阅读说明：本技术 全固体二次电池用粘结剂组合物、全固体二次电池用浆料组合物、全固体二次电池用功能层和全固体二次电池 (Binder composition for all-solid-state secondary battery, slurry composition for all-solid-state secondary battery, functional layer for all-solid-state secondary battery, and all-solid-state secondar) 是由 前田耕一郎 于 2018-12-04 设计创作，主要内容包括：本发明提供一种全固体二次电池用粘结剂组合物,其在制造全固体二次电池时的加工性优异,并且能够得到具有良好的电池特性的全固体二次电池；还提供包含该全固体二次电池用粘结剂组合物的全固体二次电池用浆料组合物；由上述全固体二次电池用浆料组合物形成的全固体二次电池用功能层；以及具有该全固体二次电池用功能层的全固体二次电池。上述全固体二次电池用粘结剂组合物包含聚合物、不饱和酸金属单体和溶剂,上述不饱和酸金属单体具有2价金属。(The invention provides a binder composition for an all-solid secondary battery, which has excellent processability in the production of the all-solid secondary battery and can obtain the all-solid secondary battery with good battery characteristics; also provided is a slurry composition for an all-solid secondary battery, which contains the binder composition for an all-solid secondary battery; a functional layer for an all-solid-state secondary battery formed from the slurry composition for an all-solid-state secondary battery; and an all-solid-state secondary battery having the functional layer for an all-solid-state secondary battery. The binder composition for all-solid secondary batteries includes a polymer, an unsaturated acid metal monomer and a solvent, wherein the unsaturated acid metal monomer has a metal having a valence of 2.)

1. A binder composition for an all-solid secondary battery, comprising a polymer, an unsaturated acid metal monomer and a solvent,

the unsaturated acid metal monomer has a metal of valence 2.

2. The binder composition for all-solid secondary batteries according to claim 1, wherein a content ratio of the unsaturated acid metal monomer is 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the polymer.

3. The binder composition for an all-solid secondary battery according to claim 1 or 2, wherein the 2-valent metal is at least 1 selected from the group consisting of calcium, magnesium, copper, and zinc.

4. The binder composition for all-solid secondary batteries according to any one of claims 1 to 3, wherein the unsaturated acid metal monomer has 2 or more double bonds.

5. The binder composition for all-solid secondary batteries according to any one of claims 1 to 4, wherein the unsaturated acid metal monomer is a (meth) acrylic acid metal monomer.

6. A slurry composition for an all-solid secondary battery, comprising the binder composition for an all-solid secondary battery according to any one of claims 1 to 5 and a solid electrolyte.

7. A functional layer for an all-solid secondary battery, which is formed from the slurry composition for an all-solid secondary battery according to claim 6.

8. An all-solid secondary battery comprising the functional layer for an all-solid secondary battery according to claim 7.

Technical Field

The present invention relates to a binder composition for an all-solid secondary battery, a slurry composition for an all-solid secondary battery, a functional layer for an all-solid secondary battery, and an all-solid secondary battery.

Background

In recent years, in addition to mobile terminals such as mobile information terminals and mobile electronic devices, secondary batteries such as lithium ion batteries are increasingly demanded for various applications such as small power storage devices for home use, electric bicycles, electric vehicles, and hybrid electric vehicles.

As such, with the expansion of applications, further improvement in the safety of secondary batteries is required. In order to ensure further improvement in the safety of the secondary battery, a method using a solid electrolyte is effective.

It is known that a polymer solid electrolyte such as polyethylene oxide can be used as the solid electrolyte (for example, refer to patent document 1). However, the polymer solid electrolyte is a combustible material, and there is still room for improvement in this respect.

As a result, an all-solid-state secondary battery has been developed which has a solid electrolyte layer containing an inorganic solid electrolyte containing an inorganic material as a nonflammable material between a positive electrode and a negative electrode and which is very safe as compared with a polymer solid electrolyte (for example, refer to patent document 2).

The solid electrolyte layer in the all-solid lithium secondary battery is formed by, for example, a method (coating method) of coating a slurry composition for a solid electrolyte layer containing solid electrolyte particles and a solvent on a positive electrode or a negative electrode and drying it (for example, refer to patent documents 3 and 4). In the case where the solid electrolyte layer is formed by the coating method, the viscosity and fluidity of the slurry composition containing the active material and the solid electrolyte need to be within the range of conditions that can be applied, and in addition to the active material and the solid electrolyte, a binder composition for an all-solid secondary battery and the like need to be added to the electrode and the solid electrolyte layer formed by drying the solvent after the slurry composition is applied, in order to exhibit the battery characteristics well. However, there is no binder composition for all-solid-state secondary batteries that can provide a slurry composition having a viscosity and a fluidity within a range of conditions that allow coating and that can provide a slurry composition with good battery characteristics.

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a binder composition for an all-solid secondary battery, which has excellent processability in the production of an all-solid secondary battery and which enables an all-solid secondary battery having good battery characteristics to be obtained.

It is another object of the present invention to provide a slurry composition for an all-solid secondary battery, which contains the binder composition for an all-solid secondary battery.

It is another object of the present invention to provide a functional layer for an all-solid-state secondary battery, which is formed from the slurry composition for an all-solid-state secondary battery.

It is another object of the present invention to provide an all-solid-state secondary battery having the functional layer for an all-solid-state secondary battery.

Means for solving the problems

As a result of intensive studies, the present inventors have found that an all-solid-state secondary battery slurry composition having excellent dispersion stability can be obtained even at a high solid content concentration of 50 mass% or more by using an unsaturated acid metal monomer having a 2-valent metal, that a functional layer for an all-solid-state secondary battery having excellent compactibility can be obtained by using the all-solid-state secondary battery slurry composition, that the resistance value of an all-solid-state secondary battery having a functional layer for an all-solid-state secondary battery can be reduced, that is, an all-solid-state secondary battery having excellent processability in the production of an all-solid-state secondary battery and having excellent battery characteristics can be obtained, and have completed the present invention.

Therefore, according to the present invention, the binder composition for an all-solid secondary battery, the slurry composition for an all-solid secondary battery, the functional layer for an all-solid secondary battery, and the all-solid secondary battery described below can be provided.

The present invention is directed to advantageously solving the above problems, and the binder composition for an all-solid secondary battery of the present invention is characterized by comprising a polymer, an unsaturated acid metal monomer having a metal of valence 2, and a solvent. By including the polymer, the unsaturated acid metal monomer having a metal of valence 2, and the solvent in the binder composition for an all-solid secondary battery as described above, the binder composition for an all-solid secondary battery has excellent processability in the production of an all-solid secondary battery, and can provide an all-solid secondary battery having good battery characteristics.

