Method for producing sulfide solid electrolyte

Abstract

Provided is a method for efficiently producing a sulfide solid electrolyte which has high ion conductivity and in which increase of particle diameters and spread of particle size distribution are suppressed, the method involving mixing, in a first solvent, raw material-containing matter that includes multiple kinds of raw materials each including at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom to obtain a solution including an electrolyte precursor, removing the solvent from the solution to obtain the electrolyte precursor, bringing the electrolyte precursor into contact with a second solvent, and subsequently heating same, wherein the second solvent differs from the first solvent and is a hydrocarbon solvent.

Description

Method for producing sulfide solid electrolyte

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

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Conventionally, batteries used for such applications have used electrolytes containing flammable organic solvents, but by making batteries all-solid-state, flammable organic solvents are not used in the battery, safety devices can be simplified, and manufacturing costs and productivity are excellent. Therefore, batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed.

[0003] Methods for producing solid electrolytes used in solid electrolyte layers are broadly divided into solid-phase methods and liquid-phase methods. Liquid-phase methods include homogeneous methods in which the solid electrolyte material is completely dissolved in a solvent, and heterogeneous methods in which the solid electrolyte material is not completely dissolved and a solid-liquid coexistence suspension is formed. For example, among the liquid-phase methods, a homogeneous method in which the solid electrolyte is dissolved in a solvent and re-precipitated is known (see, for example, Patent Document 1). Also, heterogeneous methods include a method in which raw materials such as lithium sulfide are reacted in a solvent containing a polar aprotic solvent (see, for example, Patent Documents 2 and 3). Furthermore, a method for producing a solid electrolyte using a specific compound having an amino group as a complexing agent (see, for example, Patent Documents 4 and 5) is also known. Non-Patent Document 1 describes a method for producing a solid electrolyte by using tetrahydrofuran and ethanol to precipitate Li. ６ P.S. ５ A tetrahydrofuran-ethanol precursor solution of Br was prepared, dried, and heated to obtain Li. ６ P.S. ５ It is described that a solid electrolyte having an argyrodite-type crystal structure with a composition of Br is prepared.

[0004] Non-Patent Documents 2 and 3 disclose a method for the preparation of a tetrahydrofuran-ethanol mixture of acetonitrile, tetrahydrofuran, and ethanol (volume ratio: 1:1:0.05) containing Li ２ S, P ２ S ５By adding S (molar ratio of 7:3:x (x = 3, 5, or 7)), lithium polysulfides and highly reactive sulfur radicals are generated, and after stirring for several minutes, the mixture is dried under vacuum and heated at a heating temperature of 270 ° C., 350 ° C., etc. to produce Li ７ P ３ S １１ It is described that a crystalline solid electrolyte having the following composition is produced.

[0005] Further, there is a method for producing a sulfide-based solid electrolyte by contacting a mixture containing an alkali metal sulfide and sulfur with a sulfur compound such as phosphorus sulfide (see, for example, Patent Document 6), and a method for producing a sulfide-based solid electrolyte by contacting a mixture containing Li in an organic solvent such as tetrahydrofuran or dimethoxyethane. ２ S and P ２ S ５ Also known are a sulfide solid electrolyte obtained by mixing and precipitating raw materials containing lithium, phosphorus, sulfur, and chlorine and a solvent such as ethanol (see, for example, Patent Document 7), and a method for producing a solid electrolyte in which a liquid containing the raw materials containing lithium, phosphorus, sulfur, and chlorine and a solvent such as ethanol is supplied to a liquid or gas having a temperature higher than the boiling point of the solvent, and the solvent is evaporated while the raw materials are reacted to precipitate an argyrodite-type crystal structure (see, for example, Patent Document 8).

[0006] Japanese Patent Application Publication No. 2014-191899 International Publication No. 2014 / 192309 Pamphlet International Publication No. 2018 / 054709 Pamphlet International Publication No. 2020 / 105737 Pamphlet International Publication No. 2021 / 230189 Pamphlet Japanese Patent Application Publication No. 2014-220051 Japanese Patent Application Publication No. 2015-232965 Japanese Patent Application Publication No. 2019-169459

[0007] J. Mater. Chem. A, 2019, 7, 558-566. Proceedings of the 62nd Battery Symposium, November 29, 2021, All-Solid-State Battery / Sulfide-Based Electrolyte, 3E01. Adv. Energy Sustenability Res. 2022, 2200019.

[0008] The present invention has been made in view of the above circumstances, and has an object to efficiently provide a sulfide solid electrolyte having high ionic conductivity in which an increase in particle size and a widening of particle size distribution are suppressed.

[0009] A method for producing a sulfide solid electrolyte according to the present invention includes: mixing, in a first solvent, a raw material-containing mixture containing a plurality of raw materials each containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom to obtain a solution containing an electrolyte precursor; removing the solvent from the solution to obtain an electrolyte precursor; contacting the electrolyte precursor with a second solvent; and subsequently heating, wherein the second solvent is different from the first solvent and is a hydrocarbon solvent.

[0010] According to the present invention, it is possible to efficiently provide a sulfide solid electrolyte having high ionic conductivity in which an increase in particle size and a widening of the particle size distribution are suppressed.

[0011] 1 is an X-ray diffraction spectrum of the powder obtained in Example 1. FIG. 2 is an X-ray diffraction spectrum of the powder obtained in Example 2. FIG. 3 is an X-ray diffraction spectrum of the powder obtained in Example 3. FIG. 4 is an X-ray diffraction spectrum of the powder obtained in Example 4. FIG. 5 is an X-ray diffraction spectrum of the powder obtained in Example 5. FIG. 6 is an X-ray diffraction spectrum of the powder obtained in Comparative Example 1. FIG. 7 is an X-ray diffraction spectrum of the powder obtained in Example 6. FIG. 8 is an X-ray diffraction spectrum of the powder obtained in Comparative Example 2. FIG. 9 is an X-ray diffraction spectrum of the powder obtained in Example 7. FIG. 10 is an X-ray diffraction spectrum of the powder obtained in Example 8. FIG. 11 is an X-ray diffraction spectrum of the powder obtained in Comparative Example 3.

[0012] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a numerical range expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​of the examples can also be used as the upper and lower limit values. Furthermore, preferred specifications can be arbitrarily adopted. In other words, one preferred specification can be adopted in combination with one or more other preferred specifications. It can be said that a combination of preferred items is more preferable.

[0013] (Findings Obtained by the Inventors to Achieve the Present Invention) The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found the following, which has led to the completion of the present invention.

[0014] In recent years, liquid-phase methods have been attracting attention as a method that allows for the practical application of all-solid-state batteries, not only for its versatility and applicability, but also for its ease of mass synthesis. Solid-phase methods, such as mechanical milling, involve grinding and mixing raw materials in a grinder to cause a reaction, thereby obtaining a solid electrolyte. However, these methods require high equipment costs and a large initial investment, making it difficult to reduce costs.

[0015] On the other hand, in the liquid-phase production methods of sulfide solid electrolytes disclosed in the above patent documents and non-patent documents, granulation may occur due to high-temperature heating during crystallization, resulting in large particle sizes. Therefore, when using the obtained sulfide solid electrolyte in the production of lithium-ion batteries, it becomes necessary to adjust the particle size in advance, which results in a problem of reduced production efficiency. Thus, in the production of sulfide solid electrolytes, it has become necessary to consider not only the production efficiency achieved by promoting the reaction of raw materials, but also the production efficiency in the production of lithium-ion batteries after the sulfide solid electrolyte is obtained.

[0016] The present inventors have noticed that the above-mentioned patent documents and non-patent documents disclosing the liquid phase method do not raise any problem of granulation due to heating and increasing particle size when heating for crystallization is performed. Furthermore, when attempting to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure, among sulfide solid electrolytes, heating at a high temperature of about 430°C is unavoidable, as can be seen from the production method disclosed in Patent Document 8, for example. Therefore, granulation is more likely to occur, and the tendency for particle size to increase becomes more pronounced.

[0017] The present inventors have conducted research into the granulation and particle size increase caused by heating and have found that granulation due to heating is affected by the residual solvent used during the reaction of raw materials. This tendency has been found to be particularly pronounced when solvents such as tetrahydrofuran, ethanol, and nitrogen-containing complexing agents, which are also used in the above-mentioned patent documents, are used. Thus, when the liquid-phase method, i.e., the reaction of raw materials is carried out in a solution, if heating for crystallization is carried out while the solvent remains, the residual solvent increases the bonding strength between particles, making granulation due to aggregation more likely to occur. Therefore, the present inventors contacted an electrolyte precursor obtained by removing the solvent from a solution in which raw materials are mixed in a solvent with a different solvent, and discovered that the sulfide solid electrolyte obtained by subsequent heating did not undergo granulation and exhibited suppressed increases in particle size and widening of the particle size distribution.

[0018] (Regarding various aspects of the present embodiment) A method for producing a sulfide solid electrolyte according to a first aspect of the present embodiment includes: mixing, in a first solvent, a raw material-containing mixture containing a plurality of raw materials each containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom to obtain a solution containing an electrolyte precursor; removing the solvent from the solution to obtain an electrolyte precursor; contacting the electrolyte precursor with a second solvent; and subsequently heating, wherein the second solvent is different from the first solvent and is a hydrocarbon solvent.

[0019] In the method for producing a sulfide solid electrolyte of this embodiment, the raw material ingredients are mixed in the first solvent, so a liquid phase method is adopted, which makes it possible to produce a sulfide solid electrolyte very efficiently.

[0020] The manufacturing method of this embodiment includes mixing the raw material inclusions in a first solvent, thereby obtaining a solution containing an electrolyte precursor. That is, a solvent capable of dissolving the raw materials contained in the raw material inclusions and the reaction product of these raw materials is adopted as the first solvent. By dissolving the raw materials in the solvent in this way, the reaction between the raw materials contained in the raw material inclusions proceeds quickly, and therefore the sulfide solid electrolyte can be obtained very efficiently.

[0021] Here, the term "electrolyte precursor" refers to a precursor of the sulfide solid electrolyte obtained by the manufacturing method of this embodiment, and is different from the raw materials contained in the raw material inclusions and the sulfide solid electrolyte obtained by heating. More specifically, it is a product of the reaction between the raw materials mixed with the first solvent to obtain a solution containing the electrolyte precursor in the manufacturing method of this embodiment. The presence of the "electrolyte precursor" can be confirmed, for example, by analyzing the "electrolyte precursor" by FT-IR (diffuse reflectance spectroscopy) and detecting a peak different from both the raw materials and the sulfide solid electrolyte, or by powder X-ray diffraction (XRD) measurement and the like.

[0022] In the manufacturing method of this embodiment, the solvent is removed from the solution obtained by the above mixing to obtain an electrolyte precursor, which is the solute dissolved in the solution. The obtained electrolyte precursor is then contacted with a second solvent. Here, by using a hydrocarbon solvent different from the first solvent as the second solvent, the first solvent adhering to the electrolyte precursor can be washed and removed.

[0023] The electrolyte precursor is then heated while being accompanied by the second solvent. By heating, the electrolyte precursor can produce an amorphous sulfide solid electrolyte or even a crystalline sulfide solid electrolyte, depending on the heating conditions. The first solvent adhering to the electrolyte precursor is replaced with the second solvent, which is a hydrocarbon solvent, and is removed by evaporation or combustion upon heating. Therefore, even when the electrolyte precursor is heated, granulation due to residual solvent does not occur. Furthermore, the first solvent, which contributes to the formation of the electrolyte precursor, is removed from the structure of the electrolyte precursor, and reactions such as decomposition of the electrolyte precursor proceed, resulting in the electrolyte precursor becoming a sulfide solid electrolyte. Thus, the manufacturing method of this embodiment makes it possible to efficiently provide a sulfide solid electrolyte in which particle size increase and particle size distribution widening are suppressed.

[0024] A second aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the first aspect, wherein the hydrocarbon solvent is at least one organic solvent selected from aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

[0025] When the hydrocarbon solvent of the second solvent is at least one organic solvent selected from aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, the first solvent adhering to the electrolyte precursor can be more easily washed and removed, and therefore a sulfide solid electrolyte can be obtained in which an increase in particle size and a widening of the particle size distribution are more efficiently suppressed.

[0026] A third aspect of the present embodiment is directed to the first or second aspect of the method for producing a sulfide solid electrolyte, wherein the solubility of the lithium halide in the hydrocarbon solvent at 25°C is 0.5 mass% or less.

[0027] In the manufacturing method of this embodiment, it is preferable to use a hydrocarbon solvent as the second solvent that has a low solubility of lithium halide, such that the solubility of lithium halide in the hydrocarbon solvent at 25°C is 0.5 mass% or less. By using such a hydrocarbon solvent, the lithium atoms and halogen atoms contained in the electrolyte precursor can be retained in the electrolyte precursor without being captured by the second solvent. Therefore, not only can the first solvent be washed and removed, but also a larger amount of the lithium atoms and halogen atoms supplied as raw materials can be retained in the electrolyte precursor, thereby improving ionic conductivity.

[0028] A fourth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to any one of the first to third aspects, wherein the hydrocarbon solvent is an aromatic hydrocarbon solvent. A fifth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the fourth aspect, wherein the aromatic hydrocarbon solvent is an alkylbenzene. A sixth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the fifth aspect, wherein the alkylbenzene has an alkyl group having 1 to 4 carbon atoms.

[0029] When the second solvent is an aromatic hydrocarbon solvent, particularly an alkylbenzene, and particularly an alkylbenzene having an alkyl group having 1 to 4 carbon atoms, the above-mentioned effect of using the second solvent can be obtained more efficiently.

[0030] A seventh aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to any one of the first to sixth aspects, wherein the amount of the second solvent used in the contacting is 50 parts by mass or more and 10,000 parts by mass or less per 100 parts by mass of the electrolyte precursor. By setting the amount of the second solvent used within the above range, the effect of using the second solvent described above can be more efficiently obtained.

[0031] The method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the first to seventh aspects, wherein the contacting is performed at least once.

[0032] In the production method of this embodiment, the contact may be performed once or twice or more times, which can be appropriately determined as necessary.

[0033] A ninth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to any one of the first to eighth aspects, wherein the raw material contents include elemental sulfur.

[0034] When elemental sulfur is used as a raw material, it is believed that by combining it with a raw material containing lithium atoms, such as lithium sulfide, the elemental sulfur reacts with the raw material containing lithium atoms, such as lithium sulfide, in the solvent to form lithium polysulfides, generating sulfur radicals. The sulfur radicals are highly reactive and promote reactions with other raw materials, such as diphosphorus pentasulfide and other raw materials containing halogen atoms, to generate precursors of sulfide solid electrolytes, i.e., soluble polysulfides (hereinafter simply referred to as "polysulfides") that serve as electrolyte precursors. By decomposing these polysulfides by heating or the like, a sulfide solid electrolyte with improved ionic conductivity can be efficiently produced.

