Sodium ion conductive glass ceramics

Abstract

The invention provides a sodium ion conductivity glass ceramic which is compact in structure, has high water resistance and high sodium ion conductivity and can be used for an electrolyte diaphragm for a water-based sodium ion secondary battery. The present invention relates to a sintered body which contains, in mol% in terms of oxides, 20.0% to 27.0% of a Na2O component, 30.0% to 40.0% of a ZrO2 component, 3.0% to 20.0% of a P2O5 component, and 20.0% to 40.0% of a SiO2 component, and which contains a monoclinic crystal phase represented by Na1 + xZr2SixP3-xO12 (0 < X < 3), and which contains, in terms of oxides, 20.0% to 27.0% of a Na2O component, 30.0% to 40.0% of a ZrO2 component, 3.0% to 20.0% of a P2O5 component, and 20.0% to 40.0% of a SiO2 component. And a sodium-ion-conductive glass ceramic in which the proportion of a ZrO2 crystal phase is 10% by mass or less among all the contained crystal phases, thereby solving the technical problem.

Description

Technical Field

[0001] This invention relates to a sodium-ion conductive glass-ceramic, an electrolyte separator for an aqueous sodium-ion secondary battery comprising the glass-ceramic, and a glass material for synthesizing the sodium-ion conductive glass-ceramic. Background Technology

[0002] Currently, lithium-ion rechargeable batteries are widely used in applications such as power supplies for electric vehicles and portable telephone terminals. Furthermore, primarily driven by the need to improve safety, the development of all-solid-state rechargeable batteries—which do not use liquid electrolytes (electrolytes) and whose electrode layers and electrolyte layers are entirely composed of inorganic solids—is also underway.

[0003] However, lithium, an essential component of lithium-ion secondary batteries, is not abundant, thus posing technical challenges in terms of cost and supply. Therefore, sodium, which is abundant and inexpensive, has attracted attention, and sodium-ion secondary batteries containing aqueous electrolytes (aqueous sodium-ion secondary batteries) are under development (e.g., Patent Documents 1-4).

[0004] Aqueous sodium-ion secondary batteries have a cost advantage because they can use sodium, which is abundant in seawater, as a raw material, and are also considered promising due to the ease of resource availability. Furthermore, regarding safety, which may become an issue during large-scale production, aqueous electrolytes are extremely difficult to ignite compared to the organic solvent electrolytes commonly used in lithium-ion secondary batteries, which have an ignition point of approximately 140°C. Therefore, further improvements in safety are expected.

[0005] Existing technical documents

[0006] Patent documents Patent Document 1: Japanese Patent Application Publication No. 2011-086402 Patent Document 2: Japanese Patent Application Publication No. 2012-003928 Patent Document 3: Japanese Patent Application Publication No. 2012-054208 Patent Document 4: Japanese Patent Application Publication No. 2017-124951 Summary of the Invention The technical problem that the invention aims to solve Here, in aqueous alkali metal ion secondary batteries containing aqueous electrolytes, the generation of hydrogen gas due to the electrolysis of water during charging becomes a problem. In particular, while aqueous sodium ion secondary batteries have advantages in terms of cost as mentioned above, it is said that regardless of the type of negative electrode active material used, it is difficult to suppress the generation of hydrogen gas during charging, and if the generated hydrogen gas remains on the negative electrode, it will cause polarization and make it difficult for current to flow.

[0007] To address this issue, namely, to obtain an aqueous alkali metal ion secondary battery with high electromotive force while suppressing hydrogen production, for example, in an aqueous lithium-ion secondary battery, a form has been conceived in which a lithium-ion solid electrolyte with high water resistance, high lithium-ion conductivity, and high water resistance is used as an electrolyte separator disposed between the positive and negative electrodes.

[0008] However, regarding sodium ion conductive materials, it is known that those with Na3Zr2Si2PO4... 12 Solid electrolytes with a crystalline phase, represented by the NASICON structure, are known to have poor sintering properties, making it impossible to obtain a dense and highly waterproof electrolyte membrane. It should be noted that Patent Document 4 disclosed a method of impregnating molten hydrocarbons (resins) in Na3Zr2Si2PO4. 12 A method for obtaining a highly waterproof sodium-ion conductive material by plasma treatment of the surface of a molded body (connector) to make it exhibit sodium ion conductivity, thereby filling the voids in the body, is problematic because this method uses Na3Zr2Si2PO4 to fill the voids. 12 Therefore, it's difficult to say that it has high sodium ion conductivity. Furthermore, due to the presence of hydrocarbons with low durability, the interaction between hydrocarbons and Na3Zr2Si2PO4... 12 At the interface and other joints, there is a very high possibility that long-term waterproofing cannot be achieved.

[0009] Therefore, the purpose of this invention is to provide a sodium-ion conductive glass-ceramic with a dense structure, high water resistance and high sodium-ion conductivity, which can be used as an electrolyte separator for aqueous sodium-ion secondary batteries.

[0010] Methods for solving technical problems To solve the aforementioned technical problems, the inventors conducted in-depth research and discovered that, calculated in mol% by oxides, the product contains: 20.0%–27.0% Na₂O, 30.0%–40.0% ZrO₂, 3.0%–20.0% P₂O₅, and 20.0%–40.0% SiO₂, and contains Na… 1＋x Zr2Si x P 3－x O 12 The present invention is a sodium-ion conductive glass-ceramic with a monoclinic crystal phase represented by (0 < X ​​< 3) and a ZrO2 crystal phase accounting for less than 10% by mass among all the crystal phases contained therein. This allows the glass-ceramic to have a dense structure, high water resistance and high sodium-ion conductivity, and can be preferably used as an electrolyte membrane for aqueous sodium-ion secondary batteries.

[0011] That is, the present invention includes the following embodiments <1> to <12>.

[0012] <1> A sodium-ion conductive glass-ceramic, comprising, in mol% (converted from oxides): 20.0%–27.0% Na₂O, 30.0%–40.0% ZrO₂, 3.0%–20.0% P₂O₅, and 20.0%–40.0% SiO₂, and containing Na₂O. 1＋x Zr2Si x P 3－x O 12 The monoclinic crystal phase represented by (0 < X ​​< 3), more preferably containing Na3Zr2Si2PO4. 12 The monoclinic crystal phase is represented; and the proportion of the ZrO2 crystal phase among all the crystal phases contained is less than 10% by mass.

[0013] <2> The sodium ion conductive glass-ceramic as described in <1>, wherein, in the sodium ion conductive glass-ceramic, the component ratio of Na, Zr, P and Si satisfies the condition using Na 1＋x Zr2Si x P 3－x O 12 The component ratio expressed as (0 < X ​​< 3) is more preferably satisfied by using Na3Zr2Si2PO4. 12 The component ratio is indicated.

[0014] <3> The sodium-ion conductive glass ceramic as described in <1> or <2>, wherein when the sodium-ion conductive glass ceramic is made into a sheet or plate-shaped substrate, the leakage rate per unit area and per 1 mm thickness of the substrate is less than 10.0 μL / h, or when the water leakage per unit area and per 1 mm thickness of the substrate per hour causes water electrolysis, the current at this time is less than 15 μA per unit area and per 1 mm thickness of the substrate.

[0015] <4> Sodium-ion conductive glass-ceramic as described in any one of <1> to <3>, wherein the sodium-ion conductivity at 25°C is 6.0 × 10⁻⁶. －4 S / cm or higher.

[0016] <5> Sodium-ion conductive glass ceramic as described in any one of <1> to <4>, wherein the sodium-ion conductivity at 25°C is 1.0 × 10⁻⁶. －6 Glass material powder with a conductivity of less than S / cm and a sodium ion conductivity of less than 1.0 × 10⁻⁶ at 25°C. －8 It is made by mixing and sintering crystalline material powder containing ZrO2 with a strength of S / cm.

