Solid electrolyte sheet, method for manufacturing the same, and all-solid battery having the same

Abstract

According to the present invention, a solid electrolyte sheet can be provided, wherein the solid electrolyte sheet is used as a separator layer separating the positive electrode layer and the negative electrode layer in an all-solid-state battery, the solid electrolyte sheet comprising a support substrate and a boron cluster-type solid electrolyte. Furthermore, according to the present invention, a method for manufacturing a solid electrolyte sheet can be provided, wherein the method comprises: a step of preparing a solid electrolyte solution obtained by dissolving a boron cluster-type solid electrolyte in a solvent; and a step of coating the obtained solid electrolyte solution onto a support substrate and then drying it to obtain a solid electrolyte sheet, wherein the solvent comprises one or more selected from water, alcohol solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate.

Description

Technical Field

[0001] This invention relates to a solid electrolyte sheet, a method for manufacturing the same, and an all-solid-state battery having the solid electrolyte sheet. Background Technology

[0002] In recent years, the demand for lithium-ion rechargeable batteries has been increasing in applications such as portable information terminals, portable electronic devices, electric vehicles, hybrid vehicles, and stationary energy storage systems. However, current lithium-ion rechargeable batteries use flammable organic solvents as electrolytes, thus requiring robust outer packaging to prevent leakage. Furthermore, in fields such as portable personal computers, there are also constraints on device structure due to the need for structures that mitigate the risk of electrolyte leakage.

[0003] Furthermore, as the applications of lithium-ion rechargeable batteries have expanded to mobile vehicles such as automobiles and airplanes, stationary lithium-ion rechargeable batteries need to have larger capacities. Under these circumstances, safety has received more attention than ever before, and more efforts have been devoted to the development of all-solid-state lithium-ion rechargeable batteries that do not use harmful substances such as organic solvents.

[0004] For example, as a solid electrolyte in all-solid-state lithium-ion secondary batteries, researchers have been studying the use of oxides, phosphoric acid compounds, organic polymers, sulfides, coordination hydrides, and the like.

[0005] All-solid-state batteries are broadly classified into thin-film and prismatic types. While thin-film batteries can achieve ideal interfacial bonding through vapor-phase deposition, the resulting electrode layers are only a few μm thick, and the electrode area is relatively small. This leads to lower energy storage capacity per unit cell and higher cost. Therefore, they are unsuitable for large-scale energy storage devices and electric vehicles requiring significant energy storage. On the other hand, prismatic batteries have electrode layers ranging from tens of μm to 100 μm thick, enabling the fabrication of all-solid-state batteries with high energy density.

[0006] Among solid electrolytes, sulfide solid electrolytes and coordinated hydrides have high ionic conductivity and relatively soft texture, thus readily forming solid-solid interfaces. They are also stable to lithium metal, and their development as practical solid electrolytes has been ongoing.

[0007] However, the manufacturing methods for all-solid-state batteries using these solid electrolytes involve pressing processes that require high pressure, which limits the fabrication of large electrodes and presents challenges in interfacial bonding. Furthermore, sulfide solid electrolytes and coordination hydride solid electrolytes are unstable to moisture and require special environments such as inert gas environments or ultra-low dew point drying chambers. Therefore, all-solid-state batteries require fabrication equipment that can be carried out in a relatively small space.

[0008] To address this issue, Patent Document 1 discloses a technical solution that forms a good interface using low pressing pressure by coating and bonding a soluble solid electrolyte onto the surfaces to be bonded between the positive and negative electrode layers. However, this solution presents challenges: not only do the positive and negative electrode layers themselves require high pressing pressure for molding, but the sulfide solid electrolyte gradually decomposes and generates hydrogen sulfide once dissolved in an alcohol solvent. Furthermore, short circuits may occur during discharge, necessitating improvements in cycle performance.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2015-2080 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] There is a need for a solid electrolyte sheet with good processability and low short-circuit risk, a method for manufacturing the same, and an all-solid-state battery having the solid electrolyte sheet, in such a situation.

[0014] Technical solutions for solving the problem

[0015] Therefore, the inventors of the present invention conducted in-depth research in view of the above-mentioned problems and found that the above-mentioned problems can be solved by using a solid electrolyte sheet comprising a support substrate and a boron cluster-type solid electrolyte.

[0016] That is, the present invention is as follows.

[0017] <1> A solid electrolyte sheet is used as a separator layer to separate the positive electrode layer from the negative electrode layer in an all-solid-state battery. The solid electrolyte sheet includes a support substrate and a boron cluster-type solid electrolyte.

[0018] <2> According to the above <1> The solid electrolyte sheet, wherein the supporting substrate is glass nonwoven fabric.

[0019] <3> According to the above <1> or <2> The solid electrolyte sheet, wherein the thickness of the supporting substrate is 10 μm to 300 μm.

