TW201841420A - Binder for power storage device electrodes - Google Patents

Abstract

The present invention provides a binder for power storage device electrodes, which exhibits an excellent binding capability with respect to an active material, is highly resistant to electrolytes, and with which it is possible to prepare a high-capacity power storage device. The present invention also provides a power storage device electrode composition, a power storage device electrode, and a power storage device, all of which use said binder. The present invention pertains to a binder which is used for a power storage device electrode, wherein the binder contains a polyvinyl acetal-based resin, and the polyvinyl acetal-based resin has an ethylene content of 25-50 mol% and a hydroxy group content of 15-35 mol%.

Description

 Electrode assembly electrode adhesive  

The present invention relates to a binder for an electrode for a storage battery device which is excellent in the binding property of an active material, and which has high durability to an electrolytic solution, and can produce a high-capacitance power storage device. Moreover, the present invention relates to a composition for an electric storage device electrode, an electric storage device electrode, and a power storage device using the electric energy storage device electrode adhesive.

In recent years, with the spread of portable electronic devices such as portable video recorders and portable personal computers, the demand for secondary batteries as mobile power sources has rapidly increased. Moreover, the demand for miniaturization, weight reduction, and high energy density of such a secondary battery is extremely high.

Therefore, as a secondary battery that can be reversibly charged and discharged, a lead battery, a nickel-cadmium battery, and the like have been mainstream. However, these batteries are excellent in charge and discharge characteristics, but they do not have sufficient characteristics in terms of battery weight or energy density to sufficiently satisfy a mobile power source as a portable electronic device.

Therefore, as a secondary battery, the industry is actively conducting research and development of a lithium secondary battery using lithium or a lithium alloy for a negative electrode. The lithium secondary battery has the following excellent features: high energy density, less self-discharge, and lighter weight.

The electrode of the lithium secondary battery is usually formed by kneading the active material and the binder together with the solvent, dispersing the active material to form a slurry, and then applying the slurry to the slurry by a doctor blade method or the like. The current collector is dried and thinned.

At present, the most widely used binder for the electrode (negative electrode) of a lithium secondary battery is a fluorine-based resin typified by polyvinylidene fluoride (PVDF).

However, when polyvinylidene fluoride is used to produce a slurry for an electrode, solubility in a solvent is poor, and the production efficiency is remarkably lowered.

Further, when a fluorine-based resin is used as the binder, there is a problem that the binder swells due to the electrolyte solution, and peeling occurs at the electrode interface during long-term circulation, thereby deteriorating the battery characteristics.

In response to this problem, N-methylpyrrolidone is generally used as a solvent for dissolving polyvinylidene fluoride, but there is a problem that since N-methylpyrrolidone has a high boiling point, it is in the slurry. Not only a large amount of heat energy is required in the drying step, but also N-methylpyrrolidone which is not completely dried remains in the electrode, and the performance of the battery is lowered.

On the other hand, carboxymethylcellulose or the like is used as the water-based binder. However, when carboxymethylcellulose is used, the flexibility of the resin is insufficient, so that the effect of binding the active material is insufficient. Or the problem that the adhesion of the current collector is significantly reduced.

Further, Patent Document 1 discloses that a low-crystalline carbon having a graphite interlayer distance (d002) of 0.345 to 0.370 nm is used as a negative electrode active material, and a styrene-butadiene copolymer (SBR) is used as a binder and a carboxy group is used. Methylcellulose is used as a tackifier to obtain a good negative electrode, and a battery having excellent output characteristics can be obtained.

However, since SBR is low in elasticity and low in rebound, there is a problem that the followability of the expansion and contraction of the active material is low, especially when the active material shrinks. As a result, there is a problem that conduction failure occurs between the active materials and the current collector interface, and the capacitance is lowered by repeated charge and discharge.

Further, as a negative electrode active material different from graphite, the industry is investigating that a battery capacity per unit weight is significantly larger than that of a ruthenium-based negative electrode active material such as ruthenium or ruthenium oxide.

However, since the lanthanide negative electrode active material expands and contracts violently with charge and discharge, when the use of polyvinylidene fluoride (PVDF) or SBR which is most widely used as a binder is used, there are the following problems: The expansion and contraction causes a decrease in the bondability between the active materials, resulting in a decrease in the performance of the battery.

[Previous Technical Literature]

[Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2009-158099

An object of the present invention is to provide an electrode binder for a power storage device which is excellent in the binding property of an active material and has high durability to an electrolytic solution, thereby producing a high-capacitance power storage device. Moreover, an object of the present invention is to provide a composition for an electric storage device electrode, an electric storage device electrode, and a power storage device using the electrode assembly electrode for an electrode.

The present invention relates to a binder for an electrode for an electricity storage device, which is used for a binder of an electrode of a power storage device, wherein the binder contains a polyvinyl acetal resin, and the ethylene acetal resin has an ethylene content of 25 ~50 mol%, the amount of hydroxyl groups is 15 to 35 mol%.

The invention is described in detail below.

As a result of intensive studies, the inventors of the present invention have found that a polyethylene acetal resin having a specific ethylene content and a hydroxyl group content is used as a binder for a storage device electrode, and the active material has excellent bonding properties and durability to the electrolyte. High, it can make high-capacity power storage devices. Further, by using a polyvinyl acetal resin having a specific ethylene content, when the electrolyte is swollen in the binder resin, the followability to the expansion and contraction of the active material can be sufficiently maintained, thereby completing the present invention. .

The electrode assembly for an electrical storage device of the present invention contains a polyvinyl acetal resin.

In the present invention, by using a polyvinyl acetal resin as a resin component of a binder (adhesive), the gravitational interaction acts on the polyvinyl acetal resin and the active material, and the activity can be activated with a small amount of binder. The substance is immobilized.

Further, the polyvinyl acetal resin may also exert an attractive interaction with the conductive auxiliary agent, and the distance between the active material and the conductive auxiliary agent is limited to a certain range. By setting the distance between the active material and the conductive auxiliary agent as appropriate, the dispersibility of the active material can be greatly improved.

Further, the compatibility with the current collector can be remarkably improved as compared with the case of using a resin such as PVDF. Further, in comparison with the case of using carboxymethylcellulose, the dispersibility and the binding property of the active material are excellent, and when the amount of the binder added is small, a sufficient effect can be exhibited.

In addition, the adhesive for electrode of the electrical storage device of the present invention may be composed of a resin component or may further contain a dispersion medium.

The polyvinyl acetal resin has an ethylene unit represented by the following formula (1).

When the polyvinyl acetal resin has an ethylene unit, the restoring force of the polyvinyl acetal resin is increased, and when a ruthenium compound which is strongly expanded and contracted during charge and discharge is used as an active material, the expansion and contraction can be improved. The followability inhibits the decrease in the binding between the active substances. Further, even when the electrolyte is swollen to the binder resin, the followability to the expansion and contraction of the active material can be sufficiently maintained.

In the polyethylene acetal resin, it is preferred that the ethylene unit is introduced randomly.

By randomly introducing the ethylene unit, the followability to the expansion and contraction of the active material can be further improved.

The lower limit of the content of the above ethylene unit (hereinafter also referred to as ethylene content) in the polyethylene acetal resin is 25 mol%, and the upper limit is 50 mol%. When the ethylene content is 25 mol% or more, the elongation of the polyvinyl acetal resin can be improved, and the followability to the expansion shrinkage of the active material can be sufficiently improved. When the ethylene content is 50% by mole or less, the restoring force of the polyvinyl acetal resin in the self-stretched state can be improved, and the followability to the expansion and contraction of the active material can be sufficiently improved.

A preferred lower limit of the content of the above ethylene unit is 30 mol%, and a preferred upper limit is 48 mol%.

In the above polyvinyl acetal resin, a preferred lower limit of the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit is 10%, a lower limit is preferably 15%, a preferred upper limit is 30%, and a higher limit is 25 %.

When the ratio of the ethylene unit having a chain length of 1 is 10% or more, the followability to the expansion and contraction of the active material can be further improved. When the ratio of the ethylene unit having a chain length of 1 is 30% or less, the restoring force of the polyvinyl acetal resin in a self-elongating state can be improved.

In addition, the "chain length" of the said ethylene unit means the continuous quantity of ethylene unit. In other words, "the chain length is 1" means that the ethylene unit is discontinuous, and the "ethylene unit having a chain length of 1" means an ethylene unit which is not adjacent to another ethylene unit.

The ratio of the above ethylene unit having a chain length of 1, for example, can be measured by NMR.

It is preferable that the polyvinyl acetal resin has a structural unit having a hydroxyl group represented by the following formula (2-1), a structural unit having an ethoxy group represented by the following formula (2-2), and the following formula ( 2-3) A structural unit having an acetal group and a constituent unit having an acetal group having an ionic functional group represented by the following formula (2-4).

