Method for producing sulfide solid electrolyte

Abstract

To provide a sulfide solid electrolyte mixture having high ion conductivity and being easily densified when compressed.SOLUTION: The present invention provides a sulfide solid electrolyte mixture comprising: a sulfide solid electrolyte that contains lithium atoms, sulfur atoms, and phosphorus atoms; and an electrolyte solution that contains a lithium salt and an ionic liquid, wherein the product of the values (A) and (B) defined below is 11 or more, where (A) denotes the number of moles of the lithium salt in 1 liter of the electrolyte solution and (B) denotes the content (mass%) of the electrolyte solution based on the total amount of the sulfide solid electrolyte mixture.SELECTED DRAWING: None

Description

[Technical field]

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

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

[0003] As a method for producing a solid electrolyte used in a solid electrolyte layer, Patent Documents 1 and 2 disclose an ion conductor obtained by mixing a solid electrolyte containing lithium element and the like with a small amount of an electrolytic solution. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 221042 Brochure [Patent Document 2] Patent Publication No. 2019-121455 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a sulfide solid electrolyte mixture that has high ionic conductivity and is easily densified when compressed. [Means for solving the problem]

[0006] The sulfide solid electrolyte mixture according to the present invention is The sulfide solid electrolyte mixture includes a sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms, and an electrolyte solution containing a lithium salt and an ionic liquid, and the product of the following (A) and (B) is 11 or more: (A) The number of moles of lithium salt in 1 liter of the electrolyte (B) The content (mass%) of the electrolyte based on the total amount of the sulfide solid electrolyte mixture Effect of the Invention

[0007] According to the present invention, it is possible to provide a sulfide solid electrolyte mixture that has high ionic conductivity and is easily densified when compressed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of the numerical ranges of "greater than or equal to", "less than or equal to", and "to" are values ​​that can be combined arbitrarily, and the numerical values ​​of the examples can also be used as the upper and lower limit values. Furthermore, provisions that are considered to be preferable can be adopted arbitrarily. In other words, one provision that is considered to be preferable can be adopted in combination with one or more other provisions that are considered to be preferable. It can be said that a combination of preferable things is more preferable.

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

[0010] Conventionally, known lithium-based batteries include lithium-ion secondary batteries that use an electrolytic solution containing lithium ions as an electrolyte, and all-solid-state batteries that use a sulfide-based or oxide-based solid electrolyte. However, batteries that use a mixture of a solid electrolyte and an electrolytic solution are not well known. Here, Patent Document 1 discloses a lithium battery having an ion conductor containing an oxide LLZ-based ion conductive powder and an ionic liquid, but does not teach the use of a sulfide solid electrolyte. Patent Document 2 discloses a sulfide solid electrolyte to which a solvated ionic liquid containing a lithium salt and a Lewis base is added, but as the Lewis base, glyme is specifically disclosed, and therefore, as the solvated ionic liquid, glyme-based solvated ionic liquid is essentially the only one disclosed. Patent Document 2 does not teach or suggest combining an ionic liquid consisting of an anion and a cation with the lithium salt in place of the Lewis base.

[0011] According to the inventor's investigation, even if a conventional solid electrolyte is compressed and molded into pellets, voids remain inside the pellets, and the pellets cannot be sufficiently densified. As a result of the inventor's intensive research into this problem, it was found that this is due to the fact that the particles of the solid electrolyte have difficulty sliding against each other due to the minute irregularities on their surfaces that get caught. The present inventors then tried mixing an ionic liquid with the solid electrolyte, and found that although the pellets could be densified to a certain degree, the ionic conductivity tended to decrease. As a result of further investigations, the present inventors have found that by mixing an electrolytic solution containing a lithium salt and an ionic liquid with a solid electrolyte such that the product of (A) and (B) is 11 or more, the amount of lithium salt present between the solid electrolyte particles becomes sufficient to maintain ionic conductivity, and the presence of the electrolytic solution on the surfaces of the solid electrolyte particles improves the slipperiness between the particles, so that when the solid electrolyte is compression molded, the solid electrolyte particles slide against each other to fill the voids, thereby achieving densification of the pellets, and have completed the present invention.

[0012] (Various aspects of the present embodiment) The sulfide solid electrolyte mixture according to a first aspect of the present embodiment includes a sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms, and an electrolyte solution containing a lithium salt and an ionic liquid, and the product of the following (A) and (B) is 11 or more: (A) The number of moles of lithium salt in 1 liter of the electrolyte (B) The content (mass%) of the electrolyte based on the total amount of the sulfide solid electrolyte mixture

[0013] The sulfide solid electrolyte mixture of the present embodiment can achieve both densification and high ionic conductivity simply by adding an electrolytic solution to the sulfide solid electrolyte, and does not complicate the production process, and is therefore extremely useful industrially.

[0014] The sulfide solid electrolyte mixture according to the second aspect of the present embodiment is the same as the first aspect, The (A) is 0.5 to 5.0 moles. That is it.

