Sulfide solid electrolyte and method for manufacturing same

Abstract

The present invention pertains to a sulfide solid electrolyte which comprises a crystal phase including a crystal represented by composition formula RaPbMcM'c'SdXe (3<a<7, 0<b, 0<c, 0≤c', b+c+c'=1, 3<d<6, 0.1<{(c+c') / (b+c+c')}<1.0, 1.1≤{e / (b+c+c')}≤2.0) (R represents an alkali metal element, P represents a phosphorus element, M and M' each represent an element belonging to groups 2-15 of the periodic table and capable of forming a tetrahedral coordination structure together with S, S represents a sulfur element, and X represents a halogen element), and in which, in the composition formula, the atomic number of M is higher than that of P, the atomic number of M' is lower than that of P, and the crystal has a PS4 tetrahedral structure and an MS4 tetrahedral structure.

Description

Sulfide solid electrolyte and method for producing same

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

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers. While liquid electrolytes have traditionally been used in lithium-ion secondary batteries, solid-state lithium-ion secondary batteries, which use solid electrolytes as the electrolyte, have attracted attention due to their potential for improved safety, high-speed charging and discharging, and compact housings.

[0003] Among the solid electrolytes used in all-solid-state lithium ion secondary batteries, sulfide solid electrolytes exhibit high lithium ion conductivity. Among them, argyrodite-type solid electrolytes exhibit even higher lithium ion conductivity. For example, Patent Document 1 discloses a sulfide solid electrolyte having the composition formula: Li ７－ｘ P.S. ６－Ｘ Ha Ｘ (Ha is Cl or Br) (x=0.2 to 1.8), and ＊ a ＊ b ＊ An argyrodite-type sulfide solid electrolyte having a colorimetric lightness L value of 60.0 or more is disclosed.

[0004] However, conventionally known argyrodite-type sulfide solid electrolytes easily react with water to form hydrogen sulfide (H ２ S) is easily generated, and when exposed to a moisture-containing atmosphere, the lithium ion conductivity drops significantly.

[0005] In contrast, in Non-Patent Document 1, PS ４ Instead of a tetrahedral structure, SiS ４ Tetrahedral structure and SbS ４ Argyrodite-type Li with a tetrahedral structure ６．６ [Si ０．６ Sb ０．４ ]S ５ I is disclosed. ２ It is said that the amount of sulfur generated is reduced and the decrease in lithium ion conductivity when exposed to a moisture-containing atmosphere is suppressed.

[0006] International Publication No. 2015 / 012042

[0007] Laidong Zhou et al. , “New Family of Argyrodite Thioantimonate Lithium Superionic Conductors”, J. Am. Chem. Soc. 2019, 141, 48, 19002-19013

[0008] However, the sulfide solid electrolyte described in Non-Patent Document 1 is H ２ The degree of reduction in the amount of sulfur generated and the degree of suppression of the decrease in lithium ion conductivity when exposed to a moisture-containing atmosphere are insufficient. ４ Instead of a tetrahedral structure, SiS ４ Tetrahedral structure and SbS ４ It was found that when a sulfide solid electrolyte with a tetrahedral structure was implemented in a lithium-ion battery, there were issues with reduction resistance.

[0009] Therefore, the present invention is ２ The present invention provides a sulfide solid electrolyte that generates a small amount of sulfur, is inhibited from decreasing in ionic conductivity when exposed to a moisture-containing atmosphere, and has good reduction resistance, and a method for producing the same.

[0010] MS in which a specific element, M, forms a tetracoordinate structure with S ４ By including a tetrahedral structure in the crystal, H ２ Further investigation by the present inventors has revealed that the amount of sulfur generated can be reduced and the decrease in ionic conductivity when exposed to a moisture-containing atmosphere can be suppressed. ４ In addition to the tetrahedral structure, PS ４ It was found that the coexistence of the tetrahedral structure also allows for good reduction resistance. Furthermore, by setting the content of halogen elements in the crystal composition to a certain level or more, S can be contained in the crystal. ２－ The proportion of isolated sulfur present as H ２ The inventors have found that the amount of sulfur generated can be further reduced, and have completed the present invention.

[0011] That is, the present invention relates to the following [1] to

[21] . [1] A sulfide solid electrolyte having a crystalline phase, wherein the crystalline phase is represented by the composition formula: R ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅ In the composition formula, R represents an alkali metal element, P represents phosphorus element, M represents an element of Groups 2 to 15 of the periodic table, has an atomic number larger than that of P, and is capable of forming a tetracoordinated structure with S, M' represents an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than that of P, and is capable of forming a tetracoordinated structure with S, S represents sulfur element, and X represents a halogen element, and in the composition formula, the following relationships are satisfied: 3<a<7, 0<b, 0<c, 0≦c', b+c+c'=1, 3<d<6, 0.1<{(c+c') / (b+c+c')}<1.0, and 1.1≦{e / (b+c+c')}≦2.0, and the crystal is PS ４ Tetrahedral structure and MS ４A sulfide solid electrolyte having a tetrahedral structure. [2] The sulfide solid electrolyte according to [1] above, wherein the composition formula satisfies 4<a<7. [3] The sulfide solid electrolyte according to [1] above or [2] above, wherein the composition formula satisfies 0.2<{(c+c') / (b+c+c')}<1.0. [4] The sulfide solid electrolyte according to any one of [1] to [3] above, wherein the composition formula satisfies 4<d<6. [5] The sulfide solid electrolyte according to any one of [1] to [4] above, wherein the composition formula satisfies 1.2≦{e / (b+c+c')}≦1.9. [6] The sulfide solid electrolyte according to any one of [1] to [5], wherein M in the composition formula contains at least one element selected from the group consisting of Mn, Ni, As, Mo, Co, Ag, Cd, Ir, W, Sn, Sb, Ga, Ge, In, Pb, Bi, Cu, Ti, V, Cr, Fe, Zn, Y, Zr, Nb, Ta, W, and La. [7] The sulfide solid electrolyte according to any one of [1] to [6], wherein M in the composition formula contains at least one element selected from the group consisting of Sn and Sb. [8] The sulfide solid electrolyte according to any one of [1] to [7], wherein M' in the composition formula contains at least one element selected from the group consisting of Mg, N, Si, Al, and B. [9] The sulfide solid electrolyte according to any one of [1] to [8], wherein the crystal has a crystal structure of the F-43m space group.

[10] The sulfide solid electrolyte according to any one of [1] to [9], wherein X in the composition formula contains I.

[11] The sulfide solid electrolyte according to

[10] , wherein X in the composition formula further contains Br.

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

[11] , wherein M and M' in the composition formula contain two or more elements in total.

[13] The sulfide solid electrolyte according to

[12] , wherein M and M' in the composition formula contain eight or less elements in total.

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

[13] , wherein R in the composition formula contains at least one element selected from the group consisting of Li, Na, and K.

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

[14] , wherein R in the composition formula contains Li.

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

[15] , wherein the crystal has an argyrodite-type crystal structure.

[0012]

[17] A method for producing the sulfide solid electrolyte according to any one of [1] to

[16] above, comprising the steps of: mixing raw materials containing the elements R, P, M, S, and X to obtain a raw material mixture; obtaining a melt of the raw material mixture by heat treatment; and cooling the melt to precipitate crystals, wherein among the elements, R represents an alkali metal element, P represents elemental phosphorus, M represents an element of Groups 2 to 15 of the periodic table, has an atomic number greater than that of P, and is capable of forming a tetracoordination structure with S, S represents elemental sulfur, and X represents an elemental halogen.

