Method for manufacturing solid secondary battery

Abstract

The problem to be solved by the present invention is to provide a method with which it is possible to industrially and advantageously produce a solid secondary battery having a low internal resistance and a high charge / discharge capacity. In order to solve the problem, the present invention provides a method for manufacturing a solid secondary battery, comprising: a first bonding step for obtaining a positive electrode layer-solid electrolyte layer bonded body by pressure bonding a positive electrode active material layer and a solid electrolyte layer; a second bonding step for obtaining a positive electrode layer-solid electrolyte layer-intermediate layer bonded body by pressure bonding the solid electrolyte layer and the intermediate layer of the positive electrode layer-solid electrolyte layer bonded body; a densification step in which the positive electrode layer-solid electrolyte layer-intermediate layer assembly is press-molded in the thickness direction, so that the porosity of the positive electrode active material layer and the solid electrolyte layer is 5% or less; and a third bonding step for obtaining an electrode laminate by pressure bonding the intermediate layer and the negative electrode layer of the positive electrode layer-solid electrolyte layer-intermediate layer bonded body.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a solid secondary battery. Background Art

[0002] In recent years, in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy, research and development related to secondary batteries that contribute to energy efficiency are being carried out. Among secondary batteries, solid secondary batteries having an electrode stack formed by configuring a solid electrolyte layer between a positive electrode layer and a negative electrode layer have attracted much attention due to their improved safety due to the non-flammability of the solid electrolyte and their superiority in terms of higher energy density. In order to improve the characteristics of solid secondary batteries, the provision of an intermediate layer between the solid electrolyte layer and the negative electrode layer has been explored. For example, the provision of a protective layer as an intermediate layer has been explored, wherein the protective layer is more stable than the solid electrolyte in terms of reduction decomposition, has a shear elastic modulus of 2 GPa or more, and has a shear elastic modulus difference of 50 GPa or less from that of the solid electrolyte layer (Patent Document 1).

[0003] [Prior Art Literature]

[0004] (Patent Document)

[0005] Patent Document 1: Japanese Patent Application No. 2022-055389 Summary of the Invention

[0006] [Problems to be solved by the invention]

[0007] Furthermore, in solid-state secondary batteries, the challenge is to increase the charge-discharge capacity. To increase the charge-discharge capacity, solid-state secondary batteries have explored using lithium as the negative electrode active material and increasing the density of the positive electrode active material layer and solid electrolyte layer in the positive electrode layer of the electrode stack. However, even with these densities, if the bonding strength between the positive electrode active material layer and the solid electrolyte layer is low or the bonding area is narrow, short circuits may occur due to increased internal resistance of the electrode stack and current concentration, resulting in a decrease in charge-discharge capacity.

[0008] The present invention has been developed in view of the above circumstances, and its object is to provide a method for industrially advantageously manufacturing a solid secondary battery having low internal resistance and high charge / discharge capacity, thereby contributing to improved energy efficiency.

[0009] [Technical means to solve the problem]

[0010] The present inventors have discovered that, in the manufacture of an electrode stack having an intermediate layer between the negative electrode layer and the solid electrolyte layer, the aforementioned problems can be solved by press-forming the positive electrode layer, the negative electrode layer, and the intermediate layer in the thickness direction, thereby densifying the positive electrode layer and the solid electrolyte layer and then joining the intermediate layer to the negative electrode layer. Consequently, the present invention provides the following inventions.

[0011] (1) A method for manufacturing a solid secondary battery, the solid secondary battery comprising an electrode stack, the electrode stack comprising: a positive electrode layer comprising a positive electrode current collector and a positive electrode active material layer; a negative electrode layer comprising a negative electrode current collector facing the positive electrode active material layer; a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; and an intermediate layer disposed between the negative electrode layer and the solid electrolyte layer; and the positive electrode layer, the solid electrolyte layer, the intermediate layer and the negative electrode layer are respectively bonded to adjacent layers, the method for manufacturing a solid secondary battery comprising: a first bonding step of pressurizing the positive electrode active material layer and the solid electrolyte layer The positive electrode layer-solid electrolyte layer assembly is obtained by bonding; a second bonding step is to press-bond the solid electrolyte layer of the positive electrode layer-solid electrolyte layer assembly with the intermediate layer to obtain a positive electrode layer-solid electrolyte layer-intermediate layer assembly; a high-densification step is to press-form the positive electrode layer-solid electrolyte layer-intermediate layer assembly in the thickness direction to obtain a high-density; and a third bonding step is to press-bond the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly with the negative electrode layer to obtain the electrode stack; and the porosity of the positive electrode active material layer and the solid electrolyte layer after the third bonding step is less than 5%.

[0012] (1) The manufacturing method of the solid secondary battery is to press-form the positive electrode layer-solid electrolyte layer-intermediate layer assembly obtained in the second joining process in the thickness direction by means of a high-density process, so that while the density is increased, the adhesion of the joining interfaces of the positive electrode active material layer, the solid electrolyte layer and the intermediate layer is improved. In addition, since the porosity of the positive electrode active material layer after the third joining process is within the above-mentioned range and is high-density, the capacitance becomes higher. Furthermore, since the porosity of the solid electrolyte layer after the third joining process is within the above-mentioned range and is high-density, the conductivity of the charge transfer medium is improved. As a result, the internal resistance of the obtained solid secondary battery becomes lower, and it has a high charge and discharge capacity.

[0013] (2) The method for manufacturing a solid secondary battery according to (1), wherein the pressure of the press molding in the high-density step is higher than the pressure of the press bonding in any one of the first bonding step, the second bonding step, and the third bonding step.

[0014] According to the method for manufacturing a solid secondary battery of (2), the pressure of the press forming in the high-densification process is high. Therefore, the high-densification process further reduces the porosity of each layer of the positive electrode active material layer, the solid electrolyte layer, and the intermediate layer, and further improves the adhesion of the bonding interface of each layer. As a result, the obtained solid secondary battery has a lower internal resistance and a higher charge and discharge capacity.

[0015] (3) The method for manufacturing a solid secondary battery according to (1) or (2), wherein the pressure of the press-bonding in the second bonding step is higher than the pressure of the press-bonding in the first bonding step.

