Sulfide solid electrolyte mixture, electrode mixture, and all-solid-state battery

Abstract

The present invention provides a sulfide solid electrolyte mixture which contains: a sulfide solid electrolyte that contains lithium atoms, sulfur atoms, and phosphorus atoms, the sulfide solid electrolyte having a high ion conductivity and being easily densified when compressed; and an electrolyte solution that contains a lithium salt and an ionic liquid. With respect to this sulfide solid electrolyte mixture, the product of (A) the number of moles of the lithium salt in 1 liter of the electrolyte solution and (B) the content (mass%) of the electrolyte solution based on the total amount of the sulfide solid electrolyte mixture is 11 or more.

Description

Sulfide solid electrolyte mixture, electrode mixture and all-solid-state battery

[0001] The present invention relates to a sulfide solid electrolyte mixture, an electrode mixture, and an all-solid-state battery.

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

[0003] 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 or the like with a small amount of an electrolytic solution.

[0004] International Publication No. 2019 / 221042 Pamphlet Japanese Patent Application Laid-Open No. 2019-121455

[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.

[0006] The sulfide solid electrolyte mixture according to the present invention comprises a sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms, and an electrolyte solution containing a lithium salt and an ionic liquid, wherein 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 solution, and (B) the content (mass %) of the electrolyte solution based on the total amount of the sulfide solid electrolyte mixture.

[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.

[0008] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, both end values ​​of "to" are included as the lower limit and upper limit of the numerical range, respectively, and the upper and lower limit numerical values ​​of the numerical ranges of "greater than or equal to," "less than or equal to," and "to" are numerical values ​​that can be arbitrarily combined, and numerical values ​​in the examples can also be used as the upper and lower limit numerical values. Furthermore, preferred specifications can be adopted arbitrarily. 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 things is more preferable.

[0009] (Findings Obtained by the Inventor to Achieve the Present Invention) The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found the following points, which have led to the completion of the present invention.

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

[0011] The present inventors have found that conventional solid electrolytes, even when compressed into pellets, leave voids inside, making it impossible to sufficiently densify the pellets. After extensive research, the present inventors have found that this is due to the difficulty of the particles sliding against each other due to minute irregularities on the surface of the solid electrolyte particles. The present inventors then tried mixing an ionic liquid with the solid electrolyte, and found that although the pellets could be densified to some extent, the ionic conductivity tended to decrease. Further investigations by the present inventors have found that mixing an electrolyte solution containing a lithium salt and an ionic liquid with the solid electrolyte so that the product of (A) and (B) is 11 or greater results in a sufficient amount of lithium salt present between the solid electrolyte particles, maintaining ionic conductivity, and improving interparticle sliding due to the presence of the electrolyte solution on the surface of the solid electrolyte particles. When the solid electrolyte particles are compressed into a compact, the voids are filled by sliding against each other, thereby achieving densification of the pellets. This finding led to the completion of the present invention.

[0012] (Various Forms of the Present Embodiment) A sulfide solid electrolyte mixture according to a first embodiment 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 solution; and (B) the content (mass %) of the electrolyte solution 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] A sulfide solid electrolyte mixture according to a second aspect of the present embodiment is the sulfide solid electrolyte mixture of the first aspect, wherein (A) is 0.5 to 5.0 moles.

[0015] A lithium salt content of 0.5 moles or more per liter of the electrolyte solution is preferable because the ionic conductivity of the resulting sulfide solid electrolyte mixture is higher, and a lithium salt content of 5.0 moles or less improves the solubility of the lithium salt in the electrolyte solution. Furthermore, in relation to (B), the product of (A) and (B) is likely to be 11 or more, which makes it easier to achieve both high ionic conductivity and densification.

[0016] A sulfide solid electrolyte mixture according to a third aspect of the present embodiment is the sulfide solid electrolyte mixture of the first or second aspect, wherein (B) is 8.0 to 20.0 mass %.

[0017] A content of the electrolyte solution 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 ionic conductivity by adding the electrolyte solution and densification when the sulfide solid electrolyte mixture is compression-molded, while a content of 20.0 mass% or less is preferable because the electrolyte solution is less likely to leach out when the sulfide solid electrolyte mixture is compression-molded. Furthermore, in relation to (A), the product of (A) and (B) is more likely to be 11 or more, which results in easier achievement of both high ionic conductivity and densification.

