Solid electrolyte and lithium ion battery

Abstract

The solid electrolyte contains Li, M [alpha], M [beta], M [gamma], Cl, and O, 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, and M [gamma] is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc. As a result, it is possible to provide a solid electrolyte having high ionic conductivity and high stability.

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. Furthermore, International Publication No. 2021 / 250985 (Document 3) discloses a solid electrolyte material comprising Li, M, O, and X. Here, M is at least one element selected from the group consisting of Ti, Zr, and Hf, and X is at least one element selected from the group consisting of Cl, Br, and I.

[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 to 3 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 described below as a related technique, combinations of cations exhibiting high initial conductivity and high stability were identified. However, in solid electrolytes of related techniques, ionic conductivity and stability may not be sufficient. Summary of the Invention

[0004] This invention relates to solid electrolytes, and its purpose is to provide solid electrolytes with high ionic conductivity and high stability.

[0005] The invention of Scheme 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.

[0006] According to the present invention, a solid electrolyte with high ionic conductivity and high stability 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, and is represented by the following composition formula (1).

[0011] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl 6－2d O d ···(1)

[0012] It satisfies 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 < d < 3.

[0013] The invention of Scheme 6 is a lithium-ion battery that includes any one of the solid electrolytes of Schemes 1 to 5.

[0014] 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

[0015] Figure 1 This is a longitudinal cross-sectional view showing an all-solid-state lithium-ion secondary battery. Detailed Implementation

[0016] 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.

[0017] 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 initial conductivity and high stability.

[0018] A preferred example of a solid electrolyte involved in the related technology is a compound represented by the following compositional formula.

[0019] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl6

[0020] It satisfies 0 < a, 0 < b, a + b < 1 and -0.2 ≤ c ≤ 0.2.

[0021] Next, a solid electrolyte according to one embodiment of the present invention will be described. This solid electrolyte is a Li ion-conducting material, with the addition of oxygen (O) compared to the solid electrolytes described in the related art. This solid electrolyte is used, for example, in the manufacture of all-solid-state secondary batteries. The solid electrolyte contains Li, three other cation-forming metals (Mα, Mβ, Mγ), Cl, and O. The solid electrolyte may also consist solely of Li, Mα, Mβ, Mγ, Cl, and O.

[0022] Similar to the solid electrolytes involved in the aforementioned related technologies, 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. As described below, a solid electrolyte containing at least one trivalent, tetravalent, and pentavalent element as a cation, in addition to Li, and also containing Cl and O, can achieve higher ionic conductivity and higher stability compared to the solid electrolytes involved in the related technologies. Furthermore, since this solid electrolyte does not produce hydrogen sulfide gas, it can provide a highly safe all-solid-state secondary battery.

[0023] In the solid electrolyte of this embodiment, to more reliably achieve high ionic conductivity and high stability, 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. The mass of O is, for example, less than half the mass of Cl, and preferably less than one-quarter the mass of Cl.

[0024] The preferred solid electrolyte is a compound represented by the following formula (1).

[0025] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl 6－2d O d ···(1)

[0026] The following conditions must be met: 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 < d < 3. Regarding a and b, 0.1 ≤ a ≤ 0.5 and 0.1 ≤ b ≤ 0.4 can be met. Additionally, 0.2 ≤ a + b ≤ 0.8 can be met. In one example, the relationship between a and b is a ≥ b, but a < b is also possible. Regarding c, -0.1 ≤ c ≤ 0.1 can be met, and c can be 0. Regarding d, 0 < d < 1 can be met. Preferably, 0 < d < 0.5 is met, and more preferably, 0 < d ≤ 0.4 is met. The lower limit of d can be 0.1. This solid electrolyte can be crystalline or amorphous.

[0027] 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 O. In confirming whether the unknown solid electrolyte is the compositional formula (1) described above, Li, Mα, Mβ, and Mγ can be quantified, for example, using ICP-luminescence spectrophotometry. Cl can be quantified, for example, using ion chromatography. O can be quantified, for example, using ONH analysis with an oxygen, nitrogen, and hydrogen analyzer.

[0028] The molar ratio of Li, Mα, Mβ, Mγ, Cl, and O in the above composition formula (1) is Li:Mα:Mβ:Mγ:Cl:O = 6 - (4 + a - b)(1 + c): (1 - a - b)(1 + c): a(1 + c): b(1 + c): 6 - 2d:d. In the molar ratio determined by analyzing an unknown solid electrolyte, 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 the above composition formula (1). 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, and O.

