Method for producing sulfide solid electrolyte and device for producing sulfide solid electrolyte

Abstract

The present invention provides a method for producing a sulfide solid electrolyte capable of continuously and stably producing a sulfide solid electrolyte exhibiting high lithium-ion conductivity. The present invention relates to a method for producing a sulfide solid electrolyte, the method comprising: preparing a sulfide solid electrolyte raw material based on stoichiometric ratio; supplying 0.1-20 mass% of a sulfur source relative to the total amount of the sulfide solid electrolyte raw material; heating and melting the sulfide solid electrolyte raw material; and cooling the obtained melt by contact with a cooling structure. The present invention also relates to a method for producing a sulfide solid electrolyte, the method comprising: preparing a sulfide solid electrolyte raw material based on stoichiometric ratio; heating and melting the sulfide solid electrolyte raw material; cooling the obtained melt by contact with a cooling structure; and obtaining a sulfide solid electrolyte in which the excess proportion of sulfur compared to the stoichiometric composition is 0.0-5.0 mass%.

Description

Method for producing sulfide solid electrolyte and apparatus for producing sulfide solid electrolyte

[0001] The present invention relates to a method for producing a sulfide solid electrolyte and an apparatus for producing a sulfide solid electrolyte.

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers. Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries. However, in recent years, all-solid-state lithium-ion secondary batteries, which use solid electrolytes as the electrolyte, have been attracting attention due to their potential for improved safety, high-speed charging and discharging, and compact housings.

[0003] Examples of solid electrolytes used in all-solid-state lithium ion secondary batteries include sulfide solid electrolytes.

[0004] One method for synthesizing sulfide solid electrolytes involves heating and melting sulfide solid electrolyte raw materials to prepare a melt, which is then cooled and solidified. However, this method has the problem of condensing gaseous volatile components generated from the melt during cooling and solidification, hindering stable production. In particular, in a manufacturing method in which sulfide solid electrolyte raw materials are continuously supplied into a furnace, the resulting melt is continuously discharged, and then cooled and solidified, a problem arises in that the melt condenses near the discharge outlet, hindering stable production.

[0005] Patent Document 1 discloses a method for producing solid electrolyte glass by compressing a raw material inlet, heating and melting the raw materials, cooling them, and continuously discharging them. Patent Document 2 discloses a method for producing a sulfide-based lithium ion conductive solid electrolyte by mixing the constituent compounds of a sulfide-based lithium ion conductive solid electrolyte in a predetermined stoichiometric ratio, and then heating and melting the mixture in an excess sulfur state.

[0006] Japanese Patent No. 5640665 Japanese Patent No. 3284215

[0007] However, with the technology disclosed in Patent Document 1, the flow paths are likely to solidify and become clogged when the melt is cooled, making stable production difficult. Furthermore, since the sulfide solid electrolyte is obtained in a block form, a multi-stage pulverization process is required, resulting in poor production efficiency. Furthermore, with the technology disclosed in Patent Document 2, when a chill roll is used to cool the melt, the melt wraps around the chill roll, making it difficult to continuously and stably produce the sulfide solid electrolyte.

[0008] Therefore, an object of the present invention is to provide a method for producing a sulfide solid electrolyte that solves the above-mentioned problems caused by the wrapping or adhesion of the melt around the cooling structure and enables continuous and stable production of a sulfide solid electrolyte that exhibits high lithium ion conductivity.

[0009] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by supplying a specific amount of a sulfur source to a sulfide solid electrolyte raw material mixed based on a stoichiometric ratio to produce a sulfide solid electrolyte having an excess ratio of sulfur of 0.0 to 5.0 mass % compared to the stoichiometric composition, and have completed the present invention. That is, the present invention relates to the following [1] to

[24] .

[0010] [1] A method for producing a sulfide solid electrolyte, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; supplying a sulfur source in an amount of 0.1 to 20 mass% relative to the total amount of the sulfide solid electrolyte raw material; heating and melting the sulfide solid electrolyte raw material; and cooling the resulting melt by contact with a cooling structure. [2] A method for producing a sulfide solid electrolyte, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; heating and melting the sulfide solid electrolyte raw material; and cooling the resulting melt by contact with a cooling structure, to obtain a sulfide solid electrolyte having an excess of sulfur of 0.0 to 5.0 mass% relative to the stoichiometric composition. [3] The method for producing a sulfide solid electrolyte according to [2], comprising supplying a sulfur source in an amount of 0.1 to 20 mass% relative to the total amount of the sulfide solid electrolyte raw material. [4] The method for producing a sulfide solid electrolyte according to [1] or [2], wherein the heating and melting temperature is 600 to 900°C. [5] The method for producing a sulfide solid electrolyte according to [1] or [2], wherein the cooling rate in the cooling is 10 to 10,000°C / sec. [6] The method for producing a sulfide solid electrolyte according to [1] or [3], wherein the sulfide solid electrolyte raw material is heated and melted, and then the sulfur source is supplied. [7] The method for producing a sulfide solid electrolyte according to [1] or [3], wherein the sulfide solid electrolyte raw material is heated and melted and the sulfur source is supplied simultaneously. [8] The method for producing a sulfide solid electrolyte according to [1] or [2], wherein the cooling structure is a metal roll or metal plate structure. [9] The method for producing a sulfide solid electrolyte according to [1] or [2], wherein the cooling structure is a cooling roll.

[10] The method for producing a sulfide solid electrolyte according to [9], wherein the cooling is performed by a twin-roll method, and the thickness of the sulfide solid electrolyte is adjusted by adjusting the roll gap between the twin rolls.

[11] The method for producing a sulfide solid electrolyte according to [8], wherein the cooling structure is a metal plate structure, and the metal plate is purged with an inert gas.

[12] The method for producing a sulfide solid electrolyte according to

[11] , wherein the thickness of the sulfide solid electrolyte is adjusted by adjusting an installation angle of the metal plate and an amount of purging of the inert gas.

[13] The method for producing a sulfide solid electrolyte according to [1] or [2], wherein the solid obtained after cooling is pulverized.

[14] The method for producing a sulfide solid electrolyte according to

[13] , wherein the pulverized solid is subjected to post-heat treatment.

[15] The method for producing a sulfide solid electrolyte according to [1] or [3], wherein a solid containing elemental sulfur is supplied as the sulfur source.

[16] The method for producing a sulfide solid electrolyte according to [1] or [3], wherein a liquid containing elemental sulfur is supplied as the sulfur source.

[17] The method for producing a sulfide solid electrolyte according to [1] or [3], wherein a gas containing elemental sulfur is supplied as the sulfur source.

[18] The sulfide solid electrolyte raw material is glass-ceramic, a crystalline phase having an LGPS-type crystal structure, or Li. ａ MZ ｂ Ha ｃ

[19] The method for producing a sulfide solid electrolyte according to [1] or [2], wherein the raw materials are mixed based on a stoichiometric ratio of a crystalline phase having an argyrodite-type crystal structure represented by the following compositional formula: wherein M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the argyrodite-type crystal structure, Z is at least one element selected from elements present as divalent anions in the argyrodite-type crystal structure, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and the compositional formula satisfies the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2.

[19] The method for producing a sulfide solid electrolyte according to

[18] , wherein M is P, Z is S, and Ha is Cl and Br in the argyrodite-type crystal structure.

[20] The method for producing a sulfide solid electrolyte according to [1] or [2], wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 3 mm.

[21] The method for producing a sulfide solid electrolyte according to

[20] , wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 0.9 mm.

[22] The method for producing a sulfide solid electrolyte according to

[20] , wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 0.6 mm.

[23] An apparatus for producing a sulfide solid electrolyte, used in the method for producing a sulfide solid electrolyte according to [1] or [2], comprising: a furnace body for heating and melting sulfide solid electrolyte raw materials; and a flow path for discharging a melt obtained by the heating and melting outside the furnace body, the apparatus comprising: a cooling section near a downstream end of the flow path for cooling the melt; and a cooling structure for cooling the melt.

[24] The apparatus for producing a sulfide solid electrolyte according to

[23] , wherein the melt is continuously discharged outside the furnace body.

[0011] The present invention solves the above-mentioned problems and provides a method for producing a sulfide solid electrolyte, which enables stable and continuous production of the sulfide solid electrolyte. The obtained sulfide solid electrolyte can achieve high lithium ion conductivity. Furthermore, the present invention provides an apparatus for producing a sulfide solid electrolyte, which can be suitably used in the production method.

[0012] FIG. 1 is a flowchart of a method for producing a sulfide solid electrolyte according to a first embodiment of the present invention. FIG. 2 is a flowchart of a method for producing a sulfide solid electrolyte according to another embodiment of the present invention. FIG. 3 is a flowchart of a method for producing a sulfide solid electrolyte according to another embodiment of the present invention. FIG. 4 is a cross-sectional schematic diagram showing an example of an apparatus for producing a sulfide solid electrolyte according to an embodiment of the present invention. FIG. 5 is a cross-sectional schematic diagram for explaining another example of an apparatus for producing a sulfide solid electrolyte in a production method according to an embodiment of the present invention. FIG. 6 is a cross-sectional schematic diagram for explaining another example of an apparatus for producing a sulfide solid electrolyte in a production method according to an embodiment of the present invention.

[0013] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired without departing from the spirit of the present invention. Furthermore, the use of "to" to indicate a numerical range means that the numerical values ​​before and after the range are included as the lower and upper limits. Furthermore, in this specification, "mass" is synonymous with "weight." Furthermore, in the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic for the purpose of clearly explaining the present invention and do not necessarily accurately represent the size or scale of an actual device, etc.

[0014] <Method for Producing Sulfide Solid Electrolyte> A method for producing a sulfide solid electrolyte according to a first embodiment of the present invention (hereinafter also referred to as the present production method) is characterized by including: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; supplying a sulfur source in an amount of 0.1 to 20 mass % relative to the total amount of the sulfide solid electrolyte raw material; heating and melting the sulfide solid electrolyte raw material; and cooling the resulting melt by contact with a cooling structure.

[0015] A method for producing a sulfide solid electrolyte according to a second embodiment of the present invention includes the steps of preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio, heating and melting the sulfide solid electrolyte raw material, cooling the resulting melt by contact with a cooling structure, and obtaining a sulfide solid electrolyte having an excess ratio of sulfur of 0.0 to 5.0 mass % compared to the stoichiometric composition.

