Solid electrolyte and battery

Abstract

A solid electrolyte according to the present invention contains A, Mα, Mβ, Mγ and Cl; A represents at least one element that is selected from the group consisting of Li and Na; Mα represents at least one element that is selected from the group consisting of Zr and Hf; Mβ represents at least one element that is selected from the group consisting of Ta and Nb; Mγ represents at least one element that is selected from the group consisting of Gd, Yb, Dy, Er, Ho, Eu and Sc; and the amount of substance of Cl is higher than the amount of substance of A. Consequently, the present invention is able to provide a solid electrolyte which has a high ionic conductivity and high stability.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte and a battery. [Citation of Related Applications] This 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 the entire disclosures of these applications are incorporated herein.

Background Art

[0002] In recent years, there has been a strong demand for miniaturization and improved reliability (safety) of batteries that serve as power sources for electronic devices. For this reason, all-solid-state batteries using solid electrolytes have attracted attention. Further, halides are known as solid electrolytes that do not contain sulfur, and Li3YCl6 exhibits high lithium ion conductivity at room temperature (see, for example, Japanese Patent No. 6934626 (Document 1)). In International Publication No. 2020 / 070956 (Document 2), a halide solid electrolyte material represented by Li 6-4b+ab (Zr 1-a M a ) b X6 is disclosed. Here, M is at least one element selected from the group consisting of Al, Ga, Bi, Sc, Sm, and Sb, X is a halogen element, and 0 < a < 1 and 0 < b < 1.5 are satisfied.

[0003] Further, in "Na2ZrCl6 enabling highly stable 3 V all-solid-state Na-ion batteries" by Hiram Kwak et al. (Energy Storage Materials, 2021, Vol. 37, pp. 47-54) (Document 3), it is reported that Na2ZrCl6 exhibits high sodium ion conductivity at room temperature. In addition, in the specification of US Patent Application Publication No. 2021 / 43966 (Document 4), (Li x M1 y )(M2) 3-δ (M3) 2-ω O12-z X z An oxide containing a compound represented by is disclosed, and the oxide has a garnet structure. Also, in Example 19 of Document 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.

[0004] By the way, when the inventors of the present application prepared the chloride electrolyte powder disclosed in Documents 1 and 2 and left it in a dry room controlled at a dew point of -40°C, it was found that the electrolyte decomposed and could not maintain the initial lithium ion conductivity, that is, the stability was low. The same was found for Na2ZrCl6 disclosed in Document 3.

Summary of the Invention

[0005] The present invention is directed to a solid electrolyte, and an object thereof is to provide a solid electrolyte having high ionic conductivity and high stability.

[0006] The invention of Aspect 1 is a solid electrolyte containing 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 substance of Cl is larger than the amount of substance of A.

[0007] According to the present invention, a solid electrolyte having high ionic conductivity and high stability can be provided.

[0008] The invention of Aspect 2 is the solid electrolyte of Aspect 1, wherein A contains Li.

[0009] The invention of Aspect 3 is the solid electrolyte of Aspect 1 or 2, wherein Mα contains Zr.

[0010] The invention of Aspect 4 is the solid electrolyte of any one of Aspects 1 to 3, wherein Mβ contains Ta.

[0011] The invention of Aspect 5 is the solid electrolyte of any one of Aspects 1 to 4, wherein Mγ contains Gd or Yb.

[0012] The invention of Aspect 6 is the solid electrolyte of any one of Aspects 1 to 5, which is represented by the following compositional formula, A 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6 0 < a, 0 < b, a + b < 1, and -0.2 ≤ c ≤ 0.2 are satisfied.

[0013] The invention of Aspect 7 is the solid electrolyte of any one of Aspects 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.

[0014] The invention of Aspect 8 is the solid electrolyte of any one of Aspects 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.

[0015] The invention of Aspect 9 is the solid electrolyte of any one of Aspects 1 to 8, which does not include a garnet structure.

[0016] The invention of Aspect 10 is a battery including the solid electrolyte of any one of Aspects 1 to 9.

