Method for producing a sulfide solid electrolyte, sulfide solid electrolyte, all-solid-state battery, and method for selecting raw material compounds used in the production of a sulfide solid electrolyte.

Abstract

The present invention provides a method for producing a sulfide solid electrolyte that can suppress the discharge of nitrogen into the system during the manufacturing process of the sulfide solid electrolyte, a method for selecting raw material compounds used in the production of the sulfide solid electrolyte, an all-solid-state battery equipped with the sulfide solid electrolyte, and a sulfide solid electrolyte with improved thermal stability, a method for producing the same, and an all-solid-state battery equipped with the sulfide solid electrolyte. [Solution] The sulfide solid electrolyte contains P, S, N, element A, element X, and element M as constituent elements and has a crystalline 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.

Description

[Technical Field]

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

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion non-aqueous electrolyte secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles, due to their high energy density. Generally, these non-aqueous electrolyte secondary batteries consist of an electrode body having a pair of electrically isolated electrodes, and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring ions between the two electrodes.

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

[0004] Patent Document 1 describes the production of a sulfide solid electrolyte having the composition 75Li2S-25P2S5-yLi3N using Li2S, P2S5, and Li3N as starting materials. Patent Document 2 describes the production of a sulfide solid electrolyte using a raw material composition consisting of Li2S, P2S5, LiBr, LiI, and Li3N. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-041671 [Patent Document 2] Japanese Patent Publication No. 2015-011898 [Patent Document 3] Japanese Patent Publication No. 2018-156735 [Overview of the project] [Problems that the invention aims to solve]

[0006] Patent Document 1 describes that the atmospheric stability (water resistance) of a sulfide solid electrolyte can be improved by including nitrogen (N). However, when Li3N is used as a raw material for the sulfide solid electrolyte, there is a problem in that nitrogen is released into the system.

[0007] Patent Document 2 describes that a high-Li ion conducting phase precipitates when a raw material composition containing Li2S, P2S5, LiI, and LiBr is amorphous and then heat-treated. However, there was a problem in that if the heat treatment temperature was too high, a low-Li ion conducting phase would precipitate. Patent Document 3 describes that the difference between the temperature at which the high-Li ion conducting phase is formed and the temperature at which the low-Li ion conducting phase is formed can be increased by adding Li3N, but the difference is small, at most about 30°C, and further improvement was needed.

[0008] The present invention has been made based on the circumstances described above, and one aspect of the present invention aims to provide a method for producing a sulfide solid electrolyte that can suppress the discharge of N into the system during the production process of the sulfide solid electrolyte, a method for selecting raw material compounds to be used in the production of a sulfide solid electrolyte, and an all-solid-state battery equipped with the sulfide solid electrolyte. Another aspect of the present invention aims to provide a sulfide solid electrolyte with improved thermal stability, a method for producing the same, and an all-solid-state battery equipped with the sulfide solid electrolyte. [Means for solving the problem]

[0009] One aspect of the present invention, made to solve the above 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 contains 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 to be used in the production of sulfide solid electrolytes, As candidate raw material compounds, select candidate materials containing N, element A', and element M', and use first-principles calculations to determine the defect generation energy E of N within the candidate materials. Ndefect The calculation of the above E Ndefect However, if the voltage is 4.00 eV or higher, the above candidate material is selected as the raw material compound, which is a method for selecting raw material compounds.

[0011] Another aspect of the present invention is a sulfide solid electrolyte having a crystalline structure and containing P, S, N, element A, element X, and element M as constituent elements. 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 one embodiment of the present invention, a method for producing a sulfide solid electrolyte, a method for selecting raw material compounds used in the production of a sulfide solid electrolyte, and a sulfide solid electrolyte, the discharge of N into the system during the production process of the sulfide solid electrolyte can be suppressed. According to another embodiment of the present invention, a sulfide solid electrolyte with improved thermal stability can be obtained. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a flowchart of the manufacturing process for a sulfide solid electrolyte in one embodiment of the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view showing an all-solid-state battery according to one embodiment of the present invention. [Figure 3] Figure 3 shows the XRD diffraction pattern of the sulfide solid electrolyte in the example. [Figure 4] Figure 4 shows the XRD diffraction pattern of the comparative example sulfide solid electrolyte. [Figure 5] Figure 5 shows the DSC curves of the intermediate sulfide solid electrolytes of the examples and comparative examples after milling and before heat treatment. [Figure 6] Figure 6 shows the DSC curves of the intermediate sulfide solid electrolytes of the examples and comparative examples after milling and before heat treatment. [Modes for carrying out the invention]

[0014] First, an overview of the method for producing sulfide solid electrolytes disclosed herein will be described.

[0015] A method for producing a sulfide solid electrolyte according to one aspect of the present invention 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 contains a raw material compound containing 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.

[0016] In the present invention, "composition" means a mixture obtained by mixing two or more compounds. "Raw material compound" means a specific compound that constitutes the above composition.

[0017] The inventors discovered 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, the discharge of N into the system during the manufacturing process of sulfide solid electrolytes can be suppressed, leading to the present invention.

[0018] This method for producing sulfide solid electrolytes suppresses the discharge of nitrogen (N) from the system during the manufacturing process. Therefore, it becomes easier to control the N content in the sulfide solid electrolyte. While the exact reason for this is unclear, the following reasons are speculated. In the method for producing a sulfide solid electrolyte using Li3N disclosed in Patent Documents 1 and 3, the energy for generating N defects in Li3N is small, and N2 gas is easily generated. In contrast, in the method for producing the sulfide solid electrolyte using raw material compounds containing N, element A, and element M, the defect generation energy for N is large, and N defects are less likely to be generated during the synthesis process of the sulfide solid electrolyte, thus making it difficult to generate N2 gas. Therefore, the discharge of N into the system during the manufacturing process of the sulfide solid electrolyte can be suppressed. Note that element M is calculated by first-principles calculations, which will be described later. α M β This refers to elements whose defect formation energy for N in a compound represented by N (where α and β are numerical values ​​that give the stoichiometric ratio depending on the type of element M) is 4.00 eV or greater. The definition of the defect formation energy for N will be described later.

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

[0020] According to this, the mass energy density of all-solid-state batteries equipped with sulfide solid electrolytes produced by this manufacturing method can be increased. This is because Li has the smallest atomic weight and ion size among alkali metal elements.

[0021] The raw material compound containing N, element A, and element M may be obtained by reacting a nitride of element M with a nitride of element A, or it may be an industrially manufactured and commercially available compound.

[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 those for which the defect formation energy of N, calculated by the first-principles calculations described later, is 4.10 eV or higher.

[0023] This makes it possible to more reliably suppress the discharge of nitrogen from the system during the manufacturing process of sulfide solid electrolytes.

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

[0025] This makes it possible to more reliably suppress the discharge of nitrogen from the system during the manufacturing process of sulfide solid electrolytes.

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

[0027] Preferably, the above composition contains Li as element A, with a molar ratio of 2.30 to 4.20 for Li relative to P, and a molar ratio of 0.0100 to 1.20 for N relative to P. More preferably, element A contains Li, with a molar ratio of 2.77 to 3.38 for Li relative to P, and a molar ratio of 0.280 to 0.650 for N relative to P. This makes it possible to provide a sulfide solid electrolyte with excellent atmospheric stability and high ionic conductivity at 25°C.

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

[0029] It is known that sulfide solid electrolytes containing Li, P, S, and element X produce a metastable phase with high ionic conductivity (hereinafter also referred to as HICP (High Ion Conduction Phase)) (Patent Document 2). Furthermore, it is known that the presence of N in such sulfide solid electrolytes widens 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)) (Patent Document 3). However, since Li3N is used to manufacture the sulfide solid electrolyte in Patent Document 3, N is discharged into the system during the manufacturing process of the sulfide solid electrolyte, and the effect of widening the heat treatment temperature range in which HICP is stable was not sufficiently obtained. In contrast, the method for producing the sulfide solid electrolyte suppresses the emission of nitrogen (N) from the system. Therefore, the effect of improving the thermal stability of HICP can be fully realized.

[0030] Preferably, the above composition has a molar ratio of 3.10 to 4.20 in which Li is contained relative to P, a molar ratio of 0.0600 to 0.750 in which N is contained relative to P, and a molar ratio of 0.180 to 1.30 in which X is contained relative to P.

[0031] This makes it possible to provide a sulfide solid electrolyte with high thermal stability for HICP.

[0032] Another aspect of the present invention relates to a sulfide solid electrolyte produced by the method for producing the sulfide solid electrolyte. With such a sulfide solid electrolyte, the discharge of nitrogen into the system during the production process of the sulfide solid electrolyte is suppressed, so that the various effects of containing nitrogen can be fully realized.

[0033] Another aspect of the present invention relates to an all-solid-state battery comprising a sulfide solid electrolyte manufactured by the method for manufacturing the sulfide solid electrolyte. With such an all-solid-state battery, the discharge of nitrogen into the system during the manufacturing process of the sulfide solid electrolyte is suppressed, so that the various effects of including nitrogen can be fully realized.

[0034] A method for selecting a raw material compound to be 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 to be used in the production of a sulfide solid electrolyte, comprising: selecting candidate materials containing N, element A', and element M' as candidate raw material compounds, and using first-principles calculations, determining the defect generation energy E of N inside the candidate materials. Ndefect The calculation of the above E Ndefect However, if the voltage is 4.00 eV or higher, the above candidate material is selected as the raw material compound, which is a method for selecting raw material compounds. Furthermore, if there are multiple N-occupied sites in the crystal structure of the candidate material, E is calculated for each N-occupied site. Ndefect Calculate the value and select the one with the lowest value for the candidate material E Ndefect It is used as such.

[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 manufactured using the above raw material compound, the discharge of N out 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 above raw material compound.

[0037] According to this, the discharge of N out 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 above raw material compound.

