Method for purifying lithium tetrafluoroborate

Abstract

The invention provides a purification method of lithium tetrafluoroborate, and belongs to the technical field of secondary batteries. The purification method of the lithium tetrafluoroborate comprises the following steps: adding lithium salt into a lithium tetrafluoroborate solution under the protection of nitrogen, stirring and dispersing, introducing boron trifluoride gas for reaction, and purging the solution by nitrogen after the reaction is finished; and filtering out excessive lithium salt, and concentrating, filtering and drying filtrate to obtain qualified lithium tetrafluoroborate. According to the method, the free acid hydrofluoric acid is converted into the product lithium tetrafluoroborate by adding the lithium salt and the boron trifluoride, waste is turned into wealth, the process is simple, the reaction effect is good, and the method is suitable for industrial production.

Description

Technical Field

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

[0002] Lithium tetrafluoroborate (LiBF4) has good thermal stability and is insensitive to moisture, so it has attracted a large number of scientific researchers to conduct extensive research on its preparation methods. The current methods for preparing LiBF4 mainly include the following: 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, the reaction of LiF with BF3 gas in anhydrous HF or organic solvent. The above methods will produce byproducts or carry over hydrogen fluoride, resulting in high acidity of the product and great difficulty in purification.

[0003] Patent CN103733416B reacts lithium fluoride with boron trifluoride in a chain carbonate to generate lithium tetrafluoroborate and obtain a reaction solution that dissolves it in a solvent, and removes acidic impurities by concentrating the reaction solution. CN109110774B uses hydrofluoric acid and boric acid to react to prepare an aqueous solution of tetrafluoroboric acid, which is then reacted with lithium carbonate in water to prepare lithium tetrafluoroborate, and the target product is obtained through concentrated crystallization and recrystallization. Both processes require recrystallization to obtain high-purity lithium tetrafluoroborate.

[0004] Patent CN104276579B uses borane to react with fluorine gas to generate boron trifluoride, and boron trifluoride reacts with a halogenated lithium salt dissolved in hydrogen fluoride to generate lithium tetrafluoroborate. To ensure more thorough removal of HF, 1. The filtration pressure is in the range of 0.5-2 atmospheres in absolute pressure; 2. The product is dried using hot N2 at a temperature of 40-60°C. After continuous flow for 3 hours, the N2 gas is heated to 150-200°C and dried for 4-8 hours. There are problems of high-pressure filtration danger and high cost of hot nitrogen purging, and hydrogen fluoride cannot be directly used. Summary of the invention

[0005] One object of the present invention is to provide a method for purifying lithium tetrafluoroborate to solve some problems in the prior art, such as the method of neutralizing free hydrofluoric acid with alkaline lithium salt will produce water by-product, resulting in product deterioration; the recrystallization method is widely used, but will lose a certain amount of product and reduce the yield; and the above two methods are unable to directly utilize the fluorine element in hydrofluoric acid.

[0006] To achieve the above object, the technical scheme of the purification method of lithium tetrafluoroborate of the present invention is:

[0007] A method for purifying lithium tetrafluoroborate comprises the following steps: adding lithium salt into a lithium tetrafluoroborate solution under nitrogen protection, slowly introducing boron trifluoride gas for full reaction, purging with nitrogen, filtering out excess lithium salt, concentrating the filtrate, crystallizing and drying to obtain qualified lithium tetrafluoroborate.

[0008] In order to further improve the purity of lithium tetrafluoroborate and reduce impurities, preferably, the purity of the lithium salt is ≥99.9%, the purity of boron trifluoride is ≥99.9%, and the water content of the lithium salt is ≤0.0005%.

[0009] In order to reduce the waste of raw materials while ensuring the purification effect, the molar ratio of the free acid, lithium salt and boron trifluoride in the lithium tetrafluoroborate is preferably 1:(1-1.3):1, and more preferably, the molar ratio of the free acid, lithium salt and boron trifluoride in the lithium tetrafluoroborate is 1:(1.02-1.1):1.

[0010] In order to further improve the reaction efficiency and the purification effect, preferably, the reaction temperature is -5°C to 30°C, the reaction time is 0.2 to 0.8 h, and the nitrogen purge time is 0.1 to 1 h; more preferably, the reaction temperature is 0°C to 20°C, the reaction time is 0.2 to 0.8 h, and the inert gas purge time is 0.2 to 0.8 h.

[0011] In order to further improve the purity of lithium tetrafluoroborate, after filtering out the lithium salt, the filtrate concentration temperature is ≤60°C, and the drying temperature is ≤100°C. More preferably, the filtrate concentration temperature is ≤45°C, and the drying temperature is ≤85°C.

[0012] The beneficial effects of the present invention are:

[0013] The lithium tetrafluoroborate purification method provided by the present invention converts free acid hydrofluoric acid into product lithium tetrafluoroborate by adding lithium salt and boron trifluoride, thereby realizing the transformation of waste into treasure, and removing by-product gas by purging with inert gas, and the purification effect is remarkable, and the impurities are converted into products to further improve the yield, and the method has high economic value. The method of the present invention is simple, fast in reaction, does not require post-processing, does not introduce other impurities, and is suitable for industrialization. DETAILED DESCRIPTION

[0014] The implementation manner of the present invention is further described below in conjunction with specific examples.