[0035] A raw material containing elemental sulfur is used as the raw material, and this is mixed in a first solvent to produce a soluble polysulfide, which is an electrolyte precursor. Furthermore, by heating, the polysulfide is decomposed to produce an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte, and the crystallinity of the crystalline sulfide solid electrolyte is improved. Here, by contacting the electrolyte precursor (polysulfide) with a second solvent before heating, the first solvent adhering to the electrolyte precursor can be washed and removed. Therefore, even when the electrolyte precursor (polysulfide) is heated, granulation due to residual solvent does not occur, and a sulfide solid electrolyte can be provided in which an increase in particle size and an expansion of the particle size distribution are suppressed. When a raw material containing elemental sulfur is used, heating is performed primarily for the decomposition of the polysulfide, removal of the solvent, and crystallization. Furthermore, the elemental sulfur produced by the decomposition of the polysulfide can also be removed by evaporation by heating, but methods other than heating, such as solvent washing and hydrodesulfurization, may also be used.

[0036] A tenth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the ninth aspect, wherein the first solvent is an organic solvent containing at least one atom selected from oxygen atoms and nitrogen atoms. A eleventh aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the tenth aspect, wherein the organic solvent contains at least one organic solvent selected from alcohol solvents, ether solvents, and nitrile solvents.

[0037] The second solvent is different from the first solvent and is a hydrocarbon solvent. However, in relation to the second solvent, it is preferable to use a solvent containing at least one atom selected from oxygen and nitrogen atoms, i.e., an atom called a heteroatom, as the first solvent. The use of such a first solvent promotes the generation of sulfur radicals via the reaction of elemental sulfur and lithium sulfide to form lithium polysulfides. Because sulfur radicals are highly reactive, they react with other raw materials, such as diphosphorus pentasulfide and other raw materials containing halogen atoms, and react with lithium sulfide or lithium polysulfides to promote the generation of soluble polysulfides. This soluble polysulfide is a precursor to a sulfide solid electrolyte, and upon heating, the polysulfide decomposes to rapidly form an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte, improving the crystallinity of the crystalline sulfide solid electrolyte. As a result, a sulfide solid electrolyte with few impurities and high ionic conductivity can be efficiently obtained.

[0038] Furthermore, as the solvent containing such a heteroatom, it is preferable to use at least one of an alcohol solvent, an ether solvent, and a nitrile solvent. By using these solvents, the effects of using the solvent containing the heteroatom, namely, the generation of sulfur radicals and the formation of an electrolyte precursor (polysulfide) are promoted. Furthermore, by using an alcohol solvent, an ether solvent, and a nitrile solvent in combination, the generation of sulfur radicals and the formation of an electrolyte precursor (polysulfide) are promoted in a balanced manner. As a result, a sulfide solid electrolyte with few impurities and high ionic conductivity can be efficiently obtained.

[0039] A method for producing a sulfide solid electrolyte according to a twelfth aspect of the present embodiment is any one of the ninth to eleventh aspects, wherein the heating temperature is 20°C or higher and 500°C or lower.

[0040] As described above, in the manufacturing method of this embodiment, heating the electrolyte precursor can produce an amorphous sulfide solid electrolyte or even a crystalline sulfide solid electrolyte, depending on the heating conditions. Here, when the raw material inclusions contain elemental sulfur, an electrolyte precursor (polysulfide) is produced as described above. Therefore, when the raw material inclusions contain elemental sulfur, heating not only produces the amorphous sulfide solid electrolyte or even the crystalline sulfide solid electrolyte, but also decomposes the electrolyte precursor (polysulfide). When the heating temperature is within the above range, more efficient and reliable decomposition and crystallization of the electrolyte precursor (polysulfide) are possible.

[0041] A thirteenth aspect of the present embodiment is directed to the method for producing a sulfide solid electrolyte of any one of the ninth to twelfth aspects, wherein the amount of elemental sulfur used is 0.5 mol or more relative to 1.0 mol of the lithium sulfide.

[0042] The amount of elemental sulfur used relative to lithium sulfide is not particularly limited, but is preferably a certain amount or more, such as 0.5 mol or more per 1.0 mol of lithium sulfide. This amount, which will be described in detail later, tends to be an amount in excess of the sulfur atoms required for the sulfide solid electrolyte to be obtained. In this way, the use of excess elemental sulfur promotes the generation of sulfur radicals, and as a result, a sulfide solid electrolyte with improved ionic conductivity can be efficiently produced.

[0043] A fourteenth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to any one of the first to eighth aspects, wherein the raw material content contains lithium sulfide, phosphorus sulfide, and at least one halogen atom-containing raw material selected from lithium halides and elemental halogens. A fifteenth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to any one of the first to ninth aspects, wherein the raw material content does not contain elemental sulfur.

[0044] In the manufacturing method of this embodiment, it is also preferable to use a raw material containing lithium sulfide, phosphorus sulfide, and at least one halogen atom-containing raw material selected from lithium halides and elemental halogens as the raw material containing material other than the elemental sulfur in the ninth aspect. In the manufacturing method of this embodiment, even if an electrolyte precursor using various raw material containing materials is used, it is possible to efficiently provide a sulfide solid electrolyte in which particle size increase and particle size distribution widening are suppressed. That is, in the manufacturing method of this embodiment, it is extremely important to contact the electrolyte precursor with the second solvent. According to the manufacturing method of this embodiment, it can be said that, regardless of the electrolyte precursor obtained by mixing the above-mentioned raw material containing materials with the first solvent, contacting the electrolyte precursor with the second solvent can efficiently provide a sulfide solid electrolyte in which particle size increase and particle size distribution widening are suppressed.

[0045] A method for producing a sulfide solid electrolyte according to a sixteenth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to the fourteenth or fifteenth aspect, except that, before the heating, the method comprises heat-treating the electrolyte precursor while supplying hydrogen sulfide. A method for producing a sulfide solid electrolyte according to a seventeenth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the fourteenth to sixteenth aspects, except that the first solvent includes an alcohol solvent and an ether solvent.

[0046] Heat-treating the electrolyte precursor while supplying hydrogen sulfide is particularly effective when the raw material contains lithium sulfide, phosphorus sulfide, and at least one halogen atom-containing raw material selected from lithium halides and elemental halogens, and further when the raw material does not contain elemental sulfur. In this case, the first solvent preferably contains an alcohol solvent and an ether solvent. By using such a solvent, the electrolyte precursor can be easily obtained, and therefore the sulfide solid electrolyte can be obtained more efficiently.

[0047] The electrolyte precursor is formed by mixing the raw material ingredients in the first solvent, but some of the raw materials contained in the raw material ingredients may remain as raw materials. For example, lithium sulfide (Li ２ When lithium sulfide (Li ２ S) may remain intact. Solvents containing oxygen atoms, such as alcohol solvents, which are preferably used in the production method of this embodiment, are advantageous in that they facilitate the production of an electrolyte precursor and reduce the amount of remaining raw materials, as described above. On the other hand, due to their high reactivity, they tend to react with lithium sulfide to produce lithium alkoxides such as lithium ethoxide, which may prevent lithium sulfide, which would otherwise be reactive with other raw materials, from contributing to the reaction with the other raw materials. If lithium alkoxide remains intact, the purity of the sulfide solid electrolyte decreases, and the lithium alkoxide may remain carbonized by calcination, which may result in a decrease in quality, such as a decrease in ionic conductivity.

[0048] In this way, when a solvent containing an alcohol solvent and an ether solvent is used as the first solvent, lithium alkoxide may be generated together with the electrolyte precursor. Here, by heating the electrolyte precursor while supplying hydrogen sulfide, the remaining lithium alkoxide is converted into lithium sulfide (Li ２ Specifically, the reactions shown in the following reaction formulas (1) to (3) are considered to occur.

[0049] Li ２ S+EtOH→EtOLi+LiSH (1) 2LiSH→Li２ S+H ２ S (2) 2EtOLi+H ２ S → Li ２ S+2EtOH (3)

[0050] The above reaction is carried out using lithium sulfide (Li ２ S) and ethanol (EtOH) as the alcohol solvent of the first solvent. ２ When lithium ethoxide (LiOEt) and lithium hydrosulfide (LiSH) are present in the original state, they react with ethanol as shown in reaction formula (1), producing lithium ethoxide (LiOEt) and lithium hydrosulfide (LiSH). Lithium hydrosulfide (LiSH) decomposes as shown in reaction formula (2), producing lithium sulfide (Li ２ S) and hydrogen sulfide.

[0051] As shown in reaction formula (3), lithium ethoxide (LiOEt) produced in reaction formula (1) reacts with hydrogen sulfide produced in reaction formula (2) and hydrogen sulfide supplied separately to produce lithium sulfide (Li ２ S) is produced. Lithium sulfide (Li ２ S) may react with other raw materials to form a sulfide solid electrolyte, and even if it remains as it is, it does not cause a decrease in the ionic conductivity of the sulfide solid electrolyte. In this way, by performing the heat treatment while supplying hydrogen sulfide, it is possible to suppress the remaining impurities such as lithium alkoxide and the loss of raw materials, and improve the quality of the sulfide solid electrolyte.

[0052] Furthermore, in the production method of this embodiment, the electrolyte precursor is brought into contact with the second solvent, so that the first solvent adhering to the surface of the electrolyte precursor can be removed, and impurities such as lithium alkoxide can also be removed. Therefore, in addition to the inherent effect of suppressing an increase in particle size and a widening of the particle size distribution, it is also possible to further suppress the remaining impurities such as lithium alkoxide and loss of raw materials, thereby further improving the quality of the sulfide solid electrolyte.

[0053] The method for producing a sulfide solid electrolyte according to an eighteenth aspect of the present embodiment is the seventeenth aspect, wherein, in obtaining the solution containing the electrolyte precursor, the raw material components are mixed in an ether solvent, and then an alcohol solvent is added and mixed.

[0054] As described above, the first solvent may contain an alcohol solvent and an ether solvent, or a mixed solvent containing an alcohol solvent and an ether solvent may be used all at once, or an alcohol solvent and an ether solvent may be used stepwise as in the eighteenth embodiment. Hereinafter, in describing the eighteenth embodiment, the first solvent that is first mixed with the raw material inclusions will be referred to as the 1-1 solvent, and the solvent that is subsequently used will be referred to as the 1-2 solvent.

[0055] In an eighteenth embodiment, when a solvent containing an alcohol solvent and an ether solvent is used as the first solvent, an ether solvent is used as the 1-1 solvent, and an alcohol solvent is used as the 1-2 solvent. That is, when a solvent containing an alcohol solvent and an ether solvent is used as the first solvent, the preferred order of use of the alcohol solvent and the ether solvent is specified.

[0056] In a production method employing a liquid phase process, it is preferable that lithium sulfide, diphosphorus pentasulfide, and other raw materials containing halogen atoms, such as lithium bromide, lithium iodide, and lithium chloride, are not separated in the liquid phase and contribute to the formation of the electrolyte precursor. As mentioned above, using an alcohol solvent as the first solvent is effective in promoting the formation of the electrolyte precursor, but due to its high reactivity, it is easy to convert lithium sulfide into lithium alkoxide. It is also known to be highly reactive, particularly with raw materials containing halogen atoms. Thus, when the first solvent is a solvent containing an ether solvent and an alcohol solvent, separation and loss of some of the raw materials are likely to occur.

[0057] In the eighteenth embodiment, an ether solvent is first used as the first-1 solvent to prepare a mixture with the raw material inclusions, i.e., the mixture is formed without completely dissolving the raw material inclusions. Because the raw material inclusions do not completely dissolve in the first-1 solvent, the reaction is slow, and the solvent and the raw materials form a bonded state due to some force (intermolecular force, chemical bond, etc.). In particular, the solvent forms a loose bond, which can suppress loss of raw materials.

[0058] Next, the mixture is mixed with the first-2 solvent to obtain a solution containing the electrolyte precursor. As described above, in the mixture, the raw materials contained in the raw material inclusions are held in a bonded state with each other and with the solvent, and by mixing this with the first-2 solvent, the raw materials dissolve while maintaining loose bonds with the first-1 solvent, thereby obtaining a solution in which the electrolyte precursor is dissolved.

[0059] Here, the raw materials are supplied to the first-2 solvent in a state where the raw materials are bonded to each other and further in a loosely bonded state with the first-1 solvent, thereby forming an electrolyte precursor without separation or loss due to reaction between the first-2 solvent and the raw materials, and contributing to the formation of a sulfide solid electrolyte. For example, as described above, when phosphorus sulfide (e.g., diphosphorus pentasulfide (P ２ S ５ Even when the first solvent is used, dissolution and reaction of phosphorus sulfide and its reactants in the first solvent can be suppressed, and phosphorus sulfide can be contributed to the formation of a sulfide solid electrolyte without separation or loss. In this way, by selectively using the first solvent and the first solvent, it is possible to suppress separation and loss of various raw materials such as lithium sulfide, phosphorus sulfide, and lithium halide, which are preferably used as raw materials.

[0060] A method for producing a sulfide solid electrolyte according to a nineteenth aspect of the present embodiment is any one of the fourteenth to eighteenth aspects, wherein the heating temperature in the heating is 150° C. or higher.

[0061] When the raw material content includes lithium sulfide, phosphorus sulfide, and at least one halogen atom-containing raw material selected from lithium halides and elemental halogens, heating at the above heating temperature makes it possible to more efficiently produce an amorphous sulfide solid electrolyte, and further a crystalline sulfide solid electrolyte.

[0062] The method for producing a sulfide solid electrolyte according to a twentieth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the first to nineteenth aspects, wherein the halogen atom is at least one atom selected from a chlorine atom, a bromine atom, and an iodine atom.

[0063] When the sulfide solid electrolyte contains halogen atoms, it has high ionic conductivity. Among halogen atoms, the sulfide solid electrolyte contains at least one halogen atom selected from chlorine atoms, bromine atoms, and iodine atoms, which facilitates the formation of an argyrodite-type crystal structure or a thiolicon region II-type crystal structure, which exhibits particularly high ionic conductivity.

[0064] A method for producing a sulfide solid electrolyte according to a twenty-first aspect of the present embodiment is any one of the first to twentieth aspects, wherein a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure or a thioliconregion II-type crystal structure is produced.

[0065] In the manufacturing method of this embodiment, it is possible to manufacture a desired sulfide solid electrolyte by changing the types and compounding ratios of the raw materials contained in the raw material inclusions. Crystalline sulfide solid electrolytes having an argyrodite-type crystal structure and crystalline sulfide solid electrolytes having a thiolicon region II-type crystal structure are known as sulfide solid electrolytes with extremely high ionic conductivity, and are preferable as the sulfide solid electrolyte to be obtained by the manufacturing method of this embodiment.

[0066] (Sulfide Solid Electrolyte) In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state under a nitrogen atmosphere at 25° C. The sulfide solid electrolyte in this embodiment is a solid electrolyte that contains at least one atom selected from lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, and preferably has ionic conductivity attributable to lithium atoms.