[0039] According to this, the discharge of N out of the system in the manufacturing process of the sulfide solid electrolyte can be even more 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 out 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. For such a sulfide solid electrolyte, the discharge of N out of the system in the manufacturing process of the sulfide solid electrolyte is suppressed, so various effects due to the inclusion of N can be sufficiently exhibited.

[0043] Another aspect of the present invention relates to an all-solid-state battery comprising a sulfide solid electrolyte manufactured using a raw material compound selected by the selection method. With such a sulfide solid electrolyte, the emission of nitrogen into the system during the manufacturing process is suppressed, so the various effects of containing nitrogen can be fully realized.

[0044] Another embodiment of the present invention is a sulfide solid electrolyte containing P, S, N, element A, element X, and element M as constituent elements, and having a crystalline 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] Such sulfide solid electrolytes can enhance the thermal stability of HICPs compared to sulfide solid electrolytes composed solely of Li, P, S, N, and element X.

[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 improved.

[0048] The above crystal structure is preferably such that, in X-ray diffraction measurements using CuKα rays, diffraction peaks are found at 2θ = 20.2° ± 0.5° and 23.6° ± 0.5°.

[0049] The sulfide solid electrolyte having the above-described crystalline structure provides good Li ion conductivity.

[0050] Another aspect of the present invention relates to an all-solid-state battery comprising a sulfide solid electrolyte having a crystalline structure and containing P, S, N, element A, element X, and element M as constituent elements.

[0051] One advantage of all-solid-state batteries compared to non-aqueous electrolyte batteries is their extremely high upper limit of operating temperature. This advantage is achieved because of the high thermal stability of the solid electrolyte. However, Patent Documents 2 and 3 describe that in sulfide solid electrolytes containing Li, P, S, N, Br, and I, a high-Li ion conduction phase transitions to a low-Li ion conduction phase when heated to a high temperature. In other words, 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. In contrast, the sulfide solid electrolyte has higher HICP thermal stability compared to conventional sulfide solid electrolytes that do not contain element M. Therefore, the all-solid-state battery equipped with the sulfide solid electrolyte of the present invention can fully enjoy the advantage of all-solid-state batteries, which is that the upper limit of the battery's operating temperature can be increased.

[0052] Another embodiment of the present invention is a crystalline sulfide solid electrolyte comprising 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] With such a sulfide solid electrolyte, it is possible to improve atmospheric stability and other factors by suppressing the emission of nitrogen (N) from the system during the manufacturing process of the sulfide solid electrolyte.

[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 reliably suppressing the emission of nitrogen from the system during the manufacturing process of sulfide solid electrolytes, atmospheric stability and other factors can be further improved.

[0056] The following describes in detail a method for producing a sulfide solid electrolyte according to one embodiment of the present invention, a sulfide solid electrolyte, an all-solid-state battery, and a method for selecting raw material compounds used in the production of a sulfide solid electrolyte. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood as design matters for those skilled in the art based on prior art. The present invention can be carried out based on the contents disclosed herein and common technical knowledge in the art.

[0057] <Method for producing sulfide solid electrolyte> [Embodiment] A method for producing a sulfide solid electrolyte according to one embodiment of the present invention comprises a preparation step of preparing a composition containing P, S, N, element A, and element M; a reaction step of reacting the composition to obtain an intermediate; and a heating step of heating the intermediate to obtain a sulfide solid electrolyte, wherein the composition contains 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 method for producing the sulfide solid electrolyte will be described using the case where element A contains Li as an example. Figure 1 is a flowchart showing an example of the method for producing the sulfide solid electrolyte according to this embodiment, and the following explanation will follow accordingly.

[0058] (preparation process) In this process, 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-MN-containing compounds) and one or more raw material compounds containing Li, P, and S.

[0059] In Figure 1, first, Li3N and a nitride of element M are prepared and mixed in a mortar and pestle. Next, pellets of the mixed raw material compound are produced. Then, the pellets are heat-treated to produce a Li-MN-containing compound.

[0060] The means of preparing the Li-MN-containing compound are not limited to those described above, and it may be prepared by other methods. For example, the raw materials for the Li-MN-containing compound may be two or more compounds containing N, Li, or element M. The Li-MN-containing compound may also be prepared by mechanical milling. Industrially manufactured and commercially available MN-containing compounds may also be prepared.

[0061] Li-MN-containing compounds are preferably made from lithium composite nitrides of element M. For example, 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 Examples include lithium composite nitrides such as N. Among these, Li is readily available. 3 / 2 Al 1 / 2 N, Li 3 / 2 B 1 / 2 N and Li 5 / 3 Si 1 / 3 N is preferred. Also, from the viewpoint of suppressing the precipitation of Li2S, Li 3 / 2 Al 1 / 2 N is particularly preferred, and Li is preferred from the viewpoint of improving the thermal stability of HICP. 3 / 2 B 1 / 2 N and Li 5 / 3 Si 1 / 3N is particularly preferred. From the viewpoint of suppressing the discharge of N into the system during the manufacturing process of sulfide solid electrolytes, Li 3 / 2 Al 1 / 2 N and Li 3 / 2 B 1 / 2 N is particularly preferred.

[0062] Examples of raw material compounds containing element M include oxides of element M, sulfides of element M, nitrides of element M, and alloys of element M and Li. Examples of sulfides of element M include Al2S3 and SiS2. Examples of nitrides of element M include AlN, Si3N4, BN, and Mg3N2. A single raw material compound containing element M may be used, or two or more may be used in combination.

[0063] In this manufacturing method, element M 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 viewpoint of more reliably suppressing the discharge of N from the system during the manufacturing process of sulfide solid electrolytes, element M is preferably one of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, or P, and more preferably one of Al, Ta, Si, Sc, Mg, Nb, or B. Furthermore, since they are readily available, element M is even more preferably one of Al, Si, or B. In particular, element M may be Al.

[0064] Examples of starting material compounds containing N include Li3N, PN, P3N5, S4N4, S2N2, and S4N2. Among these, Li3N is preferred. The starting material compounds containing N may be used individually or as a mixture of two or more.

[0065] Examples of Li-containing raw material compounds (also referred to as Li compounds) include Li2S, Li2O, Li3N, Li2CO3, and metallic lithium. Among these, Li2S is preferred. Li-containing raw material compounds may be used individually or as a mixture of two or more.

[0066] Examples of P-containing raw material compounds (also referred to as P compounds) include P2S3, P2S5, P2O5, P3N5, and elemental phosphorus. Among these, P2S3 and P2S5 are preferred, and P2S5 is particularly preferred. A single P-containing raw material compound may be used, or two or more may be used in mixture form.

[0067] Examples of raw material compounds containing sulfur include Li2S, P2S3, P2S5, sulfides of element M, and elemental sulfur. A single raw material compound containing sulfur may be used alone, or two or more may be used in combination.

[0068] The above composition preferably contains a Li compound, a P compound, and a Li-MN-containing compound, and more preferably at least one of the Li compound and the P compound contains S. Examples of the Li compound, P compound, and Li-MN-containing compound include lithium sulfide, phosphorus sulfide, and Li (general formula Li). α M β It is even more preferable to include a compound represented by N (where α and β are numerical values ​​that give a stoichiometric ratio depending on the type of element M).

[0069] Sulfide solid electrolytes may experience reduced atmospheric stability due to Li2S precipitation if the Li content is high, and reduced ionic conductivity if the Li content is low. Furthermore, if the N content is high, atmospheric stability may decrease due to Li2S precipitation, while if the N content is low, the effects of improved atmospheric stability due to N content may not be fully realized. From these viewpoints, it is preferable that the elemental ratios of the above composition in the mixed state simultaneously satisfy the following formula in terms of molar ratios. 2.30 ≤ Li / P ≤ 4.20 0.0100 ≤ N / P ≤ 1.20 It is more preferable that the above Li / P and N / P simultaneously satisfy the following equations. 2.36 ≤ Li / P ≤ 4.12 0.0200 ≤ N / P ≤ 1.11 It is even more preferable that the above Li / P and N / P simultaneously satisfy the following equations. 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] Further, in the above composition, the molar ratios of the respective elements of Li, P, S, N, and element M are 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 a stoichiometric ratio according to the type of element M). It is preferable to satisfy this. 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 is not specified to consist of Li₂S, P₂S₅, and Li α M β N.

[0071] In the above general formula, z is preferably more 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. Further, when 1 ≤ z ≤ 30, a sulfide solid electrolyte with enhanced 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 does not substantially contain Li₂S, which is likely to react 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 above-mentioned content ratio of Li2S and P2S5 in the above composition, a sulfide solid electrolyte with enhanced ionic conductivity at 25°C can be produced.

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

[0074] (Reaction process) In this process, a composition containing Li, P, S, N, and element M is reacted by mechanical milling to obtain an intermediate. The means of obtaining the intermediate are not limited to those shown, and other methods may be used. For example, in Figure 1, instead of mechanical milling, a melt-quenching method or the like may be used.

[0075] Mechanical milling may be dry or wet, but wet milling is preferred because it allows for more uniform mixing of the raw material compounds. Examples of mechanical milling include container-driven mills, media-stirring mills, milling with high-speed rotary grinders, roller mills, and jet mills. Examples of container-driven mills include rotary mills, vibratory mills, and planetary mills. Examples of media-stirring mills include attritors and bead mills. Examples of milling with high-speed rotary grinders include hammer mills and pin mills. Among these, container-driven mills are preferred, and planetary mills are particularly preferred.

