Solid electrolytes and batteries

Abstract

The solid electrolyte comprises A, Mα, Mβ, Mγ, and Cl, wherein 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, Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc, and the physical quantity of Cl is greater than the physical quantity of A. By doing so, it is possible to provide a solid electrolyte having high ionic conductivity and also high stability.

Description

Technology Field

[0001] The present invention relates to a solid electrolyte and a battery.

[0002] [Reference to related applications]

[0003] The present application claims the benefit of priority from international patent application PCT / JP2022 / 26960 filed on July 7, 2022 and international patent application PCT / JP2023 / 12626 filed on March 28, 2023, and all disclosures of these applications are incorporated herein. Background Technology

[0004] Recently, there has been a strong demand for miniaturization and improved reliability (safety) for batteries that serve as power sources for electronic devices. For this reason, all-solid-state batteries utilizing solid electrolytes are attracting attention. Furthermore, halides are known as sulfur-free solid electrolytes, and Li3YCl6 exhibits high lithium-ion conductivity at room temperature (see, for example, Patent Publication No. 6934626 (Reference 1)). In International Publication No. 2020 / 070956 (Reference 2), Li 6-4b+ab (Zr 1-a M a ) b A halogenated 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 also 0 < a < 1 and 0 < b < 1.5 are satisfied.

[0005] In addition, in “Na2ZrCl6-enabling high stable 3 V all-solid-state Na-ion batteries” by Hiram Kwak et al. (Energy Storage Materials, 2021, Vol. 37, pp. 47-54) (Reference 3), it is reported that Na2ZrCl6 exhibits high sodium ion conductivity at room temperature. Furthermore, in the specification of U.S. Patent Application Publication No. 2021 / 43966 (Reference 4), (Li x M1 y )(M2) 3-δ (M3) 2-ω O 12-z X z An oxide comprising a compound represented by is disclosed, and said oxide has a garnet structure. Additionally, in Example 19 of Reference 4, Li 6.8 La3Zr 0.4 Hf 0.4 Sn 0.4 Sc 0.4 Nb 0.4 O 11.8 Cl 0.2 An oxide represented by is disclosed.

[0006] However, when the inventors of the present invention produced chloride electrolyte powders disclosed in Literature 1 and 2 and placed them in a dry room controlled to a dew point of -40°C, it was found that the electrolyte decomposed and could not maintain the initial lithium ion conductivity, that is, that the stability was low. It was also found that Na2ZrCl6 disclosed in Literature 3 had low stability.

[0007] The present invention aims to provide a solid electrolyte that is suitable for solid electrolytes, has high ionic conductivity, and also has high stability.

[0008] The invention of Embodiment 1 comprises a solid electrolyte comprising A, Mα, Mβ, Mγ, and Cl, wherein 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, Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc, and the amount of Cl is greater than the amount of A.

[0009] According to the present invention, a solid electrolyte having high ionic conductivity and high stability can be provided.

[0010] The invention of Embodiment 2 is a solid electrolyte of Embodiment 1, wherein A comprises Li.

[0011] The invention of Embodiment 3 is a solid electrolyte of Embodiment 1 or 2, wherein Mα comprises Zr.

[0012] The invention of Embodiment 4 is a solid electrolyte of any one of Embodiments 1 to 3, wherein Mβ comprises Ta.

[0013] The invention of Embodiment 5 is a solid electrolyte of any one of Embodiments 1 to 4, wherein Mγ comprises Gd or Yb.

[0014] The invention of Embodiment 6 is represented by the following compositional formula as a solid electrolyte of any one of Embodiments 1 to 5, and

[0015] A 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6

[0016] 0<a, 0<b, a+b<1 and -0.2≤c≤0.2 are satisfied.

[0017] The invention of Embodiment 7 is a solid electrolyte of any one of Embodiments 1 to 6, wherein A is Li, and the value obtained by dividing the average ionic radius of Li, Mα, Mβ, and Mγ by the ionic radius of Cl is less than 0.424.

[0018] The invention of Embodiment 8 is a solid electrolyte of any one of Embodiments 1, 3 to 6, wherein A is Na, and the value obtained by dividing the average ionic radius of Na, Mα, Mβ, and Mγ by the ionic radius of Cl is less than 0.526.

[0019] The invention of Embodiment 9 is a solid electrolyte of any one of Embodiments 1 to 8 that does not include a garnet structure.

[0020] The invention of Embodiment 10 is a battery comprising a solid electrolyte of any one of Embodiments 1 to 9.

