Negative electrode layer for all-solid-state battery and all-solid-state battery

Abstract

According to one embodiment, a negative electrode layer for an all-solid-state battery is provided, comprising a negative electrode active material and a solid electrolyte, wherein the negative electrode active material is a silicon-based material and the solid electrolyte is a boron cluster-type solid electrolyte.

Description

Technical Field

[0001] This invention relates to a negative electrode layer for an all-solid-state battery and an all-solid-state battery having the negative electrode layer. The invention also relates to a method for manufacturing the negative electrode layer for an all-solid-state battery. 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 electric vehicles, and stationary energy storage systems. However, existing lithium-ion rechargeable batteries use flammable organic solvents as electrolytes, requiring robust casings to prevent leakage. Furthermore, in portable personal computers and similar devices, structural designs are needed to address the risk of electrolyte leakage, thus constraining the design of these devices.

[0003] Furthermore, its applications have expanded to mobile vehicles such as automobiles and airplanes, requiring large-capacity stationary lithium-ion secondary batteries. Under these circumstances, there is a growing emphasis on safety, and the development of all-solid-state lithium-ion secondary batteries that do not use harmful substances such as organic solvents has attracted much attention.

[0004] Among the solid electrolytes used in all-solid-state batteries, sulfide solid electrolytes and complexed hydrides possess high ionic conductivity and are relatively soft, thus readily forming solid-solid interfaces. They are also stable to lithium metal and are being developed as practical solid electrolytes. Attempts are also being made to add these solid electrolytes to the positive and / or negative electrode layers. At this point, it is necessary to appropriately select the positive and negative electrode active materials based on the technical problems to be solved, and to study the combination of these active materials with the solid electrolyte. For example, silicon-based materials can be cited as a negative electrode active material that can achieve high theoretical capacity (Patent Document 1). However, when adding conventionally used solid electrolytes to a negative electrode layer containing silicon-based materials, problems may arise due to the expansion and contraction of the silicon-based material itself during charging and discharging. As a result, voids are generated inside the negative electrode layer, causing problems such as increased resistance and capacity reduction due to repeated charge-discharge cycles. In this situation, it is necessary to appropriately select the materials and structures of each layer of the all-solid-state battery to solve various technical problems.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 7269571 Summary of the Invention

[0006] The technical problem that the invention aims to solve The purpose of this invention is to provide a negative electrode layer for obtaining a stable all-solid-state battery and an all-solid-state battery having the negative electrode layer.

[0007] Technical solutions for solving technical problems In order to solve the technical problems of the silicon-based materials mentioned above, the inventors of this invention conducted in-depth research and found that by combining silicon-based materials with a specified solid electrolyte to form a negative electrode layer, an all-solid-state battery that can operate stably even after repeated charge-discharge cycles can be obtained.

[0008] The present invention is described below, for example.

[0009] [1] A negative electrode layer for an all-solid-state battery, comprising a negative electrode active material and a solid electrolyte, wherein the negative electrode active material is a silicon-based material and the solid electrolyte is a boron cluster type solid electrolyte.

[0010] [1-1] The negative electrode layer for all-solid-state batteries as described in [1], wherein the boron cluster-type solid electrolyte contains components selected from LiCB9H. 10 LiCB 11 H 12 and Li2B 12 H 12 One or more of them.

[0011] [2] As described in [1], the negative electrode layer for all-solid-state batteries, wherein the boron cluster-type solid electrolyte is prepared according to LiCB9H. 10 / LiCB 11 H 12 The molar ratio in the range of 1.1 to 20 includes LiCB9H. 10 and LiCB 11 H 12 Solid electrolyte complex.

[0012] [3] The negative electrode layer for all-solid-state batteries as described in [2], wherein the boron cluster type solid electrolyte is prepared according to LiCB9H 10 :LiCB 11 H 12 A molar ratio of 7:3 includes LiCB9H 10 and LiCB 11 H 12 Solid electrolyte complex.

[0013] [4] The negative electrode layer as described in any one of [1] to [3], wherein the silicon-based material is selected from SiO, Si, SiN, SiC and silicon-carbon composites.

[0014] [5] The negative electrode layer for all-solid-state batteries as described in any one of [1] to [4], wherein the silicon-based material is contained in a proportion of 40 to 90% by weight relative to the total weight of the boron cluster-type solid electrolyte and the silicon-based material.

[0015] [5-1] A negative electrode layer for an all-solid-state battery as described in any one of [1] to [5], wherein the negative electrode layer for an all-solid-state battery is a negative electrode sheet having a current collector and a layer containing a negative electrode active material stacked on the current collector.

[0016] [6] A method for manufacturing an anode layer for an all-solid-state battery, comprising: a step of preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; and a step of impregnating the obtained solid electrolyte solution into a sheet containing a silicon-based material and then drying it to obtain an anode layer for an all-solid-state battery.

