Method for producing sulfide solid electrolyte

Abstract

To provide a method for producing sulfide solid electrolyte with high productivity and a small particle size.SOLUTION: A method for producing sulfide solid electrolyte includes: mixing raw material contents that include lithium atoms, phosphorus atoms, and sulfur atoms with a first solvent to obtain a precursor-containing mixture; mixing the precursor-containing mixture with a second solvent, which is incompatible with the first solvent, to obtain an emulsion; and removing the first solvent and the second solvent from the emulsion.SELECTED DRAWING: None

Description

[Technical field]

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

[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 to be used as power sources for these devices has become important. Conventionally, electrolytes containing flammable organic solvents have been used in batteries used for such purposes, but by making the battery fully solid-state, flammable organic solvents are not used in the battery, safety devices can be simplified, and manufacturing costs and productivity are excellent, so that batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed.

[0003] As a method for producing a solid electrolyte, Patent Document 1 discloses a method in which a liquid containing a solid electrolyte raw material and a solvent is supplied to a high-temperature medium and the solvent is evaporated to precipitate an argyrodite-type crystal structure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication 2019-169459 Summary of the Invention [Problem to be solved by the invention]

[0005] 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 having a small particle size with excellent productivity. [Means for solving the problem]

[0006] The method for producing a sulfide solid electrolyte according to the present invention includes the steps of: a method for producing a sulfide solid electrolyte, the method comprising: mixing a raw material containing a lithium atom, a phosphorus atom, and a sulfur atom with a first solvent to obtain a precursor-containing mixture; mixing the precursor-containing mixture with a second solvent that is incompatible with the first solvent to obtain an emulsion; and removing the first solvent and the second solvent from the emulsion; It is. Effect of the Invention

[0007] According to the present invention, a method for producing a sulfide solid electrolyte having a small particle size with excellent productivity can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] 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 the numerical ranges of "greater than or equal to", "less than or equal to", and "to" are values ​​that can be combined arbitrarily, and the numerical values ​​of the examples can also be used as the upper and lower limit values. Furthermore, provisions that are considered to be preferable can be adopted arbitrarily. In other words, one provision that is considered to be preferable can be adopted in combination with one or more other provisions that are considered to be preferable. It can be said that a combination of preferable things is more preferable.

[0009] (Findings Obtained by the Inventors to Achieve the Present Invention) As a result of intensive research aimed at solving the above problems, the present inventors have discovered the following and completed the present invention.

[0010] The method described in Patent Document 1 discloses a method in which a liquid containing a solid electrolyte raw material and a solvent is supplied to a high-temperature medium and the solvent is evaporated to precipitate an argyrodite-type crystal structure. However, it does not disclose that the particle size of the resulting solid electrolyte can be reduced by forming an emulsion using two types of solvents. It is desirable for the particle size of the sulfide solid electrolyte to be small. In lithium-ion batteries, the positive electrode material, the negative electrode material, and the electrolyte are all solid. Therefore, by reducing the particle size of the sulfide solid electrolyte, it becomes easier to form a contact interface between the active material and the sulfide solid electrolyte, and the path of ionic conduction and electronic conduction becomes good. However, the method of Patent Document 1 does not disclose any adjustment of the particle size of the resulting solid electrolyte, particularly any reduction in the particle size. In response to this, the present inventors discovered that a sulfide solid electrolyte having small particle size can be produced by mixing the raw material ingredients with a solvent, and then mixing it with another solvent to obtain an emulsion, and then removing the solvents.

[0011] (Various aspects of the present embodiment) A method for producing a sulfide solid electrolyte according to a first embodiment of the present invention includes the steps of: a method for producing a sulfide solid electrolyte, the method comprising: mixing a raw material containing a lithium atom, a phosphorus atom, and a sulfur atom with a first solvent to obtain a precursor-containing mixture; mixing the precursor-containing mixture with a second solvent that is incompatible with the first solvent to obtain an emulsion; and removing the first solvent and the second solvent from the emulsion; It is.

[0012] In the past, in order to obtain a small particle size solid electrolyte, it was common to crush the solid electrolyte afterwards using a crusher such as a bead mill. However, in the present invention, we focused on forming an emulsion by combining two types of solvents that are incompatible with each other. We thought that it would be possible to produce a small particle size sulfide solid electrolyte simply by making a solid electrolyte precursor into an emulsion and then removing the solvent. If a small particle size sulfide solid electrolyte could be obtained just by manipulating the solvent, it would be extremely efficient in terms of production efficiency.

[0013] In the manufacturing method of this embodiment, the term "precursor" refers to a precursor of a solid electrolyte that becomes a sulfide solid electrolyte by, as necessary, crystallizing by heating or in a solvent after removing the solvent. By sequentially mixing the raw material contents with the first solvent and the second solvent to form an emulsion, the solid electrolyte raw materials are uniformly mixed, and in some cases, they further react with each other to form a structure similar to the sulfide solid electrolyte to become a precursor, and it is believed that by removing the first solvent and the second solvent from this and, as necessary, crystallizing or in a solvent, the reaction between the raw materials proceeds to form the sulfide solid electrolyte. In the production method of this embodiment, the "precursor-containing mixture" is a mixture that contains at least the precursor and the first solvent, and may further contain unreacted raw materials, etc.

[0014] A method for producing a sulfide solid electrolyte according to a second aspect of the present embodiment is the same as the first aspect, one of the first solvent and the second solvent contains an alcohol solvent, and the other contains a hydrocarbon solvent having 5 to 40 carbon atoms; That is it.

[0015] When the first solvent or the second solvent contains an alcohol solvent, the raw materials are likely to be dispersed more uniformly, and therefore the electrolyte precursor can be obtained more efficiently. As a result, the production efficiency is improved and a high-quality sulfide solid electrolyte can be easily produced. Furthermore, by using a hydrocarbon solvent having 5 to 40 carbon atoms, which has low compatibility with the alcohol solvent, as the other of the first and second solvents, an emulsion can be formed efficiently.

[0016] 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 first solvent contains a hydrocarbon solvent having 5 to 40 carbon atoms, and the second solvent contains an alcohol solvent. That is it.

[0017] By including a hydrocarbon solvent in the first solvent, the solid electrolyte raw material is first uniformly dispersed in the first solvent, and then mixed with the second solvent including an alcohol solvent to form an emulsion. This makes it possible to suppress side reactions that may occur due to a long contact time between the precursor and the alcohol solvent, and as a result, it becomes easier to obtain a sulfide solid electrolyte having higher ionic conductivity.

[0018] A method for producing a sulfide solid electrolyte according to a fourth aspect of the present embodiment includes the steps of: removing one of the first solvent and the second solvent from the emulsion to obtain a slurry containing a sulfide solid electrolyte; and removing the other of the first solvent and the second solvent from the slurry to remove the first solvent and the second solvent from the emulsion. That is it.

[0019] A specific preferred method for removing the first and second solvents from an emulsion containing them is a stepwise method in which one of them is first removed and then the other is removed. By using such a method, the solvent can be easily removed and a sulfide solid electrolyte having a small particle size can be efficiently obtained.

[0020] A method for producing a sulfide solid electrolyte according to a fifth aspect of the present embodiment includes the steps of: supplying the emulsion to a medium which is higher than the boiling point of the first solvent and higher than the boiling point of the second solvent and which is liquid or gaseous, and evaporating the first solvent and the second solvent, thereby removing the first solvent and the second solvent from the emulsion; That is it.

