Method for producing solid electrolyte, method for producing separator, method for producing electrode, and method for producing power storage device

Abstract

To provide a method for producing a solid electrolyte, a method for producing a separator, a method for producing an electrode, and a method for producing a power storage device, the methods enabling reduction of interfacial resistance.SOLUTION: A method for producing a solid electrolyte comprises contacting an aprotic organic solvent in which an alkali metal salt is dissolved with a fracture surface of an oxide-based solid electrolyte, thereby forming on the fracture surface a surface layer derived from the alkali metal salt. A method for producing a separator, a method for producing an electrode, and a method for producing a power storage device each comprise a step of disposing a solid electrolyte obtained by the method for producing the solid electrolyte.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a solid electrolyte, a method for producing a separator, a method for producing an electrode, and a method for producing an electricity storage device. [Background technology]

[0002] The surface condition of a solid electrolyte affects the interfacial resistance of the solid electrolyte, and an increase in the interfacial resistance of the solid electrolyte leads to a decrease in the performance of an electricity storage device that includes the solid electrolyte. The prior art disclosed in Patent Document 1 applies heat treatment to the solid electrolyte in order to reduce the interfacial resistance of the solid electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7209636 Summary of the Invention [Problem to be solved by the invention]

[0004] In the prior art, a film containing substances in the atmosphere surrounding the solid electrolyte is formed on the surface of the solid electrolyte during or after the heat treatment, which has the problem of being ineffective in reducing the interfacial resistance of the solid electrolyte.

[0005] The present invention has been made to solve the problems, and an object of the present invention is to provide a method for manufacturing a solid electrolyte, a method for manufacturing a separator, a method for manufacturing an electrode, and a method for manufacturing an electricity storage device that can reduce interfacial resistance. [Means for solving the problem]

[0006] A first aspect for achieving this object is a method for producing an oxide-based solid electrolyte, which includes the steps of bringing an aprotic organic solvent having an alkali metal salt dissolved therein into contact with a fracture surface of the solid electrolyte, and forming a surface layer derived from the alkali metal salt on the fracture surface.

[0007] In a second embodiment, in the first embodiment, the alkali metal salt is a lithium salt.

[0008] In a third aspect, in the first or second aspect, the alkali metal salt contains one or more of fluorine, sulfur, and nitrogen.

[0009] In a fourth aspect, in any one of the first to third aspects, the alkali metal salt is lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide.

[0010] In a fifth aspect, in any one of the first to fourth aspects, the fracture surface is formed by flowing an aprotic organic solvent in which the solid electrolyte is dispersed, thereby pulverizing the solid electrolyte.

[0011] In a sixth aspect, in any one of the first to fifth aspects, the solid electrolyte has a garnet-type crystal structure containing Li, La, and Zr.

[0012] In a seventh embodiment, in the sixth embodiment, the solid electrolyte further contains Mg and Sr.

[0013] An eighth aspect is a method for producing a separator, which includes a step of arranging a solid electrolyte obtained by the method for producing a solid electrolyte according to any one of the first to seventh aspects.

[0014] A ninth aspect is a method for producing an electrode, which includes a step of arranging a solid electrolyte obtained by the method for producing a solid electrolyte according to any one of the first to seventh aspects.

[0015] A tenth aspect is a method for producing an electricity storage device, which includes a step of arranging a solid electrolyte obtained by the method for producing a solid electrolyte according to any one of the first to seventh aspects. [Effects of the Invention]

[0016] According to the method for producing a solid electrolyte of the present invention, the aprotic organic solvent having an alkali metal salt dissolved therein comes into contact with the fracture surface of the solid electrolyte, and a surface layer derived from the alkali metal salt is formed on the fracture surface, thereby reducing the interfacial resistance of the solid electrolyte. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view of an electricity storage device including an ion conductor according to a first embodiment. [Figure 2] FIG. 1 is a diagram schematically illustrating a garnet-type crystal structure. [Figure 3] FIG. 2 is a cross-sectional view of a separator. [Figure 4] FIG. 10 is a cross-sectional view of an electricity accumulation device according to a second embodiment. [Figure 5] FIG. 10 is a cross-sectional view of an electricity accumulation device according to a third embodiment. [Figure 6] 10(a) is a cross-sectional view of an insulator in the fourth embodiment, (b) is a cross-sectional view of an electrode in the fifth embodiment, and (c) is a cross-sectional view of an electrode in the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of an electricity storage device 11 including an ion conductor 10 according to a first embodiment. The electricity storage device 11 in this embodiment is a secondary battery that uses lithium ions as charge carriers. The electricity storage device 11 includes, in order, a positive electrode layer 12, a separator 15, and a negative electrode layer 16. The positive electrode layer 12, the separator 15, and the negative electrode layer 16 are housed in a case (not shown).

[0019] The positive electrode layer 12 is formed by stacking a current collecting layer 13 and an active material layer 14. The current collecting layer 13 is a conductive member. Examples of materials for the current collecting layer 13 include metals selected from Ni, Ti, Fe, and Al, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0020] The active material layer 14 includes an ion conductor 10 and an active material 20. The ion conductor 10 includes a solid electrolyte 19. The active material layer 14 may contain a conductive additive to reduce the resistance of the active material layer 14. Examples of conductive additives include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0021] The active material 20 is exemplified by a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. The metal oxide containing a transition metal is exemplified by a metal oxide containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. The metal oxide containing a transition metal is exemplified by LiCoO2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4,LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Examples include O2 and LiFePO4.

[0022] In order to suppress the reaction between the active material 20 and the solid electrolyte 19, a coating layer can be provided on the surface of the active material 20. The coating layer can be made of Al2O3, ZrO2, LiNbO3, Li4Ti5O 12 , LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4 and Li2MoO4 are examples.