[0015] The purification method of lithium tetrafluoroborate provided by the present invention converts free acid hydrofluoric acid into product lithium tetrafluoroborate by adding lithium salt and boron trifluoride, thereby realizing the transformation of waste into treasure. The free acid in lithium tetrafluoroborate is purified by inert gas purging to remove by-product gas, and the purification effect is significant. The addition of lithium salt and boron trifluoride will not introduce other metal impurities. The purification method is simple and efficient and suitable for industrialization. The principle of this process is as follows:

[0016] HF+LiX+BF 3 =LiBF 4 +HX.

[0017] Example 1

[0018] The lithium tetrafluoroborate solutions used in all the examples were obtained by dissolving lithium tetrafluoroborate crystals containing free acid in an organic solvent, ethyl methyl carbonate, and the acidity was tested before and after purification.

[0019] The purification method of lithium tetrafluoroborate of the present embodiment comprises the following steps:

[0020] Under nitrogen protection, lithium hydride was added to 2kg lithium tetrafluoroborate solution and stirred to disperse, and boron trifluoride gas was introduced for sufficient reaction. The molar ratio of free acid, lithium salt and boron trifluoride in lithium tetrafluoroborate was 1:1.02:1. The reaction temperature was 0°C, the reaction time was 0.8h, and then nitrogen was purged for 0.2h. The reaction liquid was filtered to remove lithium hydride, and the filtrate was concentrated, filtered and dried to obtain the product. The concentration temperature was 45°C and the drying temperature was 85°C.

[0021] Example 2

[0022] The purification method of lithium tetrafluoroborate of the present embodiment comprises the following steps:

[0023] Under nitrogen protection, lithium chloride was added to 2kg lithium tetrafluoroborate solution and stirred to disperse, and boron trifluoride gas was introduced for sufficient reaction. The molar ratio of free acid, lithium salt and boron trifluoride in lithium tetrafluoroborate was 1:1.06:1. The reaction temperature was 10°C, the reaction time was 0.5h, and then nitrogen was purged for 0.5h. The reaction liquid was filtered to remove lithium chloride, and the filtrate was concentrated, filtered and dried to obtain the product. The concentration temperature was 40°C and the drying temperature was 80°C.

[0024] Example 3

[0025] The purification method of lithium tetrafluoroborate of the present embodiment comprises the following steps:

[0026] Under nitrogen protection, lithium hydride is added to 2kg of lithium tetrafluoroborate solution and stirred to disperse, and boron trifluoride gas is introduced for sufficient reaction. The molar ratio of free acid, lithium salt and boron trifluoride in lithium tetrafluoroborate is 1:1.1:1. The reaction temperature is 20°C, the reaction time is 0.2h, and then nitrogen is purged for 0.8h. The reaction liquid is filtered to remove lithium hydride, and the filtrate is concentrated, filtered and dried to obtain the product. The concentration temperature is 45°C and the drying temperature is 85°C.

[0027] Comparative Example 1

[0028] The purification method of lithium tetrafluoroborate of the present embodiment comprises the following steps:

[0029] Under nitrogen protection, lithium hydride was added to 2kg of lithium tetrafluoroborate solution and stirred for reaction. The molar ratio of free acid in lithium tetrafluoroborate to lithium hydride was 1:1.02. The reaction temperature was 0°C and the reaction time was 0.8h. Then nitrogen was purged for 0.2h. The reaction solution was filtered to remove lithium hydride. The filtrate was concentrated, filtered and dried to obtain the product. The concentration temperature was 45°C and the drying temperature was 85°C.

[0030] Comparative Example 2

[0031] The purification method of lithium tetrafluoroborate of the present embodiment comprises the following steps:

[0032] Under nitrogen protection, lithium chloride was added to 2kg lithium tetrafluoroborate solution and stirred for reaction, the molar ratio of free acid in lithium tetrafluoroborate to lithium chloride was 1:1.06, the reaction temperature was 10°C, the reaction time was 0.5h, and then nitrogen was purged for 0.5h; the reaction liquid was filtered to remove lithium chloride, and the filtrate was concentrated, filtered, and dried to obtain the product, the concentration temperature was 40°C, and the drying temperature was 80°C.

[0033] Table 1 Purification effect of lithium tetrafluoroborate

[0034]

Claims

1. A method for purifying lithium tetrafluoroborate, characterized in that: The method comprises the following steps: adding lithium salt into lithium tetrafluoroborate solution under nitrogen protection, stirring and dispersing, introducing boron trifluoride gas for reaction, purging the solution with inert gas after the reaction, filtering off excess lithium salt, and concentrating, filtering and drying the filtrate to obtain qualified lithium tetrafluoroborate.

2. The method for purifying lithium tetrafluoroborate according to claim 1, characterized in that: The molar ratio of the free acid, the lithium salt and the boron trifluoride in the lithium tetrafluoroborate is 1:(1-1.06):

1.

3. The method for purifying lithium tetrafluoroborate according to claim 1, characterized in that: The lithium salt is lithium chloride or lithium hydride, with a purity of ≥99.9%, the purity of boron trifluoride is ≥99.9%, and the water content of the lithium salt is ≤0.001%.

4. The method for purifying lithium tetrafluoroborate according to claim 1, characterized in that: The reaction temperature is 0°C to 20°C, the reaction time is 0.2 to 8 hours, and the inert gas purge time is 0.2 to 0.8 hours.

5. The method for purifying lithium tetrafluoroborate according to any one of claims 1 to 4, characterized in that: The inert gas is nitrogen.

6. The method for purifying lithium tetrafluoroborate according to any one of claims 1 to 4, characterized in that: The concentration temperature is 45°C and the drying temperature is 85°C.

Images