All-solid-state battery and method for manufacturing all-solid-state battery

Abstract

The present application relates to an all-solid battery and a manufacturing method of an all-solid battery. The object is to improve the short circuit resistance of the all-solid battery. An all-solid battery has, in order, a first electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and a second electrode layer, the first solid electrolyte layer has a first surface, the second solid electrolyte layer has a second surface in contact with the first surface, the maximum height Rz1 of the first surface and the maximum height Rz2 of the second surface satisfy the following relationship (1). 0.15 ≤ Rz1 / Rz2 ≤ 0.25 … (1).

Description

Technical Field

[0001] This application discloses an all-solid-state battery and a method for manufacturing an all-solid-state battery. Background Technology

[0002] Patent Document 1 discloses the following technology: by placing two solid electrolyte layers between the positive and negative electrode layers of an all-solid-state battery, the number of pinholes penetrating between the positive and negative electrode layers is reduced. Furthermore, Patent Document 2 discloses the following technology: in an all-solid-state battery using lithium metal as the negative electrode active material, by placing two or more solid electrolytes between the positive and negative electrode layers and adjusting the material and ionic conductivity of each solid electrolyte layer, the safety and reliability of the all-solid-state battery are improved.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2014 / 010043

[0006] Patent Document 2: Japanese Patent Application Publication No. 2004-206942 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] According to the inventor's new insight, even when there are two solid electrolyte layers between the positive and negative electrode layers in an all-solid-state battery, if stress is applied to the solid electrolyte layers during charging and discharging due to the expansion or contraction of the active materials, resulting in cracks in the solid electrolyte layers, these cracks may propagate from one solid electrolyte layer to the other, causing a short circuit. Regarding this, in conventional technologies, there is still room for improvement in suppressing crack propagation in the solid electrolyte layers to improve the short-circuit withstand capability of all-solid-state batteries.

[0009] Methods for solving problems

[0010] As one of the means to solve the above-mentioned problems, this application discloses an all-solid-state battery, which has a first electrode layer, a first solid electrolyte layer, a second solid electrolyte layer and a second electrode layer in sequence. The first solid electrolyte layer has a first surface, and the second solid electrolyte layer has a second surface in contact with the first surface. The maximum height Rz1 of the first surface and the maximum height Rz2 of the second surface satisfy the following relationship (1).

[0011] 0.15≤Rz1 / Rz2≤0.25…(1)

[0012] In the all-solid-state battery of this disclosure, the second solid electrolyte layer may have a third surface on the side opposite to the second surface, and the second electrode layer may have a fourth surface in contact with the third surface. The maximum height Rz3 of the third surface and the maximum height Rz4 of the fourth surface may satisfy the following relationship (2) or (3).

[0013] 0.45≤Rz3 / Rz4≤1.00…(2)

[0014] 0.45≤Rz4 / Rz3≤1.00…(3)

[0015] In the all-solid-state battery disclosed herein, the first electrode layer may include a positive electrode active material layer, and the second electrode layer may include a negative electrode active material layer.

[0016] In the all-solid-state battery disclosed herein, the negative electrode active material layer may contain metallic lithium as the negative electrode active material.

[0017] In the all-solid-state battery of this disclosure, the positive electrode active material layer may contain sulfur as the positive electrode active material.

[0018] As one means to solve the above-mentioned problems, this application discloses a method for manufacturing an all-solid-state battery, comprising: forming a first solid electrolyte layer on the surface of a substrate to obtain a transfer material; stacking the transfer material with a first electrode layer, applying pressure P1 in the stacking direction to transfer the first solid electrolyte layer of the transfer material onto the first electrode layer, thereby obtaining a first laminate of the first electrode layer and the first solid electrolyte layer; coating a material constituting a second solid electrolyte layer onto a second electrode layer to obtain a second laminate of the second electrode layer and the second solid electrolyte layer; and after stacking the first laminate and the second laminate, applying pressure P2, which is smaller than the pressure P1, in the stacking direction to obtain an all-solid-state battery having the first electrode layer, the first solid electrolyte layer, the second solid electrolyte layer, and the second electrode layer in sequence.

[0019] In the manufacturing method disclosed herein, the first electrode layer may include a positive electrode active material layer, and the second electrode layer may include a negative electrode active material layer.

[0020] In the manufacturing method disclosed herein, the negative electrode active material layer may contain metallic lithium as the negative electrode active material.

[0021] In the manufacturing method disclosed herein, the positive electrode active material layer may contain sulfur as a positive electrode active material.

[0022] Invention Effects

[0023] In the all-solid-state battery disclosed herein, even if a crack is generated in one of the first and second solid electrolyte layers, the propagation of the crack to the other layer can be easily suppressed, thus ensuring excellent short-circuit withstand capability. Attached Figure Description

[0024] Figure 1 The structure of the all-solid-state battery 100 is shown in general.

[0025] Figure 2 The structure of the all-solid-state battery 100 is broken down and schematically shown.

[0026] Figure 3 The method for determining the maximum height Rz of the surface of the solid electrolyte layer is shown in outline.

[0027] Figure 4 An example of a process for manufacturing an all-solid-state battery 100 is shown.

[0028] Figure 5A The composition of the transfer material obtained through process S1 is shown in general.

[0029] Figure 5B The process of step S2 and the structure of the first laminate obtained through step S2 are shown in a general way.

[0030] Figure 5C The process of step S3 and the structure of the second laminate obtained through step S3 are shown in a general way.

[0031] Figure 5D The process of step S4 and the structure of the all-solid-state battery obtained through step S4 are shown in general.

[0032] Explanation of reference numerals in the attached figures

[0033] 11 First Electrode Layer

[0034] 12 Second electrode layer

[0035] 21 First solid electrolyte layer

[0036] 22 Second solid electrolyte layer

[0037] 31 Substrate

[0038] 41 Transfer materials

[0039] 51 First layer of stacked body

[0040] 52 Second layer stack

[0041] 100 All-Solid-State Battery Detailed Implementation

[0042] 1. All-solid-state battery

[0043] like Figure 1 and 2 As shown, one embodiment of the all-solid-state battery 100 sequentially includes a first electrode layer 11, a first solid electrolyte layer 21, a second solid electrolyte layer 22, and a second electrode layer 12. For example... Figure 2 As shown, the first solid electrolyte layer 21 has a first surface 21x, and the second solid electrolyte layer 22 has a second surface 22x that contacts the first surface 21x. Furthermore, the maximum height Rz1 of the first surface 21x and the maximum height Rz2 of the second surface 22x satisfy the following relationship (1).

[0044] 0.15≤Rz1 / Rz2≤0.25 … (1)

[0045] 1.1 First Electrode Layer

[0046] like Figure 1 and 2 As shown, the first electrode layer 11 may include an active material layer 11a and a current collector layer 11b. The first electrode layer 11 can be a positive electrode layer or a negative electrode layer; in particular, in the case of a positive electrode layer, high performance can be expected. That is, the first electrode layer 11 may include a positive active material layer 11a and a positive current collector layer 11b.

[0047] 1.1.1 Positive Electrode Active Material Layer

[0048] The positive electrode active material layer 11a contains at least a positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer 11a may optionally contain a solid electrolyte, a binder, and a conductive additive.