[0023] Examples of sulfur-based active materials include S, TiS2, NiS, FeS2, Li2S, MoS3, and sulfur-carbon composites. Examples of organic active materials include radical compounds such as 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, and phenazine oxide.

[0024] The separator 15 separates the positive electrode layer 12 and the negative electrode layer 16, electrically insulating them from each other. The separator 15 is made of an ion conductor 10. The ion conductor 10 includes a solid electrolyte 19 and an electrolytic solution (described below). The ion conductor 10 may further include a binder.

[0025] The negative electrode layer 16 is formed by stacking a current collecting layer 17 and an active material layer 18. The current collecting layer 17 is a conductive member. Examples of materials for the current collecting layer 17 include metals selected from Ni, Ti, Fe, Cu, and Si, alloys containing two or more of these elements, stainless steel, and carbon materials.

[0026] The active material layer 18 includes an ion conductor 10 and an active material 21. To reduce the resistance of the active material layer 18, the active material layer 18 may contain a conductive additive. Examples of the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag. The active material 21 may be Li, a Li-Al alloy, Li4Ti5O 12 Examples of the binder include graphite, In, Si, a Si—Li alloy, and SiO. As with the separator 15, the active material layers 14 and 18 may contain a binder.

[0027] The electricity storage device 11 is manufactured, for example, as follows: A solution in which a binder is dissolved in a solvent is mixed with an electrolytic solution in which an electrolyte is dissolved in a nonaqueous solvent and a solid electrolyte 19 to form a slurry. The slurry is formed into a sheet and then dried to obtain a green sheet (electrolyte sheet) for the separator 15.

[0028] An electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent is mixed with a solid electrolyte 19, and the mixture is mixed with an active material 20, and further mixed with a solution in which a binder is dissolved in a solvent to form a slurry. The slurry is applied onto the current collecting layer 13 and then dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 12.

[0029] An electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent is mixed with a solid electrolyte 19, and the mixture is mixed with an active material 21. A solution in which a binder is dissolved in a solvent is further mixed with the mixture to form a slurry. The slurry is applied onto the current collecting layer 17 and then dried to obtain a green sheet (negative electrode sheet) for the negative electrode layer 16.

[0030] The electrolyte sheet, positive electrode sheet, and negative electrode sheet are each cut to a predetermined shape, and then stacked in this order: positive electrode sheet, electrolyte sheet, negative electrode sheet, and then pressed together to form a single sheet. Terminals (not shown) are connected to the current collecting layers 13 and 17, respectively, and the device is sealed in a case (not shown), resulting in an electricity storage device 11 including a positive electrode layer 12, a separator 15, and a negative electrode layer 16. In this way, a sheet including a solid electrolyte 19 can become an electrolyte sheet, a positive electrode sheet, and a negative electrode sheet by the ion conductor 10.

[0031] The solid electrolyte 19 is a crystalline or amorphous oxide-based solid electrolyte. Examples of the solid electrolyte 19 include those having a perovskite type, a NASICON type, a LISICON type, and a garnet type structure. The perovskite type solid electrolyte is an oxide containing at least Li, Ti, and La, for example, La 2 / 3-X Li 3X Examples of the NASICON-type solid electrolyte include oxides containing at least Li, M (where M is one or more elements selected from Ti, Zr, and Ge), and P, such as Li(Al,Ti)2(PO4)3 and Li(Al,Ge)2(PO4)3. Examples of the LISICON-type solid electrolyte include oxides containing Li 14 Zn(GeO4)4 is an example. Garnet-type solid electrolytes are exemplified by composite oxides containing Li, La, and Zr. The garnet-type crystal structure has the general formula C3A2B3O 12 It is expressed as:

[0032] FIG. 2 is a diagram schematically illustrating a garnet-type crystal structure. In the garnet-type crystal structure, Sc at the C site is dodecahedrally coordinated with an oxygen atom Oa, Sa at the A site is octahedrally coordinated with an oxygen atom Oa, and Sb at the B site is tetrahedrally coordinated with an oxygen atom Oa. In the solid electrolyte 19, Li can exist in a vacancy V, which would otherwise be octahedrally coordinated with an oxygen atom Oa in a typical garnet-type crystal structure. The vacancy V is, for example, a location sandwiched between the B site Sb1 and the B site Sb2. The Li present in the vacancy V is octahedrally coordinated with an oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 forming the B site Sb1 and the tetrahedral face Fb2 forming the B site Sb2. For example, in the case of Li7La3Zr2O having a garnet-type crystal structure, 12 In the formula, La can occupy the C-site Sc, Zr can occupy the A-site Sa, and Li can occupy the B-site Sb and the vacant V.

[0033] The garnet-type crystal structure is X-ray diffraction file No. 422259 (Li7La3Zr2O) in the CSD (Cambridge Structural Database). 12 ) has an XRD pattern similar to that of No. 422259. Compared to No. 422259, solid electrolyte 19 may differ in the type of constituent elements and Li concentration, resulting in different diffraction angles and intensity ratios. A typical crystal structure of this type is a cubic system (space group Ia-3d (- indicates an overline indicating a reversal operation), JCPDS: 84-1753).

[0034] Returning to FIG. 1, the solid electrolyte 19 is typically Li7La3Zr2O 12 The solid electrolyte 19 may have some of its constituent elements substituted with other elements, or may have a small amount of other elements added without substituting the constituent elements. Examples of the other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La).

