Solid electrolytes and batteries

Abstract

This solid electrolyte includes A, M, F, and X. A is at least one element selected from the group consisting of Li, Na, and K. M is a metal element or a metalloid element other than A. X is at least one element selected from the group consisting of Cl, Br, and I. Accordingly, it is possible to provide a solid electrolyte that is highly safe and has high ionic conductivity.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte and a battery. [Reference to Related Applications] This application claims the benefit of priority from International Patent Application PCT / JP2022 / 42227, filed November 14, 2022, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] In recent years, development of solid electrolytes for use in all-solid-state batteries and the like has been progressing. For example, Japanese Patent Application Laid-Open No. 2011-129312 (Reference 1) discloses a solid electrolyte made of sulfide and an all-solid-state battery including the solid electrolyte. However, solid electrolytes made of sulfide can react with moisture in the air and generate toxic hydrogen sulfide gas. Therefore, International Publication Nos. 2021 / 161604 (Reference 2) and 2021 / 186833 (Reference 3) propose solid electrolytes made of fluorine compounds. Specifically, the solid electrolyte in Reference 2 contains Li, Zr, Al, and F. The solid electrolyte in Reference 3 contains Li, Ti, Al, M, and F, where M is Zr or Mg. In addition, "Solid Halide Electrolytes with High Lithium-Ion Conductivity for Application in 4 V Class Bulk-Type All-Solid-State Batteries" (ADVANCED MATERIALS, 2018, Vol. 30, 1803075) (Reference 4) by Tetsuya Asano and five others describes the solid electrolyte material Li3YCl6.

[0003] By the way, the solid electrolytes made of fluorine compounds in References 2 and 3 improve safety, but the lithium ion conductivity is 10 -6 It is in the S / cm range, which is not sufficient. Summary of the Invention

[0004] The present invention is directed to a solid electrolyte, and has an object to provide a solid electrolyte that is highly safe and has high ionic conductivity.

[0005] A first aspect of the invention is a solid electrolyte comprising A, M, F, and X, wherein A is at least one element selected from the group consisting of Li, Na, and K, and M is a metal element or a metalloid element other than A; comprising at least one element selected from the group consisting of Mα which is a trivalent cation, Mβ which is a tetravalent cation, and Mγ which is a divalent cation, X is at least one element selected from the group consisting of Cl, Br and I. wherein the composition formula of the solid electrolyte is A 3-b+c Mα 1-b-c Mβ b Mγ c F 6-a X a represented by, where 0 < a < 3, 0 ≤ b < 1, and 0 ≤ c < 1 are satisfied do.

[0006] According to the present invention, it is possible to provide a solid electrolyte that is highly safe and has high ionic conductivity.

[0007] A second aspect of the invention is the solid electrolyte of the first aspect, in which M contains Ga.

[0010] Aspects 3 The invention is 1 of The solid electrolyte includes M containing Zr.

[0011] Aspects 4 The invention is 1 of The solid electrolyte includes Mg.

[0012] Aspects 5 The invention is as follows: 4 A battery containing one of the solid electrolytes.

[0013] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0014]

Figure 1

Figure 2

[0015] FIG. 1 is a longitudinal 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, from top to bottom 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 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.

[0016] 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, such as NCM (Li(Ni, Co, Mn)O2). The positive electrode active material may be other lithium composite oxides, such as NCA (Li(Ni, Co, Al)O2) and LCO (LiCoO2) having a layered rock salt structure, and LNMO (LiNi 0.5 Mn 1.5 The positive electrode layer 112 may be a positive electrode active material, such as a lithium ion battery (LiFePO4), or an LFP (LiFePO4) having an olivine structure. In addition to the positive electrode active material, the positive electrode layer 112 further contains a solid electrolyte and an electron conduction aid (carbon black, etc.) described below. The positive electrode layer 112 in this embodiment is formed by integrating these materials by applying pressure or heat.

[0017] The negative electrode active material of the negative electrode layer 122 is, for example, LTO (Li4Ti5O 12Examples of the negative electrode layer 122 include compounds such as NbTiO, TiO (titanium oxide), graphite, and SiO (silicon monoxide). The negative electrode layer 122 contains a solid electrolyte, which will be described later, in addition to the negative electrode active material. The negative electrode layer 122 may further contain an electron conduction aid (carbon black, etc.). The negative electrode layer 122 in this embodiment is formed by integrating these materials by applying pressure or heat.

[0018] 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 used.

