Sheets and energy storage devices

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

[Technical Field]

[0001] This invention relates to a sheet containing an active material layer and an energy storage device. [Background technology]

[0002] Energy storage devices that include an active material in the negative electrode whose volume changes during charging and discharging may experience a rapid decrease in capacity retention as the charge-discharge cycle is repeated, due to the formation of voids between the active materials or changes in the shape of the active materials. Patent Document 1 describes a battery having a layer containing an active material and a solid electrolyte, with a capacity of 150 kgf / cm². 2 Prior art has been disclosed that involves repeatedly performing charge-discharge processes while applying the above pressure in the stacking direction to prevent a rapid decrease in capacity retention. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-35987 [Overview of the project] [Problems that the invention aims to solve]

[0004] Prior technology has the problem that the capacity retention rate fluctuates due to slight variations in pressure during the charging and discharging process.

[0005] This invention was made to solve this problem and aims to provide a sheet and an energy storage device that can improve cycle characteristics without performing a pressure-assisted charge / discharge process. [Means for solving the problem]

[0006] A first embodiment for achieving this objective is a sheet comprising an active material layer containing an active material, further comprising an oxide layer in contact with the active material layer, wherein the active material layer includes 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, and the oxide layer includes particles of an oxide-based solid electrolyte, a binder that binds the particles together, and an electrolyte.

[0007] In the second embodiment, the median diameter of the particle is 0.04 times or more and 0.6 times or less the median diameter of the active material.

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

[0009] In the fourth embodiment, in any of the first to third embodiments, the circularity of the particles is less than 0.8, preferably less than 0.72. Preferably, the circularity of the particles is 0.60 or more and less than 0.80.

[0010] The fifth embodiment is that, in any of the first to fourth embodiments, the ratio of the binder volume to the combined volume of particles, binder, and electrolyte is less than 50%, preferably 5% or more.

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

[0012] The seventh embodiment is the same as the sixth embodiment, wherein the particles further include Mg and Sr.

[0013] The eighth embodiment is an energy storage device comprising a positive electrode layer, a negative electrode layer, and a separator separating the positive electrode layer and the negative electrode layer, wherein the negative electrode layer includes a current collector layer and an active material layer, and the active material layer is part of a sheet of any of the first to seventh embodiments.

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

[0015] A tenth embodiment is the eighth embodiment, further comprising a protective layer in contact with the active material layer, wherein the protective layer includes an oxide layer of the sheet. [Effects of the Invention]

[0016] According to the sheet of the present invention, the inorganic framework reduces the volume change of the active material during charging and discharging, and the particles contained in the oxide layer combine with the inorganic framework to reduce the peeling of the oxide layer. This improves the cycle characteristics of energy storage devices including the sheet. [Brief explanation of the drawing]

[0017] [Figure 1] This is a cross-sectional view of a sheet in one embodiment. [Figure 2] This is a schematic diagram showing the crystal structure of a garnet-type crystal. [Figure 3] This is a cross-sectional view of the energy storage device in the first embodiment. [Figure 4] This is a cross-sectional view of the energy storage device in the second embodiment. [Figure 5] This is a cross-sectional view of the energy storage device in the third embodiment. [Modes for carrying out the invention]

[0018] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a schematic cross-sectional view of a sheet 10 in 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 includes a current collector layer 13 disposed on the back surface of the active material layer 11.

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

[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 material 14. In this embodiment, the inorganic skeleton 15 is provided on both the surface of the active material layer 11 (the interface between the active material layer 11 and the oxide layer 12) and between the active material 14.

[0021] Active material 14 is an alkali metal ion (Li + kaNa + , K + The material is not particularly limited as long as it is capable of reversibly intercalating and releasing ions (etc.). The mechanism of ion intercalation and release may include dissolution and precipitation of the substance, insertion and desorption of ions between crystal layers, etc. The active material 14 may be 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 alloys, composites, oxides, chalcogenides, or halides using these elements.

[0022] Active material 14 changes the electrode potential from 0V to 1V (vs.Li + From the viewpoint of keeping it within the range of / 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, allotropes of these elements, alloys, or oxides are preferred. From the viewpoint of increasing the energy density, the active material 14 is preferably one that contains elements such as Al, Si, Zn, Ge, Ag, and 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, etc., and may be a total solid solution alloy, eutectic alloy, hypoeutectic alloy, hypereutectic alloy, or peritectic alloy. The oxides are Fe2O3, CuO, MnO2, NiO, Li4Ti5O 12 H2Ti 12 O 25 Na2Ti3O7 is preferred. The active material 14 may be coated with a material or ceramic with excellent electronic 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, flaky, torus-shaped, or hollow.

[0024] The inorganic skeleton 15 is the core of the active material layer 11 and is made of an inorganic compound. The inorganic compound constituting the inorganic skeleton 15 is not particularly limited as long as it is durable against the active material 14 and the electrolyte. Examples of inorganic compounds include silicates having siloxane bonds or phosphates having aluminophosphate bonds.

