All-solid-state batteries

Abstract

To provide an all-solid battery that can prevent the occurrence of defects due to misalignment of a unit electrode body and a current collector that make up a multilayer electrode body when an all-solid battery equipped with a multilayer electrode body with a bipolar structure is assembled, and can suppress deterioration of characteristics due to moisture intruding inside, and that relates to goals 3, 7, 11 and 12 of the SDGs.SOLUTION: In an all-solid battery according to the present invention, a multilayer electrode body in which a plurality of unit electrode body each including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode are laminated, and the adjacent unit electrode bodies are connected in series via a current collector is enclosed inside an exterior body, and a resin sheet containing a desiccant is attached to the peripheral surface of the multilayer electrode body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an all-solid-state battery that can prevent defects from occurring during assembly of the all-solid-state battery including a laminated electrode body having a bipolar structure and can suppress deterioration of characteristics due to moisture penetrating inside. [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 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 have attracted attention (see, for example, Patent Documents 1 and 2). All-solid-state batteries use a molded body of a solid electrolyte that does not use an organic solvent instead of the conventional organic solvent-based electrolyte, and are highly safe with no risk of abnormal heat generation from the solid electrolyte.

[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] However, lithium batteries have a problem in that moisture entering the battery interior can cause deterioration in various characteristics, such as an increase in internal resistance and a decrease in capacity, and there is a demand for preventing such problems from occurring.

[0009] For example, Patent Document 3 proposes a technology for avoiding the occurrence of the above-mentioned problems by using a housing (exterior body) made of synthetic resin, which allows external moisture to penetrate more easily than a metal container, and by disposing a moisture absorbent inside a battery that uses a non-fluidic electrolyte layer containing, for example, a supporting electrolyte, a solvent, and a polymer for gelation.

[0010] However, in batteries with electrolytes containing solvents, some of the elements constituting the moisture absorbent may dissolve into the solvent, causing a deterioration in performance due to the moisture absorbent disposed inside the battery. In addition, there is a risk that the moisture absorbent will no longer function as a moisture absorbent if its surface becomes wet with the solvent.

[0011] Furthermore, in all-solid-state batteries, it has been proposed to use a bipolar structure in which multiple power generating elements (unit cells) are stacked and connected in series, thereby achieving higher voltage and higher capacity (Patent Document 4). In batteries with the bipolar structure, there is a possibility that the multiple power generating elements may become misaligned when they are stacked in order to assemble the battery, which may cause problems such as short circuits and increased internal resistance, and therefore measures to address this issue are required. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-40531 [Patent Document 2] Japanese Patent Application Publication No. 2017-168387 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-243357 [Patent Document 4] Patent Publication No. 2021-64584 Summary of the Invention [Problem to be solved by the invention]

[0013] 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 that can prevent defects caused by misalignment of unit electrode bodies and current collectors that constitute a laminated electrode body having a bipolar structure when assembling the all-solid-state battery, and can suppress deterioration of characteristics caused by moisture penetrating inside. [Means for solving the problem]

[0014] The all-solid-state battery of the present invention is characterized in that a laminated electrode body, which is formed by stacking a plurality of unit electrode bodies and connecting adjacent unit electrode bodies in series via a current collector, is enclosed inside an exterior body, and a resin sheet containing a desiccant is attached to the peripheral surface of the laminated electrode body. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an all-solid-state battery that can prevent misalignment of unit electrode bodies and current collectors that constitute the laminated electrode body when assembling the all-solid-state battery including the laminated electrode body having a bipolar structure, and can prevent the occurrence of short circuits and increases in internal resistance, as well as suppress deterioration of characteristics due to moisture penetrating into the battery. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a longitudinal sectional view schematically illustrating an example of an all-solid-state battery of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The all-solid-state battery of the present invention is configured such that a laminated electrode body is enclosed inside an outer casing, the laminated electrode body being formed by stacking a plurality of unit electrode bodies each having a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, and adjacent unit electrode bodies being connected in series via a current collector, and further, a resin sheet containing a desiccant is attached to the peripheral surface of the laminated electrode body, i.e., to the side surface of the laminated electrode body configured by stacking the unit electrode bodies and the current collector in a columnar shape.

[0018] In the all-solid-state battery of the present invention, a resin sheet attached to the peripheral surface of the laminated electrode body can prevent misalignment of the unit electrode bodies and current collectors that make up the laminated electrode body. Furthermore, the action of the desiccant contained in the resin sheet causes some or all of the moisture that penetrates into the exterior body to be adsorbed by the resin sheet, thereby suppressing deterioration of the solid electrolyte, active material, etc., due to moisture. This prevents the occurrence of short circuits and increases in internal resistance due to misalignment of the unit electrode bodies and current collectors, and also makes it possible to suppress deterioration of characteristics due to moisture penetrating into the interior of the all-solid-state battery of the present invention.

