Sulfide solid electrolyte and method for producing sulfide solid electrolyte

Abstract

The present invention relates to a sulfide solid electrolyte which has a crystal phase, wherein: the crystal phase has at least an argyrodite-type crystal structure; the argyrodite-type crystal structure has a crystal system of a cubic crystal and at least one selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal; and the total ratio of the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal in the crystal phase is 1-50 mass%.

Description

Sulfide solid electrolyte and method for producing sulfide solid electrolyte

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

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers. Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but all-solid-state lithium-ion batteries using solid electrolytes have attracted attention due to their potential for improved safety and high-speed charging and discharging.

[0003] Solid electrolytes are broadly classified into sulfide solid electrolytes and oxide solid electrolytes. Among them, sulfide ions constituting sulfide solid electrolytes have higher polarizability and exhibit higher ionic conductivity than oxide ions constituting oxide solid electrolytes.

[0004] As a sulfide solid electrolyte, Li １０ GeP ２ S １２ LGPS type crystals such as Li ６ P.S. ５ Argyrodite-type crystals such as Cl, Li ７ P ３ S １１ LPS crystallized glass and the like are known.

[0005] On the other hand, sulfide solid electrolytes are known to have poor water resistance because they react with water to generate hydrogen sulfide, and sulfide solid electrolytes with an argyrodite-type crystal phase are no exception.

[0006] In contrast, Patent Document 1 discloses that a solid electrolyte having excellent water resistance can be obtained by mixing a sulfide having an argyrodite-type crystal structure and phosphorus sulfide in the presence of at least one solvent selected from a nonpolar solvent and an aprotic solvent.

[0007] Japanese Patent Application Publication No. 2021-163758

[0008] However, there are concerns that the solid electrolyte obtained by Patent Document 1 may have reduced battery performance due to contamination with organic substances. In addition, there are concerns that the method described in Patent Document 1 may increase costs due to an increase in the number of steps.

[0009] Therefore, an object of the present invention is to provide an argyrodite-type sulfide solid electrolyte that has excellent water resistance while maintaining high ionic conductivity, and to provide a method for producing such a sulfide solid electrolyte.

[0010] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using an argyrodite-type sulfide solid electrolyte that also contains crystal systems other than cubic. The crystal system known as the argyrodite-type crystal structure is a cubic crystal. Although the existence of crystal systems other than cubic has been suggested, there have been no reports that such systems have actually been obtained.

[0011] In contrast, the present invention realizes crystal systems other than cubic, such as tetragonal, orthorhombic, and monoclinic, as the argyrodite-type crystal structure. By including these other crystal systems together with the cubic crystal, it is possible to achieve both high ionic conductivity and excellent water resistance in the sulfide solid electrolyte, leading to the completion of the present invention.

[0012] That is, the present invention relates to the following items [1] to

[15] : [1] A sulfide solid electrolyte having a crystalline phase, wherein the crystalline phase has at least an argyrodite-type crystal structure, the argyrodite-type crystal structure has a crystal system of a cubic crystal and at least one crystal selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal, and the proportion of the total of the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal to the total of the cubic crystal, the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal is 1 to 50 mass%. [2] The sulfide solid electrolyte according to [1], which exhibits diffraction peaks at three or more of 2θ=15.5°±0.5°, 17.9°±0.5°, 25.45°±0.5°, 29.9°±0.5°, 31.3°±0.5°, and 44.8°±0.5° in a powder X-ray diffraction pattern using Cu-Kα radiation. [3] The sulfide solid electrolyte according to [1] or [2], wherein the argyrodite-type crystal structure contains S as a constituent element. [4] The sulfide solid electrolyte according to [3], wherein the argyrodite-type crystal structure contains Ha as a constituent element, and the Ha is at least one element selected from the group consisting of F, Cl, Br, and I. [5] The sulfide solid electrolyte according to [3], wherein the argyrodite-type crystal structure contains Li ａ MZ ｂ Ha ｃIn the composition formula, M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the crystal structure, Z is at least one element selected from elements present as divalent anions in the crystal structure, Z includes S, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I, and in the composition formula, a represents a composition ratio of Li, b represents a composition ratio of Z, and c represents a composition ratio of Ha, respectively, and the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2 are satisfied. [6] The sulfide solid electrolyte according to [5], wherein the element present as a divalent to pentavalent cation in the composition formula is at least one selected from the group consisting of B (boron), Mg (magnesium), Al (aluminum), Si (silicon), P (phosphorus), Ca (calcium), Ti (titanium), V (vanadium), Fe (iron), Zn (zinc), Ga (gallium), Sr (strontium), Y (yttrium), Zr (zirconium), Nb (niobium), Mo (molybdenum), Sn (tin), Sb (antimony), Ba (barium), Ta (tantalum), W (tungsten), and Bi (bismuth). [7] The sulfide solid electrolyte according to [5] or [6], wherein the composition formula contains P as M. [8] The sulfide solid electrolyte according to [7], wherein the content ratio of P relative to the total content of M in the composition formula is 60 to 100 atoms%. [9] The sulfide solid electrolyte according to any one of [5] to [8], wherein the element present as the divalent anion in the composition formula is at least one selected from the group consisting of S (sulfur), O (oxygen), Se (selenium), and Te (tellurium).

[10] The sulfide solid electrolyte according to any one of [5] to [9], wherein the content of S relative to the total of Z in the composition formula is 60 to 100 atoms%.

[11] The sulfide solid electrolyte according to any one of [5] to

[10] , wherein the composition ratio of S as Z in the composition formula is 1 to 6.

[12] The sulfide solid electrolyte according to any one of [1] to

[11] , wherein the content ratio of the argyrodite-type crystal structure in the sulfide solid electrolyte is 51 mass% or more.

[13] The sulfide solid electrolyte according to any one of [1] to

[12] , wherein the amount of S in the composition of the argyrodite-type crystal structure is 0.5 to 3.5% in excess of the amount of S that constitutes a stoichiometric ratio.

[0013]

[14] A method for producing a sulfide solid electrolyte having a crystalline phase, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; heating the sulfide solid electrolyte raw material to obtain a melt; supplying 100 parts by mass of the sulfide solid electrolyte raw material or 7 to 24 parts by mass of a sulfur source relative to 100 parts by mass of the melt; and then cooling the melt to precipitate crystals to obtain a solid, wherein the precipitated crystals have at least an argyrodite-type crystal structure containing S as a constituent element.

[15] The method for producing a sulfide solid electrolyte according to

[14] , wherein the argyrodite-type crystal structure has a crystal system of a cubic crystal and at least one crystal selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal, and wherein the proportion of the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal to the total of the cubic crystal, the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal is 1 to 50% by mass.

[0014] According to the present invention, an argyrodite-type sulfide solid electrolyte that maintains high ionic conductivity and also has excellent water resistance can be obtained.

[0015] FIG. 1 is a flow diagram showing one aspect of a method for producing a sulfide solid electrolyte according to this embodiment. FIG. 2 is a flow diagram showing one aspect of a method for producing a sulfide solid electrolyte according to this embodiment. FIG. 3 is a flow diagram showing one aspect of a method for producing a sulfide solid electrolyte according to this embodiment. FIG. 4 shows XRD patterns of the sulfide solid electrolyte of Example 3, where FIG. 4(a) is the XRD pattern from 2θ = 10 to 100° and FIG. 4(b) is an enlarged XRD pattern of FIG. 4(a) at 2θ = 15 to 35°. FIG. 5 is an XRD pattern of the sulfide solid electrolyte of Example 5, where FIG. 5(a) is the XRD pattern from 2θ = 10 to 100° and FIG. 5(b) is an enlarged XRD pattern of FIG. 4(a) at 2θ = 15 to 35°.

[0016] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired without departing from the gist of the present invention. Furthermore, the term "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the lower and upper limits. In this specification, mass % and weight %, parts by mass and parts by weight, and ppm by mass and ppm by weight are synonymous.

[0017] <<Sulfide Solid Electrolyte>> The sulfide solid electrolyte according to this embodiment has a crystalline phase. The crystalline phase has at least an argyrodite-type crystal structure, and the argyrodite-type crystal structure has a crystal system of a cubic crystal and at least one crystal selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal. In the crystalline phase, the proportion of the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal to the total of the cubic crystal, the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal is 1 to 50 mass%.

[0018] The present inventors believed that water resistance could be improved by introducing a less symmetrical crystal system into the conventional cubic argyrodite-type sulfide solid electrolyte. As a result of extensive research, they succeeded in obtaining, for the first time, a sulfide solid electrolyte having an argyrodite-type crystal structure that has, in addition to a cubic crystal, at least one crystal system selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal.

[0019] The symmetry of the above crystal systems decreases in the order of cubic, tetragonal, orthorhombic, and monoclinic, but from the viewpoint of ionic conductivity, a higher symmetry is better, while from the viewpoint of water resistance, a lower symmetry is better, and it is difficult to achieve both. However, the inventors have conceived that by setting the ratio of the total of the tetragonal, orthorhombic, and monoclinic crystals to the total of the cubic, tetragonal, orthorhombic, and monoclinic crystals in the crystalline phase to be in the range of 1 to 50 mass%, it is possible to achieve excellent water resistance while maintaining high ionic conductivity.

