Method for manufacturing sulfide solid electrolyte, sulfide solid electrolyte, all-solid-state battery, and method for selecting raw material compound used to manufacture sulfide solid electrolyte

Abstract

To provide a method for manufacturing a sulfide solid electrolyte that suppresses discharge of N to the outside of the system in a manufacturing process of the sulfide solid electrolyte, a method for selecting a raw material compound used for manufacturing of the sulfide solid electrolyte, and an all-solid-state battery including the sulfide solid electrolyte; and a sulfide solid electrolyte having improved thermal stability, a method for manufacturing the same, and an all-solid-state battery including the sulfide solid electrolyte.SOLUTION: A sulfide solid electrolyte contains, as constituent elements, P, S, N, elemental A, elemental X, and elemental M, and has a crystal structure. A represents at least one element selected from the group consisting of Li, Na, and K. X represents at least one element selected from the group consisting of Cl, Br, and I. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a sulfide solid electrolyte, a sulfide solid electrolyte, an all-solid-state battery, and a method for selecting a raw material compound used in the manufacture of a sulfide solid electrolyte.

[0002] Non-aqueous electrolyte secondary batteries typified by lithium-ion non-aqueous electrolyte secondary batteries are widely used in electronic devices such as personal computers and communication terminals, and automobiles, etc., because of their high energy density. Generally, the non-aqueous electrolyte secondary battery includes an electrode body having a pair of electrodes electrically isolated from each other, and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring ions between both electrodes.

[0003] In recent years, sulfide solid electrolytes have attracted attention as non-aqueous electrolytes for non-aqueous electrolyte secondary batteries, and various studies have been conducted.

[0004] Patent Document 1 describes manufacturing a sulfide solid electrolyte having a composition of 75Li2S-25P2S5-yLi3N using Li2S, P2S5, and Li3N as starting materials. Patent Document 2 describes manufacturing a sulfide solid electrolyte using a raw material composition comprising Li2S, P2S5, LiBr, LiI, and Li3N.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 describes that by containing N in the sulfide solid electrolyte, the atmospheric stability (water resistance) of the sulfide solid electrolyte can be improved. However, when using Li3N as a raw material for the sulfide solid electrolyte, there was a problem that N was discharged outside the system.

[0007] Patent Document 2 describes that by amorphizing and heat-treating a raw material composition containing Li2S, P2S5, LiI, and LiBr, a high Li-ion conductive phase precipitates. However, if the heat treatment temperature is too high, there is a problem that a low Li-ion conductive phase precipitates. Patent Document 3 describes that by adding Li3N, the difference between the temperature at which a high Li-ion conductive phase is generated and the temperature at which a low Li-ion conductive phase is generated can be increased. However, the difference is as small as about 30°C at most, and further improvement has been demanded.

[0008] The present invention has been made based on the above circumstances. An object of one aspect of the present invention is to provide a method for producing a sulfide solid electrolyte capable of suppressing the discharge of N outside the system in the production process of the sulfide solid electrolyte, a method for selecting a raw material compound used in the production of the sulfide solid electrolyte, and a all-solid-state battery including the sulfide solid electrolyte. Another object of one aspect of the present invention is to provide a method for obtaining a sulfide solid electrolyte with improved thermal stability, a method for producing the same, and a all-solid-state battery including the sulfide solid electrolyte.

Means for Solving the Problems

[0009] One aspect of the present invention, which has been made to solve the above-mentioned problems, is a method for producing a sulfide solid electrolyte, comprising: preparing a composition containing P, S, N, element A, and element M; reacting the composition to obtain an intermediate; and heating the intermediate to obtain a sulfide solid electrolyte, wherein the composition comprises a raw material compound containing N, element A, and element M. A represents at least one element selected from the group consisting of Li, Na, and K. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti.

[0010] Another aspect of the present invention is a method for selecting raw material compounds used in the production of a sulfide solid electrolyte, comprising: As a candidate for the raw material compound, a candidate material containing N, element A', and element M' is selected, and the defect formation energy E of N in the candidate material is calculated using first-principles calculations. Ndefect and calculating E Ndefect is 4.00 eV or more, the candidate material is selected as the raw material compound.

[0011] Another aspect of the present invention is a sulfide solid electrolyte having a crystalline structure and containing, as constituent elements, P, S, N, element A, element X, and element M. Here, A represents at least one element selected from the group consisting of Li, Na, and K. X represents at least one element selected from the group consisting of Cl, Br, and I. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti. [Effects of the Invention]

[0012] According to the method for producing a sulfide solid electrolyte, the method for selecting raw material compounds used in the production of a sulfide solid electrolyte, and the sulfide solid electrolyte of one embodiment of the present invention, it is possible to suppress the emission of N to the outside of the system during the production process of the sulfide solid electrolyte. According to the sulfide solid electrolyte of another aspect of the present invention, a sulfide solid electrolyte with improved thermal stability can be obtained.

Brief Description of Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0014] First, an overview of the manufacturing method of the sulfide solid electrolyte disclosed by this specification will be described.

[0015] The manufacturing method of the sulfide solid electrolyte according to one aspect of the present invention is a manufacturing method of a sulfide solid electrolyte, including preparing a composition containing P, S, N, element A, and element M, reacting the above composition to obtain an intermediate, and heating the above intermediate to obtain a sulfide solid electrolyte. The composition contains a raw material compound containing N, element A, and element M, and is a manufacturing method of a sulfide solid electrolyte. Here, A represents at least one element selected from the group consisting of Li, Na, and K. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti.

[0016] In the present invention, the "composition" means a mixture formed by mixing two or more compounds. The "raw material compound" means a specific compound constituting the above composition.

[0017] The inventors have found that by using a raw material compound containing at least one element A selected from the group consisting of Li, Na, and K, at least one element M selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti, and N, it is possible to suppress the discharge of N outside the system in the manufacturing process of the sulfide solid electrolyte, and thus have reached the present invention.

[0018] According to the method for manufacturing the sulfide solid electrolyte, the discharge of N outside the system in the manufacturing process of the sulfide solid electrolyte can be suppressed. Therefore, it becomes easy to control the content of N contained in the sulfide solid electrolyte. Although the reason for this is not clear, the following reasons are speculated. In the method for manufacturing a sulfide solid electrolyte using Li3N disclosed in Patent Document 1 and Patent Document 3, the defect generation energy of N in Li3N is small, and N2 gas is likely to be generated. On the other hand, in the method for manufacturing the sulfide solid electrolyte using a raw material compound containing N, element A, and element M, the defect generation energy of N is large, and defects of N are unlikely to be generated during the synthesis process of the sulfide solid electrolyte, so N2 gas is unlikely to be generated. Therefore, the discharge of N outside the system in the manufacturing process of the sulfide solid electrolyte can be suppressed. Note that each of the elements M is an element in which the defect generation energy of N in the compound represented by Li α M β N (α and β are numerical values giving the stoichiometric ratio according to the type of element M) is 4.00 eV or more. The definition of the defect generation energy of N will be described later.

[0019] The above raw material compound containing N, element A, and element M preferably contains Li, N, element A, and element M.

[0020] According to this, the mass energy density of the all-solid-state battery including the sulfide solid electrolyte manufactured by the manufacturing method can be increased. This is because Li has the smallest atomic weight and the smallest ionic size among the alkali metal elements.

[0021] The raw material compound containing the above N, element A, and element M may be obtained by reacting a nitride of element M and a nitride of element A, or those industrially manufactured and sold may be used.

[0022] Element M is preferably one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, and P. These elements are elements for which the defect formation energy of N calculated by the first-principles calculation described later is 4.10 eV or more.

[0023] Thereby, the emission of N to the outside of the system during the manufacturing process of the sulfide solid electrolyte can be more reliably suppressed.

[0024] Element M is more preferably at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, and Nb. These elements are elements for which the defect formation energy of N calculated by the first-principles calculation described later is 4.35 eV or more.

[0025] Thereby, the emission of N to the outside of the system during the manufacturing process of the sulfide solid electrolyte can be more reliably suppressed.

[0026] The above composition preferably includes lithium sulfide, phosphorus sulfide, and the raw material compound containing the above N, element A, and element M. Since these compounds are easy to handle, the manufacturability of the sulfide solid electrolyte can be enhanced.

[0027] The above composition preferably contains Li as the above element A, the content ratio of Li to P in the above composition being 2.30 or more and 4.20 or less in molar ratio, and the content ratio of N to P in the above composition being 0.0100 or more and 1.20 or less in molar ratio. Further, it is more preferable that the above element A contains Li, the content ratio of Li to P in the above composition being 2.77 or more and 3.38 or less in molar ratio, and the content ratio of N to P in the above composition being 0.280 or more and 0.650 or less in molar ratio. Thereby, a sulfide solid electrolyte excellent in air stability and having a high ionic conductivity at 25°C can be provided.

[0028] The above composition preferably contains element X. X is at least one element selected from the group consisting of Cl, Br, and I.

[0029] It is known that a sulfide solid electrolyte containing Li, P, S, and element X forms a metastable phase with high ionic conductivity (hereinafter, also referred to as HICP (High Ion Conduction Phase)) (Patent Document 2). Further, when such a sulfide solid electrolyte contains N, it is known that the difference between the heat treatment temperature at which HICP precipitates and the heat treatment temperature at which HICP undergoes a phase transition to another phase with low ionic conductivity (hereinafter, also referred to as LICP (Low Ion Conduction Phase)) widens (Patent Document 3). However, in Patent Document 3, since a sulfide solid electrolyte is produced using Li3N, N is discharged outside the system during the production process of the sulfide solid electrolyte, and the effect of expanding the heat treatment temperature range in which HICP is stable cannot be sufficiently obtained. On the other hand, in the method for producing the sulfide solid electrolyte, the discharge of N outside the system is suppressed. Therefore, the effect of improving the thermal stability of HICP can be sufficiently exerted.

[0030] In the above composition, it is preferable that the content ratio of Li to P in the above composition is 3.10 or more and 4.20 or less in molar ratio, the content ratio of N to P in the above composition is 0.0600 or more and 0.750 or less in molar ratio, and the content ratio of X to P in the above composition is 0.180 or more and 1.30 or less in molar ratio.

[0031] As a result, a sulfide solid electrolyte with high thermal stability of HICP can be provided.

[0032] The sulfide solid electrolyte according to another aspect of the present invention is a sulfide solid electrolyte manufactured by the manufacturing method of the sulfide solid electrolyte. For such a sulfide solid electrolyte, the discharge of N to the outside of the system during the manufacturing process of the sulfide solid electrolyte is suppressed, so that various effects due to the inclusion of N can be sufficiently exerted.

[0033] The all-solid-state battery according to another aspect of the present invention includes a sulfide solid electrolyte manufactured by the manufacturing method of the sulfide solid electrolyte. For such an all-solid-state battery, the discharge of N to the outside of the system during the manufacturing process of the sulfide solid electrolyte is suppressed, so that various effects due to the inclusion of N can be sufficiently exerted.

[0034] The method for selecting a raw material compound used in the production of a sulfide solid electrolyte according to another aspect of the present invention is a method for selecting a raw material compound used in the production of a sulfide solid electrolyte, which comprises selecting a candidate material containing N, element A´, and element M´ as a candidate for the raw material compound, and calculating the defect formation energy E of N inside the candidate material using first-principles calculations. Ndefect When the calculated value of E is 4.00 eV or more, the candidate material is selected as the raw material compound. Ndefect is calculated, and when the calculated value of E is 4.00 eV or more, the candidate material is selected as the raw material compound. When there are multiple N occupancy sites in the crystal structure of the candidate material, E is calculated for each N occupancy site, and the one with the lowest value is used as the E of the candidate material. Ndefect is calculated, and the one with the lowest value is used as the E of the candidate material. Ndefect for the candidate material.

[0035] The raw material compound selected by the selection method has a large defect generation energy of N and is unlikely to generate N defects during the synthesis process of the sulfide solid electrolyte, so it is unlikely to generate N2 gas. Therefore, when the sulfide solid electrolyte is produced using the above raw material compound, the discharge of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte can be suppressed.

[0036] The above E Ndefect When it is 4.10 eV or more, it is preferable to select the candidate material as the raw material compound.

[0037] According to this, the discharge of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte can be more reliably suppressed.

[0038] The above E Ndefect When it is 4.35 eV or more, it is more preferable to select the candidate material as the raw material compound.

[0039] According to this, the discharge of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte can be further reliably suppressed.

[0040] A method for manufacturing a sulfide solid electrolyte according to another aspect of the present invention includes preparing a composition containing a raw material compound selected by a method for selecting a raw material compound used in the manufacture of the sulfide solid electrolyte, reacting the composition to obtain an intermediate, and heating the intermediate to obtain a sulfide solid electrolyte.

[0041] According to this, the discharge of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte can be suppressed. Therefore, it becomes easy to control the content of N contained in the sulfide solid electrolyte.

[0042] A sulfide solid electrolyte according to another aspect of the present invention is a sulfide solid electrolyte manufactured by the manufacturing method. With such a sulfide solid electrolyte, the discharge of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte is suppressed, so that various effects due to the inclusion of N can be sufficiently exhibited.

[0043] The all-solid-state battery according to another aspect of the present invention includes a sulfide solid electrolyte manufactured using a raw material compound selected by the selection method. With such a sulfide solid electrolyte, the emission of N to the outside of the system during the manufacturing process is suppressed, so that various effects due to the inclusion of N can be fully exhibited.

[0044] The sulfide solid electrolyte according to another aspect of the present invention is a sulfide solid electrolyte containing, as constituent elements, P, S, N, element A, element X, and element M and having a crystal structure. Here, A represents at least one element selected from the group consisting of Li, Na, and K. X represents at least one element selected from the group consisting of Cl, Br, and I. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti.

[0045] With such a sulfide solid electrolyte, the thermal stability of HICP can be enhanced as compared with a sulfide solid electrolyte composed only of Li, P, S, N, and element X. [[ID=eleven]]

[0046] It is preferable that element M is at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, and B.

[0047] According to this, the thermal stability of HICP can be further enhanced.

[0048] It is preferable that the above crystal structure has diffraction peaks at 2θ = 20.2° ± 0.5° and 23.6° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0049] By having the above crystal structure, the sulfide solid electrolyte can obtain good Li ion conductivity.

[0050] The all-solid-state battery according to another aspect of the present invention is an all-solid-state battery containing, as constituent elements, P, S, N, element A, element X, and element M and having a crystal structure, and including a sulfide solid electrolyte.

