Method for producing sulfide solid electrolyte

Abstract

Provided is a method for producing a sulfide solid electrolyte having an argyrodite crystal structure in the liquid phase, the method allowing an efficient use of a raw material-containing substance to increase the production efficiency and facilitating production of a sulfide solid electrolyte with high quality. The method for producing a sulfide solid electrolyte having an argyrodite crystal structure comprises mixing a raw material-containing substance with a first solvent to obtain a mixture, mixing said mixture with a second solvent to obtain a solution containing a solid electrolyte precursor, heating the solid electrolyte precursor while supplying hydrogen sulfide to obtain a heated solid electrolyte precursor and burning the heated solid electrolyte precursor.

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 important. Conventionally, batteries used for such applications have used electrolytes containing flammable organic solvents. However, 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, all-solid-state batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed. Furthermore, with the spread of solid electrolytes, attention is being paid to technologies for more efficiently producing solid electrolytes with higher quality.

[0003] Methods for producing solid electrolytes can be broadly divided into solid-phase methods and liquid-phase methods. In recent years, liquid-phase methods have attracted attention as a method that can easily mass-produce solid electrolytes, in addition to their versatility and applicability, in order to commercialize all-solid-state batteries. Liquid-phase methods include homogeneous methods that use a solution of the solid electrolyte material, and heterogeneous methods that use a solid-liquid coexistence suspension (slurry) without complete dissolution. In liquid-phase methods, for example, a complexing agent solution (or slurry) of the solid electrolyte raw material is prepared, the solution is dried to obtain complex crystals, and the complex crystals are then calcined to obtain a solid electrolyte of a different crystal type (see Patent Document 1). Patent Document 2 also discloses a method for producing a sulfide solid electrolyte, in which a raw material-containing solution containing the raw material and a solvent is supplied to another medium maintained at a temperature higher than that of the solvent, the solvent is volatilized, and the raw material is reacted to precipitate an argyrodite-type crystal structure.

[0004] International Publication No. 2018 / 054709 Pamphlet Japanese Patent Application Laid-Open No. 2019-169459

[0005] The present invention has been made in view of the above circumstances, and aims to provide a method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure in a liquid phase, which improves production efficiency by effectively using raw material contents, and easily produces a high-quality sulfide solid electrolyte.

[0006] The method for producing a sulfide solid electrolyte according to the present invention includes: mixing raw material ingredients with a first solvent to obtain a mixture; mixing the mixture with a second solvent to obtain a solution containing a solid electrolyte precursor; heat-treating the solid electrolyte precursor while supplying hydrogen sulfide to obtain a heated solid electrolyte precursor; and calcining the heated solid electrolyte precursor.

[0007] According to the present invention, in a method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure in a liquid phase, it is possible to provide a method for improving production efficiency by effectively using raw material contents and easily producing a high-quality sulfide solid electrolyte.

[0008] 1 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 1. FIG. 2 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Comparative Example 1. FIG. 3 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 2. FIG. 4 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 3.

[0009] 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 range expressed by "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0010] (Findings Obtained by the Inventors to Achieve the Present Invention) As a result of intensive research to solve the above-mentioned problems, the inventors have found the following and completed the present invention. As shown in Patent Documents 1 and 2, sulfide solid electrolytes having various compositions have been studied. In recent years, sulfide solid electrolytes have become more widespread, for example, due to studies of applications to automotive applications, and there is an increasing demand for higher quality sulfide solid electrolytes. Therefore, there is a growing need to improve the quality of the sulfide solid electrolytes that have already been studied, and at the same time, to develop methods for more easily producing them.

[0011] In the production method (liquid phase method) described in Patent Document 1, since several kinds of raw materials are used, it is difficult to synthesize each raw material in a complexing agent solution or slurry without separating each raw material. As a result, some of the raw materials do not contribute to the reaction, which may result in a decrease in the ionic conductivity of the solid electrolyte.

[0012] The manufacturing method described in Patent Document 2 is also a liquid phase method, and ethanol is assumed to be one of the solvents used to prepare the raw material content. Alcohol solvents such as ethanol have the advantage of facilitating the reaction of the raw materials, but they also have disadvantages. For example, some of the raw materials may not contribute to the production of solid electrolytes, which may result in a decrease in manufacturing efficiency. Lithium sulfide (Li ２ S) reacts partially with alcohol solvents such as ethanol to produce lithium alkoxides such as lithium ethoxide, and lithium sulfide (Li ２ S) and commonly used phosphorus sulfides (e.g., diphosphorus pentasulfide (P ２ S ５ )) and other raw materials, and are likely to remain as impurities, resulting in a decrease in the purity of the sulfide solid electrolyte and a decrease in ionic conductivity, leading to a decrease in quality. ２ S ５ )) dissolves in alcohol solvents such as ethanol, but when dissolved, it dissolves in other lithium sulfide (Li ２ In this way, when an alcohol solvent is used, some of the raw materials do not contribute to the reaction, making it difficult to obtain excellent production efficiency. In addition, in the production method described in Patent Document 2, when ethanol is used, Li ３ P.S. ４ However, there is also the disadvantage that improving manufacturing efficiency imposes restrictions on the raw materials used, as shown by the use of

[0013] In addition, Patent Document 2 also considers the use of other solvents, but various operations are required to obtain the raw material content. For example, when tetrahydrofuran is used, elemental sulfur must be used as a dissolving agent, and when dehydrated pyridine is used, heating is required to proceed with the reaction, and further dehydrated pyridine must be added to adjust the viscosity, and hydrogen sulfide must also be blown in.

[0014] The liquid phase production methods described in Patent Documents 1 and 2 are considered to be highly efficient in that they can produce solid electrolytes by supplying a raw material-containing liquid to a medium. However, depending on the solvent used, some of the raw materials may be lost, which can reduce production efficiency or impose restrictions on the raw materials depending on the solvent used. Furthermore, the required operations may differ depending on the solvent used, making the operations complicated. Therefore, there is room for further improvement in production efficiency, versatility, etc., in methods of producing solid electrolytes by reacting raw materials in a liquid phase using ethanol or other solvents.