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

[0019] Furthermore, the sulfide solid electrolyte mixture according to a fifth aspect of the present embodiment is any one of the first to third aspects, wherein the product of (A) and (B) is 14 to 55.

[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, wherein the product of the following (C) and (B) is 2.5 or more: (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 is preferably higher.

[0023] A sulfide solid electrolyte mixture according to a seventh aspect of the present embodiment is any one of the first to sixth aspects, wherein the lithium salt is represented by the following general formula (I): (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] As the lithium salt used in the sulfide solid electrolyte mixture of this embodiment, specifically, it is preferable to use one represented by the above general formula (I) from the viewpoint of ionic conductivity.

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

[0026] Furthermore, a sulfide solid electrolyte mixture according to a ninth aspect of the present embodiment is the sulfide solid electrolyte mixture of the eighth aspect, wherein the imidazolium cation is represented by the following general formula (II): (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] Further, in the sulfide solid electrolyte mixture according to a tenth aspect of the present embodiment, in the ninth aspect, ３ and R ４ are each independently an unsubstituted alkyl or alkenyl group having 1 to 8 carbon atoms.

[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 of 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, wherein the anion of the ionic liquid is at least one selected from the group consisting of halide ions, tetrafluoroborate, hexafluorophosphate, and those represented by the following general formula (III): (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] Further, in a sulfide solid electrolyte mixture according to a twelfth aspect of the present embodiment, in the eleventh aspect, the anion of the ionic liquid is represented by the general formula (III).

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

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

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

[0034] The sulfide solid electrolyte mixture of the present embodiment can be used in an all-solid-state battery, and more specifically, 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 this 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 solution; and (B) the content (mass %) of the electrolyte solution 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 a certain value or more. The product of (A) and (B) must be 11 or more, preferably 12.5 to 70, and more preferably 14 to 55.

[0037] For the same reasons as above, the sulfide solid electrolyte mixture of this embodiment preferably has a product of the following (C) and (B) of 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 also contain halogen atoms.

[0039] The term "solid electrolyte" includes both amorphous solid electrolytes and crystalline solid electrolytes. In this specification, a crystalline solid electrolyte is a solid electrolyte in which peaks derived from the solid electrolyte are observed in an X-ray diffraction pattern in X-ray diffraction measurement, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present. That is, a crystalline solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as a crystalline solid electrolyte has the X-ray diffraction pattern described above, it may also contain an amorphous solid electrolyte in part. Therefore, crystalline solid electrolytes include so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than its crystallization temperature. Furthermore, in this specification, an amorphous solid electrolyte is one in which a halo pattern in an X-ray diffraction pattern in X-ray diffraction measurement is observed in which substantially no peaks other than those derived from the material are present, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present.

[0040] The sulfide solid electrolyte contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably further contains halogen atoms. Representative examples include Li ２ S-P ２ S ５ Solid electrolytes composed of lithium sulfide and phosphorus sulfide such as Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiBr-LiCl, is preferred, and Li ２ S-P ２ S ５ A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and two types of lithium halides, such as LiBr-LiCl, is more preferred. The types of atoms constituting the sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0041] In the amorphous solid electrolyte, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms is preferably 1.0 to 1.8:0.1 to 0.8:1.0 to 2.0:0.01 to 0.6, more preferably 1.1 to 1.7:0.2 to 0.6:1.2 to 1.8:0.05 to 0.5, and even more preferably 1.2 to 1.6:0.25 to 0.5:1.3 to 1.7:0.08 to 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 to 1.8: 0.1 to 0.8: 1.0 to 2.0: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 0.2 to 0.6: 1.2 to 1.8: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 0.25 to 0.5: 1.3 to 1.7: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 0.3 to 0.45: 1.4 to 1.7: 0.04 to 0.18: 0.04 to 0.18. By setting the composition ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, a solid electrolyte having a higher ionic conductivity, particularly a thiolisiconregion II crystal structure or an argyrodite crystal structure, can be easily obtained. 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 preferred, and in particular, one having a thiolisiconregion II crystal structure or an argyrodite crystal structure is preferred.

[0042] The shape of the sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (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 then, if necessary, by heating the pulverized product to obtain a heat-treated product.

