Method for producing sulfide solid electrolyte

Abstract

The present invention provides a method for producing a sulfide solid electrolyte, comprising: a first step for obtaining a mixture by mixing raw material-containing substances containing lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms in an organic solvent; a second step in which the mixture is irradiated with microwaves of 0.5-700 W / g and heated to 50-360 DEG C; and a third step in which the mixture is cooled to 20-70 DEG C and the second step and the third step are repeated 2-50 times, whereby the sulfide solid electrolyte can be produced by reducing the heating temperature using a liquid phase method. And can efficiently produce a high-quality sulfide solid electrolyte in which granulation caused by heating is suppressed and the particle size is maintained.

Description

Technical Field

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

[0002] In recent years, with the rapid spread of information-related devices and communication devices such as personal computers, video cameras and mobile phones, the development of batteries used as their power sources has also attracted attention. Among them, lithium-ion batteries have attracted attention due to their high energy density.

[0003] In the past, an electrolyte containing a flammable organic solvent was used in a battery for such a purpose, and therefore, a safety device for suppressing the temperature rise during a short circuit, a structure for preventing a short circuit, and improvements in materials were required. In contrast, by changing the electrolyte to a solid electrolyte and making the battery fully solid, a flammable organic solvent is not used in the battery, and the safety device is simplified, and the manufacturing cost and productivity are excellent, so a battery in which the electrolyte is replaced by a solid electrolyte layer is developed.

[0004] The solid electrolyte manufacturing method used for the solid electrolyte layer is roughly divided into a solid phase method and a liquid phase method. The liquid phase method includes a uniform method in which the solid electrolyte material is completely dissolved in a solvent, and an inhomogeneous method in which the solid electrolyte material is not completely dissolved but a suspension is formed in which solid and liquid coexist.

[0005] For example, as a solid phase method, there is a method of mechanically grinding raw materials such as lithium sulfide and phosphorus pentasulfide using a ball mill, a bead mill, etc., and performing a heat treatment as needed to produce an amorphous or crystalline solid electrolyte (for example, see Patent Document 1). In addition, as a uniform method in a liquid phase method, there is a method of dissolving a solid electrolyte in a solvent and reprecipitating it (for example, see Patent Document 2), and as an inhomogeneous method, there is a method of reacting solid electrolyte raw materials such as lithium sulfide in a solvent containing a polar aprotic solvent (for example, see Patent Documents 3 and 4, Non-Patent Document 1).

[0006] In addition, 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 3 PS 4 The composition of the electrolyte.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: International Publication No. 2017 / 159667

[0010] Patent Document 2: Japanese Patent Application Publication No. 2014-191899

[0011] Patent Document 3: International Publication No. 2014 / 192309

[0012] Patent Document 4: International Publication No. 2018 / 054709

[0013] Patent Document 5: Japanese Patent Application Publication No. 2020-15661

[0014] Non-patent literature

[0015] Non-patent document 1: CHEMISTRY OF MATERIALS, 2017, No. 29, pp. 1830-1835

[0016] Non-patent document 2: Journal of Materials Chemistry A, 2018, No. 6, pp. 21261-21265

[0017] Non-patent document 3: Journal of Materials Chemistry A, 2018, No. 9, pp. 400-405 Summary of the invention

[0018] Technical problem to be solved by the invention

[0019] The present invention has been made in view of such actual conditions, and an object of the present invention is to provide a method for producing a sulfide solid electrolyte, which adopts a liquid phase method, reduces the heating temperature, and can efficiently produce a sulfide solid electrolyte having a high quality by suppressing granulation caused by heating and maintaining the particle size.

[0020] Solutions for solving the above technical problems

[0021] The method for producing the sulfide solid electrolyte of the present invention is:

[0022] A method for producing a sulfide solid electrolyte comprises: a first step of mixing a raw material containing lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms in an organic solvent to obtain a mixture; a second step of irradiating the mixture with microwaves of 0.5 to 700 W / g to heat the mixture to 50 to 360° C.; and a third step of cooling the mixture to 20 to 70° C., and repeating the second step and the third step 2 to 50 times.

[0023] Effects of the Invention

[0024] According to the present invention, a method for producing a sulfide solid electrolyte can be provided, which can reduce the heating temperature by using a liquid phase method, and efficiently produce a sulfide solid electrolyte having high quality while suppressing granulation caused by heating and maintaining the particle size. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 1.

[0026] Figure 2 This is the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 2.

[0027] Figure 3 This is the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 3.

[0028] Figure 4 This is the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Example 4.

[0029] Figure 5 This is an X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Comparative Example 1. DETAILED DESCRIPTION

[0030] Hereinafter, an embodiment of the present invention (hereinafter sometimes referred to as "the present embodiment") is described. In addition, in this specification, the upper and lower limits of the numerical ranges of "above", "below", and "to" are numerical values ​​that can be combined arbitrarily, and the numerical values ​​of the embodiments can also be used as the upper and lower limits.

[0031] (Discovery made by the inventors to complete the present invention)

[0032] The present inventors have conducted intensive studies to solve the above-mentioned technical problems and, as a result, have found the following matters and have completed the present invention.

[0033] The solid phase method has the following characteristics: it is easy to obtain a solid electrolyte with good purity, centered on a solid phase reaction, and thus it is easy to achieve high ion conductivity, but it is not suitable for mass production. In recent years, with the goal of practical application of all-solid batteries, research has been conducted on large-scale industrial production (mass production), and the liquid phase method has attracted attention as a method that can be synthesized simply and in large quantities in addition to its versatility and applicability.

[0034] In the liquid phase method, firing is usually performed for the purpose of increasing the crystallinity of the sulfide solid electrolyte. In particular, in the case of making a sulfide solid electrolyte having an argyrodite-type crystal structure, firing at a high temperature of about 400°C is required. In addition, if such high-temperature firing is performed, the particle size becomes larger than before firing due to granulation, so pulverization is sometimes required, resulting in high cost of the sulfide solid electrolyte. In addition, if high-temperature firing is required, problems such as promoting corrosion of the reaction equipment may sometimes occur, so sometimes the cost of the sulfide solid electrolyte may be increased due to increased equipment costs.

[0035] The present inventors have focused on the following situation: In the conventional methods for producing sulfide solid electrolytes by the liquid phase method disclosed in the above-mentioned Patent Documents 2 to 4 and Non-Patent Document 1, no particular study on firing is conducted, and no mention is made of the problem of granulation and increase in particle size due to high-temperature firing. In addition, in the case of obtaining a sulfide solid electrolyte having an argyrodite-type crystal structure, it can be seen from the conventional methods for producing by the liquid phase method disclosed in these documents and the method for producing by the above-mentioned Non-Patent Document 3 that firing at a high temperature is inevitable.

[0036] Therefore, the inventors of the present invention have conducted in-depth research on the method for producing a sulfide solid electrolyte, especially on the operation of firing, and have found that by subjecting a mixture of raw material contents mixed in an organic solvent to microwave irradiation, the heating temperature can be suppressed to a low level and granulation caused by heating can be suppressed. The reduction in heating temperature not only reduces the energy consumed for heating, but also reduces equipment costs as described above. In addition, granulation caused by heating can be suppressed and the particle size can be maintained, and pulverization after heating is not required, so it is extremely effective in achieving efficiency and cost reduction in manufacturing.

[0037] It can be said that Patent Document 5 and Non-Patent Documents 2 and 3 describe the use of microwave irradiation in a sulfide solid electrolyte. However, in the production methods disclosed in these documents, microwave irradiation is performed using Li 2 S and P 2 S 5 Manufacturing 3 PS 4 In the case of using an electrolyte (lithium thiophosphate) composed of 2,4-dimethyl-1-nitrogen, the material containing halogen atoms is not subjected to microwave irradiation. In addition, although Patent Document 5 and Non-Patent Document 2 describe the manufacture of an amorphous sulfide solid electrolyte by microwave irradiation, a crystalline sulfide solid electrolyte such as one having an argyrodite-type crystal structure is not manufactured. Furthermore, Non-Patent Document 3 describes the microwave irradiation as described above, but also performs sintering at a high temperature.

[0038] Therefore, in view of the conventional production methods, it is a surprising phenomenon that the heating temperature can be lowered and a sulfide solid electrolyte in which granulation due to heating is suppressed and the particle size is maintained can be produced by performing an extremely simple operation such as microwave irradiation instead of the calcination operation in the conventional production methods.

[0039] In this specification, "solid electrolyte" refers to an electrolyte that maintains a solid state at 25°C in a nitrogen atmosphere. The "sulfide solid electrolyte" obtained by the manufacturing method of this embodiment refers to a solid electrolyte containing alkali metal atoms, sulfur atoms, phosphorus atoms and halogen atoms, and having ionic conductivity caused by alkali metal atoms such as lithium atoms. In addition, the above-mentioned "sulfide solid electrolyte" may also contain metal atoms such as Ge, Na, K, Mg, Ca, Al, Si, Sb, Ti, and Zr.

[0040] In this specification, "sulfide solid electrolyte" includes both crystalline sulfide solid electrolyte and amorphous sulfide solid electrolyte. In this specification, crystalline sulfide solid electrolyte refers to a solid electrolyte in which a peak derived from a solid electrolyte is observed in an X-ray diffraction pattern in an X-ray diffraction measurement, and is a material that is independent of whether or not there is a peak derived from a raw material of the solid electrolyte. That is, the crystalline sulfide solid electrolyte includes a crystal structure derived from a solid electrolyte, and a part of it may be a crystal structure derived from the solid electrolyte, or all of it may be a crystal structure derived from the solid electrolyte. In addition, as long as the crystalline sulfide solid electrolyte has the above-mentioned X-ray diffraction pattern, it may also include an amorphous sulfide solid electrolyte (also referred to as a "glass component") in a part thereof. Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte (glass component) to a crystallization temperature or above.

[0041] In this specification, an amorphous sulfide solid electrolyte (glass component) means that in X-ray diffraction measurement, the X-ray diffraction pattern is a halo pattern in which substantially no peaks other than peaks derived from the material are observed, regardless of the presence or absence of peaks derived from the raw materials of the solid electrolyte.