[0016] According to the method for manufacturing a solid secondary battery of (3), by reducing the pressure of the press bonding in the first bonding step, the positive electrode layer and the solid electrolyte layer of the positive electrode layer-solid electrolyte layer assembly are softened and pre-compressed, and the pressure of the press bonding in the second bonding step is increased. This increases the contact area between the solid electrolyte layer and the intermediate layer while the intermediate layer is soft and has appropriate porosity, thereby improving adhesion. The softness and appropriate porosity of the intermediate layer facilitate uniform transfer of the charge transfer medium to the entire surface of the negative electrode during charging.

[0017] (4) The method for manufacturing a solid secondary battery according to any one of (1) to (3), wherein the pressure of the press bonding in the third bonding step is higher than the pressure of the press bonding in the first bonding step and lower than the pressure of the press bonding in the second bonding step.

[0018] According to the method for manufacturing a solid secondary battery of (4), the pressure of the pressurized bonding in the third bonding step is within the above-mentioned range. Therefore, the intermediate layer and the negative electrode layer can be bonded without excessively pressurizing the intermediate layer, thereby maintaining the intermediate layer in a soft state with appropriate porosity. In addition, the structural collapse of the positive electrode layer and the solid electrolyte layer can be suppressed, short circuits can be prevented, and internal resistance can be reduced.

[0019] (5) A method for manufacturing a solid secondary battery according to any one of (1) to (4), wherein the reduction rate of the porosity of the positive electrode active material layer caused by press forming in the high-densification step is 77% or more, and the reduction rate of the porosity of the solid electrolyte layer caused by press forming is 85% or more.

[0020] The porosity reduction rate is a value calculated by the following formula (1).

[0021] Porosity reduction rate (%) = (porosity before high-densification process - porosity after high-densification process) / porosity before high-densification process × 100 (1)

[0022] According to the method for manufacturing a solid secondary battery of (5), the porosity reduction rate of the positive electrode active material layer and the porosity reduction rate of the solid electrolyte layer after the high-densification process are within the above-mentioned range, so the positive electrode active material layer and the solid electrolyte layer are high-density. As a result, the effective reaction area within the positive electrode active material layer and the solid electrolyte layer is increased, and the adhesion between the interfaces of the layers is improved. Therefore, the internal resistance of the obtained solid secondary battery is further reduced, and the charge and discharge capacity is further increased.

[0023] (6) The method for producing a solid secondary battery according to any one of (1) to (5), wherein the temperature of the press molding in the high-density step is within a range of 60° C. to 200° C.

[0024] According to the method for manufacturing a solid secondary battery of (6), the temperature of the press forming in the high-densification process is within the above-mentioned range. Therefore, the high-densification process further reduces the porosity of each layer of the positive electrode active material layer, the solid electrolyte layer, and the intermediate layer, and more effectively improves the adhesion of the bonding interface of each layer. As a result, the obtained solid secondary battery has a lower internal resistance and a higher charge and discharge capacity.

[0025] (7) The method for producing a solid secondary battery according to any one of (1) to (6), wherein the pressure forming in the density increasing step is performed by isostatic pressing.

[0026] According to the method for manufacturing a solid secondary battery of (7), the press forming in the high-densification process is performed by isostatic pressing. Therefore, the high-densification process uniformly reduces the porosity of each layer of the positive electrode active material layer, the solid electrolyte layer, and the intermediate layer, and uniformly improves the adhesion of the bonding interface of each layer. As a result, the obtained solid secondary battery has a lower internal resistance and a higher charge and discharge capacity.

[0027] (8) The method for manufacturing a solid secondary battery according to any one of (1) to (7), wherein the complex elastic modulus of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly after the high-density step is less than 1 GPa.

[0028] According to the manufacturing method of the solid secondary battery of (8), the composite elastic modulus of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly after the high-densification process is within the above-mentioned range, and the intermediate layer is soft, so the contact area of the interface between the solid electrolyte layer and the intermediate layer, and between the intermediate layer and the negative electrode layer, is increased, which can improve the adhesion. In addition, the intermediate layer follows the expansion and contraction of the negative electrode layer during charging and discharging, which allows the positive electrode layer and the negative electrode layer to react uniformly in the surface and thickness direction. As a result, the internal resistance of the obtained solid secondary battery is further reduced, and current concentration can be suppressed and short circuits can be prevented.

[0029] (9) The method for manufacturing a solid secondary battery according to any one of (1) to (8), wherein the porosity of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly after the high-densification step is within a range of 40% to 70%.

[0030] According to the method for manufacturing a solid secondary battery of (9), the porosity of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly after the high-densification step is within the above-mentioned range, so an electrode stack having pores in the intermediate layer can be obtained. The intermediate layer having pores is flexible and can therefore follow the changes in the thickness of the negative electrode layer that occur with charge and discharge. As a result, the solid secondary battery obtained has a steadily low internal resistance and a stable and high charge and discharge capacity.

[0031] (10) The method for producing a solid secondary battery according to any one of (1) to (9), wherein the intermediate layer contains amorphous carbon particles.

[0032] According to the method for manufacturing a solid secondary battery of (10), the intermediate layer contains amorphous carbon particles, so the conductivity of the charge transfer medium in the intermediate layer is improved. As a result, the obtained solid secondary battery has a lower internal resistance and a more stable and high charge and discharge capacity.

[0033] (Effects of the Invention)

[0034] According to the present invention, a solid secondary battery having low internal resistance and high charge and discharge capacity can be manufactured industrially advantageously. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a cross-sectional view showing an example of a solid secondary battery obtained by the method for manufacturing a solid secondary battery according to one embodiment of the present invention.

[0036] Figure 2 This is a diagram illustrating one step of a method for manufacturing a solid secondary battery according to one embodiment of the present invention, and is a cross-sectional view illustrating a state where a positive electrode layer and a solid electrolyte layer are press-bonded.

[0037] Figure 3 This is a diagram illustrating one step of a method for manufacturing a solid secondary battery according to one embodiment of the present invention, and is a cross-sectional view illustrating a state where a solid electrolyte layer and an intermediate layer are press-bonded.

[0038] Figure 4 This is a diagram illustrating one step of a method for manufacturing a solid secondary battery according to one embodiment of the present invention, and is a cross-sectional view illustrating a state where an intermediate layer and a negative electrode layer are press-bonded. DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments shown below are for illustrative purposes only and are not intended to limit the present invention.

[0040] Figure 1 1 is a cross-sectional view showing an example of a solid secondary battery obtained by a method for manufacturing a solid secondary battery according to an embodiment of the present invention. Figure 1 As shown, the solid secondary battery 1 includes an electrode stack 10 and an outer package 60 that houses the electrode stack 10 .