[0025] Silicates are compounds whose main molecular framework consists of Si and O, and examples include alkali metal silicates, guanidine compound silicates, and ammonium compound silicates. Silicates include polysilicates such as orthosilicate (A4SiO4), metasilicate (A2SiO3), pyrosilicate (A6Si2O7), disilicate (A2Si2O5), and tetrasilicate (A2Si4O9), as well as A2Si2O5, A2Si3O7, A2Si4O9, etc., and may be hydrates (A = alkali metal element, guanidine compound, or ammonium compound). Some of the Si sites in the siloxane bond may be substituted with transition metal elements such as Al, Zr, Ti, Mg, Mo, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y.

[0026] Silicates are crystalline or amorphous structures represented by the general formula A2O·nSiO2. In the general formula, A is one or more of Li, Na, K, triethanolammonium group, tetramethanolammonium group, tetraethanolammonium group, or granidine group, and n is between 0.5 and 5.0.

[0027] Preferably, A in the general formula is Li or Na, and n is 1.6 to 3.9, more preferably 2.0 to 3.5. From the viewpoint of mechanical strength, bonding properties, and wear resistance of the skeleton, Na is preferred for A. When A is Li, an inorganic skeleton 15 with high ionic conductivity is obtained, resulting in excellent input / output characteristics for the energy storage device (described later). Even if A is Na, if n exceeds 5.0, the bonding properties of the active material 14 tend to decrease. If n is less than 0.5, the viscosity increases, making it difficult to form the inorganic skeleton 15 between the active material 14.

[0028] The silicate is preferably amorphous. Because amorphous silicates are isotropic and lack directionality, they are less prone to cracking in a specific direction, thus greatly improving the lifespan of the active material layer 11. Furthermore, their resistance to hydrofluoric acid is improved, making hydrofluoric acid-induced disintegration of the active material layer 11 less likely.

[0029] Examples of phosphates of inorganic skeleton 15 include aluminum phosphate, magnesium phosphate, and calcium phosphate. Examples of aluminum phosphate include monoaluminum phosphate (Al(H2PO4)3), aluminum hydrogen phosphate (Al2(H2PO4)3), and aluminum metaphosphate (Al(PO3)3). Examples of magnesium phosphate include monoaluminum phosphate (Mg(H2PO4)3), magnesium hydrogen phosphate (MgHPO4), and magnesium metaphosphate (Mg(PO3)2). Examples of calcium phosphate include monoaluminum phosphate (Ca(H2PO4)3), calcium hydrogen phosphate (CaHPO4), tricalcium phosphate (Ca3(H2PO4)2), and calcium metaphosphate (Ca(PO3)2). These may also be hydrates.

[0030] When phosphates are heated, water is removed from the hydroxyl group, forming a covalent bond between P and O, and a dehydration condensation reaction occurs. This dehydration condensation reaction can occur at up to six sites per molecule, centered around the transition metal, resulting in a three-dimensional polymer of transition metal phosphate. In other words, phosphates are compounds whose main molecular framework consists of P, O, and a transition metal (M).

[0031] Phosphates have a crystalline or amorphous structure represented by the general formula M·nHxPO4. In the general formula, M is one or more of Al, Ca, and Mg, and a portion of M may be substituted with transition metal elements such as Cu, Fe, Ba, Ti, Mn, Mo, Mg, Si, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y. In the general formula, x is between 0 and 2, and n is between 0.5 and 5. Al is preferred for M from the viewpoint of mechanical strength, bonding properties, and wear resistance of the inorganic skeleton 15. X is preferably between 1 and 2, more preferably 2, from the viewpoint of bonding properties of the active material 14. N is preferably between 0.5 and 5.0, more preferably 2.5 and 3.5, from the viewpoint of mechanical strength, bonding properties, and wear resistance of the inorganic skeleton 15. Phosphates are also preferably amorphous, similar to silicates.

[0032] Sheet 10 is manufactured as follows, for example. The active material layer 11 is obtained by creating a film of slurry on the current collector layer 13 by mixing a binder solution with the active material 14, and then drying it. One method for providing the inorganic skeleton 15 to 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 of silicate dissolved in basic water, or an aqueous solution of phosphate dissolved in acidic water. The aqueous solution may also contain a surfactant.

[0033] The skeleton-forming agent can be applied by methods such as immersing the active material layer 11 in a tank containing the skeleton-forming agent, dropping the skeleton-forming agent onto the surface of the active material layer 11, spraying the atomized skeleton-forming agent onto the active material layer 11, screen printing, curtain method, spin coating, gravure coating, die coating, etc. The skeleton-forming agent applied to the surface of the active material layer 11 penetrates from the surface into the interior of the active material layer 11 and enters between the active materials 14. This results in 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 an inorganic skeleton 15 in the active material layer 11 is to use a skeleton-forming agent as a binder when granulating the active material 14. Examples of granulation methods for the active material include fluidized bed granulation, agitation granulation, rolling granulation, spray drying, extrusion granulation, rolling granulation, and coating granulation. By these methods, aggregated granules of the active material 14 containing the skeleton-forming agent are created, and when the aggregated granules are dried, a granulated product is obtained in which the inorganic skeleton 15 is bound to the active material 14. The granulated product is bound to the current collector layer 13 with a binder to form the active material layer 11. This results in an electrode sheet containing an active material layer 11 in which the inorganic skeleton 15 is provided between the active material 14, and a current collector layer 13. It is preferable that the skeleton-forming agent is included in the granulated product in an amount of 0.2% by mass or more and 30% by mass or less.

