JP2018160400A - Binder for power storage device electrodes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a binder for power storage device electrodes, which has adhesiveness and stickiness and which can impart large toughness and flexibility to resultant electrodes; a composition for power storage device electrodes, containing the binder for power storage device electrodes; a power storage device electrode; and a power storage device.SOLUTION: A binder for power storage device electrodes is one to be used for electrodes of power storage devices. The binder comprises: a binder resin (A) having a storage elastic modulus of 1×10to 1×10Pa under the conditions of 50°C and 10 Hz; and a binder resin (B) having a storage elastic modulus of 1×10to 1×10Pa under the conditions of 50°C and 10 Hz. The binder includes the binder resin (A) of 85 to 99.9 wt.% and the binder resin (B) of 0.1 to 15 wt.% to a total of 100 wt.% of the binder resin (A) and the binder resin (B).SELECTED DRAWING: None

Description

The present invention relates to a binder for an electricity storage device electrode that has adhesiveness and tackiness and can impart toughness and flexibility to the obtained electrode. Furthermore, the present invention relates to an electrical storage device electrode composition, an electrical storage device electrode, and an electrical storage device containing the electrical storage device electrode binder.

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.
As a structure of the charge / discharge part of the lithium secondary battery, a stacked battery in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, or a wound battery such as a cylindrical battery is used. The wound battery can increase the effective electrode area for a small volume, and can increase the capacity and output.

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.

On the other hand, carboxymethylcellulose or the like is used as the aqueous binder, but when carboxymethylcellulose is used, the resin becomes insufficiently flexible, and the effect of binding the active material becomes insufficient. There has been a problem that the adhesive strength to the current collector is significantly reduced.
In Patent Document 1, low crystal carbon having a graphite interlayer distance (d002) of 0.345 to 0.370 nm as a negative electrode active material, styrene-butadiene copolymer (SBR) as a binder, and carboxymethyl cellulose as a thickener. It has been shown that a favorable negative electrode can be obtained by using it, and a battery having excellent output characteristics can be obtained.
However, since SBR has low elasticity and low resilience, there is a problem that the followability of the active material to expansion and contraction is low, and in particular, the binder peels when the active material contracts. As a result, there is a problem in that conduction failure occurs between the active materials and at the current collector interface, and the capacity decreases due to repeated charge and discharge.

In addition, a method using a binder resin having high elasticity and high resilience has also been proposed. However, in a wound battery, non-uniform stress distribution occurs in the wound body due to expansion and contraction of the active material during charging and discharging. There is a problem in that the capacity is reduced due to the occurrence of pressure on the electrode, peeling between the active materials and the current collector interface, cracking of the electrode, and squeezing of the electrode end.

JP 2009-158099 A

An object of this invention is to provide the binder for electrical storage device electrodes which has adhesiveness and adhesiveness and can provide toughness and a softness | flexibility to the electrode obtained. Furthermore, it aims at providing the composition for electrical storage device electrodes containing this binder for electrical storage device electrodes, an electrical storage device electrode, and an electrical storage device.

The present invention relates to a binder used in the electrode of the electric storage device, 50 ° C., a storage modulus at 10Hz is 1 × ¹⁰ 8 ~1 × binder resin is ^{10 10} Pa (A), and, 50 ° C., at 10Hz A binder resin (B) having a storage elastic modulus of 1 × 10 ⁵ to 1 × 10 ⁷ Pa is contained, and the binder resin is used with respect to a total of 100% by weight of the binder resin (A) and the binder resin (B). It is an electrical storage device electrode binder containing (A) 85 to 99.9 wt% and 0.1 to 15 wt% of the binder resin (B).
The present invention is described in detail below.

As a result of intensive investigations, the present inventors have found that a binder resin used in the composition for an electricity storage device electrode is composed mainly of a binder resin having a high elasticity and a high resilience, a low elasticity and a low resilience. It has been found that by adding a constant amount, it is possible to impart adhesiveness to the binder itself. In particular, when used in a wound battery such as a cylindrical battery, it is possible to suppress cracking of the electrode and twisting of the electrode end, and to suppress a decrease in capacity due to repeated charge and discharge. The headline and the present invention have been completed.

The binder for an electricity storage device electrode of the present invention contains a binder resin (A).
In the binder resin (A), the lower limit of the storage elastic modulus at 50 ° C. and 10 Hz is 1 × 10 ⁸ Pa, and the upper limit is 1 × 10 ¹⁰ Pa.
When the storage elastic modulus of the binder resin (A) is 1 × 10 ⁸ Pa or more, the binder resin does not become too soft, and the deformation of the binder resin is reduced even during repeated charge and discharge. Separation of the substance can be suppressed. When the storage elastic modulus of the binder resin (A) is 1 × 10 ¹⁰ Pa or less, the binder resin does not become too hard, and the adhesion between the active materials and the current collector interface can be improved.
The storage elastic modulus of the binder resin (A) has a preferable lower limit of 2.0 × 10 ⁸ Pa, a more preferable lower limit of 3.0 × 10 ⁸ Pa, a preferable upper limit of 2.5 × 10 ⁹ Pa, and a more preferable upper limit. 1.5 × 10 ⁹ Pa.
In addition, the storage elastic modulus in 50 degreeC and 10 Hz can be measured by using a dynamic viscoelasticity measuring apparatus.

The binder resin (A) preferably has a weight average molecular weight of 10,000 to 10,000,000, more preferably 20,000 to 5,000,000.

As for the glass transition temperature of the binder resin (A), a preferable lower limit is 55 ° C., a more preferable lower limit is 60 ° C., a preferable upper limit is 250 ° C., and a more preferable upper limit is 140 ° C.

Examples of the binder resin (A) include polyvinyl acetal resins, polyacrylonitrile, (meth) acrylic acid ester homopolymers, polyamide imides, and the like. Of these, polyvinyl acetal resins are preferable.

Examples of polyacrylonitrile include a homopolymer of acrylonitrile, and a copolymer of acrylonitrile and an alkyl ester of acrylic acid, an alkyl ester of methacrylic acid, or the like.

Examples of (meth) acrylate homopolymers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, alkyl acrylates such as octyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate And homopolymers such as alkyl esters of methacrylic acid such as butyl methacrylate and octyl methacrylate. Of these, polymethyl methacrylate is preferably used.

Polyamideimide is a degeneracy of acid components such as trimellitic acid, pyromellitic acid and polyamic acid and diamines such as aromatic diamine and aliphatic diamine, or diisocyanates such as aromatic diisocyanate and aliphatic diisocyanate. Coalescence is mentioned.

