Method for preparing battery-grade lithium fluoride from lithium sulfate brine

Abstract

The invention belongs to the technical field of lithium ion battery materials, and discloses a method for preparing battery-grade lithium fluoride from lithium sulfate brine. The method comprises the following preparation steps: (1) preparing lithium oxalate: putting lithium sulfate brine into a reaction kettle, then adding barium oxalate for reaction, filtering, taking filtrate, concentrating, cooling and crystallizing to obtain lithium oxalate; (2) removing barium from lithium oxalate: dissolving lithium oxalate with deionized water, and performing deep barium removal in a resin impurity removal manner to ensure that the concentration of barium ions is less than or equal to 5ppm; and (3) charging reaction: adding the barium-removed lithium oxalate solution into an ammonium fluoride solution, stirring to react, filtering after the reaction is completed, taking a solid phase, washing, and drying to obtain the battery-grade lithium fluoride. According to the method disclosed by the invention, the battery-grade lithium fluoride can be prepared by adopting the lithium sulfate brine with high sodium level, the technological process is simple and short, the loss of lithium is reduced, and the raw material cost in the whole process is low.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a method for preparing battery-grade lithium fluoride by using lithium sulfate brine. BACKGROUND

[0002] With the increasing popularity of new energy in various countries, the research on new energy materials is more and more in-depth. As the main research object of new energy and its wide use, the demand for reducing the production cost of lithium ion batteries is more and more urgent. As one of the raw materials of lithium ion batteries, the demand for lithium fluoride is increasing. At present, most of the lithium sources for preparing lithium fluoride are concentrated in high-purity lithium carbonate or high-purity lithium salt, and the requirements for raw lithium salt are very strict.

[0003] The reaction process using high-purity lithium carbonate as raw material mainly passes high-purity lithium carbonate into carbon dioxide gas for carbonation reaction to obtain lithium bicarbonate solution, and then reacts with hydrofluoric acid to obtain lithium fluoride. The reaction process using high-purity lithium salt as raw material mainly reacts high-purity soluble lithium salt, such as high-purity lithium chloride, lithium nitrate, lithium bromide, lithium sulfate, etc. with hydrofluoric acid or soluble fluorine salt to obtain lithium fluoride.

[0004] The above existing preparation schemes of lithium fluoride are generally concentrated in preferentially purifying lithium-containing substances, and then preparing lithium fluoride or converting into an intermediate state with high purity and low impurities for reaction to prepare lithium fluoride. The lithium loss of this kind is also high, and the cost is high.

[0005] High-sodium lithium sulfate brine is derived from lithium sulfate obtained by ore extraction. The main ions in the lithium sulfate brine include Li, Na, K, Ca, Mg, Al, Fe, SO4 2-Although most impurities have been removed through the processes of adjusting the alkali, removing impurities, and removing calcium carbonate, these impurity removal methods do not remove Na and K ions. However, there are few methods for preparing lithium fluoride under the condition of high Na and K content. The technology for preparing battery-grade lithium fluoride using lithium sulfate brine with high Na and K content is not mature. These ions are entrained in lithium fluoride during the preparation process, resulting in lithium fluoride impurities that do not meet the battery-grade standard. Although Na and K in the brine can be removed by resin and membrane treatment, freezing, and other methods, or by using purified lithium carbonate or an intermediate state with high purity and low impurities to prepare lithium fluoride, these methods have high requirements for resins and membranes, are complex, have high energy consumption and cost, and are not conducive to industrial production. This is because lithium sulfate brine has high Na and K content. In order to control the Na and K content for the preparation of battery-grade lithium fluoride, resin is used to remove Na and K. However, since lithium, sodium, and potassium are monovalent ions, lithium loss is high, and the cost of the resin is high. In addition, sulfate ions in lithium sulfate brine also need to be removed. If lithium sulfate is used to prepare lithium carbonate, and then lithium fluoride is prepared, due to the high Na and K content of lithium sulfate brine, only industrial-grade lithium carbonate can be prepared. The lithium fluoride prepared from industrial-grade lithium carbonate does not meet the battery-grade standard. Therefore, further purification of lithium carbonate is required to prepare qualified lithium fluoride. SUMMARY

