JP7358151B2 - Composition for all-solid-state batteries - Google Patents

Description

The present invention provides an all-solid-state battery composition that has excellent dispersibility and adhesion of active materials and electrolytes, reduces viscosity decrease and dimensional change over time, and can prevent battery deterioration and failure due to moisture absorption. and an all-solid-state battery using the all-solid-state battery composition.

In recent years, with the spread of portable electronic devices such as portable video cameras and portable personal computers, the demand for secondary batteries as mobile power sources has rapidly increased. Further, there are very high demands for such secondary batteries to be smaller, lighter, and have higher energy density.
As described above, water-soluble batteries such as lead batteries and nickel-cadmium batteries have traditionally been the mainstream secondary batteries that can be charged and discharged repeatedly, but these water-soluble batteries have excellent charge and discharge characteristics. However, in terms of battery weight and energy density, it cannot be said that the battery has sufficiently satisfactory characteristics as a mobile power source for portable electronic devices.

Therefore, as a secondary battery, research and development of lithium secondary batteries using lithium or lithium alloy for the negative electrode is actively conducted. This lithium secondary battery has excellent features such as high energy density, low self-discharge, and light weight.
The electrodes of lithium secondary batteries are usually made by kneading the active material and binder with a solvent, dispersing the active material to form a slurry, and then applying this slurry onto a current collector using a doctor blade method or the like and drying it to form a thin film. It is formed by

Currently, fluororesins represented by polyvinylidene fluoride (PVDF) are most widely used as binders for electrodes of lithium secondary batteries.
However, when a fluororesin is used as a binder, while it is possible to create a flexible thin film, the binding between the current collector and the active material is poor, so some or all of the active material is removed during the battery manufacturing process. There was a risk that it would peel off or fall off from the current collector. Furthermore, when the battery is charged and discharged, lithium ions are repeatedly inserted and released within the active material, which may cause the active material to peel off or fall off from the current collector.

In order to solve these problems, attempts have been made to use binders other than PVDF. However, when a conventional resin is used, a new problem has arisen in that the resin decomposes or deteriorates when a voltage is applied to the electrode. When such resin deterioration occurs, problems such as a decrease in charge/discharge capacity and peeling of electrodes occur.

On the other hand, Patent Document 1 describes a binder for a non-aqueous secondary battery comprising a copolymer of an acidic functional group-containing monomer and an amide group-containing monomer.
However, when such a binder is used, the dispersibility of the active material becomes low and the viscosity of the electrode composition becomes high, so it takes time for paste filtration, which increases the process time, and it also causes problems during coating. It was easy for uneven construction to occur. Furthermore, since the density of the active material in the electrode is reduced, the capacity of the resulting battery is insufficient.
Furthermore, when such a resin is used, the flexibility of the electrode becomes low, causing cracking and peeling from the current collector, resulting in a problem of reduced battery durability.

Patent Document 2 discloses a binder composition for a secondary battery positive electrode containing a predetermined amount of an aromatic vinyl unit, a nitrile group unit, a hydrophilic group unit, and a linear alkylene unit.
However, even when such a composition is used, the dispersibility of the active material is low and the viscosity of the electrode composition is high, so paste filtration takes time, the process time becomes longer, and coating Occasionally, coating unevenness was likely to occur. Furthermore, if an electrode composition is prepared with a high moisture content, acidic gas will be generated from inside the battery due to the influence of moisture, which may cause expansion, ignition, or explosion of the battery.
Furthermore, since the density of the active material in the electrode is reduced, the capacity of the resulting battery is insufficient.

On the other hand, since lithium secondary batteries employ a liquid electrolyte, there is a problem in that short circuits between the positive electrode and the negative electrode are likely to occur. In order to solve these problems, safety is ensured by solidifying the electrolyte using polymers, inorganic ceramics, etc. that are chemically stable even in a wide potential window, rather than using a liquid electrolyte. All-solid-state batteries are being developed and put into practical use.

For example, Patent Document 3 discloses an active material slurry in which an active material is dispersed in a solvent containing a lithium ion conductive binder, and a solid state in which a sulfide solid electrolyte is dispersed in a solvent containing a lithium ion conductive binder. A method of manufacturing an all-solid-state battery using an electrolyte slurry is disclosed.
However, even when such a technique is used, the problem that the dispersibility of the active material and solid electrolyte deteriorates over time remains unsolved.

Patent No. 5708872 Japanese Patent Application Publication No. 2013-179040 Japanese Patent Application Publication No. 2010-33918

The present invention provides an all-solid-state battery composition that has excellent dispersibility and adhesion of active materials and electrolytes, reduces viscosity decrease and dimensional change over time, and can prevent battery deterioration and failure due to moisture absorption. The object of the present invention is to provide an all-solid-state battery using the all-solid-state battery composition.