[0020] We have found that sulfide solid electrolytes with the above characteristics can be obtained by, for example, using a melt-quenching method in which a sulfide solid electrolyte raw material is heated and melted, then cooled to precipitate crystals, by reducing the supply amount of sulfur source compared to conventional methods and controlling it within an appropriate range. Furthermore, we have found that if an argyrodite-type sulfide solid electrolyte having multiple crystal systems is obtained and then further heat-treated, it undergoes a phase change to a more highly symmetrical crystal system, such as monoclinic to orthorhombic, orthorhombic to tetragonal, or tetragonal to cubic, respectively. Therefore, the proportion of each crystal system can be controlled by appropriately changing the heat-treatment conditions.

[0021] <Composition> In this embodiment, the argyrodite-type crystal structure has the composition formula Ag ８ GeS ６ This is a crystalline structure possessed by a group of compounds derived from minerals represented by the formula: When the sulfide solid electrolyte is used in a lithium ion battery, the argyrodite-type crystalline structure preferably contains Li (lithium) as a constituent element. When used in a sodium ion battery or a potassium ion battery, it preferably contains Na (sodium) or K (potassium) as a constituent element. Note that the above does not in any way exclude the inclusion of Na or K as a constituent element when the sulfide solid electrolyte is used in a lithium ion battery.

[0022] The argyrodite-type crystal structure of this embodiment preferably contains, as the element group M, at least one element selected from the group consisting of Na, K, and elements present as divalent to pentavalent cations in the crystal structure. Among these, elements present as divalent to pentavalent cations include, for example, B (boron), Mg (magnesium), Al (aluminum), Si (silicon), P (phosphorus), Ca (calcium), Ti (titanium), V (vanadium), Fe (iron), Zn (zinc), Ga (gallium), Sr (strontium), Y (yttrium), Zr (zirconium), Nb (niobium), Mo (molybdenum), Sn (tin), Sb (antimony), Ba (barium), Ta (tantalum), W (tungsten), and Bi (bismuth). These elements present as divalent to pentavalent cations may contain one type or two or more types.

[0023] From the viewpoint of the oxidation-reduction potential of the element, it is preferable that the element group M contains P, and it is preferable that it mainly contains P. In this specification, "mainly contains" means that, in the case of P, the content ratio of P with respect to the total content of the element group M is 60 atoms% (at%) or more, and the content ratio may be 60 to 100 at%. Furthermore, the content ratio may be 60 at% or more, 70 at% or more, or 80 at% or more. The upper limit of the content ratio is not particularly limited, and may be 100 at%, but may also be 98 at% or less, 97 at% or less, or 95 at% or less.

[0024] When the element group M contains an element other than P, for example, at least one element selected from the group consisting of Na, K, Mg, and Ca may be contained. These are elements that may be contained as impurities in the sulfide solid electrolyte raw material. Note that the above does not in any way exclude intentional inclusion of elements other than P or inclusion of large amounts of elements other than P.

[0025] The argyrodite-type crystal structure of this embodiment preferably contains, as element group Z, at least one element selected from the group consisting of elements that exist as divalent anions in the crystal structure. For example, it is more preferable to contain at least one element selected from the group consisting of S (sulfur), O (oxygen), Se (selenium), and Te (tellurium).

[0026] From the viewpoint of lithium ion conductivity, the element group Z preferably contains S (sulfur), and preferably contains S as the main component. The content ratio of S with respect to the total of the element group Z is preferably 60 to 100 at%. Here, the content ratio may be 60 at% or more, 70 at% or more, or 80 at% or more. Furthermore, the upper limit of the content ratio is not particularly limited, and may be 100 at%, but may also be 98 at% or less, 97 at% or less, 95 at% or less, or 90 at% or less.

[0027] In addition, when S is included as the element group Z, a part of S may be Ha or BH in addition to the above-mentioned O, Se, and Te. ４ , CN, etc.

[0028] The argyrodite-type crystal structure is a PS crystal structure containing P as the element group M and S as the element group Z, which have a tetrahedral structure. ４ ３－ It is preferable to take the following formula: ４ In some of the tetrahedra, P may be substituted with other elements, or one or more of the four S may be substituted with other elements. Also, all tetrahedral structures do not have to have the same configuration.

[0029] The argyrodite-type crystal structure in this embodiment preferably contains Ha as a constituent element. Here, Ha is at least one element selected from the group consisting of F, Cl, Br, and I. From the viewpoint of ease of forming the argyrodite-type crystal structure, the Ha preferably contains at least one of Cl and Br, more preferably contains Br, and even more preferably contains Cl. Furthermore, from the viewpoint of further improving lithium ion conductivity, the Ha is more preferably a mixture of Cl and Br.

[0030] That is, a preferred embodiment of the argyrodite-type crystal structure in this embodiment is Li ａ MZ ｂ Ha ｃ In the composition formula, M is at least one element selected from Na, K, and elements that exist as divalent to pentavalent cations in the crystal structure, Z is at least one element selected from elements that exist as divalent anions in the crystal structure, and Ha is at least one element selected from the group consisting of F, Cl, Br, and I. Here, M corresponds to the element group M, and Z corresponds to the element group Z. That is, it is preferable that M contains P, and it is also preferable that Z contains S, and it is more preferable that M contains P and Z contains S.

[0031] In the above composition formula, a represents the composition ratio of Li, b represents the composition ratio of Z, and c represents the composition ratio of Ha. Here, it is preferable that one or more of the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2 are satisfied, more preferably two or more of the relationships are satisfied, and even more preferably all three relationships are satisfied.

[0032] The composition ratios of a to c in the above composition formula more preferably satisfy the relationships of 5<a<7, 4<b<6, and 1<c<2, even more preferably satisfy the relationships of 5.1<a<6.3, 4<b<5.3, and 1.4≦c≦1.9, and even more preferably satisfy the relationships of 5.2<a<6.2, 4.1<b<5.2, and 1.5≦c≦1.8.

[0033] That is, a is preferably 5 or more, more preferably greater than 5, even more preferably greater than 5.1, even more preferably greater than 5.2, and preferably 7 or less, more preferably less than 7, even more preferably less than 6.3, and even more preferably less than 6.2. b is preferably 4 or more, more preferably greater than 4, even more preferably greater than 4.1, and preferably 6 or less, more preferably less than 6, even more preferably less than 5.3, and even more preferably less than 5.2. c is preferably greater than 1, more preferably 1.3 or more, even more preferably 1.4 or more, even more preferably 1.5 or more, and preferably 2 or less, more preferably less than 2, even more preferably 1.9 or less, and even more preferably 1.8 or less.

[0034] Composition formula Li ａ MZ ｂ Ha ｃ In the formula, b, which indicates the composition ratio of Z, is preferably 4 or more, and preferably 6 or less, as described above. This composition ratio is a composition ratio including S. That is, when Z is composed of S and one or more other elements, it is preferable that the total composition ratio of these elements is within the above range. Furthermore, when Z is composed of S and one or more other elements, the composition ratio of S is preferably 1 to 6. Specifically, it is preferably 1 or more, more preferably 2 or more, more preferably 3 or more, and more preferably 4 or more, and is preferably 6 or less, and more preferably less than 6. When Z is composed only of S, the composition ratio of S is the same as the above preferred range of b.

[0035] <Crystalline Phase> The crystal phase in this embodiment has an argyrodite-type crystal structure. Conventionally, only a cubic crystal has been obtained as an argyrodite-type crystal structure. Although the existence of other crystal systems has been suggested, no examples have actually been obtained. In contrast, the argyrodite-type crystal structure in this embodiment has a cubic crystal system and at least one crystal system selected from the group consisting of a tetragonal crystal system, an orthorhombic crystal system, and a monoclinic crystal system.

[0036] Examples of cubic crystals include space group P-43m (No. 215) and space group F-43m (No. 216). Examples of tetragonal crystals include space group P-42m (No. 111). Examples of orthorhombic crystals include space group Cmm2 (No. 35). Examples of monoclinic crystals include space group Cm (No. 8). However, none of these are limited to the above space groups.

[0037] The argyrodite-type crystal structure of this embodiment may further have other crystal systems in addition to those described above. Examples of other crystal systems include trigonal crystals. Examples of trigonal crystals include space group R3m (No. 160).

[0038] In the powder X-ray diffraction (XRD) pattern using Cu-Kα radiation (λ=1.5418 Å), the sulfide solid electrolyte according to this embodiment preferably exhibits diffraction peaks at three or more of 2θ=15.5°±0.5°, 17.9°±0.5°, 25.45°±0.5°, 29.9°±0.5°, 31.3°±0.5°, and 44.8°±0.5°, more preferably at four or more positions, and even more preferably at all six positions. All of the above correspond to diffraction peaks of a cubic argyrodite crystal.