[0015] When the content of the lithium salt in 1 liter of the electrolyte is 0.5 moles or more, the ionic conductivity of the resulting sulfide solid electrolyte mixture is higher, and when the content is 5.0 moles or less, the solubility of the lithium salt in the electrolyte is good. In addition, in relation to (B), the product of (A) and (B) is easily set to 11 or more, and as a result, it is easy to achieve both high ionic conductivity and densification.

[0016] The sulfide solid electrolyte mixture according to the third aspect of the present embodiment is the first or second aspect described above, The (B) is 8.0 to 20.0% by mass. That is it.

[0017] A content of the electrolyte of 8.0 mass% or more based on the total amount of the sulfide solid electrolyte mixture is preferable from the viewpoint of the effect of improving ion conductivity by adding the electrolyte and densification when the sulfide solid electrolyte mixture is compression molded, and a content of 20.0 mass% or less is preferable because the electrolyte is less likely to leach out when the sulfide solid electrolyte mixture is compression molded. In addition, in relation to (A), the product of (A) and (B) is easily made 11 or more, and as a result, high ion conductivity and densification are easily achieved at the same time.

[0018] The sulfide solid electrolyte mixture according to a fourth aspect of the present embodiment is any one of the first to third aspects described above, The product of (A) and (B) is 12.5 to 70. That is it.

[0019] In addition, the sulfide solid electrolyte mixture according to a fifth aspect of the present embodiment is any one of the first to third aspects described above, The product of (A) and (B) is 14 to 55. That is it.

[0020] When the product of (A) and (B) is within the above range, the solubility of the lithium salt in the electrolyte is good, which is more preferable from the viewpoint of achieving both ease of densification and ionic conductivity, and also because the electrolyte is less likely to leach out during compression molding.

[0021] The sulfide solid electrolyte mixture according to a sixth aspect of the present embodiment is any one of the first to fifth aspects, The product of the following (C) and (B) is 2.5 or more: That is it. (C) The number of moles of lithium salt per mole of ionic liquid in the electrolyte solution

[0022] When the product of (C) and (B) is within the above range, the ionic conductivity of the resulting sulfide solid electrolyte mixture becomes higher, which is preferable.

[0023] The sulfide solid electrolyte mixture according to a seventh aspect of the present embodiment is any one of the first to sixth aspects, The lithium salt is represented by the following general formula (I): That is it. [ka] (In the formula, R 1 and R 2 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.)

[0024] Specifically, as the lithium salt used in the sulfide solid electrolyte mixture of the present embodiment, it is preferable to use one represented by the above general formula (I) from the viewpoint of ion conductivity.

[0025] The sulfide solid electrolyte mixture according to an eighth aspect of the present embodiment is any one of the first to seventh aspects, The cation of the ionic liquid is at least one selected from the group consisting of ammonium, imidazolium cation, pyridinium cation, pyrrolidinium cation, piperidinium cation, and phosphonium cation. That is it.

[0026] In addition, the sulfide solid electrolyte mixture according to a ninth aspect of the present embodiment is the same as the eighth aspect, The imidazolium cation is represented by the following general formula (II): [ka] (In the formula, R 3 and R 4 are each independently a hydrogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 18 carbon atoms; R 5 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0027] In addition, the sulfide solid electrolyte mixture according to a tenth aspect of the present embodiment is the same as the ninth aspect, In the general formula (II), R 3 and R 4 each independently represents an unsubstituted alkyl or alkenyl group having 1 to 8 carbon atoms; That is it.

[0028] Use of the above-mentioned ionic liquid is preferable because the presence of an electrolytic solution containing the ionic liquid between sulfide solid electrolyte particles improves the slipperiness between the particles and improves the ionic conductivity between the particles, thereby improving the ionic conductivity in the entire sulfide solid electrolyte mixture.

[0029] The sulfide solid electrolyte mixture according to an eleventh aspect of the present embodiment is any one of the first to tenth aspects, The anion of the ionic liquid is at least one selected from the group consisting of a halide ion, a tetrafluoroborate ion, a hexafluorophosphate ion, and an anion represented by the following general formula (III): That is it. [ka] (In the formula, R 6 and R 7 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.)

[0030] In addition, the sulfide solid electrolyte mixture according to a twelfth aspect of the present embodiment is the same as the eleventh aspect, The anion of the ionic liquid is represented by the general formula (III). That is it.

[0031] The sulfide solid electrolyte mixture according to a thirteenth aspect of the present embodiment is any one of the first to twelfth aspects, The sulfide solid electrolyte has an argyrodite-type crystal structure. That is it.

[0032] Specifically, the sulfide solid electrolyte used in this embodiment preferably has an argyrodite crystal structure.

[0033] An all-solid-state battery according to a fourteenth aspect of the present embodiment includes the sulfide solid electrolyte mixture according to any one of the first to thirteenth aspects in a solid electrolyte layer. An electrode mixture according to a fifteenth aspect of the present embodiment contains the sulfide solid electrolyte mixture according to any one of the first to thirteenth aspects and an electrode active material. Further, an all-solid-state battery according to a sixteenth aspect of the present embodiment includes the electrode mixture according to the fifteenth aspect in an electrode mixture layer.

