All-solid-state battery

Abstract

To provide means enabling suppression of short-circuiting at an end portion of a power generation element of an all-solid battery.SOLUTION: An all-solid battery is provided, comprising a power generation element in which a negative electrode active material layer, a solid electrolyte layer, a carbon-containing layer, and a positive electrode active material layer are sequentially laminated. In the all-solid battery, when seeing the power generation element in a plan view, the positive electrode active material layer is comprised of: a center portion that includes both lithium-free positive electrode active material and lithium-containing positive electrode active material; and an outer peripheral edge portion that includes the lithium-free positive electrode active material and arbitrarily includes the lithium-containing positive electrode active material. A capacity [mAh] of the lithium-containing positive electrode active material included in the center portion of the positive electrode active material layer is equal to or more than that of carbon material included in a region overlapped with the center portion of the positive electrode active material layer, of the carbon-containing layer. A capacity [mAh] of the lithium-containing positive electrode active material included in the outer peripheral edge portion of the positive electrode active material layer is less than that of carbon material included in a region overlapped with the outer peripheral edge portion of the positive electrode active material layer, of the carbon-containing layer.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery. [Background technology]

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. The automotive industry is pinning its hopes on reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and there has been active development of secondary batteries, such as those for driving motors, which hold the key to putting these vehicles into practical use.

[0003] Secondary batteries for driving motors are required to have extremely high output characteristics and high energy compared to consumer lithium secondary batteries used in mobile phones, laptops, etc. Therefore, lithium secondary batteries, which have the highest theoretical energy of all practical batteries, have attracted attention and are currently being rapidly developed.

[0004] Currently widely used lithium secondary batteries use flammable organic electrolytes, and these liquid-based lithium secondary batteries require stricter safety measures against leakage, short circuits, overcharging, and other issues than other batteries.

[0005] Therefore, in recent years, there has been active research and development into all-solid-state lithium secondary batteries that use oxide- or sulfide-based solid electrolytes. Solid electrolytes are materials primarily composed of ionic conductors that allow ionic conduction in a solid state. For this reason, all-solid-state lithium secondary batteries do not, in principle, encounter the various problems associated with flammable organic electrolytes that occur in conventional liquid-based lithium secondary batteries. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the output density and energy density of the battery.

[0006] Conventionally, one type of all-solid-state lithium secondary battery known is a so-called lithium deposition type, in which lithium metal is deposited on a negative electrode current collector during charging (see, for example, Patent Document 1). During charging of such a lithium deposition type all-solid-state lithium secondary battery, lithium metal is deposited between the solid electrolyte layer and the negative electrode current collector. Patent Document 1 discloses a technique in which a fine particle layer (carbon-containing layer) containing fine particles such as amorphous carbon (e.g., carbon black) is disposed between the negative electrode current collector and the solid electrolyte layer, which constitute the power generating element of the lithium secondary battery. According to Patent Document 1, with this configuration, when lithium metal is deposited between the fine particle layer and the negative electrode current collector during charging, the fine particle layer acts as a protective layer for the lithium metal layer and suppresses the growth of dendrites from the lithium metal layer, thereby preventing short-circuiting of the lithium secondary battery and resulting capacity reduction. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2019 / 0157723 Summary of the Invention [Problem to be solved by the invention]

[0008] However, according to the study of the present inventors, it has been found that even if the technique described in Patent Document 1 is used, there are still cases where it is not possible to prevent short circuits at the ends of the power generating element.

[0009] Therefore, an object of the present invention is to provide a means capable of suppressing short circuits at the ends of a power generating element of an all-solid-state battery. [Means for solving the problem]

[0010] The present inventors conducted extensive research to solve the above-mentioned problems. During this research, they discovered that during initial charging, when lithium migrates from the positive electrode side to the negative electrode side, lithium is absorbed into the carbon material contained in the carbon-containing layer interposed between the negative electrode current collector and the solid electrolyte layer, thereby imparting lithium conductivity to the carbon-containing layer. Based on this discovery, by disposing a lithium-containing positive electrode active material containing a sufficient amount of lithium to impart lithium conductivity to the carbon-containing layer only in the center of the positive electrode active material layer, sufficient lithium conductivity is imparted only to the region of the carbon-containing layer that overlaps with the center of the positive electrode active material layer (the center of the carbon-containing layer) when the power generating element is viewed in plan. Meanwhile, the lithium conductivity of the other region (the outer peripheral edge of the carbon-containing layer) remains low. This suppresses charge / discharge reactions at the edges of the power generating element, thereby solving the above-mentioned problems. This led to the completion of the present invention.

[0011] An all-solid-state battery according to one embodiment of the present invention includes a power generating element including: an anode active material layer including at least one anode active material selected from the group consisting of metallic lithium and a lithium-containing alloy; a cathode active material layer including a lithium-free cathode active material and a lithium-containing cathode active material; a solid electrolyte layer interposed between the anode active material layer and the cathode active material layer; and a carbon-containing layer interposed between the anode active material layer and the solid electrolyte layer and including a carbon material capable of absorbing lithium. The positive electrode active material layer is characterized in that, when the power-generating element is viewed from above, the positive electrode active material layer is composed of a central portion containing both the lithium-free positive electrode active material and the lithium-containing positive electrode active material, and an outer peripheral portion containing the lithium-free positive electrode active material and optionally containing the lithium-containing positive electrode active material; and the capacity [mAh] of the lithium-containing positive electrode active material contained in the central portion of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer that overlaps with the central portion of the positive electrode active material layer, and the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer is less than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer that overlaps with the outer peripheral portion of the positive electrode active material layer. [Effects of the Invention]

