JP2017183241A - Binder for power storage device electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a binder for a power storage device electrode, which is superior in active material dispersibility, defoamability and adhesiveness, which is high in endurance against an electrolyte solution, and which enables the manufacturing a high-capacity lithium secondary battery even with a small addition amount of a binder; and a composition for a power storage device electrode, a power storage device electrode, and a power storage device which are each arranged by use of the binder for a power storage device electrode.SOLUTION: A binder for a power storage device electrode is a binder to be used for an electrode of a power storage device. The binder comprises a polyvinyl acetal-based resin fluid dispersion including microparticles made of a polyvinyl acetal based resin of which the amount of hydroxyl groups is 30-60 mol%, a nonionic surfactant and an aqueous medium.SELECTED DRAWING: None

Description

The present invention is a power storage device that is excellent in dispersibility, defoaming, and adhesiveness of an active material, has high durability against an electrolytic solution, and can produce a high-capacity lithium secondary battery even when the amount of binder added is small. The present invention relates to a binder for device electrodes.
The present invention also relates to a composition for an electricity storage device electrode using the binder for an electricity storage device electrode, an electricity storage device electrode, and an electricity storage device.

In recent years, with the widespread use of portable electronic devices such as portable video cameras and portable personal computers, the demand for secondary batteries as mobile power sources has increased rapidly. In addition, there are very high demands for such secondary batteries to be reduced in size, weight, and energy density.
Thus, as a secondary battery that can be repeatedly charged and discharged, a lead battery, a nickel-cadmium battery, and the like have been mainly used. However, although these batteries are excellent in charge / discharge characteristics, it cannot be said that they have characteristics that are sufficiently satisfactory as a mobile power supply for portable electronic devices in terms of battery weight and energy density.

Therefore, research and development of lithium secondary batteries using lithium or a lithium alloy as a negative electrode as a secondary battery has been actively conducted. This lithium secondary battery has excellent characteristics such as high energy density, low self-discharge, and light weight.
An electrode of a lithium secondary battery is usually a thin film obtained by kneading an active material and a binder together with a solvent, dispersing the active material into a slurry, applying the slurry on a current collector by a doctor blade method or the like, and drying the slurry. It is formed by forming.

Currently, in particular, fluorine-based resins represented by polyvinylidene fluoride (PVDF) are most widely used as binders for electrodes (negative electrodes) of lithium secondary batteries.
However, polyvinylidene fluoride has a problem that, when producing a slurry for an electrode, the solubility in a solvent is poor and the production efficiency is remarkably lowered.
On the other hand, N-methylpyrrolidone is generally used as a slurry solvent for dissolving polyvinylidene fluoride, but N-methylpyrrolidone has a high boiling point, and thus requires a large amount of heat energy in the slurry drying step. In addition, N-methylpyrrolidone that has not been completely dried remains in the electrode, thereby degrading the performance of the battery.

In order to solve such a problem, a method of using an aqueous slurry using water as a solvent has been studied as an electrode slurry used for a positive electrode and a negative electrode. In such a method, carboxymethyl cellulose is generally used as the water-soluble binder resin.
However, when carboxymethyl cellulose is used, there is a problem that the flexibility of the resin is insufficient and the ability to bind the active material and the adhesive force to the current collector are remarkably insufficient.
On the other hand, Patent Document 1 attempts to disperse styrene / butadiene latex as a binder. In this case, however, the organic component is excessively added, so the amount of active material added is relatively high. Therefore, there has been a new problem that the capacity of the battery is reduced.

In addition to the active material, it is common to add a conductive aid as a constituent material of the electrode slurry. However, the conductive aid has a small particle diameter and a large specific surface area, and thus tends to cause poor dispersion. However, there was a problem that the performance of the active material could not be sufficiently extracted.
On the other hand, Patent Document 2 proposes to improve the dispersibility of the conductive additive by using a polyvinylpyrrolidone polymer as a dispersant.
Patent Document 3 proposes to improve battery characteristics by adding a fluorine-based nonionic surfactant in the positive electrode mixture layer.
Further, Patent Document 4 proposes to improve the battery characteristics by providing a coating layer made of a conductive assistant or a mixture of a conductive assistant and a polymer dispersant on the surface of the active material (graphite). .

However, the method of Patent Document 2 has a problem in that the graphite and the conductive assistant are electrically repelled, so that the current collection at the electrode becomes insufficient and the output characteristics cannot be improved.
In addition, in the method of Patent Document 3, since the adsorption force of the surfactant to the graphite surface is weak, it is necessary to add a large amount of surfactant. The battery characteristics could not be improved due to the decrease.
Further, in the method of Patent Document 4, even if a coating layer is provided, the conductivity between graphite is insufficient, and the internal resistance in the electrode is increased, resulting in a new problem that battery characteristics deteriorate. It was.

In addition, the electrode slurry made of an aqueous medium is generally subjected to vacuum defoaming treatment in order to remove bubbles present in the electrode slurry in the production process, but when the defoaming treatment is insufficient, The remaining bubbles volatilized when the electrode was dried to generate pinholes, resulting in electrode defects.

Japanese Patent Laid-Open No. 5-74461 Japanese Patent Laid-Open No. 2003-157846 JP 2002-75330 A JP 2003-142097 A

The present invention is a power storage device that is excellent in dispersibility, defoaming, and adhesiveness of an active material, has high durability against an electrolytic solution, and can produce a high-capacity lithium secondary battery even when the amount of binder added is small. It aims at providing the binder for device electrodes. Moreover, the composition for electrical storage device electrodes, electrical storage device electrodes, and electrical storage devices using the electrical storage device electrode binder are provided.

The present invention is a binder used for an electrode of an electricity storage device, and is a polyvinyl acetal resin dispersion containing fine particles comprising a polyvinyl acetal resin having a hydroxyl amount of 30 to 60 mol%, a nonionic surfactant, and an aqueous medium It is the binder for electrical storage device electrodes which consists of.
The present invention is described in detail below.

As a result of intensive studies, the present inventors use a polyvinyl acetal resin dispersion containing fine particles made of a polyvinyl acetal resin having a specific amount of hydroxyl groups and a nonionic surfactant as a binder for an electricity storage device electrode. The present invention was completed by discovering that the active material has excellent dispersibility, defoaming and adhesiveness, high durability against electrolytes, and that a high-capacity lithium secondary battery can be produced even when the amount of binder added is small. I came to let you.
In particular, since the binder for an electricity storage device electrode of the present invention is excellent in adsorptivity with an active material, it is not necessary to add a large amount when preparing an electrode slurry, and sufficiently ensure electrical conductivity between active materials, A stable power storage device with little increase in internal resistance can be manufactured.

