A preparation method of sodium tetrafluoroborate

Abstract

The invention belongs to the technical field of new energy batteries, and particularly relates to a method for preparing sodium tetrafluoroborate. The method uses relatively cheap and readily available ammonium fluoride, sodium bicarbonate, and boron trichloride gas as raw materials, wherein ammonium fluoride and sodium bicarbonate are added to an organic solvent and stirred uniformly to obtain a dispersion, boron trichloride gas is introduced, the dispersion is fully reacted, nitrogen is purged from the reaction liquid, and the filtrate is filtered to obtain a filtrate, which is concentrated, crystallized, filtered, washed, and dried to obtain sodium tetrafluoroborate. The method has the advantages of simple process, rapid and thorough reaction, no water by-product, and reduced preparation cost of sodium tetrafluoroborate while achieving a yield and purity equivalent to or even superior to that of existing sodium tetrafluoroborate.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion batteries, and in particular relates to a method for preparing sodium tetrafluoroborate. Background Art

[0002] Sodium-ion batteries have the advantages of abundant resources and low cost. Electrolytes are ionic charge carriers necessary for electrochemical reactions and have an important influence on electrochemical performance. Sodium tetrafluoroborate can be used as the main salt or additive in sodium-ion battery electrolytes and has good oxidation stability under high voltage.

[0003] Although products with high purity can be obtained according to the existing preparation processes of sodium tetrafluoroborate, these preparation processes still have the defect of high preparation cost in terms of the actual situation of industrial production. For example, patent CN202211036289.3 discloses a one-step method for preparing sodium tetrafluoroborate at room temperature: fluorine-boron compounds and sodium salts of oxygen-containing acid radicals are dispersed in a non-aqueous solvent, reacted at room temperature for 10 to 24 hours, solid-liquid separation is performed, and the solvent in the resulting solution is evaporated to obtain a high-purity solid product, sodium tetrafluoroborate. This method has high raw material (fluorine-boron compound) cost and long reaction time, which is not conducive to industrialization; patent CN20098 Patent 0159908.4 provides a method for continuously manufacturing sodium tetrafluoroborate, in which boron trifluoride gas reacts with fluoride in an organic solvent to prepare sodium tetrafluoroborate. The raw material boron trifluoride is expensive and difficult to react completely after complexation with the solvent, which affects product quality and increases the cost of subsequent purification. Patent CN201610406229.4 discloses a method for preparing lithium tetrafluoroborate, in which a compound containing a weak acid radical lithium salt and BF3 is mixed uniformly in a solvent in a certain ratio for reaction, solid-liquid separation, concentration, crystallization, and purification are performed to obtain a LiBF4 product. This method also has the problem that the raw material boron trifluoride is expensive and difficult to react completely after complexation with the solvent.

[0004] In general, although the existing sodium tetrafluoroborate preparation process obtains a high-purity product, the selection of expensive raw materials, the long production cycle, and the increased energy consumption caused by the more complicated purification operations all increase the preparation cost to varying degrees, affecting the company's profits. Summary of the Invention

[0005] In order to overcome the technical defects of the existing technology, the present invention uses relatively cheap and easily available ammonium fluoride, sodium bicarbonate, and boron trichloride gas as raw materials, and designs a technical solution based on a preparation mechanism different from the existing one, so as to synergistically achieve the purpose of reducing the preparation cost of sodium tetrafluoroborate, thereby reducing the production cost of the enterprise and increasing the enterprise's profits.

[0006] To achieve the above object, the present invention adopts a technical solution: a method for preparing sodium tetrafluoroborate, comprising the following steps: adding ammonium fluoride and sodium bicarbonate to an organic solvent and stirring uniformly to obtain a dispersion liquid, introducing boron trichloride gas, reacting at 15°C to 30°C for 0.6 to 1 hour, and then reacting at a constant temperature under ultrasonic conditions for 1 to 1.7 hours to obtain a reaction liquid; purging the reaction liquid with nitrogen, filtering to obtain a filtrate, concentrating the filtrate for crystallization, filtering, washing, and drying in a protective atmosphere to obtain sodium tetrafluoroborate; wherein the purity of ammonium fluoride and sodium bicarbonate is not less than 99.9%, and the moisture content is not higher than 0.002%; the purity of boron trichloride is not less than 99.9%; and the molar ratio of ammonium fluoride, sodium bicarbonate, and boron trichloride is 4.05 to 4.1:1:1.

[0007] The reaction principle of the present invention is:

[0008] 4NH4F+NaHCO3+BCl3=NaBF4+3NH4Cl+NH4HCO3

[0009] Preferably, the organic solvent is one or a mixture of dichloromethane, methanol, ethanol, n-propanol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetone and acetonitrile, and the water content of the organic solvent is less than 5 ppm.

[0010] Preferably, the temperature during concentration is ≤55° C.; after concentration and crystallization, the filter cake is washed with dichloromethane.

[0011] Preferably, the protective gas is nitrogen, and the drying temperature is 90°C to 95°C.

