Secondary battery

Abstract

To provide a means enabling suppression of the occurrence of short circuit in a secondary battery comprising a solid electrolyte layer.SOLUTION: The present invention provides a secondary battery 10 including a positive electrode layer 11, a negative electrode layer 12, and a solid electrolyte layer 13 disposed between the positive electrode layer 11 and the negative electrode layer 12. The positive electrode layer 11 includes a positive electrode current collector foil 14, a positive electrode active material layer 15 disposed on the positive electrode current collector foil 14, and a solid electrolyte layer support member 16 disposed in such a manner as to be in contact with at least a part of an outer peripheral side surface of the positive electrode active material layer 15. The solid electrolyte layer support member 16 includes at least one step part provided on the side in contact with the positive electrode active material layer 15. At least a part of an outer peripheral part of the positive electrode active material layer 15 is sandwiched between the step part and the solid electrolyte layer 13, and / or is sandwiched between the step part and the positive electrode current collector foil 14.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] Conventionally, secondary batteries have been known that include a solid electrolyte layer between a positive electrode layer and a negative electrode layer. Such secondary batteries minimize the amount of flammable organic solvent used, significantly reducing the possibility of battery degradation even in the event of a short circuit. This allows for significantly improved battery performance compared to currently available lithium-ion batteries that use electrolyte solutions.

[0003] On the other hand, secondary batteries equipped with a solid electrolyte layer use a solid electrolyte, and therefore, if the contact between the positive electrode layer and the solid electrolyte layer and between the negative electrode layer and the solid electrolyte layer is not sufficiently maintained, the resistance within the battery increases, making it difficult to exhibit excellent battery characteristics.

[0004] Conventionally, a pressurizing process has been performed in the manufacturing process of secondary batteries to improve contact between the positive electrode layer or negative electrode layer and the solid electrolyte layer. In this pressurizing process, a pressure difference occurs in a portion of a laminate including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer that is not laminated. This pressure difference can cause microscopic defects in the solid electrolyte layer. During the charge / discharge process of the battery, cracks are generated and grow in the solid electrolyte layer due to such defects. As lithium grows through these cracks, a short circuit may occur between the positive electrode layer and the negative electrode layer.

[0005] For example, Patent Document 1 discloses an all-solid-state battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode current collector, a positive electrode active material layer disposed on the positive electrode current collector, and an inactive member disposed on one side of the positive electrode active material layer, and the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on the negative electrode current collector.

[0006] In this all-solid-state battery, the inactive member is located on the side of the positive electrode active material layer and is in contact with the solid electrolyte layer, thereby suppressing cracks in the solid electrolyte layer that are generated due to the pressure difference during the pressurization process in the solid electrolyte layer that is not in contact with the positive electrode active material layer, thereby preventing short circuits. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-77644 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the all-solid-state battery configuration described in Patent Document 1, when external force is applied to the all-solid-state battery, stress concentrates in the solid electrolyte layer located above the boundary between the positive electrode active material layer and the inactive member, each of which is made of materials with different physical properties. Furthermore, the bond strength between the positive electrode active material layer and the inactive member, each of which is made of materials with different physical properties, is low and vulnerable to tensile force, so there is a possibility that they will peel off when external force is applied. This may cause a problem of short-circuiting the all-solid-state battery.

[0009] Therefore, an object of the present invention is to provide a means for suppressing the occurrence of short circuits in a secondary battery having a solid electrolyte layer. [Means for solving the problem]

[0010] A secondary battery according to one embodiment of the present invention includes a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer includes a positive electrode current collector foil, a positive electrode active material layer disposed on the positive electrode current collector foil, and a solid electrolyte layer support material disposed so as to contact at least a portion of the outer peripheral side surface of the positive electrode active material layer. The solid electrolyte layer support material includes at least one step portion provided on the side in contact with the positive electrode active material layer, and at least a portion of the outer peripheral portion of the positive electrode active material layer is sandwiched between the step portion and the solid electrolyte layer and / or between the step portion and the positive electrode current collector foil. [Effects of the Invention]

[0011] According to the present invention, the solid electrolyte layer support material includes a step portion on the cathode active material layer side, thereby increasing the bonding strength between the cathode layer and the solid electrolyte layer support material in the stacking direction of the battery and increasing resistance to tensile forces. Therefore, even when stress is concentrated on the solid electrolyte layer located above the interface between the cathode active material layer and the solid electrolyte layer support material when the battery is pressurized, peeling between the cathode active material layer and the solid electrolyte layer support material can be suppressed, thereby suppressing short circuits in the secondary battery. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of a main part illustrating the configuration of a secondary battery according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating the configuration of a secondary battery according to the second embodiment. [Figure 3] FIG. 3 is a cross-sectional view illustrating the configuration of a secondary battery according to the third embodiment. [Figure 4] Fig. 4 is a cross-sectional view illustrating the configuration of a secondary battery according to a fourth embodiment, and Fig. 4(a) and (b) each show a cross-sectional view of a pair of outer peripheral portions arranged opposite each other in the surface direction of the secondary battery. [Figure 5] FIG. 5 is a cross-sectional view illustrating the configuration of a secondary battery according to a fifth embodiment. [Figure 6] FIG. 6 is a cross-sectional view illustrating the configuration of a secondary battery according to a sixth embodiment. [Figure 7]FIG. 7 is a cross-sectional view illustrating the configuration of a secondary battery according to a seventh embodiment. [Figure 8] FIG. 8 is a cross-sectional view illustrating the configuration of a secondary battery according to an eighth embodiment. [Figure 9] 9A and 9B are cross-sectional views illustrating the configuration of a secondary battery according to a ninth embodiment, in which (a) is a cross-sectional view of the outer periphery of the secondary battery according to this embodiment, and (b) is a cross-sectional view of the outer periphery of a comparative embodiment. [Figure 10] FIG. 10 is a cross-sectional view illustrating the configuration of a secondary battery according to a tenth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] One aspect of the present invention is a secondary battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the positive electrode layer including a positive electrode current collector foil, a positive electrode active material layer disposed on the positive electrode current collector foil, and a solid electrolyte layer support material disposed so as to be in contact with at least a portion of an outer peripheral side surface of the positive electrode active material layer, the solid electrolyte layer support material including at least one step portion provided on a side in contact with the positive electrode active material layer, and at least a portion of the outer peripheral portion of the positive electrode active material layer being sandwiched between the step portion and the solid electrolyte layer and / or the step portion and the positive electrode current collector foil.