[0012] According to the present invention, it is possible to suppress short circuits at the ends of the power generating element of an all-solid-state battery. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view showing the appearance of a flat laminated type all-solid-state lithium secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line 2-2 shown in FIG. [Figure 3] FIG. 3 is a plan view of a positive electrode active material layer included in a stacked battery according to one embodiment of the present invention. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing the state of a cell layer included in a stacked battery according to one embodiment of the present invention before the initial charge. [Figure 5] FIG. 5 is an enlarged cross-sectional view showing the state of a cell layer included in a stacked battery according to one embodiment of the present invention after initial charging. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing a positive electrode active material layer included in a stacked battery according to one embodiment of the present invention. [Figure 7] FIG. 7 is an enlarged cross-sectional view showing a positive electrode active material layer included in a stacked battery according to another embodiment of the present invention. [Figure 8] FIG. 8 is an enlarged cross-sectional view showing a positive electrode active material layer included in a stacked battery according to still another embodiment of the present invention. [Figure 9] FIG. 9 is an enlarged cross-sectional view showing a positive electrode active material layer included in a stacked battery according to still another embodiment of the present invention. [Figure 10] FIG. 10 is a graph showing the charge / discharge curves of the test cell. [Figure 11] FIG. 11 is a graph showing a charging curve in measuring the capacity of a carbon material. [Figure 12] FIG. 12 is an enlarged cross-sectional view showing the state of a cell layer included in a stacked battery according to another embodiment of the present invention before the initial charge. [Figure 13]FIG. 13 is an enlarged cross-sectional view showing a state before the initial charge of a unit cell layer included in a stacked battery according to still another embodiment of the present invention. [Figure 14] FIG. 14 is an enlarged cross-sectional view showing the state of a cell layer included in a stacked battery according to still another embodiment of the present invention before the initial charge. [Figure 15] FIG. 15 is an enlarged cross-sectional view showing the state of a cell layer included in a stacked battery according to still another embodiment of the present invention before the initial charge. DETAILED DESCRIPTION OF THE INVENTION

[0014] An all-solid-state battery according to one embodiment of the present invention includes a power generating element including: an anode active material layer including at least one anode active material selected from the group consisting of metallic lithium and a lithium-containing alloy; a cathode active material layer including a lithium-free cathode active material and a lithium-containing cathode active material; a solid electrolyte layer interposed between the anode active material layer and the cathode active material layer; and a carbon-containing layer interposed between the anode active material layer and the solid electrolyte layer and including a carbon material capable of absorbing lithium. The positive electrode active material layer is characterized in that, when the power-generating element is viewed from above, the positive electrode active material layer is composed of a central portion containing both the lithium-free positive electrode active material and the lithium-containing positive electrode active material, and an outer peripheral portion containing the lithium-free positive electrode active material and optionally containing the lithium-containing positive electrode active material; and the capacity [mAh] of the lithium-containing positive electrode active material contained in the central portion of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer that overlaps with the central portion of the positive electrode active material layer, and the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer is less than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer that overlaps with the outer peripheral portion of the positive electrode active material layer.

[0015] The present embodiment will be described below with reference to the drawings. However, the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiment. In the description of the drawings, the same elements are given the same reference numerals and redundant 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.

[0016] FIG. 1 is a perspective view showing the appearance of a flat-layered all-solid-state lithium secondary battery according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1. The layered structure allows the battery to be compact and have a high capacity. In this specification, the flat-layered non-bipolar all-solid-state lithium secondary battery shown in FIGS. 1 and 2 (hereinafter also simply referred to as a "layered battery") will be used as an example for detailed explanation. However, in terms of the internal electrical connection configuration (electrode structure) of the lithium secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0017] 1, the stacked battery 10a has a flat, rectangular shape, with a negative electrode current collector 25 and a positive electrode current collector 27 extending from both sides for extracting power. The power generating element 21 is wrapped in the battery exterior material (laminate film 29) of the stacked battery 10a, and the periphery is heat-sealed, with the negative electrode current collector 25 and positive electrode current collector 27 extending to the outside.

[0018] 2, the stacked battery 10a of this embodiment has a structure in which a flat, generally rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, a carbon-containing layer 14, and a negative electrode are stacked. The positive electrode has a structure in which positive electrode active material layers 15 are disposed on both sides of a positive electrode current collector 11". The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode current collector 11'. The positive electrode, solid electrolyte layer 17, carbon-containing layer 14, and negative electrode are laminated in this order so that one positive electrode active material layer 15 faces an adjacent stack of a carbon-containing layer 14 and a negative electrode active material layer 13 with the solid electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, solid electrolyte layer 17, carbon-containing layer 14, and negative electrode constitute one unit cell layer 19. Therefore, the stacked battery 10a shown in FIG. 2 can also be said to have a structure in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. Note that a constraining pressure is applied to the stacked battery 10a in the stacking direction of the power generating element 21 by a pressure member (not shown). Therefore, the volume of the power generating element 21 is kept constant.

[0019] Negative electrode current collector 11′ and positive electrode current collector 11″ are respectively attached with negative electrode current collector (tab) 25 and positive electrode current collector (tab) 27 that are electrically connected to the respective electrodes (positive and negative electrodes), and are structured so as to be sandwiched between the ends of laminate film 29, which is the battery outer casing material, and extended to the outside of laminate film 29. Positive electrode current collector 27 and negative electrode current collector 25 may be attached to positive electrode current collector 11″ and negative electrode current collector 11′ of the respective electrodes by ultrasonic welding, resistance welding, or the like, via positive electrode leads and negative electrode leads (not shown) as necessary.

[0020] Fig. 3 is a plan view of a positive electrode active material layer included in a stacked battery according to one embodiment of the present invention. As shown in Fig. 3, in this embodiment, the positive electrode active material layer 15 is composed of two regions, a central portion 15a and an outer peripheral portion 15b (a square-shaped region of the positive electrode active material layer 15 excluding the central portion 15a), when the power generating element 21 is viewed from above.

[0021] FIG. 4 is an enlarged cross-sectional view of a cell layer included in a stacked battery according to one embodiment of the present invention, showing the state before the initial charge. FIG. 5 is an enlarged cross-sectional view of a cell layer included in a stacked battery according to one embodiment of the present invention, showing the state after the initial charge. In FIGS. 4 and 5, gray areas in the positive electrode active material layer and the carbon-containing layer indicate the presence of lithium. In the state before the initial charge shown in FIG. 4, the central portion 15a of the positive electrode active material layer 15 contains a lithium-free positive electrode active material (indicated by "□") and a lithium-containing positive electrode active material (indicated by gray "◯"). The outer peripheral portion 15b of the positive electrode active material layer 15 contains a lithium-free positive electrode active material but does not contain a lithium-containing positive electrode active material. The capacity [mAh] of the lithium-containing positive electrode active material is equal to or greater than the capacity [mAh] of the carbon material (indicated by "△") included in the region 14a of the carbon-containing layer 14 that overlaps with the central portion 15a of the positive electrode active material layer (the center of the carbon-containing layer). When the battery having the configuration shown in FIG. 4 is charged, as shown in FIG. 5, in a plan view of the power-generating element, lithium is absorbed into the carbon material contained in region 14a of carbon-containing layer 14 (lithium-containing positive electrode active material that has released lithium is indicated by a circle, and carbon material that has absorbed lithium is indicated by a gray triangle). This makes region 14a lithium-conductive. On the other hand, other region 14b (the outer peripheral portion of the carbon-containing layer) of carbon-containing layer 14 does not overlap with central portion 15a of the positive electrode active material layer (because it overlaps with outer peripheral portion 15b of the positive electrode active material layer (which contains a lithium-free positive electrode active material and does not contain a lithium-containing positive electrode active material)), and therefore lithium is not absorbed into the carbon material. Therefore, the lithium conductivity of region 14b is low, and lithium migration is hindered in this region. This suppresses charge / discharge reactions in the region overlapping with outer peripheral portion 15b of positive electrode active material layer 15, thereby preventing short-circuiting at the end of power-generating element 21.