[0017] The above objects and other objects, features, aspects, and advantages will be clarified by the following detailed description of the invention with reference to the accompanying drawings.

Brief Description of the Drawings

[0018]

Figure 1

Mode for Carrying Out the Invention

[0019] FIG. 1 is a longitudinal 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 in 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 contains a positive electrode active material. The negative electrode 12 includes a current collector 121 and a negative electrode layer 122. The negative electrode layer 122 contains a negative electrode active material.

[0020] The positive electrode active material of the positive electrode layer 112 preferably contains a lithium composite oxide. A preferred positive electrode active material is a lithium composite oxide having a layered rock salt structure, for example, NCM (Li(Ni,Co,Mn)O2). The positive electrode active material may be other lithium composite oxides, for example, NCA (Li(Ni,Co,Al)O2), LCO (LiCoO2) having a layered rock salt structure, LNMO (LiNi 0.5 Mn 1.5 O4) having a spinel-type structure, LFP (LiFePO4) having an olivine-type structure, etc. The positive electrode layer 112 further contains a solid electrolyte and an electron conduction aid (such as carbon black) described later in addition to the positive electrode active material. The positive electrode layer 112 in the present embodiment is an integrated body of these substances by pressure or heating.

[0021] As the negative electrode active material of the negative electrode layer 122, for example, LTO (Li4Ti5O 12) Compounds such as NTO (Nb2TiO7), TiO2 (titanium oxide), graphite, and SiO (silicon monoxide) can be mentioned. The negative electrode layer 122 contains, in addition to the negative electrode active material, the solid electrolyte described below. The negative electrode layer 122 may further contain an electron conduction auxiliary agent (such as carbon black). The negative electrode layer 122 in the present embodiment is formed by integrating these substances by pressure or heating.

[0022] The configurations and materials of the positive electrode 11 and the negative electrode 12 of the all-solid-state secondary battery 1 are not limited to those described above, and various other configurations and materials can be adopted.

[0023] The electrolyte layer 13 is made of a solid electrolyte (hereinafter also referred to as "the present solid electrolyte") according to an embodiment of the present invention, or contains the solid electrolyte. The solid electrolyte is a lithium (Li) ion conductive material. The solid electrolyte contains a lithium (Li) element, three other metal (Mα, Mβ, Mγ) elements serving as cations, and a chlorine (Cl) element. The solid electrolyte may be composed of Li, Mα, Mβ, Mγ, and Cl.

[0024] 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 solid electrolyte containing at least one element each of trivalent, tetravalent, and pentavalent elements in addition to Li as a cation, as will be described later, high lithium ion conductivity and high stability are achieved. Further, since hydrogen sulfide gas is not generated in the solid electrolyte, the all-solid-state secondary battery 1 with high safety is provided.

[0025] In this solid electrolyte, Mα preferably contains Zr, and Mα may be only Zr. Thereby, as will be described later, it is possible to suppress a decrease in lithium ion conductivity due to the influence of water or the like in the air, and more reliably improve stability. Mβ preferably contains Ta, and Mβ may be only Ta. Thereby, as in the examples described later, the lithium ion conductivity can be restored by heat treatment. Mγ preferably contains Gd or Yb, and Mγ may be only Gd or Yb, or only Gd and Yb. Thereby, as in the examples described later, it is possible to more reliably improve the lithium ion conductivity immediately after synthesis (initial stage). The amount of substance of Li is, for example, larger than the amount of substance of any of Mα, Mβ, and Mγ, and preferably larger than the total amount of substance of Mα, Mβ, and Mγ. In one example, the amount of substance of Mα is larger than the amount of substance of any of Mβ and Mγ, but it may also be smaller. Typically, the amount of substance of Cl is larger than the amount of substance of Li. The amount of substance of Cl is, for example, larger than the amount of substance of any of Li, Mα, Mβ, and Mγ, and may also be larger than the total amount of substance of Li, Mα, Mβ, and Mγ.