In the present invention, by using a polyvinyl acetal resin as the binder resin (A), an attractive interaction acts on the active material, and the active material can be fixed with a small amount of the binder. In addition, it has 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, the dispersibility of an active material is improved significantly by making the distance of an active material and a conductive support agent 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.

The minimum with the preferable amount of hydroxyl groups of the said polyvinyl acetal type resin is 30 mol%, and a preferable upper limit is 60 mol%. When the amount of the hydroxyl group is 30 mol% or more, it is possible to suppress the resin component from eluting into the electrolytic solution when the electrode is immersed in the electrolytic solution with sufficient resistance to the electrolytic solution. When the hydroxyl group content is 60 mol% or less, the stability of the polyvinyl acetal resin in an aqueous medium is improved, and the active material can be sufficiently dispersed while suppressing the aggregation of the binder resin.
A more preferred lower limit of the hydroxyl group content is 35 mol%, and a more preferred upper limit is 55 mol%.

As for the degree of acetalization of the polyvinyl acetal-based resin, a preferable lower limit is 40 mol% and a preferable upper limit is 70 mol% in all acetalization degrees, regardless of whether a single aldehyde or a mixed aldehyde is used. When the degree of acetalization is 40 mol% or more, the resin has good flexibility, and sufficient adhesive force to the current collector can be exhibited. When the degree of acetalization is 70 mol% or less, it is possible to suppress the elution of the resin component into the electrolytic solution when the electrode is immersed in the electrolytic solution with sufficient resistance to the electrolytic solution. As for the said acetalization degree, a more preferable minimum is 45 mol% and a more preferable upper limit is 65 mol%.

The preferable lower limit of the amount of acetyl groups in the polyvinyl acetal resin is 0.2 mol%, and the preferable upper limit is 20 mol%. When the acetyl group content is 0.2 mol% or more, the flexibility of the resin can be improved. When the amount of the acetyl group is 20 mol% or less, the resistance to the electrolytic solution is sufficient, and elution of the resin component into the electrolytic solution when the electrode is immersed in the electrolytic solution can be suppressed. A more preferable lower limit of the amount of the acetyl group is 1 mol%.

The preferable lower limit of the degree of polymerization of the polyvinyl acetal resin is 250, and the preferable upper limit is 4000. When the degree of polymerization is 250 or more, the resistance to the electrolytic solution is sufficient, and the elution of the electrode into the electrolytic solution can be suppressed. When the degree of polymerization is 4000 or less, sufficient adhesive strength with the active material can be obtained, and a decrease in the discharge capacity of the lithium secondary battery can be suppressed. The minimum with said more preferable polymerization degree is 280, and a more preferable upper limit is 3500.

The polyvinyl acetal resin 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 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 particularly excellent. Can be.
In addition, as said salt, sodium salt, potassium salt, etc. are mentioned.

The preferable lower limit of the content of the ionic functional group in the polyvinyl acetal resin is 0.01 mmol / g, and the preferable upper limit is 1 mmol / g. When the content of the ionic functional group is 0.01 mmol / g or more, the dispersibility of the polyvinyl acetal-based resin in the composition for a lithium secondary battery electrode, and the active material and conductivity assist when used as an electrode. The dispersibility of the agent can be sufficiently improved. When the content of the ionic functional group is 1 mmol / g or less, the durability of the binder in the battery can be improved, and the discharge capacity of the lithium secondary battery can be improved. The content of the ionic functional group in the polyvinyl acetal resin has a more preferable lower limit of 0.02 mmol / g and a more preferable upper limit of 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 active material and the dispersibility of a conductive support agent excellent in the tolerance with respect to electrolyte solution and an electrode, it is preferable to exist directly in a polyvinyl acetal type resin structure.
When the ionic functional group is present directly 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 an acetal bond It is preferable that the molecular structure has an ionic functional group bonded thereto. Further, 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 polyvinyl acetal resin in the composition for a lithium secondary battery electrode, and improves the dispersibility of the active material and the conductive assistant when used as an electrode. In addition to being able to be particularly excellent, since deterioration of the binder when the battery is made is suppressed, a decrease in the discharge capacity of the 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, a method of reacting an aldehyde with the above-mentioned modified polyvinyl alcohol raw material having an ionic functional group to acetalize, after producing a polyvinyl acetal resin, another functional group having reactivity to the functional group of the polyvinyl acetal resin And a method of reacting with a compound having a group and an ionic functional group.

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. . Among these, 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, and 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 (1-1): The structural unit which has an acetyl group represented by 1-2), the structural unit which has an acetal group represented by the following formula (1-3), and the ionic functional group represented by the following formula (1-4) It is preferable to have a structural unit having an acetal group containing
As a result, the dispersibility of the polyvinyl acetal resin, the dispersibility of the active material and the conductive additive can be made particularly excellent, and the adhesive strength 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.

In Formula (1-3), R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. In Formula (1-4), R ² represents an alkylene group having 1 to 20 carbon atoms or an aromatic ring. X represents an ionic 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%. Moreover, when two ionic functional groups are introduced by one acetal bond, the content of the acetal bond having the ionic functional group is preferably about 0.05 to 5 mol%. Further, in order to increase both the dispersibility of the polyvinyl acetal resin and the flexibility of the resin and the adhesive force to the current collector, the content of the acetal bond having an ionic functional group in the polyvinyl acetal resin is The total acetal bond is preferably 0.5 to 20 mol%.
By making the content of the ionic functional group in the polyvinyl acetal resin within the above range, the dispersibility of the polyvinyl acetal resin in the composition for a lithium secondary battery electrode is improved, and the resistance to the electrolyte and the electrode In this case, the dispersibility of the active material and the conductive additive can be made excellent. Furthermore, since the deterioration of the binder when used as a battery is suppressed, a decrease in the discharge capacity of the lithium secondary battery can be suppressed.

The 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, the method of acetalizing after making the aldehyde which has the said ionic functional group react beforehand with a polyvinyl alcohol raw material is mentioned. Also, when acetalizing polyvinyl alcohol, the aldehyde raw material is mixed with the aldehyde having the ionic functional group and acetalized, and after producing the polyvinyl acetal resin, the aldehyde having the ionic functional group is reacted. Methods 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 polyvinyl acetal resin in the composition for a lithium secondary battery electrode, the dispersibility of the active material and the conductive assistant when used as an electrode, the battery The durability of the binder 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 (2). When the polyvinyl acetal resin has a structural unit represented by the following general formula (2), the dispersibility 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 are particularly high. It can be excellent.