[0017] [7] The method as described in [6], wherein the solvent comprises at least one selected from water, alcohol solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate and ethyl acetate.

[0018] [8] The method as described in [6] or [7], wherein the boron cluster solid electrolyte is prepared according to LiCB9H 10 / LiCB 11 H 12 The molar ratio in the range of 1.1 to 20 includes LiCB9H. 10 and LiCB 11 H 12 Solid electrolyte complex.

[0019] [9] As described in [8], wherein the boron cluster solid electrolyte is prepared according to LiCB9H 10 :LiCB 11 H 12 A molar ratio of 7:3 includes LiCB9H 10 and LiCB 11 H 12 Solid electrolyte complex.

[0020]

[10] The method of any one of [6] to [9], wherein the silicon-based material is selected from SiO, Si, SiN, SiC and silicon-carbon composites.

[0021]

[11] The method of any one of [6] to [9], wherein the drying is performed at atmospheric pressure at a temperature of 40 to 180°C for 30 minutes to 5 hours, and then at a temperature of 100 to 300°C for 1 to 25 hours under vacuum.

[0022]

[12] An all-solid-state battery having a positive electrode layer, a negative electrode layer and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the negative electrode layer is any one of [1] to [5-1] for an all-solid-state battery.

[0023]

[13] The all-solid-state battery as described in

[12] , wherein the solid electrolyte layer comprises a boron cluster-type solid electrolyte.

[0024]

[14] The all-solid-state battery as described in

[13] , wherein the solid electrolyte layer is a solid electrolyte sheet comprising a support substrate and a boron cluster-type solid electrolyte supported on the support substrate.

[0025] The effects of the invention According to the present invention, it is possible to provide a negative electrode layer for obtaining an all-solid-state battery capable of stable operation, and an all-solid-state battery having the negative electrode layer. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view of the all-solid-state battery involved in the implementation method.

[0027] Figure 2 This is a graph showing the charge-discharge test results of Example 1.

[0028] Figure 3 This is a graph showing the charge-discharge test results of Comparative Example 1.

[0029] Figure 4 This is a graph showing the charge-discharge test results of Comparative Example 2. Detailed Implementation

[0030] The embodiments of the present invention will be described in detail below. The materials, structures, etc., described below are not limited to the present invention, and various modifications can be made within the scope of the spirit of the present invention.

[0031] first, Figure 1 This represents the cross-section of the all-solid-state battery involved in the implementation method.

[0032] The all-solid-state battery 10 described in the embodiments is, for example, an all-solid-state lithium-ion secondary battery, which can be used in various devices such as mobile phones, personal computers, and automobiles. The all-solid-state battery 10 has a structure in which a solid electrolyte layer 2 is disposed between the positive electrode layer 1 and the negative electrode layer 3.

[0033] 1. Negative electrode layer According to one embodiment of the present invention, a negative electrode layer for an all-solid-state battery is provided, which includes a negative electrode active material and a solid electrolyte, wherein the negative electrode active material is a silicon-based material and the solid electrolyte is a boron cluster type solid electrolyte.

[0034] All-solid-state batteries using silicon-based materials and boron cluster-type solid-state electrolytes in the negative electrode layer exhibit minimal degradation even after repeated charge-discharge cycles, suppressing capacity decline due to long-term use and thus enabling stable long-term operation. In other words, by using the negative electrode layer described in this embodiment, an all-solid-state battery with excellent cycle characteristics can be obtained. This is believed to be due to the boron cluster-type solid-state electrolyte's ability to suppress the expansion and contraction of silicon-based materials during charge and discharge. Although the specific mechanism is not yet clear, it is speculated that the boron cluster-type solid-state electrolyte "follows" the expansion and contraction of the silicon-based materials. This "following" of the boron cluster-type solid-state electrolyte is considered to contribute to good charge-discharge cycle performance.

[0035] The all-solid-state battery described in this embodiment solves the aforementioned technical problem of cycle characteristics while using silicon-based materials that help increase theoretical capacity, which is truly groundbreaking. In other words, the all-solid-state battery described in this embodiment has the advantages of large capacity and long-term stable operation.

[0036] Boron cluster-type solid electrolytes are a type of complex hydride, which are compounds with a cluster structure based on boron. Generally, a closed (cage-like) cluster structure is preferred for exhibiting 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, considering the increasing trend in ionic conductivity, boron cluster-type solid electrolytes with carbon in their framework are preferred. Examples of such compounds include LiCB9H. 10 and LiCB 11 H 12 These boron cluster-type solid electrolytes can be used individually or in combination of two or more. The following shows LiCB9H... 10 and LiCB 11 H 12 Its chemical structure. As a boron cluster-type solid electrolyte, LiCB9H is preferred. 10 With LiCB 11 H 12 A solid electrolyte complex, more preferably containing LiCB9H 10 and LiCB 11 H 12 And LiCB9H 10 / LiCB 11 H 12Solid electrolyte complexes with a molar ratio in the range of 1.1 to 20 (more preferably 1.25 to 10, even more preferably 1.5 to 9).