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0015] [First embodiment] A secondary battery 10 according to a first embodiment of the present invention will be described.

[0016] FIG. 1 is a schematic cross-sectional view illustrating the configuration of a secondary battery 10 according to this embodiment. The secondary battery 10 according to this embodiment is a so-called stacked-type battery that houses a power generating element, which is made up of multiple stacked cell layers, sealed in a laminate film, which is a battery exterior material. The stacked-type battery allows for a compact battery with high capacity. However, the cell layers housed in the secondary battery 10 to which the present invention is applied do not necessarily have to be multiple layers; a single layer may also be used. Furthermore, the external appearance and internal electrical connection state (electrode structure) of the secondary battery 10 according to this embodiment are not particularly limited. The external appearance of the secondary battery 10 may be, for example, a flattened rectangular shape, or a circular or elliptical shape. Alternatively, the secondary battery 10 may be a cylindrical type that houses a single or multiple cell layers wound together. Furthermore, the electrode structure of the secondary battery 10 may be either a non-bipolar type (internal parallel connection type) or a bipolar type (internal series connection type). That is, aspects other than the configuration of the secondary battery 10 described below are not particularly limited, regardless of whether they are publicly known or not.

[0017] As shown in the figure, the secondary battery 10 includes a positive electrode layer 11, a negative electrode layer 12, a solid electrolyte layer 13, a positive electrode current collector foil 14, a positive electrode active material layer 15, a solid electrolyte layer support 16, a negative electrode current collector foil 17, and a negative electrode active material layer 18.

[0018] More specifically, the secondary battery 10 includes a positive electrode layer 11 having a positive electrode active material layer 15 containing a positive electrode active material disposed on the surface of a positive electrode current collector foil 14 and a solid electrolyte layer support material 16 disposed so as to contact the outer peripheral side surface of the positive electrode active material layer 15, and a negative electrode layer 12 having a negative electrode active material layer 18 containing a negative electrode active material disposed on the surface of a negative electrode current collector foil 17, and further includes a solid electrolyte layer 13 disposed between the positive electrode layer 11 and the negative electrode layer 12. In this embodiment, the solid electrolyte layer support material 16 is disposed so as to contact the outer peripheral side surface of the positive electrode active material layer 15 over the entire periphery of the positive electrode active material layer 15.

[0019] The solid electrolyte layer support material 16 includes a step portion 16a on the side that contacts the positive electrode active material layer 15, and the outer periphery of the positive electrode active material layer 15 is sandwiched between the step portion 16a and the solid electrolyte layer 13 along the entire periphery of the positive electrode active material layer 15. This allows the solid electrolyte layer support material 16 to contact the outer periphery of the positive electrode active material layer 15 and also the solid electrolyte layer 13, thereby suppressing cracks in the solid electrolyte layer that are not in contact with the positive electrode active material layer 15 due to a pressure difference during the pressurization process. Furthermore, during the pressurization process, the outer periphery of the positive electrode active material layer 15 and the step portion of the solid electrolyte layer support material 16 are pressed together with a strong force in the stacking direction, increasing the bonding strength of the adhesive surfaces and making them more resistant to tensile forces. As a result, peeling between the positive electrode active material layer 15 and the solid electrolyte layer support material 16 can be suppressed, thereby suppressing short-circuiting in the secondary battery.

[0020] In this embodiment, the solid electrolyte layer support material 16 extends to the outer peripheral edge of the solid electrolyte layer 13. This can suppress the occurrence of cracks at the outer peripheral edge of the solid electrolyte layer 13. However, the solid electrolyte layer support material 16 does not have to extend to the outer peripheral edge of the solid electrolyte layer 13, and may extend beyond the outer peripheral edge.

[0021] Furthermore, in the configuration of the all-solid-state battery described in Patent Document 1, if a gap is formed between the positive electrode active material layer and the inactive member, the pressing pressure applied to the solid electrolyte layer above the gap during or after installation, which is a pressurization process aimed at densifying and strengthening the solid electrolyte layer, may be insufficient, resulting in a risk of the solid electrolyte layer being insufficient in strength. In contrast, by providing a step portion 16a on the side of the solid electrolyte layer support 16 that contacts the positive electrode active material layer 15, as in this embodiment, the width of such a gap is reduced, thereby preventing a lack of strength in the solid electrolyte layer 13.

[0022] Next, components constituting the secondary battery according to one embodiment of the present invention will be described.

