Solid electrolytes and lithium-ion batteries

Abstract

This solid electrolyte includes 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 at least one type of group selected from the group consisting of 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–. As a result, it is possible to provide a solid electrolyte having excellent reduction resistance.

Description

[[Technical Field]]

[0001] The present invention relates to a solid electrolyte and a lithium ion battery. [[Background Art]]

[0002] In recent years, there has been a strong demand for miniaturization and improved reliability (safety) for batteries that serve as power sources for electronic devices. For this reason, all-solid-state batteries using solid electrolytes have attracted attention. Halides are known as sulfur-free solid electrolytes, and Li3YCl6 exhibits high Li ion conductivity at room temperature (see, for example, Japanese Patent No. 6934626 (Document 1)). Furthermore, in International Publication No. WO 2020 / 070956 (Document 2), Li 6-4b+ab (Zr 1-a M a ) b A halide solid electrolyte material represented by X6 is disclosed. Here, M is at least one element selected from the group consisting of Al, Ga, Bi, Sc, Sm and Sb, X is a halogen element, and 0<a<1 and 0<b<1.5 are satisfied.

[0003] As mentioned above, although chloride electrolytes such as Li3YCl6 exhibit high ionic conductivity at room temperature, information regarding their stability is not disclosed. When the inventors of the present application produced the solid electrolytes disclosed in Documents 1 and 2 above and allowed them to stand in a dry room controlled at a dew point of -40°C, the electrolytes decomposed and the initial ionic conductivity could not be maintained, that is, it was found that the stability (or moisture resistance) is low. Accordingly, in order to improve the stability of chloride electrolytes, the inventors of the present application produced Li x In MCl6, materials were prepared by combining various cations (M), and a combination of cations with high stability was searched for. As a result, as described later in the related art, a combination of cations that exhibits high ionic conductivity and high stability was identified. On the other hand, in all-solid-state batteries, in order to improve energy density, it is also required to improve the reduction resistance of solid electrolytes. [[Summary of Invention]]

[0004] The present invention is directed to a solid electrolyte, and aims to provide a solid electrolyte excellent in reduction resistance.

[0005] The invention of aspect 1 is a solid electrolyte comprising Li, Mα, Mβ, Mγ, Cl , Mδ 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, and Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu and Sc, 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, A is 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 - is at least one selected from the group consist and the solid electrolyte is represented by the following formula (1), Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl 6 ·n(Mδ x A y )···(1) 0<a, 0<b, a+b<1, -0.2≤c≤0.2, 0<n, 0<x, and 0<y are satisfied, and when the valence of Mδ is s and the valence of A is t, s×x=t×y is satisfied ing of.

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

[0007] The invention of embodiment 2 is the solid electrolyte of embodiment 1, wherein Mα contains Zr.

[0008] The invention of embodiment 3 is a solid electrolyte according to embodiment 1 or 2, wherein Mβ contains Ta.

[0009] The invention of embodiment 4 is a solid electrolyte according to any one of embodiments 1 to 3, wherein Mγ comprises Gd, Yb, or Er.

[0010] The invention of embodiment 5 is a solid electrolyte according to any one of embodiments 1 to 4, wherein A is SO4 2- CO3 2- , PO4 3- , BO2 - , BO3 3- , PO3 - NO3 - or TFSI - Includes.

[0012] manner 6 The invention is described in aspects 1 to 5 It is a lithium-ion battery containing one of the following solid electrolytes.

[0013] The aforementioned objectives, as well as other objectives, features, embodiments, and advantages, will be revealed by the detailed description of the present invention below, with reference to the attached drawings. [Brief explanation of the drawing]

[0014] [Fig. 1] This is a longitudinal cross-sectional view showing an all-solid-state lithium-ion secondary battery. [Modes for carrying out the invention]

[0015] First, a solid electrolyte according to the related art of the present invention will be described. The solid electrolyte according to the related art is a lithium (Li) ion conductive material, and contains a lithium (Li) element, three other types of metal (Mα, Mβ, Mγ) elements serving as cations, and a chlorine (Cl) element.