[0034] The sulfide solid electrolyte mixture of the present embodiment can be used in an all-solid-state battery. More specifically, the sulfide solid electrolyte mixture can be used together with an electrode active material to form an electrode mixture for an all-solid-state battery, or can be used to form a solid electrolyte layer provided between a positive electrode mixture layer and a negative electrode mixture layer.

[0035] (Sulfide solid electrolyte mixture) As described above, the sulfide solid electrolyte mixture of the present embodiment contains a sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms, and an electrolyte solution containing a lithium salt and an ionic liquid, and the product of the following (A) and (B) is 11 or more. (A) The number of moles of lithium salt in 1 liter of the electrolyte (B) The content (mass%) of the electrolyte based on the total amount of the sulfide solid electrolyte mixture

[0036] The sulfide solid electrolyte mixture of this embodiment has high ionic conductivity and is easily densified when compressed, because the product of (A) and (B) is equal to or greater than a certain value. The product of the above (A) and (B) must be 11 or more, is preferably 12.5 to 70, and more preferably 14 to 55.

[0037] For the same reasons as above, in the sulfide solid electrolyte mixture of this embodiment, the product of the following (C) and the above (B) is preferably 2.5 or more, more preferably 3.0 to 20.0, and even more preferably 3.3 to 15.0. (C) The number of moles of lithium salt per mole of ionic liquid in the electrolyte solution

[0038] (Sulfide solid electrolyte) In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state under a nitrogen atmosphere at 25° C. The sulfide solid electrolyte in this embodiment is a solid electrolyte that contains at least lithium atoms, sulfur atoms, and phosphorus atoms and has ionic conductivity due to the lithium atoms, and may further contain halogen atoms.

[0039] The term "solid electrolyte" includes both amorphous solid electrolytes and crystalline solid electrolytes. In this specification, the crystalline solid electrolyte is a solid electrolyte in which a peak derived from the solid electrolyte is observed in the X-ray diffraction pattern in the X-ray diffraction measurement, and it does not matter whether or not there is a peak derived from the raw material of the solid electrolyte. That is, the crystalline solid electrolyte includes a crystal structure derived from the solid electrolyte, and a part of the crystal structure may be derived from the solid electrolyte, or the whole of the crystal structure may be derived from the solid electrolyte. And, as long as the crystalline solid electrolyte has the above-mentioned X-ray diffraction pattern, a part of the crystalline solid electrolyte may include an amorphous solid electrolyte. Therefore, the crystalline solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte to a crystallization temperature or higher. In this specification, the term "amorphous solid electrolyte" refers to an amorphous solid electrolyte that has a halo pattern in which no peaks other than those derived from the material are substantially observed in an X-ray diffraction pattern obtained by X-ray diffraction measurement, regardless of whether or not there are peaks derived from the raw materials of the solid electrolyte.

[0040] The sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably further contains halogen atoms. Representative examples include solid electrolytes composed of lithium sulfide and phosphorus sulfide, such as Li2S-P2S5; solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, and Li2S-P2S5-LiBr-LiCl, are preferred, and solid electrolytes composed of lithium sulfide, phosphorus sulfide, and two types of lithium halides, such as Li2S-P2S5-LiBr-LiCl, are more preferred. The types of atoms constituting the sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectroscopic analyzer.

[0041] In the above amorphous solid electrolyte, 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 further 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, more preferably 1.2-1.6:0.25-0.5:1.3-1.7:0.03-0.2:0.03-0.2, and even 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 having a higher ionic conductivity, particularly having a thiolithicon region II type crystal structure or an argyrodite type crystal structure. As the sulfide solid electrolyte used in the sulfide solid electrolyte mixture of this embodiment, from the viewpoint of obtaining high ionic conductivity, a crystalline sulfide solid electrolyte is preferable, and among them, one having a thiolicon region II type crystal structure or an argyrodite type crystal structure is preferable.

[0042] The shape of the sulfide solid electrolyte is not particularly limited, but may be, for example, a particulate shape. The average particle size (D 50 ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 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.

[0043] The sulfide solid electrolyte can be produced, for example, by pulverizing a raw material containing at least lithium atoms, sulfur atoms, and phosphorus atoms to obtain a pulverized product, and further heating the pulverized product as necessary to obtain a heat-treated product.

[0044] The crystalline sulfide solid electrolyte obtained by the heating may contain the thiolicon region II type crystal structure or may contain it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it contains it as the main crystal. In this specification, "containing it as the main crystal" means that the ratio of the target crystal structure among the crystal structures is 80% or more, preferably 90% or more, and more preferably 95% or more. In addition, from the viewpoint of obtaining higher ionic conductivity, it is preferable that the crystalline sulfide solid electrolyte does not contain crystalline Li3PS4 (β-Li3PS4).

[0045] In addition, the composition ratio of the atoms contained in the crystalline sulfide solid electrolyte is preferably within the range of the composition ratio according to the composition formula corresponding to each of the above various crystal structures and within the range of the composition ratio of each atom of the above amorphous sulfide solid electrolyte. When within the range of the composition ratio of each atom, among the above crystal structures, it becomes easier to form a thiolsilicon region II-type crystal structure or an argyrodite-type crystal structure.