[0035] The solid electrolyte 19 is, for example, Li6La3Zr 1.5 W0.5 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 , Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 , Li 6.25 La3Zr2Ga 0.25 O 12 , Li 6.4 La3Zr 1.4 Ta 0.6 O 12 , Li 6.5 La3Zr 1.75 Te 0.25 O 12 , Li 6.75 La3Zr 1.75 Nb 0.25 O 12 , Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 , Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 , Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 , Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 , Li 6.20 Ba 0.30 La 2.95 Rb 0.05 Zr2O 12 include the following.

[0036] The solid electrolyte 19 preferably contains at least one of Mg and element A (A is at least one element selected from the group consisting of Ca, Sr, and Ba) in which the molar ratio of each element satisfies all of the following (1) to (3), or contains both Mg and element A in which the molar ratio of each element satisfies all of the following (4) to (6). The element A is preferably Sr, as this increases the ionic conductivity of the solid electrolyte 19. (1) 1.33≦Li / (La+A)≦3 (2) 0≦Mg / (La+A)≦0.5 (3) 0≦A / (La+A)≦0.67 (4) 2.0≦Li / (La+A)≦2.6 (5) 0.01≦Mg / (La+A)≦0.14 (6) 0.04≦A / (La+A)≦0.17

[0037] The median diameter of the circle-equivalent diameter of the solid electrolyte 19 appearing in the cross section of the separator 15 is preferably 0.5 to 10 μm, and more preferably 0.5 to 6 μm, in order to ensure that the surface area of ​​the solid electrolyte 19 is of an appropriate size and to ensure the amount of Li ions that can move between the solid electrolyte 19 and the electrolytic solution present on the surface of the solid electrolyte 19.

[0038] To determine the median diameter of the solid electrolyte 19, first, a scanning electron microscope (SEM) image of the solid electrolyte 19 appearing on the cross section of the separator 15 (a polished surface, a surface obtained by irradiating with a focused ion beam (FIB), or a surface obtained by ion milling) is analyzed, and the circle-equivalent diameter is calculated from the area of ​​each particle of the solid electrolyte 19, and the volume-based particle size distribution is determined. The median diameter is the circle-equivalent diameter at which the cumulative frequency in the particle size distribution is 50%. To ensure accuracy, the image for determining the particle size distribution is taken from a 400 μm area of ​​the separator 15. 2 The area shall be equal to or greater than this.

[0039] The ionic conductor 10 may contain one or more other solid electrolytes in addition to the solid electrolyte 19 having a garnet-type crystal structure containing Li, La, and Zr. Examples of other solid electrolytes include crystalline or amorphous oxide-based solid electrolytes such as perovskite-type, NASICON-type, and LISICON-type, and hydride-based solid electrolytes.

[0040] The perovskite-type solid electrolyte is an oxide containing at least Li, Ti, and La, for example, La 2 / 3-X Li 3X Examples of the NASICON-type solid electrolyte include oxides containing at least Li, M (where M is one or more elements selected from Ti, Zr, and Ge), and P, such as Li(Al,Ti)2(PO4)3 and Li(Al,Ge)2(PO4)3. Examples of the LISICON-type solid electrolyte include oxides containing Li 14 An example of a hydride-based solid electrolyte is Zn(GeO4). Examples of hydride-based solid electrolytes include hydrides of alkali metals or alkaline earth metals containing at least one element from Group 13 of the Periodic Table of Elements (e.g., B, Al, Ga, In, Ta). Examples include LiBH4 and LiAlH4.

[0041] FIG. 3 is a cross-sectional view of the separator 15 (see FIG. 1). The separator 15 includes a solid electrolyte 19 provided with a surface layer 22 and an electrolyte solution 23 (nonaqueous electrolyte solution) in which the electrolyte is dissolved in a nonaqueous solvent. The electrolyte is a compound used for exchanging cations between the positive electrode layer 12 and the negative electrode layer 16. The anions of the electrolyte are halide ions (I - ,Cl - ,Br - etc.),SCN - ,BF4 - ,BF3(CF3) - ,BF3(C2F5) - ,PF6 - ,ClO4 - ,SbF6 - ,N(SO2F)2 - ,N(SO2CF3)2 - ,N(SO2C2F5)2 - ,B(C6H5)4 -,B(O2C2H4)2 - ,C(SO2F)3 - ,C(SO2CF3)3 - ,CF3COO - ,CF3SO2O - ,C6F5SO2O - ,B(O2C2O2)2 - ,RCOO - (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group).

[0042] The anion of the electrolyte is N(SO2F)2, which has a sulfonyl group -S(=O)2-. - ,N(SO2CF3)2 - ,N(SO2C2F5)2 - Sulfonylimides such as PF6 - The halophosphate ions, such as sulfonylimide anions, are preferably used. This is because sulfonylimide anions are less susceptible to increases in electrolyte viscosity and decreases in ionic conductivity even when the salt concentration is high, while halophosphate ions have a high degree of dissociation. Both are preferred because they can form a highly stable and low-resistance coating (SEI), which reduces the reductive decomposition of the non-aqueous solvent and widens the reduction-side potential window.

[0043] Non-aqueous solvents are broadly classified into molecular solvents, which are mostly composed of molecules, and ionic liquids, which are composed of cations and anions. As molecular solvents, aprotic organic solvents are preferred because they broaden the potential window of non-aqueous electrolytes. Examples of aprotic organic solvents include cyclic esters, chain esters, aliphatic carboxylic acid esters, phosphate esters, nitriles, amides, sulfur compounds, ketones, ethers, nitro compounds, fluorous solvents, and sulfone-based solvents. Mixtures of these solvents are also acceptable.

[0044] Examples of cyclic esters include carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, and lactones such as β-propiolactone, γ-butyrolactone, δ-valerolactone, α-pyrone, and coumarin. Examples of chain esters include carbonate esters such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, and benzonitrile.