[0037] The aforementioned solid electrolyte complex is preferably used in Raman spectroscopy measurements based on LiCB9H. 10 749cm -1 (±5cm) -1 ) and based on LiCB 11 H 12 763cm -1 (±5cm) -1 Peaks are present at each of the following locations. Although peaks may also be present in other regions, the peaks that exhibit their respective characteristics are those described above.

[0038] A more preferred boron cluster-type solid electrolyte is one containing LiCB9H. 10 and LiCB 11 H 12 And LiCB9H 10 :LiCB 11 H 12 A solid electrolyte complex with a molar ratio of approximately 7:3. This was achieved using LiCB9H... 10 :LiCB 11 H 12 A mixture of approximately 7:3 molar ratio yields a material with higher ionic conductivity (>1 mS / cm).

[0039] 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 compounds with purity within the above range, the desired crystals can be easily obtained.

[0040] LiCB9H 10 With LiCB 11 H 12 The mixing can be carried out in the atmosphere under a homogeneous solvent. There are no particular limitations on the solvent; examples include nitrile solvents such as water and acetonitrile, ether solvents such as tetrahydrofuran and diethyl ether, alcohol solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, methanol, ethanol, and propanol, and solvents such as acetone, ethyl acetate, methyl acetate, toluene, dichloromethane, and chloroform. From a safety perspective, alcohol solvents such as water, ethanol, and isopropanol are particularly preferred, with water being more preferred. As for alcohol solvents, those with 3 or fewer carbon atoms are more preferred.

[0041] For example, using water as a solvent to mix LiCB9H 10 and LiCB 11 H12 LiCB9H can be obtained by distilling water away from the mixed aqueous solution using an evaporator. 10 With LiCB 11 H 12 A composite mixture in a specified molar ratio. Depending on the type of solvent, the solvent removal in the evaporator and the powder drying time vary, with alcohol-based solvents tending to have shorter drying times.

[0042] In the negative electrode layer, the boron cluster solid electrolyte is preferably contained in a proportion of 10 to 85% by weight, more preferably 15 to 80% by weight, and particularly preferably 20 to 75% by weight, relative to the total weight of the boron cluster solid electrolyte and the silicon-based material.

[0043] There are no particular limitations on silicon-based materials as long as they contain silicon. Examples include Si, SiO, and Si-C composite materials, with Si and SiO being preferred, and SiO being more preferred. Using Si or SiO as the negative electrode active material is preferred because it results in a lower equilibrium potential at the negative electrode, higher energy density of the battery, and higher operating voltage.

[0044] In the negative electrode layer, the silicon-based material is preferably contained in a proportion of 15 to 90% by weight, more preferably 20 to 85% by weight, and particularly preferably 25 to 80% by weight, relative to the total weight of the boron cluster-type solid electrolyte and the silicon-based material.

[0045] The structure and manufacturing method of the negative electrode layer are not particularly limited, and can be carried out according to structures and manufacturing methods known in the art, such as using a negative electrode sheet. The negative electrode sheet, for example, has a structure in which a layer containing a negative electrode active material is laminated on a current collector. The layer containing the negative electrode active material has voids, allowing it to be impregnated with a solid electrolyte solution (also referred to as "electrolyte" in this specification). As the current collector for the negative electrode layer, stainless steel foil, copper foil, nickel, etc., can be used. Alternatively, a current collector with a carbon-coated surface can also be used.

[0046] As a method for manufacturing the negative electrode sheet, known methods can be used. For example, a coating solution is prepared by mixing the negative electrode active material, solvent, and other materials (binder, conductive additive, etc., described later). This coating solution is applied to the current collector by a doctor blade method, spin coating, or spray coating, and then dried to form a layer containing the negative electrode active material on the current collector. Alternatively, a layer containing the negative electrode active material can also be formed on the current collector by a vapor phase method (e.g., vapor deposition). Then, a solid electrolyte solution is further impregnated and dried, thereby producing a negative electrode sheet carrying a solid electrolyte.

[0047] Therefore, according to one embodiment of the present invention, a method for manufacturing a negative electrode layer for an all-solid-state battery is provided, comprising: a step of preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; and a step of impregnating the obtained solid electrolyte solution into a sheet containing a silicon-based material, and then drying it to obtain a negative electrode layer for an all-solid-state battery.