[0019] The electrolyte layer 13 is made of or includes a solid electrolyte according to the present invention (hereinafter also referred to as "the present solid electrolyte"). The solid electrolyte is a lithium (Li) ion conductive material. The solid electrolyte includes lithium element (Li), an element (M) that is a metal element or a semimetal element other than Li, fluorine element (F), and an element X described below. M may be only one type of element, or may include two or more types of elements. An example of M is an element that forms a trivalent cation. M preferably includes gallium (Ga), or may consist solely of Ga. M may also include another element that forms a trivalent cation together with Ga, an example of such an element being aluminum (Al).

[0020] In this specification, metalloid elements are boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Metal elements are elements included in Groups 1 to 12 of the periodic table excluding hydrogen, and elements included in Groups 13 to 16 of the periodic table excluding the above metalloids and C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming inorganic compounds with halogen compounds.

[0021] X is at least one element selected from the group consisting of chlorine (Cl), bromine (Br), and iodine (I). More preferably, X contains Cl and may be only Cl. Typically, X replaces some of the F. For example, the amount of substance of X in this solid electrolyte is less than or equal to the amount of substance of F, but may also be greater than the amount of substance of F. This solid electrolyte does not contain sulfide and does not generate hydrogen sulfide gas. Therefore, a highly safe all-solid-state secondary battery 1 is provided. As will be described later, in this solid electrolyte, a high lithium ion conductivity of 1×10 -5 S / cm or more is achieved.

[0022] In a preferred solid electrolyte, the composition formula is Li3MF 6-a X a ···(1) represented by, and 0 < a < 6 is satisfied. In the composition formula (1), it is more preferable that 1 < a < 6 is satisfied, and it is even more preferable that 1 < a < 4 is satisfied. Here, M is an element that becomes a trivalent cation and may contain two or more elements (for example, Ga and Al).

[0023] In another preferred solid electrolyte, the above M contains Mα that becomes a trivalent cation and Mβ that becomes a tetravalent cation. In this case, the composition formula of the solid electrolyte is Li 3-b Mα 1-b Mβ b F 6-a X a ···(2) represented by, and 0 < a < 6 and 0 < b < 1 are satisfied. Also in the composition formula (2), it is more preferable that 1 < a < 6 is satisfied, and it is even more preferable that 1 < a < 4 is satisfied. In an example of this solid electrolyte, Mα is Ga and Mβ is zirconium (Zr). For example, the amount of substance of Mα is greater than or equal to the amount of substance of Mβ, but may also be less than the amount of substance of Mβ.

[0024] In this solid electrolyte, M may include Mγ which is a divalent cation. For example, M includes Mα and optionally includes Mβ and / or Mγ. In this case, the composition formula of the solid electrolyte is Li 3-b+c Mα 1-b-c Mβ b Mγ c F 6-a X a ···(3) represented by 0 < a < 6, 0 ≤ b < 1, and 0 ≤ c < 1 being satisfied. In the composition formula (3) as well, it is more preferable that 1 < a < 6 is satisfied, and it is even more preferable that 1 < a < 4 is satisfied. An example of Mγ is magnesium (Mg). For example, the amount of substance of Mα is greater than or equal to the total amount of substances of Mβ and Mγ, but it may also be less than the total amount of substances.

[0025] In the confirmation of whether an unknown solid electrolyte conforms to the composition formula (1), (2), or (3), for example, for Li, Ga, Al, Zr, and Mg, it can be quantified by ICP-emission spectrometry or the like. For F and Cl, for example, it can be quantified by ion chromatography. When this solid electrolyte contains elements other than those described above, a measurement method capable of quantifying the element is appropriately selected.

[0026] In the above composition formula (1), the molar ratio of Li, M, F, and X is Li:M:F:X = 3:1:6 - a:a. In the molar ratio obtained by analyzing an unknown solid electrolyte, if the value of Li is 0.90×3 or more and 1.10×3 or less, it is considered that the above composition formula (1) is satisfied for Li. It is more preferable that the value of Li is 0.95×3 or more and 1.05×3 or less. The same applies to M, F, and X. Also, for the above composition formula (2) as well, similar to the above composition formula (1), if each value of the molar ratio of Li, Mα, Mβ, F, and X obtained by analysis is within the range of ±10% (preferably ±5%) of the value of the above composition formula (2), it is considered that the above composition formula (2) is satisfied. The same applies to the above composition formula (3) and the composition formulas (4) to (7) described later.