[0021] According to this method, the emulsion can be supplied to a medium maintained at a high temperature, and the first solvent and the second solvent can be removed almost simultaneously, which is preferable from the viewpoint of efficiently obtaining a sulfide solid electrolyte having a small particle size.

[0022] A method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment includes the steps of: The first solvent contains a complexing agent. That is it.

[0023] Here, the complexing agent means a compound capable of forming a complex. When the solvent contains a complexing agent, the formation of the complex is promoted, and the dispersion state of the solid electrolyte raw material is easily maintained uniformly. Therefore, all the raw materials contained in the raw material content are easily contributed to the formation of the sulfide solid electrolyte, and as a result, it is easy to obtain a sulfide solid electrolyte having a higher ionic conductivity.

[0024] A method for producing a sulfide solid electrolyte according to a seventh aspect of the present embodiment is the same as the first to sixth aspects described above, The raw material further contains a halogen atom. That is it.

[0025] When the raw material contains halogen atoms, it becomes easier to obtain a sulfide solid electrolyte that exhibits higher ionic conductivity.

[0026] The method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is the same as the first to seventh aspects, except that The method further includes removing the first solvent and the second solvent from the emulsion, and then heat-treating the sulfide solid electrolyte to crystallize it. That is it.

[0027] By heat-treating a sulfide solid electrolyte, a crystalline structure is formed or its crystallinity is improved (i.e., it is "crystallized"), resulting in a high-quality sulfide solid electrolyte.

[0028] A method for producing a sulfide solid electrolyte according to a ninth aspect of the present embodiment is the same as the first to eighth aspects described above, The ratio of the first solvent to the second solvent is 10:90 to 90:10 by mass ratio. That is it. In addition, the method for producing a sulfide solid electrolyte according to a tenth aspect of the present embodiment is the same as the first to ninth aspects, except that The ratio of the raw material content to the first solvent is 1.0 g or more and 20.0 g or less per 100 ml of the first solvent; That is it.

[0029] The ratio of the first solvent to the second solvent and the ratio of the raw material contents to the first solvent vary depending on various factors such as which of the first solvent or the second solvent contains an alcohol solvent, the raw material contents used, and the crystal structure of the desired sulfide solid electrolyte. However, by keeping the ratio within the above range, for example, it is possible to more efficiently obtain a sulfide solid electrolyte having a small particle size.

[0030] A method for producing a sulfide solid electrolyte according to an eleventh aspect of the present embodiment includes the steps of: The stirring power when mixing the precursor-containing mixture with the second solvent is 0.01 W / m 3 That's all. That is it.

[0031] In the production method of the present embodiment, the droplet size of the emulsion can be made smaller by increasing the stirring power when forming the emulsion, which is preferable from the viewpoint of making the resulting sulfide solid electrolyte smaller in diameter. The stirring power is expressed by the following general formula and can be adjusted by the rotation speed, blade shape, etc. Agitation power (W / m 3 )=Np×ρ×n 3 ×d 5 / V Np: Power number (-) ρ: Density (kg / m 3 ) n: rotation speed (rps) d: Wing span (m) V: Capacity (m 3 )

[0032] (solid electrolyte) In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state under a nitrogen atmosphere at 25° C. The solid electrolyte in this embodiment is a solid electrolyte that contains lithium atoms, sulfur atoms, and phosphorus atoms and has ionic conductivity due to the lithium atoms.

[0033] The term "solid electrolyte" includes both amorphous solid electrolytes and crystalline solid electrolytes. In this specification, the crystalline solid electrolyte is a solid electrolyte in which a peak derived from the solid electrolyte is observed in the X-ray diffraction pattern in the X-ray diffraction measurement, and it does not matter whether or not there is a peak derived from the raw material of the solid electrolyte. That is, the crystalline solid electrolyte includes a crystal structure derived from the solid electrolyte, and a part of the crystal structure may be derived from the solid electrolyte, or the whole of the crystal structure may be derived from the solid electrolyte. And, as long as the crystalline solid electrolyte has the above-mentioned X-ray diffraction pattern, a part of the crystalline solid electrolyte may include an amorphous solid electrolyte. Therefore, the crystalline solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte to a crystallization temperature or higher. In this specification, the term "amorphous solid electrolyte" refers to an amorphous solid electrolyte that has a halo pattern in which no peaks other than those derived from the material are substantially observed in an X-ray diffraction pattern obtained by X-ray diffraction measurement, regardless of whether or not there are peaks derived from the raw materials of the solid electrolyte.

[0034] [Method of manufacturing sulfide solid electrolyte] The method for producing the sulfide solid electrolyte of the present embodiment includes the steps of: a method for producing a sulfide solid electrolyte, the method comprising: mixing a raw material containing a lithium atom, a phosphorus atom, and a sulfur atom with a first solvent to obtain a precursor-containing mixture; mixing the precursor-containing mixture with a second solvent that is incompatible with the first solvent to obtain an emulsion; and removing the first solvent and the second solvent from the emulsion; It is.

[0035] Obtaining a Precursor-Containing Mixture The manufacturing method of this embodiment includes mixing a raw material containing lithium atoms, phosphorus atoms, and sulfur atoms with a first solvent to obtain a precursor-containing mixture. In the manufacturing method of this embodiment, the ingredients will first be described.

[0036] (Raw material content) The raw material content used in this embodiment contains lithium atoms, sulfur atoms, and phosphorus atoms, preferably lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and more specifically, a substance containing one or more selected from the group consisting of these atoms (hereinafter, also referred to as "solid electrolyte raw material"). As the halogen atoms, chlorine atoms, bromine atoms, and iodine atoms are preferred, and chlorine atoms and bromine atoms are more preferred, and it is preferable that the raw material content contains at least two types of halogen atoms.

[0037] The raw materials contained in the raw material contents include, for example, lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; diphosphorus trisulfide (P 2 S 3 ), diphosphorus pentasulfide (P 2 S 5 ) and other phosphorus sulfides; various phosphorus fluorides (PF 3 , P.F. 5 ), various phosphorus chlorides (PCl 3 , PCl 5 , P 2 Cl 4 ), various phosphorus bromides (PBr 3 , PBr 5 ), various phosphorus iodides (PI 3 , P 2 I 4 Phosphorus halides such as thiophosphoryl fluoride (PSF 3 ), thiophosphoryl chloride (PSCl 3 ), thiophosphoryl bromide (PSBr 3 ), thiophosphoryl iodide (PSI 3 ), thiophosphoryl dichloride fluoride (PSCl 2 F), thiophosphoryl dibromide fluoride (PSBr 2a source material consisting of at least two atoms selected from the above four atoms, such as fluorine (F 2 ), Chlorine (Cl 2 ), Bromine (Br 2 ), iodine (I 2 ), preferably chlorine (Cl 2 ), Bromine (Br 2 ) are representative examples.

[0038] Examples of materials that can be used as raw materials other than those mentioned above include raw materials that contain at least one atom selected from the above four types of atoms and also contain atoms other than the four types of atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, and tin sulfide (SnS, SnS 2 ), metal sulfides such as aluminum sulfide and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium, such as sodium halides such as sodium iodide, sodium fluoride, sodium chloride and sodium bromide; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides and bismuth halides; phosphorus oxychloride (POCl 3 ), phosphorus oxybromide (POBr 3 ) and other phosphorus oxyhalides;

[0039] Among the raw materials contained in the raw material contents, lithium sulfide, diphosphorus trisulfide (P 2 S 3 ), diphosphorus pentasulfide (P 2 S 5 ) and other phosphorus sulfides, fluorine (F 2 ), Chlorine (Cl 2 ), Bromine (Br 2 ), iodine (I 2Preferred are halogen elements such as lithium fluoride, lithium chloride, lithium bromide, lithium iodide, and lithium halides. When oxygen atoms are introduced into the solid electrolyte, preferred are lithium oxide, lithium hydroxide, and phosphate compounds such as lithium phosphate.