[0044] The crystalline sulfide solid electrolyte obtained by the heating may contain, for example, the thiolisiconregion II type crystal structure or the argyrodite type 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, the crystalline sulfide solid electrolyte contains crystalline Li ３ P.S. ４ (β-Li ３ P.S. ４ ) is preferably not included.

[0045] 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 thiolisiconregion II crystal structure or an argyrodite crystal structure, among the above crystal structures. The crystal structure of the sulfide solid electrolyte contained in the sulfide solid electrolyte mixture of this embodiment is preferably a thiolisiconregion II crystal structure or an argyrodite crystal structure, and more preferably an argyrodite crystal structure.

[0046] The crystalline sulfide solid electrolyte may be Li ７ P.S. ６ A preferred example of the crystalline sulfide solid electrolyte is an argyrodite-type crystal structure having a structural skeleton in which part of P is substituted with Si. The composition formula of the argyrodite-type crystal structure is, for example, the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is −0.6 to 0.6, y is 0.1 to 0.6) The argyrodite-type crystal structure represented by this composition formula is a cubic or orthorhombic crystal, preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0047] The composition formula of the argyrodite-type crystal structure is Li ７－ｘ－２ｙ P.S. 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 a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The composition formula of the argyrodite-type crystal structure is preferably the composition formula Li ７－ｘ P.S. ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8). The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and 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°. Note that these peak positions may vary within a range of ±0.5°.

[0048] The sulfide solid electrolyte contained in the sulfide solid electrolyte mixture of this embodiment contains lithium atoms, phosphorus atoms, and sulfur atoms, and preferably halogen atoms. ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ ”, “Compositional formula Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ " and "Composition formula Li ７－ｘ P.S. ６－ｘ Ha ｘ However, when the sulfide solid electrolyte mixture of the present embodiment has the same diffraction peak as the "argyrodite-type crystal structure," it can be said that the sulfide solid electrolyte contained in the sulfide solid electrolyte mixture of the present embodiment has an argyrodite-type crystal structure formed by lithium atoms, phosphorus atoms, and sulfur atoms, preferably lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. In this regard, although no explanation is given regarding the composition formula, this is not limited to the argyrodite-type crystal structure, but also applies to the thiolisiconregion II-type crystal structure.

[0049] (Method for Producing Sulfide Solid Electrolyte Mixture) As described above, the sulfide solid electrolyte contained in the sulfide solid electrolyte mixture of this embodiment 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 then, if necessary, heating the pulverized product to obtain a heat-treated product. The sulfide solid electrolyte mixture can then be produced by mixing the obtained sulfide solid electrolyte with an electrolytic solution. The electrolytic solution containing a lithium salt and an ionic liquid contained in the sulfide solid electrolyte mixture of this embodiment will be described together with the method for producing the sulfide solid electrolyte mixture.

[0050] (Raw material inclusions) The raw material inclusions contain lithium atoms, sulfur atoms, and phosphorus atoms, and more specifically, contain a substance containing one or more selected from the group consisting of these atoms (hereinafter also referred to as "solid electrolyte raw material"). The raw material inclusions used in this embodiment preferably contain two or more solid electrolyte raw materials. Furthermore, the raw material inclusions may further contain halogen atoms.

[0051] Examples of the solid electrolyte raw material contained in the raw material content include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ phosphorus sulfides such as various phosphorus fluorides (PF ３ , P.F. ５ ), various phosphorus chlorides (PCl ３ , PCl ５ , P ２ Cl ４ ), various phosphorus bromides (PBr ３ , PBr ５ ), various phosphorus iodides (PI ３ , P ２ I ４ ) and the like; phosphorus halides such as thiophosphoryl fluoride (PSF ３ ), thiophosphoryl chloride (PSCl ３ ), thiophosphoryl bromide (PSBr ３), thiophosphoryl iodide (PSI ３ ), thiophosphoryl fluoride dichloride (PSCl ２ F), thiophosphoryl fluoride dibromide (PSBr ２ a source material consisting of at least two atoms selected from the above four types of atoms, such as thiophosphoryl halides, e.g., fluorine (F); ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Representative examples include simple halogen atoms such as

[0052] 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 also 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; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, and tin sulfide (SnS, SnS ２ metal sulfides such as aluminum sulfide and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium such as sodium halides such as sodium iodide, sodium fluoride, sodium chloride and sodium bromide; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides and bismuth halides; phosphorus oxychloride (POCl ３ ), phosphorus oxybromide (POBr ３ ) and the like; and the like.

