Solid electrolyte, ion conductor, sheet, and power storage device

Abstract

Provided are a solid electrolyte (19) capable of improving conductivity, an ion conductor (10), a sheet (15), and a power storage device (11). The solid electrolyte has a garnet-type crystal structure containing Li, La, Zr, and O, wherein the sulfur mass concentration measured by carbon / sulfur analysis using a combustion infrared absorption method is at least 0.01%, and the sulfur abundance obtained from a peak intensity at a binding energy of 160-174 eV in spectra obtained by X-ray photoelectron spectroscopy is at most 30 times the Li-O-derived oxygen abundance obtained from a peak intensity at a binding energy of 528.5 eV. The ion conductor includes a solid electrolyte and an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent. The sheet includes an ion conductor and a binder for binding a solid electrolyte. The power storage device includes a solid electrolyte.

Description

Solid electrolyte, ionic conductor, sheet and electricity storage device

[0001] The present invention relates to a solid electrolyte, an ion conductor, a sheet, and an electricity storage device.

[0002] Oxides containing Li, La, and Zr and having a garnet-type crystal structure have ionic conductivity and high electrochemical stability, and therefore, Patent Document 1 discloses a prior art technique in which such oxides are used as solid electrolytes in electricity storage devices.

[0003] Patent No. 6797619

[0004] However, the solid electrolyte has problems in terms of conductivity, such as high interfacial resistance.

[0005] The present invention has been made to solve this problem, and has an object to provide a solid electrolyte, an ion conductor, a sheet, and an electricity storage device that can improve the electrical conductivity.

[0006] A first aspect for achieving this object is a solid electrolyte having a garnet-type crystal structure containing Li, La, Zr, and O, in which the mass concentration of sulfur measured by carbon-sulfur analysis using combustion infrared absorption spectroscopy is 0.01% or more, and the amount of sulfur present, obtained from the peak intensity in the binding energy range of 160 eV to 174 eV in a spectrum obtained by X-ray photoelectron spectroscopy, is 30 times or less the amount of oxygen present derived from Li—O, obtained from the peak intensity at a binding energy of 528.5 eV.

[0007] In the second aspect, in the first aspect, a peak derived from sulfur oxides is present in a binding energy range of 166 eV to 170 eV in a spectrum obtained by X-ray photoelectron spectroscopy.

[0008] In a third aspect, in the first or second aspect, the mass concentration of carbon measured by carbon-sulfur analysis is 0.1% or more, and the amount of carbon present, obtained from the peak intensity in the binding energy range of 280 eV to 294 eV in a spectrum obtained by X-ray photoelectron spectroscopy, is 30 times or less the amount of oxygen present derived from Li—O, obtained from the peak intensity at a binding energy of 528.5 eV.

[0009] In a fourth aspect, in any one of the first to third aspects, the proportion of the amount of carbon dioxide generated between room temperature and 500°C to the amount of carbon dioxide generated between room temperature and 1000°C, as measured by thermal generated gas mass spectrometry, is 5% or more and 49% or less.

[0010] A fifth aspect is the composition of any one of the first to fourth aspects, further comprising Mg and Sr.

[0011] A sixth aspect is an ion conductor, which includes the solid electrolyte according to any one of the first to fifth aspects and an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent.

[0012] A seventh aspect is a sheet comprising the solid electrolyte of any one of the first to fifth aspects, or the ion conductor of the sixth aspect.

[0013] An eighth aspect is an electrode, which includes the solid electrolyte according to any one of the first to fifth aspects, or the ion conductor according to the sixth aspect.

[0014] A ninth aspect is an electrode that is in contact with a protective layer containing the solid electrolyte of any one of the first to fifth aspects, or in contact with a protective layer containing the ion conductor of the sixth aspect.

[0015] A tenth aspect is a separator, which includes the solid electrolyte according to any one of the first to fifth aspects, or the ion conductor according to the sixth aspect.

[0016] An eleventh aspect is a separator that is in contact with a protective layer containing the solid electrolyte of any one of the first to fifth aspects, or in contact with a protective layer containing the ion conductor of the sixth aspect.

[0017] A twelfth aspect is an electricity storage device, which includes the electrode according to the eighth or ninth aspect, or the separator according to the tenth or eleventh aspect.

[0018] According to the solid electrolyte of the present invention, the mass concentration of sulfur measured by carbon-sulfur analysis using the combustion infrared absorption method is 0.01 wt % or more, and therefore electrical conductivity can be improved.

