Solid secondary battery and manufacturing method therefor

Abstract

To provide a solid secondary battery with which an increase in internal resistance and internal short-circuiting hardly occurs, and which has a high charge / discharge capacity.SOLUTION: A solid secondary battery 1 comprises an electrode laminate 10 including a cathode layer 20 having a cathode active material layer 22, a solid electrolyte layer 40, an intermediate layer 50, and an anode layer 30, with the cathode layer 20, the solid electrolyte layer 40, the intermediate layer 50, and the anode layer 30 being joined to the adjacent layer, respectively. The composite modulus of the cathode active material layer 22 before the cathode layer 20 and the solid electrolyte layer 40 are joined is less than 30 GPa, the composite modulus of the solid electrolyte layer 40 is less than 15 GPa, the composite modulus of the solid electrolyte layer 40 before the solid electrolyte layer 40 and the intermediate layer 50 are joined is less than 18 GPa, and the composite modulus of the intermediate layer 50 is less than 1 GPa. The composite modulus of each of the cathode active material layer 22, the solid electrolyte layer 40, the intermediate layer 50, and the anode layer 30 of the electrode laminate 10 satisfies the relationship: intermediate layer 50<layer 30<electrolyte layer 40<active material layer 22.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid secondary battery and a method for manufacturing the same. [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. Among secondary batteries, solid-state secondary batteries, which have an electrode stack in which a solid electrolyte layer is disposed between a positive electrode layer and a negative electrode layer, have attracted particular attention due to their superior safety due to the non-flammable nature of the solid electrolyte and their higher energy density. To improve the performance of solid-state secondary batteries, the provision of an intermediate layer between the solid electrolyte layer and the negative electrode layer has been considered. For example, the provision of a protective layer, which is more stable with respect to reductive decomposition than a solid electrolyte and has a shear modulus of 2 GPa or more and a difference in shear modulus from the solid electrolyte layer of 50 GPa or less, has been considered as the intermediate layer (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Application No. 2022-055389 Summary of the Invention [Problem to be solved by the invention]

[0004] Increasing the charge / discharge capacity of solid-state secondary batteries is a challenge. To achieve this, the use of lithium as the negative electrode active material and the densification of the positive electrode active material layer and solid electrolyte layer of the positive electrode layer of the electrode laminate have been considered. However, even if the positive electrode active material layer and solid electrolyte layer are densified, if the adhesion between the positive electrode active material layer and the solid electrolyte layer of the positive electrode layer is too low or the contact area is too small, lithium ions, which serve as the charge transfer medium, may precipitate in locations other than the negative electrode layer during charging. If the precipitation location of the charge transfer medium during charging is inappropriate, the internal resistance of the electrode laminate may increase or an internal short circuit may occur due to current concentration, resulting in a decrease in charge / discharge capacity.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a solid secondary battery that is less likely to cause an increase in internal resistance or an internal short circuit and has a high charge / discharge capacity, and a method for manufacturing the same, which will ultimately contribute to improving energy efficiency. [Means for solving the problem]

[0006] The present inventors have discovered that the above-mentioned problems can be solved by adjusting the composite elastic modulus of each layer when joining adjacent layers in an electrode laminate having a positive electrode layer, a negative electrode 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 have completed the present invention.

[0007] 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 each bonded to an adjacent layer; wherein the positive electrode active material layer has a composite elastic modulus of less than 30 GPa and the solid electrolyte layer has a composite elastic modulus of less than 15 GPa before bonding the positive electrode layer and the solid electrolyte layer; the solid electrolyte layer has a composite elastic modulus of less than 18 GPa and the intermediate layer has a composite elastic modulus of less than 1 GPa before bonding the solid electrolyte layer and the intermediate layer; and the composite elastic moduli of the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer of the electrode laminate satisfy the relationship intermediate layer<negative electrode layer<solid electrolyte layer<positive electrode active material layer.

[0008] In the solid secondary battery (1), the composite elastic modulus of the positive electrode layer and solid electrolyte layer before bonding, and the composite elastic modulus of the solid electrolyte layer and intermediate layer before bonding, are within the above-mentioned ranges. Therefore, the electrode laminate obtained by bonding these layers has high adhesion at the contact interface of each layer. This ensures appropriate deposition position of the charge transfer medium during charging. Furthermore, the composite elastic modulus of each layer of the electrode laminate satisfies the above-mentioned relationship, and the positive electrode active material layer has the highest composite elastic modulus and is a high-density layer, resulting in a high electrical capacity of the positive electrode layer. Therefore, this solid secondary battery is less likely to experience an increase in internal resistance or internal short-circuiting, and has a high charge / discharge capacity.

[0009] (2) The solid secondary battery according to (1), wherein the relative density of the positive electrode active material layer before bonding the positive electrode layer and the solid electrolyte layer is less than 75%, the relative density of the solid electrolyte layer is less than 75%, the relative density of the solid electrolyte layer before bonding the solid electrolyte layer and the intermediate layer is less than 85%, the relative density of the intermediate layer is less than 40%, and the relative density of the intermediate layer is the smallest among the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer of the electrode laminate.

[0010] In the solid secondary battery (2), the relative densities of the positive electrode layer and the solid electrolyte layer before bonding, and the relative densities of the solid electrolyte layer and the intermediate layer before bonding, are within the above-mentioned ranges. Therefore, the electrode laminate obtained by bonding these layers has higher adhesion at the contact interface of each layer. This results in a more appropriate deposition position of the charge transfer medium during charging. Furthermore, since the relative densities of each layer of the electrode laminate satisfy the above-mentioned relationship and the positive electrode active material layer has a high relative density, the electric capacity of the positive electrode layer is higher.

[0011] (3) The solid secondary battery according to (1) or (2), wherein the developed area ratio of the contact interface between each of the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer is 0.2 or more.

[0012] In the solid secondary battery (3), the developed area ratio of the contact interface between each layer of the electrode laminate is within the above range, and the surface area of ​​the contact interface between each layer is large, so the adhesion of the contact interface between each layer of the electrode laminate is further improved, and therefore the deposition position of the charge transfer medium during charging is more appropriate.

[0013] (4) The solid secondary battery according to any one of (1) to (3), wherein the intermediate layer of the electrode laminate has a composite elastic modulus of less than 1 GPa.

[0014] In the solid secondary battery (4), the composite elastic modulus of the intermediate layer, which has the lowest composite elastic modulus among the layers of the electrode laminate, is within the above range. Therefore, the reaction area of ​​the contact interface between the solid electrolyte layer and the intermediate layer and between the negative electrode layer and the solid electrolyte layer can be increased, and the direct current resistance at a high current density can be reduced.