In the binder composition for an all-solid secondary battery according to the present invention, the content of the unsaturated acid metal monomer is preferably 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the polymer. By setting the content of the unsaturated acid metal monomer to 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the polymer, the effect of adding the unsaturated acid metal monomer (i.e., the effect of increasing the solid content concentration of the slurry composition for an all-solid secondary battery) can be obtained, and the agglomeration of the polymer particles (binder agglomeration) can be suppressed.

In addition, the binder composition for an all-solid secondary battery of the present invention preferably has at least 1 of the 2-valent metals selected from the group consisting of calcium, magnesium, copper, and zinc. By making the 2-valent metal at least 1 selected from the group consisting of calcium, magnesium, copper, and zinc, an all-solid secondary battery having more excellent processability and more favorable battery characteristics can be obtained when the all-solid secondary battery is manufactured.

In the binder composition for an all-solid-state secondary battery according to the present invention, the unsaturated acid metal monomer preferably has 2 or more double bonds. By providing the unsaturated acid metal monomer with 2 or more double bonds, an all-solid secondary battery having more excellent processability and more favorable battery characteristics can be obtained when the all-solid secondary battery is manufactured.

In the binder composition for an all-solid-state secondary battery according to the present invention, the unsaturated acid metal monomer is preferably a (meth) acrylic acid metal monomer. By using the (meth) acrylic acid metal monomer as the unsaturated acid metal monomer, an all-solid secondary battery having more excellent processability and more favorable battery characteristics can be obtained when the all-solid secondary battery is manufactured.

The present invention is also directed to advantageously solve the above problems, and a slurry composition for an all-solid secondary battery according to the present invention is characterized by containing the binder composition for an all-solid secondary battery and a solid electrolyte. In this way, if the binder composition for an all-solid secondary battery and the solid electrolyte are contained, the dispersion stability of the slurry composition for an all-solid secondary battery can be improved.

In addition, in order to advantageously solve the above problems, the present invention provides a functional layer for an all-solid-state secondary battery, which is formed from the slurry composition for an all-solid-state secondary battery. Thus, if the slurry composition for an all-solid secondary battery is used, the pressing performance of the functional layer for an all-solid secondary battery can be improved.

In addition, in order to advantageously solve the above problems, an all-solid-state secondary battery according to the present invention is characterized by having the functional layer for an all-solid-state secondary battery. Thus, if the functional layer for an all-solid-state secondary battery is provided, the resistance value of the all-solid-state secondary battery can be reduced.

Effects of the invention

According to the present invention, a binder composition for an all-solid secondary battery, which is excellent in processability in the production of an all-solid secondary battery and can provide an all-solid secondary battery having good battery characteristics, can be obtained; a slurry composition for an all-solid secondary battery, which contains the binder composition for an all-solid secondary battery; a functional layer for an all-solid-state secondary battery formed from the slurry composition for an all-solid-state secondary battery; and an all-solid-state secondary battery having the functional layer for an all-solid-state secondary battery.

Detailed Description

(Binder composition for all-solid-state secondary batteries)

The binder composition for all-solid-state secondary batteries according to the present invention will be described below. The binder composition for an all-solid secondary battery is characterized by comprising a polymer, an unsaturated acid metal monomer and a solvent, wherein the unsaturated acid metal monomer has a metal having a valence of 2.

The solid content concentration of the binder composition for a solid electrolyte battery used in the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5.6% by mass or more, and preferably 40% by mass or less, more preferably 15% by mass or less, and still more preferably 7% by mass or less. When the solid content concentration of the binder composition for a solid electrolyte battery is 1% by mass or more, a slurry that can be easily coated can be obtained. In addition, if the solid content concentration of the binder composition for a solid electrolyte battery is 40 mass% or less, the handling such as weighing can be easily performed.

In the binder composition for an all-solid secondary battery of the present invention, when the polymer is present in the aqueous dispersion, it is necessary to exchange water for a solvent in an organic solvent. The solvent exchange can be carried out by a known method, for example, by adding an aqueous dispersion of a polymer and an organic solvent to a rotary evaporator, reducing the pressure, and carrying out the solvent exchange and dehydration at a predetermined temperature.

In addition, the amount of water in the organic solvent containing the polymer after the solvent exchange (the amount of water in the binder composition) is preferably less than 1000ppm, more preferably less than 500ppm, still more preferably less than 100ppm, yet more preferably 95ppm or less, particularly preferably 90ppm or less, and most preferably 85ppm or less.

The binder composition for an all-solid secondary battery of the present invention can be used for at least 1 of a positive electrode active material layer, a negative electrode active material layer, or a solid electrolyte layer. The positive electrode has a positive electrode active material layer on a current collector, and the negative electrode has a negative electrode active material layer on a current collector. In addition, the positive electrode active material layer and the negative electrode active material layer may be collectively referred to as an electrode active material layer.

< polymers >

For example, in the case where the binder composition for an all-solid secondary battery is used for the solid electrolyte layer, the polymer contained in the binder composition for an all-solid secondary battery of the present invention may bind the solid electrolytes contained in the solid electrolyte layer to each other to form the solid electrolyte layer.

The polymer contained in the binder composition for an all-solid secondary battery of the present invention is preferably a particulate polymer obtained by polymerizing or copolymerizing a monomer composition.

[ particulate Polymer ]

The average particle diameter of the particulate polymer is preferably 0.1 μm or more, more preferably 0.15 μm or more, and preferably 1 μm or less, more preferably 0.70 μm or less. This is because if the average particle diameter of the particulate polymer is 0.1 μm or more and 1 μm or less, the number of contact points between the solid electrolyte particles and the contact area increase, and as a result, the internal resistance becomes small. The average particle diameter of the particulate polymer is a number average particle diameter that can be determined by measuring the particle size distribution by laser refraction.

The glass transition temperature of the particulate polymer is preferably 0 ℃ or lower, more preferably-10 ℃ or lower, particularly preferably-32 ℃ or lower, preferably-60 ℃ or higher, more preferably-50 ℃ or higher, and still more preferably-43 ℃ or higher. When the glass transition temperature of the particulate polymer is 0 ℃ or lower, the phenomenon of excessive glass transition temperature and insufficient adhesive force can be suppressed. Further, if the glass transition temperature of the particulate polymer is-60 ℃ or higher, the battery performance can be suppressed from being lowered at low temperatures.

The type of the particulate polymer is not particularly limited, and preferred examples thereof include a conjugated diene polymer, a (meth) acrylate polymer, and the like.

[ [ conjugated diene polymer ] ]

The conjugated diene polymer is not particularly limited as long as it is a conjugated diene monomer unit obtained by polymerizing a conjugated diene monomer, and may be any of a conjugated diene homopolymer and a conjugated diene copolymer.

The conjugated diene polymer may be a conjugated diene homopolymer or a conjugated diene copolymer, each of which is used alone or in combination of 2 or more.

Homopolymers of conjugated dienes

The conjugated diene homopolymer is not particularly limited as long as it is a polymer obtained by polymerizing only a conjugated diene monomer, and examples thereof include commercially used and usual polymers such as polybutadiene, polyisoprene, polycyanobutadiene, and polypentadiene.