[0021] The aforementioned objectives and other objectives, features, modes, and advantages will become clear from the detailed description of the present invention below with reference to the attached drawings. Brief explanation of the drawing

[0022] Figure 1 is a cross-sectional view showing an all-solid-state lithium-ion secondary battery. Specific details for implementing the invention

[0023] FIG. 1 is a 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) has, in order from the top of FIG. 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 positive electrode (11) includes a current collector (111) and a positive electrode layer (112). The positive electrode layer (112) includes 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) includes a negative electrode active material.

[0024] 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 having a layered rock salt structure, for example, NCM (Li(Ni,Co,Mn)O2). The positive electrode active material may be other lithium composite oxides, for example, NCA (Li(Ni,Co,Al)O2) having a layered rock salt structure, LCO (LiCoO2), or LNMO (LiNi) having a spinel-type structure. 0.5 Mn 1.5 It may also be O4), LFP (LiFePO4) having an olivine-type structure, etc. The positive electrode layer (112) further comprises, in addition to the positive electrode active material, a solid electrolyte and an electron conductivity aid (carbon black, etc.) described later. In this embodiment, the positive electrode layer (112) is formed by integrating these materials by applying pressure or heating.

[0025] As the negative electrode active material of the negative electrode layer (122), for example, LTO (Li4Ti5O 12 Examples of compounds include NTO (Nb2TiO7), TiO2 (titanium oxide), graphite, and SiO (silicon monoxide). The negative electrode layer (122) includes, in addition to the negative electrode active material, a solid electrolyte described later. The negative electrode layer (122) may further include an electron conductivity aid (such as carbon black). In this embodiment, the negative electrode layer (122) is formed by integrating these materials by applying pressure or heating.

[0026] 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 those described above, and various other compositions and materials may be adopted.

[0027] The electrolyte layer (13) comprises a solid electrolyte according to one embodiment of the present invention (hereinafter also referred to as “the solid electrolyte”) or comprises said solid electrolyte. said solid electrolyte is a lithium (Li) ion conductive material. said solid electrolyte comprises a lithium (Li) element, three other types of metal elements (Mα, Mβ, Mγ) that become cations, and a chlorine (Cl) element. said solid electrolyte may also comprise Li, Mα, Mβ, Mγ and Cl.

[0028] Mα is an element that becomes 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 becomes 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 becomes 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 above solid electrolyte containing at least one trivalent, tetravalent, and pentavalent element each in addition to Li as a cation, high lithium ion conductivity and high stability are realized as described below. Furthermore, since hydrogen sulfide gas is not generated in the said solid electrolyte, a high-safety all-solid-state secondary battery (1) is provided.

[0029] In the present solid electrolyte, it is preferable that Mα contains Zr, and Mα may be Zr alone. By doing so, as described below, the decrease in lithium ion conductivity caused by the influence of water in the air can be suppressed, thereby more reliably improving stability. It is preferable that Mβ contains Ta, and Mβ may be Ta alone. By doing so, lithium ion conductivity can be restored by heat treatment, as described in the examples below. It is preferable that Mγ contains Gd or Yb, and Mγ may be Gd or Yb alone, or Gd and Yb alone. By doing so, lithium ion conductivity immediately after synthesis (initial), as described in the examples below, can be more reliably improved. The amount of Li is, for example, greater than any amount of Mβ, Mα, and Mγ, and preferably greater than the sum of the amounts of Mα, Mβ, and Mγ. In one example, the amount of Mα is greater than any amount of Mβ and Mγ, but may be smaller. Typically, the amount of Cl is greater than the amount of Li. The amount of Cl may be, for example, greater than any amount of Li, Mα, Mβ, and Mγ, and greater than the sum of the amounts of Li, Mα, Mβ, and Mγ.

[0030] A preferred solid electrolyte is a compound represented by the following compositional formula (1), and

[0031] Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6… (1)

[0032] 0 < a, 0 < b, a+b < 1, and -0.2 ≤ c ≤ 0.2 are satisfied. For a and b, 0.1 ≤ a ≤ 0.4 and 0.1 ≤ b ≤ 0.4 may be satisfied. Additionally, 0.1 ≤ a+b ≤ 0.6 may be satisfied. For c, -0.1 ≤ c ≤ 0.1 may be satisfied, and c may be 0. The above solid electrolyte may be crystalline or amorphous.

[0033] When confirming whether an unknown solid electrolyte is the solid electrolyte in question, chemical analysis is performed on the unknown solid electrolyte to determine whether the constituent elements are Li, Mα, Mβ, Mγ, and Cl. In confirming whether the unknown solid electrolyte is of 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.