[0015] (5) The solid secondary battery according to any one of (1) to (4), wherein the relative density of the intermediate layer of the electrode laminate is in the range of 30% or more and 60% or less.

[0016] The solid-state secondary battery (5) has an intermediate layer with a relative density within the above range and a flexible intermediate layer, which can adapt to changes in the thickness of the negative electrode layer during charging and discharging. This results in a stable low internal resistance and a stable high charge / discharge capacity. Furthermore, the uniform reaction across the electrode surface and thickness suppresses localized current concentration, contributing to the prevention of short circuits.

[0017] (6) The solid secondary battery according to any one of (1) to (5), wherein the intermediate layer of the electrode laminate contains amorphous carbon particles.

[0018] In the solid secondary battery (6), the intermediate layer contains amorphous carbon particles, which improves the conductivity of the charge transfer medium. This allows the electrode stack to deposit at a more suitable location during charging.

[0019] (7) A solid secondary battery 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 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, wherein the positive electrode layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer each comprise an electrode laminate joined to an adjacent layer, and the developed area ratio of the contact interface between each of the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer is all 0.2 or more.

[0020] In the solid secondary battery (7), the developed area ratio of the contact interface between each layer of the electrode laminate is within the above range, and the surface area of ​​the contact interface between each layer is large, so the electrode laminate has high adhesion at the contact interface between each layer. Therefore, the electrode laminate has an appropriate deposition position for the charge transfer medium during charging. Therefore, this solid secondary battery is less likely to experience an increase in internal resistance or an internal short circuit, and has a high charge / discharge capacity.

[0021] (8) The solid secondary battery according to (7), wherein the developed area ratio of the contact interface between the positive electrode active material layer and the solid electrolyte layer is the highest, the developed area ratio of the contact interface between the solid electrolyte layer and the intermediate layer is the next highest, and the developed area ratio of the contact interface between the intermediate layer and the negative electrode layer is the lowest.

[0022] In the solid secondary battery (8), the developed area ratio of the contact interface between each layer of the electrode stack satisfies the above relationship, and the surface area of ​​the contact interface between the positive electrode active material layer and the solid electrolyte layer is the largest, so the contact interface between the positive electrode active material layer and the solid electrolyte layer has high adhesion, facilitating the transfer of the charge transfer medium between the positive electrode active material layer and the solid electrolyte layer. Therefore, this solid secondary battery has lower internal resistance and higher charge / discharge capacity.

[0023] (9) The solid secondary battery according to (7) or (8), wherein the developed area ratio of the contact interface between the positive electrode active material layer and the solid electrolyte layer is in the range of 1.5 to 3.0 times the developed area ratio of the contact interface between the solid electrolyte layer and the intermediate layer, and the developed area ratio of the contact interface between the solid electrolyte layer and the intermediate layer is in the range of 2.0 to 5.0 times the developed area ratio of the contact interface between the intermediate layer and the negative electrode layer.

[0024] In the solid secondary battery (9), the developed area ratio of the contact interface between the positive electrode active material layer and the solid electrolyte layer and the developed area ratio of the contact interface between the solid electrolyte layer and the intermediate layer are within the above ranges, which further enhances the adhesion of the contact interface between the positive electrode active material layer and the solid electrolyte layer, making it easier for the charge transfer medium to move between the positive electrode active material layer and the solid electrolyte layer. As a result, this solid secondary battery has even lower internal resistance and even higher charge / discharge capacity.

[0025] (10) A method for manufacturing a solid secondary battery comprising an electrode stack including: a cathode layer having a cathode current collector and a cathode active material layer; an anode layer having an anode current collector facing the cathode active material layer; a solid electrolyte layer disposed between the cathode layer and the anode layer; and an intermediate layer disposed between the anode layer and the solid electrolyte layer, wherein the cathode layer, the solid electrolyte layer, the intermediate layer, and the anode layer are each bonded to an adjacent layer, the method comprising: a first bonding step of bonding the cathode active material layer and the solid electrolyte layer to obtain a cathode layer-solid electrolyte layer assembly; a second bonding step of bonding an electrolyte layer and the intermediate layer to obtain a cathode layer-solid electrolyte layer-intermediate layer assembly; and a third bonding step of bonding the intermediate layer of the cathode layer-solid electrolyte layer-intermediate layer assembly and the anode layer to obtain the electrode laminate, wherein the composite elastic modulus of the cathode active material layer before bonding in the first bonding step is less than 30 GPa and the composite elastic modulus of the solid electrolyte layer before bonding is less than 10 GPa, and the composite elastic modulus of the solid electrolyte layer before bonding in the second bonding step is less than 18 GPa and the composite elastic modulus of the intermediate layer before bonding is less than 1 GPa.

[0026] In the method for producing a solid secondary battery (10), the composite elastic modulus of each layer bonded in the first bonding step and the second bonding step is set within the above range, so that an electrode laminate having high adhesion at the contact interface of each layer can be obtained. Therefore, the solid secondary battery obtained by this method for producing a solid secondary battery is less likely to have an increase in internal resistance or an internal short circuit, and has a high charge / discharge capacity. [Effects of the Invention]

[0027] According to the present invention, it is possible to provide a solid secondary battery that is less likely to cause an increase in internal resistance or an internal short circuit and has a high charge / discharge capacity, and a method for producing the same. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a cross-sectional view showing a solid secondary battery according to one embodiment of the present invention. [Figure 2]1 is a cross-sectional photograph showing a contact interface between a positive electrode active material layer and a solid electrolyte layer of a solid secondary battery according to one embodiment of the present invention. [Figure 3] FIG. 2 is a cross-sectional view showing a step of a method for manufacturing a solid secondary battery according to an embodiment of the present invention, illustrating a state in which a positive electrode layer and a solid electrolyte layer are joined together. [Figure 4] FIG. 2 is a cross-sectional view showing a step of a method for manufacturing a solid secondary battery according to an embodiment of the present invention, illustrating a state in which a solid electrolyte layer and an intermediate layer are joined together. [Figure 5] FIG. 2 is a cross-sectional view showing a step of a method for manufacturing a solid secondary battery according to an embodiment of the present invention, illustrating a state in which an intermediate layer and a negative electrode layer are joined together. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below are merely examples of the present invention, and the present invention is not limited to the following.

[0030] FIG. 1 is a cross-sectional view showing a solid secondary battery according to one embodiment of the present invention. As shown in FIG. 1, the solid secondary battery 1 includes an electrode laminate 10 and an exterior body 60 that houses the electrode laminate 10.