[0067] The term "sulfide solid electrolyte" includes both amorphous sulfide solid electrolytes and crystalline sulfide solid electrolytes. In this specification, a crystalline sulfide solid electrolyte refers to a sulfide solid electrolyte in which a peak derived from the solid electrolyte is observed in an X-ray diffraction pattern in an X-ray diffraction measurement, regardless of whether or not a peak derived from the raw materials of the sulfide solid electrolyte is present. That is, a crystalline sulfide solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as the crystalline sulfide solid electrolyte has the X-ray diffraction pattern described above, it may also contain an amorphous sulfide solid electrolyte in part. Therefore, crystalline sulfide solid electrolytes include so-called glass ceramics obtained by heating an amorphous sulfide solid electrolyte to a temperature equal to or higher than the crystallization temperature. In this specification, the amorphous sulfide solid electrolyte refers to an X-ray diffraction pattern in X-ray diffraction measurement that has a halo pattern in which no peaks other than those derived from the material are substantially observed, regardless of whether or not there are peaks derived from the raw materials of the sulfide solid electrolyte.

[0068] [Method for Producing Sulfide Solid Electrolyte] The method for producing a sulfide solid electrolyte of the present embodiment includes: mixing, in a first solvent, a raw material-containing mixture containing a plurality of raw materials each containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom to obtain a solution containing an electrolyte precursor; removing the solvent from the solution to obtain an electrolyte precursor; contacting the electrolyte precursor with a second solvent; and subsequently heating, wherein the second solvent is different from the first solvent and is a hydrocarbon solvent.

[0069] As described above, according to the production method of this embodiment, by contacting the electrolyte precursor with the second solvent, it is possible to obtain an effect of efficiently providing a sulfide solid electrolyte in which an increase in particle size and a widening of the particle size distribution are suppressed, regardless of the electrolyte precursor obtained by mixing the above-mentioned raw material inclusions with the first solvent. As such, in the production method of this embodiment, it is extremely important to contact the electrolyte precursor with the second solvent, and therefore the contacting process will be described first.

[0070] [Contacting the Electrolyte Precursor with the Second Solvent] The production method of this embodiment includes contacting the electrolyte precursor obtained in obtaining a solution containing the electrolyte precursor with the second solvent. As a result, as described above, granulation due to heating caused by the remaining first solvent does not occur, and it is possible to provide a sulfide solid electrolyte in which an increase in particle size and a widening of the particle size distribution are suppressed.

[0071] (Second Solvent) The second solvent used in the production method of this embodiment is different from the first solvent and is required to be a hydrocarbon solvent. By using such a second solvent, granulation due to heating caused by the remaining first solvent does not occur, and it is possible to provide a sulfide solid electrolyte in which an increase in particle size and a widening of the particle size distribution are suppressed.

[0072] The hydrocarbon solvent of the second solvent preferably includes hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents. More specifically, representative and preferred examples include aliphatic hydrocarbon solvents such as hexane, pentane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane; alicyclic hydrocarbon solvents such as cyclohexane and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene.

[0073] Among the above hydrocarbon solvents, aromatic hydrocarbon solvents are preferred, and alkylbenzenes such as toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene are more preferred. The number of carbon atoms in the alkyl group of the alkylbenzene is preferably 1 or more, with the upper limit being preferably 4 or less, more preferably 3 or less, and even more preferably 2 or less. Here, the number of carbon atoms in the alkyl group is the number of carbon atoms in one alkyl group, and when there are multiple alkyl groups, it is preferable that there are multiple alkyl groups having the above number of carbon atoms. In the production method of this embodiment, the above hydrocarbon solvents can be used alone or in combination.

[0074] Furthermore, the hydrocarbon solvent of the second solvent preferably has a lithium halide solubility of 0.5 mass % or less at 25° C. When the hydrocarbon solvent has a low lithium halide solubility at 25° C. within the above range, the lithium atoms and halogen atoms contained in the electrolyte precursor are not taken up by the second solvent as described above, and can be retained in the electrolyte precursor. This not only suppresses an increase in particle size and a widening of the particle size distribution, but also improves the ionic conductivity of the resulting solid electrolyte.

[0075] From the same viewpoint, the solubility is more preferably 0.4% by mass or less, and even more preferably 0.2% by mass or less. There is no particular restriction on the lower limit of the solubility, and 0% by mass, i.e., no solubility at all, is preferable, but in reality it is 0.01% by mass or more.

[0076] The amount of the second solvent used in the contact is not particularly limited as long as it can remove the first solvent, and may be, for example, 50 parts by mass or more and 10,000 parts by mass or less relative to 100 parts by mass of the electrolyte precursor. From the viewpoint of more efficient and reliable removal of the first solvent, the amount is preferably 100 parts by mass or more, more preferably 300 parts by mass or more, and even more preferably 500 parts by mass or more, with the upper limit being preferably 8,000 parts by mass or less, more preferably 5,000 parts by mass or less, and even more preferably 3,000 parts by mass or less.

[0077] The electrolyte precursor is preferably contacted with the second solvent at least once, but from the viewpoint of more efficient and reliable removal of the first solvent, the number of times is preferably two or more, and the upper limit is preferably eight or less, more preferably four or less.

[0078] The method for contacting the electrolyte precursor with the second solvent is not particularly limited as long as they are in contact with each other, and may be, for example, a method commonly referred to as solvent washing, in which the electrolyte precursor and the second solvent are mixed and then decanted or filtered using a glass filter to remove the second solvent.

[0079] The temperature conditions for contacting the electrolyte precursor with the second solvent are not particularly limited and are, for example, −10 to 130° C., preferably 10 to 120° C., and more preferably room temperature (20° C.) to 110° C. Within the above temperature range, an increase in particle size and an increase in particle size distribution can be easily suppressed. Furthermore, from the viewpoint of reducing the particle size and narrowing the particle size distribution in addition to suppressing an increase in particle size and an increase in particle size distribution, the temperature is preferably 40 to 130° C., more preferably 60 to 120° C., even more preferably 80 to 110° C., and even more preferably 90 to 105° C.

[0080] [Regarding steps other than the above-described contacting] Next, steps other than "contacting the electrolyte precursor with the second solvent", "obtaining a solution containing the electrolyte precursor", "obtaining the electrolyte precursor", and "heating" will be described in order.

[0081] As described above, in the production method of this embodiment, any electrolyte precursor obtained by mixing the above-mentioned raw material inclusions with a first solvent can be brought into contact with a second solvent to efficiently produce a sulfide solid electrolyte in which particle size increase and particle size distribution expansion are suppressed. The electrolyte precursor varies mainly depending on the raw materials contained in the raw material inclusions, and is preferably divided into the following two forms (i) and (ii) depending on the raw material inclusions. Therefore, the raw material inclusions will be described separately for the following cases: Embodiment (i) When elemental sulfur is contained; and Embodiment (ii) When lithium sulfide, phosphorus sulfide, and at least one halogen atom-containing raw material selected from lithium halide and elemental halogen are contained.

[0082] Although the raw materials contained in the raw material inclusions are different between embodiments (i) and (ii), the operations of "obtaining a solution containing an electrolyte precursor," "obtaining an electrolyte precursor," "contacting the electrolyte precursor with a second solvent," and "heating" are performed in both embodiments. However, due to the different raw materials, the conditions for "obtaining a solution containing an electrolyte precursor," "obtaining an electrolyte precursor," and "heating" among the above-mentioned various operations may differ. On the other hand, the conditions may be common. Furthermore, the raw material inclusions employed in the manufacturing method of this embodiment are preferably those of embodiments (i) and (ii) above, but are not limited to these embodiments. Below, the explanation will begin with "obtaining a solution containing an electrolyte precursor," "obtaining an electrolyte precursor," and "heating" in embodiment (i). However, the contents of embodiment (ii) and parts that also apply to other embodiments also apply to embodiment (ii) and other embodiments unless otherwise specified.

[0083] [Embodiment (i)] In embodiment (i), the raw material content contains a plurality of raw materials each containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom, and also contains elemental sulfur.

[0084] [Obtaining a Solution Containing an Electrolyte Precursor] The manufacturing method of this embodiment includes preparing an electrolyte precursor before contacting the electrolyte precursor with a second solvent. That is, the manufacturing method includes mixing, in a first solvent, a raw material content containing a plurality of raw materials containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom to obtain a solution containing an electrolyte precursor. The raw material content will first be described regarding obtaining a solution containing an electrolyte precursor.

[0085] (Raw material inclusions) The raw material inclusions used in this embodiment are inclusions containing multiple raw materials containing at least one atom selected from lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and in the case of embodiment (i), the raw material inclusions contain elemental sulfur. The atoms contained in the raw material inclusions are at least one atom selected from lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and from the viewpoint of improving ionic conductivity, the raw material inclusions preferably contain lithium atoms, sulfur atoms, and phosphorus atoms, and more preferably contain lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms.

[0086] In embodiment (i), examples of raw materials other than elemental sulfur contained in the raw material content include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides; various phosphorus fluorides (PF ３ , P.F. ５ ), various phosphorus chlorides (PCl ３ , PCl ５ , P ２ Cl ４ ), various phosphorus bromides (PBr ３ , PBr ５ ), various phosphorus iodides (PI ３ , P ２ I ４ ) and the like; phosphorus halides such as thiophosphoryl fluoride (PSF ３ ), thiophosphoryl chloride (PSCl ３ ), thiophosphoryl bromide (PSBr ３ ), thiophosphoryl iodide (PSI３ ), thiophosphoryl fluoride dichloride (PSCl ２ F), thiophosphoryl fluoride dibromide (PSBr ２ a source material consisting of at least two atoms selected from the above four types of atoms, such as thiophosphoryl halides, e.g., fluorine (F); ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), preferably chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ) are typical examples.

[0087] Examples of materials that can be used as raw materials other than those mentioned above include raw materials that contain at least one atom selected from the above four types of atoms and also contain atoms other than the four types of atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, and tin sulfide (SnS, SnS ２ metal sulfides such as aluminum sulfide and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium such as sodium halides such as sodium iodide, sodium fluoride, sodium chloride and sodium bromide; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides and bismuth halides; phosphorus oxychloride (POCl ３ ), phosphorus oxybromide (POBr ３ ) and the like; and the like.

[0088] In the case of embodiment (i), the raw material content only needs to contain elemental sulfur, and in consideration of the ease of forming polysulfides, it is preferable to contain lithium sulfide among the above. ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, fluorine (F２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide are preferred. When oxygen atoms are introduced into the solid electrolyte, lithium oxide, lithium hydroxide, and phosphate compounds such as lithium phosphate are preferred.

[0089] The halogen atom is preferably a chlorine atom, a bromine atom, or an iodine atom, and is preferably at least one selected from these, and more preferably a combination of a chlorine atom and a bromine atom, or a bromine atom and an iodine atom. Therefore, the lithium halide is preferably lithium chloride, lithium bromide, or lithium iodide, and more preferably a combination of lithium chloride and lithium bromide, or a combination of lithium bromide and lithium iodine. The halogen element is chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), and chlorine (Cl ２ ) and bromine (Br ２ ), bromine (Br ２ ) and iodine (I ２ The lithium halide and the halogen element may be used alone or in combination of two or more kinds.

[0090] In embodiment (i), preferred combinations of raw materials including elemental sulfur include, for example, a combination of lithium sulfide, elemental sulfur, diphosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, elemental sulfur, diphosphorus pentasulfide, and an elemental halogen. Furthermore, preferred lithium halides include lithium chloride, lithium bromide, and lithium iodide, with combinations of lithium chloride and lithium bromide, and lithium bromide and lithium iodide being more preferred. Preferred halogen elements include chlorine, bromine, and iodine, with combinations of chlorine and bromine, and bromine and iodine being more preferred.

[0091] Lithium sulfide, which is one of the preferred raw materials, can be produced by, for example, combining lithium hydroxide with elemental sulfur. Therefore, when lithium sulfide is contained as a raw material component, the lithium sulfide may be, for example, a commercially available lithium sulfide, or may be lithium sulfide obtained by reacting another raw material containing lithium atoms, such as lithium hydroxide, with a raw material containing sulfur atoms, such as elemental sulfur.

[0092] In this embodiment, PS ４ Li containing structure ３ P.S. ４ can also be used as part of the raw material. ３ P.S. ４ This is prepared by manufacturing or the like and used as a raw material. ３ P.S. ４ The content is preferably 60 to 100 mol %, more preferably 65 to 90 mol %, and even more preferably 70 to 80 mol %.

[0093] Also, Li ３ P.S. ４ When using a halogen atom, Li ３ P.S. ４ The content of the halogen element is preferably 1 to 50 mol %, more preferably 10 to 40 mol %, even more preferably 20 to 30 mol %, and even more preferably 22 to 28 mol %.

[0094] The lithium sulfide used in this embodiment is preferably in the form of particles. ５０ ) is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.5 μm or more and 100 μm or less, and even more preferably 1 μm or more and 20 μm or less. ５０) is the particle size at which, when a particle size distribution cumulative curve is drawn, the cumulative total, starting from the smallest particle size, reaches 50% (by volume) of the total, and the volume distribution refers to an average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device. Furthermore, among the above-mentioned examples of raw materials, solid raw materials preferably have an average particle size similar to that of the lithium sulfide particles, i.e., within the same range as that of the lithium sulfide particles.

[0095] (Regarding the blending ratio of raw materials) In the embodiment (i), when elemental sulfur and lithium sulfide are used, the amount of elemental sulfur used relative to lithium sulfide can be adopted without any particular limitation. When elemental sulfur is used, as described above, elemental sulfur reacts with lithium sulfide to form lithium polysulfides, generating sulfur radicals, and then promotes the reaction with other raw materials to obtain polysulfides, which are electrolyte precursors.

[0096] The amount of elemental sulfur used relative to lithium sulfide cannot be generalized because it varies depending on the type of sulfide solid electrolyte to be obtained by the production method of the present embodiment. However, when the sulfide solid electrolyte contains lithium atoms, phosphorus atoms, and sulfur atoms, the amount of elemental sulfur used relative to 1.0 mole of lithium sulfide is preferably 0.5 moles or more, and more preferably 0.7 moles or more.

[0097] When the sulfide solid electrolyte contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, it is preferably used in an excess amount of more than 1.0 mol per 1.0 mol of lithium sulfide, more preferably 1.2 mol or more, more preferably 1.5 mol or more, and even more preferably 1.7 mol or more. Using an excess of elemental sulfur in this way promotes the generation of sulfur radicals, resulting in the efficient production of a sulfide solid electrolyte with improved ionic conductivity. In either case, there is no particular upper limit, but from the viewpoint of more efficiently obtaining a sulfide solid electrolyte, it is sufficient to use an amount of about 4.0 mol or less, preferably 3.0 mol or less.

[0098] Furthermore, when the sulfide solid electrolyte to be obtained by the production method of this embodiment contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, the amount of elemental sulfur used is preferably 110% or more, more preferably 130% or more, even more preferably 150% or more, and still more preferably 170% or more of the sulfur atoms required to achieve that composition. There is no particular upper limit, but from the viewpoint of more efficiently obtaining a sulfide solid electrolyte, it is sufficient to set the amount to about 300% or less, preferably 280% or less, more preferably 250% or less, and even more preferably 230% or less.

[0099] When lithium sulfide, elemental sulfur, diphosphorus pentasulfide, and lithium halide are used as raw materials, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 65 to 85 mol%, more preferably 70 to 82 mol%, and even more preferably 74 to 80 mol%, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity. When lithium sulfide, elemental sulfur, diphosphorus pentasulfide, lithium halide, and other raw materials used as needed are used, the content of lithium sulfide and diphosphorus pentasulfide to the total is preferably 50 to 99 mol%, more preferably 55 to 90 mol%, and even more preferably 60 to 85 mol%.