[0019] Furthermore, for example, in the case of a battery having an electrolyte solution containing a solvent (including one that has been made into a gel state using a polymer or the like), if a desiccant is placed inside the exterior body, there is a risk that some of the elements that make up the desiccant will dissolve into the solvent of the electrolyte solution, impairing the battery characteristics, or that the surface of the desiccant will become wet with the solvent, causing it to lose its moisture absorption function.However, an all-solid-state battery that does not use an electrolyte solution containing a solvent can prevent such problems from occurring.

[0020] The desiccant in the resin sheet containing the desiccant may be any desiccant capable of adsorbing moisture that penetrates into the battery, and the mechanism of adsorption may be either chemical adsorption or physical adsorption. Specific examples include desiccants that chemically adsorb moisture, such as calcium oxide, calcium chloride, magnesium perchlorate, barium oxide, barium perchlorate, phosphorus pentoxide, strontium oxide, and magnesium sulfate; and desiccants that physically adsorb moisture, such as synthetic zeolite and silica gel. Calcium oxide is preferred. One type of desiccant may be used, or two or more types may be used.

[0021] From the viewpoint of moisture adsorption, the desiccant should have a BET specific surface area of ​​10m 2 / g or more, and the specific surface area is preferably 30m 2 / g or more is more preferable, and 40m 2 The BET specific surface area of ​​the desiccant referred to in this specification is a value determined by the BET method in accordance with Japanese Industrial Standards (JIS) K 6217, and can be measured, for example, using a specific surface area measuring device based on the nitrogen adsorption method ("Macsorb HM model e-1201" manufactured by Mountech Co., Ltd.).

[0022] The resin sheet containing a desiccant is formed by molding a composition containing a desiccant and a resin into a sheet, and the resin in the resin sheet serves to retain the desiccant contained in the sheet. The resin can be the same as the various resins used inside batteries such as lithium batteries, such as separators and electrode binders. Specific examples include polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers; polyesters such as polyethylene terephthalate and copolymer polyesters; fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); and styrene-butadiene rubber. Polyolefins and fluororesins are preferred. One type of resin may be used, or two or more types may be used.

[0023] In the resin sheet containing a desiccant, the content of the desiccant is preferably 30% by mass or more, more preferably 50% by mass or more, from the viewpoint of further enhancing the moisture adsorption performance inside the battery. However, if the amount of the desiccant in the resin sheet is too large, for example, there is a risk that the composition cannot be formed into a sheet, so the content of the desiccant in the resin sheet is preferably 95% by mass or less, more preferably 85% by mass or less.

[0024] In a resin sheet containing a desiccant, the only component other than the desiccant may be resin, or it may further contain other components (such as surfactants, antistatic agents, pigments, indicators, fragrances, lubricant fillers, and antioxidants). The resin content in the resin sheet is, for example, preferably 5% by mass or more, more preferably 15% by mass or more, and preferably 70% by mass or less, and more preferably 50% by mass or less. Furthermore, when the resin sheet contains components other than the desiccant and resin, the content of the components may be set within ranges such that the desiccant and resin contents each satisfy the above-mentioned preferred values.

[0025] There are no particular restrictions on the thickness of the resin sheet containing the desiccant, but it is usually preferable to make it 50 μm or more in order to obtain a certain level of moisture absorption, and it is preferable to make it 500 μm or less in order to reduce the proportion of the resin sheet in the battery's internal volume and prevent a decrease in battery capacity.

[0026] When a composition containing a desiccant and a resin is formed into a sheet to produce a resin sheet, it is preferable to thoroughly dry the desiccant and the like before blending them into the composition. In mixing the desiccant and the resin, the resin may be heated as needed to melt the resin before mixing.

[0027] Furthermore, from the viewpoint of moisture adsorption, it is preferable that the resin is fibrillated. For example, when PTFE or the like is used, the resin can be fibrillated by dry-mixing the resin with a desiccant and rolling the resulting mixture.

[0028] The resin sheet containing the desiccant may be a commercially available product, such as flexible seal-type desiccants "Dry Keep TFREE-Z (product name)" and "Dry Keep Film Extra (product name)" manufactured by Sasaki Chemical Co., Ltd.

[0029] A longitudinal cross-sectional view schematically illustrating an example of an all-solid-state battery of the present invention is shown in Figure 1. The all-solid-state battery 1 shown in Figure 1 has a coin-shaped (also called button-shaped) exterior body consisting of an exterior can 3, a sealing can 4, and a gasket 5, and has a laminated electrode body 2 formed by stacking two unit electrode bodies 20, 20 enclosed therein.