[0022] The main components of the all-solid-state lithium secondary battery according to this embodiment will be described below.

[0023] [Current collector] The current collector has a function of mediating the transfer of electrons from the electrode active material layer. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

[0024] Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, and copper. Other examples include clad materials of nickel and aluminum, and clad materials of copper and aluminum. Furthermore, foils in which aluminum is coated on a metal surface 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 by sputtering.

[0025] Furthermore, examples of the resin having electrical conductivity include resins in which a conductive filler is added to a non-conductive polymer material.

[0026] The current collector may have a single layer structure made of a single material, or may have a laminate structure made of an appropriate combination of layers made of these materials. From the viewpoint of reducing the weight of the current collector, it is preferable that the current collector includes at least a conductive resin layer made of a resin having electrical conductivity. Furthermore, from the viewpoint of blocking the movement of lithium ions between the cell layers, a metal layer may be provided on a part of the current collector. Furthermore, if the negative electrode active material layer and the positive electrode active material layer described later are electrically conductive and can perform a current collecting function, it is not necessary to use a current collector as a separate member from these electrode active material layers. In such a configuration, the negative electrode active material layer described later constitutes the negative electrode, and the positive electrode active material layer described later constitutes the positive electrode.

[0027] [Negative electrode active material layer] In the all-solid-state battery according to this embodiment, the negative electrode active material layer essentially contains at least one negative electrode active material selected from the group consisting of metallic lithium and lithium-containing alloys. The lithium-containing alloy is not particularly limited, but examples thereof include alloys of Li with at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. In some cases, two or more negative electrode active materials may be used in combination. Of course, negative electrode active materials other than those listed above may also be used as long as they essentially contain metallic lithium or a lithium-containing alloy.

[0028] A preferred embodiment of the all-solid-state battery is a so-called lithium deposition type battery in which metallic lithium is deposited on the negative electrode current collector during charging. In this case, the layer of metallic lithium deposited on the negative electrode current collector during charging serves as the negative electrode active material layer. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer may not be present during full discharge, but in some cases, a negative electrode active material layer consisting of a certain amount of metallic lithium may be present during full discharge.

[0029] In another preferred embodiment, the all-solid-state battery has a negative electrode including a negative electrode current collector and a layer of a lithium-containing alloy disposed thereon as a negative electrode active material layer, wherein the thickness of the negative electrode active material layer increases as lithium is absorbed into the lithium-containing alloy during charging, and decreases as lithium is released from the lithium-containing alloy during discharging.

[0030] The thickness of the negative electrode active material layer when fully charged varies depending on the configuration of the intended all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

[0031] [Carbon-containing layer] The carbon-containing layer is a layer interposed between the negative electrode active material layer and the solid electrolyte layer, and contains a carbon material capable of absorbing lithium.

[0032] The carbon material is not particularly limited, but examples thereof include carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNT), graphite, hard carbon, etc. Among these, carbon black is preferred, and at least one selected from the group consisting of acetylene black, Ketjen Black (registered trademark), furnace black, channel black, and thermal lamp black is more preferred.

[0033] The content of the carbon material in the carbon-containing layer is not particularly limited, but is preferably in the range of 50 to 100 mass%, more preferably in the range of 70 to 100 mass%, even more preferably in the range of 90 to 100 mass%, and particularly preferably in the range of 95 to 100 mass%.

[0034] The carbon-containing layer may be composed solely of a carbon material as long as a free-standing film can be produced using only the carbon material, but may also contain a binder if necessary. Examples of binders include, but are not limited to, thermoplastic polymers such as polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen atoms), polyethylene, polypropylene, polymethylpentene, polybutene, polyethernitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene-propylene-diene copolymer, styrene-butadiene-styrene block copolymer and its hydrogenated derivatives, styrene-isoprene-styrene block copolymer and its hydrogenated derivatives, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and polychlorotrifluoroethylene (PCTF). Examples of the fluororesin include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), epoxy resin, and carboxymethyl cellulose.Among these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are more preferable.

[0035] The binder content in the carbon-containing layer is not particularly limited, but is preferably in the range of 1 to 10 mass %, and more preferably in the range of 2 to 5 mass %. If the binder content is 1 mass % or more, a carbon-containing layer having sufficient strength can be formed. If the binder content is 10 mass % or less, a decrease in energy density can be suppressed.

[0036] The carbon-containing layer preferably does not contain any components other than the carbon material and the binder. Thus, according to a preferred embodiment, the carbon-containing layer is made of only the carbon material, or only the carbon material and the binder.

[0037] The thickness of the carbon-containing layer is not particularly limited, but is preferably in the range of 1 to 50 μm, more preferably in the range of 5 to 40 μm, and even more preferably in the range of 10 to 30 μm. When the thickness of the carbon-containing layer is 1 μm or more, the functions of the carbon-containing layer can be fully exhibited. When the thickness of the carbon-containing layer is 50 μm or less, a decrease in energy density can be suppressed.

[0038] [Solid electrolyte layer] The solid electrolyte layer contains a solid electrolyte as a main component and is a layer interposed between the negative electrode active material layer and the positive electrode active material layer. The solid electrolyte is not particularly limited, but examples thereof include sulfide solid electrolytes and oxide solid electrolytes. From the viewpoint of high ionic conductivity, the solid electrolyte preferably contains a sulfide solid electrolyte.

[0039] 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-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, 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.

[0040] 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 and LiI-LiBr-Li3PS 4、 Examples of sulfide solid electrolytes having a Li4P2S7 skeleton include Li-PS-based solid electrolytes called LPS (e.g., Li7P3S 11 ) can be mentioned. In addition, examples of sulfide solid electrolytes include Li (4-x) Ge (1-x) P xAn LGPS or the like represented by S4 (where 0 < x < 1) 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).

