Active material recovery method

Abstract

Provided is an active material recovery method for recovering active material from an all-solid state secondary battery member which includes an active material layer containing an active material and an oxide-based solid electrolyte, includes a solid electrolyte containing a lithium-containing oxide including Li, B, and O, lithium salt, and water, and in this solid electrolyte, the value of the ratio of lithium salt content to lithium-containing oxide content is 0.001 to 1.5 in molar ratio, and the value of the ratio of water content relative to the same is 1 to 12 in molar ratio. The method performs solid-liquid separation after bringing the all-solid state secondary battery member and an aqueous medium into contact.

Description

Active material recovery method

[0001] The present invention relates to a method for recovering active material from an all-solid-state secondary battery component.

[0002] Traditionally, secondary batteries, such as lithium-ion secondary batteries, have used liquid electrolytes with high ionic conductivity. However, liquid electrolytes pose safety issues due to their flammability. Furthermore, their liquid form makes compact construction difficult, and increasing battery size poses capacity limitations. In contrast, all-solid-state secondary batteries using inorganic solid electrolytes are expected to be one of the next-generation batteries that can address these issues. Furthermore, the recent development of inorganic solid electrolytes with ionic conductivity comparable to that of liquid electrolytes has led to rapid advances in the performance of all-solid-state secondary batteries. As a result, their applications have expanded to a wide range of applications, including mobile devices such as mobile phones, laptops, and game consoles, as well as various medical devices. Furthermore, electric vehicles equipped with all-solid-state secondary batteries have become increasingly popular due to environmental concerns. As a result, the production volume of all-solid-state secondary batteries has rapidly increased, and the amount of all-solid-state secondary battery waste has also increased year by year.

[0003] All-solid-state secondary batteries contain resources such as active materials containing rare metal elements, such as cobalt. The reserves of these rare metal elements are limited. Furthermore, environmental sustainability has become a growing concern in recent years. Therefore, technologies for recovering and reusing resources from all-solid-state secondary batteries are desired. For example, a technology for recovering a cathode active material or its components from an all-solid-state secondary battery or its components has been proposed. Specifically, Patent Document 1 describes a "method for treating a battery component containing at least a cathode active material containing Li and a sulfide solid electrolyte material containing Li, the method comprising: a contacting step of contacting the battery component with a treatment solution to generate hydrogen sulfide and dissolve Li contained in the sulfide solid electrolyte material in the treatment solution; a cathode active material recovery step of recovering the cathode active material, which is an insoluble component, from the treatment solution containing dissolved Li; and a Li compound recovery step of recovering Li compounds from the treatment solution from which the cathode active material, which is an insoluble component, has been recovered." Furthermore, Patent Document 2 describes "a method for recovering positive electrode active material components from a positive electrode composite of a solid-state battery, the method comprising the steps of: applying mechanical energy to a positive electrode composite including a positive electrode active material having a coating layer on its surface and a solid electrolyte, thereby increasing the exposed surface of the positive electrode active material; and bringing the increased exposed surface of the positive electrode active material into contact with a treatment liquid, thereby dissolving the positive electrode active material components in the treatment liquid."

[0004] International Publication No. 2010 / 106618 Japanese Patent Application Laid-Open No. 2016-033876

[0005] However, the processing method described in Patent Document 1 involves separating and recovering a positive electrode active material from a sulfide-based solid electrolyte in an all-solid-state secondary battery using a sulfide-based solid electrolyte as an inorganic solid electrolyte by decomposing the sulfide-based solid electrolyte. This processing method actively generates highly toxic hydrogen sulfide, necessitating safety measures. This leads to increased costs due to the construction of manufacturing facilities and reduced operational efficiency, and concerns remain regarding safety, making it difficult to implement industrially. On the other hand, the recovery method described in Patent Document 2 is said to be able to efficiently recover positive electrode active material components from a positive electrode composite containing a sulfide-based solid electrolyte as an inorganic solid electrolyte by dissolving the sulfide-based solid electrolyte in a dispersion medium. However, this method recovers positive electrode active material components at the elemental level, and for reuse, the recovered elements must be converted (synthesized) into a predetermined compound. Therefore, reusing the recovered positive electrode active material components as a positive electrode active material requires complex processes.

[0006] Oxide-based solid electrolytes are highly stable in the atmosphere, generally do not generate toxic substances such as hydrogen sulfide, and are therefore safe materials. Therefore, research and development of all-solid-state secondary batteries using oxide-based solid electrolytes has been progressing. However, Patent Documents 1 and 2 do not discuss a method for recovering positive electrode active material components from a positive electrode composite in which an oxide-based solid electrolyte coexists as an inorganic solid electrolyte. While various methods for recovering positive electrode active material from all-solid-state secondary batteries have been known, few methods for recovering positive electrode active material from all-solid-state secondary batteries using oxide-based solid electrolytes have been investigated. One reason for this is that when an oxide-based solid electrolyte is used, the positive electrode active material is typically sintered together with the oxide-based solid electrolyte at high temperatures, and the positive electrode active material integrated with the oxide-based solid electrolyte by sintering cannot be efficiently separated and recovered from the oxide-based solid electrolyte by a simple operation (step).

[0007] An object of the present invention is to provide a method for recovering active material easily and with high recovery efficiency, even from battery components derived from all-solid-state secondary batteries using an oxide-based solid electrolyte.

[0008] The present inventors have discovered that an oxide-based solid electrolyte containing a lithium-containing oxide containing Li, B, and O, such as lithium tetraborate, a lithium salt, and water in predetermined proportions can form a firmly bound solid electrolyte layer and an active material layer by pressure treatment (layer formation characteristics) without being subjected to high-temperature sintering treatment or without blending a binder such as an organic polymer. Further investigation into this oxide-based solid electrolyte has led to the discovery that the lithium-containing oxide containing Li, B, and O itself is poorly soluble in water, and that the oxide-based solid electrolyte forms a slurry-like aqueous dispersion at a high solids concentration, but that when the solids concentration is reduced, the oxide-based solid electrolyte exhibits solubility in water (hereinafter referred to as "water solubility" for convenience) that cannot be exhibited by conventional oxide-based solid electrolytes, thereby forming an aqueous solution or aqueous dispersion. Further investigations based on these findings led to the idea that by utilizing the unique properties of the oxide-based solid electrolyte, namely its layer-forming properties and water solubility, it would be possible to recover an active material even from an active material layer containing the oxide-based solid electrolyte. Following this, the inventors conducted various studies and found that by contacting an active material layer containing the oxide-based solid electrolyte and an active material with water, the active material can be separated and recovered from the oxide-based solid electrolyte by a simple operation (step), with high recovery efficiency, and safely, even without a special environment. The present invention was completed as a result of further investigations based on these findings.

[0009] That is, the above-mentioned problems have been solved by the following means. <1> A method for recovering an active material from an all-solid-state secondary battery member including an active material layer containing an active material and an oxide-based solid electrolyte, wherein the oxide-based solid electrolyte comprises a solid electrolyte containing a lithium-containing oxide containing Li, B, and O, a lithium salt, and water, wherein the ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte is 0.001 to 1.5 in molar ratio and the ratio of the content of water to the content of the lithium-containing oxide is 1 to 12 in molar ratio, and the method for recovering an active material comprises contacting the all-solid-state secondary battery member with an aqueous medium, followed by solid-liquid separation. <2> The method according to <1>, wherein the lithium-containing oxide contains amorphous lithium tetraborate. <3> The method according to <1> or <2>, wherein the all-solid-state secondary battery member is contacted with an aqueous medium in the atmosphere, followed by solid-liquid separation. <4> The recovery method according to any one of <1> to <3>, wherein the contact causes the oxide-based solid electrolyte to elute into the aqueous medium and disperse the active material in the aqueous medium. <5> The recovery method according to any one of <1> to <4>, wherein the active material is a positive electrode active material. <6> The recovery method according to <5>, wherein the positive electrode active material is a positive electrode active material containing a rare metal element. <7> The recovery method according to any one of <1> to <6>, wherein the all-solid-state secondary battery component is a component derived from a battery stack including a positive electrode active material layer containing a positive electrode active material and an oxide-based solid electrolyte, or a negative electrode active material layer containing a negative electrode active material and an oxide-based solid electrolyte, wherein both of the oxide-based solid electrolytes comprise a solid electrolyte containing a lithium-containing oxide containing Li, B, and O, a lithium salt, and water, and wherein the molar ratio of the lithium salt content to the lithium-containing oxide content in the solid electrolyte is 0.001 to 1.5, and the molar ratio of the water content to the lithium-containing oxide content is 1 to 12.

[0010] When describing a numerical range in the present invention or specification, if the upper and lower limits of the numerical range are described separately, any of the upper and lower limits can be appropriately combined to form a specific numerical range. On the other hand, when describing multiple numerical ranges expressed using "to", the upper and lower limits forming the numerical range are not limited to the specific combinations written before and after "to" as a specific numerical range, and can be a numerical range obtained by appropriately combining the upper and lower limits of each numerical range. Note that in the present invention or specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits.

[0011] The active material recovery method of the present invention can recover active materials from all-solid-state secondary battery components easily and with high recovery efficiency. The above and other features and advantages of the present invention will become more apparent from the following description, which is given with reference to the accompanying drawings as appropriate.

[0012] Fig. 1 is a cross-sectional view schematically showing an example of the configuration of an all-solid-state secondary battery. Fig. 2 is a diagram showing an example of an X-ray diffraction pattern for explaining the X-ray diffraction characteristics of a preferred embodiment of solid electrolyte (I), which is an oxide-based solid electrolyte contained in the active material layer of an all-solid-state secondary battery member used in the present invention. Fig. 3 is a diagram showing an example of the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of solid electrolyte (I), which is an oxide-based solid electrolyte contained in the active material layer of an all-solid-state secondary battery member used in the present invention. Fig. 4 is a diagram showing the solid state distribution function G(r) of a preferred embodiment of solid electrolyte (I), which is an oxide-based solid electrolyte contained in the active material layer of an all-solid-state secondary battery member used in the present invention. ７ 5 shows an example of a spectrum obtained when Li-NMR measurement is performed at 20° C. or 120° C. FIG. ７ 6 is a diagram showing an example of a spectrum obtained when Li-NMR measurement is performed at 20° C. or 120° C. FIG. 6 is a diagram showing a solid state of a preferred embodiment of the solid electrolyte (I), which is an oxide-based solid electrolyte contained in the active material layer of the all-solid-state secondary battery member used in the present invention. ７FIG. 7 is a diagram showing an example of a spectrum obtained when Li-NMR measurement is performed at 20° C. FIG. 7 is a diagram showing waveform separation of the peaks shown in FIG. 6. FIG. 8 is a diagram showing an example of a Raman spectrum of a preferred form of solid electrolyte (I), which is an oxide-based solid electrolyte contained in the active material layer of the all-solid-state secondary battery member used in the present invention. FIG. 9 is a diagram showing the Raman spectrum of lithium tetraborate crystal. FIG. 10 is a diagram showing the Raman spectrum of powdered Li ２ B ４ O ７ 11 shows the reduced pair distribution function G(r) obtained by X-ray total scattering measurement of the crystal. ２ B ４ O ７ FIG. 1 shows the X-ray diffraction pattern of the crystal.

[0013] [Active Material Recovery Method] The active material recovery method of the present invention (hereinafter also referred to as the "method of the present invention") is a method for recovering an active material as a compound from an all-solid-state secondary battery component including an active material layer containing an active material and an oxide-based solid electrolyte, as described below. This method involves contacting the all-solid-state secondary battery component with an aqueous medium, followed by solid-liquid separation. Specifically, in the step of contacting the all-solid-state secondary battery component including an active material layer formed using the layer-forming properties of the oxide-based solid electrolyte with an aqueous medium, the oxide-based solid electrolyte is dissolved (dissolved or dispersed) in the aqueous medium by utilizing the water solubility of the oxide-based solid electrolyte, while the water-insoluble active material is dispersed (in a solid state) in the aqueous medium. This allows the active material present in the active material layer to be separated (isolated) from the oxide-based solid electrolyte simply and with high recovery efficiency. Furthermore, the method of the present invention can be safely performed in the atmosphere (environment). Such a method of the present invention can also be referred to as a method for producing recovered active material.

[0014] The details of the reason for this are not yet clear, but it is thought to be as follows. As described above, the oxide-based solid electrolyte described below has unique properties that cannot be achieved with conventional oxide-based solid electrolytes. That is, this oxide-based solid electrolyte exhibits excellent binding properties, and even without high-temperature sintering, it can firmly bind the oxide-based solid electrolyte itself and solid particles such as active materials and conductive additives, thereby forming constituent layers (solid electrolyte layer, active material layer, etc.) of all-solid-state secondary batteries that exhibit good ionic conductivity. Therefore, it is believed that a constituent layer formed using an oxide-based solid electrolyte exhibiting such layer-forming properties is likely to be easily disintegrated or crushed upon contact with an aqueous medium, as the firmly bound state of the solid particles is released. Furthermore, this oxide-based solid electrolyte exhibits water solubility at low concentrations. Therefore, as the constituent layer disintegrates in an aqueous medium, the oxide-based solid electrolyte dissolves (dissolves) in the aqueous medium, and the water-insoluble active materials and the like disperse in the aqueous medium. By subjecting the resulting solid-liquid separation, the oxide-based solid electrolyte and the active material, etc. can be separated and recovered at a high recovery rate by a simple process of simply contacting the oxide-based solid electrolyte with an aqueous medium and then performing solid-liquid separation. In this way, the present invention utilizes the unique properties of the oxide-based solid electrolyte, namely, the layer-forming property and water solubility, which will be described later, to enable the active material to be recovered easily and with a high recovery efficiency, which was not possible with conventional all-solid-state secondary batteries using oxide-based solid electrolytes.

[0015] [All-Solid-State Secondary Battery Components] The all-solid-state secondary battery components to which the method of the present invention is applied may be any component derived from an all-solid-state secondary battery, including an active material layer containing an active material and an oxide-based solid electrolyte, as described below, and the form thereof is not particularly limited. Examples include all-solid-state secondary batteries themselves, as well as components of all-solid-state secondary batteries and materials for manufacturing all-solid-state secondary batteries. Components of all-solid-state secondary batteries include the individual constituent layers of all-solid-state secondary batteries and battery stacks of multiple constituent layers. Materials for manufacturing all-solid-state secondary batteries include layer-forming compositions (slurries) for forming the constituent layers. Examples of battery stacks include stacks containing active material layers (positive electrode active material layers or negative electrode active material layers). Specific examples include stacks (positive electrode stacks, negative electrode stacks) of a current collector and an active material layer (positive electrode active material layer or negative electrode active material layer), stacks of an active material layer (at least one of the positive electrode active material layer and the negative electrode active material layer) and a solid electrolyte layer, and stacks of these stacks and a current collector. The constituent layers and stacks include sheet-shaped and rectangular-shaped ones. The active material layer contained in the all-solid-state secondary battery component may be either a positive electrode active material layer or a negative electrode active material layer as long as it contains an active material and an oxide-based solid electrolyte described below. However, a positive electrode active material layer is preferred because it allows the recovery of a positive electrode active material containing a rare metal element. That is, the active material (also referred to as an electrode active material) to be recovered may be either a positive electrode active material or a negative electrode active material, but a positive electrode active material is preferred, and a positive electrode active material containing a rare metal element is more preferred. Examples of all-solid-state secondary battery components used in recovering the positive electrode active material include a positive electrode active material layer alone, a positive electrode laminate consisting of a positive electrode current collector and a positive electrode active material layer, and a laminate consisting of an active material and a solid electrolyte layer, such as a laminate consisting of a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer.

[0016] Among the active material layers contained in the all-solid-state secondary battery component, the active material layer containing the active material to be recovered contains an oxide-based solid electrolyte, as described below. On the other hand, the other active material layers and solid electrolyte layers do not necessarily contain the oxide-based solid electrolyte, as described below, as the solid electrolyte. However, considering the workability of the method of the present invention, it is preferable that they contain the oxide-based solid electrolyte, as described below. For example, in a laminate of a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer, if all of the constituent layers contain the oxide-based solid electrolyte, as described below, the target active material can be recovered easily and efficiently. The all-solid-state secondary battery component may be an all-solid-state secondary battery, a constituent member, or the like, as is, or may be broken, crushed, cut, or the like. The shape, size, etc. are not particularly limited, but considering the work efficiency, recovery rate, etc., an embodiment that increases the contact area with the aqueous medium is preferred, and is determined appropriately.

[0017] <All-Solid-State Secondary Battery> The all-solid-state secondary battery that can be used as an all-solid-state secondary battery component is not particularly limited as long as it includes the active material layer, and may be a used all-solid-state secondary battery or an unused all-solid-state secondary battery, for example, a scrapped product, a non-standard all-solid-state secondary battery, etc.

[0018] The configuration of the all-solid-state secondary battery is not particularly limited, but typically has a configuration in which a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer are laminated in this order, and includes a configuration in which these constituent layers are continuously laminated. The positive electrode active material layer is preferably formed on a positive electrode current collector to constitute the positive electrode. The negative electrode active material layer is preferably formed on a negative electrode current collector to constitute the negative electrode. In the present invention, each constituent layer (including current collectors, etc.) that constitutes the all-solid-state secondary battery may have a single-layer structure or a multi-layer structure. The basic configuration of an all-solid-state secondary battery is shown in FIG. 1. As viewed from the negative electrode side, an all-solid-state secondary battery 10 has a negative electrode current collector 1, a negative electrode active material layer 2, a solid electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5, in this order. Each layer is in contact with each other and has an adjacent structure. By adopting such a structure, electrons (e － ) is supplied to the solid electrolyte layer 3, and lithium ions (Li ＋On the other hand, during discharge, the lithium ions (Li ＋ ) is returned to the positive electrode side through the solid electrolyte layer 3, and electrons are supplied to the operating part 6. In the illustrated example, a light bulb is used as a model for the operating part 6, and it is lit by discharge.

