Solid electrolyte, method for producing solid electrolyte, and battery

Abstract

The solid electrolyte contains Na, M [alpha], M [beta], and F, where M [alpha] is at least one element that is a trivalent cation, and M [beta] is at least one element that is a tetravalent or higher cation. As a result, it is possible to provide a solid electrolyte having high ion conductivity. Preferably, M [beta] is an element having a tetravalent cation, the solid electrolyte contains a component represented by the compositional formula Na3-xM [alpha] 1-xM [beta] xF6, and 0 < x < 1 is satisfied.

Description

Technical Field

[0001] This invention relates to solid electrolytes and batteries.

[0002] [Reference to relevant applications]

[0003] This application claims priority to International Patent Application PCT / JP2023 / 35747 filed on September 29, 2023, and Japanese Patent Application JP2024-86422 filed on May 28, 2024, the entire disclosure of which is incorporated herein by reference. Background Technology

[0004] In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as their power source has increased significantly. In batteries used for such applications, organic electrolytes, obtained by dissolving the electrolyte in flammable organic solvents, have traditionally been used as the medium for ion movement. Batteries containing organic electrolytes have the potential to cause safety-related problems. Therefore, to inherently ensure safety, all-solid-state batteries using solid electrolytes instead of organic electrolytes are being developed. In all-solid-state batteries, the electrolyte is a non-flammable material, thus enabling a higher level of safety.

[0005] In addition, in response to the recent rapid changes in the social landscape aimed at achieving carbon neutrality, the demand for decarbonized electric vehicles (EVs) and large lithium-ion batteries that provide a stable supply of renewable energy has increased rapidly. In addition to Co and Ni, which have been rare elements in the past, the unstable supply and high cost of Li have also become a problem.

[0006] Therefore, Japanese Patent Application Publication No. 2023-48155 (Document 1) and Japanese Patent Publication No. 7230772 (Document 2) disclose a solid electrolyte as a Na ion conductor. The solid electrolyte in Document 1 has the characteristic of using Na... x M 1 2－（y＋Z） M 2 y M 3 z The compound represented by (AO4)3, M 1 M 2 and M 3 The sources are Hf, Mg, Sc, In, Y, Ca, or Zr, and A is P, Si, S, or a combination thereof. In the preparation of the solid electrolyte in Reference 2, the Na source, Y source, and Si source are mixed and calcined to produce Na5YSi4O. 12 The sintered body is formed and then sintered. Before sintering, Na3YSi3O9 powder is added.

[0007] However, in the manufacturing of solid electrolytes in references 1 and 2, high-temperature sintering (heat treatment) is required for densification, etc. In battery manufacturing, when the solid electrolyte before sintering is mixed with the positive or negative electrode active material and then sintered, high resistivity sometimes occurs due to the reaction between the solid electrolyte and the active material. Therefore, there is a need for novel Na-ion solid electrolytes that can achieve densification using methods such as compression molding and possess high ionic conductivity. Summary of the Invention

[0008] The purpose of this invention is to provide a solid electrolyte with high ionic conductivity.

[0009] The invention of Scheme 1 is a solid electrolyte containing Na, Mα, Mβ and F, wherein Mα is at least one element that is a trivalent cation and Mβ is at least one element that is a quadrivalent or higher cation.

[0010] According to the present invention, a solid electrolyte with high ionic conductivity can be provided.

[0011] Scheme 2 is based on the solid electrolyte of Scheme 1, wherein Mβ is an element with a tetravalent cation, and the solid electrolyte contains Na 3－x Mα 1－x Mβ x The component represented by F6 satisfies 0 < x < 1.

[0012] The invention of Scheme 3 is based on the solid electrolyte of Scheme 2, wherein the composition formula satisfies 0.1≤x≤0.85.

[0013] Scheme 4 is based on the solid electrolyte of Scheme 1, wherein the element with a tetravalent cation is designated as Mβ. 1 Let the element that is a pentavalent cation be designated as Mβ. 2 Let the element that is a hexavalent cation be designated as Mβ. 3 When the solid electrolyte contains Na 3－x－2y－3z Mα 1－（x＋y＋z） Mβ 1 x Mβ 2 y Mβ 3 z The components represented by F6 satisfy 0≤x<1, 0≤y<1, 0≤z<1, and 0<(x+y+z)<1.

[0014] The invention of Scheme 5 is based on the solid electrolyte of Scheme 4, wherein the composition formula satisfies 0.1≤x≤0.85.

[0015] The invention of Scheme 6 is based on the solid electrolyte of any one of Schemes 1 to 5, wherein Mα includes Al or Ga.

[0016] The invention of Scheme 7 is based on the solid electrolyte of any one of Schemes 1 to 6, wherein Mβ includes Si, P or Ge.

[0017] The invention of Scheme 8 is based on the solid electrolyte of any one of Schemes 1 to 7, wherein the X-ray diffraction pattern obtained by using X-ray diffraction measurement of CuKα rays has peaks in the range of diffraction angle 2θ of 18 to 21°, 21 to 24°, 31 to 34°, and 45 to 48°, respectively.