[0042] [Method for producing sulfide solid electrolyte]

[0043] The method for producing a sulfide solid electrolyte according to the first aspect of the present embodiment is as follows:

[0044] A method for producing a sulfide solid electrolyte comprises: a first step of mixing a raw material containing lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms in an organic solvent to obtain a mixture; a second step of irradiating the mixture with microwaves of 0.5 to 700 W / g to heat the mixture to 50 to 360° C.; and a third step of cooling the mixture to 20 to 70° C., and repeating the second step and the third step 2 to 50 times.

[0045] Conventionally, in particular, when manufacturing a crystalline sulfide solid electrolyte, a crystallization step by firing is required. Among them, when manufacturing a sulfide solid electrolyte having an argyrodite-type crystal structure, an extremely high temperature of about 400° C. is required during firing, which may increase equipment costs, increase particle size due to granulation, and energy consumption for heating, as described above. Therefore, the present inventors have focused on heating by microwave irradiation for the firing operation.

[0046] Heating by microwave irradiation is heating that increases the temperature of a target substance by irradiating the target substance with microwaves. The inventors of the present invention considered whether it is possible to suppress the temperature of the reaction system as a whole by selectively heating the raw material content containing a substance that becomes a raw material of a sulfide solid electrolyte and reacting it by making full use of the characteristic of heating the target substance by microwave irradiation. Furthermore, it was considered whether it is possible to suppress the temperature of the reaction system as a whole by selectively heating the raw material content by microwave irradiation in an organic solvent, so that the organic solvent can absorb the heat of the raw material content.

[0047] In addition, the present inventors discovered that if the temperature of the raw material content is only maintained high, the reaction between the solid electrolyte raw materials contained in the raw material content will not proceed sufficiently. During the period when the raw material content is irradiated with a specific high-output microwave, the reaction between the solid electrolyte raw materials will be promoted, thereby completing the present invention.

[0048] The manufacturing method of the present embodiment is a manufacturing method in which a sulfide solid electrolyte can be obtained while lowering the heating temperature, and a sulfide solid electrolyte having a high quality and suppressing granulation caused by heating and maintaining the particle size can be obtained by simply performing an extremely simple operation of irradiating microwaves at a specific output power. Moreover, by lowering the heating temperature, not only can the equipment cost be reduced, but also the energy consumption spent on heating can be reduced. In addition, by suppressing granulation caused by heating and maintaining the particle size, a pulverization process after heating is not required. As a result, the manufacturing method of the present embodiment can achieve efficiency in the manufacture of a sulfide solid electrolyte, achieve low cost, and obtain a sulfide solid electrolyte with high quality.

[0049] The method for producing a sulfide solid electrolyte according to the second aspect of the present embodiment is as follows:

[0050] In the method for producing a sulfide solid electrolyte of the first aspect, after the second step, a heat preservation step of irradiating the mixture with microwaves and maintaining the mixture at a temperature of 80 to 360° C. for 1 to 300 minutes is provided, and then the third step is performed.

[0051] By maintaining the mixture at a predetermined temperature in the heat-retaining step, the reaction between the solid electrolyte raw materials is promoted, and it is expected that a higher-quality sulfide solid electrolyte can be efficiently obtained.

[0052] A method for producing a sulfide solid electrolyte according to a third aspect of the present embodiment is as follows:

[0053] In the method for producing a sulfide solid electrolyte according to the first or second aspect, the organic solvent has a dielectric loss factor of 10.0 or less at 25°C.

[0054] In the third aspect, an organic solvent having a prescribed dielectric loss factor is used as the organic solvent.

[0055] The energy loss of a substance when it is placed in an electromagnetic field generated by microwave irradiation is the sum of the conductive loss, dielectric loss, and magnetic loss. When a liquid is placed in an electromagnetic field generated by microwave irradiation, dielectric loss occurs, and the energy of the electric field is converted into thermal energy to generate heat. In other words, it can be said that the less dielectric loss there is, the more efficiently the energy generated by microwave irradiation can be consumed by the raw material content.

[0056] The dielectric loss factor is a loss factor in a proportional relationship with the dielectric loss, and the dielectric loss factor has the following relationship with the dielectric loss.

[0057] Dielectric loss = πfε 0 ε”|E| 2

[0058] (f: frequency (1 / sec), ε 0 : Dielectric constant of vacuum, ε”: Dielectric loss factor of material, |E|: Electric field (V / m)

[0059] Thus, the dielectric loss factor becomes an index showing 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 content can be heated more selectively, so the sulfide solid electrolyte can be produced more efficiently.

[0060] A fourth method for producing a sulfide solid electrolyte according to the present embodiment is as follows:

[0061] In the method for producing a sulfide solid electrolyte according to any one of the first to third aspects, the boiling point of the organic solvent is 50° C. or higher.

[0062] In the fourth aspect, an organic solvent having a predetermined boiling point is used as the organic solvent.

[0063] The higher the boiling point of the organic solvent, the more the amount of organic solvent volatilization can be suppressed when the raw material content is selectively heated, and the raw material content can be more uniformly maintained in the organic solvent. Therefore, it is easy to selectively heat the raw material content and the amount of organic solvent used can be reduced.

[0064] A method for producing a sulfide solid electrolyte according to a fifth aspect of the present embodiment is as follows:

[0065] In the method for producing a sulfide solid electrolyte according to any one of the first to fourth aspects, the organic solvent is an aromatic solvent.

[0066] In the fifth embodiment, an aromatic solvent, that is, an organic solvent having an aromatic ring is used as the organic solvent.

[0067] Aromatic solvents, which are organic solvents having an aromatic ring, easily satisfy the properties of the second and third embodiments, namely, dielectric loss factor and boiling point, and thus, the sulfide solid electrolyte can be produced more efficiently.

[0068] A sixth method for producing a sulfide solid electrolyte according to the present embodiment is as follows:

[0069] In the method for producing a sulfide solid electrolyte according to any one of the first to fifth aspects, the content of the raw material content contained in the mixture is 1 mass % to 20 mass %.

[0070] In the sixth aspect, the content of the raw material content in the mixture is set to a predetermined range. Since the amount of the organic solvent used can be reduced, the sulfide solid electrolyte can be produced more efficiently.

[0071] A method for producing a sulfide solid electrolyte according to a seventh aspect of the present embodiment is as follows:

[0072] In the method for producing a sulfide solid electrolyte according to any one of the first to sixth aspects, in the second step, the mixture is irradiated with microwaves of 130 to 700 W / g.

[0073] In the seventh aspect, the output power of the microwave irradiated in the second step is set to a predetermined range. According to the seventh aspect, the reaction between the solid electrolyte raw materials is efficiently promoted, and a sulfide solid electrolyte with higher quality can be obtained.

[0074] The method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is as follows:

[0075] In the method for producing a sulfide solid electrolyte according to any one of the first to seventh aspects, in the second step, the mixture is heated to 150 to 360°C.

[0076] A method for producing a sulfide solid electrolyte according to a ninth aspect of the present embodiment is as follows:

[0077] In the method for producing a sulfide solid electrolyte according to any one of the second to eighth aspects, in the heat-retaining step, the mixture is heated to 150 to 360°C.

[0078] In the eighth aspect, the temperature of the mixture is heated to within a prescribed range. In the ninth aspect, the temperature of the mixture is maintained within a prescribed range.

[0079] As described above, for example, when a sulfide solid electrolyte having an argyrodite type crystal structure is to be produced, the conventional production method requires sintering at a high temperature of about 400° C. However, according to the production method of the present embodiment, a sulfide solid electrolyte having an argyrodite type crystal structure can be produced even under low temperature conditions of 150° C. to 360° C.

[0080] A method for producing a sulfide solid electrolyte according to a tenth aspect of the present embodiment is as follows:

[0081] In the method for producing a sulfide solid electrolyte according to any one of the first to ninth aspects, in the temperature-retaining step, the mixture is maintained at the temperature for 1 to 240 minutes.

[0082] In the tenth aspect, the time for maintaining the temperature of the mixture in the heat-retaining step within the range is set within a predetermined range. By setting the time for maintaining the temperature of the mixture within the predetermined range, a sulfide solid electrolyte having excellent quality can be produced more efficiently.

[0083] The method for producing a sulfide solid electrolyte according to an eleventh aspect of the present embodiment is as follows:

[0084] In the method for producing a sulfide solid electrolyte according to any one of the first to tenth aspects, the second step and the third step are repeated 2 to 20 times.

[0085] In the eleventh embodiment, the number of times the second step and the third step are repeated is set within a predetermined range from the viewpoint of both productivity and quality of the sulfide solid electrolyte. The method for producing a sulfide solid electrolyte according to the twelfth embodiment of the present embodiment is,

[0086] In the method for producing a sulfide solid electrolyte according to any one of the first to eleventh aspects, the sulfide solid electrolyte is a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure.

[0087] In the twelfth embodiment, the obtained sulfide solid electrolyte is a sulfide solid electrolyte having an argyrodite crystal structure. As described above, according to the conventional manufacturing method, the sulfide solid electrolyte having an argyrodite crystal structure needs to be fired at a high temperature of about 400°C. However, according to the manufacturing method of this embodiment, the heating temperature can be reduced to 50°C or more and 360°C or less. That is, in the case of manufacturing a sulfide solid electrolyte having an argyrodite crystal structure, the advantages of the manufacturing method of this embodiment can be more flexibly utilized.

[0088] [Get the mixture]

[0089] The production method of this embodiment includes mixing raw material contents including lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms in an organic solvent to obtain a mixture. The following describes how to obtain the mixture starting from the raw material contents.

[0090] (Ingredients contained in raw materials)

[0091] The raw material content includes lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms. As the raw material content, there is no particular limitation as long as it is a substance containing these atoms, and examples include substances containing alone or containing multiple substances containing at least one atom selected from these atoms as the raw material content. It is preferred to contain two or more substances selected from the following substances: a substance containing at least one atom selected from lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms. Therefore, the sulfide solid electrolyte obtained by the manufacturing method of this embodiment contains lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms.

