Positive electrode for all-solid-state secondary battery, power generation element, and all-solid-state secondary battery

Abstract

The present invention provides: an all-solid-state secondary battery which has excellent charge and discharge cycle characteristics under high temperature conditions; and a positive electrode and a power generation element for constituting the all-solid-state secondary battery.　A positive electrode for an all-solid-state secondary battery according to the present invention has an overall void fraction of a molded body of a positive electrode mixture and a sheet-like porous metal base material of 14-21%. A power generation element according to the present invention is used for an all-solid-state secondary battery, and is provided with: a positive electrode that has a sheet-like porous metal base material and a molded body of a positive electrode mixture that contains a positive electrode active material and a solid electrolyte; a negative electrode that has a sheet-like porous metal base material and a molded body of a negative electrode mixture that contains a negative electrode active material; and a solid electrolyte layer. The overall void fraction of the molded body of the positive electrode mixture, the sheet-like porous metal base material of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the sheet-like porous metal base material of the negative electrode is 14-22%. An all-solid-state secondary battery according to the present invention comprises a positive electrode according to the present invention or a power generation element according to the present invention.

Description

Positive electrode for all-solid-state secondary battery, power generating element and all-solid-state secondary battery

[0001] The present invention relates to an all-solid-state secondary battery having excellent charge-discharge cycle characteristics at high temperatures, and a positive electrode and a power generating element for constituting the all-solid-state secondary battery.

[0002] As batteries, non-aqueous electrolyte batteries such as lithium ion batteries using an organic electrolyte are widely used. However, in recent years, as the range of application fields expands, there has been a demand for higher capacity and use in high-temperature environments, which has led to an increased demand for improved safety, for example.

[0003] For these reasons, attention is being drawn to all-solid-state batteries, which can ensure excellent heat resistance by using a molded solid electrolyte instead of an organic electrolyte solution that uses an organic solvent, which is a flammable liquid.

[0004] Various studies are currently being conducted on all-solid-state batteries. For example, Patent Document 1 discloses that in an all-solid-state secondary battery having a laminated electrode body in which a positive electrode having a molded body of a positive electrode mixture containing a positive electrode active material powder of primary particles having a lithium niobium-containing oxide formed on the surface, a conductive additive, and a sulfide-based solid electrolyte, a negative electrode having a molded body of a negative electrode mixture containing a negative electrode active material powder, a conductive additive, and a sulfide-based solid electrolyte, and a solid electrolyte layer are integrated, the load characteristics and high-temperature characteristics can be improved by, for example, setting the porosity of the molded body of the positive electrode mixture to 10% or less.

[0005] Japanese Patent Application Laid-Open No. 2021-163582

[0006] The all-solid-state secondary battery described in Patent Document 1 can exhibit excellent charge-discharge cycle characteristics, for example, even in an environment of about 100° C. However, in a temperature environment higher than this (for example, an environment of about 150° C.), it is not easy to maintain high levels of charge-discharge cycle characteristics even with the all-solid-state secondary battery described in Patent Document 1, and in this respect, there is still room for improvement.

[0007] 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 secondary battery having excellent charge-discharge cycle characteristics at high temperatures, as well as a positive electrode and a power-generating element for constituting the all-solid-state secondary battery.

[0008] The positive electrode for an all-solid-state secondary battery of the present invention comprises a molded body of a positive electrode mixture containing a positive electrode active material and a solid electrolyte, and a sheet-like porous metal substrate, and is characterized in that the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate is 14 to 21%.

[0009] The power generating element of the present invention is used in an all-solid-state secondary battery, and comprises a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode comprises a molded body of a positive electrode mixture containing a positive electrode active material and a solid electrolyte, and a sheet-like porous metal substrate, and the negative electrode comprises a molded body of a negative electrode mixture containing a negative electrode active material, and a sheet-like porous metal substrate, and the overall porosity of the molded body of the positive electrode mixture, the sheet-like porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the sheet-like porous metal substrate of the negative electrode is 14 to 22%.

[0010] Furthermore, the all-solid-state secondary battery of the present invention is characterized in that a power generation element having a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode is housed in an exterior body, and the positive electrode is the positive electrode for an all-solid-state secondary battery of the present invention, or the power generation element is the power generation element of the present invention.

[0011] According to the present invention, it is possible to provide an all-solid-state secondary battery having excellent charge-discharge cycle characteristics at high temperatures, as well as a positive electrode and a power generating element for constituting the all-solid-state secondary battery.

[0012] 3 is an exploded perspective view of the cell assembly of FIG. 3; and FIG. 4 is a cross-sectional view taken along line II of FIG. 2. The cell assembly of FIG. 3 is an exploded perspective view of the cell assembly of FIG. 3; and FIG. 4 is a cross-sectional view of the cell assembly of FIG. 3; and FIG. 4 is a graph showing the relationship between the overall porosity of the positive electrode mixture molded body and the sheet-like porous metal substrate in the positive electrode and the evaluation results of high-temperature charge-discharge cycle characteristics of the all-solid-state secondary batteries of Examples and Comparative Examples. The graph showing the relationship between the overall porosity of the positive electrode mixture molded body, the positive electrode sheet-like porous metal substrate, the solid electrolyte layer, the negative electrode mixture molded body, and the negative electrode sheet-like porous metal substrate in the power generation element and the evaluation results of high-temperature charge-discharge cycle characteristics of the all-solid-state secondary batteries of Examples and Comparative Examples. 1 is a graph showing the relationship between the overall porosity of the molded positive electrode mixture and the sheet-like porous metal substrate in the positive electrode of the all-solid-state secondary batteries of Examples and Comparative Examples, and the remaining capacity after storage for 1000 hours at 105° C. FIG. 2 is a graph showing the relationship between the overall porosity of the molded positive electrode mixture, the sheet-like porous metal substrate of the positive electrode, the solid electrolyte layer, the molded negative electrode mixture, and the sheet-like porous metal substrate of the negative electrode in the power generation element of the all-solid-state secondary batteries of Examples and Comparative Examples, and the remaining capacity after storage for 1000 hours at 105° C.

[0013] In a positive electrode having a molded body of a positive electrode mixture, the porosity is reduced to minimize the gap between the positive electrode active material and the solid electrolyte, thereby enabling good contact between them, thereby increasing the ionic conductivity within the molded body of the positive electrode mixture and reducing the internal resistance of the positive electrode. Therefore, in an all-solid-state secondary battery using such a positive electrode, the internal resistance is reduced, and good discharge characteristics can be ensured.

[0014] However, when such an all-solid-state secondary battery is repeatedly charged and discharged in an environment of, for example, about 150 ° C, its resistance rapidly increases. This is because, in such a high-temperature environment, the reactivity at the interface between the positive electrode active material and the solid electrolyte in the molded positive electrode mixture increases, causing deterioration of the solid electrolyte. However, if the porosity of the molded positive electrode mixture is very low, the positive electrode active material and the solid electrolyte are in good contact, which is thought to cause the deterioration of the solid electrolyte to progress more quickly. Furthermore, when the positive electrode includes a sheet-shaped porous metal substrate as a current collector together with the molded positive electrode mixture (hereinafter, the sheet-shaped porous metal substrate in the positive electrode and the sheet-shaped porous metal substrate in the negative electrode may be simply referred to as the "porous metal substrate"), as described below, the contact area between the molded positive electrode mixture and the porous metal substrate is large, and therefore, in such a high-temperature environment, a reaction occurs between the solid electrolyte in the molded positive electrode mixture and the porous metal substrate, making the deterioration of the solid electrolyte more likely to progress.

[0015] Therefore, the present inventors conducted extensive research and found that, when the overall porosity of the molded body of the positive electrode mixture and the porous metal substrate in the positive electrode, and the overall porosity of the molded body of the positive electrode mixture, the porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the porous metal substrate of the negative electrode in the power generation element are adjusted to specific values, it is possible to improve the charge-discharge cycle characteristics in a high-temperature environment while minimizing the deterioration of the discharge characteristics of the all-solid-state secondary battery at room temperature, and have completed the present invention.

[0016] As will be shown in the examples described later, the inventors have found through their studies that the tendency of deterioration of battery characteristics relative to the overall porosity of the molded positive electrode mixture and porous metal substrate in the positive electrode, and the overall porosity of the molded positive electrode mixture, porous metal substrate of the positive electrode, solid electrolyte layer, molded negative electrode mixture, and porous metal substrate of the negative electrode in the power generating element, is significantly different when an all-solid-state secondary battery is stored in an environment of about 100°C (e.g., 105°C) compared to when it is stored in a harsher environment (e.g., 150°C), and the present invention was completed based on such new findings. Details of the present invention are described below.

[0017] <Positive electrode for all-solid-state secondary battery> The positive electrode for an all-solid-state secondary battery of the present invention (hereinafter simply referred to as "positive electrode") has a molded body of a positive electrode mixture containing a positive electrode active material and a solid electrolyte, and a sheet-like porous metal substrate.

[0018] In the positive electrode of the present invention, from the viewpoint of improving the charge-discharge cycle characteristics in a high-temperature environment in an all-solid-state secondary battery using the positive electrode, the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate is 14% or more, preferably 15% or more, and more preferably 16% or more. If the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate is too large, the discharge characteristics of the all-solid-state secondary battery at room temperature tend to decrease, and the charge-discharge cycle characteristics in a high-temperature environment also tend to decrease. Therefore, in the positive electrode of the present invention, from the viewpoint of improving the charge-discharge cycle characteristics of the all-solid-state secondary battery using the positive electrode in a high-temperature environment while suppressing the decrease in discharge characteristics at room temperature as much as possible, the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate is 21% or less, preferably 20% or less.

[0019] The overall porosity of the positive electrode mixture molded body and the sheet-shaped porous metal substrate referred to in this specification is a value calculated from the true density and composition ratio of each material constituting the positive electrode mixture molded body and the sheet-shaped porous metal substrate, and the overall mass and volume of the positive electrode mixture molded body and the sheet-shaped porous metal substrate.In the examples described below, since the shape of the positive electrode is circular in plan view, the thickness and diameter were measured with a micrometer to calculate the volume.