Thereby, the dispersibility of the polyvinyl acetal resin, the dispersibility of the active material and the conductive auxiliary agent are particularly excellent, and the adhesion to the current collector and the resistance to the electrolytic solution can be particularly excellent. In particular, the discharge capacity reduction of the lithium secondary battery can be suppressed.

In the above formula (2-3), R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and in the formula (2-4), R ² represents an alkylene group or aroma having 1 to 20 carbon atoms. Ring, X represents an ionic functional group.

Examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a decyl group, an undecyl group, and a decyl group. Dialkyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl and the like. Among them, a methyl group, an ethyl group, and a propyl group are preferred.

Examples of the alkylene group having 1 to 20 carbon atoms include a linear alkyl group, a branched alkyl group, and a cyclic alkyl group.

Examples of the linear alkylene group include a methylene group, an ethylidene group, a n-propyl group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethyl group, and a tenth. Methyl and the like. Examples of the branched alkylene group include a methylmethylene group, a methylexylethyl group, a 1-methylamylpentyl group, and a 1,4-dimethylexenebutyl group. Examples of the cyclic alkyl group include a cyclopropyl group, a cyclopentene group, and a cyclohexylene group. Among them, a linear alkyl group is preferred, and a methylene group, an ethyl group, and a propyl group are more preferred, and a methylene group and an ethyl group are further preferred.

The ionic functional group is preferably 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 amine group, and the like. Functional group. Among them, a carboxyl group, a sulfonic acid group, and the like are more preferred, and a sulfonic acid group and a salt thereof are particularly preferable.

The lower limit of the content of the constituent unit having a hydroxyl group (hereinafter also referred to as the amount of hydroxyl groups) in the polyvinyl acetal resin is 15 mol%, and the upper limit is 35 mol%. When the amount of the hydroxyl group is 15 mol% or more, the resistance to the electrolytic solution can be sufficiently improved, and when the electrode is immersed in the electrolytic solution, the elution of the resin component into the electrolytic solution can be suppressed. When the amount of the hydroxyl group is 35 mol% or less, hydrogen bonding between the polymer chains of the polyvinyl acetal resin can be suppressed, and the flexibility can be improved.

A preferred lower limit of the amount of the above hydroxyl group is 17 mol%, a preferred upper limit is 32 mol%, a more preferred upper limit is 30 mol%, and a further preferred upper limit is 25 mol%.

A preferred lower limit of the ratio of the ethylene content to the amount of the hydroxyl group (ethylene content/hydroxyl group) in the polyvinyl acetal resin is 1.4, and a preferred upper limit is 3.2.

In the polyvinyl acetal resin, the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 to the entire hydroxyl group-containing constituent unit is preferably 25% or less. When the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 is 25% or less, the resistance to the electrolytic solution can be sufficiently improved, and the resin component is not swollen by the electrolytic solution, and the battery characteristics can be improved.

A more preferable upper limit of the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 is 23%, and a preferred upper limit is 18%.

Further, the lower limit of the ratio of the constituent unit having a hydroxyl group having a chain length of 1 is not particularly limited, and a preferred lower limit is 5%.

In addition, the "chain length" of the said hydroxyl group-containing structural unit means the continuous number of the structural unit containing a hydroxyl group. In other words, "the chain length is 1" means that the constituent unit having a hydroxyl group is discontinuous, and the "constituting unit having a hydroxyl group having a chain length of 1" means a constituent unit having a hydroxyl group which is not adjacent to another constituent unit having a hydroxyl group.

The ratio of the hydroxyl group-containing constituent unit can be calculated, for example, by dissolving a polyvinyl acetal resin in deuterated dimethyl hydrazine so as to have a concentration of 1% by weight, and measuring proton NMR or carbon NMR.

In the polyvinyl acetal resin, in order to set the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 to the above range, it is necessary to appropriately adjust the amount of the acetal group, and the amount of the acetal group is not too low or too high. Moreover, the amount of hydroxyl groups is also poorly low or too high. In order to set the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 in an appropriate range, the amount of the acetal group is preferably about 20 to 55 mol%, and the amount of the hydroxyl group is preferably about 15 to 30 mol%. Further, in order to adjust the ratio of the hydroxyl group-containing constituent unit having a chain length of 1, it is effective to carry out the acetal ring detachment by dissolving the polyvinyl acetal resin in an alcohol under acidic conditions and heating it. With the bonding again, the ratio of the constituent units having a hydroxyl group having a chain length of 1 is adjusted. Specifically, a method in which a polyvinyl acetal resin is dissolved in an acidic isopropyl alcohol and then reacted at a high temperature of about 70 to 80 ° C is exemplified. Moreover, it is preferable to adjust the reaction time or the acid concentration in order to adjust the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 in the polyvinyl acetal resin in the above-described appropriate range. When the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 in the polyvinyl acetal resin is set to be low, it is preferred to increase the reaction time, and it is preferred to increase the acid concentration. When the ratio of the hydroxyl group-containing constituent unit having a chain length of 1 in the polyvinyl acetal resin is set to be high, the reaction time is preferably shortened, and the acid concentration is preferably lowered. The preferred reaction time is from 0.1 to 10 hours, and the preferred acid concentration is from pH 1 to 3.5.

When the content of the constituent unit having an acetal group (hereinafter also referred to as an amount of acetal group) in the polyvinyl acetal resin is acetalized using either an aldehyde alone or a mixed aldehyde, The lower limit is preferably 20 mol%, and the upper limit is 55 mol%, based on the total amount of acetal.

When the total amount of the acetal group is 20 mol% or more, the flexibility of the resin can be sufficiently improved, and the adhesion to the current collector can be improved. When the amount of the acetal group is 55 mol% or less, the resistance to the electrolytic solution can be sufficiently improved, and the resin component can be prevented from being eluted into the electrolytic solution when the electrode is immersed in the electrolytic solution.

A more preferred lower limit of the amount of the acetal group is 23 mol%, and a more preferred upper limit is 50 mol%.

Further, in the present specification, the amount of the acetal group in which the acetal group amount coefficient is derived from the aldehyde-modified hydroxyl group is specifically calculated by the formation of two hydroxyl groups by acetalization. In addition to the aldehyde group, an amount obtained by adding a hemiacetal group formed of one hydroxyl group is also added.

A preferred lower limit of the ratio of the ethylene content to the amount of the acetal group (ethylene content / acetal amount) in the polyvinyl acetal resin is 0.5, a lower limit is 1.0, and a preferred upper limit is 2.0, more preferably 2.0. The upper limit is 1.8.

It is preferred that the acetal ring structure of the polyvinyl acetal resin has a meso/racemo ratio of less than 10. If the meso/racemic ratio of the above acetal ring structure is less than 10, the stability in a wide temperature range can be improved, and the characteristics of the obtained battery can be improved. A preferred lower limit of the above meso/racemic ratio is 1, a lower limit is 5, and a higher limit is 8.

Further, in the present invention, the "meso/racemic ratio of the acetal ring structure" is in the three-dimensional structure of the acetal ring, and the amount of the acetal group having a meso acetal ring is relatively The ratio of the amount of the acetal group of the racemic acetal ring. The racemic acetal ring system has an acetal ring structure formed by a hydroxyl group having a row structure, and the meso acetal ring system has an acetal ring structure formed of a hydroxyl group having the same row structure. The meso/racemic ratio can be measured, for example, by dissolving a polyvinyl acetal resin in a solvent such as dimethyl hydrazine, and measuring proton NMR at a measurement temperature of 150 ° C, and comparing it to 4.5 ppm. The peak derived from the meso acetal ring structure and the integrated value derived from the peak of the racemic acetal ring structure appearing near 4.2 ppm. Further, it can be measured by measuring carbon NMR and comparing the peak derived from the meso acetal ring structure near 100 ppm with the peak derived from the racemic acetal ring structure near 94 ppm. value.

In order to set the meso/racemic ratio of the acetal ring structure in the polyvinyl acetal resin to the above range, it is necessary to appropriately adjust the amount of the acetal group, and the amount of the acetal group is not too low or too high. Moreover, the amount of hydroxyl groups is also poorly low or too high. In order to set the meso/racemic ratio in an appropriate range, the amount of the acetal group is preferably about 20 to 55 mol%, and the amount of the hydroxyl group is preferably about 15 to 30 mol%.

In order to adjust the meso/racemic ratio, it is effective to carry out the detachment and re-bonding of the acetal ring by dissolving the polyvinyl acetal resin in an alcohol under acidic conditions and heating it. The ratio of meso acetal rings. Specifically, a method in which a polyvinyl acetal resin is dissolved in an acidic isopropyl alcohol and then reacted at a high temperature of about 70 to 80 ° C is exemplified. In addition, in order to adjust the ratio of the meso-type acetal ring in the polyvinyl acetal resin to the above-mentioned appropriate range, it is preferred to adjust the reaction time or the acid concentration in the polyvinyl acetal resin. When the ratio of the meso acetal ring is set to be high, it is preferred to extend the reaction time, and it is preferred to increase the acid concentration. When the ratio of the meso acetal ring in the polyvinyl acetal resin is set to be low, the reaction time is preferably shortened, and the acid concentration is preferably lowered. The preferred reaction time is from 0.1 to 10 hours, and the preferred acid concentration is from pH 1 to 3.5.

