Method for producing sulfide solid electrolyte

Abstract

To provide a method for producing a sulfide solid electrolyte that features superior productivity and a particularly small particle size.SOLUTION: A method for producing a sulfide solid electrolyte includes mixing a raw material containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms to give an electrolyte precursor, and heating the electrolyte precursor while it is sealed in a pressure-resistant vessel in the presence of a solvent and a dispersant with a carbon number of 8 or more in its molecules.SELECTED DRAWING: None

Description

[Technical Field]

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

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

[0003] A method using an autoclave is known as a method for producing a solid electrolyte used in a solid electrolyte layer. For example, Patent Document 1 discloses a method in which a raw material mixture is calcined in an autoclave, then heated at a high temperature in an electric furnace to obtain an argyrodite-type solid electrolyte, and then a surfactant and a solvent are added and stirred, followed by removal of the solvent. Patent Document 2 also discloses a method in which a raw material mixture is heated in an autoclave in the presence of a high-boiling-point solvent to obtain an argyrodite-type solid electrolyte. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 029315 Brochure [Patent Document 2] International Publication No. 2021 / 054412 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] In the method described in Patent Document 1, an argyrodite-type solid electrolyte is first produced, and then a surfactant or the like is added and stirred for the purpose of providing a water-resistant coating. In addition, in the method described in Patent Document 2, a complexing agent is used, but the electrolyte precursor is not calcined in the presence of a surfactant or the like. In these conventional manufacturing methods that include a firing process, particles grow large, making it difficult to obtain fine solid electrolyte particles suitable for solid electrolyte layers with particle sizes on the submicron order. When the particles grow large, further particle size reduction is required, reducing production efficiency. Furthermore, the low-boiling-point complexing agent and solvent used in the previous process are difficult to heat at high temperatures, and impurities generated in the previous process may cause the particles to grow, so they had to be removed first.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a method for producing a sulfide solid electrolyte with excellent productivity and particularly small particle size. [Means for solving the problem]

[0007] The method for producing a sulfide solid electrolyte according to the present invention includes the steps of: Mixing raw materials containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms to obtain an electrolyte precursor; heating the electrolyte precursor in a sealed pressure-resistant container in the presence of a solvent and a dispersant having 8 or more carbon atoms in its molecule; A method for producing a sulfide solid electrolyte, is. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a sulfide solid electrolyte with excellent productivity and particularly small particle size. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a SEM (scanning electron microscope) photograph of the solid electrolyte obtained in Example 1. [Figure 2] 1 is a SEM (scanning electron microscope) photograph of the solid electrolyte obtained in Example 2. [Figure 3] 1 is a SEM (scanning electron microscope) photograph of the solid electrolyte obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a numerical range expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values. Furthermore, preferred specifications can be arbitrarily adopted. In other words, one preferred specification can be adopted in combination with one or more other preferred specifications. It can be said that a combination of preferred items is more preferable.

[0011] (Findings Obtained by the Inventors to Achieve the Invention) As a result of extensive research aimed at solving the above problems, the present inventors have discovered the following and have completed the present invention.

[0012] Known solid electrolytes used in all-solid-state batteries include those having an argyrodite-type crystal structure and those having a thiolisiconregion II-type crystal structure. Patent Documents 1 and 2 disclose a method for producing a solid electrolyte having an argyrodite-type crystal structure, in which a hydrocarbon-based organic solvent is added to raw material components containing lithium atoms, sulfur atoms, phosphorus atoms, etc., and the raw materials are brought into contact with the raw materials to prepare an electrolyte precursor, which is then fired to produce a solid electrolyte having an argyrodite-type crystal structure, and then a microparticulation step is performed in which a solvent is added and the mixture is stirred.

[0013] The present inventors, taking into consideration that the fewer production steps required, the more advantageous it is industrially, thought that by heating the electrolyte precursor in the presence of a dispersant in a sealed state using an autoclave or the like, it might be possible to suppress aggregation of the particulate electrolyte precursor, and thus completed the present invention.

[0014] (Sulfide solid electrolyte) First, the terms used in this specification will be explained. In this specification, the term "solid electrolyte" refers to an electrolyte that remains solid at 25° C. under a nitrogen atmosphere. The sulfide solid electrolyte in this embodiment also contains at least lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms.

[0015] The term "solid electrolyte" includes both amorphous solid electrolytes and crystalline solid electrolytes. In this specification, a crystalline solid electrolyte refers to a solid electrolyte in which a peak derived from the solid electrolyte is observed in an X-ray diffraction pattern in an X-ray diffraction measurement, regardless of whether or not a peak derived from the raw material of the solid electrolyte is present. That is, a crystalline solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a part of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as the crystalline solid electrolyte has the X-ray diffraction pattern described above, it may also include an amorphous solid electrolyte in part. Therefore, a crystalline solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than the crystallization temperature. In addition, in this specification, an amorphous solid electrolyte refers to an X-ray diffraction pattern obtained by X-ray diffraction measurement that shows a halo pattern in which peaks other than those derived from the material are not substantially observed, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present.

[0016] (Various aspects of this embodiment) A method for producing a sulfide solid electrolyte according to a first aspect of the present embodiment includes the steps of: Mixing raw materials containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms to obtain an electrolyte precursor; heating the electrolyte precursor in a sealed pressure-resistant container in the presence of a solvent containing a dispersant having a linear or branched hydrocarbon group having 8 or more carbon atoms; A method for producing a sulfide solid electrolyte, is.

[0017] In the method for producing a sulfide solid electrolyte of this embodiment, an electrolyte precursor is heated in a sealed pressure vessel in the presence of a specific dispersant, thereby producing a sulfide solid electrolyte while preventing particles of the electrolyte precursor from aggregating with each other. Therefore, the sulfide solid electrolyte obtained by the manufacturing method of this embodiment does not show particle growth due to aggregation, and has a particle size small enough that subsequent atomization treatment is not necessary.

[0018] As a dispersant that can be used in the production method of this embodiment, among dispersants generally known as dispersants having a hydrophilic group and a hydrophobic group, it is necessary to use one that has a linear or branched hydrocarbon group having 8 or more carbon atoms, from the viewpoint of increasing the interparticle distance between the electrolyte precursor particles. If only a general hydrocarbon solvent is used, the electrolyte precursor particles will aggregate, and the particle size of the obtained sulfide solid electrolyte will be large.

[0019] The method for producing a sulfide solid electrolyte according to the present embodiment is extremely useful industrially because it can produce a sulfide solid electrolyte having such a small particle size that subsequent atomization treatment is not necessary.

[0020] A method for producing a sulfide solid electrolyte according to a second aspect of the present embodiment is the same as the first aspect, except that: The boiling point of the dispersant is 170°C or higher. That is it.

[0021] The dispersant used in the production method of this embodiment is exposed to high temperatures when the electrolyte precursor is heated in a sealed pressure-resistant container, so it is preferable to use one with a high boiling point.