[0041] The electrode stack 10 is a stack comprising a positive electrode layer 20, a negative electrode layer 30, a solid electrolyte layer 40 disposed between the positive electrode layer 20 and the negative electrode layer 30, and an intermediate layer 50 disposed between the negative electrode layer 30 and the solid electrolyte layer 40. The positive electrode layer 20 includes a positive electrode current collector 21 and a substrate laminated on one surface (at Figure 1 The positive electrode active material layer 22 (the lower surface in the figure) is formed on the positive electrode current collector 21. The positive electrode current collector 21 is connected to the positive electrode terminal 26 via the positive electrode lead 25. The negative electrode layer 30 includes the negative electrode current collector 31 and a metal layer 32 laminated on the surface of the negative electrode current collector 31 on the solid electrolyte layer 40 side. The negative electrode current collector 31 is connected to the negative electrode terminal 36 via the negative electrode lead 35. The negative electrode current collector 31 faces the positive electrode active material layer 22. The positive electrode layer 20, the solid electrolyte layer 40, the intermediate layer 50, and the negative electrode layer 30 are each bonded to the adjacent layers. Parts of the positive electrode terminal 26 and the negative electrode terminal 36 are exposed from the outer packaging body 60. Figure 1 The solid secondary battery 1 is shown in a discharged state. When charging, lithium ions, the charge transfer medium released from the positive electrode active material layer 22, pass through the solid electrolyte layer 40 and the intermediate layer 50 and precipitate on the surface of the metal layer 32 of the negative electrode layer 30, forming a lithium precipitation layer and increasing the thickness of the negative electrode layer 30. Passing through the intermediate layer 50 allows the lithium precipitation layer to be uniformly formed on the surface of the metal layer 32. The lithium precipitation layer functions as a negative electrode active material layer, releasing lithium ions during discharge. Therefore, in the solid secondary battery 1, the thickness of the negative electrode layer 30 changes with charging and discharging.

[0042] The positive electrode active material layer 22, the solid electrolyte layer 40, and the intermediate layer 50 of the electrode stack 10 have pores. The porosity of the positive electrode active material layer 22 and the solid electrolyte layer 40 is set to 5% or less. The porosity of the positive electrode active material layer 22 and the solid electrolyte layer 40 may also be 3% or less. The porosity of the intermediate layer 50 may be greater than that of the positive electrode active material layer 22 and the solid electrolyte layer 40. The porosity of the intermediate layer 50 may be, for example, in the range of 10 times or more and 40 times or less relative to the positive electrode active material layer 22 and the solid electrolyte layer 40. The porosity of the intermediate layer 50 may also be, for example, in the range of 40% or more and 70% or less. The porosity may be, for example, a value calculated as follows: the weight, area, and film thickness of the material constituting the intermediate layer 50 are measured, the volume-based filling rate (%) of the intermediate layer 50 is calculated, and the following formula (2) is used to calculate the porosity based on the obtained filling rate. The porosity is a value measured after the electrode stack 10 is manufactured and before the electrode stack 10 is charged and discharged.

[0043] Porosity (%) = 100 - Filling rate (%) (2)

[0044] The calculation method for the "filling rate" in formula (2) is not limited to the method described above. The filling rate may also be calculated as the percentage of the density of the intermediate layer 50 after molding relative to the true density of the material constituting the intermediate layer 50. Furthermore, the filling rate may be calculated based on the pore volume, which is measured by instrumental analysis using, for example, the BET method, porosimetry, or gas diffusion method. Alternatively, the filling rate may be calculated by image analysis using, for example, a scanning electron microscope.

[0045] The complex elastic modulus of each of the positive electrode active material layer 22, solid electrolyte layer 40, intermediate layer 50, and metal layer 32 of the electrode stack 10 may be, for example, in the following relationship: intermediate layer 50 < metal layer 32 < solid electrolyte layer 40 < positive electrode active material layer 22. The complex elastic modulus of the intermediate layer 50 may be, for example, in the range of 0.1 GPa to 2.0 GPa. The complex elastic modulus of the metal layer 32 may be, for example, in the range of 2 times to 10 times the complex elastic modulus of the intermediate layer 50. The complex elastic modulus of the metal layer 32 may be, for example, in the range of 1.0 GPa to 4.0 GPa. The complex elastic modulus of the solid electrolyte layer 40 may be, for example, in the range of 5 times to 20 times the complex elastic modulus of the metal layer 32. The complex elastic modulus of the solid electrolyte layer 40 may be, for example, in the range of 10 GPa to 50 GPa. The complex elastic modulus of the positive electrode active material layer 22 may be, for example, 2 to 5 times greater than the complex elastic modulus of the solid electrolyte layer 40. The complex elastic modulus of the positive electrode active material layer 22 may be, for example, 50 GPa to 200 GPa. The complex elastic modulus is a value measured by nanoindentation. The complex elastic modulus is a value measured after the electrode stack 10 is manufactured and before the electrode stack 10 is charged or discharged.

[0046] The positive electrode current collector 21 is not particularly limited in material or shape as long as it has the function of collecting current from the positive electrode layer 20. Examples of materials for the positive electrode current collector 21 include aluminum, aluminum alloys, stainless steel, nickel, iron, and titanium, with aluminum, aluminum alloys, and stainless steel being preferred. Examples of the shape of the positive electrode current collector 21 include foil and plate.

[0047] The positive electrode active material layer 22 contains at least one positive electrode active material. There is no particular limitation on the positive electrode active material, and materials used in the positive electrode layer of a general solid secondary battery can be used. As the positive electrode active material, for example, a layered active material containing lithium, a spinel type active material, an olivine type active material, etc. can be used. Specific examples of positive electrode active materials include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNiO2, etc. p Mn q Co r O2 (p + q + r = 1), LiNi p Al q Co r O2 (p + q + r = 1), lithium manganate (LiMn2O4), Li 1+x Mn 2-x-yHeterogeneous element substituted Li-Mn spinel represented by MO4 (x+y=2, M is selected from at least one of Al, Mg, Co, Fe, Ni and Zn), lithium titanate (an oxide containing Li and Ti), lithium metal phosphate (LiMPO4, M is selected from at least one of Fe, Mn, Co and Ni), etc.

[0048] The average particle size of the positive electrode active material can be, for example, in the range of 0.5 μm to 20 μm. In this embodiment, the average particle size is a value measured by a laser diffraction scattering method.