[18] A method for producing the sulfide solid electrolyte according to

[17] above, wherein the cooling is performed by slow cooling at a cooling rate of 0.01 to 2000°C / sec.

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

[17] or

[18] , wherein the raw material mixture further contains a raw material containing an element M', wherein M' is an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than that of P, and is capable of forming a tetracoordination structure with S.

[20] The method for producing a sulfide solid electrolyte according to any one of

[17] to

[19] , further comprising, after precipitating the crystals, performing a post-heat treatment by heating.

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

[20] , wherein the post-heat treatment is performed at a temperature of 300 to 600°C for 10 minutes to 20 hours in an inert atmosphere with a dew point of -20°C or lower.

[0013] According to the present invention, H ２ A sulfide solid electrolyte is obtained that generates a small amount of sulfur, suppresses a decrease in ionic conductivity when exposed to a moisture-containing atmosphere, and has good reduction resistance. Therefore, a secondary battery incorporating the sulfide solid electrolyte has excellent battery characteristics.

[0014] 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 an XRD pattern of the sulfide solid electrolyte of Example 1. FIG. 4 is an XRD pattern of the sulfide solid electrolyte of Example 3. FIG. 5 is an XRD pattern of the sulfide solid electrolyte of Example 5. FIG. 6 is an XRD pattern of the sulfide solid electrolyte of Example 7. FIG. 7 is an XRD pattern of the sulfide solid electrolyte of Example 9. FIG. 8 is an XRD pattern of the sulfide solid electrolyte of Example 11.

[0015] 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. 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 % have the same meaning.

[0016] The sulfide solid electrolyte according to this embodiment has a crystalline phase. ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅThe present invention includes a crystal represented by the formula: In this composition, R represents an alkali metal element, P represents phosphorus, M represents an element of Groups 2 to 15 of the periodic table, has an atomic number larger than that of P, and is capable of forming a tetracoordination structure with S, M' represents an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than that of P, and is capable of forming a tetracoordination structure with S, S represents sulfur, and X represents a halogen. In addition, in the above composition, a to e and c', which represent the molar content ratios (composition ratios) of each element, satisfy the following relationship: Here, when two or more elements are contained as each of the elements represented by R, M, M', and X, a, c, c', and e, which represent the composition ratios of R, M, M', and X, respectively, represent the sum of the two or more elements. 3<a<7, 0<b, 0<c, 0≦c′, b+c+c′=1, 3<d<6, 0.1<{(c+c′) / (b+c+c′)}<1.0, and 1.1≦{e / (b+c+c′)}≦2.0. In addition to the above, the crystal in this embodiment is PS ４ Tetrahedral structure and MS ４ It has a tetrahedral structure.

[0017] <Crystalline Phase> The composition formula of the crystal contained in the crystalline phase in this embodiment is R ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅ As described above, R in the above composition formula represents an alkali metal element. Specifically, it is preferable that at least one selected from the group consisting of Li, Na, and K is contained, more preferably that at least one of Li and Na is contained, and even more preferably that Li is contained. Here, the alkali metal element means a carrier of the solid electrolyte. That is, when the sulfide solid electrolyte according to this embodiment is used in a lithium ion battery, R preferably contains Li. Furthermore, when the sulfide solid electrolyte according to this embodiment is used in a sodium ion battery, R preferably contains Na. Furthermore, when the sulfide solid electrolyte according to this embodiment is used in a potassium ion battery, R preferably contains K.

[0018] The composition formula showing the crystal in this embodiment: R ａ Pｂ M ｃ M' ｃ’ S ｄ X ｅ In the formula, when the sum of the composition ratios of P, M, and M', (b+c+c'), is taken as the standard, i.e., when b+c+c'=1, the composition ratio a of R representing an alkali metal element is more than 3 and less than 7, preferably more than 4 and less than 7, more preferably more than 5 and less than 7, even more preferably more than 5.2 and less than 6.8, and even more preferably more than 5.4 and less than 6.5. Here, the composition ratio a is more than 3, preferably more than 4, more preferably more than 5, even more preferably more than 5.2, and even more preferably more than 5.4, from the viewpoint of precipitating the target crystalline phase. In addition, the composition ratio a is set to be greater than 3 from the viewpoint of improving ionic conductivity and suppressing the reaction of hydrogen sulfide (H ２ S) from the viewpoint of reducing the amount of generation, it is less than 7, preferably less than 6.8, and more preferably less than 6.5.

[0019] In the composition formula, P (phosphorus element), M, and M' are elements that can form a four-coordinate structure with S (sulfur element). ４ Tetrahedral structure and MS ４ It has a tetrahedral structure and, optionally, further comprises M'S ４ It also has a tetrahedral structure. Here, M is an element of Groups 2 to 15 of the periodic table, has an atomic number larger than that of P, and can form a tetrahedral structure with S. Furthermore, M' is an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than that of P, and can form a tetrahedral structure with S. The crystal in this embodiment is the above MS in which M is coordinated with S. ４ By having a tetrahedral structure, H ２ The amount of sulfur generated can be reduced, and the decrease in ionic conductivity when exposed to a moisture-containing atmosphere can be suppressed. ４ In addition to the tetrahedral structure, M'S ４ The above effect can be preferably obtained by further having a tetrahedral structure.

[0020] For this reason, the present inventors have ４ Compared to tetrahedrons, MS ４ The tetrahedron is H ２It is believed that this is because it is difficult for the OH to bond with the tetrahedral structure. The above can be explained based on the HSAB (Hard and Soft Acids and Bases) rule. The HSAB rule introduces the concepts of hard and soft in the reactivity of acids and bases. Similarly, in the tetrahedral structure, OH － H consisting of hard bases such as ２ It is thought that a tetrahedral structure with a weak acid as the central element is less likely to react with O. ４ P that forms a tetrahedron ５＋ is classified as a hard acid, but P ５＋ The elements that can be said to form weaker acids than P are those in groups 2 to 15 of the periodic table and have atomic numbers greater than P.

[0021] M is not particularly limited as long as it is an element of Groups 2 to 15 of the periodic table, has an atomic number greater than that of P, and can form a tetracoordinate structure with S, and examples thereof include Mn, Ni, As, Mo, Co, Ag, Cd, Ir, W, Sn, Sb, Ga, Ge, In, Pb, Bi, Cu, Ti, V, Cr, Fe, Zn, Y, Zr, Nb, Ta, W, and La. That is, it is preferable that M contains at least one element selected from the group consisting of Mn, Ni, As, Mo, Co, Ag, Cd, Ir, W, Sn, Sb, Ga, Ge, In, Pb, Bi, Cu, Ti, V, Cr, Fe, Zn, Y, Zr, Nb, Ta, W, and La. Among these, hydrogen sulfide (H ２ From the viewpoint that the lithium ion conductivity is unlikely to decrease even when exposed to a moisture-containing atmosphere, Sn, Sb, Bi, Ti, V, Cr, Fe, Zn, Y, Zr, Nb, Ta, W, and La are more preferable, Sn, Sb, Bi, Ti, Cr, Fe, Zn, Y, Zr, and Nb are even more preferable, Sn, Sb, Bi, Y, Zr, and Nb are still more preferable, and at least one of Sn and Sb is particularly preferable.

[0022] Furthermore, by employing the manufacturing method described later, the crystal of this embodiment can also be realized to contain two or more elements as M. This allows for the formation of multiple MSs according to desired properties. ４ It can be a crystal with a tetrahedral structure.

[0023] Here, when two or more elements are contained as M, M preferably contains at least one of Sn and Sb, and more preferably contains Sn and Sb.

