Sulfide solid electrolyte, method for producing same, electrode mixture, solid electrolyte layer, and all-solid-state lithium ion secondary battery

Abstract

The present invention relates to a sulfide solid electrolyte which contains Li, P, S and Ha and has an argyrodite-type crystal structure having a plurality of PS4 tetrahedrons (T1) in which some of the elements may be substituted, the number of the elements as the vertices of the PS4 tetrahedrons (T1) being 16 in the unit cell, and the number of the elements as the vertices of the PS4 tetrahedrons (T1) being 16. Average value # imgabs0 # of distance delta when corresponding to each position of S element at 16e position of PS4 tetrahedron T2 of space group F-43m

Description

Technical Field

[0001] The present invention relates to a sulfide solid electrolyte and a method for manufacturing the same. Further, the present invention also relates to an electrode mixture, a solid electrolyte layer, and an all-solid-state lithium-ion secondary battery including the above sulfide solid electrolyte. Background Art

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers.

[0003] Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but there are concerns such as leakage and fire, and the housing needs to be enlarged for safety design. In addition, the battery life is short and the operating temperature range is narrow, which also need to be improved urgently.

[0004] On the other hand, all-solid-state lithium-ion secondary batteries using a solid electrolyte as the electrolyte of the lithium-ion secondary battery have attracted attention in terms of expected improvement in safety, high-speed charge and discharge, and miniaturization of the housing.

[0005] Solid electrolytes can be roughly classified into sulfide solid electrolytes and oxide solid electrolytes. Sulfide ions constituting the sulfide solid electrolyte have a larger polarizability than oxide ions constituting the oxide solid electrolyte, and exhibit higher lithium-ion conductivity. As sulfide solid electrolytes, LGPS-type crystals such as Li 10 GeP 2 S 12 and the like, thiogermanate-type crystals such as Li 6 PS 5 Cl, and LPS crystallized glass such as Li 7 P 3 S 11 crystallized glass are known.

[0006] As an example of a disclosed thiogermanate-type sulfide solid electrolyte, Patent Document 1 can be cited. The sulfide solid electrolyte disclosed in Patent Document 1 has a crystal structure of a cubic system belonging to the space group F-43m, and contains a composition formula: Li 7－x PS 6－X Ha X (Ha is Cl or Br) (x = 0.2 to 1.8), and the L value of the L * a * b * color system is 60.0 or more. The purpose is to improve the charge and discharge efficiency and cycle characteristics by increasing the lithium-ion conductivity and decreasing the electron conductivity.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: WO 2015 / 012042 SUMMARY OF THE INVENTION

[0010] In contrast, sulfide solid electrolytes require further improvement in lithium ion conductivity.

[0011] Accordingly, an object of the present invention is to provide a novel sulfide solid electrolyte having improved lithium ion conductivity and a method for producing the same. Another object is to provide an electrode mixture, a solid electrolyte layer, and an all-solid-state lithium secondary battery including the above sulfide solid electrolyte.

[0012] The inventors of the present invention repeatedly conducted in-depth studies and found that: by forming a PS tetrahedron having a structural deformation introduced therein with respect to the PS tetrahedron in the conventional thiogermanate crystal structure belonging to the space group F-43m, the above problems can be solved, and thus the present invention has been completed. 4 tetrahedron, a PS tetrahedron into which a structural deformation is introduced can be formed, 4 and the present invention has been completed.

[0013] That is, the present invention relates to the following [1] to

[13] .

[0014] [1] A sulfide solid electrolyte containing Li element, P element, S element, and Ha element, having a thiogermanate crystal structure,

[0015] wherein the above Ha element is at least one element selected from F, Cl, Br, and I,

[0016] the above crystal structure has a plurality of PS tetrahedrons T centered on the above P element and having the above 4 S elements as vertices, 4 tetrahedron T 1 ,

[0017] in a part of the above PS 4 tetrahedron T 1 the above P element may be replaced with at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element, and Ge element,

[0018] in a part of the above PS 4 tetrahedron T 1 at least a part of the above S element may be replaced with at least one element selected from O element and the above Ha element,

[0019] in the above crystal structure, there are 16 elements as the above vertices of the above PS 4 tetrahedron T 1 in the unit cell,

[0020] making the above 16 elements and the PS 4 tetrahedron T 2When corresponding to 16 S elements at the vertex equivalent to the 16e position, the above-mentioned PS 4 tetrahedron T 1 For each position of the above-mentioned 16 elements and the above-mentioned PS corresponding thereto 4 tetrahedron T 2 The average value of the distance Δ from each position of the above-mentioned 16 S elements of the tetrahedron T is

[0021] [2] The sulfide solid electrolyte according to [1] above, wherein a part of the above-mentioned PS 4 tetrahedron T 1 The above-mentioned P element is replaced by the above-mentioned Si element.

[0022] [3] The sulfide solid electrolyte according to [1] or [2] above, wherein a part of the above-mentioned PS 4 tetrahedron T 1 At least a part of the above-mentioned S element is replaced by the above-mentioned O element.

[0023] [4] The sulfide solid electrolyte according to any one of [1] to [3] above, wherein as the above-mentioned Ha element, at least two selected from F, Cl, Br, and I are included.

[0024] [5] The sulfide solid electrolyte according to any one of [1] to [4] above, wherein the average value of the above-mentioned distance Δ is

[0025] [6] The sulfide solid electrolyte according to any one of [1] to [5] above, wherein the unit cell has an axial length of and a space group P1 with axial angles α = β = γ = 90°.

[0026] [7] An electrode mixture for a lithium-ion secondary battery, comprising the sulfide solid electrolyte according to any one of [1] to [6] above and an active material.

[0027] [8] A solid electrolyte layer for a lithium-ion secondary battery, comprising the sulfide solid electrolyte according to any one of [1] to [6] above.

[0028] [9] An all-solid-state lithium-ion secondary battery, comprising the sulfide solid electrolyte according to any one of [1] to [6] above.

[0029]

[10] A method for manufacturing a sulfide solid electrolyte, comprising the following steps:[[]]

[0030] Mixing raw materials containing Li element, P element, S element, and Ha element to obtain a raw material mixture,[[]]

[0031] The above raw material mixture is heated at a temperature of 760 °C or higher to obtain a melt of a completely melted intermediate compound,

[0032] The above melt is cooled to precipitate argyrodite-type crystals, and

[0033] The above-precipitated crystals are heat-treated at 350 to 500 °C;

[0034] The above-mentioned Ha element is at least one element selected from F, Cl, Br, and I,

[0035] The above sulfide solid electrolyte contains an argyrodite-type crystal structure.

[0036]

[11] The method for manufacturing a sulfide solid electrolyte according to the above

[10] , wherein the above raw materials further contain at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element, Ge element, and O element.

[0037]

[12] The method for manufacturing a sulfide solid electrolyte according to the above

[10] or

[11] , wherein the heating at a temperature of 760 °C or higher is carried out under an inert atmosphere for 10 minutes to 10 hours.

