Method for producing sulfide solid electrolyte

Abstract

Provided is a method for producing a sulfide solid electrolyte, the method comprising mixing a starting material-containing substance containing a lithium atom, a phosphorus atom, a sulfur atom and a halogen atom in an organic solvent to produce a mixture and subjecting the mixture to irradiation with microwaves. Thus, a method for producing a sulfide solid electrolyte is provided, in which a heating temperature is decreased by employing a liquid phase method to suppress the granulation by heating and therefore a sulfide solid electrolyte that keeps the particle diameters thereof can be efficiently produced.

Description

Method for producing sulfide solid electrolyte

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

[0002] In recent years, the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones has placed great importance on the development of batteries for use as their power sources. Lithium-ion batteries, in particular, have attracted attention due to their high energy density. Traditionally, batteries used for such applications have used electrolytes containing flammable organic solvents, necessitating the installation of safety devices to suppress temperature rise during short circuits, as well as improvements in the structure and materials to prevent short circuits. In response to this issue, development is underway to develop batteries that use solid electrolytes, eliminating the need for flammable organic solvents, simplifying safety devices, and improving manufacturing costs and productivity.

[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, a solid-phase method is known in which raw materials such as lithium sulfide and diphosphorus pentasulfide are mechanically milled using a device such as a ball mill or a bead mill, and then heated as necessary to produce an amorphous or crystalline solid electrolyte (see, for example, Patent Document 1). Among liquid-phase methods, a homogeneous method is known in which a solid electrolyte is dissolved in a solvent and then reprecipitated (see, for example, Patent Document 2). A heterogeneous method is known in which a solid electrolyte raw material such as lithium sulfide is reacted in a solvent containing a polar aprotic solvent (see, for example, Patent Documents 3 and 4, and Non-Patent Document 1).

[0004] As a method for producing a solid electrolyte, Patent Document 5 and Non-Patent Documents 2 and 3 disclose a method for producing amorphous Li by irradiating lithium sulfide and diphosphorus pentasulfide in an organic solvent with microwaves. ３ P.S. ４ It is disclosed to prepare an electrolyte of the composition.

[0005] International Publication No. 2017 / 159667 Pamphlet Japanese Patent Application Laid-Open No. 2014-191899 International Publication No. 2014 / 192309 Pamphlet International Publication No. 2018 / 054709 Pamphlet Japanese Patent Application Laid-Open No. 2020-15661

[0006] “CHEMISTRY OF MATERIALS”, 2017, No. 29, pp. 1830-1835 “Journal of Materials Chemistry A”, 2018, No. 6, pp. 21261-21265 “Journal of Materials Chemistry A”, 2018, No. 9, pp. 400-405

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a method for producing a sulfide solid electrolyte, which employs a liquid phase method, reduces the heating temperature, and suppresses granulation due to heating, thereby enabling efficient production of a sulfide solid electrolyte with particle size maintained.

[0008] The method for producing a sulfide solid electrolyte according to the present invention includes: mixing raw material components containing lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms in an organic solvent to obtain a mixture; and irradiating the mixture with microwaves.

[0009] According to the present invention, it is possible to provide a method for producing a sulfide solid electrolyte, which employs a liquid phase method, reduces the heating temperature, and suppresses granulation due to heating, thereby enabling efficient production of a sulfide solid electrolyte with particle size maintained.

[0010] 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 Example 2. FIG. 3 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 3. FIG. 4 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Comparative Example 1. FIG. 5 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Comparative Example 2. FIG. 6 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Comparative Example 3. FIG. 7 is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Comparative Example 4.

[0011] 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.

[0012] (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 discovered the following and completed the present invention. The solid-phase method is primarily based on a solid-phase reaction, and since it is easy to obtain a solid electrolyte with high purity, it is easy to achieve high ionic conductivity, but it is characterized by being unsuitable for mass production. In recent years, with a view to commercializing all-solid-state batteries, efforts have been made to increase the size (mass production) for industrial production, and the liquid-phase method has attracted attention as a method that not only has versatility and applicability but also allows for simple and large-scale synthesis.

[0013] In the liquid-phase method, firing is generally performed for the purpose of improving the crystallinity of the sulfide solid electrolyte. In particular, when producing a sulfide solid electrolyte having an argyrodite-type crystal structure, firing at a high temperature of about 400°C is required. Furthermore, firing at such a high temperature causes granulation, resulting in larger particle sizes than before firing, which may require a pulverization process, ultimately leading to higher costs for the sulfide solid electrolyte. Furthermore, the need for firing at a high temperature may cause problems such as accelerated corrosion of reaction equipment, which may lead to higher costs for the sulfide solid electrolyte due to increased equipment costs.

[0014] The present inventors have noticed that the conventional liquid-phase production methods for sulfide solid electrolytes disclosed in Patent Documents 2 to 4 and Non-Patent Document 1, etc., do not particularly consider calcination, and do not raise any issue of the problem of granulation caused by high-temperature calcination resulting in an increase in particle size. Furthermore, when attempting to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure, among sulfide solid electrolytes, calcination at high temperatures is unavoidable, as is clear from the conventional liquid-phase production methods disclosed in these documents and the production method described in Non-Patent Document 3.

[0015] Therefore, the present inventors conducted extensive research, particularly on the calcination process, in a method for producing a sulfide solid electrolyte. They discovered that irradiating a mixture of raw material components in an organic solvent with microwaves can reduce the heating temperature and suppress granulation due to heating. Reducing the heating temperature not only reduces the energy required for heating, but also reduces equipment costs, as described above. Furthermore, suppressing granulation due to heating and maintaining particle size eliminates the need for a pulverization process after heating, which is extremely effective in improving production efficiency and reducing costs.

[0016] It can be said that Patent Document 5, Non-Patent Documents 2 and 3 describe microwave irradiation in sulfide solid electrolytes. However, in the manufacturing methods disclosed in these documents, microwave irradiation is performed on Li ２ S and P ２ S ５ Using Li ３ P.S. ４ Microwave irradiation is employed when producing an electrolyte (lithium thiophosphate) of the composition, and microwave irradiation is not performed on those containing halogen atoms. Furthermore, Patent Document 5 and Non-Patent Document 2 describe the production of an amorphous sulfide solid electrolyte by microwave irradiation, but do not involve the production of a crystalline sulfide solid electrolyte, such as one having an argyrodite-type crystal structure. Non-Patent Document 3 also describes that microwave irradiation is performed as described above, while high-temperature firing is also performed. Therefore, in light of conventional manufacturing methods, it is a surprising phenomenon that a sulfide solid electrolyte can be produced that maintains particle size by reducing the heating temperature and suppressing granulation due to heating through the extremely simple operation of microwave irradiation instead of the firing operation used in conventional manufacturing methods.

[0017] In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state at 25°C under a nitrogen atmosphere. The "sulfide solid electrolyte" obtained by the production method of this embodiment refers to a solid electrolyte that contains alkali metal atoms, sulfur atoms, phosphorus atoms, and halogen atoms and has ionic conductivity due to alkali metal atoms such as lithium atoms. The above-mentioned "sulfide solid electrolyte" may also contain metal atoms such as Ge, Na, K, Mg, Ca, Al, Si, Sb, Ti, and Zr.

[0018] In this specification, the term "sulfide solid electrolyte" includes both crystalline sulfide solid electrolytes 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 X-ray diffraction 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 thereof. 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 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 X-ray diffraction measurement, and it does not matter whether or not there are peaks derived from the raw materials of the solid electrolyte.

[0020] [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, comprising: mixing raw material components containing lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms in an organic solvent to obtain a mixture; and irradiating the mixture with microwaves.

[0021] Conventionally, particularly when producing a crystalline sulfide solid electrolyte, a crystallization step by calcination has been required. In particular, when producing a sulfide solid electrolyte having an argyrodite-type crystal structure, an extremely high heating temperature of about 400°C is required during calcination. As described above, this can result in increased equipment costs, an increase in particle size due to granulation, and energy consumption for heating. Therefore, the present inventors focused on heating by microwave irradiation as the calcination operation.

[0022] Heating by microwave irradiation involves irradiating a target substance with microwaves, causing the molecules of the substance to vibrate and raising the temperature of the substance through frictional heat. The inventors considered whether it would be possible to suppress the temperature of the entire reaction system by utilizing the characteristic of microwave irradiation, which heats the target substance, and selectively heating and reacting raw material contents containing compounds that serve as raw materials for sulfide solid electrolytes. They then considered whether it would be possible to suppress the temperature of the entire reaction system by selectively heating the raw material contents in an organic solvent by microwave irradiation, allowing the organic solvent to absorb the heat from the raw material contents, thereby suppressing the temperature of the entire reaction system, and arrived at the present invention.

