Preparation method of tetrafluoroborate

Abstract

The invention relates to the technical field of battery electrolytes, and the embodiment of the invention discloses a preparation method of tetrafluoroborate, and the method comprises the following steps: introducing excessive boron trifluoride into a lithium fluoride solution to react to generate lithium tetrafluoroborate, and obtaining a first reaction solution; adding sodium fluoride into the first reaction solution to obtain a second reaction solution containing sodium tetrafluoroborate; filtering the second reaction liquid to obtain a sodium tetrafluoroborate solid and filtrate; obtaining a lithium tetrafluoroborate solid based on the filtrate; excessive boron trifluoride is adopted to react with lithium fluoride, the situation that fluorine ions in the product exceed the standard due to lithium fluoride residues caused by the fact that lithium fluoride of residual micro powder is difficult to filter can be avoided, sodium fluoride is added to react with excessive residual boron trifluoride after the excessive boron trifluoride reacts with lithium fluoride, the situation that the acid value and moisture of the product exceed the standard is avoided, and the product quality is improved. Sodium fluoride is easy to remove through subsequent filtration, and finally high-purity lithium tetrafluoroborate and sodium tetrafluoroborate are obtained.

Description

Technical Field

[0001] The present application relates to the technical field of battery electrolytes, and in particular to a method for preparing tetrafluoroborate. Background Art

[0002] High-purity tetrafluoroborate has the advantages of low moisture, low temperature sensitivity and good safety performance in the application of electrolytes in lithium batteries or sodium batteries. At present, the preparation processes of tetrafluoroborate include aqueous solution method, gas-solid reaction method and non-aqueous solution method. Since tetrafluoroborate is extremely easy to absorb water, for example, in the process of preparing lithium tetrafluoroborate by aqueous solution method, lithium tetrafluoroborate will appear in the form of monohydrate and needs to be dehydrated at about 200°C. Heating at about 200°C will cause the lithium tetrafluoroborate salt to decompose, which will cause the battery cycle performance to decrease when used as an electrolyte material. Therefore, the aqueous solution method is not suitable for the preparation of battery-grade products. The gas-solid reaction method such as solid-gas contact method has relatively high requirements for equipment and preparation process. The tetrafluoroborate generated by the reaction is wrapped on the surface of the solid raw material fluoride salt, which is not conducive to the in-depth reaction, uneven reaction and low production efficiency.

[0003] The non-aqueous solution method usually uses high-purity fluoride salt and boron trifluoride as raw materials to react in an organic solution. It has low requirements for production operations and equipment, high yield, and is suitable for large-scale production. For example, CN110272056A, CN105293512A, etc. mix lithium fluoride and boron trifluoride in an organic solvent to react to generate lithium tetrafluoroborate, and then obtain lithium tetrafluoroborate crystals through steps such as concentration and crystallization. However, lithium fluoride has low solubility in organic solvents, and organic solvents are easy to form suspensions (slurries), while micro-powdered lithium fluoride is difficult to filter, which makes it difficult to circulate organic solvents containing lithium fluoride, and the production process is difficult to be continuous. Moreover, even a trace amount of lithium fluoride residue will cause the fluoride ions in the product to exceed the standard, making it difficult to achieve a high-purity product. In CN102803142A, a slightly excessive amount of boron trifluoride gas is introduced so that the tetrafluoroborate solution can be circulated in the production system. However, excessive boron trifluoride gas often causes the acid value, moisture, etc. of the product to exceed the standard, and still does not meet the purity requirements of high-quality tetrafluoroborate. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a method for preparing tetrafluoroborate to solve the problem that the acid value and water content of the product exceed the standard when preparing tetrafluoroborate in a non-aqueous solution, and the residual lithium fluoride causes the fluoride ion in the product to exceed the standard.

[0005] Specifically, the present application provides a method for preparing tetrafluoroborate, the method comprising: Passing an excess amount of boron trifluoride into a lithium fluoride solution to react and generate lithium tetrafluoroborate to obtain a first reaction solution; adding sodium fluoride to the first reaction solution to obtain a second reaction solution containing sodium tetrafluoroborate; Filtering the second reaction liquid to obtain sodium tetrafluoroborate solid and filtrate; Lithium tetrafluoroborate solid was obtained based on the filtrate.