The binder for an electricity storage device electrode of the present invention comprises a polyvinyl acetal resin dispersion containing fine particles comprising a polyvinyl acetal resin, a nonionic surfactant, and an aqueous medium.
In the present invention, by containing a nonionic surfactant, it is possible to disperse the active material and other components satisfactorily, and it is excellent in antifoaming properties, and it is possible to firmly bond the active materials. As a result, when used as an electrode of an electricity storage device, battery performance can be sufficiently extracted.

Examples of the nonionic surfactant include polyoxyethylene polyoxypropylene block copolymers, polyoxyalkylene alkyl ethers, polyoxyalkylene alkyl phenyl ethers, polyoxyalkylene alkyl fatty acid esters, polyoxyalkylene glyceryl ether fatty acid esters, Examples include polyoxyalkylene styrenated phenyl ether, polyoxyalkylene allyl phenyl ether, polyoxyalkylene sorbitan fatty acid ester, sorbitan fatty acid ester, and polyoxyalkylene. Among these, at least one selected from the group consisting of polyoxyethylene polyoxypropylene block copolymers, polyoxyalkylene alkyl ethers, and polyoxyalkylene glyceryl ether fatty acid esters is preferable.

The polyoxyalkylene alkyl ethers are preferably polyoxyethylene alkyl ethers, polyoxypropylene alkyl ethers, and polyoxyethylene / polyoxypropylene alkyl ethers. Moreover, it is preferable to use a C12-20 thing as an alkyl group.

Examples of the polyoxyalkylene include polyethylene oxide, polypropylene oxide, and polybutylene oxide. The average added mole number of the polyoxyalkylene is preferably adjusted to a range of 1 to 50 moles.

Examples of the fatty acid include heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, and isostearic acid.

Commercially available surfactants can be used as the nonionic surfactant, and examples thereof include Epan Series, Neugen Series, DKS Series (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and the like.

When the nonionic surfactant has an ethylene oxide chain, the preferable lower limit of the ethylene oxide content is 5% by weight, and the preferable upper limit is 90% by weight. By setting the ethylene oxide content within the above range, the defoaming effect can be further enhanced. A more preferable lower limit of the ethylene oxide content is 10% by weight, and a more preferable upper limit is 85% by weight.

The nonionic surfactant has a preferred lower limit of 300 and a preferred upper limit of 25,000 for the weight average molecular weight. By making the said weight average molecular weight into the above-mentioned range, a defoaming effect can be improved further. The more preferable lower limit of the weight average molecular weight is 900, and the more preferable upper limit is 16000.

The nonionic surfactant has a preferred lower limit of the HLB value of 8.0 and a preferred upper limit of 20.0. By setting the HLB value within the above range, the defoaming effect can be further enhanced. A more preferable lower limit of the HLB value is 9.6, and a more preferable upper limit is 19.3.
The HLB value can be calculated by the Griffin method using the following formula.
HLB value = 20 × sum of formula weight of hydrophilic part / molecular weight

In the binder for an electricity storage device electrode of the present invention, the content of the nonionic surfactant is preferably 0.01 to 15% by weight of fine particles made of a polyvinyl acetal resin. By setting the content to be within the above range, the defoaming effect can be further enhanced. A more preferable lower limit of the content is 0.1% by weight, and a more preferable upper limit is 10% by weight.

The polyvinyl acetal resin dispersion contains fine particles made of a polyvinyl acetal resin.
In the present invention, by using a polyvinyl acetal resin as a resin component of the binder (binder), an attractive interaction works between the fine particles made of the polyvinyl acetal resin and the active material, and the active material is fixed with a small amount of the binder. Can be
Further, the fine particles exert an attractive interaction with the conductive auxiliary agent, and the distance between the active material and the conductive auxiliary agent can be kept within a certain range. Thus, dispersibility of the active material is greatly improved by making the distance between the active material and the conductive additive moderate.
Furthermore, compared with the case of using a resin such as PVDF, the adhesiveness with the current collector can be remarkably improved. In addition, compared with the case where carboxymethyl cellulose is used, the active material is excellent in dispersibility and adhesiveness, and a sufficient effect can be exhibited even when the amount of the binder added is small.
Furthermore, by making the binder into a fine particle shape, it is possible to partially adhere (point contact) without covering the entire surface of the active material and the conductive additive. As a result, the contact between the electrolytic solution and the active material is improved, and even when a large current is applied when used in a lithium battery, lithium ion conduction is sufficiently maintained, and a decrease in battery capacity can be suppressed. The advantage is obtained.

The lower limit of the amount of hydroxyl groups in the polyvinyl acetal resin constituting the polyvinyl acetal resin fine particles is 30 mol%, and the upper limit is 60 mol%. When the amount of the hydroxyl group is less than 30 mol%, the resistance to the electrolytic solution becomes insufficient, and when the electrode is immersed in the electrolytic solution, the resin component may be eluted in the electrolytic solution. If exceeding, not only is it difficult to synthesize industrially, but the stability of the fine particles of the polyvinyl acetal resin in the aqueous medium is reduced, the coalescence of the particles occurs, and the active material is sufficiently dispersed. It becomes difficult.
A preferable lower limit of the hydroxyl group content is 35 mol%, and a preferable upper limit is 55 mol%.

The acetalization degree of the polyvinyl acetal resin constituting the polyvinyl acetal resin fine particles is preferably in the range of 40 to 70 mol% in terms of the total acetalization degree, regardless of whether a single aldehyde or a mixed aldehyde is used. When the total degree of acetalization is less than 40 mol%, the flexibility of the resin is remarkably deteriorated and the adhesive force to the current collector becomes insufficient. When the degree of acetalization exceeds 70 mol%, the resistance to the electrolytic solution becomes insufficient, and the resin component may be eluted in the electrolytic solution when the electrode is immersed in the electrolytic solution. More preferably, it is 45-65 mol%.

The polyvinyl acetal resin constituting the polyvinyl acetal resin fine particles has a preferable lower limit of the acetyl group amount of 0.2 mol% and a preferable upper limit of 20 mol%. When the amount of acetyl groups in the polyvinyl acetal resin is less than 0.2 mol%, the flexibility is remarkably lowered and the adhesion to the aluminum foil may be insufficient, and the amount of acetyl groups exceeds 20 mol%. And the tolerance with respect to electrolyte solution becomes inadequate, and when an electrode is immersed in electrolyte solution, a resin component may elute in electrolyte solution. A more preferable lower limit of the amount of the acetyl group is 1 mol%.

In particular, the preferable lower limit of the degree of polymerization of the polyvinyl acetal resin constituting the polyvinyl acetal resin fine particles is 250, and the preferable upper limit is 4000. If the degree of polymerization is less than 250, the resistance to the electrolytic solution is insufficient, and thus the electrode may be eluted into the electrolytic solution and short-circuited. When the polymerization degree exceeds 4000, the adhesive force with the active material becomes insufficient, and the discharge capacity of the lithium secondary battery may be reduced. The minimum with said more preferable polymerization degree is 280, and a more preferable upper limit is 3500.

