Manufacturing method of solid state battery

Abstract

To provide a manufacturing method of a solid state battery capable of improving a bonding property of a solid electrolyte layer in contact with a positive electrode layer with the positive electrode layer.SOLUTION: A manufacturing method of a solid state battery comprises a laminate forming step of forming a solid electrolyte layer-positive electrode layer laminate. The laminate forming step includes: a transfer pressing step of transferring and pressing a first solid electrolyte layer onto a positive electrode active material layer in a positive electrode layer; a first pressurizing step of pressurizing the positive electrode layer to which the first solid electrolyte layer has been transferred and the first solid electrolyte layer; and a second pressurizing step of disposing a second solid electrolyte layer on the first solid electrolyte layer and pressurizing them after the first pressurizing step. A pressing pressure in the transfer pressing step is lower than a pressing pressure in the first pressing step. A content of a binder contained in the first solid electrolyte layer is equal to or higher than a content of the binder contained in the second solid electrolyte layer.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

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

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] Known examples of such secondary batteries include solid-state batteries such as lithium metal batteries and lithium ion secondary batteries, in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer.

[0004] Known technology relating to solid-state batteries includes technology relating to all-solid-state batteries having a first solid electrolyte layer adjacent to a negative electrode and a second solid electrolyte layer located between the first solid electrolyte layer and a positive electrode, where the first solid electrolyte layer has a smaller Young's modulus than the second solid electrolyte layer (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-108202 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology disclosed in Patent Document 1 aims to suppress deterioration of the interfacial contact between the solid electrolyte layer and the positive and negative electrode layers, and to suppress voltage drop during self-discharge. On the other hand, forming the positive electrode active material layer as thick as possible is considered as a means for increasing the capacity of a solid battery. A thick positive electrode active material layer is preferably densified by pressing, during which the positive electrode active material layer is likely to stretch. Therefore, it is preferable that the solid electrolyte layer in contact with the positive electrode active material layer be configured so that it can follow the stretching of the positive electrode active material layer during pressing, thereby improving the bonding strength with the positive electrode active material layer.

[0007] The present invention has been made in view of the above, and has an object to provide a method for manufacturing a solid state battery that can improve the bonding between a solid electrolyte layer in contact with a positive electrode layer and the positive electrode layer. [Means for solving the problem]

[0008] (1) A method for manufacturing a solid-state battery, comprising: a cathode layer including a cathode current collector layer and a cathode active material layer; and a laminate-forming step of laminating a solid electrolyte layer on the cathode active material layer to form a solid electrolyte layer-cathode layer laminate, the laminate-forming step comprising: a transfer press step of transferring and pressing a first solid electrolyte layer onto the cathode active material layer of the cathode layer; a first pressurizing step of pressing the cathode layer to which the first solid electrolyte layer has been transferred and the first solid electrolyte layer; and a second pressurizing step of placing and pressing a second solid electrolyte layer on the first solid electrolyte layer after the first pressurizing step, wherein the press pressure in the transfer press step is lower than the pressurizing pressure in the first pressurizing step, and the first solid electrolyte layer has a binder content equal to or greater than the binder content in the second solid electrolyte layer.

[0009] According to the invention (1), it is possible to provide a method for manufacturing a solid-state battery that can improve the bonding between the positive electrode layer and the solid electrolyte layer that is in contact with the positive electrode layer.

[0010] (2) The method for producing a solid-state battery according to (1), wherein the pressing pressure in the transfer pressing step is lower than the pressing pressure in the second pressing step.

[0011] According to the invention (2), the solid electrolyte layer in contact with the positive electrode layer can easily extend following the positive electrode layer in the second pressurizing step, thereby improving the bondability with the positive electrode layer.

[0012] (3) The method for producing a solid-state battery according to (1) or (2), wherein the thickness of the first solid electrolyte layer is thinner than the thickness of the second solid electrolyte layer.

[0013] According to the invention of (3), the solid electrolyte layer in contact with the positive electrode layer can easily extend following the positive electrode layer, thereby improving the bonding strength with the positive electrode layer.