[0039] In the sulfide solid electrolyte according to this embodiment, in an XRD pattern using Cu-Kα radiation, diffraction peaks are preferably shown at 5 or more of 2θ = 15.6° ± 0.5°, 17.9° ± 0.5°, 17.95° ± 0.5°, 25.45° ± 0.5°, 25.5° ± 0.5°, 29.9° ± 0.5°, 30.0° ± 0.5°, 31.35° ± 0.5°, 44.8° ± 0.5°, and 44.9° ± 0.5°, more preferably at 7 or more positions, and even more preferably at all 10 positions. All of the above correspond to diffraction peaks of a tetragonal argyrodite type.

[0040] In the sulfide solid electrolyte according to this embodiment, in an XRD pattern using Cu-Kα radiation, diffraction peaks are preferably shown at 5 or more of 2θ = 15.3 ° ± 0.5 °, 15.5 ° ± 0.5 °, 17.75 ° ± 0.5 °, 17.9 ° ± 0.5 °, 25.3 ° ± 0.5 °, 25.4 ° ± 0.5 °, 25.65 ° ± 0.5 °, 29.75 ° ± 0.5 °, 29.85 ° ± 0.5 °, 30.1 ° ± 0.5 °, 31.2 ° ± 0.5 °, 31.5 ° ± 0.5 °, 44.8 ° ± 0.5 °, and 45.0 ° ± 0.5 °, more preferably at 9 or more positions, and even more preferably at all 14 positions. All of the above correspond to diffraction peaks of an orthorhombic argyrodite crystal.

[0041] In the sulfide solid electrolyte according to this embodiment, in an XRD pattern using Cu-Kα radiation, diffraction peaks are preferably shown at 5 or more of 2θ = 15.3 ° ± 0.5 °, 15.6 ° ± 0.5 °, 17.85 ° ± 0.5 °, 25.05 ° ± 0.5 °, 25.35 ° ± 0.5 °, 25.7 ° ± 0.5 °, 29.75 ° ± 0.5 °, 29.85 ° ± 0.5 °, 29.9 ° ± 0.5 °, 30.05 ° ± 0.5 °, 30.9 ° ± 0.5 °, 31.4 ° ± 0.5 °, 44.9 ° ± 0.5 °, and 45.1 ° ± 0.5 °, more preferably at 9 or more positions, and more preferably at all 14 positions. All of the above correspond to monoclinic argyrodite-type diffraction peaks.

[0042] Although the diffraction peaks of the above crystal systems partially overlap, by performing XRD measurement and Rietveld analysis of the obtained XRD pattern under the following conditions, the peaks representing each crystal system can be separated, and the argyrodite-type crystal structure constituting the sulfide solid electrolyte can be distinguished for each crystal system.

[0043] The XRD measurement is carried out under the following conditions: radiation source: CuKα radiation (λ=1.5418 Å), tube voltage: 45 kV, tube current: 200 mA, scan angle: 10 to 120°, scan speed: 5° / min, number of steps: 0.01° / step.

[0044] Crystal structure refinement by Rietveld analysis is carried out using the program RIETAN-FP.

[0045] Toraya's extended Pseudo-Voigt function is used as the profile function, and fitting is performed so that the reliability factor Rwp (R-weighted pattern), a general guideline, is less than 10% for the entire analysis range. The analysis range is 2θ = 10 to 120°, and the optimized parameters are the background parameter, mass fraction, profile parameter, and lattice constant. Structural parameters (only atomic displacement parameters are optimized), zero-point shift parameter, and preferred orientation parameter are fixed at their initial values ​​and are not optimized. Refinement of each atomic coordinate is performed according to the space group of each phase.

[0046] The mass fraction of each phase (quantitative determination of the crystalline and amorphous phases) is determined as follows after the XRD pattern is refined by the Rietveld method. Since the crystalline concentration of 10% by mass of Si mixed as an internal standard always exceeds 10% by mass, the mass fraction of each phase is calculated by correcting the concentration of the lithium-containing argyrodite-type sulfide solid electrolyte so that the crystalline Si concentration is 10% by mass. The mass fraction of the amorphous phase is calculated by subtracting the sum of these concentrations from 100% by mass.

[0047] The initial structures for crystal structure refinement are argyrodite crystals of cubic, tetragonal, orthorhombic, and monoclinic structures, Si crystals, and LiX (X = Cl, Br). For argyrodite crystals of tetragonal, orthorhombic, and monoclinic structures other than the cubic structure, symmetry operations are performed in accordance with the determinants of the transformation matrix described in Reference 1 below, and the axes are further standardized to refine the crystal structure. (Reference 1: Th. Hahn, International Tables for Crystallography, Volume A: Space-Group Symmetry, first online ed., 2006, Wiley, ISBN: 978-0-7923-6590-7)

[0048] The determinant of the transformation matrix is ​​as follows:

[0049]

[0050] The above can be realized when crystals having an argyrodite-type crystal structure are precipitated by the manufacturing method described below.

[0051] The content (crystallinity) of the crystalline phase in the sulfide solid electrolyte according to this embodiment is preferably 50% by mass or more, and preferably 50 to 100% by mass. From the viewpoint of ensuring ionic conductivity, the content is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. On the other hand, the content may be 100% by mass, i.e., the solid electrolyte may consist of only the crystalline phase. However, from the viewpoint of obtaining the effect of expanding the elastic deformation region due to the presence of the amorphous phase, the content is preferably 99% by mass or less, and more preferably 95% by mass or less.

[0052] The content of the argyrodite-type crystal structure in the sulfide solid electrolyte according to this embodiment is preferably 51% by mass or more, and preferably 70 to 100% by mass. From the viewpoint of ensuring ionic conductivity, the content is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. On the other hand, the content may be 100% by mass, i.e., the sulfide solid electrolyte may be composed solely of argyrodite-type crystals. However, from the viewpoint of obtaining the effect of expanding the elastic deformation region due to the presence of an amorphous phase and from the possibility of containing other crystalline phases derived from the raw materials, the content may be 99% by mass or less, 95% by mass or less, or 90% by mass or less.

[0053] In this embodiment, the proportion of the crystalline phase having an argyrodite-type crystal structure relative to the total crystalline phase is preferably 51% by mass or more, and more preferably 70 to 100% by mass. Here, the proportion is more preferably 80% by mass or more, and the higher the better. Examples of crystalline phases that may be present other than the argyrodite-type crystal structure include LiHa (lithium halide) derived from the raw materials.

[0054] In the crystalline phase having an argyrodite-type crystal structure in this embodiment, the total proportion of tetragonal, orthorhombic, and monoclinic crystals relative to the total of cubic, tetragonal, orthorhombic, and monoclinic crystals is preferably 1 to 50 mass%. That is, the proportion of cubic crystals relative to the total of cubic, tetragonal, orthorhombic, and monoclinic crystals is preferably 50 to 99 mass%. From the viewpoint of water resistance, the total proportion of tetragonal, orthorhombic, and monoclinic crystals is preferably 1 mass% or more, more preferably 5 mass% or more, and even more preferably 10 mass% or more, with a higher proportion being preferable. On the other hand, from the viewpoint of ionic conductivity, it is preferably 50 mass% or less, more preferably 45 mass% or less, and even more preferably 40 mass% or less, with a lower proportion being preferable.

[0055] The proportions of the tetragonal, orthorhombic, monoclinic and trigonal crystals relative to the total can be determined taking into consideration the symmetry of the crystal system.

[0056] Furthermore, as mentioned above, if an argyrodite-type sulfide solid electrolyte having multiple crystal systems is obtained and then further heat-treated, the phase changes stepwise to a more symmetrical crystal system, such as monoclinic to orthorhombic, orthorhombic to tetragonal, and tetragonal to cubic. Therefore, the respective proportions of tetragonal, orthorhombic, and monoclinic tend to be tetragonal ≧ orthorhombic ≧ monoclinic.

[0057] The lattice constant of the argyrodite-type crystal structure in this embodiment is preferably 9.70 to 10.50 Å, more preferably 9.70 to 10.45 Å, even more preferably 9.70 to 10.40 Å, even more preferably 9.75 to 10.30 Å, and particularly preferably 9.75 to 10.20 Å. Here, from the viewpoint of maintaining high lithium ion conductivity, the lattice constant is preferably 9.70 Å or more, and more preferably 9.75 Å or more. From the same viewpoint, the lattice constant is preferably 10.50 Å or less, more preferably 10.45 Å or less, even more preferably 10.40 Å or less, even more preferably 10.30 Å or less, and particularly preferably 10.20 Å or less.

[0058] In this embodiment, the crystallite diameter of the argyrodite-type crystal structure is preferably 100 to 3000 Å. Here, from the viewpoint of ionic conductivity, the crystallite diameter is preferably 100 Å or more, more preferably 200 Å or more, and even more preferably 300 Å or more. Furthermore, considering that the crystallite diameter inevitably becomes smaller as the particle size becomes finer, from the viewpoint of achieving the desired particle size D50 and BET specific surface area for the sulfide solid electrolyte, the crystallite diameter is preferably 3000 Å or less, more preferably 2500 Å or less, and even more preferably 2000 Å or less. Note that the crystallite diameter in this specification is a value determined together with the strain value when the XRD pattern of the sulfide solid electrolyte powder is analyzed using the Williamson-Hall method.