[0023] The production method of this embodiment is a production method in which, by simply performing the extremely simple operation of microwave irradiation, not only can a sulfide solid electrolyte be obtained while reducing the heating temperature, but also a sulfide solid electrolyte with particle size maintained by suppressing granulation due to heating. Reducing the heating temperature not only leads to a reduction in equipment costs, but also reduces the energy consumption required for heating. Furthermore, suppressing granulation due to heating and maintaining particle size eliminates the need for a pulverization treatment after heating. As a result, the production method of this embodiment can improve the efficiency of production of a sulfide solid electrolyte and reduce costs.

[0024] A second aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the first aspect, wherein the integrated irradiation energy during irradiation of microwaves at an output of 140 W / g or more per unit mass of the raw material contained in the mixture is 1.0 kW s / g or more.

[0025] By irradiating the mixture with microwaves so as to satisfy the above-mentioned predetermined conditions, the reaction between the solid electrolyte raw materials in the raw material contents contained in the mixture is more easily promoted, thereby making it easier to obtain a sulfide solid electrolyte with a higher degree of crystallinity and higher ionic conductivity.

[0026] A method for producing a sulfide solid electrolyte according to a third aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the organic solvent has a dielectric loss factor of 10.0 or less at 25° C. The third aspect is such that the organic solvent in the first aspect has a predetermined dielectric loss factor.

[0027] The energy loss when a substance is placed in an electromagnetic field irradiated with microwaves is the sum of conductive loss, dielectric loss, and magnetic loss. When a liquid is placed in an electromagnetic field irradiated with microwaves, dielectric loss occurs, converting the energy of the electric field into thermal energy and generating heat. In other words, the lower the dielectric loss, the more efficiently the energy from microwave irradiation can be consumed by the raw material contents.

[0028] The dielectric loss factor is proportional to the dielectric loss, and the dielectric loss factor and the dielectric loss have the following relationship: Dielectric loss = πfε ０ ε” |E| ２ (f: frequency (1 / sec), ε ０ : dielectric constant of vacuum, ε": dielectric loss factor of material, |E|: electric field (V / m)

[0029] Thus, the dielectric loss factor is an index of the ease of heating by microwaves, and the smaller the dielectric loss factor, the smaller the dielectric loss. Therefore, when the dielectric loss factor of the organic solvent used in the production method of this embodiment is 10.0 or less, the raw material contents can be heated more selectively, and therefore the sulfide solid electrolyte can be produced more efficiently.

[0030] A fourth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the boiling point of the organic solvent is 50° C. or higher. The fourth aspect is a method for producing a sulfide solid electrolyte, wherein the organic solvent in any one of the first to third aspects has a predetermined boiling point.

[0031] The higher the boiling point of the organic solvent, the more the amount of the organic solvent that volatilizes when the raw material content is selectively heated can be suppressed, and the raw material content can be more uniformly maintained in the organic solvent. Therefore, it is easier to selectively heat the raw material content and it is possible to reduce the amount of organic solvent used.

[0032] A fifth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the organic solvent is an aromatic solvent. The fifth aspect is a method for producing a sulfide solid electrolyte, wherein the organic solvent in any one of the first to fourth aspects is an aromatic solvent, i.e., an organic solvent having an aromatic ring.

[0033] Aromatic solvents, which are organic solvents having an aromatic ring, tend to satisfy the properties, i.e., the dielectric loss factor and boiling point, required in the third and fourth aspects, and therefore enable the production of sulfide solid electrolytes more efficiently.

[0034] A sixth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the mixture contains a raw material ingredient in an amount of 1 mass % or more and 20 mass % or less.

[0035] In a sixth aspect, in any one of the first to fifth aspects, the content of the raw material components contained in the mixture is set to a predetermined range, which allows the amount of organic solvent used to be reduced, making it possible to more efficiently produce a sulfide solid electrolyte.

[0036] A method for producing a sulfide solid electrolyte according to a seventh aspect of the present embodiment is a method for producing a sulfide solid electrolyte, comprising: irradiating the mixture with microwaves and heating the mixture at a temperature of 150°C or higher and 360°C or lower.

[0037] In a seventh embodiment, in any one of the first to sixth embodiments, the temperature of the mixture is heated to within a predetermined range. As described above, for example, to produce a sulfide solid electrolyte having an argyrodite-type crystal structure, conventional manufacturing methods require firing at a high temperature of approximately 400°C. However, according to the manufacturing method of this embodiment, it is possible to produce a sulfide solid electrolyte having an argyrodite-type crystal structure even under low-temperature conditions of 150°C or higher and 360°C or lower.

[0038] A method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the raw material contents include lithium sulfide, phosphorus sulfide, and lithium halide.

[0039] In the eighth embodiment, in any one of the first to seventh embodiments, specific compounds of lithium sulfide, phosphorus sulfide, and lithium halide are used as the raw material ingredients. By employing raw material ingredients containing such compounds, it becomes possible to more efficiently produce a sulfide solid electrolyte.

[0040] A method for producing a sulfide solid electrolyte according to a ninth aspect of the present embodiment is a method for producing a sulfide solid electrolyte, wherein the sulfide solid electrolyte is a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure.

[0041] In a ninth aspect, the sulfide solid electrolyte obtained by the manufacturing method of any one of the first to eighth aspects is a sulfide solid electrolyte having an argyrodite-type crystal structure. As described above, a sulfide solid electrolyte having an argyrodite-type crystal structure requires firing at a high temperature of about 400°C according to conventional manufacturing methods. However, according to the manufacturing method of this embodiment, it is possible to reduce the heating temperature to, for example, 150°C or higher and 360°C or lower. In other words, when manufacturing a sulfide solid electrolyte having an argyrodite-type crystal structure, it is possible to make better use of the features of the manufacturing method of this embodiment.

[0042] A tenth aspect of the present embodiment provides a method for producing a sulfide solid electrolyte, which is the method for producing a sulfide solid electrolyte according to any one of the first to ninth aspects, in which the raw material inclusions contain a raw material sulfide solid electrolyte as a raw material.

[0043] A method for producing a sulfide solid electrolyte according to an eleventh aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to the tenth aspect, further comprising: mixing and pulverizing a raw material inclusion B containing at least two types of compounds in a solvent to obtain a raw material mixture; and calcining the raw material mixture to obtain the raw material sulfide solid electrolyte.

[0044] A method for producing a sulfide solid electrolyte according to a twelfth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to the eleventh aspect, wherein the heating temperature in the calcination is 150°C or higher and 300°C or lower.

[0045] [Obtaining a mixture] The production method of this embodiment includes mixing raw material components containing lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms in an organic solvent to obtain a mixture. Hereinafter, obtaining the mixture will be described starting with the raw material components.

[0046] (Raw material inclusions) The raw material inclusions contain lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. There are no particular limitations on the raw material inclusions as long as they contain these atoms, and examples include inclusions containing a compound containing at least one atom selected from these atoms, either singly or in combination as a raw material. The inclusions preferably contain two or more compounds selected from compounds containing at least one atom selected from lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. Therefore, the sulfide solid electrolyte obtained by the production method of this embodiment contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms.

[0047] Compounds that can be used as raw materials contain at least one atom of a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom, and more specifically, alkali metal sulfides such as lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; alkali metal halides such as lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; and sodium halides such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; 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 (PSI ３ ), thiophosphoryl fluoride dichloride (PSCl ２ F), thiophosphoryl fluoride dibromide (PSBr ２ a raw material consisting of at least two elements selected from the above four elements, such as thiophosphoryl halides, e.g., fluorine (F); ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), preferably bromine (Br ２ ), iodine (I ２ ) are typical examples.

[0048] Compounds that can be used as raw materials other than those mentioned above include, for example, compounds containing at least one atom selected from the above four types of atoms and also containing atoms other than the four types of atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; 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; 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.

[0049] In this embodiment, the halogen atom can vary depending on the sulfide solid electrolyte to be obtained, and therefore cannot be generalized. However, from the viewpoint of more easily obtaining a sulfide solid electrolyte having high ionic conductivity, among halogen atoms, chlorine atoms, bromine atoms, and iodine atoms are preferred. These atoms may be used alone or in combination. Furthermore, for example, when a sulfide solid electrolyte having a thiolicon region II crystal structure, which will be described later, is to be obtained, bromine atoms and iodine atoms are more preferred. Furthermore, when a sulfide solid electrolyte having an argyrodite crystal structure is to be obtained, chlorine atoms and bromine atoms are more preferred.