[0035] A slurry is prepared by mixing an electrolyte solution (an electrolyte dissolved in a solvent) with particles 16, and then mixing in a binder solution. After tape formation, the mixture is dried to obtain a green sheet (oxide sheet) for the oxide layer 12. After cutting the electrode sheet and oxide sheet into predetermined shapes, the electrode sheet and oxide sheet are stacked and pressed together to form a single unit. This yields sheet 10. Alternatively, the slurry can be applied to the electrode sheet to form the oxide layer 12 on the active material layer 11.

[0036] When the skeletal-forming agent contains silicates, it is preferable that it also contains alkali-resistant inorganic particles. Furthermore, when the skeletal-forming agent contains phosphates, it is preferable that it also contains acid-resistant inorganic particles. When the aggregate-forming agent contains inorganic particles, if the skeletal-forming agent is applied to the active material layer 11, inorganic particles are present on the surface of the active material layer 11, and inorganic particles also penetrate into the active material layer 11. When aggregated particles of the active material 14 containing the skeletal-forming agent are formed, inorganic particles are present between the active material 14.

[0037] When inorganic particles are included in the inorganic skeleton 15, voids are formed between the inorganic particles. This allows vapor to escape through these voids during the drying of the skeleton-forming agent, reducing the occurrence of blistering of the inorganic skeleton 15 caused by trapped vapor. Furthermore, the voids formed between the inorganic particles reduce the occurrence of delamination and cracking of the inorganic skeleton 15 due to volume shrinkage of salt during the drying of the skeleton-forming agent.

[0038] Examples of alkali-resistant inorganic particles include oxides, hydroxides, nitrides, carbides, carbonates, and sulfates 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 less susceptible to oxidative and reductive decomposition during charging and discharging of energy storage devices and has low irreversible capacity, it is preferable to include Al2O3, ZrO2, TiO2, SiO2, CeO, Y2O3, AlN, WC, SiC, B4C, BN, TaC, TiC, TiB2, HfB2, Si3N4, TiN, Al2(SO4)3, and ZrSiO4.

[0039] In the inorganic framework 15, it is preferable that inorganic particles make up 20% to 95% by mass of the total amount of silicate or phosphate and inorganic particles. Furthermore, the median diameter of the volume-based particle size distribution of the inorganic particles, measured by laser diffraction-scattering particle size distribution analysis, is preferably 0.2 μm to 20 μm. The inorganic framework 15 has high strength and excellent heat resistance, and excellent binding properties for the active material 14, so the inorganic framework 15 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 rubbery polymers such as fluorinated resins, polyolefins, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether, polyimide, polyamide, polyamideimide, and styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer. One or more of these may be used in combination.

[0041] There are no particular restrictions on vinylidene fluoride polymers as long as they contain -CH2CF2-. 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-containing 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 ethers. Examples of non-halogen-containing copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, their esters or salts; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or more copolymerizable monomers polymerize 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 fibers, conductive polymers, and conductive glass. One or more of these may be used in combination.

[0043] The proportion of the conductive material relative to the total of the active material 14, binder, and conductive material in the active material layer 11 is preferably 0 to 20% by mass. When the content of the conductive material exceeds 20% by mass, the proportion of the active material 14 decreases, which tends to result in lower capacity density.

[0044] The active material layer 11 may contain oxide-based solid electrolyte particles. The proportion of the particles relative to the total of the active material 14, binder, and solid electrolyte particles in the active material layer 11 is preferably 0 to 20% by mass. When the content of the particles exceeds 20% by mass, the proportion of the active material 14 decreases, which tends to result in lower capacity density.

[0045] The proportion of the binder relative to the total of the active material 14, conductive material, and particles in the active material layer 11 is preferably 0.1 to 60% by mass, and more preferably 0.5 to 30% by mass. When the proportion of the binder is less than 0.1% by mass, the strength of the active material layer 11 decreases, and the active material 14 tends to easily fall off. When the proportion of the binder exceeds 60% by mass, electrical resistance tends to increase and 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 oxide-based solid electrolyte particles 16, a binder, and an electrolytic solution. Examples of the solid electrolyte include β-alumina, NASICON-based materials, LISICON-based materials, oxides having a perovskite structure, and oxides having a garnet-type structure.

[0047] NASICON-based materials are generally represented by the general formula A x M2(TO4)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. Specific examples include Na3V2(PO4)3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Ge x Ti 2-x (PO4)3. LISICON-based materials include Li 4-2x Zn xGeO4 (0 ≤ x ≤ 1) is an example. Oxides having a perovskite structure include Li x La (1-x) / 3 NbO3, La 2 / 3-X Li 3X One example is TiO3 (0 ≤ x ≤ 1). The crystal structure of garnet-type oxides is given by the general formula C3A2B3O 12 It is represented as follows. Oxides with a garnet-type structure are preferred because they have excellent reduction resistance.