[0048] Solid electrolyte solutions can be obtained by mixing boron cluster-type solid electrolytes with solvents. The solvent used is not particularly limited as long as it can dissolve the boron cluster-type solid electrolyte, but solvents that do not react with it are preferred. Examples of such solvents include water, alcoholic solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate; one or more of these can be used. Water, methanol, tetrahydrofuran, and acetonitrile are preferred solvents, with methanol being more preferable. Water and alcoholic solvents have good compatibility with boron cluster-type compounds and can achieve high solubility, therefore they are preferred as solvents.

[0049] As long as a solid electrolyte solution can be obtained, its preparation method is not particularly limited. For example, when using LiCB9H... 10 With LiCB 11 H 12 In the case of a solid electrolyte complex, LiCB9H can be used. 10 Aqueous solution and LiCB 11 H 12 The aqueous solution is mixed and dried to obtain a powder of the solid electrolyte complex. This powder is then dissolved in methanol to obtain a solid electrolyte solution. Alternatively, LiCB9H can also be used... 10 methanol solution with LiCB 11 H 12 A solid electrolyte solution is prepared by mixing the solvent with a methanol solution. Solid electrolyte solutions can also be prepared using other solid electrolytes. Furthermore, the specific solvent described here is an example and does not preclude the use of other solvents.

[0050] While the optimal 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, aiming for optimal viscosity during coating, it is preferably in the range of 5% to 70% by weight. Using this concentration range allows the solid electrolyte solution to penetrate deep into the pores of the negative electrode, while also ensuring good solid electrolyte deposition efficiency. More preferably, the concentration of the solid component in the solid electrolyte solution is in the range of 20% to 60% by weight, and even more preferably in the range of 30% to 50% by weight.

[0051] As a method for impregnating a solid electrolyte solution into an electrode sheet, known impregnation methods can be used. Vacuum impregnation is preferred for penetrating deep into the pores of the electrode layer. Furthermore, heating reduces the viscosity of the solution, thus enabling more effective penetration into the pores.

[0052] After the solid electrolyte solution is impregnated into the negative electrode, the solvent is removed by drying, thereby allowing the solid electrolyte to precipitate into the voids of the negative electrode, resulting in a negative electrode loaded with the solid electrolyte. The drying process is not particularly limited as long as the solvent is removed to the desired degree. For example, it is preferable to dry at atmospheric pressure at a temperature of 40–180°C (more preferably 45–175°C) for 30 minutes to 5 hours (more preferably 1–4 hours), followed by further drying under vacuum at a temperature of 100–300°C (more preferably 105–295°C) for 1–25 hours (more preferably 2–24 hours). Such drying conditions allow for efficient solvent evaporation, leading to the precipitation of the solid electrolyte. Under these conditions, problems such as side reactions or solvent foaming that prevent the solid electrolyte from densely precipitating are less likely to occur. Furthermore, heating under an inert gas flow or under vacuum can further promote solvent evaporation.

[0053] For anode sheets carrying solid electrolytes after drying, calendering can make the electrode layer more compact. The calendering method is not particularly limited, but the rolling method used in manufacturing electrode sheets for lithium-ion batteries is preferred. The rolling method has the advantage of high continuous production capacity, but the pressure applied is lower than that of uniaxial pressing and isostatic pressing. In this case, the pressure is preferably 0.1 MPa to 100 MPa, more preferably 1 MPa to 80 MPa. Previously, very high pressures were required when molding the powder itself, but by using a method that precipitates the solid electrolyte from the solid electrolyte solution, a dense solid electrolyte is formed in the gaps of the electrode layer, thus eliminating the need for high pressures such as 300 MPa required for particle deformation. This post-drying calendering aims to fill small cracks caused by thermal expansion and contraction, and small gaps created by solvent evaporation; the rolling method achieves sufficient results in this regard.

[0054] The negative electrode layer can contain materials conventionally used in this technical field, other than the silicon-based materials and boron cluster-type solid electrolytes mentioned above. Examples of such materials include adhesives and conductive additives. The adhesives used for the negative electrode layer are not particularly limited; examples include polyimide compounds, polysiloxanes, polyalkylene glycols, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and acrylic compounds. Thickeners such as carboxymethyl cellulose (CMC) can also be used as needed. The conductive additives are not particularly limited as long as they possess the required conductivity; examples include conductive additives made of carbon materials. Specifically, carbon black, acetylene black, Ketjen black, and carbon fibers can be included. Furthermore, cellulose nanofibers made from plant materials can also be included. These materials can be added at any time depending on the structure of the negative electrode layer. For example, when the negative electrode layer is the aforementioned negative electrode sheet, a coating solution can be prepared by mixing the negative electrode active material, solvent, and the other materials mentioned above (adhesives, conductive additives, etc.), and then applied to the current collector. Alternatively, where permitted, the other materials mentioned above may be mixed into the solid electrolyte solution.

