Sheet and power storage device

Abstract

The present invention provides a sheet (10) which is capable of improving the cycle characteristics, and a power storage device (20). The sheet includes an active material layer (11) that contains an active material (14), and an oxide layer (12) that is in contact with the active material layer. The active material layer includes an inorganic skeleton (15) which is provided on a surface of the active material layer, the surface being in contact with the oxide layer, and / or among the active material. The oxide layer contains particles (16) of an oxide-based solid electrolyte, a binder that binds the particles, and an electrolyte solution. The power storage device includes a positive electrode layer (21), a negative electrode layer, and a separator (12) that separates the positive electrode layer and the negative electrode layer from each other. The negative electrode layer includes a current collector layer (13) and an active material layer. The active material layer is a part of the sheet.

Description

Seat and power storage device

[0001] The present invention relates to a sheet including an active material layer and an electricity storage device.

[0002] In an electricity storage device containing in the negative electrode an active material whose volume changes during charging and discharging, repeated charge and discharge cycles can cause voids to form between the active materials or changes in the shape of the active material, resulting in a rapid decrease in capacity retention. Patent Document 1 describes a battery having a layer containing an active material and a solid electrolyte, which is subjected to a pressure of 150 kgf / cm ２ A prior art technique has been disclosed in which charge / discharge treatment is repeated multiple times while applying the above pressure in the stacking direction, thereby preventing a sudden decrease in capacity retention rate.

[0003] JP 2014-35987 A

[0004] The prior art has a problem in that the capacity retention rate varies due to slight variations in pressure during charge and discharge processes.

[0005] The present invention has been made to solve this problem, and has an object to provide a sheet and an electricity storage device that can improve cycle characteristics without performing charge / discharge treatment under pressure.

[0006] A first aspect for achieving this object is a sheet comprising an active material layer containing an active material, further comprising an oxide layer in contact with the active material layer, the active material layer including an inorganic skeleton provided on at least one of the surface of the active material layer in contact with the oxide layer and between the active material, the oxide layer including particles of an oxide-based solid electrolyte, a binder binding the particles, and an electrolytic solution.

[0007] In a second aspect, in the first aspect, the median diameter of the particles is 0.04 to 0.6 times the median diameter of the active material.

[0008] In a third aspect, in the first or second aspect, the Young's modulus of the oxide layer is 0.05 to 6.50 MPa.

[0009] In a fourth aspect, in any one of the first to third aspects, the circularity of the particles is less than 0.8, preferably less than 0.72, and more preferably 0.60 or more and less than 0.80.

[0010] In a fifth aspect, in any one of the first to fourth aspects, the ratio of the volume of the binder to the combined volume of the particles, the binder, and the electrolyte solution is less than 50%, and preferably 5% or more.

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

[0012] In a seventh embodiment, in the sixth embodiment, the particles further contain Mg and Sr.

[0013] An eighth aspect is an electricity storage device comprising a positive electrode layer, a negative electrode layer, and a separator separating the positive electrode layer and the negative electrode layer, the negative electrode layer including a current collecting layer and an active material layer, and the active material layer is part of the sheet of any one of the first to seventh aspects.

[0014] In a ninth aspect, in the eighth aspect, the separator includes an oxide layer of a sheet.

[0015] In a tenth aspect, in the eighth aspect, a protective layer is further provided in contact with the active material layer, the protective layer including an oxide layer of the sheet.

[0016] According to the sheet of the present invention, the inorganic skeleton reduces the volume change of the active material during charge and discharge, and the particles contained in the oxide layer and the inorganic skeleton combine to reduce peeling of the oxide layer, thereby improving the cycle characteristics of an electricity storage device including the sheet.

[0017] Fig. 1 is a cross-sectional view of a sheet according to one embodiment; Fig. 2 is a diagram schematically showing a garnet-type crystal structure; Fig. 3 is a cross-sectional view of an electricity storage device according to a first embodiment; 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;

[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 a sheet 10 according to one embodiment. The sheet 10 includes an active material layer 11 and an oxide layer 12 in contact with the surface of the active material layer 11. In this embodiment, the sheet 10 also includes a current collecting layer 13 disposed on the back surface of the active material layer 11.

[0019] The current collecting layer 13 is not particularly limited as long as it is a material that has electronic conductivity and can conduct current to the active material layer 11. For example, conductive materials such as C, Ti, Cr, Ni, Cu, Fe, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Al, and Au, or alloys containing two or more of these conductive materials (e.g., stainless steel) can be used for the current collecting layer 13. When Fe is used for the current collecting layer 13, it is preferably coated with Ni, Cu, or the like to prevent oxidation. The shape of the current collecting layer 13 is also not limited, and examples include a wire, rod, plate, foil, and porous shape.

[0020] The active material layer 11 includes an active material 14 and an inorganic skeleton 15 provided on at least one of the surface of the active material layer 11 and between the active materials 14. In this embodiment, the inorganic skeleton 15 is provided both on the surface of the active material layer 11 (at the interface between the active material layer 11 and the oxide layer 12) and between the active materials 14.

[0021] The active material 14 is an alkali metal ion (Li ＋ , Na ＋ , K. ＋ The active material 14 is not particularly limited as long as it is a material capable of reversibly absorbing and releasing ions (such as ions). The ion absorption and release mechanism may be dissolution or precipitation of a substance, or insertion and desorption of ions between crystalline layers. The active material 14 may be, for example, one or more elements selected from the group consisting of Li, Na, K, C, Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, W, Pb, and Bi, or an alloy, composite, oxide, chalcogenide, or halide using these elements.