[0026] A preferred solid electrolyte is a compound represented by the following compositional formula (1), Li 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6···(1) 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. Also, 0.1 ≤ a + b ≤ 0.6 may be satisfied. For c, -0.1 ≤ c ≤ 0.1 may be satisfied, or c may be 0. The solid electrolyte may be crystalline or amorphous.

[0027] When confirming whether an unknown solid electrolyte is this solid electrolyte, chemical analysis is performed on the unknown solid electrolyte to check whether the constituent elements are Li, Mα, Mβ, Mγ, and Cl. In the confirmation of whether the unknown solid electrolyte conforms to the above composition formula (1), for Li, Mα, Mβ, and Mγ, they can be quantified by, for example, ICP-emission spectrometry. For Cl, it can be quantified by, for example, ion chromatography.

[0028] In the composition formula (1), the molar ratios of Li, Mα, Mβ, Mγ, and Cl are Li:Mα:Mβ:Mγ:Cl = 6-(4+a-b)(1+c):(1-a-b)(1+c):a(1+c):b(1+c):6. In the molar ratios obtained by the analysis of the unknown solid electrolyte, if the value of Li is not less than 0.90×{6-(4+a-b)(1+c)} and not more than 1.10×{6-(4+a-b)(1+c)}, it is considered that the above composition formula (1) is satisfied for Li. More preferably, the value of Li is not less than 0.95×{6-(4+a-b)(1+c)} and not more than 1.05×{6-(4+a-b)(1+c)}. The same applies to Mα, Mβ, and Mγ.

[0029] In a preferred solid electrolyte, the value obtained by dividing the average ionic radii 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. The average ionic radius ratio is more preferably less than 0.422, and even more preferably less than 0.420. In such a solid electrolyte, as will be described later, the stability can be more reliably improved. 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 contained in the solid electrolyte is calculated based on Equation (1).

[0030] (Equation (1)) rc = Σ(rC·RC) / ΣRC Here, rC represents the ionic radius of the elements (i.e., cations) contained 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 a solid electrolyte where the average ionic radius ratio is less than 0.424, it is considered that the bonding distance between the cation and Cl becomes shorter, and the bonding force between the cation-Cl becomes higher. And it is presumed that this high bonding force improves the stability as a material.

[0031] This solid electrolyte is produced, for example, by 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 so as to have a predetermined molar ratio.

[0032] Subsequently, the mixture is subjected to a milling treatment (mechanochemical milling). Here, in an example of the milling treatment, a planetary ball mill is used. In a planetary ball mill, since the pot rotates while the stage on which the pot is placed revolves, it is possible to generate extremely high impact energy. The milling treatment may be performed using other types of grinders. By the above milling treatment, the powder of this solid electrolyte used for the positive electrode layer 112, the negative electrode layer 122, or the electrolyte layer 13 is obtained. In this example of the treatment, the milling treatment is performed at room temperature, but conditions such as temperature may be appropriately changed. This solid electrolyte may be produced by methods other than the milling treatment, such as firing.

[0033] This solid electrolyte may contain sodium (Na) instead of lithium (Li), or may contain Na together with Li. That is, the solid electrolyte contains A, Mα, Mβ, Mγ, and Cl, and A is at least one element selected from the group consisting of Li and Na. Mα, Mβ, and Mγ are the same as described above. Even when A is Na, as will be described later, high (sodium) ion conductivity and high stability are achieved. The solid electrolyte may consist of A, Mα, Mβ, Mγ, and Cl. In this case, the total mass of A, Mα, Mβ, Mγ, and Cl with respect to the entire solid electrolyte is, for example, 95% by mass or more. Typically, the amount of substance of Cl is larger than the amount of substance of A. The amount of substance of Cl may be larger than the amount of substance of any element contained in the solid electrolyte. Different from the oxide described in US Patent Application Publication No. 2021 / 43966 (Document 4 above), it is preferable that this solid electrolyte does not contain a garnet structure. Whether it contains a garnet structure or not can be confirmed by X-ray diffraction analysis.

