A method for preparing lithium fluoride and a method for preparing lithium hexafluorophosphate
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-15
- Publication Date
- 2026-08-14
AI Technical Summary
[0005]本发明提供一种氟化锂制备方法及六氟磷酸锂制备方法，旨在解决六氟磷酸锂生产过程中设备腐蚀严重及六氟磷酸锂产品水分偏高的问题
现有技术生产氟化锂的工艺中，碳酸氢锂溶液是弱碱性的，pH在8左右，溶液中有大量碳酸氢根(HCO3-)，加入氢氟酸生成氟化锂沉淀时，氟化锂晶体会裹挟[HCO3-]，即氟化锂产品中会含有LiHCO3杂质，后续用该氟化锂制备六氟磷酸锂时，杂质LiHCO3与溶剂HF反应生成水，反应式为LiHCO3+ HF → LiF↓+ H2O + CO2↑，从而把水分引入反应体系，该水分正是上述(1)和(2)两个问题的真正原因。
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Figure CN122561992A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium battery electrolyte technology, specifically relating to a method for preparing lithium fluoride and a method for preparing lithium hexafluorophosphate. Background Technology
[0002] Lithium fluoride (LiF) is one of the essential raw materials for preparing lithium hexafluorophosphate, a lithium battery electrolyte. Lithium hexafluorophosphate is usually prepared by reacting lithium fluoride with phosphorus pentafluoride in anhydrous hydrogen fluoride. The quality of lithium fluoride is one of the important factors affecting the quality of lithium hexafluorophosphate products.
[0003] The commonly used method for preparing lithium fluoride is as follows: lithium carbonate is dispersed in water to form a slurry, then carbon dioxide is passed through to generate a lithium bicarbonate solution, followed by the addition of hydrofluoric acid to form a lithium fluoride precipitate. The precipitate is then filtered and dried to obtain the lithium fluoride product. The chemical reactions involved include: Li2CO3+ H2O + CO2→ 2LiHCO3 (a) LiHCO3+ HF → LiF↓+ H2O + CO2↑ (b).
[0004] However, the following problems frequently occur when using LiF prepared by this method to produce hexafluorophosphate (LiPF6): (1) severe equipment corrosion, and (2) high moisture content in the lithium hexafluorophosphate product. Those skilled in the art know that the production of LiPF6 from LiF and PF5 strictly requires anhydrous raw materials and must be carried out in an anhydrous environment. They also know that anhydrous hydrogen fluoride is not highly corrosive; for example, when storing anhydrous hydrofluoric acid in steel containers, the corrosive ability increases exponentially only when water is present. Production personnel have repeatedly tested the moisture content of the raw materials LiF, PF5, and anhydrous hydrogen fluoride, as well as the equipment's sealing performance. The raw materials have extremely low moisture content, and the equipment is well-sealed, so there is absolutely no factor introducing moisture. Therefore, the source of the moisture remains unclear, and the above problems (1) and (2) cannot be resolved. Summary of the Invention
[0005] This invention provides a method for preparing lithium fluoride and a method for preparing lithium hexafluorophosphate, aiming to solve the problems of severe equipment corrosion and high moisture content in lithium hexafluorophosphate products during the production process.
[0006] To achieve the above-mentioned objectives, the technical solution adopted by the present invention includes two aspects: the first aspect is a method for preparing lithium fluoride, and the second aspect is a method for preparing lithium hexafluorophosphate.
[0007] A method for preparing lithium fluoride includes the following steps: first, adding an acidic solution to a reaction vessel, then simultaneously adding a lithium bicarbonate solution and a hydrofluoric acid solution, stirring the reaction to produce lithium fluoride precipitate, keeping the reaction system continuously acidic, then separating the solid and liquid, and drying the solid to obtain the lithium fluoride product.
[0008] Furthermore, the acidic solution is a dilute hydrofluoric acid solution, preferably with a pH value of 1-2.
[0009] Furthermore, the feeding rates of the lithium bicarbonate solution and the hydrofluoric acid solution satisfy a solute molar ratio of 1:0.5-2.
[0010] Furthermore, the lithium bicarbonate solution is a saturated solution, and the hydrofluoric acid solution concentration is 10-50 wt%.
[0011] Furthermore, the temperature of the reaction system is controlled between 0-100℃.
[0012] Furthermore, the pH of the system is 4-5 at the end of the reaction. Under these conditions, a small amount of acid is used while still ensuring an acidic environment.
[0013] Furthermore, the mother liquor after solid-liquid separation is reused as the acidic solution.