[0053] Among the above, lithium sulfide, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２Preferred examples of the solid electrolyte raw materials include a halogen atom such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide, and a lithium halide such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. When oxygen atoms are introduced into the solid electrolyte, preferred examples of the solid electrolyte raw materials include a combination of lithium sulfide, phosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, phosphorus pentasulfide, and a halogen atom. Preferred examples of the lithium halide include lithium bromide and lithium chloride, and preferred examples of the halogen atom include bromine and chlorine.

[0054] In this embodiment, PS ４ Li containing structure ３ P.S. ４ can also be used as part of the raw material. ３ P.S. ４ This is prepared by manufacturing or the like and used as a raw material. ３ P.S. ４ The content is preferably 60 to 100 mol %, more preferably 65 to 90 mol %, and even more preferably 70 to 80 mol %.

[0055] The lithium sulfide used in this embodiment is preferably in the form of particles. ５０ ) is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.5 μm or more and 100 μm or less, and even more preferably 1 μm or more and 20 μm or less. 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 an 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.

[0056] 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, with the upper limit being 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 still more preferably 74 to 80 mol%. Furthermore, when attempting to obtain a sulfide solid electrolyte having a thiolicon region II type crystal structure, in addition to the above ranges, particularly 74 to 78.5 mol%, 74 to 78 mol%, and 74 to 76 mol% are preferred, and when attempting to obtain a sulfide solid electrolyte having an argyrodite type crystal structure, in addition to the above ranges, particularly 76 to 83 mol%, 77 to 80 mol%, and 78 to 80 mol% are preferred.

[0057] (Crusher) When obtaining a crushed product, the raw material content is crushed using a crusher. A crusher is literally a device used for crushing, but it can also stir and mix at the same time as crushing.

[0058] The grinder can be any grinder that can mix the solid electrolyte raw materials without any particular limitations, and for example, a media-type grinder that uses grinding media can be used.

[0059] Media-type mills are broadly classified into vessel-driven mills and media-agitated mills. Examples of vessel-driven mills include agitation tanks, grinding tanks, and combinations thereof, such as ball mills and bead mills. Examples of media-agitated mills include impact mills such as cutter mills, hammer mills, and pin mills; tower mills and other tower-type mills; agitation tank mills such as attritors, aquamizers, and sand grinders; flow-through tank mills such as Viscomill and pearl mills; flow-through pipe mills; annular mills such as Coball mills; continuous dynamic mills; and single- or multi-shaft kneaders. Considering the ease of adjusting the particle size of the resulting pulverized product, it is preferable to use ball mills and bead mills, which are exemplified as vessel-driven mills, and planetary mills are particularly preferred.

[0060] These pulverizers can be appropriately selected depending on the desired scale, etc. For relatively small scales, container-driven pulverizers such as ball mills and bead mills can be used, while for large scales or mass production, other types of pulverizers may be used.

[0061] The size of the beads and balls used in the ball mill and 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 and balls include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0062] When a ball mill or a bead mill is used, the rotation speed varies depending on the scale of the treatment and cannot be generalized, but is usually 10 rpm or more, preferably 20 rpm or more, more preferably 50 rpm or more, with the upper limit being 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. Furthermore, the milling time in this case varies depending on the scale of the treatment and cannot be generalized, but is usually 0.5 hours or more, preferably 1 hour or more, more preferably 2 hours or more, with the upper limit being 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.

[0063] The sulfide solid electrolyte may be prepared by mixing the raw material components 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, an aliphatic amine is preferred, and an aliphatic diamine is more preferred.

[0064] When a crystalline sulfide solid electrolyte is produced, heating may be further included. When an amorphous sulfide solid electrolyte (glass component) is obtained by the above mixing, a crystalline sulfide solid electrolyte can be obtained by heating, and when a crystalline sulfide solid electrolyte is obtained, a crystalline sulfide solid electrolyte with improved crystallinity can be obtained.

[0065] For example, when obtaining an amorphous sulfide solid electrolyte, 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. There is no particular restriction on the lower limit, but it may be set to about −40 ° C. or more, which is 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 can be obtained more efficiently and reliably.

[0066] 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.

[0067] 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, and the temperature is set to preferably 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 upper limit, but it may 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.