[0045] Examples of amides include formamide, N-methylformamide, dimethylformamide, N-methylacetamide, dimethylacetamide, N-methylpropioamide, hexamethylphosphoramide, and N-methylpyrrolidone. Examples of sulfur compounds include dimethyl sulfoxide, sulfolane, dimethylthioformamide, and N-methylthiopyrrolidone. Examples of ketones include acetone, 4-methyl-2-pentanone, and acetylacetone. Examples of ethers include tetrahydrofuran and monoglyme. Examples of nitro compounds include nitromethane and nitrobenzene. Fluorous solvents are compounds in which the hydrogen atoms of hydrocarbons are replaced with fluorine atoms, and their derivatives.

[0046] Examples of sulfone solvents include trimethylene sulfone, sulfolane, difluorosulfolane, dimethyl sulfolane, monofluorosulfolane, 3-methyl sulfolane, ethyl methyl sulfone, and ethyl isopropyl sulfone. Sulfone solvents are preferred because of their high thermal stability.

[0047] The reaction in which an electrolyte dissolves in a molecular solvent and dissociates into free ions proceeds more easily the higher the relative dielectric constant of the solvent and the easier it is for ions to solvate, so a solvent with a relatively high relative dielectric constant εr (εr>20) is preferred. Examples of molecular solvents with a relative dielectric constant greater than 20 include cyclic esters, nitriles, amides, sulfur compounds, acetone, acetylacetone, and nitro compounds. Of course, it is possible to mix a solvent with a relative dielectric constant greater than 20 with a solvent with a relative dielectric constant of 20 or less to adjust the viscosity of the solvent, etc.

[0048] Ionic liquids are compounds consisting of cations and anions, and are liquid at room temperature and normal pressure. If the solvent of a non-aqueous electrolyte is an ionic liquid, the flame retardancy of the non-aqueous electrolyte can be improved. The ionic liquid is preferably one having one or more cation species selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium.

[0049] The anion component of the ionic liquid is not particularly limited. The anion component is BF4 - ,N(SO2F)2 - Inorganic anions such as B(C6H5)4 - ,CH3SO3 - ,CF3SO3 - ,N(SO2CF3)2 - ,N(SO2C4F9)2 - Examples of organic anions include:

[0050] The ionic liquid may be a solvated ionic liquid, such as a sulfone-based solvent such as sulfolane or a sulfolane derivative, or a glyme-based solvent such as tetraglyme, in which an electrolyte is dissolved.

[0051] The ionic conductor 10 may contain a binder that binds the solid electrolyte 19. Examples of binders include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, and rubber-like polymers such as styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0052] Examples of vinylidene fluoride polymers include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and copolymerizable monomers. Examples of copolymerizable monomers include halogen-containing monomers (excluding vinylidene fluoride) and non-halogen copolymerizable monomers. Examples of halogen-containing monomers include chlorine-containing monomers such as vinyl chloride; and fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ether. Examples of non-halogen copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, and esters or salts thereof; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or more copolymerizable monomers are polymerized with vinylidene fluoride to form the copolymer.

[0053] The surface layer 22 is provided on the fractured surface of the solid electrolyte 19. The surface layer 22 is formed by bringing an aprotic organic solvent (hereinafter referred to as the "specific solvent") having an alkali metal salt dissolved therein into contact with the fractured surface of the solid electrolyte 19 in the presence of the specific solvent or in an inert atmosphere. The specific solvent containing alkali metal ions reacts with atoms and molecules appearing on the fractured surface of the solid electrolyte 19, and the surface layer 22 derived from the alkali metal salt is formed on the fractured surface. The surface layer 22 formed on the fractured surface can reduce the interfacial resistance of the solid electrolyte 19.

[0054] Examples of means for contacting the fracture surface of the solid electrolyte 19 with a specific solvent include an operation of breaking the solid electrolyte 19 in an inert atmosphere to form a new fracture surface on the solid electrolyte 19, and then contacting the fracture surface with a specific solvent, and an operation of forming a new fracture surface on the solid electrolyte 19 in a specific solvent. Examples of the inert atmosphere include an atmosphere of a rare gas such as helium, neon, or argon, or a nitrogen gas. Examples of an operation of forming a new fracture surface on the solid electrolyte 19 in a specific solvent include a so-called wet grinding operation in which the specific solvent in which the solid electrolyte 19 is dispersed is flowed and the solid electrolyte 19 is pulverized in the specific solvent. Wet grinding is preferably performed in an inert atmosphere. To perform wet grinding in an inert atmosphere, a grinder is placed in the inert atmosphere and the device is operated.

[0055] During wet pulverization, the ratio of solid electrolyte 19 to the slurry obtained by dispersing solid electrolyte 19 in a specific solvent is preferably 30 wt % or more and 70 wt % or less. If the ratio is less than 30 wt %, the yield will be low, and if the ratio exceeds 70 wt %, there will tend to be solid electrolyte 19 that cannot come into contact with the specific solvent, and the ratio of solid electrolyte 19 that does not have surface layer 22 will increase.

[0056] The cation of the alkali metal salt that constitutes the specific solvent is Li + ,Na + ,K + The cation of the alkali metal salt is preferably the same as the charge carrier of the electricity storage device 11. The anion of the alkali metal salt is preferably a halide ion (I - ,Cl - ,Br - etc.),SCN - ,BF4 - ,BF3(CF3) - ,BF3(C2F5) - ,PF6 - ,ClO4 - ,SbF6 - ,N(SO2F)2 - ,N(SO2CF3)2 - ,N(SO2C2F5)2 - ,B(C6H5)4 - ,B(O2C2H4)2 - ,C(SO2F)3- ,C(SO2CF3)3 - ,CF3COO - ,CF3SO2O - ,C6F5SO2O - ,B(O2C2O2)2 - ,RCOO - (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group).