[0027] The solid electrolyte is manufactured, for example, by the following method. First, a powder of a fluoride containing Li, a powder of a fluoride containing M, and a powder of a halide containing Li (LiX) are prepared. Then, these powders are weighed and mixed to a predetermined molar ratio. The fluoride containing Li is, for example, LiF (lithium fluoride). Since Li and F are also contained in other powders, it is possible to omit the fluoride containing Li. When M is Ga, the fluoride containing Ga is, for example, GaF3 (gallium fluoride). When M is Ga and Al, the fluoride containing Al is, for example, AlF3 (aluminum fluoride). When M is Ga and Zr, the fluoride containing Zr is, for example, ZrF4 (zirconium fluoride). When M is Ga and Mg, the fluoride containing Mg is, for example, MgF2 (magnesium fluoride). Examples of halides containing Li (LiX) include LiCl (lithium chloride), LiBr (lithium bromide), and LiI (lithium iodide). As a raw material, a halide containing M may be used, and examples of the halide include GaCl3 (gallium chloride) and ZrCl4 (zirconium chloride), and may also be a bromide containing M or an iodide containing M.

[0028] Next, the mixture is subjected to mechanical milling (mechanochemical milling). Here, a planetary ball mill is used as an example of mechanical milling. In a planetary ball mill, the pot rotates on its axis while the stage on which the pot is placed revolves, making it possible to generate very high impact energy. The mechanical milling may also be performed using other types of grinders. The above mechanical milling process produces the present solid electrolyte used in the positive electrode layer 112, the negative electrode layer 122, or the electrolyte layer 13. In this example, the mechanical milling process is performed at room temperature, but conditions such as temperature may be changed as appropriate. The present solid electrolyte may also be produced by methods other than mechanical milling, such as firing.

[0029] This solid electrolyte may contain sodium (Na) or potassium (K) instead of lithium, and may contain two or more elements among Li, Na, and K. That is, the solid electrolyte contains A, M, F, and X, and A is at least one element selected from the group consisting of Li, Na, and K. M and X are the same as described above. Even when A is Na, as will be described later, high (sodium) ion conductivity is achieved. The same applies when A is K.

[0030] Considering the case where this solid electrolyte contains Na or K, the above compositional formula (1) is A3MF 6-a X a ···(4) represented by, and similar to the compositional formula (1), 0 < a < 6 is satisfied.

[0031] Also, the above compositional formula (2) is A 3-b Mα 1-b Mβ b F 6-a X a ···(5) represented by, and similar to the compositional formula (2), 0 < a < 6 and 0 < b < 1 are satisfied.

[0032] Furthermore, the above compositional formula (3) is A 3-b+c Mα 1-b-c Mβ b Mγ c F 6-a X a ···(6) represented by, and similar to the compositional formula (3), 0 < a < 6, 0 ≤ b < 1, and 0 ≤ c < 1 are satisfied. Note that Na and K can be quantified by ICP-emission spectrometry or the like.

[0033] In the production of a solid electrolyte in which A is Na, NaF (sodium fluoride), NaCl (sodium chloride), NaBr (sodium bromide), NaI (sodium iodide), etc. are used instead of LiF or the above-mentioned LiX, etc. Similarly, in the production of a solid electrolyte in which A is K, KF (potassium fluoride), KCl (potassium chloride), KBr (potassium bromide), KI (potassium iodide), etc. are used.

[0034] The all-solid-state secondary battery 1 using a solid electrolyte in which A contains Na may be an all-solid-state sodium-ion secondary battery. In this case, an example of the positive electrode active material of the positive electrode layer 112 is Na(Fe,Mn)O2. Other examples of the positive electrode active material include layered compounds such as NaCoO2, NaNiO2, NaMnO2, Na(Ni,Co,Mn)O2, NaFeO2, and Na(Ni,Mn,Fe,Ti)O2; spinel-type NaMn2O4; polyanion-type Na3V2(PO4)3, Na2Fe2(SO4)3, Na2Mn2(SO4)3, NaFePO4, NaMnPO4, Na4Fe7(PO4)6, and Na3V(PO3)3N; and pyrophosphate-based Na2MnP2O7 and Na2FeP2O7. Furthermore, an example of the negative electrode active material of the negative electrode layer 122 is hard carbon. Other examples of the negative electrode active material include metals such as Na, In, Sn, and Sb, alloys of these metals with Na, graphite, SiO, TiO2, Fe2O3, Na 4 / 3 Ti 5 / 3 O4, Na2Ti6O 13 , Na 0.66 [Li 0.22 Ti 0.78 ]O2, Na3V2(PO4)3, SnO, Li4Ti5O 12 The all-solid-state secondary battery 1 may be an all-solid-state potassium ion secondary battery, in which case known materials are used as the positive electrode active material and the negative electrode active material.

