Sodium compound having nasicon structure

Abstract

Provided is a method by which a sodium compound that has a NASICON structure and has a single phase as observed by x-ray diffraction can be produced in an industrially advantageous manner.　The present invention is a production method for a sodium compound that has a NASICON structure and contains at least sodium, zirconium, silicon, and phosphorus. The production method is characterized by firing a reaction precursor that contains sodium, zirconium, silicon, and phosphorus and has an infrared absorption spectrum that has at least an absorption peak that has a maximum value at 950–1050 cm-1 and an absorption peak that has a maximum value at 1060–1150 cm-1 at 800°C–1100°C.

Description

Sodium compounds having the NASICON structure

[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.

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

[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 of sodium ion conductor having a NASICON structure as a solid electrolyte.

[0004] Patent Document 1 describes a method for hydrolyzing a precursor solution containing sodium, zirconium, silicon, and phosphorus to form a gel, 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 to obtain Na ３ Zr ２ (SiO ４ ) ２ (P.O. ４ A method for synthesizing a solid electrolyte represented by the formula (II) has been proposed.

[0005] JP 2010-15782 A

[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 by which a sodium compound having a NASICON structure and being a single phase as measured by X-ray diffraction can be obtained in an industrially advantageous manner.

[0008] In view of the above-mentioned 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 being single-phase as measured by 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, thereby completing 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, －１ and an absorption peak with a maximum value 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 in which an absorption peak having 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] The present invention (3) also provides the method for producing a sodium compound having a NASICON structure according to (1) or (2), characterized in that the reaction precursor is obtained by carrying out the following steps: 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-pulverizing the sodium-containing heat-treated product slurry; and a fifth step of drying the sodium-containing heat-treated product slurry after the fourth step.

[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 contained in 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 the 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), characterized in that the sodium compound having a NASICON structure is represented by the following general formula (1): ｇ Zr ｈ Si ｉ P ｊ O ｋ (1) (Wherein, 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 that 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 (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 the method for producing a sodium compound having a NASICON structure according to (10) or (11), characterized in that in the first step, the M source is further contained in the mixed slurry.

[0021] The present invention (13) also provides a method for producing the sodium compound having the NASICON structure of (1), which is characterized by being used as a solid electrolyte.

[0022] According to the present invention, it is possible to provide an industrially advantageous method for obtaining a sodium compound having a NASICON structure and being a single phase as measured by X-ray diffraction.

[0023] X-ray diffraction pattern of the reaction precursor obtained in Example 1. FT-IR chart of the reaction precursor obtained in Example 1. X-ray diffraction pattern of the sodium compound having a NASICON structure obtained in Example 1. X-ray diffraction pattern of the sodium compound having a NASICON structure obtained in Example 2. SEM image of the sodium compound having a NASICON structure obtained in Example 2. X-ray diffraction pattern of the reaction precursor obtained in Comparative Example 1. FT-IR chart of the reaction precursor obtained in Comparative Example 1. X-ray diffraction pattern of the sodium compound having a NASICON structure obtained in Comparative Example 1.

[0024] The present invention will be described below 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, which contains sodium, zirconium, silicon, and phosphorus and has an infrared absorption spectrum of at least 950 to 1050 cm －１and an absorption peak with a maximum value in the range of 1060 to 1150 cm －１ The reaction precursor, which exhibits an absorption peak with 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): ｇ Zr ｈ Si ｉ P ｊ O ｋ　　 (1) (Wherein, 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 2.7≦g≦3.3, preferably 2.8≦g≦3.2, from the viewpoint of synthesizing a solid electrolyte having a single-phase NASICON structure in terms of X-ray diffraction. Furthermore, in the general formula (1), h is 1.7≦h≦2.3, preferably 1.8≦h≦2.2, from the viewpoint of synthesizing a solid electrolyte having a single-phase NASICON structure in terms of X-ray diffraction. Furthermore, in the general formula (1), i is 1.7≦i≦2.3, preferably 1.8≦i≦2.2, from the viewpoint of synthesizing a solid electrolyte having a single-phase NASICON structure in terms of X-ray diffraction. In addition, in the general formula (1), j is preferably 0.8≦j≦1.2, and more preferably 0.9≦j≦1.1, 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, k in the general formula (1) is preferably 10≦k≦14, and more 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 The absorption peak (first absorption peak) has a maximum value in the range of 1060 to 1150 cm －１ An absorption peak (second absorption peak) having a maximum value in the range of 950 to 1050 cm is observed. －１Preferably, the range is 960 to 1040 cm －１ The maximum value of the second absorption peak is more preferably in the range of 1060 to 1150 cm －１ Preferably, the wavelength is in the range of 1070 to 1140 cm －１ For example, Fig. 2 shows an FT-IR spectrum 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. In the FT-IR chart of Fig. 2, the maximum value (peak top) is 990 cm －１ The peak (first absorption peak) and the maximum (peak top) are located near 1100 cm －１ A peak (second absorption peak) is observed nearby.