In formula (2), 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 ⁵ 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, a method of reacting an aldehyde with the above-mentioned modified polyvinyl alcohol raw material having an ionic functional group to acetalize, after producing a polyvinyl acetal resin, another functional group having reactivity to the functional group of the polyvinyl acetal resin And a method of reacting with a compound having a group and an ionic functional group.

As a method for producing the modified polyvinyl alcohol raw material having the 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 (3), The method of saponifying the ester site | part of the obtained copolymer resin with an alkali or an acid is mentioned.

In formula (3), 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 (3), 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 its salt are used, the dispersibility of the polyvinyl acetal resin in the composition for the lithium secondary battery electrode is improved, and the resistance to the electrolytic solution and the active material and conductivity when the electrode is used. The dispersibility of the auxiliary agent can be made excellent. Furthermore, since the deterioration of the binder in the battery is suppressed, it is preferable because the reduction in the discharge capacity of the lithium secondary battery can be suppressed. 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 ⁸ 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 (2) 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 (2), the general formula ( The content of the structural unit shown in 2) is preferably about 0.05 to 5 mol%. In addition, when two ionic functional groups are introduced by the general formula (2), the content of the structural unit represented by the general formula (2) should be about 0.025 to 2.5 mol%. Is preferred.
By making the content of the ionic functional group in the polyvinyl acetal resin within the above range, the dispersibility of the polyvinyl acetal resin in the composition for a lithium secondary battery electrode is improved, and the resistance to the electrolyte and the electrode In this case, the dispersibility of the active material and the conductive additive can be made excellent. Furthermore, since the deterioration of the binder when used as a battery is suppressed, a decrease in the discharge capacity of the lithium secondary battery can be suppressed.

The polyvinyl acetal resin preferably has a structural unit represented by the following formula (4). In formula (4), R ⁹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
By having the structural unit represented by the following formula (4), it has excellent binding properties and good resistance to the electrolytic solution, so that the resin component swells with the electrolytic solution or the resin component is in the electrolytic solution. Elution can be suppressed. As a result, the electrode density of the obtained electrode can be improved.

In the formula (4), the alkyl group having 1 to 20 carbon atoms represented by R ^9, not particularly limited, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl Group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group and the like.
In view of the above R ⁹ , the binding properties between the active materials and between the active material and the current collector can be made more excellent, and the swelling resistance against the electrolytic solution can be made higher. To propyl groups are preferred.

The minimum with preferable content of the structural unit represented by the said Formula (4) in the said polyvinyl acetal type-resin is 0.3 mol%. The effect which improves the tolerance with respect to electrolyte solution can fully be exhibited as content of the structural unit represented by the said Formula (4) is 0.3 mol% or more. Moreover, the flexibility of the resin becomes good, and the occurrence of cracks and cracks can be suppressed.
The more preferable lower limit of the content of the structural unit represented by the above formula (4) is 0.4 mol%, the more preferable lower limit is 0.5 mol%, the preferable upper limit is 5 mol%, and the more preferable upper limit is 3 mol%. A more preferred upper limit is 2 mol%.

The content of the structural unit represented by the above formula (4) can be calculated by the following method.
Specifically, polyvinyl acetal resin is dissolved in deuterated dimethyl sulfoxide so that the concentration becomes 1% by weight, proton NMR is measured at a measurement temperature of 150 ° C., and peak (a) appearing near 4.8 ppm is obtained. Using the integrated values of the peak (b) appearing near 4.2 ppm, the peak (c) appearing near 1.0 to 1.8 ppm, and the peak (d) appearing near 0.9 ppm, the following formula is used. be able to.
Content (mol%) of structural unit represented by formula (4) = {(ab-2) / [(c-4d / 3) / 2]} × 100

The content of the structural unit represented by the formula (4) in the polyvinyl acetal resin is preferably set high when the hydroxyl group content of the polyvinyl acetal resin is high. When the amount of hydroxyl groups in the polyvinyl acetal resin is high, the binder is easily hardened by intermolecular hydrogen bonding, so that cracks and cracks are likely to occur. However, the content of the structural unit represented by the above formula (4) By increasing the value, the flexibility of the resin becomes good and the occurrence of cracks and cracks can be suppressed.
On the other hand, when the amount of hydroxyl groups in the polyvinyl acetal resin is low, the content of the structural unit represented by the above formula (4) in the polyvinyl acetal resin is preferably set low.
When the amount of hydroxyl groups in the polyvinyl acetal resin is low, the flexibility of the resin is sufficiently exhibited even in the range where the content of the structural unit represented by the above formula (4) is low, and the occurrence of cracks and cracks is suppressed. In addition, the resistance to the electrolytic solution can be increased.

As a method for producing a polyvinyl acetal resin having a structural unit represented by the above formula (4) in the polyvinyl acetal resin, for example, a modified polyvinyl alcohol having a structural unit represented by the above formula (4) A method of reacting an aldehyde with a raw material to acetalize is mentioned. Moreover, when producing a polyvinyl acetal resin, a method in which a compound having reactivity with a functional group of a polyvinyl alcohol raw material is allowed to act so that the structural unit represented by the formula (4) is held in the molecule is mentioned. It is done. Furthermore, after producing a polyvinyl acetal resin, a compound having reactivity with a functional group of the polyvinyl acetal resin is reacted to retain the structural unit represented by the formula (4) in the molecule. Is mentioned. Especially, after producing a polyvinyl acetal resin from the point of being easy to adjust productivity and content of the structural unit represented by Formula (4), it reacts with respect to the functional group of this polyvinyl acetal resin. A method of reacting a compound having a property to retain the structural unit represented by the formula (4) in the molecule is preferable.

As a method of reacting a compound having reactivity with the functional group of the polyvinyl acetal resin, a geminal diol compound having two hydroxyl groups per carbon atom with respect to one hydroxyl group of the polyvinyl acetal resin is used. Examples thereof include a method of dehydration condensation, a method of adding an aldehyde compound to one hydroxyl group of the polyvinyl acetal resin, and the like. Especially, since it is easy to adjust productivity and content of the structural unit represented by Formula (4), the method of adding an aldehyde compound with respect to one hydroxyl group of polyvinyl acetal type resin is suitable.

As a method for adding an aldehyde compound to one hydroxyl group of the polyvinyl acetal resin, for example, after dissolving the polyvinyl acetal resin in isopropyl alcohol adjusted to an acidic condition, under a high temperature condition of about 70 to 80 ° C. Examples include a method of reacting an aldehyde. Moreover, in order to adjust content of the structural unit represented by the said Formula (4) in the said polyvinyl acetal type-resin so that it may become the said appropriate range, it is preferable to adjust the said reaction time and acid concentration. When the content of the structural unit represented by the above formula (4) in the polyvinyl acetal resin is set low, it is preferable to increase the reaction time and to increase the acid concentration. When the content of the structural unit represented by the above formula (4) in the polyvinyl acetal resin is set high, it is preferable to shorten the reaction time, and it is preferable to reduce the acid concentration. A preferable reaction time is 0.1 to 10 hours, and a preferable acid concentration is 0.5 mM to 0.3 M.

