JP2010205449A - Electrolyte layer for all-solid secondary battery, laminate for all-solid secondary battery, and all-solid secondary battery - Google Patents

Abstract

An object of the present invention is to provide an electrolyte layer for an all-solid-state secondary battery that is made of a solid electrolyte material and a soft polymer and has high flexibility and excellent battery characteristics. Moreover, the all-solid-state secondary battery provided with the said electrolyte layer for all-solid-state secondary batteries, a positive electrode, and a negative electrode is provided.
A solid electrolyte layer for an all-solid-state secondary battery including a solid electrolyte material and a soft polymer as a binder, and the soft polymer preferably has a glass transition temperature of 15 ° C. or lower. A positive electrode, a laminate for an all solid secondary battery comprising the solid electrolyte layer for an all solid secondary battery and a negative electrode in this order, and a positive electrode and a negative electrode of the laminate for an all solid secondary battery are provided with a current collector. All-solid secondary battery.
[Selection figure] None

Description

  The present invention relates to a solid electrolyte layer for use in an all-solid secondary battery such as an all-solid lithium ion secondary battery, a laminate for an all-solid secondary battery using the same, and an all-solid secondary battery.

In recent years, the demand for secondary batteries such as high-performance lithium batteries used in personal digital assistants, portable electronic devices, small household power storage devices, motorcycles powered by motors, electric vehicles, hybrid electric vehicles, etc. has increased. Yes.
As the applications used expand, further improvements in safety and performance of secondary batteries are required. As a method for ensuring safety, it is effective to use an inorganic solid electrolyte instead of the organic solvent electrolyte.

Inorganic solid electrolytes are nonflammable in nature and are safer materials than commonly used organic solvent electrolytes. For this reason, development of an all-solid-state battery using the electrolyte and having high safety is proceeding (Patent Document 1).
An all solid state battery has a solid electrolyte layer made of an inorganic material as an electrolyte layer between a positive electrode and a negative electrode.

  Various processes for producing an all-solid battery have been proposed. A method of mixing a positive electrode active material or a negative electrode active material and a solid electrolyte material, press-molding the mixture into a pellet form, a solid electrolyte material, and a positive electrode active material A method is disclosed in which a substance, a negative electrode active material, or the like is dispersed and suspended in a solvent together with a binder, a plasticizer, and the like, and applied, molded, and fired on a substrate. (Patent Document 2)

In the latter method of coating and molding, a step of slurrying the positive or negative electrode active material with a solvent, a binder and a plasticizer, a step of slurrying a solid electrolyte material with a solvent, a binder and a plasticizer, and a current collector material A slurry is made together with a solvent, a binder and a plasticizer, and each slurry is applied and molded onto a base material such as a current collector foil to produce a green sheet, followed by a firing step to produce an all-solid battery. A technique is disclosed.
Moreover, an acrylic resin, a methacryl resin, a cellulose resin etc. are disclosed as a binder.

  However, since the all-solid-state secondary battery manufactured in the above-described process produces an all-solid-state secondary battery through the firing process, the obtained solid electrolyte layer, the positive electrode, and the negative electrode may be wound with poor flexibility. There was a problem that it was difficult. In addition, after slurrying, coating, and molding the solid electrolyte material, the positive electrode active material, and the negative electrode active material, it is necessary to burn off the binder and the plasticizer in the firing process, which increases the production process and increases the manufacturing cost. there were.

JP 59-151770 JP2007-227362

  Accordingly, an object of the present invention is to provide an electrolyte layer for an all-solid secondary battery having a high packing density of the solid electrolyte and an excellent winding property, a laminate for an all-solid secondary battery, and an all-solid secondary battery having an excellent productivity. The purpose is to provide.

The inventors of the present invention use a soft polymer as a binder when slurrying and applying a solid electrolyte material, a positive electrode active material, and a negative electrode active material when producing an all-solid-state secondary battery. It has been found that the contact between the solid electrolyte materials becomes good without developing the process, and high battery characteristics are exhibited. In addition, since the binder baking process is not performed, the production process is simplified, the production cost is reduced, and the presence of a soft polymer improves the strength and adhesion of the solid electrolyte layer, the positive electrode, and the negative electrode. I found.
Furthermore, applying a slurry to form a solid electrolyte layer, etc., and applying a soft polymer as a binder when drying, suppresses a sudden increase in viscosity of the coating film during drying and improves the drying density It has been found that it is possible to produce a good all-solid secondary battery having a high filling rate.