The method for acetalization is not particularly limited, and a conventionally known method can be used. Examples thereof include a method of adding various aldehydes to an aqueous solution of polyvinyl alcohol in the presence of an acid catalyst such as hydrochloric acid.

The aldehyde used for the acetalization is not particularly limited. For example, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, amylaldehyde, hexylaldehyde, heptylaldehyde, 2-ethylhexylaldehyde, Examples include cyclohexyl aldehyde, furfural, glyoxal, glutaraldehyde, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, β-phenylpropionaldehyde and the like. Of these, acetaldehyde or butyraldehyde is preferable in terms of productivity and property balance. These aldehydes may be used alone or in combination of two or more.

The polyvinyl alcohol may be a saponified copolymer obtained by copolymerizing the vinyl ester and an α-olefin. Furthermore, it is good also as polyvinyl alcohol which copolymerizes the said ethylenically unsaturated monomer and contains the component originating in an ethylenically unsaturated monomer. Also used is a terminal polyvinyl alcohol obtained by copolymerizing a vinyl ester monomer such as vinyl acetate with an α-olefin in the presence of a thiol compound such as thiol acetic acid or mercaptopropionic acid, and saponifying it. be able to. The α-olefin is not particularly limited, and examples thereof include methylene, ethylene, propylene, isopropylene, butylene, isobutylene, pentylene, hexylene, cyclohexylene, cyclohexylethylene, and cyclohexylpropylene.

The polyvinyl acetal resin constituting the polyvinyl acetal resin fine particles preferably has an ionic functional group. The ionic functional group is at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfinic acid group, a sulfenic acid group, a phosphoric acid group, a phosphonic acid group, an amino group, and a salt thereof. Functional groups are preferred. Of these, carboxyl groups, sulfonic acid groups, and salts thereof are more preferable, and sulfonic acid groups and salts thereof are particularly preferable. When the polyvinyl acetal resin has an ionic functional group, the dispersibility of the fine particles composed of the polyvinyl acetal resin in the composition for a lithium secondary battery electrode is improved, and the dispersibility of the active material and the conductive auxiliary agent is improved. It can be made particularly excellent.
In addition, as said salt, sodium salt, potassium salt, etc. are mentioned.

The content of the ionic functional group in the polyvinyl acetal resin is preferably 0.01 to 1 mmol / g. When the content of the ionic functional group is less than 0.01 mmol / g, the dispersibility of the fine particles in the composition for a lithium secondary battery electrode, and the dispersion of the active material and the conductive assistant when used as an electrode When it exceeds 1 mmol / g, the durability of the binder in the battery may be reduced, and the discharge capacity of the lithium secondary battery may be reduced. The more preferable content of the ionic functional group in the polyvinyl acetal resin is 0.02 to 0.5 mmol / g. The content of the ionic functional group can be measured by using NMR.

The presence form of the ionic functional group may be directly present in the polyvinyl acetal resin structure, or may be present in the graft chain of a polyvinyl acetal resin containing a graft chain (hereinafter also simply referred to as a graft copolymer). You may do it. Especially, since it can make the dispersibility of the active material at the time of setting it as an electrode and an electrode, and the dispersibility of a conductive support agent, it is preferable to exist directly in a polyvinyl acetal type resin structure.
When the ionic functional group is directly present in the polyvinyl acetal resin structure, it is a chain molecular structure in which the ionic functional group is bonded to carbon constituting the main chain of the polyvinyl acetal resin, or through an acetal bond. Thus, a molecular structure in which an ionic functional group is bonded is preferable, and a molecular structure in which an ionic functional group is bonded through an acetal bond is particularly preferable.
The presence of the ionic functional group in the above structure improves the dispersibility of the fine particles comprising the polyvinyl acetal resin in the composition for the lithium secondary battery electrode, and the active material and the conductive auxiliary agent when used as an electrode are improved. While dispersibility can be made especially excellent, since the deterioration of the binder at the time of setting it as a battery is suppressed, the fall of the discharge capacity of a lithium secondary battery can be suppressed.

The method for producing the polyvinyl acetal resin having the ionic functional group directly in the polyvinyl acetal resin structure is not particularly limited. For example, the modified polyvinyl alcohol raw material having the ionic functional group is reacted with an aldehyde. Examples include a method for acetalization, a method for producing a polyvinyl acetal resin, and a method for reacting it with a compound having another functional group and an ionic functional group that are reactive to the functional group of the polyvinyl acetal resin. .

When the polyvinyl acetal resin has an ionic functional group via an acetal bond, the acetal bond and the ionic functional group are preferably connected by a chain or cyclic alkyl group or an aromatic ring. In particular, it is preferably connected by an alkylene group having 1 or more carbon atoms, a cyclic alkylene group having 5 or more carbon atoms, an aryl group having 6 or more carbon atoms, or the like, in particular, an alkylene group having 1 or more carbon atoms or an aromatic ring. It is preferable that it is connected by.
As a result, the resistance to the electrolytic solution and the dispersibility of the active material and the conductive additive when used as an electrode can be improved, and the deterioration of the binder when used as a battery is suppressed, so that the lithium secondary A decrease in the discharge capacity of the battery can be suppressed.
Examples of the aromatic substituent include aromatic rings such as a benzene ring and a pyridine ring, and condensed polycyclic aromatic groups such as a naphthalene ring and an anthracene ring.

When the polyvinyl acetal resin has an ionic functional group via an acetal bond, the polyvinyl acetal resin is a structural unit having a hydroxyl group represented by the following formula (1), the following formula (2) A structural unit having an acetyl group, a structural unit having an acetal group represented by the following formula (3), and a structural unit having an acetal group containing an ionic functional group represented by the following formula (4) It is preferable that it has.
As a result, the dispersibility of the fine particles comprising the polyvinyl acetal resin, the dispersibility of the active material and the conductive auxiliary agent can be made particularly excellent, and the adhesion to the current collector and the resistance to the electrolyte solution are also particularly excellent. Therefore, a reduction in the discharge capacity of the lithium secondary battery can be particularly suppressed.

式（３）中、Ｒ^１は水素原子又は炭素数１〜２０のアルキル基を表し、式（４）中、Ｒ^２は炭素数１〜２０のアルキレン基又は芳香環を表し、Ｘはイオン性官能基を表す。

In formula (3), R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, in formula (4), R ² represents an alkylene group or aromatic ring having 1 to 20 carbon atoms, and X is ionic. Represents a functional group.