The binder resin (A) is preferably in the form of fine particles. When the binder resin (A) is in the form of fine particles, 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 a lithium battery is used, the conduction of lithium ions is sufficiently maintained, and a decrease in battery capacity can be suppressed. The advantage is obtained. Among these, fine particles made of a polyvinyl acetal resin are preferable.
The binder resin (A) preferably has a volume average particle size of 10 to 1000 nm. When the volume average particle diameter is 10 nm or more, the dispersibility of the active material and the conductive auxiliary agent when used as an electrode can be improved, and the discharge capacity of the lithium secondary battery can be improved. Moreover, since the binder does not cover all the surfaces of the active material and the conductive additive and the contact property between the electrolytic solution and the active material can be improved when the thickness is 1000 nm or less, a lithium battery is used at a large current. In this case, the lithium ion is sufficiently conducted, and the battery capacity can be improved. A more preferable volume average particle diameter of the polyvinyl acetal resin in the form of fine particles is 15 to 800 nm, and a more preferable volume average particle diameter is 15 to 700 nm.
The volume average particle size 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 binder resin (A) is preferably 40%. When the CV value is 40% or less, there is no presence of fine particles having a large particle size, and the deterioration of the stability of the composition for a lithium secondary battery electrode due to sedimentation of the large particle size is suppressed. Can do.
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.

When a polyvinyl acetal resin is used as the binder resin (A), the production method is not particularly limited. For example, after the step of preparing a polyvinyl acetal resin, the polyvinyl acetal resin such as tetrahydrofuran, acetone, toluene, methyl ethyl ketone, ethyl acetate, methanol, ethanol, butanol, isopropyl alcohol, etc. is dissolved in the polyvinyl acetal resin. There is a method in which a fine solvent is prepared by precipitating a polyvinyl acetal resin by dissolving in an organic solvent and then adding a poor solvent such as water little by little and removing the organic solvent by heating and / or decompressing. Moreover, after adding the solution which melt | dissolved the said polyvinyl acetal type resin in a lot of water, the method of heating and / or decompressing as needed and removing an organic solvent, and depositing a polyvinyl acetal resin, and producing microparticles | fine-particles is mentioned. It is done. Further, there may be mentioned 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.

The binder for an electricity storage device electrode of the present invention contains a binder resin (B).
The binder resin (B) has a lower limit of storage elastic modulus at 50 ° C. and 10 Hz of 1 × 10 ⁵ Pa and an upper limit of 1 × 10 ⁷ Pa.
When the storage elastic modulus of the binder resin (B) is 1 × 10 ⁵ Pa or more, elution of the binder resin can be suppressed. When the storage elastic modulus of the binder resin (B) is 1 × 10 ⁷ Pa or less, the stress dispersibility of the binder resin can be improved and cracking of the electrode can be prevented.
The storage elastic modulus of the binder resin (B) has a preferable lower limit of 5.0 × 10 ⁵ Pa, a more preferable lower limit of 7.0 × 10 ⁵ Pa, a preferable upper limit of 9.0 × 10 ⁶ Pa, and a more preferable upper limit. It is 6.0 × 10 ⁶ Pa.
In addition, the storage elastic modulus in 50 degreeC and 10 Hz can be measured by using a dynamic viscoelasticity measuring apparatus.

The binder resin (B) preferably has a weight average molecular weight of 10,000 to 10,000,000.

The glass resin transition temperature of the binder resin (B) has a preferable lower limit of −30 ° C., a more preferable lower limit of −10 ° C., a preferable upper limit of 53 ° C., and a more preferable upper limit of 49 ° C.

Examples of the binder resin (B) include styrene-acrylic copolymers, styrene-diene copolymers, and acrylic acid copolymers.

Examples of the styrene-acrylic copolymer include a copolymer using styrene or a styrene derivative and acrylic acid, acrylic acid ester, methacrylic acid, and methacrylic acid ester as monomers.
As acrylic acid ester or methacrylic acid ester, acrylic acid or methacrylic acid alkyl ester having an alkyl group such as methyl group or ethyl group, acrylic acid or methacrylic acid ester having an aliphatic ring such as cyclohexyl group or cyclopentyl group, Examples include esters of acrylic acid or methacrylic acid having an aromatic ring such as a phenyl group and a benzyl group.
Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, ( T-butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (meth) acrylic acid Examples include cyclohexyl, methyl cyclohexyl (meth) acrylate, t-butylcyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, and the like, and 2-ethylhexyl (meth) acrylate is preferred.
The styrene-acrylic copolymer may be a block copolymer or a random copolymer.
The content of the styrene structural unit in the styrene-acrylic copolymer is preferably 50 to 90% by weight.

Examples of the styrene-diene copolymer include a copolymer of styrene or a styrene derivative and a conjugated diene.
Examples of the conjugated diene include 1,3-butadiene, isoprene, 1,3-pentadiene and the like.
The styrene-diene copolymer may be a block copolymer or a random copolymer.
The content of the styrene structural unit in the styrene-diene copolymer is preferably 50 to 90% by weight.

Examples of the acrylic acid-based copolymer include copolymers of acrylic acid or methacrylic acid and other monomers.
Other monomers include alkyl esters of acrylic acid or methacrylic acid having an alkyl group such as methyl group or ethyl group, esters of acrylic acid or methacrylic acid having an aliphatic ring such as cyclohexyl group or cyclopentyl group, phenyl group And acrylic acid esters or methacrylic acid esters such as acrylic acid or methacrylic acid ester having an aromatic ring such as benzyl group, and olefinic monomers such as ethylene, propylene and butylene.
The content of acrylic acid structural units or methacrylic acid structural units in the acrylic acid copolymer is preferably 50 to 90% by weight.

The shape of the binder resin (B) is not particularly limited, but is preferably a fine particle shape.
When the binder resin (B) is in the form of fine particles, the volume average particle diameter is preferably 10 to 1000 nm, and more preferably 15 to 700 nm.