[0048] Figure 2 schematically shows a garnet-type crystal structure. In a garnet-type crystal structure, the C site Sc is dodecahedral coordinated with the oxygen atom Oa, the A site Sa is octahedral coordinated with the oxygen atom Oa, and the B site Sb is tetrahedral coordinated with the oxygen atom Oa. In a typical garnet-type crystal structure, Li may be present in the void V, which is the site where the oxygen atom Oa would normally be octahedral coordinated with the solid electrolyte 19. The void V is, for example, the area sandwiched between B site Sb1 and B site Sb2. The Li present in void V is octahedral coordinated with the oxygen atom Oa that constitutes an octahedron including the tetrahedral face Fb1 forming B site Sb1 and the tetrahedral face Fb2 forming B site Sb2. For example, Li7La3Zr2O has a garnet-type crystal structure. 12 In this case, La may occupy site C (Sc), Zr may occupy site A (Sa), and Li may occupy site B (Sb) and the void V.

[0049] Garnet-type crystal structures can be identified by X-ray diffraction. The garnet-type crystal structure is found in the Cambridge Structural Database (CSD) X-ray diffraction file No. 422259 (Li7La3Zr2O 12 It has an XRD pattern similar to ). The solid electrolyte may differ from No. 422259 in terms of the types of constituent elements and Li concentration, so the diffraction angle and intensity ratio may differ. A typical crystal structure of this type is cubic (space group Ia-3d (- indicates an overline meaning reversal operation), JCPDS:84-1753).

[0050] Solid electrolytes with a garnet-type crystal structure are typically Li7La3Zr2O12 Examples include: The solid electrolyte is Li7La3Zr2O 12 Some of the constituent elements may be substituted with other elements, or trace amounts of other elements may be added without substituting any constituent elements. Examples of 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).

[0051] Solid electrolytes include, for example, Li6La3Zr 1.5 W 0.5 O 12 Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 Li 6.25 La3Zr2Ga 0.25 O 12 Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 6.5 La3Zr 1.75 Te 0.25 O 12 Li 6.75 La3Zr 1.75 Nb 0.25 O 12 Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 Li 6.46 Ga 0.23 La3Zr 1.85 Y 0.15 O 12 Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 Li 7.05 La 3.00 Zr 1.95 Gd0.05 O 12 Li 6.20 Ga 0.30 La 2.95 Rb 0.05 Zr2O 12 These are some examples.

[0052] The solid electrolyte is preferably one that contains Mg and at least one of element A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba), and the molar ratio of each element satisfies all of (1) to (3) below, or one that contains both Mg and element A, and the molar ratio of each element satisfies all of (4) to (6) below. Element A is preferably Sr in order to increase 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] Let's return to Figure 1 for explanation. The binder contained in the oxide layer 12 binds the solid electrolyte particles 16 together. Examples of binders include rubbery polymers such as fluorinated resins, polyolefins, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether, polyimide, polyamide, polyamideimide, and styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer. One or more of these may be used in combination.

[0055] There are no particular restrictions on vinylidene fluoride polymers as long as they contain -CH2CF2-. 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-containing 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 ethers. Examples of non-halogen-containing copolymerizable monomers include olefins such as ethylene and propylene; acrylic monomers such as acrylic acid, methacrylic acid, their esters or salts; and vinyl monomers such as acrylonitrile, vinyl acetate, and styrene. One or more copolymerizable monomers polymerize with vinylidene fluoride to form a copolymer.

[0056] The oxide layer 12 may consist of the binder and electrolyte separated, or it may consist of a mixture of the binder and electrolyte in a gel-like state. The solvent for dissolving the binder may also be contained in the oxide layer 12. The binder is preferably one with a potential window wider than the potential window of the electrolyte.

[0057] An electrolyte is a solution in which an electrolyte is dissolved in a solvent. The solvent is not particularly limited as long as it is capable of dissolving the electrolyte. Examples of solvents include carbonate esters, aliphatic carboxylic acid esters, phosphate esters, γ-lactones, ethers, nitriles, sulfolanes, dimethyl sulfoxides, fluorescein solvents, and ionic liquids. Mixtures of these are also acceptable.

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

[0059] Examples of the aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Examples of the phosphate ester include trimethyl phosphate. Examples of the γ-lactones include γ-butyrolactone. Examples of the ethers include chain ethers such as 1,3-dioxolane and 1,2-dialkoxyethane, and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran. Examples of the nitriles include acetonitrile and propionitrile. A fluorous solvent is a compound obtained by substituting a fluorine atom for a hydrogen atom of a hydrocarbon and a derivative thereof.