[0019] FIG. 1 is a cross-sectional view of an electricity storage device including an ion conductor according to a first embodiment; FIG. 2 is a diagram schematically showing a garnet-type crystal structure; FIG. 3 is a cross-sectional view of a separator; FIG. 4 is a cross-sectional view of an electricity storage device according to a second embodiment; FIG. 5 is a cross-sectional view of an electricity storage device according to a third embodiment; (a) is a cross-sectional view of an insulator according to a fourth embodiment, (b) is a cross-sectional view of an electrode according to a fifth embodiment, and (c) is a cross-sectional view of an electrode according to a sixth embodiment; FIG. 6 is an S2p spectrum of a solid electrolyte obtained by X-ray photoelectron spectroscopy; and FIG. 7 is a result of thermal evolved gas mass spectrometry.

[0020] 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).

[0021] 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 a metal selected from Ni, Ti, Fe, and Al, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0022] 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 the conductive additive include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0023] Examples of the active material 20 include a metal oxide containing a transition metal, a sulfur-based active material, and an organic active material. Examples of the metal oxide containing a transition metal include a metal oxide containing Li and one or more elements selected from Mn, Co, Ni, Fe, Cr, and V. Examples of the metal oxide containing a transition metal include LiCoO ２ , LiNi ０．８ Co ０．１５ Al ０．０５ O２ , LiMn ２ O ４ , LiNiVO ４ , LiNi ０．５ Mn １．５ O ４ , LiNi １／３ Mn １／３ Co １／３ O ２ and LiFePO ４ is exemplified.

[0024] 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 is made of Al ２ O ３ , ZrO ２ , LiNbO ３ , Li ４ Ti ５ O １２ , LiTaO ３ , LiNbO ３ , LiAlO ２ , Li ２ ZrO ３ , Li ２ WO ４ , Li ２ TiO ３ , Li ２ B ４ O ７ , Li ３ P.O. ４ and Li ２ MoO ４ is exemplified.

[0025] The sulfur-based active material is S, TiS ２ , NiS, FeS ２ , Li ２ S, MoS ３ 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.

[0026] 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 later). The ion conductor 10 may further include a binder.

[0027] 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 a metal selected from Ni, Ti, Fe, Cu, and Si, an alloy containing two or more of these elements, stainless steel, and a carbon material.

[0028] 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, Li, ４ Ti ５ O １２ , 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.

[0029] The electricity storage device 11 is manufactured, for example, as follows: A slurry is produced by mixing an electrolyte solution, in which a lithium salt is dissolved in a nonaqueous solvent, with the solid electrolyte 19, and then mixing the mixture with a solution in which a binder is dissolved in a solvent. The slurry is formed into a sheet and then dried to obtain a green sheet (electrolyte sheet) for the separator 15.

[0030] A slurry is prepared by mixing an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent with a solid electrolyte 19, mixing the active material 20 with the solid electrolyte, and then mixing a solution in which a binder is dissolved in a solvent with the mixed solution. 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.

[0031] A slurry is prepared by mixing an active material 21 with a solid electrolyte 19 and an electrolyte solution prepared by dissolving a lithium salt in a non-aqueous solvent, and then mixing with a solution prepared by dissolving a binder in a solvent. 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.

[0032] 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 an integrated unit. 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.

[0033] The solid electrolyte 19 is a composite oxide containing Li, La, and Zr and having a garnet-type crystal structure. This type of garnet-type crystal structure is represented by the general formula C ３ A ２ B ３ O １２ It is expressed as:

[0034] FIG. 2 is a diagram schematically showing a garnet-type crystal structure. In the garnet-type crystal structure, the C site Sc is dodecahedrally coordinated with an oxygen atom Oa, the A site Sa is octahedrally coordinated with an oxygen atom Oa, and the B site Sb is tetrahedrally coordinated with an oxygen atom Oa. In the solid electrolyte 19, Li can exist in a position that would be octahedrally coordinated with an oxygen atom Oa in a normal garnet-type crystal structure, but that becomes a void V. The void V is, for example, a position sandwiched between the B site Sb1 and the B site Sb2. The Li present in the void V is octahedrally coordinated with an oxygen atom Oa that forms an octahedron including the tetrahedral face Fb1 that forms the B site Sb1 and the tetrahedral face Fb2 that forms the B site Sb2. For example, Li having a garnet-type crystal structure ７ La ３ Zr ２ O 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 void V.

[0035] The garnet-type crystal structure is X-ray diffraction file No. 422259 (Li) in the Cambridge Structural Database (CSD). ７ La ３ Zr ２ O １２ ) has an XRD pattern similar to that of No. 422259. Compared with No. 422259, the type of constituent elements and the Li concentration of the solid electrolyte 19 may differ, and therefore the diffraction angle and intensity ratio may differ. A typical crystal structure of this type is a cubic system (space group Ia-3d (- indicates an overline that indicates a reversal operation), JCPDS: 84-1753).

[0036] Returning to FIG. 1, the solid electrolyte 19 is typically Li ７ La ３ Zr ２ O 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).