[0057] The anion of the alkali metal salt is N(SO2F)2, which has a sulfonyl group -S(=O)2-. - ,N(SO2CF3)2 - ,N(SO2C2F5)2 - Sulfonylimides such as PF6 - Halophosphate ions such as these are preferably used. Sulfonylimide anions are less susceptible to increased viscosity and decreased ionic conductivity in specific solvents even at high salt concentrations, while halophosphate ions have a high degree of dissociation. Examples of imide salts include lithium bis(fluorosulfonyl)imide LiN(SO2F)2 and lithium bis(trifluoromethanesulfonyl)imide LiN(SO2CF3)2.

[0058] The alkali metal salt preferably contains one or more of fluorine, sulfur, and nitrogen, in order to reduce the electrical resistance of the surface layer 22. There are no limitations on the concentration of the alkali metal salt in the specific solvent, but an example of this is 0.2 to 4.0 mol / L, in order to reduce the electrical resistance of the surface layer 22.

[0059] When the electrolytic solution 23 contains an aprotic organic solvent, the specific solvent may be the same type of solvent as the aprotic organic solvent contained in the electrolytic solution 23 or a different type of solvent, but is preferably the same type of solvent as the aprotic organic solvent contained in the electrolytic solution 23. This is to prevent different components from being mixed into the electrolytic solution 23.

[0060] The aprotic organic solvent constituting the specific solvent may be an inert solvent, because the alkali metal salt will dissociate. Examples of the inert solvent include benzene, carbon tetrachloride, saturated hydrocarbons, and fluorine-based inert solvents. Examples of the fluorine-based inert solvent include perfluoropolyether, perfluorocarbon, perfluoromethylcyclohexane, hydrofluoroether, and fluorous solvents.

[0061] The aprotic organic solvent constituting the specific solvent is preferably a carbonate-based solvent (chain or cyclic carbonate ester) or one containing one or more of halogen, nitrogen, and sulfur in the functional group (excluding inert solvents), because this increases the reactivity between the solid electrolyte 19 and the specific solvent. The elimination of the active functional group results in the formation of a low-resistance surface layer 22.

[0062] The solid electrolyte 19 has a surface layer 22 formed on the fracture surface by bringing a specific solvent into contact with the fracture surface, and the specific solvent adheres to the surface layer 22. When the adhered specific solvent is removed, the surface layer 22 of the solid electrolyte 19 appears.

[0063] The surface layer 22 can be analyzed by X-ray photoelectron spectroscopy (XPS). XPS irradiates the surface layer 22 of the solid electrolyte 19 with X-rays in a vacuum and measures the spectrum of the kinetic energy of the electrons emitted by photoionization, thereby obtaining information about the abundance ratio of the elements that make up the surface layer 22. When irradiating with X-rays from an AlKα radiation source, the mean free path in a solid of photoelectrons having energy equivalent to the kinetic energy of the electrons emitted from the surface layer 22 is 2 nm or less, so the thickness of the surface layer 22 analyzed by XPS is estimated to be about 10 nm.

[0064] When the solid electrolyte 19 has a garnet-type crystal structure containing Li, La, and Zr, the ratio of the total of the abundance ratio (area intensity) of Li2S, the area intensity of LiF, and the area intensity of Li3N divided by the area intensity of other lithium compounds (excluding Li2CO3) when the kinetic energy spectrum of electrons emitted from the surface (surface layer 22) of the solid electrolyte 19 is measured by XPS is preferably 0.1 or more. This is to reduce the electrical resistance of the surface layer 22.

[0065] In the ion conductor 10, the ratio of the volume of the solid electrolyte 19 to the total volume of the solid electrolyte 19 and the electrolytic solution 23 is preferably 52% or more and less than 100%, and more preferably 61% or more and less than 100%. The combination of the solid electrolyte 19 and the electrolytic solution 23 can reduce the interfacial resistance of the solid electrolyte 19, thereby increasing the operational stability of the electricity storage device 11 in which the ion conductor 10 is disposed.

[0066] The contents (volume %) of solid electrolyte 19 and electrolyte solution 23 are determined by freezing separator 15 or embedding separator 15 in a tetrafunctional epoxy resin or the like and then analyzing a randomly selected area of ​​the cross section of separator 15 at a magnification of 5000 times using an SEM equipped with an energy dispersive X-ray spectrometer (EDS). The analysis involves identifying the distribution of La, Zr, and S and performing image analysis of the contrast of the backscattered electron image to identify the areas of solid electrolyte 19 and electrolyte solution 23, and the proportion of the area in the cross section of separator 15 is considered to be the proportion of the volume of ion conductor 10 in separator 15 to obtain the contents (volume %) of solid electrolyte 19 and electrolyte solution 23.

[0067] The ionic conductivity of the ionic conductor 10 is determined by the types and salt concentrations of the solid electrolyte 19 and the electrolyte solution 23. The lithium ionic conductivity of the ionic conductor 10 at 25° C. is 1.0×10 -5 The ionic conductivity is preferably S / cm or more in order to ensure the output density of the electricity storage device 11 including the ionic conductor 10.

[0068] A second embodiment will be described with reference to Fig. 4. In the first embodiment, an electricity storage device 11 in which a solid electrolyte 19 is disposed in a separator 15 is described. In the second embodiment, a case in which an ion conductor 10 is used in a liquid-based lithium-ion battery in which charge carriers pass through a separator 25 is described. The same parts as those described in the first embodiment are given the same reference numerals, and the following description will be omitted. Fig. 4 is a cross-sectional view of an electricity storage device 24 in the second embodiment.