[0050] In this embodiment, from the viewpoint of more easily obtaining a sulfide solid electrolyte having high ionic conductivity, examples of compounds that can be used as raw materials include, among the above, alkali metal sulfides such as lithium sulfide and sodium sulfide, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２Among the alkali metal sulfides, lithium sulfide is preferred, and among the phosphorus sulfides, diphosphorus pentasulfide is preferred.

[0051] As mentioned above, raw materials containing halogen atoms can vary depending on the sulfide solid electrolyte to be obtained, so it is difficult to generalize. However, among the halogen elements, chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ) is preferred, and among the lithium halides, lithium chloride, lithium bromide, and lithium iodide are preferred. Furthermore, when a sulfide solid electrolyte having a thiolithium region II crystal structure is to be obtained, the halogen element is preferably bromine (Br ２ ), iodine (I ２ ) is more preferable, and lithium bromide and lithium iodide are more preferable as lithium halides. In addition, when it is intended to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure, chlorine (Cl ２ ), bromine (Br ２ ) is more preferred, and as the lithium halide, lithium chloride and lithium bromide are more preferred.

[0052] The combination of compounds that can be used as raw materials is preferably a combination of lithium sulfide, phosphorus sulfide, and lithium halide, or a combination of lithium sulfide, phosphorus sulfide, and a simple halogen, and more preferably a combination of lithium sulfide, phosphorus sulfide, and lithium halide. Here, diphosphorus pentasulfide is preferred as the phosphorus sulfide, and the lithium halide and simple halogen may be selected according to the sulfide solid electrolyte to be obtained, as described above.

[0053] In this embodiment, compounds that can be used as raw materials include PS ４ Li including units etc. ３ P.S. ４ The sulfide solid electrolyte obtained by the production method of this embodiment has a main structure containing Li. ３ P.S. ４By using a lithium-containing structure such as the above as a raw material, the composition ratio of the structure is increased compared to when a compound such as lithium sulfide is used as a raw material and a sulfide solid electrolyte is formed by synthesizing the compound through a reaction between the compounds. ４ The fraction can be improved and high ionic conductivity can be obtained.

[0054] In this embodiment, the sulfide solid electrolyte (hereinafter also referred to as "raw sulfide solid electrolyte") that can be used as a compound used as a raw material has a molecular structure of Li ３ P.S. ４ Amorphous sulfide solid electrolyte having the structure ("amorphous Li ３ P.S. ４ "), or crystalline sulfide solid electrolytes ("crystalline Li ３ P.S. ４ "). ) and the like are preferred. In addition, an amorphous sulfide solid electrolyte having a structure containing halogen atoms, which will be described later as an "amorphous sulfide solid electrolyte", or a crystalline sulfide solid electrolyte, or a precursor equivalent thereto (such as the "calcined product" described later), can also be used. When the raw material inclusion contains a raw material sulfide solid electrolyte as a raw material, higher Joule heating is obtained due to the ionic conductivity of the raw material sulfide solid electrolyte, which makes it easier to promote the reaction, improves the crystallinity of the obtained sulfide solid electrolyte, and makes it easier to obtain a sulfide solid electrolyte with higher ionic conductivity. In addition, in consideration of obtaining high ionic conductivity, the raw material sulfide solid electrolyte is preferably Li ４ P ２ S ７ An amorphous or crystalline sulfide solid electrolyte that does not contain a structure is preferred. These raw sulfide solid electrolytes can be produced by conventional production methods such as mechanical milling, slurry method, and melt quenching method, or commercially available products can also be used.

[0055] The sulfide solid electrolyte used as a raw material (raw sulfide solid electrolyte) may be amorphous or crystalline, or may contain both amorphous and crystalline components. In either case, when a compound containing a halogen atom is used as a raw material, the dispersibility of the halogen atom is improved, which makes it easier for the halogen atom to bond with the lithium atom, sulfur atom, and phosphorus atom in the solid electrolyte, resulting in a sulfide solid electrolyte with higher ionic conductivity.

[0056] In this embodiment, when lithium sulfide is used as a raw material, 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 reached when the particle size distribution integral curve is drawn and the integral is calculated sequentially 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 analyzer. 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. The particle size of the raw material compound may be adjusted by pulverization or the like, as necessary.

[0057] When lithium sulfide, diphosphorus pentasulfide, and lithium halide are used as raw materials, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide cannot be generalized because it varies depending on the sulfide solid electrolyte to be obtained. However, from the viewpoint of obtaining higher chemical stability and high ionic conductivity, the ratio is preferably 60 mol% or more, more preferably 65 mol% or more, and even more preferably 68 mol% or more, with the upper limit being preferably 85 mol% or less, more preferably 83 mol% or less, and even more preferably 80 mol% or less.

[0058] 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 55 mol% or more, more preferably 58 mol% or more, even more preferably 60 mol% or more, and the upper limit is preferably 100 mol% or less, more preferably 90 mol% or less, even more preferably 80 mol% or less, and still more preferably 70 mol% or less.

[0059] When lithium bromide and lithium iodide are used in combination as the lithium halide, from the viewpoint of obtaining high ionic conductivity, the ratio of lithium bromide to the total of lithium bromide and lithium iodide 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. Furthermore, when lithium bromide and lithium chloride are used in combination as the lithium halide, the ratio of lithium bromide to the total of lithium bromide and lithium chloride is the same as the ratio of lithium bromide to the total of lithium bromide and lithium iodide described above.

[0060] [Organic Solvent] In the production method of this embodiment, the raw material components are mixed in an organic solvent. As the solvent used in mixing the raw material components, various solvents widely known as organic solvents can be used.

[0061] As the solvent, a wide variety of solvents that have conventionally been used in the production of solid electrolytes can be used, and examples thereof include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

[0062] Examples of aliphatic hydrocarbons include saturated aliphatic hydrocarbons such as pentane, hexane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane, as well as unsaturated aliphatic hydrocarbons corresponding to the above saturated aliphatic hydrocarbons such as pentene and hexene. Examples of alicyclic hydrocarbons include saturated alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, as well as unsaturated aliphatic hydrocarbons corresponding to the above saturated alicyclic hydrocarbons such as cyclohexene and methylcyclohexene. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, mesitylene, ethylbenzene, tert-butylbenzene, biphenyl, naphthalene, tetrahydronaphthalene (tetralin, cyclohexylbenzene), anthracene, and the like.

[0063] In addition to the above hydrocarbon solvents, examples of the solvent include solvents containing heteroatoms such as atoms other than carbon and hydrogen atoms, for example, nitrogen atoms, oxygen atoms, sulfur atoms, halogen atoms, etc. Preferred examples of the solvent containing an oxygen atom as a heteroatom include ether solvents, ester solvents, alcohol solvents, aldehyde solvents, and ketone solvents.

[0064] Preferred examples of the 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 (diphenyl oxide).

[0065] 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.

[0066] Preferred examples of the solvent include alcohol solvents such as ethanol and butanol; aldehyde solvents such as formaldehyde, acetaldehyde and dimethylformamide; and ketone solvents such as acetone and methyl ethyl ketone.

[0067] Examples of solvents containing a nitrogen atom as a heteroatom include solvents having a group containing a nitrogen element, such as an amino group, an amide group, a nitro group, a nitrile group, etc. For example, preferred examples of solvents having an amino group (amine solvents) include aliphatic amines such as diethylamine, triethylamine, ethylenediamine, diaminopropane, dimethylethylenediamine, diethylethylenediamine, dimethyldiaminopropane, tetramethyldiaminomethane, tetramethylethylenediamine (TMEDA), and tetramethyldiaminopropane (TMPDA); alicyclic amines such as cyclopropanediamine, cyclohexanediamine, and bisaminomethylcyclohexane; heterocyclic amines such as isophoronediamine, pyridine, methylpyridine, dimethylpyridine, methylethylpyridine, piperazine, dipiperidylpropane, and dimethylpiperazine; and aromatic amines such as phenyldiamine, tolylenediamine, naphthalenediamine, methylphenylenediamine, dimethylnaphthalenediamine, dimethylphenylenediamine, tetramethylphenylenediamine, tetramethylnaphthalenediamine, and dimethylaniline.