In the binder for an electricity storage device electrode of the present invention, the content of the binder resin (A) is 85 to 99.9% by weight with respect to a total of 100% by weight of the binder resin (A) and the binder resin (B). is there.
When the content of the binder resin (A) is 85% by weight or more, the followability of the active material to expansion and contraction can be improved, and peeling between the active materials and the current collector interface can be suppressed. When the content of the binder resin (A) is 99.9% by weight or less, it is possible to improve the stress dispersibility of the binder resin and suppress cracking of the electrode and bending of the electrode end.
As for content of the said binder resin (A), a more preferable minimum is 90 weight% and a more preferable upper limit is 95 weight%.

In the binder for an electricity storage device electrode of the present invention, the content of the binder resin (B) is 0.1 to 15% by weight with respect to a total of 100% by weight of the binder resin (A) and the binder resin (B). is there.
When the content of the binder resin (B) is 0.1% by weight or more, the stress dispersibility of the binder resin can be improved, and cracking of the electrode and bending of the electrode end can be suppressed. When the content of the binder resin (B) is 15% by weight or less, it is possible to improve followability to the expansion and contraction of the active material, and to suppress separation between the active materials and the current collector interface.
As for content of the said binder resin (B), a more preferable minimum is 3 weight% and a more preferable upper limit is 10 weight%.

The ratio between the storage elastic modulus of the binder resin (A) and the storage elastic modulus of the binder resin (B) (the storage elastic modulus of the binder resin (A) / the storage elastic modulus of the binder resin (B)) has a preferable lower limit. 400, a more preferred lower limit is 430, a preferred upper limit is 280, and a more preferred upper limit is 250.

The binder for an electricity storage device electrode of the present invention may further contain an aqueous medium.
By containing the aqueous medium, the solvent remaining on the electrode can be reduced.
The aqueous medium may be water alone, and a solvent other than water may be added in addition to the 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. The upper limit with preferable addition amount of solvents other than the said water is 30 weight part with respect to 100 weight part of water, and a more preferable upper limit is 20 weight part.

Although the total content of the binder resin (A) and the binder resin (B) in the binder for an electricity storage device electrode of the present invention is not particularly limited, the preferred lower limit is 2% by weight and the preferred upper limit is 60% by weight. When the total content of the binder resin (A) and the binder resin (B) is 2% by weight or more, the binder resin for the active material when the binder is mixed with the active material to obtain a composition for an electricity storage device electrode As a result, the adhesive strength to the current collector can be improved. When the total content of the binder resin (A) and the binder resin (B) is 60% by weight or less, the stability of the binder resin in the dispersion medium is improved and the dispersibility of the active material is improved. It is possible to suppress a decrease in discharge capacity of an electricity storage device such as a lithium secondary battery. The total content of the binder resin (A) and the binder resin (B) is more preferably 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.

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.

Although the total content of the binder resin (A) and the binder resin (B) in the composition for an electricity storage device electrode of the present invention is not particularly limited, the preferred lower limit is 0.1 weight with respect to 100 parts by weight of the active material. Parts, and the preferred upper limit is 12 parts by weight. When the total content is 0.1 parts by weight or more, the adhesion to the current collector can be sufficiently improved, and when the total content is 12 parts by weight or less, the discharge capacity of the lithium secondary battery is suppressed from decreasing. can do. More preferably, it is 0.5 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 cobalt oxide (LiCoO 2), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co—Ni—Mn, lithium composite oxide of Ni—Mn—Al, Ni—Co—Al lithium composite oxide, lithium manganate (LiMn ₂ O ₄ ), lithium phosphate compound (LiXMPO ₄ , where M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V , Ca, Sr, Ba, Ti, Al, Si, B, and Mo, 0 ≦ X ≦ 2)) and the like. Further, an iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to be present during reduction firing. These compounds may be partially element-substituted.
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.
Moreover, you may use silicon (Si, SiO, Si alloy) with high lithium ion storage capability as a negative electrode active material.

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.

In addition to the above-mentioned active material, conductive additive, polyvinyl acetal resin, and aqueous medium, the composition for an electricity storage device electrode of the present invention, if necessary, a flame retardant aid, a thickener, an antifoaming agent, Additives such as 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 polyvinyl acetal resin, the aqueous medium, and various additives to be added as necessary are ball milled. And a method of mixing using various mixers such as a blender mill and a three-roller.

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 electrical storage device obtained using such an electrical storage device electrode composition is 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.

ADVANTAGE OF THE INVENTION This invention can provide the binder for electrical storage device electrodes which has adhesiveness and adhesiveness and can provide toughness and a softness | flexibility to the electrode obtained. Furthermore, the composition for electrical storage device electrodes, the electrical storage device electrode, and the electrical storage device containing the binder for electrical storage device electrodes can be provided.

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 fine particles of polyvinyl acetal resin)
Polyvinyl acetal resin (polymerization degree 1100, butyralization degree 52 mol%, hydroxyl group amount 47.8 mol%, acetyl group amount 0.2 mol%) 20 weight in a reaction vessel equipped with a thermometer, a stirrer and a cooling tube Parts were dissolved in 80 parts by weight of isopropanol. Thereafter, 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 the mixture was reacted at 70 ° C. for 4 hours. Next, 0.2 part by weight of butyraldehyde and 1 part by weight of 12M concentrated hydrochloric acid were added, and after reacting at 82 ° C. for 6 hours, the reaction solution was cooled and the resin was purified by a reprecipitation method. Finally, the resin was recovered by drying. Next, the obtained resin was dissolved again in 80 parts by weight of isopropanol, and 200 parts by weight of water was added dropwise. Next, after maintaining the liquid temperature at 30 ° C. and evaporating isopropanol and water by stirring under reduced pressure, the solution is concentrated until the solid content becomes 20% by weight, and fine particles composed of polyvinyl acetal resin (hereinafter referred to as polyvinyl acetate). A dispersion liquid (also referred to as acetal resin fine particles) dispersed therein (content of polyvinyl acetal resin fine particles: 20% by weight) was prepared.
When the obtained polyvinyl acetal resin was measured by NMR, the content of the structural unit represented by the formula (4) (R ⁹ is a propyl group in the formula (4)) was 1 mol%, and the degree of butyralization was 51 mol%. , Hydroxyl group amount 45 mol%, acetyl group amount 0.2 mol%, amount of ionic functional group contained in polyvinyl acetal resin 0.2 mmol / g, acetal bond having ionic functional group (formula (1-4) Among them, the content of R ² was a benzene ring and X was sodium sulfonate) was 2.8 mol%. Moreover, when the volume average particle diameter of the obtained polyvinyl acetal resin fine particles was measured with a transmission electron microscope, it was 90 nm and Tg (glass transition temperature) was 83 ° C.

