Production method for sulfide solid electrolyte and sulfide solid electrolyte

Abstract

The present invention provides a method for producing a sulfide solid electrolyte having high ion conductivity and high thermal stability without complicating the production process, with a production method for sulfide solid electrolytes that includes: obtaining an electrolyte precursor by mixing a raw-material-containing substance containing at least one type selected from lithium atoms, sulfur atoms, and phosphorus atoms, and a complexing agent containing a compound having two or more hetero atoms in a molecule; mixing the electrolyte precursor in a solvent containing an oxygen-atom-containing compound having a relative permittivity of 3.2 or higher at 25°C; obtaining a pulverized substance by pulverizing the mixture; and, obtaining the sulfide solid electrolyte by removing the solvent from the pulverized substance.

Description

Method for producing sulfide solid electrolyte and sulfide solid electrolyte

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

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become 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] From the viewpoint of the performance and manufacturing of all-solid-state lithium batteries, a method for manufacturing a solid electrolyte used in a solid electrolyte layer that has a small particle size is required. In all-solid-state lithium batteries, the cathode material, the anode material, and the electrolyte are all solid. Therefore, a small particle size of the solid electrolyte has the advantage of facilitating the formation of a contact interface between the active material and the solid electrolyte, thereby improving the paths for ionic and electronic conduction. As a method for reducing the particle size (also referred to as "microparticulation"), for example, a manufacturing method has been disclosed that includes a step of adding an ether compound to a coarse-grained sulfide solid electrolyte material and micronizing it by a pulverization process (see, for example, Patent Documents 1 and 2).

[0004] Furthermore, as a method for producing a solid electrolyte, a liquid phase method has attracted attention as a method that can easily synthesize a large amount of the solid electrolyte. However, since it is difficult to precipitate the solid electrolyte while maintaining the dispersion state of the atoms that constitute the solid electrolyte in the liquid phase method, a method for producing a solid electrolyte through an electrolyte precursor using a complexing agent has been disclosed (see, for example, Patent Documents 3 and 4).

[0005] JP 2013-20894 A JP 2017-100907 A International Publication No. 2020 / 105736 International Publication No. 2020 / 105737

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a sulfide solid electrolyte having high ionic conductivity and high thermal stability without complicating the production process.

[0007] The method for producing a crystalline sulfide solid electrolyte according to the present invention includes: mixing a raw material containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms with a complexing agent having two or more heteroatoms in the molecule to obtain an electrolyte precursor; pulverizing the electrolyte precursor in a solvent containing an oxygen atom-containing compound having a relative dielectric constant at 25°C of 3.2 or more to obtain a pulverized product; and removing the solvent from the pulverized product to obtain a sulfide solid electrolyte.

[0008] According to the present invention, it is possible to provide a sulfide solid electrolyte having high ionic conductivity and high thermal stability without complicating the manufacturing process.

[0009] 1 is a DTA curve of the amorphous solid electrolyte obtained in Example 1. FIG. 2 is a DTA curve of the amorphous solid electrolyte obtained in Comparative Example 3. FIG. 3 is a DTA curve of the crystalline solid electrolyte obtained in Example 1. FIG. 4 is a DTA curve of the crystalline solid electrolyte obtained in Comparative Example 3.

[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 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.

[0011] (Findings Obtained by the Inventor to Achieve the Present Invention) The inventors conducted extensive research to solve the above-mentioned problems, and as a result, discovered the following and completed the present invention. In the production methods described in Patent Documents 1 and 2, a dispersant is added when grinding coarse particles, but a complexing agent having two or more heteroatoms is not used, resulting in a problem of difficulty in maintaining the dispersion of the atoms constituting the solid electrolyte. On the other hand, in the production methods described in Patent Documents 3 and 4, a complexing agent is used in a liquid-phase process to produce a solid electrolyte, thereby maintaining the dispersion of the atoms constituting the solid electrolyte. However, the complexing agent, which has a high affinity for lithium, tends to remain in the solid electrolyte, which may reduce ionic conductivity. Furthermore, the resulting solid electrolyte may undergo a continuous change in crystal structure at high temperatures, resulting in a phase transition to a phase with lower ionic conductivity, resulting in reduced thermal stability. For these reasons, a method for efficiently producing a sulfide solid electrolyte having high ionic conductivity and high thermal stability has been desired.

[0012] The present inventors have found that ionic conductivity and thermal stability can be improved by adding a specific solvent to an electrolyte precursor produced using a complexing agent, subjecting the resulting mixture to a pulverization treatment, and then removing the solvent.

[0013] In this embodiment, we have discovered that a sulfide solid electrolyte having high ionic conductivity and thermal stability can be produced by pulverizing the electrolyte precursor in a solvent containing an oxygen-containing compound having a dielectric constant of 3.2 or more at 25°C to obtain a pulverized product, and then removing the solvent to obtain a sulfide solid electrolyte. This embodiment is an extremely excellent production method because the ionic conductivity of the sulfide solid electrolyte is improved simply by pulverizing the electrolyte precursor in a specific solvent. Conventional liquid-phase production methods result in the resulting sulfide solid electrolyte undergoing continuous changes in crystal structure with increasing temperature. However, in this embodiment, pulverization using a specific solvent is performed to obtain a sulfide solid electrolyte in which a clear exothermic crystallization peak is observed between 270 and 310°C in differential thermal analysis (DTA), indicating a phase transition to a crystalline phase with lower ionic conductivity. A sulfide solid electrolyte in which such an exothermic crystallization peak is observed at higher temperatures exhibits minimal change in crystal structure in the temperature range below the exothermic crystallization peak, thereby suppressing the decrease in ionic conductivity associated with the change in crystal structure. Therefore, it is believed to be a sulfide solid electrolyte with excellent thermal stability.

[0014] The method for producing a sulfide solid electrolyte according to the first to eleventh aspects of this embodiment will be described below. The method for producing a sulfide solid electrolyte according to the first aspect of this embodiment includes: mixing a raw material containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms with a complexing agent having two or more heteroatoms in the molecule to obtain an electrolyte precursor; pulverizing the electrolyte precursor in a solvent containing an oxygen-containing compound having a relative dielectric constant of 3.2 or more at 25°C to obtain a pulverized product; and removing the solvent from the pulverized product to obtain a sulfide solid electrolyte.

[0015] In the solid electrolyte manufacturing methods described in Patent Documents 1 and 2, a dispersant is added when grinding coarse particles, but a complexing agent with two or more heteroatoms is not used when mixing the sulfide solid electrolyte material. This makes it difficult to maintain the dispersion of the atoms constituting the solid electrolyte, and the resulting solid electrolyte does not have high ionic conductivity. Furthermore, in the solid electrolyte manufacturing methods described in Patent Documents 3 and 4, a sulfide solid electrolyte obtained by mixing raw material ingredients containing lithium and the like with a complexing agent is crushed and granulated using a bead mill with or without a solvent. However, because the specified solvent specified in the present invention is not used, the complexing agent remaining inside the solid electrolyte cannot be completely removed, and the resulting solid electrolyte has insufficient ionic conductivity. Furthermore, solid electrolytes obtained using a complexing agent may experience a phenomenon in which their crystal structure continuously changes with increasing temperature, posing challenges in terms of thermal stability. In contrast, in the present invention, it has been found that by subjecting an electrolyte precursor produced using a complexing agent having two or more heteroatoms to a pulverization treatment in a solvent containing an oxygen atom-containing compound with a high relative dielectric constant, the amount of residual complexing agent can be reduced, and a solid electrolyte with high ionic conductivity can be produced.

[0016] A method for producing a sulfide solid electrolyte according to a second aspect of the present embodiment is the same as the method for producing a sulfide solid electrolyte according to the first aspect, except that the oxygen atom-containing compound is an ether compound. Using an ether compound as the oxygen atom-containing compound is preferable from the viewpoint of removing a complexing agent coordinated to lithium and improving the ionic conductivity of the solid electrolyte.

[0017] A method for producing a sulfide solid electrolyte according to a third aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to the second aspect, in which the ether compound is an aliphatic ether having 1 to 20 carbon atoms. Examples of the ether compound that makes it easy to remove the complexing agent coordinated to lithium include an aliphatic ether having 1 to 20 carbon atoms.

[0018] A method for producing a sulfide solid electrolyte according to a fourth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the first to third aspects, in which the ether compound is represented by the following general formula (1): １ -O-R ２ ...(1) (wherein, R １ and R ２ are each independently a linear alkyl group having 1 to 20 carbon atoms, a branched alkyl group having 3 to 20 carbon atoms, or a cycloalkyl group having 5 to 20 carbon atoms.) More specifically, as the ether compound, it is preferable to use the compound represented by the above general formula (1) from the viewpoint of efficiently removing the complexing agent coordinated to lithium.

[0019] In addition, in the method for producing a sulfide solid electrolyte according to the fifth aspect of the present embodiment, R １ and R ２ and R in general formula (1) are the same group. １ and R ２ are identical groups.

[0020] A method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the first to fifth aspects, further comprising heating the electrolyte precursor. From the viewpoint of further improving ionic conductivity, it is preferable to heat the electrolyte precursor to crystallize it.

[0021] A seventh aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to any one of the first to sixth aspects, further comprising heating the sulfide solid electrolyte. The sulfide solid electrolyte is preferably heated to crystallize it, from the viewpoint of further improving ionic conductivity.

[0022] A method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the first to seventh aspects, in which the complexing agent is a compound having a tertiary amino group. Using a compound having a tertiary amino group as the complexing agent is preferable from the viewpoint of improving ionic conductivity, because the complexing agent is easily removed by the oxygen-containing compound.