The present invention for solving the above-mentioned problems includes the following matters as a gist.
(1) An electrolyte layer for an all-solid-state secondary battery including a solid electrolyte material and a soft polymer.
(2) The electrolyte for an all-solid secondary battery as described in (1) above, wherein the soft polymer has a glass transition temperature of 15 ° C. or lower. (3) The positive electrode, or the all-solid-state secondary electrode described in (1) or (2) above. An all-solid-state secondary battery laminate comprising a secondary battery composition and a negative electrode in this order.
(4) The laminate for an all-solid-state secondary battery according to (3), wherein the positive polymer and the negative electrode contain the soft polymer and a solid electrolyte material.
(5) The all-solid-state secondary battery which comprises a collector in the positive electrode and negative electrode of the said laminated body for all-solid-state secondary batteries.

  ADVANTAGE OF THE INVENTION According to this invention, the laminated body for all-solid-state secondary batteries excellent in the electrolyte layer for all-solid-state secondary batteries excellent in flexibility and adhesiveness, and a high packing density and the performance can be obtained. In addition, the present invention can produce an all-solid secondary battery with excellent productivity and low cost.

The present invention will be described in detail below.
(Electrolyte layer for all-solid-state secondary battery)
The electrolyte layer for an all-solid-state secondary battery in the present invention includes a soft polymer and a solid electrolyte material. The electrolyte layer for an all-solid-state secondary battery can be obtained by applying and drying a slurry composition obtained by mixing a soft polymer composition containing a soft polymer and an organic solvent and a solid electrolyte material.
Details will be described below.

(Soft polymer)
As soft polymers, polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, ethyl acrylate / butyl acrylate / styrene copolymer, ethyl acrylate / butyl acrylate / acrylonitrile copolymer, ethyl acrylate / butyl An acrylic soft polymer which is a homopolymer of acrylic acid or a methacrylic acid derivative, such as an acrylate / acrylonitrile / glycidyl methacrylate copolymer, or a copolymer with a monomer copolymerizable therewith;
Isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene / butadiene / Diene-based soft polymers such as styrene block copolymer, isoprene / styrene block copolymer, styrene / isoprene / styrene block copolymer;
Silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer, etc. Olefinic soft polymers of
Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
Epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
Examples thereof include other soft polymers such as natural rubber, polypeptide, protein, polyester-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, and polyamide-based thermoplastic elastomer.
These soft polymers may have a cross-linked structure or may have a functional group introduced by modification.

Among these, a polymer having a glass transition temperature of 15 ° C. or lower is particularly preferable. When the glass transition temperature of the binder is 15 ° C. or lower, it is possible to increase the binding property between the solid electrolyte materials when pressure is applied to the solid electrolyte layer, thereby improving the contact area between the solid electrolyte materials. High battery performance can be obtained.
Furthermore, when the glass transition temperature is 15 ° C. or lower, when the slurry composition is applied and dried, there is no sudden increase in viscosity during drying, and the packing density is high and the contact area between the solid electrolyte materials is high. A large electrolyte layer for an all-solid-state secondary battery can be obtained.

  In the present invention, the porosity in the solid electrolyte layer is preferably low, and is preferably 10% by volume or less from the viewpoint of ionic conductivity. Further, it is more preferably 7% by volume or less, and most preferably 4% by volume or less. In order to set the porosity to 10% by volume or less, it is preferable to apply pressure.

In addition, by setting the glass transition temperature of the soft polymer in the above range, flexibility can be given to the solid electrolyte layer and the laminate for an all-solid secondary battery, so that cracks can occur during roll winding and winding. It can be made highly flexible with no chipping.
From these viewpoints, among the soft polymers, acrylic soft polymers, isobutylene soft polymers, and diene soft polymers are preferable. In particular, an acrylic soft polymer is preferable from the viewpoint of being stable in redox and easily obtaining a battery having a long life.

