JP6459691B2 - All solid state secondary battery - Google Patents

Description

  The present invention relates to an all solid state secondary battery such as an all solid state lithium ion secondary battery.

  In recent years, secondary batteries such as lithium-ion batteries have been used in various applications such as small-sized electric power storage devices for home use, electric motorcycles, electric vehicles, and hybrid electric vehicles in addition to portable terminals such as portable information terminals and portable electronic devices. Demand is increasing.

  As the use expands, further improvements in the safety of secondary batteries are required. In order to ensure safety, a method of preventing liquid leakage and a method of using a solid electrolyte instead of a flammable organic solvent electrolyte are effective.

  As a solid electrolyte, a polymer solid electrolyte using polyethylene oxide or the like is known (Patent Document 1), but the polymer solid electrolyte is a combustible material. As a solid electrolyte, an inorganic solid electrolyte made of an inorganic material has also been proposed (Patent Document 2, etc.). Compared to a polymer solid electrolyte, an inorganic solid electrolyte is a solid electrolyte made of an inorganic substance and is a nonflammable substance, and has a very high safety compared to a commonly used organic solvent electrolyte. As described in Patent Document 2, development of an all-solid secondary battery having high safety using an inorganic solid electrolyte is progressing.

  The all solid state secondary battery has an inorganic solid electrolyte layer as an electrolyte layer between a positive electrode and a negative electrode. In Patent Document 3 and Patent Document 4, all the solid electrolyte layers formed by a method (coating method) in which a slurry composition for a solid electrolyte layer containing solid electrolyte particles and a solvent is applied on a positive electrode or a negative electrode and dried. A solid lithium secondary battery is described. When forming an electrode or an electrolyte layer by a coating method, it is necessary that the viscosity and fluidity of a slurry composition containing an active material and an electrolyte are within the range of conditions for coating. On the other hand, additives such as a binder other than the active material and the electrolyte are important for the electrode and the electrolyte layer formed by applying the slurry composition and then drying the solvent in order to develop the characteristics as a battery. Therefore, in patent document 5, it is proposed to use an acrylate polymer for a binder.

Japanese Patent No. 4134617 JP 59-151770 A JP 2009-176484 A JP 2009-2111950 A International Publication No. 2011/105574

  However, according to the study of the present inventor, in the all solid lithium secondary battery described in Patent Documents 3 and 4, the ion conductivity inside the solid electrolyte layer and inside the active material layer is not sufficient. In some cases, capacity characteristics and cycle characteristics are insufficient, and Patent Document 5 proposes an all-solid secondary battery with good battery characteristics. However, a battery with higher characteristics is required.

  An object of this invention is to provide the all-solid-state secondary battery with a favorable battery characteristic.

  As a result of intensive studies, the present inventors have found that the above object can be achieved by including two types of solid electrolyte particles having different particle diameter ranges and a binder having a specific structure in the solid electrolyte layer. It came to be completed.

That is, according to the present invention,
(1) An all-solid secondary battery having 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 between these positive and negative electrode active material layers, wherein the thickness of the solid electrolyte layer The solid electrolyte layer has a particle diameter of 10 to 40% by weight of particles having a particle diameter of 0.1 μm or more and less than 1.0 μm, and a particle diameter of 60 to less than 20 μm. An all-solid secondary battery comprising solid electrolyte particles containing 90 wt% and a binder containing a polymer having a gel structure;
(2) The all-solid-state secondary battery according to (1), wherein the solid electrolyte particles are sulfide glass composed of Li ₂ S and P ₂ S ₅ ,
(3) The all-solid-state secondary battery according to (1) or (2), wherein the binder includes 10 to 90 wt% of the polymer having the gel structure.
(4) The all-solid-state secondary battery according to any one of (1) to (3), wherein the polymer having the gel structure is an acrylate polymer.

  According to the present invention, a solid electrolyte battery having good charge / discharge performance can be obtained by including two types of solid electrolyte particles having different particle diameter ranges and a binder having a specific structure in the solid electrolyte layer. This is because the solid electrolyte layer can be densified by combining two types of solid electrolyte particles having different particle diameter ranges, so that the number of contact points and the contact area between the solid electrolyte particles increase. This seems to be because an all-solid secondary battery having a low internal resistance can be provided. In addition, according to the present invention, in order to develop high battery performance using solid electrolyte particles having a specific particle size, an all-solid secondary with low internal resistance can be obtained by using a binder containing a polymer having a gel structure. A battery can be provided.

(All-solid secondary battery)
The all solid state secondary battery of the present invention 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 between these positive and negative electrode active material layers. The solid electrolyte layer has a thickness of 2 to 20 μm, a particle diameter of 10 to 40 wt% of particles having a particle diameter of 0.1 μm or more and less than 1.0 μm, and a particle diameter of 1.0 μm or more to less than 20 μm. The solid electrolyte particle containing 60-90 wt% and the binder containing the polymer which has a gel structure are contained. The positive electrode has a positive electrode active material layer on the current collector, and the negative electrode has a negative electrode active material layer on the current collector. Hereinafter, (1) the solid electrolyte layer, (2) the positive electrode active material layer, and (3) the negative electrode active material layer will be described in this order.

(1) Solid electrolyte layer The solid electrolyte layer used in the present invention has a thickness of 2 to 20 μm, particles having a particle diameter of 0.1 μm or more and less than 1.0 μm, 10 to 40 wt%, and a particle diameter of 1.0 μm. As mentioned above, the solid electrolyte particle which contains 60-90 wt% of particles less than 20 micrometers, and the binder containing the polymer which has a gel structure are contained.
The solid electrolyte layer is formed by applying and drying a slurry composition for a solid electrolyte layer containing solid electrolyte particles and a binder on a positive electrode active material layer or a negative electrode active material layer described later. The slurry composition for a solid electrolyte layer is produced by mixing solid electrolyte particles, a binder, an organic solvent, and other components added as necessary.

