Sodium composite metal sulfate material and method for producing sodium composite metal sulfate material

Abstract

To propose a sodium composite metal sulfate material with improved ionic conductivity and a method for producing a sodium composite metal sulfate material with improved ionic conductivity.SOLUTION: The sodium composite metal sulfate material comprises a solid solution which is a sodium composite metal sulfate in which a part of Zn in Na6Zn(SO4)4 is substituted with a trivalent or higher metal M. The method for producing a sodium composite metal sulfate material comprises a stirring step of adding, to a solvent, compound I containing sodium, compound II containing zinc, and compound III containing metal M (wherein at least one of compound I, compound II, and compound III is a sulfate) and stirring, and a drying step of evaporating and drying a stirred product obtained by the stirring step to dryness.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a sodium composite metal sulfate-based material and a method for manufacturing the sodium composite metal sulfate-based material.

Background Art

[0002] Conventionally, a lithium-ion secondary battery using an electrolyte as a secondary battery is known. However, since the lithium material is expensive, the lithium-ion secondary battery has a problem that the product price becomes high. Therefore, a sodium secondary battery using a solid electrolyte has attracted attention because of the merit of the material price. For example, in Patent Document 1, a sodium secondary battery including Na , , , , Fe2(SO4)3(0 < x≦2) is disclosed, and it is disclosed that a solid electrolyte may be used as the electrolyte.

[0003] In addition, as another problem of a secondary battery using an electrolyte, a risk such as leakage of the electrolyte has been pointed out. Therefore, research on an all-solid-state secondary battery using a solid electrolyte has been conducted. For example, in Patent Document 2, an oxide-based solid electrolyte represented by Na a (B 1-b S b )O c has been proposed. In addition, in Patent Document 3, an oxide-based solid electrolyte represented by the general formula Lix Lay M1zM 2n O 12 (1≦x≦7, 2≦y≦4, 0≦z≦3, 0≦n≦3, M1 = Zr or Ta, M2 = Nb) and various sulfide-based solid electrolytes such as a Li2S-P2S5 system have been proposed.

Prior Art Documents

[0005] As mentioned above, oxide-based and sulfide-based solid electrolytes have been proposed for use in all-solid-state secondary batteries. However, oxide-based solid electrolytes require sintering at temperatures exceeding 1000°C during production, which presents manufacturing process disadvantages. Furthermore, sulfide-based solid electrolytes are toxic because they react with water vapor to generate hydrogen sulfide. Therefore, there is a need for proposals for compounds other than oxide-based and sulfide-based compounds that can also be used as solid electrolytes.

[0006] The present inventors have noticed that when an all-solid-state sodium secondary battery is manufactured, the use of a solid electrolyte of the same type as the sulfate-based positive electrode active material (i.e., a sulfate-based solid electrolyte) as disclosed in Cited Document 1 can bring about various advantages, such as a reduction in the electrical resistance at the interface between the positive electrode active material and the solid electrolyte and an improvement in electrical connection therebetween. The present inventors then attempted to provide a sodium sulfate-based compound that can be suitably used as a solid electrolyte for all-solid-state sodium secondary batteries, and arrived at the present invention.

[0007] That is, the present invention has been made in consideration of the above-mentioned problems, and proposes a sodium composite metal sulfate-based material with improved ionic conductivity and a method for manufacturing a sodium composite metal sulfate-based material with improved ionic conductivity. [Means for solving the problem]

[0008] The sodium composite metal sulfate material of the present invention is characterized by including a solid solution that is a sodium composite metal sulfate in which part of the Zn in Na6Zn(SO4)4 is substituted with a metal M that is trivalent or higher.

[0009] The method for producing a sodium composite metal sulfate material of the present invention is characterized by comprising a stirring step of adding a compound I containing sodium, a compound II containing zinc, and a compound III containing a metal M to a solvent (wherein at least one of compound I, compound II, and compound III is a sulfate) and stirring the mixture, and a drying step of evaporating and drying the mixture obtained by the stirring step. [Effects of the Invention]

[0010] The sodium composite metal sulfate material of the present invention has improved ionic conductivity compared to conventional sodium composite metal sulfate materials and can exhibit higher ionic conductivity than conventional sulfate compounds. The sodium composite metal sulfate material of the present invention can exhibit ionic conductivity at a level that allows it to be used favorably as a solid electrolyte for, for example, an all-solid-state sodium secondary battery. Furthermore, the method for producing a sodium composite metal sulfate material of the present invention is easy to operate and can produce a sodium composite metal sulfate material at a relatively low temperature. [Brief explanation of the drawings]