The method for producing the soft polymer is not particularly limited, and any method such as a solution polymerization method, 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, lithium persulfate, and the like.
Among these, as the polymerization initiator in the present invention, an organic peroxide and an azo compound are preferable, and an organic peroxide is more preferable. This is because the reactivity with a solid electrolyte material described later is low.

  In the present invention, the polystyrene equivalent weight average molecular weight determined by GPC of the soft polymer is preferably 5,000 to 1,000,000, and more preferably 10,000 to 500,000. By setting the weight average molecular weight of the soft polymer within the above range, it is possible to increase the temporal stability of the slurry composition and improve the strength of the coating film.

(Soft polymer composition)
The soft polymer composition used in the present invention contains the soft polymer and an organic solvent.
The content of the soft polymer in the soft polymer composition is preferably 1% by weight to 20% by weight, and more preferably 2% by weight to 10% by weight in terms of solid content.
By setting the solid content concentration of the soft polymer in the soft polymer composition within the above range, solution viscosity and solution viscosity suitable for coating can be obtained.

  Examples of the organic solvent contained in the soft polymer composition used in the present invention include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ethylmethylketone and cyclohexanone. Ketones; esters such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, and ethylene Examples include alcohols such as glycol and ethylene glycol monomethyl ether; amides such as N-methylpyrrolidone and N, N-dimethylformamide, and fluorines such as hydrofluoroether. These solvents may be used alone or in admixture of two or more and appropriately selected from the viewpoint of drying speed and environment. Among these, in the present invention, it is preferable to use a nonpolar solvent selected from aromatic hydrocarbons from the viewpoint of reactivity with the solid electrolyte material.

In the soft polymer composition used in the present invention, the water content in the soft polymer composition measured by the Karl Fischer method is preferably smaller, preferably 1000 ppm or less, more preferably 800 ppm or less, and most preferably 500 ppm or less. is there. By setting the water content in the soft polymer composition within the above range, the solid electrolyte material described later can be prevented from being deteriorated by water, and a stable slurry composition can be produced.
As a technique for reducing the water content in the soft polymer composition, a technique for dehydrating the soft polymer composition with a molecular sieve may be mentioned.

The soft polymer composition used in the present invention preferably has a lower metal content. As the metal ion species included, Fe ions measured by ICP emission spectroscopic analysis are preferably 9 ppm or less, Ni ions are 10 ppm or less, and Cu ions are 2 ppm or less. Furthermore, Fe ions are preferably 1 ppm or less, Ni ions are 1 ppm or less, and Zn ions are 1 ppm or less.
This is because when the metal ion species in the soft polymer composition is within the above range, metal ion crosslinking between the soft polymers does not occur, and the soft polymer composition exhibits high stability over time.

Moreover, it is preferable that there are few electroconductive particle-like foreign materials contained in a soft polymer composition as metal content. As a preferable range of the amount of conductive particulate foreign matter contained in the soft polymer composition, the amount of particulate foreign matter having a size of 20 μm or less is 10 ppm or less, more preferably 5 ppm or less.
Since the amount of conductive particulate foreign matter contained in the soft polymer composition is in the above range, a secondary battery can be stably produced with a high yield without short-circuiting when an all-solid secondary battery is formed. Is possible.

  In order to reduce the metal ion species and the particulate metal foreign matter, the technique is not limited. For example, it is achieved by applying a step of removing the metal species using a magnetic force to the soft polymer composition.

The soft polymer composition used in the present invention preferably has a low halogen (F, Cl, Br, I) ion concentration. Specifically, the halogen ion concentration measured by ICP emission spectroscopic analysis is preferably 5 ppm or less. More preferably, it is 0.5 ppm or less.
By setting the halogen ion concentration contained in the soft polymer composition within the above range, it is possible to suppress the reactivity with a solid electrolyte material described later and to prepare a slurry composition having high temporal stability.