[0060] An ionic liquid is a compound composed of a cation and an anion, and is liquid at normal temperature and normal pressure. If the solvent of the electrolytic solution is an ionic liquid, the flame retardancy of the electrolytic solution can be improved. The ionic liquid is preferably one that uses at least one selected from the group consisting of ammonium, imidazolium, pyrrolidinium, and piperidinium as the cation species.

[0061] The anion component of the ionic liquid is not particularly limited. The anion component is BF4 - , N(SO2F)2 - and other inorganic anions, B(C6H5)4 - , CH3SO3 - , CF3SO3 - , N(SO2CF3)2 - , N(SO2C4F9)2 - and other organic anions. N(SO2F)2 - is abbreviated as [FSI] - : bis(fluorosulfonyl)imide anion, and N(SO2CF3)2 - is abbreviated as [TFSI] - : it is sometimes called bis(trifluoromethanesulfonyl)imide anion.

[0062] Examples of the ionic liquid include 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). Mixtures of these may also be used.

[0063] The ionic liquid may be a solvated ionic liquid. Examples of the solvated ionic liquid include those obtained by dissolving an electrolyte in a sulfone-based solvent such as sulfolane or a sulfolane derivative, or a glyme-based solvent such as tetraglyme.

[0064] The electrolyte is a compound used for transferring cations. The cation of the electrolyte is an alkali metal ion. The anion of the electrolyte is a halide ion (I - , Cl - , Br - etc.), SCN - , BF4 - , BF3(CF3) - , BF3(C2F5) - , PF6 - , ClO4 - , SbF6 - , N(SO2F)2 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , B(C6H5)4 - , B(O2C2H4)2 - , C(SO2F)3 -,C(SO2CF3)3 - CF3COO - CF3SO2O - ,C6F5SO2O - ,B(O2C2O2)2 - RCOO - Examples include (where R is an alkyl group having 1-4 carbon atoms, a phenyl group, or a naphthyl group). The electrolyte may also be a mixture of these.

[0065] The salt concentration of the electrolyte in the electrolyte solution is 0.2 mol / dm³ 3 The above is preferable, and preferably 0.5 mol / dm 3 That concludes the explanation. As the salt concentration increases, the number of solvent molecules coordinating to the carrier ions increases and the number of uncoordinated solvents decreases, thus reducing the interfacial resistance of particle 16. The salt concentration of the electrolyte is 4.0 mol / dm³. 3 The following is preferable: Salt concentration of electrolyte is 4.0 mol / dm³ 3 This is because beyond a certain point, the ionic conductivity tends to decrease significantly due to the increased viscosity of the electrolyte.

[0066] The oxide layer 12 has a ratio of the volume of particles 16 to the total volume of the particles 16 and the electrolyte that is 52% or more and less than 100%, preferably 61% or more and less than 100%. The combination of particles 16 and the electrolyte reduces the interfacial resistance of the particles 16, so the ion transport rate of the oxide layer 12 can be made greater than that of a typical electrolyte. As a result, the stability of operation of the energy storage device (described later) including the oxide layer 12 is increased. It is preferable that the ratio of the binder volume to the combined volume of particles 16, binder and electrolyte is less than 50% of the oxide layer 12, as this allows for an appropriate maintenance of the tensile modulus of the oxide layer 12.

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

[0068] The cross-sections of the oxide layer 12 used for analysis are polished surfaces, surfaces obtained by irradiation with a focused ion beam (FIB), and surfaces obtained by ion milling. Polished surfaces are, for example, surfaces 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. Therefore, the particles 16 tend to get caught on the surface of the active material layer 11 at the interface between the active material layer 11 containing the inorganic skeleton 15 and the oxide layer 12. Since the particles 16 of the oxide layer 12 are bound together 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 interface between the active material layer 11 and the oxide layer 12 to peel off.

[0070] To reduce the 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 low 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 of ​​12 μm vertically and 9 μm horizontally in the cross-section of the oxide layer 12. After acquiring the SEM image, image analysis is performed using known image analysis software (for example, WinROOF®, manufactured by Mitani Corporation).

[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 binarized to extract image edges. In the binarization process, the brightness (luminance) of each pixel in the SEM image is binarized using a predetermined threshold (e.g., threshold 0-25). By binarizing the pixels and eliminating intermediate tones, a binarized image is obtained in which the edges (grain boundaries) of the particles 16 are emphasized.

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

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

[0074] The median diameter of the equivalent circular diameter of particle 16 is preferably 0.04 times or more and 0.60 times or less of the median diameter of the equivalent circular diameter of active material 14. The equivalent circular diameter of active material 14 refers to the diameter of a circle having an area equivalent to the area S of the active material 14 that appears in the cross-section.

[0075] To determine the median diameter of particles 16 and active material 14, the cross-sectional SEM image is analyzed to calculate the equivalent circular diameter from the area S of each particle 16, and the volume-based particle size distribution is determined. Similarly, the equivalent circular diameter is calculated from the area S of each active material 14, and the volume-based particle size distribution is determined. The median diameter is the equivalent circular diameter at which the cumulative frequency in the particle size distribution reaches 50%. To ensure accuracy, the SEM image used to determine the particle size distribution is 400 μm of the oxide layer 12 and active material layer 11. 2 The area shall be as stated above.