[0035] Next, experimental examples of solid electrolytes will be described. The following experiments were carried out in a glove box in an argon (Ar) atmosphere with a dew point of -60°C or less. The conditions and measurement results of Experimental Examples 1 to 21 are shown in Tables 1 and 2. Experimental Examples 2 to 21 are examples of the present invention containing X (here, Cl), and Experimental Example 1 is a comparative example that does not contain X. In the column of composition formula in Tables 1 and 2, the composition formula of the solid electrolyte is represented by A 3-b+c Mα 1-b-c Mβ b Mγ c F 6-a X a The values ​​of a, b, and c are also shown when Mα is Ga or Ga and Al, Mβ is Zr, and Mγ is Mg.

[0036] [Table 1]

[0037] [Table 2]

[0038] (Experimental Example 1) Commercially available LiF powder and GaF powder were prepared as raw materials. These powders were weighed so that the molar ratio of LiF:GaF was 3:1, and mechanically milled using a planetary ball mill to obtain a solid electrolyte.

[0039] (Experimental Example 2) In addition to the LiF powder and GaF3 powder, commercially available LiCl powder was prepared and weighed so that the molar ratio of LiF:LiCl:GaF3 was 2.9:0.1:1. The same treatment as in Experimental Example 1 was carried out to obtain a solid electrolyte.

[0040] (Experimental Example 3) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, and GaF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3 was 2.7:0.3:1.

[0041] (Experimental Example 4) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, and GaF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3 was 2.4:0.6:1.

[0042] (Experimental Example 5) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, and GaF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3 was 2:1:1.

[0043] (Experimental Example 6) In addition to LiF powder, LiCl powder, and GaF powder, commercially available ZrF powder was prepared and weighed so that the molar ratio of LiF:LiCl:GaF:ZrF was 2.2:0.6:0.8:0.2. The same treatment as in Experimental Example 1 was carried out to obtain a solid electrolyte.

[0044] (Experimental Example 7) In addition to LiF powder, LiCl powder, and GaF powder, commercially available AlF powder was prepared and weighed so that the molar ratio of LiF:LiCl:GaF:AlF was 2.4:0.6:0.8:0.2. The same treatment as in Experimental Example 1 was carried out to obtain a solid electrolyte.

[0045] (Experimental Example 8) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, GaF3 powder, and AlF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3:AlF3 was 2.4:0.6:0.5:0.5.

[0046] (Experimental Example 9) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, GaF3 powder, and AlF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3:AlF3 was 2.4:0.6:0.3:0.7.

[0047] (Experimental Example 10) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, and GaF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3 was 1.5:1.5:1.

[0048] (Experimental Example 11) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, and GaF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3 was 1:2:1.

[0049] (Experimental Example 12) A solid electrolyte was obtained by the same treatment as in Experimental Example 1, except that LiCl powder and GaF3 powder were used and weighed out so that the molar ratio of LiCl:GaF3 was 3:1.

[0050] (Experimental Example 13) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, GaF3 powder, and AlF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3:AlF3 was 1:2:0.8:0.2.

[0051] (Experimental Example 14) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, GaF3 powder, and AlF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3:AlF3 was 1:2:0.7:0.3.

[0052] (Experimental Example 15) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, GaF3 powder, and AlF3 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3:AlF3 was 1:2:0.6:0.4.

[0053] (Experimental Example 16) In addition to LiF powder, LiCl powder, and GaF powder, commercially available MgF powder was prepared and weighed so that the molar ratio of LiF:LiCl:GaF:MgF was 1.1:2:0.9:0.1. The same treatment as in Experimental Example 1 was carried out to obtain a solid electrolyte.

[0054] (Experimental Example 17) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, GaF3 powder, and MgF2 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3:MgF2 was 1.3:2:0.7:0.3.

[0055] (Experimental Example 18) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that LiF powder, LiCl powder, GaF3 powder, and MgF2 powder were used and weighed so that the molar ratio of LiF:LiCl:GaF3:MgF2 was 1.4:2:0.6:0.4.

[0056] (Experimental Example 19) Commercially available NaF powder, NaCl powder, and GaF3 powder were prepared and weighed out so that the molar ratio of NaF:NaCl:GaF3 was 1:2:1, and the same treatment as in Experimental Example 1 was carried out to obtain a solid electrolyte.