[0014] A method for preparing lithium hexafluorophosphate involves dissolving lithium fluoride obtained by the above method in anhydrous hydrogen fluoride, introducing phosphorus pentafluoride gas, and filtering and drying after the reaction to obtain the lithium hexafluorophosphate product.
[0015] Furthermore, the temperature of the reaction system is controlled between 0 and 19°C.
[0016] Furthermore, after the reaction is complete, the temperature is lowered to -30 to 0°C, and then filtered.
[0017] Compared with the prior art, the present invention has the following beneficial effects: In existing processes for producing lithium fluoride, the lithium bicarbonate solution is weakly alkaline, with a pH of around 8, and contains a large amount of bicarbonate ions (HCO3-). - When hydrofluoric acid is added to form lithium fluoride precipitate, the lithium fluoride crystals will be encapsulated with [HCO3]. - That is, lithium fluoride products contain LiHCO3 impurities. When lithium hexafluorophosphate is prepared from this lithium fluoride, the impurity LiHCO3 reacts with the solvent HF to generate water. The reaction formula is LiHCO3 + HF → LiF↓ + H2O + CO2↑, thus introducing water into the reaction system. This water is the real reason for the above two problems (1) and (2).
[0018] This application introduces an acidic solution into the reaction system beforehand, and then simultaneously adds lithium bicarbonate solution and hydrofluoric acid solution to control the reaction system to remain acidic at all times, so that [HCO3] - Rapid decomposition and non-persistence prevent lithium fluoride crystals from being trapped within [HCO3]. -This means that the lithium fluoride product no longer contains LiHCO3 impurities, and no water is generated during the subsequent preparation of lithium hexafluorophosphate using this lithium fluoride. This effectively solves the problems of severe equipment corrosion and high moisture content in the lithium hexafluorophosphate product. Furthermore, the mother liquor after solid-liquid separation can be reused as the initial acidic solution for the reaction without increasing production costs, making it suitable for widespread use. Attached Figure Description
[0019] Figure 1 Images showing the phenolphthalein indicator detection of lithium fluoride products in Examples 1-3.
[0020] Figure 2 Image showing the phenolphthalein indicator test of lithium fluoride product in Comparative Example 1. Detailed Implementation
[0021] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. These embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention or the method of implementing the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] Example 1 A method for preparing lithium fluoride.
[0023] At 20℃, 800g of 1wt% hydrofluoric acid aqueous solution (pH 1) was first added to a 5L reactor. Then, 8.5wt% lithium bicarbonate solution and 40wt% hydrofluoric acid solution were added simultaneously. The lithium bicarbonate solution was added at a rate of 80g / min and the hydrofluoric acid solution was added at a rate of 5g / min. The mixture was stirred while adding the materials for 10 minutes. The addition was then stopped and the mixture was allowed to stand for 10 minutes. At this point, the pH was 1.8. The mixture was then filtered, washed, and dried in a vacuum chamber at 110℃ for 2 hours to obtain lithium fluoride product.
[0024] Example 2 A method for preparing lithium fluoride.
[0025] At 25℃, 800g of a 0.12wt% hydrofluoric acid aqueous solution (pH 2) was first added to a 5L reactor. Then, an 8.5wt% lithium bicarbonate solution and a 30wt% hydrofluoric acid solution were added simultaneously. The lithium bicarbonate solution was added at a rate of 40g / min, and the hydrofluoric acid solution was added at a rate of 4g / min. The mixture was stirred while adding the solutions for 20min. The addition was then stopped and the mixture was allowed to stand for 10min. At this point, the pH was 1.9. The mixture was then filtered, washed, and dried in a vacuum chamber at 110℃ for 2h to obtain the lithium fluoride product.
[0026] Example 3 A method for preparing lithium fluoride.
[0027] At 30℃, 800g of a 0.4wt% hydrofluoric acid aqueous solution with a pH of 1.5 was first added to a 5L reactor. Then, a 7wt% lithium bicarbonate solution and a 49wt% hydrofluoric acid solution were added simultaneously. The lithium bicarbonate solution was added at a rate of 108.6g / min, and the hydrofluoric acid solution was added at a rate of 4.1g / min. The mixture was stirred while being added for 10 minutes. The addition was then stopped and the mixture was allowed to stand for 10 minutes. At this point, the pH was 2.5. The mixture was then filtered, washed, and dried in a vacuum chamber at 110℃ for 2 hours to obtain the lithium fluoride product.
[0028] Example 4 A method for preparing lithium fluoride.
