Method for purifying lithium tetrafluoroborate

Abstract

The invention belongs to the technical field of secondary batteries, and discloses a purification method of lithium tetrafluoroborate. The method comprises the following steps: mixing a lithium tetrafluoroborate solution with lithium hydride in a protective atmosphere, and then introducing boron trifluoride gas for reaction; and after the reaction is finished, carrying out nitrogen purging, then filtering, and sequentially carrying out concentration crystallization and drying on the obtained filtrate to obtain purified lithium tetrafluoroborate. According to the lithium tetrafluoroborate purification method provided by the invention, free hydrofluoric acid in the lithium tetrafluoroborate solution is converted into the target product lithium tetrafluoroborate by utilizing lithium hydride and boron trifluoride, the content of free acid can be effectively reduced, the process is simple, the purification effect is good, other impurity ions cannot be introduced into the used lithium hydride and boron trifluoride, and waste can be turned into wealth; the method is simple, efficient and good in application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and particularly to a purification method of lithium tetrafluoroborate. Background Art

[0002] Lithium tetrafluoroborate is an additive for lithium battery electrolytes, with good chemical stability and thermal stability, which can broaden the working temperature range of lithium batteries and improve the high and low temperature discharge performance of the batteries. At present, the main preparation method of lithium tetrafluoroborate is to introduce boron trifluoride gas into hydrogen fluoride containing lithium fluoride, and crystallize to obtain lithium tetrafluoroborate. The product in this system may have a high acidity (residual hydrogen fluoride).

[0003] Patent CN116040658B discloses a purification process of lithium tetrafluoroborate. Pure water is added to the crude lithium tetrafluoroborate for hydrolysis reaction, an alkaline lithium salt is added, filtered, concentrated, crystallized and filtered to obtain lithium tetrafluoroborate hydrate; dried under reduced pressure, then added with a non-aqueous polar solvent to stir and dissolve, filtered, concentrated under reduced pressure, added with a non-polar solvent for crystallization, washed and filtered, and vacuum dried to obtain the lithium tetrafluoroborate product. This method has a long process flow, introducing water will cause product deterioration and yield reduction.

[0004] Therefore, how to provide a purification method of lithium tetrafluoroborate with a simple process and high purification efficiency is an urgent problem to be solved at present. Summary of the Invention

[0005] The purpose of the present invention is to provide a purification method of lithium tetrafluoroborate, which solves the problems of long process flow and product deterioration caused by introducing water in the prior art.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a purification method of lithium tetrafluoroborate, including the following steps:

[0008] Under a protective atmosphere, mix the lithium tetrafluoroborate solution with lithium hydride, and then introduce boron trifluoride gas for reaction; after the reaction is completed, purge with nitrogen, then filter, and the obtained filtrate is sequentially concentrated and crystallized, dried to obtain purified lithium tetrafluoroborate, thus completing the purification of the lithium tetrafluoroborate.

[0009] Preferably, in the above purification method of lithium tetrafluoroborate, the molar ratio of free acid, lithium hydride, and boron trifluoride in the lithium tetrafluoroborate solution is 1:1 to 1.5:1.

[0010] Preferably, in the above purification method of lithium tetrafluoroborate, the purity of the lithium hydride ≥ 99.9%; the water content of the lithium hydride ≤ 0.001%; the purity of the boron trifluoride ≥ 99.9%.

[0011] Preferably, in the above purification method of lithium tetrafluoroborate, the temperature of the reaction is 0 - 35°C; the time of the reaction is 0.2 - 2 h.

[0012] Preferably, in the above purification method of lithium tetrafluoroborate, the time of nitrogen purging is 0.1 - 1 h.

[0013] Preferably, in the above purification method of lithium tetrafluoroborate, the temperature of concentration and crystallization is ≤60°C; the temperature of drying is 70 - 90°C.

[0014] Preferably, in the above purification method of lithium tetrafluoroborate, the lithium tetrafluoroborate solution is a dimethyl carbonate solution of lithium tetrafluoroborate containing free acid.