[0030] In the all-solid-state battery 1, the sealing can 4 is fitted into the opening of the outer can 3 via a gasket 5, and the open end of the outer can 3 is tightened inward, whereby the gasket 5 comes into contact with the sealing can 4, sealing the opening of the outer can 3 and forming an airtight structure inside the battery.

[0031] Each of the individual unit electrode bodies 20, 20 is configured by laminating a positive electrode 21 and a negative electrode 22 with a solid electrolyte layer 23 interposed therebetween. A current collector 6 is disposed between the positive electrode 21 of the unit electrode body 20 on the upper side in the figure and the negative electrode 22 of the unit electrode body 20 on the lower side in the figure, and the upper unit electrode body 20 and the lower unit electrode body 20 are connected in series via this current collector 6. Therefore, the positive electrode 21 of the upper unit electrode body 20, the current collector 6, and the negative electrode 22 of the lower unit electrode body 20 form a bipolar structure.

[0032] 1, although not shown, the inner surface of the sealed can 4 is electrically connected to the negative electrode 22 of the upper unit electrode body 20 via a current collector, thereby also serving as the negative electrode terminal, and the inner surface of the outer can 3 is electrically connected to the positive electrode 21 of the lower unit electrode body 20 via a current collector, thereby also serving as the positive electrode terminal. Depending on the application of the battery, the outer can may also serve as the negative electrode terminal, and the sealed can may also serve as the positive electrode terminal.

[0033] In the all-solid-state battery 1, a resin sheet 7 containing a desiccant is attached to the peripheral surface of the laminated electrode body 2.

[0034] For example, in the case of a coin-type battery having an exterior body (battery container) having an exterior can and a sealing can as shown in FIG. 1, moisture is likely to penetrate from the vicinity of the peripheral edge of the exterior can (between the exterior can 3 and the gasket 5 in the case of battery 1 in FIG. 1) or from the vicinity of the peripheral edge of the sealing can (between the sealing can 4 and the gasket 5 in the case of battery 1 in FIG. 1). Therefore, in an all-solid-state battery, by attaching a resin sheet containing a desiccant to the peripheral surface of the laminated electrode body, not only can it be prevented from misaligning the unit electrode bodies and current collectors that make up the laminated electrode body as described above, but also the desiccant in the resin sheet on the surface of the laminated electrode body adsorbs the moisture before the infiltrating moisture reaches the laminated electrode body, making it possible to suppress a deterioration in battery characteristics due to a reaction between the solid electrolyte or active material of the laminated electrode body and moisture.

[0035] There are no particular restrictions on the position where the resin sheet containing the desiccant is attached to the peripheral surface of the laminated electrode body, as long as it can prevent the unit electrode bodies and current collectors from shifting positions, and it may be attached to a part of the peripheral surface of the laminated electrode body. However, from the viewpoint of more effectively absorbing moisture that has entered, it is preferable that the area be as large as possible, and it is more preferable to attach the resin sheet to the entire peripheral surface of the laminated electrode body.

[0036] As will be described later, in all-solid-state batteries, the solid electrolyte layer contains a solid electrolyte, and the positive electrode also usually contains a solid electrolyte, and the negative electrode also sometimes contains a solid electrolyte. However, when at least one of the positive electrode, negative electrode, and solid electrolyte layer contains a solid electrolyte that is highly reactive with moisture, such as a sulfide-based solid electrolyte, a hydride solid electrolyte, or a part of an oxide-based solid electrolyte, the effect of the present invention, which suppresses deterioration of characteristics due to moisture that has penetrated inside, becomes more pronounced.

[0037] The all-solid-state battery of the present invention includes a primary battery and a secondary battery.

[0038] (positive electrode) The positive electrode of the all-solid-state battery includes a positive electrode mixture containing a positive electrode active material and a solid electrolyte, and examples thereof include a positive electrode consisting of only a compact of the positive electrode mixture, and a positive electrode mixture having a structure in which a layer (positive electrode mixture layer) consisting of a compact of the positive electrode mixture is formed on a current collector.

[0039] When the all-solid-state battery is a primary battery, the same positive electrode active material as that used in conventionally known non-aqueous electrolyte primary batteries can be used. 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 a Li content of 3.5% by mass or less, preferably 2% by mass or less, more preferably 1.5% by mass or less, and particularly preferably 1% by mass or less), Li a Ti 5 / 3Lithium-containing composite oxides such as O4 (4 / 3 ≤ a < 7 / 3); vanadium oxides; niobium oxides; titanium oxides; sulfides such as iron disulfide; graphite fluoride; silver sulfides such as Ag2S; nickel oxides such as NiO2; etc. can be mentioned.