[0011] [Figure 1] 1 shows X-ray diffraction charts obtained using the powders of Examples 1-1 to 1-8 after evaporation to dryness and the powder of a reference substance after evaporation to dryness. [Figure 2] 1 shows X-ray diffraction charts obtained using the powders of Examples 2-1 to 2-8 after evaporation to dryness and the powder of a reference substance after evaporation to dryness. [Figure 3] 1 shows X-ray diffraction charts of Examples 2-1 to 2-3 after dehydration treatment and a reference substance after dehydration treatment. [Figure 4] 1 is an X-ray diffraction chart of the powder obtained after evaporation to dryness in Example 3-2. [Figure 5] (5A) is an SEM photograph of the pulverized product of Example 4-1, (5B) is an SEM photograph of the pulverized product of Example 2-2, (5C) is an SEM photograph of the pulverized product of Example 4-2, and (5D) is an SEM photograph of the pulverized product of Example 4-3. [Figure 6](6A) is an SEM photograph of the press-molded body of Example 2-2, (6B) is an SEM photograph of the press-molded body of Example 4-2, and (6C) is an SEM photograph of the press-molded body of Example 4-3. [Figure 7] 1 is an SEM photograph of the pulverized product of Example 4-4. [Figure 8] (8A) is an SEM photograph of the pulverized product of Example 4-5, and (8B) is an SEM photograph of the pulverized product of Example 4-6. [Figure 9] 1 is a process diagram showing an example of a method for producing a sodium composite metal sulfate material of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Sodium composite metal sulfate-based material] The sodium composite metal sulfate material of the present invention is a material containing a solid solution that is a sodium composite metal sulfate in which part of the Zn in Na6Zn(SO4)4 is substituted with a metal M that is trivalent or higher. The present invention exhibits significantly higher ionic conductivity than the conventional sodium complex metal sulfate, Na6Zn(SO4)4·2H2O. Although the reason for this improvement in ionic conductivity is unclear, it is presumed that by substituting a portion of the Zn in Na6Zn(SO4)4 with another metal having an ionic radius different from that of the Zn, the lattice constant changes while maintaining the crystal structure of Na6Zn(SO4)4, changing the interatomic distance, which in turn facilitates the movement of sodium ions, resulting in high ionic conductivity. The sodium composite metal sulfate material of the present invention includes an embodiment containing only the sodium composite metal sulfate, which is a solid solution, and an embodiment containing the sodium composite metal sulfate together with other materials or impurities, such as precipitates generated during the production of the sodium composite metal sulfate.

[0013] Although conventional oxide-based solid electrolytes are highly safe, they require a high sintering temperature exceeding 1000 degrees during manufacturing. Conventional sulfide-based solid electrolytes, on the other hand, can be manufactured without requiring high temperatures, but they have a problem of low safety because hydrogen sulfide is generated when they come into contact with water vapor. In contrast, the sodium composite metal sulfate-based material of the present invention does not require as high a temperature as oxide-based solid electrolytes during manufacturing and can be manufactured at a relatively low temperature of, for example, 150 degrees or less. Also, it can exhibit good chemical stability compared to sulfide-based solid electrolytes.

[0014] The sodium composite metal sulfate contained in the sodium composite metal sulfate-based material of the present invention can be represented by the following general formula (1). [Formula 1] Na A Zn B M C (SO4)4·····(1) (However, in the formula, 0 < A < 6, 0 < B < 1, 0 < C < 1, and M is a metal with a charge of +3 or more).

[0015] In the present invention, the sodium composite metal sulfate contained in the general formula (1) may be a hydrate or an anhydride. That both the hydrate and the anhydride of the sodium composite metal sulfate represented by the general formula (1) exhibit higher ionic conductivity than Na6Zn(SO4)4 will be shown in the examples described later. When the sodium composite metal sulfate contained in the general formula (1) is a hydrate, it is preferable because there is a tendency for a more significant improvement in ionic conductivity compared to the anhydride. On the other hand, when the sodium composite metal sulfate contained in the general formula (1) is an anhydride, it is preferable in that it can be used at high temperatures compared to the hydrate and has a wide range of applications.

[0016] In the present invention, the metal M with a valence of +3 or more that is substituted for a part of Zn may be any metal that can form a solid solution as a sulfate containing sodium, zinc, and metal M. For example, preferred examples of the metal M include aluminum, gallium, zirconium, and indium.

[0017] More specifically, when the metal M is aluminum, the sodium complex metal sulfate of the present invention is represented by the following general formula (2) or (3). [Formula 2] Na 6-C Zn 1-C Al C (SO4)4·2H2O (0 <C<1)···(2) [Formula 3] Na 6-C Zn 1-C Al C (SO4)4(0 <C<1)···(3)

[0018] When the metal M is gallium, the sodium complex metal sulfate of the present invention is represented by the following general formula (4) or (5). [Formula 4] Na 6-C Zn 1-C Ga C (SO4)4·2H2O (0 <C<1)···(4) [Formula 5] Na 6-C Zn 1-C Ga C (SO4)4(0 <C<1)···(5)

[0019] When the metal M is zirconium, the sodium composite metal sulfate of the present invention is represented by the following general formula (6) or (7). [Formula 6] Na 6-2C Zn 1-C Zr C (SO4)4·2H2O(0 <C<1)···(6) [Formula 7] Na 6-2C Zn 1-C Zr C (SO4)4(0 <C<1)···(7)

[0020] When the metal M is indium, the sodium composite metal sulfate in the present invention is represented by the following general formula (8) or general formula (9). [Formula 8] Na 6-2C Zn 1-C In C (SO4)4·2H2O(0 < C < 1) ··· (8) [Formula 9] Na 6-2C Zn 1-C In C (SO4)4(0 < C < 1) ··· (9)

[0021] Whether the sodium composite metal sulfate material of the present invention is composed only of a solid solution or contains inclusions or the like can be confirmed from the X-ray diffraction chart of the sample. For example, FIG. 1 is an X-ray diffraction chart of Example 1 represented by the general formula (2) Na 6-C Zn 1-C Al C (SO4)4·2H2O (0 < C < 1). Specifically, taking Na6Zn(SO4)4 as a reference (C = 0), theoretically, the value of C is changed in 12 steps so as to replace Zn in such a reference compound with Al in 5% increments, and it is the X-ray diffraction of the material obtained by implementing the production method of the present invention. As is clear from FIG. 1, from C = 0.05 to C = 0.40, the peak pattern shows a single phase, and within the solid solubility limit, Zn and Al are substituted, and it is confirmed that a sodium composite metal sulfate-based material substantially composed only of a solid solution was produced. On the other hand, when C ≥ 0.45, peaks that are not present in the single-phase pattern occur, and Al or a compound containing Al that was not solid-dissolved appears as an inclusion.