The conjugated diene homopolymer may be used alone in 1 kind, or 2 or more kinds may be used in combination at an arbitrary ratio.

Among these, polybutadiene and polyisoprene are preferable, and polybutadiene is more preferable, from the viewpoint of easy availability.

Examples of the conjugated diene monomer constituting the conjugated diene monomer unit in the conjugated diene homopolymer include 1, 3-butadiene, isoprene, 2, 3-dimethyl-1, 3-butadiene, 1, 3-pentadiene, 1, 3-hexadiene, chloroprene, and cyanobutadiene. The conjugated diene monomer may be used alone in 1 kind, or 2 or more kinds may be used in combination at an arbitrary ratio.

Among these, 1, 3-butadiene and isoprene are preferable, and 1, 3-butadiene is more preferable, from the viewpoint of easy availability.

Here, the polymerization method of the conjugated diene polymer is not particularly limited, and may be appropriately selected according to the purpose of use.

Conjugated diene copolymer

The conjugated diene copolymer is not particularly limited as long as it is a copolymer containing at least a conjugated diene monomer unit (monomer unit composed of a conjugated diene monomer). As the conjugated diene monomer constituting the conjugated diene monomer unit, the same monomers as those used for polymerization of the above-mentioned conjugated diene homopolymer can be used.

The monomer constituting the monomer unit other than the conjugated diene monomer unit in the conjugated diene copolymer is not particularly limited as long as it is a monomer copolymerizable with the conjugated diene monomer, and examples thereof include a cyano group-containing vinyl monomer, an amino group-containing vinyl monomer, a pyridyl group-containing vinyl monomer, an alkoxy group-containing vinyl monomer, and an aromatic vinyl monomer. The above-mentioned monomer copolymerizable with the conjugated diene monomer may be used alone in 1 kind, or 2 or more kinds may be used in combination in an arbitrary ratio.

Among these, from the viewpoint of reactivity, aromatic vinyl monomers and cyano group-containing vinyl monomers are preferable, and aromatic vinyl monomers are more preferable.

When the conjugated diene copolymer is formed from an aromatic vinyl monomer and a conjugated diene monomer unit, that is, when the conjugated diene copolymer is a copolymer of an aromatic vinyl compound and a conjugated diene compound, the vinyl structure derived from the conjugated diene compound is preferably 10% by mass or more, and preferably 60% by mass or less, of the structural units derived from the conjugated diene compound.

Aromatic vinyl monomers

Examples of the aromatic vinyl monomer include styrene, α -methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2, 4-diisopropylstyrene, 2, 4-dimethylstyrene, 4-tert-butylstyrene, 5-tert-butyl-2-methylstyrene, N-dimethylaminoethylstyrene, N-diethylaminoethylstyrene and the like, and 1 kind of the aromatic vinyl monomer may be used alone or 2 or more kinds may be used in combination at an optional ratio.

Of these, styrene and α -methylstyrene are preferred.

Cyano-containing vinyl monomers

Examples of the cyano group-containing vinyl monomer include acrylonitrile and methacrylonitrile. Further, the above-mentioned cyano group-containing vinyl monomers may be used alone in 1 kind, or 2 or more kinds may be used in combination in an optional ratio.

The ratio of the monomer unit derived from the conjugated diene monomer and the monomer unit derived from the monomer copolymerizable with the conjugated diene monomer in the conjugated diene copolymer can be appropriately selected depending on the purpose, but is preferably 70/30 to 100/0, more preferably 80/20 to 100/0 in terms of the mass ratio of "monomer unit derived from the conjugated diene monomer/monomer unit derived from the monomer copolymerizable with the conjugated diene monomer". When the mass ratio of the "monomer unit derived from a conjugated diene monomer/the monomer unit derived from a monomer copolymerizable with the conjugated diene monomer" is 70/30 to 100/0, an all-solid secondary battery having more excellent processability in the production of the all-solid secondary battery and more excellent battery characteristics can be obtained.

[ [ (meth) acrylate-based Polymer ] ]

The (meth) acrylate polymer is not particularly limited as long as it is a polymer obtained by polymerizing a (meth) acrylate monomer.

In the present specification, "(meth) acrylate" means acrylate or methacrylate.

- (meth) acrylate-based monomer-

Examples of the (meth) acrylate monomer include: alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, 2-ethylhexyl acrylate, 2-methoxyethyl acrylate, and 2-ethoxyethyl acrylate; 2- (perfluoroalkyl) ethyl acrylates such as 2- (perfluorobutyl) ethyl acrylate and 2- (perfluoropentyl) ethyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, tridecyl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and 2-ethylhexyl methacrylate; 2- (perfluoroalkyl) ethyl methacrylate such as 2- (perfluorobutyl) ethyl methacrylate and 2- (perfluoropentyl) ethyl methacrylate; benzyl acrylate; benzyl methacrylate, and the like. The (meth) acrylate monomer may be used alone in 1 kind, or 2 or more kinds may be used in combination at an arbitrary ratio.

Among these, n-butyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate are preferable from the viewpoint of reactivity.

The monomer constituting the monomer unit other than the (meth) acrylate monomer unit ((monomer unit composed of a (meth) acrylate monomer) in the (meth) acrylate polymer is not particularly limited as long as it is a monomer copolymerizable with the (meth) acrylate monomer, and examples thereof include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid, amide monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α -methylstyrene, and divinylbenzene, amide monomers such as acrylamide, N-methylolacrylamide, and acrylamido-2-methylpropanesulfonic acid, α -unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile, olefins such as ethylene and propylene, diene monomers such as butadiene and isoprene, halogen atom-containing monomers such as vinyl chloride and vinylidene chloride, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, vinyl ethers such as methyl vinyl ether, vinyl ethers such as butyl ether, methyl vinyl ketone, ethyl ketone, vinyl pyrrolidone monomer, vinyl ketone monomer, vinyl pyrrolidone, vinyl ether monomer, vinyl ketone.

In addition, among monomers constituting monomer units other than the (meth) acrylate monomer unit (monomer unit constituted by a (meth) acrylate monomer) in the (meth) acrylate polymer, a monomer having a plurality of functional groups can be used as a crosslinking agent. Examples of monomers that can be used as the crosslinking agent include: carboxylic acid esters having 2 or more carbon-carbon double bonds such as Ethylene Glycol Dimethacrylate (EGDMA), diethylene glycol dimethacrylate, trimethylolpropane triacrylate, etc.; glycidyl group-containing monomers such as glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether.

Here, when a proper amount of a crosslinking agent such as Ethylene Glycol Dimethacrylate (EGDMA) is added, the entire system can be prevented from being hardened, the adhesive force of the adhesive can be prevented from being lowered, and the occurrence of breakage and chipping can be prevented.