[0016] Mα is an element that forms a tetravalent cation, and is at least one element selected from the group consisting of zirconium (Zr) and hafnium (Hf). Mβ is an element that forms a pentavalent cation, and is at least one element selected from the group consisting of tantalum (Ta) and niobium (Nb). Mγ is an element that forms a trivalent cation, and is at least one element selected from the group consisting of gadolinium (Gd), ytterbium (Yb), dysprosium (Dy), erbium (Er), holmium (Ho), europium (Eu) and scandium (Sc). In the solid electrolyte containing at least one each of trivalent, tetravalent, and pentavalent elements as cations in addition to Li, high ionic conductivity and high stability are achieved.

[0017] A preferred example of the solid electrolyte according to the related art is a compound represented by the following composition formula, Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6 0<a, 0<b, a+b<1, and -0.2≦c≦0.2 are satisfied.

[0018] Next, a solid electrolyte according to one embodiment of the present invention will be described. The solid electrolyte is a Li ion conductive material, and is a composite of the solid electrolyte according to the above related art and a metal salt of an anion described later. The solid electrolyte is used, for example, in the manufacture of an all-solid-state secondary battery. The solid electrolyte contains a Li element, three other types of metal (Mα, Mβ, Mγ) elements serving as cations, a Cl element, and A that is an anion. The solid electrolyte may be composed only of Li, Mα, Mβ, Mγ, Cl and A.

[0019] Similar to the solid electrolytes related to the above-mentioned technologies, Mα is an element that forms a tetravalent cation and is at least one element selected from the group consisting of Zr and Hf. Mβ is an element that forms a pentavalent cation and is at least one element selected from the group consisting of Ta and Nb. Mγ is an element that forms a trivalent cation and is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu and Sc. Because the solid electrolyte contains at least one each of trivalent, tetravalent, and pentavalent elements in addition to Li as cations, high ionic conductivity and high stability are achieved in the solid electrolyte according to this embodiment.

[0020] Anion A is 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 - It is at least one selected from the group consisting of [list of elements]. Anion A is also called a polyanion. A solid electrolyte containing anion A has high reduction resistance, as will be described later. 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 may be any other element. Even if anion A contains sulfur (S), anion A is stable, so hydrogen sulfide gas is not generated in the solid electrolyte. Therefore, a highly safe all-solid-state secondary battery can be provided.

[0021] In the solid electrolyte according to the present embodiment, to more reliably achieve high reduction resistance, Mα preferably contains Zr, and Mα may be only Zr. In addition, Mβ preferably contains Ta, and Mβ may be only Ta. Further, Mγ preferably contains Gd, Yb or Er, and Mγ may be only Gd, Yb or Er. Mγ may contain two or more elements selected from Gd, Yb and Er. The molar amount of Li is, for example, greater than the molar amount of any of Mα, Mβ and Mγ, and preferably greater than the total molar amount of Mα, Mβ and Mγ. The molar amount of Cl is, for example, greater than the total molar amount of Li, Mα, Mβ and Mγ.

[0022] The anion A is preferably SO4 2- , CO3 2- , PO4 3- , BO2 - , BO3 3- , PO3 - , NO3 - or TFSI - , and may be only SO4 2- , CO3 2- , PO4 3- , BO2 - , BO3 3- , PO3 - , NO3 - or TFSI - . The anion A may contain two or more types of these anions. The molar amount of anion A is, for example, smaller than the molar amount of Li.

[0023] A preferred solid electrolyte is a compound represented by the following formula (1): Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6·n(Mδ x A y )···(1) 0 < a, 0 < b, a + b < 1, -0.2 ≦ c ≦ 0.2, 0 < n, 0 < x, and 0 < y are satisfied. Further, when the valence of Mδ is s and the valence of A is t, s×x = t×y is satisfied. Furthermore, 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. For a and b, 0.1 ≦ a ≦ 0.5 and 0.1 ≦ b ≦ 0.4 may be satisfied. Further, 0.2 ≦ a + b ≦ 0.8 may be satisfied. The relationship between a and b may satisfy a ≧ b or a < b. For c, -0.1 ≦ c ≦ 0.1 may be satisfied, and c may be 0. For n, 0 < n ≦ 3 may be satisfied, or 0 < n ≦ 2 may be satisfied. The solid electrolyte may be crystalline or amorphous.

