All-solid-state battery negative electrode layer and all-solid-state battery

Abstract

An all-solid-state battery negative electrode layer according to one embodiment of the present invention includes a negative electrode active material and a solid electrolyte. The negative electrode active material is a silicon-based material, and the solid electrolyte is a boron cluster-type solid electrolyte.

Description

Anode layer for all-solid-state battery and all-solid-state battery

[0001] The present invention relates to an anode layer for use in an all-solid-state battery and an all-solid-state battery including the same. The present invention also relates to a method for producing an anode layer for an all-solid-state battery.

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

[0003] Furthermore, their use is expanding to mobile vehicles such as automobiles and airplanes, requiring stationary lithium-ion secondary batteries with large capacities. Under these circumstances, safety is becoming more important than ever, and efforts are being made to develop all-solid-state lithium-ion secondary batteries that do not use hazardous substances such as organic solvents.

[0004] Among the solid electrolytes used in all-solid-state batteries, sulfide solid electrolytes and complex hydrides have high ionic conductivity and are relatively soft, making them easy to form solid-solid interfaces. They are also stable against metallic lithium, and their development as practical solid electrolytes is progressing. These solid electrolytes have also been added to the positive electrode layer and / or negative electrode layer. In such cases, it is necessary to appropriately select the positive electrode and negative electrode active materials and consider the combination of these active materials with the solid electrolyte depending on the problem to be solved. For example, silicon-based materials are known as negative electrode active materials that can achieve high theoretical capacity (Patent Document 1). However, adding conventional solid electrolytes to negative electrode layers containing silicon-based materials can cause problems, such as the silicon-based material itself expanding and contracting during charging and discharging. This can result in the formation of voids within the negative electrode layer, leading to problems such as increased resistance and a decrease in capacity due to repeated charge-discharge cycles. Under these circumstances, there is a need to appropriately select the materials and configuration of each layer of all-solid-state batteries to resolve various issues.

[0005] Patent No. 7269571

[0006] An object of the present invention is to provide an anode layer for obtaining an all-solid-state battery that can operate stably, and an all-solid-state battery including the anode layer.

[0007] The present inventors have conducted extensive research to solve the problems associated with silicon-based materials, and have found that by combining a silicon-based material with a predetermined solid electrolyte to form an anode layer, it is possible to obtain an all-solid-state battery that can operate stably even after repeated charge-discharge cycles. The present invention is, for example, as follows: [1] An anode layer for an all-solid-state battery, comprising an anode active material and a solid electrolyte, wherein the anode active material is a silicon-based material, and the solid electrolyte is a boron cluster-type solid electrolyte. [1-1] The boron cluster-type solid electrolyte is LiCB ９ H １０ , LiCB １１ H １２ , and Li ２ B １２ H １２[2] The negative electrode layer for an all-solid-state battery according to [1], comprising one or more selected from the following: ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ The negative electrode layer for an all-solid-state battery according to [1], wherein the boron cluster-type solid electrolyte is a solid electrolyte composite containing LiCB at a molar ratio of 1.1 to 20. ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ : LiCB １１ H １２ [4] The anode layer for an all-solid-state battery according to [2], which is a solid electrolyte composite containing the boron cluster-type solid electrolyte and the silicon-based material in a molar ratio of 7:3. [4] The anode layer for an all-solid-state battery according to any of [1] to [3], wherein the silicon-based material is selected from the group consisting of SiO, Si, SiN, SiC, and a Si-carbon composite. [5] The anode layer for an all-solid-state battery according to any of [1] to [4], wherein the silicon-based material is contained in an amount of 40 to 90 wt % based on the total weight of the boron cluster-type solid electrolyte and the silicon-based material. [5-1] The anode layer for an all-solid-state battery according to any of [1] to [5], which is an anode sheet comprising a current collector and a layer containing a negative electrode active material laminated on the current collector. [6] A method for producing a negative electrode layer for an all-solid-state battery, the method comprising: preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; and impregnating a sheet containing a silicon-based material with the obtained solid electrolyte solution, and then drying the sheet to obtain a negative electrode layer for an all-solid-state battery. [7] The method according to [6], wherein the solvent contains at least one selected from the group consisting of water, alcohol-based solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate. [8] The boron cluster-type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB９ H １０ / LiCB １１ H １２ The method according to [6] or [7], wherein the boron cluster-type solid electrolyte is a solid electrolyte composite containing LiCB at a molar ratio of 1.1 to 20. ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ : LiCB １１ H １２ The method according to [8], wherein the silicon-based material is a solid electrolyte composite containing silicon and silicon at a molar ratio of 7:3.