[0015] As described above, in a method for producing a solid electrolyte by a liquid phase method, separation or loss of a portion of the raw materials, which does not contribute to the reaction, has been a factor in reducing production efficiency and preventing the production of a high-quality solid electrolyte. Further investigation into this problem has revealed that raw materials containing halogen atoms, such as lithium bromide, lithium iodide, and lithium chloride, which are used to produce a solid electrolyte having an argyrodite-type crystal structure, are particularly susceptible to the separation and loss described above.

[0016] Therefore, when examining the solvent to be used in the method for producing a solid electrolyte by the liquid phase method, the inventors have focused on the affinity of the solvent with the raw materials used in producing the solid electrolyte, and have conducted research into how to prevent separation and loss of part of the raw materials. As a result, they have discovered that by selectively using a solvent that dissolves the raw materials and a solvent that does not dissolve the raw materials, it is possible to obtain a high-quality solid electrolyte while solving the problem associated with employing the liquid phase method, namely, the problem that separation and loss of part of the raw materials do not contribute to the reaction and result in reduced production efficiency.

[0017] 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" of this embodiment is a solid electrolyte that contains lithium atoms, sulfur atoms, phosphorus atoms, and at least one halogen atom selected from chlorine atoms and bromine atoms, and has ionic conductivity attributable to the lithium atoms.

[0018] The term "sulfide solid electrolyte" includes both crystalline sulfide solid electrolytes having a crystalline structure and amorphous sulfide solid electrolytes. In this specification, a crystalline sulfide solid electrolyte is a solid electrolyte in which a peak derived from the solid electrolyte is observed in the X-ray diffraction pattern in powder X-ray diffraction (XRD) measurement, regardless of whether or not a peak derived from the raw material of the 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 include an amorphous sulfide solid electrolyte (also referred to as a "glass component") as a portion of the crystalline sulfide solid electrolyte. Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte (glass component) to a temperature above the crystallization temperature.

[0019] In this specification, the term "amorphous sulfide solid electrolyte (glass component)" refers to a solid electrolyte in which the X-ray diffraction pattern is a halo pattern in which no peaks other than those derived from the material are observed in powder X-ray diffraction (XRD) measurement, regardless of whether or not there are peaks derived from the raw materials of the solid electrolyte. In this embodiment, the distinction between crystalline and amorphous applies to both sulfide solid electrolytes and modified sulfide solid electrolytes.

[0020] A method for producing a sulfide solid electrolyte according to a first aspect of the present embodiment is a method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure, comprising: mixing raw material ingredients with a first solvent to obtain a mixture; mixing the mixture with a second solvent to obtain a solution containing a solid electrolyte precursor; heat-treating the solid electrolyte precursor while supplying hydrogen sulfide to obtain a heated solid electrolyte precursor; and calcining the heated solid electrolyte precursor.

[0021] As mentioned above, the conventional methods for producing solid electrolytes described in Patent Documents 1 and 2 have the problem that some of the raw materials used are separated and lost, which does not contribute to the reaction and reduces production efficiency. According to the method for producing a sulfide solid electrolyte of the first embodiment, a mixture with the raw material contents is first prepared by using a first solvent, that is, a mixture is formed without completely dissolving the raw material contents. Because the raw material contents do not completely dissolve in the first solvent, the reaction is slow, and a bond is formed between the solvent and the raw materials due to some force (intermolecular force, chemical bond, etc.). In particular, a loose bond is formed with the solvent, which suppresses separation and loss of the raw materials.

[0022] Next, the mixture is mixed with a second solvent to obtain a solution containing a solid electrolyte precursor. As described above, in the mixture, the raw materials contained in the raw material inclusions are held in a bonded state between the raw materials and the solvent, and by mixing this with a second solvent, the raw materials are dissolved while maintaining a loose bond with the first solvent, and a solution in which the solid electrolyte precursor is dissolved is obtained. Here, the raw materials are supplied to the second solvent in a state in which the raw materials form a bonded state between themselves and in a loose bond with the first solvent, thereby forming a solid electrolyte precursor without causing loss due to separation or reaction between the second 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 )) is used, dissolution and reaction of phosphorus sulfide and its reactants in the second solvent can be suppressed, and therefore phosphorus sulfide can be contributed to the formation of a sulfide solid electrolyte without being separated or lost.

[0023] The solid electrolyte precursor obtained by mixing the mixture with the second solvent is a reaction product in which the raw materials contained in the mixture form a bonded state, and is obtained by dissolving the raw materials themselves in the second solvent and reacting with each other. By calcining while supplying hydrogen sulfide, which will be described later, a sulfide solid electrolyte having an argyrodite-type crystal structure is obtained. Therefore, the solid electrolyte precursor obtained by mixing the mixture with the second solvent is thought to have a structure that easily forms an argyrodite-type crystal structure.

[0024] The method for producing a sulfide solid electrolyte according to the first embodiment further comprises heating the solid electrolyte precursor while supplying hydrogen sulfide to obtain a heated solid electrolyte precursor. As described above, by using the first solvent and the second solvent appropriately, the raw materials are bonded together, which makes it possible to reduce separation and loss of the raw materials compared to conventional production methods. However, there are cases where some raw materials remain as they are. For example, lithium sulfide (Li ２ When lithium sulfide (Li ２ If lithium alkoxide (LiS) is present in an intact state, it will produce lithium alkoxide as described above, and will not contribute to the reaction with other raw materials. If lithium alkoxide remains as it is, the purity of the sulfide solid electrolyte will decrease, and the lithium alkoxide may remain carbonized by calcination, resulting in a decrease in quality such as a decrease in ionic conductivity. However, in the method for producing a sulfide solid electrolyte according to the first embodiment, lithium alkoxide is converted into lithium sulfide (LiS) by performing a heat treatment while supplying hydrogen sulfide. ２ Specifically, the reactions shown in the following reaction formulas (1) to (3) are thought to occur.

[0025] Li ２ S+EtOH→EtOLi+LiSH (1) 2LiSH→Li ２ S+H ２ S (2) 2EtOLi+H ２ S → Li ２S+2EtOH (3)

[0026] The above reaction is carried out using lithium sulfide (Li ２ S) as the second solvent, and ethanol (EtOH) as the second 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 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.