[0040] Also, when the all-solid-state battery is a secondary battery, the same positive electrode active materials as those used in conventionally known non-aqueous electrolyte secondary batteries, that is, active materials capable of occluding and releasing Li (lithium) ions can be used. Specifically, Li 1-x M 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, 0 ≤ x ≤ 1, 0 ≤ r ≤ 1), spinel-type lithium manganese composite oxide represented by [[ID=ll]] r Mn (1-s-t) 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 ≤ 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 1-x Co 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, 0 ≤ x ≤ 1, 0 ≤ r ≤ 0.5), lithium cobalt composite oxide represented by 1-x Ni 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, 0 ≤ x ≤ 1, 0 ≤ r ≤ 0.5), lithium nickel composite oxide represented by 1+s-xM 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≦x≦1, 0≦r≦0.5, 0≦s≦1), Li 2-x M 1-r N r Examples include pyrophosphate compounds 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≦x≦2, 0≦r≦0.5), and these may be used alone or in combination of two or more.

[0041] 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 load characteristics of the battery.

[0042] The average particle diameter of various particles (positive electrode active material, solid electrolyte, 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 particles using a particle size distribution analyzer (e.g., a Microtrac particle size distribution analyzer "HRA9320" manufactured by Nikkiso Co., Ltd.). 50 ) means

[0043] 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.

[0044] If the positive electrode active material and the solid electrolyte come into direct contact within the positive electrode mixture compact, the solid electrolyte may oxidize to form a resistance layer, resulting in a decrease in ionic conductivity within the compact. 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 a decrease in ionic conductivity within the compact due to oxidation of the solid electrolyte.

[0045] The reaction suppression layer may be made of any material that has ion conductivity and can suppress the reaction between the positive electrode 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, and Zr, more specifically, Nb-containing oxides such as LiNbO3, Li3PO4, Li3BO3, Li4SiO4, Li4GeO4, LiTiO3, LiZrO3, and Li2WO4. The reaction suppression layer may contain only one of these oxides, or may contain 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.

[0046] 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.

[0047] 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.

[0048] The content of the positive electrode active material in the positive electrode mixture is preferably 60 to 98 mass %.

[0049] 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, its content is preferably 1 to 10 mass %.

[0050] The positive electrode mixture may contain a binder. Specific examples include fluororesins such as PVDF. Note that, for example, when a sulfide-based solid electrolyte is contained in the positive electrode mixture (described in detail below), the positive electrode mixture may not contain a binder if good moldability can be ensured in forming a compact from the positive electrode mixture without using a binder.

[0051] 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 the positive electrode mixture contains a sulfide-based solid electrolyte and thus can obtain formability without the need for a binder, 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).

[0052] The solid electrolyte contained in the positive electrode mixture is not particularly limited as long as it has lithium ion conductivity, and for example, a sulfide-based solid electrolyte, a hydride-based solid electrolyte, a halide-based solid electrolyte, an oxide-based solid electrolyte, etc. can be used.

[0053] Examples of sulfide-based solid electrolytes include particles of Li2S-P2S5, Li2S-SiS2, Li2S-P2S5-GeS2, and Li2S-B2S3-based glass. In addition, thio-LISICON-type electrolytes (Li 10 GeP2S 12 , Li9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 such as Li 12-12a-b+c+6d-e M 1 3+a-b-c-d M 2 b M 3 c M 4 d M 5 12-e X e (where M 1 is Si, Ge or Sn, M 2 is P or V, M 3 is Al, Ga, Y or Sb, M 4 is Zn, Ca, or Ba, M 5 is either S or S and O, X is F, Cl, Br or I, 0 ≦ a < 3, 0 ≦ b + c + d ≦ 3, 0 ≦ e ≦ 3), or those of the argyrodite type [such as Li6PS5Cl, Li 7-f+g PS 6-x Cl x+y (where 0.05 ≦ f ≦ 0.9, -3.0f + 1.8 ≦ g ≦ -3.0f + 5.7), 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.

[0054] Examples of the hydride-based solid electrolyte include LiBH4, a solid solution of LiBH4 and the following alkali metal compounds (for example, those having a molar ratio of LiBH4 to the alkali metal compound of 1:1 to 20:1). 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.

[0055] Examples of the halide-based solid electrolyte include 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 in addition, for example, known ones described in International Publication No. 2020 / 070958 and International Publication No. 2020 / 070955 can be used.

[0056] Examples of the oxide-based solid electrolyte include garnet-type Li7La3Zr2O 12 , NASICON-type Li 1+O Al 1+O Ti 2-O (PO4)3, Li 1+p Al 1+p Ge 2-p (PO4)3, perovskite-type Li 3q La 2 / 3-q TiO3, and the like.