[0018] The invention of Scheme 9 is based on the solid electrolyte of any one of Schemes 1 to 8, wherein the half-width of the strongest peak in the X-ray diffraction pattern obtained by X-ray diffraction measurement using CuKα rays is greater than 0.4°.

[0019] The invention of Scheme 10 is a method for manufacturing a solid electrolyte, comprising the following steps: a) when Mα is set as at least one element having a trivalent cation and Mβ is set as at least one element having a quadrivalent or higher cation, mixing a substance containing Na, Mβ and F with Na3MαF6 to obtain a mixture, or mixing a substance containing Na, Mβ and F, MαF3 and NaF to obtain a mixture; and b) mechanically grinding the mixture.

[0020] The invention of Scheme 11 is a battery comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the solid electrolyte of any one of Schemes 1 to 9 is included in at least one of the positive electrode, the negative electrode, and the electrolyte layer.

[0021] The above-mentioned objectives, as well as other objectives, features, solutions, and advantages, will become clear from the following detailed description of the invention with reference to the accompanying drawings. Attached Figure Description

[0022] Figure 1 This is a longitudinal cross-sectional view of an all-solid-state secondary battery.

[0023] Figure 2 This is a diagram showing the manufacturing process of solid electrolytes.

[0024] Figure 3 This is a diagram showing the X-ray diffraction pattern obtained from a solid electrolyte.

[0025] Figure 4 This is a graph showing the relationship between the molar ratio of Na2SiF6 and its ionic conductivity at room temperature.

[0026] Figure 5 This is a graph showing the relationship between the molar ratio of Na2SiF6 and its ionic conductivity at 120℃.

[0027] Figure 6 This is a graph showing the results of the charge-discharge test.

[0028] Figure 7 This is a graph showing the results of the potential window measurement. Detailed Implementation

[0029] Figure 1 This is a longitudinal cross-sectional view showing an all-solid-state sodium-ion secondary battery 1 (hereinafter referred to as "all-solid-state secondary battery 1"). All-solid-state secondary battery 1... Figure 1 Starting from the top, the electrode comprises, in sequence: a positive electrode 11, an electrolyte layer 13, and a negative electrode 12. Specifically, the electrolyte layer 13 is disposed 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.

[0030] One example of the positive electrode active material in the positive electrode layer 112 is Na(Fe,Mn)O2. Other examples of positive electrode active materials include: layered compounds such as NaCoO2, NaNiO2, NaMnO2, Na(Ni,Co,Mn)O2, NaFeO2, Na(Ni,Mn,Fe,Ti)O2, spinel-type NaMn2O4, polyanionic compounds such as Na3V2(PO4)3, Na2Fe2(SO4)3, Na2Mn2(SO4)3, NaFePO4, NaMnPO4, Na4Fe7(PO4)6, Na3V(PO3)3N, and pyrophosphate-based compounds such as Na2MnP2O7 and Na2FeP2O7. In addition to the positive electrode active material, the positive electrode layer 112 also contains the solid electrolyte described later. The positive electrode layer 112 may further contain electron conduction aids (such as carbon black). One example of the positive electrode layer 112 is obtained by integrating these materials using pressure or other methods.

[0031] One example of the negative electrode active material in negative electrode layer 122 is hard carbon. Other examples of negative electrode active materials include: metals such as Na, In, Sn, and Sb; alloys of these metals and Na; graphite; SiO; TiO2; Fe2O3; and 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 In addition to the negative electrode active material, the negative electrode layer 122 also contains the solid electrolyte described later. The negative electrode layer 122 may further contain an electron conduction aid (such as carbon black). One example of the negative electrode layer 122 is obtained by integrating these materials using pressure or the like.

[0032] The composition and materials of the positive electrode 11 and negative electrode 12 of the all-solid secondary battery 1 are not limited to the above-mentioned composition and materials, and various other compositions and materials can be used.

[0033] The electrolyte layer 13 is composed of, or contains, a solid electrolyte according to one embodiment of the present invention (hereinafter also referred to as "the solid electrolyte"). The solid electrolyte is a sodium (Na) ion-conducting material. The solid electrolyte comprises sodium (Na), at least one element as a trivalent cation (Mα), at least one element as a quadrivalent or higher cation (Mβ), and fluorine (F). The solid electrolyte may consist only of Na, Mα, Mβ, and F. Mα is typically a metallic element. Mβ is a metallic or non-metallic element. In one example, the mass of Na is greater than the mass of Mα and Mβ, and the mass of F is greater than the mass of Na. As described later, a high ion conductivity (typically sodium ion conductivity) can be achieved in this solid electrolyte. Furthermore, the solid electrolyte is non-flammable and chemically stable. The solid electrolyte is typically a non-sulfide system, and in one example, does not contain sulfur (S) (which may be included as an unavoidable impurity).