[0040] The halogen atom is preferably a chlorine atom, a bromine atom, or an iodine atom, and is preferably at least one selected from these. Therefore, the lithium halide is preferably lithium chloride, lithium bromide, or lithium iodide, and the halogen element is preferably chlorine (Cl 2 ), Bromine (Br 2 ), iodine (I 2 ) is preferable. These may be used alone or in combination of two or more kinds.

[0041] Preferred examples of the combination of raw materials include a combination of lithium sulfide, diphosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, diphosphorus pentasulfide, and a simple halogen. As the lithium halide, lithium chloride, lithium bromide, and lithium iodide are preferred, and as the simple halogen, chlorine, bromine, and iodine are preferred.

[0042] In this embodiment, PS 4 Structure containing Li 3 P.S. 4 can also be used as part of the raw materials. 3 P.S. 4 The above is prepared by manufacturing or otherwise and used as a raw material. Li relative to total raw materials 3 P.S. 4 The content is preferably from 60 to 100 mol %, more preferably from 65 to 90 mol %, and further preferably from 70 to 80 mol %.

[0043] Also, Li 3 P.S. 4 When using a halogen atom, Li 3 P.S. 4The content of the halogen element relative to the total amount is preferably from 1 to 50 mol %, more preferably from 10 to 40 mol %, further preferably from 20 to 30 mol %, and even more preferably from 22 to 28 mol %.

[0044] The lithium sulfide used in this embodiment is preferably in the form of particles. The average particle size of lithium sulfide particles (D 50 In this specification, the average particle size (D 50 ) is the particle size at which the particle size distribution cumulative curve is accumulated from the smallest particle size to 50% (volume basis) of the total, and the volume distribution is the average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device. In addition, among the above-mentioned examples of raw materials, solid raw materials preferably have an average particle size similar to that of the lithium sulfide particles, that is, within the same range as the average particle size of the lithium sulfide particles.

[0045] When lithium sulfide, diphosphorus pentasulfide, and lithium halide are used as raw materials, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 70 to 82 mol%, more preferably 72 to 80 mol%, and even more preferably 74 to 80 mol%, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity. When lithium sulfide, diphosphorus pentasulfide, lithium halide, and other raw materials used as necessary are used, the content of lithium sulfide and diphosphorus pentasulfide relative to the total of these is preferably 50 to 100 mol%, more preferably 55 to 85 mol%, and even more preferably 60 to 80 mol%.

[0046] When lithium chloride and lithium bromide are used in combination as the lithium halide, from the viewpoint of improving ion conductivity, the ratio of lithium chloride to the total of lithium chloride and lithium bromide is preferably 1 to 99 mol%, more preferably 10 to 80 mol%, further preferably 20 to 70 mol%, and particularly preferably 25 to 45 mol%.

[0047] In the case where a halogen element is used as a raw material, and lithium sulfide and diphosphorus pentasulfide are used, the ratio of the number of moles of lithium sulfide excluding the same number of moles of lithium sulfide as the halogen element to the total number of moles of lithium sulfide and diphosphorus pentasulfide excluding the same number of moles of lithium sulfide as the halogen element is preferably within the range of 60 to 90%, more preferably within the range of 65 to 85%, even more preferably within the range of 68 to 82%, even more preferably within the range of 72 to 78%, and particularly preferably within the range of 73 to 77%. This is because higher ion conductivity can be obtained at these ratios. From the same viewpoint, when lithium sulfide, diphosphorus pentasulfide, and a halogen element are used, the content of the halogen element relative to the total amount of lithium sulfide, diphosphorus pentasulfide, and the halogen element is preferably 1 to 50 mol%, more preferably 2 to 40 mol%, even more preferably 3 to 25 mol%, and even more preferably 3 to 15 mol%.

[0048] When lithium sulfide, diphosphorus pentasulfide, a halogen element, and a lithium halide are used, the content of the halogen element (α mol %) and the content of the lithium halide (β mol %) relative to the total amount thereof preferably satisfy the following formula (2), more preferably satisfy the following formula (3), even more preferably satisfy the following formula (4), and even more preferably satisfy the following formula (5). 2≦2α+β≦100…(2) 4≦2α+β≦80 …(3) 6≦2α+β≦50 …(4) 6≦2α+β≦30 …(5)

[0049] When two types of halogens are used as simple substances, the molar number of one halogen atom in the substance is A1 and the molar number of the other halogen atom in the substance is A2, and A1:A2 is preferably 1 to 99:99 to 1, more preferably 10:90 to 90:10, even more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0050] (First Solvent) As the first solvent used in the present embodiment, a wide variety of solvents that have conventionally been used in the production of solid electrolytes can be used. Examples of the first solvent include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; solvents containing carbon atoms such as alcohol solvents, ester solvents, aldehyde solvents, ketone solvents, ether solvents, and solvents containing carbon atoms and heteroatoms; and the like. The first solvent may be appropriately selected from these solvents.

[0051] More specifically, examples of the solvent include aliphatic hydrocarbon solvents such as hexane, pentane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane; alicyclic hydrocarbon solvents such as cyclohexane and methylcyclohexane; aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene, chlorotoluene, and bromobenzene; alcohol solvents such as ethanol and butanol; aldehyde solvents such as formaldehyde, acetaldehyde, and dimethylformamide, and ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as dibutyl ether, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole; and solvents containing carbon atoms and hetero atoms such as acetonitrile, dimethyl sulfoxide, and carbon disulfide.

[0052] Among these solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, ether solvents, and alcohol solvents are preferred. As the first solvent, these solvent components may be used alone, or a combination of a plurality of solvent components may be used.

[0053] The first solvent used in the present embodiment preferably contains an alcohol solvent and a complexing agent from the viewpoint of promoting the reaction of the solid electrolyte raw materials, while preferably contains a complexing agent and a hydrocarbon solvent from the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte while promoting the reaction of the solid electrolyte raw materials.

[0054] (alcohol solvent) Specific examples of alcohol solvents include primary and secondary aliphatic alcohols such as methanol, ethanol, isopropanol, butanol, and 2-ethylhexyl alcohol; polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, and hexanediol; alicyclic alcohols such as cyclopentanol, cyclohexanol, and cyclopentylmethanol; aromatic alcohols such as butylphenol, benzyl alcohol, phenethyl alcohol, naphthol, and diphenylmethanol; and alkoxy alcohols such as methoxyethanol, propoxyethanol, and butoxyethanol. As the alcohol solvent, among the various solvents mentioned above, aliphatic alcohols are preferred, primary aliphatic alcohols are more preferred, methanol and ethanol are further preferred, and ethanol is particularly preferred.