[0017] <6> Sodium-ion conductive glass-ceramics as described in any one of <1> to <5>, wherein, among all the crystalline phases contained therein, the sodium-ion conductive glass-ceramic is...1＋x Zr2Si x P 3－x O 12 The proportion of the monoclinic crystal phases represented by (0 < X ​​< 3), more preferably Na3Zr2Si2PO4. 12 The proportion of the monoclinic crystal phase is 70% or more by mass.

[0018] <7> Sodium-ion conductive glass-ceramic as described in any one of <1> to <6>, wherein, in all the crystalline phases contained therein, the sodium-ion conductive glass-ceramic is included. 1＋x Zr2Si x P 3－x O 12 The monoclinic crystal phase represented by (0 < X ​​< 3) includes Na 1＋x Zr2Si x P 3－x O 12 The proportion of crystalline phases represented by (0 < X ​​< 3) is more preferably represented by Na3Zr2Si2PO4. 12 The proportion of the crystalline phase is 83% by mass or more.

[0019] <8> Sodium-ion conductive glass ceramics as described in any one of <1> to <7>, wherein all of the contained sodium ions are used in the process of... 1＋x Zr2Si x P 3－x O 12 Among the crystalline phases represented by (0 < X ​​< 3), Na3Zr2Si2PO4 is used. 12 The proportion of the monoclinic crystal phase is above 85% by mass.

[0020] <9> Sodium ion conductive glass ceramics as described in any one of <1> to <8>, wherein the proportion of the amorphous phase is 10% by mass or more.

[0021] <10> An electrolyte separator for an aqueous sodium-ion secondary battery, comprising sodium-ion conductive glass-ceramic as described in any one of <1> to <9>.

[0022] <11> A glass material for synthesizing sodium-ion conductive glass-ceramics, comprising, in mol% (converted from oxides): 30.0%–40.0% Na₂O, 0%–5.0% ZrO₂, 5.0%–35.0% P₂O₅, and 30.0%–60.0% SiO₂, wherein the ratio of Na, P, and Si satisfies the requirement of Na… 1＋x Zr2Si x P 3－x O 12The component ratio excluding Zr in the component ratio expressed as (0 < X ​​< 3), more preferably satisfying the condition of using Na3Zr2Si2PO4. 12 The component ratio represented is the component ratio after removing Zr.

[0023] <12> The glass material for synthesizing sodium ion conductive glass ceramics as described in <11>, wherein the glass transition temperature (Tg) is above 600°C.

[0024] The effects of the invention According to the present invention, a sodium-ion conductive glass-ceramic with a dense structure, high water resistance, and high sodium-ion conductivity can be provided. Furthermore, by using this sodium-ion conductive glass-ceramic, an excellent electrolyte separator for aqueous sodium-ion secondary batteries can be provided. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the device used in the embodiment to measure water resistance (a particle leakage detector using water column pressure).

[0026] Figure 2 The graph shows the water resistance measurement results of Comparative Example 2 and Example 3.

[0027] Figure 3 This is a graph showing the powder X-ray diffraction measurement results of the sintered particles in Example 3.

[0028] Figure 4 This is a secondary electron image of the fracture surface of the sintered particles of Comparative Example 1 (instead of the photograph in the attached figure).

[0029] Figure 5 yes Figure 4 A magnified image of the secondary electron image (instead of the photograph in the attached image).

[0030] Figure 6 This is a secondary electron image of the fracture surface of the sintered particles of Comparative Example 2 (instead of the photograph in the attached figure).

[0031] Figure 7 yes Figure 6 A magnified image of the secondary electron image (instead of the photograph in the attached image).

[0032] Figure 8 This is a secondary electron image of the fracture surface of the sintered particles in Example 3 (instead of the photograph in the accompanying figure).

[0033] Figure 9 yes Figure 8 A magnified image of the secondary electron image (instead of the photograph in the attached image).

[0034] Figure 10This is a reflected electron image of the fracture surface of the sheet-like sintered body of Example 5 (instead of the photograph in the accompanying drawing).

[0035] Figure 11 The image shown is a reflected electron image of the fracture surface of the sheet-like sintered body of Comparative Example 3 (instead of the photograph in the attached figure). Detailed Implementation

[0036] The present invention will be described.

[0037] This invention relates to a sodium-ion conductive glass-ceramic, comprising, in mol% (based on oxide content) 20.0%–27.0% Na₂O, 30.0%–40.0% ZrO₂, 3.0%–20.0% P₂O₅, and 20.0%–40.0% SiO₂, using Na₂O as the base metal. 1+x Zr2Si x P 3-x O 12 The monoclinic crystalline phase represented by (0 < X ​​< 3), wherein the proportion of the ZrO2 crystalline phase in all the included crystalline phases is 10% by mass or less, and an electrolyte separator for an aqueous sodium-ion secondary battery comprising the glass ceramic. Hereinafter, they are sometimes referred to as "sodium-ion conductive glass ceramic of the present invention" and "electrolyte separator for an aqueous sodium-ion secondary battery of the present invention," respectively.

[0038] Furthermore, the present invention also includes a glass material for synthesizing sodium-ion conductive glass-ceramics, wherein, based on mol% of oxides, it contains 30.0%–40.0% Na₂O, 0%–5.0% ZrO₂, 5.0%–35.0% P₂O₅, and 30.0%–60.0% SiO₂, and the composition ratio of Na, P, and Si satisfies the requirement of Na… 1+x Zr2Si x P 3-x O 12 (0 < X ​​< 3) represents the component ratio after removing Zr. Hereinafter, in this specification, it will sometimes be referred to as "the glass material for the synthesis of sodium ion conductive glass-ceramics of the present invention".

[0039] It should be noted that, unless otherwise specified, the content of the components contained in the sodium-ion conductive glass ceramic of the present invention or the glass material for synthesizing the sodium-ion conductive glass ceramic of the present invention is expressed as mol% converted from oxides (hereinafter, unless otherwise specified, mol% also means mol% converted from oxides). The content expressed as "mol% converted from oxides" means: assuming that the oxides, complex salts, metal fluorides, etc. used as raw materials for the sodium-ion conductive glass ceramic of the present invention or the glass material for synthesizing the sodium-ion conductive glass ceramic of the present invention are all decomposed and converted into oxides during melting, the total number of moles of the generated oxides is 100 mol%, representing the content of oxides of each component contained in the sodium-ion conductive glass ceramic of the present invention or in the glass material for synthesizing the sodium-ion conductive glass ceramic of the present invention.

[0040] <The composition and components of glass ceramics with sodium ion conductivity> First, the composition and components of the glass ceramic constituting the sodium ion conductivity of the present invention will be described in detail.

[0041] Na₂O is an essential component for imparting sodium ion conductivity to the lithium-sodium ion conductive glass-ceramic of this invention. In other words, it can be described as a component that significantly contributes to sodium ion conductivity. 1＋x Zr2SixP 3－x O 12 (0 < X ​​< 3) represents the essential components of the monoclinic crystal phase. Therefore, the lower limit of the Na₂O content is 20.0 mol%, preferably 21.0 mol%, more preferably 22.0 mol%, even more preferably 22.5 mol%, and even more preferably 23.0 mol%. On the other hand, based on the ease of forming Na... 1＋x Zr2SixP 3－x O 12 (0 < X ​​< 3) indicates the crystallization of monoclinic crystals. Therefore, the upper limit of the Na2O content is 27 mol%, preferably 26.0 mol%, and more preferably 25.0 mol%.

[0042] The P2O5 component is used to make the sodium ion conductive glass ceramic of the present invention contain Na. 1＋x Zr2SixP 3－x O 12 The monoclinic crystal phase represented by (0 < X ​​< 3) is an essential component necessary for excellent sodium ion conductivity. Therefore, the lower limit of the P2O5 content is 3.0 mol%, preferably 5.0 mol%, and more preferably 8.0 mol%. Furthermore, based on the ease of forming Na... 1＋x Zr2SixP3－x O 12 (0 < X ​​< 3) indicates the crystallization of monoclinic crystals. The upper limit of the content of P2O5 is 20.0 mol%, preferably 18.0 mol%, more preferably 16.0 mol%, even more preferably 14.0 mol%, further preferably 12.0 mol%, and even more preferably 10.0 mol%.