[0022] The active material 14 is used to set the electrode potential from 0 V to 1 V (vs. Li ＋ From the viewpoint of keeping the content of the active material 14 within the range of 0.1 wt % / Li, at least one element selected from the group consisting of Li, Na, K, C, Mg, Al, Si, Ti, Zn, Ge, Fe, Mn, Ag, Cu, In, Sn, and Pb, or an allotrope, alloy, or oxide of these elements is preferred. From the viewpoint of increasing the energy density, the active material 14 preferably contains an element such as Al, Si, Zn, Ge, Ag, or Sn.

[0023] The alloy as the active material 14 is preferably Si—Al, Al—Zn, Si—Mg, Si—La, Al—Ge, Si—Ge, Si—Ag, Si—Sn, Si—Ti, Si—Y, Si—Cr, Si—Ni, Si—Zr, Si—V, Si—Nb, Si—Mo, Zn—Sn, Ge—Ag, Ge—Sn, Ge—Sb, Ag—Sn, Ag—Ge, Sn—Sb, or the like, and may be a complete solid solution alloy, a eutectic alloy, a hypoeutectic alloy, a hypereutectic alloy, or a peritectic alloy. ２ O ３ , CuO, MnO ２ , NiO, Li ４ Ti ５ O １２ , H ２ Ti １２ O ２５ , Na ２ Ti ３ O ７ etc. are preferred. The active material 14 may be coated with a material or ceramics having excellent electron conductivity. Two or more materials may be used for the active material 14. The shape of the active material 14 is not particularly limited, and may be spherical, elliptical, faceted, strip-shaped, fibrous, scale-shaped, torus-shaped, or hollow.

[0024] The inorganic skeleton 15 is made of an inorganic compound and is the core of the active material layer 11. There are no particular restrictions on the inorganic compound that constitutes the inorganic skeleton 15, as long as it is durable against the active material 14 and the electrolyte solution. Examples of inorganic compounds include those containing silicates having siloxane bonds or phosphates having aluminophosphate bonds.

[0025] Silicates are compounds whose main molecular skeleton is composed of Si and O, and examples thereof include alkali metal silicates, silicates of guanidine compounds, and silicates of ammonium compounds. Silicates include orthosilicates (A ４ SiO ４ ), metasilicate (A ２ SiO ３ ), pyrosilicate (A ６ Si ２ O ７ ), disilicate (A ２ Si ２ O ５ ), tetrasilicate (A ２ Si ４ O９ ), polysilicates such as A ２ Si ２ O ５ , A ２ Si ３ O ７ , A ２ Si ４ O ９ and the like, and may be a hydrate (A=alkali metal element, guanidine compound, or ammonium compound). A portion of the Si sites in the siloxane bond may be substituted with a transition metal element such as Al, Zr, Ti, Mg, Mo, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, or Y.

[0026] The silicate has the general formula A ２ O.nSiO ２ In the general formula, A is at least one of Li, Na, K, a triethanolammonium group, a tetramethanolammonium group, a tetraethanolammonium group, and a granidine group, and n is 0.5 or more and 5.0 or less.

[0027] Preferably, A in the general formula is Li or Na, and n is 1.6 or more and 3.9 or less, more preferably 2.0 or more and 3.5 or less. A is preferably Na from the viewpoint of the mechanical strength, binding property, and abrasion resistance of the skeleton. When A is Li, an inorganic skeleton 15 with high ionic conductivity is obtained, resulting in excellent input / output characteristics of the electricity storage device (described later). Even when A is Na, if n exceeds 5.0, the binding property of the active material 14 tends to decrease. If n is less than 0.5, the viscosity increases, and it tends to be difficult to form the inorganic skeleton 15 between the active materials 14.

[0028] The silicate is preferably amorphous. Amorphous silicate has no directionality and is isotropic, making it less likely to crack in a specific direction and significantly improving the life of the active material layer 11. Furthermore, its resistance to hydrofluoric acid is improved, making it less likely for the active material layer 11 to collapse due to hydrofluoric acid.

[0029] The phosphate salt of the inorganic skeleton 15 is exemplified by aluminum phosphate salt, magnesium phosphate salt, and calcium phosphate salt. The aluminum phosphate salt is aluminum monophosphate salt (Al(H ２ P.O.４ ) ３ ), aluminum hydrogen phosphate (Al ２ (H ２ P.O. ４ ) ３ ), aluminum metaphosphate (Al(PO ３ ) ３ Examples of magnesium phosphate salts include monobasic magnesium phosphate (Mg(H ２ P.O. ４ ) ３ ), magnesium hydrogen phosphate (MgHPO ４ ), magnesium metaphosphate (Mg(PO ３ ) ２ Calcium phosphate salts include monocalcium phosphate salts (Ca(H ２ P.O. ４ ) ３ ), calcium hydrogen phosphate (CaHPO ４ ), tricalcium phosphate salt (Ca ３ (H ２ P.O. ４ ) ２ ), calcium metaphosphate (Ca(PO ３ ) ２ These may be hydrates.

[0030] When phosphate is heated, water is removed from the hydroxyl groups, forming a covalent bond between P and O, resulting in a dehydration condensation reaction. This dehydration condensation reaction can occur at up to six sites per molecule centered on the transition metal, resulting in a three-dimensional polymerized transition metal phosphate. In other words, phosphate is a compound whose main molecular structure is P, O, and a transition metal (M).

[0031] Phosphates have the general formula M.nHxPO ４It has a crystalline or amorphous structure represented by the formula: M is one or more of Al, Ca, and Mg, and a portion of M may be substituted with a transition metal element such as Cu, Fe, Ba, Ti, Mn, Mo, Mg, Si, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, or Y. In the formula, x is 0 or more and 2 or less, and n is 0.5 or more and 5 or less. M is preferably Al from the viewpoint of the mechanical strength, binding ability, and wear resistance of the inorganic skeleton 15. x is preferably 1-2, more preferably 2, from the viewpoint of the binding ability of the active material 14. n is preferably 0.5-5.0, more preferably 2.5-3.5, from the viewpoint of the mechanical strength, binding ability, and wear resistance of the inorganic skeleton 15. As in the case of silicates, phosphates are preferably amorphous.