(Solid electrolyte particles)
The solid electrolyte is used in the form of particles. Since the solid electrolyte particles are those that have undergone a pulverization step, they are not completely spherical but irregular. In general, the size of the fine particles is measured by a method of measuring the scattered light by irradiating the laser light to the particles. In this case, the particle diameter is a value assuming that the shape of one particle is spherical. When a plurality of particles are measured together, the proportion of particles having a corresponding particle size can be expressed as a particle size distribution. The solid electrolyte particles forming the solid electrolyte layer are often shown as an average particle diameter as measured by this method.

  In the solid electrolyte layer, reducing the resistance of ion conduction is effective for improving battery performance. The ionic conduction resistance of the solid electrolyte layer is greatly influenced by the particle diameter of the solid electrolyte particles. In general, the ion transfer resistance inside the solid electrolyte particles is smaller than the transfer resistance between the particles. However, if the average particle size of the solid electrolyte particles is too large, the voids in the electrolyte layer become large and the ion migration resistance value becomes large. On the other hand, when the average particle size is too small, there is a problem that the resistance between particles becomes too large, the viscosity of the slurry composition for the solid electrolyte layer becomes high, and the thickness control of the solid electrolyte layer becomes difficult. Therefore, it is necessary to set the average particle size within an appropriate range, but the battery performance is improved by controlling not only the average particle size but also the particle size distribution state within a specific range.

  In the present invention, particles having a particle diameter of 0.1 μm or more and less than 1.0 μm are combined in a proportion of 10 to 40 wt%, and particles of 1.0 μm or more and less than 20 μm are combined in a ratio of 90 to 60 wt%. Since the particles can be densified, the internal resistance can be reduced.

  In the present invention, the solid electrolyte particles may have a single particle size distribution, or a mixture of a plurality of types of solid electrolyte particles having different average particle diameters to obtain solid electrolyte particles having a multimodal particle size distribution. Particles having a size of 0.1 μm or more and less than 1.0 μm may be 10 to 40 wt%, and particles having a size of 1.0 μm or more and less than 20 μm may be 90 to 60 wt%.

  When the particle size distribution of the solid electrolyte particles is unimodal, the average particle size is preferably 0.5 to 10 μm. When the average particle diameter of the solid electrolyte particles is in the above range, a slurry composition for a solid electrolyte layer having good dispersibility and coating property can be obtained.

  The solid electrolyte particles are not particularly limited as long as they have lithium ion conductivity, but preferably contain a crystalline inorganic lithium ion conductor or an amorphous inorganic lithium ion conductor.

Examples of crystalline inorganic lithium ion conductors include Li ₃ N, LIICON (Li ₁₄ Zn (GeO ₄ ) ₄ ), perovskite type Li _0.5 La _0.5 TiO ₃ , LIPON (Li _{3 + y} PO _4-x N _x ), Thio-LISICON (Li _3.25 Ge _0.25 P _0.75 S ₄ ) and the like.

The amorphous inorganic lithium ion conductor is not particularly limited as long as it contains S (sulfur atom) and has ion conductivity (sulfide solid electrolytic particles). Here, when the all-solid secondary battery in the present invention is an all-solid lithium secondary battery, as the sulfide solid electrolyte material to be used, Li ₂ S and sulfides of elements of Groups 13 to 15 are used. What uses the raw material composition containing this can be mentioned. Examples of a method for synthesizing a sulfide solid electrolyte material using such a raw material composition include an amorphization method. Examples of the amorphization method include a mechanical milling method and a melt quenching method, and among them, the mechanical milling method is preferable. This is because according to the mechanical milling method, processing at room temperature is possible, and the manufacturing process can be simplified.

Examples of the Group 13 to Group 15 elements include Al, Si, Ge, P, As, and Sb. Specific examples of the sulfides of elements belonging to Group 13 to Group 15 include Al ₂ S ₃ , SiS ₂ , GeS ₂ , P ₂ S ₃ , P ₂ S ₅ , As ₂ S ₃ , and Sb _2. S ₃ etc. can be mentioned. Among these, in the present invention, it is preferable to use a Group 14 or Group 15 sulfide. In particular, in the present invention, a sulfide solid electrolyte material using a raw material composition containing Li ₂ S and a sulfide of an element belonging to Group 13 to Group 15 is Li ₂ S—P ₂ S _5. The material is preferably a Li ₂ S—SiS ₂ material, a Li ₂ S—GeS ₂ material or a Li ₂ S—Al ₂ S ₃ material, and more preferably a Li ₂ S—P ₂ S ₅ material. This is because Li ion conductivity is excellent.

  Moreover, it is preferable that the sulfide solid electrolyte material in this invention has bridge | crosslinking sulfur. It is because ion conductivity becomes high by having bridge | crosslinking sulfur. Furthermore, when the sulfide solid electrolyte material has cross-linked sulfur, the reactivity with the positive electrode active material is usually high, and a high resistance layer is likely to occur. However, in the present invention, since two types of solid electrolyte particles having different particle diameter ranges are used at a specific ratio, the generation of a high resistance layer can be suppressed, and as a result, the internal resistance of the all-solid secondary battery is reduced. The effects of the present invention can be sufficiently exhibited. Note that “having bridging sulfur” can also be determined by taking into consideration, for example, a measurement result by a Raman spectrum, a raw material composition ratio, a measurement result by NMR, and the like.

The molar fraction of Li ₂ S in the Li ₂ S—P ₂ S ₅ material or the Li ₂ S—Al ₂ S ₃ material is, for example, from the viewpoint of obtaining a sulfide solid electrolyte material having crosslinked sulfur more reliably. It is preferable to be in the range of 50 to 74%, particularly in the range of 60 to 74%.

  The sulfide solid electrolyte material in the present invention may be sulfide glass, or may be crystallized sulfide glass obtained by heat-treating the sulfide glass. The sulfide glass can be obtained, for example, by the above-described amorphization method. Crystallized sulfide glass can be obtained, for example, by heat-treating sulfide glass.

In particular, in the present invention, the sulfide solid electrolyte material is preferably a crystallized sulfide glass represented by Li ₇ P ₃ S ₁₁ . This is because the Li ion conductivity is particularly excellent. As a method for synthesizing Li ₇ P ₃ S ₁₁ , for example, a sulfide glass is synthesized by mixing Li ₂ S and P ₂ S ₅ at a molar ratio of 70:30 and amorphizing with a ball mill. Li ₇ P ₃ S ₁₁ can be synthesized by heat-treating the obtained sulfide glass at 150 ° C. to 360 ° C.