[0043] The ZrO2 component is used to make the sodium ion conductive glass ceramic of this invention contain Na. 1＋x Zr2SixP 3－x O 12 The monoclinic crystal phase (0 < X ​​< 3) is an essential component necessary for excellent sodium ion conductivity. Furthermore, it contributes to improving the water resistance of the sodium ion conductive glass-ceramic of the present invention. Therefore, the lower limit of the ZrO2 content is 30.0 mol%, preferably 31.0 mol%, more preferably 33.0 mol%. Additionally, based on the ease of forming with Na… 1＋x Zr2SixP 3－x O 12 For reasons such as the monoclinic crystal phase represented by (0 < X ​​< 3) and the ease of reducing the proportion of ZrO2 crystal phase, the upper limit of the ZrO2 content is 40.0 mol%, preferably 39.0 mol%, more preferably 37.0 mol%, and even more preferably 35.0 mol%.

[0044] The SiO2 component is also used to ensure that the sodium-ion conductive glass ceramic of this invention contains Na. 1＋x Zr2SixP 3－x O 12 The monoclinic crystal phase represented by (0 < X ​​< 3) is an essential component necessary for excellent sodium ion conductivity. Furthermore, it contributes to improving the compactness (water resistance) of the sodium ion conductive glass-ceramic of the present invention. Therefore, the lower limit of the SiO2 content is 20.0 mol%, preferably 23.0 mol%, more preferably 25.0 mol%, further preferably 27.0 mol%, and even more preferably 30.0 mol%. Additionally, based on the ease of forming Na... 1＋x Zr2SixP 3－x O 12 (0 < X ​​< 3) indicates the crystallization of monoclinic crystals. Therefore, the upper limit of the SiO2 content is 40.0 mol%, preferably 39.0 mol%, more preferably 37.0 mol%, and even more preferably 35.0 mol%.

[0045] The sodium-ion conductive glass-ceramic of the present invention may consist only of the aforementioned essential components, but as optional components, it may further include one or more components selected from the group consisting of Al2O3, Y2O3, Sc2O3, CaO, and MgO. Furthermore, as long as it does not significantly affect the sodium-ion conductivity of the sodium-ion conductive glass-ceramic of the present invention, it may also contain a small amount of Li2O or K2O (e.g., a total of 5.0 mol% or less).

[0046] The Al2O3, Y2O3, and Sc2O3 components are optional components that can further improve the sodium ion conductivity of the sodium ion conductive glass ceramic of the present invention. It should be noted that the content of Al2O3, Y2O3, and Sc2O3 is preferably 10.0 mol% or less, more preferably 8.0 mol% or less, even more preferably 5.0 mol% or less, and even more preferably 3.0 mol% or less.

[0047] CaO and MgO are optional components that can further improve the sodium ion conductivity of the sodium ion conductive glass ceramic of the present invention. It should be noted that the content of both CaO and MgO is preferably 10.0 mol% or less, more preferably 8.0 mol% or less, even more preferably 5.0 mol% or less, and even more preferably 3.0 mol% or less.

[0048] It should be noted that the sodium-ion conductive glass ceramic of the present invention preferably contains as little sulfur (S) as possible (e.g., less than 1 mol%, further less than 0.1 mol%, etc.), and more preferably none at all. By reducing the S content, the possibility of generating harmful gases such as hydrogen sulfide in aqueous sodium-ion secondary batteries using the sodium-ion conductive glass ceramic of the present invention as the electrolyte separator can be reduced. Furthermore, it is also preferable to minimize zinc (Zn), arsenic (As), antimony (Sb), and lead (Pb), and more preferably none at all. This is because these are harmful substances. Furthermore, from the viewpoint of generating electronic conductivity, it is also preferable to minimize bismuth (Bi) and tellurium (Te), and more preferably none at all. In addition, the sodium-ion conductive glass ceramic of the present invention is an inorganic material and substantially does not contain hydrocarbon components such as resins.

[0049] <Crystalline and amorphous phases contained in sodium ion-conducting glass ceramics> The sodium-ion conductive glass-ceramic of the present invention has the above-described components, and further contains sodium... 1＋x Zr2Si x P 3－x O 12The monoclinic crystal phase is represented by (0 < X ​​< 3). In other words, it contains at least Na with a NASICON structure. 1＋x Zr2Si x P 3－ x O 12 (0 < X ​​< 3) represents monoclinic crystalline phase and glassy phase (amorphous phase) sodium ion conductivity glass ceramics. It should be noted that the value of X is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1 or more. The upper limit is preferably 2.5 or less. In particular, when Na... 1＋x Zr2Si x P 3－x O 12 The monoclinic crystal phase represented by (0 < X ​​< 3) is Na3Zr2Si2PO4. 12 When the monoclinic crystal phase is represented, that is, when the sodium ion conductive glass ceramic of the present invention contains Na3Zr2Si2PO4, it indicates that the crystal phase is monoclinic. 12 When representing a monoclinic crystalline phase, it is highly preferred due to the ease of obtaining high sodium ion conductivity. Furthermore, in the sodium ion conductive glass-ceramic of the present invention, the proportion of ZrO2 crystalline phase (i.e., the mass percentage of ZrO2 crystalline phase in the total mass of the crystalline phases) among all the crystalline phases contained (all the crystalline phases contained in the sodium ion conductive glass-ceramic of the present invention) is 10% by mass or less. This, combined with the above-described structure, allows for the combination of a dense structure and high sodium ion conductivity. It should be noted that the proportion of this ZrO2 crystalline phase is preferably 9% by mass or less, more preferably 8% by mass or less.

[0050] Here, "glass ceramic" refers to a crystalline phase synthesized by mixing glass (amorphous material) with other materials and then heat-treating it, including both crystalline and amorphous phases formed by heat treatment. In other words, it is a mixture of ceramic and glass. Additionally, "monoclinic crystalline phase" refers to a crystalline structure determined by X-ray diffraction measurements, in which two of the three crystal axes are orthogonal to each other, and only the third axis is oblique to the aforementioned two axes. Alternatively, in space group representation, it can be represented as I2 / a (15) or C2 / c (15). Furthermore, the composition and proportion of the aforementioned crystalline phase can be measured and analyzed by powder X-ray diffraction (the same applies to the composition and proportion of the crystalline phase below).

[0051] In particular, the sodium-ion conductive glass-ceramic of the present invention preferably has the following structure: the ratio of Na, Zr, P to Si in the total of the crystalline and amorphous phases (i.e., the glass-ceramic as a whole) satisfies the requirement of Na... 1＋x Zr2Si x P 3－x O 12 The component ratio is expressed as (0 < X ​​< 3). This can also be described as the crystallization process caused by sintering during glass and ceramic manufacturing, etc., using Na... 1＋x Zr2Si x P 3－x O 12 The compositional shift of the crystalline phase represented by (0 < X ​​< 3) is almost negligible. Furthermore, when Na is used... 1＋x Zr2Si x P 3－x O 12 The component ratio expressed as (0 < X ​​< 3) is calculated using Na3Zr2Si2PO4. 12 When the component ratio is expressed, it is more preferred. In other words, when the component ratio of Na, Zr, P and Si in the sodium ion conductive glass ceramic of the present invention satisfies the condition of Na3Zr2Si2PO4, it is preferred. 12 When the component ratio is expressed, it is more preferred.

[0052] It should be noted that the sodium-ion conductive glass-ceramic of the present invention includes, among all the crystalline phases contained therein, a monoclinic crystalline phase using Na... 1＋x Zr2Si x P 3－x O 12 The proportion of the crystalline phase represented by (0 < X ​​< 3) is preferably 83% by mass or more, more preferably 85% by mass or more, even more preferably 88% by mass or more, and even more preferably 90% by mass or more. In particular, when Na3Zr2Si2PO4 is used... 12 It is more preferable when the proportion of the crystalline phase is within the above-described range. However, the sodium-ion conductive glass-ceramic of the present invention may also contain a portion of the crystalline phase other than those described above.