[0020] <4> According to the above <1> ~ <3> In any one of the solid electrolyte sheets, the boron cluster type solid electrolyte is LiCB9H 10 / LiCB 11 H 12 The molar ratio range of 1.1 to 20 contains LiCB9H. 10 and LiCB 11 H12 Solid electrolyte complex.

[0021] <5> According to the above <4> The solid electrolyte sheet, wherein the boron cluster type solid electrolyte is LiCB9H 10 ∶LiCB 11 H 12 A molar ratio of 7:3 contains LiCB9H 10 and LiCB 11 H 12 Solid electrolyte complex.

[0022] <6> A solid-state battery, wherein a positive electrode layer, an insulating layer, and a negative electrode layer are sequentially stacked, wherein the insulating layer is as described above. <1> ~ <5> The solid electrolyte sheet as described in any one of the following.

[0023] <7> A method for manufacturing a solid electrolyte sheet, comprising:

[0024] The process for preparing a solid electrolyte solution by dissolving a boron cluster-type solid electrolyte in a solvent; and

[0025] The process involves coating the obtained solid electrolyte solution onto a support substrate and then drying it to obtain a solid electrolyte sheet.

[0026] The solvents mentioned above include one or more selected from water, alcohol solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate and ethyl acetate.

[0027] <8> According to the above <7> In the manufacturing method described above, the supporting substrate is glass nonwoven fabric.

[0028] <9> According to the above <7> or <8> In the manufacturing method described above, the thickness of the support substrate is 10 μm to 300 μm.

[0029] <10> According to the above <7> ~ <9> In any one of the manufacturing methods, the boron cluster type solid electrolyte is LiCB9H 10 / LiCB 11 H 12 The molar ratio range of 1.1 to 20 contains LiCB9H. 10 and LiCB 11 H 12 Solid electrolyte complex.

[0030] <11> According to the above <10> In the aforementioned manufacturing method, the boron cluster-type solid electrolyte is LiCB9H. 10 ∶LiCB 11 H 12 A molar ratio of 7:3 contains LiCB9H10 and LiCB 11 H 12 Solid electrolyte complex.

[0031] <12> According to the above <7> ~ <11> In any one of the manufacturing methods, the concentration of the solid component in the solid electrolyte solution is 5% to 70% by mass.

[0032] <13> According to the above <7> ~ <12> In any one of the manufacturing methods, the above drying is carried out at atmospheric pressure and at a temperature of 40°C to 200°C for 30 minutes to 5 hours, and then under vacuum at a temperature of 100°C to 300°C for 1 to 30 hours.

[0033] <14> According to the above <7> ~ <13> The manufacturing method according to any one of the above-mentioned methods includes a step of densifying the support substrate by rolling it with a roller after the above-mentioned drying.

[0034] Invention Effects

[0035] This invention provides a solid electrolyte sheet with excellent processability and low short-circuit risk, a method for manufacturing the same, and an all-solid-state battery having the solid electrolyte sheet. Attached Figure Description

[0036] Figure 1 A graph showing the charge-discharge curves of the all-solid-state battery prepared in Example 1.

[0037] Figure 2 A graph showing the cycle characteristics of the all-solid-state battery fabricated in Example 1.

[0038] Figure 3 A graph showing the charge-discharge curves of the Li battery prepared in Comparative Example 1.

[0039] Figure 4 A graph showing the charge-discharge curves of the all-solid-state battery prepared in Comparative Example 2. Detailed Implementation

[0040] The solid electrolyte sheet of the present invention, its manufacturing method, and an all-solid-state battery having the solid electrolyte sheet will be described in detail below. It should be noted that the materials and structures described below are not intended to limit the present invention, and various modifications can be made within the scope of the present invention. It should also be noted that in this specification, when "~" is used to indicate a numerical range, the values ​​at both ends are included.

[0041] [Solid Electrolyte Tablets]

[0042] The solid electrolyte sheet of the present invention is used as an isolation layer separating the positive electrode layer and the negative electrode layer in an all-solid-state battery, and includes a support substrate and a boron cluster type solid electrolyte.

[0043] The solid electrolyte sheet of the present invention can be manufactured by impregnating a solid electrolyte solution containing a boron cluster-type solid electrolyte into a support substrate capable of penetrating the solution, removing the solvent, and allowing the solid electrolyte to precipitate inside and on the surface of the support substrate.

[0044] <Supporting substrate>

[0045] The solid electrolyte sheet of the present invention functions as an insulating layer separating the positive electrode layer from the negative electrode layer. Therefore, the supporting substrate is required to have high insulation properties. Although not particularly limited, the separator membrane used for electrolytes can be used. Examples include glass nonwoven fabric, glass fiber filter paper, polyolefin separator membrane, cellulose separator membrane, and nonwoven fabric separator membranes other than glass nonwoven fabric. The porosity of the separator membrane is preferably 40% to 95%, more preferably 70% to 95%. This is because the solid electrolyte forms in the voids, thus increasing the proportion of the solid electrolyte as an ion conductor. In addition, the heat resistance temperature is preferably 200°C or higher. Although from the viewpoint of heat resistance, it is desirable to use a glass nonwoven fabric without organic binders, it may contain organic binders depending on the type.

