Method for producing sulfide solid electrolyte and sulfide solid electrolyte

Abstract

The present invention provides a method for producing a sulfide solid electrolyte capable of enhancing solubility of a raw material when producing the sulfide solid electrolyte by a melting method. The present invention relates to a method for producing a sulfide solid electrolyte containing at least one element of Sn, Si and Sb by heating and melting a sulfide solid electrolyte raw material containing at least one element of Sn, Si and Sb in a gas atmosphere containing a sulfur element and cooling and solidifying the obtained melt, wherein the heating and melting increases the valence of the element contained in the sulfide solid electrolyte raw material.

Description

Method for producing sulfide solid electrolyte and sulfide solid electrolyte

[0001] The present invention relates to a method for producing a sulfide solid electrolyte and 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. Meanwhile, in recent years, all-solid-state lithium ion secondary batteries, which use solid electrolytes as the electrolyte, have been attracting attention due to the promise of improved safety, high-speed charging and discharging, and smaller cases. Examples of solid electrolytes used in all-solid-state lithium ion secondary batteries include sulfide solid electrolytes. The most common sulfide solid electrolytes are Li-P-S-based crystallized glass, Li-P-S-Ha-based crystallized glass, and Li-P-S-Ha-based argyrodite-type crystals.

[0003] On the other hand, H ２ From the viewpoint of suppressing the generation of S and the decrease in ionic conductivity due to exposure to moisture, the PS contained in sulfide solid electrolytes ４ A new type of sulfide solid electrolyte is also known in which a part or all of the sulfide is replaced by another tetrahedral structure. For example, Non-Patent Document 1 discloses a sulfide solid electrolyte having an argyrodite-type crystal structure, such as PS ４ Another tetrahedral structure of SbS ４ Li replaced with ６．６ [Si ０．６ Sb ０．４ ]S ５ In addition, Non-Patent Document 2 describes Li ６．５ [P ０．２５ Si ０．２５ Ge ０．２５ Sb ０．２５ ]S ５ I is listed.

[0004] Laidong Zhou et al., “New Family of Argyrodite Thioantimonate Lithium Superionic Conductors”, J. Am. Chem. Soc. 2019, 141, 48, 19002‐19013Jing Lin et al., “A High-Entropy Multicationic Substituted Lithium Argyrodite Superionic Solid Electrolyte”, ACS Materials Lett. 2022, 4, 2187-2194

[0005] The typical method for producing such a new type of sulfide solid electrolyte is to perform pretreatment by mechanical milling, then seal the sample in a vacuum sealed tube and heat treat it for a long time to obtain a sulfide solid electrolyte. ４ In addition, SnS ４ , SiS ４ , and SbS ４ As described above, in order to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb through pretreatment by mechanical milling, it has been necessary to apply a huge amount of energy during production, making it impractical to mass-produce the sulfide solid electrolyte by mechanical milling.

[0006] The present inventors have focused on the melting method, rather than the mechanical milling method, as a method for producing the sulfide solid electrolyte. ４ Another tetrahedral structure of SnS ４ It has become clear that replacing the raw materials with sulfide or sulfur dioxide increases the melting point of the raw materials, resulting in poor solubility of the raw materials. Poor solubility of the raw materials can lead to problems such as difficulty in designing heating devices such as heaters suitable for melting, corrosion of furnace materials and containers due to high heating temperatures, increased volatilization of constituent components, and an increase in the amount of heat required for cooling. Furthermore, low solubility of the raw materials can make it difficult to obtain a homogeneous sulfide solid electrolyte, which may result in a decrease in lithium ion conductivity.

[0007] An object of the present invention is to provide a method for producing a sulfide solid electrolyte that can increase the solubility of raw materials when producing a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb by a melting method.

[0008] As a result of extensive research, the present inventors have found that, when a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb is produced by a melting method, the solubility of the raw material can be improved by increasing the valence of at least one element selected from Sn, Si, and Sb contained in the sulfide solid electrolyte raw material through heating and melting, i.e., by making the valence of the element contained in the sulfide solid electrolyte to be produced greater than the valence of the element contained in the sulfide solid electrolyte raw material. Furthermore, the present inventors have found that, when a sulfide solid electrolyte is produced by a melting method, an excess Ha compound relative to the target composition of the sulfide solid electrolyte to be produced is added to the sulfide solid electrolyte raw material and melted by heating, and at least a portion of the excess Ha compound relative to the target composition is replaced with Ha. ２ Furthermore, the present inventors have found that, in producing a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb by a melting method, an excess amount of Ha compound relative to a target composition of the sulfide solid electrolyte to be produced is added to the sulfide solid electrolyte raw material, and the mixture is heated and melted, and at least a portion of the excess amount of Ha compound relative to the target composition is volatilized as Ha. ２ or HHa, and then increasing the valence of at least one element selected from Sn, Si, and Sb contained in the sulfide solid electrolyte raw material by heating and melting, that is, making the valence of the element contained in the sulfide solid electrolyte to be greater than the valence of the element contained in the sulfide solid electrolyte raw material, thereby finding that the solubility of the raw material can be improved.

[0009] That is, a first embodiment of the present invention relates to a method for producing a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb by heating and melting a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb in a gas atmosphere containing elemental sulfur, and cooling and solidifying the resulting melt, wherein the valence of the element contained in the sulfide solid electrolyte raw material is increased by the heating and melting.

[0010] A second embodiment of the present invention is a method for producing a sulfide solid electrolyte, comprising: adding a Ha compound in excess of a target composition of the sulfide solid electrolyte to a sulfide solid electrolyte raw material; and heating and melting the resulting mixture in a gas atmosphere containing a sulfur element or a halogen element; and melting at least a portion of the Ha compound in excess of the target composition with a Ha compound. ２ and the resulting melt is cooled and solidified. ２、 And Ha in the HHa represents at least one element selected from halogen elements.

[0011] In a third embodiment of the present invention, there is provided a method for producing a sulfide solid electrolyte, comprising: adding an excess amount of a Ha compound to a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb, relative to a target composition of the sulfide solid electrolyte produced by the method; and heating and melting the resulting mixture in a gas atmosphere containing a sulfur element or a halogen element; and melting at least a portion of the excess amount of the Ha compound relative to the target composition by melting the resulting mixture in a gas atmosphere containing a sulfur element or a halogen element. ２ or HHa, and the resulting melt is cooled and solidified to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb, wherein the valence of the element contained in the sulfide solid electrolyte raw material is increased by heating and melting. ２、 And Ha in the HHa represents at least one element selected from halogen elements.

[0012] According to each embodiment of the present invention, the solubility of raw materials can be increased when producing a sulfide solid electrolyte by a melting method. This eliminates the need for excessively high heating temperatures, eliminating the difficulty of configuring a heating device, such as a heater, suitable for melting. Furthermore, problems such as corrosion of furnace materials or containers, increased volatilization of constituent components, and increased heat dissipation required during cooling due to high heating temperatures can be avoided. Furthermore, the high solubility of raw materials makes it easier to obtain a homogeneous sulfide solid electrolyte, thereby improving lithium ion conductivity.

[0013] Fig. 1 is a flow diagram showing a method for producing a sulfide solid electrolyte according to a first embodiment of the present invention. Fig. 2 is a flow diagram showing a method for producing a sulfide solid electrolyte according to a second embodiment of the present invention. Fig. 3 is a flow diagram showing a method for producing a sulfide solid electrolyte according to a third embodiment of the present invention.

[0014] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with any modifications within the scope of the present invention. The term "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0015] First Embodiment: Method for Producing Sulfide Solid Electrolyte A method for producing a sulfide solid electrolyte according to a first embodiment comprises heating and melting a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb in a gas atmosphere containing elemental sulfur, and cooling and solidifying the resulting melt to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb, wherein the heating and melting increases the valence of the element contained in the sulfide solid electrolyte raw material.

