solid-state batteries

Abstract

This relieves the stress caused by the expansion and contraction of the positive electrode active material. [Solution] The device comprises a positive electrode layer containing a positive electrode active material containing sulfur, a negative electrode layer containing a negative electrode active material containing lithium, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises a plurality of spaced-apart columnar structures, and the aspect ratio [β / α] obtained from the diameter α of the surface of the columnar structure in contact with the solid electrolyte layer and the dimension β of the columnar structure in the thickness direction of the positive electrode layer is 2 or more, and the aspect ratio is less than or equal to the aspect ratio at which the buckling stress obtained by Euler's buckling formula for the columnar structure is greater than the stress due to the confinement pressure acting on the columnar structure.

Description

[Technical Field]

[0001] This disclosure relates to solid-state batteries. [Background technology]

[0002] In recent years, the importance of secondary batteries has increased, and in addition to secondary batteries with electrolytes, the development of solid-state batteries using solid electrolytes is progressing. All-solid-state batteries, an example of a solid-state battery, are batteries that have a solid electrolyte layer instead of an electrolyte, and because they do not use flammable organic solvents, safety devices can be simplified, and they are superior in terms of manufacturing cost and productivity. Patent documents 1 and 2 disclose so-called LiS batteries, which use sulfur (S) as the positive electrode active material and lithium (Li) as the negative electrode active material. LiS batteries are attracting attention as solid-state batteries that can achieve both high gravimetric energy density and low cost.

[0003] However, several technical challenges have been pointed out regarding LiS batteries. According to Patent Document 1, a problem with LiS batteries is that the sulfur, which is the positive electrode active material, expands and contracts during charging and discharging, interrupting the ion and electron conduction pathways. Regarding this point, Patent Document 1 discloses a method of mixing sulfur and Li2S in a predetermined ratio when manufacturing the positive electrode composite material for a LiS battery. It is said that by mixing Li2S into the positive electrode composite material, the effects of expansion and contraction of the active material can be mitigated from the first charge and discharge. Furthermore, Patent Document 2 mentions that in LiS batteries, sulfur dissolves into the electrolyte during oxidation-reduction reactions, degrading the battery life, and if an appropriate electrolyte cannot be selected, Li2S, which is a sulfur reducer, precipitates and can no longer participate in electrochemical reactions. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-026199 [Patent Document 2] Japanese Patent Publication No. 2003-123840 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in a solid-state battery comprising a positive electrode layer containing a positive electrode active material containing sulfur, a negative electrode layer containing a negative electrode active material containing lithium, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the positive electrode active material containing sulfur expands and contracts during charging and discharging, generating large internal stresses in a direction perpendicular to the stacking direction of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer. This causes cracks in the solid electrolyte layer, leading to problems such as short circuits and a decrease in rate characteristics due to damage to the conduction path.

[0006] Therefore, in view of the above-mentioned circumstances, this disclosure aims to provide a solid-state battery that has a positive electrode layer capable of relieving the stress generated in the positive electrode layer due to the expansion and contraction of the positive electrode active material, and that can prevent the occurrence of cracks in the solid electrolyte layer. [Means for solving the problem]

[0007] To achieve the above-mentioned objectives, the inventors conducted diligent studies and found that by including a plurality of columnar structures having a predetermined aspect ratio in the positive electrode layer, stress caused by the expansion and contraction of the positive electrode active material can be alleviated, thereby preventing cracking of the solid electrolyte layer. This led to the completion of this disclosure. This disclosure includes the following: <1> A solid-state battery comprising a positive electrode layer containing a positive electrode active material containing sulfur, a negative electrode layer containing a negative electrode active material containing lithium, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises a plurality of spaced-apart columnar structures, the aspect ratio [β / α] obtained from the diameter α of the surface of the columnar structure in contact with the solid electrolyte layer and the dimension β of the columnar structure in the thickness direction of the positive electrode layer is 2 or more, and the aspect ratio is less than or equal to the aspect ratio at which the buckling stress obtained by Euler's buckling formula for the columnar structure is greater than the stress due to the confinement pressure acting on the columnar structure. <2>The solid-state battery according to <1>, wherein the columnar structure has a cross-sectional shape that becomes smaller in diameter toward the surface in contact with the solid electrolyte layer. <3>The solid-state battery according to <1> or <2>, wherein the plurality of columnar structures are in contact with each other on the side opposite to the surface in contact with the solid electrolyte layer. <4>The solid-state battery according to any one of <1> to <3>, wherein the plurality of columnar structures are arranged in a concentric, lattice, or honeycomb pattern. <5>The solid-state battery according to any one of <1> to <4>, wherein the positive electrode layer contains a solid electrolyte containing sulfur and phosphorus.