[0022] Similarly, FIG. 2 is the general formula (4) Na 6-C Zn 1-C Ga C(SO4)4·2H2O (0 < C < 1) is the X-ray diffraction chart of Example 2. As is clear from FIG. 2, from C = 0.05 to C = 0.15, the peak pattern shows a single phase, and it is confirmed that Zn and Ga are substituted within the solid solubility limit, and it is confirmed that a sodium composite metal sulfate-based material consisting substantially only of a solid solution is produced. On the other hand, when C = 0.20 or more, a peak pattern significantly different from the single-phase pattern is shown (see particularly frames 1 and 2 in FIG. 2), and Ga that was not solid-dissolved or a compound containing Ga appears as an inclusion.

[0023] FIG. 3 is the X-ray diffraction chart of the anhydride obtained by subjecting the material represented by the general formula (4) Na 6-C Zn 1-C Ga C (SO4)4·2H2O (0 < C < 1) to dehydration treatment by heat treatment under reduced pressure for C = 0.15, C = 0.10, C = 0.5, and C = 0.

[0024] Similarly, FIG. 4 is the X-ray diffraction chart of Example 3-2 represented by the general formula (6) Na 6-2C Zn 1-C Zr C (SO4)4·2H2O (C = 0.1). As is clear from FIG. 4, it is confirmed that Zn and Zr are substituted within the solid solubility limit in Example 3-2, and it is confirmed that a sodium composite metal sulfate-based material consisting substantially only of a solid solution is produced.

[0025] The production method of the present invention described later can avoid the mixing of inclusions by substituting Zn and metal M within the solid solubility limit, and can provide a material showing better conductivity. However, even when Zn and metal M are substituted beyond the solid solubility limit and a solid solution and inclusions (by-products) are mixed, it can show higher conductivity than conventional Na6Zn(SO4)4.

[0026] Based on the X-ray diffraction results shown in FIG. 1, from the viewpoint of being a stable composite metal and being likely to sufficiently show high ionic conductivity, the general formula (1) Na AZn B M C (SO4)4 (where 0 < A < 6, 0 < B < 1, 0 < C < 1, and M is a metal with a charge of +3 or more), when M = Al, it is preferable that 0 < C < 0.45, and more preferably 0 < C ≤ 0.40. Also from the same perspective, based on the X-ray diffraction results shown in FIG. 2, in the general formula (1), when M = Ga, it is preferable that 0 < C < 0.20, and more preferably 0 < C ≤ 0.15. Also from the same perspective, although illustration is omitted, in the general formula (1), when M = Zr, it is more preferable that 0 < C ≤ 0.1.

[0027] The sodium composite metal sulfate-based material of the present invention can show a significantly higher ionic conductivity compared to Na6Zn(SO4)4, and the ionic conductivity is preferably 0.1×10 -6 S / cm -1 or more, more preferably 1.0×10 -6 S / cm -1 or more, and particularly preferably a sodium composite metal sulfate-based material that can show an ionic conductivity of 1.0×10 -5 S / cm or more, which is comparable to that of conventional oxide-based solid electrolytes. For example, when M in the general formula (1) is one selected from aluminum, gallium, zirconium, and indium, it is preferable because excellent ionic conductivity can be shown. -1 In particular, when M is indium, it tends to show excellent ionic conductivity, so the sodium composite metal sulfate-based material of the present invention in which a part of zinc (Zn) is substituted with indium (In) is particularly preferable. -4

[0028] ​​From the viewpoint of exhibiting higher ionic conductivity, the sodium composite metal sulfate material is preferably formed into a press-molded body. In particular, a press-molded body formed using a sodium composite metal sulfate material consisting essentially of sodium composite metal sulfate is preferred. When the sodium composite metal sulfate material is a press-molded body, the average particle size of the particulate sodium composite metal sulfate constituting the press-molded body is more preferably 0.08 μm to 0.20 μm, and even more preferably 0.08 μm to 0.15 μm. By setting the average particle size to 0.15 μm or less, the specific surface area of ​​the composite metal can be sufficiently increased. On the other hand, by setting the average particle size to 0.08 μm or more, it is easy to prevent aggregation of fine particles and prevent a substantial decrease in the specific surface area. The average particle size within the above preferred range can be easily achieved by performing a pulverization step in the manufacturing method of the present invention described below. Similarly, from the viewpoint of exhibiting higher ionic conductivity, in a press-molded body formed using a sodium composite metal sulfate-based material, the ratio of the number of particulate sodium composite metal sulfate particles having a particle size of 0.20 μm or more to the total number of particulate sodium composite metal sulfate particles contained in the press-molded body is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less. Although the particle sizes are polydisperse, a moderately small number of large particles allows for high density and higher ionic conductivity. This reduction in the proportion of relatively large particles can be achieved, for example, by changing various conditions in the milling step carried out in the manufacturing method of the present invention, which will be described later. In particular, it is particularly preferred that the particulate sodium composite metal sulfate constituting the press-molded body has an average particle size of 0.08 μm or more and 0.20 μm or less, and that in the sodium composite metal sulfate-based material, the number of particulate sodium composite metal sulfate having a particle size of 0.20 μm or more relative to the total number of particles of particulate sodium composite metal sulfate contained in the material is 20% or less. The average particle size and particle size are measured by image analysis. Specifically, in the present invention, the average particle size refers to the number-based average particle size obtained by analyzing an image obtained by analyzing an SEM image, and the particle size is confirmed in the particle size distribution (number-based frequency distribution).

[0029] The average particle size of the particulate sodium composite metal sulfate contained in the sodium composite metal sulfate material is measured by the method described in Examples below. Also, the ratio of the number of particulate sodium composite metal sulfate having a particle size of 0.20 μm or more to the total number of particulate sodium composite metal sulfate particles contained in the sodium composite metal sulfate material is measured by the method described in Examples below.