(binder)
The binder is for binding solid electrolyte particles to form a solid electrolyte layer. As a binder, it is known from Patent Document 5 that an acrylate polymer is suitable. Although it is preferable to use an acrylate polymer as a binder from the standpoint that the withstand voltage can be increased and the energy density of the all-solid-state secondary battery can be increased, there is a demand for higher performance.

  The acrylate polymer can be obtained by a solution polymerization method or an emulsion polymerization method. The polymer usually obtained is a linear polymer and is soluble in an organic solvent. When such a polymer is used as a binder, it is dissolved in an organic solvent and used as a binder.

  In the present invention, a polymer having a gel structure is used as a binder, but an acrylate polymer is preferably used as the polymer having a gel structure.

  An acrylate-based polymer is a polymer containing an acrylate or methacrylate (hereinafter sometimes abbreviated as “(meth) acrylate”) and a repeating unit (polymerized unit) obtained by polymerizing these derivatives. , (Meth) acrylate homopolymers, copolymers of (meth) acrylates, and copolymers of (meth) acrylates with other monomers copolymerizable with the (meth) acrylates.

  Examples of (meth) acrylates include acrylic acid such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, and benzyl acrylate. Alkyl esters; acrylic acid alkoxyalkyl esters such as 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate; acrylics such as 2- (perfluorobutyl) ethyl acrylate and 2- (perfluoropentyl) ethyl acrylate 2- (perfluoroalkyl) ethyl acid; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and t-butyl methacrylate, 2-ethylhexyl methacrylate Methacrylic acid alkyl esters such as lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate and benzyl methacrylate; 2- (methacrylic acid 2- (perfluorobutyl) ethyl methacrylate and 2- (perfluoropentyl) ethyl methacrylate 2- ( Perfluoroalkyl) ethyl; Among these, in the present invention, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, acrylic acid due to high adhesion to the solid electrolyte. Preferred are alkyl acrylates such as 2-ethylhexyl and benzyl acrylate; alkoxyalkyl acrylates such as -2-methoxyethyl acrylate and -2-ethoxyethyl acrylate.

  The content ratio of the monomer unit derived from (meth) acrylate in the acrylate polymer is usually 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more. In addition, the upper limit of the content ratio of the monomer unit derived from (meth) acrylate in the acrylate polymer is usually 100% by mass or less, and preferably 99% by mass or less.

  The acrylate polymer may be a copolymer of (meth) acrylate and a monomer copolymerizable with the (meth) acrylate. Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; two or more carbon-carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate. Carboxylic acid esters having a double bond; styrene monomers such as styrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, hydroxymethyl styrene, α-methyl styrene, divinylbenzene; acrylamide Amide monomers such as methacrylamide, N-methylolacrylamide and acrylamide-2-methylpropanesulfonic acid; α, β-unsaturated nitrification of acrylonitrile, methacrylonitrile, etc. Compound; Olefin such as ethylene and propylene; Diene monomer such as butadiene and isoprene; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; Methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, etc. Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole. Among these, styrene monomers, amide monomers, and α, β-unsaturated nitrile compounds are preferable from the viewpoint of affinity for organic solvents. The content of the copolymerizable monomer in the acrylate polymer is usually 40% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less.

  The binder used in the present invention includes a polymer having a gel structure. An indicator of having a gel structure is the gel fraction. The gel fraction is a value indicating the weight ratio of the components insoluble in the organic solvent because the polymer chains are bonded or entangled, and is a polymer gel having a gel structure in the present invention. The fraction is 50 to 95%, preferably 70 to 85%. If the gel fraction is too small, it tends to flow at high temperatures. Moreover, when the gel fraction is too high, the binding force as a binder may be reduced.

  In the present invention, in order to give the polymer contained in the binder a gel structure, generally a method of copolymerizing a compound capable of functioning as a crosslinking agent or a monomer capable of forming a self-crosslinking structure upon polymerization of the polymer Is mentioned.

  In order to adjust the gel fraction to a predetermined range, it is preferable to copolymerize the crosslinking agent as described above. Examples of the crosslinking agent include monomers having two or more double bonds. Examples thereof include polyfunctional acrylate compounds such as polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and ethylene glycol dimethacrylate, and polyfunctional aromatic compounds such as divinylbenzene. A polyfunctional acrylate compound such as ethylene glycol dimethacrylate is preferred.

  Although the usage-amount of a crosslinking agent changes with the kinds, Preferably it is 0.01-5 mass parts with respect to 100 mass parts of total amounts of a monomer, More preferably, it is 0.05-1 mass part.

  Examples of monomers that can easily form a self-crosslinking structure include diene monomers such as butadiene and isoprene, and unsaturated nitrile compounds such as acrylonitrile. A method of copolymerizing acrylonitrile is preferable.

In the present invention, the use of the polymer having the gel structure and the polymer not having the gel structure as the binder can improve the coatability of the slurry. The ratio of the polymer having a gel structure is 10 to 90 wt% of the total with the polymer having no gel structure. If the ratio of the polymer not having the gel structure is too large, the characteristics of the polymer having the gel structure are difficult to be exhibited, so that the battery performance is deteriorated.
In addition, as the polymer having no gel structure, in the above-mentioned acrylate polymer, a compound that can function as a crosslinking agent or a monomer that can form a self-crosslinking structure is not copolymerized at the time of polymerization of the polymer, that is, Those having no gel structure can be used.

  As a method for producing the acrylate polymer, any method of polymerization in a dispersion system such as a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization method, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used.

  Examples of the polymerization initiator used for polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Organic peroxides, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like.

  The glass transition temperature (Tg) of the binder is preferably −50 to 25 ° C., more preferably −45 from the viewpoint of obtaining an all-solid secondary battery having excellent strength and flexibility and high output characteristics. -15 ° C, particularly preferably -40 to 5 ° C. The glass transition temperature of the binder can be adjusted by combining various monomers.

