WO2021187366A1 - Binder suitable for electricity storage device electrodes, binder solution, electricity storage device electrode slurry, electricity storage device electrode, and electricity storage device - Google Patents

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), r_i 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

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

This patent application claims priority under the Paris Convention with respect to Japanese Patent Application No. 2020-0448997 (filed on March 16, 2020), which is hereby incorporated by reference in its entirety. It shall be incorporated into the book.
The present invention relates to a binder, a binder solution, a storage device electrode slurry, a power storage device electrode, and a power storage device suitable for a power storage device electrode.

In recent years, mobile terminals such as mobile phones, notebook personal computers, and pad-type information terminal devices have become remarkably widespread. Mobile terminals are required to be more comfortable to carry, and with the rapid progress of miniaturization, thinning, weight reduction and high performance, batteries used in mobile terminals are also becoming smaller, thinner, lighter and lighter. High performance is required. Lithium-ion secondary batteries are often used as power storage devices used as power sources for such mobile terminals. For non-aqueous electrolyte batteries such as lithium ion secondary batteries, positive and negative electrodes are installed via a separator, and LiPF ₆ , LiBF ₄ , LiTFSI (lithium (bistrifluoromethylsulfonylimide)), LiFSI (lithium (bisfluorosulfonylimide)). It has a structure in which these electrodes are housed in a container together with an electrolytic solution in which a lithium salt such as)) is dissolved in an organic liquid such as ethylene carbonate.

The negative electrode and positive electrode constituting the power storage device are usually obtained by dissolving or dispersing a binder and a thickener in water or a solvent, and mixing the active material, a conductive auxiliary agent (conducting agent), or the like with the binder and a thickener. Is applied to the current collector and then dried with water or a solvent to form a mixed layer.

From the viewpoint of reducing the burden on the environment and the convenience of the manufacturing equipment, the movement to use an aqueous medium for the electrode slurry is rapidly advancing, especially in the manufacturing of the negative electrode. As the binder used for such an electrode slurry for an aqueous medium, a vinyl alcohol-based polymer (hereinafter, also referred to as "PVA"), an acrylic-based polymer such as acrylic acid, a binder of an amide / imide-based polymer, and the like are known. (For example, Patent Documents 1 and 2).

On the other hand, in the production of the positive electrode, an electrode slurry using a solvent is generally used. Examples of such a solvent include organic solvents such as N-methyl-2-pyrrolidone, dimethylformamide, N, N-dimethylacetamide, N, N-dimethylmethanesulfonamide, and hexamethylphosphoric triamide. As the binder used for such an electrode slurry for an organic solvent, vinylidene fluoride-based polymer, tetrafluoroethylene-based polymer, fluororubber and the like are known (for example, Patent Documents 3 and 4).

Japanese Unexamined Patent Publication No. 11-250915 JP-A-2017-59527 JP-A-2017-107827 Japanese Unexamined Patent Publication No. 2013-37955

However, in any of the production of the negative electrode and the positive electrode described in Patent Documents 1 to 4, a slurry (electrode) obtained by mixing a binder, a solvent (water or a solvent), an active material, a conductive additive (conductivity-imparting agent), or the like is mixed. Slurry) has many problems as shown below, for example, due to the influence of various conditions in the preparation of the slurry and the form of the material such as the binder in the slurry when the electrode is formed by applying the slurry to the current collector. Was occurring.

When using resin powder as a binder, it is necessary to dissolve the resin powder in water or a solvent (N-methyl-2-pyrrolidone (NMP), etc.) in advance, but in the case of water-soluble resin powder, piping In the silo or silo, the particles constituting the powder are fused to form agglomerates, which may cause gel-like lumps at the time of dissolution. When the slurry is prepared using a binder solution containing a large amount of gel-like lumps, it becomes difficult to disperse the active material in the slurry, and as a result, it becomes difficult to form the electrodes uniformly, and the performance is sufficiently low. It was not possible to obtain resistance and high discharge capacity. Due to the water-soluble and hygroscopic properties of the water-soluble resin powder, there is a problem that such agglomerates are likely to be generated and gel-like lumps are likely to occur at the time of dissolution, especially in a high humidity environment. ..

Therefore, the present invention is less likely to cause gel-like lumps when the water-soluble resin powder is dissolved, and is preferably a uniform electrode (an electrode having a small film thickness variation of the coating electrode), especially when used as a power storage device electrode. It is an object of the present invention to provide a binder that can form a storage device electrode having a low resistance and a high discharge capacity.

The above object is achieved by the present invention including the following preferred embodiments.
[1] A binder containing a water-soluble resin powder, which is a binder.
The water-soluble resin powder is composed of particles having an average particle diameter of 100 to 2,000 μm.
With respect to 50 particles arbitrarily extracted from the particles having a particle size of 100 to 1,000 μm contained in the water-soluble resin powder, the following formula (1) of each particle is used.

[In equation (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 horns that the particle has,
However, when the number of corners of the particle is 9 or more, the radius of curvature of 8 corners is adopted in ascending order of radius of curvature, and N is 8.]
A binder in which the average value PA of the degree of 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 vinyl alcohol-based polymer has a viscosity average degree of polymerization of 200 to 5,000 and a saponification degree of 35 to 99.99 mol%.
[4] The following formula (2)
PA × S ≧ 18 (2)
[In the formula (2), PA is the same as the above definition, and S is the saponification degree (mol%) of the vinyl alcohol polymer].
The binder according to any one of claims 1 to 3, wherein the water-soluble resin powder has an average particle size of 100 to 1,000 μm.
[5] The binder according to any one of [1] to [4], wherein the content of particles having a particle size of 100 to 1,000 μm is 50% by mass or more in the water-soluble resin powder.
[6] A power storage device electrode containing the binder according to any one of [1] to [5].
[7] A binder solution for a power storage device electrode containing the binder according to any one of [1] to [5] and water.
[8] The binder solution for a power storage device electrode according to [7], which contains N-methyl-2-pyrrolidone.
[9] A storage device electrode slurry containing the binder solution for a power storage device electrode according to [7] or [8] and an active material.
[10] The storage device electrode slurry according to [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 power storage device electrode comprising a cured body and a current collector of the power storage device electrode slurry according to [9] or [10].
[12] A power storage device including the power storage device electrode according to [11].
[13] The present invention includes a step of obtaining a crude powder of the water-soluble resin by crushing a resin solid containing the water-soluble resin, and a step of processing the surface of particles constituting the crude powder [1]. The method for producing a binder according to any one of [5].

According to the present invention, gel-like lumps are less likely to occur when the water-soluble resin powder is dissolved, and when used as a power storage device electrode, a suitable uniform electrode (electrode having a small thickness variation of the coated electrode) is formed. It is possible to provide a binder for a power storage device electrode, which has a low resistance and a high discharge capacity.

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

[In equation (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 horns that the particle has,
However, when the number of corners of the particle is 9 or more, the radius of curvature of 8 corners is adopted in ascending order of radius of curvature, and N is 8.]
The average value PA (hereinafter, also referred to as “average circularity”) of the circularity P represented by is 0.1 to 0.8.