[0049] As the positive electrode active material, any material known as a positive electrode active material in all-solid-state batteries can be used. Two materials with different potentials (charge / discharge potentials) for adsorbing and releasing specified ions can be selected from known active materials. The material exhibiting the higher potential is used as the positive electrode active material, and the material exhibiting the lower potential is used as the negative electrode active material (described later). For example, in the case of constructing a lithium-ion battery, lithium cobalt oxide, lithium nickel oxide, and LiNi oxide can be used as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3Various lithium-containing composite oxides such as O2, lithium manganese oxide, and spinel-based lithium compounds; sulfur or sulfur compounds, etc. The positive electrode active material can be a single type or a mixture of two or more types. In particular, when the positive electrode active material layer 11a contains sulfur as the positive electrode active material, even better results can be expected. That is, it is believed that sulfur, as the positive electrode active material, expands and contracts significantly during charging and discharging. The stress accompanying this expansion and contraction tends to remain between the positive electrode active material layer and the solid electrolyte layer. This stress is not mitigated, thus easily causing cracks in the solid electrolyte layer. According to the technology disclosed herein, the propagation of cracks generated in the solid electrolyte layer is suppressed, and the short-circuit withstand capability of the all-solid-state battery is easily improved. To suppress reactions caused by contact between the positive electrode active material and the solid electrolyte, a coating layer such as a lithium niobate layer, a lithium titanate layer, or a lithium phosphate layer can also be provided on the surface of the positive electrode active material. The positive electrode active material can be, for example, in particle form, and its size is not particularly limited. The particles of the positive electrode active material can be solid particles or hollow particles. The particles of the positive electrode active material can be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle size of the positive electrode active material can be, for example, 1 nm or more, 5 nm or more, or 10 nm or more; alternatively, it can be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. It should be noted that the average particle size mentioned in this application refers to the particle size (median particle size, D50) at which the cumulative value of the particle size distribution on a volume basis determined by laser diffraction / scattering is 50%.

[0050] As a solid electrolyte that can be contained in the positive electrode active material layer 11a, materials known as solid electrolytes for all-solid-state batteries can be used. The solid electrolyte can be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, inorganic solid electrolytes have higher ionic conductivity compared to organic polymer electrolytes. Furthermore, they exhibit superior heat resistance compared to organic polymer electrolytes. Examples of inorganic solid electrolytes include lithium lanthanum zirconate, LiPON, and Li... 1+ X Al X Ge 2-X(PO4)3, Li-SiO glass, Li-Al-SO glass and other oxide solid electrolytes; Li2S, P2S5, Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5-GeS2 and other sulfide solid electrolytes. Sulfide solid electrolytes, in particular, exhibit excellent performance. Solid electrolytes can be amorphous or crystalline. A single solid electrolyte can be used alone, or two or more can be used in combination. The solid electrolyte contained in the positive electrode active material layer 11a can be in particle form. Solid electrolyte particles can be primary particles or secondary particles formed by the aggregation of multiple primary particles. The average particle size of the solid electrolyte can be, for example, 10 nm or more, 0.1 μm or more, 0.5 μm or more, or 1 μm or more; or it can be less than 100 μm, less than 50 μm, 10 μm or less.

[0051] The binder contained in the positive electrode active material layer 11a may be at least one selected from butadiene rubber (BR) based binders, butene rubber (IIR) based binders, acrylate butadiene rubber (ABR) based binders, styrene butadiene rubber (SBR) based binders, polyvinylidene fluoride (PVdF) based binders, polytetrafluoroethylene (PTFE) based binders, etc.

[0052] The conductive additive that may be included in the positive electrode active material layer 11a may be at least one selected from carbon materials such as acetylene black and Ketjen black, and metal materials such as nickel, aluminum, and stainless steel. The conductive additive may be in particulate or fibrous form, and its size is not particularly limited.

[0053] The content of each component in the positive electrode active material layer 11a can be the same as in the conventional form. The positive electrode active material layer 11a may, for example, contain 10% to 90% by mass of positive electrode active material, 0% to 60% by mass of solid electrolyte, 0% to 30% by mass of conductive additive, and optionally a binder as the remainder. The shape of the positive electrode active material layer 11a can also be the same as in the conventional form. From the viewpoint of more easily constructing an all-solid-state battery 100, the positive electrode active material layer 11a can be sheet-like. The thickness of the positive electrode active material layer 11a is not particularly limited, and for example, it can be 0.1 μm or more and 2 mm or less. The lower limit can be 1 μm or more, and the upper limit can be 1 mm or less.

[0054] 1.1.2 Positive current collector layer

[0055] The positive electrode current collector layer 11b can be a typical positive electrode current collector layer used in all-solid-state batteries. The positive electrode current collector layer 11b can be composed of metal foil or metal mesh. In particular, metal foil has excellent processability. The positive electrode current collector layer 11b can also be composed of multiple metal foils. Examples of metals constituting the positive electrode current collector layer 11b include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. Especially from the viewpoint of ensuring oxidation resistance, the positive electrode current collector layer 11b may contain Al. For purposes such as adjusting resistance, the positive electrode current collector layer 11b can have any coating on its surface. Furthermore, when the positive electrode current collector layer 11b is composed of multiple metal foils, any layer can be formed between these multiple metal foils. The thickness of the positive electrode current collector layer 11b is not particularly limited. For example, it can be above 0.1μm or above 1μm, or below 1mm or below 100μm.

[0056] 1.2 First Solid Electrolyte Layer

[0057] like Figure 1 and Figure 2 As shown, the first solid electrolyte layer 21 is disposed between the first electrode layer 11 and the second solid electrolyte layer 22, and can contact both of them. That is, the first solid electrolyte layer 21 may have a first surface 21x that contacts the second solid electrolyte layer 22, and may also have a fifth surface 21y that contacts the first electrode layer 11.

[0058] The first solid electrolyte layer 21 contains at least a solid electrolyte. In addition to the solid electrolyte, the first solid electrolyte layer 21 may also contain an adhesive, etc.

[0059] The solid electrolyte contained in the first solid electrolyte layer 21 may be the same as or different from the solid electrolyte contained in the positive electrode active material layer 11a. The solid electrolyte may be the aforementioned inorganic solid electrolyte, particularly the aforementioned sulfide solid electrolyte, which exhibits excellent performance. The solid electrolyte may be amorphous or crystalline. Only one type of solid electrolyte may be used, or two or more types may be used in combination. The solid electrolyte contained in the first solid electrolyte layer 21 may be in particulate form. The average particle size of the solid electrolyte may, for example, be 10 nm or more, 0.1 μm or more, 0.5 μm or more, or 1 μm or more; alternatively, it may be 100 μm or less, 50 μm or less, 10 μm or less, or 5 μm or less.

[0060] The binder contained in the first solid electrolyte layer 21 may be the same as or different from the binder contained in the positive electrode active material layer 11a. For example, it may be at least one of the following: butadiene rubber (BR) based binder, butene rubber (IIR) based binder, acrylate butadiene rubber (ABR) based binder, styrene butadiene rubber (SBR) based binder, polyvinylidene fluoride (PVdF) based binder, polytetrafluoroethylene (PTFE) based binder, etc.

[0061] There is no particular limitation on the content of solid electrolyte and binder in the first solid electrolyte layer 21. The first solid electrolyte layer 21 may, for example, contain 80% or more or 90% or more of solid electrolyte and 20% or less or 10% or less of binder. In particular, when the first solid electrolyte layer 21 contains 0.6% or more and 10% or less of binder, high performance is easily ensured. The first solid electrolyte layer 21 may, for example, be in sheet form. The thickness of the first solid electrolyte layer 21 is not particularly limited, and may, for example, be 0.1 μm or more and 2 mm or less. The lower limit may be 1 μm or more, and the upper limit may be 1 mm or less. The first solid electrolyte layer 21 may be thicker or thinner than the second solid electrolyte layer 22 described later; a thicker layer is considered more effective.

[0062] 1.3 Second Solid Electrolyte Layer

[0063] like Figure 1 and Figure 2 As shown, the second solid electrolyte layer 22 is disposed between the first solid electrolyte layer 21 and the second electrode layer 12, and can contact both of them. That is, the second solid electrolyte layer 22 may have a second surface 22x that contacts the first solid electrolyte layer 21, and may also have a third surface 22y that contacts the second electrode layer 12.

