Solid electrolyte and lithium ion battery

Abstract

Provided is a solid electrolyte exhibiting high stability in a dry room in which the dew point is controlled to -40°C while having high conductivity associated with inclusion of Br, the solid electrolyte being capable of significantly recovering reduced conductivity through heat treatment. This solid electrolyte comprises Li, Mα, Mβ, Mγ, Cl, and Br, 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, Nb, and Mo; and Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, Sc, and Al.

Description

Solid electrolyte and lithium-ion batteries

[0001] The present disclosure relates to solid electrolytes and lithium-ion batteries.

[0002] In recent years, there has been a strong demand for smaller size and improved reliability (safety) for batteries that serve as power sources for electronic devices. Therefore, all-solid-state batteries, which use solid electrolytes instead of liquid electrolytes, have attracted attention. One typical type of solid electrolyte is a sulfide-based solid electrolyte. However, because sulfide-based solid electrolytes can generate toxic hydrogen sulfide, solid electrolytes that do not belong to the sulfide-based solid electrolyte category are desired from a safety perspective.

[0003] Halides have been proposed as sulfur-free solid electrolytes. For example, Patent Document 1 (Japanese Patent No. 7316571) discloses a sulfur-free solid electrolyte containing Li ３－３ δ －ａ Y １＋ δ －ａ M ａ Cl ６－ｘ－ｙ Br ｘ I ｙ (wherein M is Zr and / or Hf, and −1<δ<1, 0.1≦a≦0.9, 0<(3−3δ−a), 0<(1+δ−a), 0≦x≦6, 0≦y≦6, and (x+y)≦6) is disclosed. ２．５ Y ０．５ Zr ０．５ Cl ６ The solid electrolyte having the above composition exhibits high lithium ion conductivity at room temperature, and the Li ２．５ Y ０．５ Zr ０．５ Cl ５ It is disclosed that a solid electrolyte having a composition of Br exhibits even higher conductivity.

[0004] Furthermore, Patent Document 2 (WO2024 / 010065) discloses a solid electrolyte containing A, Mα, Mβ, Mγ, and Cl, in which A is at least one element selected from the group consisting of Li and Na, 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, and the amount of substance of Cl is greater than the amount of substance of A.

[0005] Patent No. 7316571 WO2024 / 010065

[0006] As mentioned above, Li ２．５ Y ０．５ Zr ０．５ Cl ６ , Li ２．５ Y ０．５ Zr ０．５ Cl ５ It is known that chloride electrolytes such as Br (see Patent Document 1) exhibit high conductivity at room temperature, but there have been no reports on the stability of these electrolytes. Therefore, the inventors prepared the chloride electrolyte powder disclosed in Patent Document 1 and placed it in a dry room controlled at a dew point of −40°C. They found that the electrolyte decomposed and could not maintain its initial conductivity. Furthermore, they found that a composition in which Br is doped into some of the Cl sites improved conductivity, but its stability in a dry room controlled at a dew point of −40°C decreased.

[0007] The present inventors have now discovered that Li, M α , M β , M γ In solid electrolytes containing Cl and Br, M α , M β and M γ The present inventors have found that by employing a specific metal element as the Br, it is possible to provide a solid electrolyte that exhibits high stability in a dry room controlled at a dew point of −40°C while still having high conductivity due to the inclusion of Br, and that can significantly recover any decreased conductivity by heat treatment.

[0008] Therefore, an object of the present invention is to provide a solid electrolyte that has high conductivity due to the inclusion of Br, yet exhibits high stability in a dry room controlled at a dew point of −40° C., and further, is capable of significantly recovering reduced conductivity by heat treatment.

[0009] According to the present disclosure, the following aspects are provided: [Aspect 1] Li, M α , M β , M γ a solid electrolyte containing Cl and Br, α is at least one element selected from the group consisting of Zr and Hf, and M β is at least one element selected from the group consisting of Ta, Nb, and Mo, and M γ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, Sc, and Al. α The solid electrolyte according to aspect 1, wherein M comprises Zr. β The solid electrolyte according to aspect 1 or 2, wherein M comprises Ta. γ [Aspect 5] A solid electrolyte according to any one of Aspects 1 to 3, wherein the solid electrolyte is a solid electrolyte having the following composition formula: Li6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) １＋ｃ Cl ６－２ｄ－ｅ－ｆ O ｄ F ｅ Br ｆ and a + b < 1, -0.2 ≦ c ≦ 0.2, 0 ≦ d < 3, 0 ≦ e < 6, and 0 < f < 6. [Aspect 6] A lithium ion battery comprising the solid electrolyte according to any one of aspects 1 to 5.

