Method for producing sulfide solid electrolyte

Abstract

To provide a method for producing a sulfide solid electrolyte which exhibits excellent productivity and product quality in a liquid-phase process.SOLUTION: A method for producing a sulfide solid electrolyte comprises mixing a material composition containing lithium, phosphorus and sulfur atoms with a pyridine compound represented by the general formula (1) in the figure, where R1 is a hydrocarbon group having 1 to 6 carbon atoms, and n is an integer from 1 to 5.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Conventionally, batteries used for such applications have used electrolytes containing flammable organic solvents. However, 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 improved. Therefore, all-solid-state batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed. In particular, for automotive applications, higher capacity and higher output are required, and the demand for safety is ever increasing.

[0003] Methods for producing solid electrolytes used in solid electrolyte layers are broadly divided into solid-phase methods and liquid-phase methods. Liquid-phase methods include homogeneous methods in which the solid electrolyte material is completely dissolved in a solvent, and heterogeneous methods in which the solid electrolyte material is not completely dissolved and is left as a solid-liquid coexisting suspension. For example, Patent Document 1 proposes a method for producing a solid electrolyte by mixing a solid electrolyte raw material with a complexing agent containing a compound having at least two tertiary amino groups in its molecule. Patent Document 2 also discloses a method for producing a solid electrolyte using a specific compound as a complexing agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 105737 Brochure [Patent Document 2] International Publication No. 2021 / 132173 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a liquid phase method for producing a sulfide solid electrolyte with excellent productivity and high quality. [Means for solving the problem]

[0006] The method for producing a sulfide solid electrolyte according to the present invention includes the steps of: A method for producing a sulfide solid electrolyte, the method comprising mixing a raw material containing lithium atoms, phosphorus atoms, and sulfur atoms with a pyridine compound represented by the following general formula (1): [ka] (In the formula, R 1 is a hydrocarbon group having 1 to 6 carbon atoms, and n is an integer of 1 to 5. is. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a liquid phase method for producing a sulfide solid electrolyte with excellent productivity and high quality. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an X-ray diffraction pattern of the crystalline sulfide solid electrolyte obtained in Example 1. [Figure 2] 1 is an X-ray diffraction pattern of the crystalline sulfide solid electrolyte obtained in Example 2. [Figure 3] 1 is an X-ray diffraction pattern of the crystalline sulfide solid electrolyte obtained in Comparative Example 1. [Figure 4] 1 is an X-ray diffraction pattern of the crystalline sulfide solid electrolyte obtained in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a numerical range expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values. Furthermore, preferred specifications can be arbitrarily adopted. In other words, one preferred specification can be adopted in combination with one or more other preferred specifications. It can be said that a combination of preferred items is more preferable.

[0010] (Findings gained by the inventors to arrive at the present invention) As a result of extensive research aimed at solving the above problems, the present inventors have discovered the following and have completed the present invention.

[0011] In the method for producing a solid electrolyte using a complexing agent, the complexing agent has a significant effect on the ionic conductivity and other properties of the resulting solid electrolyte. Therefore, in search of a better complexing agent, various compounds have been investigated as complexing agents. Specifically, amine compounds containing a ring structure are known as complexing agents (see Patent Document 2). However, in recent years, there has been an increasing demand for improved performance of batteries using solid electrolytes, and there is a need to search for complexing agents that can produce solid electrolytes with higher ionic conductivity.

[0012] The present inventors have investigated the suitability of compounds with various structures as solvents or complexing agents, and through the investigation, have discovered that a solid electrolyte with high ionic conductivity can be produced by using a compound having a hydrocarbon group on a pyridine skeleton as a solvent or complexing agent.

[0013] (Various aspects of this embodiment) A method for producing a sulfide solid electrolyte according to a first aspect of the present embodiment includes the steps of: A method for producing a sulfide solid electrolyte, the method comprising mixing a raw material containing lithium atoms, phosphorus atoms, and sulfur atoms with a pyridine compound represented by the following general formula (1): [ka] (In the formula, R 1 is a hydrocarbon group having 1 to 6 carbon atoms, and n is an integer of 1 to 5. is.

[0014] In the method for producing a sulfide solid electrolyte of the present embodiment, by using a pyridine compound having a specific substituent (a compound having a pyridine ring) as a solvent or a complexing agent, as described above, a sulfide solid electrolyte having higher ionic conductivity can be obtained.

[0015] A method for producing a sulfide solid electrolyte according to a second aspect of the present embodiment includes the steps of: In the first embodiment, in the general formula (1), 1 is an alkyl or alkenyl group having 1 to 4 carbon atoms, and n is 1 or 2; That is it.

[0016] Further, a method for producing a sulfide solid electrolyte according to a third aspect of the present embodiment includes the steps of: In the first or second embodiment, the R 1 is bonded to at least one of the 2- and 4-positions of the pyridine skeleton, That is it.

[0017] Further, a method for producing a sulfide solid electrolyte according to a fourth aspect of the present embodiment includes the steps of: In any one of the first to third embodiments, the pyridine compound is 2-methylpyridine or 4-methylpyridine. That is it.

[0018] As the solvent or complexing agent used in the production method of this embodiment, a pyridine compound having a specific substituent as described above can be used. However, from the viewpoint of easily achieving the effects of the present invention, it is possible to use a pyridine compound having a specific substituent R 1is preferably an alkyl or alkenyl group having 1 to 4 carbon atoms, n is preferably 1 or 2, and R 1 is more preferably bonded to at least one of the 2-position and 4-position of the pyridine skeleton, and more specifically, the pyridine compound is particularly preferably 2-methylpyridine or 4-methylpyridine.

[0019] A method for producing a sulfide solid electrolyte according to a fifth aspect of the present embodiment includes: In any one of the first to fourth embodiments, the raw material-containing material contains lithium sulfide and diphosphorus pentasulfide. That is it.

[0020] By using lithium sulfide and diphosphorus pentasulfide as the raw material components, a sulfide solid electrolyte having high ionic conductivity can be easily obtained efficiently.

[0021] Further, a method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment includes the steps of: In the fifth embodiment, the lithium sulfide is previously contacted with an alcohol. That is it.

[0022] By using lithium sulfide that has been brought into contact with alcohol beforehand as the lithium sulfide used in the raw material ingredients, a sulfide solid electrolyte having higher ionic conductivity can be more efficiently obtained.

[0023] A method for producing a sulfide solid electrolyte according to a seventh aspect of the present embodiment includes: In any one of the first to sixth embodiments, the method further comprises heating the electrolyte precursor obtained by the mixing. That is it.

[0024] By heating the electrolyte precursor, the sulfide solid electrolyte can be obtained efficiently.

[0025] A method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment includes: In any one of the first to seventh embodiments, the obtained sulfide solid electrolyte contains a thiolithium region II crystal structure. That is it.

[0026] Further, a method for producing a sulfide solid electrolyte according to a ninth aspect of the present embodiment includes the steps of: In any one of the first to eighth embodiments, the sulfide solid electrolyte does not have diffraction peaks at 2θ=17.5° and 26.1° in X-ray diffraction measurement using CuKα rays. That is it.