[0076] The intermediate obtained in the reaction step may have a crystalline structure, but it is preferably a so-called sulfide glass. "Sulfide glass" refers to a sulfide solid electrolyte containing an amorphous structure. When the intermediate is sulfide glass, there is less crystalline phase with low atmospheric stability, such as Li2S, and a sulfide solid electrolyte 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 an intermediate at a temperature above its 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 thermometer (DSC). For example, Li7P3S 11 To obtain a crystalline structure, the heat treatment temperature is preferably between 250°C and 400°C, and to obtain a β-Li3PS4 crystalline structure, the heat treatment temperature is preferably between 200°C and 400°C. Furthermore, to obtain a first crystalline 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 measurements using CuKα rays, the heat treatment temperature is preferably between 250°C and 400°C. This is because if heat treatment is performed at a high temperature such as 500°C, there is a possibility of a phase transition to the stable phase Li4P2S6.

[0078] [Differentiation] The method for producing a sulfide solid electrolyte according to 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 embodiments.

[0079] In the above embodiment, a Li2S-P2S5-based sulfide solid electrolyte was described as an example, but LGPS-type sulfide solid electrolytes and argyrodite-type sulfide solid electrolytes may also be produced by this manufacturing method. Examples of LGPS-type sulfide solid electrolytes include Li 10 GeP2S 12 Examples include Li 10 GeP2S 12 The crystal structure having the crystalline phase exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 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°. Examples of argyrodite-type sulfide solid electrolytes include Li6PS5Cl. The crystalline structure of Li6PS5Cl, which has a crystalline phase, exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 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°.

[0080] [Example 1] As a modification example 1, an embodiment for producing an LGPS-type sulfide solid electrolyte will be described. An LGPS-type sulfide solid electrolyte can be produced by adding a raw material compound containing Ge to the composition in the above preparation step. Examples of raw material compounds containing Ge include GeS2. When producing an LGPS-type sulfide solid electrolyte, it is preferable that the elemental ratios of the composition simultaneously satisfy the following formula in molar ratio. 5.01 ≤ Li / P ≤ 5.61 0.0051 ≤ N / P ≤ 0.41 By setting the elemental content ratio in the above composition to the above range, Li 10 GeP2S 12 This method allows for the production of a sulfide solid electrolyte having a crystalline phase and high ionic conductivity at 25°C.

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

[0082] In the second modification, a raw material compound containing element X is added to the above composition to produce a crystalline sulfide solid electrolyte containing Li, P, S, N, element X, and element M. This makes it possible to produce a sulfide solid electrolyte having HICP and improved thermal stability of the HICP.

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

[0084] In the modified example 2, when the composition contains both Br and I, the amount of Br relative to the total amount of Br and I in the composition is preferably 1 mol% or more and 99 mol%, and more preferably 5 mol% or more and 80 mol%.

[0085] When the content of Li 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, leading to 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 crystalline phase of lithium halide may remain in the sulfide solid electrolyte, which may reduce the ionic conductivity. When the content is low, there is a risk that the effect of containing element X cannot be fully exerted. From these viewpoints, it is preferable that the composition in the preparation process of the modified example 2 simultaneously satisfies the following formulas in terms of the elemental ratio in the mixed state, each in 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] It is preferable that the above composition satisfies the molar ratio of each element of Li, P, S, N, element X, and element M as 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). More preferably, 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 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. 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, and 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, and it is more preferable that 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 the stoichiometric ratio 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 not lower 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).

[0090] In Modified Example 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 specific crystal structure C. Among these crystal phases, HICP has the highest ionic conductivity. Therefore, in the heat treatment step in Modified Example 2, the lower limit of the heat treatment temperature is the formation temperature T of HICP H or higher, which is preferable. Also, the upper limit of the heat treatment temperature is preferably the formation temperature T of β-Li3PS4 β or lower, and more preferably the formation temperature T of LICP L or the formation temperature T of specific crystal structure C C or lower. T H , T L , T C and T β can be determined by XRD measurement. The sulfide solid electrolyte produced in Modified Example 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 Modified Example 2, there is an advantage that a sulfide solid electrolyte having a high ionic conductivity can be produced without requiring strict temperature control in the heat treatment step. β -T H is preferably ≧40°C, more preferably ≧50°C, even more preferably ≧60°C, and particularly preferably ≧70°C. β -T H β -T H β -T H β -T H

[0091]

[0092] ​​​​​"HICP" refers to a crystalline phase that has diffraction peaks at 2θ = 20.2°±0.5° and 23.6°±0.5° in X-ray diffraction measurements using CuKα rays. This crystal structure is the crystalline phase described in Patent Document 2, etc., and is a crystalline phase with high Li ion conductivity. "LICP" refers to a crystalline phase that has diffraction peaks at 2θ = 21.0°±0.5° and 28.0°±0.5° in X-ray diffraction measurements using CuKα rays. This crystal structure is the crystalline phase described in Patent Document 2, etc., and is a crystalline phase with low Li ion conductivity. "Specific Crystal Structure C" refers to a crystalline phase that has diffraction peaks at 2θ = 17.5°±0.5° and 24.9°±0.5° in X-ray diffraction measurements using CuKα rays. "β-Li3PS4" represents a crystalline phase that exhibits 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 measurements using CuKα rays.

[0093] X-ray diffraction measurements using CuKα rays as described herein are performed according to the following procedure. A solid electrolyte powder to be measured is packed into an airtight X-ray diffraction sample holder under an argon atmosphere with a dew point of -50°C or lower. Powder X-ray diffraction measurements are performed using an X-ray diffractometer (Rigaku's "MiniFlex II"). The radiation source is CuKα rays, the tube voltage is 30kV, and the tube current is 15mA. The diffracted X-rays are passed through a 30μm thick Kβ filter and detected by a high-speed one-dimensional detector (model: D / teX Ultra 2). The sampling width is 0.01°, the scan speed is 5° / min, the diverging slit width is 0.625°, the receiving slit width is 13mm (OPEN), and the scattering slit width is 8mm.

[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 into the system during the production process of the sulfide solid electrolyte. In selecting elements A and M that would produce such effects, the 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 according to 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 N defect formation energy E Ndefect 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 non-empirically predicting physical properties, 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 atoms, structural 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 N defect formation energy E Ndefect is the energy value required to remove N from the crystal structure to generate a defect. The N defect formation energy is a value calculated using the total energy E perfect of a crystal structure without defects, the total energy E Nvacancy of a crystal structure containing N defects, and the chemical potential μ N of N atoms, and is defined by the following formula (1). E Ndefect = (E Nvacancy + μ N ) - E perfect Formula (1) That is, the procedure for calculating the N defect formation energy E Ndefect is as follows. (a) Obtain the composition and crystal structure of the candidate material. (b) Chemical potential μ of the N atom to be removed as a defect N Calculate. (c) Total energy E of a defect-free crystal structure perfect This is calculated using structural optimization calculations. (d) Total energy E of the crystal structure containing N defects Nvacancy This is calculated using structural optimization calculations. (e) Defect generation energy E of N according to equation (1) Ndefect Calculate. If there are multiple N-occupied sites in the crystal structure of the candidate material, E is calculated for each N-occupied site. Ndefect Calculate the value and select the one with the lowest value for the candidate material E Ndefect It is used as such. The composition and crystal structure of the candidate materials can be arbitrarily selected from those available in known publications and databases. The candidate materials are not particularly limited as long as they are compounds containing N, element A', and element M', but it is preferable that they are compounds that are stable at room temperature and pressure.

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

[0099] In this embodiment, α M' βFor candidate materials represented by N (where α and β are values ​​that give the stoichiometric ratio depending on the type of element M), and for Li3N, the defect formation energy of N was calculated. Specifically, Li was selected as element A'. For 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, and C were evaluated. For the first-principles calculations, the Vienna Ab-initio Simulation Package (VASP) software was used. The calculation conditions were as follows: The k-points were set so that the k-resolution value was approximately 1000. The k-resolution is the product of the number of atoms in the model and the k-points in the a, b, and c axes. Cutoff energy of plane wave basis function: 520 eV Approximation method for exchange-correlation interaction: GGA+U Pseudopotential: PAW(PBEsol) k point:k-resolution≒1000 Convergence conditions for SCF calculation: 10 -4 eV Occupancy of each atomic site (Occ.): 1 For first-principles calculations of materials containing transition metal elements such as V, Cr, Mn, Fe, Co, and Ni, where the 3d orbital is the outermost shell orbital and the 3d orbital is not closed in the stable valence state of the cation, and electrons exist in the 3d orbital, see Hubbard's U shown in Table 1. eff The values ​​were used as calculation conditions. This reflected the electron localization effect in the d orbital in the calculation. Hubbard's U is shown in Table 1. eff The values ​​are taken from the calculation conditions of first-principles calculations performed in the crystal structure database Materials Project (https: / / materialsproject.org / #search / materials) (as of August 22, 2019). By searching the database for materials containing V, Cr, Mn, Fe, Co, and Ni, U eff The value was retrieved.

[0100] [Table 1]

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

[0102] [Table 2]

[0103] Table 3 shows the element M', the chemical composition of each candidate material, and the defect generation energy E for N. Ndefect This indicates.

[0104] [Table 3]

[0105] Table 3 shows the defect generation energy E for N in Li3N, where N defects are easily generated. Ndefect It can be seen that the voltage is 2.94 eV. Furthermore, the elements V, Y, Ga, Ca, Ce, Sn, Zn, Ge, Cr, Mn, Sr, In, Co, Ni, and Fe are all Li α M' β Defect generation energy E in N Ndefect It can be seen that the voltage is small, less than 3.88 eV. For this reason, in candidate materials containing any of V, Y, Ga, Ca, Ce, Sn, Zn, Ge, Cr, Mn, Sr, In, Co, Ni, or Fe as element M', it is predicted that N defects will easily form, and the effect of the present invention in suppressing the discharge of N out of the system during the manufacturing process of sulfide solid electrolytes will not be obtained, or the effect will be small. On the other hand, the elements Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, and Ti are Li α M' β Defect generation energy E in N NdefectIt can be seen that the voltage is large, at 4.00 eV or more. Therefore, it is predicted that if the candidate material contains any of Al, Ta, Si, Sc, Mg, Nb, B, Hf, C, P, Zr, or Ti as element M', it is highly likely that the effects of the present invention will be exerted, as N defects are less likely to be generated and N will be suppressed from being released into the system during the manufacturing process of sulfide solid electrolytes.