[0068] Preferred examples of solvents having a nitrile group (nitrile solvents) include acetonitrile, propionitrile, 3-chloropropionitrile, benzonitrile, 4-fluorobenzonitrile, tert-butyronitrile, isobutyronitrile, acrylonitrile, cyclohexylnitrile, capronitrile, isocapronitrile, malononitrile, and fumaronitrile. Other preferred examples include solvents containing a nitrogen atom, such as dimethylformamide and nitrobenzene.

[0069] Preferred examples of solvents containing a halogen atom as a heteroatom include dichloromethane, chlorobenzene, trifluoromethylbenzene, chlorobenzene, chlorotoluene, bromobenzene, etc. Preferred examples of solvents containing a sulfur atom include dimethyl sulfoxide, carbon disulfide, etc.

[0070] The amount of organic solvent used is such that the content of the total amount of the raw material ingredients relative to the total amount of the raw material ingredients and the organic solvent is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and still more preferably 8% by mass or more, with the upper limit being preferably 20% by mass or less, more preferably 17% by mass or less, even more preferably 15% by mass or less, and still more preferably 12% by mass or less. When the amount of organic solvent used is within the above range, the raw material ingredients are more likely to be uniformly maintained in the organic solvent, making it easier for the raw material ingredients to be selectively heated by microwave irradiation, and allowing the sulfide solid electrolyte to be produced more efficiently.

[0071] (Dielectric Loss Factor and Boiling Point of Organic Solvent) Among the above organic solvents, the organic solvent used in the production method of this embodiment is preferably one having a dielectric loss factor of 10.0 or less at 25°C. By using an organic solvent having a dielectric loss factor of 10.0 or less, the raw material contents can be heated more selectively, thereby enabling the sulfide solid electrolyte to be produced more efficiently. From this perspective, the dielectric loss factor of the organic solvent is more preferably 8.0 or less, even more preferably 5.0 or less, even more preferably 1.0 or less, and particularly preferably 0.5 or less. There is no particular restriction on the lower limit, and it is usually 0.01 or more. The dielectric loss factor in this specification is the dielectric loss factor at 25°C at 2.45 GHz, and is a measured value measured according to a conventional method. For example, the relative permittivity and dielectric loss tangent can be measured using a dielectric constant measuring device (e.g., various devices such as an LCR meter, an impedance material analyzer, a network analyzer, a TDR measuring device, or a pulse THz spectroscopy device) and the dielectric loss factor can be calculated.

[0072] Among the organic solvents described above, those having a boiling point of 50°C or higher are preferred for use in the production method of this embodiment. A boiling point of 50°C or higher suppresses the amount of volatilization of the organic solvent when the raw material content is selectively heated, and also allows the raw material content to be more uniformly maintained in the organic solvent, making it easier to selectively heat the raw material content and reducing the amount of organic solvent used. From this perspective, the boiling point of the organic solvent is more preferably 65°C or higher, even more preferably 75°C or higher, even more preferably 100°C or higher, and particularly preferably 200°C or higher.

[0073] Among the organic solvents exemplified above, aromatic solvents having an aromatic ring, such as aromatic hydrocarbon solvents, aromatic ether solvents, and aromatic ester solvents, as well as aliphatic hydrocarbons, alicyclic hydrocarbons, ether solvents (excluding the above-mentioned aromatic ether solvents), ester solvents (excluding the above-mentioned aromatic ester solvents), solvents having an amino group (amine solvents), and solvents containing a halogen atom are more preferred, and among these, aromatic solvents having an aromatic ring are particularly preferred. These organic solvents are likely to satisfy the above-mentioned dielectric loss factor and boiling point conditions, and allow for selective heating of the raw material contents, making it possible to more efficiently produce a sulfide solid electrolyte.

[0074] The aromatic solvent is preferably an aromatic hydrocarbon solvent or an aromatic ether, more preferably an aromatic ether, and the aromatic hydrocarbon solvent is preferably benzene, toluene, xylene, biphenyl, naphthalene, or tetrahydronaphthalene (tetralin, cyclohexylbenzene), and the aromatic ether is preferably diphenyl ether (diphenyl oxide).

[0075] As the aliphatic hydrocarbon, pentane and hexane are preferred, and as the alicyclic hydrocarbon, cyclohexane is preferred. As the ether solvent (excluding the above-mentioned aromatic ether solvents), aliphatic ethers and alicyclic ethers are preferred, with diethyl ether and tetrahydrofuran being particularly preferred. As the ester solvent (excluding the above-mentioned aromatic ester solvents), aliphatic esters are preferred, with ethyl acetate being particularly preferred.

[0076] As the solvent having an amino group (amine solvent), aliphatic amines and heterocyclic amines are preferred, and triethylamine and pyridine are particularly preferred. As the solvent containing a halogen atom, dichloromethane is preferred.

[0077] [Mixing] The production method of this embodiment requires mixing the raw material ingredients in the organic solvent to obtain a mixture. The mixture becomes a slurry (suspension) in which the raw material ingredients are dispersed in the organic solvent. By mixing the raw material ingredients to obtain a mixture, the raw material ingredients can be more uniformly maintained in the organic solvent, making it easier to selectively heat the raw material ingredients, and enabling the efficient production of a sulfide solid electrolyte.

[0078] Mixing the raw material ingredients in an organic solvent to obtain a mixture can be performed using, for example, a mixer. It can also be performed using a stirrer, a grinder, or the like. Mixing of the raw materials can occur using a stirrer, and grinding of the raw materials occurs using a grinder, but mixing also occurs at the same time. In other words, it can be said that the mixture can be obtained by subjecting the raw material ingredients to stirring, mixing, grinding, or a combination of these processes in an organic solvent. In the production method of this embodiment, mixing can be performed using a stirrer, a mixer, or a grinder. However, from the viewpoint of efficiently obtaining a slurry (suspension) in which the raw material ingredients are dispersed in an organic solvent, it is preferable to use either a stirrer or a mixer, and it is more preferable to use a mixer.

[0079] Examples of the stirrer or mixer include a mechanical stirring mixer that is equipped with stirring blades in a reaction vessel and can stir (also referred to as mixing by stirring or stirring and mixing). Examples of the mechanical stirring mixer include a high-speed stirring mixer and a double-arm mixer. Examples of the high-speed stirring mixer include a vertical-axis rotary mixer and a horizontal-axis rotary mixer, and either type of mixer may be used.

[0080] 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.

[0081] When a mechanical stirring mixer is used, the rotation speed of the stirring blades can be adjusted appropriately depending on the volume of the fluid in the reaction vessel, the temperature, the shape of the stirring blades, etc., and is not particularly limited. However, it is usually sufficient to set the rotation speed at about 5 rpm or more and 400 rpm or less. From the viewpoint of more efficiently promoting the reaction of the raw materials, the rotation speed is preferably 10 rpm or more and 300 rpm or less, more preferably 15 rpm or more and 250 rpm or less, and even more preferably 20 rpm or more and 200 rpm or less.

[0082] The temperature conditions when mixing is performed using a mixer are not particularly limited, and are, for example, usually −30 to 120° C., preferably −10 to 100° C., more preferably 0 to 80° C., and even more preferably 10 to 60° C. The mixing time is usually 0.1 to 500 hours, and from the viewpoint of achieving a more uniform dispersion state of the raw materials and promoting the reaction, is preferably 1 to 450 hours, more preferably 10 to 425 hours, even more preferably 20 to 400 hours, and still more preferably 40 to 375 hours.

[0083] As the pulverizer, for example, a media-type pulverizer using a pulverizing medium can be used. Media-type pulverizers are broadly classified into container-driven pulverizers and media-agitation pulverizers. Container-driven pulverizers include agitation tanks, grinding tanks, or combinations thereof, such as ball mills and bead mills. Examples of media-agitation pulverizers include impact pulverizers such as cutter mills, hammer mills, and pin mills; tower-type pulverizers such as tower mills; agitation tank pulverizers such as attritors, aquamizers, and sand grinders; flow-tank pulverizers such as Viscomill and pearl mills; flow-tube pulverizers; annular pulverizers such as Coball mills; continuous dynamic pulverizers; and single- or multi-shaft kneaders. Among these, considering the ease of adjusting the particle size of the resulting sulfide, the ball mills and bead mills exemplified as container-driven pulverizers are preferred, and planetary pulverizers are particularly preferred.

[0084] These pulverizers can be appropriately selected depending on the desired scale, etc. For relatively small scales, container-driven pulverizers such as ball mills and bead mills can be used, while for large scales or mass production, other types of pulverizers may be used.