(Solid electrolyte material)
Examples of the solid electrolyte material contained in the electrolyte layer for an all-solid secondary battery in the present invention include the following.
The solid electrolyte material is not particularly limited as long as it has lithium ion conductivity, but at least one selected from the group consisting of Ti, Al, La, Ge, Si, Ce, Ga, In, P, and S And an alkali metal salt mainly composed of lithium, such as lithium acetate and isopropoxy lithium.
The solid electrolyte material has the following general formula (1):
Li _{1 + X} Al _X Ti _2-X (PO ₄ ) ₃ (1) (0 ≦ x ≦ 2)
It is also preferable to contain the phosphoric acid compound represented by these. Further, the solid electrolyte materials include lithium ion conductive NASICON type compounds, sulfides such as Li ₂ S / P ₂ S ₅ , lithium ion conductive oxides such as Li _0.34 La _0.51 TiO _2.94 , A phosphoric acid compound such as LiPON may be included.

(Slurry composition)
The slurry composition used in the present invention contains the soft polymer, the solid electrolyte material, and the organic solvent.

  0.1-20 mass parts is preferable with respect to 100 mass parts of solid electrolyte materials, and, as for the content rate of the soft polymer in a slurry composition, 0.5-10 mass parts is more preferable. By making the content ratio of the soft polymer in the slurry composition within the above range, the electrolyte layer for an all-solid secondary battery and the all-solid-state secondary battery excellent in battery characteristics without increasing the contact resistance between the solid electrolyte particles. A laminate and an all-solid secondary battery can be obtained.

10-80 mass% is preferable and, as for the content rate of the solid electrolyte material in a slurry composition, 20-70 mass% is more preferable.
This is because by setting the content ratio of the solid electrolyte material in the slurry composition within the above range, the viscosity and viscosity of the slurry composition suitable for coating can be obtained.

  Examples of the organic solvent contained in the slurry composition used in the present invention include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone. Esters such as ethyl acetate, butyl acetate, γ-butyrolactone, ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, Examples include alcohols such as ethylene glycol monomethyl ether; amides such as N-methylpyrrolidone and N, N-dimethylformamide. These solvents may be used alone or in admixture of two or more and appropriately selected from the viewpoint of drying speed and environment. Among these, in the present invention, it is preferable to use a nonpolar solvent selected from aromatic hydrocarbons from the viewpoint of reactivity with the solid electrolyte material.

As for the content rate of the organic solvent in a slurry composition, 20-80 mass parts is preferable with respect to 100 mass parts of solid electrolyte materials, Furthermore, 30-70 mass parts is preferable.
This is because when the content ratio of the organic solvent in the slurry composition is within the above range, good coating properties can be obtained while maintaining the dispersibility of the solid electrolyte.

In addition to the above components, the slurry composition used in the present invention may further contain other components having functions of a dispersant, a leveling agent, and an antifoaming agent. These are not particularly limited as long as they do not affect the battery reaction.
Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. The dispersant is selected according to the solid electrolyte material used.

The content ratio of the dispersant in the slurry composition is preferably within a range that does not affect the battery characteristics, and specifically 10 mass% or less.
Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs during coating or to improve the smoothness of the electrode.
The content ratio of the leveling agent in the slurry composition is preferably in a range that does not affect the battery characteristics, and specifically 10 mass% or less.

  The slurry composition is obtained by mixing a solid electrolyte material, a soft polymer, an additive added as necessary, and an organic solvent using a mixer. In the mixing, the above components may be supplied to a mixer all at once and mixed and dispersed. As the mixer, a ball mill, a sand mill, a pigment disperser, a pulverizer, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, and the like can be used. Therefore, it is preferable.

(Method for producing electrolyte layer for all-solid-state secondary battery)
The method for producing the electrolyte layer for an all-solid-state secondary battery in the present invention is not particularly limited as long as it is a method of applying the slurry composition onto the substrate.
For example, it is applied by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating, or the like. The amount to be applied is not particularly limited, but is an amount such that the thickness of the active material layer formed after removing the organic solvent is usually 0.005 to 5 mm, preferably 0.01 to 2 mm. 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 adjusted so that the organic solvent volatilizes as soon as possible within a speed range in which stress concentration usually occurs and the electrolyte layer cracks or the electrolyte layer does not peel from the current collector.