[0037] The solid electrolyte 19 is, for example, Li ６ La ３ Zr １．５ W ０．５ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Al ０．２ O １２ , Li ６．１５ La ３ Zr １．７５ Ta ０．２５ Ga ０．２ O １２ , Li ６．２５ La ３ Zr ２ Ga ０．２５ O １２ , Li ６．４ La ３ Zr １．４ Ta ０．６ O１２ , Li ６．５ La ３ Zr １．７５ Te ０．２５ O １２ , Li ６．７５ La ３ Zr １．７５ Nb ０．２５ O １２ , Li ６．９ La ３ Zr １．６７５ Ta ０．２８９ Bi ０．０３６ O １２ , Li ６．４６ Ga ０．２３ La ３ Zr 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 Zr ２ O １２ Examples include:

[0038] 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), with the molar ratio of each element satisfying all of the following (1) to (3), or contains both Mg and element A, with the molar ratio of each element satisfying all of the following (4) to (6). Element A is preferably Sr, in order to increase 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

[0039] 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.

[0040] To determine the median diameter of the solid electrolyte 19, first, an image of the solid electrolyte 19 that appears 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 using a scanning electron microscope (SEM), and the circle-equivalent diameter is calculated from the area of ​​each particle of the solid electrolyte 19, and a 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 400 μm particles of the separator 15. ２ The area shall be equal to or greater than this.

[0041] 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, Zr, and O. Examples of the 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.

[0042] The perovskite-type solid electrolyte is an oxide containing at least Li, Ti, and La, for example, La ２／３－Ｘ Li ３Ｘ TiO ３ The NASICON type solid electrolyte is an oxide containing at least Li, M (M is one or more elements selected from Ti, Zr, and Ge), and P, such as Li(Al,Ti) ２ (P.O. ４ ) ３ and Li(Al,Ge) ２ (P.O. ４ ) ３ The LISICON type solid electrolyte is Li １４ Zn(GeO ４ ) ４Examples of hydride-based solid electrolytes include hydrides of alkali metals or alkaline earth metals, and include at least one element from Group 13 of the Periodic Table of Elements (e.g., B, Al, Ga, In, and Ta). For example, LiBH ４ , LiAlH ４ Examples include:

[0043] FIG. 3 is a cross-sectional view of the separator 15 (see FIG. 1). The ionic conductor 10 contains an electrolyte solution 23 (non-aqueous electrolyte solution) in which a lithium salt is dissolved in a non-aqueous solvent. The lithium salt is a compound used for exchanging cations between the positive electrode layer 12 and the negative electrode layer 16. The anion of the lithium salt is a halide ion (I － , Cl － ,Br － etc.), SCN － , BF ４ － , BF ３ (CF ３ ) － , BF ３ (C ２ F ５ ) － , P.F. ６ － , ClO ４ － , SbF ６ － , N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ２ F ５ ) ２ － , B(C ６ H ５ ) ４ － , B(O ２ C ２ H ４ ) ２ － , C(SO ２ F) ３ － , C(SO ２ CF ３ ) ３－ , C.F. ３ COO － , C.F. ３ SO ２ O － , C ６ F ５ SO ２ O － , B(O ２ C ２ O ２ ) ２ － , RCOO － (R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group).

[0044] The anion of the lithium salt is a sulfonyl group -S(=O) ２ - N(SO ２ F) ２ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ２ F ５ ) ２ － Sulfonylimides such as PF ６ － The sulfonylimide anion is less susceptible to increases in the viscosity of the electrolyte and decreases in ionic conductivity even when the salt concentration is high, while the halophosphate ion has a high degree of dissociation. Both are preferred because they can form a highly stable and low-resistance coating (SEI) that reduces the reductive decomposition of the non-aqueous solvent and widens the reduction-side potential window.

[0045] 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. Among molecular solvents, aprotic solvents are preferred because they broaden the potential window of non-aqueous electrolytes. Examples of aprotic 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.

[0046] 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.

[0047] 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 derivatives thereof.

[0048] 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.

[0049] 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 more easily ions are solvated, 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. It is of course 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 in order to adjust the viscosity of the solvent, etc.

[0050] 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 preferably contains one or more cation species selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium.

[0051] The anion component of the ionic liquid is not particularly limited. ４ － , N(SO ２ F) ２ － inorganic anions such as B(C ６ H ５ ) ４ － , CH ３ SO ３ － , C.F. ３ SO ３ － , N(SO ２ CF ３ ) ２ － , N(SO ２ C ４ F ９ ) ２ － Examples of organic anions include:

[0052] 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 a lithium salt is dissolved.

