Manufacturing method for solid-state battery

Abstract

To provide a method for manufacturing a solid-state battery that can improve the strength of a solid electrolyte layer and suppress deterioration of battery performance.SOLUTION: In a method for manufacturing a solid-state battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, the solid electrolyte layer includes a solid electrolyte and a filler, and the filler includes an easily meltable material having a melting point or melting temperature of less than 150°C, and the method includes a crack determination step of determining whether cracks have occurred in the solid electrolyte layer, and a heating step of heating the solid-state battery when it is determined in the crack determination step that cracks have occurred in the solid electrolyte layer.SELECTED DRAWING: Figure 3

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] In recent years, technologies related to solid-state batteries using solid electrolytes that have high energy density and high thermal safety have been proposed. Patent Document 1 discloses a technology for the purpose of providing a method for producing a crack-resistant solid electrolyte layer, in which a solid electrolyte composition in which a specific amount of fibrous organic filler having a specific aspect ratio is dispersed is used to form a solid electrolyte layer so that the ratio (D50 / d) of the median diameter D50 of the organic filler in the solid electrolyte layer to the average length d of the organic filler as a starting material is 1 or more and 5 or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-184438 Summary of the Invention [Problem to be solved by the invention]

[0005] The manufacturing process of a solid-state battery may include a step of pressing a laminated solid electrolyte layer and an electrode layer together in order to improve the electrical characteristics of the solid-state battery. In this case, if the solid electrolyte layer contains a reinforcing material such as a filler, cracks may occur in the solid electrolyte layer when the load is removed, due to factors such as a difference in Young's modulus between the reinforcing material and the solid electrolyte particles, which may result in a deterioration in battery performance.

[0006] 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 strength of the solid electrolyte layer and suppress deterioration of battery performance. [Means for solving the problem]

[0007] (1) The present invention relates to a method for manufacturing a solid-state battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, wherein the solid electrolyte layer includes a solid electrolyte and a filler, and the filler includes an easily meltable material having a melting point or melting temperature of less than 150°C, the method comprising: a crack determination step of determining whether or not cracks have occurred in the solid electrolyte layer; and a heating step of heating the solid-state battery when it is determined in the crack determination step that cracks have occurred in the solid electrolyte layer.

[0008] According to the invention (1), it is possible to provide a method for manufacturing a solid state battery that can improve the strength of the solid electrolyte layer and suppress the deterioration of battery performance.

[0009] (2) The method for producing a solid-state battery according to (1), wherein the heating step is a step of heating and pressurizing the solid-state battery.

[0010] According to the invention of (2), the molten, easily meltable material can be suitably filled into the cracks.

[0011] (3) The method for manufacturing a solid-state battery according to (1) or (2), wherein the crack determination step is a step of determining that a crack has occurred in the solid electrolyte layer when the electrical characteristics of the solid-state battery are below a predetermined threshold, and the predetermined threshold is at least one of a predetermined threshold and a threshold determined based on an initial value in a charge / discharge cycle of the solid-state battery.

[0012] According to the invention (3), even if cracks occur in the solid electrolyte layer, the deterioration of the battery performance can be suitably determined.

[0013] (4) The method for producing a solid state battery according to any one of (1) to (3), wherein the filling material includes a fibrous filler.

[0014] According to the fourth aspect of the present invention, the filler can be uniformly dispersed in the solid electrolyte slurry, and the solid electrolyte layer can be given toughness and improved in strength against external pressure.

[0015] (5) The method for producing a solid-state battery according to any one of (1) to (4), wherein the filler includes a fibrous filler and a coating layer that coats a surface of the filler, and at least a portion of the coating layer includes the easily meltable material.

[0016] According to the invention (5), the filler can be uniformly dispersed in the solid electrolyte slurry, and the easily meltable material can be efficiently filled into the cracks that have occurred.

[0017] (6) The method for producing a solid-state battery according to any one of (1) to (5), wherein the easily meltable material is mixed with a material having ion conductivity.