[0053] Furthermore, based on reasons such as making it easier to improve the conductivity of sodium ions, Na is used among all the crystalline phases contained therein. 1＋ x Zr2Si x P 3－x O 12 The proportion of the monoclinic crystalline phase (the mass percentage of that crystalline phase in the total mass of the crystalline phase) represented by (0 < X ​​< 3) is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more. In particular, when Na3Zr2Si2PO4 is used... 12 It is more preferable when the proportion of the monoclinic crystalline phase is within the above-mentioned range. Furthermore, although not limited, it is preferable to include all the Na-containing... 1＋x Zr2Si x P3－x O 12 Among the crystalline phases represented by (0 < X ​​< 3), Na3Zr2Si2PO4 is used. 12 The proportion of the monoclinic crystalline phase is preferably 85% by mass or more, more preferably 88% by mass or more, and even more preferably 90% by mass or more.

[0054] The sodium-ion conductive glass-ceramic of the present invention is preferably obtained by mixing and sintering powders with a sodium-ion conductivity of 1.0 × 10⁻⁶ at 25°C. －6 Glass material powder with a conductivity of less than S / cm; and sodium ion conductivity of less than 1.0 × 10⁻⁶ at 25°C. －8 Crystalline material powders containing ZrO2 (such as zirconia powder) with a S / cm (including materials that do not substantially have sodium ion conductivity). The reason for this is that the resulting powder, formed by mixing and sintering, uses Na... 1＋x Zr2Si x P 3－x O 12 (0 < X ​​< 3) indicates that the crystalline phase of monoclinic crystals is unlikely to undergo compositional shift (the ZrO2 component in the crystalline material powder is easily facilitated by Na). 1＋x Zr2Si x P 3－x O 12 (The formation of the monoclinic crystalline phase, where 0 < X ​​< 3), readily yields glass-ceramics with a dense structure and high sodium ion conductivity. Therefore, a dense electrolyte film is easily formed. The glass material powder described below is preferably an example of the sodium ion conductivity glass-ceramic synthesis powder of the present invention. Furthermore, the crystalline material powder containing ZrO2 preferably contains more than 30 mol% ZrO2.

[0055] Furthermore, the sodium-ion conductive glass-ceramic of the present invention, as described above, contains not only the aforementioned crystalline phase but also a certain amount or more of an amorphous phase, resulting in a dense structure and high water resistance. This water resistance is maintained over a long period. While the proportion of the amorphous phase is not limited, it is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more in the sodium-ion conductive glass-ceramic of the present invention. The upper limit is preferably less than 50% by mass, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

[0056] The proportion of the amorphous phase can be measured, for example, by forming the sodium-ion conductive glass-ceramic of the present invention into a sheet-like sintered body with a film thickness of 1 μm or more and 1000 μm or less, fracturing and grinding it to obtain a fracture surface, and then calculating the area of ​​the amorphous phase in the fracture surface (i.e., calculating the proportion of the amorphous phase in the total area of ​​the fracture surface). It should be noted that the "film thickness" refers to the straight-line distance between the two surfaces (main surfaces) of the sheet-like sintered body, and is a value obtained by measuring the film thickness at any 10 locations using known equipment and calculating the average value. The same applies below.

[0057] Furthermore, while the water resistance of the sodium-ion conductive glass-ceramic of the present invention is not limited, it is preferably configured such that when the sodium-ion conductive glass-ceramic of the present invention is made into a sheet or plate-shaped substrate, the water resistance per unit area (unit area of ​​the main surface, 1 cm²) of the substrate is [value missing]. 2 The leakage rate per 1 mm thickness is 10.0 μL / h or less. The upper limit is preferably 8.0 μL / h or less, more preferably 5.0 μL / h or less, and even more preferably 2.0 μL / h or less.

[0058] Here, "leak rate" refers to: using Figure 1 The apparatus shown (a particle leakage detector using water column pressure) uses the values ​​obtained from evaluation using a completely impermeable glass plate as a baseline. Measurements are performed on one sample for 3–5 days in a constant temperature bath controlled at 25°C. The leakage amount (transmission volume, μL) of water (liquid water) in the substrate is measured, and the leakage rate per hour per unit area (1 cm²) is calculated. 2 The leakage rate is measured in units of 1 mm thick water. It should be noted that the water column pressure used is between 250 mmAq and 50 mmAq. Additionally, to minimize errors caused by air inside the container, the amount of air inside should be reduced as much as possible, and atmospheric pressure correction should be performed.

[0059] Alternatively, the sodium-ion conductive glass-ceramic of the present invention, due to the leakage of water (i.e., 1 cm² per hour per unit area). 2 The electrolysis of water (including water seeping in at a thickness of 1 mm) generates an electric current. When the current is converted, the current per unit area of ​​the substrate and per 1 mm thickness is 15 μA or less, more preferably 10 μA or less, and even more preferably 2 μA or less. Furthermore, this current can also be directly evaluated by electrochemical methods.

[0060] Furthermore, the sodium ion conductive glass-ceramic of the present invention, while possessing high water resistance, also exhibits high sodium ion conductivity, with a preferred sodium ion conductivity of 6.0 × 10⁻⁶ at 25°C. －4 S / cm or higher, more preferably 7.0×10－4 S / cm or higher, and more preferably 8.0×10 －4 S / cm or higher, more preferably 9.0 × 10⁻⁶ －4 S / cm or higher, and more preferably 1.0×10 －3 S / cm or higher.

[0061] <Electrolyte separator for aqueous sodium-ion secondary batteries containing sodium-ion conductive glass ceramics> The sodium-ion conductive glass-ceramic of the present invention possesses the aforementioned high water resistance and high sodium-ion conductivity, and also exhibits water resistance. Therefore, it is preferably used as an electrolyte separator for aqueous sodium-ion secondary batteries (i.e., a solid electrolyte separator disposed between the positive and negative electrodes of an aqueous sodium-ion secondary battery to separate the aqueous electrolyte). In other words, the electrolyte separator for aqueous sodium-ion secondary batteries of the present invention, comprising the sodium-ion conductive glass-ceramic of the present invention, exhibits excellent water resistance and sodium-ion conductivity, making it very useful as an electrolyte separator for aqueous sodium-ion secondary batteries. In the electrolyte separator for aqueous sodium-ion secondary batteries of the present invention, the content of the sodium-ion conductive glass-ceramic of the present invention is only required to be greater than 50% by mass, more preferably 60% by mass or more, and even more preferably greater than 65% by mass.

[0062] The shape of the electrolyte membrane for the aqueous sodium-ion secondary battery of the present invention is not limited as long as it functions as a membrane. Its shape (overall shape) is preferably cylindrical, single-sided closed cylindrical, elliptical single-sided closed cylindrical, honeycomb structure cylindrical, or plate-shaped.

[0063] Here, "cylindrical" refers to a cylindrical shape in which the top and bottom surfaces are approximately circular (approximately circular with a major-to-minor axis ratio of less than 1.5) and are not closed (without diaphragms on the top and bottom surfaces), with the sides forming the periphery of the cylinder functioning as diaphragms; "one-sided closed cylindrical" refers to a cylindrical shape in which one of the top or bottom surfaces is closed by a diaphragm, while the other is not closed; "elliptical one-sided closed cylindrical" refers to a cylindrical shape in which both the top and bottom surfaces of the one-sided closed cylindrical are elliptical (elliptical with a major-to-minor axis ratio of 1.5 or greater); "honeycomb structure cylindrical" refers to a cylindrical shape in which the internal voids are honeycomb structure; "plate-like" refers to a plate-like shape (plate-like) having two main surfaces, a front and a back, that function as diaphragms.