[0046] As the above crystalline sulfide solid electrolyte, a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure formed by substituting a part of P with Si and having a structural skeleton of Li7PS6 is also preferably mentioned. As the composition formula of the argyrodite-type crystal structure, for example, the composition formula Li 7-x P 1-y Si y S6 and Li 7+x P 1-y Si y S6 (where x is -0.6 to 0.6 and y is 0.1 to 0.6) represents a crystal structure. The argyrodite-type crystal structure represented by this composition formula is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα rays, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0047] As the composition formula of the above argyrodite-type crystal structure, the composition formula Li 7-x-2y PS 6-x-y Cl x (0.8 ≦ x ≦ 1.7, 0 < y ≦ -0.25x + 0.5) is also mentioned. The argyrodite-type crystal structure represented by this composition formula is preferably cubic, and in X-ray diffraction measurement using CuKα rays, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. In addition, as the composition formula of the above argyrodite-type crystal structure, the composition formula Li 7-x PS 6-x Ha x(Ha is Cl or Br, and x is preferably 0.2 to 1.8). The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0° in X-ray diffraction measurement using CuKα radiation. The positions of these peaks may vary within a range of ±0.5°.

[0048] (Raw material content) The raw material content includes lithium atoms, sulfur atoms, and phosphorus atoms, and more specifically includes a substance including one or more selected from the group consisting of these atoms (hereinafter, also referred to as "solid electrolyte raw material"). The raw material content used in this embodiment preferably includes two or more solid electrolyte raw materials. The raw material contents may further include halogen atoms.

[0049] Examples of solid electrolyte raw materials contained in the raw material content include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5); 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); thiophosphori fluorides, Representative examples of such materials include raw materials consisting of at least two atoms selected from the above four types of atoms, such as thiophosphoryl halides, such as thiophosphoryl chloride (PSCl3), thiophosphoryl bromide (PSBr3), thiophosphoryl iodide (PSI3), thiophosphoryl fluoride dichloride (PSCl2F), and thiophosphoryl fluoride dibromide (PSBr2F); and elemental halogens, such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2).

[0050] Examples of usable solid electrolyte raw materials other than those mentioned above include solid electrolyte raw materials containing at least one atom selected from the above four types of atoms and containing atoms other than the four types of atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; metal sulfides such as silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS, SnS2), 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 (POCl3) and phosphorus oxybromide (POBr3).

[0051] Among the above, lithium sulfide, phosphorus sulfide such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5), halogen elements such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2), and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide are preferred. In addition, when oxygen atoms are introduced into the solid electrolyte, phosphoric acid compounds such as lithium oxide, lithium hydroxide, and lithium phosphate are preferred. As the combination of the solid electrolyte raw materials, for example, a combination of lithium sulfide, diphosphorus pentasulfide, and lithium halides, and a combination of lithium sulfide, diphosphorus pentasulfide, and halogen elements are preferred, and lithium bromide and lithium chloride are preferred as lithium halides, and bromine and chlorine are preferred as halogen elements.

[0052] In this embodiment, Li3PS4 containing the PS4 structure can be used as a part of the raw material. Specifically, Li3PS4 is prepared in advance by manufacturing or the like, and used as the raw material. The content of Li3PS4 in the total of the raw materials is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and further preferably 70 to 80 mol%.

[0053] The lithium sulfide used in the present embodiment is preferably in particulate form. The average particle size of lithium sulfide particles (D 50 In this specification, the average particle size (D 50 ) is the particle size at which the particle size distribution cumulative curve is accumulated from the smallest particle size to 50% (volume basis) of the total, and the volume distribution is the average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device. In addition, among the above-mentioned examples of raw materials, solid raw materials preferably have an average particle size similar to that of the lithium sulfide particles, that is, within the same range as the average particle size of the lithium sulfide particles.

[0054] 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 even more preferably 74 mol% or more, and the upper limit is preferably 85 mol% or less, more preferably 83 mol% or less, and even 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 even more preferably 74 to 80 mol%. Furthermore, when a sulfide solid electrolyte having a thiolithium region II type crystal structure is to be obtained, in addition to the above range, 74 to 78.5 mol%, 74 to 78 mol%, and 74 to 76 mol% are particularly preferred. When a sulfide solid electrolyte having an argyrodite type crystal structure is to be obtained, in addition to the above range, 76 to 83 mol%, 77 to 80 mol%, and 78 to 80 mol% are particularly preferred.

[0055] (Crusher) When obtaining the pulverized product, the raw material content is pulverized using a pulverizer. A grinder is a device used to grind materials, as the name suggests, but it can also stir and mix materials at the same time.

[0056] The pulverizer can be any type that can mix the solid electrolyte raw materials without any particular limitations. For example, a media type pulverizer using a pulverizing medium can be used.