[0055] 2. Positive electrode layer As the positive electrode layer, a positive electrode layer known in the art for lithium-ion batteries using solid-state electrolytes can be used. Similar to the description of the negative electrode layer above, it can be an electrode sheet (i.e., a positive electrode sheet) having a layer containing a positive electrode active material stacked on a current collector, or it can be a powder-molded positive electrode composite material, or a metal foil or alloy foil. In the case of the positive electrode sheet, stainless steel foil or aluminum foil can be used as the current collector, and the surface of the current collector can also be coated with carbon. The manufacturing method of the positive electrode sheet is the same as that described for the negative electrode sheet above.

[0056] As the positive electrode active material contained in the positive electrode layer, any material capable of releasing lithium ions during charging and absorbing 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, a positive electrode active material potential of 3.0V or less (based on lithium) is preferred because it suppresses the reaction at the interface between the active material and the solid electrolyte, resulting in a lower interfacial resistance. More preferably, the positive electrode active material potential is 1.0 to 2.7V (based on lithium).

[0057] As metal oxides containing transition metals, particles or thin films comprising metal oxides of any one or more of the transition metals Mn, Co, Ni, Fe, Cr, and V, and lithium can be used. While not particularly limited, 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. In addition, Fe2O3, Cr3O8, V2O5, MnO2, etc., can also be used. Among them, LiCoO2, LiMnO2, LiMn2O4, and LiNi are preferred. 0.8 Co 0.15 Al 0.05 O2, LiNi 0.5 Mn 0.5 O2, Li2NiMn3O8, LiFePO4, LiCoPO4, LiMnPO4, LiVOPO4, LiNiO2 and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2.

[0058] In addition, to suppress reactions with solid electrolytes, coatings can be applied to the particles or thin films of these positive electrode active materials. Examples of coatings include LiNbO3 and Li4Ti5O3. 12 LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4 and LiBO2.

[0059] As a sulfur-based positive electrode active material, there are no particular limitations, but specific examples include S, sulfur-carbon complexes, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, Li2S, MoS3, sulfur-modified polyacrylonitrile, erythrine (dithiooxazone), and disulfide compounds. Among these, TiS2, TiS3, TiS4, NiS, NiS2, FeS2, Li2S, MoS3, sulfur-modified polyacrylonitrile, sulfur-carbon complexes, and erythrine (dithiooxazone) are preferred.

[0060] 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, quinone compounds, radialene compounds, tetracyanoquinone dimethane, and phenazine oxides. Among these, free radical compounds and quinone compounds have larger theoretical capacities and can better maintain discharge capacity, and are therefore preferred.

[0061] There are no particular limitations on the binder used for the positive electrode layer; for example, polyimide-based, acrylic-based, polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and ethylene-vinyl alcohol copolymer (EVOH) can be used. Thickeners such as carboxymethyl cellulose (CMC) can also be used as needed. The same material as the negative electrode layer can be used as the conductive additive. The positive electrode layer can contain a solid electrolyte, which can be a boron cluster-type solid electrolyte like the negative electrode layer, or other solid electrolytes commonly used in all-solid-state batteries.

[0062] When neither the positive nor negative electrode layer contains Li as an active material, such as when a sulfur-based positive electrode active material is used in the positive electrode layer, it is necessary to dope either active material with lithium.

[0063] 3. Solid electrolyte layer The solid electrolyte layer is located between the positive electrode layer and the negative electrode layer. As long as it contains a solid electrolyte, its structure and manufacturing method are not limited. For example, the solid electrolyte layer can be fabricated separately, then inserted between the positive and negative electrode layers and calendered to form an all-solid-state battery. As a method for fabricating the solid electrolyte layer, for example, it is possible to compress solid electrolyte powder into granular form. As the solid electrolyte, conventionally used solid electrolytes in the field can be used, but the boron cluster-type solid electrolyte described above for the negative electrode layer is preferred. Therefore, according to one embodiment of the present invention, the solid electrolyte layer comprises a boron cluster-type solid electrolyte.

[0064] Alternatively, a solid electrolyte solution can be impregnated into a support substrate capable of being impregnated, and then the solvent can be removed, thereby precipitating the solid electrolyte and producing a solid electrolyte sheet. According to one embodiment, the solid electrolyte layer is a solid electrolyte sheet comprising a support substrate and a boron cluster-type solid electrolyte supported on the support substrate. Since the solid electrolyte layer also functions as a separator separating the positive and negative electrode layers, the support substrate of the solid electrolyte sheet is required to have high insulation properties. Examples of such support substrates include glass fiber filter paper, polyolefin-based separators, cellulose-based separators, and nonwoven fabric-based separators, among which glass fiber filter paper and nonwoven fabric-based separators with high porosity and excellent heat resistance are preferred. By using a support substrate with high porosity, more solid electrolyte solution can be impregnated, and the amount of solid electrolyte precipitated also increases. Using a solid electrolyte layer with high loading capacity in an all-solid-state battery can achieve high ion conductivity. Furthermore, since the heating-induced shut-off function seen in some separators is not generated, the space for solid electrolyte precipitation is not lost due to the shut-off function. The thickness of the support substrate is preferably 10μm to 300μm, more preferably 50μm to 200μm.