[0010] FIG. 1 is a schematic cross-sectional view showing an example of an all-solid-state battery according to the present invention.

[0011] Solid Electrolyte The solid electrolyte according to the present invention isα , M β , M γ , Cl and Br. α is at least one element selected from the group consisting of Zr and Hf. β is at least one element selected from the group consisting of Ta, Nb and Mo. γ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, Sc and Al. α , M β , M γ By employing specific constituent elements in a solid electrolyte containing Cl and Br, it is possible to provide a solid electrolyte that has high conductivity due to the inclusion of Br, yet exhibits high stability in a dry room controlled at a dew point of −40° C., and furthermore, is capable of significantly recovering reduced conductivity by heat treatment.

[0012] As mentioned above, when the present inventors prepared the chloride electrolyte powder disclosed in Patent Document 1 and left it in a dry room controlled at a dew point of -40°C, it was found that the electrolyte decomposed and the initial conductivity could not be maintained. In addition, it was found that a composition in which Br is doped into a part of the Cl site improves conductivity, but the stability in a dry room controlled at a dew point of -40°C decreases. Therefore, in order to improve the stability of the chloride electrolyte, the present inventors ｘ MClyBr ｚ In the composition system (M is a cation), materials were prepared with various cations, and a search was made for cations with good stability and their combinations. As a result of examining various cations and various combinations, M α Zr, M β As Ta, M γ Li containing Gd and / or Yb in combination as ｘ (M α , M β , M γ ) Cl ｙ Br ｚ Although the solid electrolyte represented by the composition formula contains Br, it has a high initial conductivity (10 at room temperature). －４ S / cm) and high stability (after 16 hours in a dry room, the conductivity is 10―４ It was found that a high conductivity (S / cm or more) could be achieved. Similar trends were also confirmed for combinations of elements other than those mentioned above. Furthermore, it was confirmed that the conductivity, once reduced, could be restored by placing the solid electrolyte of the above composition in a dry room and then heat-treating it at 150°C. The present invention is based on these findings and successfully solves the above-mentioned problems. As a result, it is possible to provide a high-conductivity solid electrolyte material that can be handled in a dry room environment with a dew point of -40°C and is highly applicable to battery fabrication processes.

[0013] As described above, the solid electrolyte of the present invention is α , M β , M γ The solid electrolyte is not particularly limited as long as it is a halide containing these elements and having the properties of a solid electrolyte. ｘ (M α , M β , M γ ) Cl ｙ Br ｚ In the basic composition, a part of the Cl site may be doped with Br, or may be doped with not only Br but also O and / or F. Specifically, such a solid electrolyte has the following composition formula: Li6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) １＋ｃ Cl ６－２ｄ－ｅ－ｆ O ｄ F ｅ Br ｆ (wherein 0<a, 0<b, a+b<1, −0.2≦c≦0.2, 0≦d<3, 0≦e<6, and 0<f<6) is preferable. The solid electrolyte may be crystalline or amorphous.

[0014] M α is an element that becomes a tetravalent cation. α is at least one element selected from the group consisting of Zr and Hf, and typically includes Zr.

[0015] M βis an element that becomes a pentavalent cation. β is at least one element selected from the group consisting of Ta, Nb and Mo, and typically includes Ta. β The coefficient a by which the above equations are multiplied satisfies 0<a (where a+b<1), preferably 0<a≦0.8, and more preferably 0.1≦a≦0.5.

[0016] M γ is an element that becomes a trivalent cation. γ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, Sc and Al, and typically contains at least one element selected from the group consisting of Gd, Yb and Er. γ The coefficient b by which a is multiplied satisfies 0<b (where a+b<1), preferably 0<b≦0.8, and more preferably 0.25≦b≦0.75.

[0017] The coefficient c is in the range of −0.2≦c≦0.2, preferably −0.15≦c≦0.15, more preferably −0.1≦c≦0.1, and typically c=0.