[0051] One of the advantages of all-solid-state batteries compared to non-aqueous electrolyte batteries is that the upper limit of the operating temperature is extremely high. This advantage is obtained because the solid electrolyte has high thermal stability. However, Patent Document 2 and Patent Document 3 describe that a sulfide solid electrolyte containing Li, P, S, N, Br, and I undergoes a phase transition from a high Li-ion conduction phase to a low Li-ion conduction phase when the heating temperature is high. That is, the operating temperature of an all-solid-state battery equipped with such a sulfide solid electrolyte was limited by the phase transition temperature of the high Li-ion conduction phase. On the other hand, the sulfide solid electrolyte has higher thermal stability of HICP compared to conventional sulfide solid electrolytes that do not contain element M. Therefore, an all-solid-state battery equipped with the sulfide solid electrolyte of the present invention can fully enjoy the advantage of an all-solid-state battery that can increase the upper limit of the operating temperature of the battery.

[0052] The sulfide solid electrolyte according to another aspect of the present invention is a crystalline sulfide solid electrolyte containing P, S, N, element A, and element M. Here, A represents at least one element selected from the group consisting of Li, Na, and K. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti.

[0053] For such a sulfide solid electrolyte, by suppressing the emission of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte, the atmospheric stability and the like can be enhanced.

[0054] It is preferable that element M is at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, and B.

[0055] According to this, by more surely suppressing the emission of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte, the atmospheric stability and the like can be further enhanced.

[0056] Hereinafter, a method for manufacturing a sulfide solid electrolyte, a sulfide solid electrolyte, an all-solid-state battery, and a method for selecting a raw material compound used in the manufacture of a sulfide solid electrolyte according to an embodiment of the present invention will be described in detail. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the content disclosed in this specification and common general knowledge in the relevant field.

[0057] <Method for manufacturing sulfide solid electrolyte> [Embodiment] A method for manufacturing a sulfide solid electrolyte according to an embodiment of the present invention includes a preparation step of preparing a composition containing P, S, N, element A, and element M, a reaction step of reacting the above composition to obtain an intermediate, and a heating step of heating the above intermediate to obtain a sulfide solid electrolyte. The above composition includes a raw material compound containing N, element A, and element M. Here, A is at least one element selected from the group consisting of Li, Na, and K. M is at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti. In this embodiment, the case where Li is contained as element A will be taken as an example to explain the method for manufacturing the sulfide solid electrolyte. FIG. 1 is a flowchart showing an example of the method for manufacturing the sulfide solid electrolyte according to this embodiment, and will be described below accordingly.

[0058] (Preparation step) In this step, a composition containing Li, P, S, N, and element M is prepared. The above composition is preferably a mixture of one or more raw material compounds containing N, Li, and element M (hereinafter also referred to as Li-M-N-containing compounds) and one or more raw material compounds containing Li, P, and S.

[0059] In FIG. 1, first, Li3N and a nitride of element M are prepared and mixed in a mortar or the like. Next, pellets of the above mixed raw material compounds are manufactured. Next, the above pellets are heat-treated to manufacture a Li-M-N-containing compound.

[0060] Note that the means for preparing the Li-M-N-containing compound is not limited to this, and it may be prepared by other methods. For example, the raw materials of the Li-M-N-containing compound may be two or more compounds containing any one of N, Li, and element M. The Li-M-N-containing compound may be prepared by mechanical milling. As the M-N-containing compound, one that is industrially manufactured and sold may be prepared.

[0061] As the Li-M-N-containing compound, a lithium composite nitride of element M is preferably used. Examples of the lithium composite nitride of element M include Li 3 / 2 Al 1 / 2 N, Li 3 / 2 B 1 / 2 N, Li 5 / 3 Si 1 / 3 N, Li 9 / 5 Si 3 / 10 N, Li 7 / 4 P 1 / 4 N, LiMgN, LiHf 1 / 2 N, Li 3 / 2 Sc 1 / 2 N, LiZr 1 / 2 N, Li 5 / 3 Ti 1 / 3 N, Li 4 / 3 Ta 1 / 3 N, Li 7 / 4 Ta 1 / 4 N, Li 7 / 4 Nb 1 / 4 N, LiC 1 / 2 Lithium composite nitrides such as N and the like can be mentioned. Among these, Li 3 / 2 Al 1 / 2 N, Li 3 / 2 B 1 / 2 N, and Li 5 / 3 Si 1 / 3 N are preferred. Also, from the viewpoint of suppressing the precipitation of Li2S, Li 3 / 2 Al 1 / 2 N is particularly preferred, and from the viewpoint of improving the thermal stability of HICP, Li 3 / 2 B 1 / 2 N and Li 5 / 3 Si 1 / 3N is particularly preferred. From the perspective of suppressing the discharge of N outside the system in the manufacturing process of the sulfide solid electrolyte, Li 3 / 2 Al 1 / 2 N and Li 3 / 2 B 1 / 2 N is particularly preferred.

[0062] Examples of the raw material compound containing element M include an oxide of element M, a sulfide of element M, a nitride of element M, an alloy of element M and Li, etc. Examples of the sulfide of element M include Al2S3, SiS2, etc. Examples of the nitride of element M include AlN, Si3N4, BN, Mg3N2, etc. The raw material compound containing element M may be used alone or in combination of two or more.

[0063] Element M in the manufacturing method may be at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti, and is not particularly limited. Among these, from the perspective of more reliably suppressing the discharge of N outside the system in the manufacturing process of the sulfide solid electrolyte, element M is preferably any one of Al, Ta, Si, Sc, Mg, Nb, B, and Hf, more preferably any one of Al, Ta, Si, Sc, Mg, and Nb. Further, since it is easily available, element M is more preferably any one of Al, Si, and B. In particular, element M may be Al.

[0064] Examples of the raw material compound containing N include Li3N, PN, P3N5, S4N4, S2N2, S4N2, etc. Among these, Li3N is preferred. The raw material compound containing N may be used alone or in combination of two or more.

[0065] Examples of the raw material compound containing Li (also referred to as Li compound) include Li2S, Li2O, Li3N, Li2CO3, metallic lithium, etc. Among these, Li2S is preferred. The raw material compound containing Li may be used alone or in combination of two or more.

[0066] Examples of the raw material compound containing P (also referred to as P compound) include P2S3, P2S5, P2O5, P3N5, elemental phosphorus, etc. Among these, P2S3 and P2S5 are preferred, and P2S5 is particularly preferred. The raw material compound containing P may be used alone or in combination of two or more.

[0067] Examples of the raw material compound containing S include Li2S, P2S3, P2S5, sulfide of element M, elemental sulfur, etc. The raw material compound containing S may be used alone or in combination of two or more.

[0068] The above composition preferably contains a Li compound, a P compound, and a Li-M-N-containing compound, and it is more preferable that at least one of the above Li compound and the above P compound contains S. As the Li compound, the P compound, and the Li-M-N-containing compound, lithium sulfide, phosphorus sulfide, and a compound represented by the general formula Li α M β N (α and β are numerical values giving the stoichiometric ratio according to the type of element M) is more preferably contained.

[0069] In the case of a sulfide solid electrolyte, when the Li content is high, Li2S precipitates, resulting in a decrease in air stability, and when it is low, there is a risk of a decrease in ionic conductivity. Also, when the N content is high, Li2S precipitates, resulting in a decrease in air stability, and when it is low, there is a risk that the effects such as the improvement of air stability by containing N cannot be fully exerted. From these viewpoints, it is preferable that the above composition simultaneously satisfies the following formulas in terms of the elemental ratio in the mixed state, each in molar ratio. 2.30 ≦ Li / P ≦ 4.20 0.0100 ≦ N / P ≦ 1.20 It is more preferable that the above Li / P and the above N / P simultaneously satisfy the following formulas respectively. 2.36 ≦ Li / P ≦ 4.12 0.0200 ≦ N / P ≦ 1.11 It is even more preferable that the above Li / P and the above N / P simultaneously satisfy the following formulas respectively. 2.36 ≤ Li / P ≤ 4.00 0.0600 ≤ N / P ≤ 0.900 It is more preferable that the above Li / P and the above N / P simultaneously satisfy the following equations respectively. 2.60 ≤ Li / P ≤ 3.40 0.190 ≤ N / P ≤ 0.710 It is particularly preferable that the above Li / P and the above N / P simultaneously satisfy the following equations respectively. 2.77 ≤ Li / P ≤ 3.38 0.280 ≤ N / P ≤ 0.650

[0070] In addition, in the above composition, the molar ratios of the respective elements of Li, P, S, N, and element M are represented by the general formula (100 - z)(yLi₂S·(1 - y)P₂S₅)·zLi α M β N (where 0 < z ≤ 40, 0.50 ≤ y ≤ 0.75, α and β are numerical values that give the stoichiometric ratio according to the type of element M). According to this, a sulfide solid electrolyte excellent in air stability and ionic conductivity at 25°C can be produced. Note that the above general formula shows the content ratios of Li, S, P, N, and element M, and the above composition α M β N does not specify that it consists of.

[0071] In the above general formula, z is preferably greater than 0 and 40 or less, and more preferably 1 or more and 30 or less. When z in the above general formula is within the above range, a sulfide solid electrolyte excellent in air stability and ionic conductivity can be produced. Furthermore, when 1 ≤ z ≤ 30, a sulfide solid electrolyte with increased ionic conductivity at 25°C can be produced. When 10 ≤ z ≤ 40, a so-called cross-linked sulfur P₂S₇ 4- (S₃P - S - PS₃) is reduced, and a sulfide solid electrolyte excellent in air stability that substantially does not contain Li₂S, which easily reacts with water, can be produced.

[0072] In the above general formula, y is preferably 0.50 or more and 0.75 or less, and more preferably 0.67 or more and 0.70 or less. By having the content ratios of Li2S and P2S5 in the above composition within the above ranges, a sulfide solid electrolyte with enhanced ionic conductivity at 25°C can be produced.

[0073] In the above general formula, α and β are numerical values that give a stoichiometric ratio according to the type of element M. The values of α and β are not particularly limited, and for example, 0.80 ≤ α ≤ 3.0 and 0.10 ≤ β ≤ 1.2 may be acceptable.

[0074] (Reaction step) In this step, the above composition is reacted by performing mechanical milling on a composition containing Li, P, S, N, and element M to obtain an intermediate. Note that the means for obtaining the intermediate is not limited to this, and it may be obtained by other methods. For example, in FIG. 1, instead of mechanical milling, a melt quenching method or the like may be performed.

[0075] Mechanical milling may be either dry or wet, but wet milling is preferred because it can mix the raw material compounds more uniformly. Examples of mechanical milling include container-driven mills, media agitation mills, milling by high-speed rotary grinders, roller mills, jet mills, etc. Examples of container-driven mills include rotary mills, vibration mills, planetary mills, etc. Examples of media agitation mills include attritors, bead mills, etc. Examples of milling by high-speed rotary grinders include hammer mills, pin mills, etc. Among these, container-driven mills are preferred, and planetary mills are particularly preferred.

[0076] The intermediate obtained in the reaction step may have a crystal structure, but is preferably a so-called sulfide glass. "Sulfide glass" means a sulfide solid electrolyte containing an amorphous structure. When the intermediate is a sulfide glass, a sulfide solid electrolyte with few crystal phases of low atmospheric stability such as Li2S and with high dispersion of N, element M, etc. can be obtained.

[0077] (Heat treatment process) In this process, a sulfide solid electrolyte is produced by heat-treating the intermediate at a temperature equal to or higher than the crystallization temperature. The heat treatment may be carried out under a reduced-pressure atmosphere or under an inert gas atmosphere. The crystallization temperature can be determined by measurement using a differential scanning calorimeter (DSC). For example, Li7P3S 11 In order to obtain a crystal structure, the heat treatment temperature is preferably 250°C or higher and 400°C or lower. In order to obtain a β-Li3PS4 crystal structure, the heat treatment temperature is preferably 200°C or higher and 400°C or lower. Also, in order to obtain a first crystal structure having diffraction peaks at 2θ = 17.9° ± 0.5°, 19.1° ± 0.5°, 29.1° ± 0.5°, and 29.8° ± 0.5° in X-ray diffraction measurement using CuKα radiation, the heat treatment temperature is preferably 250°C or higher and 400°C or lower. This is because when heat-treated at a high temperature such as 500°C, there is a possibility of phase transition to the stable phase Li4P2S6.

[0078] [Modification example] The method for producing a sulfide solid electrolyte according to the present invention is not limited to the above-described embodiment, and can be implemented in various modified and improved forms in addition to the above-described aspects.

[0079] In the above embodiment, a Li2S-P2S5-based sulfide solid electrolyte has been described as an example, but an LGPS-type sulfide solid electrolyte or an argyrodite-type sulfide solid electrolyte may also be produced by the production method. Examples of the LGPS-type sulfide solid electrolyte include Li 10 GeP2S 12 and the like. A crystal structure having a crystal phase of Li 10 GeP2S 12 has diffraction peaks at positions of 2θ = 14.4° ± 0.5°, 20.1° ± 0.5°, 20.4° ± 0.5°, 26.9° ± 0.5°, 29.5° ± 0.5°, and 47.3° ± 0.5° in X-ray diffraction measurement using CuKα radiation. Examples of the argyrodite-type sulfide solid electrolyte include Li6PS5Cl and the like. The crystal structure having the crystal phase of Li6PS5Cl has diffraction peaks at positions of 2θ = 15.6° ± 0.5°, 25.5° ± 0.5°, 30.0° ± 0.5°, 31.4° ± 0.5°, 45.0° ± 0.5°, and 52.5° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0080] [Modification Example 1] As Modification Example 1, an embodiment of manufacturing an LGPS-type sulfide solid electrolyte will be described. By adding a raw material compound containing Ge to the composition in the above preparation step, an LGPS-type sulfide solid electrolyte can be manufactured. Examples of the raw material compound containing Ge include GeS2 and the like. When manufacturing an LGPS-type sulfide solid electrolyte, it is preferable that the composition simultaneously satisfies the following formula in terms of the elemental ratio in molar ratio. 5.01 ≦ Li / P ≦ 5.61 0.0051 ≦ N / P ≦ 0.41 By setting the content ratio of the elements in the above composition within the above range, a sulfide solid electrolyte having a crystal phase of Li 10 GeP2S 12 and having a high ionic conductivity at 25°C can be manufactured.