As described above, the water-soluble resin powder contained in the binder of the present invention has an average roundness PA of 0.1 to 0.8, preferably 0.12 to 0.7, and more preferably 0. It is .14 to 0.65, more preferably 0.16 to 0.6.

When the average degree of roundness is within the above-mentioned specific range, agglomerates due to fusion of the resin powder are less likely to occur in the piping or silo as compared with the conventional binder made of water-soluble resin powder. The reason for this is not always 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, the fusion of the particles is unlikely to occur.

The water-soluble resin is not particularly limited as long as it has a solubility of 1 g or more of the resin in 100 g of water. For example, such water-soluble resins include vinyl alcohol-based polymers and derivatives thereof, acrylic polymers and derivatives such as (meth) acrylic acid, cellulose derivatives such as carboxymethyl cellulose, alginic acid and its neutralized products, and polyvinyl. Examples include pyrrolidone.

Of these, vinyl alcohol-based polymers and their derivatives have good affinity for active materials used in power storage devices such as carbon materials, metals, and metal oxides, and are therefore preferably used as water-soluble resins. ..

When PVA is used as the water-soluble resin, it is usually the main component of the water-soluble resin powder. The main component means the component having the highest content on a mass basis. The content of PVA in the non-volatile content of the water-soluble resin powder is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 90% by mass or more, and even more preferably 99% by mass or more. .. The upper limit of the content of PVA in the non-volatile content of the water-soluble resin powder may be 100% by mass. Non-volatile components other than PVA that may be contained in the water-soluble resin powder include resins other than PVA, surfactants, plasticizers, defoaming agents, additives such as viscosity modifiers, and compounds used during production. And so on. The content of the 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 the volatile matter that can be contained in the water-soluble resin powder include alcohol and water.

A vinyl alcohol-based polymer (also referred to as "polyvinyl alcohol" or simply "PVA") is a polymer having a vinyl alcohol unit as a monomer unit (that is, a constituent unit). PVA is usually obtained by saponifying a polyvinyl ester. The ratio of vinyl alcohol units to all monomer units in PVA is preferably 35 mol% or more, more preferably 50 mol% or more, further preferably 70 mol% or more, and more preferably 80 mol% or more or 90 mol% or more. It may be even more preferable. By setting the ratio of the vinyl alcohol unit to the above lower limit value or more, the passability is enhanced particularly in a high humidity environment, and the water-soluble resin powder in the present invention can be efficiently produced by a production method that undergoes crushing and surface processing. It will be easier to manufacture. On the other hand, the ratio of the vinyl alcohol unit may be 100 mol%, but is preferably 99.99 mol% or less, and more preferably 99 mol% or less.

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

PVA may have a monomer unit (constituent unit) other than the vinyl alcohol unit and the vinyl ester unit. Examples of the monomer giving the other monomer unit include α-olefins such as ethylene, propylene, 1-butene, isobutene and 1-hexene; acrylic acid and methacrylic acid; acrylics such as methyl acrylate and ethyl acrylate. Acid ester; Methacrylate ester such as methyl methacrylate and ethyl methacrylate; acrylamide derivative such as N-methylacrylamide and N-ethylacrylamide; Methacrylate derivative such as N-methylmethacrylate and N-ethylmethacrylate; Methylvinyl ether, Vinyl ethers such as 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; propyl allyl Allyl ethers such as ethers, butyl allyl ethers, and hexyl allyl ethers; monomers having an oxyalkylene group; isopropenyl acetate; 3-butene-1-ol, 4-penten-1-ol, 5-hexene-1-ol , 7-octen-1-ol, 9-decene-1-ol, 3-methyl-3-buten-1-ol and other hydroxy group-containing α-olefins; vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxy Monomers having a silyl group such as silane, vinyl triethoxysilane, vinyl methyl diethoxysilane, vinyl dimethyl ethoxysilane, 3- (meth) acrylamide propyltrimethoxysilane, 3- (meth) acrylamide propyltriethoxysilane, etc. Can be mentioned. Among these, α-olefin, acrylic acid, methacrylic acid, acrylic acid ester and methacrylic acid ester are preferable.

The ratio of the above-mentioned other monomer units to the total monomer units in PVA may be preferably 20 mol% or less, and more preferably 10 mol% or less. On the other hand, the ratio of the other monomer units may be, for example, 0.1 mol% or more, and may be 1 mol% or more.

The viscosity average degree of polymerization of PVA is not particularly limited, but is preferably 200 or more, more preferably 250 or more, further preferably 400 or more, and particularly preferably 600 or more. The viscosity average degree of polymerization is preferably 5,000 or less, more preferably 4,500 or less, and even more preferably 3,500 or less. By setting the viscosity average degree of polymerization within the above range, industrial production of resin particles having the above average degree of roundness becomes easy. The viscosity average degree of polymerization can be measured according to JIS K6726: 1994. That is, PVA can be re-saponified to a saponification degree of 99.5 mol% or more, purified, and then determined by the following formula from the ultimate viscosity [η] (unit: liter / g) measured in water at 30 ° C.
Viscosity average degree of polymerization = ([η] × 1,0000 / 8.29) (1 / 0.62)

The average particle size 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 size is 100 μm or more, dust explosion is less likely to occur, and safety can be improved. The average particle size is 2,000 μm or less, preferably 1,500 μm or less, more preferably 1,000 μm or less, still more preferably 850 μm or less. When the average particle size is 2000 μm or less, it becomes easy to dissolve in a solvent, the generation of gel-like lumps is suppressed, and a uniform electrode can be produced.

The average particle size of the water-soluble resin powder (that is, the particles constituting the water-soluble resin powder) can be measured according to the method described in JIS K7369: 2009.

Average roundness of the water-soluble resin powder (that is, particles constituting the water-soluble resin powder) in the present invention (roundness P of 50 particles arbitrarily extracted from particles having a particle size of 100 to 1,000 μm) It is important that the average value PA) of is 0.1 or more, preferably 0.2 or more, more preferably 0.25 or more, further preferably 0.3 or more, particularly preferably 0.33 or more, and 0. .35 or higher may be highly preferred. By setting the average roundness to 0.1 or more, it becomes easy to dissolve in a solvent, the generation of gel-like lumps is suppressed, and a uniform electrode can be produced. On the other hand, it is important that the average degree of roundness is 0.8 or less, preferably 0.7 or less. By setting the average roundness 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 roundness of less than or equal to the above upper limit can be effectively produced by a production method of crushing and surface processing.