[0031] The electrode laminate 10 is a laminate including 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 positive electrode active material layer 22 laminated on one surface (the lower surface in FIG. 1 ) of the positive electrode current collector 21. The positive electrode current collector 21 is connected to a positive electrode terminal 26 via a positive electrode lead wire 25. The negative electrode layer 30 includes a negative electrode current collector 31 and a metal layer 32 laminated on the surface of the negative electrode current collector 31 facing the solid electrolyte layer 40. The negative electrode current collector 31 is connected to a negative electrode terminal 36 via a negative electrode lead wire 35. The negative electrode current collector 31 faces the positive electrode active material layer 22. The positive electrode layer 20, solid electrolyte layer 40, intermediate layer 50, and negative electrode layer 30 are each bonded to adjacent layers. Portions of the positive electrode terminal 26 and negative electrode terminal 36 are exposed from the exterior casing 60. The solid secondary battery 1 shown in FIG. 1 is in a discharged state. When the solid secondary battery 1 is charged, lithium ions, which serve as a charge transfer medium, are released from the positive electrode active material layer 22 and pass through the solid electrolyte layer 40 and intermediate layer 50. They are deposited on the surface of the metal layer 32 of the negative electrode layer 30, forming a lithium deposit layer, and the thickness of the negative electrode layer 30 increases. By passing through the intermediate layer 50, a lithium deposit layer can be uniformly formed on the surface of the metal layer 32. The lithium deposit layer acts as a negative electrode active material layer and releases lithium ions during discharge. Therefore, the thickness of the negative electrode layer 30 of the solid secondary battery 1 changes during charge and discharge.

[0032] The composite 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 laminate 10 satisfies the relationship intermediate layer 50<metal layer 32<solid electrolyte layer 40<positive electrode active material layer 22. The composite elastic modulus of the intermediate layer 50 may be, for example, in the range of 0.1 GPa to 2.0 GPa. The composite elastic modulus of the metal layer 32 may be, for example, in the range of 2 to 10 times the composite elastic modulus of the intermediate layer 50. The composite elastic modulus of the metal layer 32 may be, for example, in the range of 1.0 GPa to 4.0 GPa. The composite elastic modulus of the solid electrolyte layer 40 may be, for example, in the range of 5 to 20 times the composite elastic modulus of the metal layer 32. The composite elastic modulus of the solid electrolyte layer 40 may be, for example, in the range of 10 GPa to 50 GPa. The composite elastic modulus of the positive electrode active material layer 22 may be, for example, in the range of 2 to 5 times the composite elastic modulus of the solid electrolyte layer 40. The composite elastic modulus of the positive electrode active material layer 22 may be, for example, in the range of 50 GPa to 200 GPa. The composite elastic modulus is a value measured by a nanoindentation method. The composite elastic modulus is a value measured after the electrode stack 10 is manufactured and before the electrode stack 10 is charged and discharged.

[0033] Of the layers in the electrode stack 10, the intermediate layer 50 has the smallest relative density. The relative density of the intermediate layer 50 may be, for example, in the range of 30% to 60%. The relative densities of the positive electrode active material layer 22, the solid electrolyte layer 40, and the metal layer 32 may be, for example, in the range of 1.5 to 3.3 times. The relative densities of the positive electrode active material layer 22, the solid electrolyte layer 40, and the metal layer 32 may be, for example, 95% or more. The relative density is a value calculated, for example, by the following formula (1). In formula (1), the "packing density" can be calculated by measuring the area density and thickness of each layer. Relative density (%) = Packing density (g / cc) / True density (g / cc) × 100 (1)

[0034] The method for calculating the relative density is not limited to the above method, and it may be calculated by instrumental analysis using a BET method, a porosimeter, gas diffusion, etc., or image analysis using a scanning electron microscope, etc. The relative density is a value measured after the electrode stack 10 is manufactured and before charging and discharging the electrode stack 10.

[0035] The composite elastic modulus of the positive electrode active material layer 22 before bonding the positive electrode layer 20 and the solid electrolyte layer 40 is less than 30 GPa, and the composite elastic modulus of the solid electrolyte layer 40 is less than 15 GPa. Details of the composite elastic modulus and relative density of the positive electrode active material layer 22 and the solid electrolyte layer 40 before bonding will be described later.

[0036] The composite elastic modulus of the solid electrolyte layer 40 before bonding to the intermediate layer 50 is less than 18 GPa, and the composite elastic modulus of the intermediate layer 50 is less than 1 GPa. Details of the composite elastic modulus and relative density of the solid electrolyte layer 40 and intermediate layer 50 before bonding will be described later.

[0037] The developed area ratio (Sdr) of the contact interface between each of the positive electrode active material layer 22, the solid electrolyte layer 40, the intermediate layer 50, and the metal layer 32 of the electrode laminate 10 may be, for example, 0.2 or more. The developed area ratio is an index showing how much the surface area of ​​a defined region has increased relative to the area of ​​the defined region.

[0038] 2 is a cross-sectional photograph showing the contact interface between the solid electrolyte layer and the intermediate layer of a solid secondary battery according to one embodiment of the present invention. The method for measuring the developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 will be described with reference to FIG. 2, taking the developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 as an example. Any two points (A and B in FIG. 2) are set on a cross-sectional photograph of the solid electrolyte layer 40 and the intermediate layer 50. The linear distance between the two points (hereinafter referred to as the AB linear length) is measured, and the square of the AB linear length is defined as the area of ​​the defined region. The distance of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 between the two points (hereinafter referred to as the AB interface length) is measured, and the square of the AB interface length is defined as the surface area of ​​the defined region. The area of ​​the defined region obtained [(AB linear length) 2 ] and the surface area of ​​the defined region [(AB interface length)2 ] and calculate the development area ratio using the following formula. Development area ratio = {(AB interface length) 2 -(AB straight line length) 2} / (AB straight line length) 2

[0039] The developed area ratio of each layer of the electrode laminate 10 may be such that the developed area ratio of the contact interface between the positive electrode active material layer 22 and the solid electrolyte layer 40 is the highest, the developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 is the next highest, and the developed area ratio of the contact interface between the intermediate layer 50 and the metal layer 32 is the lowest. The developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 may be, for example, in a range of 1.5 to 3.0 times the developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50. The developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 may be, for example, in a range of 2.0 to 3.0. The developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 may be, for example, in a range of 2.0 to 5.0 times the developed area ratio of the contact interface between the intermediate layer 50 and the metal layer 32. The developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 may be, for example, in the range of 1.0 to 2.0. The developed area ratio of the contact interface between the intermediate layer 50 and the metal layer 32 may be, for example, in the range of 0.1 to 1.0.