[0092] The material that can be used as the raw material is a material containing at least one of a lithium atom, a phosphorus atom, a sulfur atom and a halogen atom. More specifically, representative examples include: alkali metal sulfides such as lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; sodium halides such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; phosphorus trisulfide (P 2 S 3 ), phosphorus pentasulfide (P 2 S 5 ) and other phosphorus sulfides; various phosphorus fluorides (PF 3 PF 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 other phosphorus halides; thiophosphoryl fluoride (PSF 3 ), thiophosphoryl chloride (PSCl 3 ), thiophosphoryl bromide (PSBr 3 ), phosphoryl iodide (PSI 3 ), thiophosphoryl fluoride dichloride (PSCl 2 F), thiophosphoryl fluoride dibromide (PSBr 2 F) and other thiophosphoryl halides; compounds consisting of at least two elements selected from the above four elements; fluorine (F 2 ), chlorine (Cl 2 ), bromine (Br 2 ), iodine (I 2 ) and other halogen monomers, preferably bromine (Br 2 ), iodine (I 2 ).

[0093] Examples of compounds other than the above that can be used as raw materials include compounds containing at least one atom selected from the above four atoms and atoms other than the four atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS, SnS 2 ), aluminum sulfide, zinc sulfide and other metal sulfides; phosphoric acid compounds such as sodium phosphate and lithium phosphate; aluminum halide, silicon halide, germanium halide, arsenic halide, selenium halide, tin halide, antimony halide, tellurium halide, bismuth halide and other metal halides; phosphorus oxychloride (POCl 3 ), phosphorus oxybromide (POBr 3 ) and other halogen phosphorus oxides; etc.

[0094] In this embodiment, the halogen atom can be changed according to the desired sulfide solid electrolyte and cannot be generalized, but from the viewpoint of more easily obtaining a sulfide solid electrolyte with high ion conductivity, chlorine atoms, bromine atoms, and iodine atoms are preferred among the halogen atoms. In addition, these atoms can be used alone or in combination of multiple types.

[0095] In addition, for example, when it is desired to obtain a sulfide solid electrolyte having a sulfide crystalline lithium superion conductor region type II crystal structure as described later, bromine atoms and iodine atoms are more preferred. Furthermore, when it is desired to obtain a sulfide solid electrolyte having an argyrodite type crystal structure, chlorine atoms and bromine atoms are more preferred.

[0096] In this embodiment, from the viewpoint of more easily obtaining a sulfide solid electrolyte having high ion conductivity, among the above-mentioned substances, preferred materials for use as raw materials are alkali metal sulfides such as lithium sulfide and sodium sulfide, phosphorus trisulfide (P 2 S 3 ), phosphorus pentasulfide (P 2 S 5 ) and other phosphorus sulfides, fluorine (F 2 ), chlorine (Cl 2 ), bromine (Br 2 ), iodine (I 2 ) and other halogen monomers, lithium fluoride, lithium chloride, lithium bromide, lithium iodide and other lithium halides, lithium sulfide is preferred among the alkali metal sulfides, and phosphorus pentasulfide is preferred among the phosphorus sulfides.

[0097] As described above, the raw material containing halogen atoms cannot be generalized because it can be changed according to the desired sulfide solid electrolyte. However, among the halogen monomers, chlorine (Cl 2 ), bromine (Br 2 ), iodine (I 2 ), lithium chloride, lithium bromide, and lithium iodide are preferred among the lithium halides. Furthermore, when a sulfide solid electrolyte having a type II crystal structure in the sulfide crystalline lithium superion conductor region is desired, bromine (Br 2 ), iodine (I 2 ), lithium bromide and lithium iodide are more preferred as lithium halides. In addition, when a sulfide solid electrolyte having an argyrodite-type crystal structure is desired, chlorine (Cl 2 ), bromine (Br 2 ), as the lithium halide, lithium chloride and lithium bromide are more preferred.

[0098] As a combination of substances that can be used as raw materials, a combination of lithium sulfide, phosphorus sulfide and lithium halide, a combination of lithium sulfide, phosphorus sulfide and a halogen monomer is preferred, and a combination of lithium sulfide, phosphorus sulfide and lithium halide is more preferred. Here, phosphorus pentasulfide is preferred as phosphorus sulfide, and lithium halide and halogen monomer can be selected according to the desired sulfide solid electrolyte as described above.

[0099] In addition, in the present embodiment, as the compound that can be used as the raw material, preferably, there can be mentioned PS 4 Unit Li 3 PS 4 In the sulfide solid electrolyte obtained by the production method of this embodiment, Li 3 PS 4As a raw material, a structure containing lithium such as lithium sulfide is used as a raw material, thereby, compared with the case where a sulfide solid electrolyte is synthesized by a reaction between the compounds as a raw material, the composition ratio of the structure can be increased, that is, the PS can be increased. 4 fraction, and high ionic conductivity can be obtained.

[0100] In the present embodiment, as the sulfide solid electrolyte that can be used as the raw material compound (hereinafter also referred to as "raw material sulfide solid electrolyte"), preferably, there can be mentioned Li 3 PS 4 Amorphous sulfide solid electrolyte (also called "amorphous Li 3 PS 4 ”), or crystalline sulfide solid electrolyte (also known as “crystalline Li 3 PS 4 ”) etc. In addition, an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte having a structure containing halogen atoms, which will be described later as an “amorphous sulfide solid electrolyte”, and a precursor thereof (such as a “calcined product” described later) can also be used.

[0101] In addition, in order to obtain high ion conductivity, the raw material sulfide solid electrolyte preferably does not contain Li 4 P 2 S 7 Amorphous or crystalline sulfide solid electrolytes of structure. These raw material sulfide solid electrolytes can use solid electrolytes produced by conventional production methods such as mechanical grinding, slurry method, melt quenching method, etc., or commercial products can be used. In addition, solid electrolytes produced by a solution method synthesized by completely dissolving the raw materials can also be used.

[0102] The sulfide solid electrolyte used as a raw material (raw material sulfide solid electrolyte) may be amorphous, crystalline, or a sulfide solid electrolyte containing an amorphous sulfide solid electrolyte and a crystalline sulfide solid electrolyte. In any case, when a compound containing halogen atoms is used as a raw material, the dispersibility of the halogen atoms is improved, and the halogen atoms are easily bonded to the lithium atoms, sulfur atoms, and phosphorus atoms in the solid electrolyte, resulting in a sulfide solid electrolyte having higher ion conductivity.

[0103] In the present embodiment, when lithium sulfide is used as a raw material, the lithium sulfide is preferably in the form of particles.

[0104] The average particle size of lithium sulfide particles (D 50) is preferably 10 μm to 2000 μm, more preferably 30 μm to 1500 μm, and even more preferably 50 μm to 1000 μm. In this specification, the average particle size (D 50 ) is the particle size when the particle size distribution cumulative curve is drawn from the smallest particle to 50% of the total, and the volume distribution is, for example, the average particle size that can be measured using a laser diffraction / scattering particle size distribution measuring device. In addition, among the raw materials exemplified as the above raw materials, the solid raw material preferably has an average particle size of the same degree as the above lithium sulfide particles, that is, the average particle size is preferably within the same range as the average particle size of the above lithium sulfide particles. The particle size of the compound as the raw material can be adjusted by pulverization or the like as needed.

[0105] When lithium sulfide, phosphorus pentasulfide and lithium halide are used as raw materials, the ratio of lithium sulfide to the total of lithium sulfide and phosphorus pentasulfide varies depending on the desired sulfide solid electrolyte and cannot be generalized, but is preferably 60 mol% or more, more preferably 65 mol% or more, and further preferably 68 mol% or more, from the viewpoint of obtaining higher chemical stability and high ion conductivity, and the upper limit is preferably 85 mol% or less, more preferably 83 mol% or less, and further preferably 80 mol% or less.

[0106] When lithium sulfide, phosphorus pentasulfide, lithium halide, and other raw materials used as needed are used, the content of lithium sulfide and phosphorus pentasulfide relative to the total of these is preferably 55 mol% or more, more preferably 58 mol% or more, and further preferably 60 mol% or more. The upper limit is preferably 100 mol% or less, more preferably 90 mol% or less, further preferably 80 mol% or less, and further preferably 70 mol% or less.

[0107] When lithium bromide and lithium iodide are used in combination as the lithium halide, from the viewpoint of obtaining high ion 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, further preferably 40 mol% or more, further preferably 50 mol% or more, and the upper limit is preferably 99 mol% or less, more preferably 90 mol% or less, further preferably 80 mol% or less, further preferably 70 mol% or less.

[0108] 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.

[0109] [Organic solvents]

[0110] In the production method of this embodiment, the above-mentioned raw material content is mixed in an organic solvent. As the solvent used for mixing the raw material content, various solvents called organic solvents can be widely used.

[0111] As the solvent, a wide range of solvents conventionally used in the production of solid electrolytes can be adopted, and examples thereof include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

[0112] Examples of aliphatic hydrocarbons include saturated aliphatic hydrocarbons such as pentane, hexane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane and tridecane, and unsaturated aliphatic hydrocarbons such as pentene and hexene corresponding to the above saturated aliphatic hydrocarbons. Examples of alicyclic hydrocarbons include saturated alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, and unsaturated aliphatic hydrocarbons such as cyclohexene and methylcyclohexene corresponding to the above saturated alicyclic hydrocarbons.

[0113] Examples of the aromatic hydrocarbon solvent include benzene, toluene, xylene, mesitylene, ethylbenzene, tert-butylbenzene, biphenyl, naphthalene, tetralin (tetrahydronaphthalene, cyclohexylbenzene), and anthracene.

[0114] In addition to the above-mentioned hydrocarbon solvents, there may be mentioned solvents containing atoms other than carbon atoms and hydrogen atoms, for example, heteroatoms such as nitrogen atoms, oxygen atoms, sulfur atoms and halogen atoms.