[0064] The second solid electrolyte layer 22 contains at least a solid electrolyte. In addition to the solid electrolyte, the second solid electrolyte layer 22 may also contain an adhesive, etc.

[0065] The solid electrolyte contained in the second solid electrolyte layer 22 may be the same as or different from the solid electrolyte contained in the positive electrode active material layer 11a and the first solid electrolyte layer 21. In particular, a solid electrolyte of the same type as that contained in the first solid electrolyte layer 21 may be used. The solid electrolyte may be the aforementioned inorganic solid electrolyte, especially the aforementioned sulfide solid electrolyte, which has excellent performance. The solid electrolyte may be amorphous or crystalline. Only one type of solid electrolyte may be used, or two or more types may be used in combination. The solid electrolyte contained in the second solid electrolyte layer 22 may be in particulate form. The average particle size of the solid electrolyte may, for example, be 10 nm or more, 0.1 μm or more, 0.5 μm or more, or 1 μm or more; alternatively, it may be less than 100 μm, less than 50 μm, 10 μm, or less than 5 μm. The solid electrolyte contained in the first solid electrolyte layer 21 and the solid electrolyte contained in the second solid electrolyte layer 22 may have substantially the same particle size. For example, the ratio D1 / D2 of the average particle size D1 of the solid electrolyte contained in the first solid electrolyte layer 21 to the average particle size D2 of the solid electrolyte contained in the second solid electrolyte layer 22 can be 0.5 or more, 0.7 or more, or 0.9 or more, or it can be 1.5 or less, 1.3 or less, or 1.1 or less.

[0066] The binder contained in the second solid electrolyte layer 22 may be the same as or different from the binder contained in the positive electrode active material layer 11a and the first solid electrolyte layer 21. For example, it may be selected from at least one of the following: butadiene rubber (BR) based binder, butene rubber (IIR) based binder, acrylate butadiene rubber (ABR) based binder, styrene butadiene rubber (SBR) based binder, polyvinylidene fluoride (PVdF) based binder, polytetrafluoroethylene (PTFE) based binder, etc.

[0067] There is no particular limitation on the content of solid electrolyte and binder in the second solid electrolyte layer 22. For example, the second solid electrolyte layer 22 may contain 80% or more or 90% or more of solid electrolyte and 20% or less or 10% or less of binder. In particular, when the second solid electrolyte layer 22 contains 0.6% or more and 10% or less of binder, high performance is easily ensured. The second solid electrolyte layer 22 may be, for example, sheet-like. There is no particular limitation on the thickness of the second solid electrolyte layer 22; for example, it may be 0.1 μm or more and 2 mm or less. The lower limit may be 1 μm or more, and the upper limit may be 1 mm or less. The second solid electrolyte layer 22 may be thicker or thinner than the first solid electrolyte layer 21 described above; thinner is considered more efficient. Furthermore, in the all-solid-state battery 100, such as... Figure 1 and Figure 2As shown, the areas of the surfaces 22x and 22y of the second solid electrolyte layer 22 can be larger than the area of ​​the surface 11x of the first electrode layer 11 and the areas of the surfaces 21x and 22y of the first solid electrolyte layer 21.

[0068] 1.4 Second Electrode Layer

[0069] like Figure 1 and 2 As shown, the second electrode layer 12 may include an active material layer 12a and a current collector layer 12b. The second electrode layer 12 can be a positive electrode layer or a negative electrode layer, and in particular, when it is a negative electrode layer, high performance can be expected. That is, the second electrode layer 12 may include a negative electrode active material layer 12a and a negative electrode current collector layer 12b.

[0070] 1.4.1 Negative Electrode Active Material Layer

[0071] The negative electrode active material layer 12a contains at least a negative electrode active material. In addition to the negative electrode active material, the negative electrode active material layer 12a may optionally contain a solid electrolyte, a binder, and a conductive additive.

[0072] Known active materials can be used as the negative electrode active material. For example, in the case of a lithium-ion battery, silicon-based active materials such as Si, Si alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; and metallic lithium (elemental lithium or lithium alloys) can be used as the negative electrode active material. It should be noted that metallic lithium, as the negative electrode active material, is softer than other active materials. When high pressure is applied to seal the metallic lithium with the second solid electrolyte layer 22, it is possible for the metallic lithium to enter the gaps in the second solid electrolyte layer 22 and reach the positive electrode side. In addition, it is difficult to transfer the second solid electrolyte layer 22 onto the surface of the soft metallic lithium. Regarding this, in the technology disclosed herein, by adopting the manufacturing method described later, even if the negative electrode active material layer 12a contains metallic lithium as the negative electrode active material, it is easy to properly seal the negative electrode active material layer 12a with the second solid electrolyte layer 22, and it is easy to ensure the ion conduction path at the interface between the negative electrode active material layer 12a and the second solid electrolyte layer 22. Therefore, dendrite growth caused by poor contact during battery charging and discharging can be easily suppressed. The negative electrode active material can be in particle form, or it can be in foil form as described later.

[0073] The solid electrolyte, binder, and conductive additive that may be contained in the negative electrode active material layer 12a may be appropriately selected from substances exemplified as substances that may be contained in the positive electrode active material layer 11a.

[0074] The content of each component in the negative electrode active material layer 12a can be the same as before. The negative electrode active material layer 12a may, for example, contain 10% by mass or more and 100% by mass of negative electrode active material, 0% by mass or more and 60% by mass of solid electrolyte, 0% by mass or more and 30% by mass of conductive additive, and optionally a binder as the remainder. The shape of the negative electrode active material layer 12a can also be the same as before. From the viewpoint of making it easier to construct the all-solid-state battery 100, the negative electrode active material layer 12a can be sheet-like. There is no particular limitation on the thickness of the negative electrode active material layer 12a; for example, it can be 0.1 μm or more and 2 mm or less. The lower limit can be 1 μm or more, and the upper limit can be 1 mm or less. In the all-solid-state battery 100, a layer made of metallic lithium (e.g., a metallic lithium foil) can be used as the negative electrode active material layer 12a. Furthermore, in the all-solid-state battery 100, such as... Figure 1 and Figure 2 As shown, the area of ​​the surface 12x of the second electrode layer 12 can be greater than the area of ​​the surface 11x of the first electrode layer 11 and the areas of the surfaces 21x and 21y of the first solid electrolyte layer 21.

[0075] 1.4.2 Negative Electrode Current Collector Layer

[0076] For the negative electrode current collector layer 12b, any general negative electrode current collector layer used in all-solid-state batteries can be employed. The negative electrode current collector layer 12b can be composed of metal foil or metal mesh, or it can be composed of carbon sheets. In particular, metal foils and carbon sheets have excellent processability. The negative electrode current collector layer 12b can also be composed of multiple metal foils or carbon sheets. Examples of metals constituting the negative electrode current collector layer 12b include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. Especially from the viewpoint of ensuring resistance to reduction and the difficulty of alloying with lithium, the negative electrode current collector layer 12b can contain at least one metal selected from Cu, Ni, and stainless steel, or it can be composed of carbon sheets. For purposes such as adjusting resistance, the negative electrode current collector layer 12b can also have any coating on its surface. Furthermore, when the negative electrode current collector layer 12b is composed of multiple metal foils, any layer can be formed between these multiple metal foils. There is no particular limitation on the thickness of the negative electrode current collector layer 12b. For example, it can be 0.1 μm or more, or 1 μm or less, or 1 mm or less.

[0077] 1.5 Relationship between surface roughness

[0078] like Figure 2As shown, the first electrode layer 11 may have a sixth surface 11x that contacts the first solid electrolyte layer 21. Additionally, the first solid electrolyte layer 21 may also have a first surface 21x that contacts the second solid electrolyte layer 22, and a fifth surface 21y that contacts the sixth surface 11x of the first electrode layer 11. Furthermore, the second solid electrolyte layer 22 may have a second surface 22x that contacts the first surface 21x of the first solid electrolyte layer 21, and a third surface 22y that contacts the second electrode layer 12. Moreover, the second electrode layer 12 may also have a fourth surface 12x that contacts the third surface 22y of the second solid electrolyte layer 22. Each surface may have a predetermined surface roughness. The relationship between the various surface roughnesses will be explained below.