[0055] (Hydrocarbon Solvent) As described above, examples of the hydrocarbon solvent include aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents. One or more solvents selected from these can be used, but it is preferable to use a solvent selected from aliphatic hydrocarbon solvents. Regarding the carbon number of the hydrocarbon solvent, it is preferable to use a hydrocarbon solvent having 5 to 40 carbon atoms, which has low compatibility with alcohol solvents, it is more preferable to use a hydrocarbon solvent having 6 to 30 carbon atoms, and it is even more preferable to use a hydrocarbon solvent having 7 to 20 carbon atoms.

[0056] The first solvent used in the present embodiment preferably contains a complexing agent, which will be described below, as a part thereof.

[0057] (Complexing Agent) As described above, the complexing agent is a compound that easily forms a complex with the solid electrolyte raw material contained in the raw material content. For example, lithium sulfide and diphosphorus pentasulfide, which are preferably used as solid electrolyte raw materials, and Li 3 P.S. 4 and a solid electrolyte raw material containing a halogen atom (hereinafter, these are also collectively referred to as "solid electrolyte raw material, etc.").

[0058] The complexing agent can be used without any particular limitation as long as it has the above-mentioned properties, and is preferably a compound containing an atom having a high affinity with lithium atoms, such as a nitrogen atom, an oxygen atom, a chlorine atom, or other heteroatom, and more preferably a compound having a group containing such a heteroatom, because such a heteroatom or group containing such a heteroatom can be coordinated (bonded) with lithium.

[0059] It is considered that the heteroatoms present in the molecules of the complexing agent have a high affinity with lithium atoms and have a property of easily forming a complex (hereinafter, also simply referred to as a "complex") by bonding with the solid electrolyte raw material, etc. Therefore, it is considered that a complex is formed by mixing the above-mentioned solid electrolyte raw material with the complexing agent, and the dispersion state of the solid electrolyte raw material, particularly the dispersion state of the halogen atoms, is easily maintained uniformly, and as a result, a sulfide solid electrolyte with high ionic conductivity is obtained.

[0060] Whether the complexing agent is capable of forming a complex with the solid electrolyte raw material or the like can be directly confirmed by an infrared absorption spectrum measured by, for example, FT-IR analysis (diffuse reflectance method).

[0061] In the production method of this embodiment, the complexing agent is preferably a compound containing an oxygen atom as a heteroatom. The compound containing an oxygen atom is preferably a compound having one or more functional groups selected from an ether group and an ester group as a group containing an oxygen atom, and among these, a compound having an ether group is particularly preferred. That is, as a complexing agent containing an oxygen atom, an ether compound is particularly preferred.

[0062] Examples of the ether compound include ether compounds such as aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, and these can be used alone or in combination of two or more kinds.

[0063] More specifically, examples of aliphatic ethers include monoethers such as dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, and tert-butyl methyl ether; diethers such as dimethoxymethane, dimethoxyethane, diethoxymethane, and diethoxyethane; polyethers having three or more ether groups, such as diethylene glycol dimethyl ether (diglyme) and triethylene oxide glycol dimethyl ether (triglyme); and ethers containing hydroxyl groups, such as diethylene glycol and triethylene glycol. The aliphatic ether preferably has 2 or more carbon atoms, more preferably 3 or more, and even more preferably 4 or more carbon atoms, and the upper limit is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic ether is preferably 1 or more, and the upper limit is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0064] Examples of alicyclic ethers include ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane, and dioxolane. Examples of heterocyclic ethers include furan, benzofuran, benzopyran, dioxene, dioxin, morpholine, methoxyindole, and hydroxymethyldimethoxypyridine. The alicyclic ether and heterocyclic ether preferably have 3 or more, more preferably 4 or more, and the upper limit thereof is preferably 16 or less, more preferably 14 or less.

[0065] Examples of aromatic ethers include methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, diphenyl ether, benzyl phenyl ether, and naphthyl ether. The aromatic ether preferably has 7 or more, more preferably 8 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0066] The ether compound used in the present embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom.

[0067] Among the above ether compounds, from the viewpoint of obtaining higher ionic conductivity, aliphatic ethers are preferred, and dimethoxyethane and tetrahydrofuran are more preferred.

[0068] Examples of the ester compound include ester compounds such as aliphatic esters, alicyclic esters, heterocyclic esters, and aromatic esters, and these can be used alone or in combination of two or more kinds.

[0069] More specifically, examples of aliphatic esters include formic acid esters such as methyl formate, ethyl formate, triethyl formate, etc.; acetate esters such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, etc.; propionate esters such as methyl propionate, ethyl propionate, propyl propionate, butyl propionate, etc.; oxalate esters such as dimethyl oxalate, diethyl oxalate, etc.; malonate esters such as dimethyl malonate, diethyl malonate, etc.; and succinate esters such as dimethyl succinate, diethyl succinate, etc.

[0070] The number of carbon atoms in the aliphatic ester is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, with the upper limit being preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic ester is preferably 1 or more, more preferably 2 or more, and the upper limit being preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0071] Examples of the alicyclic esters include methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, dimethyl cyclohexanedicarboxylate, dibutyl cyclohexanedicarboxylate, and dibutyl cyclohexenedicarboxylate. Examples of the heterocyclic esters include methyl pyridinecarboxylate, ethyl pyridinecarboxylate, propyl pyridinecarboxylate, methyl pyrimidinecarboxylate, ethyl pyrimidinecarboxylate, and lactones such as acetolactone, propiolactone, butyrolactone, and valerolactone.

[0072] The alicyclic ester and heterocyclic ester each preferably have 3 or more, more preferably 4 or more, and the upper limit thereof is preferably 16 or less, more preferably 14 or less.

[0073] Examples of aromatic esters include benzoic acid esters such as methyl benzoate, ethyl benzoate, propyl benzoate, and butyl benzoate; phthalic acid esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, butyl benzyl phthalate, and dicyclohexyl phthalate; and trimellitic acid esters such as trimethyl trimellitate, triethyl trimellitate, tripropyl trimellitate, tributyl trimellitate, and trioctyl trimellitate.

[0074] The aromatic ester preferably has 8 or more, more preferably 9 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0075] The ester compound used in the present embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom.

[0076] Among the above ester compounds, from the viewpoint of obtaining higher ionic conductivity, aliphatic esters are preferred, acetate esters are more preferred, and ethyl acetate is particularly preferred.

[0077] When the first solvent contains a complexing agent and an alcohol solvent, the ratio of the complexing agent in the first solvent is preferably 1.0 to 50 volume %, more preferably 5.0 to 40 volume %, and even more preferably 10 to 30 volume %, in terms of the volume ratio of the complexing agent to the total amount of the first solvent. The ratio of the alcohol solvent in the first solvent is preferably 50 to 99% by volume, more preferably 60 to 95% by volume, and even more preferably 70 to 90% by volume, in terms of the volume ratio of the alcohol solvent to the total amount of the first solvent. Furthermore, the ratio of the total amount of the complexing agent and the alcohol solvent in the first solvent is preferably 50 to 100% by volume, more preferably 70 to 100% by volume, and even more preferably 90 to 100% by volume, based on the total amount of the first solvent.

[0078] On the other hand, when the first solvent contains a complexing agent and a hydrocarbon solvent, the ratio of the complexing agent in the first solvent is preferably 1.0 to 50 volume %, more preferably 5.0 to 40 volume %, and even more preferably 10 to 30 volume %, in terms of the volume ratio of the complexing agent to the total amount of the first solvent. The ratio of the hydrocarbon solvent in the first solvent is preferably 50 to 99% by volume, more preferably 60 to 95% by volume, and even more preferably 70 to 90% by volume, in terms of the volume ratio of the hydrocarbon solvent to the total amount of the first solvent. The ratio of the total amount of the complexing agent and the hydrocarbon solvent in the first solvent is preferably 50 to 100% by volume, more preferably 70 to 100% by volume, and even more preferably 90 to 100% by volume, based on the total amount of the first solvent.