[0016] 1 shows a flowchart of a production method according to a first embodiment of the present invention. In the production method according to the first embodiment of the present invention, a sulfide solid electrolyte raw material is first prepared based on a stoichiometric ratio (step S1), a sulfur source is supplied in an amount of 0.1 to 20 mass % relative to the total amount of the sulfide solid electrolyte raw material (step S2), and the sulfide solid electrolyte raw material is heated and melted (step S3) to obtain a melt (step S4). The resulting melt is then cooled by contact with a cooling structure (step S5), and a sulfide solid electrolyte is obtained (step S7).

[0017] In a manufacturing method according to a second embodiment of the present invention, a sulfide solid electrolyte raw material is prepared based on a stoichiometric ratio (Step S1), and the sulfide solid electrolyte raw material is heated and melted (Step S3) to obtain a melt (Step S4). The resulting melt is then cooled by contact with a cooling structure (Step S5), to obtain a sulfide solid electrolyte having an excess of sulfur of 0.0 to 5.0 mass% compared to the stoichiometric composition (Step S7). The manufacturing method according to the second embodiment of the present invention may also include supplying a sulfur source in an amount of 0.1 to 20 mass% based on the total amount of the sulfide solid electrolyte raw material (Step S2).

[0018] In a production method according to another embodiment of the present invention, if necessary, the sulfide solid electrolyte raw material may be heated and melted (step S3) and then the sulfur source may be supplied (step S2), or the heating and melting of the sulfide solid electrolyte raw material (step S3) and the supply of the sulfur source (step S2) may be performed simultaneously, as shown in Fig. 2. Furthermore, in a production method according to another embodiment of the present invention, if necessary, the solid obtained after cooling (step S5) may be pulverized (step S6a), and the pulverized solid may be subjected to a post-heat treatment (step S6b), as shown in Fig. 3.

[0019] In the production method according to the embodiment of the present invention, the sulfide solid electrolyte raw material and the sulfur source may be supplied into a furnace body. As the furnace body, a known furnace having a heating section and conventionally used for heating and melting solid electrolyte raw materials can be appropriately used, and the material and size of the furnace body can also be selected arbitrarily.

[0020] (Sulfide solid electrolyte raw material) In this production method, a sulfide solid electrolyte raw material (hereinafter sometimes simply referred to as a "sulfide solid electrolyte raw material" or "raw material") is prepared based on a stoichiometric ratio. The sulfide solid electrolyte raw materials can be mixed to form a raw material mixture. That is, the sulfide solid electrolyte raw materials can be mixed and used in a predetermined stoichiometric ratio according to the composition of the target sulfide solid electrolyte. In this production method, various raw materials can be used as the sulfide solid electrolyte raw material.

[0021] As the raw materials constituting the raw material mixture, commercially available sulfide solid electrolyte raw materials may be used, or a sulfide solid electrolyte raw material produced from a material may be used. Furthermore, these sulfide solid electrolyte raw materials may be further subjected to a known pretreatment. That is, the present production method may appropriately include a step of producing a raw material mixture and a step of subjecting the raw material mixture to a pretreatment.

[0022] The sulfide solid electrolyte raw material will be specifically described below. The sulfide solid electrolyte raw material usually contains an alkali metal element (R) and a sulfur element (S).

[0023] Examples of the alkali metal element (R) include lithium (Li), sodium (Na), and potassium (K), among which lithium (Li) is preferred. As the alkali metal element (R), an alkali metal element alone or a substance (component) containing an alkali metal element, such as a compound containing an alkali metal element, can be used in appropriate combination. Among these, as the lithium element, an alkali metal element alone or a substance (component) containing Li, such as a compound containing Li, can be used in appropriate combination.

[0024] Examples of substances containing lithium element (Li) include lithium sulfide (Li ２ S), lithium iodide (LiI), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ O), lithium nitride (Li ３ Examples of the material include lithium compounds such as lithium ion (Li), lithium hydroxide (LiOH), and metallic lithium. As the material containing lithium element (Li), it is preferable to use lithium sulfide from the viewpoint of obtaining a sulfide material.

[0025] As the sulfur element (S), simple S or a substance (component) containing S such as a compound containing S can be used in appropriate combination.

[0026] Examples of substances containing sulfur (S) include diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ), other sulfur compounds containing phosphorus, elemental sulfur, and compounds containing sulfur. ２ S, CS ２ , Na ２ S, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), antimony sulfide (Sb ２ S ３ ), copper sulfide (CuS, Cu２ S, Cu １－ｘ S, etc.), tin sulfide (SnS ２ ), tungsten sulfide (WS ２ From the viewpoint of obtaining a sulfide material, the substance containing sulfur element (S) is preferably phosphorus sulfide, and diphosphorus pentasulfide (P ２ S ５ ) is more preferable. These substances may be used alone or in combination of two or more. Phosphorus sulfide can be considered as a compound that serves as both an S-containing substance and a P-containing substance described later.

[0027] From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, the raw material mixture preferably further contains phosphorus (P). As the phosphorus (P), a suitable combination of P-containing substances (components), such as simple P or P-containing compounds, can be used.

[0028] Examples of substances containing phosphorus (P) include diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ As a substance containing elemental phosphorus (P), from the viewpoint of further exerting the effects of the present invention, phosphorus sulfide, which is highly volatile, is preferred, and diphosphorus pentasulfide (P ２ S ５ These substances may be used alone or in combination of two or more.

[0029] As described above, in this production method, sulfide solid electrolyte raw materials prepared based on a stoichiometric ratio are used. The raw material mixture can be obtained, for example, by mixing the above raw materials in a predetermined stoichiometric ratio corresponding to the composition of the target sulfide solid electrolyte. Examples of the mixing method include mixing in a mortar, mixing using a media such as a planetary ball mill, and medialess mixing such as a pin mill, a powder mixer, or airflow mixing.

[0030] An example of a preferred combination of alkali metal elements and sulfur elements contained in the raw material mixture is Li ２S and P ２ S ５ The combination of Li ２ S and P ２ S ５ When these are combined, the molar ratio of Li to P, Li / P, is preferably 40 / 60 or more, more preferably 50 / 50 or more. The molar ratio of Li to P, Li / P, is preferably 88 / 12 or less. The molar ratio of Li to P, Li / P, is preferably 40 / 60 to 88 / 12, more preferably 50 / 50 to 88 / 12. P ２ S ５ Li ２ By adjusting the mixture ratio so that the amount of Li is relatively small compared to S, ２ Melting point of S is ２ S ５ The low boiling point of the sulfur component makes it easier to suppress the volatilization of the sulfur component and the phosphorus component during the heat treatment.

[0031] On the other hand, since lithium sulfide is expensive, lithium compounds other than lithium sulfide, metallic lithium, etc. may be used from the viewpoint of reducing the production cost of the sulfide solid electrolyte. Specifically, in this case, the raw material may be a substance containing Li, such as metallic lithium, lithium iodide (LiI), or lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ It is preferable that the catalyst contains at least one selected from the group consisting of lithium ion (LiO) and lithium hydroxide (LiOH). These substances may be used alone or in combination of two or more.

[0032] The raw material mixture may contain further substances (compounds, etc.) in addition to the above substances depending on the composition of the desired sulfide solid electrolyte or as additives, etc.

[0033] For example, when a sulfide solid electrolyte containing a halogen element such as F, Cl, Br, or I is produced, the raw material mixture preferably contains a halogen element (Ha). In this case, the raw material mixture preferably contains a compound containing a halogen element. Examples of the compound containing a halogen element include lithium halides (LiHa) such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides such as sodium chloride (NaCl), and barium fluoride (BaF ２ ), barium halides, boron halides, yttrium chloride (YCl ３ yttrium halides such as indium chloride (InCl ３ indium halides such as zirconium chloride (ZrCl ４ ), zirconium halides such as lanthanum fluoride (LaF ２ As the compound containing a halogen element, lithium halide is preferred, and LiCl, LiBr, and LiI are more preferred, from the viewpoint of the reactivity of the raw material. These compounds may be used alone or in combination of two or more.

[0034] Note that an alkali metal halide such as lithium halide is also a compound containing an alkali metal element such as Li. When the raw material mixture contains an alkali metal halide, part or all of the alkali metal element such as Li in the raw material mixture may be derived from the alkali metal halide such as lithium halide.

[0035] When the raw material mixture contains a halogen element (Ha) and phosphorus element (P), the molar equivalent of Ha relative to P in the raw material mixture is preferably 0.2 molar equivalents or more, and more preferably 0.5 molar equivalents or more, from the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte. Furthermore, from the viewpoint of the stability of the resulting sulfide solid electrolyte, the molar equivalent of Ha is preferably 4 molar equivalents or less, and more preferably 3 molar equivalents or less.

[0036] The sulfide solid electrolyte obtained may be an amorphous sulfide solid electrolyte depending on the purpose. By facilitating the formation of an amorphous phase, an amorphous sulfide solid electrolyte can be obtained even if the cooling rate is reduced when an amorphous phase is obtained by rapid cooling, and the load on the equipment can be reduced.

[0037] In addition, from the viewpoint of imparting moisture resistance to the sulfide solid electrolyte, SiO ２ , B ２ O ３ , GeO ２ , Al ２ O ３ , P ２ O ５ , ZrO ２ , Ta ２ O ５ , TiO ２ , La ２ O ３ It is also preferable to contain oxides such as: These compounds may be used alone or in combination of two or more.

[0038] The oxide may be contained in the raw material mixture or may be added separately when the raw material mixture is heated and melted. The amount of the oxide added is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, based on the total amount of the raw material mixture. The amount added is preferably 50% by mass or less, more preferably 40% by mass or less.

[0039] The raw material may also contain a compound that will serve as a crystal nucleus, as described below.

[0040] This production method is particularly suitable when the raw material mixture contains a highly volatile compound. Examples of the highly volatile compound include LiI and B. ２ S ３ , S, Se, Sb ２ S ３ , and P ２ S ５ etc.

