A method for preparing sodium hexafluorophosphate

Abstract

This invention provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) dissolving sodium hydrogen fluoride solid in an organic solvent, then adding phosphorus pentachloride solid, reacting to obtain a reaction mixture; (2) filtering the reaction mixture to obtain a filtrate, then evaporating and crystallizing the filtrate to obtain crude sodium hexafluorophosphate crystals; then dissolving the crude sodium hexafluorophosphate crystals in an organic solvent for multiple recrystallizations to obtain the sodium hexafluorophosphate; wherein, the organic solvent in step (1) includes any one or a combination of at least two of ethylene glycol dimethyl ether, propylene carbonate, acetonitrile, and ethyl acetate. The sodium hexafluorophosphate prepared by the method provided by this invention has high yield and purity, and the reaction conditions are mild, the operation is safe, and the preparation process is simple.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical materials technology and relates to a method for preparing sodium hexafluorophosphate. Background Technology

[0002] With the rapid development of energy storage technology, sodium-ion batteries, with their advantages of abundant resources, low cost, and high safety, have become an important supplement to lithium-ion batteries, showing broad application prospects in large-scale energy storage, low-speed electric vehicles, and other fields. Sodium hexafluorophosphate (NaPF6), as the core electrolyte salt of sodium-ion battery electrolyte, directly affects the battery's cycle stability, rate performance, and lifespan.

[0003] Currently, the mainstream preparation method for sodium hexafluorophosphate (NaPF6) mainly uses anhydrous hydrogen fluoride as a solvent, reacting phosphorus pentachloride with hydrogen fluoride salts. However, this method has many drawbacks: on the one hand, anhydrous hydrogen fluoride is highly corrosive and toxic, posing extremely high safety risks during storage, transportation, and production. It requires stringent standards for equipment materials and protective measures, resulting in high equipment protection and construction costs, and may cause environmental pollution and health hazards during storage, transportation, and use. On the other hand, in systems using hydrogen fluoride or hydrofluoric acid, raw materials (such as phosphorus pentachloride) and side reactions easily generate chlorine-containing impurities (such as HCl, POCl3, etc.), which may lead to residual moisture and acidity (HF). These impurities are difficult to completely remove through simple processes, affecting the purity of NaPF6 and limiting its application in high-end sodium-ion batteries (especially power and energy storage batteries) that require high safety and long cycle life. In other words, the reaction system easily introduces chlorine-containing impurities, subsequent purification processes are complex and energy-intensive, and it is difficult to reduce the impurity content to the stringent standards required for battery applications. Thirdly, existing methods generally involve multi-stage reactions, complex post-processing and purification steps (such as high-temperature vacuum distillation to remove harmful solvents, cumbersome adsorption and impurity removal, and complex drying procedures), resulting in a long overall process flow, complex operation, high energy consumption, poor production continuity, and unfavorable product purity control. The reasons for the above problems in the existing technology are as follows: (1) Choosing anhydrous hydrogen fluoride or high-concentration hydrofluoric acid as a solvent can provide a fluorine source and reaction environment for the reaction, but its inherent danger leads to structural defects in process safety. (2) In the hydrogen fluoride or hydrofluoric acid system, phosphorus pentafluoride (PF5) is usually generated in situ from PCl5 and HF, or directly using PF5 gas. In this process, the introduction of chlorine (from PCl5 or chlorine impurities in the solvent) and the sensitivity of the hydrogen fluoride system to trace moisture will inevitably lead to chloride ions (Cl - (3) Impurities in commonly used systems of sodium hexafluorophosphate (such as Cl) -The physicochemical properties of substances such as water and residual acid are similar to those of other substances, making it difficult for traditional precipitation, adsorption, or simple distillation methods to meet battery-grade purity requirements (e.g., Cl). - <10ppm, H2O<20ppm), must rely on energy-intensive and high-loss multi-stage recrystallization, high-temperature and high-pressure distillation or complex adsorption processes. (4) In order to achieve high purity, existing technologies often simply superimpose multiple independent unit operations (synthesis, purification, crystallization, drying), lacking synergistic optimization of reaction and separation processes, resulting in equipment redundancy and cumbersome processes.