[0064] Furthermore, the thickness of the electrolyte membrane for the aqueous sodium-ion secondary battery of the present invention is not limited, but is preferably 0.01 mm or more, more preferably 0.1 mm or more. Its upper limit is preferably 1 mm or less, more preferably 0.5 mm or less. It should be noted that this "membrane thickness" also refers to the straight-line distance between the two surfaces (main surfaces) of the electrolyte membrane for the aqueous sodium-ion secondary battery, and is a value obtained by measuring the membrane thickness at any 10 locations using known equipment and calculating its average value.

[0065] Furthermore, its density is not particularly limited; for example, it can be 2.0 g / cm³. 3 The above can also be 2.5 g / cm³. 3 The above can also be 3.0 g / cm³ 3 The above can be 3.1 g / cm³. 3 That's all. Furthermore, the sodium-ion conductive glass-ceramic of the present invention, having the same density as described above, can be used to construct the electrolyte separator for an aqueous sodium-ion secondary battery of the present invention, having the density described above.

[0066] In addition, the electrolyte separator for aqueous sodium-ion secondary batteries of the present invention can also be implemented in a form that is joined with a porous support plate in order to make it a thin film and maintain its strength.

[0067] <Composition and Components of Glass Materials for Sodium Ion Conductivity Glass-Ceramic Synthesis> Next, the composition and components of the glass material constituting the sodium ion conductive glass ceramic of the present invention, which can be synthesized by mixing and sintering with a crystalline material containing ZrO2, will be described in detail.

[0068] The Na₂O component is an essential component necessary to impart sodium ion conductivity to the sodium ion conductive glass ceramic of the present invention synthesized using the glass material for synthesizing sodium ion conductive glass ceramics of the present invention. Therefore, the lower limit of the Na₂O content is 30.0 mol%, preferably 31.0 mol%, more preferably 33.0 mol%, even more preferably 35.0 mol%, and even more preferably 36.0 mol%. On the other hand, the sodium ion conductive glass ceramic of the present invention synthesized based on the glass material for synthesizing sodium ion conductive glass ceramics of the present invention readily forms sodium ion conductivity. 1＋x Zr2Si x P 3－x O 12 (0 < X ​​< 3) indicates the crystallization of monoclinic crystals. Therefore, the upper limit of the Na2O content is 40.0 mol%, preferably 39.0 mol%, and more preferably 38.0 mol%.

[0069] The P2O5 component is used to ensure that the sodium-ion conductive glass ceramic of the present invention, synthesized using the glass material for synthesizing sodium-ion conductive glass ceramics of the present invention, contains sodium. 1＋x Zr2Si x P 3－x O 12 The monoclinic crystal phase represented by (0 < X ​​< 3) is an essential component necessary for excellent sodium ion conductivity. Therefore, the lower limit of the P2O5 content is 5.0 mol%, preferably 8.0 mol%, more preferably 10.0 mol%, and even more preferably 12.0 mol%. Furthermore, the sodium ion conductive glass-ceramic of the present invention, synthesized based on the glass material for synthesizing sodium ion conductive glass-ceramics using the present invention, readily forms sodium ion conductive glass-ceramics. 1＋ x Zr2Si x P 3－x O 12 (0 < X ​​< 3) indicates the crystallization of monoclinic crystals. The upper limit of the content of P2O5 is 35.0 mol%, preferably 30.0 mol%, more preferably 25.0 mol%, even more preferably 22.0 mol%, further preferably 20.0 mol%, and even more preferably 15.0 mol%.

[0070] The SiO2 component also allows the sodium-ion conductive glass ceramic of the present invention, synthesized using the glass material for synthesizing sodium-ion conductive glass ceramics of the present invention, to contain Na. 1＋x Zr2Si x P 3－x O 12 The monoclinic crystal phase represented by (0 < X ​​< 3) is an essential component necessary for excellent sodium ion conductivity. Furthermore, it contributes to improving the compactness (water resistance) of the synthesized sodium ion conductive glass-ceramic of the present invention. Therefore, the lower limit of the SiO2 content is 30.0 mol%, preferably 33.0 mol%, more preferably 35.0 mol%, even more preferably 38.0 mol%, even more preferably 40.0 mol%, even more preferably 42.0 mol%, and even more preferably 45.0 mol%. In addition, the sodium ion conductive glass-ceramic of the present invention synthesized using the glass material for synthesizing the sodium ion conductive glass-ceramic of the present invention readily forms with Na… 1+ x Zr2Si x P 3-x O 12 (0 < X ​​< 3) indicates the crystallization of monoclinic crystals. Therefore, the upper limit of the SiO2 content is 60.0 mol%, preferably 56.0 mol%, more preferably 53.0 mol%, and even more preferably 50.0 mol%.

[0071] ZrO2 is an optional component that can be included in the glass material for synthesizing sodium-ion conductive glass-ceramics according to the present invention. The inclusion of ZrO2 improves the water resistance of the glass material. However, based on the viewpoint of facilitating glass formation of the glass material for synthesizing sodium-ion conductive glass-ceramics according to the present invention, the upper limit of the ZrO2 content in the glass material for synthesizing sodium-ion conductive glass-ceramics according to the present invention is preferably 5.0 mol%, more preferably 3.0 mol%, and even more preferably 1.0 mol%. Furthermore, it is also possible to substantially omit the ZrO2 component.

[0072] The glass material for synthesizing sodium-ion conductive glass-ceramics of the present invention may consist only of the aforementioned essential components. However, as optional components, in addition to ZrO2, it may contain one or more components selected from the group consisting of Al2O3, Y2O3, Sc2O3, CaO, and MgO, as described above. Furthermore, as long as it does not affect the sodium-ion conductivity of the sodium-ion conductive glass-ceramics of the present invention synthesized using it, a small amount of Li2O or K2O may be included. The content of these components may be the same as that in the sodium-ion conductive glass-ceramics of the present invention described above. In addition, similarly to the sodium-ion conductive glass-ceramics of the present invention described above, it is preferable to minimize the presence of sulfur (S), zinc (Zn), arsenic (As), antimony (Sb), lead (Pb), bismuth (Bi), or tellurium (Te), and more preferably, to omit them altogether.

[0073] Furthermore, the glass material for synthesizing sodium-ion conductive glass-ceramics of the present invention comprises the above-mentioned components, and is configured such that the component ratio of Na, P and Si satisfies the requirement of Na 1＋x Zr2Si x P 3－x O 12 The component ratio (0 < X ​​< 3) represents the component ratio excluding Zr. It should be noted that the value of X can be the same as described above. Therefore, by mixing and sintering with a crystalline material containing ZrO2, the sodium-ion conductive glass-ceramic of the present invention described above can be synthesized. In particular, when Na... 1＋x Zr2Si x P 3－x O 12 The component ratio expressed as (0 < X ​​< 3) is calculated using Na3Zr2Si2PO4. 12 When the component ratio is expressed, that is, when the component ratio of Na, P and Si satisfies the condition Na3Zr2Si2PO4, then... 12 When the component ratio expressed is excluding Zr, the sodium-ion conductive glass-ceramic of the present invention, obtained by mixing and sintering with a crystalline material containing ZrO2, tends to contain Na3Zr2Si2PO4.12 It represents a monoclinic crystal phase and is highly preferred because it readily exhibits high sodium ion conductivity.

[0074] Furthermore, in the glass material for synthesizing sodium ion conductive glass-ceramics of the present invention, the components mentioned above, such as Al2O3, Y2O3, and ZrO2, which impart water resistance to the glass material, are preferably 5 mol% or less, more preferably 3 mol% or less. This is because improving water resistance increases the flexibility of the manufacturing method, improves shelf life and facilitates storage, thus enhancing quality stability and reducing costs.

[0075] It should be noted that the total content of these components used to impart water resistance (e.g., Al2O3, Y2O3, and ZrO2) can be less than 20 mol%, more preferably less than 10 mol%. If too much of these components are added, composition shift can easily occur when the material is mixed and sintered with a crystalline material containing ZrO2 to produce a sodium-ion conductive glass-ceramic, and the sodium-ion conductivity and density can easily decrease.