[0085] Furthermore, as will be described later, when the mixture is in a liquid state involving a liquid such as a solvent or in a slurry state during mixing, a wet mill that can handle wet milling is preferred. Typical examples of wet mills include wet bead mills, wet ball mills, and wet vibration mills. Wet bead mills that use beads as milling media are preferred because they allow for free adjustment of milling conditions and are easily adaptable to smaller particle sizes. Dry mills, such as dry media mills (e.g., dry bead mills, dry ball mills, and dry vibration mills) and dry non-media mills (e.g., jet mills), can also be used.

[0086] Furthermore, when the material to be mixed is in a liquid state or a slurry state, a flow-through mill that can perform a circulation operation to circulate the material as needed can also be used. Specifically, a mill that circulates the material between a mill (pulverizing mixer) that pulverizes the slurry and a temperature holding tank (reaction vessel) can be used.

[0087] The size of the beads or balls used in the ball mill or bead mill may be appropriately selected depending on the desired particle size, processing amount, etc. For example, the diameter of the beads is usually 0.05 mmφ or more, preferably 0.1 mmφ or more, more preferably 0.3 mmφ or more, with the upper limit being usually 5.0 mmφ or less, preferably 3.0 mmφ or less, more preferably 2.0 mmφ or less. The diameter of the balls is usually 2.0 mmφ or more, preferably 2.5 mmφ or more, more preferably 3.0 mmφ or more, with the upper limit being usually 20.0 mmφ or less, preferably 15.0 mmφ or less, more preferably 10.0 mmφ or less. Examples of materials include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0088] Furthermore, when a ball mill or a bead mill is used, the rotation speed varies depending on the scale of the treatment and cannot be generalized, but is usually 10 rpm or more, preferably 20 rpm or more, more preferably 50 rpm or more, with the upper limit being usually 1,000 rpm or less, preferably 900 rpm or less, more preferably 800 rpm or less, and even more preferably 700 rpm or less. Furthermore, the milling time in this case varies depending on the scale of the treatment and cannot be generalized, but is usually 0.5 hours or more, preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more, with the upper limit being usually 100 hours or less, preferably 72 hours or less, more preferably 48 hours or less, and even more preferably 36 hours or less.

[0089] By selecting the size and material of the medium (beads, balls) used, the rotor rotation speed, time, etc., it is possible to perform mixing, stirring, pulverization, or a combination of these processes, and it is possible to adjust the particle size, etc. of the resulting sulfide.

[0090] The content of the raw material ingredients contained in the mixture obtained by mixing is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and even more preferably 8% by mass or more, with the upper limit being preferably 20% by mass or less, more preferably 17% by mass or less, even more preferably 15% by mass or less, and even more preferably 12% by mass or less. When the content of the raw material ingredients is within the above range, the raw material ingredients are more likely to be uniformly maintained in the organic solvent, and therefore the raw material ingredients are more likely to be selectively heated by microwave irradiation, allowing the sulfide solid electrolyte to be produced more efficiently.

[0091] [Microwave Irradiation] In the production method of this embodiment, it is necessary to irradiate the mixture obtained by the above-mentioned mixing with microwaves. By irradiating the mixture containing the raw material ingredients and the organic solvent with microwaves, the raw material ingredients are selectively heated, and a sulfide solid electrolyte is obtained.

[0092] As a microwave generator for irradiating microwaves, for example, an irradiation device equipped with a high-frequency oscillator for emitting microwaves can be used, and if the scale is small, a commercially available microwave oven or the like can also be used.

[0093] The microwave frequency is not particularly limited as long as it is within the range of about 0.3 GHz or more and 3000 GHz or less. In consideration of more efficient heating of the raw material contents and ease of obtaining microwave generators, the frequency is preferably 0.5 GHz or more, more preferably 1.0 GHz or more, and even more preferably 1.5 GHz or more, with the upper limit being preferably 100 GHz or less, more preferably 10.0 GHz or less, and even more preferably 6.0 GHz or less.

[0094] The output power cannot be generalized because it varies depending on the type of organic solvent contained in the mixture to be irradiated with microwaves, the amount of the mixture, etc., but in consideration of more efficiently heating the raw material contents, the output power is preferably 10 W or more, more preferably 50 W or more, and even more preferably 100 W or more, with the upper limit being preferably 500 kW or less, more preferably 300 kW or less, and even more preferably 200 kW or less.

[0095] The microwave irradiation time cannot be generalized because it varies depending on the type of organic solvent contained in the mixture to be microwave irradiated, the amount of the mixture, etc., but in consideration of more efficient heating of the raw material contents, it is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 3 minutes or more, with the upper limit being preferably 360 minutes or less, more preferably 300 minutes or less, and even more preferably 240 minutes or less. Furthermore, with regard to the heating temperature, the irradiation time for maintaining the highest temperature is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 3 minutes or more, with the upper limit being preferably 240 minutes or less, more preferably 210 minutes or less, even more preferably 190 minutes or less, and even more preferably 180 minutes or less.

[0096] The heating temperature by microwave irradiation cannot be generally determined because it varies depending on the composition of the sulfide solid electrolyte to be obtained, whether an amorphous or crystalline sulfide solid electrolyte is to be obtained, but the temperature of the mixture is preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 230°C or higher, with the upper limit being preferably 360°C or lower, more preferably 350°C or lower, even more preferably 310°C or lower, and still more preferably 275°C or lower.

[0097] The heating temperature by microwave irradiation can vary depending on the composition of the sulfide solid electrolyte to be obtained, whether it is amorphous or crystalline, as described above. That is, the heating temperature by microwave irradiation can control whether the sulfide solid electrolyte to be obtained is amorphous or crystalline.

[0098] For example, the temperature required for crystallization of the resulting raw sulfide solid electrolyte, i.e., the amorphous sulfide solid electrolyte, is determined by subjecting the amorphous sulfide solid electrolyte to differential thermal analysis (DTA) at a temperature increase rate of 10°C / min using a differential thermal analyzer (DTA device), and the peak top temperature of the exothermic peak observed at the lowest temperature is determined as the crystallization temperature. If the raw material contents in the mixture obtained by the above mixing, which are to be heated by microwave irradiation, are heated to a temperature higher than the crystallization temperature, a crystalline sulfide solid electrolyte is obtained, and if the raw material contents are heated to a temperature lower than the crystallization temperature, an amorphous sulfide solid electrolyte is obtained.

[0099] When producing a crystalline sulfide solid electrolyte, from the viewpoint of obtaining a crystalline sulfide solid electrolyte more stably and efficiently, the temperature of the raw material inclusions is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher relative to the crystallization temperature. There is no particular limitation on the upper limit, but it may be about 40 ° C. or lower. On the other hand, when producing an amorphous sulfide solid electrolyte, from the viewpoint of obtaining a more stably and efficiently amorphous sulfide solid electrolyte, the temperature of the raw material inclusions is preferably 5 ° C. or lower, more preferably 10 ° C. or lower, and even more preferably 20 ° C. or lower relative to the crystallization temperature. It may be set to be equal to or higher than the boiling point of the organic solvent contained in the mixture. The lower limit is not particularly limited as long as it is equal to or higher than the boiling point of the organic solvent contained in the mixture. For example, it may be set to about −40 ° C. or higher, which is the temperature at the top of the exothermic peak observed at the lowest temperature.

[0100] In the production method of this embodiment, since the raw material inclusions are selectively heated as described above, the temperature of the raw material inclusions themselves is considered to be higher than the temperature of the organic solvent (considered to be the same as the temperature of the mixture). Therefore, in the production method of this embodiment, although the temperature of the mixture obtained by the above mixing can be known, the temperature of the raw material inclusions in the mixture is indirectly known from the temperature of the mixture.

[0101] According to the examples described below, a sulfide solid electrolyte having an argyrodite-type crystal structure is obtained by setting the temperature of the mixture at 250°C. Considering that, as mentioned above, a sulfide solid electrolyte having an argyrodite-type crystal structure requires firing at a high temperature of about 400°C according to conventional methods, the temperature of the raw material inclusions themselves can be considered to be the temperature of the mixture + about 150°C. Strictly speaking, this can vary depending on the type and content of the organic solvent in the mixture, but it is advisable to determine whether the temperature of the raw material inclusions themselves has reached the crystallization temperature and set the heating temperature based on a guideline of about 150°C above the temperature of the mixture.