[0015] As can be seen from the above technical solutions, compared with the prior art, the present invention has the following beneficial effects:

[0016] The purification method of lithium tetrafluoroborate provided by the present invention uses lithium hydride and boron trifluoride to convert free hydrofluoric acid in the lithium tetrafluoroborate solution into the target product lithium tetrafluoroborate, which can effectively reduce the content of free acid. The process is simple, the purification effect is good, and the raw materials lithium hydride and boron trifluoride used will not introduce other impurity ions, and it can turn waste into treasure. The method is simple and efficient, and has good application prospects. Specific Embodiments

[0017] The present invention provides a purification method of lithium tetrafluoroborate, comprising the following steps:

[0018] Under a protective atmosphere, mix the lithium tetrafluoroborate solution with lithium hydride, and then introduce boron trifluoride gas for reaction; after the reaction is completed, conduct nitrogen purging, and then filter. The obtained filtrate is successively subjected to concentration and crystallization, and drying to obtain purified lithium tetrafluoroborate, thus completing the purification of the lithium tetrafluoroborate.

[0019] In the present invention, the protective atmosphere is preferably nitrogen.

[0020] In the present invention, the molar ratio of free acid, lithium hydride, and boron trifluoride in the lithium tetrafluoroborate solution is preferably 1:1 - 1.5:1, more preferably 1:1.02 - 1.2:1, and even more preferably 1:1.02:1. The raw material dosage of the present invention can improve the reaction conversion rate and does not waste raw materials.

[0021] In the present invention, the purity of the lithium hydride is preferably ≥99.9%; the water content of the lithium hydride is preferably ≤0.001%; the purity of the boron trifluoride is preferably ≥99.9%. The present invention controls the impurity and water content of the raw materials, further improving the purity of lithium tetrafluoroborate.

[0022] In the present invention, the method of mixing the lithium tetrafluoroborate solution with lithium hydride is preferably to add lithium hydride to the lithium tetrafluoroborate solution and then stir and disperse.

[0023] In the present invention, the temperature of the reaction is preferably 0 - 35°C, more preferably 5 - 15°C, and even more preferably 5°C; the reaction time is preferably 0.2 - 2 h, more preferably 0.6 - 1.2 h, and even more preferably 0.6 h. The reaction temperature and time of the present invention can further improve the purification efficiency.

[0024] In the present invention, the time of nitrogen purging is preferably 0.1 - 1 h, more preferably 0.5 - 1 h, and even more preferably 1 h.

[0025] In the present invention, the temperature of concentration and crystallization is preferably ≤60°C, more preferably ≤50°C, and even more preferably 45°C; the drying temperature is preferably 70 - 90°C, more preferably 75 - 85°C, and even more preferably 80°C.

[0026] In the present invention, the lithium tetrafluoroborate solution is preferably a dimethyl carbonate solution of lithium tetrafluoroborate containing free acid.

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Example 1

[0029] This example provides a method for purifying lithium tetrafluoroborate, including the following steps:

[0030] Under a nitrogen atmosphere, lithium hydride is added to 1000 g of lithium tetrafluoroborate solution (acidity is 105 ppm) and stirred and dispersed, and then boron trifluoride gas is introduced for reaction. The molar ratio of free acid, lithium hydride, and boron trifluoride in the lithium tetrafluoroborate solution is 1:1.02:1. The reaction temperature is 5°C and the time is 0.6 h. After the reaction, nitrogen is used for purging for 1 h, and then the reaction solution is filtered to remove excessive lithium hydride. The obtained filtrate is concentrated and crystallized at 45°C and then dried at 80°C to obtain purified lithium tetrafluoroborate.

[0031] Among them, the purity of lithium hydride ≥99.9%, the water content of lithium hydride ≤0.001%, and the purity of boron trifluoride ≥99.9%.