[0029] The solid electrolyte involved in this embodiment is manufactured, for example, using the following method. First, powders containing a Li compound, a compound containing Mα, a compound containing Mβ, and a compound containing Mγ are prepared. Of these compounds, some are chlorides, and the remaining compounds are oxides. Oxides and chlorides containing the same metal element can also be prepared. For example, the Li-containing chloride is LiCl, and the Li-containing oxide is Li₂O. For example, the Mα-containing chloride is MαCl₄, and the Mα-containing oxide is MαO₂. For example, the Mβ-containing chloride is MβCl₅, and the Mβ-containing oxide is Mβ₂O₅. For example, the Mγ-containing chloride is MγCl₃, and the Mγ-containing oxide is Mγ₂O₃. These powders are weighed and mixed according to a predetermined molar ratio.

[0030] Next, the mixture is subjected to milling (mechanical-chemical milling). Here, in one example of milling, 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, the solid electrolyte according to this embodiment is obtained. 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 electrolyte is described. In this example, the milling process is performed at room temperature; however, conditions such as temperature can be appropriately changed. The solid electrolyte involved in this embodiment can also be manufactured using methods other than milling, such as sintering.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Next, examples and comparative examples of solid electrolytes will be described. Tables 1 to 5 show the composition and evaluation results of the solid electrolytes of Examples 1 to 8 and Comparative Examples 1 to 6. It should be noted that the solid electrolytes of Comparative Examples 1, 3 to 6 are solid electrolytes involved in the above-mentioned related art.

[0035] [Table 1]

[0036]

[0037] [Table 2]

[0038]

[0039] [Table 3]

[0040]

[0041] [Table 4]

[0042]

[0043] [Table 5]

[0044]

[0045] (Example 1)

[0046] [Electrolyte preparation]

[0047] In an argon atmosphere with a dew point below -60°C, LiCl, ZrCl4, TaCl5, and Gd2O3, used as raw material powders, were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:Gd2O3 = 1.7:0.5:0.4:0.05, and then pulverized and mixed in a mortar. The resulting mixture was placed in a zirconia jar and milled using a planetary ball mill at 300 rpm for 20 hours to obtain solid electrolyte powder.

[0048] [Exposure Test]

[0049] The solid electrolyte powder was placed in a shallow dish and left to stand (exposed) in a drying chamber with the dew point controlled at -40°C for 16 hours.

[0050] [Conductivity Measurement]

[0051] Solid electrolyte powder is placed in a mold consisting of a resin sleeve and upper and lower punches made of SUS (stainless steel), and uniaxial pressing is performed under pressure of 150 MPa. Wires are connected to the upper and lower punches, and impedance is measured at room temperature to calculate the lithium-ion conductivity (hereinafter also referred to as "ion conductivity").

[0052] [Stability Evaluation]

[0053] Impedance measurements were performed on the solid electrolyte powder immediately after milling using a planetary ball mill (after synthesis) and the solid electrolyte powder exposed in a drying chamber for 16 hours, and the ionic conductivity was calculated. Table 1 shows the ionic conductivity of the freshly milled solid electrolyte powder (i.e., the initial conductivity) in the "After Synthesis" column, and the ionic conductivity of the solid electrolyte powder exposed in a drying chamber for 16 hours in the "Exposed for 16 hours" column (the same applies to Tables 2 to 5). Furthermore, the retention rate of ionic conductivity was calculated in the stability evaluation. The retention rate of ionic conductivity after 16 hours of exposure was calculated using (100 × (ionic conductivity after 16 hours of exposure) / (ionic conductivity after synthesis)). It can be said that the higher this retention rate, the higher the stability (moisture resistance).

[0054] (Example 2)

[0055] In the preparation of the electrolyte in Example 1 above, LiCl, Li2O, ZrCl4, TaCl5 and Gd2O3, which are used as raw material powders, were weighed according to the molar ratio of LiCl:Li2O:ZrCl4:TaCl5:Gd2O3 = 1.4:0.15:0.5:0.4:0.05. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0056] (Example 3)

[0057] In the preparation of the electrolyte in Example 1 above, LiCl, Li2O, ZrCl4, TaCl5 and Gd2O3, which are used as raw material powders, were weighed in a molar ratio of LiCl:Li2O:ZrCl4:TaCl5:Gd2O3 = 1.0:0.35:0.5:0.4:0.05. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0058] (Example 4)

[0059] In the preparation of the electrolyte in Example 1 above, LiCl, Li2O, ZrCl4, TaCl5 and Gd2O3, which are used as raw material powders, were weighed in a molar ratio of LiCl:Li2O:ZrCl4:TaCl5:Gd2O3 = 0.5:0.6:0.5:0.4:0.05. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0060] (Example 5)

