Method for purifying mixture of sodium tetrafluoroborate and sodium difluoro (oxalato) borate

Abstract

The invention discloses a method for purifying a mixture of sodium tetrafluoroborate and sodium difluoro (oxalato) borate, which comprises the following steps of: mixing the mixture of sodium tetrafluoroborate and sodium difluoro (oxalato) borate with an ionic liquid by taking the ionic liquid as a purification reagent, dissolving sodium tetrafluoroborate in the ionic liquid, filtering and drying to obtain solid sodium difluoro (oxalato) borate; according to the method, high-purity solid sodium difluoro (oxalato) borate can be obtained, the solid sodium difluoro (oxalato) borate is very suitable for being used as an electrolyte additive of a liquid sodium-ion battery, the purification process is simple and efficient, and the yield is high.

Description

Technical Field

[0001] The invention belongs to the field of battery electrolyte additives, and in particular relates to a method for purifying a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate. Background Art

[0002] The key component of liquid sodium-ion batteries is the electrolyte. Like traditional lithium-ion batteries, the addition of additives can effectively improve the performance of liquid sodium-ion batteries. Electrolyte sodium salts are key electrolyte additives for liquid sodium-ion batteries. Currently, commonly used electrolyte sodium salts include sodium hexafluorophosphate, sodium perchlorate, and sodium bis(trifluoromethanesulfonylimide). However, using any of them alone will have certain defects, such as sodium hexafluorophosphate is easily hydrolyzed, and sodium bis(trifluoromethanesulfonylimide is easy to corrode aluminum foil, which is difficult to meet the application of high-performance sodium-ion batteries.

[0003] Sodium difluorooxalatoborate is considered by current technology to be an ideal sodium salt for electrolytes because it is compatible with a variety of solvents, and the electrolytes prepared have good compatibility, a wide electrochemical window, and good cycle stability, which can significantly enhance the electrochemical stability of the electrolyte. However, the existing process for producing sodium difluorooxalatoborate uses sodium oxalate and a boron trifluoride complex as raw materials for reaction and purification to obtain sodium difluorooxalatoborate. The process does not use a strong acidic additive, and is an environmentally friendly production method; but the disadvantage of this method is that there will be a large amount of sodium tetrafluoroborate in the synthesized sodium difluorooxalatoborate product, which is difficult to completely separate by extraction or crystallization.

[0004] Therefore, the applicant hopes to seek technical solutions to solve the above technical problems. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for purifying a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate, which can obtain high-purity solid sodium difluorooxalatoborate, which is very suitable as an electrolyte additive for liquid sodium ion batteries, and the purification process of the present invention is simple, efficient, and has a high yield.

[0006] The technical solution adopted by the present invention is as follows: A method for purifying a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate comprises the following steps: using an ionic liquid as a purification reagent, mixing the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate with the ionic liquid, dissolving the sodium tetrafluoroborate in the ionic liquid, and obtaining solid sodium difluorooxalatoborate after filtering and drying.

[0007] Preferably, the ionic liquid comprises any one of the following structural formulas: , , . Preferably, the method comprises the following steps: S1), mixing a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate with an ionic liquid, wherein during the mixing process, the mixture is heated and stirred so that the sodium tetrafluoroborate is dissolved in the ionic liquid to obtain a solid-liquid mixture; S2), filtering and separating the solid-liquid mixture to obtain a filtered solid, and then drying the filtered solid to obtain solid sodium difluorooxalatoborate.

[0008] Preferably, the mass ratio of the ionic liquid to the sodium tetrafluoroborate is in the range of 1-5:1, preferably 1-2:1.

[0009] Preferably, during the mixing process, the mixed material is heated, wherein the heating temperature range is set at 40-60°C, preferably 50-60°C.

[0010] Preferably, during the mixing process, the mixed material is stirred, wherein the stirring time is 1.0-4.0 h, preferably 1.0-2.0 h.

[0011] Preferably, in the step S2), the filtered solid is rinsed with water before being dried.

[0012] Preferably, the mass ratio of the water to the filtered solid is in the range of 2-5:1, preferably 2-3:1.

[0013] Preferably, in the step S2), the filtered solid is dried by vacuum rotary evaporation.

[0014] Preferably, the vacuum degree of the vacuum rotary evaporation ranges from -0.06 KPaG to -0.12 KPaG; the temperature of the vacuum rotary evaporation is 120-150°C, preferably 140-150°C; and the drying time is 24-72h, preferably 24-48h.