  From the viewpoint of suppressing the increase in the resistance of the solid electrolyte layer by inhibiting the movement of lithium while maintaining the binding property between the solid electrolyte particles, the content of the binder in the slurry composition for the solid electrolyte layer, Preferably it is 0.1-10 mass parts with respect to 100 mass parts of solid electrolyte particles, More preferably, it is 0.5-7 mass parts, Most preferably, it is 0.5-5 mass parts.

(Organic solvent)
Examples of the organic solvent include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ethers such as dimethyl ether, methyl ethyl ether, diethyl ether, and cyclopentyl methyl ether; ethyl acetate and acetic acid And esters such as butyl. These solvents can be used singly or in combination of two or more, and can be appropriately selected and used from the viewpoint of drying speed and environment. Among them, in the present invention, from the viewpoint of easiness of drying of the slurry, the fragrance It is preferable to use a nonpolar solvent selected from group hydrocarbons.

  The content of the organic solvent in the solid electrolyte layer slurry composition is determined from the viewpoint of obtaining good coating properties while maintaining the dispersibility of the solid electrolyte particles in the solid electrolyte layer slurry composition. Preferably it is 10-700 mass parts with respect to 100 mass parts of particle | grains, More preferably, it is 30-500 mass parts.

  In addition to the above components, the solid electrolyte layer slurry composition may contain components having functions of a dispersant, a leveling agent, and an antifoaming agent as other components added as necessary. These components are not particularly limited as long as they do not affect the battery reaction.

(Dispersant)
Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. A dispersing agent is selected according to the solid electrolyte particle to be used. The content of the dispersant in the slurry composition for the solid electrolyte layer is preferably within a range that does not affect the battery characteristics. Specifically, the content is 10 parts by mass or less with respect to 100 parts by mass of the solid electrolyte particles.

(Leveling agent)
Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs when the slurry composition for the solid electrolyte layer is applied to the surface of the positive electrode active material layer or the negative electrode active material layer, which will be described later. Can be improved. The content of the leveling agent in the solid electrolyte layer slurry composition is preferably in a range that does not affect the battery characteristics, and specifically, is 10 parts by mass or less with respect to 100 parts by mass of the solid electrolyte particles.

(Defoamer)
Examples of the antifoaming agent include mineral oil antifoaming agents, silicone antifoaming agents, and polymer antifoaming agents. An antifoaming agent is selected according to the solid electrolyte particle to be used. The content of the antifoaming agent in the solid electrolyte layer slurry composition is preferably in a range that does not affect the battery characteristics, and specifically, 10 parts by mass or less with respect to 100 parts by mass of the solid electrolyte particles.

(2) 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 containing a positive electrode active material, solid electrolyte particles, and a positive electrode binder to the surface of a current collector, which will be described later, and drying. It is formed. The positive electrode active material layer slurry composition is produced by mixing a positive electrode active material, solid electrolyte particles, a positive electrode binder, an organic solvent, and other components added as necessary.

(Positive electrode active material)
The positive electrode active material is a compound that can occlude and release lithium ions. The positive electrode active material is roughly classified into those made of inorganic compounds and those made of organic compounds.

Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. As the transition metal, Fe, Co, Ni, Mn and the like are used. Specific examples of inorganic compounds used in the positive electrode active material include lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO ₄ ; TiS ₂ , TiS ₃ , non- Transition metal sulfides such as crystalline MoS ₂ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ It is done. These compounds may be partially element-substituted.

  Examples of the positive electrode active material made of an organic compound include polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, and N-fluoropyridinium salts. The positive electrode active material may be a mixture of the above inorganic compound and organic compound.

  The average particle size of the positive electrode active material used in the present invention is such that the all-solid-state secondary battery having a large charge / discharge capacity can be obtained from the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, and the positive electrode active material layer From the viewpoint of easy handling of the slurry composition for use and easy handling when producing the positive electrode, it is usually 0.1 to 50 μm, preferably 1 to 20 μm. The average particle size can be determined by measuring the particle size distribution by laser diffraction.

(Solid electrolyte particles)
The same solid electrolyte particles as those exemplified in the solid electrolyte layer can be used.

  The weight ratio of the positive electrode active material to the solid electrolyte particles is preferably positive electrode active material: solid electrolyte particles = 90: 10 to 50:50, more preferably positive electrode active material: solid electrolyte particles = 60: 40 to 80:20. is there. When the weight ratio of the positive electrode active material is too small, the amount of the positive electrode active material in the battery is reduced, leading to a decrease in capacity as a battery. On the other hand, if the weight ratio of the solid electrolyte particles is too small, sufficient conductivity cannot be obtained, and the positive electrode active material cannot be used effectively, leading to a decrease in capacity as a battery.

(Binder for positive electrode)
As the binder for the positive electrode, those exemplified for the solid electrolyte layer can be used.

  The content of the positive electrode binder in the positive electrode active material layer slurry composition is 100 mass parts of the positive electrode active material from the viewpoint of preventing the positive electrode active material from falling off the electrode without inhibiting the battery reaction. On the other hand, it is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass.

  The organic solvent in the positive electrode active material layer slurry composition and other components added as necessary can be the same as those exemplified for the solid electrolyte layer. The content of the organic solvent in the positive electrode active material layer slurry composition is preferably based on 100 parts by mass of the positive electrode active material from the viewpoint of obtaining good coating properties while maintaining the dispersibility of the solid electrolyte. Is 20 to 80 parts by mass, more preferably 30 to 70 parts by mass.

  In addition to the above components, the positive electrode active material layer slurry composition may contain additives that exhibit various functions, such as a conductive agent and a reinforcing material, as other components added as necessary. These 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 usually includes carbon powders such as acetylene black, carbon black and graphite, and fibers and foils of various metals.

(Reinforcing material)
As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used.

(3) Negative electrode active material layer The negative electrode active material layer contains a negative electrode active material.

