Preparation method of high-purity bisfluorosulfonylimide

Abstract

This invention discloses a method for preparing high-purity bis(fluorosulfonyl)imide, comprising the following steps: A1. Under inert gas protection, crude bis(fluorosulfonyl)imide is dissolved in an organic solvent and kept at -50 to 17°C for 1 to 5 hours; A2. An ammonium salt is added to the reaction system described in A1, and the reaction is carried out for 0.5 to 5 hours, followed by heating to 17 to 80°C and reacting for another 0.5 to 5 hours to obtain the reaction product; the reaction product includes an insoluble chloride salt and a fluorosulfonate; A3. High-purity bis(fluorosulfonyl)imide is obtained by vacuum distillation. This invention features a simple process, low energy consumption, high product yield, and effective removal of impurities such as chloride ions and fluorosulfonate ions, making it suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the preparation of bis(fluorosulfonyl)imide, and more particularly to a purification method for high-purity bis(fluorosulfonyl)imide. Background Technology

[0002] Lithium difluorosulfonylimide is a novel lithium salt with many advantages such as high conductivity, high thermal stability, resistance to hydrolysis, and suppression of battery gas expansion. It is considered to be the next generation of lithium-ion battery electrolyte salt.

[0003] In existing technologies, bis(fluorosulfonyl)imide is the main raw material for preparing lithium bis(fluorosulfonyl)imide, with a boiling point of 170℃ and a melting point of 17℃. Currently, bis(fluorosulfonyl)imide is commonly prepared using aminosulfonic acid, sulfonyl chloride, and chlorosulfonic acid as raw materials, or chlorosulfonic acid isocyanate and chlorosulfonic acid as raw materials, followed by fluorination with anhydrous hydrogen fluoride or fluoride salts to produce bis(fluorosulfonyl)imide. This reaction readily generates hydrogen chloride and fluorosulfonic acid, which are difficult to remove by distillation, resulting in the purity of the subsequent bis(fluorosulfonyl)imide metal salt failing to meet the requirements of electrolytes.

[0004] To improve the purity of bis(fluorosulfonyl)imide metal salts, current research focuses on increasing the purity of its raw material, bis(fluorosulfonyl)imide.

[0005] Patent CN113912028A discloses a method for purifying crude bis(fluorosulfonyl)imide by adding an acid or alkali metal salt to the product. This method can reduce the chloride ion concentration in bis(fluorosulfonyl)imide to below 10 ppm, but the impurity removal process is time-consuming, has a low yield, cannot remove other anionic impurities such as fluorosulfonic acid, and the introduction of alkali metals may cause an increase in cations.

[0006] Patent CN113710649A discloses a method for purifying bis(fluorosulfonyl)imide by reacting gaseous ammonia with fluorosulfonic acid to produce ammonium fluorosulfonate. However, the ammonia used in this method is a hazardous chemical, making the operation inconvenient, and the ammonia readily reacts with bis(fluorosulfonyl)imide, leading to a reduced product yield.

[0007] Patents CN111634895A and CN110697668B disclose a method for removing impurities by dissolving crude bis(fluorosulfonyl)imide in a solvent, followed by cooling crystallization and washing. This method separates the components based on their melting points; however, single crystallization is ineffective against hydrogen chloride and fluorosulfonic acid impurities in the bis(fluorosulfonyl)imide product. To achieve the desired purity, the crystallization process must be repeated continuously, resulting in cumbersome operation and low yield.

[0008] In summary, the existing purification methods for bis(fluorosulfonyl)imide not only easily lead to a large loss of bis(fluorosulfonyl)imide products, but also have problems such as being cumbersome to operate, having high energy consumption and high pollution, or only targeting a certain impurity. They cannot remove impurities such as hydrogen chloride and fluorosulfonic acid at the same time, and the purity of bis(fluorosulfonyl)imide is still difficult to meet the requirements of subsequent electrolyte salts. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention proposes a method for preparing high-purity bis(fluorosulfonyl)imide that is simple in process, low in energy consumption, high in product yield, effectively removes impurities such as chloride ions and fluorosulfonic acid ions, and is suitable for industrial production.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for preparing high-purity difluorosulfonyl imide, the method comprising the following steps:

[0012] A1. Under inert gas protection, crude difluorosulfonamide is dissolved in an organic solvent and kept at -50 to 17°C for 1 to 5 hours.

