JP2016181472A - All-solid secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-solid secondary battery having excellent battery characteristics.SOLUTION: An all-solid secondary battery 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. Thickness of the solid electrolyte layer is 2 to 20 μm, and the solid electrolyte layer contains a binder including a particulate polymer whose average particle size is 0.1 to 1 μm.SELECTED DRAWING: None

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. An inorganic solid electrolyte made of an inorganic material has also been proposed as a solid electrolyte (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, an all-solid lithium secondary in which a solid electrolyte layer is formed by applying and drying a slurry composition for a solid electrolyte layer containing solid electrolyte particles and a solvent on a positive electrode or a negative electrode. A battery is described. When an electrode or an electrolyte layer is formed 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 that can be applied. 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 by the present inventors, 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. However, Patent Document 5 proposes an all-solid secondary battery with good battery characteristics, but a battery with higher characteristics is demanded.

  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 inventor has found that the above object can be achieved by using a binder containing a particulate polymer having a specific particle diameter, and has completed the present invention.

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 contains an all-solid-state secondary battery containing a binder containing a particulate polymer having an average particle diameter of 0.1 to 1 μm,
(2) The all-solid secondary battery according to (1), wherein the binder contains 10 to 90 wt% of the particulate polymer,
(3) The all-solid-state secondary battery according to (1) or (2), wherein the particulate polymer is an acrylate polymer containing a monomer unit derived from (meth) acrylate.
(4) The all-solid-state secondary battery according to any one of (1) to (3) obtained by using a binder composition in which the particulate polymer is dispersed in an organic solvent.

  According to the present invention, by using a particulate polymer having a specific particle size as a binder, a solid electrolyte battery with good charge / discharge performance can be obtained. This is because the use of a binder having a specific particle diameter increases the number of contact points and the contact area between the solid electrolyte particles, thereby providing an all-solid-state secondary battery having a low internal resistance. I think that the.

(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. Moreover, the thickness of a solid electrolyte layer is 2-20 micrometers, and a solid electrolyte layer contains the binder containing the particulate polymer whose average particle diameter is 0.1-1 micrometer. 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 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 Here, the binder contains a particulate polymer having an average particle diameter of 0.1 to 1 μm. 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 in the form of particles because it has been subjected to a pulverization process, but is not a perfect sphere but an indefinite shape. 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.

  The average particle diameter of the solid electrolyte particles is preferably 0.3 to 1.3 μm from the viewpoint of obtaining a slurry composition for a solid electrolyte layer having good dispersibility and coating properties. The average particle diameter of the solid electrolyte particles is a number average particle diameter that can be obtained by measuring the particle size distribution by laser diffraction.

  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 the crystalline inorganic lithium ion conductor 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 electrolyte material). 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 this invention, since the binder containing the particulate polymer which has a specific particle diameter is used, the effect of this invention that generation | occurrence | production of a high resistance layer can be suppressed can fully be 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. Here, it is preferable to use an acrylate-based polymer as a binder from the viewpoint that the withstand voltage can be increased and the energy density of the all-solid-state secondary battery can be increased, but 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.
In general, the binder uses a linear polymer in order to obtain a high binding force. However, if the binder completely covers the surface of the solid electrolyte particles, the ionic conductivity at the contact point is lowered. Therefore, in the present invention, a binder containing a particulate polymer is used.

  As the kind of polymer used for the binder, an acrylate polymer is preferable. 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, and (meth) acrylate. Specifically, a polymer containing a monomer unit derived from (a) a homopolymer of (meth) acrylate, a copolymer of (meth) acrylate, and other monomers copolymerizable with (meth) acrylate and the (meth) acrylate. And a copolymer with a monomer.

  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, due to the high adhesion to the solid electrolyte, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, acrylic acid 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, preferably 95% by mass or less.

  The acrylate polymer can 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, divinyl benzene, etc. Amide monomers such as acrylamide, methacrylamide, N-methylolacrylamide, and acrylamide-2-methylpropanesulfonic acid; α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile Olefins such as ethylene and propylene; Diene monomers such as butadiene and isoprene; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether Vinyl 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. Of these, styrene monomers, amide monomers, and α, β-unsaturated nitrile compounds are preferred from the viewpoint of solubility in organic solvents. The content of the copolymerizable monomer unit 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 particulate polymer of the present invention is a polymer that is particulate when dispersed in an organic solvent and that is also particulate when dried.

  As a method for obtaining a particulate polymer, there is a method in which a monomer is polymerized with a crosslinking agent when the polymer is emulsion-polymerized or dispersed-polymerized in an aqueous or solvent system. Moreover, in order to obtain a particulate polymer, it is preferable to copolymerize a crosslinking agent when polymerizing.