The lower limit of the content of the constituent unit having an ethyl fluorene group (hereinafter, also referred to as the amount of acetyl group) in the polyvinyl acetal resin is 0.2 mol%, and the upper limit is preferably 20 mol%.

When the amount of the acetyl group of the polyvinyl acetal resin is 0.2 mol% or more, the flexibility can be sufficiently improved, and the adhesion to the metal foil can be sufficiently improved. When the amount of the ethyl hydrazide is 20 mol% or less, the resistance to the electrolytic solution can be made sufficient, and when the electrode is immersed in the electrolytic solution, the resin component is eluted into the electrolytic solution.

A more preferred lower limit of the amount of the above-mentioned ethyl group is 1 mol%.

A preferred lower limit of the degree of polymerization of the polyvinyl acetal resin is 250, and a preferred upper limit is 4,000.

When the degree of polymerization is 250 or more, the resistance to the electrolytic solution can be made sufficient, and the electrode can be prevented from being eluted into the electrolytic solution to prevent short-circuiting. When the degree of polymerization is 4,000 or less, the adhesion to the active material can be sufficiently increased, and the decrease in discharge capacity of the electrical storage device can be suppressed.

A lower limit of the above polymerization degree is 280, and a more preferable upper limit is 3,500.

The method for producing the polyvinyl acetal resin having the ethylene unit is not particularly limited, and examples thereof include a method of acetalizing an ethylene-modified polyvinyl alcohol having an ethylene unit in a specific ratio in a main chain; A method in which an ethylene unit is introduced after acetalization of a modified polyvinyl alcohol.

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

The aldehyde used in the above acetalization is not particularly limited. For example, formaldehyde (including paraformaldehyde), acetaldehyde (including paraacetaldehyde), propionaldehyde, butyraldehyde, valeraldehyde, hexanal, heptaldehyde, 2-ethylhexanal, An aliphatic monoaldehyde such as cyclohexanal. Further, examples thereof include furfural, benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenyl group. An aromatic monoaldehyde such as propionaldehyde. Further, dialdehydes such as glyoxal and glutaraldehyde can be mentioned. Among them, acetaldehyde or butyraldehyde is suitable in terms of productivity and balance of properties. These aldehydes may be used singly or in combination of two or more.

The polyvinyl alcohol may be obtained by saponifying a copolymer obtained by copolymerizing a vinyl ester and an α-olefin. Further, the ethylenically unsaturated monomer may be further copolymerized to form a polyvinyl alcohol containing a component derived from an ethylenically unsaturated monomer. Further, 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 sulfuric acid or mercaptopropionic acid may be used. And saponify it. The α-olefin is not particularly limited, and examples thereof include methylene, ethylene, propylene, isopropylene, butene, isobutylene, pentene, hexene, cyclohexene, cyclohexylethylene, and cyclohexylpropene.

Moreover, it is preferable that the polyvinyl acetal resin constituting the fine particles of the polyvinyl acetal resin has an ionic functional group. The ionic functional group is preferably 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 amine group, and the like. Functional group. Among them, a carboxyl group, a sulfonic acid group, and the like are more preferred, and a sulfonic acid group and a salt thereof are particularly preferable. By having an ionic functional group in the polyvinyl acetal resin, the dispersibility of the fine particles composed of the polyvinyl acetal resin can be improved in the composition for a lithium secondary battery electrode, and the active material and the conductive auxiliary can be used. The dispersibility of the agent is particularly excellent.

Further, examples of the salt include a sodium salt and a potassium salt.

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 0.01 mmol/g or more, the dispersibility of the fine particles in the composition for a lithium secondary battery electrode and the dispersibility of the active material and the conductive auxiliary agent when the electrode is formed can be made good. . When the content of the ionic functional group is 1 mmol/g or less, the durability of the binder when the battery is formed can be improved, and the discharge capacity of the lithium secondary battery can be improved. A more preferred lower limit of the content of the ionic functional group in the polyvinyl acetal resin is 0.02 mmol/g, and a more preferred upper limit is 0.5 mmol/g. The content of the above ionic functional group can be measured by using NMR.

The form of the ionic functional group may be directly present in the structure of the polyvinyl acetal resin, or may be present in a polyvinyl acetal resin (hereinafter, also simply referred to as a graft copolymer) containing a graft chain. Graft chain. Among them, it is preferable that the resistance to the electrolytic solution and the dispersibility of the active material and the conductive auxiliary agent at the time of forming the electrode are excellent in the structure of the polyvinyl acetal resin.

When the ionic functional group is directly present in the structure of the polyvinyl acetal resin, it is preferred that the ionic functional group is bonded to a chain molecular structure constituting the carbon of the main chain of the polyvinyl acetal resin, or ionic A molecular structure in which a functional group is bonded via an acetal bond. Further, a molecular structure in which an ionic functional group is bonded via an acetal bond is particularly preferable.

By allowing the ionic functional group to have the above-described structure, the dispersibility of the fine particles composed of the polyvinyl acetal resin can be improved in the composition for a lithium secondary battery electrode, and the active material and the conductive auxiliary agent when the electrode is formed can be obtained. The dispersibility is particularly excellent. Further, since the deterioration of the adhesive when the battery is formed can be suppressed, the discharge capacity reduction of the lithium secondary battery can be suppressed.

The method of 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 a modified polyvinyl alcohol raw material having the above ionic functional group to carry out acetalization, and after preparing a polyvinyl acetal-based resin, and having the polyvinyl acetal-based resin A method in which a functional group-reactive other functional group and a compound having an ionic functional group are reacted.

When the polyvinyl acetal resin has an ionic functional group via an acetal bond, it is preferred that the acetal bond and the ionic functional group are linked by a chain or a cyclic alkyl group or an aromatic ring. In particular, it is preferably an alkyl group having 1 or more carbon atoms, a cyclic alkyl group having 5 or more carbon atoms, an aryl group having 6 or more carbon atoms, and the like, and particularly preferably an alkyl group having a carbon number of 1 or more and aroma. Family ring connection.

Thereby, the resistance to the electrolytic solution and the dispersibility of the active material and the conductive auxiliary agent at the time of forming the electrode can be excellent, and the deterioration of the adhesive when the battery is formed can be suppressed, so that the lithium secondary can be suppressed. The discharge capacitance of the battery is reduced.

Examples of the aromatic substituent include an aromatic ring such as a benzene ring or a pyridine ring, a condensed polycyclic aromatic group such as a naphthalene ring or an anthracene ring, and the like.

The content of the acetal bond having an ionic functional group in the polyvinyl acetal resin is preferably adjusted such that the content of the ionic functional group in the polyvinyl acetal resin is within the above-mentioned appropriate range. In order to set the content of the ionic functional group in the polyvinyl acetal resin to the above-mentioned appropriate range, for example, when one ionic functional group is introduced by one acetal bond, it is preferred to have an ionic functional group. The content of the acetal bond is set to about 0.1 to 10 mol%. Further, when two ionic functional groups are introduced by one acetal bond, the content of the acetal bond having an ionic functional group is preferably about 0.05 to 5 mol%. Further, in order to increase the dispersibility of the fine particles composed of the polyvinyl acetal resin, the flexibility of the resin, and the adhesion to the current collector, it is preferable that the polyvinyl acetal resin has an ion. The content of the acetal bond of the functional group is 0.5 to 20 mol% of the total acetal bond.

When the content of the ionic functional group in the polyvinyl acetal resin is within the above range, the dispersibility of the fine particles composed of the polyvinyl acetal resin can be improved in the lithium secondary battery electrode composition. The resistance to the electrolytic solution and the dispersibility of the active material and the conductive auxiliary agent when the electrode is formed are excellent. Further, since the deterioration of the adhesive when the battery is formed can be suppressed, the discharge capacity reduction of the lithium secondary battery can be suppressed.

The method of producing the polyvinyl acetal resin having an ionic functional group via an acetal bond in the polyvinyl acetal resin structure is not particularly limited. For example, a method in which an aldehyde having the above ionic functional group is reacted with a polyvinyl alcohol raw material in advance and then acetalized is used. Further, a method in which an aldehyde having the above ionic functional group is mixed with an aldehyde raw material and acetalization is carried out when acetalizing polyvinyl alcohol is used. Further, a method of reacting an aldehyde having the above ionic functional group, and the like after producing a polyvinyl acetal resin can be mentioned.

Examples of the aldehyde having the ionic functional group include an aldehyde having a sulfonic acid group, an aldehyde having an amine group, an aldehyde having a phosphate group, and an aldehyde having a carboxyl group.

Examples of the aldehyde having a sulfonic acid group include disodium 4-methylmercaptobenzene-1,3-disulfonate, sodium 4-methylsulfonatesulfonate, sodium 2-methylsulfonatesulfonate, and the like. .