[0027] According to the manufacturing method of this embodiment, a sulfide solid electrolyte containing a thiolisiconregion II crystal structure can be efficiently obtained by a simple method. More specifically, the sulfide solid electrolyte containing the thiolisiconregion II crystal structure does not have the above-mentioned predetermined diffraction peak.

[0028] [Sulfide solid electrolyte] In this specification, the term "sulfide solid electrolyte" refers to an electrolyte that maintains a solid state under a nitrogen atmosphere at 25° C. The sulfide solid electrolyte in this embodiment is a sulfide solid electrolyte that contains lithium, sulfur, and phosphorus and has ionic conductivity due to the lithium element.

[0029] The term "sulfide solid electrolyte" includes both crystalline sulfide solid electrolytes having a crystalline structure and amorphous sulfide solid electrolytes. In this specification, a crystalline sulfide solid electrolyte is a solid electrolyte in which peaks derived from the solid electrolyte are observed in the X-ray diffraction pattern in powder X-ray diffraction (XRD) measurement, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present. That is, a crystalline sulfide solid electrolyte includes a crystalline structure derived from the solid electrolyte, and the crystalline structure may be partially or entirely 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 partially contain an amorphous sulfide solid electrolyte (also referred to as a "glass component"). Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte (glass component) above its crystallization temperature.

[0030] In addition, in this specification, the amorphous sulfide solid electrolyte (glass component) refers to one in which the X-ray diffraction pattern in powder X-ray diffraction (XRD) measurement is a halo pattern in which no peaks other than those derived from the material are observed, and it does not matter whether or not there are peaks derived from the raw materials of the solid electrolyte.

[0031] [Method for producing sulfide solid electrolyte] The method for producing a sulfide solid electrolyte of this embodiment includes mixing a raw material containing lithium atoms, phosphorus atoms, and sulfur atoms with a predetermined pyridine compound.

[0032] (Raw material content) The raw material contents used in this embodiment contain lithium atoms, phosphorus atoms, and sulfur atoms. Furthermore, from the viewpoint of improving ionic conductivity, the raw material contents used in this embodiment preferably further contain halogen atoms. More specifically, the raw material contents are contents containing substances containing these atoms (hereinafter also referred to as "solid electrolyte raw materials"), and preferably contain two or more solid electrolyte raw materials.

[0033] Representative examples of solid electrolyte raw materials include raw materials containing at least two types of atoms selected from the above-mentioned atoms, such as lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; and phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5), as well as raw materials consisting of one type of atom selected from the above-mentioned atoms, such as elemental halogens such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2); elemental phosphorus; and elemental sulfur.

[0034] Among the above, preferred solid electrolyte raw materials containing lithium atoms, sulfur atoms, and phosphorus atoms include lithium sulfide; and phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5). Of the phosphorus sulfides, diphosphorus pentasulfide is preferred.

[0035] Among the above, either a simple halogen or lithium halide can be preferably used as the solid electrolyte raw material containing a halogen atom. The halogen atoms contained in the raw material are preferably fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, more preferably chlorine atoms, bromine atoms, and iodine atoms, and even more preferably bromine atoms and iodine atoms. The solid electrolyte raw material preferably contains these halogen atoms. Therefore, as the halogen element, chlorine (Cl2), bromine (Br2), and iodine (I2) are more preferred, and bromine (Br2) and iodine (I2) are more preferred. As the lithium halide, lithium chloride, lithium bromide, and lithium iodide are more preferred, and lithium bromide and lithium iodide are even more preferred. These can be used alone or in combination.

[0036] Preferred examples of the combination of solid electrolyte raw materials contained in the raw material inclusions include a combination of lithium sulfide, phosphorus sulfide, and lithium halide, a combination of lithium sulfide, phosphorus sulfide, and a simple halogen, and a combination of lithium sulfide, phosphorus sulfide, lithium halide, and a simple halogen. More preferred examples include a combination of lithium sulfide, phosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, phosphorus pentasulfide, and a simple halogen. In the above combinations, lithium bromide and lithium iodide are preferred as the lithium halide, and bromine and iodine are preferred as the simple halogen. As mentioned above, the solid electrolyte raw material containing halogen atoms can be selected depending on the type of sulfide solid electrolyte to be obtained.

[0037] The raw material inclusions contain a solid electrolyte raw material containing at least two types of atoms selected from the above-mentioned atoms. Examples of solid electrolyte raw materials other than those mentioned above include phosphorus halides such as various phosphorus fluorides (PF3, PF5), various phosphorus chlorides (PCl3, PCl5, P2Cl4), various phosphorus bromides (PBr3, PBr5), and various phosphorus iodides (PI3, P2I4); and thiophosphoryl halides such as thiophosphoryl fluoride (PSF3), thiophosphoryl chloride (PSCl3), thiophosphoryl bromide (PSBr3), thiophosphoryl iodide (PSI3), thiophosphoryl fluoride dichloride (PSCl2F), and thiophosphoryl fluoride dibromide (PSBr2F).

[0038] Examples of solid electrolyte raw materials other than those mentioned above that are contained in the raw material inclusion include solid electrolyte raw materials that contain at least one atom selected from the above atoms and also contain atoms other than the atom. More specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; metal sulfides such as silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS, SnS), aluminum sulfide, and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium, 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; and phosphorus oxyhalides such as phosphorus oxychloride (POCl) and phosphorus oxybromide (POBr). When oxygen atoms are introduced into the solid electrolyte, lithium oxide, lithium hydroxide, and phosphate compounds such as lithium phosphate are preferred.

[0039] In this embodiment, Li3PS4 containing the PS4 structure can also be used as the solid electrolyte raw material. Specifically, Li3PS4 may be prepared in advance by manufacturing or the like and used as the raw material. In this case, preferred combinations of solid electrolyte raw materials contained in the raw material contents include a combination of Li3PS4 and the lithium halide, a combination of Li3PS4 and the elemental halogen, and a combination of Li3PS4 and the lithium halide and the elemental halogen.

[0040] The solid electrolyte raw material such as lithium sulfide used in this embodiment is preferably in the form of particles. The average particle size of the solid electrolyte raw material (D 50 ) is preferably 0.1 to 1000 μm, more preferably 0.5 to 100 μm, and even more preferably 1 to 20 μm. 50) is the particle size at which, when a particle size distribution cumulative curve is drawn, the cumulative total, starting from the smallest particle size, reaches 50% (by volume) 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 similar to that of the lithium sulfide particles, i.e., within the same range as that of the lithium sulfide particles.

[0041] When the raw material contains lithium sulfide, diphosphorus pentasulfide, and lithium halide, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 60 mol% or more, more preferably 65 mol% or more, even more preferably 70 mol% or more, and still more preferably 74 mol% or more, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity, and the upper limit is preferably 85 mol% or less, more preferably 83 mol% or less, and still more preferably 80 mol% or less. The range is typically preferably 60 to 85 mol%, more preferably 65 to 83 mol%, even more preferably 70 to 80 mol%, and still more preferably 74 to 80 mol%. Furthermore, when a sulfide solid electrolyte having a thiolicon region II crystal structure is to be obtained, in addition to the above ranges, particularly preferably 74 to 78.5 mol%, 74 to 78 mol%, or 74 to 76 mol%, and when a sulfide solid electrolyte having an argyrodite crystal structure is to be obtained, in addition to the above ranges, particularly preferably 76 to 83 mol%, 77 to 80 mol%, or 78 to 80 mol%.