[0020] The positive electrode active material is not particularly limited as long as it is a positive electrode active material used in known non-aqueous electrolyte secondary batteries, that is, an active material capable of absorbing and releasing Li ions. Specific examples of the positive electrode active material include LiM ｒ Mn ２－ｒ O ４ (wherein 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), a spinel-type lithium manganese composite oxide represented by Liｒ Mn （１－ｓ－ｒ） Ni ｓ M ｔ O （２－ｕ） F ｖ (wherein 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, and 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), a layered compound represented by １－ｒ M ｒ O ２ (wherein 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 O ２ (wherein 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), a lithium nickel composite oxide represented by Li １＋ｓ M １－ｒ N ｒ P.O. ４ F 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), Li ２ M １－ｒ N ｒ P ２ O ７ (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), and the like. Among these, only one type may be used, or two or more types may be used in combination.

[0021] The average particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 0.5 μm or more, and is preferably 25 μm or less, more preferably 10 μm or less, from the viewpoint of reducing side reactions that cause battery capacity degradation and increasing the density of the molded body of the positive electrode mixture. 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 diameter within the above range is used, a large interface with the solid electrolyte can be secured within the molded body of the positive electrode mixture, thereby further improving the load characteristics of the all-solid-state secondary battery.

[0022] The average particle diameter of the positive electrode active material and the average particle diameter of other particles (negative electrode active material, solid electrolyte, etc.) referred to in this specification are the 50% diameter value (D) in the volume-based integrated fraction when the integrated volume is calculated from particles with small particle sizes using a particle size distribution measuring device (e.g., a Microtrac particle size distribution measuring device "HRA9320" manufactured by Nikkiso Co., Ltd.). ５０ ) means

[0023] The positive electrode active material preferably has a reaction suppression layer on its surface for suppressing reaction with the solid electrolyte contained in the molded positive electrode mixture. By providing a reaction suppression layer on the surface of the positive electrode active material for suppressing reaction with the solid electrolyte and preventing direct contact between the positive electrode active material and the solid electrolyte, it is possible to more effectively suppress a decrease in ionic conductivity in the molded positive electrode mixture due to deterioration of the solid electrolyte.

[0024] The reaction suppression layer may be made of a 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, Zr, Ta, and W, more specifically, LiNbO ３ Nb-containing oxides such as Li ３ P.O. ４ , Li ３ BO ３ , Li ４ SiO ４ , Li ４ GeO ４ , LiTiO ３, LiZrO ３ , Li ２ WO ４ The reaction suppression layer may contain only one of these oxides, or may contain two or more of them, or may contain a composite compound of two or more of these oxides. Among these oxides, it is preferable to use an Nb-containing oxide, such as LiNbO ３ It is more preferable to use

[0025] The reaction suppression layer is preferably present on the surface in an amount of 0.1 to 2.0 parts 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.

[0026] 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.

[0027] The content of the positive electrode active material in the positive electrode mixture is preferably 20 to 95 mass %.

[0028] The molded body of the positive electrode mixture contains a solid electrolyte. The solid electrolyte is not particularly limited as long as it has Li ion conductivity, and examples of the solid electrolyte that can be used include sulfide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and oxide-based solid electrolytes.

[0029] The sulfide-based solid electrolyte is Li ２ S-P ２ S ５ , Li ２ S-SiS ２ , Li ２ S-P ２ S ５ -GeS ２ , Li ２ S-B ２ S ３ In addition to particles of glass, thio-LISICON type particles [Li １０ GeP ２ S １２ , Li ９．５４ Si １．７４ P １．４４S １１．７ Cl ０．３ Li12-12a-b+c+6d-eM, etc. １ ３＋ａ－ｂ－ｃ－ｄ M ２ ｂ M ３ ｃ M ４ ｄ M ５ １２－ｅ X ｅ (However, 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, and X is F, Cl, Br or I, 0≦a<3, 0≦b+c+d≦3, 0≦e≦3], or argyrodite type [Li ６ P.S. ５ Li, such as Cl ７－ｋ P.S. ６－ｋ X ｋ (wherein X represents one or more halogen elements, and 0.2<k<2.0), Li ７－ｆ＋ｇ P.S. ６－ｆ Cl ｆ＋ｇ (wherein 0.05≦g≦0.9, −3.0f+1.8≦g≦−3.0f+5.7), Li ７－ｈ P.S. ６－ｈ Cl ｉ Br ｊ (where h=i+j, 0<h≦1.8, 0.1≦i / j≦10.0) can also be used.

[0030] Examples of hydride-based solid electrolytes include LiBH ４ , LiBH ４ and a solid solution of the following alkali metal compound (e.g., LiBH ４and the alkali metal compound in a molar ratio of 1:1 to 20:1. The alkali metal compound in the solid solution may be at least one selected from the group consisting of lithium halides (LiI, LiBr, LiF, LiCl, etc.), rubidium halides (RbI, RbBr, RbF, RbCl, etc.), cesium halides (CsI, CsBr, CsF, CsCl, etc.), lithium amide, rubidium amide, and cesium amide.

[0031] Examples of halide-based solid electrolytes include monoclinic LiAlCl ４ , defect spinel type or layer structure LiInBr ４ , monoclinic Li ６－３ｍ Y ｍ X ６ (wherein 0 < m < 2 and X = Cl or Br), and other known compounds described in, for example, WO 2020 / 070958 and WO 2020 / 070955 can also be used.

[0032] Examples of oxide-based solid electrolytes include Li ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -TiO ２ Li-based glass ceramics ２ O-Al ２ O ３ -SiO ２ -P ２ O ５ -GeO ２ Lithium-ion-based glass ceramics, garnet-type ７ La ３ Zr ２ O １２ , NASICON type Li １＋Ｏ Al １＋Ｏ Ti ２－Ｏ (P.O. ４ ) ３ , Li １＋ｐ Al １＋ｐ Ge ２－ｐ (P.O. ４ ) ３ , perovskite-type Li ３ｑ La２／３－ｑ TiO ３ Examples include:

[0033] Among these solid electrolytes, sulfide-based solid electrolytes are preferred because of their high Li ion conductivity, sulfide-based solid electrolytes containing Li and P are more preferred, and argyrodite-type sulfide-based solid electrolytes are even more preferred because of their particularly high Li ion conductivity and high chemical stability.

[0034] The content of the solid electrolyte in the positive electrode mixture is preferably 4 to 80 mass %.

[0035] The molded body of the positive electrode mixture can contain a conductive additive. Examples of the conductive additive for the positive electrode include carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), graphite (natural graphite, artificial graphite), graphene, vapor-grown carbon fiber, carbon nanofiber, carbon nanotube, and other carbon materials; powders of Cu, Ni, Al, Au, and Pd alone or alloys thereof, or porous bodies thereof; and the like. These may be used alone or in combination of two or more.

[0036] In molding a positive electrode mixture containing graphene as a conductive additive, increasing the surface pressure during pressing orients the graphene. However, after the molded body of the positive electrode mixture is removed from the molding die, the graphene springs back, causing microcracks within the molded body. All-solid-state secondary batteries using a positive electrode having a molded body of a positive electrode mixture with such cracks are more likely to experience a decrease in charge-discharge cycle characteristics in high-temperature environments. However, with the positive electrode of the present invention, even when graphene is used as the conductive additive, the decrease in charge-discharge cycle characteristics of the all-solid-state secondary battery in high-temperature environments can be effectively suppressed. Therefore, in the present invention, when graphene is used as the conductive additive for the positive electrode, the effect is more pronounced.

[0037] The content of the conductive additive in the positive electrode mixture is preferably 0.1 to 15 mass %.

[0038] The molded body of the positive electrode mixture may contain a binder, but it does not have to contain a binder if good moldability can be ensured without using a binder, such as in the case of a positive electrode in which a sulfide-based solid electrolyte is contained and a powder of the positive electrode mixture is charged into a molding die and compacted.

[0039] Examples of the binder to be contained in the molded body of the positive electrode mixture include fluororesins such as polyvinylidene fluoride (PVDF).

[0040] When a binder is required in the molded body of the positive electrode mixture, the content thereof in the positive electrode mixture is preferably 15% by mass or less, and preferably 0.5% by mass or more. On the other hand, when a binder is not required in the molded body of the positive electrode mixture from the viewpoint of moldability, the content thereof in the positive electrode mixture 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).

[0041] The sheet-like porous metal substrate for the positive electrode of the present invention functions as a current collector in the positive electrode. Plain woven wire mesh, expanded metal, and the like can be used as the porous metal substrate. However, due to its higher current collection efficiency, it is preferable to use a foamed metal porous body (such as "Celmet (registered trademark)" manufactured by Sumitomo Electric Industries, Ltd.). The material of the porous metal substrate for the positive electrode can be aluminum, titanium, nickel, tungsten, or an alloy thereof (such as a nickel-chromium alloy, a nickel-tin alloy, a titanium-aluminum alloy, or a titanium-aluminum-vanadium alloy); austenitic stainless steel (such as SUS304 or SUS316); or the like.

[0042] In the positive electrode, at least a portion of the positive electrode mixture penetrates into the pores of the porous metal substrate, thereby improving the adhesion between the porous metal substrate and the molded body of the positive electrode mixture, and also increasing the contact area between the molded body of the positive electrode mixture and the porous metal substrate, thereby making it possible to further reduce the resistance of the positive electrode.

[0043] That is, it is preferable that at least a portion of the positive electrode mixture is filled into the pores of the porous metal substrate. More specifically, it is preferable that at least a portion of the porous metal substrate of the positive electrode, including the end portion of the positive electrode mixture on the molded body side, is embedded in the surface layer of the molded body of the positive electrode mixture and is integrated with the molded body of the positive electrode mixture.