[0004] Therefore, developing a method for preparing sodium hexafluorophosphate with mild reaction conditions, safe operation, high product purity, and simple preparation process has become a key requirement for promoting the large-scale development of the sodium-ion battery industry. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing sodium hexafluorophosphate.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) Dissolve sodium fluoride (NaHF2) solid in an organic solvent, then add phosphorus pentachloride (PCl5) solid, react, and obtain the reaction mixture; (2) The mixture after the reaction is filtered to remove insoluble impurities and obtain filtrate. Then the filtrate is evaporated and crystallized to obtain crude sodium hexafluorophosphate crystals. Then, taking advantage of the difference in solubility between sodium hexafluorophosphate and impurities in organic solvents, the crude sodium hexafluorophosphate crystals are dissolved in organic solvents and recrystallized multiple times to gradually improve the purity of the product and obtain the sodium hexafluorophosphate. The organic solvent in step (1) includes any one or a combination of at least two of ethylene glycol dimethyl ether, propylene carbonate, acetonitrile, and ethyl acetate.

[0007] The method for preparing sodium hexafluorophosphate provided by this invention uses solid phosphorus pentachloride and solid sodium hydrogen fluoride as reaction raw materials, and replaces the high-risk anhydrous hydrogen fluoride with a low-toxicity and weakly corrosive organic solvent to construct a homogeneous reaction environment. This significantly reduces production safety risks and equipment costs while improving the reaction rate and conversion rate of the raw materials, achieving a synergy between safety and efficiency. The organic solvent used in this invention is volatile and easy to remove, eliminating the need for complex instruments (such as high-temperature vacuum distillation equipment), further reducing post-processing costs and operational complexity.

[0008] This invention suppresses the formation of byproducts at the source by optimizing reaction conditions, and then uses the difference in solubility between products and impurities in organic solvents to deeply remove residual impurities through multiple recrystallization processes. The entire chain of impurity control is optimized, which can meet the stringent requirements of high-end batteries.

[0009] This invention features an innovative reaction route that requires no special atmosphere or equipment. It uses solid PCl5 and solid NaHF2 to react directly in an organic solvent, resulting in a mild and controllable reaction that reduces the generation of byproducts from the source.

[0010] Preferably, the molar ratio of phosphorus pentachloride solid and sodium fluoride solid in step (1) is 1:(1~6), such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, etc., but not limited to the listed values. Other unlisted values ​​within this range are also applicable. Preferably, it is 1:(3~6). If the proportion of sodium fluoride solid is too low, it will affect the reaction conversion efficiency. If the proportion of sodium fluoride solid is too high, more reaction raw materials will remain, increasing the difficulty of impurity removal.

[0011] Preferably, in step (1), the ratio of the total mass of sodium bifluoride solid and phosphorus pentachloride solid to the mass of organic solvent is 1:(10~24), for example 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] Preferably, the step (1) of dissolving sodium fluoride solid in an organic solvent specifically includes: mixing sodium fluoride solid and an organic solvent, heating to 60~100℃ (e.g., 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc., but not limited to the listed values, other unlisted values ​​within this range are also applicable) and stirring to dissolve.

[0013] Preferably, the reaction temperature in step (1) is 20~60℃, such as 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 20~50℃ being the preferred temperature. If the reaction temperature is too low, the reaction rate will be low; if the reaction temperature is too high, the impurity content will increase, and the substance will change color.

[0014] Preferably, the reaction time in step (1) is 6 to 48 hours, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 24 hours, 30 hours, 34 hours, 36 hours, 40 hours, 44 hours, 48 ​​hours, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 24 to 48 hours being the preferred option. By controlling the reaction time within a suitable range, the purity of the product can be higher, and the reaction efficiency can also be higher.

[0015] Preferably, the reaction in step (1) is carried out under stirring conditions.

[0016] Preferably, the evaporation and crystallization temperature in step (2) is 40~60℃, such as 40℃, 45℃, 50℃, 55℃, 60℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. By controlling the evaporation and crystallization temperature within this range, it can be ensured that sodium hexafluorophosphate will not undergo high-temperature hydrolysis and deterioration during this process.

[0017] Preferably, step (2) involves evaporating and crystallizing the filtrate to obtain crude sodium hexafluorophosphate crystals, specifically including: evaporating and concentrating the filtrate under reduced pressure at 40~60℃ (e.g., 40℃, 45℃, 50℃, 55℃, 60℃, etc., but not limited to the listed values; other unlisted values ​​within this range are also applicable) to precipitate crude sodium hexafluorophosphate crystals.