Advantages of the Invention

[0008] In the solid-state battery according to the present disclosure, after repeated charge and discharge, the stress generated in the positive electrode layer can be relaxed, the occurrence of cracks in the solid electrolyte layer can be prevented, and cracks in the solid electrolyte layer can be prevented.

Brief Description of the Drawings

[0009] [Figure 1] It is a cross-sectional view of the main part of the solid-state battery shown as an embodiment of the present disclosure. [Figure 2] It is a perspective view of the main part schematically showing the columnar structure in the solid-state battery shown as an embodiment of the present disclosure. [Figure 3] It is a schematic diagram of the columnar structure for explaining the aspect ratio calculated for the columnar structure. [Figure 4] It is a cross-sectional view of the main part of the solid-state battery shown as another embodiment of the present disclosure.

Modes for Carrying Out the Invention

[0010] The solid-state battery according to this disclosure comprises a positive electrode layer containing a positive electrode active material containing sulfur, a negative electrode layer containing a negative electrode active material containing lithium, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises a plurality of spaced-apart columnar structures. In the solid-state battery according to this disclosure, the aspect ratio [β / α] obtained from the diameter α of the surface of the columnar structure in contact with the solid electrolyte layer and the dimension β of the columnar structure in the thickness direction of the positive electrode layer is 2 or more, and the aspect ratio is less than or equal to the aspect ratio at which the buckling stress obtained by Euler's buckling formula for the columnar structure is greater than the stress due to the confinement pressure on the columnar structure.

[0011] The solid-state battery of this disclosure comprises a plurality of columnar structures arranged spaced apart from each other, and the shape of these columnar structures is defined to have the aspect ratio described above. As a result, in the solid-state battery of this disclosure, even if the sulfur-containing positive electrode active material repeatedly expands and contracts with charging and discharging, the stress generated in the positive electrode layer can be relieved, and cracking of the solid electrolyte layer can be prevented. This is presumed to be because, since a gap is formed between the columnar structures, the expansion of the positive electrode active material, i.e., the expansion of the columnar structures, is absorbed by this gap, resulting in the relief of the stress generated in the positive electrode layer.

[0012] Here, Euler's buckling equation is given by the following formula for buckling stress σ. Equation: σ = nπ 2 E / λl 2 In the above formula, n is the terminal condition coefficient, and when both ends are fixed as in the columnar structure described above, n=4. In the above formula, π represents pi (3.14), and E represents the Young's modulus. In the above formula, λ is the aspect ratio of the columnar structure (as described above [β(μm) / α(μm)]), and l is the length of the columnar structure β (μm).

[0013] In the solid-state battery of this disclosure, by setting the aspect ratio of the columnar structure to 2 or more, even if the columnar structure expands as described above, the expansion is absorbed by the spacing between the columnar structures, preventing the occurrence of cracks in the solid electrolyte layer. In particular, the aspect ratio of the columnar structure is preferably 2.5 or more, more preferably 3 or more, even more preferably 3.5 or more, and even more preferably 4 or more. Furthermore, the upper limit of the aspect ratio of the columnar structure is defined so that the buckling stress is greater than the constraining pressure applied to the columnar structure, as described above. As a result, even when constraining pressure is applied to the columnar structure, the columnar structure can maintain its shape without buckling. The constraining pressure is the pressure applied in the stacking direction of the laminate including the positive electrode layer, solid electrolyte layer, and negative electrode layer, and is, for example, the pressure applied by a constraining member to the laminate or the pressure applied by housing the laminate inside the outer casing.