[0102] Furthermore, when irradiating the mixture with microwaves, it is preferable to irradiate with microwaves at a high output power of at least a certain level and with an integrated irradiation energy of at least a certain level. Specifically, microwaves are irradiated at a high output power of 140 W / g or more, and the integrated irradiation energy per unit mass of the raw material contained in the mixture during the high-output microwave irradiation is preferably 1.0 kW·s / g or more, more preferably 3.0 kW·s / g or more, and even more preferably 5.0 kW·s / g or more. By irradiating with microwaves under the above conditions, the reaction between the solid electrolyte raw materials in the raw material contained in the mixture is promoted, and the crystallinity and ionic conductivity of the resulting sulfide solid electrolyte are improved.

[0103] [Drying] The manufacturing method of this embodiment may include drying the fluid obtained by the microwave irradiation. The obtained fluid contains the sulfide solid electrolyte produced by the microwave irradiation, the remaining organic solvent, etc., and is usually in the form of a slurry (suspension). Therefore, by drying the fluid, a powder of the sulfide solid electrolyte is obtained.

[0104] Drying can be performed by irradiating the mixture with microwaves and drying the resulting fluid at a temperature that depends on the type of solvent, typically at 5 to 200°C, preferably 10 to 180°C, and more preferably 15 to 160°C, under reduced pressure (vacuum drying) using a vacuum pump or the like to volatilize the solvent.

[0105] Drying may be carried out by filtering the fluid using a glass filter or the like, by solid-liquid separation by decantation, or by solid-liquid separation using a centrifugal separator or the like.

[0106] The drying may be carried out by any of the above-mentioned reduced pressure drying (vacuum drying), filtration, and solid-liquid separation. For example, reduced pressure drying (vacuum drying) may be carried out after filtration or solid-liquid separation.

[0107] [Production of raw materials contained in raw material inclusions] As described above, the raw materials contained in the raw material inclusions have a molecular structure of Li ３ P.S. ４A sulfide solid electrolyte such as a sulfide solid electrolyte (lithium thiophosphate) having the structure can be preferably used. Hereinafter, a method for producing the sulfide solid electrolyte (raw material sulfide solid electrolyte) used in the raw material inclusion will be described, mainly with respect to the molecular structure of Li ３ P.S. ４ A sulfide solid electrolyte (lithium thiophosphate) having the structure will be described.

[0108] As described above, the raw sulfide solid electrolyte can be produced by a conventional production method such as a mechanical milling method, a slurry method, or a melt quenching method, and preferably by a production method including: mixing and pulverizing raw material components containing at least two types of compounds in a solvent to obtain a raw material mixture; and calcining the raw material mixture to obtain a calcined product.

[0109] (Raw material contents) As the raw material contents containing at least two compounds (to distinguish from the raw material contents used in the above-mentioned "obtaining a mixture", the raw material contents used in "obtaining a mixture" will be referred to as "raw material contents A", and the raw material contents used in "producing the raw materials contained in the raw material contents" will be referred to as "raw material contents B"), raw material contents B containing lithium sulfide and phosphorus sulfide, which are raw material compounds, is preferably used, and diphosphorus pentasulfide is preferred as the phosphorus sulfide. The amounts of lithium sulfide and phosphorus sulfide used may be appropriately determined depending on the sulfide solid electrolyte to be obtained, and lithium sulfide and diphosphorus pentasulfide are used to produce Li ３ P.S. ４ When a sulfide solid electrolyte having the structure is to be obtained, the molar ratio may be 3:1. When another sulfide solid electrolyte is to be obtained, the molar ratio may be used according to the sulfide solid electrolyte, and when a sulfide solid electrolyte containing a halogen atom is to be obtained, a raw material compound containing a halogen atom according to the sulfide solid electrolyte may be used. The molar ratio according to the sulfide solid electrolyte, the raw material compound to be used, and the like are the same as those explained above for the raw material content A.

[0110] The compound contained in the raw material content B may be crushed in advance before use. The crushing may be performed using a crusher described as a crusher that can be used to obtain the above mixture, and for example, a pin mill, particularly a pin mill having a constant volume feeder, is preferably used.

[0111] (Mixing and Pulverization) The method for producing a raw material sulfide solid electrolyte includes mixing and pulverizing a raw material inclusion B containing at least two compounds in a solvent to obtain a raw material mixture. For example, phosphorus sulfide and diphosphorus pentasulfide that may be contained in the raw material inclusion B are pre-pulverized as necessary, weighed out in amounts corresponding to the desired raw material sulfide solid electrolyte, and roughly mixed to obtain raw material inclusion B, which is then mixed and pulverized in a solvent to obtain the raw material mixture.

[0112] The raw material mixture contains compounds that are raw materials contained in raw material inclusion B, and it is believed that these compounds mainly form fine crystals. This is because the mixing and grinding of the raw material compounds promotes the atomization of the compounds contained in raw material inclusion B. It is also believed that some of the raw material compounds react to form a raw material sulfide solid electrolyte.

[0113] The raw material components B may be mixed and pulverized using any of the pulverizers described above as being usable for obtaining the mixture, and media-type pulverizers such as ball mills and bead mills are preferred. Alternatively, kneaders such as single-screw or multi-screw kneaders may also be used.

[0114] As the solvent used in the mixing and grinding, an organic solvent is preferably used. The organic solvent may be appropriately selected from the organic solvents used in obtaining the mixture. Among the above organic solvents, hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents are preferred, aromatic hydrocarbon solvents are more preferred, and toluene and xylene are particularly preferred.

[0115] In addition, as the solvent used in the mixing and grinding, it is also preferable to use the above-mentioned solvent containing a hetero atom, and it is more preferable to use it in combination with the above-mentioned hydrocarbon solvent.Among the solvents containing a hetero atom, a solvent containing an oxygen atom and a solvent containing a nitrogen atom are preferred, and as the solvent containing an oxygen atom, an ether solvent is preferred, and as the solvent containing a nitrogen atom, a solvent containing a nitrile group (nitrile solvent) is preferred, and a solvent containing a nitrile group (nitrile solvent) is more preferred.As the ether solvent, tetrahydrofuran, diethyl ether, etc. are preferred, and as the nitrile solvent, propionitrile, isocapronitrile, isobutyronitrile are preferred.

[0116] The solvent used in the mixing and grinding is preferably a combination of the hydrocarbon solvent and the heteroatom-containing solvent. In this case, the content of the heteroatom-containing solvent relative to the total amount of the solvent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, and the upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0117] The raw material ingredient B and the solvent to be mixed and pulverized usually form a slurry (suspension). The content of the raw material ingredient B in the slurry to be mixed and pulverized may be appropriately selected from the range of the content of the raw material ingredient A in the mixture to obtain the above mixture.

[0118] (Causticizing) The method for producing a raw sulfide solid electrolyte includes calcining a raw material mixture obtained by mixing and pulverizing the raw material contents B to obtain a calcined product. The calcination promotes the reaction of raw material compounds contained in the raw material mixture to produce a raw sulfide solid electrolyte, and also removes the solvent, thereby obtaining a powdered raw sulfide solid electrolyte. In other words, the calcined product obtained by calcining becomes the raw sulfide solid electrolyte.

[0119] The method of calcination is not particularly limited, and examples thereof include methods using a hot plate, autoclave, vacuum heating device, argon gas atmosphere furnace, calcination furnace, etc. In addition, methods using a shear-type dryer such as an FM mixer or Nauta mixer, a stationary furnace such as a hearth kiln, or a rotary furnace such as a rotary kiln, and further, industrially, a horizontal dryer having a heating means and a feeding mechanism, a horizontal vibration fluidized dryer, etc. The calcination method may be selected depending on the processing amount to be calcined.

[0120] The heating temperature and time in the calcination cannot be generalized because they vary depending on the composition of the calcined product and whether an amorphous or crystalline calcined product is intended to be obtained. For example, the heating temperature is preferably 150°C or higher, more preferably 160°C or higher, and even more preferably 170°C or higher, with the upper limit being preferably 300°C or lower, more preferably 280°C or lower, and even more preferably 250°C or lower.

[0121] As described above, the raw sulfide solid electrolyte may be either amorphous or crystalline, but is preferably amorphous from the viewpoint of improving the dispersibility of halogen atoms, facilitating bonding between the halogen atoms and lithium atoms, sulfur atoms, and phosphorus atoms in the sulfide solid electrolyte, and thereby obtaining a sulfide solid electrolyte having higher ionic conductivity. Therefore, the heating temperature in the calcination is preferably a temperature at which an amorphous raw sulfide solid electrolyte is obtained, and may be determined by the method starting from the crystallization temperature, as described above for the heating temperature by microwave irradiation.