[0059] <Applications> The sulfide solid electrolyte according to this embodiment is suitable for use in electrode mixtures and solid electrolyte layers used in lithium ion secondary batteries, and is particularly suitable for all-solid-state lithium secondary batteries. That is, the electrode mixture is used in lithium ion secondary batteries and contains the solid electrolyte and an active material. The solid electrolyte layer is used in lithium ion secondary batteries and contains the solid electrolyte. The all-solid-state lithium secondary battery contains the solid electrolyte.

[0060] The electrode mixture, the solid electrolyte layer, and the all-solid-state lithium secondary battery may further contain another solid electrolyte. The other solid electrolyte is not particularly limited, and examples thereof include Li ３ P.S. ４ , Li ４ P ２ S ６ , Li ７ P ３ S １１ Solid electrolytes called LPS systems, such as Li １０ GeP ２ S １２ Solid electrolytes called LGPS-based electrolytes such as those described above, thiolisicone-type solid electrolytes, oxide-containing solid electrolytes, Li ２ S, LiHa, etc.

[0061] The active material contained in the electrode mixture may be a conventionally known material. For example, the positive electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions, intercalate and deintercalate lithium ions, or dope and dedope counter anions of the lithium ions. Specific examples include lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, composite metal oxides, and polyanion olivine-type positive electrodes.

[0062] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions, desorb and insert (intercalate) lithium ions, or dope and dedope counter anions of the lithium ions. Specific examples include lithium metal, carbonaceous materials such as graphite, hard carbon, and soft carbon, metals capable of forming alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0063] The solid electrolyte layer may contain the sulfide solid electrolyte according to the present embodiment, but may also contain other additives such as a binder. Conventionally known binders can be used, including butadiene rubber, acrylate butadiene rubber, styrene butadiene rubber, polyvinylidene fluoride, and polytetrafluoroethylene. The binder content in the solid electrolyte layer may also be within a conventionally known range.

[0064] The all-solid-state lithium secondary battery is not particularly limited as long as it includes a positive electrode and a negative electrode in addition to the sulfide solid electrolyte according to this embodiment. The positive electrode and the negative electrode may be an electrode mixture containing the sulfide solid electrolyte according to this embodiment. The positive electrode active material may be the same as the positive electrode active material described in the electrode mixture, and the positive electrode may further include a positive electrode current collector, a binder, a conductive additive, and the like, as necessary. The positive electrode current collector may be made of aluminum, an alloy thereof, a thin metal plate such as stainless steel, or the like.

[0065] The negative electrode active material can be the same as the negative electrode active material described in the electrode mixture, and the negative electrode may further contain, as necessary, a negative electrode current collector, a binder, a conductive additive, etc. The negative electrode current collector can be a thin metal plate such as copper or aluminum.

[0066] <<Method for Producing Sulfide Solid Electrolyte>> The method for producing a sulfide solid electrolyte according to this embodiment is not particularly limited as long as the argyrodite-type crystal structure of the crystalline phase has at least one crystal system selected from the group consisting of cubic, tetragonal, orthorhombic, and monoclinic. In particular, it is preferable to obtain the sulfide solid electrolyte described in the above <<Sulfide Solid Electrolyte>>. The preferred aspects of the produced sulfide solid electrolyte are the same as those described in the above <<Sulfide Solid Electrolyte>>. For example, the argyrodite-type crystal structure preferably contains S as a constituent element, more preferably P and S as constituent elements, and even more preferably P, S, and Ha as constituent elements. Here, Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

[0067] The method for producing the sulfide solid electrolyte according to this embodiment may be, but is not limited to, the melt quenching method described above, a solid-phase synthesis method such as mechanical milling, or a liquid-phase synthesis method. In any of these methods, sulfur volatilizes from the sulfide solid electrolyte raw material prepared based on the stoichiometric ratio due to heat during the production process. Furthermore, in the liquid-phase synthesis method, in addition to the volatilization of sulfur due to heat, sulfur leakage into the solvent is also considered. In contrast, in the method for producing the sulfide solid electrolyte according to this embodiment, it has been found that by reducing the amount of sulfur source supplied to compensate for the volatilized or leaked sulfur compared to conventional methods, crystals having an argyrodite-type crystal structure that also has a crystal system other than a cubic crystal can be obtained.

[0068] Although the reason for this is unclear, if the amount of sulfur source added is sufficiently in excess of the stoichiometric ratio, only highly symmetric and stable cubic crystals are precipitated. However, if the amount added is slightly in excess, it has the effect of making it easier to obtain a crystalline system with low symmetry, and as a result, it becomes easier to obtain crystals in which cubic crystals coexist with tetragonal crystals, orthorhombic crystals, and monoclinic crystals.

[0069] The method for producing the sulfide solid electrolyte according to this embodiment is preferably a melt-quenching method from the viewpoint of obtaining the desired sulfide solid electrolyte in a shorter time.

[0070] Among the methods for producing a sulfide solid electrolyte according to this embodiment, one aspect of the melt quenching method includes the following steps: Step 1: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; Step 2: heating the sulfide solid electrolyte raw material to obtain a melt; Step 3: supplying 7 to 24 parts by mass of a sulfur source to 100 parts by mass of the sulfide solid electrolyte raw material obtained in Step 1 or 100 parts by mass of the melt obtained in Step 2; Step 4: subsequently cooling the melt to precipitate crystals and obtain a solid. The crystals precipitated in Step 4 have at least an argyrodite-type crystal structure containing S as a constituent element. Furthermore, the argyrodite-type crystal structure has a crystal system consisting of a cubic crystal and at least one crystal system selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal. The solid obtained in Step 4 functions as an electrolyte and can therefore be used as the sulfide solid electrolyte according to this embodiment.

[0071] Furthermore, the method may further include the following step 5 after step 4. Step 5: a step of performing a post-heat treatment after step 4 When step 5 is further carried out, it is sufficient that the obtained crystal has at least an argyrodite-type crystal structure containing S as a constituent element, and the argyrodite-type crystal structure has a crystal system of a cubic crystal and at least one crystal selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal. When step 5 is carried out, the solid obtained in step 5 can be the sulfide solid electrolyte of this embodiment.

[0072] <First Aspect and Second Aspect> A first aspect, which is one aspect of the production method according to the present embodiment, will be described. In the first aspect of the present embodiment, as shown in Fig. 1 , a sulfur source is supplied to a sulfide solid electrolyte raw material based on a stoichiometric ratio in step S1 (steps 1 and 3). Next, in step S2, the sulfide solid electrolyte raw material, to which the sulfur source has been supplied and which has become in a sulfur-excess state, is heated to obtain a melt (step 2). Then, in step S3, the obtained melt is cooled to precipitate crystals, thereby obtaining a solid (sulfide solid electrolyte) (step 4).

[0073] A second aspect, which is one aspect of the production method according to this embodiment, will be described. In the second aspect of this embodiment, as shown in FIG. 2 , in step S′1, a sulfide solid electrolyte raw material is heated based on a stoichiometric ratio to obtain a melt A (steps 1 and 2). Next, in step S′2, a sulfur source is supplied to the melt A to obtain a melt B in which sulfur is in an excess state (step 3). Then, in step S′3, the obtained melt B is cooled to precipitate crystals, thereby obtaining a solid (sulfide solid electrolyte) (step 4).

[0074] In either the first embodiment or the second embodiment, the solid obtained in step S3 or step S'3, which is step 4, may be further subjected to a post-heat treatment to obtain a sulfide solid electrolyte. Specifically, as shown in Fig. 3, the solid obtained in step 4 may be pulverized as desired in step S4, and then subjected to a post-heat treatment in step S5 to obtain a sulfide solid electrolyte.

[0075] This will be explained in detail below.

[0076] <Sulfide Solid Electrolyte Raw Material> The sulfide solid electrolyte raw material in this embodiment is based on a stoichiometric ratio. That is, the sulfide solid electrolyte raw material is a mixture of raw materials in a predetermined stoichiometric ratio according to the composition of the target sulfide solid electrolyte.

[0077] The sulfide solid electrolyte raw material in this embodiment may be a commercially available product or a manufactured product. In addition, before being used as a sulfide solid electrolyte raw material, known pretreatment may be appropriately performed.

[0078] Next, each raw material constituting the sulfide solid electrolyte raw material in this embodiment will be described.

[0079] The raw materials may be appropriately determined depending on the composition of the desired sulfide solid electrolyte, but typically, at least a raw material containing an alkali metal element (R) and a raw material containing sulfur element (S) are used. In addition to the above, it is preferable to use a raw material containing phosphorus element (P), and it is also preferable to use a raw material containing a halogen element (Ha).

[0080] Examples of the alkali metal element (R) include lithium element (Li), sodium element (Na), and potassium element (K). Among these, when the sulfide solid electrolyte is applied to a lithium ion battery, a raw material containing lithium element (Li) is preferred. As the alkali metal element (R), an appropriate combination of substances (components) containing alkali metal elements, such as an alkali metal element alone or a compound containing an alkali metal element, can be used. Among these, as the lithium element, an appropriate combination of substances (components) containing Li, such as an alkali metal element or a compound containing Li, can be used.