The content of the acetal bond having an ionic functional group in the polyvinyl acetal resin is preferably adjusted so that the content of the ionic functional group in the polyvinyl acetal resin is within the appropriate range. In order to make the content of the ionic functional group in the polyvinyl acetal resin within the above suitable range, for example, when one ionic functional group is introduced by one acetal bond, it has an ionic functional group The content of the acetal bond is preferably about 0.1 to 10 mol%, and when two ionic functional groups are introduced by one acetal bond, the acetal having an ionic functional group The bond content is preferably about 0.05 to 5 mol%. In addition, in order to increase both the dispersibility of the fine particles comprising the polyvinyl acetal resin, the flexibility of the resin, and the adhesion to the current collector, the acetal bond having an ionic functional group in the polyvinyl acetal resin is used. The content is preferably 0.5 to 20 mol% of all acetal bonds.
By making the content of the ionic functional group in the polyvinyl acetal resin within the above range, the dispersibility of the fine particles composed of the polyvinyl acetal resin in the composition for a lithium secondary battery electrode is improved, and the electrolyte solution has Dispersion of the active material and conductive additive when used as an electrode and an electrode can be improved, and further, the deterioration of the binder when used as a battery is suppressed, so the discharge capacity of the lithium secondary battery is reduced. Can be suppressed.

A method for producing a polyvinyl acetal resin having an ionic functional group through an acetal bond in the polyvinyl acetal resin structure is not particularly limited. For example, an aldehyde having the ionic functional group is previously added to a polyvinyl alcohol raw material. Method of acetalizing after reacting, Method of acetalizing by mixing aldehyde raw material with aldehyde having the above ionic functional group when acetalizing polyvinyl alcohol, After creating polyvinyl acetal resin, said ionic functional group And the like.

Examples of the aldehyde having an ionic functional group include an aldehyde having a sulfonic acid group, an aldehyde having an amino group, an aldehyde having a phosphate group, and an aldehyde having a carboxyl group. Specifically, for example, 4-formylbenzene-1,3-disulfonate disodium, sodium 4-formylbenzenesulfonate, sodium 2-formylbenzenesulfonate, 3-pyridinecarbaldehyde hydrochloride, 4-diethylaminobenzaldehyde hydrochloride 4-dimethylaminobenzaldehyde hydrochloride, betaine aldehyde chloride, (2-hydroxy-3-oxopropoxy) phosphoric acid, pyridoxal 5-phosphate, terephthalaldehyde acid, isophthalaldehyde acid and the like.

The polyvinyl acetal resin has an ionic functional group through an acetal bond, the ionic functional group is a sulfonic acid group or a salt thereof, and the acetal bond and the ionic functional group are connected by a benzene ring. It is particularly preferable. Since the polyvinyl acetal resin has such a molecular structure, the dispersibility of the fine particles composed of the polyvinyl acetal resin in the composition for a lithium secondary battery electrode, the dispersion of the active material and the conductive auxiliary agent when used as an electrode The durability of the binder when used as a battery can be made particularly excellent.

When the polyvinyl acetal resin has a chain molecular structure in which an ionic functional group is bonded to carbon constituting the main chain of the polymer, it preferably has a structural unit represented by the following general formula (5). When the polyvinyl acetal resin has a structural unit represented by the following general formula (5), the dispersibility of the fine particles composed of the polyvinyl acetal resin in the composition for a lithium secondary battery electrode, and the durability of the binder when used as a battery The property can be made particularly excellent.

In formula (5), C represents a carbon atom of the polymer main chain, R ³ represents a hydrogen atom or a methyl group, R ⁴ represents an alkylene group having 1 or more carbon atoms, and R ⁵ represents an ionic functional group. .

R ³ is particularly preferably a hydrogen atom.
Examples of R ⁴ include a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, an isobutylene group, a sec-butylene group, and a tert-butylene group. Of these, R ⁴ is preferably a methylene group.
R ⁴ may be a structure substituted with a substituent having a hetero atom. Examples of the substituent include an ester group, an ether group, a sulfide group, an amide group, an amine group, a sulfoxide group, a ketone group, and a hydroxyl group.

The method for producing a polyvinyl acetal resin in which an ionic functional group is directly present in the polyvinyl acetal resin structure is not particularly limited. For example, the modified polyvinyl alcohol raw material having the ionic functional group is reacted with an aldehyde to obtain an acetal And a method of reacting with a compound having another functional group reactive with the functional group of the polyvinyl acetal resin and a compound having an ionic functional group.

As a method for producing the modified polyvinyl alcohol having an ionic functional group, for example, after copolymerizing a vinyl ester monomer such as vinyl acetate and a monomer having a structure represented by the following general formula (6), The method of saponifying the ester site | part of the obtained copolymer resin with an alkali or an acid is mentioned.

In formula (6), R ⁶ represents a hydrogen atom or a methyl group, R ⁷ represents an alkylene group having 1 or more carbon atoms, and R ⁸ represents an ionic functional group.

It does not specifically limit as a monomer which has a structure shown in the said General formula (6), For example, carboxyl groups and polymeric functional groups, such as 3-butenoic acid, 4-pentenoic acid, 5-hexenoic acid, and 9-decenoic acid, are included. Sulfonic acid groups such as allylsulfonic acid, 2-methyl-2-propene-1-sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3- (methacryloyloxy) propanesulfonic acid and polymerizable functional groups , Those having an amino group and a polymerizable functional group such as N, N-diethylallylamine, and salts thereof.
In particular, when allyl sulfonic acid and a salt thereof are used, the dispersibility of the fine particles comprising the polyvinyl acetal resin in the composition for a lithium secondary battery electrode is improved, and the resistance to the electrolytic solution and the activity when the electrode is used are improved. Suitable for excellent dispersibility of substances and conductive assistants, and further, since deterioration of the binder in the case of a battery can be suppressed, a decrease in the discharge capacity of the lithium secondary battery can be suppressed. It is. In particular, it is preferable to use sodium allyl sulfonate.
These monomers may be used independently and may use 2 or more types together.

R ⁶ is particularly preferably a hydrogen atom.
Examples of R ⁷ include a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, an isobutylene group, a sec-butylene group, and a tert-butylene group. Of these, R ⁷ is preferably a methylene group.
R ⁷ may be a structure substituted with a substituent having a hetero atom. Examples of the substituent include an ester group, an ether group, a sulfide group, an amide group, an amine group, a sulfoxide group, a ketone group, and a hydroxyl group.

The content of the structural unit represented by the general formula (5) in the polyvinyl acetal resin is preferably adjusted so that the content of the ionic functional group in the polyvinyl acetal resin is within the appropriate range. In order to make the content of the ionic functional group in the polyvinyl acetal resin within the appropriate range, for example, when one ionic functional group is introduced by the general formula (5), the general formula ( The content of the structural unit shown in 5) is preferably about 0.05 to 5 mol%, and when two ionic functional groups are introduced by the general formula (5), the above general formula The content of the structural unit shown in (5) is preferably about 0.025 to 2.5 mol%.
By making the content of the ionic functional group in the polyvinyl acetal resin within the above range, the dispersibility of the fine particles composed of the polyvinyl acetal resin in the composition for a lithium secondary battery electrode is improved, and the electrolyte solution has Dispersion of the active material and conductive additive when used as an electrode and an electrode can be improved, and further, the deterioration of the binder when used as a battery is suppressed, so the discharge capacity of the lithium secondary battery is reduced. Can be suppressed.