[0040] There are no particular limitations on the material or shape of the positive electrode current collector 21, 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, and among these, aluminum, aluminum alloys, and stainless steel are preferred. Examples of the shape of the positive electrode current collector 21 include a foil shape and a plate shape.

[0041] The positive electrode active material layer 22 contains at least one type of positive electrode active material. There are no particular limitations on the positive electrode active material, and any material used in the positive electrode layers of general solid secondary batteries 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 the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNi p Mn q Co r O2(p+q+r=1), LiNi p Al q Co r O2 (p+q+r=1), lithium manganese oxide (LiMn2O4), Li 1+x Mn 2-x-y Examples include heteroelement-substituted Li-Mn spinel represented by MO4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (oxide containing Li and Ti), and lithium metal phosphate (LiMPO4, M=at least one selected from Fe, Mn, Co, and Ni).

[0042] The average particle size of the positive electrode active material may be, for example, in the range of 1 μm to 20 μm. In this embodiment, the average particle size is a value measured by a laser diffraction scattering method.

[0043] The positive electrode active material layer 22 may optionally contain a solid electrolyte from the viewpoint of improving lithium ion conductivity. It may also optionally contain a conductive additive to improve conductivity. Furthermore, it may also optionally contain a binder from the viewpoint of exhibiting flexibility, etc. There are no particular limitations on the solid electrolyte, conductive additive, and binder, and those used in the positive electrode layers of general solid secondary batteries may be used.

[0044] The material of the positive electrode lead wire 25 may be the same as or different from the material of the positive electrode current collector 21. The positive electrode lead wire 25 may be integrally connected to the positive electrode current collector 21. In this embodiment, the positive electrode lead wire 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 the material of the positive electrode lead wire 25. The positive electrode terminal 26 may be integrally connected to the positive electrode lead wire 25. In this embodiment, the positive electrode terminal 26 and the positive electrode lead wire 25 are separate members and are electrically connected to each other.

[0045] The material and shape of the negative electrode current collector 31 are not particularly limited 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 the shape of the negative electrode current collector 31 include a foil shape, a plate shape, and the like.

[0046] The metal layer 32 is not particularly limited in material or shape as long as it has the function of densely depositing lithium ions. A metallic lithium layer or a layer of a metal that forms an alloy with lithium can be used as the metal layer 32. Examples of metals that form an alloy with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. The metal that forms the metal layer 32 may be in the form of a powder or a thin film. By using the anode layer 30 having this metal layer 32, a uniform lithium deposit layer can be formed on the surface of the metal layer 32.

[0047] The material of the negative electrode lead wire 35 may be the same as or different from the material of the negative electrode current collector 31. The negative electrode lead wire 35 may be integrally connected to the negative electrode current collector 31. In this embodiment, the negative electrode lead wire 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 the material of the negative electrode lead wire 35. The negative electrode terminal 36 may be integrally connected to the negative electrode lead wire 35. In this embodiment, the negative electrode terminal 36 and the negative electrode lead wire 35 are separate members and are electrically connected to each other.

[0048] The solid electrolyte layer 40 contains at least one type of solid electrolyte. The solid electrolyte layer 40 can conduct lithium ions between the positive electrode layer 20 and the negative electrode layer 30 via the solid electrolyte.

[0049] The solid electrolyte is not particularly limited as long as it has lithium ion conductivity, but for example, a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, a halide solid electrolyte, etc. can be used.

[0050] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, etc. The sulfide solid electrolyte may have an argyrodite-type crystal structure.

[0051] Examples of oxide solid electrolytes include 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 Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., LiLaZrO 12 Examples of perovskite oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3).

[0052] The average particle size of the solid electrolyte contained in solid electrolyte layer 40 may be equal to or smaller than the average particle size of the cathode active material contained in cathode active material layer 22. The ratio D50SE / D50Cathode of the average particle size D50SE of the solid electrolyte to the average particle size D50Cathode of the cathode active material may be greater than 0.1 and equal to or less than 1.0. The average particle size of the solid electrolyte may be, for example, equal to or greater than 0.5 μm and equal to or less than 10 μm.

[0053] The solid electrolyte layer 40 may contain a binder. There are no particular restrictions on the binder, and any binder that is used in the solid electrolyte layer of a general solid secondary battery can be used.

[0054] The solid electrolyte layer 40 may have a porous substrate inside. The porous substrate may be, for example, a woven fabric or a nonwoven fabric. A solid electrolyte having a porous substrate inside has increased strength.

[0055] The intermediate layer 50 is electronically conductive and has voids through which lithium metal can pass. The voids in the intermediate layer 50 give the intermediate layer 50 flexibility that allows it to follow changes in the thickness of the negative electrode layer 30 that occur during 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, and the durability of the solid secondary battery 1 can be improved.

[0056] The intermediate layer 50 may contain a material having lithium metal conductivity and a material having electronic conductivity. For example, amorphous carbon particles can be used as the material having lithium metal conductivity. For example, metal can be used as the material having electronic conductivity. The metal may be in the form of particles. The metal particles may be contained in the intermediate layer 50 in a state of being mixed with amorphous carbon particles, or may be contained in the intermediate layer 50 in a state of being supported on amorphous carbon particles. Furthermore, the metal may be present on the surface of the amorphous carbon particles as a film, or may be impregnated into the interior of the amorphous carbon particles.

[0057] Examples of amorphous carbon particles that can be used include 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, as well as coke, activated carbon, carbon nanotubes (CNTs), fullerenes, and graphene. Some of the carbon atoms in the amorphous carbon particles may be substituted with atoms such as B, P, S, O, and N by chemical treatment such as a liquid-phase method or a gas-phase method.

[0058] Particles of a metal that forms an alloy or an intermetallic compound with lithium ions can be used as the metal contained in the intermediate layer 50. 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.

[0059] When the intermediate layer 50 contains 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 electrolyte particles 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 be, for example, in the range of 0.02 μm to 0.06 μm. The average particle size of the metal particles may be, for example, in the range of 0.06 μm to 0.1 μm.

[0060] The exterior body 60 is expandable and contractible in accordance with changes in the thickness of the negative electrode layer 30 due to charging and discharging. A laminate film can be used as the material for the exterior body 60. The laminate film can be a three-layer laminate film having an inner resin layer, a metal layer, and an outer resin layer stacked in this order from the inside. 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.

[0061] A method for manufacturing the solid secondary battery 1 of this embodiment will be described. Figures 3 to 5 are diagrams showing steps of the method for manufacturing the solid secondary battery according to one embodiment of the present invention. The method for manufacturing the solid secondary battery 1 of this embodiment includes three bonding steps: a first bonding step, a second bonding step, and a third bonding step.