[0032] The sheet 10 is manufactured, for example, as follows. The active material layer 11 is obtained by forming a slurry film on the current collecting layer 13, in which a solution in which a binder is dissolved is mixed with the active material 14, and then drying the film. One method of providing the inorganic skeleton 15 on the active material layer 11 is to apply a skeleton-forming agent to the surface of the active material layer 11, and then heat the active material layer 11 to, for example, 110-160°C to harden the skeleton-forming agent. The skeleton-forming agent is an aqueous solution in which a silicate is dissolved in basic water, or an aqueous solution in which a phosphate is dissolved in acidic water. A surfactant may be included in the aqueous solution.

[0033] The skeleton-forming agent can be applied by a method such as immersing the active material layer 11 in a tank containing the skeleton-forming agent, dripping the skeleton-forming agent onto the surface of the active material layer 11, spraying atomized skeleton-forming agent onto the active material layer 11, screen printing, curtain coating, spin coating, gravure coating, or die coating. The skeleton-forming agent applied to the surface of the active material layer 11 penetrates from the surface of the active material layer 11 to the interior and enters between the active materials 14. This provides an electrode sheet in which an inorganic skeleton 15 is provided on the surface of the active material layer 11 and between the active materials 14.

[0034] Another method for providing the active material layer 11 with the inorganic skeleton 15 is to use a skeleton-forming agent as a binder when granulating the active material 14. Examples of active material granulation methods include fluidized bed granulation, stirring granulation, tumbling granulation, spray drying, extrusion granulation, tumbling granulation, and coating granulation. By using these methods, agglomerated granules of the active material 14 containing the skeleton-forming agent are produced. The agglomerated granules are then dried to obtain a granulated product in which the active material 14 is bound by the inorganic skeleton 15. The granulated product is bound onto the current collecting layer 13 with a binder to form the active material layer 11. This provides an electrode sheet including the active material layer 11 and the current collecting layer 13, in which the inorganic skeleton 15 is provided between the active materials 14. The skeleton-forming agent is preferably contained in an amount of 0.2% by mass or more and 30% by mass or less relative to the granulated product.

[0035] Separately from the electrode sheet, a slurry is prepared by mixing an electrolyte solution, in which an electrolyte is dissolved in a solvent, with particles 16, and then mixing this with a solution in which a binder is dissolved. After tape casting, the mixture is dried to obtain a green sheet (oxide sheet) for the oxide layer 12. After the electrode sheet and oxide sheet are cut into predetermined shapes, the electrode sheet and oxide sheet are stacked and pressed together to form an integrated body. This produces the sheet 10. The slurry may be applied onto the electrode sheet to form the oxide layer 12 on the active material layer 11.

[0036] When the skeleton forming agent contains silicate, it is preferable that it further contains alkali-resistant inorganic particles. Also, when the skeleton forming agent contains phosphate, it is preferable that it further contains acid-resistant inorganic particles. When the aggregate forming agent contains inorganic particles, when the skeleton forming agent is applied to the active material layer 11, the inorganic particles are present on the surface of the active material layer 11 and also penetrate into the active material layer 11. When agglomerates of active material 14 containing the skeleton forming agent are formed, the inorganic particles are present among the active material 14.

[0037] When inorganic particles are contained in the inorganic skeleton 15, voids are formed between the inorganic particles, which allows steam to escape through the voids when the skeleton-forming agent dries, reducing swelling of the inorganic skeleton 15 that would otherwise occur due to trapped steam. Furthermore, the voids formed between the inorganic particles reduce peeling and cracking of the inorganic skeleton 15 that would otherwise occur due to volumetric shrinkage of the salt when the skeleton-forming agent dries.

[0038] Examples of alkali-resistant inorganic particles include oxides, hydroxides, nitrides, carbides, carbonate compounds, and sulfate compounds of at least one element selected from the group consisting of Al, Zr, Ti, Si, Mo, Sr, Ba, B, W, Ta, Ce, Hf, and Y. From the viewpoint of being a material that is resistant to oxidative decomposition or reductive decomposition during charging and discharging of an electricity storage device and has a small irreversible capacity, Al ２ O ３ , ZrO ２ , TiO ２ , SiO ２ , CeO, Y ２ O ３ , AlN, WC, SiC, B ４ C, BN, TaC, TiC, TiB ２ , HfB ２ , Si ３ N ４ , TiN, Al ２ (SO ４ ) ３ , ZrSiO ４ It is preferred that the compound contains:

[0039] In the inorganic skeleton 15, the inorganic particles preferably account for 20% by mass or more and 95% by mass or less of the total of the silicate or phosphate and the inorganic particles. Furthermore, the median particle size of the inorganic particles, measured by a laser diffraction / scattering particle size distribution measurement method, is preferably 0.2 μm or more and 20 μm or less. The inorganic skeleton 15 has high strength, excellent heat resistance, and excellent binding ability for the active material 14, and therefore firmly fixes the active material 14 to the active material layer 11.

[0040] The active material layer 11 may contain a binder that binds the active material 14. Examples of binders include fluorinated resins, polyolefins, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether, polyimide, polyamide, polyamideimide, 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. These may be used alone or in combination.

[0041] Vinylidene fluoride polymers are -CH ２ CF ２ - is not particularly limited as long as it contains. 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.

[0042] The active material layer 11 may contain a conductive material that imparts electronic conductivity. The conductive material is not particularly limited as long as it has electronic conductivity, and examples include metals such as Ni, Pt, and Ag; carbon materials such as carbon black, acetylene black, ketjen black, and carbon fiber; conductive polymers; and conductive glass. One or more of these may be used in combination.

