Solid electrolyte sheet, method for producing same, and all-solid-state battery having said solid electrolyte sheet

Abstract

The present invention makes it possible to provide a solid electrolyte sheet to be used as a separator layer that separates a positive electrode layer from a negative electrode layer in an all-solid-state battery, the solid electrolyte sheet comprising a support base material and a boron cluster-type solid electrolyte. Furthermore, the present invention makes it possible to provide a method for producing a solid electrolyte sheet, the method comprising a step for preparing a solid electrolyte solution obtained by dissolving a boron cluster-type solid electrolyte in a solvent, and a step for obtaining a solid electrolyte sheet by applying the obtained solid electrolyte solution to a support base material and then drying the result, wherein the solvent contains at least one substance selected from the group consisting of water, alcohol-based solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate.

Description

Solid electrolyte sheet, manufacturing method thereof, and all-solid-state battery having the solid electrolyte sheet

[0001] The present invention relates to a solid electrolyte sheet, a method for producing the same, and an all-solid-state battery having the solid electrolyte sheet.

[0002] In recent years, demand for lithium-ion secondary batteries has been increasing for applications such as personal digital assistants (PDAs), portable electronic devices, electric vehicles (EVs), hybrid electric vehicles (HEVs), and even stationary energy storage systems. However, current lithium-ion secondary batteries use flammable organic solvents as electrolytes, and require robust packaging to prevent leakage of the organic solvent. Furthermore, restrictions on the design of portable personal computers and other devices are being placed on their construction, such as the need to incorporate measures to protect against the risk of electrolyte leakage.

[0003] Furthermore, their applications have expanded to mobile vehicles such as automobiles and airplanes, requiring stationary lithium-ion secondary batteries with large capacities. Under these circumstances, safety is becoming more important than ever, and efforts are being made to develop all-solid-state lithium-ion secondary batteries that do not use harmful substances such as organic solvents. For example, the use of oxides, phosphate compounds, organic polymers, sulfides, complex hydrides, etc. as solid electrolytes in all-solid-state lithium-ion secondary batteries has been considered.

[0004] All-solid-state batteries are broadly classified into thin-film and bulk types. Thin-film batteries utilize vapor deposition to form ideal interfacial junctions, but the electrode layer is only a few micrometers thick and the electrode area is small, resulting in low energy storage per cell and high costs. Therefore, they are unsuitable for use in large-scale energy storage devices or electric vehicles, which require the storage of large amounts of energy. On the other hand, the thickness of the electrode layer of bulk batteries can be made from several tens of micrometers to 100 micrometers, making it possible to fabricate all-solid-state batteries with high energy density.

[0005] Among solid electrolytes, sulfide solid electrolytes and complex hydrides have high ionic conductivity and are relatively soft, making them easy to form solid-solid interfaces. They are also stable against metallic lithium, and development is underway to develop them as practical solid electrolytes.

[0006] However, the manufacturing methods for all-solid-state batteries using these solid electrolytes require pressing techniques that require high pressure, which limits the ability to manufacture large electrodes and poses challenges in interfacial bonding. Furthermore, sulfide solid electrolytes and complex hydride solid electrolytes are unstable in the presence of moisture, requiring special environments such as an inert gas atmosphere or an ultra-low dew point dry room. Therefore, there is a need for equipment that can manufacture all-solid-state batteries in a small space.

[0007] To address this issue, it has been disclosed that a good interface can be formed with low press pressure by applying a solution of solid electrolyte to the mating surfaces of the positive electrode layer and negative electrode layer and then laminating them together (Patent Document 1). However, the positive electrode layer and negative electrode layer themselves must be formed with high press pressure, and there is also the issue that dissolving a sulfide solid electrolyte in an alcohol solvent gradually decomposes the sulfide solid electrolyte, generating hydrogen sulfide. In addition, short circuits can occur during discharge, so improvements in cycle performance are needed.

[0008] Japanese Patent Application Laid-Open No. 2015-2080

[0009] Under these circumstances, it is desired to provide a solid electrolyte sheet that is easy to process and has a low risk of short circuiting, a method for producing the same, and an all-solid-state battery that includes the solid electrolyte sheet.

[0010] Therefore, the present inventors have conducted extensive research in view of the above-mentioned problems and have found that the above-mentioned problems can be solved by a solid electrolyte sheet including a support substrate and a boron cluster-type solid electrolyte.

