Solid electrolyte, electrochemical device, and sodium battery

Abstract

Provided is a solid electrolyte having high ion conductivity. This solid electrolyte is represented by a composition formula: Na6-(4+a-b)(1+c)(Mα (1-a-b)Mβ aMγ b)(1+c)Cl6-2dOd, 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 serving as a trivalent cation, and 0.3 < a, 0 < b, a+b < 1, -0.2 ≤ c ≤ 0.2, and 0 ≤ d < 3 are satisfied.

Description

Solid Electrolyte, Electrochemical Device, and Sodium Battery

[0001] The present disclosure relates to a solid electrolyte, an electrochemical device, and a sodium battery.

[0002] In recent years, there have been strong demands for miniaturization and improved reliability (safety) of batteries that serve as power sources for electronic devices. For this reason, all-solid-state batteries that use a solid electrolyte instead of an electrolytic solution have attracted attention. For example, development of inexpensive all-solid-state sodium batteries with abundant resource availability is underway.

[0003] Here, sulfide-based solid electrolytes are mentioned as one of the representative types of solid electrolytes. However, since sulfide-based solid electrolytes can generate toxic hydrogen sulfide, solid electrolytes that do not belong to sulfide-based solid electrolytes are desired from the viewpoint of safety.

[0004] Halides are known as solid electrolytes that do not contain sulfur. For example, Non-Patent Document 1 (Hiram Kwak et al., Energy Storage Materials, Vol. 37, 2021, pp. 47-54) discloses Na ２ ZrCl ６ that the solid electrolyte represented by the composition exhibits high sodium ion conductivity (1.8×10 －５ S / cm) at room temperature. Further, Non-Patent Document 2 (Kota Motohashi et al., ACS Materials Letters, Vol. 6, 2024, pp. 1178-1183) discloses NaTaCl ６ that the solid electrolyte represented by the composition exhibits high sodium ion conductivity (6.2×10 －５ S / cm) at 25°C. Furthermore, Patent Document 1 (WO2024 / 010065A1) discloses a solid electrolyte containing, in addition to Li or Na as cations, at least one each of trivalent, tetravalent, and pentavalent elements, and it is stated that high ionic conductivity and high stability are achieved according to such a solid electrolyte. In fact, Patent Document 1 discloses Na １．８ Zr ０．６ Ta ０．３ Gd ０．１ Cl６ The sodium ion conductivity of the solid electrolyte represented by the composition is 8.2 × 10⁻⁶. －５ S / cm, Na １．９ Zr ０．５ Ta ０．３ Yb ０．２ Cl ６ The sodium ion conductivity of the solid electrolyte represented by the composition is 8.3 × 10⁻⁶. －５ It has been shown to be S / cm.

[0005] WO2024 / 010065A1

[0006] Hiram Kwak et al., "Na2ZrCl6 enabling highly stable 3 V all-solid-state Na-ion batteries", Energy Storage Materials, Vol. 37, 2021, pp. 47-54Kota Motohashi et al., "NaTaCl6: Chloride as the End-Member of Sodium-Ion Conductors", ACS Materials Letters, Vol. 6, 2024, pp. 1178-1183

[0007] The solid electrolytes shown in Patent Document 1 and Non-Patent Documents 1 and 2 do not exhibit sufficiently high sodium ion conductivity at room temperature, and further improvements in ionic conductivity are desired.

[0008] The present inventors have now discovered that Na, M α M β M γ , and in a solid electrolyte containing Cl, M α M β and M γ As such, elements that become tetravalent, pentavalent, and trivalent cations are adopted, and M β We discovered that ionic conductivity can be improved by increasing the elemental composition ratio of the material beyond a predetermined value.

[0009] Therefore, an object of the present invention is to provide a solid electrolyte having high ionic conductivity.