[0115] As the solvent containing an oxygen atom as a hetero atom, for example, in addition to ether solvents and ester solvents, alcohol solvents, aldehyde solvents and ketone solvents can be preferably exemplified.

[0116] As the ether solvent, for example, preferably there can be mentioned aliphatic ethers such as dimethyl ether, diethyl ether, tert-butyl methyl ether, dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) or diethylene glycol, triethylene glycol; alicyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane; heterocyclic ethers such as furan, benzofuran, benzopyran; aromatic ethers such as methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, diphenyl ether (diphenyl ether).

[0117] As the ester solvent, for example, preferably exemplified are methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate; aliphatic esters such as methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate; alicyclic esters such as methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, dimethyl cyclohexanedicarboxylate; heterocyclic esters such as methyl pyridinecarboxylate, methyl pyrimidinecarboxylate, acetyl lactone, propiolactone, butyrolactone, valerolactone; aromatic esters such as methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, trimethyl trimellitate, triethyl trimellitate.

[0118] In addition, preferably, there can be mentioned alcohol solvents such as ethanol and butanol; aldehyde solvents such as formaldehyde, acetaldehyde and dimethylformamide; ketone solvents such as acetone and methyl ethyl ketone.

[0119] Examples of the solvent containing a nitrogen atom as a hetero atom include solvents having a group containing a nitrogen element such as an amino group, an amide group, a nitro group or a nitrile group.

[0120] For example, as solvents having an amino group (amine solvents), preferably exemplified are 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, picoline, dimethylpyridine, methylethylpyridine, piperazine, dipiperidylpropane, and dimethylpiperazine; aromatic amines such as phenylenediamine, toluenediamine, naphthalenediamine, methylphenylenediamine, dimethylnaphthalenediamine, dimethylphenylenediamine, tetramethylphenylenediamine, tetramethylnaphthalenediamine, and dimethylaniline.

[0121] In addition, as solvents having a nitrile group (nitrile solvents), preferably acetonitrile, propionitrile, 3-chloropropionitrile, benzonitrile, 4-fluorobenzonitrile, tert-butylnitrile, isobutylnitrile, acrylonitrile, cyclohexanenitrile, capronitrile, isocronitrile, malononitrile, fumaronitrile and the like are mentioned, and preferably solvents containing nitrogen atoms such as dimethylformamide and nitrobenzene are mentioned.

[0122] As the solvent containing a halogen atom as a hetero atom, preferably, dichloromethane, chlorobenzene, trifluorotoluene, chlorobenzene, chlorotoluene, bromobenzene and the like are exemplified.

[0123] Furthermore, as the solvent containing a sulfur atom, dimethyl sulfoxide, carbon disulfide, etc. can be preferably exemplified.

[0124] Regarding the amount of the organic solvent used, the amount used is such that the total amount of the raw material content relative to the total amount of the raw material content and the organic solvent is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, and further preferably 8% by mass or more, and the upper limit is preferably 20% by mass or less, more preferably 17% by mass or less, further preferably 15% by mass or less, and further preferably 12% by mass or less. If the amount of the organic solvent used is within the above range, it is easy to uniformly maintain the raw material content in the organic solvent, so it is easy to selectively heat the raw material content by microwave irradiation, and the sulfide solid electrolyte can be produced more efficiently.

[0125] (Dielectric loss factor and boiling point of organic solvents)

[0126] As the organic solvent used in the manufacturing method of the present embodiment, among the above organic solvents, an organic solvent having a dielectric loss factor of 10.0 or less at 25°C is preferred. This is because, by using an organic solvent having a dielectric loss factor of 10.0 or less, the raw material content can be heated more selectively, so the sulfide solid electrolyte can be manufactured more efficiently. From this point of view, the dielectric loss factor of the organic solvent is more preferably 8.0 or less, further preferably 5.0 or less, further preferably 1.0 or less, and particularly preferably 0.5 or less. There is no particular restriction as the lower limit, and it is usually 0.01 or more.

[0127] The dielectric loss factor in this specification is a dielectric loss factor at 2.45 GHz and 25° C., and is a measured value measured based on a conventional method. For example, the dielectric loss factor can be calculated by measuring the relative dielectric constant and the dielectric loss tangent using a dielectric constant measuring device (e.g., an LCR meter, an impedance material analyzer, a network analyzer, a TDR measuring device, a pulse THz spectroscopy, and other various devices).

[0128] As the organic solvent used in the production method of the present embodiment, among the above-mentioned organic solvents, an organic solvent having a boiling point of 50°C or higher is preferred. This is because if the boiling point is 50°C or higher, the amount of organic solvent volatilization 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, so it is easy to selectively heat the raw material content, and the amount of organic solvent used can be reduced. From such a viewpoint, the boiling point of the organic solvent is more preferably 65°C or higher, more preferably 75°C or higher, more preferably 100°C or higher, and particularly preferably 200°C or higher.

[0129] Among the above-mentioned organic solvents, aromatic solvents with aromatic rings 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 with amino groups (amine solvents), and solvents containing halogen atoms are more preferred, and aromatic solvents with aromatic rings are particularly preferred. These organic solvents are organic solvents that easily meet the above-mentioned dielectric loss factor and boiling point conditions, and are easy to selectively heat the raw material content, and can more efficiently produce sulfide solid electrolytes.

[0130] As the aromatic solvent, it is preferred to select from aromatic hydrocarbon solvents and aromatic ethers, more preferably aromatic ethers. In addition, as the aromatic hydrocarbon solvent, preferably benzene, toluene, xylene, biphenyl, naphthalene, tetralin (tetralin, cyclohexylbenzene), in addition, as the aromatic ether, preferably diphenyl ether (diphenyl ether).

[0131] As the aliphatic hydrocarbon, pentane and hexane are preferred, and as the alicyclic hydrocarbon, cyclohexane is preferred.

[0132] As the ether solvent (excluding the above aromatic ether solvents), aliphatic ethers and alicyclic ethers are preferred, and diethyl ether and tetrahydrofuran are preferred. As the ester solvent (excluding the above aromatic ester solvents), aliphatic esters are preferred, and ethyl acetate is preferred.

[0133] As the solvent having an amino group (amine solvent), aliphatic amines and heterocyclic amines are preferred, and among them, triethylamine and pyridine are preferred.

[0134] Furthermore, as the solvent containing a halogen atom, dichloromethane is preferred.

[0135] [1st step]

[0136] The first step is a step of mixing the raw material contents in the organic solvent to obtain a mixture. The mixture thus obtained becomes a slurry (suspension) in which the raw material contents are dispersed in the organic solvent. By mixing to obtain a mixture, the raw material contents can be more uniformly maintained in the organic solvent, so that the raw material contents can be selectively heated easily, and the sulfide solid electrolyte can be efficiently produced.

[0137] The first step can be carried out, for example, using a mixer. In addition, a stirrer, a pulverizer, etc. can also be used. This is because even if a stirrer is used, the raw materials can be mixed, and the pulverizer can be used to pulverize the raw materials while mixing them. That is, it can also be said that the mixture is a substance obtained by stirring, mixing, pulverizing or any combination of the raw material contents in an organic solvent.

[0138] In the manufacturing method of this embodiment, mixing can be carried out using any of a stirrer, a mixer, and a pulverizer, but from the viewpoint of efficiently obtaining a slurry (suspension) in which the raw material-containing substance is dispersed in an organic solvent, it is preferred to use any of a stirrer and a mixer, and it is more preferred to use a mixer.

[0139] As agitators and mixers, for example, a mechanical stirring mixer having stirring blades in a reaction tank and capable of stirring (also referred to as mixing brought by stirring, stirring and mixing) can be exemplified. As mechanical stirring mixers, high-speed stirring mixers, double-arm mixers, etc. can be exemplified. In addition, as high-speed stirring mixers, vertical axis rotating mixers, horizontal axis rotating mixers, etc. can be exemplified, and any type of mixer can also be used.

[0140] The shape of the stirring blade used in the mechanical stirring mixer may be a blade type, an arm type, an anchor type, a paddle type, a stirring paddle type, a belt type, a multi-stage blade type, a double-arm type, a bucket type, a double-shaft blade type, a flat blade type, a C-blade type, etc. From the viewpoint of more efficiently promoting the reaction of the raw materials, a bucket type, a flat blade type, a C-blade type, an anchor type, a paddle type, a stirring paddle type is preferred, and an anchor type, a paddle type, a stirring paddle type is more preferred.

[0141] When a mechanical stirring mixer is used, the rotation speed of the stirring blade can be appropriately adjusted according to the capacity, temperature, shape of the stirring blade, etc. of the fluid in the reaction tank, without any particular limitation, and is usually set to about 5 rpm to about 400 rpm. From the viewpoint of more efficiently promoting the reaction of the raw materials, it is preferably 10 rpm to 300 rpm, more preferably 15 rpm to 250 rpm, and further preferably 20 rpm to 200 rpm.

[0142] The temperature conditions for mixing 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 further preferably 10 to 60° C. The mixing time is usually 0.1 to 500 hours, and is preferably 1 to 450 hours, more preferably 10 to 425 hours, further preferably 20 to 400 hours, and further preferably 40 to 375 hours from the viewpoint of making the dispersion state of the raw materials more uniform and promoting the reaction.

[0143] As the pulverizer, for example, a media type pulverizer using pulverizing media can be used.

[0144] The media pulverizer is roughly divided into a container-driven pulverizer and a media-stirring pulverizer. As the container-driven pulverizer, a stirring tank, a crushing tank, or a ball mill or a bead mill in which these are combined can be cited. In addition, as the media-stirring pulverizer, there can be cited: impact pulverizers such as a cutter mill, a hammer mill, and a pin mill; tower-type pulverizers such as a tower mill; stirring tank-type pulverizers such as a grinder, a wet sand mill (aquamizer), and a sand mill; flow-through trough-type pulverizers such as a viscose mill and a coarse crusher; flow-through tube-type pulverizers; annular pulverizers such as a combined ball mill; a continuous dynamic pulverizer; various pulverizers such as a single-shaft or multi-shaft kneading machine. Among them, if the ease of adjusting the particle size of the obtained sulfide is considered, the ball mill and bead mill exemplified as the container-driven pulverizer are preferred, and a planetary pulverizer is preferred.