The present invention provides an all-solid-state battery composition containing an active material and/or a solid electrolyte, a binder, and an organic solvent, wherein the binder contains a polyvinyl acetal resin, and the polyvinyl acetal resin has an alkylene oxide group. A composition for an all-solid battery, comprising a structural unit having an alkylene oxide group, the content of the structural unit having an alkylene oxide group is 0.01 to 20 mol%, the amount of hydroxyl groups is 16 to 32 mol%, and the degree of polymerization is 250 to 5000. It is a thing.
The present invention will be explained in detail below.

As a result of extensive studies, the present inventors have found that by using a polyvinyl acetal resin having a predetermined structure as a binder for forming an all-solid-state battery, the dispersibility and adhesiveness of the active material and solid electrolyte are excellent. In addition, we have discovered that it is possible to prevent battery deterioration and failure due to moisture absorption by reducing viscosity decline and dimensional changes over time, and that high-capacity all-solid-state batteries can be manufactured even when the amount of binder added is small. was completed.
In particular, if the all-solid-state battery composition absorbs moisture during the electrode manufacturing process, the water present in the cell during battery manufacturing may react with lithium, causing battery deterioration and failure. The all-solid-state battery composition of the present invention can reduce hygroscopicity and prevent battery deterioration and failure.

The all-solid-state battery composition of the present invention contains an active material and/or a solid electrolyte.
The all-solid-state battery composition of the present invention may be used for electrodes or electrolyte layers.
Moreover, when used for an electrode, it may be used for both a positive electrode and a negative electrode. Therefore, the active material includes a positive electrode active material and a negative electrode active material.

Examples of the positive electrode active material include lithium-containing composite metal oxides such as lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. Specific examples include LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ and the like.
Note that these may be used alone or in combination of two or more.

As the negative electrode active material, for example, materials conventionally used as negative electrode active materials of secondary batteries can be used, such as spherical natural graphite, natural graphite, artificial graphite, amorphous carbon, carbon black, or Examples include those in which different elements are added to these components.

It is preferable that the composition for an all-solid-state battery of the present invention contains a conductivity imparting agent (conductivity aid).
Examples of the conductivity imparting agent include carbon materials such as graphite, acetylene black, carbon black, Ketjenblack, and vapor-grown carbon fiber. In particular, acetylene black and carbon black are preferable as the conductivity imparting agent for the positive electrode, and acetylene black and scaly graphite are particularly preferable as the conductivity imparting agent for the negative electrode.

The above-mentioned solid electrolyte is not particularly limited, and the same one as the above-mentioned active material may be used.
Specifically, for example, low melting point glass such as LiO ₂ /Al ₂ O ₃ /SiO ₂ -based inorganic glass, lithium sulfur-based glass such as Li ₂ S-M _x S _y (M=B, Si, Gc, P), etc. , lithium cobalt composite oxides such as LiCoO ₂ and lithium manganese composite oxides such as LiMnO ₄ . In addition, lithium nickel composite oxide, lithium vanadium composite oxide, lithium zirconium composite oxide, lithium hafnium composite oxide, lithium silicate (Li _3.5 Si _0.5 P _0.5 O ₄ ), lithium titanium phosphate (LiTi ₂ (PO ₄ ) ₃ ), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the like. Furthermore, lithium germanium phosphate (LiGe ₂ (PO ₄ ) ₃ ), Li ₂ O-SiO ₂ , Li ₂ O-V ₂ O ₅ -SiO ₂ , Li ₂ O-P ₂ O ₅ -B ₂ O ₃ , Li Examples include lithium oxide compounds such as ₂ O-GeO ₂ Ba and Li ₁₀ GeP ₂ S ₁₂ . Note that the average particle diameter of the solid electrolyte is preferably 0.05 to 50 μm.

The all-solid-state battery composition of the present invention contains a polyvinyl acetal resin. In the present invention, by using polyvinyl acetal resin as a binder, an attractive interaction occurs between the hydroxyl group of the polyvinyl acetal resin and the oxygen atom of the active material, resulting in a structure in which the active material is surrounded by the polyvinyl acetal resin. . Further, another hydroxyl group within the same molecule also exerts an attractive interaction with the conductivity imparting agent, so that the distance between the active material and the conductivity imparting agent can be kept within a certain range. By arranging the active material and the conductivity imparting agent at a suitable distance from each other in a characteristic structure in this way, the dispersibility of the active material is greatly improved. Furthermore, similar effects can be obtained when the above polyvinyl acetal resin is used in the electrolyte layer.
Furthermore, the adhesion to the current collector can be improved compared to the case where resin such as PVDF is used. Furthermore, it has the advantage of being excellent in solvent solubility and expanding the range of solvent selection.