[0011] That is, the present invention is as follows. <1> A solid electrolyte sheet used as a separator layer separating a positive electrode layer and a negative electrode layer in an all-solid-state battery, the solid electrolyte sheet comprising a support substrate and a boron cluster-type solid electrolyte. <2> The solid electrolyte sheet according to the above <1>, wherein the support substrate is a glass nonwoven fabric. <3> The solid electrolyte sheet according to the above <1> or <2>, wherein the support substrate has a thickness of 10 μm to 300 μm. <4> The boron cluster-type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ <5> The solid electrolyte sheet according to any one of the above items <1> to <3>, wherein the boron cluster-type solid electrolyte is a solid electrolyte composite containing LiCB in a molar ratio range of 1.1 to 20. ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ : LiCB １１ H １２<4> above, wherein the solid electrolyte composite contains a boron cluster-type solid electrolyte in a molar ratio of 0.01 to 0.03. <6> An all-solid-state battery having a positive electrode layer, a separator layer, and a negative electrode layer stacked in this order, wherein the separator layer is the solid electrolyte sheet according to any one of <1> to <5> above. <7> A method for producing a solid electrolyte sheet, comprising the steps of: preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; and applying the obtained solid electrolyte solution to a support substrate and drying it to obtain a solid electrolyte sheet, wherein the solvent comprises one or more selected from the group consisting of water, alcohol-based solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate. <8> The method according to <7> above, wherein the support substrate is a glass nonwoven fabric. <9> The method according to <7> or <8> above, wherein the support substrate has a thickness of 10 μm to 300 μm. <10> The boron cluster-type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ <11> The method for producing a solid electrolyte composite according to any one of the above items <7> to <9>, wherein the boron cluster-type solid electrolyte is a solid electrolyte composite containing LiCB in a molar ratio of 1.1 to 20. ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ : LiCB １１ H １２<10> The method for producing a solid electrolyte composite according to the above <10>, wherein the solid electrolyte composite contains a molar ratio of 0.01 to 0.02 of 0.01 to 0.03. <12> The method for producing a solid electrolyte composite according to the above <7> to <11>, wherein the solid content concentration of the solid electrolyte solution is 5% by mass to 70% by mass. <13> The method for producing a solid electrolyte composite according to the above <7> to <12>, wherein the drying is performed at a temperature of 40°C to 200°C under atmospheric pressure for 30 minutes to 5 hours, and further at a temperature of 100°C to 300°C for 1 to 30 hours under vacuum. <14> The method for producing a solid electrolyte composite according to the above <7> to <13>, comprising, after the drying, a step of rolling the support substrate using a roll press to densify it.

[0012] According to the present invention, it is possible to provide a solid electrolyte sheet that is excellent in processability and has a low risk of short circuiting, a method for producing the same, and an all-solid-state battery that includes the solid electrolyte sheet.

[0013] Fig. 1 is a diagram showing charge / discharge curves of the all-solid-state battery produced in Example 1. Fig. 2 is a diagram showing cycle characteristics of the all-solid-state battery produced in Example 1. Fig. 3 is a diagram showing charge / discharge curves of the Li battery produced in Comparative Example 1. Fig. 4 is a diagram showing charge / discharge curves of the all-solid-state battery produced in Comparative Example 2.

[0014] The solid electrolyte sheet of the present invention, its manufacturing method, and an all-solid-state battery including the solid electrolyte sheet are specifically described below. Note that the materials and configurations described below do not limit the present invention and can be modified in various ways within the scope of the present invention. Note that in this specification, when a numerical range is indicated using "to," the numerical values ​​at both ends are included.

[0015] [Solid Electrolyte Sheet] The solid electrolyte sheet of the present invention is used as a separator layer separating a positive electrode layer and a negative electrode layer in an all-solid-state battery, and includes a support substrate and a boron cluster-type solid electrolyte. The solid electrolyte sheet of the present invention can be produced by impregnating a support substrate capable of soaking in a solution with a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved, and then removing the solvent to deposit the solid electrolyte inside and on the surface of the support substrate.

[0016] <Support Substrate> The solid electrolyte sheet of the present invention serves as a separator layer separating the positive electrode layer and the negative electrode layer. Therefore, the support substrate must be highly insulating. While not particularly limited, separators used in electrolytes can be used. Examples include glass nonwoven fabric, glass fiber filter paper, polyolefin-based separators, cellulose-based separators, and nonwoven fabric separators other than glass nonwoven fabric. Among these, the porosity of the separator is preferably 40% to 95%, more preferably 70% to 95%. This is because the solid electrolyte is formed in the voids, increasing the proportion of the solid electrolyte, which is an ion conductor. Furthermore, the heat resistance temperature is preferably 200°C or higher. From the standpoint of heat resistance, glass nonwoven fabrics that do not contain an organic binder are desirable, although organic binders may be present depending on the type. The thickness of the support substrate used in the present invention is preferably 10 μm to 300 μm, more preferably 50 μm to 200 μm.

