Method for producing sodium compounds having a NASICON structure

Abstract

To provide an industrially advantageous method for obtaining a single-phase sodium compound having a NASICON structure by X-ray diffraction.SOLUTION: A method for producing a sodium compound having a NASICON structure and containing at least sodium, zirconium, silicon and phosphorus is provided. The method comprises calcining at 800 to 1100°C a reaction precursor which contains sodium, zirconium, silicon, and phosphorus and in which absorption peaks with maxima in the range of at least 950 to 1050 cm-1 and 1060 to 1150 cm-1 are observed in the infrared absorption spectrum.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing a sodium compound having a NASICON structure, which is useful as a solid electrolyte, etc. [Background technology]

[0002] Non-aqueous lithium secondary batteries are used as power sources for portable devices, notebook computers, electric vehicles, industrial robots, etc. In recent years, in place of non-aqueous lithium secondary batteries that use electrolytes containing flammable organic solvents, the development of all-solid-state lithium ion batteries that use highly safe solid electrolytes has been actively pursued.

[0003] On the other hand, there are concerns about the global rise in the cost of lithium as a raw material, and sodium has also been attracting attention as an alternative material to lithium. For example, Patent Document 1 proposes a sodium-ion all-solid-state battery that uses a sodium compound that is a sodium ion conductor having a NASICON structure as a solid electrolyte.

[0004] Patent Document 1 proposes a method for synthesizing a solid electrolyte represented by Na3Zr2(SiO4)2(PO4) by hydrolyzing a precursor solution containing sodium, zirconium, silicon, and phosphorus, gelling it, leaving it for one day, aging the gel, drying it at 120°C for 24 hours, crushing it, and calcining it at 750°C for 5 hours to obtain a precursor powder, which is then fired at 1000°C for 5 hours. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-15782 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the solid electrolyte synthesis method of Patent Document 1, it takes a long time to obtain a reaction precursor, making it difficult to industrially advantageously obtain a sodium compound that has a NASICON structure and is single-phase in terms of X-ray diffraction.

[0007] Therefore, an object of the present invention is to provide a method for obtaining a sodium compound having a NASICON structure and a single phase in terms of X-ray diffraction, which is industrially advantageous. [Means for solving the problem]

[0008] In view of the above circumstances, the present inventors have conducted extensive research and have found that in a method for producing a sodium compound having a NASICON structure and containing at least sodium, zirconium, silicon and phosphorus, by using a specific reaction precursor containing sodium, zirconium, silicon and phosphorus, a sodium compound having a NASICON structure and having a single phase in terms of X-ray diffraction can be obtained in a relatively short period of time, and that the reaction precursor can be obtained by an industrially advantageous method by carrying out a series of steps, and have completed the present invention.

[0009] That is, the present invention (1) is A method for producing a sodium compound having a NASICON structure and containing at least sodium, zirconium, silicon and phosphorus, comprising the steps of: Contains sodium, zirconium, silicon and phosphorus and has an infrared absorption spectrum of at least 950 to 1050 cm -1 Absorption peaks with maximum values ​​in the range of 1060 to 1150 cm -1 The present invention provides a method for producing a sodium compound having a NASICON structure, which comprises calcining a reaction precursor having an absorption peak with a maximum value in the range of 800 to 1100°C.

[0010] The present invention (2) also provides a method for producing a sodium compound having a NASICON structure according to (1), characterized in that the reaction precursor is an amorphous reaction precursor.

[0011] In addition, the present invention (3) relates to the reaction precursor, A first step of mixing a zirconium source, a silicon source, and phosphoric acid to prepare a mixed slurry; A second step of heat-treating the mixed slurry to obtain a heat-treated slurry; A third step of adding a sodium source to the heat-treated slurry to obtain a sodium-containing heat-treated slurry; A fourth step of wet-pulverizing the sodium-containing heat-treated slurry; A fifth step of drying the sodium-containing heat-treated slurry after the fourth step; The present invention provides a method for producing a sodium compound having a NASICON structure according to (1) or (2), which is characterized in that the compound is obtained by carrying out the steps of:

[0012] The present invention (4) also provides a method for producing a sodium compound having a NASICON structure according to (1) or (2), characterized in that the silicon source is precipitated silica.

[0013] The present invention (5) also provides a method for producing a sodium compound having a NASICON structure according to (3), characterized in that in the first step, a surfactant is further added to the mixed slurry.

[0014] The present invention (6) also provides a method for producing a sodium compound having a NASICON structure according to (3), characterized in that the sodium source is sodium hydroxide.

[0015] The present invention (7) also provides a method for producing a sodium compound having a NASICON structure according to (3), characterized in that the heat treatment temperature in the second step is 50 to 120°C.