[0024] When confirming whether an unknown solid electrolyte is the solid electrolyte according to the present embodiment, chemical analysis is performed on the unknown solid electrolyte to confirm whether the constituent elements are Li, Mα, Mβ, Mγ, Cl, and the constituent elements of A. In confirming whether an unknown solid electrolyte satisfies the above formula (1), Li, Mα, Mβ, and Mγ can be quantified, for example, by ICP-optical emission spectrometry or the like. Cl can be quantified, for example, by ion chromatography or the like. For the constituent elements of the anion A, a measurement method capable of quantifying the element is appropriately selected. O, N, and H can be quantified, for example, by ONH analysis using an oxygen-nitrogen-hydrogen analyzer, and F can be quantified, for example, by ion chromatography or the like. C can be quantified, for example, by a carbon-sulfur analyzer (CS meter) or the like, and other elements can be quantified by ICP-optical emission spectrometry or the like.

[0025] In equation (1) above, the molar ratios of Li, Mα, Mβ, Mγ, Cl, Mδ, and A are Li:Mα:Mβ:Mγ:Cl:Mδ:A = 6-(4+ab)(1+c):(1-ab)(1+c):a(1+c):b(1+c):6:nx:ny. In the molar ratios determined by analysis of an unknown solid electrolyte, if the value of Li is 0.90×{6-(4+ab)(1+c)} or greater and 1.10×{6-(4+ab)(1+c)} or less, then equation (1) above is considered to be satisfied for Li. It is more preferable that the value of Li is 0.95×{6-(4+ab)(1+c)} or greater and 1.05×{6-(4+ab)(1+c)} or less. The same applies to Mα, Mβ, Mγ, Cl, Mδ, and A.

[0026] The solid electrolyte according to this embodiment is manufactured, for example, by the following method. First, a chloride powder containing Li, a chloride powder containing Mα, a chloride powder containing Mβ, and a chloride powder containing Mγ are prepared. The chloride containing Li is, for example, LiCl. The chloride containing Mα is, for example, MαCl4. The chloride containing Mβ is, for example, MβCl5. The chloride containing Mγ is, for example, MγCl3. These powders are weighed and mixed in a predetermined molar ratio.

[0027] Once the mixture is prepared, it is subjected to milling (mechanochemical milling). In one example of milling, a planetary ball mill is used. In a planetary ball mill, the pot rotates on its own axis while the stage on which the pot rests revolves, making it possible to generate very high impact energy. Milling may also be carried out using other types of grinders. The above milling process yields a solid electrolyte containing Li, Mα, Mβ, Mγ, and Cl. This solid electrolyte is the solid electrolyte before compounding (the solid electrolyte related to the above-mentioned related technologies), and in the following description, the synthesis of this solid electrolyte will also be referred to as "pre-synthesis". In this example, the milling process is carried out at room temperature, but the temperature and other conditions may be changed as appropriate.

[0028] Next, the metal salt of anion A and the pre-synthesized solid electrolyte are weighed and mixed in a predetermined molar ratio. Then, the mixture is milled in the same manner as described above to obtain the solid electrolyte according to this embodiment. This solid electrolyte is a composite of the pre-synthesized solid electrolyte and the metal salt of the anion. This solid electrolyte is used in the manufacture of the positive electrode layer 112, the negative electrode layer 122, or the electrolyte layer 13 in the all-solid-state secondary battery 1 (see Figure 1) described later. In the manufacture of the solid electrolyte according to this embodiment, it is not necessarily required that the solid electrolyte (solid electrolyte without anion A) be pre-synthesized. A composite solid electrolyte may be manufactured without pre-synthesis by milling a mixture of the raw materials for the solid electrolyte used in pre-synthesis (e.g., LiCl, MαCl4, MβCl5, MγCl3) and the metal salt of anion A. Furthermore, this solid electrolyte may be manufactured by methods other than milling, such as calcination.

