Method for producing solid-state battery

Abstract

To provide a method for producing a solid-state battery, with which a short circuit can be suppressed.SOLUTION: There is provided a method for producing a solid-state battery that includes a cathode layer, an anode layer, and a solid electrolyte layer disposed between the cathode layer and the anode layer and that uses a deposition-dissolution reaction of metal lithium. The method includes: a deposition step of depositing a protective layer having Li ion conductivity on a deposition surface while using one side of the solid electrolyte layer as the deposition surface; and a step of, after the deposition step, obtaining a laminate in which the anode layer, the protective layer, the solid electrolyte layer and the cathode layer are laminated in this order and pressing the laminate. In the deposition step, the protective layer is deposited on the deposition surface such that an area of the protective layer is smaller than an area of the solid electrolyte layer when the laminate is planarly viewed from a side of the anode layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a solid-state battery. [Background technology]

[0002] Various techniques have been proposed for solid-state batteries as disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 141241 [Patent Document 2] Japanese Patent Application Publication No. 2023-149739 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses that a protective layer selected from Li and metals that can be alloyed with Li is applied to the negative electrode layer side of a solid electrolyte layer by a vapor deposition method. When applying the protective layer, the protective layer may creep into the positive electrode layer via the side of the solid electrolyte layer, causing a short circuit in the solid battery.

[0005] The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a method for manufacturing a solid-state battery that can suppress short circuits. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A method for manufacturing a 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, the method utilizing a deposition-dissolution reaction of metallic lithium, a film-forming step of forming a protective layer having Li ion conductivity on one surface of the solid electrolyte layer as a film-forming surface; a step of obtaining a laminate in which the negative electrode layer, the protective layer, the solid electrolyte layer, and the positive electrode layer are laminated in this order after the film-forming step, and pressing the laminate, In the film-forming step, the protective layer is formed on the film-forming surface such that an area of the protective layer is smaller than an area of the solid electrolyte layer when the laminate is viewed in plan from the negative electrode layer side.

[0007] <2> In the film-forming step, when the laminate is viewed from above from the negative electrode layer side, the solid electrolyte layer extends outward from all outer edges of the protective layer. <1> A method for manufacturing the solid state battery according to claim 1.

[0008] <3> In the film forming step, the protective layer is formed on the film forming surface by sputtering. <1> or <2> 10. A method for manufacturing the solid state battery according to claim 9.

[0009] <4> The protective layer contains at least one of an In element and an Sn element. <1> ~ <3> 10. A method for producing the solid-state battery according to claim 9.

[0010] <5> A method for manufacturing a 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, the method utilizing a deposition-dissolution reaction of metallic lithium, a film-forming step of forming a protective layer having Li ion conductivity on one surface of the solid electrolyte layer as a film-forming surface; a step of obtaining a laminate in which the negative electrode layer, the protective layer, the solid electrolyte layer, and the positive electrode layer are laminated in this order after the film-forming step, and pressing the laminate, the solid electrolyte layer includes a first solid electrolyte layer and a second solid electrolyte layer, a second solid electrolyte layer formed on the first solid electrolyte layer, the second solid electrolyte layer being laminated on the surface of the first solid electrolyte layer opposite to the first solid electrolyte layer, and the second solid electrolyte layer being pressed to obtain the second solid electrolyte layer. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a method for manufacturing a solid-state battery that can suppress short circuits. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a part of the solid-state battery of Example 1. As shown in FIG. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a part of the solid-state battery of Example 2. As shown in FIG. [Figure 3] FIG. 3 shows a part of the solid-state battery of Example 3, (1) a schematic cross-sectional view and (2) a schematic plan view. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a part of the solid-state battery of Comparative Example 1. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a solid-state battery that does not characterize the present disclosure) can be understood as design matters for a person skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. In the present disclosure, unless otherwise specified, the average particle size of particles is the median diameter (D50) value, which is the particle size at 50% of the cumulative value in the volume-based particle size distribution measured by laser diffraction / scattering particle size distribution measurement.

