not only for lithium manganese dioxide batteries but also for alkaline dry batteries and the like.

[0099] · Fabrication of the positive electrode for a lithium manganese dioxide battery The positive electrode slurry obtained as described above was coated on a current collector of aluminum foil (CST8G, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). After primary drying with a hot air dryer at 80°C for 30 minutes, rolling treatment was performed using a roll press (manufactured by Hozen Co., Ltd.). Then, after punching out as an electrode for a battery (φ14 mm), a positive electrode for a coin battery was fabricated by secondary drying under reduced pressure conditions at 140°C for 3 hours. The uniformity of the electrode of the fabricated positive electrode for a coin battery was evaluated by the method described above. The results are summarized in Table 3 below. Note that the obtained electrode can be used not only for lithium manganese dioxide batteries but also for alkaline dry batteries and the like.

[0100] · Fabrication of a lithium manganese dioxide battery The positive electrode for the battery obtained as described above was transferred to a glove box (manufactured by Miwa Seisakusho Co., Ltd.) under an argon gas atmosphere. A metallic lithium foil (thickness 0.2 mm, φ16 mm) was used for the negative electrode, a polypropylene-based separator (Celgard #2400, manufactured by Polypore) was used, and a mixed solvent system (1M-LiPF6, EC / EMC = 3 / 7 vol%, 2 mass% VC) in which vinylene carbonate (VC) was added to ethylene carbonate (EC) and ethyl methyl carbonate (EMC) for lithium hexafluorophosphate (LiPF6) was used for the electrolytic solution and injected. With such a configuration, a coin cell (2032 type) was fabricated. For the fabricated coin cell, the discharge capacity and the DC resistance value were measured by the method described above. The results are summarized in Table 3 below.

[0101] · Preparation of slurry for negative electrode of nickel-metal hydride battery The binder aqueous solution with a solid content concentration of 5 mass% described above, the hydrogen storage alloy as the negative electrode active material, and Super-P (manufactured by Timcal) as the conductive aid (conductive imparting agent) were put into a dedicated container and kneaded using a planetary stirrer (ARE-250, manufactured by Shinchi Co., Ltd.) to prepare a slurry for the negative electrode. At the time of charging, the solid content in the binder aqueous solution was 3 parts by mass, the solid content of the hydrogen storage alloy was 95 parts by mass, and the solid content of Super-P was 2 parts by mass. That is, the composition ratio of the active material, the conductive aid, and the binder in the slurry for the negative electrode is, as a solid content, hydrogen storage alloy:conductive aid:binder = 95:2:3 (mass ratio).

[0102] · Fabrication of negative electrode for nickel-metal hydride battery The slurry for the negative electrode obtained as described above was applied onto a current collector made of iron punching metal (thickness: 60 μm, hole diameter: 1.2 mm, aperture ratio: 40%) with nickel plating on the surface using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). After primary drying with a hot air dryer at 80°C for 30 minutes, rolling treatment was performed using a roll press (manufactured by Hozen Co., Ltd.). Thereafter, after punching out as an electrode for a battery (φ14 mm), a negative electrode for a coin cell was produced by secondary drying under reduced pressure conditions at 140°C for 3 hours. The uniformity of the electrodes of the produced negative electrode for a coin cell was evaluated by the method described above. The results are summarized in Table 3 below.

[0103] · Preparation of Slurry for Positive Electrode of Nickel-Metal Hydride Battery The binder aqueous solution with a solid content concentration of 5% by mass described above, nickel hydroxide as a positive electrode active material, and Super-P (manufactured by Timcal) as a conductive auxiliary agent (conductive imparting agent) were put into a dedicated container and kneaded using a planetary stirrer (ARE-250, manufactured by Shin Kee Co., Ltd.) to prepare a slurry for a positive electrode. At the time of charging, the solid content in the binder aqueous solution was 3 parts by mass, the solid content of nickel hydroxide was 95 parts by mass, and the solid content of Super-P was 2 parts by mass. That is, the composition ratio of the active material, conductive auxiliary agent, and binder in the slurry for the positive electrode was, as a solid content, nickel hydroxide: conductive auxiliary agent: binder = 95:2:3 (mass ratio).

[0104] · Fabrication of Positive Electrode for Nickel-Metal Hydride Battery The slurry for the positive electrode obtained as described above was applied onto a current collector made of nickel foam (basis weight (areal density) of about 300 g / m 2 , thickness of about 1.0 mm) using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). After primary drying with a hot air dryer at 80°C for 30 minutes, rolling treatment was performed using a roll press (manufactured by Hozen Co., Ltd.). Thereafter, after punching out as an electrode for a battery (φ14 mm), a positive electrode for a coin cell was produced by secondary drying under reduced pressure conditions at 140°C for 3 hours. The uniformity of the electrodes of the produced positive electrode for a coin cell was evaluated by the method described above. The results are summarized in Table 3 below.