[0018] Preferably, the organic solvent in step (2) includes any one or a combination of at least two of ethylene glycol dimethyl ether, propylene carbonate, acetonitrile, and ethyl acetate.

[0019] Preferably, the number of times mentioned in step (2) is 2 to 4 times, for example, 2 times, 3 times or 4 times.

[0020] Preferably, step (2) further includes a drying step after dissolving the crude sodium hexafluorophosphate crystals in an organic solvent for multiple recrystallizations.

[0021] Preferably, the drying is vacuum drying.

[0022] Preferably, the vacuum drying temperature is 50~80℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The vacuum drying time is 24~48 hours, such as 24 hours, 36 hours, 40 hours, 48 ​​hours, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] As a preferred embodiment of the present invention, the preparation method includes the following steps: (1) Mix sodium hydrogen fluoride solid and organic solvent, heat to 60~100℃ and stir to dissolve. After the solution cools to 20~30℃, add phosphorus pentachloride solid and react at 20~60℃ with stirring for 6~48h to obtain the reaction mixture. The molar ratio of solid phosphorus pentachloride to solid sodium bifluoride is 1:(1~6), and the ratio of the total mass of solid sodium bifluoride and solid phosphorus pentachloride to the mass of organic solvent is 1:(10~24). (2) The mixture after the reaction is filtered to obtain the filtrate. Then the filtrate is concentrated by vacuum evaporation at 40~60℃ to precipitate crude sodium hexafluorophosphate crystals. Then the crude sodium hexafluorophosphate crystals are dissolved in an organic solvent for recrystallization 2~4 times. Finally, the crystals are dried under vacuum at 50~80℃ for 24~48 hours to obtain the sodium hexafluorophosphate. The organic solvents mentioned in steps (1) and (2) each independently include any one or a combination of at least two of ethylene glycol dimethyl ether, propylene carbonate, acetonitrile, and ethyl acetate.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses a low-toxicity and weakly corrosive organic solvent to replace the high-risk anhydrous hydrogen fluoride as the reaction solvent, and constructs a homogeneous reaction environment. This not only significantly reduces the production safety risks and equipment costs, but also improves the reaction rate and conversion rate of the raw materials, achieving a synergy between safety and efficiency.

[0025] (2) This invention suppresses the generation of byproducts from the source by optimizing reaction conditions, and then uses the difference in solubility between products and impurities by organic solvents to deeply remove residual impurities by multiple recrystallization processes. The whole chain optimizes impurity control and can meet the stringent requirements of high-end batteries.

[0026] (3) The reaction route of this invention is innovative, requiring no special atmosphere or equipment. It uses solid PCl5 and solid NaHF2 to react directly in an organic solvent. The reaction is mild and controllable, reducing the generation of by-products from the source. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0029] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0030] Example 1 This embodiment provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) Synthesis of crude sodium hexafluorophosphate: 700 mL of dry ethylene glycol dimethyl ether solvent was added to a reaction beaker, and 18.6 g of NaHF2 solid was added. The temperature was raised to 100 °C and stirred to dissolve. After the solution was cooled to 25 °C, 20.8 g of PCl5 solid was slowly added. After the reaction was completed, the temperature was maintained at 30 °C and stirred for 24 hours to obtain the reaction mixture.

[0031] (2) Purification of crude sodium hexafluorophosphate: After the reaction is completed, the mixture after the reaction is filtered while hot to remove insoluble impurities and obtain filtrate. Then, the filtrate is concentrated by vacuum evaporation at 40°C to precipitate crude sodium hexafluorophosphate crystals. Then, the crude sodium hexafluorophosphate crystals are dissolved in ethylene glycol dimethyl ether for the first recrystallization. Subsequently, the crystals are dissolved in ethylene glycol dimethyl ether for the second and third recrystallization to further remove residual ethylene glycol dimethyl ether and impurities. Finally, the crystals are vacuum dried at 60°C for 24 hours to obtain a white solid of sodium hexafluorophosphate with high purity, which is the sodium hexafluorophosphate.

[0032] Example 2 This embodiment provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) Synthesis of crude sodium hexafluorophosphate: 800 mL of dry acetonitrile solvent was added to a reaction beaker, and 37.2 g of NaHF2 solid was added. The temperature was raised to 80 °C and stirred to dissolve. After the solution was cooled to 25 °C, 20.8 g of PCl5 solid was slowly added. After the reaction was completed, the temperature was maintained at 40 °C and stirred for 36 hours to obtain the reaction mixture.