(Preparation of polyacrylonitrile resin fine particle dispersion)
In a polymerization reaction vessel, 250 parts by weight of water, 25 parts by weight of colloidal silica (20% by weight, manufactured by Asahi Denka Co., Ltd.) and 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF) as a dispersion stabilizer, 1.8% by weight of 1N hydrochloric acid The aqueous dispersion medium was prepared.
Next, from 67 parts by weight of acrylonitrile and a polymerization initiator (0.8 part by weight of 2,2′-azobisisobutyronitrile, 0.6 part by weight of 2,2′-azobis (2,4-dimethylvaleronitrile)) The resulting oily mixture was added to an aqueous dispersion medium and suspended to prepare a dispersion. The resulting dispersion was reacted at 60 ° C. for 20 hours while stirring and mixing with an ultrasonic homogenizer to obtain a reaction product. The obtained reaction product is repeatedly filtered and washed with water to disperse a dispersion of polyacrylonitrile-based fine particles (hereinafter also referred to as polyacrylonitrile-based resin fine particles) (content of polyacrylonitrile-based resin fine particles: 20 wt. %). Moreover, when the volume average particle diameter of the obtained polyacrylonitrile-based resin fine particles was measured with a transmission electron microscope, it was 260 nm and Tg was 113 ° C.

(Preparation of plasticized polyvinyl acetal resin 1)
100 parts by weight of the obtained polyvinyl acetal resin fine particles were weighed, and 5 parts by weight of triethylene glycol-2-ethylhexanoate was added to prepare a plasticized polyvinyl acetal resin 1. The obtained plasticized polyvinyl acetal resin 1 was in the form of fine particles, and as measured by transmission electron microscopic amount, the volume average particle diameter was 90 nm and Tg was 78 ° C.

(Preparation of plasticized polyvinyl acetal resin 2)
100 parts by weight of the obtained polyvinyl acetal resin fine particles were weighed, and 50 parts by weight of triethylene glycol-2-ethylhexanoate was added to prepare a plasticized polyvinyl acetal resin 2. The obtained plasticized polyvinyl acetal resin 2 was in the form of fine particles, and as measured by transmission electron microscopic amount, the volume average particle diameter was 90 nm and Tg was 43 ° C.

Example 1
(Preparation of composition for positive electrode of lithium secondary battery)
To 95 parts by weight of the dispersion of the obtained polyvinyl acetal resin fine particles, styrene-butadiene copolymer latex (styrene content unit content 50% by weight, butadiene structural unit content 50% by weight, Tg 8 ° C., volume average particle diameter 180 nm). The binder was prepared by adding 5 parts by weight of a solid content of 50% by weight and 115 parts by weight of water as a solvent.
With respect to 20 parts by weight of the obtained binder (2 parts by weight of the resin component), 50 parts by weight of lithium cobaltate (manufactured by Nippon Chemical Industry Co., Ltd., Cell Seed C-5) as the positive electrode active material, and acetylene black (electrochemical as the conductive assistant) 1 part by weight of Kogyo Co., Ltd., Denka Black) and 1 part by weight of carboxymethyl cellulose (manufactured by Daicel Finechem, CMC Daicel # 2200) as a thickener were added and mixed to obtain a composition for a lithium secondary battery positive electrode.

(Example 2)
Instead of styrene-butadiene copolymer latex, styrene-acrylic copolymer latex (styrene unit content 50% by weight, acrylic ester (2-ethylhexyl acrylate) unit content 50% by weight, Tg 15 ° C., volume average) A composition for a lithium secondary battery positive electrode was obtained in the same manner as in Example 1 except that the particle diameter was 200 nm and the solid content was 50% by weight.

(Example 3)
Instead of styrene-butadiene copolymer latex, acrylic acid copolymer latex (2-ethylhexyl acrylate unit content 60% by weight, ethyl methacrylate unit content 40% by weight, Tg 12 ° C., volume average particle diameter 200 nm, A lithium secondary battery positive electrode composition was obtained in the same manner as in Example 1 except that the solid content was 50% by weight.

Example 4
A lithium secondary battery positive electrode composition was obtained in the same manner as in Example 1 except that a dispersion of polyacrylonitrile resin fine particles was used instead of the dispersion of polyvinyl acetal resin fine particles.

(Example 5)
A lithium secondary battery positive electrode composition was prepared in the same manner as in Example 1 except that the binder was prepared so that the blending ratio of the polyvinyl acetal resin fine particles and the styrene-butadiene copolymer was 99.0: 1.0. Obtained.

(Example 6)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 1 except that spherical natural graphite (Nippon Graphite Industries Co., Ltd., CGB-20) was added as the negative electrode active material instead of the positive electrode active material.

(Example 7)
It replaced with the positive electrode active material, and obtained the composition for lithium secondary battery negative electrodes like Example 2 except having added spherical natural graphite (Nippon Graphite Industries Co., Ltd. make, CGB-20) as a negative electrode active material.

(Example 8)
It replaced with the positive electrode active material, and obtained the composition for lithium secondary battery negative electrodes like Example 3 except having added spherical natural graphite (Nippon Graphite Industries Co., Ltd. make, CGB-20) as a negative electrode active material.

Example 9
It replaced with the positive electrode active material, and obtained the composition for lithium secondary battery negative electrodes like Example 4 except having added spherical natural graphite (Nippon Graphite Industries Co., Ltd. make, CGB-20) as a negative electrode active material.

(Example 10)
It replaced with the positive electrode active material, and obtained the composition for lithium secondary battery negative electrodes like Example 5 except having added spherical natural graphite (Nippon Graphite Industries Co., Ltd. make, CGB-20) as a negative electrode active material.

(Example 11)
Example 1 except that 45 parts by weight of spherical natural graphite (CGB-20, manufactured by Nippon Graphite Industries Co., Ltd.) and 5 parts by weight of silicon (SiO, manufactured by Titanium Technologies, Inc.) were added as the negative electrode active material instead of the positive electrode active material. In the same manner as above, a composition for a negative electrode of a lithium secondary battery was obtained.

(Example 12)
Example 2 except that 45 parts by weight of spherical natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20) and 5 parts by weight of silicon (SiO, manufactured by Osaka Titanium Technologies) were added as the negative electrode active material instead of the positive electrode active material. In the same manner as above, a composition for a negative electrode of a lithium secondary battery was obtained.

(Example 13)
Example 3 except that 45 parts by weight of spherical natural graphite (CGB-20, manufactured by Nippon Graphite Industries Co., Ltd.) and 5 parts by weight of silicon (SiO, manufactured by Titanium Technologies, Inc.) were added as the negative electrode active material instead of the positive electrode active material. In the same manner as above, a composition for a negative electrode of a lithium secondary battery was obtained.