The drying temperature is a temperature at which the organic solvent is sufficiently volatilized. Specifically, 50 to 250 ° C is preferable, and 80 to 200 ° C is more preferable.
This is because by setting the content in the above range, it is possible to form a good electrolyte layer for an all-solid-state secondary battery without thermal decomposition of the soft polymer.

  Although it does not specifically limit about drying time, Usually, it is performed in the range for 10 to 60 minutes.

Further, the electrode may be stabilized by pressing the current collector after drying. Examples of the pressing method include, but are not limited to, a mold press and a calendar press.
The substrate to be applied is not particularly limited as long as the organic solvent contained in the slurry composition is resistant, and examples thereof include a carrier film such as polyester. Alternatively, the slurry composition may be applied to a base material on which a positive electrode or negative electrode material is formed on a current collector, which will be described later, and dried to form an electrolyte layer for an all-solid secondary battery.

(Laminated body for all-solid-state secondary battery)
The all-solid-state secondary battery laminate in the present invention is formed by laminating a positive electrode, an electrolyte layer for an all-solid-state secondary battery, and a negative electrode in this order.
The positive electrode active material contained in the positive electrode is a compound that can occlude and release lithium ions. Active materials for positive electrodes are 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 the inorganic compound used for the positive electrode active material include transition metal oxides such as MnO, V ₂ O ₅ , V ₆ O1 ₃ , and TiO ₂ , lithium such as lithium nickelate, lithium cobaltate, and lithium manganate. And transition metal sulfides such as TiS ₂ , FeS, and MoS ₂ . 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 particle diameter of the positive electrode active material used in the present invention is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the 50% volume cumulative diameter is Usually, it is 0.1-50 micrometers, Preferably it is 1-20 micrometers. When the 50% volume cumulative diameter is within this range, a secondary battery having a large charge / discharge capacity can be obtained, and handling in producing an electrode slurry and an electrode described later is easy. The 50% volume cumulative diameter can be determined by measuring the particle size distribution by laser diffraction.

  Examples of the negative electrode active material contained in the negative electrode include carbon allotropes such as graphite and coke. The 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. The particle diameter of the negative electrode active material is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics, a 50% volume cumulative diameter is usually The thickness is 1 to 50 μm, preferably 15 to 30 μm.

  The positive electrode and the negative electrode preferably include a solid electrolyte material. This is because when the solid electrolyte material is contained in the positive electrode and the negative electrode, the contact area between the solid electrolyte material, the positive electrode active material and the negative electrode active material is increased, and high battery characteristics can be exhibited.

  The ratio of the solid electrolyte material contained in a positive electrode or a negative electrode is 10 to 80 weight% in a positive electrode or a negative electrode, Preferably it is 20 to 60 weight%. By setting it as the said range, the all-solid-state secondary battery which shows the favorable battery characteristic with which the capacity | capacitance and the output were balanced can be obtained.

  The positive electrode and the negative electrode are formed by mixing the positive electrode active material or the negative electrode active material together with a binder in an organic solvent to produce an active material slurry, and applying and drying it on a current collector foil.

  The binder is preferably the same as the soft polymer because an electrolyte material is mixed in the active material slurry, but is not limited thereto.

  Examples of the organic solvent contained in the active material slurry include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate, Esters such as butyl acetate, γ-butyrolactone, ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether And alcohols such as N-methylpyrrolidone and N, N-dimethylformamide. These solvents may be used alone or in admixture of two or more and appropriately selected from the viewpoint of drying speed and environment. Among these, in the present invention, it is preferable to use a nonpolar solvent selected from aromatic hydrocarbons from the viewpoint of reactivity with the solid electrolyte material.

In addition to the positive electrode active material or the negative electrode active material, the binder, and the organic solvent, the active material slurry may further contain other components having functions of a dispersant, a leveling agent, and an antifoaming agent. . These are not particularly limited as long as they do not affect the battery reaction.
Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. The dispersant is selected according to the solid electrolyte material used.