[0033] (2) Purification of crude sodium hexafluorophosphate: After the reaction is completed, the mixture after the reaction is filtered while hot to remove insoluble impurities and obtain filtrate. Then, the filtrate is concentrated by vacuum evaporation at 50°C to precipitate crude sodium hexafluorophosphate crystals. Then, the crude sodium hexafluorophosphate crystals are dissolved in acetonitrile for the first recrystallization. Subsequently, the crystals are dissolved in acetonitrile for the second and third recrystallization to further remove residual acetonitrile and impurities. Finally, the crystals are vacuum dried at 60°C for 24 hours to obtain a white solid of sodium hexafluorophosphate with high purity, which is the sodium hexafluorophosphate.

[0034] Example 3 This embodiment provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) Synthesis of crude sodium hexafluorophosphate: 900 mL of dry ethyl acetate solvent was added to a reaction beaker, and 18.6 g of NaHF2 solid was added. The temperature was raised to 90 °C and stirred to dissolve. After the solution was cooled to 25 °C, 20.8 g of PCl5 solid was slowly added. After the reaction was completed, the temperature was maintained at 25 °C and stirred for 48 hours to obtain the reaction mixture.

[0035] (2) Purification of crude sodium hexafluorophosphate: After the reaction is completed, the mixture after the reaction is filtered while hot to remove insoluble impurities and obtain filtrate. Then, the filtrate is concentrated by vacuum evaporation at 55°C to precipitate crude sodium hexafluorophosphate crystals. Then, the crude sodium hexafluorophosphate crystals are dissolved in ethylene glycol dimethyl ether for the first recrystallization. Subsequently, the crystals are dissolved in ethylene glycol dimethyl ether for the second and third recrystallization to further remove residual ethylene glycol dimethyl ether and impurities. Finally, the crystals are vacuum dried at 60°C for 24 hours to obtain a white solid of sodium hexafluorophosphate with high purity, which is the sodium hexafluorophosphate.

[0036] Example 4 This embodiment provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) Synthesis of crude sodium hexafluorophosphate: 1000 mL of dry acetonitrile solvent was added to a reaction beaker, and 12.4 g of NaHF2 solid was added. The temperature was raised to 60 °C and stirred to dissolve. After the solution was cooled to 25 °C, 20.8 g of PCl5 solid was slowly added. After the reaction was completed, the temperature was maintained at 25 °C and stirred for 48 hours to obtain the reaction mixture.

[0037] (2) Purification of crude sodium hexafluorophosphate: After the reaction is completed, the mixture after the reaction is filtered while hot to remove insoluble impurities and obtain filtrate. Then, the filtrate is concentrated by vacuum evaporation at 60°C to precipitate crude sodium hexafluorophosphate crystals. Then, the crude sodium hexafluorophosphate crystals are dissolved in propylene carbonate for the first recrystallization and filtered. Subsequently, the crystals are dissolved in propylene carbonate for the second and third recrystallization to remove impurities. Finally, the crystals are vacuum dried at 60°C for 24 hours to obtain a white solid of sodium hexafluorophosphate with high purity, which is the sodium hexafluorophosphate.

[0038] Example 5 This embodiment provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) Synthesis of crude sodium hexafluorophosphate: 600 mL of dry propylene carbonate solvent was added to a reaction beaker, and 18.6 g of NaHF2 solid was added. The temperature was raised to 70 °C and stirred to dissolve. After the solution was cooled to 25 °C, 20.8 g of PCl5 solid was slowly added. After the reaction was completed, the temperature was maintained at 50 °C and stirred for 24 hours to obtain the reaction mixture.

[0039] (2) Purification of crude sodium hexafluorophosphate: After the reaction is completed, the mixture after the reaction is filtered while hot to remove insoluble impurities and obtain filtrate. Then, the filtrate is concentrated by vacuum evaporation at 40°C to precipitate crude sodium hexafluorophosphate crystals. Then, the crude sodium hexafluorophosphate crystals are dissolved in propylene carbonate for the first recrystallization. Subsequently, the crystals are dissolved in propylene carbonate for the second and third recrystallization to further remove residual propylene carbonate and impurities. Finally, the crystals are vacuum dried at 60°C for 24 hours to obtain a white solid of sodium hexafluorophosphate with high purity, which is the sodium hexafluorophosphate.