[0023] A method for producing a sulfide solid electrolyte according to a ninth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to any one of the first to eighth aspects, in which the solvent further contains a hydrocarbon compound. When the solvent further contains a hydrocarbon compound, the complexing agent and the oxygen-containing compound can be easily removed, which is preferable from the viewpoint of improving ionic conductivity.

[0024] A tenth aspect of the present embodiment is a method for producing a sulfide solid electrolyte according to the ninth aspect, wherein the solvent contains 50 to 99.5 mass % of the hydrocarbon compound and 0.5 to 50 mass % of the oxygen atom-containing compound. It is preferable from the viewpoint of improving ionic conductivity if the contents of the hydrocarbon compound and the oxygen atom-containing compound in the solvent are within the above ranges.

[0025] A sulfide solid electrolyte according to an eleventh aspect of this embodiment is a sulfide solid electrolyte containing 0.1 to 0.9 mass % of a complexing agent that contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms and has two or more heteroatoms in the molecule, and 0.01 to 0.5 mass % of an oxygen-atom-containing compound that has a relative dielectric constant of 3.2 or more at 25° C. The sulfide solid electrolyte obtained by the above-mentioned production method of the present invention contains very small amounts of the complexing agent and the oxygen-atom-containing compound.

[0026] A sulfide solid electrolyte according to a twelfth aspect of this embodiment is the sulfide solid electrolyte according to the eleventh aspect, which exhibits a crystallization exothermic peak in differential thermal analysis (DTA) at 270 to 310° C. The sulfide solid electrolyte of the present invention has a small amount of residual complexing agent or oxygen atom-containing compound, but if it exhibits a crystallization exothermic peak in differential thermal analysis (DTA) at 270 to 310° C., there is little change in the crystal structure in the temperature range below the crystallization exothermic peak, and therefore a decrease in ionic conductivity due to a change in the crystal structure is unlikely to occur, resulting in good thermal stability.

[0027] The sulfide solid electrolyte according to the thirteenth aspect of the present embodiment has a specific surface area of ​​1 to 20 m ２ The sulfide solid electrolyte according to the eleventh or twelfth aspect has a specific surface area of ​​0.1 to 1.5 μm / g and an average particle size (D50) of 0.1 to 10 μm. When the sulfide solid electrolyte of the present invention has a specific surface area and an average particle size within the above ranges, the specific surface area of ​​the particle surfaces of the solid electrolyte is reduced, improving the ionic conductivity of the solid electrolyte while facilitating the formation of a contact interface between the active material and the solid electrolyte, which is preferable from the viewpoint of improving the paths for ionic conduction and electronic conduction.

[0028] The manufacturing method of this embodiment will be described in more detail below in accordance with the above-described embodiment.

[0029] [Method for Producing Sulfide Solid Electrolyte] The method for producing a sulfide solid electrolyte of the present embodiment includes: mixing a raw material containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms with a complexing agent having two or more heteroatoms in the molecule to obtain an electrolyte precursor; pulverizing the electrolyte precursor in a solvent containing an oxygen atom-containing compound having a relative dielectric constant of 3.2 or more at 25°C to obtain a pulverized product; and removing the solvent from the pulverized product to obtain a sulfide solid electrolyte.

[0030] <Obtaining an Electrolyte Precursor> In this embodiment, "obtaining an electrolyte precursor" requires mixing a raw material component described later with a complexing agent described later. By mixing the raw material component with the complexing agent and complexing the raw material component, Li can be obtained even in the liquid phase method or the heterogeneous method. ３ P.S.４ These compounds are preferred because they form complexes containing lithium atoms, phosphorus atoms, sulfur atoms, etc., and can suppress separation of specific components, thereby enabling the production of a homogeneous solid electrolyte.

[0031] (Solid Electrolyte) In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state at 25°C under a nitrogen atmosphere. The solid electrolyte in this embodiment is a solid electrolyte that contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms and has ionic conductivity due to the lithium atoms. The term "solid electrolyte" includes both crystalline sulfide solid electrolytes having a crystalline structure and amorphous sulfide solid electrolytes.

[0032] In this specification, a crystalline sulfide solid electrolyte refers to a solid electrolyte in which peaks derived from the solid electrolyte are observed in an X-ray diffraction pattern in X-ray diffraction measurement, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present. That is, the crystalline sulfide solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as the crystalline sulfide solid electrolyte has the X-ray diffraction pattern described above, it may also contain an amorphous solid electrolyte as a portion thereof. Therefore, crystalline sulfide solid electrolytes include so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than the crystallization temperature. Furthermore, in this specification, an amorphous solid electrolyte refers to an X-ray diffraction pattern in X-ray diffraction measurement that has a halo pattern in which substantially no peaks other than those derived from the material are observed, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present.

[0033] (Mixing) The "mixing" in this embodiment is preferably carried out using a stirrer or a mixer.

[0034] Examples of the stirrer and mixer include a mechanical stirring mixer that is equipped with stirring blades in a reaction vessel and can stir (also referred to as mixing by stirring or stirring mixing). Examples of the mechanical stirring mixer include a high-speed stirring mixer and a double-arm mixer. Examples of the high-speed stirring mixer include a vertical-axis rotary mixer and a horizontal-axis rotary mixer, and either type of mixer may be used.

[0035] Examples of the shape of the stirring blade used in a mechanical stirring mixer include blade type, arm type, anchor type, paddle type, full zone type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, C-type blade type, etc., and from the viewpoint of more efficiently promoting the reaction of the raw materials, the shovel type, flat blade type, C-type blade type, anchor type, paddle type, full zone type, etc. are preferred, with the anchor type, paddle type, and full zone type being more preferred. When performing on a small scale, it is also preferable to use a Schlenk bottle with a stirring bar or a separable flask equipped with a rotor blade.

[0036] When a mechanical stirring mixer is used, the rotation speed of the stirring blades can be adjusted appropriately depending on the volume of the fluid in the reaction vessel, the temperature, the shape of the stirring blades, etc., and is not particularly limited. However, it is usually sufficient to set the rotation speed at about 5 rpm or more and 400 rpm or less. From the viewpoint of more efficiently promoting the reaction of the raw materials, the rotation speed is preferably 10 rpm or more and 300 rpm or less, more preferably 15 rpm or more and 250 rpm or less, and even more preferably 20 rpm or more and 230 rpm or less.

[0037] The temperature conditions when mixing using a mixer are not particularly limited, and are, for example, usually −30 to 120°C, preferably −10 to 100°C, more preferably 0 to 80°C, and even more preferably 10 to 60°C. Mixing without external temperature control is also preferred. The mixing time is usually 0.1 to 500 hours, and from the viewpoint of more uniform dispersion of the raw materials and accelerating the reaction, it is preferably 1 to 450 hours, more preferably 10 to 425 hours, even more preferably 20 to 400 hours, and even more preferably 30 to 300 hours.

[0038] (Raw Material Contents) The raw material contents used in this embodiment are required to contain lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Specific examples of solid electrolyte raw materials contained in the raw material contents include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides; various phosphorus fluorides (PF ３ , P.F. ５ ), various phosphorus chlorides (PCl ３ , PCl ５ , P ２ Cl ４ ), various phosphorus bromides (PBr ３ , PBr ５ ), various phosphorus iodides (PI ３ , P ２ I ４ ) and the like; phosphorus halides such as thiophosphoryl fluoride (PSF ３ ), thiophosphoryl chloride (PSCl ３ ), thiophosphoryl bromide (PSBr ３ ), thiophosphoryl iodide (PSI ３ ), thiophosphoryl fluoride dichloride (PSCl ２ F), thiophosphoryl fluoride dibromide (PSBr ２ a source material consisting of at least two atoms selected from the above four types of atoms, such as thiophosphoryl halides, e.g., fluorine (F); ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ), preferably bromine (Br ２ ), iodine (I ２ ) are typical examples.

[0039] Examples of materials that can be used as raw materials other than those mentioned above include raw materials containing at least one atom selected from the above four types of atoms and other atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, and tin sulfide (SnS, SnS ２ metal sulfides such as aluminum sulfide and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium such as sodium halides such as sodium iodide, sodium fluoride, sodium chloride and sodium bromide; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides and bismuth halides; phosphorus oxychloride (POCl ３ ), phosphorus oxybromide (POBr ３ ) and the like; and the like.

[0040] Among the above, 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 ２ Preferred examples of the halogen compound include lithium fluoride, lithium chloride, lithium bromide, and lithium iodide, and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. When oxygen atoms are introduced into the solid electrolyte, preferred examples of the halogen compound include lithium oxide, lithium hydroxide, and lithium phosphate. Preferred examples of the combination of raw materials include lithium sulfide, phosphorus pentasulfide, and a lithium halide, and lithium sulfide, phosphorus pentasulfide, and a halogen compound. Preferred examples of the lithium halide include lithium bromide and lithium iodide, and preferred examples of the halogen compound include bromine and iodine.

[0041] In this embodiment, PS ４ Li containing structure３ P.S. ４ can also be used as part of the raw material. ３ P.S. ４ This is prepared by manufacturing or the like and used as a raw material. ３ P.S. ４ The content is preferably 60 to 100 mol %, more preferably 65 to 90 mol %, and even more preferably 70 to 80 mol %.

[0042] Also, Li ３ P.S. ４ When using a halogen atom, Li ３ P.S. ４ The content of the halogen element is preferably 1 to 50 mol %, more preferably 10 to 40 mol %, even more preferably 20 to 30 mol %, and even more preferably 22 to 28 mol %.