[0046] The thickness of the support substrate used in this invention is preferably 10μm to 300μm, and more preferably 50μm to 200μm.

[0047] <Boron Cluster Type Solid Electrolyte>

[0048] Boron cluster-type solid electrolytes are coordination hydrides, compounds with a boron-based framework and a cluster structure. Typically, if the cluster structure is closed (cage-like), it exhibits high stability to water and alcohols. LiCB9H is a specific example of a boron cluster-type solid electrolyte. 10 LiCB 11 H 12 Li2B 12 H 12 Among these, since the ionic conductivity tends to increase, boron cluster-type solid electrolytes with carbon in the framework are preferred. Examples of such compounds include LiCB9H. 10 and LiCB 11 H 12 However, it is not limited to this. The following shows LiCB9H. 10 and LiCB 11 H 12 Its chemical structure.

[0049]

[0050] The boron cluster-type solid electrolyte used in this invention is preferably LiCB9H. 10 / LiCB 11 H 12 The molar ratio range of LiCB9H is 1.1 to 20 (more preferably 1.25 to 10, and even more preferably 1.5 to 9). 10 and LiCB 11 H 12 Solid electrolyte complex.

[0051] The aforementioned solid electrolyte complex is preferably obtained by Raman spectrometry from LiCB9H. 10 749cm －1 (±5cm) －1 ) and derived from LiCB 11 H 12 763cm －1 (±5cm) －1 It has a peak. Although it may also have peaks in other regions, the peaks that show their respective characteristics are those described above.

[0052] In this invention, in particular, the boron cluster-type solid electrolyte is preferably LiCB9H. 10 ∶LiCB 11 H 12 A molar ratio of 7:3 contains LiCB9H 10 and LiCB 11 H 12 A solid electrolyte complex. Through the use of LiCB9H 10 ∶LiCB 11 H 12 A molar ratio of 7:3 will be able to form a high ionic conductor (>1 mS / cm).

[0053] LiCB9H as a raw material 10 and LiCB 11 H 12 Commercially available products can be used. Furthermore, its purity is preferably 95% or higher, more preferably 98% or higher. By using a compound with a purity within the above range, the desired crystals can be easily obtained.

[0054] LiCB9H 10 and LiCB 11 H 12 The mixture can be mixed using homogeneous solvents in the atmosphere.

[0055] As a mixing method, it can also be carried out in a solvent. There are no particular limitations on the solvent, and examples include water, nitrile solvents such as acetonitrile, ether solvents such as tetrahydrofuran and diethyl ether, alcohol solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, methanol, ethanol, and propanol, acetone, ethyl acetate, methyl acetate, toluene, dichloromethane, and chloroform. For safety, alcohol solvents such as water, ethanol, and isopropanol are particularly preferred, and water is more preferred. Among alcohol solvents, those with 3 or fewer carbon atoms are more preferred.

[0056] For example, using water as a solvent with LiCB9H 10 and LiCB 11 H 12 By mixing and then distilling the water away from the mixed aqueous solution using an evaporator, LiCB9H can be obtained. 10 With LiCB 11 H 12 Compounds mixed in a specified molar ratio. Depending on the type of solvent, there are differences in solvent removal by distillation and powder drying time; the drying time is shorter when using alcohol-based solvents.

[0057] [Manufacturing method of solid electrolyte sheets]

[0058] The method for manufacturing the solid electrolyte sheet of the present invention includes (1) a step of preparing a solid electrolyte solution by dissolving a boron cluster type solid electrolyte in a solvent; and (2) a step of coating the obtained solid electrolyte solution onto a support substrate and then drying it to obtain a solid electrolyte sheet.

[0059] <Preparation process of solid electrolyte solution>

[0060] The solid electrolyte solution preparation process in this invention involves dissolving a boron cluster-type solid electrolyte in a solvent to prepare the solid electrolyte solution.

[0061] The boron cluster solid electrolyte used in this process is the same as the boron cluster solid electrolyte mentioned above, and the preferred example is also the same.

[0062] The solvent used in this process includes one or more selected from water, alcohol solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate and ethyl acetate, wherein methanol, tetrahydrofuran and acetonitrile are preferred, and methanol is more preferred.

[0063] As long as a solid electrolyte solution can be obtained, there are no particular limitations on its preparation method. For example, when using LiCB9H... 10 With LiCB 11 H 12 In the case of a solid electrolyte complex, LiCB9H can be used. 10Aqueous solution of LiCB 11 H 12 After mixing and drying an aqueous solution to obtain a powder of a solid electrolyte complex, the powder is dissolved in methanol to form a solid electrolyte solution. Alternatively, LiCB9H can be used... 10 methanol solution with LiCB 11 H 12 The mixture obtained by mixing the methanol solution is used as a solid electrolyte solution. Solid electrolyte solutions can also be prepared in the same way when using other solid electrolytes. Furthermore, the specific solvent described in this example is merely one example and does not preclude the description of using other solvents.