[0100] When lithium bromide and lithium iodide are used in combination as the lithium halide, from the viewpoint of improving ionic conductivity, the ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 80 mol%, even more preferably 35 to 80 mol%, and particularly preferably 45 to 70 mol%. Furthermore, when lithium bromide and lithium chloride are used in combination as the lithium halide, from the viewpoint of improving ionic conductivity, the ratio of lithium bromide to the total of lithium bromide and lithium chloride is preferably 1 to 99 mol%, more preferably 15 to 75 mol%, even more preferably 25 to 60 mol%, and particularly preferably 35 to 45 mol%.

[0101] When a halogen element is used as a raw material, and lithium sulfide, elemental sulfur, or diphosphorus pentasulfide is used, the ratio of the number of moles of lithium sulfide excluding the same number of moles of lithium sulfide as the halogen element to the total number of moles of lithium sulfide and diphosphorus pentasulfide excluding the same number of moles of lithium sulfide as the halogen element is preferably within the range of 60 to 90%, more preferably within the range of 65 to 85%, even more preferably within the range of 68 to 82%, even more preferably within the range of 72 to 78%, and particularly preferably within the range of 73 to 77%. This is because higher ionic conductivity can be obtained with these ratios. Furthermore, from the same viewpoint, when lithium sulfide, elemental sulfur, diphosphorus pentasulfide, and a halogen element are used, the content of the halogen element relative to the total amount of lithium sulfide, diphosphorus pentasulfide, and the halogen element is preferably 1 to 50 mol%, more preferably 2 to 40 mol%, even more preferably 3 to 25 mol%, and even more preferably 3 to 15 mol%.

[0102] When lithium sulfide, elemental sulfur, diphosphorus pentasulfide, elemental halogen, and lithium halide are used, the content of elemental halogen (α mol %) and the content of lithium halide (β mol %) relative to the total amount of lithium sulfide, diphosphorus pentasulfide, elemental halogen, and lithium halide preferably satisfy the following formula (2), more preferably satisfy the following formula (3), even more preferably satisfy the following formula (4), and still more preferably satisfy the following formula (5): 2≦2α+β≦100 (2) 4≦2α+β≦80 (3) 6≦2α+β≦50 (4) 6≦2α+β≦30 (5)

[0103] When two types of halogens are used as simple substances, the molar number of one halogen atom in the substance is A1, and the molar number of the other halogen atom in the substance is A2, and the ratio A1:A2 is preferably 1 to 99:99 to 1, more preferably 10:90 to 90:10, even more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0104] When two kinds of halogen elements are used, and the two kinds of halogen elements are bromine and iodine, where A1 is the number of moles of bromine and A2 is the number of moles of iodine, A1:A2 is preferably 1:99 to 99:1, more preferably 20:80 to 80:20, even more preferably 35:65 to 80:20, and even more preferably 45:55 to 70:30. When the two kinds of halogen elements are bromine and chlorine, B1 is the number of moles of bromine and B2 is the number of moles of chlorine, and B1:B2 is preferably 1:99 to 99:1, more preferably 15:85 to 75:25, even more preferably 25:75 to 60:40, and even more preferably 35:45 to 65:55.

[0105] The above blending ratio of raw materials makes it easier to obtain the thiolicon region II type crystal structure and the argyrodite type crystal structure, which are preferred crystal structures of the sulfide solid electrolyte obtained by the production method of this embodiment.

[0106] (First Solvent) In the above embodiment (i), the first solvent used when mixing the raw materials may be a solvent different from the second solvent, in relation to the second solvent. As the first solvent, a hydrocarbon solvent exemplified as the second solvent, other than the hydrocarbon solvent used as the second solvent, can also be used, but it is preferable to use a solvent containing a heteroatom. Preferred examples of heteroatoms contained in the solvent include oxygen atoms, nitrogen atoms, sulfur atoms, chlorine atoms, and phosphorus atoms, and among these, oxygen atoms and nitrogen atoms are preferred. The solvent containing a heteroatom may contain one type of these heteroatoms or may contain multiple types.

[0107] Examples of such heteroatom-containing solvents include oxygen-containing solvents such as alcohol solvents, ether solvents, ester solvents, aldehyde solvents, and ketone solvents; nitrogen-containing solvents such as amine solvents and nitrile solvents; and oxygen- and nitrogen-containing solvents such as amide solvents. Among these, alcohol solvents and ether solvents are preferred as oxygen-containing solvents, and nitrile solvents are preferred as nitrogen-containing solvents. The use of these solvents promotes the generation of sulfur radicals and the formation of an electrolyte precursor (polysulfide), efficiently producing a sulfide solid electrolyte with few impurities and high ionic conductivity.

[0108] These solvents may be used alone or in combination, and it is particularly preferable to use at least one organic solvent selected from alcohol solvents, ether solvents, and nitrile solvents, and it is more preferable to use a combination of alcohol solvents, ether solvents, and nitrile solvents.Since the generation of sulfur radicals and the formation of the electrolyte precursor (polysulfide) are promoted in a balanced manner, a sulfide solid electrolyte with few impurities and high ionic conductivity can be efficiently obtained.

[0109] (Alcohol Solvent) Examples of the alcohol solvent include aliphatic alcohols, alicyclic alcohols, heterocyclic alcohols, and aromatic alcohols. In consideration of availability and cost, aliphatic alcohols, alicyclic alcohols, and aromatic alcohols are preferred, and aliphatic alcohols are more preferred.

[0110] Representative and preferred examples of aliphatic alcohols include saturated or unsaturated monohydric aliphatic alcohols such as methanol, ethanol, various propanols, allyl alcohol, various butanols, and various buteneols; and saturated or unsaturated polyhydric aliphatic alcohols such as various propanediols, various propenediols, various butanediols, various butenediols, various hexanediols, various hexenediols, various butanetriols, erythritol, pentaerythritol, and dipentaerythritol. In this specification, "various" means that all possible isomers are included, for example, in the case of various butanols, such as 1-butanol, 2-butanol, 2-methyl-1-propanol, and 1,1-dimethylethanol. Furthermore, even if "various" is not used, compounds described in a format in which the substitution position number is not specified include all possible isomers.

[0111] The aliphatic hydrocarbon group in the aliphatic alcohol may be linear or branched, saturated or unsaturated. The number of carbon atoms in the aliphatic alcohol is preferably 1 or more, more preferably 2 or more, and is preferably 12 or less, more preferably 8 or less, and even more preferably 4 or less.

[0112] The aliphatic alcohol may be partially substituted, and preferred examples thereof include alkanolamines in which a portion of the alcohol is substituted with an amino group, such as ethanolamine, propanolamine, and dimethylethanolamine, and alcohols in which a portion of the alcohol is substituted with a halogen atom, such as fluoroalcohols.

[0113] Typical preferred examples of the alicyclic alcohol include mono- or polyhydric saturated or unsaturated monocyclic alicyclic alcohols such as cyclopropanol, methylcyclopropanol, cyclopropanemethanol, cyclobutanol, cyclobutenol, cyclopentanol, cyclopentenol, cyclohexanol, methylcyclohexanol, cyclohexenol, cyclohexanediol, and cyclohexanetriol; and mono- or polyhydric polycyclic alicyclic alcohols such as cyclopentyl cyclopentanol, cyclohexyl cyclohexanol, cyclohexylphenyl cyclohexanol, and bicyclohexanol.

[0114] The number of carbon atoms in the alicyclic alcohol is preferably 3 or more, and the upper limit is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less.

[0115] The alicyclic alcohol may be partially substituted, and preferred examples thereof include those partially substituted with saturated or unsaturated hydrocarbon groups (including linear and branched ones) such as alkyl groups and alkenyl groups, for example, those partially substituted with amino groups such as aminomethylcyclopropanol, and those partially substituted with halogen atoms. In addition, the alicyclic alcohol may be substituted with a substituent such as an amide group or a cyano group.

[0116] Typical preferred examples of heterocyclic alcohols include monocyclic heterocyclic alcohols such as oxetaneol, oxetanemethanol, furfuryl alcohol, tetrahydrofurfuryl alcohol, tetrahydropyranmethanol, morpholineethanol, and pyridinemethanol; and polycyclic condensed heterocyclic alcohols such as benzofuranmethanol and dihydrobenzofuranmethanol.

[0117] The number of carbon atoms in the heterocyclic alcohol is preferably 3 or more, and the upper limit is preferably 24 or less, more preferably 18 or less, and even more preferably 12 or less. The heterocyclic alcohol may be partially substituted, similar to the above-mentioned alicyclic alcohol.

[0118] Typical preferred examples of aromatic alcohols include monocyclic aromatic alcohols such as benzyl alcohol, salicylic alcohol, benzenedimethanol, methoxyphenylmethanol, trimethoxyphenylmethanol, and phenethyl alcohol; polycyclic aromatic alcohols such as diphenylmethanol and triphenylmethanol; and condensed polycyclic aromatic alcohols such as naphthalenemethanol, anthracenemethanol, benzofuranmethanol, and dihydrobenzofuranmethanol.

[0119] The aromatic alcohol preferably has 7 or more carbon atoms, and the upper limit is preferably 24 or less, more preferably 20 or less, and even more preferably 16 or less. The aromatic alcohol may be partially substituted, similar to the above-mentioned alicyclic alcohol.

[0120] The above examples are merely representative examples of preferred alcohol solvents, and the solvents that can be used in the production method of this embodiment are not limited to the above examples.

[0121] The alcohol solvent may be any of primary, secondary, and tertiary alcohols, preferably primary alcohols, and may also be monohydric alcohols having one hydroxyl group or polyhydric alcohols having two or more hydroxyl groups, preferably monohydric alcohols.

[0122] (Ether Solvent) Examples of the ether solvent include aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers. In consideration of availability and cost, aliphatic ethers, alicyclic ethers, and aromatic ethers are preferred, aliphatic ethers and alicyclic ethers are more preferred, and alicyclic ethers are even more preferred.

[0123] Representative preferred examples of aliphatic ethers include monoethers such as dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, and tert-butyl methyl ether; diethers such as dimethoxymethane, dimethoxyethane, diethoxymethane, and diethoxyethane; polyethers having three or more ether groups such as diethylene glycol dimethyl ether (diglyme) and triethylene oxide glycol dimethyl ether (triglyme); and ethers containing a hydroxyl group such as diethylene glycol and triethylene glycol.

[0124] The number of carbon atoms in the aliphatic ether is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, and the upper limit is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The aliphatic alcohol may be linear or branched.

[0125] Typical preferred examples of the alicyclic ether include monocyclic alicyclic ethers such as ethylene oxide, propylene oxide, furan, tetrahydrofuran, pyran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane, dioxene, dioxine, and dioxolane; and polycyclic alicyclic ethers such as dicyclopentyl ether and dicyclohexyl ether.

[0126] Representative preferred examples of heterocyclic ethers include monocyclic heterocyclic ethers such as morpholine and hydroxymethyldimethoxypyridine; and polycyclic fused heterocyclic ethers such as benzofuran, benzopyran, dibenzofuran and methoxyindole. The number of carbon atoms in the alicyclic ether or heterocyclic ether is preferably 3 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 10 or less.

[0127] Representative preferred examples of aromatic ethers include monocyclic aromatic ethers such as methyl phenyl ether (anisole) and ethyl phenyl ether; polycyclic aromatic ethers such as dibenzyl ether, diphenyl ether and benzyl phenyl ether; and condensed polycyclic aromatic ethers such as benzyl naphthyl ether and bisnaphthyl ether.

[0128] The aromatic ether preferably has 7 or more carbon atoms, more preferably 8 or more carbon atoms, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less carbon atoms.

[0129] The ether compound used in the present embodiment may be substituted with a substituent such as a linear or branched hydrocarbon group, such as an alkyl group or an alkenyl group, an alkoxyl group (the alkyl group may be linear or branched), a hydroxyl group, an amino group, an amide group or a cyano group, or a halogen atom.

[0130] Among the above ether compounds, from the viewpoint of obtaining higher ionic conductivity, alicyclic ethers are preferred, monocyclic alicyclic ethers are more preferred, and tetrahydrofuran is particularly preferred.

[0131] (Nitrile Solvent) Examples of nitrile solvents include aliphatic nitriles, alicyclic nitriles, heterocyclic nitriles, and aromatic nitriles. In view of availability and cost, aliphatic nitriles are preferred.

[0132] Typical preferred aliphatic nitriles include saturated or unsaturated aliphatic nitriles having one nitrile group, such as acetonitrile, acrylonitrile, methoxyacetonitrile, propionitrile, methoxypropionitrile, and butyronitrile; and saturated or unsaturated aliphatic nitriles having two or more nitrile groups, such as propanedinitrile, propanetricarbonitrile, butanedinitrile, butenedinitrile, butanetricarbonitrile, pentanedinitrile, pentanetricarbonitrile, hexanedinitrile, hexenedinitrile, hexanetricarbonitrile, and methylenepentanedinitrile.

[0133] The number of carbon atoms in the aliphatic nitrile is preferably 2 or more, and the upper limit is preferably 10 or less, more preferably 8 or less, and even more preferably 4 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic nitrile is preferably 1 or more, and the upper limit is preferably 8 or less, more preferably 6 or less, and even more preferably 2 or less. The aliphatic hydrocarbon group in the aliphatic nitrile may be linear or branched.

[0134] Typical preferred examples of the alicyclic nitrile include monocyclic or polycyclic alicyclic nitriles having one nitrile group, such as cyanocyclopropane, cyclobutanecarbonitrile, hydroxycyclobutanecarbonitrile, oxocyclobutanecarbonitrile, cyclopentanecarbonitrile, furancarbonitrile, tetrahydropyrancarbonitrile, cyclohexanecarbonitrile, and bicyclobutanecarbonitrile; and alicyclic nitriles having two or more nitrile groups, such as furandicarbonitrile, cyclobutanedicarbonitrile, cyclopentanedicarbonitrile, cyclohexanedicarbonitrile, and cyclohexanetricarbonitrile.

[0135] Typical preferred examples of the heterocyclic nitrile include monocyclic heterocyclic nitriles having one or more nitrile groups, such as morpholinecarbonitrile, tetrahydrofurfurylcarbonitrile, cyanopyridine, pyridinedicarbonitrile, pyridinetricarbonitrile, and furfurylmalononitrile; and polycyclic or polycyclic condensed heterocyclic nitriles having one or more nitrile groups, such as benzofurancarbonitrile, dibenzofurandicarbonitrile, and dicyanobipyridine.

[0136] The number of carbon atoms in the alicyclic nitrile and heterocyclic nitrile is preferably 3 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 10 or less.

[0137] Typical preferred examples of aromatic nitriles include monocyclic aromatic nitriles having one or more nitrile groups, such as phenylacetonitrile, cyanotoluene, benzonitrile, benzenedicarbonitrile, and benzenetricarbonitrile; and polycyclic or condensed polycyclic aromatic nitriles having one or more nitrile groups, such as biphenyldicarbonitrile, phenylcyclobutanecarbonitrile, naphthalenecarbonitrile, naphthalenedicarbonitrile, naphthalenetricarbonitrile, anthracenecarbonitrile, and cyclopentylbenzonitrile.