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

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

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

[0079] The active material layer 23 contains an active material 24 and particles 25. A conductive material may be included in the active material layer 23 to lower its resistance. Examples of conductive materials include carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag.

[0080] Examples of active materials 24 include metal oxides containing transition metals, sulfur-based active materials, and organic active materials. Examples of metal oxides containing transition metals include metal oxides containing one or more elements selected from Mn, Co, Ni, Fe, Cr, and V, and Li. Examples of metal oxides containing transition metals include LiCoO2 and LiNi 0.8 Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi 0.5 Mn 1.5 O4, LiSa 1 / 3 Mn 1 / 3 Co 1 / 3 O2 and LiFePO4 are examples.

[0081] Examples of sulfur-based active materials include S,TiS2,NiS,FeS2,Li2S,MoS3, and sulfur-carbon composites. Examples of organic active materials include radical compounds such as 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyl vinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, and phenazine oxide.

[0082] 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 Al2O3, ZrO2, LiNbO3, Li4Ti5O 12 Examples include LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, and Li2MoO4.

[0083] The active material layer 23 may contain a binder that binds the active material 24. Examples of binders include rubbery polymers such as fluorinated resins, polyolefins, polyvinylpyrrolidone, polyvinyl alcohol, cellulose ether, polyimide, polyamide, polyamideimide, and styrene-butadiene rubber. Examples of fluorinated resins include vinylidene fluoride polymers, polychlorotrifluoroethylene, polyvinyl fluoride, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer. One or more of these may be used in combination.

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

[0085] The energy storage device 20 is manufactured, for example, as follows: A slurry is made by mixing a mixture of active material 24 and particles 25 with a solution in which a binder has been dissolved. After applying the slurry onto the current collector layer 22, it is dried to obtain a green sheet (positive electrode sheet) for the positive electrode layer 21.

[0086] After cutting sheet 10 and the positive electrode sheet into predetermined shapes, sheet 10 and the positive electrode sheet are stacked and pressed together to form a single unit. Terminals (not shown) are connected to the current collector layers 13 and 22, respectively, and the device is sealed in a case (not shown) to obtain an energy storage device 20 including a positive electrode layer 21, a separator, and a negative electrode layer.

[0087] Examples of energy storage devices 20 include a stacked type in which positive electrode layers 21 and negative electrode layers are alternately stacked with a separator in between, and a wound type in which positive electrode layers 21 and negative electrode layers are wound in a spiral shape with a separator in between. Examples of energy storage devices 20 include electrochemical capacitors and semi-solid batteries. Since energy storage devices 20 do not require the treatment of repeatedly charging and discharging while applying pressure in the stacking direction of the energy storage device to improve cycle characteristics, the energy storage device can be of various types.

[0088] In the energy storage device 20, the inorganic framework 15 reduces the volume change of the active material 14 in the negative electrode layer during charging and discharging. Furthermore, the particles 16 contained in the oxide layer 12 and the inorganic framework 15 work together to reduce the peeling of the oxide layer 12 caused by the volume change of the active material 14 during charging and discharging. This improves and stabilizes the cycle characteristics of the energy storage device 20.

[0089] A second embodiment will be described with reference to Figure 4. In the first embodiment, the case in which the oxide layer 12 is used as a separator was described. In the second embodiment, the case in which the oxide layer 12 is used as a protective layer will be described. Parts identical to those described in the first embodiment are denoted by the same reference numerals and their descriptions are omitted below. Figure 4 is a schematic cross-sectional view of the energy storage device 30 in the second embodiment. The energy storage device 30 is a liquid-based alkali metal ion battery.

[0090] The energy storage device 30 includes, in 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 consists of a current collector layer 22 and an active material layer 32 superimposed on each other. The active material layer 32 contains an active material 24. To lower the resistance of the active material layer 32, the active material layer 32 may contain conductive additives such as carbon black, acetylene black, Ketjen black, carbon fiber, Ni, Pt, and Ag.

[0091] The separator 33 is exemplified by a porous material that is durable against the active materials 14 and 24 contained in the positive electrode layer 31 and sheet 10, as well as the electrolyte, and allows alkali metal ions to pass through but does not have electron conductivity. Examples of porous materials include nonwoven fabrics and porous membranes made of cellulose, polypropylene, polyethylene, etc. Another example of a separator 33 is one in which a gel-like electrolyte with ion conductivity is arranged, or one in which a mixture of a solid electrolyte with ion conductivity and the electrolyte is arranged. The electrolyte is the same as that described in the first embodiment, so its description is omitted.

[0092] An oxide layer 12 (protective layer) is placed between the separator 33 and the active material layer 11. The oxide layer 12 is formed by sheet lamination, coating onto the separator 33, etc. The oxide layer 12 interposed between the active material layer 11 and the separator 33 reduces short circuits caused by alkali metal dendrite growth.