[0105] ·Fabrication of Nickel-Hydrogen Battery Using the negative electrode and positive electrode for nickel-hydrogen battery obtained as described above, a coin battery was fabricated. As the separator, a polypropylene-based material (Celgard #2400, manufactured by Polypore) was used, and an alkaline electrolyte containing NaOH was injected as the electrolyte. As the alkaline electrolyte, an aqueous solution containing 7.5 mol / L of NaOH was used. With such a configuration, a coin battery (2032 type) was fabricated. For the fabricated coin battery, the discharge capacity and DC resistance value were measured by the method described above. The results are summarized in Table 3 below.

[0106] [Example 1] Production of Resin Powder 1 of PVA1 Into a 250 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and an initiator addition port, 112.5 kg of vinyl acetate and 37.5 kg of methanol (75% by mass of vinyl acetate: 25% by mass of methanol) were charged, and the system was purged with nitrogen for 30 minutes while bubbling nitrogen. The temperature of the reactor was started to rise, and when the internal temperature reached 60 °C, 35 g of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. When the polymerization rate reached 50%, cooling was carried out to stop the polymerization. The solid content concentration at the end of polymerization was 37.0%. Subsequently, methanol was added intermittently at 30 °C under reduced pressure to remove the unreacted vinyl acetate monomer, and a methanol solution of polyvinyl acetate (PVAc) (concentration 35%) was obtained. Further, 1.86 kg of an alkaline solution (10% methanol solution of sodium hydroxide) was added to 54.05 kg of a methanol solution of PVAc prepared by adding methanol thereto (20 kg of PVAc in the solution) for saponification (PVAc concentration in the saponification solution 30%, molar ratio of sodium hydroxide to vinyl acetate units in PVAc 0.02 mol%). Since a gel-like substance (resin solid) was formed about 1 minute after the addition of the alkaline solution, this was pulverized in a pulverizer (mixer) for 5 minutes. After leaving the pulverized product at 40 °C for 1 hour to allow saponification to proceed, 50 kg of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, filtration was carried out to obtain a white solid, and 200 kg of methanol was added thereto and left standing for washing at room temperature for 3 hours. After repeating the above washing operation 3 times, the white solid obtained by centrifugal dewatering was left in a dryer at 65 °C for 2 days to obtain a crude powder of PVA1. The degree of polymerization of PVA1 was 1,700, and the degree of saponification was 98.5 mol%. Next, the crude powder of PVA1 was filled into a Lodige mixer "FKM130D" equipped with a Becker type shovel manufactured by Chuo Kiko Co., Ltd. Surface treatment was carried out at a rotation speed of 160 rpm for 3 hours at room temperature in a nitrogen atmosphere. As a result, resin powder 1 having an average particle diameter of 650 μm and an average circularity of 0.25 was obtained.

[0107] [Examples 2 to 10, 15 to 16] Resin powder 2 of PVA2 and the like were obtained in the same manner as in Example 1 except that the conditions described in Table 1 were used.

[0108] [Example 11] Into a 250 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a comonomer dropping port, and an initiator addition port, 120.0 kg of vinyl acetate and 30.0 kg of methanol (80 mass% vinyl acetate: 20 mass% methanol) were charged, and the system was purged with nitrogen for 30 minutes while bubbling nitrogen. The temperature of the reactor was started to rise, and when the internal temperature reached 60 °C, 2.5 kg of acetaldehyde and 35 g of 2,2'-azobisisobutyronitrile (AIBN) were added to initiate polymerization. When the polymerization rate reached 50%, cooling was carried out to stop the polymerization. The solid content concentration at the end of polymerization was 39.3%. Hereinafter, except that the conditions described in Table 1 were adopted, the same procedure as in Example 1 was carried out to obtain 11 resin powders of PVA11.

[0109] [Example 12] Polymerization and saponification were carried out in the same manner as in Example 2 described in JP-A-2019-011282 to obtain a crude powder of ethylene-modified PVA (PVA12) having a degree of polymerization of 1850, a degree of saponification of 98.5 mol%, and an ethylene unit content of 6 mol%. Hereinafter, except that the conditions described in Table 1 were adopted, the same procedure as in Example 1 was carried out to obtain 12 resin powders of PVA12.

[0110] [Example 13] Into a 250 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a comonomer dropping port, and an initiator addition port, 112.5 kg of vinyl acetate, 37.5 g of methanol (75 mass% vinyl acetate: 25 mass% methanol), and 220 ml of a methanol solution in which methyl methacrylate was dissolved at 24 mass% were charged, and the system was purged with nitrogen for 30 minutes while bubbling nitrogen. The temperature of the reactor was started to rise, and when the internal temperature reached 60 °C, 25 g of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. While sequentially charging 11 L of the above methanol solution of methyl methacrylate, cooling was carried out when the polymerization rate reached 40% to stop the polymerization. The solid content concentration at the end of polymerization was 28.0%. Hereinafter, except that the conditions described in Table 1 were adopted, the same procedure as in Example 1 was carried out to obtain 13 resin powders of PVA13.