[0022] A method for producing a sulfide solid electrolyte according to a third aspect of the present embodiment is the same as the first or second aspect, The dispersant is at least one selected from the group consisting of an anionic dispersant having a linear or branched hydrocarbon group having 8 to 30 carbon atoms, a cationic dispersant having a linear or branched hydrocarbon group having 8 to 30 carbon atoms, and a nonionic dispersant having a linear or branched hydrocarbon group having 8 to 30 carbon atoms. That is it. Further, a method for producing a crystalline sulfide solid electrolyte according to a fourth aspect of the present embodiment is a method for producing a crystalline sulfide solid electrolyte according to any one of the first to third aspects, The dispersant is a sulfonate. That is it.

[0023] The dispersant used in the production method of this embodiment may be any dispersant generally known as a dispersant having a linear or branched hydrocarbon group having 8 or more carbon atoms, as described above. Specifically, it is preferable to use a dispersant selected from the group consisting of an anionic dispersant having a linear or branched hydrocarbon group having 8 to 30 carbon atoms, a cationic dispersant having a linear or branched hydrocarbon group having 8 to 30 carbon atoms, and a nonionic dispersant having a linear or branched hydrocarbon group having 8 to 30 carbon atoms. Of these anionic dispersants, sulfonates are particularly preferred.

[0024] A method for producing a crystalline sulfide solid electrolyte according to a fifth aspect of the present embodiment is the same as any one of the first to fourth aspects, except that: The temperature when the electrolyte precursor is heated is 250°C or higher and 500°C or lower. That is it.

[0025] When a crystalline sulfide solid electrolyte is obtained by the production method of this embodiment, the heating temperature is preferably within the above range.

[0026] A method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment is the same as any of the first to fifth aspects, except that: The internal pressure in the pressure-resistant container when the electrolyte precursor is heated is 0.35 MPa or more and 2.0 MPa or less. That is it. Further, a method for producing a sulfide solid electrolyte according to a seventh aspect of the present embodiment is the same as any one of the first to sixth aspects, except that: The pressure-resistant vessel is an autoclave. That is it.

[0027] In the production method of this embodiment, the pressure conditions when the electrolyte precursor is sealed in a pressure-resistant container and heated are set within the above range, and an autoclave apparatus is used as the pressure-resistant container, so that the electrolyte precursor can be efficiently heated.

[0028] The method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is the same as any one of the first to seventh aspects, except that: The raw material contains at least chlorine as the halogen atom. That is it.

[0029] As a specific embodiment for producing a sulfide solid electrolyte having an argyrodite-type crystal structure, the halogen atoms contained in the raw materials preferably contain chlorine.

[0030] A method for producing a sulfide solid electrolyte according to a ninth aspect of the present embodiment is the same as any of the first to eighth aspects, except that: The boiling point of the solvent is 190°C or higher. That is it.

[0031] As with the dispersant described above, the solvent used in the manufacturing method of this embodiment is exposed to high temperatures when the electrolyte precursor is heated in a sealed pressure-resistant container, and therefore it is preferable to use a solvent with a high boiling point.

[0032] A tenth aspect of the present embodiment provides a method for producing a sulfide solid electrolyte according to any one of the first to ninth aspects, The solvent further comprises one or more selected from aromatic hydrocarbon solvents and ether solvents. That is it.

[0033] The solvent used in the production method of the present embodiment is preferably one that has excellent heat resistance and is unlikely to adversely affect the quality of the sulfide solid electrolyte, and specifically, aromatic hydrocarbon solvents and ether-based solvents are preferably used.

[0034] A method for producing a sulfide solid electrolyte according to an eleventh aspect of the present embodiment is the same as any of the first to tenth aspects, except that: When the heating is performed, the amount of the dispersant is 0.1 to 20 mass% relative to the amount of the electrolyte precursor. That is it.

[0035] The amount of dispersant used in the production method of the present embodiment is preferably within the above range from the viewpoint of reducing the amount of dispersant remaining in the produced sulfide solid electrolyte while ensuring the interparticle distance of the particulate electrolyte precursor.

[0036] A method for producing a sulfide solid electrolyte according to a twelfth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the first to eleventh aspects, When the heating is performed, the ratio of the amount of the electrolyte precursor to the total amount of the electrolyte precursor and the solvent is 0.50 to 50 mass %. That is it.

[0037] In the manufacturing method of this embodiment, it is preferable to set the amount of the electrolyte precursor within the above range from the viewpoint of suppressing aggregation of the electrolyte precursor during heating and improving productivity.

[0038] [Method for producing sulfide solid electrolyte] The method for producing the sulfide solid electrolyte of this embodiment includes the steps of: Mixing raw materials containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms to obtain an electrolyte precursor; heating the electrolyte precursor in a sealed pressure-resistant container in the presence of a solvent and a dispersant having 8 or more carbon atoms in its molecule; A method for producing a sulfide solid electrolyte, is.

[0039] [Mixing raw materials containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms to obtain an electrolyte precursor] In the method for producing a sulfide solid electrolyte of this embodiment, raw material components containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms are mixed to obtain an electrolyte precursor.

[0040] (Raw material content) As the solid electrolyte raw material contained in the raw material inclusion used in this embodiment, from the viewpoint of obtaining a sulfide solid electrolyte containing a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom, a raw material containing one type of atom selected from a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom is preferably used, and by combining one or more types of raw materials, the raw material inclusion as a whole may contain a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom. Examples of such solid electrolyte raw materials containing lithium atoms, sulfur atoms, and phosphorus atoms include lithium sulfide (Li2S) and phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5).

[0041] The lithium sulfide is preferably in particulate form. The average particle size (D50) of the lithium sulfide particles is preferably 0.1 μm or more and 300 μm or less, more preferably 1 μm or more and 100 μm or less, even more preferably 3 μm or more and 50 μm or less, and particularly preferably 5 μm or more and 30 μm or less. In this specification, the average particle size (D50) is the particle size at which 50% of the particles in a particle size distribution cumulative curve are accumulated, starting from the smallest particle size, and the volume distribution refers to the average particle size that can be measured, for example, using a laser diffraction / scattering particle size distribution analyzer. Furthermore, the other solid raw materials used in this embodiment preferably have an average particle size similar to that of the lithium sulfide particles, i.e., within the same range as the average particle size of the lithium sulfide particles.

[0042] Furthermore, from the viewpoint of improving ion conductivity, a solid electrolyte raw material containing a halogen atom is used as the solid electrolyte raw material. Raw materials containing halogen atoms include lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; phosphorus halides such as various phosphorus fluorides (PF3, PF5), various phosphorus chlorides (PCl3, PCl5, P2Cl4), various phosphorus bromides (PBr3, PBr5), and various phosphorus iodides (PI3, P2I4); thiophosphoryl fluoride (PSF3), thiophosphoryl chloride (PSCl3), thiophosphoryl bromide (PSBr3), and thiophosphoryl iodide (P Representative examples of the halogen atom include compounds comprising at least two elements selected from the four types of atoms mentioned above, i.e., lithium atom, phosphorus atom, sulfur atom, and halogen atom, such as thiophosphoryl halides such as thiophosphoryl dichloride (PSClF), thiophosphoryl fluoride dibromide (PSBrF), and the like; and elemental halogens such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), with chlorine (Cl), bromine (Br), and iodine (I) being preferred.