[0014] More specifically, the upper limit of the aspect ratio of the columnar structure is calculated as a value dependent on the dimensions β of the columnar structure, the Young's modulus of the positive electrode active material, and the confinement pressure, as is clear from Euler's buckling formula mentioned above. For example, if the confinement pressure is 1 MPa, the Young's modulus of the sulfur in the positive electrode active material layer is 10 GPa, and the dimensions β of the columnar structure are 78 μm, then it can be calculated that buckling will occur if the aspect ratio is 64.89 or higher. In this case, the upper limit of the aspect ratio can be set to 64 or less. However, the upper limit of the aspect ratio is not limited to 64 or less; for example, it can be 60 or less, preferably 50 or less, more preferably 40 or less, and even more preferably 30 or less.

[0015] Here, the columnar structure may be any shape, such as a cylinder, polygonal prism, frustocone, or frustocone. In particular, when the columnar structure is a polygonal prism or frustocone, it is preferable that the corners in the cross-section are not acute (i.e., obtuse), so it is preferable to make it a square prism or a polygonal prism or frustocone of a square or larger. Making the columnar structure a cylinder, frustocone, polygonal prism of a square or larger, or frustocone of a square or larger increases its mechanical strength, thus preventing cracks caused by expansion and contraction of the columnar structure due to charging and discharging. These columnar structures can be formed, for example, by laser processing after forming a positive electrode layer containing positive electrode active material in layers.

[0016] The surface in contact with the solid electrolyte layer in a columnar structure varies depending on the shape of the columnar structure, such as a cylinder, polygonal prism, frustocone, or frustoconical pyramid, and can be circular or polygonal. The diameter α of the surface in contact with the solid electrolyte layer in a columnar structure can be the diameter if the surface is circular, the dimension of the major axis or the average dimension of the major and minor axes if the surface is elliptical, or the dimension of the maximum length within the surface or the average dimension of the maximum and minimum lengths within the surface if the surface is polygonal.

[0017] Figure 1 shows one embodiment of a laminate in the solid-state battery of the present disclosure, including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. As shown in Figure 1, the laminate constituting the solid-state battery of the present disclosure comprises a positive electrode layer 1, a solid electrolyte layer 2, and a negative electrode layer 3. Although not shown, a positive electrode current collector is provided on the side of the positive electrode layer 1 opposite to the contact surface with the solid electrolyte layer 2, and a negative electrode current collector is provided on the side of the negative electrode layer 3 opposite to the contact surface with the solid electrolyte layer 2. In particular, in the laminate constituting the solid-state battery of the present disclosure, the positive electrode layer 1 comprises a plurality of spaced-apart columnar structures 4. A cross-section of the laminate shown in this example is shown in Figure 1, but the shape of the laminate when viewed from above is not particularly limited and may be any shape such as circular, rectangular, polygonal, etc.

[0018] The multiple columnar structures 4 may be arranged randomly or in a regular pattern. In particular, it is preferable that the spacing between adjacent columnar structures 4 is approximately equal. Approximately equal spacing between adjacent columnar structures 4 means that the nearest neighbor distance at the upper end faces of the closest columnar structures 4 is approximately equal in distance. Approximately equal distance means that the difference between the maximum distance and the minimum distance is within 25%, preferably within 20%, more preferably within 15%, and even more preferably within 10%. By making the spacing between adjacent columnar structures 4 approximately equal, it is possible to avoid localized increases in internal stress due to the expansion of the columnar structures 4, and stress can be relieved throughout the entire positive electrode layer 1.