[0044] In addition, the porous metal substrate composed of the foamed metal porous body as described above is usually compressed and reduced in thickness when manufacturing a positive electrode together with a positive electrode mixture, so that the thickness before use in the positive electrode is greater than the thickness in the positive electrode. For example, the thickness of the porous metal substrate before compression is preferably 0.1 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.5 mm or more, while preferably 3 mm or less, more preferably 2 mm or less, and particularly preferably 1.5 mm or less. For example, in the manufacturing method of a power generation element described below, the porous metal substrate is compressed in the thickness direction when manufacturing a positive electrode through a process of pressing the positive electrode mixture (a provisionally molded body of the positive electrode mixture) and the porous metal substrate, and its thickness becomes the value described below.

[0045] The porosity of the porous metal substrate before compression is, for example, in the process of pressurizing the porous metal substrate and the cathode mixture (a provisionally molded body of the cathode mixture), in order to facilitate filling of the cathode mixture into the pores of the porous metal substrate and to facilitate integration of the metal substrate and the molded body of the cathode mixture, it is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. On the other hand, in order to increase the volume of the porous metal substrate to a certain level and increase the conductivity, its porosity is preferably 99.5% or less, more preferably 99% or less, and even more preferably 98.5% or less.

[0046] Furthermore, in the case of a positive electrode in which at least a portion of the porous metal substrate, including the end portion on the side of the molded body of the positive electrode mixture, is embedded in the surface layer portion of the molded body of the positive electrode mixture and is integrated with the molded body of the positive electrode mixture, the thickness of the portion of the porous metal substrate that is embedded in the molded body of the positive electrode mixture is preferably 10% or more, and more preferably 20% or more, of the thickness of the porous metal substrate (the thickness of the entire porous metal substrate, including the thickness of the portion where the molded body of the positive electrode mixture coexists; unless otherwise specified, the same applies hereinafter to the thickness of the porous metal substrate), from the viewpoint of more reliably integrating the porous metal substrate and the molded body of the positive electrode mixture.

[0047] In a positive electrode in which at least a portion of the porous metal substrate, including the end portion on the side of the molded body of the positive electrode mixture, is embedded in the surface layer portion of the molded body of the positive electrode mixture and integrated with the molded body of the positive electrode mixture, the conductive path in the exterior body of the all-solid-state secondary battery (the conductive path that the exterior body has in order to connect the power generation element to the terminal for connecting with an external device, etc., which the battery exterior body has. This also includes the conductive sheet and lead in FIG. 5 described later) In order to reduce the resistance when contacted with the conductive path, the end of the porous metal substrate opposite the molded body side of the positive electrode mixture (hereinafter sometimes referred to as the surface side end) is not embedded in the molded body of the positive electrode mixture, and it is desirable that the end of the positive electrode (surface of the positive electrode) is composed only of the porous metal substrate. That is, for example, in the manufacturing method of a power generation element described later, when manufacturing a positive electrode through a process of pressurizing the positive electrode mixture (provisional molded body of the positive electrode mixture) and the porous metal substrate, the porous metal substrate is compressed in the thickness direction, and the pores at the surface side end of the porous metal substrate are crushed and eliminated, and only the porous metal substrate is exposed on the surface of the positive electrode. It is desirable. However, some of the pores at the surface end of the porous metal substrate may not be crushed and remain as pores, or may be filled with a positive electrode mixture. A portion of the positive electrode mixture may be exposed to the surface of the positive electrode together with the surface end of the porous metal substrate, as long as it does not significantly affect the contact resistance with the conductive path. That is, as long as the surface end of the porous metal substrate can be exposed to the electrode surface, the entire porous metal substrate (100% of the thickness of the porous metal substrate) may be embedded in the surface layer of the molded positive electrode mixture. By filling the pores of the porous metal substrate up to the surface of the positive electrode with the positive electrode mixture, the integration of the molded positive electrode mixture and the porous metal substrate can be more reliably achieved.

[0048] 1 shows a scanning electron microscope (SEM) photograph for explaining the surface state of the positive electrode (note that the SEM photograph shown in FIG. 1 is not a photograph of the surface of the positive electrode of the present invention, but a photograph of a positive electrode having a surface state similar to that of the positive electrode of the present invention, and is shown only for the purpose of explaining the surface state of the positive electrode of the present invention). On the surface of the positive electrode shown in FIG. 1, the end of the porous metal substrate 201b is exposed, and part of the positive electrode mixture 201c also enters the pores present at the end of the porous metal substrate 201b and is thereby exposed on the surface of the positive electrode.

[0049] However, since the contact resistance between the porous metal substrate and the conductive path of the all-solid-state secondary battery increases as the proportion (area ratio) of the positive electrode mixture exposed on the surface of the positive electrode increases, the proportion of the area of ​​the exposed positive electrode mixture on the surface of the positive electrode is preferably 50% or less, more preferably 25% or less, even more preferably 15% or less, and particularly preferably 10% or less in plan view.

[0050] In the positive electrode, when at least a portion of the metal substrate is embedded in the surface layer portion of the molded body of the positive electrode mixture, from the viewpoint of more reliably integrating the porous metal substrate and the molded body of the positive electrode mixture, the thickness of the porous metal substrate is the overall thickness of the molded body of the positive electrode mixture (including the thickness of the portion coexisting with the porous metal substrate. Unless otherwise specified, the "thickness of the molded body of the positive electrode mixture" referred to below means the "total thickness of the molded body of the positive electrode mixture"). It is preferably 1% or more, more preferably 2% or more, and particularly preferably 3% or more. Furthermore, from the viewpoint of improving the filling property of the positive electrode mixture in the positive electrode, the thickness of the porous metal substrate is preferably 30% or less, more preferably 20% or less, and particularly preferably 10% or less of the thickness of the molded body of the positive electrode mixture.

[0051] In the positive electrode, the thickness of the porous metal substrate (thickness when formed into a positive electrode) is preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 30 μm or more, while it is preferably 300 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less.

[0052] The thickness of the molded body of the positive electrode mixture in the positive electrode is preferably 0.2 mm or more, more preferably 0.5 mm or more, and even more preferably 0.7 mm or more, and is preferably 3 mm or less, more preferably 2 mm or less, and even more preferably 1.5 mm or less.

[0053] The thickness of the porous metal substrate and the molded body of the positive electrode mixture in the positive electrode, and the thickness of the porous metal substrate and the molded body of the negative electrode mixture in the negative electrode described later are each determined by the maximum value of the thickness direction width of the region in which the porous metal substrate can be confirmed and the region in which the positive electrode mixture or the negative electrode mixture can be confirmed in an image obtained by observing a cross section of the thickness direction of the positive electrode or the negative electrode by SEM at a magnification of 50 to 1000 times. Further, the thickness of the portion of the porous metal substrate embedded in the molded body of the positive electrode mixture or the molded body of the negative electrode mixture is determined by the maximum value of the thickness direction width of the portion where the region in which the porous metal substrate can be confirmed and the region in which the positive electrode mixture or the negative electrode mixture can be confirmed overlap.

[0054] The proportion (area ratio) of the positive electrode mixture exposed on the surface of the positive electrode and the proportion (area ratio) of the negative electrode mixture exposed on the surface of the negative electrode described below are determined by the ratio (A / B) of the total area of ​​the positive electrode mixture or the negative electrode mixture: A to the total area of ​​the positive electrode or the negative electrode: B in an image of the surface of the positive electrode or the negative electrode observed with an SEM at a magnification of 50 to 200 times.

[0055] The positive electrode of the present invention can be produced, for example, by a method of press-molding a powdered positive electrode mixture and a porous metal substrate together; or a method of press-molding a powdered positive electrode mixture once to form a provisionally molded body, and then press-molding this provisionally molded body and a porous metal substrate together; but it is more preferable to produce it by the method of producing the power generation element of the present invention described below.

[0056] If the surface pressure during pressure molding is too high, the overall porosity of the molded body of the positive electrode mixture and the porous metal substrate becomes too small. Therefore, in order to ensure the above-mentioned porosity, it is necessary to adjust the surface pressure. Specifically, it is preferable to set the surface pressure at about the level described in the method for producing a power generation element, which will be described later.

[0057] <Power generating element> The power generating element of the present invention has a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode. The positive electrode of the power generating element has a molded body of a positive electrode mixture containing a positive electrode active material and a solid electrolyte, and a sheet-like porous metal substrate. The negative electrode of the power generating element has a molded body of a negative electrode mixture containing a negative electrode active material, and a sheet-like porous metal substrate.

[0058] In the power generation element of the present invention, from the viewpoint of improving the charge-discharge cycle characteristics in a high-temperature environment in an all-solid-state secondary battery using the same, the overall porosity of the molded body of the positive electrode mixture, the sheet-like porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the sheet-like porous metal substrate of the negative electrode is 14% or more, and preferably 15% or more. Note that if the overall porosity of the molded body of the positive electrode mixture, the sheet-like porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the sheet-like porous metal substrate of the negative electrode is too large, the discharge characteristics of the all-solid-state secondary battery at room temperature tend to deteriorate, and the charge-discharge cycle characteristics in a high-temperature environment also tend to deteriorate. Therefore, in the positive electrode of the present invention, from the viewpoint of improving the charge-discharge cycle characteristics of an all-solid-state secondary battery using the same in a high-temperature environment while suppressing as much as possible a deterioration in discharge characteristics at room temperature, the overall porosity of the molded body of the positive electrode mixture, the sheet-like porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the sheet-like porous metal substrate of the negative electrode is 22% or less, and preferably 20% or less.

[0059] As used herein, the porosity of the positive electrode mixture molded body, the positive electrode sheet-shaped porous metal substrate, the solid electrolyte layer, the negative electrode mixture molded body, and the negative electrode sheet-shaped porous metal substrate is the true density and composition ratio of each material constituting the positive electrode mixture molded body, the positive electrode sheet-shaped porous metal substrate, the solid electrolyte layer, the negative electrode mixture molded body, and the negative electrode sheet-shaped porous metal substrate, and the positive electrode mixture molded body, the positive electrode sheet-shaped porous metal substrate, the solid electrolyte layer, the negative electrode mixture molded body, and the negative electrode sheet-shaped porous metal substrate It is a value calculated from the total mass and volume. Note that, in the examples described below, since the shape of the power generation element is circular in plan view, the thickness and diameter were measured with a micrometer to calculate the volume.

[0060] The positive electrode of the power generating element can be the positive electrode of the present invention.

