Solid electrolyte and lithium ion battery

Abstract

The solid electrolyte contains Li, M [alpha], M [beta], M [gamma], Cl, and A, where M [alpha] is at least one element selected from the group consisting of Zr and Hf, M [beta] is at least one element selected from the group consisting of Ta and Nb, M [gamma] is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc, and A is at least one element selected from the group consisting of OH <->, AlO2 <->, SO3 <->, SO4 < 2->, SiO3 < 2->, SiO4 < 4->, Si2O76 <->, CO3 < 2->, PO4 < 3->, P2O74 <->, BO2 <->, BO33 <->, PO3 <->, NO3 This makes it possible to provide a solid electrolyte having excellent reduction resistance.

Description

Technical Field

[0001] This invention relates to solid electrolytes and lithium-ion batteries. Background Technology

[0002] In recent years, there has been a strong demand for miniaturization and improved reliability (safety) of batteries used as power sources for electronic devices. Therefore, all-solid-state batteries using solid electrolytes have attracted considerable attention. As sulfur-free solid electrolytes, halides are known, with Li3YCl6 exhibiting high Li-ion conductivity at room temperature (see, for example, Japanese Patent No. 6934626 (Reference 1)). Furthermore, International Patent Publication No. 2020 / 070956 (Reference 2) discloses a method using Li... 6－4b＋ab (Zr) 1－a M a ) b X6 represents a halide solid electrolyte material. Here, M is at least one element selected from the group consisting of Al, Ga, Bi, Sc, Sm and Sb, and X is a halogen element, satisfying 0 < a < 1 and 0 < b < 1.5.

[0003] As mentioned above, chloride electrolytes such as Li3YCl6 exhibit high ionic conductivity at room temperature; however, information regarding their stability is not disclosed. The inventors of this invention prepared the solid electrolytes disclosed in documents 1 and 2 above and placed them in a dry chamber with a dew point controlled at -40°C. As a result, the electrolytes decomposed, indicating that they could not maintain their initial ionic conductivity, i.e., their stability (or moisture resistance) was low. Therefore, in order to improve the stability of the chloride electrolyte, the inventors of this invention... x In MCl6, materials were fabricated by combining various cations (M), and combinations of cations with high stability were explored. As a result, as explained below as a related technology, combinations of cations exhibiting high ionic conductivity and high stability were identified. On the other hand, in all-solid-state batteries, improving the reduction tolerance of the solid electrolyte is also required to increase energy density. Summary of the Invention

[0004] This invention relates to solid electrolytes, and its purpose is to provide solid electrolytes with excellent reduction tolerance.

[0005] Scheme 1 is a solid electrolyte comprising Li, Mα, Mβ, Mγ, Cl, and A, wherein Mα is at least one element selected from the group consisting of Zr and Hf, Mβ is at least one element selected from the group consisting of Ta and Nb, Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc, and A is an element selected from OH. － AlO2 － SO3 － 、SO4 2－SiO3 2－ SiO4 4－ Si2O7 6－ CO3 2－ PO4 3－ P2O7 4－ BO2 － BO3 3－ PO3 － NO3 － BF4 － PF6 － ClO4 － B(C2O4) 2－ CH3COO － TFSI － and FSI － At least one of the groups formed.

[0006] According to the present invention, a solid electrolyte with excellent reduction tolerance can be provided.

[0007] The invention of Scheme 2 is based on the solid electrolyte of Scheme 1, wherein Mα includes Zr.

[0008] The invention of Scheme 3 is based on the solid electrolyte of Scheme 1 or 2, wherein Mβ includes Ta.

[0009] The invention of Scheme 4 is based on the solid electrolyte of any one of Schemes 1 to 3, wherein Mγ includes Gd, Yb or Er.

[0010] The invention of Scheme 5 is based on the solid electrolyte of any one of Schemes 1 to 4, wherein A includes SO4. 2－ CO3 2－ PO4 3－ BO2 － BO3 3－ PO3 － NO3 － or TFSI － .

[0011] The invention of Scheme 6 is based on the solid electrolyte of any one of Schemes 1 to 5, and is represented by the following formula (1).