[0015] Preferably, the yield of the solid sodium difluorooxalatoborate is not less than 98%, and the purity is not less than 99%.

[0016] It should be particularly noted that the "mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate" involved in the present application can be a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate in any proportion. Since the sodium difluorooxalatoborate product obtained by the environmentally friendly process route adopted by the sodium salt of the electrolyte (using sodium oxalate and boron trifluoride complex as raw materials for reaction and purification to obtain sodium difluorooxalatoborate) contains a large amount of sodium tetrafluoroborate, it is difficult to completely separate it by extraction or crystallization. Therefore, it is particularly suitable to use the purification method provided by the present invention to purify the sodium difluorooxalatoborate product.

[0017] The present invention adopts ionic liquid as a purification reagent, mixes a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate with the ionic liquid, so that the sodium tetrafluoroborate is dissolved in the ionic liquid, and then the solid-liquid mixture is filtered and dried to obtain high-purity solid sodium difluorooxalatoborate, which is very suitable as an electrolyte additive for liquid sodium ion batteries. The purification process of the present invention is simple, efficient, and has a high yield. DETAILED DESCRIPTION

[0018] This embodiment provides a method for purifying a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate, using an ionic liquid as a purification reagent, mixing the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate with the ionic liquid, dissolving the sodium tetrafluoroborate in the ionic liquid, and obtaining solid sodium difluorooxalatoborate after filtering and drying.

[0019] Preferably, in this embodiment, the ionic liquid comprises any one of the following structural formulas: , , ; Specifically and preferably, 1-hexyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium tetrafluoroborate or 1-allyl-3-ethylimidazolium tetrafluoroborate can be used as the ionic liquid in the embodiments of the present application.

[0020] Preferably, in this embodiment, the method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate comprises the following steps: S1), mixing a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate with an ionic liquid, wherein during the mixing process, the mixture is heated and stirred so that the sodium tetrafluoroborate is dissolved in the ionic liquid to obtain a solid-liquid mixture; preferably, in this embodiment, the mass ratio of the ionic liquid to the sodium tetrafluoroborate is in the range of 1-5:1, preferably 1-2:1; during the mixing process, the mixture is heated and stirred, wherein the heating temperature range is set at 40-60°C, more preferably 50-60°C; the stirring time is 1.0-4.0h, more preferably 1.0-2.0h; S2), filtering and separating the solid-liquid mixture to obtain a filtered solid, and then drying the filtered solid to obtain solid sodium difluorooxalate borate; preferably, in this step S2), the filtered solid is pre-rinsed with water before drying the filtered solid; preferably, the mass ratio of water to the filtered solid is in the range of 2-5:1, more preferably 2-3:1; preferably, in this step S2), the filtered solid is dried by vacuum rotary evaporation; preferably, the vacuum degree of vacuum rotary evaporation is in the range of -0.06KPaG to -0.12KPaG, more preferably -0.09KPaG to -0.099KPaG; the temperature of vacuum rotary evaporation is 120-150°C, more preferably 140-150°C; the drying time is 24-72h, more preferably 24-48h.

[0021] Preferably, in this embodiment, the yield of the obtained solid sodium difluorooxalatoborate is not less than 98%, and the purity is not less than 99%.

[0022] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0023] On the basis of the above implementation contents, in order to verify the technical effects achieved by this application, this application further proposes the following embodiments: It should be noted that the sources of the reagent raw materials used in the following examples are as follows: 1-Hexyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate were purchased from MacLean Reagent Co., Ltd.; 1-allyl-3-ethylimidazolium tetrafluoroborate was purchased from Wuhan Smac Biotechnology Co., Ltd.; Sodium tetrafluoroborate and sodium difluorooxalatoborate were purchased from MacLean Reagent Co., Ltd.; Unless otherwise specified, other reagents and raw materials are common commercially available products.

[0024] The testing method of the following embodiments is as follows: The product structure was characterized by nuclear magnetic resonance (NMR) using a Bruker AVANCE II 500 MHz spectrometer.