[0042] When the raw material content includes lithium sulfide, diphosphorus pentasulfide, lithium halide, and other raw materials used as needed, the content of lithium sulfide and diphosphorus pentasulfide relative to the total of these is preferably 50 mol% or more, more preferably 55 mol% or more, and even more preferably 60 mol% or more, and the upper limit is preferably 100 mol% or less, more preferably 90 mol% or less, even more preferably 85 mol% or less, and even more preferably 80 mol% or less. The range is typically preferably 50 to 100 mol%, more preferably 55 to 90 mol%, even more preferably 60 to 85 mol%, and even more preferably 60 to 80 mol%. Furthermore, when a sulfide solid electrolyte having a thiolicon region II crystal structure is to be obtained, in addition to the above ranges, particularly preferably 65 to 90 mol%, 70 to 85 mol%, or 75 to 83 mol%, and when a sulfide solid electrolyte having an argyrodite crystal structure is to be obtained, in addition to the above ranges, particularly preferably 50 to 78 mol%, 55 to 70 mol%, or 55 to 65 mol%.

[0043] When the raw material contains a combination of lithium bromide and lithium iodide as lithium halides, from the viewpoint of improving ionic conductivity, the ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 mol% or more, more preferably 20 mol% or more, even more preferably 35 mol% or more, and even more preferably 45 mol% or more, and the upper limit is preferably 99 mol% or less, more preferably 90 mol% or less, even more preferably 75 mol% or less, and even more preferably 60 mol% or less. The range is typically preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 35 to 75 mol%, and even more preferably 45 to 60 mol%. When attempting to obtain a sulfide solid electrolyte having a thiolicon region II crystal structure, the content is particularly preferably 40 to 75 mol %, 40 to 65 mol %, or 45 to 55 mol % in addition to the above range.

[0044] Furthermore, when the raw material contains a combination of lithium bromide and lithium chloride as the lithium halide, from the viewpoint of improving ionic conductivity, the ratio of lithium bromide to the total of lithium bromide and lithium chloride is preferably 1 mol% or more, more preferably 15 mol% or more, even more preferably 25 mol% or more, and even more preferably 35 mol% or more, with the upper limit being preferably 99 mol% or less, more preferably 75 mol% or less, even more preferably 60 mol% or less, and even more preferably 45 mol% or less. The range is typically preferably 1 to 99 mol%, more preferably 15 to 75 mol%, even more preferably 25 to 60 mol%, and even more preferably 35 to 45 mol%. Furthermore, when it is desired to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure, in addition to the above range, the content is particularly preferably 25 to 45 mol %, or 35 to 40 mol %.

[0045] When the raw material inclusions include elemental halogens as raw materials, including lithium sulfide and diphosphorus pentasulfide, the ratio of the number of moles of lithium sulfide excluding the same number of moles of lithium sulfide as the elemental halogen to the total number of moles of lithium sulfide and diphosphorus pentasulfide excluding the same number of moles of lithium sulfide as the elemental halogen 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 at these ratios.

[0046] From the same viewpoint, when the raw material contains lithium sulfide, diphosphorus pentasulfide, and an elemental halogen, the content of the elemental halogen relative to the total amount of lithium sulfide, diphosphorus pentasulfide, and the elemental halogen 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%.

[0047] When the raw material contains lithium sulfide, diphosphorus pentasulfide, an elemental halogen, and a lithium halide, the content of the elemental halogen (α mol %) and the content of the lithium halide (β mol %) relative to the total amount of lithium sulfide, diphosphorus pentasulfide, the elemental halogen, and the lithium halide preferably satisfy the following formula (1), more preferably satisfy the following formula (2), even more preferably satisfy the following formula (3), and even more preferably satisfy the following formula (4): 2≦2α+β≦100…(1) 4≦2α+β≦80 …(2) 6≦2α+β≦50 …(3) 6≦2α+β≦30 …(4)

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

[0049] When the raw material contains two types of halogen elements, and the two types of halogen elements are bromine and iodine, the moles of bromine are A1 and the moles of iodine are A2, respectively, and A1:A2 is preferably 1:99 to 99:1, more preferably 20:80 to 80:20, even more preferably 35:65 to 80:20, and even more preferably 45:55 to 70:30. Furthermore, when the two types of halogen atoms are bromine and chlorine, where the number of moles of bromine is B1 and the number of moles of chlorine is B2, the B1:B2 ratio is preferably 1:99 to 99:1, more preferably 15:85 to 75:25, even more preferably 25:75 to 60:40, and even more preferably 35:45 to 65:55.

[0050] Furthermore, when the raw material inclusion contains Li3PS4, the content of Li3PS4 relative to the total amount of raw materials contained in the raw material inclusion is preferably 60 to 100 mol%, more preferably 60 to 90 mol%, and even more preferably 65 to 80 mol%. As mentioned above, Li3PS4 may be manufactured and used. In this case, it is obtained by reacting lithium sulfide with diphosphorus pentasulfide in a 3:1 molar ratio. When Li3PS4 is used as a solid electrolyte raw material, the compounding ratio with other raw materials, such as lithium halide or elemental halogen, may be similar to that used when lithium sulfide and diphosphorus pentasulfide are used. For example, when lithium sulfide and diphosphorus pentasulfide are reacted in a 3:1 molar ratio, 2 moles of Li3PS4 are obtained, which corresponds to a total of 4 moles of lithium sulfide and diphosphorus pentasulfide. Therefore, when lithium sulfide and diphosphorus pentasulfide are used, the moles of lithium sulfide and diphosphorus pentasulfide should be doubled compared to the number of moles of Li3PS4 used. When Li3PS4 and a simple halogen are used, the amount of the simple halogen relative to Li3PS4 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 %.

[0051] (solvent) In the method for producing a sulfide solid electrolyte of this embodiment, a solvent may be used, and the solvent may contain a complexing agent. The complexing agent is a compound that can form a complex by coordinating (bonding) with the solid electrolyte raw material contained in the raw material inclusions, particularly with lithium atoms contained in the raw material inclusions. In this embodiment, at least a pyridine compound represented by the general formula (1) described below is used as the solvent or complexing agent.

[0052] As the solvent used in this embodiment, a wide variety of solvents that have been conventionally used in the production of solid electrolytes can be used, including hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, as well as compounds containing heteroatoms such as nitrogen atoms, oxygen atoms, halogen atoms such as chlorine atoms, and sulfur atoms. Here, compounds containing heteroatoms tend to function as compounds capable of forming complexes, and are therefore preferably used as complexing agents. Therefore, pyridine compounds, which will be described later, are solvents containing heteroatoms. , which also corresponds to a complexing agent as described below.