The average roundness of the water-soluble resin powder (that is, the particles constituting the water-soluble resin powder) can be determined by the following method. Arbitrarily 50 particles are extracted from the particles having a particle size of 100 to 1,000 μm (or a particle size of 106 to 1,000 μm based on a sieving net) in the water-soluble resin powder. Particles having a particle size of 100 to 1,000 μm are sorted as particles that have passed through a sieving net with a nominal opening of 1,000 μm (16 mesh) and have not passed through a sieving net with a nominal opening of 106 μm (150 mesh) in sieving. can do. The mechanical sieving can be performed by, for example, the method described in JIS K7369: 2009. The extracted one particle, the projection view area of the apparent is maximized, eight corners (corner is less than eight in ascending order of the radius of curvature r _i, that is, when the 7 or less, all that extract the corner), for measuring the radius of curvature r _i of each the corner. Further, the radius R of the maximum inscribed circle of the particle is measured based on the projection drawing that maximizes the apparent area. The number of angles of the particle is N (when the number of angles of the particle is 9 or more, N is 8), and based on the measured _ri and R, the circle of one particle is calculated by the following formula (1). Polishing degree P is required. A low degree of roundness P indicates that the particles have many angular corners, and a high degree of roundness indicates that the particles are rounded.

[In equation (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 horns that the particle has,
However, when the number of corners of the particle is 9 or more, the radius of curvature of 8 corners is adopted in ascending order of radius of curvature, and N is 8.]

The above-mentioned circularity P is measured for the extracted 50 particles, and the average value PA of the circularity P of these 50 particles is obtained. This average value PA is the average degree of roundness.

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 of 106 to 1,000 μm based on a sieve net) is not particularly limited, but is 50% by mass or more. Is preferable, 55% by mass or more is more preferable, and 60% by mass or more is further preferable. 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, fusion of the particles is less likely to occur in the piping or silo, and gel-like lumps are less likely to occur when the resin powder is dissolved. Become. Along with this, when used as a binder solution for electrode fabrication, 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 is determined by using a sieve net having a nominal opening of 1,000 μm (16 mesh) and a sieve net having a nominal opening of 106 μm (150 mesh). It can be obtained according to the method described in 2009.

The water-soluble resin powder (that is, the particles constituting the water-soluble resin powder) in the present invention preferably satisfies the following formula (2), satisfies the following formula (2), and has an average particle size of 100 to 1. More preferably, it is 000 μm. In such a case, it is possible to suppress the fusion of particles and the generation of agglomerates, especially under high humidity. According to the study by the present inventor, the higher the average degree of circularity, the less likely it is that the particles will be fused. On the other hand, especially under high humidity, the water-soluble resin powder containing PVA having a low degree of saponification is affected by its hygroscopicity and the like, so that particles are easily fused. Therefore, by setting the product (PA × S) of the average value PA (average circularity) of the circularity P and the saponification degree S of PVA to a predetermined value or more, the fusion of particles is suppressed even under high humidity. be able to.
PA × S ≧ 18 (2)
In the formula (2), PA is the average value of the degree of roundness P. S is the saponification degree (mol%) of PVA.

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

The angle of repose measured after adjusting the humidity of the water-soluble resin powder in the present invention in an atmosphere of 20 ° C. and 30% humidity for one week is preferably less than 38 °, more preferably less than 35 °. The angle of repose measured after adjusting the humidity of the water-soluble resin powder in the present invention in an atmosphere of 20 ° C. and 65% humidity for one week is preferably less than 40 °, more preferably less than 38 °. When the angle of repose of the water-soluble resin powder is so 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, but may be, for example, 25 ° or more, or 30 ° or more. The angle of repose of the water-soluble resin powder can be controlled within the above range by controlling the average roundness and the average particle size. The angle of repose of the water-soluble resin powder can be measured according to the method described in JIS 9301-2-2: 1999.

<Manufacturing method of 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 of obtaining a crude powder of the water-soluble resin by pulverizing a resin solid containing the water-soluble resin (step B), and a step of processing the surface of particles contained in the crude powder (step C).
including.

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

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

In the polymerization step, the 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 a massive polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among these methods, a lumpy polymerization method performed without a solvent and a solution polymerization method performed using a solvent such as alcohol are preferable, and a solution polymerization method of polymerizing in the presence of a lower alcohol is more preferable. As the lower alcohol, an alcohol having 3 or less carbon atoms is preferable, methanol, ethanol, n-propanol and isopropanol are more preferable, and methanol is even more preferable. When carrying out the polymerization reaction by the massive polymerization method or the solution polymerization method, either a batch method or a continuous method can be adopted as the reaction method.

Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like. Be done. Of these, vinyl acetate is preferable.

Examples of the initiator used in the polymerization reaction include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2'-azobis (4-methoxy). Azo-based initiators such as −2,4-dimethylvaleronitrile); known initiators such as organic peroxide-based initiators such as benzoyl peroxide and n-propylperoxycarbonate can be mentioned. The polymerization temperature at the time of carrying out the polymerization reaction is not particularly limited, but a range of 5 ° C. or higher and 200 ° C. or lower is suitable.

When polymerizing the vinyl ester monomer, a copolymerizable monomer 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 coexist for the purpose of adjusting the degree of polymerization of the obtained PVA. Examples of the chain transfer agent include aldehydes such as acetaldehyde, propionaldehyde, butylaldehyde and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone and cyclohexanone; mercaptans such as 2-hydroxyethanethiol; thiocarboxylic acids such as thioacetic acid; trichloroethylene and perchloro. Examples thereof include halogenated hydrocarbons such as ethylene, and among them, aldehydes and ketones are preferably used. The amount of the chain transfer agent added is determined according to the chain transfer constant of the chain transfer agent to be added and the degree of polymerization of the target PVA, but is generally 0.1 to 10% by mass with respect to the vinyl ester used. Is preferable.

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. Alcohol decomposition or hydrolysis using a conventionally known basic catalyst such as sodium hydroxide, potassium hydroxide or sodium methoxyde, or an acidic catalyst such as p-toluenesulfonic acid is used for the saponification reaction of the vinyl ester polymer. The reaction is applicable. Examples of the solvent used in the saponification reaction include 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. These can be used alone or in combination of two or more. Among these, it is convenient and preferable to carry out the saponification reaction in the presence of sodium hydroxide, which is a basic catalyst, using methanol or a mixed solution of methanol and methyl acetate as a solvent.

The saponification step can be performed by a belt type reactor, a kneader type reactor, a tower type reactor, or the like. By going through the saponification step, a resin solid containing PVA can be obtained. The content ratio of PVA in the non-volatile content 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 further preferably 99% by mass or more. The non-volatile content in the resin solid may be substantially PVA as a main component, but may contain impurities such as sodium acetate, by-products and the like.

(Step B)
In step B, a resin solid containing a water-soluble resin such as PVA is pulverized. As a result, a crude powder containing a water-soluble resin can be obtained. The above pulverization can be performed by a known pulverizer. As the crusher, an apparatus capable of controlling the degree of crushing such as crushing strength is preferable in order to adjust the average particle size and the like of the particles constituting the obtained crude powder and eventually the finally obtained resin powder. In addition to adjusting the crushing strength, the average particle size and the like of the particles constituting the obtained crude powder can also be controlled by the treatment time and the like. The average particle size of the particles constituting the crude powder is not limited, but when the surface processing is performed in the step C described later, the resin powder finally obtained in consideration of the reduction in particle size due to the step. It is preferable to set it to be equal to or larger than the average particle size of the body. For example, by setting the average particle size of the particles constituting the crude powder to 100 to 3000 μm, a resin powder having a desired average particle size can be finally obtained. The obtained crude powder may be saponified again. Further, the obtained crude powder may be subjected to a cleaning treatment for reducing impurities such as sodium acetate, by-products and the like, and a drying treatment for reducing volatile components. The resin solid substance before crushing may be subjected to a cleaning treatment or a drying treatment.