[0057] (Experimental Example 20) A solid electrolyte was obtained by the same treatment as in Experimental Example 1, except that NaCl powder and GaF3 powder were used and weighed so that the molar ratio of NaCl:GaF3 was 3:1.

[0058] (Experimental Example 21) A solid electrolyte was obtained in the same manner as in Experimental Example 1, except that NaF powder, NaCl powder, GaF3 powder, and AlF3 powder were used and weighed so that the molar ratio of NaF:NaCl:GaF3:AlF3 was 1:2:0.7:0.3.

[0059] <Measurement of ionic conductivity> The solid electrolyte was placed in a mold consisting of a resin sleeve and upper and lower metal punches and uniaxially pressed. Wires were connected to the upper and lower punches, and impedance measurements were performed at room temperature to calculate the ionic conductivity (lithium ionic conductivity in Experimental Examples 1 to 18, and sodium ionic conductivity in Experimental Examples 19 to 21). In Table 1, the ionic conductivity is shown in the column labeled "Conductivity."

[0060] <Construction of all-solid-state batteries> The solid electrolyte of Experimental Example 14, Li3YCl6 as a solid electrolyte, LiFePO4 (LFP) as a positive electrode active material, carbon fiber as a conductive additive, and Li4Ti5O as a negative electrode active material 12 Li3YCl6 was prepared based on "Solid Halide Electrolytes with High Lithium-Ion Conductivity for Application in 4 V Class Bulk-Type All-Solid-State Batteries" by Tetsuya Asano and five others (ADVANCED MATERIALS, 2018, Vol. 30, pp. 1803075) (reference 4 mentioned above). LFP, the solid electrolyte of Experimental Example 14, and carbon fiber were weighed out in a weight ratio of 30:30:1 and mixed in a mortar to obtain a positive electrode powder mixture. LTO, Li3YCl6, and carbon fiber were weighed out in a weight ratio of 30:40:1 and mixed in a mortar to obtain a negative electrode powder mixture. 100 mg of Li3YCl6 was placed in a mold (inner diameter φ10 mm) consisting of a PEEK resin sleeve and upper and lower SUS punches and uniaxially pressed. One of the punches was removed, and 30 mg of the positive electrode powder was added, followed by uniaxial pressing again. Next, the punch opposite to the side where the positive electrode powder was added was removed, and 40 mg of the negative electrode powder was added, followed by uniaxial pressing. This resulted in the construction of an all-solid-state battery in which the positive electrode was formed from LFP and the solid electrolyte of Experimental Example 14, the electrolyte layer was formed from Li3YCl6, and the negative electrode was formed from LTO and Li3YCl6.

[0061] <Charge / discharge test> A current collecting wire was connected to the upper and lower punches, and a charge-discharge test was carried out at room temperature. The charging conditions were a cut-off voltage of 2.2 V and a current of 300 μA / cm. 2 After constant current (cc) charging, 30 μA / cm 2 The battery was charged at a constant voltage (cv) with a cut-off current of 1.0 V and a discharge current of 300 μA / cm. 2 After constant current (cc) discharge of 30 μA / cm 2 A constant voltage (CV) discharge was performed with a cut-off current of .

[0062] FIG. 2 shows the discharge curves obtained in the charge-discharge test. In FIG. 2, the solid line L1 indicates the initial discharge curve, and the dashed line L2 indicates the discharge curve at the 20th cycle. The results of the charge-discharge test showed that the discharge capacity per positive electrode weight was 46 mAh / g-positive electrode. Furthermore, the capacity retention rate at 20 cycles was 99%, meaning that the discharge capacity did not decrease even at the 20th cycle, and charge-discharge could be appropriately repeated. Thus, it was confirmed that the solid electrolyte of Experimental Example 14 functions as a Li-ion solid electrolyte for all-solid-state batteries.

[0063] <Evaluation of Experimental Examples> As shown in Table 1, Experimental Examples 2 to 18, which contained X (here, Cl), had higher lithium ion conductivity than Experimental Example 1, which did not contain X. In a Li-ion conductive material, the inclusion of an anion with a larger ionic radius weakens the binding force of the monovalent cation Li ion, making the Li ion more mobile, which is thought to increase ionic conductivity. The ionic radius of an F ion is 1.33 Å, while the ionic radius of a Cl ion is 1.81 Å. Although the details are not entirely clear, it is presumed that the solid electrolytes of Experimental Examples 2 to 18 achieved high ionic conductivity by containing Cl, which has a larger ionic radius than F (i.e., by replacing some F with X). For the same reason, it is thought that high ionic conductivity was also achieved in the solid electrolytes of Experimental Examples 19 to 21, which were Na compounds (Na-ion conductive materials).