Examples of the aldehyde having an amine group include 3-pyridinecarbaldehyde hydrochloride, 4-diethylaminobenzaldehyde hydrochloride, 4-dimethylaminobenzaldehyde hydrochloride, and methylhydrazine methyl three. Betaine Aldehyde Chloride and the like.

Examples of the aldehyde having a phosphoric acid group include (2-hydroxy-3-oxopropoxy)phosphoric acid and pyridoxal 5-phosphate. Examples of the aldehyde having a carboxyl group include p-quinalduronic acid and isophthalic acid.

Among them, an aldehyde having a sulfonic acid group and an aldehyde having a carboxyl group are preferred, and sodium 2-methylsulfonylbenzenesulfonate and p-hydroxyaldehyde are more preferred.

The polyvinyl acetal resin preferably has an ionic functional group via an acetal bond, and the ionic functional group is a sulfonic acid group or a salt thereof, and the acetal bond and the ionic functional group are linked by a benzene ring. By having such a molecular structure of the polyvinyl acetal resin, the dispersibility of fine particles composed of a polyvinyl acetal resin in the composition for a lithium secondary battery electrode can be used, and the active material when the electrode is formed and The dispersibility of the conductive auxiliary agent and the durability of the adhesive when the battery is formed are particularly excellent.

When the polyvinyl acetal resin is a chain-like molecular structure in which an ionic functional group is bonded to a carbon constituting a main chain of the polymer, it preferably has a structural unit represented by the following formula (3). When the polyvinyl acetal resin has a structural unit represented by the following formula (3), the dispersibility of the fine particles composed of the polyvinyl acetal resin in the lithium secondary battery electrode composition can be obtained. The durability of the adhesive when forming a battery is particularly excellent.

In the formula (3), 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.

As the above R ³ , a hydrogen atom is particularly preferable.

Examples of the above R ⁴ include a methylene group, an ethylidene group, a propyl group, an extended isopropyl group, a butyl group, an isobutyl group, a second butyl group, and a third butyl group. Among them, the above R ^{4 is} preferably a methylene group.

The above 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, a guanamine group, an amine group, a fluorenylene group, a ketone group, and a hydroxyl group.

The method of producing the polyvinyl acetal resin in which the 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 a modified polyvinyl alcohol raw material having the above ionic functional group to carry out acetalization; and after producing a polyvinyl acetal resin, and having a functional group for the polyvinyl acetal resin A method in which a reactive other functional group and a compound having an ionic functional group are reacted.

The method of producing a modified polyvinyl alcohol raw material having the ionic functional group, for example, after copolymerizing a vinyl ester monomer such as vinyl acetate with a monomer having a structure represented by the following formula (4) A method of saponifying an ester moiety of a obtained copolymer resin using a base or an acid.

In the formula (4), 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.

The monomer having the structure represented by the above formula (4) is not particularly limited, and examples thereof include a monomer having a carboxyl group and a polymerizable functional group, a monomer having a sulfonic acid group and a polymerizable functional group, and an amine. a monomer having a base and a polymerizable functional group, a salt thereof, and the like.

Examples of the monomer having a carboxyl group and a polymerizable functional group include 3-butenoic acid, 4-pentenoic acid, 5-hexenoic acid, and 9-decenoic acid. Examples of the monomer having a sulfonic acid group and a polymerizable functional group include allylsulfonic acid, 2-methyl-2-propene-1-sulfonic acid, and 2-propenylamine-2-methylpropane. Sulfonic acid, 3-(methacryloxy)propanesulfonic acid, and the like. Examples of the monomer having an amine group and a polymerizable functional group include N,N-diethylallylamine and the like.

When the allyl sulfonic acid and its salt are used, the dispersibility of the fine particles composed of the polyvinyl acetal resin can be improved in the composition for the electrode of the lithium secondary battery, and the resistance to the electrolyte can be made. The dispersibility of the active material and the conductive auxiliary agent when the electrode is formed is excellent. Further, since deterioration of the binder at the time of forming the battery can be suppressed, it is possible to suppress a decrease in discharge capacitance of the lithium secondary battery, which is preferable. It is especially preferred to use sodium allyl sulfonate.

These monomers may be used singly or in combination of two or more.

As the above R ⁶ , a hydrogen atom is particularly preferable.

Examples of the above R ⁷ include a methylene group, an ethylidene group, a propyl group, an extended isopropyl group, a butyl group, an isobutyl group, a second butyl group, and a third butyl group. Among them, the above R ^{7 is} preferably a methylene group.

The above 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 thioether group, a decylamino group, an amine group, a fluorenylene group, a ketone group, and a hydroxyl group.

A preferred lower limit of the ratio of the ethylene content of the polyethylene acetal resin to the content of the acetal bond having the ionic functional group (the content of the ethylene/the content of the acetal bond having an ionic functional group) is 9, A lower limit is preferably 15 and a preferred upper limit is 75, and a higher limit is 65.

The content of the structural unit represented by the above formula (3) 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 above-mentioned appropriate range. In order to set the content of the ionic functional group in the polyvinyl acetal resin to the above-mentioned appropriate range, for example, when one ionic functional group is introduced by the above formula (3), the above formula is preferred. The content of the structural unit represented by (3) is set to about 0.05 to 5 mol%. In the case where two ionic functional groups are introduced by the above formula (3), the content of the structural unit represented by the above formula (3) is preferably set to about 0.025 to 2.5 mol%.

When the content of the ionic functional group in the polyvinyl acetal resin is within the above range, the dispersibility of the fine particles composed of the polyvinyl acetal resin can be improved in the composition for a lithium secondary battery electrode, and The resistance to the electrolytic solution and the dispersibility of the active material and the conductive auxiliary agent when the electrode is formed are excellent. Further, since the deterioration of the adhesive when the battery is formed can be suppressed, the discharge capacity reduction of the lithium secondary battery can be suppressed.

The polyvinyl acetal resin preferably has a constituent unit represented by the following formula (5) (hereinafter also referred to as a hemiacetal group). In the formula (5), R ⁹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.

By the constituent unit represented by the following formula (5), the bonding property is excellent, and the resistance to the electrolytic solution can be improved, and the resin component can be inhibited from swelling by the electrolytic solution or the resin component can be eluted into the electrolytic solution. As a result, the electrode density of the obtained electrode can be increased.

In the above formula (5), the alkyl group having 1 to 20 carbon atoms represented by R ⁹ is not particularly limited, and examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, and a heptyl group. Octyl, decyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, ten Nonaalkyl, eicosyl and the like.

The above-mentioned R ^{9 is} preferably a propyl group from the viewpoint that the binding properties of the active materials and the active material to the current collector are more excellent, and the swelling resistance of the electrolytic solution is made higher.

The preferred upper limit of the content of the constituent unit represented by the above formula (5) (hereinafter also referred to as the amount of hemiacetal group) in the polyvinyl acetal resin is 1 mol%.

When the amount of the above-mentioned hemiacetal group is 1 mol% or less, the flexibility of the resin becomes good, and generation of cracks or cracks can be suppressed.

A preferred lower limit of the amount of the above-mentioned hemiacetal group is 0.1 mol%, a more preferred lower limit is 0.5 mol%, and a more preferred upper limit is 0.8 mol%.

Further, the amount of the above-mentioned hemiacetal group can be calculated by the following method.

Specifically, a polyvinyl acetal resin was dissolved in deuterated dimethyl hydrazine at a concentration of 1% by weight, and proton NMR was measured at a measurement temperature of 150 °C. According to the obtained results, the peak appearing near 4.8 ppm (a), the peak appearing near 4.2 ppm (b), the peak appearing near 1.0 to 1.8 ppm (c), and the peak appearing near 0.9 ppm The integral value of (d) is calculated by the following formula.

Hemiacetal group amount (% by mole) = {(a-b/2) / [(c-4d/3)/2]} × 100

The amount of the above-mentioned hemiacetal group in the polyvinyl acetal resin is preferably set to be high when the amount of the hydroxyl group of the polyvinyl acetal resin is high. When the amount of hydroxyl groups in the polyvinyl acetal resin is high, the binder tends to be hard due to hydrogen bonding between the molecules, so that cracks or cracks are likely to occur, but the resin is softened by increasing the amount of the hemiacetal group. The sex becomes good and it can suppress the occurrence of cracks or cracks.

On the other hand, when the amount of the hydroxyl group of the polyvinyl acetal resin is low, the amount of the above-mentioned hemiacetal group in the polyvinyl acetal resin is preferably set to be low.

When the amount of the hydroxyl group of the polyvinyl acetal resin is low, the flexibility of the resin is sufficiently exhibited in the range where the amount of the hemiacetal group is low, and cracking or cracking can be suppressed, and The electrolyte is highly resistant.