[0014] 1. First embodiment The present disclosure provides a method for manufacturing a 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, and utilizing a deposition-dissolution reaction of metallic lithium, the method comprising: a film-forming step of forming a protective layer having Li ion conductivity on one surface of the solid electrolyte layer as a film-forming surface; a step of obtaining a laminate in which the negative electrode layer, the protective layer, the solid electrolyte layer, and the positive electrode layer are laminated in this order after the film-forming step, and pressing the laminate, In the film-forming step, the protective layer is formed on the film-forming surface so that the area of the protective layer is smaller than the area of the solid electrolyte layer when the laminate is viewed in plan from the negative electrode layer side.

[0015] Methods for improving the energy density of solid-state batteries include the use of lithium-based active materials such as metallic lithium and the creation of anode-free batteries, which eliminate the need for a negative electrode layer during fabrication. In these cases, methods for improving the cycle and rate characteristics of solid-state batteries include the introduction of a metal protective layer, such as Sn, between the negative electrode layer and the solid electrolyte layer on the solid electrolyte layer side. However, when introducing the protective layer, the protective layer may adhere to the periphery of the solid electrolyte layer or even to the positive electrode side of the solid electrolyte layer, potentially causing a short circuit in the solid-state battery due to contact with the positive electrode terminal. One measure to prevent short circuits when a protective layer is introduced into a solid-state battery is to protect the periphery of the positive electrode with an insulating material such as a polymer insulating film. In the present disclosure, a protective layer that is smaller than the solid electrolyte layer is placed on the negative electrode side of the solid electrolyte layer. By making the protective layer smaller than the solid electrolyte layer, adhesion of the protective layer to the peripheral edge of the solid electrolyte layer or to the positive electrode side of the solid electrolyte layer is prevented, and a short circuit in the solid battery when the protective layer is introduced is suppressed. The present disclosure can prevent a short circuit in a solid-state battery caused by the protective layer wrapping around the side of the solid electrolyte layer and reaching the positive electrode layer during the film formation process. In addition, an insulating member is not required, simplifying the configuration of the solid-state battery.

[0016] The solid-state battery of the present disclosure includes a positive electrode including a positive electrode layer, a negative electrode including a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and utilizes a deposition-dissolution reaction of metallic lithium. The solid-state battery of the present disclosure includes a protective layer between the negative electrode layer and the solid electrolyte layer. In the present disclosure, a solid-state battery refers to a battery containing a solid electrolyte. The solid-state battery may be a semi-solid-state battery that contains a solid electrolyte and a liquid-based material, or an all-solid-state battery that does not contain a liquid-based material. When a set of a positive electrode, a solid electrolyte layer, and a negative electrode is considered as a power generation unit, the solid-state battery may have only one power generation unit or may have two or more power generation units. When the solid-state battery has two or more power generation units, the power generation units may be connected in series or in parallel. When the solid state battery is viewed from above from the positive electrode layer side, the area of the positive electrode layer may be smaller than or the same as the area of the solid electrolyte layer. When the solid-state battery is viewed from above from the negative electrode layer side, the area of the protective layer is smaller than the area of the solid electrolyte layer, which eliminates the need for an insulator around the positive electrode to prevent short circuits. When the aspect ratio is different, such as when the solid state battery has a rectangular shape in plan view, the solid electrolyte layer may extend from the outer edge of the protective layer toward the outside of the protective layer only in the region of the side where the positive electrode terminal is present. When the solid state battery is viewed from above from the negative electrode layer side, the area of the negative electrode layer may be smaller than the area of the solid electrolyte layer, or may be smaller than or the same as the area of the protective layer. The area of the positive electrode layer and the area of the negative electrode layer may be the same or different, and from the viewpoint of suppressing the deposition of Li metal dendrites, the area of the positive electrode layer may be smaller than the area of the negative electrode layer. When the solid state battery is viewed from above from the positive electrode layer side, the solid electrolyte layer may extend outward from all outer edges of the positive electrode layer. When the solid state battery is viewed from above from the negative electrode layer side, the solid electrolyte layer may extend outward from all outer edges of the protective layer. When the solid state battery is viewed from above from the negative electrode layer side, the protective layer may extend outward from all outer edges of the negative electrode layer. When the solid state battery is viewed from above from the negative electrode layer side, the solid electrolyte layer may extend outward from all outer edges of the negative electrode layer.