[0027] The reaction precursor is preferably an amorphous reaction precursor. In the present invention, the reaction precursor being amorphous means that in X-ray diffraction analysis, only a broad peak is observed in the range of 2θ=10 to 70°, and no sharp diffraction peak (half width of 1.0° or less) is observed. Therefore, the reaction precursor is preferably an amorphous reaction precursor. ２ HPO ４ ) is not observed in the range of 2θ=31.5 to 32.5° (half-value width is 1.0° or less).

[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 and an absorption peak with a maximum value in the range of 1060 to 1150 cm －１ The method for producing a sodium compound having a NASICON structure of the present invention is characterized by the fact that the reactive precursor exhibiting an absorption peak with a maximum value in the range of 800 to 1100°C is calcined at 800 to 1100°C. That is, 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 reactive precursor containing at least sodium, zirconium, silicon, and phosphorus. Step B: A step of calcining the obtained reactive precursor at 800 to 1100°C.

[0029] (Step A) Step A contains at least 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 value 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 of

[0030] The step A is preferably a step having the following steps: 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-pulverizing the sodium-containing heat-treated product slurry; and a fifth step of drying the wet-pulverized 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 the phosphoric acid in the solvent, thereby preparing 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 inert to the raw materials, and examples thereof include alcohols such as ethanol, propanol, and butanol, and methyl ethyl ketone. In the case of a mixed solvent of water and a hydrophilic organic solvent, the mixing ratio of water to the hydrophilic organic solvent is appropriately selected.

[0033] In the first step, examples of the zirconium source include compounds containing zirconium element, such as zirconium oxide, zirconium hydroxide, and zirconium carbonate. Among these, zirconium hydroxide is preferred from the viewpoint of being a highly reactive reaction precursor. 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 Zr element in the zirconium source to Si element in the silicon source in the mixed slurry is 0.8 to 1.2, preferably 0.9 to 1.1. When the amount of the zirconium source added to the mixed slurry is within the above range, it becomes possible to synthesize a sodium compound having a NASICON structure and being single-phase in terms of X-ray diffraction.

[0035] In the first step, examples of the silicon source include compounds containing silicon, such as precipitated silica and amorphous silica, such as fumed silica. Among these, precipitated silica is preferred from the viewpoints of reactivity and ease of handling. The silicon source may be a single type or a combination of two or more types.

[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 solution of phosphoric acid.

[0037] The amount of phosphoric acid added is an amount that results in a molar ratio (P / Si) of P element in the 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 that has a NASICON structure and is single-phase in terms of X-ray diffraction.

[0038] In the first step, a surfactant may be added to the slurry as needed to form a mixed slurry further containing a surfactant. By including a surfactant, the zirconium source, the silicon source, and the phosphoric acid are 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, and 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 per 100 parts by mass of the silicon source.

[0041] In the first step, the order of adding the zirconium source, silicon source, phosphoric acid, and optionally the surfactant 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 Step 2 are amorphous and no diffraction peaks are detected in X-ray diffraction analysis. Therefore, although the details are not clear, the present inventors speculate that by heat-treating the mixed slurry obtained in Step 1 in Step 2, the phosphoric acid and the zirconium source in the mixed slurry react (see, for example, Japanese Patent No. 6190023), and the resulting 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., preferably 70 to 105° C. When the heat treatment temperature is within the above range, it becomes possible to complete the reaction between the zirconium source and 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 allowing the phosphoric acid and the zirconium source to react with each other.