[0079] 1.5.1 Relationship at the interface between the first solid electrolyte layer and the second solid electrolyte layer

[0080] In the all-solid-state battery 100, it is important that the maximum height Rz1 of the first surface 21x and the maximum height Rz2 of the second surface 22x satisfy the relationship described above (1). That is, the ratio Rz1 / Rz2 of Rz1 to Rz2 is 0.15 or more and 0.25 or less. It can be said that this ratio Rz1 / Rz2 represents the contact state between the first solid electrolyte layer 21 and the second solid electrolyte layer 22. According to the inventor's new insight, when the ratio Rz1 / Rz2 is too small, the difference in surface roughness between the first solid electrolyte layer 21 and the second solid electrolyte layer 22 is too large, so a large number of voids are easily generated between the first solid electrolyte layer 21 and the second solid electrolyte layer 22, making it difficult to ensure a sufficient ion conduction path between the first solid electrolyte layer 21 and the second solid electrolyte layer 22. On the other hand, when the ratio Rz1 / Rz2 is about 1.00, the unevenness of the surface of the first solid electrolyte layer 21 and the unevenness of the surface of the second solid electrolyte layer 22 engage with each other, and the contact area between the first solid electrolyte layer 21 and the second solid electrolyte layer 22 becomes larger. In this case, although it is easy to ensure the ion conduction path, the first solid electrolyte layer 21 and the second solid electrolyte layer 22 tend to follow each other. Therefore, if a crack occurs in one of the first solid electrolyte layer 21 or the second solid electrolyte layer 22, a crack is also likely to occur in the other layer. In addition, cracks generated in one layer can easily propagate to the other layer. As a result, it is difficult to improve the short-circuit withstand capability of the all-solid-state battery. However, as described above, by making the ratio Rz1 / Rz2 between 0.15 and 0.25, the necessary ion conduction path is ensured between the first solid electrolyte layer 21 and the second solid electrolyte layer 22, and the first solid electrolyte layer 21 and the second solid electrolyte layer 22 are not excessively tightly bonded. Therefore, it is also possible to suppress the propagation of cracks from one layer to the other.

[0081] In the all-solid-state battery 100, the specific value of the maximum height Rz1 of the first surface 21x of the first solid electrolyte layer 21 is not particularly limited. For example, it can be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more, or it can be 3.0 μm or less, 2.0 μm or less, 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less. Similarly, in the all-solid-state battery 100, the specific value of the maximum height Rz2 of the second surface 22x of the second solid electrolyte layer 22 is not particularly limited. For example, it can be 0.5 μm or more, 0.8 μm or more, 1.0 μm or more, or 1.5 μm or more, or it can be 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, or 2.0 μm or less.

[0082] 1.5.2 Relationship at the interface between the second solid electrolyte layer and the second electrode layer

[0083] In the all-solid-state battery 100, the second solid electrolyte layer 22 may have a third surface 22y on the side opposite to the second surface 22x, or it may have a fourth surface 12x in contact with the third surface 22y. In this case, the maximum height Rz3 of the third surface 22y and the maximum height Rz4 of the fourth surface 12x may satisfy the following relationship (2) or (3).

[0084] 0.45≤Rz3 / Rz4≤1.00…(2)

[0085] 0.45≤Rz4 / Rz3≤1.00…(3)

[0086] By setting the ratio Rz3 / Rz4 or Rz4 / Rz3 to 0.45 or higher, the unevenness of the surface of the second solid electrolyte layer 22 engages with the unevenness of the surface of the second electrode layer 12, increasing the contact area between the second solid electrolyte layer 22 and the second electrode layer 12. This facilitates the establishment of an ion conduction path between the second solid electrolyte layer 22 and the second electrode layer 12. Furthermore, crack propagation does not need to be suppressed between the second solid electrolyte layer 22 and the second electrode layer 12. Even if a crack propagates from the second electrode layer 12 to the second solid electrolyte layer 22, as described above, crack propagation from the second solid electrolyte layer 22 to the first solid electrolyte layer 21 is suppressed, thus ensuring sufficient short-circuit withstand capability in the all-solid-state battery 100. There is no particular upper limit for the ratio Rz3 / Rz4 or Rz4 / Rz3; as described above, it can be 1.00 or lower, or 0.90 or lower, 0.80 or lower, 0.70 or lower, 0.60 or lower, or 0.50 or lower.

[0087] In the all-solid-state battery 100, the specific value of the maximum height Rz3 of the third surface 22y of the second solid electrolyte layer 22 is not particularly limited. For example, it can be 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, 0.8 μm or more, or 1.0 μm or more, or it can be less than 5.0 μm, less than 4.0 μm, less than 3.0 μm, or less than 2.0 μm. Similarly, the specific value of the maximum height Rz4 of the fourth surface 12x of the second electrode layer 12 is not particularly limited. For example, it can be 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, 0.8 μm or more, or 1.0 μm or more, or it can be less than 5.0 μm, less than 4.0 μm, less than 3.0 μm, or less than 2.0 μm.

[0088] 1.5.3 Relationship at the interface between the first solid electrolyte layer and the first electrode layer

[0089] In the all-solid-state battery 100, the first solid electrolyte layer 21 may have a fifth surface 21y on the side opposite to the first surface 21x, and the first electrode layer 11 may have a sixth surface 11x in contact with the fifth surface 21y. In this case, the maximum height Rz5 of the fifth surface 21y and the maximum height Rz6 of the sixth surface 11x can satisfy the following relationship (4) or (5). Thus, the unevenness of the surface of the first solid electrolyte layer 21 and the unevenness of the surface of the first electrode layer 11 engage with each other, which can increase the contact area between the first solid electrolyte layer 21 and the first electrode layer 11, and easily ensure the ion conduction path between the first solid electrolyte layer 21 and the first electrode layer 11.

[0090] 0.45≤Rz5 / Rz6≤1.00…(4)

[0091] 0.45≤Rz6 / Rz5≤1.00…(5)

[0092] 1.5.4 Method for determining the maximum height Rz

[0093] In this application, the maximum surface height Rz of each layer can be determined by observing the cross-section of the all-solid-state battery using methods such as SEM. For example, as Figure 3As shown, a two-dimensional image of the cross-section near the interface between the first solid electrolyte layer 21 and the second solid electrolyte layer 22 of the all-solid-state battery 100 is obtained by cross-sectional observation using SEM or similar methods. For each of the first solid electrolyte layer 21 and the second solid electrolyte layer 22, the two-dimensional image contains convexities of five or more surfaces. Two vertices P1 and P2 of these convexities are identified, and a straight line L1 connecting P1 and P2 is determined. Here, it is confirmed that there are no convexities (convexities protruding from the straight line L1) on the extension of the straight line L1 exceeding the height of P1 and P2. Next, a parallel line L2 is assumed to be parallel to the straight line L1, and this parallel line L2 intersects the bottom point B1 of the deepest recess on the surface of the solid electrolyte layer. Here, it is confirmed that there are no recesses (recesses deeper than the position of the parallel line L2) on the extension of the parallel line L2 exceeding the depth of B1. The distance H1 between the straight line L1 and the parallel line L2 is set as the maximum height Rz.