[0081] [Modification Example 2] As Modification Example 2, an embodiment of manufacturing a sulfide solid electrolyte containing Li, P, S, N, element X, and element M as constituent elements and having a crystal structure will be described. X is at least one element selected from the group consisting of Cl, Br, and I.

[0082] In Modification Example 2, by adding a raw material compound containing element X to the above composition, a sulfide solid electrolyte containing Li, P, S, N, element X, and element M and having crystallinity is manufactured. According to this, a sulfide solid electrolyte having HICP and having improved thermal stability of HICP can be manufactured.

[0083] Examples of the raw material compound containing element X include lithium halides, sulfur halides, phosphorus halides, M η X σ (However, η = 1 or 2, and σ is an integer from 1 to 10.) Examples include halides of element M represented by the formula. Examples of lithium halides include LiCl, LiBr, LiI, etc. Examples of sulfur halides include SCl2, S2Cl2, SBr2, S2Br2, SI2, S2I2, etc. Examples of phosphorus halides include PCl3, PCl5, POCl3, PBr3, PBr5, POBr3, PI3, PCI4, P2I4, etc. Examples of the halides of the above element M include AlBr3, BBr3, AlCl3, AlBr3, AlI3, SiCl3, SiCl4, SiBr4, SiI4, SiBrI3, SiBr2I2, SiBr3I, BCl3, BBr3, BI3, etc. Among these, lithium halides and phosphorus halides are preferred, and lithium halides are more preferred. As lithium halides, LiBr and LiI are preferred. The raw material compound containing element X may be used alone or in combination of two or more. Also, the above composition may contain one kind of element X alone or two or more kinds. In particular, from the viewpoint of increasing the ionic conductivity at 25 °C, it is preferable to contain Br or I alone as element X, and it is more preferable to contain Br alone. It is also preferable to contain Br and I simultaneously.

[0084] In Modification 2, when the above composition contains Br and I simultaneously, the content of Br with respect to the total amount of Br and I in the above composition is preferably 1 mol% or more and 99 mol% or less, and more preferably 5 mol% or more and 80 mol% or less.

[0085] When the content of Li is high, Li2S precipitates, resulting in a decrease in air stability. When the content of Li is low, there is a risk that HICP will not precipitate. In addition, when the content of N is high, Li2S precipitates, leading to a decrease in air stability. When the content of N is low, there is a risk that the effect of containing N cannot be fully exerted. Further, when the content of element X is high, a crystal phase of lithium halide may remain in the sulfide solid electrolyte, reducing the ionic conductivity. When the content of element X is low, there is a risk that the effect of containing element X cannot be fully exerted. From these viewpoints, in the composition in the preparation process of Modification 2, it is preferable that the elemental ratios in the mixed state simultaneously satisfy the following formulas in terms of molar ratio. 3.10 ≦ Li / P ≦ 4.20 0.0600 ≦ N / P ≦ 0.750 0.180 ≦ X / P ≦ 1.30 Moreover, it is more preferable that the above Li / P, the above N / P, and the above X / P simultaneously satisfy the following formulas. 3.10 ≦ Li / P ≦ 3.90 0.0900 ≦ N / P ≦ 0.750 0.180 ≦ X / P ≦ 1.00

[0086] In the above composition, the molar ratios of the respective elements of Li, P, S, N, element X, and element M are represented by the general formula (100 - z){(1 - y)[xLi2S·(1 - x)P2S5]·yLi α M β N}·zLiX (where 0.50 ≦ x ≦ 0.80, 0 < y ≦ 0.50, 5 ≦ z ≦ 40, α and β are numerical values giving the stoichiometric ratio according to the type of element M), and it is preferable that x, y, and z are 0.67 ≦ x ≦ 0.73, 0.10 ≦ y ≦ 0.30, and 10 ≦ z ≦ 30, respectively. Thereby, the thermal stability of HICP can be improved. Moreover, when the above composition contains two types of elements X1 and X2 as element X, the above general formula is (100 - z1 - z2){(1 - y)[xLi2S·(1 - x)P2S5]·yLi α M βN·z1LiX1·z2LiX2 (where 0.50 ≦ x ≦ 0.80, 0 < y ≦ 0.50, 5 ≦ (z1 + z2) ≦ 40, and α and β are numerical values that give stoichiometric ratios according to the type of element M) can also be represented. In this case, it is preferable that x, y, z1, and z2 are 0.67 ≦ x ≦ 0.73, 0.10 ≦ y ≦ 0.30, and 10 ≦ (z1 + z2) ≦ 30, respectively. Note that the above general formula shows the content ratios of Li, S, P, N, element M, and element X, and the above composition does not specify that it consists of Li2S, P2S5, Li α M β N, and LiX.

[0087] In the above general formula, when element M is either Al or B, α = 2 / 3 and β = 1 / 2 may be used. In this case, it is preferable that x, y, and z are 0.50 ≦ x ≦ 0.80, 0 < y ≦ 0.50, and 5 ≦ z ≦ 40, respectively. More preferably, 0.60 ≦ x ≦ 0.75, 0.050 ≦ y ≦ 0.40, and 10 ≦ z ≦ 30. Even more preferably, 0.67 ≦ x ≦ 0.73, 0.10 ≦ y ≦ 0.30, and 15 ≦ z ≦ 25.

[0088] The raw materials used in the reaction process of Modification Example 2 preferably include a Li compound, a P compound, a halogen compound, and a Li-M-N-containing compound. More preferably, at least one of the above Li compound and the above P compound contains an S element. Further, as the above Li compound, the above P compound, the above halogenated compound, and the above Li-M-N-containing compound, lithium sulfide, phosphorus sulfide, lithium halide, and a compound represented by the general formula Li α M β N (α and β are numerical values that give stoichiometric ratios according to the type of element M) are more preferably contained.

[0089] In the heat treatment step of Modification Example 2, a sulfide solid electrolyte is produced by heat-treating the intermediate at a temperature equal to or higher than the crystallization temperature. The heat treatment may be performed under a reduced pressure atmosphere or under an inert gas atmosphere. The crystallization temperature can be determined by measurement using a differential scanning calorimeter (DSC).

[0090] In Modification 2, a sulfide solid electrolyte having HICP is produced. It is presumed that HICP further undergoes a phase transition to β-Li3PS4 after undergoing a phase transition to either LICP or a specific crystal structure C. Among these crystal phases, HICP has the highest ionic conductivity. Therefore, in the heat treatment step in Modification 2, the lower limit of the heat treatment temperature is preferably equal to or higher than the production temperature T of HICP. H Also, the upper limit of the heat treatment temperature is preferably equal to or lower than the production temperature T of β-Li3PS4, and more preferably equal to or lower than the production temperature T of LICP β or the production temperature T of the specific crystal structure C. T L 、T C 、T H 、T L 、T C and T β can be determined by XRD measurement. For the sulfide solid electrolyte produced in Modification 2, T β -T H is preferably ≧40°C, more preferably ≧50°C, even more preferably ≧60°C, and particularly preferably ≧70°C. β -T H For the sulfide solid electrolyte produced in Modification 2, it is preferably that T β -T H ≧50°C, more preferably ≧60°C, even more preferably ≧70°C, and particularly preferably ≧80°C. β -T H ≧60°C, even more preferably ≧70°C, and particularly preferably ≧80°C. β -T H ≧70°C is particularly preferred.

[0091] The sulfide solid electrolyte produced in Modification 2 has a wide heat treatment temperature range in which the ionic conductivity does not decrease. That is, even if the heat treatment temperature deviates from the intended temperature in the heat treatment step, there is little risk that the ionic conductivity of the produced sulfide solid electrolyte will decrease. Therefore, according to the embodiment of Modification 2, there is an advantage that a sulfide solid electrolyte having high ionic conductivity can be produced without requiring strict temperature control in the heat treatment step.

[0092] Note that "HICP" represents a crystal phase having diffraction peaks at 2θ = 20.2° ± 0.5° and 23.6° ± 0.5° in X-ray diffraction measurement using CuKα radiation. This crystal structure is the crystal phase described in Patent Document 2 and the like, and is a crystal phase with high Li ion conductivity. "LICP" is a crystal phase having diffraction peaks at 2θ = 21.0° ± 0.5° and 28.0° ± 0.5° in X-ray diffraction measurement using CuKα radiation. This crystal structure is the crystal phase described in Patent Document 2 and the like, and is a crystal phase with low Li ion conductivity. "Specific crystal structure C" represents a crystal phase having diffraction peaks at 2θ = 17.5° ± 0.5° and 24.9° ± 0.5° in X-ray diffraction measurement using CuKα radiation. "β-Li3PS4" represents a crystal phase having diffraction peaks at 2θ = 17.5° ± 0.5°, 18.1° ± 0.5°, 29.1° ± 0.5°, 29.9° ± 0.5°, and 31.2° ± 0.5° in X-ray diffraction measurement using CuKα radiation.

[0093] The X-ray diffraction measurement using CuKα radiation in this specification is performed by the following procedure. A hermetic sample holder for X-ray diffraction measurement is filled with a solid electrolyte powder to be measured under an argon atmosphere with a dew point of -50°C or lower. Powder X-ray diffraction measurement is performed using an X-ray diffractometer ("MiniFlex II" manufactured by Rigaku). The radiation source is CuKα radiation, the tube voltage is 30 kV, the tube current is 15 mA, and the diffracted X-rays are detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2) through a Kβ filter with a thickness of 30 μm. The sampling width is 0.01°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm.

[0094] <Method for Selecting Raw Material Compounds> According to the method for producing a sulfide solid electrolyte of the present invention, by using a raw material compound containing N, element A, and element M, it is possible to suppress the release of N outside the system during the production process of the sulfide solid electrolyte. In selecting element A and element M that can obtain such an effect, the present inventors used first-principles calculations. Hereinafter, a method for selecting a raw material compound used in the production of a sulfide solid electrolyte according to an embodiment of the present invention will be described.

[0095] In this embodiment, the raw material compound is selected by the procedures shown in (1) to (3). (1) Select a candidate material containing N, element A´, and element M´, where the first nearest neighbor atoms of the above element A´ and the above element M´ are N. (2) Using first-principles calculations, calculate the defect formation energy E Ndefect of N inside the above candidate material. (3) When the above E Ndefect is 4.00 eV or more, select the above candidate material as the above raw material compound.

[0096] First-principles calculation is a calculation method for predicting physical properties non-empirically, and it is a method that can calculate the total energy of a model containing atoms with known atomic numbers and spatial coordinates, and the electronic energy band structure. By calculating the forces acting on the atoms, structure optimization becomes possible, and lattice constants, stable structures at 0 K, band gaps, etc. can be calculated. The calculation methods are roughly divided into two types: the "wave function theory" type and the "density functional theory" type. The calculation method used in this specification is based on density functional theory.

[0097] The defect formation energy E Ndefect of N is the energy value required to remove N from the crystal structure to generate a defect. The defect formation energy of N is the total energy E perfect of the crystal structure without defects, the total energy E Nvacancy of the crystal structure containing N defects, and the chemical potential μ N of the N atom, and is calculated using the following formula (1). E Ndefect = (E Nvacancy + μ N ) - E perfect Formula (1) That is, the procedure for calculating the defect formation energy E Ndefect of N is as follows. (a) Obtain the composition and crystal structure of the candidate material. (b) Calculate the chemical potential μ of the N atom to be desorbed as a defect. N Calculate it. (c) Calculate the total energy E of the defect-free crystal structure by a structure optimization calculation. perfect Calculate it by a structure optimization calculation. (d) Calculate the total energy E of the crystal structure containing N defects by a structure optimization calculation. Nvacancy Calculate it by a structure optimization calculation. (e) Calculate the defect formation energy E of N according to formula (1). Ndefect Calculate it. When there are multiple N occupancy sites in the crystal structure of the candidate material, calculate E for each N occupancy site, and use the one with the lowest value as E of the candidate material. Ndefect Calculate it, and use the one with the lowest value as E of the candidate material. Ndefect Use it. The composition and crystal structure of the candidate material can be arbitrarily selected from those available from known publications, databases, etc. The candidate material is not particularly limited as long as it is a compound containing N, element A´, and element M´, but it is preferably a compound stable under normal temperature and pressure.

[0098] In this embodiment, element A´ is a metal element. Element M´ is an element other than nitrogen belonging to any of Groups 2 to 15 of the periodic table and is different from element A´. N is a nitrogen element. Element A´ is not particularly limited, but is preferably any of an alkali metal element, an alkaline earth metal element, and an aluminum element, more preferably at least one selected from Li, Na, K, Mg, Ca, Al, and even more preferably Li. This makes it easier to operate the sulfide solid electrolyte as a battery.

[0099] In this embodiment, Li α M´ βFor the candidate material represented by N (where α and β are numerical values giving the stoichiometric ratio according to the type of element M), and for Li3N, the defect formation energy of N was calculated. That is, Li was selected as element A´. As element M´, B, Mg, Al, Si, P, Ca, Sr, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Sr, Y, Zr, Nb, In, Sn, Ce, Hf, Ta, C were evaluated. In the first-principles calculation, the computational software Vienna Ab-initio Simulation Package (VASP) was used. The calculation conditions are as follows. The k-points were set so that the value of k-resolution was about 1000. k-resolution is the product of the number of atoms in the model and the k-points in the a, b, and c axis directions. Cutoff energy of plane-wave basis functions: 520 eV Approximation method for exchange-correlation interaction: GGA+U Pseudopotential: PAW(PBEsol) k-points: k-resolution ≒ 1000 Convergence condition for SCF calculation: 10 -4 eV Occupancy (Occ.) of each atomic site: 1 For the first-principles calculation of materials containing transition metal elements V, Cr, Mn, Fe, Co, Ni in which the 3d orbit is the outermost shell orbit and the 3d orbit is not closed-shell and there are electrons in the 3d orbit in the state of a cation with a stable valence, the Hubbard U eff values shown in Table 1 were used as calculation conditions. Thereby, the localization effect of electrons in the d orbit was reflected in the calculation. The Hubbard U eff values shown in Table 1 were cited from the calculation conditions of the first-principles calculation performed in the crystal structure database Materials Project (https: / / materialsproject.org / #search / materials) (as of August 22, 2019). By searching for materials containing V, Cr, Mn, Fe, Co, Ni in the database, the U eff values were obtained.

[0100]

Table 1

[0101] In addition, in the above procedure (d), in order to reduce the interaction between N defects, a calculation model cell was designed such that the lattice constants a, b, and c were all about 10 Å within the range where the total number of atoms did not exceed 200. Table 2 shows the lattice constants used in the calculation of some candidate materials.