[0032] Example 2

[0033] This example provides a method for purifying lithium tetrafluoroborate, including the following steps:

[0034] Under a nitrogen atmosphere, lithium hydride was added to 1000 g of a lithium tetrafluoroborate solution (acidity 300 ppm) and stirred to disperse, then boron trifluoride gas was introduced for reaction. The molar ratio of free acid, lithium hydride, and boron trifluoride in the lithium tetrafluoroborate solution was 1:1.2:1. The reaction temperature was 5 °C and the time was 1.2 h. After the reaction, nitrogen was used for purging for 1 h, then the reaction solution was filtered to remove excess lithium hydride, and the obtained filtrate was concentrated and crystallized at 40 °C and then dried at 80 °C to obtain purified lithium tetrafluoroborate.

[0035] Among them, the purity of lithium hydride ≥ 99.9%, the water content of lithium hydride ≤ 0.001%, and the purity of boron trifluoride ≥ 99.9%.

[0036] Example 3

[0037] This example provides a method for purifying lithium tetrafluoroborate, including the following steps:

[0038] Under a nitrogen atmosphere, lithium hydride was added to 1000 g of a lithium tetrafluoroborate solution (acidity 450 ppm) and stirred to disperse, then boron trifluoride gas was introduced for reaction. The molar ratio of free acid, lithium hydride, and boron trifluoride in the lithium tetrafluoroborate solution was 1:1.1:1. The reaction temperature was 15 °C and the time was 1 h. After the reaction, nitrogen was used for purging for 1 h, then the reaction solution was filtered to remove excess lithium hydride, and the obtained filtrate was concentrated and crystallized at 45 °C and then dried at 80 °C to obtain purified lithium tetrafluoroborate.

[0039] Among them, the purity of lithium hydride ≥ 99.9%, the water content of lithium hydride ≤ 0.001%, and the purity of boron trifluoride ≥ 99.9%.

[0040] The acidity of lithium tetrafluoroborate before and after purification by the purification methods of Examples 1 to 3 is shown in Table 1.

[0041] Table 1 Acidity of lithium tetrafluoroborate before and after purification

[0042]

[0043] As can be seen from Table 1, the purification method of lithium tetrafluoroborate provided by the present invention can convert free hydrofluoric acid into the main product of lithium tetrafluoroborate through a chemical reaction, can effectively reduce the content of free acid in the lithium tetrafluoroborate solution, realize turning waste into treasure, and the addition of lithium hydride and boron trifluoride will not introduce other impurities, and the method is simple and efficient.

[0044] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A purification method of lithium tetrafluoroborate, characterized in that It includes the following steps: Under a protective atmosphere, lithium tetrafluoroborate solution is mixed with lithium hydride, and then boron trifluoride gas is introduced for reaction; after the reaction is completed, nitrogen purging is carried out, and then filtration is performed. The obtained filtrate is successively concentrated for crystallization and dried to obtain purified lithium tetrafluoroborate, thus completing the purification of the lithium tetrafluoroborate.

2. The purification method of lithium tetrafluoroborate according to claim 1, characterized in that The molar ratio of free acid, lithium hydride, and boron trifluoride in the lithium tetrafluoroborate solution is 1:1 to 1.5:

1.

3. The purification method of lithium tetrafluoroborate according to claim 2, characterized in that, The purity of the lithium hydride ≥ 99.9%; the water content of the lithium hydride ≤ 0.001%; the purity of the boron trifluoride ≥ 99.9%.

4. A purification method of lithium tetrafluoroborate according to claim 1 or 2, characterized in that, The temperature of the reaction is 0 to 35 °C; the time of the reaction is 0.2 to 2 h.

5. A purification method of lithium tetrafluoroborate according to claim 4, characterized in that, The time of the nitrogen purging is 0.1 to 1 h.

6. The purification method of lithium tetrafluoroborate according to claim 5, characterized in that, The temperature of the concentration and crystallization is ≤ 60 °C; the temperature of the drying is 70 to 90 °C.

7. A purification method of lithium tetrafluoroborate according to claim 1 or 6, characterized in that, The lithium tetrafluoroborate solution is a dimethyl carbonate solution of lithium tetrafluoroborate containing free acid.

Images