[0057] Media-type mills are broadly classified into vessel-driven mills and media-agitation mills. Examples of vessel-driven mills include agitation tanks, grinding tanks, and combinations thereof such as ball mills and bead mills. Examples of media-agitation mills include impact mills such as cutter mills, hammer mills, and pin mills; tower mills and other tower-type mills; attritors, aquamizers, sand grinders and other agitation tank-type mills; visco mills, pearl mills and other circulation tank-type mills; circulation pipe mills; annular mills such as coball mills; continuous dynamic mills; and single-shaft or multi-shaft kneaders. Considering the ease of adjusting the particle size of the resulting pulverized product, it is preferable to use a ball mill or a bead mill, which are given as examples of the container-driven pulverizer, and among these, a planetary type mill is preferable.

[0058] These pulverizers can be appropriately selected depending on the desired scale, etc. For relatively small-scale operations, container-driven pulverizers such as ball mills and bead mills can be used, while for large-scale operations or mass production, other types of pulverizers may be used.

[0059] The size of the beads or balls used in the above-mentioned 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 mmφ or more, preferably 0.1 mmφ or more, more preferably 0.3 mmφ or more, with the upper limit being usually 5.0 mmφ or less, preferably 3.0 mmφ or less, more preferably 2.0 mmφ or less. The diameter of the balls is usually 2.0 mmφ or more, preferably 2.5 mmφ or more, more preferably 3.0 mmφ or more, with the upper limit being usually 20.0 mmφ or less, preferably 15.0 mmφ or less, more preferably 10.0 mmφ 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.

[0060] When a ball mill or bead mill is used, the rotation speed varies depending on the scale of processing and cannot be generally determined, but is usually 10 rpm or more, preferably 20 rpm or more, and more preferably 50 rpm or more, and the upper limit is usually 1,000 rpm or less, preferably 900 rpm or less, more preferably 800 rpm or less, and even more preferably 700 rpm or less. In this case, the grinding time varies depending on the scale of processing and cannot be generalized, but is usually 0.5 hours or more, preferably 1 hour or more, and more preferably 2 hours or more, and the upper limit is usually 100 hours or less, preferably 72 hours or less, more preferably 48 hours or less, even more preferably 24 hours or less, and even more preferably 10 hours or less.

[0061] The sulfide solid electrolyte may be prepared by mixing the above-mentioned raw material ingredients and then contacting them with a complexing agent or a solvent. The complexing agent preferably contains a heteroatom such as a nitrogen atom or an oxygen atom, and more preferably has a group containing at least two heteroatoms in the molecule. More specifically, the complexing agent is preferably an aliphatic amine, and more preferably an aliphatic diamine.

[0062] In the case of producing a crystalline sulfide solid electrolyte, heating may be further included. When an amorphous sulfide solid electrolyte (glass component) is obtained by the above mixing, a crystalline sulfide solid electrolyte is obtained by heating, and when a crystalline sulfide solid electrolyte is obtained, a crystalline sulfide solid electrolyte with improved crystallinity is obtained.

[0063] For example, when obtaining an amorphous sulfide solid electrolyte, the heating temperature may be determined according to 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) at a temperature rise rate of 10°C / min using a differential thermal analyzer (DTA device), and 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 temperature of the top of the exothermic peak observed on the lowest temperature side. There is no particular limit to the lower limit, but the heating temperature may be set to about -40°C or more, which is the temperature of the top of the exothermic peak observed on the lowest temperature side. By setting the temperature range, an amorphous sulfide solid electrolyte can be obtained more efficiently and reliably.

[0064] The heating temperature for obtaining an amorphous sulfide solid electrolyte cannot be generally defined because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained. However, it is usually 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.

[0065] When obtaining a crystalline sulfide solid electrolyte, the heating temperature may be determined according to 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) at a temperature rise rate of 10°C / min using a differential thermal analyzer (DTA device), and the 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 on the lowest temperature side. There is no particular limit to the upper limit, but it may be about 40°C or lower. By setting the temperature range, a crystalline sulfide solid electrolyte can be obtained more efficiently and reliably.

[0066] 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 crystalline sulfide solid electrolyte to be obtained. Generally, however, the heating temperature is 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 heating temperature is preferably 600° C. or lower, more preferably 550° C. or lower, and even more preferably 500° C. or lower.

[0067] The heating time is not particularly limited as long as the desired amorphous sulfide solid electrolyte or crystalline sulfide solid electrolyte can be obtained, but is preferably, for example, 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.

[0068] The heating is preferably performed in an inert gas atmosphere (e.g., nitrogen atmosphere, argon atmosphere) or a reduced pressure atmosphere (particularly in a 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. Also, for industrial purposes, a horizontal dryer having a heating means and a feeding mechanism, a horizontal vibration fluidized dryer, etc. may be used, and may be selected according to the amount of processing to be heated.

[0069] (mixture) Specifically, the sulfide solid electrolyte mixture of the present embodiment can be produced by mixing the sulfide solid electrolyte and the electrolytic solution.