[0034] Considering the case where this solid electrolyte contains Na, the above compositional formula (1) is represented as the following compositional formula (2), A 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6···(2) Similar to the compositional formula (1), 0 < a, 0 < b, a + b < 1, and -0.2 ≤ c ≤ 0.2 are satisfied. Note that Na can be quantified by ICP-emission spectrometry or the like.

[0035] 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, similar to the case where A is Li, referred to as the "average ionic radius ratio") is less than 0.526. The average ionic radius ratio is more preferably less than 0.520, and even more preferably less than 0.515. In such a solid electrolyte, as will be described later, the stability can be more reliably improved. The lower limit of the average ionic radius ratio is not particularly limited, but for example, it is 0.480. The average ionic radius ratio when A is Na is determined in the same manner as when A is Li.

[0036] In the production of a solid electrolyte where A is Na, instead of the powder of a chloride containing Li, a powder of a chloride containing Na is used. The chloride containing Na is, for example, NaCl. Then, the powder of the chloride containing Na, the powder of the chloride containing Mα, the powder of the chloride containing Mβ, and the powder of the chloride containing Mγ are mixed and subjected to a milling process to obtain a powder of the solid electrolyte where A is Na.

[0037] The all-solid-state secondary battery 1 using a solid electrolyte containing Na as A 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, for example, layered compounds such as NaCoO2, NaNiO2, NaMnO2, Na(Ni,Co,Mn)O2, NaFeO2, Na(Fe,Mn)O2, Na(Ni, Mn, Fe, Ti)O2, etc., spinel-type NaMn2O4, etc., polyanion-type Na3V2(PO4)3, Na2Fe2(SO4)3, NaFePO4, Na4Fe7(PO4)6, Na3V(PO3)3N, etc. can be mentioned. Also, as the negative electrode active material of the negative electrode layer 122, for example, metals such as Na, In, Sn, Sb, etc., Na alloys, graphite, hard carbon, Na 4 / 3 Ti 5 / 3 O4, Na2Ti6O 13 、Na 0.66 [Li 0.22 Ti 0.78Examples include O2, Na3V2(PO4)3, SnO, etc. A includes Li and Na, and the ions conducting in all-solid-state secondary battery 1 may be both Li ions and Na ions.

[0038] Next, examples and comparative examples of this solid electrolyte when A is Li will be described. Tables 1 and 2 show the compositions, evaluation results, etc. of the solid electrolytes of Examples 1 to 21.

[0039] [Table 1]

[0040] [Table 2]

[0041] (Example 1) [Preparation of electrolyte] In an argon atmosphere having a dew point of -60°C or lower, LiCl, ZrCl4, TaCl5, and GdCl3 as raw material powders were weighed so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 1.7:0.5:0.4:0.1, and these raw material powders were pulverized and mixed in a mortar. The obtained mixed powder was put into a zirconia pot together with zirconia balls, and subjected to milling treatment at 300 rpm for 20 h (hours) using a planetary ball mill to obtain a solid electrolyte powder.

[0042] [Exposure test] The solid electrolyte powder was put into a petri dish and left (exposed) in a dry room with the dew point controlled at -40°C for 16 h.

[0043] [Heat treatment] The solid electrolyte powder left (exposed) in the dry room for 16 h was heat-treated at 150°C.

[0044] [Conductivity measurement] A mold consisting of a resin sleeve and upper and lower punches made of SUS (stainless steel) was charged with solid electrolyte powder and pressed at 150 MPa for uniaxial press molding. Conductive wires were connected to the upper and lower punches, and impedance measurement was performed at room temperature to calculate the lithium ion conductivity (in Examples 22 to 23 and Comparative Examples 10 to 11 described later, it is sodium ion conductivity, and hereinafter, it is also simply referred to as "ion conductivity").

[0045] [Stability evaluation] Impedance measurements were performed on the solid electrolyte powder immediately after milling (after synthesis) in a planetary ball mill, the solid electrolyte powder exposed to the dry room for 16 h, and the solid electrolyte powder heat-treated after exposure to calculate the ion conductivity. In Table 1, the ion conductivity of the solid electrolyte powder immediately after milling (i.e., the initial conductivity) is shown in the column of "after synthesis", the ion conductivity of the solid electrolyte powder exposed to the dry room for 16 h is shown in the column of "16 h exposure", and the ion conductivity of the solid electrolyte powder heat-treated after exposure is shown in the column of "16 h exposure + heat treatment" (the same applies to Table 2 and Tables 3 and 4 described later).