[0068] The heating temperature for obtaining a crystalline sulfide solid electrolyte cannot be generally specified because it varies depending on the composition and structure of the resulting crystalline sulfide solid electrolyte. However, it is usually preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher. There is no particular upper limit, but it is preferably 600°C or lower, more preferably 550°C or lower, and even more preferably 500°C or lower.

[0069] 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.

[0070] Heating is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum). 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 include methods using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, and a firing furnace. In addition, industrially, a horizontal dryer or a horizontal vibration fluidized dryer having a heating means and a feeding mechanism can also be used, and the method may be selected depending on the amount of heat to be processed.

[0071] (Mixing) Specifically, the sulfide solid electrolyte mixture of this embodiment can be produced by mixing the sulfide solid electrolyte and the electrolytic solution.

[0072] As the device for mixing the sulfide solid electrolyte and the electrolytic solution, the device used for mixing the solid electrolyte raw materials described above can be used, and it is preferable to use a pulverizer such as a ball mill, a bead mill, etc. The details of the pulverizer and pulverization 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.

[0073] (Electrolyte Solution) 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 electrolyte 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 electrolyte solution.

[0074] The number of moles of the lithium salt in 1 liter of the electrolyte solution (the 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.

[0075] 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 even more preferably 12.0 to 17.0 mass%.

[0076] Furthermore, the number of moles of lithium salt per mole of ionic liquid in the electrolyte solution (the above (C)) is preferably 0.15 to 1.00 moles, more preferably 0.20 to 0.95 moles, and particularly preferably 0.50 to 0.80 moles, from the viewpoint of the ionic conductivity of the resulting sulfide solid electrolyte mixture and the solubility of the lithium salt.

[0077] (Lithium Salt) As the lithium salt, any lithium salt that is typically used in the electrolyte of a lithium ion battery can be used. For example, a lithium salt having an anion of at least one selected from halide ions, tetrafluoroborate, hexafluorophosphate, and a salt represented by the following general formula (I) is preferably used, and a lithium salt having an anion represented by the following general formula (I) is more preferably used.

[0078] (In the formula, R １ and R ２ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.

[0079] (Ionic Liquid) As the ionic liquid, any ionic liquid that is typically used in the electrolyte of a lithium ion battery can be used. Specifically, the cation is preferably at least one 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):

[0080] (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.

[0081] In the general formula (II), R ３ and R ４ are each independently an unsubstituted alkyl or alkenyl group having 1 to 8 carbon atoms.

[0082] The ionic liquid preferably has an anion of at least one selected from the group consisting of halide ions, tetrafluoroborate, hexafluorophosphate, and those represented by the following general formula (III). (In the formula, R ６ and R ７ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.

[0083] 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. Here, the ionic conductivity in this specification is measured by the method described in the examples.

[0084] (Applications) The sulfide solid electrolyte mixture of this embodiment has good lithium ion conductivity and is therefore suitable for use in all-solid-state batteries and the like. When used in an all-solid-state battery, the sulfide solid electrolyte mixture of this embodiment may be used in the positive electrode layer, negative electrode layer, or electrolyte layer of the all-solid-state battery. When used in the positive electrode layer or negative electrode layer, it is preferably used as an electrode mixture containing the sulfide solid electrolyte mixture of this embodiment and an electrode active material. These layers can be produced by known methods.

[0085] 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 of a material that reacts with the solid electrolyte mixture, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used.

[0086] 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.

[0087] (Measurement of Powder XRD Diffraction) Powder X-ray diffraction (XRD) measurement was 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 leveled with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured under the following conditions without being exposed to air. Measurement device: D2 PHASER, manufactured by Bruker Corporation Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: focusing method Slit configuration: Soller slit 4°, divergence slit 1 mm Detector: semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scan speed: 0.02 deg, 0.4 sec / step

[0088] (Preparation of pellets) 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.

[0089] (Measurement of ionic conductivity) The circular pellet (diameter: 10 mm, cross-sectional area S: 0.785 cm) obtained by the above pellet preparation process was 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: 5 MHz to 100 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was 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

[0090] (Measurement of pellet density) 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 pellet production.