[0061] As the negative electrode active material in the molded negative electrode mixture for the negative electrode of the power generation element, for example, one or a mixture of two or more carbon-based materials capable of absorbing and releasing lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be used. Furthermore, simple substances, compounds, and alloys thereof containing elements such as Si, Sn, Ge, Bi, Sb, and In; compounds that can be charged and discharged at low voltages close to those of lithium metal, such as lithium-containing nitrides or lithium-containing oxides; lithium metal; and lithium / aluminum alloys can also be used as the negative electrode active material. For example, Li ４ Ti ５ O １２ and TiO ２ , NbO ２．５－δ (0≦δ≦0.5), MoO ３－δ (0≦δ≦1), WO ３－δ (0≦δ≦1), TiNb ２ O ７ Metal oxides such as WS ２ , MoS ２ or a mixture of two or more of these metal sulfides can also be used as the negative electrode active material.

[0062] The content of the negative electrode active material in the negative electrode mixture is preferably 50 to 95 mass %.

[0063] A solid electrolyte can be contained in the molded body of the negative electrode mixture. The solid electrolyte contained in the molded body of the negative electrode mixture can be the same as the various solid electrolytes exemplified above as the solid electrolytes that can be contained in the molded body of the positive electrode mixture. Among the solid electrolytes exemplified above, it is more preferable to use a sulfide-based solid electrolyte, and it is even more preferable to use an argyrodite-type sulfide-based solid electrolyte, because they have high Li ion conductivity and have the function of improving the moldability of the molded body of the negative electrode mixture.

[0064] The content of the solid electrolyte in the negative electrode mixture is preferably 4 to 70 mass %.

[0065] The molded negative electrode mixture may contain a conductive additive. Specific examples include carbon materials such as graphite (natural graphite, artificial graphite), graphene, carbon black, vapor-grown carbon fiber, carbon nanofiber, and carbon nanotube. The content of the conductive additive in the negative electrode mixture is preferably 1 to 10 mass %.

[0066] The molded body of the negative electrode mixture may contain a binder, but it does not have to contain a binder if good moldability can be ensured without using a binder, such as in the case of a negative electrode in which a sulfide-based solid electrolyte is contained and powder of the negative electrode mixture is charged into a molding die and compacted.

[0067] When a binder is required in the molded negative electrode mixture, the content thereof in the negative electrode mixture is preferably 15% by mass or less, and preferably 0.5% by mass or more. On the other hand, when good moldability can be obtained in the molded negative electrode mixture without the inclusion of 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 included).

[0068] As with the positive electrode, the sheet-like porous metal substrate that functions as the current collector for the negative electrode can be made of a plain woven wire mesh, expanded metal, or the like, but it is preferable to use a foamed porous metal (such as Celmet (registered trademark) from Sumitomo Electric Industries, Ltd.) The material for the porous metal substrate for the negative electrode can be aluminum, titanium, nickel, tungsten, or an alloy thereof (such as a nickel-chromium alloy, a nickel-tin alloy, a titanium-aluminum alloy, or a titanium-aluminum-vanadium alloy); austenitic stainless steel (such as SUS304 or SUS316); or the like.

[0069] In the case of the negative electrode, at least a portion of the negative electrode mixture penetrates into the pores of the porous metal substrate, thereby improving the adhesion between the porous metal substrate and the molded body of the negative electrode mixture, and increasing the contact area between the molded body of the negative electrode mixture and the porous metal substrate, thereby making it possible to further reduce the resistance of the negative electrode.

[0070] That is, it is preferable that at least a portion of the negative electrode mixture is filled into the pores of the porous metal substrate. More specifically, it is preferable that at least a portion of the porous metal substrate of the negative electrode, including the end portion of the negative electrode mixture on the molded body side, is embedded in the surface layer portion of the molded body of the negative electrode mixture and is integrated with the molded body of the negative electrode mixture.

[0071] In addition, such a porous metal substrate usually has a thickness before use in a negative electrode (power generating element) that is greater than the aforementioned thickness (thickness within the negative electrode) (for example, the thickness before compression is preferably 0.1 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.5 mm or more, while preferably 3 mm or less, more preferably 2 mm or less, and particularly preferably 1.5 mm or less), and is compressed in the thickness direction during the production of the power generating element described below, so that the thickness becomes the value described below.

[0072] The porosity of the porous metal substrate before compression is preferably 80% or more, more preferably 90% or more, and particularly preferably 95% or more, in order to facilitate the filling of the pores of the porous metal substrate with the negative electrode mixture in the process of pressurizing the porous metal substrate and the negative electrode mixture, and to facilitate the integration of the porous metal substrate and the molded body of the negative electrode mixture. On the other hand, in order to increase the amount of the substrate by a certain amount or more and to increase the conductivity, the porosity is preferably 99.5% or less, more preferably 99% or less, and particularly preferably 98.5% or less.

[0073] In the negative electrode, the thickness of the portion of the porous metal substrate that is embedded in the molded body of the negative electrode mixture is preferably 10% or more, and more preferably 20% or more, of the thickness of the porous metal substrate (the thickness of the entire porous metal substrate, including the thickness of the portion where the molded body of the negative electrode mixture coexists; unless otherwise specified, the same applies hereinafter to the thickness of the porous metal substrate), from the viewpoint of more reliably integrating the porous metal substrate and the molded body of the negative electrode mixture.

[0074] Even in a negative electrode in which at least a portion of the porous metal substrate, including the end portion on the negative electrode mixture molding side, is embedded in the surface layer of the negative electrode mixture molding and integrated with the negative electrode mixture molding, for the same reasons as in the case of the positive electrode, the end portion of the porous metal substrate opposite the negative electrode mixture molding side is not embedded in the negative electrode mixture molding, and the end portion of the negative electrode (the surface of the negative electrode) is preferably composed only of the porous metal substrate. That is, for example, during the production of the power generation element described below, when the porous metal substrate is compressed in the thickness direction, it is desirable that the pores at the end of the porous metal substrate are crushed and disappear, and only the porous metal substrate is exposed on the surface of the negative electrode. However, some of the pores at the end of the porous metal substrate may not be crushed and may be filled with the negative electrode mixture, and a portion of the negative electrode mixture may be exposed on the surface of the negative electrode together with the end of the porous metal substrate, as long as it does not significantly affect the contact resistance with the conductive path of the battery.

[0075] However, since the contact resistance between the porous metal substrate and the conductive path of the battery exterior increases as the proportion (area ratio) of the negative electrode mixture exposed on the surface of the negative electrode increases, it is desirable that the proportion of the area of ​​the exposed negative electrode mixture on the negative electrode surface be 50% or less in plan view, more desirably 25% or less, even more desirably 15% or less, and particularly desirably 10% or less.

[0076] In the negative electrode, when at least a portion of the porous metal substrate is embedded in the molded body of the negative electrode mixture, from the viewpoint of more reliably integrating the porous metal substrate and the molded body of the negative electrode mixture, the thickness of the porous metal substrate is the overall thickness of the molded body of the negative electrode mixture (including the thickness of the portion coexisting with the porous metal substrate. Unless otherwise specified, the "thickness of the molded body of the negative electrode mixture" referred to below means the "total thickness of the molded body of the negative electrode mixture"). It is preferably 1% or more, more preferably 2% or more, and particularly preferably 3% or more. Furthermore, from the viewpoint of improving the filling property of the molded body of the negative electrode mixture in the negative electrode, the thickness of the porous metal substrate is preferably 30% or less, more preferably 20% or less, and particularly preferably 10% or less of the thickness of the molded body of the negative electrode mixture.

[0077] In the negative electrode, the thickness of the porous metal substrate is preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 30 μm or more, while it is preferably 300 μm or less, more preferably 200 μm or less, and particularly preferably 100 μm or less. The thickness of the molded body of the negative electrode mixture is preferably 0.2 mm or more, more preferably 0.5 mm or more, and particularly preferably 0.7 mm or more, while it is preferably 2 mm or less, more preferably 1.7 mm or less, and particularly preferably 1.5 mm or less.

[0078] The overall porosity of the molded negative electrode mixture and the sheet-like porous metal substrate of the negative electrode (a porosity determined in the same manner as the overall porosity of the molded positive electrode mixture and the sheet-like porous metal substrate of the positive electrode) is preferably 14% or more, more preferably 15% or more, and is preferably 21% or less.

[0079] The negative electrode can be manufactured by, for example, a method of press-molding a powdered negative electrode mixture together with a porous metal substrate; a method of press-molding a powdered negative electrode mixture once to form a provisionally molded body, and then press-molding this provisionally molded body together with a porous metal substrate; or the like. However, it is more preferable to manufacture the negative electrode by the method of manufacturing a power generation element described below.

[0080] Specific examples of the solid electrolyte constituting the solid electrolyte layer of the power generation element include the same solid electrolytes as those exemplified above as the solid electrolytes that can be contained in the molded body of the positive electrode mixture. Among the solid electrolytes exemplified above, it is more preferable to use a sulfide-based solid electrolyte, and it is even more preferable to use an argyrodite-type sulfide-based solid electrolyte, because they have high Li ion conductivity and also have the function of improving the moldability of the solid electrolyte layer.

[0081] The solid electrolyte layer may contain a binder such as an acrylic resin or a fluororesin to maintain its shape.

[0082] The thickness of the solid electrolyte layer is preferably 10 to 200 μm.

[0083] The porosity of the solid electrolyte layer (determined in the same manner as the porosity of the molded body of the positive electrode mixture and the entire sheet-like porous metal substrate) is preferably 15 to 24%.

[0084] The solid electrolyte layer can be produced, for example, by pressure molding a powdered solid electrolyte (or a mixture of a solid electrolyte and a binder), but it is more preferable to produce it by the method for producing a power generating element described below.

[0085] The power generating element can be manufactured, for example, by a manufacturing method including the following first to third steps.

[0086] In the first step, the electrode mixture (positive electrode mixture or negative electrode mixture) is placed in a mold and pressure-molded to form a temporary molded body of the electrode mixture. The surface pressure of the pressure-molding in the first step is preferably, for example, 30 to 500 MPa.