(Step C)
In step C, the surface of the particles constituting the crude powder is processed. When a resin solid containing a water-soluble resin such as PVA is crushed, the obtained crude powder usually has a very sharp-edged shape. Therefore, in step C, a water-soluble powder having rounded corners and an average degree of roundness within a predetermined range can be efficiently obtained.

The apparatus used in step C is not particularly limited as long as the surface of the crude powder can be polished. For example, the surface polishing proceeds when the powder filling container rotates and the powders come into contact with each other. A rotary kiln, a planetary motion mixer that can give three-dimensional motion to the contents by a screw blade that revolves in the container, so that the paddle and screw in the container rotate and the internal powder is polished by the rotation. Mixers and the like. Examples of the mixer include a high-speed mixer, a Henschel mixer, a turbulizer, a radige mixer and the like. Among these, from the viewpoint of processing efficiency, a mixer is preferable, and a turbulizer and a radige mixer are more preferable. Further, in the step C, the surface processing of the crude powder may be performed while heating.

The method for producing the water-soluble resin powder in the present invention may also include a sieving step for adjusting the average particle size. Further, after the step C, a cleaning treatment or a drying treatment may be performed.

<Binder solution for power storage device electrodes>
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 polyvalent basic acids such as citric acid, tartaric acid and aspartic acid and salts thereof, condensates thereof, and inorganic substances such as fumed silica and alumina. The amount of these additions is not particularly limited, but is usually preferably 0.01 part by mass or more and 10 parts by mass or less, more preferably 0.02 parts by mass or more and 8 parts by mass or less, still more preferably, with respect to 100 parts by mass of PVA. Is 0.05 parts by mass or more and 5 parts by mass or less. The more the material for adjusting the viscosity is contained, the more the viscosity of the binder of the present invention in the solution state can be increased. The smaller the particle size of the inorganic substance, the easier it is to increase the viscosity of the binder in the solution state.

The binder of the present invention or the binder solution for the power storage device electrode of the present invention described later can further contain a compounding agent as long as the effects of the present invention are not impaired. Examples of the compounding agent include a light stabilizer, an ultraviolet absorber, a freeze stabilizer, a thickener, a leveling agent, a rheology stabilizer, a thixoxing agent, an antifoaming agent, a plasticizer, a lubricant, and a preservative. Anti-corrosive agents, anti-static agents, anti-static agents, anti-yellowing agents, pH adjusters, film-forming aids, curing catalysts, cross-linking reaction catalysts, cross-linking agents (glioxal, urea resin, melamine resin, polyvalent metal salts, Polyhydric isocyanate, polyamide epichlorohydrin, etc.), dispersants, etc. can be mentioned. It can be selected or combined according to each purpose. The content of the compounding agent is, for example, 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, based on the total amount of the binder or the binder solution for the power storage device electrode.

The binder of the present invention is obtained by dissolving a water-soluble resin, particularly PVA, and a component other than the water-soluble resin contained as necessary in a solvent (for example, water or NMP) to prepare a solution, and removing the solvent. May be good. Further, the solution may be used as it is for the preparation of a slurry which follows as a binder solution for a power storage device electrode of the present invention, which will be described later. 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 the cured product of the slurry composition of the present invention in a state of being mixed with components such as an active material.

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 viewpoint of reducing the environmental load and the convenience of the equipment. On the other hand, when the solvent is NMP, it is preferable because the active material in the slurry is not deteriorated, especially when it is applied as a slurry for a positive electrode.

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

The binder solution is prepared by mixing a water-soluble resin such as PVA, a solvent (for example, water or NMP), and a component other than the aqueous solution resin as described above, which is contained if necessary, by a known method, for example, stirring. And get it. The mixing temperature and mixing time can be appropriately adjusted according to the type of solvent. The binder solution indicates a solution in which the above-mentioned water-soluble resin is dissolved in a solvent. In the dissolved state, the mass of the water-soluble resin completely dissolved in the solvent, particularly PVA, is preferably based on the total mass (100% by mass) of the water-soluble resin used in preparing the binder solution. It means a state of 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 99% by mass or more, and even more preferably 100% by mass.

The content of the water-soluble resin, particularly PVA, in the binder solution of the present invention is 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, based on the total amount of the binder solution. Is 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 adhesiveness 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 prevent the active material from rapidly aggregating when forming the electrode.

<Storage device electrode slurry>
The power storage device electrode slurry as an embodiment of the present invention contains the above-mentioned binder solution and active material.

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

As the negative electrode active material, for example, a material conventionally used as a negative electrode active material of a power storage device can be used. Examples are conductive such as amorphous carbon, artificial graphite, natural graphite (graphite), mesocarbon microbeads (MCMB), pitch carbon fiber, carbon black, activated carbon, carbon fiber, hard carbon, soft carbon, mesoporous carbon and polyacene. Carbonous materials such as sex polymers, silicon-based compounds such as _{Si and SiO x , composite metal oxides represented by SnO x} and LiTIO _x , other metal oxides, lithium metals, lithium-based metals such as lithium alloys, Examples thereof include metal compounds such as TiS ₂ and LiTiS ₂ , composite materials of metal oxides and carbonaceous materials, hydrogen storage alloys and the like. These negative electrode active materials can be used alone or in combination of two or more.

As the positive electrode active material, for example, a material conventionally used as a positive electrode active material of a power storage device can be used. Examples are transitions such as TiS ₂ , TiS ₃ , amorphous MoS ₃ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O-P ₂ O ₅ , MoO ₃ , V ₂ O ₅ and V ₆ O _13. Examples include metal oxides, lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ , manganese dioxide, nickel hydroxide, nickel oxyhydroxide, and the like. These positive electrode active materials can be used alone or in combination of two or more.

The slurry may contain a conductive auxiliary agent. The conductive auxiliary agent is used to increase the output of the power storage device, and can be appropriately selected depending on the case where it is used for the positive electrode or the negative electrode. Examples thereof include graphite, acetylene black, carbon black, Ketjen black, vapor-grown carbon fiber and the like. Among these, acetylene black is preferable from the viewpoint that the output of the obtained power storage device can be easily increased.

When the slurry contains a conductive auxiliary agent, the content of the conductive auxiliary agent is preferably 0.1 part by mass or more and 15 parts by mass or less, and more preferably 1 part by mass or more and 10 parts by mass with respect to 100 parts by mass of the active material. Hereinafter, it is more preferably 3 parts by mass or more and 10 parts by mass or less. When the content of the conductive auxiliary agent is within this range, a sufficient conductive auxiliary effect can be obtained without lowering the battery capacity to which the slurry is applied.