[0034] When Mβ is an element with a tetravalent cation, this solid electrolyte is, for example, Na3MαF6 and Na2MβF6 (Na2Mβ will be discussed later). 1 The mixture of NaF and MβF4 (F6) can be used instead of Na2MβF6. When Na3MαF6 and Na2MβF6 are mixed in a mass ratio of (1-x):x (where 0 < x < 1), the composition of this solid electrolyte is given by NaF. 3－x Mα 1－x Mβ x F6 indicates that, considering measurement errors, the molar ratio of Na, Mα, Mβ, and F is a:b:c:d (i.e., Na...). a Mα b Mβ c F dComponents satisfying 0.9(3-x)≤a≤1.1(3-x), 0.9(1-x)≤b≤1.1(1-x), 0.9x≤c≤1.1x, and 5.4≤d≤6.6 can be considered as components expressed by the above composition formula. Since 0 < x < 1, the above conditions for a to d are equivalent to 1.8 < a < 3.3, 0 < b < 1.1, 0 < c < 1.1, and 5.4≤d≤6.6. In the above composition formula, it is preferable to satisfy 0.1≤x≤0.85, and more preferably 0.2≤x≤0.6. This further improves ionic conductivity. Through the manufacturing method of the solid electrolyte, a, b, c, and d can be outside the above ranges. Furthermore, depending on the required ionic conductivity of the solid electrolyte, x can be less than 0.1 or greater than 0.85.

[0035] The trivalent cation Mα is included in Group 13 elements (Al, Ga, etc.), Group 3 elements (Sc, etc.), transition metal elements (Fe, Mn, etc.), and rare earth elements (Y, Ho, etc.). Preferably, Mα includes aluminum (Al) or gallium (Ga). Mα can include both Al and Ga. An example of Na3MαF6 is Na3AlF6 or Na3GaF6. When Mβ is a tetravalent cation, Mβ is included in Group 4 elements (Zr, etc.) and Group 14 elements (Si, Ge, etc.). Preferably, Mβ includes silicon (Si) or germanium (Ge). Mβ can include both Si and Ge. An example of Na2MβF6 is Na2SiF6 or Na2GeF6. For example, in solid electrolytes containing Na3AlF6 and Na2SiF6, the ionic conductivity is higher than that of the Na3AlF6 monomer. The reason is not necessarily clear, but one possible explanation is that through mechanical grinding, as described later, Al and Si are mixed in a Na-containing crystalline structure (e.g., Si). 4＋ Compared to Al 3＋ (and solid solution), thus resulting in Na deficiency. The same applies to the case where Na3MαF6 is a compound other than Na3AlF6 (e.g., Na3GaF6), Na2MβF6 is a compound other than Na2SiF6 (e.g., Na2GeF6), and Mβ is an element with a cation other than tetravalent (e.g., pentavalent cation, hexavalent cation, etc.).

[0036] As described above, Mβ is one or more elements among cations with a valence of 4 or higher, for example, it may include elements with a valence of 5 or 6. Elements with a valence of 4 are designated as Mβ. 1 Let the element that is a pentavalent cation be designated as Mβ. 2 Let the element that is a hexavalent cation be designated as Mβ. 3 In the case of solid electrolytes, the composition formula is based on Na.3－x－2y－ 3z Mα 1－（x＋y＋z） Mβ 1 x Mβ 2 y Mβ 3 z F6 represents the formula. The above formula satisfies 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, and 0 < (x + y + z) < 1. Considering measurement errors, etc., then Na, Mα, and Mβ... 1 Mβ 2 Mβ 3 The mass ratio of F is a:b:c1:c2:c3:d (i.e., Na) a Mα b Mβ 1 c1 Mβ 2 c2 Mβ 3 c3 F d The components satisfying 0.9(3-x-2y-3z)≤a≤1.1(3-x-2y-3z), 0.9(1-(x+y+z))≤b≤1.1(1-(x+y+z)), 0.9x≤c1≤1.1x, 0.9y≤c2≤1.1y, 0.9z≤c3≤1.1z, and 5.4≤d≤6.6 can be considered as components represented by the above composition formula. In the above composition formula, 0.1≤x≤0.85 can be satisfied. The element Mβ, exhibiting a pentavalent cation... 2 Examples include phosphorus (P), vanadium (V), niobium (Nb), tantalum (Ta), and antimony (Sb). The element Mβ is a hexavalent cation. 3 Examples include molybdenum (Mo) and tungsten (W). Depending on the manufacturing method of the solid electrolyte, this solid electrolyte can be represented by formulas other than the above-mentioned composition formulas.

[0037] As described below, the X-ray diffraction pattern obtained by X-ray diffraction measurement using CuKα rays for this solid electrolyte preferably has peaks in the ranges of 18–21°, 21–24°, 31–34°, and 45–48°, respectively, at diffraction angles 2θ. Furthermore, the half-width at half-maximum (WHM) of the strongest peak in the X-ray diffraction pattern is preferably 0.4° or greater. In such a solid electrolyte, crystallinity is moderately reduced, resulting in higher ionic conductivity. It should be noted that this solid electrolyte can be amorphous.