[0043] The lithium sulfide used in this embodiment is preferably in the form of particles. The average particle diameter (D ５０ ) is preferably 10 μm or more and 2000 μm or less, more preferably 30 μm or more and 1500 μm or less, and even more preferably 50 μm or more and 1000 μm or less. ５０ ) is the volume-average particle size at which, when a particle size distribution cumulative curve is drawn on a volume basis, the cumulative total, starting from the smallest particle size, reaches 50% of the total, and the volume distribution refers to the average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device. Furthermore, among the above-mentioned examples of raw materials, solid raw materials preferably have an average particle size approximately the same as that of the lithium sulfide particles, that is, within the same range as that of the lithium sulfide particles.

[0044] 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 80 mol%, more preferably 72 to 78 mol%, and even more preferably 74 to 78 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 needed are used, the content of lithium sulfide and diphosphorus pentasulfide to the total is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 80 mol%. Furthermore, when lithium bromide and lithium iodide are used in combination as the lithium halide, the ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%, from the viewpoint of improving ionic conductivity.

[0045] When 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 ionic conductivity can be obtained with these ratios. Furthermore, 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%.

[0046] When lithium sulfide, diphosphorus pentasulfide, an elemental halogen, and a lithium halide are used, the content of the elemental halogen (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):

[0047] 2≦2α+β≦100 (2) 4≦2α+β≦80 (3) 6≦2α+β≦50 (4) 6≦2α+β≦30 (5)

[0048] When two types of halogens are used as simple substances, the molar number of one halogen atom in the substance is designated as A1, and the molar number of the other halogen atom in the substance is designated as A2. The ratio A1:A2 is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, even more preferably 20:80 to 80:20, and still more preferably 30:70 to 70:30.

[0049] Furthermore, when the two types of halogen atoms are bromine and iodine, where the number of moles of bromine is B1 and the number of moles of iodine is B2, the ratio B1:B2 is preferably 1:99 to 99:1, more preferably 15:85 to 90:10, even more preferably 20:80 to 80:20, still more preferably 30:70 to 75:25, and particularly preferably 35:65 to 75:25.

[0050] When mixing the raw material ingredients with a complexing agent described below, it is preferable to mix the raw material mixture with a solvent described below to form a slurry, since this will result in the raw material mixture becoming a uniform complex.

[0051] (Complexing Agent) In this specification, the complexing agent is Li, which is preferably used as a raw material for solid electrolytes. ２ S and P ２ S ５ Li obtained from ３ P.S. ４ and capable of forming a complex containing a halogen atom, preferably Li ３ P.S. ４ and the formed Li ３ P.S. ４The complexing agent used in this embodiment may be a single type or two or more types, but it is required that the number of heteroatoms in the molecule is two or more. ３ P.S. ４ A complexing agent capable of forming a complex containing a halogen atom is used.

[0052] In order to efficiently form a complex, the amount of complexing agent added when mixing in this embodiment is preferably such that the molar ratio of the complexing agent to the total molar amount of Li atoms contained in the raw material content is 0.5 or more and 7.0 or less, more preferably 0.6 or more and 5.5 or less, and even more preferably 0.8 or more and 3.5 or less.

[0053] The complexing agent used in this embodiment is not particularly limited as long as it has the above-mentioned properties and has two or more heteroatoms in the molecule, and is preferably a compound containing an atom having a high affinity with lithium atoms, 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 heteroatom or group containing such a heteroatom can coordinate (bond) with lithium.

[0054] The heteroatoms present in the molecules of the complexing agent have a high affinity with lithium atoms, and the PS main skeleton of the solid electrolyte produced by this embodiment ４ Li containing structure ３ P.S. ４ It is also believed that the compound has the ability to easily form a complex by bonding with a raw material containing lithium atoms and halogen atoms, such as lithium halide. Therefore, by mixing the raw material with a complexing agent, the complex is formed, and it becomes possible to precipitate various components while maintaining the dispersed state even in the precipitation step, and an electrolyte precursor in which halogen atoms are more uniformly dispersed and fixed (hereinafter, the substance obtained by mixing the raw material containing at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms with the complexing agent will also be referred to as an electrolyte precursor) can be obtained, and as a result, it is believed that a solid electrolyte with high ionic conductivity can be obtained.

[0055] Therefore, the complexing agent is required to have at least two heteroatoms in the molecule, and more preferably has a group containing at least two heteroatoms in the molecule. ３ P.S. ４ A raw material containing lithium and a halogen, such as lithium halide, can be bound via at least two heteroatoms in the molecule. Among heteroatoms, a nitrogen atom is preferred, and an amino group is preferred as a group containing a nitrogen atom. That is, an amine compound is preferred as a complexing agent.

[0056] The amine compound is not particularly limited as long as it has an amino group in the molecule, as it can promote the formation of a complex, but a compound having at least two amino groups in the molecule is preferred. ３ P.S. ４ and lithium and halogen-containing materials such as lithium halide can be bonded via at least two nitrogen atoms in the molecule.

[0057] Examples of such amine compounds include aliphatic amines, alicyclic amines, heterocyclic amines, and aromatic amines, and these can be used alone or in combination.

[0058] More specifically, typical and preferred examples of the aliphatic amine include aliphatic primary diamines such as ethylenediamine, diaminopropane, and diaminobutane; aliphatic secondary diamines such as N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N'-dimethyldiaminopropane, and N,N'-diethyldiaminopropane; and aliphatic tertiary diamines such as N,N,N',N'-tetramethyldiaminomethane, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetramethyldiaminopropane, N,N,N',N'-tetraethyldiaminopropane, N,N,N',N'-tetramethyldiaminobutane, N,N,N',N'-tetramethyldiaminopentane, and N,N,N',N'-tetramethyldiaminohexane. In the examples given in this specification, for example, in the case of diaminobutane, unless otherwise specified, all isomers of butane, such as linear and branched isomers, are included in addition to isomers relating to the position of the amino group, such as 1,2-diaminobutane, 1,3-diaminobutane, and 1,4-diaminobutane.

[0059] The number of carbon atoms in the aliphatic amine is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, and the upper limit is 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 amine is preferably 2 or more, and the upper limit is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0060] Representative preferred examples of the alicyclic amine include alicyclic primary diamines such as cyclopropanediamine and cyclohexanediamine; alicyclic secondary diamines such as bisaminomethylcyclohexane; and alicyclic tertiary diamines such as N,N,N',N'-tetramethyl-cyclohexanediamine and bis(ethylmethylamino)cyclohexane. Representative preferred examples of the heterocyclic amine include heterocyclic primary diamines such as isophoronediamine; heterocyclic secondary diamines such as piperazine and dipiperidylpropane; and heterocyclic tertiary diamines such as N,N-dimethylpiperazine and bismethylpiperidylpropane. The number of carbon atoms in the alicyclic amine and heterocyclic amine is preferably 3 or more, more preferably 4 or more, and preferably 16 or less, more preferably 14 or less.

[0061] Representative preferred examples of aromatic amines include aromatic primary diamines such as phenyldiamine, tolylenediamine, and naphthalenediamine; aromatic secondary diamines such as N-methylphenylenediamine, N,N'-dimethylphenylenediamine, N,N'-bismethylphenylphenylenediamine, N,N'-dimethylnaphthalenediamine, and N-naphthylethylenediamine; and aromatic tertiary diamines such as N,N-dimethylphenylenediamine, N,N,N',N'-tetramethylphenylenediamine, N,N,N',N'-tetramethyldiaminodiphenylmethane, and N,N,N',N'-tetramethylnaphthalenediamine. The number of carbon atoms in the aromatic amine is preferably 6 or more, more preferably 7 or more, and even more preferably 8 or more, with the upper limit being preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0062] The amine compound used in this 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. Although diamine is given as a specific example, the amine compound that can be used in this embodiment is not limited to diamine, and can also be used, for example, imidazole compounds such as imidazole and methylimidazole, and polyamines having three or more amino groups such as diethylenetriamine, N,N',N"-trimethyldiethylenetriamine, N,N,N',N",N"-pentamethyldiethylenetriamine, triethylenetetramine, N,N'-bis[(dimethylamino)ethyl]-N,N'-dimethylethylenediamine, hexamethylenetetramine, or tetraethylenepentamine.

[0063] Among the above, from the viewpoint of obtaining higher ionic conductivity, a tertiary amine having a tertiary amino group as the amino group is preferred, a tertiary diamine having two tertiary amino groups is more preferred, a tertiary diamine having two tertiary amino groups at both ends is even more preferred, and an aliphatic tertiary diamine having tertiary amino groups at both ends is even more preferred. Among the above amine compounds, the aliphatic tertiary diamine having tertiary amino groups at both ends is preferably tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, or tetraethyldiaminopropane, and in consideration of ease of availability, etc., tetramethylethylenediamine or tetramethyldiaminopropane is preferred.

[0064] Furthermore, compounds having a nitrogen atom as a heteroatom and a group other than an amino group, such as a nitro group or an amide group, can also provide the same effect.

[0065] It is preferable to use a complexing agent having a relative dielectric constant of less than 3.2 at 25° C., since this facilitates substitution of the complexing agent with the oxygen atom-containing compound during the pulverization treatment described below.

[0066] In this embodiment, when the raw material ingredients and the complexing agent are mixed, a complexing agent other than the above-mentioned ones having two or more heteroatoms in the molecule may be further added.

[0067] (Solvent) In this embodiment, a solvent may be added when mixing the raw material inclusions and the complexing agent. When a solid complex is formed in a liquid complexing agent, if the complex is easily soluble in the complexing agent, separation of the components may occur. Therefore, by using a solvent in which the complex is insoluble, the elution of components in the electrolyte precursor can be suppressed. Furthermore, mixing the raw material inclusions and the complexing agent using a solvent promotes complex formation, allowing the various components to be more evenly present, and an electrolyte precursor in which the halogen atoms are more dispersed and fixed can be obtained, which results in the effect of obtaining a solid electrolyte with high ionic conductivity.

