Solid electrolytes and lithium-ion batteries

Abstract

This solid electrolyte contains Li, Mα, Mβ, Mγ, Cl, and O, 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. Thus, it is possible to provide a solid electrolyte that has high ion conductivity and that is highly stable.

Description

[Technical Field]

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

[0002] In recent years, there have been strong demands for miniaturization and improved reliability (safety) for batteries used as power sources for electronic devices. Therefore, all-solid-state batteries using a solid electrolyte have attracted attention. Halides are known as solid electrolytes containing no sulfur, and Li3YCl6 exhibits high Li ion conductivity at room temperature (see, for example, Japanese Patent No. 6934626 (Document 1)). Further, 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. Further, International Publication No. WO 2021 / 250985 (Document 3) discloses a solid electrolyte material containing Li, M, O and X. Here, M is at least one selected from the group consisting of Ti, Zr and Hf, and X is at least one selected from the group consisting of Cl, Br and I.

[0003] As described above, chloride electrolytes such as Li3YCl6 exhibit high ionic conductivity at room temperature, but information on stability is not disclosed. The inventors of the present application produced the solid electrolytes disclosed in Documents 1 to 3 mentioned above and allowed them to stand in a dry room controlled at a dew point of -40°C, and found that the electrolyte decomposed and the initial ionic conductivity could not be maintained, that is, the stability (or moisture resistance) was low. Therefore, the inventors of the present application, in order to improve the stability of the chloride electrolyte, Li xIn MCl₆, materials were produced by combining various cations (M), and a search was conducted for combinations of cations with high stability. As a result, as described later as related art, a combination of cations exhibiting high initial conductivity and high stability was identified. However, the solid electrolytes of the related art do not necessarily have sufficient ionic conductivity and stability. Summary of the Invention

[0004] The present invention is directed to a solid electrolyte, and an object of the present invention is to provide a solid electrolyte that has high ionic conductivity and high stability.

[0005] The invention according to aspect 1 is a solid electrolyte, comprising Li, Mα, Mβ, Mγ, Cl and O, 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 wherein the solid electrolyte is represented by the following compositional formula (1), Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl 6-2d O d ···(1) 0<a, 0<b, a+b<1, -0.2≤c≤0.2, and 0<d<3 are satisfied .

[0006] According to the present invention, a solid electrolyte having high ionic conductivity and high stability can be provided.

[0007] The invention according to aspect 2 is the solid electrolyte according to aspect 1, wherein Mα comprises Zr.

[0008] The invention according to aspect 3 is the solid electrolyte according to aspect 1 or 2, wherein Mβ comprises Ta.

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

[0011] Aspect 5 the invention is 4 a lithium ion battery comprising the solid electrolyte according to any one of

[0012] The above object and other objects, features, aspects and advantages of the present invention will become apparent from the detailed description of the invention given below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013]

Fig. 1

[0014] First, a solid electrolyte according to 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 lithium (Li) element, three other types of metal elements that serve as cations (Mα, Mβ, Mγ), and chlorine (Cl) element.

[0015] 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, as cations, at least one each of trivalent, tetravalent, and pentavalent elements in addition to Li, high initial conductivity and high stability are achieved.

[0016] A preferred example of a 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.

[0017] Next, a solid electrolyte according to an embodiment of the present invention will be described. The solid electrolyte is a Li-ion conductive material, and is obtained by adding oxygen (O) to the solid electrolyte according to the related art described above. The solid electrolyte is used, for example, for manufacturing an all-solid-state secondary battery. The solid electrolyte includes elemental Li, three other types of metal (Mα, Mβ, Mγ) elements that serve as cations, elemental Cl, and elemental O. The solid electrolyte may consist only of Li, Mα, Mβ, Mγ, Cl, and O.

[0018] Similar to the solid electrolyte according to the related art described above, 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. For a solid electrolyte that contains at least one each of trivalent, tetravalent, and pentavalent elements as cations in addition to Li, and further contains Cl and O, as will be described later, higher ionic conductivity and higher stability are achieved than the solid electrolyte according to the related art. In addition, since hydrogen sulfide gas is not generated from the solid electrolyte, a highly safe all-solid-state secondary battery can be provided.

[0019] In the solid electrolyte according to the present embodiment, in order to more reliably achieve high ionic conductivity and high stability, 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 amount of Li substance is, for example, greater than the amount of any of Mα, Mβ and Mγ substances, and is preferably greater than the total amount of Mα, Mβ and Mγ substances. The amount of Cl substance is, for example, greater than the total amount of Li, Mα, Mβ and Mγ substances. The amount of O substance is, for example, less than 1 / 2 of the amount of Cl substance, and preferably less than 1 / 4 of the amount of Cl substance.