[0065] The solid electrolyte solution used here can be the same as the solid electrolyte solution impregnated into the negative electrode sheet, and the preparation method is also the same.

[0066] After applying the solid electrolyte solution to the support substrate, it is dried to remove the solvent, allowing the solid electrolyte to precipitate and densely fill the voids in the support substrate.

[0067] Drying can be carried out using the same methods and conditions as the drying process described above when impregnating the negative electrode layer with a solid electrolyte solution.

[0068] After the solid electrolyte is precipitated by drying, the solid electrolyte layer is preferably densified by calendering. As described above, the calendering method using a roll press (rolling method) has the advantage of high continuous production capacity, but the pressure applied is lower than that of the uniaxial pressing method and the isostatic pressing method. However, since the solid electrolyte precipitated from the solid electrolyte solution is relatively dense, and the boron cluster type solid electrolyte is relatively soft, the solid electrolyte layer can be sufficiently densified even with a lower pressure applied. Thus, as a solid electrolyte layer, a solid electrolyte sheet obtained by impregnating the solid electrolyte solution into a support substrate has excellent processability. In addition, such a solid electrolyte sheet also has the advantage of low short-circuit risk.

[0069] Alternatively, a solid electrolyte layer can be formed by coating the surface of the electrode layer (negative electrode layer or positive electrode layer) with a solid electrolyte solution, and then removing the solvent to allow the solid electrolyte to precipitate. The solid electrolyte solution described above for the negative electrode layer can be used as the solid electrolyte solution.

[0070] The coating of the solid electrolyte solution can be performed using known methods, such as blade coating, spin coating, and spray coating. Solvent removal can be performed using the same method as the drying process described above after impregnating the solid electrolyte solution into the negative electrode. Alternatively, when impregnating the electrode with the solid electrolyte solution, it is possible to simultaneously impregnate the electrode with the solid electrolyte solution and form a solid electrolyte layer by coating the surface of the electrode layer with the solid electrolyte solution.

[0071] The thickness of the solid electrolyte layer is preferably 1 to 300 μm, more preferably 5 to 100 μm. By using this range, short circuits due to an excessively thin solid electrolyte layer and increased resistance due to an excessively thick layer are less likely to occur.

[0072] 4. All-solid-state batteries The above layers are fabricated and stacked to create an all-solid-state battery, but there are no particular limitations on the fabrication and stacking methods for each layer. For example, there are methods such as dispersing solid electrolytes or electrode active materials in a solvent to form a slurry, applying it by means of a doctor blade or spin coating, and then calendering it into a film; vapor phase methods such as vacuum evaporation, ion plating, sputtering, and laser ablation to form and stack the film; and pressing methods such as hot pressing or cold pressing without heating to shape powder and then stacking it.

[0073] As described above, it is more preferable to form the negative electrode layer as a sheet and the solid electrolyte layer as particles or solid electrolyte sheets, so that they can be overlapped with the positive electrode layer and rolled to manufacture an all-solid-state battery. The pressure applied at this time is preferably 0.0001 MPa to 100 MPa, more preferably 0.0005 MPa to 20 MPa, and particularly preferably 0.001 MPa to 10 MPa.

[0074] Since boron cluster-type solid electrolytes also have the ability to act as binders, the bonding effect on these sheets is high. Regarding calendering methods, for example, it can be implemented through rolling.

[0075] The foregoing has described several embodiments of the present invention, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, and also within the scope of the invention described in the claims and its equivalents.

[0076] Example The present invention will be described in detail below through embodiments, but the content of the present invention is not limited thereto.

[0077] <Example 1: All-solid-state battery of SiO + LCBH / LCBH particles / Li> (1) Preparation of boron cluster type solid electrolyte Prepare LiCB9H respectively 10 Aqueous solutions and LiCB 11 H 12 Aqueous solution, according to the formation of LiCB9H 10 :LiCB 11 H 12 A 7:3 molar ratio aqueous solution was mixed. Then, the water in the mixed aqueous solution was removed by distillation using an evaporator to obtain a boron cluster-type solid electrolyte. The following will describe the process according to LiCB9H... 10 :LiCB 11 H 12 A boron cluster-type solid electrolyte with a molar ratio of 7:3 is also called "LCBH".

[0078] (2) Preparation of solid electrolyte solution Methanol was added to the LCBH prepared in (1) above to make the solid content concentration 40% by weight, and a methanol solution of LCBH was prepared by manual stirring. All these steps were carried out in a dry environment with a dew point below -60°C.