The polyvinyl acetal resin includes a structural unit having an alkylene oxide group.
By having such structural units, the above polyvinyl acetal resin can have excellent resistance to electrolyte, adhesion with current collectors, and ionic conductivity, and when the amount of binder added is reduced. However, it has the advantage of being able to produce high-capacity all-solid-state batteries.

The polyvinyl acetal resin includes a structural unit having an alkylene oxide group.
The structural unit having an alkylene oxide group is preferably a structural unit represented by the following formula (1).
By having the structural unit represented by the following formula (1), the oxygen atom present in the alkylene oxide group coordinates with the lithium ion and has a conductive path even in the solid, whereas the counter ion is not transported. It has the advantage of increasing the ion transfer number.

式（１）中、Ｒ^１は、炭素数が２～６であるアルキレンオキサイド基を有する基を表す。

In formula (1), R ¹ represents a group having an alkylene oxide group having 2 to 6 carbon atoms.

The alkylene oxide group having 2 to 6 carbon atoms is preferably an ethylene oxide group, a propylene oxide group, a butylene oxide group, a pentylene oxide group, a hexylene oxide group, or a combination of two or more of these. However, ethylene oxide groups are preferred.
Examples of the structural unit represented by the above formula (1) include those having multiple ethylene oxide groups in the structural unit such as polyethylene glycol, those having a single ethylene glycol unit in the structural unit, and non-continuous Examples include those having multiple ethylene glycol units or polyethylene glycol units.
The structural unit represented by the above formula (1) is preferably a structural unit having an alkylene oxide group (ethylene oxide group) represented by the following formula (2).

式（２）中、Ｒ^２及びＲ^３は、Ｃ及びＯからなる群より選択される少なくとも１種を有する連結基又は単結合を表し、ｎは整数を表す。

In formula (2), R ² and R ³ represent a linking group or a single bond having at least one selected from the group consisting of C and O, and n represents an integer.

The above R ² is a linking group or a single bond having at least one selected from the group consisting of C and O. The above R ² is preferably an alkylene group having 1 to 10 carbon atoms or a carbonyl group. When the number of carbon atoms in R ² is within the above range, the alkylene oxide structural unit does not depart too far from the main chain, and the hydroxyl group and the oxygen atom of the alkylene oxide unit interact with each other, so that the alkylene oxide is effectively It can expand.
Examples of the above R ² include a methylene group, an ethylene group, a carbonyl group, and an ether group. Moreover, the above R ² may be a single bond.
The above R ³ is a linking group or a single bond having at least one selected from the group consisting of C and O. The above R ³ is preferably an ethylene group having 1 to 10 carbon atoms or a carbonyl group. Examples of the above R ³ include a methylene group, an ethylene group, a propylene group, a carbonyl group, and an ether group. Moreover, the above R ³ may be a single bond.
Further, the integer n, which is the number of repeats of the alkylene oxide, is not particularly limited, but is preferably from 2 to 50, more preferably from 5 to 20. When the number of repetitions of alkylene oxide is within the above range, it becomes possible to efficiently transport only lithium ions.

The lower limit of the content of the structural unit having an alkylene oxide group in the polyvinyl acetal resin is 0.01 mol%, and the upper limit is 20 mol%. By setting the above content to 0.01 mol% or more, the lithium ion transfer number can be increased, and by setting the above content to 20 mol% or less, electrolyte resistance and voltage resistance can be maintained. can. The preferable lower limit of the content is 0.05 mol%, and the preferable upper limit is 15 mol%. A more preferable upper limit is 12 mol%.

The polyvinyl acetal resin has a structural unit having an acetal group.
The content of the structural unit having the acetal group (degree of acetalization) in the polyvinyl acetal resin is preferably 20 to 80 mol%. By setting the degree of acetalization to 20 mol% or more, the solubility in a solvent is improved and it can be suitably used as a composition. By setting the degree of acetalization to 80 mol% or less, the resistance to the electrolyte becomes sufficient, and when the electrode is immersed in the electrolyte, the resin component can be prevented from eluting into the electrolyte. More preferably, it is 30 to 65 mol%. More preferably, it is 30 to 60 mol%.
In this specification, the degree of acetalization refers to the ratio of the number of hydroxyl groups acetalized with butyraldehyde to the number of hydroxyl groups in polyvinyl alcohol. In addition, since the acetal group of polyvinyl acetal resin is acetalized from two hydroxyl groups, the method for calculating the degree of acetalization is to count the two hydroxyl groups that have been acetalized. Calculate the mole % of degree.
In addition, in this specification, the degree of acetalization means the content of the structural unit having an acetal group with respect to the entire polyvinyl acetal resin.