[0027] Furthermore, by calcining the heated solid electrolyte precursor obtained by the heat treatment, an argyrodite-type crystal structure is formed and the crystallinity is improved, so that a high-quality sulfide solid electrolyte having an argyrodite-type crystal structure can be obtained.

[0028] As described above, by selectively using the first solvent and the second solvent, and by carrying out the heat treatment and calcination while supplying hydrogen sulfide, it is possible to solve the problem of a portion of the raw materials being separated and lost, which does not contribute to the reaction and reduces production efficiency, and it becomes possible to easily produce a high-quality sulfide solid electrolyte with reduced impurities and high ionic conductivity.

[0029] In a method for producing a sulfide solid electrolyte according to a second aspect of the present embodiment, the second solvent is an alcohol solvent. When the second solvent is an alcohol solvent, separation and loss of raw materials are less likely to occur, and therefore the solid electrolyte precursor can be obtained more efficiently, resulting in improved production efficiency and making it possible to easily produce a high-quality sulfide solid electrolyte.

[0030] A method for producing a sulfide solid electrolyte according to a third aspect of this embodiment is characterized in that the first solvent is a solvent different from the second solvent and contains at least one of an oxygen atom and a nitrogen atom. When the first solvent is a solvent different from the second solvent and contains at least one of an oxygen atom and a nitrogen atom, the raw materials interact with each other to an extent that they do not dissolve in the solvent, making it easier for the raw materials to form a bonded state due to some force (such as an intermolecular force or a chemical bond) between themselves or between the raw materials and the first solvent, thereby suppressing separation and loss of the raw materials. As a result, it is possible to improve production efficiency and easily produce a high-quality sulfide solid electrolyte.

[0031] A fourth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the first solvent is at least one oxygen atom-containing solvent selected from ester solvents, ether solvents, aldehyde solvents, and ketone solvents. A fifth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the first solvent is at least one nitrogen atom-containing solvent selected from amine solvents, amide solvents, nitro solvents, and nitrile solvents.

[0032] When the first solvent is one of the above, it is possible to improve production efficiency and easily produce a high-quality sulfide solid electrolyte, as explained in the method for producing a sulfide solid electrolyte according to the third embodiment.

[0033] In the method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment, the heat treatment is carried out at 200° C. or higher. By setting the temperature of the heat treatment at 200° C. or higher, lithium alkoxide can be converted into Li２ S can suppress deterioration in quality such as a decrease in ionic conductivity due to the inclusion of lithium alkoxide, and Li ２ Since it becomes easier to obtain a sulfide solid electrolyte having a desired argyrodite-type crystal structure without any deviation in composition due to loss of S, it becomes possible to improve production efficiency and easily produce a high-quality sulfide solid electrolyte.

[0034] A seventh aspect of the present embodiment is a method for producing a sulfide solid electrolyte, which comprises mixing the raw material inclusions and the first solvent using a mixer or a stirrer. An eighth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, which comprises mixing the mixture and the second solvent using a mixer or a stirrer. Because the raw material inclusions and the first solvent, and the mixture and the second solvent can be mixed using a mixer or a stirrer, i.e., mixing can be performed without using equipment that requires a large amount of energy, such as a grinder, these methods can be said to be highly efficient.

[0035] In the method for producing a sulfide solid electrolyte according to a ninth aspect of this embodiment, the mixture contains a reaction product of the raw material contents. The mixture is obtained by mixing the raw material contents with the first solvent, and as described above, the raw materials or the raw materials and the first solvent form a bonded state due to some force (intermolecular force, chemical bond, etc.), which can be considered as a "reaction product." For example, when lithium sulfide (Li ２ S) and phosphorus sulfides (e.g., diphosphorus pentasulfide (P ２ S ５ )) is used, part of it is Li ３ P.S. ４ The reaction products include Li ３ P.S. ４ Also included are those having properties as solid electrolytes such as those mentioned above.

[0036] Li ３ P.S. ４ The reaction products formed by the bonding of the raw materials, such as lithium sulfide (Li ２S) and phosphorus sulfides (e.g., diphosphorus pentasulfide (P ２ S ５ )) and other raw materials are not liberated, so separation and loss of raw materials are unlikely to occur. ３ P.S. ４ The reaction product forms a loose bond with the first solvent, which protects it from the second solvent and can serve as the basic structure of a sulfide solid electrolyte, making it easier to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure. As a result, a solid electrolyte precursor can be obtained more efficiently, which in turn improves production efficiency and makes it possible to easily produce a high-quality sulfide solid electrolyte.

[0037] In a tenth aspect of the present embodiment, the raw material inclusions in the method for producing a sulfide solid electrolyte include lithium sulfide. In an eleventh aspect of the present embodiment, the raw material inclusions in the method for producing a sulfide solid electrolyte include phosphorus sulfide. In a twelfth aspect of the present embodiment, the raw material inclusions in the method for producing a sulfide solid electrolyte include a lithium halide selected from lithium chloride and lithium bromide.

[0038] These forms define the raw materials that are preferable as raw material contents. By using raw materials defined by these forms, it becomes easier to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure.

[0039] In a thirteenth aspect of the present embodiment, a method for producing a sulfide solid electrolyte is provided in which the amount of the first solvent used is 100 mL or more and 1,000 mL or less per 100 g of the raw material content. In a fourteenth aspect of the present embodiment, a method for producing a sulfide solid electrolyte is provided in which the amount of the second solvent used is 200 mL or more and 2,000 mL or less per 100 g of the raw material content. By setting the amounts of the first solvent and the second solvent used within the above ranges, each solvent functions efficiently, allowing a solid electrolyte precursor to be obtained more efficiently, resulting in improved production efficiency and enabling a high-quality sulfide solid electrolyte to be easily produced.

[0040] The method for producing the sulfide solid electrolyte of this embodiment will be described in more detail below in accordance with the above aspects.

[0041] [Method for Producing Sulfide Solid Electrolyte] A method for producing a sulfide solid electrolyte according to a first aspect of the present embodiment is a method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure, comprising: mixing a raw material inclusion with a first solvent to obtain a mixture; mixing the mixture with a second solvent to obtain a solution containing a solid electrolyte precursor; heat-treating the solid electrolyte precursor while supplying hydrogen sulfide to obtain a heated solid electrolyte precursor; and calcining the heated solid electrolyte precursor.