[0069] The electricity storage device 24 includes, in that order, a positive electrode layer 12, a separator 25, and a negative electrode layer 16. These are housed in a case (not shown). The separator 25 is made of a porous material that is durable against the active materials 20, 21 and the electrolyte solution 23 contained in the positive electrode layer 12 and the negative electrode layer 16, and that allows charge carriers (lithium ions) to pass through but does not have electronic conductivity. Examples of the separator 25 include nonwoven fabrics and porous films made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc. The electricity storage device 24 of the second embodiment includes an ion conductor 10 in the positive electrode layer 12 and the negative electrode layer 16, and therefore has increased operational stability similar to the electricity storage device 11 of the first embodiment.

[0070] A third embodiment will be described with reference to Fig. 5. In the first and second embodiments, the positive electrode layer 12, separator 15, and negative electrode layer 16 contain the ion conductor 10. In the third embodiment, the protective layers 29 and 32 contain the ion conductor 10. The same parts as those described in the first and second embodiments are designated by the same reference numerals, and the following description will be omitted. Fig. 5 is a cross-sectional view of an electricity storage device 26 in the third embodiment.

[0071] The power storage device 26 includes, in order, a positive electrode layer 27, a separator 25, and a negative electrode layer 30. These are housed in a case (not shown). The power storage device 26 is a liquid-based lithium-ion battery that uses a non-aqueous electrolyte solution as the electrolyte.

[0072] The positive electrode layer 27 is formed by stacking the current collecting layer 13 and an active material layer 28. The active material layer 28 contains an active material 20. In order to reduce the resistance of the active material layer 28, the active material layer 28 may contain a conductive additive such as carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, or Ag.

[0073] A protective layer 29 is disposed between the separator 25 and the negative electrode layer 30. The protective layer 29 includes an ion conductor 10.

[0074] The negative electrode layer 30 is formed by stacking an active material layer 31, a protective layer 32, and a current collecting layer 17 in this order. The active material layer 31 is made of, for example, Li, a Li-Al alloy, a Li-Sn alloy, a Li-Si alloy, a Li-Mg alloy, a Li-Si alloy, or a Si-Li alloy. The protective layer 32 contains an ion conductor 10. The protective layers 29 and 32 are arranged by stacking sheet-like compacts made of a slurry containing the ion conductor 10, or by applying a slurry containing the ion conductor 10 to the separator 25 or the current collecting layer 17, or the like.

[0075] The solid electrolyte 19, which has a garnet-type crystal structure containing Li, La, and Zr and is contained in the ion conductor 10, is resistant to reduction by the metallic lithium of the active material layer 31, and therefore the protective layer 29 increases the operational stability of the electricity storage device 26. Furthermore, the protective layer 29 suppresses short circuits caused by dendrite growth of metallic lithium. The protective layer 32 interposed between the active material layer 31 and the current collecting layer 17 suppresses deterioration of the current collecting layer 17.

[0076] Fourth to sixth embodiments will be described with reference to Fig. 6. Note that the same parts as those described in the first to third embodiments are given the same reference numerals and the description thereof will be omitted. Fig. 6(a) is a cross-sectional view of an insulator 33 in the fourth embodiment.

[0077] The insulator 33 includes a separator 25 and a protective layer 29 in contact with the separator 25. The separator 25 includes a first interface 34 and a second interface 35 opposite the first interface 34, and the protective layer 29 is disposed at the first interface 34 and the second interface 35. The protective layer 29 disposed on the separator 25 can reduce short circuits caused by dendritic growth of metallic lithium contained in the electricity storage device. Even if a short circuit occurs in the electricity storage device and the separator 25 attempts to thermally deform, the presence of the protective layer 29 allows the shape of the separator 25 to be maintained, thereby suppressing the occurrence of thermal runaway in the electricity storage device.

[0078] 6(b) is a cross-sectional view of an electrode 36 according to a fifth embodiment. The electrode 36 includes a positive electrode layer 12 and a protective layer 29 in contact with the active material layer 14 of the positive electrode layer 12. The electrode 36 has the protective layer 29 disposed at an interface 37 of the active material layer 14 opposite the surface on which the current collecting layer 13 is disposed. The protective layer 29 disposed at the interface 37 of the active material layer 14 can reduce dendrite growth from the negative electrode layer 16 of the electricity storage device.

[0079] 6(c) is a cross-sectional view of an electrode 38 according to a sixth embodiment. The electrode 38 includes a negative electrode layer 16 and a protective layer 29 in contact with the active material layer 18 of the negative electrode layer 16. The electrode 38 has the protective layer 29 disposed at an interface 39 opposite the surface of the active material layer 18 on which the current collecting layer 17 is disposed. The protective layer 29 disposed at the interface 39 of the active material layer 18 can reduce dendrite growth from the negative electrode layer 16 of the electricity storage device.

[0080] The insulator 33 is disposed in the electricity storage device in place of the separator 25 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. The insulator 33 may omit one of the two protective layers 29 disposed at the interfaces 34, 35 of the separator 25.

[0081] The electrode 36 is disposed in the electricity storage device in place of the positive electrode layers 12, 27 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. The electrode 38 is disposed in the electricity storage device in place of the negative electrode layers 16, 30 of the electricity storage device 24 of the second embodiment or the electricity storage device 26 of the third embodiment. [Example]

[0082] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0083] (Preparation of solid electrolyte) Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12 Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed out so that the composition satisfies the following formula: Li2CO3 was used in an excess of approximately 15 mol% in elemental terms to account for the volatilization of Li during firing. The weighed raw materials and ethanol were placed in a nylon pot along with zirconia balls and ground and mixed in a ball mill for 15 hours. The slurry removed from the pot was dried, placed on an MgO plate, and calcined at 1200°C for 10 hours. The calcined powder was crushed in a mortar and pestle, and the powder that passed through a 250 μm mesh was used as calcined powder. The calcined powder was placed in an MgO sheath and further fired at 1100°C for 4 hours. The fired powder was crushed in a mortar and pestle, and the powder that passed through a 250 μm mesh was collected to obtain a solid electrolyte powder (hereinafter referred to as "LLZ").