[0040] Example 6 This embodiment provides a method for preparing sodium hexafluorophosphate, the method comprising the following steps: (1) Synthesis of crude sodium hexafluorophosphate: 600 mL of dry ethylene glycol dimethyl ether solvent was added to a reaction beaker, and 6.2 g of NaHF2 solid was added. The temperature was raised to 100 °C and stirred to dissolve. After the solution was cooled to 25 °C, 20.8 g of PCl5 solid was slowly added. After the reaction was completed, the temperature was maintained at 30 °C and stirred for 24 hours to obtain the reaction mixture.

[0041] (2) Purification of crude sodium hexafluorophosphate: After the reaction is completed, the mixture after the reaction is filtered while hot to remove insoluble impurities and obtain filtrate. Then, the filtrate is concentrated by vacuum evaporation at 40°C to precipitate crude sodium hexafluorophosphate crystals. Then, the crude sodium hexafluorophosphate crystals are dissolved in ethylene glycol dimethyl ether for the first recrystallization. Subsequently, the crystals are dissolved in ethylene glycol dimethyl ether for the second and third recrystallization to further remove residual ethylene glycol dimethyl ether and impurities. Finally, the crystals are vacuum dried at 60°C for 24 hours to obtain a white solid of sodium hexafluorophosphate with high purity, which is the sodium hexafluorophosphate.

[0042] Example 7 The only difference between this embodiment and embodiment 1 is that the reaction temperature in step (1) is 60°C and the reaction time is 12 hours.

[0043] Example 8 The only difference between this embodiment and Embodiment 1 is that recrystallization is performed twice in step (2).

[0044] Example 9 The only difference between this embodiment and embodiment 1 is that the reaction temperature in step (1) is 10°C and the reaction time is 48 hours.

[0045] Example 10 The only difference between this embodiment and Embodiment 1 is that the reaction temperature in step (1) is 70°C and the reaction time is 6 hours.

[0046] Comparative Example 1 The only difference between this comparative example and Example 1 is that the organic solvent (ethylene glycol dimethyl ether solvent) in step (1) is replaced with an equal weight of anhydrous ethanol.

[0047] Comparative Example 2 The only difference between this comparative example and Example 1 is that recrystallization is performed once in step (2).

[0048] The performance of sodium hexafluorophosphate provided in the embodiments and comparative examples of the present invention was tested using the following methods: (1) Purity: The purity of the product was determined by nuclear magnetic resonance phosphorus spectroscopy (31P NMR) and nuclear magnetic resonance fluorine spectroscopy (11F NMR); (2) Yield: The formula for calculating the yield is: .

[0049] The performance test results are shown in Table 1.

[0050] Table 1 As can be seen from Table 1, the sodium hexafluorophosphate prepared by the preparation methods provided in Examples 1-8 of this invention all have high yields (>82%, preferably >85%) and purity (≥98.5%, preferably ≥99%), and the sodium hexafluorophosphate prepared under the preferred conditions has even higher yields and purity.

[0051] Compared with Example 1, the sodium hexafluorophosphate prepared by the method provided in Comparative Example 1 had a purity that decreased from 99.5% to 96.8% and a yield that decreased from 87.3% to 72.3%, with significant decreases in both purity and yield, highlighting the key influence of the reaction solvent on the reaction system. The sodium hexafluorophosphate prepared by the method provided in Comparative Example 2 had a purity that decreased from 99.5% to 98.2%, with a significant decrease in purity, confirming the necessity of multiple recrystallization processes for deep removal of trace impurities and improvement of product purity. The yield will experience normal losses as the number of purification cycles increases.

[0052] In summary, the method for preparing sodium hexafluorophosphate provided by this invention exhibits significant advantages in multiple dimensions. Regarding production safety and ease of operation, this process replaces the traditional high-risk hydrogen fluoride system with a low-toxicity, weakly corrosive organic solvent, eliminating safety hazards such as leakage of highly toxic media and strong equipment corrosion at the source, significantly reducing safety protection costs and environmental risks during production. Simultaneously, the integrated "one-step synthesis-selective crystallization" process eliminates the complex multi-stage reactions and cumbersome high-temperature distillation for impurity removal found in traditional processes, shortening the production cycle and reducing the technical requirements for operators, facilitating continuous and large-scale production. In terms of product performance, the sodium hexafluorophosphate prepared by this method possesses both high yield and high purity: by precisely controlling the raw material ratio and reaction parameters during the reaction process, side reactions are effectively suppressed, and the target product yield remains stable at over 82%; after multiple purifications, the product purity can reach over 99.0%.