[0064] To achieve the optimal viscosity for coating the support substrate, the concentration of the solid component in the solid electrolyte solution (the concentration of the solid electrolyte) varies depending on the type of boron cluster-type solid electrolyte and solvent, but is preferably in the range of 5% to 70% by mass. At concentrations lower than this range, the precipitation efficiency of the solid electrolyte may deteriorate. On the other hand, at higher concentrations, there is a possibility that it may become difficult to penetrate deep into the pores due to increased viscosity. The concentration of the solid component in the solid electrolyte solution is more preferably in the range of 20% to 60% by mass, and even more preferably in the range of 30% to 50% by mass.

[0065] <Coating and drying process for support substrate>

[0066] The coating and drying process of the support substrate in this invention involves coating the solid electrolyte solution obtained in the above-mentioned solid electrolyte solution preparation process onto the support substrate and then drying it to obtain a solid electrolyte sheet.

[0067] The support substrate used in this process is the same as the support substrate mentioned above, and the preferred example is also the same.

[0068] As a method for coating a solid electrolyte solution onto a support substrate, known methods for coating and impregnating the electrode sheet with electrolyte can be used, such as blade coating, spin coating, and spray coating. Among these, it is preferable to drop the solid electrolyte solution onto the support substrate and then uniformly coat it using a wire rod coating method.

[0069] In the solid electrolyte sheet, the content of solid electrolyte is preferably 40 to 90% by mass, more preferably 45 to 85% by mass, and particularly preferably 50 to 80% by mass, relative to the total mass of the support substrate and the solid electrolyte.

[0070] After the solid electrolyte solution is coated on the support substrate, the solvent is removed by drying to allow the solid electrolyte to precipitate out, thereby tightly filling the voids in the support substrate with solid electrolyte.

[0071] Drying is performed 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), followed by drying under vacuum 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). This drying process allows for efficient solvent evaporation and the precipitation of solid electrolytes. When solvent evaporation is performed at temperatures exceeding this range, side reactions or solvent foaming may occur, preventing the dense precipitation of solid electrolytes. Furthermore, heating under a stream of inert gas or under vacuum can promote solvent evaporation.

[0072] In this invention, it is preferable to include a process of densifying the support substrate by rolling after the above-mentioned drying.

[0073] Although the rolling method (rolling process) offers high continuous productivity, the pressing pressure is lower than that of the uniaxial pressing method and 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 relatively soft, even with lower pressing pressure, the solid electrolyte can still be sufficiently dense.

[0074] The pressing pressure using the rolling method is preferably 0.1 MPa to 100 MPa, more preferably 1 MPa to 80 MPa. Conventional solid-state battery molding requires very high pressing pressures to deform and densify the powder itself. However, in this invention, by precipitating the solid electrolyte from the solid electrolyte solution, the solid electrolyte can be densely formed in the voids of the supporting substrate, thus eliminating the need for pressing pressures as high as, for example, 300 MPa required to deform the particles. In the preferred embodiment of this invention, the purpose of calendering after drying is to fill small cracks caused by thermal expansion / contraction and small voids generated during solvent evaporation; the rolling method achieves sufficiently good results in this regard.

[0075] [All-solid-state battery]

[0076] The all-solid-state battery of the present invention comprises a positive electrode layer, an insulating layer, and a negative electrode layer stacked sequentially, wherein the insulating layer is the solid electrolyte sheet of the present invention. It should be noted that the positive electrode layer and the negative electrode layer are collectively referred to as electrode layers.

[0077] As the electrode layer used in this invention, an electrode layer for lithium-ion batteries using an electrolyte can be employed. In this invention, a positive electrode sheet with a positive electrode layer formed on the current collector and a negative electrode sheet with a negative electrode layer formed on the current collector can also be used. It should be noted that the positive electrode sheet and the negative electrode sheet are collectively referred to as electrode sheets.

[0078] The positive electrode layer is typically formed of a positive electrode active material, a binder, and a conductive additive, while the negative electrode layer is typically formed of a negative electrode active material, a binder, and a conductive additive. These electrode layers have voids, allowing the electrolyte to be impregnated within them. It should be noted that one electrode layer (positive or negative) can be made of metal foil or alloy foil, while the other electrode can use the electrode sheet containing a boron cluster-type solid electrolyte as used in this invention.

[0079] As current collectors, the positive electrode layer typically uses stainless steel or aluminum foil, while the negative electrode layer uses stainless steel or copper foil. It should be noted that current collectors with carbon coating on their surface can also be used.