[0019] Each constituent layer of the all-solid-state secondary battery will be described.

[0020] <Positive electrode active material layer> The positive electrode active material layer is a layer formed by forming a positive electrode active material, or a positive electrode active material together with a solid electrolyte, preferably a conductive additive, and further other components described below within a range that does not impair the effects of the present invention. The positive electrode active material layer may not contain the conductive additive, other components, etc. Note that the positive electrode active material layer usually does not contain a negative electrode active material.

[0021] (Solid Electrolyte) When the positive electrode active material layer contains a solid electrolyte (usually an inorganic solid electrolyte), the type of this solid electrolyte is not particularly limited, and oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes can be used. Furthermore, sulfide-based solid electrolytes can also be used within the scope of the present invention, as long as the effects of the present invention are not impaired. From the viewpoint of emphasizing high safety in implementation under atmospheric conditions, oxide-based solid electrolytes can be used, and from the viewpoints of workability and recovery efficiency, it is preferable to use an oxide-based solid electrolyte (solid electrolyte (I)) described below. The positive electrode active material layer may contain one or more solid electrolytes. The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, and the total content with the positive electrode active material is preferably 50 to 99.9 mass%, more preferably 70 to 99.5 mass%, and even more preferably 90 to 99 mass%.

[0022] (Positive Electrode Active Material) The positive electrode active material itself can be a wide variety of positive electrode active materials that can be used in conventional all-solid-state secondary batteries. A preferred embodiment of the positive electrode active material is described below. The positive electrode active material is an active material capable of inserting and releasing ions of metals belonging to Group 1 or Group 2 of the periodic table, and is preferably capable of reversibly inserting (also referred to as occluding) and releasing lithium ions. The positive electrode active material is not particularly limited, and a transition metal oxide is preferred, and a transition metal oxide containing a transition metal element Ma (one or more elements selected from Co, Ni, Fe, Mn, Cu, and V) is more preferred. Furthermore, this transition metal oxide may be mixed with element Mb (a metal element from Group 1 (Ia) of the periodic table other than lithium, an element from Group 2 (IIa), an element such as Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, or B). The amount of element Mb mixed is preferably 0 to 30 mol% relative to the amount of transition metal element Ma (100 mol%). More preferably, the transition metal oxide is synthesized by mixing so that the Li / Ma molar ratio is 0.3 to 2.2. Specific examples of the transition metal oxide include (MA) a transition metal oxide having a layered rock salt structure, (MB) a transition metal oxide having a spinel structure, (MC) a lithium-containing transition metal phosphate compound, (MD) a lithium-containing transition metal halide phosphate compound, and (ME) a ​​lithium-containing transition metal silicate compound.

[0023] (MA) Examples of transition metal oxides having a layered rock salt structure include LiCoO ２ (lithium cobalt oxide [LCO]), LiNiO ２ (Lithium nickel oxide [LNO]), LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ (nickel cobalt lithium aluminum oxide [NCA]), LiNi １／３ Mn １／３ Co １／３ O ２ (Lithium nickel manganese cobalt oxide [NMC]), LiNi ０．５ Mn ０．５ O ２ (lithium manganese nickel oxide), and Li ２ MnO ３ -LiNiMnCoO２ Examples include:

[0024] (MB) Examples of transition metal oxides having a spinel structure include LiMn ２ O ４ (LMO), LiNi ０．５ Mn １．５ O ４ ([LNMO]), LiCoMnO ４ , Li ２ FeMn ３ O ８ , Li ２ CuMn ３ O ８ , Li ２ CrMn ３ O ８ , and Li ２ NiMn ３ O ８ Examples include:

[0025] (MC) Examples of lithium-containing transition metal phosphate compounds include LiFePO ４ ([LFP]) and Li ３ Fe ２ (P.O. ４ ) ３ Olivine-type iron phosphate salts such as LiFeP ２ O ７ Iron pyrophosphate salts such as LiMnPO ４ Olivine-type manganese phosphate salts such as [(LMP)], LiNiPO ４ Olivine-type nickel phosphate salts such as [(LNP)], LiCoPO ４ Olivine-type cobalt phosphate salts such as [(LCP)], Li ２ CoP ２ O ７ Olivine-type cobalt pyrophosphate salts such as Li ３ V ２ (P.O. ４ ) ３ Examples of suitable vanadium phosphate salts include monoclinic NASICON type vanadium phosphate salts such as (lithium vanadium phosphate).

[0026] (MD) Examples of lithium-containing transition metal halide phosphate compounds include Li ２ FePO ４ Fluorophosphate iron salts such as F, Li２ MnPO ４ Fluorophosphate manganese salts such as F, and Li ２ CoPO ４ Fluorophosphate cobalt salts such as F are also included.

[0027] (ME) Examples of lithium-containing transition metal silicate compounds include Li ２ FeSiO ４ , Li ２ MnSiO ４ , and Li ２ CoSiO ４ Examples include:

[0028] Among the above-mentioned positive electrode active materials, those containing rare metal elements and those that contribute to improving the performance of all-solid-state secondary batteries can be used because they can be recovered and recycled. For example, transition metal oxides having a layered rock salt structure (MA) can be preferably used, and LiCoO ２ , LiNi １／３ Co １／３ Mn １／３ O ２ , LiNi ０．５ Mn １．５ O ４ , LiFePO ４ , Li ２ CoP ２ O ７ Here, the term "rare metal element" generally refers to an expensive metal element that is present in small amounts in the earth's crust and in circulation, but in the present invention, it refers to a non-ferrous metal element that constitutes an active material for an all-solid-state secondary battery, and examples thereof include elements such as lithium, cobalt, nickel, manganese, titanium, and niobium.

[0029] The shape of the positive electrode active material is not particularly limited and is usually particulate. The volume average particle diameter of the positive electrode active material is not particularly limited and is, for example, preferably 0.1 to 50 μm, more preferably 1 to 20 μm, and even more preferably 3 to 15 μm. The volume average particle diameter of the positive electrode active material can be determined in the same manner as the volume average particle diameter of the negative electrode active material described below. The positive electrode active material obtained by the calcination method may be used after washing with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

[0030] The positive electrode active material may be surface-coated with a surface coating agent, sulfur, or phosphorus, as described below, or further with actinic rays, in the same manner as the negative electrode active material described below.

[0031] The positive electrode active material layer may contain one or more positive electrode active materials. The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably 10 to 97 mass%, more preferably 30 to 95 mass%, even more preferably 40 to 93 mass%, and particularly preferably 50 to 90 mass%.

[0032] The positive electrode active material layer may contain components (other components) other than the solid electrolyte and the active material. For example, the positive electrode active material layer may contain one or more of a conductive additive, a binder (described later), a lithium salt, and the like. (Conductive additive) As the conductive additive, a commonly known conductive additive can be used. Examples of the conductive additive include electron-conductive materials such as graphites (e.g., natural graphite, artificial graphite), carbon blacks (e.g., acetylene black, ketjen black, furnace black), amorphous carbons (e.g., needle coke), vapor-grown carbon fibers (e.g., carbon nanotubes), and carbonaceous materials (e.g., graphene, fullerene). Conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyphenylene derivatives may also be used. In addition to the conductive additives described above, conventional conductive additives that do not contain carbon atoms, such as metal powder or metal fibers, may also be used. A conductive additive refers to a material that does not insert or release ions (e.g., Li) during charging and discharging of a battery and does not function as an active material. Therefore, among conductive additives, those that can function as an active material in the active material layer when the battery is charged and discharged are classified as active materials rather than conductive additives. Whether or not a conductive additive functions as an active material when the battery is charged and discharged is not uniquely determined, but is determined by its combination with the active material. The conductive additive is preferably particulate. When the conductive additive is particulate, the volume average particle diameter of the conductive additive (measured in the same manner as for the negative electrode active material) is not particularly limited, but is preferably, for example, 0.02 to 1.0 μm. The content of the conductive additive in the positive electrode active material layer is not particularly limited, but is preferably, for example, 0 to 10 mass %, and more preferably 1 to 5 mass %.

[0033] (Binder) The positive electrode active material layer may contain various binders (binding agents). Aqueous binders are preferred because they can be easily removed in the method of the present invention. The content of the binder in the positive electrode active material layer is not particularly limited, but is preferably 10% by mass or less, more preferably 1 to 5% by mass. As the water-soluble binder, a polymer containing a repeating unit having at least one structure selected from the group consisting of a structure containing a hydroxy group, a structure containing a pyrrolidone ring, and a structure containing an oxyalkylene group can be used. As the water-soluble binder containing a repeating unit having a structure containing a hydroxy group, polysaccharides or polyvinyl alcohol are preferred. Polysaccharides include polysaccharide derivatives and alkali metal salts thereof. As the polysaccharide derivative, cellulose-based polymers are preferred, and more preferably those in which at least a portion of the hydroxy groups are substituted with at least one selected from alkyl groups, hydroxyalkyl groups, and carboxyalkyl groups, with carboxymethylcellulose being particularly preferred. As the water-soluble binder containing a repeating unit having a structure containing a pyrrolidone ring, polyvinylpyrrolidone is preferred. As the water-soluble binder containing a repeating unit having a structure containing an oxyalkylene group, polyethylene glycol and polyethylene oxide are preferred.

[0034] The thickness of the positive electrode active material layer is not particularly limited, and is, for example, preferably 10 to 1,000 μm, more preferably 20 to 500 μm, and even more preferably 50 to 300 μm.

[0035] <Positive Electrode Current Collector> The positive electrode current collector is an electron conductor. The positive electrode current collector is typically in the form of a film sheet. Examples of materials for the positive electrode current collector include aluminum (Al), aluminum alloys (Al alloys), copper (Cu), stainless steel, nickel, and titanium, with aluminum, aluminum alloys, or copper being preferred. Examples of positive electrode current collectors include those having a coating layer (thin film) of carbon, nickel, titanium, or silver on the surface of aluminum or stainless steel. When the positive electrode current collector also functions as a positive electrode active material layer (in other words, when the positive electrode active material layer also functions as a positive electrode current collector), it is not necessary for the positive electrode current collector to have two layers, a positive electrode current collector and a positive electrode active material layer, and a single-layer configuration may also be used. The thickness of the positive electrode current collector is not particularly limited, but can be 1 to 500 μm, preferably 10 to 100 μm.

[0036] <Solid Electrolyte Layer> The solid electrolyte layer is a layer formed by forming a solid electrolyte, or a solid electrolyte together with a conductive additive, the other components described above, etc., in a layer shape within a range that does not impair the effects of the present invention. The solid electrolyte layer does not need to contain the conductive additive, the other components, etc.

[0037] (Solid Electrolyte) The type of solid electrolyte contained in the solid electrolyte layer is not particularly limited, and examples thereof include oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes. Furthermore, sulfide-based solid electrolytes can also be used as long as the effects of the present invention are not impaired. From the viewpoint of emphasizing high safety in implementation under atmospheric conditions, oxide-based solid electrolytes can be used. From the viewpoint of workability and recovery efficiency, the following oxide-based solid electrolytes are preferably used. A preferred oxide-based solid electrolyte contains a lithium-containing oxide containing the elements Li, B, and O (also simply referred to as a "lithium-containing oxide"), water, and a lithium salt. In this solid electrolyte, the ratio of the lithium salt content to the lithium-containing oxide content (lithium salt / lithium-containing oxide) is 0.001 to 1.5 in molar ratio. Furthermore, in the solid electrolyte, the ratio of the water content to the lithium-containing oxide content (water / lithium-containing oxide) is 1 to 12 in molar ratio. A solid electrolyte containing the above components in the above molar ratio is also referred to as "solid electrolyte (I)." The solid electrolyte (I) is usually an inorganic solid electrolyte. Note that the lithium-containing oxide may be called a lithium salt depending on its type, for example, lithium tetraborate may be called a lithium salt of boric acid. However, as long as it is an oxide containing the elements Li, B, and O, it is classified as the lithium-containing oxide rather than the lithium salt described below.

[0038] The solid electrolyte (I) exhibits elastic properties that are prone to plastic deformation. As a result, in a constituent layer containing the solid electrolyte (I) formed by pressure treatment or the like, the adhesion between the solid electrolytes (I) and / or the adhesion between the solid electrolyte (I) and other components present in the constituent layer is improved, thereby reducing interfacial resistance and achieving better ionic conductivity. By using this solid electrolyte (I), a constituent layer exhibiting excellent ionic conductivity can be formed by pressure treatment or the like, even though it is a highly safe oxide-based solid electrolyte, without being subjected to high-temperature sintering treatment. Furthermore, as described above, the solid electrolyte (I) has the property of exhibiting solubility in water when its concentration is reduced, forming an aqueous solution or aqueous dispersion.

[0039] The water contained in the solid electrolyte (I) includes at least bound water. While the reason why the solid electrolyte (I) exhibits high lithium ion conductivity is unclear, it is believed that in the solid electrolyte (I), a soft hydration layer is likely to form on the surface of the lithium-containing oxide, and this hydration layer contains a large amount of lithium derived from the lithium salt, resulting in enhanced ionic conductivity. Here, in the present invention and specification, "bound water" refers to water other than water present as free water or OH groups bound to the lithium-containing oxide. Even if the solid electrolyte (I) contains the above amount of water, it is in the form of solid particles (including a state in which solid particles are bound together) and functions as a solid electrolyte for an all-solid-state secondary battery. In other words, the solid electrolyte (I) contains bound water that is not or is difficult to remove under normal drying conditions. Note that the solid electrolyte (I) may contain free water as long as it is in the form of solid particles (a state that can be handled as a powder) and functions as a solid electrolyte for an all-solid-state secondary battery. That is, in the present invention, the "all-solid-state secondary battery" also includes a form in which the solid electrolyte contains water, as long as the solid electrolyte can be treated as solid particles (solid powder). The solid electrolyte (I) used in the present invention, in which the ratio of the water content to the lithium-containing oxide content is 12 or less in molar ratio, is neither in a paste-like nor gel-like state, but in a state of solid particles (solid powder).

[0040] In the present invention, the solid electrolyte (I) is preferably in an amorphous state (synonymous with a non-crystalline state or an amorphous state) from the viewpoint of more easily exhibiting elastic properties that are prone to plastic deformation. The "amorphous state" of the solid electrolyte (I) means that it satisfies the following X-ray diffraction characteristics.

[0041] (X-ray diffraction characteristics) In the X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα rays, none of the following peaks is present: a first peak having a peak top in the range of a diffraction angle 2θ of 21.6 to 22.0° and a full width at half maximum of 0.65° or less; a second peak having a peak top in the range of a diffraction angle 2θ of 25.4 to 25.8° and a full width at half maximum of 0.65° or less; a third peak having a peak top in the range of a diffraction angle 2θ of 33.4 to 33.8° and a full width at half maximum of 0.65° or less; and a fourth peak having a peak top in the range of a diffraction angle 2θ of 34.4 to 34.8° and a full width at half maximum of 0.65° or less; or In the X-ray diffraction pattern, when at least one peak (hereinafter referred to as "peak X") among the first peak, second peak, third peak, and fourth peak is present, at least one peak among peak X has an intensity ratio of 5.0 or less as calculated by the intensity measurement method described below.

[0042] -Intensity measurement method- The average intensity (Av1) in the range of +0.45° to +0.55° from the diffraction angle 2θ at the peak top of Peak X is calculated, and the average intensity (Av2) in the range of -0.55° to -0.45° from the diffraction angle 2θ at the peak top of Peak X is calculated, and the arithmetic average value of Av1 and Av2 is calculated. The ratio of the peak intensity at the peak top of Peak X to this arithmetic average value (peak intensity at the peak top of Peak X / arithmetic average value) is defined as the intensity ratio.

[0043] The X-ray diffraction characteristics will be described in more detail. In the X-ray diffraction pattern obtained from X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, if none of the first peak, second peak, third peak, and fourth peak is present, the X-ray diffraction characteristics are satisfied, and the solid electrolyte (I) is in an amorphous state. In addition, in the X-ray diffraction pattern obtained from X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, if the peak X is present, and at least one peak of the peak X has an intensity ratio of 5.0 or less obtained by the intensity measurement method, the X-ray diffraction characteristics are also satisfied, and the solid electrolyte (I) is in an amorphous state. Here, the full width at half maximum (FWHM) of the peak means the peak width (°) at 1 / 2 of the peak intensity at the peak top.

[0044] The intensity measurement method will be described in more detail with reference to FIG. 2. FIG. 2 is a diagram showing an example of peak X appearing in a diffraction pattern obtained by X-ray diffraction measurement of solid electrolyte (I) using CuKα radiation. In the X-ray diffraction pattern shown in FIG. 2, a specific peak whose peak top intensity exhibits intensity 1 is shown. In the intensity measurement method, as shown in FIG. 2, an average intensity (Av1) in the range of +0.45° to +0.55° from the diffraction angle 2θ of the peak top of peak X is calculated, and an average intensity (Av2) in the range of −0.55° to −0.45° from the diffraction angle 2θ of the peak top of peak X is further calculated. Next, the arithmetic average values ​​of Av1 and Av2 are calculated, and the ratio of intensity 1 to the arithmetic average value is determined as the intensity ratio.