[0084] (Preparation of sintered body) A binder was added to the calcined powder, and the mixture was pulverized and mixed in an inert solvent for 60 hours in a ball mill. The slurry was removed from the pot and dried to obtain the raw material powder for the solid electrolyte. The raw material powder was placed in a mold with an inner diameter of 32.5 mm and pressed to obtain a disk with a diameter of 32.5 mm and a thickness of approximately 2.5 mm. The disk was then pressed using a cold isostatic press at 1.5 t / cm. 2The compact was covered with the raw material powder and sintered in air at 1100°C for 4 hours to obtain a sintered body (hereinafter referred to as "LLZ sintered body").

[0085] (Comparative Example 1) The LLZ and the inert solvent were placed in a zirconia pot together with zirconia balls so that the mass ratio of the LLZ to the combined mass of the fluorine-based inert solvent containing perfluorocarbon as the main component and the LLZ was 50 wt%. The pot was sealed under an argon atmosphere, and the LLZ was wet-pulverized in a ball mill. The slurry removed from the pot was air-dried under an argon atmosphere to obtain the solid electrolyte of Comparative Example 1.

[0086] Example 1 The solid electrolyte (powder) of Comparative Example 1 was immersed in sulfolane (specific solvent) in which lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved so that the lithium salt concentration was 2.7 mol / L, and the mixture was left at room temperature for 7 days. The specific solvent was removed by suction filtration, and the removed powder was naturally dried under an argon atmosphere to obtain the solid electrolyte of Example 1.

[0087] Example 2 LLZ and the specific solvent were placed in a zirconia pot together with zirconia balls so that the mass ratio of LLZ to the combined mass of LLZ and dimethyl carbonate (specific solvent) in which LiFSI was dissolved to a lithium salt concentration of 2.7 mol / L was 50 wt%. The pot was sealed under an argon atmosphere, and the LLZ was wet-pulverized in a ball mill. The slurry removed from the pot was air-dried under an argon atmosphere to obtain the solid electrolyte (powder) of Example 2.

[0088] Dimethyl carbonate (specific solvent) in which LiFSI was dissolved so that the lithium salt concentration was 2.7 mol / L was dropped onto waterproof abrasive paper to which silicon carbide abrasive (grain size 320 specified in JIS R6010:2000) was fixed, and each circular surface of the LLZ sintered body was wet-polished under an argon atmosphere. This resulted in a solid electrolyte (sintered body) in Example 2 in which both sides of the LLZ sintered body were polished.

[0089] (Comparative Example 2) A solid electrolyte (powder and sintered body) of Comparative Example 2 was obtained in the same manner as in Example 1, except that the solvent used in the wet grinding was changed to dimethyl carbonate (in which lithium salt was not dissolved).

[0090] (Comparative Example 3) The solid electrolyte (powder) of Comparative Example 3 was obtained by dry pulverization using a jet mill in which the LLZs were caused to collide with each other in an argon atmosphere.

[0091] A solid electrolyte (sintered body) in Comparative Example 3 was obtained in the same manner as in Example 2, except that each circular surface of the LLZ sintered body was dry-polished under an argon atmosphere using waterproof abrasive paper to which silicon carbide abrasive (grain size 320 as specified in JIS R6010:2000) was fixed.

[0092] (XPS spectrum measurement) The solid electrolytes (powder) in Examples 1 and 2 and Comparative Examples 1 to 3 were stored in a transfer vessel under an argon atmosphere. After being introduced into an XPS analyzer, the surface of the solid electrolyte was analyzed. The XPS conditions were: X-ray: monochromated AlKα radiation, pass energy: 112 eV, and analysis area: 100 μmΦ. In Example 1 and Comparative Example 1, the area intensities of Li2S, LiF, Li3N, and other lithium compounds were measured from the spectra obtained by XPS. In Example 2 and Comparative Examples 2 and 3, the area intensities of Li2CO3, LiF, Li2S, and other lithium compounds were measured from the spectra obtained by XPS. The results are shown in Tables 1 and 2.

[0093] [Table 1]

[0094] [Table 2]

[0095] According to Table 1, in Comparative Example 1, almost no Li2S was detected compared to the intensity of LiF derived from the fluorine-based inert solvent, whereas in Example 1, the intensity of LiF derived from LiFSI and the intensity of Li2S were almost the same. Example 1 revealed that by bringing the specific solvent into contact with the interface of the solid electrolyte, a surface layer derived from the alkali metal salt constituting the specific solvent can be formed.

[0096] According to Table 2, in Comparative Examples 2 and 3, no LiF or Li2S was detected, whereas in Example 2, the total intensity of LiF and Li2S was approximately 0.14 times the intensity of lithium compounds (excluding LiF, Li2S, and Li2CO3).

[0097] (Interface resistance measurement) The solid electrolytes (sintered bodies) in Example 2 and Comparative Examples 2 and 3 were sandwiched between insulating cylinders with gaskets interposed between them. Electrolyte solution was poured into the cylinders on both sides of the solid electrolyte. The electrolyte solution used was dimethyl carbonate, the same as the specific solvent, in which LiFSI was dissolved to a lithium salt concentration of 2.7 mol / L. A working electrode and a reference electrode made of metallic lithium were immersed in the electrolyte solution, and AC impedance was measured using the four-terminal method. The AC impedance measurement conditions were a temperature of 25°C, a voltage of 10 mV, and a frequency of 1 MHz to 10 mHz. The impedance at the solid electrolyte / electrolyte interface was separated using a Nyquist plot, and the interfacial resistance was determined. The results are shown in Table 2.