(Example 14)
Example 4 except that 45 parts by weight of spherical natural graphite (Nippon Graphite Industries Co., Ltd., CGB-20) and 5 parts by weight of silicon (SiO, manufactured by Osaka Titanium Technologies) were added as the negative electrode active material instead of the positive electrode active material. In the same manner as above, a composition for a negative electrode of a lithium secondary battery was obtained.

(Example 15)
Example 5 except that 45 parts by weight of spherical natural graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-20) and 5 parts by weight of silicon (SiO, manufactured by Osaka Titanium Technologies) were added as the negative electrode active material instead of the positive electrode active material. In the same manner as above, a composition for a negative electrode of a lithium secondary battery was obtained.

(Comparative Example 1)
A binder was prepared by adding 100 parts by weight of water as a solvent to 100 parts by weight of the resulting dispersion of polyvinyl acetal resin fine particles.
Except having used the obtained binder, it carried out similarly to Example 1, and obtained the composition for lithium secondary battery positive electrodes.

(Comparative Example 2)
A binder was prepared by adding 400 parts by weight of water as a solvent to 100 parts by weight of a styrene-butadiene copolymer latex (volume average particle diameter 180 nm, solid content 50% by weight).
Except having used the obtained binder, it carried out similarly to Example 1, and obtained the composition for lithium secondary battery positive electrodes.

(Comparative Example 3)
To 95 parts by weight of the obtained dispersion of fine particles of polyvinyl acetal resin, 5 parts by weight of a dispersion of plasticized polyvinyl acetal resin 2 (content of plasticized polyvinyl acetal resin 2: 20% by weight), water 100 as a solvent. A binder was prepared by adding parts by weight.
Except having used the obtained binder, it carried out similarly to Example 1, and obtained the composition for lithium secondary battery positive electrodes.

(Comparative Example 4)
To 80 parts by weight of the obtained dispersion of the polyvinyl acetal resin fine particles, 20 parts by weight of a dispersion of the plasticized polyvinyl acetal resin 2 (content of the plasticized polyvinyl acetal resin 2: 20% by weight), 100% water as a solvent. A binder was prepared by adding parts by weight.
Except having used the obtained binder, it carried out similarly to Example 1, and obtained the composition for lithium secondary battery positive electrodes.

(Comparative Example 5)
Except having used the binder obtained by the comparative example 1, it carried out similarly to Example 6, and obtained the composition for lithium secondary battery negative electrodes.

(Comparative Example 6)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 6 except that the binder obtained in Comparative Example 2 was used.

(Comparative Example 7)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 6 except that the binder obtained in Comparative Example 3 was used.

(Comparative Example 8)
A composition for a lithium secondary battery negative electrode was obtained in the same manner as in Example 6 except that the binder obtained in Comparative Example 4 was used.

(Comparative Example 9)
A lithium secondary battery negative electrode composition was prepared in the same manner as in Example 6 except that the binder was prepared so that the blending ratio of the polyvinyl acetal resin fine particles and the styrene-butadiene copolymer was 80.0: 20.0. Obtained.

(Comparative Example 10)
Example 6 is used except that instead of the dispersion of the polyvinyl acetal resin fine particles, a dispersion of the plasticized polyvinyl acetal resin 1 (content of the plasticized polyvinyl acetal resin 1: 20% by weight) is used. Similarly, a composition for a lithium secondary battery negative electrode was obtained.

(Comparative Example 11)
Comparative Example 7 except that instead of the dispersion of plasticized polyvinyl acetal resin 2, a dispersion of plasticized polyvinyl acetal resin 1 (content of plasticized polyvinyl acetal resin 1: 20% by weight) was used. Similarly, a composition for a lithium secondary battery negative electrode was obtained.

(Comparative Example 12)
Except having used the binder obtained by the comparative example 1, it carried out similarly to Example 11, and obtained the composition for lithium secondary battery negative electrodes.

(Comparative Example 13)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 11 except that the binder obtained in Comparative Example 2 was used.

(Comparative Example 14)
Except having used the binder obtained by the comparative example 3, it carried out similarly to Example 11, and obtained the composition for lithium secondary battery negative electrodes.

(Comparative Example 15)
A lithium secondary battery negative electrode composition was obtained in the same manner as in Example 11 except that the binder obtained in Comparative Example 4 was used.

<Evaluation>
Polyvinyl acetal resin fine particles, plasticized polyvinyl acetal resin, styrene-butadiene copolymer latex, styrene-acrylic copolymer latex and acrylic acid copolymer latex used in Examples and Comparative Examples, Examples and Comparative Examples The following evaluation was performed about the composition for secondary battery electrodes (for positive electrodes, for negative electrodes) obtained in (1). The results are shown in Tables 1 and 2.

(1) Storage elastic modulus About polyvinyl acetal resin fine particles and plasticized polyvinyl acetal resin used in Examples and Comparative Examples, DVA-200 (manufactured by IT Measurement Control Co., Ltd.) was used, and the frequency was 10 Hz and 5 ° C / min. It heated at the temperature increase rate, and measured the storage elastic modulus in 50 degreeC and 10 Hz. Moreover, about the styrene-butadiene copolymer latex, the styrene-acrylic copolymer latex, and the acrylic acid copolymer latex, the resin component was separated by removing water, and the storage elastic modulus was measured in the same manner.

(2) Dispersibility (average dispersion diameter)
After mixing and diluting 10 parts by weight of the compositions for lithium secondary battery electrodes obtained in Examples and Comparative Examples and 90 parts by weight of water, the mixture was diluted with an ultrasonic disperser (manufactured by SNDI, “US-303”). Stir for minutes. 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.

(3) Adhesiveness (peeling force)
About the composition for lithium secondary battery positive electrodes obtained in Examples 1-5 and Comparative Examples 1-4, the adhesiveness with respect to aluminum foil was evaluated, and obtained in Examples 6-15 and Comparative Examples 5-15. About the composition for lithium secondary battery negative electrodes, the adhesiveness with respect to copper foil was evaluated.

(3-1) Adhesive to aluminum foil A composition for a lithium secondary battery positive electrode is coated on an aluminum foil (thickness: 15 μm) so that the film thickness after drying is 40 μm, and dried. A test piece having an electrode formed in a sheet shape was obtained.
This sample was cut into a length of 10 cm and a width of 5 cm, and using AUTOGRAPH (manufactured by Shimadzu Corporation, “AGS-J”), the electrode sheet was pulled up while fixing the test piece until the electrode sheet completely peeled from the aluminum foil. The required peel force (N) was measured.

(3-2) Adhesiveness to copper foil In the above "(3-1) 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 15 µm).