[0038]

[13] The method for manufacturing a sulfide solid electrolyte according to any one of the above

[10] to

[12] , wherein the above heat treatment is carried out under an inert atmosphere for 10 minutes to 10 hours.

[0039] According to the present invention, a novel sulfide solid electrolyte with improved lithium ion conductivity is obtained. Therefore, the output characteristics and low temperature characteristics of a lithium ion secondary battery using an electrode mixture and a solid electrolyte layer containing the above sulfide solid electrolyte are excellent. In addition, a all-solid-state lithium ion secondary battery having such excellent characteristics is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a diagram showing the state of the PS 4 tetrahedron T 1 and a part of it existing in the unit cell of the crystal structure of the sulfide solid electrolyte of the present embodiment.

[0041] Figure 2 is a diagram showing the state of the PS 4 tetrahedron T 1 and a part of it and other elements existing in the unit cell of the crystal structure of the sulfide solid electrolyte of the present embodiment.

[0042] Figure 3 is a diagram for explaining the method of obtaining the average value of the distance Δ in the present embodiment,Figure 3 (a) shows the PS tetrahedron T present in the unit cell in the space group F-43m, 4 one of the 2 figures. Figure 3 (b) shows the PS tetrahedron T present in the unit cell of the crystal structure of the present embodiment, 4 one of the 1 figures.

[0043] Figure 4 is a flowchart showing the manufacturing method of the sulfide solid electrolyte of the present embodiment.

[0044] Figure 5 is a chart showing the results of the PDF analysis of the sulfide solid electrolyte of Example 1. DETAILED DESCRIPTION

[0045] Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments and can be arbitrarily modified and implemented within the scope not departing from the gist of the present invention. In addition, "~" indicating a numerical range is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value.

[0046] <Sulfide Solid Electrolyte>

[0047] The sulfide solid electrolyte of the present embodiment (hereinafter, sometimes simply referred to as "solid electrolyte") contains Li element, P element, S element and Ha element and has a thiogermanate-type crystal structure. Here, the Ha element in this specification refers to at least one element selected from F, Cl, Br and I.

[0048] The crystal structure of the sulfide solid electrolyte of the present embodiment has a plurality of PS tetrahedrons T centered on the P element and having 4 S elements as vertices. 4 Among them, the P element of a part of the PS tetrahedrons T can be replaced with at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element and Ge element. In addition, at least a part of the S element of a part of the PS tetrahedrons T can be replaced with at least one element selected from O element and Ha element. 1 4 1 4 1

[0049] The PS tetrahedrons T of the crystal structure of the sulfide solid electrolyte of the present embodiment have 16 elements as vertices existing in the unit cell. Making the above 16 elements coincide with the PS tetrahedrons T constituting the space group F-43m 4 1 4 2When corresponding to the 16 S elements of the vertices of PS 4 tetrahedron T 1 The positions of the 16 elements of and the corresponding PS 4 tetrahedron T 2 The average value of the distance Δ from the positions of the 16 S elements of is The PS of the above space group F-43m 4 tetrahedron T 2 The vertices of are equivalent to the 16e positions.

[0050] The larger the average value of the above distance Δ, it means that in the crystal structure of the sulfide solid electrolyte, PS 4 tetrahedron T 1 The structure of and the PS in the previous thiogermanate-type crystal structure belonging to the space group F-43m 4 The tetrahedron is more deformed in structure compared to the tetrahedron.

[0051] It can be seen that in the sulfide solid electrolyte of the present embodiment, by the average value of the above distance Δ being Introducing the structural deformation within the above range, thereby improving the lithium ion conductivity of the sulfide solid electrolyte.

[0052] Hereinafter, the above structural deformation will be described.

[0053] The PS existing in the unit cell in the crystal structure of the sulfide solid electrolyte of the present embodiment 4 tetrahedron T 1 The state of is shown in Figure 1 and Figure 2 PS 4 tetrahedron T 1 There are 16 elements as vertices of in the unit cell.

[0054] Figure 1 shows the PS existing in the unit cell 4 tetrahedron T 1 and a part of its state. Only the P element and the S element are shown. The elements marked with the symbols S1 to S16 represent the S elements as the above vertices. The elements without symbols other than these are P elements.

[0055] Figure 2 shows the PS existing in the unit cell 4 tetrahedron T 1 and a part of it and the state of other elements. It is a view from the a-axis direction showing the state of the Li element and the Ha element in addition to the P element and the S element. The PS 4 tetrahedron T 1 is composed of the P element at the 4b position and the S element at the 16e position. The adjacent PS 4 tetrahedron T1 There are a Li element at the 48h position and an S element / Ha element at the 4a position with respect to each other.

[0056] In Figure 1 and Figure 2 among the S elements shown as S1 to S16, four S elements shown as S1 to S4 become the vertices of one PS 4 tetrahedron T 1 The other 12 S elements, S5 to S16, become the vertices of 12 mutually different PS 4 tetrahedron T 1 The vertices.

[0057] When the above 16 elements S1 to S16 as vertices in this embodiment are made to correspond to the 16 vertices (corresponding to the 16e position) of the PS 4 tetrahedron T 2 in the space group F-43m, i.e., the elements S'1 to S'16, the positions of the 16 elements as the respective vertices of the PS 4 tetrahedron T 1 and the positions of the 16 elements as the respective vertices of the PS 4 tetrahedron T 2 The average value of the distance Δ between the positions of the 16 elements as the respective vertices is 0.05 to That is, the distance Δ1 between S1 and S'1, the distance Δ2 between S2 and S'2, and so on up to the distance Δ16 between S16 and S'16 are obtained, and the distance Δ as the average value of Δ1 to Δ16 is

[0058] Using Figure 3 The method for obtaining the average value of the above distance Δ will be described.

[0059] Figure 3 In (a) of 4 tetrahedron T 2 One of the PSs existing in the unit cell in the space group F-43m is shown, Figure 3 In (b) of 4 tetrahedron T 1 One of the PSs existing in the unit cell of the crystal structure in this embodiment is shown. Figure 3 In (a) of 4 tetrahedron T 2 Only one PS Figure 3 Composed of the central P element and the four vertex elements S'1 to S'4 corresponding to the 16e position is drawn, but actually, there are 12 vertex elements, S'5 to S'16, in the same unit cell. Similarly, Figure 3 In (b) of 4Tetrahedron T 1 , but in fact, there are 12 elements S5 to S16 as vertices in the same unit cell. It should be noted that the elements S1 to S16 as vertices correspond to the elements S’1 to S’16 as vertices in sequence respectively.

[0060] Let Figure 3 the distance between the position of the element S’1 in (a) and the position of the element S1 in (b) corresponding to the element S’1 be Δ1. Here, the positions of all P elements in the unit cell of the space group F-43m are the same as the positions of all P elements in the unit cell of the crystal structure of this embodiment. It should be noted that Figure 3 in (a) of Figure 3 and Figure 3 in (b) of

[0061] For the sake of convenience, a straight line connecting the P element and the element S’1 is drawn in (a) and (b) to make the distance Δ1 easy to understand. Similarly, the distance Δ2 between the element S’2 and the element S2, the distance Δ3 between the element S’3 and the element S3, and so on until the distance Δ16 between the element S’16 and the element S16 are calculated in sequence. The value represented by the average value of the distances Δ1 to Δ16, that is, {(Δ1 + Δ2 + ··· + Δ16) / 16}, is used as the average value of the above distance Δ.