[0038] Figure 2 This is a diagram illustrating the manufacturing process of this solid electrolyte. In the following description, Na3AlF6 will be used as Na3MαF6 and Na2MβF6 will be used as Na2MβF6. 1The process of manufacturing this solid electrolyte by mixing Na2SiF6 with F6 is described. First, Na3AlF6 powder is prepared. In preparing the Na3AlF6 powder, for example, commercially available NaF (sodium fluoride) powder and commercially available AlF3 (aluminum fluoride) powder are weighed and mixed at a mass ratio of 3:1. Next, the resulting mixture is heated (e.g., to 1050°C), and then pulverized to obtain Na3AlF6 powder. Na3AlF6 powder can also be generated using other methods.

[0039] In addition, Na2SiF6 powder is prepared. Commercially available Na2SiF6 powder is used. Of course, Na2SiF6 powder can be generated using well-known methods. Then, Na3AlF6 powder and Na2SiF6 powder are mixed to obtain a mixture (step S11). In this mixture, the mass percentage of Na2SiF6 in the total mass percentage of Na3AlF6 and Na2SiF6 is greater than 0% and less than 100%. This percentage is preferably 10% or more and 85% or less, more preferably 20% or more and 60% or less.

[0040] Next, the mixture is subjected to mechanical grinding (step S12). In one example of this mechanical grinding process, a planetary ball mill is used. In a planetary ball mill, the jar rotates on its own axis while the platform carrying the jar revolves around it, thus generating very high impact energy. Mechanical grinding can also be performed using other types of pulverizers. Through the above mechanical grinding process, powder of the solid electrolyte used in the positive electrode layer 112, negative electrode layer 122, or electrolyte layer 13 is obtained. In this example, the mechanical grinding process is performed at room temperature; however, the temperature and other conditions can be appropriately varied.

[0041] As described above, Mβ can include elements that are pentavalent cations or hexavalent cations. In the manufacture of this solid electrolyte, instead of Na, Mβ... 1 And compounds composed of F (e.g., Na2Mβ) 1 F6, the above is Na2SiF6), or, in addition to this compound, compounds composed of Na, Mβ can be used. 2 And compounds composed of F (such as NaPF6), containing Na, Mβ 2 and mixtures of F (e.g., a mixture of NaF and NbF5), or containing Na, Mβ 3And mixtures of F (e.g., a mixture of NaF and MoF6), etc. In this way, substances containing Na, Mβ, and F (typically substances composed of Na, Mβ, and F) can be used. This substance is a compound composed of Na, Mβ, and F, and / or a mixture containing Na, Mβ, and F (typically a mixture composed of Na, Mβ, and F). In step S11, a mixture is obtained by mixing a substance containing Na, Mβ, and F with Na3MαF6 (Na3AlF6 in the above example), and in step S12, the mixture is mechanically ground to produce this solid electrolyte.

[0042] Figure 3 This diagram shows the X-ray diffraction (XRD) pattern obtained by powder X-ray diffraction for this solid electrolyte, and also shows the X-ray diffraction pattern of the solid electrolyte (Experimental Example 6 described later) obtained by setting the molar ratio of Na₂SiF₆ to 50%. In this measurement, CuKα rays were used as the X-ray source in the X-ray diffraction apparatus. (Image...) Figure 3 Thus, the X-ray diffraction pattern of the solid electrolyte manufactured by mechanical grinding exhibits relatively broad peaks in the diffraction angle 2θ ranges of 18–21°, 21–24°, 31–34°, and 45–48°, respectively. According to... Figure 3 It is believed that the Na3AlF6 and Na2SiF6 particles are miniaturized or partially amorphized due to the very high impact energy from the mechanical grinding process. Furthermore, the crystalline structure is disrupted by strain and dislocations within the crystals, particularly at the particle interfaces. Therefore, the ionic conductivity of this solid electrolyte is considered to be improved. Accordingly, this solid electrolyte can be further or completely amorphized. For more reliable improvement of the ionic conductivity of this solid electrolyte, the half-width of the strongest peak (e.g., a peak in the range of 18–21°) in the X-ray diffraction pattern is preferably 0.4° or more, and more preferably 0.5° or more. Figure 3 In the X-ray diffraction pattern, the half-width of the strongest peak is 0.66°. There is no specific upper limit to this half-width, for example, it could be 3.0°. It should be noted that the half-width of the peak is determined by automatic fitting in the X-ray diffraction pattern using the XRD data analysis software JADE.

[0043] Next, Experimental Examples 1 to 10 of the solid electrolyte will be described. Experimental Examples 2 to 10 are embodiments of the present invention, and Experimental Example 1 is a comparative example. The following experiments were conducted in a glove box or a dry room with a dew point below -40°C.

[0044] (Experimental Example 1)

[0045] Commercially available NaF powder and AlF3 powder were prepared as raw materials. The raw materials were weighed and mixed at a NaF:AlF3 ratio of 3:1 (mass ratio). The resulting mixture was heated at 1050°C, and then pulverized using a mortar and pestle to obtain Na3AlF6 powder. The Na3AlF6 powder was mechanically ground using a planetary ball mill to obtain a solid electrolyte powder containing only Na3AlF6 powder.