[0017] <Boron cluster type solid electrolyte> A boron cluster type solid electrolyte is a type of complex hydride, and is a compound having a cluster structure with boron as the basic skeleton. Generally, if this cluster structure is closed (cage-shaped), it exhibits high stability against water and alcohol. Specific examples of boron cluster type solid electrolytes include LiCB ９ H １０ , LiCB １１ H １２ , Li ２ B １２ H １２ Among them, boron cluster type solid electrolytes having carbon in the skeleton are preferred because they tend to have high ionic conductivity. Examples of such compounds include LiCB ９ H １０ and LiCB １１ H １２ Examples include, but are not limited to, LiCB ９ H １０ and LiCB １１ H １２ The chemical structure of

[0018] The boron cluster type solid electrolyte used in the present invention is, among others, LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ The solid electrolyte composite preferably contains LiCB in a molar ratio range of 1.1 to 20 (more preferably 1.25 to 10, and even more preferably 1.5 to 9). ９ H １０ Based on 749cm －１ (±5cm －１ ) and LiCB １１ H １２ Based on 763cm －１ (±5cm －１ ) respectively. Peaks may also be present in other regions, but the peaks that show the characteristics of each are as described above. In the present invention, in particular, the boron cluster type solid electrolyte is ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ : LiCB １１ H １２ It is preferable that the solid electrolyte composite contains LiCB in a molar ratio of 7:3. ９ H １０ : LiCB １１ H １２ By mixing them at a molar ratio of 7:3, a high ionic conductor (>1 mS / cm) can be formed.

[0019] The raw material LiCB ９ H １０ and LiCB １１ H １２ As the crystalline crystalline ester, commercially available crystalline esters can be used. The purity of the crystalline crystalline ester is preferably 95% or more, and more preferably 98% or more. By using a compound having a purity within the above range, it is easy to obtain the desired crystals.

[0020] LiCB ９ H １０ and LiCB １１ H １２ The mixing with the above can be carried out in the air or in a homogeneous solvent. As a method of mixing, it can also be carried out in a solvent. The solvent is not particularly limited, but examples thereof include water, nitrile solvents such as acetonitrile, ether solvents such as tetrahydrofuran and diethyl ether, N,N-dimethylformamide, N,N-dimethylacetamide, alcohol solvents such as methanol, ethanol, and propanol, acetone, ethyl acetate, methyl acetate, toluene, methylene chloride, and chloroform. Among these solvents, in view of safety, alcohol solvents such as water, ethanol, and isopropanol are particularly preferred, and water is more preferred. As the alcohol solvent, those having 3 or less carbon atoms are more preferred. For example, when LiCB is mixed using water as a solvent, ９ H １０ and LiCB １１ H １２ The water was removed from the mixed aqueous solution using an evaporator, and LiCB ９ H １０ and LiCB １１ H １２ A compound containing a mixture of these at a specified molar ratio can be obtained. The solvent evaporation and powder drying times vary depending on the solvent type, and the drying time is shorter when an alcohol-based solvent is used.

[0021] [Method for Producing Solid Electrolyte Sheet] The method for producing a solid electrolyte sheet of the present invention includes: (1) a step of preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; and (2) a step of applying the obtained solid electrolyte solution to a support substrate and then drying the applied solution to obtain a solid electrolyte sheet.

[0022] <Preparation step of solid electrolyte solution> The preparation step of the solid electrolyte solution in the present invention is a step of dissolving a boron cluster-type solid electrolyte in a solvent to prepare a solid electrolyte solution. The boron cluster-type solid electrolyte used in this step is the one described above, and preferred examples are also the same. The solvent used in this step includes one or more selected from the group consisting of water, alcohol-based solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate, and among these, methanol, tetrahydrofuran, and acetonitrile are preferably used, and methanol is more preferably used. As long as a solid electrolyte solution can be obtained, the preparation method is not particularly limited, but for example, LiCB ９ H １０ and LiCB １１ H １２ When using a solid electrolyte composite with LiCB ９ H １０ and LiCB １１ H １２ The resulting mixture is mixed with an aqueous solution of LiCB and dried to obtain a powder of the solid electrolyte composite, which is then dissolved in methanol to obtain a solid electrolyte solution. ９ H １０ Methanol solution and LiCB １１ H １２ A solid electrolyte solution can also be prepared by mixing the above-mentioned methanol solution with the above-mentioned solid electrolyte. When using other solid electrolytes, a solid electrolyte solution can be prepared in the same manner. The specific solvents described here are merely examples, and do not preclude the use of other solvents.

[0023] The solids concentration (solid electrolyte concentration) in the solid electrolyte solution is preferably in the range of 5% by mass to 70% by mass, although the optimum value varies depending on the type of boron cluster-type solid electrolyte and solvent, so as to achieve an optimal viscosity when applied to a support substrate. At concentrations lower than this range, the precipitation efficiency of the solid electrolyte may be reduced. On the other hand, at higher concentrations, there is a concern that the increased viscosity may make it difficult for the solid electrolyte to penetrate deep into the pores. The solids concentration in the solid electrolyte solution is more preferably in the range of 20% by mass to 60% by mass, and even more preferably in the range of 30% by mass to 50% by mass.