[0093] A third embodiment will be described with reference to Figure 5. In the second embodiment, a case was described in which an oxide layer 12 is placed between the separator 33 and the active material layer 11 to form a protective layer. In the third embodiment, a case will be described in which an oxide layer 12 is placed between the active material layer 11 and the current collector layer 13 to form a protective layer. Parts identical to those described in the first or second embodiment are denoted by the same reference numerals and their descriptions are omitted below. Figure 5 is a schematic cross-sectional view of the energy storage device 40 in the third embodiment. The energy storage device 40 is a liquid-based alkali metal ion battery.

[0094] The energy 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 collector layer 13. These are housed in a case (not shown). The oxide layer 12 (protective layer) positioned between the active material layer 11 and the current collector layer 13 is provided by sheet lamination, coating onto the current collector layer 13, etc. The oxide layer 12 interposed between the active material layer 11 and the current collector layer 13 reduces deterioration of the current collector layer 13. [Examples]

[0095] The present invention will be described in more detail by 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 Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed accordingly. Li2CO3 was kept in excess by approximately 15 mol% elementally, considering the volatilization of Li during calcination. The weighed raw materials and organic solvents were placed in a nylon pot along with zirconia balls and ground and mixed in a ball mill for 15 hours. After drying the slurry removed from the pot, it was placed on an MgO plate and calcined at 900°C for 1 hour and then at 1200°C for 10 hours. The calcined powder was placed on an MgO plate and calcined at 1100°C for 4 hours in an inert gas atmosphere. The calcined powder was then ground for various times in a wet planetary ball mill in an air-free environment, and then dried to obtain various particles of solid electrolyte.

[0097] (Preparation of electrolyte solution) The electrolyte LiN(SO2F)2(LiFSI) was dissolved in the ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (P13FSI) to obtain a salt concentration of 2.1 mol / dm³. 3 We obtained the electrolyte.

[0098] (Fabrication of oxide layer) After mixing particles and electrolyte in a mortar in a particle:electrolyte ratio of 61:39 (vol%), a binder solution of poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) dissolved in carbonate ester was added in various proportions and mixed using a rotating and rotating agitator to obtain various oxide layer slurries. After degassing the oxide layer slurry that passed through a filter with a pore size of 25 μm, it was coated onto a polyethylene terephthalate film and dried to obtain various oxide layers.

[0099] A rectangular specimen was prepared by punching out the oxide layer into a rectangle 30 mm long and 10 mm wide. A gauge mark with a distance of 10 mm between the gauge marks was marked on the specimen, and the Young's modulus of the oxide layer specimen 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 O2, particles, vapor-grown carbon fiber (VGCF) (conductive material), and electrolyte were mixed in the ratio of active material:particles:conductive material:electrolyte = 81.5:6.2:0.4:11.9 (wt%) to obtain a mixture. Then, 4 wt% of binder solution was added to the mixture and mixed using a rotating agitator to obtain a cathode slurry. The cathode slurry that passed through a filter with a pore size of 25 μm was degassed, and then applied to aluminum foil (current collector layer) and dried to obtain a cathode layer (thickness approximately 20 μm).

[0101] A slurry for the oxide layer was applied to the side of the positive electrode layer opposite to the current collector layer, and dried to obtain a positive electrode sheet in which an oxide layer was laminated on the positive electrode layer.

[0102] (Fabrication of the negative electrode layer) Active material Si(D 50 A binder solution, prepared by dissolving polyvinylidene fluoride in carbonate ester, was added to a mixture of active material and conductive material, with the ratio of acetylene black (conductive material), VGCF (conductive material), and polyvinylidene fluoride (binder) being 92:4.2:0.8:3 (wt%). This binder solution was then mixed using a rotating and rotating agitator to obtain a negative electrode slurry. The negative electrode slurry that passed through a filter with a pore size of 25 μm was degassed, and then applied to a stainless steel film and dried to obtain a negative electrode layer (approximately 20 μm thick).

[0103] After weighing Na2CO3 and SiO2 to form Na2O·3SiO2, the mixture was heated to over 1000°C and melted. After cooling, the Na2O·3SiO2 was dissolved in water to obtain an aggregate-forming agent at a ratio of 5% by mass. After immersing the active material layer in the aggregate-forming agent, it was heated to 160°C to obtain a negative electrode layer in which an inorganic skeleton was formed on the active material layer. A slurry for the oxide layer was applied to the side of the negative electrode layer opposite the current collector 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-sections of the oxide layer and the active material layer were acquired, and the circularity of the particles in the oxide layer, the median diameter of the equivalent circle diameter of the particles in the oxide layer, and the median diameter of the equivalent circle diameter of the active material were measured. The circularity was rounded to the fourth decimal place. The ratio of median diameters was obtained by dividing the median diameter of the particles by the median diameter of the active material. The ratio of median diameters was rounded to the third decimal place.

[0105] (Creation of evaluation cells) The oxide layers of the positive electrode sheet and the negative electrode sheet were overlapped and pressed together using a roll press. After connecting terminals to each current collector layer, the cells were sealed under vacuum to obtain the evaluation cells for samples No. 1-6.