[0122] The heating time is preferably 0.1 hour or more, more preferably 0.2 hour or more, and even more preferably 0.25 hour or more, and the upper limit is preferably 8 hours or less, more preferably 6 hours or less, and even more preferably 4 hours or less.

[0123] The calcination 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). An inert gas atmosphere containing hydrogen gas may also be used, as this can prevent deterioration (e.g., oxidation) of the raw material sulfide solid electrolyte.

[0124] Furthermore, drying may be carried out before the calcination. By drying, the solvent contained in the raw material mixture can be removed in advance. The drying method may be the same as that used for drying the fluid obtained by microwave irradiation.

[0125] The raw material sulfide solid electrolyte obtained by the above manufacturing method has a molecular structure mainly consisting of Li ３ P.S. ４ However, when the compounding ratio (molar ratio) of the raw materials used in the raw material contents B is changed, or when a raw material compound containing a halogen atom is used, for example, a sulfide solid electrolyte corresponding to the change can be obtained.

[0126] Molecular structure: Li ３ P.S. ４ In the case of a sulfide solid electrolyte (lithium thiophosphate) having the above-mentioned structure, calcination at the preferred heating temperature results in an amorphous sulfide solid electrolyte. Furthermore, for example, when a blending ratio of raw materials is adopted that results in a sulfide solid electrolyte having an argyrodite-type crystal structure (described later), the calcined product is merely an intermediate, and although the details are unknown because the state may change depending on the microwave irradiation conditions, it is thought to be a precursor that produces a sulfide solid electrolyte having an argyrodite-type crystal structure when irradiated with microwaves.

[0127] [Sulfide Solid Electrolyte] The sulfide solid electrolyte obtained by the manufacturing method of this embodiment is either an amorphous sulfide solid electrolyte (glass component) or a crystalline sulfide solid electrolyte. Whether it is amorphous or crystalline can be adjusted by the heating temperature by microwave irradiation.

[0128] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte obtained 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-P２ S ５ - LiBr, Li ２ S-P ２ S ５ - LiI-LiBr, etc., sulfide solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide; 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 sulfide solid electrolyte such as LiI is preferable. 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 preferred example of the solid electrolyte is a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and a lithium halide, such as LiI-LiBr. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0129] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle size (D ５０ ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.

[0130] (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 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, Li７ P.S. ６ Crystal structure, Li ７ P ３ S １１ Examples of the crystalline sulfide solid electrolyte obtained by the production method of this embodiment include a crystalline structure having peaks at 2θ = 20.2° and 23.6° in X-ray diffraction measurement using CuKα rays (for example, JP 2013-16423 A). In addition, from the viewpoint of obtaining higher ionic conductivity, the following argyrodite-type crystalline structure and thiolicon region II-type crystalline structure are preferred.

[0131] The above Li ７ P.S. ６ The structural skeleton of the compound has the composition formula Li 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－ｙ Cl 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°. 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°. ７P.S. ６ A crystal structure basically having the structural skeleton shown in the figure is also called an argyrodite-type crystal structure. Note that the positions of these peaks may vary within a range of ±0.5°.

[0132] Also, 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 Also included are crystal structures similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725).

[0133] As used herein, the term "thiolicon region II crystal structure" refers to a 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 ４This indicates that the crystalline sulfide solid electrolyte obtained by the production method of this embodiment has either the thio-lisicon region II type crystal structure or a crystal structure similar to the thio-lisicon region II type. Furthermore, the crystalline sulfide solid electrolyte obtained by the production method of this embodiment may have the thio-lisicon region II type crystal structure or may have it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it has it as the main crystal. In this specification, "having 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 production method of this embodiment has either the crystalline Li ３ P.S. ４ (β-Li ３ P.S. ４ ) is preferably not included.

[0134] 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 ｘS ４ Diffraction 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°.

[0135] As described above, in this embodiment, when the thiolicon region II crystal structure is obtained, crystalline Li ３ P.S. ４ (β-Li ３ P.S. ４ The sulfide solid electrolyte obtained by the production method of this embodiment preferably does not contain crystalline Li ３ P.S. ４ The diffraction peaks at 2θ=17.5° and 26.1° seen in the thiolicon region II crystal structure are not present, or even if they are present, they are extremely small peaks compared to the diffraction peaks of the thiolicon region II crystal structure.

[0136] The shape of the crystalline sulfide solid electrolyte 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.

[0137] (Uses of sulfide solid electrolyte) The sulfide solid electrolyte obtained by the production method of this embodiment has high ionic conductivity and excellent battery performance, and is therefore suitable for use in batteries. The sulfide solid electrolyte obtained by the production method of this embodiment may be used in any of a positive electrode layer, a negative electrode layer, and an electrolyte layer. Each layer can be produced by a known method.

[0138] 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.

[0139] 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.

[0140] (Preparation Example 1: Preparation of Raw Material Sulfide Solid Electrolyte) Lithium sulfide (Li ２ S) was pulverized under a nitrogen atmosphere using a pin mill equipped with a constant volume feeder (model number "100UPZ", manufactured by Hosokawa Micron Corporation) (feeding rate: 80 g / min, disk rotation speed: 18,000 rpm). ２ S ５ Lithium bromide (LiBr, manufactured by Honjo Chemical Co., Ltd.), and lithium chloride (LiCl, manufactured by Honjo Chemical Co., Ltd.) were also pulverized using the pin mill. ２ S ５ The charging rates of lithium bromide (LiBr) and lithium chloride (LiCl) were 140 g / min, 230 g / min, and 250 g / min, respectively, and the rotation speed of the disk was 18,000 rpm.

[0141] Next, in a glove box under a nitrogen atmosphere, each compound pulverized as described above was mixed with a mixture of 100% ammonium hydroxide and 100% ammonium hydroxide in a molar ratio of Li ２ S:P ２ S ５ The ratio of the raw materials was 47.5:12.5:15.0:25.0, and a total of 110 g was weighed out and placed in a glass container. The container was then shaken to roughly mix. 110 g of the crudely mixed raw materials was dispersed in a mixed solvent of 720 mL of dehydrated toluene (manufactured by Wako Pure Chemical Industries) and 2.9 mL of dehydrated isobutyronitrile (manufactured by Kishida Chemical) (2 wt% relative to the raw materials) under a nitrogen atmosphere to obtain a slurry of approximately 10% by mass. The slurry was mixed and pulverized using a bead mill (LMZ015, manufactured by Ashizawa Finetech Co., Ltd.) while maintaining the nitrogen atmosphere. Specifically, 456 g of zirconia beads with a diameter of 0.5 mm were used as the milling medium, and the bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 mL / min. The slurry was then introduced into the mill and circulated for 1 hour to obtain a raw material mixture.

[0142] 400 mL of the mixture of raw materials obtained above was placed in an autoclave (volume: 500 mL, made of SUS316) equipped with a stirrer and a heating oil bath, and heat-treated at 200° C. for 2 hours while stirring at a rotation speed of 350 rpm. After the treatment, the mixture was dried under reduced pressure to distill off the solvent, and a calcined product was obtained.

[0143] Example 1 The raw sulfide solid electrolyte obtained in Preparation Example 1 was used as the raw material. 1.5 g of the raw sulfide solid electrolyte obtained in Preparation Example 1 was mixed with 13.5 g of a solvent containing biphenyl and diphenyl oxide ("DAWTHERM A Heat Medium (trade name)" manufactured by Dow Chemical Japan, biphenyl content: 27% by mass) to obtain a mixture (slurry concentration: 10% by mass). The resulting mixture was placed in a microwave irradiation device ("Initiator+ (model number)" manufactured by Biotage), and microwave irradiation (frequency: 2.45 GHz) was initiated. The mixture was maintained at 250°C for 30 minutes, and then microwave irradiation was stopped. The solvent in the resulting mixture was replaced with toluene under vacuum, and the mixture was dried at room temperature until the solvent was completely removed. The mixture was then dried at 180°C for 4 hours to obtain a sulfide solid electrolyte powder. When the mixture was irradiated with microwaves at an output of 140 W / g or more per unit mass of the raw material content, the cumulative irradiation energy was 78 kW·s / g.