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 adhesiveness 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 content range is more preferably 0.2 parts by mass or more and 18 parts by mass or less, further preferably 0.5 parts 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.

The slurry may contain additives such as flame-retardant aids, thickeners, defoamers, leveling agents, and adhesion-imparting agents, if necessary, in addition to binders, active materials, conductive aids and solvents. can. 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.

The slurry is prepared by mixing binders, active materials and, if necessary, conductive aids, solvents and additives by conventional methods, for example using a mixer such as a ball mill, blender mill, three rolls or the like. Obtainable.

<Storage device electrode>
The power storage device electrode as an embodiment of the present invention includes the cured body and the current collector of the above-mentioned slurry. The cured product of the slurry is a cured product obtained by removing the solvent in the slurry by drying or the like.

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

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

The method of 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 product derived from the slurry composition.

Examples of the electrode rolling method include a mold press and a roll press. The press pressure is preferably 1 MPa or more and 40 MPa or less from the viewpoint of easily increasing the battery capacity.

In the electrode of the present invention, the thickness of the current collector is preferably 1 μm or more and 200 μm or less, and more preferably 2 μm or more and 150 μm or less. The thickness of the cured product is preferably 10 μm or more and 800 μm, and 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.

<Power storage device>
The power storage device as one embodiment of the present invention includes the above-mentioned power storage device electrode as a negative electrode and / or a positive electrode.

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 hydrogen battery, an alkaline dry battery, and the like.

The power storage device of the present invention has excellent electrode uniformity, low electrical resistance, and high discharge capacity.

The discharge capacity of the power storage device can be calculated by using, for example, a method of performing a charge / discharge test using a commercially available charge / discharge tester, as shown in Examples described later.

The electrolytic solution contained in the power storage device is a solution that dissolves the electrolyte in a solvent. The electrolyte may be in the form of a liquid or a gel as long as it is used in a normal battery, and an electrolyte that exhibits a function as a battery may be appropriately selected depending on the type of the negative electrode active material and the positive electrode active material. Specific electrolytes, for example, suitably can be used known lithium salt in the nonaqueous electrolyte _{battery, LiClO 4, LiBF 6, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , CF ₃ SO ₃ Li, CH ₃ SO ₃ Li, LiCF ₃ SO ₃ , _{Li C 4} F ₉ SO ₃ , Li (CF ₃ SO) _{2) 2} N, include lower aliphatic carboxylic acid lithium, and the like. Examples of batteries using an aqueous electrolyte include an alkaline aqueous solution containing potassium hydroxide, sodium hydroxide, and lithium hydroxide as solutes.

The solvent contained in the electrolytic solution is not particularly limited. Specific examples thereof include carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate and vinylene carbonate, lactones such as γ-butyl lactone, trimethoxymethane and 1,2-dimethoxy. Ethers such as ethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetraxide, sulfoxides such as dimethylsulfoxide, oxolanes such as 1,3-dioxolane and 4-methyl-1,3-dioxolane, acetonitrile and Nitrogen-containing compounds such as 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, Examples thereof include jiglimes, triglimes, sulfolans, oxazolidinones such as 3-methyl-2-oxazolidinone, 1,3-propane sulton, and sulton such as 1,4-butane sulton and nafta sulton, water and the like. These can be used alone or in combination of two or more. When a gel-like electrolytic solution is used, 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.

When the electrode of the present invention is used for 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.

In one of the preferred embodiments, the power storage device of the present invention includes the electrode of the present invention as a negative electrode and a conventional electrode as a positive electrode. The positive electrode is not particularly limited as long as it is a positive electrode normally used for a power storage device.

Alternatively, in one of the preferred embodiments, the power storage device of the present invention includes the electrode of the present invention as a positive electrode and a conventional electrode as a negative electrode. The negative electrode is not particularly limited as long as it is a negative electrode normally used for a power storage device.

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

The method for manufacturing the power storage device of the present invention is not particularly limited, but for example, it can be manufactured as follows. That is, the negative electrode and the positive electrode are overlapped with each other via a separator such as a polypropylene porous membrane, wound and / or folded according to the shape of the battery, put into a battery container, and the electrolytic solution is injected to seal the battery. The shape of the battery may be any of known coin type, button type, sheet type, cylindrical type, square type, flat type and the like.

The power storage device of the present invention is useful for various uses. For example, it is very useful as a battery used in a mobile terminal that requires miniaturization, thinning, weight reduction, and high performance. Further, it can be suitably used for batteries of equipment requiring flexibility, for example, winding type dry batteries and laminated type batteries.

The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples. The physical property values of each PVA used in each of the Examples and Comparative Examples described later, the evaluation of the binder aqueous solution and the NMP solution containing each PVA, the evaluation in the electrode application, and the evaluation in the battery application were measured according to the following methods.

[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 degree of saponification of PVA is less than 99.5 mol%, it is saponified until the degree of saponification becomes 99.5 mol% or more, and the obtained PVA is subjected to the ultimate viscosity measured at 30 ° C. in water. Using [η] (liter / g), the viscosity average degree of polymerization was determined by the following formula.
Viscosity average degree of polymerization = ([η] × 1,0000 / 8.29) (1 / 0.62)

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

[Average particle size of particles constituting (water-soluble) resin powder and content of particles having a particle size of 100 to 1,000 μm]
Using a JIS standard sieve, the average particle size of the resin powder and the particle size of 100 to 1,000 μm (or the particle size of 106 to 1,000 μm based on the sieving net) according to the method described in JIS K7369: 2009. The particle content was determined.

[Average roundness of (water-soluble) resin powder]
Particles having a particle size of 100 to 1,000 μm (or a particle size of 106 to 1,000 μm based on a sieving net) were selected by the above-mentioned sieving, and any 50 particles were extracted from these particles. For these particles, based on the expansion 100 times the ratio image using the Keyence Corporation Ltd. digital microscope VHX-900, obtains the radius R of the curvature radius r _i and the maximum inscribed circle, the circle of each particle Migakudo I asked for P. The average value PA of the circularity P of 50 particles was obtained and used as the average circularity.

[Angle of repose of (water-soluble) resin powder]
The resin powder was humidity-controlled for 1 week in an atmosphere of 20 ° C. and 30% humidity or 20 ° C. and 65% humidity. Then, the angle of repose of the resin powder was measured using a multi-tester MT-1001 manufactured by Seishin Enterprise Co., Ltd. The angle of repose was measured according to 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 it is that particles will fuse in the pipe or silo and agglomerates will form.

[Evaluation of solubility of (water-soluble) resin powder]
In order to confirm the solubility of the resin powder in the solvent (water or NMP), water or 95 parts by mass of NMP was added to 5 parts by mass of PVA, the temperature was raised to 95 ° C. with stirring, and the mixture was heated and stirred for 4 hours to obtain PVA. The state of dissolution was visually observed. After cooling, it was passed through a wire mesh having a mesh size of 3 mm, and the solubility was evaluated according to the following criteria. When the evaluation is A, when it is used as a binder, the uniformity of the electrode can be improved.
A: No residue is found on the wire mesh.
B: A transparent gel-like lump is confirmed on the wire mesh.
C: An opaque gel-like lump is confirmed on the wire mesh.