[0076] Furthermore, the glass material for synthesizing sodium-ion conductive glass-ceramics of the present invention, based on the ease of synthesizing the sodium-ion conductive glass-ceramics of the present invention, preferably has a glass transition temperature (Tg) of 600°C or higher, more preferably 650°C or higher, even more preferably 680°C or higher, and even more preferably 730°C or higher. Its upper limit can be 900°C or lower, or 850°C or lower, or even 800°C or lower. Additionally, for the same reason, its crystallization temperature (Tc) is preferably 650°C or higher, more preferably 700°C or higher, even more preferably 720°C or higher, and even more preferably 780°C or higher. Its upper limit can be 950°C or lower, or 900°C or lower, or even 850°C or lower.

[0077] Furthermore, the sodium-ion conductive glass material for synthesizing glass-ceramics of the present invention, having the aforementioned constituent components and elements, is an amorphous material. Therefore, the sodium-ion conductive glass material for synthesizing glass-ceramics of the present invention substantially does not contain a crystalline phase. Additionally, the preferred form of the sodium-ion conductive glass material for synthesizing glass-ceramics of the present invention is the powder form described below.

[0078] <Manufacturing methods, etc.> Next, the sodium-ion conductive glass ceramic of the present invention, the electrolyte membrane for an aqueous sodium-ion secondary battery comprising the present invention, and the manufacturing method of the glass material for synthesizing the sodium-ion conductive glass ceramic of the present invention used in its synthesis will be described in detail.

[0079] First, the method for manufacturing the glass material for synthesizing sodium-ion conductive glass-ceramics according to the present invention will be described. The glass material for synthesizing sodium-ion conductive glass-ceramics according to the present invention can be manufactured using conventional methods for amorphous inorganic materials, such as sintering or melting of inorganic materials and vitrification. It should be noted that, regarding the dissolution issue in the case of melting after pre-firing, although not limited, a temperature of 1000°C or higher is preferred, more preferably 1200°C or higher and 1450°C or lower. The inorganic material used for manufacturing is not limited, but sodium dihydrogen phosphate (NaH2PO4), sodium carbonate (Na2CO3), orthophosphoric acid (H3PO4), silicon dioxide (SiO2), etc., are preferred.

[0080] Here, the glass material for synthesizing sodium ion conductive glass-ceramics of the present invention, based on the viewpoint of easy vitrification, requires that the content of ZrO2 component be less than 5.0 mol%, as described above.

[0081] Furthermore, the sodium-ion conductive glass-ceramic of the present invention and the electrolyte membrane for an aqueous sodium-ion secondary battery containing the present invention can be obtained by mixing a glass material for synthesizing the sodium-ion conductive glass-ceramic of the present invention obtained in the above manner with a crystalline material containing ZrO2 (e.g., zirconium oxide powder), and molding it into a film or the like (e.g., pressure molding) as needed, and sintering it at a sintering temperature of, for example, 1000°C or higher and less than 1250°C. In particular, based on the reason that it is easy to simultaneously achieve density and sodium-ion conductivity, the sintering temperature is preferably 1100°C or higher and less than 1200°C. When the sintering temperature is higher than 1250°C, it is easy for the ZrO2 crystalline phase to form due to thermal decomposition.

[0082] It should be noted that if the glass material for synthesizing sodium ion conductive glass-ceramic of the present invention and the crystalline material containing ZrO2 are both in powder form, the above-mentioned mixing and molding are easy to carry out, and therefore preferred.

[0083] For example, based on reasons such as the ease of adjusting the membrane thickness when forming the electrolyte membrane for aqueous sodium-ion secondary batteries, the average particle size (D) of these powders is... 90 The particle size is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less. Alternatively, after mixing these powders, they can be pulverized to achieve the aforementioned average particle size. Here, "average particle size" refers to the average particle size based on volume (90% volumetric particle size) measured by a laser diffraction particle size distribution measuring device. 90 The same applies below.

[0084] Furthermore, regarding these powders, as described above, the sodium ion conductivity of the glass material powder for synthesizing sodium ion conductive glass-ceramics of the present invention is preferably 1.0 × 10⁻⁶ at 25°C. －6 For crystalline powders containing ZrO2, the sodium ion conductivity at 25°C is preferably less than 1.0 × 10⁻⁶ S / cm or less. －8 S / cm. In other words, the sodium ion conductive glass-ceramic of the present invention preferably has a sodium ion conductivity of 1.0 × 10⁻⁶ at 25°C. －6 The sodium ion conductivity glass material powder of the present invention, with a sodium ion conductivity of less than S / cm, has a sodium ion conductivity of less than 1.0 × 10⁻⁶ at 25°C. －8 It is obtained by mixing and sintering crystalline material powder containing ZrO2 with a strength of S / cm.

[0085] The embodiments described above are merely examples to facilitate understanding of the present invention and are not intended to limit the present invention. That is to say, various changes and modifications can be made to the components described above, as long as they do not depart from the spirit of the present invention, and the present invention naturally includes its equivalents.

[0086] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the technical concept of the present invention.

[0087] Example <Sodium-ion conductive glass ceramics and preparation of comparative samples> The fabrication of sodium-ion conductive glass ceramics involves preparing a raw material glass (a glass material for synthesizing sodium-ion conductive glass ceramics), mixing zirconium oxide (a crystalline material containing ZrO2) into it, and then molding and sintering it. Specifically, it is fabricated using the following method.

[0088] As raw materials, NaH2PO4, Na2CO3, and SiO2 were mixed to achieve the component ratios shown in Table 1 below (mol% converted from oxides). The mixture was then placed in a plastic bag and gently shaken to mix. The mixture was then placed in a platinum crucible and pre-fired at 1000°C for 1 hour. After this pre-firing, the mixture was melted in a melting furnace at a temperature above 1300°C with thorough stirring and cast onto a metal casting plate. Subsequently, the mixture was pulverized using an impact mill to pass through a sieve with a mesh size of less than 106 μm, thereby obtaining the raw material glass of Examples 1-4.

[0089] Table 1

[0090] The thermal properties (glass transition temperature Tg, crystallization temperature Tc) of the obtained raw glass samples were measured using a differential thermal analyzer (NETZSCH STA409PC). The results are shown in Table 2 below. It should be noted that the sodium ion conductivity of these raw glass samples at 25°C was 1.0 × 10⁻⁶. －6 Below S / cm.

[0091] Table 2

[0092] The pulverized glass (passed through a 106μm sieve) and zirconium oxide powder (manufactured by Daiichi Rare Element Chemical Industry Co., Ltd., UEP-100: substantially free of sodium ion conductivity) were mixed to the stoichiometric ratios shown in Table 3 below. The mixture was then pulverized using 1-propanol, φ2mm zirconium oxide beads (manufactured by Nikkato, YTZ beads), and a 500cc zirconium oxide container, at 250 rpm for 2 hours (5 minutes of pulverization followed by 1 minute of pause) using a planetary ball mill (manufactured by Fritsch Japan, P-5). The average particle size of the pulverized slurry was measured using a particle size analyzer (laser diffraction particle size distribution measuring device, manufactured by Spectris). The average particle size was expressed in terms of D... 90 The particles were measured to be less than 2μm, confirming that they had been thoroughly pulverized. The pulverized slurry was separated from the zirconium oxide beads using a sieve, and the resulting slurry was dried using a rack-type solvent recovery dryer (manufactured by Creation Chemical Co., Ltd.).

[0093] On the other hand, as a comparative sample, Na3Zr2Si2PO4 manufactured by Toyoshima Corporation was used. 12 The slurry was pulverized using 1-propanol, φ2mm zirconia beads (Nikkato YTZ beads), and a 500cc zirconia container, at 250 rpm for 2 hours (5 minutes of pulverization followed by 1 minute of pause) using a planetary ball mill (Fritsch Japan P-5). The average particle size of the pulverized slurry was measured using a particle size analyzer (laser diffraction particle size distribution measuring device, Spectris). The average particle size was expressed in terms of D... 90 The particles were measured to be less than 2 μm, confirming that they had been thoroughly pulverized. Subsequently, the pulverized slurry was separated from the zirconium oxide beads using a sieve, and the resulting slurry was dried using a rack-type solvent recovery dryer (manufactured by Chuangzao Chemical Co., Ltd.) (Comparative Example 1).