[0145] These pulverizers can be appropriately selected according to the desired scale, etc. For a relatively small scale, a container-driven pulverizer such as a ball mill or a bead mill can be used. In the case of large-scale or mass production, other types of pulverizers can also be used.

[0146] Furthermore, as described later, when the mixture is in a liquid state accompanied with a liquid such as a solvent or in a slurry state during mixing, a wet pulverizer capable of wet pulverization is preferred.

[0147] As wet pulverizers, wet bead mills, wet ball mills, wet vibration mills, etc. can be representatively cited. From the perspective of being able to freely adjust the conditions of the pulverization operation and being easy to handle materials with smaller particle sizes, wet bead mills using beads as pulverization media are preferred. In addition, dry pulverizers such as dry bead mills, dry ball mills, dry vibration mills, and dry non-media pulverizers such as jet mills can also be used.

[0148] In addition, when the object to be mixed is in a liquid state or a slurry state, a flow-through pulverizer can be used, which can be circulated as needed. Specifically, a pulverizer that circulates between a pulverizer (pulverizing mixer) for pulverizing slurry and a temperature-maintaining tank (reaction container) can be cited.

[0149] The size of the beads or balls used in the above-mentioned ball mill or bead mill can be appropriately selected according to the desired particle size, processing volume, 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, and the upper limit is usually 5.0 mmφ or less, preferably 3.0 mmφ or less, and more preferably 2.0 mmφ or less. In addition, the diameter of the balls is usually 2.0 mmφ or more, preferably 2.5 mmφ or more, and more preferably 3.0 mmφ or more, and the upper limit is usually 20.0 mmφ or less, preferably 15.0 mmφ or less, and more preferably 10.0 mmφ or less.

[0150] In addition, examples of the material include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconium oxide and silicon nitride; and minerals such as agate.

[0151] When a ball mill or a bead mill is used, the rotation speed cannot be generally specified because it varies according to the scale of treatment, but is usually 10 rpm or more, preferably 20 rpm or more, and more preferably 50 rpm or more, and the upper limit is usually 1,000 rpm or less, preferably 900 rpm or less, more preferably 800 rpm or less, and further preferably 700 rpm or less.

[0152] The pulverization time in this case cannot be generally stated because it varies depending on the scale of treatment, but is usually 0.5 hours or more, preferably 1 hour or more, more preferably 5 hours or more, and further preferably 10 hours or more, and the upper limit is usually 100 hours or less, preferably 72 hours or less, more preferably 48 hours or less, and further preferably 36 hours or less.

[0153] By selecting the size and material of the medium (beads, balls) used, the rotation speed and time of the rotor, etc., mixing, stirring, pulverization, or any combination of these can be performed, and the particle size of the obtained sulfide can be adjusted.

[0154] The content of the raw material content contained in the mixture obtained by mixing is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, and further preferably 8% by mass or more, and the upper limit is preferably 20% by mass or less, more preferably 17% by mass or less, further preferably 15% by mass or less, and further preferably 12% by mass or less. If the content of the raw material content is within the above range, it is easy to uniformly maintain the raw material content in the organic solvent, so it is easy to selectively heat the raw material content by microwave irradiation, and the sulfide solid electrolyte can be produced more efficiently.

[0155] [Step 2]

[0156] In the second step, the mixture obtained in the first step is irradiated with microwaves at 0.5 to 700 W / g to heat to 50 to 360° C. By irradiating the mixture containing the raw material content and the organic solvent with microwaves, the raw material content is selectively heated, and the reaction between the solid electrolyte raw materials is promoted.

[0157] As a microwave generating device for irradiating microwaves, for example, an irradiation device including a high-frequency oscillator for oscillating microwaves can be used, and if the scale is small, a commercially available microwave oven or the like can also be used.

[0158] There is no particular limitation on the frequency of the microwave as long as it is within the range of about 0.3 GHz to about 3000 GHz. Taking into account more efficient heating of the raw material contents and the ease of obtaining a microwave generating device, the frequency is preferably above 0.5 GHz, more preferably above 1.0 GHz, and further preferably above 1.5 GHz. The upper limit is preferably below 100 GHz, more preferably below 10.0 GHz, and further preferably below 6.0 GHz.

[0159] 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. However, in consideration of more efficient heating of the raw material contents, the output power needs to be 0.5 to 700 W / g, preferably 60 W / g or more, more preferably 100 W / g or more, and further preferably 130 W / g or more. The upper limit needs to be 700 W / g or less, more preferably 300 W / g or less, and further preferably 280 W / g or less.

[0160] The microwave irradiation time in the second step may be any time that can raise the temperature of the mixture to 50 to 360° C., and may vary depending on the type of organic solvent contained in the mixture to be irradiated with microwaves, the amount of the mixture, etc., and cannot be generalized, but is preferably 1 minute or more, more preferably 2 minutes or more, and even more preferably 3 minutes or more, and the upper limit is preferably 360 minutes or less, more preferably 300 minutes or less, and even more preferably 240 minutes or less.

[0161] The heating temperature by microwave irradiation can be changed according to the composition of the desired sulfide solid electrolyte, whether an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte is desired, and cannot be generalized, but the temperature of the mixture is 50 to 360°C, preferably 150°C or more, more preferably 200°C or more, and further preferably 230°C or more, and the upper limit is preferably 350°C or less, more preferably 310°C or less, and further preferably 275°C or less.

[0162] The heating temperature by microwave irradiation can be changed according to the composition of the desired sulfide solid electrolyte, and whether it is amorphous or crystalline, as described above. That is, whether an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte is produced can be controlled by the heating temperature by microwave irradiation.

[0163] For example, the temperature required for crystallization of the obtained raw material sulfide solid electrolyte, that is, the temperature of the peak top of the exothermic peak observed on the lowest temperature side by differential thermal analysis (DTA) of the amorphous sulfide solid electrolyte under the condition of a temperature increase of 10°C / min using a differential thermal analyzer (DTA device) is defined as the crystallization temperature. Then, if the temperature of the raw material content in the mixture obtained by the above mixing as the heating target by microwave irradiation is heated to a temperature higher than the crystallization temperature, a crystalline sulfide solid electrolyte can be obtained, and if the temperature is heated to a temperature lower than the crystallization temperature, an amorphous sulfide solid electrolyte can be obtained.

[0164] In the case of 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 content is preferably 5° C. or more, more preferably 10° C. or more, and further preferably 20° C. or more relative to the crystallization temperature. The upper limit is not particularly limited, but may be about 40° C. or less.

[0165] On the other hand, in the case of producing an amorphous sulfide solid electrolyte, from the viewpoint of obtaining an amorphous sulfide solid electrolyte more stably and efficiently, the temperature of the raw material content is preferably 5°C or less, more preferably 10°C or less, and further preferably 20°C or less relative to the crystallization temperature and is 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, and can be, for example, the temperature of the peak top of the exothermic peak observed on the lowest temperature side is about -40°C or more.

[0166] In the manufacturing method of this embodiment, since the raw material content is selectively heated as described above, it can be considered that the temperature of the raw material content itself is higher than the temperature of the organic solvent (which can be considered to be the same as the temperature of the mixture). Therefore, in the manufacturing method of this embodiment, the temperature of the mixture obtained by the above mixing can be grasped, and the temperature of the raw material content in the mixture is indirectly grasped based on the temperature of the mixture.

[0167] According to the examples described below, by setting the temperature of the mixture to 250°C, a sulfide solid electrolyte having an argyrodite type crystal structure can be obtained. Considering that the sulfide solid electrolyte having an argyrodite type crystal structure requires sintering at a high temperature of about 400°C according to the conventional method as described above, it can be considered that the temperature of the raw material content itself is about the temperature of the mixture + 150°C. Strictly speaking, although the heating temperature can also be changed depending on the type of organic solvent in the mixture, its content, etc., the temperature of the raw material content itself can be used as a reference to determine whether the crystallization temperature has been reached, and thus the heating temperature can be set.

[0168] [Heat preservation process]

[0169] In the production method of this embodiment, after performing the second step, a heat preservation step may be further included, and then the third step may be performed.

[0170] In the heat preservation step, the mixture is irradiated with microwaves and maintained at a temperature of 80 to 360° C. for 1 to 300 minutes. More specifically, the temperature setting is the same as in the second step. In the heat preservation step, the temperature of the mixture may be varied within the range of 80 to 360° C., but is preferably maintained within a range of ±20° C., more preferably within a range of ±10° C., with the target temperature in the second step as the center.

[0171] In addition, the irradiation time of microwaves in the heat-retaining step is 1 minute or more, preferably 2 minutes or more, more preferably 3 minutes or more, and the upper limit is 300 minutes or less, preferably 240 minutes or less, more preferably 210 minutes or less, further preferably 190 minutes or less, and further preferably 180 minutes or less.

[0172] The output of the microwaves irradiated in the heat-retaining step is preferably about 0 to 133 W / g, more preferably about 0 to 100 W / g, and the irradiation may be intermittent.

[0173] [Step 3]

[0174] In the third step, the mixture is cooled to 20 to 70° C. The mixture is temporarily cooled and then irradiated with microwaves of a predetermined high output in the second step again, thereby suppressing problems such as granulation caused by excessive heating and promoting the reaction between the solid electrolyte raw materials.

[0175] The mixture may be cooled by keeping it at room temperature, or by actively cooling the container holding the mixture by bringing it into contact with a heat medium such as water. Alternatively, the reaction container may be cooled by blowing air directly into it.

[0176] [Repetition of the second and third steps]

[0177] In the manufacturing method of this embodiment, the second step, the heat preservation step and the third step, which are provided as needed, need to be repeated 2 to 50 times, preferably 2 to 20 times, and more preferably 3 to 10 times. In addition, the number of repetitions of the second step and the third step is a value that is counted for the first time.