[0019] Examples of arranging multiple columnar structures 4 in a regular manner can be seen in Figures 2(a), 2(b), and 2(c). In the example shown in Figure 2(a), the multiple columnar structures 4 are each cylindrical and are arranged in multiple concentric rows. In the example shown in Figure 2(b), the multiple columnar structures 4 are each cylindrical and are arranged in a grid pattern. In the example shown in Figure 2(c), the multiple columnar structures 4 are each hexagonal prisms and are arranged in a honeycomb pattern. In all of these cases, because the multiple columnar structures 4 are arranged regularly, it is possible to avoid localized increases in internal stress due to the expansion of the columnar structures 4, and stress can be relieved throughout the entire positive electrode layer 1.

[0020] Furthermore, as described above, the aspect ratio of the columnar structure 4 is determined by [β / α], which is the diameter α of the surface of the columnar structure 4 that is in contact with the solid electrolyte layer 2, and the dimension β of the positive electrode layer 1 in the thickness direction for the columnar structure 4. More specifically, for a cylindrical or polygonal columnar structure 4, as shown in Figure 3(a), dimension a corresponds to diameter α and dimension b corresponds to dimension β. Also, as shown in Figure 3(b), if the columnar structure 4 is a quadrangular prism with a rectangular cross-sectional shape, the diagonal of the rectangle between side a and side c is taken as diameter α. In this case as well, dimension b corresponds to dimension β.

[0021] Furthermore, in the solid-state battery of this disclosure, it is preferable that the columnar structure 4 has a cross-sectional shape that becomes smaller in diameter toward the surface in contact with the solid electrolyte layer 2. Examples of columnar structures 4 having a cross-sectional shape that becomes smaller in diameter toward the surface in contact with the solid electrolyte layer 2 include the truncated cone or truncated polygonal columnar structure 4 shown in Figure 4. When the columnar structure 4 has a cross-sectional shape that becomes smaller in diameter toward the surface in contact with the solid electrolyte layer 2, even if the columnar structure 4 repeatedly expands and contracts with charging and discharging, stress can be relieved in the region of the positive electrode layer 1 close to the solid electrolyte layer 2, and the occurrence of cracks in the solid electrolyte layer 2 can be reliably prevented.

[0022] Furthermore, in the solid-state battery of this disclosure, it is preferable that the multiple columnar structures 4 are in contact on the side opposite to the surface in contact with the solid electrolyte layer 2. In other words, the multiple columnar structures 4 are spaced apart on the side in contact with the solid electrolyte layer 2, and the spacing between them gradually narrows towards the side opposite to the surface in contact with the solid electrolyte layer 2, until they are in contact on the surface in contact with the solid electrolyte layer 2. Examples of shapes in which the multiple columnar structures 4 are in contact on the side opposite to the surface in contact with the solid electrolyte layer 2 include the frustoconical or frustopyramidal columnar structures 4 shown in Figure 4. Although the multiple columnar structures 4 shown in Figure 4 are in contact on the side opposite to the surface in contact with the solid electrolyte layer 2, the solid-state battery of this disclosure is not limited to this configuration. In the solid-state battery of this disclosure, the multiple columnar structures 4 may be in contact from the side opposite to the surface in contact with the solid electrolyte layer 2 up to a height of 1 / 10, preferably up to a height of 1 / 5, more preferably up to a height of 1 / 3, in the thickness direction of the positive electrode layer 1. This case is also included in the form in which they are in contact on the side opposite to the surface in contact with the solid electrolyte layer 2. By configuring the multiple columnar structures 4 to contact the solid electrolyte layer 2 on the opposite side from the surface in contact with it, the volume of the multiple columnar structures 4 can be increased, thereby improving battery performance. In this case, the solid electrolytes repel each other, reducing stress in the direction perpendicular to the stacking direction.

[0023] The solid-state battery of this disclosure, configured as described above, will now be explained in more detail. However, the technical scope of the solid-state battery of this disclosure is not limited to the following description.