[0043] Examples of materials that can be used as raw materials other than those mentioned above include raw materials that contain at least one atom selected from the lithium atom, phosphorus atom, sulfur atom, and halogen atom, and also contain atoms other than the four types of atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; metal sulfides such as silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS, SnS), aluminum sulfide, and zinc sulfide; sodium phosphate; phosphate compounds such as thorium and lithium phosphate; halides of alkali metals other than lithium, such as sodium halides such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides, and bismuth halides; phosphorus oxyhalides such as phosphorus oxychloride (POCl3) and phosphorus oxybromide (POBr3); and the like.

[0044] In the method for producing a sulfide solid electrolyte of the present embodiment, "mixing raw material components containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms to obtain an electrolyte precursor" preferably includes, more specifically, the following steps (i) and (ii): (i) a mixing step of mixing raw materials containing lithium atoms, sulfur atoms, and phosphorus atoms to obtain a first precursor having a Li3PS4 structure; (ii) A step of mixing the first precursor obtained in the step (i) with a solid electrolyte raw material containing halogen atoms to obtain an electrolyte precursor.

[0045] (Step (i)) The first precursor obtained in the step (i) has a Li3PS4 structure from the viewpoint of improving ionic conductivity. The first precursor may contain unreacted solid electrolyte raw materials in addition to the Li3PS4 structure. Among the above, it is preferable to use lithium sulfide (Li2S) and phosphorus sulfide such as diphosphorus trisulfide (P2S3) or diphosphorus pentasulfide (P2S5) as the raw materials used in step (i). In this case, the compounding ratio of lithium sulfide and phosphorus sulfide is not particularly limited as long as it is within the range in which the Li3PS4 structure can be formed. 3- From the viewpoint of efficiently forming the structure, when diphosphorus pentasulfide is used as phosphorus sulfide, the ratio of the number of moles of lithium sulfide to the total number of moles of lithium sulfide and diphosphorus pentasulfide is preferably within a range of 60 to 90%, more preferably within a range of 65 to 85%, even more preferably within a range of 70 to 80%, still more preferably within a range of 72 to 78%, and particularly preferably within a range of 73 to 77%.

[0046] Step (i) is preferably carried out in the presence of a complexing agent. The complexing agent is a substance capable of forming a complex with lithium atoms, and reacts with the sulfide containing lithium atoms contained in the solid electrolyte raw material to form a precursor containing lithium atoms, sulfur atoms, and phosphorus atoms, preferably PS4 3- The complex obtained by forming a complex with the lithium atom is a complex containing a lithium atom, a sulfur atom, a phosphorus atom, and a complexing agent, and the complexing agent is preferably removed from the complex (also simply referred to as "decomplexation") to form PS4 3- Among the structures, amorphous Li3PS4 and crystalline Li3PS4 can be obtained.

[0047] The complexing agent can be any agent having the above properties, and is preferably a compound containing an atom having a high affinity with lithium atoms, such as a heteroatom such as a nitrogen atom, an oxygen atom, or a chlorine atom, and more preferably a compound having a group containing such a heteroatom, because such a group can form a coordinate bond with lithium. Preferred examples of the heteroatom include a nitrogen atom, an oxygen atom, and a halogen atom such as a chlorine atom.

[0048] Specific examples of complexing agents include ester-based solvents such as ethyl acetate and butyl acetate; aldehyde-based solvents such as formaldehyde, acetaldehyde, and dimethylformamide; ketone-based solvents such as acetone and methyl ethyl ketone; ether-based solvents such as diethyl ether, diisopropyl ether, dibutyl ether, tetrahydrofuran, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole; halogen-containing aromatic hydrocarbon solvents such as trifluoromethylbenzene, nitrobenzene, chlorobenzene, chlorotoluene, and bromobenzene; amine-based solvents such as tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, tetraethyldiaminopropane, cyclopropanediamine, tolylenediamine, and tetraethylenepentamine; nitrile-based solvents such as acetonitrile, methoxyacetonitrile, propionitrile, methoxypropionitrile, and benzonitrile; and solvents containing carbon atoms and heteroatoms such as dimethyl sulfoxide and carbon disulfide. Among these, the complexing agent is preferably an amine-based solvent, an ether-based solvent, or a nitrile-based solvent, more preferably an ether-based solvent, and among these, diethyl ether, diisopropyl ether, dibutyl ether, or tetrahydrofuran is preferred, more preferably tetrahydrofuran. Furthermore, the complexing agent is preferably one in which the solid electrolyte raw material is not or hardly dissolved, and from this viewpoint, the amine-based solvent or the ether-based solvent is preferred.

[0049] In addition to the complexing agent, various solvents can be used, such as aliphatic hydrocarbon solvents such as hexane, pentane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane; alicyclic hydrocarbon solvents such as cyclohexane and methylcyclohexane; aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene; and paraffinic solvents such as oligomers obtained by polymerizing at least one normal paraffin, such as normal butene and normal propylene, to a degree of polymerization of about 3 to 10, and hydrogenated products thereof, normal paraffinic solvents, and oligomers obtained by polymerizing at least one paraffin, including at least isoparaffin, from among isobutene, normal butene, normal propylene, and isopropylene, to a degree of polymerization of about 3 to 10, and hydrogenated products thereof, and isoparaffinic solvents.

[0050] When the solid electrolyte raw material and the complexing agent are mixed in a liquid phase, the amount of the complexing agent used relative to the solid electrolyte raw material is preferably 1 to 50 mass %, more preferably 2 to 30 mass %, even more preferably 3 to 20 mass %, and still more preferably 5 to 15 mass %, in terms of the content of the solid electrolyte raw material relative to the total amount of the solid electrolyte raw material and the complexing agent.

[0051] A precursor (e.g., a Li3PS4 structure) containing the Li3PS4 structure can be synthesized by mixing the solid electrolyte raw materials and the complexing agent. It can also be synthesized by further pulverization, kneading, or a combination of these processes. The processes of mixing, pulverization, kneading, and the like may occur simultaneously and therefore cannot be clearly distinguished. Mixing the solid and powder raw materials exemplified as raw materials that can be included in the solid electrolyte raw material may result in kneading. At the same time, the solid electrolyte raw materials may collide with each other and be pulverized or kneaded. Furthermore, pulverization itself may also serve as mixing or kneading. The synthesis of the precursor in this mixing process can be achieved by repeatedly contacting the raw materials with each other by applying force, such as rotation or vibration, to the various raw materials included in the solid electrolyte raw material. This contact may be accompanied by other processes, such as pulverization or kneading, as long as it includes at least a mixing process.