[0045] If the above X-ray diffraction characteristics are satisfied, it means that there is no or almost no crystalline structure in the solid electrolyte (I), and that the solid electrolyte is in an amorphous state. In other words, the first to fourth peaks are peaks mainly derived from the crystalline structure in the solid electrolyte (e.g., the crystalline structure of lithium tetraborate), and the absence of these peaks means that the solid electrolyte is in an amorphous state. Furthermore, even if at least one of the first to fourth peaks is present, the intensity ratio of at least one of the peaks X present is 5.0 or less, which means that there is almost no crystalline structure in the solid electrolyte (I) that inhibits the effects of the present invention. Note that, for example, a peak derived from a specific component (e.g., a lithium salt) may overlap with any of the first to fourth peaks described above. However, in an amorphous solid electrolyte, all of the first to fourth peaks are usually reduced. Therefore, even if a peak due to the specific component happens to overlap with any of the first to fourth peaks and a single large peak appears, the presence of at least one peak X with an intensity ratio below a predetermined value indicates that the solid electrolyte (I) is in an amorphous state.

[0046] The X-ray diffraction measurement is carried out using CuKα rays under measurement conditions of 0.01° / step and 3° / min.

[0047] In the X-ray diffraction pattern obtained by X-ray diffraction measurement of the solid electrolyte (I) using CuKα radiation, none of the above-mentioned first peak, second peak, third peak, and fourth peak is present, or even if at least one peak X among the above-mentioned first peak, second peak, third peak, and fourth peak is present, it is preferable that the intensity ratio of at least one peak among the peaks X is 3.0 or less. Among these, it is more preferable that none of the above-mentioned first peak, second peak, third peak, and fourth peak is present, or even if at least one peak X among the above-mentioned first peak, second peak, third peak, and fourth peak is present, the intensity ratio of at least one peak among the peaks X is 2.0 or less.

[0048] In the X-ray diffraction pattern, if two or more peaks have their peak tops in the range of 21.6 to 22.0° and their full width at half maximum is 0.65° or less, the peak with the highest diffracted X-ray intensity is selected as the first peak, and the X-ray diffraction characteristics are determined. In the X-ray diffraction pattern, if two or more peaks have their peak tops in the range of 25.4 to 25.8° and their full width at half maximum is 0.65° or less, the peak with the highest diffracted X-ray intensity is selected as the second peak, and the X-ray diffraction characteristics are determined. In the X-ray diffraction pattern, if two or more peaks have their peak tops in the range of 33.4 to 33.8° and their full width at half maximum is 0.65° or less, the peak with the highest diffracted X-ray intensity is selected as the third peak, and the X-ray diffraction characteristics are determined. Furthermore, in the X-ray diffraction pattern, if there are two or more peaks whose peak tops are located in the range of 34.4 to 34.8° and whose full width at half maximum is 0.65° or less, the peak with the greatest diffracted X-ray intensity is selected as the fourth peak, and the X-ray diffraction characteristics are determined.

[0049] (X-ray total scattering characteristics) The solid electrolyte (I) preferably satisfies the following requirement A-1 as an X-ray total scattering characteristic. Furthermore, when the solid electrolyte (I) satisfies the above X-ray diffraction characteristics, the solid electrolyte (I) usually satisfies the following requirement A-2.

[0050] - Requirement A-1 - In the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), there is a first peak whose peak top is located in the range of r 1.43±0.2 Å and a second peak whose peak top is located in the range of r 2.40±0.2 Å, and the G(r) at the peak top of the first peak exceeds 1.0, and the G(r) at the peak top of the second peak is 0.8 or more.

[0051] - Requirement A-2 - In the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), the absolute value of G(r) is less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å.

[0052] When the solid electrolyte (I) satisfies requirements A-1 and A-2, it has a short-range ordered structure related to the B-O and B-B interatomic distances, but has almost no long-range ordered structure, so that the oxide solid electrolyte itself is softer than conventional lithium-containing oxides and exhibits elastic properties that make it more susceptible to plastic deformation. As a result, it is presumed that in a layer containing the solid electrolyte (I) formed by pressure treatment or the like, adhesion between the solid electrolytes (I) themselves and / or adhesion between the solid electrolyte (I) and other components present in the constituent layer is improved, thereby reducing interfacial resistance and achieving better ionic conductivity. Requirements A-1 and A-2 will be described in more detail with reference to the drawings.

[0053] FIG. 3 shows an example of the reduced pair distribution function G(r) obtained by X-ray total scattering measurement of the solid electrolyte (I). The vertical axis of FIG. 3 is the reduced pair distribution function obtained by Fourier transform of the X-ray scattering, and indicates the probability that an atom exists at a position of distance r. The X-ray total scattering measurement can be performed using SPring-8 BL04B2 (accelerating voltage 61.4 keV, wavelength 0.2019 Å). The scattering intensity I obtained by the experiment ｏｂｓ The reduced pair distribution function G(r) is obtained by converting the scattering intensity I ｏｂｓ is expressed by the following formula (1): The structure factor S(Q) is calculated by the coherent scattering I ｃｏｈ is obtained by dividing by the product of the number of atoms N and the square of the atomic scattering factor f. ｏｂｓ =I ｃｏｈ +I ｉｎｃｏｈ +I 蛍光 (1)

[0054]

[0055] The structure factor S(Q) is used for PDF (Pair Distribution Function) analysis. In the above formula (2), the required intensity is the coherent scattering I ｃｏｈ Incoherent scattering I ｉｎｃｏｈ and X-ray fluorescence I 蛍光 is the scattering intensity I obtained by blank measurement, subtraction using the theoretical formula, and the detector discriminator. ｏｂｓCoherent scattering I ｃｏｈ is expressed by Debye's scattering formula (the following formula (3)) (N: total number of atoms, f: atomic scattering factor, r ｉｊ : interatomic distance between i and j).

[0056]

[0057] If we focus on an arbitrary atom and let the atomic density at a distance r be ρ(r), the number of atoms present within a sphere with a radius of r-r+d(r) is 4πr ２ Since ρ(r)dr, the above formula (3) can be expressed as the following formula (4).

[0058]

[0059] The average density of atoms is ρ ０ Then, by transforming the above equation (4), the following equation (5) is obtained.

[0060]

[0061] From the above formula (5) and formula (2), the following formula (6) is obtained.

[0062]

[0063] The pair distribution function g(r) is expressed by the following equation (7).

[0064]

[0065] From the above formulas (6) and (7), the following formula (8) is obtained.

[0066]

[0067] As described above, the pair distribution function can be determined by the Fourier transform of the structure factor S(Q). To make it easier to observe medium- and long-range order, the pair distribution function g(r) is converted to the equation G(r) = 4πr(g(r)-1), which gives the reduced pair distribution function G(r) (Figure 3). g(r), which oscillates around 0, represents the density difference from the average density at each interatomic distance. If there is a correlation at a specific interatomic distance, the average density will be higher than 1. Therefore, it reflects the distance and coordination number of elements corresponding to local to medium distances. As order disappears, ρ(r) approaches the average density, and g(r) approaches 1. Therefore, in an amorphous structure, the larger r becomes, the less order there is, so g(r) becomes 1, i.e., G(r) becomes 0.

[0068] In requirement A-1, as shown in FIG. 3, in the reduced pair distribution function G(r) obtained from X-ray total scattering measurement of the solid electrolyte (I), there is a first peak P1 whose peak top is located in the range of r = 1.43 ± 0.2 Å, and a second peak P2 whose peak top is located in the range of r = 2.40 ± 0.2 Å, and the G(r) at the peak top of the first peak P1 is greater than 1.0 (preferably 1.2 or greater), and the G(r) at the peak top of the second peak P2 is greater than 0.8 (preferably greater than 1.0). In FIG. 3, the peak top of the first peak P1 is located at 1.43 Å, and the peak top of the second peak P2 is located at 2.40 Å. At the position of 1.43 Å, there is a peak assigned to the interatomic distance of B (boron)-O (oxygen). Furthermore, at the position of 2.40 Å, there is a peak assigned to the interatomic distance of B (boron)-B (boron). In other words, the observation of the two peaks (first peak and second peak) means that a periodic structure corresponding to the two interatomic distances is present in the solid electrolyte (I).

[0069] In requirement A-2, the absolute value of G(r) is less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å, as shown in Figure 3. As described above, the absolute value of G(r) being less than 1.0 when r is in the range of more than 5 Å and not more than 10 Å means that there is almost no long-range ordered structure in the solid electrolyte (I).

[0070] In the reduced pair distribution function G(r), there may be peaks other than the first peak and the second peak in the range of r being 5 Å or less.

[0071] There is no particular limitation on the method for making the solid electrolyte (I) amorphous. For example, in preparing the solid electrolyte (I), a method is used in which a lithium-containing oxide that has been subjected to mechanical milling is used as a raw material. This mechanical milling may be performed in the presence of a lithium salt.

[0072] -Mechanical milling- Mechanical milling is a process in which a sample is pulverized while applying mechanical energy. Examples of mechanical milling include milling using a ball mill, a vibration mill, a turbo mill, or a disk mill. Milling using a ball mill is preferred from the viewpoint of obtaining an amorphous solid electrolyte (I) with good productivity. Examples of ball mills include a vibration ball mill, a rotary ball mill, and a planetary ball mill, with a planetary ball mill being more preferred.

[0073] The conditions for the milling treatment using a ball mill (hereinafter referred to as ball milling treatment) are adjusted appropriately depending on the object to be treated. The material of the milling balls (media) is not particularly limited, and examples thereof include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred. The average particle size of the milling balls is not particularly limited, and is preferably 1 to 10 mm, more preferably 3 to 7 mm, from the viewpoint of enabling the solid electrolyte (I) to be produced with good productivity. The average particle size is determined by measuring the diameters of 50 randomly selected milling balls and calculating the arithmetic mean thereof. When the milling balls are not spherical, the major axis is taken as the diameter. The number of milling balls is not particularly limited, and ball milling treatment is usually performed using 10 to 100 balls, preferably 40 to 60 balls.

[0074] The material of the grinding pot in the ball milling process is not particularly limited, and examples thereof include agate, silicon nitride, zirconia, alumina, and iron-based alloys, with stabilized zirconia (YSZ) being preferred.

[0075] The rotation speed of the ball milling treatment is not particularly limited and can be, for example, 200 to 700 rpm, preferably 350 to 550 rpm. The treatment time of the ball milling treatment is not particularly limited and can be, for example, 10 to 200 hours, preferably 20 to 140 hours. The atmosphere in which the ball milling treatment is performed may be air or an inert gas atmosphere (e.g., argon gas, helium gas, nitrogen gas, etc.).

[0076] The method for producing the solid electrolyte (I) using the lithium-containing oxide that has been subjected to mechanical milling treatment preferably involves the following steps 1A to 3A. Step 1A: A step of subjecting the lithium-containing oxide to mechanical milling treatment in the presence of a lithium salt. Step 2A: A step of mixing the product obtained in step 1A with water. Step 3A: A step of removing water from the dispersion liquid obtained in step 2A to obtain the solid electrolyte (I).

[0077] In step 1A, the amount of the lithium salt used is not particularly limited, and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention.

[0078] In the above-mentioned step 2A, the amount of water used is not particularly limited. For example, the amount of water used can be 10 to 200 parts by mass, and preferably 50 to 150 parts by mass, per 100 parts by mass of the product obtained in step 1A. The method for mixing the product obtained in step 1A with water is not particularly limited, and they may be mixed all at once, or water may be added stepwise to the product obtained in step 1A and mixed. When mixing, ultrasonic treatment may be performed as necessary. The time for ultrasonic treatment is not particularly limited, and may be, for example, 10 minutes to 5 hours.

[0079] Step 3A is a step of removing water from the dispersion obtained in step 2A to obtain a solid electrolyte (I). The method for removing water from the dispersion obtained in step 2A is not particularly limited, and water may be removed by heat treatment or vacuum drying treatment. The drying conditions are not particularly limited, and for example, ordinary drying conditions applied to general drying treatments can be appropriately applied, such as the drying conditions applied in the examples. Examples of ordinary drying conditions include air drying (<30% RH), desiccator drying (<5% RH), and heating to 100°C for 30 minutes to 2 hours.

[0080] Before the step 1A, a step 0 may be carried out in which the lithium-containing oxide is subjected to mechanical milling in an environment in which no lithium salt is present.

[0081] As a method for producing the solid electrolyte (I), it is also preferable to carry out the following steps 1B to 3B instead of the above steps 1A to 3A. Step 1B: A step of subjecting a lithium-containing oxide to mechanical milling treatment; Step 2B: A step of mixing the product obtained in step 1B with water and a lithium salt; Step 3B: A step of removing water from the dispersion obtained in step 2B to obtain the solid electrolyte (I).

[0082] The method of performing steps 1B to 3B differs from the method of performing steps 1A to 3A in that a lithium salt is mixed with a lithium-containing oxide that has been subjected to mechanical milling in the presence of water. Therefore, the difference between step 1B and step 1A is that in step 1A, mechanical milling is performed in the presence of a lithium salt, whereas in step 1B, mechanical milling is performed without using a lithium salt. Therefore, in step 2B, the product obtained in step 1B is mixed with water and a lithium salt. The procedure of step 2B is not particularly limited, and may be a method of simultaneously mixing the product obtained in step 1B with water and a lithium salt (Method 1), a method of mixing the product obtained in step 1B with water to prepare a dispersion, and then mixing the resulting dispersion with a lithium salt (Method 2), or a method of mixing the product obtained in step 1B with water to prepare dispersion 1, mixing a lithium salt with water to prepare solution 2, and then mixing dispersion 1 with solution 2 (Method 3). When the product obtained in Step 1B is mixed with water, a dispersion treatment such as ultrasonic treatment may be appropriately performed. In Method 2, when the dispersion obtained by mixing the product obtained in Step 1B with water is mixed with a lithium salt, if the amount of lithium salt is too large, the resulting liquid is likely to gel, and the amount of lithium salt to be mixed is limited. In contrast, in Method 3, even when the product obtained in Step 1B and the lithium salt are mixed in approximately equimolar amounts, gelation of the liquid is unlikely to occur, and a larger amount of lithium salt can be mixed. From this perspective, Method 3 is preferred. The procedures of Step 3B and Step 3A are the same.

[0083] As a method for producing the solid electrolyte (I), it is also preferable to carry out the following steps 1C to 3C instead of the above steps 1A to 3A. Step 1C: A step of subjecting a lithium-containing oxide to mechanical milling treatment; Step 2C: A step of mixing the product obtained in step 1C with water; Step 3C: A step of mixing the product obtained by removing water from the dispersion liquid obtained in step 2C with a lithium salt to obtain the solid electrolyte (I).

[0084] The procedures of Step 1C and Step 1B are the same. The procedures of Step 2C and Step 2A are the same. Step 3C differs from Steps 3A and 3B in that a product obtained by removing water from the dispersion obtained in Step 2C is mixed with a lithium salt. In Step 3C, the amount of lithium salt used is not particularly limited and is appropriately adjusted so as to obtain the solid electrolyte (I) defined in the present invention. The method for mixing the product obtained by removing water from the dispersion obtained in Step 2C with the lithium salt is not particularly limited, and a method in which a solution obtained by dissolving the lithium salt in water is impregnated into the product and the two are mixed may be used.

[0085] (Component Composition of Solid Electrolyte (I)) In the solid electrolyte (I), the ratio of the content of the lithium salt to the content of the lithium-containing oxide is 0.001 to 1.5 in molar ratio, and the ratio of the content of the water is 1 to 12 in molar ratio. The ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte (I) is preferably 0.001 to 1.2 in molar ratio, more preferably 0.01 to 1.2, still more preferably 0.1 to 1.2, and particularly preferably 0.5 to 1.2. Furthermore, the ratio of the content of the water to the content of the lithium-containing oxide in the solid electrolyte (I) is preferably 2 to 12 in molar ratio, more preferably 3 to 11. Furthermore, this molar ratio is also preferably 2 to 10, also preferably 2 to 8, also preferably 2 to 7, and also preferably 3 to 7. The molar amounts of the lithium-containing oxide, lithium salt, and water in the solid electrolyte (I) can be determined based on elemental analysis. Examples of the elemental analysis include the elemental analysis methods described later in the elemental composition of the solid electrolyte (I). The molar amount of water can also be determined by the Karl Fischer method.

[0086] The water content in the solid electrolyte (I) is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less. The water content in the solid electrolyte (I) is also preferably 30% by mass or less, and even more preferably 25% by mass or less. The water content in the solid electrolyte (I) is usually 5% by mass or more, preferably 10% by mass or more, and even preferably 15% by mass or more. Therefore, the water content in the solid electrolyte (I) is preferably 5 to 50% by mass, more preferably 5 to 45% by mass, even more preferably 10 to 40% by mass, particularly preferably 10 to 35% by mass, also preferably 10 to 30% by mass, also preferably 15 to 30% by mass, and even preferably 15 to 25% by mass. The lithium-containing oxide content in the solid electrolyte (I) is preferably 20 to 80% by mass, more preferably 20 to 75% by mass, and even more preferably 25 to 70% by mass. The content of the lithium salt in the solid electrolyte (I) is preferably 0.5 to 60 mass%, more preferably 1.0 to 55 mass%, even more preferably 2.0 to 50 mass%, and also preferably 5.0 to 50 mass%.