[0023] [Current collecting foil] The material constituting the positive electrode current collector foil and the negative electrode current collector foil (hereinafter collectively referred to as "current collector foil") is not particularly limited as long as it functions as a current collector foil applicable in the technical field of secondary batteries. Known materials may be used as the constituent material of the current collector foil, such as metals and conductive resins.

[0024] Specifically, metals used as constituent materials of the current collector foil include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition, a clad material of nickel and aluminum, or a clad material of copper and aluminum, may also be used. A foil having a metal surface coated with aluminum may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electronic conductivity, battery operating potential, and adhesion of the negative electrode active material to the current collector foil by sputtering.

[0025] The conductive resin used as the constituent material of the current collector foil may be a resin obtained by adding a conductive filler to a non-conductive polymer material as required.

[0026] In particular, examples of non-conductive polymeric materials include polyethylene (PE; high density polyethylene (HDPE) or low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS).

[0027] The positive electrode current collector foil and the negative electrode current collector foil may be made of the same material, or different materials may be selected from the materials listed above as constituent materials for the current collector foil.

[0028] The lengths of the positive and negative electrode current collector foils in the cross section of the battery in the stacking direction are not particularly limited as long as they maintain their function as current collectors and do not cause short circuits due to contact with the negative electrode in the case of a positive electrode current collector foil or the positive electrode in the case of a negative electrode current collector foil. The negative electrode current collector foil is preferably larger than the outer dimensions of the negative electrode active material layer and smaller than the outer dimensions of the solid electrolyte layer support material when the solid electrolyte layer support material is made of an insulating material. Furthermore, when the solid electrolyte layer support material is made of a conductive material, the negative electrode current collector foil is preferably smaller than the outer dimensions of the solid electrolyte layer.

[0029] [Negative electrode layer] The negative electrode layer includes a negative electrode current collector foil and a negative electrode active material layer. The material constituting the negative electrode active material layer is not particularly limited, but examples thereof include carbon materials, metal oxides, elemental metals, silicon materials, tin materials, and lithium (Li)-containing materials.

[0030] Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon.

[0031] Examples of metal oxides include Nb2O5 and Li4Ti5O 12 etc.

[0032] Furthermore, silicon or tin may be used as a material for forming the negative electrode active material layer. Here, silicon and tin belong to the 14th group of elements, and it is known that when these are used as materials for the negative electrode active material of a non-aqueous electrolyte secondary battery, the capacity can be significantly improved. These simple substances can absorb and release a large number of charge carriers (lithium ions, etc.) per unit volume (mass), and therefore can be materials that can realize a high-capacity negative electrode active material. Here, it is preferable to use Si simple substance as the silicon material. Similarly, SiO 2 disproportionated into two phases, a Si phase and a silicon oxide phase, can be used. xIt is also preferable to use silicon oxides such as (0.3≦x≦1.6). In this case, the range of x is more preferably 0.5≦x≦1.5, and even more preferably 0.7≦x≦1.2. Furthermore, an alloy containing silicon may be used as the silicon material. On the other hand, examples of tin materials include simple Sn, tin alloys (Cu-Sn alloys, Co-Sn alloys), amorphous tin oxides, and tin silicon oxides. Among these, examples of amorphous tin oxides include SnB 0.4 P 0.6 O 3.1 Examples of tin silicon oxide include SnSiO3.

[0033] The lithium-containing material is not particularly limited as long as it is an active material containing lithium, and examples thereof include metallic lithium and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li and at least one of In, Al, Si, and Sn. Furthermore, in some cases, the negative electrode active material may be formed by combining any two or more of the above-exemplified constituent materials. Of course, negative electrode active materials other than those listed above may also be used. In terms of high capacity, metallic lithium, silicon materials, tin materials, or combinations thereof are preferably used as the negative electrode active material, and metallic lithium is particularly preferred.

[0034] The shape of the negative electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. In particular, when the negative electrode active material is particulate, its average particle size (D50) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. The average particle size (D50) of the negative electrode active material can be measured by a laser diffraction scattering method.

[0035] The negative electrode active material layer preferably further contains a solid electrolyte. Specific solid electrolytes contained in the negative electrode active material layer can be selected from the same solid electrolytes as those contained in the solid electrolyte layer described below. The inclusion of a solid electrolyte in the negative electrode active material layer can improve the ionic conductivity of the negative electrode active material layer. Examples of solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes, and sulfide solid electrolytes are preferred.

[0036] Examples of sulfide solid electrolytes include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (where m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In). The term "LiS-P2S5" refers to a sulfide solid electrolyte obtained using a raw material composition containing LiS and P2S5, and the same applies to other terms.

[0037] The sulfide solid electrolyte may have, for example, a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of sulfide solid electrolytes having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Examples of sulfide solid electrolytes having a Li4P2S7 skeleton include Li-PS-based solid electrolytes known as LPS (for example, Li7P3S 11) can be mentioned. Also, as the sulfide solid electrolyte, for example, Li (4-x) Ge (1-x) P x S4 (where x satisfies 0 < x < 1), such as LGPS, may be used. Among them, the sulfide solid electrolyte is preferably a sulfide solid electrolyte containing P element, and more preferably a material mainly composed of Li2S - P2S5. Further, the sulfide solid electrolyte may contain halogen (F, Cl, Br, I).

[0038] Also, when the sulfide solid electrolyte is of the Li2S - P2S5 system, the ratio of Li2S and P2S5 is preferably within the range of Li2S:P2S5 = 50:50 to 100:0 in molar ratio, and among them, Li2S:P2S5 = 70:30 to 80:20 is preferable.