[0070] As a device for mixing the sulfide solid electrolyte and the electrolytic solution, the above-mentioned device for mixing the raw materials for the solid electrolyte can be used, and it is preferable to use a grinder such as a ball mill or a bead mill. The details of the pulverizer and pulverizing conditions used for mixing the sulfide solid electrolyte and the electrolytic solution are the same as those for mixing the solid electrolyte raw materials described above.

[0071] (electrolyte) The electrolyte solution in this embodiment contains a lithium salt and an ionic liquid as described above. The total content of the lithium salt and the ionic liquid in the above-mentioned electrolytic solution is preferably 50 to 100 mass %, more preferably 80 to 100 mass %, even more preferably 90 to 100 mass %, and particularly preferably 95 to 100 mass %, based on the total amount of the electrolytic solution.

[0072] The number of moles of the lithium salt in 1 liter of the above-mentioned electrolytic solution (above (A)) is preferably 0.5 to 5.0 mol, more preferably 0.7 to 4.0 mol, and particularly preferably 2.0 to 3.0 mol, from the viewpoints of the ionic conductivity of the resulting sulfide solid electrolyte mixture and the solubility of the lithium salt.

[0073] The content of the electrolytic solution (the above (B)) based on the total amount of the sulfide solid electrolyte mixture is preferably 8.0 to 20.0 mass %, more preferably 10.0 to 18.0 mass %, and further preferably 12.0 to 17.0 mass %.

[0074] Furthermore, the number of moles of the lithium salt per mole of the ionic liquid in the electrolytic solution (above (C)) is preferably 0.15 to 1.00 mol, more preferably 0.20 to 0.95 mol, and particularly preferably 0.50 to 0.80 mol, from the viewpoints of the ionic conductivity of the resulting sulfide solid electrolyte mixture and the solubility of the lithium salt.

[0075] (Lithium salts) As the lithium salt, any of those typically used in the electrolyte of lithium ion batteries can be used. For example, those in which the anion is one or more selected from halide ions, tetrafluoroborate, hexafluorophosphate, and those represented by the following general formula (I) are preferably used, and those in which the anion is represented by the following general formula (I) are more preferably used.

[0076] [ka] (In the formula, R 1 and R 2 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.)

[0077] (Ionic Liquid) As the ionic liquid, any ionic liquid that is usually used in the electrolyte of a lithium ion battery can be used. Specifically, the cation is preferably one or more selected from the group consisting of ammonium, imidazolium cation, pyridinium cation, pyrrolidinium cation, piperidinium cation, and phosphonium cation, and more preferably one represented by the following general formula (II):

[0078] [ka] (In the formula, R 3 and R 4 are each independently a hydrogen atom or a substituted or unsubstituted hydrocarbon group having 1 to 18 carbon atoms; R 5 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0079] In the general formula (II), R 3 and R 4 are each preferably an unsubstituted alkyl or alkenyl group having 1 to 8 carbon atoms.

[0080] The ionic liquid preferably has an anion which is at least one selected from the group consisting of a halide ion, tetrafluoroborate, hexafluorophosphate, and an anion represented by the following general formula (III). [ka] (In the formula, R 6 and R 7 are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.)

[0081] The ionic conductivity of the sulfide solid electrolyte mixture of this embodiment is preferably 0.5 mS / cm or more, more preferably 1.0 mS / cm or more, even more preferably 2.0 mS / cm or more, and particularly preferably 3.0 mS / cm or more. In this specification, the ionic conductivity is measured by the method described in the Examples.

[0082] (Application) The sulfide solid electrolyte mixture of the present embodiment has good lithium ion conductivity and is therefore suitable for use in all-solid-state batteries and the like. When the sulfide solid electrolyte mixture of the present embodiment is used in an all-solid-state battery, it may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer of the all-solid-state battery, and when it is used in the positive electrode layer or the negative electrode layer, it is preferably used as an electrode mixture containing the sulfide solid electrolyte mixture of the present embodiment and an electrode active material. Each of these layers can be produced by a known method.

[0083] In addition, the all-solid-state battery preferably uses 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 in which a material that reacts with the solid electrolyte mixture, such as Au, Pt, Al, Ti, or Cu, is coated with Au or the like can be used. EXAMPLES

[0084] 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.

[0085] (Powder XRD diffraction measurement) Powder X-ray diffraction (XRD) measurements were carried out as follows. The sulfide solid electrolyte powder obtained in the examples and comparative examples was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm, and smoothed with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured under the following conditions without exposing it to air. Measurement equipment: D2 PHASER, manufactured by Bruker Corporation Tube voltage: 30kV Tube current: 10mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: Solar slit 4°, divergence slit 1mm Detector: Semiconductor detector Measurement range: 2θ=10-60deg Step width, scan speed: 0.02 deg, 0.4 sec / step

[0086] (Pellet preparation) 300 mg of the powder obtained in each of the examples and comparative examples was weighed and filled into a powder compression molding jig (φ10 mm) consisting of a cylindrical mold and upper and lower punches, and then compressed at 400 MPa using a uniaxial press to produce circular pellets.