[Evaluation of electrode uniformity (homogeneity) when applying negative and positive electrodes]
In order to evaluate the uniformity (homogeneity) of the negative electrode and the positive electrode produced in each of the examples and comparative examples described later, the film thickness variation of the battery coating electrode was used as an index, and four electrodes were measured at three points each. rice field. Judgment of ◎, ○, △, × was made according to the following criteria. Those with a rating of ◎ and ○ are excellent in discharge capacity and DC resistance, and those with a rating of ◎ are particularly excellent.
⊚: Variation with respect to average film thickness is 1 μm or less ◯: Variation with respect to average film thickness is greater than 1 μm and 2 μm or less Δ: Variation with respect to average film thickness is greater than 2 μm and 3 μm or less ×: With average film thickness On the other hand, the variation is larger than 3 μm.

[Discharge capacity and DC resistance of lithium-ion secondary battery in negative electrode application]
The coin batteries produced in each of the Examples and Comparative Examples described later were tested 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, a constant current charge of 0.2 C (about 1 mA / cm ² ) is performed up to 0.01 V with respect to the lithium potential, and a constant voltage charge of 0.01 V with respect to the lithium potential becomes a current of 0.02 mA. I went to. In the discharge, a constant current discharge of ^{0.2 C (about 0.5 mA / cm 2} ) was performed up to 1.5 V with respect to the lithium potential. The coin battery was placed in a constant temperature bath at 25 ° C., initial charge / discharge was performed under the above conditions, and the discharge capacity and DC resistance were measured.

[Discharge capacity and DC resistance of lithium-ion secondary battery in positive electrode application]
The coin batteries produced in each of the Examples and Comparative Examples described later were tested 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 of ^{0.2 C (about 1 mA / cm 2} ) was performed up to 4.2 V with respect to the lithium potential. In the discharge, a constant current discharge of 0.2 C (about 0.5 mA / cm ² ) was performed up to 3 V with respect to the lithium potential. The coin battery was placed in a constant temperature bath at 25 ° C., initial charge / discharge was performed under the above conditions, and the discharge capacity and DC resistance were measured.

[Discharge capacity of lithium manganese dioxide battery in positive electrode application, DC resistance]
The coin batteries produced in each of the Examples and Comparative Examples described later were tested 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 before discharging was defined as the DC resistance value. Pre-discharge was performed so that the battery voltage became 3.2 V, and then constant resistance discharge (15 kΩ) was performed, and the discharge capacity up to 2.0 V was measured.

[Discharge capacity and DC resistance of nickel-metal hydride batteries when applying positive and negative electrodes]
The coin batteries produced in each of the Examples and Comparative Examples described later were tested using a commercially available charge / discharge tester (TOSCAT3100, manufactured by Toyo System). The coin battery is placed in a constant temperature bath at 25 ° C., charged at 0.2 C, and then charged / discharged at 0.4 C until the battery voltage reaches 1.0 V. The charging / discharging operation is repeated 5 times for initial activation. rice field. The resistance value when a current of 0.1 mA was passed for 3 seconds after the initial activation was taken as the DC resistance value. The capacity when the coin battery after the initial activation was charged at 0.1 C and discharged at 0.2 C until the voltage of the battery became 1.0 V was measured and used as the discharge capacity.

-Preparation of slurry for negative electrode of lithium ion secondary battery The above-mentioned aqueous binder solution having a solid content concentration of 5% by mass, artificial graphite as a negative electrode active material (FSN-1, manufactured by Sugisugi, China), and a conductive auxiliary agent (conductivity-imparting agent). Super-P (manufactured by Timcal Co., Ltd.) was put into a special container and kneaded using a planetary stirrer (ARE-250, manufactured by Shinky Co., Ltd.) to prepare a slurry for a negative electrode. At the time of charging, the solid content in the binder aqueous solution was 3 parts by mass, the solid content of 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, the conductive auxiliary agent, and the binder in the slurry for the negative electrode is graphite powder: conductive auxiliary agent: binder = 96: 1: 3 (mass ratio) as the solid content.

-Manufacture of negative electrode for lithium ion secondary battery Copper foil (CST8G, manufactured by Fukuda Metal Leaf Powder Industry Co., Ltd.) was used for the slurry for negative electrode obtained as described above using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). It was painted on the current collector. After primary drying in a hot air dryer for 30 minutes at 80 ° C., rolling treatment was performed using a roll press (manufactured by Hosen Co., Ltd.). Then, after punching as a battery electrode (φ14 mm), a negative electrode for a coin battery was prepared by secondary drying under reduced pressure conditions at 140 ° C. for 3 hours. With respect to the produced negative electrode for coin batteries, the uniformity of the electrodes was evaluated by the method described above. The results are summarized in Table 3 below.

-Manufacture of lithium ion secondary battery The negative electrode for the battery obtained as described above was transferred to a glove box (manufactured by Miwa Seisakusho Co., Ltd.) in an argon gas atmosphere. Metallic lithium foil (thickness 0.2 mm, φ16 mm) is used for the positive electrode, polypropylene (Cellguard # 2400, made by Polypore) is used for the separator, and ethylene _{hexafluorophosphate (LiPF 6) is used as the electrolytic solution.} It was injected using _{a mixed solvent system (1M-LiPF 6} , EC / EMC = 3/7 vol%, VC ₂ % by mass) in which vinylene carbonate (VC) was added to carbonate (EC) and ethylmethyl carbonate (EMC). A coin battery (2032 type) was manufactured with such a configuration. With respect to the produced 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.

-Preparation of slurry for positive electrode of lithium ion secondary battery Furthermore, the above-mentioned binder NMP solution having a solid content concentration of about 5% by mass, NCM as a positive electrode active material (manufactured by Nippon Kagaku Kogyo Co., Ltd., "Celseed C-5H"), and conductivity. Super-P (manufactured by Timcal Co., Ltd.) as an auxiliary agent (conductivity-imparting agent) was put into a special container and kneaded using a planetary stirrer (ARE-250, manufactured by Shinky Co., Ltd.) to prepare a slurry for a positive electrode. At the time of charging, the solid content in the binder NMP solution was 3 parts by mass, the 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, the conductive auxiliary agent, and the binder in the slurry for the positive electrode is NCM powder: conductive auxiliary agent: binder = 95: 2: 3 (mass ratio) as the solid content.

-Manufacture of positive electrode for lithium ion secondary battery Aluminum foil (CST8G, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) was used to prepare the positive electrode slurry obtained as described above using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). It was painted on the current collector. After primary drying in a hot air dryer for 30 minutes at 80 ° C., rolling treatment was performed using a roll press (manufactured by Hosen Co., Ltd.). Then, after punching as a battery electrode (φ14 mm), a positive electrode for a coin battery was prepared by secondary drying under reduced pressure conditions at 140 ° C. for 3 hours. With respect to the produced positive electrode for coin batteries, the uniformity of the electrodes was evaluated by the method described above. The results are summarized in Table 3 below.