[ Process for producing particulate Polymer ]

The method for producing the particulate polymer is not particularly limited, and examples thereof include emulsion polymerization, suspension polymerization, and the like.

Among these, the emulsion polymerization method is preferred in view of easy control of particle size. In the emulsion polymerization method, for example, the monomer may be emulsion-polymerized in an aqueous dispersion of the seed particles.

The polymerization method may be any of a batch method, a semi-continuous method, and a continuous method. In addition, as the polymerization pressure, polymerization temperature and polymerization time, known conditions can be adopted.

[ [ emulsion polymerization method ] ]

The emulsion polymerization process is generally carried out according to conventional methods. For example, the method is carried out according to the method described in "laboratory chemistry lecture" volume 28 (publisher: Wanshan, Japan chemical society Co., Ltd.). Namely, the emulsion polymerization method is a method as follows: a solution of (i) water, (ii) additives such as a dispersant, an emulsifier, and a crosslinking agent, (iii) a polymerization initiator, and (iv) a monomer is added to a closed vessel equipped with a stirrer and a heating device to have a predetermined composition, and the monomer composition in the vessel is stirred to emulsify the monomer in water, stirred, and heated to initiate polymerization. Alternatively, the emulsion polymerization method may be a method in which the monomer composition is emulsified and then charged into a closed vessel to initiate the reaction in the same manner. In the emulsion polymerization, various additives such as a surfactant (emulsifier), a polymerization initiator, a molecular weight regulator (chain transfer agent), a chelating agent, an electrolyte, and a deoxidizer, which are generally used in the emulsion polymerization reaction, can be used as auxiliary materials for polymerization.

Surfactants (emulsifiers) -

As the surfactant (emulsifier) used in the emulsion polymerization method, any surfactant can be used as long as a desired particulate polymer can be obtained, and examples thereof include sodium Dodecylbenzenesulfonate (DBS), sodium lauryl sulfate, sodium dodecyldiphenylether disulfonate, sodium dialkylsulfosuccinate, and the like. The surfactant may be used alone in 1 kind, or 2 or more kinds may be used in combination at an optional ratio.

The amount of the surfactant is arbitrary as long as a desired particulate polymer can be obtained, and is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the total amount of monomers used for producing the particulate polymer. If the amount of the surfactant is 0.5 parts by mass or more, emulsion polymerization can be stably performed. Further, if the amount of the surfactant is 10 parts by mass or less, the influence on the battery can be reduced.

Polymerization initiators

In addition, a polymerization initiator is generally used in the polymerization reaction. As the polymerization initiator, any polymerization initiator can be used as long as the desired particulate polymer can be obtained, and examples thereof include sodium persulfate (NaPS), Ammonium Persulfate (APS), potassium persulfate (KPS), and the like. The polymerization initiator may be used alone in 1 kind, or 2 or more kinds may be used in combination in an optional ratio.

Among these, sodium persulfate and potassium persulfate are preferable, and potassium persulfate is more preferable, from the viewpoint of suppressing the reduction in the cycle characteristics of the obtained all-solid secondary battery.

Chain transfer agents (molecular weight regulators)

Further, in the polymerization reaction, the polymerization system may contain a chain transfer agent (molecular weight regulator). examples of the chain transfer agent (molecular weight regulator) include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan, xanthate compounds such as dimethyl disulfide, and diisopropyl disulfide xanthate, terpinolene, thiuram compounds such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, and tetramethyl thiuram monosulfide, phenol compounds such as 2, 6-di-t-butyl-4-methylphenol, and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as methylene chloride, methylene bromide, and carbon tetrabromide, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, diphenylethylene, and α -methylstyrene dimer, 1 kind of the above-mentioned molecular weight regulator may be used alone, or 2 or more kinds may be used in combination at an optional ratio.

< unsaturated acid Metal monomer >

The unsaturated acid metal monomer is not particularly limited as long as it has a metal having a valence of 2, and examples thereof include (meth) acrylic acid metal monomers such as calcium dimethacrylate, magnesium dimethacrylate, copper dimethacrylate, zinc dimethacrylate, calcium diacrylate, magnesium diacrylate, copper diacrylate and zinc diacrylate.

The unsaturated acid metal monomer may be used alone in 1 kind, or 2 or more kinds may be used in combination at an arbitrary ratio.

Among these, magnesium diacrylate and copper diacrylate are preferable, and magnesium diacrylate is more preferable, from the viewpoint of water solubility.

The number of double bonds in the unsaturated acid metal monomer is preferably 2 or more, more preferably 2.

It is also presumed that the addition of the unsaturated acid metal monomer can crosslink the surface of the polymer without lowering the dispersion stability of the polymer.

The content of the unsaturated acid metal monomer is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and particularly preferably 0.3 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, particularly preferably 4 parts by mass or less, and most preferably 3 parts by mass or less, based on 100 parts by mass of the polymer. If the content of the unsaturated metal monomer is 0.01 parts by mass or more per 100 parts by mass of the polymer, the effect of adding the unsaturated acid metal monomer (the effect of increasing the solid content concentration of the slurry composition for an all-solid secondary battery) can be obtained. Further, if the content ratio of the unsaturated acid metal monomer to 100 parts by mass of the polymer is 10 parts by mass or less, a crosslinked structure is formed on the surface of the polymer particles, and thereby the aggregation of the polymer particles with each other (binder aggregation) can be suppressed.

< solvent >

The solvent contained in the binder composition for an all-solid secondary battery of the present invention is not particularly limited, and examples thereof include organic solvents having a boiling point of 100 ℃ or higher and 250 ℃ or lower.

As the organic solvent having a boiling point of 100 ℃ or higher and 250 ℃ or lower, there may be preferably mentioned, for example, aromatic hydrocarbons such as toluene (boiling point: 111 ℃) and xylene (boiling point: 144 ℃); ethers such as cyclopentyl methyl ether (boiling point: 106 ℃ C.); esters such as butyl acetate (boiling point: 126 ℃ C.), butyl butyrate (boiling point: 164 ℃ C.), and the like.

When the boiling point of the organic solvent exceeds 250 ℃, the temperature required for the drying step in the production of an electrode or the like becomes high, and thus the apparatus becomes large.

The organic solvent having a boiling point of 100 ℃ or higher and 250 ℃ or lower may be used alone in 1 kind, or 2 or more kinds may be used in combination at an optional ratio.

Among these, xylene is preferable from the viewpoint of easy availability.

In addition, as the organic solvent in the solvent exchange from water to the organic solvent, it is preferable to use the organic solvent having a boiling point of 100 ℃ or more and 250 ℃ or less as exemplified above.

When the binder composition for an all-solid secondary battery of the present invention is used, the processability in the production of an all-solid secondary battery is excellent, and an all-solid secondary battery having good battery characteristics can be obtained.

(slurry composition for all-solid-state secondary battery)

The slurry composition for an all-solid secondary battery of the present invention contains the binder composition for an all-solid secondary battery of the present invention and a solid electrolyte.