[0039] Also, the sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid phase method. The sulfide glass can be obtained, for example, by performing mechanical milling (such as a ball mill) on the raw material composition. Also, the crystallized sulfide glass can be obtained, for example, by performing heat treatment on the sulfide glass at a temperature above the crystallization temperature. Also, the ionic conductivity (for example, Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is, for example, 1×10 -5 S / cm or more is preferable, and 1×10 -4 S / cm or more is more preferable. The value of the ionic conductivity of the solid electrolyte can be measured by the alternating current impedance method.

[0040] Examples of the oxide solid electrolyte include compounds having a NASICON-type structure. As an example of a compound having a NASICON-type structure, a compound represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 ≤ x ≤ 2) (LAGP), a compound represented by the general formula Li 1+x Al x Ti 2-x(PO4)3 (0≦x≦2) (LATP) and the like. Another example of an oxide solid electrolyte is LiLaTiO (for example, Li 0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ) etc.

[0041] The shape of the solid electrolyte may be, for example, a particulate shape such as a spherical shape or an oval spherical shape, or a thin film shape. When the solid electrolyte is particulate, its average particle size (D50) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle size (D50) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

[0042] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably within the range of 40 to 99 mass %, and more preferably within the range of 50 to 90 mass %, for example.

[0043] The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably in the range of 1 to 60 mass %, more preferably in the range of 10 to 50 mass %. However, when lithium metal is used as the material of the negative electrode active material, the content of the solid electrolyte in the negative electrode active material layer is preferably zero. Note that, examples of the form of lithium metal used here include lithium metal foil, lithium alloy metal foil (alloy species: Mg, Al, In, etc.), and lithium vapor-deposited on a substrate (substrate: SUS foil, Al foil, etc.).

[0044] The negative electrode active material layer may further contain at least one of a conductive additive and a binder in addition to the above-mentioned negative electrode active material and solid electrolyte.

[0045] Examples of conductive additives include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNTs), and carbon black (specifically, acetylene black, Ketjenblack (registered trademark), furnace black, channel black, thermal lamp black, etc.).

[0046] Furthermore, the material used as the binder is not particularly limited, and any known material may be used as long as it functions as a binder applicable in the technical field of secondary batteries. Examples of binders include polyvinylidene fluoride (PVDF), styrene-butadiene copolymer rubber (SBR), and polyimide.

[0047] The negative electrode active material layer may further contain additives such as a filler, a coating agent, a dispersant, and an ion-conductive auxiliary in addition to the negative electrode active material, solid electrolyte, binder, and conductive auxiliary.

[0048] The thickness of the negative electrode active material layer varies depending on the intended configuration of the secondary battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[0049] [Positive electrode layer] The positive electrode layer includes a positive electrode current collector foil, a positive electrode active material layer disposed on the positive electrode current collector foil, and a solid electrolyte layer support disposed so as to contact at least a portion of the outer peripheral side surface of the positive electrode active material layer.

[0050] The positive electrode active material constituting the positive electrode active material layer may be a material containing sulfur (sulfur element or a sulfur compound) or a material not containing sulfur (metal compound, etc.). In particular, it is preferable to form the positive electrode active material layer using a material containing sulfur.

[0051] Examples of the sulfur-containing material include particles or thin films of elemental sulfur (S), organic sulfur compounds, or inorganic sulfur compounds. In particular, the sulfur-containing material is preferably a substance that can release lithium ions during charging and absorb lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0052] Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitriles typified by the compounds described in WO 2010 / 044437, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), polycarbon sulfide, etc. Among these, disulfide compounds, sulfur-modified polyacrylonitriles, and rubeanic acid are preferred, and sulfur-modified polyacrylonitriles are particularly preferred.

[0053] As the disulfide compound, a dithiobiurea derivative, a compound having a thiourea group, a thioisocyanate group, or a thioamide group is more preferred.

[0054] Here, sulfur-modified polyacrylonitrile is a modified polyacrylonitrile containing sulfur atoms, which is obtained by mixing sulfur powder with polyacrylonitrile and heating the mixture under an inert gas or under reduced pressure. Its estimated structure is, for example, as shown in Chem. Mater. 2011, 23, 5024-5028, in which polyacrylonitrile is ring-closed to form a polycyclic ring, and at least a part of S is bonded to C. The compound described in this document has a peak at 1330 cm in the Raman spectrum. -1 and 1560cm -1 There is a strong peak signal near 307 cm -1 , 379cm -1 , 472cm -1 , 929cm -1 There is a peak nearby.

[0055] On the other hand, inorganic sulfur compounds are preferred due to their excellent stability. Specific examples include elemental sulfur (S), S-carbon composites, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, Li2S, MoS2, and MoS3. Of these, S, S-carbon composites, TiS2, TiS3, TiS4, FeS2, and MoS2 are preferred, with elemental sulfur (S), S-carbon composites, TiS2, and FeS2 being more preferred, and elemental sulfur (S) being particularly preferred. Here, the term "S-carbon composite" refers to a composite containing sulfur powder and a carbon material, which are combined by heat treatment or mechanical mixing. More specifically, the composite may be one in which sulfur is distributed on the surface or within the pores of the carbon material, one in which sulfur and the carbon material are uniformly dispersed at the nano-level and aggregated to form particles, or one in which the carbon material is distributed on the surface or within fine sulfur powder, or a combination of these.