[0030] In order to exhibit higher ionic conductivity, the specific surface area of ​​the particulate sodium composite metal sulfate contained in the sodium composite metal sulfate-based material is 8.00 m 2 / g or more is preferable, and 8.50m 2 / g or more is more preferable, and 9.00m 2 / g or more is more preferable, and 9.50m 2 In order to realize the preferred range of the specific surface area, for example, it is advisable to adjust the average particle size of the particulate sodium composite metal sulfate contained in the sodium composite metal sulfate-based material to fall within an appropriate range, and also adjust the proportion of large particle sizes in all particles of the particulate sodium composite metal sulfate to be appropriately small.

[0031] The specific surface area of ​​the particulate sodium composite metal sulfate contained in the sodium composite metal sulfate material can be determined by gas adsorption method.

[0032] The sodium composite metal sulfate material of the present invention described above can be applied to various technical fields by taking advantage of its excellent ionic conductivity, and can be suitably used, for example, as a solid electrolyte for all-solid-state sodium secondary batteries.

[0033] When the sodium composite metal sulfate material of the present invention is used as a solid electrolyte, for example, a particulate sodium composite metal sulfate material may be produced by the manufacturing method of the present invention described below, and then press-molded at room temperature to produce a high-density pressed compact. The pressure during such press-molding may be, for example, about 90 MPa to 250 MPa. By such press-molding, the present invention can provide a solid electrolyte with a high density of 60% or more, further 70% or more, further 80% or more, and particularly 90% or more relative density. It is believed that the reason for this high density achieved by press-molding at room temperature is that the sodium composite metal sulfate material of the present invention is flexible because the bonding strength between atoms in the crystal structure is changed by replacing a portion of Zn with a trivalent or higher metal M, resulting in the material becoming flexible. The relative density is measured by a method described in the examples below.

[0034] [Method of manufacturing sodium composite metal sulfate-based material] A method for producing the sodium composite metal sulfate material of the present invention will be described below. The production method of the present invention is suitable as a method for producing the sodium composite metal sulfate material of the present invention described above. However, the method for producing the sodium composite metal sulfate material of the present invention is not limited to the production method of the present invention.

[0035] The production method of the present invention includes a stirring step of adding a sodium-containing compound I, a zinc-containing compound II, and a metal M-containing compound III to a solvent and stirring the mixture, and a drying step of evaporating the mixture obtained by the stirring step to dryness. Note that at least one of the compounds I, II, and III is a sulfate. The production method of the present invention may further include a grinding step of grinding the powder obtained by the drying step after evaporation to dryness to a small particle size. Optionally, a press molding step, as described below, may be carried out after the drying step or the grinding step. The production method of the present invention does not require high-temperature treatment, such as high-temperature sintering required for producing oxide compounds used in solid electrolytes, and therefore the production method of the present invention is energy efficient and preferable from the viewpoint of environmental protection. In addition, the production method of the present invention also has good production efficiency because it does not require cooling of the heated product immediately after production.

[0036] One embodiment of the manufacturing method of the present invention will be described below. FIG. 9 will be used as appropriate for the description. FIG. 9 is a process diagram showing one embodiment of the manufacturing method of the present invention for manufacturing a material containing a sodium complex metal sulfate of the general formula (4) or (5) in which a portion of Zn has been substituted with Ga. FIG. 9 shows an embodiment that further includes a pulverization step and a press-molding step in addition to the stirring step and drying step. However, the present invention also encompasses manufacturing methods that do not include the pulverization step and / or the press-molding step. Although not shown in FIG. 9, the manufacturing method of the present invention may also include an anhydrification treatment at any timing to obtain an anhydrous sodium complex metal sulfate from the hydrated sodium complex metal sulfate. Details of the anhydrification treatment will be described later.

[0037] <Mixing process> The stirring step is a step of mixing and stirring a compound that is a material for producing a sodium composite metal sulfate with a solvent. When producing a sodium complex metal sulfate hydrate in which the metal M is Ga, for example, as shown in Figure 9, Na2SO4 can be used as the sodium-containing compound I, ZnSO4·7H2O as the zinc-containing compound II, and Ga2(SO4)3·16H2O as the metal M (gallium)-containing compound III. Furthermore, when producing a sodium complex metal sulfate hydrate in which the metal M is Al, for example, Na2SO4 can be used as the sodium-containing compound I, ZnSO4·7H2O as the zinc-containing compound II, and Al2(SO4)3·16H2O as the metal M (aluminum)-containing compound III. Furthermore, when producing a sodium complex metal sulfate hydrate in which the metal M is Zr, for example, Na2SO4 can be used as the sodium-containing compound I, ZnSO4·7H2O as the zinc-containing compound II, and Zr(SO4)2·4H2O as the metal M (zirconium)-containing compound III. Furthermore, when producing a sodium complex metal sulfate hydrate in which the metal M is In, for example, Na2SO4 can be used as the sodium-containing compound I, ZnSO4·7H2O can be used as the zinc-containing compound II, and In2(SO4)3·16H2O can be used as the metal M (indium)-containing compound III.

[0038] The solvent for dissolving Compounds I to III in the stirring step is not particularly limited, and examples thereof include water and alcohol. The solvent used in the stirring step may be one type or a combination of two or more types. From the viewpoint of being able to adjust the drying temperature low in the drying step described below, it is preferable that the solvent has a boiling point of 200°C or less. In the embodiment shown in FIG. 9, water (ion-exchanged water) is first used as the first solvent, Compounds I to III are added, and then ethanol is further added as the second solvent. In this way, using water and ethanol in combination is preferable in that the boiling point of the solvent can be substantially lowered and the temperature in the production process can be kept low. However, the use of ethanol as the second solvent can be omitted. In FIG. 9, when a portion of zinc is substituted with gallium, the proportion of substituted gallium (i.e., the value of C in the above general formula (4)) can be adjusted by the amounts of compounds I to III used in the stirring step.