[0062] Here, the positions of the above elements S1 to S16 are obtained by neutron diffraction measurement of the sulfide solid electrolyte. Specifically, the crystal periodic structure is analyzed by Rietveld analysis of the obtained neutron diffraction pattern, and the PDF (pair-distribution function) analysis is performed on the neutron scattering pattern. It should be noted that the Rietveld analysis is carried out in the space group F-43m, and the PDF analysis is carried out in the space group P1. The positions of the elements S1 to S16 are obtained independently through the above analysis, and the distances Δ1 to Δ16 are accurately obtained, so that the local structure deformation can be analyzed.

[0063] The details of the above neutron diffraction measurement are described.

[0064] The conditions of the neutron diffraction measurement are as follows.

[0065] The neutron diffraction measurement is carried out, for example, by the iMATERIA (Ibaraki Materials Structure Analysis Instrument) in BL20 of the high-intensity proton accelerator facility J-PARC (Japan Proton Accelerator Research Complex).

[0066] The sulfide solid electrolyte as a sample is filled in a cylinder with a diameter of 6 mm × a height of 50 mm and a volume of about 1.4 cm 3A cylindrical container made of vanadium.

[0067] The diffractometer uses a neutron TOF (Time-of-Flight) type, and the detector uses a 90-degree arrangement (resolution Δd / d = 0.5%). The measurement range is (DF mode), the measurement time is about 20 minutes, and neutron diffraction patterns and neutron scattering patterns are obtained.

[0068] The structure refinement of the obtained neutron diffraction pattern based on Rietveld analysis is carried out using Z-Rietveld software [refer to the following references 1, 2]. The initial structure parameters of the sulfide solid electrolyte for crystal structure refinement use ICSD No.259201 (Li 5.4 PS 4.4 CL 0.8 Br 0.8 ) registered in the ICSD (Inorganic Crystal Structure Database).

[0069] The refinement of the coordinates of each atom is carried out according to the cubic crystal system of F-43m, space group No.216.

[0070] After calculating the structure factor S(Q) (absorption correction, polarization correction, non-interference scattering correction, atomic scattering factor) for the obtained neutron scattering pattern, G(r) is derived by Fourier transform. The PDF (Pair Distribution Function) analysis is carried out using PDFgui software [refer to the following reference 3], and the analysis range r is In addition, the initial structure of the PDF analysis uses the structure obtained from the Rietveld analysis of the above neutron diffraction pattern.

[0071] The refinement of the coordinates of each atom in the PDF analysis is different from that in the Rietveld analysis and is carried out according to the triclinic crystal system of P1, space group No.1.

[0072] [Reference 1] R.Oishi, M.Yonemura, Y.Nishimaki, S.Torii, A.Hoshikawa, T.Ishigaki, T.Morishima, K.Mori, T.Kamiyama, “Rietveld analysis software for J-PARC”, Nucl.Instr.Meth.Phys.Res.A., 2009, 600, 94-96.doi:10.1016 / j.nima.2008.11.056

[0073] [Reference 2] R. Oishi-Tomiyasu, M. Yonemura, T. Morishima, A. Hoshikawa, S. Torii, T. Ishigaki, T. Kamiyama, “Application of matrix decomposition algorithms for singular matrices to the Pawley method in Z-Rietveld”, J. Appl. Cryst., 2012, 45, 299-308. doi:10.1107 / S0021889812003998

[0074] [Reference 3] C. L. Farrow, P. Juhas, J. W. Liu, D. Bryndin, E. S. Bozin, J. Bloch, Th. Proffen, S. J. L. Billinge, “PDFfit2 and PDFgui: computer programs for studying nanostructure in crystals”, J. Phys.: Condens. Matter., 2007, 19, 335219. doi:10.1088 / 0953-8984 / 19 / 33 / 335219

[0075] The average value of the above distance Δ of the sulfide solid electrolyte of this embodiment is Preferably More preferably Particularly preferably By having an average value of the distance Δ of the above structural deformation, the lithium ion conductivity is improved.

[0076] The reason is not yet clear, but it is considered that in the case of PS of the crystal system that conforms to the space group F-43m without structural deformation 4 tetrahedron T 2 the lithium ions adjacent to the S element as the vertex are localized, and it is difficult to conduct lithium ions over a long distance. In contrast, it is considered that PS with an average value of the distance Δ of the above structural deformation 4 tetrahedron T 1 has its local structure disrupted, and the delocalization of lithium ions promotes the long-distance conduction of lithium ions. That is, it is considered that located in PS 4 tetrahedron T 1Due to the structural deformation, the lithium ions around the specific S element at the vertex are prone to move to the surroundings of adjacent other S elements. As a result, the lithium ion conductivity is improved.

[0077] From the perspective of the above-mentioned improvement in lithium ion conductivity, the average value of the above distance Δ is above, preferably above. In addition, if PS 4 tetrahedron T 1 has too large a structural deformation, the thiogermanate crystal structure cannot be maintained. Therefore, the average value of the above distance Δ is below. From the perspective of the manufacturing cost brought by the necessary heat treatment temperature, it is preferably below, more preferably below.

[0078] Each value of Δ1 to Δ16, which is the basis for the average value of the distance Δ, is preferably more preferably even more preferably Here, from the perspective of obtaining high lithium ion conductivity, each value of Δ1 to Δ16 is preferably above, more preferably above, even more preferably above. In addition, from the perspective of maintaining the thiogermanate crystal structure, each value of Δ1 to Δ16 is preferably below, more preferably below, even more preferably below.

[0079] Among the 16 distances of Δ1 to Δ16, the number of distances Δ within the above range is preferably 12 or more, more preferably 14 or more, and even more preferably all 16.

[0080] It should be noted that in a part of multiple PS 4 tetrahedron T 1 as the central element, the P element can be replaced by at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element and Ge element. In addition, in a part of multiple PS 4 tetrahedron T 1 at least a part of the S element as the vertex can be replaced by at least one element selected from O element and Ha element.

[0081] Even in such a case, the above method can be directly used to calculate the average value of the above distance Δ. That is, for the PS 4 tetrahedron T 2, instead of replacing the P element and the S element with the above elements respectively, keep the state where the central element is the P element and the vertex elements are the S elements, and calculate the distances Δ1 to Δ16 respectively for analysis. This is because the displacement of the bond lengths and bond angles in the tetrahedron caused by replacing the P element and the S element with other elements has a negligible impact on the distances Δ1 to Δ16.

[0082] As described above, multiple PS 4 tetrahedron T 1 The P element as the central element in a part of the tetrahedron can be replaced with at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element, and Ge element.