[0081] Examples of raw materials containing lithium element (Li) include lithium sulfide (Li ２ S ｘ (0.05≦x≦0.95)), lithium halides such as lithium iodide (LiI), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ O), lithium nitride (Li ３ Examples of the raw material include lithium compounds such as lithium hydroxide (LiOH), lithium nitrate (LiN), and metallic lithium. Here, lithium sulfide and lithium sulfate are raw materials containing Li, and at the same time, they also correspond to raw materials containing sulfur element (S). Lithium halide is a raw material containing Li, and at the same time, they also correspond to raw materials containing halogen element (Ha). These may be used alone or in combination of two or more. From the viewpoint of obtaining a sulfide material, it is preferable to use lithium sulfide as the raw material containing lithium element (Li).

[0082] As the sulfur element (S), simple S or a substance (component) containing S such as a compound containing S can be used in appropriate combination.

[0083] Examples of raw materials containing sulfur element (S) include diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５), other sulfur compounds containing phosphorus, elemental sulfur, compounds containing sulfur, etc. Phosphorus sulfide is a raw material containing S, and also corresponds to a raw material containing phosphorus element (P). When sulfur halide is used, it is a raw material containing sulfur element (S) and also corresponds to a raw material containing halogen element (Ha). In addition, as mentioned above, lithium sulfide (Li ２ S ｘ (0.05≦x≦0.95)) may be used. These may be used alone or in combination of two or more.

[0084] Sulfur-containing compounds include H ２ S, CS ２ , Na ２ S, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), antimony sulfide (Sb ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ S, etc.), tin sulfide (SnS ２ ), tungsten sulfide (WS ２ ) etc.

[0085] Among the raw materials containing sulfur element (S), lithium sulfide and phosphorus sulfide are preferable. As phosphorus sulfide, diphosphorus pentasulfide (P ２ S ５ ) is more preferred.

[0086] From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, the sulfide solid electrolyte raw material preferably further contains phosphorus (P). As the phosphorus (P), a suitable combination of P-containing substances (components), such as simple P or P-containing compounds, can be used.

[0087] Examples of raw materials containing phosphorus (P) include diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, sodium phosphate (Na ３P.O. ４ ) and elemental phosphorus. When a phosphorus halide is used, it is a raw material containing phosphorus element (P) and also a raw material containing halogen element (Ha). As the raw material containing phosphorus element (P), phosphorus sulfide is preferred, from the viewpoint of preventing the inclusion of elements other than elements constituting the target sulfide solid electrolyte, and diphosphorus pentasulfide (P ２ S ５ These substances may be used alone or in combination of two or more.

[0088] Examples of raw materials containing a halogen element (Ha) include lithium halides (LiHa) such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, barium halides, boron halides, yttrium halides, indium halides, zirconium halides, and lanthanum halides. Among these, from the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte, lithium halides are preferred, LiCl, LiBr, and LiI are more preferred, and LiCl and LiBr are even more preferred.

[0089] In addition to the above, for example, raw materials containing silicon element (Si), raw materials containing aluminum element (Al), raw materials containing tin element (Sn), raw materials containing indium element (In), raw materials containing copper element (Cu), raw materials containing antimony element (Sb), raw materials containing germanium element (Ge), etc. can be appropriately adopted according to the composition of the desired sulfide solid electrolyte.

[0090] Examples of raw materials containing Si include SiO ２ , SiS ２ Among them, from the viewpoint of lithium ion conductivity, SiO ２ These compounds may be used alone or in combination of two or more.

[0091] Examples of raw materials containing Al include Al ２ S ３ , Al２ O ３ , AlCl ３ Among them, from the viewpoint of lithium ion conductivity, Al ２ S ３ , AlCl ３ is preferred, and Al ２ S ３ These compounds may be used alone or in combination of two or more.

[0092] Examples of raw materials containing Sn include SnS, SnS ２ , SnO, SnO ２ , SnCl ２ Among them, from the viewpoint of lithium ion conductivity, SnS ２ , SnCl ２ is preferred, and SnS ２ These compounds may be used alone or in combination of two or more.

[0093] Examples of raw materials containing In include In ２ O ３ , In ２ S ３ , InCl ３ Among them, from the viewpoint of lithium ion conductivity, In ２ S ３ , InCl ３ is preferred, In ２ S ３ These compounds may be used alone or in combination of two or more.

[0094] Examples of raw materials containing Cu include Cu ２ O, CuO, Cu ２ S, CuS, CuCl ２ Among them, from the viewpoint of lithium ion conductivity, CuS, CuCl ２ These compounds may be used alone or in combination of two or more.

[0095] Examples of raw materials containing Sb include Sb ２ O ３ , Sb ２ S３ , SbCl ３ Among them, from the viewpoint of lithium ion conductivity, Sb ２ S ３ , SbCl ３ is preferred, and Sb ２ S ３ These compounds may be used alone or in combination of two or more.

[0096] Examples of raw materials containing Ge include GeO ２ , GeS, GeS ２ , GeCl ２ Among them, from the viewpoint of lithium ion conductivity, GeS ２ , GeCl ２ is preferred, and GeS ２ These compounds may be used alone or in combination of two or more.

[0097] In step 1 of the manufacturing method according to this embodiment, when preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio, the raw materials constituting the sulfide solid electrolyte raw material are mixed in a predetermined stoichiometric ratio according to the composition of the target sulfide solid electrolyte. The mixing method is not particularly limited, and examples thereof include mixing in a mortar, mixing using a media such as a planetary ball mill, and medialess mixing such as a pin mill, a powder mixer, and airflow mixing. The raw materials may be made amorphous by mixing before heating.

[0098] <Supply of Sulfur Source> In the production method according to this embodiment, in step 3, 7 to 24 parts by mass of a sulfur source is supplied relative to 100 parts by mass of the sulfide solid electrolyte raw material obtained in step 1. Alternatively, in step 3, the sulfide solid electrolyte raw material obtained in step 1 may be heated to form a melt (step 2), and 7 to 24 parts by mass of a sulfur source may be supplied relative to 100 parts by mass of the melt. Alternatively, the sulfur source may be supplied to both the sulfide solid electrolyte raw material and the melt. In this case, the sulfur source may be supplied in an amount such that the total amount of the supplied sulfur source falls within the above range.

[0099] In the production process of a sulfide solid electrolyte, sulfur (S) in particular is easily volatilized. Therefore, when raw materials are prepared based on the stoichiometric ratio of the target sulfide solid electrolyte, the composition of the actually obtained sulfide solid electrolyte will have less sulfur than the target composition. To prevent this composition deviation, a sufficient amount of sulfur source has conventionally been supplied to ensure that the amount of sulfur (S) lost through volatilization is compensated for. In this case, the obtained sulfide solid electrolyte has a slight excess of S compared to the sulfide solid electrolyte with the stoichiometric ratio. Specifically, the molecular weight of the obtained sulfide solid electrolyte is approximately 104% or more of the molecular weight of the sulfide solid electrolyte with the stoichiometric ratio, resulting in a composition with excess S.

[0100] In contrast to this, in the present embodiment, the amount of sulfur source supplied in excess is reduced compared to the conventional case, and the composition of the obtained sulfide solid electrolyte is made to be in an S-deficient state compared to the composition of sulfide solid electrolytes obtained conventionally.

[0101] Specifically, in the past, the molecular weight of the obtained sulfide solid electrolyte relative to the molecular weight of a stoichiometric sulfide solid electrolyte was approximately 104% or more, i.e., the excess S amount was 4% or more. However, the molecular weight ratio of the sulfide solid electrolyte obtained in this embodiment is preferably 100.5 to 103.5%, i.e., the excess S amount is 0.5 to 3.5%. Here, the excess S amount refers to the excess amount (proportion) of S in the composition of the argyrodite-type crystal structure relative to the amount of S that results in a stoichiometric ratio. Here, from the viewpoint of maintaining a certain proportion of the cubic argyrodite-type crystal structure and maintaining high ionic conductivity, the excess S amount is preferably 0.5% or more, more preferably 0.7% or more, even more preferably 1.0% or more, and even more preferably 1.2% or more. Furthermore, in the argyrodite-type crystal structure, from the viewpoint of increasing the proportion of other crystal systems with lower symmetry than cubic crystals and realizing better water resistance, the excess S content is preferably 3.5% or less, more preferably 3.3% or less, even more preferably 3.0% or less, and even more preferably 2.5% or less.

[0102] It has been found that this allows the argyrodite-type crystal structure of the resulting sulfide solid electrolyte to be realized in a state in which not only a cubic crystal but also other crystal systems with lower symmetry can exist together. It has also been found that this improves the water resistance of the sulfide solid electrolyte. Here, the other crystal systems with lower symmetry preferably include at least one crystal system selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal.