[0064] As described above, this solid electrolyte contains A, M, F, and X. A is at least one element selected from the group consisting of Li, Na, and K. M is a metal element or a metalloid element other than A. X is at least one element selected from the group consisting of Cl, Br, and I. Thus, by including X having an ionic radius larger than that of F in the solid electrolyte, high ionic conductivity can be achieved. Further, since the solid electrolyte does not contain sulfide and does not generate hydrogen sulfide gas, its safety is enhanced.

[0065] In a preferred solid electrolyte, as in Experimental Examples 2 to 21, M contains Ga. Thereby, the ionic conductivity can be more reliably improved.

[0066] In a preferred solid electrolyte, the composition formula is A3MF 6-a X a ···(4) represented by 0 < a < 6 being satisfied. Thereby, a solid electrolyte having high ionic conductivity can be preferably realized. As in Experimental Examples 10 to 21, it is more preferable that 1 < a < 6 is satisfied, and it is even more preferable that 1 < a < 4 is satisfied. Thereby, the ionic conductivity can be significantly improved.

[0067] Preferably, as in Experimental Examples 2 to 21, M contains at least one element selected from the group consisting of Mα which is a trivalent cation, Mβ which is a tetravalent cation, and Mγ which is a divalent cation. Further, the composition formula is A 3-b+c Mα 1-b-c Mβ b Mγ c F 6-a X a ···(6) represented by 0 < a < 6, 0 ≤ b < 1, and 0 ≤ c < 1 being satisfied. Thereby, the ionic conductivity can be more reliably improved.

[0068] M may include both Mα which is a trivalent cation and Mβ which is a tetravalent cation. In this case, the composition formula is A 3-b Mα 1-b Mβ b F 6-a X a ···(5) represented by, and 0 < a < 6 and 0 < b < 1 are satisfied. Thereby, a solid electrolyte having high ionic conductivity can be preferably realized as in Experimental Example 6 in which a part of Ga is replaced with Zr.

[0069] Similarly, M may include both Mα which is a trivalent cation and Mγ which is a divalent cation. In this case, the composition formula is A 3+c Mα 1-c Mγ c F 6-a X a ···(7) represented by, and 0 < a < 6 and 0 < c < 1 are satisfied. Thereby, a solid electrolyte having high ionic conductivity can be preferably realized as in Experimental Examples 16 to 18 in which a part of Ga is replaced with Mg.

[0070] In this solid electrolyte and the all-solid-state secondary battery 1, various modifications are possible.

[0071] This solid electrolyte may be represented by other than the above composition formulas (1) to (7).

[0072] This solid electrolyte may be mixed with other substances (which may contain A such as Li.) and used as an electrolyte material. In this case, it is preferable that this solid electrolyte is the component having 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.

[0073] The present solid electrolyte used in the all solid state secondary battery 1 does not necessarily need to be contained in all of the positive electrode 11, the negative electrode 12, and the electrolyte layer 13, but may be contained in at least one of the positive electrode 11, the negative electrode 12, and the electrolyte layer 13. Furthermore, the present solid electrolyte may be used in batteries other than all solid state secondary batteries, and may be used for purposes other than batteries.

[0074] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0075] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention. [Explanation of symbols]

[0076] 1. All-solid-state lithium-ion secondary battery 11 Positive electrode 12 Negative electrode 13 Electrolyte layer

Claims

1. A solid electrolyte, A, M, F and X, A is at least one element selected from the group consisting of Li, Na, and K; M is a metal element or a metalloid element other than A, and includes at least one element selected from the group consisting of Mα, which becomes a trivalent cation, Mβ, which becomes a tetravalent cation, and Mγ, which becomes a divalent cation; X is at least one element selected from the group consisting of Cl, Br, and I; The composition formula of the solid electrolyte is represented by A 3-b+c Mα 1-bc Mβ b Mγ c F 6-a X a , A solid electrolyte in which 0<a<3, 0≦b<1, and 0≦c<1 are satisfied.

2. 2. The solid electrolyte according to claim 1, A solid electrolyte in which M contains Ga.

3. 2. The solid electrolyte according to claim 1, A solid electrolyte in which M contains Zr.

4. 2. The solid electrolyte according to claim 1, A solid electrolyte in which M comprises Mg.

5. A battery comprising the solid electrolyte according to any one of claims 1 to 4.

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