[0041] In an embodiment of the present invention, the sulfide solid electrolyte raw material is a crystallized glass, a crystalline phase having an LGPS-type crystal structure, or a Li ａ MZ ｂ Ha ｃIn the composition formula, M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the argyrodite-type crystal structure, Z is at least one element selected from elements present as divalent anions in the argyrodite-type crystal structure, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I; and it is preferable that the composition formula satisfy the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2.

[0042] Li ａ MZ ｂ Ha ｃ In one preferred embodiment, M is P, Z is S, and Ha is Cl and Br in the argyrodite-type crystal structure represented by the following composition formula: ａ MZ ｂ Ha ｃ The composition formula will be described in detail later.

[0043] (Apparatus for Producing Sulfide Solid Electrolyte) Here, an apparatus for producing a sulfide solid electrolyte that can be used in the present invention (hereinafter also referred to as the present production apparatus) will be described with reference to FIG. 4 . FIG. 4 is a cross-sectional schematic diagram showing an example of an apparatus for producing a sulfide solid electrolyte according to an embodiment of the present invention. In FIG. 4 , the apparatus for producing a sulfide solid electrolyte 1 includes a furnace body 10 for heating and melting a sulfide solid electrolyte raw material, and a flow path 12 for discharging a melt 11 obtained by the heating and melting outside the furnace body. A cooling section 14 for cooling the melt 11 is provided near a downstream end 18 of the flow path 12. A sulfide solid electrolyte 31 obtained by cooling the melt 11 may be contained in a container 20.

[0044] In the present manufacturing apparatus 1, it is preferable that the supply of the sulfide solid electrolyte raw material into the furnace body 10 and the discharge of the melt 11, which will be described below, out of the furnace body 10 are carried out continuously, and the effects of the present invention are further enhanced when this continuous manufacturing method is adopted. The continuous supply of the sulfide solid electrolyte raw material into the furnace body 10 is preferably a fixed amount supply, and the method for fixed amount supply is not particularly limited, but examples include methods using a screw feeder, a table feeder, air current conveyance, etc.

[0045] The present invention also relates to a sulfide solid electrolyte manufacturing apparatus used in the sulfide solid electrolyte manufacturing method of the present invention, the apparatus comprising: a furnace body for heating and melting a sulfide solid electrolyte raw material; a flow path for discharging a melt obtained by the heating and melting outside the furnace body; and a cooling section comprising a cooling structure for cooling the melt near a downstream end of the flow path. It is preferable that the melt is continuously discharged outside the furnace body.

[0046] (Supply of Sulfur Source) In the production method according to an embodiment of the present invention, 0.1 to 20 mass% of a sulfur source is supplied relative to the total amount of the raw material mixture (sulfide solid electrolyte raw material). By supplying 0.1 to 20 mass% of a sulfur source, a sulfide solid electrolyte can be obtained in which the excess amount of sulfur compared to the stoichiometric composition is within a predetermined range. The form of the sulfur source is not particularly limited, and the sulfur source may be a solid containing elemental sulfur, a liquid containing elemental sulfur, or a gas containing elemental sulfur. Furthermore, the sulfur source may be supplied to the sulfide solid electrolyte raw material before mixing, to a raw material mixture containing the sulfide solid electrolyte raw material, or to a melt obtained by heating and melting the sulfide solid electrolyte raw material.

[0047] When a gas containing elemental sulfur is supplied as the sulfur source, the sulfide solid electrolyte raw material may be heated and melted in a gas atmosphere containing elemental sulfur to supply the sulfur source. Heating and melting the raw material mixture in a gas atmosphere containing elemental sulfur introduces sulfur into the melt. This suppresses sulfur volatilization during heating, allowing the composition of the resulting sulfide solid electrolyte to be appropriately controlled, making it easier to obtain a sulfide solid electrolyte having an excess of sulfur of 0.0 to 5.0 mass% compared to the stoichiometric composition. The gas containing elemental sulfur may be, for example, a gas containing a compound containing elemental sulfur or elemental sulfur, such as sulfur gas, hydrogen sulfide gas, or carbon disulfide gas.

[0048] The gas containing elemental sulfur may be obtained by supplying a solid or liquid containing elemental sulfur as a sulfur source to the sulfide solid electrolyte raw material or a melt obtained by heating and melting the sulfide solid electrolyte raw material, and then heating the sulfur source to generate a gas containing elemental sulfur. By supplying a solid or liquid containing elemental sulfur as a sulfur source to the sulfide solid electrolyte raw material, the sulfur source is also heated when the sulfide solid electrolyte raw material is heated and melted, so that the sulfide solid electrolyte raw material can be heated and melted in an atmosphere of the generated gas containing elemental sulfur. Alternatively, a solid or liquid containing elemental sulfur as a sulfur source may be supplied to a melt obtained by heating and melting the sulfide solid electrolyte raw material.

[0049] Alternatively, the gas atmosphere containing elemental sulfur may be obtained by introducing sulfur vapor obtained in advance into the furnace body. For example, sulfur is heated at 200 to 450°C to generate sulfur vapor, and N ２ A gas atmosphere containing elemental sulfur can be obtained by transporting an inert gas such as argon gas or helium gas into the furnace as a carrier gas.

[0050] When a solid containing elemental sulfur is supplied as a sulfur source, the sulfur source is not particularly limited as long as it is elemental sulfur or a sulfur compound. For example, elemental sulfur, hydrogen sulfide, carbon disulfide and other organic sulfur compounds, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３), copper sulfide (CuS, Cu ２ S, Cu １－ｘ Examples of the sulfur source include polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubber vulcanized with sulfur, etc. As the sulfur source, sulfur powder is preferably used.

[0051] When a liquid containing elemental sulfur is supplied as a sulfur source, the sulfur source is not particularly limited as long as it is elemental sulfur or a sulfur compound. For example, elemental sulfur, hydrogen sulfide, carbon disulfide and other organic sulfur compounds, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ S, etc.), polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubbers that have been subjected to sulfur vulcanization treatment, etc.

[0052] The supply amount of the sulfur source must be 0.1 to 20 mass% relative to the total amount of the sulfide solid electrolyte raw material. If the supply amount of the sulfur source is less than 0.1 mass%, the effect of suppressing sulfur volatilization cannot be obtained. Furthermore, if the supply amount of the sulfur source exceeds 20 mass%, the melt wraps around the quench roll used in the cooling process, making continuous, stable production impossible. The inventors speculate that this is because the melting point of sulfur is lower than that of the electrolyte, and if the supply amount of the sulfur source exceeds 20 mass%, the melt does not completely solidify during quenching, causing excess sulfur to wrap around the roll. The supply amount of the sulfur source is preferably 1 mass% or more, more preferably 3 mass% or more, and even more preferably 5 mass% or more relative to the total amount of the sulfide solid electrolyte raw material. Furthermore, the supply amount is preferably 15 mass% or less, more preferably 10 mass% or less.

[0053] (Heat Melting) In a production method according to an embodiment of the present invention, a sulfide solid electrolyte raw material mixed based on a stoichiometric ratio is heated and melted. The heat melting temperature is not particularly limited, but is preferably 600°C or higher, more preferably 630°C or higher, even more preferably 650°C or higher, and particularly preferably 700°C or higher, from the viewpoint of homogenizing the melt in a short time. The heat melting temperature is preferably 1000°C or lower, more preferably 950°C or lower, even more preferably 900°C or lower, even more preferably 800°C or lower, and particularly preferably 750°C or lower, from the viewpoint of suppressing deterioration or decomposition of components in the melt due to heating. The heat melting temperature is preferably 600°C or higher but not higher than 900°C, more preferably 630°C or higher but not higher than 850°C, and even more preferably 650°C or higher but not higher than 800°C. Heating to the above temperatures can be performed, for example, by heating units (reference numeral 17 in FIG. 4 ) provided on the wall and bottom of the furnace body. The heating section 17 of the furnace body is not particularly limited, but for example, heaters that heat the object by passing an electric current through a heat generating material such as a Kanthal heater, a SiC heater, or a carbon heater, heaters that perform radiant heating such as a halogen heater, or a high-frequency induction heating device can be appropriately used to maintain the temperature inside the furnace body 10.

[0054] The heat-melting time for obtaining a melt is not particularly limited, but may be, for example, 0.5 hours or more, 1 hour or more, or 2 hours or more. Furthermore, the heat-melting time may be long as long as deterioration or decomposition of the components in the melt due to heating is acceptable. A practical range is preferably 100 hours or less, more preferably 50 hours or less, and even more preferably 25 hours or less.

[0055] The pressure during heating and melting is not particularly limited, but for example, normal pressure or slight pressure is preferred, and normal pressure is more preferred.

[0056] From the viewpoint of preventing side reactions with water vapor, oxygen, etc. during heat melting, the dew point in the furnace is preferably −20° C. or lower, and although there is no particular lower limit, it is usually −80° C. or higher. The oxygen concentration is preferably 1000 ppm by volume or lower.

[0057] (Discharge of Melt Outside Furnace Body) Subsequently, the obtained melt 11 may be discharged to a container 20 or the like outside the furnace body 10 through a flow path 12 as shown in Fig. 4. The flow path 12 may have a heating section for heating.

[0058] The flow path 12 is preferably capable of continuously discharging the melt 11 from the furnace body 10 and has a throttle portion capable of adjusting the flow rate and flow speed of the melt 11. That is, the flow path 12 preferably has a throttle portion. Furthermore, the throttle portion is more preferably in the form of a nozzle that is capable of adjusting the discharge amount and discharge speed of the melt 11 and that prevents a large amount of the melt 11 from being instantaneously discharged from the furnace body 10. That is, the throttle portion is preferably in the form of a nozzle.

[0059] The presence of a constricted portion in the flow path 12 has the following effects: Heating the outlet without a constricted portion would result in a large overall heat capacity and require a lot of energy, whereas the presence of a constricted portion in the flow path 12 makes it possible to locally reduce the heat capacity and not require as much energy; localized heating prevents excessive temperature rise in the melt 11 and makes it easier to maintain the crystal structure of the resulting sulfide solid electrolyte; installation of a heating unit for heating the flow path 12 having a constricted portion is simplified; installing a flow path 12 having a constricted portion near the cooling unit rapidly cools the high-temperature melt 11 and suppresses gas generation from the melt 11; this suppresses the adhesion of agglomerates derived from the gas and enables stable operation of the device; local temperature control is possible, so that stopping the operation of the heating unit solidifies the melt 11 and makes it possible to stop the outflow.