The content ratio of the dispersant in the active material slurry is preferably within a range that does not affect the battery characteristics, and specifically 10 mass% or less.
Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By mixing the surfactant, it is possible to prevent the repelling that occurs during coating or to improve the smoothness of the electrode.
The content ratio of the leveling agent in the active material slurry is preferably within a range that does not affect the battery characteristics, and is specifically 10% by mass or less.

  The active material slurry may contain additives that exhibit various functions such as a conductive material and a reinforcing material. The conductive material 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. As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used.

  The active material slurry is obtained by mixing a positive electrode active material or a negative electrode active material, a solid electrolyte material, a binder, additives that are added as necessary, a conductive agent, a reinforcing agent, and an organic solvent using a mixer. . In the mixing, the above components may be supplied to a mixer all at once and mixed and dispersed. A ball mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, Hobart mixer, etc. can be used as a mixer. Is preferable.

  The method for applying the active material slurry to the current collector is not particularly limited. For example, it is applied by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating, or the like. The amount to be applied is not particularly limited, but is an amount such that the thickness of the active material layer formed after removing the organic solvent is usually 0.005 to 5 mm, preferably 0.01 to 2 mm. 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. Further, the electrode may be stabilized by pressing the current collector 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, 50 to 250 ° C is preferable, and 80 to 200 ° C is more preferable.
This is because by setting the drying temperature within the above range, it is possible to form an excellent electrolyte layer for an all-solid secondary battery without thermal decomposition of the soft polymer.

  Although it does not specifically limit about drying time, Usually, it is performed in the range of 10 minutes-60 minutes.

On the positive electrode surface coated and dried by the above method, a modification layer may be provided at the interface in order to reduce the contact resistance between the solid electrolyte layer and the positive electrode. For the modification layer, a lithium ion conductive oxide material is preferable, and examples thereof include Li ₄ Ti ₅ O ₁₂ and LiNbO ₃ .

(All-solid secondary battery)
The all-solid-state secondary battery in the present invention is obtained by laminating a current collector on the positive electrode and the negative electrode of a laminate for an all-solid-state secondary battery.

  The current collector is not limited as long as it has conductivity, but usually from copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, indium, lithium, or alloys thereof. A plate-like body or a foil-like body is used. Although the thickness of metal foil is not specifically limited, Usually, 1-50 micrometers, Preferably it is 1-30 micrometers. If the current collector is too thin, the mechanical strength will be weakened, which may cause production problems such as breakage and wrinkling, and if it is too thick, the capacity of the battery as a whole will decrease. Tend to. The current collector is preferably one whose surface is roughened in order to increase the adhesive strength with the active material layer. 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 current collector surface in order to increase the adhesive strength and conductivity with the active material layer.

The following aspects can be considered as a concrete manufacturing method of the all-solid-state secondary battery in the present invention.
Aspect I: An active material slurry for forming a positive electrode or a negative electrode is applied to the surface of the current collector to form a positive electrode or a negative electrode, and a slurry composition is further applied and dried from above to form an electrolyte layer for an all-solid-state secondary battery. A positive electrode or a negative electrode formed on the current collector is further laminated.
Aspect II: The positive electrode and the negative electrode are formed on separate current collectors. Further, the electrolyte layer for an all-solid-state secondary battery applied and formed on the carrier film is sandwiched and laminated between the positive electrode and the negative electrode.
In any of the above embodiments, pressurization may be performed after or before lamination in order to improve contact at each interface of the positive electrode, the solid electrolyte layer, and the negative electrode and improve battery characteristics. The method of applying pressure is not particularly limited, and examples thereof include a flat plate press, a roll press, and CIP (Cold Isostatic Press), but are not particularly limited.
The pressure for pressing is preferably in the range of 5 to 700 MPa, more preferably 7 to 500 MPa.
This is because by setting the pressure to be pressed within the above range, the resistance at each interface of the positive electrode, the solid electrolyte layer and the negative electrode, and further, the contact resistance between particles in each layer is lowered, and good battery characteristics are exhibited. The pressure in the above range may be applied in a state constituting a battery of an all-solid secondary battery.