[0106] The candidate material is N with a defect generation energy E Ndefect The larger the value of E, the less likely N defects are to form, and it is predicted that the emission of N out of the system during the manufacturing process of sulfide solid electrolytes can be further suppressed. For this reason, in this embodiment, the defect formation energy E of N in the candidate material is Ndefect The radiation level is 4.00 eV or higher, preferably 4.10 eV or higher, more preferably 4.20 eV or higher, even more preferably 4.30 eV or higher, and particularly preferably 4.35 eV or higher.

[0107] In this embodiment, calculations were performed for the case where element A' includes Li. That is, Li α M' β First-principles calculations were performed using N as a model. However, the present invention is not limited to this. Element A' can be any metallic element; for example, candidate materials containing any of Na, K, Mg, Ca, or Al may be selected as element A', and a starting compound may be selected using first-principles calculations.

[0108] <Sulfide solid electrolyte> [Embodiment 1] A sulfide solid electrolyte according to one embodiment of the present invention is a composition containing P, S, N, element A, and element M, and is manufactured by a manufacturing method comprising: preparing a raw material compound containing N, element A, and element M; reacting the composition to obtain an intermediate; and heating the intermediate to obtain a sulfide solid electrolyte. The sulfide solid electrolyte will be described below using the case in which element A contains Li as an example.

[0109] The sulfide solid electrolyte has a crystalline structure. "Having a crystalline structure" means that in X-ray diffraction measurements, peaks originating from the crystalline structure of the sulfide solid electrolyte are observed in the X-ray diffraction pattern. The sulfide solid electrolyte may contain amorphous regions.

[0110] Examples of the crystal structures of the sulfide solid electrolyte include HICP, LGPS type, argyrodite type, and Li7P3S. 11 Examples include the Thio-LISICON system. Among these, the crystal structures mentioned above, from the viewpoint of lithium ion conductivity, include HICP, LGPS type, argyrodite type, and Li7P3S. 11 Li7P3S is preferred because it has high stability with respect to Li. 11 More preferably, the first crystal structure has a crystalline phase of Li4P2S6 or β-Li3PS4, or a first crystal structure has 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 measurements using CuKα rays. Among these, the first crystal structure has 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 measurements using CuKα rays, due to its high lithium ion conductivity.

[0111] The first crystal structure described above may include specific crystal structure A, which has 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 above X-ray diffraction measurement, or specific crystal structure B, which has diffraction peaks at 2θ = 17.9°±0.5°, 19.1°±0.5°, 29.1°±0.5° and 29.8°±0.5° in the above X-ray diffraction measurement, and does not have a diffraction peak at 30.9°±0.5°. With the above configuration, a sulfide solid electrolyte can be obtained that can increase the initial Coulomb efficiency of an all-solid-state battery equipped with the solid electrolyte.

[0112] In the first crystal structure described above, the diffraction peak may have a range of 2θ that is within ±0.3° or within ±0.1°.

[0113] The above Li7P3S 11 The crystal structure having the crystalline phase exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 2θ = 17.8°±0.5°, 18.5°±0.5°, 23.7°±0.5°, 29.6°±0.5°, and 30.0°±0.5°.

[0114] Examples of the above LGPS-type sulfide solid electrolyte include Li 10 GeP2S 12 Examples include Li 10 GeP2S 12 The crystal structure having the crystalline phase exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 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°.

[0115] Examples of the above-mentioned argyrodite-type sulfide solid electrolytes include Li6PS5Cl. The crystalline structure of Li6PS5Cl, which has a crystalline phase, exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 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°.

[0116] The crystalline structure of Li4P2S6 having the above-mentioned crystalline phase exhibits diffraction peaks at the positions 2θ = 16.9°±0.5°, 27.1°±0.5°, 32.1°±0.5°, and 32.5°±0.5° in X-ray diffraction measurements using CuKα rays.

[0117] The crystalline structure having the β-Li3PS4 crystalline phase, as described above, exhibits diffraction peaks at the following positions in X-ray diffraction measurements using CuKα rays: 2θ = 17.5°±0.5°, 18.1°±0.5°, 29.1°±0.5°, 29.9°±0.5°, and 31.2°±0.5°.

[0118] The sulfide solid electrolyte preferably contains an anionic structure of so-called ortho composition as its main component. For example, if the sulfide solid electrolyte is a Li2S-P2S5 solid electrolyte, then PS4 3- It is preferable that the structure is included as the main component. Here, "main component" means that the proportion of a particular component in the total components is 50 mol% or more.

[0119] When the sulfide solid electrolyte contains an ortho-composition anionic structure as the main component, the content of the ortho-composition anionic structure relative to the total anionic structure 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%, even more preferably 80 mol% or more and less than 100 mol%, and particularly preferably 90 mol% or more and less than 100 mol%.

[0120] It is preferable that the sulfide solid electrolyte substantially does not contain crosslinked sulfur. Since crosslinked sulfur reacts with water to produce hydrogen sulfide, substantially omitting crosslinked sulfur can improve atmospheric stability. For example, if the sulfide solid electrolyte is a Li2S-P2S5 solid electrolyte, it is preferable that it substantially does not contain the S3P-S-PS3 structure. The substantial absence of crosslinked sulfur can be confirmed by the fact that no peak corresponding to the crosslinked sulfur structure is detected when the Raman spectrum is measured with a laser at an excitation wavelength of 532 nm. For example, the substantial absence of the S3P-S-PS3 structure can be confirmed by the fact that when the Raman spectrum is measured with a laser at an excitation wavelength of 532 nm, a peak corresponding to the crosslinked sulfur structure is not detected. -1 This can be confirmed by the absence of a peak being detected. Furthermore, the sulfide solid electrolyte may contain a small amount of crosslinked sulfur. In this case, the intensity of the peak attributed to the anionic structure of the ortho composition in the Raman spectroscopy measurement is I O The intensity of the peak attributed to crosslinked sulfur is I P Ratio I P / I OHowever, it is preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.35 or less. For example, if the sulfide solid electrolyte is a Li2S-P2S5 solid electrolyte, then PS4 3- 417cm (due to structural reasons) -1 The peak intensity in the above I O This corresponds to 402cm derived from the S3PS-PS3 structure. -1 The peak intensity in the above I P It corresponds to this.

[0121] It is preferable that the sulfide solid electrolyte is substantially free of Li2S. Since Li2S reacts with water to produce hydrogen sulfide, substantially free of Li2S improves atmospheric stability. Here, "substantially free of Li2S" means that the crystalline structure does not have 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 measurements using CuKα rays.

[0122] Sulfide solid electrolytes may experience reduced atmospheric stability due to Li2S precipitation if the Li content is high, and reduced ionic conductivity if the Li content is low. Furthermore, if the N content is high, atmospheric stability may decrease due to Li2S precipitation, while if the N content is low, the effects of improved atmospheric stability due to N content may not be fully realized. From these viewpoints, it is preferable that the sulfide solid electrolyte has elemental ratios that simultaneously satisfy the following formula 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 N / P simultaneously satisfy the following equations. 2.36 ≤ Li / P ≤ 4.12 0.0200 ≤ N / P ≤ 1.11 It is even more preferable that the above Li / P and N / P simultaneously satisfy the following equations. 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 formulas 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 formulas respectively. 2.77 ≦ Li / P ≦ 3.38 0.280 ≦ N / P ≦ 0.650

[0123] As the sulfide solid electrolyte, it 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, α and β are numerical values giving the stoichiometric ratio according to the type of element M). By having the sulfide solid electrolyte have the 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 using the following method. Under an argon atmosphere with a dew point of -50°C or lower, 120 mg of the sample powder is placed in a powder molder with an inner diameter of 10 mm, and then uniaxially press-molded using a hydraulic press at a pressure of 50 MPa or less per sample area. After the pressure is released, SUS316L powder is placed on the top and bottom surfaces of the sample as current collectors, and then uniaxially press-molded for 5 minutes at a pressure of 360 MPa per pellet area to obtain a pellet for ionic conductivity measurement. This pellet for ionic conductivity measurement is inserted into a Hosen HS cell and the AC impedance is measured. 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 a solid electrolyte in an all-solid-state battery.

[0127] [Embodiment 2] Another embodiment of the present invention provides a sulfide solid electrolyte containing 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 element selected from the group consisting of Al, B, and Si as element M, or it may contain Al as element M.

[0129] If the sulfide solid electrolyte has a high Li content, Li2S will precipitate, reducing its atmospheric stability. If the Li content is low, HICP may not precipitate. Similarly, if the N content is high, Li2S will precipitate, reducing its atmospheric stability. If the N content is low, the effects of containing N may not be fully realized. Furthermore, if the element X content is high, the lithium halide crystalline phase may remain in the sulfide solid electrolyte, reducing its ionic conductivity. If the element X content is low, the effects of containing element X may not be fully realized. Due to these circumstances, it is preferable that the sulfide solid electrolyte simultaneously satisfies the following equations in molar ratio 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 stoichiometric ratios depending on the type of element M), and it is more preferable that x, y, and z are 0.67 ≤ x ≤ 0.73, 0.1 ≤ y ≤ 0.3, and 10 ≤ z ≤ 30, respectively. By 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 types of 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 stoichiometric ratios depending on the type of element M), and in this case, it is preferable that x, y, z1, and z2 are 0.67 ≤ x ≤ 0.73, 0.1 ≤ y ≤ 0.3, 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 as consisting 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 radiation.

