Method for efficiently purifying lithium tetrafluoroborate

Abstract

The invention belongs to the technical field of secondary batteries, and discloses a method for efficiently purifying lithium tetrafluoroborate. The method comprises the following steps: mixing a lithium tetrafluoroborate solution with lithium fluoride in a protective atmosphere, and then introducing boron trichloride 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 method, free acid hydrogen fluoride in the lithium tetrafluoroborate solution is converted into a lithium tetrafluoroborate main product through chemical reaction, complicated reaction and post-treatment processes are not needed, the free acid content of the product can be effectively reduced, impurities are converted into the product, the yield is further improved, and the production benefit is improved. Meanwhile, other metal impurities cannot be introduced by adding lithium fluoride and boron trichloride, and the purification method is simple, safe, efficient, remarkable in purification effect, low in equipment investment and suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of secondary batteries, and in particular to a method for efficiently purifying lithium tetrafluoroborate. Background Art

[0002] Lithium tetrafluoroborate (LiBF4) has good chemical stability and thermal stability, is insensitive to environmental moisture, and is expected to become an excellent electrolyte system in the field of energy storage and power batteries. At present, there are mainly the following methods for preparing LiBF4: 1. Gas-solid reaction method, such as the reaction of solid LiF with BF3 gas; 2. Aqueous solution method, such as the reaction of lithium source with tetrafluoroboric acid aqueous solution; 3. Non-aqueous solution method, LiF reacts with BF3 gas in anhydrous HF or organic solvent. After the above methods prepare the crude lithium tetrafluoroborate, it is necessary to further remove HF to obtain high-purity lithium tetrafluoroborate, but these existing purification processes all have the problems of high acidity of the prepared products, difficulty in purification, and high cost.

[0003] For example, patent CN104276579A uses borane to react with fluorine gas to generate boron trifluoride, which is then reacted with a halogenated lithium salt in hydrogen fluoride to generate lithium tetrafluoroborate. After the reaction, in order to ensure more thorough removal of HF, high-pressure filtration and long-term hot nitrogen purging are used to remove the acid; the purification process of this method has the problems of high-pressure filtration danger and high hot nitrogen purging cost, and hydrogen fluoride cannot be directly used.

[0004] Patent CN103733416A reacts lithium fluoride with boron trifluoride in a chain carbonate to generate lithium tetrafluoroborate and obtain a reaction solution that is dissolved in a solvent, and removes acidic impurities by concentrating the reaction solution. CN109110774A uses hydrofluoric acid and boric acid to react to prepare an aqueous solution of tetrafluoroboric acid, and then reacts with lithium carbonate in water to prepare lithium tetrafluoroborate, and obtains the target product through concentrated crystallization and recrystallization. Both processes require recrystallization to obtain high-purity lithium tetrafluoroborate, and the purification cost is high and the yield is low.

[0005] Therefore, the existing preparation methods of lithium tetrafluoroborate have problems to varying degrees such as high product acidity and high purification cost (safety cost, complex process and production cost caused by low yield, etc.). Summary of the invention

[0006] The object of the present invention is to provide a method for efficiently purifying lithium tetrafluoroborate, so as to solve the problems of high product acidity and high purification cost (safety cost, complex process and production cost caused by low yield, etc.) existing in the existing lithium tetrafluoroborate preparation process.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for efficiently purifying lithium tetrafluoroborate, comprising the following steps:

[0009] Under a protective atmosphere, a lithium tetrafluoroborate solution is mixed with lithium fluoride, and then boron trichloride gas is introduced to react; after the reaction is completed, nitrogen is purged, and then filtered, and the obtained filtrate is concentrated, crystallized, and dried in turn to obtain purified lithium tetrafluoroborate, that is, the efficient purification of lithium tetrafluoroborate is completed.

[0010] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the molar ratio of lithium fluoride, boron trichloride and free acid in the lithium tetrafluoroborate solution is 1-1.3:1:3.

[0011] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the molar ratio of lithium fluoride, boron trichloride and free acid in the lithium tetrafluoroborate solution is 1.02-1.1:1:3.

[0012] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the purity of the lithium fluoride is ≥99.9%; the water content of the lithium fluoride is ≤0.001%; ​​and the purity of the boron trichloride is ≥99.9%.

[0013] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the reaction temperature is 0 to 30° C.; and the reaction time is 0.1 to 1.2 h.

[0014] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the nitrogen purging time is 0.1 to 1 hour.

[0015] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the temperature of the concentration and crystallization is ≤60°C; and the temperature of the drying is ≤95°C.

[0016] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the lithium tetrafluoroborate solution is obtained by dissolving lithium tetrafluoroborate crystals containing free acid in an organic solvent; and the organic solvent is dimethyl carbonate.

[0017] Preferably, in the above-mentioned method for efficiently purifying lithium tetrafluoroborate, the protective atmosphere is nitrogen.