[0087] - Lithium-containing oxide - As described above, the lithium-containing oxide constituting the solid electrolyte (I) contains Li, B, and O. The lithium-containing oxide is Li ２＋ｘ B ４＋ｙ O ７＋ｚ (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) is preferred. That is, when the molar amount of B is 4.00 and the molar amount of Li is expressed, it is preferred that the molar amount of Li is 1.58 to 2.49 (i.e., 1.7×4 / 4.3 to 2.3×4 / 3.7) and the molar amount of O is 6.23 to 7.89 (i.e., 6.7×4 / 4.3 to 7.3×4 / 3.7). In other words, when the molar amount of B contained is 4.00, it is preferred that the relative value of the molar amount of Li contained is 1.58 to 2.49 and the molar amount of O is 6.23 to 7.89. Typical examples of such lithium-containing oxides include lithium tetraborate (Li ２ B ４ O ７The lithium-containing oxide may be Li １＋ｘ B ３＋ｙ O ５＋ｚ A compound represented by (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) is also preferred. As such a lithium-containing oxide, lithium triborate (LiB ３ O ５ The lithium-containing oxide may be Li ３＋ｘ B １１＋ｙ O １８＋ｚ Compounds represented by (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) are also preferred. As such lithium-containing oxides, typically Li ３ B １１ O １８ The lithium-containing oxide may be Li ３＋ｘ B ７＋ｙ O １２＋ｚ Compounds represented by (-0.3<x<0.3, -0.3<y<0.3, -0.3<z<0.3) are also preferred. As such lithium-containing oxides, typically Li ３ B ７ O １２ Therefore, the lithium-containing oxide can be ２＋ｘ B ４＋ｙ O ７＋ｚ , the above Li １＋ｘ B ３＋ｙ O ５＋ｚ , Li ３＋ｘ B １１＋ｙ O １８＋ｚ , and Li ３＋ｘ B ７＋ｙ O １２＋ｚ In place of the lithium-containing oxide described above, or together with the lithium-containing oxide described above, LiBO may be used as the lithium-containing oxide. ５ , Li ２ B ７ O １２ , LiB ２ O ３ (OH)H ２ O and Li ４ B ８ O １３ (OH) ２(H ２ O) ３ At least one of the following may also be used. In the solid electrolyte (I), the lithium-containing oxide is preferably in an amorphous state. That is, in the solid electrolyte (I), it is preferable that the lithium-containing oxide is also in a desired amorphous state so that the solid electrolyte (I) is in the above-mentioned amorphous state. Among them, the lithium-containing oxide is preferably lithium tetraborate in an amorphous state.

[0088] - Lithium Salt - The lithium salt constituting the solid electrolyte (I) is not particularly limited, and Li ＋ and an anion, and Li ＋ and an organic anion are preferred, and Li ＋ and a salt composed of an organic anion having a halogen atom is more preferred. The lithium salt constituting the solid electrolyte (I) preferably contains two or more specific elements selected from the group consisting of elements of Group 3 of the periodic table, elements of Group 4 of the periodic table, elements of Group 13 of the periodic table, elements of Group 14 of the periodic table, elements of Group 15 of the periodic table, elements of Group 16 of the periodic table, elements of Group 17 of the periodic table, and H. As the lithium salt constituting the solid electrolyte (I), for example, a compound represented by the following formula (1) is preferred. Formula (1) LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) R ｆ１ and R ｆ２ R each independently represents a halogen atom or a perfluoroalkyl group. ｆ１ and R ｆ２ may be the same or different. ｆ１ and R ｆ２ When R is a perfluoroalkyl group, the number of carbon atoms in the perfluoroalkyl group is not particularly limited. ｆ１ and R ｆ２is preferably a halogen atom or a perfluoroalkyl group having 1 to 6 carbon atoms, more preferably a halogen atom or a perfluoroalkyl group having 1 to 2 carbon atoms, and even more preferably a halogen atom. When the volume of the terminal group increases, steric hindrance increases, which becomes a factor that inhibits ion conduction. ｆ１ and R ｆ２ When is a perfluoroalkyl group, it is preferable that the number of carbon atoms is small.

[0089] The lithium salt that can be contained in the solid electrolyte (I) is not limited to the compound represented by the above formula (1). Examples of lithium salts that can be contained in the solid electrolyte (I) used in the present invention are shown below.

[0090] (L-1) Inorganic lithium salt: LiPF ６ , LiBF ４ , LiAsF ６ , and LiSbF ６ Inorganic fluoride salts such as LiClO ４ , LiBrO ４ , and LiIO ４ perhalogenates such as LiAlCl ４ Inorganic chloride salts such as

[0091] (L-2) Fluorine-containing organic lithium salt: LiCF ３ SO ３ perfluoroalkanesulfonates such as LiN(CF ３ SO ２ ) ２ , LiN(CF ３ CF ２ SO ２ ) ２ , LiN(FSO ２ ) ２ (In this specification, Li(FSO ２ ) ２ N), and LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ Fluorosulfonylimide salts or perfluoroalkanesulfonylimide salts such as LiC(CF ３ SO ２ ) ３perfluoroalkanesulfonylmethide salts such as Li[PF ５ (CF ２ CF ２ CF ３ ) )], Li[PF ４ (CF ２ CF ２ CF ３ ) ２ ], Li[PF ３ (CF ２ CF ２ CF ３ ) ３ ], Li[PF ５ (CF ２ CF ２ CF ２ CF ３ ) )], Li[PF ４ (CF ２ CF ２ CF ２ CF ３ ) ２ ] and Li[PF ３ (CF ２ CF ２ CF ２ CF ３ ) ３ Fluoroalkyl fluorophosphates (preferably perfluoroalkyl fluorophosphates) such as:

[0092] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate and lithium difluorooxalatoborate.

[0093] In addition to the above, examples of lithium salts include LiF, LiCl, LiBr, LiI, and Li ２ SO ４ , LiNO ３ , Li ２ CO ３ , C.H. ３ COOLi, LiAsF ６ , LiSbF ６ , LiAlCl ４ , and LiB(C ６ H ５ ) ４ Among them, LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF６ , LiClO ４ , Li(R ｆ１１ SO ２ ), LiN(R ｆ１１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１１ SO ２ ) (R ｆ１２ SO ２ ) is preferred, and LiPF ６ , LiBF ４ , LiN(R ｆ１１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１１ SO ２ ) (R ｆ１２ SO ２ In these examples, R ｆ１１ and R ｆ１２ each independently represents a perfluoroalkyl group, preferably having 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and even more preferably 1 or 2 carbon atoms. ｆ１１ and R ｆ１２ may be the same or different. In addition, LiNO ３ and 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide lithium are also preferred.

[0094] Here, the solid electrolyte (I) is an electrolyte comprising specific amounts of a lithium-containing oxide, a lithium salt, and water, and in the solid electrolyte (I), the lithium salt may be present as a dissociated ion, or the dissociated ion may be present in a form doped in the lithium-containing oxide. In this case, the lithium salt may be present in the solid electrolyte (I) in a state that is no longer present in the form of a lithium salt, and such a solid electrolyte is also included in the solid electrolyte (I).

[0095] (Elemental Composition of Solid Electrolyte (I)) The component composition of the solid electrolyte (I) has been described based on the compounds constituting the solid electrolyte (I). Next, the solid electrolyte (I) will be described from the perspective of a preferred elemental composition. That is, in one embodiment of the present invention, the solid electrolyte (I) can be specified by its elemental composition, for example, as follows, without having "lithium-containing oxide" and "lithium salt" as invention-specifying matters. The solid electrolyte (I) contained in the all-solid-state secondary battery component preferably has a molar amount of Li of 1.58 to 3.49 (preferably 1.58 to 3.00, more preferably 1.90 to 3.00, and even more preferably 2.00 to 3.00) when the molar amount of B in the solid electrolyte (I) is 4.00. Furthermore, when the molar amount of B in the solid electrolyte (I) is 4.00, the molar amount of O is preferably 6.23 to 25.00 (preferably 6.50 to 23.00, more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, particularly preferably 10.00 to 18.00). Furthermore, when the molar amount of B in the solid electrolyte (I) is 4.00, the molar amounts of elements other than B, Li, and O are each preferably 0.001 to 10.00 (preferably 0.001 to 6.00, more preferably 0.01 to 5.00).

[0096] The content of each element is determined by ordinary elemental analysis. As an elemental analysis method, for example, Li and B are analyzed by ICP-OES (inductively coupled plasma optical emission spectrometry), N and the like are analyzed by an inert gas fusion method, and, for example, F and S are analyzed by combustion ion chromatography. O can be calculated by adding up the analyzed masses of elements other than O and calculating the difference from the total amount of powder. Note that the method for calculating the content of each element is not limited to the above, and the content of one element may be estimated from the analysis results of the content of other elements, taking into account the structure of the compound used. From the content of each element calculated by elemental analysis, the molar amounts of Li, O, and other elements are calculated when the molar amount of B is 4.00.

[0097] In a preferred embodiment of the solid electrolyte (I), in addition to Li, B, and O, the solid electrolyte (I) further contains one or more, more preferably two or more, elements (E) selected from Group 4 elements, Group 15 elements, Group 16 elements, Group 17 elements, Si, C, Sc, and Y. Examples of Group 4 elements include Ti, Zr, Hf, and Rf. Examples of Group 15 elements include N, P, As, Sb, Bi, and Mc. Examples of Group 16 elements include S, Se, Te, Po, and Lv. Examples of Group 17 elements include F, Cl, Br, I, At, and Ts. Among these, it is preferable to contain one or more elements (E) selected from F, Cl, Br, I, S, P, Si, Se, Te, C, Sb, As, Sc, Y, Zr, Ti, Hf, and N, and more preferably to contain two or more. The types of elements (E) contained in the solid electrolyte (I) may be three or more, preferably two to five, and more preferably two to four. A suitable embodiment of the solid electrolyte (I) is preferably to contain two or more elements (E) selected from F, S, N, P, and C, more preferably to contain two or more elements (E) selected from F, S, C, and N, and even more preferably to contain three elements (E) of F, S, and N.

[0098] In the solid electrolyte (I) containing one or more (preferably two or more) of the above element (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of Li is expressed, the molar amount of Li is preferably 1.58 to 3.49. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of Li contained is preferably 1.58 to 3.49. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of Li is expressed, the molar amount of Li is preferably 1.58 to 3.00, more preferably 1.90 to 3.00, and even more preferably 2.00 to 3.00.

[0099] In the solid electrolyte (I) containing one or more (preferably two or more) of the above element (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of O is expressed, the molar amount of O is preferably 6.23 to 25.00. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of O contained is preferably 6.23 to 25.00. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of O is expressed, the molar amount of O is preferably 6.50 to 23.00, more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, and particularly preferably 10.00 to 18.00.

[0100] In the solid electrolyte (I) containing one or more (preferably two or more) of the above-mentioned element (E), when the molar amount of B in the solid electrolyte (I) is 4.00 and the molar amount of the element (E) is expressed, the molar amount of each element (E) is preferably 0.001 to 10.00. In other words, when the molar amount of B contained is 4.00, the relative value of the molar amount of each element (E) contained is preferably 0.001 to 10.00. In particular, when the molar amount of B contained in the solid electrolyte (I) is 4.00 and the molar amount of the element (E) is expressed, the molar amount of each element (E) is preferably 0.001 to 6.00, and more preferably 0.01 to 5.00.

[0101] One preferred embodiment of the elemental composition of the solid electrolyte (I) containing one or more (preferably two or more) of the above element (E) is a solid electrolyte containing Li, B, O, F, S, and N, in which, when the molar amount of B is 4.00, the molar amount of Li is 1.58 to 3.49 (preferably 1.58 to 3.00, more preferably 1.90 to 3.00, and even more preferably 2.00 to 3.00), and the molar amount of O is 6.23 to 25.00 (preferably 6.50 to 23.00). 0.00, more preferably 8.00 to 23.00, even more preferably 10.00 to 23.00, particularly preferably 10.00 to 18.00), the molar amount of F is 0.001 to 10.00 (preferably 0.01 to 10.00), the molar amount of S is 0.001 to 2.00 (preferably 0.01 to 2.00), and the molar amount of N is 0.001 to 1.00 (preferably 0.005 to 1.00).

[0102] The solid electrolyte (I) contained in the all-solid-state secondary battery component is preferably in the amorphous state described above, and as a result, the solid electrolyte (I) preferably exhibits the following properties in addition to the above-described X-ray diffraction properties:

[0103] (solid ７ Li-NMR spectrum characteristics) The solid electrolyte (I) is a solid electrolyte (I). ７ Li-NMR measurement is carried out at 20°C and 120°C, and the full width at half maximum ratio calculated from the obtained spectrum by the following method is preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less. There is no particular lower limit, but it is often 10% or more. The above full width at half maximum ratio is determined by the solid electrolyte (I). ７ Li-NMR measurements are performed at 20°C and 120°C, respectively, and the full width at half maximum (FWHM 1) of a peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained by measurement at 20°C and the full width at half maximum (FWHM 2) of a peak appearing in the chemical shift range of -100 to +100 ppm in the spectrum obtained by measurement at 120°C are determined. The full width at half maximum (FWHM) of the peak is then calculated as a percentage {(FWHM 2 / FWHM 1) x 100 (%)}. The full width at half maximum (FWHM) of the peak means the width (ppm) at half the height (H) of the peak (H / 2). The above characteristics will be explained below with reference to FIG. 4. In FIG. 4, the solid electrolyte (I) ７ The figure shows an example of the spectrum obtained when Li-NMR measurement was performed at 20°C or 120°C. The solid line spectrum shown at the bottom of Figure 4 is the spectrum of the solid ７ The spectrum obtained when Li-NMR measurement was performed at 20°C, and the spectrum shown by the dashed line at the top of Figure 4 is the spectrum of the solid ７ This is the spectrum obtained when Li-NMR measurement was performed at 120°C. ７ In Li-NMR measurement, Li ＋When the mobility of Li is high, the peak obtained is sharper. In the embodiment shown in FIG. 4, when the spectrum at 20° C. is compared with the spectrum at 120° C., the spectrum at 120° C. is sharper. In other words, in the embodiment shown in FIG. 4, due to the presence of Li defects, etc., ＋ This indicates that the mobility of Li is increased. Such a solid electrolyte (I) is prone to plastic deformation due to the above-mentioned defect structure, and ＋ For reference, the solid state hopping of a typical lithium tetraborate crystal is ７ When Li-NMR measurements are performed at 20°C or 120°C, the spectrum measured at 20°C, represented by the solid line in the lower part of Fig. 5, and the spectrum measured at 120°C, represented by the dashed line in the upper part of Fig. 5, tend to have approximately the same shape. In other words, lithium tetraborate crystals are free of Li defects and, as a result, have a high elastic modulus and are not prone to plastic deformation.

[0104] The above solid ７ The Li-NMR measurement conditions are as follows: a 4 mm HX CP-MAS probe is used, and the measurement is performed using a single pulse method, with a 90° pulse width of 3.2 μs, an observation frequency of 155.546 MHz, an observation width of 1397.6 ppm, a repetition time of 15 sec, integration once, and a MAS rotation speed of 0 Hz.

[0105] The solid electrolyte (I) is a solid ７ When a spectrum obtained by Li-NMR measurement at 20°C is subjected to waveform separation of a first peak appearing in the range of -100 to +100 ppm, it is preferable that a second peak having a chemical shift in the range of -3 to +3 ppm and a full width at half maximum of 5 ppm or less is present, and the ratio of the area intensity of the second peak to the area intensity of the first peak is 0.5% or more. The ratio of the area intensity is more preferably 2% or more, even more preferably 5% or more, particularly preferably 10% or more, and most preferably 15% or more. In an embodiment of the present invention in which the solid electrolyte (I) contains water, the solid of the solid electrolyte (I) ７ The Li-NMR spectrum characteristics tend to be as described above. There is no particular upper limit to the ratio of the area intensity, but it is often 50% or less.

[0106] The above characteristics will be explained below with reference to Fig. 6 and Fig. 7. Fig. 6 shows the solid electrolyte (I) ７ An example of a spectrum obtained when Li-NMR measurement was performed at 20°C is shown in Figure 6. As shown in Figure 6, a peak (corresponding to the first peak) is observed in the range of -100 to +100 ppm for the solid electrolyte (I), and within this first peak, a small peak is observed near the chemical shift of 0 ppm, as surrounded by a dashed line. As described above, Li ＋ When the mobility of the first peak is high, the peak is observed sharply, which is thought to be the influence of the second peak. Next, FIG. 7 shows the waveform separation of the first peak. As shown in FIG. 7, the first peak is separated into a small peak (corresponding to the second peak) represented by a solid line and a large peak represented by a dashed line. The second peak appears in a chemical shift range of -3 to +3 ppm and has a full width at half maximum of 5 ppm or less. For the solid electrolyte (I), the ratio of the area intensity of the second peak represented by the solid line in FIG. 7 to the area intensity of the first peak (the peak before waveform separation) represented by FIG. 6 ((area intensity of the second peak / area intensity of the first peak) × 100 (%)) is preferably within the above range. Examples of waveform separation methods include methods using known software, such as WaveMetrics' graph processing software Igor Pro.

[0107] (Raman Spectral Characteristics) The solid electrolyte (I) has a Raman spectrum of 600 to 850 cm －１ The coefficient of determination obtained by linear regression analysis by the least squares method in the wavenumber region of 0.9400 or more is preferably 0.9600 or more, more preferably 0.9800 or more. There is no particular upper limit, but it is usually 1.0000 or less.

[0108] The Raman spectral characteristics are described with reference to FIG. 8 . First, the Raman spectrum of the solid electrolyte (I) is acquired. Raman imaging is used to measure the Raman spectrum. Raman imaging is a microspectroscopic technique that combines Raman spectroscopy with microscopy. Specifically, it involves scanning excitation light over a sample to detect measurement light containing Raman scattered light and visualizing the distribution of components based on the intensity of the measurement light. The Raman imaging measurement conditions are: 27°C, atmospheric air, 532 nm excitation light, 100x objective lens, mapping point scanning, 1 μm steps, 1 second exposure time per point, 1 integration, and a measurement range of 70 μm × 50 μm. However, depending on the film thickness of the sample, the measurement range may be narrower. Furthermore, principal component analysis (PCA) is performed on the Raman spectral data to remove noise. Specifically, in the PCA process, spectra are recombined using components with an autocorrelation coefficient of 0.6 or higher.