[0056] Further, sulfur-free materials include metal oxides, particularly lithium metal composite oxides, such as layered rock salt compounds such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and Li(Ni-Mn-Co)O2, LiMn2O4, and LiNi 0.5 Mn 1.5 Examples of lithium metal composite oxides include spinel-type compounds such as LiFePO4 and LiMnPO4, olivine-type compounds such as LiFeSiO4 and LiMnSiO4, and Si-containing compounds such as LiFeSiO4 and LiMnSiO4. 12 Examples include:

[0057] In some cases, two or more positive electrode active materials may be used in combination. Of course, positive electrode active materials other than those mentioned above may also be used.

[0058] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, its average particle size (D50) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. In this specification, the average particle size (D50) of the active material can be measured by a laser diffraction scattering method.

[0059] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably within the range of 40 to 99 mass %, and more preferably within the range of 50 to 90 mass %, for example.

[0060] Like the negative electrode active material layer, the positive electrode active material layer may further contain at least one of a conductive additive and a binder. Furthermore, it may further contain additives such as a filler, a coating agent, a dispersant, and an ion-conductive additive. The specific forms of the conductive additive and binder that can be contained in the positive electrode active material layer 15 are the same as those described above, and therefore, detailed description thereof will be omitted here.

[0061] The thickness of the positive electrode active material layer varies depending on the intended configuration of the secondary battery 10, but is preferably within the range of 0.1 to 1000 μm, for example.

[0062] As described above, the solid electrolyte layer support material includes at least one step portion provided on the side that contacts the positive electrode active material layer. The term "step portion" refers to a portion where the thickness of the solid electrolyte layer support material decreases from the outside toward the center in a cross section of the battery in the stacking direction. The number of step portions is not particularly limited, but from the viewpoint of further demonstrating the effects of the present invention, it is preferably 1 to 4 steps, more preferably 1 to 3 steps, even more preferably 1 to 2 steps, and most preferably 2 steps as shown in FIG. 1 . The "number of step portions" refers to the total number of times the thickness of the solid electrolyte layer support material decreases, with one step being defined as a portion where the thickness of the solid electrolyte layer support material decreases from the outside toward the center in a cross section of the battery in the stacking direction.

[0063] There are no particular limitations on the method for producing the step portion of the solid electrolyte layer support material. For example, the step portion may be formed by stacking multiple sheets, or by molding using a mold.

[0064] In the step portion of the solid electrolyte layer support, the shape of the inner peripheral side surface that contacts the outer peripheral side surface of the positive electrode active material layer is not limited, and may be angular or rounded (arc-shaped). The rounded shape of the inner peripheral side surface of the step portion can be formed by applying a rounded shape using a mold, and particularly excellent effects can be obtained by making the rounded shape (radius) the same as the height of the step portion.

[0065] The thickness of the solid electrolyte layer support material may be approximately the same as that of the positive electrode layer, and the difference in thickness from the positive electrode layer is preferably within 10%, more preferably within 5%.

[0066] The constituent material of the solid electrolyte layer support is preferably chemically stable with respect to battery materials such as the solid electrolyte layer. Furthermore, the solid electrolyte layer support does not need to be composed of only one type of material, but may be composed of a combination of multiple types of materials. For example, the solid electrolyte layer support may be a laminate of multiple sheets composed of different materials, a laminate of multiple sheets with different thicknesses, or a laminate of sheets with different physical properties such as Young's modulus.

[0067] Here, if a sheet with high bending rigidity is used as a constituent material of the solid electrolyte layer support material, adhesion to the solid electrolyte layer may decrease after pressing. Therefore, when the solid electrolyte layer support material is a laminate of multiple sheets made of different materials, for example, when the laminate is made of sheets with different rigidities, it is preferable to configure the sheet that contacts the outer peripheral side surface of the positive electrode active material layer to have the highest bending rigidity among the sheets that make up the laminate. In this case, it is more effective to configure the sheet that contacts the solid electrolyte layer to have the lowest bending rigidity.

[0068] The solid electrolyte layer support material does not need to be electronically insulating and may be electronically conductive as long as it is not in contact with the negative electrode active material layer. For example, the solid electrolyte layer support material may be made of a conductive resin, metal, metal oxide, or a mixture thereof, or may be made of the same material as the current collector foil.

[0069] [Solid electrolyte layer] The solid electrolyte layer of the secondary battery contains a solid electrolyte as a main component and is a layer interposed between the positive electrode layer and the negative electrode layer. The specific form of the solid electrolyte contained in the solid electrolyte layer is the same as that described above, and therefore a detailed description thereof will be omitted here.

[0070] The content of the solid electrolyte in the solid electrolyte layer is, for example, preferably in the range of 10 to 100 mass %, more preferably in the range of 50 to 100 mass %, and even more preferably in the range of 90 to 100 mass %.

[0071] The solid electrolyte layer may further contain a binder in addition to the above-described solid electrolyte. The specific form of the binder that can be contained in the solid electrolyte layer is the same as that described above, and therefore detailed description thereof will be omitted here.

[0072] The thickness of the solid electrolyte layer varies depending on the intended configuration of the secondary battery, but is preferably within the range of 0.1 to 1000 μm, and more preferably within the range of 0.1 to 300 μm, for example.

[0073] [Method for manufacturing secondary batteries] An example of a method for producing a secondary battery will be described below.

[0074] (1) Preparation of the solid electrolyte layer support material A resin sheet is prepared as a support for the solid electrolyte layer, and an opening of the same size as the cathode active material layer is formed at the position where the cathode active material layer is to be installed. This results in a frame-shaped sheet. The step portion is formed in advance by molding.