[0053] The ionic conductor 10 may contain a binder that binds the solid electrolyte 19. Examples of the binder include fluorinated resins, polyolefins, polyimides, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ethers, styrene-butadiene rubber, and other rubber-like polymers. Examples of the fluorinated resin include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene-chlorotrifluoroethylene copolymers.

[0054] 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 a copolymer.

[0055] Because the solid electrolyte 19 is highly reactive, handling the solid electrolyte 19 in an inert gas atmosphere will result in a reaction with traces of moisture and carbon dioxide present in the inert gas, resulting in the formation of resistive phases such as lithium hydroxide and lithium carbonate on the surface of the solid electrolyte 19. Therefore, in this embodiment, the solid electrolyte 19 is wet-polished (wet-pulverized) in the presence of a sulfur-containing solution in an inert gas atmosphere. The solution immediately contacts the surface of the solid electrolyte 19 from which the resistive phase has been removed by polishing, and the components of the solution react with the solid electrolyte 19 to form a surface layer 22. Immediately after polishing, the solution used in the wet polishing remains on the surface layer 22 of the solid electrolyte 19. Removing the adhered solution reveals the surface layer 22 of the solid electrolyte 19.

[0056] The light elements (non-metallic elements) carbon and sulfur contained in the solid electrolyte 19 including the surface layer 22 can be quantitatively analyzed by oxygen flow combustion-infrared absorption spectroscopy. The solid electrolyte 19 including the surface layer 22 has a sulfur mass concentration of 0.01% or more as measured using a high-frequency induction heating furnace-type carbon / sulfur analyzer. The solid electrolyte 19 is composed of a composite oxide having a garnet-type crystal structure containing Li, La, and Zr, and does not contain sulfur. Therefore, sulfur is presumed to be contained in the surface layer 22. Sulfide ions have a higher polarizability than oxide ions and have a smaller effect of capturing lithium ions, and are therefore thought to have higher ionic conductivity than oxides. The presence of the sulfur-containing surface layer 22 in the solid electrolyte 19 reduces interfacial resistance. As a result, the conductivity of the solid electrolyte 19 can be improved.

[0057] The solid electrolyte 19 including the surface layer 22 can be analyzed by X-ray photoelectron spectroscopy (XPS). XPS involves irradiating the surface layer 22 of the solid electrolyte 19 with X-rays in a vacuum and measuring the spectrum of the kinetic energy of electrons emitted by photoionization, thereby obtaining information about the abundance ratio of elements constituting the surface layer 22. Since the mean free path in a solid of photoelectrons having energy equivalent to the kinetic energy of electrons emitted from the surface layer 22 when the surface layer 22 is irradiated with X-rays using an AlKα radiation source is 2 nm or less, the thickness of the surface layer 22 analyzed by XPS is estimated to be about 10 nm.

[0058] In the XPS S2p spectrum of the solid electrolyte 19, a peak exists in the binding energy range of 166 eV to 170 eV. Since the peak existing in the range of 166 eV to 170 eV in the S2p spectrum is derived from sulfur oxide, it is presumed that sulfur exists as an oxide in the surface layer 22. Since the surface layer 22 of the solid electrolyte 19 contains sulfur oxide, the interface resistance of the solid electrolyte 19 can be further reduced.

[0059] On the other hand, if the volume of the surface layer 22 becomes too large, there is a risk of an increase in resistance. Therefore, in XPS, the amount of sulfur present, obtained from the peak intensity in the binding energy range of 160 eV to 174 eV, is preferably 30 times or less the amount of oxygen present, derived from Li—O, obtained from the peak intensity at a binding energy of 528.5 eV.

[0060] The carbon content of the solid electrolyte 19 including the surface layer 22 is also measured by oxygen flow combustion-infrared absorption spectroscopy. The solid electrolyte 19 is made of a composite oxide having a garnet-type crystal structure containing Li, La, and Zr, and does not contain carbon. Therefore, it is presumed that carbon is contained in the surface layer 22 as lithium carbonate or the like.

[0061] The carbon component of the surface layer 22 is thought to exist as a compound containing lithium, and acts as an ion-conducting substance, although not as conductive as sulfide ions, so that as the mass concentration of carbon measured by a high-frequency induction heating furnace-type carbon-sulfur analyzer increases, the electrical conductivity of the surface layer 22 tends to increase. To ensure the electrical conductivity of the surface layer 22, the mass concentration of carbon is preferably 0.1% or more.

[0062] On the other hand, if the volume of the surface layer 22 becomes too large, there is a risk of an increase in resistance. Therefore, in XPS, the amount of carbon present, obtained from the peak intensity in the binding energy range of 280 eV to 294 eV, is preferably 30 times or less the amount of oxygen present, derived from Li—O, obtained from the peak intensity at a binding energy of 528.5 eV.