[0178] By repeating these steps, the quality of the sulfide solid electrolyte obtained by promoting the reaction between the solid electrolyte raw materials in the second step is improved, and granulation due to heating in the third step can be suppressed.

[0179] The temperature conditions, time, etc. of the second step, the heat preservation step provided as necessary, and the third step in each repeated process may be the same or different, but are preferably the same in consideration of ease of operation.

[0180] [dry]

[0181] The manufacturing method of this embodiment may further include drying the fluid obtained by repeating the above-mentioned second step, the heat preservation step provided as needed, and the fourth step. The obtained fluid contains the sulfide solid electrolyte generated by microwave irradiation, the residual organic solvent, etc., and usually becomes a slurry (suspension). Therefore, by drying the fluid, a powder of the sulfide solid electrolyte can be obtained.

[0182] The fluid obtained by irradiating the mixture with microwaves can be dried at a temperature corresponding to the type of the solvent.

[0183] Furthermore, the drying can be performed by drying under reduced pressure (vacuum drying) using a vacuum pump or the like at usually 5 to 200°C, preferably 10 to 180°C, and more preferably 15 to 160°C to volatilize the solvent.

[0184] The fluid may be dried by filtration using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge or the like.

[0185] Drying can be performed 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 performed after filtration or solid-liquid separation.

[0186] [Manufacturing of raw materials contained in raw material contents]

[0187] As the raw material contained in the raw material content, as described above, Li 3 PS 4The following is a method for producing a sulfide solid electrolyte (raw material sulfide solid electrolyte) used in a raw material containing material, mainly focusing on a sulfide solid electrolyte having Li 3 PS 4 The structure will be described as a sulfide solid electrolyte (lithium thiophosphate) having a molecular structure.

[0188] As described above, the raw material sulfide solid electrolyte can be produced by conventional production methods such as mechanical grinding, slurry method, and melt quenching method. Preferably, it can be produced by the following production method, which includes:

[0189] A raw material mixture is obtained by mixing and pulverizing a raw material content containing at least two compounds in a solvent;

[0190] The raw material mixture is pre-calcined to obtain a pre-calcined product.

[0191] (Ingredients contained in raw materials)

[0192] As a raw material containing at least two compounds (in order to distinguish from the raw material containing material used in the above-mentioned first step, the raw material containing material used in the first step is referred to as "raw material containing material A", and the raw material containing material used in "manufacturing of raw materials contained in the raw material containing material" is referred to as "raw material containing material B"), it is preferred to use raw material containing material B containing raw material compounds, namely lithium sulfide and phosphorus sulfide, and phosphorus pentasulfide is preferred as phosphorus sulfide. The amount of lithium sulfide and phosphorus sulfide used can be appropriately determined according to the desired sulfide solid electrolyte. When lithium sulfide and phosphorus pentasulfide are used to obtain a sulfide solid electrolyte having Li 3 PS 4 In the case of a sulfide solid electrolyte having a structure of 3:1, it may be used in a molar ratio of 3:1.

[0193] In addition, when it is desired to obtain another sulfide solid electrolyte, it can be used in a molar ratio corresponding to the sulfide solid electrolyte. In addition, when it is desired to obtain a sulfide solid electrolyte containing halogen atoms, a compound as a raw material containing halogen atoms corresponding thereto can be used. The molar ratio corresponding to the sulfide solid electrolyte, the compound as the raw material used, etc. are the same as the description of the raw material content A described above.

[0194] The compound contained in the raw material content B may be pulverized before use. The pulverization may be carried out using any pulverizer described as being usable in the step of obtaining the mixture, and for example, a pin mill is preferably used, and a pin mill having a quantitative feeder is particularly preferably used.

[0195] (Mixing and crushing)

[0196] The method for producing a raw material sulfide solid electrolyte comprises: mixing and pulverizing a raw material content B containing at least two compounds in a solvent to obtain a raw material mixture. For example, phosphorus sulfide and phosphorus pentasulfide that may be contained in the raw material content B are pulverized in advance as needed, and the pulverized material is weighed in an amount corresponding to the desired raw material sulfide solid electrolyte, and roughly mixed to obtain a raw material content B, which is mixed and pulverized in a solvent to obtain a raw material mixture.

[0197] The raw material mixture contains the compounds as raw materials contained in the raw material content B, and it is considered that these compounds are mainly compounds formed into fine particle crystals. This is because the compound contained in the raw material content B is finely divided by mixing and pulverizing the raw material compounds. In addition, it is considered that part of the raw material compounds reacts to form a raw material sulfide solid electrolyte.

[0198] The raw material content B may be mixed and pulverized using any of the pulverizers described above as being usable in the step of obtaining the mixture, and preferably a media pulverizer such as a ball mill or a bead mill. Alternatively, a kneader such as a single-shaft or multi-shaft kneader may be used.

[0199] As the solvent used in the above mixing and pulverizing, an organic solvent is preferably used. The organic solvent may be appropriately selected from the organic solvents used in the above step of obtaining the mixture.

[0200] 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.

[0201] Furthermore, as the solvent used in the above mixing and pulverizing, it is also preferable to use the above heteroatom-containing solvent, and it is more preferable to use it in combination with the above hydrocarbon solvent.

[0202] Among the solvents containing heteroatoms, solvents containing oxygen atoms and solvents containing nitrogen atoms are preferred. As solvents containing oxygen atoms, ether solvents are preferred. As solvents containing nitrogen atoms, solvents containing nitrile groups (nitrile solvents) are preferred. Among these, solvents containing nitrile groups (nitrile solvents) are more preferred. As ether solvents, tetrahydrofuran, diethyl ether, etc. are preferred. As nitrile solvents, propionitrile, isohexanenitrile, and isobutyronitrile are preferred.

[0203] As the solvent used in the above-mentioned mixing and pulverizing, it is preferred to use the above-mentioned hydrocarbon solvent in combination with the above-mentioned solvent containing heteroatoms. In this case, the content of the solvent containing heteroatoms relative to the total amount of the solvent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, further preferably 0.3% by mass or more, and as an upper limit, it is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 1% by mass or less.

[0204] The raw material component B and the solvent to be mixed and pulverized usually form a slurry (suspension). The content of the raw material component B in the slurry to be mixed and pulverized can be appropriately selected from the range of the content of the raw material component A in the mixture in the step of obtaining the mixture.

[0205] (Pre-burn)

[0206] The method for producing a raw material sulfide solid electrolyte includes: pre-calcining a raw material mixture obtained by mixing and pulverizing the raw material content B to obtain a pre-calcined product. By pre-calcining, the reaction of the raw material compound contained in the raw material mixture is promoted to generate a raw material sulfide solid electrolyte, and the solvent is removed, so that a powdered raw material sulfide solid electrolyte can be obtained. That is, the pre-calcined product obtained by pre-calcining becomes a raw material sulfide solid electrolyte.

[0207] The method of pre-calcination is not particularly limited, and examples thereof include methods using a hot plate, an autoclave, a vacuum heating device, an argon atmosphere furnace, a firing furnace, etc. In addition, a method using a shearing dryer such as an FM mixer, a NAUTA mixer, a static furnace such as a hearth kiln, a rotary furnace such as a rotary kiln, etc. can be used, and a horizontal dryer with a heating unit and a feeding mechanism, a horizontal vibration fluidized dryer, etc. can also be used industrially. The method of pre-calcination can be selected according to the processing volume of the pre-calcination.

[0208] The heating temperature and time during the calcination process can be changed according to the composition of the calcined product and whether an amorphous calcined product or a crystalline calcined product is desired, and therefore cannot be generalized. However, for example, the heating temperature is preferably 150° C. or higher, more preferably 160° C. or higher, and further preferably 170° C. or higher, and the upper limit is preferably 300° C. or lower, more preferably 280° C. or lower, and further preferably 250° C. or lower.

[0209] As described above, the raw material sulfide solid electrolyte may be either amorphous or crystalline, but is preferably amorphous from the viewpoint of improving the dispersibility of halogen atoms, facilitating the bonding of halogen atoms with lithium atoms, sulfur atoms, and phosphorus atoms in the sulfide solid electrolyte, and obtaining a sulfide solid electrolyte having higher ion conductivity.

[0210] Therefore, the heating temperature in the calcination is preferably a temperature at which an amorphous raw material sulfide solid electrolyte can be obtained, and may be determined by the method described above with respect to the heating temperature by microwave irradiation, using the crystallization temperature as a starting point.

[0211] The heating time is preferably 0.1 hour or longer, more preferably 0.2 hour or longer, and even more preferably 0.25 hour or longer, and the upper limit is preferably 8 hours or shorter, more preferably 6 hours or shorter, and even more preferably 4 hours or shorter.

[0212] The calcination is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere, an argon atmosphere) or in a reduced pressure atmosphere (particularly in a vacuum). In addition, an inert gas atmosphere containing hydrogen may also be used. This is because it can prevent the degradation (e.g., oxidation) of the raw material sulfide solid electrolyte.

[0213] In addition, drying may be performed before calcination. By drying, the solvent contained in the raw material mixture can be removed in advance. The drying method is the same as that of drying the fluid obtained by microwave irradiation.

[0214] The raw material sulfide solid electrolyte obtained by the above production method is assumed to mainly have Li 3 PS 4 The structure is a sulfide solid electrolyte (lithium thiophosphate) of the molecular structure, but depending on the blending ratio (molar ratio) of the raw materials used in the raw material content B, and, for example, when a compound containing a halogen atom is used as a raw material, a corresponding sulfide solid electrolyte can of course be obtained.

[0215] In the case of Li 3 PS 4 In the case of a sulfide solid electrolyte (lithium thiophosphate) having a molecular structure, if calcination is performed at the above-mentioned preferred heating temperature, an amorphous sulfide solid electrolyte is obtained.

[0216] In addition, for example, in the case where a blending ratio that can obtain a sulfide solid electrolyte with an argyrodite type crystal structure described later is used as the blending ratio of the raw materials, the calcined product is only an intermediate, and its state will change depending on the conditions of microwave irradiation, etc., so its details are unknown, but it can be considered to be a precursor of a sulfide solid electrolyte that generates an argyrodite type crystal structure when microwave irradiation is performed.