[0138] The aromatic nitrile preferably has 7 or more carbon atoms, more preferably 8 or more carbon atoms, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less carbon atoms.

[0139] The ether compound used in the present embodiment may be substituted with a substituent such as a linear or branched hydrocarbon group, such as an alkyl group or an alkenyl group, an alkoxyl group (the alkyl group may be linear or branched), a hydroxyl group, an amino group, an amide group or a cyano group, or a halogen atom.

[0140] (Other Solvents Having Heteroatoms) Preferred examples of the amine solvents exemplified as solvents having heteroatoms other than the alcohol solvents, ether solvents, and nitrile solvents include aliphatic amines such as ethylenediamine, diaminopropane, dimethylethylenediamine, tetramethylethylenediamine (TMEDA), and tetramethyldiaminopropane (TMPDA); alicyclic amines such as cyclopropanediamine and cyclohexanediamine; heterocyclic aromatic amine solvents such as pyridine; and amide solvents such as dimethylformamide, dimethylacetamide, hexamethylphosphoramide, and N-methylpyrrolidone.

[0141] (Other Solvents) When the solvent containing a heteroatom is used as the first solvent in obtaining a solution containing an electrolyte precursor, other solvents than the first solvent may be hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents exemplified as the second solvent.

[0142] In this case, the amount of the other solvent used is preferably as small as possible, for example, preferably 50.0 parts by volume or less, more preferably 30.0 parts by volume or less, and even more preferably 15.0 parts by volume or less, relative to 100.0 parts by volume of the first solvent used. Of course, it is preferable to use only the first solvent without using any other solvent.

[0143] (Amount of First Solvent Used) In the production method of the present embodiment, when an alcohol solvent is used as the first solvent, the amount of the alcohol solvent used is preferably 0.005 mol or more, more preferably 0.010 mol or more, even more preferably 0.015 mol or more, and still more preferably 0.020 mol or more, relative to 1.0 mol of lithium sulfide used as a raw material, and the upper limit is preferably 20.0 mol or less, more preferably 16.0 mol or less, and even more preferably 10.0 mol or less.

[0144] Furthermore, when at least one organic solvent selected from alcohol solvents, ether solvents, and nitrile solvents is used, and an alcohol solvent is used, the total amount of the ether solvent and the nitrile solvent used is preferably 2.0 parts by volume or more, more preferably 5.0 parts by volume or more, even more preferably 15.0 parts by volume or more, still more preferably 50.0 parts by volume or more, and particularly preferably 150.0 parts by volume or more, relative to 1.0 part by volume of the alcohol solvent used, and the upper limit is preferably 10,000.0 parts by volume or less, more preferably 9,000.0 parts by volume or less, even more preferably 8,000.0 parts by volume or less, and still more preferably parts by volume or less.

[0145] (Mixing) In the production method of this embodiment, a raw material content containing raw materials is mixed in the first solvent. By mixing the raw material content in the first solvent, a solution containing an electrolyte precursor is obtained. In embodiment (i), the electrolyte precursor (polysulfide) is generated via sulfur radicals, so that a sulfide solid electrolyte with few impurities and high ionic conductivity can be efficiently obtained.

[0146] The method for mixing the raw material ingredients in the first solvent is not particularly limited. The first solvent and the raw material ingredients can be mixed in a device capable of mixing the raw material ingredients in the first solvent. For example, it is preferable to supply the first solvent into a tank, operate the stirring blade, and then gradually add the raw material ingredients. It is also preferable to supply the raw material ingredients into a tank, operate the stirring blade, and then gradually add the first solvent. Since a good mixing state of the raw material ingredients is obtained, the dispersion of the raw material ingredients is improved, and the generation of sulfur radicals and the formation of the electrolyte precursor (polysulfide) are promoted. However, when a halogen element is used as a raw material, the raw material may not be solid. Specifically, fluorine and chlorine are gaseous, and bromine is liquid at room temperature and normal pressure. In such cases, for example, if the raw material is liquid, it can be supplied into the tank together with the solvent separately from other solid raw materials. Alternatively, if the raw material is gaseous, it can be supplied by blowing it into the solvent containing the solid raw material.

[0147] There are no particular restrictions on the order in which the raw materials of the raw material content are added and mixed, but in consideration of work efficiency, it is preferable to mix all the raw materials at the same time, that is, all at once.

[0148] Furthermore, in order to improve the solubility of the raw materials, further suppress the generation of impurities, and more efficiently obtain a sulfide solid electrolyte having high ionic conductivity, it is preferable to perform split mixing in which the raw materials are divided into two raw material groups, raw material group 1 and 2, and raw material group 1 is mixed first and then raw material group 2 is mixed.

[0149] When separate mixing is performed, raw material group 1 preferably contains elemental sulfur. This promotes the formation of sulfur radicals, and more efficiently produces a sulfide solid electrolyte with high ionic conductivity. From a similar perspective, a combination of raw material group 1 containing a raw material containing at least one atom selected from lithium atoms, phosphorus atoms, and sulfur atoms, elemental sulfur, and lithium sulfide, and raw material group 2 containing a raw material containing a halogen atom is preferred. This is because raw material group 1 contains elemental sulfur and lithium sulfide, and the reaction between these promotes the formation of sulfur radicals via lithium polysulfides. From a similar perspective, a combination of raw material group 1 containing a raw material containing a halogen atom, elemental sulfur, and lithium sulfide, and raw material group 2 containing a raw material containing a phosphorus atom and sulfur atom is also preferred.

[0150] In the production method of this embodiment, the order in which the raw materials are charged and mixed may be selected depending on whether importance is attached to work efficiency or to the ionic conductivity of the sulfide solid electrolyte.

[0151] As described above, in the manufacturing method of this embodiment, the raw material contained in the raw material content is PS ４ Li containing structure ３ P.S. ４ can be prepared in advance by production or the like and used. ３ P.S. ４ can be produced by blending, for example, lithium sulfide and diphosphorus pentasulfide in a molar ratio of 75:25. In the production method of this embodiment, when diphosphorus pentasulfide is used in addition to lithium sulfide as raw materials, a raw material group 1 containing lithium sulfide and diphosphorus pentasulfide in a predetermined molar ratio, such as 75:25, and containing elemental sulfur, can be mixed in a solvent, and then a raw material group 2 containing a raw material containing a halogen atom, such as lithium halide, and other remaining raw materials required for producing the desired sulfide solid electrolyte, for example, a raw material group containing the shortage of lithium sulfide, can be added and mixed. ３ P.S. ４A sulfide solid electrolyte can be obtained more efficiently by forming an electrolyte precursor (polysulfide) containing the basic structure of

[0043] . Here, the predetermined molar ratio of lithium sulfide to diphosphorus pentasulfide is preferably 55-85:15-45, more preferably 60-80:20-40, and even more preferably 65-75:25-35.

[0152] The manufacturing method of this embodiment is characterized by including mixing the raw material ingredients in a first solvent. That is, since the raw material ingredients only need to be mixed and not pulverized, the manufacturing method can be performed without using equipment commonly referred to as a pulverizer, such as a media-type pulverizer such as a ball mill or a bead mill, which is typically used for pulverizing raw materials. In this manufacturing method of this embodiment, simply mixing the raw material ingredients in the solvent mixes the solvent and raw materials, generating a polysulfide, which is an electrolyte precursor. When this polysulfide is decomposed by heating or the like, an amorphous sulfide solid electrolyte, or even a crystalline sulfide solid electrolyte, can be formed. The raw material mixture in the solvent may be pulverized using a pulverizer to shorten the mixing time or to achieve finer powder to obtain the electrolyte precursor. However, as described above, it is preferable not to use a pulverizer.

[0153] An example of a device for mixing the raw material ingredients in the first solvent is a mechanical agitation mixer equipped with an agitator blade in a tank. Examples of mechanical agitation mixers include high-speed agitation mixers and double-arm mixers, and high-speed agitation mixers are preferably used from the viewpoint of improving the uniformity of the raw materials in the mixture of raw material ingredients and obtaining higher ionic conductivity. Examples of high-speed agitation mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used.

[0154] Examples of the shape of the impeller used in a mechanical stirring mixer include anchor type, blade type, arm type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, C-type blade type, etc., and from the viewpoint of improving the uniformity of the raw materials and obtaining higher ionic conductivity, the shovel type, flat blade type, C-type blade type, etc. are preferred. Furthermore, in a mechanical stirring mixer, it is preferable to install a circulation line that discharges the material to be stirred outside the mixer and then returns it to the mixer. This allows raw materials with a high specific gravity, such as lithium halide, to be stirred without settling or stagnation, enabling more uniform mixing.

[0155] The location of the circulation line is not particularly limited, but it is preferably installed in a location where it discharges from the bottom of the mixer and returns to the top of the mixer. This makes it easier to mix uniformly by using convection caused by circulation to carry out the materials that tend to settle. Furthermore, it is preferable that the return port is located below the liquid surface of the material to be mixed. This can prevent the material to be mixed from splashing and adhering to the wall surfaces inside the mixer.

[0156] The mixing time for mixing the raw material ingredients in the first solvent is not particularly limited as an upper limit, but considering efficiency, it is preferably 240 minutes or less, more preferably 60 minutes or less, even more preferably 30 minutes or less, and even more preferably 15 minutes or less, and the lower limit is usually 0.1 minutes or more, preferably 1 minute or more, and even more preferably 3 minutes or more. Furthermore, the temperature conditions for mixing the raw material ingredients in the solvent are not particularly limited, and are, for example, −30 to 100° C., preferably −10 to 50° C., and more preferably about room temperature (20° C.) (for example, about room temperature ±5° C.).

[0157] [Obtaining Electrolyte Precursor] The manufacturing method of this embodiment includes removing the first solvent from the solution obtained by obtaining the above-described solution containing the electrolyte precursor, thereby obtaining the electrolyte precursor. In the manufacturing method of this embodiment, since a solution containing the electrolyte precursor is obtained, it is necessary to remove the solvent from the solution to obtain a powder of the electrolyte precursor. This is because the electrolyte precursor dissolved in the solution cannot be brought into contact with the second solvent.

[0158] The method for removing the solvent from the solution containing the electrolyte precursor is not particularly limited, but may be, for example, a method by drying.

[0159] As for the drying conditions, the drying temperature cannot be generalized because it varies depending on the pressure conditions under which drying is performed, the boiling point of the first solvent, etc., but is usually 5° C. or higher and lower than 200° C., preferably 20° C. to 190° C., more preferably 35 to 175° C., and even more preferably 50 to 160° C. Furthermore, as for the pressure conditions, although normal pressure or pressurized pressure can be used, reduced pressure drying (vacuum drying) using a vacuum pump or the like is preferred.

[0160] The drying time is usually 1 minute to 10 hours, preferably 10 minutes to 8 hours, more preferably 30 minutes to 6 hours, and even more preferably 1 hour to 5 hours.

[0161] In this way, a powder of the electrolyte precursor that dissolves in the solution containing the electrolyte precursor is obtained by a method such as drying, etc. By obtaining the electrolyte precursor and making it into a powder of the electrolyte precursor, the electrolyte precursor can be brought into contact with the second solvent.

[0162] In embodiment (i), obtaining the electrolyte precursor may be performed by the same operation as the "first heating" in the "heating" section described below, or may be performed separately in "first heating-1" and "first heating-2." The heating temperature in the "first heating" is 20°C or higher and lower than 150°C, as described below, and is substantially within the range of the drying temperature in the "method by drying" described above. Therefore, even when the temperature conditions for the "first heating" described below are taken into consideration, granulation due to heating caused by residual solvent is unlikely to occur. Note that the same operation as the "first heating" described above in obtaining the electrolyte precursor may be performed on a solution containing the electrolyte precursor, that is, on a solution containing the electrolyte precursor and the first solvent, and there is no need to replace the first solvent with the second solvent.

[0163] The electrolyte precursor is obtained by the same operation as the "first heating" described below, and after contacting the electrolyte precursor with the second solvent, heating may be performed by the methods of "first heating" and "second heating", or the "first heating" may be omitted and "second heating" may be performed. Here, when the "first heating" is performed, it may be performed separately as "first heating-1" and "first heating-2". In either case, by performing the electrolyte precursor by the same operation as the "first heating", granulation is less likely to occur as described above, and therefore the particle size and particle size distribution can be made smaller, and an increase in particle size and a change in particle size distribution can be more effectively suppressed.

[0164] Details of obtaining the electrolyte precursor in embodiment (ii) will be described later. The electrolyte precursor may be obtained by the same operation as the "first heating" in the "heating" of embodiment (i), or may be obtained by dividing it into "first heating-1" and "first heating-2".

[0165] [Heating] The production method of this embodiment includes removing the solvent from the solution containing the electrolyte precursor to obtain an electrolyte precursor, bringing the electrolyte precursor into contact with a second solvent, and then heating the resulting electrolyte precursor.

[0166] The heating temperature is not particularly limited as long as it is equal to or higher than room temperature, and although it cannot be generally determined because room temperature may vary, it is usually preferably equal to or higher than 20° C., with the upper limit preferably equal to or lower than 500° C. If the heating temperature is within the above range, decomposition of polysulfides, removal of the solvent and removal of elemental sulfur, as well as crystallization can be more efficiently carried out.

[0167] In embodiment (i), heating can be performed to form a sulfide solid electrolyte by decomposing the produced polysulfide (i.e., electrolyte precursor), to remove elemental sulfur produced by decomposition of the polysulfide, and to remove the solvent and crystallize the resulting mixture. The heating temperature in embodiment (i) is preferably within the above-mentioned range, i.e., 20°C or higher and 500°C or lower.

[0168] In the embodiment (i), the heating is preferably carried out in multiple stages, for example, a heating step (first heating) is carried out mainly for decomposing the produced polysulfides, removing the solvent, and removing elemental sulfur, followed by a heating step (second heating) for crystallization. More specifically, the heating step is preferably carried out by a first heating step at a heating temperature of 20° C. or higher but lower than 150° C., and a second heating step at a heating temperature of 150° C. or higher but 500° C. or lower.

[0169] The heating temperature in the first heating may be 20°C or higher and lower than 150°C. For example, heating at a lower temperature may be followed by heating at a higher temperature; that is, the first heating may be performed by further multi-stage heating. Typically, solvent removal begins at 20°C or higher, decomposition of polysulfides begins at 60°C or higher, and sulfur removal begins at 100°C or higher. By performing multi-stage heating at heating temperatures appropriate for these purposes, each purpose can be achieved more efficiently, making it easier to obtain a sulfide solid electrolyte with improved ionic conductivity. In particular, by reliably removing elemental sulfur, the generation of impurities due to remaining elemental sulfur can be further suppressed, making it easier to obtain a sulfide solid electrolyte with improved ionic conductivity.