[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 radiation. 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 radiation H [[ID=2U]]with respect to the diffraction peak intensity I at 2θ = 21.0° ± 0.5° LThe diffraction peak intensity ratio I L / I H is, 0 L / I H Preferably, it is <3.2, 0 L / I H It is more preferable that it be <2.5, 0 L / I H It is even more preferable that it be <2.0, and 0 L / I H A diffraction peak intensity ratio of <1.0 is even more preferable. L / I H This indicates the relative abundance of HICP and LICP contained in the sulfide solid electrolyte. In other words, the diffraction peak intensity ratio I L / I H A small value indicates that the amount of LICP is relatively small compared to HICP.

[0135] The ionic conductivity of the sulfide solid electrolyte in Embodiment 2 at 25°C is 2.0 × 10⁻⁶. -3 It is preferable that the ratio is S / cm or higher, and 2.5 × 10 -3 It is more preferable that the ratio is S / cm or higher, and 3.0 × 10 -3 It is even more preferable that the ratio is 4.0 × 10 -3 A value of S / cm or higher is particularly preferable. The above configuration can improve the high-rate discharge performance of the all-solid-state battery equipped with the sulfide solid electrolyte.

[0136] <All-solid-state battery> The all-solid-state battery comprises a negative electrode layer, a solid electrolyte layer, and a positive electrode layer. Figure 2 is a schematic cross-sectional view showing an all-solid-state battery in one 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 arranged via a solid electrolyte layer 3. The negative electrode layer 1 has a negative electrode substrate layer 4 and a negative electrode mixture layer 5, with the negative electrode substrate layer 4 being the outermost layer of the negative electrode layer 1. The positive electrode layer 2 has a positive electrode substrate layer 7 and a positive electrode mixture layer 6, with the positive electrode substrate layer 7 being the outermost layer of the positive electrode layer 2. In the all-solid-state battery 10 shown in Figure 2, the positive electrode mixture layer 6, solid electrolyte layer 3, negative electrode mixture layer 5, and negative electrode substrate layer 4 are stacked on the positive electrode substrate layer 7 in this order.

[0137] ​​​​In this 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. Because the negative electrode layer 1, the solid electrolyte layer 3, the positive electrode layer 2, or a combination thereof, contains 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 are further enhanced.

[0138] The all-solid-state battery may also use other solid electrolytes in addition to the sulfide solid electrolyte. The other solid electrolyte may be a sulfide solid electrolyte other than the sulfide solid electrolyte, or it may be an oxide-based solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a pseudo-solid electrolyte.

[0139] Other sulfide solid electrolytes besides the aforementioned sulfide solid electrolytes are preferably those with high Li ion conductivity, such as 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, and Li2S-P2S5-Z. m S 2n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga.) Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li δ XO ε (However, δ and ε are positive numbers, and X is one of P, Si, Ge, B, Al, Ga, or In.) Li 10 GeP2S 12 These are some examples. Among these, Li2S-P2S5 and Li are chosen from the viewpoint of good lithium-ion conductivity. 10 GeP2S 12The following are preferred. As for Li2S-P2S5, xLi2S·(100-x)P2S5 (70≦x≦80) is preferred.

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

[0141] (Negative electrode base material layer) The negative electrode substrate layer 4 is a conductive layer. The material of the negative electrode substrate 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 steel alloys can be used.

[0142] The lower limit of the average thickness of the negative electrode substrate layer 4 is preferably 3 μm, more preferably 5 μm, and even more preferably 8 μm. The upper limit of the average thickness of the negative electrode substrate layer 4 is preferably 200 μm, more preferably 100 μm, and even more preferably 50 μm. By setting the average thickness of the negative electrode substrate layer 4 to be above the lower limit, the strength of the negative electrode substrate layer 4 can be sufficiently increased, so that the negative electrode layer 1 can be formed well. By setting the average thickness of the negative electrode substrate layer 4 to be below the upper limit, the volume of other components can be sufficiently secured.

[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 negative electrode composite containing the negative electrode active material and the sulfide solid electrolyte. The negative electrode mixture may optionally contain other solid electrolytes, conductive agents, binders, fillers, and other optional components besides the sulfide solid electrolyte.

[0144] <Negative electrode active material> Typically, materials capable of intercalating and releasing lithium ions are used as negative electrode active materials. Specific examples of negative electrode active materials include metallic lithium; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide and Sn oxide; polyphosphate compounds; carbon materials such as graphite and non-graphitizable carbon (easily graphitizable or poorly graphitizable carbon); and lithium metal composite oxides such as lithium titanate.

[0145] The lower limit of the negative electrode active material content in the negative electrode mixture is preferably 10% by mass, and more preferably 15% by mass. The upper limit of the negative electrode active material content is preferably 60% by mass, more preferably 70% by mass, even more preferably 80% by mass, particularly preferably 90% by mass, and may also be 95% by mass. By setting the negative electrode active material content within the above range, the electrical capacity 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 using 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 composites include composites having chemical or physical bonds between the negative electrode active material and the sulfide solid electrolyte, and composites in which the negative electrode active material and the sulfide solid electrolyte are mechanically combined. In these composites, the negative electrode active material and the sulfide solid electrolyte are present within a single particle, and examples include those in which the negative electrode active material and the sulfide solid electrolyte form an aggregated state, and those in which a film containing the sulfide solid electrolyte is formed on at least a part of the surface of the negative electrode active material. The above-mentioned negative electrode mixture or negative electrode complex 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 mixture constitute a negative electrode mixture or negative electrode complex, thereby improving 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, and 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, further 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. 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 a conductive agent include carbon blacks such as natural or artificial graphite, furnace black, acetylene black, and ketjen black, metals, and conductive ceramics. The shape of the conductive agent includes powdery, fibrous, and the like. The content of the conductive agent in the above negative electrode mixture can be, for example, 0.5% by mass or more and 30% by mass or less. The above 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. The main components of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and carbon.

[0151] The lower limit of the average thickness of the negative electrode mixture layer 5 is preferably 30 μm, and more preferably 60 μm. The upper limit of the average thickness of the negative electrode mixture layer 5 is preferably 1000 μm, more preferably 500 μm, and even more preferably 200 μm. By setting the average thickness of the negative electrode mixture layer 5 to or above the lower limit, an all-solid-state battery with high energy density can be obtained. By setting the average thickness of the negative electrode mixture layer 5 to or below the upper limit, an all-solid-state battery with a negative electrode that has excellent rate characteristics and high active material utilization can be obtained.

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

[0153] [Positive electrode layer] The positive electrode layer 2 comprises a positive electrode base layer 7 and a positive electrode mixture layer 6 laminated on the surface of the positive electrode base layer 7. Similar to the negative electrode layer 1, the positive electrode layer 2 may have an intermediate layer between the positive electrode base 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 substrate layer) The positive electrode substrate layer 7 can have the same configuration as the negative electrode substrate layer 4. The material of the positive electrode substrate layer 7 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 steel alloys can be used.

[0155] The lower limit of the average thickness of the positive electrode substrate layer 7 is preferably 3 μm, more preferably 5 μm. The upper limit of the average thickness of the positive electrode substrate layer 7 is preferably 200 μm, more preferably 100 μm, and even more preferably 50 μm. By setting the average thickness of the positive electrode substrate layer 7 to be above the lower limit, the strength of the positive electrode substrate layer 7 can be sufficiently increased, thereby enabling good formation of the positive electrode layer 2. By setting the average thickness of the positive electrode substrate layer 7 to be below the upper limit, sufficient volume for other components can be secured.

[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 positive electrode composite containing a positive electrode active material and a solid electrolyte. A sulfide solid electrolyte may be used as the solid electrolyte. 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, conductive agent, binder, and filler, as needed. The positive electrode mixture layer may also be in a form that does not contain a solid electrolyte.

[0157] <Cathode active material> As the positive electrode active material contained in the positive electrode mixture layer 6, known materials commonly used in all-solid-state batteries can be used. For example, Li x M e O y (Me represents at least one transition metal) A composite oxide (Li having a layered α-NaFeO2 type crystal structure) x CoO2, Li x KiO2, Li x MnO3, Li x Ni α Co (1-α) O2, Li x Ni α Mn β Co (1-α-β) Li such as O2, which has a spinel-type crystal structure x Mn2O4, Li x Ni α Mn (2-α) O4, etc., Li w Me x (AO y ) zExamples of polyanion compounds represented by (Me represents at least one transition metal, and A represents, for example, P, Si, B, V, etc.) include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The 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 may be used in mixture form.

[0158] Positive electrode active materials include 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 compounds other than those represented by the above general formula, such as MnO2, FeO2, TiO2, V2O5, V6O 13 Materials with a redox potential greater than that of the negative electrode material, such as TiS2, can be used.

[0159] The lower limit of the content of positive electrode active material in the positive electrode mixture is preferably 10% by mass, and more preferably 15% by mass. The upper limit of the content of positive electrode active material is preferably 60% by mass, more preferably 70% by mass, even more preferably 80% by mass, particularly preferably 90% by mass, and may also be 95% by mass. By setting the content of positive electrode active material within the above range, the electrical capacity of the all-solid-state battery can be increased.

[0160] <Positive electrode mixture or positive electrode composite> The above-mentioned positive electrode mixture is a mixture produced by mixing positive electrode active material and solid electrolyte, etc., using mechanical milling or the like, similar to the case of the negative electrode. For example, a mixture of positive electrode active material and solid electrolyte, etc., can be obtained by mixing particulate positive electrode active material and particulate solid electrolyte, etc. Similar to the case of the negative electrode, the positive electrode composites mentioned above include composites having chemical or physical bonds between the positive electrode active material and the solid electrolyte, and composites in which the positive electrode active material and the solid electrolyte are mechanically combined. The above composites have the positive electrode active material and the solid electrolyte present within a single particle, and examples include those in which the positive electrode active material and the solid electrolyte form an aggregated state, and those in which a film containing the solid electrolyte is formed on at least a part of the surface of the positive electrode active material. The above-mentioned cathode mixture or cathode complex may contain a solid electrolyte other than the sulfide solid electrolyte. The positive electrode active material and solid electrolyte contained in the positive electrode mixture constitute a positive electrode mixture or positive electrode composite, thereby improving ionic conductivity.