[0217] [Sulfide solid electrolyte]

[0218] The sulfide solid electrolyte obtained by the production method of this embodiment is either an amorphous sulfide solid electrolyte (glass component) or a crystalline sulfide solid electrolyte. Whether to make an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte can be adjusted by the heating temperature by microwave irradiation.

[0219] (Amorphous sulfide solid electrolyte)

[0220] The amorphous sulfide solid electrolyte obtained by the production method of this embodiment contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. As a representative amorphous sulfide solid electrolyte, for example, Li 2 SP 2 S 5 -LiI, Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -LiI-LiBr, etc., sulfide solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide; solid electrolytes containing other atoms such as oxygen atoms and silicon atoms, such as Li 2 SP 2 S 5 -Li 2 O-LiI、Li 2 S-SiS 2 -P 2 S 5 -LiI and other sulfide solid electrolytes. From the viewpoint of obtaining higher ion conductivity, Li 2 SP 2 S 5 -LiI, Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -LiI-LiBr, etc. Solid electrolytes composed of lithium sulfide, phosphorus sulfide and lithium halide.

[0221] The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed by, for example, an ICP emission spectrometer.

[0222] The shape of the amorphous sulfide solid electrolyte is not particularly limited, and may be, for example, a particle shape. The average particle size (D 50 ) For example, the range of 0.01 μm to 500 μm and 0.1 to 200 μm can be exemplified.

[0223] (Crystalline sulfide solid electrolyte)

[0224] The crystalline sulfide solid electrolyte obtained by the production method of this embodiment may be a so-called glass ceramic obtained by heating an amorphous solid electrolyte to a crystallization temperature or higher. As its crystal structure, Li 3 PS 4 Crystal structure, Li 4 P 2 S 6 Crystal structure, Li 7 PS 6 Crystal structure, Li 7 P 3 S 11 Crystal structure, a crystal structure having peaks near 2θ=20.2° and near 23.6° (for example, Japanese Patent Application Publication No. 2013-16423), etc. In addition, as the crystalline sulfide solid electrolyte obtained by the production method of this embodiment, from the viewpoint of obtaining higher ion conductivity, the following argyrodite type crystal structure and sulfide crystalline lithium superion conductor region II type crystal structure can be preferably exemplified.

[0225] The above-mentioned Li 7 PS 6 The structural framework of the composition formula is Li 7-x P 1- y Si y S 6 Li 7+x P 1-y Si y S 6 The crystal structure represented by (x is -0.6 to 0.6, y is 0.1 to 0.6) is cubic or orthorhombic, preferably cubic, and has peaks mainly appearing at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0° in X-ray diffraction measurement using CuKα rays. 7-x-2y PS 6-x-y Cl x(0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) represents a crystal structure preferably cubic, and in X-ray diffraction measurements using CuKα radiation, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°. In addition, the above-mentioned one with the compositional formula Li 7-x PS 6-x Ha x (where Ha is Cl or Br, and x is preferably 0.2 - 1.8) represents a crystal structure preferably cubic, and in X-ray diffraction measurements using CuKα radiation, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°. These basically have a crystal structure with a structural framework of Li 7 PS 6 and is also called a thiogermanate-type crystal structure.

[0226] In addition, these peak positions can fluctuate within a range of ±0.5°.

[0227] Furthermore, examples include Li 4-x Ge 1-x P x S 4 type thio-lithium superionic conductor region II (thio-LISICON Region II) crystal structure (refer to Kanno et al., Journal of The Electrochemical Society, 148(7) A742 - 746 (2001)), and a crystal structure similar to Li 4-x Ge 1-x P x S 4 type thio-lithium superionic conductor region II (thio-LISICON Region II) (refer to Solid State Ionics, 177(2006), 2721 - 2725), etc.

[0228] In this specification, "thio-lithium superionic conductor region II crystal structure" means Li 4-x Ge 1-x P x S 4 type thio-lithium superionic conductor region II (thio-LISICON Region II) crystal structure, and a crystal structure similar to Li 4-x Ge 1-x P x S 4Any crystal structure similar to the thio-LISICON Region II type. In addition, the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be a crystalline sulfide solid electrolyte having the above-mentioned thio-LISICON Region II type crystal structure, or may be a crystalline sulfide solid electrolyte having the thio-LISICON Region II type crystal structure as a main crystal. From the viewpoint of obtaining higher ionic conductivity, it is preferred to have the thio-LISICON Region II type crystal structure as a main crystal. In this specification, "having as a main crystal" means that the proportion of the crystal structure as the object in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more. In addition, from the viewpoint of obtaining higher ionic conductivity, the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment preferably does not contain crystalline Li 3 PS 4 (β-Li 3 PS 4 ).

[0229] In X-ray diffraction measurements using CuKα radiation, Li 3 PS 4 The diffraction peaks of the crystal structure appear near 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, for example. 4 P 2 S 6 The diffraction peaks of the crystal structure appear at around 2θ=16.9°, 27.1°, and 32.5°. 7 PS 6 The diffraction peaks of the crystal structure appear near 2θ=15.3°, 25.2°, 29.6°, and 31.0°, for example. 7 P 3 S 11 The diffraction peaks of the crystal structure appear near 2θ=17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, for example. 4-x Ge 1-x P x S 4 The diffraction peaks of the thio-LISICON Region II crystal structure appear at 2θ=20.1°, 23.9°, and 29.5°, which are similar to those of Li 4-x Ge 1-x P x S 4The diffraction peaks of the crystal structure similar to the thio-LISICON Region II type appear, for example, near 2θ=20.2 and 23.6°. In addition, these peak positions can fluctuate within a range of ±0.5°.

[0230] As described above, in the case where the type II crystal structure of the sulfide crystalline lithium superion conductor region is obtained in the present embodiment, it is preferable that the crystalline Li 3 PS 4 (β-Li 3 PS 4 ). The sulfide solid electrolyte obtained by the manufacturing method of this embodiment does not have a crystalline Li 3 PS 4 The observed diffraction peaks at 2θ=17.5° and 26.1° are at a level where, even if they exist, they are only extremely small compared with the diffraction peaks of the type II crystal structure of the sulfide crystallized lithium superion conductor region.

[0231] The shape of the crystalline sulfide solid electrolyte is not particularly limited, and may be, for example, a particle shape. The average particle size (D 50 ) For example, the range of 0.01 μm to 500 μm and 0.1 to 200 μm can be exemplified.

[0232] (Application of sulfide solid electrolyte)

[0233] The sulfide solid electrolyte obtained by the manufacturing method of this embodiment has high ion conductivity and excellent battery performance, and is therefore suitable for use in batteries. The sulfide solid electrolyte obtained by the manufacturing method of this embodiment can be used for any of the positive electrode layer, the negative electrode layer, and the electrolyte layer. In addition, each layer can be manufactured by a known method.

[0234] In addition, the battery preferably uses a current collector in addition to the positive electrode layer, the electrolyte layer and the negative electrode layer, and the current collector can use a known current collector. For example, a layer obtained by coating a substance that reacts with the solid electrolyte such as Au, Pt, Al, Ti or Cu can be used.

[0235] Example

[0236] Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples at all.

[0237] (Preparation Example 1: Preparation of raw material sulfide solid electrolyte)

[0238] Lithium sulfide (Li 2O3) was pulverized using a pin mill equipped with a quantitative feeder (“100UPZ (model)”, manufactured by Hosokawa Micron Co., Ltd.) under a nitrogen atmosphere. 2 S) (input speed: 80 g / min, rotation speed of the circular plate: 18000 rpm).

[0239] In addition, for phosphorus pentasulfide (P 2 S 5 , Italmatch Japan), lithium bromide (LiBr, Honjo Chemical Co., Ltd.) and lithium chloride (LiCl, Honjo Chemical Co., Ltd.) were also ground using the above-mentioned pin mill. 2 S 5 ) was added at a rate of 140 g / min, lithium bromide (LiBr) was added at a rate of 230 g / min, lithium chloride (LiCl) was added at a rate of 250 g / min, and the rotation speed of the circular plate was 18000 rpm.

[0240] Next, in a glove box under a nitrogen atmosphere, the compounds crushed in the above step were weighed so that the molar ratio was Li 2 S:P 2 S 5 : LiBr: LiCl = 47.5: 12.5: 15.0: 25.0, and a total of 110 g of the obtained substance was placed in a glass container, and the container was shaken for rough mixing.

[0241] 110g of the raw material after rough mixing was dispersed in a mixed solvent of 720mL of dehydrated toluene (Wako Pure Chemical Industries, Ltd.) and 2.9mL of dehydrated isobutyronitrile (Kishida Chemicals, Ltd.) (2wt% relative to the raw material) under a nitrogen atmosphere to prepare a slurry of about 10 mass%. The slurry was kept in a nitrogen atmosphere and mixed and crushed using a bead mill (LMZ015, Ashizawa Finetech Co., Ltd.). Specifically, 456g of zirconia beads with a diameter of 0.5mm were used as a crushing medium, and the bead mill was operated under the conditions of a circumference of 12m / s and a flow rate of 500mL / min, and the slurry was put into the mill and circulated for 1 hour to obtain a mixture of raw materials.

[0242] 400 mL of the raw material mixture obtained above was placed in an autoclave (500 mL capacity, made of SUS316) equipped with a stirrer and a heating oil bath, and heated at 200° C. for 2 hours while stirring at 350 rpm. After the treatment, the mixture was dried under reduced pressure and the solvent was distilled off to obtain a calcined product.

[0243] (Example 1)

[0244] The raw material sulfide solid electrolyte obtained in Preparation Example 1 was used as the raw material content.

[0245] 1.5 g of the raw material sulfide solid electrolyte obtained in Preparation Example 1 was mixed with 13.5 g of a solvent containing biphenyl and diphenyl ether as an organic solvent ("DAWTHERMA thermal medium (trade name)", manufactured by Dow Chemical Japan Co., Ltd., biphenyl content: 27% by mass) to obtain a mixture (slurry concentration: 10% by mass).