[0052] In this embodiment, the mixing, pulverizing, kneading, or a combination thereof can be performed using, for example, a mechanical agitation mixer equipped with an agitating blade in a tank. Examples of mechanical agitation mixers include high-speed agitation mixers and double-arm mixers, and high-speed agitation mixers are preferably used from the viewpoint of promoting a reaction through more uniform contact between the various raw materials contained in the raw material content and obtaining higher ionic conductivity. Examples of high-speed agitation mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used. Examples of the shape of the stirring blades used in mechanical stirring mixers include blade type, arm type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, C-shaped blade type, etc., and from the viewpoint of promoting reaction through more uniform contact between the various raw materials contained in the raw material content and obtaining higher ionic conductivity, the shovel type, flat blade type, C-shaped blade type, etc. are preferred.

[0053] The above treatment can also be carried out using, for example, a media-type grinder. Media-type mills are broadly classified into vessel-driven mills and media-agitation mills. Vessel-driven mills include agitation tanks, grinding tanks, and combinations thereof, such as ball mills and bead mills. Ball mills and bead mills can be of any of various types, including rotary, rolling, vibrating, and planetary types.

[0054] Examples of media agitation type grinders include impact grinders such as cutter mills, hammer mills, and pin mills; tower-type grinders such as tower mills; agitation tank-type grinders such as attritors, aquamizers, and sand grinders; flow tank-type grinders such as Viscomill and pearl mills; flow pipe-type grinders; annular-type grinders such as Coball mills; and continuous dynamic grinders. Alternatively, the mixing can be carried out using, for example, a single-screw or multi-screw kneader.

[0055] In step (i), it is preferable to employ a process using a mechanical stirring mixer in order to more efficiently synthesize a precursor containing the Li3PS4 structure (such as the Li3PS4 structure), particularly a complex containing lithium, sulfur, phosphorus, and the complexing agent.

[0056] The temperature for synthesizing the complex in step (i) is not particularly limited, but can be adjusted within the range of, for example, 20 to 100°C. It may be around room temperature (23°C), but heating may be used to accelerate the synthesis reaction in a short time. Higher temperatures are preferred under non-drying conditions such as reflux. For example, it can be 50 to 90°C, more preferably around 80°C. The synthesis time may be about 0.5 to 100 hours, and in consideration of production efficiency, it is preferably 1 to 90 hours, and more preferably 3 to 75 hours.

[0057] The product obtained by the above synthesis is a first precursor containing a lithium atom, a sulfur atom, and a phosphorus atom, more specifically, a complex formed from a lithium atom, a sulfur atom, a phosphorus atom, and the complexing agent.

[0058] (drying process) When a complexing agent or a solvent is used in step (i), the production method of this embodiment may include a drying step to remove the complexing agent or the solvent from the obtained slurry. When a slurry containing a complex from which amorphous and crystalline Li3PS4 can be obtained in step (i) as described above, the complexing agent and the solvent can be removed from the slurry by drying in the drying step, thereby obtaining complex crystals. By removing the complexing agent and solvent, impurities are reduced, and ionic conductivity can be expected to improve. On the other hand, when the above step (i) is performed in a liquid phase, a slurry containing the first precursor is obtained. However, drying this slurry may lead to the formation of aggregates. Furthermore, when the aggregates are subjected to heating as required (described below), they become larger calcined bodies, which may prevent the production of a solid electrolyte with a small particle size. In such cases, a pulverization process is preferable.

[0059] The precursor containing the complexing agent and solvent can be dried at a temperature according to the type of the remaining complexing agent and solvent, for example, at a temperature equal to or higher than the boiling point of the remaining complexing agent or solvent. The drying temperature is, for example, usually 5 to 100°C, preferably 10 to 90°C, and more preferably 20 to 85°C. Alternatively, the precursor can be dried under reduced pressure (vacuum) using a vacuum pump or the like. The drying time is not particularly limited, but is preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and even more preferably 1 hour or more. The upper limit of the drying time is not particularly limited, but is preferably 24 hours or less, more preferably 12 hours or less, even more preferably 6 hours or less, and even more preferably 3 hours or less.

[0060] The drying may be performed by filtering the first precursor together with the complexing agent and the solvent using a glass filter or the like, by solid-liquid separation by decantation, or by solid-liquid separation using a centrifuge, etc. In this embodiment, after the solid-liquid separation, drying may be performed under the above temperature conditions. Specifically, solid-liquid separation can be easily performed by decantation, in which the first precursor together with the complexing agent and the solvent is transferred to a container, and after the first precursor has precipitated, the supernatant solvent is removed. Alternatively, solid-liquid separation can be easily performed by filtration using, for example, a glass filter with a pore size of about 10 to 200 μm, preferably 20 to 150 μm.

[0061] (Heating process) The manufacturing method of this embodiment preferably includes, in addition to step (iii) described below, a heating step of heating the first precursor obtained in step (i) above or the first precursor that has further been subjected to a drying step. Specifically, after the above step (i) and drying step, the complexing agent and solvent are removed from the slurry, and the slurry is further heated while adjusting the heating temperature to obtain crystalline Li3PS4. Generally, when a solid electrolyte is heated, it may become thickened by burning, which increases the particle size. In this embodiment, by producing the first precursor before the step (ii) described below, the particle size of the resulting solid electrolyte can be made smaller, thereby making it possible to reduce the particle size and improve the ionic conductivity at the same time.

[0062] The heating temperature in the heating step is not particularly limited as long as a first precursor having a Li3PS4 structure is obtained, but is, for example, preferably 140°C or higher, more preferably 145°C or higher, even more preferably 150°C or higher, and even more preferably 170°C or higher, and although there is no particular upper limit, is preferably 300°C or lower, more preferably 275°C or lower, even more preferably 225°C or lower, and even more preferably 200°C or lower. Within the above temperature range, the first precursor having a Li3PS4 structure can be produced more efficiently, and mainly crystalline Li3PS4 can be obtained. Furthermore, when mainly amorphous Li3PS4 is to be obtained, the upper limit should be 150°C or less, preferably 140°C or less, and more preferably 135°C or less. There is no particular lower limit, but the lower limit should be about 100°C or more, and preferably 105°C or more.

[0063] The treatment time of the heating step is not particularly limited as long as a first precursor having a Li3PS4 structure is obtained, but for example, it is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 1 hour or more, and even more preferably 4 hours or more. The upper limit of the heating time is not particularly limited, but it is preferably 24 hours or less, more preferably 18 hours or less, even more preferably 12 hours or less, and even more preferably 10 hours or less.