[0049] From the perspective of improving lithium ion conductivity, the positive electrode active material layer 22 may optionally contain a solid electrolyte. Furthermore, a conductive additive may optionally be included to improve conductivity. Furthermore, from the perspective of exhibiting flexibility, a binder may optionally be included. The solid electrolyte, conductive additive, and binder are not particularly limited, and substances used in the positive electrode layer of a general solid secondary battery may be used.

[0050] The material of the positive electrode lead 25 may be the same as or different from that of the positive electrode current collector 21. The positive electrode lead 25 may also be integrally connected to the positive electrode current collector 21. In this embodiment, the positive electrode lead 25 is formed by extending the positive electrode current collector 21 and is integrally connected to the positive electrode current collector 21. The material of the positive electrode terminal 26 may be the same as or different from that of the positive electrode lead 25. The positive electrode terminal 26 may also be integrally connected to the positive electrode lead 25. In this embodiment, the positive electrode terminal 26 and the positive electrode lead 25 are separate components, but are electrically connected.

[0051] The negative electrode current collector 31 is not particularly limited in material or shape as long as it has the function of collecting current from the negative electrode layer 30. Examples of materials for the negative electrode current collector 31 include nickel, copper, and stainless steel. Examples of shapes for the negative electrode current collector 31 include foil and plate.

[0052] As long as the metal layer 32 has the function of densely depositing lithium ions, there are no particular restrictions on the material and shape. As the metal layer 32, a metallic lithium layer or a layer of a metal that can form an alloy with lithium can be used. Examples of metals that can form alloys with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. The metal forming the metal layer 32 can be in powder form or in thin film form. By using the negative electrode layer 30 having this metal layer 32, a uniform lithium deposition layer can be formed on the surface of the metal layer 32.

[0053] The material of the negative electrode lead 35 may be the same as or different from that of the negative electrode current collector 31. The negative electrode lead 35 may also be integrally connected to the negative electrode current collector 31. In this embodiment, the negative electrode lead 35 is formed by extending the negative electrode current collector 31 and is integrally connected to the negative electrode current collector 31. The material of the negative electrode terminal 36 may be the same as or different from that of the negative electrode lead 35. The negative electrode terminal 36 may also be integrally connected to the negative electrode lead 35. In this embodiment, the negative electrode terminal 36 and the negative electrode lead 35 are separate components, but are electrically connected.

[0054] The solid electrolyte layer 40 contains at least one solid electrolyte and can conduct lithium ions between the positive electrode layer 20 and the negative electrode layer 30 via the solid electrolyte.

[0055] The solid electrolyte is not particularly limited as long as it has lithium ion conductivity, and for example, a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, a halide solid electrolyte, or the like can be used.

[0056] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, etc. The sulfide solid electrolyte may have an argyrodite-type crystal structure.

[0057] Examples of oxide solid electrolytes include sodium superionic conductor (Na superionic conductor, NASICON) type oxides, garnet type oxides, and perovskite type oxides. Examples of NASICON type oxides include oxides containing Li, Al, Ti, P, and O (e.g., Li 1.5 Al 0.5 Ti 1.5 (PO4)3). Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., Li7La3Zr2O 12 Examples of perovskite-type oxides include oxides containing Li, La, Ti, and O (eg, LiLaTiO 3 ).

[0058] The average particle size of the solid electrolyte contained in the solid electrolyte layer 40 may be equal to or smaller than the average particle size of the positive electrode active material contained in the positive electrode active material layer 22. Average particle size D50 of the solid electrolyte SE The average particle size D50 of the positive electrode active material Cathode Ratio D50 SE / D50 CathodeIt may be in the range of greater than 0.1 and less than 1.0. The average particle size of the solid electrolyte may be in the range of, for example, 0.5 μm to 10 μm.

[0059] The solid electrolyte layer 40 may also contain a binder. The binder is not particularly limited, and any substance used in a solid electrolyte layer of a general solid secondary battery can be used.

[0060] The solid electrolyte layer 40 may also have a porous substrate inside. As the porous substrate, for example, woven fabric or non-woven fabric can be used. A solid electrolyte having a porous substrate inside has high strength.

[0061] The intermediate layer 50 has electron conductivity and pores through which lithium metal can pass. The pores in the intermediate layer 50 provide flexibility, allowing it to adapt to changes in the thickness of the negative electrode layer 30 that occur with charge and discharge. Therefore, even when the solid secondary battery 1 is repeatedly charged and discharged, the interfacial adhesion between the layers of the electrode stack 10 can be maintained, thereby improving the durability of the solid secondary battery 1.

[0062] The intermediate layer 50 may also include a substance having lithium metal conductivity and a substance having electron conductivity. Amorphous carbon particles, for example, may be used as the substance having lithium metal conductivity. A metal, for example, may be used as the substance having electron conductivity. The metal may also be in the form of particles. The metal particles may be included in the intermediate layer 50 in the form of a mixture with the amorphous carbon particles or in the form of being supported by the amorphous carbon particles. Furthermore, the metal may be present as a film on the surface of the amorphous carbon particles or may be impregnated within the amorphous carbon particles.

[0063] Amorphous carbon particles can include, for example, easily graphitizable carbon (soft carbon) and non-graphitizable carbon (hard carbon). Specific examples of amorphous carbon particles include carbon blacks such as acetylene black, furnace black, and Ketjen black, coke, activated carbon, carbon nanotubes (CNTs), fullerenes, and graphene. Some of the carbon atoms in the amorphous carbon particles can also be replaced with atoms such as boron, phosphorus, sulfur, oxygen, and nitrogen through chemical treatments such as liquid-phase or vapor-phase methods.

[0064] As the metal contained in the intermediate layer 50, particles of a metal that forms an alloy or an intermetallic compound with lithium ions can be used. For example, examples of metals that form an alloy or an intermetallic compound with lithium include Ag, Au, Pt, Pd, Si, Al, Bi, Sn, Zn, Ga, and In.

[0065] When the intermediate layer 50 includes a mixture of amorphous carbon particles and metal particles, the average particle size of the mixture may be smaller than the average particle size of the solid electrolyte contained in the solid electrolyte layer 40. This allows the intermediate layer 50 to penetrate into the gaps between the solid electrolytes present at the interface of the solid electrolyte layer 40, thereby increasing the developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 and improving the adhesion between the solid electrolyte layer 40 and the intermediate layer 50. The average particle size of the amorphous carbon particles may also be, for example, within the range of 0.02 μm to 0.06 μm. The average particle size of the metal particles may also be, for example, within the range of 0.06 to 0.1 μm.