[0083] For example, from the viewpoint of further improving the lithium ion conductivity, it is preferable to replace the P element with the Si element. The proportion of replacing the P element with the Si element is preferably 0.01 to 50%, more preferably 0.1 to 40%. Here, from the viewpoint of obtaining higher lithium ion conductivity, the above replacement proportion is preferably 0.01% or more, more preferably 0.1% or more. On the other hand, from the viewpoint of crystallinity, the above proportion is preferably 50% or less, more preferably 40% or less. However, the replacement proportion can also be 0%, that is, not replaced with the Si element. In addition, the PS 4 tetrahedron T 1 can increase the structural deformation by containing the Si element. Moreover, the PS 4 tetrahedron T 1 can further increase its structural deformation by containing the O element and the above Si element at the same time.

[0084] In addition, when elements other than the Si element, such as Al element, Sn element, In element, Cu element, Sb element, and Ge element, are contained in the raw materials used in the manufacture of the sulfide solid electrolyte whether intentionally or mixed in during the manufacturing process, they can be replaced from the P element. However, the proportion of the element replaced from the P element, including the total proportion of the above replacement with the Si element, is preferably 50% or less.

[0085] It should be noted that in this specification, the substitution ratio of the elements constituting the crystal structure is obtained by performing X-ray diffraction (XRD) measurement and Rietveld analysis on the obtained XRD pattern.

[0086] As described above, multiple PS 4 tetrahedron T 1 At least a part of the S element as the vertex in a part of the tetrahedron can be replaced with at least one X element selected from O element and Ha element. That is, the PS 4 tetrahedron T 1 a part of which can also be P(S + X)4 Tetrahedron. Here, the X element refers to at least one element selected from the O element and the Ha element.

[0087] P(S + X) 4 The tetrahedron means a PSX tetrahedron having 1 S element and 3 X elements with respect to the P element of the central element 3 tetrahedron, a PS having 2 S elements and 2 X elements 2 X 2 tetrahedron, or a PS having 3 S elements and 1 X element 3 tetrahedron of such a structure as the X tetrahedron. In the case of PS with two or more X elements 2 X 2 tetrahedron or PS 1 X 3 In the case of, the plurality of X elements may be the same element or different elements.

[0088] In addition, at least a part of the S element as the vertex of P(S + X) 4 The P element as the vertex of the tetrahedron can also be replaced by at least one element selected from the above Si element, Al element, Sn element, In element, Cu element, Sb element and Ge element.

[0089] PS 4 tetrahedron T 1 In, from the viewpoint of maintaining high lithium ion conductivity, PS 4 tetrahedron is preferred. From the viewpoint of improving water resistance, P(S + O) 4 tetrahedron in which at least a part of the S element is replaced by the O element is preferred.

[0090] When at least a part of the S element is replaced by at least one X element selected from the O element and the Ha element, as PS 4 tetrahedron T 1 and P(S + X) 4 As an index of the ratio of tetrahedrons, the ratio of the X element to the total of the S element and the X element constituting the vertex of the tetrahedron is preferably 0.01 to 25%, more preferably 0.1 to 20%. Here, from the viewpoint of obtaining the effect of substitution, the above ratio is preferably 0.01% or more, more preferably 0.1% or more. On the other hand, from the viewpoint of maintaining high lithium ion conductivity, the above ratio is preferably 25% or less, more preferably 20% or less. However, the case where all tetrahedrons have a P element as the central element and all the elements as the vertices are S elements, that is, the above ratio is 0%, is not excluded.

[0091] In addition to the above, a part of the S element and the X element that form the vertices of the tetrahedron can be further substituted with other elements or groups. Examples of the elements or groups that can be substituted include Se, Te, BH 4 , CN, etc. These elements or groups can be substituted regardless of whether they are intentionally included in the raw materials used in the production of the solid electrolyte or are mixed in during the production process. However, the elements and groups other than the S element among the elements that form the vertices of the tetrahedron, with the total proportion also including the above-mentioned X element, are preferably 50% or less, more preferably 25% or less, and still more preferably 20% or less.

[0092] The unit cell of the crystal structure of the sulfide solid electrolyte of the present embodiment preferably has an axial length of and a space group P1 with axial angles α = β = γ = 90°. This means that even if the axial lengths a = b = c and the axial angles α = β = γ = 90°, due to the structural deformation of the PS 4 tetrahedron T 1 , there are no symmetry axes, mirror symmetry planes, etc., and the symmetry is low. It should be noted that the above does not exclude space groups other than the space group P1, and other space groups such as the space group Pm can also be adopted.

[0093] The axial length is preferably more preferably even more preferably particularly preferably Here, from the viewpoint of maintaining high lithium ion conductivity, the axial length is preferably or more, more preferably or more. In addition, from the same viewpoint, the axial length is preferably or less, more preferably or less, even more preferably or less, particularly preferably or less.

[0094] The crystal structure of the sulfide solid electrolyte of the present embodiment is of the argyrodite type, and the argyrodite-type crystal structure refers to the crystal structure of the compound group derived from the mineral represented by the composition formula Ag 8 GeS 6 .

[0095] In addition to the fact that at least a part of the S element of the sulfide solid electrolyte of the present embodiment can be substituted with the Ha element, the Ha element is also contained.

[0096] The Ha element is at least one element selected from F, Cl, Br, and I. From the viewpoint of lithium ion conductivity, it is preferable that the sulfide solid electrolyte of the present embodiment contains at least two of them.

[0097] The sulfide solid electrolyte of the present embodiment more preferably contains at least one element selected from Cl, Br, and I, and further preferably contains two or more elements as the Ha element.

[0098] In addition, the sulfide solid electrolyte of the present embodiment further preferably contains at least one of Cl and Br, and particularly preferably contains Cl and Br as the Ha element.

[0099] The thiogermanate crystal structure of the sulfide solid electrolyte of the present embodiment preferably adopts the above structure. As a composition formula, it is preferably represented by Li a PS b Ha c satisfying the relationship of 5 ≤ a ≤ 7, 4 ≤ b ≤ 6, and 1.3 ≤ c ≤ 2. The above element ratio more preferably satisfies the relationship of 5.1 < a < 6.3, 4 < b < 5.3, and 1.4 ≤ c ≤ 1.9, and further preferably satisfies the relationship of 5.2 < a < 6.2, 4.1 < b < 5.2, and 1.5 ≤ c ≤ 1.8.

[0100] That is, a is preferably 5 or more, more preferably greater than 5.1, and further preferably greater than 5.2. In addition, it is preferably 7 or less, more preferably less than 6.3, and further preferably less than 6.2. b is preferably 4 or more, more preferably greater than 4, and further preferably greater than 4.1. In addition, it is preferably 6 or less, more preferably less than 5.3, and further preferably less than 5.2. c is preferably 1.3 or more, more preferably 1.4 or more, and further preferably 1.5 or more. In addition, it is preferably 2 or less, more preferably 1.9 or less, and further preferably 1.8 or less.