[0029] Figure 1 is a longitudinal cross-sectional view showing an all-solid-state lithium-ion secondary battery 1 (hereinafter simply referred to as "all-solid-state secondary battery 1"). The all-solid-state secondary battery 1 uses a solid electrolyte according to this embodiment. The all-solid-state secondary battery 1 has, in order from top to bottom in Figure 1, a positive electrode 11, an electrolyte layer 13, and a negative electrode 12. That is, the electrolyte layer 13 is provided 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 consists of or contains the solid electrolyte according to 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.

[0030] The positive electrode active material of the positive electrode layer 112 preferably contains a lithium composite oxide. A preferred positive electrode active material is a lithium composite oxide having a layered rock salt structure, for example, NCM(Li(Ni,Co,Mn)O2). The positive electrode active material may also be other lithium composite oxides, for example, NCA(Li(Ni,Co,Al)O2) having a layered rock salt structure, LCO(LiCoO2), and LNMO(LiNi) having a spinel-type structure. 0.5 Mn1.5 The material may be O4, or an LFP (LiFePO4) having an olivine-type structure. The positive electrode layer 112 contains a solid electrolyte according to this embodiment in addition to the positive electrode active material. The positive electrode layer 112 may further contain an electron conduction aid (such as carbon black). An example of the positive electrode layer 112 is obtained by integrating these materials by pressurization or heating.

[0031] For example, LTO(Li4Ti5O) is used as the negative electrode active material for the negative electrode layer 122. 12 Compounds such as ), NTO (Nb2TiO7), TiO2 (titanium dioxide), graphite, and SiO (silicon monoxide) are examples. The negative electrode layer 122 contains the solid electrolyte according to this embodiment in addition to the negative electrode active material. The negative electrode layer 122 may further contain an electron conduction aid (such as carbon black). An example of the negative electrode layer 122 is obtained by integrating these materials by pressurization or heating. The configuration and materials of the positive electrode 11 and negative electrode 12 of the all-solid-state secondary battery 1 are not limited to those described above, and various other configurations and materials can be used.

[0032] Next, examples and comparative examples of solid electrolytes will be described. Table 1 shows the composition and evaluation results of the solid electrolytes for Examples 1 to 10 and Comparative Example 1. The solid electrolyte for Comparative Example 1 is the solid electrolyte related to the above-mentioned related technology.

[0033] [Table 1]

[0034] (Example 1) [Pre-synthesis of solid electrolytes] In an argon atmosphere with a dew point of -60°C or lower, LiCl, ZrCl4, TaCl5, and YbCl3 were weighed out as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:YbCl3 = 2.0:0.6:0.2:0.2, and these raw material powders were ground and mixed in a mortar. The resulting mixture was placed in a zirconia pot and milled at 300 rpm for 20 hours using a planetary ball mill to pre-synthesize a chloride-based solid electrolyte.

[0035] [Compounding with Li salts containing polyanions] In an argon atmosphere with a dew point of -60°C or lower, the solid electrolyte pre-synthesized above and Li2SO4 were weighed in a molar ratio of 1:0.15, and these were ground and mixed in a mortar. The resulting mixed powder was placed in a zirconia pot and milled at 300 rpm for 20 hours using a planetary ball mill to obtain a solid electrolyte containing polyanions.

[0036] [Evaluation of reduction stability] Solid electrolyte powder was placed in a mold consisting of a resin sleeve and upper and lower punches made of SUS (stainless steel), and uniaxial press molding was performed under pressure of 150 MPa. Afterward, the lower punch was removed, Li metal foil was applied to the surface of the compacted molded body, and the lower punch was reinserted and pressurized at 50 MPa. Wires were connected to the upper and lower punches, and cyclic voltammetry measurements were performed at room temperature.

[0037] In the cyclic voltammetry measurement, the scan speed was set to 1 mV / sec, and the working electrode was scanned from the OCV (Open Circuit Voltage) at the time of cell construction down to -1.0 V (vs. Li) in the reduction direction. To quantify the stability with respect to the reduction potential, the reduction current per unit area of ​​the working electrode was measured to be -20 μA / cm² when scanning from OCV in the reduction direction. 2 The potential at which the value exceeded a certain threshold was defined as the reduction initiation potential. In Table 1, the obtained values ​​are shown in the "Reduction Initiation Potential" column.