[0006] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, obtaining lithium tetrafluoroborate solid based on the filtrate comprises: The filtrate is concentrated and then a poor solvent is added to obtain lithium tetrafluoroborate solid.

[0007] In the above embodiment of the method for preparing tetrafluoroborate, the poor solvent is selected from at least one of toluene, dichloromethane, dichloroethane, trichloropropane, tetrachloroethane, xylene and isopropyl ether.

[0008] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, a poor solvent is added to the second filtrate, the temperature is lowered to 0-10° C., filtered, and vacuum dried to obtain lithium tetrafluoroborate solid.

[0009] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, the solvent in the lithium fluoride solution is selected from at least one of ethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0010] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, the molar ratio of lithium fluoride to boron trifluoride is 1:(1.1-2).

[0011] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, the ratio of the molar difference between the boron trifluoride and the lithium fluoride to the molar amount of the sodium fluoride is 1:(1-2), preferably 1:(1-1.2), and further preferably 1:(1-1.1).

[0012] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, the reaction temperature of excess boron trifluoride and lithium fluoride solution is 20-60°C.

[0013] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, after an excess amount of boron trifluoride is introduced into a lithium fluoride solution to react and generate lithium tetrafluoroborate, the method further comprises: keeping the temperature for 1 to 6 hours.

[0014] In the above-mentioned embodiment of the method for preparing tetrafluoroborate, sodium fluoride is added to the first reaction solution, and the reaction is carried out by heat preservation for 0.5-6 hours, and the temperature is lowered to 20-25° C. and then filtered to obtain a filtrate.

[0015] One or more of the above embodiments of the present application have at least one or more of the following beneficial effects: using excess boron trifluoride to react with lithium fluoride can avoid the problem that the remaining micro-powdered lithium fluoride is difficult to filter and the problem that the fluoride ions in the product exceed the standard due to the residual lithium fluoride can be avoided; adding sodium fluoride to react with the excess remaining boron trifluoride after the excess boron trifluoride reacts with lithium fluoride can avoid the acid value and moisture content of the product exceeding the standard, and the excess sodium fluoride can be easily removed by filtering later, so that high-purity lithium tetrafluoroborate and sodium tetrafluoroborate are finally obtained.

[0016] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. DETAILED DESCRIPTION

[0017] Some embodiments of the present application are described below. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the protection scope of the present application.

[0018] As described in the background technology, the current preparation methods of tetrafluoroborate include aqueous solution method, gas-solid reaction method and non-aqueous solution method, among which the gas-solid reaction method has high requirements for equipment and preparation operation, and it is difficult to achieve large-scale production. In the preparation process of the aqueous solution method, due to the extremely easy water absorption of tetrafluoroborate, it is difficult to dry and remove water. After being applied to the battery, the performance of the battery is poor, and the yield is not high. Therefore, the non-aqueous solution method with low requirements for production operation and equipment and high yield is widely used. In the process of preparing tetrafluoroborate by the current non-aqueous solution method, in order to ensure that the raw materials are fully reacted and the yield is improved, the amount of a certain raw material is often increased. For example, when preparing lithium tetrafluoroborate, an excess of boron trifluoride gas is usually introduced into an organic solvent containing lithium fluoride, but an excess of boron trifluoride gas will cause the acid value, moisture, etc. of the product to exceed the standard, and the micro-powdered lithium fluoride is difficult to filter, and an excess of lithium fluoride will also cause the fluoride ion in the product to exceed the standard.

[0019] In order to solve the above problems, the present application creatively proposes a method for preparing tetrafluoroborate, firstly, an excess of boron trifluoride is reacted with lithium fluoride, which can avoid the problem that the remaining micro-powdered lithium fluoride is difficult to filter and the residual lithium fluoride causes the fluoride ion in the product to exceed the standard, and then sodium fluoride is added after the reaction of boron trifluoride and lithium fluoride to react with the excess remaining boron trifluoride, so as to avoid the acid value and moisture content of the product exceeding the standard, and the sodium fluoride is easily removed by filtration later, so as to finally obtain high-purity lithium tetrafluoroborate and sodium tetrafluoroborate at the same time.