[0080] As the positive electrode active material contained in the positive electrode layer, any material that can release lithium ions during charging and absorb lithium ions during discharging can be used without particular restrictions. Examples include metal oxides containing transition metals, sulfur-based positive electrode active materials, organic positive electrode active materials, and FeF3 and VF3 utilizing a conversion reaction. In this invention, it is preferable that the potential of the positive electrode active material is 3.0V or less, based on lithium, to suppress the reaction at the interface between the active material and the boron cluster-type solid electrolyte, thereby reducing the interface resistance. More preferably, the potential of the positive electrode active material is 1.0 to 2.7V, based on lithium.

[0081] As a metal oxide containing a transition metal, particles or thin films containing one or more transition metals selected from Mn, Co, Ni, Fe, Cr, and V, and lithium can be used. There are no particular limitations, but specific examples include LiCoO2, LiCo2O4, LiMnO2, LiMn2O4, LiMnCoO4, Li2MnCoO4, and LiNi. 0.8 Co 0.15 Al 0.05 O2, LiNi 0.5 Mn 0.5 O2, Li2NiMn3O8, LiVO2, LiV3O3, LiCrO2, LiFePO4, LiCoPO4, LiMnPO4, LiVOPO4, LiNiO2, LiNi2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li2FeSiO4, Li2MnSiO4, LiFeBO3, etc. Alternatively, Fe2O3, Cr3O8, V2O5, MnO2, etc., can also be used. Among these, LiCoO2, LiMnO2, LiMn2O4, and LiNi are preferred. 0.8 Co 0.15 Al 0.05 O2, LiNi 0.5 Mn 0.5O2, Li2NiMn3O8, LiFePO4, LiCoPO4, LiMnPO4, LiVOPO4, LiNiO2 and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0082] It should be noted that, for the purpose of inhibiting reactions with solid electrolytes, these positive electrode active materials can also be coated with a coating layer on particles, films, etc., of the positive electrode active material. Examples of coating layers include LiNbO3 and Li4Ti5O3. 12 LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4 and LiBO2.

[0083] There are no particular limitations on sulfur-based positive electrode active materials, but specific examples include S, sulfur-carbon composite materials, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, Li2S, MoS3, sulfur-modified polyacrylonitrile, erythrone (dithiooxazone), and disulfide compounds. Among these, TiS2, TiS3, TiS4, NiS, NiS2, FeS2, Li2S, MoS3, sulfur-modified polyacrylonitrile, sulfur-carbon composite materials, and erythrone (dithiooxazone) are preferred.

[0084] As an organic cathode active material, there are no particular limitations, but specific examples include free radical compounds such as 2,2,6,6-tetramethylpiperidinoxy-4-yl methacrylate and polytetramethylpiperidinoxy vinyl ether, as well as quinone compounds, annulopene compounds, tetracyano-p-benzodiquinone dimethane, and phenazine oxides. Among these, free radical compounds and quinone compounds are preferred because they have large theoretical capacities and can maintain discharge capacity relatively well.

[0085] As the negative electrode active material contained in the negative electrode layer, examples include Si-based negative electrode materials, metallic active materials, and carbon-based active materials. Examples of Si-based negative electrode materials include composite materials such as Si, SiO, and Si-C. Examples of metallic active materials include, for instance, Li4Ti5O. 12 Examples of active materials include Li, In, Al, Sn, and alloys of these metals. On the other hand, examples of carbon-based active materials include mesophase carbon microspheres (MCMB), highly oriented pyrolytic graphite (HOPG), hard carbon, and soft carbon. Among these, to improve the energy density and operating voltage of the battery, it is preferable to use an active material with a lower equilibrium potential as the negative electrode. Examples of such negative electrode active materials include Li, carbon-based active materials, and Si-based negative electrode materials.

[0086] There are no particular limitations on the binder used as the positive electrode layer, but materials such as polyimide-based, acrylic-based, polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and ethylene-vinyl alcohol copolymer (EVOH) can be used. Carboxymethyl cellulose (CMC) and other thickeners can also be used as needed.

[0087] There are no particular limitations on the adhesive used as the negative electrode layer, but materials such as polyimide-based, polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and acrylic-based materials can be used. Carboxymethyl cellulose (CMC) and other tackifiers may also be used as needed.

[0088] The conductive additives used in the electrode layer are not particularly limited as long as they possess the required conductivity, but examples include conductive additives made of carbon materials. Specifically, examples include carbon black, acetylene black, Ketjen black, and carbon fibers. Additionally, examples include cellulose nanofibers made from plant materials.

[0089] As a method for fabricating electrode sheets, known methods can be employed. For example, a coating solution can be prepared by mixing a positive or negative electrode active material with a binder, a conductive additive, and an organic solvent. The electrode sheet with an electrode layer formed on the current collector can be fabricated by applying the coating solution onto the current collector using a doctor blade method, spin coating method, or spray coating method and then drying it.

[0090] All-solid-state batteries can be fabricated by stacking and rolling individual cells together.