[0024] <Cathode active material> In the solid-state battery of this disclosure, the positive electrode layer contains sulfur as a positive electrode active material. The positive electrode layer contains at least sulfur as a positive electrode active material, and may further optionally contain an electrolyte, a conductive additive, a binder, etc. The positive electrode layer may also contain various other additives. The content of each component in the positive electrode layer can be appropriately determined according to the desired battery performance. For example, with the entire positive electrode layer (total solid content) as 100% by mass, the content of the positive electrode active material may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or 100% by mass or less, or 90% by mass or less. The thickness of the positive electrode layer is not particularly limited and may be, for example, 0.1 μm or more, 1 μm or more, or 10 μm or more, or 2 mm or less, 1 mm or less, or 500 μm or less.

[0025] As mentioned above, at least sulfur is used as the positive electrode active material. The sulfur can be any material capable of functioning as a positive electrode active material, and may be elemental sulfur or a sulfur compound. For example, the positive electrode active material may be elemental sulfur. For example, S8 sulfur can be used as an elemental sulfur. S8 sulfur has three crystalline forms: α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), and γ-sulfur (monoclinic sulfur), and any of these crystalline forms may be used. The amount of positive electrode active material contained in the positive electrode layer is not particularly limited and may be appropriately determined according to the desired battery performance. For example, the positive electrode layer may contain 10% to 80% by mass of positive electrode active material. The lower limit of the positive electrode active material content may be 15% or more by mass, 20% or more by mass, or 25% or more by mass. The upper limit of the positive electrode active material content may be 70% or less by mass, or 60% or less by mass.

[0026] A portion or all of the positive electrode active material may be solid-dissolved in a sulfur-containing compound, as described later. In other words, the positive electrode layer may contain a solid solution of the positive electrode active material and a sulfur-containing compound. Furthermore, the sulfur in the positive electrode active material and the sulfur in the sulfur-containing compound may have a chemical bond (SS bond). Examples of sulfur-containing compounds include boron-containing sulfur compounds containing boron and sulfur, and phosphorus-containing sulfur compounds containing phosphorus and sulfur. Either or both of the boron-containing sulfur compound and the phosphorus-containing sulfur compound can be used as the sulfur compound. The positive electrode layer may contain only the positive electrode active material and the sulfur-containing compound, or it may further contain other elements (e.g., Ge, Sn, Si, or Al).

[0027] The sulfur-containing compound in the positive electrode layer can take various forms. For example, the positive electrode layer may contain a sulfur-containing compound having an ortho composition structure. That is, a sulfur-containing compound having boron and sulfur may have an ortho structure of boron. Specifically, the ortho structure of boron is the BS3 structure. Also, a sulfur-containing compound having phosphorus and sulfur may have an ortho structure of phosphorus. Specifically, the ortho structure of phosphorus is the PS4 structure. Furthermore, the sulfur-containing compound may have an ortho structure of an M element (where M is, for example, Ge, Sn, Si, or Al). Examples of ortho structures of an M element include the GeS4 structure, SnS4 structure, SiS4 structure, and AlS3 structure. In addition, the positive electrode mixture may contain sulfides as sulfur-containing compounds. That is, a sulfur-containing compound having boron and sulfur may have a boron sulfide (B2S3). On the other hand, a sulfur-containing compound having phosphorus and sulfur may have a phosphorus sulfide (e.g., P2S5). Furthermore, sulfur-containing compounds are sulfides of element M (M x S y ) may have ) where x and y are integers that give electrical neutrality with S depending on the type of M. sulfide (M x S y Examples of these sulfides include GeS2, SnS2, SiS2, and Al2S3. Furthermore, these sulfides may also be, for example, residues from the starting materials.

