Solid electrolyte sheet and all-solid-state battery

Abstract

The present invention provides: an all-solid-state battery which has excellent reliability; and a solid electrolyte sheet with which the all-solid-state battery can be configured.　A solid electrolyte sheet according to the present invention is characterized by comprising: a solid electrolyte layer A which comprises a porous base material and a solid electrolyte that is held by the porous base material, and which contains a solid electrolyte a that reacts with lithium metal to oxidize the lithium; and a solid electrolyte layer B which contains a solid electrolyte b that has a lower reactivity with lithium metal than the solid electrolyte a. The solid electrolyte sheet is also characterized in that the solid electrolyte layer B is disposed on at least one surface of the solid electrolyte sheet. An all-solid-state battery according to the present invention comprises a positive electrode, a negative electrode, and a solid electrolyte layer, and is characterized by comprising a solid electrolyte sheet according to the present invention as the solid electrolyte layer in such a manner that the solid electrolyte layer B of the solid electrolyte sheet faces the negative electrode.

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery having excellent reliability and a solid electrolyte sheet that can be used to form the all-solid-state battery. [Background technology]

[0002] In recent years, with the development of portable electronic devices such as mobile phones and laptop personal computers, and the practical application of electric vehicles, there has been a growing demand for small, lightweight batteries with high capacity and high energy density.

[0003] Currently, lithium batteries, particularly lithium-ion batteries, that can meet this demand use lithium-containing composite oxides such as lithium cobalt oxide (LiCoO) and lithium nickel oxide (LiNiO) as the positive electrode active material, graphite or the like as the negative electrode active material, and an organic electrolyte solution containing an organic solvent and a lithium salt as the non-aqueous electrolyte.

[0004] Furthermore, with the further development of devices that use lithium-ion batteries, there is a demand for longer life, higher capacity, and higher energy density of lithium-ion batteries, as well as a high demand for the reliability of these longer life, higher capacity, and higher energy density lithium-ion batteries.

[0005] However, the organic electrolyte used in lithium-ion batteries contains flammable organic solvents, which can cause the organic electrolyte to generate excessive heat in the event of an abnormality such as a short circuit. Furthermore, with the recent trend toward higher energy density in lithium-ion batteries and an increasing amount of organic solvent in the organic electrolyte, there is a growing demand for greater reliability in lithium-ion batteries.

[0006] In light of the above, all-solid-state lithium batteries (all-solid-state batteries) that do not use organic solvents are also being considered. All-solid-state lithium batteries use a molded body of a solid electrolyte that does not use organic solvents instead of the conventional organic solvent-based electrolyte, and are highly reliable without the risk of abnormal heat generation from the solid electrolyte. Therefore, there are high expectations for them, especially in product fields that require high-capacity secondary batteries.

[0007] Furthermore, because all-solid-state batteries are not only highly safe but also highly reliable, environmentally resistant, and have a long lifespan, they are expected to be maintenance-free batteries that can continue to contribute to social development while also contributing to safety and security. Providing all-solid-state batteries to society will contribute to the achievement of Goal 3 (Ensure healthy lives and promote well-being for all at all ages), Goal 7 (Ensure access to affordable, reliable, sustainable, and modern energy for all), Goal 11 (Make cities inclusive, safe, resilient, and sustainable cities and human settlements), and Goal 12 (Ensure sustainable consumption and production patterns) out of the 17 Sustainable Development Goals (SDGs) established by the United Nations.

[0008] Various studies have also been conducted on all-solid-state batteries. For example, Patent Documents 1 to 4 propose filling pores in a porous substrate such as a nonwoven fabric with a solid electrolyte to produce a solid electrolyte sheet that has both lithium ion conductivity and strength, and using this solid electrolyte sheet to construct an all-solid-state secondary battery.

[0009] Of these, Patent Document 4 shows that by making the thickness of the porous substrate 70% or more of the thickness of the entire solid electrolyte sheet, the mechanical strength of the solid electrolyte sheet can be improved, and damage to the solid electrolyte and separation of the solid electrolyte from the porous substrate can be prevented even when the area of ​​the solid electrolyte sheet is increased. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-153460 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-139482 [Patent Document 3] International Publication No. 2019 / 208347 [Patent Document 4] International Publication No. 2020 / 054081 Summary of the Invention [Problem to be solved by the invention]

[0011] The technology described in Patent Document 4 makes it possible to increase the size of an all-solid-state battery, thereby increasing its capacity. However, when an all-solid-state battery is increased in capacity, the problem of short circuiting due to lithium dendrites that precipitate during charging becomes more likely to occur. Therefore, it is necessary to improve the reliability of all-solid-state batteries so that the occurrence of such problems can be better suppressed even when the capacity is increased.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an all-solid-state battery with excellent reliability and a solid electrolyte sheet that can be used to form the all-solid-state battery. [Means for solving the problem]

[0013] The solid electrolyte sheet of the present invention comprises a porous substrate and a solid electrolyte held by the porous substrate, and is characterized in that it has a solid electrolyte layer A containing a solid electrolyte a that reacts with metallic lithium to oxidize lithium, and a solid electrolyte layer B containing a solid electrolyte b that is less reactive with metallic lithium than the solid electrolyte a, and the solid electrolyte layer B is disposed on at least one surface of the solid electrolyte sheet.

[0014] The all-solid-state battery of the present invention includes a positive electrode, a negative electrode, and a solid electrolyte layer, and is characterized in that the solid electrolyte layer includes the solid electrolyte sheet of the present invention, and the solid electrolyte layer B of the solid electrolyte sheet faces the negative electrode. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an all-solid-state battery with excellent reliability and a solid electrolyte sheet that can be used to form the all-solid-state battery. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a solid electrolyte sheet of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically illustrating another example of the solid electrolyte sheet of the present invention. [Figure 3] FIG. 1 is a cross-sectional view schematically illustrating an example of an all-solid-state battery of the present invention. [Figure 4] FIG. 10 is a graph showing voltage changes during charge-discharge cycles of a cell using the solid electrolyte sheet of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Solid electrolyte sheet> The solid electrolyte sheet of the present invention comprises a porous substrate and a solid electrolyte held by the porous substrate, and has a solid electrolyte layer A containing a solid electrolyte a that reacts with metallic lithium to oxidize lithium, and a solid electrolyte layer B containing a solid electrolyte b that is less reactive with metallic lithium than the solid electrolyte a, and the solid electrolyte layer B is disposed on at least one surface of the solid electrolyte sheet.

[0018] In an all-solid-state battery having the solid electrolyte sheet of the present invention as a solid electrolyte layer, even if lithium dendrites precipitate on the surface of the negative electrode during charging, the growth of lithium dendrites within the solid electrolyte layer (solid electrolyte sheet) is inhibited by the solid electrolyte a contained in the solid electrolyte layer A, which reacts with metallic lithium to oxidize lithium, and the lithium dendrites are prevented from reaching the positive electrode. Therefore, by using the solid electrolyte sheet of the present invention, an all-solid-state battery can be formed that can suppress the occurrence of short circuits due to the precipitation of lithium dendrites.