[0075] Alternatively, the step portion can be formed by stacking multiple sheets. For example, a sheet having an opening of the same size as the positive electrode active material layer at the position where the positive electrode active material layer is to be installed and a sheet having an opening smaller than the size of the positive electrode active material layer are fabricated. The size of the small opening is preferably the minimum outer dimension of the positive electrode layer, including tolerances, minus 1.0 mm or less, and more preferably minus 0.5 mm or less.

[0076] (2) Preparation of the positive electrode layer The solid electrolyte layer support material prepared above is placed on both sides of the positive electrode current collector foil together with a positive electrode active material layer having the above dimensions, and they are simultaneously heat-pressed using, for example, a roll press to prepare the positive electrode layer. When a step structure is formed by stacking multiple sheets, the sheets may be heat-pressed together in advance, or the heat-pressing treatment may be performed simultaneously when integrating them with the positive electrode active material layer 15.

[0077] (3) Fabrication of secondary batteries Next, a solid electrolyte layer is formed on both sides of the positive electrode layer 11 prepared above by hot pressing or by coating with a solid electrolyte layer slurry. Furthermore, a negative electrode active material layer is formed on both sides of the solid electrolyte layer by hot pressing or by coating with a negative electrode active material layer slurry. Negative electrode current collector foils are placed on both sides of the laminate obtained in this way to obtain a power generating element for a secondary battery. Finally, leads are connected to the power generating element as needed, and the power generating element is placed inside an exterior body such as an aluminum laminate film and vacuum sealed to complete the secondary battery.

[0078] [Second embodiment] The secondary battery 10 according to the second embodiment will be described below. Note that the same elements as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

[0079] 2 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. As shown in the figure, the secondary battery 10 of this embodiment differs from the secondary battery 10 of the first embodiment in that the space between the inner peripheral side surface of a step portion 16a that is not in contact with the outer peripheral side surface of the positive electrode active material layer 15 and the outer peripheral side surface of the positive electrode active material layer 15 is filled with a solid electrolyte layer 13.

[0080] The above-described configuration can prevent pressure loss of the solid electrolyte layer 13 between the step portion 16a of the solid electrolyte layer support material 16 and the outer peripheral side surface of the positive electrode active material layer 15 during the pressurization process. As a result, a lack of strength of the solid electrolyte layer 13 located in the upper portion between the step portion 16a of the solid electrolyte layer support material 16 and the outer peripheral side surface of the positive electrode active material layer 15 is prevented, and stress concentration in this portion is also suppressed. This prevents peeling between the solid electrolyte layer support material 16 and the positive electrode active material layer 15, and more reliably prevents the occurrence of a short circuit in the secondary battery 10.

[0081] [Third embodiment] The secondary battery according to the third embodiment will be described below. Note that the same elements as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

[0082] 3 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. As shown in the figure, the secondary battery 10 of this embodiment differs from the secondary battery 10 of the first embodiment in that the outer periphery of the positive electrode active material layer 15 is sandwiched between the solid electrolyte layer 13 and a step portion 16a that is closest to the solid electrolyte layer 13 in the stacking direction of the battery.

[0083] The above-described configuration reduces the width of the gap between the solid electrolyte layer support material 16 and the outer periphery of the positive electrode active material layer 15. As a result, the strength of the solid electrolyte layer 13 located in the upper portion between the step portion 16a of the solid electrolyte layer support material 16 and the outer periphery of the positive electrode active material layer 15 is reduced, and stress concentration in this portion is reduced. This reduces peeling between the solid electrolyte layer support material 16 and the positive electrode active material layer 15, making it possible to more reliably prevent short circuits in the secondary battery 10.

[0084] [Fourth embodiment] The secondary battery 10 according to the fourth embodiment will be described below. Note that the same elements as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

[0085] FIG. 4 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. Also, (a) and (b) of FIG. 4 each show cross-sectional views of a pair of outer peripheral portions arranged opposite each other in the plane direction of the secondary battery 10. As shown in the figure, the secondary battery 10 of this embodiment differs from the secondary battery 10 of the first embodiment in that, in a pair of step portions 16a arranged opposite each other in the positive electrode active material layer 15, the lengths of the step portions 16a from the outside toward the center in the cross section in the stacking direction of the battery (length L1 shown in (a) of FIG. 4 and length L2 shown in (b) of FIG. 4) are different from each other. Furthermore, when performing roll pressing or the like, it is preferable that the length of the step portion 16a on the downstream side is longer.

[0086] With the above-described configuration, when the displacement of each member downstream of the press increases during roll pressing or the like, the step portion 16a is wider on the downstream side, which makes it possible to prevent the positive electrode active material layer 15 from climbing up onto the uppermost surface of the solid electrolyte layer support material 16 or preventing the positive electrode active material layer 15 from not resting on any of the steps of the step portion 16a.

[0087] [Fifth embodiment] The secondary battery 10 according to the fifth embodiment will be described below. Elements similar to those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0088] 5 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. As shown in the figure, the secondary battery 10 of this embodiment differs from the secondary battery 10 of the first embodiment in that the inner peripheral side surface of the step portion 16a, which contacts the outer peripheral side surface of the positive electrode active material layer 15, has an R-shape.

[0089] With the above-described configuration, when a bending input is applied to the secondary battery 10, the inner peripheral side surface of the step portion is not angular, which reduces the stress concentration on the solid electrolyte layer 13 and the positive electrode active material layer 15. As a result, damage to these components can be suppressed, and local current concentration during battery use and the resulting battery degradation can be prevented.