[0103] The sulfur source is preferably supplied in an amount of 7 to 24 parts by mass per 100 parts by mass of the sulfide solid electrolyte raw material or a melt thereof. From the viewpoint of maintaining a certain proportion of the cubic argyrodite-type crystal structure and maintaining high ionic conductivity, the supply ratio of the sulfur source is preferably 7 parts by mass or more, more preferably 8 parts by mass or more, more preferably 9 parts by mass or more, and even more preferably 10 parts by mass or more. Furthermore, from the viewpoint of increasing the proportion of crystal systems with lower symmetry other than cubic in the argyrodite-type crystal structure and achieving better water resistance, the supply ratio is preferably 24 parts by mass or less, more preferably 22 parts by mass or less, even more preferably 20 parts by mass or less, and even more preferably 18 parts by mass or less.

[0104] The form of the sulfur source to be supplied to the sulfide solid electrolyte raw material or its melt is not particularly limited. For example, it may be any of a gas, a solid, or a liquid. Furthermore, two or more sulfur sources may be supplied in combination.

[0105] When the sulfur source is supplied as a gas, a gas containing elemental sulfur is used. Examples of the gas containing elemental sulfur include a gas of a compound containing elemental sulfur, such as sulfur gas, hydrogen sulfide gas, carbon disulfide gas, and sulfur dioxide gas, and a gas containing elemental sulfur.

[0106] The gas containing elemental sulfur may be obtained by supplying a solid or liquid containing elemental sulfur as a sulfur source to a sulfide solid electrolyte raw material or a melt thereof, and heating the sulfur source to generate a gas containing elemental sulfur.

[0107] When a solid or liquid containing elemental sulfur is supplied as a sulfur source to the sulfide solid electrolyte raw material, the sulfur source is also heated to generate a gas containing elemental sulfur when the sulfide solid electrolyte raw material is heated to obtain a melt in the subsequent step 2. As a result, the sulfide solid electrolyte raw material is heated in a gas atmosphere containing elemental sulfur to obtain a melt. However, the above does not exclude an embodiment in which a solid or liquid containing elemental sulfur is supplied as a sulfur source to the melt of the sulfide solid electrolyte raw material.

[0108] Alternatively, sulfur vapor obtained in advance may be introduced into a furnace containing a sulfide solid electrolyte raw material or a melt thereof to create a gas atmosphere containing elemental sulfur. For example, sulfur may be heated at 200 to 450°C to generate sulfur vapor, and N ２ By transporting an inert gas such as argon gas or helium gas as a carrier gas into the furnace, a gas atmosphere containing sulfur elements can be created.

[0109] When the sulfur source is supplied in a liquid form, any elemental sulfur or sulfur compound can be used as the sulfur source. For example, elemental sulfur, hydrogen sulfide, organic sulfur compounds such as carbon disulfide, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ S, etc.), polysulfides such as sodium polysulfide, polysulfides, rubbers that have been subjected to sulfur vulcanization treatment, etc.

[0110] When the sulfur source is supplied as a solid, the sulfur source is not particularly limited as long as it is elemental sulfur or a sulfur compound. For example, elemental sulfur, hydrogen sulfide, carbon disulfide and other organic sulfur compounds, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘExamples of the sulfur source include polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubber vulcanized with sulfur, etc. As the sulfur source, sulfur powder is preferably used.

[0111] <Heating (Melted Material)> In the production method according to the present embodiment, in Step 2, the sulfide solid electrolyte raw material obtained in Step 1, or the sulfide solid electrolyte raw material containing excess sulfur obtained by supplying a sulfur source to the sulfide solid electrolyte raw material obtained in Step 1 in Step 3, is heated to obtain a melted material.

[0112] A heat-resistant container is used for obtaining a molten material by heating. Specific examples include heat-resistant containers made of carbon, heat-resistant containers containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, and mullite, heat-resistant containers containing nitrides such as silicon nitride and boron nitride, and heat-resistant containers containing carbides such as silicon carbide. These heat-resistant containers may be bulk-formed from the above-mentioned materials, or may be containers on which a layer of carbon, oxide, nitride, carbide, or the like is formed, such as a carbon-coated quartz tube.

[0113] The heating temperature when obtaining the melt is not particularly limited, but from the viewpoint of homogenizing the melt in a short time, for example, 550 to 1000°C is preferable. Here, from the viewpoint of meltability, the heating temperature is preferably 550°C or higher, more preferably 600°C or higher, even more preferably 630°C or higher, even more preferably 650°C or higher, and particularly preferably 700°C or higher. Furthermore, from the viewpoint of suppressing deterioration or decomposition of components in the melt, the heating temperature is preferably 1000°C or lower, more preferably 950°C or lower, even more preferably 900°C or lower, even more preferably 850°C or lower, particularly preferably 800°C or lower, and particularly preferably 750°C or lower.

[0114] The heating time for obtaining the melt is not particularly limited and varies depending on the scale, but may be, for example, 10 minutes to 100 hours. From the viewpoint of smoothly progressing the reaction, the heating time is preferably 10 minutes or more, and may be 30 minutes or more, 45 minutes or more, 1 hour or more, or 2 hours or more. Furthermore, the heating time may be longer as long as it is within an acceptable range for deterioration or decomposition of the components in the melt, and is not particularly limited. From the viewpoint of a practical range, i.e., productivity, etc., the heating time may be 100 hours or more, 50 hours or less, 25 hours or less, 10 hours or less, 9.5 hours or less, or 9 hours or less. Furthermore, the heating temperature and heating time may be adjusted according to the concentration of the sulfur source to be supplied, etc.

[0115] The pressure at which the melt is obtained by heating is not particularly limited, but for example, normal pressure or slight pressure is preferred, and normal pressure is more preferred.

[0116] The dew point when obtaining a melt by heating is preferably −20° C. or lower from the viewpoint of preventing side reactions with water vapor, oxygen, etc., and although there is no particular lower limit, it is usually about −80° C. Furthermore, the oxygen concentration in the atmosphere when obtaining a melt by heating is preferably 1000 ppm by volume or lower.

[0117] The complete dissolution of the molten material by heating can be confirmed by the absence of peaks derived from crystals in high-temperature X-ray diffraction measurement.

[0118] In order to increase the crystallinity of the resulting sulfide solid electrolyte, a compound that serves as a crystal nucleus may be added to the resulting melt. This facilitates crystal precipitation during cooling. Alternatively, the compound that serves as a crystal nucleus may be added to the sulfide solid electrolyte raw material or the sulfide solid electrolyte raw material containing excess sulfur before melting.

[0119] Examples of compounds that can become crystal nuclei include oxides, oxynitrides, nitrides, carbides, other chalcogen compounds, and halides. The compounds that can become crystal nuclei are preferably compounds that have a certain degree of compatibility with the melt. However, compounds that are completely incompatible with the melt cannot become crystal nuclei.

[0120] When a compound that becomes a crystal nucleus is added, the content of the compound in the melt is preferably 0.01 to 20% by mass. From the viewpoint of enhancing crystallinity, the content is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. From the viewpoint of ionic conductivity, the content is preferably 20% by mass or less, more preferably 10% by mass or less.

[0121] <Cooling (Crystallization)> In the production method according to this embodiment, in step 4, the melt of the sulfide solid electrolyte raw material to which the sulfur source has been supplied, or the melt to which the sulfur source has been supplied, is cooled to precipitate crystals having at least an argyrodite-type crystal structure, thereby obtaining a solid. By appropriately controlling the amount of the sulfur source supplied, the obtained argyrodite-type crystal structure includes not only a cubic crystal but also other crystal systems. Examples of other crystal systems include at least one selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal, and two or all three crystal systems may be used.

[0122] When there is only one type of other crystal system, tetragonal or orthorhombic is preferred, with tetragonal being more preferred. When there are two types of other crystal systems, tetragonal and orthorhombic are preferred. This corresponds to the fact that when the argyrodite-type crystal structure is subjected to a heat treatment of a certain level or more, it undergoes a phase change to a highly symmetrical crystal system, such as from monoclinic to orthorhombic, from orthorhombic to tetragonal, and from tetragonal to cubic, in a stepwise manner.

[0123] The cooling conditions for cooling the molten material vary depending on the composition, the target crystallization rate, and the like. The cooling rate is not particularly limited as long as the desired crystals are precipitated, but is preferably, for example, 1 to 10,000°C / min. From the viewpoint of productivity, the cooling rate is preferably 1°C / min or more, more preferably 5°C / min or more, even more preferably 10°C / min or more, even more preferably 30°C / min or more, and may be 50°C / min or more, or may be 100°C / min or more. Furthermore, from the viewpoint of increasing the crystallization rate, the cooling rate is preferably 10,000°C / min or less, more preferably 5,000°C / min or less, even more preferably 2,000°C / min or less, even more preferably 1,000°C / min or less, even more preferably 800°C / min or less, and particularly preferably 500°C / min or less.

[0124] The atmosphere during cooling is not particularly limited, but may be a gas atmosphere containing S element or an inert atmosphere, as in the case of the heat treatment. When the melt is obtained in a vacuum sealed tube, the cooling may also be performed while the melt is still in the vacuum sealed tube.

[0125] In this way, the solid from which crystals are precipitated in step 4 can be used as the sulfide solid electrolyte. If necessary, the solid may be further subjected to a pulverization treatment, a stabilization treatment by heating, or the like before being used as the sulfide solid electrolyte.