[0039] As described above, a mixture obtained by adding compounds I to III to a solvent is stirred. The stirring conditions are not particularly limited. However, from the viewpoint of sufficiently dissolving compounds I to III in the solvent and satisfactorily producing a sodium composite metal sulfate material from the target compound, the temperature of the mixture during stirring is preferably 50°C or higher and lower than the boiling point of the solvent, more preferably 65°C or higher and 90°C or lower. From the same viewpoint, the stirring time is also preferably 30 minutes to 2 hours, more preferably 40 minutes to 1 hour 40 minutes, and even more preferably 50 minutes to 1 hour 20 minutes. Figure 9 shows an example in which the temperature of the mixture was adjusted to 80°C and stirred continuously for 1 hour. The stirring speed may be adjusted to within the range of 400 rpm to 600 rpm, for example.

[0040] <Drying process> After the stirring step described above, a drying step is carried out. The drying temperature should be adjusted to a temperature above the boiling point of the solvent used. The end of the drying step should be determined based on the moisture content measured with a moisture meter. Specifically, the drying step should be terminated when it is confirmed that the moisture content of the dried powder is 0.1% or less. The drying method is not particularly limited, and for example, the solution after the stirring step can be dried in an oven adjusted to a predetermined temperature, thereby obtaining a powder after evaporation to dryness.

[0041] <Crushing process> The powder obtained by the drying step after evaporation to dryness is further pulverized into smaller particles to produce a pulverized product. The pulverization method is not particularly limited, but it is preferable to use a ball mill, and in particular, it is preferable to use a planetary ball mill, from the viewpoint that the pulverized product to be produced can be easily adjusted to fine particles.

[0042] When a ball mill is used as the mill in the pulverization step, the stirring conditions of the ball mill are preferably a rotation speed of 300 rpm to 500 rpm, more preferably 350 rpm to 450 rpm. If the rotation speed is too slow, the pulverized product may not be sufficiently refined, making it difficult to achieve high density. If the rotation speed is too fast, the pulverized product may be refined too much, causing ultrafine particles to aggregate, increasing the apparent particle size and substantially reducing the specific surface area of ​​the material. Furthermore, when a ball mill is used as the mill in the milling step, stirring is preferably carried out at a rotation speed within the above-mentioned preferred range for 10 minutes to 360 minutes, more preferably for 30 minutes to 240 minutes, which makes it easy to adjust the milled product into particulate matter with an appropriately small particle size and to produce particulate sodium composite metal sulfate with a large specific surface area.

[0043] When the pulverization step is carried out using a ball mill such as a planetary ball mill, the diameter of the balls used is not particularly limited, but is preferably 0.2 mm or more and 3.0 mm or less, and more preferably 0.3 mm or more and 1.0 mm or less. By using balls with an appropriately small diameter, the contact area between the balls and the powder after evaporation to dryness, which is the material to be pulverized, can be increased, and the frequency of collision between the balls and the powder after evaporation to dryness can be increased, resulting in improved pulverization efficiency.

[0044] <Press molding process> The press-molding step is an optional step in the manufacturing method of the present invention. However, by performing the press-molding step, the density of the sodium composite metal sulfate-based material of the present invention can be increased, thereby providing a material exhibiting superior ionic conductivity. This press-molding step may be cold pressing performed at a low temperature such as room temperature. The pressure during press-molding is not particularly limited, but can be performed at a relatively low pressure of, for example, about 90 MPa to 250 MPa.

[0045] <Anhydrification treatment> The dehydration treatment is a treatment for removing water molecules from a sodium composite metal sulfate hydrate to form an anhydrous sodium composite metal sulfate. The anhydrous sodium composite metal sulfate of the present invention can be used at higher temperatures than a hydrate. The dehydration treatment may be any treatment capable of removing water molecules from the sodium complex metal sulfate hydrate, and for example, the dehydration treatment (hereinafter also referred to as dehydration treatment I) can be carried out by heat treatment under reduced pressure. The dehydration treatment I is preferably carried out after the above-mentioned pulverization step and before the press-molding step, but may also be carried out at other times. The dehydration treatment I can be carried out, for example, by heating at a temperature of about 150°C to 400°C for about 30 minutes to 10 hours in an environment reduced to about 1 / 100 to 1 / 1500 of atmospheric pressure (1 atmosphere). However, the degree of reduced pressure, heating temperature, and heating time are not limited to these. In another embodiment, an anhydrification treatment (hereinafter also referred to as an anhydrification treatment II) may be carried out simultaneously with the above-described pulverization step. When the anhydrification treatment II is carried out, the pulverization step is preferably carried out in a low-humidity environment. Stirring during the pulverization step can remove water molecules from the sodium complex metal sulfate hydrate. In another embodiment, an anhydration treatment (hereinafter also referred to as an anhydration treatment III) may be carried out simultaneously with the drying step described above. When the anhydration treatment III is carried out, the drying step is preferably carried out under reduced pressure, and heat treatment is preferably carried out at a high temperature sufficient to remove water molecules from the compound. When the anhydration treatment III is carried out, subsequent steps are preferably carried out in a low-humidity environment to prevent the compound from absorbing moisture and becoming a hydrate again during subsequent steps. [Example]

[0046] The present invention will be described in more detail below with reference to examples of the present invention, but the present invention is not limited to the examples described below. Each of the examples described below was produced according to the production method of the present invention.