[0064] The heating step may be carried out in an inert gas atmosphere (e.g., nitrogen atmosphere, argon atmosphere) or a reduced pressure atmosphere (particularly in vacuum), because this can prevent deterioration (e.g., oxidation) of the precursor obtained by the synthesis and mixing described above. The heating method is not particularly limited, and examples thereof include a method using a hot plate, an autoclave, a vacuum heating device, an argon gas atmosphere furnace, a calcination furnace, etc. Furthermore, industrially, a horizontal dryer or a horizontal vibration fluidized dryer having a heating means and a feeding mechanism can also be used, and the method may be selected depending on the amount of processing to be heated.

[0065] The first precursor having the Li3PS4 structure thus obtained is typically a complex that can be decomposed to obtain the amorphous and crystalline Li3PS4, amorphous Li3PS4, crystalline Li3PS4 (β-Li3PS4), etc. In addition, the first precursor having the Li3PS4 structure includes these PS4 3- The structure may be of a single type or may contain a mixture of multiple types. In this embodiment, the Li3PS4 structure is formed once and then subjected to subsequent steps, thereby obtaining a solid electrolyte with small particle size and high ionic conductivity.

[0066] The Li3PS4 structure contained in the first precursor thus obtained is a solid 31 P-NMR measurement can be used to observe the PS4 3- From the viewpoint of ionic conductivity, the crystal structure consisting of phosphorus and sulfur atoms is PS4 3-Structures other than the structure, e.g. P2S7 4- Structure, P2S6 4- Structure (P x S y a- It is preferable that the PS4 does not contain a crystal structure such as the PS4 structure. 3- This makes it easier to obtain a precursor containing the structure.

[0067] (Step (ii)) Step (ii) is a step of mixing the first precursor obtained in step (i) with a solid electrolyte raw material containing halogen atoms to obtain an electrolyte precursor.

[0068] Specific examples of solid electrolyte raw materials containing halogen atoms include lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide, and elemental halogens such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Among the lithium halides, lithium chloride, lithium bromide, and lithium iodide are preferred, with lithium chloride and lithium bromide being more preferred. Furthermore, among the halogen elements, chlorine (Cl2), bromine (Br2), and iodine (I2) are preferred, with chlorine (Cl2) and bromine (Br2) being more preferred. As a combination of solid electrolyte raw materials containing halogen atoms, a combination of lithium chloride and lithium bromide, or a combination of chlorine (Cl2) and bromine (Br2) is preferable.

[0069] In the production method of this embodiment, the solid electrolyte raw material containing a halogen atom may be added together with other solid electrolyte raw materials in the step (i). However, from the viewpoint of more reliably forming the Li3PS4 structure, improving ionic conductivity, and more reliably reducing the particle size, it is preferable to add the solid electrolyte raw material after the step (i).

[0070] The compounding ratio of the various solid electrolyte raw materials used in the solid electrolyte raw material of this embodiment may be appropriately determined depending on the desired crystal structure. As an example, the compounding ratio of the various raw materials in a crystalline solid electrolyte having an argyrodite-type crystal structure, which is one of the preferred crystalline solid electrolytes obtained by the manufacturing method of this embodiment, will be described below. The argyrodite-type crystal structure will be described later.

[0071] For example, when the crystalline Li3PS4 (β-Li3PS4) obtained in step (i) is blended with lithium sulfide and lithium halide, the molar ratio of these raw materials (Li3PS4:Li2S:lithium halide) is preferably 15-55:3-25:20-80, more preferably 20-45:5-20:30-70, even more preferably 25-40:8-18:40-60, and still more preferably 30-35:10-15:50-55.

[0072] When lithium chloride and lithium bromide are used in combination as the lithium halide, the ratio of the number of moles of lithium bromide to the total number of moles of lithium chloride and lithium bromide is preferably 1 to 70%, more preferably 10 to 60%, even more preferably 20 to 50%, and even more preferably 30 to 40%.

[0073] (Crushing process) The manufacturing method of this embodiment preferably includes a pulverization step in which the electrolyte precursor obtained in the above step (ii) is pulverized. By heating the pulverized material obtained in this pulverization step in the step (iii) described below, a crystalline solid electrolyte can be easily obtained even at a lower heating temperature. Furthermore, by performing this pulverization step, a solid electrolyte having a small particle size and high ionic conductivity can be efficiently obtained.

[0074] The specific pulverization method in the pulverization step is not particularly limited, but from the viewpoint of more efficient pulverization, mechanical milling is preferred because it makes it easier to obtain a solid electrolyte with high ionic conductivity. Mechanical milling is a treatment using a media mill, which is exemplified as a method for synthesizing the first precursor in the above step (i), and media mills are broadly classified into container-driven mills and media-agitation mills, with container-driven mills such as ball mills and bead mills being preferred. Various types of ball mills and bead mills can be mentioned, including rotary, rolling, vibrating, and planetary types, and any of these may be used.

[0075] The pulverization step is preferably carried out in a liquid phase. By carrying out pulverization in a liquid phase, pulverization may be accelerated. Therefore, in the production method of this embodiment, the pulverization step may be carried out without removing the complexing agent and solvent used in the step (i) above, or after completing the step (i), the complexing agent and solvent may be removed, and then a new solvent may be added, followed by pulverization in a liquid phase. The solvent used in the above-mentioned grinding step may be, for example, the complexing agent and solvent exemplified in the synthesis of the first precursor in the above-mentioned step (i). Preferred solvents are aromatic hydrocarbon solvents, ether solvents, and nitrile solvents, more preferably aromatic hydrocarbon solvents and nitrile solvents, still more preferably toluene, xylene, ethylbenzene, tert-butylbenzene, and isobutyronitrile, and even more preferably toluene and isobutyronitrile. In this case, the amount of the solvent used relative to the solid electrolyte raw material is the same as the amount of the complexing agent used in the above step (i).

[0076] The average particle size (D50) of the pulverized material obtained in this pulverization step is preferably 0.01 μm to 100 μm, more preferably 0.03 μm to 50 μm, even more preferably 0.05 μm to 10 μm, and even more preferably 0.1 μm to 3 μm. If the average particle size of the pulverized material is within the above range, the desired crystalline solid electrolyte can be more easily obtained even at a lower heating temperature in step (iii), and the progress of particle growth can be suppressed, allowing the particle size to be maintained small. As a result, a crystalline solid electrolyte with a small particle size can be more efficiently obtained.

[0077] In this embodiment, the average particle size of the pulverized product can be adjusted to fall within the above range by adjusting the conditions of the pulverization treatment. For example, when mechanical milling using a media-type pulverizer is used in the pulverization treatment, the average particle size can be adjusted by adjusting the particle size, shape, and amount of zirconia balls, zirconia beads, etc. used in the pulverizer, the operating conditions (rotation speed, etc.) of the pulverizer, the amount of solvent used relative to the precursor, etc.