[0087] In the next step, a porous metal substrate is placed on the temporary molded body of the electrode mixture pressure-molded in step 1, and then in step 3, the temporary molded body of the electrode mixture and the porous metal substrate are pressed together. By pressing in step 3, the electrode mixture is further compressed while the porous metal substrate is embedded in the electrode mixture from the end on the electrode mixture side, and the porous metal substrate is compressed in the thickness direction, so that the molded body of the electrode mixture (the molded body of the positive electrode mixture or the molded body of the negative electrode mixture) and the porous metal substrate are integrated to form an electrode (positive electrode or negative electrode).

[0088] As described above, in this third step, the porous metal substrate is compressed in the thickness direction, and the degree of compression is such that, from the viewpoint of more reliably bonding the porous metal substrate and the molded body of the electrode mixture, the thickness of the porous metal substrate after compression is preferably 30% or less of the thickness before compression, more preferably 20% or less, and particularly preferably 10% or less. Furthermore, from the viewpoint of retaining a certain amount of electrode mixture in the voids of the porous metal substrate and increasing the bonding strength between the porous metal substrate and the molded body of the electrode mixture, the thickness of the porous metal substrate after compression in the third step is preferably 1% or more of the thickness before compression, more preferably 2% or more.

[0089] The surface pressure during pressing in the third step is, for example, preferably 200 MPa or more, more preferably 250 MPa or more, preferably 550 MPa or less, and more preferably 500 MPa or less. By pressing at such a surface pressure, it is possible to adjust the overall porosity of the molded body of the positive electrode mixture and the porous metal substrate to the above-mentioned value, or to adjust the overall porosity of the molded body of the positive electrode mixture, the sheet-like porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the sheet-like porous metal substrate of the negative electrode to the above-mentioned value.

[0090] Furthermore, by going through the first to third steps, it is possible to obtain an electrode (positive electrode or negative electrode) in which at least a portion of the porous metal substrate, including the end portion thereof on the molded body side of the electrode mixture (a certain range in the thickness direction from the end portion of the porous metal substrate), is embedded in the molded body of the electrode mixture and is integrated with the molded body of the electrode mixture, and the other end portion of the porous metal substrate is exposed on the surface of the electrode.

[0091] If the surface pressure during the application of pressure in the third step becomes too high, cracks may occur when the porous metal substrate is compressed. However, even if the substrate is broken into pieces, the ends of the pieces can contribute to reducing the contact resistance as long as they are exposed on the surface of the electrode.

[0092] A positive electrode and a negative electrode are prepared through the first, second and third steps, and are then arranged on both sides of a solid electrolyte layer, and pressurized as necessary to produce a power generating element.

[0093] Furthermore, before the first step, a preliminary step may be provided in which the solid electrolyte is poured into a mold and pressure-molded to form a temporary solid electrolyte body, and an electrode mixture (a positive electrode mixture or a negative electrode mixture) is placed on the temporary solid electrolyte body pressure-molded in this preliminary step. Thereafter, the first step, the second step, and the third step are carried out in sequence, thereby producing an integrated product of the solid electrolyte layer and the electrode (a positive electrode or a negative electrode), which can be used to manufacture a power generation element.

[0094] The surface pressure during pressure molding in the preliminary step is preferably set to, for example, 30 to 200 MPa.

[0095] Furthermore, the power generating element can also be manufactured as an integrally molded body by forming one of the positive and negative electrodes on one side of the solid electrolyte layer through the preliminary step, the first step, the second step, and the third step, and then sequentially performing the first step, the second step, and the third step on the other side of the solid electrolyte layer to form the other electrode (negative electrode or positive electrode).

[0096] Furthermore, it is particularly preferable to manufacture a power generating element as an integrally molded body by carrying out the first and second steps from the preliminary step to form an integrated body of a provisionally molded body of a positive electrode mixture or a negative electrode mixture and a porous metal substrate on one side of the provisionally molded body of a solid electrolyte layer, then carrying out the first and second steps on the other side of the solid electrolyte layer to form an integrated body of a provisionally molded body of a negative electrode mixture or a positive electrode mixture and a porous metal substrate, and subsequently carrying out the third step to form a positive electrode, a solid electrolyte layer, and a negative electrode. In this case, by applying pressure in the third step at the above-mentioned surface pressure, it becomes easy to adjust the overall porosity of the molded body of a positive electrode mixture and the porous metal substrate, as well as the overall porosity of the molded body of a positive electrode mixture, the sheet-like porous metal substrate of a positive electrode, the solid electrolyte layer, the molded body of a negative electrode mixture, and the sheet-like porous metal substrate of a negative electrode, to the above-mentioned value.

[0097] In this specification, the term "integrally molded body" in the context of a power generation element refers to a power generation element obtained by using a single molding die to form a positive electrode, a solid electrolyte layer, and a negative electrode to form a power generation element, continuously forming each layer without removing the layer from the die, and then removing the resulting power generation element from the die after it has all of the layers. A power generation element obtained by this procedure is presumed to have a different structure at the interface between the positive electrode (molded body of the positive electrode mixture) and the solid electrolyte layer, and at the interface between the negative electrode (molded body of the negative electrode mixture) and the solid electrolyte layer, from a power generation element obtained by molding the positive electrode, the solid electrolyte layer, and the negative electrode separately, laminating these, and applying pressure to the entirety. For example, the power generation element obtained by this procedure is expected to have a higher degree of adhesion between the positive electrode and the solid electrolyte layer, and between the negative electrode and the solid electrolyte layer, and to ensure better properties.

[0098] <All-solid-state secondary battery> The all-solid-state secondary battery of the present invention includes a power generation element having a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode, housed in an exterior body, and the positive electrode is the positive electrode of the present invention, or the power generation element is the power generation element of the present invention. The all-solid-state secondary battery of the present invention may include one power generation element or multiple power generation elements.

[0099] When the positive electrode of the all-solid-state secondary battery is the positive electrode of the present invention, the negative electrode and the solid electrolyte layer can be the same as the negative electrode and the solid electrolyte layer of the power generating element of the present invention.

[0100] An example of the all-solid-state secondary battery of the present invention will be described below with reference to the drawings. Fig. 2 is an external perspective view of the all-solid-state secondary battery, and Fig. 3 is a cross-sectional view taken along line II in Fig. 2.

[0101] The all-solid-state secondary battery 1 shown in FIGS. 2 and 3 includes a cell assembly 21 having an electrode body 20 formed by stacking six power generation elements 20 a, 20 b, 20 c, 20 d, 20 e, and 20 f, housed in an exterior body made up of a cylindrical exterior can 10 with a bottom and a lid 50.

[0102] The outer can 10 has a bottom surface 101 and a side surface 102. A plurality of recesses 103 extending from the lower end toward the upper direction in the figure are formed on the outer peripheral wall surface of the side surface 102 by, for example, pressing. This increases the rigidity of the outer can 10, and therefore prevents the outer can 10 from being easily crushed or damaged when a strong external force is applied to the outer can 10.

[0103] Furthermore, by forming the recess 103, a protrusion that protrudes toward the inside of the exterior can 10 is formed on the inner peripheral wall surface of the side surface 102 of the exterior can 10 at the position where the recess 103 is formed. This protrusion comes into contact with the side surface of the cell assembly 21 (the side surface of the electrode body 20) when the cell assembly 21 having the electrode body 20 is housed inside the exterior can 10. This prevents the cell assembly 21 (the electrode body 20 housed therein) from vibrating inside the exterior can 10.

[0104] The recess 103 does not have to be formed in the exterior can 10. In this case, for example, the cell assembly 21 (electrode body 20) and the inner peripheral wall surface of the side surface 102 of the exterior can 10 can be fixed by adhesive. Also, a sealing member made of a non-conductive material such as resin may be disposed in the gap between the cell assembly 21 (electrode body 20) and the inner peripheral wall surface of the side surface 102 of the exterior can 10 to fill the gap.

[0105] The exterior can 10 can be made of aluminum, stainless steel, nickel alloy, or the like.

[0106] The lid 50 has a metal terminal 52 attached to a metal body 51 via an insulator 53 made of resin (e.g., polypropylene), glass hermetic, ceramic hermetic, or the like. When using an electrolyte that decomposes due to atmospheric moisture, such as a sulfide or hydride, as the solid electrolyte, it is desirable to use a more airtight glass hermetic or ceramic hermetic. The lid 50 is inserted into the opening of the outer can 10, and the opening of the outer can 10 is sealed by welding the joint between the two, thereby sealing the interior of the battery. An insulating sheet 54 is attached to the underside of the body 51 of the lid 50 (the surface facing the inside of the battery). A connection lead 60 is attached to the surface of the terminal 52 facing the inside of the battery for electrically connecting the electrode body 20 and the terminal 52.

[0107] The main body 51 and terminals 52 of the lid 50 can be made of aluminum, stainless steel, nickel alloy, or the like.

[0108] The cell assembly 21 includes an electrode body 20 , a holder 22 , a positive electrode lead 30 , and a negative electrode lead 40 .

[0109] 4 shows an exploded perspective view of the cell assembly 21. In the cell assembly 21, six power generation elements 20a, 20b, 20c, 20d, 20e, and 20f and insulating plates 210a, 210b, 210c, 210d, and 210e interposed therebetween are arranged in the vertical direction in the figure to form the electrode body 20. In this manner, a plurality of power generation elements can be accommodated in the cylindrical outer can, and the size of the all-solid-state battery can be increased.

[0110] Each of the individual power generating elements 20a, 20b, 20c, 20d, 20e, and 20f of the electrode assembly 20 is configured by sequentially stacking a positive electrode 201, a solid electrolyte layer 203, and a negative electrode 202. These power generating elements 20a, 20b, 20c, 20d, 20e, and 20f are stacked vertically in the drawing and connected in parallel to each other as described below to configure the electrode assembly 20. Note that in Figs. 3 and 4, in order to avoid complicating the drawings, the molded body of the positive electrode mixture and the porous metal substrate of the positive electrode 201 are not distinguished from each other, and the molded body of the negative electrode mixture and the porous metal substrate of the negative electrode 202 are not distinguished from each other.