The above structural unit having an acetal group can be obtained by acetalization using an aldehyde.
The preferable lower limit of the number of carbon atoms (the number of carbon atoms excluding the aldehyde group) of the aldehyde is 1, and the preferable upper limit is 11. By setting the number of carbon atoms within the above range, the hydrophobicity of the resin becomes low, so that purification efficiency is improved and the content of Na ions can be reduced.
Specific examples of the aldehyde include alkyl aldehydes such as acetaldehyde, butyraldehyde and propionaldehyde, and aldehydes having a vinyl group (vinyl aldehyde) such as benzaldehyde and acrolein. Among them, alkyl aldehydes are preferred.
Further, the acetal group is preferably at least one selected from the group consisting of a butyral group, a benzacetal group, an acetoacetal group, a propionacetal group, and a vinyl acetal group. Among these, at least one selected from the group consisting of a butyral group, an acetoacetal group, a propionacetal group, and a vinyl acetal group is preferable.

In the polyvinyl acetal resin, the ratio of the portion acetalized with acetaldehyde to the portion acetalized with butyraldehyde is preferably 0/100 to 50/50. This makes the polyvinyl acetal resin flexible and improves its adhesion to the current collector. More preferably, the ratio (molar ratio) of the part acetalized with acetaldehyde to the part acetalized with butyraldehyde is 0/100 to 20/80.

The polyvinyl acetal resin has a structural unit having a hydroxyl group.
The lower limit of the content of the structural unit having a hydroxyl group (the amount of hydroxyl groups) in the polyvinyl acetal resin is 16 mol%, and the upper limit is 32 mol%. By setting the amount of hydroxyl groups to 16 mol% or more, the resistance to the electrolyte can be improved and the resin can be prevented from eluting into the electrolytic solution, and by setting it to 32 mol% or less, the flexibility of the resin can be improved. Therefore, the adhesion to the current collector becomes sufficient.
The preferable lower limit of the amount of hydroxyl groups is 17 mol%, and the preferable upper limit is 30 mol%.
A more preferable lower limit is 20 mol%, and a more preferable upper limit is 25 mol%. In addition, in this specification, the amount of hydroxyl groups means the content of the structural unit having a hydroxyl group with respect to the whole polyvinyl acetal resin.

It is preferable that the polyvinyl acetal resin has a structural unit having an acetyl group.
The preferable lower limit of the content of structural units having an acetyl group (acetyl group amount) in the polyvinyl acetal resin is 0.1 mol%, and the preferable upper limit is 20 mol%. By setting the amount of acetyl groups to 0.1 mol% or more, the flexibility of the resin can be improved and the adhesive strength to the current collector can be made sufficient, and by setting the amount of acetyl groups to 20 mol% or less, By doing so, the resistance to the electrolyte can be improved and short circuits caused by elution into the electrolyte can be prevented. A more preferable lower limit of the amount of acetyl groups is 1 mol%, a more preferable upper limit is 15 mol%, an even more preferable lower limit is 2 mol%, and an even more preferable upper limit is 10 mol%.
In addition, in this specification, the acetyl group amount means the content of the structural unit which has an acetyl group with respect to the whole polyvinyl acetal resin.

In the above polyvinyl acetal resin, the ratio of the content of structural units having an alkylene oxide group to the content of structural units having a hydroxyl group (content of structural units having an alkylene oxide group/content of structural units having a hydroxyl group) is , preferably 0.0003 to 1.2. By setting it within the above range, the ion transfer number can be increased while maintaining properties such as adhesiveness and hygroscopicity. More preferably, it is 0.01 to 0.8.
In addition, in the above polyvinyl acetal resin, the total amount of the content of the structural units having a hydroxyl group and the content of the structural units having an alkylene oxide group (content of the structural units having a hydroxyl group + the content of the structural units having an alkylene oxide group) content) is preferably 17 to 40 mol%. By setting it within the above range, the ion transfer number can be increased while maintaining properties such as adhesiveness and hygroscopicity. More preferably, it is 20 to 37 mol%. A more preferable lower limit is 23 mol%, and an even more preferable upper limit is 35 mol%.

The polyvinyl acetal resin may have an ionic functional group other than an alkylene oxide group. The ionic functional group is at least one selected from the group consisting of carboxyl group, sulfonic acid group, sulfinic acid group, sulfenic acid group, phosphoric acid group, phosphonic acid group, amino group, and salts thereof. Functional groups are preferred. Among these, carboxyl groups, sulfonic acid groups, and salts thereof are more preferred, and sulfonic acid groups and salts thereof are particularly preferred. Since the polyvinyl acetal resin has an ionic functional group, the active material and the conductive additive can have particularly excellent dispersibility in the composition for an all-solid-state battery.
Note that the above-mentioned salts include sodium salts, potassium salts, and the like.

The preferred lower limit of the degree of polymerization of the polyvinyl acetal resin is 250, and the upper limit is 5,000. By setting the degree of polymerization to 250 or more, industrial availability becomes easy. By setting the degree of polymerization to 5000 or less, it becomes possible to lower the solution viscosity and sufficiently disperse the active material. The preferable lower limit of the degree of polymerization is 300, the preferable upper limit is 4,000, the more preferable lower limit is 400, and the more preferable upper limit is 3,000.