[0043] The proportion of the conductive material to the total of the active material 14, binder, and conductive material in the active material layer 11 is preferably 0 to 20 mass %. If the conductive material exceeds 20 mass %, the proportion of the active material 14 decreases, and the capacity density tends to decrease.

[0044] The active material layer 11 may contain particles of an oxide-based solid electrolyte. The proportion of the particles to the total of the active material 14, binder, and solid electrolyte particles in the active material layer 11 is preferably 0 to 20 mass %. If the proportion of the particles exceeds 20 mass %, the proportion of the active material 14 decreases, and the capacity density tends to decrease.

[0045] The proportion of the binder relative to the total of the active material 14, binder, conductive material, and particles in the active material layer 11 is preferably 0.1 to 60 mass %, and more preferably 0.5 to 30 mass %. If the proportion of the binder is less than 0.1 mass %, the strength of the active material layer 11 tends to decrease and the active material 14 tends to easily fall off. If the proportion of the binder exceeds 60 mass %, the electrical resistance tends to increase and the capacity density tends to decrease.

[0046] The oxide layer 12 is in contact with the surface of the active material layer 11. The oxide layer 12 includes particles 16 of an oxide-based solid electrolyte, a binder, and an electrolytic solution. Examples of the solid electrolyte include β-alumina, a NASICON-based material, a LISICON-based material, an oxide having a perovskite structure, and an oxide having a garnet structure.

[0047] NASICON-based materials are represented by the general formula A ｘ M ２ (TO ４ ) ３ Examples of A include Na and Li, examples of M include Zr, Ti, V, Mn, Cr, Fe, Ni, Al, and Ge, and examples of T include P, Si, and As. For example, Na ３ V ２ (P.O. ４ ) ３ , Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ , Li １＋ｘ Ge ｘ Ti ２－ｘ (P.O. ４ )３ LISICON-based materials include Li ４－２ｘ Zn ｘ GeO ４ (0≦x≦1). Oxides having a perovskite structure include Li ｘ La （１－ｘ）／３ NbO ３ , La ２／３－Ｘ Li ３Ｘ TiO ３ (0≦x≦1). The crystal structure of a garnet-type oxide is represented by the general formula C ３ A ２ B ３ O １２ Oxides having a garnet structure are preferred because they have excellent resistance to reduction.

[0048] 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.

[0049] The garnet-type crystal structure can be identified by X-ray diffraction. The garnet-type crystal structure is identified by 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 to No. 422259, the solid electrolyte may differ in the type of constituent elements, Li concentration, etc., 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 indicating a reversal operation), JCPDS: 84-1753).

[0050] Solid electrolytes with a garnet-type crystal structure are typically Li ７ La ３ Zr ２ O １２ The solid electrolyte is Li ７ La ３ Zr ２ O １２ A part of the constituent elements may be substituted with another element, or a small amount of another element may be added without substituting the constituent elements. Examples of the other element 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).

[0051] The solid electrolyte 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 O １２ , Li ６．５ La ３ Zr １．７５ Te ０．２５ O１２ , 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 Ga ０．３０ La ２．９５ Rb ０．０５ Zr ２ O １２ Examples include:

[0052] The solid electrolyte 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, as this increases the ionic conductivity of the solid electrolyte.

[0053] (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

[0054] Returning to FIG. 1 , the binder contained in the oxide layer 12 binds the solid electrolyte particles 16 together. Examples of the binder include fluorinated resins, polyolefins, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether, polyimide, polyamide, polyamideimide, and rubber-like polymers such as styrene-butadiene rubber. 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. These may be used alone or in combination.

[0055] Vinylidene fluoride polymers are -CH ２ CF ２ - is not particularly limited as long as it contains. 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.

[0056] In the oxide layer 12, the binder and the electrolyte may be present separately, or the binder and the electrolyte may be mixed and formed into a gel. A solvent that dissolves the binder may be contained in the oxide layer 12. The binder preferably has a wider potential window than the electrolyte.

[0057] The electrolytic solution is a solution in which an electrolyte is dissolved in a solvent. There are no particular limitations on the solvent as long as the electrolyte is soluble in the solvent. Examples of the solvent include carbonate esters, aliphatic carboxylic acid esters, phosphate esters, γ-lactones, ethers, nitriles, sulfolane, dimethyl sulfoxide, fluorous solvents, and ionic liquids. A mixture of these may also be used.

[0058] Examples of carbonate esters include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate, and chain carbonate esters such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

[0059] Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Examples of phosphate esters include trimethyl phosphate. Examples of γ-lactones include γ-butyrolactone. Examples of ethers include chain ethers such as 1,3-dioxolane and 1,2-dialkoxyethane, and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran. Examples of nitriles include acetonitrile and propionitrile. Fluorous solvents are compounds in which the hydrogen atoms of hydrocarbons are substituted with fluorine atoms, and derivatives thereof.

[0060] Ionic liquids are compounds consisting of cations and anions, and are liquid at room temperature and pressure. If the solvent of an electrolyte is an ionic liquid, the flame retardancy of the 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.

[0061] 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 N(SO ２ F) ２ － is abbreviated as [FSI] － : It is called bis(fluorosulfonyl)imide anion, and N(SO ２ CF ３ ) ２ － abbreviated as [TFSI] － : It is sometimes called bis(trifluoromethanesulfonyl)imide anion.

[0062] The ionic liquids were N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME-FSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEME-TFSI), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI-FSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), N-butyl-N-methylpiperidinium bis(fluorosulfonyl)imide, N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13-FSI), and N-methyl-N-propylpyrrolidinium. Bis(trifluoromethanesulfonyl)imide (P13-TFSI) is an example. A mixture of these may also be used.

[0063] 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.