[0024] <Coating and Drying Process on Support Substrate> The coating and drying process on support substrate in the present invention is a process of coating a support substrate with the solid electrolyte solution obtained in the above-described solid electrolyte solution preparation process, followed by drying to obtain a solid electrolyte sheet. The support substrate used in this process is the same as that described above, and preferred examples are also the same. Methods for coating the support substrate with the solid electrolyte solution include known methods of coating and impregnating an electrode sheet with an electrolyte solution, such as a doctor blade method, a spin coating method, and a spray coating method. Among these, dropping the solid electrolyte solution onto the support substrate and uniformly applying it by wire coating is preferred. In the solid electrolyte sheet, the solid electrolyte is preferably contained in an amount of 40 to 90% by mass, more preferably 45 to 85% by mass, and particularly preferably 50 to 80% by mass, based on the total mass of the support substrate and the solid electrolyte.

[0025] After applying the solid electrolyte solution to the support substrate, the solution is dried to remove the solvent and deposit the solid electrolyte, densely filling the voids in the support substrate with the solid electrolyte. Drying is preferably carried out at atmospheric pressure at a temperature of 40°C to 200°C (more preferably 120°C to 180°C) for 30 minutes to 5 hours (more preferably 1 to 3 hours), and further at a temperature of 100°C to 300°C (more preferably 150°C to 200°C) for 1 to 30 hours (more preferably 20 to 25 hours) under vacuum. This drying method allows the solvent to be efficiently evaporated, resulting in the deposition of the solid electrolyte. If the solvent is evaporated at a temperature higher than this range, side reactions may occur or the solvent may foam, potentially preventing the solid electrolyte from being densely deposited. Furthermore, heating under an inert gas stream or in a vacuum can promote the evaporation of the solvent.

[0026] The present invention preferably includes a step of rolling the support substrate using a roll press to densify it after the drying. Although the rolling method using a roll press (roll press method) has high continuous productivity, the pressing pressure is lower than that of the uniaxial pressing method or the isostatic pressing method. Because the solid electrolyte precipitated from the solid electrolyte solution is relatively dense, and the boron cluster-type solid electrolyte is soft, rolling at a low pressing pressure can sufficiently densify the solid electrolyte. The pressing pressure used in the roll press method is preferably 0.1 MPa to 100 MPa, and more preferably 1 MPa to 80 MPa. Conventional molding of all-solid-state batteries required extremely high pressing pressure to deform and densify the powder itself. However, in the present invention, by precipitating the solid electrolyte from the solid electrolyte solution, a dense solid electrolyte is formed in the voids of the support substrate, eliminating the need for high pressing pressures, such as 300 MPa, which would deform the particles. In a preferred embodiment of the present invention, rolling after drying is carried out for the purpose of filling small cracks that occur due to expansion and contraction caused by thermal changes and small voids that occur when the solvent volatilizes, and a sufficient effect can be obtained by the roll press method.

[0027] [All-Solid-State Battery] The all-solid-state battery of the present invention comprises a positive electrode layer, a separator layer, and a negative electrode layer stacked in this order, with the separator layer being the solid electrolyte sheet of the present invention. The positive electrode layer and the negative electrode layer are collectively referred to as electrode layers. The electrode layers used in the present invention may be electrode layers for lithium-ion batteries that use an electrolyte solution. In the present invention, a positive electrode sheet in which a positive electrode layer is formed on a current collector, and a negative electrode sheet in which a negative electrode layer is formed on a current collector, may also be used. The positive electrode sheet and the negative electrode sheet are collectively referred to as electrode sheets. The positive electrode layer is typically formed from a positive electrode active material, a binder, and a conductive additive, while the negative electrode layer is typically formed from a negative electrode active material, a binder, and a conductive additive. These electrode layers have voids and can be impregnated with an electrolyte solution. It is also possible to use a metal foil or an alloy foil for either the positive electrode layer or the negative electrode layer, and an electrode sheet containing the boron cluster-type solid electrolyte used in the present invention for the other electrode. As the current collector, stainless steel foil or aluminum foil is generally used for the positive electrode layer, and stainless steel foil or copper foil is generally used for the negative electrode layer. However, current collectors with a carbon-coated surface can also be used.