[0144] The obtained sulfide solid electrolyte powder was subjected to powder XRD diffraction measurement by the following method. The results are shown in Figure 1. As shown in Figure 1, diffraction peaks at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°, which are attributable to the argyrodite-type crystal structure, were confirmed.

[0145] The ionic conductivity was measured by the following method and found to be 1.2 mS / cm. The average particle size was measured by the following method and found to be 3.5 μm (D ５０ ) and the Li used as a raw material ３ P.S. ４ The average particle size of 3.4 μm (D ５０ ) was almost the same as

[0146] (Measurement of Ion Conductivity) In this example, the measurement of ion conductivity was carried out as follows. A 10 mm diameter (cross-sectional area S: 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 100 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 defined 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

[0147] (Powder X-ray Diffraction (XRD) Measurement) In this specification, powder X-ray diffraction (XRD) measurement 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 sealed with Kapton film for XRD and measured under the following conditions without being exposed to air. Measuring device: M03xhf (model number, manufactured by Mac Science Co., Ltd.) Tube voltage: 40 kV Tube current: 40 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: focusing method Slit configuration: divergence slit 0.5°, scattering slit 0.5°, receiving slit 0.3 mm, monochromator used Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.05 deg, 10 seconds / step

[0148] (Average particle size) In this specification, the average particle size was measured as follows. For the powders obtained in the examples and comparative examples, the particle size at a cumulative volume percentage of 50% (D ５０ ) was measured and used as the average particle size.

[0149] (Examples 2 and 3) As Example 2, a sulfide solid electrolyte of Example 2 was obtained in the same manner as Example 1, except that the time for which the temperature of the mixture in Example 1 was maintained at 250°C was changed to 60 minutes. Furthermore, as Example 3, a sulfide solid electrolyte of Example 3 was obtained in the same manner as Example 1, except that the slurry concentration of the mixture in Example 1 was changed from 10% by mass to 5% by mass, and the time for which the temperature was maintained at 250°C was changed to 180 minutes. Note that, when microwave irradiation was performed on the mixture in Example 2, the cumulative irradiation energy during microwave irradiation at an output of 140 W / g or more per unit mass of the raw material content was 107 kW·s / g. Furthermore, the cumulative irradiation energy in Example 3 was 175 kW·s / g. The ionic conductivity, powder X-ray diffraction (XRD), and average particle size of the obtained sulfide solid electrolyte were measured using the methods described above.

[0150] The results of powder X-ray diffraction (XRD) of the sulfide solid electrolytes obtained in Examples 2 and 3 are shown in Figures 2 and 3, respectively. As shown in these figures, it was confirmed that the sulfide solid electrolytes obtained in Examples 2 and 3, like the sulfide solid electrolyte of Example 1, have diffraction peaks at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°, which are derived from an argyrodite-type crystal structure.

[0151] The ionic conductivities were 1.9 mS / cm and 1.3 mS / cm, respectively. The average particle diameters were 3.7 μm (D ５０ ), 3.2 μm (D ５０ ) and the Li used as a raw material ３ P.S. ４ The average particle size of 3.4 μm (D ５０ ) was almost the same as

[0152] (Comparative Examples 1 and 2) The raw material components in Example 1 were mixed without using an organic solvent, and the mixture was left to stand in a 250°C furnace for 30 minutes and 60 minutes, and then removed from the furnace to obtain powders of Comparative Examples 1 and 2, respectively. The obtained powders were subjected to powder XRD diffraction measurements. The results are shown in Figures 4 and 5. As shown in these figures, the powders obtained in Comparative Examples 1 and 2 did not exhibit the diffraction peaks attributable to the argyrodite-type crystal structure that were observed in the powders obtained in the above examples.

[0153] (Comparative Example 3) A powder was obtained in the same manner as in Comparative Example 1, except that the powder was left to stand in a 300°C furnace for 10 minutes. The obtained powder was subjected to powder XRD diffraction measurement. The results are shown in Figure 6. As shown in Figure 6, the powder obtained in Comparative Example 3 did not exhibit any diffraction peaks attributable to an argyrodite-type crystal structure, which were observed in the powders obtained in the above examples.

[0154] (Comparative Example 4) A powder was obtained in the same manner as in Comparative Example 1, except that the powder was left to stand in a 320°C furnace for 60 minutes. The obtained powder was subjected to powder XRD diffraction measurement. The results are shown in Figure 7. As shown in Figure 7, the powder obtained in Comparative Example 4 did not exhibit any diffraction peaks attributable to an argyrodite-type crystal structure, which were observed in the powders obtained in the above Examples.

[0155] (Reference Example) In the above Example 1, microwave irradiation (frequency: 2.45 GHz) was performed under the same conditions as in Example 1, except that only the organic solvent was placed in the microwave irradiation device. As a result, it was confirmed that the mixture was heated to 140° C. Considering that the temperature of the mixture (slurry) containing the raw material ingredients and the organic solvent reached 250° C. in Example 1, it can be seen that the raw material ingredients are preferentially heated by microwave irradiation.

[0156] Example 4 A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the mixture was irradiated with microwaves at an output of 300 W for 465 seconds, and then intermittently irradiated with microwaves at an output of 200 W or less to maintain the temperature of the mixture at 250°C. The cumulative irradiation energy during microwave irradiation at an output of 140 W / g or more per gram of raw material contained in the mixture was 93 kW·s / g. The ionic conductivity of the obtained sulfide solid electrolyte powder was measured in the same manner as in Example 1, and was found to be 0.35 mS / cm, and the average particle size was 2.28 μm (D ５０ ) was.

[0157] Example 5 A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the mixture was irradiated with microwaves at an output of 400 W for 401 seconds, and then intermittently irradiated with microwaves at an output of 200 W or less to maintain the temperature of the mixture at 250°C. The cumulative irradiation energy during microwave irradiation at an output of 140 W / g or more per gram of raw material contained in the mixture was 107 kW·s / g. The ionic conductivity of the obtained sulfide solid electrolyte powder was measured in the same manner as in Example 1, and was found to be 1.9 mS / cm, and the average particle size was 3.68 μm (D ５０ ) was.

[0158] Example 6 A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the mixture was irradiated with microwaves at an output of 300 W for a total of 1,089 seconds in two separate sessions, and then intermittently irradiated with microwaves at an output of 200 W or less to maintain the temperature of the mixture at 250°C. The cumulative irradiation energy per gram of raw material contained in the mixture was 218 kW·s / g. The ionic conductivity of the obtained sulfide solid electrolyte powder was measured in the same manner as in Example 1, and was found to be 1.4 mS / cm, and the average particle size was 2.54 μm (D ５０ ) was.

[0159] According to the production method of this embodiment, a liquid phase method is employed, the heating temperature is reduced, and granulation due to heating is suppressed, thereby enabling efficient production of a sulfide solid electrolyte that maintains particle size. The sulfide solid electrolyte obtained by the production method of this embodiment 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 raw materials containing lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms in an organic solvent to obtain a mixture; subjecting the mixture to microwave irradiation; A method for producing a sulfide solid electrolyte, comprising:

2. 2. The method for producing a sulfide solid electrolyte according to claim 1, wherein the integrated irradiation energy during irradiation of microwaves at an output of 140 W / g or more per unit mass of the raw material contained in the mixture is 1.0 kW s / g or more.

3. 3. The method for producing a sulfide solid electrolyte according to claim 1, wherein the organic solvent has a dielectric loss factor of 10.0 or less at 25°C.

4. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the boiling point of the organic solvent is 50°C or higher.

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

6. 3. The method for producing a sulfide solid electrolyte according to claim 1, wherein the content of the raw material contained in the mixture is 1% by mass or more and 20% by mass or less.

7. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the microwave irradiation is performed and the mixture is heated at 150°C or higher and 360°C or lower.

8. 3. The method for producing a sulfide solid electrolyte according to claim 1, wherein the raw material contains lithium sulfide, phosphorus sulfide, and lithium halide.

9. 3. The method for producing a sulfide solid electrolyte according to claim 1, wherein the sulfide solid electrolyte is a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure.

10. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the raw material inclusions contain a raw material sulfide solid electrolyte as a raw material.

11. Furthermore, a raw material mixture B containing at least two compounds is mixed and pulverized in a solvent to obtain a raw material mixture; and calcining the raw material mixture to obtain the raw material sulfide solid electrolyte. The method for producing the sulfide solid electrolyte according to claim 10.

12. The method for producing a sulfide solid electrolyte according to claim 11, wherein the heating temperature in the calcination is 150°C or higher and 300°C or lower.