[0041] 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 terms of molar ratio, and more preferably Li2S:P2S5 = 70:30 to 80:20.

[0042] 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 a raw material composition. Also, the crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass at a temperature above the crystallization temperature. The ionic conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25°C) is, for example, 1×10 -5 S / cm or more, and more preferably 1×10 -4 S / cm or more. The value of the ionic conductivity of the solid electrolyte can be measured by an alternating current impedance method.

[0043] 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), etc. are included. Also, as another example of the oxide solid electrolyte, LiLaTiO (for example, Li0.34 La 0.51 TiO3), LiPON (e.g., Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (e.g., Li7La3Zr2O 12 ) etc.

[0044] 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 diameter (D 50 ) 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. 50 ) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

[0045] 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 %.

[0046] 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.

[0047] The thickness of the solid electrolyte layer varies depending on the configuration of the intended all-solid-state battery, but from the viewpoint of improving the volumetric energy density of the battery, it is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. On the other hand, there is no particular restriction on the lower limit of the thickness of the solid electrolyte layer, but it is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0048] [Cathode active material layer] In the all-solid-state battery according to this embodiment, the positive electrode active material layer essentially contains a lithium-free positive electrode active material and a lithium-containing positive electrode active material.

[0049] (Lithium-free positive electrode active material) In this specification, the term "lithium-free positive electrode active material" refers to a positive electrode active material that does not contain lithium element. Examples of the lithium-free positive electrode active material include, but are not limited to, transition metal oxides, transition metal fluorides, and sulfur-based positive electrode active materials.

[0050] Specific examples of transition metal oxides and transition metal fluorides include titanium oxide (TiO2), niobium oxide (Nb2O3), tungsten oxide (WO3), iron(II) fluoride (FeF2), vanadium pentoxide (VO5), iron oxide (FeO X ), manganese dioxide (MnO2), etc.

[0051] Examples of sulfur-based positive electrode active materials include particles or thin films of organic or inorganic sulfur compounds. Any material can be used as long as it utilizes the oxidation-reduction reaction of sulfur to release lithium ions during charging and absorb lithium ions during discharging. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), and polycarbonate, as typified by the compounds described in International Publication No. 2010 / 044437. Among these, disulfide compounds, sulfur-modified polyacrylonitrile, and rubeanic acid are preferred, with sulfur-modified polyacrylonitrile being particularly preferred. Disulfide compounds containing dithiobiurea derivatives, thiourea groups, thioisocyanates, or thioamide groups are more preferred. On the other hand, inorganic sulfur compounds are preferred due to their excellent stability. Specific examples include sulfur (S), S-carbon composites, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, MoS2, and MoS3. Among these, S, S-carbon composites, TiS2, TiS3, TiS4, FeS2, and MoS2 are preferred, with S, S-carbon composites, TiS2, and FeS2 being more 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, one in which the carbon material is distributed on the surface or within fine sulfur powder, or a combination of these.

[0052] In some cases, two or more types of lithium-free positive electrode active materials may be used in combination. Of course, lithium-free positive electrode active materials other than those mentioned above may also be used.

[0053] (Lithium-containing positive electrode active material) In this specification, the lithium-containing positive electrode active material refers to a positive electrode active material containing lithium element. The lithium-containing positive electrode active material is not particularly limited, but may be a layered rock salt type active material such as LiCoO2, LiMnO2, LiNiO2, LiVO2, Li(Ni-Mn-Co)O2, Li(Ni-Co-Al)O2, LiMn2O4, LiNi 0.5 Mn 1.5 Examples of oxide active materials include spinel-type active materials such as LiFePO4 and LiMnPO4, olivine-type active materials such as LiFeSiO4 and LiMnSiO4, and Si-containing active materials such as LiFeSiO4 and LiMnSiO4. 12 Among these, composite oxides containing lithium and nickel are preferably used, more preferably Li(Ni-Mn-Co)O2 (hereinafter also referred to as "NMC composite oxide") or Li(Ni-Co-Al)O2 (hereinafter also referred to as "NCA composite oxide"), and oxides in which part of the transition metal has been substituted with other elements, and particularly preferably NMC composite oxide. NMC composite oxides and NCA composite oxides have a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co arranged in an orderly manner) atomic layers are alternately stacked with oxygen atomic layers interposed between them, and contain one Li atom per atom of the transition metal M. The amount of Li that can be extracted is twice that of spinel-type lithium manganese oxides, i.e., the supply capacity is doubled, resulting in high capacity.

[0054] As mentioned above, the NMC composite oxide and the NCA composite oxide also include composite oxides in which a portion of the transition metal element is replaced with another metal element. In this case, the other element may be Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu, Ag, or Zn. Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, or Cr is preferred, and Ti, Zr, P, Al, Mg, or Cr is more preferred. From the viewpoint of improving cycle performance, Ti, Zr, Al, Mg, or Cr is even more preferred. However, the other metal element that can replace the transition metal element of the NCA composite oxide is one other than Al. More specifically, LiNi0.8 Co 0.1 Al 0.1 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.88 Mn 0.06 Co 0.06 O2 and LiNi 0.5 Mn 0.3 Co 0.2 Examples include O2.

[0055] In some cases, two or more kinds of lithium-containing positive electrode active materials may be used in combination. Of course, lithium-containing positive electrode active materials other than those mentioned above may also be used.

[0056] 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 diameter (D 50 ) 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.

[0057] The content of the positive electrode active material (the total amount of the lithium-free positive electrode active material and the lithium-containing positive electrode active material) in the positive electrode active material layer is not particularly limited, but is preferably within a range of, for example, 40 to 100 mass %, and more preferably within a range of 50 to 90 mass %.

[0058] The positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive additive, and a binder, as necessary. The specific forms of the solid electrolyte and the binder are the same as those described above, and therefore detailed description thereof will be omitted here.

[0059] The conductive additive is not particularly limited, but examples thereof include 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, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). Furthermore, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives. Among these conductive additives, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, more preferably at least one selected from the group consisting of aluminum, stainless steel, silver, gold, and carbon, and even more preferably at least one carbon. These conductive additives may be used alone or in combination.

[0060] The conductive additive is preferably in the form of particles or fibers. When the conductive additive is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, scale, or spindle shape.