(Negative electrode active material)
Examples of the negative electrode active material include carbon allotropes such as graphite and coke. The negative electrode active material composed of the allotrope of carbon can also be used in the form of a mixture with a metal, a metal salt, an oxide, or the like or a cover. Moreover, as a negative electrode active material, lithium alloys, such as oxides and sulfates, such as silicon, tin, zinc, manganese, iron, nickel, lithium metal, Li-Al, Li-Bi-Cd, Li-Sn-Cd, Lithium transition metal nitride, silicon, etc. can be used. In the case of a metal material, a metal foil or a metal plate can be used as an electrode as it is, but it may be in the form of particles.

  In this case, the negative electrode active material layer is formed by applying a slurry composition for a negative electrode active material layer containing a negative electrode active material, solid electrolyte particles, and a negative electrode binder to the surface of a current collector, which will be described later, and drying. The slurry composition for a negative electrode active material layer is produced by mixing a negative electrode active material, solid electrolyte particles, a negative electrode binder, an organic solvent, and other components added as necessary. The solid electrolyte particles, the organic solvent, and other components added as necessary in the slurry composition for the negative electrode active material layer can be the same as those exemplified for the positive electrode active material layer. .

  When the negative electrode active material is in the form of particles, the average particle size of the negative electrode active material is usually 1 to 50 μm, preferably 15 to 30 μm, from the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics.

  The weight ratio of the negative electrode active material to the solid electrolyte particles is preferably negative electrode active material: solid electrolyte particles = 90: 10 to 50:50, more preferably negative electrode active material: solid electrolyte particles = 60: 40 to 80:20. is there. If the weight ratio of the negative electrode active material is too small, the amount of the negative electrode active material in the battery is reduced, leading to a decrease in capacity as a battery. On the other hand, if the weight ratio of the solid electrolyte particles is too small, sufficient conductivity cannot be obtained and the negative electrode active material cannot be used effectively, leading to a reduction in capacity as a battery.

(Binder for negative electrode)
When the negative electrode active material is in the form of particles, those exemplified for the solid electrolyte layer can be used as the negative electrode binder.

  When the negative electrode active material is in a particulate form, the content of the negative electrode binder in the slurry composition for the negative electrode active material layer can prevent the electrode active material from dropping from the electrode without inhibiting the battery reaction. From 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass with respect to 100 parts by mass of the negative electrode active material.

(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 has electrical conductivity and is electrochemically durable, but from the viewpoint of heat resistance, for example, Metal materials such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum are preferable. Among these, aluminum is particularly preferable for the positive electrode, and copper is particularly preferable for the negative electrode. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. In order to increase the adhesive strength between the current collector and the positive and negative electrode active material layers described above, the current collector is preferably used after being subjected to a roughening treatment. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used. Further, an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and conductivity between the current collector and the positive / negative electrode active material layer.

(Production of slurry composition for solid electrolyte layer)
The solid electrolyte layer slurry composition is obtained by mixing the above-described solid electrolyte particles, a binder, an organic solvent, and other components added as necessary.

(Production of slurry composition for positive electrode active material layer)
The slurry composition for the positive electrode active material layer is obtained by mixing the positive electrode active material, the solid electrolyte particles, the positive electrode binder, the organic solvent, and other components added as necessary.

(Manufacture of slurry composition for negative electrode active material layer)
The slurry composition for the negative electrode active material layer is obtained by mixing the negative electrode active material, the solid electrolyte particles, the negative electrode binder, the organic solvent, and other components added as necessary.

  The method for mixing the slurry composition is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a bead mill, a planetary mixer, a sand mill, a roll mill, and a planetary kneader may be used. From the viewpoint of suppressing aggregation of solid electrolyte particles, a planetary mixer and a ball mill Alternatively, a method using a bead mill is preferable.

  The viscosity of the slurry composition for a solid electrolyte layer produced as described above is 10 to 500 mPa · s, preferably 15 to 400 mPa · s, more preferably from the viewpoint of improving the dispersibility and coating property of the slurry composition. Is 20 to 300 mPa · s. If the viscosity of the slurry composition is too low, the slurry composition for the solid electrolyte layer tends to sag. On the other hand, when the viscosity of the slurry composition is too high, it is difficult to reduce the thickness of the solid electrolyte layer.

  The viscosity of the slurry composition for a positive electrode active material layer and the slurry composition for a negative electrode active material layer produced as described above is from 3000 to 50000 mPa · s, from the viewpoint of improving the dispersibility and coatability of the slurry composition. Preferably it is 4000-30000 mPa * s, More preferably, it is 5000-100000 mPa * s. If the viscosity of the slurry composition is too low, the active material and solid electrolyte particles in the slurry composition will easily settle. Moreover, when the viscosity of this slurry composition is too high, the uniformity of a coating film will be lost.

(All-solid secondary battery)
The all solid state secondary battery of the present invention 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 between these positive and negative electrode active material layers. The thickness of the solid electrolyte layer is 2 to 20 μm, preferably 3 to 15 μm, more preferably 5 to 12 μm. When the thickness of the solid electrolyte layer is in the above range, the internal resistance of the all-solid secondary battery can be reduced. If the thickness of the solid electrolyte layer is too thin, the all-solid secondary battery is likely to be short-circuited. Moreover, when the thickness of the solid electrolyte layer is too thick, the internal resistance of the battery increases.

  The positive electrode in the all-solid-state secondary battery of the present invention is manufactured by applying the positive electrode active material layer slurry composition onto a current collector and drying to form a positive electrode active material layer. Moreover, the negative electrode in the all-solid-state secondary battery of this invention can be used as it is, when using metal foil. When the negative electrode active material is in the form of particles, the negative electrode active material layer slurry composition is applied onto a current collector different from the positive electrode current collector and dried to form a negative electrode active material layer. Manufactured. Next, the solid electrolyte layer slurry composition is applied on the formed positive electrode active material layer or negative electrode active material layer and dried to form a solid electrolyte layer. And an all-solid-state secondary battery element is manufactured by bonding together the electrode which did not form a solid electrolyte layer, and the electrode which formed said solid electrolyte layer.