[0042] (Raw Material Contents) The raw material contents used in the manufacturing method of this embodiment contain raw materials for the sulfide solid electrolyte. The sulfide solid electrolyte obtained by the manufacturing method of this embodiment is a sulfide solid electrolyte having an argyrodite-type crystal structure, and contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. That is, the raw material contents essentially contain a plurality of raw materials having atoms selected from lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. As halogen atoms, chlorine atoms, bromine atoms, and iodine atoms are preferred, and chlorine atoms and bromine atoms are more preferred. It is preferable that the raw material contents contain at least two types of halogen atoms.

[0043] The raw materials used in the manufacturing method of this embodiment 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 , P２ I ４ ) and the like; phosphorus halides such as thiophosphoryl fluoride (PSF ３ ), thiophosphoryl chloride (PSCl ３ ), thiophosphoryl bromide (PSBr ３ ), thiophosphoryl iodide (PSI ３ ), thiophosphoryl fluoride dichloride (PSCl ２ F), thiophosphoryl fluoride dibromide (PSBr ２ and thiophosphoryl halides such as fluorine (F). ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Representative examples include simple halogen atoms such as

[0044] 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 alkali metals, sulfur atoms, and phosphorus atoms, and preferably further halogen atoms, and also contain atoms other than the above 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.

[0045] In this embodiment, from the viewpoint of more easily obtaining a sulfide solid electrolyte having high ionic conductivity, among alkali metal atoms, lithium atoms and sodium atoms are preferred, with lithium atoms being more preferred, and among halogen atoms, chlorine atoms, bromine atoms and iodine atoms are preferred, with chlorine atoms and bromine atoms being more preferred. These atoms may be used alone or in combination.

[0046] From the same viewpoint, compounds that can be used as raw materials include alkali metal sulfides such as lithium sulfide and sodium sulfide, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Preferred are phosphorus sulfides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. Examples of compounds containing halogen atoms include lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ It is preferable to use lithium halide and a halogen atom alone or in combination, that is, it is preferable to use at least one selected from lithium halide and a halogen atom. It goes without saying that when lithium halide or a halogen atom alone is used or when lithium halide and a halogen atom are used in combination, multiple kinds of lithium halides and multiple kinds of halogen atoms can be used.

[0047] Among alkali metal sulfides, lithium sulfide is preferred, among phosphorus sulfides, diphosphorus pentasulfide is preferred, and among halogen elements, chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), and chlorine (Cl ２ ), bromine (Br ２ Among lithium halides, lithium chloride, lithium bromide, and lithium iodide are preferred, and lithium chloride and lithium bromide are more preferred. When a lithium halide is used, it is particularly preferred to use lithium chloride and lithium bromide in combination.

[0048] Preferred examples of combinations of compounds that can be used as raw materials include a combination of lithium sulfide, diphosphorus pentasulfide, and a lithium halide, a combination of lithium sulfide, diphosphorus pentasulfide, and a simple halogen, and a combination of lithium sulfide, diphosphorus pentasulfide, lithium halide, and a simple halogen. Of these, the combination of lithium sulfide, diphosphorus pentasulfide, and lithium halide is preferred.

[0049] In this embodiment, the above-mentioned examples can be used alone or in combination of two or more kinds.

[0050] In this embodiment, PS ４ Li including structure etc. ３ P.S. ４ It is also possible to use solid electrolytes such as Li as a raw material. ３ P.S. ４ By using a solid electrolyte such as lithium sulfide (Li ２ S), phosphorus sulfide (e.g., diphosphorus pentasulfide (P ２ S ５ )) and other separation and loss can be suppressed, and Li ３ P.S. ４ The reaction products such as the above can be the basic structure of a sulfide solid electrolyte, and therefore, a sulfide solid electrolyte having an argyrodite-type crystal structure can be easily obtained.

[0051] On the other hand, Li ３ P.S. ４ In order to obtain a solid electrolyte such as lithium sulfide (Li ２ S) and phosphorus sulfide (e.g., diphosphorus pentasulfide (P ２ S ５)) and is produced by conventional production methods such as mechanical milling, slurry, melt quenching, etc. Therefore, the production efficiency of the production method of this embodiment may be reduced. In the production method of this embodiment, as described above, by mixing the raw material content with the first solvent, a reaction product is obtained in which the raw materials form a loose bond state due to some force (intermolecular force, etc.), thereby suppressing separation and loss of the raw materials. In consideration of this, in the production method of this embodiment, the raw materials are Li ３ P.S. ４ There is no strong need to use reaction products such as

[0052] In the present embodiment, when lithium sulfide is used as the compound containing an alkali metal, the lithium sulfide is preferably in the form of particles. ５０ ) is preferably 10 μm or more and 2000 μm or less, more preferably 30 μm or more and 1500 μm or less, and even more preferably 50 μm or more and 1000 μm or less. ５０ ) is the particle size at which 50% of the total particle size is obtained by accumulating the particle size distribution cumulative curve from the smallest particle size, and the volume distribution is the 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.

[0053] (Regarding the blending ratio of raw materials in the raw material content) When lithium sulfide and diphosphorus pentasulfide are used, the amount of lithium sulfide used relative to the total amount of lithium sulfide and phosphorus sulfide is preferably 65 mol% or more, more preferably 70 mol% or more, and even more preferably 76 mol% or more, and the upper limit is preferably 85 mol% or less, more preferably 80 mol% or less, and even more preferably 79 mol% or less. When the amount of lithium sulfide used is within the above range, a sulfide solid electrolyte having an argyrodite-type crystal structure is easily obtained.

[0054] When lithium sulfide, diphosphorus pentasulfide, lithium halide, and other raw materials used as needed are used, the content of lithium sulfide and diphosphorus pentasulfide relative to the total of these is preferably 45 mol% or more, more preferably 47 mol% or more, and even more preferably 50 mol% or more, with the upper limit being preferably 80 mol% or less, more preferably 65 mol% or less, and even more preferably 58 mol% or less. When the contents of lithium sulfide and diphosphorus pentasulfide are within the above ranges, a sulfide solid electrolyte having an argyrodite-type crystal structure is easily obtained.