[0006] In view of the defects and deficiencies of the prior art, the purpose of the present application is to provide a method for preparing battery-grade lithium fluoride using lithium sulfate brine. The preparation method of the present application can well prepare battery-grade lithium fluoride using lithium sulfate brine. The method prepares lithium oxalate, reduces the sulfate content in the brine, and correspondingly reduces the Na and K content in the lithium oxalate. The method uses a spraying and multi-point simultaneous feeding method, reduces the feeding rate, controls the feeding time, reduces the crystallization rate, and improves the crystallization. The method can effectively prevent the entrainment of Na and K in the lithium fluoride crystallization process, and remove most of the Na and K impurities in the lithium fluoride through high-temperature water washing, thereby improving the quality of the lithium fluoride.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] A method for preparing battery-grade lithium fluoride using lithium sulfate brine, comprising the following preparation steps:

[0009] (1) Lithium oxalate preparation: lithium sulfate brine is placed in a reaction kettle, and then barium oxalate is added for reaction. The filtrate is concentrated and then crystallized by cooling to obtain lithium oxalate;

[0010] (2) Lithium oxalate barium removal: the lithium oxalate obtained in step (1) is dissolved in deionized water and then subjected to deep barium removal by resin impurity removal to ensure that the barium ion concentration is ≦5 ppm;

[0011] (3) Feeding reaction: the lithium oxalate solution after removing barium is added to the ammonium fluoride solution for stirring reaction, after the reaction is completed, filtration is performed, the solid phase is washed, dried, and battery-grade lithium fluoride is obtained.

[0012] Further, the lithium sulfate brine in step (1) contains Li + : 5-30 g / L, Na + : 1-6 g / L, K + : ≦1 g / L, and the remaining impurities are ≦5 ppm.

[0013] Further, the molar ratio of the amount of barium oxalate added in step (1) to lithium sulfate in the lithium sulfate brine is 1:1-1:1.2.

[0014] Further, the reaction temperature in step (1) is controlled at 30-90°C, and the reaction time is 0.5-2 h.

[0015] Further, the temperature for cooling crystallization in step (1) is 10-20°C.

[0016] Further, the resin impurity removal in step (2) refers to deep barium removal using Purolite S940 ion exchange resin at room temperature at a flow rate of 0.5-1 BV / h.

[0017] Further, the mass fraction of the ammonium fluoride solution in step (3) is 31%-35%.

[0018] Further preferably, the ammonium fluoride solution is prepared by mixing hydrofluoric acid and ammonia water, or is prepared by mixing ammonium fluoride and deionized water.

[0019] Further, the lithium oxalate solution in step (3) is added to the ammonium fluoride solution in a multi-point spray feeding manner, and the feeding time is controlled at 1-3 h.

[0020] Further, the stirring reaction temperature in step (3) is 20-35°C, the time is 30 min-60 min, and the stirring speed is 200 r / min-300 r / min.

[0021] Further, the washing in step (3) refers to high-temperature stirring washing using deionized water at a temperature of 80-100°C.

[0022] Further preferably, the high-temperature stirring washing is performed 1-3 times, each time for 5 min-30 min, and the deionized water usage is 200%-500% of the mass of the solid phase product.

[0023] Further, the purity of the battery-grade lithium fluoride in step (3) is ≥ 99.95%, the particle size is 5-20 μm, Na + ≤ 10 ppm, K + ≤ 5 ppm, and the remaining impurities ≤ 1 ppm.

[0024] The principle of the present application is that the lithium sulfate brine contains a high content of sodium ions and potassium ions. Since lithium ions, sodium ions and potassium ions are monovalent ions, directly removing sodium and potassium by using resin will result in high lithium loss, and the cost of such resin is relatively high. In addition, since the solubility difference between lithium sulfate and sodium sulfate and potassium sulfate is relatively small, it is difficult to effectively reduce the content of sodium and potassium at a low lithium loss by means of crystallization purification. The present application first converts lithium sulfate into lithium oxalate, thereby expanding the solubility difference between lithium salt and sodium salt and potassium salt. By cooling and crystallization, lithium oxalate is crystallized and precipitated, and most of the sodium ions and potassium ions are left in the solution. The obtained lithium oxalate crystal contains very little sodium and potassium, which can effectively reduce the content of sodium and potassium. A small amount of barium, potassium and sodium is entrained in the lithium oxalate crystallization process. Resin is used to further remove barium. By using the multi-point spraying dispersion feeding reaction mode, the feeding rate is reduced, the feeding time is prolonged, and the crystallization rate is controlled, thereby making the crystallization more perfect, effectively preventing the small amount of entrained sodium and potassium in the lithium oxalate crystal from being entrained in the lithium fluoride crystallization process, and preparing battery-grade lithium fluoride.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] (1) The preparation method of the present application can not only prepare battery-grade lithium fluoride from lithium sulfate brine with high sodium level, but also has a simple process flow, short process flow, reduces the loss of lithium, and the raw material cost of the whole process is low.