The fine particles made of the polyvinyl acetal resin preferably have a volume average particle diameter of 10 to 500 nm. When the volume average particle diameter exceeds 500 nm, the dispersibility of the active material and the conductive additive when used as an electrode may be reduced, and the discharge capacity of the lithium secondary battery may be reduced. On the other hand, when the thickness is less than 10 nm, the binder may cover all the surfaces of the active material and the conductive auxiliary agent, and the electrolyte solution becomes difficult to come into contact with the active material. Lithium ion conduction may decrease, and battery capacity may decrease. The more preferable volume average particle diameter of the fine particles made of the polyvinyl acetal resin is 15 to 300 nm, and the more preferable volume average particle diameter is 15 to 200 nm.
The volume average particle size of the fine particles comprising the polyvinyl acetal resin can be measured using a laser diffraction / scattering particle size distribution measuring device, a transmission electron microscope, a scanning electron microscope, or the like.

The upper limit of the CV value of the volume average particle diameter of the fine particles comprising the polyvinyl acetal resin is preferably 40%. When the CV value exceeds 40%, fine particles having a large particle size exist, and a stable composition for a lithium secondary battery electrode may not be obtained due to sedimentation of the large particle size particles. is there.
The preferable upper limit of the CV value is 35%, the more preferable upper limit is 32%, and the more preferable upper limit is 30%. The CV value is a numerical value indicated by a percentage (%) of a value obtained by dividing the standard deviation by the volume average particle diameter.

The binder for an electricity storage device electrode of the present invention contains an aqueous medium as a dispersion medium.
By using an aqueous medium as the dispersion medium, the solvent remaining on the electrode can be reduced as much as possible, and a lithium secondary battery can be manufactured.
In addition, in the binder for electrical storage device electrodes of this invention, an aqueous medium may be only water and in addition to the said water, you may add solvents other than water.
As the solvent other than water, a solvent having solubility in water and high volatility is preferable, and examples thereof include alcohols such as isopropyl alcohol, normal propyl alcohol, ethanol, and methanol. The said solvent may be used independently and may use 2 or more types together. A preferable upper limit of the amount of the solvent other than water is 30 parts by weight with respect to 100 parts by weight of water, and a more preferable upper limit is 20 parts by weight.

Although content of the microparticles | fine-particles which consist of the said polyvinyl acetal type resin in the binder for electrical storage device electrodes of this invention is not specifically limited, A preferable minimum is 2 weight% and a preferable upper limit is 60 weight%. When the content of the fine particles composed of the polyvinyl acetal resin is less than 2% by weight, the fine particles composed of the polyvinyl acetal resin with respect to the active material when the binder is mixed with the active material to obtain a composition for an electricity storage device electrode. When the amount is less than 60% by weight, the stability of the fine particles of the polyvinyl acetal resin in the aqueous medium decreases, When coalescence occurs, it becomes difficult to sufficiently disperse the active material, and the discharge capacity of an electricity storage device such as a lithium secondary battery may be reduced. More preferably, it is 5 to 50% by weight.

The binder for an electricity storage device electrode of the present invention is a binder used for an electrode of an electricity storage device.
Examples of the electricity storage device include a lithium secondary battery, an electric double layer capacitor, and a lithium ion capacitor. Especially, it can be used especially suitably for a lithium secondary battery and a lithium ion capacitor.

The method for producing the binder for an electricity storage device electrode of the present invention is not particularly limited. For example, after performing the step of producing a polyvinyl acetal resin, the polyvinyl acetal resin is converted into tetrahydrofuran, acetone, toluene, methyl ethyl ketone, ethyl acetate. Or dissolved in an organic solvent in which polyvinyl acetal resin such as methanol, ethanol, butanol, isopropyl alcohol is dissolved, and then a poor solvent such as water is added little by little, and the organic solvent is removed by heating and / or reducing pressure. A method for producing fine particles by precipitating a polyvinyl acetal resin, adding a solution in which the polyvinyl acetal resin is dissolved in a large amount of water, and then heating and / or reducing pressure as necessary to remove the organic solvent, Polyvinyl acetal resin is deposited and fine And a method of preparing a child, a method in which a polyvinyl acetal resin is heated at a temperature equal to or higher than the glass transition temperature of the polyvinyl acetal resin and kneaded with a kneader or the like, and water is added little by little under heat and pressure. .
Among them, since the volume-average particle diameter of the fine particles made of the obtained polyvinyl acetal resin is small and fine particles with a narrow particle size distribution can be obtained, the polyvinyl acetal resin is dissolved after dissolving the polyvinyl acetal resin in an organic solvent. A method of producing fine particles by precipitation is preferred.
In the above production method, fine particles comprising a polyvinyl acetal resin may be prepared and dried, and then dispersed in an aqueous medium. The solvent used in the production of the fine particles comprising a polyvinyl acetal resin is used as an aqueous medium as it is. May be.

It can be set as the composition for electrical storage device electrodes by adding an active material to the binder for electrical storage device electrodes of this invention. Such a binder for an electricity storage device electrode of the present invention and a composition for an electricity storage device electrode containing an active material are also one aspect of the present invention.

The content of the fine particles comprising the polyvinyl acetal resin in the power storage device electrode composition of the present invention is not particularly limited, but the preferred lower limit is 0.5 parts by weight and the preferred upper limit is 12 parts with respect to 100 parts by weight of the active material. Parts by weight. If the content of the fine particles comprising the polyvinyl acetal resin is less than 0.5 parts by weight, the adhesive force to the current collector may be insufficient. If the content exceeds 12 parts by weight, the lithium secondary battery The discharge capacity may be reduced. More preferably, it is 1 to 5 parts by weight.

The composition for an electricity storage device electrode of the present invention contains an active material.
The composition for an electricity storage device electrode of the present invention may be used for either a positive electrode or a negative electrode, or may be used for both a positive electrode and a negative electrode. Accordingly, the active material includes a positive electrode active material and a negative electrode active material.

Examples of the positive electrode active material include lithium-containing composite metal oxides such as lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. Specific examples include LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , and LiFeO.
In addition, these may be used independently and may use 2 or more types together.

As said negative electrode active material, the material conventionally used as a negative electrode active material of a lithium secondary battery can be used, for example, natural graphite (graphite), artificial graphite, amorphous carbon, carbon black, or The thing which added the different element to these components is mentioned. Of these, graphite is preferable, and spherical natural graphite is particularly preferable.