[0102]

Table 2

[0103] Table 3 shows the element M´, the chemical composition of each candidate material, and the N defect formation energy E Ndefect thereof.

[0104]

Table 3

[0105] From Table 3, it can be seen that the N defect formation energy E Ndefect in Li3N where N defects are likely to be generated is 2.94 eV. In addition, for each of the elements V, Y, Ga, Ca, Ce, Sn, Zn, Ge, Cr, Mn, Sr, In, Co, Ni, and Fe, it can be seen that the N defect formation energy E α M´ β in Li Ndefect N is as small as 3.88 eV or less. Therefore, in candidate materials containing any one of V, Y, Ga, Ca, Ce, Sn, Zn, Ge, Cr, Mn, Sr, In, Co, Ni, and Fe as the element M´, N defects are likely to be generated, and it is predicted that the effect of the present invention of suppressing the discharge of N out of the system in the manufacturing process of the sulfide solid electrolyte cannot be obtained or the effect is small. On the other hand, for each of the elements Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti, the N defect formation energy E α M´ β in Li NdefectIt can be seen that it is as large as 4.00 eV or more. Therefore, if it is a candidate material containing any one of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti as the element M', it is predicted that N defects are unlikely to be generated, and there is a very high possibility that the effect of the present invention of suppressing the discharge of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte will be exhibited.

[0106] The candidate material has a larger N defect generation energy E Ndefect The larger the value, the less likely N defects are to be generated, and it is predicted that the discharge of N to the outside of the system in the manufacturing process of the sulfide solid electrolyte can be further suppressed. Therefore, in the present embodiment, the N defect generation energy E Ndefect of the candidate material is 4.00 eV or more, preferably 4.10 eV or more, more preferably 4.20 eV or more, still more preferably 4.30 eV or more, and particularly preferably 4.35 eV or more.

[0107] In the present embodiment, calculations were performed for the case where Li is included as the element A'. That is, first-principles calculations were performed using Li α M' β N as a model. However, the present invention is not limited to this. The element A' may be a metal element. For example, as the element A', a candidate material containing any one of Na, K, Mg, Ca, and Al may be selected, and a raw material compound may be selected using first-principles calculations.

[0108] <Sulfide solid electrolyte> [Embodiment 1] The sulfide solid electrolyte according to an embodiment of the present invention is a composition containing P, S, N, element A, and element M, and includes preparing a raw material compound containing N, element A, and element M, reacting the above composition to obtain an intermediate, and heating the above intermediate to obtain a sulfide solid electrolyte. Hereinafter, the case where Li is contained as element A will be taken as an example to describe the sulfide solid electrolyte.

[0109] The sulfide solid electrolyte has a crystalline structure. "Having a crystalline structure" means that, in an X-ray diffraction measurement, peaks attributable to the crystalline structure of the sulfide solid electrolyte are observed in the X-ray diffraction pattern. The sulfide solid electrolyte may contain an amorphous portion.

[0110] Examples of the crystal structure of the sulfide solid electrolyte include HICP, LGPS, argyrodite, and Li7P3S 11 Among these, the crystal structure is preferably HICP, LGPS, argyrodite, or Li7P3S from the viewpoint of lithium ion conductivity. 11 Among these, Li7P3S is preferred because it has high stability against Li. 11 From the viewpoint of stability to the atmosphere, it is preferable that the material contains a crystal structure having a crystalline phase of Li4P2S6 or β-Li3PS4, or a first crystal structure having diffraction peaks at 2θ=17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, and 29.8°±0.5° in X-ray diffraction measurement using CuKα radiation, and among these, the first crystal structure having diffraction peaks at 2θ=17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, and 29.8°±0.5° in X-ray diffraction measurement using CuKα radiation is more preferable because of its high lithium ion conductivity.

[0111] The first crystal structure may include specific crystal structure A having diffraction peaks at 2θ=17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, 29.8°±0.5°, and 30.9°±0.5° in the X-ray diffraction measurement, or specific crystal structure B having diffraction peaks at 2θ=17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5°, and 29.8°±0.5° but no diffraction peak at 30.9°±0.5° in the X-ray diffraction measurement. The above configuration provides a sulfide solid electrolyte that can increase the initial coulombic efficiency of an all-solid-state battery including the solid electrolyte.

[0112] The diffraction peaks in the above first crystal structure may be within the range of ±0.3° or within the range of ±0.1° in terms of the above 2θ.

[0113] The above Li7P3S 11 The crystal structure having a crystal phase of has diffraction peaks at positions of 2θ = 17.8° ± 0.5°, 18.5° ± 0.5°, 23.7° ± 0.5°, 29.6° ± 0.5°, 30.0° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0114] Examples of the above LGPS-type sulfide solid electrolyte include, for example, Li 10 GeP2S 12 and the like. The crystal structure having a crystal phase of Li 10 GeP2S 12 has diffraction peaks at positions of 2θ = 14.4° ± 0.5°, 20.1° ± 0.5°, 20.4° ± 0.5°, 26.9° ± 0.5°, 29.5° ± 0.5°, 47.3° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0115] Examples of the above argyrodite-type sulfide solid electrolyte include, for example, Li6PS5Cl and the like. The crystal structure having a crystal phase of Li6PS5Cl has diffraction peaks at positions of 2θ = 15.6° ± 0.5°, 25.5° ± 0.5°, 30.0° ± 0.5°, 31.4° ± 0.5°, 45.0° ± 0.5°, 52.5° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0116] The crystal structure having a crystal phase of the above Li4P2S6 has diffraction peaks at positions of 2θ = 16.9° ± 0.5°, 27.1° ± 0.5°, 32.1° ± 0.5°, 32.5° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0117] The crystal structure having a crystal phase of the above β-Li3PS4 has diffraction peaks at positions of 2θ = 17.5° ± 0.5°, 18.1° ± 0.5°, 29.1° ± 0.5°, 29.9° ± 0.5°, 31.2° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0118] The sulfide solid electrolyte preferably contains, as a main component, an anion structure of a so-called ortho composition. For example, when the sulfide solid electrolyte is a Li2S-P2S5-based solid electrolyte, it preferably contains a PS4 3- structure as a main component. Here, "main component" means that the proportion of a specific component in all components is 50 mol% or more.

[0119] When the sulfide solid electrolyte contains an anion structure of an ortho composition as a main component, the content of the anion structure of the ortho composition with respect to all anion structures constituting the sulfide solid electrolyte is 50 mol% or more and less than 100 mol%, preferably 60 mol% or more and less than 100 mol%, more preferably 70 mol% or more and less than 100 mol%, still more preferably 80 mol% or more and less than 100 mol%, and particularly preferably 90 mol% or more and less than 100 mol%.

[0120] The sulfide solid electrolyte preferably does not substantially contain crosslinked sulfur. Since crosslinked sulfur reacts with water to generate hydrogen sulfide, the atmospheric stability can be improved by not substantially containing crosslinked sulfur. For example, when the sulfide solid electrolyte is a Li2S-P2S5-based solid electrolyte, it preferably does not substantially contain an S3P-S-PS3 structure. The fact that crosslinked sulfur is not substantially contained can be confirmed by the fact that no peak corresponding to the crosslinked sulfur structure is detected when measuring the Raman spectrum with a laser having an excitation wavelength of 532 nm. For example, the fact that the S3P-S-PS3 structure is not substantially contained can be confirmed by the fact that no peak is detected at 402 cm -1 when measuring the Raman spectrum with a laser having an excitation wavelength of 532 nm. Note that the sulfide solid electrolyte may contain a small amount of crosslinked sulfur. In this case, the intensity I of the peak attributed to the anion structure of the ortho composition in the Raman spectrum measurement O relative to the intensity I of the peak attributed to crosslinked sulfur P of the ratio I P / I Ois preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.35 or less. For example, when the sulfide solid electrolyte is a Li2S-P2S5-based solid electrolyte, PS4 3- The peak intensity at 417 cm -1 corresponding to the above I O and the peak intensity at 402 cm corresponding to the S3PS-PS3 structure -1 corresponding to the above I P .

[0121] The sulfide solid electrolyte preferably does not substantially contain Li2S. Since Li2S reacts with water to produce hydrogen sulfide, the atmospheric stability can be improved by not substantially containing Li2S. Here, "not substantially containing Li2S" means not including a crystal structure having diffraction peaks at 2θ = 27.0 ± 0.5°, 31.2 ± 0.5°, 44.8 ± 0.5°, and 53.1 ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0122] When the content of Li in the sulfide solid electrolyte is high, Li2S precipitates, resulting in a decrease in atmospheric stability. When the content is low, there is a risk of a decrease in ionic conductivity. In addition, when the content of N is high, Li2S precipitates, resulting in a decrease in atmospheric stability. When the content is low, there is a risk that the effects such as the improvement of atmospheric stability due to the inclusion of N cannot be fully exerted. From these viewpoints, the sulfide solid electrolyte preferably simultaneously satisfies the following formula in terms of elemental ratio in molar ratio. 2.30 ≦ Li / P ≦ 4.20 0.0100 ≦ N / P ≦ 1.20 The above Li / P and the above N / P more preferably simultaneously satisfy the following formula. 2.36 ≦ Li / P ≦ 4.12 0.0200 ≦ N / P ≦ 1.11 The above Li / P and the above N / P even more preferably simultaneously satisfy the following formula. 2.36 ≦ Li / P ≦ 4.00 0.0600 ≦ N / P ≦ 0.900 It is more preferable that the above Li / P and the above N / P simultaneously satisfy the following equations respectively. 2.60 ≦ Li / P ≦ 3.40 0.190 ≦ N / P ≦ 0.710 It is particularly preferable that the above Li / P and the above N / P simultaneously satisfy the following equations respectively. 2.77 ≦ Li / P ≦ 3.38 0.280 ≦ N / P ≦ 0.650

[0123] The sulfide solid electrolyte preferably has a composition represented by the general formula (100−z)(yLi2S·(1−y)P2S5)·zLi α M β N (where 0 < z ≦ 40, 0.50 ≦ y ≦ 0.75, and α and β are numerical values giving a stoichiometric ratio according to the type of element M). By having the sulfide solid electrolyte have a composition represented by the above general formula, the air stability and the ionic conductivity at 25° C. can be improved. The above general formula shows the content ratios of Li, S, P, N, and element M, and the above composition does not specify that the composition consists of Li2S, P2S5, and Li α M β N.

[0124] As the lower limit of the ionic conductivity of the sulfide solid electrolyte at 25° C., 0.4×10 -3 S / cm is preferable, 1.0×10 -3 S / cm is more preferable, and 1.5×10 -3 S / cm is even more preferable. By having the ionic conductivity of the sulfide solid electrolyte at 25° C. within the above range, the rate characteristics of the all-solid-state battery can be improved.

[0125] The ionic conductivity of the sulfide solid electrolyte at 25°C is determined by measuring the AC impedance by the following method. In an argon atmosphere with a dew point of -50°C or lower, 120 mg of sample powder is put into a powder molding machine with an inner diameter of 10 mm, and then uniaxially pressed and molded at a pressure of 50 MPa or less per sample area using a hydraulic press. After releasing the pressure, SUS316L powder is put on the upper and lower surfaces of the sample as a current collector, and then a pellet for measuring ionic conductivity is obtained by uniaxially pressing and molding at a pressure of 360 MPa per pellet area for 5 minutes. This pellet for measuring ionic conductivity is inserted into an HS cell manufactured by Hokusen Co., Ltd. to measure the AC impedance. The measurement conditions are an applied voltage amplitude of 20 mV, a frequency range of 1 MHz to 100 mHz, and a measurement temperature of 25°C.

[0126] Thus, the sulfide solid electrolyte can be suitably used as the solid electrolyte of an all-solid-state battery.

[0127] [Embodiment 2] The sulfide solid electrolyte according to another embodiment of the present invention contains Li, P, S, N, element X, and element M. Element X represents at least one element selected from the group consisting of Cl, Br, and I.

[0128] The sulfide solid electrolyte may contain one selected from the group consisting of Al, B, and Si as element M, or may contain Al as element M.

[0129] When the content of Li in the sulfide solid electrolyte is high, Li2S precipitates, resulting in a decrease in air stability. When the content is low, there is a risk that HICP will not precipitate. Also, when the content of N is high, Li2S precipitates, resulting in a decrease in air stability. When the content is low, there is a risk that the effect of containing N cannot be fully exerted. Further, when the content of element X is high, a crystal phase of lithium halide may remain in the sulfide solid electrolyte, decreasing the ionic conductivity. When the content is low, there is a risk that the effect of containing element X cannot be fully exerted. Due to these circumstances, it is preferable that the sulfide solid electrolyte simultaneously satisfies the following equations in molar ratios for the content ratio of Li to P (Li / P), the content ratio of N to P (N / P), and the content ratio of X to P (X / P) with respect to the above P. 3.10 < Li / P < 4.20 0.0600 < N / P < 0.750 0.180 < X / P < 1.30 Moreover, it is more preferable that the above Li / P, N / P, and X / P simultaneously satisfy the following equations. 3.10 < Li / P < 3.90 0.0900 < N / P < 0.750 0.180 < X / P < 1.00

[0130] The sulfide solid electrolyte preferably has a composition represented by the general formula (100-z){(1-y)[xLi2S·(1-x)P2S5]·yLi α M β N}·zLiX (where 0.50 ≦ x ≦ 0.80, 0 < y ≦ 0.50, 5 ≦ z ≦ 40, α and β are numerical values giving the stoichiometric ratio according to the type of element M), and more preferably, x, y, and z are 0.67 ≦ x ≦ 0.73, 0.10 ≦ y ≦ 0.30, and 10 ≦ z ≦ 30, respectively. By the sulfide solid electrolyte having the composition represented by the above general formula, the thermal stability of HICP can be improved. Moreover, when the sulfide solid electrolyte contains two elements X1 and X2 as element X, the above general formula can also be represented as (100-z1-z2){(1-y)[xLi2S·(1-x)P2S5]·yLi α M β N}·z1LiX1·z2LiX2 (where 0.50 ≦ x ≦ 0.80, 0 < y ≦ 0.50, 5 ≦ (z1+z2) ≦ 40, α and β are numerical values giving the stoichiometric ratio according to the type of element M), and in this case, it is preferable that x, y, z1, and z2 are 0.67 ≦ x ≦ 0.73, 0.10 ≦ y ≦ 0.30, and 10 ≦ (z1+z2) ≦ 30, respectively. The above general formula indicates the content ratios of Li, S, P, N, element M, and element X. The above composition is not specified to consist of Li2S, P2S5, Li α M β N, and LiX.