[0034] The molar ratio of Li, Mα, Mβ, Mγ, and Cl in the above compositional formula (1) is Li:Mα:Mβ:Mγ:Cl = 6-(4+ab)(1+c):(1-ab)(1+c):a(1+c):b(1+c):6. In the molar ratio obtained by analysis of an unknown solid electrolyte, if the value of Li is 0.90×{6-(4+ab)(1+c)} or higher and 1.10×{6-(4+ab)(1+c)} or lower, it is considered that the above compositional formula (1) is satisfied with respect to Li. It is more preferable that the value of Li is 0.95×{6-(4+ab)(1+c)} or higher and 1.05×{6-(4+ab)(1+c)} or lower. The same applies to Mα, Mβ, and Mγ.

[0035] In a preferred solid electrolyte, the value obtained by dividing the average ionic radius of Li, Mα, Mβ, and Mγ by the ionic radius of Cl (hereinafter referred to as the "average ionic radius ratio") is less than 0.424. More preferably, the average ionic radius ratio is less than 0.422, and even more preferably, less than 0.420. In such a solid electrolyte, stability can be more reliably improved as described below. The lower limit of the average ionic radius ratio is not particularly limited, but is, for example, 0.395. The average ionic radius (rc) of Li, Mα, Mβ, and Mγ included in the solid electrolyte is calculated based on Equation 1.

[0036] (Mathematical Formula 1)

[0037] rc=Σ(rC·RC) / ΣRC

[0038] Here, rC represents the ionic radius of the elements (i.e., cations) included in Li, Mα, Mβ, and Mγ. RC represents the amount of substance of each element. By dividing the average ionic radius (rc) of Li, Mα, Mβ, and Mγ by the ionic radius (ra) of Cl, the average ionic radius ratio (rc / ra) is obtained. In solid electrolytes where the average ionic radius ratio is less than 0.424, it is thought that the bonding distance between the cation and Cl is shortened, and the bonding force between the cation and Cl increases. Furthermore, it is estimated that the magnitude of this bonding force improves the stability of the material.

[0039] The present solid electrolyte is prepared, for example, according to the following method. First, a powder of a chloride containing Li, a powder of a chloride containing Mα, a powder of a chloride containing Mβ, and a powder of a chloride containing Mγ are prepared. The chloride containing Li is, for example, LiCl. The chloride containing Mα is, for example, MαCl4. The chloride containing Mβ is, for example, MβCl5. The chloride containing Mγ is, for example, MγCl3. These powders are weighed and mixed in a predetermined molar ratio.

[0040] Next, the mixture is milled (mechanochemical milling). Here, as an example of the milling process, a planetary ball mill is used. In a planetary ball mill, since the pot rotates while the stage carrying the pot revolves, it is possible to generate very high impact energy. The milling process may also be performed using other types of grinders. Through the above milling process, a powder of the solid electrolyte used for the positive electrode layer (112), negative electrode layer (122), or electrolyte layer (13) can be obtained. In the present example of the process, the milling process is performed at room temperature, but conditions such as temperature may be appropriately changed. The solid electrolyte may also be manufactured by a process other than milling, such as calcination.

[0041] The present solid electrolyte may contain sodium (Na) instead of Li, or may contain Na along with Li. That is, the present solid electrolyte comprises A, Mα, Mβ, Mγ, and Cl, wherein A is at least one element selected from the group consisting of Li and Na. Mα, Mβ, and Mγ are the same as above. Even when A is Na, high (sodium) ion conductivity and high stability are realized as described below. The present solid electrolyte may also comprise A, Mα, Mβ, Mγ, and Cl. In this case, the total mass of A, Mα, Mβ, Mγ, and Cl relative to the entire solid electrolyte is, for example, 95 mass% or more. Typically, the amount of substance of Cl is greater than the amount of substance of A. The amount of substance of Cl may be greater than the amount of substance of any element included in the solid electrolyte. Unlike the oxide described in U.S. Patent Application Publication No. 2021 / 43966 (Reference 4 above), the present solid electrolyte preferably does not contain a garnet structure. Whether or not it contains a garnet structure can be confirmed by X-ray diffraction analysis.

[0042] When considering the case where the solid electrolyte contains Na, the above composition formula (1) is expressed as the following composition formula (2), and

[0043] A 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6… (2)

[0044] Similar to the composition formula (1), 0<a, 0<b, a+b<1, and -0.2≤c≤0.2 are satisfied. Additionally, Na can be quantified by ICP-emission spectroscopy or the like.