[0046] Also, in the stability evaluation, the retention rate of the ion conductivity was calculated. The retention rate of the ion conductivity after 16 h of exposure was determined by (100×(ion conductivity after 16 h of exposure) / (ion conductivity after synthesis)). The retention rate of the ion conductivity after 16 h of exposure + heat treatment was determined by (100×(ion conductivity after 16 h of exposure + heat treatment) / (ion conductivity after synthesis)).

[0047] [Calculation of average ion radius ratio] The average ionic radius ratio of the solid electrolyte in Example 1 was calculated using Equation (1) above. Here, the solid electrolyte in 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 ratios of Li, Zr, Ta, and Gd are 1.700:0.500:0.400:0.100. Therefore, the average ionic radius rc of the cations was calculated to be 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 to be 0.410 by calculating rc / ra. In the column of "meeting rc / ra < 0.424" in Table 1, when the average ionic radius ratio is less than 0.424, the evaluation is "○", and when it is 0.424 or more, the evaluation is "×" (the same applies to Tables 2 and 3).

[0048] (Example 2) In the preparation of the electrolyte in Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 1.8:0.6:0.3:0.1.

[0049] (Example 3) In the preparation of the electrolyte in Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 1.9:0.7:0.2:0.1.

[0050] (Example 4) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 2.0:0.8:0.1:0.1.

[0051] (Example 5) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 1.9:0.5:0.3:0.2.

[0052] (Example 6) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 2.0:0.6:0.2:0.2.

[0053] (Example 7) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 2.1:0.7:0.1:0.2.

[0054] (Example 8) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 2.1:0.5:0.2:0.3.

[0055] (Example 9) In the production of the electrolyte of Example 1 above, an electrolyte was produced and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and GdCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3 = 2.3:0.5:0.1:0.4.

[0056] (Example 10) In the production of the electrolyte of Example 1 above, an electrolyte was produced and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and YbCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:YbCl3 = 1.7:0.5:0.4:0.1.

[0057] (Example 11) In the production of the electrolyte of Example 1 above, an electrolyte was produced and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and YbCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:YbCl3 = 1.9:0.5:0.3:0.2.

[0058] (Example 12) In the production of the electrolyte of Example 1 above, an electrolyte was produced and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and YbCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:YbCl3 = 2.1:0.5:0.2:0.3.

[0059] (Example 13) In the production of the electrolyte of Example 1 above, an electrolyte was produced and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and YbCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:YbCl3 = 2.3:0.5:0.1:0.4.

[0060] (Example 14) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, GdCl3, and YbCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:GdCl3:YbCl3 = 2.2:0.4:0.2:0.2:0.2.

[0061] (Example 15) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, NbCl5, and YbCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:NbCl5:YbCl3 = 1.9:0.5:0.3:0.2.

[0062] (Example 16) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, HfCl4, TaCl5, and YbCl3 were weighed as raw material powders so that the molar ratio was LiCl:HfCl4:TaCl5:YbCl3 = 1.9:0.5:0.3:0.2.

[0063] (Example 17) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and HoCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:HoCl3 = 1.9:0.7:0.2:0.1.

[0064] (Example 18) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and DyCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:DyCl3 = 1.9:0.7:0.2:0.1.

[0065] (Example 19) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and ErCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:ErCl3 = 1.9:0.7:0.2:0.1.

[0066] (Example 20) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and ScCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:ScCl3 = 1.8:0.6:0.3:0.1.

[0067] (Example 21) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, TaCl5, and EuCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5:EuCl3 = 1.8:0.6:0.3:0.1.

[0068] Table 3 shows the compositions, evaluation results, etc. of the solid electrolytes of Comparative Examples 1 to 9.