[0131] In the above general formula, when element M is any one of Al, B, and Sc, α = 2 / 3 and β = 1 / 2 may be applicable. In this case, x, y, and z are preferably 0.50 ≦ x ≦ 0.80, 0 < y ≦ 0.50, and 5 ≦ z ≦ 40, more preferably 0.60 ≦ x ≦ 0.75, 0.050 ≦ y ≦ 0.40, and 10 ≦ z ≦ 30, and even more preferably 0.67 ≦ x ≦ 0.73, 0.10 ≦ y ≦ 0.30, and 15 ≦ z ≦ 25.

[0132] The sulfide solid electrolyte preferably contains Br or I alone as element X, and more preferably contains Br alone. It is also preferable to contain Br and I simultaneously. When the sulfide solid electrolyte contains Br and I simultaneously, the content of Br with respect to the total amount of Br and I contained in the sulfide solid electrolyte is preferably 1 mol% or more and 99 mol% or less, and more preferably 5 mol% or more and 80 mol% or less.

[0133] The sulfide solid electrolyte preferably contains HICP. That is, it preferably contains a crystal structure having diffraction peaks at 2θ = 20.2° ± 0.5° and 23.6° ± 0.5° in X-ray diffraction measurement using CuKα rays.

[0134] The sulfide solid electrolyte preferably does not contain LICP. That is, it preferably does not contain a crystal structure having diffraction peaks at 2θ = 21.0° ± 0.5° and 28.0° ± 0.5° in X-ray diffraction measurement using CuKα rays. The sulfide solid electrolyte may contain a small amount of LICP. In this case, the diffraction peak intensity I at 2θ = 20.2° ± 0.5° in X-ray diffraction measurement using CuKα rays H with respect to the diffraction peak intensity I at 2θ = 21.0° ± 0.5° LThe diffraction peak intensity ratio I L / I H is preferably 0 < I L / I H < 3.2, more preferably 0 < I L / I H < 2.5, even more preferably 0 < I L / I H < 2.0, and still more preferably 0 < I L / I H < 1.0. The diffraction peak intensity ratio I L / I H indicates the abundance ratio of HICP and LICP contained in the sulfide solid electrolyte. That is, a small diffraction peak intensity ratio I L / I H indicates that the amount of LICP is relatively small with respect to HICP.

[0135] The ionic conductivity of the sulfide solid electrolyte of Embodiment 2 at 25 °C is preferably 2.0×10 -3 S / cm or more, more preferably 2.5×10 -3 S / cm or more, even more preferably 3.0×10 -3 S / cm or more, and particularly preferably 4.0×10 -3 S / cm or more. With the above configuration, the high-rate discharge performance of the all-solid-state battery including the sulfide solid electrolyte can be improved.

[0136] <All-solid-state battery> The all-solid-state battery includes a negative electrode layer, a solid electrolyte layer, and a positive electrode layer. FIG. 2 is a schematic cross-sectional view showing an all-solid-state battery according to an embodiment of the present invention. The all-solid-state battery 10, which is a secondary battery, has a negative electrode layer 1 and a positive electrode layer 2 disposed with a solid electrolyte layer 3 therebetween. The negative electrode layer 1 has a negative electrode base material layer 4 and a negative electrode mixture layer 5, and the negative electrode base material layer 4 is the outermost layer of the negative electrode layer 1. The positive electrode layer 2 has a positive electrode base material layer 7 and a positive electrode mixture layer 6, and the positive electrode base material layer 7 is the outermost layer of the positive electrode layer 2. In the all-solid-state battery 10 shown in FIG. 2, a positive electrode mixture layer 6, a solid electrolyte layer 3, a negative electrode mixture layer 5, and a negative electrode base material layer 4 are laminated in this order on the positive electrode base material layer 7.

[0137] In the all-solid-state battery, the negative electrode layer 1, the solid electrolyte layer 3, the positive electrode layer 2, or a combination thereof contains the sulfide solid electrolyte. Since the all-solid-state battery has the negative electrode layer 1, the solid electrolyte layer 3, the positive electrode layer 2, or a combination thereof containing the sulfide solid electrolyte, the initial Coulomb efficiency is excellent. Since the sulfide solid electrolyte has excellent reduction resistance, it is preferable that the negative electrode layer 1 and / or the solid electrolyte layer 3 contain the sulfide solid electrolyte. With the above configuration, the effects of the present invention become even more excellent.

[0138] The all-solid-state battery may also be used in combination with other solid electrolytes other than the sulfide solid electrolyte. As the other solid electrolyte, a sulfide solid electrolyte other than the sulfide solid electrolyte may be used, or an oxide-based solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a pseudo solid electrolyte may be used.

[0139] As the sulfide solid electrolyte other than the sulfide solid electrolyte, it is preferably highly Li-ion conductive. For example, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-Li3N, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S 2n (However, m and n are positive numbers, and Z is any one of Ge, Zn, and Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li δ XO ε (However, δ and ε are positive numbers, and X is any one of P, Si, Ge, B, Al, Ga, and In.), Li 10 GeP2S 12 etc. can be mentioned. Among these, from the viewpoint of good lithium ion conductivity, Li2S-P2S5 or Li 10 GeP2S 12etc. are preferable. As Li2S-P2S5, xLi2S·(100-x)P2S5 (70≦x≦80) is preferable.

[0140] [Negative electrode layer] The negative electrode layer 1 includes a negative electrode base material layer 4 and a negative electrode mixture layer 5 laminated on the surface of the negative electrode base material layer 4. The negative electrode layer 1 may have an intermediate layer (not shown) between the negative electrode base material layer 4 and the negative electrode mixture layer 5.

[0141] (Negative electrode base material layer) The negative electrode base material layer 4 is a layer having conductivity. The material of the negative electrode base material layer 4 is not limited as long as it is a conductor. For example, one or more metals selected from the group consisting of copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, indium, and alloys containing one or more of these, and stainless alloys can be mentioned.

[0142] As the lower limit of the average thickness of the negative electrode base material layer 4, 3 μm is preferable, 5 μm is more preferable, and 8 μm is even more preferable. As the upper limit of the average thickness of the negative electrode base material layer 4, 200 μm is preferable, 100 μm is more preferable, and 50 μm is even more preferable. By setting the average thickness of the negative electrode base material layer 4 to be not less than the above lower limit, the strength of the negative electrode base material layer 4 can be made sufficiently high, so that the negative electrode layer 1 can be formed well. By setting the average thickness of the negative electrode base material layer 4 to be not more than the above upper limit, sufficient volume of other components can be ensured.

[0143] (Negative electrode mixture layer) The negative electrode mixture layer 5 can be formed from a so-called negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a negative electrode mixture or a negative electrode composite containing a negative electrode active material and the sulfide solid electrolyte. The negative electrode mixture may contain optional components such as a solid electrolyte other than the sulfide solid electrolyte, a conductive agent, a binder, and a filler, as necessary.

[0144] 〈Negative electrode active material〉 As the negative electrode active material, a material that can occlude and release lithium ions is usually used. Specific examples of the negative electrode active material include metallic lithium; metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxide and Sn oxide; polyphosphoric acid compounds; carbon materials such as graphite (graphite) and non-graphitic carbon (easily graphitizable carbon or hardly graphitizable carbon); lithium metal composite oxides such as lithium titanate, and the like.

[0145] As the lower limit of the content of the negative electrode active material in the negative electrode binder, 10% by mass is preferable, and 15% by mass is more preferable. As the upper limit of the content of the negative electrode active material, 60% by mass is preferable, 70% by mass is more preferable, 80% by mass is still more preferable, 90% by mass is particularly preferable, and 95% by mass may be used. By setting the content of the negative electrode active material within the above range, the capacitance of the all-solid-state battery can be increased.

[0146] 〈Negative electrode mixture or negative electrode composite〉 The above-mentioned negative electrode mixture is a mixture produced by mixing the negative electrode active material and the sulfide solid electrolyte by mechanical milling or the like. For example, a mixture of the negative electrode active material and the sulfide solid electrolyte can be obtained by mixing particulate negative electrode active material and particulate sulfide solid electrolyte. Examples of the above-mentioned negative electrode composite include a composite having a chemical or physical bond between the negative electrode active material and the sulfide solid electrolyte, and a composite in which the negative electrode active material and the sulfide solid electrolyte are mechanically combined. The above composite is one in which the negative electrode active material and the sulfide solid electrolyte are present in one particle. For example, those in which the negative electrode active material and the sulfide solid electrolyte form an aggregated state, those in which a sulfide solid electrolyte-containing film is formed on at least a part of the surface of the negative electrode active material, and the like can be mentioned. The above-mentioned negative electrode mixture or negative electrode composite may contain a solid electrolyte other than the sulfide solid electrolyte. The negative electrode active material and the sulfide solid electrolyte contained in the negative electrode binder constitute the negative electrode mixture or negative electrode composite, thereby improving the ionic conductivity.

[0147] When the negative electrode mixture contains a solid electrolyte, the lower limit of the content of the solid electrolyte in the negative electrode mixture may be 5% by mass, preferably 10% by mass. The upper limit of the content of the solid electrolyte in the negative electrode mixture is preferably 90% by mass, more preferably 85% by mass, even more preferably 80% by mass, and particularly preferably 75% by mass. By setting the content of the solid electrolyte within the above range, the capacitance of the all-solid-state battery can be increased. The negative electrode mixture may contain the sulfide solid electrolyte or may contain a solid electrolyte other than the sulfide solid electrolyte.

[0148] 〈Any other optional components〉 The above conductive agent is not particularly limited. Examples of such conductive agents include carbon blacks such as natural or artificial graphite, furnace black, acetylene black, and ketjen black, metals, and conductive ceramics. Examples of the shape of the conductive agent include powder form and fibrous form. The content of the conductive agent in the negative electrode mixture can be, for example, 0.5% by mass or more and 30% by mass or less. The negative electrode mixture may not contain a conductive agent.

[0149] The above binder is not particularly limited. Examples include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyimide, and polyacrylic acid; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0150] The above filler is not particularly limited. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and carbon.

[0151] As the lower limit of the average thickness of the negative electrode mixture layer 5, 30 μm is preferable, and 60 μm is more preferable. As the upper limit of the average thickness of the negative electrode mixture layer 5, 1000 μm is preferable, 500 μm is more preferable, and 200 μm is even more preferable. By setting the average thickness of the negative electrode mixture layer 5 to be equal to or greater than the above lower limit, a all-solid-state battery having a high energy density can be obtained. By setting the average thickness of the negative electrode mixture layer 5 to be equal to or less than the above upper limit, a all-solid-state battery including a negative electrode excellent in rate characteristics and having a high active material utilization rate can be obtained.

[0152] (Intermediate layer) The above intermediate layer is a coating layer on the surface of the negative electrode base material layer 4, and by containing conductive particles such as carbon particles, the contact resistance between the negative electrode base material layer 4 and the negative electrode mixture layer 5 is reduced. The configuration of the intermediate layer is not particularly limited, and for example, it can be formed of a composition containing a resin binder and conductive particles.

[0153] [Positive electrode layer] The positive electrode layer 2 includes a positive electrode base material layer 7 and a positive electrode mixture layer 6 laminated on the surface of the positive electrode base material layer 7. Similar to the negative electrode layer 1, the positive electrode layer 2 may have an intermediate layer between the positive electrode base material layer 7 and the positive electrode mixture layer 6. This intermediate layer can have the same configuration as the intermediate layer of the negative electrode layer 1.

[0154] (Positive electrode base material layer) The positive electrode base material layer 7 can have the same configuration as the negative electrode base material layer 4. The material of the positive electrode base material layer 7 is not limited as long as it is a conductor. For example, copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, gold, silver, iron, platinum, chromium, tin, indium, and an alloy containing one or more of these, and one or more metals selected from the group consisting of stainless alloys can be mentioned.

[0155] As the lower limit of the average thickness of the positive electrode substrate layer 7, 3 μm is preferable, and 5 μm is more preferable. As the upper limit of the average thickness of the positive electrode substrate layer 7, 200 μm is preferable, 100 μm is more preferable, and 50 μm is even more preferable. By setting the average thickness of the positive electrode substrate layer 7 to be not less than the above lower limit, the strength of the positive electrode substrate layer 7 can be sufficiently increased, so that the positive electrode layer 2 can be formed well. By setting the average thickness of the positive electrode substrate layer 7 to be not more than the above upper limit, the volume of other components can be sufficiently ensured.

[0156] (Positive electrode mixture layer) The positive electrode mixture layer 6 can be formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture may contain a positive electrode mixture or a positive electrode composite containing a positive electrode active material and a solid electrolyte. As the above solid electrolyte, the sulfide solid electrolyte may be used. The positive electrode mixture forming the positive electrode mixture layer 6, like the negative electrode mixture, may contain optional components such as a solid electrolyte, a conductive agent, a binder, and a filler as necessary. Note that the positive electrode mixture layer may be in a form that does not contain a solid electrolyte.

[0157] 〈Positive electrode active material〉 As the positive electrode active material contained in the positive electrode mixture layer 6, known ones usually used in all-solid-state batteries can be used. Examples of the above positive electrode active material include Li x M e O y (Me represents at least one transition metal) composite oxide (Li having a layered α-NaFeO2-type crystal structure x CoO2, Li x NiO2, Li x MnO3, Li x Ni α Co (1-α) O2, Li x Ni α Mn β Co (1-α-β) O2, etc., Li x Mn2O4, Li x Ni α Mn (2-α) O4, etc.), Li w Me x (AO y ) z(Me represents at least one transition metal, and A represents, for example, P, Si, B, V, etc.) Polyanion compounds represented by (such as LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc.) can be mentioned. Elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode active material layer, one of these compounds may be used alone, or two or more of them may be mixed and used.

[0158] As the positive electrode active material, lithium alloys such as Li-Al, Li-In, Li-Sn, Li-Pb, Li-Bi, Li-Ga, Li-Sr, Li-Si, Li-Zn, Li-Cd, Li-Ca, Li-Ba, and MnO2, FeO2, TiO2, V2O5, V6O 13 , materials such as TiS2 with a redox potential nobler than that of the negative electrode material can be used.