[0079] From the viewpoint of efficiently forming an emulsion, the ratio of the first solvent to the second solvent is preferably 10:90 to 90:10 in mass ratio (mass ratio of the first solvent:mass ratio of the second solvent), more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0080] (mixture) In the manufacturing method of this embodiment, the above-mentioned raw material ingredients and a first solvent are mixed to obtain a precursor-containing mixture. Here, the ratio of the raw material content to the first solvent is preferably 1.0 g or more and 20.0 g or less, more preferably 1.5 g or more and 15.0 g or less, and even more preferably 2.0 g or more and 12.0 g or less, per 100 ml of the first solvent, from the viewpoint of obtaining a sulfide solid electrolyte with a small particle size.

[0081] There is no particular limitation on the method for mixing the raw material ingredients and the first solvent, and the raw material ingredients and the first solvent may be mixed by putting them into an apparatus capable of mixing the raw material ingredients and the solvent. However, when a halogen element is used as the solid electrolyte raw material, the solid electrolyte raw material may not be solid, specifically, fluorine and chlorine are gaseous, and bromine is liquid, at room temperature and normal pressure. In such a case, for example, when the solid electrolyte raw material is liquid, it may be supplied into the tank together with the solvent separately from the other solid solid electrolyte raw materials, and when the solid electrolyte raw material is gas, it may be supplied by blowing into the solvent mixed with the solid solid electrolyte raw material.

[0082] The manufacturing method of this embodiment is characterized by including mixing the raw material ingredients with the first solvent. At that time, mixing can be performed by a method that does not use a device generally called a pulverizer, such as a media type pulverizer such as a ball mill or a bead mill, which is used for the purpose of pulverizing the solid electrolyte raw material, to obtain a mixture containing a precursor of the solid electrolyte (precursor-containing mixture). In order to shorten the mixing time for obtaining the precursor or to pulverize the mixture into fine particles, the raw material ingredients and the first solvent may be mixed together and then pulverized by a pulverizer.

[0083] The device for mixing the raw material ingredients and the first solvent may be, for example, a mechanical stirring mixer equipped with stirring blades in a tank. The mechanical stirring mixer may be a high-speed stirring mixer, a double-arm mixer, etc., and the high-speed stirring mixer is preferably used from the viewpoint of increasing the uniformity of the solid electrolyte raw material in the mixture of the solid electrolyte raw material and the solvent and obtaining a higher ion conductivity. In addition, the high-speed stirring mixer may be a vertical shaft rotating mixer, a horizontal shaft rotating mixer, etc., and either type of mixer may be used.

[0084] The shape of the impeller used in the mechanical stirring mixer includes anchor type, blade type, arm type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, C-type blade type, etc., and from the viewpoint of improving the uniformity of the solid electrolyte raw material and obtaining a higher ion conductivity, the shovel type, flat blade type, C-type blade type, etc. are preferred. In addition, the mechanical stirring mixer may be provided with a circulation line that discharges the material to be stirred outside the mixer and then returns it to the inside of the mixer. This allows the heavy raw material to be stirred without settling or stagnating, making it possible to mix more uniformly.

[0085] The location of the circulation line is not particularly limited, but it is preferable to install it at a location where it can be discharged from the bottom of the mixer and returned to the top of the mixer. This makes it easier to uniformly mix the solid electrolyte raw material, which tends to settle, by carrying it on the convection caused by the circulation. Furthermore, it is preferable that the return port is located below the liquid surface of the object to be mixed. This can prevent the object to be mixed from splashing and adhering to the wall surface inside the mixer.

[0086] The temperature conditions when mixing the solid electrolyte raw material and the first solvent are not particularly limited, and are, for example, −30 to 100° C., preferably −10 to 50° C., and more preferably about room temperature (23° C.) (for example, about room temperature ±5° C.) The mixing time is about 0.1 to 150 hours, and from the viewpoint of more uniform mixing and obtaining higher ionic conductivity, is preferably 1 to 120 hours, more preferably 4 to 100 hours, and even more preferably 8 to 80 hours.

[0087] When a complexing agent is used as the first solvent, a complex is formed by mixing the solid electrolyte raw material and the complexing agent. More specifically, the complex is considered to be formed by the lithium atom, sulfur atom, phosphorus atom, and halogen atom contained in the solid electrolyte raw material being directly bonded to each other with and / or without the complexing agent due to the action of the complexing agent and the lithium atom, sulfur atom, phosphorus atom, and halogen atom contained in the solid electrolyte raw material. That is, in the manufacturing method of this embodiment, the complex obtained by mixing the solid electrolyte raw material and the complexing agent can be said to be composed of the complexing agent, lithium atom, sulfur atom, phosphorus atom, and halogen atom. The complex obtained in this embodiment is not completely soluble in the complexing agent, which is a liquid, and is usually a solid, so that the complex is obtained as a suspension in which the complex is suspended in a solvent containing the complex.

[0088] Mixing the Precursor-Containing Mixture with a Second Solvent The manufacturing method of this embodiment is as follows: mixing the precursor-containing mixture with a second solvent that is immiscible with the first solvent to obtain an emulsion; Includes. By mixing the precursor-containing mixture with the second solvent to form an emulsion, the precursors contained in the precursor-containing mixture dispersed in the emulsion are scattered in the form of islands throughout the emulsion. Therefore, the sulfide solid electrolyte obtained upon removing the first solvent and the second solvent described below has a small particle size without the need for subsequent crushing treatment or the like.

[0089] (Second Solvent) As described above, the second solvent used in the present embodiment is required to be incompatible with the first solvent described above, and thus an emulsion can be formed by mixing the precursor-containing mixture including the first solvent with the second solvent. Details of the second solvent that can be selected are the same as those given above for the first solvent, except that the second solvent must be incompatible with the first solvent selected as above.

[0090] Specific examples of combinations of the first and second solvents include those in which one of the first and second solvents contains an alcohol solvent and the other contains a hydrocarbon solvent having 5 to 40 carbon atoms. More specific examples of combinations include the following embodiments (1) to (4). (1) The first solvent contains an alcohol solvent, and the second solvent contains a hydrocarbon solvent having 5 to 40 carbon atoms. (2) The first solvent contains a hydrocarbon solvent having 5 to 40 carbon atoms, and the second solvent contains an alcohol solvent. (3) The first solvent contains a complexing agent and an alcohol solvent, and the second solvent contains a hydrocarbon solvent having 5 to 40 carbon atoms. (4) The first solvent contains a complexing agent and a hydrocarbon solvent having 5 to 40 carbon atoms, and the second solvent contains an alcohol solvent. Among the above embodiments (1) to (4), (1) and (3) in which the first solvent contains an alcohol solvent have the advantage that the reaction between the solid electrolyte raw materials tends to proceed quickly, whereas (2) and (4) in which the second solvent contains an alcohol solvent have the advantage that the contact time between the precursor and the alcohol solvent is shortened, making side reactions less likely to occur. In addition, in the cases of (3) and (4) in which the first solvent contains a complexing agent, the formation of a complex in the precursor is promoted and the solid electrolyte raw material is uniformly dispersed, making it easier to obtain a sulfide solid electrolyte having higher ionic conductivity.