[0014] (4) The method for producing a solid state battery according to any one of (1) to (3), wherein the content of the binder in the first solid electrolyte layer is 5% by volume or more and 25% by volume or less.

[0015] According to the invention of (4), the solid electrolyte layer in contact with the positive electrode layer can easily extend following the positive electrode layer, thereby improving the bonding strength with the positive electrode layer.

[0016] (5) The method for producing a solid state battery according to any one of (1) to (4), wherein the first solid electrolyte layer contains a fluorine-based binder.

[0017] According to the fifth aspect of the present invention, the first solid electrolyte layer can be easily pressed under high pressure and thinned.

[0018] (6) The method for producing a solid state battery according to any one of (1) to (5) or (2), wherein the first solid electrolyte layer has a thickness of 3 μm or more and 15 μm or less.

[0019] According to the sixth aspect of the present invention, a solid-state battery can be obtained in which the first solid electrolyte layer is preferably thinned.

[0020] (7) The method for producing a solid state battery according to any one of (1) to (6), wherein the pressing pressure in the transfer pressing step is 100 MPa.

[0021] According to the seventh aspect of the invention, the solid electrolyte layer in contact with the positive electrode layer can easily extend in accordance with the positive electrode layer in the first pressurizing step, thereby improving the bondability with the positive electrode layer.

[0022] (8) The method for producing a solid state battery according to any one of (1) to (7), wherein the pressing pressure in the second pressing step is 150 MPa.

[0023] According to the invention of (8), the second solid electrolyte layer is not pressurized too much but is pressurized appropriately, thereby improving the bonding between the second solid electrolyte layer and the third solid electrolyte layer. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a conceptual cross-sectional view showing the configuration of a solid-state battery according to an embodiment of the present invention. [Figure 2A] 1A to 1C are diagrams illustrating some steps in a method for manufacturing a solid-state battery according to an embodiment of the present invention. [Figure 2B] 1A to 1C are diagrams illustrating some steps in a method for manufacturing a solid-state battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] [Solid battery] As shown in Fig. 1, a solid-state battery 1 manufactured by the manufacturing method according to the present invention has an electrode laminate in which an anode layer 2, a solid electrolyte layer 4, and a cathode layer 3 are laminated in this order. In this embodiment, the structure in which the anode layer 2, the solid electrolyte layer 4, the cathode layer 3, the solid electrolyte layer 4, and the anode layer 2 are laminated in this order as shown in Fig. 1 will be described as the laminate structure of the solid-state battery 1. However, the structure of the solid-state battery 1 is not limited to the above. In addition to the electrode laminate shown in Fig. 1, the solid-state battery 1 may have a configuration that can be used in a solid-state battery, such as an exterior body.

[0026] The solid electrolyte layer 4 in the solid battery 1 has at least a first solid electrolyte layer 43 disposed on the cathode layer 3 side and a second solid electrolyte layer 42 disposed adjacent to the first solid electrolyte layer 43. The solid electrolyte layer 4 may also have a third solid electrolyte layer 41 disposed on the anode layer 2 side. In this embodiment, the solid electrolyte layer 4 will be described as being composed of the above three layers. An intermediate layer 5 may be optionally disposed between the anode layer 2 and the solid electrolyte layer 4.

[0027] The solid state battery 1 is not particularly limited, but may be a lithium ion solid state secondary battery or a lithium metal secondary battery.

[0028] (negative electrode layer) The negative electrode layer 2 has a negative electrode active material layer 21 and a negative electrode current collector layer 22. The negative electrode active material layer 21 is not particularly limited and can be made of a material that can be used as a negative electrode active material in a solid-state battery. Examples of the negative electrode active material that makes up the negative electrode active material layer 21 include silicon-based active materials such as lithium metal, lithium alloys, Si, and Si alloys, and lithium titanate (Li4Ti5O 12 transition metal oxides such as TiO2, Nb2O3 and WO3, metal sulfides, metal nitrides, carbon materials such as graphite, soft carbon and hard carbon, metallic indium, etc.