[0111] [Example 14] The pulverization time by the pulverizer was shortened to 2 minutes and the pulverization was coarser than in Example 1. Resin powder 14 of PVA14 was obtained in the same manner as in Example 2.

[0112] [Examples 17 to 19] Resin powder 17 of PVA17 etc. were obtained in the same manner as in Example 2, except that the surface treatment was performed with the apparatus described in Table 1 instead of the Lodige mixer.

[0113] [Example 20] The pulverization time by the pulverizer was lengthened to 10 minutes and the pulverization was finer than in Example 1. Resin powder 20 of PVA20 etc. were obtained in the same manner as in Example 2, except that the surface treatment by the Lodige mixer was not performed.

[0114] [Comparative Example 1] The pulverization time by the pulverizer was shortened to 1 minute and the pulverization was coarser than in Example 14. Resin powder 1' of PVA1' was obtained in the same manner as in Example 2.

[0115] [Comparative Example 2] Resin powder 2' of PVA2' was obtained in the same manner as in Example 2, except that the surface treatment by the Lodige mixer was not performed.

[0116] Table 2 shows the degree of polymerization and degree of saponification of each PVA obtained in Examples 1 to 20 and Comparative Examples 1 to 2, the average circularity, average particle diameter, and content of particles with a particle diameter of 100 to 1,000 μm of each resin powder, and the product of the average circularity and the degree of saponification.

[0117] [Evaluation] For each resin powder obtained in Examples 1 to 20 and Comparative Examples 1 to 2, the angle of repose after conditioning in an atmosphere of 20°C and 30% humidity and 20°C and 65% humidity was measured by the above method. The measurement results are shown in Table 2.

[0118] The solubility of each resin powder obtained in Examples 1 to 20 and Comparative Examples 1 and 2 in water and NMP, the electrode uniformity (electrode homogeneity) when used as an electrode binder for each energy storage device, and the energy storage device characteristics are shown in Table 3.

[0119]

Table 1

[0120]

Table 2

[0121]

Table 3

[0122] As shown in Table 3, when the resin powders of Examples 1 to 20 were used as binders, uniform electrodes were obtained because gel-like lumps were less likely to occur when dissolved in water or NMP. As a result, a battery having a high discharge capacity and a low DC resistance was obtained. On the other hand, when the resin powder of Comparative Example 1 having a large average particle diameter and the resin powder of Comparative Example 2 having a small average circularity were used as binders, gel-like lumps were likely to occur when dissolved in water or NMP. Along with this, the uniformity of the electrodes was impaired, resulting in a decrease in discharge capacity and an increase in DC resistance.

Claims

1. A binder containing a water-soluble resin powder, wherein the water-soluble resin powder is composed of particles having an average particle diameter of 100 to 2,000 μm, for 50 particles arbitrarily extracted from the particles having a particle diameter of 100 to 1,000 μm contained in the water-soluble resin powder, for each of the following formulas (1) of each particle 【Number 1】 [In formula (1), r i is the radius of curvature for each angle of the particle, R is the radius of the largest inscribed circle of the particle, N is the number of corners of the particle, however, when the number of corners of the particle is 9 or more, the curvature radii of 8 corners are adopted in ascending order of the curvature radius, and N is 8] A binder in which the average value PA of the circularity P represented by is 0.1 to 0.

8.

2. The binder according to claim 1, wherein the water-soluble resin is a vinyl alcohol-based polymer.

3. The binder according to claim 2, wherein the viscosity average degree of polymerization of the vinyl alcohol-based polymer is 200 to 5,000, and the saponification degree is 35 to 99.99 mol%.

4. The following formula (2) PA × S ≧ 18 (2) [In formula (2), PA is the same as defined above, and S is the saponification degree (mol%) of the vinyl alcohol-based polymer] The binder according to any one of claims 2 to 3, which satisfies and the water-soluble resin powder has an average particle diameter of 100 to 1,000 μm.

5. The binder according to any one of claims 1 to 4, wherein the content of particles having a particle diameter of 100 to 1,000 μm in the water-soluble resin powder is 50% by mass or more.

6. A storage device electrode containing the binder according to any one of claims 1 to 5.

7. A binder solution for a storage device electrode containing the binder according to any one of claims 1 to 5 and water.

8. The binder solution for a storage device electrode according to claim 7, containing N-methyl-2-pyrrolidone.

9. A storage device electrode slurry containing the binder solution for a storage device electrode according to claim 7 or 8 and an active material.

10. The storage device electrode slurry according to claim 9, wherein the content of the binder is 0.1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the active material.

11. A step of obtaining a coarse powder of the water-soluble resin by pulverizing a resin solid containing the water-soluble resin, and A step of processing the surface of the particles constituting the coarse powder A method for producing the binder according to any one of claims 1 to 5, including.

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