[0016] The inventors' research has revealed that the tetrahedral PS ４ At least a part of the SnS of another tetrahedral structure ４ , SiS ４ , and SbS ４It has become clear that when producing a sulfide solid electrolyte in which Sn is replaced with Sn, Si, or Sb, i.e., a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb, the solubility of the raw material is reduced due to factors such as an increase in the melting point of the raw material. In response to this, the present inventors have discovered that the solubility of the raw material can be improved by selecting a sulfide solid electrolyte raw material such that the valence of at least one element selected from Sn, Si, and Sb contained in the sulfide solid electrolyte raw material increases upon heating and melting. In other words, by producing a sulfide solid electrolyte in such a way that the valence of at least one element selected from Sn, Si, and Sb contained in the sulfide solid electrolyte finally produced in this embodiment is greater than the valence of the element contained in the sulfide solid electrolyte raw material. The mechanism of this action is not clear, but is presumed to be as follows. That is, the sulfide solid electrolyte raw material is selected so that the valence of at least one element of Sn, Si, and Sb contained in the sulfide solid electrolyte raw material increases upon heating and melting. In other words, in order to make the valence of the element contained in the sulfide solid electrolyte finally produced in this embodiment larger than the valence of the element contained in the sulfide solid electrolyte raw material, a substance having a small valence of the element is used as the sulfide solid electrolyte raw material. For example, when the element is Sn, SnS, which has a large valence of Sn, is used. ２ Since the valence of the elements in the raw materials is low, Sn, especially Li, which is the main component and has a high melting point, is absorbed from the surroundings during the initial melting reaction. ２ As a result, it is presumed that the initial solubility of the raw material is improved by lowering the melting point of the raw material. ４ SnS ４ and Li ４ SiS ４ It is presumed that the initial solubility of the raw material is improved because the raw material can be melted while avoiding crystal precipitation. Note that this embodiment is not to be interpreted as being limited to the above-mentioned mechanism of action.

[0017] The method for producing a sulfide solid electrolyte according to the first embodiment includes the following steps, as shown in Fig. 1: (Step S11) A step of heating and melting a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb in a gas atmosphere containing elemental sulfur; (Step S12) A step of cooling and solidifying the resulting melt to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb. Each step will be described below.

[0018] <Step S11: Heating and Melting a Sulfide Solid Electrolyte Raw Material Containing at Least One of Sn, Si, and Sb in a Gas Atmosphere Containing Elemental Sulfur> Sulfide Solid Electrolyte Raw Material Containing at Least One of Sn, Si, and Sb In the method for producing a sulfide solid electrolyte according to the first embodiment, a sulfide solid electrolyte raw material containing at least one of Sn, Si, and Sb (hereinafter collectively referred to as the present raw material) is used as the raw material. In other words, at least one of a sulfide solid electrolyte raw material containing Sn, a sulfide solid electrolyte raw material containing Si, and a sulfide solid electrolyte raw material containing Sb is used as the raw material.

[0019] Among the raw materials, examples of sulfide solid electrolyte raw materials containing Sn (hereinafter also referred to as Sn-containing raw materials) include Sn (Sn simple substance) and SnS. Furthermore, multi-component compounds such as R-M-Sn-S (R is a monovalent cation, and M is a divalent or higher cation) may also be used. Of these, Sn and SnS are preferred, with Sn being the most preferred, because they have a lower valence than the Sn contained in the sulfide solid electrolyte finally produced in this embodiment, and can enhance the solubility of the raw materials. The valence of Sn contained in the sulfide solid electrolyte finally produced is tetravalent because it is electrochemically stable, and the Sn-containing raw materials are zero-valent in the case of Sn and divalent in the case of SnS.

[0020] The molar equivalent of Sn in the Sn-containing raw material is preferably 0.2 to 1 molar equivalent, more preferably 0.5 to 1 molar equivalent, and even more preferably 0.7 to 1 molar equivalent.

[0021] Among the raw materials, examples of the sulfide solid electrolyte raw material containing Sb (hereinafter also referred to as Sb-containing raw material) include Sb (single Sb), Sb ２ S ３ In addition, multi-component compounds such as R-M-Sb-S (R is a monovalent cation, and M is a divalent or higher cation) may also be used. Among these, Sb, Sb, and Sb are preferred because they have a lower valence than Sb contained in the sulfide solid electrolyte finally produced in this embodiment and can increase the solubility of the raw materials. ２ S ３ The valence of Sb contained in the sulfide solid electrolyte finally produced is pentavalent because it is electrochemically stable. ２ S ３ In the case of , it is trivalent.

[0022] The molar equivalent of Sb in the Sb-containing raw material is preferably 0.1 to 1 molar equivalent, more preferably 0.2 to 1 molar equivalent, and even more preferably 0.3 to 1 molar equivalent.

[0023] Among the raw materials, examples of sulfide solid electrolyte raw materials containing Si (hereinafter also referred to as Si-containing raw materials) include Si (Si element). Alternatively, they may be multi-component compounds such as R-M-Si-S (R is a monovalent cation, and M is a divalent or higher cation). Among these, Si is preferred, and Si is most preferred, because it has a lower valence than Si contained in the sulfide solid electrolyte finally produced in this embodiment and can enhance the solubility of the raw materials. The valence of Si contained in the sulfide solid electrolyte finally produced is tetravalent because it is electrochemically stable, whereas the Si-containing raw material has a valence of zero in the case of Si.

[0024] The molar equivalent of Si in the Si-containing raw material is preferably 0.2 to 1 molar equivalent, more preferably 0.5 to 1 molar equivalent, and even more preferably 0.7 to 1 molar equivalent.

[0025] From the viewpoint of ionic conductivity, the constituent components of the sulfide solid electrolyte preferably contain at least one of Sn, Si, and Sb, and more preferably contain Sb.

[0026] The raw material typically contains a sulfide solid electrolyte raw material containing, as elements other than the Sn, Si, and Sb, substances such as an alkali metal element (R) and sulfur element (S). Examples of the alkali metal element (R) include lithium element (Li), sodium element (Na), and potassium element (K). When the resulting sulfide solid electrolyte is to be applied to a lithium ion secondary battery, the raw material preferably contains a sulfide solid electrolyte raw material containing, as the alkali metal element (R), a substance such as lithium element (Li).

[0027] As the source of the alkali metal element (R), an appropriate combination of an alkali metal element, a substance containing an alkali metal element such as a simple substance of the alkali metal element or a compound containing an alkali metal element can be used. When the alkali metal element (R) is lithium element (Li), an appropriate combination of Li-containing substances such as simple substance of Li or a compound containing Li can be used as the lithium element.

[0028] As a material containing lithium element (Li), that is, a sulfide solid electrolyte raw material containing lithium element (Li), for example, lithium sulfide (Li ２ S), lithium iodide (LiI), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ Examples of the substance containing lithium element (Li) include lithium compounds such as lithium hydroxide (LiOH), lithium ion (LiO), and metallic lithium. The substance containing lithium element (Li) may be used alone or in combination of two or more.

[0029] As the substance containing lithium element (Li), it is preferable to use lithium sulfide from the viewpoint of obtaining a sulfide material. Furthermore, when the obtained sulfide solid electrolyte contains a halogen element, it is also preferable to include lithium halide (LiHa, where Ha is a halogen element) as the substance containing lithium element (Li). Lithium halide will be described later.

[0030] As the sulfur element (S) source, a suitable combination of substances containing S, such as simple S or compounds containing S, can be used. The sulfur element (S)-containing substance, i.e., the sulfide solid electrolyte raw material containing sulfur element (S), may be used alone or in combination of two or more. ２ S is a compound that contains both a substance containing sulfur element (S) and the above-mentioned substance containing lithium element (Li). ２ S ５ is a compound that contains both a substance containing sulfur element (S) and a substance containing phosphorus element (P) as described later. Furthermore, SnS is a compound that contains both a substance containing sulfur element (S) and a substance containing Sn as described above. ２ S ３ is a compound that serves as both a substance containing sulfur element (S) and the above-mentioned substance containing Sb.

[0031] Examples of substances containing sulfur element (S) include phosphorus pentasulfide (P ２ S ５ ), diphosphorus trisulfide (P ２ S ３ ), other sulfur compounds containing phosphorus, elemental sulfur, and compounds containing sulfur. ２ S, CS ２ , 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.

[0032] From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, the raw material preferably further contains a substance containing phosphorus (P), i.e., a sulfide solid electrolyte raw material containing phosphorus (P). As the source of phosphorus (P), an appropriate combination of substances containing P, such as simple P or a compound containing P, can be used. One type of substance containing phosphorus (P) may be used, or two or more types may be used in combination.

[0033] The substance containing phosphorus (P) is the above-mentioned diphosphorus pentasulfide (P ２ S ５ ), for example, diphosphorus trisulfide (P ２ S ３ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ ) and elemental phosphorus.

[0034] When the present raw materials are mixed and charged into a heating furnace and then heated and melted, the mixing ratio of the present raw materials may be determined appropriately depending on the composition of the desired sulfide solid electrolyte. When the present raw materials are mixed and charged into a heating furnace and then heated and melted, the mixing ratio of the present raw materials may be determined appropriately depending on the composition of the desired sulfide solid electrolyte.