[0029] At 70°C, 800g of the filtrate from Example 2 was first added to a 5L reactor, with a pH of 1.9. Then, an 8wt% lithium bicarbonate solution and a 10wt% hydrofluoric acid solution were added simultaneously. The lithium bicarbonate solution was added at a rate of 60.8g / min, and the hydrofluoric acid solution was added at a rate of 13.3g / min. The mixture was stirred while being added for 15 minutes. The addition was then stopped and the mixture was allowed to stand for 10 minutes. At this point, the pH was 4. The mixture was then filtered, washed, and the solid was dried in a vacuum chamber at 110°C for 2 hours to obtain the lithium fluoride product.
[0030] Comparative Example 1 A method for preparing lithium fluoride.
[0031] At 20℃, 1000g of 8.5wt% lithium bicarbonate solution was first added to a 5L reactor, followed by dropwise addition of 40wt% hydrofluoric acid solution at a rate of 7.5g / min. The mixture was stirred while adding the solution for 10 minutes, then the addition was stopped and the mixture was allowed to stand for 10 minutes. At this point, the pH was 1.8. The mixture was then filtered, washed, and the solid was dried in a vacuum chamber at 110℃ for 2 hours to obtain lithium fluoride product.
[0032] Detection example The lithium fluoride products from Examples 1-3 and Comparative Example 1 were ground to 200 mesh. 100 ml of purified water was placed in a beaker, 3 drops of phenolphthalein indicator were added, then 10 g of the ground lithium fluoride was added. After stirring for 1 minute, the mixture was allowed to stand and the color was observed. The products from Examples 1-3 were colorless. Figure 1 Comparative Example 1 product is red, such as Figure 2 This result demonstrates that the comparative lithium fluoride product contains lithium bicarbonate impurities. The hydrolysis of lithium bicarbonate makes the solution weakly alkaline, causing the phenolphthalein indicator to turn red.
[0033] Example 5 A method for preparing lithium hexafluorophosphate.
[0034] At 15°C, 9g of lithium fluoride obtained in Example 1 was dissolved in 100g of anhydrous hydrogen fluoride in a closed reactor. Then, 50g of high-purity phosphorus pentafluoride was introduced and reacted for 10 minutes. The mixture was then cooled to -5°C, filtered, and the solid was dried in a vacuum chamber at 90°C for 3 hours to obtain lithium hexafluorophosphate. The moisture content was found to be 4ppm.
[0035] Comparative Example 2 A method for preparing lithium hexafluorophosphate.
[0036] At 15°C, 9g of lithium fluoride obtained from Comparative Example 1 was dissolved in 100g of anhydrous hydrogen fluoride in a closed reactor. Then, 50g of high-purity phosphorus pentafluoride was introduced and reacted for 10 minutes. The mixture was then cooled to -5°C, filtered, and the solid was dried in a vacuum chamber at 90°C for 3 hours to obtain lithium hexafluorophosphate. The moisture content was determined to be 17ppm.
Claims
1. A method for preparing lithium fluoride, characterized in that, Includes the following steps: An acidic solution is first added to the reactor, followed by the simultaneous addition of lithium bicarbonate solution and hydrofluoric acid solution. The reaction is stirred to produce lithium fluoride precipitate, maintaining the acidity of the reaction system. Then, the solid and liquid are separated, and the solid is dried to obtain the lithium fluoride product.
2. The method according to claim 1, characterized in that, The acidic solution is an aqueous solution of hydrofluoric acid.
3. The method according to claim 2, characterized in that, The pH value of the acidic solution is 1-2.
4. The method according to claim 1, characterized in that, The feeding rates of the lithium bicarbonate solution and hydrofluoric acid solution satisfy a solute molar ratio of 1:0.5-2.
5. The method according to claim 4, characterized in that, The lithium bicarbonate solution is a saturated solution, and the hydrofluoric acid solution concentration is 10-50 wt%.
6. The method according to claim 1, characterized in that, The temperature of the reaction system is controlled between 0-100℃.
7. The method according to claim 1, characterized in that, The pH of the system was 4-5 at the end of the reaction.
8. The method according to claim 1, characterized in that, The mother liquor after solid-liquid separation is reused as the acidic solution.
9. A method for preparing lithium hexafluorophosphate, characterized in that, Lithium fluoride prepared by any of the methods of claims 1-8 is reacted with phosphorus pentafluoride in anhydrous hydrogen fluoride, and then filtered and dried to obtain lithium hexafluorophosphate.
10. The method according to claim 9, characterized in that, The reaction temperature is 0 to 19°C, and after the reaction is completed, the temperature is lowered to -30 to 0°C.