[0111] The electrode body 20 is formed by stacking each power generating element 20a, 20b, 20c, 20d, 20e, and 20f so that the positive and negative electrodes of adjacent power generating elements face each other with insulating plates 210a, 210b, 210c, 210d, and 210e interposed therebetween.

[0112] A positive electrode tab 204 and a negative electrode tab 205 can be attached to the positive electrode 201 and the negative electrode 202 of each of the power generation elements 20a, 20b, 20c, 20d, 20e, and 20f, respectively. Then, by connecting the positive electrode tabs 204 of all the power generation elements to the positive electrode lead 30 and the negative electrode tabs 205 of all the power generation elements to the negative electrode lead 40 by welding or the like, each of the power generation elements 20a, 20b, 20c, 20d, 20e, and 20f in the electrode body 20 can be connected in parallel.

[0113] The positive electrode tab 204 can be attached to the porous metal substrate of the positive electrode 201 by welding or the like, and the negative electrode tab 205 can also be attached to the porous metal substrate of the negative electrode 202 by welding or the like.

[0114] The electrode body 20 is held from below, the sides, and above by a holder 22. The holder 22 is composed of a first holding portion 23 that holds the bottom and sides of the electrode body 20, and a second holding portion 24 that is positioned above the electrode body 20. The first holding portion 23 has a bottom holding portion 231 and multiple side holding portions 232 (four in FIG. 4 ) that extend upward in the figure from the bottom holding portion 231. A hook-shaped bent portion 232 a is provided above the side holding portion 232.

[0115] To hold the electrode body 20 with the holder 22, for example, the electrode body 20 is placed on the bottom holding portion 231 of the first holding portion 23 via a sheet 233 made of a silicone material or the like, and the second holding portion 24 is then placed above the electrode body 20. The bent portion 232a at the tip of the side holding portion 232 of the first holding portion 23 is fitted into a fixing portion provided on the second holding portion 24, thereby fixing the side holding portion 232 and the second holding portion 24. In this way, the electrode body 20 is held within the holder 22 formed by the first holding portion 23 and the second holding portion 24.

[0116] The sheet 233 does not have to be used, but by using it, the electrode body 20 can be easily rotated within the holder 22, which makes it easier to align the electrodes, for example, when welding the positive electrode tab 204 to the positive electrode lead 30 or welding the negative electrode tab 205 to the negative electrode lead 40.

[0117] The side surfaces of the cell assembly 21 can be covered with a heat-shrinkable tube 213 made of insulating resin such as polyethylene or various elastomers. This heat-shrinkable tube 213 can insulate the electrode body 20 from the metal outer can 10, for example.

[0118] In addition, the side surfaces and parts of the upper and lower surfaces of each of the power generating elements 20a, 20b, 20c, 20d, 20e, and 20f can also be covered with a heat-shrinkable tube 212 made of insulating resin such as polyethylene or various elastomers.

[0119] In an all-solid-state secondary battery having a plurality of power generating elements, these power generating elements may be connected in parallel to each other as shown in FIG. 3, or may be connected in series to each other.

[0120] When the cell assembly 21 is enclosed in the exterior body, first, a buffer sheet 104 is placed on the inner bottom surface of the exterior can 10 as needed, and then the cell assembly 21 is placed on top of that. The negative electrode lead 40 of the cell assembly 21 is connected to the inner surface of the exterior can 10 by, for example, welding, etc. This allows the exterior can 10 to also serve as the negative electrode terminal.

[0121] Furthermore, the positive electrode lead 30 of the cell assembly 21 is connected to the connection lead 60 of the lid 50 by welding or the like. This allows the terminal 52 to function as a positive electrode terminal. Thereafter, the lid 50 is placed over the open end of the outer can 10 and sealed. In this manner, the all-solid-state secondary battery 1 can be obtained.

[0122] A part of the positive electrode lead 30 (for example, a part located on the upper surface side of the cell assembly 21) is exposed and not covered with the heat shrink tube 213. Therefore, in order to prevent contact between the exposed part of the positive electrode lead 30 and the outer casing 10, the exposed part of the positive electrode lead 30 may be covered with an insulating seal 206.

[0123] Although FIG. 3 shows an all-solid-state secondary battery in which the outer can 10 also functions as a negative electrode terminal and the terminal 52 functions as a positive electrode terminal, the battery may also be configured so that the outer can 10 also functions as a positive electrode terminal and the terminal 52 functions as a negative electrode terminal, as necessary.

[0124] 5 is a cross-sectional view schematically illustrating another example of the all-solid-state secondary battery of the present invention. The all-solid-state secondary battery 2 shown in Fig. 5 is configured by enclosing a power generating element 20g having a positive electrode 201, a negative electrode 202, and a solid electrolyte layer 203 interposed therebetween in an exterior body formed by an exterior container 300 and a lid 310.

[0125] External terminals 320 and 330 for electrically connecting the all-solid-state secondary battery 2 to an application device are provided on the bottom surface of the outer container 300 in the figure. The external terminal 320 is electrically connected to the positive electrode 201 of the power generating element 20g through a conductive path 321. The external terminal 330 is electrically connected to the negative electrode 202 of the power generating element 20g through a lead 340 and a conductive path 331.

[0126] The positive electrode 201 has a molded positive electrode mixture body 201a and a porous metal substrate 201b, and the entire porous metal substrate 201b, including the end portion thereof on the side of the molded positive electrode mixture body 201a, is embedded in the surface layer portion of the molded positive electrode mixture body 201a. That is, the entire location of the porous metal substrate 201b corresponds to the region where the molded positive electrode mixture body and the porous metal substrate coexist, i.e., the surface layer portion of the molded positive electrode mixture body. Furthermore, in the positive electrode 201, the end portion of the porous metal substrate 201b opposite the molded positive electrode mixture body 201a side (the lower end portion in FIG. 5 ) is exposed to the surface. The dotted line in the positive electrode 201 indicates the boundary between the region in the positive electrode mixture molded body 201a where the porous metal substrate does not coexist and the region in which the positive electrode mixture molded body and the porous metal substrate coexist, and corresponds to the end of the porous metal substrate 201b on the positive electrode mixture molded body 201a side.

[0127] The negative electrode 202 has a molded negative electrode mixture body 202a and a porous metal substrate 202b, and the entire porous metal substrate 202b, including the end portion thereof on the side of the molded negative electrode mixture body 202a, is embedded in the surface layer portion of the molded negative electrode mixture body 202a. That is, the entire location of the porous metal substrate 202b corresponds to the region where the molded negative electrode mixture body and the porous metal substrate coexist, i.e., the surface layer portion of the molded negative electrode mixture body. Furthermore, in the negative electrode 202, the end portion of the porous metal substrate 202b opposite the molded negative electrode mixture body 202a side (the upper end portion in FIG. 5 ) is exposed to the surface. The dotted line in the negative electrode 202 indicates the boundary between the region in the negative electrode mixture molded body 202a where the porous metal substrate does not coexist and the region where the negative electrode mixture molded body and the porous metal substrate coexist, and corresponds to the end of the porous metal substrate 202b on the negative electrode mixture molded body 202a side.

[0128] A conductive sheet (metal foil, foamed metal porous body, etc.) 360 is arranged on the surface of the porous metal substrate 201b of the positive electrode 201 (the surface opposite to the side of the molded body 201a of the positive electrode mixture), and the positive electrode 201 is in contact with the porous metal substrate 201, thereby establishing electrical conduction with the conductive sheet 360, and this conductive sheet 360 is in electrical conduction with the electrical conduction path 321.

[0129] 5, a spacer 350 having the effect of pressing the power generating element 20g toward the conductive sheet 360 is disposed between the lead 340 and the lid 310, and the effect of this spacer 350 improves the electrical connection between the lead 240 and the negative electrode 202 and the conductive path 331, the electrical connection between the positive electrode 201 and the conductive sheet 360, and the electrical connection between the conductive sheet 360 and the conductive path 321. A rubber plate, a metal spring (such as a leaf spring), or the like can be used as the spacer 350.

[0130] In an exterior package consisting of a case having an exterior container and a sealing member as shown in Fig. 5, the exterior container can be made of ceramics or resin. The lid can be made of ceramics, resin, or metal (such as an iron-nickel alloy or an iron-nickel-cobalt alloy, or an iron-based alloy). Furthermore, in the exterior container, the external terminals and the conductive paths connecting the electrodes of the electrode stack to the external terminals can be made of metals such as manganese, cobalt, nickel, copper, molybdenum, silver, palladium, tungsten, platinum, and gold, or alloys containing these metals.

[0131] The outer container and the lid can be sealed by bonding them together with an adhesive. In addition, when a metal lid is used, the lid side of the side wall of the recess in the outer container can be made of metal (an iron-based alloy such as an iron-nickel alloy or an iron-nickel-cobalt alloy), and the lid can be welded to this or brazed with an alloy such as gold-tin (Au-Sn) to achieve sealing.

[0132] Furthermore, when both the outer container and the lid are made of ceramic, they can be sealed by welding with low-melting glass.

[0133] In addition to those shown in FIGS. 2, 3, and 5, flat (coin-shaped or button-shaped) exterior bodies having an exterior can and a sealing can; those made of a metal laminate film; and the like can also be applied to the exterior bodies of the all-solid-state secondary battery of the present invention.

[0134] The shape of the exterior body in a plan view may be circular or may be polygonal such as quadrilateral (square or rectangle).

[0135] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0136] (Example 1) Lithium titanate (Li) having an average particle size of 2 μm ４ Ti ５ O １２ , negative electrode active material) and a sulfide-based solid electrolyte (Li ６ P.S. ５ Cl) and graphene (conductive additive) were mixed in a mass ratio of 50:41:9 to prepare a negative electrode mixture.

[0137] In addition, LiNbO ３ LiCoO having an average particle size of 5 μm on which a coating layer of ２ (positive electrode active material) and a sulfide-based solid electrolyte (Li ６ P.S. ５ Cl) and graphene were mixed in a mass ratio of 65:30.7:4.3 to prepare a positive electrode mixture.