[0091] In this invention, the preferred method includes the following steps: for example, bonding the negative electrode layer to the solid electrolyte sheet in a manner that provides a solid electrolyte sheet between the positive electrode layer and the negative electrode layer, and then bonding the solid electrolyte sheet to the positive electrode layer. The pressing pressure during bonding the negative electrode layer to the solid electrolyte sheet and the pressing pressure during bonding the positive electrode layer to 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.

[0092] Because boron cluster-type solid electrolytes also possess the ability to act as binders, they exhibit high bonding effectiveness against these sheets. Regarding calendering methods, this can be achieved, for example, through rolling.

[0093] Example

[0094] The present invention will be described in more detail below through embodiments, but the embodiments are not limited to these embodiments.

[0095] (Example 1)

[0096] Synthesis of Boron Cluster-Type Solid Electrolytes

[0097] Prepare LiCB9H respectively 10 Aqueous solutions and LiCB 11 H 12 The aqueous solutions were mixed in a molar ratio of 7:3. Then, the water in the mixed aqueous solution was removed by distillation using an evaporator. The following section will discuss LiCB9H... 10 With LiCB 11 H 12 Compounds mixed in a 7:3 molar ratio (boron cluster type solid electrolyte) are designated as "LCBH".

[0098] <Preparation of Solid Electrolyte Solutions>

[0099] Add methanol to the LCBH prepared as described above to make the solid component concentration reach 40 wt%, and stir manually to prepare LCBH / MeOH solution (solid electrolyte solution).

[0100] <Preparation of Solid Electrolyte Tablets>

[0101] Glass nonwoven fabric support substrate (Advantec) ® The LCBH / MeOH solution obtained above (prepared with GC-50, 190 μm thickness) was added dropwise and uniformly coated using a wire rod coating method to ensure the solution penetrated the interior. Simultaneously, any remaining LCBH / MeOH solution was removed. Next, pre-drying was performed in a constant-temperature desiccator at atmospheric pressure, at 160°C for 2 hours. Then, further vacuum drying was carried out in a vacuum desiccator at 180°C for 15 hours to produce a solid electrolyte sheet. The mass per unit area of ​​the above-mentioned glass nonwoven fabric support substrate is 5.05 mg / cm². 2 In contrast, the solid electrolyte sheet obtained by coating with the above-mentioned LCBH / MeOH solution and then drying has a mass per unit area of ​​12.79 mg / cm². 2 That is, the content ratio of solid electrolyte to the total mass of the supporting substrate and solid electrolyte is approximately 60% by mass.

[0102] <Densification of Solid Electrolyte Sheets>

[0103] To achieve densification of the solid electrolyte sheet obtained above, a benchtop hot roller press (manufactured by Hosen Co., Ltd., HSPR-60150HL-A) was used in an unheated state, with the pressing pressure set to 50 MPa and the gap width between the rollers being 50 μm. It should be noted that the above-described processes 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 below -60°C.

[0104] <Preparation of Negative Electrode Slurry>

[0105] In preparing the negative electrode slurry, SiO (a carbon-coated powder with an average particle size of 6 μm) was used as the negative electrode active material, polyimide-based binder (UBE Corporation, U-varnish A) was used as the adhesive, and acetylene black (Nippon Denka Co., Ltd., DENKA BRACK Li-100) was used as the conductive additive. The SiO:acetylene black:polyimide-based binder were weighed according to a composition of 80:5:15 wt%, and mixed with N-methyl-2-pyrrolidone (NMP) solvent using a rotation-revolution mixer (Thinky Corporation, ARE-310) at 2000 rpm for 20 min to prepare the negative electrode slurry.

[0106] <Fabrication of Negative Electrode Composite Layer>

[0107] The aforementioned negative electrode slurry was coated onto a 10 μm thick stainless steel foil (current collector) using a benchtop coating machine (TESTER SANGYO CO., LTD., FILMCOATER, PI-1210). Pre-drying was then performed using a constant-temperature desiccator at 80°C for 10 minutes. After pre-drying, vacuum heating treatment was conducted using a vacuum constant-temperature desiccator at 240°C for 15 hours to fabricate the negative electrode composite layer (electrode). It should be noted that the electrode's capacity density is 1.0 mAh / cm³. 2 .

[0108] <Making of Negative Electrode Sheets>

[0109] A solid electrolyte solution prepared according to the above-described solid electrolyte sheet fabrication method was dropwise added to the surface of the obtained negative electrode composite layer (electrode). The solid electrolyte solution was then permeated and evenly distributed into the interior of the negative electrode composite layer using a wire rod coating method, while removing any remaining solid electrolyte solution. Next, pre-drying was performed in a constant-temperature desiccator at atmospheric pressure, at 160°C, for 2 hours. This process from solid electrolyte solution coating to pre-drying was repeated twice. Then, further vacuum heating drying was performed in a vacuum desiccator at 180°C, for 15 hours, to produce a negative electrode sheet with a solid electrolyte layer formed inside the negative electrode composite layer. All of this process was carried out in a dry environment with a dew point below -60°C.