[0064] An electrolyte is a compound used to donate and accept cations. The cations of electrolytes are alkali metal ions. The anions of electrolytes are halide ions (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), etc. The electrolyte may be a mixture of these.

[0065] The salt concentration of the electrolyte in the electrolyte solution is 0.2 mol / dm ３ or more, preferably 0.5 mol / dm ３ As the salt concentration increases, the number of solvent molecules coordinated to carrier ions increases and the amount of uncoordinated solvent decreases, thereby reducing the interfacial resistance of the particles 16. The salt concentration of the electrolyte is 4.0 mol / dm ３ The salt concentration of the electrolyte is preferably 4.0 mol / dm or less. ３ This is because, when the temperature exceeds this value, the ionic conductivity tends to decrease significantly due to an increase in the viscosity of the electrolyte.

[0066] In the oxide layer 12, the ratio of the volume of the particles 16 to the total volume of the particles 16 and the electrolyte solution is 52% or more and less than 100%, and preferably 61% or more and less than 100%. The interfacial resistance of the particles 16 can be reduced by combining the particles 16 with the electrolyte solution, so that the ionic transport number of the oxide layer 12 can be made larger than that of a typical electrolyte solution. As a result, the operational stability of an electricity storage device (described below) including the oxide layer 12 is improved. It is preferable that the volume ratio of the binder to the combined volume of the particles 16, the binder, and the electrolyte solution is less than 50%, because this allows the tensile modulus of the oxide layer 12 to be maintained at an appropriate level.

[0067] The content (volume %) of the particles 16, binder, and electrolyte is determined by analyzing 10 or more randomly selected locations on the cross section of the oxide layer 12 at a magnification of 5000x using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). The analysis involves identifying element distribution and performing image analysis of the contrast of backscattered electron images to determine the area of ​​the particles 16, the area of ​​the binder, and the area of ​​the electrolyte. The content (volume %) of the particles 16 is obtained by regarding the ratio of the area of ​​the particles 16 to the total area of ​​the particles 16 and the electrolyte as the volume ratio. The content (volume %) of the binder is also obtained by regarding the ratio of the area of ​​the binder to the total area of ​​the particles 16, the area of ​​the binder, and the area of ​​the electrolyte as the volume ratio.

[0068] The cross section of the oxide layer 12 used for analysis is a polished surface, a surface obtained by irradiating with a focused ion beam (FIB), or a surface obtained by ion milling. The polished surface is, for example, a surface obtained by freezing the oxide layer 12 or by embedding and solidifying the oxide layer 12 in a tetrafunctional epoxy resin or the like and then polishing it.

[0069] The oxide-based solid electrolyte particles 16 contained in the oxide layer 12 are harder than particles of other solid electrolytes, such as sulfide-based solid electrolytes, and therefore the particles 16 are more likely to get caught on the surface of the active material layer 11 at the interface between the oxide layer 12 and the active material layer 11, which includes the inorganic skeleton 15. Because the particles 16 of the oxide layer 12 are bound to each other by a binder, the oxide layer 12 expands and contracts to follow changes in the volume of the active material 14 in the active material layer 11. This makes it difficult for the active material layer 11 and the oxide layer 12 to peel off from each other at the interface.

[0070] In order to reduce peeling of the oxide layer 12 due to friction between the oxide layer 12 and the active material layer 11, it is desirable that the particles 16 contained in the oxide layer 12 have a small circularity (are angular). The circularity of the particles 16 is determined from an SEM image of the particles 16 appearing in the cross section of the oxide layer 12. The SEM image is an enlarged image of a rectangular area measuring 12 μm in length and 9 μm in width on the cross section of the oxide layer 12. After the SEM image is acquired, image analysis is performed using known image analysis software (for example, WinROOF (registered trademark), manufactured by Mitani Shoji Co., Ltd.).

[0071] In image analysis, the size of each SEM image is calibrated based on the scale bar attached to the SEM image, and then the SEM image is subjected to binarization processing in order to extract the edges of the image. In the binarization processing, the brightness (brightness) of each pixel in the SEM image is converted into two levels using a predetermined threshold (for example, a threshold of 0-25). By converting the pixels into two levels and eliminating intermediate gradations, a binarized image is obtained in which the edges (grain boundaries) of the particles 16 are emphasized.

[0072] Using the obtained binary image, the area S of the particle 16 and the perimeter (total length of the edge) L of the particle 16 with area S are calculated by a known image analysis method. The circularity of the particle 16 is 4πS / L ２In order to strengthen the adhesion of particles 16 to the surface of active material layer 11, the average circularity of 20 randomly selected particles 16 is preferably less than 0.8, and more preferably less than 0.72. It is even more preferable that the circularity of particles 16 is 0.1 or more and 0.5 or less.

[0073] In order to strengthen the adhesion of particles 16 to the surface of active material layer 11, the particle diameter of particles 16 contained in oxide layer 12 is preferably in the range of 0.8 to 10 μm, more preferably in the range of 1 to 6 μm, in terms of the median equivalent circle diameter. The equivalent circle diameter of particle 16 refers to the diameter of a circle having an area equivalent to the area S of particle 16 as seen in a cross section.

[0074] The median diameter of the equivalent circle diameters of particles 16 is preferably 0.04 to 0.60 times the median diameter of the equivalent circle diameters of active material 14. The equivalent circle diameter of active material 14 refers to the diameter of a circle having an area equivalent to the area S of active material 14 when exposed in cross section.

[0075] To determine the median diameter of the particles 16 and the active material 14, the SEM image of the cross section is analyzed, the circle-equivalent diameter is calculated from the area S of each particle 16, and the volume-based particle size distribution is determined. Similarly, the circle-equivalent diameter is calculated from the area S of each active material 1416, 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 SEM image for determining the particle size distribution is taken from the oxide layer 12 and the active material layer 11 within 400 μm ２ The area shall be equal to or greater than this.