[0057] 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 preferred is the argyrodite-type sulfide-based solid electrolyte which has high lithium ion conductivity and high chemical stability.

[0058] Note that from the viewpoint of reducing grain boundary resistance, the average particle diameter of the solid electrolyte is preferably 0.1 μm or more, more preferably 0.2 μm or more. On the other hand, from the viewpoint of forming a sufficient contact interface between the active material and the solid electrolyte, it is preferably 10 μm or less, more preferably 5 μm or less.

[0059] The content of the solid electrolyte in the positive electrode mixture is preferably 4 to 40% by mass.

[0060] When a current collector is used for the positive electrode, as the current collector, metal foils such as aluminum and stainless steel, punching metal, mesh, expanded metal, foamed metal; carbon sheet; and the like can be used.

[0061] The compact of the positive electrode mixture can be formed, for example, by compressing a positive electrode mixture prepared by mixing a positive electrode active material with a conductive additive, a binder, a solid electrolyte, and the like, which are added as needed, by pressure molding or the like.

[0062] In the case of a positive electrode having a current collector, it can be produced by bonding a molded body of the positive electrode mixture formed by the above-mentioned method to the current collector by, for example, pressing.

[0063] Alternatively, the positive electrode mixture and a solvent may be mixed to prepare a positive electrode mixture-containing composition, which may then be applied to a substrate such as a current collector or a solid electrolyte layer that faces the positive electrode, dried, and then pressed to form a molded body of the positive electrode mixture.

[0064] The solvent for the positive electrode mixture-containing composition can be water or an organic solvent such as N-methyl-2-pyrrolidone (NMP). When a solid electrolyte is also included in the positive electrode mixture-containing composition, it is preferable to select a solvent that is less likely to deteriorate the solid electrolyte. In particular, sulfide-based solid electrolytes and hydride-based solid electrolytes undergo chemical reactions with trace amounts of water, so nonpolar aprotic solvents such as hydrocarbon solvents such as hexane, heptane, octane, nonane, decane, decalin, toluene, and xylene are preferred. Ultra-dehydrated solvents with a water content of 0.001% by mass (10 ppm) or less are particularly preferred. Fluorine-based solvents such as "Vertrel®" from Mitsui DuPont Fluorochemicals, "Zeorolla®" from Nippon Zeon, and "Novec®" from Sumitomo 3M can also be used, as well as nonaqueous organic solvents such as dichloromethane and diethyl ether.

[0065] From the viewpoint of increasing the density and reducing the porosity of the positive electrode mixture, and further reducing the internal resistance of the positive electrode, it is more preferable that the positive electrode mixture be compressed and molded by pressure molding or the like.

[0066] The thickness of the positive electrode mixture compact is usually 50 μm or more, but is preferably 200 μm or more from the viewpoint of increasing the capacity of the battery. The thickness of the positive electrode mixture compact is usually 3000 μm or less, but is preferably 500 μm or less from the viewpoint of increasing the output of the battery.

[0067] In the case of a positive electrode produced by forming a positive electrode mixture layer made of a compact of a positive electrode mixture on a current collector using a positive electrode mixture-containing composition containing a solvent, the thickness of the positive electrode mixture layer is preferably 50 to 1000 μm, and more preferably 500 μm or less from the viewpoint of increasing the output of the battery.

[0068] (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.

[0069] 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 molded body (pellet, etc.) obtained by molding the negative electrode mixture, and 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.

[0070] When the negative electrode has a molded body of a negative electrode mixture, examples of the negative electrode active material include carbon materials such as graphite, simple substances containing elements such as Si and Sn, compounds (oxides, etc.), and alloys thereof. Lithium metal and lithium alloys (lithium-aluminum alloys, lithium-indium alloys, etc.) can also be used as the negative electrode active material.

[0071] The content of the negative electrode active material in the negative electrode mixture is preferably 10 to 99 mass %.

[0072] 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 1 to 10 mass %.

[0073] 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 in detail below), if good moldability can be ensured in forming a compact from the negative electrode mixture without using a binder, the negative electrode mixture may not contain a binder.

[0074] 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 the negative electrode mixture contains a sulfide-based solid electrolyte and thus can be molded without a binder, 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).

[0075] In a negative electrode having a compact of a negative electrode mixture, a solid electrolyte is contained in the negative electrode mixture. Specific examples include the same solid electrolytes as those exemplified above as those that can be contained in the positive electrode mixture. Among the solid electrolytes exemplified above, it is more preferable to use a sulfide-based solid electrolyte because it has high lithium ion conductivity and has the function of improving the formability of the negative electrode mixture.