[0063] When the thermal decomposition behavior of the solid electrolyte 19 including the surface layer 22 is confirmed by thermally evolved gas mass spectrometry (TPD-MS), the amount of carbon dioxide generated between room temperature and 500°C preferably accounts for 5% or more of the amount of carbon dioxide generated between room temperature and 1000°C. The room temperature is defined in accordance with JIS Z8703:1983.

[0064] TPD-MS confirms the amount of carbon dioxide generated per unit area of ​​the surface layer 22 of the solid electrolyte 19. When the solid electrolyte 19 is a sintered body having a certain size, the dimensions of the sintered body are measured to calculate the area of ​​the surface layer 22. When the solid electrolyte 19 is a powder, the area of ​​the surface layer 22 is calculated based on the specific surface area of ​​the powder determined by gas adsorption method.

[0065] It is presumed that the carbon dioxide generated between room temperature and 500°C is derived from an organic material having lithium ion conductivity, such as lithium alkyl carbonate, contained in the surface layer 22. If the proportion of carbon dioxide generated between room temperature and 500°C is 5% or more, the organic material contained in the surface layer 22 can further reduce the interfacial resistance of the solid electrolyte 19.

[0066] The proportion of the amount of carbon dioxide generated between room temperature and 500°C to the amount of carbon dioxide generated between room temperature and 1000°C is preferably 49% or less. If the proportion of the amount of carbon dioxide generated between room temperature and 500°C exceeds 49%, the contents of the surface layer 22 will be biased toward organic components, which may reduce the stability and protective function of the inorganic components. By setting the proportion of the amount of carbon dioxide generated between room temperature and 500°C to 49% or less, the ion conduction network of the inorganic components can become dominant.

[0067] The lithium salt concentration of the nonaqueous electrolyte is preferably 4.0 mol / kg or less. This is because if the salt concentration of the nonaqueous electrolyte exceeds 4.0 mol / kg, the viscosity of the nonaqueous electrolyte increases, which significantly reduces the lithium ion conductivity. The salt concentration of the nonaqueous electrolyte is determined, for example, as follows. Here, the ionic conductor 10 constituting the separator 15 will be described, but the ionic conductor 10 constituting the active material layers 14 and 18 can also be determined in the same manner.

[0068] First, the separator 15 is crushed and immersed in a solvent, and the nonaqueous electrolyte contained in the separator 15 is dissolved in the solvent, and then the separator 15 is separated into a solid component and a liquid component using a centrifuge. The Li content of the separated liquid component is determined by high-frequency inductively coupled plasma spectroscopy (ICP).

[0069] The type of nonaqueous solvent contained in separator 15 is identified by, for example, gas chromatography-mass spectrometry (GC-MS). The nonaqueous solvent of which type has been identified (hereinafter referred to as a "standard substance") and separator 15 are analyzed by thermogravimetric differential thermal analysis (TG-DTA). The analysis results of the standard substance and the analysis results of separator 15 are compared to identify the content of nonaqueous solvent contained in separator 15. The molar concentration (mol / kg) of the lithium salt in the nonaqueous electrolyte is calculated based on the Li content in the liquid component and the content of the nonaqueous solvent in separator 15.

[0070] 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 non-aqueous electrolyte solution 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 non-aqueous electrolyte solution 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.

[0071] The contents (volume %) of the solid electrolyte 19 and the non-aqueous electrolyte solution are determined by freezing the separator 15 or embedding the separator 15 in a tetrafunctional epoxy resin or the like and then analyzing a randomly selected cross section of the 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 a backscattered electron image to identify the areas of the solid electrolyte 19 and the non-aqueous electrolyte solution, and the proportions of these areas in the cross section of the separator 15 are regarded as the proportions of the volume of the ion conductor 10 in the separator 15 to obtain the contents (volume %) of the solid electrolyte 19 and the non-aqueous electrolyte solution.

[0072] The Li ion conductivity of the ionic conductor 10 is determined by the type and salt concentration of the solid electrolyte 19 and the non-aqueous electrolyte. The lithium ion conductivity of the ionic conductor 10 at 25° C. is 1.0×10 －５ The ionic conductivity is preferably 25 S / cm or more in order to ensure the output density of the electricity storage device 11 including the ionic conductor 10.

[0073] A second embodiment will be described with reference to Fig. 4. In the first embodiment, an electricity storage device 11 using a solid electrolyte 19 as the electrolyte was described. In the second embodiment, a case where an ion conductor 10 is used in a liquid-based lithium-ion battery using a nonaqueous electrolyte solution as the electrolyte will be 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.

[0074] The power storage device 24 includes, in 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 electrolyte contained in the positive electrode layer 12 and the negative electrode layer 16, and that allows lithium ions to pass through but does not have electronic conductivity. Examples of the separator 25 include nonwoven fabrics and porous membranes made of cellulose, polypropylene, polyethylene, polyimide, alumina, etc. The nonaqueous electrolyte is the same as that described in the first embodiment, so its description will be omitted.