In the polyvinyl acetal resin, as a method for producing the polyvinyl acetal resin having the above-mentioned hemiacetal group, for example, an aldehyde is reacted with a modified polyvinyl alcohol raw material having the above-mentioned hemiacetal group. A method of acetalization. Moreover, in the case of producing a polyvinyl acetal-based resin, a method of reacting a compound reactive with a functional group of a polyvinyl alcohol raw material to form a semi-acetal group in the molecule can be mentioned. Further, a method in which a compound having reactivity with a functional group of the polyvinyl acetal resin is reacted after a polyvinyl acetal resin is produced, and a semi-acetal group is retained in the molecule, and the like. Among them, in terms of productivity and easy adjustment of the amount of the hemiacetal group, it is preferred to react a compound having reactivity with the functional group of the polyvinyl acetal resin after the production of the polyvinyl acetal resin. A method of maintaining a semi-acetal group in a molecule.

As a method of reacting a compound reactive with the functional group of the polyvinyl acetal resin, a geminal diol compound having two hydroxyl groups and having a hydroxyl group on one carbon atom is exemplified. A method of dehydrating condensation of one hydroxyl group of a resin; a method of adding an aldehyde compound to one hydroxyl group of a polyvinyl acetal resin, and the like. Among them, in terms of productivity and easy adjustment of the amount of the hemiacetal group, a method of adding an aldehyde compound to one hydroxyl group of the polyvinyl acetal resin is suitable.

The method of adding the aldehyde compound to one hydroxyl group of the polyvinyl acetal resin is, for example, a method in which a polyvinyl acetal resin is dissolved in an acidic isopropyl alcohol at a temperature of about 70 to 80 ° C. A method of reacting an aldehyde under conditions, and the like. Further, in order to adjust the amount of the above-mentioned hemiacetal group in the polyvinyl acetal resin so as to be in the above-described appropriate range, it is preferred to adjust the reaction time or the acid concentration. When the amount of the above-mentioned hemiacetal group in the polyvinyl acetal resin is set to be low, the reaction time is preferably extended, and the acid concentration is preferably increased. When the amount of the above-mentioned hemiacetal group in the polyvinyl acetal resin is set to be high, the reaction time is preferably shortened, and the acid concentration is preferably lowered. The preferred reaction time is from 0.1 to 10 hours, and the preferred acid concentration is from pH 1 to 3.5.

The preferred lower limit of the ratio of the ethylene content to the amount of the above-mentioned hemiacetal group (the ethylene content / the amount of the semi-acetal group) in the polyvinyl acetal resin is 105, and the lower limit is 110, and the upper limit is 540. A better upper limit is 500.

The polyethylene acetal resin may have a crosslinked structure. By having the crosslinked structure of the polyvinyl acetal resin, aggregation of the binder resin can be suppressed, and the bonding between the active materials and the current collector interface can be uniformly controlled to suppress the decrease in the bonding property, and the battery capacitance can be suppressed even by the reverse charging and discharging. reduce.

The method of crosslinking the polyvinyl acetal resin, for example, a method of acetalizing polyvinyl alcohol with a polyfunctional aldehyde, and adding a polyvinyl acetal resin obtained by acetalizing polyvinyl alcohol. A method of a crosslinking agent, and the like.

Among them, in view of obtaining a polyvinyl acetal resin having a sufficient degree of crosslinking, a method of adding a crosslinking agent to a polyvinyl acetal resin obtained by acetalizing polyvinyl alcohol is preferred. Further, by using a method of adding a crosslinking agent to a polyvinyl acetal resin, the uncrosslinked polyvinyl acetal resin having a fine particle shape can be crosslinked with each other to form a crosslinked polyethylene. Acetal based resin.

In the method of acetalizing polyvinyl alcohol by a polyfunctional aldehyde, the degree of crosslinking of the obtained polyvinyl acetal resin is insufficient, and the effect of suppressing aggregation is not sufficiently exhibited. Further, when the obtained polyvinyl acetal resin is formed into a crosslinked structure by a polyfunctional aldehyde, the polymer chain of the polyvinyl acetal resin may be in a state of being connected to each other and may have high viscosity, and the specific physical properties may not be obtained.

Examples of the crosslinking agent include a polyfunctional aldehyde, a polyfunctional epoxide, a melamine resin, an urethane resin, a polyfunctional isocyanate, and a phenol-formaldehyde resin.

Examples of the polyfunctional aldehyde include malondialdehyde, succinaldehyde, glutaraldehyde, terephthalaldehyde, isophthalaldehyde, and o-phthalaldehyde. Examples of the polyfunctional epoxide include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, diglycerin polyglycidyl ether, glycerin polyglycidyl ether, and polyethylene glycol diglycidyl ether. Examples of the polyfunctional isocyanate include toluene 2,4-diisocyanate, 1,6-diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate. Among them, from the viewpoint of high crosslinking reactivity of the resin, a polyfunctional aldehyde is preferred, and glutaraldehyde is particularly preferred.

It is preferred that the polyethylene acetal resin has a degree of crosslinking at 25 ° C of 5% by weight or more.

When the degree of crosslinking is 5% by weight or more, the polyvinyl acetal resin is sufficiently crosslinked, and the dispersibility of the binder resin can be improved.

The degree of crosslinking described above is more preferably 10% by weight or more. Further, the degree of crosslinking is preferably 75% by weight or less, more preferably 70% by weight or less.

The above-mentioned degree of crosslinking means a weight ratio (% by weight) of the insoluble component to the weight of the polyvinyl acetal resin (before immersion) when immersed in a specific solvent.

Moreover, the degree of crosslinking at 25 ° C means the degree of crosslinking when immersed in a solvent at 25 ° C.

It is preferred that the polyvinyl acetal resin contains a component derived from a crosslinking agent.

The component derived from the crosslinking agent may be a component derived from a crosslinking agent such as a polyfunctional aldehyde, a polyfunctional epoxide, a melamine resin, an amine ester resin, a polyfunctional isocyanate or a phenol-formaldehyde resin.

Examples of the polyfunctional aldehyde include malondialdehyde, succinaldehyde, glutaraldehyde, terephthalaldehyde, isophthalaldehyde, and o-phthalaldehyde. Examples of the polyfunctional epoxide include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, diglycerin polyglycidyl ether, glycerin polyglycidyl ether, and polyethylene glycol diglycidyl ether. Examples of the polyfunctional isocyanate include toluene 2,4-diisocyanate, 1,6-diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.

The content of the component derived from the crosslinking agent in the polyvinyl acetal resin is preferably 0.015 mol%, and preferably 10 mol%, based on the mass of the material. When the content of the component derived from the crosslinking agent is 0.015 mol% or more, the polyvinyl acetal resin is sufficiently crosslinked, and the dispersibility of the binder resin can be improved. When the content of the component derived from the crosslinking agent is 10 mol% or less, the flexibility of the binder resin can be sufficiently improved. A more preferred lower limit of the content of the component derived from the crosslinking agent is 0.025 mol%, and a more preferred upper limit is 5 mol%.

The content of the above-mentioned component derived from the crosslinking agent can be measured, for example, by NMR.

The ratio of the content of the component derived from the crosslinking agent to the amount of the hydroxyl group (the content of the component derived from the crosslinking agent / the amount of the hydroxyl group) is preferably 0.03 in terms of a molar ratio, and the upper limit is preferably 33. When the ratio is 0.03 or more, the polyvinyl acetal resin is sufficiently crosslinked, and the dispersibility of the binder resin can be improved. When the ratio is 33 or less, the flexibility of the binder resin can be sufficiently improved. A lower limit of the ratio of the content of the component derived from the crosslinking agent to the amount of the above hydroxyl group is preferably 0.05, and the upper limit is more preferably 15.

Preferably, the polyvinyl acetal resin is in the form of fine particles.

By making the polyvinyl acetal resin into a fine particle shape, it is possible to partially carry out the bonding (point contact) without covering the entire surface of the active material and the conductive auxiliary agent. As a result, it is possible to obtain an advantage that the contact between the electrolytic solution and the active material is good, and in the case of using a lithium battery, even if a large current is applied, the conduction of lithium ions is sufficiently maintained, and the decrease in battery capacitance can be suppressed.

It is preferred that the fine particle-shaped polyvinyl acetal resin has a volume average particle diameter of 50 to 700 nm. When the volume average particle diameter is 700 nm or less, the dispersibility of the active material and the conductive auxiliary agent at the time of electrode formation can be improved, and the discharge capacity of the lithium secondary battery can be improved. Further, when the thickness is 50 nm or more, the contact between the electrolyte and the active material can be improved without covering the entire surface of the active material and the conductive auxiliary agent, so that when a lithium battery is used at a large current, the conduction of lithium ions is changed. Fully, it can increase battery capacitance. A more preferable volume average particle diameter of the polyvinyl acetal resin having a microparticle shape is 60 to 600 nm, and further preferably a volume average particle diameter of 90 to 500 nm.