[0017] The solid-state battery may optionally include an exterior body that houses the positive electrode layer, the negative electrode layer, the solid electrolyte layer, and the like. The material of the exterior body is not particularly limited as long as it is stable against the solid electrolyte, and examples thereof include metals such as aluminum, polypropylene, polyethylene, and resins such as acrylic resin.

[0018] Examples of the shape of the solid-state battery include coin type, laminate type, cylindrical type, and square type.

[0019] The solid-state battery may be a primary battery or a secondary battery. Examples of uses of the solid-state battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the solid-state battery may be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The solid-state battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), or as a power source for electrical appliances such as information processing devices.

[0020] [Protective layer] The protective layer may contain a metal having Li ion conductivity, such as Sn, In, Mg, Ag, Si, Ga, Zn, Sb, Bi, and Al, and may be an alloy containing two or more of these metals, an alloy of one or more of these metals with Li, or at least one of In and Sn. The shape of the protective layer may be any shape as long as the area of the protective layer is smaller than the area of the solid electrolyte layer. The protective layer may have holes therein in a plan view. The shape and number of the holes are not particularly limited. The thickness of the protective layer may be 0.1 μm or more, or 1 μm or less.

[0021] [Positive electrode] The positive electrode includes a positive electrode layer and, if necessary, a positive electrode current collector.

[0022] [Positive electrode layer] The positive electrode layer contains a positive electrode active material, and may also contain a solid electrolyte, a conductive material, a binder, and the like, as necessary.

[0023] The positive electrode active material may be, for example, sulfur alone, a sulfur mixture of sulfur with carbon, phosphorus, and lithium, lithium nickel cobalt aluminum oxide (NCA), LiCoO2, LiNi x Co 1-x O2(0 <x<1)、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Examples of the Li-Mn spinel substituted with different elements include O2, LiMnO2, LiMn2O4, LiNiO2, LiVO2, Li-Mn spinel substituted with different elements, lithium titanate, lithium metal phosphate, LiCoN, Li2SiO3, and Li4SiO4. The Li-Mn spinel substituted with different elements is, for example, LiMn 1.5 Ni 0.5 O4, LiMn 1.5 Al 0.5 O4, LiMn 1.5 Mg 0.5 O4, LiMn 1.5 Co 0.5 O4, LiMn 1.5 Fe 0.5 O4 and LiMn 1.5 Zn 0.5 O4, etc. Lithium titanate is, for example, Li4Ti5O 12 Lithium metal phosphates include, for example, LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4. The shape of the positive electrode active material is not particularly limited, but may be in the form of particles (positive electrode active material particles).The average particle size of the positive electrode active material particles is not particularly limited, and may be 1 nm to 100 μm. A coating layer containing a Li-ion conductive compound may be formed on the surface of the positive electrode active material, because this can suppress the reaction between the positive electrode active material and the solid electrolyte. Examples of Li-ion conductive compounds include LiNbO3 and Li4Ti5O 12, and Li3PO4. The thickness of the coating layer is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the coating layer is, for example, 100 nm or less, and may be 20 nm or less. The coverage of the coating layer on the surface of the positive electrode active material is, for example, 70% or more, and may be 90% or more.

[0024] Known conductive materials can be used, such as carbon materials and metal particles. Examples of carbon materials include acetylene black (AB), furnace black, VGCF, carbon nanotubes, and carbon nanofibers. Among them, from the viewpoint of electron conductivity, at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers may be used. Examples of metal particles include particles of Ni, Cu, Fe, and SUS. The content of the conductive material in the positive electrode layer is not particularly limited.

[0025] Examples of the solid electrolyte include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, hydride solid electrolytes, halide solid electrolytes, and nitride solid electrolytes, as well as organic polymer electrolytes such as polymer electrolytes. A relatively soft sulfide solid electrolyte may be used as the solid electrolyte to prevent the positive electrode layer and the negative electrode layer from peeling off from the solid electrolyte layer and further reduce the resistance of the solid battery. Only one type of solid electrolyte may be used alone, or two or more types may be used in combination.