[0094] Alternatively, after peeling off each layer from the solid-state battery to expose the surface of each layer, Rz can be measured on the exposed surface according to JIS B0601:2001. Alternatively, after exposing the surface of each layer, the surface can be molded using resin or the like, and Rz can be measured on the resin or the like with a surface that is substantially the same as the surface, according to JIS B0601:2001, and this is considered as the Rz of the surface of each layer. In this case, using the SE-600 manufactured by Kosaka Research Institute Co., Ltd., Rz can be obtained under measurement conditions of a measurement length of 8 mm and a cutoff value of 0.5 mm for a sample cut to 10 mm × 10 mm. It is acceptable as long as either the Rz obtained from the above image analysis or the Rz measured according to the JIS standard satisfies the above relationship.

[0095] 1.5.5 Supplementary information on surface roughness

[0096] It should be noted that in an all-solid-state battery, on a surface A of an electrode layer, unevenness is formed approximately consistently over the entire surface of surface A; similarly, on a surface B of a solid electrolyte layer, unevenness is formed approximately consistently over the entire surface of surface B. In other words, the maximum height Rz of each layer's surface is substantially related to the arithmetic mean roughness Ra of each layer's surface. That is, it can be said that by determining the maximum height Rz of each layer's surface, the unevenness state pervading the entire surface of each layer can be represented.

[0097] In the all-solid-state battery 100, there is no particular limitation on the ratio or specific value of the arithmetic mean roughness Ra of the surfaces 11x, 12x, 21x, 21y, 22x, and 22y of each layer 11, 12, 21, and 22. For example, in the relationship with Rz mentioned above, the ratio Ra / Rz can be greater than 0.1 and less than 0.2.

[0098] 1.6 Other Components

[0099] The all-solid-state battery 100 only needs to have at least the above-mentioned layers, and may also have other components. The components described below are examples of other components that the all-solid-state battery 100 may have.

[0100] 1.6.1 Outer Packaging

[0101] The all-solid-state battery 100 can be a structure in which the aforementioned layers are housed inside an outer packaging body. More specifically, the portion other than the electrodes or terminals used to extract power from the all-solid-state battery 100 to the outside can be housed inside the outer packaging body. The outer packaging body can be any packaging body known as a battery packaging body. For example, a laminated film can be used as the outer packaging body. Furthermore, multiple all-solid-state batteries 100 can be electrically connected and optionally stacked to form a battery pack. In this case, the battery pack can also be housed inside a known battery casing.

[0102] 1.6.2 Sealing Resin

[0103] In the all-solid-state battery 100, each of the aforementioned layers can be sealed with resin. For example, at least the sides (surfaces along the stacking direction) of the laminate composed of each layer can be sealed with resin. This easily suppresses the mixing of moisture into the interior of each layer. As the sealing resin, known thermosetting resins and thermoplastic resins can be used.

[0104] 1.6.3 Constraint Members

[0105] The all-solid-state battery 100 may have constraint members for constraining each layer in the stacking direction. By applying constraint pressure to each layer along the stacking direction using the constraint members, the internal resistance of each layer is easily reduced. In this case, the constraint pressure is usually smaller than the pressures P1 and P2 described later, for example, it can be less than 50 MPa, less than 30 MPa, or less than 10 MPa, or more than 0.1 MPa or more.

[0106] 2. Manufacturing method of all-solid-state batteries

[0107] The technology disclosed herein also has aspects that constitute a method for manufacturing all-solid-state batteries. For example... Figure 4 and Figure 5A As shown in ~D, one embodiment of a method for manufacturing an all-solid-state battery includes: forming a first solid electrolyte layer 21 on the surface of a substrate 31 to obtain a transfer material 41 (step S1, reference). Figure 5AAfter stacking the transfer material 41 and the first electrode layer 11, pressure P1 is applied in the stacking direction to transfer the first solid electrolyte layer 21 of the transfer material 41 onto the first electrode layer 11, thereby obtaining a first laminate 51 of the first electrode layer 11 and the first solid electrolyte layer 21 (step S2, reference). Figure 5B ); The material 22a constituting the second solid electrolyte layer 22 is coated onto the second electrode layer 12 to obtain the second laminate 52 of the second electrode layer 12 and the second solid electrolyte layer 22 (step S3, refer to Figure 5C After stacking the first laminate 51 and the second laminate 52, a pressure P2 smaller than the pressure P1 is applied in the stacking direction to obtain an all-solid-state battery 100 having the first electrode layer 11, the first solid electrolyte layer 21, the second solid electrolyte layer 22 and the second electrode layer 12 in sequence (step S4, see reference). Figure 5D ).

[0108] 2.1 Process S1

[0109] like Figure 4 and Figure 5A As shown, in process S1, a first solid electrolyte layer 21 is formed on the surface of the substrate 31 to obtain the transfer material 41.

[0110] As for the substrate 31, it is sufficient that it can be peeled off from the first solid electrolyte layer 21 after pressure P1 is applied in the process S2 described later. For example, metal foil, resin film, etc. can be used as the substrate 31.

[0111] In step S1, there is no particular limitation on the method for forming the first solid electrolyte layer 21 on the surface of the substrate 31. For example, the transfer material 41 can be obtained by coating a slurry containing the material constituting the first solid electrolyte layer 21 onto the surface of the substrate 31 and then drying it. Alternatively, the transfer material 41 can be obtained by dry molding the material constituting the first solid electrolyte layer 21 together with the substrate 31.

[0112] 2.2 Process S2

[0113] like Figure 4 and Figure 5B As shown, in process S2, after the transfer material 41 and the first electrode layer 11 are laminated, pressure P1 is applied in the lamination direction.

[0114] As described above, the first electrode layer 11 may have an active material layer 11a and a current collector layer 11b. In this case, for example, the first electrode layer 11 can be obtained by coating a slurry containing a material constituting the active material layer 11a onto the surface of the current collector layer 11b and then drying it. Alternatively, the first electrode layer 11 can be obtained by dry molding the material constituting the active material layer 11a together with the current collector layer 11b.

[0115] In step S2, for example, the first solid electrolyte layer 21 of the transfer material 41 is overlapped with the active material layer 11a of the first electrode layer 11, and pressure P1 is applied in the stacking direction to make the interface between the first solid electrolyte layer 21 and the active material layer 11a tightly bonded. Pressure P1 can be a pressure capable of plastically deforming the solid electrolyte contained in the first solid electrolyte layer 21. Specifically, pressure P1 can be greater than 100 MPa, 200 MPa or more, 300 MPa or more, 400 MPa or more, 500 MPa or more, or 600 MPa or more. There is no particular upper limit to the pressure P1, as long as it is a pressure sufficient to prevent damage to each layer. There is no particular limitation on the pressurization method in step S2; various pressurization methods such as CIP, HIP, roll forming, uniaxial pressing, and molding can be used.

[0116] It should be noted that in step S2 and step S4 described later, "applying pressure in the stacking direction" means applying pressure P1 or pressure P2 at least in the stacking direction, which may include pressure P1 or pressure P2 in the stacking direction as well as pressure in directions other than the stacking direction.

[0117] In process S2, after the transfer material 41 and the first electrode layer 11 are stacked and pressurized as described above, the substrate 31 is removed by peeling off the transfer material 41, thereby obtaining the first laminate 51 of the first electrode layer 11 and the first solid electrolyte layer 21.

[0118] 2.3 Process S3

[0119] like Figure 4 and Figure 5C As shown, in process S3, the material 22a constituting the second solid electrolyte layer 22 is coated onto the second electrode layer 12 to obtain a second laminate 52 of the second electrode layer 12 and the second solid electrolyte layer 22.

[0120] As described above, the second electrode layer 12 may have an active material layer 12a and a current collector layer 12b. In this case, for example, the second electrode layer 12 can be obtained by coating a slurry containing a material constituting the active material layer 12a onto the surface of the current collector layer 12b and then drying it. Alternatively, the second electrode layer 12 can be obtained by dry molding the material constituting the active material layer 12a together with the current collector layer 12b. More specifically, the second electrode layer 12 can also be obtained by attaching a lithium metal foil serving as the active material layer 12a to the surface of a metal foil serving as the current collector layer 12b.