[0016] The present invention (8) also provides a method for producing a sodium compound having a NASICON structure according to (3), characterized in that the drying in the fifth step is carried out by spray drying.

[0017] The present invention (9) also provides a method for producing a sodium compound having a NASICON structure according to (1), wherein the sodium compound having a NASICON structure is represented by the following general formula (1): Na g Zr h S i P j O k (1) (In the formula, g is 2.7≦g≦3.3, h is 1.7≦h≦2.3, i is 1.7≦i≦2.3, j is 0.8≦j≦1.2, and k is 10≦k≦14.)

[0018] The present invention (10) also provides a method for producing a sodium compound having a NASICON structure according to (1), characterized in that the reaction precursor further contains an M source having an M element which is a metal element other than sodium and zirconium.

[0019] The present invention (11) also provides a method for producing a sodium compound having a NASICON structure according to the above (10), wherein the M source contains one or more elements selected from Mg, Zn, Cu, Fe, Cr, Mn, Ni, V, W, Li, K, Ca, Sr, Ba, Ti, Hf, Nb, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho.

[0020] The present invention (12) also provides a method for producing a sodium compound having a NASICON structure according to (10) or (11), characterized in that in the first step, the mixed slurry further contains the M source.

[0021] The present invention (13) also provides a method for producing the sodium compound having the NASICON structure according to (1), which is characterized in that it is used as a solid electrolyte. Effect of the Invention

[0022] According to the present invention, there can be provided a method for obtaining a sodium compound having a NASICON structure and being a single phase in terms of X-ray diffraction, in an industrially advantageous manner. [Brief description of the drawings]

[0023] [Figure 1] FIG. 2 is an X-ray diffraction pattern of the reaction precursor obtained in Example 1. [Diagram 2] FIG. 2 is an FT-IR chart of the reaction precursor obtained in Example 1. [Diagram 3] 1 is an X-ray diffraction diagram of the sodium compound having a NASICON structure obtained in Example 1. [Figure 4] 1 is an X-ray diffraction diagram of the sodium compound having a NASICON structure obtained in Example 2. [Diagram 5] 1 is an SEM image of the sodium compound having a NASICON structure obtained in Example 2. [Figure 6] FIG. 2 is an X-ray diffraction diagram of the reaction precursor obtained in Comparative Example 1. [Figure 7] FIG. 4 is an FT-IR chart of the reaction precursor obtained in Comparative Example 1. [Figure 8] 1 is an X-ray diffraction diagram of a sodium compound having a NASICON structure obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, the present invention will be described based on preferred embodiments. The method for producing a sodium compound having a NASICON structure of the present invention is a method for producing a sodium compound having a NASICON structure and containing at least sodium, zirconium, silicon and phosphorus, comprising the steps of: Contains sodium, zirconium, silicon and phosphorus and has an infrared absorption spectrum of at least 950 to 1050 cm -1 Absorption peaks with maximum values ​​in the range of 1060 to 1150 cm -1 The reaction precursor, which exhibits an absorption peak having a maximum value in the range of 800 to 1100°C, is fired at 800 to 1100°C.

[0025] The sodium compound having a NASICON structure obtained by the method for producing a sodium compound having a NASICON structure of the present invention is basically represented by the following general formula (1). Na g Zr h S i P j O k (1) (In the formula, g is 2.7≦g≦3.3, h is 1.7≦h≦2.3, i is 1.7≦i≦2.3, j is 0.8≦j≦1.2, and k is 10≦k≦14.) In the general formula (1), g is preferably 2.7≦g≦3.3, more preferably 2.8≦g≦3.2, from the viewpoint of synthesizing a solid electrolyte having a single phase NASICON structure and being single phase in terms of X-ray diffraction. In addition, in the general formula (1), h is preferably 1.7≦h≦2.3, more preferably 1.8≦h≦2.2, from the viewpoint of synthesizing a solid electrolyte having a single phase NASICON structure and being single phase in terms of X-ray diffraction. In addition, in the general formula (1), it is preferable that i is 1.7≦i≦2.3, and preferably 1.8≦i≦2.2, from the viewpoint of synthesizing a solid electrolyte having a single phase NASICON structure and being single phase in terms of X-ray diffraction. In addition, j in the general formula (1) is preferably 0.8≦j≦1.2, and more preferably 0.9≦j≦1.1, from the viewpoint of synthesis of a solid electrolyte having a single phase NASICON structure and being single phase in terms of X-ray diffraction. In addition, k in the general formula (1) is 10≦k≦14, and preferably 11≦k≦12.