[0026] Examples of sulfide solid electrolytes include solid electrolytes containing Li, A, and S. The A element is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The sulfide solid electrolyte may further contain at least one of O and a halogen element. Examples of the halogen element (X) include F, Cl, Br, and I. The sulfide solid electrolyte may be glass (amorphous), glass ceramic, or crystalline. When the sulfide solid electrolyte is crystalline, it has a crystalline phase. Examples of the crystalline phase include a Thio-LISICON-type crystalline phase, an LGPS-type crystalline phase, and an argyrodite-type crystalline phase. Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-SiS2, Li2S-GeS2, and Li2S-P2S5-GeS2. The term "Li2S-P2S5" refers to a material made using a raw material composition containing Li2S and P2S5, and the same applies to other terms. The molar ratio of each element in the sulfide solid electrolyte can be controlled by adjusting the content of each element in the raw materials. The molar ratio and composition of each element in the sulfide solid electrolyte can be measured, for example, by ICP atomic emission spectrometry.

[0027] The oxide solid electrolyte may contain, for example, Li element, Z element (Z is Nb, B, Al, Si, P, Examples of oxide solid electrolytes include solid electrolytes containing at least one of Ti, Zr, Mo, W, and S, and O. Examples of oxide solid electrolytes include Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4, and Li 3+x PO4-x N x (1≦x≦3) etc. may also be used. The hydride solid electrolyte contains, for example, Li and a complex anion containing hydrogen. The complex anion may be, for example, (BH4). - , (NH2) - , (AlH4) - , and (AlH6) 3- etc. Examples of halogenated solid electrolytes include LiF, LiCl, LiBr, LiI, and LiI-Al2O3. An example of the nitrogenated solid electrolyte is Li3N.

[0028] The solid electrolyte may be solid electrolyte particles. The average particle size (D50) of the solid electrolyte particles is not particularly limited, but may be 0.1 μm or more and 100 μm or less. The content of the solid electrolyte in the positive electrode layer is not particularly limited, but may be, for example, in the range of 1% to 80% by mass when the total mass of the positive electrode layer is taken as 100% by mass.

[0029] Examples of binders include rubber-based binders and fluoride-based binders. Examples of rubber-based binders include butadiene rubber, hydrogenated butadiene rubber, styrene butadiene rubber (SBR), hydrogenated styrene butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, acrylonitrile butadiene rubber (ABR), and ethylene propylene rubber. Examples of fluoride-based binders include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, and fluororubber. The content of the binder in the positive electrode layer is not particularly limited.

[0030] The thickness of the positive electrode layer is not particularly limited.

[0031] The positive electrode layer can be formed by a conventionally known method. For example, a positive electrode active material and, if necessary, other components are put into a solvent and stirred to prepare a positive electrode slurry, and the positive electrode slurry is applied to one surface of a support such as a positive electrode current collector and dried to obtain a positive electrode layer. Examples of the solvent include butyl acetate, butyl butyrate, heptane, and N-methyl-2-pyrrolidone. The method for applying the positive electrode slurry onto one surface of a support such as a positive electrode current collector is not particularly limited, and examples thereof include a doctor blade method, a metal mask printing method, an electrostatic application method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, and a screen printing method. The support can be appropriately selected from those having self-supporting properties and is not particularly limited, and examples thereof include metal foils such as Cu and Al foils.

[0032] [Positive electrode current collector] The positive electrode current collector may be a known metal that can be used as a current collector for solid-state batteries. Examples of such metals include metal materials containing one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge, and In. Examples of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. The form of the positive electrode current collector is not particularly limited, and it can be in various forms such as a foil form, a mesh form, or the like.

[0033] [Negative electrode] The negative electrode includes a negative electrode layer and, if necessary, a negative electrode current collector.