[0076] The content of the solid electrolyte in the negative electrode mixture is preferably 4 to 49 mass %.

[0077] When a current collector is used in a negative electrode having a molded body of a negative electrode mixture, the current collector can be made of copper or nickel foil, punched metal, mesh, expanded metal, foamed metal; carbon sheet; or the like.

[0078] The compact of the negative electrode mixture can be formed, for example, by compressing a negative electrode mixture prepared by mixing a negative electrode active material, and optionally a conductive additive, a solid electrolyte, a binder, etc., by pressure molding, etc. A negative electrode composed only of a compact of the negative electrode mixture can be produced by the above-mentioned method.

[0079] In the case of a negative electrode having a current collector, it can be produced by bonding a molded body of the negative electrode mixture formed by the above-mentioned method to the current collector by, for example, pressing.

[0080] Furthermore, in the case of a negative electrode having a current collector, the negative electrode can also be produced by a method in which a negative electrode mixture-containing composition (paste, slurry, etc.) in which a negative electrode active material, and further, optionally added conductive additives, a solid electrolyte, a binder, etc. are dispersed in a solvent is applied to a current collector, dried, and then pressure-molded, as necessary, by calendering or other means, to form a molded body of the negative electrode mixture (negative electrode mixture layer) on the surface of the current collector.

[0081] 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 positive electrode mixture-containing composition containing a solid electrolyte.

[0082] From the viewpoint of increasing the density and reducing the porosity of the negative electrode mixture, and further reducing the internal resistance of the negative electrode, it is more preferable that the negative electrode mixture be formed by compressing the negative electrode mixture by pressure molding or the like.

[0083] The thickness of the negative electrode mixture compact is usually 50 μm or more, but from the viewpoint of increasing the capacity of the battery, it is preferably 200 μm or more. The thickness of the negative electrode mixture compact is usually 3000 μm or less, but from the viewpoint of increasing the output of the battery, it is preferably 500 μm or less.

[0084] In the case of a negative electrode produced by forming a negative electrode mixture layer made of a compact of a negative electrode mixture on a current collector using a negative electrode mixture-containing composition containing a solvent, the thickness of the negative electrode mixture layer is preferably 50 to 1000 μm, and more preferably 500 μm or less from the viewpoint of increasing the output of the battery.

[0085] 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.

[0086] 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).

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] Furthermore, 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.

[0092] (solid electrolyte layer) The solid electrolyte constituting the solid electrolyte layer interposed between the positive electrode and the negative electrode can be one or more of the various sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes exemplified above for use in the positive electrode. However, to improve battery characteristics, it is preferable to include a sulfide-based solid electrolyte, and it is more preferable to include an argyrodite-type sulfide-based solid electrolyte. It is even more preferable to include a sulfide-based solid electrolyte in both the positive electrode and the solid electrolyte layer, and it is even more preferable to include an argyrodite-type sulfide-based solid electrolyte.

[0093] The solid electrolyte layer may have a porous body such as a resin nonwoven fabric as a support.

[0094] The solid electrolyte layer can be formed by a method of compressing the solid electrolyte by pressure molding or the like; a method of dispersing the solid electrolyte in a solvent to prepare a composition for forming the solid electrolyte layer, applying the composition to a substrate, a positive electrode, or a negative electrode, drying the composition, and optionally performing pressure molding such as pressing; or the like; however, it is more preferable to employ the method of compressing the solid electrolyte.

[0095] It is desirable to select a solvent that is unlikely to deteriorate the solid electrolyte as the solvent used in the solid electrolyte layer-forming composition, and it is preferable to use the same solvents as those exemplified above as the solvents for the positive electrode mixture-containing composition containing the solid electrolyte.

[0096] The thickness of the solid electrolyte layer is preferably 100 to 400 μm.

[0097] (Laminated electrode body) The positive electrode and the negative electrode are stacked as unit electrode bodies with a solid electrolyte layer interposed therebetween, and a plurality of such unit electrode bodies are stacked in order with current collectors interposed therebetween to form a stacked electrode body, which is used in the battery.

[0098] The current collector interposed between the unit electrode bodies can be made of a metal that does not react with Li, such as copper, nickel, or iron, or an alloy containing such a metal (including stainless steel), such as foil, punched metal, mesh, expanded metal, or foamed metal; or a carbon sheet. The thickness of the current collector interposed between the unit electrode bodies is preferably 10 to 200 μm.

[0099] The current collector and the adjacent unit electrode body may simply be stacked, or the current collector and the positive electrode or negative electrode adjacent to the current collector may be integrated by bonding or the like.