[0019] Furthermore, the solid electrolyte sheet of the present invention has, in addition to the solid electrolyte layer A, a solid electrolyte layer B containing a solid electrolyte b that is less reactive with metallic lithium than the solid electrolyte a. This solid electrolyte layer B can contain the solid electrolyte b, for example, a sulfide-based solid electrolyte having an argyrodite structure. Therefore, in the solid electrolyte sheet of the present invention, the solid electrolyte layer A can efficiently suppress the growth of lithium ion dendrites, while the solid electrolyte layer B can ensure good lithium ion conductivity. Therefore, an all-solid-state battery including the solid electrolyte sheet of the present invention (the all-solid-state battery of the present invention) can suppress the occurrence of short circuits due to lithium dendrites while ensuring good battery characteristics, thereby improving its reliability.

[0020] 1 and 2 are cross-sectional views schematically illustrating an example of a solid electrolyte sheet. The solid electrolyte sheet 10 in FIG. 1 is a two-layered sheet having a solid electrolyte layer A20 containing a solid electrolyte a that reacts with metallic lithium to oxidize the lithium, and a solid electrolyte layer B30 containing a solid electrolyte b that is less reactive with metallic lithium than the solid electrolyte a. The solid electrolyte sheet 10 has a porous substrate, which is shared by the solid electrolyte layers A20 and B30. At least a portion of the solid electrolyte layer A20 is formed by retaining the solid electrolyte a within the pores of the porous substrate. At least a portion of the solid electrolyte layer B30 is formed by retaining the solid electrolyte b within the pores of the porous substrate.

[0021] The solid electrolyte sheet 11 in FIG. 2 is a three-layer sheet having solid electrolyte layers B30 and B30 above and below the solid electrolyte layer A20. The solid electrolyte sheet 11 also has a porous substrate, and the solid electrolyte layer A20 and the two solid electrolyte layers B30 and B30 share the porous substrate. The solid electrolyte layer A20 is formed entirely with a solid electrolyte a held within the pores of the porous substrate. The two solid electrolyte layers B30 are formed, at least in part, with a solid electrolyte b held within the pores of the porous substrate.

[0022] As shown in Figures 1 and 2, in the solid electrolyte sheet, a solid electrolyte layer B is disposed on at least one surface of the solid electrolyte sheet. When an all-solid-state battery is formed using a solid electrolyte sheet as a solid electrolyte layer, the battery reaction is inhibited when the solid electrolyte a comes into contact with the negative electrode. Therefore, when forming an all-solid-state battery, it is necessary to have the solid electrolyte layer B of the solid electrolyte sheet face the negative electrode, and therefore the solid electrolyte layer B is disposed on at least one surface of the solid electrolyte sheet.

[0023] Although the edge of the porous substrate may be exposed on the surface of the solid electrolyte sheet together with the solid electrolyte, it is preferable that the surface and its vicinity of the solid electrolyte sheet are free of the porous substrate and comprise only the solid electrolyte (and a binder, etc., described below). That is, the porous substrate may be present throughout the entire thickness of the solid electrolyte sheet, but to prevent the porous substrate from inhibiting ion conduction at the interfaces between the positive and negative electrodes and the solid electrolyte sheet, it is preferable that the porous substrate be present only in a portion (inner side of the solid electrolyte sheet) of the solid electrolyte layer A and solid electrolyte layer B disposed on the surface of the solid electrolyte sheet, and that the surface and its vicinity of the solid electrolyte sheet are formed only of the solid electrolyte (and a binder, etc.). In other words, it is preferable that the surface of the porous substrate in the solid electrolyte sheet is covered with the solid electrolyte (and a binder, etc.).

[0024] In the case of a two-layer solid electrolyte sheet as shown in Figure 1, one of the solid electrolyte layers A and B may have a porous substrate in part or all of it, and the other may have no porous substrate (formed only of a solid electrolyte (and a binder, etc.)). In the case of a three-layer solid electrolyte sheet as shown in Figure 2, one of the two solid electrolyte layers B may have a porous substrate in part or all of it, and the other may have no porous substrate (formed only of a solid electrolyte (and a binder, etc.)).

[0025] The solid electrolyte layer A of the solid electrolyte sheet contains a solid electrolyte a that reacts with metallic lithium to oxidize it, and the solid electrolyte may include at least one element selected from Ti, Ge, Sn, Al, and Si. Specific examples of such solid electrolytes include La. 0.05 Li 0.35 TiO3(LLTO), Li 1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP), Li 10 SnP2S 12 (LSPS), Li 1.4 Al 0.5 Ti 1.6 (PO4)3(LATP), Li 10 GeP2S 12 (LGPS), Li2O-Al2O3-SiO2-P2O5-TiO2, etc.

[0026] The solid electrolyte layer A may contain, together with the solid electrolyte a, a solid electrolyte b that is less reactive with metallic lithium than the solid electrolyte a (for example, a mixture of the solid electrolyte a and the solid electrolyte b may be contained in the solid electrolyte layer A). Examples of the solid electrolyte b include various solid electrolytes exemplified below. Among these solid electrolytes, it is preferable to use a sulfide-based solid electrolyte, and it is more preferable to use a solid electrolyte having an argyrodite structure, because this can further improve the lithium ion conductivity of the solid electrolyte layer A and further enhance the characteristics of an all-solid-state battery formed using the solid electrolyte sheet.

[0027] When the solid electrolyte layer A contains the solid electrolyte b together with the solid electrolyte a, from the viewpoint of satisfactorily ensuring the effect of inhibiting the growth of lithium dendrites, the content of the solid electrolyte a in the entire solid electrolyte contained in the solid electrolyte layer A is preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 40% by mass or more.

[0028] In the solid electrolyte layer A, since only the solid electrolyte a may be used as the solid electrolyte, the upper limit of the content of the solid electrolyte a in all the solid electrolytes contained in the solid electrolyte layer A is 100% by mass. However, from the viewpoint of ensuring a good effect (for example, the effect of improving lithium ion conductivity) by using the solid electrolyte b together with the solid electrolyte a in the solid electrolyte layer A, the content of the solid electrolyte a in all the solid electrolytes contained in the solid electrolyte layer A is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0029] The solid electrolyte b to be contained in the solid electrolyte layer B has a lower reactivity with metallic lithium than the solid electrolyte a, and preferably has little or no action of reacting with metallic lithium to oxidize lithium, and is not particularly limited as long as it has lithium ion conductivity. For example, sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, etc. can be used. The solid electrolyte of the solid electrolyte layer B may be composed only of the solid electrolyte b, but may contain the solid electrolyte a as long as it does not inhibit the battery reaction.

[0030] Examples of the sulfide-based solid electrolyte include particles such as Li2S-P2S5, Li2S-SiS2, Li2S-P2S5-GeS2, and Li2S-B2S3-based glasses. In recent years, those having an argyrodite-type structure (such as Li6PS5Cl, etc., Li 7-f+g PS 6-f Cl f+g (where 0.05 ≤ f ≤ 0.9, -3.0f + 1.8 ≤ g ≤ -3.0f + 5.7), those represented by Li 7-h PS 6-h Cl i Br j (where h = i + j, 0 < h ≤ 1.8, 0.1 ≤ i / j ≤ 10.0), etc.] can also be used.