[0026] The reaction precursor used in the method for producing a sodium compound having a NASICON structure of the present invention contains sodium, zirconium, silicon and phosphorus, and has an infrared absorption spectrum of at least 950 to 1050 cm. -1 Absorption peaks with a maximum value in the range of 1060 to 1150 cm (first absorption peak) -1 The maximum value of the first absorption peak is observed in the range of 950 to 1050 cm. -1 Preferably, the wavelength is in the range of 960 to 1040 cm-1 It is more preferable that the maximum value of the second absorption peak is in the range of 1060 to 1150 cm. -1 Preferably, the wavelength is in the range of 1070 to 1140 cm -1 For example, FT-IR of an example of the form of the reaction precursor used in the method for producing a sodium compound having a NASICON structure of the present invention is shown in FIG. -1 The peak (first absorption peak) and the maximum (peak top) are located near 1100 cm -1 A nearby peak (second absorption peak) is observed.

[0027] The reaction precursor is preferably an amorphous reaction precursor. In the present invention, the reaction precursor being amorphous means that only a broad peak is observed in the range of 2θ=10 to 70° in X-ray diffraction analysis, and no sharp diffraction peak (half width is 1.0° or less) is observed. Therefore, the reaction precursor is preferably such that no sharp diffraction peak (half width is 1.0° or less) derived from sodium hydrogen phosphate (Na2HPO4) is observed in the range of 2θ=31.5 to 32.5° in X-ray diffraction analysis.

[0028] The method for producing a sodium compound having a NASICON structure of the present invention contains at least sodium, zirconium phosphorus and silicon, and has an infrared absorption spectrum of at least 950 to 1050 cm -1 Absorption peaks with maximum values ​​in the range of 1060 to 1150 cm -1 The reaction precursor, which exhibits an absorption peak having a maximum value in the range of 800 to 1100°C, is fired at 800 to 1100°C. In other words, the method for producing a sodium compound having a NASICON structure of the present invention basically comprises the following steps: Step A: A step of preparing a reaction precursor containing at least sodium, zirconium, silicon and phosphorus. Step B: A step of calcining the obtained reaction precursor at 800 to 1100°C.

[0029] (Step A) The step A includes a step of forming a compound containing at least sodium, zirconium, silicon and phosphorus, and having an infrared absorption spectrum of at least 950 to 1050 cm -1 Absorption peaks with maximum values ​​in the range of 1060 to 1150 cm -1 This is a step of preparing a reaction precursor in which an absorption peak having a maximum value in the range is observed.

[0030] It is preferable that Step A comprises a first step of mixing a zirconium source, a silicon source, and phosphoric acid to prepare a mixed slurry, a second step of heat-treating the mixed slurry to obtain a heat-treated product slurry, a third step of adding a sodium source to the heat-treated product slurry to obtain a sodium-containing heat-treated product slurry, a fourth step of wet-grinding the sodium-containing heat-treated product slurry, and a fifth step of drying the wet-ground sodium-containing heat-treated product slurry to obtain a reaction precursor.

[0031] The first step is a step of adding a zirconium source, a silicon source, and phosphoric acid to a solvent and stirring the mixture to mix the zirconium source, the silicon source, and phosphoric acid in the solvent to prepare a mixed slurry.

[0032] In the first step, the solvent is a water solvent or a mixed solvent of water and a hydrophilic organic solvent. The hydrophilic organic solvent is not particularly limited as long as it is inactive against the raw material, and examples thereof include alcohols such as ethanol, propanol, butanol, and methyl ethyl ketone. In the case of a mixed solvent of water and a hydrophilic organic solvent, the mixing ratio of water and the hydrophilic organic solvent is appropriately selected.

[0033] In the first step, the zirconium source may be, for example, a compound having a zirconium element, such as zirconium oxide, zirconium hydroxide, or zirconium carbonate. Among these, zirconium hydroxide is preferred from the viewpoint of being a reaction precursor having excellent reactivity. The zirconium source may be a single type or a combination of two or more types.

[0034] The amount of the zirconium source added is an amount such that the molar ratio (Zr / Si) of the Zr element in the zirconium source to the Si element in the silicon source in the mixed slurry is 0.8 to 1.2, preferably 0.9 to 1.1. By adding the amount of the zirconium source to the mixed slurry within the above range, it becomes possible to synthesize a sodium compound having a NASICON structure and a single phase in terms of X-ray diffraction.

[0035] In the first step, the silicon source may be, for example, a compound having silicon element, such as precipitated silica, amorphous silica such as fumed silica, etc. Among these, precipitated silica is preferred from the viewpoint of reactivity and ease of handling. The silicon source may be one type alone or two or more types in combination.