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

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

[12] An all-solid-state battery comprising 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 the all-solid-state battery negative electrode layer according to any one of [1] to [5-1].

[13] The all-solid-state battery according to

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

[14] The all-solid-state battery according to

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

[0008] According to the present invention, it is possible to provide an anode layer for obtaining an all-solid-state battery that can operate stably, and an all-solid-state battery including the anode layer.

[0009] 1 is a cross-sectional view of an all-solid-state battery according to an embodiment. 2 is a diagram showing the results of a charge-discharge test of Example 1. 3 is a diagram showing the results of a charge-discharge test of Comparative Example 1. 4 is a diagram showing the results of a charge-discharge test of Comparative Example 2.

[0010] Hereinafter, embodiments of the present invention will be described in detail. The materials, configurations, etc. described below do not limit the present invention, and various modifications can be made within the scope of the present invention. First, a cross-sectional view of an all-solid-state battery according to an embodiment is shown in FIG. 1. The all-solid-state battery 10 according to the embodiment is, for example, an all-solid-state lithium-ion secondary battery, and can be used in various devices such as mobile phones, personal computers, automobiles, etc. The all-solid-state battery 10 has a structure in which a solid electrolyte layer 2 is disposed between a positive electrode layer 1 and a negative electrode layer 3.

[0011] 1. Negative Electrode Layer According to one embodiment of the present invention, there is provided 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.

[0012] All-solid-state batteries using a silicon-based material and a boron cluster-type solid electrolyte in the anode layer exhibit minimal deterioration even after multiple charge-discharge cycles. The decrease in charge-discharge capacity over long periods of use can be minimized, allowing for stable long-term use. In other words, by using the anode layer according to the embodiment, an all-solid-state battery with excellent cycle characteristics can be obtained. This is thought to be due to the boron cluster-type solid electrolyte's ability to suppress the expansion and contraction of the silicon-based material caused by charge and discharge. While the specific mechanism is unclear, it is speculated that the boron cluster-type solid electrolyte "follows" the expansion and contraction of the silicon-based material. This "following" of the boron cluster-type solid electrolyte is thought to contribute to the excellent charge-discharge cycle performance. The all-solid-state batteries according to the embodiment are revolutionary in that they can solve the above-mentioned cycle characteristic issues while using a silicon-based material that contributes to an increase in theoretical capacity. In other words, the all-solid-state batteries according to the embodiment have the advantages of large capacity and stable operation over long periods of time.

[0013] A boron cluster-type solid electrolyte is a type of complex hydride, and is a compound having a cluster structure with boron as the basic skeleton. In general, if this cluster structure is closed (cage-shaped), it is preferable because it shows high stability against water and alcohol. Specific examples of boron cluster-type solid electrolytes include LiCB ９ H １０ , LiCB １１ H １２ , Li ２ B １２ H １２ Among them, boron cluster type solid electrolytes having carbon in the skeleton are preferred because they tend to have high ionic conductivity. Examples of such compounds include LiCB ９ H １０ and LiCB １１ H １２ These boron cluster type solid electrolytes may be used alone or in combination of two or more. ９ H １０ and LiCB １１ H １２ The chemical structure of

[0014] As a boron cluster type solid electrolyte, LiCB ９ H １０ and LiCB １１ H １２ Preferably, the solid electrolyte composite is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ It is more preferable that the solid electrolyte composite contains LiCB in a molar ratio of 1.1 to 20 (more preferably 1.25 to 10, and even more preferably 1.5 to 9). ９ H １０ Based on 749cm －１ (±5cm －１ ) and LiCB １１ H １２Based on 763cm －１ (±5cm －１ It is preferable that the peaks are in the respective regions. Peaks may also be present in other regions, but the peaks that show the characteristics of each region are as described above.

[0015] More preferably, the boron cluster type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ : LiCB １１ H １２ = approximately 7:3 molar ratio. ９ H １０ : LiCB １１ H １２ By mixing them at a molar ratio of about 7:3, a material with higher ionic conductivity (>1 mS / cm) is obtained.

[0016] The raw material LiCB ９ H １０ and LiCB １１ H １２ As the crystalline crystalline ester, commercially available crystalline esters can be used. The purity of the crystalline crystalline ester is preferably 95% or more, and more preferably 98% or more. By using a compound having a purity within the above range, it is easy to obtain the desired crystals.