[0075] In the electricity storage device 24 of the second embodiment, the ion conductor 10 is contained in the positive electrode layer 12 and the negative electrode layer 16, and therefore, the stability of operation is increased, similar to the electricity storage device 11 of the first embodiment.

[0076] A third embodiment will be described with reference to Fig. 5. In the first and second embodiments, the positive electrode layer 12, the separator 15, and the 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The solid electrolyte 19 contained in the ion conductor 10 has a garnet-type crystal structure containing Li, La, Zr, and O, and is resistant to reduction by the metallic lithium of the active material layer 31, so 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.

[0082] 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.

[0083] 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, with the protective layer 29 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.

[0084] 6(b) is a cross-sectional view of an electrode 36 according to the 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.

[0085] 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.

[0086] The insulator 33 is disposed in the electric storage device in place of the separator 25 of the electric storage device 24 of the second embodiment or the electric 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.

[0087] 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 in the second embodiment or the electricity storage device 26 in 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 in the second embodiment or the electricity storage device 26 in the third embodiment.

[0088] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0089] (Preparation of solid electrolyte) Li ６．９５ Mg ０．１５ La ２．７５ Sr ０．２５ Zr ２．０ O １２ So that Li ２ CO ３ , MgO, La(OH) ３ , SrCO ３ , ZrO ２ was weighed. ２ CO ３ Considering the volatilization of Li during firing, the amount of Li was in excess of about 15 mol% in elemental terms. The weighed raw materials and ethanol were placed in a nylon pot together with zirconia balls and ground and mixed in a ball mill for 15 hours. The slurry removed from the pot was dried, then placed on an MgO plate and pre-fired at 1200°C for 10 hours. A binder was added to the pre-fired material, and the material was ground and mixed in an inert solvent for 60 hours in a ball mill. The slurry removed from the pot was dried to obtain a raw material powder for the solid electrolyte.

[0090] 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 about 2.5 mm. The disk was pressed with a cold isostatic press at a pressure of 1.5 t / cm ２ The compact was covered with the raw material powder and sintered in the air at 1100° C. for 4 hours to obtain a sintered body of the solid electrolyte.

[0091] (Example) Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in dimethyl carbonate to prepare a non-aqueous solution with a lithium salt concentration of 2.7 mol / L. The sintered solid electrolyte and the non-aqueous solution were placed in a nylon pot together with zirconia balls, and the sintered solid was wet-pulverized in a ball mill for 15 hours. The slurry removed from the pot was subjected to solid-liquid separation, and the separated solid portion was washed with dimethyl carbonate and dried to obtain the solid electrolyte of this example.

[0092] (Comparative Example) Using a dry jet mill (Nano Jetmizer (registered trademark) NJ-50 model, manufactured by Aisin Nano Technologies Co., Ltd.), the sintered body of the solid electrolyte was dry-pulverized by passing it through the jet mill twice in a nitrogen atmosphere, thereby obtaining a solid electrolyte for the comparative example.

[0093] (Quantitative Analysis of Carbon and Sulfur) The solid electrolytes in the Examples and Comparative Examples were placed in ceramic crucibles and burned in a high-frequency induction heating furnace in an oxygen stream. Carbon was gasified as carbon dioxide and carbon monoxide, and sulfur was gasified as sulfur dioxide. The generated gas was introduced into a non-dispersive infrared detector, and carbon and sulfur were detected as mass versus extraction time. The mass of the solid electrolyte (sample) before combustion was measured in advance to determine the sample mass, and the detected masses of carbon and sulfur were divided by the sample mass to calculate the mass concentrations of carbon and sulfur, respectively.

[0094] (XPS Spectral Measurement) The solid electrolytes in the examples and comparative examples 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: 140 eV, and analysis area: 100 μmΦ. The abundance ratio (atom%) of oxygen derived from Li—O obtained from the peak intensity at a binding energy of 528.5 eV (O1s spectrum), the abundance ratio (atom%) of sulfur obtained from the peak intensity in the binding energy range of 160 eV to 174 eV (S2p spectrum), and the abundance ratio (atom%) of carbon obtained from the peak intensity in the binding energy range of 280 eV to 294 eV (C1s spectrum) were measured.

[0095] Fig. 7 shows the S2p spectrum of the solid electrolyte by XPS, in which the horizontal axis represents the binding energy value of the measured electrons to the atomic nucleus, and the vertical axis represents the photoelectron intensity.