[0027] (2) By converting lithium sulfate brine into lithium oxalate to prepare lithium fluoride, the intermediate purification is reduced, and the content of sodium and potassium in lithium oxalate can be very easily controlled, thereby reducing the cost of intermediate purification. Since the solution contains a certain amount of barium, resin is needed to remove barium. Compared with resin for removing sodium and potassium, the lithium loss is low during the process of removing barium by resin, and the cost of resin is not high.

[0028] (3) By further using the multi-point spraying dispersion feeding reaction mode, the feeding rate is reduced, the feeding time is prolonged, and the crystallization rate is controlled, thereby making the crystallization more perfect, effectively preventing the sodium and potassium from being entrained in the lithium fluoride crystallization process, and improving the quality of lithium fluoride.

[0029] (4) By using the method of high-temperature water washing, the impurities in lithium fluoride can be effectively removed, because the solubility of impurities is large at high temperature. DETAILED DESCRIPTION

[0030] The application will be further described in detail below with reference to examples, but the embodiments of the application are not limited thereto.

[0031] Example 1

[0032] A method for preparing battery-grade lithium fluoride from lithium sulfate brine, comprising the following preparation steps:

[0033] (1) Preparation of lithium oxalate: lithium sulfate brine (Li2SO4: 10.4 g / L, Na2SO4: 4.6 g / L, K2SO4: 0.65 g / L, and other impurities < 5 ppm) is placed in a reaction kettle, and barium oxalate is added in a lithium sulfate to barium molar ratio of 1:1.1 for reaction, the reaction temperature is controlled at 60°C, the reaction time is 1 h, after the reaction is completed, filtration is performed, the filtrate is concentrated, and then cooled to 15°C for crystallization, the precipitate is obtained by filtration, and washed with deionized water to obtain lithium oxalate. + :10.4g / L, Na + :4.6g / L, K + :0.65g / L, and other impurities < 5 ppm) is placed in a reaction kettle, and barium oxalate is added in a lithium sulfate to barium molar ratio of 1:1.1 for reaction, the reaction temperature is controlled at 60°C, the reaction time is 1 h, after the reaction is completed, filtration is performed, the filtrate is concentrated, and then cooled to 15°C for crystallization, the precipitate is obtained by filtration, and washed with deionized water to obtain lithium oxalate.

[0034] (2) Barium removal from lithium oxalate: the lithium oxalate obtained in step (1) is dissolved with deionized water to obtain a lithium oxalate solution. Then, deep barium removal is performed on the lithium oxalate solution at room temperature by passing it through a Purolite S940 ion exchange resin at a flow rate of 0.75 BV / h, so that the barium ion concentration is ≤5 ppm.

[0035] (3) Feeding reaction: the lithium oxalate solution after barium removal is fed into a 32% mass fraction ammonium fluoride solution (prepared by mixing 40% hydrofluoric acid and ammonia water in a molar ratio of 1:1, at a temperature of 25°C) by means of multi-point spray feeding, and stirred for reaction, the feeding time is controlled at 2 h, the feeding temperature is 30°C, and the stirring speed is 250 r / min; after the feeding is completed, stirring and heat preservation are continued for 40 min. After the reaction is completed, filtration is performed, the solid phase is washed with 400% deionized water for stirring twice, each time for 20 min, the stirring and washing temperature is 90°C, and after filtration, drying is performed to obtain battery-grade lithium fluoride (purity 99.99%, particle size D50 = 7.53 μm, Na2SO4 concentration 5 ppm, K2SO4 concentration 3 ppm, and other impurities < 1 ppm). + :10.4g / L, Na + :4.6g / L, K + :0.65g / L, and other impurities < 5 ppm) is placed in a reaction kettle, and barium oxalate is added in a lithium sulfate to barium molar ratio of 1:1.1 for reaction, the reaction temperature is controlled at 60°C, the reaction time is 1 h, after the reaction is completed, filtration is performed, the filtrate is concentrated, and then cooled to 15°C for crystallization, the precipitate is obtained by filtration, and washed with deionized water to obtain lithium oxalate.