[0046] (Experimental Example 2)

[0047] In addition to the Na3AlF6 powder mentioned above, commercially available Na2SiF6 powder was prepared. Na3AlF6:Na2SiF6 was weighed and mixed at a mass ratio of 90:10, and then mechanically ground using a planetary ball mill to obtain Na3AlF6-Na2SiF6 powder as a solid electrolyte powder. As described above, when Na3MαF6 and Na2MβF6 are mixed at a mass ratio of (1-x):x (where 0 < x < 1), the composition formula is Na... 3－x Mα 1－x Mβ x F6 represents the solid electrolyte powder with the formula Na, where Mα and Mβ are Al and Si, respectively, and x is 0.1. 2.9 Al 0.9 Si 0.1 F6 indicates.

[0048] (Experimental Example 3)

[0049] Weigh the Na3AlF6:Na2SiF6 mixture according to a mass ratio of 80:20. Otherwise, perform the same treatment as in Experimental Example 2 to obtain the product with the composition formula Na... 2.8 Al 0.8 Si 0.2 F6 indicates solid electrolyte powder.

[0050] (Experimental Example 4)

[0051] Weigh the Na3AlF6:Na2SiF6 mixture according to a mass ratio of 70:30. Otherwise, perform the same treatment as in Experimental Example 2 to obtain the product with the composition formula Na. 2.7 Al 0.7 Si 0.3 F6 indicates solid electrolyte powder.

[0052] (Experimental Example 5)

[0053] Weigh the Na3AlF6:Na2SiF6 mixture according to a mass ratio of 60:40. Otherwise, perform the same treatment as in Experimental Example 2 to obtain the product with the composition formula Na... 2.6 Al0.6 Si 0.4 F6 indicates solid electrolyte powder.

[0054] (Experimental Example 6)

[0055] Weigh the Na3AlF6:Na2SiF6 mixture according to a 50:50 (substance ratio), and otherwise perform the same treatment as in Experimental Example 2 to obtain the product with the composition formula Na 2.5 Al 0.5 Si 0.5 F6 indicates solid electrolyte powder.

[0056] (Experimental Example 7)

[0057] Weigh the Na3AlF6:Na2SiF6 mixture according to a mass ratio of 20:80. Otherwise, perform the same treatment as in Experimental Example 2 to obtain the product with the composition formula Na. 2.2 Al 0.2 Si 0.8 F6 indicates solid electrolyte powder.

[0058] (Experimental Example 8)

[0059] Commercially available NaF powder and commercially available GaF3 (gallium fluoride) powder were prepared as raw materials. The raw materials were weighed and mixed at a NaF:GaF3 ratio of 3:1 (mass ratio). The resulting mixture was heated at 1050°C, and then pulverized using a mortar and pestle to obtain Na3GaF6 powder. Next, the mixture was weighed at a Na3GaF6:Na2SiF6 ratio of 50:50 (mass ratio) and mechanically ground using a planetary ball mill to obtain Na2SiF6 powder. 2.5 Ga 0.5 Si 0.5 F6 indicates solid electrolyte powder.

[0060] (Experimental Example 9)

[0061] In addition to the Na3AlF6 powder mentioned above, commercially available NaPF6 powder was prepared. Na3AlF6:NaPF6 was weighed and mixed at a mass ratio of 67:33, and then mechanically ground using a planetary ball mill to obtain Na3AlF6-NaPF6 powder as a solid electrolyte powder. This solid electrolyte powder has the composition formula Na... 2.34 Al 0.67 P 0.33 F6 indicates.

[0062] (Experimental Example 10)

[0063] The Na3AlF6:NaPF6:Na2SiF6 mixture was weighed and mixed in a mass ratio of 10:80:10, and then mechanically ground using a planetary ball mill to obtain Na3AlF6-NaPF6-Na2SiF6 powder as a solid electrolyte powder. This solid electrolyte powder has the composition formula Na... 1.3 Al 0.1 Si 0.1 P 0.8 F6 indicates.

[0064] <Determination of Ion Conductivity>

[0065] Solid electrolyte powder was placed into a mold consisting of a resin sleeve and upper and lower punches made of SUS (stainless steel), and uniaxially pressed under a pressure of 150 MPa. Wires were connected to the upper and lower punches, and impedance measurements were performed at room temperature to 120°C to calculate the ionic conductivity.

[0066] Table 1 shows the molar ratios of Na3AlF6 or Na3GaF6 and Na2SiF6 and / or NaPF6 in the solid electrolyte powders of Experimental Examples 1 to 10, as well as their ionic conductivity at room temperature and 120°C. Additionally, the half-widths (WHMs) of each peak, calculated using the aforementioned method, are also shown for X-ray diffraction patterns obtained from a portion of the solid electrolyte powder. Figure 4 and Figure 5 This is a graph showing the relationship between the percentage (mol%) of Na2SiF6 in the total amount of Na3AlF6 and Na2SiF6 and its ionic conductivity. Figure 4 The figure shows the ionic conductivity at room temperature. Figure 5 The ionic conductivity at 120°C is shown in the figure.