[0053] (pyridine compounds) In the method for producing a sulfide solid electrolyte of this embodiment, a pyridine compound represented by the following general formula (1) (sometimes simply referred to as a "pyridine compound" in this specification) is used as a solvent or complexing agent. In this embodiment, examples of complexing agents other than pyridine compounds include compounds containing heteroatoms such as the nitrogen atom, oxygen atom, halogen atom such as chlorine atom, and sulfur atom.

[0054] [ka] (In the formula, R 1 is a hydrocarbon group having 1 to 6 carbon atoms, and n is an integer of 1 to 5.

[0055] The complexing agent used in this embodiment may be a single type, or two or more types, or two or more different pyridine compounds. That is, the complexing agent used in this embodiment may be not only the pyridine compound, but also other complexing agents other than the pyridine compound. As the other complexing agent, one capable of forming a complex containing Li3PS4 and a halogen atom is typically used. As described above, the complexing agent is a compound capable of coordinating (bonding) with a lithium atom to form a complex, and therefore is a compound that easily forms a complex containing Li3PS4. Furthermore, a compound containing a heteroatom such as a halogen atom is preferably used, and therefore a complex containing a halogen atom is also easily formed.

[0056] As the complexing agent, any compound having a heteroatom can be used without particular limitation. The heteroatoms present in the molecules of the complexing agent, such as nitrogen, oxygen, and chlorine, have a high affinity with lithium atoms and are thought to have the property of easily bonding with the solid electrolyte raw material contained in the raw material content to form a complex (hereinafter also simply referred to as a "complex"). Therefore, by mixing the solid electrolyte raw material with the complexing agent, a complex is formed, which is thought to make it easier to maintain the uniform dispersion state of the solid electrolyte raw material, particularly the dispersion state of the halogen atoms.

[0057] R in the general formula (1) 1 The hydrocarbon group represented by the formula (I) may be an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, but is preferably an aliphatic hydrocarbon group, more preferably a saturated aliphatic hydrocarbon group, further preferably an alkyl or alkenyl group having 1 to 4 carbon atoms, and particularly preferably a methyl group. The pyridine compound may further comprise a compound having R at least one of the 2- and 4-positions on the pyridine skeleton. 1 is bonded to at least one of the 2- and 4-positions of the pyridine skeleton, since it is easy to obtain a sulfide solid electrolyte having a thiolithium region II crystal structure, which will be described later. 1 If R is bonded to the 6th position, 1 may be bonded. In addition, R in the general formula (1) 1 If there are multiple R 1 may be the same or different from each other. More specifically, the pyridine compound is preferably 2-methylpyridine or 4-methylpyridine.

[0058] The amount of the pyridine compound used per gram of the total mass of the raw material ingredients is preferably 0.1 to 30 mL, more preferably 0.5 to 20 mL, and even more preferably 1.5 to 15 mL, from the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte.

[0059] (Other complexing agents) In this embodiment, other complexing agents may be added to the pyridine compound. Examples of other complexing agents include compounds having a group containing a heteroatom, such as oxygen or a halogen element, such as chlorine, which have a high affinity with lithium. Specific examples of compounds containing oxygen include ester solvents such as ethyl acetate and butyl acetate; aldehyde solvents such as formaldehyde, acetaldehyde, and dimethylformamide; ketone solvents such as acetone and methyl ethyl ketone; and ether solvents such as diethyl ether, diisopropyl ether, dibutyl ether, tetrahydrofuran, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole. In addition, a compound having a group such as an amino group, a nitro group, or an amide group containing a nitrogen element as a heteroatom can also provide the same effect. In this embodiment, the content of the pyridine compound in the complexing agent is preferably as high as possible, specifically 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably 100% by mass, i.e., it is particularly preferred that the entire amount of the complexing agent is the pyridine compound.

[0060] (Other solvents) In this embodiment, a solvent other than the pyridine compound (hereinafter also referred to as "other solvent") may be used as the solvent when mixing the raw material ingredients with the pyridine compound. When a solid complex is formed in a liquid complexing agent, the complex dissolves in the complexing agent (solvent), which improves the dispersion of the resulting sulfide solid electrolyte raw material, facilitating the production of the desired sulfide solid electrolyte.

[0061] (mixture) The production method of this embodiment includes mixing the raw material ingredients with a pyridine compound.

[0062] In this embodiment, the raw material ingredients and the pyridine compound may be mixed in either a solid or liquid form. However, since the solid electrolyte raw material contained in the raw material ingredients contains a solid, and the pyridine compound is liquid, they are usually mixed in a form (slurry) in which the solid electrolyte raw material is present in the liquid pyridine compound. Furthermore, when mixing the raw material ingredients and the pyridine compound, the above-mentioned solvent or other complexing agent may be further mixed as needed. Hereinafter, in the description of the mixing of the raw material ingredients and the pyridine compound, unless otherwise specified, the same applies to the description of mixing with the solvent or other complexing agent used as needed.

[0063] There is no particular limitation on the method for mixing the raw material ingredients and the pyridine compound, and the raw material ingredients and the pyridine compound may be mixed by adding them to a device capable of mixing them. For example, it is preferable to supply the pyridine compound into a tank, operate the stirring blades, and then gradually add the raw material ingredients, since this improves the mixing state of the raw material ingredients and the dispersibility of the raw material. However, when a halogen element is used as the solid electrolyte raw material contained in the raw material content, the solid electrolyte raw material may not be solid. Specifically, fluorine and chlorine are gaseous, and bromine is liquid at room temperature and normal pressure. In such a case, for example, when the solid electrolyte raw material is liquid, it may be supplied into the tank together with a pyridine compound separately from other solid solid electrolyte raw materials. When the solid electrolyte raw material is gaseous, it may be supplied by blowing into the mixture of the pyridine compound and the solid solid electrolyte raw material.

[0064] In the manufacturing method of this embodiment, a solid electrolyte raw material and a pyridine compound are mixed. However, mixing the solid electrolyte raw material and the pyridine compound is sufficient; pulverization is not required. Therefore, the solid electrolyte raw material can be manufactured by a method that does not use equipment commonly referred to as a pulverizer, such as a media-type pulverizer such as a ball mill or a bead mill, which is typically used for pulverizing solid electrolyte raw materials. In the manufacturing method of this embodiment, simply mixing the solid electrolyte raw material and the pyridine compound allows the solid electrolyte raw material contained in the raw material content to mix with the pyridine compound, thereby forming a complex, i.e., an electrolyte precursor. Note that the mixture of the raw material and the pyridine compound may be pulverized using a pulverizer to shorten the mixing time for obtaining the complex or to achieve finer powder. However, as described above, it is preferable not to use a pulverizer.

[0065] An example of an apparatus for mixing the solid electrolyte raw material and the pyridine compound is a mechanical agitation mixer equipped with an agitator blade in a tank. Examples of mechanical agitation mixers include high-speed agitation mixers and double-arm mixers. High-speed agitation mixers are preferred from the viewpoint of improving the uniformity of the solid electrolyte raw material in the mixture of the solid electrolyte raw material and the complexing agent and achieving higher ionic conductivity. Examples of high-speed agitation mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers. Either type of mixer may be used.