[0066] The outer packaging 60 is capable of expanding and contracting as the thickness of the negative electrode layer 30 changes due to charge and discharge. A laminated film can be used as the material for the outer packaging 60. A laminated film can have a three-layer structure, comprising an inner resin layer, a metal layer, and an outer resin layer, stacked in this order from the inside. Optionally, the outer resin layer can be, for example, a polyamide (nylon) layer or a polyethylene terephthalate (PET) layer, the metal layer can be, for example, an aluminum layer, and the inner resin layer can be, for example, a polyethylene layer or a polypropylene layer.

[0067] A method for manufacturing the solid secondary battery 1 of this embodiment will be described. Figures 2 to 4 This diagram illustrates one step of a method for manufacturing a solid secondary battery according to one embodiment of the present invention. The method for manufacturing a solid secondary battery 1 according to this embodiment includes a first bonding step, a second bonding step, a high-density bonding step, and a third bonding step.

[0068] In the first bonding step, Figure 2 As shown, the positive electrode layer 20 with the positive electrode lead 25 is press-bonded to the solid electrolyte layer 40 to obtain the positive electrode layer-solid electrolyte layer assembly 11. The porosity of the positive electrode active material layer 22 of the positive electrode layer 20 before bonding can be, for example, in the range of 30% to 50%. The porosity of the solid electrolyte layer 40 before bonding can be, for example, in the range of 30% to 50%. The porosity of the positive electrode active material layer 22 before bonding can be equal to or different from the porosity of the solid electrolyte layer 40. The porosity of the solid electrolyte layer 40 before bonding can be, for example, in the range of 0.6 times to 1.7 times the porosity of the positive electrode active material layer 22 before bonding.

[0069] As a method for joining the positive electrode layer 20 and the solid electrolyte layer 40, a pressing method can be used, for example. As a pressing machine, for example, a roller press or a uniaxial forming pressing device can be used. The joining pressure during press joining is, for example, in the range of 50 MPa to 300 MPa, the joining time is, for example, in the range of 0.1 seconds to 5 minutes, and the joining temperature is, for example, in the range of 20°C to 200°C. The reduction rate of the porosity of the positive electrode active material layer 22 caused by press joining in the first joining step can be, for example, in the range of 10% to 60%. The reduction rate of the porosity of the solid electrolyte layer 40 can be, for example, in the range of 10% to 60%. In addition, the reduction rate of the porosity is a value calculated by the following formula (3).

[0070] Porosity reduction rate (%) = (porosity before the first bonding step - porosity after the first bonding step) / porosity before the first bonding step × 100 (3)

[0071] In the second bonding process, Figure 3 As shown, the solid electrolyte layer 40 and the intermediate layer 50 of the positive electrode layer-solid electrolyte layer assembly 11 are press-bonded to obtain the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12. The porosity of the solid electrolyte layer 40 before the second bonding can be, for example, in the range of 25% or more and 40% or less. The porosity of the intermediate layer 50 before the second bonding can be, for example, in the range of 70% or more and 90% or less. The porosity of the solid electrolyte layer 40 before the second bonding can be smaller than the porosity of the intermediate layer 50 before bonding. The porosity of the solid electrolyte layer 40 can also be, for example, in the range of 0.25 times or more and 0.6 times or less relative to the porosity of the intermediate layer 50 before bonding.

[0072] As a method for joining the solid electrolyte layer 40 and the intermediate layer 50 of the positive electrode layer-solid electrolyte layer assembly 11 in the second joining step, for example, pressing can be used. A press machine, for example, can be used. The joining pressure during press joining is, for example, in the range of 100 MPa to 600 MPa, the joining time is, for example, in the range of 0.1 seconds to 5 minutes, and the joining temperature is, for example, in the range of 20°C to 200°C. The joining pressure in the second joining step can be higher than the joining pressure in the first joining step. The joining pressure in the second joining step can also be, for example, in the range of 1.5 times to 12 times the joining pressure in the first joining step. The reduction rate of the porosity of the positive electrode active material layer 22 due to press forming in the second joining step can be, for example, in the range of 20% to 80%. The reduction rate of the porosity of the solid electrolyte layer 40 can be, for example, in the range of 20% to 80%. The reduction rate of the porosity of the intermediate layer 50 may be, for example, within a range of 20% to 60%. The reduction rate of the porosity is a value calculated by the following formula (4).

[0073] Porosity reduction rate (%) = (porosity before the second bonding step - porosity after the second bonding step) / porosity before the second step × 100 (4)

[0074] In the densification step, the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12 obtained in the second joining step is press-formed in the thickness direction to achieve a high density. As a joining method for the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12, isostatic pressing, for example, can be used. As a press, a cold isostatic press (CIP) or a hot isostatic press (HIP) can be used. The forming pressure during press forming is, for example, in the range of 600 MPa to 1200 MPa, the forming time is, for example, in the range of 0.1 seconds to 5 minutes, and the forming temperature is, for example, in the range of 60°C to 200°C. The forming pressure during the densification step can be higher than the joining pressure during press joining in any of the first, second, and third joining steps. The forming pressure during the densification step can also be, for example, in the range of 2 to 24 times the joining pressure of the first joining step. The forming pressure during the densification step can also be, for example, in the range of 1.1 to 12 times the joining pressure of the second joining step. The molding pressure in the high-densification step may be in a range of, for example, 1.2 times or more and 20 times or less relative to the bonding pressure in the third bonding step.

[0075] The reduction rate of the porosity of the positive electrode active material layer 22 caused by the press forming in the high-densification process can be, for example, 77% or more, or can be in the range of 80% or more and 95% or less. The reduction rate of the porosity of the solid electrolyte layer 40 can be, for example, 85% or more, or can be in the range of 88% or more and 95% or less. The reduction rate of the porosity of the intermediate layer 50 can be in the range of 0% or more and 30% or less. In addition, the reduction rate of porosity is a value calculated by the above-mentioned formula (1).

[0076] The densification process is used to densify the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12. The porosity of the positive electrode active material layer 22 and the solid electrolyte layer 40 of the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12 after the densification process can be 5% or less. However, if the intermediate layer 50 is excessively densified, the electrical properties of the electrode stack 10 may be reduced. Therefore, the densification process can be performed by making the porosity of the intermediate layer 50 after the densification process within a range of 40% to 70%. In addition, the densification process can be performed by making the complex elastic modulus of the intermediate layer 50 after the densification process less than 1 GPa.