[0020] The present application will be described in detail below through specific embodiments.

[0021] Specifically, the present invention provides a method for preparing tetrafluoroborate, the method comprising: S1. Excessive boron trifluoride is introduced into a lithium fluoride solution to react and generate lithium tetrafluoroborate, thereby obtaining a first reaction solution.

[0022] S2. Add sodium fluoride to the first reaction solution to obtain a second reaction solution containing sodium tetrafluoroborate.

[0023] S3. Filter the second reaction solution to obtain sodium tetrafluoroborate solid and filtrate.

[0024] S4. Obtain lithium tetrafluoroborate solid based on the filtrate.

[0025] The use of excess boron trifluoride to react with lithium fluoride can avoid the problem of residual micro-powdered lithium fluoride being difficult to filter and residual lithium fluoride causing excessive fluoride ions in the product. After the reaction of boron trifluoride and lithium fluoride, sodium fluoride is added to react with the excess remaining boron trifluoride to avoid excessive acid value and water content of the product, and finally obtain high-purity lithium tetrafluoroborate and sodium tetrafluoroborate at the same time. The purification of sodium tetrafluoroborate can be obtained by dissolving, filtering and removing sodium fluoride, and then recrystallizing.

[0026] In S2 of the present application, sodium fluoride is added to consume the boron trifluoride remaining after the reaction with lithium fluoride, thereby avoiding excessive boron trifluoride causing the acid value, moisture content, etc. of the product to exceed the standard. In some embodiments of the present application, step S4 includes: The filtrate was concentrated and then a poor solvent was added to obtain lithium tetrafluoroborate as a solid.

[0027] The term "poor solvent" refers to a solvent with a weak solubility for the solute. Lithium tetrafluoroborate has a low solubility in a poor solvent and has a weak intermolecular interaction with the solvent, so that lithium tetrafluoroborate can be crystallized. By selecting a suitable poor solvent, good lithium tetrafluoroborate crystals can be obtained while keeping impurities in solution.

[0028] In some embodiments of the present application, the poor solvent is selected from at least one of toluene, dichloromethane, dichloroethane, trichloropropane, tetrachloroethane, xylene, and isopropyl ether. The solubility of lithium tetrafluoroborate in toluene, dichloromethane, dichloroethane, trichloropropane, tetrachloroethane, xylene, and isopropyl ether is relatively low.

[0029] In some embodiments of the present application, after adding a poor solvent to the second filtrate, the temperature is cooled to 0-10°C for filtration, and vacuum dried to obtain lithium tetrafluoroborate solid. Optionally, the temperature is cooled to 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, or any temperature within the above temperature range.

[0030] In some embodiments of the present application, the solvent in the lithium fluoride solution is selected from at least one of ethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0031] There is a great difference in the solubility of sodium tetrafluoroborate and lithium tetrafluoroborate in different solvents. Lithium tetrafluoroborate has very good solubility in ethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Subsequent crystallization requires the addition of poor solvents such as toluene, dichloromethane, dichloroethylene, trichloropropane, tetrachloroethane, xylene, and isopropyl ether to crystallize. Sodium tetrafluoroborate is insoluble in ethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. The reaction solvent of lithium fluoride and boron trifluoride is selected from at least one of ethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. After sodium fluoride is added to react to generate sodium tetrafluoroborate, sodium tetrafluoroborate can be precipitated first, and then at least one of poor solvents such as toluene, dichloromethane, dichloroethane, trichloropropane, tetrachloroethane, xylene, and isopropyl ether is added to precipitate lithium tetrafluoroborate, so that high-purity lithium tetrafluoroborate crystals can be obtained.

[0032] In some embodiments of the present application, the molar ratio of lithium fluoride to boron trifluoride is 1:(1.1-2).