[0100] The number of unit electrode bodies that an all-solid-state battery has is not particularly limited as long as it is plural, and can be two, three, four, or more as needed. However, in the case of a flat battery such as that shown in FIG. 1, for example, if the number of unit electrode bodies is too large, the thickness of the battery becomes too large, which may undermine the advantage of the flat shape, and therefore the number is usually four or less.

[0101] (exterior body) The exterior body of an all-solid-state battery is, for example, a battery container having an exterior can and a sealing can as shown in Fig. 1. That is, an all-solid-state battery using such a battery container as the exterior body becomes a coin-type (button-type) battery.

[0102] In the case where the exterior body of the all-solid-state battery is a battery container having an exterior can and a sealing can, examples include a case in which the exterior can and the sealing can are crimped and sealed via a gasket as shown in FIG. 1, and a case in which the exterior can and the sealing can are bonded with a resin.

[0103] The outer can and sealing can can be made of stainless steel or other materials. Materials such as polypropylene and nylon can be used for the gasket. If heat resistance is required for the battery's intended use, heat-resistant resins with melting points exceeding 240°C, such as fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene ether (PEE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), can also be used. If the battery is intended for use in applications requiring heat resistance, a glass hermetic seal can also be used for the sealing.

[0104] The shape of the exterior body, which is a battery container having an exterior can and a sealing can, in a plan view may be circular or polygonal such as quadrilateral (square or rectangle).In the case of a polygon, the corners may be curved.

[0105] Furthermore, a laminate film exterior made of a metal laminate film such as an aluminum laminate film can also be used as the exterior of the all-solid-state battery.

[0106] 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. [Example]

[0107] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0108] Example 1 <Preparation of unit electrode body> Lithium titanate (Li4Ti5O 12 , negative electrode active material) and a sulfide-based solid electrolyte (Li 5.4 PS4.4 Cl 0.8 Br 0.8 ) and graphene (conductive additive) were mixed in a mass ratio of 50:41:9 to prepare a negative electrode mixture.

[0109] In addition, a LiCoO2 (positive electrode active material) with an average particle size of 5 μm and a LiNbO3 coating layer formed on its surface and a sulfide-based solid electrolyte (Li 7.0 PS 5.4 Cl 1.2 ) was mixed with carbon black and vapor grown carbon fiber (VGCF) in a mass ratio of 70:26.8:1.1:2.1 to prepare a positive electrode mixture.

[0110] Next, a sulfide-based solid electrolyte (Li 5.4 PS 4.4 Cl 0.8 Br 0.8 ) powder was placed in a powder molding die and subjected to low-pressure molding using a press to form a provisionally molded layer of a solid electrolyte layer. Furthermore, the negative electrode mixture was placed on the upper surface of the provisionally molded layer of the solid electrolyte layer and subjected to low-pressure molding to form a provisionally molded layer of a negative electrode on the provisionally molded layer of the solid electrolyte layer.

[0111] Furthermore, after the mold was turned upside down, the positive electrode mixture was placed on the upper surface of the provisionally molded layer of the solid electrolyte layer in the mold (the surface opposite to the surface having the provisionally molded layer of the negative electrode), and the entire mold was pressurized with 1300 MPa (13 tf / cm 2 ) to fabricate two unit electrode bodies each having a thickness of 0.75 mm, in which the negative electrode, solid electrolyte layer, and positive electrode were integrated.

[0112] <Fabrication of laminated electrode body> Flexible graphite sheet "PERMA-FOIL" (product name) manufactured by Toyo Tanso Co., Ltd. (thickness: 0.1 mm, apparent density: 1.1 g / cm 3One of these sheets was placed on top of the positive electrode of one of the two unit electrode bodies, and the remaining unit electrode body was placed on top of this graphite sheet with the negative electrode side facing the graphite sheet, thereby obtaining a stacked electrode body having two unit electrode bodies connected in series via the graphite sheet (current collector). Furthermore, a flexible seal-type desiccant "Dry Keep TFREE-Z (product name)" manufactured by Sasaki Chemical Co., Ltd. was attached to the entire periphery of the stacked electrode body to fix the unit electrode body and current collector.

[0113] <Battery assembly> One of the graphite sheets punched out as described above was placed on the inner bottom surface of a stainless steel sealing can fitted with a polyphenylene sulfide ring gasket, and a laminated electrode assembly was placed on top of it, with the exposed surface of the negative electrode facing the graphite sheet. The remaining graphite sheet was then placed on the exposed surface of the laminated electrode assembly, and a stainless steel outer can was placed over it. The open end of the outer can was then crimped inward to seal, producing an all-solid-state secondary battery (coin-type all-solid-state secondary battery) with the structure shown in Fig. 1. The sealing can and the graphite sheet placed between the outer can and the laminated electrode assembly are not shown in Fig. 1.