[0109] An example of the Raman spectrum of the solid electrolyte (I) is shown in Fig. 8. In the graph shown in Fig. 8, the vertical axis represents the Raman intensity and the horizontal axis represents the Raman shift. －１ The coefficient of determination (coefficient of determination R ２ ) is calculated from 600 to 850 cm of the Raman spectrum in FIG. －１ In the wavenumber region, a regression line (thick line in FIG. 8) is obtained by the least squares method, and the coefficient of determination R ２ The coefficient of determination is calculated between 0 (no linear correlation) and 1 (perfect linear correlation of the measured values) depending on the linear correlation of the measured values. In the solid electrolyte (I), as shown in FIG. 8, －１ As a result, a high coefficient of determination is observed. ２ corresponds to the square of the correlation coefficient (Pearson's product-moment correlation coefficient). More specifically, in this specification, the coefficient of determination R ２ is calculated by the following formula: １ and y１ represents the wave number in the Raman spectrum and the Raman intensity corresponding to that wave number, and x ２ is the (additive) mean of the wavenumber, and y ２ represents the (additive) average of the Raman intensities.

[0110]

[0111] On the other hand, for reference, the Raman spectrum of a typical lithium tetraborate crystal is shown in Figure 9. As shown in Figure 9, in the case of a typical lithium tetraborate crystal, the peak at 716 to 726 cm －１ , and 771 to 785 cm －１ When such a peak is present, a peak is observed in the wave number region of 600 to 850 cm －１ When a linear regression analysis by the least squares method is performed in the wave number region, the coefficient of determination is calculated, and the coefficient of determination is less than 0.9400. In other words, the coefficient of determination being 0.9400 or more indicates that the solid electrolyte (I) contains almost no crystalline structure. As a result, the solid electrolyte (I) has the property of being easily plastically deformed and the property of Li ＋ It is believed that the compound has excellent ion hopping properties such as the above.

[0112] (Infrared absorption spectrum characteristics) The solid electrolyte (I) has an infrared absorption spectrum of 800 to 1600 cm －１ 3000 to 3500 cm for the maximum absorption intensity in the wave number region －１ The ratio of the maximum absorption intensity in the wave number region (3000 to 3500 cm －１ Maximum absorption intensity in the wavenumber region / 800 to 1600 cm －１ The ratio of the maximum absorption intensity in the wave number region of 3000 to 3500 cm of the infrared absorption spectrum is preferably 1 / 5 or more (0.2 or more). In particular, the ratio is preferably 3 / 10 or more, and more preferably 2 / 5 or more. There is no particular upper limit, but it is preferably 1 or less. －１ The O-H stretching vibration mode is observed in the wavenumber region of 800 to 1600 cm －１In the wavenumber region of 800 to 1600 cm, the B-O stretching vibration mode is observed. In the solid electrolyte (I), a strong absorption intensity due to the O-H stretching vibration mode is observed, which indicates that a large number of OH groups and / or a large amount of water are contained. In such a solid electrolyte (I), ions such as lithium ions tend to move easily, and as a result, ionic conductivity tends to be improved. In addition, in the wavenumber region of 800 to 1600 cm, －１ In the wavenumber region, vibrational modes originating from lithium salts can also be observed.

[0113] The infrared absorption spectrum measurement conditions can be as follows: Objective lens: 32x Cassegrain type (NA 0.65), Detector: MCT-A, Measurement range: 650 to 4000 cm －１ , resolution: 4cm －１ The infrared absorption spectrum obtained was compared with that of atmospheric water and CO. ２ Correction is performed to remove signals from the sample, and then offset correction is performed on the background to set the absorption intensity to 0. After vacuum drying at 40° C. for 2 hours, measurement is performed under atmospheric pressure.

[0114] The ionic conductivity (27°C) of the solid electrolyte (I) is not particularly limited, and from the viewpoint of application to various uses, it is 1.0 × 10 －５ S / cm or more is preferable, and 1.0 × 10 －４ S / cm or more is more preferable, and 1.0 × 10 －３ S / cm or more is more preferable, and 3.0×10 －３ The upper limit is not particularly limited, but is preferably 1.0 × 10 －２ In many cases, it is less than 1000 kJ / cm.

[0115] Furthermore, it is also preferable that the solid electrolyte (I) exhibits the following characteristics or physical properties.

[0116] (Mass Loss Rate) When the solid electrolyte (I) is heated to 800°C, the mass loss rate is preferably 20 to 40% by mass, more preferably 25 to 35% by mass. The mass loss caused by the heating is believed to be due to the removal of water contained in the solid electrolyte (I). The inclusion of such water in the solid electrolyte (I) can further improve lithium ion conductivity. In the heat treatment, the solid electrolyte (I) is heated at a temperature increase rate of 20°C / sec from 25°C to 800°C. A known thermogravimetric differential thermal analysis (TG-DTA) device can be used to measure the mass loss. The mass loss rate is calculated by {(mass at 25°C - mass at 800°C) / mass at 25°C} x 100. To measure the mass loss rate, the solid electrolyte (I) is previously subjected to vacuum drying at 40°C for 2 hours. The mass loss rate is measured in the atmosphere.

[0117] The solid electrolyte layer may contain one or more solid electrolytes. The content of the solid electrolyte in the solid electrolyte layer is not particularly limited and can be 100 mass %, but is preferably 50 to 99.9 mass %, more preferably 70 to 99.5 mass %, and even more preferably 90 to 99 mass %.

[0118] The solid electrolyte layer may contain components (other components) other than the solid electrolyte. For example, the solid electrolyte layer may contain one or more of the above-mentioned conductive additives, binders, lithium salts, etc. The contents of these components are not particularly limited, but can be set to the same as the contents in the above-mentioned positive electrode active material layer.

[0119] The thickness of the solid electrolyte layer is not particularly limited, and is, for example, preferably 10 to 1,000 μm, more preferably 20 to 500 μm, and even more preferably 30 to 100 μm.

[0120] <Negative electrode active material layer> The negative electrode active material layer is a layer formed by forming a negative electrode active material, or a negative electrode active material together with a solid electrolyte, preferably a conductive additive, and further the above-mentioned other components, etc., in a layered form, within a range that does not impair the effects of the present invention. The negative electrode active material layer may not contain the conductive additive, other components, etc. Note that the negative electrode active material layer usually does not contain a positive electrode active material.

[0121] (Solid Electrolyte) When the negative electrode active material layer contains a solid electrolyte (usually an inorganic solid electrolyte), the type of this solid electrolyte is not particularly limited, and oxide-based solid electrolytes, halide-based solid electrolytes, and hydride-based solid electrolytes can be used. Furthermore, sulfide-based solid electrolytes can also be used within a range that does not impair the effects of the present invention. From the viewpoint of emphasizing high safety in implementation under atmospheric conditions, oxide-based solid electrolytes can be used, and from the viewpoints of workability and recovery efficiency, the above-mentioned oxide-based solid electrolyte (solid electrolyte (I)) is preferably used. The negative electrode active material layer may contain one or more solid electrolytes. The content of the solid electrolyte in the negative electrode active material layer is not particularly limited, and the total content together with the negative electrode active material is preferably 50 to 99.9 mass%, more preferably 70 to 99.5 mass%, and even more preferably 90 to 99 mass%.

[0122] (Negative electrode active material) The negative electrode active material itself can be a wide variety of negative electrode active materials that can be used in ordinary all-solid-state secondary batteries. A preferred form of the negative electrode active material is described below. The negative electrode active material is an active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table, and is preferably one that can reversibly insert and release lithium ions. The negative electrode active material is not particularly limited, and examples thereof include carbonaceous materials, oxides of metal elements or semimetal elements, elemental lithium, lithium alloys, and negative electrode active materials that can form alloys with lithium.

[0123] The carbonaceous material used as the negative electrode active material is a material essentially composed of carbon. Examples include carbon black such as petroleum pitch and acetylene black (AB), graphite (natural graphite, artificial graphite such as vapor-grown graphite), and carbonaceous materials obtained by calcining various synthetic resins such as PAN (polyacrylonitrile)-based resins or furfuryl alcohol resins. Further examples include various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA (polyvinyl alcohol)-based carbon fibers, lignin carbon fibers, glassy carbon fibers, and activated carbon fibers, as well as mesophase microspheres, graphite whiskers, and flat graphite. These carbonaceous materials can also be divided into difficult-to-graphitize carbonaceous materials (also called hard carbon) and graphite-based carbonaceous materials depending on the degree of graphitization. Furthermore, the carbonaceous material preferably has the interplanar spacing, density, or crystallite size described in JP-A-62-022066, JP-A-2-006856, and JP-A-3-045473. The carbonaceous material does not need to be a single material, and a mixture of natural graphite and artificial graphite described in JP-A-5-090844 and graphite having a coating layer described in JP-A-6-004516 can also be used. As the carbonaceous material, hard carbon or graphite is preferred, and graphite is more preferred.

[0124] The oxide of a metal element or a metalloid element used as a negative electrode active material is not particularly limited as long as it is an oxide capable of absorbing and releasing lithium, and examples thereof include oxides of metal elements (metal oxides), composite oxides of metal elements, composite oxides of metal elements and metalloid elements, and oxides of metalloid elements (metalloid oxides). Note that composite oxides of metal elements and composite oxides of metal elements and metalloid elements are also collectively referred to as metal composite oxides. Examples of these oxides include oxides of iron, for example, Fe ３ O ４Preferred examples include amorphous oxides, and even more preferred are chalcogenides, which are reaction products of metal elements and elements of Group 16 of the periodic table. In the present invention, the term "metalloid element" refers to an element exhibiting properties intermediate between those of metal elements and nonmetal elements, and typically includes six elements: boron, silicon, germanium, arsenic, antimony, and tellurium, and three elements: selenium, polonium, and astatine. Furthermore, "amorphous" refers to an X-ray diffraction method using CuKα radiation that exhibits a broad scattering band with a peak in the 2θ range of 20 to 40°, and may also have crystalline diffraction lines. The strongest intensity of the crystalline diffraction lines observed in the 2θ range of 40 to 70° is preferably 100 times or less, more preferably 5 times or less, the intensity of the diffraction line at the peak of the broad scattering band observed in the 2θ range of 20 to 40°, and even more preferably does not have crystalline diffraction lines.

[0125] Among the compound group consisting of the amorphous oxides and chalcogenides, amorphous oxides or the chalcogenides of metalloid elements are more preferred, and (composite) oxides or chalcogenides consisting of one element selected from Groups 13 (IIIB) to 15 (VB) of the periodic table (e.g., Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) or a combination of two or more of these elements are even more preferred. ２ O ３ , GeO, PbO, PbO ２ , Pb ２ O ３ , Pb ２ O ４ , Pb ３ O ４ , Sb ２ O ３ , Sb ２ O ４ , Sb ２ O ８ Bi ２ O ３ , Sb ２ O ８ Si ２ O ３ , Sb ２ O ５ , Bi ２ O ３ , Bi ２O ４ , GeS, PbS, PbS ２ , Sb ２ S ３ or Sb ２ S ５ As the negative electrode active material that can be used in combination with the amorphous oxide mainly containing Sn, Si, or Ge, a carbonaceous material that can occlude and / or release lithium ions or lithium metal, lithium alone, a lithium alloy, or a negative electrode active material that can be alloyed with lithium is preferred.

[0126] The oxides of metal elements or semimetal elements (particularly metal (composite) oxides) and the chalcogenides preferably contain at least one of titanium and lithium as a constituent component in terms of high current density charge / discharge characteristics. Examples of metal composite oxides containing lithium (lithium composite metal oxides) include composite oxides of lithium oxide and the metal oxides, metal composite oxides, or chalcogenides. More specifically, Li ２ SnO ２ The negative electrode active material (for example, a metal oxide) preferably contains titanium element (titanium oxide). Specifically, Li ４ Ti ５ O １２ Lithium titanate (LTO) is preferred in that it has excellent rapid charge / discharge characteristics due to small volume fluctuations during absorption and desorption of lithium ions, and it can suppress electrode deterioration and improve the life of the all-solid-state secondary battery.

[0127] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy that is commonly used as a negative electrode active material for all-solid-state secondary batteries, and examples thereof include lithium aluminum alloys.

[0128] The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is one that is commonly used as a negative electrode active material for all-solid-state secondary batteries. Examples of the negative electrode active material include negative electrode active materials (alloys) containing silicon or tin, as well as metals such as Al and In. A negative electrode active material containing silicon (silicon-containing active material) is preferred, as it enables higher battery capacity, and a silicon-containing active material having a silicon content of 50 mol% or more of the total constituent elements is more preferred. Generally, negative electrodes containing these negative electrode active materials (e.g., Si negative electrodes containing silicon-containing active materials, Sn negative electrodes containing tin-containing active materials) can absorb more Li ions than carbon negative electrodes (e.g., graphite and acetylene black). That is, the amount of Li ions absorbed per unit mass increases. This increases the battery capacity. As a result, there is an advantage in that the battery operating time can be extended.

[0129] Examples of silicon-containing active materials include silicon materials such as Si and SiOx (0<x≦1), and silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (e.g., LaSi ２ , VSi ２ , La—Si, Gd—Si, and Ni—Si), or textured active materials (e.g., LaSi ２ / Si). Other examples include SnSiO ３ , and SnSiS ３ Examples of the active material containing silicon and tin include: SiOx itself can be used as a negative electrode active material (semi-metal oxide); and since SiOx generates Si during operation of an all-solid-state secondary battery, it can be used as a negative electrode active material (precursor material) that can be alloyed with lithium. Examples of the negative electrode active material containing tin include Sn, SnO, and SnO. ２ , SnS, SnS ２ and active materials containing the silicon and tin elements.

[0130] In terms of battery capacity, the negative electrode active material is preferably a negative electrode active material that can be alloyed with lithium, more preferably the above-mentioned silicon material or silicon-containing alloy (alloy containing silicon element), and even more preferably silicon (Si) or a silicon-containing alloy.

[0131] It is also preferable to use titanium-niobium composite oxide as the negative electrode active material. Titanium-niobium composite oxide has a high theoretical volumetric capacity density, and is expected to enable a long life and rapid charging. Examples of titanium-niobium composite oxides include TiNb ２ O ７ (TNO) can be mentioned.

[0132] The shape of the negative electrode active material is not particularly limited, but particulate is preferred. The volume-average particle size of the negative electrode active material is not particularly limited, but is preferably 0.1 to 50 μm, more preferably 1.0 to 20 μm, and even more preferably 3.0 to 15 μm. The volume-average particle size is measured using the following procedure. The negative electrode active material is diluted with water (or heptane in the case of a substance unstable in water) in a 20 mL sample bottle to prepare a 1% by mass dispersion. The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used for testing immediately thereafter. Using this dispersion sample, data is acquired 50 times using a laser diffraction / scattering particle size distribution analyzer LA-920 (trade name, manufactured by HORIBA) at a temperature of 25°C using a quartz measurement cell to obtain the volume-average particle size. For other detailed conditions, etc., please refer to the description of Japanese Industrial Standards (JIS) Z 8828:2013, "Particle Size Analysis - Dynamic Light Scattering Method," as necessary. Five samples are prepared for each level and the average value is used.

[0133] The surface of the negative electrode active material may be coated with an oxide such as another metal oxide or a carbon-based material. Examples of the surface coating agent include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds, such as Li ４ Ti ５ O １２ , Li ２ Ti ２ O ５ , LiTaO ３ , LiNbO３ , LiAlO ２ , Li ２ ZrO ３ , Li ２ WO ４ , Li ２ TiO ３ , Li ２ B ４ O ７ , Li ３ P.O. ４ , Li ２ MoO ４ , Li ３ BO ３ , LiBO ２ , Li ２ CO ３ , Li ２ SiO ３ , SiO ２ , TiO ２ , ZrO ２ , Al ２ O ３ , B ２ O ３ , Li ３ AlF ６ Carbon-based materials such as C, SiC, and SiOC (carbon-doped silicon oxide) can also be used as the surface coating material. The surface of the negative electrode active material may be surface-treated with sulfur or phosphorus. Furthermore, the surface of the negative electrode active material may be surface-treated with active light or active gas (e.g., plasma) before or after the surface coating.

[0134] The negative electrode active material layer may contain one or more negative electrode active materials. The content of the negative electrode active materials in the negative electrode active material layer is not particularly limited, but is preferably 10 to 90 mass %, more preferably 20 to 85 mass %, still more preferably 30 to 80 mass %, and even more preferably 40 to 75 mass %.

[0135] The negative electrode active material layer may contain one or more components (other components) other than the solid electrolyte and the active material. Examples of the other components include those described for the positive electrode active material layer, and the contents thereof are also as described above.

[0136] The thickness of the negative electrode active material layer is not particularly limited, and is, for example, preferably 10 to 1,000 μm, more preferably 20 to 500 μm, and even more preferably 50 to 300 μm.

[0137] <Negative Electrode Current Collector> The current collector constituting the negative electrode layer is an electron conductor. The negative electrode current collector is usually in the form of a film sheet. Examples of materials constituting the negative electrode current collector include aluminum, copper, copper alloys, stainless steel, nickel, and titanium, with aluminum, copper, copper alloys, or stainless steel being preferred. Examples of negative electrode current collectors include those having a coating layer (thin film) of carbon, nickel, zinc, titanium, aluminum, gold, or silver on the surface of aluminum, copper, copper alloys, or stainless steel. When the negative electrode current collector also functions as a negative electrode active material layer (in other words, when the negative electrode active material layer also functions as a negative electrode current collector), it is not necessary for the negative electrode current collector to have two layers, i.e., a negative electrode current collector and a negative electrode active material layer, and a single-layer configuration may also be used. The thickness of the negative electrode current collector is not particularly limited, but can be 1 to 500 μm, preferably 10 to 100 μm.

[0138] In the present invention, when the positive electrode active material layer or the negative electrode active material layer contains a solid electrolyte, the solid electrolytes contained in the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer may be the same or different from one another, but are preferably the above-mentioned oxide-based solid electrolyte.