[0028] The positive electrode active material contained in the positive electrode layer is not particularly limited as long as it is a material that can release lithium ions during charging and absorb lithium ions during discharging. For example, metal oxides containing transition metals, sulfur-based positive electrode active materials, organic positive electrode active materials, FeF using a conversion reaction, etc. ３ and VF ３ In the present invention, it is preferable that the potential of the positive electrode active material is 3.0 V or less versus lithium, since this suppresses the reaction at the interface between the active material and the boron cluster-type solid electrolyte, thereby reducing the interfacial resistance. More preferably, the potential of the positive electrode active material is 1.0 to 2.7 V versus lithium.

[0029] As the metal oxide containing a transition metal, particles or a thin film of a metal oxide containing lithium and any one or more of the transition metals Mn, Co, Ni, Fe, Cr, and V can be used. Specific examples include, but are not limited to, LiCoO ２ , LiCo２ O₄, LiMnO ２ , LiMn ２ O ４ , LiMnCoO₄, Li ２ MnCoO₄, LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiNi ０．５ Mn ０．５ O ２ , Li ２ NiMn ３ O ８ , LiVO ２ , LiV ３ O ３ , LiCrO ２ , LiFePO ４ , LiCoPO ４ , LiMnPO ４ , LiVOPO ４ , LiNiO ２ , LiNi ２ O₄, LiNi １／３ Co １／３ Mn １／３ O ２ , Li ２ FeSiO ４ , Li ２ MnSiO ４ , LiFeBO ３ etc. can be mentioned. Also, Fe ２ O ３ , Cr ３ O ８ , V ２ O ５ , MnO ２ etc. can also be used. Among them, LiCoO ２ , LiMnO ２ , LiMn ２ O ４ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiNi ０．５ Mn ０．５ O ２ , Li ２ NiMn ３ O ８ , LiFePO ４ , LiCoPO ４ , LiMnPO４ , LiVOPO ４ , LiNiO ２ and LiNi １／３ Co １／３ Mn １／３ O ２ In addition, for the purpose of suppressing the reaction with the solid electrolyte, it is possible to provide a coating layer on the particles or thin film of these positive electrode active materials. As the type of coating layer, 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 , Li ２ MoO ４ and LiBO ２ Examples include:

[0030] The sulfur-based positive electrode active material is not particularly limited, but specifically includes S, sulfur-carbon composite, TiS ２ , TiS ３ , TiS ４ , NiS, NiS ２ , CuS, FeS ２ , Li ２ S, MoS ３ , sulfur-modified polyacrytonitrile, rubeanic acid (dithiooxamide), disulfide compounds, etc. ２ , TiS ３ , TiS ４ , NiS, NiS ２ , FeS ２ , Li ２ S, MoS ３ , sulfur-modified polyacrytonitrile, sulfur-carbon composite, and rubeanic acid (dithiooxamide) are preferred.

[0031] The organic positive electrode active material is not particularly limited, but specific examples include radical compounds typified by 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyvinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, phenazine oxide, etc. Among these, radical compounds and quinone compounds are preferred because they have a large theoretical capacity and can maintain a relatively good discharge capacity.

[0032] The negative electrode active material contained in the negative electrode layer can be, for example, a Si-based negative electrode material, a metal active material, or a carbon-based active material. Examples of the Si-based negative electrode material include Si, SiO, and Si—C composite materials. Examples of the metal active material include Li ４ Ti ５ O １２ , Li, In, Al, Sn, and alloys of these metals. On the other hand, examples of the carbon-based active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Among these, it is preferable to use an active material that lowers the equilibrium potential as a negative electrode, since this improves the energy density of the battery and increases the operating voltage. Examples of such negative electrode active materials include Li, carbon-based active materials, and Si-based negative electrode materials.

[0033] The binder used in the positive electrode layer is not particularly limited, but examples thereof include polyimides, acrylics, polysiloxanes, polyalkylene glycols, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), ethylene-vinyl alcohol copolymers (EVOH), and the like. If necessary, thickeners such as carboxymethyl cellulose (CMC) can also be used. The binder used in the negative electrode layer is not particularly limited, but examples thereof include polyimides, polysiloxanes, polyalkylene glycols, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), acrylics, and the like. If necessary, thickeners such as carboxymethyl cellulose (CMC) can also be used.

[0034] The conductive additive used in the electrode layer is not particularly limited as long as it has the desired conductivity, but examples thereof include conductive additives made of carbon materials. Specific examples include carbon black, acetylene black, ketjen black, and carbon fiber. Other examples include cellulose nanofibers made from plants.

[0035] The electrode sheet can be produced by a known method. For example, a coating liquid is prepared by mixing a positive electrode active material or a negative electrode active material with a binder, a conductive additive, and an organic solvent. This coating liquid is applied to a current collector by a doctor blade method, a spin coating method, a spray coating method, or the like, and then dried to produce an electrode sheet in which an electrode layer is formed on a current collector.