[0024] The number of types of elements M is preferably 1 to 8, more preferably 2 to 5, and even more preferably 2 to 4. Here, the number of types of elements M constituting the crystal in this embodiment is preferably 1 or more, and when M' is not included, it is preferably 2 or more. In addition, there is no particular upper limit on the number of types of elements M, but in the case of PS ４ From the viewpoint of optimally obtaining the effect of having a tetrahedral structure in the crystal, eight or fewer types are preferred, five or fewer types are more preferred, and four or fewer types are even more preferred. Furthermore, M and M' in the composition formula representing the crystal in this embodiment preferably contain a total of two to eight types of elements, two to five types are more preferred, and two to four types are even more preferred. That is, the types of the elements are preferably two or more types, and eight or fewer types are preferred, five or fewer types are more preferred, and four or fewer types are even more preferred.

[0025] When Sb is contained as M, the proportion of Sb relative to the total composition ratio c of M is preferably 15 to 100% in atomic ratio, more preferably 30 to 90%, and even more preferably 40 to 80%. Here, from the viewpoint of improving water resistance and ionic conductivity, the proportion of Sb is preferably 15% or more, more preferably 30% or more, and even more preferably 40% or more. Furthermore, the proportion of Sb may be 100%, i.e., only Sb may be contained as M. On the other hand, from the viewpoint of being able to improve ionic conductivity by further mixing different types of elements, the proportion of Sb is preferably 90% or less, more preferably 80% or less.

[0026] When Sn is contained as M, the proportion of Sn relative to the total composition ratio c of M is preferably 5 to 80% in atomic ratio, more preferably 10 to 50%, and even more preferably 20 to 40%. From the viewpoint of improving water resistance, the proportion of Sn is preferably 5% or more, more preferably 10% or more, and even more preferably 20% or more. Furthermore, although the proportion of Sn may be 100%, from the viewpoint of increasing ionic conductivity, the proportion of Sn is preferably 80% or less, more preferably 50% or less, and even more preferably 40% or less.

[0027] The crystal in this embodiment may contain M' as a constituent element in addition to the above-mentioned R, P, M, S, and X. M' is an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than that of P, and can form a tetracoordination structure with S. Examples of M' include Mg (magnesium), N (nitrogen), Si (silicon), Al (aluminum), and B (boron). That is, it is preferable that M' contains at least one element selected from the group consisting of Mg, N, Si, Al, and B.

[0028] That is, the crystal in this embodiment is MS ４ Other tetrahedral structures include M'S ４ It may further have a tetrahedral structure, which is preferable in terms of ion conductivity. ４ The tetrahedral structure is, for example, MgS ４ Tetrahedral structure, NS ４ Tetrahedral structure, SiS ４ Tetrahedral structure, AlS ４ Tetrahedral structure and BS ４ It may be at least one selected from the group consisting of tetrahedral structures, and SiS ４ Tetrahedral structure, AlS ４ Tetrahedral structure and BS ４ Among them, from the viewpoint of ionic conductivity, SiS ４ It preferably comprises a tetrahedral structure.

[0029] The crystal in this embodiment is ４ Tetrahedral structure and optionally M'S ４ In addition to the tetrahedral structure, PS４ It also has a tetrahedral structure. ４ Tetrahedral structure, MS ４ Tetrahedral structure and M'S ４ Compared with the case where only the tetrahedral structure is used, better reduction resistance can be achieved.

[0030] P.S. ４ Tetrahedral structure, MS ４ Tetrahedral structure, and M'S ４ The proportion of the tetrahedral structure is represented by the composition ratio b of P (phosphorus element), the composition ratio c of M, and the composition ratio c' of M' in the composition formula. Here, the ratio represented by {(c + c') / (b + c + c')} is greater than 0.1 and less than 1.0, preferably greater than 0.2 and less than 1.0, also preferably 0.2 to 0.9, more preferably 0.3 to 0.85, and even more preferably 0.4 to 0.7. Here, from the viewpoint of water resistance, the ratio is greater than 0.1 and preferably 0.2 or greater, more preferably greater than 0.2, even more preferably 0.3 or greater, and even more preferably 0.4 or greater. Furthermore, from the viewpoint of reduction resistance, the ratio is less than 1.0 and preferably 0.9 or less, more preferably 0.85 or less, and even more preferably 0.7 or less. The tetrahedral structure can be confirmed by structural analysis of XRD patterns, solid-state NMR measurement, etc., and the composition ratio of each element can be confirmed by composition analysis, etc. The composition ratios b, c, and c' of P, M, and M' have the following relationship: 0<b, 0<c, 0≦c', and b+c+c'=1.

[0031] The composition ratio d of S, which is a sulfur element, is greater than 3 and less than 6, preferably greater than 4 and less than 6, more preferably greater than 4 and less than 5.3, and even more preferably greater than 4.1 and less than 5.2. Here, the S is a component of PS in the crystal of this embodiment. ４ Tetrahedral structure and MS ４ Tetrahedral structure, optionally M'S ４ In addition to forming a tetrahedral structure, S ２－ It can exist as isolated sulfur. ４ Tetrahedral structure, MS ４ Tetrahedral structure and M'S ４From the viewpoint of forming an adequate tetrahedral structure, the composition ratio d is greater than 3, preferably greater than 4, and more preferably greater than 4.1. Moreover, from the viewpoint of reducing the proportion of isolated sulfur and realizing good water resistance, the composition ratio d is less than 6, preferably less than 5.3, and more preferably less than 5.2.

[0032] The crystal in this embodiment contains a halogen element represented by X as a constituent element. Examples of halogen elements include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Among these, from the viewpoint of improving ionic conductivity, it is preferable to contain at least one selected from the group consisting of chlorine, bromine, and iodine, more preferably at least one of bromine and iodine, and even more preferably iodine. Furthermore, from the viewpoint of improving ionic conductivity, it is also preferable to contain two or more halogen elements. In this case, it is preferable to contain at least two selected from the group consisting of chlorine, bromine, and iodine, and more preferably bromine and iodine.

[0033] The composition ratio e of X, which is a halogen element contained in the crystal in this embodiment, is the ratio to the sum of the composition ratios of P, M, and M', that is, the ratio expressed as {e / (b+c+c')}, is 1.1 or more and 2.0 or less, preferably 1.2 or more and 1.9 or less, more preferably 1.3 or more and 1.8 or less, and even more preferably 1.4 or more and 1.7 or less. Here, the halogen element is S, which is isolated sulfur. ２－ By entering the site, the proportion of isolated sulfur can be reduced. From this viewpoint, the ratio is 1.1 or more, preferably 1.2 or more, more preferably 1.3 or more, and even more preferably 1.4 or more. Furthermore, from the viewpoint of obtaining the target crystalline phase, the ratio is 2.0 or less, preferably 1.9 or less, more preferably 1.8 or less, and even more preferably 1.7 or less.

[0034] The crystal in this embodiment may further contain other elements as constituent elements in addition to the above-mentioned R, P, M, optionally M', S and X. Examples of other elements include N, C and O. These elements include CN, CO ｎ , NO ｎ , S.O. ｎ The crystal may be present in the form of the above.