The content of the polyvinyl acetal resin in the composition for an all-solid-state battery of the present invention is not particularly limited, but the preferable lower limit is 0.2% by weight, and the preferable upper limit is 5% by weight. By setting the content of the polyvinyl acetal resin to 0.2% by weight or more, the adhesive strength to the current collector can be improved, and by setting the content to 5% by weight or less, the discharge capacity of the all-solid-state battery can be improved. can be done. More preferably, it is 0.5 to 3% by weight.

The polyvinyl acetal resin is obtained by acetalizing polyvinyl alcohol with an aldehyde.
In particular, the method for producing the polyvinyl acetal resin includes a method in which polyvinyl alcohol having a structural unit having the alkylene oxide group is prepared in advance and then acetalized. Other examples include a method of acetalizing polyvinyl alcohol that does not have a structural unit having the alkylene oxide group, and then adding a moiety that will become the structural unit having the alkylene oxide group.

As a method for producing polyvinyl alcohol having a structural unit having an alkylene oxide group, for example, after copolymerizing an alkylene oxide group-containing monomer and a vinyl ester such as vinyl acetate, the resulting copolymer is Examples include a method in which an acid or alkali is added to an alcohol solution to saponify it.
Further, the polyvinyl alcohol having a structural unit having an alkylene oxide group preferably has a degree of saponification of 80.0 to 99.9 mol%. By setting it within the above range, it becomes possible to achieve both flexibility of the obtained electrode and resistance to the electrolytic solution. A more preferable lower limit of the degree of saponification is 85.0 mol%, an even more preferable lower limit is 88.0 mol%, a more preferable upper limit is 99.8 mol%, an even more preferable upper limit is 98.0 mol%, and an especially preferable upper limit is 95 mol%. .0 mol%.

As a method for producing polyvinyl alcohol having a structural unit having an alkylene oxide group, for example, after copolymerizing a hydroxyalkyl vinyl ether containing an oxyalkylene group and vinyl acetate, an alcohol solution of the obtained copolymer is added. Examples include a method of saponification by adding an acid or an alkali. In addition to the above-mentioned hydroxyalkyl vinyl ethers, poly(alkylene glycol) vinyl ethers such as dialkylene glycol vinyl ether and trialkylene glycol monovinyl ether may also be used.
Further, examples of the method for adding the moiety corresponding to R ² of the structural unit represented by the above formula (2) include a method of changing the type of the alkyl vinyl ether.

Polyvinyl alcohol that does not have a structural unit having an alkylene oxide group can be obtained, for example, by saponifying a copolymer of vinyl ester and alkylene. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and the like. Among them, vinyl acetate is preferred from the viewpoint of economy.

The polyvinyl alcohol may be one copolymerized with an alkylenically unsaturated monomer within a range that does not impair the effects of the present invention. Examples of the alkylenically unsaturated monomer include unsaturated carboxylic acid, acrylonitrile methacrylonitrile, acrylamide, methacrylamide, trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, acrylamide-2-methylpropane. Examples include sulfonic acid and its sodium salt. Examples of the unsaturated carboxylic acids include acrylic acid, methacrylic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride).
Examples of the alkylenically unsaturated monomers include ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroalkylene, and vinyl sulfone. Examples include sodium acid, sodium allylsulfonate, and the like.
Additionally, terminal-modified polyvinyl alcohol obtained by copolymerizing a vinyl ester monomer such as vinyl acetate with alkylene in the presence of a thiol compound such as thiol acetic acid or mercaptopropionic acid and saponifying the copolymerization may also be used. Can be done.

The polyvinyl alcohol may be a saponified copolymer of the vinyl ester and α-olefin. Furthermore, the above ethylenically unsaturated monomer may be copolymerized to produce polyvinyl alcohol containing a component derived from the alkylenically unsaturated monomer. Additionally, terminal polyvinyl alcohol obtained by copolymerizing a vinyl ester monomer such as vinyl acetate with an α-olefin in the presence of a thiol compound such as thiol acetic acid or mercaptopropionic acid and saponifying the copolymer is also used. be able to. The α-olefin is not particularly limited, and includes, for example, methylene, alkylene, propylene, isopropylene, butylene, isobutylene, pentylene, hexylene, cyclohexylene, cyclohexylalkylene, cyclohexylpropylene, and the like.

The composition for an all-solid-state battery of the present invention may further contain a polyvinylidene fluoride resin in addition to the polyvinyl acetal resin.
By using the above-mentioned polyvinylidene fluoride resin in combination, the resistance to electrolyte solution can be further improved and the discharge capacity can be improved.