[0121] In step S3, for example, a slurry containing the material constituting the second solid electrolyte layer 22 is coated onto the surface of the active material layer 12a of the second electrode layer 12 and then dried to obtain the second laminate 52. Here, in step S3, the second laminate 52 may or may not be pressurized. If pressurized, a pressure lower than the aforementioned pressure P1 is applied. Especially when a layer containing lithium metal is used as the active material layer 12a, since lithium metal is soft, if a large pressure is applied to the second laminate 52, the lithium metal may excessively penetrate into the interior of the second solid electrolyte layer 22. Regarding this, in step S3, by using a coating method, even without pressurizing the second laminate 52, the second solid electrolyte layer 22 and the second electrode layer 12 can be tightly bonded within the second laminate 52, and after step S4 described later, the aforementioned ratio of Rz3 / Rz4 or Rz4 / Rz3 can be easily achieved.

[0122] In process S3, the second laminate 52 is obtained by coating, and the second laminate 52 is not pressurized, or is pressurized with a pressure less than the pressure P1. As a result, unevenness originating from solid electrolyte particles, etc., is easily retained on the second surface 22x of the second solid electrolyte layer 22. That is, the maximum height Rz2 of the second surface 22x is easily increased, and the ratio Rz1 / Rz2 mentioned above is easily satisfied.

[0123] On the other hand, if a transfer method similar to that used in steps S1 and S2 is employed in step S3, the maximum height Rz2 of the second surface 22x of the second solid electrolyte layer 22 is equal to the maximum height Rz1 of the first surface 21x of the first solid electrolyte layer 21, making it difficult to satisfy the aforementioned ratio Rz1 / Rz2. Furthermore, when the active material layer 12a of the second electrode layer 12 is a layer containing soft metallic lithium, it is inherently difficult to transfer the second solid electrolyte layer 22 onto the surface of the active material layer 12a.

[0124] 2.4 Process S4

[0125] like Figure 4 and Figure 5DAs shown, in step S4, after the first stacked body 51 and the second stacked body 52 are stacked, a pressure P2 smaller than the pressure P1 is applied in the stacking direction to obtain an all-solid-state battery 100 having a first electrode layer 11, a first solid electrolyte layer 21, a second solid electrolyte layer 22 and a second electrode layer 12 in sequence.

[0126] In step S4, it is not necessary to bond the first laminate 51 to the second laminate 52; pressure is only applied to achieve a moderate level of contact between the first laminate 51 and the second laminate 52. Furthermore, as mentioned above, when lithium metal is used as the active material in the electrode layer, there are concerns that excessive pressure could lead to unnecessary deformation of the lithium metal, penetration into the solid electrolyte layer, and short circuits. Moreover, excessive pressure could eliminate the surface irregularities of the second surface 22x of the second solid electrolyte layer 22, making it difficult to achieve the aforementioned Rz1 / Rz2 ratio. Regarding this, it is important that the pressure P2 in step S4 is lower than the pressure P1 in step S2. Specifically, the pressure P2 can be less than 200 MPa, 180 MPa or less, 150 MPa or less, 120 MPa or less, or 100 MPa or less. There is no particular limitation on the lower limit of the pressure P2; any pressure sufficient to ensure adequate contact at the interface of the battery materials is acceptable. There are no particular restrictions on the pressure application method in process S4. Various pressure application methods such as CIP, HIP, roller pressing, uniaxial pressing, and molding can be used.

[0127] 2.5 Other processes

[0128] The manufacturing method of an all-solid-state battery may also include steps such as housing the all-solid-state battery obtained as described above in an outer packaging, and installing terminals and other components required for the battery. Explanations of obvious steps in the manufacturing method of an all-solid-state battery are omitted.

[0129] Example

[0130] The following embodiments are shown to further illustrate the technology of this disclosure in detail, but the technology of this disclosure is not limited to the following embodiments.

[0131] 1. Comparative Example 1

[0132] 1.1 Fabrication of positive electrode composite material

[0133] As starting materials for the positive electrode composite, 1.05 g of sulfur (S), 0.852 g of P2S5, and 0.57 g of VGCF were used, and the starting materials were compounded by mechanical grinding. Specifically, the above starting materials were weighed in a glove box with a dew point temperature below -70°C and then mixed in an agate mortar for 15 minutes. A 45 mL jar (made of ZrO2) and zirconium oxide balls (pre-dried at 60°C) were prepared. Approximately 96g (about 500 pieces) of the mixed powder is placed in a container together with the zirconia balls. The mixture is mechanically ground at 500 rpm for 1 hour, stopped for 15 minutes, then rotated in the opposite direction and mechanically ground at 500 rpm for 1 hour, and stopped for 15 minutes. This process is repeated for 48 hours to obtain the positive electrode composite material.

[0134] 1.2 Fabrication of the first electrode layer

[0135] A solution of mesitylene containing 5% SBR and mesitylene were added to a polypropylene container and mixed with a shaker for 3 minutes. The positive electrode material (S8-P2S5 / C) was then added, and the mixing was repeated twice, once with a shaker for 3 minutes and again with an ultrasonic disperser for 30 seconds. Next, using a doctor blade with a 250 μm gap, the positive electrode material slurry obtained immediately after mixing in the ultrasonic disperser for 5 seconds was coated onto an Al foil serving as the positive electrode current collector layer. After visually confirming that the coated positive electrode material surface was dry, it was further dried on a hot plate at 100°C for 30 minutes, thus obtaining the positive electrode layer as the first electrode layer.

[0136] 1.3 Fabrication of the first solid electrolyte layer

[0137] A heptane solution containing 5% by mass of ABR, heptane, and butyl butyrate were added to a polypropylene container and mixed with a shaker for 3 minutes. Then, a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5 series solid electrolyte, D50 = 0.5 μm) was added, and the mixing was repeated twice, once with a shaker for 3 minutes and once with an ultrasonic dispersion device for 30 seconds. Next, using a coater with a 350 μm gap, the solid electrolyte slurry, obtained immediately after mixing in the ultrasonic dispersion device for 5 seconds, was coated onto an Al foil as a substrate. After visually confirming that the surface of the coated solid electrolyte was dry, it was further dried on a hot plate at 165°C for 30 minutes, thereby obtaining a transfer material consisting of a substrate and a solid electrolyte layer. The amount of ABR contained in the solid electrolyte layer was 0.6% by mass.

[0138] 1.4 Fabrication of the Second Solid Electrolyte Layer

[0139] A transfer material consisting of a substrate and a solid electrolyte layer was obtained using the same method as that used to fabricate the first solid electrolyte layer. The amount of ABR contained in the solid electrolyte layer was 0.6% by mass.

[0140] 1.5 Fabrication of an all-solid-state battery

[0141] After overlapping a transfer material on the surface of the positive electrode layer and pressing it at 600 MPa, the substrate is peeled off from the transfer material, thereby transferring a first solid electrolyte layer onto the surface of the positive electrode layer, resulting in a first laminate having a positive current collector layer, a positive active material layer, and a first solid electrolyte layer in sequence. Next, the transfer material is overlapped again on the surface of the first solid electrolyte layer of the first laminate and pressed at 600 MPa, then the substrate is peeled off from the transfer material, resulting in a second laminate having a positive current collector layer, a positive active material layer, a first solid electrolyte layer, and a second solid electrolyte layer in sequence. Then, a lithium foil serving as a negative active material layer and a Ni foil serving as a negative current collector layer are laminated on the surface of the second solid electrolyte layer of the second laminate, and pressed at 100 MPa, resulting in an all-solid-state battery having a positive current collector layer, a positive active material layer, a first solid electrolyte layer, a second solid electrolyte layer, a negative active material layer, and a negative current collector layer in sequence. The obtained all-solid-state battery is sealed in a laminate and then evaluated by constraint at 10 MPa in the lamination direction.