[0101] Here, when a part of the P element is replaced by other elements, the total of the P element and other elements is set to 1, and preferably a, b, and c with respect to it are within the above ranges. In addition, when a part of the S element is replaced by the O element, it is preferably that the total of the S element and the O element is within the above range of b.

[0102] From the viewpoint of obtaining good lithium ion conductivity when used in a lithium ion secondary battery, the smaller the secondary particle size of the sulfide solid electrolyte of the present embodiment, the better. Specifically, it is preferably 10 μm or less, more preferably 3 μm or less, and further preferably 1 μm or less. The lower limit of the secondary particle size is not particularly limited and is usually 0.1 μm or more.

[0103] The secondary particle size can be measured using a Microtrac device.

[0104] The lithium ion conductivity of the sulfide solid electrolyte of the present embodiment at 25 °C is preferably 3.0×10 －3 S / cm or more, more preferably 3.5×10 －3above S / cm, more preferably 4.0×10 －3 S / cm or more, and the higher the better. The upper limit of the lithium ion conductivity is not particularly limited, and is usually 1×10

[0105] －1 S / cm or less.

[0106] It should be noted that the lithium ion conductivity can be measured by the AC impedance method.

[0107] The solid electrolyte of the present embodiment is suitable for use in electrode binders and solid electrolyte layers used in lithium ion secondary batteries, and is particularly suitable for all-solid-state lithium ion secondary batteries.

[0108] That is, the electrode binder of the present embodiment is used in a lithium ion secondary battery and contains the above-mentioned solid electrolyte and an active material.

[0109] In addition, the solid electrolyte layer of the present embodiment is used in a lithium ion secondary battery and contains the above-mentioned solid electrolyte.

[0110] In addition, the all-solid-state lithium ion secondary battery of the present embodiment contains the above-mentioned solid electrolyte.

[0111] The above-mentioned electrode binder, solid electrolyte layer, and all-solid-state lithium ion secondary battery may further contain other solid electrolytes. The other solid electrolytes are not particularly limited. For example, solid electrolytes having a thio-LISICON crystal structure known in the past, Li 3 PS 4 、Li 4 P 2 S 6 、Li 2 S、LiHa, etc. can be cited.

[0112] The active material contained in the electrode binder can be a conventionally known material.

[0113] For example, as the positive electrode active material, as long as it can reversibly occlude and release lithium ions, deintercalate and intercalate lithium ions, or dope and dedope the equilibrium anion of the lithium ions, there is no particular limitation. Specifically, lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, composite metal oxides, polyanion olivine type positive electrodes, etc. can be cited.

[0114] The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions, deintercalate and intercalate (intercalation) lithium ions, or dope and dedope the counter anions of the lithium ions. Specifically, examples thereof include carbon-based materials such as lithium metal, graphite, hard carbon, and soft carbon, metals that can form alloys with lithium such as aluminum, silicon, and tin, amorphous oxides such as silicon oxide and tin oxide, and lithium titanate.

[0115] The solid electrolyte layer only needs to contain the solid electrolyte of the present embodiment. In addition, additives such as a binder may be further contained.

[0116] As the binder, conventionally known substances can be used. For example, butadiene rubber, acrylate butadiene rubber, styrene butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, etc. can be cited. The content of the binder in the solid electrolyte layer only needs to be within a conventionally known range.

[0117] The all-solid-state lithium ion secondary battery is not particularly limited as long as it includes the solid electrolyte of the present embodiment, a positive electrode, and a negative electrode. In addition, the positive electrode and the negative electrode may also be electrode mixtures containing the solid electrolyte of the present embodiment.

[0118] As the positive electrode active material, the same positive electrode active material as that described in the electrode mixture can be used. The positive electrode may further contain a positive electrode current collector, a binder, a conductive assistant, etc. as needed. As the positive electrode current collector, metal thin plates such as aluminum, its alloy, and stainless steel can be used.

[0119] As the negative electrode active material, the same negative electrode active material as that described in the electrode mixture can be used. The negative electrode may further contain a negative electrode current collector, a binder, a conductive assistant, etc. as needed. As the negative electrode current collector, metal thin plates such as copper and aluminum can be used.

[0120] <Manufacturing method of sulfide solid electrolyte>

[0121] The manufacturing method of the sulfide solid electrolyte of the present embodiment is not particularly limited as long as the crystal structure described in the above <sulfide solid electrolyte> can be obtained.

[0122] As one embodiment, for example, as Figure 4 shown, it sequentially includes the following steps S1 to S4.

[0123] Step S1 is a step of mixing raw materials containing Li element, P element, S element, and Ha element to obtain a raw material mixture.

[0124] Step S2 is a step of heating the raw material mixture obtained in step S1 at a temperature of 760 °C or higher to obtain a melt of a completely melted intermediate compound.

[0125] Step S3 is a step of cooling the melt obtained in step S2 to precipitate argyrodite type crystals.

[0126] Step S4 is a step of heat-treating the precipitated crystals obtained in step S3 at 350 to 500°C.

[0127] Each step is explained.

[0128] In step S1, in which raw materials containing Li, P, S and Ha are mixed to obtain a raw material mixture, a raw material mixture containing a PS 4 Tetrahedron T 1 The raw material is a raw material of each element of P element and S element, and Li element and Ha element. When a part of P element and S element is substituted with other elements as described above, it is preferred that other elements are also contained as raw materials. Specifically, the raw material further contains at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element, Ge element and O element.

[0129] As the raw material containing the Li element, the P element, the S element, the Ha element, and other elements as necessary, a conventionally known raw material can be used.

[0130] Specifically, Li simple substance or a compound containing Li, P simple substance or a compound containing P, S simple substance or a compound containing S, and a compound containing Ha can be used in appropriate combination. In the case of further containing the element O, an oxide can be used as the above-mentioned compound. In addition, the above-mentioned compound can also be a compound containing two or more of Li, P, S and Ha. For example, as a compound that serves as both a compound containing S and a compound containing P, phosphorus pentasulfide (P 2 S 5 ) etc. In addition, examples of compounds that serve as both a compound containing Li and a compound containing Ha include lithium halides.

[0131] Examples of the compound containing Li include lithium sulfide (Li 2 S), lithium carbonate (Li 2 CO 3 ), lithium sulfate (Li 2 SO 4 ), lithium oxide (Li 2 O) and lithium compounds such as lithium hydroxide (LiOH), etc. From the viewpoint of easy handling, lithium sulfide is preferred.

[0132] On the other hand, since lithium sulfide is expensive, from the viewpoint of suppressing manufacturing costs, lithium compounds other than lithium sulfide, metallic lithium, etc. are preferred. Specifically, those preferably selected are one or more selected from metallic lithium, lithium carbonate (Li 2 CO 3 ), lithium sulfate (Li 2 SO 4 ), lithium oxide (Li 2 O), and lithium hydroxide (LiOH). They may be used alone or in combination of two or more.