[0033] The amount of boron trifluoride is excessive to maximize the reaction and consumption of lithium fluoride, thereby reducing the residual amount of lithium fluoride in the form of fine powder that is difficult to filter.

[0034] In some embodiments of the present application, the sodium fluoride added is used to consume excess boron trifluoride, and the molar amount of sodium fluoride should be greater than or equal to the molar difference between boron trifluoride and lithium fluoride, and the molar difference between boron trifluoride and lithium fluoride refers to the molar amount of boron trifluoride minus the molar amount of lithium fluoride. Specifically, the ratio of the molar amount of boron trifluoride minus the molar amount of lithium fluoride to the molar amount of sodium fluoride is 1: (1-2). However, in order to reduce unnecessary waste and obtain a better yield of lithium tetrafluoroborate, the input amount of sodium fluoride should not be too large. The above ratio range is preferably 1: (1-1.2), and further preferably 1: (1-1.1). For example, it can be 1: 1.01, 1: 1.02, 1: 1.03, 1: 1.04, 1: 1.05, 1: 1.06, 1: 1.07, 1: 1.08, 1: 1.09, 1: 1, 1: 1.1, 1: 1.12, 1: 1.13, 1: 1.14, 1: 1.15, 1: 1.16, 1: 1.17, 1: 1.18, 1: 1.19, 1: 1.2, or any value within the above range.

[0035] In some embodiments of the present application, the reaction temperature of excess boron trifluoride and lithium fluoride solution is 20-60° C. Optionally, the reaction temperature of excess boron trifluoride and lithium fluoride solution can be 60° C., 58° C., 55° C., 50° C., 45° C., 40° C., 38° C., 35° C., 30° C., 28° C., 25° C., 20° C., or any temperature value within the above temperature range.

[0036] In some embodiments of the present application, after an excess of boron trifluoride is introduced into a lithium fluoride solution to react and generate lithium tetrafluoroborate, the solution is kept warm for 1 to 6 hours. Optionally, the solution is kept warm for 1 hour, 1.5 hours, 2 hours, 3 hours, 3 hours, 4 hours, 5 hours, 6 hours, or any time value within the above time range.

[0037] In some embodiments of the present application, after adding sodium fluoride to the first reaction solution, the method further comprises: Keep the reaction warm for 0.5-6h, then cool to 20-25℃.

[0038] Optionally, the reaction is kept warm for 0.5h, 1.5h, 2h, 3h, 4h, 5h, 6h, or any time value within the above time range. The temperature is lowered to 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, or any temperature value within the above temperature range.

[0039] The present application is further described in detail below in conjunction with the embodiments. It should be noted that the following embodiments are only used to illustrate the present application and are not used to limit the scope of protection claimed in the present application, and cannot be understood as limiting the scope of protection of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the contents of the present application above still belong to the scope of protection of the present application.

[0040] In the following examples, the reagents, materials and instruments used are all commercially available products and can be purchased unless otherwise specified.

[0041] Embodiment 1: 25.94g (1.0mol) of lithium fluoride was added to 500g of acetonitrile solution, the temperature was controlled at 50-60°C, 74.59g (1.1mol) of boron trifluoride was introduced, and the solution was passed through for about 1 hour. After the solution was passed through, the solution was kept warm at 50-60°C for 1 hour. 4.20g of sodium fluoride (0.1mol) was added, and the solution was kept warm for half an hour and then cooled to 20-25°C for filtration. The filter cake was rinsed with acetonitrile and then vacuum dried to obtain 10.87g of sodium tetrafluoroborate. The filtrate was concentrated to about 180g under reduced pressure, 300g of poor solvent toluene was added dropwise, the solution was cooled to 0-5°C for filtration, and the filter cake was vacuum dried to obtain 90.1g of lithium tetrafluoroborate.