[0161] When the positive electrode mixture contains a solid electrolyte, the lower limit of the solid electrolyte content may be 5% by mass, and 10% by mass is preferred. The upper limit of the solid electrolyte content in the positive 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 solid electrolyte content within the above range, the electrical capacity of the all-solid-state battery can be increased.

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

[0163] [Solid electrolyte layer] The solid electrolyte layer 3 contains an electrolyte for the solid electrolyte layer. In addition to the sulfide solid electrolyte described above, other examples of electrolytes for the solid electrolyte layer include oxide-based solid electrolytes, other sulfide solid electrolytes, dry polymer electrolytes, gel polymer electrolytes, and pseudo-solid electrolytes. Among these, sulfide solid electrolytes are preferred, and more preferred, from the viewpoint of good ionic conductivity and ease of interface formation. Because the solid electrolyte layer 3 contains the sulfide solid electrolyte, the solid electrolyte layer can exhibit high ionic conductivity, thereby reducing the internal resistance of the all-solid-state battery.

[0164] The content of the sulfide solid electrolyte relative to the total amount of 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, even 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 consists solely of the sulfide solid electrolyte. In particular, since the sulfide solid electrolyte containing element X has high thermal stability, by configuring the all-solid-state battery as described above, the advantages of an all-solid-state battery, such as being able to raise the upper limit of the battery's operating temperature, can be fully enjoyed.

[0165] The electrolyte for the solid electrolyte layer may have a crystalline structure or may be amorphous without a crystalline 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 to 50 μm, and more preferably 3 μm to 20 μm. 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 reliably insulating the positive electrode and the negative electrode.

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

[0168] (Process for producing sulfide solid electrolytes) In this process, for example, a sulfide solid electrolyte is prepared by the method for producing the sulfide solid electrolyte.

[0169] (Negative electrode mixture preparation process) In this step, a negative electrode mixture is prepared for forming the negative electrode layer. If the negative electrode mixture contains a mixture or complex of a negative electrode active material and the sulfide solid electrolyte, this step includes mixing the negative electrode active material and the sulfide solid electrolyte using, for example, a mechanical milling method, to prepare a mixture or complex of the negative electrode active material and the sulfide solid electrolyte.

[0170] (Electrolyte fabrication process for solid electrolyte layer) In this process, the electrolyte for the solid electrolyte layer is prepared. In this process, the electrolyte for the solid electrolyte layer can be obtained by processing a predetermined material by mechanical milling. Alternatively, the electrolyte for the solid electrolyte layer may be prepared by heating the predetermined material for the solid electrolyte layer above its melting temperature using a melt-and-cool method, melting and mixing the two in a predetermined ratio, and then rapidly cooling. Other methods for synthesizing the electrolyte for the solid electrolyte layer include, for example, a solid-phase method of firing under reduced pressure, a liquid-phase method such as dissolution extraction, a gas-phase method (PLD), and firing under an argon atmosphere after mechanical milling. If the electrolyte for the solid electrolyte layer is a sulfide solid electrolyte, the sulfide solid electrolyte preparation process described above is performed in the process for preparing the electrolyte for the solid electrolyte layer.

[0171] (Cathode mixture preparation process) In this process, a positive electrode mixture is prepared for forming the positive electrode layer. There are no particular restrictions on the method for preparing the positive electrode mixture, and it can be appropriately selected according to the purpose. Examples include compression molding of the positive electrode active material, mechanical milling of a predetermined material of the positive electrode mixture, and sputtering of the positive electrode active material using a target material. If the positive electrode mixture contains a mixture or composite of the positive electrode active material and the sulfide solid electrolyte, this process includes mixing the positive electrode active material and the sulfide solid electrolyte using, for example, a mechanical milling method, to prepare a mixture or composite of the positive electrode active material and the sulfide solid electrolyte.

[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, solid electrolyte layer, and positive electrode layer may be formed sequentially or in reverse order, and the order of formation of each layer is not particularly limited. The negative electrode layer is formed by pressure molding of the negative electrode substrate and negative electrode mixture, the solid electrolyte layer is formed by pressure molding of the electrolyte for the solid electrolyte layer, and the positive electrode layer is formed by pressure molding of the positive electrode substrate and positive electrode mixture.

[0173] The negative electrode layer, solid electrolyte layer, and positive electrode layer may be laminated by pressure molding the negative electrode substrate, negative electrode mixture, electrolyte for the solid electrolyte layer, positive electrode substrate, and positive electrode mixture at the same time. Alternatively, the positive electrode layer, 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 embodiments described above, and can be implemented in various modified and improved forms in addition to those described above.

[0175] In the above embodiments, a raw material compound containing only N, Li, and element M was described as an example of a raw material compound containing N, element A, and element M, but the present invention is not limited thereto. For example, the raw material compound containing N, element A, and element M may further contain other elements as long as it does not hinder the solving of the problem of the present invention.

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

[0177] The present invention will be described in more detail below through demonstration experiments, but the present invention is not limited to the following embodiments.

[0178] First, Examples 1, 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 demonstrate the effect of the method for producing a sulfide solid electrolyte according to one embodiment of the present invention on suppressing the discharge of nitrogen into the system. [Example 1] The following process results in 80(0.70Li2S·0.30P2S5)·20Li 3 / 2 Al 1 / 2 N was synthesized. (preparation process) Li3N and AlN were weighed in a molar ratio of 1.2:1, mixed in a mortar, and then pelletized. Next, the mixture was heat-treated at 750°C for 1 hour. 3 / 2 Al 1 / 2 N was fabricated. Li was fabricated. 3 / 2 Al 1 / 2 N's main phase was determined by XRD measurement to be Li 3 / 2 Al 1 / 2 We confirmed that it is N. Next, in a glove box with an argon atmosphere and a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich) and Li 3 / 2 Al 1 / 2 After weighing out N in a molar ratio of 56:24:20, the mixture was prepared in a mortar to prepare a composition containing Li, P, S, N, and Al. (Reaction process) The above composition was placed in a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls. Milling was performed for 45 hours at a rotational speed of 510 rpm using a planetary ball mill (FRITSCH, model number Premium line P-7) to obtain an intermediate. (Heat treatment process) The above intermediate 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 but not exceeding 100°C below the crystallization temperature. The crystallization temperature was determined by DSC measurement. The DSC measurement was performed under the following conditions: a DSC apparatus (Rigaku Thermo Plus DSC8230) was used, a sealed SUS pan was used, and the temperature was increased from room temperature to 400°C at a rate of 10°C / min. The composition prepared using the above synthesis procedure was designated as sample a, the intermediate as sample b, and the sulfide solid electrolyte as sample c.

[0179] [Example 2] Except for the following changes to the preparation process, the procedure was the same as in Example 1: 80(0.70Li2S·0.30P2S5)·20Li 3 / 2 B 1 / 2 N was synthesized. (preparation process) Li3N and BN were weighed in a molar ratio of 1.1:1, mixed in a mortar, and then pelletized. Next, the mixture was heat-treated at 800°C for 10 minutes. 3 / 2 B 1 / 2 N was fabricated. Li was fabricated. 3 / 2 B 1 / 2 N's main phase was determined by XRD measurement to be Li 3 / 2 B 1 / 2 We confirmed that it is N. Next, in a glove box with an argon atmosphere and a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich) and Li 3 / 2 B 1 / 2 After weighing out N in a molar ratio of 56:24:20, the mixture was prepared 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 modified 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 in a molar ratio of 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] Except for the following changes to the preparation process, the procedure was the same as in Example 1: 80(0.70Li2S·0.30P2S5)·20Li 3 / 2 Al 1 / 2 N was synthesized. (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 in a molar ratio of 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] Except for the following changes to the preparation process, the procedure was the same as in Example 1: 80(0.70Li2S·0.30P2S5)·20Li 7 / 4 V 1 / 4 N was synthesized. (preparation process) Li3N and VN were weighed in a molar ratio of 3:1, mixed in a mortar, and then pelletized. Next, the Li3N was heat-treated at 750°C for 10 hours. 7 / 4 V 1 / 4 N was fabricated. Li was fabricated. 7 / 4 V 1 / 4 N's main phase was determined by XRD measurement to be Li 7 / 4 V 1 / 4 We confirmed that it is N. Next, in a glove box with an argon atmosphere and a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich) and Li 7 / 4 V 1 / 4 After weighing out N in a molar ratio of 56:24:20, the mixture was prepared in a mortar to prepare a composition containing Li, P, S, N, and V.

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

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

[0185] Table 4 shows the XRD patterns and ionic conductivity (σ) at 25°C for Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3. 25Table 4 shows that all sulfide solid electrolytes in the examples and comparative examples exhibited peaks in their XRD spectra, confirming the presence of specific crystal structure A. Specific crystal structure A is a crystal structure that exhibits 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 measurements. Furthermore, it was confirmed that the sulfide solid electrolytes in Example 1, Example 2, and Comparative Example 3 exhibited similar ionic conductivity. 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] For each sample in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the content of Li, B, Al, and P in the sample was determined using an ICP emission spectrometer. Furthermore, for each sample in Example 1, Example 2, and Comparative Examples 1 through 3, the content of N in the sample was determined using an oxygen, nitrogen, and hydrogen analyzer. From these analysis results, the rate of change in the N content of the sample was calculated. Table 5 shows the analysis results. In the table, "No change" indicates that the rate of change in the N content relative to sample a was ±5% by mass or less.