[0036] The phosphoric acid used in the first step is not particularly limited as long as it is industrially available. The phosphoric acid may be an aqueous phosphoric acid solution.

[0037] The amount of phosphoric acid added is an amount that provides a molar ratio (P / Si) of P element in phosphoric acid to Si element in the silicon source in the slurry of 0.4 to 0.6, preferably 0.45 to 0.55. By adding phosphoric acid in the above range, it becomes possible to synthesize a sodium compound having a NASICON structure and a single phase in terms of X-ray diffraction.

[0038] In the first step, if necessary, a surfactant may be added to the slurry to form a mixed slurry further containing a surfactant. By including a surfactant, the zirconium source, the silicon source, and the phosphoric acid can be easily stirred, and a uniform mixed slurry can be formed. That is, the mixed slurry may be (i) one obtained by mixing a zirconium source, a silicon source, and phosphoric acid, or (ii) one obtained by mixing a zirconium source, a silicon source, phosphoric acid, and a surfactant.

[0039] As the surfactant, an anionic surfactant is preferred because it can reduce the viscosity of the slurry. For example, ammonium polycarboxylate, polyacrylic acid, etc. are particularly preferred because they can suppress adhesion of the slurry inside the spray drying apparatus.

[0040] In the first step, when a surfactant is added to the mixed slurry, the amount of the surfactant added is preferably 1 to 10 parts by mass relative to 100 parts by mass of the silicon source.

[0041] In the first step, the order of adding the zirconium source, the silicon source, the phosphoric acid, and the surfactant used as needed to the solvent is not particularly limited.

[0042] The second step is a step of heat-treating the mixed slurry obtained in the first step to obtain a heat-treated slurry.

[0043] The components contained in the heat-treated slurry obtained in the second step are amorphous and no diffraction peaks are detected in the X-ray diffraction analysis. Therefore, although the details are not clear, the inventors presume that in the second step, by heat-treating the mixed slurry obtained in the first step, the phosphoric acid and the zirconium source in the mixed slurry react (for example, see Japanese Patent No. 6190023), and the obtained heat-treated slurry becomes a slurry containing a silicon source and an amorphous compound containing phosphorus and zirconium.

[0044] In the second step, the heat treatment temperature is 50 to 120° C., and preferably 70 to 105° C. When the heat treatment temperature is within the above range, it becomes possible to complete the reaction of the zirconium source with phosphoric acid in an industrially advantageous manner.

[0045] In the second step, the pH of the heat-treated slurry is preferably 3.5 to 7.0 from the viewpoint of reacting the phosphoric acid with the zirconium source.

[0046] In the second step, in order to increase the reactivity of the mixed slurry, it is preferable to carry out a heat treatment while stirring.

[0047] The third step is a step of adding a sodium source to the heat-treated slurry obtained in the second step to obtain a sodium-containing heat-treated slurry.

[0048] The components contained in the sodium-containing heat-treated slurry obtained in the third step are amorphous in X-ray diffraction analysis, and no diffraction peaks are detected.Thus, although the details are not clear, the present inventors speculate that in the third step, by adding a sodium source to the heat-treated slurry obtained in the second step, the components contained in the heat-treated slurry, for example, the silicon source and the sodium source react, and the resulting sodium-containing heat-treated slurry becomes a slurry containing an amorphous compound containing silicon and sodium, and an amorphous compound containing phosphorus and zirconium.

[0049] In the third step, examples of the sodium source include sodium carbonate, sodium bicarbonate, and sodium hydroxide. Among these, sodium hydroxide is preferred from the viewpoint of reactivity. The sodium source may be one type alone or a combination of two or more types.

[0050] The timing of addition of the sodium source may be such that the sodium source is added to the heated heat-treated slurry after the second step, or to the heat-treated slurry that has been cooled to near room temperature, preferably below 50°C, after the second step. However, it is preferable to add the sodium source to the heat-treated slurry that has been cooled to near room temperature, preferably below 45°C, after the second step, in order to suppress an increase in the viscosity of the slurry.

[0051] The amount of the sodium source added is an amount such that the molar ratio (Na / Si) of the Na element in the sodium source to the Si element in the heat-treated slurry is 1.2 to 1.8, preferably 1.3 to 1.7. By adding the amount of the sodium source within the above range, it becomes possible to synthesize a sodium compound having a NASICON structure and a single phase in terms of X-ray diffraction.

[0052] In the third step, the pH of the sodium-containing heat-treated slurry is preferably 7 to 13 from the viewpoint of sufficiently reacting the sodium source with the heat-treated slurry.

[0053] In the third step, the reaction is preferably carried out under stirring in order to increase the reactivity between the components in the heat-treated slurry obtained in the second step and the sodium source.