[0035] The mixing ratio or input ratio of the raw materials is not particularly limited. For example, the molar ratio S / R of sulfur (S) to alkali metal (R) in the raw materials is preferably 0.65 / 0.35 or less, and more preferably 0.5 / 0.5 or less, from the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte.

[0036] When the raw materials are charged into a heating furnace, they are preferably mixed at a predetermined stoichiometric ratio according to the raw materials. The method for mixing the raw materials is not particularly limited, but examples thereof include mixing in a mortar, mixing using media such as a planetary ball mill, and medialess mixing such as a pin mill, a powder mixer, and airflow mixing.

[0037] On the other hand, since lithium sulfide is expensive, in order to reduce the production cost of the sulfide solid electrolyte, lithium compounds other than lithium sulfide, metallic lithium, etc. may be used in addition to lithium sulfide. Specifically, in this case, the raw material is a substance containing Li, that is, as a sulfide solid electrolyte raw material containing lithium element (Li), metallic lithium, lithium halide (LiHa), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２These may be used alone or in combination of two or more.

[0038] The raw material may contain a sulfide solid electrolyte raw material containing a further substance (compound, etc.) in addition to the above substances, depending on the composition of the target sulfide solid electrolyte, or as an additive, etc. For example, when producing a sulfide solid electrolyte containing a halogen element (Ha) such as F, Cl, Br, or I, the raw material preferably contains a sulfide solid electrolyte raw material containing a halogen element.

[0039] Compounds containing halogen elements, i.e., sulfide solid electrolyte raw materials containing halogen elements, include lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. Among these, from the viewpoint of reactivity, lithium halides are preferred, LiCl, LiBr, and LiI are more preferred, and LiCl and LiBr are even more preferred. These compounds may be used alone or in combination of two or more.

[0040] In addition, since an alkali metal halide such as lithium halide is also a compound containing an alkali metal element such as Li, it can also serve as a source of the alkali metal element (R) in the raw material.

[0041] As will be described later, the sulfide solid electrolyte obtained by the production method according to this embodiment may be amorphous depending on the purpose. When the obtained sulfide solid electrolyte contains an amorphous phase, the amorphous phase is easily formed even if the quenching rate is reduced during quenching, and from the viewpoint of reducing the equipment load, the raw material is preferably B ２ S ３ , GeS ２ , Al ２ S ３ It is preferable that the sulfide solid electrolyte raw material contains a sulfide such as the above. These may be used alone or in combination of two or more.

[0042] From the viewpoint of imparting moisture resistance to the obtained sulfide solid electrolyte, it is preferable to use SiO as a constituent of the sulfide solid electrolyte. ２ , B ２ O ３ , GeO ２ , Al ２ O ３ , P ２ O ５ These may be used alone or in combination of two or more.

[0043] When the raw material is heated, the sulfides and oxides may be contained in the raw material or may be added separately during heating.

[0044] The amount of the sulfide and oxide added is preferably 0.1 to 50 mass%, more preferably 0.5 to 40 mass%, based on the total amount of the raw material. Here, the amount is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and is preferably 50 mass% or less, more preferably 40 mass% or less.

[0045] The raw material may further contain a compound that will serve as a crystal nucleus, which will be described later.

[0046] Heat Melting In step S11 in this embodiment, the raw material is placed in, for example, a heating furnace and heated to melt it.

[0047] As the furnace body in the heating furnace used for heating and melting, a conventionally known furnace having a heating section can be used as appropriate, and the material and size of the furnace body can also be selected arbitrarily.

[0048] The temperature for heat melting is not particularly limited as long as the raw material is melted, but is preferably 600°C or higher, more preferably 600 to 1000°C, even more preferably 630 to 950°C, even more preferably 650°C or higher but less than 900°C, and particularly preferably 650°C or higher but less than 850°C. Here, from the viewpoint of homogenizing the melt in a short time, the heat melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher. Furthermore, from the viewpoint of suppressing deterioration or decomposition of components in the melt, the heat melting temperature is preferably 1000°C or lower, more preferably 950°C or lower, even more preferably less than 900°C, and particularly preferably less than 850°C. The heat melting temperature is the temperature of the melt produced in the furnace and can be adjusted by the heating unit provided in the furnace.

[0049] The heating and melting time is not particularly limited as long as the raw material is melted, but may be, for example, 0.5 hours or more, 1 hour or more, or 2 hours or more.

[0050] The pressure during heating and melting is not particularly limited as long as the raw material is melted, but for example, normal pressure or slight pressure is preferred, and normal pressure is more preferred.

[0051] From the viewpoint of preventing side reactions between the melt and water vapor, oxygen, etc. during heating and melting, the dew point inside the furnace is preferably −20° C. or lower, and although there is no particular lower limit, it is usually −80° C. or higher. In addition, the oxygen concentration inside the furnace is preferably 1000 ppm by volume or lower.

[0052] In this embodiment, the heat melting is performed in a gas atmosphere containing elemental sulfur. By heat melting the raw material in a gas atmosphere containing elemental sulfur, sulfur is introduced into the resulting melt, thereby suppressing changes in the sulfur composition due to volatilization. The gas also serves as a source of sulfur for the raw material, promoting dissolution and achieving a target composition. Examples of the gas containing elemental sulfur include sulfur gas, hydrogen sulfide gas, carbon disulfide gas, and other gases containing compounds containing elemental sulfur or elemental sulfur.

[0053] The gas atmosphere containing elemental sulfur may be obtained by supplying a sulfur source to a melt obtained by heating and melting the raw material, and then heating the sulfur source to generate a gas containing elemental sulfur. In this case, the sulfur source is not particularly limited as long as it is elemental sulfur or a sulfur compound that can generate a gas containing elemental sulfur by heating. 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 sulfur powder, polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubbers vulcanized with sulfur, etc. As the sulfur source, sulfur powder is preferably used.

[0054] 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 gas, argon gas, or helium gas into the furnace body as a carrier gas.

[0055] Alternatively, the gas atmosphere containing elemental sulfur may be obtained by incorporating a sulfur source into the raw material, which heats the raw material and melts it in the presence of the generated gas atmosphere containing elemental sulfur.

[0056] In this embodiment, any one of the above methods for obtaining a gas atmosphere containing elemental sulfur may be adopted, or a combination of a plurality of methods may be adopted.

[0057] The heat melting in this embodiment may be performed on the intermediate after the raw material is heat treated and then the intermediate is synthesized.

[0058] In the heat treatment in the intermediate synthesis step, the temperature at which the raw material is heated is preferably 250°C or higher, more preferably 255°C or higher, and even more preferably 260°C or higher. A temperature of at least the lower limit value is preferred because it facilitates the reaction of synthesizing the intermediate. In addition, the temperature is preferably 500°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower. By keeping the temperature at or below the upper limit value, the P in the raw material can be easily removed. ２ S ５ This is preferable because it suppresses the evaporation of low-boiling point components such as methyl methyl ketone and the like, and facilitates the reaction of synthesizing an intermediate containing a compound of the target composition.

[0059] To obtain an intermediate by heat treatment, it is preferable to hold the temperature within the above-mentioned preferred temperature range for a certain period of time. The temperature range during holding is more preferably within a certain temperature range, for example, preferably within ±15°C of the reference temperature, more preferably within ±10°C. The holding time is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, even more preferably 15 minutes or more, and particularly preferably 20 minutes or more. Even when heated at the above-mentioned preferred temperature, if the holding time is insufficient, it is thought that the reaction is likely to proceed insufficiently. Holding the temperature for 1 minute or more provides the conditions for the reaction to proceed and obtain an intermediate, and is therefore preferable. The holding time is determined based on the P in the raw material. ２ S ５ From the viewpoint of suppressing the volatilization of components with low boiling points such as the above, the boiling time is preferably 600 minutes or less, and more preferably 500 minutes or less.

[0060] The holding time can be further shortened in some cases when the raw material is subjected to a predetermined treatment. Examples of such treatment include reducing the particle size of the raw material, removing or modifying the oxide layer on the surface of the particles contained in the raw material as much as possible by etching or the like, making the particles porous, adjusting the mixing conditions of the raw material to improve the homogeneity of the raw material, and thereby increasing the reactivity between the particles contained in the raw material. In this case, the holding time is preferably 1 second or more, more preferably 10 seconds or more, and even more preferably 20 seconds or more. The holding time is determined based on the P content in the raw material. ２ S ５From the viewpoint of suppressing the evaporation of low boiling point components such as the above, the time is preferably 10 minutes or less, and more preferably 5 minutes or less.