[0066] Examples of the shape of the stirring blade used in the mechanical stirring mixer include blade type, arm type, anchor type, paddle type, full zone type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, and C-type blade type. From the viewpoint of improving the uniformity of the solid electrolyte raw material and obtaining higher ionic conductivity, the shovel type, flat blade type, C-type blade type, and the like are preferred.

[0067] Furthermore, in a mechanical stirring mixer, it is preferable to install a circulation line that discharges the material to be stirred outside the mixer and then returns it to the mixer, which allows raw materials with a high specific gravity, such as lithium halide, to be stirred without settling or remaining, enabling more uniform mixing. The location of the circulation line is not particularly limited, but it is preferably installed at a location where it discharges from the bottom of the mixer and returns to the top of the mixer. This makes it easier to uniformly mix the solid electrolyte raw material, which tends to settle, by using convection caused by circulation. Furthermore, it is preferable that the return port is located below the liquid surface of the material to be mixed. This can prevent the material to be mixed from splashing and adhering to the wall surfaces inside the mixer.

[0068] The temperature conditions when mixing the solid electrolyte raw material and the pyridine compound are not particularly limited and are, for example, −30 to 100° C., preferably −10 to 50° C., and more preferably about room temperature (23° C.) (for example, about room temperature ±5° C.) The mixing time is about 0.1 to 150 hours, and from the viewpoint of more uniform mixing and obtaining higher ionic conductivity, is preferably 1 to 120 hours, more preferably 4 to 100 hours, and even more preferably 8 to 80 hours.

[0069] By mixing the solid electrolyte raw material with the pyridine compound, a complex is formed between the solid electrolyte raw material and the pyridine compound. As described above, the complex corresponds to the electrolyte precursor. More specifically, it is considered that the lithium atoms, sulfur atoms, and phosphorus atoms contained in the solid electrolyte raw material, the halogen atoms contained as needed, and the pyridine compound interact with each other to bond these atoms directly with and / or without the pyridine compound. That is, in the production method of this embodiment, the complex obtained by mixing the solid electrolyte raw material with the pyridine compound, i.e., the electrolyte precursor, can be said to be composed of the pyridine compound, lithium atoms, sulfur atoms, and phosphorus atoms, and further halogen atoms used as needed. The complex obtained in this embodiment is not completely soluble in the liquid pyridine compound and is usually solid, so that a suspension (containing an electrolyte precursor) in which the complex is suspended in the pyridine compound and a solvent used as needed is obtained. Therefore, the method for producing a solid electrolyte in this embodiment corresponds to a heterogeneous system in a so-called liquid phase method.

[0070] By selecting the size and material of the medium (beads or balls) used, the rotor rotation speed, time, etc., it is possible to perform mixing, stirring, pulverization, or a combination of these processes, and it is possible to adjust the particle size, etc. of the resulting crystalline sulfide solid electrolyte.

[0071] (Obtaining the electrolyte precursor) In the method for producing the sulfide solid electrolyte of the present embodiment, it is preferable that the mixing yields an electrolyte precursor containing lithium atoms, sulfur atoms, and phosphorus atoms, the pyridine compound, and further, if necessary, halogen atoms. More specifically, it is preferable that the pyridine compound is used as a solvent or complexing agent, the raw material contains a substance group C containing lithium atoms, sulfur atoms, and phosphorus atoms, and a substance group D containing halogen atoms, and that the mixing is carried out by the following (i) to (iii). (i) A portion of lithium sulfide is dissolved in alcohol, and then the alcohol is distilled off to obtain alcohol-treated lithium sulfide. (ii) Lithium sulfide, diphosphorus pentasulfide, and a solvent are mixed to obtain a solution. (iii) The alcohol-treated lithium sulfide and a pyridine compound are mixed to form a slurry, and the slurry is mixed with the solution obtained in (ii) above.

[0072] By carrying out the above (i), lithium sulfide is atomized, its reactivity with other solid electrolyte raw materials and pyridine compounds is improved, and the finally obtained sulfide solid electrolyte tends to have a thiolicon region II crystal structure. Therefore, it is preferable to use lithium sulfide that has been contacted with an alcohol in advance. As the alcohol used in (i), specifically, ethanol is preferably used.

[0073] The alcohol-treated lithium sulfide obtained in (i) may be further added with a solvent or a pyridine compound to form a slurry, which may then be used for mixing in (iii). The solvent used in (ii) above is preferably the pyridine compound, but other than that, the above-mentioned ester solvents, aldehyde solvents, ketone solvents, ether solvents, nitrile solvents, etc. can also be used. As the ester solvent, an aliphatic ester is more preferable, an ester of a monovalent fatty acid and a monovalent alcohol is even more preferable, an ester of a monovalent saturated fatty acid and a monovalent alcohol is even more preferable, and ethyl acetate is particularly preferable.

[0074] In the above (i), the heating temperature during distillation of the alcohol is preferably increased stepwise, with the final heating temperature preferably being 150°C or higher, more preferably 180°C or higher, and particularly preferably 220°C or higher. The heating time is preferably 4 hours or longer, more preferably 8 hours or longer, and particularly preferably 10 hours or longer. There are no particular limitations on the upper limit of the heating time, but it is preferably, for example, 48 hours or shorter, more preferably 24 hours or shorter.

[0075] In addition to the above-mentioned solvents, the solvent used in (ii) above may also include, for example, nitrile solvents such as acetonitrile and propionitrile. Also, various solvents may be mixed and used, such as alicyclic hydrocarbon solvents such as cyclohexane and methylcyclohexane; aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene; and paraffinic solvents such as oligomers obtained by polymerizing at least one normal paraffin, such as normal butene and normal propylene, to a degree of polymerization of about 3 to 10, and hydrogenated products thereof, normal paraffinic solvents, and isoparaffinic solvents obtained by polymerizing at least one paraffin, including at least isoparaffin, from among isobutene, normal butene, normal propylene, and isopropylene, to a degree of polymerization of about 3 to 10, and hydrogenated products thereof.

[0076] By carrying out the above steps (ii) and (iii), lithium sulfide, diphosphorus pentasulfide, and the pyridine compound react with each other, and the electrolyte precursor contained in the resulting slurry partially contains Li3PS4. Here too, in addition to the pyridine compound, a solvent may be further added and mixed.

[0077] In the above step (iii), all of the solid electrolyte raw materials come into contact with each other, and the reaction is accelerated, so that the electrolyte precursor can be obtained efficiently.

[0078] (Dry) The production method of this embodiment may include drying the electrolyte precursor-containing material after obtaining the electrolyte precursor-containing material by the mixing. By heating the electrolyte precursor obtained by drying the electrolyte precursor-containing material, the electrolyte precursor can be heated more directly, and therefore the complexing agent such as the pyridine compound can be separated and removed more efficiently from the electrolyte precursor.