[0068] The method for producing a solid electrolyte according to this embodiment is a so-called heterogeneous method, and it is preferable that the complex does not completely dissolve in the liquid complexing agent but precipitates. The solubility of the complex can be adjusted by adding a solvent. Halogen atoms, in particular, tend to dissolve from the complex, so adding a solvent suppresses the dissolution of halogen atoms to obtain the desired complex. As a result, a sulfide solid electrolyte with high ionic conductivity can be obtained via an electrolyte precursor in which components such as halogens are dispersed, which is preferable.

[0069] A preferred example of a solvent having such properties is a solvent having a solubility parameter of 10 or less. In this specification, the solubility parameter is a value δ ((cal / cm)) calculated by the following formula (1), which is described in various documents, such as "Chemical Handbook" (published in 2004, revised 5th edition, Maruzen Co., Ltd.). ３ ) １／２ ) and is also called the Hildebrand parameter or SP value.

[0070] (In equation (1), ΔH is the molar heat of heat, R is the gas constant, T is the temperature, and V is the molar volume.)

[0071] By using a solvent with a solubility parameter of 10 or less, halogen atoms, halogen-containing raw materials such as lithium halide, and even halogen-containing components constituting the co-crystal contained in the complex (e.g., an aggregate formed by bonding lithium halide and a complexing agent) can be made relatively less soluble compared to the complexing agent. This makes it easier to fix halogen atoms in the complex, and halogen atoms are present in a well-dispersed state in the resulting electrolyte precursor and, further, in the solid electrolyte, making it easier to obtain a solid electrolyte with high ionic conductivity. In other words, the solvent used in this embodiment preferably has the property of not dissolving the complex. From the same perspective, the solubility parameter of the solvent is preferably 9.5 or less, more preferably 9.0 or less, and even more preferably 8.5 or less.

[0072] More specifically, the solvent used in the present embodiment can be a wide variety of solvents that have conventionally been used in the production of solid electrolytes. The solvent is preferably at least one selected from nonpolar solvents and aprotic polar solvents. Among these, a solvent having a solubility parameter within the above-mentioned range may be appropriately selected and used. Examples of the solvent include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; and solvents containing carbon atoms such as alcohol-based solvents, ester-based solvents, aldehyde-based solvents, ketone-based solvents, and solvents containing carbon atoms and heteroatoms. Among these, a solvent having a solubility parameter within the above-mentioned range may be appropriately selected and used.

[0073] More specifically, examples of such solvents include aliphatic hydrocarbon solvents such as hexane (7.3), pentane (7.0), 2-ethylhexane, heptane (7.4), octane (7.5), decane, undecane, dodecane, and tridecane; alicyclic hydrocarbon solvents such as cyclohexane (8.2) and methylcyclohexane; aromatic hydrocarbon solvents such as benzene, toluene (8.8), xylene (8.8), mesitylene, ethylbenzene (8.8), tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene (9.5), chlorotoluene (8.8), and bromobenzene; and solvents containing carbon atoms and heteroatoms such as acetonitrile (11.9) and carbon disulfide. The values ​​in parentheses in the above examples are SP values.

[0074] Among these solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents are preferred, and from the viewpoint of obtaining a more stable and high ionic conductivity, heptane, cyclohexane, toluene, ethylbenzene, and particularly cyclohexane are preferred. The solvent used in this embodiment is preferably an organic solvent exemplified above, and is an organic solvent different from the complexing agent. In this embodiment, these solvents may be used alone or in combination.

[0075] It is preferable to use a solvent having a relative dielectric constant of less than 3.2 at 25° C., since this facilitates substitution of the complexing agent with the oxygen atom-containing compound during the pulverization treatment described below.

[0076] (Crushing Treatment) The mixture of the raw material-containing substance and the complexing agent obtained as described above can be further crushed to promote the formation of a complex. The details of the crushing treatment are the same as those when crushing the electrolyte precursor described below in a solvent containing an oxygen-containing compound having a dielectric constant of 3.2 or more at 25°C.

[0077] (Removal of Complexing Agent, etc.) In this embodiment, since the electrolyte precursor is often a suspension, a step of removing the complexing agent and, if necessary, a solvent (hereinafter, sometimes referred to as "complexing agent, etc.") by an operation such as drying or solid-liquid separation may be included. This results in a powder of the electrolyte precursor. Removing the complexing agent, etc. before the heating described below is preferable because it allows for efficient heating. Note that the removal of the complexing agent, etc. and the subsequent heating may be performed in the same step.

[0078] The drying can be performed at a temperature appropriate for the complexing agent remaining in the electrolyte precursor and the type of solvent used if necessary. For example, the drying can be performed at a temperature equal to or higher than the boiling point of the complexing agent or solvent. Furthermore, the drying can be performed by volatilizing the complexing agent and solvent by drying under reduced pressure (vacuum drying) using a vacuum pump or the like at typically 5 to 100°C, preferably 10 to 85°C, more preferably 15 to 70°C, and even more preferably at about room temperature (23°C) (e.g., about room temperature ±5°C). Unlike complexing agents, solvents are less likely to be incorporated into the complex. Therefore, the amount of solvent that can be contained in the complex is typically 3% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less.

[0079] The solid-liquid separation may be carried out by filtration using a glass filter or the like, decantation, a centrifuge, or the like. In this embodiment, after the solid-liquid separation, drying may be further carried out under the above-mentioned temperature conditions. Specifically, the solid-liquid separation can be carried out by decantation, in which the suspension is transferred to a container, and after the solid has precipitated, the supernatant complexing agent and the solvent added as needed are removed, or by filtration using a glass filter with a pore size of about 10 to 200 μm, preferably 20 to 150 μm.

[0080] The complex is characterized in that it is composed of a complexing agent, a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom, and in that a peak different from the peaks derived from the raw materials is observed in the X-ray diffraction pattern in X-ray diffraction measurement, and preferably includes a cocrystal composed of a complexing agent, a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom. When the raw materials are simply mixed, only the peaks derived from the raw materials are observed, but when the raw materials are mixed with the complexing agent, a peak different from the peaks derived from the raw materials is observed, and therefore the complex has a structure that is clearly different from the raw materials themselves contained in the raw materials.

[0081] The content of the complexing agent in the complex varies depending on the molecular weight of the complexing agent, but is usually about 10% by mass to 70% by mass, preferably 15% by mass to 65% by mass.

[0082] (Decomplexation Treatment) In the manufacturing method of this embodiment, the electrolyte precursor may be heated to undergo a complexation treatment, thereby converting the electrolyte precursor into a complex decomposition product. As described below, the complex decomposition product essentially functions as a solid electrolyte. (Heating the Electrolyte Precursor) By including a step of heating the electrolyte precursor, the complexing agent in the electrolyte precursor is removed, and a complex decomposition product containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms is obtained. Here, the removal of the complexing agent in the electrolyte precursor is supported by the fact that the results of X-ray diffraction patterns, gas chromatography analysis, etc. clearly show that the complexing agent forms a co-crystal with the electrolyte precursor, and also by the fact that the solid electrolyte obtained by removing the complexing agent by heating the electrolyte precursor has the same X-ray diffraction pattern as a solid electrolyte obtained by a conventional method without using a complexing agent.

[0083] In this embodiment, the complex decomposition product is obtained by removing the complexing agent from the electrolyte precursor by heating the electrolyte precursor. The less the complexing agent in the complex decomposition product, the better. However, the complexing agent may be contained to an extent that does not impair the performance of the complex decomposition product. The content of the complexing agent in the complex decomposition product is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0084] The heating temperature of the electrolyte precursor may be determined depending on the structure of the complex decomposition product obtained by heating the electrolyte precursor, for example. Specifically, the electrolyte precursor is subjected to differential thermal analysis (DTA) at a temperature increase rate of 10°C / min using a differential thermal analyzer (DTA device). The heating temperature is preferably set to 5°C or lower, more preferably 10°C or lower, and even more preferably 20°C or lower, starting from the temperature at the top of the exothermic peak observed at the lowest temperature. The lower limit is not particularly limited, but may be about −40°C or higher than the temperature at the top of the exothermic peak observed at the lowest temperature. By setting the temperature within this range, the complex decomposition product can be obtained more efficiently and reliably. The heating temperature cannot be generally specified because it varies depending on the structure of the complex decomposition product to be obtained, but is typically preferably 190°C or lower, more preferably 180°C or lower, and even more preferably 170°C or lower. The lower limit is not particularly limited, but is preferably 90°C or higher, more preferably 110°C or higher, and even more preferably 130°C or higher.

[0085] The heating time is not particularly limited as long as it is a time that allows the desired complex decomposition product and crystalline sulfide solid electrolyte to be obtained, but is, for example, 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 heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less.

[0086] Furthermore, heating is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum). This is because deterioration (e.g., oxidation) of the complex decomposition product and the crystalline sulfide solid electrolyte can be prevented. The heating method is not particularly limited, and examples thereof include methods using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, and a calcination furnace. 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 heat to be processed.

[0087] (Complex Decomposition Product) The complex decomposition product obtained by this embodiment contains a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom. Representative examples include Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -LiI-LiBr, etc., solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide; and solid electrolytes further containing other atoms such as oxygen atoms and silicon atoms, for example, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a solid electrolyte such as Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and a lithium halide, such as —LiI—LiBr, is preferred. The types of atoms constituting the complex decomposition product can be confirmed, for example, by an ICP emission spectrometer.