[0061] From the viewpoint of shortening the retention time, i.e., shortening the reaction time in the intermediate synthesis step, it is preferable to reduce the particle size of the raw material. Furthermore, if the particle size (D50) of the raw material is too large, it may affect the homogeneity of the sulfide solid electrolyte, and from this viewpoint as well, it is preferable that the particle size (D50) of the raw material is relatively small. From these viewpoints, specifically, the particle size (D50) of the raw material is preferably 1 mm or less, more preferably 500 μm or less, even more preferably 250 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0062] Although the smaller the particle size, the more preferable, the practical lower limit is about 0.1 μm, and 1 μm or more is preferable, and 5 μm or more is more preferable. Furthermore, from the viewpoint of suppressing production costs, for example, it is also preferable that the particle size of the raw material is 10 μm or more, more preferably 100 μm or more, and even more preferably 250 μm or more.

[0063] As described above, the raw material may be a mixture of multiple substances (compounds, etc.). The raw material may also be in the form of a mixture of multiple substances with different particle sizes. In this case, it is preferable that the particle sizes of each substance are within the above range. In this specification, the particle size (D50) of the raw material refers to the median diameter (D50) obtained from the volume-based particle size distribution chart obtained by measuring the particle size distribution using a laser diffraction particle size distribution analyzer MT3300EXII manufactured by Microtrac.

[0064] The pressure during the heat treatment in the intermediate synthesis step is not particularly limited, but is preferably, for example, normal pressure to slightly increased pressure, and more preferably normal pressure.

[0065] The heat treatment in the intermediate synthesis step is preferably carried out under an inert gas atmosphere to prevent side reactions between the raw material and water vapor, oxygen, etc. ２ Examples of suitable gases include gas, argon gas, and helium gas. The dew point during the 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 or lower.

[0066] In the intermediate synthesis process, intermediates with different compositions depending on the purpose can be obtained by adjusting the compounds contained in the raw material and their mixing ratios, and by controlling the conditions during the heat treatment. The obtained intermediate may be used in the heat-melting process directly in the heating furnace used for intermediate synthesis without being removed from the heat-resistant container, or it may be removed and temporarily stored after cooling to room temperature. It is also possible to combine multiple intermediates with different compositions that have been removed and stored and use them in the heat-melting process.

[0067] Examples of intermediate compositions include Li ４ P ２ S ６ , Li ３ P.S. ４ In the heat-melting step, the amount of sulfur introduced into the intermediate can be controlled under a gas atmosphere containing sulfur element, and in that case, the intermediate can be made of Li, P, and S. ４ P ２ S ６ , Li ３ P.S. ４ and a compound in which one or more of Sb, Sn, and Si are substituted at the phosphorus site of the compound. ４ P ２ S ６ , Li ３ P.S. ４ and compounds in which one or more of Sb, Sn and Si are substituted at the phosphorus site of the above compounds are thermodynamically stable, and therefore are also preferred from the viewpoint of stability during temporary storage of intermediates.

[0068] Here, the reaction occurring in the intermediate synthesis step depends on the composition of the target sulfide solid electrolyte, but typically involves the reaction of Li contained in the raw material. ２ S and P ２ S ５ begins to react at about 250°C, and Li ４ P ２ S ６ , Li ３ P.S. ４and a compound in which one or more of Sb, Sn, and Si are substituted at the phosphorus site of the compound. ２ S and P ２ S ５ The reaction may start from a Li-containing substance (compound, etc.) or a P-containing substance (compound, etc.) in a stage prior to obtaining each of them. In order to essentially accelerate this reaction, it is preferable to increase the reactivity between particles contained in the raw material by reducing the particle size of the raw material, removing or modifying the oxide layer on the surface of the particles contained in the raw material as much as possible by etching or the like, making the particles porous, adjusting the mixing conditions of the raw material, and improving the homogeneity of the raw material. In particular, in this reaction, it is preferable to increase the reactivity between particles contained in the raw material by reducing the particle size of the raw material, removing or modifying the oxide layer on the surface of the particles contained in the raw material as much as possible by etching or the like, making the particles porous, adjusting the mixing conditions of the raw material, improving the homogeneity of the raw material, etc. ２ S ５ Li is the first to react ２ The particle size of S is likely to affect the intermediate formation reaction. Therefore, from the viewpoint of promoting the intermediate formation reaction, it is preferable that the raw material contains Li ２ S or Li ２ It is preferable to make the particle size of the substance (compound, etc.) containing Li finer before obtaining S. ２ It is believed that reducing the crystallinity of the surface of S and increasing the surface area other than atomization are also effective from the above viewpoint. ２ S and P ２ S ５ It is believed that reacting with the above also contributes to promoting the intermediate formation reaction.

[0069] When producing a sulfide solid electrolyte containing a halogen element, the intermediate preferably contains a compound containing a halogen element. Note that when the raw material contains a sulfide solid electrolyte raw material containing a lithium halide such as LiCl, LiBr, or LiI, the composition of these compounds is unlikely to change within the temperature range during heat treatment, and therefore the resulting intermediate may also contain a lithium halide.

[0070] By going through the intermediate synthesis process, it is possible to suppress the volatilization of sulfur and phosphorus components in the raw material compared to obtaining the target sulfide solid electrolyte directly from the raw material, and therefore Li ４P ２ S ６ , Li ３ P.S. ４ Compounds with clear compositional information containing Li, P, and S, such as compounds in which one or more of Sb, Sn, and Si are substituted for the phosphorus site of the compound, can be synthesized as intermediates. Because these intermediates are thermodynamically stable, they can be extracted by lowering the temperature to room temperature after the heat treatment during intermediate synthesis. Composition analysis of the extracted intermediates can be performed, making it possible to determine the amount of sulfur required for the heat-melting process. Furthermore, by starting from the raw material and producing an intermediate with a specific composition, it becomes easier to set the heat-melting conditions more appropriately to match the intermediate composition. This allows for appropriate control of the amount of sulfur introduced under a gas atmosphere containing elemental sulfur, reducing the likelihood of compositional deviation. Furthermore, by heat-melting an intermediate with a composition closer to the target sulfide solid electrolyte than the raw material, the resulting sulfide solid electrolyte can be made homogeneous in composition. Additionally, by combining and heat-melting multiple intermediates with different compositions, it becomes easier to produce sulfide solid electrolytes with different compositions, physical properties, and performance. Furthermore, the raw materials of Sn, Si, and Sb and lithium halide may be mixed in the required amounts after synthesis of the intermediate, and then transferred to the subsequent melting step.

[0071] <Step S12: Cooling and solidifying the obtained melt to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb> The production method according to this embodiment includes cooling and solidifying the melt obtained in step S11 to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb. Cooling the melt produces a solid sulfide solid electrolyte.

[0072] In step S12, the melt obtained in step S11 is discharged at any time from a discharge port provided in the furnace body, and the process proceeds to a cooling and solidifying step. A known method can be used to cool the melt, and there is no particular limitation. For example, from the viewpoint of increasing the cooling rate, cooling using a twin roller, which is generally considered to have the fastest rapid cooling rate, is preferred.

[0073] From the viewpoint of maintaining the composition of the melt obtained in step S11, 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. There is no particular upper limit to the cooling rate, but the cooling rate of the twin rollers is, for example, 1,000,000° C. / sec or less.

[0074] When an amorphous sulfide solid electrolyte is desired, it is preferable to perform quenching at a higher cooling rate. The cooling rate during quenching is preferably 10°C / sec or higher, more preferably 100°C / sec or higher, even more preferably 500°C / sec or higher, and particularly preferably 700°C / sec or higher. The upper limit of the cooling rate during quenching is not particularly limited, but the cooling rate of the twin rollers is, for example, 1,000,000°C / sec or lower.

[0075] On the other hand, a sulfide solid electrolyte having a crystalline phase may be obtained by slow cooling during the cooling and solidification step. Alternatively, a sulfide solid electrolyte having both a crystalline phase and an amorphous phase may be obtained. The cooling rate during slow cooling is preferably 0.01 to 500°C / sec, more preferably 0.05 to 450°C / sec. It may also be 0.01 to 10°C / sec, or 0.05 to 5°C / sec. Here, the cooling rate is preferably 0.01°C / sec or more, more preferably 0.05°C / sec or more, and is preferably 500°C / sec or less, more preferably 450°C / sec or less. The cooling rate may also be 10°C / sec or less, or 5°C / sec or less. The cooling rate may be adjusted appropriately depending on the crystallization conditions.