[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 product slurry obtained in Step 3 are amorphous and no diffraction peaks are detected in X-ray diffraction analysis. Therefore, although the details are not clear, the present inventors speculate that, in Step 3, by adding a sodium source to the heat-treated product slurry obtained in Step 2, the components contained in the heat-treated product slurry, for example, the silicon source and the sodium source, react with each other, and the resulting sodium-containing heat-treated product 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 a single type or a combination of two or more types.

[0050] The sodium source may be added to the heated heat-treated slurry after the second step, or to the heat-treated slurry that has been cooled to around room temperature, preferably 50°C or below, after the second step. However, adding the sodium source to the heat-treated slurry that has been cooled to around room temperature, preferably 45°C or below, after the second step is preferred, as this can prevent an increase in the viscosity of the slurry.

[0051] The amount of the sodium source added is an amount such that the molar ratio of Na in the sodium source to Si in the heat-treated slurry (Na / Si) is 1.2 to 1.8, preferably 1.3 to 1.7. When the amount of the sodium source added is within the above range, it becomes possible to synthesize a sodium compound having a NASICON structure and being 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 allowing the sodium source and the heat-treated slurry to react sufficiently.

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

[0055] In the fourth step, the solids concentration of the sodium-containing heat-treated product slurry to be wet-pulverized is 5 to 40% by mass, preferably 10 to 30% by mass. Having the solids concentration of the sodium-containing heat-treated product slurry within this range ensures good operability and efficient pulverization. Therefore, after performing the third step, the solids concentration of the sodium-containing heat-treated product slurry may be adjusted to the above-mentioned solids concentration, and then the fourth step may be performed.

[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 because it can efficiently obtain fine particles.

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

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

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

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

[0065] In 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 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 moisture absorption by the powder 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 via Step A, a sodium compound having a NASICON structure and being a single phase in terms of X-ray diffraction can be obtained.

[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 set 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 keeping the calcination temperature within the above range, it becomes possible to industrially advantageously obtain a sodium compound having a NASICON structure that is 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. Furthermore, in step B, the fired product obtained in the first firing may be fired multiple times as necessary. Alternatively, in order to homogenize the powder properties, the fired product may be pulverized, remixed, or the like, and then refired.

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

[0071] In step B, if necessary, crushing, grinding, classification, etc. can be carried out 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 Na ３ Zr ２ Si ２ P.O. １２ It is preferable that the crystalline silicon be represented by the formula (I), have a NASICON structure, and be 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, as needed.

[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 may be, 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 a combination of two or more types.

[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 prepare 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 in the silicon source in the slurry is 0.01 to 0.5, preferably 0.01 to 0.3. When the amount of the M source added is within the above range, it becomes possible to synthesize a sodium compound that has a NASICON structure and is a single phase in terms of X-ray diffraction. When two or more types 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 sum of the number of moles of each M element.

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

[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 determined by SEM observation is the average particle size of primary particles obtained from a scanning electron microscope (SEM) photograph, and is determined by randomly extracting 100 primary particles from the scanning electron microscope (SEM) observation, measuring the horizontal Feret 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 20 m ２ When the BET specific surface area is in the above range, it is possible to obtain a dense sintered body.

[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, and 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.

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

[0086] <Evaluation equipment> X-ray diffraction analysis: Rigaku Ultima IV was used. Cu-Kα was used as the radiation source. 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 , Number of accumulations: 256, Measurement wave number range: 400 to 4000 cm －１ The measurement was carried out by the ATR method, and ATR correction and spectrum smoothing processing were carried out.