[0079] Drying methods include filtration using a glass filter or the like, solid-liquid separation by decantation, and solid-liquid separation using a centrifuge, etc. Specifically, solid-liquid separation can be easily performed by decantation, in which the suspension is transferred to a container, a solid is precipitated, and then the supernatant pyridine compound and a solvent used 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] Alternatively, the material can be dried by heating using a dryer or the like. The electrolyte precursor-containing material may be dried under any pressure condition, such as under pressure, normal pressure, or reduced pressure, and is preferably dried under normal pressure or reduced pressure. In particular, when drying at a lower temperature is required, it is preferable to dry the material under reduced pressure, or even under vacuum, using a vacuum pump or the like.

[0081] The temperature conditions for drying may be a temperature equal to or higher than the boiling point of the remaining pyridine compound or the solvent used as needed. The boiling point varies depending on the type of pyridine compound and solvent used, so the specific temperature conditions cannot be generalized, but the temperature is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher, with the upper limit being preferably 110°C or lower, more preferably 85°C or lower, and even more preferably 70°C or lower.

[0082] As for the pressure conditions, as mentioned above, normal pressure or reduced pressure is preferable. When reduced pressure is used, specifically, the pressure is preferably 85 kPa or less, more preferably 80 kPa or less, and even more preferably 70 kPa or less. The lower limit may be a vacuum (0 KPa). Considering the ease of adjusting the pressure, the pressure is preferably 1 kPa or more, more preferably 2 kPa or more, and even more preferably 3 kPa or more.

[0083] In the production method of this embodiment, when drying is performed, drying may be performed while heating after the solid-liquid separation. Furthermore, in the manufacturing method of this embodiment, drying may or may not be performed. That is, in the manufacturing method of this embodiment, the electrolyte precursor to be heated may be in a state contained in an electrolyte precursor-containing material, or may be a dried electrolyte precursor obtained by drying.

[0084] (heating) The method for producing the sulfide solid electrolyte of the present embodiment preferably includes heating. Examples of heating include heating the electrolyte precursor obtained by the mixing to remove a complexing agent such as a pyridine compound and a solvent from the electrolyte precursor; heating the electrolyte precursor from which the complexing agent has been removed to obtain a crystalline sulfide solid electrolyte; when an amorphous sulfide solid electrolyte can be obtained by removing the complexing agent from the electrolyte precursor, heating the amorphous sulfide solid electrolyte to obtain a crystalline sulfide solid electrolyte; and heating the electrolyte precursor to obtain a crystalline sulfide solid electrolyte.

[0085] By heating, the complexing agent such as the pyridine compound in the electrolyte precursor is removed, and a sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and optionally halogen atoms is obtained. Here, the removal of the complexing agent from the electrolyte precursor is supported by the fact that it can be confirmed from the results of X-ray diffraction patterns, gas chromatography analysis, etc. that the complexing agent constitutes the electrolyte precursor (complex), and also by the fact that the sulfide solid electrolyte obtained by removing the complexing agent from the electrolyte precursor has the same X-ray diffraction pattern as the sulfide solid electrolyte obtained by a conventional method without using a complexing agent.

[0086] In the production method of this embodiment, a crystalline sulfide solid electrolyte may be obtained by heating an electrolyte precursor, or a sulfide solid electrolyte that can become an amorphous sulfide solid electrolyte may be obtained by first heating an electrolyte precursor to obtain an amorphous sulfide solid electrolyte and then heating the amorphous sulfide solid electrolyte. In other words, the production method of this embodiment can also produce an amorphous sulfide solid electrolyte.

[0087] In the production method of this embodiment, whether to obtain an amorphous sulfide solid electrolyte, a crystalline sulfide solid electrolyte, or an amorphous sulfide solid electrolyte and then a crystalline sulfide solid electrolyte, or a crystalline sulfide solid electrolyte directly from an electrolyte precursor is appropriately selected as desired, and can be adjusted by the heating temperature, heating time, etc.

[0088] For example, when obtaining an amorphous sulfide solid electrolyte (including when removing a complexing agent from an electrolyte precursor), the heating temperature may be determined depending on the structure of the crystalline sulfide solid electrolyte obtained by heating the amorphous sulfide solid electrolyte. Specifically, the amorphous sulfide solid electrolyte is subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) at a temperature increase rate of 10°C / min. The heating temperature is preferably set to 5°C or less, more preferably 10°C or less, and even more preferably 20°C or less, starting from the peak-top temperature of the exothermic peak observed at the lowest temperature. The lower limit is not particularly limited, but may be set to about −40°C or more, the peak-top temperature of the exothermic peak observed at the lowest temperature. By setting the temperature range in this way, an amorphous sulfide solid electrolyte (an electrolyte precursor from which a complexing agent has been removed) can be obtained more efficiently and reliably.

[0089] The heating temperature for obtaining an amorphous sulfide solid electrolyte (including the heating temperature for removing the complexing agent from the electrolyte precursor) cannot be generally specified because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained. However, it is generally preferably 135°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower. There is no particular lower limit, but it is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher.

[0090] When obtaining a crystalline sulfide solid electrolyte, the heating temperature may be determined depending on the structure of the crystalline sulfide solid electrolyte, and is preferably higher than the heating temperature for obtaining an amorphous sulfide solid electrolyte. Specifically, the amorphous sulfide solid electrolyte is subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) at a temperature increase rate of 10°C / min. The heating temperature is preferably set to 5°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher, starting from the peak top temperature of the exothermic peak observed at the lowest temperature. There is no particular upper limit, but it should be about 40°C or lower. By setting the temperature range in this way, a crystalline sulfide solid electrolyte can be obtained more efficiently and reliably.

[0091] The heating temperature for obtaining a crystalline sulfide solid electrolyte cannot be generally defined because it varies depending on the composition and structure of the resulting crystalline sulfide solid electrolyte. However, it is generally preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 140°C or higher. There is no particular upper limit, but it is preferably 400°C or lower, more preferably 300°C or lower, even more preferably 250°C or lower, and particularly preferably 200°C or lower.

[0092] The heating time is not particularly limited as long as it is a time that allows a desired amorphous sulfide solid electrolyte or 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.

[0093] Heating is preferably carried out in an inert gas atmosphere (e.g., nitrogen atmosphere, argon atmosphere) or a reduced pressure atmosphere (particularly in vacuum). For example, an inert gas atmosphere containing a certain concentration of hydrogen may be used. This is because deterioration (e.g., oxidation) of the crystalline sulfide solid electrolyte can be prevented. The heating method is not particularly limited, and examples thereof include a method using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, a baking furnace, etc. Furthermore, industrially, a horizontal dryer having a heating means and a feeding mechanism, a horizontal vibration fluidized dryer, etc. may also be used, and the method may be selected depending on the amount of processing to be heated.