[0188] [Table 5]

[0189] Table 5 shows that in Examples 1 and 2, the nitrogen content in samples a, b, and c remained almost unchanged. In other words, in Examples 1 and 2, the nitrogen content remained almost unchanged even after going through the reaction and heat treatment processes, indicating that the discharge of nitrogen into the system was suppressed. On the other hand, in Comparative Examples 1, 2, and 3, it can be seen that the nitrogen content in samples a, b, and c decreases in the order of a, b, and c. In other words, in Comparative Examples 1, 2, and 3, the nitrogen content decreases with each step of the reaction and heat treatment process, and nitrogen is discharged out of the system. Based on the above, it has been demonstrated that Al and B, which were selected based on first-principles calculations to predict their emission reduction effects on N, actually provide effective results. Furthermore, it has also been demonstrated that V, which was predicted to have no emission reduction effect on N using first-principles calculations, does not actually provide any effect.

[0190] Next, Examples 3 to 20 and Comparative Examples 4 to 8 demonstrate the effect of improving the thermal stability of a sulfide solid electrolyte according to one embodiment of the present invention. [Example 3] Through the following process, the composition formula 85(0.80(0.70Li2S·0.30P2S5)·0.20Li 3 / 2 Al 1 / 2 A sulfide solid electrolyte represented by N)·10LiBr·5LiI was synthesized. Li3N and AlN were weighed in a molar ratio of 1.2:1, mixed in a mortar, and then pelletized. Next, the mixture was heat-treated at 750°C for 1 hour. 3 / 2 Al 1 / 2 N was fabricated. Li was fabricated. 3 / 2 Al 1 / 2 N's main phase was determined by XRD measurement to be Li 3 / 2 Al 1 / 2 We confirmed that it is N. Next, in a glove box with an argon atmosphere with 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 in a molar ratio of 47.6:20.4:10:5:17 and then mixed in a mortar. This mixed sample was placed in a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls. Milling was performed for 45 hours at a rotational speed of 510 rpm using a planetary ball mill (FRITSCH, model number Premium line P-7). The sample was heat-treated at 245 °C for 2 hours to obtain the sulfide solid electrolyte of Example 3. The heat treatment temperature was set to be above the crystallization temperature but not more than 100 °C above the crystallization temperature. The crystallization temperature was determined by taking a portion of the sample after milling and subjecting it to DSC measurement. The DSC measurement was performed under the following conditions: a DSC device (Rigaku, Thermo Plus DSC8230) was used, a sealed SUS pan was used, and 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 sulfide solid electrolytes of Comparative Examples 4 and 5 were synthesized in the same manner as in Example 3, except that the composition of the sulfide solid electrolyte was 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.

[0192] [Examples 4 to 7, Comparative Example 6] The composition of the sulfide solid electrolyte is 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 / 3Except for changing the composition to N)·12LiBr·8LiI and 80(0.6975Li2S·0.25P2S5·0.035Li3N)·12LiBr·8LiI, and setting the heat treatment temperatures to 255°C, 275°C, 270°C, 270°C, and 250°C, respectively, the sulfide solid electrolytes of Examples 4 to 7 and Comparative Example 6 were synthesized in the same manner as in Example 3. In addition to the sample with a heat treatment temperature of 255°C, the sulfide solid electrolyte of Example 4 was also synthesized with heat treatment temperatures of 215°C, 230°C, 275°C, 290°C, and 310°C. In addition to the sample with a heat treatment temperature of 275°C, the sulfide solid electrolyte of Example 5 was also synthesized with heat treatment temperatures of 235°C, 290°C, 310°C, and 330°C. In addition to the sample with a heat treatment temperature of 270°C, the sulfide solid electrolyte of Example 6 was also synthesized with heat treatment temperatures of 230°C, 270°C, 290°C, 310°C, and 330°C. In addition to the sample with a heat treatment temperature of 270°C, the sulfide solid electrolyte of Example 7 was also synthesized with heat treatment temperatures of 230°C, 290°C, 310°C, and 330°C. In addition, for 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 order from lowest to highest heat treatment temperature.

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

[0194] [Examples 9 to 11, Comparative Example 8] The composition of the sulfide solid electrolyte is 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 Except for changing the composition to N)·30LiBr and 90(0.72Li2S·0.25P2S5·0.020Li3N)·10LiBr, and setting the heat treatment temperatures to 265°C, 250°C, 240°C, and 225°C, respectively, the sulfide solid electrolytes of Examples 9, 10, 11, and Comparative Example 8 were synthesized in the same manner as in Example 3.

[0195] [Examples 12 and 13] The composition of the sulfide solid electrolyte is 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 The sulfide solid electrolytes of Examples 12 and 13 were synthesized in the same manner as in Example 3, except that N)·20LiI was used and the heat treatment temperatures were set to 255°C and 240°C, respectively.

[0196] [Examples 14 to 17] The composition of the sulfide solid electrolyte is 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 N)·12LiBr·8LiI was changed and the heat treatment temperature was set to 250°C for each.

[0197] [Examples 18 to 20] The composition of the sulfide solid electrolyte is 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 Except for changing the material to N)·20LiBr·15LiI and setting the heat treatment temperatures to 230°C, 195°C, and 185°C, respectively, the sulfide solid electrolytes of Examples 18 to 20 were synthesized in the same manner as in Example 3.

[0198] The sulfide solid electrolytes of Examples 3 to 20 have the general formula (100-z1-z2){(1-y)[xLi2S·(1-x)P2S5]·yLi α M β The formula is represented as 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 crystalline phase that has diffraction peaks at 2θ = 20.2°±0.5° and 23.6°±0.5° in X-ray diffraction measurements using CuKα rays. "LICP" represents a crystalline phase that has diffraction peaks at 2θ = 21.0°±0.5° and 28.0°±0.5° in X-ray diffraction measurements using CuKα rays. "Specific Crystal Structure C" represents a crystalline phase that has diffraction peaks at 2θ = 17.5°±0.5° and 24.9°±0.5° in X-ray diffraction measurements using CuKα rays. "β-Li3PS4" represents a crystalline phase that has 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 measurements using CuKα rays. "Unknown" represents a peak whose crystalline phase is unassigned. Furthermore, Figure 3 shows the XRD patterns of Examples 4-1 to 4-6. Figure 4 shows the XRD patterns of Comparative Examples 6-1 to 6-3.

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

[0201] (3) DSC DSC measurements were performed using the following method: A DSC device (Rigaku Thermo Plus DSC8230) was used, and the temperature was increased from room temperature to 400°C at a rate of 10°C / min using a sealed stainless steel pan.

[0202] For the sulfide solid electrolytes of Examples 4 to 7, Examples 14 to 17, and Comparative Example 6, intermediates after milling but before heat treatment were subjected to DSC measurement. Figures 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] Table 6 shows that the sulfide solid electrolytes of Comparative Examples 4 and 5 generate LICP when the heat treatment temperature is 225°C, and their ionic conductivity at 25°C decreases. On the other hand, the sulfide solid electrolyte of Example 3, which contains Li, P, S, N, Br, I, and Al, does not generate LICP and exhibits high ionic conductivity despite being heat-treated at a higher temperature than the sulfide solid electrolytes of Comparative Examples 4 and 5. In other words, it can be seen that the lower limit of the heat treatment temperature at which the ionic conductivity decreases is higher for the sulfide solid electrolyte of Example 3 than for the sulfide solid electrolytes of Comparative Examples 4 and 5.

[0212] Table 7 shows that the sulfide solid electrolytes of Examples 4 to 7 exhibit high ionic conductivity without the formation of LICP, even though they were heat-treated at a higher temperature than the sulfide solid electrolyte of Comparative Example 6. In other words, it can be seen that the lower limit of the heat treatment temperature at which ionic conductivity decreases is higher for the sulfide solid electrolytes of Examples 4 to 7 than for the sulfide solid electrolyte of Comparative Example 6.

[0213] Table 8 shows that the sulfide solid electrolyte of Example 8 exhibits higher ionic conductivity despite being heat-treated at a higher temperature than the sulfide solid electrolyte of Comparative Example 7. In other words, the lower limit of the heat treatment temperature at which ionic conductivity decreases is higher for the sulfide solid electrolyte of Example 8 than for the sulfide solid electrolyte of Comparative Example 7. This is thought to be because the phase transition of HICP to LICP was suppressed in the sulfide solid electrolyte of Example 8.

[0214] Table 9 shows that the sulfide solid electrolytes of Examples 9 to 11 all exhibit higher ionic conductivity despite being heat-treated at higher temperatures than the sulfide solid electrolyte of Comparative Example 8. Furthermore, it can be seen that even when the sulfide solid electrolyte contains only Br as element X, the effect of the present invention, which improves the thermal stability of the high Li ion conducting phase of the sulfide solid electrolyte, can be obtained. Furthermore, comparing Example 9 and Comparative Example 8, which have the same Br content, it can be seen that neither HICP nor LICP was formed in Comparative Example 8, while HICP was formed in Example 9. In other words, when the sulfide solid electrolyte contains Li, P, S, N, element X, and element M, it was observed that HICP can be formed with a smaller amount of element X compared to when element M is not present.

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

[0216] Table 11 shows that the sulfide solid electrolytes of Example 6 and Examples 15 to 17 exhibited high ionic conductivity (HICP) despite being heat-treated at temperatures higher than those of the sulfide solid electrolyte of Comparative Example 6. In other words, it can be seen that the lower limit of the heat treatment temperature at which ionic conductivity decreases is higher for the sulfide solid electrolytes of these examples compared to the sulfide solid electrolyte of Comparative Example 6. Furthermore, Figure 6 shows that the sulfide solid electrolytes of Example 6 and Examples 14 to 17 exhibit a larger temperature difference between the crystallization peak presumed to originate from HICP and the crystallization peak originating from β-Li3PS4 compared to the sulfide solid electrolyte of Comparative Example 6. For example, in Comparative Example 6, the crystallization peak presumed to originate from HICP and the crystallization peak originating from β-Li3PS4 were observed at around 190°C and 260°C, respectively, while in Example 14, they were observed at around 190°C and 280°C, respectively. From this, it can be understood that in the sulfide solid electrolytes of the examples, the temperature range in which HICP exists stably is broadened, and the thermal stability of the high-Li ion conducting phase is improved. The crystallization peaks in Figure 6 that are presumed to originate from HICP are those observed in the range of approximately 180°C to 220°C. The crystallization peaks in Figure 6 that originate from β-Li3PS4 are those observed around 345°C, 280°C, 300°C, 310°C, 335°C, and 260°C in Examples 6, 14 to 16, and Comparative Example 6, respectively. From the above, it can be seen that even when the N / P ratio of P in 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 conducting phase can be obtained.