[0036] An all-solid-state battery can be fabricated by stacking and rolling the sheets. In the present invention, it is preferable to include, for example, a step of laminating an anode layer and a solid electrolyte sheet together, and then laminating the solid electrolyte sheet and a cathode layer together, so that a solid electrolyte sheet is disposed between the cathode layer and the anode layer. The pressing pressure when laminating the anode layer and the solid electrolyte sheet, and the pressing pressure when laminating the cathode layer and the solid electrolyte sheet, are preferably 0.001 MPa to 100 MPa, more preferably 1 MPa to 80 MPa, and particularly preferably 10 MPa to 60 MPa. The boron cluster-type solid electrolyte also functions as a binder, and is therefore highly effective in bonding these sheets together. The rolling method can be, for example, a roll press method.

[0037] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples.

[0038] Example 1 Synthesis of boron cluster-type solid electrolyte LiCB ９ H １０ and LiCB １１ H １２ The aqueous solutions were mixed so that the molar ratio was 7:3. Next, the water in the mixed aqueous solution was removed using an evaporator. ９ H １０ and LiCB １１ H １２ A compound (boron cluster type solid electrolyte) in which these are mixed in a molar ratio of 7:3 is referred to as "LCBH."

[0039] <Preparation of Solid Electrolyte Solution> Methanol was added to the LCBH prepared above so that the solid content concentration was 40 wt %, and an LCBH / MeOH solution (solid electrolyte solution) was prepared by manual stirring.

[0040] <Preparation of Solid Electrolyte Sheet> The LCBH / MeOH solution obtained above was dropped onto a glass nonwoven fabric support substrate (GC-50, manufactured by Advantec, thickness 190 μm), and uniformly applied using a wire coater, allowing it to penetrate to the interior. At the same time, excess LCBH / MeOH solution was removed. Next, temporary drying was carried out using a constant temperature dryer under atmospheric pressure at 160°C for 2 hours. Thereafter, vacuum heating was further carried out in a vacuum constant temperature dryer under vacuum at 180°C for 15 hours to prepare a solid electrolyte sheet. The mass per unit area of ​​the glass nonwoven fabric support substrate alone was 5.05 mg / cm ２ On the other hand, the mass per unit area of ​​the solid electrolyte sheet obtained by applying the LCBH / MeOH solution and drying it was 12.79 mg / cm ２ That is, the solid electrolyte was contained in a proportion of about 60 mass % with respect to the total mass of the supporting substrate and the solid electrolyte.

[0041] <Densification of Solid Electrolyte Sheet> To densify the solid electrolyte sheet obtained above, roll pressing was carried out without heating using a tabletop hot roll press (HSPR-60150HL-A, manufactured by Hosen Co., Ltd.) under conditions of a press pressure of 50 MPa and a slit width between rolls of 50 μm. The above steps of <Preparation of Solid Electrolyte Solution>, <Fabrication of Solid Electrolyte Sheet>, and <Densification of Solid Electrolyte Sheet> were all carried out in a dry environment with a dew point of −60° C. or lower.

[0042] <Preparation of Negative Electrode Slurry> When preparing the negative electrode slurry, SiO (carbon-coated powder having an average particle size of 6 μm) was used as the negative electrode active material, a polyimide binder (U-Varnish A, manufactured by UBE) was used as the binding agent (binder), and acetylene black (DENKA BLACK Li-100, manufactured by Denka Co., Ltd.) was used as the conductive additive. Each of these was weighed out to give a composition of SiO:acetylene black:polyimide binder = 80:5:15 wt %, and the mixture was kneaded together with N-methyl-2-pyrrolidone (NMP) solvent using a rotation / revolution mixer (ARE-310, manufactured by Thinky Co., Ltd.) at 2000 rpm for 20 minutes to prepare the negative electrode slurry.

[0043] <Preparation of Negative Electrode Composite Layer> The negative electrode slurry obtained above was applied to a stainless steel foil (thickness 10 μm) of a current collector (current collector) using a desktop coater (FILMCOATER, PI-1210, manufactured by Tester Sangyo Co., Ltd.), and pre-dried in a constant temperature oven at 80°C for 10 minutes. After pre-drying, a vacuum heat treatment was carried out in a vacuum constant temperature oven at 240°C for 15 hours to prepare a negative electrode composite layer (electrode). The capacity density of the electrode was 1.0 mAh / cm ２ It was.

[0044] <Preparation of Negative Electrode Sheet> The solid electrolyte solution prepared in the preparation of the solid electrolyte sheet was dropped onto the surface of the negative electrode composite layer (electrode) obtained above, and the solid electrolyte solution was penetrated and homogenized into the interior of the negative electrode composite layer using a wire coater. At the same time, excess solid electrolyte solution was removed. Then, pre-drying was performed in a constant temperature dryer under atmospheric pressure at 160°C for 2 hours. This operation from coating the solid electrolyte solution to pre-drying was repeated twice. Then, vacuum heating and drying was performed in a vacuum constant temperature dryer under vacuum conditions at 180°C for 15 hours to prepare a negative electrode sheet in which a solid electrolyte layer was formed inside the negative electrode composite layer. This process was all performed in a dry environment with a dew point of -60°C or less.