[0170] For example, when heating at a lower temperature (first heating-1), the heating temperature is preferably 20°C or higher, with the upper limit preferably being less than 60°C, more preferably being 50°C or lower. By setting the temperature range in this way, it becomes possible to remove the solvent. Next, when heating at a higher temperature (first heating-2), the heating temperature is preferably 60°C or higher, more preferably 65°C or higher, even more preferably 75°C or higher, still more preferably 95°C or higher, and particularly preferably 110°C or higher, with the upper limit being less than 150°C, more preferably 145°C or lower, even more preferably 135°C or lower, and still more preferably 130°C or lower. By setting the temperature range in this way, it becomes possible to mainly decompose polysulfides and remove sulfur.

[0171] As for the first heating, as described above, depending on the heating temperature, any of solvent removal, decomposition of polysulfides, and sulfur removal can be performed. Therefore, various embodiments can be taken by adjusting the heating temperature. For example, if the heating temperature of the first heating is 60°C or higher (less than 100°C), it is possible to remove the solvent and decompose the polysulfides. This is referred to as first heating-1, and by performing heating at 100°C or higher (less than 150°C) as first heating-2, it is possible to remove sulfur. In this case, first heating-2 is not performed, and sulfur removal can be performed by a method other than heating, i.e., solvent washing, hydrodesulfurization, etc., and then second heating can be performed. Methods for removing sulfur, such as solvent washing and hydrodesulfurization, will be described later.

[0172] Furthermore, for example, if the heating temperature of the first heating is set to 20°C or higher (less than 60°C), the solvent can be removed, and this is designated as First Heating-1. If First Heating-2 is heated at 60°C or higher (less than 100°C), the polysulfides can be decomposed, and then First Heating-3 is heated at 100°C or higher (less than 150°C) to remove sulfur. In this case, three-stage heating can be performed. In place of First Heating-3, sulfur can be removed by a method other than heating, as described above. Also, by setting the heating temperature of First Heating-2 to 100°C or higher (less than 150°C), decomposition of polysulfides and removal of sulfur can be performed simultaneously.

[0173] The above has described the case where the first heating is performed by multi-stage heating. However, if the heating temperature of the first heating is set to 100°C or higher, for example, removal of the solvent, decomposition of polysulfides, and removal of sulfur can be performed, and therefore multi-stage heating is not necessary.

[0174] The heating time of the first heating is not particularly limited as long as it is at least long enough to remove the solvent, but is, for example, preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and even more preferably 1 hour or more. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less.

[0175] The pressure conditions during the first heating are preferably normal pressure or reduced pressure. When reduced pressure is used, specifically, the pressure is preferably 85 kPa or less, more preferably 80 kPa or less, and even more preferably 70 kPa or less. The lower limit may be a vacuum (0 kPa). In consideration of ease of pressure adjustment, the pressure is preferably 1 kPa or more, more preferably 2 kPa or more, and even more preferably 3 kPa or more.

[0176] Furthermore, the heating is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum). For example, an inert gas atmosphere containing a certain concentration of hydrogen may be used. This is because deterioration (e.g., oxidation) of the sulfide solid electrolyte can be prevented.

[0177] As described above, "obtaining an electrolyte precursor" can be performed by the same operation as the above-mentioned "first heating." In this case, the "first heating" may be omitted or may be performed. However, considering that multi-stage heating at heating temperatures according to the purpose can achieve each purpose more efficiently, it is preferable to perform the "first heating."

[0178] The heating temperature in the second heating cannot be generally determined because it varies depending on the sulfide solid electrolyte to be produced. However, taking into consideration the relationship with the first heating, the heating temperature is sufficient as long as it is 150°C or higher and 500°C or lower, preferably 160°C or higher, more preferably 200°C or higher, and even more preferably 240°C or higher, with the upper limit being preferably 480°C or lower, more preferably 460°C or lower, and even more preferably 440°C or lower.

[0179] The second heating may also be performed in multiple stages, similar to the first heating. Performing multiple stages as the second heating can ensure more reliable crystallization. When performing multiple stages of heating, for example, the heating temperature at a lower heating temperature (second heating-1) is preferably 150°C or higher but lower than 270°C, and the heating temperature at a higher heating temperature (second heating-2) is preferably 270°C or higher but 500°C. The lower limit of second heating-1 is preferably the lower limit temperature of the second heating, and the upper limit is preferably 265°C or lower, more preferably 255°C or lower. The upper limit of second heating-2 is preferably the upper limit temperature of the second heating, and the lower limit is preferably 290°C or higher, more preferably 340°C or higher, and even more preferably 375°C or higher.

[0180] The heating time and pressure conditions in the second heating are the same as those in the first heating, and it is also preferable that the heating is performed in an inert gas atmosphere.

[0181] The heating method is not particularly limited, and examples thereof include methods using various heating devices such as a hot plate, a vacuum heating device, an argon gas atmosphere furnace, a baking furnace, a vacuum baking furnace, etc. Furthermore, industrially, a horizontal dryer or a horizontal vibration fluidized dryer having a heating means and a feeding mechanism can also be used, and the method may be selected depending on the amount of processing to be heated.

[0182] (Sulfur Removal) In embodiment (i), elemental sulfur is used as the raw material, and the electrolyte precursor is a polysulfide. Therefore, sulfur can be removed by heating as described above, but excess sulfur may remain. In this case, sulfur may be removed by a method other than heating. For example, when the first heating temperature is set to less than 100°C, sulfur removal is preferably performed by a method other than heating. Examples of methods for removing sulfur include solvent removal and hydrodesulfurization.

[0183] The solvent washing method involves washing the powder that has undergone the first heating step with a solvent that dissolves sulfur, such as an aromatic hydrocarbon solvent (e.g., benzene, toluene, or xylene) or a sulfur-containing organic solvent (e.g., carbon disulfide). Contacting the electrolyte precursor with the second solvent in the manufacturing method of this embodiment can also be considered a form of solvent washing. Therefore, contacting the electrolyte precursor with the second solvent before heating can remove sulfur in addition to removing the solvent attached to the electrolyte precursor. Therefore, sulfur removal may not be necessary, and, as described above, sulfur removal may be performed when more reliable solvent removal is desired, such as when the temperature of the first heating step is set to less than 100°C.

[0184] The method of solvent washing for removing sulfur is a method in which the powder that has been subjected to the first heating is washed with a solvent that dissolves sulfur, such as an aromatic hydrocarbon solvent such as benzene, toluene, or xylene; or a sulfur-containing organic solvent such as carbon disulfide, to remove the sulfur.

[0185] The hydrodesulfurization method involves mixing the powder that has been subjected to the first heating with a hydrodesulfurization catalyst, and passing hydrogen through the mixture while heating at 300 to 450° C., thereby removing sulfur through a hydrodesulfurization reaction. Preferred examples of the hydrodesulfurization catalyst include porous catalysts containing nickel, molybdenum, cobalt, tungsten, or the like as active metal elements, such as NiMo catalysts, CoMo catalysts, and NiW catalysts.

[0186] (Amorphous Sulfide Solid Electrolyte) In embodiment (i) of the production method of the present embodiment, the first heating step, which is mainly for removing the solvent, is performed to produce an amorphous sulfide solid electrolyte.

[0187] The amorphous sulfide solid electrolyte produced by the manufacturing method of this embodiment contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and representative examples thereof include Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２S ５ - LiBr, Li ２ S-P ２ S ５ -LiI-LiBr, etc., solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide; and solid electrolytes further containing other atoms such as oxygen atoms and silicon atoms, for example, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a solid electrolyte such as Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and a lithium halide, such as LiI-LiBr, is preferred. The types of atoms constituting the sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0188] In the sulfide solid electrolyte (amorphous sulfide solid electrolyte and crystalline sulfide solid electrolyte) obtained by the production method of this embodiment, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms is preferably 1.0 to 1.8: 0.1 to 0.8: 1.0 to 2.0: 0.01 to 0.6, more preferably 1.1 to 1.7: 0.2 to 0.6: 1.2 to 1.8: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 0.25 to 0.5: 1.3 to 1.7: 0.08 to 0.4. Furthermore, when bromine and iodine, or bromine and chlorine are used in combination as halogen atoms, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, bromine, and iodine (or chlorine) is preferably 1.0 to 1.8: 0.1 to 0.8: 1.0 to 2.0: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 0.2 to 0.6: 1.2 to 1.8: 0.02 to 0.25: 0.02 to 0.25, even more preferably 1.2 to 1.6: 0.25 to 0.5: 1.3 to 1.7: 0.03 to 0.2: 0.03 to 0.2, and still more preferably 1.35 to 1.45: 0.3 to 0.45: 1.4 to 1.7: 0.04 to 0.18: 0.04 to 0.18. By setting the composition ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte having a higher ionic conductivity and a crystal structure described below, particularly a thiolisiconregion II crystal structure or an argyrodite crystal structure.

[0189] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle size (D ５０ ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 200.0 μm or less, further 100.0 μm or less, 90.0 μm or less, 80.0 μm or less, or 70.0 μm or less.

[0190] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be a so-called glass ceramic obtained by heating an amorphous sulfide solid electrolyte to a crystallization temperature or higher, and its crystalline structure may be Li ３ P.S.４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ P.S. ６ Crystal structure, Li ７ P ３ S １１ Preferred examples include a crystalline structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP-A-2013-16423).

[0191] Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Preferred examples include crystal structures similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725).

[0192] The crystal structure of the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment is preferably a thiolicon region II crystal structure among the above, in that higher ionic conductivity can be obtained. Here, the "thiolicon region II crystal structure" means a structure in which Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the thio-LISICON region II type has a similar crystal structure.

[0193] The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may contain the above-mentioned thiolicon region II type crystal structure or may contain it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it contains it as the main crystal. In this specification, "containing it as the main crystal" means that the proportion of the target crystal structure among the crystal structures is 80% or more, preferably 90% or more, and more preferably 95% or more. Furthermore, from the viewpoint of obtaining higher ionic conductivity, the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment contains crystalline Li ３ P.S. ４ (β-Li ３ P.S. ４ ) is preferably not included.

[0194] In X-ray diffraction measurement using CuKα radiation, Li ３ P.S. ４ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°. ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=16.9°, 27.1°, and 32.5°. ７ P.S. ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=15.3°, 25.2°, 29.6°, and 31.0°. ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II crystal structure appear, for example, at 2θ=20.1°, 23.9°, and 29.5°, and Li ４－ｘ Ge １－ｘ P ｘ S ４Diffraction peaks of a crystal structure similar to that of thio-LISICON Region II type appear, for example, at 2θ=20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0195] The above Li ７ P.S. ６ A preferred example of the crystalline sulfide solid electrolyte is an argyrodite-type crystal structure having a structural skeleton in which part of P is substituted with Si. The composition formula of the argyrodite-type crystal structure is, for example, the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is −0.6 to 0.6, y is 0.1 to 0.6) The argyrodite-type crystal structure represented by this composition formula is a cubic or orthorhombic crystal, preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0196] The composition formula of the argyrodite-type crystal structure is Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5) is also included. The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The composition formula of the argyrodite-type crystal structure is preferably the composition formula Li ７－ｘ P.S. ６－ｘ Ha ｘ(Ha is Cl or Br, and x is preferably 0.2 to 1.8). The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has peaks that appear mainly at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Note that these peak positions may vary within a range of ±0.5°.

[0197] Among the above, the crystalline sulfide solid electrolyte obtained by the production method of this embodiment is preferably a crystalline sulfide solid electrolyte having a thiolicon region II type crystal structure or an argyrodite type crystal structure.

[0198] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 200.0 μm or less, further 100.0 μm or less, 90.0 μm or less, 80.0 μm or less, or 70.0 μm or less.

[0199] [Embodiment (ii)] In the case of embodiment (ii), the raw material-containing material includes a plurality of raw materials containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom, and also includes lithium sulfide, phosphorus sulfide, and at least one halogen atom-containing raw material selected from a lithium halide and an elemental halogen.

[0200] [Obtaining a Solution Containing an Electrolyte Precursor] Obtaining a solvent containing an electrolyte precursor in embodiment (ii) will be described starting with the raw material contents.

[0201] (Raw material content) The raw material content employed in embodiment (ii) contains a plurality of raw materials containing at least one atom selected from lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, and contains at least one halogen atom-containing raw material selected from lithium sulfide, phosphorus sulfide, lithium halide, and elemental halogen. Furthermore, the raw material content employed in embodiment (ii) preferably does not contain elemental sulfur. Thus, the raw materials used in embodiments (i) and (ii) are different.

[0202] The raw material contents employed in embodiment (ii) differ from the raw material contents of embodiment (i) in that they contain phosphorus sulfide, lithium halide, and elemental halogen as raw materials. However, for raw materials other than these, the raw materials exemplified as the raw material contents of embodiment (i) above can be employed.

[0203] The blending ratio of the raw materials in embodiment (ii) can be the same as that described in embodiment (i) above. For example, in embodiment (i) above, when lithium sulfide, elemental sulfur, diphosphorus pentasulfide, and lithium halide are used, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide contains elemental sulfur, but this can also be applied to embodiment (ii) which does not contain elemental sulfur. By adopting such blending ratios, it becomes easier to obtain the thiolicon region II crystal structure and the argyrodite crystal structure, which are preferred crystal structures of the sulfide solid electrolyte obtained by the manufacturing method of this embodiment.

[0204] (First Solvent) In embodiment (ii), the first solvent used when mixing the raw materials may be a solvent different from the second solvent in relation to the second solvent, and a hydrocarbon solvent other than the hydrocarbon solvent used as the second solvent may be used, and it is preferable to use a solvent containing a heteroatom, as in embodiment (i) above.

[0205] In embodiment (ii), among the solvents containing heteroatoms, alcohol solvents and ether solvents are preferred. The alcohol solvents and ether solvents may be used alone or in combination of two or more kinds, and alcohol solvents and ether solvents are particularly preferred. Examples of these solvents include the same solvents as those described in embodiment (i) above.

[0206] (1-1 Solvent and 1-2 Solvent) In embodiment (ii), the first solvent used when mixing the raw materials is preferably used in such a manner that the raw material-containing substance is mixed in an ether solvent (1-1 solvent), and then an alcohol solvent (1-2 solvent) is added and mixed. When the first solvent includes a mixed solvent containing multiple solvents, by using the 1-1 solvent and the 1-2 solvent appropriately, it is possible to suppress separation and loss of various raw materials such as lithium sulfide, phosphorus sulfide, and lithium halide, which are preferably used as raw materials.

[0207] When the first solvent contains an alcohol solvent and an ether solvent, the 1-1 solvent is preferably an ether solvent, and the 1-2 solvent is preferably an alcohol solvent.

[0208] As the 1-1 solvent, in addition to ether solvents, ester solvents and amine solvents are also preferably used among solvents containing heteroatoms such as oxygen atoms and nitrogen atoms. Of these, ether solvents are preferred. Furthermore, among ether solvents, alicyclic ethers are preferred, and tetrahydrofuran is particularly preferred.

[0209] The amount of solvent 1-1 used is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 350 mL or more, and still more preferably 450 mL or more per 100 g of the raw material content, and the upper limit is preferably 1000 mL or less, more preferably 850 mL or less, even more preferably 700 mL or less, and still more preferably 550 mL or less.