[0010] The following embodiments are provided according to this disclosure: [Embodiment 1] The following composition formula: Na6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) （１＋ｃ） Cl ６－２ｄ O ｄ It is represented as M 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 and Nb, and M γ is a solid electrolyte that is at least one element that forms a trivalent cation, satisfying 0.3 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 ≤ d < 3. [Aspect 2] M γ The solid electrolyte according to Embodiment 1, wherein the element is at least one element selected from the group consisting of lanthanide elements that form a trivalent cation. [Embodiment 3] M γ The solid electrolyte according to embodiment 1 or 2, wherein the element is at least one element selected from the group consisting of La, Sm, Gd, Dy, Ho, Er, and Yb. [Embodiment 4] M γ A solid electrolyte according to any one of embodiments 1 to 3, wherein the element is at least one element selected from the group consisting of Gd, Ho, and Er. [Embodiment 5] A solid electrolyte according to any one of embodiments 1 to 4, satisfying 0.4 ≤ a. [Embodiment 6] A solid electrolyte according to any one of embodiments 1 to 5, satisfying 0 < b ≤ 0.3. [Embodiment 7] A solid electrolyte according to any one of embodiments 1 to 6, satisfying 0 < d ≤ 0.3. [Embodiment 8] M α A solid electrolyte according to any one of embodiments 1 to 7, wherein the solid electrolyte contains Zr. [Embodiment 9] M β A solid electrolyte according to any one of embodiments 1 to 8, wherein the solid electrolyte is Ta. [Embodiment 10] An electrochemical device comprising the solid electrolyte according to any one of embodiments 1 to 9. [Embodiment 11] A sodium battery comprising the solid electrolyte according to any one of embodiments 1 to 9.

[0011] This is a schematic cross-sectional view showing an example of a sodium battery according to the present invention.

[0012] Solid Electrolyte The solid electrolyte according to this disclosure has the following compositional formula: Na6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) （１＋ｃ） Cl ６－２ｄ O ｄ It is represented by the above composition formula, M 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 and Nb. γ is at least one element that forms a trivalent cation. The above composition formula satisfies 0.3 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 ≤ d < 3. Thus, Na, M α M β M γ , and in a solid electrolyte containing Cl, M α M β and M γ As such, elements that become tetravalent, pentavalent, and trivalent cations are adopted, and M β By increasing the elemental composition ratio of the sodium ion to a predetermined value, the sodium ion conductivity can be improved. In this specification, "sodium ion conductivity" and "sodium ion conductivity" may be referred to as "ionic conductivity" and "ionic conductivity," respectively.

[0013] As mentioned above, various halogen-based solid electrolytes that do not contain sulfur have been reported (see, for example, Non-Patent Documents 1 and 2 and Patent Document 1), but conventional halogen-based solid electrolytes do not have sufficiently high sodium ion conductivity at room temperature (hereinafter referred to as room temperature conductivity), and further improvement in conductivity was desired. This problem is successfully solved by the present invention. That is, the inventors of the present invention have found that Na ｘ MCl ６ In the composition system (where M is a cation), various combinations of cations (M) and various composition ratios were investigated. As a result, in the aforementioned composition formula, M α As Zr and / or Hf, M βTa and / or Nb, M γ As a combination of elements that form a trivalent cation, M β By making the coefficient a greater than 0.3, a high room temperature conductivity (for example, 1.0 × 10) can be achieved. －４ It was found to exhibit a conductivity greater than S / cm. Although the mechanism is not entirely clear, it is thought that the presence of at least one element each of trivalent, tetravalent, and pentavalent cations in addition to Na, and a large amount of elements that form pentavalent cations (i.e., Ta and / or Nb), contributes to the high ionic conductivity.

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

[0015] M β M is an element that forms a pentavalent cation. β is at least one element selected from the group consisting of Ta and Nb, preferably containing Ta. β The coefficient a in this equation satisfies 0.3 < a (where a + b < 1), preferably 0.4 ≤ a, more preferably 0.4 ≤ a ≤ 0.8, and particularly preferably 0.5 ≤ a ≤ 0.8.

[0016] M γ is at least one element that forms a trivalent cation. γ It is preferable that is at least one element selected from the group consisting of lanthanide elements that form a trivalent cation. Examples of such lanthanide elements include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, more preferably La, Sm, Gd, Dy, Ho, Er, and Yb, and even more preferably Gd, Ho, and Er. γ The coefficient b multiplied by satisfies 0 < b (where a + b < 1), preferably 0 < b ≤ 0.5, more preferably 0 < b ≤ 0.3, and even more preferably 0.1 ≤ b ≤ 0.3.