[0246] The obtained mixture was placed in a microwave irradiation apparatus ("Initiator+ (Microwave Synthesizer+) (Model)", manufactured by BIOTAGE), and microwave irradiation (output power: 300 W, frequency: 2.45 GHz) was started to raise the temperature of the mixture to 250°C (second step).

[0247] Next, the output power of the microwave was varied from 0 to 200 W (the device automatically changed the output power (W) to maintain the temperature) at any time, and the temperature of the mixture was maintained at 250° C. for 30 minutes (heat-keeping step).

[0248] Furthermore, the microwave irradiation was stopped, and the obtained mixture was air-purged (air-blown) to be cooled to 50° C. (third step).

[0249] Then, after repeating the above-mentioned series of heating based on microwave irradiation, temperature maintenance and cooling of the mixture, the heat preservation step and the third step (number of repetitions: 2 times), the solvent is replaced with toluene under vacuum, dried at room temperature until the solvent disappears, and then dried at 180°C for 4 hours to obtain a powder of a sulfide solid electrolyte.

[0250] The powder XRD diffraction of the obtained sulfide solid electrolyte was measured by the following method. The results are shown in Figure 1 .according to Figure 1 Diffraction peaks at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0° derived from the argyrodite type crystal structure were confirmed.

[0251] The ionic conductivity was measured by the method described below and found to be 0.7 mS / cm.

[0252] In addition, the average particle size was measured by the following method and the average particle size was 2.23 μm (D 50 ), and Li 3 PS 4 The average particle size is 2.53 μm (D 50 ) are roughly the same.

[0253] (Measurement of ionic conductivity)

[0254] In this example, the measurement of ion conductivity was performed as follows.

[0255] The sulfide solid electrolyte is formed into a 10 mm diameter (cross-sectional area S: 0.785 cm 2 ), round particles with a height (L) of 0.1 to 0.3 cm are used to make a sample. The top and bottom of the sample are taken as electrode terminals, and the AC impedance method is used for measurement at 25°C (frequency range: 1 MHz to 100 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. Near the right end of the arc observed in the high-frequency side area, the real part Z'(Ω) at the point where -Z"(Ω) is the smallest is taken as the bulk resistance R(Ω) of the electrolyte, and the ionic conductivity σ(S / cm) is calculated according to the following formula.

[0256] R=ρ(L / S)

[0257] σ=1 / ρ

[0258] (Powder X-ray Diffraction (XRD) Measurement)

[0259] In this specification, powder X-ray diffraction (XRD) measurement is performed as follows.

[0260] The powders obtained in the examples and comparative examples were filled into a groove with a diameter of 20 mm and a depth of 0.2 mm and leveled with glass to prepare a sample. The sample was sealed with a kapton film for XRD and measured under the following conditions in a manner that it was not in contact with air.

[0261] Measuring device: M03xhf (model, manufactured by MAC SCIENCE Co., Ltd.)

[0262] Tube voltage: 40kV

[0263] Tube current: 40mA

[0264] X-ray wavelength: Cu-Kα ray

[0265] Optical system: Concentration method

[0266] Slit composition: divergence slit 0.5°, scattering slit 0.5°, receiving slit 0.3mm, using monochromator

[0267] Detector: Semiconductor detector

[0268] Measuring range: 2θ = 10-60 degrees

[0269] Step width, scanning speed: 0.05deg, 10 seconds / step

[0270] (Average particle size)

[0271] In this specification, the measurement of the average particle size is performed as follows.

[0272] The powders obtained in the examples and comparative examples were measured using a laser diffraction particle size distribution measuring apparatus ("LA-950 (trade name)", manufactured by Horiba, Ltd.) to measure the particle size (D) at a cumulative volume percentage of 50%. 50 ), as the average particle size.

[0273] (Example 2)

[0274] A sulfide solid electrolyte was obtained in the same manner as in Example 1 except that a series of steps from microwave irradiation to cooling were performed a total of three times (number of repetitions of the second step, the heat-retaining step, and the third step: 3 times).

[0275] The ion conductivity of the obtained sulfide solid electrolyte was measured by the above method and the result was 1.4 mS / cm.

[0276] In addition, the average particle size of the obtained sulfide solid electrolyte was measured by the above method, and the average particle size was 2.35 μm (D 50 ).

[0277] Furthermore, the powder X-ray diffraction (XRD) of the obtained sulfide solid electrolyte powder was measured by the above method. The results are shown in Figure 2 .like Figure 2 As shown, it was confirmed that the sulfide solid electrolyte obtained in Example 2 also had diffraction peaks at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0° derived from the argyrodite type crystal structure, similarly to the sulfide solid electrolyte in Example 1.

[0278] (Example 3)

[0279] A sulfide solid electrolyte was obtained in the same manner as in Example 1 except that a series of steps from microwave irradiation to cooling was performed a total of 4 times (number of repetitions of the second step, the heat-retaining step, and the third step: 4 times).

[0280] The ionic conductivity of the obtained sulfide solid electrolyte was measured by the above method and the result was 2.1 mS / cm.

[0281] In addition, the average particle size of the obtained sulfide solid electrolyte was measured by the above method, and the average particle size was 2.34 μm (D 50 ).

[0282] Furthermore, the powder X-ray diffraction (XRD) of the obtained sulfide solid electrolyte powder was measured by the above method. The results are shown in Figure 3 .like Figure 3 As shown, it was confirmed that the sulfide solid electrolyte obtained in Example 3 also had diffraction peaks at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0° derived from the argyrodite type crystal structure, similarly to the sulfide solid electrolyte in Example 1.

[0283] (Example 4)

[0284] In Example 1, a sulfide solid electrolyte was obtained in the same manner as in Example 1 except that the microwave irradiation step was performed as follows.

[0285] The obtained mixture is placed in a microwave irradiation device, and microwave irradiation (output power: 300 W, frequency: 2.45 GHz) is started. After the temperature of the mixture reaches 300°C, the output power is changed at any time between 0 and 200 W (the device automatically changes the output power (W) for temperature maintenance) to maintain the temperature of the mixture at 300°C for 30 minutes, then the microwave irradiation is stopped, and the obtained mixture is cooled to 50°C by air purge (blowing air).

[0286] Then, after repeating the series of steps from the above-mentioned microwave irradiation to cooling twice (the number of repetitions of the second step, the heat preservation step and the third step: 3 times), the solvent is replaced with toluene under vacuum, dried at room temperature until the solvent disappears, and then dried at 180°C for 4 hours to obtain a powder of a sulfide solid electrolyte.

[0287] The ion conductivity of the obtained sulfide solid electrolyte was measured by the above method and the result was 2.6 mS / cm.

[0288] In addition, the average particle size of the obtained sulfide solid electrolyte was measured by the above method, and the average particle size was 2.18 μm (D 50 ).

[0289] Furthermore, the powder X-ray diffraction (XRD) of the obtained sulfide solid electrolyte powder was measured by the above method. The results are shown in Figure 4 .like Figure 4 As shown, it was confirmed that the sulfide solid electrolyte obtained in Example 4 also had diffraction peaks at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0° derived from the argyrodite type crystal structure, similarly to the sulfide solid electrolyte in Example 1.

[0290] (Comparative Example 1)

[0291] A sulfide solid electrolyte was obtained in the same manner as in Example 1 except that a series of steps from microwave irradiation to cooling were performed only once (number of repetitions of the second step, the heat-retaining step, and the third step: 1 time).

[0292] The ion conductivity of the obtained sulfide solid electrolyte was measured by the above method and the result was 0.4 mS / cm.

[0293] In addition, the average particle size of the obtained sulfide solid electrolyte was measured by the above method, and the average particle size was 2.28 μm (D 50 ).

[0294] Furthermore, the powder X-ray diffraction (XRD) of the obtained sulfide solid electrolyte powder was measured by the above method. The results are shown in Figure 5 .like Figure 5 As shown, in the powder obtained in Comparative Example 1, no diffraction peak derived from the argyrodite type crystal structure confirmed in the powder obtained in the above Examples was confirmed.

[0295] Industrial Applicability

[0296] According to the production method of this embodiment, a sulfide solid electrolyte can be efficiently produced by adopting a liquid phase method, lowering the heating temperature, suppressing granulation caused by heating and maintaining the 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 or communication devices such as personal computers, video cameras and mobile phones.

Claims

1. A method for producing a sulfide solid electrolyte, characterized in that: include: The first step is to mix raw materials containing lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms in an organic solvent to obtain a mixture; the second step is to irradiate the mixture with 0.5 to 700 W / g microwaves to heat it to 50 to 360° C.; and the third step is to cool the mixture to 20 to 70° C., and repeat the second and third steps 2 to 50 times.

2. The method for producing a sulfide solid electrolyte according to claim 1, wherein: After the second step, the mixture is irradiated with microwaves and maintained at a temperature of 80 to 360° C. for 1 to 300 minutes, and then the third step is performed.

3. The method for producing a sulfide solid electrolyte according to claim 1 or 2, 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 any one of claims 1 to 3, wherein: The boiling point of the organic solvent is 50° C. or higher.

5. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 4, wherein: The organic solvent is an aromatic solvent.

6. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 5, wherein: The content of the raw material-containing substance contained in the mixture is 1 mass % or more and 20 mass % or less.

7. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 6, wherein: In the second step, the mixture is irradiated with microwaves at 130 to 700 W / g.

8. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 7, wherein: In the second step, the mixture is heated to 150 to 360°C.

9. The method for producing a sulfide solid electrolyte according to any one of claims 2 to 8, wherein: In the heat-retaining step, the mixture is maintained at a temperature of 150 to 360°C.

10. The method for producing a sulfide solid electrolyte according to any one of claims 2 to 9, wherein: In the heat-retaining step, the mixture is maintained at the temperature for 1 to 240 minutes.

11. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 10, wherein: The second step and the third step are repeated 2 to 20 times.

12. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 11, wherein: The sulfide solid electrolyte is a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure.

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