[0067] Table 1

[0068]

[0069] The solid electrolyte powders in Examples 2 to 8, which contain Na₂SiF₆, exhibit higher ionic conductivity at room temperature and 120°C than the solid electrolyte powder in Example 1, which does not contain Na₂SiF₆. Looking at Examples 1 to 7, which contain Na₃AlF₆, the results are as follows... Figure 4 and Figure 5As shown, the ionic conductivity increases at room temperature and 120°C as the Na₂SiF₆ content approaches 50%. If the Na₂SiF₆ content increases further, the ionic conductivity decreases. In Example 7, where the Na₂SiF₆ content is 80%, the ionic conductivity is sufficiently high compared to the solid electrolyte powder in Example 1. Therefore, it is concluded that a higher ionic conductivity than that of the solid electrolyte powder in Example 1 can be ensured by maintaining a Na₂SiF₆ content greater than 0% and less than 100% (i.e., satisfying 0 < x < 1).

[0070] Furthermore, considering the results of Experiment 2 with a Na₂SiF₆ content of 10% and Experiment 7 with a Na₂SiF₆ content of 80%, it can be concluded that if the Na₂SiF₆ content is 10% or more and 85% or less (0.1 ≤ x ≤ 0.85), the ionic conductivity is sufficiently increased. A Na₂SiF₆ content of 20% or more and 60% or less (0.2 ≤ x ≤ 0.6) is more preferable, thereby achieving a sufficiently high ionic conductivity more reliably. Additionally, the solid electrolyte powders in Experiments 9 and 10, which contain NaPF₆, exhibited higher ionic conductivity at room temperature and 120°C than the solid electrolyte powder in Experiment 1. It should be noted that the solid electrolyte powders in Experiments 3 and 6, for which X-ray diffraction measurements were performed, exhibited peaks in the X-ray diffraction patterns within the diffraction angle 2θ ranges of 18–21°, 21–24°, 31–34°, and 45–48°, respectively. Furthermore, the half-width of the strongest peak was 0.4° or more.

[0071] <The Making of an All-Solid-State Battery 1>

[0072] Na(Fe,Mn)O2 (positive electrode active material powder), solid electrolyte powder, and electron conduction aid powder are weighed and mixed to obtain the positive electrode blended powder. Separately, hard carbon (negative electrode active material powder), solid electrolyte powder, and electron conduction aid powder are weighed and mixed to obtain the negative electrode blended powder. The solid electrolyte powder is placed into a mold consisting of a PEEK resin sleeve and SUS upper and lower punches, and uniaxially pressed at 150 MPa. The positive electrode blended powder is placed on top of the pressed solid electrolyte powder and integrated using 150 MPa pressure. The negative electrode blended powder is placed on the opposite side of the pressed solid electrolyte powder and integrated using 150 MPa pressure. Thus, a battery consisting of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is manufactured.

[0073] <Charge and Discharge Test 1>

[0074] After connecting the upper and lower punches with wires, the above battery was left static in a thermostat at 120 °C for a cc-cv (Constant Current-Constant Voltage) charge-discharge test. During the charge-discharge test, the cc current density was set to 300 μA / cm 2 , the cv current density was 30 μA / cm 2 , and the cut-off voltage was 4.25 - 1.50 V. In the battery using the solid electrolyte powder of Experimental Example 1 (Comparative Example), the discharge capacity per unit of positive electrode active material was 0 mAh / g. That is, the resistance was relatively high and charge-discharge could not be carried out. In the battery using the solid electrolyte powder of Experimental Example 6 (Example), the discharge capacity per unit of positive electrode active material was 31 mAh / g.

[0075] <Full Solid-State Battery Fabrication 2>

[0076] The solid electrolyte powder of Experimental Example 6, commercially available NaCrO2 powder as the positive electrode active material powder, and commercially available acetylene black as the electron conduction assistant powder were weighed and mixed at a weight ratio of 50:50:3 to obtain the blended powder for the positive electrode. 100 mg of the solid electrolyte powder was placed into a PEEK resin mold with an inner diameter of φ10 mm and press-molded. One punch was removed, 3.3 mg of the blended powder for the positive electrode was placed in, and press-molded. Additionally, another punch was removed, a Na metal foil was placed, and then the punch was put back and fixed with a screw, thus constructing the battery.

[0077] <Charge-Discharge Test 2>

[0078] The above battery was placed in a thermostat at 60 °C for a cc charge-discharge test at 50 μA. The charge cut-off voltage was set to 3.6 V, and the discharge cut-off voltage was set to 2.0 V. Figure 6 is a graph showing the results of the charge-discharge test. Figure 6 The vertical axis represents voltage, and the horizontal axis represents capacity density. Additionally, the first to fourth charge curves were marked with L11, L12, L13, L14, and the first to fourth discharge curves were marked with L21, L22, L23, L24. As Figure 6 such, in the above battery, charge-discharge of multiple cycles could be stably repeated, and it was confirmed that this solid electrolyte functioned as a Na solid electrolyte.