[0055] Furthermore, when a combination of lithium chloride and lithium bromide is used as the lithium halide, the proportion of lithium chloride to the total of lithium chloride and lithium bromide is preferably 1 mol% or more, more preferably 20 mol% or more, even more preferably 40 mol% or more, still more preferably 50 mol% or more, and the upper limit is preferably 99 mol% or less, more preferably 90 mol% or less, even more preferably 80 mol% or less, and still more preferably 70 mol% or less. When the proportion of lithium chloride is within the above range, a sulfide solid electrolyte having an argyrodite-type crystal structure is easily obtained.

[0056] (First Solvent) In the manufacturing method of this embodiment, as described above, two types of solvents, a first solvent and a second solvent, are used. Examples of the first solvent include a solvent that can be mixed with the raw material inclusion to obtain a mixture, i.e., a solvent that has the property of not dissolving the raw materials contained in the raw material inclusion and the reaction product formed by the raw materials bonding together. Here, "not dissolving" does not strictly mean "not dissolving" at all, but rather allows for some dissolution. Specifically, "not dissolving" includes cases where the solubility (at 25°C) of the raw materials and the reaction product is less than 1 g / 100 mL.

[0057] The first solvent is preferably a solvent different from the second solvent described below and containing at least either an oxygen atom or a nitrogen atom. Specific examples of such a first solvent include at least one oxygen atom-containing solvent selected from ether solvents, ester solvents, aldehyde solvents, and ketone solvents; and at least one nitrogen atom-containing solvent selected from amine solvents, amide solvents, nitro solvents, and nitrile solvents.

[0058] Preferred examples of the solvent containing an oxygen atom, such as an ether solvent, include aliphatic ethers such as dimethyl ether, diethyl ether, tert-butyl methyl ether, dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether (diglyme), triethylene oxide glycol dimethyl ether (triglyme), diethylene glycol, and triethylene glycol; alicyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, and dioxane; heterocyclic ethers such as furan, benzofuran, and benzopyran; and aromatic ethers such as methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, and diphenyl ether.

[0059] Preferred examples of the ester solvent include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, and isopropyl acetate; aliphatic esters such as methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, and diethyl succinate; alicyclic esters such as methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, and dimethyl cyclohexanedicarboxylate; heterocyclic esters such as methyl pyridinecarboxylate, methyl pyrimidinecarboxylate, acetolactone, propiolactone, butyrolactone, and valerolactone; and aromatic esters such as methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, trimethyl trimellitate, and triethyl trimellitate.

[0060] Preferred examples of the aldehyde solvent include formaldehyde, acetaldehyde, and dimethylformamide, and preferred examples of the ketone solvent include acetone and methyl ethyl ketone.

[0061] Examples of the solvent containing a nitrogen atom include solvents having a group containing a nitrogen atom, such as an amino group, an amide group, a nitro group, or a nitrile group, i.e., amine solvents, amide solvents, nitro solvents, and nitrile solvents. Preferred examples of the amine solvent include aliphatic amines such as ethylenediamine, diaminopropane, dimethylethylenediamine, diethylethylenediamine, dimethyldiaminopropane, tetramethyldiaminomethane, tetramethylethylenediamine (TMEDA), and tetramethyldiaminopropane (TMPDA); alicyclic amines such as cyclopropanediamine, cyclohexanediamine, and bisaminomethylcyclohexane; heterocyclic amines such as isophoronediamine, piperazine, dipiperidylpropane, and dimethylpiperazine; and aromatic amines such as phenyldiamine, tolylenediamine, naphthalenediamine, methylphenylenediamine, dimethylnaphthalenediamine, dimethylphenylenediamine, tetramethylphenylenediamine, and tetramethylnaphthalenediamine.

[0062] Preferred examples of the amide solvent include dimethylformamide, diethylformamide, dimethylacetamide, methoxydimethylpropanamide, hexamethylphosphoric triamide, hexamethylphosphorous triamide, and N-methylpyrrolidone.

[0063] Preferred examples of nitro solvents include nitrobenzene, and preferred examples of nitrile solvents include acetonitrile, methoxyacetonitrile, acrylonitrile, propionitrile, isobutyronitrile, methoxypropionitrile, and benzonitrile.

[0064] As the first solvent, among the various solvents described above, ether solvents, ester solvents, and amine solvents are preferred, and ether solvents are more preferred. Furthermore, among ether solvents, alicyclic ethers are preferred, and tetrahydrofuran is particularly preferred.

[0065] The amount of the first solvent used is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 350 mL or more, and even 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 even more preferably 550 mL or less.

[0066] (Second Solvent) The second solvent may be a solvent that can be mixed with the mixture obtained by mixing the raw material components with the first solvent to obtain a solution containing a solid electrolyte precursor, i.e., a solvent that has the property of dissolving the reaction product formed by bonding the raw materials contained in the mixture, and further the solid electrolyte precursor. Here, the "dissolving property" specifically means that the solubility (at 25°C) of the reaction product and the solid electrolyte precursor is 1 g / 100 mL or more.

[0067] As described above, the second solvent is a solvent different from the first solvent, and specifically, an alcohol solvent is preferably used. Examples of the alcohol solvent include primary and secondary aliphatic alcohols such as methanol, ethanol, isopropanol, butanol, and 2-ethylhexyl alcohol; polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, and hexanediol; alicyclic alcohols such as cyclopentanol, cyclohexanol, and cyclopentylmethanol; aromatic alcohols such as butylphenol, benzyl alcohol, phenethyl alcohol, naphthol, and diphenylmethanol; and alkoxy alcohols such as methoxyethanol, propoxyethanol, and butoxyethanol.

[0068] As the second solvent, among the various solvents mentioned above, aliphatic alcohols are preferred, primary aliphatic alcohols are more preferred, methanol and ethanol are even more preferred, and ethanol is particularly preferred.

[0069] The amount of the second solvent used is preferably 200 mL or more, more preferably 400 mL or more, even more preferably 700 mL or more, and even more preferably 900 mL or more per 100 g of raw material content, and the upper limit is preferably 2000 mL or less, more preferably 1700 mL or less, even more preferably 1400 mL or less, and even more preferably 1100 mL or less.