[0217] Table 12 shows that even when the ratio of element X to P in the sulfide solid electrolyte, X / P, 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 seen that when the sulfide solid electrolyte of Comparative Example 6 is heat-treated at a temperature of 250°C or higher, HICP undergoes a phase transition to LICP and β-Li3PS4. Furthermore, it can be seen that the ionic conductivity at 25°C decreases significantly as a result. On the other hand, from Examples 4-1 to 4-6, it can be seen 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. Furthermore, from Examples 5-1 to 5-5, it can be seen that the sulfide solid electrolyte of Example 5 also has high ionic conductivity (HICP) over a wide temperature range and can maintain high ionic conductivity. Furthermore, Examples 6-1 to 6-5 and Examples 7-1 to 7-5 demonstrate that even when element M contains B and Si instead of Al, the effects of the present invention, which maintain high ionic conductivity over a wide temperature range, can be obtained. In other words, as can be seen from Table 13, the sulfide solid electrolytes of Examples 4 to 7 have a wider range of heat treatment temperatures over which ionic conductivity does not decrease. Furthermore, a comparison of Examples 6 and 7 with Examples 4 and 5 in Table 13 reveals that when the sulfide solid electrolyte contains either Si or B as element M, there is a heat treatment temperature range of at least 80°C in which the ionic conductivity does not decrease, and the high-Li ion-conducting phase exhibits particularly excellent thermal stability. The peak around 210°C in the DSC curves of Examples 6 and 7 in Figure 5 is a crystallization peak presumed to originate from HICP. Therefore, it can also be inferred that in Examples 6 and 7, there is a heat treatment temperature range of 100°C in which the ionic conductivity does not decrease. The reason for these results is not clear, but for example, it is possible that the strength of the bond energy between either Si or B and N was a value suitable for exhibiting the effects of the present invention.

[0219] As is clear from Tables 6 to 13, the sulfide solid electrolytes of the examples showed an increase in the lower limit of the heat treatment temperature at which ionic conductivity decreases, and a widening of the heat treatment temperature range at which ionic conductivity does not decrease. In other words, the sulfide solid electrolytes containing Li, P, S, N, element X, and element M exhibited excellent thermal stability of HICP. This is thought to be because the emission of N into the system during the manufacturing process was suppressed, allowing the thermal stability-improving effect of containing N in the sulfide solid electrolyte to be fully realized.

[0220] A method for producing a sulfide solid electrolyte according to one embodiment of the present invention has been shown to suppress the emission of N into the system, as well as suppress the precipitation of Li2S. Suppressing the precipitation of Li2S is preferable because it improves the atmospheric stability of the sulfide solid electrolyte.

[0221] In other words, Examples 21 to 41, Comparative Example 9, and Comparative Example 10 suggest that the method for producing a sulfide solid electrolyte according to one embodiment of the present invention can suppress the precipitation of Li2S.

[0222] [Example 21] The following process results in 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 with N, z=1, y=0.70, i.e., 99(0.7Li2S·0.3P2S5)·1Li 3 / 2 Al 1 / 2 N was synthesized. Li3N and AlN were weighed in a molar ratio of 1.2:1, mixed in a mortar, and then pelletized. Next, the mixture was heat-treated at 750°C for 1 hour. 3 / 2 Al 1 / 2 N was created. Next, in a glove box with an argon atmosphere and a dew point of -50°C or lower, Li2S (99.98%, Aldrich), P2S5 (99%, Aldrich) and Li 3 / 2 Al 1 / 2 N was weighed in a molar ratio of 69.3:29.7:1.0 and then mixed in a mortar. This mixed sample was placed in a sealed 80 mL zirconia pot containing 160 g of 4 mm diameter zirconia balls. Milling was performed for 45 hours at a rotational speed of 510 rpm using a planetary ball mill (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 performed at a temperature above the crystallization temperature and below the crystallization temperature plus 100°C. The crystallization temperature was determined by measuring DSC. DSC measurement was performed under the following conditions: a DSC device (Rigaku, Thermo Plus DSC8230) was used, a sealed SUS pan was used, and the temperature was raised from room temperature to 400°C at a rate of 10°C / min.

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

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

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

[0226] [Examples 37 to 41] Li3N and Si3N4 were weighed in a molar ratio of 5.1:1, mixed in a mortar, pelletized, and then heat-treated at 800°C for 10 minutes. 5 / 3 Si 1 / 3 N was created. Fabricated Li 5 / 3 Si 1 / 3 Regarding N, XRD measurements revealed that the main phase is Li5 / 3Si 1 / 3 We confirmed that it is N. The chemical formula of the sulfide solid electrolyte is (100-z)(yLi2S·(1-y)P2S5)·zLi α M β Li in N α M β N to Li5 / 3 Si 1 / 3 The sulfide solid electrolytes of Examples 37 to 41 were synthesized in the same manner as in Example 21, except that N was changed and the value of z was changed to 1.5, 15, 20, 30, and 45.

[0227] [Comparative Example 9] The chemical formula of the sulfide solid electrolyte is (100-z)(yLi2S·(1-y)P2S5)·zLi α M β Li in N α M β The sulfide solid electrolyte of Comparative Example 9 was synthesized in the same manner as in Example 21, except that N was changed to Li3N and the value of z was changed to 20.

[0228] [Comparative Example 10] The chemical formula of the sulfide solid electrolyte is (100-z)(yLi2S·(1-y)P2S5)·zLi α M β The sulfide solid electrolyte of Comparative Example 10 was synthesized in the same manner as in Comparative Example 9, except that y=0.68 was set at N and the value of z was changed to 16.

[0229] [evaluation] (1) XRD, ionic conductivity (σ) X-ray diffraction measurements were performed using the method described above. Additionally, the ionic conductivity at 25°C (σ) was measured. 25 The AC impedance was determined by measuring it using the method described above with a Bio-Logic VMP-300.

[0230] (2) Raman spectroscopy The Raman spectrum was measured using the following method. A laser Raman spectrophotometer ("LabRAM HR Revolution" manufactured by Horiba, Ltd.) was used, with an excitation laser wavelength of 532 nm (YAG laser) and a grating of 600 gr / mm, at 100 cm². -1 From 1800cm -1 Raman spectroscopy measurements were performed in the wavenumber range.

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

[0232] [Table 14]

[0233] In the sulfide solid electrolyte of Comparative Example 9, only peaks originating from the Li2S crystal structure were observed. This result indicates that Li2S precipitates easily when Li3N is used. The reason for these results is not entirely clear, but it is thought that Li3N reacts dramatically with other starting compounds to precipitate Li2S.

[0234] In Examples 21 to 35 and Examples 37 to 40, no Li2S peak was observed. In particular, a comparison of the examples with z=20 and y=0.70 (Examples 26, 35, 39, and Comparative Example 9) confirmed that the precipitation of Li2S was suppressed in the sulfide solid electrolytes of the examples.

[0235] Furthermore, in Examples 27 to 29, 32, 39, and 40, the sulfide solid electrolytes all showed no Li2S peak despite having a higher Li / P ratio compared to the sulfide solid electrolyte of Comparative Example 10. In particular, in Example 29, the Li / P ratio was 4.00, which is higher than that of Comparative Examples 9 and 10, yet no Li2S peak was observed. In Examples 26 and 35, the sulfide solid electrolytes showed no Li2S peak despite having approximately the same Li / P ratio as the sulfide solid electrolyte of Comparative Example 10. Despite the sulfide solid electrolyte of Example 32 having approximately the same y value and Li / P ratio as Comparative Example 10, no Li2S peak was observed. In sulfide solid electrolytes, Li2S tends to precipitate when the Li content is high. However, given the results obtained above, it is suggested that the method for producing the sulfide solid electrolyte in the example suppresses the precipitation of Li2S.

[0236] In other words, a comparison of Examples 28, 29, 36, 40, and 41 suggests that the suppression of Li2S precipitation is significant when Al is included as element M.

[0237] From the above, it is suggested that the precipitation of Li2S is suppressed in the method for producing the sulfide solid electrolyte of the example. The reason why the precipitation of Li2S can be suppressed by the inclusion of element M in the sulfide solid electrolyte is thought to be as follows: When Li3N is used as the starting material for a sulfide-based solid electrolyte containing N, Li3N and P2S5 react dramatically, releasing N2 and causing Li2S to precipitate. This is thought to be because the defect generation energy of N in Li3N is small. In contrast, in the present invention, Li α M β Because the defect formation energy for N in N is greater than that for Li3N, the reaction proceeds slowly during the synthesis of sulfide-based solid electrolytes, suppressing the release of N2 and the precipitation of Li2S.

[0238] Although the present invention has been described in detail above, the embodiments described above are merely illustrative, and the invention disclosed herein includes various modifications and changes to the above-described examples. [Industrial applicability]

[0239] The all-solid-state battery equipped with a sulfide solid electrolyte according to the present invention is suitably used, for example, as a lithium-ion all-solid-state battery for HEVs. [Explanation of Symbols]

[0240] 1. Negative electrode layer 2 Positive electrode layer 3 Solid electrolyte layer 4 Negative electrode base material layer 5. Negative electrode mixture layer 6. Cathode mixture layer 7. Positive electrode substrate layer 10 All-solid-state battery

Claims

[Claim 1] A sulfide solid electrolyte having a crystalline structure and containing P, S, N, element A, element X, and element M as constituent elements. 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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