[0159] As the lower limit of the content of the positive electrode active material in the positive electrode binder, 10% by mass is preferable, and 15% by mass is more preferable. As the upper limit of the content of the positive electrode active material, 60% by mass is preferable, 70% by mass is more preferable, 80% by mass is further preferable, 90% by mass is particularly preferable, and 95% by mass may also be used. By setting the content of the positive electrode active material within the above range, the capacitance of the all-solid-state battery can be increased.

[0160] 〈Positive electrode mixture or positive electrode composite〉 The above positive electrode mixture is a mixture prepared by mechanically milling the positive electrode active material, solid electrolyte, etc. in the same manner as in the case of the negative electrode. For example, a mixture of the positive electrode active material and the solid electrolyte, etc. can be obtained by mixing the particulate positive electrode active material and the particulate solid electrolyte, etc. Similar to the case of the negative electrode, the above positive electrode composite includes a composite having a chemical or physical bond between a positive electrode active material and a solid electrolyte, a composite in which a positive electrode active material and a solid electrolyte are mechanically combined, and the like. The above composite has a positive electrode active material and a solid electrolyte existing within one particle. For example, those in which the positive electrode active material and the solid electrolyte form an aggregated state, those in which a solid electrolyte-containing film is formed on at least a part of the surface of the positive electrode active material, and the like can be mentioned. The above positive electrode mixture or positive electrode composite may contain a solid electrolyte other than the sulfide solid electrolyte. By the positive electrode active material and the solid electrolyte contained in the positive electrode binder constituting the positive electrode mixture or the positive electrode composite, the ionic conductivity can be improved.

[0161] When the positive electrode binder contains a solid electrolyte, the lower limit of the content of the solid electrolyte may be 5% by mass, and 10% by mass is preferable. The upper limit of the content of the solid electrolyte in the positive electrode binder is preferably 90% by mass, more preferably 85% by mass, still more preferably 80% by mass, and particularly preferably 75% by mass. By setting the content of the solid electrolyte within the above range, the electric capacity of the all-solid-state battery can be increased.

[0162] The lower limit of the average thickness of the positive electrode binder layer 6 is preferably 30 μm, and more preferably 60 μm. The upper limit of the average thickness of the positive electrode binder layer 6 is preferably 1000 μm, more preferably 500 μm, still more preferably 200 μm. By setting the average thickness of the positive electrode binder layer 6 to be equal to or greater than the above lower limit, an all-solid-state battery having a high energy density can be obtained. By setting the average thickness of the positive electrode binder layer 6 to be equal to or less than the above upper limit, an all-solid-state battery equipped with a negative electrode having excellent high-rate discharge performance and a high active material utilization rate can be obtained.

[0163] [Solid electrolyte layer] The solid electrolyte layer 3 contains an electrolyte for the solid electrolyte layer. Examples of the electrolyte for the solid electrolyte layer include, in addition to the above-mentioned sulfide solid electrolyte, oxide-based solid electrolytes, other sulfide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, pseudo solid electrolytes, and the like. Among these, sulfide solid electrolytes are preferred from the viewpoints of good ionic conductivity and easy interface formation, and the sulfide solid electrolyte is more preferred. By containing the sulfide solid electrolyte in the solid electrolyte layer 3, the solid electrolyte layer can exhibit high ionic conductivity, and thus the internal resistance of the all-solid-state battery can be reduced.

[0164] The content of the sulfide solid electrolyte with respect to the total amount of the solid electrolyte contained in the all-solid-state battery is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, still more preferably 80% by mass or more and 100% by mass or less, and even more preferably 90% by mass or more and 100% by mass or less. In particular, it is preferable that the solid electrolyte contained in the all-solid-state battery is composed only of the sulfide solid electrolyte. In particular, since the sulfide solid electrolyte containing the element X has high thermal stability, by configuring the all-solid-state battery as described above, the advantage of the all-solid-state battery that can increase the upper limit of the operating temperature of the battery can be fully enjoyed.

[0165] ]> The electrolyte for the solid electrolyte layer may have a crystal structure or may be amorphous without a crystal structure. Oxides such as Li3PO4, halogens, halogen compounds, etc. may be added to the electrolyte for the solid electrolyte layer.

[0166] The average thickness of the solid electrolyte layer 3 is preferably 1 μm or more and 50 μm or less, and more preferably 3 μm or more and 20 μm or less. By setting the average thickness of the solid electrolyte layer 3 within the above range, it is possible to increase the energy density of the all-solid-state battery while surely insulating the positive electrode and the negative electrode.

[0167] <Manufacturing method of all-solid-state battery> The manufacturing method of the all-solid-state battery mainly includes, for example, a sulfide solid electrolyte manufacturing step, a negative electrode mixture manufacturing step, an electrolyte for the solid electrolyte layer manufacturing step, a positive electrode mixture manufacturing step, and a lamination step of laminating a negative electrode layer, a solid electrolyte layer, and a positive electrode layer.

[0168] (Sulfide solid electrolyte manufacturing step) In this step, for example, a sulfide solid electrolyte is manufactured by the manufacturing method of the sulfide solid electrolyte.

[0169] (Negative electrode mixture manufacturing step) In this step, a negative electrode mixture for forming a negative electrode layer is manufactured. When the negative electrode mixture contains a mixture or composite of a negative electrode active material and the sulfide solid electrolyte, in this step, for example, the negative electrode active material and the sulfide solid electrolyte are mixed using a mechanical milling method or the like, and the step includes manufacturing a mixture or composite of the negative electrode active material and the sulfide solid electrolyte.

[0170] (Electrolyte for solid electrolyte layer manufacturing step) In this step, the electrolyte for the solid electrolyte layer for forming the solid electrolyte layer is manufactured. In this step, a predetermined material of the electrolyte for the solid electrolyte layer can be obtained by treating it by a mechanical milling method. The electrolyte for the solid electrolyte layer may be manufactured by heating a predetermined material of the electrolyte for the solid electrolyte layer above the melting temperature and melt-mixing the two at a predetermined ratio and then quenching by a melt quenching method. Other synthesis methods of the electrolyte for the solid electrolyte layer include, for example, a solid phase method of vacuum encapsulation and firing, a liquid phase method such as dissolution precipitation, a vapor phase method (PLD), and firing in an argon atmosphere after mechanical milling. When the electrolyte for the solid electrolyte layer is the sulfide solid electrolyte, in the manufacturing step of the electrolyte for the solid electrolyte layer, the above-mentioned sulfide solid electrolyte manufacturing step is performed.

[0171] (Positive electrode mixture manufacturing step) In this process, a positive electrode mixture for forming a positive electrode layer is produced. The method for producing the positive electrode mixture is not particularly limited and can be appropriately selected according to the purpose. For example, compression molding of a positive electrode active material, mechanical milling treatment of a predetermined material of the positive electrode mixture, sputtering using a target material of the positive electrode active material, etc. can be mentioned. When the positive electrode mixture contains a mixture or composite including a positive electrode active material and the sulfide solid electrolyte, in this process, for example, the positive electrode active material and the sulfide solid electrolyte are mixed using a mechanical milling method or the like, and a mixture or composite of the positive electrode active material and the sulfide solid electrolyte is produced.

[0172] (Lamination process) In this process, a negative electrode layer having a negative electrode substrate layer and a negative electrode mixture layer, a solid electrolyte layer, and a positive electrode layer having a positive electrode substrate layer and a positive electrode mixture layer are laminated. In this process, the negative electrode layer, the solid electrolyte layer, and the positive electrode layer may be formed sequentially, or vice versa, and the order of formation of each layer is not particularly limited. The above negative electrode layer is formed by pressure molding a negative electrode substrate and a negative electrode mixture, the above solid electrolyte layer is formed by pressure molding an electrolyte for the solid electrolyte layer, and the above positive electrode layer is formed by pressure molding a positive electrode substrate and a positive electrode mixture.

[0173] The negative electrode layer, the solid electrolyte layer, and the positive electrode layer may be laminated by pressure molding the negative electrode substrate, the negative electrode mixture, the electrolyte for the solid electrolyte layer, the positive electrode substrate, and the positive electrode mixture at once. The positive electrode layer, the negative electrode layer, or these layers may be pre-formed and laminated by pressure molding with the solid electrolyte layer.

[0174] <Other embodiments> The present invention is not limited to the above embodiments, and can be implemented in various modified and improved forms in addition to the above aspects.

[0175] In the above embodiment, as the raw material compound containing N, element A, and element M, a raw material compound containing only N, Li, and element M was described as an example. However, the present invention is not limited to this. For example, the raw material compound containing N, element A, and element M may further contain other elements as long as it does not interfere with the solution of the problems of the present invention.

[0176] The configuration of the all-solid-state battery according to the present invention is not particularly limited. For example, it may include other layers other than the negative electrode layer, the positive electrode layer, and the solid electrolyte layer, such as an intermediate layer or an adhesive layer.

Example

[0177] Hereinafter, the present invention will be described more specifically by demonstration experiments, but the present invention is not limited to the following examples.

[0178] First, the effect of suppressing the discharge of N to the outside of the system in the method for producing a sulfide solid electrolyte according to an embodiment of the present invention will be shown from Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3. [Example 1] By the following treatment, 80(0.70Li2S·0.30P2S5)·20Li 3 / 2 Al 1 / 2 N was synthesized. (Preparation step) Li3N and AlN were weighed so that the molar ratio was 1.2:1, mixed in a mortar, and then pelletized. Next, heat treatment was performed at 750 ° C for 1 hour to produce Li 3 / 2 Al 1 / 2 N. The produced Li 3 / 2 Al 1 / 2 N was confirmed to have a main phase of Li 3 / 2 Al 1 / 2 N by XRD measurement. Next, in a glove box with an argon atmosphere having a dew point of -50 ° C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), and Li 3 / 2 Al 1 / 2 N were weighed so that the molar ratio was 56:24:20, and then mixed in a mortar to prepare a composition containing Li, P, S, N, and Al. (Reaction Engineering) The above composition was put into a sealed 80 mL zirconia pot containing 160 g of zirconia balls with a diameter of 4 mm. Milling treatment was carried out for 45 hours at a revolution speed of 510 rpm using a planetary ball mill (manufactured by FRITSCH, model number Premium line P-7) to obtain an intermediate product. (Heat Treatment Process) The above intermediate product was heat-treated for 2 hours to obtain a sulfide solid electrolyte. This heat treatment was carried out at a temperature above the crystallization temperature and not exceeding 100 °C above the crystallization temperature. The crystallization temperature was determined by measuring DSC. The DSC measurement was carried out under the following conditions. That is, using a DSC apparatus (manufactured by Rigaku, Thermo Plus DSC8230), a sealed pan made of SUS was used, and the temperature was raised from room temperature to 400 °C at a rate of 10 °C / min. The composition prepared by the above synthesis procedure was designated as sample a, the intermediate product as sample b, and the sulfide solid electrolyte as sample c.

[0179] [Example 2] Except that the preparation process was changed as follows, the same procedure as in Example 1 was followed to synthesize 80(0.70Li2S·0.30P2S5)·20Li 3 / 2 B 1 / 2 N. (Preparation Process) Li3N and BN were weighed so that the molar ratio was 1.1:1, mixed in a mortar, and then pelletized. Next, they were heat-treated at 800 °C for 10 minutes to prepare Li 3 / 2 B 1 / 2 N. The prepared Li 3 / 2 B 1 / 2 N was confirmed by XRD measurement to have a main phase of Li 3 / 2 B 1 / 2 N. Next, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), and Li 3 / 2 B 1 / 2 [[ID=4O]]N were weighed so that the molar ratio was 56:24:20, and then mixed in a mortar to prepare a composition containing Li, P, S, N, and B.

[0180] [Comparative Example 1] 56.8Li2S·27.0P2S5·16.2Li3N was synthesized in the same manner as in Example 1, except that the preparation process was changed as follows. (Preparation Process) In a glove box under an argon atmosphere with a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), and Li3N were weighed so that the molar ratio was 56.8:27.0:16.2, and then mixed in a mortar to prepare a composition containing Li, P, S, and N.

[0181] [Comparative Example 2] 80(0.70Li2S·0.30P2S5)·20Li 3 / 2 Al 1 / 2 N was synthesized in the same manner as in Example 1, except that the preparation process was changed as follows. (Preparation Process) In a glove box under an argon atmosphere with a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), Li3N, and AlN were weighed so that the molar ratio was 56:24:10:10, and then mixed in a mortar to prepare a composition containing Li, P, S, N, and Al.

[0182] [Comparative Example 3] 80(0.70Li2S·0.30P2S5)·20Li 7 / 4 V 1 / 4 N was synthesized in the same manner as in Example 1, except that the preparation process was changed as follows. (Preparation Process) Li3N and VN were weighed so that the molar ratio was 3:1, mixed in a mortar, and then pelletized. Next, they were heat-treated at 750°C for 10 hours to produce Li 7 / 4 V 1 / 4 N. The produced Li 7 / 4 V 1 / 4 N was confirmed by XRD measurement to have a main phase of Li 7 / 4 V 1 / 4 N. Next, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), and Li were weighed in a molar ratio of 56:24:20 in a glove box under an argon atmosphere with a dew point of -50 °C or lower, and then mixed in a mortar to prepare a composition containing Li, P, S, N, and V. 7 / 4 V 1 / 4 N, and after mixing them in a mortar, a composition containing Li, P, S, N, and V was prepared.

[0183] [Evaluation] (1) XRD X-ray diffraction measurement was performed by the following method. Using an airtight sample holder for X-ray diffraction measurement, the sulfide solid electrolyte powders of the examples and comparative examples were filled under an argon atmosphere with a dew point of -50 °C or lower. Powder X-ray diffraction measurement was performed using an X-ray diffractometer ("miniFlex II" manufactured by Rigaku). The radiation source was CuKα radiation, the tube voltage was 30 kV, the tube current was 15 mA, and the diffracted X-rays were detected by a high-speed one-dimensional detector (model number: D / teX Ultra2) through a Kβ filter with a thickness of 30 μm. The sampling width was 0.01°, the scan speed was 5° / min, the divergence slit width was 0.625°, the receiving slit width was 13 mm (OPEN), and the scattering slit width was 8 mm.

[0184] (2) Ionic conductivity (σ) The ionic conductivity (σ 25 ) was determined by measuring the alternating current impedance at 25 °C using the method described above with "VMP-300" manufactured by (Bio-Logic). Also, for some of the examples and comparative examples, the ionic conductivities at each temperature of -30 °C, -20 °C, -10 °C, 0 °C, and 50 °C were also measured, and the activation energy (E a ) was calculated using the Arrhenius equation.