[0020] A preferred solid electrolyte is a compound represented by the following composition formula (1), Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl 6-2d O d ···(1) 0<a, 0<b, a+b<1, -0.2≤c≤0.2, and 0<d<3 are satisfied. For a and b, 0.1≤a≤0.5, and 0.1≤b≤0.4 may be satisfied. In addition, 0.2≤a+b≤0.8 may be satisfied. In one example, the relationship between a and b is a≥b, but a<b may also be satisfied. For c, -0.1≤c≤0.1 may be satisfied, or c may be 0. For d, 0<d<1 may be satisfied. Preferably, 0<d<0.5 is satisfied, more preferably 0<d≤0.4 is satisfied. The lower limit of d may be 0.1. The solid electrolyte may be crystalline or amorphous.

[0021] To confirm whether an unknown solid electrolyte is the solid electrolyte according to this embodiment, a chemical analysis is performed on the unknown solid electrolyte to confirm whether its constituent elements are Li, Mα, Mβ, Mγ, Cl, and O. In confirming whether the unknown solid electrolyte has the above composition formula (1), Li, Mα, Mβ, and Mγ can be quantified, for example, by ICP-emission spectroscopy. Cl can be quantified, for example, by ion chromatography. O can be quantified, for example, by ONH analysis using an oxygen-nitrogen-hydrogen analyzer.

[0022] The molar ratios of Li, Mα, Mβ, Mγ, Cl, and O in the above compositional formula (1) are Li:Mα:Mβ:Mγ:Cl:O=6-(4+ab)(1+c):(1-ab)(1+c):a(1+c):b(1+c):6-2d:d. 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, it is considered that the above compositional formula (1) is 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, and O.

[0023] The solid electrolyte according to this embodiment is manufactured, for example, by the following method. First, powders of a Li-containing compound, a Mα-containing compound, a Mβ-containing compound, and a Mγ-containing compound are prepared. Of these compounds, some are chlorides and the remaining compounds are oxides. Oxides and chlorides containing the same metal element may be prepared. A Li-containing chloride is, for example, LiCl, and a Li-containing oxide is, for example, Li2O. A Mα-containing chloride is, for example, MαCl4, and an Mα-containing oxide is, for example, MαO2. A Mβ-containing chloride is, for example, MβCl5, and an Mβ-containing oxide is, for example, Mβ2O5. A Mγ-containing chloride is, for example, MγCl3, and an Mγ-containing oxide is, for example, Mγ2O3. These powders are weighed and mixed in a predetermined molar ratio.

[0024] Next, the mixture is milled (mechanochemical milling). In this example, a planetary ball mill is used for the milling process. 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. The milling process may also be carried out using other types of grinders. The solid electrolyte according to this embodiment is obtained by the above milling process. 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 this example, the milling process is carried out at room temperature, but the temperature and other conditions may be changed as appropriate. The solid electrolyte according to this embodiment may also be manufactured by methods other than milling, such as firing.

[0025] 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.

[0026] 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 Mn 1.5 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.

[0027] For example, LTO(Li4Ti5O) is used as the negative electrode active material for the negative electrode layer 122. 12Examples of compounds include ), NTO (Nb2TiO7), TiO2 (titanium dioxide), graphite, and SiO (silicon monoxide). 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.

[0028] Next, examples and comparative examples of solid electrolytes are described. Tables 1 to 5 show the composition and evaluation results of the solid electrolytes for Examples 1 to 8 and Comparative Examples 1 to 6. The solid electrolytes for Comparative Examples 1, 3 to 6 are solid electrolytes related to the above-mentioned related technologies.

[0029] [Table 1]

[0030] [Table 2]

[0031] [Table 3]

[0032] [Table 4]

[0033] [Table 5]

[0034] (Example 1) [Preparation of electrolytes] In an argon atmosphere with a dew point of -60°C or lower, LiCl, ZrCl4, TaCl5, and Gd2O3 were weighed out as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:Gd2O3 = 1.7:0.5:0.4:0.05, 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 obtain a solid electrolyte powder.

[0035] [Exposure test] The solid electrolyte powder was placed in a petri dish and left to stand (exposed) for 16 hours in a dry room controlled to a dew point of -40°C.

[0036] [Conductivity measurement] A mold consisting of a resin sleeve and upper and lower punches made of SUS (stainless steel) was filled with solid electrolyte powder and uniaxially press-molded under pressure of 150 MPa. Wires were connected to the upper and lower punches, and impedance measurements were performed at room temperature to calculate lithium ion conductivity (hereinafter also simply referred to as "ionic conductivity").