[0138] Next, a sulfide-based solid electrolyte (Li ６ P.S. ５ A powder of HCl) was placed in a powder molding die and subjected to pressure molding at a surface pressure of 59 MPa using a press to form a provisionally molded body of a solid electrolyte. Furthermore, the negative electrode mixture was placed on the upper surface of the provisionally molded body of the solid electrolyte and pressure molding was performed at a surface pressure of 47 MPa to form a provisionally molded body of the negative electrode mixture on the provisionally molded body of the solid electrolyte.

[0139] Furthermore, a circular piece (thickness: 1.2 mm, porosity: 98%) of nickel foamed porous metal (nickel Celmet (registered trademark)) manufactured by Sumitomo Electric Industries, Ltd. was placed on the pre-molded body of the negative electrode mixture, and pressure molding was performed at a surface pressure of 196 MPa to form an integrated body of the solid electrolyte pre-molded body, the pre-molded body of the negative electrode mixture, and the porous metal substrate (current collector) for the negative electrode.

[0140] Furthermore, after the mold was turned upside down, the positive electrode mixture was placed on the upper surface of the provisionally molded solid electrolyte body in the mold (the side opposite to the surface having the provisionally molded negative electrode mixture body), and molding was performed with a surface pressure of 47 MPa, thereby forming a provisionally molded positive electrode body on the provisionally molded solid electrolyte body.

[0141] Next, a cut piece of the same nickel foamed porous metal body used for the negative electrode was placed on the provisionally molded positive electrode body formed on the provisionally molded solid electrolyte body, and pressure molding was performed at a surface pressure of 441 MPa to obtain a power generation element having a positive electrode in which a porous metal substrate was embedded in the surface layer portion of the molded positive electrode mixture body, a solid electrolyte layer, and a negative electrode in which a porous metal substrate was embedded in the surface layer portion of the molded negative electrode mixture body.

[0142] In the obtained power generation element, the thickness of the molded body of the positive electrode mixture, the thickness of the porous metal substrate of the positive electrode (the thickness of the portion not embedded in the molded body of the positive electrode mixture; the same applies to the thickness of the porous metal substrate of the positive electrode in each of the Examples and Comparative Examples described later), the thickness of the molded body of the negative electrode mixture, the thickness of the porous metal substrate of the negative electrode (the thickness of the portion not embedded in the molded body of the negative electrode mixture; the same applies to the thickness of the porous metal substrate of the negative electrode in each of the Examples and Comparative Examples described later), the thickness of the solid electrolyte layer, and the thickness of the entire power generation element (the thickness of the molded body of the positive electrode mixture, the porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the porous metal substrate of the negative electrode). The overall thickness of the material. The same applies to the overall thickness of the power generation element in each of the examples and comparative examples described below.) was 0.75 mm, 0.07 mm, 1.32 mm, 0.07 mm, 0.14 mm, and 2.35 mm, respectively, the overall porosity of the molded body of the positive electrode mixture and the porous metal substrate in the positive electrode was 16.0%, the overall porosity of the molded body of the negative electrode mixture and the porous metal substrate in the negative electrode was 16.0%, the porosity of the solid electrolyte layer was 16.7%, and the overall porosity of the molded body of the positive electrode mixture, the porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the porous metal substrate of the negative electrode in the power generation element was 15.2%.

[0143] The outer container (ceramic depth 2.5 mm) had a cross-sectional structure similar to that shown in FIG. 5 , was made of ceramics, and had a seal ring made of an iron-nickel-cobalt alloy placed on the top of the sidewall. The same nickel foamed metal porous material used for the positive and negative electrodes was cut to a diameter of 7.25 mm and placed on the inner bottom surface of the container. The power generation element was placed on top of it, with the positive electrode facing downwards. A lead (Ni foil) was placed on the negative electrode of the power generation element, and a 400 μm thick rubber sheet (spacer) was then placed on top of that. A lid made of an iron-nickel-cobalt alloy was then placed on the sidewall of the recess in the outer container. The rubber sheet was compressed in the thickness direction while the lid and outer container were welded together, sealing the outer container and the lid, resulting in an all-solid-state secondary battery. In the resulting all-solid-state secondary battery, the rubber sheet serving as a spacer was compressed in the thickness direction, causing the power generation element to press against the conductive sheet made of foamed metal porous material. The thickness of the conductive sheet in the all-solid-state secondary battery was 200 μm.

[0144] Example 2 A power generating element was produced in the same manner as in Example 1, except that the surface pressure during pressure molding after placing the porous metal substrate on the preform of the positive electrode was changed to 392 MPa.

[0145] In the obtained power generation element, the thickness of the molded positive electrode mixture, the thickness of the porous metal substrate of the positive electrode, the thickness of the molded negative electrode mixture, the thickness of the porous metal substrate of the negative electrode, the thickness of the solid electrolyte layer, and the thickness of the entire power generation element were 0.76 mm, 0.07 mm, 1.31 mm, 0.07 mm, 0.14 mm, and 2.35 mm, respectively. The overall porosity of the molded positive electrode mixture and porous metal substrate in the positive electrode was 17.1%, the overall porosity of the molded negative electrode mixture and porous metal substrate in the negative electrode was 17.1%, the porosity of the solid electrolyte layer was 17.9%, and the overall porosity of the molded positive electrode mixture, porous metal substrate of the positive electrode, solid electrolyte layer, molded negative electrode mixture, and porous metal substrate of the negative electrode in the power generation element was 16.9%.

[0146] An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the power generating element was used.

[0147] Example 3 A power generating element was produced in the same manner as in Example 1, except that the surface pressure during pressure molding after placing the porous metal substrate on the preform of the positive electrode was changed to 294 MPa.

[0148] In the obtained power generation element, the thickness of the molded positive electrode mixture, the thickness of the porous metal substrate of the positive electrode, the thickness of the molded negative electrode mixture, the thickness of the porous metal substrate of the negative electrode, the thickness of the solid electrolyte layer, and the thickness of the entire power generation element were 0.76 mm, 0.07 mm, 1.31 mm, 0.07 mm, 0.15 mm, and 2.36 mm, respectively. The overall porosity of the molded positive electrode mixture and porous metal substrate in the positive electrode was 17.1%, the overall porosity of the molded negative electrode mixture and porous metal substrate in the negative electrode was 19.4%, and the porosity of the solid electrolyte layer was 20.8%. The overall porosity of the molded positive electrode mixture, porous metal substrate of the positive electrode, solid electrolyte layer, molded negative electrode mixture, and porous metal substrate of the negative electrode in the power generation element was 20.4%.

[0149] An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the power generating element was used.

[0150] Comparative Example 1 A power generating element was produced in the same manner as in Example 1, except that the surface pressure during pressure molding after placing the porous metal substrate on the provisionally molded body of the positive electrode was changed to 588 MPa.

[0151] In the obtained power generation element, the thickness of the molded positive electrode mixture, the thickness of the porous metal substrate of the positive electrode, the thickness of the molded negative electrode mixture, the thickness of the porous metal substrate of the negative electrode, the thickness of the solid electrolyte layer, and the thickness of the entire power generation element were 0.75 mm, 0.07 mm, 1.31 mm, 0.07 mm, 0.15 mm, and 2.34 mm, respectively, the overall porosity of the molded positive electrode mixture and porous metal substrate in the positive electrode was 13.1%, the overall porosity of the molded negative electrode mixture and porous metal substrate in the negative electrode was 13.1%, the porosity of the solid electrolyte layer was 13.7%, and the overall porosity of the molded positive electrode mixture, porous metal substrate of the positive electrode, solid electrolyte layer, molded negative electrode mixture, and porous metal substrate of the negative electrode in the power generation element was 12.2%.

[0152] An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the power generating element was used.

[0153] Comparative Example 2 A power generating element was produced in the same manner as in Example 1, except that the surface pressure during pressure molding after placing the porous metal substrate on the provisionally molded body of the positive electrode was changed to 196 MPa.

[0154] In the obtained power generation element, the thickness of the molded positive electrode mixture, the thickness of the porous metal substrate of the positive electrode, the thickness of the molded negative electrode mixture, the thickness of the porous metal substrate of the negative electrode, the thickness of the solid electrolyte layer, and the thickness of the entire power generation element were 0.79 mm, 0.07 mm, 1.33 mm, 0.07 mm, 0.16 mm, and 2.42 mm, respectively, the porosity of the entire positive electrode mixture molded body and porous metal substrate in the positive electrode was 22.0%, the porosity of the entire negative electrode mixture molded body and porous metal substrate in the negative electrode was 22.0%, the porosity of the entire solid electrolyte layer was 25.0%, and the porosity of the entire positive electrode mixture molded body, porous metal substrate of the positive electrode, solid electrolyte layer, negative electrode mixture molded body, and porous metal substrate of the negative electrode in the power generation element was 23.6%.

[0155] An all-solid-state secondary battery was fabricated in the same manner as in Example 1, except that the power generating element was used.

[0156] The following evaluations were carried out on each of the all-solid-state secondary batteries of the Examples and Comparative Examples.

[0157] <Initial Resistance Measurement> The all-solid-state secondary batteries of Examples and Comparative Examples were charged at a constant current of 4.0 mA in a room temperature (25° C.) environment until the voltage reached 2.6 V, and then charged at a constant voltage of 2.6 V until the current reached 0.05 mA, and then discharged at a constant current of 1.0 mA until the voltage reached 1.0 V. Thereafter, the internal resistance of each battery was measured at an applied voltage of 10 mV and 1 kHz to determine the initial resistance.

[0158] <High-Temperature Charge-Discharge Cycle Characteristics> For the all-solid-state secondary batteries of Examples and Comparative Examples, constant current charging, constant voltage charging, and constant current discharging were performed under the same conditions as when measuring the initial resistance, and the discharge capacity (initial capacity) was measured.

[0159] Next, each battery was subjected to constant current charging at a current value of 8.0 mA in an environment of 150°C until the voltage reached 2.6 V, followed by constant voltage charging at a current value of 2.6 V for 10 minutes, and then discharged at a current value of 8.0 mA for 2 minutes. This series of operations was repeated, and the time (cycle time) at which the voltage during discharge reached 1.8 V was determined to evaluate the high-temperature charge-discharge cycle characteristics.