[0034] [Negative electrode layer] The negative electrode layer is sufficient as long as it is present at least during charging, and may or may not be present during production and full discharge. The negative electrode layer contains a negative electrode active material and may optionally contain at least one of a solid electrolyte, a conductive material, and a binder. The negative electrode layer may contain, as the negative electrode active material, for example, a lithium-based active material, a carbon-based active material, an oxide-based active material, an Si-based active material, or the like. Examples of lithium-based active materials include metallic lithium and lithium alloys, etc. Examples of metal elements contained in lithium alloys other than lithium include Mg, Ag, In, Sn, Si, Ga, Au, and Pt. Examples of carbon-based active materials include graphite, hard carbon, and soft carbon. An example of the oxide-based active material is lithium titanate. Examples of Si-based active materials include simple Si, Si alloys, and silicon oxide. The negative electrode active material may be in the form of particles, for example. The average particle size of the negative electrode active material particles is not particularly limited and may be 1 nm to 100 μm. Examples of the conductive material, solid electrolyte, and binder used in the negative electrode layer include the same conductive materials, solid electrolytes, and binders as those exemplified as the conductive material, solid electrolyte, and binder that can be contained in the positive electrode layer. The thickness of the negative electrode layer may be 0.1 μm or more and 100 μm or less.

[0035] [Negative electrode current collector] The material of the negative electrode current collector may be a material that does not alloy with Li, such as SUS, copper, or nickel. The negative electrode current collector may be in the form of, for example, a foil or a plate. The shape of the negative electrode current collector in plan view is not particularly limited, but may be, for example, a circle, an ellipse, a rectangle, or any polygonal shape. The thickness of the negative electrode current collector varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm.

[0036] [Solid electrolyte layer] The solid electrolyte layer contains a solid electrolyte and, if necessary, a binder and the like. The solid electrolyte layer may be a layer consisting of one layer, or may be a layer consisting of two layers, a first solid electrolyte layer and a second solid electrolyte layer. Examples of the solid electrolyte include the solid electrolytes that can be contained in the positive electrode layer described above. When two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to form a multilayer structure. The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, but may be, for example, 50 mass % or more and 99 mass % or less. Examples of the binder include the binders that can be contained in the positive electrode layer described above. When the solid electrolyte layer contains a binder, the content of the binder may be 0% by mass to 10% by mass with respect to the total amount of the solid electrolyte layer. The thickness of the solid electrolyte layer may be 10 μm or more from the viewpoint of suppressing short circuits in the solid battery, and may be 100 μm or less from the viewpoint of reducing the resistance of the solid battery.

[0037] The solid electrolyte layer can be formed, for example, by the following method. A solid electrolyte layer may be formed by preparing a solid electrolyte slurry containing a solid electrolyte, a binder, and a solvent, and applying the solid electrolyte slurry onto a release film. Examples of the solvent include the solvents that can be used to prepare the positive electrode slurry described above.

[0038] The method for manufacturing a solid-state battery according to the present disclosure includes (1) a film-forming step and (2) a pressing step.

[0039] (1) Film formation process The film-forming step is a step of forming a protective layer having Li ion conductivity on one surface of the solid electrolyte layer as a film-forming surface. In the film-forming step, the protective layer is formed on the film-forming surface so that the area of the protective layer is smaller than the area of the solid electrolyte layer when the laminate is viewed from above from the negative electrode layer side. In the film formation step, when a laminate in which the anode layer, the protective layer, the solid electrolyte layer, and the cathode layer are laminated in this order is viewed from above from the anode layer side, the solid electrolyte layer may extend outward from all outer edges of the protective layer. In the film formation step, the film formation method is not particularly limited, and may be vapor deposition, ion plating, sputtering, chemical vapor deposition (CVD), or the like. In the film-forming step, the protective layer may be formed on the film-forming surface by sputtering in order to form the protective layer uniformly.

[0040] (2) Pressing process The pressing step is a step of obtaining a laminate in which the negative electrode layer, the protective layer, the solid electrolyte layer, and the positive electrode layer are laminated in this order after the film-forming step, and pressing the laminate.