[0070] (Other Solvents) In the production method of this embodiment, other solvents besides the first solvent and the second solvent can also be used. Examples of other solvents include solvents that do not have heteroatoms such as oxygen atoms or nitrogen atoms. Examples of such solvents include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

[0071] Examples of aliphatic hydrocarbons include hexane, pentane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane. Examples of alicyclic hydrocarbons include cyclohexane and methylcyclohexane. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene.

[0072] When the other solvent is used, it may be used in combination with the first solvent or the second solvent. There is no particular limitation on the amount of the other solvent used.

[0073] (Obtaining the Mixture) In the manufacturing method of this embodiment, the mixture is obtained by mixing the raw material contents described above with the first solvent. As described above, the mixture contains the reaction product in which the raw materials are bonded together by some force (such as intermolecular force or chemical bond), the first solvent, and the raw materials themselves.

[0074] The mixing of the raw material ingredients and the first solvent can be carried out using, for example, a mixer or a stirrer. It can also be carried out using a pulverizer. By using a pulverizer, the reaction tends to proceed more quickly, but the equipment costs become higher. In the production method of this embodiment, these factors are comprehensively considered and either a mixer, a stirrer or a pulverizer can be adopted. In the production method of this embodiment, when considering the equipment costs in particular as production efficiency, it is preferable to mix the raw material ingredients and the first solvent using equipment called a mixer or a stirrer. In other words, it can be said that the mixing of solvent 1 and raw material 1 can be carried out by stirring, mixing, or a process combining these.

[0075] Examples of the agitator or mixer include a mechanical agitation mixer that is equipped with a stirring blade in a mixing tank and is capable of agitation (also referred to as mixing by agitation or agitation mixing). Examples of the mechanical agitation mixer include a high-speed agitation mixer and a double-arm mixer. Examples of the high-speed agitation mixer include a vertical-axis rotary mixer and a horizontal-axis rotary mixer, and either type of mixer may be used.

[0076] Examples of the shape of the stirring blade used in the mechanical stirring mixer include blade type, arm type, anchor type, paddle type, full zone 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 promoting the reaction of the raw materials more efficiently, the shovel type, flat blade type, C-type blade type, anchor type, paddle type, full zone type, etc. are preferred, with the anchor type, paddle type, and full zone type being more preferred.

[0077] When a mechanical stirring mixer is used, the rotation speed of the stirring blades can be adjusted appropriately depending on the volume of the mixture in the mixing tank, the temperature, the shape of the stirring blades, etc., and is not particularly limited. However, it is usually about 5 rpm or more and 500 rpm or less. From the viewpoint of more efficiently preparing a solution, the rotation speed is preferably 25 rpm or more, more preferably 50 rpm or more, and even more preferably 100 rpm or more, with the upper limit being preferably 450 rpm or less, more preferably 400 rpm or less, and even more preferably 350 rpm or less.

[0078] The temperature conditions when mixing is performed using a stirrer or mixer 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 quantities, 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.

[0079] (Obtaining a Solution) In the production method of this embodiment, a solution containing a solid electrolyte precursor is obtained by mixing the above mixture with a second solvent. The solution containing a solid electrolyte precursor contains a first solvent, a second solvent, and a solid electrolyte precursor, and the solid electrolyte precursor is present in a dissolved state.

[0080] The mixing of the mixture with the second solvent is similar to the mixing of the raw material ingredients with the first solvent, and can be carried out using, for example, a mixer or a stirrer. The mixer or a stirrer that can be used to mix the mixture with the second solvent can be selected from the mixers and agitators exemplified above as the mixers and agitators that can be used to mix the raw material ingredients with the first solvent.

[0081] The temperature conditions when mixing is performed using a stirrer or mixer 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.

[0082] (Drying) The solution containing the solid electrolyte precursor may be dried before the heat treatment while supplying hydrogen sulfide, which will be described later. That is, the production method of this embodiment may include drying the solution containing the solid electrolyte precursor. By drying and volatilizing the first solvent and the second solvent contained in the solution, hydrogen sulfide supplied in the heat treatment, which will be described later, becomes more likely to come into contact with the solid components contained in the solution, particularly lithium alkoxide, which facilitates the reaction shown in the above reaction formula (3) to proceed, making it easier to convert lithium alkoxide into lithium sulfide. This makes it possible to efficiently suppress quality degradation, such as a decrease in ionic conductivity, and to obtain a high-quality sulfide solid electrolyte.

[0083] Drying can be performed at a temperature depending on the types of the first and second solvents used in the above mixture. For example, drying can be performed at a temperature equal to or higher than the boiling points of the first and second solvents. The drying temperature cannot be generalized because it varies depending on the pressure conditions under which drying is performed and the boiling points of the first and second solvents. It is typically 5°C or higher but lower than 200°C, preferably 20°C to 190°C, more preferably 35°C to 175°C, and even more preferably 50°C to 160°C. While normal pressure or increased pressure is possible, reduced-pressure drying (vacuum drying) using a vacuum pump or the like is preferred. The drying time is typically 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.

[0084] (Obtaining a Heated Solid Electrolyte Precursor by Heat Treatment While Supplying Hydrogen Sulfide) The manufacturing method of this embodiment includes obtaining a heated solid electrolyte precursor by heating the solid electrolyte precursor while supplying hydrogen sulfide. By performing the heat treatment while supplying hydrogen sulfide, impurities contained in the solution, such as lithium alkoxide, which may be generated as a reaction product between lithium sulfide and the second solvent, can be converted to lithium sulfide. Next, by calcining the obtained heated solid electrolyte precursor, an argyrodite-type crystal structure is formed and its crystallinity is improved, resulting in a sulfide solid electrolyte having a high-quality argyrodite-type crystal structure. Furthermore, if the above drying is not performed, the first solvent and the second solvent contained in the solution can be removed.

[0085] 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.

[0086] The heating temperature for the heat treatment cannot be generally defined because it can vary depending on the types of the first solvent and the second solvent, but is preferably a temperature lower than the calcination temperature described below, and can be selected from a temperature range that is usually preferably 200° C. or higher, more preferably 250° C. or higher, even more preferably 350° C. or higher, and even more preferably 400° C. or higher, with the upper limit preferably being 700° C. or lower, more preferably 600° C. or lower, even more preferably 500° C. or lower, and even more preferably 450° C. or lower. 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.