[0062] In the first bonding step, as shown in FIG. 3 , the cathode layer 20 with the cathode lead wire 25 attached and the solid electrolyte layer 40 are bonded to obtain a cathode layer-solid electrolyte layer assembly 11. In the first bonding step, the composite elastic modulus of the cathode active material layer 22 before bonding is less than 30 GPa, and the composite elastic modulus of the solid electrolyte layer 40 before bonding is less than 10 GPa. The composite elastic modulus of the cathode active material layer 22 before bonding may be, for example, in the range of 0.09 GPa to 20 GPa. The composite elastic modulus of the solid electrolyte layer 40 before bonding may be, for example, in the range of 0.06 GPa to 8 GPa. The composite elastic modulus of the solid electrolyte layer 40 before bonding may be equal to or different from the composite elastic modulus of the cathode active material layer 22 before bonding. The composite elastic modulus of the solid electrolyte layer 40 before bonding may be, for example, in the range of 0.01 to 100 times the composite elastic modulus of the cathode active material layer 22 before bonding.

[0063] The relative density of the positive electrode active material layer 22 before bonding the positive electrode layer 20 and the solid electrolyte layer 40 may be less than 75%, and the relative density of the solid electrolyte layer 40 may be less than 75%. The relative density of the positive electrode active material layer 22 before bonding may be, for example, in the range of 50% to 70%. The relative density of the solid electrolyte layer 40 before bonding may be, for example, in the range of 50% to 70%. The relative density of the solid electrolyte layer 40 before bonding may be the same as or different from the relative density of the positive electrode active material layer 22 before bonding. The relative density of the solid electrolyte layer 40 before bonding may be, for example, in the range of 0.7 to 1.4 times the relative density of the positive electrode active material layer 22 before bonding.

[0064] The positive electrode layer 20 and the solid electrolyte layer 40 can be bonded, for example, by a pressing method. A roll press can be used as the press. The bonding conditions, such as the bonding pressure, bonding time, and bonding temperature, are such that the composite elastic modulus of the solid electrolyte layer 40 after bonding is less than 18 GPa. The pressing conditions may be such that the ratio of the relative density of the solid electrolyte layer 40 after bonding to the relative density before bonding (relative density after bonding / relative density before bonding) is in the range of 1.05 to 1.5, or the ratio of the composite elastic modulus of the solid electrolyte layer 40 before bonding (composite elastic modulus after bonding / composite elastic modulus before bonding) is in the range of 20 to 150.

[0065] In the second bonding step, as shown in FIG. 4 , the solid electrolyte layer 40 and the intermediate layer 50 of the cathode layer-solid electrolyte layer assembly 11 are bonded to obtain a cathode layer-solid electrolyte layer-intermediate layer assembly 12. In the second bonding step, the solid electrolyte layer 40 has a composite elastic modulus of less than 18 GPa before bonding, and the intermediate layer 50 has a composite elastic modulus of less than 1 GPa. The composite elastic modulus of the solid electrolyte layer 40 before bonding may be, for example, in the range of 5 GPa to 15 GPa. The composite elastic modulus of the intermediate layer 50 before bonding may be, for example, in the range of 0.05 GPa to 0.4 GPa. The composite elastic modulus of the solid electrolyte layer 40 before bonding may be higher than the composite elastic modulus of the intermediate layer 50 before bonding. The composite elastic modulus of the solid electrolyte layer 40 before bonding may be, for example, in the range of 20 to 200 times the composite elastic modulus of the intermediate layer 50 before bonding.

[0066] The relative density of the solid electrolyte layer 40 before bonding the solid electrolyte layer 40 and the intermediate layer 50 may be less than 85%, and the relative density of the intermediate layer 50 may be less than 40%. The relative density of the solid electrolyte layer 40 before bonding may be, for example, in the range of 60% to 80%. The relative density of the intermediate layer 50 before bonding may be, for example, in the range of 10% to 30%. The relative density of the solid electrolyte layer 40 before bonding may be higher than the relative density of the intermediate layer 50 before bonding. The relative density of the solid electrolyte layer 40 before bonding may be, for example, in the range of 2 to 8 times the relative density of the intermediate layer 50 before bonding.

[0067] The solid electrolyte layer 40 and the intermediate layer 50 can be bonded, for example, by a pressing method. A roll press can be used as the press. The pressing conditions, such as the bonding pressure, bonding time, and bonding temperature, may be such that the ratio of the relative density of the intermediate layer 50 after bonding to the relative density before bonding (relative density after bonding / relative density before bonding) is in the range of 1.3 to 4.5, or the ratio of the composite elastic modulus of the intermediate layer 50 before bonding (composite elastic modulus after bonding / composite elastic modulus before bonding) is in the range of 2 to 10. The pressing conditions may be such that the composite elastic modulus of the intermediate layer 50 after bonding is less than 1 GPa, or such that the relative density of the intermediate layer 50 after bonding is in the range of 30% to 60%.

[0068] In the third bonding step, as shown in FIG. 5 , the intermediate layer 50 of the positive electrode layer-solid electrolyte layer-intermediate layer assembly 12 is bonded to the negative electrode layer 30 with the negative electrode lead wire 35 to obtain the electrode laminate 10. The composite elastic modulus of the intermediate layer 50 before bonding may be less than 1.0 GPa, and the composite elastic modulus of the metal layer 32 may be less than 5.0 GPa. The composite elastic modulus of the intermediate layer 50 before bonding may be, for example, in the range of 0.05 GPa to 0.9 GPa. The composite elastic modulus of the metal layer 32 before bonding may be, for example, in the range of 0.05 GPa to 10 GPa. The composite elastic modulus of the metal layer 32 before bonding may be higher than the composite elastic modulus of the intermediate layer 50 before bonding. The composite elastic modulus of the metal layer 32 before bonding may be, for example, in the range of 2 to 100 times the composite elastic modulus of the intermediate layer 50 before bonding.

[0069] The relative density of the intermediate layer 50 before bonding to the negative electrode layer 30 may be less than 40%, and the relative density of the metal layer 32 may be 95% or more. The relative density of the intermediate layer 50 before bonding may be, for example, in the range of 30% or more and 50% or less.

[0070] The intermediate layer 50 and the negative electrode layer 30 can be bonded, for example, by a pressing method. A roll press can be used as the press. The pressing conditions, such as the bonding pressure, bonding time, and bonding temperature, may be such that the ratio of the relative density of the intermediate layer 50 after bonding to the relative density before bonding (relative density after bonding / relative density before bonding) is in the range of 1.0 to 2.0, or the ratio of the composite elastic modulus of the intermediate layer 50 before bonding (composite elastic modulus after bonding / composite elastic modulus before bonding) is in the range of 2 to 5. The pressing conditions may be such that the composite elastic modulus of the intermediate layer 50 after bonding is less than 1 GPa, or such that the relative density of the intermediate layer 50 after bonding is in the range of 30% to 60%.