[0036] Example 2

[0037] A method for preparing battery-grade lithium fluoride from lithium sulfate brine, comprising the following preparation steps:

[0038] (1) Preparation of lithium oxalate: lithium sulfate brine (Li2SO4: 10.4 g / L, Na2SO4: 4.6 g / L, K2SO4: 0.65 g / L, and other impurities < 5 ppm) is placed in a reaction kettle, and barium oxalate is added in a lithium sulfate to barium molar ratio of 1:1.1 for reaction, the reaction temperature is controlled at 60°C, the reaction time is 1 h, after the reaction is completed, filtration is performed, the filtrate is concentrated, and then cooled to 15°C for crystallization, the precipitate is obtained by filtration, and washed with deionized water to obtain lithium oxalate. + :10.4g / L, Na + :4.6g / L, K +(0.25 g / L, other impurities < 5 ppm) was placed in a reaction vessel, and barium oxalate was added at a molar ratio of lithium sulfate to barium of 1:1. The reaction temperature was controlled at 30℃ and the reaction time was 2 h. After the reaction was completed, the mixture was filtered, the filtrate was concentrated and cooled to 10℃ to crystallize, the precipitate was filtered and washed with deionized water to obtain lithium oxalate.

[0039] (2) Barium removal with lithium oxalate: The lithium oxalate obtained in step (1) is dissolved in deionized water to obtain a lithium oxalate solution. Then, at room temperature, it is passed through Purolite S940 ion exchange resin for deep barium removal at a flow rate of 0.5 BV / h to make the barium ion concentration ≤ 5 ppm.

[0040] (3) Feeding reaction: The barium-removed lithium oxalate solution was added to a 31% ammonium fluoride solution (prepared by mixing ammonium fluoride and deionized water) using a multi-point spray feeding method. The reaction was stirred for 1 hour, the feeding temperature was 20℃, and the stirring speed was 300 r / min. After feeding, the reaction was continued for 60 minutes with stirring and heat preservation. After the reaction was completed, the mixture was filtered, and the solid phase was washed twice with 200% deionized water with stirring. Each washing time was 30 minutes, and the washing temperature was 80℃. After filtration and drying, battery-grade lithium fluoride (purity 99.96%, particle size D50 = 6.38 μm, Na) was obtained. + The concentration is 4 ppm, K + The concentration is 2 ppm, and other impurities are <1 ppm.

[0041] Example 3

[0042] A method for preparing battery-grade lithium fluoride using lithium sulfate brine includes the following preparation steps:

[0043] (1) Preparation of lithium oxalate: Lithium sulfate brine (Li + 15.0 g / L, Na + 5.8g / L, K + (Lithium oxalate) with a concentration of 0.84 g / L and other impurities <5 ppm was placed in a reaction vessel. Barium oxalate was added at a molar ratio of lithium to barium of 1:1.2. The reaction temperature was controlled at 45℃ and the reaction time was 0.5 h. After the reaction was completed, the mixture was filtered, the filtrate was concentrated, and then cooled to 20℃ to crystallize. The precipitate was filtered and washed with deionized water to obtain lithium oxalate.

[0044] (2) Barium removal with lithium oxalate: The lithium oxalate obtained in step (1) is dissolved in deionized water to obtain a lithium oxalate solution. Then, at room temperature, it is passed through Purolite S940 ion exchange resin for deep barium removal at a flow rate of 1 BV / h to make the barium ion concentration ≤5 ppm.

[0045] (3) Feeding reaction: the barium-removed lithium oxalate solution was added into the 35% ammonium fluoride solution (prepared by mixing ammonium fluoride and deionized water) by multi-point spray feeding, the feeding time was controlled for 3 h, the feeding temperature was 35°C, and the stirring speed was 200 r / min; after the feeding was completed, the stirring was continued for 30 min. After the reaction was completed, filtration was performed, the solid phase was stirred with 500% deionized water for two times, each time for 5 min, the stirring temperature was 100°C, and after filtration, drying was performed to obtain the battery-grade lithium fluoride (purity 99.98%, particle size D50 = 7.69 μm, Na + concentration 8 ppm, K + concentration 5 ppm, and other impurities < 1 ppm).