[0060] The flow rate of the melt 11 passing through the flow channel 12 may be determined taking into consideration the scale of the production apparatus, the type of desired sulfide solid electrolyte, etc., and is not particularly limited, but may be, for example, 4.0 kg / min or less. By setting the flow rate of the melt 11 passing through the flow channel 12 to 4.0 kg / min or less, the amount of heat generated when heating the flow channel 12 can be reduced. For example, when a nozzle-shaped throttle portion of the flow channel 12 is employed, the above flow rate can be adjusted by adjusting the size of the cross section of the nozzle in a direction perpendicular to the direction in which the melt 11 flows.

[0061] The flow path 12 may have a heating unit, and is heated, for example, by a heating unit installed along the flow direction of the flow path. This heating prevents the melt 11 from solidifying until it reaches a cooling unit described below, and prevents adhesion of gas-derived aggregates of the melt 11 to the flow path 12 and other peripheral equipment. The heating unit in the flow path 12 is not particularly limited, and examples thereof include heaters that heat an object by passing an electric current through a heat-generating material such as a Kanthal heater, a SiC heater, and a carbon heater; heaters that perform radiant heating such as a halogen heater; a high-frequency induction heating device; an electric current heating device; and the like, which can maintain the temperature of the melt 11 flowing through the flow path 12 at a desired temperature.

[0062] The heating temperature of the flow channel 12 may be appropriately determined depending on the type of sulfide solid electrolyte raw material, etc., but is preferably 500°C or higher, more preferably 525°C to 1000°C, and even more preferably 550°C to 950°C.

[0063] (Cooling of the melt) Subsequently, the melt 11 that has passed through the flow path 12 reaches the cooling section 14 provided near the downstream end 18 of the flow path, where the melt 11 can be cooled. In the manufacturing method according to an embodiment of the present invention, the obtained melt is cooled and solidified by contact with a cooling structure. The cooling structure is a structure that cools the melt. The cooling structure may be a structure that cools the inside or a structure that cools the outside, but from the viewpoint of cooling efficiency, a structure that cools the inside is preferable. Examples of the cooling structure include a cooling metal body, which is a structure made of metal, and a cooling ceramic, which is a structure made of ceramic. The shape of the cooling structure is not particularly limited, but examples include a cooling roll and a cooling plate. The cooling structure is preferably a cooling roll.

[0064] The cooling metal body is not particularly limited, and examples thereof include cooled structures such as metal rolls and metal plates. For example, the inside or outside of a metal structure may be cooled by water cooling or the like to form a metal cooling body. The cooling structure is preferably a metal roll or metal plate structure. The cooling ceramic is not particularly limited, and examples thereof include cooled structures such as ceramic rolls and ceramic plates. For example, the inside or outside of a ceramic structure may be cooled by water cooling or the like to form a cooling ceramic. Furthermore, the cooling structure may be partially or entirely made of metal, or partially or entirely made of ceramics. For example, the inside may be made of metal and the surface may be coated with another material such as ceramics.

[0065] Examples of contact with a cooling structure include contact with a cooling roll or a quenching twin roll by a roll method, and contact using a cooling plate such as a cooling metal plate, and contact with a quenching twin roll is preferred.

[0066] The contact with the cooling roll by the roll method may be carried out by a known roll method using a metal roll, and the method is not particularly limited as long as it is a roll method. More specific methods of cooling using rolls include, for example, a method in which the melt is poured into a water-cooled narrow gap to be quenched, as typified by a twin roll method; and a single roll method in which the melt is sprayed onto a roll rotating at high speed to be quenched. In an embodiment of the present invention, cooling is preferably carried out by the twin roll method, and more preferably by a roll method using a quenching twin roll.

[0067] When a melt is poured into a narrow gap by a twin-roll method or the like to form a thin sulfide solid electrolyte, the cooling efficiency is excellent, and a flake-like, fibrous, powder-like, or other form can be obtained. When a melt is poured between twin rolls and cooled by the twin-roll method, the thickness of the melt and the resulting solid (sulfide solid electrolyte) after pouring is preferably relatively thin, from the viewpoint of improving cooling efficiency. Specifically, the thickness is preferably 5 mm or less, more preferably 3 mm or less, even more preferably 2 mm or less, particularly preferably 0.9 mm or less, and most preferably 0.6 mm or less. The lower limit of the thickness is not particularly limited, but may be 0.1 mm or more, 0.2 mm or more, or even 0.3 mm or more. More specifically, the thickness is preferably 0.1 to 5 mm, more preferably 0.1 to 3 mm, even more preferably 0.1 to 0.9 mm, and particularly preferably 0.1 to 0.6 mm. The thickness of the resulting solid can be adjusted by adjusting the roll gap between the twin rolls. In an embodiment of the present invention, cooling of the melt is carried out by a twin roll method, and in one preferred embodiment, the thickness of the sulfide solid electrolyte is adjusted by adjusting the roll gap between the twin rolls.

[0068] Cooling using a metal plate is not particularly limited as long as it uses a cooled metal plate. For example, the melt can be poured from the end portion 18 of the flow path onto a cooled metal plate and cooled. In cooling using a metal plate, it is preferable that the location where the metal plate is installed is the cooling area, and the inside of the metal plate may be cooled, the outside of the metal plate may be cooled, or both may be used. Examples of cooling the metal plate include cooling with a liquid such as water or oil. In an embodiment of the present invention, it is preferable to water-cool the inside of the metal plate from the viewpoint of heat dissipation.

[0069] When the metal plate is cooled with a liquid, it is preferable to circulate the liquid inside the metal plate. The liquid may be circulated continuously or intermittently, and is preferably circulated continuously from the viewpoint of the amount of heat removal. The type, flow rate, and temperature of the liquid may be determined taking into consideration the scale of the production apparatus, the type of desired sulfide-based solid electrolyte, etc., and are not particularly limited. The temperature of the liquid may be, for example, 0°C or higher and 30°C or lower, or may be room temperature. The flow rate of the liquid may be, for example, 1.0 L / min or higher.

[0070] When a metal plate is used for the cooling, there are no particular limitations on the material of the metal plate, and examples thereof include iron, copper, stainless steel such as SUS304, aluminum, and titanium, with stainless steel being preferred. The size of the metal plate is not particularly limited, and can be determined taking into consideration the scale of the production equipment and the type of desired sulfide-based solid electrolyte, but can be, for example, 50 mm or more in width and 100 mm or more in length. There are also no particular limitations on the thickness of the metal plate, and it can be, for example, 20 mm or more.

[0071] The installation angle of the metal plate is not particularly limited, and may be 30° to 60° with respect to the horizontal direction. The lower limit of the installation angle of the metal plate may be 35° or more, or 40° or more with respect to the horizontal direction. The upper limit may be 55° or less, or 50° or less. The melt flowing onto the metal plate may be pressed by another metal body. The other metal body may be cooled or uncooled. Pressing with another metal body enhances the cooling effect and allows the thickness of the resulting solid to be adjusted. The material of the other metal body is not particularly limited, and examples include iron, copper, stainless steel such as SUS304, aluminum, and titanium, with stainless steel being preferred. The shape and size of the other metal body are also not particularly limited, and may be a metal plate.

[0072] The metal plate may be purged with an inert gas. Purging with the inert gas allows the obtained solid to be peeled off from the metal plate. Purging with the inert gas may be performed continuously or intermittently, and is preferably performed continuously from the viewpoint of not leaving the solid near the flow-down point. The type, flow rate, and temperature of the inert gas may be determined taking into consideration the scale of the production apparatus, the type of desired sulfide-based solid electrolyte, etc., and are not particularly limited. Examples of the inert gas include helium gas, neon gas, nitrogen gas, and argon gas, with nitrogen gas being preferred. The temperature of the inert gas may be, for example, −100° C. or higher and 50° C. or lower, or may be room temperature. The flow rate of the inert gas may be, for example, 1.0 L / min or higher.

[0073] In one preferred embodiment of the present invention, the cooling structure is a metal plate structure, and the metal plate is purged with an inert gas. The thickness of the obtained solid can be adjusted by adjusting the installation angle of the metal plate and the amount of purged inert gas.

[0074] The obtained solid can be obtained in any shape, but a pellet-shaped solid is preferable because it is easy to recover. Pellets include plate-shaped, flake-shaped, and fibrous shapes. By obtaining a pellet-shaped solid, it is possible to crush the solid in a single step without requiring multiple crushing steps. When the melt is cooled by a conventional method, multiple crushing steps are required, such as crushing the melt into a size that is easy to handle, such as a block, and then crushing the resulting solid into pellets that can be used in a mill. However, in the production method according to an embodiment of the present invention, the melt is cooled by contact with a cooling structure, making it easy to obtain a pellet-shaped solid.

[0075] Among pellets, flakes are preferred from the viewpoint of crushing efficiency, flakes having a thickness of 0.1 to 3 mm are more preferred, thin plates having a thickness of 0.1 to 0.9 mm are particularly preferred, and thin plates having a thickness of 0.1 to 0.6 mm are most preferred.

[0076] From the viewpoint of maintaining the composition obtained by heat melting, the cooling rate is preferably 0.01°C / sec or more, more preferably 0.05°C / sec or more, and even more preferably 0.1°C / sec or more. Although the upper limit of the cooling rate is not particularly determined, the cooling rate in the twin roll method, which is generally considered to have a fast quenching rate, is 10 ７ The cooling rate is 0.4 °C / sec or less. The cooling rate can also be adjusted by the outflow rate of the melt. When using the roll method, the cooling rate can also be adjusted by the roll gap and rotation speed of the twin rolls.

[0077] Here, when it is desired to obtain an amorphous sulfide solid electrolyte, it is preferable to obtain a solid by quenching the melt obtained by heating and melting. Specifically, the cooling rate in the quenching is preferably 10°C / sec or more, more preferably 100°C / sec or more, even more preferably 500°C / sec or more, and even more preferably 700°C / sec or more. In addition, although there is no particular upper limit for the cooling rate, the cooling rate in the twin-roll method, which is generally considered to have a fast quenching rate, is 10 ７ In the manufacturing method according to the embodiment of the present invention, the cooling rate is preferably 10 to 10,000° C. / sec.