[0185] Table 4 shows the XRD patterns and the ionic conductivity (σ 25) is shown. As shown in Table 4, for the sulfide solid electrolytes of all examples and comparative examples, peaks were observed in the XRD spectrum, and it was confirmed that they have a specific crystal structure A. Note that the specific crystal structure A is a crystal structure having diffraction peaks at 2θ = 17.9° ± 0.5°, 19.1° ± 0.5°, 29.1° ± 0.5°, 29.8° ± 0.5°, and 30.9° ± 0.5° in X-ray diffraction measurement. Also, it was confirmed that the sulfide solid electrolytes of Example 1, Example 2, and Comparative Example 3 exhibit similar ionic conductivities. Therefore, it can be said that Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 have similar structures.

[0186]

Table 4

[0187] Regarding each sample of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the contents of Li, B, Al, and P in the sample were determined using an ICP emission spectrometer. Also, regarding each sample of Example 1, Example 2, and Comparative Examples 1 to 3, the content of N in the sample was determined using an oxygen / nitrogen / hydrogen analyzer. From this analysis result, the change rate of the content ratio of N in the sample was calculated. Table 5 shows the analysis results. Note that in the table, "no change" indicates that the change rate of the content ratio of N with respect to sample a was ±5 mass% or less.

[0188]

Table 5

[0189] From Table 5, it can be seen that in Example 1 and Example 2, the content ratio of N in sample a, sample b, and sample c hardly changes. That is, in Example 1 and Example 2, it can be seen that the N content rate hardly changes even after passing through each of the reaction step and the heat treatment step, and the discharge of N to the outside of the system is suppressed. On the other hand, in Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that the N content ratios in Sample a, Sample b, and Sample c decrease in the order of Sample a, Sample b, and Sample c. That is, in Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that the N content rate decreases with each step of the reaction step and the heat treatment step, and N is discharged out of the system. From the above, it was demonstrated that the effects were actually obtained for Al and B, which were predicted and selected using first-principles calculations for the N emission suppression effect. Furthermore, it was also demonstrated that the effect was not actually obtained for V, for which it was predicted that the N emission suppression effect could not be obtained using first-principles calculations.

[0190] Next, Examples 3 to 20 and Comparative Examples 4 to 8 show the effect of improving the thermal stability of the sulfide solid electrolyte according to one embodiment of the present invention. [Example 3] By the following treatment, a sulfide solid electrolyte represented by the composition formula 85(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·10LiBr·5LiI was synthesized. Li3N and AlN were weighed so that the molar ratio was 1.2:1, mixed in a mortar, and then pelletized. Next, they were heat-treated at 750°C for 1 hour to produce Li 3 / 2 Al 1 / 2 N. The produced Li 3 / 2 Al 1 / 2 N was confirmed to have a main phase of Li 3 / 2 Al 1 / 2 N by XRD measurement. Next, in a glove box with an argon atmosphere having a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), LiBr (99.999%, Aldrich), LiI (99.999%, Aldrich), and Li 3 / 2 Al 1 / 2N was weighed so that the molar ratio became 47.6:20.4:10:5:17, and then mixed in a mortar. This mixed sample was put into a sealed 80 mL zirconia pot containing 160 g of zirconia balls with a diameter of 4 mm. Milling treatment was performed for 45 hours at a revolution speed of 510 rpm using a planetary ball mill (manufactured by FRITSCH, model number Premium line P-7). Heat treatment was carried out at 245 °C for 2 hours to obtain the sulfide solid electrolyte of Example 3. This heat treatment temperature was set to be above the crystallization temperature and not more than 100 °C higher than the crystallization temperature. The crystallization temperature was determined by taking out a part of the sample after the milling treatment and subjecting it to DSC measurement. The DSC measurement was carried out under the following conditions. That is, using a DSC device (manufactured by Rigaku, Thermo Plus DSC8230), using a sealed pan made of SUS, the temperature was raised from room temperature to 400 °C at a rate of 10 °C / min.

[0191] [Comparative Example 4, Comparative Example 5] The compositions of the sulfide solid electrolytes were changed to 85(0.75Li2S·0.25P2S5)·10LiBr·5LiI and 85(0.72Li2S·0.25P2S5·0.020Li3N)·10LiBr·5LiI, and the heat treatment temperature was set to 225 °C in both cases. Otherwise, the sulfide solid electrolytes of Comparative Example 4 and Comparative Example 5 were synthesized in the same manner as in Example 3.

[0192] [Examples 4 to 7, Comparative Example 6] The compositions of the sulfide solid electrolytes were 80(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·12LiBr·8LiI, 80(0.70(0.67Li2S·0.33P2S5)·0.30Li 3 / 2 Al 1 / 2 N)·12LiBr·8LiI, 80(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 B 1 / 2 N)·12LiBr·8LiI, 80(0.80(0.70Li2S·0.30P2S5)·0.20Li 5 / 3 Si 1 / 3Changed to 80(0.6975Li2S·0.25P2S5·0.035Li3N)·12LiBr·8LiI and 80(0.6975Li2S·0.25P2S5·0.035Li3N)·12LiBr·8LiI, and synthesized the sulfide solid electrolytes of Examples 4 to 7 and Comparative Example 6 in the same manner as in Example 3, except that the heat treatment temperatures were 255°C, 275°C, 270°C, 270°C, and 250°C, respectively. In addition, for the sulfide solid electrolyte of Example 4, in addition to the sample with a heat treatment temperature of 255°C, samples with heat treatment temperatures of 215°C, 230°C, 275°C, 290°C, and 310°C were also synthesized. For the sulfide solid electrolyte of Example 5, in addition to the sample with a heat treatment temperature of 275°C, samples with heat treatment temperatures of 235°C, 290°C, 310°C, and 330°C were also synthesized. For the sulfide solid electrolyte of Example 6, in addition to the sample with a heat treatment temperature of 270°C, samples with heat treatment temperatures of 230°C, 270°C, 290°C, 310°C, and 330°C were also synthesized. For the sulfide solid electrolyte of Example 7, in addition to the sample with a heat treatment temperature of 270°C, samples with heat treatment temperatures of 230°C, 290°C, 310°C, and 330°C were also synthesized. Also, for the sulfide solid electrolyte of Comparative Example 6, in addition to the sample with a heat treatment temperature of 250°C, samples with heat treatment temperatures of 210°C and 230°C were also synthesized. The sulfide solid electrolytes synthesized at each heat treatment temperature are designated as Examples 4-1 to 4-6, Examples 5-1 to 5-5, Examples 6-1 to 6-5, Examples 7-1 to 7-5, and Comparative Examples 6-1 to 6-3 in ascending order of heat treatment temperature.

[0193] [Example 8, Comparative Example 7] The composition of the sulfide solid electrolyte was changed to 75(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·15LiBr·10LiI and 75(0.72Li2S·0.25P2S5·0.020Li3N)·15LiBr·10LiI, and synthesized the sulfide solid electrolytes of Example 8 and Comparative Example 7 in the same manner as in Example 1, except that the heat treatment temperatures were 215°C and 195°C, respectively.

[0194] [Examples 9 to 11, Comparative Example 8] The composition of the sulfide solid electrolyte was changed to 90(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·10LiBr, 80(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·20LiBr, 70(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·30LiBr, 90(0.72Li2S·0.25P2S5·0.020Li3N)·10LiBr. Except that the heat treatment temperatures were set to 265°C, 250°C, 240°C, and 225°C respectively, the sulfide solid electrolytes of Example 9, Example 10, Example 11, and Comparative Example 8 were synthesized in the same manner as in Example 3.

[0195] [Example 12, Example 13] The composition of the sulfide solid electrolyte was changed to 90(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·10LiI, 80(0.80(0.7Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 N)·20LiI. Except that the heat treatment temperatures were set to 255°C and 240°C respectively, the sulfide solid electrolytes of Example 12 and Example 13 were synthesized in the same manner as in Example 3.

[0196] [Example 14 to Example 17] The composition of the sulfide solid electrolyte was changed to 80(0.97(0.745Li2S·0.255P2S5)·0.03Li 3 / 2 B 1 / 2 N)·12LiBr·8LiI, 80(0.95(0.74Li2S·0.26P2S5)·0.05Li 3 / 2 B 1 / 2 N)·12LiBr·8LiI, 80(0.90(0.73Li2S·0.27P2S5)·0.10Li 3 / 2 B 1 / 2 N)·12LiBr·8LiI, 80(0.85(0.715Li2S·0.285P2S5)·0.15Li 3 / 2 B1 / 2 The sulfide solid electrolytes of Examples 14 to 17 were synthesized in the same manner as in Example 3, except that the composition was changed to 12LiBr·8LiI·12LiN and the heat treatment temperature was set to 250°C for each.

[0197] [Examples 18 to 20] The composition of the sulfide solid electrolyte was changed to 75(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 B 1 / 2 N)·15LiBr·10LiI, 70(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 B 1 / 2 N)·17LiBr·13LiI, 65(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 B 1 / 2 N)·20LiBr·15LiI, and the sulfide solid electrolytes of Examples 18 to 20 were synthesized in the same manner as in Example 3, except that the heat treatment temperatures were set to 230°C, 195°C, and 185°C, respectively.

[0198] The sulfide solid electrolytes of Examples 3 to 20 are represented by the general formula (100 - z1 - z2){(1 - y)[xLi2S·(1 - x)P2S5]·yLi α M β N}·z1LiX1·z2LiX2. The sulfide solid electrolytes of Comparative Examples 5 to 7 are represented by the general formula (100 - z1 - z2){(x - 1.5y)Li2S·(1 - x)P2S5·yLi3N}·z1LiX1·z2LiX2.

[0199] Tables 6 to 12 show the crystal structures identified from the XRD patterns of Examples 3 to 20 and Comparative Examples 4 to 8. Table 13 shows the crystal structures identified from the XRD patterns of Examples 4-1 to 4-6, Examples 5-1 to 5-5, Examples 6-1 to 6-5, Examples 7-1 to 7-5, and Comparative Examples 6-1 to 6-3. In the table, "HICP" represents a crystal phase having diffraction peaks at 2θ = 20.2° ± 0.5° and 23.6° ± 0.5° in X-ray diffraction measurement using CuKα radiation. "LICP" represents a crystal phase having diffraction peaks at 2θ = 21.0° ± 0.5° and 28.0° ± 0.5° in X-ray diffraction measurement using CuKα radiation. "Specific crystal structure C" represents a crystal phase having diffraction peaks at 2θ = 17.5° ± 0.5° and 24.9° ± 0.5° in X-ray diffraction measurement using CuKα radiation. "β-Li3PS4" represents a crystal phase having diffraction peaks at 2θ = 17.5° ± 0.5°, 18.1° ± 0.5°, 29.1° ± 0.5°, 29.9° ± 0.5°, and 31.2° ± 0.5° in X-ray diffraction measurement using CuKα radiation. "Unknown" represents peaks with an unknown crystal phase assignment. Also, the XRD patterns of Examples 4-1 to 4-6 are shown in FIG. 3. The XRD patterns of Comparative Examples 6-1 to 6-3 are shown in FIG. 4.

[0200] Tables 6 to 12 show the ionic conductivity (σ 25 ) and the activation energy (E a ) at 25 °C for Examples 3 to 20 and Comparative Examples 4 to 8. Table 13 shows the ionic conductivity (σ 25 ) and the activation energy (E a ) at 25 °C for Examples 4-1 to 4-6, Examples 5-1 to 5-5, Examples 6-1 to 6-5, Examples 7-1 to 7-5, and Comparative Examples 6-1 to 6-3.

[0201] (3) DSC DSC measurement was performed by the following method. Using a DSC apparatus (manufactured by Rigaku Corporation, Thermo Plus DSC8230) and a sealed pan made of SUS, the temperature was raised from room temperature to 400 °C at a rate of 10 °C / min.

[0202] For the sulfide solid electrolytes of Examples 4 to 7, Examples 14 to 17, and Comparative Example 6, the intermediate after milling and before heat treatment was subjected to DSC measurement. FIGS. 5 and 6 show the DSC curves of these samples.

[0203]

Table 6

[0204]

Table 7

[0205]

Table 8

[0206]

Table 9

[0207]

Table 10

[0208]

Table 11

[0209]

Table 12

[0210]

Table 13

[0211] From Table 6, it can be seen that for the sulfide solid electrolytes of Comparative Example 4 and Comparative Example 5, when the heat treatment temperature was 225°C, LICP was generated and the ionic conductivity at 25°C decreased. On the other hand, the sulfide solid electrolyte of Example 3 containing Li, P, S, N, Br, I, and Al showed high ionic conductivity without generating LICP even though it was heat treated at a higher temperature than the sulfide solid electrolytes of Comparative Example 4 and Comparative Example 5. That is, it can be understood that in the sulfide solid electrolyte of Example 3, the lower limit of the heat treatment temperature at which the ionic conductivity decreases compared to the sulfide solid electrolytes of Comparative Example 4 and Comparative Example 5 has increased.

[0212] From Table 7, it can be seen that the sulfide solid electrolytes of Examples 4 to 7 showed high ionic conductivity without generating LICP even though they were heat treated at a higher temperature than the sulfide solid electrolyte of Comparative Example 6. That is, it can be understood that in the sulfide solid electrolytes of Examples 4 to 7, the lower limit of the heat treatment temperature at which the ionic conductivity decreases compared to the sulfide solid electrolyte of Comparative Example 6 has increased.

[0213] From Table 8, it can be seen that the sulfide solid electrolyte of Example 8 showed higher ionic conductivity even though it was heat treated at a higher temperature than the sulfide solid electrolyte of Comparative Example 7. That is, it can be understood that in the sulfide solid electrolyte of Example 8, the lower limit of the heat treatment temperature at which the ionic conductivity decreases compared to the sulfide solid electrolyte of Comparative Example 7 has increased. This is presumably because the phase transition from HICP to LICP was suppressed in the sulfide solid electrolyte of Example 8.

[0214] From Table 9, it can be seen that the sulfide solid electrolytes of Examples 9 to 11 all showed higher ionic conductivity even though they were heat treated at a higher temperature than the sulfide solid electrolyte of Comparative Example 8. Also, it can be seen that the effect of the present invention of improving the thermal stability of the high Li-ion conductive phase of the sulfide solid electrolyte can be obtained even when the sulfide solid electrolyte contains only Br as the element X. Also, comparing Example 9 and Comparative Example 8 with the same Br content, it can be seen that in Comparative Example 8, neither HICP nor LICP was generated, while in Example 9, HICP was generated. That is, when the sulfide solid electrolyte contains Li, P, S, N, element X, and element M, an effect was recognized that HICP can be generated with a lower content of element X compared to the case where element M is not included.