[0041] The positive electrode layer, negative electrode layer, and solid electrolyte layer used in the pressing step may be the same as those exemplified in the solid state battery described above. The pressure for pressing the laminate in the pressing step is not particularly limited, but may be 400 MPa or less, 392 MPa or less, or 300 MPa or less from the viewpoint of suppressing a short circuit in the solid state battery. The pressing method is not particularly limited, and examples thereof include cold isostatic pressing and roll pressing. The solid electrolyte contained in the solid electrolyte layer is not easily deformed by the pressing in the pressing step, and therefore the solid electrolyte contained in the solid electrolyte layer after the pressing is performed can be considered to be the same as the solid electrolyte contained in the solid electrolyte layer before the pressing is performed.

[0042] 2. Second embodiment The present disclosure provides a method for manufacturing a 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, and utilizing a deposition-dissolution reaction of metallic lithium, the method comprising: a film-forming step of forming a protective layer having Li ion conductivity on one surface of the solid electrolyte layer as a film-forming surface; a step of obtaining a laminate in which the negative electrode layer, the protective layer, the solid electrolyte layer, and the positive electrode layer are laminated in this order after the film-forming step, and pressing the laminate, the solid electrolyte layer includes a first solid electrolyte layer and a second solid electrolyte layer, In the film-forming step, one surface of the first solid electrolyte layer is used as the film-forming surface, and the protective layer is formed on the film-forming surface. Then, the second solid electrolyte layer is laminated and pressed on the surface of the first solid electrolyte layer opposite to the film-forming surface, thereby obtaining the solid electrolyte layer.

[0043] When the solid electrolyte layer has a first solid electrolyte layer and a second solid electrolyte layer, in the film formation step, one surface of the first solid electrolyte layer is used as a film formation surface, a protective layer is formed on the film formation surface, and then the second solid electrolyte layer is laminated on the surface opposite to the film formation surface of the first solid electrolyte layer and pressed to obtain the solid electrolyte layer. The pressing method and pressing pressure for the solid electrolyte layer may be the same as the pressing method and pressing pressure for the laminate described above. By forming a two-layer solid electrolyte layer, introducing a protective layer onto the anode layer side of the solid electrolyte layer, and then joining the anode layer side of the solid electrolyte layer to the cathode layer side of the solid electrolyte layer, it is possible to prevent the protective layer from wrapping around the cathode layer side of the solid electrolyte layer and the cathode layer, even if the area of the protective layer is the same as the area of the solid electrolyte layer when viewed from above from the anode layer side of the laminate. In the second embodiment, the area of the laminate surface of the protective layer may be the same as or smaller than the area of the laminate surface of the solid electrolyte layer. [Example]

[0044] Example 1 [Preparation of positive electrode] NCA was used as the positive electrode active material, and a sulfide solid electrolyte was used as the solid electrolyte. Using butyl butyrate as a solvent, NCA, a binder, and a conductive material were mixed so as to have a mass composition ratio of NCA:solid electrolyte:binder:conductive material=84.7:13.4:0.6:1.27 to prepare a positive electrode slurry. Next, the obtained positive electrode slurry was applied onto an aluminum foil serving as a positive electrode current collector with a coating gap of 225 μm. Thereafter, the obtained coating film was pre-dried at 60°C for a predetermined time, and then fully dried at 165°C for 1 hour, and coated on the positive electrode current collector with a basis weight of 18.7 mg / cm 2 , design capacity 3.0mAh / cm 2 A positive electrode having a positive electrode layer of the above formula was obtained. [Preparation of solid electrolyte layer] As the solid electrolyte, sulfide solid electrolyte particles with an average particle size (D50) of 2.0 μm were used. Using butyl butyrate as a solvent, the sulfide solid electrolyte and the binder were mixed so that the mass composition ratio of sulfide solid electrolyte:binder was 92.6:7.4, thereby obtaining a solid electrolyte slurry. Next, the solid electrolyte slurry was applied onto the release film with a coating gap of 325 μm. Thereafter, the resulting coating film was pre-dried at room temperature for about 3 hours and then fully dried at 165°C for 1 hour. Two coated foils with a diameter of 14.5 mm were punched out from the dried coated foil, and the coated surfaces of the two coated foils were overlapped and pressed at 7 tons. After pressing, the release film was peeled off to obtain a free-standing solid electrolyte layer. [Creating protective layer] A protective layer of Sn was formed on the free-standing solid electrolyte layer by sputtering to a thickness of 0.1 μm. In plan view, the area of the protective layer was made smaller than the area of the solid electrolyte layer. When making the area of the protective layer smaller than the area of the solid electrolyte layer, a mask of an appropriate size was applied to the solid electrolyte layer during sputtering. [Preparation of negative electrode] A 1.0 μm thick Mg foil was used as the negative electrode active material. Ni foil was used as the negative electrode current collector. The Mg foil and Ni foil were each punched to a diameter of 14.5 mm, and a negative electrode layer made of Mg foil was formed on the negative electrode current collector, resulting in a negative electrode with the negative electrode layer formed on the negative electrode current collector. [Fabrication of solid-state batteries] The fabricated positive electrode was punched out to a diameter of 11.28 mm, and a fabricated free-standing solid electrolyte layer with a diameter of 14.5 mm was placed between the positive electrode and the fabricated negative electrode to obtain a laminate. The positive electrode terminal was made of Al, and the negative electrode terminal was made of Ni. The laminate was vacuum-sealed in an exterior body made of a laminate film with positive and negative electrode terminals attached to it, to obtain a cell. The sealed cell was isostatically pressed at 392 MPa using CIP (cold isostatic pressing) to produce a laminate cell, which is a solid-state battery.