[0079] (3) Preparation of negative electrode slurry As the negative electrode active material, SiO (a powder with an average particle size of 6 μm coated with carbon) was used; as the binder, a polyimide-based binder (U-Varnish A, manufactured by UBE Corporation) was used; and as the conductive additive, acetylene black (DENKA BRACK Li-100, manufactured by Denka Corporation) was used. The materials were weighed according to a composition of SiO:acetylene black:polyimide binder = 80:5:15 (wt%), and placed together with N-methyl-2-pyrrolidone (NMP) solvent in a rotary-revolutionary mixer (Thinky, ARE-310). The mixture was kneaded at 2000 rpm for 20 minutes to obtain the negative electrode slurry.

[0080] (4) Coating of negative electrode paste (fabrication of negative electrode sheet) The negative electrode slurry obtained in (3) above was coated onto a stainless steel foil (10 μm thick) serving as the current collector using a benchtop coating machine (Tester Industrial Manufacturing, FILMCOATER, PI-1210). The foil was then temporarily dried using a constant-temperature dryer (80°C, 10 minutes). The temporarily dried negative electrode was further subjected to vacuum heating treatment using a vacuum constant-temperature dryer (vacuum, 240°C, 15 hours). The electrode capacity density was 1.0 mAh / cm³. 2 The weight per unit area is 8.58 mg / cm³. 2 The calculated SiO content per unit area in the negative electrode is 0.71 mg / cm².2 .

[0081] (5) Loading of solid electrolyte on negative electrode The solid electrolyte solution obtained in (2) was dropped onto the surface of the negative electrode obtained in (4), and coated with a wire rod to penetrate into the interior of the negative electrode and homogenize it, while removing excess solid electrolyte solution. Then, it was temporarily dried in a constant temperature desiccator (atmospheric pressure, 160°C, 2 hours). The operation from dropping the solid electrolyte solution to temporary drying was repeated twice. Afterward, it was further dried in a vacuum constant temperature desiccator (vacuum, 180°C, 15 hours) to obtain a negative electrode with solid electrolyte loaded inside. After this process, the unit area weight of the negative electrode became 10.67 mg / cm³. 2 The weight of LCBH formed internally was calculated to be 2.09 mg / cm³. 2 All these processes are carried out in a dry environment with a dew point below -60°C.

[0082] (6) Fabrication of solid electrolyte layer The LCBH powder prepared in (1) above was fed into a powder molding machine with a diameter of 12 mm and cold-pressed into a disc shape at a pressure of 35 MPa. The molded product, i.e., the disc-shaped particles, was removed to obtain a solid electrolyte layer. At this time, care should be taken not to allow the particles to break or be damaged. All these processes were carried out in a dry environment with a dew point below -60°C.

[0083] (7) Fabrication of all-solid-state batteries The negative electrode sheet carrying the solid electrolyte obtained in (5) above was punched into a disc shape with a diameter of 11 mm using an electrode punching manual punch press (manufactured by Nogami Giken Co., Ltd.) as a test electrode. This 11 mm diameter test electrode was overlapped with the 12 mm diameter LCBH particles obtained in (6) above, and placed in a 12 mm diameter powder forming machine, and cold-pressed into a disc shape at a pressure of 35 MPa. Next, a 11 mm diameter Li foil (manufactured by Honjo Metals Co., Ltd., thickness 200 μmm) was cold-pressed onto the side of the LCBH particles opposite to the test electrode at a pressure of 5 MPa to make them tightly sealed. For the resulting laminate, a CR2032 type coin cell was fabricated as an all-solid-state battery. All these processes were carried out in a dry environment with a dew point of -60°C or below.

[0084] (8) Charge and discharge test The all-solid-state battery obtained in (7) above was placed in a thermostat set at 60°C, with a charge / discharge current of 0.05 mA / cm. 2 Constant current charge-discharge tests were performed under operating voltage conditions ranging from 1.20 to 0.01V. Figure 2 The results (charge-discharge curves) are shown. (From...) Figure 2 It can be seen that the all-solid-state battery involved in the implementation method does not significantly decrease its charge and discharge capacity even after repeated cycles, and operates stably.

[0085] <Comparative Example 1: All-solid-state battery of SiO+3LiBH4-LiI / LCBH particles / Li> Except for using 3LiBH4-LiI as the solid electrolyte supported on the negative electrode, the same operation as in Example 1 was performed.

[0086] In the process of loading a solid electrolyte onto the negative electrode, a solution of 3LiBH4-LiI dissolved in THF to achieve a 3LiBH4-LiI concentration of 25% by weight was used as the solid electrolyte solution. This solid electrolyte solution was dropped onto the surface of the negative electrode obtained in Example 1 (4), and coated with a wire rod to allow it to penetrate into the interior of the negative electrode and homogenize it, while removing excess solid electrolyte solution. Then, temporary drying was performed using a constant temperature desiccator (atmospheric pressure, 60°C, 2 hours). The operation from dropping the solid electrolyte solution to temporary drying was repeated 3 times. Afterward, further vacuum heating drying was performed using a vacuum constant temperature desiccator (vacuum, 120°C, 15 hours) to obtain a negative electrode with a solid electrolyte loaded inside. All these processes were carried out in a dry environment with a dew point below -60°C.