[0078] [The electrolyte precursor is heated in the presence of a solvent and a dispersant having 8 or more carbon atoms in the molecule, while the container is sealed in a pressure-resistant container.] In the method for producing a sulfide solid electrolyte of the present embodiment, the above-mentioned step of "heating an electrolyte precursor in a sealed pressure-resistant vessel in the presence of a solvent and a dispersant having 8 or more carbon atoms in the molecule" preferably includes, more specifically, the following step (iii): (iii) A step of heating the electrolyte precursor obtained in the above step (ii) in a sealed pressure-resistant container in the presence of a solvent containing a dispersant having a linear or branched hydrocarbon group having 8 or more carbon atoms.

[0079] (Step (iii)) The method for producing a crystalline solid electrolyte of this embodiment preferably includes a step of pulverizing the electrolyte precursor obtained in step (ii) above, if necessary, by the pulverization step, and then heating the resulting mixture in a sealed pressure-resistant container in the presence of a solvent containing a dispersant having a linear or branched hydrocarbon group having 8 or more carbon atoms. As described above, the electrolyte precursor is preferably a precursor containing a Li3PS4 structure. Also, as described above, the electrolyte precursor is preferably a pulverized product obtained by the pulverization step. In the manufacturing method of this embodiment, by going through step (iii), a reaction between the Li3PS4 structure contained in the electrolyte precursor, preferably the electrolyte precursor containing the Li3PS4 structure, and a raw material containing a halogen element occurs, whereby the halogen element is incorporated into the Li3PS4 structure and crystallizes, thereby obtaining a crystalline solid electrolyte containing lithium, sulfur, phosphorus, and a halogen element.

[0080] By heating in step (iii), the diffusion distance of each element in the particles is shortened, making it easier to obtain a desired crystalline solid electrolyte. In the production method of this embodiment, by employing this step of obtaining a solid electrolyte by heating using a pressure-resistant container in the presence of a solvent containing the dispersant, the dispersant can promote the formation of a solid electrolyte while maintaining the interparticle distance between the electrolyte precursor particles, making it possible to suppress an increase in particle size.

[0081] The solvent used in step (iii) must contain a dispersant having a linear or branched hydrocarbon group having 8 or more carbon atoms, as described above. As the dispersant, among those generally known as dispersants having a hydrophilic group and a hydrophobic group, it is necessary to use one having a linear or branched hydrocarbon group having 8 or more carbon atoms from the viewpoint of maintaining a relatively wide interparticle distance between electrolyte precursor particles and from the viewpoint of the need for a relatively high boiling point because the electrolyte precursor is heated in a sealed state in a pressure-resistant vessel. Furthermore, from the viewpoint of it being preferable to remove impurities as much as possible to obtain a sulfide solid electrolyte with high conductivity, and therefore a dispersant that is easy to remove after the heating is preferred, and from the viewpoint of ensuring solubility by keeping the carbon number at a certain level or less, the dispersant is less likely to precipitate and is therefore more effective in dispersing the electrolyte precursor, dispersants having a linear or branched hydrocarbon group having 30 or less carbon atoms are preferred, dispersants having a linear or branched hydrocarbon group having 8 to 30 carbon atoms are more preferred, and dispersants having a linear or branched hydrocarbon group having 8 to 24 carbon atoms are even more preferred. The dispersant preferably has 8 to 40 carbon atoms in its entire molecule, more preferably 10 to 32 carbon atoms, and even more preferably 12 to 24 carbon atoms.

[0082] As the dispersant, it is preferable to use one or more selected from anionic dispersants, cationic dispersants, and nonionic dispersants. Specific examples of the anionic dispersant include carboxylates, sulfonates, sulfates, and phosphates. Using a sulfonate as a dispersant is preferable because the sulfonate ions, which are anions of the cations contained in the sulfide solid electrolyte and lithium ions in particular, tend to interact with each other. This allows the dispersant to be adsorbed onto the surface of the sulfide solid electrolyte particles, resulting in improved dispersibility due to steric hindrance. Furthermore, alkylbenzene sulfonates, such as sodium dodecylbenzene sulfonate, are particularly preferred as the dispersant. For the same reasons as described above, the alkyl group in the alkylbenzene sulfonate is preferably a linear or branched alkyl group having 30 or less carbon atoms, more preferably a linear or branched alkyl group having 8 to 30 carbon atoms, and even more preferably a linear or branched alkyl group having 8 to 24 carbon atoms. Specific examples of the cationic dispersant include amine salts and ammonium salts. Specific examples of the nonionic dispersant include esters, ethers, amides, and amines, with aliphatic amines such as oleylamine being particularly preferred. The dispersant preferably has a boiling point of 170°C or higher, more preferably 250°C or higher, and even more preferably 300°C or higher.

[0083] The amount of the dispersant relative to the amount of the electrolyte precursor when the heating is performed is preferably 0.1 to 20 mass %, more preferably 0.5 to 15 mass %, and even more preferably 1.0 to 10 mass %, from the viewpoint of reducing the amount of the dispersant remaining in the produced sulfide solid electrolyte while ensuring the interparticle distance of the particulate electrolyte precursor.

[0084] If a pulverization step is performed after producing a crystalline solid electrolyte having a desired crystal structure in the above step (iii), the ionic conductivity may decrease due to destruction of the crystal structure, etc. From this viewpoint, it is preferable that the production method of this embodiment does not include a pulverization step after step (iii).

[0085] The method for heating the electrolyte precursor obtained in step (ii), preferably the pulverized product obtained in the pulverization step, is not particularly limited as long as it is a method performed in a sealed pressure-resistant container, and any method can be adopted, for example, a method using a pressure-resistant container such as an autoclave. Among them, an autoclave is preferred from the viewpoint of suppressing the increase in particle size in step (iii). In the production method of this embodiment, the electrolyte precursor is heated in a sealed state in a pressure-resistant vessel, thereby increasing the pressure in the pressure-resistant vessel and enabling efficient production of a solid electrolyte. Here, even if the pressure-resistant vessel is equipped with a safety valve, it can be said that the electrolyte precursor is in a sealed state in the pressure-resistant vessel under normal heating conditions.

[0086] The heating temperature in step (iii) may be adjusted appropriately depending on the desired solid electrolyte. For example, when producing a solid electrolyte having an argyrodite-type crystal structure, the heating temperature is preferably 250°C or higher and 500°C or lower, more preferably 280°C or higher and 470°C or lower, even more preferably 320°C or higher and 450°C or lower, and still more preferably 360°C or higher and 430°C or lower.

[0087] The heating time in step (iii) may be adjusted appropriately depending on the desired solid electrolyte, and is, for example, preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, and even more preferably 15 minutes or more. The upper limit of the heating time is not particularly limited, but is preferably 10 hours or less, more preferably 5 hours or less, even more preferably 3 hours or less, and even more preferably 2 hours or less.

[0088] The internal pressure in the pressure vessel in step (iii) is preferably 0.35 MPa or more and 2.0 MPa or less, more preferably 0.50 MPa or more and 1.5 MPa or less, and even more preferably 0.80 MPa or more and 1.2 MPa or less.