[0018] As can be seen from the above composition formula, not only Cl but also Br, optionally O, and optionally F can be present at the Cl site. The coefficient f multiplied by Br is 0<f<6, preferably 0<f≦2.0, and more preferably 0.3≦f≦1.0. O is an optional element, and the coefficient d multiplied by O is 0≦d<3, preferably 0≦d<0.5, and more preferably 0≦d≦0.4. F is also an optional element, and the coefficient e multiplied by F is 0≦e<6, preferably 0≦e≦2, and more preferably 0≦e≦1.

[0019] When determining whether an unknown solid electrolyte is the above-mentioned solid electrolyte, chemical analysis is performed on the unknown solid electrolyte to determine whether the constituent elements are Li, M, α , M β , M γ , Cl 、 It is sufficient to confirm whether the unknown solid electrolyte has the above composition formula, for example, Li, M α , M β and M γcan be quantified using an ICP-emission spectrophotometer. 、 F and Br can be quantified by ion chromatography, and O can be quantified by ONH analysis using an oxygen, nitrogen, and hydrogen analyzer.

[0020] Lithium-ion battery According to a preferred embodiment of the present invention, there is provided a lithium-ion battery containing the solid electrolyte of the present invention. This lithium-ion battery is preferably a lithium-ion secondary battery, more preferably an all-solid-state lithium-ion secondary battery. An all-solid-state lithium-ion secondary battery is particularly preferred. Figure 1 schematically shows an example of a lithium-ion battery 10 according to the present invention.

[0021] The positive electrode 12 includes a positive electrode active material. The positive electrode active material preferably includes a lithium composite oxide. Examples of lithium composite oxides include lithium nickel manganese oxide (LNMO) (typically LiNi ０．５ Mn １．５ O ４ ), lithium nickel cobalt manganese oxide (NCM) (typically Li(Ni,Co,Mn)O ２ ), lithium cobalt oxide (LCO) (typically LiCoO ２ ), lithium nickel cobalt aluminate (NCA) (typically Li(Ni,Co,Al)O ２ ) and lithium iron phosphate (LFP) (typically LiFePO ４ ), and combinations thereof. NCM, LCO, and NCA have a layered rock salt structure. LNMO has a spinel structure. LFP has an olivine structure. A lithium composite oxide having a layered rock salt structure, such as NCM, is preferred. The positive electrode 12 preferably further contains a solid electrolyte and / or an electron conductive additive (carbon black, etc.) in addition to the positive electrode active material. The positive electrode 12 in this embodiment is formed by integrating these materials by pressure or heat. Therefore, as shown in FIG. 1, the positive electrode 12 is typically in the form of a positive electrode layer. When the positive electrode 12 contains a solid electrolyte, it is preferable to use such a solid electrolyte as described below.

[0022] The negative electrode 14 is 0.1 V (vs. Li / Li ＋ ) or more, and includes a negative electrode active material capable of inserting and desorbing lithium ions. Examples of the negative electrode active material include lithium titanate (LTO) (typically Li ４ Ti ５ O １２ ), SiO, Si or Si alloy, and TiO ２ The negative electrode active material is preferably LTO, SiO, or TiO in view of non-flammability. ２ In terms of cycleability, LTO is particularly preferred. Although LTO is typically known to have a spinel structure, it can also have other structures during charge and discharge. For example, LTO can have Li ４ Ti ５ O １２ (spinel structure) and Li ７ Ti ５ O １２ The reaction proceeds in the coexistence of two phases, a solid electrolyte (rock salt structure) and a solid electrolyte (rock salt structure). Therefore, LTO is not limited to a spinel structure. From the viewpoint of improving ionic conductivity, it is preferable that the negative electrode 14 further contains a solid electrolyte in addition to the negative electrode active material. The negative electrode 14 may further contain an electron conduction aid (carbon black, etc.). The negative electrode 14 in this embodiment is formed by integrating these materials by pressure or heat. Therefore, as shown in FIG. 1, the negative electrode 14 is typically in the form of a negative electrode layer. When the negative electrode 14 contains a solid electrolyte, it is preferable to use the solid electrolyte according to the present invention described above.

[0023] The electrolyte layer 16 is a layer containing an electrolyte and disposed between the positive electrode 12 and the negative electrode 14. Typically, the electrolyte layer 16 contains a solid electrolyte, and is preferably made of a solid electrolyte. In this case, the electrolyte layer 16 can be said to also function as a separator. The solid electrolyte contained in the electrolyte layer 16 is preferably the solid electrolyte according to the present invention described above.