[0069] [Table 3]

[0070] (Comparative Example 1) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl and YCl3 were weighed as raw material powders so that the molar ratio was LiCl:YCl3 = 3:1.

[0071] (Comparative Example 2) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl and ZrCl4 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4 = 2:1.

[0072] (Comparative Example 3) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated 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 was 3:1.

[0073] (Comparative Example 4) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, and SmCl3 were weighed as raw material powders so that the molar ratio of LiCl:ZrCl4:SmCl3 was 2.1:0.9:0.1.

[0074] (Comparative Example 5) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, and BiCl3 were weighed as raw material powders so that the molar ratio of LiCl:ZrCl4:BiCl3 was 2.1:0.9:0.1.

[0075] (Comparative Example 6) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, and GdCl3 were weighed as raw material powders so that the molar ratio of LiCl:ZrCl4:GdCl3 was 2.3:0.7:0.3.

[0076] (Comparative Example 7) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, and YbCl3 were weighed as raw material powders so that the molar ratio of LiCl:ZrCl4:YbCl3 was 2.3:0.7:0.3.

[0077] (Comparative Example 8) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, and YCl3 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:YCl3 = 2.5:0.5:0.5.

[0078] (Comparative Example 9) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that LiCl, ZrCl4, and TaCl5 were weighed as raw material powders so that the molar ratio was LiCl:ZrCl4:TaCl5 = 1.7:0.7:0.3.

[0079] As shown in Tables 1 to 3, in the solid electrolytes of Examples 1 to 21, the ionic conductivity after synthesis was 4.8×10 -4 S / cm or more in all cases, and the ionic conductivity after exposure for 16 h was 3.9×10 -5 S / cm or more. On the other hand, in the solid electrolytes of Comparative Examples 1 to 9, at least one of the ionic conductivity after synthesis and the ionic conductivity after exposure for 16 h 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).

[0080] Also, in the solid electrolytes of Examples 1 to 8, 10 to 21, compared with Comparative Examples 1 to 9, the ionic conductivity after exposure for 16 h and the ionic conductivity after exposure for 16 h + heat treatment were high, and the ionic conductivity after exposure for 16 h + heat treatment was 1.0×10 -4 S / cm or more. Also, the retention rate of the ionic conductivity after exposure for 16 h was higher than that of Comparative Examples 1 to 9. Therefore, it can be seen that the solid electrolytes of Examples 1 to 8, 10 to 21 with an average ionic radius ratio (rc / ra) of less than 0.424 are materials with higher stability.

[0081] In the solid electrolytes of Examples 1 to 21, the detailed mechanism by which the stability is improved is not clear, but it is considered that containing at least one kind each of trivalent, tetravalent, and pentavalent elements in addition to Li as a cation contributes to the stability. Further, from the viewpoint of improving the stability, it is preferable that the average ionic radius ratio is smaller than 0.424 as described above. A smaller average ionic radius ratio indicates a shorter bond distance between the cation and Cl, and it is considered that the binding force between the cation and Cl is high. It is presumed that this high binding force improves the stability of the material.

[0082] Comparing Comparative Examples 1 to 3, in Comparative Example 2 in which the solid electrolyte contains Zr, the ionic conductivity after 16 h of exposure is high. Also, in Examples 1 to 4 and Examples 5 to 7, as the ratio of Zr increases, the ionic conductivity after 16 h of exposure tends to increase. Therefore, it is considered that the stability is more surely improved when the solid electrolyte contains Zr. The reason for this is not clear, but in the solid electrolyte containing Zr, it has been confirmed that the stability against water is improved, and this is considered to contribute to the improvement of the ionic conductivity after 16 h of exposure. Also, when Hf, which is a tetravalent cation like Zr, is used instead of Zr or together with Zr, the stability is considered to be improved. Actually, in Example 16, Hf is used instead of Zr, and in this case too, a certain degree of high ionic conductivity is obtained after 16 h of exposure.