[0045] In a preferred solid electrolyte where A is Na, the value obtained by dividing the average ionic radii of Na, Mα, Mβ, and Mγ by the ionic radius of Cl (hereinafter referred to as the "average ionic radius ratio," as in the case where A is Li) is less than 0.526. More preferably, the average ionic radius ratio is less than 0.520, and even more preferably, less than 0.515. In such a solid electrolyte, stability can be more reliably improved as described below. The lower limit of the average ionic radius ratio is not particularly limited, but is, for example, 0.480. The average ionic radius ratio in the case where A is Na is obtained in the same way as in the case where A is Li.

[0046] In the preparation of a solid electrolyte where A is Na, a chloride powder containing Na is used instead of a chloride powder containing Li. The chloride containing Na is, for example, NaCl. Then, by mixing the chloride powder containing Na, the chloride powder containing Mα, the chloride powder containing Mβ, and the chloride powder containing Mγ, and performing a milling process, a solid electrolyte powder where A is Na can be obtained.

[0047] The all-solid-state secondary battery (1) using a solid electrolyte containing Na may be an all-solid-state sodium ion secondary battery. In this case, as the positive electrode active material of the positive electrode layer (112), examples include layered compounds such as NaCoO2, NaNiO2, NaMnO2, Na(Ni,Co,Mn)O2, NaFeO2, Na(Fe,Mn)O2, Na(Ni,Mn,Fe,Ti)O2, spinel-type NaMn2O4, polyanionic-type Na3V2(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na4Fe7(PO4)6, Na3V(PO3)3N, etc. Additionally, as the negative electrode active material of the negative electrode layer (122), examples include metals such as Na, In, Sn, Sb, Na alloy, graphite, hard carbon, Na 4 / 3 Ti 5 / 3 O4, Na2Ti6O13 , Na 0.66 [Li 0.22 Ti 0.78 Examples include O2, Na3V2(PO4)3, SnO, etc. A may contain Li and Na, and the conductive ions in the all-solid-state secondary battery (1) may be both Li ions and Na ions.

[0048] Next, examples and comparative examples of the present solid electrolyte in which A is Li will be described. Tables 1 and 2 show the composition, evaluation results, etc. of the solid electrolytes of Examples 1 to 21.

[0049] [Table 1]

[0050]

[0051] [Table 2]

[0052]

[0053] (Example 1)

[0054] [Preparation of Electrolytes]

[0055] In an argon atmosphere having a dew point of -60℃ or lower, 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, and these raw material powders were ground and mixed in a mortar. The obtained mixed powder was placed in a zirconia pot together with zirconia jade and milled using a planetary ball mill at 300 rpm for 20 h (hours) to obtain a solid electrolyte powder.

[0056] [Exposure Test]

[0057] The solid electrolyte powder was placed in a petri dish and left to stand for 16 hours in a dry room controlled to a dew point of -40℃ (dew point).

[0058] [Heat Treatment]

[0059] Solid electrolyte powder that had been left in a dry room for 16 hours (exposed) was heat-treated at 150°C.

[0060] [Conductivity Measurement]

[0061] Solid electrolyte powder was introduced into a mold containing a resin sleeve and upper and lower punches made of SUS (stainless steel), and uniaxial press molding was performed by applying pressure of 150 MPa. A wire was connected to the upper and lower punches, and impedance measurements were performed at room temperature to calculate the lithium ion conductivity (in Examples 22-23 and Comparative Examples 10-11 described later, it is sodium ion conductivity, and hereinafter also referred to simply as "ion conductivity").

[0062] [Stability Assessment]

[0063] The impedance of the solid electrolyte powder immediately after milling with a planetary ball mill (after synthesis), the solid electrolyte powder exposed in a dry room for 16 hours, and the solid electrolyte powder heat-treated after exposure was measured to calculate the ionic conductivity. In Table 1, the ionic conductivity of the solid electrolyte powder immediately after milling (i.e., initial conductivity) is shown in the column "After Synthesis," the ionic conductivity of the solid electrolyte powder exposed in a dry room for 16 hours is shown in the column "Exposure 16 hours," and the ionic conductivity of the solid electrolyte powder heat-treated after exposure is shown in the column "Exposure 16 hours + Heat Treatment" (the same applies to Table 2 and Tables 3 and 4 described later).

[0064] In addition, the retention rate of ion conductivity was calculated in the stability evaluation. The retention rate of ion conductivity after 16 h of exposure was calculated by (100 × (ion conductivity after 16 h of exposure) / (ion conductivity after synthesis)). The retention rate of ion conductivity after 16 h of exposure + heat treatment was calculated by (100 × (ion conductivity after 16 h of exposure + heat treatment) / (ion conductivity after synthesis)).