[0078] On the other hand, slow cooling can be performed during cooling to crystallize at least a portion of the solid, thereby obtaining a sulfide solid electrolyte having a specific crystal structure or a sulfide solid electrolyte composed of a crystalline phase and an amorphous phase. When slowly cooling, the cooling rate is preferably 0.01°C / sec or more, more preferably 0.05°C / sec or more. Furthermore, the cooling rate is preferably 500°C / sec or less, more preferably 450°C / sec or less. The cooling rate may be 10°C / sec or less, or may be 5°C / sec or less. The cooling rate may be adjusted appropriately depending on the crystallization conditions. Here, the crystal contained in the sulfide solid electrolyte is preferably an ion-conductive crystal. Specifically, the ion-conductive crystal is a crystal having a lithium ion conductivity of 10 －４ S / cm, more preferably 10 －３ The crystals are larger than S / cm.

[0079] When it is desired that the solid obtained after cooling be a sulfide solid electrolyte containing a crystalline phase, it is preferable to include a compound that will become a crystal nucleus in the melt obtained by heat melting. This makes it easier for crystals to precipitate during cooling. The method for including the compound that will become a crystal nucleus in the melt is not particularly limited, but examples include adding the compound that will become a crystal nucleus to the raw material or the heated raw material, or adding the compound that will become a crystal nucleus to the melt during heat melting.

[0080] Examples of compounds that can become crystal nuclei include oxides, oxynitrides, nitrides, carbides, other chalcogen compounds, and halides. Compounds that can become crystal nuclei are preferably compounds that have a certain degree of compatibility with the melt. Note that compounds that are completely incompatible with the melt cannot become crystal nuclei.

[0081] When the solid obtained after cooling is intended to be a sulfide solid electrolyte containing a crystalline phase, the content of the compound that will become the crystal nuclei in the melt is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. On the other hand, from the viewpoint of suppressing a decrease in lithium ion conductivity, the content of the compound that will become the crystal nuclei in the melt is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0082] When the solid obtained after cooling is to be an amorphous sulfide solid electrolyte, it is preferable that the melt does not contain a compound that will become a crystal nucleus, or that the content of the compound is a predetermined amount or less. Specifically, the content of the compound that will become a crystal nucleus in the melt is preferably 1 mass% or less, more preferably 0.1 mass% or less. The content of the compound that will become a crystal nucleus in the melt may be less than 0.01 mass%.

[0083] In the present production method, the sulfide solid electrolyte obtained by cooling the melt may be subjected to known post-treatments, etc. Examples of post-treatments include a step of further subjecting the sulfide solid electrolyte to post-heat treatment in order to obtain desired properties, and a step of subjecting the sulfide solid electrolyte to pulverization in order to obtain a desired shape, etc.

[0084] This manufacturing method will be described with reference to the drawings. First, an example in which a twin-roll method is used for the cooling will be described. The twin-roll method is well known, and for example, as shown in FIG. 4 , melt 11 supplied from a flow path 12 is introduced between twin rolls consisting of water-cooled rolls 142 and 144 as a cooling section 14. After solidifying between the rolls 142 and 144, the melt is discharged in the form of a plate or flakes. The rolls 142 and 144 are installed near the downstream end of the flow path 12. Specifically, the distance from the downstream end is preferably 5 mm to 500 mm, more preferably 10 mm to 300 mm. The sulfide solid electrolyte solidified between the rolls 142 and 144 and discharged in the form of a plate can be powdered as needed.

[0085] Next, an example in which cooling using a metal plate is employed as the cooling method will be described. For example, as shown in FIG. 5 , melt 11 supplied from flow channel 12 is poured onto metal plate 145 as cooling unit 14, cooled and solidified on metal plate 145, and then recovered in the form of a plate or flakes. The thickness of the resulting solid may be adjusted by purging inert gas 146 onto metal plate 145 in the direction of the arrow to promote the casting and cooling of melt 11. Furthermore, melt 11 poured onto metal plate 145 may be pressed by another metal body 147 as shown in FIG. 6 . The melt 11 may be pressed by another metal body 147, for example, in the direction of the arrow. The sulfide solid electrolyte solidified on metal plate 145 and recovered in the form of a plate may be powdered as needed. That is, the solid obtained after cooling may be pulverized.

[0086] As described above, cooling by contact with a cooling structure is a method for rapidly cooling the melt, but from the viewpoint of suppressing gas generation, it is desirable that the melt be sufficiently heated until just before being rapidly cooled. Furthermore, it is preferable that the heating section of the flow path 12 be installed at a certain distance from the furnace body 10 to suppress the heat generated by the heating section from being transmitted to the furnace body 10.

[0087] On the other hand, in the present production apparatus, it is preferable to provide a heat insulating layer between the furnace body 10 and the flow path 12. Alternatively, it is preferable to provide a heat insulating layer between the furnace body 10 and the heating unit. The presence of the heat insulating layer can suppress the heat generated by heating the flow path 12 from propagating to the furnace body 10, making it possible to maintain the heating and melting conditions performed in the furnace body 10 at desired settings, and improving the quality of the obtained sulfide solid electrolyte.

[0088] The material of the heat insulating layer is not particularly limited, but examples thereof include ceramic fiber board, carbon fiber insulation, brick, calcium silicate material, rock rule material, etc. The heat insulating layer is preferably disposed over almost the entire bottom of the furnace body 10. The thickness of the heat insulating layer in the direction parallel to the flow direction of the melt 11 in the flow channel 12 is preferably, for example, 10 mm or more and 500 mm or less, and more preferably 20 mm or more and 250 mm or less.

[0089] (Post-heat treatment) In the present manufacturing method, the solid obtained after cooling the melt may be heated to perform a post-heat treatment. When the solid obtained by cooling the melt is an amorphous sulfide solid electrolyte or a sulfide solid electrolyte containing an amorphous phase, crystallization is promoted by performing a post-heat treatment by heating the solid electrolyte again. Furthermore, by reheating a sulfide solid electrolyte containing sulfide solid electrolyte crystals, ions in the crystal structure can be rearranged and the lithium ion conductivity can be increased. Note that the post-heat treatment refers to at least one of heating the solid obtained by cooling to crystallize it and rearranging ions in the crystal structure.

[0090] For example, the temperature in the post-heat treatment of the argyrodite-type crystal is preferably 300 to 550° C., more preferably 350 to 500° C., and even more preferably 400 to 450° C. Here, from the viewpoint of suitably obtaining the effects of the post-heat treatment and from the viewpoint of shortening the time for the post-heat treatment, the temperature for the post-heat treatment is preferably 300° C. or higher, more preferably 350° C. or higher, and even more preferably 400° C. or higher. Furthermore, from the viewpoint of preventing sintering of particles, the temperature for the post-heat treatment is preferably 550° C. or lower, more preferably 500° C. or lower, and even more preferably 450° C. or lower.

[0091] The post-heat treatment time is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, even more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. From the viewpoint of production stability, the post-heat treatment time is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and particularly preferably 1 hour or more. From the viewpoint of production cost, the post-heat treatment time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0092] The atmosphere for the post-heat treatment is preferably an inert atmosphere. Examples of the inert atmosphere include a nitrogen gas atmosphere, an argon gas atmosphere, and a helium gas atmosphere. The dew point during the post-heat treatment is preferably −20° C. or lower, and although there is no particular lower limit, it is usually about −80° C. The oxygen concentration is preferably 1000 ppm by volume or lower.

[0093] (Pulverization) The obtained sulfide solid electrolyte may be further pulverized to further reduce the particle size. Examples of pulverization methods include wet pulverization. In the case of wet pulverization, the type of solvent used is not particularly limited. However, since sulfide solid electrolytes tend to react with moisture and deteriorate, it is preferable to use a non-aqueous organic solvent. The type of non-aqueous organic solvent is not particularly limited, but examples include hydrocarbon solvents, organic solvents containing hydroxy groups, organic solvents containing ether groups, organic solvents containing carbonyl groups, organic solvents containing ester groups, organic solvents containing amino groups, organic solvents containing formyl groups, organic solvents containing carboxy groups, organic solvents containing amide groups, organic solvents containing benzene rings, organic solvents containing mercapto groups, organic solvents containing thioether groups, organic solvents containing thioester groups, organic solvents containing disulfide groups, and alkyl halides. Examples of hydrocarbon solvents include cyclohexane, heptane, octane, and toluene. Cyclohexane, heptane, and octane are preferred due to their low saturated water concentration. In addition, from the viewpoint of adjusting the water concentration, it is also preferable to use a mixed solvent in which these hydrocarbon solvents are mixed with toluene, dibutyl ether, or the like. From the viewpoint of preventing a decrease in lithium ion conductivity due to the reaction of the sulfide solid electrolyte with water during pulverization of the sulfide solid electrolyte, it is preferable that the water concentration of the non-aqueous organic solvent is low. The water concentration of the non-aqueous organic solvent may be, for example, 170 ppm by mass or less, 150 ppm by mass or less, 120 ppm by mass or less, or 100 ppm by mass or less.

[0094] The wet grinding method may be carried out using a grinder such as a ball mill, a planetary ball mill, a bead mill, etc. In the wet grinding, in addition to the above-mentioned solvent, an ether compound, an ester compound, or a nitrile compound may be added as an additive (dispersant).

[0095] If a solvent or additive remains in the sulfide solid electrolyte obtained through wet pulverization, a drying step may be carried out. Drying conditions may include a temperature of 100°C or higher and 200°C or lower. The drying time is not particularly limited and may be, for example, 10 minutes or longer and 24 hours or shorter. The drying step may also be carried out under reduced pressure, for example, an absolute pressure of 50 kPa or lower. The drying step may be carried out using a hot plate, a drying furnace, an electric furnace, or the like.

[0096] This production method can be used to produce various solid electrolytes, specific examples of which are shown in Tables 1 and 2. That is, the solid electrolytes shown in the representative composition column can be produced by melt-synthesizing the raw materials shown in the raw material column of Table 1 or Table 2. Note that the examples shown in Tables 1 and 2 are merely examples, and the scope of application of the present invention is not limited to these.