[0045] <Preparation of All-Solid-State Battery> An all-solid-state battery was prepared by stacking the negative electrode sheet obtained above as a test electrode, the solid electrolyte sheet obtained above as a separator layer, and Li as a counter electrode in this order. First, the solid electrolyte sheet obtained above was punched out to a diameter of 13 mm using an electrode punching hand punch (manufactured by Nogami Giken Co., Ltd.) to prepare a test sheet. The negative electrode sheet obtained above was also punched out to a disk shape of 11 mm diameter using a hand punch to prepare a test electrode. The solid electrolyte sheet punched out to a diameter of 13 mm using the hand punch was overlapped with the negative electrode composite layer surface of the negative electrode sheet punched out to a diameter of 11 mm so that they were in contact, and then cold-pressed at 50 MPa using a uniaxial powder molding press to adhere them together. Furthermore, a 12 mm diameter Li foil (manufactured by Honjo Metals Co., Ltd., 200 μm thick) was placed on the opposite side of the solid electrolyte sheet from the negative electrode sheet, and again cold pressed at 20 MPa using a uniaxial powder molding press to obtain a laminate of the negative electrode sheet, solid electrolyte sheet, and Li. A CR2032 coin cell was fabricated from this laminate to form an all-solid-state battery. This process was carried out in a dry environment with a dew point of −60°C or below.

[0046] <Charge / Discharge Test> The all-solid-state battery obtained above was placed in a thermostatic chamber set to 60°C, and a charge / discharge current was set to 0.05 mA / cm ２ A constant current charge / discharge test was carried out with the operating voltage range of 1.20 to 0.01 V. Figure 1 shows the charge / discharge curve of the all-solid-state battery produced in Example 1. The initial charge capacity was 2737 mAh / g, and the initial discharge capacity was 1651 mAh / g. The results shown in Figure 1 show that the all-solid-state battery produced in Example 1 is capable of stable charge / discharge from the second cycle onwards. In addition, from the fourth cycle onwards, the charge / discharge current was increased to 0.1 mA / cm. ２ The cycle characteristics are shown in Figure 2, which shows that the all-solid-state battery prepared in Example 1 was capable of stable charge and discharge without short circuiting for 100 cycles.

[0047] Comparative Example 1 <Preparation of Li Battery Using Electrolyte> The negative electrode composite layer (electrode) obtained in <Preparation of Negative Electrode Composite Layer> in Example 1 was punched into a disk shape with a diameter of 11 mm using an electrode punch hand punch (manufactured by Nogami Giken Co., Ltd.) to prepare a test electrode. A 14 mm diameter Li foil (manufactured by Honjo Metals Co., Ltd., t = 500 μm) was used as the counter electrode of this test electrode, a 16 mm diameter glass fiber filter (manufactured by Advantec, GA-100, t = 500 μm) and a polyolefin microporous membrane (PP / PE / PP microporous membrane, t = 25 μm) were used as the separator, and 1 mol / L LiPF ６ A CR2032-type coin cell (Li battery) was fabricated using EC / DEC (=50 / 50, Vol%) (LBG-96533, manufactured by Kishida Chemical Co., Ltd.). This process was all carried out in a dry environment with a dew point of −60°C or below.

[0048] <Charge / Discharge Test> The Li battery obtained above was placed in a thermostatic chamber set at 60°C, and a charge / discharge current was applied at 0.05 mA / cm ２ A constant current charge / discharge test was carried out with the operating voltage range set to 1.20 to 0.01 V. Figure 3 shows the charge / discharge curve of the Li battery produced in Comparative Example 1. The charge / discharge curve is similar to that shown in Figure 1, and the obtained discharge capacity was also the same. From this, it can be seen that Example 1, although being an all-solid-state battery, has the same performance as a Li battery using an electrolyte solution, and that the solid electrolyte sheet produced in Example 1 is useful for all-solid-state batteries. In addition, ６ In the Li battery of Comparative Example 1 using the solid electrolyte sheet, the electrolyte solution reacts and decomposes, resulting in poor high-temperature stability, and there is also a constant risk of leakage. However, with the all-solid-state battery using the solid electrolyte sheet produced in Example 1, there is no need to worry about this.

[0049] Comparative Example 2 <Preparation of Coating Solution> In the same manner as in <Preparation of Solid Electrolyte Solution> in Example 1, a 30 wt % LCBH / MeOH solution was prepared, to which a 100% by mass mixture of LCBH:nanoSiO ２ (Fumed silica, primary particle diameter 5-50 nm, secondary particle diameter approximately 300 nm) = 80:20 ２ Add the nano SiO ２This process was carried out in a dry environment with a dew point of −60° C. or less.