[0087] (Example 1) <First Step> Zirconium hydroxide (average particle size 5 μm, BET specific surface area 208 m) with a purity of 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 m２ 661.1 g of ammonium hydroxide (89.4% by weight, calculated as silica) and 564.8 g of phosphoric acid (water content 15% by weight) were charged in this order to prepare a mixed slurry (1). <Step 2> Next, the mixed slurry (1) was heated to 80°C at 30°C / h with stirring, held at 80°C for 4 hours, and then allowed to cool to room temperature (25°C) to obtain a heat-treated product slurry (2). The pH of the heat-treated product slurry (2) was 4.1. <Step 3> Next, 2360.0 g of 25% by weight sodium hydroxide was added to the heat-treated product slurry (2) over 20 minutes with stirring to obtain a sodium-containing heat-treated product slurry (3). The pH of the sodium-containing heat-treated product slurry (3) was 13.5. <Step 4> Next, the sodium-containing heat-treated product slurry was supplied to a media-agitation bead mill charged with zirconia beads having a diameter of 0.5 mm, and wet-pulverized. The average particle size of the solids in the sodium-containing heat-treated product slurry after wet pulverization, as determined by laser diffraction / scattering, was 2.1 μm. The pH of the sodium-containing heat-treated product slurry after wet pulverization was 11.4. <Fifth Step> Next, the sodium-containing heat-treated product slurry (3) after wet pulverization was supplied to a spray dryer set at 220°C at a supply 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% based on the solids. X-ray diffraction analysis of the obtained reaction precursor revealed that it was an amorphous composition (Figure 1). Furthermore, FT-IR analysis revealed that the respective －１ and 1110 cm －１ Peaks (first and second absorption peaks) with maximal values ​​were confirmed (FIG. 2). <Step B> Next, the obtained reaction precursor was 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 Na ３ Zr ２ Si ２ P.O. １２ (Figure 3).

[0088] (Example 2) <Steps 1 to 5> 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 fired in the atmosphere at 915°C for 4 hours to obtain a fired product. The fired product was then pulverized in a jet mill to obtain a pulverized product. X-ray diffraction analysis of the obtained pulverized product revealed that the pulverized product was composed of a single-phase Na SiO 2 having a NASICON structure. ３ Zr ２ Si ２ P.O. １２ (Fig. 4). ３ Zr ２ Si ２ P.O. 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) with a purity of 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 / g, purity in terms of silica: 89.4%) 661.1g, sodium triphosphate (Na ３ P.O. ４ ) and 806.1 g of zirconia beads having a diameter of 0.5 mm were charged in this order to prepare a mixed slurry (1). Next, the slurry was supplied to a media-agitated bead mill charged with zirconia beads having a diameter of 0.5 mm, and wet-pulverized. The average particle size of the solid content in the slurry after wet-pulverization, as determined by laser diffraction and scattering, was 2.3 μm. Next, the lithium-containing heat-treated product slurry was supplied to a spray dryer set at 220° C. at a supply rate of 2.4 L / h, and a dried product was obtained. Visual observation 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 that sodium hydrogen phosphate (Na ２ HPO ４ ) was observed (Figure 6). In addition, FT-IR analysis revealed a peak at 1100 cm －１A peak was confirmed at 1000°C (Fig. 7). 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 resulting calcined product revealed that the calcined product was a single-phase Na SiO 2 -based compound without a NASICON structure. ３ Zr ２ Si ２ P.O. １２ The peak intensity ratio between near 2θ=30° and near 2θ=50° was 3.62 (FIG. 8).

[0090] (Comparative Example 2) The reaction precursor obtained in the same manner as in Comparative Example 1 was fired in the air at 950°C for 4 hours to obtain a fired product. The fired product was then pulverized in a jet mill to obtain a pulverized product. X-ray diffraction analysis of the pulverized product revealed that Na ３ Zr ２ Si ２ P.O. １２ Heterogeneous phase ZrO ２ It included:

Claims

1. A method for producing a sodium compound having a NASICON structure and containing at least sodium, zirconium, silicon and phosphorus, comprising: －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. A method for producing a sodium compound having a NASICON structure as described in claim 1 or 2, characterized in that the reaction precursor is obtained by carrying out the following steps: 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 sodium-containing heat-treated product slurry after the fourth step.

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

6. A method for producing a sodium compound having a NASICON structure as described in claim 3, characterized in that the sodium source is sodium hydroxide.

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

8. A method for producing a sodium compound having a NASICON structure as described in 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): 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.) 10. 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. A method for producing a sodium compound having a NASICON structure as described in 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. A method for producing the sodium compound having the NASICON structure described in claim 1, which is used as a solid electrolyte.

Images