[0076] When it is desired to obtain a sulfide solid electrolyte containing a crystalline phase, in order to facilitate crystal precipitation, it is preferable to include a compound that will become a crystal nucleus in the melt obtained in step S11. The method for including the compound that will become a crystal nucleus in the melt is not particularly limited, but examples thereof include a method of adding the compound that will become a crystal nucleus to the raw material, and a method of directly adding the compound that will become a crystal nucleus to the melt that has been heated and melted.

[0077] 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.

[0078] The amount of the compound that becomes the crystal nuclei added to the melt is preferably 0.01 to 20 mass%, more preferably 0.1 to 20 mass%, and even more preferably 1 to 10 mass%. From the viewpoint of favorably forming a crystalline phase in the resulting sulfide solid electrolyte, the amount added is preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and even more preferably 1 mass% or more. Furthermore, from the viewpoint of suppressing a decrease in lithium ion conductivity, the amount added is preferably 20 mass% or less, and more preferably 10 mass% or less.

[0079] When a sulfide solid electrolyte having a large amorphous phase is desired, a compound serving as a crystal nucleus is not added to the melt, or if added, the amount of the compound added is preferably 1% by mass or less, more preferably 0.1% by mass or less. The amount may also be 0.01% by mass or less.

[0080] The cooling and solidification is preferably carried out under normal pressure. "Under normal pressure" means that the pressure is not controlled during cooling. Specifically, the pressure is about 0.8 to 1.2 atm.

[0081] In the manufacturing method according to the present embodiment, the sulfide solid electrolyte obtained in step S12 may be reheated for heat treatment. This heat treatment may be particularly effective when the sulfide solid electrolyte is amorphous or contains an amorphous phase. The heat treatment may also rearrange ions within the crystal structure to increase lithium ion conductivity.

[0082] The heat treatment refers to at least one of a heat treatment for crystallizing the obtained solid and a heat treatment for rearranging ions in the crystal structure. That is, the heat treatment also includes a crystallization treatment by heating of an amorphous sulfide solid electrolyte or a sulfide solid electrolyte containing an amorphous phase.

[0083] In the production method according to this embodiment, it is preferable to perform the above steps S11 and S12 as a continuous process. That is, it is preferable to continuously obtain the sulfide solid electrolyte by heating and melting the raw material, and then continuously discharging the resulting melt and transferring it to a step of cooling and solidifying it. In this way, it is preferable to continuously produce the sulfide solid electrolyte.

[0084] By continuously producing sulfide solid electrolyte, a series of processes, including heating and melting the raw material, discharging the melt, and cooling and solidifying it, can be carried out continuously, allowing sulfide solid electrolyte to be produced in large quantities more efficiently in a short period of time.

[0085] In a more preferred embodiment of the continuous process, in step S11, the raw material is first heated and melted in an amount sufficient to form at least a melt surface within the furnace. Here, the melt surface refers to a liquid surface formed by the melt covering the entire bottom surface of the furnace. Once a melt surface is formed within the furnace, the temperature of the raw material subsequently added to the melt rises rapidly and the raw material melts instantaneously. Therefore, as the raw material is added, a continuous melt is generated one after another. This melt is continuously discharged and subjected to a cooling and solidification process, thereby continuously producing a sulfide solid electrolyte in a short period of time. This continuous production of a sulfide solid electrolyte allows a large amount of sulfide solid electrolyte to be produced in a short period of time. Furthermore, the shortening of the production process also reduces the volatilization of the raw material during the production process.

[0086] In the manufacturing method according to the present embodiment, the processes of steps S11 and S12 may be carried out in a batch manner. The batch manner is a method in which the raw material is charged into a furnace, heated and melted, and then the entire amount is discharged, and means that the contents of the furnace are all replaced every time the manufacturing method according to the present embodiment is carried out.

[0087] Sulfide Solid Electrolyte The sulfide solid electrolyte obtained by the production method according to this embodiment contains at least one element selected from Sn, Si, and Sb. Examples include Li-P-M-S-based and Li-P-M-S-Ha-based sulfide solid electrolytes having an argyrodite-type crystal structure (M is at least one element selected from B, Al, Si, Ga, Ge, In, Sn, Pb, Bi, and other transition metals), sulfide solid electrolytes having an LGPS-type crystal structure, and Li-P-S-Ha-based and Li-P-Sn-S(-Ha)-based crystallized glasses.

[0088] In the manufacturing method according to this embodiment, as described above, it is important that the valence of at least one element selected from Sn, Si, and Sb contained in the sulfide solid electrolyte raw material increases upon heating and melting. In other words, it is important that the valence of at least one element selected from Sn, Si, and Sb contained in the resulting sulfide solid electrolyte is greater than the valence of the element contained in the sulfide solid electrolyte raw material. This can improve the solubility of the raw material. The valences of Sn, Si, and Sb contained in the resulting sulfide solid electrolyte can be determined by analyzing the XRD pattern structure of the resulting crystal and examining the coordination number and coordination distance of the element. To examine the valences of the elements in more detail, methods such as the Mössbauer method and XPS can be used to determine the valence of Sn, Si-NMR, XPS, and XAFS can be used to determine the valence of Si, and XAFS can be used to determine the valence of Sb.

[0089] Of the constituent components of the sulfide solid electrolyte obtained by the production method according to this embodiment, the molar equivalent of the elements Sn, Si, and Sb is preferably 0.001 to 0.3 molar equivalents in total, more preferably 0.01 to 0.2 molar equivalents, and even more preferably 0.02 to 0.1 molar equivalents.

[0090] When the sulfide solid electrolyte obtained by the production method according to this embodiment contains a halogen (Ha) and a phosphorus (P), the molar equivalent of the halogen (Ha) relative to the phosphorus (P) of the constituent components of the sulfide solid electrolyte is preferably 0.2 to 4 molar equivalents, more preferably 0.5 to 3 molar equivalents. Furthermore, when the sulfide solid electrolyte obtained by the production method according to this embodiment contains a halogen (Ha) and a sulfur (S), the molar equivalent of the halogen (Ha) relative to the sulfur (S) of the constituent components of the sulfide solid electrolyte is preferably 0.01 to 1.0 molar equivalents, more preferably 0.05 to 0.5 molar equivalents. From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, the molar equivalent of the halogen is preferably 0.01 molar equivalents or more, more preferably 0.05 molar equivalents or more. From the viewpoint of the stability of the resulting sulfide solid electrolyte, the molar equivalent of the halogen is preferably 0.5 molar equivalents or less, more preferably 0.25 molar equivalents or less. When the powder raw material contains two or more halogen elements, it is preferable that the total content thereof falls within the above-mentioned range of molar equivalents.

[0091] The sulfide solid electrolyte obtained by the production method according to this embodiment preferably has a molar ratio (P / X) of P to the total amount X of P, Sn, Si, and Sb contained in the sulfide solid electrolyte of 0.1 or more and 0.9 or less. When P / X is 0.1 or more, the battery characteristics are good. Furthermore, when P / X is 0.9 or less, the water resistance is good. The P / X is more preferably 0.1 or more, even more preferably 0.25 or more, particularly preferably 0.4 or more, and more preferably 0.9 or less, even more preferably 0.75 or less, particularly preferably 0.5 or less.

[0092] The sulfide solid electrolyte obtained by the manufacturing method according to the present embodiment preferably contains iodine from the viewpoint of improving ionic conductivity and reducing resistance. ４ Another tetrahedral structure of SnS ４By replacing the iodine with other iodine-containing sulfide solid electrolytes, the melting point of the raw materials increases, and the solubility of the raw materials decreases. Therefore, in the past, when producing the sulfide solid electrolyte by a melting method, it was necessary to increase the heating temperature, which resulted in the volatilization of iodine, making it impossible to obtain a sulfide solid electrolyte containing a sufficient amount of iodine. On the other hand, in the present invention, the solubility of the raw materials is increased as described above, and therefore, a sulfide solid electrolyte containing a sufficient amount of iodine can be obtained without the need to increase the heating temperature excessively.