[0045] FIG. 1 is a schematic cross-sectional view showing a part of the solid-state battery of Example 1. As shown in FIG. The solid-state battery 100 has a positive electrode layer 10, a solid electrolyte layer 20, and a negative electrode layer 30, with a protective layer 40 between the solid electrolyte layer 20 and the negative electrode layer 30. For convenience, the positive electrode current collector, the negative electrode current collector, the positive electrode terminal, the negative electrode terminal, and the laminate film are omitted from Fig. 1. In Example 1, the area of the stacking surface of the positive electrode layer 10 is smaller than the area of the stacking surface of the solid electrolyte layer 20, the area of the stacking surface of the negative electrode layer 30 is smaller than the area of the stacking surface of the solid electrolyte layer 20, the area of the stacking surface of the positive electrode layer 10 is smaller than the area of the stacking surface of the negative electrode layer 30, and the area of the stacking surface of the protective layer 40 is smaller than the area of the stacking surface of the solid electrolyte layer 20. The area of the laminated surface of the protective layer 40 is smaller than the area of the laminated surface of the solid electrolyte layer 20, so that the protective layer 40 is prevented from wrapping around the positive electrode layer 10, and a short circuit can be prevented.

[0046] Example 2 In [Preparation of solid electrolyte layer], two coated foils with a diameter of 14.5 mm were punched out from the dried coated foil, the release films of the two coated foils were peeled off, one was used as the first solid electrolyte layer and the other was used as the second solid electrolyte layer, one surface of the first solid electrolyte layer was used as the film formation surface, a 0.1 μm thick Sn film was formed on the film formation surface by sputtering as a protective layer, and then the second solid electrolyte layer was laminated on the surface opposite to the film formation surface of the first solid electrolyte layer and pressed at 7 tons to obtain a solid electrolyte layer having a protective layer on the surface facing the first solid electrolyte layer. A solid battery was prepared in the same manner as in Example 1, except for this. Fig. 2 is a cross-sectional view showing a part of the solid state battery of Example 2. In Fig. 2, the positive electrode current collector, negative electrode current collector, positive electrode terminal, negative electrode terminal, and laminate film are omitted for convenience. The solid-state battery 200 has a positive electrode layer 10, a second solid electrolyte layer 22, a first solid electrolyte layer 21, and a negative electrode layer 30, and has a protective layer 40 between the first solid electrolyte layer 21 and the negative electrode layer 30. By forming the solid electrolyte layer into two layers and joining the first solid electrolyte layer 21 and the second solid electrolyte layer 22 after introducing the protective layer 40 into the first solid electrolyte layer 21, it is possible to prevent the protective layer 40 from wrapping around the second solid electrolyte layer 22 and the positive electrode layer 10, thereby preventing a short circuit.