When the polyvinylidene fluoride resin is contained, the weight ratio of the polyvinyl acetal resin to the polyvinylidene fluoride resin is preferably 0.5:9.5 to 7:3.
By setting it within such a range, it is possible to provide resistance to electrolyte solutions while having adhesive strength to a current collector, which is significantly lacking in polyvinylidene fluoride.
A more preferable weight ratio of the polyvinyl acetal resin and polyvinylidene fluoride resin is 1:9 to 4:6.

The preferable lower limit of the content of the polyvinyl acetal resin in the all-solid battery composition of the present invention is 0.01 parts by weight, and the preferable upper limit is 20 parts by weight, based on 100 parts by weight of the active material and/or solid electrolyte. By setting the content of the polyvinyl acetal resin to 0.01 parts by weight or more, the adhesive force to the current collector can be improved, and by setting the content to 20 parts by weight or less, the discharge capacity of the all-solid-state battery can be improved. It becomes possible to do so.
The content of the polyvinyl acetal resin in the composition for an all-solid-state battery of the present invention has a preferable lower limit of 0.01 parts by weight and a preferable upper limit of 200 parts by weight based on 100 parts by weight of the conductive additive.
Further, the content of the entire binder in the composition for an all-solid-state battery of the present invention is not particularly limited, but the preferable lower limit is 1% by weight, and the preferable upper limit is 30% by weight. By setting the binder content to 1% by weight or more, the adhesive strength to the current collector can be improved, and by setting the content to 30% by weight or less, it is possible to improve the discharge capacity of the all-solid-state battery. becomes.

The all-solid-state battery composition of the present invention contains an organic solvent.
The organic solvent is not particularly limited as long as it can dissolve the polyvinyl acetal resin, and examples thereof include cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, toluene, isopropyl alcohol, N-methylpyrrolidone, ethanol, distilled Examples include water. Among them, N-methylpyrrolidone is preferred.
The above organic solvents may be used alone or in combination of two or more.

The content of the organic solvent in the all-solid battery composition of the present invention is not particularly limited, but the preferred lower limit is 20% by weight, and the preferred upper limit is 50% by weight. By setting the content of the organic solvent to 20% by weight or more, the viscosity can be lowered and the paste can be applied easily, and by setting the content to 50% by weight or less, unevenness may occur when the solvent is dried. can be prevented. A more preferable lower limit is 25% by weight, and a more preferable upper limit is 40% by weight.

In addition to the above-mentioned active material and/or solid electrolyte, polyvinyl acetal resin, and organic solvent, the composition for an all-solid-state battery of the present invention may optionally include a flame retardant aid, a thickener, an antifoaming agent, Additives such as leveling agents and adhesion agents may be added.

The method for producing the composition for an all-solid-state battery of the present invention is not particularly limited. Examples include methods of mixing using various mixers such as a Lee mixer, a disper, a ball mill, a blender mill, and a three-roll mixer.

The all-solid-state battery composition of the present invention is applied, for example, on a conductive substrate and then dried to form an electrode and an electrolyte layer.
An all-solid-state battery using the all-solid-state battery composition of the present invention is also an aspect of the present invention.
Various coating methods can be used to apply the all-solid battery composition of the present invention onto a conductive substrate, including, for example, an extrusion coater, a reverse roller, a doctor blade, an applicator, etc. .

According to the present invention, an all-solid-state battery that has excellent dispersibility and adhesion of active materials and electrolytes, reduces viscosity decrease and dimensional change over time, and can prevent battery deterioration and failure due to moisture absorption. A composition and an all-solid-state battery using the composition for an all-solid-state battery can be provided.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

(Synthesis of polyvinyl acetal resin A1)
Add 350 parts by weight of alkylene oxide group-containing polyvinyl alcohol A having a constitutional unit having an alkylene oxide group (ethylene oxide group) represented by the following formula (2) to 3000 parts by weight of pure water, and stir at a temperature of 90°C for about 2 hours. and dissolved. The alkylene oxide group-containing polyvinyl alcohol A has a degree of polymerization of 250, a degree of saponification of 97.8 mol%, and a content of structural units having an alkylene oxide group represented by the following formula (2) [alkylene oxide group content] 0.01 mol%, n in formula (2) is 10, R ² = single bond, R ³ = single bond.
This solution was cooled to 40°C, 230 parts by weight of hydrochloric acid with a concentration of 35% by weight was added thereto, the temperature was lowered to 5°C, 82.8 parts by weight of n-butyraldehyde was added, and this temperature was maintained. An acetalization reaction was carried out to precipitate a reaction product. Thereafter, the reaction was completed by maintaining the liquid temperature at 30° C. for 3 hours, and the mixture was neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin A1.