[0046] Example 4

[0047] A method for preparing battery-grade lithium fluoride from lithium sulfate brine, comprising the following preparation steps:

[0048] (1) Preparation of lithium oxalate: lithium sulfate brine (Li + : 29.6 g / L, Na + : 6.0 g / L, K + : 0.98 g / L, and other impurities < 5 ppm) was placed in a reaction kettle, and barium oxalate was added in a molar ratio of 1:1.1 of lithium sulfate to barium for reaction, the reaction temperature was controlled at 90°C, and the reaction time was 1 h; after the reaction was completed, filtration was performed, the filtrate was concentrated, and then cooled to 15°C for crystallization, the precipitate was filtered and washed with deionized water to obtain lithium oxalate.

[0049] (2) Barium removal from lithium oxalate: the lithium oxalate obtained in step (1) was dissolved with deionized water to obtain a lithium oxalate solution. Then, deep barium removal was performed by passing the solution through Purolite S940 ion exchange resin at a flow rate of 0.75 BV / h at room temperature, so that the barium ion concentration was ≦5 ppm.

[0050] (3) Feeding reaction: the barium-removed lithium oxalate solution was added into the 35% ammonium fluoride solution (prepared by mixing ammonium fluoride and deionized water) by multi-point spray feeding, the feeding time was controlled for 3 h, the feeding temperature was 35°C, and the stirring speed was 200 r / min; after the feeding was completed, the stirring was continued for 30 min. After the reaction was completed, filtration was performed, the solid phase was stirred with 500% deionized water for two times, each time for 5 min, the stirring temperature was 100°C, and after filtration, drying was performed to obtain the battery-grade lithium fluoride (purity 99.98%, particle size D50 = 7.69 μm, Na + concentration 8 ppm, K +Concentration 3 ppm, other impurities <1 ppm).

[0051] Comparative Example 1

[0052] This comparative example is compared with Example 1, and the lithium sulfate brine is directly reacted with the ammonium fluoride solution. The specific steps are as follows:

[0053] The lithium sulfate brine (Li + : 10.4 g / L, Na + : 4.6 g / L, K + : 0.65 g / L, other impurities <5 ppm) is added to the 32% ammonium fluoride solution (40% hydrofluoric acid and ammonia water are mixed in a molar ratio of 1:1, and the temperature is 25°C) by a multi-point spraying feeding method. The feeding time is controlled for 2 h, the feeding temperature is 30°C, and the stirring speed is 250 r / min. After the feeding is completed, the stirring is maintained for 40 min. After the reaction is completed, the solid phase is filtered, washed with 400% deionized water for two times, each time for 20 min, the stirring and washing temperature is 90°C, and then dried after filtration to obtain lithium fluoride (purity 99.92%, particle size D50 = 12.53 μm, Na + : 24 ppm, K + : 16 ppm, other impurities <1 ppm).

[0054] It can be seen from the comparison between this comparative example and Example 1 that the lithium fluoride product prepared by converting the lithium sulfate brine into lithium oxalate can significantly reduce the Na + , K + content, so as to reach the quality standard of battery-grade lithium fluoride.

[0055] Comparative Example 2

[0056] This comparative example is compared with Example 1, and the lithium oxalate solution is added by a one-time feeding method instead of a multi-point spraying feeding method. The specific steps are as follows:

[0057] Steps (1)-(2) are the same as those in Example 1.

[0058] (3) feeding reaction: the lithium oxalate solution after removing barium was added to the 32% mass fraction of ammonium fluoride solution (40% hydrofluoric acid and ammonia water were mixed according to a molar ratio of 1:1, and the temperature was 25°C) for stirring reaction, the feeding time was controlled within 2h, the feeding temperature was 30°C, and the stirring speed was 250r / min; after the feeding was completed, the stirring was maintained for 40min for reaction. After the reaction was completed, filtration was performed, the solid phase was stirred with 400% deionized water for washing twice, each time for 20min, the stirring and washing temperature was 90°C, after filtration, drying was performed, and lithium fluoride was obtained (purity 99.91%, particle size D50=16.35μm, Na + concentration 18ppm, K + concentration 16ppm, and the rest of the impurities were less than 1ppm).