[0017] LiCB ９ H １０ and LiCB １１ H １２The mixture can be mixed in the air or in a homogeneous solvent. The solvent is not particularly limited, but examples thereof include water, nitrile solvents such as acetonitrile, ether solvents such as tetrahydrofuran and diethyl ether, N,N-dimethylformamide, N,N-dimethylacetamide, alcohol solvents such as methanol, ethanol, and propanol, acetone, ethyl acetate, methyl acetate, toluene, methylene chloride, and chloroform. Among these solvents, alcohol solvents such as water, ethanol, and isopropanol are particularly preferred for safety reasons, and water is more preferred. As the alcohol solvent, one having 3 or less carbon atoms is more preferred. For example, when LiCB is mixed using water as a solvent, ９ H １０ and LiCB １１ H １２ and the water is removed from the mixed aqueous solution by an evaporator to obtain LiCB. ９ H １０ and LiCB １１ H １２ A composite can be obtained in which the above two compounds are mixed in a specified molar ratio. Depending on the type of solvent, the time required to remove the solvent in an evaporator and to dry the powder varies, with alcohol-based solvents tending to have shorter drying times.

[0018] In the negative electrode layer, the boron cluster-type solid electrolyte is contained in an amount of preferably 10 to 85 wt %, more preferably 15 to 80 wt %, and particularly preferably 20 to 75 wt %, based on the total weight of the boron cluster-type solid electrolyte and the silicon-based material.

[0019] The silicon-based material is not limited as long as it contains silicon, but examples thereof include Si, SiO, and Si-C composite materials, preferably Si and SiO, and more preferably SiO. The use of Si or SiO as the negative electrode active material is preferable in that the equilibrium potential of the negative electrode is lowered, improving the energy density of the battery and increasing the operating voltage.

[0020] In the negative electrode layer, the silicon-based material is contained in a proportion of preferably 15 to 90 wt %, more preferably 20 to 85 wt %, and particularly preferably 25 to 80 wt %, based on the total weight of the boron cluster-type solid electrolyte and the silicon-based material.

[0021] The structure and fabrication method of the negative electrode layer are not particularly limited and may follow structures and fabrication methods known in the art. For example, a negative electrode sheet may be used. The negative electrode sheet 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 solution" in this specification). Stainless steel foil, copper foil, nickel, etc. may be used as the current collector for the negative electrode layer. Note that a current collector with a carbon-coated surface may also be used.

[0022] Known methods can be used to prepare the negative electrode sheet. For example, a coating solution is prepared by mixing a negative electrode active material, a solvent, and other materials (such as a binder and a conductive additive) described below. This coating solution is applied to a current collector by a doctor blade method, spin coating method, or spray coating method, 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 be formed on the current collector by a gas phase method (e.g., vapor deposition). A solid electrolyte solution is then impregnated into the current collector and the resulting layer is dried to produce a negative electrode sheet carrying a solid electrolyte.

[0023] Therefore, according to one embodiment of the present invention, there is provided a method for producing a negative electrode layer for an all-solid-state battery, the method comprising: preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent; impregnating a sheet containing a silicon-based material with the obtained solid electrolyte solution, and then drying the sheet to obtain a negative electrode layer for an all-solid-state battery.

[0024] The solid electrolyte solution is obtained by mixing a boron cluster-type solid electrolyte with a solvent. The solvent used here is not particularly limited as long as it can dissolve the boron cluster-type solid electrolyte, but a solvent that does not react with the boron cluster-type solid electrolyte is preferred. Examples of such solvents include water, alcohol-based solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate, and one or more of these may be used. The solvent is preferably water, methanol, tetrahydrofuran, or acetonitrile, and more preferably methanol. Water and alcohol-based solvents are preferred as solvents because they are compatible with boron cluster-type compounds and provide high solubility.

[0025] As long as a solid electrolyte solution can be obtained, the preparation method is not particularly limited. For example, ９ H １０ and LiCB １１ H １２ When using a solid electrolyte composite with LiCB ９ H １０ and LiCB １１ H １２ The resulting mixture is mixed with an aqueous solution of LiCB and dried to obtain a powder of the solid electrolyte composite, which is then dissolved in methanol to obtain a solid electrolyte solution. ９ H １０ Methanol solution and LiCB １１ H １２ A solid electrolyte solution can also be prepared by mixing the above-mentioned methanol solution with the above-mentioned solid electrolyte. When using other solid electrolytes, a solid electrolyte solution can be prepared in the same manner. The specific solvents described here are merely examples, and do not preclude the use of other solvents.