[0047] Example 1 As Example 1, a sodium composite metal sulfate material of the present invention containing a composite metal of the following general formula (2) and / or (3) in which a portion of Zn is substituted with Al was produced. In Example 1, the blending amounts of the materials used were adjusted so that the value of C calculated based on the valence was 0.05 to 0.40 in increments of 0.05, and Examples 1-1 to 1-8 with different values ​​of C were produced as follows. [Formula 10] Na 6-C Zn 1-C Al C (SO4)4·2H2O (0 <C<1)···(2) [Formula 11] Na 6-C Zn 1-C Al C (SO4)4(0 <C<1)···(3)

[0048] (Example 1-2) That is, following the process sequence shown in Figure 9, a mixed solution was obtained by adding 0.7226 g of Na2SO4 (Fujifilm Wako Pure Chemical Industries, purity 99%) as compound I, 0.4418 g of ZnSO4·7H2O (Fujifilm Wako Pure Chemical Industries, purity 99.5%) as compound II, and 0.0292 g of Al2(SO4)3 (Kojundo Chemical Research Institute, purity 99%) as compound III to a container containing 20 ml of ion-exchanged water as the first solvent. The mixture was adjusted to a temperature of 80°C and stirred with a stirrer at 200 rpm for 1 hour to obtain a mixed solution. The mixture was placed in an oven adjusted to 150°C and dried until the moisture content was 0.1% by mass or less relative to the total mass, resulting in a powder after evaporation to dryness. The powder after evaporation to dryness obtained as described above was subjected to a planetary ball mill (PM100, manufactured by Retsch) and pulverized under conditions of a ball diameter of 0.3 mm, a rotation speed of 400 rpm, and a pulverization time of 1 hour to obtain a sodium composite metal sulfate material (pulverized product) of Example 1-2 in which Zn was substituted with Al at a ratio such that the value of C in general formula (2) and / or (3) was 0.05.

[0049] The pulverized products obtained as described above were press-molded as follows: Each pulverized product was pre-molded at room temperature under a pressure of 95 MPa for 1 minute, and then pressed at a pressure of 190 MPa for 1 minute to obtain a pellet-shaped pressed compact having a diameter of 10 mm and a thickness of 1 to 2 mm.

[0050] (Examples 1-1, 1-3 to 1-8) Pulverized products of Examples 1-1 and 1-3 to 1-8 were obtained by the same manufacturing method as in Example 1-2, except that the amounts of the compounds I to III added were adjusted so that the C values ​​of the obtained sodium composite metal sulfate materials would be the values ​​shown in Table 1. Then, each of the pulverized products obtained as described above was press-molded by the same method as in Example 1-1 to obtain press-molded bodies.

[0051] (Comparative Example 1) As a comparative example, NaZn(SO)·2H O was prepared. Specifically, a pulverized product of the reference compound was produced in the same manner as in Example 1, except that Al(SO)·16H O was not used. A press-molded body of the reference compound was obtained by the same press-molding method as in Example 1, except that the pulverized product was used.

[0052] The press-molded bodies of Examples 1-1 to 1-8 and Comparative Example 1 obtained as described above were subjected to the density (g / cm 3 ), relative density (%), ionic conductivity (×10 -6 The X-ray powder diffraction (XRD) was measured and is shown in Table 1. The powder X-ray diffraction patterns of Examples 1-1 to 1-8 and Comparative Example 1 using CuKα radiation are shown in Figure 1. In the peak patterns shown in Figure 1, a peak was observed at a diffraction angle 2θ of approximately 17.5°, confirming that each pulverized product was a hydrate.

[0053] The density (g / cm 3 ) was measured by measuring the diameter and thickness of the disk-shaped pellet with a micrometer to determine the pellet volume, and then measuring the weight of the pellet. The relative density (%) was determined by calculating the ratio (percentage) of density to the theoretical density of the sodium composite metal sulfate. In addition, the ionic conductivity (×10 -6 S / cm) was measured by the conventional AC impedance method.

[0054] Example 2 As Example 2, a sodium composite metal sulfate material of the present invention was produced, which contains a composite metal of the following general formula (4) and / or (5) in which a portion of Zn is substituted with Ga. In Example 2, the blending amounts of the materials used were adjusted so that the value of C calculated based on the valence was 0.05 to 0.40 in increments of 0.05, and Examples 2-1 to 2-8 with different values ​​of C were carried out. [Formula 12] Na 6-C Zn 1-C Ga C (SO4)4·2H2O (0 <C<1)···(4) [Formula 13] Na 6-C Zn 1-C Ga C (SO4)4(0 <C<1)···(5)

[0055] (Example 2-2) Specifically, following the process sequence shown in Figure 9, 0.7226 g of Na2SO4 (Fujifilm Wako Pure Chemical Industries, purity 99%) as compound I, 0.4418 g of ZnSO4·7H2O (Fujifilm Wako Pure Chemical Industries, purity 99.5%) as compound II, and 0.0611 g of Ga2(SO4)3·16H2O (Kojundo Chemical Research Institute, purity 99.9%) as compound III were added to a container containing 20 mL of ion-exchanged water as the first solvent. Subsequently, approximately 5 mL to 15 mL of ethanol was added to the same container as the second solvent to obtain a mixed solution. Using the above mixed solution, a sodium composite metal sulfate material (pulverized product) of Example 2-2 was obtained in the same manner as in Example 1-2.

[0056] (Examples 2-1, 2-3 to 2-8) The pulverized products of Examples 2-1, 2-3 to 2-8 were obtained by the same manufacturing method as in Example 2-2, except that the amounts of the compounds I to III added were adjusted so that the C value of the obtained sodium composite metal sulfate material was the value shown in Table 2. Furthermore, using Examples 2-1 to 2-3 obtained as described above, press-molded bodies were produced in the same manner as in Example 1, and the density, relative density, and ionic conductivity were measured in the same manner as in Example 1. The measurement results are shown in Table 2. Furthermore, a chart of the powder X-ray diffraction patterns using CuKα rays for Examples 2-1 to 2-8 is shown in Figure 2. In the peak pattern shown in Figure 2, a peak was observed at a diffraction angle 2θ of around 17.5°, confirming that each pulverized product was a hydrate.