[0054] The fourth step is a step of wet-pulverizing the sodium-containing heat-treated slurry obtained in the third step. That is, the sodium-containing heat-treated slurry obtained in the third step is wet-pulverized to obtain a slurry in which each raw material is finely dispersed and uniformly dispersed. The components in the sodium-containing heat-treated slurry obtained in the third step are amorphous and have a softer particle strength than those of crystalline components, so that the slurry can be easily made into a slurry in which each raw material is finely dispersed and uniformly dispersed.

[0055] In the fourth step, the solid content of the sodium-containing heat-treated product slurry to be wet-pulverized is 5 to 40% by mass, preferably 10 to 30% by mass. When the solid content of the sodium-containing heat-treated product slurry is in the above range, the operability is good and the pulverization process can be carried out efficiently. Therefore, after carrying out the third step, the solid content of the sodium-containing heat-treated product slurry may be adjusted to the above solid content before carrying out the fourth step.

[0056] Examples of the wet grinding method include a bead mill, a ball mill, a wet jet mill, etc. Among these, a bead mill is preferred since fine particles can be efficiently obtained.

[0057] It is preferable to carry out wet pulverization until the average particle size of the solid content of the sodium-containing heat-treated product slurry after wet pulverization reaches 0.1 to 3 μm, preferably 0.1 to 1.5 μm, as measured by a laser scattering / diffraction method, in order to obtain a reaction precursor having excellent reactivity.

[0058] In the fourth step, from the viewpoint of reacting the sodium source with the silica source, the pH of the sodium-containing heat-treated product slurry after wet-pulverization is preferably 7 to 13. The present inventors presume that the wet-pulverization promotes the reaction between the sodium source and the heat-treated product slurry that was unreacted with the sodium source in the third step, and therefore the pH becomes lower than that of the sodium-containing heat-treated product slurry.

[0059] In the fourth step, in order to perform the wet pulverization more efficiently, a dispersant may be added to the sodium-containing heat-treated slurry before the wet pulverization. Examples of the dispersant include various surfactants.

[0060] The fifth step is a step of drying the sodium-containing heat-treated slurry after wet pulverization obtained in the fourth step to obtain a reaction precursor.

[0061] The reaction precursor obtained in the fifth step has a peak at 950 to 1050 cm -1 Absorption peaks with a maximum value in the range of 1060 to 1150 cm (first absorption peak) -1 The reaction precursor has an absorption peak (secondary absorption peak) with a maximum value in the range of 960 to 1040 cm. -1 Preferably, the wavelength is in the range of 970 to 1030 cm -1 It is more preferable that the maximum value of the second absorption peak is in the range of 1070 to 1140 cm -1 Preferably, the wavelength is in the range of 1080 to 1130 cm -1It is more preferable that the maximum value of the first absorption peak and the maximum value of the second absorption peak are in the above-mentioned ranges, since it is possible to industrially advantageously obtain a sodium compound having a NASICON structure and being single-phase in terms of X-ray diffraction.

[0062] The molar ratio of Na:Zr:Si:P in the reaction precursor obtained in the fifth step is preferably 2.7-3.3:1.7-2.3:1.7-2.3:0.8-1.2.

[0063] In the fifth step, the method for drying the sodium-containing heat-treated slurry after wet pulverization is not particularly limited, but drying by spray drying is preferred because it allows a reaction precursor in which the raw material particles are densely packed, making it possible to industrially advantageously obtain a sodium compound that is single-phase in terms of X-ray diffraction and has a NASICON structure.

[0064] In the spray drying, the sodium-containing heat-treated product slurry after wet pulverization is atomized by a predetermined means, and the resulting fine droplets are dried to obtain a reaction precursor. The sodium-containing heat-treated product slurry after wet pulverization can be atomized, for example, by using a rotating disk or a pressure nozzle, and either method can be used in the fifth step.

[0065] In the spray drying, the size of the atomized droplets is not particularly limited, but is 1 to 40 μm, preferably 5 to 30 μm. The amount of the slurry to be supplied to the spray drying apparatus is preferably determined taking this into consideration.

[0066] The drying temperature in the spray dryer is preferably adjusted so that the hot air inlet temperature is 150 to 300°C, preferably 200 to 250°C, and the hot air outlet temperature is 80 to 200°C, preferably 100 to 170°C, since this prevents the powder from absorbing moisture and makes it easier to recover the powder.

[0067] (Step B) In the present invention, by providing step B, which is a step of calcining the reaction precursor prepared through step A, it is possible to obtain a sodium compound having a NASICON structure and a single phase in terms of X-ray diffraction.