[0071] The above manufacturing method provides an electrode laminate 10 having a positive electrode layer 20 including a positive electrode current collector 21 and a positive electrode active material layer 22, a negative electrode layer 30 including a negative electrode current collector 31 facing the positive electrode active material layer 22, 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, wherein the positive electrode layer 20, the solid electrolyte layer 40, the intermediate layer 50, and the negative electrode layer 30 are each bonded to an adjacent layer. The obtained electrode laminate 10 may be optionally pressed in the stacking direction to densify each layer of the electrode laminate 10.

[0072] The solid secondary battery 1 can be manufactured as follows: The positive electrode lead wire 25 of the obtained electrode laminate 10 is connected to the positive electrode terminal 26, and the negative electrode lead wire 35 is connected to the negative electrode terminal 36. Next, the electrode laminate 10 is housed in an exterior body 60 so that the ends of the positive electrode terminal 26 and the negative electrode terminal 36 protrude, and the exterior body 60 is sealed.

[0073] In the solid secondary battery 1 of this embodiment configured as described above, the composite elastic modulus of the positive electrode layer 20 and the solid electrolyte layer 40 before bonding, and the composite elastic modulus of the solid electrolyte layer 40 and the intermediate layer 50 before bonding, are within the above-described ranges. Therefore, the electrode laminate 10 obtained by bonding these layers exhibits high adhesion at the contact interface of each layer. This facilitates lithium deposition on the metal layer 32 of the negative electrode layer 30 during charging, ensuring an appropriate lithium deposition location during charging. Furthermore, the composite elastic modulus of each layer of the electrode laminate 10 satisfies the above-described relationship, and the positive electrode active material layer 22 has the highest composite elastic modulus and is a high-density layer, resulting in a high electrical capacity of the positive electrode layer 20. Therefore, the solid secondary battery 1 is less susceptible to increases in internal resistance and internal short circuits, and has a high charge / discharge capacity.

[0074] In the solid secondary battery 1, when the relative densities of the positive electrode layer 20 and the solid electrolyte layer 40 before bonding and the relative densities of the solid electrolyte layer 40 and the intermediate layer 50 before bonding are within the above ranges, the adhesion of the contact interfaces of the layers of the electrode stack 10 obtained by bonding them is improved. This makes the position of lithium deposition during charging more appropriate. Furthermore, since the relative densities of the layers of the electrode stack 10 satisfy the above relationship and the relative density of the positive electrode active material layer 22 is high, the electric capacity of the positive electrode layer 20 is high.

[0075] In the solid secondary battery 1, when the relative density of the intermediate layer 50 is within the above range, the intermediate layer 50 is flexible and can follow the changes in thickness of the negative electrode layer 30 that occur during charge and discharge. This results in a stable low internal resistance and a stable high charge and discharge capacity. Furthermore, when the intermediate layer 50 contains amorphous carbon particles, lithium conductivity is improved. Therefore, the electrode stack 10 has a more appropriate lithium deposition position during charge.

[0076] In the solid secondary battery 1, when the developed area ratios of the contact interfaces between the layers of the electrode laminate 10 are all within the above range, the surface area of ​​the contact interfaces between the layers is large, and therefore the contact interfaces of the layers in the electrode laminate 10 have high adhesion. As a result, the electrode laminate 10 has an appropriate position for lithium deposition during charging. Therefore, the solid secondary battery 1 is less likely to experience an increase in internal resistance or an internal short circuit, and has a high charge / discharge capacity.

[0077] In the solid secondary battery 1, when the developed area ratio of the contact interface between each layer of the electrode stack 10 satisfies the above relationship, the surface area of ​​the contact interface between the positive electrode active material layer 22 and the solid electrolyte layer 40 is the largest, which increases the adhesion of the contact interface between the positive electrode active material layer 22 and the solid electrolyte layer 40 and facilitates the movement of lithium between the positive electrode active material layer 22 and the solid electrolyte layer 40. Therefore, the solid secondary battery 1 has a lower internal resistance and a higher charge / discharge capacity.

[0078] In the solid secondary battery 1, the developed area ratio of the contact interface between the positive electrode active material layer 22 and the solid electrolyte layer 40 and the developed area ratio of the contact interface between the solid electrolyte layer 40 and the intermediate layer 50 are within the above ranges, so that the adhesion of the contact interface between the positive electrode active material layer 22 and the solid electrolyte layer 40 is further improved, and lithium ions move more easily between the positive electrode active material layer 22 and the solid electrolyte layer 40. Therefore, the solid secondary battery 1 has an even lower internal resistance and an even higher charge / discharge capacity.

[0079] In the method for manufacturing the solid secondary battery 1 of this embodiment, the composite elastic modulus of each layer bonded in the first bonding step and the second bonding step is set within the above range, so it is possible to obtain an electrode laminate 10 in which the contact interfaces of each layer have high adhesion. Therefore, the solid secondary battery 1 obtained by the method for manufacturing the solid secondary battery 1 of this embodiment is less likely to suffer from an increase in internal resistance or an internal short circuit, and has a high charge / discharge capacity.

[0080] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the solid secondary battery 1 of this embodiment, the negative electrode layer 30 includes the metal layer 32. However, the metal layer 32 may be omitted, and lithium may be deposited on the surface of the negative electrode current collector 31. Alternatively, the metal layer 32 may be replaced with a layer containing a negative electrode active material capable of absorbing and releasing lithium ions. 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, SiO2, metal sulfides, metal nitrides, and carbon materials such as artificial graphite, natural graphite, graphite, soft carbon, and hard carbon. The negative electrode active material layer may optionally contain a solid electrolyte to improve lithium ion conductivity. It may also optionally contain a conductive additive to improve conductivity. Furthermore, it may optionally contain a binder to achieve flexibility. The solid electrolyte, conductive additive, and binder may be those commonly used in solid secondary batteries.

[0081] Furthermore, although the solid secondary battery 1 of this embodiment is a lithium battery using lithium as a charge transfer medium, the present invention is not limited to this. The solid secondary battery 1 of this embodiment may be, for example, a battery using sodium, potassium, magnesium, calcium, aluminum, zinc, or fluorine as a charge transfer medium.

[0082] The present invention will be described in detail below using examples, but the present invention is not limited to these examples.