[0098] As shown in Table 2, the interface resistance in Example 2 was 10 Ωcm 2 In contrast, Comparative Example 2 was 22 Ωcm 2 and Comparative Example 3 is 79 Ωcm 2It was clear that the solid electrolyte in Example 2, which was wet-polished using a specific solvent containing an alkali metal salt and an aprotic organic solvent, had reduced interfacial resistance compared to the solid electrolyte in Comparative Example 2, which was wet-polished using an aprotic organic solvent, and the solid electrolyte in Comparative Example 3, which was dry-polished. The examples revealed that the interfacial resistance of the solid electrolyte can be reduced by contacting the interface of an oxide-based solid electrolyte with a specific solvent containing an alkali metal salt and an aprotic organic solvent.

[0099] Oxide-based solid electrolytes with a garnet-type crystal structure containing Li, La, and Zr have the excellent characteristics of having bulk conductivity comparable to that of nonaqueous electrolytes and being electrochemically stable against metallic lithium. However, because oxide-based solid electrolytes have high interfacial resistance, it is difficult for energy storage devices that use compacts formed by pressing solid electrolyte particles to achieve battery characteristics that are practically usable. In contrast, the examples demonstrate that solid electrolytes that can reduce interfacial resistance can be obtained. Therefore, energy storage devices that use compacts formed by pressing solid electrolyte particles can be obtained that achieve battery characteristics that are practically usable, without having to form and sinter the solid electrolyte particles into a high-density sintered body.

[0100] The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0101] In the embodiment, the electricity storage device 11 has been described as including a positive electrode layer 12 in which an active material layer 14 is provided on one side of a current collecting layer 13, and an negative electrode layer 16 in which an active material layer 18 is provided on one side of a current collecting layer 17, but the present invention is not necessarily limited to this. For example, it is of course possible to apply each element in the embodiment to an electricity storage device including electrode layers in which an active material layer 14 and an active material layer 18 are provided on both sides of a current collecting layer 13 (so-called bipolar electrodes). If bipolar electrodes and separators 15 are alternately stacked and housed in a case (not shown), an electricity storage device with a so-called bipolar structure can be obtained.

[0102] In the embodiment, the active material layers 14, 18 and the separator 15 all contain the ion conductor 10, but this is not necessarily limited to this. The electricity storage device only needs to have at least one of the active material layers 14, 18 and the separator 15 contain the ion conductor 10.

[0103] In the embodiment, the solid electrolyte 19 uses lithium ions as a charge carrier, but this is not necessarily limited to this. Other charge carriers may be alkali metal ions such as sodium ions and potassium ions, depending on the type of solid electrolyte 19.

[0104] In the embodiments, the power storage devices 11, 24, and 26 are described as being made of lithium-ion batteries, but this is not necessarily limited to this. It is clear that other power storage devices may include the solid electrolyte 19. Examples of other power storage devices include electrochemical capacitors. Examples of electrochemical capacitors include redox capacitors that utilize redox reactions and hybrid capacitors that are asymmetric cells that combine an electric double layer capacitor with a solid electrolyte 19.

[0105] Although not described in the embodiment, it is of course possible to dispose a protective layer 29 between the active material layer 18 and the separators 15, 25, or between the current collecting layer 17 and the active material layer 18. Disposing a protective layer 29 between the active material layer 18 and the separators 15, 25 can reduce short circuits caused by dendrites. Disposing a protective layer 29 between the current collecting layer 17 and the active material layer 18 can reduce deterioration of the current collecting layer 17. [Explanation of symbols]

[0106] 11,24,26 Energy storage devices 12 Positive electrode layer (electrode) 15 Separator 16 Negative electrode layer (electrode) 19 Solid electrolyte 22 Surface layer 25 Separator

Claims

1. A method for producing an oxide-based solid electrolyte, comprising: a process for producing a solid electrolyte, the process comprising contacting a fractured surface of the solid electrolyte with an aprotic organic solvent having an alkali metal salt dissolved therein, and forming a surface layer derived from the alkali metal salt on the fractured surface.

2. 2. The method for producing a solid electrolyte according to claim 1, wherein the alkali metal salt is a lithium salt.

3. 2. The method for producing a solid electrolyte according to claim 1, wherein the alkali metal salt contains at least one of fluorine, sulfur, and nitrogen.

4. 2. The method for producing a solid electrolyte according to claim 1, wherein the alkali metal salt is lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide.

5. 2. The method for producing a solid electrolyte according to claim 1, wherein the fracture surface is produced by flowing the aprotic organic solvent in which the solid electrolyte is dispersed, thereby pulverizing the solid electrolyte.

6. 2. The method for producing a solid electrolyte according to claim 1, wherein the solid electrolyte has a garnet-type crystal structure containing Li, La, and Zr.

7. The method for producing a solid electrolyte according to claim 6, wherein the solid electrolyte further contains Mg and Sr.

8. A method for producing a separator, comprising the step of arranging a solid electrolyte obtained by the method for producing a solid electrolyte according to any one of claims 1 to 7.

9. A method for producing an electrode, comprising the step of arranging a solid electrolyte obtained by the method for producing a solid electrolyte according to any one of claims 1 to 7.

10. A method for producing an electricity storage device, comprising the step of arranging a solid electrolyte obtained by the method for producing a solid electrolyte according to any one of claims 1 to 7.

Images