[0093] The sulfide solid electrolyte obtained by the production method according to this embodiment preferably contains 0.001 to 0.1 molar equivalents of iodine, more preferably 0.01 to 0.05 molar equivalents, and even more preferably 0.02 to 0.04 molar equivalents.

[0094] The sulfide solid electrolyte obtained by the production method according to this embodiment 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 lithium ion conductivity, the crystalline phase is preferably an argyrodite-type crystalline phase.

[0095] From the viewpoint of ionic conductivity, the sulfide solid electrolyte obtained by the production method according to the present embodiment preferably contains at least Sb among the elements Sn, Si, and Sb.

[0096] The lithium ion conductivity of the sulfide solid electrolyte obtained by the production method according to the present embodiment is 5.0 × 10 from the viewpoint of battery characteristics when used in a lithium ion secondary battery. －１ The lithium ion conductivity in this specification is a value measured using an AC impedance measuring device (for example, a potentiostat / galvanostat VSP manufactured by Bio-Logic Sciences Instruments) under the conditions of a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C.

[0097] The sulfide solid electrolyte obtained by the production method according to this embodiment 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 optical emission spectrometry, atomic absorption spectrometry, and ion chromatography. For example, P, Si, Sn, Sb, and S can be measured by ICP optical emission spectrometry, Li can be measured by atomic absorption spectrometry, and Ha can be measured by ion chromatography.

[0098] Second Embodiment: Method for Producing Sulfide Solid Electrolyte A method for producing a sulfide solid electrolyte according to a second embodiment is a method for producing a sulfide solid electrolyte, the method comprising: adding a Ha compound in excess of a target composition of the sulfide solid electrolyte produced by the method to a sulfide solid electrolyte raw material; heating and melting the resulting mixture in a gas atmosphere containing a sulfur element or a halogen element; and melting at least a portion of the Ha compound in excess of the target composition by adding Ha. ２ or HHa, and the resulting melt is cooled and solidified. ２、 and Ha in HHa represents at least one element selected from halogen elements.

[0099] According to the research of the present inventors, it was found that the solubility of the raw material can be increased by adding an excess amount of Ha compound to the sulfide solid electrolyte raw material relative to the target composition of the sulfide solid electrolyte to be produced. The mechanism of action is not clear, but it is speculated as follows. That is, it is speculated that a halide raw material with a low melting point promotes the melting reaction. In addition, since the excess amount of Ha compound added relative to the target composition may block the ion conduction path, it is possible to replace at least a part of it with Ha. ２ Alternatively, it is volatilized as HHa. Note that this embodiment is not to be construed as being limited to the above-mentioned mechanism of action.

[0100] The method for producing a sulfide solid electrolyte according to the second embodiment includes the following steps, as shown in Fig. 2. (Step S21) Adding an excess amount of Ha compound to a sulfide solid electrolyte raw material relative to a target composition of the sulfide solid electrolyte to be produced, and heating and melting the mixture in a gas atmosphere containing elemental sulfur or elemental halogen, and melting at least a portion of the excess amount of Ha compound relative to the target composition. ２ or a step of volatilizing it as HHa. (Step S22) A step of cooling and solidifying the obtained melt. Each step will be described below.

[0101] <Step S21: Adding an excess amount of a Ha compound to a sulfide solid electrolyte raw material relative to a target composition of the sulfide solid electrolyte to be produced, and heating and melting the mixture in a gas atmosphere containing a sulfur element or a halogen element, and melting at least a portion of the excess amount of the Ha compound relative to the target composition. ２ or HHa) > Sulfide solid electrolyte raw material The raw material (the raw material) described in the first embodiment can be used as the sulfide solid electrolyte raw material. For example, a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb may be used, or another raw material may be used.

[0102] Ha Compound Examples of the Ha compound added to the sulfide solid electrolyte raw material include LiHa, Ha ２ , HHa, etc. ２ and HHa are added as gases. The Ha compound is preferably LiHa. Examples of LiHa include LiI, LiBr, LiCl, etc., and LiI is particularly preferred from the viewpoint of ease of volatilization. By using a LiHa compound that is easy to volatilize, as will be described later, it is possible to reduce the amount of Ha after heating and melting. ２ When LiHa is used, it is preferable to adjust the amount of Li in the sulfide solid electrolyte raw material so that the resulting sulfide solid electrolyte does not contain excessive Li. ２ Examples of the chlorine atom include Cl. ２ , F ２ ,Br ２ , I ２Examples of HHa include HCl, HF, HBr, and HI.

[0103] An excess of a Ha compound is added to the target composition of the sulfide solid electrolyte produced by the method of this embodiment. This increases the solubility of the raw materials. Here, the "target composition" refers to the composition of the sulfide solid electrolyte to be produced by the method of this embodiment, and for example, Li ３．３ [P ０．７ Sn ０．３ ]S ４ Furthermore, "an excess of Ha compound relative to the target composition of the sulfide solid electrolyte to be produced" specifically means that the actual analytical value of the composition of the obtained solid electrolyte is larger than the charged value shown in Table 1 in the examples described later.

[0104] The amount of the Ha compound added is preferably 1.001 times or more, more preferably 1.01 times or more, and even more preferably 1.04 times or more of the target composition of the sulfide solid electrolyte to be produced, and is preferably 2 times or less, more preferably 1.8 times or less, and even more preferably 1.5 times or less.

[0105] Heat Melting In step S21 of this embodiment, for example, in a heating furnace, a Ha compound is added to a sulfide solid electrolyte raw material, and the mixture is heated and melted under a gas atmosphere containing sulfur element or halogen element. The conditions for the heat melting can be the same as those described above in the first embodiment. In particular, as described later, at least a part of the Ha compound in excess of the target composition added can be melted by adding Ha. ２ Alternatively, in order to volatilize it as HHa, it is preferable to extend the melting time or replace the atmosphere in the furnace as heating and melting conditions.

[0106] The sulfide solid electrolyte raw material is heated and melted in a gas atmosphere containing elemental sulfur or halogen. By heating and melting in a gas atmosphere containing elemental sulfur or halogen, sulfur or halogen is introduced into the resulting melt, thereby suppressing changes in the sulfur or halogen composition due to volatilization. This gas also serves as a source of sulfur or halogen to the raw material, promoting dissolution and achieving a target composition. Examples of the sulfur-containing gas include sulfur gas, hydrogen sulfide gas, carbon disulfide gas, and other compounds containing sulfur or gases containing elemental sulfur. Examples of the halogen-containing gas include gases containing elemental halogen, hydrogen halide gas, and gases containing metal halide elements.

[0107] In step S21 of this embodiment, at least a part of the added excess Ha compound relative to the target composition is replaced with Ha. ２ When the Ha compound is LiHa, at least a part of the excess LiHa is converted into Ha. ２ Specifically, when LiHa is LiI, at least a part of the excess LiI is converted to I ２ Or volatilized as HI. Ha compounds are ２ In the case of excess Ha ２ At least a part of ２ Or, it is evaporated as HHa. Specifically, Ha ２ is Cl ２ In the case of excess Cl ２ At least a part of ２ When the Ha compound is HHa, at least a part of the excess HHa is evaporated as Ha. ２ Specifically, when HHa is HCl, at least a part of the excess HCl is evaporated to Cl. ２ Or stripped as HCl.

[0108] <Step S22: Step of cooling and solidifying the obtained melt> In step S22 of this embodiment, the melt obtained in step S21 is cooled and solidified. The cooling and solidification conditions and the like can be the same as those described in the first embodiment.

[0109] Third Embodiment: Method for Producing Sulfide Solid Electrolyte A method for producing a sulfide solid electrolyte according to a third embodiment includes adding an excess LiHa compound relative to a target composition of the sulfide solid electrolyte produced by the method to a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb, and heating and melting the resulting mixture in a gas atmosphere containing a sulfur element or a halogen element, and then replacing at least a portion of the excess LiHa compound relative to the target composition with Ha. ２ The melt is cooled and solidified to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb, and the valence of the element contained in the sulfide solid electrolyte raw material is increased by the heating and melting. ２、 and Ha in HHa represents at least one element selected from halogen elements.

[0110] The method for producing a sulfide solid electrolyte according to the third embodiment includes the following steps, as shown in Fig. 3. (Step S31) Adding an excess LiHa compound to a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb, relative to a target composition of the sulfide solid electrolyte to be produced, and heating and melting the mixture in a gas atmosphere containing elemental sulfur or elemental halogen, and replacing at least a portion of the excess LiHa compound relative to the target composition with Ha. ２ or HHa. (Step S32) A step of cooling and solidifying the obtained melt to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb. Each step will be described below.