The solid content concentration of the slurry composition for an all-solid secondary battery of the present invention is preferably 40% by mass or more, more preferably 55% by mass or more, particularly preferably 60% by mass or more, most preferably 62% by mass or more, preferably 70% by mass or less, more preferably 65% by mass or less. If the solid content concentration of the slurry composition for an all-solid secondary battery is 40 mass% or more, the process of coating and drying can be facilitated, the drying time can be shortened, the amount of heat required for drying can be reduced, and the workability in the production of an all-solid secondary battery can be improved.

< solid electrolyte >

The solid electrolyte is generally in the form of particles because it is an electrolyte that has undergone a pulverization step. Here, the granular shape does not mean a perfect spherical shape but means an irregular shape.

The size of the solid electrolyte particle can be measured as an average particle diameter by a method of irradiating the particle with laser light and measuring scattered light, and the like. The particle diameter in this case is a value assuming that the shape of the particles is spherical. When a plurality of particles are measured together, the presence ratio of particles having a corresponding particle diameter can be expressed as a particle size distribution.

The average particle diameter of the solid electrolyte particles is preferably 0.3 μm or more, more preferably 0.5 μm or more, and particularly preferably 1.0 μm or more, and is preferably 1.3 μm or less, more preferably 1.2 μm or less, from the viewpoint of dispersibility and coatability of the slurry composition for a solid secondary battery. The average particle diameter of the solid electrolyte particles is a number average particle diameter that can be determined by measuring the particle size distribution by laser refraction.

The solid electrolyte is not particularly limited, and examples thereof include a crystalline inorganic lithium ion conductor, an amorphous inorganic lithium ion conductor, and the like.

In addition, the solid electrolyte can be used alone in 1, also can be used in 2 or more in an optional ratio combination.

Among these, amorphous inorganic lithium ion conductors are preferable in view of conductivity.

[ crystalline inorganic lithium ion conductor ]

The crystalline inorganic lithium ion conductor is not particularly limited, and examples thereof include L i₃N、LISICON(Li₁₄Zn(GeO₄)₄) Perovskite type L i_0.5La_0.5TiO₃Garnet type L i₇La₃Zr₂O₁₀、LIPON(Li_3+yPO_4-xN_x)、Thio-LISICON(Li_3.25Ge_0.25P_0.75S₄) And the like.

[ amorphous inorganic lithium ion conductor ]

The amorphous inorganic lithium ion conductor is not particularly limited, and L i-Si-S-O glass, L i-P-S glass, and the like can be given.

Among these, a conductor (sulfide solid electrolyte material) containing S (sulfur atom) and having ion conductivity is preferable from the viewpoint of conductivity.

Here, in the case where the all-solid secondary battery using the binder composition for an all-solid secondary battery of the present invention is an all-solid lithium secondary battery, the sulfide solid electrolyte material preferably contains L i and P amorphous sulfides, and more preferably contains L i₂S and a sulfide of a group 13 to group 15 element. Examples of a method for synthesizing a sulfide solid electrolyte material using such a raw material composition includeA mechanical polishing method, a melt quenching method, and the like. Among these, mechanical polishing is preferable because the treatment can be performed at room temperature and the production process can be simplified.

Since the amorphous sulfide containing L i and P has high lithium ion conductivity, the use of the amorphous sulfide as an inorganic solid electrolyte can reduce the internal resistance of the battery and improve the output characteristics.

From the viewpoint of reducing the internal resistance of the battery and improving the output characteristics, the amorphous sulfide containing L i and P preferably contains L i₂S and P₂S₅More preferably L i₂S∶P₂S₅L i with the molar ratio of 65: 35-85: 15₂S and P₂S₅The sulfide glass produced from the mixed raw materials of (1) and (2) further, it is preferable that L i of the amorphous sulfide containing L i and P is L i₂S∶P₂S₅L i with the molar ratio of 65: 35-85: 15₂S and P₂S₅The mixed raw material (C) is preferably L i from the viewpoint of maintaining the lithium ion conductivity in a high state₂S∶P₂S₅The molar ratio of (A) to (B) is 68: 32-80: 20.

Examples of the sulfide of an element of group 13 to group 15 include Al₂S₃、SiS₂、GeS₂、P₂S₃、P₂S₅、As₂S₃、Sb₂S₃And the like.

The sulfide of the group 13 to group 15 element may be used alone in 1 kind, or 2 or more kinds may be used in combination in an optional ratio.

Of these, group 14 or group 15 sulfides are preferable, and P is more preferable from the viewpoint of reducing the internal resistance of the battery and improving the output characteristics₂S₅。

[ [ sulfide solid electrolyte material ] ]

As a use containing L i₂S and a sulfide of an element of groups 13 to 15The sulfide solid electrolyte material of the composition includes, for example, L i₂S-P₂S₅Materials, L i₂S-SiS₂Materials, L i₂S-GeS₂Materials, L i₂S-Al₂S₃Materials, and the like.

Of these, L i is preferable from the viewpoint of excellent ion conductivity of L i₂S-P₂S₅A material.

In addition, to the extent that the ion conductivity is not lowered, other than L i described above₂S、P₂S₅In addition, the sulfide solid electrolyte material may further contain Al selected from₂S₃、B₂S₃And SiS₂At least 1 sulfide as a starting material. When the sulfide is added, the glass component in the sulfide solid electrolyte material can be stabilized.

Likewise, sulfide solid electrolyte materials other than L i₂S and P₂S₅In addition, the compound can also contain L i₃PO₄、Li₄SiO₄、Li₄GeO₄、Li₃BO₃And L i₃AlO₃At least 1 kind of lithium orthooxolate. When the lithium orthooxolate is contained, the glass component in the sulfide solid electrolyte material can be stabilized.

L i from the viewpoint of more reliably obtaining a sulfide solid electrolyte material having crosslinked sulfur₂S-P₂S₅Materials, L i₂S-SiS₂Materials, L i₂S-GeS₂Materials, L i₂S-Al₂S₃L i in sulfide solid electrolyte material of material or the like₂The mole percentage of S is preferably 50% or more, more preferably 60% or more, and preferably 74% or less.

Further, the sulfide solid electrolyte material preferably has crosslinking sulfur from the viewpoint of being able to increase ion conductivity. Here, "having crosslinking sulfur" can be determined from, for example, a measurement result by raman spectroscopy, a raw material composition ratio, a measurement result by NMR, and the like.

In addition, when the sulfide solid electrolyte material has crosslinking sulfur, the sulfide solid electrolyte material generally has high reactivity with the positive electrode active material, and a high resistance layer is easily formed. However, since the binder composition for an all-solid secondary battery generally contains a copolymer containing an aromatic vinyl compound monomer unit and a conjugated diene compound monomer unit, the effect of the present invention, that is, the generation of a high-resistance layer can be sufficiently exhibited.