[0057] The crushed products of Examples 2-1 to 2-3 were mixed at 1×10 -3 The heat-treated product was heated at 290°C for 4 hours in an environment reduced to atmospheric pressure, yielding a heat-treated product. The reference material was also subjected to the same heat treatment as described above to obtain a heat-treated product. Figure 3 shows the powder X-ray diffraction pattern chart using CuKα radiation of the heat-treated product obtained as described above. The chart in Figure 3 confirmed that the heat-treated products of Examples 2-1 to 2-3 and the heat-treated product of the reference material were anhydrates. It was also confirmed that the heat treatment described above was effective as an anhydrification treatment. These heat-treated products were then press-molded into pressed compacts in the same manner as in Example 1-1, and their ionic conductivity was measured. The measurement results are shown in Table 2. The press-molded products of the heat-treated products listed in Table 2 were obtained by pressing the heat-treated anhydrates, and have structures that do not contain water of crystallization. As shown in Table 2, it was confirmed that the ionic conductivity of the anhydrates of Examples 2-1 to 2-3 was significantly higher than that of the corresponding reference substances (anhydrates). Furthermore, when the ionic conductivity of the hydrates of Examples 2-1 to 2-3 was compared with that of the anhydrates of Examples 2-1 to 2-3, it was confirmed that the ionic conductivity of the hydrates was significantly improved.

[0058] Example 3 As Example 3, a sodium composite metal sulfate material of the present invention was produced, which contains a composite metal of the following general formula (6) and / or (7) in which a portion of Zn is substituted with Zr. In Example 3, the blending amounts of the materials used were adjusted so that the value of C calculated based on the valence was 0.05 to 0.40 in increments of 0.05, and Examples 3-1 to 3-8 with different values ​​of C were carried out. [Formula 14] Na 6-2C Zn 1-C Zr C (SO4)4·2H2O (0 <C<1)···(6) [Formula 15] Na 6-2C Zn 1-C Zr C (SO4)4(0 <C<1)···(7)

[0059] (Example 3-2) Specifically, following the process sequence shown in Figure 9, 0.7106 g of Na2SO4 (manufactured by Fujifilm Wako Pure Chemical Industries, purity 99%) as compound I, 0.4418 g of ZnSO4·7H2O (manufactured by Fujifilm Wako Pure Chemical Industries, purity 99.5%) as compound II, and 0.0619 g of Zr(SO4)2·4H2O (manufactured by Kojundo Chemical Laboratory, purity 98%) as compound III were added to a container containing 20 ml of ion-exchanged water as the first solvent to obtain a mixed solution. Using the above mixed solution, a sodium composite metal sulfate material (pulverized product) of Example 3-2 was obtained in the same manner as in Example 1-2.

[0060] Example 3-1 The pulverized product of Example 3-1 was obtained by the same manufacturing method as in Example 3-2, except that the amounts of compounds I to III added were adjusted so that the C value of the resulting sodium composite metal sulfate material would be the value shown in Table 3. Furthermore, using Examples 3-1 and 3-2 obtained as described above, press-molded bodies were produced in the same manner as in Example 1-2, and the density, relative density, and ionic conductivity were measured in the same manner as in Example 1-2. The measurement results are shown in Table 3. A powder X-ray diffraction pattern chart using CuKα radiation for Example 3-2 is shown in Figure 4. In the peak pattern shown in Figure 4, a peak was observed at a diffraction angle 2θ of approximately 17.5°, confirming that Example 3-2 used was a hydrate.

[0061] Example 4 Examples 4-1 to 4-6 were produced by press molding in the same manner as in Example 2-2, except that the pulverization conditions were changed as shown in Table 4. Example 4-7 was obtained by carrying out the steps up to the drying step in Example 2-2, but carrying out the press molding step without carrying out the pulverization step. The density, relative density, and ionic conductivity of the press-molded bodies of Examples 4-1 to 4-7 were measured using the same methods as in Example 1. The measurement results are shown in Table 4. Furthermore, for Examples 2-2, 4-2, and 4-3, the average particle size (μm) of the particles constituting the press-molded bodies was determined, and the ratio of the number of particles with a particle size of 0.20 μm or more to the total number of particles constituting the press-molded body was calculated. The results are shown in Table 4. The density, relative density, and ionic conductivity of the press-molded body obtained using the powder after evaporation to dryness in Examples 4-7 were measured in the same manner as in Example 1. As a result, the density was 2.37 g / cm 3 , relative density 85.9%, ionic conductivity 3.73(×10 -6 S / cm).

[0062] The average particle size (μm) and the ratio of the number of particles with a particle size of 0.20 μm or more to the total number of particles constituting the press-molded body were both determined by image analysis using a scanning electron microscope (SU1510 manufactured by Hitachi High-Technologies Corporation).

[0063] In order to confirm the state of the granular sodium composite metal sulfate resulting from changes in the grinding conditions for some examples, the following SEM photographs were taken and are shown in FIGS. 5 to 8. Figure 5A is an SEM photograph of the pulverized product of Example 4-1, Figure 5B is an SEM photograph of the pulverized product of Example 2-2, Figure 5C is an SEM photograph of the pulverized product of Example 4-2, and Figure 5D is an SEM photograph of the pulverized product of Example 4-3. FIG. 6A is an SEM photograph of the press-molded body of Example 2-2, FIG. 6B is an SEM photograph of the press-molded body of Example 4-2, and FIG. 6C is an SEM photograph of the press-molded body of Example 4-3. FIG. 7 is an SEM photograph of the pulverized product of Example 4-4. FIG. 8A is an SEM photograph of the pulverized product of Example 4-5, and FIG. 8B is an SEM photograph of the pulverized product of Example 4-6.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] [Table 4]