[0091] (Example 1) (1-1) Preparation of Raw Material Sulfide Solid Electrolyte In a glove box under a nitrogen atmosphere, each compound was crushed and mixed in a molar ratio of Li ２ S:P ２ S ５ The raw materials were weighed so that the ratio of LiBr:LiCl was 47.5:12.5:15.0:25.0, and the mixture was placed in a glass container and roughly mixed by shaking the container. The roughly mixed raw materials were dispersed in a mixed solvent of dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and dehydrated isobutyronitrile (manufactured by Kishida Chemical Co., Ltd.) under a nitrogen atmosphere to obtain a raw material mixture slurry of approximately 10% by mass. The raw material mixture slurry was mixed and pulverized using a bead mill (LMZ015, manufactured by 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 a raw material mixture.

[0092] (1-2) Heating (crystallization) step The raw material mixture obtained in (1-1) above was heated in an electric furnace (F-1 404-A, manufactured by Tokyo Glass Instruments Co., Ltd.) in a glove box under a nitrogen atmosphere. ２ O ３The raw material mixture was placed in a sagger (999-60S, manufactured by Tokyo Glass Instruments Co., Ltd.) and heated in an electric furnace at 410 to 430°C for at least one hour. The sagger was then removed from the electric furnace and slowly cooled to obtain an argyrodite-type solid electrolyte. X-ray diffraction (XRD) measurement of the obtained sulfide solid electrolyte revealed peaks at 2θ = 25.5 ± 1.0 deg and 29.9 ± 1.0 deg, etc., attributable to the argyrodite-type crystal structure.

[0093] (1-3) Microparticulation Step The obtained argyrodite-type solid electrolyte was dispersed in a mixed solvent of dehydrated toluene (manufactured by Fujifilm 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 pulverized 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 step was used.

[0094] (1-4) Mixing Step In a glove box under an inert gas atmosphere, 34 g of zirconia balls with a diameter of 5.0 mm were placed in a 45 mL zirconia container, and 1.70 g of the microparticulated argyrodite-type sulfide solid electrolyte obtained in (1-3) above and 0.30 g of an electrolyte solution having a mole number of lithium salt per liter of electrolyte solution ((A) above) of 1.0 mole were placed. Here, the electrolyte solution consisted of 13 mass% lithium bis(fluorosulfonyl)imide and 87 mass% 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide. Furthermore, the content of the electrolyte solution ((B) above) based on the total amount of the sulfide solid electrolyte mixture was 15.0 mass%.

[0095] The container was sealed, then removed from the glove box, placed on a small ball mill rotating stand, and mixed for 1 hour at 600 rpm. The container was then placed back in the glove box, and the zirconia balls were separated from the contents using a 300 μm SUS sieve to obtain a sulfide solid electrolyte mixture.

[0096] The obtained sulfide solid electrolyte mixture powder was used to prepare pellets, and the ionic conductivity was measured. The ionic conductivity was 3.8 mS / cm. The density of the obtained pellets was also measured. It was 1.90 g / cm. ３ It was.

[0097] 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 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.

[0098] The obtained sulfide solid electrolyte mixture powder was used to prepare pellets, and the ionic conductivity was measured. The ionic conductivity was 4.0 mS / cm. The density of the obtained pellets was measured and found to be 1.91 g / cm. ３ It was.

[0099] Example 3 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 liter of the electrolyte solution was 3.2 moles was used. Here, the electrolyte solution consisted of 37 mass % lithium bis(fluorosulfonyl)imide and 63 mass % 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide.

[0100] The obtained sulfide solid electrolyte mixture powder was used to prepare pellets, and the ionic conductivity was measured. The ionic conductivity was 3.7 mS / cm. The density of the obtained pellets was measured and found to be 1.94 g / cm. ３ It was.

[0101] Comparative Example 1 The particulate argyrodite-type sulfide solid electrolyte obtained in Example 1 (1-3) was used as it was to prepare pellets, and the ionic conductivity was measured. The ionic conductivity was 4.8 mS / cm. The density of the obtained pellets was measured and found to be 1.65 g / cm. ３ It was.

[0102] Comparative Example 2 Pellets were prepared in the same manner as in Example 1 (1-4), except that 1.80 g of a 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.

[0103] Comparative Example 3 Pellets were prepared in the same manner as in Example 1 (1-4), except that 1.70 g of a particulate 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.

[0104] 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 containing 1.0 moles of lithium salt per liter of electrolyte solution ((A) above) were mixed to obtain a sulfide solid electrolyte mixture. The electrolyte solution consisted of 13% by mass of lithium bis(fluorosulfonyl)imide and 87% by mass of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide. The content of the electrolyte solution ((B) above) based on the total mass of the sulfide solid electrolyte mixture was 10.0% by mass.