The sulfide solid electrolyte material may be a sulfide glass, or may be a crystallized sulfide glass obtained by heat-treating the sulfide glass. Here, the "sulfide glass" can be obtained by, for example, the above-described amorphization method. The crystallized sulfide glass can be obtained by, for example, heat-treating sulfide glass.

From the viewpoint of ion conductivity of L i, the crystallized sulfide glass is preferably L i₇P₃S₁₁Here, as synthesis L i₇P₃S₁₁E.g. by mixing L i₂S and P₂S₅Mixing them at a molar ratio of 70: 30, crystallizing the mixture in a ball mill to synthesize a sulfide glass, and heat-treating the sulfide glass at 150 to 360 ℃ to synthesize L i₇P₃S₁₁。

(functional layer for all-solid-State Secondary Battery)

The functional layer for an all-solid secondary battery of the present invention is formed using the slurry composition for an all-solid secondary battery of the present invention, and is at least one layer, preferably all layers, of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer.

The functional layer for an all-solid secondary battery of the present invention is a solid electrolyte layer formed by applying the slurry composition for an all-solid secondary battery of the present invention on a positive electrode active material layer or a negative electrode active material layer, which will be described later, and drying the applied slurry composition.

(all-solid secondary battery)

The all-solid-state secondary battery of the present invention has the functional layer for the all-solid-state secondary battery of the present invention. That is, the all-solid-state secondary battery of the present invention is obtained by forming at least one layer of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer using the binder composition for an all-solid-state secondary battery of the present invention, and preferably by forming all the layers. Here, the all-solid-state secondary battery of the present invention generally includes a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and a solid electrolyte layer formed between these positive and negative electrode active material layers. The positive electrode has a positive electrode active material layer on a current collector, and the negative electrode has a negative electrode active material layer on a current collector. The solid electrolyte layer, the positive electrode active material layer, and the negative electrode active material layer will be described below.

< solid electrolyte layer >

In the case where the functional layer for an all-solid secondary battery of the present invention is a solid electrolyte layer, the solid electrolyte layer is formed by applying a slurry composition for a solid electrolyte layer on the surface of a current collector described later and drying the applied slurry composition. The slurry composition for a solid electrolyte layer is produced by mixing a solid electrolyte, a binder (polymer) for a solid electrolyte layer, an unsaturated acid metal monomer having a metal of valence 2, an organic solvent, and other components added as needed.

When the functional layer for an all-solid secondary battery of the present invention is not a solid electrolyte layer, the solid electrolyte layer is not particularly limited, and any of the solid electrolyte layers described in, for example, japanese patent laid-open nos. 2012 and 243476, 2013 and 143299, and 2016 and 143614 can be used.

[ solid electrolyte ]

As the solid electrolyte, the same solid electrolyte as exemplified in the slurry composition for an all-solid secondary battery can be used.

[ Binder for solid electrolyte layer ]

The binder for the solid electrolyte layer may be used to bind the solid electrolyte to form the solid electrolyte layer. The binder for the solid electrolyte layer may contain a polymer constituting a binder composition for an all-solid-state secondary battery.

[ unsaturated acid Metal monomer ]

As the unsaturated acid metal monomer, the same monomers as exemplified in the binder composition for an all-solid secondary battery can be used.

[ organic solvent ]

The organic solvent can be preferably used as "the organic solvent having a boiling point of 100 ℃ or higher and 250 ℃ or lower" exemplified in the binder composition for an all-solid secondary battery.

[ other ingredients ]

The slurry composition for a solid electrolyte layer may contain, in addition to the above components (solid electrolyte, binder for a solid electrolyte layer, unsaturated acid metal monomer, and organic solvent), additives exhibiting various functions such as a conductive agent and a reinforcing material as other components added as necessary. These additives are not particularly limited as long as they do not affect the battery reaction.

[ [ conductive agent ] ]

The conductive agent is not particularly limited as long as it can impart conductivity, and examples thereof include carbon powders such as acetylene black, carbon black, and graphite; fibers of various metals; various metal foils, and the like.

[ [ reinforcing material ] ]

As the reinforcing material, an inorganic filler or an organic filler in a spherical shape, a plate shape, a rod shape, or a fiber shape can be used.

[ [ non-conductive particles ] ]

As the non-conductive particles, there are no particular limitations, and various inorganic particles and organic particles can be used, for example.

Examples of the inorganic particles include aluminum oxide (alumina), silicon oxide, magnesium oxide, titanium oxide, and BaTiO₂Oxide particles such as ZrO and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles of silicon, diamond, or the like; insoluble ionic crystal particles such as barium sulfate, calcium fluoride, barium fluoride and the like; and clay fine particles such as talc and montmorillonite.

Examples of the organic particles include various crosslinked polymer particles such as polyethylene, polystyrene, polydivinylbenzene, a crosslinked product of a styrene-divinylbenzene copolymer, polyimide, polyamide, polyamideimide, melamine resin, phenol resin, and a benzoguanamine-formaldehyde condensate; heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramide, polyacetal, and thermoplastic polyimide.

< Positive electrode active Material layer >

In the case where the functional layer for an all-solid secondary battery of the present invention is a positive electrode active material layer, the positive electrode active material layer is formed by applying a slurry composition for a positive electrode active material layer to the surface of a current collector described later and drying the applied slurry composition. The slurry composition for a positive electrode active material layer is produced by mixing a positive electrode active material, a solid electrolyte, a binder (polymer) for a positive electrode, an unsaturated acid metal monomer having a metal with a valence of 2, an organic solvent, and other components added as needed.

When the functional layer for an all-solid-state secondary battery of the present invention is not a positive electrode active material layer, the positive electrode active material layer is not particularly limited, and any positive electrode active material layer described in, for example, japanese patent laid-open nos. 2016-.

[ Positive electrode active Material ]

The positive electrode active material is a compound capable of storing and releasing lithium ions. Examples of the positive electrode active material include a positive electrode active material formed of an inorganic compound, a positive electrode active material formed of an organic compound, and a mixture of an inorganic compound and an organic compound.

The average particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and further preferably 50 μm or less, more preferably 20 μm or less, from the viewpoints of (i) load characteristics, charge-discharge cycle characteristics, charge-discharge capacity, and other battery characteristics, (ii) treatment of the slurry composition for a positive electrode active material layer, and (iii) treatment in the production of a positive electrode. The average particle diameter of the positive electrode active material is a number average particle diameter that can be determined by measuring the particle size distribution by laser refraction.

[ [ positive electrode active material formed of inorganic compound ] ]

Examples of the positive electrode active material made of an inorganic compound include (i) a transition metal oxide, (ii) a composite oxide of lithium and a transition metal such as Fe, Co, Ni, or Mn (lithium-containing composite metal oxide), and (iii) a transition metal sulfide.