[0215] From Table 10, it can be seen that even when the sulfide solid electrolyte contains only I as element X, a sulfide solid electrolyte containing HICP can be obtained.

[0216] From Table 11, it can be seen that the sulfide solid electrolytes of Example 6 and Examples 15 to 17 show the presence of HICP and high ionic conductivity even though they were heat-treated at a temperature higher than that of the sulfide solid electrolyte of Comparative Example 6. That is, it can be understood that for the sulfide solid electrolytes of these examples, the lower limit of the heat treatment temperature at which the ionic conductivity decreases compared to the sulfide solid electrolyte of Comparative Example 6 has increased. Also, from FIG. 6, it can be seen that for the sulfide solid electrolytes of Example 6 and Examples 14 to 17, the temperature difference between the crystallization peak presumed to be derived from HICP and the crystallization peak derived from β-Li3PS4 is larger compared to the sulfide solid electrolyte of Comparative Example 6. For example, in Comparative Example 6, the crystallization peak presumed to be derived from HICP and the crystallization peak derived from β-Li3PS4 were observed at around 190°C and around 260°C, respectively, while in Example 14, they were observed at around 190°C and around 280°C, respectively. From this, it can be understood that for the sulfide solid electrolytes of the examples, the temperature range in which HICP stably exists expands, and the thermal stability of the high Li ion conduction phase improves. Note that the crystallization peak presumed to be derived from HICP in FIG. 6 indicates the peak observed in the range of approximately 180°C to 220°C. The crystallization peak derived from β-Li3PS4 in FIG. 6 indicates the peaks observed at around 345°C, around 280°C, around 300°C, around 310°C, around 335°C, and around 260°C in Example 6, Examples 14 to 16, and Comparative Example 6, respectively. From the above, it can be understood that even when the content ratio N / P of N to P of the sulfide solid electrolyte is 0.060, 0.10, 0.21, 0.31, or 0.42, the effect of improving the thermal stability of the high Li ion conduction phase can be obtained.

[0217] From Table 12, it can be understood that even when the content ratio X / P of element X to P of the sulfide solid electrolyte is 0.52, 0.70, 0.90, or 1.12, a sulfide solid electrolyte containing HICP can be obtained.

[0218] From Comparative Examples 6-1 to 6-3 shown in Table 13, it can be understood that in the sulfide solid electrolyte of Comparative Example 6, when the heat treatment temperature is 250°C or higher, HICP undergoes a phase transition to LICP and β-Li3PS4. Also, it can be understood that the ionic conductivity at 25°C decreases significantly accordingly. On the other hand, from Examples 4-1 to 4-6, it can be understood that in the sulfide solid electrolyte of Example 4, HICP exists even when the heat treatment temperature is increased to 290°C, and high ionic conductivity can be maintained. Also, from Examples 5-1 to 5-5, it can be understood that in the sulfide solid electrolyte of Example 5, HICP exists in a wide temperature range, and high ionic conductivity can be maintained. Furthermore, from Examples 6-1 to 6-5 and Examples 7-1 to 7-5, it can be understood that even when B and Si are contained instead of Al as element M, the effect of the present invention of maintaining high ionic conductivity in a wide temperature range can be obtained. That is, from Table 13, it can be understood that in the sulfide solid electrolytes of Examples 4 to 7, the temperature range of heat treatment in which the ionic conductivity does not decrease expands. Also, from the comparison between Examples 6 and 7 and Examples 4 and 5 in Table 13, when the sulfide solid electrolyte contains either Si or B as element M, it can be seen that there exists a heat treatment temperature range of at least 80 °C over which the ionic conductivity does not decrease, indicating particularly excellent thermal stability of the high Li-ion conducting phase. Note that the peak near 210 °C in the DSC curves of Examples 6 and 7 in Figure 5 is a crystallization peak presumably derived from HICP. Therefore, it can also be inferred that in Examples 6 and 7, there exists a heat treatment temperature range of 100 °C over which the ionic conductivity does not decrease. The reason for obtaining such results is not clear, but for example, it is considered that the bond energy strength between either Si or B and N was a value suitable for exerting the effects of the present invention.

[0219] As is clear from Tables 6 to 13, it was confirmed that for the sulfide solid electrolytes of the examples, the lower limit of the heat treatment temperature at which the ionic conductivity decreases increased, and the heat treatment temperature range over which the ionic conductivity does not decrease widened. That is, the sulfide solid electrolytes containing Li, P, S, N, element X, and element M were excellent in the thermal stability of HICP. This is presumably because the discharge of N to the outside of the system in the manufacturing process was suppressed, and thus the effect of improving the thermal stability due to the inclusion of N in the sulfide solid electrolyte was fully exerted.

[0220] It is suggested that the method for manufacturing a sulfide solid electrolyte according to an embodiment of the present invention can suppress the discharge of N to the outside of the system and can also suppress the precipitation of Li2S. Suppressing the precipitation of Li2S is preferable because it can improve the air stability of the sulfide solid electrolyte.

[0221] That is, from Examples 21 to 41, Comparative Example 9, and Comparative Example 10, it is suggested that the method for manufacturing a sulfide solid electrolyte according to an embodiment of the present invention can suppress the precipitation of Li2S.

[0222] [Example 21] By the following treatment, the composition formula (100 - z)(yLi2S·(1 - y)P2S5)·zLi α M βLi in N α M β N is Li 3 / 2 Al 1 / 2 A sulfide solid electrolyte where N is, z = 1, and y = 0.70, i.e., 99(0.7Li2S·0.3P2S5)·1Li 3 / 2 Al 1 / 2 N was synthesized. Li3N and AlN were weighed so that the molar ratio was 1.2:1, mixed in a mortar, and then pelletized. Next, they were heat-treated at 750°C for 1 hour to produce Li 3 / 2 Al 1 / 2 N. Next, inside a glove box with an argon atmosphere having a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich), and Li 3 / 2 Al 1 / 2 N were weighed so that the molar ratio was 69.3:29.7:1.0, and then mixed in a mortar. This mixed sample was put into a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls. Milling treatment was performed for 45 hours at a revolution speed of 510 rpm using a planetary ball mill (manufactured by FRITSCH, model number Premium line P-7). Heat treatment was performed for 2 hours to obtain the sulfide solid electrolyte of Example 1. This heat treatment was carried out at a temperature that was at or above the crystallization temperature and at or below the crystallization temperature plus 100°C. The crystallization temperature was determined by measuring DSC. The DSC measurement was carried out under the following conditions. That is, using a DSC device (manufactured by Rigaku, Thermo Plus DSC8230), using a sealed pan made of SUS, the temperature was raised from room temperature to 400°C at 10°C / min.

[0223] [Examples 22 to 29] Composition formula of the sulfide solid electrolyte (100 - z)(yLi2S·(1 - y)P2S5)·zLi α M β Except that the value of z in N was changed to 5, 7, 10, 15, 20, 25, 30, 40, the sulfide solid electrolytes of Examples 22 to 29 were synthesized in the same manner as in Example 21.

[0224] [Examples 30 to 32] Composition formula of sulfide solid electrolyte: (100 - z)(yLi₂S·(1 - y)P₂S₅)·zLi α M β In N, except that y = 0.67 and the value of z was changed to 20, 25, and 30 respectively, the sulfide solid electrolytes of Examples 30 to 32 were synthesized in the same manner as in Example 21.

[0225] [Examples 33 to 36] Li₃N and BN were weighed so that the molar ratio was 1.1:1, mixed in a mortar, pelletized, and then heat-treated at 800 °C for 10 minutes to prepare Li 3 / 2 B 1 / 2 N. For the prepared Li 3 / 2 B 1 / 2 N, it was confirmed by XRD measurement that the main phase was Li 3 / 2 B 1 / 2 N. Composition formula of sulfide solid electrolyte: (100 - z)(yLi₂S·(1 - y)P₂S₅)·zLi α M β In N, Li α M β N was changed to Li 3 / 2 B 1 / 2 N, and except that the value of z was changed to 1, 10, 20, and 30, the sulfide solid electrolytes of Examples 33 to 36 were synthesized in the same manner as in Example 21.

[0226] [Examples 37 to 41] Li₃N and Si₃N₄ were weighed so that the molar ratio was 5.1:1, mixed in a mortar, pelletized, and then heat-treated at 800 °C for 10 minutes to prepare Li 5 / 3 Si 1 / 3 N. For the prepared Li 5 / 3 Si 1 / 3 N, it was confirmed by XRD measurement that the main phase was Li₅ / ₃Si 1 / 3 N. Composition formula of sulfide solid electrolyte: (100 - z)(yLi₂S·(1 - y)P₂S₅)·zLi α M β In N, Li α M β N was changed to Li5 / 3 Si 1 / 3 Except for changing Si to N and changing the values of z to 1.5, 15, 20, 30, and 45, the sulfide solid electrolytes of Examples 37 to 41 were synthesized in the same manner as in Example 21.

[0227] [Comparative Example 9] Composition formula of sulfide solid electrolyte: (100 - z)(yLi2S·(1 - y)P2S5)·zLi α M β Li in N α M β Except for changing N to Li3N and changing the value of z to 20, the sulfide solid electrolyte of Comparative Example 9 was synthesized in the same manner as in Example 21.

[0228] [Comparative Example 10] Composition formula of sulfide solid electrolyte: (100 - z)(yLi2S·(1 - y)P2S5)·zLi α M β In N, except for setting y = 0.68 and changing the value of z to 16, the sulfide solid electrolyte of Comparative Example 10 was synthesized in the same manner as in Comparative Example 9.

[0229] [Evaluation] (1) XRD, ionic conductivity (σ) X-ray diffraction measurement was performed by the above method. Also, the ionic conductivity (σ 25 ) at 25 °C was obtained by measuring the alternating current impedance by the above method using "VMP-300" manufactured by (Bio-Logic).

[0230] (2) Raman spectroscopic analysis The Raman spectrum was measured by the following method. Using a laser Raman spectrophotometer ("LabRAM HR Revolution" manufactured by Horiba, Ltd.), under the conditions of an excitation laser wavelength of 532 nm (YAG laser) and a grating of 600 gr / mm, Raman spectroscopic measurement was performed in the wavenumber range from 100 cm -1 to 1800 cm -1 .

[0231] Table 14 shows the ionic conductivity at 25°C, the crystal structure identified from the XRD pattern, and the Raman spectrum of Examples 21 to 41, Comparative Example 9, and Comparative Example 10. In the table, "Specific Crystal Structure A" represents a crystal phase having diffraction peaks at 2θ = 17.9° ± 0.5°, 19.1° ± 0.5°, 29.1° ± 0.5°, 29.8° ± 0.5°, 30.9° ± 0.5° in X-ray diffraction measurement using CuKα radiation. "Specific Crystal Structure B" represents a crystal phase having diffraction peaks at 2θ = 17.9° ± 0.5°, 19.1° ± 0.5°, 29.1° ± 0.5°, 29.8° ± 0.5° in X-ray diffraction measurement using CuKα radiation. "-" indicates that the measurement was not performed.

[0232]

Table 14

[0233] In the sulfide solid electrolyte of Comparative Example 9, only the peaks derived from the crystal structure of Li2S were observed. From this result, it can be seen that Li2S is likely to precipitate when Li3N is used. The reason for such a result is not clear, but it is considered that Li3N reacts violently with other raw material compounds to precipitate Li2S.

[0234] In Examples 21 to 35 and Examples 37 to 40, the peaks of Li2S were not observed. Among them, from the comparison of the examples (Examples 26, 35, 39, and Comparative Example 9) where z = 20 and y = 0.70, it was confirmed that the precipitation of Li2S was suppressed in the sulfide solid electrolyte of the examples.

[0235] In addition, although the sulfide solid electrolytes of Examples 27 to 29, Example 32, Example 39, and Example 40 all had a higher Li / P content ratio of Li to P than the sulfide solid electrolyte of Comparative Example 10, no peak of Li2S was observed. In particular, in Example 29, the Li / P content ratio was 4.00, which was higher than those of Comparative Example 9 and Comparative Example 10, yet no peak of Li2S was observed. For the sulfide solid electrolytes of Example 26 and Example 35, although the Li / P was substantially the same as that of the sulfide solid electrolyte of Comparative Example 10, no peak of Li2S was observed. For the sulfide solid electrolyte of Example 32, although the value of y was substantially the same as that of Comparative Example 10 and the Li / P was also the same, no peak of Li2S was observed. In the case of sulfide solid electrolytes, Li2S tends to precipitate when the Li content is high. However, since the above results were obtained, it is suggested that the precipitation of Li2S is suppressed in the method for manufacturing the sulfide solid electrolyte of the examples.

[0236] That is, from the comparison of Example 28, Example 29, Example 36, Example 40, and Example 41, it was suggested that when Al was included as element M, the suppression of Li2S precipitation was remarkable.

[0237] From the above, it was suggested that the precipitation of Li2S is suppressed in the method for manufacturing the sulfide solid electrolyte of the examples. As a reason why the precipitation of Li2S can be suppressed by the sulfide solid electrolyte containing element M, the following can be considered. When Li3N is used as a starting material for a sulfide-based solid electrolyte containing N, Li3N and P2S5 react violently to release N2 and Li2S precipitates. This is presumably because the defect formation energy of N in Li3N is small. In contrast, in the present invention, α M β the defect formation energy of N in

[0238] Although the present invention has been described in detail above, the above embodiments are merely examples, and the invention disclosed herein includes various modifications and changes of the above specific examples.

Industrial Applicability

[0239] The all-solid-state battery including the sulfide solid electrolyte according to the present invention is suitably used, for example, as a lithium-ion all-solid-state battery for HEV.

Explanation of Signs

[0240] 1 Negative electrode layer 2 Positive electrode layer 3 Solid electrolyte layer 4 Negative electrode substrate layer 5 Negative electrode binder layer 6 Positive electrode binder layer 7 Positive electrode substrate layer 10 All-solid-state battery

Claims

【Claim 1】 A sulfide solid electrolyte containing, as constituent elements, P, S, N, element A, element X, and element M and having a crystal structure. Here, A represents at least one element selected from the group consisting of Li, Na, and K. X represents at least one element selected from the group consisting of Cl, Br, and I. M represents at least one element selected from the group consisting of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti.

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