  The method for applying the slurry composition for the positive electrode active material layer and the slurry composition for the negative electrode active material layer to the current collector is not particularly limited. For example, the doctor blade method, the dip method, the reverse roll method, the direct roll method, the gravure method It is applied by the extrusion method, brush coating or the like. The amount to be applied is not particularly limited, but is such an amount that the thickness of the active material layer formed after removing the organic solvent is usually 5 to 300 μm, preferably 10 to 250 μm. The drying method is not particularly limited, and examples thereof include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying conditions are usually adjusted so that the organic solvent volatilizes as quickly as possible within a speed range in which stress concentration occurs and the active material layer cracks or the active material layer does not peel from the current collector. Furthermore, you may stabilize an electrode by pressing the electrode after drying. Examples of the pressing method include, but are not limited to, a mold press and a calendar press.

  The drying temperature is a temperature at which the organic solvent is sufficiently volatilized. Specifically, from the viewpoint that a good active material layer can be formed without thermal decomposition of the positive and negative electrode binders, 50 to 250 ° C is preferable, and 80 to 200 ° C is more preferable. Although it does not specifically limit about drying time, Usually, it is performed in the range for 10 to 60 minutes.

  The method for applying the slurry composition for the solid electrolyte layer to the positive electrode active material layer or the negative electrode active material layer is not particularly limited, and the current collection of the slurry composition for the positive electrode active material layer and the slurry composition for the negative electrode active material layer described above is performed. The gravure method is preferable from the viewpoint that a thin solid electrolyte layer can be formed. The amount to be applied is not particularly limited, but is such an amount that the thickness of the solid electrolyte layer formed after removing the organic solvent is 2 to 20 μm, preferably 3 to 15 μm. The drying method, drying conditions, and drying temperature are also the same as those of the positive electrode active material layer slurry composition and the negative electrode active material layer slurry composition described above.

  Furthermore, you may pressurize the laminated body which bonded together the electrode which formed said solid electrolyte layer, and the electrode which did not form a solid electrolyte layer. The pressurizing method is not particularly limited, and examples thereof include a flat plate press, a roll press, and a CIP (Cold Isostatic Press). The pressure for press-pressing is preferably 5 to 700 MPa, more preferably from the viewpoint that the resistance at each interface between the electrode and the solid electrolyte layer, and further, the contact resistance between particles in each layer is reduced to show good battery characteristics. Is 7 to 500 MPa. Note that the solid electrolyte layer and the active material layer may be compressed by pressing, and may be thinner than before pressing. When pressing is performed, the thickness of the solid electrolyte layer and the active material layer in the present invention may be such that the thickness after pressing is in the above range.

  There is no particular limitation on whether the positive electrode active material layer or the negative electrode active material layer is coated with the slurry composition for the solid electrolyte layer, but the solid electrolyte layer slurry is applied to the active material layer having the larger particle diameter of the electrode active material to be used. It is preferable to apply the composition. When the particle diameter of the electrode active material is large, irregularities are formed on the surface of the active material layer. Therefore, the irregularities on the surface of the active material layer can be reduced by applying the slurry composition. Therefore, when the electrode formed with the solid electrolyte layer and the electrode not formed with the solid electrolyte layer are bonded and laminated, the contact area between the solid electrolyte layer and the electrode is increased, and the interface resistance can be suppressed. .

  The obtained all-solid-state secondary battery element is put into a battery container as it is or wound or folded according to the shape of the battery, and sealed to obtain an all-solid-state secondary battery. If necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate or the like can be placed in the battery container to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

  Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to these examples. Each characteristic is evaluated by the following method. Note that “parts” and “%” in this example are “parts by mass” and “mass%”, respectively, unless otherwise specified.

<Measurement of thickness of solid electrolyte layer>
According to JIS K5600-1-7: 1999, the cross-section of the solid electrolyte layer of the all-solid-state secondary battery after pressing is set to 5000 times by using a scanning electron microscope (S-4700, manufactured by Hitachi High-Tech Fielding Co., Ltd.). Ten points were randomly measured and calculated from the average value.

<Particle size measurement>
In accordance with JIS Z8825-1: 2001, the particle size was measured with a laser analyzer (Laser diffraction particle size distribution analyzer SALD-3100 manufactured by Shimadzu Corporation).

<Battery characteristics: Output characteristics>
A 5-cell all solid state secondary battery was charged to 4.3 V by a constant current method of 0.1 C, and then discharged to 3.0 V at 0.1 C to obtain a 0.1 C discharge capacity a. Thereafter, the battery was charged to 4.3 V at 0.1 C, and then discharged to 3.0 V at 10 C to obtain a 10 C discharge capacity b. Using the average value of the five cells as a measured value, the capacity retention represented by the ratio (b / a (%)) of the electric capacity between 10C discharge capacity b and 0.1C discharge capacity a was determined.

<Battery characteristics: Charging / discharging cycle characteristics>
Using the obtained all-solid-state secondary battery, the battery was charged at a constant current until it reached 4.2 V by a method of constant current constant voltage charging at 25 ° C. and 0.5 C, and then charged at a constant voltage. A charge / discharge cycle was carried out to discharge to 3.0 V at a constant current of 5 C. The charge / discharge cycle was performed up to 50 cycles, and the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity was determined as the capacity retention rate. The larger the value, the smaller the capacity loss due to repeated charging / discharging, that is, the smaller the internal resistance, so that the deterioration of the active material and the binder can be suppressed, and the charge / discharge cycle characteristics are excellent.

Example 1
<Production of polymer having gel structure>
In a glass container with a stirrer, 55 parts of ethyl acrylate, 45 parts of butyl acrylate, 1 part of ethylene glycol dimethacrylate as a crosslinking agent, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and as a polymerization initiator After adding 0.5 parts of potassium persulfate and stirring sufficiently, the mixture was heated to 70 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, cooling was started and the reaction was stopped to obtain an aqueous dispersion of a polymer having a gel structure.
And pH was adjusted to 7 using 10 wt% NaOH aqueous solution to the obtained aqueous dispersion.

  The obtained aqueous dispersion of polymer was dried using a petri dish made of PTFE to produce a film. The obtained film was immersed in THF for 24 hours and then filtered through a 200 mesh SUS wire mesh. The filtered wire mesh was dried at 100 ° C. for 1 hour, and the value obtained by dividing the weight of the wire mesh by the weight of the film was the gel fraction, and the gel fraction was 95 wt%.