[0087] 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 (23° 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.

[0088] 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.

[0089] (Caking the heated solid electrolyte precursor) The manufacturing method of this embodiment includes calcining the heated solid electrolyte precursor. By calcining the heated solid electrolyte precursor, an argyrodite-type crystal structure is formed and the crystallinity is improved, thereby obtaining a sulfide solid electrolyte having a high-quality argyrodite-type crystal structure.

[0090] The heating temperature for calcination cannot be generally defined because it varies depending on the types of the first solvent and second solvent. However, it is preferably higher than the heating temperature during the heat treatment. It is usually preferably 200°C or higher, more preferably 250°C or higher, even more preferably 350°C or higher, and even more preferably 400°C or higher. The upper limit can be selected from a temperature range of preferably 700°C or lower, more preferably 600°C or lower, even more preferably 500°C or lower, and even more preferably 450°C or lower. The calcination temperature refers to the maximum temperature during calcination. The calcination 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 refers to the time during which the calcination heating temperature is maintained. In the production method of this embodiment, it is preferable to maintain a constant temperature for the above-mentioned calcination time.

[0091] The calcination method is not particularly limited, and examples thereof include methods using a vacuum heating device, a calcination furnace, an autoclave, etc. Furthermore, industrially, a horizontal dryer having a heating means and a feeding mechanism, a horizontal vibration fluidized dryer, etc. may also be used, and the method may be selected depending on the amount of heat to be processed.

[0092] The calcination can be carried out by transferring the heated solid electrolyte precursor obtained by heat treatment while supplying hydrogen sulfide to a calcination device, for example. The calcination can be carried out continuously with the heat treatment, and the calcination can be carried out while supplying the hydrogen sulfide used in the heat treatment, or by stopping the supply of hydrogen sulfide. Typical examples of the heat treatment and calcination include: (i) placing a solid electrolyte precursor in a furnace at room temperature (23°C), heating the furnace while supplying hydrogen sulfide, and then calcining at the calcination temperature while supplying hydrogen sulfide or stopping the supply of hydrogen sulfide; (ii) placing a solid electrolyte precursor in a furnace set at a predetermined heating temperature, performing a heat treatment while supplying hydrogen sulfide to obtain a heated solid electrolyte precursor, and then placing the heated solid electrolyte precursor in a furnace set at a calcination temperature, and calcining while supplying hydrogen sulfide or without supplying hydrogen sulfide; (iii) placing a solid electrolyte precursor in a furnace set at a predetermined heating temperature, performing a heat treatment while supplying hydrogen sulfide, and then calcining while raising the temperature from the heating temperature to the calcination temperature; and the like.

[0093] (Sulfide Solid Electrolyte) The sulfide solid electrolyte obtained by the above production method is a sulfide solid electrolyte having an argyrodite-type crystal structure.

[0094] The argyrodite crystal structure is ７ P.S. ６ The structure basically has the following structural skeleton, and a part of P is replaced with Si. For example, the structure has the following composition formula: ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ The crystal structure represented by the formula (x is -0.6 to 0.6, y is 0.1 to 0.6) 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°. ７－ｘ－２ｙ P.S. ６－ｘ－ｙCl ｘ The crystal structure represented by (0.8≦x≦1.7, 0<y≦−0.25x+0.5) 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°. In addition, the composition formula Li ７－ｘ P.S. ６－ｘ Ha ｘ The crystal structure represented by the formula (where Ha is Cl or Br, and x is preferably 0.2 to 1.8) 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°. Note that these peak positions may vary within a range of ±0.5°.

[0095] The shape of the sulfide solid electrolyte having an argyrodite-type crystal structure obtained by the production method of this embodiment is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０ ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.

[0096] (Applications) As described above, the sulfide solid electrolyte having an argyrodite-type crystal structure obtained by the method for producing a sulfide solid electrolyte of this embodiment is a high-quality sulfide solid electrolyte with few impurities and high ionic conductivity. Therefore, it has excellent battery performance and can be suitably used in batteries. The sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte 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.

[0097] The battery preferably includes a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used, such as a layer of Au, Pt, Al, Ti, or Cu, which reacts with the solid electrolyte, coated with Au or the like.

[0098] 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.

[0099] (Measurement of Ion Conductivity) In the present example, the ion conductivity was measured as follows. Using the sulfide solid electrolyte powders obtained in the examples and comparative examples, a sample having a diameter of 6 to 10 mm (cross-sectional area S: 0.283 to 0.785 cm 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: 1 MHz to 0.1 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

[0100] (Powder X-ray Diffraction Measurement) In the present examples, powder X-ray diffraction measurement (XRD) was carried out as follows. The powders obtained in the examples and comparative examples were filled into a groove 20 mm in diameter and 0.2 mm deep, and leveled with glass to prepare a sample. This sample was measured under the following conditions, without being exposed to air, using an airtight sample stage sealed with Kapton film. Measurement equipment: MiniFlex, manufactured by Rigaku Corporation Tube voltage: 40 kV Tube current: 150 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: focusing method Slit configuration: Soller slit 2.5°, divergence slit 0.625°, Kβ filter (Ni plate) used Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 2.5 deg, 0.02 deg / sec

[0101] Example 1 In an argon atmosphere, 0.597 g (0.0127 mol) of lithium sulfide, 0.759 g (0.0034 mol) of diphosphorus pentasulfide, 0.289 g (0.0068 mol) of lithium chloride (LiCl), and 0.356 g (0.0041 mol) of lithium bromide (LiBr) were introduced into a 100 mL eggplant-shaped flask. A stirring bar was added, and 10 mL of tetrahydrofuran was added as a first solvent while stirring with a stirrer. Mixing was carried out at room temperature (23°C) for 12 hours (rotation speed: 300 rpm). The above raw material contents and the reaction product (Li ３ P.S. ４ A mixture containing tetrahydrofuran and a first solvent (tetrahydrofuran) was obtained. Next, 20 mL of ethanol was added as a second solvent, and the mixture was mixed for an additional 5 minutes at room temperature (23°C) to prepare a solution containing a solid electrolyte precursor. The resulting solution was dried under vacuum at 150°C for 2 hours to obtain a solid electrolyte precursor. The resulting solid electrolyte precursor was placed in an alumina boat and subjected to a heat treatment in which the temperature was increased from room temperature (23°C) to 430°C at a rate of 5°C / min while supplying hydrogen sulfide at a flow rate of 100 cc / min. Subsequently, the mixture was calcined at 430°C for 2 hours while supplying hydrogen sulfide under the same conditions, and then cooled to room temperature. The resulting sulfide solid electrolyte was a white powder. Powder XRD diffraction analysis was performed on the resulting sulfide solid electrolyte. The results are shown in Figure 1. The ionic conductivity was also measured, and found to be 5.9 mS / cm.