[0050] <Preparation of Negative Electrode Sheet> The coating solution obtained above was applied to the surface of the negative electrode composite layer (electrode) obtained in <Preparation of Negative Electrode Composite Layer> in Example 1 using a wire coater, and then pre-dried using a constant temperature dryer at atmospheric pressure and 160 ° C for 2 hours. This coating-pre-drying process was repeated five times, and finally vacuum heating and drying was performed in a vacuum constant temperature dryer at 180 ° C for 15 hours. Furthermore, in order to densify the negative electrode sheet obtained above, roll pressing was performed using a tabletop hot roll press machine (manufactured by Hosen Co., Ltd., HSPR-60150HL-A) without heating, with a slit width between the rolls of 0 μm. A negative electrode sheet was obtained in which a solid electrolyte layer was formed inside and on the surface of the negative electrode composite layer. This process was all carried out in a dry environment with a dew point of -60 ° C or less.

[0051] <Preparation of all-solid-state battery> The negative electrode sheet obtained above was punched out to a diameter of 12 mm using an electrode punching hand punch (manufactured by Nogami Giken Co., Ltd.) to prepare a test sheet. The 12 mm diameter test sheet punched out with the hand punch was superimposed on an 11 mm diameter Li foil (manufactured by Honjo Metals Co., Ltd., thickness 200 μm) and cold pressed at 5 MPa using a powder molding uniaxial pressure press to adhere the foil. A CR2032 type coin cell was prepared from this laminate to prepare an all-solid-state battery. All of these steps were carried out in a dry environment with a dew point of -60 ° C or less.

[0052] <Charge / Discharge Test> The all-solid-state battery obtained above was placed in an incubator set at 60°C, and a constant current charge / discharge test was performed in the same manner as in Example 1. Figure 4 shows the charge / discharge curve of the all-solid-state battery prepared in Comparative Example 2. A short circuit was confirmed in the second cycle for the all-solid-state battery prepared in Comparative Example 2. Even when the method of the example described in WO2020-184340 was applied to LCBH, good cycle performance was not obtained. This shows that the solid electrolyte sheet is superior to the solid electrolyte formation method described in WO2020-184340.

Claims

1. A solid electrolyte sheet used as a separator layer separating a positive electrode layer and a negative electrode layer in an all-solid-state battery, the solid electrolyte sheet comprising a supporting substrate and a boron cluster-type solid electrolyte.

2. The solid electrolyte sheet according to claim 1, wherein the supporting substrate is a nonwoven glass fabric.

3. The solid electrolyte sheet according to claim 1 or 2, wherein the thickness of the supporting substrate is 10 μm to 300 μm.

4. The boron cluster type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ The solid electrolyte sheet according to any one of claims 1 to 3, which is a solid electrolyte composite containing a molar ratio of 0.1 to 0.25 ...

5. The boron cluster type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ :LiCB １１ H １２ 5. The solid electrolyte sheet according to claim 4, wherein the solid electrolyte composite contains the metal oxide and the metal oxide in a molar ratio of 7:

3.

6. An all-solid-state battery comprising a positive electrode layer, a separator layer, and a negative electrode layer laminated in this order, wherein the separator layer is the solid electrolyte sheet according to any one of claims 1 to 5.

7. A method for producing a solid electrolyte sheet, comprising: preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; and applying the obtained solid electrolyte solution to a supporting substrate and drying it to obtain a solid electrolyte sheet, wherein the solvent comprises one or more selected from the group consisting of water, alcohol-based solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate.

8. The method according to claim 7, wherein the supporting substrate is a nonwoven glass fabric.

9. The method according to claim 7 or 8, wherein the thickness of the supporting substrate is 10 μm to 300 μm.

10. The boron cluster type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ The method according to any one of claims 7 to 9, wherein the solid electrolyte composite is a solid electrolyte composite having a molar ratio of 0.1 to 0.

5.

11. The boron cluster type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ :LiCB １１ H １２ The method according to claim 10, wherein the solid electrolyte composite is a composite containing the metal oxide and the metal oxide in a molar ratio of 7:

3.

12. The method according to any one of claims 7 to 11, wherein the solid content of the solid electrolyte solution is 5% by mass to 70% by mass.

13. The method according to any one of claims 7 to 12, wherein the drying is carried out at atmospheric pressure at a temperature of 40°C to 200°C for 30 minutes to 5 hours, and further carried out under vacuum at a temperature of 100°C to 300°C for 1 to 30 hours.

14. The method according to any one of claims 7 to 13, further comprising a step of rolling and densifying the support substrate using a roll press after the drying.

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