[0042] Embodiment 2: 25.94g (1.0mol) of lithium fluoride was added to 500g of dimethyl carbonate solution, the temperature was controlled at 40-50°C, 101.71g (1.5mol) of boron trifluoride was introduced, and the introduction was completed in about 2 hours. After the introduction, the temperature was kept at 40-50°C for 1.5 hours. 21.41g (0.51mol) of sodium fluoride was added, and the reaction was kept for 1 hour and then cooled to 20-25°C and filtered. The filter cake was rinsed with dimethyl carbonate and then vacuum dried to obtain 55.22g of sodium tetrafluoroborate. The filtrate was concentrated to about 180 grams, 300g of poor solvent o-xylene was added dropwise, the temperature was cooled to 5-10°C and filtered, and the filter cake was vacuum dried to obtain 89g of lithium tetrafluoroborate.

[0043] Embodiment 3: 25.94g (1.0mol) of lithium fluoride was added to 500g of diethyl carbonate solution, the temperature was controlled at 20-30°C, 135.62g (2.0mol) of boron trifluoride was introduced, and the solution was passed through for about 3 hours. After the solution was passed through, the solution was kept warm at 20-30°C for 3 hours. 42.83g (1.02mol) of sodium fluoride was added, and the solution was kept warm for 3 hours and then cooled to 20-25°C and filtered. The filter cake was rinsed with diethyl carbonate and then vacuum dried to obtain 110.38g of sodium tetrafluoroborate. The filtrate was concentrated to about 180 grams, 300g of poor solvent dichloromethane was added dropwise, the solution was cooled to 5-10°C and filtered, and the filter cake was vacuum dried to obtain 90.5g of lithium tetrafluoroborate.

[0044] Embodiment 4: 500g ethylene glycol dimethyl ether solution, add 25.94g (1.0mol) lithium fluoride, temperature control 50 ~ 60 ℃, pass 81.37g (1.2mol) boron trifluoride, about 1 hour pass, pass through, after completion 50 ℃ ~ 60 ℃ insulation 2 hours, add 10.08g (0.24mol) sodium fluoride, insulation reaction 1 hour after cooling to 20-25 ℃ filtration, filter cake rinsed with ethylene glycol dimethyl ether after vacuum drying to obtain 23.52g sodium tetrafluoroborate, the filtrate was concentrated to about 180 grams under reduced pressure, 300g poor solvent tetrachloroethane was added dropwise, cooled to 0-5 ℃ filtration, the filter cake was vacuum dried to obtain 88g lithium tetrafluoroborate.

[0045] Embodiment 5: 25.94g (1.0mol) of lithium fluoride was added to 500g of ethyl methyl carbonate solution, the temperature was controlled at 25-35°C, 88.15g (1.3mol) of boron trifluoride was introduced, and the introduction was completed in about 4 hours. After the introduction, the temperature was kept at 25-35°C for 4 hours, 15.12g (0.36mol) of sodium fluoride was added, and the reaction was kept for 2 hours and then cooled to 20-25°C and filtered. The filter cake was rinsed with ethyl methyl carbonate and then vacuum dried to obtain 35.28g of sodium tetrafluoroborate. The filtrate was concentrated to about 180 grams under reduced pressure, 300g of poor solvent dichloroethane was added dropwise, the temperature was cooled to 0-5°C and filtered, and the filter cake was vacuum dried to obtain 88.5g of lithium tetrafluoroborate.

[0046] Embodiment 6: 25.94g (1.0mol) of lithium fluoride was added to 500g of dimethyl carbonate solution, the temperature was controlled at 25-35°C, 128.83g (1.9mol) of boron trifluoride was introduced, and the introduction was completed in about 4 hours. After the introduction, the temperature was kept at 25-35°C for 4 hours, 41.99g (1.0mol) of sodium fluoride was added, and the reaction was kept for 4 hours and then cooled to 20-25°C and filtered. The filter cake was rinsed with dimethyl carbonate and vacuum dried to obtain 102.71g of sodium tetrafluoroborate. The filtrate was concentrated to about 180 grams, 300g of poor solvent trichloropropane was added dropwise, the temperature was cooled to 0-5°C and filtered, and the filter cake was vacuum dried to obtain 91.5g of lithium tetrafluoroborate.