[0024] At least one of the positive electrode 12, the negative electrode 14, and the electrolyte layer 16 contains a solid electrolyte according to the present invention. The solid electrolyte exhibits high ionic conductivity (e.g., lithium ion conductivity). Furthermore, this solid electrolyte is non-flammable and chemically stable, and does not generate hydrogen sulfide gas, thereby realizing an inherently safe lithium-ion battery 10. However, it is not necessary for all of the positive electrode 12, the negative electrode 14, and the electrolyte layer 16 to contain the solid electrolyte; at least one of them may contain the solid electrolyte.

[0025] The solid electrolyte according to the present invention may be mixed with other substances 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 wt % or more, more preferably 60 wt % or more, and even more preferably 70 wt % or more.

[0026] As described above, in the lithium ion battery 10 of the present invention, sulfide-free materials can be used for the positive electrode 12, the negative electrode 14, and the electrolyte layer 16. In other words, it is preferable that no part of the positive electrode 12, the negative electrode 14, or the electrolyte layer 16 contains sulfide. This makes it possible to provide an intrinsically safe lithium ion battery 10 that does not generate toxic gases such as hydrogen sulfide.

[0027] The lithium-ion battery 10 preferably further includes a positive electrode current collector 18 and a negative electrode current collector 20. The positive electrode current collector 18 is preferably provided on the surface of the positive electrode 12 opposite the electrolyte layer 16, and the negative electrode current collector 20 is preferably provided on the surface of the negative electrode 14 opposite the electrolyte layer 16. Examples of materials that can be used to form the positive electrode current collector 18 and the negative electrode current collector 20 include aluminum (Al), copper (Cu), titanium (Ti), nickel (Ni), stainless steel (SUS), carbon, platinum (Pt), platinum (Pt) / palladium (Pd), gold (Au), silver (Ag), and ITO (indium-tin oxide).

[0028] The container 22 is not particularly limited as long as it can accommodate a single lithium-ion battery 10 or a stack of multiple lithium-ion batteries 10 stacked in series or parallel. In particular, if the lithium-ion battery 10 is an all-solid-state battery, there is no concern about electrolyte leakage, so a relatively simple container shape can be adopted for the container 22. For example, a chip shape for mounting on an electronic circuit or a laminate cell shape (e.g., a multi-layer product of aluminum (Al) / polypropylene (PP)) for thin and wide space applications can be adopted.

[0029] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0030] Example 1 (1) Preparation of electrolyte: In an argon atmosphere having a dew point of −60° C. or less, LiCl, LiBr, ZrCl ４ , ZrF ４ , HfCl ４ , TaCl ５ , MoCl ５ , Gd ２ O ３ , YbCl ３ , DyCl ３ , ErCl ３ , and HoCl ３ Each raw material powder was mixed with LiCl:LiBr:ZrCl ４ : ZrF ４ : HfCl ４ : TaCl ５ : MoCl ５ : Gd ２ O ３ : YbCl ３ : DyCl ３ : ErCl ３ : HoCl ３ The raw material powders were weighed to have a molar ratio of 1.8:0.5:0.125:0.075:0.2:0.1:0.05:0.025:0.05:0.1:0.2:0.05, and were mixed by pulverization in a mortar. The resulting mixed powder was placed in a zirconia pot and milled for 20 hours at 300 rpm using a planetary ball mill to obtain a solid electrolyte powder.

[0031] (2) Conductivity Measurement The solid electrolyte powder was placed in a mold consisting of a resin sleeve and upper and lower stainless steel punches, and uniaxially pressed under a pressure of 150 MPa. Impedance measurements were performed at room temperature with leads connected to the upper and lower punches, and the lithium ion conductivity (hereinafter referred to as the initial conductivity C １ The results are shown in Table 1.

[0032] (3) Exposure Test The solid electrolyte powder was placed in a petri dish and allowed to stand in a dry room controlled at a dew point of −40° C. for 16 hours.

[0033] (4) Heat Treatment The solid electrolyte powder was left standing in a dry room for 16 hours and then heat treated at 150°C.

[0034] (5) Stability Evaluation The solid electrolyte powders that were left standing in the dry room in the above (3) and the solid electrolyte powders that were heat-treated in the above (4) were each subjected to impedance measurement at room temperature in the same manner as in the above (2), and the lithium ion conductivity of each powder was calculated. ２ and conductivity C after exposure test and heat treatment ３ Each of these is set to the initial conductivity C １ The conductivity retention rate of each powder was calculated by dividing the measured value by 100 and multiplying by 100. The results are shown in Table 1.