[0013] A2. Add the ammonium salt to the reaction system described in A1, react for 0.5–5 hours, then raise the temperature to 17–80°C and react for another 0.5–5 hours to obtain the reaction products; the reaction products include insoluble chloride salts and fluorosulfonates;

[0014] A3. High-purity difluorosulfonyl imide was obtained by vacuum distillation.

[0015] The crude difluorosulfonylimide comprises at least one of hydrogen chloride or fluorosulfonic acid.

[0016] This invention involves reacting ammonium salts with impurities such as hydrogen chloride or fluorosulfonic acid in bis(fluorosulfonyl)imide to generate insoluble ammonium salts. The insoluble salts and high-boiling-point weak acids are then removed through separation to obtain high-purity bis(fluorosulfonyl)imide. However, during purification, ammonium salts readily react with bis(fluorosulfonyl)imide, leading to a decrease in the yield of the bis(fluorosulfonyl)imide product. This invention utilizes a solid-liquid mixture of bis(fluorosulfonyl)imide and an organic solvent for impurity removal, effectively avoiding side reactions between the ammonium salt and bis(fluorosulfonyl)imide.

[0017] The organic solvent should be able to dissolve bis(fluorosulfonyl)imide and ammonium salt. Specifically, the organic solvent is selected from at least one of alkanes, alkenes, and halogenated hydrocarbons; preferably, the organic solvent is selected from at least one of haloalkanes and halogenated hydrocarbons; more preferably, the organic solvent is selected from at least one of dichloromethane or dichloroethane.

[0018] The organic solvent has a moisture content of less than 100 ppm; preferably, the organic solvent has a moisture content of less than 50 ppm.

[0019] In step A1, the inert gas is selected from at least one of high-purity nitrogen, high-purity argon, and high-purity helium; preferably, the inert gas is high-purity nitrogen or high-purity argon.

[0020] Preferably, in step A1, the crude difluorosulfonamide is dissolved in an organic solvent under an inert gas atmosphere and kept at a temperature of -30 to 17°C for 2 to 4 hours.

[0021] The ammonium salt is an inorganic or organic ammonium salt. The inorganic ammonium salt is selected from at least one of ammonium aminosulfonate, ammonium molybdate, ammonium tungstate, ammonium phosphate, or ammonium polyphosphate; preferably, the inorganic ammonium salt is selected from at least one of ammonium molybdate, ammonium tungstate, or ammonium phosphate. The organic ammonium salt is selected from at least one of carbamate, ammonium oxalate, ammonium citrate, ammonium malate, ammonium tartrate, ammonium benzoate, ammonium salicylate, ammonium succinate, ammonium glycinate, or ammonium ethylenediaminetetraacetate; preferably, the organic ammonium salt is selected from at least one of ammonium carbamate, ammonium citrate, ammonium oxalate, or ammonium succinate.

[0022] The moisture in the ammonium salt will cause the difluorosulfonyl imide to decompose during the reaction, which can easily lead to a large loss of the difluorosulfonyl imide product. Therefore, the moisture content in the ammonium salt is not higher than 0.1%; preferably, the moisture content in the ammonium salt is not higher than 0.01%.

[0023] In step A2, if there are too many dissociable ammonium ions in the ammonium salt, it can easily lead to an increase in ammonium ion concentration. These ammonium ions can then react with the crude difluorosulfonyl imide, thus reducing the product yield. Conversely, if there are too few dissociable ammonium ions in the ammonium salt, hydrogen chloride and fluorosulfonic acid impurities in the crude difluorosulfonyl imide will not be completely removed. Specifically, the ratio of the number of moles of dissociable ammonium ions in the ammonium salt to the sum of the number of moles of chloride ions and fluorosulfonic acid ions in the crude difluorosulfonyl imide is (1–4):1, preferably (1–2):1, and more preferably (1–1.2):1.

[0024] In step A2, the reaction temperature is -50 to 17°C, the reaction time is 0.5 to 5 hours, and then the temperature is raised to 17 to 80°C for another 0.5 to 5 hours; preferably, the reaction temperature is -30 to 17°C, the reaction time is 0.5 to 4 hours, and then the temperature is raised to 20 to 70°C for another 0.5 to 4 hours; more preferably, the reaction temperature is -15 to 17°C, the reaction time is 1 to 3 hours, and then the temperature is raised to 25 to 60°C for another 1 to 3 hours.