[0061] When the conductive additive is particulate, its average particle size (primary particle size) is not particularly limited, but is preferably 0.01 to 10 μm from the viewpoint of the electrical properties of the battery. In this specification, the "particle size of the conductive additive" refers to the longest distance L between any two points on the contour line of the conductive additive. The value of the "average particle size of the conductive additive" is calculated as the average particle size of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0062] When the positive electrode active material layer contains a conductive additive, the content of the conductive additive in the positive electrode active material layer is not particularly limited, but is preferably 0 to 10 mass %, more preferably 2 to 8 mass %, and even more preferably 4 to 7 mass %, relative to the total mass of the positive electrode active material layer. Within such a range, a stronger electron conduction path can be formed in the positive electrode active material layer, which can effectively contribute to improving battery characteristics.

[0063] The all-solid-state battery according to this embodiment is characterized in that, when viewed from above, the cathode active material layer comprises a central portion containing both a lithium-free cathode active material and a lithium-containing cathode active material, and an outer peripheral portion containing the lithium-free cathode active material and optionally a lithium-containing cathode active material; and the capacity [mAh] of the lithium-containing cathode active material contained in the central portion of the cathode active material layer is equal to or greater than the capacity [mAh] of the carbon material contained in the carbon-containing layer in the region overlapping with the central portion of the cathode active material layer, and the capacity [mAh] of the lithium-containing cathode active material contained in the outer peripheral portion of the cathode active material layer is less than the capacity [mAh] of the carbon material contained in the carbon-containing layer in the region overlapping with the outer peripheral portion of the cathode active material layer. This configuration provides sufficient lithium conductivity to the carbon-containing layer in the region overlapping with the central portion of the cathode active material layer (the central portion of the carbon-containing layer). Meanwhile, the lithium conductivity of the remaining region (the outer peripheral portion of the carbon-containing layer) remains low. This suppresses charge / discharge reactions at the ends of the power generating element of the all-solid-state battery, making it less likely that a short circuit will occur at the ends. Note that the outer peripheral edge portion may contain a lithium-containing positive electrode active material, as long as the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer that overlaps with the outer peripheral edge portion of the positive electrode active material layer. However, from the viewpoint of further suppressing a short circuit at the ends of the power generating element, it is preferable that the outer peripheral edge portion does not contain a lithium-containing positive electrode active material.

[0064] In this specification, the "center" and "outer peripheral portion" of the positive electrode active material layer are determined by the following methods, depending on whether the outer peripheral portion contains no lithium-containing positive electrode active material or a lithium-containing positive electrode active material. That is, when the outer peripheral portion does not contain a lithium-containing positive electrode active material, elemental mapping of lithium can be performed using energy dispersive X-ray spectroscopy (EDX) on an image of the positive electrode active material layer in the planar direction observed with a scanning electron microscope (SEM), and the counted number of lithium elements can be used as an indicator for determination. More specifically, the point where lithium elements are first observed from the outer peripheral edge of the positive electrode active material layer toward the inside is defined as the boundary between the center and the outer peripheral portion. The region enclosed by this boundary (including the boundary) is then determined as the "center," and the remaining region is determined as the "outer peripheral portion." On the other hand, when the outer peripheral portion of the positive electrode active material layer contains a lithium-containing positive electrode active material, the all-solid-state battery according to this embodiment is initially charged. This causes lithium to be released from the lithium-containing positive electrode active material present in the center and outer peripheral portion of the positive electrode active material layer, and lithium to be absorbed into the carbon-containing layer. In the all-solid-state battery according to the present embodiment, the capacity [mAh] of the lithium-containing positive electrode active material contained in the central portion of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the carbon material contained in the carbon-containing layer in the region overlapping with the central portion of the positive electrode active material layer, whereas the capacity [mAh] of the lithium-containing positive electrode active material contained in the peripheral portion of the positive electrode active material layer is less than the capacity [mAh] of the carbon material contained in the carbon-containing layer in the region overlapping with the peripheral portion of the positive electrode active material layer. Therefore, the carbon material contained in the carbon-containing layer in the region overlapping with the central portion of the positive electrode active material layer has absorbed lithium up to the upper limit of its absorption capacity after the initial charge and is therefore unable to absorb any more lithium. In contrast, the carbon material contained in the carbon-containing layer in the region overlapping with the peripheral portion of the positive electrode active material layer has not absorbed lithium up to the upper limit of its absorption capacity even after the initial charge and is therefore able to absorb further lithium. Therefore, by determining whether the carbon material contained in the carbon-containing layer can absorb further lithium after the initial charge, it is possible to determine whether the corresponding position of the positive electrode active material layer is the peripheral portion or the central portion.

[0065] In the all-solid-state battery according to this embodiment, the boundary between the center and the outer peripheral edge of the positive electrode active material layer is located inside the outer peripheral edge of the positive electrode active material layer. In other words, the "outer peripheral edge" exists around the entire outer peripheral edge of the positive electrode active material layer. This configuration can suppress short circuits at the end of the power generating element. Furthermore, since lithium-free positive electrode active materials are less expensive than lithium-containing positive electrode active materials, the cost of the all-solid-state battery can be reduced by forming a positive electrode active material layer using a lithium-free positive electrode active material and a sufficient amount of lithium-containing positive electrode active material to impart lithium conductivity to the carbon-containing layer.

[0066] The shape and size of the center and outer periphery of the power generating element when viewed in plan are not particularly limited. When the positive electrode active material layer is rectangular, the shape of the center when viewed in plan is preferably also rectangular. In this case, the outer periphery is a square shape defined by the positive electrode active material layer excluding the center. From the viewpoint of improving the energy density of the all-solid-state battery, the size of the center when viewed in plan is preferably as large as possible, as long as a sufficient outer periphery can be secured to prevent short circuits. Specifically, the ratio of the size of the center to the size of the positive electrode active material layer is preferably 0.80 to 0.98, more preferably 0.85 to 0.98, even more preferably 0.90 to 0.98, and particularly preferably 0.95 to 0.98. The width of the outer periphery (the distance from the outer periphery of the positive electrode active material layer to the boundary between the center and the outer periphery) is not particularly limited, but is preferably 1 mm to 5 cm, more preferably 2 mm to 3 cm, and even more preferably 5 mm to 2 cm. By keeping the width of the outer periphery within the above range, short circuits at the ends of the power generating element can be further suppressed.