[0037] [Stability evaluation] Impedance measurements were performed on solid electrolyte powder immediately after milling (after synthesis) using a planetary ball mill, and on solid electrolyte powder exposed to a dry room for 16 hours, and the ionic conductivity was calculated. In Table 1, the ionic conductivity of the solid electrolyte powder immediately after milling (i.e., initial conductivity) is shown in the "After Synthesis" column, and the ionic conductivity of the solid electrolyte powder exposed to a dry room for 16 hours is shown in the "16h Exposure" column (the same applies to Tables 2 to 5). In addition, the retention rate of ionic conductivity was calculated for stability evaluation. The retention rate of ionic conductivity after 16 hours of exposure was calculated as (100 × (ionic conductivity after 16 hours of exposure) / (ionic conductivity after synthesis)). A higher retention rate indicates higher stability (moisture resistance).

[0038] (Example 2) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the raw material powders LiCl, Li2O, ZrCl4, TaCl5, and Gd2O3 were weighed in a molar ratio of LiCl:Li2O:ZrCl4:TaCl5:Gd2O3 = 1.4:0.15:0.5:0.4:0.05. The electrolyte was then tested and evaluated.

[0039] (Example 3) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the raw material powders LiCl, Li2O, ZrCl4, TaCl5, and Gd2O3 were weighed in a molar ratio of LiCl:Li2O:ZrCl4:TaCl5:Gd2O3 = 1.0:0.35:0.5:0.4:0.05. The electrolyte was then tested and evaluated.

[0040] (Example 4) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the raw material powders LiCl, Li2O, ZrCl4, TaCl5, and Gd2O3 were weighed in a molar ratio of LiCl:Li2O:ZrCl4:TaCl5:Gd2O3 = 0.5:0.6:0.5:0.4:0.05. The electrolyte was then tested and evaluated.

[0041] (Example 5) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the raw material powders LiCl, ZrCl4, TaCl5, GdCl3, and Gd2O3 were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3:Gd2O3 = 2.0:0.6:0.2:0.1:0.05. The electrolyte was then tested and evaluated.

[0042] (Example 6) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the raw material powders LiCl, ZrCl4, TaCl5, and Gd2O3 were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:Gd2O3 = 1.9:0.5:0.3:0.1. The electrolyte was then tested and evaluated.

[0043] (Example 7) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, Li2O, ZrCl4, TaCl5, and YbCl3 were weighed as raw material powders in a molar ratio of LiCl:Li2O:ZrCl4:TaCl5:YbCl3 = 1.7:0.15:0.6:0.2:0.2. The electrolyte was then tested and evaluated.

[0044] (Example 8) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, Li2O, ZrCl4, TaCl5, and ErCl3 were weighed as raw material powders in a molar ratio of LiCl:Li2O:ZrCl4:TaCl5:ErCl3 = 1.15:0.3:0.25:0.5:0.25. The electrolyte was then tested and evaluated.

[0045] (Comparative Example 1) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3 = 1.7:0.5:0.4:0.1. The electrolyte was then tested and evaluated.

[0046] (Comparative Example 2) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, and TiO2 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:TiO2 = 2.0:0.7:0.3. The electrolyte was then tested and evaluated.

[0047] (Comparative Example 3) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that the raw material powders LiCl, ZrCl4, TaCl5, and GdCl3 were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3 = 2.0:0.6:0.2:0.2. The electrolyte was then tested and evaluated.

[0048] (Comparative Example 4) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3 = 1.9:0.5:0.3:0.2. The electrolyte was then tested and evaluated.

[0049] (Comparative Example 5) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and YbCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:YbCl3 = 2.0:0.6:0.2:0.2. The electrolyte was then tested and evaluated.

[0050] (Comparative Example 6) In the preparation of the electrolyte in Example 1 described above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and ErCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:ErCl3 = 1.75:0.25:0.5:0.25. The electrolyte was then tested and evaluated.

[0051] As shown in Table 1, in the solid electrolytes of Examples 1 to 4, where the composition ratios of Li, Zr, Ta, and Gd were the same but the ratio of O was different, the ionic conductivity after synthesis was 9.3 × 10⁻⁶ in all cases. -4 The ionic conductivity is greater than S / cm and the ionic conductivity after 16 hours of exposure is 2.7 × 10⁻⁶. -4The ionic conductivity was 18% or higher, and the retention rate of ionic conductivity was 18% or higher. Thus, the solid electrolytes of Examples 1 to 4, which contain O, are materials that achieve both high ionic conductivity and high stability. In contrast, the solid electrolyte of Comparative Example 1, which has the same composition ratio of Li, Zr, Ta, and Gd as Examples 1 to 4 but does not contain O, had ionic conductivity after synthesis, ionic conductivity after 16 hours of exposure, and retention rate of ionic conductivity that were lower than the above values ​​for Examples 1 to 4. Furthermore, the solid electrolyte of Comparative Example 2 contains Li, Zr, Cl, and O, but does not contain Mβ and Mγ, and had ionic conductivity after synthesis, ionic conductivity after 16 hours of exposure, and retention rate of ionic conductivity that were lower than the above values ​​for Examples 1 to 4. Therefore, in order to further increase ionic conductivity and stability, it can be said that it is important to include at least one each of trivalent, tetravalent, and pentavalent elements as cations in addition to Li, and to also include O.