Further, the volume average particle diameter of the polyvinyl acetal resin can be measured by a laser diffraction/scattering particle size distribution measuring apparatus, 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 above-mentioned fine particle-shaped polyvinyl acetal resin is preferably 40%. When the CV value is 40% or less, fine particles having a large particle diameter are not present, and the stability of the composition for a lithium secondary battery electrode caused by precipitation of large-sized particles can be suppressed.

A preferred upper limit of the above CV value is 35%, a more preferred upper limit is 32%, and a preferred upper limit is 30%. Further, the CV value is a value expressed by a percentage (%) of a value obtained by dividing the standard deviation by the volume average particle diameter.

When the polyvinyl acetal resin is in the form of fine particles, the lower limit of the surface potential of the polyvinyl acetal resin is preferably -60 mV, more preferably -55 mV, and the upper limit is -30 mV, more preferably upper limit. It is -35mV.

Further, the surface potential can be measured, for example, by a zeta potentiometer or the like.

A preferred lower limit of the glass transition temperature of the polyethylene acetal resin is 20 ° C, a lower limit is 25 ° C, a preferred upper limit is 50 ° C, and a higher limit is 45 ° C.

When the glass transition temperature is not less than the above preferred lower limit and not more than the above preferred lower limit, when the active material is repeatedly expanded and contracted by repeated charge and discharge, the bonding property between the active materials can be maintained, and the decrease in discharge capacity can be suppressed.

Further, the glass transition temperature can be measured, for example, by using a differential scanning calorimeter or the like.

Preferably, the electrode binder for an electrical storage device of the present invention contains a dispersion containing the polyethylene acetal resin and a dispersion medium.

As the above dispersion medium, an aqueous medium can be preferably used.

By using an aqueous medium as the above dispersion medium, the solvent remaining in the electrode can be greatly reduced, and a lithium secondary battery can be produced.

Further, in the electrode binder for a storage device of the present invention, the aqueous medium may be only water, and a solvent other than water may be added in addition to the above water.

The solvent other than the above-mentioned water is preferably an alcohol having solubility in water and having high volatility, and examples thereof include alcohols such as isopropyl alcohol, n-propanol, ethanol, and methanol. These solvents may be used singly or in combination of two or more. A preferred upper limit of the amount of the solvent other than the above water is 30 parts by weight, more preferably 20 parts by weight, based on 100 parts by weight of water.

The content of the polyethylene acetal resin in the electrode binder for a storage device of the present invention is not particularly limited, and a preferred lower limit is 2% by weight, and a preferred upper limit is 60% by weight. When the content of the polyethylene acetal resin is 2% by weight or more, the amount of the polyvinyl acetal resin relative to the active material can be sufficiently increased when the binder is mixed with the active material to form a composition for an electric storage device electrode. To improve the adhesion to the collector. When the content of the polyvinyl acetal resin is 60% by weight or less, the stability of the polyvinyl acetal resin in an aqueous medium can be improved, and the dispersibility of the active material can be improved, and a power storage device such as a lithium secondary battery can be suppressed. The discharge capacitance is reduced. A more preferred lower limit of the content of the polyethylene acetal resin is 5% by weight, and a more preferred upper limit is 50% by weight.

The electrode adhesive for an electrical storage device of the present invention is an adhesive for an electrode of an electrical storage device.

Examples of the power storage device include a lithium secondary battery, an electric double layer capacitor, and a lithium ion capacitor. Among them, it can be suitably used for a lithium secondary battery or a lithium ion capacitor.

The method for producing the electrode binder for a storage device of the present invention is not particularly limited. For example, after the step of producing a polyvinyl acetal resin, the polyethylene acetal resin is dissolved in an organic solvent capable of dissolving the polyvinyl acetal resin, and then a small amount of a poor solvent such as water is gradually added thereto. Then, the organic solvent is removed by heating and/or depressurization, whereby the polyvinyl acetal resin is precipitated to prepare fine particles. In addition, a solution in which the polyvinyl acetal resin is dissolved is added to a large amount of water, and then heated and/or reduced pressure as necessary to remove an organic solvent, and a polyvinyl acetal resin is precipitated to prepare fine particles. . Furthermore, the polyvinyl acetal type resin is heated by a kneader or the like while heating the polyethylene acetal resin at a glass transition temperature or higher, and a small amount of water is gradually added under heat and pressure. Mix and practice. Examples of the organic solvent include tetrahydrofuran, acetone, toluene, methyl ethyl ketone, ethyl acetate or methanol, ethanol, butanol, and isopropyl alcohol.

In particular, since the obtained polyvinyl acetal resin has a small volume average particle diameter and can obtain fine particles having a narrow particle size distribution, it is preferred to dissolve the polyethylene acetal resin in an organic solvent to form a polyethylene. A method in which an acetal resin is precipitated to prepare fine particles.

Further, in the above production method, a polyvinyl acetal resin having a fine particle shape can be produced and dried, and then dispersed in an aqueous medium, and a solvent used for producing a polyvinyl acetal resin having a fine particle shape can be used as it is. As an aqueous medium.

By adding an active material to the electrode for a storage device electrode of the present invention, a composition for an electrode of a power storage device can be obtained. Such a composition for an electric storage device electrode containing the binder for an electrode for an electrical storage device of the present invention and an active material is also one of the inventions.

The content of the polyethylene acetal resin in the electrode assembly for a storage device of the present invention is not particularly limited, and is preferably 0.5 parts by weight, and preferably 12 parts by weight, based on 100 parts by weight of the active material. When the content of the polyethylene acetal resin is 0.5 parts by weight or more, the adhesion to the current collector can be sufficiently improved. When the content of the polyethylene acetal resin is 12 parts by weight or less, the decrease in discharge capacity of the lithium secondary battery can be suppressed. A more preferred lower limit of the content of the polyethylene acetal resin is 0.8 parts by weight, and a more preferred upper limit is 5 parts by weight.

The electrode assembly for an electrical storage device of the present invention contains an active material.

The electrode composition for a storage device of the present invention can be used for any of the positive electrode and the negative electrode, and can also be used for both the positive electrode and the negative electrode. Therefore, as the active material, there are a positive electrode active material and a negative electrode active material.

Examples of the positive electrode active material include particles containing lithium and a transition metal element as an oxide of a constituent metal element (lithium transition metal oxide), and a phosphate containing a lithium and a transition metal element as a constituent metal element.

Examples of the oxide containing lithium and a transition metal element as a constituent metal element include lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), and lithium manganese oxide (for example, LiMri ₂ O _{4 ).} Or such a composite (for example, LiNi _0.5 Mn _1.5 O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) or the like. Examples of the phosphate containing lithium and a transition metal element as a constituent metal element include lithium manganese phosphate (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ). Furthermore, these may be used alone or in combination of two or more.

As the negative electrode active material, for example, a material which has been conventionally used as a negative electrode active material for a lithium secondary battery can be used, and examples thereof include a carbon-based material such as graphite, natural graphite, graphite carbon, or amorphous carbon, and a lithium transition metal oxide. A lithium transition metal nitride, a ruthenium compound such as ruthenium or osmium oxide, or the like.

It is preferable that the electrode composition for an electricity storage device of the present invention contains a conductive auxiliary agent.

The conductive auxiliary agent is used to increase the output of the power storage device, and may be used depending on the case of the positive electrode and the negative electrode.

Examples of the conductive auxiliary agent include graphite, acetylene black, carbon black, ketjen black, and vapor-grown carbon fibers. Among them, acetylene black is preferred.

In addition to the above-mentioned active material, a conductive auxiliary agent, fine particles composed of a polyvinyl acetal resin, a polyvinyl alcohol-based resin, or an aqueous medium, the electrode composition for an electrical storage device of the present invention may be added as needed. Additives such as fuel additives, tackifiers, defoamers, leveling agents, and adhesion imparting agents.

The method for producing the electrode assembly for the electrical storage device of the present invention is not particularly limited, and for example, various mixing devices such as a ball mill, a stirring mill, and a three-roll mill are used, and the active material, the conductive auxiliary agent, and the polyethylene are mixed. A method of forming fine particles of an acetal resin, a polyvinyl alcohol resin, an aqueous medium, and various additives as needed.

The electrode assembly for a storage device of the present invention is formed by, for example, applying onto a conductive substrate and drying the electrode to form a storage device electrode. Such an electric storage device electrode and an electric storage device obtained by using the composition for an electric storage device electrode are also one of the inventions.

As a coating method for applying the electrode assembly for an electrical storage device of the present invention to a conductive substrate, for example, various coatings such as an extrusion coater, a reverse roller, a doctor blade, an applicator, and the like can be used. Cloth method.

Further, it is preferred to carry out the pressurization step so as to achieve an appropriate electrode density after being applied onto the conductive substrate. The above pressurizing step preferably uses a roll press.

According to the present invention, it is possible to provide a binder for a storage device electrode of a storage device having a high capacitance, which is excellent in the binding property of an active material and has high durability to an electrolytic solution. Moreover, it is possible to provide a composition for an electric storage device electrode, an electric storage device electrode, and a power storage device using the electric energy storage device electrode adhesive.