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

[0107] (Measurement of capacity retention rate) The evaluation cells in No. 1-6 and the comparative example were repeatedly charged and discharged at a rate of 0.1C, and the ratio of the discharge capacity at 10 cycles to the initial discharge capacity (capacity retention rate) was measured. The ratio of the binder in the oxide layer, the circularity of the oxide layer particles, 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 represents the ratio of the binder volume to the combined volume of the particles constituting the oxide layer, the binder, and the electrolyte (the same applies to Table 2).

[0108] [Table 1]

[0109] As shown in Table 1, the evaluation cells No. 1-6 and the comparative example had the same ratio of circularity to median diameter of the particles constituting the oxide layer. It was found that the evaluation cells No. 1-6, which had an inorganic skeleton in the negative electrode layer, could achieve a higher capacity retention rate compared to the comparative example, which did not have an inorganic skeleton in the negative electrode layer. In other words, the evaluation cells No. 1-6 showed improved cycle characteristics compared to the comparative example.

[0110] According to the evaluation cells in No. 1-6, the capacity retention rate tended to decrease as the proportion of binder in the oxide layer increased. It was found that the evaluation cells in No. 1-5, with a binder proportion of less than 50 vol%, could achieve a higher capacity retention rate compared to the evaluation cell in No. 6, with a binder proportion of 50 vol%.

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

[0112] (Experiment 2) The 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 proportion of binder in the oxide layer, the circularity of the particles contained in the oxide layer, and the ratio of median diameters were varied. The evaluation cells for No. 7-14 were repeatedly charged and discharged at a rate of 0.1C, and the ratio of the discharge capacity after 10 cycles to the initial discharge capacity (capacity retention rate) was measured. The proportion of binder in the oxide layer, the circularity of the particles in the oxide layer, the Young's modulus of the oxide layer, the ratio of median diameters, and the capacity retention rate are shown in Table 2.

[0113] [Table 2]

[0114] In evaluation cells No. 7-13, where the binder ratio was equal, the volume retention rate tended to decrease as the particle roundness increased. It was found that evaluation cells No. 7-11, where the particle roundness was less than 0.72, could achieve a higher volume retention rate compared to evaluation cells No. 12 and 13, where the particle roundness was 0.742 or higher.

[0115] Among the evaluation cells in samples No. 7-11, the capacity retention rates of evaluation cells in samples No. 7, 9, and 11 were higher than those of evaluation cells in samples No. 8 and 10. The median diameter ratio for samples No. 7, 9, and 11 was between 0.04 and 0.60, while the median diameter ratio for samples No. 8 and 10 was outside the range of 0.04-0.60. It became clear that a high capacity retention rate can be achieved when the median diameter of the particles is between 0.04 and 0.60 times the median diameter of the active material.

[0116] In evaluation cell No. 14, where the binder ratio was 4 vol%, the Young's modulus of the oxide layer was less than 0.05 MPa. The capacity retention rate of evaluation cell No. 14 was lower than that of evaluation cells No. 7-13, and was equivalent to that of evaluation cells No. 12 and 13. To increase the capacity retention rate, it was found that a Young's modulus of 0.05 MPa or higher is preferable for the oxide layer, and 0.07 MPa or higher is more preferable.

[0117] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0118] In the embodiments described, a sheet 10 and energy storage devices 20, 30 were described in which an oxide layer 12 is disposed on the surface of the active material layer 11 and a current collector layer 13 is disposed on the back surface of the active material layer 11, and an energy storage device 40 was described in which an oxide layer 12 is disposed on the surface of the active material layer 11 and a separator 33 is disposed on the back surface of the active material layer 11. However, the embodiments are not necessarily limited to these. It is naturally possible to place the oxide layer 12 on both the surface and back surface of the active material layer 11, for example, by providing the oxide layer 12 between the active material layer 11 and the current collector layer 13 of the sheet 10. [Explanation of Symbols]

[0119] 10 sheets 11 Active material layer 12. Oxide layer 14 Active material 15 Inorganic skeleton 16 particles 20, 30, 40 Energy storage devices 33 Separator

Claims

1. A sheet comprising an active material layer containing an active material, The active material layer is further comprising an oxide layer in contact with the active material layer, The active material layer includes 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 and the oxide layer. The oxide layer comprises particles of an oxide-based solid electrolyte, a binder that binds the particles together, and an electrolyte solution. A sheet in which the Young's modulus of the oxide layer is 0.05 MPa or higher, and the circularity of the particles is less than 0.

72.

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

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

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

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

6. The sheet according to claim 5, further comprising Mg and Sr as the particles.

7. It comprises a positive electrode layer, a negative electrode layer, and a separator that separates the positive electrode layer and the negative electrode layer, The negative electrode layer is an energy storage device comprising a current collector layer and an active material layer, The active material layer is part of the sheet described in claim 1 or 2, in this energy storage device.

8. The energy storage device according to claim 7, wherein the separator includes the oxide layer of the sheet.

9. The active material layer is further provided with a protective layer in contact with the active material layer, The energy storage device according to claim 7, wherein the protective layer includes the oxide layer of the sheet.

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