[0017] In the above compositional formula, a + b, which is the sum of coefficients a and b, satisfies a + b < 1, preferably a + b ≤ 0.9, more preferably 0.5 ≤ a + b ≤ 0.9, and even more preferably 0.7 ≤ a + b ≤ 0.8.

[0018] The coefficient c is set to allow for a predetermined tolerance range, taking into account measurement errors in the composition of the solid electrolyte. From this viewpoint, the coefficient c satisfies -0.2 ≤ c ≤ 0.2, preferably -0.15 ≤ c ≤ 0.15, more preferably -0.1 ≤ c ≤ 0.1, and typically c = 0.

[0019] As can be seen from the above compositional formula, not only Cl but also O may be present at the Cl site, if desired. O is an arbitrary element, and the coefficient d multiplied by O satisfies 0 ≤ d < 3, preferably 0 ≤ d < 0.5, more preferably 0 ≤ d ≤ 0.4, and even more preferably 0 ≤ d ≤ 0.3.

[0020] The solid electrolyte of this disclosure has a concentration of 1.0 × 10 at room temperature (e.g., 25°C). －４ Preferably, it exhibits a sodium ion conductivity of more than S / cm, and more preferably 2.0 × 10⁻⁶. －４ S / cm or more, more preferably 5.0 × 10 －４ The conductivity should be S / cm or higher. Since a higher sodium ion conductivity is desirable, there is no upper limit, but it is typically 1.0 × 10⁻⁶. －１ Less than S / cm, more typically 1.0 × 10⁻⁶ －２ It is less than or equal to S / cm.

[0021] To confirm whether an unknown solid electrolyte is the above-mentioned solid electrolyte, a chemical analysis should be performed on the unknown solid electrolyte to determine if its constituent elements are Na, M α M β M γ It is sufficient to check whether it is , Cl, or O. Furthermore, to check whether an unknown solid electrolyte has the above compositional formula, for example, Na, M α M β and M γcan be quantified using an ICP-optical emission spectrometer. Cl can be quantified by ion chromatography. O can be quantified by ONH analysis using an oxygen / nitrogen / hydrogen analyzer or the like.

[0022] The solid electrolyte of the present disclosure may be produced by any method. For example, sodium chloride (NaCl), M α chloride, M β chloride, and M γ chloride raw material powders are weighed and mixed at a predetermined molar ratio, and the obtained mixed powder is milled, whereby a solid electrolyte can be favorably produced. When the solid electrolyte contains O, instead of or together with the above chlorides, M α oxide, M β oxide, and / or M γ oxide may be used.

[0023] Electrochemical Device According to a preferred aspect of the present disclosure, an electrochemical device including the solid electrolyte of the present disclosure is provided. The electrochemical device of the present disclosure is not particularly limited as long as it is a device that mutually converts electrical energy and chemical energy using a chemical reaction. Preferable examples of electrochemical devices include primary batteries, secondary batteries, fuel cells, electrolyzers, sensors, and the like. A particularly preferable example of an electrochemical device is a sodium battery described below.

[0024] Sodium Battery According to a preferred aspect of the present disclosure, a sodium battery including the solid electrolyte of the present disclosure is provided. FIG. 1 schematically shows an example of a sodium battery 10 according to the present disclosure. The sodium battery 10 typically includes a positive electrode 12, a negative electrode 14, and an electrolyte layer 16 disposed between the positive electrode 12 and the negative electrode 14. The sodium battery 10 of this embodiment is preferably a sodium ion secondary battery, and more preferably an all-solid sodium ion secondary battery. However, the sodium battery 10 is not limited to all-solid batteries, and may be a battery that uses a combination of a solid material (such as a solid electrolyte) called a semi-solid battery and a liquid material (such as an electrolytic solution or ionic liquid), or may be another type of battery.