[0139] <Other Configurations> In the present invention, a functional layer appropriately applied to an all-solid-state secondary battery may be provided between or on the outside of each of the negative electrode current collector, the negative electrode active material layer, the solid electrolyte layer, the positive electrode active material layer, and the positive electrode current collector, and a member such as a casing or a packaging body may also be provided.

[0140] <Manufacturing of All-Solid-State Secondary Battery> An all-solid-state secondary battery can be manufactured by referring to a typical manufacturing method for an all-solid-state secondary battery, except that the above-mentioned oxide-based solid electrolyte (solid electrolyte (I)) is used as the solid electrolyte constituting the active material layer containing the active material to be recovered. That is, the all-solid-state secondary battery can be manufactured by including a step of obtaining a laminate comprising a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer arranged in this order. Here, the amount of water in the solid electrolyte (I) used may or may not satisfy the amount specified in the present invention. The manufacturing method for an all-solid-state secondary battery can also include a step of subjecting the formed constituent layer to a drying treatment, as necessary, in order to adjust the amount of water in the solid electrolyte (I) contained in the constituent layer, such as the active material layer, to the amount specified in the present invention, regardless of the amount of water in the solid electrolyte (I) used. This drying step for the constituent layer may be performed at any stage after the formation of the constituent layer, as long as the solid electrolyte (I) in the constituent layer in the resulting secondary battery can have the amount of water specified in the present invention. In order to more reliably set the water content within the range specified in the present invention, it is preferable to subject a laminate having at least a positive electrode active material layer, a solid electrolyte layer, and a negative electrode active material layer arranged in this order to a drying treatment while the laminate is placed in a battery cell. The drying method is not particularly limited, and the water content of the solid electrolyte (I) in the constituent layers can be reduced to within the range specified in the present invention by, for example, using a desiccator, subjecting the laminate to vacuum drying, subjecting the laminate to vacuum freeze-drying, or subjecting the laminate to heat treatment.

[0141] The all-solid-state secondary battery is preferably formed by sealing a laminate comprising a positive electrode current collector, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector arranged in this order. By sealing, it is possible to more reliably prevent moisture from entering the constituent layers after the drying process. The sealing method is not particularly limited, and any method that can block or suppress the intrusion of moisture (atmospheric air) can be used. For example, the laminate can be sealed by closing the lid of a housing (battery cell) that houses the laminate via a gasket such as an O-ring. Furthermore, the cell resistance can be improved by heating the resulting laminate (e.g., at 80°C for 2 hours).

[0142] Furthermore, the method for forming the laminate in which the positive electrode current collector, the positive electrode active material layer, the solid electrolyte layer, the negative electrode active material layer, and the negative electrode current collector are arranged in this order is not particularly limited, and examples of the method for forming each constituent layer include formation by coating a dispersion liquid and compaction of powder.

[0143] One embodiment of a method for manufacturing an all-solid-state secondary battery includes a manufacturing method that includes applying a dispersion of a solid electrolyte (I) to form a constituent layer, particularly an active material layer. This method can be adopted because the solid electrolyte (I) can be easily prepared as an aqueous dispersion (solid electrolyte slurry). Specifically, the positive electrode active material layer and the negative electrode active material layer can be formed by applying a dispersion of the active material and the solid electrolyte (I), respectively. When components other than the active material, such as a conductive additive, are contained, a dispersion in which these components are also dispersed is used. The dispersion medium for the dispersion of the solid electrolyte (I) and the dispersion of the active material can be appropriately selected taking into consideration the reactivity with the components contained in the dispersion. For example, when the solid electrolyte (I) is contained, an aqueous dispersion is preferable, and when a sulfide-based solid electrolyte is contained, an organic solvent dispersion is preferable.

[0144] Examples of methods for manufacturing all-solid-state secondary batteries include applying a cathode-forming composition (cathode slurry) containing a cathode active material to a metal foil cathode current collector to form a cathode active material layer, then applying a solid electrolyte layer-forming dispersion (solid electrolyte slurry) containing a solid electrolyte to the cathode active material layer to form a solid electrolyte layer, and then applying a negative electrode-forming composition (negative electrode slurry) containing a negative electrode active material to the solid electrolyte layer to form a negative electrode active material layer, and then overlaying a negative electrode current collector (metal foil) on the negative electrode active material layer. If necessary, the entire structure may be subjected to a pressure treatment to obtain an all-solid-state secondary battery as shown in FIG. Alternatively, the method for forming each layer may be reversed to form a negative electrode active material layer, a solid electrolyte layer, and a positive electrode active material layer on the negative electrode current collector, and if necessary, the entire structure may be subjected to a pressure treatment to produce an all-solid-state secondary battery.

[0145] Here, the solid electrolyte (I) is contained in a composition containing the active material to be recovered, for example, in at least one of a positive electrode-forming composition and a negative electrode-forming composition, and may also be contained in a solid electrolyte layer-forming dispersion liquid.

[0146] Alternatively, the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer may be separately prepared, stacked, and optionally pressurized to produce an all-solid-state secondary battery. In this case, a support such as a nonwoven fabric may be provided as needed during the formation of each layer, allowing each layer to be a free-standing film.

[0147] Another embodiment of the method for producing an all-solid-state secondary battery is a production method that includes applying pressure to powder of the solid electrolyte (I) to form a constituent layer, particularly an active material layer. The solid electrolyte (I) can be easily plastically deformed by pressure, and is itself soft and plastically deformed, acting like a binder to contribute to improving the binding between solid particles or layers. Therefore, by this method, a constituent layer that exhibits high ionic conductivity can be obtained without undergoing a sintering treatment at high temperatures (in other words, without sintering).

[0148] Specifically, the positive electrode active material layer and the negative electrode active material layer can be formed by pressure molding the powders (active material, solid electrolyte (I), and other components) that constitute each layer. More specifically, the powder that constitutes the positive electrode active material layer (hereinafter referred to as positive electrode composite powder), the powder that constitutes the solid electrolyte layer (hereinafter referred to as solid electrolyte powder), and the powder that constitutes the negative electrode active material layer (hereinafter referred to as negative electrode composite powder) are used, and the powders that constitute each layer are pressed into a predetermined shape to form pellets for each layer. These pellets are then stacked on a positive or negative electrode current collector and pressed, whereby an all-solid-state secondary battery can also be produced. For example, a solid electrolyte powder is filled into a predetermined mold and pressure-molded to form a solid electrolyte pellet, a negative electrode composite powder is filled on one side of the obtained solid electrolyte pellet and pressure-molded to form a negative electrode composite pellet, and a positive electrode composite powder is filled on the other side of the obtained solid electrolyte pellet and pressure-molded to form a positive electrode composite pellet, thereby obtaining a powder compact in which the positive electrode composite pellet, solid electrolyte pellet, and negative electrode composite pellet are stacked in this order. Subsequently, the obtained powder compact is placed on a negative electrode current collector (metal foil) with the negative electrode composite pellet on the bottom, and a positive electrode current collector (metal foil) is further placed on top of the positive electrode composite pellet, and the entire assembly is subjected to a pressure treatment to obtain an all-solid-state secondary battery as shown in FIG.

[0149] There are no particular limitations on the method for preparing the solid electrolyte powder. For example, it can be prepared by freeze-vacuum drying a solid electrolyte layer-forming dispersion (solid electrolyte slurry) containing a solid electrolyte. There are no particular limitations on the method for preparing the negative electrode composite powder. For example, it can be prepared by mixing a previously prepared solid electrolyte powder with components for forming a negative electrode active material layer, including a negative electrode active material. There are no particular limitations on the method for preparing the positive electrode composite powder. For example, it can be prepared by mixing a previously prepared solid electrolyte powder with components for forming a positive electrode active material layer, including a positive electrode active material. There are no particular limitations on the pressure conditions when preparing the negative electrode composite pellets, solid electrolyte pellets, and positive electrode composite pellets. For example, the pellets can be prepared by applying a pressure of 50 to 300 MPa for about 10 seconds. In addition, the pressure bonding between the negative electrode composite pellet and the negative electrode current collector, and the positive electrode composite pellet and the positive electrode current collector can also be performed using a pressure of about 60 MPa. There is no particular limitation on the order in which the pellets for each layer are formed, and for example, the pellets may be formed in the order of anode composite pellets, solid electrolyte pellets, and cathode composite pellets. Alternatively, an all-solid-state secondary battery can be manufactured by separately preparing anode composite pellets, solid electrolyte pellets, and cathode composite pellets, stacking the obtained pellets, sandwiching the stacked pellets between cathode and anode current collectors, and applying pressure.

[0150] Here, the solid electrolyte (I) is contained in a composite containing the active material to be recovered, for example, in at least one of the positive electrode composite and the negative electrode composite, and may further be contained in a powder of the solid electrolyte.

[0151] The method for producing an all-solid-state secondary battery is not limited to the method described above, as long as it is capable of forming a constituent layer containing the solid electrolyte (I) together with the recovered active material.

[0152] It is preferable to initialize the all-solid-state secondary battery after production or before use. The initialization method is not particularly limited, and can be performed, for example, by performing initial charge and discharge under an increased pressure, and then releasing the pressure until the pressure falls within the range of the pressure conditions during use of the secondary battery.

[0153] <Applications of All-Solid-State Secondary Batteries> All-solid-state secondary batteries can be used in a variety of applications. While there are no particular limitations on the application mode, examples of applications include electronic devices such as notebook computers, pen-input PCs, mobile PCs, e-book players, mobile phones, cordless phone handsets, pagers, handheld terminals, mobile fax machines, mobile copiers, mobile printers, headphone stereos, video movie players, LCD TVs, handheld vacuum cleaners, portable CD players, mini-discs, electric shavers, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, and backup power supplies. Other consumer applications include automobiles, electric vehicles, motors, lighting fixtures, toys, game consoles, road conditioners, clocks, flash devices, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). Furthermore, all-solid-state secondary batteries can be used for various military and space applications. They can also be combined with solar cells.

[0154] [Recovery Method of the Present Invention] The recovery method of the present invention includes a step of contacting the components derived from the all-solid-state secondary battery described above with an aqueous medium, and a step of subjecting the treated liquid obtained in this step to solid-liquid separation.

[0155] <Contacting Step> The aqueous medium used in this contacting step is a medium containing water, and may contain a hydrophilic solvent and a water-soluble solvent in addition to water. The water is not particularly limited, but (ultra) pure water, ion-exchanged water, etc. can be used. Examples of hydrophilic solvents and water-soluble solvents include alcohol solvents such as methanol and ethanol, ketone solvents such as acetone and methyl ethyl ketone, polyhydric alcohol solvents such as diethylene glycol and glycerin, and ether solvents such as propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether. The content of the water-soluble solvent in the aqueous medium is not particularly limited, but is preferably 50% by mass or less. It is preferable to use water as the aqueous medium.

[0156] The contacting method is not particularly limited as long as it is a method that can contact the all-solid-state secondary battery component with an aqueous medium and dissolve (extract) the oxide-based solid electrolyte into the aqueous medium, and any conventional method can be appropriately adopted. Examples include a method of immersing the all-solid-state secondary battery component in an aqueous medium, a method of passing the aqueous medium through the all-solid-state secondary battery component, and a method of spraying the aqueous medium onto the all-solid-state secondary battery component. Among these, the immersion method is preferred in terms of workability and recovery efficiency. In the immersion method, it is preferable to irradiate the aqueous medium in which the all-solid-state secondary battery component is immersed with ultrasound and to agitate the aqueous medium, as this can promote the dissolution of the oxide-based solid electrolyte and increase the amount of elution. The ultrasound irradiation conditions and agitation conditions are appropriately set.

[0157] The contact conditions are not particularly limited, but are appropriately set to conditions that allow the oxide-based solid electrolyte to dissolve in the aqueous medium, taking into consideration workability, recovery efficiency, and the contact method. The amount of aqueous medium used relative to the all-solid-state secondary battery component is not uniquely determined by the contact method. For example, in an aqueous medium containing an oxide-based solid electrolyte, the concentration of the oxide-based solid electrolyte can be 10 mass% or less, preferably 5 mass% or less. The amount of aqueous medium used relative to 1 g of the all-solid-state secondary battery component can be, for example, 10 g or more, preferably 20 g or more. More specifically, in the immersion method, the amount of aqueous medium used relative to 1 g of the all-solid-state secondary battery component is preferably 100 to 1000 g, and even more preferably 10 to 100 g. The contact temperature can be, for example, 10 to 80°C, preferably 15 to 60°C, and more preferably 20 to 40°C. The contact temperature usually refers to the temperature of the aqueous medium (in which the all-solid-state secondary battery component is immersed). However, when an all-solid-state secondary battery component is immersed in the aqueous medium at the aforementioned temperature, the temperature can be the temperature of the all-solid-state secondary battery component. The contact time can be, for example, 0.5 to 60 minutes, preferably 1 to 30 minutes, and more preferably 5 to 20 minutes. The contacting step can be carried out under an appropriate environment, such as in a special environment or special equipment typically employed as a countermeasure against the generation of toxic compounds. Since the method of the present invention uses an all-solid-state secondary battery component containing the oxide-based solid electrolyte, the contacting step can be carried out safely. Taking advantage of this safety, the contacting step can also be carried out in the atmosphere, which provides excellent workability. The pH of the aqueous medium is not particularly limited.

[0158] By bringing the all-solid-state secondary battery component into contact with the aqueous medium as described above, the oxide-based solid electrolyte is eluted from the active material layer of the all-solid-state secondary battery component into the aqueous medium, and a treated liquid in which the active material is dispersed in a solid state in the aqueous medium is obtained.

[0159] <Solid-Liquid Separation Step> In the method of the present invention, the treated liquid obtained in the contacting step is then subjected to solid-liquid separation. Here, "solid-liquid separation" is used as a typical technique for separating the aqueous medium and insoluble components in the treated liquid. However, in the present invention, the term "solid-liquid separation" is not limited to this, as long as the aqueous medium and insoluble components can be separated. The solid-liquid separation step separates insoluble components, such as the active material dispersed in the treated liquid, from liquid components, such as the aqueous medium, specifically, dissolved components, such as the oxide-based solid electrolyte (its components), dissolved in the treated liquid. Conventional solid-liquid separation methods can be applied as the solid-liquid separation method without any particular limitations. From the viewpoint of workability, filtration is preferred. Examples of filtration methods include natural filtration, reduced-pressure filtration (suction filtration), pressure filtration, and centrifugal filtration, and various filtration devices can be used. The solid-liquid separation conditions are appropriately set, and a filter capable of collecting the target active material as a filtered residue is used. The ambient temperature for solid-liquid separation can be within a normal temperature range, for example, 15 to 30°C, taking into account factors such as workability. The solid-liquid separation process, like the contacting process, can be performed in a special environment or special equipment, but can also be performed in the atmosphere. The contacting process and solid-liquid separation process can be performed continuously, in which case, for example, a mixing tank equipped with a filter can be used. If the insoluble components contain components other than the target active material, the target active material alone can be separated into solid and liquid in the solid-liquid separation process. Alternatively, the insoluble components can be separated together in the solid-liquid separation process, and then the active material can be isolated from the other components in the isolation process described below. Furthermore, when centrifugation is used as the solid-liquid separation method, for example, the density difference between the positive electrode active material and the negative electrode active material can be utilized to separate the two active materials into, for example, a sedimentary component and a supernatant floating component simultaneously with the separation of the oxide-based solid electrolyte. The centrifugal filtration conditions cannot be uniquely determined based on the densities of the two active materials to be separated, but can be appropriately set taking into account the density difference, etc. For example, the rotation speed may be 2,000 to 150,000 rpm, and the treatment time may be 1 to 20 minutes.

[0160] <Other Steps> The method of the present invention may include steps other than the above steps (referred to as "other steps"). The other steps are not particularly limited, and examples of pre-treatment steps include a step of charging or discharging an all-solid-state secondary battery, a step of removing a housing, packaging, etc. from an all-solid-state secondary battery, a step of disassembling or crushing an all-solid-state secondary battery to obtain all-solid-state secondary battery components, and a step of peeling a current collector from an all-solid-state secondary battery component. Examples of post-treatment steps include a step of purifying the recovered material, a step of washing the recovered material, a step of drying the recovered material, a step of pulverizing or crushing the recovered material, and a step of classifying the recovered material. Examples of the step of purifying the recovered material include recrystallization, reprecipitation, a method using column chromatography, and a method of eliminating organic matter. The above-mentioned other steps can be performed using conventional methods and conditions.

[0161] When the recovered material obtained by the method of the present invention contains a positive electrode active material and a negative electrode active material, and further contains solid components such as a conductive additive, a process for isolating the target active material from the recovered material can be performed as a separate process from the solid-liquid separation process. An appropriate method can be applied to the isolation process depending on the type and characteristics of each component contained in the recovered material. Isolation methods utilizing the specific gravity difference between each component (classification method) are preferred because they are easy to work with and can isolate components with high purity. Specific examples include centrifugation, air separation, and sedimentation. Isolation methods utilizing the particle size difference between each component (classification method) can also be applied. In particular, when the particle size distributions of each component do not overlap, simple classification methods are preferred. Typically, each component is separated using a filter capable of retaining particles intermediate the particle size distributions of the components to be separated. On the other hand, when the particle size distributions of each component overlap, isolation methods utilizing the specific gravity difference, especially centrifugation, are preferred. It is anticipated that separation of the positive electrode active material and the negative electrode active material at high purity may be difficult to perform, and therefore, if possible, it is preferable to use an all-solid-state secondary battery component in which the positive electrode active material layer and the negative electrode active material layer have been separated in advance.