[0026] The solids concentration (solid electrolyte concentration) in the solid electrolyte solution is preferably in the range of 5 to 70 wt % so as to achieve optimal viscosity during application, although the optimal value varies depending on the type of boron cluster-type solid electrolyte and solvent. By achieving this concentration range, the solid electrolyte solution is impregnated deep into the pores of the negative electrode sheet, and the solid electrolyte deposition efficiency is also improved. The solids concentration in the solid electrolyte solution is more preferably in the range of 20 to 60 wt %, and even more preferably in the range of 30 to 50 wt %. Known impregnation methods can be used to impregnate the electrode sheet with the solid electrolyte solution. Among these, vacuum impregnation is preferred to achieve deep impregnation into the pores of the electrode layer. Furthermore, heating reduces the viscosity of the solution, allowing for more efficient deep impregnation into the pores.

[0027] After impregnating the negative electrode sheet with the solid electrolyte solution, the sheet is dried to remove the solvent, resulting in the solid electrolyte being deposited in the voids of the negative electrode sheet, resulting in a negative electrode sheet supported with the solid electrolyte. Drying is not particularly limited as long as it is performed under conditions that allow the desired degree of solvent removal. For example, drying is preferably performed under atmospheric pressure at a temperature of 40 to 180°C (more preferably 45 to 175°C) for 30 to 5 hours (more preferably 1 to 4 hours), followed by further drying under vacuum at a temperature of 100 to 300°C (more preferably 105 to 295°C) for 1 to 25 hours (more preferably 2 to 24 hours). These drying conditions allow for efficient volatilization of the solvent, resulting in the precipitation of the solid electrolyte. Under these conditions, problems such as side reactions or foaming of the solvent, which prevents the solid electrolyte from being densely precipitated, are unlikely to occur. Furthermore, heating under an inert gas flow or vacuum can also promote solvent volatilization.

[0028] The dried negative electrode sheet carrying the solid electrolyte can be rolled to further densify the electrode layer. While the rolling method is not particularly limited, it is preferable to use the roll press method used in producing electrode sheets for lithium-ion batteries. While the roll press method has the advantage of high continuous productivity, the press pressure is lower than that of uniaxial pressing and isostatic pressing. In this case, the press pressure is preferably 0.1 MPa to 100 MPa, and more preferably 1 MPa to 80 MPa. While extremely high press pressures were required when molding powder itself, by adopting a method in which the solid electrolyte is precipitated from a solid electrolyte solution, the solid electrolyte is densely formed in the voids of the electrode layer, eliminating the need for high press pressures, such as 300 MPa, which would deform the particles. The purpose of this rolling after drying is to fill small cracks that occur due to expansion and contraction caused by thermal changes and small voids that occur when the solvent evaporates, and the roll press method can provide sufficient results.

[0029] The negative electrode layer may contain materials commonly used in the relevant technical field other than the silicon-based materials and boron cluster-type solid electrolytes described above. Examples of such materials include binders and conductive additives. The binder used in the negative electrode layer is not particularly limited, but examples include polyimide-based compounds, polysiloxanes, polyalkylene glycols, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and acrylic compounds. If necessary, a thickener such as carboxymethyl cellulose (CMC) can also be used. The conductive additive is not particularly limited as long as it has the desired conductivity, but examples include conductive additives made from carbon materials. Specific examples include carbon black, acetylene black, ketjen black, and carbon fiber. Other examples include cellulose nanofibers derived from plants. These materials can be added at any time depending on the configuration of the negative electrode layer. For example, when the negative electrode layer is a negative electrode sheet as described above, a coating liquid can be prepared by mixing a negative electrode active material, a solvent, and other materials as described above (binder, conductive additive, etc.), and the coating liquid can be applied to a current collector. Alternatively, if permitted, other materials as described above may be mixed into a solid electrolyte solution.

[0030] 2. Positive Electrode Layer The positive electrode layer can be any positive electrode layer known in the art for lithium-ion batteries using solid electrolytes. As described above for the negative electrode layer, it may be in the form of an electrode sheet (i.e., a positive electrode sheet) having a configuration in which a layer containing a positive electrode active material is laminated on a current collector, or a pressed powder molded body of a positive electrode composite, or a metal foil or alloy foil may be used. In the case of a positive electrode sheet, a stainless steel foil or an aluminum foil may be used as the current collector, and the surface of the current collector may be carbon-coated. The method for producing the positive electrode sheet is the same as that described above for the negative electrode sheet.

[0031] The positive electrode active material contained in the positive electrode layer is not particularly limited as long as it is a material that can release lithium ions during charging and absorb lithium ions during discharging. For example, metal oxides containing transition metals, sulfur-based positive electrode active materials, organic positive electrode active materials, FeF using a conversion reaction, etc. ３ and VF ３ In the present invention, it is preferable that the potential of the positive electrode active material is 3.0 V or less versus lithium, since this suppresses the reaction at the interface between the active material and the solid electrolyte and reduces the interfacial resistance. More preferably, the potential of the positive electrode active material is 1.0 to 2.7 V versus lithium.