[0077] In the third bonding step, Figure 4 As shown, the electrode stack 10 is obtained by press-bonding the intermediate layer 50 of the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12 and the negative electrode layer 30 with the negative electrode lead 35 .

[0078] As a method for joining the intermediate layer 50 and the negative electrode layer 30, a pressing method can be used, for example. As a pressing machine, for example, a roller press or a uniaxial forming pressing device can be used. The bonding pressure during press bonding is, for example, in the range of 60 MPa to 500 MPa, the bonding time is, for example, in the range of 0.1 seconds to 5 minutes, and the bonding temperature is, for example, in the range of 20°C to 200°C. The bonding pressure of the third bonding process can be higher than the bonding pressure of the first bonding process and lower than the bonding pressure of the second bonding process. The bonding pressure of the third bonding process can also be in the range of, for example, 1.2 times to 10 times relative to the bonding pressure of the first bonding process. The bonding pressure of the third bonding process can also be in the range of, for example, 0.1 times to 0.9 times relative to the bonding pressure of the second bonding process.

[0079] By the above manufacturing method, the following electrode stack 10 is obtained, wherein the electrode stack 10 comprises: a positive electrode layer 20 having a positive electrode collector 21 and a positive electrode active material layer 22; a negative electrode layer 30 having a negative electrode collector 31 opposite to the positive electrode active material layer 22; a solid electrolyte layer 40 arranged between the positive electrode layer 20 and the negative electrode layer 30; and an intermediate layer 50 arranged between the negative electrode layer 30 and the solid electrolyte layer 40; and the positive electrode layer 20, the solid electrolyte layer 40, the intermediate layer 50 and the negative electrode layer 30 are respectively bonded to adjacent layers.

[0080] The solid secondary battery 1 can be manufactured as follows. The negative electrode lead 35 connected to the positive electrode lead 25 and positive electrode terminal 26 of the obtained electrode stack 10 is connected to the negative electrode terminal 36. The electrode stack 10 is then housed in an outer packaging 60 with the ends of the positive electrode terminal 26 and the negative electrode terminal 36 protruding, and the outer packaging 60 is sealed.

[0081] In the manufacturing method of the solid secondary battery 1 of this embodiment having the above structure, the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12 obtained in the second joining step is press-formed in the thickness direction by a high-density step, and the adhesion of the joining interfaces of the positive electrode active material layer 22, the solid electrolyte layer 40, and the intermediate layer 50 is improved. In addition, since the porosity of the positive electrode active material layer 22 after the third joining step is within the above-mentioned range and is high-density, the capacitance is increased. Furthermore, since the porosity of the solid electrolyte layer 40 after the third joining step is within the above-mentioned range and is high-density, the conductivity of the charge transfer medium is increased. As a result, the internal resistance of the obtained solid secondary battery 1 is reduced, and it has a high charge and discharge capacity.

[0082] In the manufacturing method of the solid secondary battery 1 of this embodiment, when the pressure of the press molding in the high-densification process meets the above-mentioned conditions, the porosity of each layer of the positive electrode active material layer 22, the solid electrolyte layer 40, and the intermediate layer 50 is further reduced by the high-densification process, and the adhesion of the bonding interface of each layer is further improved. In addition, when the reduction rate of the porosity of the positive electrode active material layer 22 and the reduction rate of the porosity of the solid electrolyte layer 40 after the high-densification process are within the above-mentioned range, the positive electrode active material layer 22 and the solid electrolyte layer 40 become high-density. As a result, the effective reaction area within the positive electrode active material layer 22 and the solid electrolyte layer 40 is increased, and the adhesion of the interfaces of each layer is improved. Therefore, the solid secondary battery 1 obtained has a lower internal resistance and a higher charge and discharge capacity. Furthermore, when the temperature of the press molding process in the densification step is within the above-mentioned range, the porosity of each of the positive electrode active material layer 22, the solid electrolyte layer 40, and the intermediate layer 50 is further reduced by the densification step, and the adhesion of the bonding interface of each layer is more reliably improved. Furthermore, when the press molding process in the densification step is performed by isostatic pressing, the porosity of each of the positive electrode active material layer 22, the solid electrolyte layer 40, and the intermediate layer 50 is uniformly reduced by the densification step, and the adhesion of the bonding interface of each layer is uniformly improved.

[0083] In the method for manufacturing the solid secondary battery 1 of this embodiment, when the pressure of the press-bonding in the second bonding step is higher than that of the first bonding step, by reducing the pressure of the press-bonding in the first bonding step, the positive electrode layer 20 and solid electrolyte layer 40 of the positive electrode layer-solid electrolyte layer assembly 11 are softened and pre-compressed, and the pressure of the press-bonding in the second bonding step is increased. This increases the contact area between the solid electrolyte layer 40 and the intermediate layer 50 while maintaining the intermediate layer 50 soft and with appropriate porosity, thereby improving adhesion. The softness and appropriate porosity of the intermediate layer 50 facilitate uniform transfer of the charge transfer medium across the entire surface of the negative electrode during charging, resulting in a higher charge-discharge capacity of the resulting solid secondary battery 1. Furthermore, when the pressure of the press-bonding in the third bonding step is higher than that of the first bonding step but lower than that of the second bonding step, the intermediate layer 50 and the negative electrode layer 30 can be bonded without excessive pressure on the intermediate layer 50, thereby maintaining the intermediate layer 50 soft and with appropriate porosity.

[0084] In the method for manufacturing a solid secondary battery 1 of this embodiment, if the composite elastic modulus of the intermediate layer 50 of the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12 after the high-densification process is within the above-mentioned range, the intermediate layer 50 is soft, so the contact area between the solid electrolyte layer 40 and the intermediate layer 50, and between the intermediate layer 50 and the negative electrode layer 30, is increased, thereby improving adhesion. In addition, the intermediate layer 50 follows the expansion and contraction of the negative electrode layer 30 during charge and discharge, which allows the positive electrode layer 20 and the negative electrode layer 30 to react uniformly in the plane and in the thickness direction. As a result, the resulting solid secondary battery 1 has a lower internal resistance, suppresses current concentration, and prevents short circuits. In addition, in the method for manufacturing a solid secondary battery 1 of this embodiment, if the porosity of the intermediate layer 50 of the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12 after the high-densification process is within the above-mentioned range, an electrode stack 10 having pores in the intermediate layer 50 can be obtained. The porous intermediate layer 50 is flexible and can therefore follow the changes in thickness of the negative electrode layer caused by charge and discharge. As a result, the solid secondary battery 1 obtained has a stably low internal resistance and a stable and high charge and discharge capacity.