[0133] Examples of the compound containing S include phosphorus sulfides such as diphosphorus trisulfide (P 2 S 3 ), diphosphorus pentasulfide (P 2 S 5 ), other sulfur compounds containing phosphorus, elemental sulfur, sulfur-containing compounds, etc. Examples of the sulfur-containing compound include H 2 S, CS 2 , iron sulfides (FeS, Fe 2 S 3 , FeS 2 , Fe 1－x S, etc.), bismuth sulfide (Bi 2 S 3 ), copper sulfides (CuS, Cu 2 S, Cu 1－x S, etc.). Among them, from the viewpoint of preventing elements other than the elements constituting the target sulfide solid electrolyte, phosphorus sulfide is preferred, and diphosphorus pentasulfide (P 2 S 5 ) is more preferred. They may be used alone or in combination of two or more. It should be noted that phosphorus sulfide is a compound that also serves as a compound containing S and a compound containing P.

[0134] Examples of the compound containing P include phosphorus sulfides such as diphosphorus trisulfide (P 2 S 3 ), diphosphorus pentasulfide (P 2 S 5 ), and phosphorus compounds such as sodium phosphate (Na 3 PO 4 ). Among them, from the viewpoint of preventing elements other than the elements constituting the target sulfide solid electrolyte, phosphorus sulfide is preferred, and diphosphorus pentasulfide (P 2 S 5 ) is more preferred. They may be used alone or in combination of two or more.

[0135] As a compound containing Ha, for example, lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, boron halides, etc. can be cited. Among them, from the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte, lithium halides are preferred, and LiCl, LiBr, and LiI are more preferred. These compounds can be used alone or in combination of two or more.

[0136] As an optional component, for raw materials containing Si element, for example, SiO 2 , SiS 2 can be cited. Among them, from the viewpoint of lithium ion conductivity, SiO 2 is more preferred. These compounds can be used alone or in combination of two or more.

[0137] As an optional component, for raw materials containing Al element, for example, Al 2 S 3 , Al 2 O 3 , AlCl 3 can be cited. Among them, from the viewpoint of lithium ion conductivity, Al 2 S 3 , AlCl 3 are preferred, and Al 2 S 3 is more preferred. These compounds can be used alone or in combination of two or more.

[0138] As an optional component, for raw materials containing Sn element, for example, SnS, SnS 2 , SnO, SnO 2 , SnCl 2 can be cited. Among them, from the viewpoint of lithium ion conductivity, SnS 2 , SnCl 2 are preferred, and SnS 2 is more preferred. These compounds can be used alone or in combination of two or more.

[0139] As an optional component, for raw materials containing In element, for example, In 2 O 3 , In 2 S 3 , InCl 3 can be cited. Among them, from the viewpoint of lithium ion conductivity, In 2 S 3 , InCl 3 are preferred, and In 2 S3 These compounds can be used alone or in combination of two or more kinds.

[0140] As an optional component, examples of the raw material containing Cu element include Cu 2 O, CuO, Cu 2 S, CuS, CuCl 2 Among them, from the viewpoint of lithium ion conductivity, CuS and CuCl are preferred 2 , and CuS is more preferred. These compounds can be used alone or in combination of two or more kinds.

[0141] As an optional component, examples of the raw material containing Sb element include Sb 2 O 3 , Sb 2 S 3 , SbCl 3 . Among them, from the viewpoint of lithium ion conductivity, Sb 2 S 3 , SbCl 3 are preferred, and Sb 2 S 3 is more preferred. These compounds can be used alone or in combination of two or more kinds.

[0142] As an optional component, examples of the raw material containing Ge element include GeO 2 , GeS, GeS 2 , GeCl 2 . Among them, from the viewpoint of lithium ion conductivity, GeS 2 , GeCl 2 are preferred, and GeS 2 is more preferred. These compounds can be used alone or in combination of two or more kinds.

[0143] The mixing of the raw materials is carried out, for example, by mixing using a mortar, mixing using a medium such as a planetary ball mill, a needle mill, a powder blender, or a medium-free mixing such as air flow mixing. The raw materials can be mixed before heating and then amorphized.

[0144] In the subsequent step S2, the raw material mixture obtained in step S1 is heated at 760 °C or higher to obtain a melt of a completely melted intermediate compound.

[0145] There are no particular limitations on the specific method for heating and melting the raw material mixture. The raw materials are placed in a heat-resistant container and heated using a heating furnace. The mixture of raw materials can be sealed in a heat-resistant container. Alternatively, melting can also be carried out in an atmosphere containing sulfur element, etc. Examples of the atmosphere containing sulfur element include a mixed gas atmosphere of a sulfur-containing gas such as sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc. and an inert gas.

[0146] As the heat-resistant container, a carbon heat-resistant container, quartz, quartz glass, borosilicate glass, aluminosilicate glass, a heat-resistant container containing oxides such as alumina, zirconia, and mullite, a heat-resistant container containing nitrides such as silicon nitride and boron nitride, a heat-resistant container containing carbides such as silicon carbide, etc. can be used. In addition, these heat-resistant containers can be integrally formed of the above materials, or can be a container having layers of carbon, oxides, nitrides, carbides, etc. such as a carbon-coated quartz tube.

[0147] When heating and melting the raw material mixture, the heating temperature is 760 °C or higher, preferably 760 - 1300 °C, more preferably 780 - 1200 °C, and further preferably 800 - 1000 °C. Here, by making the heating temperature 760 °C or higher, it is easy to introduce a structural deformation in the PS 4 tetrahedron T 1 in the resulting sulfide solid electrolyte.

[0148] Thus, it is considered that by obtaining a melt of an intermediate compound in which the raw material mixture is completely melted, the disorder of the atomic arrangement becomes larger, and the environment around the PS 4 tetrahedron T 1 becomes non-equivalent, and at the same time, a structural deformation is introduced. The introduction of this structural deformation can be increased by using a raw material containing Si element in the raw material mixture, and can be further increased by jointly using a raw material containing Si element and a raw material containing O element.

[0149] From the above viewpoints, the heating temperature is 760 °C or higher, more preferably 780 °C or higher, and further preferably 800 °C or higher. In addition, from the viewpoints of suppressing deterioration, decomposition, etc. of the components in the melt caused by heating, the heating temperature is preferably 1300 °C or lower, more preferably 1200 °C or lower, and further preferably 1000 °C or lower.

[0150] The heating and melting time is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, still more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, from the viewpoint of enabling the reaction to proceed well, the heating and melting time is preferably 10 minutes or more, more preferably 30 minutes or more, still more preferably 45 minutes or more, and particularly preferably 1 hour or more. In addition, from the viewpoints of suppressing deterioration, decomposition, etc. of the components in the melt due to heating, the heating and melting time is preferably 10 hours or less, more preferably 9.5 hours or less, still more preferably 9 hours or less.

[0151] The atmosphere for heating and melting is preferably an inert atmosphere. Examples of the inert atmosphere include a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, etc.

[0152] In addition, the dew point during heating and melting is preferably -20°C or lower, and the lower limit is not particularly limited and is usually about -80°C. The oxygen concentration is preferably 1000 ppm or lower.

[0153] In step S2, the complete melting of the intermediate compound can be confirmed by the absence of peaks from the crystal in high-temperature X-ray diffraction measurement.