[0029] The negative electrode active material layer 21 may contain other materials that can be contained in a negative electrode active material layer of a solid-state battery. Examples of such materials include a solid electrolyte, a conductive additive, and a binder. Examples of the solid electrolyte include the same solid electrolyte contained in the solid electrolyte layer 4 described below. Examples of the conductive additive include carbon black, natural graphite, carbon fiber, and carbon nanotubes. Examples of the binder include a nitrile polymer, a polyester polymer, an acrylic acid polymer, a cellulose polymer, a styrene polymer, a styrene-butadiene polymer, a vinyl acetate polymer, a urethane polymer, and a fluoroethylene polymer.

[0030] The negative electrode current collector layer 22 is not particularly limited, but may be made of copper, nickel, stainless steel, or the like. Examples of the shape of the negative electrode current collector layer 22 include foil, plate, mesh, nonwoven fabric, and foam. A portion of the negative electrode current collector layer 22 extends in a predetermined direction to form a negative electrode current collector tab 22a.

[0031] (solid electrolyte layer) The solid electrolyte layer 4 is formed between the anode layer 2 and the cathode layer 3. In this embodiment, the solid electrolyte layer 4 has a structure in which a first solid electrolyte layer 43 arranged in contact with the cathode layer, a second solid electrolyte layer 42, and a third solid electrolyte layer 41 arranged on the anode layer side are stacked in this order.

[0032] The first solid electrolyte layer 43 is disposed in contact with the positive electrode active material layer 31 of the positive electrode layer 3. The solid electrolyte constituting the first solid electrolyte layer 43 is not particularly limited, and may be any material that can be used as an electrolyte in a solid-state battery. Examples include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes, and lithium-containing salts, and polymer solid electrolytes such as polyethylene oxide. One type of the above solid electrolytes may be used, or two or more types may be used in combination.

[0033] The first solid electrolyte layer 43 contains a binder in addition to the solid electrolyte material. The binder may be the same as the binder that can be contained in the negative electrode active material layer 21. The content of the binder in the first solid electrolyte layer 43 relative to the total mass of the first solid electrolyte layer 43 is equal to or greater than the content of the binder in the second solid electrolyte layer 42 relative to the total mass of the second solid electrolyte layer 42. The upper limit of the content of the binder in the first solid electrolyte layer 43 is, for example, 25% by mass. The content of the binder in the first solid electrolyte layer 43 is preferably 10 to 30% by mass. This allows the first solid electrolyte layer 43 to easily extend following the positive electrode layer 3 when the positive electrode layer 3 is pressed. Furthermore, the pressing pressure in the transfer pressing step described below can be reduced.

[0034] The first solid electrolyte layer 43 preferably contains a fluorine-based polymer (fluorine-based binder). Examples of fluorine-based binders include PVdF (polyvinylidene fluoride). This makes it easy to perform high-pressure pressing and thinning of the solid electrolyte layer.

[0035] In addition to the solid electrolyte material and binder, the first solid electrolyte layer 43 may contain materials that can be used in the solid electrolyte layer of a solid-state battery.

[0036] The thickness of first solid electrolyte layer 43 (the length of each layer in the stacking direction) is preferably thinner than the thickness of second solid electrolyte layer 42. The thickness of first solid electrolyte layer 43 is preferably, for example, 3 to 15 μm.

[0037] The second solid electrolyte layer 42 is disposed adjacent to the first solid electrolyte layer 43. The solid electrolyte material constituting the second solid electrolyte layer 42 is not particularly limited and may be the same as the solid electrolyte material constituting the first solid electrolyte layer 43. Like the first solid electrolyte layer 43, the second solid electrolyte layer 42 may contain a binder or the like in addition to the solid electrolyte material. The content of the binder in the second solid electrolyte layer 42 is equal to or less than the content of the binder in the first solid electrolyte layer 43. The content of the binder in the second solid electrolyte layer 42 is preferably 10 to 30 mass %. This improves the energy density of the solid battery 1. The second solid electrolyte layer 42 may include a support. The support may be a three-dimensional structure such as a mesh, a woven fabric, a nonwoven fabric, an embossed body, a punched body, an expanded body, or a foamed body. The second solid electrolyte layer 42 may not include the support.