[0110] <The Making of All-Solid-State Batteries>

[0111] Using the aforementioned negative electrode as the test electrode, the aforementioned solid electrolyte sheet as the separator, and Li as the counter electrode, these layers were stacked sequentially to fabricate an all-solid-state battery. First, the aforementioned solid electrolyte sheet was punched into a 13mm diameter shape using a manual electrode punch (manufactured by Nogami Corporation) to serve as the test electrode. Additionally, the aforementioned negative electrode sheet was also punched into an 11mm diameter disc shape using the manual punch to serve as the test electrode.

[0112] A 13mm diameter solid electrolyte sheet, punched with a manual punch, is laminated with an 11mm diameter negative electrode composite material layer, and then cold-pressed at 50MPa using a uniaxial press for powder forming to tightly bond them together. Furthermore, a 12mm diameter Li foil (manufactured by Honjo Metals Co., Ltd., 200μm thick) is laminated onto the opposite side of the solid electrolyte sheet and cold-pressed again at 20MPa using the same uniaxial press, thus obtaining a laminate of the negative electrode sheet, solid electrolyte sheet, and Li. This laminate is then used to manufacture a CR2032 type button cell, serving as an all-solid-state battery. All these processes are performed in a dry environment with a dew point below -60°C.

[0113] <Charge and Discharge Test>

[0114] The all-solid-state battery obtained above was placed in a thermostat set at 60°C, and the charging and discharging current was set to 0.05 mA / cm². 2 The operating voltage range was set to 1.20~0.01V, and a constant current charge-discharge test was conducted. Figure 1 The chart shows the charge-discharge curves of the all-solid-state battery prepared in Example 1. The initial charge capacity was 2737 mAh / g, and the initial discharge capacity was 1651 mAh / g. Figure 1 The results show that the all-solid-state battery prepared in Example 1 can also achieve stable charge and discharge after the second cycle.

[0115] Additionally, after the fourth cycle, the charge / discharge current will be changed to 0.1 mA / cm. 2 The charging and discharging process was repeated. Figure 2 Its cycle characteristics indicate that the all-solid-state battery prepared in Example 1 can achieve stable charging and discharging without short circuits during 100 cycles.

[0116] (Comparative Example 1)

[0117] <Fabrication of Li-ion Batteries Using Electrolyte>

[0118] The negative electrode composite layer (electrode) obtained in Example 1, in the <Fabrication of Negative Electrode Composite Layer>, was punched using an electrode punching manual punch (manufactured by Nogami Technology Co., Ltd.) to form a circular plate with a diameter of 11 mm, which served as the 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 Advantech, GA-100, t = 500 μm) and a polyolefin microporous membrane (PP / PE / PP microporous membrane, t = 25 μm) were used as the separator. A 1 mol / L LiPF6 EC / DEC (= 50 / 50, Vol%) (manufactured by Kishida Chemical Co., Ltd., LBG-96533) was used as the electrolyte to fabricate a CR2032 type button cell (Li battery). All of this process was carried out in a dry environment with a dew point below -60°C.

[0119] <Charge and Discharge Test>

[0120] The Li battery obtained above was placed in a thermostat set at 60°C, and the charging and discharging current was set to 0.05 mA / cm². 2 The operating voltage range was set to 1.20~0.01V, and a constant current charge-discharge test was conducted. Figure 3 The charge-discharge curves of the Li battery fabricated in Comparative Example 1 are shown. The curves are plotted against the Li battery fabricated in Comparative Example 1. Figure 1 The same charge-discharge curves yielded the same discharge capacity. Therefore, although Example 1 is an all-solid-state battery, it exhibits performance equivalent to a Li battery using an electrolyte. The solid electrolyte sheet prepared in Example 1 is useful for all-solid-state batteries. Furthermore, in the Li battery of Comparative Example 1, which uses LiPF6 as the electrolyte, the electrolyte reacts and decomposes, resulting in poor high-temperature stability and a constant risk of leakage. However, the all-solid-state battery using the solid electrolyte sheet prepared in Example 1 does not have these concerns.

[0121] (Comparative Example 2)

[0122] <Preparation of Coating Solution>

[0123] Similar to the preparation of the solid electrolyte solution in Example 1, nano-SiO2 was added to a 30wt% LCBH / MeOH solution to achieve a mass ratio of LCBH:nano-SiO2 (fumed silica, primary particle size 5-50 nm, secondary particle size approximately 300 nm) = 80:20. The container was gently shaken by hand to disperse the nano-SiO2, thus preparing the coating solution. This entire process was carried out in a dry environment with a dew point below -60°C.