[0035] The crystal in this embodiment has the composition formula: R ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅ The composition ratios of the elements in the formula are 3<a<7, 0<b, 0<c, 0≦c', b+c+c'=1, 3<d<6, 0.1<{(c+c') / (b+c+c')}<1.0, and 1.1≦{e / (b+c+c')}≦2.0, but 4<a<7, 0<b, 0<c, 0≦c', b+c+c'=1, 4<d<6, 0.2<{(c+c') / (b+c+c')}<1.0, 1.2≦{e / (b+c+c')}≦1.9, or 5<a<7, 0<b, 0<c, 0≦c', b+c+c'=1, 4<d<5.3, 0.2≦{(c+c') / (

[0047] It is preferable that 5.2<a<6.8, 0<b, 0<c, 0<c', b+c+c'=1, 4.1<d<5.2, 0.3<{(c+c') / (b+c+c')}≦0.85, 1.3<{e / (b+c+c')}≦1.8 are more preferable, and 5.4<a<6.5, 0<b, 0<c, 0<c', b+c+c'=1, 4.1<d<5.2, 0.4<{(c+c') / (b+c+c')}≦0.7, 1.4<{e / (b+c+c')}≦1.7 are even more preferable.

[0036] From the viewpoint of improving ionic conductivity, the crystal in this embodiment preferably has a crystal structure of the F-43m space group, and more preferably has a cubic crystal structure of the F-43m space group. Furthermore, it is more preferable that it has an argyrodite-type crystal structure, and even more preferable that it has a cubic argyrodite-type crystal structure. Note that the argyrodite-type in this specification refers to a crystal having the composition formula Ag ８ GeS ６ This is the crystal structure of a group of compounds derived from minerals represented by the formula:

[0037] When the crystal in this embodiment is a cubic crystal of the F-43m space group, the lattice constant is preferably 10.25 to 10.45 Å, more preferably 10.30 to 10.42 Å. That is, the lattice constant is preferably 10.25 Å or more, more preferably 10.30 Å or more, and is preferably 10.45 Å or less, more preferably 10.42 Å or less. The lattice constant of the crystal can be determined by Rietveld analysis of the XRD pattern or from representative peak positions. When determining from representative peak positions, it is desirable to calculate an average value using two or more peaks.

[0038] The sulfide solid electrolyte according to this embodiment may consist of only the crystalline phase made of the above crystals, or may contain other crystalline phases or an amorphous phase.

[0039] The content of the crystals in the sulfide solid electrolyte according to this embodiment is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 70 to 90% by mass. From the viewpoint of improving 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. The content of the crystals may be 100% by mass, i.e., the sulfide solid electrolyte according to this embodiment may consist solely of the crystals. On the other hand, from the viewpoint of formability, the content is preferably less than 100% by mass, and more preferably 90% by mass or less.

[0040] When the crystals in this embodiment have a crystal structure of the F-43m space group, the content of the crystals in the sulfide solid electrolyte is the same as above, i.e., preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and may be 100% by mass, less than 100% by mass, or 90% by mass or less.

[0041] <Sulfide Solid Electrolyte> The secondary particle diameter of the sulfide solid electrolyte according to this embodiment is preferably small from the viewpoint of obtaining good ionic conductivity when used in a secondary battery. Specifically, the secondary particle diameter is preferably 10 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. The lower limit of the secondary particle diameter is not particularly limited, but is usually 0.1 μm or more. The secondary particle diameter can be measured using a microtrack device.

[0042] The lithium ion conductivity of the sulfide solid electrolyte according to this embodiment at 25° C. is 0.1×10 －３ S / cm or more is preferable, and 1×10 －３ S / cm or more is more preferable, and 2×10 －３ The upper limit of the lithium ion conductivity is not particularly limited, but it is usually 1×10 －１ The lithium ion conductivity is 0.05 S / cm or less. The lithium ion conductivity can be measured by an AC impedance method. Specifically, the lithium ion conductivity is a value measured using an AC impedance measuring device (for example, a potentiostat / galvanostat VSP manufactured by Bio-Logic Sciences Instruments) under the following conditions: a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C.

[0043] The sulfide solid electrolyte according to this embodiment can be identified by analyzing the elemental composition using various methods such as crystal structure analysis by X-ray diffraction (XRD) measurement, ICP emission spectrometry measurement, atomic absorption spectrometry measurement, and ion chromatography measurement. For example, P, M, M', and S can be measured by ICP emission spectrometry measurement, R can be measured by atomic absorption spectrometry measurement, and X can be measured by ion chromatography measurement.

[0044] The sulfide solid electrolyte according to this embodiment is suitable for use in electrode mixtures and solid electrolyte layers used in secondary batteries, and is particularly suitable for all-solid-state secondary batteries, and more suitable for all-solid-state lithium-ion secondary batteries. That is, the electrode mixture is used in secondary batteries and contains the sulfide solid electrolyte and an active material. The solid electrolyte layer is used in secondary batteries and contains the sulfide solid electrolyte.

[0045] The electrode mixture, the solid electrolyte layer, and the all-solid-state lithium ion secondary battery may further contain another solid electrolyte. The other solid electrolyte is not particularly limited, and examples thereof include a conventionally known solid electrolyte having an argyrodite-type crystal structure, Li ３ P.S. ４ Examples of suitable solid electrolytes include solid electrolytes having an LGPS type crystal structure, and Li-PS-Ha (Ha is a halogen element) type crystallized glass type solid electrolytes.

[0046] 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 alkali metal ions, intercalate and deintercalate alkali metal ions, or dope and dedope counter anions of the alkali metal ions. Here, the alkali metal ion is preferably lithium ion. Specific examples of the positive electrode active material include lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, composite metal oxides, and polyanion olivine-type positive electrodes.

[0047] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release alkali metal ions, detach and insert (intercalate) alkali metal ions, or reversibly dope and dedope counter anions of the alkali metal ions. Here, the alkali metal ions are preferably lithium ions. Specific examples of the negative electrode active material include lithium metal, carbon-based materials such as graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0048] 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.

[0049] The all-solid-state 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.

[0050] 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.

[0051] <<Method for Producing Sulfide Solid Electrolyte>> The method for producing the sulfide solid electrolyte according to this embodiment is not particularly limited as long as it can produce the sulfide solid electrolyte described above in <<Sulfide Solid Electrolyte>>. Preferred aspects of the resulting sulfide solid electrolyte are also the same as the preferred aspects described above in <<Sulfide Solid Electrolyte>>.

[0052] As shown in Fig. 1, one example of the method for producing a sulfide solid electrolyte according to this embodiment includes the following steps in order: Step S1: A step of mixing raw materials containing the elements R, P, M, S, and X to obtain a raw material mixture; Step S2: A step of obtaining a melt of the raw material mixture obtained in Step S1 by heat treatment; Step S3: A step of cooling the melt obtained in Step S2 to precipitate crystals.

[0053] The raw material mixture in step S1 may further contain a raw material containing an element M'.

[0054] Among the elements in step S1, R represents an alkali metal element, P represents phosphorus, M represents an element of Groups 2 to 15 of the periodic table, has an atomic number larger than that of P, and can form a tetracoordination structure with S, M' represents an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than that of P, and can form a tetracoordination structure with S, S represents sulfur, and X represents a halogen element.

[0055] 2, the manufacturing method according to this embodiment may further include the following step S4 after the step S3: Step S4: A step of performing a post-heat treatment by heating after the crystals are precipitated in step S3.

[0056] Each step will be explained in order.

[0057] <Step S1: Mixing> Step S1 in this embodiment is a step of mixing raw materials containing elements R, P, M, and optionally M', S, and X to obtain a raw material mixture. Among the elements in the above step, R represents an alkali metal element, P represents phosphorus element, M represents an element of Groups 2 to 15 of the periodic table that has an atomic number larger than that of P and can form a tetracoordination structure with S, M' represents an element of Groups 2 to 15 of the periodic table that has an atomic number smaller than that of P and can form a tetracoordination structure with S, S represents sulfur element, and X represents a halogen element.