[0067] In the all-solid-state battery according to this embodiment, both the lithium-free positive electrode active material and the lithium-containing positive electrode active material are contained in the central portion. Because the positive electrode active material layer has lithium conductivity, the arrangement of the lithium-free positive electrode active material and the lithium-containing positive electrode active material in the stacking direction in the central portion is not limited. FIG. 6 is an enlarged cross-sectional view showing a state before the first charge of a positive electrode active material layer contained in a stacked battery according to one embodiment of the present invention. In the embodiment of FIG. 6, the lithium-containing positive electrode active material is uniformly present throughout the entire thickness direction of the central portion. Other embodiments of the positive electrode active material layer include those shown in FIGS. 7 to 9. In the embodiment of FIG. 7, the lithium-containing positive electrode active material is present only in a half-thickness region on the solid electrolyte layer side of the central portion. In the embodiment of FIG. 8, the lithium-containing positive electrode active material is present only in a half-thickness region on the opposite side of the solid electrolyte layer side of the central portion.

[0068] In the all-solid-state battery according to this embodiment, the thickness of the central portion of the positive electrode active material layer and the thickness of the peripheral edge portion may be the same or different, as shown in FIGS. 6 to 8 . An example of a case in which the thickness of the central portion and the thickness of the peripheral edge portion are different is an embodiment in which the central portion is relatively thick and the peripheral edge portion is relatively thin, as shown in FIG. 9 . However, from the viewpoint of applying a uniform pressure in the planar direction when applying a constraining pressure in the stacking direction of the power generating element, it is preferable that the thickness of the central portion and the thickness of the peripheral edge portion are close to each other. More specifically, the ratio of the thickness of the central portion of the positive electrode active material layer to the thickness of the peripheral edge portion is preferably 0.90 to 1.10, more preferably 0.95 to 1.05, even more preferably 0.98 to 1.02, and particularly preferably 1.00. In this specification, the thickness of the central portion refers to a value calculated as the arithmetic average of thicknesses measured at several to several tens of different locations. The same applies to the thickness of the peripheral edge portion.

[0069] The all-solid-state battery according to this embodiment is also characterized in that the capacity [mAh] of the lithium-containing positive electrode active material contained in the center of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer overlapping with the center of the positive electrode active material layer, and the capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral portion of the positive electrode active material layer is less than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer overlapping with the outer peripheral portion of the positive electrode active material layer. The inventors have found from the following experimental results that the above-mentioned configuration imparts to the carbon-containing layer sufficient lithium conductivity to enable the battery to function during initial charging (the carbon-containing layer is activated), and as a result, the battery can function.

[0070] <<Preparation of test cell>> First, a lithium symmetric cell was prepared as a test cell. More specifically, a positive electrode current collector (SUS foil), metallic lithium, a solid electrolyte layer (Li6PS5Cl), a carbon-containing layer (prepared using furnace black as a carbon material in accordance with paragraphs "0136" to "0138" of U.S. Patent Application Publication No. 2019 / 0157723), metallic lithium, and a negative electrode current collector (SUS foil) were stacked in this order. Then, the positive electrode current collector (made of SUS) and the negative electrode current collector (made of SUS) were sandwiched and sealed in a pressurized container capable of blocking the outside air under a confining pressure of 20 MPa to prepare a test cell.

[0071] <Charge / Discharge Test> Next, a charge / discharge test was carried out on the test cell by the following method. The measurement was carried out in a constant temperature bath set at 25° C. The charge / discharge conditions were as follows:

[0072] [Voltage range] -2.0~2.0V [Charging process] 0.2mA / cm 2 [Discharge process]0.2mA / cm 2 [Termination condition] Current capacity 6.0mAh / cm 2 .

[0073] Figure 10 is a graph showing the charge / discharge curves of the test cell. When charging was performed as the first operation, charging and subsequent discharging were possible, as shown in Figure 10. When discharging was performed as the first operation, the overvoltage became large, as shown in Figure 10, and it was found that the cell did not function as a battery.

[0074] The above results suggest that in an all-solid-state battery having a carbon-containing layer on the negative electrode side, lithium released from the positive electrode active material during initial charging is absorbed into the carbon material in the carbon-containing layer, thereby exhibiting battery function. This shows that even in an all-solid-state battery containing a lithium-free positive electrode active material as the positive electrode active material, the battery can be made to function by incorporating a lithium-containing positive electrode active material having a capacity equal to or greater than the capacity of the carbon material contained in the carbon-containing layer into the positive electrode active material and performing an initial charge equal to or greater than the capacity of the carbon material.

[0075] By applying the above findings, it is possible to control the lithium conductivity of the carbon-containing layer at a corresponding position in a planar view of the power generating element by adjusting the amount of lithium-containing positive electrode active material in the positive electrode active material layer. Therefore, by controlling the arrangement of the lithium-containing positive electrode active material in the positive electrode active material layer so that the capacity [mAh] of the lithium-containing positive electrode active material contained in the center of the positive electrode active material layer is equal to or greater than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer overlapping with the center of the positive electrode active material layer, and the capacity [mAh] of the lithium-containing positive electrode active material contained in the peripheral edge of the positive electrode active material layer is less than the capacity [mAh] of the carbon material contained in the region of the carbon-containing layer overlapping with the peripheral edge of the positive electrode active material layer, it is possible to maintain sufficiently high lithium conductivity in the center of the carbon-containing layer while maintaining low lithium conductivity in the peripheral edge. As a result, charge / discharge reactions at the edges of the power generating element of the all-solid-state battery are suppressed, making short circuits less likely to occur at the edges.

[0076] Here, the "capacity of the lithium-containing positive electrode active material" can be measured using a so-called half-cell comprising a positive electrode active material layer containing the target lithium-containing positive electrode active material, a solid electrolyte, a conductive additive, and a binder; a solid electrolyte layer; and metallic lithium as the negative electrode. For example, the cell is placed in an evaluation jig capable of ensuring an inert atmosphere while applying an appropriate surface pressure (preferably 100 MPa or less, e.g., 20 MPa). The cell is then connected to a charge / discharge device and charged at 25°C at a constant current (preferably 1 / 20 [C], more preferably 1 / 100 [C]) (a constant current is passed from the positive electrode to the negative electrode), thereby transferring lithium from the lithium-containing positive electrode active material to the negative electrode. The behavior of the cell voltage during this process is measured, and the current capacity [mAh] of the lithium-containing positive electrode active material is determined from this behavior. The cutoff voltage varies depending on the type of positive electrode active material, but the point at which the half-cell voltage sharply decreases is generally considered the terminal voltage. The time (h) from the start of charging to cutoff and the constant charging current (mA / cm 2 ) is the capacity per unit area of ​​the positive electrode active material layer [mAh / cm 2 ]. The capacity of the positive electrode active material layer, i.e., the capacity [mAh] of the lithium-containing positive electrode active material used in the half cell, can be determined by multiplying this value by the area of ​​the positive electrode active material layer. Note that if the mass [g] of the lithium-containing positive electrode active material included in the portion to be measured (the center or outer peripheral edge of the positive electrode active material layer) is different from the mass [g] of the lithium-containing positive electrode active material used in the half cell, the capacity [mAh] of the lithium-containing positive electrode active material included in the portion to be measured can be determined by multiplying the value [mAh / g] obtained by dividing the capacity [mAh] of the lithium-containing positive electrode active material used in the half cell by the mass [g] of the lithium-containing positive electrode active material included in the portion to be measured by the mass [g] of the lithium-containing positive electrode active material included in the portion to be measured.