[0210] The first and second solvents are preferably alcohol solvents, in which case aliphatic alcohols are preferred, primary aliphatic alcohols are more preferred, methanol and ethanol are even more preferred, and ethanol is particularly preferred.

[0211] The amount of the first-2 solvent used is preferably 200 mL or more, more preferably 400 mL or more, even more preferably 700 mL or more, and still more preferably 900 mL or more per 100 g of the raw material content, and the upper limit is preferably 3000 mL or less, more preferably 2000 mL or less, even more preferably 1700 mL or less, and still more preferably 1500 mL or less.

[0212] In embodiment (ii), similarly to embodiment (i) above, in addition to the first solvent, a hydrocarbon solvent such as an aliphatic hydrocarbon solvent, an alicyclic hydrocarbon solvent, or an aromatic hydrocarbon solvent exemplified as the second solvent above may be used as another solvent.

[0213] (Mixing) In the embodiment (ii), the raw material ingredients can be mixed in the first solvent by the same method as in the above embodiment (i).

[0214] As described above, when the first solvent is divided into the 1-1 solvent and the 1-2 solvent and used, mixing the raw material contents in the 1-1 solvent results in a mixture as described above, in which the raw material contents are not completely dissolved. In the mixture, the raw materials contained in the raw material contents are held in a bonded state between each other and with the solvent, and then the 1-2 solvent is added and mixed, whereby the raw materials dissolve while maintaining loose bonds with the 1-1 solvent, and a solution containing an electrolyte precursor is obtained.

[0215] When the 1-1 solvent and the 1-2 solvent are used separately, the temperature conditions for mixing the raw material contents in the 1-1 solvent are not particularly limited, and are, for example, usually −10 to 100° C., preferably 0 to 80° C., more preferably 10 to 70° C., and even more preferably 20 to 60° C. The mixing time is usually 0.1 to 500 hours, and from the viewpoint of preparing the reaction product more efficiently and in larger amounts, is preferably 1 to 400 hours, more preferably 3 to 300 hours, even more preferably 5 to 200 hours, and still more preferably 10 to 100 hours.

[0216] The mixing conditions when adding and mixing the first-second solvent include temperature conditions, and are not particularly limited, and are, for example, usually −10 to 100° C., preferably 0 to 80° C., more preferably 10 to 70° C., and even more preferably 20 to 60° C. The mixing time is usually 1 minute to 100 hours, and from the viewpoint of more efficiently preparing a larger amount of the solid electrolyte precursor, is preferably 3 minutes to 80 hours, more preferably 5 minutes to 50 hours, even more preferably 10 minutes to 10 hours, and still more preferably 20 minutes to 1 hour.

[0217] [Obtaining the Electrolyte Precursor] In embodiment (ii), after obtaining a solution containing the electrolyte precursor by the above-mentioned mixing, the solvent is removed from the solution to obtain the electrolyte precursor. To remove the solvent from the solution to obtain the electrolyte precursor, a method such as drying may be employed, as in embodiment (i) above. Furthermore, "obtaining the electrolyte precursor" in embodiment (ii) may be performed by the same operation as in the "first heating" in the "heating" of embodiment (i) above, or may be performed separately in "first heating-1" and "first heating-2".

[0218] [Heat Treatment While Supplying Hydrogen Sulfide] In embodiment (ii), it is preferable to include heat treatment of the electrolyte precursor while supplying hydrogen sulfide before heating. Heat treatment of the electrolyte precursor while supplying hydrogen sulfide (hereinafter, sometimes simply referred to as "heat treatment") may be performed after removing the solvent from a solution containing the electrolyte precursor to obtain the electrolyte precursor. Furthermore, from the viewpoint of suppressing deterioration in quality due to remaining lithium alkoxide, it is preferable to perform the heat treatment before heating. Therefore, it is preferable to perform the heat treatment after obtaining the electrolyte precursor and before heating, and before or after contacting with the second solvent.

[0219] The heat treatment is carried out while supplying hydrogen sulfide. Hydrogen sulfide may be supplied alone or diluted with an inert gas such as nitrogen gas or argon gas. When hydrogen sulfide is diluted with an inert gas and supplied, the hydrogen sulfide content is preferably 5% by volume or more, more preferably 10% by volume or more, and even more preferably 20% by volume or more. The upper limit is less than 100% by volume, preferably 90% by volume or less, more preferably 80% by volume or less, and even more preferably 70% by volume or less.

[0220] The heating temperature in the heat treatment cannot be generally defined because it can vary depending on the types of first and second solvents and the desired crystal structure, but it is preferably a temperature lower than the heating temperature in the heating described below, and can be selected from a temperature range of preferably 120° C. or higher, 130° C. or higher, 150° C. or higher, 250° C. or higher, 350° C. or higher, or 400° C. or higher, with the upper limit preferably being 700° C. or lower, 600° C. or lower, 500° C. or lower, 450° C. or lower, 350° C. or lower, 250° C. or lower, 200° C. or lower, or 160° C. Note that although a range of 250° C. or higher as the lower limit and 200° C. or lower as the upper limit is described, it goes without saying that a range of 250° C. or higher and 200° C. or lower cannot be adopted.

[0221] The heat treatment time is usually 1 minute to 10 hours, preferably 10 minutes to 8 hours, more preferably 30 minutes to 6 hours, and even more preferably 30 minutes to 2 hours.

[0222] The heat treatment can be performed by keeping the heating temperature constant, or by increasing or decreasing the temperature, or by combining these. For example, the heat treatment can be performed by placing the solid electrolyte precursor in a furnace at room temperature (20°C) and increasing the temperature in the furnace to a firing temperature described below, or by placing the solid electrolyte precursor in a furnace set to a predetermined heating temperature.

[0223] The amount of hydrogen sulfide supplied is preferably 0.01 Nm per 100 g of raw material content. ３ / h or more, more preferably 0.03 Nm ３ / h or more, more preferably 0.05 Nm ３ / h or more, and even more preferably 0.08 Nm ３ / h or more, and the upper limit is preferably 1.0 Nm ３ / h or less, more preferably 0.8 Nm ３ / h or less, more preferably 0.6 Nm ３ / h or less, and even more preferably 0.4 Nm ３ When hydrogen sulfide is diluted with an inert gas and then supplied, it is preferable that the supply amount of hydrogen sulfide is within the above range.

[0224] [Heating] The embodiment (ii) also includes heating. In the embodiment (ii), heating can remove the second solvent, form the sulfide solid electrolyte, crystallize the sulfide solid electrolyte, and the like.

[0225] The heating temperature cannot be generally defined because it may vary depending on the type of second solvent and the desired crystal structure, but as described above, it is preferably selected appropriately from the range of 20°C or higher and 500°C or lower.

[0226] In embodiment (ii), the heating temperature may be selected depending on the type of second solvent and the desired crystal structure, as described above, and is preferably 150°C or higher, 170°C or higher, 200°C or higher, 250°C or higher, 350°C or higher, or 400°C or higher, with the upper limit preferably being 700°C or lower, 600°C or lower, 500°C or lower, 450°C or lower, 350°C or lower, 250°C or lower, 200°C or lower, or 180°C or lower. The heating temperature refers to the maximum temperature during heating. Although a range of 250°C or higher as the lower limit and 200°C or lower as the upper limit is described, it goes without saying that a range of 250°C or higher and 200°C or lower is not possible. Furthermore, when heat treatment is performed, the temperature is preferably higher than the heating temperature during heat treatment.

[0227] The heating time is usually 1 minute to 10 hours, preferably 10 minutes to 8 hours, more preferably 30 minutes to 6 hours, and even more preferably 1 hour to 5 hours. The calcination time means the time for which the heating temperature for calcination is maintained. In the production method of this embodiment, it is preferable to maintain a constant temperature for the above-mentioned calcination time.

[0228] In embodiment (ii), the heating can be carried out continuously with the above-mentioned heat treatment, and the heating can be carried out while supplying the hydrogen sulfide used in the heat treatment, or the heating can be carried out after stopping the supply of hydrogen sulfide. Typical examples of heat treatment and heating include: (a) placing an electrolyte precursor in a furnace at room temperature (20°C), and heating the furnace by raising the temperature to the aforementioned heating temperature while supplying hydrogen sulfide, followed by calcining at the heating temperature while supplying hydrogen sulfide or stopping the supply of hydrogen sulfide; (b) placing an electrolyte precursor in a furnace set at a predetermined heating temperature, and performing a heat treatment while supplying hydrogen sulfide, and then placing the heat-treated electrolyte precursor in a furnace set at the heating temperature while supplying hydrogen sulfide, and heating while supplying hydrogen sulfide or without supplying hydrogen sulfide; (c) placing an electrolyte precursor in a furnace set at a predetermined heating temperature, and performing a heat treatment while supplying hydrogen sulfide, followed by calcining while raising the temperature from the heating temperature for the heat treatment to the heating temperature while supplying hydrogen sulfide or stopping the supply of hydrogen sulfide.

[0229] Also in embodiment (ii), similarly to embodiment (i), multi-stage heating such as first heating and second heating can be performed. In this case, the first heating may be divided into "first heating-1" and "first heating-2", and the second heating may be divided into "second heating-1" and "second heating-2".

[0230] (Sulfide Solid Electrolyte) In embodiment (ii) of the manufacturing method of this embodiment, an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte is produced by performing the heat treatment or heating. Whether an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte is produced can be adjusted by the heating temperature in the heat treatment or heating. In other words, this can be adjusted by setting the temperature higher or lower than the temperature (crystallization temperature) for producing a crystalline sulfide solid electrolyte having a desired crystal structure.

[0231] The amorphous sulfide solid electrolyte and the crystalline sulfide solid electrolyte obtained in embodiment (ii) are the same as the amorphous sulfide solid electrolyte and the crystalline sulfide solid electrolyte described as being obtained in embodiment (i) above.

[0232] (Applications) The sulfide solid electrolyte obtained by the production method of this embodiment is suitable for use in lithium ion batteries, particularly all-solid-state batteries, because it is suppressed from increasing in particle size and widening of particle size distribution, has high ionic conductivity, and has excellent battery performance. The sulfide solid electrolyte obtained by the production method of this embodiment may be used in a positive electrode layer, a negative electrode layer, or an electrolyte layer. Each layer can be produced by a known method.

[0233] The battery preferably includes a current collector in addition to the positive electrode layer, the electrolyte layer, and the negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used.

[0234] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0235] (Measurement of average particle diameter) A laser diffraction particle size distribution analyzer ("LA-950 (product name)" (manufactured by Horiba, Ltd.) was used to measure the particle diameter (D ５０ ) was measured and used as the average particle size. The arithmetic standard deviation of the average particle size was also calculated.

[0236] (Measurement of Powder XRD Diffraction) Powder X-ray diffraction (XRD) measurement was carried out as follows. The sulfide solid electrolyte powder obtained in the Examples and Comparative Examples was filled into a groove 20 mm in diameter and 0.2 mm deep, and leveled with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured under the following conditions without being exposed to air. Measurement device: D2 PHASER, manufactured by Bruker Corporation Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: focusing method Slit configuration: Soller slit 4°, divergence slit 1 mm, Kβ filter (Ni plate) used Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.05 deg, 0.05 deg / sec

[0237] (Measurement of Ion Conductivity) In the present example, the measurement of ion conductivity was carried out as follows. A 10 mm diameter (cross-sectional area S: 0.785 cm ) sample was taken from the crystalline sulfide solid electrolyte obtained in the examples and comparative examples. ２ ), and a height (L) of 0.1 to 0.3 cm were molded into a circular pellet to prepare a sample. Electrode terminals were attached to the top and bottom of the sample, and measurements were made at 25°C using an AC impedance method (frequency range: 5 MHz to 0.5 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula: R = ρ (L / S) σ = 1 / ρ

[0238] Example 1 In a glove box under an argon atmosphere, 0.2546 g of lithium sulfide, 0.3241 g of diphosphorus pentasulfide, and 0.3554 g of elemental sulfur were mixed in a mortar and introduced into a 100-mL reaction vessel together with a stirrer (Reaction Vessel 1). Similarly, 0.1236 g of lithium chloride and 0.1520 g of lithium bromide were mixed in a mortar and introduced into another 100-mL reaction vessel together with a stirrer (Reaction Vessel 2). Under a nitrogen atmosphere, a first solvent was added to reaction vessel 1, which was a mixed solvent of ethanol (EtOH), tetrahydrofuran (THF) and acetonitrile (ACN) (14.94 mL (the total amount of tetrahydrofuran (THF) and acetonitrile (ACN) relative to 1.0 volume part of ethanol (EtOH) was 237.1 volume parts, ethanol: tetrahydrofuran: acetonitrile = 0.0084: 1: 1 (volume ratio)). The mixture was stirred for 10 minutes with a magnetic stirrer. Next, the solution from reaction vessel 1 was added to reaction vessel 2, and the mixture was stirred for 10 minutes with a magnetic stirrer. Next, using a vacuum pump and an oil bath, the mixture was dried under reduced pressure at room temperature (20 ° C) for 1 hour, and then dried under reduced pressure at 130 ° C for 1 hour. The solvent was removed from the solution containing the electrolyte precursor, and an electrolyte precursor was obtained.

[0239] To the obtained electrolyte precursor, 30 mL of toluene (second solvent) was added at room temperature (20°C), and the mixture was stirred for 1 hour using a magnetic stirrer (rotation speed: 600 rpm). A glass filter (particle retention capacity: 1.6 μm) was used under a nitrogen atmosphere to obtain a powder of the electrolyte precursor. The obtained powder of the electrolyte precursor was heated under reduced pressure at room temperature (20°C) for 1 hour (first heating-1) and then at 130°C for 1 hour (first heating-2) using a vacuum pump and an oil bath. The powder obtained by the first heating was further heated under a nitrogen atmosphere at 250°C for 1 hour (second heating-1), and then heated under a nitrogen atmosphere at 430°C for 8 hours (second heating-2), obtaining a powder.

[0240] The powder obtained after the second heating was subjected to powder XRD diffraction measurement. The X-ray diffraction spectrum is shown in Figure 1. The powder before contact with the second solvent (hereinafter referred to as "Powder 1") and the powder obtained after the second heating (hereinafter referred to as "Powder 2") were subjected to average particle size measurement, and the average particle size (D ５０ ), and the arithmetic standard deviation were obtained. Furthermore, when the ionic conductivity of the powder obtained by heating at 430°C in Example 1 was measured, it was found to be 5.5 mS / cm.

[0241] Examples 2 to 5 Powders of Examples 2 to 5 were obtained in the same manner as in Example 1, except that the drying conditions in obtaining the electrolyte precursor, the temperature conditions in contacting the electrolyte precursor with the second solvent, and the presence or absence of stirring were changed to the conditions shown in Table 1.

[0242] The powders obtained after the second heating were subjected to powder XRD diffraction measurement. The X-ray diffraction spectra are shown in Figures 2 to 5. The average particle diameters of Powder 1 and Powder 2 were measured, and the average particle diameters (D ５０ ), and the arithmetic standard deviation were obtained. In addition, the ionic conductivity was measured for the powders obtained by heating at 430°C in Examples 2 to 5. The results are shown in Table 1.