[0111] <Step S31: Adding an excess LiHa compound to a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb relative to a target composition of the sulfide solid electrolyte to be produced, and heating and melting the resulting mixture in a gas atmosphere containing a sulfur element or a halogen element, and replacing at least a portion of the excess LiHa compound relative to the target composition with Ha. ２Step S31 is a combination of step S11 in the first embodiment and step S21 in the second embodiment, and the same steps as those described above for step S11 in the first embodiment and step S21 in the second embodiment can be employed as they are.

[0112] <Step S32: Step of Cooling and Solidifying the Obtained Melt to Produce a Sulfide Solid Electrolyte Containing at Least One of Sn, Si, and Sb> Step S32 is a combination of step S12 in the first embodiment and step S22 in the second embodiment, and the steps described above in step S12 in the first embodiment and step S22 in the second embodiment can be employed as they are.

[0113] 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.

[0114] As explained above, this specification discloses the following: 1. A method for producing a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb by heating and melting a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb in a gas atmosphere containing elemental sulfur, and cooling and solidifying the resulting melt, wherein the valence of the element contained in the sulfide solid electrolyte raw material is increased by the heating and melting. 2. A method for producing a sulfide solid electrolyte, comprising adding a Ha compound in excess of a target composition of the sulfide solid electrolyte produced by the method to the sulfide solid electrolyte raw material, and heating and melting the sulfide solid electrolyte raw material in a gas atmosphere containing elemental sulfur or halogen, and replacing at least a portion of the Ha compound in excess of the target composition with Ha. ２ or HHa, and the resulting melt is cooled and solidified.２、 and Ha in HHa represents at least one element selected from halogen elements.) 3. A method for producing a sulfide solid electrolyte, comprising: adding an excess amount of Ha compound relative to a target composition of the sulfide solid electrolyte produced by the method to a sulfide solid electrolyte raw material containing at least one element selected from Sn, Si, and Sb; heating and melting the mixture in a gas atmosphere containing sulfur element or halogen element; and melting at least a portion of the excess amount of Ha compound relative to the target composition with Ha. ２ or HHa, and the resulting melt is cooled and solidified to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb, wherein the valence of the element contained in the sulfide solid electrolyte raw material is increased by the heating and melting. (The Ha compound, the Ha ２、 and Ha in HHa represents at least one element selected from halogen elements. 4. The method for producing a sulfide solid electrolyte according to item 2 or 3 above, wherein the Ha compound is LiHa. 5. The method for producing a sulfide solid electrolyte according to item 4 above, wherein the LiHa is LiI. 6. The method for producing a sulfide solid electrolyte according to item 1 or 3 above, wherein the molar ratio (P / X) of P to the total amount X of P, Sn, Si, and Sb contained in the sulfide solid electrolyte produced by the method is 0.1 or more and 0.9 or less. 7. The method for producing a sulfide solid electrolyte according to item 6 above, wherein the sulfide solid electrolyte produced by the method contains iodine.

[0115] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1, 3, 4, 6, 7, 8, and 11 are working examples, and Examples 2, 5, 9, and 10 are comparative examples.

[0116] <Synthesis of sulfide solid electrolyte> Example 1 In a glove box adjusted to a nitrogen atmosphere with a dew point of -50°C, Li ２ S (manufactured by Sigma, purity 99.98%), P ２ S ５The raw material powders of Li (manufactured by Sigma, purity 99%), Sn (manufactured by Sigma, purity 99%), and S (manufactured by Sigma, purity 99.98%) were mixed to the charge composition (target composition) in Table 1 and thoroughly mixed in a mortar. 1 g of the resulting mixture was placed in a quartz test tube and melted at 720°C for 1 hour, and then removed. During the melting, 10 vol% sulfur gas was supplied. The composition of the resulting sulfide solid electrolyte was (Li ３．３ [P ０．７ Sn ０．３ ]S ４ ) was.

[0117] Example 2: As a raw material powder, Li ２ S (manufactured by Sigma, purity 99.98%), P ２ S ５ (manufactured by Sigma, purity 99%), SnS ２ The sulfide solid electrolyte (Li ３．３ [P ０．７ Sn ０．３ ]S ４ ) was obtained.

[0118] Example 3: As a raw material powder, Li ２ S (manufactured by Sigma, purity 99.98%), P ２ S ５ (Sigma, purity 99%), Sn (Sigma, purity 99%), S (Sigma, purity 99.98%), Si (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%), Sb ２ S ３ The sulfide solid electrolyte (LiI) of Example 3 was prepared in the same manner as in Example 1, except that the sulfide solid electrolyte (LiI) of Example 3 (manufactured by Mitsuwa Chemical Co., Ltd., purity 99.98%) and LiI (manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.9%, low moisture grade) were mixed to have the charge composition (mol) shown in Table 1, and the dissolution temperature was set to 700°C. ６．５ [P ０．２５ Si ０．３ Sn ０．２ Sb ０．２５ ]S ５ I) was obtained.

[0119] Example 4 The amount of LiI in the raw material powder used in Example 3 was increased by 10 wt % and Li ２ The sulfide solid electrolyte (Li) of Example 4 was prepared in the same manner as in Example 3, except that the amounts of S and S were adjusted to obtain the charge composition (target composition) in Table 1 except for iodine, and the dissolution temperature was set to 680°C. ６．５ [P ０．２５ Si ０．３ Sn ０．２ Sb ０．２５ ]S ５ Although the obtained composition contained a large amount of iodine, it was equivalent to the charged composition.

[0120] Example 5: As a raw material powder, Li ２ S (manufactured by Sigma, purity 99.98%), P ２ S ５ (manufactured by Sigma, purity 99%), SnS ２ (Mitsuwa Chemical Co., Ltd., purity 99.5%), SiS ２ (Mitsuwa Chemical Co., Ltd., purity 99%), Sb ２ S ５ The sulfide solid electrolyte (LiI) of Example 5 was prepared in the same manner as in Example 3, except that LiI (manufactured by Strem Chemicals, purity 98%) and LiI (manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.9%, low moisture grade) were used and the dissolution temperature was set to 730°C. ６．５ [P ０．２５ Si ０．３ Sn ０．２ Sb ０．２５ ]S ５ I) was obtained.

[0121] Example 6: As a raw material powder, Li ２ S (manufactured by Sigma, purity 99.98%), P ２ S ５ (manufactured by Sigma, purity 99%), S (manufactured by Sigma, purity 99.98%), SnS ２ (Mitsuwa Chemical Co., Ltd., purity 99.5%), SiS ２ (Mitsuwa Chemical Co., Ltd., purity 99%), Sb ２ S ５(manufactured by Strem Chemicals, purity 98%) and LiI (manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.9%, low moisture grade), the amount of LiI in the raw material powder used in Example 3 was increased by 10 wt %, and Li ２ The sulfide solid electrolyte (Li ６．５ [P ０．２５ Si ０．３ Sn ０．２ Sb ０．２５ ]S ５ Although the obtained composition contained a large amount of iodine, it was equivalent to the charged composition.

[0122] Example 7: As a raw material powder, Li ２ S (Sigma, purity 99.98%), Si (Fujifilm Wako Pure Chemical Industries, Ltd., purity 99.9%), Sb ２ S ３ The sulfide solid electrolyte (LiI) of Example 7 was prepared in the same manner as in Example 1, except that the sulfide solid electrolyte (LiI) of Example 7 (manufactured by Mitsuwa Chemical Co., Ltd., purity 99.98%), S (manufactured by Sigma, purity 99.98%), and LiI (manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.9%, low moisture grade) were mixed to have the charge composition (target composition) shown in Table 1, and the dissolution temperature was 750°C. ６．６ [Si ０．６ Sb ０．４ ]S ５ I) was obtained.

[0123] Example 8 The amount of LiI in the raw material powder used in Example 7 was increased by 10 wt % and Li ２ The sulfide solid electrolyte (Li) of Example 8 was prepared in the same manner as in Example 7, except that the amounts of S and S were adjusted to obtain the charge composition (target composition) in Table 1 except for iodine, and the dissolution temperature was set to 720°C. ６．６ [Si ０．６ Sb ０．４ ]S ５ Although the obtained composition contained a large amount of iodine, it was equivalent to the charged composition.