[0038] The thickness of the second solid electrolyte layer 42 (the length of each layer in the stacking direction) is preferably greater than the thickness of the first solid electrolyte layer 43. The thickness of the second solid electrolyte layer 42 is preferably, for example, 10 to 50 μm.

[0039] The third solid electrolyte layer 41 is an optional layer and is disposed on the anode layer side. The third solid electrolyte layer 41 may be disposed adjacent to the anode layer 2. When the solid-state battery 1 has an intermediate layer 5 as shown in FIG. 1 , the third solid electrolyte layer 41 may be disposed adjacent to the intermediate layer 5.

[0040] The solid electrolyte material constituting the third solid electrolyte layer 41 is not particularly limited, and may be the same material as the solid electrolyte material constituting the first solid electrolyte layer 43. Like the first solid electrolyte layer 43, the third solid electrolyte layer 41 may contain a binder or the like in addition to the solid electrolyte material. The content of the binder in the third solid electrolyte layer 41 relative to the total mass of the first solid electrolyte layer 43 is preferably 1 to 20 mass %. This can improve the energy density of the solid battery 1.

[0041] (positive electrode layer) The positive electrode layer 3 has a positive electrode active material layer 31 and a positive electrode current collector layer 32. In this embodiment, the positive electrode layer 3 has a configuration in which two positive electrode active material layers 31 are stacked on both sides of one positive electrode current collector layer 32. However, the configuration of the positive electrode layer 3 is not limited to the above, and the positive electrode layer 3 may have a configuration in which one positive electrode active material layer 31 is stacked on one side of one positive electrode current collector layer 32.

[0042] The positive electrode active material layer 31 is not particularly limited and can be made of a material that can be used as a positive electrode active material for a solid-state battery. Examples of the positive electrode active material that makes up the positive electrode active material layer 31 include LiCoO2, LiNiO2, LiCo x Ni y Mn z O2 (x+y+z=1), LiVO2, LiCrO2, etc., layered positive electrode active material particles, LiMn2O4, Li(Ni 0.25 Mn 0.75Examples of such positive electrode active materials include spinel-type positive electrode active materials such as LiCoPO, LiMnPO, and LiFePO; solid solution oxides (LiMnO-LiMO (M=Co, Ni, etc.)); conductive polymers such as polyaniline and polypyrrole; sulfides such as LiS, CuS, Li-Cu-S compounds, TiS, FeS, MoS, and Li-Mo-S compounds; and mixtures of sulfur and carbon. The positive electrode active material may be one of the above materials, or may be composed of two or more of the above materials.

[0043] The thickness of the positive electrode active material layer 31 (the length of each layer in the stacking direction) is preferably, for example, 3 to 15 μm, which can improve the battery capacity of the solid state battery 1.

[0044] An insulating frame 6 may be provided around the outer periphery of the positive electrode active material layer 31. The insulating frame 6 can prevent short circuits in the solid state battery 1 and improve its strength. In this embodiment, the insulating frame 6 is disposed so as to cover the side surfaces of the two positive electrode active material layers 31 formed on both sides of the positive electrode current collector layer 32. The insulating frame 6 also abuts against a portion of the stacking surface of the positive electrode current collector layer 32, and has a gap through which a positive electrode current collector tab 32a (described later) extends. The material for the insulating frame 6 is not particularly limited, but examples thereof include insulating oxides such as alumina, resins such as polyvinylidene fluoride (PVDF), and rubbers such as styrene-butadiene rubber (SBR).

[0045] The positive electrode current collector layer 32 is not particularly limited, and can be made of, for example, aluminum, stainless steel, conductive carbon (graphite, carbon nanotubes, etc.), etc. Examples of the shape of the positive electrode current collector layer 32 include foil, plate, mesh, nonwoven fabric, and foam. A portion of the positive electrode current collector layer 32 extends in a predetermined direction to form a positive electrode current collector tab 32a.