[0154] In the subsequent step S3, the melt of the intermediate compound completely melted in step S2 is cooled to precipitate a thiogermanate-type crystal.

[0155] The cooling rate is preferably 0.1 to 10000°C / second, more preferably 0.5 to 5000°C / second, still more preferably 1 to 1000°C / second. Here, from the viewpoints of improving compositional homogeneity and suppressing quality variations, the cooling rate is preferably 0.1°C / second or more, more preferably 0.5°C / second or more, still more preferably 1°C / second or more. In addition, the upper limit value of the cooling rate is not particularly limited. If considering the cooling rate of a twin roll, which is generally considered to have the fastest quenching rate, the upper limit value is 1000000°C / second or lower. From the viewpoint of actual production, the cooling rate is more preferably 10000°C / second or lower, still more preferably 5000°C / second or lower, and even more preferably 1000°C / second.

[0156] The atmosphere during cooling is preferably a low moisture content, inert atmosphere, the same as that during heating and melting in step S2.

[0157] In step S4, the thiogermanate-type crystal precipitated in step S3 is heat-treated at 350 to 500°C. Thus, the sulfide solid electrolyte of the present embodiment is obtained.

[0158] The temperature of the heat treatment is 350 to 500°C, preferably 355 to 490°C, more preferably 360 to 480°C. Here, from the viewpoint of facilitating the PS in the sulfide solid electrolyte 4Tetrahedron T 1 In consideration of introducing the concept of structural deformation, the heat treatment temperature is 350 °C or higher, preferably 355 °C or higher, more preferably 360 °C or higher. Additionally, from the perspective of preventing sintering between particles, the heat treatment temperature is 500 °C or lower, preferably 490 °C or lower, more preferably 480 °C or lower.

[0159] The heat treatment time is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, further preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, from the perspective of facilitating the introduction of structural deformation, the heat treatment time is preferably 10 minutes or more, more preferably 30 minutes or more, further preferably 45 minutes or more, and particularly preferably 1 hour or more. Additionally, from the perspective of manufacturing cost, the heating and melting time is preferably 10 hours or less, more preferably 9.5 hours or less, further preferably 9 hours or less.

[0160] The heat treatment atmosphere is preferably an inert atmosphere. Examples of the inert atmosphere include a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, etc.

[0161] In addition, the dew point during heat treatment is preferably -20 °C or lower, and the lower limit is not particularly limited and is usually around -80 °C. The oxygen concentration is preferably 1000 ppm or lower.

[0162] When the sulfide solid electrolyte obtained in the above step S4 is used in an electrode mixture for a lithium-ion secondary battery, a solid electrolyte layer, or an all-solid-state lithium-ion secondary battery, it is supplied to a conventionally known process together with other components as needed.

[0163] Examples

[0164] The following provides examples to specifically illustrate the present invention, but the present invention is not limited thereto.

[0165] Example 1 and Example 2 are examples, and Example 3 is a comparative example.

[0166] [Example 1]

[0167] Under a dry nitrogen atmosphere, to obtain a composition ratio of Li 5.4 PS 4.4 CL 0.8 Br 0.8 Lithium sulfide powder (manufactured by Sigma, purity 99.98%), phosphorus pentasulfide powder (manufactured by Sigma, purity 99%), lithium chloride powder (manufactured by Sigma, purity 99.99%), and lithium bromide powder (manufactured by Sigma, purity 99.995%) were weighed, and mixed using a mortar. Then, SiO was mixed. 2Powder (manufactured by AS ONE Corporation, obtained by pulverizing the SJT series of quartz test tubes) was placed into a carbon-coated quartz tube, and the tube was sealed under vacuum. Then, it was heated at 850 °C for 1 hour using an electric furnace to obtain a melt of a completely melted intermediate compound. Subsequently, it was cooled to room temperature at 10 °C / second to precipitate sphalerite-type crystals. Then, heat treatment was performed at 400 °C for 1 hour in a dry nitrogen atmosphere, and it was cooled to room temperature again at 1 °C / second to obtain a sulfide solid electrolyte.

[0168] [Example 2]

[0169] The heat treatment temperature after precipitating the sphalerite-type crystals was changed to 415 °C as shown in Table 1, and a sulfide solid electrolyte was obtained in the same manner as in Example 1 except for this.

[0170] [Example 3]

[0171] The heat treatment temperature after precipitating the sphalerite-type crystals was changed to 320 °C as shown in Table 1, and a sulfide solid electrolyte was obtained in the same manner as in Example 1 except for this.

[0172] [Evaluation: Neutron Diffraction Measurement]

[0173] Neutron diffraction measurements were performed on the sulfide solid electrolytes obtained in Examples 1 to 3 above.

[0174] The neutron diffraction measurements were carried out using the iMATERIA (Ibaraki Materials Structure Analysis Instrument) in BL20 of the Japan Proton Accelerator Research Complex (J-PARC), a large-intensity proton accelerator facility.

[0175] The sulfide solid electrolyte as a sample was filled into a vanadium cylindrical container with a diameter of 6 mm × height of 50 mm and a volume of approximately 1.4 cm 3 3.

[0176] A neutron TOF (Time-of-Flight) type diffractometer was used, and the detector was arranged at 90 degrees (resolution Δd / d = 0.5%).

[0177] The measurement range was (DF mode), the measurement time was approximately 20 minutes, and neutron diffraction patterns and neutron scattering patterns were obtained.

[0178] The structure refinement of the obtained neutron diffraction pattern based on Rietveld analysis was carried out using the Z-Rietveld software. Here, the initial structure parameters of the sulfide solid electrolyte for crystal structure refinement were those of ICSD No.259201 (Li 5.4 PS 4.4 CL 0.8 Br 0.8 ) registered in the ICSD (Inorganic Crystal Structure Database).

[0179] The refinement of the coordinates of each atom was carried out according to the cubic crystal system of space group F-43m, No.216.

[0180] For the obtained neutron scattering pattern, after calculating the structure factor S(Q) (absorption correction, polarization correction, non-interference scattering correction, atomic scattering factor), G(r) was derived by Fourier transform. The PDF (pair distribution function) analysis was carried out using the PDFgui software, and the analysis range r was In addition, the initial structure for the PDF analysis was the structure obtained in the above Rietveld analysis.

[0181] The refinement of the coordinates of each atom in the PDF analysis was different from that in the Rietveld analysis and was carried out according to the triclinic crystal system of space group P1, No.1.

[0182] Based on the results of the PDF analysis, the specific composition and content ratio of the sulfide solid electrolyte having a thiogermanate-type crystal structure were determined.

[0183] As an example, the figure showing the results of the PDF analysis of the sulfide solid electrolyte of Example 1 is shown in Figure 5 . Figure 5 In it, the circles represent the measured values, the dashed lines represent the calculated values, and the solid lines represent the residuals meaning the difference between the two. In addition, the specific compositions and content ratios of the sulfide solid electrolytes of Examples 1 to 3 are shown in "Composition" in Table 1. The space group, axial lengths, and axial angles of the thiogermanate-type crystal structure are also shown in "Space group", "Axial lengths a = b = c", and "Axial angles α = β = γ" of "Thiogermanate-type crystal structure" in Table 1, respectively.