[0058] Examples of the alkali metal element (R) include lithium element (Li), sodium element (Na), and potassium element (K). When the obtained sulfide solid electrolyte is applied to a lithium ion secondary battery, the raw material preferably contains a substance such as lithium element (Li) as the alkali metal element (R).

[0059] As the raw material containing an alkali metal element (R), an appropriate combination of substances containing an alkali metal element, such as an alkali metal element alone or a compound containing an alkali metal element, can be used. When the alkali metal element (R) is lithium element (Li), an appropriate combination of substances containing Li, such as Li alone or a compound containing Li, can be used as the lithium element.

[0060] Examples of raw materials containing lithium element (Li) include lithium sulfide (Li ２ S), lithium iodide (LiI), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２Examples of the raw material containing lithium element (Li) include lithium compounds such as lithium ion (LiO), lithium hydroxide (LiOH), and metallic lithium. One type of raw material containing lithium element (Li) may be used, or two or more types may be used in combination.

[0061] As the raw material containing lithium element (Li), lithium sulfide is preferably used from the viewpoint of obtaining a sulfide material. In addition, when the obtained sulfide solid electrolyte contains a halogen element, it is also preferable to use lithium halide (LiX, where X is a halogen element) as the raw material containing lithium element (Li). Lithium halide will be described later.

[0062] As the raw material containing phosphorus (P), a suitable combination of substances containing P, such as simple P or a compound containing P, can be used. The raw material containing phosphorus (P) may be used alone or in combination of two or more.

[0063] As a raw material containing phosphorus (P), diphosphorus pentasulfide (P ２ S ５ ), diphosphorus trisulfide (P ２ S ３ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ ) and elemental phosphorus.

[0064] As a raw material containing element (M), which is an element of Groups 2 to 15 of the periodic table, has an atomic number greater than P, and can form a tetracoordination structure with S, conventionally known raw materials can be used. For example, as a raw material containing element (M), a simple substance consisting of element (M), an oxide of element (M), a sulfide of element (M), or a halide of element (M) can be used in appropriate combination. Specific examples of elements are shown below.

[0065] When the element M contains tin (Sn), examples of raw materials containing tin (Sn) include Sn (single Sn), SnS, and SnS. ２ , SnO, SnO ２ , SnCl ２ Among them, from the viewpoint of lithium ion conductivity, SnS ２ , SnCl ２ is preferred, and SnS ２The raw material containing tin (Sn) may be used alone or in combination of two or more.

[0066] When the element M contains antimony (Sb), examples of raw materials containing antimony (Sb) include Sb (single Sb), Sb ２ S ３ , Sb ２ S ５ The raw material containing antimony (Sb) may be used alone or in combination of two or more.

[0067] When the element M contains germanium (Ge), 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.

[0068] When the element M contains indium (In), 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.

[0069] When the element M contains copper (Cu), the raw material containing Cu may be, for example, Cu ２ O, CuO, Cu ２ S, CuS, CuCl ２ Among them, from the viewpoint of lithium ion conductivity, CuS, CuCl ２These compounds may be used alone or in combination of two or more.

[0070] When the crystals contained in the crystalline phase of the sulfide solid electrolyte obtained by the production method according to the present embodiment contain the element M′, the raw materials in step S1 further include a raw material containing the element M′ that can form a tetracoordination structure with S.

[0071] When the element M' contains silicon (Si), examples of the raw material containing Si include Si (simple Si), SiO ２ , SiS ２ Among them, from the viewpoint of lithium ion conductivity, SiO ２ The raw material containing silicon element (Si) may be used alone or in combination of two or more.

[0072] When the element M' contains aluminum (Al), examples of raw materials containing Al include Al ２ S ３ , Al ２ 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.

[0073] As the raw material containing sulfur element (S), raw materials containing S such as simple S or compounds containing S can be used in appropriate combination. The raw material containing sulfur element (S) may be used alone or in combination of two or more. ２ S is a compound that serves as both a raw material containing sulfur element (S) and a raw material containing lithium element (Li) as described above. ２ S ５ is a compound that serves as both a raw material containing sulfur element (S) and the above-mentioned raw material containing phosphorus element (P). Furthermore, SnS is a compound that serves as both a raw material containing sulfur element (S) and the above-mentioned raw material containing Sn.２ S ３ is a compound that serves as both a raw material containing elemental sulfur (S) and a raw material containing Sb as described above.

[0074] Examples of raw materials containing sulfur element (S) include phosphorus pentasulfide (P ２ S ５ ), diphosphorus trisulfide (P ２ S ３ ), other sulfur compounds containing phosphorus, elemental sulfur, and compounds containing sulfur. ２ S, CS ２ , 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.

[0075] Examples of raw materials containing a halogen element (X) 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, and boron halides. Among these, lithium halides are preferred from the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte. These compounds may be used alone or in combination of two or more. Furthermore, the halogen may be HX or X ２ It may be introduced as a gas, and when X is Br or I, Br ２ Ya I ２ It may be introduced as

[0076] The raw materials can be mixed, for example, by mixing in a mortar, mixing using media such as a planetary ball mill, or medialess mixing such as a pin mill, a powder mixer, or airflow mixing. The raw materials may be made amorphous by mixing before heating.

[0077] <Step S2: Heat Melting> Step S2 in this embodiment is a process of obtaining a melt of the raw material mixture obtained in step S1 by heat treatment.

[0078] The specific method for heating and melting the raw material mixture is not particularly limited, and the raw materials are placed in a heat-resistant container and heated in a heating furnace. The raw material mixture may be sealed in a heat-resistant container. Alternatively, the melting may be carried out in an atmosphere containing elemental sulfur. Examples of the atmosphere containing elemental sulfur include a mixed gas atmosphere of a gas containing elemental sulfur, such as sulfur gas, hydrogen sulfide gas, or sulfur dioxide gas, and an inert gas.

[0079] The heat-resistant container may be a heat-resistant container made of carbon, a heat-resistant container containing an oxide such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, or mullite, a heat-resistant container containing a nitride such as silicon nitride or boron nitride, or a heat-resistant container containing a carbide such as silicon carbide, etc. Furthermore, these heat-resistant containers may be formed in bulk 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.

[0080] As the furnace body in the heating furnace used for heating and melting, a conventionally known furnace having a heating section can be used as appropriate, and the material and size of the furnace body can also be selected arbitrarily.

[0081] The heat-melting temperature is not particularly limited as long as the raw material mixture is melted, but is preferably 600°C or higher, more preferably 600 to 1000°C, even more preferably 630 to 950°C, even more preferably 650°C or higher but less than 900°C, and particularly preferably 650°C or higher but less than 850°C. Here, from the viewpoint of homogenizing the melt in a short time, the heat-melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher. Furthermore, from the viewpoint of suppressing deterioration or decomposition of components in the melt, the heat-melting temperature is preferably 1000°C or lower, more preferably 950°C or lower, even more preferably less than 900°C, and particularly preferably less than 850°C. The heat-melting temperature is the temperature of the melt produced in the furnace body and can be adjusted by the heating unit provided in the furnace body.

[0082] The heat-melting time is not particularly limited as long as the raw material mixture is melted, but is, for example, preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, even more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. From the viewpoint of smoothly progressing the reaction, the heat-melting 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. Furthermore, from the viewpoint of suppressing deterioration or decomposition of components in the melt due to heating, the heat-melting time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0083] The heat melting is preferably performed in an inert atmosphere, such as a nitrogen gas atmosphere, an argon gas atmosphere, or a helium gas atmosphere. Alternatively, the heat melting may be performed in a gas atmosphere containing elemental sulfur.