[0068] In step B, the calcination temperature is 800 to 1100°C, preferably 850 to 1050°C, and more preferably 900 to 1000°C. In step B, the calcination temperature can be relatively low by calcining the reaction precursor according to the method for producing a sodium compound having a NASICON structure of the present invention. By setting the calcination temperature within the above range, it becomes possible to industrially advantageously obtain a sodium compound having a NASICON structure and being single-phase in terms of X-ray diffraction.

[0069] In step B, the firing time is 1 to 20 hours, preferably 2 to 15 hours. In step B, the fired product obtained in the first firing may be fired multiple times as necessary. Alternatively, in order to make the powder characteristics uniform, the fired product may be crushed, remixed, or the like, and then fired again.

[0070] In the step B, the firing atmosphere is an air atmosphere or an inert gas atmosphere, such as argon gas, helium gas, nitrogen gas, etc.

[0071] In step B, crushing, grinding, classification, etc. can be carried out as necessary to obtain the desired sodium compound having a NASICON structure.

[0072] The crushing, pulverization, classification, etc. may be performed by a dry method or a wet method. Examples of devices for performing crushing, pulverization, classification, etc. by a dry method include a jet mill, a pin mill, a roll mill, a ball mill, a bead mill, etc. Examples of devices for performing crushing, pulverization, classification, etc. by a dry method include a ball mill, a bead mill, etc.

[0073] The sodium compound obtained by the method for producing a sodium compound having a NASICON structure of the present invention is preferably Na3Zr2Si2PO 12 It is preferable that the material has a NASICON structure and is a single phase in terms of X-ray diffraction.

[0074] Furthermore, in the production method of the present invention, it is also possible to produce a sodium compound having a NASICON structure, which contains a metal element M source as a solid solution, if necessary.

[0075] Specifically, the reaction precursor used in step A may further contain an M source having an M element other than sodium and zirconium, and then step B may be carried out. The M source is, for example, a compound having one or more elements selected from Mg, Zn, Cu, Fe, Cr, Mn, Ni, V, W, Li, K, Ca, Sr, Ba, Ti, Hf, Nb, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho as the M element. The M source is preferably a compound having one or more elements selected from Mg, Zn, and Nb. The M source may be one type alone or two or more types in combination.

[0076] When the reaction precursor contains an M source, the molar ratio of Na:(Zr+M):Si:P in the reaction precursor is preferably 2.7-3.3:1.7-2.3:1.7-2.3:0.8-1.2.

[0077] As a method for incorporating the M source into the reaction precursor, for example, in the first step of the step A, the M source may be added to the slurry as necessary to form a mixed slurry containing the M source. Examples of the M source include oxides, hydroxides, carbonates, etc. containing the M element.

[0078] The amount of the M source added is an amount such that the molar ratio (M / Si) of the M element in the M source to the Si element of the silicon source in the slurry is 0.01 to 0.5, preferably 0.01 to 0.3. By adding the amount of the M source within the above range, it is possible to synthesize a sodium compound having a NASICON structure and a single phase in terms of X-ray diffraction. When two or more kinds of M elements are added as the M source, the number of moles of the M element in atomic terms, which is the basis for calculating the above molar ratio, refers to the total number of moles of each M element.

[0079] After completion of the first step, the above-mentioned second to fifth steps are carried out under similar conditions to obtain a reaction precursor further containing an M source, and then, by carrying out the B step, a product in which the M source is contained in a solid solution in a sodium compound having a NASICON structure can be produced.

[0080] The sodium compound obtained by the method for producing a sodium compound having a NASICON structure of the present invention has an average particle size of 0.1 to 5.0 μm, preferably 0.2 to 3.0 μm, as determined by SEM observation. When the average particle size as determined by SEM observation is within the above range, a dense sintered body can be obtained.

[0081] The average particle size by SEM observation is the average particle size of primary particles obtained from a scanning electron microscope (SEM) photograph, and is calculated by randomly extracting 100 primary particles from the scanning electron microscope (SEM) observation, measuring the horizontal Feret's diameter of each particle, and averaging the diameter of the 100 particles.

[0082] The BET specific surface area of ​​the sodium compound obtained by the method for producing a sodium compound having a NASICON structure of the present invention is 1 to 30 m 2 / g, preferably 3 to 20m 2 When the BET specific surface area is within the above range, a dense sintered body can be obtained.

[0083] The sodium compound obtained by the method for producing a sodium compound having a NASICON structure of the present invention is particularly useful as a solid electrolyte.