[0083] In Comparative Example 9 containing Zr and Ta in addition to Li and Cl, the ionic conductivity after 16 h of exposure + heat treatment is higher than that in Comparative Example 2 containing only Zr. Also, in Examples 1 to 14 and 16 to 21 containing Ta, the ionic conductivity after 16 h of exposure + heat treatment is generally higher. Therefore, it is considered that the solid electrolyte can recover the ionic conductivity by heat treatment when it contains Ta. When Nb, which becomes a pentavalent cation like Ta and has the same ionic radius as Ta, is used instead of Ta or together with Ta, it is considered that the ionic conductivity is easily recovered by heat treatment. Actually, in Example 15, Nb is used instead of Ta, and in this case as well, high ionic conductivity is obtained in the 16 h of exposure + heat treatment.

[0084] In Comparative Examples 6 and 7 containing Zr and Gd or Yb in addition to Li and Cl, the ionic conductivity after synthesis (initial conductivity) is significantly higher than that in Comparative Example 2 containing only Zr. Also, in Examples 1 to 16 containing Gd or Yb, the ionic conductivity after synthesis is generally higher. Therefore, it is considered that the solid electrolyte can more surely improve the ionic conductivity after synthesis when it contains Gd or Yb. When Dy, Er, Ho, Eu, and Sc, which become trivalent cations like Gd and Yb and have an ionic radius approximate to that of Gd or Yb, are used instead of Gd or Yb or together with Gd or Yb, it is considered that the ionic conductivity after synthesis is improved. Actually, in Examples 17 to 21, Ho, Dy, Er, Sc, and Eu are used respectively, and in this case as well, high ionic conductivity is obtained after synthesis.

[0085] Next, examples and comparative examples of this solid electrolyte when A is Na will be described. Table 4 shows the compositions, evaluation results, etc. of the solid electrolytes of Examples 22 to 23 and Comparative Examples 10 to 11. In the column of "satisfying rc / ra < 0.526" in Table 4, when the average ionic radius ratio is less than 0.526, the evaluation is "○", and when it is 0.526 or more, the evaluation is "×". Also, in the calculation of the average ionic radius ratio, the ionic radius (coordination number 6) of Na is 1.02 Å.

[0086]

Table 4

[0087] (Example 22) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that NaCl, ZrCl4, TaCl5, and GdCl3 were weighed so that the molar ratio was NaCl:ZrCl4:TaCl5:GdCl3 = 1.8:0.6:0.3:0.1.

[0088] (Example 23) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that NaCl, ZrCl4, TaCl5, and YbCl3 were weighed so that the molar ratio was NaCl:ZrCl4:TaCl5:YbCl3 = 1.9:0.5:0.3:0.2.

[0089] (Comparative Example 10) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that NaCl and ZrCl4 were weighed so that the molar ratio was NaCl:ZrCl4 = 2:1.

[0090] (Comparative Example 11) In the preparation of the electrolyte of Example 1 above, an electrolyte was prepared and tested and evaluated in the same manner as in Example 1, except that NaCl, ZrCl4, and YbCl3 were weighed so that the molar ratio was NaCl:ZrCl4:YbCl3 = 2.5:0.5:0.5.

[0091] As shown in Table 4, in the solid electrolytes of Examples 22 to 23, the ionic conductivity after synthesis, the ionic conductivity after exposure for 16 h, and the ionic conductivity after exposure for 16 h + heat treatment were higher than those of the solid electrolytes of Comparative Examples 10 to 11. Thus, also in the Na ion conductor, by containing at least one kind each of trivalent, tetravalent, and pentavalent elements in addition to Na as a cation, high initial conductivity and high stability can be obtained. The solid electrolytes of Examples 22 to 23 also satisfy the above compositional formula (2).

[0092] In the solid electrolytes of Examples 22 to 23, the detailed mechanism of the improved stability is not clear, but it is considered that containing at least one kind each of trivalent, tetravalent, and pentavalent elements in addition to Na as a cation contributes to the stability. Further, from the viewpoint of improving the stability, it is preferable that the average ionic radius ratio is smaller than 0.526 as described above. A smaller average ionic radius ratio indicates a shorter bond distance between the cation and Cl, and it is considered that the bonding force between the cation and Cl is high. It is presumed that this high bonding force improves the stability as a material.