[0084] The dew point during heat melting is preferably −20° C. or lower in order to prevent side reactions between the melt and water vapor, oxygen, etc. The lower limit of the dew point is not particularly limited, but is usually about −80° C. The oxygen concentration is preferably 1000 ppm by volume or lower.

[0085] The pressure during heating and melting is not particularly limited as long as the raw material mixture is melted, but for example, normal pressure or slight pressure is preferred, and normal pressure is more preferred.

[0086] Heat melting is more preferably carried out in a temperature range of 600 to 1000°C for 10 minutes to 10 hours, and in addition to the above, it is more preferably carried out under one or more of the following conditions: in an inert atmosphere, under a dew point of -20°C or less, and under normal pressure or slight pressure, even more preferably under two or more of the following conditions, and particularly preferably under all three of the following conditions.

[0087] In step S2, whether the raw material mixture is completely melted can be confirmed by the absence of peaks derived from crystals in high-temperature X-ray diffraction measurement.

[0088] In step S2, a compound that will become a crystal nucleus may be contained in the melt in order to facilitate the precipitation of crystals in the subsequent step S3. The method for containing the compound that will become a crystal nucleus in the melt is not particularly limited, but examples thereof include a method of adding the compound that will become a crystal nucleus to raw materials, and a method of directly adding the compound that will become a crystal nucleus to the melt that has been heated and melted.

[0089] Examples of compounds that can serve as crystal nuclei include oxides, oxynitrides, nitrides, carbides, other chalcogen compounds, and halides. Compounds that can serve as crystal nuclei are preferably compounds that have a certain degree of compatibility with the melt. Note that compounds that are completely incompatible with the melt cannot serve as crystal nuclei.

[0090] <Step S3: Cooling> Step S3 in this embodiment is a step of cooling the melt obtained in step S2 to precipitate crystals. ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅ The crystals obtained in step S3 may be used as the sulfide solid electrolyte, or the crystals that have been subjected to a post-heat treatment in the subsequent step S4 may be used as the sulfide solid electrolyte.

[0091] In step S3, the molten material obtained in step S2 is discharged at any time from a discharge port provided in the furnace body, and the process proceeds to a step of cooling and solidifying. A known method can be used to cool the molten material, and there is no particular limitation. For example, from the viewpoint of increasing the cooling rate, cooling using a twin roller, which is generally considered to have the fastest quenching rate, is preferred.

[0092] The cooling rate is preferably 0.1 to 10,000°C / sec, more preferably 0.5 to 5,000°C / sec, and even more preferably 1 to 1,000°C / sec. From the viewpoint of improving compositional homogeneity and suppressing quality variations, the cooling rate is preferably 0.1°C / sec or more, more preferably 0.5°C / sec or more, and even more preferably 1°C / sec or more. The upper limit of the cooling rate is not particularly limited, but taking into account the cooling rate of a twin roller, which is generally said to have the fastest quenching rate, the upper limit is 1,000,000°C / sec or less. From the viewpoint of practical production, the cooling rate is more preferably 10,000°C / sec or less, more preferably 5,000°C / sec or less, and even more preferably 1,000°C / sec or less.

[0093] On the other hand, a sulfide solid electrolyte having a crystalline phase may be obtained by slow cooling during cooling. Alternatively, a sulfide solid electrolyte having both a crystalline phase and an amorphous phase may be obtained. When slowly cooled, the cooling rate is preferably 0.01 to 2000°C / sec, more preferably 0.01 to 1000°C / sec, even more preferably 0.01 to 750°C / sec, even more preferably 0.01 to 500°C / sec, and particularly preferably 0.05 to 450°C / sec. Alternatively, it may be 0.01 to 10°C / sec, or may be 0.05 to 5°C / sec. Here, the cooling rate is preferably 0.01°C / sec or more, more preferably 0.05°C / sec or more, and preferably 2000°C / sec or less, more preferably 1000°C / sec or less, even more preferably 750°C / sec or less, even more preferably 500°C / sec or less, and particularly preferably 450°C / sec or less. The cooling rate may be 10° C. / sec or less, or 5° C. / sec or less. The cooling rate may be adjusted appropriately depending on the crystallization conditions.

[0094] The atmosphere during cooling is preferably a low-moisture, inert atmosphere, similar to the heating and melting in step S2. Cooling and solidification is preferably carried out under atmospheric pressure. "Atmospheric pressure" here means that the pressure is not controlled during cooling. Specifically, the pressure is about 0.8 to 1.2 atm.

[0095] <Step S4: Post-heat treatment> Step S4 in this embodiment is an optional step of performing post-heat treatment by heating again after the crystals are precipitated in step S3.

[0096] The post-heat treatment in step S4 promotes crystallization if the solid obtained in step S3 contains an amorphous phase. The post-heat treatment may also rearrange ions within the crystalline structure to increase lithium ion conductivity.

[0097] That is, the post-heat treatment refers to at least one of a heat treatment for crystallizing the obtained solid and a heat treatment for rearranging ions in the crystal structure.

[0098] The temperature in the post-heat treatment is preferably 300 to 600° C., more preferably 350 to 600° C., even more preferably 355 to 550° C., and even more preferably 360 to 500° C. Here, from the viewpoint of shortening the heat treatment time, the temperature in the post-heat treatment is preferably 300° C. or higher, more preferably 350° C. or higher, even more preferably 355° C. or higher, and even more preferably 360° C. or higher. Furthermore, from the viewpoint of preventing sintering of particles, the temperature in the post-heat treatment is preferably 600° C. or lower, more preferably 550° C. or lower, and even more preferably 500° C. or lower.

[0099] The post-heat treatment time is preferably 10 minutes to 20 hours, more preferably 10 minutes to 10 hours, even more preferably 30 minutes to 9.5 hours, even more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. From the viewpoint of production stability, the heat treatment 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 post-heat treatment time is preferably 20 hours or less, more preferably 10 hours or less, even more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0100] 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.

[0101] The post-heat treatment is more preferably carried out, for example, in a temperature range of 300 to 600°C for 10 minutes to 20 hours, and in addition to the above, it is further more preferably carried out under at least one of an inert atmosphere and a condition with a dew point of -20°C or lower, and particularly preferably under both conditions.

[0102] <Effect> Composition formula: R ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅ The crystal represented by the formula (I) can be obtained not only by the manufacturing method including the above-mentioned steps S1 to S3 or S1 to S4, but also by a solid-state reaction method. Here, the solid-state reaction method is a method in which a raw material mixture obtained by mixing raw materials is further mechanically mixed using media such as mechanical milling, and then heated to cause a solid-state reaction to obtain crystals. However, especially MS ４ Crystals containing two or more elements M that form a tetrahedral structure, MS ４ Tetrahedral structure and M'S ４ To obtain crystals having a tetrahedral structure, a very large amount of energy is required. Therefore, it is unrealistic from the viewpoint of mass production. ４ Tetrahedral structure, MS ４ Tetrahedral structure and M'S ４ It is difficult to achieve the desired ratio of tetrahedral structures. ２ Unreacted substances such as S tend to remain in the main raw materials, which reduces ionic conductivity and ２ This causes an increase in the amount of sulfur generated.