[0065] [Calculation of Average Ionic Radius Ratio]

[0066] The average ionic radius ratio of the solid electrolyte of Example 1 was calculated using the aforementioned Equation 1. Here, the solid electrolyte of Example 1 contains Li, Zr, Ta, and Gd as cations and Cl as an anion. The ionic radii (coordination number 6) of Li, Zr, Ta, Gd, and Cl are 0.76 Å, 0.72 Å, 0.64 Å, 0.938 Å, and 1.81 Å, respectively. The molar ratio of Li, Zr, Ta, and Gd is 1.700:0.500:0.400:0.100. Therefore, the average ionic radius (rc) of the cation was calculated as 0.741 Å by calculating (1.700×0.76+0.500×0.72+0.400×0.64+0.100×0.938) / (1.700+0.500+0.400+0.100). The ionic radius (ra) of the anion is 1.81 Å. Therefore, the average ionic radius ratio was calculated as 0.410 by calculating rc / ra. In the column "satisfies rc / ra < 0.424" in Table 1, the evaluation is marked "○" if the average ionic radius ratio is less than 0.424, and "×" if it is 0.424 or greater (the same applies to Tables 2 and 3).

[0067] (Example 2)

[0068] In the preparation of the electrolyte of Example 1 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 = 1.8:0.6:0.3:0.1, and tests and evaluations were performed.

[0069] (Example 3)

[0070] In the preparation of the electrolyte of Example 1 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 = 1.9:0.7:0.2:0.1, and tests and evaluations were performed.

[0071] (Example 4)

[0072] In the preparation of the electrolyte of Example 1 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 = 2.0:0.8:0.1:0.1, and tests and evaluations were performed.

[0073] (Example 5)

[0074] In the preparation of the electrolyte of Example 1 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, and tests and evaluations were performed.

[0075] (Example 6)

[0076] In the preparation of the electrolyte of Example 1 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 = 2.0:0.6:0.2:0.2, and tests and evaluations were performed.

[0077] (Example 7)

[0078] In the preparation of the electrolyte of Example 1 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 such that the molar ratio of LiCl:ZrCl4:TaCl5:GdCl3 was 2.1:0.7:0.1:0.2, and the electrolyte was tested and evaluated.

[0079] (Example 8)

[0080] In the preparation of the electrolyte of Example 1 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 = 2.1:0.5:0.2:0.3, and tests and evaluations were performed.

[0081] (Example 9)

[0082] In the preparation of the electrolyte of Example 1 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 = 2.3:0.5:0.1:0.4, and tests and evaluations were performed.

[0083] (Example 10)

[0084] In the preparation of the electrolyte of Example 1 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 = 1.7:0.5:0.4:0.1, and tests and evaluations were performed.

[0085] (Example 11)

[0086] In the preparation of the electrolyte of Example 1 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 = 1.9:0.5:0.3:0.2, and tests and evaluations were performed.

[0087] (Example 12)

[0088] In the preparation of the electrolyte of Example 1 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 = 2.1:0.5:0.2:0.3, and tests and evaluations were performed.

[0089] (Example 13)

[0090] In the preparation of the electrolyte of Example 1 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 = 2.3:0.5:0.1:0.4, and tests and evaluations were performed.

[0091] (Example 14)

[0092] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, GdCl3, and YbCl3 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:TaCl5:GdCl3:YbCl3 was 2.2:0.4:0.2:0.2, and tests and evaluations were performed.

[0093] (Example 15)

[0094] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, NbCl5, and YbCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:NbCl5:YbCl3 = 1.9:0.5:0.3:0.2, and tests and evaluations were performed.

[0095] (Example 16)

[0096] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, HfCl4, TaCl5, and YbCl3 were weighed as raw material powders in a molar ratio of LiCl:HfCl4:TaCl5:YbCl3 = 1.9:0.5:0.3:0.2, and tests and evaluations were performed.

[0097] (Example 17)

[0098] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and HoCl3 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:TaCl5:HoCl3 was 1.9:0.7:0.2:0.1, and the electrolyte was tested and evaluated.

[0099] (Example 18)

[0100] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and DyCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:DyCl3 = 1.9:0.7:0.2:0.1, and tests and evaluations were performed.

[0101] (Example 19)

[0102] In the preparation of the electrolyte of Example 1 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 = 1.9:0.7:0.2:0.1, and tests and evaluations were performed.

[0103] (Example 20)

[0104] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and ScCl3 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:TaCl5:ScCl3 was 1.8:0.6:0.3:0.1, and the electrolyte was tested and evaluated.