Examples of the (i) transition metal oxide include Cu₂V₂O₃Amorphous V₂O-P₂O₅、MoO₃、V₂O₅、V₆O₁₃And the like. These compounds may be partially element substituted compounds.

The lithium-containing composite metal oxide (ii) includes L iCoO₂(lithium cobaltate), L iNiO₂、LiMnO₂、LiMn₂O₄、LiFePO₄、LiFeVO₄And the like. These compounds may be partially element substituted compounds.

The transition metal sulfide (iii) may be TiS₂、TiS₃Amorphous MoS₂And the like. These compounds may be partially element substituted compounds.

[ [ positive electrode active material formed of organic compound ] ]

Examples of the positive electrode active material made of an organic compound include polyaniline, polypyrrole, polyacene, a disulfide compound, a polysulfide compound, and an N-fluoropyridinium salt.

[ solid electrolyte ]

As the solid electrolyte, the same electrolyte as exemplified in the slurry composition for an all-solid secondary battery can be used.

The mass ratio of the positive electrode active material to the solid electrolyte (positive electrode active material: solid electrolyte) is preferably 90: 10 to 50: 50, and more preferably 80: 20 to 60: 40. When the mass ratio of the positive electrode active material to the solid electrolyte is within the above range, it is possible to suppress a decrease in the mass of the positive electrode active material in the battery and a decrease in the capacity of the battery due to an excessively small mass ratio of the positive electrode active material, and it is also possible to suppress a decrease in the capacity of the battery due to an insufficient availability of conductivity and an inefficient use of the positive electrode active material due to an excessively small mass ratio of the solid electrolyte.

[ Binder for Positive electrode ]

The binder for a positive electrode is used to bind a positive electrode active material and a solid electrolyte, thereby forming a positive electrode active material layer. The binder for the positive electrode may contain a polymer constituting a binder composition for an all-solid-state secondary battery.

The content of the binder for a positive electrode in the slurry composition for a positive electrode active material layer is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 5 parts by mass or less, more preferably 4 parts by mass or less, per 100 parts by mass of the positive electrode active material, in terms of a solid content equivalent, from the viewpoint of preventing the positive electrode active material from falling off from the electrode without inhibiting the battery reaction.

[ unsaturated acid Metal monomer ]

As the unsaturated acid metal monomer, the same monomers as exemplified in the binder composition for an all-solid secondary battery can be used.

[ organic solvent ]

The organic solvent can be preferably used as "the organic solvent having a boiling point of 100 ℃ or higher and 250 ℃ or lower" exemplified in the binder composition for an all-solid secondary battery.

The content of the organic solvent in the slurry composition for a positive electrode active material layer is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and preferably 80 parts by mass or less, more preferably 70 parts by mass or less, relative to 100 parts by mass of the positive electrode active material, from the viewpoint of maintaining dispersibility of the solid electrolyte and obtaining good coating properties.

[ other ingredients ]

The slurry composition for a positive electrode active material layer may contain, as other components added as necessary, the above-mentioned conductive agent, the above-mentioned reinforcing material, the above-mentioned nonconductive particles, and other additives exhibiting various functions, in addition to the above-mentioned components (positive electrode active material, solid electrolyte, positive electrode binder, unsaturated acid metal monomer, and organic solvent). These additives are not particularly limited as long as they do not affect the battery reaction.

< negative electrode active Material layer >

In the case where the functional layer for an all-solid secondary battery of the present invention is a negative electrode active material layer, the negative electrode active material layer is formed by applying a slurry composition for a negative electrode active material layer to the surface of a current collector described later and drying the applied slurry composition. The slurry composition for a negative electrode active material layer is produced by mixing a negative electrode active material, a solid electrolyte, a binder for a negative electrode, an unsaturated acid metal monomer having a metal with a valence of 2, an organic solvent, and other components added as needed.

When the functional layer for an all-solid secondary battery of the present invention is not a negative electrode active material layer, the negative electrode active material layer is not particularly limited, and any negative electrode active material layer described in, for example, japanese patent laid-open nos. 2016-.

[ negative electrode active Material ]

Examples of the negative electrode active material include carbon allotropes such as graphite and coke, oxides or sulfates of silicon, tin, zinc, manganese, iron, nickel, and the like, metallic lithium, lithium alloys such as L i-Al, L i-Bi-Cd, L i-Sn-Cd, lithium transition metal nitrides, silicon, and the like.

When the negative electrode active material is in the form of particles, the average particle diameter of the negative electrode active material is preferably 1 μm or more, more preferably 15 μm or more, preferably 50 μm or less, and more preferably 30 μm or less, from the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and charge-discharge cycle characteristics. The average particle diameter of the negative electrode active material is a number average particle diameter that can be determined by measuring the particle size distribution by laser refraction.

[ solid electrolyte ]

As the solid electrolyte, the same electrolyte as exemplified in the slurry composition for an all-solid secondary battery can be used.

The mass ratio of the negative electrode active material to the solid electrolyte (negative electrode active material: solid electrolyte) is preferably 90: 10 to 50: 50, and more preferably 80: 20 to 60: 40. When the mass ratio of the negative electrode active material to the solid electrolyte is within the above range, it is possible to suppress a phenomenon in which the mass of the negative electrode active material in the battery decreases and the capacity of the battery decreases due to an excessively small mass ratio of the negative electrode active material, and it is also possible to suppress a phenomenon in which the conductivity cannot be sufficiently obtained and the negative electrode active material cannot be effectively used and the capacity of the battery decreases due to an excessively small mass ratio of the solid electrolyte.

[ Binder for negative electrode ]

The binder for a negative electrode is used for binding a negative electrode active material and a solid electrolyte to form a negative electrode active material layer. The binder for a negative electrode may contain a polymer constituting a binder composition for an all-solid-state secondary battery.

The content of the binder for a negative electrode in the slurry composition for a negative electrode active material layer is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 5 parts by mass or less, more preferably 4 parts by mass or less, per 100 parts by mass of the negative electrode active material, in terms of a solid content equivalent, from the viewpoint of preventing the negative electrode active material from falling off from the electrode without inhibiting the battery reaction.

[ unsaturated acid Metal monomer ]

As the unsaturated acid metal monomer, the same monomers as exemplified in the binder composition for an all-solid secondary battery can be used.

[ organic solvent ]

The organic solvent can be preferably used as "the organic solvent having a boiling point of 100 ℃ or higher and 250 ℃ or lower" exemplified in the binder composition for an all-solid secondary battery.

[ other ingredients ]

The slurry composition for a negative electrode active material layer may contain, as other components added as necessary, the above-described conductive agent, the above-described reinforcing material, the above-described nonconductive particles, and other additives exhibiting various functions, in addition to the above-described components (negative electrode active material, solid electrolyte, binder for a negative electrode, unsaturated acid metal monomer, and organic solvent). These additives are not particularly limited as long as they do not affect the battery reaction.