[0052] Tables 2-5 also compare the examples and comparative examples with the same composition ratios of Li, Mα, Mβ, and Mγ. The solid electrolytes of the examples containing O showed higher ionic conductivity after synthesis, ionic conductivity after 16 hours of exposure, and ionic conductivity retention rate compared to the solid electrolytes of the comparative examples that did not contain O. Thus, even with the same cation ratio, the presence or absence of O changes the above properties, and it was confirmed that solid electrolytes containing O improve the above properties, although the degree of improvement varies.

[0053] The reason why the ionic conductivity of solid electrolytes containing oxygen (O) improves after synthesis is not entirely clear, but it is thought that the introduction of O creates defects in the anion sites, causing structural distortion. This expands the pathways through which Li ions can move, thus improving ionic conductivity. Furthermore, the ionic radius of O is 1.40, which is smaller than that of Cl (1.81). The bond distance between oxygen and cations is shorter for oxygen due to its smaller ionic radius, and the bond force between cation and oxygen is thought to be higher than that between cation and Cl. This improvement in bond strength is presumed to improve the stability of the material.

[0054] The mechanism by which the ionic conductivity and stability after synthesis are increased is thought to be the same even when the cation species is changed. Specifically, when Hf, which is a tetravalent cation like Zr, is used in place of Zr, or together with Zr, the ionic conductivity and stability are thought to be improved. The same is true when Nb, which is a pentavalent cation like Ta, and has the same ionic radius as Ta, is used in place of Ta, or together with Ta. Furthermore, the same is true when Dy, Ho, Eu, and Sc, which are trivalent cations like Gd, Yb, and Er, and have ionic radii similar to Gd, Yb, or Er, are used in place of Gd, Yb, or Er, or together with Gd, Yb, or Er.

[0055] As described above, the solid electrolyte according to this embodiment comprises Li, Mα, Mβ, Mγ, Cl, and O. 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.

[0056] Here, the solid electrolytes of Comparative Examples 1, 3-6 are solid electrolytes related to the above-mentioned related technologies, and their ionic conductivity after synthesis is, for example, 1.0 × 10⁻⁶ at room temperature. -4 The ionic conductivity of this solid electrolyte decreases when left standing in a dry room for 16 hours, but after heat treatment at 150°C, the ionic conductivity increases to 1.0 × 10⁻⁶. -4 It has been confirmed that the conductivity can be restored to above S / cm. However, in the case of the solid electrolytes in Comparative Examples 1, 3-6, heat treatment is required to restore the ionic conductivity, which consumes a lot of electricity during the manufacturing of the solid electrolyte and consequently leads to increased manufacturing costs.

[0057] In contrast, in the solid electrolyte according to the present embodiment, doping with oxygen atoms makes the ionic conductivity after synthesis (initial conductivity) higher than that of the solid electrolytes of Comparative Examples 1 and 3 to 6, and also maintains high ionic conductivity (for example, 1.0×10 -4 S / cm or higher) even in a dry room environment with a dew point of -40°C. As described above, the solid electrolyte according to the present embodiment achieves high stability with little conductivity degradation, and eliminates the need for heat treatment to recover ionic conductivity. As a result, it becomes possible to easily manufacture a lithium ion battery by applying the solid electrolyte to an existing battery manufacturing process performed in the dry room environment. It has been confirmed that also in the solid electrolyte according to the present embodiment, the ionic conductivity can be improved by performing the same heat treatment as in Comparative Examples 1 and 3 to 6.

[0058] A preferred solid electrolyte is represented by the following composition formula (1), Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl 6-2d O d ···(1) 0<a, 0<b, a+b<1, -0.2≦c≦0.2, and 0<d<3 are satisfied. In the chloride electrolyte represented by Li x MCl 6―2d O d , by optimizing the oxygen content d, and the type and combination of the cation M, a solid electrolyte having high ionic conductivity and high stability can be more reliably achieved.

[0059] Various modifications can be made to the above solid electrolyte and the all-solid-state secondary battery 1.

[0060] The solid electrolyte containing Li, Mα, Mβ, Mγ, Cl and O may not satisfy the above composition formula (1).

[0061] 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.

[0062] 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.

[0063] The configurations in the above embodiments and each modified example may be combined as appropriate, as long as they do not contradict each other.

[0064] 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]

[0065] 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 and O, 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. The aforementioned solid electrolyte is represented by the following compositional formula (1), Li 6-(4+a-b) (1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl 6-2d O d ... (1) A solid electrolyte that satisfies 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 < d < 3.

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 lithium-ion battery comprising a solid electrolyte according to any one of claims 1 to 4.

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