[0088] The complex decomposition product obtained in this embodiment contains at least Li ２ S-P ２ S ５ When Li ２ S and P ２ S ５From the viewpoint of obtaining higher ionic conductivity, the molar ratio of Li to Li is preferably 65 to 85:15 to 35, more preferably 70 to 80:20 to 30, and even more preferably 72 to 78:22 to 28. ２ S-P ２ S ５ In the case of -LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 60 to 95 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 85 mol%. The ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

[0089] In the complex decomposition product obtained in this embodiment, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms is preferably 1.0 to 1.8:1.0 to 2.0:0.1 to 0.8:0.01 to 0.6, more preferably 1.1 to 1.7:1.2 to 1.8:0.2 to 0.6:0.05 to 0.5, and even more preferably 1.2 to 1.6:1.3 to 1.7:0.25 to 0.5:0.08 to 0.4. Further, when bromine and iodine are used in combination as halogen atoms, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine, and iodine is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 1.4 to 1.7: 0.3 to 0.45: 0.04 to 0.18: 0.04 to 0.18. By setting the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte having a thiolisiconregion II type crystal structure described below and having higher ionic conductivity.

[0090] In this specification, the average particle size (D50) is a value measured by a laser diffraction particle size distribution measurement method, and can be measured, for example, by the method described in the Examples. The shape of the complex decomposition product is not particularly limited, but may be, for example, particulate. The average particle size (D50b) of the particulate complex decomposition product is, for example, in the range of 0.01 μm to 500 μm, or further 0.1 to 200 μm.

[0091] In this specification, the specific surface area is a value measured by the BET method, and can be measured, for example, by the method described in the Examples. The specific surface area (Sb) of the complex decomposition product before the pulverization treatment is preferably 21 m ２ / g or more, more preferably 23m ２ / g or more, more preferably 25m ２ / g or more, and even more preferably 27m ２ / g or more, and the upper limit is preferably 70m ２ / g or less, more preferably 60m ２ / g or less, more preferably 50m ２ / g or less, and even more preferably 35m ２ / g or less.

[0092] <Obtaining a Pulverized Product> In this embodiment, the electrolyte precursor is required to be pulverized in a solvent containing an oxygen-atom-containing compound having a relative dielectric constant of 3.2 or more at 25° C. By pulverizing in the solvent containing the oxygen-atom-containing compound, the complexing agent remaining inside the electrolyte precursor is replaced with the oxygen-atom-containing compound and removed, eliminating the obstruction of the conduction path caused by the remaining complexing agent, resulting in a solid electrolyte having high ionic conductivity and also improving thermal stability, which is preferable.

[0093] (Solvent) The solvent used in the above-mentioned pulverization treatment may be an oxygen-containing compound having a dielectric constant of 3.2 or more at 25°C, or may be mixed with other solvents. Such other solvents are similar to those used in mixing the raw material components and the complexing agent described above, but hydrocarbon solvents are preferred. The solvent used in the pulverization treatment is preferably one containing 50 to 99.5% by mass of a hydrocarbon compound and 0.5 to 50% by mass of an oxygen-containing compound, more preferably one containing 65 to 95% by mass of a hydrocarbon compound and 5 to 35% by mass of an oxygen-containing compound, and even more preferably one containing 80 to 95% by mass of a hydrocarbon compound and 5 to 20% by mass of an oxygen-containing compound.

[0094] (Oxygen Atom-Containing Compound) In this specification, the oxygen atom-containing compound is a compound having a relative dielectric constant of 3.2 or more at 25° C. and preferably used as a raw material for solid electrolytes. ２ S and P ２ S ５ Li obtained from ３ P.S. ４ It is preferable to use a complexing agent other than the above that can form a complex containing the compound. By subjecting the electrolyte precursor obtained using the complexing agent to a pulverization treatment in a solvent containing an oxygen atom-containing compound, the complexing agent remaining inside the electrolyte precursor is replaced with the oxygen atom-containing compound and is easily removed, which is thought to improve the ionic conductivity of the sulfide solid electrolyte finally obtained.

[0095] The oxygen atom-containing compound may be any compound that contains an oxygen atom and has the above-mentioned relative dielectric constant, but a compound with a relative dielectric constant of 3.5 or more at 25° C. is preferred, and a compound with a relative dielectric constant of 3.7 or more is more preferred. The oxygen atoms present in the molecules of the oxygen atom-containing compound have a high affinity with lithium atoms, and the PS main skeleton of the solid electrolyte produced by this embodiment has a high affinity with lithium atoms. ４ Li containing structure ３ P.S. ４It is believed that the complexing agent has the ability to easily bond with the oxygen atom to form a complex. Therefore, it is believed that mixing the electrolyte precursor with the oxygen atom-containing compound promotes the removal of the complexing agent remaining inside the electrolyte precursor.

[0096] Furthermore, the oxygen atom-containing group preferably has one or more functional groups selected from an ether group and an ester group, and among these, an ether group is particularly preferred. That is, an ether compound is particularly preferred as the oxygen atom-containing compound. Furthermore, in relation to the complexing agent, it is preferable that the oxygen atom-containing compound does not contain a nitrogen atom as a heteroatom. Therefore, in this embodiment, it is preferable to use a complexing agent that contains a nitrogen atom as a heteroatom, and to use an oxygen atom-containing compound that does not contain a nitrogen atom as a heteroatom. This makes it possible to effectively utilize the functions of the complexing agent and the oxygen atom-containing compound described above, thereby improving the ionic conductivity of the resulting solid electrolyte.

[0097] Examples of such ether compounds include aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, and these compounds may be used alone or in combination.

[0098] More specifically, examples of aliphatic ethers include monoethers such as dimethyl ether, diethyl ether, diisopropyl 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 number of carbon atoms in the aliphatic ether is 1 or more, preferably 2 or more, and more preferably 3 or more, with the upper limit being preferably 20 or less, more preferably 10 or less, and even more preferably 7 or less. Furthermore, as the aliphatic ether, an aliphatic ether having a branched alkyl group on the oxygen atom, such as diisopropyl ether, is most preferably used.

[0099] Examples of alicyclic ethers include ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxolane, etc., and examples of heterocyclic ethers include morpholine, hydroxymethyldimethoxypyridine, etc. The number of carbon atoms in the alicyclic ether and heterocyclic ether is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0100] Examples of aromatic ethers include methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, diphenyl ether, benzyl phenyl ether, naphthyl ether, etc. The number of carbon atoms in the aromatic ether is preferably 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.

[0101] The ether compound used in this 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.

[0102] The ether compound used in this embodiment is preferably an aliphatic ether from the viewpoint of obtaining higher ionic conductivity.

[0103] Furthermore, it is preferable to use a symmetric ether represented by the following general formula (1) as the ether compound, since the ionic conductivity of the resulting sulfide solid electrolyte is higher. １ -O-R ２ ...(1) (wherein, R １ and R ２ are each independently a linear alkyl group having 1 to 20 carbon atoms, a branched alkyl group having 3 to 20 carbon atoms, or a cycloalkyl group having 5 to 20 carbon atoms. １ are the same group, the symmetrical ether represented by general formula (1) has a symmetrical structure with respect to the central oxygen atom.

[0104] R in the above general formula (1) １ and R ２ are each independently preferably a branched alkyl group having 3 to 20 carbon atoms, more preferably a branched alkyl group having 3 to 10 carbon atoms, and even more preferably a branched alkyl group having 3 to 8 carbon atoms. Such bulky alkyl groups can suppress excessive reactivity of the oxygen atoms of the ether compound with the electrolyte precursor. In addition, the ether compound is preferably a branched alkyl group having 3 to 20 carbon atoms, more preferably a branched alkyl group having 3 to 10 carbon atoms, and even more preferably a branched alkyl group having 3 to 8 carbon atoms. Such bulky alkyl groups can suppress excessive reactivity of the oxygen atoms of the ether compound with the electrolyte precursor. １ and R ２ It is also preferred that the groups are symmetrical ethers in which are the same group.

[0105] Examples of the ester compound include aliphatic esters, alicyclic esters, heterocyclic esters, and aromatic esters, and these compounds may be used alone or in combination.

[0106] More specifically, examples of aliphatic esters include formic acid esters such as methyl formate, ethyl formate, and triethyl formate; acetic acid esters such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and isobutyl acetate; propionic acid esters such as methyl propionate, ethyl propionate, propyl propionate, and butyl propionate; oxalic acid esters such as dimethyl oxalate and diethyl oxalate; malonic acid esters such as dimethyl malonate and diethyl malonate; and succinic acid esters such as dimethyl succinate and diethyl succinate. 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.

[0107] Examples of alicyclic esters include methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, dimethyl cyclohexanedicarboxylate, dibutyl cyclohexanedicarboxylate, and dibutyl cyclohexenedicarboxylate, while examples of heterocyclic esters include methyl pyridinecarboxylate, ethyl pyridinecarboxylate, propyl pyridinecarboxylate, methyl pyrimidinecarboxylate, ethyl pyrimidinecarboxylate, and lactones such as acetolactone, propiolactone, butyrolactone, and valerolactone. The number of carbon atoms in the alicyclic esters and heterocyclic esters is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0108] 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. The number of carbon atoms in the aromatic ester is preferably 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.

[0109] The ester compound used in this 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.

[0110] The ester compound used in this embodiment is preferably an aliphatic ester, more preferably an acetate ester, and particularly preferably ethyl acetate, from the viewpoint of obtaining higher ionic conductivity.