[0031] Examples of the hydride-based solid electrolyte include LiBH4, a solid solution of LiBH4 and the following alkali metal compound (e.g., those having a molar ratio of LiBH4 to the alkali metal compound of 1:1 to 20:1), and the like. Examples of the alkali metal compound in the solid solution include at least one selected from the group consisting of lithium halides (such as LiI, LiBr, LiF, LiCl), rubidium halides (such as RbI, RbBr, RbF, RbCl), cesium halides (such as CsI, CsBr, CsF, CsCl), lithium amide, rubidium amide, and cesium amide.

[0032] Examples of the halide-based solid electrolyte include, for example, monoclinic LiAlCl4, defective spinel-type or layered-structured LiInBr4, monoclinic Li 6-3m Y m X6 (where 0 < m < 2 and X = Cl or Br), and the like. In addition, for example, known ones described in International Publication No. 2020 / 070958 and International Publication No. 2020 / 070955 can also be used.

[0033] For the solid electrolyte b of the solid electrolyte layer B, only one of the above-exemplified ones may be used, or two or more thereof may be used in combination. Among these solid electrolytes, sulfide-based solid electrolytes are preferred because of their high lithium ion conductivity. Sulfide-based solid electrolytes containing Li and P are more preferred. Particularly, sulfide-based solid electrolytes having a high lithium ion conductivity and a highly chemically stable argyrodite-type structure are even more preferred.

[0034] The solid electrolyte contained in solid electrolyte layer A and the solid electrolyte contained in solid electrolyte layer B are preferably particles, and their size is preferably 5 μm or less, more preferably 2 μm or less, from the viewpoint of improving the filling of the pores of the porous substrate and ensuring good lithium ion conductivity and lithium dendrite growth suppression. However, if the size of the solid electrolyte particles is too small, there is a risk of reduced handleability. Furthermore, as described below, the solid electrolyte particles are preferably bound with a binder to ensure good retention in the pores of the porous substrate and good adhesion to the surface of the porous substrate. In this case, however, a larger amount of binder is required, which may increase the resistance value. Therefore, the average particle size of the solid electrolyte particles is preferably 0.3 μm or more, more preferably 0.5 μm or more.

[0035] The average particle diameter of the solid electrolyte particles and other particles (positive electrode active material, negative electrode active material, etc.) referred to in this specification is the 50% diameter value (D ) in the volume-based integrated fraction when calculating the integrated volume from small particle sizes using a particle size distribution analyzer (e.g., a Microtrac particle size distribution analyzer "HRA9320" manufactured by Nikkiso Co., Ltd.). 50 ) means

[0036] The porous substrate of the solid electrolyte sheet may be made of a fibrous material, and for example, a woven fabric, a nonwoven fabric, a mesh, or the like is preferred, with the nonwoven fabric being particularly preferred.

[0037] The fiber diameter of the fibrous material constituting the porous substrate is preferably 5 μm or less, and is preferably 0.5 μm or more.

[0038] The material of the fibrous material is not particularly limited as long as it does not react with metallic lithium and has insulating properties. For example, resins such as polyolefins such as polypropylene and polyethylene; polystyrene; aramid; polyamideimide; polyimide; nylon; polyesters such as polyethylene terephthalate (PET); polyarylate; cellulose or modified cellulose; etc. may be used. Inorganic materials such as glass, alumina, silica, and zirconia may also be used. A preferred material is polyarylate. The fibrous material may be composed of one or more of the materials exemplified above. The porous substrate may be composed of only fibrous materials of the same material, or may be composed of a combination of two or more fibrous materials of different materials.

[0039] The basis weight of the porous substrate is 10 g / m so as to be able to hold a sufficient amount of solid electrolyte to ensure good lithium ion conductivity and to ensure good lithium dendrite growth suppression function. 2 Preferably, it is 8 g / m or less. 2 It is more preferable that the thickness is 3 g / m or less, and from the viewpoint of ensuring sufficient strength, 2 It is preferable that the content is 4 g / m or more. 2 More preferably, it is equal to or greater than this.

[0040] In the solid electrolyte sheet, it is preferable to bind the solid electrolyte using a binder in order to favorably retain the solid electrolyte in the pores of the porous substrate and to improve the adhesion of the solid electrolyte covering the surface of the porous substrate to the porous substrate, thereby enhancing the shape retention of the solid electrolyte sheet.

[0041] The binder for the solid electrolyte sheet is preferably one that does not react with the solid electrolyte, and at least one resin selected from the group consisting of butyl rubber, chloroprene rubber, acrylic resin, and fluororesin is preferably used.

[0042] The thickness of the solid electrolyte sheet is preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of optimizing the distance between the positive electrode and the negative electrode of a battery using the solid electrolyte sheet and suppressing the occurrence of a short circuit or an increase in resistance, and is preferably 50 μm or less, more preferably 30 μm or less.

[0043] In the solid electrolyte sheet, the thickness of the porous substrate is preferably 85% or less, and more preferably 80% or less, of the thickness of the solid electrolyte sheet, from the viewpoint of ensuring smooth movement of lithium ions on the positive electrode side and smooth movement of lithium ions on the negative electrode side, and also of better ensuring the effect of suppressing precipitation of lithium dendrites that cause charging abnormalities, with the solid electrolyte covering the surface of the porous substrate having the above-mentioned thickness.

[0044] The porous substrate serves as a component for enhancing the shape retention of the solid electrolyte sheet. However, if the thickness ratio of the porous substrate to the solid electrolyte sheet is too small, the shape retention of the solid electrolyte sheet may be reduced. Furthermore, if the thickness ratio of the porous substrate to the solid electrolyte sheet is relatively large, the effect of smoothing the movement of lithium ions on the positive electrode side and the negative electrode side, as well as suppressing metal deposition that causes charging abnormalities, becomes more pronounced. For these reasons, the thickness of the porous substrate is preferably 30% or more, more preferably 50% or more, of the thickness of the solid electrolyte sheet.

[0045] Specifically, the thickness of the porous substrate is, for example, preferably 3 μm or more, more preferably 8 μm or more, and preferably 45 μm or less, more preferably 25 μm or less.

[0046] Furthermore, the thickness of the solid electrolyte layer A (when the solid electrolyte sheet has a plurality of solid electrolyte layers A, the total thickness of the layers) is preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of better ensuring the effect of suppressing the growth of lithium dendrites. The upper limit of the thickness of the solid electrolyte layer A is set within a range that satisfies the above-mentioned preferred thickness of the solid electrolyte sheet and the below-described preferred thickness of the solid electrolyte layer B.

[0047] Furthermore, the thickness of the solid electrolyte layer B (when the solid electrolyte sheet has a plurality of solid electrolyte layers B, the total thickness of the layers) is preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of ensuring good lithium ion conductivity. The upper limit of the thickness of the solid electrolyte layer B is set within a range that satisfies the above-mentioned preferred thickness of the solid electrolyte sheet and the preferred thickness of the solid electrolyte layer A.