[0085] In the method for manufacturing the solid secondary battery 1 of this embodiment, when the intermediate layer 50 contains amorphous carbon particles, the conductivity of the charge transfer medium in the intermediate layer is improved. As a result, the resulting solid secondary battery 1 has a lower internal resistance and a more stable and high charge and discharge capacity.

[0086] As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment.

[0087] For example, in this embodiment, the negative electrode layer 30 has a metal layer 32, but the metal layer 32 may be omitted so that lithium is deposited on the surface of the negative electrode current collector 31. In addition, a layer containing a negative electrode active material that can absorb and release lithium ions may be used instead of the metal layer 32. Examples of negative electrode active materials include lithium transition metal oxides such as lithium titanate, transition metal oxides such as TiO2, Nb2O3, and WOn, Si, SiO, metal sulfides, metal nitrides, and carbon materials such as artificial graphite, natural graphite, graphite, soft carbon, and hard carbon. From the perspective of improving lithium ion conductivity, the negative electrode active material layer may optionally contain a solid electrolyte. In addition, a conductive additive may be optionally included to improve conductivity. Furthermore, from the perspective of exhibiting flexibility, a binder may be optionally included. Regarding the solid electrolyte, conductive additive, and binder, substances commonly used in solid secondary batteries can be used.

[0088] [Example]

[0089] Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples.

[0090] (Example 1)

[0091] (Fabrication of the positive electrode layer)

[0092] As a positive electrode current collector with a positive electrode lead, an aluminum foil having a thickness of 15.0 μm was prepared.

[0093] 80 parts by mass of lithium nickel cobalt manganese composite oxide (NCM622) as the positive electrode active material, 17 parts by mass of argyrodite-type sulfide solid electrolyte as the solid electrolyte, 2 parts by mass of carbon black as the conductive additive, and 1 part by mass of SBR (styrene butadiene rubber)-based binder as the binder were mixed in this ratio. The obtained mixture was dispersed in 43 parts by mass of butyl butyrate to prepare a positive electrode active material layer slurry. A bar coater was used to obtain a unit area weight of 27 mg / cm after drying. 2 The obtained positive electrode active material layer slurry was applied to one surface of the positive electrode current collector and dried to form a positive electrode active material layer with a thickness of 80.0 μm, thereby producing a positive electrode layer. The porosity of the positive electrode active material layer was 45%, and the composite elastic modulus was 0.1 GPa. The porosity of the positive electrode active material layer was calculated using the above formula (2). In addition, the filling rate was calculated as the percentage of the density of the positive electrode active material layer after molding relative to the true density of the positive electrode active material.

[0094] (Fabrication of Solid Electrolyte Layer Transfer Sheet)

[0095] A dispersion of an argyrodite-type sulfide solid electrolyte (average particle size: 3.0 μm) was applied to a support sheet and dried to form a 100 μm thick argyrodite-type sulfide solid electrolyte layer, creating a solid electrolyte layer transfer sheet. The solid electrolyte layer had a porosity of 40% and a complex elastic modulus of 0.2 GPa.

[0096] (Production of intermediate layer transfer sheet)

[0097] 95 parts by mass of Sn particles (average particle size: 0.07 μm) as metal particles, acetylene black (average particle size: 0.05 μm) as amorphous carbon particles, and 5 parts by mass of a PVDF-based binder as a binder were mixed in this ratio. The resulting mixture was dispersed in 1000 parts by mass of NMP (N-methyl-2-pyrrolidone) to prepare an interlayer slurry. The resulting interlayer slurry was applied to a support sheet and dried to a final thickness of 3.0 μm to produce an interlayer transfer sheet. The interlayer had a porosity of 82% and a complex elastic modulus of 0.1 GPa.

[0098] (Fabrication of the negative electrode layer)

[0099] A copper foil having a thickness of 10 μm was prepared as a negative electrode current collector with a negative electrode lead.

[0100] A 40 μm thick lithium foil was rolled and laminated on the surface of the copper foil to produce the negative electrode layer.

[0101] (Fabrication of Electrode Laminate)

[0102] The solid electrolyte layer of the solid electrolyte layer transfer sheet was superimposed on the surface of the positive electrode active material layer of the positive electrode layer. Bonding was performed using a uniaxial press machine under conditions of 90 MPa bonding pressure, 3 minutes bonding time, and room temperature bonding temperature (first bonding step). The support sheet of the solid electrolyte layer transfer sheet was then removed, yielding a positive electrode layer-solid electrolyte layer assembly. Next, the intermediate layer of the intermediate layer transfer sheet was superimposed on the surface of the solid electrolyte layer of the positive electrode layer-solid electrolyte layer assembly. Bonding was performed using a uniaxial press machine under conditions of 290 MPa bonding pressure, 5 minutes bonding time, and room temperature bonding temperature (second bonding step). The support sheet of the intermediate layer transfer sheet was then removed, yielding a positive electrode layer-solid electrolyte layer-intermediate layer assembly. The resulting positive electrode layer-solid electrolyte layer-intermediate layer assembly was press-formed using an isostatic press at a forming pressure of 980 MPa, a forming time of 5 minutes, and a forming temperature of 120°C to achieve high density (densification step). Subsequently, the metal lithium foil of the negative electrode layer was superimposed on the surface of the intermediate layer of the densified positive electrode layer-solid electrolyte layer-intermediate layer assembly and bonded using a uniaxial press at a bonding pressure of 180 MPa, a bonding time of 2 minutes, and a bonding temperature of room temperature (third bonding step). This resulted in an electrode stack. The bonding pressures of the first bonding step, the second bonding step, the forming pressure and forming temperature of the densification step, and the bonding pressure of the third bonding step are shown in Table 1 below.

[0103] (Examples 2-3)

[0104] An electrode laminate was obtained in the same manner as in Example 1 except that the molding temperature in the high-density step was changed to the temperature shown in Table 1 below.

[0105] (Comparative Example 1)

[0106] An electrode laminate was obtained in the same manner as in Example 1 except that the molding temperature in the high-density step was set to room temperature.

[0107] (Comparative Examples 2-3)

[0108] An electrode laminate was obtained in the same manner as in Example 1 except that the molding temperature in the high-density step was set to room temperature and the molding pressure was set to the pressure shown in Table 1 below.