[0018] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0019] The lithium tetrafluoroborate purification method provided by the present invention converts the free acid hydrogen fluoride in the lithium tetrafluoroborate solution into the main lithium tetrafluoroborate product through a chemical reaction, does not require a complicated reaction and post-processing process, can effectively reduce the free acid content of the product, and converts impurities into products to further improve the yield and production efficiency. At the same time, the addition of lithium fluoride and boron trichloride will not introduce other metal impurities, the purification method is simple, safe and efficient, the purification effect is significant, the equipment investment is low, and it is suitable for industrial production. DETAILED DESCRIPTION

[0020] The present invention provides a method for efficiently purifying lithium tetrafluoroborate, comprising the following steps:

[0021] Under a protective atmosphere, a lithium tetrafluoroborate solution is mixed with lithium fluoride, and then boron trichloride gas is introduced to react; after the reaction is completed, nitrogen is purged, and then filtered, and the obtained filtrate is concentrated, crystallized, and dried in turn to obtain purified lithium tetrafluoroborate, that is, the efficient purification of lithium tetrafluoroborate is completed.

[0022] In the present invention, the reaction principle involved is as follows:

[0023] 3HF+LiF+BCl3=LiBF4+3HCl

[0024] In the present invention, the lithium tetrafluoroborate solution is preferably obtained by dissolving lithium tetrafluoroborate crystals containing free acid in an organic solvent; the organic solvent is preferably dimethyl carbonate. The lithium tetrafluoroborate solutions described in Examples 1 to 3 of the present invention are all dimethyl carbonate solutions of lithium tetrafluoroborate.

[0025] In the present invention, the protective atmosphere is preferably nitrogen.

[0026] In the present invention, the lithium tetrafluoroborate solution and lithium fluoride are preferably mixed by adding lithium fluoride to the lithium tetrafluoroborate solution and then stirring.

[0027] In the present invention, the molar ratio of the free acid in the lithium fluoride, boron trichloride and lithium tetrafluoroborate solution is preferably 1 to 1.3:1:3, and more preferably 1.02 to 1.1:1:3.

[0028] In the present invention, the purity of the lithium fluoride is preferably ≥99.9%; the water content of the lithium fluoride is preferably ≤0.001%, and more preferably ≤0.0005%.

[0029] In the present invention, the purity of the boron trichloride is preferably ≥99.9%.

[0030] In the present invention, the reaction temperature is preferably 0 to 30° C., more preferably 5 to 15° C.; the reaction time is preferably 0.1 to 1.2 h, more preferably 0.2 to 1 h.

[0031] In the present invention, the nitrogen purge time is preferably 0.1 to 1 h, more preferably 0.2 to 0.6 h.

[0032] In the present invention, the purpose of the filtration is to remove excess lithium fluoride.

[0033] In the present invention, the temperature of the concentration and crystallization is preferably ≤60°C, and more preferably ≤50°C.

[0034] In the present invention, the drying temperature is preferably ≤95°C, and more preferably ≤85°C.

[0035] 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 them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] This embodiment provides a method for efficiently purifying lithium tetrafluoroborate, comprising the following steps:

[0038] Under a nitrogen protective atmosphere, 0.42 g of lithium fluoride was added to 10000 g of lithium tetrafluoroborate solution (acidity of 95 ppm) and stirred and dispersed, and 1.857 g of boron trichloride gas was introduced for reaction at a temperature of 5°C for 1 h. After the reaction was completed, nitrogen was used for purging for 0.5 h, and then the excess lithium fluoride was removed by filtration. The obtained filtrate was concentrated and crystallized at 50°C and then dried at 85°C to obtain purified lithium tetrafluoroborate.

[0039] The purity of lithium fluoride is ≥99.9%, the water content of lithium fluoride is ≤0.0005%, the purity of boron trichloride is ≥99.9%, and the molar ratio of free acid in the lithium fluoride, boron trichloride and lithium tetrafluoroborate solution is 1.02:1:3.

[0040] After purification according to the above method, the acidity of lithium tetrafluoroborate was 5 ppm.

[0041] Example 2

[0042] This embodiment provides a method for efficiently purifying lithium tetrafluoroborate, comprising the following steps:

[0043] Under a nitrogen protective atmosphere, 1.102 g of lithium fluoride was added to 10000 g of lithium tetrafluoroborate solution (acidity of 240 ppm) and stirred and dispersed, and 4.692 g of boron trichloride gas was introduced for reaction at a temperature of 10°C and a reaction time of 0.6 h. After the reaction was completed, nitrogen was used for purging for 0.4 h, and then the excess lithium fluoride was removed by filtration. The obtained filtrate was concentrated and crystallized at 45°C and then dried at 80°C to obtain purified lithium tetrafluoroborate.

[0044] The purity of lithium fluoride is ≥99.9%, the water content of lithium fluoride is ≤0.0005%, the purity of boron trichloride is ≥99.9%, and the molar ratio of free acid in the lithium fluoride, boron trichloride and lithium tetrafluoroborate solution is 1.06:1:3.

[0045] After purification according to the above method, the acidity of lithium tetrafluoroborate was 8 ppm.