[0048] The proportion of the porous substrate in the solid electrolyte sheet (proportion of the actual volume excluding pores) is preferably 30% by volume or less, and more preferably 25% by volume or less, from the viewpoint of ensuring good lithium ion conductivity. However, if the proportion of the porous substrate in the solid electrolyte sheet is too small, the effect of improving the shape retention of the solid electrolyte sheet may be reduced. Therefore, from the viewpoint of further increasing the strength of the solid electrolyte sheet, the proportion of the porous substrate in the solid electrolyte sheet is preferably 5% by volume or more, and more preferably 10% by volume or more.

[0049] Furthermore, from the viewpoint of further enhancing the shape retention of the solid electrolyte sheet, the content of the binder in the solid electrolyte sheet is preferably 0.5 mass % or more, and more preferably 1 mass % or more, of the total amount of the solid electrolyte and the binder. Furthermore, from the viewpoint of restricting the amount of the binder to some extent and suppressing a decrease in lithium ion conductivity, the content of the binder is preferably 5 mass % or less, and more preferably 3 mass % or less.

[0050] Although there are no particular limitations on the method for producing the solid electrolyte sheet, it is preferable to produce the solid electrolyte sheet by a method including a step of dispersing a solid electrolyte and an optional binder in a solvent to prepare a slurry for forming a solid electrolyte layer A and a slurry for forming a solid electrolyte layer B, and then successively wet-filling these slurries into the voids of the porous substrate (filling step). Furthermore, when the surface portion of the solid electrolyte sheet is formed of a solid electrolyte layer A or a solid electrolyte layer B that does not contain a porous substrate, the filling step may involve filling the voids of the porous substrate with the slurries while forming coating films of these slurries on the surface of the porous substrate. This method improves the strength of the solid electrolyte sheet and facilitates the production of a large-area solid electrolyte sheet.

[0051] As a method for filling the voids of the porous substrate with a slurry containing a solid electrolyte, or for forming a coating film of the slurry on the surface of the porous substrate, coating methods such as screen printing, doctor blade method, and dipping method can be used.

[0052] The slurry is prepared by adding a solid electrolyte and, if necessary, a binder to a solvent and mixing them. It is preferable to select a solvent for the slurry that is less likely to deteriorate the solid electrolyte. In particular, sulfide-based and hydride-based solid electrolytes undergo chemical reactions even with trace amounts of water, so nonpolar aprotic solvents, such as hydrocarbon solvents like hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene, are preferred. It is particularly preferable to use ultra-dehydrated solvents with a water content of 0.001% by mass (10 ppm) or less. Fluorine-based solvents such as "Vertrel®" from DuPont-Mitsui Fluorochemicals, "Zeorolla®" from Zeon Corporation, and "Novec®" from Sumitomo 3M Company, as well as nonaqueous organic solvents such as dichloromethane and diethyl ether can also be used.

[0053] After filling the voids in the porous substrate with the slurry or forming a coating of the slurry on the surface of the porous substrate as described above, the solvent in the slurry is removed by drying, and pressure molding is performed as necessary to obtain a solid electrolyte sheet.

[0054] As mentioned above, the manufacturing method of the solid electrolyte sheet is not limited to the wet method. For example, when filling the pores of the porous substrate with the solid electrolyte (and a binder used as needed), the solid electrolyte or a mixture of the solid electrolyte and the binder may be dry-filled, followed by pressure molding. In addition, when covering the surface of the porous substrate with the solid electrolyte, a sheet obtained by molding a mixture of the solid electrolyte and the binder may be attached to the surface of a sheet of the porous substrate in which the pores are filled with the solid electrolyte.

[0055] <All-solid-state battery> The all-solid-state battery of the present invention includes a positive electrode, a negative electrode, and a solid electrolyte layer, and the solid electrolyte layer has the solid electrolyte sheet of the present invention, with the solid electrolyte layer B of the solid electrolyte sheet facing the negative electrode. The all-solid-state battery of the present invention includes primary batteries and secondary batteries.

[0056] A cross-sectional view schematically illustrating an example of the all-solid-state battery of the present invention is shown in Fig. 3. The battery 100 shown in Fig. 3 has a positive electrode 200, a negative electrode 300, and a solid electrolyte sheet 400 interposed between the positive electrode 200 and the negative electrode 300, enclosed in an exterior body formed by an exterior can 500, a sealing can 600, and a resin gasket 700 interposed between them.

[0057] The sealing can 600 is fitted into the opening of the outer can 500 via a gasket 700, and the open end of the outer can 500 is tightened inward, causing the gasket 700 to abut against the sealing can 600, thereby sealing the opening of the outer can 500 and creating an airtight structure inside the battery.

[0058] The outer can and the sealing can can be made of stainless steel, etc. The gasket material can be polypropylene, nylon, etc., and if heat resistance is required for the battery's application, fluororesin such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene ether ( PPE Heat-resistant resins with melting points exceeding 240°C, such as polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), can also be used. If the battery is used in an application that requires heat resistance, a glass hermetic seal can be used to seal the battery.

[0059] Next, components of the all-solid-state battery other than the solid electrolyte sheet will be described.

[0060] (positive electrode) Examples of the positive electrode of the all-solid-state battery include a structure in which a layer (positive electrode mixture layer) made of a compact of a positive electrode mixture containing a positive electrode active material and a solid electrolyte is formed on a current collector, a structure in which a compact of a positive electrode mixture (such as a pellet) is formed only, and a structure in which a positive electrode mixture containing a positive electrode active material and a solid electrolyte is filled into the pores of a conductive porous substrate.

[0061] When the all-solid-state battery is a primary battery, the positive electrode active material can be the same as the positive electrode active material used in conventionally known non-aqueous electrolyte primary batteries, etc. Specifically, for example, manganese dioxide, lithium-containing manganese oxides (e.g., LiMn3O6, or composite oxides having the same crystal structure as manganese dioxide (e.g., β-type, γ-type, or a mixed structure of β-type and γ-type) and containing 3.5 mass % or less, preferably 2 mass % or less, more preferably 1.5 mass % or less, and particularly preferably 1 mass % or less), Li a Ti 5 / 3 Examples include lithium-containing composite oxides such as O4 (4 / 3≦a<7 / 3); vanadium oxide; niobium oxide; titanium oxide; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as Ag2S; and nickel oxides such as NiO2.

[0062] In addition, when the all-solid-state battery is the positive electrode of a secondary battery, the same positive electrode active materials as those used in conventionally known non-aqueous electrolyte secondary batteries and the like can be used for the positive electrode active material. Specifically, LiM r Mn 2-r O4 (where M is at least one element selected from the group consisting of Li, Na, K, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Zr, Fe, Co, Ni, Cu, Zn, Al, Sn, Sb, In, Nb, Ta, Mo, W, Y, Ru, and Rh, and 0 ≦ r ≦ 1), spinel-type lithium manganese composite oxide represented by Li r Mn (1-s-r) Ni s M t O (2-u) F v (where M is at least one element selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, and W, 0.8 ≦ r ≦ 1.2, 0 < s < 0.5, 0 ≦ t ≦ 0.5, u + v < 1, -0.1 ≦ u ≦ 0.2, 0 ≦ v ≦ 0.1), layered compound represented by LiCo 1-r M r O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, V, Cr, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0 ≦ r ≦ 0.5), lithium cobalt composite oxide represented by LiNi 1-r M r O2 (where M is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and Ba, and 0 ≦ r ≦ 0.5), lithium nickel composite oxide represented by Li 1+s M 1-r N r PO4F s(wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦r≦0.5, 0≦s≦1), an olivine-type composite oxide represented by Li2M 1-r N r Examples of the positive electrode active material include one or more types of particles of various positive electrode active materials used in conventionally known non-aqueous electrolyte secondary batteries, such as a pyrophosphate compound represented by P2O7 (wherein M is at least one element selected from the group consisting of Fe, Mn, and Co, and N is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, V, and Ba, and 0≦r≦0.5).