[0028] In addition, the positive electrode layer may contain a positive electrode active material other than elemental sulfur and sulfur compounds. Examples of the positive electrode active material other than elemental sulfur and sulfur compounds include various lithium-containing compounds. The lithium-containing compounds include lithium cobalt oxide, lithium nickel oxide, Li 1±α Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2±δ , lithium manganate, spinel-based lithium compounds (Li 1+x Mn 2-x-y M y O4 (M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), such as hetero-element-substituted Li-Mn spinel, etc.), lithium titanate, lithium metal phosphate (LiMPO4, etc., M is one or more selected from Fe, Mn, Co, and Ni), and various lithium-containing oxides.

[0029] The shape of the positive electrode active material may be a general shape as the positive electrode active material of the lithium-sulfur battery. The positive electrode active material may be, for example, particulate. The positive electrode active material may be solid, hollow, have voids, or be porous. The positive electrode active material may be primary particles or secondary particles formed by aggregation of a plurality of primary particles. The average particle diameter D50 of the positive electrode active material may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter D50 referred to in this application is the particle diameter (median diameter) at the integrated value of 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0030] The electrolyte contained in the positive electrode layer may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, a higher effect is more easily obtained when the positive electrode layer contains at least a solid electrolyte. The solid electrolyte may be one of those known as solid electrolytes for batteries. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte, as described later. The electrolyte solution may contain lithium ions. The electrolyte solution may be, for example, a non-aqueous electrolyte. The composition of the electrolyte solution may be the same as that known as the composition of an electrolyte solution for batteries. For example, a solution in which a lithium salt is dissolved at a predetermined concentration in a carbonate-based solvent can be used as the electrolyte solution. Examples of carbonate-based solvents include fluoroethylene carbonate (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC). Examples of lithium salts include LiPF6.

[0031] Examples of conductive additives that may be included in the positive electrode layer include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic 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. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0032] Examples of binders that may be included in the positive electrode layer include butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, and polyimide (PI) binders. A single binder may be used alone, or two or more binders may be used in combination. <Solid electrolyte> The solid electrolyte can be used without limiting the inorganic solid electrolyte used in solid-state batteries. Such inorganic solid electrolytes can include crystalline nitrides, oxides, sulfides and oxoates, as well as amorphous glass-structured materials. Specifically, sulfide solid electrolytes that can be used include, for example, at least one selected from the group consisting of LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, Li3PS4, LiCl-LiBr-Li3PS4, LiCl-LiBr-Li2S-P2S5, and LiCl-LiBr-Li2S-SiS2. Furthermore, oxide-based solid electrolytes include, for example, Li 0.34 La 0.56 TiO3, Li 3 / 8 Sr 7 / 16 Ta 3 / 4 M 1 / 4 O3 (M=Zr or Hf), Li7La3Zr2O 12 Li 1.3 Al 0.7 Ti 1.3 (PO4)3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 3.5 Ge 0.5 V 0.5 O, Li 2.88 PO 3.73 N 0.14 , and Li 2.9 Si 0.45 PO 1.6 N 1.3 These can be cited as examples. In addition, complex hydride lithium-ion conductors and halide-based lithium-ion conductors may also be used as solid electrolytes.

[0033] <Negative electrode active material> In the solid-state battery of this disclosure, the negative electrode layer includes a negative electrode active material. The negative electrode active material in the solid-state battery of this disclosure is not particularly limited. The negative electrode layer includes at least a negative electrode active material and may optionally include an electrolyte, a conductive additive, and a binder. For example, lithium is used as the negative electrode active material. The lithium may be any material capable of functioning as a negative electrode active material, and may be metallic lithium, a lithium alloy, or a lithium compound. The negative electrode active material layer 31 may also contain a negative electrode active material other than lithium. Examples of negative electrode active materials other than lithium include Si-based active materials such as Si, Si alloys, and Si compounds, and carbon-based active materials such as graphite. The electrolyte, conductive additive, and binder that may be included in the negative electrode layer can be appropriately selected from those exemplified as possible for inclusion in the positive electrode layer. The electrolyte, conductive additive, and binder included in the negative electrode layer and the electrolyte, conductive additive, and binder included in the positive electrode layer may be of the same type or of different types.