[0126] <Pulverization> In the production method according to this embodiment, the solid obtained in step 4 may be pulverized, if desired.

[0127] In step 5, when the solid obtained in step 4 is further subjected to a post-heat treatment, pulverization may be performed at least either before or after the post-heat treatment, or both before and after the post-heat treatment. When pulverization is performed both before and after the post-heat treatment, for example, coarse pulverization may be performed before the post-heat treatment and fine pulverization may be performed after the post-heat treatment.

[0128] The pulverization method is not particularly limited, and a conventionally known method can be used. For example, pulverization may be performed by dry pulverization or wet pulverization. For wet pulverization, a pulverizer such as a ball mill, a planetary ball mill, or a bead mill can be used.

[0129] When pulverizing by wet pulverization, the type of solvent (dispersion medium) is not particularly limited, but in view of the high reactivity of the sulfide solid electrolyte with water, a non-aqueous organic solvent is preferred. The type of non-aqueous organic solvent is not particularly limited, but for example, hydrocarbon solvents, organic solvents containing a hydroxy group, organic solvents containing an ether group, organic solvents containing a carbonyl group, organic solvents containing an ester group, organic solvents containing an amino group, organic solvents containing a formyl group, organic solvents containing a carboxy group, organic solvents containing an amide group, organic solvents containing a benzene ring, organic solvents containing a mercapto group, organic solvents containing a thioether group, organic solvents containing a thioester group, organic solvents containing a disulfide group, alkyl halides, etc. can be mentioned.

[0130] Examples of hydrocarbon solvents include cyclohexane, heptane, octane, and toluene, and cyclohexane, heptane, and octane are preferred from the viewpoint of low saturated water concentration. Also, from the viewpoint of adjusting the water concentration, it is preferred to mix these hydrocarbon solvents with toluene, dibutyl ether, or the like to form mixed solvents.

[0131] The water concentration in the non-aqueous solvent is preferably as low as possible to prevent a decrease in ionic conductivity. The water concentration may be, for example, 170 ppm by mass or less, 150 ppm by mass or less, 120 ppm by mass or less, or 100 ppm by mass or less.

[0132] In the wet grinding, in addition to the above solvent, an ether compound, an ester compound, a nitrile compound or the like may be further added as an additive (dispersant).

[0133] When the solvent or additives remain in the solid (sulfide solid electrolyte) obtained through wet pulverization, the solid may be further dried by a conventionally known method, for example, using a hot plate, a drying furnace, an electric furnace, or the like.

[0134] The heating temperature during drying is not particularly limited, but may be, for example, 100°C or higher or 200°C or lower. The heating time during drying is not particularly limited, but may be, for example, 10 minutes or longer or 24 hours or shorter. The pressure during drying is not particularly limited, but may be, for example, under reduced pressure, for example, an absolute pressure of 50 kPa or lower. The drying step can be carried out using a hot plate, a drying oven, an electric oven, or the like.

[0135] <Post-heat treatment> In the manufacturing method according to this embodiment, the solid obtained in step 4 may be further subjected to a post-heat treatment. The post-heat treatment is a treatment for stabilizing the solid by heating. The stabilization involves ion rearrangement within the crystal structure and promotion of crystallization, which improves ionic conductivity. In other words, the post-heat treatment in this specification refers to at least one of heating a solid containing crystals precipitated by cooling to crystallize it, and heating it to rearrange ions within the crystal structure.

[0136] The heating temperature in the post-heat treatment is preferably, for example, 300 to 550° C. Here, from the viewpoint of preferably obtaining the effect of the post-heat treatment, the heating temperature is preferably 300° C. or higher, more preferably 350° C. or higher, and even more preferably 400° C. or higher. Furthermore, from the viewpoint of production costs, the heating temperature is preferably 550° C. or lower, more preferably 500° C. or lower, and even more preferably 450° C. or lower.

[0137] The heating time in the post-heat treatment is preferably, for example, 10 minutes to 10 hours. From the viewpoint of production stability, the heating time is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and particularly preferably 1 hour or more. From the viewpoint of production cost, the heating time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0138] The atmosphere for the post-heat treatment is preferably an inert atmosphere. Examples of the inert atmosphere include a nitrogen gas atmosphere, an argon gas atmosphere, and a helium gas atmosphere. The dew point during the post-heat treatment is preferably −20° C. or lower, and although there is no particular lower limit, it is usually about −80° C. The oxygen concentration is preferably 1000 ppm by volume or lower.

[0139] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1 to 3 are working examples, and Examples 4 to 7 are comparative examples.

[0140] [Example 1] Li ５．４ P １．０ S ４．４ Cl ０．８ Br ０．８(Li: 43.5 at%, P: 8.1 at%, S: 35.5 at%, Cl: 6.5 at%, Br: 6.5 at%) composition ratio (stoichiometric ratio) Lithium sulfide powder (Sigma, purity 99.98%), diphosphorus pentasulfide powder (Sigma, purity 99%), lithium chloride powder (Sigma, purity 99.99%), and lithium bromide powder (Sigma, purity 99.995%) were weighed and mixed in a mortar to obtain a sulfide solid electrolyte raw material (step 1). 15 parts by mass of sulfur powder (Sigma, purity 99.998%) as a sulfur source was added to 100 parts by mass of the obtained sulfide solid electrolyte raw material (step 3), and heated in a glove box under a nitrogen atmosphere with a dew point of −50 ° C. or less to obtain a molten material (step 2). The sulfide solid electrolyte raw material supplied with the sulfur source was placed in a carbon container, and the heating conditions were pressure: gauge pressure + 1 kPa, temperature: 750 °C, and time: 1 hour. It was confirmed that the resulting molten material was completely dissolved. The molten material was then poured into a carbon container and cooled to room temperature at a cooling rate of 300 °C / min, yielding a block-shaped solid (step 4). The resulting solid was pulverized in a nitrogen atmosphere using a pin mill (Hosokawa Micron Corporation, 100UPZ) at 15,000 rpm for 1 hour to obtain a powder. Furthermore, the powder was subjected to a post-heat treatment by heating at 430 °C for 1 hour in a nitrogen atmosphere with a dew point of -50 °C or less (step 5), and then cooled to room temperature at a cooling rate of 300 °C / min to obtain a sulfide solid electrolyte powder.

[0141] [Examples 2 to 7] Powders of sulfide solid electrolytes of Examples 2 to 7 were obtained in the same manner as in Example 1, except that the supply ratio of the sulfur source in step 3 was changed from 15 parts by mass to each of the supply ratios shown in Table 1.

[0142] [Evaluation: Composition Analysis] The obtained sulfide solid electrolyte was weighed in a glove box and dissolved in an alkaline aqueous solution, and composition analysis was performed for each element. Specifically, P was analyzed by ICP optical emission spectroscopy (apparatus: Hitachi High-Tech Science Corporation, model PS3520UVDDII), Li was analyzed by atomic absorption spectrometry (apparatus: Hitachi High-Tech Corporation, model ZA3300; when measuring Li, CsCl was added so that the solution concentration became 0.1%), and Cl and Br were analyzed by ion chromatography (apparatus: Thermo Fisher Scientific, model ICS-2100 (column: AS11HC), H ２ O ２ The sulfide solid electrolyte was measured by adding a small amount of HCl and diluting with ultrapure water), and S was measured by oxygen flow combustion-infrared absorption method (apparatus: EMIA-expert carbon and sulfur analyzer manufactured by Horiba, Ltd.). For the oxygen flow combustion-infrared absorption method, a sulfide solid electrolyte sealed in a Sn container in a glove box with a dew point of -50°C or less was used as a sample. The composition of each sulfide solid electrolyte determined as a result of the above is shown in the "Actual composition" column of "Sulfide solid electrolyte" in Table 1.

[0143] Furthermore, using the above results, the difference in molecular weight of the sulfide solid electrolyte obtained in each example relative to the molecular weight of the stoichiometric ratio, which is the target composition, was calculated as the excess sulfur ratio (excess S amount). The results are shown in "Excess S amount (mass %)" under "Sulfide solid electrolyte" in Table 1.

[0144] [Evaluation: Powder X-ray Diffraction Measurement] Powder X-ray diffraction (XRD) measurement was performed on the obtained sulfide solid electrolyte. For the XRD measurement, Si powder was mixed as an internal standard with the sulfide solid electrolyte powder of each example, and an X-ray diffraction measurement (Rigaku Corporation, SmartLab) was performed using a holder not exposed to the atmosphere. The measurement conditions were as follows: radiation source: CuKα radiation (λ = 1.5418 Å), tube voltage: 45 kV, tube current: 200 mA, scan angle: 10 to 120°, scan speed: 5° / min, number of steps: 0.01° / step.