[0076] The oxide layer 12 preferably has a Young's modulus (tensile modulus) of 0.05 to 6.50 MPa because the oxide layer 12 expands and contracts to follow changes in the volume of the active material 14 in the active material layer 11. The Young's modulus is measured in accordance with JIS K7161-1:2014.

[0077] An electricity storage device 20 using the sheet 10 will be described with reference to Fig. 3. Fig. 3 is a cross-sectional view of the electricity storage device 20 according to the first embodiment. The electricity storage device 20 includes, in order, a positive electrode layer 21 and the sheet 10. The positive electrode layer 21 includes, in order, a current collecting layer 22 and an active material layer 23.

[0078] The current collecting layer 22 is not particularly limited as long as it is a material that has electronic conductivity and can pass current through the active material layer 23. For example, conductive materials such as C, Ti, Cr, Ni, Cu, Fe, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Al, and Au, or alloys containing two or more of these conductive materials (e.g., stainless steel) can be used for the current collecting layer 22. When Fe is used for the current collecting layer 22, it is preferably coated with Ni or Cu to prevent oxidation. The shape of the current collecting layer 22 is also not limited, and examples include a wire, rod, plate, foil, and porous shape.

[0079] The active material layer 23 includes an active material 24 and particles 25. The active material layer 23 may contain a conductive material to reduce the resistance of the active material layer 23. Examples of the conductive material include carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, and Ag.

[0080] Examples of the active material 24 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 O ２ , 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.

[0081] The sulfur-based active material is S, TiS ２ , NiS, FeS ２ , Li ２ S, MoS ３Examples 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.

[0082] In order to suppress the reaction between the active material 24 and the particles 25, a coating layer can be provided on the surface of the active material 24. 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.

[0083] The active material layer 23 may contain a binder that binds the active material 24. Examples of binders include fluorinated resins, polyolefins, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether, polyimide, polyamide, polyamideimide, 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. These may be used alone or in combination.

[0084] In the electricity storage device 20, the active material layer 11 and the current collecting layer 13 of the sheet 10 constitute a negative electrode layer, and the oxide layer 12 of the sheet 10 constitutes a separator that separates the positive electrode layer 21 from the negative electrode layer. Because the oxide layer 12 contains an electrolyte, the interface resistance of the particles 16 contained in the oxide layer 12 can be reduced.

[0085] The electricity storage device 20 is manufactured, for example, as follows: A solution in which a binder is dissolved is mixed with a mixture of the active material 24 and the particles 25 to form a slurry. The slurry is applied onto the current collecting layer 22 and then dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 21.

[0086] After cutting the sheet 10 and the positive electrode sheet to a predetermined shape, the sheet 10 and the positive electrode sheet are stacked and pressed together to form an integrated unit. Terminals (not shown) are connected to the current collecting layers 13 and 22, respectively, and the resulting assembly is sealed in a case (not shown), thereby obtaining an electricity storage device 20 including a positive electrode layer 21, a separator, and a negative electrode layer.

[0087] The power storage device 20 may be, for example, a stacked type in which positive electrode layers 21 and negative electrode layers are alternately stacked with a separator interposed therebetween, or a wound type in which positive electrode layers 21 and negative electrode layers are spirally wound with a separator sandwiched therebetween. The power storage device 20 may be, for example, an electrochemical capacitor or a semi-solid battery. The power storage device 20 does not require repeated charging and discharging multiple times while applying pressure in the stacking direction of the power storage device in order to improve cycle characteristics, and therefore may be of various types.

[0088] In the electricity storage device 20, the inorganic skeleton 15 reduces the volume change of the active material 14 in the negative electrode layer during charge and discharge. Furthermore, the particles 16 contained in the oxide layer 12 combine with the inorganic skeleton 15 to reduce peeling of the oxide layer 12 that accompanies the volume change of the active material 14 during charge and discharge. This allows the cycle characteristics of the electricity storage device 20 to be improved and stabilized.

[0089] A second embodiment will be described with reference to Fig. 4. In the first embodiment, the oxide layer 12 is used as a separator. In the second embodiment, the oxide layer 12 is used as a protective layer. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted. Fig. 4 is a schematic cross-sectional view of an electricity storage device 30 in the second embodiment. The electricity storage device 30 is a liquid alkali metal ion battery.

[0090] The electricity storage device 30 includes, in this order, a positive electrode layer 31, a separator 33, and a sheet 10. These are housed in a case (not shown). The positive electrode layer 31 includes a current collecting layer 22 and an active material layer 32 superimposed on each other. The active material layer 32 includes an active material 24. In order to reduce the resistance of the active material layer 32, the active material layer 32 may include a conductive additive such as carbon black, acetylene black, ketjen black, carbon fiber, Ni, Pt, or Ag.

[0091] The separator 33 is exemplified by a porous body that is durable against the active materials 14, 24 and electrolyte solution contained in the positive electrode layer 31 and the sheet 10, and that allows alkali metal ions to pass through but does not have electronic conductivity. Examples of the porous body include a nonwoven fabric or a porous membrane made of cellulose, polypropylene, polyethylene, or the like. The separator 33 is also exemplified by one in which an ion-conductive gel electrolyte is disposed, or one in which a mixture of an ion-conductive solid electrolyte and an electrolyte solution is disposed. The electrolyte solution is the same as that described in the first embodiment, and therefore its description will be omitted.

[0092] An oxide layer 12 (protective layer) is disposed between the separator 33 and the active material layer 11. The oxide layer 12 is disposed by sheet lamination, coating on the separator 33, or the like. The oxide layer 12 interposed between the active material layer 11 and the separator 33 reduces short circuits caused by dendrite growth of alkali metals.