[0012] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl6·n(Mδ) x A y )···(1)

[0013] The following conditions must be met: 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, 0 < n, 0 < x, and 0 < y. When the valence of Mδ is set to s and the valence of A is set to t, s × x = t × y is satisfied. Mδ is at least one element selected from the group consisting of Li, Zr, Hf, Ta, Nb, Gd, Yb, Dy, Er, Ho, Eu, and Sc.

[0014] The invention of Scheme 7 is a lithium-ion battery that includes any one of the solid electrolytes of Schemes 1 to 6.

[0015] The above-mentioned objectives, as well as other objectives, features, solutions, and advantages, will become clear from the following detailed description of the invention with reference to the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a longitudinal cross-sectional view showing an all-solid-state lithium-ion secondary battery. Detailed Implementation

[0017] First, the solid electrolyte involved in the related technology of this invention will be described. The solid electrolyte involved in the related technology is a lithium (Li) ion conductive material, which contains lithium (Li) element, three other metal elements (Mα, Mβ, Mγ) that are cations, and chlorine (Cl) element.

[0018] Mα is an element with a tetravalent cation, and is selected from at least one element in the group consisting of zirconium (Zr) and hafnium (Hf). Mβ is an element with a pentavalent cation, and is selected from at least one element in the group consisting of tantalum (Ta) and niobium (Nb). Mγ is an element with a trivalent cation, and is selected from at least one element in the group consisting of gadolinium (Gd), ytterbium (Yb), dysprosium (Dy), erbium (Er), holmium (Ho), europium (Eu), and scandium (Sc). This solid electrolyte, which contains at least one trivalent, tetravalent, and pentavalent element as a cation in addition to Li, can achieve high ionic conductivity and high stability.

[0019] A preferred example of a solid electrolyte involved in the related technology is a compound represented by the following compositional formula.

[0020] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl6

[0021] It satisfies 0 < a, 0 < b, a + b < 1 and -0.2 ≤ c ≤ 0.2.

[0022] Next, a solid electrolyte according to one embodiment of the present invention will be described. This solid electrolyte is a Li ion-conducting material, obtained by combining a solid electrolyte according to the aforementioned related technologies with a metal salt of anion described later. This solid electrolyte is used, for example, in the manufacture of all-solid-state secondary batteries. The solid electrolyte contains Li, three other metals (Mα, Mβ, Mγ) that are cations, Cl, and A as an anion. The solid electrolyte may also consist only of Li, Mα, Mβ, Mγ, Cl, and A.

[0023] Similar to the solid electrolytes described above, Mα is an element with a tetravalent cation, and is at least one element selected from the group consisting of Zr and Hf. Mβ is an element with a pentavalent cation, and is at least one element selected from the group consisting of Ta and Nb. Mγ is an element with a trivalent cation, and is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc. Since the solid electrolytes described in this embodiment contain at least one trivalent, tetravalent, and pentavalent element in addition to Li as cations, they can also achieve high ionic conductivity and high stability.

[0024] Anion A is selected from OH- － AlO2 － SO3 － 、SO4 2－ SiO3 2－ SiO4 4－ Si2O7 6－ CO3 2－ PO4 3－ P2O7 4－ BO2 － BO3 3－ PO3 － NO3 － BF4 － PF6 － ClO4 － B(C2O4) 2－ CH3COO － TFSI － and FSI －At least one of the constituent elements. Anion A is also called a polyanion. Solid electrolytes containing anion A exhibit high reduction resistance, as described below. The metal element of the metal salt of anion A is preferably at least one element selected from the group consisting of Li, Zr, Hf, Ta, Nb, Gd, Yb, Dy, Er, Ho, Eu, and Sc. The metal element of the metal salt can also be other elements. Even when anion A contains sulfur (S), the solid electrolyte does not produce hydrogen sulfide gas because anion A is stable. Therefore, a highly safe all-solid-state secondary battery can be provided.