[0145] The obtained XRD patterns were subjected to refinement of the crystal structure by the Rietveld method using the program RIETAN-FP. The specific analysis method was as described above, and the structure with the lowest Rwp value was determined as the crystal structure of each example. The crystallinity (mass%) of the sulfide solid electrolyte, the content (mass%) of argyrodite-type crystals relative to the entire crystalline phase, and the proportions (parts by mass) of cubic, tetragonal, orthorhombic, and monoclinic crystals relative to a total of 100 parts by mass of the entire crystalline system of the argyrodite-type crystals are shown in the "Crystalline Properties" section of Table 1. The Rwp values ​​of each example were all low; for example, the Rwp value of Example 2 was 3.544, the Rwp value of Example 3 was 3.901, and the Rwp value of Example 5 was 4.691.

[0146] For the sulfide solid electrolytes of Examples 3 and 5, the XRD patterns for 2θ = 10 to 100° are shown in Figures 4(a) and 5(a), and the XRD patterns for the range of 2θ = 15 to 35° are enlarged in Figures 4(b) and 5(b), respectively. It was confirmed that Examples 1 and 2 had tetragonal and orthorhombic crystals in addition to cubic crystals. It was confirmed that Examples 3 and 5 to 7 had tetragonal, orthorhombic, and monoclinic crystals in addition to cubic crystals. The diffraction peaks of the XRD pattern using Cu-Kα radiation shown by the tetragonal, orthorhombic, and monoclinic crystals are as described above, but the sulfide solid electrolyte of Example 1 has diffraction peaks at 2θ = 15.6 °, 17.9 °, 17.95 °, 25.45 °, 25.5 °, 29.9 °, 30.0 °, 31.35 °, 44.8 °, and 44.9 ° as a tetragonal crystal. It was confirmed that it has diffraction peaks at positions. Also, as an orthorhombic crystal, it was confirmed that it has diffraction peaks at 2θ = 15.3 °, 15.5 °, 17.75 °, 17.9 °, 25.3 °, 25.4 °, 25.65 °, 29.75 °, 29.85 °, 30.1 °, 31.2 °, 31.5 °, 44.8 °, and 45.0 °. The sulfide solid electrolyte of Example 2 was confirmed to have diffraction peaks at 2θ = 15.6°, 17.9°, 17.95°, 25.45°, 25.5°, 29.9°, 30.0°, 31.35°, 44.8°, and 44.9° as a tetragonal crystal. It was also confirmed to have diffraction peaks at 2θ = 15.3°, 15.5°, 17.75°, 17.9°, 25.3°, 25.4°, 25.65°, 29.75°, 29.85°, 30.1°, 31.2°, 31.5°, 44.8°, and 45.0° as an orthorhombic crystal. The sulfide solid electrolyte of Example 3 was confirmed to have diffraction peaks at 2θ = 15.6°, 17.9°, 17.95°, 25.45°, 25.5°, 29.9°, 30.0°, 31.35°, 44.8°, and 44.9° as a tetragonal crystal. It was also confirmed to have diffraction peaks at 2θ = 15.3°, 15.5°, 17.75°, 17.9°, 25.3°, 25.4°, 25.65°, 29.75°, 29.85°, 30.1°, 31.2°, 31.5°, 44.8°, and 45.0° as an orthorhombic crystal.Furthermore, it was confirmed that the monoclinic crystal had diffraction peaks at 2θ=15.3°, 15.6°, 17.85°, 25.05°, 25.35°, 25.7°, 29.75°, 29.85°, 29.9°, 30.05°, 30.9°, 31.4°, 44.9°, and 45.1°.

[0147] [Evaluation: Lithium Ion Conductivity] The obtained sulfide solid electrolyte was pulverized in a mortar, 100 mg was weighed out, and a measurement sample was obtained by pressure molding at 380 MPa to an area with a diameter of 10 mm. The lithium ion conductivity of the measurement sample was measured using an AC impedance measurement device (potentiostat / galvanostat VSP, manufactured by Bio-Logic Sciences Instruments). The measurement conditions were a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C. The results are shown in Table 1 under "Lithium Ion Conductivity (mS / cm)."

[0148] [Evaluation: Water Resistance] The obtained sulfide solid electrolyte was pulverized in a mortar and passed through a 100 μm sieve to obtain a powder with a D50 of approximately 10 to 20 μm. 20 mg of the obtained powder was weighed as a sample, and nitrogen gas with a dew point of −20° C. was flowed at a flow rate of 0.5 L / min for 5 hours. ２ The amount of sulfur generated was measured and normalized by dividing it by the weight of the sample (20 mg). ２ The amount of sulfur generated (mL / g) is shown in the table below.

[0149]

[0150] The above results confirmed that an argyrodite-type crystal structure having tetragonal, orthorhombic, and monoclinic crystal systems was realized. Furthermore, by including at least one crystal system selected from the group consisting of tetragonal, orthorhombic, and monoclinic, which has lower symmetry than cubic crystal systems, together with cubic crystal systems within a certain range, it was possible to achieve excellent water resistance while maintaining high lithium ion conductivity.

[0151] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2024-089124) filed on May 31, 2024, the contents of which are incorporated herein by reference.

Claims

1. A sulfide solid electrolyte having a crystalline phase, wherein the crystalline phase has at least an argyrodite-type crystal structure, the argyrodite-type crystal structure has a crystal system of a cubic crystal and at least one crystal selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal, and the proportion of the total of the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal to the total of the cubic crystal, the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal is 1 to 50 mass%.

2. The sulfide solid electrolyte according to claim 1, which exhibits diffraction peaks at three or more of 2θ = 15.5° ± 0.5°, 17.9° ± 0.5°, 25.45° ± 0.5°, 29.9° ± 0.5°, 31.3° ± 0.5°, and 44.8° ± 0.5° in a powder X-ray diffraction pattern using Cu-Kα radiation.

3. The sulfide solid electrolyte according to claim 1 or 2, wherein the argyrodite-type crystal structure contains S as a constituent element.

4. The sulfide solid electrolyte according to claim 3, wherein the argyrodite-type crystal structure contains Ha as a constituent element, and the Ha is at least one element selected from the group consisting of F, Cl, Br, and I.

5. The argyrodite-type crystal structure is Li ａ MZ ｂ Ha ｃ 3. The sulfide solid electrolyte according to claim 1, wherein the sulfide solid electrolyte is represented by a composition formula: wherein in the composition formula, M is at least one element selected from Na, K, and elements present as divalent to pentavalent cations in the crystal structure; Z is at least one element selected from elements present as divalent anions in the crystal structure, Z includes S; and Ha is at least one element selected from the group consisting of F, Cl, Br, and I; and in the composition formula, a represents a composition ratio of Li, b represents a composition ratio of Z, and c represents a composition ratio of Ha, respectively, and the relationships 5≦a≦7, 4≦b≦6, and 1<c≦2 are satisfied.

6. The sulfide solid electrolyte according to claim 5, wherein the element present as a divalent to pentavalent cation in the composition formula is at least one element selected from the group consisting of B (boron), Mg (magnesium), Al (aluminum), Si (silicon), P (phosphorus), Ca (calcium), Ti (titanium), V (vanadium), Fe (iron), Zn (zinc), Ga (gallium), Sr (strontium), Y (yttrium), Zr (zirconium), Nb (niobium), Mo (molybdenum), Sn (tin), Sb (antimony), Ba (barium), Ta (tantalum), W (tungsten), and Bi (bismuth).

7. The sulfide solid electrolyte according to claim 5, wherein M in the composition formula contains P.

8. The sulfide solid electrolyte according to claim 7, wherein in the composition formula, the content ratio of P to the total of M is 60 to 100 atoms %.

9. The sulfide solid electrolyte according to claim 5, wherein the element present as a divalent anion in the composition formula is at least one element selected from the group consisting of S (sulfur), O (oxygen), Se (selenium), and Te (tellurium).

10. The sulfide solid electrolyte according to claim 5, wherein in the composition formula, the content of S relative to the total of Z is 60 to 100 atoms %.

11. The sulfide solid electrolyte according to claim 5, wherein in the composition formula, the composition ratio of S as Z is 1 to 6.

12. The sulfide solid electrolyte according to claim 1 or 2, wherein the content of the argyrodite-type crystal structure in the sulfide solid electrolyte is 51 mass % or more.

13. The sulfide solid electrolyte according to claim 1 or 2, wherein the amount of S in the composition of the argyrodite-type crystal structure is 0.5 to 3.5% in excess of the amount of S that results in a stoichiometric ratio.

14. A method for producing a sulfide solid electrolyte having a crystalline phase, comprising: preparing a sulfide solid electrolyte raw material based on a stoichiometric ratio; heating the sulfide solid electrolyte raw material to obtain a melt; supplying 100 parts by mass of the sulfide solid electrolyte raw material or 7 to 24 parts by mass of a sulfur source per 100 parts by mass of the melt; and then cooling the melt to precipitate crystals and obtain a solid, wherein the precipitated crystals have at least an argyrodite-type crystal structure containing S as a constituent element.

15. The method for producing a sulfide solid electrolyte according to claim 14, wherein the argyrodite-type crystal structure has a crystal system of a cubic crystal and at least one crystal selected from the group consisting of a tetragonal crystal, an orthorhombic crystal, and a monoclinic crystal, and the proportion of the total of the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal to the total of the cubic crystal, the tetragonal crystal, the orthorhombic crystal, and the monoclinic crystal is 1 to 50 mass%.

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