[0093] As described above, the present solid electrolyte contains 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 solid electrolyte has high ionic conductivity (initial conductivity), and high ionic conductivity is maintained even in a dry room environment with a dew point of -40°C, and has high stability. Therefore, it becomes possible to easily manufacture a lithium ion battery or a sodium ion battery by applying the solid electrolyte to an existing battery manufacturing process performed in the dry room environment. To achieve higher initial conductivity and stability, it is preferable that A contains Li, and it is more preferable that A is Li.

[0094] Preferably, this solid electrolyte is represented by the following compositional formula: A 6-(4+a-b)(1+c) (Mα (1-a-b) Mβ a Mγ b ) 1+c Cl6 0 < a, 0 < b, a + b < 1, and -0.2 ≤ c ≤ 0.2 are satisfied. Thereby, a solid electrolyte having high ionic conductivity and high stability can be more reliably realized.

[0095] When A is Li, preferably, the value obtained by dividing the average ionic radius of Li, Mα, Mβ, and Mγ by the ionic radius of Cl (that is, the average ionic radius ratio) is less than 0.424. Thereby, the stability of the solid electrolyte can be more reliably improved.

[0096] 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. Thereby, the stability of the solid electrolyte can be more reliably improved.

[0097] Various modifications are possible for this solid electrolyte and the all-solid-state secondary battery 1.

[0098] This solid electrolyte containing Li, Mα, Mβ, Mγ, and Cl may not satisfy the above compositional formula (1). Also, the average ionic radius ratio may be 0.424 or more. Similarly, this solid electrolyte containing Na, Mα, Mβ, Mγ, and Cl may not satisfy the above compositional formula (2). Also, the average ionic radius ratio may be 0.526 or more.

[0099] This solid electrolyte may be mixed with other substances (which may contain Li or Na) and used as an electrolyte material. In this case, it is preferable that this solid electrolyte is the component with the largest mass ratio among the components contained in the electrolyte material, that is, the main component. The mass ratio of the main component in the electrolyte material is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more.

[0100] This solid electrolyte used in the all-solid-state secondary battery 1 does not necessarily have to be contained in all of the positive electrode 11, negative electrode 12, and electrolyte layer 13, and it may be contained in at least one of the positive electrode 11, negative electrode 12, and electrolyte layer 13. Further, this solid electrolyte may be used in batteries other than all-solid-state secondary batteries, and may also be used for applications other than batteries.

[0101] The configurations in the above embodiments and each modification may be appropriately combined as long as they do not contradict each other.

[0102] Although the invention has been described and explained in detail, the above description is illustrative and not restrictive. Therefore, it can be said that numerous modifications and variations are possible without departing from the scope of the present invention.

Explanation of Reference Numerals

[0103] 1 All-solid-state secondary battery 11 Positive electrode 12 Negative electrode 13 Electrolyte layer

Claims

1. 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 substance of Cl is greater than the amount of substance of A.

2. The solid electrolyte according to Claim 1, wherein A contains Li.

3. The solid electrolyte according to Claim 1, wherein Mα contains Zr.

4. The solid electrolyte according to Claim 1, wherein Mβ contains Ta.

5. The solid electrolyte according to Claim 1, wherein Mγ contains Gd or Yb.

6. The solid electrolyte according to Claim 1, which is represented by the following composition formula: A ６－（４＋ａ－ｂ）（１＋ｃ） (Mα （１－ａ－ｂ） Mβ ａ Mγ ｂ ) １＋ｃ Cl ６ 0 < a, 0 < b, a + b < 1, and -0.2 ≤ c ≤ 0.

2.

7. The solid electrolyte according to Claim 1, 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.

8. The solid electrolyte according to Claim 1, 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.

9. The solid electrolyte according to Claim 1, which does not contain a garnet structure.

10. A battery comprising the solid electrolyte according to any one of Claims 1 to 9.

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