[0087] (Measurement of ionic conductivity) The circular pellet obtained by the above pellet preparation process (diameter: 10 mm, cross-sectional area S: 0.785 cm 2 ) was used as a sample. The initial cell length (L0) of the powder compression molding jig was measured in advance, and the thickness of the pellet (L) was calculated by taking the difference between this and the cell length (L1) after pellet molding. Electrode terminals were attached to the top and bottom of the sample, and measurements were made at 25°C using the AC impedance method (frequency range: 5MHz to 100Hz, amplitude: 10mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula. R=ρ(L / S) σ=1 / ρ

[0088] (Pellet density measurement) The pellet volume was calculated from the product of the pellet thickness (L) and its cross-sectional area (S), and the pellet density was calculated by dividing the pellet volume by the powder mass weighed in the above pellet production.

[0089] Example 1 (1-1) Preparation of raw sulfide solid electrolyte In a glove box under a nitrogen atmosphere, each of the ground compounds was weighed out so that the molar ratio of Li2S:P2S5:LiBr:LiCl was 47.5:12.5:15.0:25.0, and the compounds were placed in a glass container and roughly mixed by shaking the container. The crudely mixed raw materials were dispersed in a mixed solvent of dehydrated toluene (Fujifilm Wako Pure Chemical Industries, Ltd.) and dehydrated isobutyronitrile (Kishida Chemical Co., Ltd.) under a nitrogen atmosphere to obtain a raw material mixture slurry of approximately 10 mass%. The raw material mixture slurry was mixed and ground using a bead mill (LMZ015, Ashizawa Finetech Co., Ltd.) while maintaining the nitrogen atmosphere. The treated slurry was placed in a nitrogen-substituted Schlenk flask and then dried under reduced pressure to prepare the raw material mixture.

[0090] (1-2) Heating (crystallization) process The raw material mixture obtained in (1-1) above was heated in an electric furnace (F-1 404-A, manufactured by Tokyo Glass Machinery Co., Ltd.) in a glove box under a nitrogen atmosphere. Specifically, the raw material mixture was placed in an Al2O3 sagger (999-60S, manufactured by Tokyo Glass Machinery Co., Ltd.) and heat-treated in an electric furnace at 410 to 430°C for one hour or more. Thereafter, the sagger was removed from the electric furnace and slowly cooled to obtain an argyrodite-type solid electrolyte. The obtained sulfide solid electrolyte was subjected to X-ray diffraction (XRD) measurement, and peaks derived from an argyrodite-type crystal structure were observed at 2θ=25.5±1.0 deg and 29.9±1.0 deg in the XRD pattern.

[0091] (1-3) Micronization process The obtained argyrodite-type solid electrolyte was dispersed in a mixed solvent of dehydrated toluene (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) and dehydrated isobutyronitrile (manufactured by Kishida Chemical Co., Ltd.) under a nitrogen atmosphere to obtain a solid electrolyte slurry. The slurry was mixed and ground using a bead mill (LMZ015, manufactured by Ashizawa Finetech Co., Ltd.) while maintaining the nitrogen atmosphere. The solid electrolyte slurry after the treatment was placed in a nitrogen-substituted Schlenk flask and then dried under reduced pressure to obtain a microparticulated argyrodite-type sulfide solid electrolyte. In the examples and comparative examples, the microparticulated argyrodite-type sulfide solid electrolyte obtained by this process was used.

[0092] (1-4) Mixing process In a glove box under an inert gas atmosphere, 34 g of zirconia balls having a diameter of 5.0 mm were placed in a 45 mL zirconia container, and 1.70 g of the finely divided argyrodite-type sulfide solid electrolyte obtained in (1-3) above and 0.30 g of an electrolyte solution in which the number of moles of lithium salt per 1 liter of the electrolyte solution (above (A)) was 1.0 mol were further placed in the container. Here, the electrolyte solution consisted of 13 mass% lithium bis(fluorosulfonyl)imide and 87 mass% 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, and the content of the electrolyte solution (above (B)) based on the total mass of the sulfide solid electrolyte mixture was 15.0 mass%.

[0093] After sealing the container, it was removed from the glove box and placed on a small ball mill rotating stand, where mixing was carried out at 600 rpm for 1 hour. The container was placed back in the glove box, and the zirconia balls were separated from the contents using a SUS sieve with 300 μm openings, to obtain a sulfide solid electrolyte mixture.

[0094] The obtained sulfide solid electrolyte mixture powder was used to prepare pellets, and the ionic conductivity was measured, and the ionic conductivity was found to be 3.8 mS / cm. The density of the resulting pellets was measured and found to be 1.90 g / cm 3 It was.

[0095] Example 2 A sulfide solid electrolyte mixture was obtained in the same manner as in Example 1, except that in the above (1-4), an electrolyte solution in which the number of moles of lithium salt (above (A)) per 1 liter of the electrolyte solution was 2.4 moles was used. Here, the electrolyte solution consisted of 29 mass % lithium bis(fluorosulfonyl)imide and 71 mass % 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide.