[0046] (middle class) The intermediate layer 5 is disposed between the anode layer 2 and the solid electrolyte layer 4. For example, when the solid battery 1 is a lithium metal battery, the intermediate layer 5 has the function of uniformly depositing lithium metal. Therefore, the interface between the intermediate layer 5 and the solid electrolyte layer 4 is stabilized. When the solid battery 1 is a lithium metal secondary battery having the intermediate layer 5, the solid battery 1 may be an anode-free battery in which the anode active material layer 21 is not present during the initial charge. In this case, a lithium metal layer is formed as the anode active material layer 21 after the initial charge / discharge.

[0047] The material constituting the intermediate layer 5 is not particularly limited, and examples thereof include metals capable of forming an alloy with lithium and amorphous carbon. Examples of metals capable of forming an alloy with lithium include tin (Sn), silicon (Si), zinc (Zn), magnesium (Mg), gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), and antimony (Sb). The metal capable of forming an alloy with lithium may be nanoparticles. Examples of amorphous carbon include carbon blacks such as acetylene black, furnace black, and ketjen black, coke, and activated carbon. The amorphous carbon may be graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), CNT (carbon nanotube), fullerene, or graphene. The intermediate layer may contain a binder in addition to the above materials.

[0048] [Solid-state battery manufacturing method] A method for manufacturing a solid-state battery according to this embodiment will be described below with reference to Figures 2A and 2B. The method for manufacturing a solid-state battery according to this embodiment is a method for manufacturing a solid-state battery having an electrode stack La in which an anode layer, an intermediate layer, a solid electrolyte layer, and a cathode layer are stacked in this order. The method for manufacturing a solid-state battery according to this embodiment includes a stack formation step of stacking a solid electrolyte layer 4 on the cathode active material layer 31 of the cathode layer 3 to form a solid electrolyte layer-cathode layer stack.

[0049] The laminate forming step includes a transfer pressing step, a first pressure applying step, and a second pressure applying step, in this order.

[0050] As shown in FIG. 2A, the transfer press step is a step of transferring and pressing the first solid electrolyte layer 43 onto the positive electrode active material layer 31 of the positive electrode layer 3. Specific examples of methods for performing the transfer press step include a method of transferring using a solid electrolyte layer transfer sheet. The solid electrolyte layer transfer sheet can be obtained, for example, by dispersing the material constituting the first solid electrolyte layer 43 in a solvent, applying a slurry to a support sheet, and drying the slurry.

[0051] In the transfer press step, the first solid electrolyte layer 43 is transferred onto the cathode active material layer 31 of the cathode layer 3 and pressed under conditions of 50 to 500 MPa at room temperature (e.g., 10 to 35°C). The pressure in the transfer press step is lower than the pressure in the first press step. The pressure in the transfer press step is preferably 100 MPa. The pressure is also preferably lower than the pressure in the second press step. Because the binder content of the first solid electrolyte layer 43 is relatively high, the pressure in the transfer press step can be reduced. Furthermore, by setting the pressure in the transfer press step as low as possible, the amount of stretching of the first solid electrolyte layer 43 in the transfer press step can be reduced. Therefore, room for stretching of the first solid electrolyte layer 43 can be left in the subsequent first press step, etc., and the first solid electrolyte layer 43 can be stretched in accordance with the cathode layer 3. This improves the bonding strength of the first solid electrolyte layer 43 to the cathode active material layer 31.

[0052] The first pressurizing step is a step of pressing the laminate L1 (laminate of the positive electrode layer 3 and the first solid electrolyte layer 43) obtained by the transfer pressing step. The first pressurizing step densifies (increases the density of) the positive electrode active material layer 31 in the positive electrode layer 3. The pressing conditions in the first pressurizing step can be, for example, a temperature of 25 to 100°C and a pressure of 800 to 1200 MPa.