[0103] In contrast, by employing the manufacturing method according to the present embodiment including the above-described steps S1 to S3 or steps S1 to S4, the PS ４ In addition to the tetrahedral structure, MS ４ Crystals containing two or more elements M that form a tetrahedral structure, and M'S ４ Even if the crystal further contains the element M' that constitutes the tetrahedral structure, the desired crystal can be produced with excellent productivity. ４When two or more elements M are used to form the tetrahedral structure, or when MS ４ In addition to the tetrahedral structure, M'S ４ This is very suitable when the material also has a tetrahedral structure. In particular, by adjusting the conditions of steps S3 and S4, the structure of the resulting crystal and its performance as a sulfide solid electrolyte can be controlled. The reason for this is believed to be that by heating and melting the raw material mixture and then cooling it, the constituent components become uniform in the molten state, and by cooling it, a crystal structure in which the constituent components are uniformly dispersed can be obtained. Note that the production method according to this embodiment should not be interpreted as being limited to the above-mentioned mechanism of action.

[0104] Regarding the uniformity of the constituent components, especially PS ４ Tetrahedron, MS ４ Tetrahedron, M'S ４ Although the tetrahedrons tend to be non-uniform, the uniformity of this tetrahedron structure can be determined by Rietveld structural analysis of the XRD pattern. In particular, when the crystal structure has an F-43m space group, it can be easily determined by the presence or absence of a diffraction pattern of the (111) plane on the low-angle side of the (200) plane. That is, when a diffraction pattern of the (111) plane is obtained, PS ４ Tetrahedron, MS ４ Tetrahedron, M'S ４ It can be said that the tetrahedrons are not uniformly dispersed.

[0105] 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 11, 15, and 16 are working examples, and Examples 12 to 14 are comparative examples.

[0106] Examples 1 to 14: Raw materials containing each element were weighed and mixed in a mortar in a dry nitrogen gas atmosphere so as to have the composition ratios shown in Table 1 to obtain a raw material mixture. The raw materials containing each element were lithium sulfide powder (manufactured by Sigma, purity 99.98%) as a raw material containing Li and S, diphosphorus pentasulfide powder (manufactured by Sigma, purity 99%) as a raw material containing P and S, and SnS as a raw material containing Sn. ２ Sb powder (manufactured by Mitsuwa Chemical Co., Ltd., purity 99.5%) was used as a raw material containing Sb. ２ S ３SiS powder (manufactured by Mitsuwa Chemical Co., Ltd., purity 99.98%) was used as a raw material containing Si. ２ Lithium bromide powder (manufactured by Sigma, purity 99.995%) was used as a raw material containing Br and Li, lithium iodide powder (manufactured by Tokyo Chemical Industry Co., Ltd., purity 99.9%, low moisture grade) was used as a raw material containing I and Li, and lithium chloride powder (manufactured by Sigma, purity 99%) was used as a raw material containing Cl and Li. ２ S ３ When powder was used, a sulfur raw material (manufactured by Sigma, purity 99.98%) was also used to adjust the composition.

[0107] The raw material mixture obtained above was placed in a quartz tube and vacuum sealed. It was then heated in an electric furnace at 700 to 800°C for 1 hour to obtain a completely dissolved molten material. It was then cooled to room temperature at a rate of 1 to 5°C / second, and crystals were precipitated to obtain a sulfide solid electrolyte.

[0108] Table 1 shows the composition formula: ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅ The ratio expressed as {(c+c') / (b+c+c')}, the ratio expressed as {e / (b+c+c')}, and the proportion of isolated sulfur are also shown. Here, the proportion of isolated sulfur means the value expressed as {d-(b+c+c') x 4} when the molar sum of elements P, M, and M' that can form a tetrahedron by bonding with sulfur is normalized to 1.

[0109] Example 15 and Example 16 The crystals obtained in Example 7 were further subjected to post-heat treatment in a dry nitrogen gas atmosphere at 400°C for 1 hour (Example 15) or at 450°C for 1 hour (Example 16), and then cooled again to room temperature at a rate of 1°C / second, thereby obtaining a sulfide solid electrolyte.

[0110] Evaluation X-ray Diffraction Measurement (XRD) For the sulfide solid electrolytes of Examples 1 to 16, the sulfide solid electrolytes were pulverized in a mortar and passed through a 100 μm sieve to obtain powders with a D50 of approximately 10 to 20 μm. Here, D50 refers to the volume-based median diameter. XRD measurements were performed on the obtained powders using an X-ray diffractometer (Rigaku Corporation, SmartLab) under the following conditions in an environment not exposed to the atmosphere: Radiation source: CuKα radiation (λ = 1.5418 Å), tube voltage: 45 kV, tube current: 200 mA, scan angle: 10 to 100°, scan rate: 5° / min, number of steps: 0.01° / step. Silicon was mixed as an internal standard to a concentration of 10% by mass, and measurements were performed.

[0111] As an example, XRD patterns of the sulfide solid electrolytes of Examples 1, 3, 5, 7, 9, and 11 are shown in FIGS. 3 to 8. From the XRD patterns, it was confirmed that crystals of the same composition as those shown in Table 1 were obtained in all of Examples 1 to 14. Furthermore, it was confirmed that Examples 15 and 16 had the same composition as those in Example 7. Furthermore, although the composition remained unchanged, it was suggested that the crystal structure had changed from that of Example 7 due to post-heat treatment. The peak at 2θ = 28.5° in FIGS. 3 to 8 is a Si internal standard. The broad peak observed at 2θ = 16 to 17° is a peak derived from the window material of the XRD holder not exposed to air. All of the crystals obtained above were cubic argyrodite-type crystals with a crystal structure in the F-43m space group.

[0112] Furthermore, in Examples 1 to 3, PS ４ Tetrahedral structure, SnS ４ Tetrahedral structure, and SbS ４ The tetrahedral structure is shown in Examples 4 and 9 as PS ４ Tetrahedral structure, SiS ４ Tetrahedral structure, SnS ４ Tetrahedral structure, and SbS ４ The tetrahedral structure is PS in Examples 5 to 8, 10, 11, 15 and 16. ４ Tetrahedral structure, SiS ４ Tetrahedral structure, and SbS ４ The tetrahedral structure is shown in Examples 12 and 13 as PS ４ In Example 14, the tetrahedral structure is SiS４ Tetrahedral structure, and SbS ４ The Rietveld analysis of the XRD patterns confirmed that the crystals each had a tetrahedral structure. Furthermore, the absence of a diffraction pattern (diffraction peak) of the (111) plane on the low-angle side of the (200) plane in the XRD patterns confirmed that the tetrahedral structures were uniformly distributed.

[0113] <Lithium Ion Conductivity> The sulfide solid electrolytes of Examples 1 to 16 were pulverized in a mortar and passed through a 100 μm sieve to obtain powders with a D50 of approximately 10 to 20 μm. Here, D50 refers to the volume-based median diameter. The resulting powders were used as samples, and their lithium ion conductivity was measured using an AC impedance measuring device (Bio-Logic Sciences Instruments, potentiostat / galvanostat VSP). 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.

[0114] <Water resistance: H ２ Amount of S Generated> The sulfide solid electrolytes of Examples 1 to 14 were crushed in a mortar and passed through a 100 μm sieve to obtain powders with a D50 of approximately 10 to 20 μm. 20 mg of the powder obtained above was weighed out as a sample, and nitrogen gas with a dew point of −20° C. was flowed through the sample at a flow rate of 0.5 L / min for 5 hours. The amount of H generated during this process was 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.