  The crosslinking agent is a monomer containing a plurality of double bonds. Examples thereof include polyfunctional acrylate compounds such as polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane trimethacrylate, and pentaerythritol tetraacrylate, and polyfunctional aromatic compounds such as divinylbenzene. A polyfunctional aromatic compound such as divinylbenzene is preferred.

  Although the usage-amount of a crosslinking agent changes with the kinds, Preferably it is 0.01-8 mass parts with respect to 100 mass parts of total amounts of a monomer, More preferably, it is 0.05-5 mass parts.

  If the addition amount of the crosslinking agent is small, when dried on the substrate, it spreads in a hemispherical shape on the substrate surface, and the area of the adhering portion spreads more than 10 times the particle size, covering the surface of the solid electrolyte particles. It is not preferable because it becomes the same state. Moreover, when there is too much addition amount of a crosslinking agent, the adhesive force of a polymer will fall and it will no longer show the function as a binder.

  The average particle diameter of the particulate polymer is 0.1 to 1 μm, preferably 0.15 to 0.70 μm. When the average particle diameter of the particulate polymer is in the above range, a solid electrolyte battery having good charge / discharge performance can be obtained. This is presumably because the use of a particulate polymer having an average particle diameter in the above range increases the number of contact points and the contact area between the solid electrolyte particles, resulting in a decrease in internal resistance. The average particle size of the particulate polymer is a number average particle size that can be determined by measuring the particle size distribution by laser diffraction.

  Further, the binder used in the present invention may contain a binder component other than the particulate polymer. The content of the particulate polymer in the binder used in the present invention is preferably 10 to 90 wt%, more preferably 20 to 80 wt%, from the viewpoint of obtaining a solid electrolyte battery with good charge / discharge performance.

  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 from the viewpoint of drying speed and environment, and among them, in the present invention, from the viewpoint of reactivity with solid electrolyte particles, ether Are preferred.

  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 the form of particles, the content of the negative electrode binder in the slurry composition for the negative electrode active material layer is determined from the viewpoint of preventing the electrode active material from dropping from the electrode without inhibiting the battery reaction. Preferably it is 0.1-5 mass parts with respect to 100 mass parts of active materials, More preferably, it is 0.2-4 mass parts.

(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 can be mentioned. From the viewpoint that aggregation of solid electrolyte particles can be suppressed, a planetary mixer, a ball mill Alternatively, a method using a bead mill is preferable.

(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 an amount such that the thickness of the solid electrolyte layer formed after removing the organic solvent is usually 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 was measured with a scanning electron microscope (S-4700, manufactured by Hitachi High-Tech Fielding Co., Ltd.) and the electrolyte layer thickness was increased 5000 times. Ten points were randomly measured and calculated from the average value.

<Particle size measurement>
According to JIS Z8825-1: 2001, a particle size (number average particle size) of 50% cumulative from the fine particle side of the cumulative particle size distribution by a laser analyzer (Laser diffraction particle size distribution measuring device SALD-3100 manufactured by Shimadzu Corporation) Was measured.

<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 5 C to obtain a 5 C discharge capacity b. Using the average value of 5 cells as a measured value, the capacity retention represented by the ratio (b / a (%)) of the electric capacity between 5C 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 constant current constant voltage charging method of 0.5 C at 25 ° 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
<Manufacture of particulate polymer>
In a 5 MPa pressure vessel with a stirrer, 30 parts of ethyl acrylate, 70 parts of butyl acrylate, 1 part of ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and After adding 0.5 parts of potassium persulfate as a polymerization initiator and stirring sufficiently, the polymerization was started by heating to 70 ° C. When the polymerization conversion rate reached 96%, cooling was started and the reaction was stopped to obtain an aqueous dispersion of particulate polymer. The average particle size was 0.24 μm.
And pH was adjusted to 7 using 10 wt% NaOH aqueous solution to the obtained aqueous dispersion.

The solid content concentration of the obtained aqueous dispersion of particulate polymer was 38 wt%. 500 parts by mass of cyclopentyl methyl ether was added to 100 parts by mass of the obtained aqueous dispersion, and the temperature of the water bath was reduced at 80 ° C. with a rotary evaporator to perform solvent exchange and dehydration operations.
An organic solvent dispersion of a particulate polymer having a water concentration of 38 ppm and a solid content concentration of 7.5 wt% was obtained by dehydration.