[0093] A third embodiment will be described with reference to Fig. 5. In the second embodiment, an oxide layer 12 is disposed between the separator 33 and the active material layer 11 to serve as a protective layer. In the third embodiment, an oxide layer 12 is disposed between the active material layer 11 and the current collecting layer 13 to serve as a protective layer. The same parts as those described in the first or second embodiment are designated by the same reference numerals, and the following description will be omitted. Fig. 5 is a schematic cross-sectional view of an electricity storage device 40 in the third embodiment. The electricity storage device 40 is a liquid alkali metal ion battery.

[0094] The electricity storage device 40 includes, in order, a positive electrode layer 31, a separator 33, an active material layer 11, an oxide layer 12, and a current collecting layer 13. These are housed in a case (not shown). The oxide layer 12 (protective layer) disposed between the active material layer 11 and the current collecting layer 13 is provided by sheet lamination, coating on the current collecting layer 13, or the like. The oxide layer 12 interposed between the active material layer 11 and the current collecting layer 13 reduces deterioration of the current collecting layer 13.

[0095] The present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples.

[0096] (Experiment 1) (Preparation of solid electrolyte particles) 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 ３In consideration of the volatilization of Li during firing, the amount of Li was in excess of about 15 mol% in terms of element. The weighed raw materials and organic solvent 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 900°C for 1 hour and at 1200°C for 10 hours. The pre-fired powder was placed on an MgO plate and fired at 1100°C for 4 hours in an inert gas atmosphere. The fired powder was ground for various times in a wet planetary ball mill in an environment not exposed to air, and then dried to obtain various particles of solid electrolyte.

[0097] (Preparation of Electrolyte) The ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) was dissolved in the electrolyte LiN(SO ２ F) ２ (LiFSI) was dissolved, and the salt concentration was 2.1 mol / dm ３ The electrolyte solution was obtained.

[0098] (Preparation of oxide layer) Particles and electrolyte solution were mixed in a mortar to a particle:electrolyte ratio of 61:39 (vol%), and then a binder solution prepared by dissolving poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) in carbonate ester was added in various ratios and mixed using a planetary centrifugal mixer to obtain various slurries for the oxide layer. Of the slurries for the oxide layer, those that passed through a filter with a pore size of 25 μm were degassed, and then coated on a polyethylene terephthalate film and dried to obtain various oxide layers.

[0099] The oxide layer was punched into a rectangle of 30 mm in length and 10 mm in width to prepare a test piece. A gauge line with a distance of 10 mm between the gauge lines was marked on the test piece, and the Young's modulus of the test piece of the oxide layer was determined in accordance with JIS K7161-1:2014.

[0100] (Preparation of Positive Electrode Sheet) Active Material LiNi １／３ Mn １／３ Co １／３ O ２The particles, vapor-grown carbon fiber VGCF (conductive material), and electrolyte were mixed in a ratio of active material:particles:conductive material:electrolyte = 81.5:6.2:0.4:11.9 (wt%) to obtain a mixture, and then 4 wt% of binder solution was added to the mixture and mixed using a planetary stirrer to obtain a positive electrode slurry. The positive electrode slurry passed through a filter with a pore size of 25 μm was degassed and then applied to aluminum foil (current collecting layer) and dried to obtain a positive electrode layer (thickness: approximately 20 μm).

[0101] The oxide layer slurry was applied to the surface of the positive electrode layer opposite the current collecting layer, and dried to obtain a positive electrode sheet in which the oxide layer was laminated on the positive electrode layer.

[0102] (Preparation of negative electrode layer) Active material Si(D ５０ A binder solution prepared by dissolving polyvinylidene fluoride in carbonate ester in a ratio of 92:4.2:0.8:3 (wt%) was added to the mixture of active material and conductive material, and the mixture was mixed using a planetary centrifugal mixer to obtain a negative electrode slurry. The negative electrode slurry was filtered through a 25 μm pore size filter, degassed, and then coated on a stainless steel film and dried to obtain a negative electrode layer (thickness: approximately 20 μm).

[0103] Na ２ O.3SiO ２ So that Na ２ CO ３ and SiO ２ After weighing, the mixture was heated to 1000°C or higher to melt. ２ O.3SiO ２ The active material layer was immersed in the aggregate-forming agent and then heated to 160°C to obtain a negative electrode layer in which an inorganic skeleton was formed in the active material layer. The oxide layer slurry was applied to the surface of the negative electrode layer opposite the current collecting layer and dried to obtain various negative electrode sheets in which an oxide layer was laminated on the negative electrode layer.

[0104] SEM images of the cross section of the oxide layer and the active material layer were taken, and the circularity of the oxide layer particles, the median circle-equivalent diameter of the oxide layer particles, and the median circle-equivalent diameter of the active material particles were measured. The circularity was rounded to four decimal places. The median particle diameter was divided by the median particle diameter of the active material to determine the median diameter ratio. The median diameter ratio was rounded to two decimal places.

[0105] (Preparation of Evaluation Cell) The oxide layer of the positive electrode sheet and the oxide layer of the negative electrode sheet were superimposed and pressed together by a roll press. After connecting terminals to each of the current collecting layers, the resultant was sealed in a vacuum state to obtain an evaluation cell for Sample No. 1-6.

[0106] For comparison, an evaluation cell of the comparative example was obtained in the same manner as the evaluation cell of No. 1, except that the negative electrode layer was not provided with an inorganic skeleton.

[0107] (Measurement of Capacity Retention Rate) Evaluation cells Nos. 1-6 and the comparative example were repeatedly charged and discharged at a rate of 0.1 C, and the ratio of the discharge capacity at 10 cycles to the initial discharge capacity (capacity retention rate) was measured. The binder ratio in the oxide layer, the circularity of the particles in the oxide layer, the Young's modulus of the oxide layer, the median diameter ratio, and the capacity retention rate are shown in Table 1. The binder (vol %) shown in Table 1 indicates the ratio of the volume of the binder to the combined volume of the particles, binder, and electrolyte solution constituting the oxide layer (the same applies to Table 2).