(Example)
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard.
In the examples and comparative examples, various physical properties are evaluated as follows.

<Porosity>
Here, the porosity is a ratio of pores contained in a unit volume, and is represented by the following formula.
Porosity (%) = (true density−bulk density) / true density × 100
Here, the true density is the density of the substance itself that can be measured by a known method such as Archimedes method. On the other hand, the bulk density is a density obtained by dividing the weight of an object by an apparent volume, and is a density including holes on the surface of the object and internal vacancies. As a measuring method, the weight and volume of a sample processed into a shape that can be easily measured (square shape or cylindrical shape) can be measured, and the weight / volume can be obtained.
The obtained porosity was judged according to the following criteria.
A: Porosity of less than 4% B: Porosity of 4% or more and less than 7% C: Porosity of 7% or more and less than 10% D: Porosity of 10% or more

<Winding characteristics>
The winding characteristics of the prepared electrolyte layer for an all-solid-state secondary battery were evaluated by the following procedure.
The film on which the solid electrolyte layer was produced was subjected to a flexibility test according to a mandrel test (JIS K 5600). A mandrel having a diameter of 3 mmφ was used, and the mandrel was attached to the mandrel so that the solid electrolyte layer was on the outside, and the surface was observed with a digital microscope. A ten-sheet flexibility test was performed to determine whether the test was acceptable.
A: 1 out of 10 sheets is not cracked. B: 1 to 3 out of 10 sheets are cracked.
C: Cracks are observed in 4 to 9 sheets out of 10 sheets.
D: Cracks are observed in all 10 sheets.

<Battery internal resistance evaluation>
The produced all solid state secondary battery was charged at a constant current and a constant voltage up to 5.0 V at 10 μA, cut off the current, left for 10 minutes, and then discharged at 10 μA. The battery internal resistance (kΩ) was calculated from the voltage drop value one second after the discharge at 10 μA.
A: Less than 20 kΩ B: 20 kΩ or more and less than 60 kΩ C: 60 kΩ or more and less than 100 kΩ D: 100 kΩ or more

Example 1
(Preparation of electrolyte layer for all-solid-state secondary battery)
In an ampoule bottle, 10.38 parts of ethyl acrylate, 10.25 parts of n-butyl acrylate, 3.75 parts of acrylonitrile, 36.56 parts of p-xylene and 0.0122 part of benzoyl peroxide as an initiator are sealed. The solution was kept in a hot water bath at 80 ° C. for 5 hours to obtain a solution containing an ethyl acrylate / butyl acrylate / acrylonitrile copolymer having a solid concentration of 20%.
Thereafter, the solution was diluted with p-xylene to a solid content concentration of 8%, and dehydrated with a molecular sieve to obtain a binder solution (soft polymer composition). It was -23 degreeC when the glass transition temperature of the obtained soft polymer was measured.
As a solid electrolyte material, 10 parts of lithium sulfide (Li ₂ S—P ₂ S ₅ ) and 18.75 parts of the binder solution are mixed, mixed with zirconia beads of 1 mmφ in a bead mill for 5 minutes, and solid A slurry composition for electrolyte was obtained.
The obtained slurry composition for electrolyte was applied on a carrier film made of polyester by a doctor blade method and dried at 120 ° C. for 20 minutes to obtain a solid electrolyte layer for an all-solid-state secondary battery.
The porosity and winding characteristics of the electrolyte layer for an all-solid-state secondary battery formed on the obtained carrier film were evaluated. The results are shown in Table 1.

(Positive electrode)
30 parts of LiCoO _2, 14 parts of lithium sulfide (Li ₂ S—P ₂ S ₅ ), 0.6 part of powdered acetylene black (manufactured by Denki Kagaku Kogyo) and 15 parts of the soft polymer composition obtained above The mixture was put into a container, 130 parts of Zr beads were added, and mixed for 10 minutes (autorotation: 2200 rpm, revolution: 500 rpm) with a bead mill to obtain a positive electrode active material slurry.
The positive electrode active material slurry obtained above was applied onto an aluminum foil (20 μm) and dried at 120 ° C. for 20 minutes. The film thickness after drying was 30 μm.