[0091] When mixing the precursor-containing mixture with the second solvent, it is preferable to stir more vigorously to disperse the precursor more uniformly in the emulsion. Specifically, the stirring power is set to 0.010 W / m 3 More preferably, it should be 1.00 W / m 3 More preferably, it should be 10.0 W / m or more. 3 More preferably, it is equal to or higher.

[0092] [Removing the first and second solvents] The manufacturing method of this embodiment is as follows: removing the first solvent and the second solvent from the emulsion; Includes.

[0093] Specific methods for removing the first solvent and the second solvent from the emulsion include the stepwise removal described below in (1) and the collective removal described below in (2). (1) removing one of the first solvent and the second solvent from the emulsion to obtain a slurry containing a sulfide solid electrolyte, and removing the other of the first solvent and the second solvent from the slurry. (2) Removing the first and second solvents from the emulsion by supplying the emulsion to a medium that is hotter than the boiling point of the first solvent and hotter than the boiling point of the second solvent and that is liquid or gas, and evaporating the first and second solvents.

[0094] Furthermore, specific examples of the above-mentioned stepwise removal mode (1) include the following modes (1-1) and (1-2). (1-1) The first solvent is removed from the emulsion to obtain a slurry containing a sulfide solid electrolyte, and then the second solvent is removed from the slurry. (1-2) The second solvent is removed from the emulsion to obtain a slurry containing a sulfide solid electrolyte, and then the first solvent is removed from the slurry.

[0095] In the above-mentioned stepwise removal, the first solvent and the second solvent are removed stepwise. As a specific method for removing the first solvent or the second solvent in the first step (i.e., the step of removing the first solvent in embodiment (1-1) or the step of removing the second solvent in embodiment (1-2)), it is preferable to remove the first solvent or the second solvent while maintaining the dispersed state of the emulsion from the viewpoint of preventing aggregation of the precursor. Therefore, it is preferable to perform the removal by a drying treatment under normal pressure or reduced pressure, rather than a liquid-liquid separation treatment using a centrifuge or the like. The drying treatment may be carried out at room temperature, or may be carried out while heating using a dryer or the like. The drying treatment may be carried out under any pressure condition, including pressure, normal pressure, and reduced pressure, but is preferably carried out under normal pressure or reduced pressure. In particular, when drying at a lower temperature is required, it is preferable to dry under reduced pressure, or even under vacuum, using a vacuum pump or the like. The temperature conditions for drying may be a temperature equal to or higher than the boiling point of the solvent to be removed. Since the temperature conditions may vary depending on the types of the first and second solvents used, the specific temperature conditions cannot be generally stated, but the temperature is preferably 5°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, still more preferably 50°C or higher, and particularly preferably 100°C or higher, with the upper limit being preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 150°C or lower.

[0096] As for the pressure conditions, as described above, normal pressure or reduced pressure is preferable. In the case of reduced pressure, specifically, the pressure is preferably 85 kPa or less, more preferably 80 kPa or less, and even more preferably 70 kPa or less. The lower limit may be a vacuum (0 Kpa). Considering the ease of adjusting the pressure, the pressure is preferably 1 kPa or more, more preferably 2 kPa or more, and even more preferably 3 kPa or more.

[0097] When removing the remaining first solvent or second solvent from the slurry obtained as described above, a drying treatment may be performed at a higher temperature or under reduced pressure conditions, but if the first solvent or second solvent remaining in the slurry has a high boiling point, it is preferable to remove it by solid-liquid separation such as filtration, centrifugation, decantation, etc. Furthermore, the sulfide solid electrolyte obtained in this manner may be washed by repeatedly adding a low boiling point solvent and removing it by solid-liquid separation, or may be dried after adding it.

[0098] In the above-mentioned embodiment (2) of simultaneous removal, the first solvent and the second solvent are removed almost simultaneously by supplying the emulsion to a medium heated to a high temperature, and a sulfide solid electrolyte can be produced, which is excellent in terms of production efficiency.

[0099] (A medium heated above the boiling point of the solvent) The medium used in the manufacturing method of this embodiment that is heated to a temperature higher than the boiling points of the first solvent and the second solvent may be either a gas or a liquid. When a liquid medium is used, a high-boiling point liquid medium having a boiling point higher than that of the solvent is used. The high-boiling point liquid medium is preferably one that does not react with or dissolve the resulting particulate sulfide solid electrolyte, and therefore, it is preferable to use a hydrocarbon compound.

[0100] The hydrocarbon compound used as the medium may be selected from those exemplified as solvents that can be used in obtaining the precursor-containing mixture, and one having a higher boiling point may be used. Preferred examples include those described as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, and more preferred examples include those described as aliphatic hydrocarbon solvents and alicyclic hydrocarbon solvents.

[0101] Considering that the high-boiling liquid medium is likely to have a boiling point higher than that of the solvent, the carbon number of the high-boiling liquid medium is preferably 8 or more, more preferably 10 or more, and the upper limit is preferably 40 or less, more preferably 20 or less, and even more preferably 16 or less, and examples of aliphatic hydrocarbon compounds include those having such a carbon number.

[0102] Examples of aliphatic hydrocarbon compounds that are preferably used as high-boiling point liquid solvents include aliphatic hydrocarbon compounds such as octane, 2-ethylhexane, decane, undecane, dodecane, and tridecane. The high-boiling point liquid medium may be used alone or in combination of two or more of the above-listed high-boiling point liquid mediums.

[0103] Specific examples of the gas medium include inert gases such as nitrogen and argon, but hydrogen sulfide and mixtures of hydrogen sulfide and inert gases can also be used.

[0104] (heating) In the manufacturing method of this embodiment, the medium is heated to a temperature higher than the boiling points of the first solvent and the second solvent. Here, when the first solvent and the second solvent are each a mixture of multiple components, the boiling point of each solvent refers to the boiling point of the component that has the highest boiling point among the components contained in each solvent, provided that the boiling points of trace components contained in the solvent at a ratio of 3 mass% or less are not taken into consideration. In addition, the medium is preferably heated to a temperature 20° C. or more higher than the boiling points of the first solvent and the second solvent, more preferably heated to a temperature 40° C. or more higher, and even more preferably heated to a temperature 60° C. or more higher.

[0105] When the medium is a liquid, the specific temperature to which the medium is heated is preferably 120°C or higher and 500°C or lower, more preferably 150°C or higher and 450°C or lower, and even more preferably 170°C or higher and 400°C or lower, from the viewpoint of efficiently evaporating the solvent while suppressing decomposition of the precursor. When the medium is a gas, the specific temperature to which the medium is heated is preferably 120°C or higher and 700°C or lower, more preferably 150°C or higher and 600°C or lower, and even more preferably 170°C or higher and 500°C or lower, for the same reasons as above.

[0106] The pressure conditions when the emulsion is supplied to the heated medium are not particularly limited, but from the viewpoint of efficiently removing the solvent, normal pressure or reduced pressure is preferable.

[0107] (Method of supply) Specific methods for supplying the emulsion to the medium in the embodiment of collective removal (2) above include injection, dripping, and spraying. From the viewpoint of atomizing the resulting sulfide solid electrolyte, it is preferable to reduce the amount of precursor contained in one drop, and therefore it is preferable to supply the precursor-containing material to the medium by dripping or spraying. More specific examples include injection or dripping using a tube pump, and spraying using a microspray. Here, in order to atomize and homogenize the solid electrolyte, it is preferable to supply the precursor-containing mixture in a constant amount at a time. The supply amount can be appropriately adjusted depending on the medium used, temperature, etc., but when the precursor-containing mixture is dropped into the medium, it is preferable to supply the precursor-containing mixture in a constant amount at a small amount per supply port, for example, about 0.1 to 10 liters / minute.