[0061] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4, TaCl5, GdCl3 and Gd2O3, which are used as raw material powders, were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3:Gd2O3 = 2.0:0.6:0.2:0.1:0.05. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0062] (Example 6)

[0063] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4, TaCl5 and Gd2O3, which are used as raw material powders, were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:Gd2O3 = 1.9:0.5:0.3:0.1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0064] (Example 7)

[0065] In the preparation of the electrolyte in Example 1 above, LiCl, Li2O, ZrCl4, TaCl5 and YbCl3, which are used as raw material powders, are weighed according to the molar ratio of LiCl:Li2O:ZrCl4:TaCl5:YbCl3 = 1.7:0.15:0.6:0.2:0.2. Otherwise, the electrolyte is prepared in the same manner as in Example 1, and tests and evaluations are carried out.

[0066] (Example 8)

[0067] In the preparation of the electrolyte in Example 1 above, LiCl, Li2O, ZrCl4, TaCl5 and ErCl3, which are used as raw material powders, were weighed according to the molar ratio of LiCl:Li2O:ZrCl4:TaCl5:ErCl3 = 1.15:0.3:0.25:0.5:0.25. 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] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4, TaCl5 and GdCl3, which are used as raw material powders, were weighed in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3 = 1.7:0.5:0.4:0.1. Otherwise, the electrolyte was prepared in the same manner as in Example 1, and the tests and evaluations were carried out.

[0070] (Comparative Example 2)

[0071] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4 and TiO2, which are used as raw material powders, are weighed in a molar ratio of LiCl:ZrCl4:TiO2 = 2.0:0.7:0.3. Otherwise, the electrolyte is prepared in the same manner as in Example 1, and tests and evaluations are carried out.

[0072] (Comparative Example 3)

[0073] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4, TaCl5 and GdCl3, which are used as raw material powders, are weighed in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3 = 2.0:0.6:0.2:0.2. Otherwise, the electrolyte is prepared in the same manner as in Example 1, and tests and evaluations are carried out.

[0074] (Comparative Example 4)

[0075] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4, TaCl5 and GdCl3, which are used as raw material powders, are weighed in a molar ratio of LiCl:ZrCl4:TaCl5:GdCl3 = 1.9:0.5:0.3:0.2. Otherwise, the electrolyte is prepared in the same manner as in Example 1, and tests and evaluations are carried out.

[0076] (Comparative Example 5)

[0077] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4, TaCl5 and YbCl3, which are used as raw material powders, are weighed in a molar ratio of LiCl:ZrCl4:TaCl5:YbCl3 = 2.0:0.6:0.2:0.2. Otherwise, the electrolyte is prepared in the same manner as in Example 1, and tests and evaluations are carried out.

[0078] (Comparative Example 6)

[0079] In the preparation of the electrolyte in Example 1 above, LiCl, ZrCl4, TaCl5 and ErCl3, which are used as raw material powders, are weighed in a molar ratio of LiCl:ZrCl4:TaCl5:ErCl3 = 1.75:0.25:0.5:0.25. Otherwise, the electrolyte is prepared in the same manner as in Example 1, and tests and evaluations are carried out.

[0080] As shown in Table 1, in the solid electrolytes of Examples 1-4, which have the same composition ratio of Li, Zr, Ta, and Gd but different O ratios, the synthesized ionic conductivity is 9.3 × 10⁻⁶. －4 For samples with a conductivity above S / cm, the ionic conductivity after 16 hours of exposure was 2.7 × 10⁻⁶. － 4The ionic conductivity is above S / cm, and the retention rate of ionic conductivity is above 18%. The solid electrolytes of Examples 1-4, which contain O, are materials that possess 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 1-4 but does not contain O, has lower ionic conductivity after synthesis, lower ionic conductivity after 16 hours of exposure, and lower retention rate of ionic conductivity than those in Examples 1-4. Furthermore, the solid electrolyte of Comparative Example 2 contains Li, Zr, Cl, and O, but does not contain Mβ and Mγ; its ionic conductivity after synthesis, lower ionic conductivity after 16 hours of exposure, and lower retention rate of ionic conductivity than those in Examples 1-4. Therefore, it can be said that in order to achieve higher ionic conductivity and stability, it is very important that, in addition to Li, the cation contains at least one trivalent, one tetravalent, and one pentavalent element, and also contains O.