[0079] <Potential Window Measurement>

[0080] 100 mg of the solid electrolyte powder from Example 6 was placed into a PEEK resin mold with an inner diameter of φ10 mm and pressed into shape. One punch was removed, Na metal foil was placed on top, the punch was replaced, and the mold was secured with screws, thus obtaining a single cell for measurement. In the potential window measurement, the single cell was placed in a 60°C constant temperature bath, and the potential was measured at -0.5 to 5V (vsNa). ＋ Within the range of / Na), a voltage scan was performed at 10mV / sec to obtain a cyclic voltammetry diagram. Figure 7 This is a graph showing the results of the potential window measurement. Figure 7 The vertical axis represents current, and the horizontal axis represents voltage. As a result of the potential window measurement, it was confirmed that no current flowed up to 5V (no electrolysis occurred in the solid electrolyte), indicating that this solid electrolyte possesses high electrochemical stability (oxidation resistance).

[0081] Figure 2 In step S11, Na3AlF6, generated from NaF and AlF3, is mixed with Na2SiF6. However, Na3AlF6 can be mixed directly without generating Na3AlF6. In this case, the molar ratio of NaF to AlF3 can be other than 3:1. When NaF, AlF3, and Na2SiF6 are mixed, a solid electrolyte with high ionic conductivity can also be produced by mechanically grinding the mixture in step S12. Additionally, in step S11, Na3MαF6 (where Mα is a trivalent cation) other than Na3AlF6 can be used, as well as Na2Mβ (other than Na2SiF6). 1 F6 (where Mβ) 1 It is an element that exhibits a tetravalent cation. Other examples of Na3MαF6 besides Na3AlF6 include Na3GaF6, Na3CrF6, and Na3LaF6. Other examples of Na2MβF6 besides Na2SiF6 are also mentioned. 1 F6 can be, for example, Na2GeF6, Na2TiF6, Na2ZrF6, etc. As mentioned above, Mβ... 2 Let Mβ be an element with a pentavalent cation. 3 When denoted as a hexavalent cation, replace Na₂Mβ. 1 F6, or, except Na2Mβ 1 Besides F6, Na and Mβ can be used. 2 And compounds composed of F (e.g., NaPF6, NaVF6), and compounds composed of Na, Mβ 3And mixtures of F (such as mixtures of NaF and MoF6 or WF6). Furthermore, MαF3 other than AlF3 and NaF can be directly mixed with Na2MβF6. Examples of MαF3 other than AlF3 include GaF3, CrF3, LaF3, BiF3, and YF3.

[0082] As explained above, this solid electrolyte contains Na, Mα, Mβ, and F, where Mα is at least one element with a trivalent cation, and Mβ is at least one element with a quadrivalent or higher cation. Therefore, a solid electrolyte with high ionic conductivity can be provided. As a result, an all-solid-state secondary battery with high output power can be realized.

[0083] However, among solid electrolytes, those based on sulfides are widely known to react with moisture to produce hydrogen sulfide gas. On the other hand, oxide-based solid electrolytes that do not produce gases like hydrogen sulfide are also under development; however, these typically require densification through high-temperature sintering to improve ionic conductivity, leading to high resistance due to reactions with the active material during battery manufacturing. In contrast, this solid electrolyte is made of a non-flammable and chemically stable material, thus providing an inherently safe ion battery. Furthermore, this solid electrolyte achieves densification using compression molding rather than sintering, preventing reactions with the active material during battery manufacturing. Moreover, even when using negative electrode active materials with low action potentials, such as graphite, a stable charge-discharge negative electrode can be formed. This solid electrolyte uses inexpensive and resource-risk-free sodium, thus providing an inexpensive and readily available all-solid-state secondary battery.

[0084] Preferably, Mβ is an element with a tetravalent cation, and this solid electrolyte contains an element with the formula Na. a Mα b Mβ c F d The components represented satisfy 0.9(3-x)≤a≤1.1(3-x), 0.9(1-x)≤b≤1.1(1-x), 0.9x≤c≤1.1x, 5.4≤d≤6.6, and 0<x<1. Therefore, a higher ionic conductivity can be achieved more reliably.

[0085] Preferred option: The element with a tetravalent cation is designated as Mβ. 1 Let the element that is a pentavalent cation be designated as Mβ. 2 Let the element that is a hexavalent cation be designated as Mβ. 3 At that time, this solid electrolyte contains Na 3－x－2y－3z Mα 1－（x＋y＋z） Mβ 1 x Mβ2 y Mβ 3 z The component represented by F6 satisfies 0≤x<1, 0≤y<1, 0≤z<1, and 0<(x+y+z)<1. Therefore, a higher ionic conductivity can be achieved more reliably.

[0086] When confirming whether an unknown solid electrolyte is this solid electrolyte, a chemical analysis is performed on the unknown solid electrolyte to confirm whether the constituent elements are Na, Mα, Mβ, and F. Furthermore, in confirming whether the unknown solid electrolyte has the above-mentioned composition, for example, regarding Na, Al, Si, and P, quantification can be performed using an ICP-luminescence spectrophotometer. Regarding F, quantification can be performed using ion chromatography. If this solid electrolyte contains element Mα other than Al, and element Mβ other than Si and P, appropriate methods for determining quantifiable elements Mα and Mβ are selected.