[0038] Furthermore, in the reduction stability evaluation, the amount of electricity generated by reductive decomposition was calculated. Using the operating potential of graphite, which is common as the negative electrode active material of lithium-ion batteries (0.1V vs. Li), as a reference, the amount of electricity (unit: coulombs [C]) accumulated from the reduction initiation potential up to 0.1V was calculated to quantitatively evaluate the stability of the negative electrode with respect to potential. In Table 1, the obtained values ​​are shown in the column "Amount of electricity generated by decomposition up to 0.1V".

[0039] (Example 2) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and Li2SO4 were weighed in a molar ratio of 1:0.33 during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0040] (Example 3) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and Li2SO4 were weighed in a 1:1 molar ratio during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0041] (Example 4) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and Li2CO3 were weighed in a 1:1 molar ratio during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0042] (Example 5) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and Li3PO4 were weighed in a 1:1 molar ratio during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0043] (Example 6) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and Li3BO3 were weighed in a 1:1 molar ratio during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0044] (Example 7) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and LiPO3 were weighed in a 1:1 molar ratio during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0045] (Example 8) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and LiBO2 were weighed in a 1:1 molar ratio during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0046] (Example 9) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and LiNO3 were weighed in a 1:1 molar ratio during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0047] (Example 10) In the electrolyte preparation process of Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the pre-synthesized solid electrolyte and LiTFSI were weighed in a molar ratio of 1:0.5 during the compounding process with the polyanion-containing Li salt. The electrolyte was then tested and evaluated.

[0048] (Comparative Example 1) The process of compounding with a polyanion-containing Li salt was omitted, and the pre-synthesized solid electrolyte was tested and evaluated.

[0049] As shown in Table 1, the solid electrolytes of Examples 1 to 10, which were compounded with a pre-synthesized solid electrolyte and a polyanion (metal salt thereof), showed a decrease in reduction in the reduction initiation potential and a reduction in the amount of decomposition electricity down to 0.1V compared to the solid electrolyte of Comparative Example 1, which was not compounded. Thus, it was confirmed that compounding a pre-synthesized solid electrolyte with a polyanion suppresses the reductive decomposition reaction of the solid electrolyte and improves its reduction resistance.

[0050] Although the reason why reduction tolerance is improved in composite solid electrolytes is not necessarily clear, compounding with polyanions disrupts the crystal structure of the pre-synthesized solid electrolyte and promotes amorphization. It is considered that the disruption of the crystal structure allows cations to interact not only with Cl but also with polyanions, thereby achieving stabilization. It is presumed that such structural changes contribute to the improvement of reduction tolerance.

[0051] Furthermore, in Examples 1 to 3 using the same type of polyanion, the ratio of the substance amount of the metal salt of the polyanion to the substance amount of the pre-synthesized solid electrolyte was varied, and it was confirmed that reduction tolerance tends to increase as the ratio increases. Therefore, the ratio is preferably 0.33 or more, more preferably 0.5 or more. The ratio may be 1 or more, and it is considered that the addition amount of polyanion is effective for improving reduction tolerance in a wide range. From the viewpoint of improving reduction tolerance, the upper limit of the ratio is not particularly limited, but from the viewpoint of suitably maintaining the properties of the pre-synthesized solid electrolyte, the ratio is, for example, 3 or less, preferably 2 or less.

[0052] It is considered that the mechanism by which reduction tolerance is improved remains the same even when the polyanion species is changed. Therefore, as polyanions, OH - , AlO2 - , SO3 - , SiO3 2- , SiO4 4- , Si2O7 6- , P2O7 4- , BF4 - , PF6 - , ClO4 - , B(C2O4) 2- , CH3COO - and FSI - It is considered that reduction tolerance is improved when any of the above is used.

[0053] Regarding pre-synthesized solid electrolytes, when Hf, which forms a tetravalent cation similar to Zr, is used in place of Zr or together with Zr, it is thought that the reduction resistance will be improved by compounding it with a polyanion. The same applies when Nb, which forms a pentavalent cation similar to Ta and has the same ionic radius as Ta, is used in place of Ta or together with Ta. Furthermore, the same applies when Gd, Dy, Er, Ho, Eu, and Sc, which form a trivalent cation similar to Yb and have an ionic radius approximating Yb, are used in place of Yb or together with Yb.