[0081] Tables 2-5 also compare examples and comparative examples with the same composition ratio of Li, Mα, Mβ, and Mγ. Compared with the solid electrolyte of the comparative example without O, the solid electrolyte of the example containing O showed increased ionic conductivity after synthesis, ionic conductivity after 16 hours of exposure, and ionic conductivity retention rate. Thus, at the same cation ratio, the above properties change depending on whether O is included. While the magnitude of the increase varies among solid electrolytes containing O, an improvement in the aforementioned properties is confirmed.

[0082] The reason for the increased ionic conductivity in solid electrolytes containing oxygen is not entirely clear. However, the introduction of oxygen creates defects at the anion sites, causing structural deformation. It is believed that this expands the migration path of Li ions, thus increasing ionic conductivity. Furthermore, the ionic radius of O is 1.40, while that of Cl is less than 1.81. The smaller ionic radius of O shortens the bonding distance with the cation, suggesting that the bonding force between cation and O is stronger than that between cation and Cl. It is presumed that this increased bonding force improves the stability of the material.

[0083] It is believed that even if the type of cation changes, the mechanism for increased ionic conductivity and stability after synthesis remains the same. Specifically, it is believed that replacing Zr with Hf, which is a tetravalent cation like Zr, or using it together with Zr, also improves ionic conductivity and stability. Similarly, replacing Ta with Nb, which is a pentavalent cation like Ta and has the same ionic radius as Ta, or using it together with Ta, also yields the same result. Furthermore, replacing Gd, Yb, or Er with Dy, Ho, Eu, and Sc, which are trivalent cations like Gd, Yb, and Er and have ionic radii similar to Gd, Yb, or Er, or using them together with Gd, Yb, or Er, also yields the same result.

[0084] As explained above, the solid electrolyte involved in this embodiment includes 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.

[0085] Here, the solid electrolytes of Comparative Examples 1, 3 to 6 are solid electrolytes involved in the aforementioned related technologies, and the synthesized ionic conductivity is, for example, 1.0 × 10⁻⁶ at room temperature. －4 The ionic conductivity of this solid electrolyte decreases when left to stand in a drying chamber for 16 hours; however, subsequent heat treatment at 150°C confirms that the ionic conductivity recovers to 1.0 × 10⁻⁶. －4 S / cm or higher. However, in the solid electrolytes of Comparative Examples 1, 3 to 6, heat treatment is required to restore the ionic conductivity. Therefore, a large amount of electricity is consumed during the manufacture of the solid electrolytes, resulting in increased manufacturing costs.

[0086] In contrast, the solid electrolyte of this embodiment, by doping with oxygen atoms, increases the synthesized ionic conductivity (initial conductivity) compared to the solid electrolytes of Comparative Examples 1, 3 to 6. Furthermore, it maintains a high ionic conductivity (e.g., 1.0 × 10⁻⁶) even in a dry chamber environment with a dew point of -40°C. －4 (S / cm or higher). In this way, the solid electrolyte according to this embodiment exhibits less conductivity degradation, achieves high stability, and eliminates the need for heat treatment to restore ionic conductivity. As a result, this solid electrolyte can be applied in existing battery manufacturing processes carried out in this dry chamber environment, easily manufacturing lithium-ion batteries. It should be noted that, in the solid electrolyte according to this embodiment, an increase in ionic conductivity was also confirmed by performing the same heat treatment as in Comparative Examples 1, 3-6.

[0087] The preferred solid electrolyte is represented by the following compositional formula (1),

[0088] Li 6－（4＋a－b）（1＋c） (Mα) （1－a－b） Mβ a Mγ b ) 1＋c Cl 6－2d O d ···(1)

[0089] It satisfies 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 < d < 3. By using Li... x MCl 6―2d O dBy optimizing the types and combinations of oxygen content d and cation M in the chloride electrolyte, a solid electrolyte with high ionic conductivity and high stability can be more reliably realized.

[0090] Various modifications can be made to the above-mentioned solid electrolyte and all-solid secondary battery 1.

[0091] Solid electrolytes containing Li, Mα, Mβ, Mγ, Cl and O may not satisfy the above composition formula (1).

[0092] 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.

[0093] 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.

[0094] The components in the above-described embodiments and their variations can be appropriately combined as long as they do not contradict each other.

[0095] 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.

[0096] Description of Reference Numerals

[0097] 1. All-solid-state lithium-ion secondary battery

[0098] 11 Positive electrode

[0099] 12 Negative electrode

[0100] 13 Electrolyte layer

Claims

1. A solid electrolyte, wherein, It contains Li, Mα, Mβ, Mγ, Cl, and O. 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.

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, 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) It satisfies 0 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 < d < 3.

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

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