[0087] The other processes are carried out in the same manner as in Example 1 to produce an all-solid-state battery.

[0088] The obtained all-solid-state battery was subjected to charge-discharge tests under the same conditions as in Example 1. Figure 3 Indicates the result. (By) Figure 3 It can be seen that the all-solid-state battery in Comparative Example 1 basically did not operate.

[0089] <Comparative Example 2: All-solid-state battery of SiO+3LiBH4-LiI / 3LiBH4-LiI particles / Li> Except for using 3LiBH4-LiI as the material for the solid electrolyte layer, the same procedures as in Comparative Example 1 were performed. More specifically, the process of fabricating the solid electrolyte layer was the same as in Comparative Example 1, except that 3LiBH4-LiI powder was used instead of LCBH powder.

[0090] The obtained all-solid-state battery was subjected to charge-discharge tests under the same conditions as in Example 1 and Comparative Example 1. Figure 4 The result is indicated in the text. Figure 4 It can be seen that the all-solid-state battery in Comparative Example 2 basically did not operate.

[0091] Explanation of reference numerals in the attached figures 1: Positive electrode layer; 2: Solid electrolyte layer; 3: Negative electrode layer; 10: All-solid-state battery.

Claims

1. A negative electrode layer for an all-solid-state battery, characterized in that: It comprises a negative electrode active material and a solid electrolyte, wherein the negative electrode active material is a silicon-based material and the solid electrolyte is a boron cluster-type solid electrolyte.

2. The negative electrode layer for all-solid-state batteries as described in claim 1, characterized in that: The boron cluster type solid electrolyte is prepared according to LiCB9H. 10 / LiCB 11 H 12 The molar ratio in the range of 1.1 to 20 includes LiCB9H. 10 and LiCB 11 H 12 Solid electrolyte complex.

3. The negative electrode layer for all-solid-state batteries as described in claim 2, characterized in that: The boron cluster type solid electrolyte is prepared according to LiCB9H. 10 :LiCB 11 H 12 A molar ratio of 7:3 includes LiCB9H 10 and LiCB 11 H 12 Solid electrolyte complex.

4. The negative electrode layer as described in any one of claims 1 to 3, characterized in that: The silicon-based materials are selected from SiO, Si, SiN, SiC, and silicon-carbon composite materials.

5. The negative electrode layer for an all-solid-state battery as described in any one of claims 1 to 4, characterized in that: The silicon-based material is contained in a proportion of 40 to 90% by weight relative to the total weight of the boron cluster solid electrolyte and the silicon-based material.

6. A method for manufacturing a negative electrode layer for an all-solid-state battery, characterized in that, include: The steps for preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; and The process involves impregnating the obtained solid electrolyte solution into a sheet containing silicon-based materials and then drying it to obtain the negative electrode layer for all-solid-state batteries.

7. The method as described in claim 6, characterized in that: The solvent comprises at least one selected from water, alcohol solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate.

8. The method as described in claim 6 or 7, characterized in that: The boron cluster type solid electrolyte is prepared according to LiCB9H. 10 / LiCB 11 H 12 The molar ratio in the range of 1.1 to 20 includes LiCB9H. 10 and LiCB 11 H 12 Solid electrolyte complex.

9. The method as described in claim 8, characterized in that: The boron cluster type solid electrolyte is prepared according to LiCB9H. 10 :LiCB 11 H 12 A molar ratio of 7:3 includes LiCB9H 10 and LiCB 11 H 12 Solid electrolyte complex.

10. The method according to any one of claims 6 to 9, characterized in that: The silicon-based materials are selected from SiO, Si, SiN, SiC, and silicon-carbon composite materials.

11. The method according to any one of claims 6 to 10, characterized in that: The drying process is carried out at atmospheric pressure and a temperature of 40–180°C for 30 minutes to 5 hours, followed by a process under vacuum at a temperature of 100–300°C for 1–25 hours.

12. An all-solid-state battery, characterized in that: It comprises a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The negative electrode layer is the negative electrode layer for all-solid-state batteries as described in claim 1.

13. The all-solid-state battery as described in claim 12, characterized in that: The solid electrolyte layer contains a boron cluster-type solid electrolyte.

14. The all-solid-state battery as described in claim 13, characterized in that: The solid electrolyte layer is a solid electrolyte sheet comprising a supporting substrate and a boron cluster-type solid electrolyte supported on the supporting substrate.

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