[0096] The obtained sulfide solid electrolyte mixture powder was used to prepare pellets, and the ionic conductivity was measured, and the ionic conductivity was found to be 4.0 mS / cm. The density of the resulting pellets was measured and found to be 1.91 g / cm 3 It was.

[0097] Example 3 In the above (1-4), a sulfide solid electrolyte mixture was obtained in the same manner as in Example 1, except that an electrolyte solution in which the number of moles of lithium salt (above (A)) per 1 liter of the electrolyte solution was 3.2 moles was used. Here, the electrolyte solution consisted of 37% by mass of lithium bis(fluorosulfonyl)imide and 63% by mass of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide.

[0098] The obtained sulfide solid electrolyte mixture powder was used to prepare pellets, and the ionic conductivity was measured, and the ionic conductivity was found to be 3.7 mS / cm. The density of the resulting pellets was measured and found to be 1.94 g / cm 3 It was.

[0099] Comparative Example 1 The finely divided argyrodite-type sulfide solid electrolyte obtained in Example 1 (1-3) was used as it was to prepare a pellet, and the ionic conductivity was measured, and the ionic conductivity was found to be 4.8 mS / cm. The density of the resulting pellets was measured and found to be 1.65 g / cm 3 It was.

[0100] Comparative Example 2 A pellet was prepared in the same manner as in Example 1 (1-4), except that 1.80 g of the particulate argyrodite-type sulfide solid electrolyte and 0.20 g of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide as an ionic liquid were added, and the ionic conductivity was measured. The ionic conductivity was 3.4 mS / cm. The density of the resulting pellets was measured and found to be 1.85 g / cm 3 It was.

[0101] Comparative Example 3 A pellet was prepared in the same manner as in Example 1 (1-4), except that 1.70 g of the finely divided argyrodite-type sulfide solid electrolyte and 0.30 g of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide as an ionic liquid were added, and the ionic conductivity was measured. The ionic conductivity was 3.2 mS / cm. The density of the resulting pellets was measured and found to be 1.91 g / cm 3 It was.

[0102] (Reference example) In the same manner as in (1-4) of Example 1, 1.80 g of a particulate argyrodite-type sulfide solid electrolyte and 0.20 g of an electrolyte solution in which the number of moles of lithium salt per 1 L of the electrolyte solution (above (A)) was 1.0 mol were charged and mixed to obtain a sulfide solid electrolyte mixture. Here, the electrolyte solution was composed of 13 mass% lithium bis(fluorosulfonyl)imide and 87 mass% 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, and the content of the electrolyte solution (above (B)) based on the total mass of the sulfide solid electrolyte mixture was 10.0 mass%.

[0103] [Table 1]

[0104] As shown in Table 1, the pellets obtained using the sulfide solid electrolyte mixtures of Examples 1 to 3, which were mixtures of a sulfide solid electrolyte and an electrolytic solution and in which the product of (A) and (B) was 11 or more, had high ionic conductivity and high density. In contrast, in Comparative Example 1, when pellets were produced using the sulfide solid electrolyte itself without using an electrolytic solution, the resulting pellets had a low density. On the other hand, the pellets obtained in Comparative Examples 2 and 3, in which an ionic liquid not containing a lithium salt was used as the electrolyte, had low ionic conductivity. It should be noted that although the Reference Example is similar to Comparative Example 5 of Patent Document 2, the product of (A) and (B) is 10, and it has become clear that this does not belong to the present invention. In Comparative Example 5 of Patent Document 2, the ratio A of the ionic liquid to the sulfide solid electrolyte is 10% by volume (therefore, the ratio of the ionic liquid to the total amount of the sulfide solid electrolyte and the ionic liquid is about 9.1% by volume). However, details such as whether the volume of the sulfide solid electrolyte is an apparent volume or not and what its density is were unclear, so for the sake of convenience, this Reference Example is provided in which the content of the electrolytic solution (above (B)) based on the total amount of the sulfide solid electrolyte mixture is 10.0% by mass. Furthermore, in this Example 1, when the volume % was calculated using the lattice constant obtained from the peak obtained by powder XRD diffraction measurement, the theoretical density of the solid electrolyte calculated from the composition ratio, and the density of the electrolyte, the result was 23.9 volume %, which was larger than the mass %. This is because the theoretical density of the solid electrolyte is larger than the density of the electrolyte, and such a calculation result is obtained. In other words, although the theoretical density of the solid electrolyte used in Comparative Example 5 of Patent Document 2 is not certain, the value of (B) in Comparative Example 5 is smaller than 9.1 mass % unless the theoretical density of the solid electrolyte is smaller than the density of the electrolyte. Even if estimated from the density of the raw materials used, the probability that the theoretical density of the solid electrolyte will be smaller than the density of the electrolyte is low, and therefore, it is reasonably assumed that the value of the product of (A) and (B) will be smaller than 10 in the above Reference Example. [Industrial Applicability]

[0105] The sulfide solid electrolyte mixture of the present embodiment has good lithium ion conductivity and is easily densified when compressed. The sulfide solid electrolyte mixture of this embodiment is suitable for use as an electrode mixture or a lithium ion battery, particularly for lithium ion batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

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