[0111] Furthermore, in this embodiment, when obtaining the above-mentioned electrolyte precursor, it is preferable to mix a solvent containing an oxygen atom-containing compound after the complex formation reaction by the complexing agent has progressed to a certain extent. The method for determining the appropriate timing for adding the oxygen atom-containing compound is not particularly limited. For example, when lithium sulfide is used as one of the raw materials, a greater effect can be achieved by adding the oxygen atom-containing compound when the remaining amount of lithium sulfide present in the system has decreased to a certain value. Specifically, the complex formation reaction can be further accelerated by adding the oxygen atom-containing compound when the remaining amount of lithium sulfide has decreased to preferably 35 mol % or less, more preferably 30 mol % or less, and even more preferably 25 mol % or less relative to the amount of lithium sulfide added.

[0112] The amount of the oxygen atom-containing compound added is determined by the amount of Li that can be produced from the raw material. ３ P.S. ４ The molar ratio of the amount of the oxygen atom-containing compound added to the total molar amount of the above is preferably 0.8 or more and 5.0 or less, more preferably 1.2 or more and 4.0 or less, and even more preferably 1.5 or more and 3.0 or less.

[0113] By mixing the raw materials with the oxygen atom-containing compound, the lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms contained in the raw materials can act on the oxygen atom-containing compound to replace the complexing agent, thereby making it possible to remove the complexing agent remaining in the electrolyte precursor.

[0114] (Pulverization Treatment) In this embodiment, the pulverization treatment may be performed by any method capable of pulverizing particles of the electrolyte precursor to expose a fresh surface or to atomize the particles. However, it is preferable to use a pulverizer. The pulverization treatment using a pulverizer is a method that has been conventionally adopted as a mechanical milling method. As the pulverizer, for example, a media-type pulverizer using a pulverization medium can be used. Media-type pulverizers are broadly classified into a container-driven pulverizer and a media-agitating pulverizer. Examples of the container-driven pulverizer include an agitation tank, a pulverization tank, or a combination thereof, such as a ball mill or a bead mill. Examples of the media-agitating pulverizer include impact pulverizers such as a cutter mill, a hammer mill, or a pin mill; a tower-type pulverizer such as a tower mill; an agitation tank pulverizer such as an attritor, an aquamizer, or a sand grinder; a flow-through tank pulverizer such as a Viscomill or a pearl mill; a flow-through pipe pulverizer; an annular pulverizer such as a Co-ball mill; a continuous dynamic pulverizer; and a single- or multi-shaft kneader. Among these, in consideration of ease of adjusting the particle size of the resulting sulfide, a ball mill or a bead mill, which are exemplified as the container-driven crusher, are preferred.

[0115] These pulverizers can be appropriately selected depending on the desired scale, etc. For relatively small scales, container-driven pulverizers such as ball mills and bead mills can be used, while for large scales or mass production, other types of pulverizers may be used.

[0116] Furthermore, as will be described later, when the material is in a liquid state involving a liquid such as a solvent or in a slurry state during the grinding process, a wet grinder that can handle wet grinding is preferred. Typical examples of wet grinders include wet bead mills, wet ball mills, and wet vibration mills. Wet bead mills that use beads as grinding media are preferred because they allow for free adjustment of grinding operation conditions and are easily adaptable to smaller particle sizes. Dry grinders such as dry media grinders, such as dry bead mills, dry ball mills, dry planetary ball mills, and dry vibration mills, and dry non-media grinders, such as jet mills, can also be used.

[0117] Furthermore, when the material to be mixed is in a liquid state or a slurry state, a flow-through mill that can perform a circulation operation to circulate the material as needed can also be used. Specifically, a mill that circulates the material between a mill (pulverizing mixer) that pulverizes the slurry and a temperature holding tank (reaction vessel) can be used.

[0118] The size of the beads or balls used in the ball mill or bead mill may be appropriately selected depending on the desired particle size, processing amount, etc. For example, the diameter of the beads is usually 0.05 mm or more, preferably 0.1 mm or more, more preferably 0.2 mm or more, with the upper limit being usually 5.0 mm or less, preferably 3.0 mm or less, more preferably 2.0 mm or less. The diameter of the balls is usually 2.0 mm or more, preferably 2.5 mm or more, more preferably 3.0 mm or more, with the upper limit being usually 30.0 mm or less, preferably 20.0 mm or less, more preferably 15.0 mm or less.

[0119] The amount of beads or balls used varies depending on the scale of treatment and cannot be generalized, but is usually 100 g or more, preferably 200 g or more, and more preferably 300 g or more, with the upper limit being 5.0 kg or less, more preferably 3.0 kg or less, and even more preferably 1.0 kg or less. Examples of materials for the beads or balls include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0120] Regarding the peripheral speed of the rotating body, low and high peripheral speeds cannot be generally defined because they can vary depending on, for example, the particle size, material, and amount of the media used in the mill. For example, in the case of a device that does not use ball or bead milling media, such as a high-speed rotating thin-film agitator, milling mainly occurs even at relatively high peripheral speeds, and granulation is difficult to occur. On the other hand, in the case of a device that uses milling media, such as a ball mill or bead mill, milling is possible at low peripheral speeds and granulation is possible at high peripheral speeds, as described above. Therefore, under the same conditions for the milling device, milling media, etc., the peripheral speed at which milling is possible is lower than the peripheral speed at which granulation is possible. Therefore, for example, under conditions where granulation is possible above a peripheral speed of 6 m / s, a low peripheral speed means less than 6 m / s, and a high peripheral speed means 6 m / s or higher. By milling the electrolyte precursor in a solvent containing an oxygen-containing compound at any peripheral speed, the amount of complexing agent remaining in the electrolyte precursor can be reduced. The peripheral speed is preferably 1 m / s or higher, more preferably 2 m / s or higher, and even more preferably 3 m / s or higher. During the pulverization, the electrolyte precursor may be granulated.

[0121] The grinding time varies depending on the scale of the treatment and cannot be generalized, but is usually 10 minutes or more, preferably 20 minutes or more, more preferably 30 minutes or more, and even more preferably 45 minutes or more, with the upper limit being usually 72 hours or less, preferably 65 hours or less, and more preferably 52 hours or less.

[0122] By selecting the size and material of the medium (beads or balls) used, the rotor rotation speed, time, etc., mixing, stirring, pulverization, or a combination of these processes can be performed, and the particle size, etc. of the resulting sulfide can be adjusted. In the pulverization process, a solvent containing the oxygen atom-containing compound having a relative dielectric constant of 3.2 or more can be added to and mixed with the electrolyte precursor.

[0123] (Pulverized Product) The pulverized product has the same chemical characteristics as the electrolyte precursor described above, but its specific surface area is different from that of the electrolyte precursor. The pulverized product after pulverization has a larger specific surface area than the electrolyte precursor before pulverization. However, since it is affected by the specific surface area of ​​the electrolyte precursor used in the pulverization, it cannot be generalized, but the specific surface area (Sa) of the pulverized product is preferably 0.5 m as a lower limit. ２ / g or more, more preferably 1.0m ２ / g or more, more preferably 2.0m ２ / g or more, and the upper limit is preferably 30m ２ / g or less, more preferably 20m ２ / g or less, more preferably 15m ２ / g or less, and even more preferably 12m ２ In this embodiment, the ratio (Sb / Sa) of the specific surface area (Sa) of the pulverized product to the specific surface area (Sb) of the electrolyte precursor before pulverization is preferably 1.0 or more and 10.0 or less, more preferably 2.0 or more and 8.0 or less, and even more preferably 3.0 or more and 7.0 or less, from the viewpoint of increasing the ionic conductivity of the sulfide solid electrolyte.

[0124] The shape of the pulverized product is not particularly limited, but may be, for example, particulate. The average particle diameter (D50a) of the particulate pulverized product is preferably not granulated by pulverization, and may be, for example, in the range of 0.01 μm to 500 μm, or even 0.1 to 200 μm. In this embodiment, the ratio (D50b / D50a) of the average particle diameter (D50b) of the electrolyte precursor before pulverization to the average particle diameter (D50a) of the pulverized product is preferably 1.0 or more and 100.0 or less, more preferably 2.0 or more and 80.0 or less, and even more preferably 2.5 or more and 70.0 or less, from the viewpoint of increasing the ionic conductivity of the sulfide solid electrolyte.

[0125] <Removing Solvent from the Pulverized Product> In this embodiment, it is necessary to remove the solvent from the pulverized product to obtain a sulfide solid electrolyte. The method for removing the solvent from the pulverized product can be performed by drying or solid-liquid separation, similar to the method for removing the complexing agent described above. Specific details of the drying and solid-liquid separation are also the same as those described for removing the complexing agent described above.

[0126] (Heating Sulfide Solid Electrolyte) In this embodiment, a step of heating the sulfide solid electrolyte may be further provided. Heating is preferable because the amorphous sulfide solid electrolyte crystallizes, resulting in a crystalline sulfide solid electrolyte with high ionic conductivity. Furthermore, removing the solvent to obtain a crystalline sulfide solid electrolyte is preferable because the crystallinity is further improved. When the amorphous sulfide solid electrolyte is heated to obtain a crystalline sulfide solid electrolyte, the heating temperature may be determined depending on the structure of the crystalline sulfide solid electrolyte. Preferably, the heating temperature is higher than the drying temperature for obtaining an amorphous sulfide solid electrolyte. Specifically, the sulfide solid electrolyte is subjected to differential thermal analysis (DTA) at a heating rate of 10°C / min using a differential thermal analyzer (DTA device). The temperature is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher, starting from the temperature of the top of the exothermic peak observed at the lowest temperature. The upper limit is not particularly limited, but may be about 40°C or lower. By setting the temperature range as described above, a crystalline sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining the crystalline sulfide solid electrolyte cannot be generally specified because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained, but is usually preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher. There is no particular upper limit, but the temperature is preferably 300°C or lower, more preferably 280°C or lower, and even more preferably 250°C or lower.