[0142] 2. Comparative Example 2

[0143] Except that the amount of ABR contained in the first solid electrolyte layer and the second solid electrolyte layer is set to 10% by mass, an all-solid-state battery was fabricated in the same manner as in Comparative Example 1.

[0144] 3. Comparative Example 3

[0145] Except that the amount of ABR contained in the first solid electrolyte layer is set to 0.6% by mass, and the amount of ABR contained in the second solid electrolyte layer is set to 10% by mass, the all-solid-state battery was manufactured in the same manner as in Comparative Example 1.

[0146] 4. Example 1

[0147] 4.1 Fabrication of the first layer

[0148] Similar to Comparative Example 1, a transfer material was prepared to serve as the first electrode layer, consisting of a positive electrode layer and a first solid electrolyte layer. Then, the transfer material was overlapped on the surface of the positive electrode layer and pressed at 600 MPa. The substrate was then peeled off from the transfer material, thereby transferring the first solid electrolyte layer onto the surface of the positive electrode layer, resulting in a first laminate having a positive current collector layer, a positive active material layer, and a first solid electrolyte layer in sequence.

[0149] 4.2 Fabrication of the Second Layer

[0150] A Li foil (70 μm thick) was adhered to the surface of a Ni foil serving as the negative electrode current collector layer, thus obtaining a negative electrode layer serving as the second electrode layer. Meanwhile, a heptane solution containing 5% by mass of ABR, heptane, and butyl butyrate were added to a polypropylene container and mixed using a shaker for 3 minutes. Here, a sulfide solid electrolyte (LiI-LiBr-Li2S-P2S5 series solid electrolyte, D50 = 0.5 μm) was added, and the mixing was repeated twice, once with a shaker for 3 minutes and once with an ultrasonic dispersion device for 30 seconds. Next, using a coater with a 350 μm gap, the solid electrolyte slurry obtained immediately after mixing in the ultrasonic dispersion device for 5 seconds was coated onto the Li foil of the negative electrode layer. After visually confirming that the surface of the coated solid electrolyte was dry, it was further dried on a hot plate at 165°C for 30 minutes, thereby obtaining a second laminate of the second solid electrolyte layer and the negative electrode layer serving as the second electrode layer. The amount of ABR contained in the solid electrolyte layer was 0.6% by mass.

[0151] 4.3 Fabrication of All-Solid-State Batteries

[0152] The first and second laminates were stacked and pressed at 100 MPa to obtain an all-solid-state battery having, sequentially, a positive electrode current collector layer, a positive electrode active material layer, a first solid electrolyte layer, a second solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer. The obtained all-solid-state battery was sealed in a laminate and then evaluated by constraint at 10 MPa in the lamination direction.

[0153] 5. Example 2

[0154] Except that the amount of ABR contained in the first and second solid electrolyte layers is set to 10% by mass, the all-solid-state battery is fabricated in the same manner as in Example 1.

[0155] 6. Example 3

[0156] Except that the amount of ABR contained in the first solid electrolyte layer is set to 0.6% by mass, and the amount of ABR contained in the second solid electrolyte layer is set to 10% by mass, the all-solid-state battery is manufactured in the same manner as in Example 1.

[0157] 7. Example 4

[0158] Instead of Li foil as the negative electrode active material layer, Li-Mg alloy foil was used, and otherwise, an all-solid-state battery was fabricated in the same manner as in Example 3.

[0159] 8. Evaluation methods for all-solid-state batteries

[0160] 8.1 Surface Roughness Measurement

[0161] For each all-solid-state battery involved in the embodiments and comparative examples, the maximum surface height Rz of each layer at the interface between the first solid electrolyte layer and the second solid electrolyte layer was measured. The method for measuring Rz is as described above. The results are shown in Table 1 below.

[0162] 8.2 Short-circuit withstand capability

[0163] The all-solid-state battery was homogenized by placing it in a constant-temperature bath at 60°C for 3 hours. Then, it was subjected to an amplitude of 0.46 mA / cm². 2 The current density was used for discharging and charging. The cutoff voltage was 1.5-3.1V. For each of the all-solid-state batteries involved in the examples and comparative examples, the maximum charge capacity obtained until a short circuit was reached was measured and taken as the "short-circuit withstand capacity" to evaluate the short-circuit withstand performance of the all-solid-state battery. It can be said that the larger the short-circuit withstand capacity, the better the short-circuit withstand performance. The results are shown in Table 1 below.

[0164] [Table 1]

[0165]

[0166] 9. Evaluation Results

[0167] In Table 1, Comparative Example 1 and Example 1, Comparative Example 2 and Example 2, and Comparative Example 3 and Example 3 are compared based on the binder dosage. Example 4 can be considered a variation of Example 3. The results shown in Table 1 indicate that at the interface between the first and second solid electrolyte layers, when the ratio Rz1 / Rz2 of the maximum height Rz1 of the surface of the first solid electrolyte layer to the maximum height Rz2 of the surface of the second solid electrolyte layer is within the range of 0.15 or more and 0.25 or less, the all-solid-state battery exhibits excellent short-circuit withstand performance (Examples 1-4). On the other hand, it is known that if the ratio Rz1 / Rz2 approaches 1.00, the short-circuit withstand performance of the all-solid-state battery decreases (Comparative Examples 1-3). This is believed to be based on the following mechanism.

[0168] First, when the ratio Rz1 / Rz2 is too small, the difference in surface roughness between the first and second solid electrolyte layers is too large. Therefore, it is believed that a large number of voids are easily generated between the first and second solid electrolyte layers, making it difficult to ensure a sufficient ion conduction path between them. Consequently, it is considered that the battery cannot guarantee sufficient capacity. Regarding this point, in Examples 1-4, it is believed that by setting the ratio Rz1 / Rz2 to 0.15 or higher, the necessary ion conduction path is ensured between the first and second solid electrolyte layers, thus guaranteeing sufficient capacity.

[0169] On the other hand, when the ratio Rz1 / Rz2 is around 1.00, it is believed that the surface irregularities of the first solid electrolyte layer and the second solid electrolyte layer interlock, increasing the contact area between them. Therefore, while it is easier to ensure the ion conduction path, the first and second solid electrolyte layers tend to follow each other. If a crack occurs in one of these layers, it is likely to propagate to the other. Regarding this, in Comparative Examples 1-3, it was believed that the short-circuit withstand capacity of the all-solid-state battery decreased due to the propagation of this crack. On the other hand, in Examples 1-4, it was believed that by keeping the ratio Rz1 / Rz2 below 0.25, the propagation of cracks in the solid electrolyte layer was suppressed, and the short-circuit withstand capacity of the all-solid-state battery increased.

[0170] 10. Supplement

[0171] Furthermore, the inventors have also confirmed the following through experiments. First, for either the first or second laminate, after fabrication by coating, when the first and second laminates are overlapped and pressurized at 100 MPa, except for the ratio Rz1 / Rz2 at the interface between the first and second solid electrolyte layers approaching 1.00, it is difficult to ensure ion conduction pathways at the interface between the positive electrode layer and the first solid electrolyte layer, resulting in a smaller maximum battery capacity. Consequently, the short-circuit withstand capacity also decreases. In this regard, fabricating either the first or second laminate using a transfer method has advantages.