It is preferable that the composition for electrical storage device electrodes of this invention contains a conductive support agent.
The conductive auxiliary agent is used to increase the output of the electricity storage device, and when used for the positive electrode, an appropriate one can be used depending on the use for the negative electrode.
Examples of the conductive aid include graphite, acetylene black, carbon black, ketjen black, and vapor grown carbon fiber. Of these, acetylene black is preferable.

The composition for an electricity storage device electrode of the present invention includes, in addition to the above-mentioned active material, conductive additive, fine particles comprising a polyvinyl acetal resin, and an aqueous medium, a flame retardant aid, a thickener, Additives such as foaming agents, leveling agents and adhesion promoters may be added. Especially, when coating the electrical storage device electrode composition on a current collector, it is preferable to add a thickener since the coating film can be made uniform.

The method for producing the composition for an electricity storage device electrode of the present invention is not particularly limited. For example, the active material, the conductive additive, the fine particles comprising a polyvinyl acetal resin, the nonionic surfactant, the aqueous medium, and the necessity There is a method of mixing various additives to be added according to various mixers such as a ball mill, a blender mill, and a three roll.

For example, the composition for an electricity storage device electrode of the present invention is applied on a conductive substrate and dried to form an electricity storage device electrode. An electrode and an electricity storage device obtained using such a composition for an electricity storage device electrode are also one aspect of the present invention.
As an application method for applying the composition for an electricity storage device electrode of the present invention to a conductive substrate, various application methods such as an extrusion coater, a reverse roller, a doctor blade, an applicator and the like can be employed.

According to the present invention, the active material is excellent in dispersibility, defoaming and adhesiveness, can improve the electrode density of the obtained electrode, has high durability against the electrolytic solution, and has a small amount of binder added. Even in this case, it is possible to provide a storage device electrode binder capable of producing a high-capacity lithium secondary battery, and a storage device electrode composition, storage device electrode, and storage device using the storage device electrode binder.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Preparation of dispersion of polyvinyl acetal resin fine particles 1)
In a reaction vessel equipped with a thermometer, a stirrer, and a cooling tube, polyvinyl acetal resin (degree of polymerization 1000, degree of butyralization 52.4 mol%, hydroxyl content 46.4 mol%, acetyl group content 1.2 mol%) 20 A part by weight was dissolved in 80 parts by weight of isopropanol, 1 part by weight of sodium 2-formylbenzenesulfonate and 0.05 part by weight of 12M concentrated hydrochloric acid were added to the solution, and reacted at 75 ° C. for 4 hours. The reaction solution was cooled, and 200 parts by weight of water was added dropwise. Next, the liquid temperature was kept at 30 ° C., and the isopropanol and water were volatilized by stirring while reducing the pressure. Then, the solution was concentrated until the solid content became 20% by weight, and the fine particles 1 (hereinafter referred to as polyvinyl acetate) composed of a polyvinyl acetal resin. A dispersion (content of fine particles 1 made of polyvinyl acetal resin: 20% by weight) in which acetal resin fine particles 1 are dispersed was prepared.
When the obtained polyvinyl acetal resin was measured by NMR, the degree of butyralization was 52.0 mol%, the hydroxyl group amount was 44.0 mol%, the acetyl group amount was 1.0 mol%, and the ions contained in the polyvinyl acetal resin. The amount of the functional functional group was 0.2 mmol / g, and the content of the acetal bond having the ionic functional group was 3.0 mol%. Moreover, it was 100 nm when the volume average particle diameter of the microparticles | fine-particles 1 which consist of obtained polyvinyl acetal type resin was measured with the transmission electron microscope.

(Preparation of dispersion of polyvinyl acetal resin fine particles 2)
20 parts by weight of polyvinyl acetal resin (polymerization degree 1000, butyralization degree 70 mol%, hydroxyl group amount 28.2 mol%, acetyl group amount 1.8 mol%) in a reaction vessel equipped with a thermometer, a stirrer and a condenser Was dissolved in 80 parts by weight of isopropanol, 1 part by weight of sodium 2-formylbenzenesulfonate and 0.05 part by weight of 12M concentrated hydrochloric acid were added to the solution, and reacted at 75 ° C. for 4 hours. The reaction solution was cooled, and 200 parts by weight of water was added dropwise. Next, the liquid temperature was kept at 30 ° C., and the isopropanol and water were volatilized by stirring while reducing the pressure, and then concentrated until the solid content became 20% by weight. Fine particles 2 made of polyvinyl acetal resin (hereinafter referred to as polyvinyl acetate). A dispersion (content of fine particles 2 made of polyvinyl acetal resin: 20% by weight) in which acetal resin fine particles 2 are dispersed was prepared.
When the obtained polyvinyl acetal resin was measured by NMR, the degree of butyralization was 69.5 mol%, the amount of hydroxyl group was 26.2 mol%, the amount of acetyl group was 1.5 mol%, and the ions contained in the polyvinyl acetal resin. The amount of the functional functional group was 0.2 mmol / g, and the content of the acetal bond having the ionic functional group was 2.8 mol%. Moreover, it was 100 nm when the volume average particle diameter of the microparticles | fine-particles 2 which consist of obtained polyvinyl acetal type resin was measured with the transmission electron microscope.

(Preparation of dispersion of polyvinyl acetal resin fine particles 3)
In a reaction vessel equipped with a thermometer, a stirrer, and a cooling tube, polyvinyl acetal resin (degree of polymerization 1000, degree of butyralization 35.5 mol%, hydroxyl content 63.3 mol%, acetyl group content 1.2 mol%) 20 A part by weight was dissolved in 80 parts by weight of isopropanol, 1 part by weight of sodium 2-formylbenzenesulfonate and 0.05 part by weight of 12M concentrated hydrochloric acid were added to the solution, and reacted at 75 ° C. for 4 hours. The reaction solution was cooled, and 200 parts by weight of water was added dropwise. Next, the liquid temperature was kept at 30 ° C., and the isopropanol and water were volatilized by stirring while reducing the pressure. Then, the solution was concentrated to a solid content of 20% by weight, and fine particles 3 made of polyvinyl acetal resin (hereinafter referred to as polyvinyl acetate). A dispersion (content of fine particles 3 made of polyvinyl acetal resin: 20% by weight) in which acetal resin fine particles 3 are dispersed was prepared.
When the obtained polyvinyl acetal resin was measured by NMR, the degree of butyralization was 34.0 mol%, the hydroxyl group amount was 62.0 mol%, the acetyl group amount was 1.0 mol%, and the ions contained in the polyvinyl acetal resin. The amount of the functional functional group was 0.2 mmol / g, and the content of the acetal bond having the ionic functional group was 3.0 mol%. Moreover, it was 100 nm when the volume average particle diameter of the microparticles | fine-particles 3 which consist of obtained polyvinyl acetal type resin was measured with the transmission electron microscope.