[0084] The sodium compound obtained by the method for producing a sodium compound having a NASICON structure of the present invention can be used, for example, as a solid electrolyte for a sodium ion all-solid-state battery, but can also be used as a sintering aid that promotes sintering of all-solid-state batteries such as a lithium ion all-solid-state battery and a magnesium ion all-solid-state battery. EXAMPLES

[0085] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0086] <Evaluation device> X-ray diffraction analysis: Rigaku UltimaIV was used. The radiation source used was Cu-Kα. The measurement conditions were a tube voltage of 40 kV, a tube current of 40 mA, and a scanning speed of 0.1° / sec. Infrared absorption spectrum (FT-IR) analysis: Infrared absorption spectrum analysis of the reaction precursor was performed using a JASCO FTIR-6600 with a resolution of 4 cm -1 , 256 integrations, measurement wave number range: 400-4000 cm -1 The measurements were performed under the following conditions: The ATR method was used, and ATR correction and spectrum smoothing processing were performed.

[0087] Example 1 <1st process> Zirconium hydroxide (average particle size 5 μm, BET specific surface area 208 m, purity 28.1% in terms of zirconium oxide) was added to 7 L of pure water at room temperature (25°C) while stirring using a three-one motor stirrer. 2 / g,) 4318.5 g, anionic surfactant (ammonium polycarboxylate: SN Dispersant 5468 manufactured by Sannopro Co., Ltd.) 249 g, precipitated silica (Nipsil-AQ manufactured by Tosoh Silica Co., Ltd., BET specific surface area 210 m 2 661.1 g of phosphate (water content: 15% by mass), 661.1 g of phosphate buffer solution (water content: 15% by mass, purity: 89.4%), and 564.8 g of phosphoric acid were charged in this order to prepare a mixed slurry (1). <Second process> Next, the mixed slurry (1) was heated to 80°C at 30°C / h under stirring, and then kept at 80°C for 4 hours, and then allowed to cool to room temperature (25°C) to obtain a heat-treated slurry (2). The pH of the heat-treated slurry (2) was 4.1. <3rd process> Next, 2360.0 g of 25% by mass sodium hydroxide was added to the heat-treated slurry (2) over a period of 20 minutes with stirring to obtain a sodium-containing heat-treated slurry (3). The pH of the sodium-containing heat-treated slurry (3) was 13.5. <4th process> The sodium-containing heat-treated slurry was then fed to a media-agitation bead mill containing zirconia beads with a diameter of 0.5 mm, and wet-pulverized. The average particle size of the solid matter in the sodium-containing heat-treated slurry after wet-pulverization was 2.1 μm, as determined by a laser diffraction / scattering method. The pH of the sodium-containing heat-treated slurry after wet-pulverization was 11.4. <5th process> Next, the wet-pulverized sodium-containing heat-treated slurry (3) was fed to a spray dryer set at 220°C at a feed rate of 2.4 L / h to obtain a reaction precursor as a dried product. Visual observation of the inside of the spray dryer revealed that there was little internal adhesion, and the recovery rate was 95% on a solid content basis. X-ray diffraction analysis of the obtained reaction precursor revealed that it was an amorphous composition (Figure 1). In addition, FT-IR analysis revealed that the reaction precursor had a peak at 990 cm -1 and 1110cm -1 Peaks with maximum values ​​(first and second absorption peaks) were confirmed (Figure 2). <Step B> The resulting reactive precursor was then calcined in air at 900°C for 4 hours to obtain a calcined product. X-ray diffraction analysis of the calcined product revealed that the calcined product was a single-phase Na3Zr2Si2PO 12 (Figure 3).

[0088] Example 2 <1st to 5th process> A reaction precursor was obtained in the same manner as in Example 1. <Step B> The reaction precursor obtained in the same manner as in Example 1 was calcined in air at 915°C for 4 hours to obtain a calcined product. The calcined product was then pulverized in a jet mill to obtain a pulverized product. X-ray diffraction analysis of the resulting pulverized product showed that the pulverized product was a single-phase Na3Zr2Si2PO 12 (Figure 4). The obtained Na3Zr2Si2PO 12 The SEM photograph is shown in FIG.