[0025] In the solid electrolyte of this embodiment, to more reliably achieve high reduction tolerance, Mα preferably includes Zr, but Mα may also be only Zr. Additionally, Mβ preferably includes Ta, but Mβ may also be only Ta. Furthermore, Mγ preferably includes Gd, Yb, or Er, but Mγ may also be only Gd, Yb, or Er. Mγ may include two or more elements selected from Gd, Yb, and Er. The mass of Li is, for example, greater than the mass of any one of Mα, Mβ, and Mγ, and preferably greater than the combined mass of Mα, Mβ, and Mγ. The mass of Cl is, for example, greater than the combined mass of Li, Mα, Mβ, and Mγ.

[0026] Anion A preferably includes SO4. 2－ CO3 2－ PO4 3－ BO2 － BO3 3－ PO3 － NO3 － or TFSI － It can also be just SO4 2－ CO3 2－ PO4 3－ BO2 － BO3 3－ PO3 － NO3 － or TFSI － Anion A can include two or more of these anions. The molar mass of anion A is, for example, smaller than that of Li.

[0027] The preferred solid electrolyte is a compound represented by the following formula (1).

[0028] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl6·n(Mδ) x A y )···(1)

[0029] The following conditions must be met: 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, 0 < n, 0 < x, and 0 < y. Furthermore, when the valence of Mδ is set to s and the valence of A is set to t, s × x = t × y is satisfied. Additionally, Mδ is at least one element selected from the group consisting of Li, Zr, Hf, Ta, Nb, Gd, Yb, Dy, Er, Ho, Eu, and Sc. Regarding a and b, 0.1 ≤ a ≤ 0.5 and 0.1 ≤ b ≤ 0.4 are satisfied. Additionally, 0.2 ≤ a + b ≤ 0.8 is satisfied. The relationship between a and b can be a ≥ b or a < b. Regarding c, -0.1 ≤ c ≤ 0.1 is satisfied, and c can be 0. Regarding n, 0 < n ≤ 3 or 0 < n ≤ 2 is satisfied. This solid electrolyte can be crystalline or amorphous.

[0030] When confirming whether an unknown solid electrolyte is the solid electrolyte involved in this embodiment, a chemical analysis is performed on the unknown solid electrolyte to confirm whether the constituent elements are Li, Mα, Mβ, Mγ, Cl, and A. In confirming whether the unknown solid electrolyte is the one in formula (1) above, for example, Li, Mα, Mβ, and Mγ can be quantified using ICP-luminescence spectrophotometry. For example, Cl can be quantified using ion chromatography. For the constituent element of the anion A, an appropriate determination method for quantifying the element is selected. For example, O, N, and H can be quantified using ONH analysis with an oxygen, nitrogen, and hydrogen analyzer. For example, F can be quantified using ion chromatography. For example, C can be quantified using a carbon and sulfur analyzer (CS meter). Other elements can be quantified using ICP-luminescence spectrophotometry.

[0031] The molar ratio of Li, Mα, Mβ, Mγ, Cl, Mδ, and A in equation (1) above is Li:Mα:Mβ:Mγ:Cl:Mδ:A = 6 - (4 + a - b)(1 + c): (1 - a - b)(1 + c): a(1 + c): b(1 + c): 6:nx:ny. In the molar ratios obtained by analyzing unknown solid electrolytes, if the value of Li is 0.90 × {6 - (4 + a - b)(1 + c)} or higher and 1.10 × {6 - (4 + a - b)(1 + c)} or lower, then Li is considered to satisfy equation (1) above. More preferably, the value of Li is 0.95 × {6 - (4 + a - b)(1 + c)} or higher and 1.05 × {6 - (4 + a - b)(1 + c)} or lower. The same applies to Mα, Mβ, Mγ, Cl, Mδ, and A.

[0032] The solid electrolyte involved in this embodiment is manufactured, for example, using the following method. First, powders containing Li chloride, Mα chloride, Mβ chloride, and Mγ chloride are prepared. The Li chloride is, for example, LiCl. The Mα chloride is, for example, MαCl4. The Mβ chloride is, for example, MβCl5. The Mγ chloride is, for example, MγCl3. These powders are weighed and mixed according to a predetermined molar ratio.