[0089] Furthermore, by carrying out the heating in an inert gas atmosphere (for example, a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum), deterioration (for example, oxidation) of the resulting solid electrolyte can be prevented.

[0090] When heating in step (iii), it is not preferable to dry the material beforehand or simultaneously with crystallization, because drying may increase the average particle size. Therefore, in the production method of this embodiment, it is preferable to avoid drying as much as possible.

[0091] In the heating in step (iii), the complexing agent and solvent used in steps (i) and (ii) may not be removed, and the electrolyte precursor obtained in these steps together with the complexing agent and solvent may be heated as is. Alternatively, the complexing agent and solvent accompanying the electrolyte precursor may be replaced in advance with a high-boiling point solvent. However, from the viewpoint of production efficiency, it is not preferable to perform a solvent replacement operation, and therefore it is preferable to subject the pulverized product obtained in the pulverization step to heating in step (iii) as is. As the solvent that can be used in step (iii), as a solvent component other than the dispersant, those explained as solvents that can be used in step (i) above can be used. It is preferable to use a solvent that has a higher boiling point than the complexing agent and solvent used in the complexing step, and in particular, it is preferable to use a solvent that is generally considered to be a high-boiling point solvent, such as a mixture of an aromatic hydrocarbon solvent and an aromatic ether solvent.

[0092] In the production method of this embodiment, after the step (iii), it is preferable to remove the solvent including the dispersant by performing solid-liquid separation such as decantation, or by the same method as in the drying step described above. The conditions in the drying step for removing the solvent, such as the drying temperature and drying time, are the same as those in the drying step described above.

[0093] (crystal structure of solid electrolyte) Examples of the solid electrolyte obtained by the manufacturing method of this embodiment include Li6PS5X, Li 7-x PS 6-x X xExamples of the all-dielectric type crystal structure include those represented by (X = Cl, Br, I; x = 0.0 to 1.8) (see JP-A-2011-096630 and JP-A-2013-211171). The diffraction peaks of these all-dielectric type crystal structures appear around, for example, 2θ = 15.3°, 17.7°, 31.1°, 44.9°, and 47.7°.

[0094] Examples of the all-dielectric type crystal structure also include the following. A crystal structure represented by the compositional formula Li having the above-mentioned structural framework of Li7PS6 and in which part of P is substituted with Si 7-x P 1-y Si y S6 and Li 7+x P 1-y Si y The crystal structure represented by S6 (x is -0.6 to 0.6, y is 0.1 to 0.6) is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα rays, has peaks mainly appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The above compositional formula Li 7-x-2y PS 6-x-y Cl x The crystal structure represented by (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) is preferably cubic, and in X-ray diffraction measurement using CuKα rays, has peaks mainly appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The above compositional formula Li 7-x PS 6-x Ha x The crystal structure represented by (Ha is Cl or Br, and x is preferably 0.2 to 1.8) is preferably cubic, and in X-ray diffraction measurement using CuKα rays, has peaks mainly appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Note that these peak positions may shift within a range of ±0.5°.

[0095] The crystal structure of the solid electrolyte obtained by the production method of this embodiment is preferably an argyrodite-type crystal structure, since this structure provides higher ionic conductivity. The solid electrolyte obtained by the manufacturing method of this embodiment may have the argyrodite-type crystal structure or may have it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it has it as the main crystal. In this specification, "having it as the main crystal" means that the proportion of the target crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more.

[0096] Furthermore, from the viewpoint of obtaining higher ionic conductivity, the solid electrolyte obtained by the manufacturing method of this embodiment preferably does not contain crystalline Li3PS4 (β-Li3PS4). Whether or not a solid electrolyte does not contain crystalline Li3PS4 (β-Li3PS4) can be confirmed by the presence or absence of diffraction peaks at 2θ = 17.5° and 26.1° that are typical of crystalline Li3PS4. In this specification, a solid electrolyte is considered to be free of crystalline Li3PS4 (β-Li3PS4) if it does not have such diffraction peaks, or if it does have such peaks, the detected peaks are extremely small compared to the diffraction peaks of the argyrodite-type crystal structure.

[0097] The solid electrolyte obtained by the production method of this embodiment has an average particle size (D50) measured by a laser diffraction / scattering particle size distribution measurement method of preferably 0.01 μm or more and 100 μm or less, more preferably 0.03 μm or more and 50 μm or less, even more preferably 0.05 μm or more and 10 μm or less, and still more preferably 0.1 μm or more and 3.0 μm or less. Furthermore, the solid electrolyte obtained by the production method of this embodiment has a particle size at 90% cumulative volume (D90) measured by a laser diffraction / scattering particle size distribution measurement method of preferably 0.10 μm or more and 20.0 μm or less, more preferably 0.40 μm or more and 15.0 μm or less, and even more preferably 0.60 μm or more and 9.0 μm or less. [Example]

[0098] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0099] Example 1 Lithium sulfide and diphosphorus pentasulfide were weighed out in a molar ratio of 75:25 and added to a 6-liter stirrer-equipped reaction vessel under a nitrogen atmosphere. After adding toluene, the stirring blade was turned on and tetrahydrofuran (THF) was added dropwise at 20°C. After stirring for 72 hours, the reaction was stopped and PS4 3- The 3THF adduct complex of Li3PS4 with the structure was obtained. Next, the 3THF adduct of Li3PS4 was subjected to a reduced pressure drying treatment at 80°C for 2 hours, and then to a heat treatment at 180°C for 6 hours to obtain PS4 3- Crystalline Li3PS4 (β-Li3PS4) having the structure was obtained. The identity of the material was confirmed by powder X-ray diffraction measurements using an X-ray diffraction (XRD) device (SmartLab device, Rigaku Corporation) showing diffraction peaks at 17.5° and 25.7°. Lithium sulfide (LiS), lithium chloride (LiCl), and lithium bromide (LiBr) were added to the resulting crystalline Li3PS4 (β-Li3PS4) in molar ratios of 40:100:60, based on a 75:25 molar ratio of lithium sulfide to diphosphorus pentasulfide. Dowther mA solvent (Dow Chemical, 30% biphenyl, 70% diphenyl ether) was added in an amount equivalent to 10% by mass of the total of these materials. Furthermore, sodium dodecylbenzenesulfonate (boiling point: 444°C) was added as a dispersant in an amount equivalent to 5% by mass of the total of the above materials. The mixture was milled for 2 hours using a bead mill (Labostar Mini LMZ015, Ashizawa Finetech Co., Ltd.) to obtain a slurry containing the ground electrolyte precursor. Zirconia beads with a diameter of 0.3 mm were used for this milling process. The particle size distribution of the ground electrolyte precursor was measured, and the average particle size (D50) was 0.2 μm. The slurry obtained as described above was sealed in an autoclave and heated at 395° C. for 30 minutes, during which the internal pressure of the autoclave was 0.90 MPa. The solvent was then removed using a cannula, and dehydrated toluene was added and stirred, followed by decantation to remove the solvent, and the mixture was then heated and dried at 180°C for 2 hours to obtain a solid electrolyte having an argyrodite-type crystal structure. Powder X-ray diffraction measurement confirmed that the obtained solid electrolyte had an argyrodite-type crystal structure, as diffraction peaks appeared at 15.3°, 17.7°, 31.1°, 44.9°, and 47.7°. The particle size distribution of the obtained solid electrolyte was measured, and the average particle size (D50) was 0.82 μm, and the particle size at 90% of the cumulative volume (D90) was 1.7 μm. Furthermore, a SEM (scanning electron microscope) photograph of the solid electrolyte obtained in Example 1 is shown in FIG.