[0108] (Heat treatment) In the manufacturing method of the present embodiment, the sulfide solid electrolyte obtained as described above may be used as it is, or may further include heat-treating the sulfide solid electrolyte. By heat-treating the sulfide solid electrolyte obtained as described above, a crystal structure is formed or the crystallinity is improved, so that a high-quality sulfide solid electrolyte can be obtained.

[0109] The heating temperature in the heat treatment is usually preferably 130° C. or higher, more preferably 140° C. or higher, and even more preferably 150° C. or higher, and the upper limit is preferably 700° C. or lower, more preferably 600° C. or lower, and even more preferably 500° C. or lower. The heating temperature means the maximum temperature during the heat treatment. The heat treatment time can be adjusted appropriately depending on the apparatus and amount used, but is usually 1 minute to 24 hours, preferably 10 minutes to 20 hours, more preferably 30 minutes to 16 hours, and even more preferably 1 hour to 12 hours. The heat treatment time means the time during which the heating temperature is maintained during the heat treatment.

[0110] The method of heat treatment is not particularly limited, and examples thereof include a method using a vacuum heating device, a calcination furnace, etc. Furthermore, for industrial purposes, a roller hearth kiln or a rotary kiln having a heating means and a feeding mechanism can also be used, and the method may be selected according to the amount of heat treatment.

[0111] (Amorphous sulfide solid electrolyte) The sulfide solid electrolyte obtained by the manufacturing method of this embodiment is either an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte. The amorphous sulfide solid electrolyte obtained by the manufacturing method of the present embodiment contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Representative examples include 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., which are solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide; and solid electrolytes containing other atoms such as oxygen and silicon atoms, e.g., Li 2 SP 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 -P 2 S 5 In order to obtain a higher ionic conductivity, a solid electrolyte such as Li-LiI is preferable. 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 An amorphous sulfide solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as -LiI-LiBr, is preferred. The types of atoms constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectroscopic analyzer.

[0112] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be a so-called glass ceramic obtained by heating an amorphous sulfide solid electrolyte to a crystallization temperature or higher, and the crystal structure thereof may be Li 3 P.S. 4 Crystal structure, Li 4 P 2 S 6 Crystal structure, Li 7 P.S. 6 Crystal structure, Li 7 P 3 S 11 Examples of such structures include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0113] Li 4-x Ge 1-x P x S 4 Thio-LISICON Region II crystal structure (Kanno et al., Journal of The Electrochemical Society, 148(7)A742-746(2001)), Li 4-x Ge 1-x P x S 4 Also included are crystal structures similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725). The crystal structure of the crystalline sulfide solid electrolyte obtained by the method for producing a solid electrolyte of this embodiment is preferably the thio-LISICON Region II type crystal structure among the above, since it has a higher ionic conductivity. Here, the "thio-LISICON Region II type crystal structure" refers to a Li 4-x Ge 1-x P x S 4 Thio-LISICON Region II crystal structure, Li 4-x Ge 1-x P x S 4This indicates that the crystal structure is either similar to that of the thio-LISICON Region II type.

[0114] The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may contain the above-mentioned thiolicon region II type crystal structure or may contain it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it contains it as the main crystal. In this specification, "containing it as the main crystal" means that the ratio of the target crystal structure among the crystal structures 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 may contain crystalline Li 3 P.S. 4 (β-Li 3 P.S. 4 ) is preferably not included.

[0115] In X-ray diffraction measurements using CuKα radiation, Li 3 P.S. 4 Diffraction peaks of the crystal structure appear, for example, at 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, and Li 4 P 2 S 6 Diffraction peaks of the crystal structure appear, for example, at 2θ = 16.9°, 27.1°, and 32.5°, and Li 7 P.S. 6 Diffraction peaks of the crystal structure appear, for example, at 2θ = 15.3°, 25.2°, 29.6°, and 31.0°. 7 P 3 S 11 Diffraction peaks of the crystal structure appear, for example, at 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°. 4-x Ge 1-x P x S 4Diffraction peaks of the thio-LISICON Region II type crystal structure appear, for example, near 2θ = 20.1°, 23.9°, and 29.5°, and Li 4-x Ge 1-x P x S 4 Diffraction peaks of a crystal structure similar to the thio-LISICON Region II type appear, for example, near 2θ = 20.2 and 23.6°. Note that these peak positions may shift within a range of ±0.5°.

[0116] The above-mentioned Li 7 PS 6 Crystalline sulfide solid electrolytes having a framework structure of and having an argyrodite-type crystal structure formed by substituting a part of P with Si are also preferably mentioned. As a composition formula of the argyrodite-type crystal structure, for example, the composition formula Li 7-x P 1-y Si y S 6 And Li 7+x P 1-y Si y S 6 (where x is -0.6 to 0.6 and y is 0.1 to 0.6). The argyrodite-type crystal structure represented by this composition formula is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα rays, 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°.

[0117] As a composition formula of the argyrodite-type crystal structure, the composition formula Li 7-x-2y PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) is also mentioned. The argyrodite-type crystal structure represented by this composition formula is preferably cubic, and in X-ray diffraction measurement using CuKα rays, 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°. The formula for the argyrodite crystal structure is Li 7-x P.S. 6-x Ha x (Ha is Cl or Br, and x is preferably 0.2 to 1.8). The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0° in X-ray diffraction measurement using CuKα radiation. The positions of these peaks may vary within a range of ±0.5°.

[0118] (Properties of sulfide solid electrolyte) The sulfide solid electrolyte obtained by the production method of this embodiment has a particulate shape. The average particle size (D 50 ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is preferably 15 μm or less, more preferably 9.0 μm or less, and further preferably 4.0 μm or less. In this way, the sulfide solid electrolyte obtained by the production method of this embodiment has a small average particle size within the above range by setting the ratio of the raw material contents to the solvent to a certain level or less. Therefore, in the manufacturing method of this embodiment, it is not necessary to carry out a pulverization (atomization) process.

[0119] Similarly, the particle size at 10% of the cumulative volume of the sulfide solid electrolyte (D 10 ) is preferably 0.05 μm or more and 10.0 μm or less, more preferably 0.50 μm or more and 6.0 μm or less, and even more preferably 1.0 μm or more and 3.0 μm or less. In addition, the particle size at 90% of the cumulative volume of the sulfide solid electrolyte (D 90 ) is preferably 0.10 μm or more and 20.0 μm or less, more preferably 1.0 μm or more and 15.0 μm or less, and even more preferably 2.5 μm or more and 8.0 μm or less.

[0120] (Application) The sulfide solid electrolyte obtained by the manufacturing method of the present embodiment has excellent coating suitability and can be used in the manufacture of batteries without using a solvent, etc., and can efficiently exhibit excellent battery performance. In addition, since it has high ionic conductivity and excellent battery performance, it is suitable for use in batteries. The sulfide solid electrolyte obtained by the manufacturing method of the present embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer. Each of these layers can be manufactured by a known method.

[0121] In addition, the battery preferably uses a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used. EXAMPLES

[0122] 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.