[0025] Example 1: A mixture containing 10g of sodium tetrafluoroborate and 5g of sodium difluorooxalatoborate was added to 20g of 1-hexyl-3-methylimidazole tetrafluoroborate, and the mixture was heated and stirred at a temperature of 55°C for 1h, and 7.21g of filtered solid was obtained by filtration; then 14.5g of deionized water was added to rinse the filtered solid; then vacuum rotary evaporation was performed at -0.095KPaG and 140°C for 24h to obtain 4.92g of solid, the yield of sodium difluorooxalatoborate was 98.4%, the purity of sodium difluorooxalatoborate was 99.9%, and the product structure analysis was as follows: Product structure characterization: 19F NMR (d-DMSO): δ -150.03 (d, 2F); 11B NMR (d-DMSO): δ 1.98 (s, 1F).

[0026] Example 2: A mixture containing 5 g of sodium tetrafluoroborate and 10 g of sodium difluorooxalatoborate was added to 10 g of 1-ethyl-3-methylimidazole tetrafluoroborate, heated and stirred at 60 ° C for 2 h, and filtered to obtain 13.6 g of filtered solid; then 50 g of deionized water was added to rinse the filtered solid; then vacuum rotary evaporation was performed at -0.095 KPaG and 150 ° C for 48 h to obtain 9.91 g of solid, the yield of sodium difluorooxalatoborate was 99.1%, the purity of sodium difluorooxalatoborate was 99.8%, and the product structure analysis was as follows: Product structure characterization: 19F NMR (d-DMSO): δ -150.03 (d, 2F); 11B NMR (d-DMSO): δ 1.98 (s, 1F).

[0027] Example 3: A mixture containing 10 g of sodium tetrafluoroborate and 10 g of sodium difluorooxalatoborate was added to 15 g of 1-allyl-3-ethylimidazole tetrafluoroborate, and the mixture was heated and stirred at 55° C. for 1.5 h, and 14.2 g of a filtered solid was obtained by filtration; then 35 g of deionized water was added to rinse the filtered solid, and then vacuum rotary drying was performed at -0.095 KPaG and 150° C. for 48 h to obtain 9.90 g of a solid, the yield of sodium difluorooxalatoborate was 99.0%, and the purity of sodium difluorooxalatoborate was 99.8%.

[0028] Product structure characterization: 19F NMR (d-DMSO): δ -150.03 (d, 2F); 11B NMR (d-DMSO): δ 1.98 (s, 1F).

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0030] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for purifying a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate, characterized in that: The ionic liquid is used as a purification reagent, and a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate is mixed with the ionic liquid, wherein the sodium tetrafluoroborate is dissolved in the ionic liquid, and solid sodium difluorooxalatoborate is obtained after filtering and drying.

2. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 1, characterized in that: The ionic liquid includes any one of the following structural formulas: 、 、 。 3. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 1, characterized in that: The steps are as follows: S1), mixing a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate with an ionic liquid, wherein during the mixing process, the mixture is heated and stirred so that the sodium tetrafluoroborate is dissolved in the ionic liquid to obtain a solid-liquid mixture; S2), filtering and separating the solid-liquid mixture to obtain a filtered solid, and then drying the filtered solid to obtain solid sodium difluorooxalatoborate.

4. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 1, 2 or 3, characterized in that: The mass ratio of the ionic liquid to the sodium tetrafluoroborate is in the range of 1-5:1, preferably 1-2:

1.

5. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 1, 2 or 3, characterized in that: During the mixing process, the mixed material is heated, wherein the heating temperature range is set at 40-60°C, preferably 50-60°C.

6. A method for purifying a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 1, 2 or 3, characterized in that: During the mixing process, the mixed material is stirred, wherein the stirring time is 1.0-4.0 hours, preferably 1.0-2.0 hours.

7. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 3, characterized in that: In the step S2), the filtered solid is rinsed with water before being dried.

8. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 6, characterized in that: The mass ratio of the water to the filtered solid is in the range of 2-5:1, preferably 2-3:

1.

9. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 3, characterized in that: In the step S2), the filtered solid is dried by vacuum rotary evaporation.

10. The method for purifying the mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 8, characterized in that: The vacuum degree of the vacuum rotary evaporation ranges from -0.06 KPaG to -0.12 KPaG; the temperature of the vacuum rotary evaporation is 120-150°C, preferably 140-150°C; and the drying time is 24-72h, preferably 24-48h.

11. A method for purifying a mixture of sodium tetrafluoroborate and sodium difluorooxalatoborate according to claim 1, 2 or 3, characterized in that: The yield of the solid sodium difluorooxalatoborate is not less than 98%, and the purity is not less than 99%.

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