[0032] As the metal oxide containing a transition metal, particles or a thin film of a metal oxide containing lithium and any one or more of the transition metals Mn, Co, Ni, Fe, Cr, and V can be used. Specific examples include, but are not limited to, LiCoO ２ , LiCo ２ O4, LiMnO ２ , LiMn ２ O ４ , LiMnCoO4, Li ２ MnCoO4, LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiNi ０．５ Mn ０．５ O ２ , Li ２ NiMn ３ O ８ , LiVO ２ , LiV ３ O ３ , LiCrO ２ , LiFePO ４ , LiCoPO ４ , LiMnPO ４ , LiVOPO ４ , LiNiO ２ , LiNi ２ O4, LiNi １／３ Co １／３ Mn １／３ O ２ , Li ２ FeSiO ４ , Li ２ MnSiO４ , LiFeBO ３ Also, Fe ２ O ３ , Cr ３ O ８ , V ２ O ５ , MnO ２ Among them, LiCoO ２ , LiMnO ２ , LiMn ２ O ４ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiNi ０．５ Mn ０．５ O ２ , Li ２ NiMn ３ O ８ , LiFePO ４ , LiCoPO ４ , LiMnPO ４ , LiVOPO ４ , LiNiO ２ and LiNi １／３ Co １／３ Mn １／３ O ２ In addition, for the purpose of suppressing the reaction with the solid electrolyte, it is possible to provide a coating layer on the particles or thin film of these positive electrode active materials. As the type of coating layer, LiNbO ３ , Li ４ Ti ５ O １２ , LiTaO ３ , LiNbO ３ , LiAlO ２ , Li ２ ZrO ３ , Li ２ WO ４ , Li ２ TiO ３ , Li ２ B ４ O ７ , Li ３ P.O. ４ , Li ２ MoO ４ and LiBO ２ Examples include:

[0033] The sulfur-based positive electrode active material is not particularly limited, but specifically includes S, sulfur-carbon composite, TiS ２ , TiS ３ , TiS ４ , NiS, NiS ２ , CuS, FeS ２ , Li ２ S, MoS ３ , sulfur-modified polyacrytonitrile, rubeanic acid (dithiooxamide), disulfide compounds, etc. ２ , TiS ３ , TiS ４ , NiS, NiS ２ , FeS ２ , Li ２ S, MoS ３ , sulfur-modified polyacrytonitrile, sulfur-carbon composite, and rubeanic acid (dithiooxamide) are preferred.

[0034] The organic positive electrode active material is not particularly limited, but specific examples include radical compounds typified by 2,2,6,6-tetramethylpiperidinoxyl-4-yl methacrylate and polytetramethylpiperidinoxyvinyl ether, quinone compounds, radialene compounds, tetraciaquinodimethane, phenazine oxide, etc. Among these, radical compounds and quinone compounds are preferred because they have a large theoretical capacity and can maintain a relatively good discharge capacity.

[0035] The binder used in the positive electrode layer is not particularly limited, and examples thereof include polyimides, acrylics, polysiloxanes, polyalkylene glycols, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and ethylene-vinyl alcohol copolymers (EVOH). Thickeners such as carboxymethyl cellulose (CMC) can also be used as needed. The conductive additive can be the same as that used in the negative electrode layer. The positive electrode layer may contain a solid electrolyte, which may be a boron cluster-type solid electrolyte, as in the negative electrode layer, or another solid electrolyte commonly used in all-solid-state batteries. When neither the positive electrode layer nor the negative electrode layer contains Li as an active material, for example, when a sulfur-based positive electrode active material is used in the positive electrode layer, one of the active materials must be doped with lithium.

[0036] 3. Solid Electrolyte Layer The solid electrolyte layer is located between the positive electrode layer and the negative electrode layer. Its configuration and manufacturing method are not limited as long as it contains a solid electrolyte. For example, a solid electrolyte layer can be manufactured separately, then inserted between the positive electrode layer and the negative electrode layer and rolled to form an all-solid-state battery. One example of a method for manufacturing a solid electrolyte layer is to compress and mold a solid electrolyte powder to produce a pellet-shaped solid electrolyte layer. While solid electrolytes commonly used in this field can be used as the solid electrolyte, it is preferable to use the boron cluster-type solid electrolyte described above for the negative electrode layer. Therefore, according to one embodiment of the present invention, the solid electrolyte layer contains a boron cluster-type solid electrolyte.