[0077] The "capacity of a carbon material" can be measured using a so-called half cell comprising metallic lithium as a positive electrode, a solid electrolyte layer, and a carbon-containing layer containing the target carbon material as a negative electrode and a negative electrode current collector. For example, the cell is placed in an evaluation jig that can ensure an inert atmosphere while applying an appropriate surface pressure (preferably 40 MPa or less, e.g., 20 MPa). The cell is then connected to a charge / discharge device and a constant current (preferably 0.2 mA / cm) is applied at 25°C. 2 , more preferably 0.05 mA / cm 2 , and more preferably 0.01 mA / cm 2 ), lithium is transferred from the positive electrode to the carbon-containing layer and negative electrode. Figure 11 shows the results of measuring the behavior of the cell voltage during this process. It is known that the standard electrode potential of carbon materials generally changes depending on their degree of lithiation, and that this potential is higher than the electrode potential of metallic lithium. Therefore, before the start of charging, the cell voltage shows a negative value. As the charging reaction progresses and the degree of lithiation of the carbon material increases, its standard electrode potential gradually approaches that of metallic lithium, and eventually becomes almost equal to the potential of metallic lithium, so the cell voltage saturates at a certain point. In Figure 11, in region (a) from the start of charging to the point of saturation (the point at which the slope of the curve becomes 0), lithium is absorbed into the carbon material. In region (b) after saturation, lithium accumulates at the negative electrode. The time (h) from the start of charging to the point of saturation and the constant charging current (mA / cm 2 ) is the capacity of the carbon-containing layer per unit area [mAh / cm 2]. Then, by calculating the product of this value and the area of ​​the carbon-containing layer, the capacity of the carbon-containing layer, i.e., the capacity [mAh] of the carbon material used in the half cell, can be determined. Note that when the mass [g] of the carbon material contained in the portion to be measured (the center or outer peripheral portion of the carbon-containing layer) is different from the mass [g] of the carbon material used in the half cell, the capacity [mAh] of the carbon material contained in the portion to be measured can be determined by multiplying the value [mAh / g] obtained by dividing the capacity [mAh] of the carbon material used in the half cell by the mass [g] of the carbon material used in the half cell by the mass [g] of the carbon material contained in the portion to be measured.

[0078] The ratio of the capacity [mAh] of the lithium-containing positive electrode active material contained in the center of the positive electrode active material layer to the capacity [mAh] of the carbon material contained in the center of the carbon-containing layer (capacity [mAh] of lithium-containing positive electrode active material / capacity [mAh] of carbon material) is essentially 1 or more, and from the viewpoint of improving energy density and reducing costs, it is preferably 1 to 2, more preferably 1 to 1.5, and even more preferably 1 to 1.2.

[0079] The manufacturing method of the positive electrode active material layer according to this embodiment is not particularly limited, and known vapor deposition methods or coating methods can be appropriately adopted. Specific examples of vapor deposition methods include: (i) masking the portion of the substrate surface that will form the outer peripheral edge, and simultaneously or sequentially vapor-depositing a lithium-free positive electrode active material and a lithium-containing positive electrode active material to form a central portion. Then, masking the surface of the central portion and the area outside the portion that will form the outer peripheral edge of the positive electrode active material layer, and removing the masking material from the outer peripheral edge. Then, vapor-depositing a lithium-free positive electrode active material on the exposed portion of the substrate to form the outer peripheral edge; and (ii) masking the portion of the substrate surface that will form the central portion and the area outside the portion that will form the outer peripheral edge of the positive electrode active material layer, and vapor-depositing a lithium-free positive electrode active material to form the outer peripheral edge. Then, masking the surface of the outer peripheral edge, and removing the masking material from the central portion. Then, vapor-depositing a lithium-free positive electrode active material and a lithium-containing positive electrode active material on the exposed portion of the substrate to form the central portion. Specific examples of the coating method include: (iii) a method in which a portion of the substrate surface that will form the outer peripheral edge is masked, and a slurry containing a lithium-free positive electrode active material and a lithium-containing positive electrode active material is coated and dried to form a central portion. Then, the surface of the central portion and the area outside the portion that will become the outer peripheral edge of the positive electrode active material layer are masked, and the masking material from the outer peripheral edge is removed. Then, a slurry containing a lithium-free positive electrode active material is coated and dried to form a peripheral edge portion on the exposed portion of the substrate; and (iv) a method in which a portion of the substrate surface that will form the central portion and the area outside the portion that will become the outer peripheral edge of the positive electrode active material layer are masked, and a slurry containing a lithium-free positive electrode active material is coated and dried to form a peripheral edge portion. Then, the surface of the outer peripheral edge is masked, and the masking material from the central portion is removed. Then, a slurry containing a lithium-free positive electrode active material and a lithium-containing positive electrode active material is coated and dried to form a central portion.In the coating methods (iii) and (iv), a slurry containing both a lithium-free positive electrode active material and a lithium-containing positive electrode active material was used to form the central portion. However, a slurry containing only a lithium-free positive electrode active material as the positive electrode active material and a slurry containing only a lithium-containing positive electrode active material as the positive electrode active material may be separately prepared. The slurry containing only a lithium-free positive electrode active material as the positive electrode active material is then coated and dried, followed by a slurry containing only a lithium-containing positive electrode active material, to form a two-layer central portion. Alternatively, the slurry containing only a lithium-containing positive electrode active material as the positive electrode active material may be coated and dried, followed by a slurry containing only a lithium-free positive electrode active material, to form a two-layer central portion.