[0127] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the above heating may be a so-called glass ceramic obtained by heating a sulfide solid electrolyte to a crystallization temperature or higher, and its crystalline structure may be Li ３ P.S. ４Crystal 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).

[0128] Also, Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples of the crystal structure include a crystal structure 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 present production method is preferably the thio-lisicon region II type crystal structure among the above, since it can provide higher ionic conductivity. Here, the "thio-lisicon region II type crystal structure" refers to a structure in which Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４This indicates that the crystalline sulfide solid electrolyte obtained by this production method has either a crystal structure similar to the thio-lisicon region II type. Furthermore, the crystalline sulfide solid electrolyte obtained by this production method may have the thio-lisicon region II type crystal structure or may have it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it has it as the main crystal. In this specification, "having it as the main crystal" means that the proportion of the target crystal structure among the crystal structures is 80% or more, preferably 90% or more, and more preferably 95% or more. Furthermore, from the viewpoint of obtaining higher ionic conductivity, the crystalline sulfide solid electrolyte obtained by this production method has either a crystal structure similar to the thio-lisicon region II type crystal structure or a crystal structure similar to the thio-lisicon region II type crystal structure. ３ P.S. ４ (β-Li ３ P.S. ４ ) is preferably not included.

[0129] In X-ray diffraction measurement using CuKα radiation, Li ３ P.S. ４ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°. ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=16.9°, 27.1°, and 32.5°. ７ P.S. ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=15.3°, 25.2°, 29.6°, and 31.0°. ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II crystal structure appear, for example, at 2θ=20.1°, 23.9°, and 29.5°, and Li ４－ｘ Ge １－ｘ P ｘ S４ Diffraction peaks of a crystal structure similar to that of thio-LISICON Region II type appear, for example, at 2θ=20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0130] As described above, in this embodiment, when the thiolicon region II crystal structure is obtained, crystalline Li ３ P.S. ４ (β-Li ３ P.S. ４ ) is preferably not included.

[0131] The above Li ７ P.S. ６ The structural skeleton of the compound has the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ The crystal structure represented by the formula (x is -0.6 to 0.6, y is 0.1 to 0.6) is a cubic or orthorhombic crystal, preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ The crystal structure represented by (0.8≦x≦1.7, 0<y≦−0.25x+0.5) is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. ７－ｘ P.S. ６－ｘ Ha ｘThe crystal structure represented by the formula (where Ha is Cl or Br, and x is preferably 0.2 to 1.8) is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Note that these peak positions may vary within a range of ±0.5°.

[0132] Furthermore, the crystalline sulfide solid electrolyte obtained by this production method preferably has a half-width of the maximum peak, including the background at 2θ = 10 to 40 °, of Δ2θ = 0.32 or less in X-ray diffraction measurement using CuKα radiation. By possessing such properties, higher ionic conductivity is obtained, and battery performance is improved. From the same viewpoint, the half-width of the maximum peak is more preferably Δ2θ = 0.30 or less, and even more preferably Δ2θ = 0.28 or less. A typical example of a crystalline sulfide solid electrolyte having such properties is one having a thiolicon region II crystal structure.

[0133] The half width can be calculated as follows. A range of the maximum peak ±2° is used. If the ratio of the Lorentz function is A (0≦A≦1), the peak intensity correction value is B, the 2θ maximum peak is C, the peak position in the range used for calculation (C±2°) is D, the half width is E, the background is F, and the intensity of each peak in the peak range used for calculation is G, then when the variables are A, B, C, D, E, and F, the following is calculated for each peak position: H=G-{B×{A / (1+(D-C) ２ / E ２ )+(1-A)×exp(-1×(D-C) ２ / E ２ )}+F} The half-width can be determined by summing up H within the range of the peak C to be calculated ±2° and minimizing the total value with GRG nonlinearity using the solver function of spreadsheet software Excel (Microsoft).

[0134] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ５０) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.

[0135] The volume-based average particle size of the crystalline sulfide solid electrolyte obtained by this manufacturing method is 3 μm or more, which is the same as the average particle size of the sulfide solid electrolyte of the present embodiment. Also, the specific surface area of ​​the crystalline sulfide solid electrolyte obtained by this manufacturing method, measured by the BET method, is 20 m or more, which is the same as the specific surface area of ​​the sulfide solid electrolyte of the present embodiment. ２ / g or more.

[0136] [Sulfide Solid Electrolyte] The sulfide solid electrolyte of this embodiment contains 0.1 to 0.9 mass% of a complexing agent containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms and having two or more heteroatoms in the molecule, and 0.01 to 0.5 mass% of an oxygen-containing compound having a dielectric constant at 25°C of 3.2 or more. The sulfide solid electrolyte obtained by the above-mentioned method for producing a sulfide solid electrolyte has a content of the complexing agent having two or more heteroatoms in the molecule and the oxygen-containing compound having a dielectric constant at 25°C of 3.2 or more within the above-mentioned ranges due to the production process. Here, details of the complexing agent having two or more heteroatoms in the molecule and the oxygen-containing compound having a dielectric constant at 25°C of 3.2 or more are the same as those described in the above-mentioned method for producing a sulfide solid electrolyte. Note that examples of methods for measuring the complexing agent having two or more heteroatoms in the molecule and the oxygen-containing compound having a dielectric constant at 25°C of 3.2 or more can be mentioned. From the viewpoint of improving ionic conductivity, the content of the complexing agent having two or more heteroatoms in the molecule in the sulfide solid electrolyte of this embodiment is preferably 0.1 to 0.75 mass%, more preferably 0.1 to 0.5 mass%. Furthermore, from the viewpoint of improving ionic conductivity, the content of the oxygen-containing compound having a relative dielectric constant of 3.2 or more at 25°C in the sulfide solid electrolyte of this embodiment is preferably 0.01 to 0.3 mass%, more preferably 0.01 to 0.2 mass%. In this embodiment, by pulverizing the electrolyte precursor using an oxygen-containing compound having a relative dielectric constant of 3.2 or more at 25°C, the interaction between Li ions and the complexing agent is inhibited by the oxygen-containing compound. The pulverized product is then subjected to a drying treatment or a heat treatment to reduce the content of the oxygen-containing compound and the complexing agent. By setting the content of the complexing agent and the oxygen-containing compound remaining inside the sulfide solid electrolyte after crystallization in this manner within the above-mentioned numerical range, conductivity can be improved without inhibiting the conduction path.

[0137] Moreover, from the viewpoint of thermal stability, the sulfide solid electrolyte of this embodiment preferably exhibits a crystallization exothermic peak of 270 to 310° C. in differential thermal analysis (DTA), more preferably exhibits a crystallization exothermic peak of 280 to 310° C., and even more preferably exhibits a crystallization exothermic peak of 290 to 310° C. Here, the above-mentioned crystallization exothermic peak can be defined as, for example, an increase in heat flow of 0.3 W / g or more in differential thermal analysis (DTA).

[0138] Furthermore, the sulfide solid electrolyte of this embodiment has a specific surface area of ​​1 to 20 m ２ / g and an average particle size (D50) of 0.1 to 10 μm.

[0139] (Uses of sulfide solid electrolyte) The sulfide solid electrolyte of this embodiment has high ionic conductivity, excellent battery performance, and is less likely to generate hydrogen sulfide, and is therefore suitable for use in batteries. It is particularly suitable when lithium element is used as the conductive species. The sulfide solid electrolyte of this embodiment may be used in a positive electrode layer, a negative electrode layer, or an electrolyte layer. Each layer may be manufactured by a known method.

[0140] The battery preferably includes a current collector in addition to the positive electrode layer, the electrolyte layer, and the negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the crystalline sulfide solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used.

[0141] 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.

[0142] (1) Measurement methods are described below: (1-1) Volume-based average particle size (D50) Measurement was performed using a laser diffraction / scattering particle size distribution analyzer (Partica LA-950 (model number), manufactured by Horiba, Ltd.).

[0143] A mixture of dehydrated toluene (FUJIFILM Wako Pure Chemical Industries, Ltd., special grade) and tertiary butyl alcohol (FUJIFILM Wako Pure Chemical Industries, Ltd., special grade) in a weight ratio of 93.8:6.2 was used as the dispersion medium. 50 mL of the dispersion medium was injected into the flow cell of the device and circulated. The measurement target was then added, ultrasonicated, and the particle size distribution was measured. The amount of measurement target added was adjusted so that the red light transmittance (R) corresponding to the particle concentration on the measurement screen specified by the device was 80-90% and the blue light transmittance (B) was 70-90%. The calculation conditions used were 2.16 as the refractive index of the measurement target and 1.49 as the refractive index of the dispersion medium. The number of repetitions in the distribution configuration was fixed at 15, and particle size calculations were performed.

[0144] (1-2) Measurement of Specific Surface Area The specific surface area was determined by the BET flow method (three-point method) using nitrogen gas as the adsorbate in accordance with JIS R 1626:1996.

[0145] (1-3) Ion Conductivity Measurement In this example, the ion conductivity was measured as follows. A 10 mm diameter (cross-sectional area S: 0.785 cm) sample was taken from the sulfide solid electrolyte. ２ ), and a height (L) of 0.1 to 0.3 cm were molded into a circular pellet to prepare a sample. Electrode terminals were attached to the top and bottom of the sample, and measurements were made at 25°C using an AC impedance method (frequency range: 1 MHz to 100 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was defined as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula: R = ρ (L / S) σ = 1 / ρ

[0146] (1-4) X-ray diffraction (XRD) measurement The obtained crystalline product was measured by XRD measurement. The sample powder produced in each example was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm and leveled with glass. This sample was sealed with Kapton film for XRD and measured without exposing it to air. Measurement was performed using a powder X-ray diffraction measurement device D2 PHASER manufactured by BRUKER Co., Ltd. under the following conditions.