[0087] A preferred method for manufacturing this solid electrolyte includes the following steps: when Mα is at least one element with a trivalent cation and Mβ is at least one element with a quadratic or higher cation, mixing a substance containing Na, Mβ, and F with Na3MαF6 to obtain a mixture, or mixing a substance containing Na, Mβ, and F, MαF3, and NaF to obtain a mixture (step S11); and mechanically grinding the mixture (step S12). Accordingly, a solid electrolyte with high ionic conductivity can be readily provided. When Mβ is an element with a quadratic cation, a preferred method includes the following steps: mixing Na3MαF6 and Na2MβF6 to obtain a mixture, or mixing MαF3, NaF, and Na2MβF6 to obtain a mixture (step S11); and mechanically grinding the mixture (step S12). Accordingly, a solid electrolyte with high ionic conductivity can be provided more reliably.

[0088] This solid electrolyte, its manufacturing method, and the battery can be modified in various ways.

[0089] The X-ray diffraction pattern obtained from this solid electrolyte may have peaks in all or part of the diffraction angle 2θ ranges of 18–21°, 21–24°, 31–34°, and 45–48°. Furthermore, the half-width of the strongest peak in the X-ray diffraction pattern may be less than 0.4°.

[0090] This solid electrolyte can be mixed with other substances (including Na₂O₃) to be used as an electrolyte material. In this case, the solid electrolyte is preferably the component with the largest mass percentage in the electrolyte material, i.e., the main component. The mass percentage of the main component in the electrolyte material is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0091] The solid electrolyte used in the all-solid-state secondary battery 1 does not necessarily need to be included in all of the positive electrode 11, negative electrode 12, and electrolyte layer 13; it is sufficient that it is included in at least one of the positive electrode 11, negative electrode 12, and electrolyte layer 13. Furthermore, this solid electrolyte can be used in batteries other than all-solid-state secondary batteries, and also for applications other than batteries. The solid electrolyte can be manufactured using processes other than mechanical grinding.

[0092] The components in the above-described embodiments and their variations can be appropriately combined as long as they do not contradict each other.

[0093] Although the invention has been described in detail, the description is illustrative and not limiting. Therefore, it can be said that numerous modifications and solutions can be adopted without departing from the scope of the invention.

[0094] Explanation of reference numerals in the attached figures

[0095] 1. All-solid-state sodium-ion secondary battery

[0096] 11 Positive electrode

[0097] 12 Negative electrode

[0098] 13 Electrolyte layer

[0099] Steps S11 and S12

Claims

1. A solid electrolyte, wherein, It includes Na, Mα, Mβ and F, where Mα is at least one element that is a trivalent cation and Mβ is at least one element that is a cation with a valence of four or more.

2. The solid electrolyte according to claim 1, wherein, Mβ is an element with a tetravalent cation, and the solid electrolyte contains elements with the formula Na. 3－x Mα 1－x Mβ x F6 indicates the component. It satisfies 0 < x < 1.

3. The solid electrolyte according to claim 2, wherein, In the given formula, 0.1 ≤ x ≤ 0.85 is satisfied.

4. The solid electrolyte according to claim 1, wherein, Let the element that is a tetravalent cation be designated as Mβ. 1 Let the element that is a pentavalent cation be designated as Mβ. 2 Let the element that is a hexavalent cation be designated as Mβ. 3 When the solid electrolyte contains Na 3－x－2y－3z Mα 1－（x＋y＋z） Mβ 1 x Mβ 2 y Mβ 3 z F6 indicates the component. It satisfies 0≤x<1, 0≤y<1, 0≤z<1, and 0<(x+y+z)<1.

5. The solid electrolyte according to claim 4, wherein, In the given formula, 0.1 ≤ x ≤ 0.85 is satisfied.

6. The solid electrolyte according to claim 1, wherein, Mα includes Al or Ga.

7. The solid electrolyte according to claim 1, wherein, Mβ includes Si, P, or Ge.

8. The solid electrolyte according to claim 1, wherein, The X-ray diffraction pattern obtained by using CuKα rays X-ray diffraction measurement has peaks in the diffraction angle 2θ ranges of 18–21°, 21–24°, 31–34°, and 45–48°, respectively.

9. The solid electrolyte according to claim 1, wherein, In the X-ray diffraction pattern obtained by using CuKα rays, the half-width of the strongest peak is greater than 0.4°.

10. A method for manufacturing a solid electrolyte, comprising the following steps: a) When Mα is set as at least one element with a trivalent cation and Mβ is set as at least one element with a quadrivalent or higher cation, a mixture is obtained by mixing a substance containing Na, Mβ, and F with Na3MαF6, or a mixture is obtained by mixing a substance containing Na, Mβ, and F, MαF3, and NaF; and b) The mixture is subjected to mechanical grinding.

11. A battery comprising: positive electrode; Negative electrode; and An electrolyte layer is disposed between the positive electrode and the negative electrode. The solid electrolyte according to any one of claims 1 to 9 comprises at least one of the positive electrode, the negative electrode, and the electrolyte layer.

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