[0089] Comparative Example 1 Zirconium hydroxide (average particle size 5 μm, BET specific surface area 208 m, purity 28.1% in terms of zirconium oxide) was added to 7 L of pure water at room temperature (25°C) while stirring using a three-one motor stirrer. 2 / g,) 4318.5 g, anionic surfactant (ammonium polycarboxylate: SN Dispersant 5468 manufactured by Sannopro Co., Ltd.) 249 g, precipitated silica (Nipsil-AQ manufactured by Tosoh Silica Co., Ltd., BET specific surface area 210 m 2 A mixed slurry (1) was prepared by charging 661.1 g of sucrose (0.1 g / g, purity calculated as silica: 89.4%) and 806.1 g of sodium triphosphate (Na3PO4) in that order. The slurry was then fed to a media-agitation bead mill containing zirconia beads with a diameter of 0.5 mm and wet-milled. The average particle size of the solids in the slurry after wet-milling was 2.3 μm, as determined by a laser diffraction / scattering method. Next, the lithium-containing heat-treated slurry was fed to a spray dryer set at 220°C at a feed rate of 2.4 L / h to obtain a dried product. Visual inspection of the inside of the spray dryer revealed that there was little internal adhesion, and the recovery rate was 95% based on the solid content. X-ray diffraction analysis of the obtained dried product revealed a peak derived from sodium hydrogen phosphate (Na2HPO4) (Figure 6). In addition, FT-IR analysis revealed a peak at 1100 cm -1 A peak was confirmed (Figure 7). The resulting reaction precursor was then calcined in air at 900°C for 4 hours to obtain a calcined product. X-ray diffraction analysis of the calcined product revealed that the calcined product was a single-phase Na3Zr2Si2PO 12 (Figure 8) In addition, the peak intensity ratio near 2θ=30° and near 2θ=50° was 3.62.

[0090] Comparative Example 2 The reaction precursor obtained by the same method as in Comparative Example 1 was calcined in air at 950°C for 4 hours to obtain a calcined product. The calcined product was then pulverized in a jet mill to obtain a pulverized product. X-ray diffraction analysis of the resulting pulverized product revealed that Na3Zr2Si2PO 12 It contained a different phase, ZrO2.

Claims

1. A method for producing a sodium compound having a NASICON structure and containing at least sodium, zirconium, silicon and phosphorus, comprising the steps of: Contains sodium, zirconium, silicon and phosphorus and has an infrared absorption spectrum of at least 950 to 1050 cm －１ and an absorption peak with a maximum in the range of 1060 to 1150 cm －１ A method for producing a sodium compound having a NASICON structure, comprising calcining a reaction precursor having an absorption peak with a maximum value in the range of 800 to 1100°C.

2. The method for producing a sodium compound having a NASICON structure according to claim 1, characterized in that the reaction precursor is an amorphous reaction precursor.

3. The reaction precursor is A first step of mixing a zirconium source, a silicon source, and phosphoric acid to prepare a mixed slurry; A second step of heat-treating the mixed slurry to obtain a heat-treated slurry; a third step of adding a sodium source to the heat-treated slurry to obtain a sodium-containing heat-treated slurry; A fourth step of wet-grinding the sodium-containing heat-treated slurry; A fifth step of drying the sodium-containing heat-treated slurry after the fourth step; The method for producing a sodium compound having a NASICON structure according to claim 1 or 2, characterized in that the compound is obtained by carrying out the steps of:

4. 3. The method for producing a sodium compound having a NASICON structure according to claim 1 or 2, characterized in that the silicon source is precipitated silica.

5. 4. The method for producing a sodium compound having a NASICON structure according to claim 3, characterized in that in the first step, a surfactant is further added to the mixed slurry.

6. The method for producing a sodium compound having a NASICON structure according to claim 3, characterized in that the sodium source is sodium hydroxide.

7. The method for producing a sodium compound having a NASICON structure according to claim 3, characterized in that the heat treatment temperature in the second step is 50 to 120°C.

8. The method for producing a sodium compound having a NASICON structure according to claim 3, characterized in that the drying in the fifth step is carried out by spray drying.

9. The method for producing a sodium compound having a NASICON structure according to claim 1, characterized in that the sodium compound having a NASICON structure is represented by the following general formula (1): No ｇ Zr ｈ Yes ｉ P ｊ O ｋ (1) (In the formula, g is 2.7≦g≦3.3, h is 1.7≦h≦2.3, i is 1.7≦i≦2.3, j is 0.8≦j≦1.2, and k is 10≦k≦14.)

10. 2. The method for producing a sodium compound having a NASICON structure according to claim 1, characterized in that the reaction precursor further contains an M source having an M element which is a metal element other than sodium and zirconium.

11. The method for producing a sodium compound having a NASICON structure according to claim 10, characterized in that the M source contains one or more elements selected from Mg, Zn, Cu, Fe, Cr, Mn, Ni, V, W, Li, K, Ca, Sr, Ba, Ti, Hf, Nb, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy and Ho.

12. The method for producing a sodium compound having a NASICON structure according to claim 10 or 11, characterized in that in the first step, the M source is further contained in the mixed slurry.

13. The method for producing a sodium compound having a NASICON structure according to claim 1, characterized in that it is used as a solid electrolyte.

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