(Negative electrode)
12.5 parts of graphite, 12.5 parts of lithium sulfide (Li ₂ S—P ₂ S ₅ ), and 15 parts of the soft polymer composition obtained above were charged into a resin container, and 130 parts of Zr beads were added. Was added for 2 minutes (rotation: 2200 rpm, revolution: 500 rpm) with a bead mill to obtain a negative electrode active material slurry.
The negative electrode active material slurry obtained above was applied onto a copper foil (20 μm) and dried at 120 ° C. for 20 minutes. The film thickness after drying was 20 μm.

(Preparation of all-solid-state secondary battery)
The slurry composition for solid electrolyte obtained above was applied onto the surface of the positive electrode active material of the positive electrode and dried at 120 ° C. for 30 minutes. The film thickness of the solid electrolyte layer after drying was 6 μm.
The positive electrode and the negative electrode laminated with a solid electrolyte layer are punched out to 12 mmφ each, and then the surfaces of the solid electrolyte layer and the negative electrode are combined and press-pressed at a pressure of 10 MPa, and the positive electrode / solid electrolyte layer provided with a current collector A negative electrode laminate was obtained.
Table 1 shows the results of producing a coin-type battery from the obtained laminate and evaluating the battery internal resistance.

(Example 2)
In Example 1, a flexible polymer composition was obtained in the same manner as in Example 1 except that the amount of acrylonitrile was 7.5 parts when obtaining the binder solution. The glass transition temperature of the obtained soft polymer was −10 ° C.
In Example 1, a slurry composition, a solid electrolyte layer, a laminate, and a battery were produced in the same manner as in Example 1 except that the soft polymer composition obtained above was used as the soft polymer composition. Each evaluation was performed. These results are shown in Table 1.

(Comparative Example 1)
(Preparation of slurry composition)
In Example 1, polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., ESREC BM-S, glass transition temperature 61 ° C.) as a binder and n-butyl acetate as an organic solvent were used in the same manner as in Example 1, A slurry composition and an electrolyte layer for an all-solid secondary battery were prepared.
The resulting solid electrolyte layer for an all-solid-state secondary battery was evaluated for porosity and winding characteristics. The results are shown in Table 1.

(Positive electrode)
In Example 1, polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., ESREC BM-S: glass transition temperature: 61 ° C.) was used as the binder, and n-butyl acetate was used as the organic solvent in the same manner as in Example 1. A positive electrode was produced.

(Negative electrode)
In Example 1, polyvinyl butyral resin (manufactured by Sekisui Chemical Co., Ltd., ESREC BM-S: glass transition temperature: 61 ° C.) was used as the binder, and n-butyl acetate was used as the organic solvent in the same manner as in Example 1. A negative electrode was produced.

(Preparation of all-solid-state secondary battery)
In Example 1, a current collector was obtained in the same manner as in Example 1 except that the positive electrode, the solid electrolyte layer for all-solid secondary battery, and the negative electrode were used as the positive electrode, the solid electrolyte layer for all-solid-state secondary battery, and the negative electrode. A laminate of a positive electrode / solid electrolyte layer / negative electrode provided with a body was prepared, and a coin-type battery was manufactured using the laminate, and each evaluation was performed. These results are shown in Table 1.

Claims (5)

  An electrolyte layer for an all-solid secondary battery using a soft polymer as a solid electrolyte material and a binder.   The electrolyte layer for an all-solid-state secondary battery according to claim 1, wherein the soft polymer has a glass transition temperature of 15 ° C or lower.   A laminate for an all-solid-state secondary battery comprising the positive electrode, the electrolyte layer for an all-solid-state secondary battery according to claim 1 and a negative electrode in this order.   The laminate for an all-solid-state secondary battery according to claim 3, wherein the positive electrode and the negative electrode include the soft polymer and a solid electrolyte material.   An all-solid secondary battery comprising a current collector on a positive electrode and a negative electrode of the laminate for an all-solid secondary battery.