[0012] The beneficial effects achieved by the present invention are:

[0013] The present invention comprehensively addresses both raw material costs and process energy consumption, synthesizes sodium tetrafluoroborate through a one-step process, has a simple process, a rapid and thorough reaction, and produces no water by-product. While achieving a yield of more than 95% and a purity of more than 99.9% that is equivalent to or even superior to existing sodium tetrafluoroborate, the preparation cost of sodium tetrafluoroborate is reduced, providing a technical basis for the sustainable development of enterprises. DETAILED DESCRIPTION

[0014] The present invention will be further described below through specific examples.

[0015] Example 1

[0016] At 20°C, 151.7 g, i.e. 4.1 mol, of ammonium fluoride and 84 g of sodium bicarbonate were added to 300 g of dimethyl carbonate containing 5 ppm of water, and stirred thoroughly to obtain a dispersion. 117.3 g, i.e. 1 mol, of boron trichloride gas was introduced for 0.6 h. The mixture was kept at 20°C under ultrasonic conditions for 1.5 h to obtain a reaction solution. The residual boron trichloride gas was purged with nitrogen for 0.5 h; the mixture was filtered, and the filtrate was concentrated under reduced pressure at 50°C, filtered, and the filter cake was washed with 600 g of dichloromethane and dried at 95°C under nitrogen to obtain 105.27 g of sodium tetrafluoroborate with a purity of 99.92% and a yield of 95.8%.

[0017] Example 2

[0018] At 30°C, 149.85g, i.e. 4.05mol, of ammonium fluoride and 84g of sodium bicarbonate were added to 280g of dimethyl carbonate containing 2ppm of water, and stirred thoroughly to obtain a dispersion. 117.3g, i.e. 1mol of boron trichloride gas was introduced for 1h. The reaction was carried out at 30°C under ultrasonic conditions for 1h to obtain a reaction solution. The residual boron trichloride gas was purged with nitrogen for 0.3h; the reaction solution was filtered, and the filtrate was concentrated under reduced pressure at 45°C, filtered, and the filter cake was washed with 800g of dichloromethane and dried at 90°C under nitrogen to obtain 105.69g of sodium tetrafluoroborate with a purity of 99.94% and a yield of 96.2%.

[0019] Example 3

[0020] At 15°C, 151.7 g, i.e. 4.1 mol, of ammonium fluoride and 84 g of sodium bicarbonate were added to 260 g of dimethyl carbonate containing 5 ppm of water and stirred thoroughly to obtain a dispersion. 117.3 g, i.e. 1 mol, of boron trichloride gas was introduced for 0.5 h. The mixture was kept at 15°C under ultrasonic conditions for 1.7 h to obtain a reaction solution. The residual boron trichloride gas was purged with nitrogen for 0.6 h. The mixture was filtered, and the filtrate was concentrated under reduced pressure at 50°C, filtered, and the filter cake was washed with 700 g of dichloromethane and dried at 90°C under nitrogen to obtain 104.5 g of sodium tetrafluoroborate with a purity of 99.9% and a yield of 95.1%.

[0021] Comparative Example 1

[0022] At 15°C, 148 g, i.e. 4 mol, of ammonium fluoride and 84 g of sodium bicarbonate were added to 260 g of dimethyl carbonate containing 5 ppm of water, and stirred thoroughly to obtain a dispersion. 120.8 g, i.e. 1.03 mol, of boron trichloride gas was introduced for 0.5 h. The reaction was carried out at a constant temperature under ultrasonic conditions for 1.7 h to obtain a reaction solution. The residual boron trichloride gas was purged with nitrogen for 0.6 h; the mixture was filtered, and the filtrate was concentrated under reduced pressure at 50°C, filtered, and the filter cake was washed with 700 g of dichloromethane and dried at 90°C under nitrogen protection to obtain 100.46 g of sodium tetrafluoroborate with a purity of 98.8% and a yield of 90.4%.

[0023] The above specific embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing sodium tetrafluoroborate, characterized in that: The following steps are involved: Ammonium fluoride and sodium bicarbonate are added to an organic solvent and stirred evenly to obtain a dispersion liquid, boron trichloride gas is introduced, and the mixture is reacted at 15°C to 30°C for 0.6 to 1 hour, and then the mixture is reacted at a constant temperature for 1 to 1.7 hours under ultrasonic conditions to obtain a reaction liquid; the reaction liquid is purged with nitrogen and filtered to obtain a filtrate, and the filtrate is concentrated and crystallized, filtered, washed, and dried in a protective atmosphere to obtain sodium tetrafluoroborate; wherein the purity of ammonium fluoride and sodium bicarbonate is not less than 99.9%, and the moisture content is not higher than 0.002%; the purity of boron trichloride is not less than 99.9%; and the molar ratio of ammonium fluoride, sodium bicarbonate, and boron trichloride is 4.05 to 4.1:1:

1.

2. The preparation method according to claim 1, characterized in that The organic solvent is selected from one or a mixture of dichloromethane, methanol, ethanol, n-propanol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, methyl acetate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetone and acetonitrile, and the water content of the organic solvent is less than 5ppm.

3. The preparation method according to any one of claims 1 to 2, characterized in that The temperature during concentration is ≤55°C; after concentration and crystallization, the filter cake is washed with dichloromethane.

4. The preparation method according to any one of claims 1 to 2, characterized in that The protective gas is nitrogen and the drying temperature is 90℃~95℃.