[0047] Example 3 In [Preparation of Protective Layer], a solid state battery was prepared in the same manner as in Example 1, except that the protective layer was formed by sputtering only in the region of the side where the positive electrode terminal was present, so that the solid electrolyte layer extended outward from the outer edge of the protective layer in plan view. 3A and 3B are (1) a cross-sectional view and (2) a plan view showing a part of the solid-state battery of Example 3. In Fig. 3, the same components as in Fig. 1 are assigned the same numbers, and the description thereof will be omitted. The solid-state battery 300 has a rectangular shape in a plan view, and the solid electrolyte layer 20 extends outward from the outer edge of the protective layer 40 only in the region 12 on the side where the positive electrode terminal 11 is present. This prevents the protective layer 40 from wrapping around the positive electrode terminal 11, thereby preventing a short circuit.

[0048] (Comparative Example 1) In [Preparation of Protective Layer], a solid state battery was prepared in the same manner as in Example 1, except that the area of the protective layer was set to be the same as the area of the solid electrolyte layer in plan view. Fig. 4 is a cross-sectional view showing a part of the solid state battery of Comparative Example 1. In Fig. 4, the same components as those in Fig. 1 are assigned the same numbers, and the description thereof will be omitted. In the solid-state battery 400, the area of the stacking surface of the negative electrode layer 30 is the same as the area of the stacking surface of the solid electrolyte layer 20, and the area of the stacking surface of the protective layer 40 is the same as the area of the stacking surface of the solid electrolyte layer 20. Since the area of the laminated surface of the protective layer 40 is the same as the area of the laminated surface of the solid electrolyte layer 20, the protective layer 40 spread around the positive electrode layer 10 and came into contact with the positive electrode terminal 11, causing a short circuit.

[0049] From the above, it can be seen that according to the present disclosure, short circuits in solid-state batteries can be suppressed. [Explanation of symbols]

[0050] 10 Positive electrode layer 11 Positive terminal 12 Side area where the positive terminal exists 20 Solid electrolyte layer 21 First solid electrolyte layer 22 Second solid electrolyte layer 30 negative electrode layer 40 protective layer 100 solid state battery 200 solid state battery 300 solid state battery 400 solid state battery

Claims

1. A method for manufacturing a 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, and utilizing a deposition-dissolution reaction of metallic lithium, a film-forming step of forming a protective layer having Li ion conductivity on one surface of the solid electrolyte layer as a film-forming surface; a step of obtaining a laminate in which the negative electrode layer, the protective layer, the solid electrolyte layer, and the positive electrode layer are laminated in this order after the film-forming step, and pressing the laminate, In the film-forming step, the protective layer is formed on the film-forming surface such that an area of the protective layer is smaller than an area of the solid electrolyte layer when the laminate is viewed in plan from the negative electrode layer side.

2. 2. The method for manufacturing a solid-state battery according to claim 1, wherein in the film-forming step, when the laminate is viewed in plan from the negative electrode layer side, the solid electrolyte layer extends outward from all outer edges of the protective layer.

3. The method for manufacturing a solid-state battery according to claim 1 , wherein in the film-forming step, the protective layer is formed on the film-forming surface by sputtering.

4. The method for manufacturing a solid-state battery according to claim 1 , wherein the protective layer contains at least one of an In element and an Sn element.

5. A method for manufacturing a 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, and utilizing a deposition-dissolution reaction of metallic lithium, a film-forming step of forming a protective layer having Li ion conductivity on one surface of the solid electrolyte layer as a film-forming surface; a step of obtaining a laminate in which the negative electrode layer, the protective layer, the solid electrolyte layer, and the positive electrode layer are laminated in this order after the film-forming step, and pressing the laminate, the solid electrolyte layer includes a first solid electrolyte layer and a second solid electrolyte layer, a second solid electrolyte layer formed on the first solid electrolyte layer, the second solid electrolyte layer being laminated on the surface opposite to the first solid electrolyte layer, and the second solid electrolyte layer being pressed to obtain the second solid electrolyte layer.

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