[0114] (Comparative Example 1) Two unit electrode bodies and three graphite sheets serving as current collectors were prepared in the same manner as in Example 1. One of the graphite sheets was placed on the inner bottom surface of a stainless steel sealing can fitted with a polyphenylene sulfide annular gasket, and one of the two unit electrode bodies was placed on top of it with the positive electrode side facing the graphite sheet. Next, one of the graphite sheets was placed on top of that, and the other unit electrode body was placed on top of that with the positive electrode side facing the graphite sheet, thereby forming a laminated electrode body.

[0115] No flexible seal-type desiccant was attached to the peripheral surface of the laminated electrode body, and the remaining graphite sheet was placed on the surface of the laminated electrode body where the positive electrode was exposed. Thereafter, a coin-type all-solid-state secondary battery was produced in the same manner as in Example 1.

[0116] (Comparative Example 2) A coin-type all-solid-state secondary battery was fabricated in the same manner as in Comparative Example 1, except that a sealed can in which a flexible seal-type desiccant was previously cut to a width of 1 mm and attached to the entire periphery of the inner surface was used.

[0117] The all-solid-state secondary batteries of Example 1 and Comparative Examples 1 and 2 were subjected to the following evaluations.

[0118] <Evaluation of internal resistance during battery assembly> Ten batteries each from Example 1 and Comparative Examples 1 and 2 were charged and discharged, and then an AC voltage of 1 kHz was applied to measure the internal resistance of the battery. The average value of the ten batteries was calculated to evaluate the effect of misalignment in the laminated electrode body.

[0119] <Evaluation of internal resistance during high-temperature storage> Next, the batteries were stored in a thermostatic chamber at 60°C and a relative humidity of 90% for 80 days, and then the batteries were removed and allowed to cool to room temperature. An alternating current of 1 kHz was then applied to measure the internal resistance of the batteries after high-temperature storage, and the average value for 10 batteries was calculated.

[0120] For the batteries of Example 1 and Comparative Examples 1 and 2, the difference between the internal resistance of the battery after high-temperature storage and the internal resistance of the battery before storage (increase in internal resistance) was calculated and compared.

[0121] The results of the evaluations are shown in Table 1. In Table 1, the internal resistance during battery assembly and the increase in internal resistance during high-temperature storage are shown as relative values, with the value for the battery of Comparative Example 1 taken as 100.

[0122] [Table 1]

[0123] In the battery of Example 1, the unit electrode bodies and graphite sheets of the laminated electrode body were stacked without any shifting and secured by a flexible seal-type desiccant, so no shifting occurred during the battery assembly process, and the internal resistance of the battery could be reduced.

[0124] On the other hand, in the batteries of Comparative Examples 1 and 2, misalignment occurred in the unit electrode bodies or graphite sheets when they were stacked or sealed, resulting in a decrease in the area where they faced each other. In addition, uneven pressure was applied to the unit electrode bodies during sealing, causing cracks, and as a result, the internal resistance after assembly was higher than that of the battery of Example 1.

[0125] Furthermore, when a battery is stored in a high-temperature, high-humidity environment, moisture gradually penetrates into the battery through the sealed portion, and reacts with the solid electrolyte, etc., increasing the internal resistance of the battery. However, as shown in Table 1, in the batteries of Example 1 and Comparative Example 2, in which a resin sheet containing a desiccant (flexible seal-type desiccant) was placed on the periphery of the laminated electrode body or the inner surface of the sealed can, the amount of moisture reacting with the solid electrolyte, etc., was reduced, and the increase in internal resistance was suppressed. [Explanation of symbols]

[0126] 1 All-solid-state battery 2. Unit electrode body 21 Positive electrode 22 Negative electrode 23 Solid electrolyte layer 3 Outer can 4 Sealed cans 5 Gasket 6 Current collector 7 Resin sheet containing desiccant

Claims

1. An all-solid-state battery in which a stacked electrode body is formed by stacking a plurality of unit electrode bodies, each having a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, and adjacent unit electrode bodies are connected in series via a current collector, and the stacked electrode body is sealed inside an exterior body, The adjacent unit laminate bodies and the current collectors connecting these unit laminate bodies to each other are not bonded to each other, An all-solid-state battery, characterized in that a resin sheet containing a desiccant is attached to the peripheral surface of the laminated electrode body.

2. 2. The all-solid-state battery according to claim 1, wherein at least one of the positive electrode, the negative electrode, and the solid electrolyte layer that constitute the laminated electrode body contains a sulfide-based solid electrolyte.

3. 3. The all-solid-state battery according to claim 1, wherein the resin sheet has a thickness of 500 μm or less.

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