[0090] [Sixth embodiment] The secondary battery 10 according to the sixth embodiment will be described below. Note that the same elements as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

[0091] 6 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. As shown in the figure, the secondary battery 10 of this embodiment differs from the secondary battery 10 of the first embodiment in that the solid electrolyte layer support material 16 is a stack of solid electrolyte layer support material sheets 19, and step portions 16a are provided in the solid electrolyte layer support material 16. Here, in this embodiment, each solid electrolyte layer support material sheet 19 has a thickness corresponding to the thickness of each step portion 16a in the stacking direction of the battery.

[0092] By adopting the above-described configuration, a separate processing step for forming the step portion 16a is not required when manufacturing the solid electrolyte layer support material 16, and therefore the manufacturing cost of the secondary battery 10 can be reduced.

[0093] [Seventh embodiment] The secondary battery 10 according to the seventh embodiment will be described below. Elements similar to those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0094] 7 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. As shown in the figure, the secondary battery 10 of this embodiment differs from the secondary battery 10 of the first embodiment in that the solid electrolyte layer support material 16 is a laminate of solid electrolyte layer support material sheets 19 and 20, and a step portion 16a is provided on the solid electrolyte layer support material 16. Here, in this embodiment, of the solid electrolyte layer support material sheets 19 and 20 constituting the laminate, the sheet in contact with the outer peripheral side surface of the positive electrode active material layer 15 is configured to have the highest bending rigidity.

[0095] The above-described configuration makes it possible to increase the rigidity of the solid electrolyte layer support material 16 while maintaining the adhesion between the solid electrolyte layer support material 16 and the solid electrolyte layer 13. This makes it possible to suppress bending input to the solid electrolyte layer 13 located between the solid electrolyte layer support material 16 and the outer peripheral side surface of the positive electrode active material layer 15.

[0096] [Eighth embodiment] The secondary battery 10 according to the eighth embodiment will be described below. Elements similar to those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0097] 8 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. As shown in the figure, the secondary battery 10 of this embodiment differs from the secondary battery 10 of the first embodiment in that the solid electrolyte layer support material 16 is made of substantially the same material as the positive electrode current collector foil 14.

[0098] The above-described configuration allows the solid electrolyte layer support material 16 to also be used as an electron conductor. Therefore, the solid electrolyte layer support material 16 does not need to be made of substantially the same material as the positive electrode current collector foil 14, and may be made of an electron-conductive material different from the constituent material of the positive electrode current collector foil 14. Note that, as such an electron-conductive material, the same materials as those mentioned above as constituent materials of the current collector foil can be used.

[0099] [Ninth embodiment] The secondary battery 10 according to the ninth embodiment will be described below. Elements similar to those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0100] 9 is a cross-sectional view illustrating the configuration of a secondary battery 10 according to this embodiment. Also, (a) in FIG. 9 is a cross-sectional view of the outer periphery of the secondary battery 10 according to this embodiment, and (b) is a cross-sectional view of the outer periphery of a comparative embodiment. As shown in the figure, the secondary battery 10 according to this embodiment differs from the comparative embodiment in that the outer periphery edge of the negative electrode active material layer 18 is disposed so as to be positioned outside the outer periphery edge of the step portion 16a that is closest to the solid electrolyte layer 13 in the stacking direction of the battery, over the entire periphery, when the battery is viewed from above.

[0101] With the above-described configuration, pressure is applied to the entire area between the solid electrolyte layer support material 16 and the positive electrode active material layer 15 during the pressurizing step including the negative electrode layer 12, thereby increasing the bonding strength between the solid electrolyte layer support material 16 and the positive electrode active material layer 15.

[0102] [Tenth embodiment] The secondary battery 10 according to the tenth embodiment will be described below. Elements similar to those in the second embodiment are given the same reference numerals, and descriptions thereof will be omitted.

[0103] 10 is a cross-sectional view illustrating the configuration of a secondary battery 10 of this embodiment. As described above, in the secondary battery 10 of the second embodiment, the outer periphery of the positive electrode active material layer 15 is sandwiched between the step portion 16a and the solid electrolyte layer 13 along the entire periphery of the positive electrode active material layer 15. In contrast, as shown in the figure, the secondary battery 10 of this embodiment differs in that the outer periphery of the positive electrode active material layer 15 is sandwiched between the step portion 16a and the positive electrode current collector foil 14 along the entire periphery of the positive electrode active material layer 15.

[0104] Even with this configuration, the solid electrolyte layer support material 16 contacts the outer periphery of the positive electrode active material layer 15 and also contacts the solid electrolyte layer 13, thereby suppressing cracks in the solid electrolyte layer that occur in the solid electrolyte layer 13 that is not in contact with the positive electrode active material layer 15 due to a pressure difference during the pressurization process. Furthermore, during the pressurization process, the outer periphery of the positive electrode active material layer 15 and the step portion of the solid electrolyte layer support material 16 are pressed with a strong force in the stacking direction, increasing the bonding strength of the adhesive surfaces and making them more resistant to tensile forces. As a result, peeling between the positive electrode active material layer 15 and the solid electrolyte layer support material 16 can be suppressed, thereby suppressing short-circuiting in the secondary battery.

[0105] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and the technical scope of the present invention is not intended to be limited to the specific configurations of the above embodiments. Furthermore, the above embodiments can be combined as appropriate.