The obtained polyvinyl acetal resin A1 was dissolved in DMSO-d ₆ (dimethyl sulfoxaside), and the amount of hydroxyl groups, degree of acetalization, amount of acetyl groups, and alkylene oxide groups were determined using ¹³ C-NMR (nuclear magnetic resonance spectrum). The content of the structural units [alkylene oxide group content] was measured. The results showed that the amount of hydroxyl groups was 20 mol%, the degree of acetalization (degree of butyralization) was 77.75 mol%, the amount of acetyl groups was 2.24 mol%, and the content of alkylene oxide groups was 0.01 mol%.

(Synthesis of polyvinyl acetal resins A2 to A45)
Polyvinyl acetal resins A2 to A45 were synthesized in the same manner as polyvinyl acetal resin A1, except that the polyvinyl alcohol (type) and n-butyraldehyde (added amount) were used as shown in Table 1.

(Synthesis of polyvinyl acetal resin B1)
350 parts by weight of alkylene oxide group-containing polyvinyl alcohol B (degree of polymerization 250, degree of saponification 98.5 mol%) having a constitutional unit having an alkylene oxide group (propylene oxide group) represented by the following formula (3) was added to pure water. 3000 parts by weight was added and stirred at a temperature of 90° C. for about 2 hours to dissolve. In addition, the alkylene oxide group-containing polyvinyl alcohol B has a content of structural units having an alkylene oxide group [alkylene oxide group content] of 5 mol%, n = 10 in formula (3), and R ⁴ = single bond. , R ⁵ =single bond structure.
This solution was cooled to 40°C, 230 parts by weight of hydrochloric acid with a concentration of 35% by weight was added thereto, the liquid temperature was lowered to 5°C, 53.5 parts by weight of n-butyraldehyde was added, and this temperature was maintained. An acetalization reaction was carried out to precipitate a reaction product. Thereafter, the liquid temperature was maintained at 30° C. for 3 hours to complete the reaction, and the mixture was neutralized, washed with water, and dried in a conventional manner to obtain a white powder of polyvinyl acetal resin B1.

式（３）中、Ｒ^４及びＲ^５は、Ｃ及びＯからなる群より選択される少なくとも１種を有する連結基又は単結合を表し、ｎは整数を表す。なお、Ｒ^４及びＲ^５としては、Ｒ^２及びＲ³と同様のものを使用することができる。

In formula (3), R ⁴ and R ⁵ represent a linking group or a single bond having at least one selected from the group consisting of C and O, and n represents an integer. Note that as R ⁴ and R ⁵ , the same ones as R ² and R ³ can be used.

The obtained polyvinyl acetal resin B1 was dissolved in DMSO-d ₆ (dimethyl sulfoxide), and the amount of hydroxyl groups, degree of acetalization, amount of acetyl groups, and alkylene oxide group content were determined using ¹³ C-NMR (nuclear magnetic resonance spectrum). It was measured. The results showed that the amount of hydroxyl groups was 30 mol%, the degree of acetalization (degree of butyralization) was 63.5 mol%, the amount of acetyl groups was 1.5 mol%, and the content of alkylene oxide groups was 5 mol%.

(Synthesis of polyvinyl acetal resins B2 to B5)
Polyvinyl acetal resins B2 to B5 were synthesized in the same manner as polyvinyl acetal resin B1, except that the polyvinyl alcohol (type) and n-butyraldehyde (addition amount) were used as shown in Table 1.

(Synthesis of polyvinyl acetal resin C1)
350 parts by weight of unmodified polyvinyl alcohol C (degree of polymerization 400, degree of saponification 86.8 mol%) was added to 3000 parts by weight of pure water, and the mixture was stirred at a temperature of 90° C. for about 2 hours to dissolve. This solution was cooled to 40°C, 230 parts by weight of hydrochloric acid with a concentration of 35% by weight was added thereto, the temperature was lowered to 5°C, 61.8 parts by weight of n-butyraldehyde was added, and this temperature was maintained. An acetalization reaction was carried out to precipitate a reaction product. Thereafter, the reaction was completed by maintaining the liquid temperature at 30° C. for 3 hours, and the mixture was neutralized, washed with water, and dried by a conventional method to obtain a white powder of polyvinyl acetal resin C1.
Table 1 shows the amount of hydroxyl groups, degree of acetalization, and amount of acetyl groups of the obtained polyvinyl acetal resin C1.

(Example 1)
(Preparation of composition for all-solid-state battery)
To 20 parts by weight of the resin solution containing the obtained polyvinyl acetal resin A1 (polyvinyl acetal resin: 2.5 parts by weight), 50 parts by weight of lithium cobalt oxide (Cellseed C-5H, manufactured by Nihon Kagaku Kogyo Co., Ltd.) as an active material, As conductivity imparting agents, 5 parts by weight of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black) and 26 parts by weight of N-methylpyrrolidone were added. Thereafter, the mixture was mixed using an Awatori Rentaro manufactured by Shinky Co., Ltd. to obtain a composition for an all-solid-state battery.