[0018] According to the sixth aspect of the present invention, the deterioration of the battery performance can be more preferably suppressed. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a laminated structure of a solid-state battery according to an embodiment of the present invention. [Figure 2] 3A and 3B are diagrams showing the configuration of a filler contained in a solid electrolyte layer according to an embodiment. [Figure 3] FIG. 2 is a cross-sectional view schematically showing the state of cracks occurring in a solid electrolyte layer. [Figure 4] 1 is a micrograph showing cracks occurring in a solid electrolyte layer. [Figure 5] 1 is a micrograph showing that cracks generated in a solid electrolyte layer are filled with resin. DETAILED DESCRIPTION OF THE INVENTION

[0020] <Solid-state battery> The solid-state battery manufactured by the method for manufacturing a solid-state battery according to the present embodiment has a laminate 10 in which a positive electrode layer 20, a negative electrode layer 30, and a solid electrolyte layer 40 are laminated, as shown in FIG. 1. In FIG. 1, the laminate 10 in which each of the above layers is laminated one by one is shown, but the number of laminations is not particularly limited. The laminate 10 is housed in an exterior body such as a laminate film and used as a solid-state battery.

[0021] (Positive electrode layer) The positive electrode layer 20 includes a positive electrode composite layer 21 and a positive electrode current collector 22.

[0022] The positive electrode composite layer 21 contains a positive electrode active material. The positive electrode composite layer 21 may further contain a solid electrolyte, a conductive assistant, a binder, etc. The solid electrolyte, the conductive assistant, the binder, etc. are not particularly limited, and substances known as electrode materials for solid secondary batteries can be applied.

[0023] The positive electrode active material is not particularly limited, and substances known as positive electrode active materials for solid secondary batteries can be used. As the positive electrode active material, for example, ternary positive electrode materials such as LiCoO2, LiNiO2, NCM (Li(NixCoyMnz)O2, (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1)), layered positive electrode active material particles such as LiVO2, LiCrO2, spinel-type positive electrode active materials such as LiMn2O4, Li(Ni 0.25 Mn 0.75 )2O4, LiCoMnO4, Li2NiMn3O8, olivine-type positive electrode active materials such as LiCoPO4, LiMnPO4, LiFePO4, etc. can be used.

[0024] The positive electrode current collector 22 is not particularly limited, and substances known as positive electrode current collectors for solid secondary batteries can be used. Examples of the positive electrode current collector 22 include metal foils such as stainless steel (SUS) foil and aluminum (Al) foil.

[0025] (Negative electrode layer) The negative electrode layer 30 includes a negative electrode mixture layer 31 and a negative electrode current collector 32 .

[0026] Negative electrode mixture layer 31 contains a negative electrode active material. Negative electrode mixture layer 31 may further contain a solid electrolyte, a conductive additive, a binder, etc. The solid electrolyte, conductive additive, binder, etc. are not particularly limited, and substances known as electrode materials for solid secondary batteries can be used.

[0027] The negative electrode active material is not particularly limited, and any known material can be used as a negative electrode active material for solid secondary batteries. For example, 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; silicon-based materials such as silicon element, silicon alloys and silicon compounds; lithium metal, lithium alloys and metallic indium.

[0028] There are no particular limitations on the material of the negative electrode current collector 32, and any known material can be used as a negative electrode current collector for solid secondary batteries. Examples of the negative electrode current collector include metal foils such as copper (Cu) foil, stainless steel (SUS) foil, and aluminum (Al) foil.

[0029] (Solid electrolyte layer) The solid electrolyte layer 40 includes a solid electrolyte and a filler. In addition to the above, the solid electrolyte layer 40 may also include a binder.

[0030] The solid electrolyte is not particularly limited, but examples thereof include sulfide-based solid electrolytes, oxide-based solid electrolytes, nitride-based solid electrolytes, and halide-based solid electrolytes.

[0031] The binder is not particularly limited, but examples thereof include polyvinylidene fluoride (PVdF), polymethyl methacrylate (PMMA), polyisobutene (PIB), styrene butadiene rubber (SBR), polyethylene-vinyl acetate copolymer (PEVA), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), etc. These may be used alone or in combination of two or more.

[0032] [Filling material] The filler includes an easily meltable material that not only improves the strength of the solid electrolyte layer 40 but also melts the easily meltable material when a crack occurs in the solid electrolyte layer 40, allowing the easily meltable material to flow into the crack and suppress a decrease in battery performance.