The invention is illustrated in more detail in the following examples, but the invention is not limited to the examples.

(Preparation of polyvinyl acetal resin)

(Synthesis Example 1)

10 parts by weight of ethylene modified polyvinyl alcohol having a polymerization degree of 1700, an ethylene content of 48.0 mol%, 10 parts by weight of hydrochloric acid having a concentration of 1.0 M, and 4.1 parts by weight of n-butyraldehyde were added to 100 parts by weight of tetrahydrofuran, and the reaction system was set up. The acetalization reaction was carried out at pH 1.3 and the liquid temperature was maintained at 65 °C. After 3.5 hours, the mixture was neutralized with pyridine, and the resin was purified by a reprecipitation method and dried to obtain a solid of an ethylene-modified polyethylene acetal resin (hereinafter also referred to as a polyvinyl acetal resin 1). . The obtained polyvinyl acetal resin 1 was dissolved in DMSO-D ₆ , and the ethylene content, the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit, the amount of hydroxyl groups, and the chain length were measured by ¹ H-NMR. The ratio of the constituent unit having a hydroxyl group of 1, the amount of the acetal group (the amount of butyral group, the amount of hemiacetal group), the meso/racemic ratio, and the amount of the ethyl group. The results are shown in Table 1.

In addition, the glass transition temperature of the obtained polyvinyl acetal resin 1 was measured in accordance with JIS K 7121 using a differential scanning calorimeter (DSC-6200R manufactured by Seiko Instruments Inc.) at a temperature increase rate of 10 ° C/min.

(Synthesis Example 2~5)

A solid of the polyvinyl acetal resin 2 to 5 was obtained in the same manner as in Synthesis Example 1 except that the amount of n-butyraldehyde was changed as shown in Table 1. The obtained polyvinyl acetal resin was dissolved in DMSO-D ₆ and the ethylene content, the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit, the amount of hydroxyl groups, and the chain length were measured by ¹ H-NMR. The ratio of the constituent unit having a hydroxyl group, the amount of the acetal group (the amount of butyraldehyde group, the amount of hemiacetal group), the meso/racemic ratio, and the amount of the ethyl group. Further, the glass transition temperature of the obtained polyvinyl acetal resin was measured.

(Synthesis Examples 6 to 9)

A solid of the polyvinyl acetal resin 6 to 9 was obtained in the same manner as in Synthesis Example 1 except that the ethylene content of the polyvinyl alcohol and the amount of the n-butyraldehyde were as shown in Table 1. The obtained polyvinyl acetal resin was dissolved in DMSO-D ₆ and the ethylene content, the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit, the amount of hydroxyl groups, and the chain length were measured by ¹ H-NMR. The ratio of the constituent unit having a hydroxyl group, the amount of the acetal group (the amount of butyraldehyde group, the amount of hemiacetal group), the meso/racemic ratio, and the amount of the ethyl group. Further, the glass transition temperature of the obtained polyvinyl acetal resin was measured.

(Preparation of polyvinyl acetal resin fine particles)

(Manufacturing Example 1)

10 parts by weight of the polyvinyl acetal resin 1 was weighed and placed in a reaction vessel equipped with a thermometer, a stirrer, and a condenser, dissolved in 60 parts by weight of isopropyl alcohol, and 2-methylmercaptobenzene was added to the solution. 0.5 parts by weight of sodium sulfonate and 0.02 parts by weight of concentrated hydrochloric acid of 12 M, the reaction system was set to pH 2.1, and reacted at 80 ° C for 4 hours. The reaction solution was cooled, and 20 parts by weight of water was added dropwise. The obtained solution was added to 20 parts by weight of water, and the liquid temperature was maintained at 30 ° C and stirred for 1 hour. Then, while maintaining the liquid temperature at 30 ° C, the mixture was stirred under reduced pressure to volatilize isopropyl alcohol and water, and then concentrated until the solid content became 25% by weight to prepare a polyvinyl acetal resin dispersed therein. A dispersion of fine particles (hereinafter also referred to as polyvinyl acetal resin fine particles 1) (content of polyvinyl acetal resin fine particles 1 : 25% by weight).

In addition, the ethylene content in the polyvinyl acetal resin fine particle 1, the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit, the amount of the hydroxyl group, the ratio of the hydroxyl group-containing constituent unit having a chain length of 1, and the acetal group. The amount (the amount of butyral group, the content of the acetal bond having an ionic functional group, the amount of the hemiacetal group), the meso/racemic ratio, and the amount of the acetyl group are shown in Table 2. Further, the volume average particle diameter of the obtained polyvinyl acetal resin fine particles 1 obtained by a transmission electron microscope was measured and found to be 300 nm. Further, the surface potential of the obtained polyvinyl acetal resin fine particles 1 was measured using a tantalum potentiometer ("Zeta Potential/Particle Sizer 380ZLS" manufactured by NICOLP). In addition, the glass transition temperature of the obtained polyvinyl acetal resin fine particles 1 was measured in accordance with JIS K 7121 using a differential scanning calorimeter (DSC-6200R manufactured by Seiko Instruments Inc.) at a temperature increase rate of 10 ° C/min.

(Manufacturing Example 2 to 8)

In the same manner as in Production Example 1, except that the type of the polyethylene acetal resin of the raw material and the amount of the sodium 2-formylbenzenesulfonate were added as shown in Table 2, a polyvinyl acetal was dispersed in the same manner as in Production Example 1. The dispersion of the resin fine particles 2 to 8 (the content of the polyvinyl acetal resin fine particles: 25% by weight).

Further, the ethylene content of the obtained polyvinyl acetal resin fine particles, the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit, the amount of the hydroxyl group, the ratio of the hydroxyl group-containing constituent unit having a chain length of 1, and the acetal The basis weight (the amount of butyraldehyde group, the content of the acetal bond having an ionic functional group, the amount of the hemiacetal group), the meso/racemic ratio, and the amount of the acetamidine group are shown in Table 2. Further, the volume average particle diameter, surface potential, and glass transition temperature of the obtained polyvinyl acetal resin fine particles were as shown in Table 2.

(Manufacturing Example 9)

Instead of sodium 2-mercaptobenzenesulfonate, p-hydroxyaldehyde was used. In addition, the polyvinyl acetal resin fine particles were dispersed in the same manner as in Production Example 1, except that the type of the raw material polyvinyl acetal resin and the amount of the uronic acid added were as shown in Table 2. 9 dispersion (content of polyvinyl acetal resin fine particles: 25% by weight).

Further, the ethylene content of the obtained polyvinyl acetal resin fine particles, the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit, the amount of the hydroxyl group, the ratio of the hydroxyl group-containing constituent unit having a chain length of 1, and the acetal The basis weight (the amount of butyraldehyde group, the content of the acetal bond having an ionic functional group, the amount of the hemiacetal group), the meso/racemic ratio, and the amount of the acetamidine group are shown in Table 2. Further, the volume average particle diameter, surface potential, and glass transition temperature of the obtained polyvinyl acetal resin fine particles were as shown in Table 2.

(Example 1)

10 parts by weight of the polyvinyl acetal resin 1 was weighed, and 90 parts by weight of N-methylpyrrolidone as a solvent was added to prepare a binder for an electrode for an electricity storage device (the content of the polyvinyl acetal resin was 10% by weight). ).

The active material and the conductive auxiliary agent were mixed at a ratio shown in Table 3 with respect to 40 parts by weight of the binder for the storage device electrode (four parts by weight of the polyvinyl acetal resin), and the composition for the storage device electrode was produced. In addition, spherical natural graphite (CGB-20 manufactured by Nippon Graphite Industries Co., Ltd.), ruthenium compound (SiO, manufactured by Osaka Titanium Technologies Co., Ltd.), and acetylene black (DENKA BLACK manufactured by Electric Chemical Industry Co., Ltd.) as a conductive auxiliary agent were used as Active substance.

(Examples 2 to 3)

In the same manner as in Example 1, except that the type of the polyethylene acetal resin was changed to the following, the electrode assembly for an electrode for an electric storage device and the electrode assembly for a storage device were prepared.

(Example 4)

1 part by weight of the polyvinyl acetal resin fine particles 1 was weighed, and 19 parts by weight of water as a solvent was added to prepare a binder for an electric storage device electrode (the content of the polyvinyl acetal resin fine particles was 5% by weight).

60 parts by weight of the binder for the storage device electrode (3 parts by weight of the polyvinyl acetal resin fine particles), the active material and the conductive auxiliary agent were mixed at a ratio shown in Table 3, and further added as a tackifier. One part by weight of carboxymethyl cellulose (manufactured by Aldrich Co., Ltd.) was mixed to prepare a composition for an electrode of a storage device.