[0243] Comparative Example 1 A powder was obtained in the same manner as in Example 1, except that the electrolyte precursor was not brought into contact with the second solvent and the first heating was not performed in Example 1. Here, "powder 1" was the powder after drying to obtain the electrolyte precursor.

[0244] The powder obtained after the second heating was subjected to powder XRD diffraction measurement. The X-ray diffraction spectrum is shown in Figure 6. The average particle size of Powder 1 and Powder 2 was measured, and the average particle size (D ５０ ), and the arithmetic standard deviation were obtained. In addition, the ionic conductivity was measured for the powder obtained by heating at 430°C in Comparative Example 1. The results are shown in Table 1.

[0245]

[0246] In Tables 1 to 3, the average particle size ratio indicates the ratio of the average particle size of the powder before and after heating, and serves as an index for determining whether granulation occurs due to heating. The closer the ratio is to 1.0, the smaller the degree of granulation due to heating. The standard deviation ratio indicates the ratio of the standard deviation of the average particle size of the powder before and after heating, and serves as an index for determining the width of the particle size distribution due to heating. The closer the ratio is to 1.0, the smaller the change in particle size distribution due to heating.

[0247] As shown in Table 1, the average particle size ratios of Examples 1 to 5 were superior to the average particle size ratio of Comparative Example 1, confirming that they were excellent in the effect of suppressing an increase in particle size. Furthermore, the standard deviation ratios were also generally excellent, confirming that the sulfide solid electrolyte obtained by the production method of this embodiment was one in which an increase in particle size and an expansion of the particle size distribution were suppressed.

[0248] According to Examples 1, 2, and 5, it was confirmed that heating and drying in the same manner as the first heating before contact with the second solvent is effective in suppressing an increase in particle size and a widening of the particle size distribution. Example 3 is an example in which the drying conditions in Example 1 were changed to room temperature (20°C), and it was confirmed that the particle size could be reduced and an increase in particle size could be suppressed. Furthermore, according to Example 4, it was confirmed that by carrying out contact with the second solvent under higher temperature conditions, the particle size could be reduced, the particle size distribution could be narrowed, and a change in the particle size distribution could be reduced while suppressing an increase in particle size.

[0249] A comparison of Examples 1 to 4 with Comparative Example 1 shows that the average particle size can be reduced by contacting the electrolyte precursor with the second solvent while stirring. On the other hand, a comparison of Example 5, in which the electrolyte precursor was contacted without stirring, with Comparative Example 1 shows that the average particle size increases when the electrolyte precursor was contacted without stirring. It is believed that contacting the electrolyte precursor with stirring suppresses or reduces aggregation of the electrolyte precursor, and as a result, the average particle size of the sulfide solid electrolyte obtained by heating also becomes smaller. From the above, it can be seen that the average particle size can be adjusted by the presence or absence of stirring and the degree of stirring.

[0250] It was also confirmed that the ionic conductivities of the sulfide solid electrolytes of the examples were all high, ranging from 5.5 to 8.1 mS / cm. This is thought to be because, as will be described later, the sulfide solid electrolytes of the examples have an argyrodite-type crystal structure that exhibits high ionic conductivity.

[0251] As shown in FIGS. 1 to 5, the powders obtained by heating at 430° C. in Examples 1 to 5 had peaks at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°, and were therefore confirmed to be crystalline sulfide solid electrolytes having an argyrodite-type crystal structure.

[0252] Example 6 In a glove box under an argon atmosphere, 60.19 g of lithium sulfide, 76.63 g of diphosphorus pentasulfide, and 84.02 g of elemental sulfur were mixed using a mixer, and half of the mixture was introduced into a 5-liter reaction vessel (reaction vessels 1-1 and 1-2) along with a stirrer. Similarly, 14.61 g of lithium chloride and 17.96 g of lithium bromide were introduced into another 5-liter reaction vessel (reaction vessel 2) along with a stirrer. Under a nitrogen atmosphere, half of a mixed solvent of ethanol (EtOH), tetrahydrofuran (THF), and acetonitrile (ACN) (3,546 mL of the total amount of tetrahydrofuran (THF) and acetonitrile (ACN) was 239.0 parts by volume relative to 1.0 part by volume of ethanol (EtOH); ethanol:tetrahydrofuran:acetonitrile = 0.0084:1:1 (volume ratio)) was added to reaction vessels 1-1 and 1-2, and the mixture was stirred for 10 minutes using a magnetic stirrer. Next, the solutions from reaction vessels 1-1 and 1-2 were added to reaction vessel 2, and further mixed by stirring with a magnetic stirrer for 1 hour. Next, the obtained solution containing the electrolyte precursor was spray-dried using a spray dryer (model "CNL-3 (product number)", manufactured by Okawara Chemical Engineering Co., Ltd.) at a spray pressure of 0.30 MPa and an inlet temperature of 150°C, to obtain an electrolyte precursor. The obtained electrolyte precursor was subjected to the same operations as in Example 1, from contact with the second solvent to the second heating, to obtain a powder of Example 6.

[0253] The powder obtained after the second heating was subjected to powder XRD diffraction measurement. The X-ray diffraction spectrum is shown in Figure 7. The average particle size of Powder 1 and Powder 2 was measured, and the average particle size (D ５０ ), and the arithmetic standard deviation were obtained. In addition, the ionic conductivity was measured for the powder obtained by heating at 430°C in Example 6. The results are shown in Table 2.

[0254] Comparative Example 2 A powder was obtained in the same manner as in Example 6, except that the electrolyte precursor was not brought into contact with the second solvent and the first heating was not performed. Here, "powder 1" was the powder after drying to obtain the electrolyte precursor.

[0255] The powder obtained after the second heating was subjected to powder XRD diffraction measurement. The X-ray diffraction spectrum is shown in Figure 8. The average particle size of Powder 1 and Powder 2 was measured, and the average particle size (D ５０ ), and the arithmetic standard deviation were obtained. In addition, the ionic conductivity was measured for the powder obtained by heating at 430°C in Comparative Example 2. The results are shown in Table 2.

[0256]

[0257] As shown in Table 2, the average particle size ratio and standard deviation ratio of Example 6 are superior to both the average particle size ratio and standard deviation ratio of Comparative Example 2, confirming that the sulfide solid electrolyte obtained by the production method of this embodiment is one in which an increase in particle size and a widening of the particle size distribution are suppressed. It was also confirmed that the sulfide solid electrolyte of Example 6 had a high ionic conductivity of 2.1 mS / cm. This is thought to be because, as will be described later, the sulfide solid electrolyte of this example has an argyrodite-type crystal structure that exhibits high ionic conductivity.

[0258] The results of Examples 1 to 5 and Example 6 also confirmed that the average particle size and arithmetic standard deviation change depending on the drying method used to remove the solvent from a solution containing an electrolyte precursor to obtain an electrolyte precursor. For example, Example 1, which employs vacuum drying, is compared with Example 6, which employs spray drying, which share the same conditions except for the drying method. Since the average particle size and arithmetic standard deviation of Example 6, which employs spray drying, are smaller than those of Example 1, it can be seen that the average particle size and arithmetic standard deviation can be reduced by employing spray drying. In other words, it can be seen that, compared to the other Examples, the average particle size can be reduced and the arithmetic standard deviation can be reduced (the particle size distribution can be narrowed).

[0259] Furthermore, as shown in FIG. 7 , the powder obtained by heating at 430°C in Example 6 had peaks at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°, and was therefore confirmed to be a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure.

[0260] Example 7 In a reaction vessel (volume: 100 mL) under a nitrogen atmosphere, 0.5960 g of lithium sulfide, 0.7588 g of diphosphorus pentasulfide, 0.2894 g of lithium chloride, and 0.3558 g of lithium bromide were introduced as raw material components. A stirrer was introduced, and 10 mL of tetrahydrofuran was added while stirring with a stirrer. Mixing was carried out at room temperature (20°C) for 24 hours (rotation speed: 300 rpm). The raw material components and the reaction product (Li ３ P.S. ４ A mixture containing ethanol (solvent 1-2) and tetrahydrofuran (solvent 1-1) was obtained. Next, 30 mL of ethanol (solvent 1-2) was added, and mixing was continued for another hour at room temperature (20°C) to prepare a solution containing an electrolyte precursor. The resulting solution was dried at room temperature under vacuum for one hour, and then dried at 130°C for one hour to remove the solvent from the solution containing the electrolyte precursor, thereby obtaining an electrolyte precursor.

[0261] To 1.2 g of the obtained electrolyte precursor, 30 mL of toluene (second solvent) was added at room temperature (20 ° C.), and the mixture was stirred for 1 hour using a magnetic stirrer (rotation speed: 600 rpm). A glass filter (particle retention capacity: 1.6 μm) was used under a nitrogen atmosphere to obtain a powder of the electrolyte precursor that had been contacted with the second solvent. The obtained electrolyte precursor powder was heated under reduced pressure at room temperature (20 ° C.) for 1 hour using a vacuum pump and an oil bath, and then heated under reduced pressure at 130 ° C. for 1 hour. The obtained powder was then heated under a nitrogen atmosphere at 250 ° C. for 1 hour, and then heated under a nitrogen atmosphere at 430 ° C. for 8 hours to obtain a powder.

[0262] The powder obtained after heating at 430°C was subjected to powder XRD diffraction measurement. The X-ray diffraction spectrum is shown in Figure 9. The powder before contact with the second solvent (hereinafter referred to as "Powder 1") and the powder obtained after heating at 430°C (hereinafter referred to as "Powder 2") were subjected to average particle size measurement, and the average particle size (D ５０ ), and the arithmetic standard deviation were obtained. In addition, the ionic conductivity was measured for the powder obtained by heating at 430°C in Example 7. The results are shown in Table 3.

[0263] Example 8 A powder was obtained in the same manner as in Example 7, except that the amounts of the raw material components and the solvent used in obtaining the solid electrolyte precursor were 0.6 times that of Example 7, and the drying conditions were the conditions shown in Table 2.

[0264] The powder obtained after heating at 430°C was subjected to powder XRD diffraction measurement. The X-ray diffraction spectrum is shown in Figure 10. The average particle size of Powder 1 and Powder 2 was measured, and the average particle size (D ５０ ), and the arithmetic standard deviation were obtained. In addition, the ionic conductivity was measured for the powder obtained by heating at 430°C. The results are shown in Table 3.

[0265] Comparative Example 3 A powder was obtained in the same manner as in Example 7, except that the drying to obtain the electrolyte precursor and the contacting of the electrolyte precursor with the second solvent were not performed. Here, "powder 1" was the powder before being heated at room temperature (20°C) under reduced pressure for 1 hour.

[0266] The powder obtained after heating at 430°C was subjected to powder XRD diffraction measurement. The X-ray diffraction spectrum is shown in Figure 11. The average particle size of Powder 1 and Powder 2 was measured, and the average particle size (D ５０ ), and the arithmetic standard deviation were obtained. In addition, the ionic conductivity was measured for the powder obtained by heating at 430°C. The results are shown in Table 3.

[0267]

[0268] As shown in Table 3, the average particle size ratios and standard deviation ratios of Examples 7 and 8 were superior to those of Comparative Example 3, confirming that the sulfide solid electrolyte obtained by the manufacturing method of this embodiment suppressed an increase in particle size and an expansion of particle size distribution. Furthermore, the average particle size and standard deviation of Examples 7 and 8 were smaller than those of Comparative Example 3, confirming that the method was effective not only in suppressing an increase in particle size and an expansion of particle size distribution, but also in reducing the particle size and particle size distribution. Furthermore, it was confirmed that the ionic conductivities were both high, at 1.7 and 3.9 mS / cm.

[0269] As shown in FIGS. 9 and 10 , the powders obtained by heating at 250° C. and 430° C. in Examples 7 and 8 had peaks at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°, and were therefore confirmed to be crystalline sulfide solid electrolytes having an argyrodite-type crystal structure.

[0270] According to the method for producing a sulfide solid electrolyte of this embodiment, it is possible to efficiently provide a sulfide solid electrolyte having high ionic conductivity and in which an increase in particle size and an expansion of particle size distribution are suppressed. The sulfide solid electrolyte obtained by the production method of this embodiment is suitable for use in lithium ion batteries, particularly lithium ion batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and in particular all-solid-state batteries.

Claims

1. A raw material-containing material is mixed in a first solvent with a mixture of multiple raw materials containing at least one atom selected from lithium, phosphorus, sulfur, and halogen atoms to obtain a solution containing an electrolyte precursor. To remove the solvent from the aforementioned solution and obtain an electrolyte precursor, The electrolyte precursor is brought into contact with the second solvent. Next, heat it. The second solvent is different from the first solvent and is a hydrocarbon solvent. A method for producing a sulfide solid electrolyte.

2. The method for producing a sulfide solid electrolyte according to claim 1, wherein the hydrocarbon solvent is at least one organic solvent selected from aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

3. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the solubility of lithium halide in the hydrocarbon solvent at 25°C is 0.5% by mass or less.

4. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the hydrocarbon solvent is an aromatic hydrocarbon solvent.

5. The method for producing a sulfide solid electrolyte according to claim 4, wherein the aromatic hydrocarbon solvent is alkylbenzene.

6. The method for producing a sulfide solid electrolyte according to claim 5, wherein the alkylbenzene has an alkyl group having 1 to 4 carbon atoms.

7. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the amount of the second solvent used in the contact is 50 parts by mass or more and 10,000 parts by mass or less per 100 parts by mass of the electrolyte precursor.

8. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the contact is performed at least once.

9. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the raw material contains elemental sulfur.

10. The method for producing a sulfide solid electrolyte according to claim 9, wherein the first solvent is an organic solvent containing at least one atom selected from oxygen atoms and nitrogen atoms.

11. The method for producing a sulfide solid electrolyte according to claim 10, wherein the organic solvent comprises at least one organic solvent selected from alcohol solvents, ether solvents, and nitrile solvents.

12. The method for producing a sulfide solid electrolyte according to claim 9, wherein the heating temperature in the heating process is 20°C or more and 500°C or less.

13. The method for producing a sulfide solid electrolyte according to claim 9, wherein the amount of elemental sulfur used is 0.5 moles or more per 1.0 mole of lithium sulfide.

14. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the raw material content includes a raw material containing at least one halogen atom selected from lithium sulfide, phosphorus sulfide, lithium halide, and elemental halogens.

15. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the raw material content does not contain elemental sulfur.

16. A method for producing a sulfide solid electrolyte according to claim 14, comprising heating the electrolyte precursor while supplying hydrogen sulfide before the aforementioned heating.

17. The method for producing a sulfide solid electrolyte according to claim 14, wherein the first solvent includes an alcohol solvent and an ether solvent.

18. A method for producing a sulfide solid electrolyte according to claim 17, wherein in order to obtain a solution containing the electrolyte precursor, the raw material components are mixed in an ether solvent, and then an alcohol solvent is added and mixed.

19. The method for producing a sulfide solid electrolyte according to claim 14, wherein the heating temperature in the heating process is 150°C or higher.

20. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the halogen atom is at least one atom selected from chlorine atoms, bromine atoms, and iodine atoms.

21. A method for producing a sulfide solid electrolyte according to claim 1 or 2, comprising producing a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure or a thiolysicon-type II crystal structure.