[0037] Alternatively, a solid electrolyte sheet can be produced by impregnating a solution-permeable support substrate with a solid electrolyte solution and then removing the solvent to precipitate the solid electrolyte. 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. Because the solid electrolyte layer also serves as a separator separating the positive electrode layer and the negative electrode layer, 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 separators. Among these, glass fiber filter paper and nonwoven fabric separators are preferred, as they have a high porosity and excellent heat resistance. Using a support substrate with a high porosity allows for a larger amount of solid electrolyte solution to be impregnated, resulting in a larger amount of precipitated solid electrolyte. Using a solid electrolyte layer with a high solid electrolyte loading in an all-solid-state battery achieves high ionic conductivity. Furthermore, since the heat-induced shutdown function seen in some separators does not occur, the space for precipitation of the solid electrolyte is not lost due to the shutdown function. The thickness of the support substrate is preferably 10 μm to 300 μm, and more preferably 50 μm to 200 μm.

[0038] The solid electrolyte solution used here can be the same as the solid electrolyte solution impregnated into the negative electrode sheet described above, and the preparation method is also similar. After the solid electrolyte solution is applied to the support substrate, it is dried to remove the solvent and precipitate the solid electrolyte, and the voids in the support substrate are densely filled with the solid electrolyte. The drying can be performed using the same method and conditions as the drying step in the impregnation of the solid electrolyte solution into the negative electrode layer described above.

[0039] After the solid electrolyte is deposited by drying, it is desirable to densify the solid electrolyte layer by rolling. As described above, the method of rolling using a roll press (roll pressing method) has the advantage of high continuous productivity, but the pressing pressure is lower than that of uniaxial pressing method and isostatic pressing method. However, because the solid electrolyte deposited from the solid electrolyte solution is relatively dense and the boron cluster-type solid electrolyte is soft, the solid electrolyte layer can be sufficiently densified even by rolling at a low pressing pressure. As such, using a solid electrolyte sheet obtained by impregnating a support substrate with a solid electrolyte solution as the solid electrolyte layer is excellent in terms of processability. Furthermore, the solid electrolyte sheet as described above also has the advantage of a low risk of short circuiting.

[0040] Alternatively, for example, a solid electrolyte layer can be formed by applying a solid electrolyte solution to the surface of an electrode layer (negative electrode layer or positive electrode layer) and then removing the solvent to precipitate the solid electrolyte. The solid electrolyte solution used for the negative electrode layer described above can be used as the solid electrolyte solution. The application of the solid electrolyte solution can be performed by known methods, such as a doctor blade method, a spin coating method, or a spray coating method. The solvent can be removed by a method similar to the drying process performed after the negative electrode sheet is impregnated with the solid electrolyte solution. Furthermore, when impregnating the electrode sheet with the solid electrolyte solution, the impregnation of the electrode sheet with the solid electrolyte solution and the formation of the solid electrolyte layer can be simultaneously performed by applying the solid electrolyte solution to the surface of the electrode layer. The thickness of the solid electrolyte layer is preferably 1 to 300 μm, more preferably 5 to 100 μm. By setting the thickness within this range, short circuits due to a solid electrolyte layer being too thin and increased resistance due to a solid electrolyte layer being too thick are less likely to occur.

[0041] 4. All-Solid-State Battery An all-solid-state battery is manufactured by preparing and stacking the above-mentioned layers, but the method for preparing and stacking each layer is not particularly limited. Examples include a method in which a solid electrolyte or an electrode active material is dispersed in a solvent to form a slurry, which is applied by a doctor blade, spin coating, or the like, and then rolled to form a film; a gas phase method in which film formation and stacking are performed using a vacuum deposition method, ion plating method, sputtering method, laser ablation method, or the like; and a pressing method in which powder is molded by hot pressing or cold pressing without applying heat, and then stacked.

[0042] As described above, it is more preferable to form the negative electrode layer as a sheet and the solid electrolyte layer as a pellet or solid electrolyte sheet. These are then stacked on top of the positive electrode layer and rolled to produce an all-solid-state battery. The pressing pressure 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. The boron cluster-type solid electrolyte also functions as a binder, and is therefore highly effective in adhering these sheets together. The rolling method can be, for example, a roll press method.

[0043] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0044] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited thereto. Example 1: All-solid-state battery of SiO+LCBH / LCBH pellet / Li (1) Preparation of boron cluster-type solid electrolyte LiCB ９ H １０ Aqueous solution and LiCB １１ H １２Aqueous solutions were prepared, and LiCB ９ H １０ : LiCB １１ H １２ The aqueous solutions were mixed so that the molar ratio of LiCB was 7:3. Next, the water in the mixed aqueous solution was removed by distillation using an evaporator to obtain a boron cluster-type solid electrolyte. ９ H １０ : LiCB １１ H １２ The boron cluster-type solid electrolyte mixed at a molar ratio of 7:3 is also referred to as "LCBH."