[0096] (Preparation of Samples for Measurement of Interface Resistance and Thermally Generated Gas Mass Analysis) Because it is difficult to measure the interface resistance of a solid electrolyte (powder), the interface resistance was measured using a sintered body of the solid electrolyte as a sample. Furthermore, thermally generated gas mass analysis was performed using a similarly prepared sample. The non-aqueous solution prepared in the Examples was dropped onto waterproof abrasive paper to which silicon carbide abrasive (particle size 320 as specified in JIS R6010:2000) was fixed, and each circular surface of the sintered body of the solid electrolyte was wet-polished under an argon atmosphere. This resulted in the samples of the Examples. The samples in the Comparative Examples were prepared by dry-polishing each circular surface of the sintered body using waterproof abrasive paper under an argon atmosphere.

[0097] (Thermal evolved gas mass spectrometry) The thermal decomposition behavior of the samples in the examples and comparative examples was measured by thermal evolved gas mass spectrometry (TPD-MS). The samples were heated in a He atmosphere at atmospheric pressure from room temperature to 1000°C at a temperature increase rate of 10°C / min, and the mass of carbon dioxide generated per unit area from room temperature to 500°C and the mass of carbon dioxide generated per unit area from room temperature to 1000°C were measured. The area of ​​the sample was calculated by measuring the diameter of the circular surface of the polished sintered body. Figure 8 shows the results of the thermal evolved gas mass spectrometry, with the heating temperature on the horizontal axis and the cumulative amount of carbon dioxide generated up to that point on the vertical axis.

[0098] (Measurement of Interface Resistance) Each sample in the Examples and Comparative Examples was fixed by sandwiching it on both sides using a cylinder made of an insulator with a gasket interposed between them. A non-aqueous electrolyte was placed in the cylinders on both sides of the sample, and a working electrode and a reference electrode made of metallic lithium were immersed in the non-aqueous electrolyte, and AC impedance was measured using a four-terminal method. The non-aqueous electrolyte used for the measurement was prepared by dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in dimethyl carbonate so that the lithium salt concentration was 3.0 mol / kg. The AC impedance measurement conditions were a temperature of 25°C, a voltage of 10 mV, and a frequency of 1 MHz-10 mHz. The impedance of the solid electrolyte / non-aqueous electrolyte interface was separated using a Nyquist plot, and the interface resistance was determined.

[0099] The carbon and sulfur mass concentrations and interface resistance obtained by carbon-sulfur analysis are shown in Table 1. The abundance ratios (atom %) of oxygen, sulfur, and carbon obtained by XPS, the ratio of the amount of sulfur to the amount of oxygen (S / O), and the ratio of the amount of carbon to the amount of oxygen (C / O) are shown in Table 2. The mass (μg / cm ) of carbon dioxide generated from room temperature to 500°C by thermal evolved gas mass spectrometry was ２ ), the mass of carbon dioxide generated from room temperature to 1000°C (μg / cm ２ ), and the ratio (%) of the mass of carbon dioxide generated between room temperature and 500°C to the mass of carbon dioxide generated between room temperature and 1000°C are shown in Table 3.

[0100]

[0101]

[0102]

[0103] As shown in Table 1, the interface resistance is 10 Ωcm in the example. ２ In contrast, the comparative example was 79 Ωcm ２ It was clear that the solid electrolyte in the example that was wet-pulverized in the presence of a non-aqueous solution had a reduced interfacial resistance compared to the solid electrolyte in the comparative example that was dry-polished.

[0104] As shown in Table 1, the mass concentration of carbon in the Examples was higher than that in the Comparative Examples. The mass concentration of carbon in the Examples was 0.10 wt % or more, while the mass concentration of carbon in the Comparative Examples was less than 0.10 wt %. The carbon in the Examples is presumed to be derived from the non-aqueous solution used when preparing the solid electrolyte in the Examples by wet pulverization and from dimethyl carbonate used for washing after pulverization. The carbon in the Comparative Examples is presumed to be derived from lithium carbonate formed on the surface of the solid electrolyte.

[0105] Furthermore, the sulfur mass concentration in the Examples was 0.01 wt% or more, while the sulfur mass concentration in the Comparative Examples was less than 0.01 wt%. The sulfur in the Examples is presumed to be derived from the sulfur component contained in the non-aqueous solution used during wet grinding, and is therefore presumed to be present on the surface of the solid electrolyte. It is presumed that the interfacial resistance in the Examples was reduced due to the influence of sulfur present on the surface of the solid electrolyte.

[0106] As shown in Table 2, the XPS measurement revealed that in the Examples, the amount of sulfur present was 30 times or less the amount of oxygen present, and the amount of carbon present was 30 times or less the amount of oxygen present. On the other hand, in the Comparative Examples, there was no sulfur present, and the amount of carbon present was more than 30 times the amount of oxygen present. It is presumed that the Examples were able to control the interface of the samples.