[0108]

[0109] As shown in Table 1, the evaluation cells No. 1-6 and the comparative example had the same circularity and median diameter ratio of the particles constituting the oxide layer. It was revealed that the evaluation cell No. 1-6, in which an inorganic skeleton was provided in the negative electrode layer, was able to increase the capacity retention rate compared to the comparative example, in which an inorganic skeleton was not provided in the negative electrode layer. In other words, the evaluation cell No. 1-6 had improved cycle characteristics compared to the comparative example.

[0110] According to the evaluation cells No. 1-6, the capacity retention rate tended to decrease as the binder ratio in the oxide layer increased. It was revealed that the evaluation cells No. 1-5, which had a binder ratio of less than 50 vol%, were able to achieve a higher capacity retention rate than the evaluation cell No. 6, which had a binder ratio of 50 vol%.

[0111] According to the evaluation cells No. 1-6, the capacity retention rate tended to decrease as the proportion of the binder in the oxide layer increased and the Young's modulus increased. It was revealed that the evaluation cells No. 1-5, in which the Young's modulus of the oxide layer was 0.07-6.17 MPa, could achieve a higher capacity retention rate than the evaluation cell No. 6, in which the Young's modulus was 12.3 MPa.

[0112] (Experiment 2) Evaluation cells for Samples No. 7-14 were prepared in the same manner as the evaluation cells for Samples No. 1-6, except that the binder ratio in the oxide layer, the circularity of the particles contained in the oxide layer, and the median diameter ratio were varied. The evaluation cells for Samples No. 7-14 were repeatedly charged and discharged at a rate of 0.1 C, and the ratio of the discharge capacity at 10 cycles to the initial discharge capacity (capacity retention) was measured. The binder ratio in the oxide layer, the circularity of the particles in the oxide layer, the Young's modulus of the oxide layer, the median diameter ratio, and the capacity retention are shown in Table 2.

[0113]

[0114] According to the evaluation cells of Samples No. 7-13, which had the same binder ratio, the capacity retention rate tended to decrease as the particle circularity increased. It was revealed that the evaluation cells of Samples No. 7-11, which had particle circularity of less than 0.72, could achieve a higher capacity retention rate than the evaluation cells of Samples No. 12 and 13, which had particle circularity of 0.742 or more.

[0115] Among the evaluation cells of Samples No. 7-11, the capacity retention rates of the evaluation cells of Samples No. 7, 9, and 11 were higher than the capacity retention rates of the evaluation cells of Samples No. 8 and 10. The median diameter ratios of Samples No. 7, 9, and 11 were 0.04 or more and 0.60 or less, whereas the median diameter ratios of Samples No. 8 and 10 were outside the range of 0.04-0.60. It was revealed that the capacity retention rate can be increased when the median diameter of the particles is 0.04 to 0.60 times the median diameter of the active material.

[0116] In the evaluation cell No. 14, which had a binder ratio of 4 vol%, the Young's modulus of the oxide layer was less than 0.05 MPa. The capacity retention rate of the evaluation cell No. 14 was smaller than that of the evaluation cells Nos. 7 to 13 and was equivalent to that of the evaluation cells Nos. 12 and 13. It was revealed that in order to increase the capacity retention rate, the Young's modulus of the oxide layer is preferably 0.05 MPa or more, and more preferably 0.07 MPa or more.

[0117] 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.

[0118] In the embodiment, the sheet 10 and electricity storage devices 20, 30 in which the oxide layer 12 is disposed on the front surface of the active material layer 11 and the current collecting layer 13 is disposed on the back surface of the active material layer 11, and the electricity storage device 40 in which the oxide layer 12 is disposed on the front surface of the active material layer 11 and the separator 33 is disposed on the back surface of the active material layer 11 have been described, but the present invention is not necessarily limited to this. It is of course possible to dispose the oxide layer 12 on both the front and back surfaces of the active material layer 11, for example, by providing the oxide layer 12 between the active material layer 11 and the current collecting layer 13 of the sheet 10.

[0119] REFERENCE SIGNS LIST 10 sheet 11 active material layer 12 oxide layer 14 active material 15 inorganic framework 16 particles 20, 30, 40 electricity storage device 33 separator

Claims

1. A sheet comprising an active material layer containing an active material, further comprising an oxide layer in contact with the active material layer, the active material layer including an inorganic skeleton provided on at least one of a surface of the active material layer in contact with the oxide layer and between the active material, the oxide layer including particles of an oxide-based solid electrolyte, a binder binding the particles, and an electrolytic solution.

2. The sheet according to claim 1, wherein the median diameter of said particles is 0.04 to 0.6 times the median diameter of said active material.

3. The sheet according to claim 1 or 2, wherein the Young's modulus of the oxide layer is 0.05-6.50 MPa.

4. The sheet according to claim 1 or 2, wherein the circularity of said particles is less than 0.

8.

5. The sheet according to claim 1 or 2, wherein the volume ratio of the binder to the combined volume of the particles, the binder and the electrolyte is less than 50%.

6. The sheet according to claim 1 or 2, wherein the particles have a garnet-type crystal structure containing Li, La and Zr.

7. The sheet of claim 6, wherein said particles further comprise Mg and Sr.

8. An electricity storage device comprising a positive electrode layer, a negative electrode layer, and a separator separating the positive electrode layer and the negative electrode layer, the negative electrode layer including a current collecting layer and an active material layer, the active material layer being part of the sheet according to claim 1 or 2.

9. The electric storage device according to claim 8, wherein the separator comprises an oxide layer of the sheet.

10. The electricity storage device according to claim 8, further comprising a protective layer in contact with the active material layer, the protective layer including an oxide layer of the sheet.

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