[0105] (Example 21)

[0106] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and EuCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:TaCl5:EuCl3 = 1.8:0.6:0.3:0.1, and tests and evaluations were performed.

[0107] Table 3 shows the composition and evaluation results of the solid electrolytes of Comparative Examples 1 to 9.

[0108] [Table 3]

[0109]

[0110] (Comparative Example 1)

[0111] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl and YCl3 were weighed as raw material powders so that the molar ratio of LiCl:YCl3 = 3:1, and tests and evaluations were performed.

[0112] (Comparative Example 2)

[0113] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl and ZrCl4 were weighed as raw material powders so that the molar ratio of LiCl:ZrCl4 = 2:1, and tests and evaluations were performed.

[0114] (Comparative Example 3)

[0115] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl and YbCl3 were weighed as raw material powders so that the molar ratio of LiCl:YbCl3 = 3:1, and tests and evaluations were performed.

[0116] (Comparative Example 4)

[0117] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, and SmCl3 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:SmCl3 was 2.1:0.9:0.1, and tests and evaluations were performed.

[0118] (Comparative Example 5)

[0119] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, and BiCl3 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:BiCl3 was 2.1:0.9:0.1, and tests and evaluations were performed.

[0120] (Comparative Example 6)

[0121] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, and GdCl3 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:GdCl3 was 2.3:0.7:0.3, and the electrolyte was tested and evaluated.

[0122] (Comparative Example 7)

[0123] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, and YbCl3 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:YbCl3 was 2.3:0.7:0.3, and the test and evaluation were performed.

[0124] (Comparative Example 8)

[0125] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, and YCl3 were weighed as raw material powders in a molar ratio of LiCl:ZrCl4:YCl3 = 2.5:0.5:0.5, and tests and evaluations were performed.

[0126] (Comparative Example 9)

[0127] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that LiCl, ZrCl4, and TaCl5 were weighed as raw material powders such that the molar ratio of LiCl:ZrCl4:TaCl5 was 1.7:0.7:0.3, and the electrolyte was tested and evaluated.

[0128] As shown in Tables 1 to 3, the ionic conductivity after synthesis of all solid electrolytes of Examples 1 to 21 is 4.8 × 10⁻⁶ -4 S / cm or higher, and also the ionic conductivity at 16 h of exposure is 3.9 × 10⁻⁶ -5 It was S / cm or higher. Meanwhile, in the solid electrolytes of Comparative Examples 1 to 9, at least one of the ionic conductivity after synthesis and the ionic conductivity after 16 h of exposure was less than the above value. Thus, the solid electrolytes of Examples 1 to 21 are materials that achieve both high ionic conductivity and high stability. The solid electrolytes of Examples 1 to 21 also satisfy the above composition formula (1).

[0129] In addition, in the solid electrolytes of Examples 1 to 8 and 10 to 21, compared to Comparative Examples 1 to 9, the ionic conductivity after 16 h of exposure and the ionic conductivity after 16 h of exposure plus heat treatment are high, and the ionic conductivity after 16 h of exposure plus heat treatment is 1.0 × 10⁻⁶. -4 It showed S / cm or higher. In addition, the retention rate of ionic conductivity after 16 h of exposure was higher than that of Comparative Examples 1 to 9. Therefore, it can be seen that the solid electrolytes of Examples 1 to 8 and 10 to 21, which have an average ionic radius ratio (rc / ra) of less than 0.424, are materials with higher stability.

[0130] In the solid electrolytes of Examples 1 to 21, although the detailed mechanism for the improvement in stability is not clear, it is believed that including at least one trivalent, tetravalent, and pentavalent element, respectively, in addition to Li as a cation, contributes to stability. Furthermore, from the perspective of improving stability, as mentioned above, it is desirable that the average ionic radius ratio be smaller than 0.424. A small average ionic radius ratio indicates that the bonding distance between the cation and Cl is short, and it is believed that the bonding force between the cation and Cl is large. It is presumed that the magnitude of this bonding force improves the stability of the material.

[0131] Comparing Comparative Examples 1 to 3, Comparative Example 2, in which the solid electrolyte contains Zr, shows a higher ionic conductivity after 16 h of exposure. Furthermore, in Examples 1 to 4 and Examples 5 to 7, there is a tendency for the ionic conductivity after 16 h of exposure to increase as the proportion of Zr increases. Therefore, it is believed that stability is more clearly improved by including Zr in the solid electrolyte. Although the reason for this is not clear, it has been confirmed that stability against water is improved in solid electrolytes containing Zr, and it is believed that this contributes to the improvement in ionic conductivity after 16 h of exposure. Additionally, it is believed that stability is improved when Hf, which is a tetravalent cation like Zr, is used instead of Zr or together with Zr. In fact, in Example 16, Hf is used instead of Zr, and in this case as well, a somewhat high ionic conductivity is obtained after 16 h of exposure.