[0147] Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: Concentration method Slit configuration: Soller slit 4° (both incident and receiving sides), divergence slit 1 mm, Kβ filter (Ni plate 0.5%), air scatter screen 3 mm) Detector: Semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.05 deg, 0.05 deg / sec

[0148] (1-5) Measurement of the contents of complexing agent and oxygen atom-containing compound The powdered crystalline solid electrolytes obtained in Example 1 and Comparative Examples 1 to 3 were dissolved in 1-pentanol, and the resulting 1-pentanol solutions were analyzed by gas chromatography to measure the contents of complexing agent and oxygen atom-containing compound. The results are shown in Table 1.

[0149] (1-6) Differential Thermal Analysis (DTA) Differential thermal analysis (DTA) was performed using a differential thermal analyzer (DTA) at a temperature increase rate of 10°C / min to measure the crystallization temperature (crystallization exothermic peak). When the heat flow increased by 0.3 W / g or more, it was considered that the crystallization exothermic peak was observed.

[0150] (1-7) Relative Dielectric Constant According to JIS C 2138:2007 “Electrical insulating materials—Method for measuring relative dielectric constant and dielectric loss tangent”, measurement was performed using Model-871 (product name, manufactured by Sanyo Trading Co., Ltd.) at a frequency of 10 kHz and 25° C.

[0151] Example 1: 13.19 g of lithium sulfide, 21.26 g of diphosphorus pentasulfide, 4.15 g of lithium bromide, and 6.40 g of lithium iodide were introduced into a 1-liter reactor equipped with an agitator under a nitrogen atmosphere. 100 mL of tetramethylethylenediamine (TMEDA) as a complexing agent and 800 mL of cyclohexane as a solvent were added, and the agitator was operated to mix by stirring. 456 g of zirconia balls (diameter: 0.5 mmφ) (bead filling rate relative to the milling chamber: 80%) were charged into a circulating bead mill ("Star Mill LMZ015 (model number)" manufactured by Ashizawa Finetech Co., Ltd.), and milling was performed for 60 minutes while circulating between the reactor and the milling chamber under the following conditions: pump flow rate: 550 mL / min, peripheral speed: 8 m / s, mill jacket temperature: 20°C, to obtain a complex slurry. The resulting complex slurry was then immediately dried under vacuum at room temperature (23°C) to obtain a powdery complex. The resulting complex was dried at 110°C under reduced pressure for 6 hours to obtain an amorphous complex decomposition product. It was then heated under reduced pressure at 160°C for 2 hours to obtain a crystalline complex decomposition product (1). Furthermore, crystallization peaks were detected at 2θ = 20.2° and 23.6° in the X-ray diffraction spectrum of the crystalline complex decomposition product (1), confirming that it had a thiolicon region II crystal structure.

[0152] Into a 1-liter reactor equipped with a stirring blade, 35 g of crystalline complex decomposition product (1), 220 g of toluene, and 35 g of diisopropyl ether (relative dielectric constant at 25 ° C: 3.8) were added. After rotating the stirring blade, a circulating bead mill (trade name: Star Mill LMZ015, manufactured by Ashizawa Finetech Co., Ltd.) was used under predetermined conditions (bead material: zirconia, bead diameter: 0.3 mmφ, bead usage amount: 456 g, pump flow rate: 650 mL / min, mill jacket temperature: 10 ° C.) at a peripheral speed of 12 m / s for 1 hour and at a peripheral speed of 4 m / s for 10 minutes. The resulting slurry was dried under vacuum (room temperature: 23 ° C.) to obtain a white powder of amorphous solid electrolyte. The obtained sample was dried under vacuum (room temperature: 23 ° C.) to obtain an amorphous solid electrolyte. Next, the mixture was heated at 180 ° C. for 2 hours under reduced pressure to obtain a crystalline solid electrolyte.

[0153] Comparative Example 1 The crystalline complex decomposition product (1) obtained in Example 1 was used as it was for comparison and subjected to various measurements.

[0154] Comparative Example 2 A crystalline solid electrolyte was obtained in the same manner as in Example 1, except that 255 g of toluene alone was used instead of 220 g of toluene and 35 g of diisopropyl ether.

[0155] Comparative Example 3 A crystalline solid electrolyte was obtained in the same manner as in Example 1, except that dibutyl ether (relative dielectric constant at 25° C.: 3.1) was used instead of diisopropyl ether.

[0156] Table 1 shows the specific surface area, average particle size (D50), contents of complexing agent and oxygen atom-containing compound having a relative dielectric constant of 3.2 or more at 25° C., and ionic conductivity of each solid electrolyte.

[0157]

[0158] The DTA curves of the amorphous solid electrolytes obtained in Example 1 and Comparative Example 3 are shown in FIGS. 1 and 2, respectively.

[0159] The results in Table 1 confirm that the crystalline solid electrolyte obtained in Example 1 had the highest ionic conductivity. Furthermore, a comparison of the DTA curves of the amorphous solid electrolytes obtained in Example 1 and Comparative Example 3 reveals a clear exothermic crystallization peak (Tc2) indicating a phase transition from thiolisicon region II to another phase only in Example 1. This suggests that in the amorphous solid electrolyte obtained in Example 1, the phase transition from thiolisicon region II to another phase is suppressed in the temperature range from Tc1 to Tc2, whereas in the amorphous solid electrolyte obtained in Comparative Example 3, the phase transition to the other phase occurs continuously in the temperature range above Tc1. Therefore, it is presumed that the ionic conductivity decreases when exposed to high temperatures during the manufacturing process of an all-solid-state battery due to its relatively low heat resistance. The DTA curves of the crystalline solid electrolytes obtained in Example 1 and Comparative Example 3 are shown in Figures 3 and 4, respectively. Comparison of the DTA curves of the crystalline solid electrolytes obtained in Example 1 and Comparative Example 3 reveals that the crystallization exothermic peak of the crystalline solid electrolyte obtained in Example 1 was observed at 270 to 310°C, and phase transition from thiolisicon region II to another phase was suppressed below 270°C. On the other hand, the crystalline solid electrolyte obtained in Comparative Example 3 exhibited a crystallization exothermic peak at approximately 220 to 240°C, and a phase transition from thiolisicon region II to another phase occurred. Therefore, it is presumed that the crystalline solid electrolyte obtained in Example 1 exhibits more suppressed phase transition and the accompanying decrease in ionic conductivity at high temperatures than the crystalline solid electrolyte obtained in Comparative Example 3, and thus has higher thermal stability. From the results of the DTA curves above, it is presumed that in Comparative Example 3, dibutyl ether readily dissolves lithium halide coordinated with a complexing agent, causing uneven distribution due to dissolution and precipitation of lithium halide, and that an impurity phase is likely to form at relatively low temperatures. On the other hand, in Example 1, it is presumed that diisopropyl ether does not easily dissolve the lithium halide coordinated with the complexing agent, and uneven distribution due to dissolution or precipitation of the lithium halide does not easily occur, and therefore an impurity phase is unlikely to be formed.

[0160] According to this embodiment, a sulfide solid electrolyte having high ionic conductivity and excellent battery performance can be produced. The sulfide solid electrolyte obtained by the production method of this embodiment is suitable for use in batteries, particularly batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. Mixing a raw material containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms with a complexing agent having two or more heteroatoms in its molecule to obtain an electrolyte precursor; pulverizing the electrolyte precursor in a solvent containing an oxygen atom-containing compound having a relative dielectric constant of 3.2 or more at 25°C to obtain a pulverized product; and removing the solvent from the pulverized product to obtain a sulfide solid electrolyte; A method for producing a sulfide solid electrolyte, comprising:

2. The method for producing a sulfide solid electrolyte according to claim 1 , wherein the oxygen atom-containing compound is an ether compound.

3. 3. The method for producing a sulfide solid electrolyte according to claim 2, wherein the ether compound is an aliphatic ether having 1 to 20 carbon atoms.

4. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, wherein the ether compound is represented by the following general formula (1): R １ -O-R ２ ・・・(1) (In the formula, R １ and R ２ are each independently a linear alkyl group having 1 to 20 carbon atoms, a branched alkyl group having 3 to 20 carbon atoms, or a cycloalkyl group having 5 to 20 carbon atoms.

5. R in the general formula (1) １ and R ２ and are the same group, the method for producing a sulfide solid electrolyte according to claim 4 .

6. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, further comprising heating the electrolyte precursor.

7. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, further comprising heating the sulfide solid electrolyte.

8. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, wherein the complexing agent is a compound having a tertiary amino group.

9. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, wherein the solvent further contains a hydrocarbon compound.

10. The method for producing a sulfide solid electrolyte according to claim 9, wherein the solvent contains 50 to 99.5 mass% of the hydrocarbon compound and 0.5 to 50 mass% of the oxygen atom-containing compound.

11. A sulfide solid electrolyte containing 0.1 to 0.9 mass % of a complexing agent that contains a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom and has two or more heteroatoms in the molecule, and 0.01 to 0.5 mass % of an oxygen atom-containing compound that has a relative dielectric constant at 25°C of 3.2 or more.

12. The sulfide solid electrolyte according to claim 11, wherein a crystallization exothermic peak is exhibited at 270 to 310 ° C. in differential thermal analysis (DTA).

13. Specific surface area is 1 to 20 m ２ The sulfide solid electrolyte according to claim 11 or 12, wherein the sulfide solid electrolyte has a molecular weight of 1000 or more and an average particle diameter (D50) of 0.1 to 10 μm.