[0033] The filler 41 is not particularly limited as long as it contains an easily meltable material, and may be in particulate form, but as shown in Fig. 2, it preferably has a fibrous filler 43 and a coating layer 42 that covers the surface of the filler 43, and the easily meltable material is contained in the coating layer 42. As shown in Fig. 3, it is expected that cracks C will originate from the filler 41, and therefore the presence of the easily meltable material on the surface of the filler 43 allows the easily meltable material to flow efficiently into the cracks C.

[0034] The filler 41 having the coating layer 42 and the filler 43 is preferably a single fiber having a minimum length of 1.0 to 10 μm, a maximum length of 100 to 1000 μm, and an aspect ratio (length-to-length ratio) of 100 or more. This allows the filler 41 to be uniformly dispersed in the solid electrolyte slurry when forming the solid electrolyte layer 40, making it easy to form the solid electrolyte layer 40. In addition, this provides toughness to the solid electrolyte layer 40, improving its strength against external pressure.

[0035] An easily meltable material is a material with a melting point or melting temperature of less than 150°C. Examples of such easily meltable materials include thermoplastic resins such as polyethylene with a melting point of less than 150°C, and resins with melting temperatures of less than 150°C, such as polystyrene, polyvinyl chloride, and ABS resin. By using an easily meltable material with a melting point or melting temperature of less than 150°C, the heating temperature at which cracks occur, as described below, can be set to a temperature lower than the degradation temperature of the binder contained in the solid electrolyte layer 40.

[0036] It is preferable that the easily meltable material is mixed with a material having ion conductivity. This improves ion conductivity when the easily meltable material is filled into the cracks, thereby more preferably suppressing the deterioration of battery performance. Examples of the material having ion conductivity include the above-mentioned solid electrolytes.

[0037] The filler 43 provides toughness to the solid electrolyte layer 40 and improves its strength against external pressure. For example, an organic filler can be used as the filler 43. Materials constituting the organic filler are not particularly limited, but examples include polyethylene terephthalate (PET), polyamide, polyimide, polycarbonate, etc. The melting point or melting temperature of the material constituting the filler 43 is preferably higher than the melting point or melting temperature of the easily meltable material.

[0038] The solid-state battery according to the present embodiment is not particularly limited, but the method for manufacturing the solid-state battery according to the present embodiment can suppress the deterioration of battery performance due to the occurrence of cracks, so that the solid-state battery is preferably a solid-state battery that expands and contracts greatly due to charging and discharging (for example, a lithium metal solid-state battery).

[0039] <Solid-state battery manufacturing method> The method for manufacturing a solid-state battery according to this embodiment includes a crack determination step of determining whether or not cracks have occurred in the solid electrolyte layer 40, and a heating step of heating the solid-state battery if it is determined in the crack determination step that cracks have occurred in the solid electrolyte layer 40. The above steps are performed after the steps of forming at least the positive electrode layer 20, the negative electrode layer 30, and the solid electrolyte layer 40, and the step of integrating the above layers by pressing or the like, i.e., the step of fabricating a solid-state battery. The method for manufacturing a solid-state battery according to this embodiment may also include a charge-discharge cycle test step for confirming the performance of the solid-state battery.

[0040] The process for forming the positive electrode layer 20 and the negative electrode layer 30 is not particularly limited, and may be, for example, a process for preparing an electrode mixture slurry and applying it onto a current collector.

[0041] The process for forming the solid electrolyte layer 40 may include, for example, the following steps: a binder is dissolved in a solvent such as butyl butyrate to prepare a binder solution; a filler is then mixed with the binder solution and stirred; solid electrolyte particles are then mixed with the binder solution and stirred; and an appropriate solvent is added to prepare a solid electrolyte slurry. The solid electrolyte slurry is then applied to the surface of the electrode layer to form the solid electrolyte layer 40.

[0042] The method for pressing the positive electrode layer 20, the negative electrode layer 30, and the solid electrolyte layer 40 to integrate them is not particularly limited, and examples thereof include known methods such as uniaxial pressing and roll pressing.