  After the completion of the polymerization reaction, for the polymer aqueous dispersion whose pH is adjusted to 7, xylene is added to 100 parts by mass of the solid content of the polymer in order to exchange the unreacted monomer and solvent from water to an organic solvent. 500 parts by mass was added and distillation under reduced pressure was performed to obtain a xylene dispersion of a polymer having a gel structure.

<Production of polymer having no gel structure>
To a 5 MPa pressure vessel with a stirrer, 55 parts of ethyl acrylate, 45 parts of butyl acrylate, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator are added After sufficiently stirring, the polymerization was started by heating to 70 ° C. When the polymerization conversion rate reached 97%, cooling was started and the reaction was stopped to obtain an aqueous dispersion of polymer.
And pH was adjusted to 7 using 10 wt% NaOH aqueous solution to the obtained aqueous dispersion.

    Next, in order to exchange the unreacted monomer and the solvent from water to an organic solvent, 500 parts by mass of xylene is added to 100 parts by mass of the solid content of the polymer, and heating and vacuum distillation is performed. A xylene solution was obtained.

<Manufacture of slurry composition for positive electrode active material layer>
Sulfide glass (Li ₂ S / P ₂ S ₅ = 70 mol) composed of 100 parts of lithium cobaltate (average particle size: 11.5 μm) as the positive electrode active material and Li ₂ S and P ₂ S ₅ as the solid electrolyte particles. % / 30 mol%, the particle diameter is 0.1 μm or more, the ratio of less than 1.0 μm is 35%, the particle diameter is 1.0 μm or more, the ratio of less than 20 μm is 65%, the average particle diameter is 2.2 μm) and 150 parts 13 parts of acetylene black as a conductive agent, 2 parts of a xylene solution of a polymer having the above-described gel structure as a positive electrode binder, and 1 part of a xylene solution of a polymer not having a gel structure corresponding to a solid part After adjusting the solid content concentration to 78% with xylene as an organic solvent, the mixture was mixed for 60 minutes with a planetary mixer. Further, the solid content concentration was adjusted to 74% with xylene, and then mixed for 10 minutes to prepare a slurry composition for a positive electrode active material layer.

<Manufacture of slurry composition for negative electrode active material layer>
Sulfide glass (Li ₂ S / P ₂ S ₅ = 70 mol% / 30 mol%) composed of 100 parts of graphite (average particle size: 20 μm) as a negative electrode active material and Li ₂ S and P ₂ S ₅ as solid electrolyte particles, As a negative electrode binder, 50 parts of particles having a particle diameter of 0.1 μm or more and less than 1.0 μm are 35%, the particle diameter is 1.0 μm or more and the ratio of less than 20 μm is 65%, and the average particle diameter is 2.2 μm. Add 2 parts of the xylene solution of the polymer having the above gel structure corresponding to the solid content, 1 part of the xylene solution of the polymer not having the gel structure corresponding to the solid content, and further add xylene as the organic solvent to obtain a solid content concentration. After adjusting to 60%, it was mixed with a planetary mixer to prepare a slurry composition for a negative electrode active material layer.

<Manufacture of slurry composition for solid electrolyte layer>
As a solid electrolyte particle, a sulfide glass composed of Li ₂ S and P ₂ S ₅ (Li ₂ S / P ₂ S ₅ = 70 mol% / 30 mol%, the particle diameter is 0.1 μm or more and less than 1.0 μm) 35%, a ratio of 1.0 μm or more and less than 20 μm is 65%, and the average particle size is 2.2 μm) and 100 parts of a xylene solution of the polymer having the gel structure described above as a binder in a solid content equivalent of 2 parts A solid electrolyte layer slurry composition is prepared by adding 1 part of a xylene solution of a polymer having no structure corresponding to the solid content, further adding xylene as an organic solvent to adjust the solid content concentration to 30%, and mixing with a planetary mixer. Was prepared.

<Manufacture of all-solid-state secondary batteries>
The positive electrode active material layer slurry composition was applied to the current collector surface and dried (110 ° C., 20 minutes) to form a positive electrode active material layer having a thickness of 50 μm to produce a positive electrode. Further, the negative electrode active material layer slurry composition was applied to another current collector surface and dried (110 ° C., 20 minutes) to form a negative electrode active material layer having a thickness of 30 μm to produce a negative electrode.

  Next, the solid electrolyte layer slurry composition was applied to the surface of the positive electrode active material layer and dried (110 ° C., 10 minutes) to form a solid electrolyte layer having a thickness of 11 μm.

  The solid electrolyte layer laminated | stacked on the surface of the positive electrode active material layer and the negative electrode active material layer of the said negative electrode were bonded together, and it pressed, and obtained the all-solid-state secondary battery. The thickness of the solid electrolyte layer of the all-solid secondary battery after pressing was 9 μm. Using this battery, output characteristics and charge / discharge cycle characteristics were evaluated. The results are shown in Table 1.

(Example 2)
An all-solid secondary battery was produced and evaluated in the same manner as in Example 1 except that the slurry composition for a solid electrolyte layer obtained below was used. In addition, the thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 7 μm. The results are shown in Table 1.

<Manufacture of slurry composition for solid electrolyte layer>
As a solid electrolyte particle, a sulfide glass composed of Li ₂ S and P ₂ S ₅ (Li ₂ S / P ₂ S ₅ = 70 mol% / 30 mol%, a particle diameter of 0.1 μm or more and less than 1.0 μm is 15%. %, 1.0 μm or more, a ratio of less than 20 μm is 85%, and the average particle size is 3.5 μm) 100 parts, and xylene solution of the polymer having the gel structure of Example 1 as a binder as 2 parts in solids, The solid electrolyte of Example 2 was prepared by adding 1 part of a xylene solution of a polymer having no gel structure corresponding to the solid content, further adding xylene as an organic solvent to adjust the solid content concentration to 30%, and mixing with a planetary mixer. A slurry composition for the layer was prepared. The viscosity of the solid electrolyte layer slurry composition was 100 mPa · s.