[0132] In Comparative Example 9, which contains Zr and Ta in addition to Li and Cl, the ionic conductivity after 16 h+ exposure heat treatment is higher compared to Comparative Example 2, which contains only Zr. Additionally, in Examples 1 to 14 and 16 to 21, which contain Ta, the ionic conductivity after 16 h+ exposure heat treatment is approximately higher. Therefore, it is believed that by including Ta in the solid electrolyte, it becomes possible to recover ionic conductivity through heat treatment. It is also believed that when Nb, which is a pentavalent cation like Ta and has the same ionic radius as Ta, is used instead of Ta or together with Ta, ionic conductivity is more easily recovered through heat treatment. In fact, in Example 15, Nb is used instead of Ta, and in this case as well, high ionic conductivity is obtained during 16 h+ exposure heat treatment.

[0133] In Comparative Examples 6 and 7, which contain Zr and Gd or Yb in addition to Li and Cl, the ionic conductivity (initial conductivity) after synthesis is significantly higher compared to Comparative Example 2, which contains only Zr. Furthermore, in Examples 1 to 16, which contain Gd or Yb, the ionic conductivity after synthesis is approximately higher. Therefore, it is believed that the ionic conductivity after synthesis is more clearly improved when the solid electrolyte contains Gd or Yb. It is also believed that the ionic conductivity after synthesis is improved when Dy, Er, Ho, Eu, and Sc, which are trivalent cations similar to Gd and Yb and have ionic radii similar to Gd or Yb, are used instead of or together with Gd or Yb. In fact, in Examples 17 to 21, Ho, Dy, Er, Sc, and Eu are used, respectively, and in these cases as well, high ionic conductivity is obtained after synthesis.

[0134] Next, examples and comparative examples of the present solid electrolyte when A is Na will be described. Table 4 shows the composition and evaluation results of the solid electrolytes of Examples 22 to 23 and Comparative Examples 10 to 11. In the column "satisfies rc / ra < 0.526" in Table 4, if the average ionic radius ratio is less than 0.526, the evaluation is marked "○", and if it is 0.526 or greater, the evaluation is marked "×". In addition, in calculating the average ionic radius ratio, the ionic radius of Na (coordination number 6) is 1.02 Å.

[0135] [Table 4]

[0136]

[0137] (Example 22)

[0138] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that NaCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders in a molar ratio of NaCl:ZrCl4:TaCl5:GdCl3 = 1.8:0.6:0.3:0.1, and tests and evaluations were performed.

[0139] (Example 23)

[0140] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that NaCl, ZrCl4, TaCl5, and YbCl3 were weighed as raw material powders such that the molar ratio of NaCl:ZrCl4:TaCl5:YbCl3 was 1.9:0.5:0.3:0.2, and the electrolyte was tested and evaluated.

[0141] (Comparative Example 10)

[0142] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that NaCl and ZrCl4 were weighed as raw material powders such that the molar ratio of NaCl:ZrCl4 = 2:1, and tests and evaluations were performed.

[0143] (Comparative Example 11)

[0144] In the preparation of the electrolyte of Example 1 above, the electrolyte was prepared in the same manner as in Example 1, except that NaCl, ZrCl4, and YbCl3 were weighed as raw material powders in a molar ratio of NaCl:ZrCl4:YbCl3 = 2.5:0.5:0.5, and tests and evaluations were performed.

[0145] As shown in Table 4, the solid electrolytes of Examples 22 to 23 had higher ion conductivity after synthesis, ion conductivity after 16 h of exposure, and ion conductivity after 16 h of exposure + heat treatment than the solid electrolytes of Comparative Examples 10 to 11. Thus, even in Na ion conductors, high initial conductivity and high stability can be obtained by including at least one trivalent, tetravalent, and pentavalent element each in addition to Na as a cation. The solid electrolytes of Examples 22 to 23 also satisfy the above composition formula (2).

[0146] In the solid electrolytes of Examples 22 to 23, although the detailed mechanism for the improvement in stability is not clear, it is believed that including at least one trivalent, tetravalent, and pentavalent element, respectively, in addition to Na as a cation, contributes to stability. Furthermore, from the perspective of improving stability, as mentioned above, it is desirable that the average ionic radius ratio be smaller than 0.526. A small average ionic radius ratio indicates that the bonding distance between the cation and Cl is short, and it is believed that the bonding force between the cation and Cl is large. It is presumed that the magnitude of this bonding force improves the stability of the material.