[0094] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte produced by the production method of this embodiment contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Representative examples include solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiS-P2S5-LiI, LiS-P2S5-LiCl, LiS-P2S5-LiBr, and LiS-P2S5-LiI-LiBr; and solid electrolytes further containing other atoms such as oxygen atoms and silicon atoms, such as LiS-P2S5-Li2O-LiI and LiS-SiS2-P2S5-LiI. From the viewpoint of obtaining higher ionic conductivity, a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and a lithium halide, such as Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, or Li2S-P2S5-LiI-LiBr, is preferred, and a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and two types of lithium halides, such as Li2S-P2S5-LiI-LiBr, is more preferred. The types of atoms constituting the sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0095] In the solid electrolyte (amorphous solid electrolyte and crystalline solid electrolyte) obtained by the method for producing a solid electrolyte of this embodiment, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms is preferably 1.0-1.8:0.1-0.8:1.0-2.0:0.01-0.6, more preferably 1.1-1.7:0.2-0.6:1.2-1.8:0.05-0.5, and even more preferably 1.2-1.6:0.25-0.5:1.3-1.7:0.08-0.4. Furthermore, when bromine and iodine, or bromine and chlorine are used in combination as halogen atoms, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, bromine, and iodine (or chlorine) is preferably 1.0-1.8:0.1-0.8:1.0-2.0:0.01-0.3:0.01-0.3, more preferably 1.1-1.7:0.2-0.6:1.2-1.8:0.02-0.25:0.02-0.25, even more preferably 1.2-1.6:0.25-0.5:1.3-1.7:0.03-0.2:0.03-0.2, and still more preferably 1.35-1.45:0.3-0.45:1.4-1.7:0.04-0.18:0.04-0.18. By setting the composition 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 with higher ionic conductivity having a crystal structure described below, particularly a thiolicon region II crystal structure or an argyrodite crystal structure.

[0096] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle size (D 50 ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 200.0 μm or less, further 100.0 μm or less, 10.0 μm or less, 1.0 μm or less, or 0.5 μm or less. (Crystalline sulfide solid electrolyte)

[0097] The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be a so-called glass ceramic obtained by heating an amorphous sulfide solid electrolyte to a crystallization temperature or higher, and its crystal structure may be Li3PS4 crystal structure, Li4P2S6 crystal structure, Li7PS6 crystal structure, Li7P3S 11 Examples of such a crystal structure include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0098] Li 4-x Ge 1-x P x S4-type 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 Examples of such a crystal structure include a crystal structure similar to the S4-based 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 manufacturing method of this embodiment 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 S4-type thio-LISICON Region II crystal structure, Li 4-x Ge 1-x P x This indicates that the crystal structure is either the S4 type thio-LISICON Region II type or similar. 4-x Ge 1-x P xThe expression "S4-based thio-LISICON Region II crystal structure" means that at the time of discovery in the literature, the crystal structure was composed of the atoms in question. The sulfide solid electrolyte obtained by the production method of this embodiment has a thio-LISICON Region II crystal structure, which means that a crystal structure exhibiting the same diffraction peak as that of the thio-LISICON Region II crystal structure is formed by the atoms (Li / P / S ( / halogen used as needed)) contained in the raw material inclusions. The same applies to the argyrodite crystal structure described below.

[0099] The crystalline sulfide solid electrolyte obtained by heating may contain the thiolicon region II crystal structure or may contain it as the main crystal. However, from the viewpoint of obtaining higher ionic conductivity, it is preferable that it contains it as the main crystal. In this specification, "containing it as the main crystal" means that the proportion of the target crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more. Furthermore, from the viewpoint of obtaining higher ionic conductivity, it is preferable that the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment does not contain crystalline Li3PS4 (β-Li3PS4).

[0100] In X-ray diffraction measurements using CuKα radiation, the diffraction peaks of the Li3PS4 crystal structure appear, for example, at 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, the diffraction peaks of the Li4P2S6 crystal structure appear, for example, at 2θ = 16.9°, 27.1°, and 32.5°, and the diffraction peaks of the Li7PS6 crystal structure appear, for example, at 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and the diffraction peaks of the Li7P3S 11 Diffraction peaks of the crystal structure appear, for example, at 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°. 4-x Ge 1-x P xDiffraction peaks of the S4 series thio-LISICON Region II type crystal structure appear near, for example, 2θ = 20.1°, 23.9°, and 29.5°, and Li 4-x Ge 1-x P x Diffraction peaks of a crystal structure similar to the S4 series thio-LISICON Region II type appear near, for example, 2θ = 20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0101] Also preferably mentioned is a crystalline sulfide solid electrolyte having the above-described structural framework of Li7PS6 and having an argyrodite-type crystal structure in which part of P is substituted with Si. Examples of the composition formula of the argyrodite-type crystal structure include the composition formula Li 7-x P 1-y Si y S6 and Li<000^043>P 1-y Si y S6 (where x is -0.6 to 0.6 and y is 0.1 to 0.6). The argyrodite-type crystal structure represented by this composition formula is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα radiation, mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0102] Examples of the composition formula of the argyrodite-type crystal structure include the composition formula Li<^000046>PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) is also included. The argyrodite-type crystal structure represented by this composition formula is preferably cubic, and in X-ray diffraction measurement using CuKα radiation, mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Also, examples of the composition formula of the argyrodite-type crystal structure include the composition formula Li 7-x PS 6-x Hax (Ha is Cl or Br, and x is preferably 0.2 to 1.8). The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. These peak positions may vary within a range of ±0.5°.

[0103] Furthermore, the composition ratio of atoms contained in the crystalline sulfide solid electrolyte is preferably a composition ratio according to a composition formula corresponding to the various crystal structures, and is within the range of the composition ratio of each atom contained in the amorphous sulfide solid electrolyte. When the composition ratio of each atom is within this range, it is easy to form a thiosilicon region II type crystal structure or an argyrodite type crystal structure, among the crystal structures.

[0104] The content of the complexing agent contained in the crystalline sulfide solid electrolyte obtained by the heating is lower than the content of the complexing agent contained in the amorphous sulfide solid electrolyte. The content of the complexing agent in the crystalline sulfide solid electrolyte is preferably 0% by mass, i.e., no complexing agent is contained at all. However, from the viewpoint of efficiently obtaining a sulfide solid electrolyte with high ionic conductivity, the content is usually 10% by mass or less, further 8% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, with the lower limit being approximately 0.01% by mass or more.

[0105] Similarly to the complexing agent, when a solvent is used, the solvent may also remain. In this case, the content of the solvent is also in the same range as the content of the complexing agent.

[0106] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle size (D 50) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 15 μm or less, further 12 μm or less, or 10 μm or less.

[0107] Furthermore, the sulfide solid electrolyte of this embodiment preferably has an ionic conductivity of 2.0 mS / cm or more, and more preferably 2.5 mS / cm or more. Specific methods for measuring ionic conductivity include the methods used in the examples.

[0108] (electrolyte precursor) The electrolyte precursor of this embodiment is an electrolyte precursor composed of lithium atoms, sulfur atoms, phosphorus atoms, and optionally halogen atoms, and a pyridine compound. The electrolyte precursor of this embodiment can be easily produced by the production method of this embodiment. As described above, the electrolyte precursor is a complex in which solid electrolyte raw materials are coordinated (bonded) via a complexing agent such as a pyridine compound. The atoms constituting the electrolyte precursor, their blending ratios, and the complexing agent such as a pyridine compound are the same as those described in the manufacturing method of this embodiment.