[0097]

[0098]

[0099] (Sulfide Solid Electrolyte) The present production method can provide a sulfide solid electrolyte having an excess of sulfur of 0.0 to 5.0 mass% relative to the stoichiometric composition. That is, the sulfide solid electrolyte obtained by the present production method has an excess of sulfur of 0.0 to 5.0 mass% relative to the stoichiometric composition of the sulfide solid electrolyte raw materials mixed based on the desired stoichiometric ratio.

[0100] Furthermore, the present production method can provide a sulfide solid electrolyte in which the excess proportion of sulfur compared to the stoichiometric composition in the sulfide solid electrolyte shown in Tables 1 and 2 is within a specific range.

[0101] The excess sulfur content compared to the stoichiometric composition is determined by subtracting the mass% of sulfur in the stoichiometric ratio (predetermined composition) from the measured mass% of the sulfur (S) content in the sample. The sulfur (S) content in the sample is quantified using oxygen flow combustion-infrared absorption spectroscopy. The sample is sealed in a Sn container in a glove box with a dew point of -50°C or less and the lid is placed on. The container is then placed in an apparatus (apparatus name: HORIBA, Ltd. Carbon / Sulfur Analyzer EMIA-Expert) and the analysis is performed.

[0102] The excess sulfur content relative to the stoichiometric composition must be 0.0 to 5.0% by mass. If the excess sulfur content is less than 0.0% by mass, the desired crystal structure cannot be obtained. Furthermore, if the excess sulfur content exceeds 5.0% by mass, the melt wraps around the quench roll used in the cooling process, preventing continuous, stable production. The inventors speculate that this is because the melting point of sulfur is lower than that of the electrolyte, and if the excess sulfur content exceeds 5.0% by mass, the melt does not completely solidify during quenching, causing the excess sulfur to wrap around the roll. The excess sulfur content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, relative to the raw material mixture. Furthermore, the excess sulfur content is preferably 4.0% by mass or less, more preferably 3.0% by mass or less.

[0103] In this manufacturing method, for example, a crystallized glass, a crystalline phase having an LGPS type crystal structure, or Li ａ MZ ｂ Ha ｃ It is possible to obtain a sulfide solid electrolyte in which the excess amount of sulfur is within a specific range compared to the stoichiometric composition, such as a crystalline phase having an argyrodite-type crystal structure represented by the composition formula Li ａ MZ ｂ Ha ｃ In the composition formula, M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the crystal structure, Z is at least one element selected from elements present as divalent anions in the crystal structure, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and the composition formula satisfies the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2. The sulfide solid electrolyte according to the embodiment of the present invention is preferably a sulfide solid electrolyte having an argyrodite-type crystal structure.

[0104] When the sulfide solid electrolyte powder according to this embodiment has an argyrodite-type crystal structure, it preferably contains a halogen (Ha) element as a constituent element, more preferably two or more kinds of Ha elements, more preferably at least one element selected from the group consisting of Cl, Br, and I, and even more preferably two or more kinds of elements.

[0105] The argyrodite-type crystal structure in this embodiment more preferably contains at least one of Cl and Br as the Ha element, and even more preferably contains Cl and Br.

[0106] When the argyrodite-type crystal structure contains two or more halogen elements, one of them is preferably Br, and the ratio of the Br content (at %) to the halogen element content (atoms %, hereinafter referred to as "at %) in the crystal structure is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7. Here, from the viewpoint of improving ionic conductivity, the ratio is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. Furthermore, from the viewpoint of suppressing a decrease in ionic conductivity, the ratio is preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.7 or less.

[0107] The argyrodite-type crystal structure preferably has the above structure, but the composition formula is Li ａ MZ ｂ Ha ｃ and it is preferable that the relationships 5≦a≦7, 4≦b≦6 and 1<c≦2 are satisfied.

[0108] In the above composition formula, M represents at least one element selected from Na, K, and elements that exist as divalent to pentavalent cations in the crystal structure, Z represents at least one element selected from elements that exist as divalent anions in the crystal structure, and Ha represents a halogen element.

[0109] Specific examples of elements M present as divalent to pentavalent cations in the above composition formula include B, Mg, Al, Si, P, Ca, Ti, V, Fe, Zn, Ga, Sr, Y, Zr, Nb, Mo, Sn, Sb, Ba, Ta, W, and Bi.

[0110] From the viewpoint of the oxidation-reduction potential of the element, it is preferable that the M mainly contains P. Specifically, "M mainly contains P" means that the ratio of the P content (at %) to the M content (at %) in the argyrodite-type crystal structure is 0.6 or more, and this ratio is preferably 0.6 to 1. This ratio is more preferably 0.7 or more, and even more preferably 0.8 or more. There is no particular upper limit to this ratio, and it may be 1, 0.98 or less, 0.97 or less, or 0.95 or less.

[0111] The M may contain, in addition to P, at least one element selected from Al, Na, K, Mg, and Ca. As a raw material for forming an argyrodite-type crystal structure, lithium sulfide (Li ２ In some cases, a mixture containing lithium sulfide (LiOH) may be preferably used. Here, it is widely known that lithium sulfide is produced from lithium hydroxide (LiOH), which may contain at least one element selected from the group consisting of Al, Na, K, Mg, and Ca (hereinafter also referred to as "R'") as an impurity. That is, M may contain R' derived from such impurities in the raw materials.

[0112] Reducing the content of R derived from impurities may require high-purity raw materials, which may increase manufacturing costs. The ratio of the R' content (at %) to the M content (at %) is preferably 0.001 to 0.4, more preferably 0.01 to 0.3. From the viewpoint of reducing manufacturing costs, the ratio is preferably 0.001 or more, more preferably 0.01 or more, and even more preferably 0.02 or more. Furthermore, from the viewpoint of suppressing a decrease in lithium ion conductivity, the ratio is preferably 0.4 or less, more preferably 0.3 or less.

[0113] The above range does not in any way preclude intentionally incorporating R' into the argyrodite-type crystal structure or incorporating more than the above-mentioned proportions. For example, in the above composition formula showing the argyrodite-type crystal structure, when Z contains O, the above R' contains at least one element selected from Al, Ca, Mg, Na and K, and the element is M. ｎ＋ It is preferable that M is present at the Li site as ｎ＋ represents a monovalent to trivalent cation. In this case, it is more preferable that R' contains Al. In this case, the content (at %) of R relative to the content (at %) of M may be higher than the above range.

[0114] In the above composition formula, Z represents at least one element selected from elements present as divalent anions in the crystal structure, such as S, O, Se, and Te. Among these, from the viewpoint of lithium ion conductivity, it is preferable that Z primarily contains S. Specifically, "Z primarily contains S" means that the ratio of the S content (at %) to the Z content (at %) in the crystal structure is 0.6 or more, and this ratio is preferably 0.6 to 1. This ratio is more preferably 0.7 or more, and even more preferably 0.8 or more. Furthermore, the upper limit of this ratio is not particularly limited, and may be 1, 0.98 or less, 0.95 or less, or 0.9 or less.

[0115] In addition, when S is contained as the above Z, a part of S may be Ha or BH in addition to the above O, Se, and Te. ４ , CN, etc.

[0116] In the above composition formula, the halogen element represented by Ha is preferably at least one element selected from the group consisting of F, Cl, Br, and I. From the viewpoint of easiness in forming an argyrodite-type crystal structure, the above Ha preferably contains at least one of Cl and Br, more preferably contains Br, and even more preferably Br alone or a mixture of Cl and Br. Furthermore, from the viewpoint of further improving lithium ion conductivity, the Ha is preferably a mixture of Cl and Br.

[0117] When Ha contains Cl and Br, where x (at%) is the Cl content in the argyrodite-type crystal structure and y (at%) is the Br content, the ratio (x / y) is preferably 0.1 to 10, more preferably 0.3 to 3, and even more preferably 0.5 to 1.6. Here, the ratio is preferably 0.1 or greater, more preferably 0.3 or greater, and even more preferably 0.5 or greater, and is preferably 10 or less, more preferably 3 or less, and even more preferably 1.6 or less. When the ratio (x / y) satisfies the above range, the interaction between lithium ions and halide ions is weakened, and lithium ion conductivity is likely to be improved. This is thought to be due to the mixed anion effect, which weakens the interaction between cations and anions by mixing bromide ions, which have a larger ionic radius than chloride ions. Furthermore, the cycle characteristics of lithium ion secondary batteries are likely to be improved.

[0118] When Ha contains Cl and Br, the ratio of the content (at%) of the elements constituting the argyrodite-type crystal structure is Li ａ MZ ｂ Cl ｃ１ Br ｃ２ When expressed as above, c1 is preferably 0.1 to 1.5, more preferably 0.3 to 1.4, and even more preferably 0.5 to 1.3. Here, c1 is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is preferably 1.5 or less, more preferably 1.4 or less, and even more preferably 1.3 or less. Furthermore, c2 is preferably 0.1 to 1.9, more preferably 0.3 to 1.6, and even more preferably 0.5 to 1.4. Here, c2 is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more, and is preferably 1.9 or less, more preferably 1.6 or less, and even more preferably 1.4 or less. When c1 and c2 each satisfy the above ranges, the proportion of halide ions in the crystal is optimized, and a stable argyrodite-type crystal is obtained while reducing the interaction between anions and lithium ions in the crystal structure. This tends to improve the lithium ion conductivity of the sulfide solid electrolyte powder. Furthermore, when c1 and c2 satisfy the above ranges, the cycle characteristics of the lithium ion secondary battery are likely to be improved.ａ MZ ｂ Cl ｃ１ Br ｃ２ In the composition formula represented by the formula (I), it is preferable that a, b, and (c1+c2) satisfy the same relationship as a, b, and c described below.

[0119] The above Li ａ MZ ｂ Ha ｃ The ratios of the elements in the composition formula represented by the formula preferably satisfy the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2, more preferably satisfy the relationships 5<a<7, 4<b<6, and 1.3<c<2, even more preferably satisfy the relationships 5.1<a<6.3, 4<b<5.3, and 1.4≦c≦1.9, and even more preferably satisfy the relationships 5.2<a<6.2, 4.1<b<5.2, and 1.5≦c≦1.8.