[0160] These results are shown in Table 1, and the relationship between the overall porosity of the molded positive electrode mixture and porous metal substrate in the positive electrode of each battery and the high-temperature charge-discharge cycle characteristics is shown in Figure 6, and the relationship between the overall porosity of the molded positive electrode mixture, porous metal substrate of the positive electrode, solid electrolyte layer, molded negative electrode mixture, and porous metal substrate of the negative electrode in the power generation element and the high-temperature charge-discharge cycle characteristics is shown in Figure 7. In the "Porosity" section of Table 1, the overall porosity of the molded positive electrode mixture and porous metal substrate in the positive electrode is listed in the "Positive Electrode" column, and the overall porosity of the molded positive electrode mixture, porous metal substrate of the positive electrode, solid electrolyte layer, molded negative electrode mixture, and porous metal substrate of the negative electrode in the power generation element is listed in the "Power Generation Element" column.

[0161]

[0162] As shown in Table 1 and FIGS. 6 and 7 , the all-solid-state secondary batteries of Examples 1 to 3, which used positive electrodes in which the molded body of the positive electrode mixture and the porous metal substrate had appropriate overall porosities, and power generation elements in which the molded body of the positive electrode mixture, the porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the porous metal substrate of the negative electrode had appropriate overall porosities, exhibited good initial resistance and good cycle time in the evaluation of high-temperature charge-discharge cycle characteristics, and were able to ensure excellent high-temperature charge-discharge cycle characteristics while maintaining high discharge characteristics at room temperature.

[0163] In contrast, the battery of Comparative Example 1, which used a positive electrode in which the overall porosity of the molded body of the positive electrode mixture and the porous metal substrate was too small, and a power generation element in which the overall porosity of the molded body of the positive electrode mixture, the porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the porous metal substrate of the negative electrode, was too small, had a short cycle time in the high-temperature charge-discharge cycle performance evaluation, and the high-temperature charge-discharge cycle performance was poor. Also, the battery of Comparative Example 2, which used a positive electrode in which the overall porosity of the molded body of the positive electrode mixture and the porous metal substrate was too large, and a power generation element in which the overall porosity of the molded body of the positive electrode mixture, the porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the porous metal substrate of the negative electrode, was too large, had a high initial resistance, and the cycle time in the high-temperature charge-discharge cycle performance evaluation was short, and both the discharge characteristics at room temperature and the high-temperature charge-discharge cycle performance were poor.

[0164] As reference data, the remaining capacity of the all-solid-state secondary batteries of the Examples and Comparative Examples when stored for 1000 hours in an environment at 105° C. was determined by the following method: The all-solid-state secondary batteries of the Examples and Comparative Examples (different from the batteries used to evaluate the high-temperature charge-discharge cycle characteristics) were subjected to constant current charging, constant voltage charging, and constant current discharging under the same conditions as those used to measure the initial resistance, and the discharge capacity (initial capacity) was measured.

[0165] After the initial capacity measurement, each battery was subjected to constant current charging and constant voltage charging under the same conditions as those used for measuring the initial resistance, and then placed in a thermostatic chamber adjusted to a temperature of 105°C. After storage for 1000 hours, the battery was removed and allowed to cool to room temperature (25°C). After that, the battery was subjected to constant current discharging under the same conditions as those used for measuring the initial resistance, and the discharge capacity (capacity after storage) was measured.

[0166] The remaining capacity (%) of each battery was calculated by dividing the post-storage capacity by the initial capacity and expressed as a percentage. These results are shown in Table 2. The relationship between the remaining capacity and the overall porosity of the positive electrode mixture molded body and the porous metal substrate is shown in Figure 8. The relationship between the remaining capacity and the overall porosity of the positive electrode mixture molded body, the porous metal substrate of the positive electrode, the solid electrolyte layer, the negative electrode mixture molded body, and the porous metal substrate of the negative electrode in the power generation element is shown in Figure 9.

[0167]

[0168] As shown in Table 2 and FIGS. 8 and 9 , when the all-solid-state secondary batteries of the Examples and Comparative Examples were stored in an environment of 105° C., the characteristics (residual capacity) decreased linearly with an increase in the overall porosity of the molded body of the positive electrode mixture and the porous metal substrate, and with an increase in the overall porosity of the molded body of the positive electrode mixture, the porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the porous metal substrate of the negative electrode in the power generating element.

[0169] In contrast, when the all-solid-state secondary batteries of the Examples and Comparative Examples were stored in a harsh environment such as at 150°C, as shown in Table 1 and Figs. 6 and 7, when the overall porosity of the positive electrode mixture molded body and the porous metal substrate, and the overall porosity of the positive electrode mixture molded body, the positive electrode porous metal substrate, the solid electrolyte layer, the negative electrode mixture molded body, and the negative electrode porous metal substrate in the power generating element were each specific values, they exhibited excellent characteristics (high-temperature charge-discharge cycle characteristics), and it was found that they exhibited behavior different from that when stored at 105°C.

[0170] 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.

[0171] The all-solid-state secondary battery of the present invention can be used in the same applications as those in which various known secondary batteries are used, but because of its excellent heat resistance, it is particularly suitable for applications in which it is used in high-temperature environments. Furthermore, the positive electrode and power generating element of the present invention can constitute the all-solid-state secondary battery of the present invention.

[0172] REFERENCE SIGNS LIST 1, 2 All-solid-state battery 10 Outer can 20 Electrode body 20a, 20b, 20c, 20d, 20e, 20f, 20g Power generation element 21 Cell assembly 22 Holder 23 First holding part 24 Second holding part 30 Positive electrode lead 40 Negative electrode lead 50 Lid body 51 Lid body main body 52 Terminal 53 Insulator 54 Insulating sheet 60 Connection lead 201 Positive electrode 201a Molded body of positive electrode mixture 201b Porous metal substrate of positive electrode 202 Negative electrode 202a Molded body of negative electrode mixture 202b Porous metal substrate of negative electrode 203 Solid electrolyte layer 204 Positive electrode tab 205 Negative electrode tab 210a, 210b, 210c, 210d, 210e Insulating plate 212, 213 Heat shrinkable tube 300 Outer container 310 Lid 320, 330 External terminal 321, 331 Conductive path 340 Lead 350 Spacer 360 Conductive sheet

Claims

1. A positive electrode for an all-solid-state secondary battery, comprising a molded body of a positive electrode mixture containing a positive electrode active material and a solid electrolyte, and a sheet-like porous metal substrate, wherein the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate is 14 to 21%.

2. The positive electrode for an all-solid-state secondary battery according to claim 1, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive.

3. A power generation element for use in an all-solid-state secondary battery, comprising a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode comprises a molded body of a positive electrode mixture containing a positive electrode active material and the solid electrolyte, and a sheet-like porous metal substrate, and the negative electrode comprises a molded body of a negative electrode mixture containing a negative electrode active material, and a sheet-like porous metal substrate, wherein the overall porosity of the molded body of the positive electrode mixture, the sheet-like porous metal substrate of the positive electrode, the solid electrolyte layer, the molded body of the negative electrode mixture, and the sheet-like porous metal substrate of the negative electrode is 14 to 22%.

4. The power generating element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive.

5. The power generating element according to claim 3, wherein the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode is 14 to 21%.

6. The power generating element according to claim 3, wherein the overall porosity of the molded negative electrode mixture and the sheet-like porous metal substrate of the negative electrode is 14 to 21%.

7. The power generating element according to claim 3, wherein the porosity of the solid electrolyte layer is 15 to 24%.

8. The power generating element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive, and the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode is 14 to 21%.

9. The power generation element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive, and the overall porosity of the molded body of the negative electrode mixture and the sheet-like porous metal substrate of the negative electrode is 14 to 21%.

10. The power generating element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive, and the porosity of the solid electrolyte layer is 15 to 24%.

11. The power generation element according to claim 3, wherein the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode is 14 to 21%, and the overall porosity of the molded body of the negative electrode mixture and the sheet-like porous metal substrate of the negative electrode is 14 to 21%.

12. The power generating element according to claim 3, wherein the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode is 14 to 21%, and the porosity of the solid electrolyte layer is 15 to 24%.

13. The power generating element according to claim 3, wherein the overall porosity of the negative electrode mixture molded body and the sheet-like porous metal substrate of the negative electrode is 14 to 21%, and the porosity of the solid electrolyte layer is 15 to 24%.

14. The power generation element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive, the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode have an overall porosity of 14 to 21%, and the molded body of the negative electrode mixture and the sheet-like porous metal substrate of the negative electrode have an overall porosity of 14 to 21%.

15. The power generation element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive, the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode is 14 to 21%, and the porosity of the solid electrolyte layer is 15 to 24%.

16. The power generation element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive, the molded body of the negative electrode mixture and the sheet-like porous metal substrate of the negative electrode have an overall porosity of 14 to 21%, and the porosity of the solid electrolyte layer is 15 to 24%.

17. The power generation element according to claim 3, wherein the overall porosity of the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode is 14 to 21%, the overall porosity of the molded body of the negative electrode mixture and the sheet-like porous metal substrate of the negative electrode is 14 to 21%, and the porosity of the solid electrolyte layer is 15 to 24%.

18. The power generation element according to claim 3, wherein the molded body of the positive electrode mixture contains graphene as a conductive additive, the molded body of the positive electrode mixture and the sheet-like porous metal substrate of the positive electrode have an overall porosity of 14 to 21%, the molded body of the negative electrode mixture and the sheet-like porous metal substrate of the negative electrode have an overall porosity of 14 to 21%, and the porosity of the solid electrolyte layer is 15 to 24%.

19. An all-solid-state secondary battery comprising a power generation element having a positive electrode, a negative electrode, and a solid electrolyte interposed between the positive electrode and the negative electrode, housed in an exterior body, wherein the positive electrode is the positive electrode for an all-solid-state secondary battery described in claim 1 or 2, or the power generation element is the power generation element described in any one of claims 3 to 18.

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