[0109] [Table 1]

[0110]

[0111] [evaluate]

[0112] (Porosity reduction rate)

[0113] The porosity reduction rates of the positive electrode active material layer and solid electrolyte layer during the first bonding step, the second bonding step, and the densification step for Examples 1 to 3 and Comparative Examples 1 to 3, as well as the porosity reduction rates of the intermediate layer during the second bonding step and the densification step, were measured. The results are shown in Table 2.

[0114] (Physical Properties of Electrode Stack)

[0115] The porosity of the positive electrode active material layer, solid electrolyte layer, and intermediate layer of the electrode stacks obtained in Examples 1 to 3 and Comparative Examples 1 to 3, as well as the complex elastic modulus of the intermediate layer, were measured. The results are shown in Table 3 below.

[0116] (Battery characteristics)

[0117] A positive terminal was connected to the positive electrode lead of the electrode stack obtained in Examples 1 to 3 and Comparative Examples 1 to 3, and a negative terminal was connected to the negative electrode lead. The electrode stack was then housed in an outer packaging body so that the ends of the positive and negative terminals protruded, and the outer packaging body was sealed to obtain a solid secondary battery. The DC resistance, 1 / 3C discharge capacity, and 1 / 3C charge and discharge capability of the obtained solid secondary battery were measured using the following methods. Each measurement was performed at 25°C. The results are shown in Table 3 below.

[0118] (DC resistance)

[0119] According to the charging state at 25℃ and SOC 50, the current density is 15.1 mA / cm 2 Voltage drop ΔV (V), current value I (A), positive electrode area Ac (cm 2 ), calculate the DC resistance (Ω·cm) using the following formula 2 ).

[0120] DC resistance (Ω·cm 2 )=voltage drop ΔV(V) / current value I(A)×positive electrode area Ac(cm 2 )

[0121] (1 / 3C discharge capacity)

[0122] The temperature is 25℃, the upper limit voltage of charge is 4.3 V, the lower limit voltage of discharge is 2.65 V, the C rate is 1 / 3C, and the current density is 1.3 mA / cm 2 Perform a charge and discharge test. The discharge capacity after the first charge is defined as the 1 / 3C discharge capacity.

[0123] (1 / 3C charge and discharge possible)

[0124] With the design capacity set at 100%, a charge / discharge capacity of 95-105% at 25°C and 1 / 3C charge / discharge, with no short-circuiting during or after charge / discharge, was considered "○." A "×" was considered if short-circuiting occurred during or after charge / discharge, the charge capacity was excessive relative to the design capacity, or the self-discharge after charge was large.

[0125] [Table 2]

[0126]

[0127] [Table 3]

[0128]

[0129] From the results of Tables 1 to 3, it can be seen that according to the manufacturing methods of Examples 1 to 3, the reduction rate of the porosity of the intermediate layer can be suppressed to a low level, while the reduction rate of the porosity of the positive electrode active material layer and the solid electrolyte layer can be increased. In the electrode stacks obtained in Examples 1 to 3, the porosity of the positive electrode active material layer and the solid electrolyte layer is low, and the porosity of the intermediate layer is kept moderate, so the expanded area ratio of the contact interface between the layers is large. Therefore, the solid secondary battery using this electrode stack has a low internal resistance and a high charge and discharge capacity. In contrast, in the manufacturing methods of Comparative Examples 1 to 3, the reduction rate of the porosity of the positive electrode active material layer and the solid electrolyte layer is low. Therefore, the solid secondary battery using the electrode stacks obtained in Comparative Examples 1 to 3 has a high DC resistance and a low charge and discharge capacity.

[0130] Reference numerals

[0131] 1Solid State Secondary Battery

[0132] 10-electrode stack

[0133] 20 positive electrode layer

[0134] 21 positive electrode collector

[0135] 22 positive electrode active material layer

[0136] 25 positive lead

[0137] 26 Positive terminal

[0138] 30 negative electrode layer

[0139] 31 negative electrode collector

[0140] 32 metal layers

[0141] 35 negative lead

[0142] 36 Negative terminal

[0143] 40 solid electrolyte layer

[0144] 50 middle layer

[0145] 60 outer packaging

Claims

1. A method for manufacturing a solid secondary battery, the solid secondary battery comprising an electrode stack, the electrode stack comprising: a positive electrode layer having a positive electrode current collector and a positive electrode active material layer; a negative electrode layer having a negative electrode current collector opposite to the positive electrode active material layer; a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; and an intermediate layer disposed between the negative electrode layer and the solid electrolyte layer; wherein the positive electrode layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer are respectively bonded to adjacent layers. The manufacturing method of the solid secondary battery includes: a first bonding step of bonding the positive electrode active material layer and the solid electrolyte layer under pressure to obtain a positive electrode layer-solid electrolyte layer bonded body; a second bonding step of press-bonding the solid electrolyte layer and the intermediate layer of the positive electrode layer-solid electrolyte layer assembly to obtain a positive electrode layer-solid electrolyte layer-intermediate layer assembly; a high-density step of press-forming the positive electrode layer-solid electrolyte layer-intermediate layer assembly in the thickness direction to achieve high density; and In a third joining step, the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly is press-joined to the negative electrode layer to obtain the electrode stack; and The porosity of the positive electrode active material layer and the solid electrolyte layer after the third joining step is 5% or less.

2. The method for manufacturing a solid secondary battery according to claim 1, wherein: The pressure of the press molding in the high-densification step is higher than the pressure of the press bonding in any of the first bonding step, the second bonding step, and the third bonding step.

3. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The pressure of the press bonding in the second bonding step is higher than the pressure of the press bonding in the first bonding step.

4. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The pressure of the press bonding in the third bonding step is higher than the pressure of the press bonding in the first bonding step, but lower than the pressure of the press bonding in the second bonding step.

5. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The reduction rate of the porosity of the positive electrode active material layer due to press molding in the high-density step is 77% or more, and the reduction rate of the porosity of the solid electrolyte layer due to press molding is 85% or more.

6. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The temperature of the press molding in the high-densification step is within a range of 60° C. to 200° C.

7. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The pressure forming in the above-mentioned high-density step is performed by isostatic pressing.

8. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The composite elastic modulus of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly after the high-density step is less than 1 GPa.

9. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The porosity of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly after the high-density step is within a range of 40% to 70%.

10. The method for manufacturing a solid secondary battery according to claim 1 or 2, wherein: The intermediate layer contains amorphous carbon particles.

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