[0124] <Making of Negative Electrode Sheets>

[0125] The coating solution obtained above was applied to the surface of the negative electrode composite layer (electrode) obtained according to the <Preparation of Negative Electrode Composite Layer> in Example 1 using a wire rod coating method. Then, it was pre-dried in a constant-temperature dryer at atmospheric pressure, at 160°C for 2 hours. This coating-pre-drying process was repeated 5 times, and finally, vacuum heating drying was performed in a vacuum constant-temperature dryer at 180°C for 15 hours. Furthermore, to achieve densification of the obtained negative electrode sheet, a benchtop hot roller press (manufactured by Hosen Co., Ltd., HSPR-60150HL-A) was used in an unheated state, with a slit width of 0 μm between the rollers. A negative electrode sheet with a solid electrolyte layer formed inside and on the surface of the negative electrode composite layer was obtained. All of this process was carried out in a dry environment with a dew point below -60°C.

[0126] <The Making of All-Solid-State Batteries>

[0127] The aforementioned negative electrode sheet was punched to a diameter of 12 mm using a manual electrode punch (manufactured by Nogami Technology Co., Ltd.), serving as a test piece. The 12 mm diameter test piece was then stacked with an 11 mm diameter Li foil (manufactured by Honjo Metals Co., Ltd., 200 μm thick), and cold-pressed at 5 MPa using a uniaxial pressure press for powder molding to ensure a tight bond. This laminate was then used to fabricate a CR2032 type button cell, serving as an all-solid-state battery. All of this process was carried out in a dry environment with a dew point below -60°C.

[0128] <Charge and Discharge Test>

[0129] The all-solid-state battery obtained above was placed in a thermostat set at 60°C and subjected to a constant current charge-discharge test in the same manner as in Example 1. Figure 4 The charge-discharge curves of the all-solid-state battery prepared in Comparative Example 2 are shown. It was confirmed that the all-solid-state battery prepared in Comparative Example 2 experienced a short circuit in the second cycle. Even when the method of the embodiment described in WO2020-184340 was applied to the LCBH, good cycle performance could not be achieved. Therefore, it can be concluded that the solid electrolyte sheet is more advantageous than the solid electrolyte formation method described in WO2020-184340.

Claims

1. A solid electrolyte sheet, characterized in that: The solid electrolyte sheet is used as an insulating layer to separate the positive electrode layer from the negative electrode layer in an all-solid-state battery. The solid electrolyte sheet comprises a support substrate and a boron cluster-type solid electrolyte.

2. The solid electrolyte sheet according to claim 1, characterized in that: The supporting substrate is glass nonwoven fabric.

3. The solid electrolyte sheet according to claim 1 or 2, characterized in that: The thickness of the support substrate is 10μm to 300μm.

4. The solid electrolyte sheet according to any one of claims 1 to 3, characterized in that: The boron cluster-type solid electrolyte is LiCB9H. 10 / LiCB 11 H 12 The molar ratio range of 1.1 to 20 contains LiCB9H. 10 and LiCB 11 H 12 Solid electrolyte complex.

5. The solid electrolyte sheet according to claim 4, characterized in that: The boron cluster-type solid electrolyte is LiCB9H. 10 ∶LiCB 11 H 12 A molar ratio of 7:3 contains LiCB9H 10 and LiCB 11 H 12 Solid electrolyte complex.

6. An all-solid-state battery, characterized in that: The all-solid-state battery consists of a positive electrode layer, an insulating layer, and a negative electrode layer stacked sequentially. The isolation layer is a solid electrolyte sheet as described in any one of claims 1 to 5.

7. A method for manufacturing a solid electrolyte sheet, characterized in that, include: The process for preparing a solid electrolyte solution by dissolving a boron cluster-type solid electrolyte in a solvent; and The process involves coating the obtained solid electrolyte solution onto a support substrate and then drying it to obtain a solid electrolyte sheet. The solvent comprises one or more selected from water, alcohol solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate.

8. The manufacturing method according to claim 7, characterized in that: The supporting substrate is glass nonwoven fabric.

9. The manufacturing method according to claim 7 or 8, characterized in that: The thickness of the support substrate is 10μm to 300μm.

10. The manufacturing method according to any one of claims 7 to 9, characterized in that: The boron cluster-type solid electrolyte is LiCB9H. 10 / LiCB 11 H 12 The molar ratio range of 1.1 to 20 contains LiCB9H. 10 and LiCB 11 H 12 Solid electrolyte complex.

11. The manufacturing method according to claim 10, characterized in that: The boron cluster-type solid electrolyte is LiCB9H. 10 ∶LiCB 11 H 12 A molar ratio of 7:3 contains LiCB9H 10 and LiCB 11 H 12 Solid electrolyte complex.

12. The manufacturing method according to any one of claims 7 to 11, characterized in that: The concentration of the solid component in the solid electrolyte solution is 5% to 70% by mass.

13. The manufacturing method according to any one of claims 7 to 12, characterized in that: The drying process is carried out under atmospheric pressure at a temperature of 40°C to 200°C for 30 minutes to 5 hours, followed by a vacuum process at a temperature of 100°C to 300°C for 1 to 30 hours.

14. The manufacturing method according to any one of claims 7 to 13, characterized in that: The manufacturing method includes a step of densifying the support substrate by calendering it using a roller after drying.

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