[0043] The crack determination step is, for example, a step of measuring the electrical characteristics of the solid-state battery and determining that cracks have occurred in the solid electrolyte layer 40 if the electrical characteristics are below a predetermined threshold. Examples of the electrical characteristics of the solid-state battery include internal voltage (V) and discharge capacity (mAh). The predetermined threshold may be, for example, a predetermined specific threshold, a threshold determined based on the initial electrical characteristics in a charge-discharge cycle test (for example, a threshold determined based on the initial internal voltage or initial discharge capacity, and an example of the threshold may be approximately 94.0% to 95.0% of the initial discharge capacity), or a combination thereof. In addition to the above, the crack determination step may also determine whether or not cracks have occurred based on the difference in Young's modulus between the materials. For example, the crack determination step may be a step of determining that cracks have occurred in the solid electrolyte layer 40 if the difference between the Young's modulus of the solid electrolyte layer 40 and the Young's modulus of the filler 43 is 0.5 GPa or more. This is because when pressure is applied to the solid electrolyte layer 40 containing the filler 43, cracks may occur due to differences in how the solid electrolyte particles and the filler are crushed and restored.

[0044] The heating step is a step of heating the solid-state battery when it is determined in the crack determination step that cracks have occurred in the solid electrolyte layer. The heating step may be a step of heating and pressurizing the solid-state battery. This allows the molten easily meltable material to be preferably filled into the cracks. Note that if it is not determined in the crack determination step that cracks have occurred in the solid electrolyte layer, it is preferable not to perform the heating step. This can suppress deterioration of the solid-state battery.

[0045] In the heating step, the temperature to which the solid-state battery is heated is equal to or higher than the melting point or melting temperature of the easily meltable material. The temperature is preferably lower than the degradation temperature of the binder contained in the solid electrolyte layer. Specifically, the temperature is preferably 50°C to 150°C. In the heating step, the pressure to which the solid-state battery is pressurized can be, for example, 1 MPa to 60 MPa.

[0046] In the heating step, the method for heating the solid-state battery is not particularly limited, and may be a method using a heater or hot air, or, if the heating step is a step of heating and pressurizing the solid-state battery, a method using a heat press may be used.

[0047] 4 and 5 are micrographs showing the results of SEM-EDX mapping analysis (C) of a cracked solid electrolyte layer 40 (containing polyethylene particles with a diameter of approximately 10 μm as a filler) after heat pressing at 150°C. The analysis was performed using a field emission scanning electron microscope (FE-SEM) S-4800 (manufactured by Hitachi High-Tech Corporation). Fig. 4 shows the SEM image, and Fig. 5 shows the EDX mapping analysis results.

[0048] 4 and 5, it is clear that the cracks generated in the solid electrolyte layer 40 are filled with carbon (C).

[0049] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Explanation of symbols]

[0050] 10 Solid-state battery (laminated body) 20 Positive electrode layer 30 negative electrode layer 40 Solid electrolyte layer 41 Filling material 42 Coating layer (easily meltable material) 43 Filler

Claims

1. A method for manufacturing a solid-state battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, comprising: the solid electrolyte layer includes a solid electrolyte and a filler, The filler includes an easily meltable material having a melting point or melting temperature of less than 150°C, a crack determination step of determining whether or not cracks have occurred in the solid electrolyte layer; a heating step of heating the solid-state battery when it is determined in the crack determination step that cracks have occurred in the solid electrolyte layer.

2. The method for manufacturing a solid-state battery according to claim 1 , wherein the heating step is a step of heating and pressurizing the solid-state battery.

3. the crack determination step is a step of determining that a crack has occurred in the solid electrolyte layer when an electrical characteristic of the solid-state battery is below a predetermined threshold value; The method for manufacturing a solid-state battery according to claim 1 , wherein the predetermined threshold is at least one of a predetermined threshold and a threshold determined based on an initial value in a charge / discharge cycle of the solid-state battery.

4. The method for manufacturing a solid-state battery according to claim 1 , wherein the filling material includes a fibrous filler.

5. The filling material includes a fibrous filler and a coating layer that coats a surface of the filler, The method for manufacturing a solid-state battery according to claim 1 , wherein at least a portion of the coating layer contains the easily meltable material.

6. The method for manufacturing a solid-state battery according to claim 1 or 2, wherein the easily meltable material is mixed with a material having ion conductivity.

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