[0025] The reaction product obtained in step A2 can be effectively removed by separation to obtain high-purity difluorosulfonylimide. The reaction product is selected from at least one of insoluble chloride salts, fluorosulfonates, or high-boiling substances.

[0026] Specifically, in step A3 of the present invention, the organic solvent in the reaction solution obtained in step A2 is distilled off by distillation, and then high-purity difluorosulfonylimide product is obtained by vacuum distillation.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The ammonium salt described in this invention can effectively reduce hydrogen chloride and fluorosulfonic acid impurities in crude difluorosulfonylimide;

[0029] 2. This invention removes impurities in a solid-liquid mixture of bis(fluorosulfonyl)imide and an organic solvent, avoiding the loss of bis(fluorosulfonyl)imide and achieving a yield of over 90%.

[0030] 3. The method of the present invention is simple in process, low in energy consumption, and suitable for industrial production. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0032] Example 1

[0033] A1. Under nitrogen protection, add 80g of crude difluorosulfonamide (chloride content 125ppm, fluorosulfonic acid content 3500ppm) and 30g of dichloromethane to a 100ml PFA three-necked flask with a stirrer, slowly cool to -5℃, and keep warm for 2 hours.

[0034] A2. Add 0.7g of ammonium molybdate, react at a reaction temperature of -5℃ for 3 hours, then raise the temperature to 25℃ and continue stirring for 1.5 hours.

[0035] A3. Filter out solid impurities, distill off the dichloromethane in the reaction solution obtained in step A2 by ordinary distillation, then heat to 80°C and distill under reduced pressure at 1000Pa to obtain 78.5g of high-purity difluorosulfonylimide product, with a yield of 98.1%.

[0036] Ion chromatography analysis showed that the high-purity difluorosulfonyl imide product contained 6 ppm of chloride ions and 18 ppm of fluorosulfonate ions.

[0037] Example 2

[0038] A1. Under nitrogen protection, add 80g of crude difluorosulfonamide (chloride content 125ppm, fluorosulfonic acid content 3500ppm) and 40g of dichloromethane to a 100ml PFA three-necked flask with a stirrer, slowly cool to -15℃, and keep warm for 4 hours.

[0039] A2. Add 0.5g of ammonium succinate, react at a reaction temperature of -15℃ for 2 hours, then raise the temperature to 35℃ and continue stirring for 2 hours;

[0040] A3. Filter out solid impurities, distill off the dichloromethane in the reaction solution obtained in step A2, then heat to 80℃ and distill under reduced pressure at 1000Pa to obtain 77.8g of high-purity difluorosulfonylimide product, with a yield of 97.3%.

[0041] Ion chromatography analysis showed that the high-purity difluorosulfonyl imide product contained 7 ppm of chloride ions and 13 ppm of fluorosulfonate ions.

[0042] Example 3

[0043] A1. Under nitrogen protection, add 80g of crude difluorosulfonamide (chloride content 125ppm, fluorosulfonic acid content 3500ppm) and 55g of dichloroethane to a 100ml PFA three-necked flask with a stirrer, slowly cool to -10℃, and keep warm for 3.5h.

[0044] A2. Add 0.26g of ammonium carbamate, react at a reaction temperature of -10℃ for 2.5h, then raise the temperature to 60℃ and continue stirring for 2h.

[0045] A3. Dichloroethane was distilled off from the reaction solution obtained in step A2, and then the temperature was raised to 80°C and distilled under reduced pressure at 1000 Pa to obtain 78.8 g of high-purity difluorosulfonyl imide product, with a yield of 98.5%.

[0046] Ion chromatography analysis showed that the high-purity difluorosulfonamide product contained 3 ppm of chloride ions and 8 ppm of fluorosulfonate ions.