[0033] After preparing the mixture, it is subjected to milling (mechanical-chemical milling). In one example of this milling process, a planetary ball mill is used. In a planetary ball mill, the jar rotates while the worktable carrying the jar revolves, thus generating very high impact energy. Milling can also be performed using other types of pulverizers. Through the above milling process, a solid electrolyte containing Li, Mα, Mβ, Mγ, and Cl is obtained. This solid electrolyte is a pre-composite solid electrolyte (the solid electrolyte involved in the aforementioned related technologies), and in the following description, the synthesis of this solid electrolyte is also referred to as "pre-synthesis." In this example, the milling process is performed at room temperature; however, conditions such as temperature can be appropriately modified.

[0034] Next, the metal salt of anion A and the pre-synthesized solid electrolyte are weighed and mixed at a specified molar ratio. Then, similar to the above operation, the mixture is milled to obtain the solid electrolyte according to this embodiment. This solid electrolyte is obtained by combining a pre-synthesized solid electrolyte with the metal salt of the anion. This solid electrolyte is used in the all-solid-state secondary battery 1 described later (see...). Figure 1 The manufacturing of the positive electrode layer 112, negative electrode layer 122, or electrolyte layer 13 in the solid electrolyte. In the manufacturing of the solid electrolyte according to this embodiment, it is not necessarily necessary to synthesize the solid electrolyte (a solid electrolyte without anion A) beforehand. By milling a mixture obtained by mixing the raw materials of the pre-synthesized solid electrolyte (e.g., LiCl, MαCl4, MβCl5, MγCl3) and a metal salt of anion A, a composite solid electrolyte can be manufactured without prior synthesis. Alternatively, this solid electrolyte can also be manufactured using operations other than milling, such as sintering.

[0035] Figure 1 This is a longitudinal cross-sectional view showing an all-solid-state lithium-ion secondary battery 1 (hereinafter referred to as "all-solid-state secondary battery 1"). The all-solid-state secondary battery 1 uses the solid electrolyte according to this embodiment. The all-solid-state secondary battery 1... Figure 1The electrode has a positive electrode 11, an electrolyte layer 13, and a negative electrode 12 arranged sequentially on top of it. Specifically, the electrolyte layer 13 is disposed between the positive electrode 11 and the negative electrode 12. The electrolyte layer 13 is a solid electrolyte layer and also serves as a separator layer. The electrolyte layer 13 is composed of, or contains, the solid electrolyte involved in this embodiment. The positive electrode 11 includes a current collector 111 and a positive electrode layer 112. The positive electrode layer 112 contains a positive electrode active material. The negative electrode 12 includes a current collector 121 and a negative electrode layer 122. The negative electrode layer 122 contains a negative electrode active material.

[0036] The positive electrode active material of the positive electrode layer 112 preferably comprises a lithium composite oxide. The preferred positive electrode active material is a lithium composite oxide with a layered rock salt structure, such as NCM (Li(Ni,Co,Mn)O2). Other lithium composite oxides can also be used, such as NCA (Li(Ni,Co,Al)O2) or LCO (LiCoO2) with a layered rock salt structure, or LNMO (LiNiO2) with a spinel-type structure. 0.5 Mn 1.5 O4), LFP (LiFePO4) with an olivine-type structure, etc. In addition to containing the positive electrode active material, the positive electrode layer 112 also contains the solid electrolyte involved in this embodiment. The positive electrode layer 112 may further contain an electron conduction aid (carbon black, etc.). One example of the positive electrode layer 112 is obtained by integrating these materials using pressure and heating.

[0037] Examples of negative electrode active materials used as negative electrode layer 122 include: LTO (Li4Ti5O) 12 Compounds such as NTO (Nb2TiO7), TiO2 (titanium oxide), graphite, and SiO (silicon monoxide) are used. The negative electrode layer 122 contains, in addition to the negative electrode active material, the solid electrolyte involved in this embodiment. The negative electrode layer 122 may further contain an electron conduction aid (carbon black, etc.). One example of the negative electrode layer 122 is obtained by integrating these materials using pressure and heating. The composition and materials of the positive electrode 11 and negative electrode 12 of the all-solid-state secondary battery 1 are not limited to the above-described composition and materials, and various other compositions and materials can be used.