[0162] The method of the present invention, which includes the above-described steps, can be carried out safely and simply even in the atmosphere, and can recover the target active material from the active material layer of an all-solid-state secondary battery component with high recovery efficiency. The recovery efficiency (recovery rate) in the method of the present invention is not unique, depending on the method and conditions used in each step. For example, the recovery efficiency (recovery rate) can be 90% by mass or more, preferably 95% by mass or more, based on 100% by mass of the active material contained in the active material layer. The method of the present invention can recover LCO and NMC, which are representative and widely used positive electrode active materials for secondary batteries in recent years, with high recovery efficiency. In particular, since the active material can be recovered as a compound with high purity, a recovered active material (recyclable material) can be produced and reused as is.

[0163] Furthermore, since the method of the present invention can recover the active material by simply contacting the all-solid-state secondary battery components with an aqueous medium, it can be carried out in a simple and safe manner at low cost, has a small environmental impact, and can be carried out on an industrial scale. Furthermore, the oxide-based solid electrolyte or its components (e.g., the above-mentioned lithium-containing oxide) dissolved in the aqueous medium can also be recovered easily.

[0164] The present invention will be described in more detail based on examples, but the present invention should not be construed as being limited to these examples. In the present invention, room temperature means 27°C. Furthermore, the production of the solid electrolyte and the production of the secondary battery described below were carried out in the air in the presence of moisture.

[0165] [Reference Example 1: Preparation by the above steps 0, 1A to 3A] Powdered Li was prepared using a ball mill (Fritsch Planetary Ball Mill P-7). ２ B ４ O ７Crystals (LBO powder) (manufactured by Rare Metallic Co., Ltd.) were ball milled under the following conditions: pot: stabilized zirconia (YSZ) (45 mL), milling balls: YSZ (average particle size: 5 mm, number: 50), rotation speed: 370 rpm (revolutions per minute), amount of LBO powder: 1 g, atmosphere: air, and ball mill treatment time: 100 hours, to obtain a finely divided lithium-containing oxide (hereinafter also referred to as "fine lithium-containing oxide"). 0.05 g of LiFSI (chemical formula: Li(FSO ２ ) ２ N) was added (5% by mass relative to the fine particles of the lithium-containing oxide), and the mixture was ball milled for another 100 hours. The obtained powder was added to water so that the powder concentration was 42% by mass, and ultrasonically dispersed for 30 minutes. Subsequently, the obtained dispersion was transferred to a glass petri dish and dried at 120°C for 2 hours in the atmosphere to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain a powdered solid electrolyte (I)-1.

[0166] <Preparation and Evaluation of Compacted Solid Electrolyte> The powdered solid electrolyte (I)-1 obtained above was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a compacted solid electrolyte (compacted powder 1). The compacted powder 1 had a cylindrical shape with a diameter of 10 mm and a thickness of 1 mm. The ionic conductivity of the compacted powder 1 obtained was measured, and the ionic conductivity of the compacted powder 1 was found to be 1.5 x 10 at 27°C. －４ S / cm and 4.0 × 10 at 60°C －４ S / cm.

[0167] The ionic conductivity of the solid electrolyte (I)-1 was calculated by placing two electrodes made of In foil so as to sandwich the powder compact 1, measuring the AC impedance between the two In electrodes in a measurement frequency range of 1 Hz to 1 MHz under conditions of a measurement temperature of 27°C or 60°C and an applied voltage of 50 mV, and analyzing the arc diameter of the obtained Cole-Cole plot (Nyquist plot).

[0168] X-ray diffraction measurement of solid electrolyte (I)-1 was carried out using CuKα radiation as described above. The measurement conditions were 0.01° / step, 3° / min. As a result, it was found that the X-ray diffraction characteristics described above were satisfied, and solid electrolyte (I)-1 was found to be in an amorphous state.

[0169] Using the solid electrolyte (I)-1 obtained above, X-ray total scattering measurements were performed using an SPring-8L04B2 (accelerating voltage: 61.4 keV, wavelength: 0.2019 Å). The sample was sealed in a 2 mmφ or 1 mmφ Kapton capillary, and the experiment was performed. The obtained data was Fourier transformed as described above to obtain a reduced pair distribution function. As a result of the analysis, in the reduced pair distribution function G(r) obtained from the X-ray total scattering measurements, within the r range of 1 to 5 Å, a first peak with a peak top of G(r) exceeding 1.0 and located at 1.43 Å, and a second peak with a peak top of G(r) exceeding 1.0 and located at 2.40 Å, were confirmed. On the other hand, in the solid electrolyte (I)-1, the peaks attributed to the B-O distance and the B-B distance observed in a typical lithium tetraborate crystal were maintained. A typical lithium tetraborate crystal has a peak top of BO. ４ Tetrahedron and BO ３ It is assumed that the structure is a diborate structure in which triangles exist in a 1:1 ratio, and that this structure is maintained in solid electrolyte (I)-1.

[0170] The solid electrolyte (I)-1 obtained above ７ The solid electrolyte (I)-1 is measured by Li-NMR at 20°C. ... ７ The ratio of the full width at half maximum (full width at half maximum 2) of the peak appearing in the chemical shift range of −100 to +100 ppm in the spectrum obtained by Li-NMR measurement at 120° C. {(full width at half maximum 2 / full width at half maximum 1)×100} was 33%. ７When a spectrum obtained by Li-NMR measurement at 20°C was subjected to waveform separation of a first peak appearing in the range of -100 to +100 ppm, a second peak having a full width at half maximum of 5 ppm or less in a chemical shift range of -3 to +3 ppm was found, and the ratio of the area intensity of the second peak to the area intensity of the first peak was 4%.

[0171] The solid electrolyte (I)-1 obtained above was subjected to infrared absorption spectroscopy under the conditions described above. In the obtained infrared absorption spectrum, －１ 3000 to 3500 cm for the maximum absorption intensity in the wave number region －１ The ratio of the maximum absorption intensities in the wave number region of 0.72 was found to be 0.72.

[0172] In the Raman spectrum of the solid electrolyte (I)-1 obtained above, －１ The coefficient of determination obtained by linear regression analysis by the least squares method in the wavenumber region of 0.9974 was 0.9974. The mass loss rate when the solid electrolyte (I)-1 was heated from 25°C to 800°C as described above was 29.8%.

[0173] Regarding the analysis of each element in the obtained solid electrolyte (I)-1, lithium and boron were quantitatively analyzed by ICP-OES, and fluorine and sulfur were quantitatively analyzed by combustion ion chromatography (combustion IC). N was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the Li salt, and O was calculated as the difference from the total amount of powder by adding up the analyzed masses of elements other than O. The results are shown in the table below.

[0174] [Reference Example 2: Preparation by the above-described steps 1B to 3B and method 2] 1 g of the fine particles of the lithium-containing oxide used in Reference Example 1 was added to water so that the concentration of the fine particles was 42 mass %, and the mixture was ultrasonically dispersed for 30 minutes. 0.05 g of LiFSI (chemical formula: Li(FSO ２ ) ２N) was added (5% by mass relative to the fine particles of the lithium-containing oxide), and ultrasonic dispersion was further carried out for 30 minutes. The obtained dispersion was transferred to a glass petri dish and dried at 120°C for 2 hours in the atmosphere to obtain a solid electrolyte film. Subsequently, the obtained film was peeled off to obtain a powdery solid electrolyte (I)-2. Various evaluations were carried out on the solid electrolyte (I)-2 in the atmosphere in the same manner as in Reference Example 1. The results are summarized in the table below.

[0175] [Reference Example 3: Preparation by the above steps 1B to 3B and method 3] Powdered Li was prepared using a ball mill (Fritsch, planetary ball mill P-7). ２ B ４ O ７ (LBO powder) (manufactured by Rare Metallic Co., Ltd.) was ball milled under the following conditions: pot: YSZ (45 ml), milling balls: YSZ (average particle size: 5 mm, weight: 70 g), rotation speed: 530 rpm (revolutions per minute), LBO powder amount: 4.2 g, atmosphere: air, ball mill treatment time: 100 hours, to obtain a fine lithium-containing oxide. The obtained fine lithium-containing oxide was added to water so that the concentration of the fine lithium-containing oxide was 42 mass%, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain dispersion 1. Next, 3.25 g of LiFSI (chemical formula: Li(FSO ２ ) ２ N) was added to water to a concentration of 87% by mass, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain Solution 2. The obtained Dispersion 1 and Solution 2 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-3. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-3 in the same manner as in Reference Example 1. The results are summarized in the table below.

[0176] Reference Example 4: Preparation by the above steps 1B to 3B and method 3 Dispersion 3 was obtained in the same manner as in the preparation of dispersion 1 in Reference Example 3. Next, 2.32 g of LiFSI (chemical formula: Li(FSO ２ ) ２N) was added to water at a concentration of 87% by mass and subjected to ultrasonic treatment for 60 minutes to obtain Solution 4. The obtained Dispersion 3 and Solution 4 were mixed and stirred and mixed with a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-4. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-4 in the same manner as in Reference Example 1. The results are summarized in the table below.

[0177] Reference Example 5: Preparation by the above-described steps 1B to 3B and method 3 Dispersion 5 was obtained in the same manner as in the preparation of dispersion 1 in Reference Example 3. Next, 4.65 g of LiFSI (chemical formula: Li(FSO ２ ) ２ N) was added to water at a concentration of 87% by mass and subjected to ultrasonic treatment for 60 minutes to obtain Solution 6. The obtained Dispersion 5 and Solution 6 were mixed and stirred and mixed with a magnetic stirrer for 60 minutes. Subsequently, the obtained dispersion was vacuum-dried at 40°C and 10 Pa for 15 hours to obtain a powdered solid electrolyte (I)-5. The obtained powdered solid electrolyte (I)-5 was immediately used to perform various evaluations in the atmosphere in the same manner as in Reference Example 1. The results are summarized in the table below.

[0178] Reference Example 6: Preparation by the above-described steps 1B to 3B and method 3 Dispersion 7 was obtained in the same manner as in the preparation of Dispersion 1 in Reference Example 3. Next, 7.13 g of LiTFSI (chemical formula: Li(F ３ CSO ２ ) ２ N) was added to water at a concentration of 87% by mass and ultrasonically treated for 60 minutes to obtain Solution 8. The obtained Dispersion 7 and Solution 8 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-6. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-6 in the same manner as in Reference Example 1. The results are summarized in the table below. In Reference Example 6, the carbon content shown in Table 1 below was estimated from the analyzed mass of sulfur, taking into account the atomic weight of each atom in the lithium salt.

[0179] Comparative Example 1 The LBO powder (powdered Li without ball milling) used in Example 1 was ２ B ４ O ７ As a result of elemental analysis of the LBO powder, the composition of the obtained powder was １．９６ B ４．００ O ６．８０ The LBO powder was compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a comparative powder compact C1. The ionic conductivity of the obtained powder compact C1 was undetectable. Furthermore, X-ray total scattering measurement was performed using the LBO powder in the same manner as in Reference Example 1 to obtain the reduced pair distribution function G(r). FIG. 10 shows the reduced pair distribution function G(r) obtained from the LBO powder. As a result of analysis, the reduced pair distribution function G(r) obtained from the X-ray total scattering measurement of the LBO powder contained a first peak (corresponding to B-O proximity) with a peak top located at 1.40 Å and a second peak (corresponding to B-B proximity) with a peak top located at 2.40 Å, and the G(r) values ​​of the peak tops of both the first and second peaks were 1.0 or greater (see FIG. 10 ). Furthermore, there were peaks with tops at 3.65 Å, 5.22 Å, 5.51 Å, and 8.54 Å, and the absolute value of G(r) at the peak top of each peak clearly exceeded 1.0 (see FIG. 10).

[0180] X-ray diffraction measurements were performed on the LBO powder of Comparative Reference Example 1 using CuKα radiation. The measurement conditions were 0.01° / step and 3° / min. FIG. 11 shows the X-ray diffraction pattern of the LBO powder of Comparative Reference Example 1. As shown in FIG. 11, the LBO powder used in Comparative Reference Example 1 exhibited multiple narrow peaks. More specifically, the strongest peak corresponding to the (1,1,2) plane was observed at a 2θ value of 21.78°. Other major diffraction peaks included a peak corresponding to the (2,0,2) plane at 25.54°, a peak corresponding to the (2,1,3) plane at 33.58°, and a peak corresponding to the (3,1,2) plane at 34.62°, and the intensities of these three peaks were approximately equal. These peaks were derived from crystalline components.

[0181] Comparative Example 2: The fine particles of the lithium-containing oxide prepared in Example 1 (powdered Li ２ B ４ O ７ As a result of elemental analysis of the fine particles of lithium-containing oxide (crystals ball-milled), the composition of the fine particles of lithium-containing oxide was １．９４ B ４．００ O ６．８０ Next, the fine particles of the lithium-containing oxide were compacted at 27°C (room temperature) under an effective pressure of 220 MPa to obtain a comparative reference compact (compacted powder R1). The ionic conductivity of the obtained compacted powder R1 was 7.5 x 10 at 27°C. －９ S / cm and 7.5 × 10 at 60 °C －８ S / cm.

[0182] In the table below, when the reduced pair distribution function G(r) obtained from X-ray total scattering measurement as described above has a first peak whose peak top is located in the r range of 1.43±0.2 Å and a second peak whose peak top is located in the r range of 2.40±0.2 Å, and the G(r) at the peak top of the first peak and the G(r) at the peak top of the second peak are greater than 1.0, the column for "short-distance G(r)" is marked with "A," and otherwise the column is marked with "B." Note that in Reference Examples 1 to 5 and Reference Examples 9 to 13 shown in the table below, the value of G(r) at the peak top of the first peak was 1.2 or greater. Furthermore, when the absolute value of G(r) in the reduced pair distribution function G(r) is less than 1.0 in the r range of greater than 5 Å and not more than 10 Å, the column for "long-distance G(r)" in the table below is marked with "A," and when the absolute value of G(r) does not satisfy the condition of less than 1.0, the column is marked with "B." Furthermore, as a result of the X-ray diffraction measurement using the above-mentioned CuKα ray, cases where the above-mentioned X-ray diffraction characteristics were satisfied were rated as "A", and cases where the above-mentioned X-ray diffraction characteristics were not satisfied were rated as "B". Note that in Reference Examples 1 to 6 and Reference Examples 7 to 13 shown in the table below, none of the first peak, second peak, third peak, and fourth peak was present in the X-ray diffraction pattern, or the intensity ratio of at least one of the first peak, second peak, third peak, and fourth peak was 2.0 or less.

[0183] In the table below, the "elemental analysis" column shows the molar amount of each element contained in the composition of the solid electrolyte (I) obtained in each Reference Example and the lithium-containing oxide in each Comparative Reference Example, as a relative value with the content of B set to "4.00". In the table below, a blank column means that the corresponding element is not contained.

[0184] In the table below, the "full width at half maximum ratio (%)", "coefficient of determination" and "mass reduction rate (%)" are as explained in the above description of Reference Example 1.

[0185] In the table below, the "area intensity ratio" is the solid ７ In Li-NMR measurement, this is the ratio of the area intensity of the second peak to the area intensity of the first peak, and the evaluation results are based on the following criteria: <Criteria for area intensity ratio> A: When the area intensity ratio is 15% or more B: When the area intensity ratio is 0.5% or more and less than 15% C: When the area intensity ratio is less than 0.5%

[0186] In the table below, the "maximum absorption intensity ratio" column indicates whether or not the above-mentioned infrared absorption spectrum characteristics are satisfied. －１ Maximum absorption intensity in the wavenumber region of 800 to 1600 cm －１ [maximum absorption intensity in the wave number region of 1000 Hz] is indicated as "A" when it is 0.20 or more, and as "B" when it is less than 0.20. In the table below, "-" means that the measured value is not shown.

[0187]

[0188]

[0189] As shown in the table above, the solid electrolytes (I)-1, (I)-2, (I)-3, (I)-4, (I)-5, and (I)-6 of Reference Examples 1 to 6 have the desired characteristics or physical properties and are excellent in ionic conductivity. Furthermore, the results of elemental analysis confirmed that the solid electrolytes in Reference Examples 3 to 6 had a higher Li content. In Reference Examples 3 to 6, an aqueous dispersion containing a lithium-containing oxide subjected to mechanical milling was mixed with an aqueous solution containing a lithium salt (Method 3 in Step 2B described above), allowing for the mixing of a larger amount of lithium salt. It is presumed that this resulted in an increased amount of Li incorporated into the solid electrolyte. Furthermore, it was also found that Reference Examples 3, 4, and 5, which used LiFSI as the lithium salt, had improved ionic conductivity. This is presumed to be due to the inclusion of highly mobile Li in the increased Li.

[0190] <Effect of Water in Solid Electrolyte> A compact (pellet) (10 mm diameter, 0.9 mm thickness) of solid electrolyte (I)-3 obtained in Reference Example 3 was vacuum-dried at 27°C under a restraint of 60 MPa, and the pressure change and ionic conductivity with respect to the vacuum drying time were investigated. The method for producing the compact and the evaluation of ionic conductivity were the same as those described above, except that the In electrode was changed to a Ti electrode. The results are shown in Table 3.

[0191]

[0192] The solid electrolyte (I)-3 of Reference Example 3 has a peak intensity of 3000 to 3500 cm in the infrared absorption spectrum. －１ Since strong absorption intensity due to the O-H stretching peak is observed in the wavenumber region, it is thought that a large number of OH groups and water are present. Furthermore, the presence of free water and bound water is presumed. In the above, the pellets were first dried by vacuum drying under conditions thought to volatilize the free water, and then further dried under more severe drying conditions, and the ionic conductivity at each stage was evaluated.

[0193] As shown in the table above, the pressure was 200 Pa after 5 minutes of drying, and the free water was considered to be in a vaporized state. However, the ionic conductivity was 3.8 × 10 －３Even with a drying time of 1080 minutes and a pressure of 15 Pa, the ionic conductivity was 5.7 × 10 －４ This result indicates that bound water exists in addition to free water, and that this contributes to ionic conductivity.