[0045] (2) Preparation of solid electrolyte solution Methanol was added to the LCBH prepared in (1) above to a solid content of 40 wt %, and the mixture was stirred by hand to prepare a methanol solution of LCBH. This process was carried out in a dry environment with a dew point of −60° C. or less.

[0046] (3) Preparation of negative electrode slurry SiO (carbon-coated powder with an average particle size of 6 μm) was used as the negative electrode active material, a polyimide binder (U-Varnish A, manufactured by UBE) was used as the binder, and acetylene black (Denka Black Li-100, manufactured by Denka Co., Ltd.) was used as the conductive additive. Each was weighed out so as to have a composition of SiO:acetylene black:polyimide binder = 80:5:15 (wt%), and placed in a rotation / revolution mixer (ARE-310, manufactured by Thinky) together with N-methyl-2-pyrrolidone (NMP) solvent, and kneaded at 2000 rpm for 20 minutes to obtain a negative electrode slurry.

[0047] (4) Coating of negative electrode slurry (preparation of negative electrode sheet) The negative electrode slurry obtained in (3) above was coated onto a stainless steel foil current collector (thickness 10 μm) using a desktop coater (FILMCOATER, PI-1210, manufactured by Tester Sangyo Co., Ltd.) and pre-dried in a constant temperature oven (80°C, 10 minutes). Furthermore, the pre-dried negative electrode sheet was subjected to a vacuum heat treatment using a vacuum constant temperature oven (vacuum, 240°C, 15 hours). The capacity density of the electrode was 1.0 mAh / cm ２ and the weight per unit area is 8.58 mg / cm ２ The weight per unit area of ​​SiO contained in this negative electrode sheet was 0.71 mg / cm２ It was calculated that:

[0048] (5) Supporting the solid electrolyte on the negative electrode sheet The solid electrolyte solution obtained in (2) above was dropped onto the surface of the negative electrode sheet obtained in (4) and was then uniformly infiltrated into the interior of the negative electrode sheet using a wire coater. At the same time, excess solid electrolyte solution was removed. This process was then temporarily dried in a constant temperature dryer (atmospheric pressure, 160°C, 2 hours). This procedure from dropping the solid electrolyte solution to temporarily drying was repeated twice. This was followed by vacuum heating and drying in a vacuum constant temperature dryer (vacuum, 180°C, 15 hours), yielding a negative electrode sheet with a solid electrolyte supported inside the negative electrode sheet. After this process, the weight per unit area of ​​the negative electrode sheet was 10.67 mg / cm. ２ The weight of the LCBH formed inside is 2.09 mg / cm ２ This process was all carried out in a dry environment with a dew point of −60° C. or less.

[0049] (6) Preparation of Solid Electrolyte Layer The LCBH powder prepared in (1) above was subjected to a powder molding machine with a diameter of 12 mm and cold-pressed into a disk shape at a pressure of 35 MPa. The molded disk-shaped pellet was extracted to obtain a solid electrolyte layer. Care was taken to prevent the pellet from collapsing or breaking. All of these steps were carried out in a dry environment with a dew point of -60°C or below.

[0050] (7) Preparation of All-Solid-State Battery The solid electrolyte-supported negative electrode sheet obtained in (5) above was punched into a 11 mm diameter disk using an electrode punching hand punch (manufactured by Nogami Giken Co., Ltd.) to form a test electrode. This 11 mm diameter test electrode and the 12 mm diameter LCBH pellet obtained in (6) above were stacked and placed in a 12 mm diameter powder molding machine and cold-pressed into a disk at a pressure of 35 MPa. Next, an 11 mm diameter Li foil (manufactured by Honjo Metals Co., Ltd., thickness 200 μm) was attached to the side opposite the test electrode of the LCBH pellet using a cold press at a pressure of 5 MPa, and tightly adhered. A CR2032-type coin cell was prepared using the resulting laminate, forming an all-solid-state battery. All of these processes were carried out in a dry environment with a dew point of -60 ° C or less.

[0051] (8) Charge / Discharge Test The all-solid-state battery obtained in (7) above was placed in a thermostat set at 60°C, and the charge / discharge current was set at 0.05 mA / cm ２ A constant current charge / discharge test was carried out with the operating voltage range of 1.20 to 0.01 V. The results (charge / discharge curves) are shown in Fig. 2. From Fig. 2, it can be seen that the all-solid-state battery according to the embodiment operated stably without a significant decrease in charge / discharge capacity even after repeated cycles.