[0025] The positive electrode 12 contains a positive electrode active material. Typically, the positive electrode active material is a substance capable of inserting and desorbing sodium. Preferable examples of the positive electrode active material include NaCoO ２ , NaNiO ２ , NaMnO ２ , Na(Ni,Co,Mn)O ２ , NaFeO ２ , Na(Fe,Mn)O ２ , Na(Ni,Mn,Fe,Cu,Zn,Sn,Ti)O ２ , Na ０．７２ Li ０．１４ Cu ０．１５ Mn ０．７１ O ２ and other layered compounds, NaMn ２ O ４ and other spinel-type compounds, Na ３ V ２ (PO ４ ) ３ , Na ２ Fe ２ (SO ４ ) ３ , NaFePO ４ , Na ４ Fe ７ (PO ４ ) ６ , Na ３ V(PO ３ ) ３ N, Na ３＋ｘ (Fe, Mn, V, Cr, Ti) ２ (PO ４ ) ３ and other polyanion-type compounds. In addition to the positive electrode active material, the positive electrode 12 preferably further contains a solid electrolyte and / or an electron conduction aid (such as carbon black). It is preferable that the positive electrode 12 in the present embodiment is obtained by integrating these substances by pressure application or heating. Therefore, as shown in FIG. 1, the positive electrode 12 is preferably in the form of a positive electrode layer. When the positive electrode 12 contains a solid electrolyte, the solid electrolyte according to the present disclosure described above may be used as such a solid electrolyte.

[0026] The negative electrode 14 contains a negative electrode active material. The negative electrode active material is typically a material from which sodium can be inserted and removed. Preferred examples of negative electrode active materials include metals such as Na, In, Sn, and Sb, Na alloys, graphite, hard carbon, and Na ４／３ Ti ５／３ O ４ Na ２ Ti ６ O １３ Na ０．６６ [Li ０．２２ Ti ０．７８ ]O ２ Na ３ LiTi ５ O １２ Na ３ V ２ (PO ４ ) ３ Examples include SnO. From the viewpoint of improving ionic conductivity, the negative electrode 14 preferably further contains a solid electrolyte in addition to the negative electrode active material. The negative electrode 14 may further contain an electron conduction aid (such as carbon black). In this embodiment, it is preferable that the negative electrode 14 is formed by integrating these materials by pressurization or heating. Therefore, as shown in Figure 1, it is preferable that the negative electrode 14 is in the form of a negative electrode layer. When the negative electrode 14 contains a solid electrolyte, the solid electrolyte according to the present disclosure described above may be used as such a solid electrolyte.

[0027] The electrolyte layer 16 is a layer containing an electrolyte, which is placed between the positive electrode 12 and the negative electrode 14. Typically, the electrolyte layer 16 contains a solid electrolyte, and preferably is composed of a solid electrolyte. In this case, the electrolyte layer 16 can be said to also function as a separator. It is preferable to use the solid electrolyte according to the present invention described above as the solid electrolyte contained in the electrolyte layer 16.

[0028] Typically, at least one of the positive electrode 12, the negative electrode 14, and the electrolyte layer 16 contains the solid electrolyte according to this disclosure. As mentioned above, this solid electrolyte exhibits high sodium ion conductivity. Furthermore, since this solid electrolyte is non-flammable, chemically stable, and does not generate hydrogen sulfide gas, it is possible to realize an essentially safe sodium 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.

[0029] The solid electrolyte according to this disclosure 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% by weight or more, more preferably 60% by weight or more, and even more preferably 70% by weight or more.

[0030] As described above, in the sodium battery 10 of this disclosure, materials that do not contain sulfides can be used for the positive electrode 12, the negative electrode 14, and the electrolyte layer 16. That is, it is preferable that no part of the positive electrode 12, the negative electrode 14, and the electrolyte layer 16 contains sulfides. By doing so, it is possible to provide a sodium battery 10 that is essentially safe and does not generate toxic gases such as hydrogen sulfide.

[0031] The sodium battery 10 preferably further comprises a positive electrode current collector 18 and a negative electrode current collector 20. The positive electrode current collector 18 is preferably provided on the side of the positive electrode 12 opposite to the electrolyte layer 16, and the negative electrode current collector 20 is preferably provided on the side of the negative electrode 14 opposite to the electrolyte layer 16. Examples of materials constituting 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), ITO (indium-tin oxide film), and the like.