[0063] When the all-solid-state battery is a secondary battery, the average particle size of the positive electrode active material is preferably 1 μm or more, more preferably 2 μm or more, and preferably 10 μm or less, more preferably 8 μm or less. The positive electrode active material may be primary particles or secondary particles formed by aggregation of primary particles. When a positive electrode active material having an average particle size within the above range is used, a large interface with the solid electrolyte contained in the positive electrode can be secured, thereby further improving the output characteristics of the battery.

[0064] When the all-solid-state battery is a secondary battery, the positive electrode active material preferably has a reaction suppression layer on its surface to suppress reaction with the solid electrolyte contained in the positive electrode.

[0065] If the positive electrode active material and the solid electrolyte come into direct contact in the positive electrode, the solid electrolyte may oxidize to form a resistance layer, which may reduce ionic conductivity in the positive electrode. By providing a reaction suppression layer on the surface of the positive electrode active material that suppresses reaction with the solid electrolyte and preventing direct contact between the positive electrode active material and the solid electrolyte, it is possible to suppress the reduction in ionic conductivity in the positive electrode due to oxidation of the solid electrolyte.

[0066] The reaction suppression layer may be made of any material that has ion conductivity and can suppress the reaction between particles of the electrode active material (cathode active material) and the solid electrolyte. Examples of materials that can form the reaction suppression layer include oxides containing Li and at least one element selected from the group consisting of Nb, P, B, Si, Ge, Ti, Zr, Ta, and W. More specifically, Nb-containing oxides such as LiNbO3, Li3PO4, Li3BO3, Li2SO4, Li4SiO4, Li4GeO4, LiTiO3, LiZrO3, and Li2WO4 are examples. The reaction suppression layer may contain only one of these oxides, or two or more of them, or may even form a composite compound of two or more of these oxides. Among these oxides, Nb-containing oxides are preferred, and LiNbO3 is more preferred.

[0067] The reaction suppression layer is preferably present on the surface in an amount of 0.1 to 1.0 part by mass per 100 parts by mass of the positive electrode active material, which allows for effective suppression of the reaction between the positive electrode active material and the solid electrolyte.

[0068] Examples of methods for forming a reaction suppression layer on the surface of a positive electrode active material include the sol-gel method, mechanofusion method, CVD method, PVD method, and ALD method.

[0069] The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 85 mass % from the viewpoint of increasing the energy density of the all-solid-state battery.

[0070] The positive electrode mixture may contain a conductive additive. Specific examples include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, carbon nanofibers, and carbon nanotubes. For example, when Ag2S is used as the active material, conductive Ag is generated during the discharge reaction, so a conductive additive need not be included. When a conductive additive is included in the positive electrode mixture, the content of the conductive additive is preferably 1.0 part by mass or more, preferably 7.0 parts by mass or less, and more preferably 6.5 parts by mass or less, based on 100 parts by mass of the positive electrode active material.

[0071] The positive electrode mixture may contain a binder. Specific examples include fluororesins such as polyvinylidene fluoride (PVDF). Note that, for example, when a sulfide-based solid electrolyte is contained in the positive electrode mixture (described later), the positive electrode mixture may not contain a binder if good moldability can be ensured in forming the positive electrode without using a binder.

[0072] When a binder is required in the positive electrode mixture, the content thereof is preferably 15% by mass or less, and preferably 0.5% by mass or more. On the other hand, when moldability can be obtained without the binder in the positive electrode mixture, the content thereof is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

[0073] The positive electrode mixture may contain a solid electrolyte.

[0074] The solid electrolyte contained in the positive electrode mixture is not particularly limited as long as it has lithium ion conductivity, and for example, the same as the solid electrolyte b or solid electrolyte a in the solid electrolyte sheet can be used. Among these, sulfide-based solid electrolytes are preferred because they have high lithium ion conductivity and also have the function of improving the formability of the positive electrode mixture, and sulfide-based solid electrolytes having an argyrodite structure are more preferred.

[0075] The average particle size of the solid electrolyte is preferably 0.1 μm or more, and more preferably 0.2 μm or more, from the viewpoint of reducing grain boundary resistance, while it is preferably 10 μm or less, and more preferably 5 μm or less, from the viewpoint of forming a sufficient contact interface between the active material and the solid electrolyte.

[0076] From the viewpoint of further increasing ionic conductivity in the positive electrode and further improving the output characteristics of the all-solid-state battery, the content of the solid electrolyte in the positive electrode mixture is preferably 10 parts by mass or more, and more preferably 15 parts by mass or more, relative to 100 parts by mass of the positive electrode active material. However, if the amount of solid electrolyte in the positive electrode mixture is too large, the amounts of other components may be reduced, and the effects of these components may be reduced. Therefore, the content of solid electrolyte in the positive electrode mixture is preferably 65 parts by mass or less, and more preferably 60 parts by mass or less, relative to 100 parts by mass of the positive electrode active material.

[0077] When a current collector is used for the positive electrode, the current collector can be made of a metal foil such as aluminum or stainless steel; a sheet-like conductive porous substrate such as punched metal, mesh, expanded metal, or foamed metal; or a carbon sheet. The sheet-like conductive porous substrate is preferably a foamed metal porous body. A specific example of a foamed metal porous body is "Celmet (registered trademark)" from Sumitomo Electric Industries, Ltd.

[0078] The positive electrode can be produced by a method in which a positive electrode mixture-containing composition (paste, slurry, etc.) obtained by dispersing a positive electrode active material, a solid electrolyte, and optionally added conductive additives, binders, etc. in a solvent is applied to a current collector, dried, and then pressure-molded, as required, by calendaring or the like, to form a molded body of the positive electrode mixture (positive electrode mixture layer) on the surface of the current collector.

[0079] As the solvent for the positive electrode mixture-containing composition, water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) can be used. However, when a solid electrolyte that is highly reactive to water is used, it is desirable to select a solvent that is less likely to deteriorate the solid electrolyte. It is preferable to use the same solvents as those exemplified above as the solvent for the slurry for forming the solid electrolyte sheet.

[0080] In addition to the above-mentioned method, the compact of the positive electrode mixture may be formed by compressing a positive electrode mixture prepared by mixing a positive electrode active material and a solid electrolyte with a conductive additive, a binder, etc., which are added as needed, by pressure molding, etc. As described above, the compact of the positive electrode mixture obtained by such a method can be used as a positive electrode as it is, or it can also be used as a positive electrode after being bonded to a current collector by pressure bonding, etc.