[0083] [Example 1] (Preparation of positive electrode layer) An aluminum foil with a thickness of 15.0 μm was prepared as a positive electrode current collector with a positive electrode lead wire. A mixture of 80 parts by mass of lithium nickel cobalt manganese composite oxide (NCM622) as the positive electrode active material, 17 parts by mass of an argyrodite-type sulfide solid electrolyte as the solid electrolyte, 2 parts by mass of carbon black as a conductive additive, and 1 part by mass of an SBR (styrene butadiene rubber) binder as the binder was prepared. The resulting mixture was dispersed in 43 parts by mass of butyl butyrate to prepare a positive electrode active material layer slurry. The resulting positive electrode active material layer slurry was applied to one surface of a positive electrode current collector to a weight per unit area of ​​27 mg / cm after drying. 2 The positive electrode active material layer had a relative density of 55% and a composite elastic modulus of 0.1 GPa.

[0084] (Preparation of solid electrolyte layer transfer sheet) A dispersion of argyrodite-type sulfide solid electrolyte (average particle size: 3.0 μm) was applied to a support sheet and dried to form an argyrodite-type sulfide solid electrolyte layer with a thickness of 100 μm. The solid electrolyte layer had a relative density of 60% and a composite elastic modulus of 0.2 GPa.

[0085] (Preparation of intermediate layer transfer sheet) A total of 95 parts by mass of Sn particles (average particle diameter: 0.07 μm) as metal particles, acetylene black (average particle diameter: 0.05 μm) as amorphous carbon particles, and 5 parts by mass of a PVDF-based binder were mixed as a binder. The resulting mixture was dispersed in 1,000 parts by mass of NMP (N-methyl-2-pyrrolidone) to prepare an intermediate layer slurry. The resulting intermediate layer slurry was applied to a support sheet and dried to produce an intermediate layer transfer sheet with a final thickness of 3.0 μm. The relative density of the intermediate layer was 18%, and the composite elastic modulus was 0.1 GPa.

[0086] (Production of negative electrode layer) A copper foil with a thickness of 10 μm was prepared as a negative electrode current collector with a negative electrode lead wire. A metallic lithium foil having a thickness of 40 μm, a relative density of 98%, and a composite elastic modulus of 2.0 GPa was rolled and laminated on the surface of the copper foil to prepare a negative electrode layer.

[0087] (Production of electrode stack) 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, and the two were bonded using a uniaxial molding press under bonding conditions of 90 MPa, a bonding time of 3 minutes, and a bonding temperature of room temperature (first bonding step). The support sheet of the solid electrolyte layer transfer sheet was then peeled off to obtain 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 laminate, and the two were bonded using a uniaxial molding press under bonding conditions of 290 MPa, a bonding time of 5 minutes, and a bonding temperature of room temperature (second bonding step). The support sheet of the intermediate layer transfer sheet was then peeled off to obtain a positive electrode layer-solid electrolyte layer-intermediate layer assembly. Next, the integrated positive electrode layer-solid electrolyte layer-intermediate layer assembly was subjected to a densification treatment using an isostatic pressing press under bonding pressure of 980 MPa, a bonding time of 5 minutes, and a bonding temperature of 120°C. Next, the metallic lithium foil of the negative electrode layer was placed on the surface of the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly, and the assembly was bonded using a uniaxial press under the conditions of a bonding pressure of 180 MPa, a bonding time of 2 minutes, and a bonding temperature of room temperature (third bonding step). In this way, an electrode laminate was obtained. The relative densities and composite elastic moduli of the positive electrode active material layer and solid electrolyte layer before bonding the positive electrode layer and solid electrolyte layer, the relative densities and composite elastic moduli of the solid electrolyte layer and intermediate layer before bonding the solid electrolyte layer and intermediate layer, and the relative densities and composite elastic moduli of the intermediate layer and negative electrode layer before bonding the intermediate layer and metallic lithium foil are shown in Table 1 below. The relative densities and composite elastic moduli of each layer of the electrode laminate are shown in Table 2 below.

[0088] [Examples 2 to 3] An electrode laminate was obtained in the same manner as in Example 1, except that the pressing conditions for joining the positive electrode layer and the solid electrolyte layer and the pressing conditions for joining the solid electrolyte layer and the intermediate layer were changed so that the composite elastic modulus before joining the solid electrolyte layer and the intermediate layer and the relative density and composite elastic modulus of the intermediate layer before joining the intermediate layer and the negative electrode layer would be the values ​​shown in Table 1. The relative density and composite elastic modulus of each layer of the electrode laminate are shown in Table 2 below.

[0089] [Comparative Example 1] An electrode laminate was obtained in the same manner as in Example 1, except that the positive electrode layer was pressed before bonding the positive electrode layer and the solid electrolyte layer, and the relative density and composite modulus of elasticity of the positive electrode active material layer were changed to the values ​​shown in the following Table 1. The relative density and composite modulus of elasticity of each layer of the electrode laminate are shown in the following Table 2.

[0090] Comparative Example 2 Before bonding the positive electrode layer and the solid electrolyte layer, the solid electrolyte layer transfer sheet was pressed to change the relative density and composite elastic modulus of the solid electrolyte layer to the values ​​shown in Table 1 below, and the relative density and composite elastic modulus of the solid electrolyte layer before bonding the solid electrolyte layer and the intermediate layer were changed, but the same procedure as in Example 1 was used to obtain an electrode laminate. The relative density and composite elastic modulus of each layer of the electrode laminate are shown in Table 2 below.

[0091] Comparative Example 3 Except for the fact that the solid electrolyte layer and the metallic lithium foil of the negative electrode layer were directly bonded without bonding an intermediate layer to the solid electrolyte, an electrode laminate was obtained in the same manner as in Example 1. The relative density and composite elastic modulus of each layer of the electrode laminate are shown in Table 2 below.

[0092] [Table 1]

[0093] [Table 2]

[0094] [evaluation] (Development area ratio of contact interface) The cross sections of the electrode laminates obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were observed using a SEM (scanning electron microscope) to measure the developed area ratio of the contact interface of each layer. The developed area ratio was measured at three locations for each layer. The average values ​​of the obtained developed area ratios are shown in Table 3 below.

[0095] (Battery characteristics) A positive electrode terminal was connected to the positive electrode lead wire of the electrode laminate obtained in Examples 1 to 3 and Comparative Examples 1 to 4, and a negative electrode terminal was connected to the negative electrode lead wire. Next, the electrode laminate was housed in an outer casing so that the ends of the positive electrode terminal and the negative electrode terminal protruded, and the outer casing was sealed to obtain a solid secondary battery. For the obtained solid secondary battery, the DC resistance, 1 / 3 C discharge capacity, whether or not 1 / 3 C charge / discharge was possible, and the lithium deposition position were measured using the following methods. Each measurement was performed at 25°C. The results are shown in Table 3 below.