-Manufacture of lithium ion secondary battery The positive electrode for the battery obtained as described above was transferred to a glove box (manufactured by Miwa Seisakusho Co., Ltd.) in an argon gas atmosphere. Metallic lithium foil (thickness 0.2 mm, φ16 mm) is used for the negative electrode, polypropylene (Cellguard # 2400, made by Polypore) is used for the separator, and ethylene _{hexafluorophosphate (LiPF 6) is used as the electrolytic solution.} It was injected using _{a mixed solvent system (1M-LiPF 6} , EC / EMC = 3/7 vol%, VC ₂ % by mass) in which vinylene carbonate (VC) was added to carbonate (EC) and ethylmethyl carbonate (EMC). A coin battery (2032 type) was manufactured with such a configuration. With respect to the produced 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.

-Preparation of slurry for positive electrode of lithium manganese dioxide battery The above-mentioned aqueous binder solution having a solid content concentration of 5% by mass, manganese dioxide as a positive electrode active material, and Super-P (manufactured by Timcal) as a conductive auxiliary agent (conductivity-imparting agent) are used. It was put into a special container and kneaded using a planetary stirrer (ARE-250, manufactured by Shinky 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 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, the conductive auxiliary agent, and the binder in the slurry for the positive electrode is manganese dioxide powder: conductive auxiliary agent: binder = 95: 2: 3 (mass ratio) as a solid content. The obtained slurry can be used not only for lithium manganese dioxide batteries but also for alkaline batteries and the like.

-Manufacture of positive electrode for lithium manganese dioxide battery The slurry for positive electrode obtained as described above was made of aluminum foil (CST8G, manufactured by Fukuda Metal Leaf Powder Industry Co., Ltd.) using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.). It was applied on the current collector. After primary drying in a hot air dryer for 30 minutes at 80 ° C., rolling treatment was performed using a roll press (manufactured by Hosen Co., Ltd.). Then, after punching as a battery electrode (φ14 mm), a positive electrode for a coin battery was prepared by secondary drying under reduced pressure conditions at 140 ° C. for 3 hours. With respect to the produced positive electrode for coin batteries, the uniformity of the electrodes was evaluated by the method described above. The results are summarized in Table 3 below. The obtained electrode can be used not only for a lithium manganese dioxide battery but also for an alkaline dry battery or the like.

-Manufacture of 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.) in an argon gas atmosphere. Metallic lithium foil (thickness 0.2 mm, φ16 mm) is used for the negative electrode, polypropylene (Cellguard # 2400, made by Polypore) is used for the separator, and ethylene _{hexafluorophosphate (LiPF 6) is used as the electrolytic solution.} It was injected using _{a mixed solvent system (1M-LiPF 6} , EC / EMC = 3/7 vol%, VC ₂ % by mass) in which vinylene carbonate (VC) was added to carbonate (EC) and ethylmethyl carbonate (EMC). A coin battery (2032 type) was manufactured with such a configuration. With respect to the produced 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.

-Preparation of nickel-metal hydride battery negative electrode slurry The above-mentioned binder aqueous solution having a solid content concentration of 5% by mass, a hydrogen storage alloy as a negative electrode active material, and Super-P (manufactured by Timcal) as a conductive auxiliary agent (conductivity-imparting agent) are used. It was put into a special container and kneaded using a planetary stirrer (ARE-250, manufactured by Shinky Co., Ltd.) to prepare a slurry for a 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 auxiliary agent, and the binder in the slurry for the negative electrode is a hydrogen storage alloy: conductive auxiliary agent: binder = 95: 2: 3 (mass ratio) as a solid content.

-Manufacture of negative electrode for nickel-metal hydride battery Iron punching metal (thickness 60 μm, pore diameter 1) whose surface was nickel-plated using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.) for the negative electrode slurry obtained as described above. It was applied on a current collector with a pore size of .2 mm and a hole opening rate of 40%). After primary drying in a hot air dryer for 30 minutes at 80 ° C., rolling treatment was performed using a roll press (manufactured by Hosen Co., Ltd.). Then, after punching as a battery electrode (φ14 mm), a negative electrode for a coin battery was prepared by secondary drying under reduced pressure conditions at 140 ° C. for 3 hours. With respect to the produced negative electrode for coin batteries, the uniformity of the electrodes was evaluated by the method described above. The results are summarized in Table 3 below.

-Preparation of slurry for positive electrode of nickel-metal hydride battery The above-mentioned aqueous solution of a binder having a solid content concentration of 5% by mass, nickel hydroxide as a positive electrode active material, and Super-P (manufactured by Timcal) as a conductive auxiliary agent (conductivity-imparting agent). It was put into a special container and kneaded using a planetary stirrer (ARE-250, manufactured by Shinky 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, the conductive auxiliary agent, and the binder in the positive electrode slurry is nickel hydroxide: conductive auxiliary agent: binder = 95: 2: 3 (mass ratio) as a solid content.

-Manufacture of positive electrode for nickel-metal hydride battery Using a bar coater (T101, manufactured by Matsuo Sangyo Co., Ltd.), a nickel foam (area density (grain) of about 300 g / m ² and thickness) was used to prepare the positive electrode slurry obtained as described above. It was applied on a current collector (about 1.0 mm). After primary drying in a hot air dryer for 30 minutes at 80 ° C., rolling treatment was performed using a roll press (manufactured by Hosen Co., Ltd.). Then, after punching as a battery electrode (φ14 mm), a positive electrode for a coin battery was prepared by secondary drying under reduced pressure conditions at 140 ° C. for 3 hours. With respect to the produced positive electrode for coin batteries, the uniformity of the electrodes was evaluated by the method described above. The results are summarized in Table 3 below.

-Manufacture of nickel-metal hydride battery A coin battery was manufactured using the negative electrode and positive electrode for the nickel-metal hydride battery obtained as described above. A polypropylene-based separator (Cellguard # 2400, manufactured by Polypore) was used, and an alkaline electrolytic solution containing NaOH was injected as an electrolytic solution. As the alkaline electrolytic solution, an aqueous solution containing NaOH at 7.5 mol / L was used. A coin battery (2032 type) was manufactured with such a configuration. With respect to the produced 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.