[0081] The thickness of the positive electrode mixture compact (positive electrode mixture layer) formed using the solvent-containing positive electrode mixture-containing composition (thickness per surface of the current collector when a current collector is used) is preferably 10 to 1000 μm. The thickness of the positive electrode mixture compact obtained by pressure molding is preferably 0.15 to 4 mm.

[0082] The thickness of the positive electrode current collector is preferably 0.01 to 0.1 mm.

[0083] Furthermore, when a conductive porous substrate is used for the positive electrode current collector, the positive electrode can be produced, for example, by filling the pores of the conductive porous substrate with the positive electrode mixture-containing composition, drying the composition, and then, if necessary, performing pressure molding such as calendaring.

[0084] Furthermore, instead of the above-described positive electrode mixture-containing composition, a positive electrode mixture containing a positive electrode active material, a solid electrolyte, and further a conductive additive and a binder, etc., but not containing a solvent, may be dry-filled into the pores of a conductive porous substrate, and the resulting mixture may be subjected to pressure molding such as calendaring as necessary, to produce a positive electrode.

[0085] In the case of a positive electrode obtained by filling the pores of a conductive porous substrate with a positive electrode mixture-containing composition or a positive electrode mixture, the thickness is preferably 30 to 4000 μm.

[0086] (Negative electrode) The negative electrode of the all-solid-state battery has, for example, a molded body of a negative electrode mixture containing a negative electrode active material, a lithium sheet, or a lithium alloy sheet. Alternatively, a conductive porous substrate having pores filled with a negative electrode mixture containing a negative electrode active material can also be used as the negative electrode.

[0087] When the negative electrode is a molded body of a negative electrode mixture containing a negative electrode active material, examples of the negative electrode include a structure in which a layer (negative electrode mixture layer) made of a molded body of the negative electrode mixture is formed on a current collector, and a structure in which only a molded body (pellet, etc.) made of a molded negative electrode mixture is formed.

[0088] Examples of the negative electrode active material include carbon materials such as graphite, lithium titanium oxides (lithium titanate, etc.), simple substances containing elements such as Si and Sn, compounds (oxides, etc.), and alloys thereof. In addition, lithium metal and lithium alloys (lithium-aluminum alloys, lithium-indium alloys, etc.) can also be used as the negative electrode active material.

[0089] The content of the negative electrode active material in the negative electrode mixture is preferably 40 to 80 mass % from the viewpoint of increasing the energy density of the battery.

[0090] The negative electrode mixture may contain a conductive additive. Specific examples include the same conductive additives as those exemplified above as those that may be contained in the positive electrode mixture. The content of the conductive additive in the negative electrode mixture is preferably 10 to 30 parts by mass relative to 100 parts by mass of the negative electrode active material.

[0091] The negative electrode mixture may contain a binder. Specific examples include the same binders as those exemplified above as binders that may be contained in the positive electrode mixture. Note that, for example, when a sulfide-based solid electrolyte is contained in the negative electrode mixture (described later), if good moldability can be ensured in forming the negative electrode mixture layer without using a binder, the negative electrode mixture may not contain a binder.

[0092] When a binder is required in the negative electrode mixture, the content thereof is preferably 15% by mass or less, and preferably 0.5% by mass or more. On the other hand, when moldability can be obtained without the binder in the negative electrode mixture, the content thereof is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0% by mass (i.e., no binder is contained).

[0093] The negative electrode mixture can contain a solid electrolyte. Specific examples thereof include the same as the solid electrolyte b in the solid electrolyte sheet. Among the solid electrolytes listed above, sulfide-based solid electrolytes are preferred because they have high lithium ion conductivity and also have the function of improving the formability of the negative electrode mixture. Sulfide-based solid electrolytes having an argyrodite structure are more preferred.

[0094] For the same reasons as in the case of the positive electrode mixture, the average particle size of the solid electrolyte in the negative electrode mixture is preferably 0.1 μm or more, more preferably 0.2 μm or more, and is preferably 10 μm or less, more preferably 5 μm or less.

[0095] From the viewpoint of further increasing ionic conductivity in the negative electrode and further improving the output characteristics of the all-solid-state battery, the content of the solid electrolyte in the negative electrode mixture is preferably 30 parts by mass or more, and more preferably 35 parts by mass or more, relative to 100 parts by mass of the negative electrode active material. However, if the amount of solid electrolyte in the negative electrode mixture is too large, the amounts of other components may be reduced, and the effects of these components may be reduced. Therefore, the content of solid electrolyte in the negative electrode mixture is preferably 130 parts by mass or less, and more preferably 110 parts by mass or less, relative to 100 parts by mass of the negative electrode active material.

[0096] When a current collector is used for a negative electrode having a molded body of a negative electrode mixture, the current collector can be a sheet-like conductive porous substrate such as copper or nickel foil, punched metal, mesh, expanded metal, or foamed metal; a carbon sheet; or the like. As the sheet-like conductive porous substrate, a foamed metal porous body is preferably used. A specific example of a foamed metal porous body is "Celmet (registered trademark)" from Sumitomo Electric Industries, Ltd.

[0097] The negative electrode can be produced by a method in which a negative electrode mixture-containing composition (paste, slurry, etc.) in which a negative electrode active material, and optionally a conductive additive, a solid electrolyte, a binder, etc. are dispersed in a solvent is applied to a current collector, dried, and then pressure-molded, as required, by calendaring or the like, to form a molded body of the negative electrode mixture (negative electrode mixture layer) on the surface of the current collector.

[0098] As the solvent for the negative electrode mixture-containing composition, an organic solvent such as water or NMP can be used. However, when the negative electrode mixture-containing composition also contains a solid electrolyte, it is desirable to select a solvent that is unlikely to deteriorate the solid electrolyte. It is preferable to use the same solvents as those exemplified above as the solvent for the slurry for forming the solid electrolyte sheet.

[0099] In addition to the above-mentioned method, the molded body of the negative electrode mixture may be formed by compressing, by pressure molding, an negative electrode mixture prepared by mixing the negative electrode active material and, if necessary, a conductive additive, a solid electrolyte, a binder, etc. As described above, the molded body of the negative electrode mixture obtained by such a method can be used as the negative electrode as it is, or it can be used as the negative electrode after being bonded to a current collector by, for example, pressure bonding.

[0100] The thickness of the negative electrode mixture compact (negative electrode mixture layer) formed using the solvent-containing negative electrode mixture-containing composition (thickness per surface of the current collector when a current collector is used) is preferably 10 to 1000 μm. The thickness of the negative electrode mixture compact obtained by pressure molding is preferably 0.15 to 4 mm.

[0101] The thickness of the negative electrode current collector is preferably 0.01 to 0.1 mm.

[0102] Furthermore, when a conductive porous substrate such as a punched metal is used as the negative electrode current collector, the negative electrode can be produced, for example, by filling the pores of the conductive porous substrate with the above-mentioned negative electrode mixture-containing composition, drying it, and then, if necessary, performing pressure molding such as calendaring. A negative electrode produced by such a method can ensure high strength, and therefore can hold a solid electrolyte sheet with a larger area.

[0103] Furthermore, instead of the above-described negative electrode mixture-containing composition, a negative electrode mixture containing a negative electrode active material, a solid electrolyte, a binder, a conductive additive, and the like, but not containing a solvent, may be dry-filled into the pores of a conductive porous substrate, and the resulting mixture may be subjected to pressure molding such as calendaring as necessary, to produce a negative electrode.