(Examples 5 to 10)

In the same manner as in Example 4, a battery electrode assembly and a battery assembly electrode assembly were produced in the same manner as in Example 4 except that the type of the polyvinyl acetal resin fine particles was changed to that shown in Table 3.

(Comparative examples 1 to 2)

In the same manner as in Example 1, except that the type of the polyethylene acetal resin was changed to the following, the electrode assembly for an electrode for an electric storage device and the electrode assembly for a storage device were prepared.

(Comparative examples 3 to 4)

In the same manner as in Example 4, a battery electrode assembly and a battery assembly electrode assembly were produced in the same manner as in Example 4 except that the type of the polyvinyl acetal resin fine particles was changed to that shown in Table 3.

(Comparative Example 5)

The styrene-butadiene copolymer (styrene constituent unit content 50%, butadiene constituent unit content 50%, particle diameter 150 to 200 nm) was mixed in the ratio shown in Table 3 instead of the polyvinyl acetal resin 1, except In the same manner as in the first embodiment, a binder for an electrode for a storage device and a composition for an electrode for a storage device were produced.

<evaluation>

The following description was carried out on the electrode assembly for an electric storage device electrode and the electrode assembly for an electric storage device obtained in the examples and the comparative examples. The results are shown in Table 3.

(1) Evaluation of elastic modulus

The electrode for the storage device electrode obtained in Examples 1 to 10 and Comparative Examples 1 to 5 was applied to the release-treated polyethylene terephthalate (PET) so that the film thickness after drying was 50 μm. The film was dried and dried to prepare a binder resin sheet.

The obtained adhesive resin sheet was cut into 10 mm × 50 mm to prepare a sheet for evaluation of elastic modulus.

The elastic modulus of the obtained sheet for evaluation of the modulus of elasticity was measured under the conditions of 23 ° C using a tensile tester (AG-IS manufactured by Shimadzu Corporation) in accordance with JIS K 7127.

(2) Evaluation of electrolyte resistance

(1) A binder resin sheet was produced in the same manner as in the evaluation of the elastic modulus, and the obtained adhesive resin sheet was cut into 30 × 50 mm to prepare an electrolyte-resistant test piece.

(dissolution, swelling evaluation)

The obtained test piece was dried at 110 ° C for 2 hours, and the weight of the obtained film was weighed, whereby the weight (a) of the film was measured.

Next, a mixed solvent of diethyl carbonate and ethylene carbonate (volume ratio: 1:1) was used as an electrolytic solution, and the obtained film was immersed in an electrolytic solution at 25 ° C for 3 days. Thereafter, the film was taken out, the electrolyte on the surface was wiped off immediately, and then weighed, whereby the weight (b) was measured.

Thereafter, the film was immersed in 500 g of pure water for 2 days to completely remove the electrolytic solution inside the film, and dried at 110 ° C for 2 hours, and then weighed, thereby measuring the weight (c).

The dissolution rate and the swelling ratio of the binder were calculated from the following formulas according to the respective weights.

Dissolution rate (%) = [(a-c) / a] × 100

Swelling rate (%) = (b-c/c) × 100

Further, a higher value of the dissolution rate means that the resin is more easily dissolved in the electrolytic solution, and a higher swelling ratio means that the resin is more likely to swell by the electrolytic solution.

(3) Recovery rate

An adhesive resin sheet was produced in the same manner as in "(1) Evaluation of elastic modulus", and the obtained adhesive resin sheet was cut into a length of 15 mm × a width of 10 mm to prepare a sheet for evaluation of recovery rate.

Using the tensile tester (AG-IS manufactured by Shimadzu Corporation), the obtained sheet for evaluation of the recovery rate was stretched to 45 mm (300%) at a tensile speed of 100 mm/min in the longitudinal direction under the conditions of 25 °C. Thereafter, the elongation state was released and left for 1 minute. Further, after elongating to a length of 45 mm/min in the longitudinal direction to 45 mm, the stretched state was released and left for 1 minute, and the operation was performed 10 times in total, and the recovery rate from the stretched state for the 10th time was calculated as follows.

Recovery rate (%) = [length of elongation state (mm) - length after placement for 1 minute (mm)] ÷ [length of elongation state (mm) - length before recovery test (mm)] × 100

Further, the recovery rate was measured in the same manner at 40 °C.

Further, a mixed solvent of diethyl carbonate and ethylene carbonate (volume ratio: 1:1) was used as an electrolytic solution, and the obtained sheet for evaluation of recovery rate was immersed in an electrolytic solution at 25 ° C for 3 days. Thereafter, the sheet for evaluation of the recovery rate was taken out, and the recovery rate in the swollen state was measured in the same manner at 25 °C.

(4) Battery performance evaluation

(a) Production of coin batteries

The components for electrical storage device electrodes obtained in Examples 1 to 10 and Comparative Examples 1 to 5 were uniformly applied onto a copper foil having a thickness of 15 μm, dried, and then pressed to be punched out. The negative electrode layer was obtained at 16 mm.

Again, use punching as 14mm of the lithium metal foil as a counter electrode, a thickness of the porous PP film of 25μm glass filter (Advantec GA-100) as a separator, containing LiPF ₆ (1M) the mixture of ethylene carbonate and diethyl carbonate of A solvent (volume ratio of 1:1) was used as an electrolyte to prepare a coin battery (CR2032 type).

(b) Charge and discharge cycle evaluation

The charge and discharge cycle was evaluated using a charge and discharge tester (manufactured by Toyo Systems Co., Ltd.) for the obtained coin battery.

The charge and discharge cycle evaluation was carried out in a voltage range of 0.1 to 1.5 V and an evaluation temperature of 25 °C. The capacity retention rate of the charge and discharge cycle evaluation is set to 100% of the discharge capacitance of the fifth cycle, and the value of the discharge capacitance of the 30th cycle divided by the discharge capacitance of the 5th cycle is set as the capacitance of the 30th cycle. Maintenance rate.

[Industrial availability]

According to the present invention, it is possible to provide a binder for a storage device electrode of a storage device having a high capacitance, which is excellent in the binding property of an active material and has high durability to an electrolytic solution. Moreover, it is possible to provide a composition for an electric storage device electrode, an electric storage device electrode, and a power storage device using the electric energy storage device electrode adhesive.

Claims (16)

 A binder for an electrode for an electricity storage device, which is a binder for an electrode of a power storage device, characterized in that the binder contains a polyvinyl acetal resin, and the ethylene content of the polyvinyl acetal resin is 25~50 mol%, the hydroxyl amount is 15~35 mol%.    The adhesive for electrical storage device electrodes according to claim 1, wherein the ratio of the ethylene content to the amount of hydroxyl groups (ethylene content/hydroxyl group) in the polyvinyl acetal resin is from 1.4 to 3.2.    The binder for a storage device electrode according to claim 1 or 2, wherein, in the polyvinyl acetal resin, the ratio of the ethylene unit having a chain length of 1 to the entire ethylene unit is 10 to 25%.    The adhesive for electrical storage device electrodes according to claim 1, 2 or 3, wherein, in the polyvinyl acetal resin, a ratio of a hydroxyl group-containing constituent unit having a chain length of 1 to a hydroxyl group-containing constituent unit is 25 %the following.    The adhesive for a storage device electrode according to claim 1, 2, 3 or 4, wherein the meso/raceo ratio of the acetal ring structure of the polyvinyl acetal resin is less than 10.    The binder for a storage device electrode according to claim 1, 2, 3, 4 or 5, which comprises a dispersion containing a polyvinyl acetal resin and an aqueous medium, wherein the polyvinyl acetal resin has a fine particle shape.    The binder for a storage device electrode according to claim 6, wherein the polyvinyl acetal resin has a volume average particle diameter of 50 to 700 nm.    The binder for a storage device electrode according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the polyvinyl acetal resin has an ionic functional group.    The adhesive for a storage device electrode according to claim 8, wherein the ionic functional group is 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 amine group, and the like. At least one functional group in the group consisting of salts.    The binder for a storage device electrode according to claim 8 or 9, wherein the polyvinyl acetal resin has an acetal bond having an ionic functional group.    The binder for a storage device electrode according to claim 10, wherein a ratio of an ethylene content in the polyvinyl acetal resin to a content of an acetal bond having an ionic functional group (ethylene content / having an ionic functional group) The content of the acetal bond is 9 to 75.    The adhesive for electrical storage device electrodes according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the polyvinyl acetal resin has a hemiacetal group.    The binder for a storage device electrode according to claim 12, wherein a ratio of the ethylene content to the amount of the hemiacetal group (the ethylene content / the amount of the hemiacetal group) in the polyvinyl acetal resin is from 105 to 540.    A composition for an electrode for a power storage device, comprising a binder for an electrode for a storage device according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or 13, and an active material, 100 parts by weight of the active material contains 0.5 to 12 parts by weight of a polyvinyl acetal resin.    An electric storage device electrode is obtained by using the composition for an electric storage device electrode according to claim 14.    A power storage device is obtained by using the electrode of the power storage device described in claim 15.