[0046] Example 3

[0047] This embodiment provides a method for efficiently purifying lithium tetrafluoroborate, comprising the following steps:

[0048] Under a nitrogen protective atmosphere, 2.574 g of lithium fluoride was added to 10000 g of lithium tetrafluoroborate solution (acidity of 540 ppm) and stirred and dispersed, and 10.557 g of boron trichloride gas was introduced for reaction at a temperature of 15 ° C and a reaction time of 0.2 h. After the reaction was completed, nitrogen was used for purging for 0.4 h, and then the excess lithium fluoride was removed by filtration. The obtained filtrate was concentrated and crystallized at 40 ° C and then dried at 80 ° C to obtain purified lithium tetrafluoroborate.

[0049] The purity of lithium fluoride is ≥99.9%, the water content of lithium fluoride is ≤0.0005%, the purity of boron trichloride is ≥99.9%, and the molar ratio of free acid in the lithium fluoride, boron trichloride and lithium tetrafluoroborate solution is 1.1:1:3.

[0050] After purification according to the above method, the acidity of lithium tetrafluoroborate was 9 ppm.

[0051] Example 4

[0052] According to the scheme of Example 1 recorded in the specification of CN103733416A, a lithium tetrafluoroborate solution was prepared, and the acidity of the obtained lithium tetrafluoroborate solution was 78 ppm, and then purified by the method of the present invention, comprising the following steps:

[0053] Under a nitrogen protective atmosphere, 0.358 g of lithium fluoride was added to 10000 g of lithium tetrafluoroborate solution (acidity of 78 ppm) and stirred and dispersed, and 1.525 g of boron trichloride gas was introduced for reaction at a temperature of 15 ° C and a reaction time of 0.2 h. After the reaction was completed, nitrogen was used for purging for 0.4 h, and then the excess lithium fluoride was removed by filtration. The obtained filtrate was concentrated and crystallized at 40 ° C and then dried at 80 ° C to obtain purified lithium tetrafluoroborate.

[0054] The purity of lithium fluoride is ≥99.9%, the water content of lithium fluoride is ≤0.0005%, the purity of boron trichloride is ≥99.9%, and the molar ratio of free acid in the lithium fluoride, boron trichloride and lithium tetrafluoroborate solution is 1.06:1:3.

[0055] After purification according to the above method, the acidity of lithium tetrafluoroborate was 4 ppm.

[0056] In summary, whether it is a solution prepared for lithium tetrafluoroborate finished crystals or a lithium tetrafluoroborate solution generated in the process of synthesizing lithium tetrafluoroborate, the purification method of the present invention can be used for deacidification, and the free acid hydrogen fluoride in the lithium tetrafluoroborate solution is converted into the main product of lithium tetrafluoroborate through a chemical reaction, without the need for complex reactions and post-treatment processes, and the free acid content of the product can be effectively reduced. The conversion of impurities into products further improves the yield and improves the production efficiency.

[0057] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for efficiently purifying lithium tetrafluoroborate, characterized in that: The following steps are involved: Under a protective atmosphere, a lithium tetrafluoroborate solution is mixed with lithium fluoride, and then boron trichloride gas is introduced to react; after the reaction is completed, nitrogen is purged, and then filtered, and the obtained filtrate is concentrated, crystallized, and dried in turn to obtain purified lithium tetrafluoroborate, that is, the efficient purification of lithium tetrafluoroborate is completed.

2. A method for efficiently purifying lithium tetrafluoroborate according to claim 1, characterized in that: The molar ratio of the free acid in the lithium fluoride, boron trichloride and lithium tetrafluoroborate solution is 1-1.3:1:

3.

3. A method for efficiently purifying lithium tetrafluoroborate according to claim 2, characterized in that: The molar ratio of free acid in the lithium fluoride, boron trichloride and lithium tetrafluoroborate solution is 1.02-1.1:1:

3.

4. A method for efficiently purifying lithium tetrafluoroborate according to claim 1 or 3, characterized in that: The purity of the lithium fluoride is ≥99.9%; the water content of the lithium fluoride is ≤0.001%; ​​and the purity of the boron trichloride is ≥99.9%.

5. A method for efficiently purifying lithium tetrafluoroborate according to claim 4, characterized in that: The reaction temperature is 0-30°C; the reaction time is 0.1-1.2h.

6. A method for efficiently purifying lithium tetrafluoroborate according to claim 3, characterized in that: The nitrogen purge time is 0.1 to 1 h.

7. A method for efficiently purifying lithium tetrafluoroborate according to claim 1 or 6, characterized in that: The temperature of the concentration and crystallization is ≤60°C; the temperature of the drying is ≤95°C.

8. A method for efficiently purifying lithium tetrafluoroborate according to claim 7, characterized in that: The lithium tetrafluoroborate solution is obtained by dissolving lithium tetrafluoroborate crystals containing free acid in an organic solvent; the organic solvent is dimethyl carbonate.

9. A method for efficiently purifying lithium tetrafluoroborate according to claim 5, characterized in that: The protective atmosphere is nitrogen.