[0094] In addition, as a comparison with the case using sintering aids, a sample was prepared using a sodium-ion conductive glass electrolyte (50 mol% Na₂O – 9 mol% SiO₂ – 41 mol% P₂O₅) as the sintering aid. This was compared to the Na₃Zr₂Si₂PO₄ manufactured by Toyoshima Corporation. 12 The aforementioned sodium-ion conductive glass electrolyte was added at a ratio of 10 wt%. The mixture was pulverized using 1-propanol, φ2mm zirconia beads (Nikkato YTZ beads), and a 500cc zirconia container, at 250 rpm for 2 hours (5 minutes of pulverization followed by 1 minute pause) via a planetary ball mill (Fritsch Japan P-5). The average particle size of the pulverized slurry was measured using a particle size analyzer (laser diffraction particle size distribution measuring device, Spectris). The average particle size was expressed in terms of D... 90 The particles were measured to be less than 2 μm, confirming that they had been thoroughly pulverized. Subsequently, the pulverized slurry was separated from the zirconium oxide beads using a sieve, and the resulting slurry was dried using a rack-type solvent recovery dryer (manufactured by Chuangzao Chemical Co., Ltd.) (Comparative Example 2).

[0095] Table 3 below shows the composition of these samples in mol% as oxides, and the composition formulas representing the composition ratios of Na, Zr, P and Si.

[0096] Table 3

[0097] The dried powders (including those that are slightly lumpy due to the drying process) were pulverized using an alumina mortar and pestle until they passed through a 500μm sieve. 1g of the pulverized powder was then molded using a φ20mm molding die under a pressure of 20kN to obtain various granules (flaky granules).

[0098] The particle was exposed to atmospheric conditions, resulting in a density exceeding 3.0 g / cm³. 3 Under certain conditions, heat treatment was carried out at a sintering temperature of 1100℃ to 1250℃ for 1 hour to obtain various sintered particles (plate-like sintered bodies) as solid electrolytes for measuring sodium ion conductivity and water resistance. The surfaces of these sintered particles were ground using #800, #2000, #5000, and #8000 water-resistant sandpaper and 1-propanol. The film thickness (mm), diameter (mm), and weight (g) were measured using vernier calipers, micrometers, and an electronic balance, and the density (g / cm³) was calculated. 3 The results are shown in Table 4 below. Under the condition of optimizing the heat treatment temperature, the density of Example 1 is the highest, and the densities of the other examples are also higher than those of the comparative example.

[0099] Table 4

[0100] <Measurement of Sodium Ion Conductivity> The sodium ion conductivity of each sintered particle after grinding was measured as follows: Gold electrodes, acting as barrier electrodes, were formed on both sides of the sintered particles after density measurement using a magnetron sputtering apparatus (Sanyu Electronics Co., Ltd., SC-701HMC). Impedance measurements were then performed using an electrochemical evaluation apparatus (Bio-Logic Co., Ltd., SP300) at 25°C, with a frequency of 0.1Hz to 7MHz, an amplitude voltage of 10mV, and an open-circuit voltage. The sodium ion conductivity (mS / cm) at 25°C was calculated. The measurement results are also shown in Table 4 above. Example 3 showed the highest sodium ion conductivity value of 1.04 mS / cm (1.04 × 10⁻⁴ mS / cm). －3 The S / cm value was approximately three times that of Comparative Example 2 with the same composition and approximately twice that of Comparative Example 1. Furthermore, the values ​​of the other examples were also higher than those of the comparative examples. On the other hand, Comparative Example 2 had the lowest sodium ion conductivity. This is presumably because only Comparative Example 2 added a sodium ion conductive glass electrolyte as a sintering aid, resulting in a compositional shift after sintering, which in turn led to an increase in resistance within the grains and at the grain boundaries.

[0101] <Measurement of Water Resistance> The water resistance of each sintered particle after grinding is determined by... Figure 1 The apparatus shown was used to measure and evaluate the leakage rate. Because the water resistance of the sample with the aforementioned gold electrodes may vary, this sample was not used; instead, sintered particles (sheet substrate) with measured density were used. This was to reduce... Figure 1 Errors caused by air inside the container were minimized, and atmospheric pressure correction was performed. Pyrex (registered trademark) glass plates with zero gas and water permeability were also evaluated and used as a baseline. Measurements were performed in a thermostatic bath controlled at 25°C. Measurements were conducted on one sample for 3–5 days. Water column pressures ranging from 250 mmAq to 50 mmAq were used. The measurement results (converted to values ​​per hour per unit area and per 1 mm thickness) for Comparative Examples 1–2 and Examples 1–4 are shown in Table 5 below. The measurement results (measured values) for Comparative Example 2 and Example 3 are also shown in… Figure 2 .

[0102] Table 5

[0103] Based on the above results, the leakage rate of Comparative Example 1 was 338 μL / h, indicating significant leakage. Although the leakage rate of Comparative Example 2 was improved to approximately 1 / 20 (18 μL / h) compared to Comparative Example 1, detectable leakage was still found.

[0104] On the other hand, regarding Examples 1-4, the leakage rate was 0.6-1.5 μL / h, with an average of 1 μL / h, which is an extremely low value. In the evaluation results for Pyrex (registered trademark) glass, the leakage rate was 1.2-2.8 μL / h, with an average of 1.7 μL / h. Therefore, the results of Examples 1-4 can be considered close to the detection limit. Regarding the per 1 mm thickness (film thickness) and per unit area of ​​1 cm²... 2 The effect of a leakage rate of 1 μL / h can be explained by considering that the electrical energy stored in the active material is consumed by the electrolysis of the leaked water. This is because the active material used in the battery has a discharge capacity of 110 mAh / g, which is generally considered low for LiMn₂O₄; its density is also 4.2 g / cm³. 3 Since it is an aqueous battery, when the active material filling rate is selected to be relatively high at 80% and the film thickness is 1 mm, the current capacity per unit area of ​​1 cm² is 37 mAh. Converting the leakage rate of 1 μL / h to the current equivalent of water electrolysis yields 1.5 μA. Dividing the current capacity of 37 mAh by 1.5 μA as the leakage current, the monthly self-discharge rate is 2.9%. Typically, the monthly self-discharge rate of aqueous nickel-metal hydride batteries is 10-30%, so although it also depends on the electrode layer film thickness, it can be considered within a practically acceptable range of 10 μL / h. Therefore, it can be seen that not only Comparative Example 1, but even Comparative Example 2 with a leakage rate of 18 μL / h is insufficient as an electrolyte separator; on the other hand, it can be confirmed that Examples 1-4 all sufficiently meet the above range.

[0105] <Analysis of Crystallized Phases> The crystalline phase composition of each sintered particle was analyzed by powder X-ray diffraction. Instead of pulverizing the samples, the ground surfaces were analyzed. The apparatus used was a Bruker D8 DISCOVER X-ray diffractometer with a tube voltage of 40 kV and 40 mA, and a Cu target (CuKα rays) was used as the X-ray source. The composition ratios were confirmed using Rietveld diffraction measurement software (TOPAS). Comparative Examples 1, 2, and 3 were evaluated. The measurement results for Example 3 are shown below. Figure 3 The composition of the identified crystalline phase can be confirmed as: monoclinic Na3Zr2Si2PO4. 12 Na3Zr2Si2PO4 with rhombohedral crystals 12Monoclinic ZrO2, tetragonal NaPO3, and monoclinic Zr(HPO4)2 were used. The results of Comparative Example 1, Comparative Example 2, and Example 3 are shown in Table 6 below (unit: mass %).