[0123] (Measurement of particle size distribution) Particle size at 10% cumulative volume (D 10 ), average particle size (D 50 ) and the particle size at 90% of the cumulative volume (D 90 ) was obtained from the particle size distribution integral curve obtained as follows. Measurements were made using a laser diffraction / scattering particle size distribution analyzer (Partica LA-950 (model number), manufactured by Horiba, Ltd.). Specifically, the powder to be measured was added to the flow cell of the device, ultrasonically treated, and then the particle size distribution was measured. In addition, the average particle size (D 50 ) was determined as the particle size that reached 50% (volume basis) of the total when the integral curve of the particle size distribution was drawn, starting from the smallest particle.

[0124] (Measurement of ionic conductivity) The sulfide solid electrolyte powders obtained in the examples and comparative examples were used to prepare a ceramic tube with a diameter of 6 to 10 mm (cross-sectional area S: 0.283 to 0.785 cm 2 ) and a height (L) of 0.1-0.3 cm were molded into a circular pellet to prepare a sample. Electrode terminals were attached to the top and bottom of the sample, and measurements were made at 25°C using an AC impedance method (frequency range: 1 MHz-0.1 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula: R=ρ(L / S) σ=1 / ρ

[0125] Example 1 0.597g of lithium sulfide, 0.759g of diphosphorus pentasulfide, 0.289g of lithium chloride, and 0.356g of lithium bromide were weighed in an anaerobic glove box, 10mL of tetrahydrofuran (THF) was added, and the mixture was stirred for 12 hours. 40mL of ethanol was then added to obtain a precursor-containing mixture. (Ratio of raw material content to solvent: 4.0g of raw material content per 100mL of solvent) To this precursor-containing mixture, 40 mL of tridecane was added and stirred at low speed (stirring power: 0.017 W / m 3 ) to obtain an emulsion.

[0126] The stirring power for the resulting emulsion was 0.017 W / m 3 The mixture was vacuum dried at room temperature for 4 hours while stirring at 40° C., and then vacuum dried at 50° C. for 2 hours to remove ethanol, thereby obtaining a slurry composed of tridecane and solids.

[0127] The solid content was separated from the above slurry by decantation. Toluene was added to the separated solid content, and then decantation was performed again to separate the solid content. This washing operation was performed three times. After that, the solid content (sulfide solid electrolyte) was recovered by vacuum drying at 150°C. The particle size distribution of the collected solids was confirmed, and the particle size distribution at 10% of the cumulative volume (D 10) is 4.5 μm, and the average particle size (D 50 ) is 8.3 μm, and the cumulative volume 90% particle size (D 90 ) was 12.4 μm.

[0128] The obtained solid content was subjected to a heat treatment at 430° C. for 8 hours. The ionic conductivity of the resulting sulfide solid electrolyte was measured and found to be 4.3 mS / cm.

[0129] Example 2 The stirring power during emulsion formation (from adding tridecane to the precursor-containing mixture to removing ethanol to obtain a slurry) was 19 W / m 3 A sulfide solid electrolyte was obtained in the same manner as in Example 1, except that an emulsion was obtained by changing the above-mentioned mixture to the above-mentioned mixture. The particle size distribution of the recovered solids was determined by the particle size at 10% cumulative volume (D 10 ) is 1.8 μm, and the average particle size (D 50 ) is 3.2 μm, and the cumulative volume 90% particle size (D 90 ) was 5.5 μm.

[0130] The obtained solid content was subjected to a heat treatment at 430° C. for 8 hours. The ionic conductivity of the resulting sulfide solid electrolyte was measured and found to be 4.2 mS / cm.

[0131] Example 3 The solid matter was recovered in the same manner as in Example 2, except that the order of addition of ethanol and tridecane was reversed. The particle size distribution of the recovered solid matter was 10% by cumulative volume (D 10 ) is 1.8 μm, and the average particle size (D 50 ) is 3.2 μm, and the cumulative volume 90% particle size (D 90 ) was 5.5 μm. Thereafter, the ionic conductivity of the sulfide solid electrolyte obtained in the same manner as in Example 2 was measured, and the ionic conductivity was 4.2 mS / cm.

[0132] Comparative Example 1 A sulfide solid electrolyte was obtained in the same manner as in Example 1, except that tridecane was not added to the precursor-containing mixture, and the mixture was directly dried in vacuum at 150° C. to obtain a sulfide solid electrolyte. The particle size distribution of the recovered solids was determined by the particle size at 10% cumulative volume (D 10 ) is 3.8 μm, and the average particle size (D 50 ) is 188.0 μm, and the particle size at 90% of the cumulative volume (D 90 ) was 355.1 μm.

[0133] The obtained solid content was subjected to a heat treatment at 430° C. for 8 hours. The ionic conductivity of the resulting sulfide solid electrolyte was measured and found to be 4.4 mS / cm.

[0134] Table 1 below shows the stirring power used when stirring the precursor-containing mixture and tridecane in Examples 1 to 3 and Comparative Example 1, and the properties of the resulting sulfide solid electrolyte.

[0135] [Table 1]

[0136] As is clear from the comparison of Examples 1 to 3 and Comparative Example 1, in Examples 1 to 3 in which the precursor-containing mixture was mixed with ethanol and tridecane to obtain an emulsion, the particle size (D 10 , D 50 , D 90 ) has become smaller. [Industrial Applicability]

[0137] The sulfide solid electrolyte obtained by the production method of this embodiment is suitably used for batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. A method for producing a sulfide solid electrolyte, comprising: mixing a raw material containing lithium atoms, phosphorus atoms, and sulfur atoms with a first solvent to obtain a precursor-containing mixture; mixing the precursor-containing mixture with a second solvent that is miscible with the first solvent to obtain an emulsion; and removing the first solvent and the second solvent from the emulsion.

2. The method for producing a sulfide solid electrolyte according to claim 1, wherein one of the first solvent and the second solvent contains an alcohol solvent and the other contains a hydrocarbon solvent having 5 to 40 carbon atoms.

3. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the first solvent contains a hydrocarbon solvent having 5 to 40 carbon atoms, and the second solvent contains an alcohol solvent.

4. A method for producing a sulfide solid electrolyte according to claim 1 or 2, comprising removing one of the first solvent and the second solvent from the emulsion to obtain a slurry containing a sulfide solid electrolyte, and removing the other of the first solvent and the second solvent from the slurry to remove the first solvent and the second solvent from the emulsion.

5. A method for producing a sulfide solid electrolyte according to claim 1 or 2, comprising supplying the emulsion to a medium that is hotter than the boiling point of the first solvent and hotter than the boiling point of the second solvent, and is in the state of a liquid or gas, and removing the first and second solvents from the emulsion by evaporating them.

6. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the first solvent contains a complexing agent.

7. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the raw material content further contains halogen atoms.

8. Furthermore, the method for producing a sulfide solid electrolyte according to claim 1 or 2, further comprising removing the first solvent and the second solvent from the emulsion, and then heating the sulfide solid electrolyte to crystallize it.

9. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the ratio of the first solvent to the second solvent is 10:90 to 90:10 by mass ratio.

10. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the ratio of the raw material content to the first solvent is 1.0 g or more and 20.0 g or less of the raw material content per 100 ml of the first solvent.

11. The stirring power used when mixing the precursor-containing mixture with the second solvent was 0.01 W / m². ３ The method for producing a sulfide solid electrolyte according to claim 1 or 2.