[0068] Example 5 As Example 5, a sodium composite metal sulfate material of the present invention was produced, which contains a composite metal of the following general formula (8) and / or (9) in which a portion of Zn is substituted with In. In Example 5, the blending amounts of the materials used were adjusted so that the value of C calculated based on the valence was 0.05 and 0.075, and Examples 5-1 and 5-2 with different values ​​of C were carried out. [Formula 16] Na 6-2C Zn 1-C In C (SO4)4·2H2O(0 <C<1)···(8) [Formula 17] Na 6-2C Zn 1-C In C (SO4)4(0 <C<1)···(9)

[0069] Specifically, following the process sequence shown in Figure 9, 0.7226 g of Na2SO4 (Fujifilm Wako Pure Chemical Industries, purity 99%) as compound I, 0.4418 g of ZnSO4·7H2O (Fujifilm Wako Pure Chemical Industries, purity 99.5%) as compound II, and 0.0571 g of In2(SO4)3·8.4H2O (Kojundo Chemical Research Institute, purity 99.9%) as compound III were added to a container containing 20 mL of ion-exchanged water as the first solvent. Subsequently, approximately 5 mL to 15 mL of ethanol was added to the same container as the second solvent to obtain a mixed solution. Using the above mixed solution, sodium composite metal sulfate materials (pulverized products) of Examples 5-1 and 5-2 were obtained in the same manner as in Example 1-2. Furthermore, using Examples 5-1 and 5-2 obtained as described above, press-molded bodies were produced in the same manner as in Example 1, and the relative density and ionic conductivity were measured in the same manner as in Example 1. The measurement results are shown in Table 5.

[0070] Example 6 As Example 6, a sodium composite metal sulfate material of the present invention was produced, which contains a composite metal of the general formula (4) and / or (5) in which a portion of Zn is substituted with Ga. In Example 6, the amounts of the materials used were adjusted so that the values ​​of C calculated based on the valence were 0.05 and 0.075, and Examples 6-1 and 6-2 with different values ​​of C were carried out. More specifically, the pulverized products of Examples 6-1 and 6-2 were obtained by the same manufacturing method as in Example 2-2. Furthermore, using Examples 6-1 and 6-2 obtained as described above, press-molded bodies were produced by the same method as in Example 1, and the relative density and ionic conductivity were measured in the same manner as in Example 1. The measurement results are shown in Table 5.

[0071] As shown in Table 5, when the substitution rate of metal M is the same and the relative density is the same, it was confirmed that the sodium composite metal sulfate material substituted with In has higher ionic conductivity than the sodium composite metal sulfate material substituted with Ga.

[0072] [Table 5]

[0073] The present invention described above encompasses the following technical ideas. (1) A sodium complex metal sulfate-based material characterized by containing a solid solution of a sodium complex metal sulfate in which part of the Zn in Na6Zn(SO4)4 is substituted with a metal M with a valence of 3 or more. (2) The sodium composite metal sulfate material according to (1) above, which is used as a solid electrolyte for a sodium secondary battery. (3) Ionic conductivity is 0.1 × 10 -6 S / cm -1 The sodium composite metal sulfate material according to (1) or (2) above. (4) The sodium composite metal sulfate-based material is a press-molded body, and the particulate sodium composite metal sulfate constituting the press-molded body has a number-based average particle size obtained by analyzing an SEM image of 0.08 μm or more and 0.20 μm or less; The sodium composite metal sulfate material according to (1) or (2) above, wherein the number of particulate sodium composite metal sulfate having a particle size of 0.20 μm or more in a particle size distribution (number-based frequency distribution) is 20% or less of the total number of particles of the particulate sodium composite metal sulfate contained in the sodium composite metal sulfate material. (5) A method for producing the sodium composite metal sulfate-based material according to (1) or (2) above, a stirring step of adding a compound I containing sodium, a compound II containing zinc, and a compound III containing a metal M to a solvent (wherein at least one of the compounds I, II, and III is a sulfate), and stirring the mixture; a drying step of evaporating the mixture obtained in the stirring step to dryness; A method for producing a sodium composite metal sulfate-based material, comprising: (6) The method for producing a sodium composite metal sulfate-based material according to (5) above, further comprising a pulverizing step of pulverizing the powder obtained by the drying step after evaporation to dryness into smaller particles. [Explanation of symbols]

[0074] Solid solubility limit...10 Frame: 20, 30

Claims

1. Na ６ Zn(SO ４ ) ４ 1. A sodium complex metal sulfate-based material comprising a solid solution of sodium complex metal sulfate in which a portion of Zn in the above formula (1) is substituted with a metal M having a valence of three or more.

2. The sodium composite metal sulfate material according to claim 1, which is used as a solid electrolyte for a sodium secondary battery.

3. Ion conductivity is 0.1 x 10 －６ S / cm －１ The sodium composite metal sulfate material according to claim 1 or 2.

4. the sodium composite metal sulfate-based material is a press-molded body, and the particulate sodium composite metal sulfate constituting the press-molded body has a number-based average particle size obtained by analyzing an SEM image of 0.08 μm or more and 0.20 μm or less; 3. The sodium composite metal sulfate-based material according to claim 1, wherein the number of particulate sodium composite metal sulfate having a particle size of 0.20 μm or more in a particle size distribution (number-based frequency distribution) is 20% or less of the total number of particles of the particulate sodium composite metal sulfate contained in the sodium composite metal sulfate-based material.

5. A method for producing the sodium composite metal sulfate-based material according to claim 1 or 2, a stirring step of adding a compound I containing sodium, a compound II containing zinc, and a compound III containing a metal M to a solvent (provided that at least one of the compound I, the compound II, and the compound III is a sulfate salt), and stirring the mixture; a drying step of evaporating the mixture obtained by the stirring step to dryness; A method for producing a sodium composite metal sulfate-based material, comprising:

6. The method for producing a sodium composite metal sulfate-based material according to claim 5, further comprising a pulverizing step of pulverizing the evaporated-to-dry powder obtained in the drying step into smaller particles.

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