[0106] In Example 3, monoclinic Na3Zr2Si2PO4 with high sodium ion conductivity was used. 12 The proportion of sodium ions is significantly higher, while the rhombohedral Na3Zr2Si2PO4 crystals have lower sodium ion conductivity. 12 The proportion of zirconium oxide, which has low sinterability, was relatively small. ZrO2 was not detected in the powders of Comparative Example 1 and Comparative Example 2 before sintering, suggesting that the ZrO2 crystalline phase was formed due to thermal decomposition during sintering.

[0107] Table 6

[0108] <Microstructure Observation I> The fine structure of the obtained sintered body particles was observed using a scanning electron microscope (JSM-IT700HR / LA, manufactured by Nippon Electron Ltd.). Comparative Examples 1, 2, and 3 were evaluated. The SEM observation results (secondary electron images) of the cross-sections of these sintered body particles are shown below. Figures 4 to 9 .

[0109] like Figure 4 As shown, in Comparative Example 1, pore sizes of 10–100 μm were confirmed to be dispersed. Furthermore, as… Figure 5 As shown in the magnified image, rough and fine gaps are confirmed to exist around the pores. It can be assumed that the large pores and the gaps observed around them significantly impair the water resistance. Furthermore, it can be inferred that although the proportion of high-density ZrO2 crystalline phase is high in the XRD measurements, the density is still only 3.01 g / cm³. 3 The reason is that thermal decomposition leads to an increase in the formation of ZrO2 crystalline phases and porosity.

[0110] In Comparative Example 2, prepared using sintering aids, although there was an improvement over Comparative Example 1, dispersed pores were still observed, and roughness and gaps were also observed around the pores in the magnified image. Figure 6 and Figure 7 ).

[0111] On the other hand, in Example 3, as Figure 8 As shown, almost no porosity was observed; and as Figure 9 As shown, even under magnification, no tiny gaps were observed. That is, a dense structure was obtained, and its sufficient waterproofness was confirmed.

[0112] <Sheet Forming Experiment> In industrial product manufacturing, there is a possibility of forming and sintering a slurry containing a binder, such as sheet molding or extrusion molding. Therefore, sheet molding tests were conducted to confirm whether a good dispersion state was maintained in this state. The example using the pulverized and dried powder of Example 3 is referred to as Example 5; the example using the pulverized and dried powder of Comparative Example 2 is referred to as Comparative Example 3.

[0113] For 100g of various pulverized and dried powders, the following components were prepared: 75.5g of 1-propanol, 2.4g of dispersant (Floren G-700, manufactured by Kyoeisha Chemical Co., Ltd.), 26.25g of binder (Oricox 2427, an acrylic polymer with very low ash residue after sintering, manufactured by Kyoeisha Chemical Co., Ltd.), 2.1g of plasticizer (DOS, manufactured by Ito Oil Co., Ltd.), and 0.14g of wetting agent (KL100, manufactured by Kyoeisha Chemical Co., Ltd.). Zirconia beads (YTZ beads, manufactured by Nikkato Co., Ltd.) with φ10mm and φ2mm diameter were then mixed in a ball mill jar for 12 hours using grinding media. After mixing, the zirconia beads were separated from the slurry, and then defoamed for 5 minutes using a defoaming device (ARV-200, manufactured by Thinky Co., Ltd.) at 1000rpm and 150Torr. Finally, the mixture was formed into sheets using the doctor blade method. The resulting molded sheet had a film thickness of 25 μm. Thirteen sheets were stacked and vacuum-packed, then isostatically pressed at 60 MPa, and finally sintered at a temperature between 1100°C and 1200°C. The density and sodium ion conductivity of the sintered sheet-like laminate (sheet-like sintered body) were approximately the same as those of the sintered body obtained by pressing powder into shape, as described above.

[0114] <Microstructure Observation II> The microstructure of the obtained lamellar laminate (lamellar sintered body) was observed using a scanning electron microscope (JSM-IT700HR / LA, manufactured by Nippon Electron Ltd.). The SEM observation results of the fracture surface of this lamellar laminate (lamellar sintered body) are shown below. Figure 10 as well as Figure 11 To confirm the composition of the sample, reflected electron microscopy was performed. The black phase was identified as amorphous, and the white phase as crystalline. In Example 5, a black amorphous phase was clearly observed (approximately 20-30% based on the area of ​​the fracture surface). Figure 10 EDS measurements showed no segregation of Zr, Si, Na, etc. It can be assumed that the target components, Na3Zr2Si2PO4, were generated simultaneously with diffusion and sintering at high temperatures. 12 And simultaneously, both amorphous and crystalline states were obtained.

[0115] On the other hand, Figure 11 In Comparative Example 3 shown, overall crystallization was confirmed, and it can be inferred that sintering aids were incorporated into the crystals. Furthermore, a large number of air bubbles were observed. The main reasons for the failure to adequately retain the amorphous phase (less than 10% based on the area of ​​the fracture surface) and the failure to form a dense, waterproof film have been confirmed through microstructure observation.

[0116] This application claims priority based on Japanese Patent Application No. 2023-179785, filed on October 18, 2023, the disclosure of which is incorporated herein by reference.

Claims

1. A sodium-ion conductive glass-ceramic, wherein, In mol% terms converted from oxides, it contains: Na₂O content: 20.0%–27.0%; ZrO2 content: 30.0%–40.0%; 3.0%–20.0% P2O5 content; and The SiO2 content is 20.0% to 40.0%, and, Contains Na 1＋x Zr2Si x P 3－x O 12 (0 < X ​​< 3) represents the monoclinic crystal phase, and the proportion of ZrO2 crystal phase among all the crystal phases contained therein is less than 10% by mass.

2. The sodium ion conductive glass-ceramic as described in claim 1, wherein, In the sodium ion conductive glass-ceramic, the component ratio of Na, Zr, P, and Si satisfies the condition that Na... 1＋x Zr2Si x P 3－x O 12 (0 < X ​​< 3) represents the component ratio.

3. The sodium-ion conductive glass-ceramic as described in claim 1, wherein, When the sodium ion conductive glass ceramic is formed into a sheet or plate substrate, the leakage rate per unit area and per 1 mm thickness of the substrate is less than 10.0 μL / h; or, when water leakage per unit area and per 1 mm thickness of the substrate per hour causes water electrolysis, the current is less than 15 μA per unit area and per 1 mm thickness of the substrate.

4. The sodium ion conductive glass-ceramic as described in claim 1 or 2, wherein, The sodium ion conductivity at 25℃ is 6.0 × 10⁻⁶. －4 S / cm or higher.

5. The sodium ion conductive glass-ceramic as described in claim 1 or 2, wherein, The sodium ion conductivity at 25℃ is 1.0 × 10⁻⁶. －6 Glass material powder with a conductivity of less than S / cm and a sodium ion conductivity of less than 1.0 × 10⁻⁶ at 25°C. －8 It is made by mixing and sintering crystalline material powder containing ZrO2 with a density of S / cm.

6. The sodium-ion conductive glass-ceramic as described in claim 1 or 2, wherein, Of all the crystalline phases contained therein, the Na 1＋x Zr2SixP 3－x O 12 (0 < X ​​< 3) indicates that the proportion of the monoclinic crystalline phase is above 70% by mass.

7. The sodium-ion conductive glass-ceramic as described in claim 1 or 2, wherein, The proportion of amorphous phase is 10% or more by mass.

8. An electrolyte separator for an aqueous sodium-ion secondary battery, comprising the sodium-ion conductive glass-ceramic as described in claim 1 or 2.

9. A glass material for synthesizing sodium-ion conductive glass-ceramics, wherein, In mol% terms converted from oxides, it contains: The Na₂O content is 30.0%–40.0%. ZrO2 content of 0% to 5.0% 5.0%–35.0% P2O5 content, and The SiO2 content is 30.0% to 60.0%, and The component ratio of Na, P and Si satisfies the requirement of using Na 1＋x Zr2SixP 3－x O 12 (0 < X ​​< 3) represents the component ratio after removing Zr.

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