[0124] Example 9: As a raw material powder, Li ２S (manufactured by Sigma, purity 99.98%), S (manufactured by Sigma, purity 99.98%), LiI (manufactured by Tokyo Kasei, purity 99.9% low moisture grade), SiS ２ (Mitsuwa Chemical Co., Ltd., purity 99%), Sb ２ S ５ The sulfide solid electrolyte (Li ６．６ [Si ０．６ Sb ０．４ ]S ５ Although the obtained composition contained a large amount of iodine, it was equivalent to the charged composition.

[0125] Example 10 In a glove box adjusted to a nitrogen atmosphere with a dew point of −50° C., LiCl, YCl ３ Each raw material powder (manufactured by Sigma, purity 99.99%) was mixed to the target composition shown in Table 1 and thoroughly mixed in a mortar. 1 g of the resulting mixture was placed in a quartz test tube, melted at 600°C for 1 hour, and then removed. The composition of the resulting solid electrolyte of Example 10 was: (Li ３ YCl ６ ) was.

[0126] Example 11 The solid electrolyte of Example 11 (Li ３ YCl ６ The composition of the obtained solid electrolyte of Example 11 was the same as the charged composition (target composition) except for chlorine.

[0127] The valences of antimony (Sb), tin (Sn), and silicon (Si) in the obtained sulfide solid electrolyte were determined by structural analysis of the XRD pattern of the obtained crystal and examining the coordination number and coordination distance of the elements. They were also determined by Raman spectroscopy and comparing the data with a database.

[0128] <Solubility Test> In the heat-melting step for producing the sulfide solid electrolytes of Examples 1 to 8, the temperature was increased in increments of 10°C from 650°C, and the solubility was evaluated based on the fluidity of the heated material and the undissolved raw material. In the heat-melting step for producing the solid electrolytes of Examples 10 and 11, the temperature was increased in increments of 10°C from 550°C, and the solubility was evaluated based on the fluidity of the heated material and the undissolved raw material. Regarding the fluidity of the heated material, a quartz test tube was tilted, and the temperature at which the liquid level followed the tilt was taken as the flow initiation temperature. Regarding the undissolved raw material, a sample was taken out at the above-mentioned flow initiation temperature, and the unmelted raw material (specifically, Li, excluding LiHa) was evaluated by XRD. ２ S.P. ２ S ５ The XRD evaluation was performed using an X-ray diffractometer (Rigaku Corporation, SmartLab) under the following conditions in an environment not exposed to the atmosphere: radiation source: CuKα radiation (λ=1.5418 Å), tube voltage: 45 kV, tube current: 200 mA, scanning angle: 10 to 100°, scanning speed: 5° / min, number of steps: 0.01° / step.

[0129] Table 1 shows the flow initiation temperature and the presence or absence of undissolved raw materials in each example.

[0130] <Lithium Ion Conductivity Evaluation> The sulfide solid electrolyte obtained in each example was further crushed in a mortar and passed through a 100 μm mesh sieve to obtain a sulfide solid electrolyte powder having a D50 of 20 μm in the volumetric particle size distribution measured by a laser diffraction particle size distribution measurement method. The powder was then compressed at a pressure of 380 kN to form a measurement sample, and the lithium ion conductivity was measured using an AC impedance measurement device (potentiostat / galvanostat VSP, manufactured by Bio-Logic Sciences Instruments). The measurement conditions were: measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, and measurement temperature: 25°C.

[0131] The lithium ion conductivity in each example is shown in Table 1.

[0132]

[0133] In Example 1, the valence of Sn in the starting materials was 0, but the valence of Sn in the resulting sulfide solid electrolyte was 4, which was higher than the valence in the starting materials. On the other hand, in Example 2, the valence of Sn in the starting materials was 4, and the valence of Sn in the resulting sulfide solid electrolyte was also 4, which was not higher than the valence in the starting materials. Therefore, Example 1 had a lower flow initiation temperature than Example 2, and no undissolved raw materials, resulting in high solubility. Furthermore, Example 1 had a higher ionic conductivity than Example 2. In Examples 3 and 4, the valences of Si, Sn, and Sb in the starting materials were 0, 0, and 3, respectively, but the valences of Si, Sn, and Sb in the resulting sulfide solid electrolyte were 4, 4, and 5, respectively, which was higher than the valence of each of the elements Si, Sn, and Sb in the starting materials. On the other hand, in Example 5, the valences of Si, Sn, and Sb in the starting materials were 4, 4, and 5, respectively, and the valences of Si, Sn, and Sb in the obtained sulfide solid electrolyte were also 4, 4, and 5, respectively, which did not increase from the valences in the starting materials. Therefore, Examples 3 and 4 had a lower flow initiation temperature than Example 5, and no undissolved raw materials were present, resulting in high solubility. Furthermore, Examples 3 and 4 had higher ionic conductivity than Example 5. In particular, in Example 4, excess LiI was added relative to the target composition, and the I in the excess LiI was replaced with I ２ As a result, the flow initiation temperature was lower than that of Example 3. In Example 6, excess LiI was added relative to the target composition, and the I in the excess LiI was replaced with I ２As a result, the flow initiation temperature was lower than in Example 5, and there was no residual raw material, resulting in high solubility. In Examples 7 and 8, the valences of Si and Sb in the starting materials were 0 and 3, respectively, but the valences of Si and Sb in the resulting sulfide solid electrolyte were 4 and 5, respectively, which were higher than the valences in the starting materials. On the other hand, in Example 9, the valences of Si and Sb in the starting materials were 4 and 5, respectively, and the valences of Si and Sb in the resulting sulfide solid electrolyte were also 4 and 5, respectively, which were not increased from the valences in the starting materials. Therefore, Examples 7 and 8 had lower flow initiation temperatures than in Example 9, and there was no residual raw material, resulting in high solubility. Furthermore, Examples 7 and 8 had higher ionic conductivity than Example 9. In particular, in Example 8, excess LiI was added relative to the target composition, and the I in the excess LiI was replaced with I ２ In Example 11, the flow starting temperature was lower than that in Example 7. ２ Gas is pumped in to remove excess Cl ２ As a result, the flow initiation temperature was lower and the ionic conductivity was higher than in Example 10, which was not subjected to such treatment.

[0134] 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. 2023-212391) filed on December 15, 2023, the contents of which are incorporated herein by reference.

Claims

1. A method for producing a sulfide solid electrolyte comprising heating and melting a sulfide solid electrolyte raw material containing at least one of Sn, Si, and Sb in a gas atmosphere containing elemental sulfur, and cooling and solidifying the resulting melt, wherein the valence of the element contained in the sulfide solid electrolyte raw material is increased by the heating and melting.

2. A method for producing a sulfide solid electrolyte, comprising: adding an excess amount of a Ha compound to a sulfide solid electrolyte raw material relative to a target composition of the sulfide solid electrolyte produced by the method; heating and melting the raw material in a gas atmosphere containing a sulfur element or a halogen element; and melting at least a portion of the excess amount of the Ha compound relative to the target composition by dissolving the raw material in a gas atmosphere containing a sulfur element or a halogen element. ２ or HHa, and the resulting melt is cooled and solidified. ２、 And Ha in the above HHa represents at least one element selected from halogen elements.

3. A method for producing a sulfide solid electrolyte, comprising: adding an excess amount of a Ha compound to a sulfide solid electrolyte raw material containing at least one element selected from the group consisting of Sn, Si, and Sb, relative to a target composition of the sulfide solid electrolyte produced by the method; heating and melting the raw material in a gas atmosphere containing a sulfur element or a halogen element; and melting at least a portion of the excess amount of the Ha compound relative to the target composition by melting the raw material with a gas atmosphere containing a sulfur element or a halogen element. ２ or HHa, and the resulting melt is cooled and solidified to produce a sulfide solid electrolyte containing at least one element selected from Sn, Si, and Sb, and the valence of the element contained in the sulfide solid electrolyte raw material is increased by the heating and melting. ２、 And Ha in the above HHa represents at least one element selected from halogen elements.

4. The method for producing a sulfide solid electrolyte according to claim 2 or 3, wherein the Ha compound is LiHa.

5. The method for producing a sulfide solid electrolyte according to claim 4, wherein the LiHa is LiI.

6. The method for producing a sulfide solid electrolyte according to claim 1 or 3, wherein a molar ratio (P / X) of P to a total amount X of P, Sn, Si, and Sb contained in the sulfide solid electrolyte produced by the method is 0.1 or more and 0.9 or less.

7. The method for producing a sulfide solid electrolyte according to claim 6, wherein the sulfide solid electrolyte produced by the method contains iodine.

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