[0038] Next, examples and comparative examples of solid electrolytes will be described. Table 1 shows the composition and evaluation results of the solid electrolytes of Examples 1 to 10 and Comparative Example 1. It should be noted that the solid electrolyte of Comparative Example 1 is the solid electrolyte involved in the above-described related art.

[0039] [Table 1]

[0040]

[0041] (Example 1)

[0042] [Prior synthesis of solid electrolytes]

[0043] In an argon atmosphere with a dew point below -60°C, LiCl, ZrCl4, TaCl5, and YbCl3, used as raw material powders, were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:YbCl3 = 2.0:0.6:0.2:0.2, and then pulverized and mixed in a mortar. The resulting mixture was placed in a zirconia container and milled using a planetary ball mill at 300 rpm for 20 hours, while a chloride-based solid electrolyte was synthesized beforehand.

[0044] [Complexation with Li salts containing polyanions]

[0045] In an argon atmosphere with a dew point below -60°C, the pre-synthesized solid electrolyte and Li₂SO₄ were weighed at a molar ratio of 1:0.15 and pulverized and mixed in a mortar. The resulting mixture was placed in a zirconia container and milled using a planetary ball mill at 300 rpm for 20 hours to obtain a solid electrolyte containing polyanions.

[0046] [Reduction Stability Evaluation]

[0047] Solid electrolyte powder was placed in a mold consisting of a resin sleeve and upper and lower SUS (stainless steel) punches, and uniaxially pressed under pressure of 150 MPa. Afterward, the lower punch was removed, Li metal foil was adhered to the surface of the pressed powder, and the lower punch was reinserted, with pressure applied at 50 MPa. Wires were connected to the upper and lower punches, and cyclic voltammetry was performed at room temperature.

[0048] In cyclic voltammetry measurements, the scan rate was set to 1 mV / sec, and the active electrode was scanned from the Open Circuit Voltage (OCV) at the time of single-cell construction towards the reduction direction up to -1.0 V (vs. Li). To quantify the stability of the reduction potential, the reduction current per unit area of ​​the active electrode was increased to over -20 μV / cm² during the scan from OCV towards the reduction direction. 2 The potential at that time is set as the reduction start potential. The obtained values ​​are shown in the "Reduction Start Potential" column in Table 1.

[0049] In addition, the charge generated during reduction stability evaluation was calculated. Using the action potential of graphite (0.1V vs. Li), a common negative electrode active material in lithium-ion batteries, as a benchmark, the reduction current flowing from the reduction initiation potential to 0.1V was added to calculate the charge (unit: coulomb [C]), thereby quantitatively evaluating the stability of the negative electrode potential. Table 1 shows the obtained values ​​in the "Decomposition Charge Reaching 0.1V" column.

[0050] (Example 2)

[0051] In the process of combining the electrolyte with the polyanionic Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and Li2SO4 were weighed at a molar ratio of 1:0.33. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0052] (Example 3)

[0053] In the process of combining the electrolyte with the polyanion-containing Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and Li2SO4 were weighed at a molar ratio of 1:1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0054] (Example 4)

[0055] In the process of combining the electrolyte with the polyanion-containing Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and Li2CO3 were weighed at a molar ratio of 1:1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0056] (Example 5)

[0057] In the process of combining the electrolyte with the polyanion-containing Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and Li3PO4 were weighed at a molar ratio of 1:1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0058] (Example 6)

[0059] In the process of combining the electrolyte with the polyanion-containing Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and Li3BO3 were weighed at a molar ratio of 1:1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0060] (Example 7)

[0061] In the process of combining the electrolyte with the polyanion-containing Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and LiPO3 were weighed at a molar ratio of 1:1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0062] (Example 8)

[0063] In the process of combining the electrolyte with the polyanion-containing Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and LiBO2 were weighed at a molar ratio of 1:1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0064] (Example 9)

[0065] In the process of combining the electrolyte with the polyanion-containing Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and LiNO3 were weighed at a molar ratio of 1:1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0066] (Example 10)

[0067] In the process of combining the electrolyte with the polyanionic Li salt in the preparation of the electrolyte in Example 1 above, the pre-synthesized solid electrolyte and LiTFSI were weighed at a molar ratio of 1:0.5. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0068] (Comparative Example 1)

[0069] The complexation with Li salts containing polyanions was omitted, and the pre-synthesized solid electrolyte was tested and evaluated.