[0053] The applicant declares that the present invention illustrates the preparation method of sodium hexafluorophosphate through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A process for the preparation of sodium hexafluorophosphate, characterized in that, The preparation method includes the following steps: (1) Dissolve sodium hydrogen fluoride solid in an organic solvent, then add phosphorus pentachloride solid, react, and obtain the reaction mixture; (2) The mixture after the reaction is filtered to obtain a filtrate, and then the filtrate is evaporated and crystallized to obtain crude sodium hexafluorophosphate crystals; then the crude sodium hexafluorophosphate crystals are dissolved in an organic solvent and recrystallized multiple times to obtain the sodium hexafluorophosphate. The organic solvent in step (1) includes any one or a combination of at least two of ethylene glycol dimethyl ether, propylene carbonate, acetonitrile, and ethyl acetate.

2. The production method according to claim 1, characterized by, The molar ratio of phosphorus pentachloride solid and sodium hydrogen fluoride solid in step (1) is 1:(1~6), preferably 1:(3~6).

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the ratio of the total mass of sodium fluoride solid and phosphorus pentachloride solid to the mass of organic solvent is 1:(10~24).

4. The preparation method according to any one of claims 1-3, characterized in that, Step (1) involves dissolving sodium hydrogen fluoride solid in an organic solvent, specifically by mixing sodium hydrogen fluoride solid with an organic solvent and heating the mixture to 60-100°C while stirring to dissolve it.

5. The preparation method according to any one of claims 1-4, characterized in that, The reaction temperature in step (1) is 20~60℃, preferably 20~50℃; Preferably, the reaction time in step (1) is 6~48h, more preferably 24~48h; Preferably, the reaction in step (1) is carried out under stirring conditions.

6. The preparation method according to any one of claims 1-5, characterized in that, The evaporation and crystallization temperature in step (2) is 40~60℃; Preferably, step (2) involves evaporating and crystallizing the filtrate to obtain crude sodium hexafluorophosphate crystals, specifically including: evaporating and concentrating the filtrate under reduced pressure at 40~60℃ to precipitate crude sodium hexafluorophosphate crystals.

7. The preparation method according to any one of claims 1-6, characterized in that, The organic solvent in step (2) includes any one or a combination of at least two of ethylene glycol dimethyl ether, propylene carbonate, acetonitrile, and ethyl acetate.

8. The preparation method according to any one of claims 1-7, characterized in that, The number of times mentioned in step (2) is 2 to 4.

9. The preparation method according to any one of claims 1-8, characterized in that, Step (2) involves dissolving crude sodium hexafluorophosphate crystals in an organic solvent and recrystallizing them multiple times, followed by a drying step. Preferably, the drying is vacuum drying; Preferably, the vacuum drying temperature is 50~80℃, and the vacuum drying time is 24~48 hours.

10. A preparation method according to any one of claims 1-9, characterized in that, The preparation method includes the following steps: (1) Mix sodium hydrogen fluoride solid and organic solvent, heat to 60~100℃ and stir to dissolve. After the solution cools to 20~30℃, add phosphorus pentachloride solid and react at 20~60℃ with stirring for 6~48h to obtain the reaction mixture. The molar ratio of solid phosphorus pentachloride to solid sodium bifluoride is 1:(1~6), and the ratio of the total mass of solid sodium bifluoride and solid phosphorus pentachloride to the mass of organic solvent is 1:(10~24). (2) The mixture after the reaction is filtered to obtain the filtrate. Then the filtrate is concentrated by vacuum evaporation at 40~60℃ to precipitate crude sodium hexafluorophosphate crystals. Then the crude sodium hexafluorophosphate crystals are dissolved in an organic solvent for recrystallization 2~4 times. Finally, the crystals are dried under vacuum at 50~80℃ for 24~48 hours to obtain the sodium hexafluorophosphate. The organic solvents mentioned in steps (1) and (2) each independently include any one or a combination of at least two of ethylene glycol dimethyl ether, propylene carbonate, acetonitrile, and ethyl acetate.

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