[0034] <Other components> In addition to the positive electrode layer containing the positive electrode active material described above, the solid electrolyte layer described above, and the negative electrode layer containing the negative electrode active material described above, the solid battery of this disclosure may also include a positive electrode current collector, a negative electrode current collector, an outer casing, a sealing resin, and a restraining member. The positive electrode current collector, negative electrode current collector, outer casing, sealing resin, and restraining member are not particularly limited, and their materials, shapes, configurations, etc., are arbitrary.

[0035] The solid-state batteries in this disclosure include all-solid-state batteries that use a solid electrolyte as the electrolyte, and semi-solid-state batteries that have a gel layer containing an electrolyte and a polymer between the electrode and the solid electrolyte, with all-solid-state batteries being preferred.

[0036] <Fabrication of Solid-State Batteries> In this disclosure, a solid-state battery can be manufactured by using the above-mentioned solid electrolyte, active material, and other components as materials to produce a laminate having a solid electrolyte layer, a positive electrode layer, and a negative electrode layer by conventionally known methods. The solid electrolyte layer, positive electrode layer, and negative electrode layer may be manufactured, for example, by a dry film deposition method without solvents, or by a wet film deposition method using solvents. As a dry film deposition method, for example, the layers may be manufactured by mixing the materials constituting each layer and pressing them. Alternatively, as a dry film deposition method, the electrodes may be manufactured by dispersing the materials constituting each layer in a dispersant to form a slurry, then applying the slurry to a predetermined substrate and drying it.

[0037] As an example of a method for manufacturing a positive electrode layer using a slurry, first, a slurry is prepared by stirring and mixing the positive electrode active material, solid electrolyte, and conductive additive in a solvent (also called a dispersion medium). The solvent is not particularly limited, but examples include 1,2,3,4-tetrahydronaphthalene, butyl acetate, butyl butyrate, mesitylene, tetralin, heptane, and N-methyl-2-pyrrolidone (NMP). Then, the obtained slurry is applied to a substrate such as a positive electrode current collector by a conventionally known method. The substrate to which the slurry is applied is not particularly limited and may be a metal foil, a positive electrode current collector, or a solid electrolyte layer. The coating method can be carried out by a known method. Examples of common methods include the doctor blade method, die coating method, gravure coating method, spray coating method, electrostatic coating method, and bar coating method.

[0038] Next, the slurry applied to the substrate, such as the positive electrode current collector, is dried. At this time, the slurry may be heated to a temperature range of 50°C to 200°C or below, or the atmosphere may be set to an inert atmosphere or a reduced-pressure atmosphere. After that, multiple columnar structures are fabricated by laser processing. Then, the positive electrode layer, solid electrolyte layer, and negative electrode layer having the columnar structures are laminated and may be restrained with a restraining member. After that, the laminated body is housed in an outer casing to manufacture the solid battery of this disclosure. [Examples]

[0039] The solid-state battery described herein will be explained below with reference to examples, but the technical scope of this disclosure is not limited to the following examples.

[0040] <Example 1, Comparative Example 1, and Comparative Example 2> S-P2S5-C composite material was prepared as the positive electrode composite material for use in Example 1, Comparative Example 1, and Comparative Example 2. First, sulfur (80°C vacuum dried), P2S5, and single-walled carbon nanotubes were mixed in a mortar in a weight ratio of 42:35:23, and stirred and mixed in a planetary ball mill for a total of 36 hours. Then, the mixture was classified by dry sieving using a 38 μm sieve to obtain the S-P2S5-C composite material for the positive electrode. A slurry was prepared by kneading the obtained S-P2S5-C composite material with a binder and solvent, and the slurry was applied to the positive electrode current collector to create the positive electrode layer.