[0070] As shown in Table 1, compared with the uncomposite solid electrolyte of Comparative Example 1, the solid electrolytes of Examples 1-10, obtained by combining the pre-synthesized solid electrolyte with the polyanion (metal salt), showed a decrease in reduction onset potential and a reduction in the amount of charge required to reach 0.1V. Thus, it was confirmed that by combining the pre-synthesized solid electrolyte with the polyanion, the reduction decomposition reaction of the solid electrolyte was suppressed, and the reduction tolerance was improved.

[0071] The reason for the increased reduction tolerance in the solid electrolyte obtained through complexation is not necessarily clear. However, complexation with polyanions leads to disordered crystal structure and amorphization of the pre-synthesized solid electrolyte. It is believed that through this disordered crystal structure, cations can interact not only with Cl- but also with polyanions, achieving stabilization. It is presumed that such structural changes contribute to improved reduction tolerance.

[0072] Furthermore, in Examples 1 to 3, which used the same type of polyanion, the ratio of the mass of the polyanion's metal salt to the mass of the pre-synthesized solid electrolyte was varied, and it was confirmed that the reduction tolerance increased with increasing ratio. Therefore, this ratio is preferably 0.33 or higher, and more preferably 0.5 or higher. This ratio can be 1 or higher, and it is considered that the amount of polyanion added is effective in improving reduction tolerance within a wide range. From the viewpoint of improving reduction tolerance, there is no particular upper limit to this ratio, but from the viewpoint of ideally maintaining the characteristics of the pre-synthesized solid electrolyte, this ratio is, for example, 3 or lower, and preferably 2 or lower.

[0073] It is believed that even if the type of polyanion changes, the mechanism for increased reduction tolerance remains the same. Therefore, it is thought that OH was used as a polyanion. － AlO2 － SO3 － SiO3 2－ SiO4 4－ Si2O7 6－ P2O7 4－ BF4 － PF6 － 、ClO4 － B(C2O4) 2－ CH3COO － and FSI － In any of the cases, reduction tolerance is improved.

[0074] Regarding pre-synthesized solid electrolytes, it is believed that when Hf, which is a tetravalent cation like Zr, is used instead of Zr or in combination with Zr, the reduction tolerance is similarly improved due to its complexation with polyanions. Similarly, the same applies when Nb, which is a pentavalent cation like Ta and has the same ionic radius as Ta, is used instead of Ta or in combination with Ta. Furthermore, the same applies when Gd, Dy, Er, Ho, Eu, and Sc, which are trivalent cations like Yb and have ionic radii similar to Yb, are used instead of Yb or in combination with Yb.

[0075] As explained above, the solid electrolyte involved in this embodiment includes Li, Mα, Mβ, Mγ, Cl, and A. Mα is at least one element selected from the group consisting of Zr and Hf. Mβ is at least one element selected from the group consisting of Ta and Nb. Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc. A is selected from OH... － AlO2 － SO3 － 、SO4 2－ SiO32－ SiO4 4－ Si2O7 6－ CO3 2－ PO4 3－ P2O7 4－ BO2 － BO3 3－ PO3 － NO3 － BF4 － PF6 － ClO4 － B(C2O4) 2－ CH3COO － TFSI － and FSI － At least one of the constituent groups. By optimizing the types and combinations of Mα, Mβ, Mγ, and A in this way, a solid electrolyte with excellent reduction tolerance can be achieved. In this solid electrolyte, the potential window is widened, thus alleviating the limitation on the operating voltage when this solid electrolyte is applied to the all-solid-state secondary battery 1, and improving the energy density of the all-solid-state secondary battery 1.