[0100] Example 2 A solid electrolyte was obtained in the same manner as in Example 1, except that oleylamine (boiling point: 350°C) was added as a dispersant to a mixture of crystalline Li3PS4 (β-Li3PS4) obtained in the same manner as in Example 1, Li2S, LiCl, LiBr, and DowthermA solvent in an amount of 10 mass% relative to the total amount of the raw materials. The particle size distribution of the obtained solid electrolyte was measured, and it was found that the average particle size (D50) was 1.4 μm and the particle size at 90% of the cumulative volume (D90) was 3.6 μm. Furthermore, a SEM (scanning electron microscope) photograph of the solid electrolyte obtained in Example 2 is shown in FIG.

[0101] Example 3 A solid electrolyte was obtained in the same manner as in Example 1, except that sodium dodecylbenzenesulfonate was added as a dispersant in an amount of 3 mass% relative to the total amount of the raw materials to a mixture of crystalline Li3PS4 (β-Li3PS4) obtained in the same manner as in Example 1, Li2S, LiCl, LiBr, and DowthermA solvent. The particle size distribution of the obtained solid electrolyte was measured, and it was found that the average particle size (D50) was 1.2 μm and the particle size at 90% of the cumulative volume (D90) was 4.4 μm.

[0102] Example 4 Lithium sulfide (LiS), diphosphorus pentasulfide (P2S5), lithium chloride (LiCl), and lithium bromide (LiBr) were pre-ground in a pin mill (100UPZ, manufactured by Hosokawa Micron Corporation) in a molar ratio of 47.5:12.5:25.0:15.0 and then mixed in a glass container. The container was then shaken to roughly mix the mixture. The resulting crude mixture was dispersed in a mixed solvent of dehydrated toluene (manufactured by Wako Pure Chemical Industries, Ltd.) and dehydrated isobutyronitrile (manufactured by Kishida Chemical Co., Ltd.) under a nitrogen atmosphere to form a slurry of approximately 10% by mass. The resulting slurry was mixed and ground in a bead mill while maintaining a nitrogen atmosphere. Specifically, 456 g of zirconia beads with a diameter of 0.5 mm were used as the grinding medium, and the bead mill was operated at a peripheral speed of 12 m / s and a flow rate of 500 ml / min. The slurry was then introduced into the mill and circulated for 1 hour. The treated slurry was placed in a nitrogen-purged Schlenk flask and dried under reduced pressure to prepare a raw material mixture. The raw material mixture obtained in the above step was dispersed in 300 ml of ethylbenzene (manufactured by Wako Pure Chemical Industries, Ltd.) to form a slurry. This slurry was placed in an autoclave (capacity 1000 ml, made of SUS316) equipped with a stirrer and a heating oil bath, and heat-treated at 200°C for 2 hours while stirring at a rotation speed of 200 rpm. After treatment, the mixture was dried under reduced pressure to distill off the solvent, and a treated product was obtained. To the calcined product obtained in the above step, DowthermA solvent was added in an amount that made the total amount 10 mass %, and further 5 mass % of sodium dodecylbenzenesulfonate was added as a dispersant, followed by mill pulverization in the same manner as in Example 1. The resulting slurry was heated directly in an autoclave at 395°C for 30 minutes. Thereafter, the solvent was removed using a cannula and the mixture was dried by heating, in the same manner as in Example 1. The particle size distribution of the obtained solid electrolyte was measured, and it was found that the average particle size (D50) was 1.4 μm and the particle size at 90% of the cumulative volume (D90) was 4.7 μm.

[0103] (Comparative Example 1) A solid electrolyte was obtained in the same manner as in Example 1, except that no dispersant was added to a mixture of crystalline Li3PS4 (β-Li3PS4) obtained in the same manner as in Example 1, Li2S, LiCl, LiBr, and DowthermA solvent. The particle size distribution of the obtained solid electrolyte was measured, and the average particle size (D50) was 4.3 μm, and the particle size at 90% of the cumulative volume (D90) was 7.6 μm. Furthermore, a SEM (scanning electron microscope) photograph of the solid electrolyte obtained in Comparative Example 1 is shown in FIG.

[0104] The average particle size (D50) and particle size at 90% cumulative volume (D90) of the solid electrolytes obtained in Examples 1 to 4 and Comparative Example 1 are shown below.

[0105] [Table 1] [Industrial Applicability]

[0106] According to the method for producing a crystalline solid electrolyte of the present embodiment, a solid electrolyte having a small particle size and high ionic conductivity can be produced, and is particularly suitable for use in producing a solid electrolyte having an argyrodite-type crystal structure. The solid electrolyte obtained by the manufacturing method of this embodiment is suitable for use in batteries, particularly in batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. A mixture of raw materials containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms is used to obtain an electrolyte precursor, and The electrolyte precursor is heated in a sealed pressure vessel in the presence of a solvent containing a dispersant having a linear or branched hydrocarbon group having 8 or more carbon atoms. A method for producing a sulfide solid electrolyte, including [the specified element].

2. The method for producing a sulfide solid electrolyte according to claim 1, wherein the boiling point of the dispersant is 170°C or higher.

3. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the dispersant is one or more selected from an anionic dispersant having linear or branched hydrocarbon groups having 8 to 30 carbon atoms, a cationic dispersant having linear or branched hydrocarbon groups having 8 to 30 carbon atoms, and a nonionic dispersant having linear or branched hydrocarbon groups having 8 to 30 carbon atoms.

4. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the dispersant is a sulfonate salt.

5. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the temperature at which the electrolyte precursor is heated is 250°C or more and 500°C or less.

6. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the internal pressure in the pressure vessel when heating the electrolyte precursor is 0.35 MPa or more and 2.0 MPa or less.

7. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the pressure vessel is an autoclave.

8. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the raw material contains at least chlorine as the halogen atom.

9. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the boiling point of the solvent is 190°C or higher.

10. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the solvent further comprises one or more selected from aromatic hydrocarbon solvents and ether-based solvents.

11. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the amount of the dispersant relative to the amount of the electrolyte precursor during the heating is 0.1 to 20% by mass.

12. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the ratio of the amount of the electrolyte precursor to the total amount of the electrolyte precursor and the solvent when performing the heating is 0.50 to 50% by mass.

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