[0032] The container 22 is not particularly limited as long as it is capable of housing a sodium battery 10 individually or a stack of multiple sodium batteries 10 arranged in series or parallel. In particular, when the sodium battery 10 is an all-solid-state battery, there is no concern about electrolyte leakage, so the container 22 can be a relatively simple container form. For example, a chip form for mounting in an electronic circuit or a laminate cell form for thin and wide space applications (e.g., a multilayer product of aluminum (Al) / polypropylene (PP)) can be used.

[0033] The present invention will be further described in detail by the following examples. However, the present invention is not limited to the following examples.

[0034] Example 1 (1) Preparation of electrolytes -NaCl, ZrCl ４ , TaCl ５ , and LaCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : LaCl ３ The raw materials were weighed to achieve a molar ratio of 1.7:0.3:0.5:0.2, and these raw material powders were ground and mixed in a mortar. The resulting mixture was placed in a zirconia pot along with zirconia pebbles, and milled at 300 rpm for 20 hours using a planetary ball mill to obtain a solid electrolyte powder.

[0035] (2) Evaluation of the electrolyte (measurement of ionic conductivity) The solid electrolyte powder obtained in (1) above was placed in a mold consisting of a resin sleeve and upper and lower punches made of stainless steel, and uniaxial press molding was performed by applying pressure at 150 MPa. Wires were connected to the upper and lower punches, and at room temperature (25°C), an electrochemical measurement system (Biological, model number: VMP3) was used to measure the AC voltage of 10 mV and frequency range of 10 ６ AC impedance measurements were performed under conditions ranging from Hz (1 MHz) to 0.1 Hz, and sodium ion conductivity was calculated from the obtained measurement results. The results are shown in Table 1.

[0036] Example 2: In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５, and SmCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : SmCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0037] Example 3: In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and GdCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : GdCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0038] Example 4: In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and DyCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : DyCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0039] Example 5 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and HoCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0040] Example 6 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and ErCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : ErCl ３The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0041] Example 7 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and YbCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : YbCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0042] Example 8: In the preparation of the electrolyte in Example 1, NaCl, HfCl ４ , TaCl ５ , and HoCl ３ Each raw material powder is mixed with NaCl:HfCl ４ : TaCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0043] Example 9: In the preparation of the electrolyte in Example 1, NaCl, HfCl ４ NbCl ５ and HoCl ３ Each raw material powder is mixed with NaCl:HfCl ４ : NbCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0044] Example 10 In the preparation of the electrolyte in Example 1, NaCl, HfCl ４ , TaCl ５ , and ErCl ３ Each raw material powder is mixed with NaCl:HfCl ４ : TaCl ５ : ErCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.2.

[0045] Example 11 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and HoCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.5:0.4:0.1.

[0046] Example 12 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and HoCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.3:0.1:0.8:0.1.

[0047] Example 13 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and HoCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.6:0.2:0.6:0.2.

[0048] Example 14 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and HoCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.8:0.2:0.5:0.3.

[0049] Example 15 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ GdCl ３and Gd ２ O ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : GdCl ３ : Gd ２ O ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.1:0.05.

[0050] Example 16 In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and Gd ２ O ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : Gd ２ O ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.7:0.3:0.5:0.1.

[0051] Example 17 (Comparison) In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and GdCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : GdCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.8:0.6:0.3:0.1. The electrolyte prepared in Example 17 corresponds to the electrolyte prepared in Example 22 of Patent Document 1 (WO2024 / 010065A1).

[0052] Example 18 (Comparison) In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and YbCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ : YbCl ３The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 1.9:0.5:0.3:0.2. The electrolyte prepared in Example 18 corresponds to the electrolyte prepared in Example 23 of Patent Document 1 (WO2024 / 010065A1).

[0053] Example 19 (Comparison) In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , and YbCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : YbCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 2.5:0.5:0.5.

[0054] Example 20 (Comparison) In the preparation of the electrolyte in Example 1, NaCl, ZrCl ４ , TaCl ５ , and HoCl ３ Each raw material powder is mixed with NaCl:ZrCl ４ : TaCl ５ :HoCl ３ The electrolyte was prepared and evaluated in the same manner as in Example 1, except that the weighing was done to achieve a molar ratio of 2.2:0.4:0.2:0.4.