[0115] <Water Resistance: Lithium Ion Conductivity Retention Rate> The sulfide solid electrolytes of Examples 1 to 14 were crushed in a mortar and passed through a 100 μm sieve to obtain powders with a D50 of approximately 10 to 20 μm. 150 mg of the resulting powder was weighed out as a sample, and nitrogen gas with a dew point of −20°C was passed through at a flow rate of 0.5 L / min for 1 hour. The sample was then heated in a vacuum at 80°C for 1 hour, and the lithium ion conductivity was measured under the same conditions as those described in the <Lithium Ion Conductivity> section above. The results are shown in Table 1 under "Conductivity (After Exposure) [mS / cm]." The lithium ion conductivity values ​​obtained in this test were calculated as the lithium ion conductivity retention rate, with the value obtained in the <Lithium Ion Conductivity> section set to 100% (reference). The results are shown in Table 1 under "Conductivity (Retention Rate) [%]."

[0116] <Reducing Resistance> The sulfide solid electrolytes of Examples 1 to 14 were crushed in a mortar and passed through a 100 μm sieve to obtain powders with a D50 of approximately 10 to 20 μm. 100 mg of the powder obtained above was pressed under 380 MPa to produce a compacted powder pellet with a diameter of 10 mm. This was used as a separator layer and placed between a lithium metal working electrode and a stainless steel (SUS) metal counter electrode, and a cyclic voltammetry test was performed under the following conditions: Sweep range: 2.0 V → 0.1 V vs. Li / Li ＋ , sweep speed: 1mV / sec

[0117] From the obtained cyclic voltammogram, the current value at a voltage of 0.1 V was used as an index to evaluate reduction resistance. The evaluation criteria were as follows: ○: −0.01 mA or more △: −0.02 mA or more to −0.01 mA or less ×: less than −0.02 mA The results are shown in the “reduction resistance” column of Table 1.

[0118]

[0119] From the above results, the sulfide solid electrolyte according to this embodiment has ２ It was found that the amount of sulfur generated was small, the decrease in ion conductivity when exposed to a moisture-containing atmosphere was suppressed, and the PS had good reduction resistance. ４ Tetrahedral structure and MS ４The coexistence of the tetrahedral structure and H ２ The amount of sulfur generated was reduced, and the decrease in ionic conductivity when exposed to a moisture-containing atmosphere was also suppressed. Furthermore, when comparing similar compositions, by increasing the composition ratio e of the halogen element (X), ２ It was found that the amount of sulfur generated could be further reduced. This is thought to be due to the fact that the proportion of isolated sulfur could be reduced.

[0120] On the other hand, in Examples 12 and 13, there is MS in the crystal. ４ It does not have a tetrahedral structure and is a PS ４ It has only a tetrahedral structure, but PS ４ Although the presence of the tetrahedral structure gave it excellent resistance to reduction, it had very low water resistance. ４ Although it has a tetrahedral structure, PS ４ This is an example that does not have a tetrahedral structure. As a result, although the retention rate of lithium ion conductivity was higher than in Examples 12 and 13, it still did not reach the results of Examples 1 to 11. ４ The lack of a tetrahedral structure resulted in poor reduction resistance.

[0121] Furthermore, the lithium ion conductivity at 25° C. of Example 7 was 2.6 mS / cm, whereas the lithium ion conductivity of Examples 15 and 16 was 7.2 mS / cm and 8.3 mS / cm, respectively. This shows that the lithium ion conductivity can be increased by further performing post-heat treatment by heating after the precipitation of crystals.

[0122] 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. 2023-206288) filed on December 6, 2023, the contents of which are incorporated herein by reference.

Claims

1. A sulfide solid electrolyte having a crystalline phase, wherein the crystalline phase has a composition formula: R ａ P ｂ M ｃ M' ｃ’ S ｄ X ｅ in which R represents an alkali metal element, P represents a phosphorus element, M represents an element of Groups 2 to 15 of the periodic table, has an atomic number larger than that of P and can form a tetracoordination structure with S, M' represents an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than that of P and can form a tetracoordination structure with S, S represents a sulfur element, and X represents a halogen element, in which the composition formula satisfies 3<a<7, 0<b, 0<c, 0≦c', b+c+c'=1, 3<d<6, 0.1<{(c+c') / (b+c+c')}<1.0, and 1.1≦{e / (b+c+c')}≦2.0, and the crystal is PS ４ Tetrahedral structure and MS ４ A sulfide solid electrolyte with a tetrahedral structure.

2. The sulfide solid electrolyte according to claim 1, wherein in the composition formula, 4<a<7 is satisfied.

3. The sulfide solid electrolyte according to claim 1, wherein the composition formula satisfies 0.2<{(c+c') / (b+c+c')}<1.

0.

4. The sulfide solid electrolyte according to claim 1, wherein in the composition formula, 4<d<6 is satisfied.

5. The sulfide solid electrolyte according to claim 1, wherein the composition formula satisfies 1.2≦{e / (b+c+c')}≦1.

9.

6. The sulfide solid electrolyte according to claim 1, wherein M in the composition formula includes at least one selected from the group consisting of Mn, Ni, As, Mo, Co, Ag, Cd, Ir, W, Sn, Sb, Ga, Ge, In, Pb, Bi, Cu, Ti, V, Cr, Fe, Zn, Y, Zr, Nb, Ta, W, and La.

7. The sulfide solid electrolyte according to claim 1, wherein M in the composition formula contains at least one of Sn and Sb.

8. The sulfide solid electrolyte according to claim 1, wherein M' in the composition formula contains at least one selected from the group consisting of Mg, N, Si, Al and B.

9. The sulfide solid electrolyte according to claim 1, wherein the crystal has a crystal structure of the F-43m space group.

10. The sulfide solid electrolyte according to claim 1, wherein X in the composition formula contains I.

11. The sulfide solid electrolyte according to claim 10, further comprising Br as X in the composition formula.

12. The sulfide solid electrolyte according to claim 1, wherein M and M' in the composition formula contain a total of two or more elements.

13. The sulfide solid electrolyte according to claim 12, wherein M and M' in the composition formula contain a total of eight or less elements.

14. The sulfide solid electrolyte according to claim 1, wherein R in the composition formula contains at least one element selected from the group consisting of Li, Na, and K.

15. The sulfide solid electrolyte according to claim 1, wherein R in the composition formula contains Li.

16. The sulfide solid electrolyte of claim 1, wherein the crystals have an argyrodite-type crystal structure.

17. A method for producing a sulfide solid electrolyte according to any one of claims 1 to 16, comprising the steps of: mixing raw materials containing the elements R, P, M, S and X to obtain a raw material mixture; obtaining a melt of the raw material mixture by heat treatment; and cooling the melt to precipitate crystals, wherein, among the elements, R represents an alkali metal element, P represents a phosphorus element, M represents an element in Groups 2 to 15 of the periodic table, has an atomic number larger than P and is capable of forming a tetracoordination structure with S, S represents a sulfur element, and X represents a halogen element.

18. The method for producing a sulfide solid electrolyte according to claim 17, wherein the cooling is carried out by slow cooling at a cooling rate of 0.01 to 2000° C. / sec.

19. The method for producing a sulfide solid electrolyte according to claim 17, wherein the raw material mixture further contains a raw material containing an element M', wherein M' is an element of Groups 2 to 15 of the periodic table, has an atomic number smaller than P, and is capable of forming a tetracoordination structure with S.

20. The method for producing a sulfide solid electrolyte according to claim 17, further comprising, after precipitating the crystals, carrying out a post-heat treatment by heating.

21. The method for producing a sulfide solid electrolyte according to claim 20, wherein the post-heat treatment is carried out at a temperature of 300 to 600° C. for 0 minutes to 20 hours in an inert atmosphere with a dew point of −20° C. or lower.

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