[0104] In the case of a negative electrode obtained by filling the pores of a conductive porous substrate with a composition containing a negative electrode mixture or a negative electrode mixture, the thickness is preferably 30 to 4000 μm.

[0105] In the case of a negative electrode having a lithium sheet or a lithium alloy sheet, one consisting of only this sheet or one consisting of this sheet stuck to a current collector is used.

[0106] Examples of alloying elements for lithium alloys include aluminum, lead, bismuth, indium, and gallium, with aluminum and indium being preferred. The proportion of alloying elements in the lithium alloy (the total proportion when multiple alloying elements are included) is preferably 50 atomic % or less (in this case, the remainder is lithium and inevitable impurities).

[0107] In addition, in the case of a negative electrode having a lithium alloy sheet, a laminate can be used in which a layer containing an alloying element for forming a lithium alloy is laminated on the surface of a lithium layer (a layer containing lithium) composed of a metal lithium foil or the like by pressure bonding, and this laminate is brought into contact with a solid electrolyte in a battery to form a lithium alloy on the surface of the lithium layer, thereby forming a negative electrode. In such a negative electrode, a laminate having a layer containing an alloying element on only one side of the lithium layer may be used, or a laminate having a layer containing an alloying element on both sides of the lithium layer may be used. The laminate can be formed, for example, by pressure bonding a metal lithium foil and a foil composed of an alloying element.

[0108] The current collector can also be used when a lithium alloy is formed in a battery to form a negative electrode. For example, a laminate having a lithium layer on one side of the negative electrode current collector and a layer containing an alloying element on the side of the lithium layer opposite the negative electrode current collector may be used, or a laminate having lithium layers on both sides of the negative electrode current collector and a layer containing an alloying element on the side of each lithium layer opposite the negative electrode current collector may be used. The negative electrode current collector and the lithium layer (metallic lithium foil) may be laminated by compression bonding or the like.

[0109] The layer containing the alloying elements in the laminate to be used as the negative electrode can be, for example, a foil composed of these alloying elements. The thickness of the layer containing the alloying elements is preferably 1 μm or more, more preferably 3 μm or more, and is preferably 20 μm or less, more preferably 12 μm or less.

[0110] The lithium layer of the laminate for use as a negative electrode may be, for example, a metallic lithium foil. The thickness of the lithium layer is preferably 0.1 to 1.5 mm. In addition, the thickness of the sheet for the negative electrode having a lithium or lithium alloy sheet is also preferably 0.1 to 1.5 mm.

[0111] When a negative electrode having a lithium sheet or a lithium alloy sheet has a current collector, the same current collectors as those exemplified above as those usable for a negative electrode having a molded body of a negative electrode mixture can be used for the current collector.

[0112] (electrode body) The positive electrode and the negative electrode can be used in a battery in the form of a laminated electrode body in which the positive electrode and the negative electrode are stacked with the solid electrolyte sheet of the present invention interposed therebetween, or in the form of a wound electrode body in which this laminated electrode body is wound. As described above, the negative electrode is opposed to the solid electrolyte layer B of the solid electrolyte sheet. On the other hand, the positive electrode can be opposed to the solid electrolyte layer A of the solid electrolyte sheet, as in the case of using a solid electrolyte sheet with a two-layer structure as shown in FIG. 1, or to the solid electrolyte layer B of the solid electrolyte sheet, as in the case of using a solid electrolyte sheet with a three-layer structure as shown in FIG. 2.

[0113] When forming the electrode assembly, it is preferable to pressure-mold the positive electrode, negative electrode, and solid electrolyte sheet in a stacked state, from the viewpoint of increasing the mechanical strength of the electrode assembly.

[0114] <Battery type> The form of the all-solid-state battery is not limited to one having an exterior body composed of an exterior can, a sealing can, and a gasket as shown in FIG. 3 , that is, one generally referred to as a coin-type battery or a button-type battery. For example, the all-solid-state battery may have an exterior body composed of a resin film or a metal-resin laminate film, an exterior body having a metallic, bottomed, tubular (cylindrical or rectangular) exterior can and a sealing structure that seals the opening, or a box-shaped exterior body made of ceramic. [Example]

[0115] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0116] Example 1 The insulating porous substrate was a nonwoven fabric (manufactured by Kurarayflex Co., Ltd., Veclus (trade name), thickness: 16 μm, basis weight: 4 g / m) made by the melt-blown method and composed of liquid crystal polyester fibers made of wholly aromatic polyester. 2 The tensile strength per basis weight of this substrate was 1.25 N / (g / m 2 Xylene (ultra-dehydrated grade) was used as the ultra-dehydrated solvent with a water content of 0.001% by mass (10 ppm) or less, and solid electrolyte a (Li 10 GeP2S 12 ), an acrylic resin binder, and a dispersant were mixed in a mass ratio of 100:3:1 with a solid content of 40%, and the mixture was stirred for 10 minutes in a Thinky mixer to prepare a uniform slurry (slurry for forming solid electrolyte layer A). The nonwoven fabric was then pulled out of the slurry and vacuum dried at 120°C for 1 hour to prepare a sheet A having a thickness of 18 μm that constitutes the solid electrolyte layer A.

[0117] In addition, a slurry for forming solid electrolyte layer B was prepared in the same manner as above, except that the solid electrolyte was a solid electrolyte b (LiPSCl) having an average particle diameter of 1.0 μm. The same nonwoven fabric as above was passed through the slurry, pulled up, and then vacuum dried at 120°C for 1 hour to produce sheet B having a thickness of 18 μm that constitutes solid electrolyte layer B.

[0118] The sheet A and the sheet B were laminated together and pressed to produce a solid electrolyte sheet in which the solid electrolyte layer A and the solid electrolyte layer B were laminated together.

[0119] Example 2 Among the solid electrolytes contained in the slurry for forming the solid electrolyte layer A, 50 mass % of the solid electrolyte a was replaced with the same solid electrolyte b as used in Example 1, and the solid electrolyte a (Li 10 GeP2S 12 A sheet A having a thickness of 18 μm and constituting a solid electrolyte layer A was produced in the same manner as in Example 1, except that the slurry was changed to one containing solid electrolyte b (LiPSCl) and solid electrolyte b (LiPSCl) in a mass ratio of 50:50. Further, a solid electrolyte sheet was produced using this sheet A in the same manner as in Example 1.

[0120] Example 3 Among the solid electrolytes contained in the slurry for forming the solid electrolyte layer A, 80 mass % of the solid electrolyte a was replaced with the same solid electrolyte b as used in Example 1, and the solid electrolyte a (Li 10 GeP2S 12 A sheet A having a thickness of 18 μm and constituting a solid electrolyte layer A was produced in the same manner as in Example 1, except that the slurry was changed to one containing Li6PS5Cl (Li6PS5Cl) and solid electrolyte b (Li6PS5Cl) in a mass ratio of 20:80. Further, a solid electrolyte sheet was produced using this sheet A in the same manner as in Example 1.