[0047] Comparative Example 1

[0048] Under nitrogen protection, 80 g of crude bis(fluorosulfonyl)imide (chloride content 125 ppm, fluorosulfonic acid content 3500 ppm) was added to a 100 ml PFA three-necked flask equipped with a stirrer, along with 0.5 g of ammonium succinate. The reaction was stirred at 60 °C for 2 h. Analysis revealed a chloride ion content of 83 ppm and a fluorosulfonic acid ion content of 1248 ppm in the product. Another 0.5 g of ammonium succinate was added, and the reaction was continued for another 3 h before the reaction was stopped. The temperature was raised to 80 °C, and the product was distilled under reduced pressure at 1000 Pa to obtain 74.5 g of high-purity bis(fluorosulfonyl)imide, with a yield of 93.1%.

[0049] Ion chromatography analysis showed that the chloride ion content of the bis(fluorosulfonyl)imide product was 47 ppm, and the fluorosulfonate ion content was 148 ppm.

[0050] Comparative Example 2

[0051] Under nitrogen protection, 80 g of crude difluorosulfonamide (chloride ion content 125 ppm, fluorosulfonic acid content 3500 ppm) was added to a 100 ml PFA three-necked flask equipped with a bubbling device, along with 0.45 g of aminosulfonic acid. Dry nitrogen was bubbled in, and the mixture was stirred at 60 °C for 10 h. The reaction was then stopped, and the mixture was distilled under reduced pressure at 1000 Pa to obtain 75.7 g of difluorosulfonamide product, with a yield of 94.6%.

[0052] Ion chromatography analysis showed that the chloride ion content of the bis(fluorosulfonyl)imide product was 63 ppm, and the fluorosulfonate ion content was 2448 ppm.

[0053] Comparative Example 3

[0054] Under nitrogen protection, 80g of crude bis(fluorosulfonyl)imide (chloride ion content 125ppm, fluorosulfonic acid content 3500ppm) was added to a 100ml PFA three-necked flask equipped with a stirrer. Stirring was started, and ammonia gas was introduced into the upper part of the reactor to maintain a slight positive pressure. After the pressure decreased, ammonia gas was introduced again, and this process was repeated until the pressure inside the reactor no longer changed, at which point the reaction was stopped. Vacuum distillation at 1000Pa yielded 62.4g of bis(fluorosulfonyl)imide product, with a yield of 78%.

[0055] Ion chromatography analysis showed that the chloride ion content of the bis(fluorosulfonyl)imide product was 34 ppm, and the fluorosulfonate ion content was 4 ppm.

Claims

1. A method for preparing high-purity difluorosulfonyl imide, characterized in that: The preparation method includes the following steps: A1. Under inert gas protection, crude difluorosulfonamide is dissolved in an organic solvent and kept at -50 to 17°C for 1 to 5 hours; wherein the organic solvent is selected from at least one of haloalkanes and haloalkanes. A2. Add the ammonium salt to the reaction system A1, react for 0.5–5 h, then raise the temperature to 17–80 °C and react for another 0.5–5 h to obtain the reaction product; the reaction product includes insoluble chloride salt and fluorosulfonate; the ammonium salt is selected from at least one of ammonium molybdate, ammonium tungstate, ammonium carbamate, ammonium oxalate, ammonium citrate, ammonium malate, ammonium tartrate, and ammonium succinate; A3. High-purity difluorosulfonyl imide was obtained by vacuum distillation.

2. The method for preparing high-purity bis(fluorosulfonyl)imide according to claim 1, characterized in that: The crude difluorosulfonamide contains hydrogen chloride and fluorosulfonic acid.

3. The method for preparing high-purity bis(fluorosulfonyl)imide according to claim 1, characterized in that: The water content of the organic solvent is less than 100 ppm.

4. The method for preparing high-purity bis(fluorosulfonyl)imide according to claim 1, characterized in that: The inert gas is high-purity nitrogen, high-purity argon, or high-purity helium.

5. The method for preparing high-purity bis(fluorosulfonyl)imide according to claim 1, characterized in that: In step A2, the ratio of the number of moles of dissociable ammonium ions in the ammonium salt to the sum of the number of moles of chloride ions and fluorosulfonic acid ions in the crude difluorosulfonyl imide is (1-4):

1.

6. The method for preparing high-purity difluorosulfonyl imide according to claim 1, characterized in that: In step A2, the reaction temperature is -30 to 17°C, the reaction time is 0.5 to 4 hours, and then the temperature is increased by 20 to 70°C and the reaction is continued for 0.5 to 4 hours to obtain the reaction product.