Example 1
(Preparation of composition for positive electrode of lithium secondary battery)
90 parts by weight of water was added to 10 parts by weight of the dispersion of the polyvinyl acetal resin fine particles 1 obtained as a binder to prepare a 2% by weight dispersion of the fine particles 1 made of the polyvinyl acetal resin. For 100 parts by weight of this dispersion, 50 parts by weight of lithium manganate (manufactured by Nippon Chemical Industry Co., Ltd., Cellseed C-5H) as the positive electrode active material and acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black) as the conductive auxiliary 4 parts by weight, 0.5 part by weight of carboxymethyl cellulose (manufactured by Aldrich) as a thickener, nonionic surfactant (polyoxyethylene polyoxypropylene block copolymer 1, Epan 740, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 1 part by weight was added and mixed to obtain a composition for a lithium secondary battery positive electrode.

(Examples 2-9)
A lithium secondary battery positive electrode composition was obtained in the same manner as in Example 1 except that the type of nonionic surfactant was changed to that shown in Table 2. In addition, the following were used as nonionic surfactant.
・ Polyoxyethylene polyoxypropylene block copolymer 2 (Epan 710, all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
・ Polyoxyethylene polyoxypropylene block copolymer 3 (Epan 785)
・ Polyoxyethylene polyoxypropylene block copolymer 4 (Epan 410)
・ Polyoxyalkylene glyceryl ether fatty acid ester (Neugen GIS-125)
・ Polyoxyethylene lauryl ether (DKS NL-50)
・ Polyoxyethylene styrenated phenyl ether (Neugen EA-207D)
・ Polyoxyalkylene decyl ether 1 (Neugen XL-50)
・ Polyoxyalkylene decyl ether 2 (Neugen TDX-80)

(Example 10)
(Preparation of composition for negative electrode of lithium secondary battery)
90 parts by weight of water was added to 10 parts by weight of a dispersion of fine particles 1 made of a polyvinyl acetal resin obtained as a binder to prepare a 2% by weight solution of a polyvinyl acetal resin. With respect to 100 parts by weight of this solution, 50 parts by weight of spherical natural graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-10) as a negative electrode active material, and 4 weights of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black) as a conductive assistant Part, 0.5 part by weight of carboxymethyl cellulose (manufactured by Aldrich) as a thickener, 0.1 part by weight of a nonionic surfactant (polyoxyethylene polyoxypropylene block copolymer 1, Epan 740, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Part was added and mixed to obtain a composition for a negative electrode of a lithium secondary battery.

(Examples 11 to 18)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 10 except that the type of nonionic surfactant was changed to that shown in Table 2.

(Comparative Examples 1 and 2)
A lithium secondary battery positive electrode composition was obtained in the same manner as in Example 1 except that the fine particles 2 and 3 made of polyvinyl acetal resin were added instead of the fine particles 1 made of polyvinyl acetal resin.

(Comparative Examples 3-5)
A lithium secondary battery positive electrode composition was obtained in the same manner as in Example 1 except that an anionic surfactant or a cationic surfactant was used instead of the nonionic surfactant. In addition, the following were used as an anionic surfactant or a cationic surfactant.
Anionic surfactant (polyoxyethylene lauryl ether phosphate 1, plysurf A208B)
Anionic surfactant (polyoxyethylene lauryl ether phosphate 2, plysurf A219B)
・ Cationic surfactant (stearyl trimethylammonium chloride, Cathogen TMS)

(Comparative Examples 6 and 7)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 10 except that the fine particles 2 and 3 made of polyvinyl acetal resin were added instead of the fine particles 1 made of polyvinyl acetal resin.

(Comparative Examples 8 to 10)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 10 except that an anionic surfactant or a cationic surfactant was used instead of the nonionic surfactant.

<Evaluation>
The following evaluation was performed about the composition for lithium secondary battery electrodes (for positive electrodes and negative electrodes) obtained by the Example and the comparative example. The results are shown in Table 2.

(1) Foaming power Evaluation was performed based on a synthetic detergent test method (Rosmiles method) of JIS K3362. Under an environment of 25 ° C., 200 ml of a sample aqueous solution having a predetermined concentration was dropped from the height of 900 mm onto the liquid surface in 30 seconds, and the height of the foam was measured as the foaming force. The height after 5 minutes was defined as the foam stability. In addition, it can be said that defoaming property is so high that the height of the foam after 5 minutes is low.

(2) Adhesiveness (peeling power)
About the composition for lithium secondary battery positive electrodes obtained in Examples 1-9 and Comparative Examples 1-5, the adhesiveness with respect to aluminum foil was evaluated, and it obtained in Examples 10-18 and Comparative Examples 6-10. About the composition for lithium secondary battery negative electrodes, the adhesiveness with respect to copper foil was evaluated. In Comparative Examples 5 and 10, since peeling occurred before measurement, it was set as “not measurable”.

(2-1) Adhesive to aluminum foil On the aluminum foil (thickness 20 μm), the composition for a lithium secondary battery electrode is applied and dried so that the film thickness after drying is 20 μm, and the aluminum foil is coated on the aluminum foil. A test piece having an electrode formed in a sheet shape was obtained.
This sample was cut into a length of 1 cm and a width of 2 cm, and the electrode sheet was pulled up while fixing the test piece using AUTOGRAPH (manufactured by Shimadzu Corporation, “AGS-J”) until the electrode sheet was completely peeled from the aluminum foil. The required peel force (N) was measured.

(2-2) Adhesiveness to copper foil In the above "(2-1) Adhesiveness to aluminum foil", the peel force was measured by exactly the same method except that the aluminum foil was changed to a copper foil (thickness 20 µm).

(3) Dispersibility (average dispersion diameter)
10 parts by weight of the obtained composition for a lithium secondary battery electrode and 90 parts by weight of water were mixed and diluted, and then stirred for 10 minutes with an ultrasonic disperser (manufactured by SNDI, “US-303”). Thereafter, the particle size distribution was measured using a laser diffraction particle size distribution meter (LA-910, manufactured by Horiba, Ltd.), and the average dispersion diameter was measured. In Comparative Examples 5 and 10, since the measured value was 100 μm or more, it was set as “not measurable”.

(4) Solvent solubility (elution rate)
(Production of electrode sheet)
On the polyethylene terephthalate (PET) film subjected to the release treatment, the lithium secondary battery electrode compositions obtained in Examples and Comparative Examples were applied and dried so that the film thickness after drying was 20 μm. A sheet was produced.
The electrode sheet was cut into a 2 cm square to prepare an electrode sheet test piece.