[0106] For example, the secondary battery according to the present embodiment does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferably an amount that allows the shape of the solid electrolyte layer formed by the solid electrolyte to be maintained and prevents leakage of the liquid electrolyte (electrolytic solution).

[0107] The following items are also included within the scope of the present invention: Item 1: A battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; the positive electrode layer includes a positive electrode current collector foil, a positive electrode active material layer disposed on the positive electrode current collector foil, and a solid electrolyte layer support disposed so as to be in contact with at least a portion of an outer peripheral side surface of the positive electrode active material layer, the solid electrolyte layer support includes at least one step portion provided on a side in contact with the positive electrode active material layer, a secondary battery, wherein at least a portion of the outer periphery of the positive electrode active material layer is sandwiched between the step portion and the solid electrolyte layer and / or between the step portion and the positive electrode current collector foil; Item 2: The secondary battery according to Item 1, wherein a space between an inner peripheral side surface of the step portion that is not in contact with the outer peripheral side surface of the positive electrode active material layer and the outer peripheral side surface of the positive electrode active material layer is filled with the solid electrolyte layer; Item 3: The secondary battery according to Item 1 or 2, wherein at least a portion of the outer periphery of the positive electrode active material layer is sandwiched between the solid electrolyte layer and a step portion that is closest to the solid electrolyte layer in the stacking direction of the battery; Item 4: The secondary battery according to any one of Items 1 to 3, wherein a pair of the step portions arranged opposite to each other in at least one of the positive electrode active material layers have different lengths from the outside toward the center in a cross section of the battery in the stacking direction; Item 5: The secondary battery according to any one of Items 1 to 4, wherein at least one of the step portions has an inner peripheral side surface that is in contact with an outer peripheral side surface of the positive electrode active material layer and has an R-shape; Item 6: The secondary battery according to Item 5, wherein the R of the R shape of the inner peripheral side surface is equal to the height of the step portion; Item 7: The secondary battery according to any one of Items 1 to 6, wherein the number of steps of the step portion is one to two; Item 8: The secondary battery according to any one of Items 1 to 7, wherein the solid electrolyte layer support material is a laminate of sheets having a thickness corresponding to the thickness of each of the step portions in the stacking direction of the battery; Item 9: The secondary battery according to Item 8, wherein, among the sheets constituting the laminate, the sheet in contact with the outer peripheral side surface of the positive electrode active material layer has the highest bending rigidity; Item 10: The secondary battery according to any one of Items 1 to 9, wherein the solid electrolyte layer support is made of substantially the same material as the positive electrode current collector foil; Item 11: The secondary battery according to any one of Items 1 to 10, wherein at least a part of the outer peripheral edge of the negative electrode active material layer is disposed so as to be located outside the outer peripheral edge of a step portion that is closest to the solid electrolyte layer in the stacking direction of the battery when the battery is viewed from above. [Explanation of symbols]

[0108] 10…Secondary battery 11...Positive electrode layer 12...Anode layer 13...Solid electrolyte layer 14...Positive current collector foil 15...Cathode active material layer 16...Solid electrolyte layer support material 16a...Step section 17...Negative electrode current collecting foil 18...Negative electrode active material layer 19...Solid electrolyte layer support sheet 20...Solid electrolyte layer support sheet L1, L2...Step length

Claims

1. a positive electrode layer, a negative electrode layer, and a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer; the positive electrode layer includes a positive electrode current collector foil, a positive electrode active material layer disposed on the positive electrode current collector foil, and a solid electrolyte layer support disposed so as to be in contact with at least a portion of an outer peripheral side surface of the positive electrode active material layer, the solid electrolyte layer support includes at least one step portion provided on a side in contact with the positive electrode active material layer, a secondary battery in which at least a portion of the outer periphery of the positive electrode active material layer is sandwiched between the step portion and the solid electrolyte layer and / or between the step portion and the positive electrode current collector foil.

2. 2. The secondary battery according to claim 1, wherein a space between an inner peripheral side surface of the step portion that is not in contact with the outer peripheral side surface of the positive electrode active material layer and the outer peripheral side surface of the positive electrode active material layer is filled with the solid electrolyte layer.

3. 3. The secondary battery according to claim 1, wherein at least a portion of the outer periphery of the positive electrode active material layer is sandwiched between the solid electrolyte layer and a step portion that is closest to the solid electrolyte layer in the stacking direction of the battery.

4. 3. The secondary battery according to claim 1, wherein a pair of the step portions arranged opposite each other in at least one of the positive electrode active material layers have different lengths from the outside toward the center in a cross section of the battery in the stacking direction.

5. The secondary battery according to claim 1 , wherein an inner peripheral side surface of at least one of the step portions that contacts an outer peripheral side surface of the positive electrode active material layer has an R-shape.

6. 3. The secondary battery according to claim 1, wherein the solid electrolyte layer support material is a laminate of sheets having a thickness corresponding to the thickness of each of the step portions in the stacking direction of the battery.

7. The secondary battery according to claim 1 , wherein the sheet in contact with the outer peripheral side surface of the positive electrode active material layer has the highest bending rigidity among the sheets constituting the laminate.

8. 3. The secondary battery according to claim 1, wherein the solid electrolyte layer support is made of substantially the same material as the positive electrode current collector foil.

9. 3. The secondary battery according to claim 1, wherein at least a part of an outer peripheral edge of the negative electrode active material layer is disposed so as to be located outward from an outer peripheral edge of a step portion that is closest to the solid electrolyte layer in a stacking direction of the battery, when the battery is viewed in plan.

Images