[0109] (Sulfide solid electrolyte) The sulfide solid electrolyte of this embodiment is a sulfide solid electrolyte that is composed of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms that are used as needed, and that contains a pyridine compound. The sulfide solid electrolyte of this embodiment can be easily produced by the production method of this embodiment described above. The atoms constituting the sulfide solid electrolyte, their blending ratios, and the complexing agent such as a pyridine compound are the same as those described in the manufacturing method of this embodiment. In the sulfide solid electrolyte of this embodiment, the "complexing agent" is used in the manufacturing process and remains in the sulfide solid electrolyte. In other words, the complexing agent contained in the sulfide solid electrolyte of this embodiment can be used to determine what solvent was used in the manufacturing process.

[0110] (Application) The sulfide solid electrolyte obtained by the production method of this embodiment has excellent coating suitability and can be used in battery production without using a solvent, etc., and can efficiently exhibit excellent battery performance. In addition, since it has high ionic conductivity and excellent battery performance, it is suitable for use in batteries. The sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be used in a positive electrode layer, a negative electrode layer, or an electrolyte layer. Each of these layers can be manufactured by a known method.

[0111] The battery preferably includes a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used, such as a layer of Au, Pt, Al, Ti, or Cu, which reacts with the solid electrolyte, coated with Au or the like. [Example]

[0112] 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.

[0113] (Powder X-ray diffraction (XRD) measurement) Powder X-ray diffraction (XRD) measurements were carried out as follows. The sulfide solid electrolyte powders obtained in the examples and comparative examples were filled into a groove 20 mm in diameter and 0.2 mm deep, and leveled with glass to prepare a sample. This sample was sealed in Kapton film for XRD and measured under the following conditions without exposing it to air. Measurement equipment: D2 PHASER, manufactured by Bruker Tube voltage: 30kV Tube current: 10mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: Soller slit 4°, divergence slit 1 mm, Kβ filter (Ni plate) Detector: Semiconductor detector Measurement range: 2θ=10-60deg Step width, scan speed: 0.05deg, 0.05deg / sec

[0114] (Production Example 1) 7.0 g of lithium sulfide was added to a Schlenk tube (volume: 500 mL) equipped with a stirrer under a nitrogen atmosphere. After starting the stirrer, 250 mL of ethanol was introduced into the vessel to completely dissolve the lithium sulfide. The resulting reaction solution was then dried under vacuum (room temperature: 23°C) to remove most of the ethanol, and 50 mL of toluene was added thereto, followed by continued drying under vacuum to remove the remaining ethanol. Next, the mixture was heated stepwise from 50°C to 200°C over 12 hours, and finally heated at 250°C for 2 hours and dried to obtain powdered ethanol-treated lithium sulfide.

[0115] Example 1 To a Schlenk tube (volume: 100 mL) equipped with a stirrer, 0.26 g of lithium sulfide and 1.23 g of diphosphorus pentasulfide were added under a nitrogen atmosphere, and 20 mL of 4-methylpyridine was further introduced and mixed to form a solution. 0.52 g of the powdered ethanol-treated lithium sulfide obtained in Production Example 1 was mixed with 30 mL of 4-methylpyridine to form a slurry, which was then added to the above solution and stirred at room temperature for 3 hours. The resulting electrolyte precursor-containing material was dried under vacuum (room temperature: 23°C) to obtain a powdered electrolyte precursor. The electrolyte precursor powder was then heated at 180°C for 5 hours under vacuum to obtain a crystalline sulfide solid electrolyte.

[0116] The obtained crystalline sulfide solid electrolyte was subjected to powder X-ray diffraction (XRD) measurement using an X-ray diffraction (XRD) device (SmartLab device, Rigaku Corporation). Crystallization peaks were detected mainly at 2θ = 20.4°, 23.6°, and 29.3° in the X-ray diffraction spectrum of the crystalline sulfide solid electrolyte (Figure 1), confirming that it had a thiolicon region II crystal structure.

[0117] Example 2 A crystalline sulfide solid electrolyte was obtained in the same manner as in Example 1, except that 2-methylpyridine was used instead of 4-methylpyridine. In the X-ray diffraction spectrum of the obtained crystalline sulfide solid electrolyte (Fig. 2), crystallization peaks were detected mainly at 2θ = 20.4°, 23.6°, and 29.3°, confirming that it had a thiolithiregion II crystal structure.

[0118] (Comparative Example 1) A crystalline sulfide solid electrolyte was obtained in the same manner as in Example 1, except that ethyl acetate was used instead of 4-methylpyridine. In the X-ray diffraction spectrum of the obtained crystalline sulfide solid electrolyte (Fig. 3), no significant crystallization peaks were detected at 2θ = 20.4°, 23.6°, and 29.3°, and the presence of the thiolicon region II crystal structure could not be confirmed.

[0119] (Comparative Example 2) A crystalline sulfide solid electrolyte was obtained in the same manner as in Example 1, except that unsubstituted pyridine was used instead of 4-methylpyridine. In the X-ray diffraction spectrum of the obtained crystalline sulfide solid electrolyte (Fig. 4), no significant crystallization peaks were detected at 2θ = 20.4°, 23.6°, and 29.3°, and the presence of the thiolicon region II crystal structure could not be confirmed.

[0120] As is clear from the comparison between Examples 1 and 2 and Comparative Examples 1 and 2, in Examples 1 and 2 in which the pyridine compound represented by general formula (1) was used as a complexing agent, it was found that a sulfide solid electrolyte having a thiolicon region II crystal structure and high ionic conductivity was obtained. [Industrial Applicability]

[0121] The crystalline sulfide solid electrolyte of this embodiment has high ionic conductivity and excellent battery performance, and is therefore suitable for use, for example, in combination with an electrode active material to form an electrode composite, or in lithium-ion batteries, which are suitable for use in, for example, automotive applications, and in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. A method for producing a sulfide solid electrolyte, comprising mixing a raw material containing lithium atoms, phosphorus atoms, and sulfur atoms with a pyridine compound represented by the following general formula (1): 【Chemical 1】 (In the formula, R １ is a hydrocarbon group having 1 to 6 carbon atoms, and n is an integer from 1 to 5.

2. In the general formula (1), the R １ is an alkyl or alkenyl group having 1 to 4 carbon atoms, and n is 1 or 2. The method for producing a sulfide solid electrolyte according to claim 1.

3. In the general formula (1), the R １ The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein

4. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, wherein the pyridine compound is 2-methylpyridine or 4-methylpyridine.

5. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 4, wherein the raw material contains lithium sulfide and diphosphorus pentasulfide.

6. 6. The method for producing a sulfide solid electrolyte according to claim 5, wherein the lithium sulfide is contacted with an alcohol in advance.

7. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 6, comprising heating the electrolyte precursor obtained by the mixing.

8. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 7, wherein the obtained sulfide solid electrolyte contains a thiolicon region II type crystal structure.

9. The method for producing a sulfide solid electrolyte according to claim 8, wherein the sulfide solid electrolyte does not have diffraction peaks at 2θ = 17.5° and 26.1° in X-ray diffraction measurement using CuKα rays.

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