[0076] Preferred option A includes SO4 2－ CO3 2－ PO4 3－ BO2 － BO3 3－ PO3 － NO3 － or TFSI － This allows for a more reliable improvement in the reduction tolerance of solid electrolytes.

[0077] The preferred solid electrolyte is represented by the following formula (1),

[0078] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl6·n(Mδ) x A y )···(1)

[0079] The following conditions must be met: 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, 0 < n, 0 < x, and 0 < y. Furthermore, when the valence of Mδ is set to s and the valence of A is set to t, s × x = t × y is satisfied. Additionally, Mδ is at least one element selected from the group consisting of Li, Zr, Hf, Ta, Nb, Gd, Yb, Dy, Er, Ho, Eu, and Sc. This allows for the more reliable realization of solid electrolytes with excellent reduction tolerance.

[0080] Various modifications can be made to the above-mentioned solid electrolyte and all-solid secondary battery 1.

[0081] Solid electrolytes containing Li, Mα, Mβ, Mγ, Cl and A may not satisfy the above equation (1).

[0082] Solid electrolytes can be mixed with other substances (which may include Li) to be used as electrolyte materials. In this case, the solid electrolyte is preferably the component with the largest mass percentage in the electrolyte material, i.e., the main component. The mass percentage of the main component in the electrolyte material is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0083] The solid electrolyte used in the all-solid-state secondary battery 1 does not necessarily need to be included in all of the positive electrode 11, negative electrode 12, and electrolyte layer 13; it is sufficient that it is included in at least one of the positive electrode 11, negative electrode 12, and electrolyte layer 13. In addition, the solid electrolyte can also be used in batteries other than all-solid-state secondary batteries, and can also be used for purposes other than batteries.

[0084] The components in the above-described embodiments and their variations can be appropriately combined as long as they do not contradict each other.

[0085] Although the invention has been described and illustrated in detail, the description is illustrative and not limiting. Therefore, it can be said that numerous modifications and solutions can be adopted without departing from the scope of the invention.

[0086] Explanation of reference numerals in the attached figures

[0087] 1. All-solid-state lithium-ion secondary battery

[0088] 11 Positive electrode

[0089] 12 Negative electrode

[0090] 13 Electrolyte layer

Claims

1. A solid electrolyte, wherein, Includes Li, Mα, Mβ, Mγ, Cl, and A. Mα is selected from at least one element in the group consisting of Zr and Hf. Mβ is selected from at least one element in the group consisting of Ta and Nb. Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc. A is selected from OH. － AlO2 － SO3 － SO4 2－ SiO3 2－ SiO4 4－ Si2O7 6－ CO3 2－ PO4 3－ P2O7 4－ BO2 － BO3 3－ PO3 － NO3 － BF4 － PF6 － ClO4 － B(C2O4) 2－ CH3COO － TFSI － and FSI － At least one of the groups formed.

2. The solid electrolyte according to claim 1, wherein, Mα includes Zr.

3. The solid electrolyte according to claim 1, wherein, Mβ includes Ta.

4. The solid electrolyte according to claim 1, wherein, Mγ includes Gd, Yb, or Er.

5. The solid electrolyte according to claim 1, wherein, A includes SO4 2－ CO3 2－ PO4 3－ BO2 － BO3 3－ PO3 － NO3 － or TFSI － .

6. The solid electrolyte according to claim 1, wherein, The following formula (1) represents, Li 6－（4＋a－b）（1＋c） (But) （1－a－b） Mb a Mg b ) 1＋c Cl6·n(Mδ x A y )···(1) When the following conditions are met: 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, 0 < n, 0 < x, and 0 < y, and the valence of Mδ is set to s and the valence of A is set to t, then s × x = t × y is satisfied. Mδ is selected from at least one element chosen from the group consisting of Li, Zr, Hf, Ta, Nb, Gd, Yb, Dy, Er, Ho, Eu, and Sc.

7. A lithium-ion battery comprising the solid electrolyte according to any one of claims 1 to 6.

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