[0102] Example 2 In Example 1, a heat treatment was performed at a heating temperature of 250°C for 1.5 hours. The heat-treated powder was transferred to a sealed container and calcined at 430°C for 2 hours without supplying hydrogen sulfide, and then cooled to room temperature to obtain a sulfide solid electrolyte. The obtained sulfide solid electrolyte was a white powder. Powder XRD diffraction measurement was performed on the obtained sulfide solid electrolyte. The results are shown in Figure 3. The ionic conductivity was also measured. The results are shown in Table 1.

[0103] Example 3 In Example 1, a heat treatment was performed at a heating temperature of 250°C for 1.5 hours. The heat-treated powder was transferred to a sealed container and calcined at 430°C for 2 hours without supplying hydrogen sulfide, and then cooled to room temperature to obtain a sulfide solid electrolyte. The obtained sulfide solid electrolyte was a white powder. Powder XRD diffraction measurement was performed on the obtained sulfide solid electrolyte. The results are shown in Figure 4. The ionic conductivity was also measured. The results are shown in Table 1.

[0104] Comparative Example 1 A sulfide solid electrolyte was obtained in the same manner as in Example 1, except that hydrogen sulfide was replaced with nitrogen gas during the heat treatment and calcination. The obtained sulfide solid electrolyte was in the form of a black powder. Powder XRD diffraction measurement was performed on the obtained sulfide solid electrolyte. The results are shown in FIG. 2. The ionic conductivity was also measured. The results are shown in Table 1.

[0105] *1. Because the heat treatment and firing were carried out consecutively, the temperature is lower than the firing temperature.

[0106] The results of Examples 1 to 3 confirmed that the sulfide solid electrolyte obtained by the manufacturing method of this embodiment was a white powder and a high-quality sulfide solid electrolyte that exhibited high ionic conductivity. Furthermore, as shown in the X-ray diffraction spectrum of FIG. 1 , the sulfide solid electrolyte obtained in Example 1 had peaks at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°, confirming that the sulfide solid electrolyte had an argyrodite-type crystal structure.

[0107] On the other hand, the sulfide solid electrolyte of Comparative Example 1, which was heat-treated without supplying hydrogen sulfide, was a black powder, and therefore contained carbonized impurities (e.g., lithium ethoxide) contained in the solid electrolyte precursor before heat treatment, and it is believed that the ionic conductivity was also lower than that of the Examples. The X-ray diffraction spectrum of Figure 2 confirmed peaks characteristic of the argyrodite-type crystal structure, similar to that of Example 1, as well as two peaks at 2θ = 22.2° and 23.3° that were not confirmed in Example 1. These peaks are presumed to be due to impurities (such as those formed from lithium ethoxide).

[0108] According to Example 1, by continuously performing the heat treatment and calcination while supplying hydrogen sulfide, a high-quality sulfide solid electrolyte was obtained that was a white powder and exhibited higher ionic conductivity than the sulfide solid electrolyte of Comparative Example 1. Furthermore, Examples 2 and 3, in which the heat treatment was performed while supplying hydrogen sulfide and then calcination was not performed without supplying hydrogen sulfide, also produced high-quality sulfide solid electrolytes that were a white powder and exhibited higher ionic conductivity than the sulfide solid electrolyte of Comparative Example 1. From the results of the Examples and Comparative Examples, it can be seen that the production method of this embodiment can produce high-quality sulfide solid electrolytes that have improved ionic conductivity and are free of impurities, simply by performing the heat treatment while supplying hydrogen sulfide. Furthermore, the sulfide solid electrolytes obtained in Examples 2 and 3 used the same raw materials and calcination temperatures as in Example 1, and had high ionic conductivities of 4.4 mS / cm and 3.2 mS / cm, respectively, and therefore have an argyrodite-type crystal structure similar to Example 1. This can be confirmed by FIGS. 3 and 4 .

[0109] According to the manufacturing method of this embodiment, a high-quality sulfide solid electrolyte having high ionic conductivity and few impurities can be efficiently manufactured. The obtained sulfide solid electrolyte is suitable for use in batteries, particularly batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. mixing the raw material contents with a first solvent to obtain a mixture; mixing the mixture with a second solvent to obtain a solution containing a solid electrolyte precursor; heat-treating the solid electrolyte precursor while supplying hydrogen sulfide to obtain a heated solid electrolyte precursor; and calcining the heated solid electrolyte precursor; Including, A method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure.

2. 2. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1, wherein the second solvent is an alcohol solvent.

3. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the first solvent is a solvent different from the second solvent and contains at least either an oxygen atom or a nitrogen atom.

4. 4. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 3, wherein the first solvent is at least one oxygen atom-containing solvent selected from the group consisting of ester solvents, ether solvents, aldehyde solvents, and ketone solvents.

5. 4. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 3, wherein the first solvent is at least one nitrogen atom-containing solvent selected from the group consisting of amine solvents, amide solvents, nitro solvents, and nitrile solvents.

6. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the heat treatment is carried out at 200°C or higher.

7. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the raw material contents and the first solvent are mixed using a mixer or a stirrer.

8. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the mixture and the second solvent are mixed using a mixer or a stirrer.

9. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the mixture contains a reaction product of the raw material ingredients.

10. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1, wherein the raw material contains lithium sulfide.

11. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1, wherein the raw material contains phosphorus sulfide.

12. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the raw material contains a lithium halide selected from lithium chloride and lithium bromide.

13. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the amount of the first solvent used is 100 mL or more and 1000 mL or less per 100 g of the raw material content.

14. 3. The method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure according to claim 1 or 2, wherein the amount of the second solvent used is 200 mL or more and 2000 mL or less per 100 g of the raw material content.