[0121] Example 4 Among the solid electrolytes contained in the slurry for forming the solid electrolyte layer A, 90 mass % of the solid electrolyte a was replaced with the same solid electrolyte b as used in Example 1, and the solid electrolyte a (Li 10 GeP2S 12A sheet A having a thickness of 18 μm and constituting a solid electrolyte layer A was produced in the same manner as in Example 1, except that the slurry was changed to one containing Li6PS5Cl (Li6PS5Cl) and solid electrolyte b (Li6PS5Cl) in a mass ratio of 10:90. Further, a solid electrolyte sheet was produced using this sheet A in the same manner as in Example 1.

[0122] Example 5 The solid electrolyte a contained in the slurry for forming the solid electrolyte layer A is Li 1.5 Al 0.5 Ge 1.5 A sheet A having a thickness of 18 μm and constituting a solid electrolyte layer A was produced in the same manner as in Example 3, except that (PO4)3 was used. Further, a solid electrolyte sheet was produced using this sheet A in the same manner as in Example 1.

[0123] Example 6 The solid electrolyte a contained in the slurry for forming the solid electrolyte layer A is Li 1.4 Al 0.5 Ti 1.6 A sheet A having a thickness of 18 μm and constituting a solid electrolyte layer A was produced in the same manner as in Example 3, except that (PO4)3 was used. Further, a solid electrolyte sheet was produced using this sheet A in the same manner as in Example 1.

[0124] Example 7 The solid electrolyte a contained in the slurry for forming the solid electrolyte layer A was 0.05 Li 0.35 A sheet A having a thickness of 18 μm and constituting a solid electrolyte layer A was produced in the same manner as in Example 3, except that TiO was used instead. Further, a solid electrolyte sheet was produced using this sheet A in the same manner as in Example 1.

[0125] Example 8 The solid electrolyte a contained in the slurry for forming the solid electrolyte layer A is Li 10 SnP2S 12 A sheet A having a thickness of 18 μm and constituting a solid electrolyte layer A was produced in the same manner as in Example 3, except for changing the thickness to 18 μm. Furthermore, a solid electrolyte sheet was produced using this sheet A in the same manner as in Example 1.

[0126] (Comparative Example 1) Instead of laminating Sheet A and Sheet B, two sheets of Sheet B were laminated to create a solid electrolyte sheet.

[0127] Each solid electrolyte sheet of the examples and comparative examples was sandwiched between two pieces of Li metal foil, and both ends of the sheet were further pressed down with two pieces of stainless steel plates to prepare a cell for evaluation.

[0128] 0.05mA / cm for each cell 2 The charge and discharge cycles were repeated 10 times at a current density of 0.1 mA / cm (the time per cycle was 40 minutes for charge and 40 minutes for discharge), and the current density was further increased to 0.1 mA / cm. 2 , 0.2mA / cm 2 , 0.4mA / cm 2 , 0.8mA / cm 2 and then 0.2mA / cm 2 1.8mA / cm at intervals 2 The current density was changed in order from 0.01 to 0.10, and 10 charge / discharge cycles were repeated in the same manner, and the change in cell voltage was measured during the cycle. The charge time and discharge time per cycle in the charge / discharge cycles are shown in Table 1. The change in voltage of the cell using the solid electrolyte sheet of Comparative Example 1 is shown in Figure 4.

[0129] [Table 1]

[0130] From the voltage change shown in FIG. 4, the cell using the solid electrolyte sheet of Comparative Example 1 had a current of 0.2 mA / cm 2 It can be seen that a short circuit occurred after the seventh charge / discharge cycle. The total amount of electricity in the charge and discharge cycles leading up to the short circuit (total amount of charge electricity + total amount of discharge electricity) was 3 mAh / cm per unit area of ​​the electrode. 2 The amount of electricity could be charged and discharged before a short circuit occurred.

[0131] Similarly, for the cells using the solid electrolyte sheets of each Example, Table 2 shows the current density at which a short circuit occurred and the total amount of charge and discharge electricity until a short circuit occurred.

[0132] [Table 2]

[0133] In the cells using the solid electrolyte sheets of Examples 1 to 8 having a laminated structure of solid electrolyte layer A and solid electrolyte layer B, solid electrolyte layer A suppressed the growth of lithium dendrites, and as shown in Table 2, short circuits were less likely to occur than in the cell using the solid electrolyte sheet of Comparative Example 1, making charging and discharging at a larger current possible.

[0134] Therefore, by assembling an all-solid-state battery using the solid electrolyte sheets of Examples 1 to 8 so that the solid electrolyte layer B faces the negative electrode, a battery in which the occurrence of short circuits due to lithium dendrites is suppressed can be constructed.

[0135] The present invention can be implemented in other forms without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the appended claims rather than the description in the above specification, and all modifications within the scope of the claims are included in the scope of the claims. [Industrial Applicability]

[0136] The all-solid-state battery of the present invention can be used in the same applications as conventionally known primary batteries and secondary batteries, but since it has a solid electrolyte instead of an organic electrolyte solution, it has excellent heat resistance and can be preferably used in applications where it is exposed to high temperatures. The solid electrolyte sheet of the present invention can constitute the all-solid-state battery of the present invention. [Explanation of symbols]

[0137] 10, 11 Solid electrolyte sheet 20 Solid electrolyte layer A 30 Solid electrolyte layer B 100 solid state battery 200 positive electrode 300 negative electrode 400 Solid Electrolyte Sheet 500 outer cans 600 sealed cans 700 gasket

Claims

1. A solid electrolyte sheet having a porous substrate and a solid electrolyte supported on the porous substrate, a solid electrolyte layer A containing a solid electrolyte a that reacts with metallic lithium to oxidize lithium, and a solid electrolyte layer B containing a solid electrolyte b that is less reactive with metallic lithium than the solid electrolyte a, the solid electrolyte layer A is formed by retaining the solid electrolyte a at least in part within the pores of the porous substrate, the solid electrolyte layer B is formed by retaining the solid electrolyte b at least in part within the pores of the porous substrate, A solid electrolyte sheet, wherein the solid electrolyte layer B is disposed on at least one surface of the solid electrolyte sheet.

2. 2. The solid electrolyte sheet according to claim 1, wherein the solid electrolyte layer B is disposed on one surface of the solid electrolyte sheet, and the solid electrolyte layer A is disposed on the other surface of the solid electrolyte sheet.

3. 2. The solid electrolyte sheet according to claim 1, wherein the solid electrolyte layer A contains a solid electrolyte a and a solid electrolyte b.

4. 2. The solid electrolyte sheet according to claim 1, wherein the solid electrolyte a contains at least one element selected from the group consisting of Ti, Ge, Sn, Al, and Si.

5. 2. The solid electrolyte sheet according to claim 1, wherein the solid electrolyte b contains a sulfide-based solid electrolyte.

6. 6. The solid electrolyte sheet according to claim 5, wherein the sulfide-based solid electrolyte is a solid electrolyte having an argyrodite structure.

7. An all-solid-state battery having a positive electrode, a negative electrode, and a solid electrolyte layer, The solid electrolyte layer comprises the solid electrolyte sheet according to any one of claims 1 to 6, a solid electrolyte layer B of the solid electrolyte sheet facing the negative electrode;

Images