[Example 1] Production of resin powder 1 of PVA1 112.5 kg of vinyl acetate and 37.5 kg of methanol (37.5 kg) in a 250 L reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, and an initiator addition port. Vinyl acetate (75% by mass: methanol: 25% by mass) was charged, and the inside of the system was replaced with nitrogen for 30 minutes while bubbling with nitrogen. When the temperature of the reactor was started and the internal temperature reached 60 ° C., 35 g of 2,2'-azobisisobutyronitrile (AIBN) was added to start the polymerization, and the polymerization rate became 50%. By the way, it was cooled and the polymerization was stopped. The solid content concentration at the time of stopping the polymerization was 37.0%. Subsequently, the unreacted vinyl acetate monomer was removed by occasionally adding methanol at 30 ° C. under reduced pressure to obtain a methanol solution (concentration 35%) of polyvinyl acetate (PVAc). Further, 1.86 kg of an alkaline solution (10% methanol solution of sodium hydroxide) was added to 54.05 kg (20 kg of PVAc in the solution) of PVAC prepared by adding methanol to the saponification (10% methanol solution of sodium hydroxide). The PVAc concentration of the saponification solution is 30%, and the molar ratio of sodium hydroxide to the vinyl acetate unit in PVAc is 0.02 mol%). A gel-like substance (resin solid substance) was formed about 1 minute after the addition of the alkaline solution, and this was pulverized with a pulverizer (mixer) for 5 minutes. The pulverized product was left at 40 ° C. for 1 hour to allow saponification to proceed, and then 50 kg of methyl acetate was added to neutralize the remaining alkali. After confirming that the neutralization was completed using a phenolphthalein indicator, a white solid was obtained by filtration, 200 kg of methanol was added thereto, and the mixture was washed at room temperature for 3 hours. After repeating the above washing operation three times, the white solid obtained by centrifugation 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 in a radige mixer "FKM130D" equipped with a Becker type excavator manufactured by Chuo Kiko Co., Ltd. The surface was processed for 3 hours at a rotation speed of 160 rpm at room temperature in a nitrogen atmosphere. As a result, a resin powder 1 having an average particle diameter of 650 μm and an average roundness of 0.25 was obtained.

[Examples 2 to 10, 15 to 16]
The resin powder 2 and the like of PVA2 were obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were satisfied.

[Example 11]
120.0 kg of vinyl acetate and 30.0 kg of methanol (80% by mass of vinyl acetate: 20% by mass of methanol) in a 250 L reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, a comonomer dropping port and an initiator addition port. ) Was charged, and the inside of the system was replaced with nitrogen for 30 minutes while bubbling with nitrogen. When the temperature of the reactor was started and the internal temperature reached 60 ° C., 2.5 kg of acetaldehyde and 35 g of 2,2'-azobisisobutyronitrile (AIBN) were added to start the polymerization, and the polymerization rate was increased. When it reached 50%, it was cooled to stop the polymerization. The solid content concentration at the time of stopping the polymerization was 39.3%. Hereinafter, the resin powder 11 of PVA11 was obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were met.

[Example 12]
Polymerization and saponification were carried out in the same manner as in Example 2 described in JP-A-2019-011282, and 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% was carried out. Coarse powder was obtained. Hereinafter, the resin powder 12 of PVA12 was obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were met.

[Example 13]
112.5 kg of vinyl acetate and 37.5 g of methanol (75% by mass of vinyl acetate: 25% by mass of methanol) in a 250 L reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, a comonomer dropping port and an initiator addition port. ), And 220 ml of a methanol solution in which methyl methacrylate was dissolved in 24% by mass was charged, and the inside of the system was replaced with nitrogen for 30 minutes while subjecting to nitrogen bubbling. When the temperature of the reactor was raised and the internal temperature reached 60 ° C., 25 g of 2,2'-azobisisobutyronitrile (AIBN) was added to start the polymerization, and the above-mentioned methyl methacrylate solution of methanol (11 L) was started. Was sequentially added and cooled when the polymerization rate reached 40% to stop the polymerization. The solid content concentration at the time of stopping the polymerization was 28.0%. Hereinafter, the resin powder 13 of PVA13 was obtained in the same manner as in Example 1 except that the conditions shown in Table 1 were met.

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

[Examples 17 to 19]
A resin powder 17 or the like of PVA17 was obtained in the same manner as in Example 2 except that the surface processing was performed by the apparatus shown in Table 1 instead of the Ladyge mixer.

[Example 20]
The resin powder 20 of PVA20 and the like were obtained in the same manner as in Example 2 except that the crushing time by the crusher was lengthened to 10 minutes, the crushing time was finer than that in Example 1, and the surface processing treatment by the Ladyge mixer was not performed. Got

[Comparative Example 1]
The resin powder 1'of PVA 1'was obtained in the same manner as in Example 2 except that the crushing time by the crusher was shortened to 1 minute and the crushing time was made coarser than in Example 14.

[Comparative Example 2]
A resin powder 2'of PVA2'was obtained in the same manner as in Example 2 except that the surface processing was not performed by the Ladyge mixer.

The degree of polymerization and saponification of each PVA obtained in Examples 1 to 20 and Comparative Examples 1 and 2, the average roundness of each resin powder, the average particle size, and the content of particles having a particle size of 100 to 1,000 μm. Table 2 shows the rate and the product of the average degree of roundness and the degree of saponification.

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

Solubility of each resin powder obtained in Examples 1 to 20 and Comparative Examples 1 and 2 in water and NMP, and electrode uniformity (electrode homogeneity) when used as an electrode binder for each power storage device. Table 3 shows the characteristics of the power storage device.

As shown in Table 3, when the resin powders of Examples 1 to 20 are used as a binder, gel-like lumps are unlikely to occur when dissolved in water or NMP, so that a uniform electrode can be obtained. 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 size and the resin powder of Comparative Example 2 having a small average roundness were used as binders, gel-like lumps were generated when dissolved in water or NMP. This is likely to occur, and as a result, the uniformity of the electrodes is impaired, resulting in a decrease in discharge capacity and an increase in DC resistance.

Claims (13)

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.
   With respect to 50 particles arbitrarily extracted from the particles having a particle size of 100 to 1,000 μm contained in the water-soluble resin powder, the following formula (1) of each particle is used.
   

   

   [In equation (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 horns that the particle has,
   However, when the number of corners of the particle is 9 or more, the radius of curvature of 8 corners is adopted in ascending order of radius of curvature, and N is 8.]
   A binder in which the average value PA of the degree of 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 1 or 2, wherein the vinyl alcohol-based polymer has an average degree of polymerization of 200 to 5,000 and a degree of saponification of 35 to 99.99 mol%.
4. The following formula (2)
   PA × S ≧ 18 (2)
   [In the formula (2), PA is the same as the above definition, and S is the saponification degree (mol%) of the vinyl alcohol polymer].
   The binder according to any one of claims 1 to 3, wherein the water-soluble resin powder has an average particle size 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 size of 100 to 1,000 μm is 50% by mass or more in the water-soluble resin powder.
6. A power storage device electrode containing the binder according to any one of claims 1 to 5.
7. A binder solution for a power storage device electrode containing the binder and water according to any one of claims 1 to 5.
8. The binder solution for a power storage device electrode according to claim 7, which contains N-methyl-2-pyrrolidone.
9. A storage device electrode slurry containing the binder solution for a power storage device electrode according to claim 7 or 8 and an active material.
10. The power 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 power storage device electrode including a cured body and a current collector of the power storage device electrode slurry according to claim 9 or 10.
12. A power storage device including the power storage device electrode according to claim 11.
13. Claims 1 to 5 include a step of obtaining a crude powder of the water-soluble resin by crushing a resin solid containing the water-soluble resin, and a step of processing the surface of particles constituting the crude powder. The method for producing a binder according to any one.