[0147] As described above, the present solid electrolyte comprises A, Mα, Mβ, Mγ, and Cl. 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. Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc. The present solid electrolyte has high ionic conductivity (initial conductivity), maintains high ionic conductivity even under a dry room environment with a dew point of -40°C, and possesses high stability. Therefore, by applying the present solid electrolyte to the conventional battery manufacturing process performed under the said dry room environment, it becomes possible to easily manufacture lithium-ion batteries or sodium-ion batteries. To achieve higher initial conductivity and stability, it is preferable that A includes Li, and it is more preferable that A is Li.

[0148] Preferably, the present solid electrolyte is represented by the following compositional formula, and

[0149] A 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6

[0150] 0<a, 0<b, a+b<1 and -0.2≤c≤0.2 are satisfied. By doing so, a solid electrolyte with high ionic conductivity and high stability can be realized more reliably.

[0151] When A is Li, preferably, the value obtained by dividing the average ionic radii of Li, Mα, Mβ, and Mγ by the ionic radius of Cl (i.e., the average ionic radius ratio) is less than 0.424. By doing so, the stability of the solid electrolyte can be improved more reliably.

[0152] When A is Na, preferably, the value obtained by dividing the average ionic radius of Na, Mα, Mβ, and Mγ by the ionic radius of Cl is less than 0.526. By doing so, the stability of the solid electrolyte can be improved more reliably.

[0153] Various modifications are possible in this solid electrolyte and all-solid secondary battery (1).

[0154] The present solid electrolyte containing Li, Mα, Mβ, Mγ, and Cl may not satisfy the composition formula (1) above. Additionally, the average ionic radius ratio may be 0.424 or higher. Likewise, the present solid electrolyte containing Na, Mα, Mβ, Mγ, and Cl may not satisfy the composition formula (2) above. Additionally, the average ionic radius ratio may be 0.526 or higher.

[0155] The present solid electrolyte may be mixed with other materials (which may include Li or Na) and used as an electrolyte material. In this case, the present solid electrolyte is preferably the component with the largest mass ratio among the components included in the electrolyte material, i.e., the main component. The mass ratio of the main component in the electrolyte material is preferably 50 mass% or more, more preferably 60 mass% or more, and even more preferably 70 mass% or more.

[0156] The solid electrolyte used in the all-solid-state secondary battery (1) does not necessarily have to be included in all of the positive electrode (11), negative electrode (12), and electrolyte layer (13), but is sufficient if it is included in at least one of the positive electrode (11), negative electrode (12), and electrolyte layer (13). In addition, the solid electrolyte may be used in a battery other than an all-solid-state secondary battery, and may be used for purposes other than batteries.

[0157] The configurations in the above embodiments and each variant may be appropriately combined as long as they do not contradict each other.

[0158] Although the invention has been described in detail, the description provided is illustrative and not limiting. Therefore, it can be said that numerous modifications or embodiments are possible without departing from the scope of the invention. Explanation of the symbols

[0159] 1 All-solid-state secondary battery 11 Straight Drama 12 plays 13 Electrolyte layer

Claims

Claim 1 A solid electrolyte comprising A, Mα, Mβ, Mγ, and Cl, wherein A is Li, 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 value obtained by dividing the average ionic radius of Li, Mα, Mβ, and Mγ by the ionic radius of Cl is less than 0.424, and the amount of substance of Cl is greater than the amount of substance of A. Claim 2 A solid electrolyte comprising A, Mα, Mβ, Mγ, and Cl, wherein A is 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, Mγ is at least one element selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu, and Sc, the value obtained by dividing the average ionic radius of Na, Mα, Mβ, and Mγ by the ionic radius of Cl is less than 0.526, and the amount of substance of Cl is greater than the amount of substance of A. Claim 3 A solid electrolyte according to claim 1 or 2, wherein Mα contains Zr. Claim 4 A solid electrolyte according to claim 1 or 2, wherein Mβ comprises Ta. Claim 5 A solid electrolyte according to claim 1 or 2, wherein Mγ comprises Gd or Yb. Claim 6 In paragraph 1 or 2, it is represented by the following composition formula, and A 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c A solid electrolyte satisfying Cl60<a, 0<b, a+b<1 and -0.2≤c≤0.

2. Claim 7 A solid electrolyte that does not include a garnet structure, in claim 1 or 2. Claim 8 A battery comprising the solid electrolyte described in paragraph 1 or 2. Claim 9 delete Claim 10 delete

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