[0047] Comparative Example 1: 25.94 g (1.0 mol) of lithium fluoride was added to 500 g of acetonitrile solution, the temperature was controlled at 50-60 ° C, 74.59 g (1.1 mol) of boron trifluoride was passed in about 1 hour, and the temperature was kept at 50-60 ° C for 1 hour after the passing. After filtering, the filtrate was concentrated to about 180 g under reduced pressure, 300 g of poor solvent toluene was added dropwise, the temperature was lowered to 0-5 ° C for filtration, and the filter cake was vacuum dried to obtain 82.5 g of lithium tetrafluoroborate.

[0048] Comparative Example 2: 25.94 g (1.0 mol) of lithium fluoride was added to 500 g of dimethyl carbonate solution, the temperature was controlled at 40-50 ° C, 67.81 g (1.0 mol) of boron trifluoride was passed in about 1 hour, and the solution was kept at 40-50 ° C for 2 hours after passing. After filtering, the filtrate was concentrated to about 180 g under reduced pressure, 300 g of poor solvent o-xylene was added dropwise, the temperature was lowered to 5-10 ° C, and the filter cake was vacuum dried to obtain 79.7 g of lithium tetrafluoroborate.

[0049] Comparative Example 3: 25.94 g (1.0 mol) of lithium fluoride was added to 500 g of diethyl carbonate solution, the temperature was controlled at 50-60 ° C, 61.71 g (0.91 mol) of boron trifluoride was passed, and the mixture was kept warm for 1 hour after passing. After filtering, the filtrate was concentrated to about 180 g under reduced pressure, 300 g of poor solvent dichloromethane was added dropwise, the temperature was lowered to 5-10 ° C, and the filter cake was vacuum dried to obtain 74.0 g of lithium tetrafluoroborate.

[0050] The yields of lithium tetrafluoroborate in the above examples and comparative examples are shown in Table 1: Table 1 Boron trifluoride Lithium fluoride Sodium fluoride Sodium tetrafluoroborate Lithium tetrafluoroborate Yield of lithium tetrafluoroborate Example 1 74.59g 25.94g 4.2g 10.87g 90.1g 96.11% (calculated as lithium fluoride) Example 2 101.71g 25.94g 21.41g 55.22g 89g 94.93% (calculated as lithium fluoride) Example 3 135.62g 25.94g 42.83g 110.38g 90.5g 96.53% (calculated as lithium fluoride) Example 4 81.37g 25.94g 10.08g 23.52g 88g 93.87% (calculated as lithium fluoride) Example 5 88.15g 25.94g 15.12g 35.28g 88.5g 94.4% (calculated as lithium fluoride) Example 6 128.83g 25.94g 41.99g 102.71g 91.5g 97.6% (calculated as lithium fluoride) Comparative Example 1 74.59g 25.94g 0 0 82.5g 88% (calculated as lithium fluoride) Comparative Example 2 67.81g 25.94g 0 0 79.7g 85% (calculated as lithium fluoride) Comparative Example 3 61.71g 25.94g 0 0 74.0g 78.93% (calculated as lithium fluoride)

[0051] The product qualities of lithium tetrafluoroborate and sodium tetrafluoroborate of the above examples and comparative examples are shown in Table 2: Table 2 Lithium tetrafluoroborate fluoride Lithium tetrafluoroborate purity Lithium Tetrafluoroborate Moisture Lithium Tetrafluoroborate Acid Value Sodium tetrafluoroborate fluoride ion Sodium tetrafluoroborate purity Sodium Tetrafluoroborate Moisture Sodium tetrafluoroborate acid value Example 1 2ppm 99.99% 25ppm 33ppm 4ppm 99.99% 36ppm 31ppm Example 2 4ppm 99.99% 24ppm 19ppm 0.79% 99.20% 25ppm 10ppm Example 3 3ppm 99.99% 17ppm 20ppm 0.76% 99.23% 30ppm 12ppm Example 4 1ppm 99.99% 15ppm 17ppm 6.61% 93.38% 29ppm 5ppm Example 5 2ppm 99.99% 11ppm 12ppm 6.68% 93.31% 35ppm 8ppm Example 6 3ppm 99.99% 16ppm 19ppm 4.09% 95.90% 21ppm 16ppm Comparative Example 1 12ppm 99.1% 120ppm 950ppm / / / / Comparative Example 2 540ppm 99.3% 110ppm 254ppm / / / / Comparative Example 3 1100ppm 99.2% 15ppm 14ppm / / / /