[0096] (DC resistance) At a temperature of 25°C and a charging state of SOC of 50, the current density was 15.1 mA / cm 2 The voltage drop ΔV (V), current value I (A), and positive electrode area Ac (cm 2 ) and the DC resistance (Ω·cm 2 ) was calculated. DC resistance (Ω cm 2 ) = Voltage drop ΔV (V) / Current value I (A) × Positive electrode area Ac (cm 2 )

[0097] (1 / 3C discharge capacity) The charge-discharge test was carried out at a temperature of 25°C, with a charge upper limit voltage of 4.3V, a discharge lower limit voltage of 2.65V, a C rate of 1 / 3C, and a current density of 1.3mA / cm2. The discharge capacity after the first charge was taken as the 1 / 3C discharge capacity.

[0098] (1 / 3C charging / discharging possible) When the design capacity is taken as 100%, if the charge / discharge capacity at 25°C and 1 / 3C charge / discharge is 95-105% and no short circuit behavior occurs during or after charge / discharge, it is marked as "Good." If short circuit behavior occurs during or after charge / discharge, the charge capacity is excessive compared to the design capacity, or the self-discharge amount after charge is large, it is marked as "Poor."

[0099] (Lithium deposition position) After one cycle, or when 1 / 3C charge / discharge was no longer possible, the solid-state secondary batteries were disassembled to check whether lithium had precipitated anywhere other than between the intermediate layer and the negative electrode layer. Cases where lithium had not precipitated anywhere other than between the intermediate layer and the negative electrode layer were marked with "Good," and cases where lithium had precipitated anywhere other than between the intermediate layer and the negative electrode layer were marked with "Poor."

[0100] [Table 3]

[0101] The results in Table 3 show that the solid secondary batteries using the electrode laminates obtained in Examples 1 to 3 have a higher developed area ratio of the contact interface between each layer, a lower DC resistance, and a larger 1 / 3C discharge capacity than the solid secondary batteries using the electrode laminates obtained in Comparative Examples 1 to 3. [Explanation of symbols]

[0102] 1 Solid state secondary battery 10 Electrode laminate 20 Positive electrode layer 21 Positive electrode current collector 22 Cathode active material layer 25 Positive lead wire 26 Positive terminal 30 negative electrode layer 31 Negative electrode current collector 32 metal layer 35 Negative lead wire 36 Negative terminal 40 Solid electrolyte layer 50 Middle Class 60 Exterior body

Claims

1. an electrode laminate including: 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 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, wherein the positive electrode layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer are each joined to an adjacent layer; a composite elastic modulus of the positive electrode active material layer before bonding the positive electrode layer and the solid electrolyte layer is less than 30 GPa, and a composite elastic modulus of the solid electrolyte layer is less than 15 GPa; a composite elastic modulus of the solid electrolyte layer before bonding the solid electrolyte layer and the intermediate layer is less than 18 GPa, and a composite elastic modulus of the intermediate layer before bonding the solid electrolyte layer and the intermediate layer is less than 1 GPa; a solid secondary battery, wherein the composite elastic modulus of each of the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer of the electrode laminate satisfies the relationship intermediate layer < negative electrode layer < solid electrolyte layer < positive electrode active material layer.

2. a relative density of the positive electrode active material layer before bonding the positive electrode layer and the solid electrolyte layer is less than 75%, and a relative density of the solid electrolyte layer is less than 75%, a relative density of the solid electrolyte layer before bonding the solid electrolyte layer and the intermediate layer is less than 85% and a relative density of the intermediate layer is less than 40%, 2. The solid secondary battery according to claim 1, wherein the relative density of the intermediate layer is the smallest among the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer of the electrode laminate.

3. 3. The solid secondary battery according to claim 1, wherein the developed area ratio of the contact interfaces between the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer is 0.2 or more.

4. The solid secondary battery according to claim 1 or 2, wherein the intermediate layer of the electrode laminate has a composite elastic modulus of less than 1 GPa.

5. 3. The solid secondary battery according to claim 1, wherein the relative density of the intermediate layer of the electrode laminate is in the range of 30% to 60%.

6. The solid secondary battery according to claim 1 or 2, wherein the intermediate layer of the electrode laminate contains amorphous carbon particles.

7. an electrode laminate including: 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 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, wherein the positive electrode layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer are each joined to an adjacent layer; a contact interface between the positive electrode active material layer, the solid electrolyte layer, the intermediate layer, and the negative electrode layer, each having a developed area ratio of 0.2 or more;

8. 8. The solid secondary battery according to claim 7, wherein the developed area ratio of the contact interface between the positive electrode active material layer and the solid electrolyte layer is the highest, the developed area ratio of the contact interface between the solid electrolyte layer and the intermediate layer is the next highest, and the developed area ratio of the contact interface between the intermediate layer and the negative electrode layer is the lowest.

9. 9. The solid secondary battery according to claim 7, wherein a developed area ratio of a contact interface between the positive electrode active material layer and the solid electrolyte layer is in a range of 1.5 to 3.0 times a developed area ratio of a contact interface between the solid electrolyte layer and the intermediate layer, and a developed area ratio of a contact interface between the solid electrolyte layer and the intermediate layer is in a range of 2.0 to 5.0 times a developed area ratio of a contact interface between the intermediate layer and the negative electrode layer.

10. a cathode layer having a cathode current collector and a cathode active material layer, an anode layer having an anode current collector facing the cathode active material layer, a solid electrolyte layer disposed between the cathode layer and the anode layer, and an intermediate layer disposed between the anode layer and the solid electrolyte layer, wherein the cathode layer, the solid electrolyte layer, the intermediate layer, and the anode layer are each joined to an adjacent layer, a first bonding step of bonding the positive electrode active material layer and the solid electrolyte layer to obtain a positive electrode layer-solid electrolyte layer bonded body; a second joining step of joining 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 third bonding step of bonding the intermediate layer of the positive electrode layer-solid electrolyte layer-intermediate layer assembly to the negative electrode layer to obtain the electrode stack; a composite elastic modulus of the positive electrode active material layer before bonding in the first bonding step is less than 30 GPa, and a composite elastic modulus of the solid electrolyte layer before bonding is less than 10 GPa; a composite elastic modulus of the solid electrolyte layer before bonding in the second bonding step is less than 18 GPa, and a composite elastic modulus of the intermediate layer before bonding is less than 1 GPa.

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