[0054] As described above, the solid electrolyte according to this embodiment comprises 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 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 -is at least one selected from the group consisting of. As described above, by optimizing the types and combinations of Mα, Mβ, Mγ and A, a solid electrolyte excellent in reduction resistance can be achieved. In this solid electrolyte, since the potential window is widened, the limitation on the operating voltage is relaxed when the solid electrolyte is applied to an all-solid-state secondary battery 1, and the energy density of the all-solid-state secondary battery 1 can be improved.

[0055] Preferably, A is SO4 2- , CO3 2- , PO4 3- , BO2 - , BO3 3- , PO3 - , NO3 - or TFSI - Thereby, the reduction resistance of the solid electrolyte can be more reliably improved.

[0056] A preferred solid electrolyte is represented by the following formula (1), Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6·n(Mδ x A y )···(1) 0<a, 0<b, a+b<1, -0.2≤c≤0.2, 0<n, 0<x, and 0<y are satisfied, and when the valence of Mδ is s and the valence of A is t, s×x=t×y is satisfied. In addition, 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. Thereby, a solid electrolyte excellent in reduction resistance can be more reliably achieved.

[0057] Various modifications can be made to the above solid electrolyte and all-solid-state secondary battery 1.

[0058] A solid electrolyte containing Li, Mα, Mβ, Mγ, Cl and A may not satisfy the above formula (1).

[0059] The solid electrolyte may be mixed with other substances (which may include Li) and used as an electrolyte material. In this case, the solid electrolyte is preferably the component with the largest mass ratio among the components contained in the electrolyte material, i.e., the main component. The mass ratio 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.

[0060] The solid electrolyte used in the all-solid-state secondary battery 1 does not necessarily need to be contained in all of the positive electrode 11, negative electrode 12, and electrolyte layer 13; it is sufficient if it is contained in at least one of the positive electrode 11, negative electrode 12, and electrolyte layer 13. Furthermore, the solid electrolyte may be used in batteries other than all-solid-state secondary batteries, and may also be used for applications other than batteries.

[0061] The configurations in the above embodiments and each modified example may be combined as appropriate, as long as they do not contradict each other.

[0062] Although the invention has been described in detail, the above description is illustrative and not limiting. Therefore, it can be said that numerous modifications and embodiments are possible as long as they do not deviate from the scope of the present invention. [Explanation of symbols]

[0063] 1. All-solid-state lithium-ion secondary battery 11 Positive electrode 12 Negative electrode 13 Electrolyte layer

Claims

1. It is a solid electrolyte, It contains Li, Mα, Mβ, Mγ, Cl, Mδ 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. 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. A is OH － , AlO ２ － , SO ３ － , SO ４ ２－ , SiO ３ ２－ , SiO ４ ４－ , Si ２ O ７ ６－ , CO ３ ２－ , PO ４ ３－ , P ２ O ７ ４－ , BO ２ － , BO ３ ３－ , PO ３ － , NO ３ － , BF ４ － , PF ６ － , ClO ４ － , B(C ２ O ４ ) ２－ , CH ３ COO － , TFSI － and FSI － is at least one selected from the group consisting of The solid electrolyte is represented by the following formula (1), Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl 6 ・n(Mδ x A y )...(1) A solid electrolyte that satisfies the following conditions: 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, 0 < n, 0 < x, and 0 < y, and where s is the valence of Mδ and t is the valence of A, then s × x = t × y.

2. A solid electrolyte according to claim 1, Mα is a solid electrolyte containing Zr.

3. A solid electrolyte according to claim 1, Mβ is a solid electrolyte containing Ta.

4. A solid electrolyte according to claim 1, Mγ is a solid electrolyte containing Gd, Yb, or Er.

5. A solid electrolyte according to claim 1, A is, SO ４ ２－ CO ３ ２－ , PO ４ ３－ , BO ２ － , BO ３ ３－ , PO ３ － NO ３ － or TFSI － A solid electrolyte containing [a specific component].

6. A lithium-ion battery comprising a solid electrolyte according to any one of claims 1 to 5.

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