[0172] Furthermore, when using lithium metal as the negative electrode active material, lithium metal is soft and cannot withstand high pressure, making it difficult to transfer a solid electrolyte layer onto the surface of the negative electrode active material layer containing lithium metal. Even if a solid electrolyte layer could be transferred onto the surface of the negative electrode active material layer under light pressure, the contact between the negative electrode active material layer and the solid electrolyte layer would be poor, raising concerns about dendrite growth during battery charging and discharging. However, by coating the surface of the negative electrode active material layer containing lithium metal with a solid electrolyte material, the contact between the negative electrode active material layer and the solid electrolyte layer is increased, making it easier to suppress dendrite growth caused by poor contact. In this regard, it is advantageous to fabricate either the first or second laminate (especially the second laminate containing lithium metal as the negative electrode active material) using a coating method.

[0173] Furthermore, when the first and second layers are stacked and pressure is applied, if the pressure is too high, in addition to causing unwanted deformation of the lithium metal, which serves as the negative electrode active material, and the penetration of lithium metal into the solid electrolyte layer, the unevenness at the interface between the first and second solid electrolyte layers is also eliminated, resulting in a ratio closer to 1.00 than Rz1 / Rz2. As a result, it is difficult to ensure sufficient short-circuit withstand capacity in all-solid-state batteries. In this regard, it is advantageous that when the first and second layers are stacked and pressure P2 is applied, this pressure P2 is smaller than the pressure P1 applied when obtaining the first layer.

[0174] It should be noted that while the above embodiments and comparative examples described a case where a lithium-sulfur battery was used as an all-solid-state battery, it is believed that the technology of this disclosure can improve the short-circuit withstand capability of all-solid-state batteries even when applied to all-solid-state batteries other than lithium-sulfur batteries. The technology of this disclosure focuses on the state of the interface between the first solid electrolyte layer and the second solid electrolyte layer, and the first electrode layer and the second electrode layer can be freely changed. For example, an active material other than sulfur can be used as the positive electrode active material, and an active material other than metallic lithium (elemental lithium and lithium alloys) can be used as the negative electrode active material. However, when using sulfur as the positive electrode active material, it is believed that the expansion and contraction of sulfur during battery charging and discharging are large, and the stress accompanying this expansion and contraction easily accumulates between the positive electrode active material layer and the solid electrolyte layer. This stress is not mitigated, making it easy for cracks to form in the solid electrolyte layer. The technology of this disclosure suppresses the propagation of cracks in the solid electrolyte layer, thereby expecting high performance. Furthermore, the technology of this disclosure is also applicable to situations where it is desirable to solve the unique problems (softness, inability to transfer solid electrolyte layers, etc.) that arise when using metallic lithium as the negative electrode active material.

[0175] Furthermore, in the above embodiments and comparative examples, an all-solid-state battery having a positive electrode layer as a first electrode layer and a negative electrode layer as a second electrode layer was illustrated. However, the technology disclosed herein can also achieve the same effect when applied to an all-solid-state battery having a negative electrode layer as a first electrode layer and a positive electrode layer as a second electrode layer.

[0176] As can be seen from the results of the above embodiments and comparative examples, the all-solid-state battery with the following configurations (1) and (2) is less prone to the propagation of cracks in the solid electrolyte layer and has excellent short-circuit resistance.

[0177] (1) It has a first electrode layer, a first solid electrolyte layer, a second solid electrolyte layer and a second electrode layer in sequence.

[0178] (2) The first solid electrolyte layer has a first surface, and the second solid electrolyte layer has a second surface in contact with the first surface. The maximum height Rz1 of the first surface and the maximum height Rz2 of the second surface satisfy the relationship 0.15≤Rz1 / Rz2≤0.25.

[0179] Furthermore, it is known that a solid-state battery having the above-described structure can be easily manufactured by a manufacturing method including the following steps S1 to S4. Also, the order of S1 to S3 described below is not limited.

[0180] (S1) A first solid electrolyte layer is formed on the surface of the substrate to obtain the transfer material.

[0181] (S2) After the transfer material and the first electrode layer are stacked, pressure P1 is applied in the stacking direction to transfer the first solid electrolyte layer of the transfer material to the first electrode layer, thereby obtaining a first laminate of the first electrode layer and the first solid electrolyte layer.

[0182] (S3) Coat the second electrode layer with the material that constitutes the second solid electrolyte layer to obtain the second laminate of the second electrode layer and the second solid electrolyte layer.

[0183] (S4) After stacking the first stack and the second stack, a pressure P2 smaller than the pressure P1 is applied in the stacking direction to obtain an all-solid-state battery having the first electrode layer, the first solid electrolyte layer, the second solid electrolyte layer and the second electrode layer in sequence.

Claims

1. An all-solid-state battery, comprising, in sequence, a first electrode layer, a first solid electrolyte layer, a second solid electrolyte layer, and a second electrode layer, wherein, The first solid electrolyte layer has a first surface, and the second solid electrolyte layer has a second surface in contact with the first surface. The maximum height Rz1 of the first surface and the maximum height Rz2 of the second surface satisfy the following relationship (1). 0.15≤Rz1 / Rz2≤0.25 … (1) The methods for measuring the maximum height Rz1 of the first surface and the maximum height Rz2 of the second surface are as follows: Near the interface between the first solid electrolyte layer and the second solid electrolyte layer, a cross-sectional observation is performed using SEM to obtain a two-dimensional image of the cross-section. In this two-dimensional image, for each of the first and second solid electrolyte layers, there are protrusions containing more than five surfaces. Two vertices of the protrusions are identified, and a straight line connecting the two vertices is determined. There are no protrusions protruding from the straight line on the extension of the straight line that have a height exceeding that of the two vertices. Assuming a parallel line to the straight line, the parallel line intersects the bottom point of the deepest recess on the surface of the solid electrolyte layer. There are no recesses with a depth exceeding that of the bottom point on the extension of the parallel line that are deeper than the position of the parallel line. The distance between the straight line and the parallel line is set as the maximum height.

2. The all-solid-state battery according to claim 1, wherein, The second solid electrolyte layer has a third surface on the side opposite to the second surface, and the second electrode layer has a fourth surface in contact with the third surface. The maximum height Rz3 of the third surface and the maximum height Rz4 of the fourth surface satisfy the following relationship (2) or (3). 0.45≤Rz3 / Rz4≤1.00 … (2) 0.45≤Rz4 / Rz3≤1.00 … (3) The methods for measuring the maximum height Rz3 of the third surface and the maximum height Rz4 of the fourth surface are the same as those in claim 1.

3. The all-solid-state battery according to claim 1 or 2, wherein, The first electrode layer includes a positive electrode active material layer, and the second electrode layer includes a negative electrode active material layer.

4. The all-solid-state battery according to claim 3, wherein, The negative electrode active material layer contains metallic lithium as the negative electrode active material.

5. The all-solid-state battery according to claim 3 or 4, wherein, The positive electrode active material layer contains sulfur, which serves as the positive electrode active material.

6. A method for manufacturing the all-solid-state battery according to claim 1, comprising: A first solid electrolyte layer is formed on the surface of the substrate to obtain the transfer material; After the transfer material is stacked with the first electrode layer, pressure P1 is applied in the stacking direction to transfer the first solid electrolyte layer of the transfer material onto the first electrode layer, thereby obtaining a first laminate of the first electrode layer and the first solid electrolyte layer. By coating the second electrode layer with a material constituting the second solid electrolyte layer, a second laminate of the second electrode layer and the second solid electrolyte layer is obtained; and After stacking the first and second stacks, a pressure P2 smaller than the pressure P1 is applied in the stacking direction to obtain an all-solid-state battery having the first electrode layer, the first solid electrolyte layer, the second solid electrolyte layer, and the second electrode layer in sequence.

7. The manufacturing method according to claim 6, wherein, The first electrode layer includes a positive electrode active material layer, and the second electrode layer includes a negative electrode active material layer.

8. The manufacturing method according to claim 7, wherein, The negative electrode active material layer contains metallic lithium as the negative electrode active material.

9. The manufacturing method according to claim 7 or 8, wherein, The positive electrode active material layer contains sulfur, which serves as the positive electrode active material.

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