[0080] After forming a cathode active material layer on the surface of the substrate by the above method, the exposed surface of the cathode active material layer is superimposed on a solid electrolyte layer and transferred to obtain a laminate of the solid electrolyte layer and the cathode active material layer. Alternatively, the cathode active material layer may be formed directly on the solid electrolyte layer instead of on the substrate. In this case, the cathode active material layer can be formed by vapor deposition or coating, similar to the method described above.

[0081] Next, the size of each layer constituting the power generating element will be described. In the all-solid-state battery according to this embodiment, when the power generating element is viewed from above, it is preferable that the outer peripheral edge of the negative electrode active material layer is located at the same position as the outer peripheral edge of the center of the positive electrode active material layer (1a), or is located outside the outer peripheral edge of the center of the positive electrode active material layer (1b) as in the embodiment shown in FIG. 12. Among these, the embodiment (1b) is more preferable. By adopting such a configuration, it is possible to prevent a decrease in capacity due to a decrease in the area mainly involved in charge and discharge.

[0082] In the all-solid-state battery according to this embodiment, when the power generating element is viewed from above, the outer peripheral edge of the carbon-containing layer is preferably located at the same position as the outer peripheral edge of the (2a) negative electrode active material layer, or is located further outward than the outer peripheral edge of the (2b) negative electrode active material layer as in the embodiment shown in Fig. 13. Among these, the embodiment (2b) is more preferable. With this configuration, the carbon-containing layer acts as a physical barrier, further suppressing short circuits at the ends of the power generating element.

[0083] In the all-solid-state battery according to this embodiment, when the power generating element is viewed from above, the outer peripheral edge of the solid electrolyte layer is preferably located at the same position as the outer peripheral edge of the (3a) carbon-containing layer, or located outside the outer peripheral edge of the (3b) carbon-containing layer as in the embodiment shown in FIG. 14. Among these, the embodiment (3b) is more preferable. This configuration can prevent a decrease in capacity due to a reduction in the area involved in charge and discharge. This configuration allows the solid electrolyte layer to act as a physical barrier, further suppressing short circuits at the ends of the power generating element.

[0084] In the all-solid-state battery according to this embodiment, it is preferable that the width of the outer peripheral edge of the positive electrode active material layer when the power generating element is viewed in plan is (4a) the same as the sum of the thickness of the positive electrode active material layer and the thickness of the solid electrolyte layer in the stacking direction of the power generating element, or (4b) greater than this sum as in the embodiment shown in Figure 15. Among these, the embodiment (4b) is more preferable. This configuration can reduce the effect of lithium diffusion in the planar direction of the positive electrode active material layer, thereby further suppressing short circuits at the ends of the power generating element.

[0085] [Positive and negative current collector plates] The material constituting the current collector plate is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate and the negative electrode current collector plate may be made of the same material or different materials.

[0086] [Positive and negative leads] The current collector and the current collecting plate may be electrically connected via a positive electrode lead or a negative electrode lead. Materials used in known lithium secondary batteries may be used as the constituent materials of the positive electrode and negative electrode leads. It is preferable that the portion removed from the outer casing be covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting the product (e.g., automobile parts, particularly electronic devices).

[0087] [Battery exterior materials] As the battery exterior material, a known metal can case can be used, or a bag-shaped case using an aluminum-containing laminate film that can cover the power generating element can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferred for the exterior body because it can easily adjust the collective pressure applied to the power generating element from the outside.

[0088] The stacked battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a driving power source for EVs and HEVs. [Explanation of symbols]

[0089] 10a stacked battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 14 carbon-containing layers, 14a The center of the carbon-containing layer; 14b the outer periphery of the carbon-containing layer; 15 positive electrode active material layer, 15a: the center of the positive electrode active material layer; 15b: an outer peripheral edge portion of the positive electrode active material layer; 17 solid electrolyte layer, 19 cell layer, 21 power generation elements, 25 negative current collector plate, 27 positive current collector plate, 29 Laminating film.

Claims

1. a negative electrode active material layer containing at least one negative electrode active material selected from the group consisting of metallic lithium and lithium-containing alloys; a positive electrode active material layer including a lithium-free positive electrode active material and a lithium-containing positive electrode active material; a solid electrolyte layer interposed between the negative electrode active material layer and the positive electrode active material layer; and an all-solid-state battery including a power generating element having a carbon-containing layer interposed between the negative electrode active material layer and the solid electrolyte layer, the carbon-containing layer containing a carbon material capable of absorbing lithium, When the power-generating element is viewed from above, the positive electrode active material layer is composed of a central portion containing both the lithium-free positive electrode active material and the lithium-containing positive electrode active material, and an outer peripheral portion containing the lithium-free positive electrode active material and optionally containing the lithium-containing positive electrode active material, a capacity [mAh] of the lithium-containing positive electrode active material contained in the central portion of the positive electrode active material layer is equal to or greater than a capacity [mAh] of the carbon material contained in a region of the carbon-containing layer that overlaps with the central portion of the positive electrode active material layer, a capacity [mAh] of the lithium-containing positive electrode active material contained in the outer peripheral edge portion of the positive electrode active material layer is less than a capacity [mAh] of the carbon material contained in a region of the carbon-containing layer that overlaps with the outer peripheral edge portion of the positive electrode active material layer.

2. The all-solid-state battery according to claim 1 , wherein an outer peripheral edge portion of the positive electrode active material layer does not contain a lithium-containing positive electrode active material.

3. 3. The all-solid-state battery according to claim 1, wherein, in a plan view of the power-generating element, an outer peripheral edge of the negative electrode active material layer is located at the same position as an outer peripheral edge of a central portion of the positive electrode active material layer, or is located outside the outer peripheral edge of the central portion of the positive electrode active material layer.

4. 4. The all-solid-state battery according to claim 1, wherein, in a plan view of the power-generating element, an outer peripheral edge of the carbon-containing layer is located at the same position as an outer peripheral edge of the negative electrode active material layer, or is located outward from the outer peripheral edge of the negative electrode active material layer.

5. 5. The all-solid-state battery according to claim 1, wherein the width of the outer peripheral edge portion of the positive electrode active material layer when the power generating element is viewed in a plan view is equal to or greater than the sum of the thickness of the positive electrode active material layer and the thickness of the solid electrolyte layer in the stacking direction of the power generating element.

6. 6. The all-solid-state battery according to claim 1, wherein a ratio of a thickness of the outer peripheral edge portion of the positive electrode active material layer to a thickness of the center portion of the positive electrode active material layer is 0.90 to 1.10.

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