[0120] That is, a is preferably 5 or more, more preferably greater than 5, even more preferably greater than 5.1, even more preferably greater than 5.2, and preferably 7 or less, more preferably less than 7, even more preferably less than 6.3, and even more preferably less than 6.2. b is preferably 4 or more, more preferably greater than 4, even more preferably greater than 4.1, and preferably 6 or less, more preferably less than 6, even more preferably less than 5.3, and even more preferably less than 5.2. c is preferably greater than 1, more preferably 1.3 or more, even more preferably 1.4 or more, even more preferably 1.5 or more, and preferably 2 or less, more preferably less than 2, even more preferably 1.9 or less, and even more preferably 1.8 or less.

[0121] Li ａ MZ ｂ Ha ｃ In one preferred embodiment, in the argyrodite-type crystal structure represented by the composition formula: M is P, Z is S, and Ha is Cl and Br.

[0122] The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte, a sulfide solid electrolyte having a specific crystal structure, or a sulfide solid electrolyte containing a crystalline phase and an amorphous phase, depending on the purpose. From the viewpoint of preventing wrapping or adhesion to the cooling structure, the crystalline phase is preferably an argyrodite-type crystalline phase.

[0123] The obtained sulfide solid electrolyte can be identified by analyzing the crystal structure by X-ray diffraction (XRD) measurement, or by analyzing the elemental composition using various methods such as ICP emission spectrometry, atomic absorption spectrometry, and ion chromatography. For example, P and S can be measured by ICP emission spectrometry, Li can be measured by atomic absorption spectrometry, and Ha can be measured by ion chromatography.

[0124] The lithium ion conductivity of the sulfide solid electrolyte according to this embodiment at 25° C. is 0.1×10 －３ S / cm or more is preferable, and 1×10 －３ S / cm or more is more preferable, and 2×10 －３ The upper limit of the lithium ion conductivity is not particularly limited, but it is usually 1×10 －１ The lithium ion conductivity is 0.05 S / cm or less. The lithium ion conductivity can be measured by an AC impedance method. Specifically, the lithium ion conductivity is a value measured using an AC impedance measuring device (for example, a potentiostat / galvanostat VSP manufactured by Bio-Logic Sciences Instruments) under the following conditions: a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C.

[0125] The sulfide solid electrolyte according to this embodiment is suitable for use in electrode mixtures and solid electrolyte layers used in secondary batteries, and is particularly suitable for all-solid-state secondary batteries, and more suitable for all-solid-state lithium-ion secondary batteries. That is, the electrode mixture is used in secondary batteries and contains the sulfide solid electrolyte and an active material. The solid electrolyte layer is used in secondary batteries and contains the sulfide solid electrolyte.

[0126] The electrode mixture, solid electrolyte layer, and all-solid-state lithium ion secondary battery may further contain other solid electrolytes in addition to the sulfide solid electrolyte according to this embodiment.

[0127] The active material contained in the electrode mixture may be a conventionally known material. The positive electrode active material is not particularly limited as long as it can reversibly absorb and release alkali metal ions, intercalate and deintercalate alkali metal ions, or dope and dedope counter anions of the alkali metal ions. Here, the alkali metal ion is preferably lithium ion. Specific examples of the positive electrode active material include lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, composite metal oxides, and polyanion olivine-type positive electrodes.

[0128] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release alkali metal ions, detach and insert (intercalate) alkali metal ions, or reversibly dope and dedope counter anions of the alkali metal ions. Here, the alkali metal ions are preferably lithium ions. Specific examples of the negative electrode active material include lithium metal, carbon-based materials such as graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0129] The solid electrolyte layer may contain the sulfide solid electrolyte according to the present embodiment, but may also contain other solid electrolytes and additives such as a binder. Conventionally known binders can be used, such as butadiene rubber, acrylate butadiene rubber, styrene butadiene rubber, polyvinylidene fluoride, and polytetrafluoroethylene. The binder content in the solid electrolyte layer may also be within a conventionally known range.

[0130] The all-solid-state secondary battery is not particularly limited as long as it includes a positive electrode and a negative electrode in addition to the sulfide solid electrolyte according to this embodiment. The positive electrode and the negative electrode may be an electrode mixture containing the sulfide solid electrolyte according to this embodiment. The positive electrode active material may be the same as the positive electrode active material described in the electrode mixture, and the positive electrode may further include a positive electrode current collector, a binder, a conductive additive, and the like, as necessary. The positive electrode current collector may be made of aluminum, an alloy thereof, a thin metal plate such as stainless steel, or the like.

[0131] The negative electrode active material can be the same as the negative electrode active material described in the electrode mixture, and the negative electrode may further contain, as necessary, a negative electrode current collector, a binder, a conductive additive, etc. The negative electrode current collector can be a thin metal plate such as copper or aluminum.

[0132] The present invention is not limited to the above-described embodiments, and various modifications can be adopted within the scope of the present invention. For example, the present invention is not limited to the above-described embodiments, and modifications and improvements can be made as appropriate. In addition, the material, shape, size, number, and location of each component in the above-described embodiments are arbitrary and not limited as long as the present invention can be achieved.

[0133] As described above, the present specification discloses the following: <1> A method for producing a sulfide solid electrolyte, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; supplying a sulfur source in an amount of 0.1 to 20 mass% relative to the total amount of the sulfide solid electrolyte raw material; heating and melting the sulfide solid electrolyte raw material; and cooling the resulting melt by contact with a cooling structure. <2> A method for producing a sulfide solid electrolyte, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; heating and melting the sulfide solid electrolyte raw material; and cooling the resulting melt by contact with a cooling structure, to obtain a sulfide solid electrolyte having an excess ratio of sulfur of 0.0 to 5.0 mass% relative to the stoichiometric composition. <3> A method for producing a sulfide solid electrolyte according to <2>, comprising supplying a sulfur source in an amount of 0.1 to 20 mass% relative to the total amount of the sulfide solid electrolyte raw material. <4> A method for producing a sulfide solid electrolyte according to any one of <1> to <3>, wherein the heating and melting temperature is 600 to 900°C. <5> The method for producing a sulfide solid electrolyte according to any one of <1> to <4>, wherein the cooling rate in the cooling is 10 to 10,000°C / second. <6> The method for producing a sulfide solid electrolyte according to <1> or <3>, wherein the sulfide solid electrolyte raw material is heated and melted, and then the sulfur source is supplied. <7> The method for producing a sulfide solid electrolyte according to <1> or <3>, wherein the heating and melting of the sulfide solid electrolyte raw material and the supply of the sulfur source are carried out simultaneously. <8> The method for producing a sulfide solid electrolyte according to any one of <1> to <7>, wherein the cooling structure is a metal roll or a metal plate structure. <9> The method for producing a sulfide solid electrolyte according to any one of <1> to <8>, wherein the cooling structure is a cooling roll. <10> The method for producing a sulfide solid electrolyte according to <9>, wherein the cooling is carried out by a twin-roll method, and the thickness of the sulfide solid electrolyte is adjusted by adjusting the roll gap between the twin rolls. <11> The method for producing a sulfide solid electrolyte according to <8>, wherein the cooling structure is a metal plate structure and an inert gas is purged into the metal plate. <12> The method for producing a sulfide solid electrolyte according to <11>, wherein a thickness of the sulfide solid electrolyte is adjusted by adjusting an installation angle of the metal plate or an amount of purged inert gas.<13> The method for producing a sulfide solid electrolyte according to any one of <1> to <12>, wherein the solid obtained after cooling is pulverized. <14> The method for producing a sulfide solid electrolyte according to <13>, wherein the pulverized solid is subjected to a post-heat treatment. <15> The method for producing a sulfide solid electrolyte according to <1> or <3>, wherein a solid containing elemental sulfur is supplied as the sulfur source. <16> The method for producing a sulfide solid electrolyte according to <1> or <3>, wherein a liquid containing elemental sulfur is supplied as the sulfur source. <17> The method for producing a sulfide solid electrolyte according to <1> or <3>, wherein a gas containing elemental sulfur is supplied as the sulfur source. <18> The sulfide solid electrolyte raw material is glass-ceramic, a crystalline phase having an LGPS-type crystal structure, or Li. ａ MZ ｂ Ha ｃ<19> The method for producing a sulfide solid electrolyte according to any one of <1> to <17>, wherein the raw materials are mixed based on a stoichiometric ratio of a crystalline phase having an argyrodite-type crystal structure represented by the following compositional formula: wherein M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the argyrodite-type crystal structure, Z is at least one element selected from elements present as divalent anions in the argyrodite-type crystal structure, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and the compositional formula satisfies the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2. <20> The method for producing a sulfide solid electrolyte according to <18>, wherein M is P, Z is S, and Ha is Cl and Br in the argyrodite-type crystal structure. <20> The method for producing a sulfide solid electrolyte according to any one of <1> to <19>, wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 3 mm. <21> The method for producing a sulfide solid electrolyte according to <20>, wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 0.9 mm. <22> The method for producing a sulfide solid electrolyte according to <20>, wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 0.6 mm. <23> An apparatus for producing a sulfide solid electrolyte, used in the method for producing a sulfide solid electrolyte according to any one of <1> to <22>, comprising: a furnace body for heating and melting sulfide solid electrolyte raw materials; and a flow path for discharging a melt obtained by the heating and melting outside the furnace body, and comprising a cooling section formed of a cooling structure for cooling the melt near a downstream end of the flow path. <24> The apparatus for producing a sulfide solid electrolyte according to <23>, wherein the melt is continuously discharged to the outside of the furnace body.

[0134] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1 to 4 are working examples, and Examples 5 to 7 are comparative examples.

[0135] Example 1: Li was dissolved in a dry nitrogen gas atmosphere. ５．４０ P １．０ S ４．４ Cl ０．８ Br ０．８Lithium sulfide powder (manufactured by Sigma, purity 99.98%), diphosphorus pentasulfide powder (manufactured by Sigma, purity 99%), lithium chloride powder, and lithium bromide powder (manufactured by Sigma, purity 99.995%) were weighed out so as to have a composition ratio of the above, and mixed in a mortar to obtain mixture 1 (step S1).