[0055] Results Table 1 shows the composition and ionic conductivity of the solid electrolytes prepared in Examples 1 to 20. Furthermore, the compositional formulas for Examples 1 to 16 are Na6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) （１＋ｃ） Cl ６－２ｄ O ｄ To confirm whether the following conditions are met or not (wherein the formula is 0.3 < a, 0 < b, a + b < 1, -0.2 ≤ c ≤ 0.2, and 0 ≤ d < 3), Table 2 shows the empirical formula and each coefficient applied to the above general formula.

[0056]

[0057]

[0058] As shown in Table 1, the solid electrolytes of Examples 1 to 16 exhibited higher sodium ion conductivity compared to the solid electrolytes of Examples 17 to 20. Specifically, the solid electrolytes of Examples 1 to 16 satisfied the above general formula and had an ionic conductivity of 1.0 × 10⁻⁶. －４ The value was greater than S / cm. On the other hand, the solid electrolytes of Examples 17-20 did not satisfy the above general formula, and their ionic conductivity was 1.0 × 10⁻⁶. －４ The value was less than or equal to S / cm. In the solid electrolytes of Examples 1 to 16, the detailed mechanism by which ionic conductivity is improved is not clear, but it is thought that the presence of at least one trivalent, tetravalent, and pentavalent element each as cations in addition to Na, and the presence of a predetermined amount of element that becomes a pentavalent cation, contributes to the manifestation of high ionic conductivity.

[0059] In the solid electrolytes of the examples (e.g., Examples 1-7) containing La, Sm, Gd, Dy, Ho, Er, or Yb as trivalent cations, high ionic conductivity has been obtained. Therefore, it is considered that high ionic conductivity can also be obtained when other elements that form trivalent cations, particularly elements with ionic radii similar to those of the above elements (e.g., lanthanide elements), are used instead of or in conjunction with these elements.

[0060] For tetravalent cations, it is thought that high ionic conductivity can also be obtained when Hf, which has an ionic radius similar to Zr, is used instead of Zr, or in conjunction with Zr. In fact, in Examples 8 and 10, Hf is used instead of Zr in Examples 5 and 6, respectively, and high ionic conductivity is obtained in these cases as well.

[0061] It is believed that high ionic conductivity can also be obtained when using Ta, which has an ionic radius similar to that of Nb, instead of Nb, or in combination with Nb, for pentavalent cations. In fact, in Example 9, Nb is used instead of Ta in Example 8, and high ionic conductivity is obtained in this case as well.

[0062] 10: Sodium battery, 12: Positive electrode, 14: Negative electrode, 16: Electrolyte layer, 18: Positive electrode current collector, 20: Negative electrode current collector, 22: Container

Claims

1. The following compositional formula: Na6-(4+a-b)(1+c)(M α （１－ａ－ｂ） M β ａ M γ ｂ ) （１＋ｃ） Cl ６－２ｄ O ｄ represented by, M α is at least one element selected from the group consisting of Zr and Hf, M β is at least one element selected from the group consisting of Ta and Nb, M γ is at least one element that forms a trivalent cation, which satisfies 0.3<a, 0<b, a+b<1, -0.2≤c≤0.2, and 0≤d<3. A solid electrolyte.

2. M γ The solid electrolyte according to claim 1, wherein the element is at least one element selected from the group consisting of lanthanide elements that form a trivalent cation.

3. M γ The solid electrolyte according to claim 1, wherein is at least one element selected from the group consisting of La, Sm, Gd, Dy, Ho, Er, and Yb.

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

5. The solid electrolyte according to claim 1, satisfying 0.4 ≤ a.

6. The solid electrolyte according to claim 1, satisfying 0 < b ≤ 0.

3.

7. The solid electrolyte according to claim 1, satisfying 0 < d ≤ 0.

3.

8. M α The solid electrolyte according to claim 1, wherein the solid electrolyte contains Zr.

9. M β The solid electrolyte according to claim 1, wherein the solid electrolyte contains Ta.

10. An electrochemical device comprising a solid electrolyte according to any one of claims 1 to 9.

11. A sodium battery comprising the solid electrolyte according to any one of claims 1 to 9.

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