[0184] As Figure 5 shown, the results of the PDF analysis indicate that the residuals are small and a PDF analysis with good accuracy was performed on the measured values. As one of the indices representing the accuracy of such a PDF analysis, the Rwp value can be cited. The Rwp value for each example was 0.161 in Example 1, 0.158 in Example 2, and 0.147 in Example 3, and it was confirmed that the values were low enough in all examples.

[0185] In addition, for the feeding composition Li 5.4 PS 4.4 CL 0.8 Br 0.8 , the composition of the obtained sulfide solid electrolyte is Li 5.30 P 0.95 Si 0.05 S 4.23 O 0.10 Cl 0.80 Br 0.80 . That is, it means that in a part of PS 4 tetrahedron T 1 , the P element is replaced by the Si element, and at least a part of the S element is replaced by the O element. It is considered that the Si element and the O element come from the SiO 2 powder added as a raw material, and a part of SiO 2 also melts together and is introduced into the crystal structure when obtaining the melt of the intermediate compound that is completely melted by heating.

[0186] In the atomic coordinates obtained by PDF analysis, the symbols S1 to S16 are assigned to 16 S elements in the unit cell. In addition, the symbols S'1 to S'16 are also assigned to 16 S elements corresponding to the 16e positions in the unit cell of the cubic crystal system of the space group No. 216, F-43m, so as to correspond to the above S1 to S16. On this basis, the distance Δ1 between S1 and S'1 is obtained, and Δ2 to Δ16 are also obtained for S2 to S16 and S'2 to S'16 in the same way respectively. Then, the value represented by {(Δ1 + Δ2 + ··· + Δ16) / 16} is obtained as the average value of the distance Δ. The results are shown in "Δave." of "thiogermanate crystal structure" in Table 1.

[0187] [Evaluation: Lithium ion conductivity]

[0188] The obtained sulfide solid electrolyte is made into a pressed powder body under a pressure of 380 kPa as a measurement sample, and measured using an alternating current impedance measurement device (manufactured by Bio-LLogic Sciences Instruments Co., Ltd., potentiostat / galvanostat VSP) to obtain the lithium ion conductivity. The measurement conditions are measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, and measurement temperature: 25 °C. The results are shown in "σ Li+ (mS / cm)" in Table 1.

[0189] [Table 1]

[0190]

[0191] Based on the above results, it can be known that the sulfide solid electrolytes of Example 1 and Example 2 have a PS with a structure deformed by introducing a tetrahedron with an average distance Δ within the range of 4 into the thiogermanate crystal structure of the space group F-43m, which was used in the past. The PS tetrahedron T 4 is formed. The above structural deformation is obtained by heating the raw material mixture at a temperature of 760 °C or higher to obtain a melt of an intermediate compound that is completely melted, and heat-treating the thiogermanate crystals precipitated by cooling the melt at 350 to 500 °C. 1 The lithium ion conductivities of the sulfide solid electrolytes of Example 1 and Example 2 are 7.0 mS / cm and 7.9 mS / cm in sequence. Compared with the lithium ion conductivity of 3.1 mS / cm of the sulfide solid electrolyte of Example 3, where the average value of the distance Δ is

[0192] and can be regarded as having no structural deformation, it shows excellent lithium ion conductivity. The present invention has been described in detail with reference to specific embodiments, but those skilled in the art can of course make various changes and modifications without departing from the spirit and scope of the present invention. This application is based on the Japanese Patent Application (Japanese Patent Application No. 2022-169459) filed on October 21, 2022, the content of which is incorporated herein by reference.

[0193] ​

Claims

1. A sulfide solid electrolyte containing Li element, P element, S element and Ha element, having a thiogermanate-type crystal structure, wherein the Ha element is at least one element selected from F, Cl, Br and I; The crystal structure has a plurality of PS with the P element as the center and 4 S elements as vertices. 4 Tetrahedron T 1 , A part of said PS 4 tetrahedron T 1 The P element of can be substituted with at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element and Ge element. A part of the said PS 4 tetrahedron T 1 At least a part of the said S element can be substituted with at least one element selected from the O element and the said Ha element, For the crystal structure, to become the PS 4 tetrahedron T 1 There are 16 elements at the vertices of the tetrahedron within the unit cell. When the 16 elements are made to correspond to 16 S elements at the vertices corresponding to the 16e positions of the PS 4 tetrahedron T 2 of the space group F-43m, the average value of the distances Δ between the positions of the 16 elements of the PS 4 tetrahedron T 1 and the positions of the corresponding 16 S elements of the PS 4 tetrahedron T 2 is 2. The sulfide solid electrolyte according to claim 1, wherein, The part of the PS 4 tetrahedron T 1 wherein the P element is replaced by the Si element.

3. The sulfide solid electrolyte according to claim 1, wherein, Said part of said PS 4 Tetrahedron T 1 At least part of the S element thereof is replaced by the O element.

4. The sulfide solid electrolyte according to claim 1, wherein, As the Ha element, it contains at least two selected from F, Cl, Br and I.

5. The sulfide solid electrolyte according to claim 1, wherein, The average value of the distance Δ is 6. The sulfide solid electrolyte according to claim 1, wherein, The unit cell has an axial length of and a space group P1 with axial angles α = β = γ = 90°.

7. An electrode mixture for a lithium ion secondary battery, comprising the sulfide solid electrolyte according to any one of claims 1 to 6 and an active material.

8. A solid electrolyte layer for a lithium ion secondary battery, comprising the sulfide solid electrolyte according to any one of claims 1 to 6.

9. A all-solid-state lithium ion secondary battery, comprising the sulfide solid electrolyte according to any one of claims 1 to 6.

10. A method for manufacturing a sulfide solid electrolyte, comprising the following steps: Mixing raw materials containing Li element, P element, S element and Ha element to obtain a raw material mixture, Heating the raw material mixture at a temperature of 760 °C or higher to obtain a melt of a completely melted intermediate compound, Cooling the melt to precipitate a thiogermanate-type crystal, and Performing heat treatment on the precipitated crystal at 350 - 500 °C; The Ha element is at least one element selected from F, Cl, Br and I, The sulfide solid electrolyte contains a thiogermanate-type crystal structure.

11. The method for manufacturing a sulfide solid electrolyte according to claim 10, wherein, The raw materials further contain at least one element selected from Si element, Al element, Sn element, In element, Cu element, Sb element, Ge element and O element.

12. The method for manufacturing a sulfide solid electrolyte according to claim 10 or 11, wherein, The heating at a temperature of 760 °C or higher is carried out under an inert atmosphere for 10 minutes to 10 hours.

13. The method for manufacturing a sulfide solid electrolyte according to claim 10 or 11, wherein, The heat treatment is carried out under an inert atmosphere for 10 minutes to 10 hours.

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