(Elution evaluation)
The weight of the obtained test piece was accurately measured, and the weight of the resin contained in the test piece was calculated from the component weight ratio contained in the sheet. Thereafter, the test piece was put in a bag-like mesh, and the total weight of the mesh bag and the test piece was accurately measured.
Next, the mesh bag containing the test piece was immersed in diethyl carbonate, which is an electrolytic solution, and left overnight at room temperature. After standing, the mesh bag was taken out and dried under conditions of 150 ° C. and 8 hours to completely dry the solvent.
After taking out from the dryer, it was left at room temperature for 1 hour and weighed. The elution amount of the resin was calculated from the weight change before and after the test, and the elution rate of the resin was calculated from the ratio between the elution amount and the weight of the resin calculated in advance, and evaluated according to the following criteria. In addition, it means that resin is easy to elute in electrolyte solution, so that the value of elution rate is high.

(5) Battery performance evaluation (5-1) Examples 1-9, Comparative Examples 1-5
(A) Preparation of coin battery The lithium secondary battery positive electrode compositions obtained in Examples 1 to 9 and Comparative Examples 1 to 5 were applied to an aluminum foil and dried to a thickness of 0.2 mm. A positive electrode layer was obtained by punching.
Moreover, the composition for lithium secondary battery negative electrodes obtained in Example 10 was applied to a copper foil and dried to a thickness of 0.2 mm, which was punched into φ12 mm to obtain a negative electrode layer.
Using a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) containing LiPF ₆ (1M) as an electrolytic solution, the positive electrode layer was impregnated with the electrolytic solution, and the positive electrode layer was then used as a positive electrode current collector. A 25-mm thick porous PP membrane (separator) impregnated with an electrolytic solution was further placed thereon.
Further, a lithium metal plate serving as a negative electrode layer was placed thereon, and a negative electrode current collector covered with insulating packing was placed thereon. Pressure was applied to the laminate with a caulking machine to obtain a sealed coin battery.

(B) Evaluation of discharge capacity and evaluation of charge / discharge cycle The obtained coin battery was subjected to a discharge capacity evaluation and a charge / discharge cycle evaluation using a charge / discharge test apparatus manufactured by Hosen Co., Ltd.
This discharge capacity evaluation and charge / discharge cycle evaluation were performed at a voltage range of 2.7 to 4.2 V and evaluation temperatures of 25 ° C. and 50 ° C. The charge / discharge cycle evaluation was calculated from the ratio of the discharge capacity at the 30th cycle to the initial discharge capacity.
In Comparative Examples 1 and 2, the aggregation of the binder was remarkable, and the coin battery could not be produced, and therefore, “not measurable” was set. Moreover, about the comparative examples 3 and 5, since dissociation of the active material by the binder eluting in electrolyte solution was confirmed and charging / discharging was not able to be performed, it was set as "measurable".

(5-2) Examples 10 to 18 and Comparative Examples 6 to 10
The lithium secondary battery positive electrode composition obtained in Example 1 was applied to an aluminum foil and dried to a thickness of 0.2 mm, which was punched into φ12 mm to obtain a positive electrode layer.
Moreover, the lithium secondary battery negative electrode compositions obtained in Examples 10 to 18 and Comparative Examples 6 to 10 were applied to a copper foil and dried to a thickness of 0.2 mm, which was punched out to φ12 mm to form a negative electrode layer. Obtained.
A sealed coin battery was obtained by the same method as (5-1) except that the obtained positive electrode layer and negative electrode layer were used, and then discharge capacity evaluation and charge / discharge cycle evaluation were performed. The charge / discharge cycle evaluation was calculated from the ratio of the discharge capacity at the 30th cycle to the initial discharge capacity.
In Comparative Examples 6 and 7, the aggregation of the binder was remarkable, and the coin battery could not be produced. Moreover, about the comparative examples 8 and 10, since dissociation of the active material by the binder eluting in electrolyte solution was confirmed and charging / discharging was not able to be performed, it was set as "measurement impossible".

According to the present invention, the active material is excellent in dispersibility, defoaming and adhesiveness, can improve the electrode density of the obtained electrode, has high durability against the electrolytic solution, and has a small amount of binder added. Even in this case, it is possible to provide a storage device electrode binder capable of producing a high-capacity lithium secondary battery, and a storage device electrode composition, storage device electrode, and storage device using the storage device electrode binder.

Claims (14)

A binder used for an electrode of an electricity storage device,
A binder for an electricity storage device electrode comprising a polyvinyl acetal resin dispersion containing fine particles comprising a polyvinyl acetal resin having a hydroxyl group content of 30 to 60 mol%, a nonionic surfactant and an aqueous medium. 2. The nonionic surfactant is at least one selected from the group consisting of polyoxyethylene polyoxypropylene block copolymers, polyoxyalkylene alkyl ethers and polyoxyalkylene glyceryl ether fatty acid esters. The binder for electrical storage device electrodes as described. The binder for an electricity storage device electrode according to claim 1, wherein the nonionic surfactant has an ethylene oxide content of 5 to 90% by weight. The binder for an electricity storage device electrode according to claim 1, wherein the nonionic surfactant has a weight average molecular weight of 300 to 25,000. The binder for an electricity storage device electrode according to claim 1, 2, 3, or 4, wherein the nonionic surfactant has an HLB value of 8.0 to 20.0. The binder for an electricity storage device electrode according to claim 1, wherein the polyvinyl acetal resin has an ionic functional group. The ionic functional group is at least one functional group selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfinic acid group, a sulfenic acid group, a phosphoric acid group, a phosphonic acid group, an amino group, and a salt thereof. The binder for an electricity storage device electrode according to claim 6, wherein: The polyvinyl acetal resin has a structural unit having a hydroxyl group represented by the following formula (1), a structural unit having an acetyl group represented by the following formula (2), and an acetal group represented by the following formula (3). The binder for an electrical storage device electrode according to claim 6 or 7, comprising a structural unit and a structural unit having an acetal group containing an ionic functional group represented by the following formula (4).

In formula (3), R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, in formula (4), R ² represents an alkylene group or aromatic ring having 1 to 20 carbon atoms, and X is ionic. Represents a functional group. The power storage device electrode binder according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the polyvinyl acetal resin has a polymerization degree of 250 to 4000. The binder for an electricity storage device electrode according to claim 6 or 7, wherein the polyvinyl acetal resin has an acetyl group content of 0.2 to 20 mol%. The power storage device electrode according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein the fine particles comprising the polyvinyl acetal resin have a volume average particle diameter of 10 to 500 nm. Binder. An electrical storage device electrode composition containing the binder for an electrical storage device electrode according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, and an active material,
An electrical storage device electrode composition comprising 0.5 to 12 parts by weight of fine particles comprising a polyvinyl acetal resin with respect to 100 parts by weight of the active material. An electrical storage device electrode comprising the electrical storage device electrode composition according to claim 12. An electricity storage device comprising the electricity storage device electrode according to claim 13.