[0035] Example 2 In the electrolyte preparation of Example 1, LiCl, LiBr, ZrCl ４ , ZrF ４ , HfCl ４ , TaCl ５ , MoCl ５ , Gd ２ O ３ , YbCl ３ , DyCl ３ , ErCl ３ , and HoCl ３ Each raw material powder was mixed with LiCl:LiBr:ZrCl ４ : ZrF ４ : HfCl ４ : TaCl ５ : MoCl ５ : Gd ２ O ３: YbCl ３ : DyCl ３ : ErCl ３ : HoCl ３ An electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 1.3:1.0:0.125:0.075:0.2:0.1:0.05:0.025:0.05:0.1:0.2:0.05.

[0036] Example 3 In the electrolyte preparation of Example 1, LiCl, LiBr, ZrCl ４ , TaCl ５ , and ErCl ３ Each raw material powder was mixed with LiCl:LiBr:ZrCl ４ : TaCl ５ : ErCl ３ An electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 1.25:0.5:0.25:0.5:0.25.

[0037] Example 4 In the electrolyte preparation of Example 1, LiCl, LiBr, ZrCl ４ , TaCl ５ , and ErCl ３ Each raw material powder was mixed with LiCl:LiBr:ZrCl ４ : TaCl ５ : ErCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 0.75:1.0:0.25:0.5:0.25.

[0038] Example 5 In the electrolyte preparation of Example 1, LiCl, LiBr, ZrCl ４ , TaCl ５ , DyCl ３ , ErCl ３ , HoCl ３ , and AlCl ３ Each raw material powder was mixed with LiCl:LiBr:ZrCl ４ : TaCl ５ : DyCl ３ : ErCl ３ : HoCl ３ : AlCl ３An electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2.3:0.3:0.2:0.1:0.3:0.1:0.2:0.1.

[0039] Example 6 In the electrolyte preparation of Example 1, LiCl, LiBr, ZrCl ４ , TaCl ５ , MoCl ５ , Gd ２ O ３ , YbCl ３ , DyCl ３ , ErCl ３ , HoCl ３ , and AlCl ３ Each raw material powder was mixed with LiCl:LiBr:ZrCl ４ : TaCl ５ : MoCl ５ : Gd ２ O ３ : YbCl ３ : DyCl ３ : ErCl ３ : HoCl ３ : AlCl ３ An electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to obtain a molar ratio of 2.2:0.45:0.15:0.05:0.05:0.025:0.05:0.35:0.15:0.05:0.1.

[0040] Example 7 (Comparative) In the electrolyte preparation of Example 1, LiCl, LiBr, YCl ３ , and ZrCl ４ Each raw material powder was mixed with LiCl:LiBr:YCl ３ : ZrCl ４ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2.0:0.5:0.5:0.5.

[0041] Example 8 (Comparative) In the electrolyte preparation of Example 1, LiCl, LiBr, YCl ３ , and ZrCl ４ Each raw material powder was mixed with LiCl:LiBr:YCl ３ : ZrCl ４The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 1.5:1.0:0.5:0.5.

[0042] Example 9 (Comparative) In the electrolyte preparation of Example 1, LiCl, LiBr, YCl ３ , and ZrCl ４ Each raw material powder was mixed with LiCl:LiBr:YCl ３ : ZrCl ４ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 0.5:2.0:0.5:0.5.

[0043] Example 10 (Reference) In the preparation of the electrolyte of Example 1, LiCl, ZrCl ４ , ZrF ４ , HfCl ４ , TaCl ５ , MoCl ５ , Gd ２ O ３ , YbCl ３ , DyCl ３ , ErCl ３ , and HoCl ３ Each raw material powder was mixed with LiCl:ZrCl ４ : ZrF ４ : HfCl ４ : TaCl ５ : MoCl ５ : Gd ２ O ３ : YbCl ３ : DyCl ３ : ErCl ３ : HoCl ３ An electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2.3:0.125:0.075:0.2:0.1:0.05:0.025:0.05:0.1:0.2:0.05.

[0044] Example 11 (Reference) In the preparation of the electrolyte of Example 1, LiCl, ZrCl ４ , TaCl ５ , and ErCl ３ Each raw material powder was mixed with LiCl:ZrCl ４ : TaCl ５ : ErCl ３The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 1.75:0.25:0.5:0.25.