[0107] According to the S2p spectrum in Figure 7, peaks not seen in the comparative example were observed in the binding energy range of 166 eV to 170 eV. These peaks are due to sulfur oxides. It is presumed that the presence of sulfur oxides on the outermost surface of the solid electrolyte reduced the interfacial resistance.

[0108] As shown in Figure 8, carbon dioxide was generated in the Examples at a lower temperature than in the Comparative Examples. As shown in Table 3, in the Examples, the proportion of the amount of carbon dioxide generated between room temperature and 500°C to the amount of carbon dioxide generated between room temperature and 1000°C, as measured by thermal evolved gas mass spectrometry, was 5% or more. On the other hand, in the Comparative Examples, this proportion was less than 5%. The reason that carbon dioxide was generated at a lower temperature in the Examples than in the Comparative Examples is thought to be due to the presence of organic matter on the surface of the solid electrolyte. It is presumed that the interfacial resistance in the Examples was reduced due to the influence of organic matter present on the surface of the solid electrolyte.

[0109] According to the examples, it has become clear that a low-resistivity surface layer can be formed on the surface of a solid electrolyte by wet-pulverizing or wet-polishing a sintered body or particles of the solid electrolyte in the presence of a non-aqueous solution to create a new surface on the surface of the solid electrolyte.

[0110] 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 electrolyte solutions and being electrochemically stable against metallic lithium. However, because oxide-based solid electrolytes have high interfacial resistance, it is difficult for energy storage devices employing compacts formed by pressure molding of solid electrolyte particles to achieve practical battery characteristics. In contrast, the examples demonstrate that solid electrolytes capable of reducing interfacial resistance can be obtained. Therefore, energy storage devices employing compacts formed by pressure molding of solid electrolyte particles can be obtained that achieve practical battery characteristics without forming and sintering the solid electrolyte particles into a high-density sintered body.

[0111] 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.

[0112] 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 this 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.

[0113] 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. It is sufficient for the power storage device that at least one of the active material layers 14, 18 and the separator 15 contains the ion conductor 10.

[0114] In the embodiments, the power storage devices 11, 24, and 26 are described as being composed 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 the solid electrolyte 19.

[0115] 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 separator 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 separator 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.

[0116] REFERENCE SIGNS LIST 10 ion conductor 11, 24, 26 electricity storage device 12 positive electrode layer (sheet, electrode) 15 separator (sheet) 16 negative electrode layer (sheet, electrode) 19 solid electrolyte 23 non-aqueous electrolyte (electrolyte) 25 separator 29, 32 protective layer

Claims

1. A solid electrolyte having a garnet-type crystal structure containing Li, La, Zr, and O, wherein the mass concentration of sulfur measured by carbon-sulfur analysis using combustion infrared absorption spectroscopy is 0.01% or more, and the amount of sulfur obtained from the peak intensity in the binding energy range of 160 eV to 174 eV in an X-ray photoelectron spectroscopy spectrum is 30 times or less the amount of oxygen derived from Li-O obtained from the peak intensity at a binding energy of 528.5 eV.

2. The solid electrolyte according to claim 1, wherein a peak attributable to sulfur oxides is present in the binding energy range of 166 eV to 170 eV in a spectrum obtained by X-ray photoelectron spectroscopy.

3. A solid electrolyte according to claim 1, wherein the mass concentration of carbon measured by the carbon-sulfur analysis is 0.1% or more, and the amount of carbon present, obtained from the peak intensity in the binding energy range of 280 eV to 294 eV in the spectrum obtained by X-ray photoelectron spectroscopy, is 30 times or less the amount of oxygen present derived from Li—O, obtained from the peak intensity at a binding energy of 528.5 eV.

4. The solid electrolyte according to claim 1, wherein the ratio of the amount of carbon dioxide generated between room temperature and 500°C to the amount of carbon dioxide generated between room temperature and 1000°C, as measured by thermal evolved gas mass spectrometry, is 5% or more and 49% or less.

5. The solid electrolyte according to any one of claims 1 to 4, further comprising Mg and Sr.

6. An ionic conductor comprising the solid electrolyte according to any one of claims 1 to 4 and an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent.

7. A sheet comprising the solid electrolyte according to any one of claims 1 to 4.

8. An electrode comprising the solid electrolyte according to any one of claims 1 to 4.

9. An electrode in contact with a protective layer containing the solid electrolyte according to any one of claims 1 to 4.

10. An electricity storage device comprising the electrode according to claim 8.

11. An electricity storage device comprising the electrode according to claim 9.

12. A separator comprising the solid electrolyte according to any one of claims 1 to 4.

13. A separator in contact with a protective layer containing the solid electrolyte according to any one of claims 1 to 4.

14. An electricity storage device comprising the separator according to claim 12.

15. An electricity storage device comprising the separator according to claim 13.

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