[0105]

[0106] 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, 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, pellets were produced using the sulfide solid electrolyte itself without using an electrolytic solution, and 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 containing no lithium salt was used as the electrolytic solution, had low ionic conductivity. Note that although the Reference Example is similar to Comparative Example 5 of Patent Document 2, the product of (A) and (B) was 10, making it 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 approximately 9.1% by volume). However, details such as whether the volume of the sulfide solid electrolyte is an apparent volume or what its density is were unknown, so for convenience, this Reference Example was provided in which the content of the electrolyte solution (above (B)) based on the total amount of the sulfide solid electrolyte mixture was 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 and the theoretical density of the solid electrolyte calculated from the composition ratio, and the density of the electrolyte solution, the result was 23.9% by volume, which was larger than the mass %. This calculation result was obtained because the theoretical density of the solid electrolyte was greater than the density of the electrolyte solution. That is, although the theoretical density of the solid electrolyte used in Comparative Example 5 of Patent Document 2 is uncertain, unless the theoretical density of the solid electrolyte is smaller than the density of the electrolytic solution, the value of (B) in Comparative Example 5 will be smaller than 9.1 mass %. Even when estimated from the densities of the raw materials used, it is unlikely that the theoretical density of the solid electrolyte will be smaller than the density of the electrolytic solution, and therefore it is reasonably presumed that the value of the product of (A) and (B) will be smaller than 10 in the above Reference Example.

[0107] The sulfide solid electrolyte mixture of this embodiment has good lithium ion conductivity and is easily densified when compressed. The sulfide solid electrolyte mixture of this embodiment is suitable for use in electrode composites and lithium ion batteries, particularly in lithium ion batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. A sulfide solid electrolyte mixture comprising a sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms, and an electrolyte solution containing a lithium salt and an ionic liquid, wherein 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 solution, and (B) the content (mass%) of the electrolyte solution based on the total amount of the sulfide solid electrolyte mixture.

2. The sulfide solid electrolyte mixture according to claim 1, wherein (A) is 0.5 to 5.0 moles.

3. The sulfide solid electrolyte mixture according to claim 1 or 2, wherein the (B) is 8.0 to 20.0 mass%.

4. The sulfide solid electrolyte mixture according to any one of claims 1 to 3, wherein the product of (A) and (B) is 12.5 to 70.

5. The sulfide solid electrolyte mixture according to any one of claims 1 to 3, wherein the product of (A) and (B) is 14 to 55.

6. The sulfide solid electrolyte mixture according to any one of claims 1 to 5, wherein the product of the following (C) and (B) is 2.5 or more: (C) the number of moles of lithium salt per mole of ionic liquid in the electrolyte solution:

7. The sulfide solid electrolyte mixture according to any one of claims 1 to 6, wherein the lithium salt is represented by the following general formula (I): (In the formula, R １ and R ２ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.

8. The sulfide solid electrolyte mixture according to any one of claims 1 to 7, wherein 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.

9. The sulfide solid electrolyte mixture according to claim 8, wherein the imidazolium cation is represented by the following general formula (II): (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.

10. In the general formula (II), R ３ and R ４ The sulfide solid electrolyte mixture according to claim 9, wherein each of the is independently an unsubstituted alkyl group or alkenyl group having 1 to 8 carbon atoms.

11. The sulfide solid electrolyte mixture according to any one of claims 1 to 10, wherein the anion of the ionic liquid is at least one selected from the group consisting of halide ions, tetrafluoroborate, hexafluorophosphate, and those represented by the following general formula (III): (In the formula, R ６ and R ７ are each independently a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms.

12. The sulfide solid electrolyte mixture according to claim 11, wherein the anion of the ionic liquid is represented by the general formula (III).

13. The sulfide solid electrolyte mixture according to any one of claims 1 to 12, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

14. An all-solid-state battery comprising a solid electrolyte layer comprising the sulfide solid electrolyte mixture according to any one of claims 1 to 13.

15. An electrode mixture comprising the sulfide solid electrolyte mixture according to any one of claims 1 to 13 and an electrode active material.

16. An all-solid-state battery comprising an electrode mixture layer comprising the electrode mixture according to claim 15.

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