[0053] As shown in Fig. 2B, the second pressurizing step is a step in which, after the first pressurizing step, a second solid electrolyte layer 42 is placed on the first solid electrolyte layer 43 of the laminate L1 (a laminate of a cathode layer 3 and a first solid electrolyte layer 43) and pressurized to obtain a solid electrolyte layer-cathode layer laminate La. The pressing conditions in the second pressurizing step can be, for example, a pressure of 50 to 500 MPa at room temperature (e.g., 10 to 35°C). The pressing conditions in the second pressurizing step are preferably 150 MPa.

[0054] The method for manufacturing a solid-state battery according to this embodiment may include other steps. For example, it may include a step for obtaining the solid-state battery 1 shown in FIG. 1. For example, it may include a step of transferring an intermediate layer 5 to the anode layer 2 to obtain an anode layer-intermediate layer laminate, a step of placing a third solid electrolyte layer 41 on the intermediate layer of the anode layer-intermediate layer laminate and pressing to obtain an anode layer-intermediate layer-solid electrolyte layer laminate, a step of placing two anode layer-intermediate layer-solid electrolyte layer laminates with their solid electrolyte layers facing each other, and placing the solid electrolyte layer-cathode layer laminate La between the facing solid electrolyte layers and pressing them together, etc.

[0055] In each of the above steps, the press joining device is not particularly limited, and a roll press device, a plate press device, and an isostatic press (CIP, WIP) device can be used. When press joining is performed using a roll press device, the conveying directions of the objects to be press joined to the roll press device may be the same direction or different directions.

[0056] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as desired within the scope that does not impair the effects of the present invention. For example, the method for manufacturing a solid-state battery of the present invention may include any steps other than those described above. [Explanation of symbols]

[0057] 1 solid state battery 2. Negative electrode layer 3 Positive electrode layer 31 Positive electrode active material layer 32 Positive electrode current collector layer 4 Solid electrolyte layer 42 Second solid electrolyte layer 43 First solid electrolyte layer

Claims

1. A method for manufacturing a solid-state battery, comprising: a stack-forming step of forming a solid electrolyte layer-positive electrode layer stack by stacking a positive electrode layer including a positive electrode current collector layer and a positive electrode active material layer, and a solid electrolyte layer on the positive electrode active material layer, The laminate forming step includes a transfer pressing step of transferring and pressing a first solid electrolyte layer onto the positive electrode active material layer of the positive electrode layer; a first pressurizing step of pressurizing the positive electrode layer to which the first solid electrolyte layer has been transferred and the first solid electrolyte layer; a second pressurizing step of placing a second solid electrolyte layer on the first solid electrolyte layer and pressurizing the second solid electrolyte layer after the first pressurizing step, the pressing pressure in the transfer pressing step is smaller than the pressing pressure in the first pressing step; a content of the binder contained in the first solid electrolyte layer being equal to or greater than a content of the binder contained in the second solid electrolyte layer;

2. The method for manufacturing a solid-state battery according to claim 1 , wherein the pressing pressure in the transfer pressing step is lower than the pressing pressure in the second pressing step.

3. 3. The method for manufacturing a solid-state battery according to claim 1, wherein the thickness of the first solid electrolyte layer is thinner than the thickness of the second solid electrolyte layer.

4. 3. The method for manufacturing a solid state battery according to claim 1, wherein the content of the binder in the first solid electrolyte layer is 5% by volume or more and 25% by volume or less.

5. The method for manufacturing a solid state battery according to claim 1 , wherein the first solid electrolyte layer contains a fluorine-based binder.

6. The method for manufacturing a solid-state battery according to claim 1 or 2, wherein the first solid electrolyte layer has a thickness of 3 μm or more and 15 μm or less.

7. The method for manufacturing a solid-state battery according to claim 1 or 2, wherein the pressing pressure in the transfer pressing step is 100 MPa.

8. The method for manufacturing a solid-state battery according to claim 1 or 2, wherein the pressing pressure in the second pressing step is 150 MPa.

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