[0059] It can be seen from the comparison results of the present comparative example and example 1 that the present application further adopts the multi-point spraying dispersion feeding reaction mode, which can effectively prevent the sodium and potassium from being entrained in the lithium fluoride crystallization process, significantly reduces the Na + , K + content in the lithium fluoride product, and improves the quality of the lithium fluoride.

[0060] Comparative examples 3-6

[0061] Comparative examples 3-6 were compared with examples 1-4 respectively, step (1) directly concentrated the lithium sulfate brine to the same volume and cooled to the same crystallization temperature for crystallization (without adding barium oxalate for reaction), and the crystallization precipitate (without washing) was taken for testing lithium loss (the reduction rate of the lithium content in the crystallization precipitate compared with the lithium content in the lithium sulfate brine) and Na + , K + removal rate (the reduction rate of the Na + , K + content in the crystallization precipitate compared with the Na + , K + content in the lithium sulfate brine), and were compared with the lithium oxalate crystallization precipitate (before deionized water washing) obtained in step (1) of examples 1-4 respectively, and the corresponding test results are shown in Table 1.

[0062] Table 1

[0063]

[0064] It can be seen from the results in Table 1 that the Na + , K + removal rate is obviously reduced by directly using the lithium sulfate brine crystallization, and the lithium loss is too high, which is not practical. The present application converts the lithium sulfate brine into lithium oxalate, which improves the Na + , K +The removal rate is high, the lithium loss is effectively reduced, and the high-sodium lithium sulfate brine is used to prepare the battery-grade lithium fluoride through a simple and low-cost process.

[0065] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are included in the protection scope of the present application.

Claims

1. A method for preparing battery-grade lithium fluoride using lithium sulfate brine, characterized in that, The preparation steps include the following: (1) Preparation of lithium oxalate: Lithium sulfate brine is placed in a reaction vessel, then barium oxalate is added to react, filtered, the filtrate is concentrated and cooled to crystallize, and lithium oxalate is obtained. (2) Removal of barium from lithium oxalate: The lithium oxalate obtained in step (1) is dissolved in deionized water and then subjected to deep barium removal by resin purification to ensure that the barium ion concentration is ≤5ppm. (3) Feeding reaction: The barium-removed lithium oxalate solution is added to the ammonium fluoride solution and stirred to react. After the reaction is completed, the mixture is filtered, the solid phase is washed and dried to obtain battery-grade lithium fluoride.

2. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The lithium sulfate brine described in step (1) contains Li + 5~30g / L, Na + 1~6g / L, K + :≦1g / L, other impurities≦5ppm.

3. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The molar ratio of barium oxalate added in step (1) to lithium sulfate in lithium sulfate brine is 1:1 to 1:1.

2.

4. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The reaction temperature in step (1) is controlled at 30℃~90℃, and the reaction time is 0.5h~2h; the temperature for cooling crystallization is 10~20℃.

5. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The resin impurity removal mentioned in step (2) refers to deep barium removal using Purolite S940 ion exchange resin at a flow rate of 0.5 to 1 BV / h at room temperature.

6. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The mass fraction of the ammonium fluoride solution in step (3) is 31% to 35%; it is prepared by mixing hydrofluoric acid and ammonia water, or by mixing ammonium fluoride and deionized water.

7. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, In step (3), the lithium oxalate solution is added to the ammonium fluoride solution using a multi-point spray feeding method, and the feeding time is controlled to be 1-3 hours.

8. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The temperature of the stirring reaction in step (3) is 20-35℃, the time is 30-60min, and the stirring speed is 200r / min-300r / min.

9. The method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The washing mentioned in step (3) refers to washing with deionized water at a high temperature of 80-100°C by stirring. The number of high-temperature stirring washes is 1-3 times, the washing time for each wash is 5-30 minutes, and the amount of deionized water used in each wash is 200%-500% of the mass of the solid product.

10. A method for preparing battery-grade lithium fluoride using lithium sulfate brine according to claim 1, characterized in that, The battery-grade lithium fluoride mentioned in step (3) has a purity of ≥99.95% and a particle size of 5–20 μm, Na + ≤10ppm, K + ≤5ppm, other impurities ≤1ppm.

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