(Examples 2 to 40, Comparative Examples 1 to 11)
An all-solid-state battery composition was obtained in the same manner as in Example 1, except that the polyvinyl acetal resin (resin type and amount added) shown in Table 2 was used.

<Evaluation>
The following evaluations were performed on the all-solid-state battery compositions obtained in Examples and Comparative Examples. The results are shown in Table 2.

(1) Adhesion (peel force)
The all-solid-state battery compositions obtained in Examples and Comparative Examples were evaluated for adhesion to aluminum foil.
An electrode composition was coated on aluminum foil (thickness: 20 μm) so that the film thickness after drying was 20 μm, and dried to obtain a test piece in which an electrode was formed in the form of a sheet on the aluminum foil.
This sample was cut into pieces 1 cm long and 2 cm wide, and using AUTOGRAPH (Shimadzu Corporation, "AGS-J"), the electrode sheet was pulled up while fixing the test piece until the electrode sheet was completely peeled off from the aluminum foil. After measuring the required peeling force (N), it was judged based on the following criteria.
○: Peeling force is over 8.0N △: Peeling force is 5.0 to 8.0N
×: Peeling force is less than 5.0N

(2) Dispersibility (surface roughness)
The surface roughness Ra of the test piece obtained in the above "(1) Adhesion" was measured based on JIS B 0601 (1994), and the surface roughness of the electrode was evaluated using the following criteria. Note that it is generally believed that the higher the dispersibility of the active material, the lower the surface roughness.
○: Ra is less than 5 μm △: Ra is 5 μm or more and 9 μm or less ×: Ra is more than 9 μm

(3) Viscosity stability over time The paste viscosity of the all-solid battery compositions obtained in Examples and Comparative Examples was measured using a B-type viscometer. The viscosity was measured on the day of paste production and one week later, and the rate of change in viscosity over time ([viscosity after one week/viscosity on the day of production] x 100) was evaluated according to the following criteria. It is generally believed that the higher the viscosity stability, the lower the rate of change in viscosity over time.
〇: Rate of change in viscosity over time is less than 1000% ×: Rate of change in viscosity over time is 1000% or more

(4) Electrode resistance measurement Regarding the electrode sheet obtained in the above "(1) Adhesiveness", the electrode resistance value was measured using an electrode resistance measuring device (manufactured by Hioki Electric Co., Ltd.), and evaluated according to the following criteria.
○: Electrode resistance value is less than 120Ω/sq △: Electrode resistance value is 120 to 150Ω/sq
×: Electrode resistance value exceeds 150Ω/sq

(5) Dimensional stability The electrode sheet obtained in "(1) Adhesiveness" above (dimensions of main surface: length 1 cm, width 2 cm) was allowed to stand at 80°C for 24 hours, and the area of the main surface before and after standing was The rate of change was measured and evaluated based on the following criteria.
○: Area change rate is 90% or more △: Area change rate is 80% or more but less than 90% ×: Area change rate is less than 80%

(6) Hygroscopicity (moisture content)
The electrode sheet obtained in "(1) Adhesiveness" above was left to stand for 24 hours in a constant temperature and humidity chamber at a temperature of 25°C and a relative humidity of 80%, and the moisture content was calculated from the weight change before and after standing. It was evaluated based on the following criteria.
○: Moisture content is less than 3% ×: Moisture content is 3% or more

According to the present invention, an all-solid-state battery that has excellent dispersibility and adhesion of active materials and electrolytes, reduces viscosity decrease and dimensional change over time, and can prevent battery deterioration and failure due to moisture absorption. A composition and an all-solid-state battery using the composition for an all-solid-state battery can be provided.

Claims (6)

An all-solid-state battery composition containing an active material and/or a solid electrolyte, a binder, and an organic solvent,
The binder contains polyvinyl acetal resin,
The polyvinyl acetal resin includes a structural unit having an alkylene oxide group, the content of the structural unit having the alkylene oxide group is 0.01 to 20 mol%, the amount of hydroxyl groups is 16 to 32 mol%, and the degree of polymerization is An all-solid-state battery composition characterized by having a molecular weight of 250 to 5,000. The all-solid-state battery composition according to claim 1, wherein the polyvinyl acetal resin has an acetalization degree of 20 to 80 mol%. 3. The all-solid battery composition according to claim 1, wherein the polyvinyl acetal resin has an acetyl group content of 0.1 to 20 mol%. 4. The composition for an all-solid-state battery according to claim 1, which contains 0.01 to 20 parts by weight of polyvinyl acetal resin based on 100 parts by weight of the active material and/or solid electrolyte. The composition for an all-solid-state battery according to claim 1, further comprising a polyvinylidene fluoride resin. An all-solid-state battery comprising the all-solid-state battery composition according to claim 1, 2, 3, 4, or 5.