[0041] For the positive electrode layer used in the solid-state battery of Example 1, a columnar structure was formed using an ultrashort pulse laser such that the aspect ratio [β / α], determined from the diameter α of the surface in contact with the solid electrolyte layer and the dimension β in the thickness direction of the positive electrode layer, was 2. In this example, multiple columnar structures were formed so as to be arranged concentrically with respect to the positive electrode layer, which has a circular top view (Figure 2(a)). Furthermore, the positive electrode layer used in the solid-state battery of Comparative Example 1 did not have a pattern formed on it (aspect ratio [β / α] = 1 / 144.6). In addition, the positive electrode layer used in the solid-state battery of Comparative Example 2 was processed in the same manner as in Example 1 so that the aspect ratio [β / α] was 1.

[0042] Furthermore, a Li2S-P2S5 system material containing a halogen was prepared as a sulfide solid electrolyte for use in Example 1, Comparative Example 1, and Comparative Example 2. A mixture of this sulfide solid electrolyte, a binder, and a solvent was then prepared. This mixture was coated onto a release film. The coated mixture was then dried. After drying, the release film was peeled off to obtain a solid electrolyte layer.

[0043] Furthermore, as the negative electrode layer used in Example 1, Comparative Example 1, and Comparative Example 2, a Li-Mg alloy layer was formed on the Ni foil, which is the negative electrode current collector.

[0044] Then, a test cell was fabricated by stacking the positive electrode layer, solid electrolyte layer, and negative electrode layer obtained above, and the following charge-discharge tests were performed. In the charge-discharge tests, the cutoff lower limit voltage was set to 1.2V, and the constant current density was 0.584mA / cm². 2 (1C = 5.84mA / cm 2 A voltage equivalent to 0.1C was applied to a test cell. Charge-discharge tests were performed at 60°C. After the charge-discharge tests, the test cells of Example 1, Comparative Example 1, and Comparative Example 2 were cut parallel to the stacking direction, and the number of cracks observed on the cut surface of the solid electrolyte layer was measured. The results are shown in Table 1.

[0045] [Table 1]

[0046] As shown in Table 1, many cracks were observed on the cross-section of the test cell of Comparative Example 1. This was presumed to be because the positive electrode layer, which contains sulfur-containing positive electrode active material, repeatedly expanded and contracted with charging and discharging, loading stress onto the solid electrolyte layer. In contrast, no cracks occurred on the cross-section of the solid electrolyte layer in the test cell of Example 1. This was presumed to be because the stress caused by the expansion and contraction of the positive electrode layer with charging and discharging was relieved, and no stress sufficient to cause cracks was loaded onto the solid electrolyte layer. Furthermore, since cracks occurred on the cross-section of the solid electrolyte layer in Comparative Example 1, it became clear that the occurrence of cracks in the solid electrolyte layer can be reliably prevented if the aspect ratio [β / α] of the columnar structure formed in the positive electrode layer is 2 or more. [Explanation of symbols]

[0047] 1...Positive electrode layer, 2...Solid electrolyte layer, 3...Negative electrode layer, 4...Columnar structure

Claims

1. The device comprises a positive electrode layer containing a positive electrode active material containing sulfur, a negative electrode layer containing a negative electrode active material containing lithium, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. A solid-state battery wherein the positive electrode layer comprises a plurality of spaced-apart columnar structures, the aspect ratio [β / α] obtained from the diameter α of the surface of the columnar structure in contact with the solid electrolyte layer and the dimension β of the columnar structure in the thickness direction of the positive electrode layer is 2 or more, and the aspect ratio is less than or equal to the ratio at which the buckling stress obtained by Euler's buckling formula for the columnar structure is greater than the stress due to the confinement pressure acting on the columnar structure.

2. The solid battery according to claim 1, wherein the columnar structure has a cross-sectional shape that becomes smaller in diameter toward the surface in contact with the solid electrolyte layer.

3. The solid battery according to claim 1, wherein the plurality of columnar structures are in contact with the solid electrolyte layer on the side opposite to the surface in contact with the solid electrolyte layer.

4. The solid battery according to claim 1, wherein the plurality of columnar structures are arranged in a concentric, grid, or honeycomb pattern.

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