(4) Electrolytic solution resistance (preparation of binder resin sheet)
On the polyethylene terephthalate (PET) film subjected to mold release treatment, the polyvinyl acetal resin solutions used in Examples and Comparative Examples were applied and dried so that the film thickness after drying was 50 μm. Produced.
The obtained binder resin sheet was cut out into 30x50 mm, and the test piece was produced.

The weight (a) of the film was measured by weighing the film obtained by drying the obtained test piece at 110 ° C. for 2 hours.
Next, a mixed solution of ethylene carbonate and diethyl carbonate (volume ratio 1: 1) was used as the electrolytic solution, and the obtained film was immersed in the electrolytic solution at 25 ° C. for 3 days. Thereafter, the film was taken out and immediately the surface electrolyte solution was wiped off and then weighed to measure the weight (b).
Thereafter, the film was immersed in 500 g of pure water for 2 days to completely remove the electrolyte inside the film, dried at 110 ° C. for 2 hours, and weighed to measure the weight (c).
From each weight, the dissolution rate and swelling rate of the binder were calculated by the following equations.
Dissolution rate (%) = [(ac) / a] × 100
Swell rate (%) = (b / c) × 100
In addition, it means that resin is easy to melt | dissolve in electrolyte solution, so that the value of a dissolution rate is high, and it means that resin is easy to swell with electrolyte solution, so that a swelling rate is high.

(5) Flexibility About the compositions for positive electrodes of lithium secondary batteries obtained in Examples 1 to 5 and Comparative Examples 1 to 4, the flexibility of the electrodes prepared using aluminum foil was evaluated, and Examples 6 to 15, About the composition for lithium secondary battery negative electrodes obtained by Comparative Examples 5-15, the softness | flexibility of the electrode produced using copper foil was evaluated.
(5-1) On a flexible aluminum foil (thickness 15 μm) using an aluminum foil, the composition for a lithium secondary battery electrode is applied and dried so that the film thickness after drying is 40 μm, and the aluminum foil A test piece having an electrode formed thereon was obtained.
This sample was cut into a length of 50 cm and a width of 2 cm, wound around a glass rod having a diameter of 2 mm and left for one day, and then the sample was unwound and the occurrence of cracks or cracks in the electrode was evaluated according to the following criteria.
◎: No cracks or cracks were observed. ○: Slight cracks or cracks were confirmed, but no peeling of the active material was confirmed. △: Cracks or cracks were confirmed, partial peeling of the active material. ×: Cracks and cracks were confirmed over the entire surface, and peeling of most of the active material was also confirmed. (5-2) Flexibility using copper foil “(5-1) Using aluminum foil The flexibility was evaluated in exactly the same manner except that the aluminum foil was changed to a copper foil (thickness 15 μm).

(6) Battery performance evaluation (6-1) Examples 1-5, Comparative Examples 1-4
(A) Production of Coin Battery The lithium secondary battery positive electrode compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were uniformly applied to an aluminum foil having a thickness of 15 μm, dried, and punched out to φ16 mm. Thus, a positive electrode layer was obtained.
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 2 and 4, when an electrolytic solution was injected into the cell, it was confirmed that the active material was peeled from the electrode due to elution of the resin component. In this state, the production of the secondary battery and the evaluation of the discharge capacity were carried out.

(6-2) Examples 6 to 15 and Comparative Examples 5 to 15
The compositions for negative electrodes of lithium secondary batteries obtained in Examples 6 to 15 and Comparative Examples 5 to 15 were uniformly applied to a copper foil having a thickness of 15 μm and dried, and punched out to φ16 mm to obtain a negative electrode layer.
A sealed coin battery was obtained by the same method as (6-1) except that the obtained negative electrode layer was 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, 8, 9, 13, and 15, when an electrolytic solution was injected into the cell, peeling of the active material from the electrode was confirmed by elution of the resin component. In this state, the production of the secondary battery and the evaluation of the discharge capacity were carried out.

(7) Electrode bending property The test piece obtained by the above “(3) Adhesiveness (peeling force)” is wound around a round bar of φ1.5 mm, and the electrode end portion is visually observed when rubbed 100 times continuously. Was evaluated according to the following criteria.
◎: No bending at the bent portion ○: There is a bend at the bent portion, but the base (aluminum foil, copper foil) cannot be confirmed ×: There is a bend at the bent portion, and the base (aluminum foil, copper foil) is Can confirm

ADVANTAGE OF THE INVENTION This invention can provide the binder for electrical storage device electrodes which has adhesiveness and adhesiveness and can provide toughness and a softness | flexibility to the electrode obtained. Furthermore, the composition for electrical storage device electrodes, the electrical storage device electrode, and the electrical storage device containing the binder for electrical storage device electrodes can be provided.

Claims (9)

A binder used for an electrode of an electricity storage device,
The binder resin (A) having a storage elastic modulus of 1 × 10 ⁸ to 1 × 10 ¹⁰ Pa at 50 ° C. and 10 Hz, and the storage elastic modulus of 1 × 10 ⁵ to 1 × 10 ⁷ Pa at 50 ° C. and 10 Hz. Containing a binder resin (B),
85 to 99.9% by weight of the binder resin (A) and 0.1 to 15% by weight of the binder resin (B) with respect to 100% by weight of the total of the binder resin (A) and the binder resin (B). % Binder for electricity storage device electrodes, characterized by containing. The binder for an electricity storage device electrode according to claim 1, wherein the binder resin (A) is at least one selected from the group consisting of polyvinyl acetal resins, polyacrylonitrile, polymethyl methacrylate, and polyamideimide. The binder resin (B) is at least one selected from the group consisting of a styrene-butadiene copolymer, a styrene-acrylic copolymer, and an acrylic acid-based copolymer. Binder for electricity storage device electrodes. The binder for an electricity storage device electrode according to claim 1, comprising a binder resin (A), a binder resin (B), and an aqueous medium. The binder for an electricity storage device electrode according to claim 1, 2, 3 or 4, wherein the binder resin (A) is in the form of fine particles. 6. The binder for an electricity storage device electrode according to claim 5, wherein the binder resin (A) has a volume average particle diameter of 10 to 1000 nm. The electrical storage device electrode binder according to claim 1, 2, 3, 4, 5, or 6, and an electrical storage device electrode composition comprising an active material, wherein the binder resin is used with respect to 100 parts by weight of the active material. The total content of (A) and binder resin (B) is 0.1-12 weight part, The composition for electrical storage device electrodes characterized by the above-mentioned. An electrical storage device electrode comprising the electrical storage device electrode composition according to claim 7. An electricity storage device comprising the electricity storage device electrode according to claim 8.