(Example 3)
The all-solid-state secondary battery was manufactured in the same manner as in Example 1 except that the solid electrolyte layer having a thickness of 18 μm was formed in the production of the all-solid-state secondary battery using the slurry composition for solid electrolyte obtained below. Manufactured and evaluated. In addition, the thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 14 μm. The results are shown in Table 1.

<Manufacture of slurry composition for solid electrolyte layer>
Sulfide glass composed of Li ₂ S and P ₂ S ₅ as solid electrolyte particles (Li ₂ S / P ₂ S ₅ = 70 mol% / 30 mol%, the ratio of particle diameter is 0.1 μm or more and less than 1.0 μm is 20 %, 1.0 μm or more, less than 20 μm is 80%, average particle size is 3.3 μm) and 100 parts of a xylene solution of the polymer having the gel structure of Example 1 as a binder, corresponding to a solid content of 2 parts, The solid electrolyte of Example 3 was prepared by adding 5 parts of a xylene solution of a polymer having no gel structure corresponding to the solid content, further adding xylene as an organic solvent to adjust the solid content concentration to 35%, and mixing with a planetary mixer. A slurry composition for the layer was prepared.

(Example 4)
In the production of the polymer having a gel structure, a polymer having a gel structure was produced in the same manner as in Example 1 except that the monomer was changed to 70 parts of 2-ethylhexyl acrylate and 30 parts of styrene. The gel fraction of this polymer was 93 wt%. In addition, in the production of the slurry composition for a solid electrolyte layer, as a binder, a polymer having no gel structure similar to that used in Example 1, with 2 parts of the xylene solution of the polymer having the gel structure corresponding to the solid content. A slurry composition for a solid electrolyte layer was prepared in the same manner as in Example 3 except that 1 part of the xylene solution was used corresponding to the solid content. Using the obtained slurry composition for a solid electrolyte layer, an all-solid secondary battery was produced in the same manner as in Example 3 and evaluated. In addition, the thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 12 μm. The results are shown in Table 1.

(Example 5)
In the production of the slurry composition for the solid electrolyte layer, as a binder, xylene solution of a polymer having a gel structure similar to that used in Example 4 is equivalent to 2 parts in solid content, which is the same as that used in Example 1 A slurry composition for a solid electrolyte layer was prepared in the same manner as in Example 4 except that 3 parts of a xylene solution of a polymer having no gel structure was used in an amount corresponding to the solid content. Using the obtained slurry composition for a solid electrolyte layer, an all-solid secondary battery was produced and evaluated in the same manner as in Example 4. In addition, the thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 11 μm. The results are shown in Table 1.

(Comparative Example 1)
In the production of the slurry composition for the solid electrolyte layer, as in Example 1, except that the polymer having a gel structure was not used as the binder and only 7 parts of the polymer having no gel structure was used corresponding to the solid content. A slurry composition for a solid electrolyte layer was prepared. Using the obtained slurry composition for a solid electrolyte layer, an all-solid secondary battery was produced in the same manner as in Example 1 and evaluated. In addition, the thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 18 μm. The results are shown in Table 1.

(Comparative Example 2)
In the production of the slurry composition for the solid electrolyte layer, as the solid electrolyte particles, sulfide glass composed of Li ₂ S and P ₂ S ₅ (Li ₂ S / P ₂ S ₅ = 70 mol% / 30 mol%, particle diameter is 0) The solid electrolyte was the same as in Example 1 except that 100 parts of 0.1 μm or more and less than 1.0 μm was 0%, 1.0 μm or more and less than 20 μm was 100%, and the average particle size was 16 μm. A slurry composition for the layer was prepared. Using the obtained slurry composition for a solid electrolyte layer, an all-solid secondary battery was produced in the same manner as in Example 1 and evaluated. In addition, the thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 25 μm. The results are shown in Table 1.

(Comparative Example 3)
In the production of the slurry composition for the solid electrolyte layer, as the solid electrolyte particles, sulfide glass composed of Li ₂ S and P ₂ S ₅ (Li ₂ S / P ₂ S ₅ = 70 mol% / 30 mol%, particle diameter is 0) (1 μm or more, less than 1.0 μm is 100%, 1.0 μm or more, less than 20 μm is 0%, average particle size is 0.7 μm) A slurry composition for a solid electrolyte layer as in Example 1, except that 1 part of the xylene solution of the polymer was used in an amount corresponding to the solid content and 7 parts of the xylene solution of the polymer having no gel structure was used in an amount equivalent to the solid content. Adjusted. Using the obtained slurry composition for a solid electrolyte layer, an all-solid secondary battery was produced in the same manner as in Example 1 and evaluated. In addition, the thickness of the solid electrolyte layer of the all-solid-state secondary battery after pressing was 7 μm. The results are shown in Table 1.

  As shown in Table 1, an all-solid-state secondary battery having 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 between these positive and negative electrode active material layers, The thickness of the electrolyte layer is 2 to 20 μm, and the solid electrolyte layer has a particle size of 10 to 40 wt% of particles of 0.1 μm or more and less than 1.0 μm, and a particle size of 1.0 μm or more and less than 20 μm. The all-solid-state secondary battery containing solid electrolyte particles containing 60 to 90 wt% of particles and a binder containing a polymer having a gel structure was excellent in both output characteristics and charge / discharge cycle characteristics.

Claims (4)

An all-solid secondary battery having 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 between these positive and negative electrode active material layers,
The thickness of the solid electrolyte layer is 2 to 20 μm,
The solid electrolyte layer has a particle diameter of 0.1 μm or more and less than 1.0 μm, 10 to 40 wt%, a particle diameter of 1.0 μm or more and less than 20 μm, and 60 to 90 wt% of solid electrolyte particles,
An all solid state secondary battery comprising a binder containing a polymer having a gel structure. The all-solid-state secondary battery according to claim 1, wherein the solid electrolyte particles are sulfide glass composed of Li ₂ S and P ₂ S ₅ .   The all-solid-state secondary battery according to claim 1, wherein the binder contains 10 to 90 wt% of the polymer having the gel structure.   The all-solid-state secondary battery according to claim 1, wherein the polymer having a gel structure is an acrylate polymer.