[0136] To the obtained mixture 1, sulfur powder (manufactured by Sigma, purity 99.998%) was added as a sulfur source so as to give an addition concentration of 1 mass % (step S2), and the mixture was placed in a carbon-coated quartz container under a nitrogen atmosphere with a dew point of −50° C. or less, and the container was sealed. The container was then placed in an electric furnace (furnace body) inside a glove box, and heated at a pressure of gauge pressure + 1 kPa and a temperature of 750° C. for 1 hour (step S3), thereby obtaining a completely dissolved molten material (melt) (step 4).

[0137] Next, the tip of the container was heated to melt the melt, and the melt was poured onto a metallic twin roll from the melt outlet and cooled to room temperature at a cooling rate of 3000°C / s (step S5), thereby obtaining a sulfide solid electrolyte in the form of a thin crystalline phase (step S7). The pressure during this process was (gauge pressure + 1 kPa), and the cooling rate was adjusted by the melt outflow rate, the roll gap of the twin rolls, and the rotation speed.

[0138] <Evaluation> <Composition> The sulfide solid electrolytes obtained in Examples 1 to 7 were weighed in a glove box and dissolved in an alkaline aqueous solution, and composition analysis was performed for each element. Specifically, P was analyzed by ICP atomic emission spectroscopy (apparatus: Hitachi High-Tech Science Corporation, model PS3520UVDDII). Li was analyzed by atomic absorption spectroscopy (apparatus: Hitachi High-Tech Corporation, model ZA3300; when measuring Li, CsCl was added so that the solution concentration became 0.1%). Cl, Br, and I were analyzed by ion chromatography (apparatus: Thermo Fisher Scientific, model ICS-2100 (column: AS11HC)). ２ O ２ A small amount of the solution was added, diluted with ultrapure water, and then the measurement was carried out.

[0139] Sulfur (S) was quantified by oxygen flow combustion-infrared absorption method (apparatus: EMIA-expert carbon and sulfur analyzer manufactured by Horiba, Ltd.). The sample was sealed in a Sn container in a glove box with a dew point of -50°C or less, and the lid was placed on the container. The container was then set in the analyzer and analysis was carried out. The results are shown in the "Composition" column in Table 3.

[0140] <Excess Sulfur Ratio> For the sulfide solid electrolyte obtained in each example, the excess sulfur ratio (excess S ratio) (mass%) was calculated by subtracting the mass% of sulfur in the stoichiometric ratio (predetermined composition) from the measured value of sulfur.

[0141] <Yield> In Examples 1 to 7, the ratio of the sulfide solid electrolyte obtained until the electrolyte adhered to the cooling structure to the mass of Mixture 1 is shown in Table 3 as the yield (mass %).

[0142] <Average Thickness and Average Particle Size> For the sulfide solid electrolytes obtained in Examples 1 to 7, the average thickness (mm) was calculated by measuring the thickness at 10 random locations using a constant pressure thickness gauge (manufactured by Teclock Corporation, product name PG-20J), and 10 flaky samples were randomly selected and their maximum lengths were measured with vernier calipers to calculate the average particle size (mm), which is shown in Table 3. However, if lumps were observed after electrolyte deposition, the thickness and particle size of the lumps were measured.

[0143] <Lithium ion conductivity 1> The sulfide solid electrolytes obtained in Examples 1 to 7 were used as samples, and lithium ion conductivity 1 was measured using an AC impedance measuring device (potentiostat / galvanostat VSP, manufactured by Bio-Logic Sciences Instruments). The measurement conditions were a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C. The results are shown in Table 3.

[0144] <Crushing and Post-Heat Treatment> The sulfide solid electrolyte obtained above was crushed in a nitrogen atmosphere using a pin mill (100UPZ manufactured by Hosokawa Micron Corporation) at 15,000 rpm for 1 hour to obtain a powder (step S6a). Post-heat treatment was performed by heating at 430°C for 1 hour (step S6b) to increase the crystallinity of the crystalline phase, and then cooled to room temperature at a cooling rate of 300°C / min to obtain a post-heat-treated sulfide solid electrolyte powder (step S7).

[0145] <Proportion of Particles of 100 μm or Less> The volume proportion of particles of 100 μm or less in the sulfide solid electrolyte powder obtained after pulverization was calculated using a laser diffraction particle size distribution analyzer (Microtrac MT3300EX II manufactured by Microtrac-Bell Corporation), and the results are shown in Table 3.

[0146] Examples 2 to 7 Sulfide solid electrolytes (sulfide solid electrolyte powders) of Examples 2 to 7 were obtained in the same manner as in Example 1, except that the concentration of sulfur powder added was changed as shown in Table 3, and evaluated in the same manner as in Example 1.

[0147]

[0148] From the above results, the sulfide solid electrolytes of Examples 1 to 4 obtained by the production method according to this embodiment did not wrap around the chill roll, enabling stable continuous production. Furthermore, preventing the wrapping around the chill roll increased the yield. Furthermore, the sulfide solid electrolytes of Examples 1 to 4 obtained by the production method according to this embodiment were able to achieve high lithium ion conductivity and were obtained as pellet-shaped solids, so they could be crushed in a single step without requiring multiple crushing steps.

[0149] On the other hand, in Examples 5 and 6, in which more than 20% by mass of the sulfur source was supplied to the sulfide solid electrolyte raw material, the excess proportion of sulfur compared to the stoichiometric composition exceeded 5.0% by mass, the sulfide solid electrolyte wrapped around the chill roll, the yield was low, and stable continuous production could not be achieved. Furthermore, in Example 7, in which no sulfur source was supplied, a sulfide solid electrolyte was obtained in which the excess proportion of sulfur compared to the stoichiometric composition was less than 0.1% by mass, the lithium ion conductivity was low, and the performance as a sulfide solid electrolyte was poor.

[0150] The present invention provides a method for producing a sulfide solid electrolyte that can continuously and stably produce a sulfide solid electrolyte exhibiting high lithium ion conductivity, and also provides an apparatus for producing a sulfide solid electrolyte that can be suitably used in the method.

[0151] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2024-066753) filed on April 17, 2024, the contents of which are incorporated herein by reference.

[0152] REFERENCE SIGNS LIST 1 Apparatus for producing sulfide solid electrolyte 10 Furnace body 11 Melt 12 Flow path 14 Cooling section 142, 144 Roll 145 Metal plate 146 Inert gas 147 Other metal plate 17 Heating section (of furnace body) 18 End section 20 Container 31 Sulfide solid electrolyte

Claims

1. A method for producing a sulfide solid electrolyte, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; supplying a sulfur source in an amount of 0.1 to 20 mass% based on the total amount of the sulfide solid electrolyte raw material; heating and melting the sulfide solid electrolyte raw material; and cooling the resulting melt by contact with a cooling structure.

2. A method for producing a sulfide solid electrolyte, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; heating and melting the sulfide solid electrolyte raw material; cooling the resulting melt by contact with a cooling structure; and obtaining a sulfide solid electrolyte having an excess ratio of sulfur of 0.0 to 5.0 mass % compared to the stoichiometric composition.

3. The method for producing a sulfide solid electrolyte according to claim 2, comprising supplying a sulfur source in an amount of 0.1 to 20 mass % based on the total amount of the sulfide solid electrolyte raw materials.

4. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the heating and melting temperature is 600 to 900°C.

5. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the cooling rate is 10 to 10,000°C / sec.

6. The method for producing a sulfide solid electrolyte according to claim 1 or 3, wherein the sulfide solid electrolyte raw material is heated and melted, and then the sulfur source is supplied.

7. The method for producing a sulfide solid electrolyte according to claim 1 or 3, wherein the heating and melting of the sulfide solid electrolyte raw material and the supply of the sulfur source are carried out simultaneously.

8. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the cooling structure is a metal roll or metal plate structure.

9. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the cooling structure is a cooling roll.

10. The method for producing a sulfide solid electrolyte according to claim 9, wherein the cooling is performed by a twin roll method, and the thickness of the sulfide solid electrolyte is adjusted by adjusting the roll gap between the twin rolls.

11. The method for producing a sulfide solid electrolyte according to claim 8, wherein the cooling structure is a metal plate structure, and the metal plate is purged with an inert gas.

12. The method for producing a sulfide solid electrolyte according to claim 11, wherein the thickness of the sulfide solid electrolyte is adjusted by adjusting the installation angle of the metal plate and the amount of purging of the inert gas.

13. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the solid obtained after the cooling is pulverized.

14. The method for producing a sulfide solid electrolyte according to claim 13, wherein the solid after the pulverization is subjected to a post-heat treatment.

15. The method for producing a sulfide solid electrolyte according to claim 1 or 3, wherein a solid containing elemental sulfur is supplied as the sulfur source.

16. The method for producing a sulfide solid electrolyte according to claim 1 or 3, wherein a liquid containing elemental sulfur is supplied as the sulfur source.

17. The method for producing a sulfide solid electrolyte according to claim 1 or 3, wherein a gas containing elemental sulfur is supplied as the sulfur source.

18. The sulfide solid electrolyte raw material is a crystallized glass, a crystalline phase having an LGPS type crystal structure, or Li ａ MZ ｂ Ha ｃ 3. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the raw materials are mixed based on a stoichiometric ratio of a crystalline phase having an argyrodite-type crystal structure represented by a composition formula: wherein in the composition formula, M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the argyrodite-type crystal structure, Z is at least one element selected from elements present as divalent anions in the argyrodite-type crystal structure, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and the composition formula satisfies the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2.

19. A method for producing a sulfide solid electrolyte according to claim 18, wherein in the argyrodite-type crystal structure, M is P, Z is S, and Ha is Cl and Br.

20. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 3 mm.

21. The method for producing a sulfide solid electrolyte according to claim 20, wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 0.9 mm.

22. The method for producing a sulfide solid electrolyte according to claim 20, wherein the sulfide solid electrolyte is in the form of a thin plate having a thickness of 0.1 to 0.6 mm.

23. A sulfide solid electrolyte manufacturing apparatus used in the sulfide solid electrolyte manufacturing method according to claim 1 or 2, comprising a furnace body for heating and melting sulfide solid electrolyte raw materials, and a flow path for discharging the molten liquid obtained by said heating and melting outside the furnace body, and a cooling section comprising a cooling structure for cooling the molten liquid near the downstream end of said flow path.

24. The apparatus for producing a sulfide solid electrolyte according to claim 23, wherein the melt is continuously discharged from the furnace body.

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