[ Current collector ]

The current collector used for forming the positive electrode active material layer and the negative electrode active material layer is not particularly limited as long as it is a current collector containing a material having conductivity and electrochemical durability, and from the viewpoint of heat resistance, for example, a current collector containing a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like is preferably used. The metal material may be used alone in 1 kind, or 2 or more kinds may be used in combination at an optional ratio.

Among these, a current collector containing aluminum is particularly preferable as the current collector for the positive electrode, and a current collector containing copper is particularly preferable as the current collector for the negative electrode.

The shape of the current collector is not particularly limited, and a sheet shape having a thickness of about 0.001mm to 0.5mm is preferable. In order to improve the adhesion strength with the positive electrode active material layer and the negative electrode active material layer, the current collector is preferably used after being subjected to a roughening treatment in advance. The roughening treatment may be performed by a mechanical polishing method, an electrolytic polishing method, a chemical polishing method, or the like. In the mechanical polishing method, polishing cloth paper to which polishing agent particles are fixed, whetstones, carborundum polishers, wire brushes having steel wires, and the like can be used. In addition, an intermediate layer such as a conductive adhesive layer may be formed on the surface of the current collector in order to improve the adhesion strength and conductivity between the current collector and the positive electrode active material layer/the negative electrode active material layer.

The mixing method of the slurry compositions (slurry composition for solid electrolyte layer, slurry composition for positive electrode active material layer, and slurry composition for negative electrode active material layer) is not particularly limited, and examples thereof include a method using a mixing device such as a stirring type, a vibrating type, or a rotary type.

Further, as a method for mixing the slurry compositions, there can be mentioned a method using a dispersion kneading apparatus such as a homogenizer, a ball mill, a bead mill, a planetary mixer, a sand mill, a roll mill, or a planetary kneader. Among these, a method using a planetary mixer, a ball mill, or a bead mill is preferable from the viewpoint of suppressing aggregation of the solid electrolyte.

< production of all-solid-State Secondary Battery >

The positive electrode in the all-solid secondary battery can be obtained by forming a positive electrode active material layer on a current collector. Here, the positive electrode active material layer may be formed by applying the slurry composition for a positive electrode active material layer on a current collector and drying the same.

In the case where the negative electrode active material is a metal foil or a metal plate, the negative electrode in the all-solid-state secondary battery can be used as it is. In addition, when the negative electrode active material is in the form of particles, the negative electrode active material may be formed on a current collector different from that of the positive electrode. Here, the negative electrode active material layer may be formed by, for example, applying the slurry composition for a negative electrode active material layer on a current collector different from a current collector of the positive electrode and drying the same.

Next, a slurry composition for a solid electrolyte layer is applied to the formed positive electrode active material layer or negative electrode active material layer, and dried to form a solid electrolyte layer. Then, the electrode on which the solid electrolyte layer is not formed and the electrode on which the solid electrolyte layer is formed are bonded to each other, thereby producing an all-solid secondary battery element.

The coating method of applying the slurry composition for an electrode active material layer to a current collector is not particularly limited, and examples thereof include a doctor blade method, a dipping method, a reverse roll coating method, a direct roll coating method, an gravure method, an extrusion method, a brush coating method, and the like.

The amount of the slurry composition for an electrode active material layer to be applied is not particularly limited, and the thickness of the electrode active material layer formed after removing the organic solvent is usually about 5 to 300 μm, preferably about 10 to 250 μm.

The method for drying the slurry composition for an electrode active material layer is not particularly limited, and examples thereof include (i) drying by warm air, hot air, low-humidity air, or the like, (ii) vacuum drying, and (iii) drying by irradiation with (far) infrared rays, electron beams, or the like. The drying conditions are generally adjusted within a speed range of a degree that stress concentration is not caused, cracks occur in the electrode active material layer, and the electrode active material layer is not peeled off from the current collector, so that the organic solvent is volatilized as quickly as possible.

Further, the dried electrode can be pressed to stabilize the electrode. Examples of the pressing method include, but are not limited to, die pressing, calender roll pressing, and the like.

The drying temperature is the temperature at which the organic solvent is sufficiently volatilized. Specifically, from the viewpoint of forming a good active material layer without thermal decomposition of the positive electrode binder and the negative electrode binder, the temperature is preferably 50 ℃ or higher, more preferably 80 ℃ or higher, preferably 250 ℃ or lower, and more preferably 200 ℃ or lower. The drying time is not particularly limited, and is usually 10 minutes to 60 minutes.

The method for applying the slurry composition for a solid electrolyte layer to the positive electrode active material layer or the negative electrode active material layer is not particularly limited, and the application can be performed by the same method as the above-described method for applying the slurry composition for an electrode active material layer to the current collector.

The amount of the slurry composition for a solid electrolyte layer to be applied is not particularly limited, and the thickness of the solid electrolyte layer formed after removing the organic solvent is usually about 2 to 20 μm, preferably about 3 to 15 μm.

The method of drying, the drying conditions and the drying temperature of the slurry composition for a solid electrolyte layer are the same as those of the above-described method of drying the slurry composition for an electrode active material layer.

Further, a laminate obtained by bonding an electrode having a solid electrolyte layer formed thereon and an electrode having no solid electrolyte layer formed thereon may be pressed.

The pressing method is not particularly limited, and examples thereof include flat plate pressing, roll pressing, CIP (ColdIsostatic Press), and the like.

The pressure for the pressing is preferably 5MPa or more, more preferably 7MPa or more, preferably 700MPa or less, more preferably 500MPa or less, from the viewpoint of reducing the electrical resistance at each interface between the electrode and the solid electrolyte layer, and further reducing the contact resistance between particles in each layer, thereby obtaining good battery characteristics.

The slurry composition for a solid electrolyte layer is not particularly limited to be applied to the positive electrode active material layer or to be applied to the negative electrode active material layer, and it is preferable to apply the slurry composition for a solid electrolyte layer to the active material layer having a larger particle size of the electrode active material. When the particle diameter of the electrode active material is large, irregularities are formed on the surface of the electrode active material layer, and therefore, the irregularities on the surface of the electrode active material layer can be alleviated by applying the slurry composition for a solid electrolyte layer. Therefore, when the electrode having the solid electrolyte layer formed thereon and the electrode having no solid electrolyte layer formed thereon are bonded and laminated, the contact area between the solid electrolyte layer and the electrode increases, and the interface resistance can be suppressed.

The all-solid-state secondary battery element obtained as described above is directly used to obtain an all-solid-state secondary battery according to the battery shape, or is wound, folded, or the like, placed in a battery container, and sealed to obtain an all-solid-state secondary battery.

In addition, a porous metal mesh can be added to the battery container as needed; a fuse; overcurrent prevention elements such as PTC elements; a guide plate, etc. to prevent a pressure rise and overcharge and discharge inside the battery.

The shape of the all-solid-state secondary battery may be any of coin-type, button-type, sheet-type, cylindrical-type, rectangular-type, flat-type, and the like, for example.