[0045] Example 12 (Reference) In the preparation of the electrolyte of Example 1, LiCl, ZrCl ４ , TaCl ５ , DyCl ３ , ErCl ３ , HoCl ３ , and AlCl ３ Each raw material powder was mixed with LiCl:ZrCl ４ : TaCl ５ : DyCl ３ : ErCl ３ : HoCl ３ : AlCl ３ An electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2.6:0.2:0.1:0.3:0.1:0.2:0.1.

[0046] Example 13 (Reference) In the preparation of the electrolyte of Example 1, LiCl, ZrCl ４ , TaCl ５ , MoCl ５ , Gd ２ O ３ , YbCl ３ , DyCl ３ , ErCl ３ , HoCl ３ , and AlCl ３ Each raw material powder was mixed with LiCl:ZrCl ４ : TaCl ５ : MoCl ５ : Gd ２ O ３ : YbCl ３ : DyCl ３ : ErCl ３ : HoCl ３ : AlCl ３ An electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2.65:0.15:0.05:0.05:0.025:0.05:0.35:0.15:0.05:0.1.

[0047] Example 14 (Reference) In the preparation of the electrolyte of Example 1, LiCl, YCl ３, and ZrCl ４ Each raw material powder was mixed with LiCl:YCl ３ : ZrCl ４ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2.5:0.5:0.5.

[0048] Results Table 1 shows the compositions and measurement results of the solid electrolytes prepared in Examples 1 to 15. In addition, the composition formula of Examples 1 to 6 was Li6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) １＋ｃ Cl ６－２ｄ－ｅ－ｆ O ｄ F ｅ Br ｆ In order to confirm that the following conditions are satisfied (wherein a>0, b>0, a+b<1, −0.2≦c≦0.2, 0≦d<3, 0≦e<6, and 0<f<6), the composition formula and each coefficient applied to the above general formula are shown in Table 2.

[0049]

[0050]

[0051] The results shown in Table 1 reveal the following: Comparison of Examples 1 and 2 (containing Br) with Reference Example 10 (containing no Br), comparison of Examples 3 and 4 (containing Br) with Reference Example 11 (containing no Br), comparison of Example 5 (containing Br) with Reference Example 12 (containing no Br), and comparison of Example 6 (containing Br) with Reference Example 13 (containing no Br), in which the comparative objects have the same composition ratios other than Cl and Br, reveals that the addition of Br not only provides a high initial conductivity, but also allows the conductivity to be maintained at a high level (although it decreases to some extent) even after 16 hours of exposure in a dry room controlled at a dew point of −40° C., and furthermore, the conductivity decreased by the exposure can be significantly recovered by heat treatment.

[0052] In contrast, the conventional Li ｘ (Y,Zr)Cl ｙ Br ｚWith regard to the composition system of the present invention, a comparison with Comparative Examples 7 to 9 (containing Br) and Reference Example 14 (containing no Br), which share the same composition ratios except for Cl and Br, reveals that although the addition of Br improved the initial conductivity, the conductivity decreased dramatically after 16 hours of exposure in a dry room controlled at a dew point of -40°C, and the conductivity decreased by the exposure could not be recovered by heat treatment. These results demonstrate that the effect of the solid electrolyte of the present invention is unexpectedly excellent.

Claims

1. Li, M α , M β , M γ a solid electrolyte containing Cl and Br, α is at least one element selected from the group consisting of Zr and Hf, and M β is at least one element selected from the group consisting of Ta, Nb, and Mo, and M γ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, Sc and Al.

2. M α The solid electrolyte of claim 1 , wherein 3. M β The solid electrolyte according to claim 1 or 2, wherein the Cr content of the Cr-based solid electrolyte is 1.0 or more and the Cr content of the Cr-based solid electrolyte is 1.0 or more.

4. M γ The solid electrolyte according to claim 1 or 2, wherein contains at least one element selected from the group consisting of Gd, Yb, and Er.

5. The following composition formula: Li6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) １＋ｃ Cl ６－２ｄ－ｅ－ｆ O ｄ F ｅ Br ｆ and a composition satisfying 0<a, 0<b, a+b<1, −0.2≦c≦0.2, 0≦d<3, 0≦e<6, and 0<f<6.

6. A lithium ion battery comprising the solid electrolyte according to claim 1 or 2.

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