<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%, number average particle diameter: 0.4 μm) 150 parts, 13 parts of acetylene black as a conductive agent, 3 parts of a cyclopentylmethyl ether dispersion of particulate polymer corresponding to solid content, 60 parts of butyl acrylate and ethyl acrylate Then, 1 part of a polymer having Mw = 150,000 was copolymerized with / 40, and the solid content was adjusted to 78% with cyclopentyl methyl ether as an organic solvent, followed by mixing with a planetary mixer for 60 minutes. Further, the solid content concentration was adjusted to 74% with cyclopentyl methyl ether, 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, Number average particle size: 0.4 μm) 50 parts, 3 parts of cyclopentylmethyl ether dispersion of particulate polymer corresponding to solid content, 1 part of polymer with Mw = 150,000 obtained by copolymerizing butyl acrylate and ethyl acrylate at 60/40 The mixture was further mixed with cyclopentyl methyl ether as an organic solvent to adjust the solid concentration to 60%, and then 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>
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%, number average particle diameter: 1.2 μm, cumulative 90% particle diameter: 2.1 μm) 100 parts, 3 parts of a cyclopentyl methyl ether dispersion of a particulate polymer corresponding to the solid content, and 1 part of a polymer with Mw = 150,000 obtained by copolymerizing butyl acrylate and ethyl acrylate at 60/40 were mixed. Further, cyclopentyl methyl ether was added as an organic solvent to adjust the solid content concentration to 30%, followed by mixing with a planetary mixer to prepare a slurry composition for a solid electrolyte layer.

<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 18 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 11 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 following solid electrolyte particles were used.

In Example 2, 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%, number average particle diameter: 0.8 μm, cumulative 90% particle size: 1.8 μm) was used. The thickness of the solid electrolyte layer before pressing was 20 μm, and the thickness after pressing was 13 μm.

Example 3
The measurement was performed in the same manner as in Example 1 except that the following polymer was used as the particulate polymer.

In a 5 MPa pressure vessel with a stirrer, 20 parts of butyl acrylate, 60 parts of 2-ethylhexyl acrylate, 20 parts of styrene, 1 part of divinylbenzene (DVB) as a crosslinking agent, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 of ion-exchanged water And 0.5 part of potassium persulfate as a polymerization initiator were added and sufficiently stirred, and then 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 particulate polymer. The average particle size was 0.28 μm.
And pH was adjusted to 7 using 10 wt% NaOH aqueous solution to the obtained aqueous dispersion.

  The solid content concentration of the obtained aqueous dispersion of particulate polymer was 38 wt%. 500 parts by mass of cyclopentyl methyl ether was added to 100 parts by mass of the obtained aqueous dispersion, and the temperature of the water bath was reduced at 80 ° C. with a rotary evaporator to perform solvent exchange and dehydration operations.

An organic solvent dispersion of a particulate polymer having a water concentration of 21 ppm and a solid content concentration of 8.5 wt% was obtained by dehydration.
A solid electrolyte layer was produced in the same manner as in Example 1 using the particulate polymer. The thickness of the solid electrolyte layer before pressing was 20 μm, and the thickness after pressing was 18 μm.

(Comparative Example 1)
The particulate polymer of Example 1 was polymerized in the same manner without adding a crosslinking agent. The average particle diameter of the obtained particulate polymer was 0.32 μm. The particulate polymer was subjected to solvent exchange with cyclopentyl methyl ether to obtain a polymer solution containing no particulates, in which the particulate polymer was dissolved. A solid electrolyte layer was prepared using this polymer solution. The thickness of the solid electrolyte layer before pressing was 33 μm, and the thickness after pressing was 25 μm. A battery was prepared and tested in the same manner as in Example 1 using the above polymer.

(Comparative Example 2)
The particulate polymer of Example 3 was polymerized in the same manner without adding a crosslinking agent. The average particle diameter of the obtained particulate polymer was 0.28 μm. The particulate polymer was subjected to solvent exchange with cyclopentyl methyl ether to obtain a polymer solution containing no particulates, in which the particulate polymer was dissolved. A solid electrolyte layer was prepared using this polymer solution. The thickness of the solid electrolyte layer before pressing was 33 μm, and the thickness after pressing was 12 μm. A battery was prepared in the same manner as in Example 3 using the polymer, and the test was performed.

  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 solid electrolyte The thickness of the layer is 2 to 20 μm, and the solid electrolyte layer contains a binder containing a particulate polymer having an average particle diameter of 0.1 to 1 μm, and output characteristics and charge / discharge of an all-solid secondary battery The cycle characteristics were good.

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 is an all-solid secondary battery containing a binder containing a particulate polymer having an average particle size of 0.1 to 1 μm.   The all-solid secondary battery according to claim 1, wherein the binder contains 10 to 90 wt% of the particulate polymer.   The all-solid-state secondary battery according to claim 1, wherein the particulate polymer is an acrylate-based polymer including a monomer unit derived from (meth) acrylate.   The all-solid-state secondary battery in any one of Claims 1-3 obtained by using the binder composition formed by disperse | distributing the said particulate polymer to the organic solvent.