[0052] <Comparative Example 1: SiO+3LiBH ４ -LiI / LCBH pellet / Li all-solid-state battery> 3LiBH was used as the solid electrolyte supported on the negative electrode sheet. ４ The same operations as in Example 1 were performed, except that 3LiBH4-LiI was used. As the solid electrolyte solution used in the process of supporting the solid electrolyte on the negative electrode sheet, a solution prepared by dissolving 3LiBH4-LiI in THF and adjusting the 3LiBH4-LiI concentration to 25 wt% was used. The solid electrolyte solution was dropped onto the surface of the negative electrode sheet obtained in (4) of Example 1, and was then wire-coated to penetrate and homogenize the inside of the negative electrode sheet. At the same time, excess solid electrolyte solution was removed. The sheet was then pre-dried in a constant-temperature oven (atmospheric pressure, 60°C, 2 hours). This procedure from the dropwise addition of the solid electrolyte solution to pre-drying was repeated three times. The sheet was then further subjected to vacuum heating and drying in a vacuum constant-temperature oven (vacuum, 120°C, 15 hours) to obtain a negative electrode sheet with a solid electrolyte supported inside. All of these processes were performed in a dry environment with a dew point of -60°C or less. Other processes were performed in the same manner as in Example 1, and an all-solid-state battery was fabricated.

[0053] A charge-discharge test was carried out on the obtained all-solid-state battery under the same conditions as in Example 1. The results are shown in Figure 3. From Figure 3, it can be seen that the all-solid-state battery of Comparative Example 1 hardly worked.

[0054] <Comparative Example 2: SiO+3LiBH ４ -LiI / 3LiBH ４ -LiI pellet / Li all-solid-state battery> 3LiBH as the material for the solid electrolyte layer ４The same operation as in Comparative Example 1 was carried out except that 3LiBH was used instead of LCBH powder in the process of preparing the solid electrolyte layer. ４ The same as Comparative Example 1 except that LiI powder was used.

[0055] The resulting all-solid-state battery was subjected to a charge-discharge test under the same conditions as in Example 1 and Comparative Example 1. The results are shown in Figure 4. From Figure 4, it can be seen that the all-solid-state battery of Comparative Example 2 hardly worked.

[0056] DESCRIPTION OF SYMBOLS 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 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.

2. The boron cluster-type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ The negative electrode layer for an all-solid-state battery according to claim 1, wherein the solid electrolyte composite contains in a molar ratio in the range of 1.1 to 20.

3. The boron cluster-type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ wherein the solid electrolyte composite contains LiCB ９ H １０ :LiCB １１ H １２ at a molar ratio of 7:3, the negative electrode layer for an all-solid-state battery according to claim 2.

4. The silicon-based material is selected from the group consisting of SiO, Si, SiN, SiC, and Si carbon composite, as described in claim 1, for the negative electrode layer of an all-solid-state battery.

5. The negative electrode layer for an all-solid-state battery according to claim 1, wherein the silicon-based material is included 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.

6. The process involves preparing a solid electrolyte solution in which a boron cluster-type solid electrolyte is dissolved in a solvent, and The obtained solid electrolyte solution is impregnated into a sheet containing a silicon-based material, and then dried to obtain a negative electrode layer for an all-solid-state battery. A method for manufacturing a negative electrode layer for an all-solid-state battery, including [the specified component].

7. The method according to claim 6, wherein the solvent comprises at least one selected from the group consisting of water, alcohol-based solvents, tetrahydrofuran, acetonitrile, toluene, N-methylpyrrolidone, dimethyl carbonate, and ethyl acetate.

8. The boron cluster-type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ / LiCB １１ H １２ The method according to claim 6, wherein the solid electrolyte composite contains in a molar ratio in the range of 1.1 to 20.

9. The boron cluster-type solid electrolyte is LiCB ９ H １０ and LiCB １１ H １２ LiCB ９ H １０ : LiCB １１ H １２ The method according to claim 8, wherein the solid electrolyte composite contains the ingredients in a molar ratio of 7:

3.

10. The method according to claim 6, wherein the silicon-based material is selected from the group consisting of SiO, Si, SiN, SiC, and Si carbon composite.

11. The method according to claim 6, wherein the drying is carried out under atmospheric pressure at a temperature of 40 to 180°C for 30 minutes to 5 hours, and further carried out under vacuum at a temperature of 100 to 300°C for 1 to 25 hours.

12. 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 an all-solid-state battery according to any one of claims 1 to 5. All-solid-state battery.

13. The all-solid-state battery according to claim 12, wherein the solid electrolyte layer includes a boron cluster-type solid electrolyte.

14. The all-solid-state battery according to claim 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.