[0194] Reference Example 7: Preparation by the above-described steps 1B to 3B and method 3 A dispersion 9 having a concentration of lithium-containing oxide fine particles of 42 mass % was obtained in the same manner as in the preparation of dispersion 1 in Reference Example 3. Next, 7.12 g of LiTFSI (chemical formula: Li(F ３ CSO ２ ) ２ N was added to water to a concentration of 87% by mass, and the mixture was subjected to ultrasonic treatment for 60 minutes to obtain Solution 10. The obtained Dispersion 9 and Solution 10 were mixed and stirred with a magnetic stirrer for 60 minutes. The obtained dispersion was then vacuum-dried at 40°C and 10 Pa for 15 hours to obtain powdered solid electrolyte (I)-7. The obtained powder was allowed to stand in the atmosphere for a certain period of time, and various evaluations were performed in the atmosphere using solid electrolyte (I)-7 in the same manner as in Reference Example 1. The results are summarized in the table below.

[0195] [Reference Example 8] A solid electrolyte (I)-8 was obtained in the same manner as in Reference Example 7, except that the contents of water and LiTFSI in the obtained solid electrolyte (I) were changed to the amounts shown in the table below, and various evaluations were carried out under air in the same manner as in Reference Example 1. The results are summarized in the table below.

[0196] [Reference Examples 9 to 13] Solid electrolytes (I)-9 to (I)-13 were obtained in the same manner as in Reference Example 7, except that LiTFSI was changed to LiFSI and the contents of water and LiFSI in the resulting solid electrolyte (I) were changed to the amounts shown in the table below. Various evaluations were carried out in the atmosphere in the same manner as in Reference Example 1. The results are summarized in the table below. However, in Reference Example 13, the powder obtained after vacuum drying was immediately used to carry out evaluation in the atmosphere.

[0197] In the table below, the "Lithium-containing oxide fine particles" column, the "Lithium salt" column, and the "Water" column represent relative molar ratios. For example, in Reference Example 7, the molar ratio of lithium salt to lithium-containing oxide fine particles is 1, and the molar ratio of water to lithium-containing oxide fine particles is 11. The molar ratios were calculated by the following method. The analysis of each element was performed by quantitatively analyzing lithium and boron using ICP-OES, and fluorine and sulfur using combustion ion chromatography (combustion IC). N was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the Li salt, and O was calculated as the difference from the total amount of solid electrolyte by adding up the analyzed masses of elements other than O. In Reference Examples 7 and 8, the carbon amount was estimated from the analyzed mass of sulfur taking into account the atomic weight of each element in the lithium salt. The molar ratio of lithium-containing oxide fine particles to lithium salt in the solid electrolyte was calculated from the molar ratio of an element (e.g., B) that is only present in the lithium-containing oxide fine particles and an element that is only present in the lithium salt. Furthermore, the molar ratio of the fine particles of the lithium-containing oxide to water was calculated by subtracting the molar ratios of O contained in the fine particles of the lithium-containing oxide and the lithium salt from the molar ratio of O in the solid electrolyte to calculate the molar amount of O derived from water, and then using the obtained molar amount of O derived from water and the molar amount of the fine particles of the lithium-containing oxide.

[0198]

[0199] The content (mass %) of each component in the solid electrolyte (I) was calculated based on the molar amount and molecular weight shown in Table 4. The results are shown in Table A below.

[0200]

[0201]

[0202] As shown in the above table, the solid electrolytes of the respective reference examples satisfied the composition defined in claim 1 of the present application, had the desired characteristics or properties, and exhibited excellent ionic conductivity.

[0203] [Production Example 1] Production of all-solid-state secondary battery In addition to the above-mentioned Reference Examples 1 to 13, a solid electrolyte having a specific composition as defined in claim 1 was prepared, and an attempt was made to recover an active material from an all-solid-state secondary battery using this. <Preparation of solid electrolyte slurry: Production of solid electrolyte (I) by the above-mentioned steps 1B to 3B and method 1> (Preparation of fine particles of lithium-containing oxide) Powdered Li ２ B ４ O ７ 45 g of crystals (LBO powder) (manufactured by Rare Metallic Co., Ltd.), 770 g of zirconia beads (average particle size: 5 mm), and 3 mL of water were placed in a 500 mL zirconia pot and sealed with a Teflon (registered trademark) ring and a zirconia lid. The LBO powder was milled using a planetary ball milling machine (P-7, manufactured by Fritsch) at 300 rpm (revolutions per minute) for 45 hours to obtain a fine lithium-containing oxide.

[0204] (Preparation of Solid Electrolyte (I)) Obtained Li ２ B ４ O ７ 10 g of powder, 15 g of water, and Li(FSO ２ ) ２ The mixture was mixed with 11 g of N(LiFSI) in a beaker and ultrasonically treated for 30 minutes using an ultrasonic cleaner to obtain a dispersion. This dispersion was further stirred for 30 minutes using a magnetic stirrer to obtain a solid electrolyte slurry. This solid electrolyte slurry was vacuum dried at 40°C and 20 Pa for 15 hours to obtain a powder. The obtained powder was stored in a desiccator (humidity 5%) for several days and then analyzed under atmospheric conditions. It was confirmed that the powder had the above-mentioned X-ray diffraction characteristics and was in an amorphous state. Furthermore, the ionic conductivity was measured using the above-mentioned method to find a value of 4.5 x 10 －３ S / cm. The molar ratio of the content of LiFSI to the content of the lithium-containing oxide was 1, and the molar ratio of the content of water was 9. The elemental composition was Li = 3, B = 4, O = 20, F = 2, S = 2, and N = 1. The solid electrolyte produced in Production Example 1 satisfied the above-mentioned properties like the solid electrolyte (I) of Reference Example 1.

[0205] <Preparation of Positive Electrode Slurry> 5.2 g of the above solid electrolyte slurry was mixed with LiCoO as a positive electrode active material. ２ (LCO, volume average particle size: 12 μm, density: 4.92 g / cm ３ 5.0 g of the above powder and 4.8 g of a 6% aqueous dispersion of carbon nanotubes (CNT) (manufactured by KJ Specialty Paper Co., Ltd.) as a conductive additive were added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain a positive electrode slurry.

[0206] <Preparation of negative electrode slurry> 7.6 g of the above solid electrolyte slurry was mixed with TiNb as a negative electrode active material. ２ O ７ (TNO, volume average particle size: 3 μm, density: 4.11 g / cm ３ 5.0 g of the above powder and 9.8 g of a 6% aqueous dispersion of CNT (manufactured by KJ Specialty Paper Co., Ltd.) as a conductive additive were added, and the mixture was stirred with a magnetic stirrer for 30 minutes to obtain a negative electrode slurry.

[0207] <Preparation of Positive Electrode Laminate [Solid Electrolyte Layer / Positive Electrode Active Material Layer / Al Current Collector]> The positive electrode slurry was applied to a 50 μm thick A4-size Al foil using a desktop coater at an applicator gap of 100 μm and a coating speed of 30 mm / s. After leaving at room temperature for 1 hour, the solid electrolyte slurry was applied in a multilayer on the positive electrode slurry coating using a desktop coater at an applicator gap of 200 μm and a coating speed of 90 mm / s. The multilayer coating was stored in a desiccator at a relative humidity of 5% or less for 12 hours to dry, and then punched out to a diameter of 10 mm using a hand punch to obtain a positive electrode laminate (solid electrolyte layer / positive electrode active material layer / Al current collector).

[0208] <Preparation of negative electrode side laminate [solid electrolyte layer / negative electrode active material layer / Al current collector]> The negative electrode slurry was applied to a 50 μm thick A4 size Al foil using a desktop coater at an applicator gap of 200 μm and a coating speed of 30 mm / s. After leaving at room temperature for 1 hour, the solid electrolyte slurry was applied in a multilayer on the negative electrode slurry coating using a desktop coater at an applicator gap of 300 μm and a coating speed of 90 mm / s. The multilayer coating was stored in a desiccator at a relative humidity of 5% or less for 12 hours to dry, and then punched out to a diameter of 10 mm using a hand punch to obtain a negative electrode side laminate (solid electrolyte layer / negative electrode active material layer / Al current collector). The positive electrode side laminate and the negative electrode side laminate were prepared using a 1.0 × 10 ５ The reaction was carried out under a pressure of 100 Pa.

[0209] <Manufacturing of All-Solid-State Secondary Battery> The above-mentioned negative electrode side laminate was placed on a 10 mm diameter SUS stand of an all-solid-state battery evaluation cell (trade name: KP-SolidCell) manufactured by Hosensha, with the solid electrolyte layer facing up, and the above-obtained positive electrode side laminate was placed on top of it with the solid electrolyte layer facing down. In this way, a laminate with a positive electrode side laminate / negative electrode side laminate structure (this laminate is referred to as a cell) was obtained. Next, a Teflon (registered trademark) tube (hereinafter referred to as a Teflon tube) with an inner diameter of 10.2 mm was inserted from the positive electrode current collector side of the cell, and a 10 mm diameter, 2 mm thick polished Ti plate was inserted through the hole at the top of the Teflon tube, and the polished Ti plate was stacked on top of the positive electrode laminate. Furthermore, a 10 mm diameter, 2 cm high Ti rod was placed on top of the polished Ti plate. Next, a grain of silica gel for water removal was placed in the cavity of the KP-Solid Cell, and the upper housing of the KP-Solid Cell was fitted and sealed with a double O-ring, four bolts, and wing nuts. The cell was constrained from above and below with a torque of 5 Nm (equivalent to 30 MPa) using a confining pressure application mechanism installed on top of the KP-Solid Cell. Next, the KP-Solid Cell was temporarily opened, the cell was removed, and any excess liquid components that had seeped out due to the application of confining pressure were wiped off. The cell was then placed in the KP-Solid Cell again in the same manner as above, and the cell was constrained from above and below (confining pressure: 5 Nm torque (equivalent to 30 MPa)). Next, with the top lid open, the KP-Solid Cell was subjected to a two-hour freeze-drying process (10 Pa, 40°C) to thoroughly remove the moisture inside the cell. After removing the KP-Solid Cell from the vacuum dryer, the top lid was closed and sealed using a double O-ring. After leaving it for 40 hours, the entire cell was heated (post-baked) at 80°C for 2 hours to produce an all-solid-state secondary battery. The positive electrode active material layer in this all-solid-state secondary battery contained 31 mass% oxide-based solid electrolyte, 67 mass% LCO, and 2 mass% CNT. The negative electrode active material layer contained 49 mass% oxide-based solid electrolyte, 46 mass% TNO, and 5 mass% CNT. The thicknesses of the positive electrode active material layer, solid electrolyte layer, and negative electrode active material layer in this all-solid-state secondary battery were 100 μm, 200 μm, and 100 μm, respectively.

[0210] [Example 1] In Example 1, a positive electrode active material and a negative electrode active material were recovered in an atmospheric environment using an unused all-solid-state secondary battery produced in Production Example 1 as follows. <Preparation of All-Solid-State Secondary Battery Components> For the all-solid-state secondary battery produced in Production Example 1, the stack of the positive electrode current collector and the positive electrode active material layer was peeled from the interface with the solid electrolyte layer using tweezers to obtain a positive electrode stack. Similarly, the stack of the negative electrode current collector and the negative electrode active material layer was peeled from the interface with the solid electrolyte layer to obtain a negative electrode stack. <Contacting Step> Next, the positive electrode stack or the negative electrode stack (10 mm diameter, 68 mg) was separately immersed in 3 mL of water (water temperature 26°C) placed in a beaker and subjected to ultrasonic treatment for 3 minutes using an ultrasonic cleaner. By performing the contacting step in this manner, the oxide-based solid electrolyte in the positive electrode active material layer or the negative electrode active material layer was dissolved into the water, and the active material and the conductive additive were dispersed. The positive electrode current collector and the negative electrode current collector that had been peeled off from the active material layers in the contacting step were removed.

[0211] <Solid-Liquid Separation Step> The treated liquid obtained by contacting the positive electrode laminate with water was suction-filtered using filter paper (manufactured by Whatman) with particle retention capacity smaller than the volume average particle diameter (particle size distribution) of LCO, and the filtered residue was washed with ultrapure water to obtain LCO. The filter paper used was designed to allow CNTs to pass through. The filter paper was then dried for 2 hours in an electric furnace set at 120°C, and 8.7 mg of LCO was recovered. The LCO recovery rate was calculated using the following formula C1 from the LCO content (8.8 mg) of the positive electrode laminate used in the contacting step and the recovered LCO (8.7 mg). The LCO recovery rate was 90 mass% or more. Formula C1: LCO recovery rate = [LCO recovery amount (g) / LCO content in the positive electrode active material layer (g)] × 100 (%) Similarly, the treated liquid obtained by contacting the negative electrode laminate with water was suction filtered using filter paper (manufactured by Whatman) having a particle retention capacity smaller than the volume average particle diameter (particle size distribution) of TNO, and the filtered residue was washed with ultrapure water to obtain TNO. The filter paper used was designed to allow CNTs to pass through. This was dried together with the filter paper in an electric furnace set at 120 ° C for 2 hours to recover 5.9 mg of TNO. When calculated using the following formula A1 from the TNO content of 6.5 mg of the negative electrode laminate used in the contacting step and the recovered TNO of 5.9 mg, the TNO recovery rate was 90 mass % or more. Formula A1: TNO recovery rate = [TNO recovery amount (g) / TNO content in the negative electrode active material layer (g)] × 100 (%)

[0212] As described above, the active materials LCO and TNO were recovered from the positive electrode laminate and the negative electrode laminate, respectively, at a high recovery rate of 90 mass% or more by a simple procedure of contacting them with water and performing solid-liquid separation. The LCO and TNO recovered in this manner had a purity sufficient for use as active material layers in all-solid-state secondary batteries. Note that each filtrate obtained in the solid-liquid separation step contains an oxide-based solid electrolyte, and if necessary, the oxide-based solid electrolyte (the lithium-containing oxide and lithium salt described above) can also be recovered from each filtrate.

[0213] [Example 2] In Example 2, the all-solid-state secondary battery produced in Production Example 1 was charged and discharged as follows, and then a positive electrode laminate and a negative electrode laminate were prepared in the same manner as in Example 1, and each laminate was subjected to a contact step in an atmospheric environment and a solid-liquid separation step. As a result, the positive electrode active material LOC and the negative electrode active material TNO were recovered with a high recovery rate, as in Example 1. <Charge and discharge of all-solid-state secondary battery> The all-solid-state secondary battery produced in Production Example 1 was charged and discharged at a current density of 0.8 mA / cm in an environment of 25°C. ２ The battery was charged at a current density of 0.8 mA / cm until the battery voltage reached 2.8 V. ２ The battery was discharged at 1000 psig until the battery voltage reached 1.5 V. This one charge and one discharge constituted one charge-discharge cycle, and 100 charge-discharge cycles were repeated under the same conditions.

[0214] In Example 2, the positive electrode laminate and the negative electrode laminate obtained from the all-solid-state secondary battery were used in the method for separating and recovering them, but the all-solid-state secondary battery itself can also be used in the method for separating and recovering them. In this case, the treated liquid obtained in the contacting step can be centrifuged, for example, to separate the positive electrode active material and the negative electrode active material by utilizing the density difference between the two active materials. Taking into consideration the results of Example 1 and the like, it can be understood that the two active materials can be separated from the other active material simultaneously with the oxide-based solid electrolyte and recovered at a high recovery rate.

[0215] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0216] This application claims priority based on Japanese Patent Application No. 2022-089966 filed in Japan on June 1, 2022, and Japanese Patent Application No. 2022-197051 filed in Japan on December 9, 2022, the contents of which are incorporated herein by reference.

[0217] REFERENCE SIGNS LIST 1 negative electrode current collector 2 negative electrode active material layer 3 solid electrolyte layer 4 positive electrode active material layer 5 positive electrode current collector 6 operating part 10 all-solid-state secondary battery

Claims

1. A method for recovering an active material from an all-solid-state secondary battery component including an active material layer containing an active material and an oxide-based solid electrolyte, comprising: the oxide-based solid electrolyte includes a solid electrolyte including a lithium-containing oxide including Li, B, and O, a lithium salt, and water, in which the ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte is 0.001 to 1.5 in terms of molar ratio, and the ratio of the content of the water is 1 to 12 in terms of molar ratio; The method for recovering an active material includes contacting the all-solid-state secondary battery component with an aqueous medium and then performing solid-liquid separation.

2. The method according to claim 1 , wherein the lithium-containing oxide comprises amorphous lithium tetraborate.

3. The method according to claim 1 or 2, wherein the all-solid-state secondary battery component is contacted with the aqueous medium in air, and then solid-liquid separation is performed.

4. The method according to claim 1 or 2, wherein the contact causes the oxide-based solid electrolyte to be dissolved in the aqueous medium, and the active material to be dispersed in the aqueous medium.

5. The method according to claim 1 or 2, wherein the active material is a positive electrode active material.

6. The recovery method according to claim 5 , wherein the positive electrode active material is a positive electrode active material containing a rare metal element.

7. 3. The method according to claim 1, wherein the all-solid-state secondary battery component is a component derived from a battery laminate including a positive electrode active material layer containing a positive electrode active material and an oxide-based solid electrolyte, or a negative electrode active material layer containing a negative electrode active material and an oxide-based solid electrolyte, and the oxide-based solid electrolyte both include a solid electrolyte containing a lithium-containing oxide containing Li, B, and O, a lithium salt, and water, and the ratio of the content of the lithium salt to the content of the lithium-containing oxide in the solid electrolyte is 0.001 to 1.5 in molar ratio, and the ratio of the content of the water is 1 to 12 in molar ratio.