[0052] With reference to Table 1 and Table 2, it can be seen that the addition of sodium fluoride after the reaction of excessive boron trifluoride with lithium fluoride can significantly improve the yield of lithium tetrafluoroborate, significantly reduce the fluorine ion impurities and moisture in the lithium tetrafluoroborate product, significantly reduce the acid value of the lithium tetrafluoroborate product, and improve the purity of the lithium tetrafluoroborate product. With reference to Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that when the molar ratio of boron trifluoride to lithium fluoride is less than or equal to 1, the yield of lithium tetrafluoroborate is significantly reduced, the fluorine ion impurities are significantly increased, and the acid value is significantly increased. In addition, as shown in Table 2, the sodium tetrafluoroborate obtained in Examples 1 to 6 has less fluorine ion impurities and moisture, high purity, and low acid value.

[0053] In summary, the method for preparing tetrafluoroborate provided in the embodiments of the present application can prepare high-purity lithium tetrafluoroborate and sodium tetrafluoroborate products. The prepared sodium tetrafluoroborate and lithium tetrafluoroborate have low acid values, and the fluoride ion and water contents are extremely low, and are suitable for use as electrolytes in batteries.

[0054] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0055] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0056] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for preparing tetrafluoroborate, characterized in that: The method comprises: Passing an excess amount of boron trifluoride into a lithium fluoride solution to react and generate lithium tetrafluoroborate to obtain a first reaction solution; adding sodium fluoride to the first reaction solution to obtain a second reaction solution containing sodium tetrafluoroborate; Filtering the second reaction liquid to obtain sodium tetrafluoroborate solid and filtrate; Lithium tetrafluoroborate solid was obtained based on the filtrate.

2. The method for preparing a tetrafluoroborate according to claim 1, characterized in that: The obtaining of lithium tetrafluoroborate solid based on the filtrate comprises: The filtrate is concentrated and then a poor solvent is added to obtain lithium tetrafluoroborate solid.

3. The method for preparing a tetrafluoroborate according to claim 2, characterized in that: The poor solvent is selected from at least one of toluene, dichloromethane, dichloroethane, trichloropropane, tetrachloroethane, xylene and isopropyl ether.

4. The method for preparing a tetrafluoroborate according to claim 2, characterized in that: After adding the poor solvent, the temperature is lowered to 0-10° C., filtered, and vacuum dried to obtain lithium tetrafluoroborate solid.

5. The method for preparing a tetrafluoroborate according to claim 1, characterized in that: The solvent in the lithium fluoride solution is selected from at least one of ethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

6. The method for preparing a tetrafluoroborate according to claim 1, characterized in that: The molar ratio of the lithium fluoride to the boron trifluoride is 1:(1.1-2).

7. The method for preparing a tetrafluoroborate according to claim 1, characterized in that: The ratio of the molar difference between the boron trifluoride and the lithium fluoride to the molar amount of the sodium fluoride is 1:(1-2).

8. The method for preparing a tetrafluoroborate according to claim 1, characterized in that: The reaction temperature of the excess boron trifluoride and the lithium fluoride solution is 20-60°C.

9. The method for preparing a tetrafluoroborate according to claim 8, characterized in that: After an excess amount of boron trifluoride is introduced into the lithium fluoride solution to react and generate lithium tetrafluoroborate, the solution is kept warm for 1 to 6 hours.

10. The method for preparing a tetrafluoroborate according to claim 1, characterized in that: After adding sodium fluoride to the first reaction solution, the reaction is kept warm for 0.5-6 hours, and the temperature is lowered to 20-25° C. and filtered to obtain a filtrate.