A method for preparing a bifluorosulfimide alkali metal liquid salt

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to a preparation method of a double-fluorosulfonylimide alkali liquid salt. First, crude double-fluorosulfonylimide acid is added into a low-temperature melting and crystallization device for purification, and the purified double-fluorosulfonylimide acid is obtained through crystallization, sweating and other processes; then the purified double-fluorosulfonylimide acid is reacted with an alkali metal chloride salt in a good solvent at low temperature, and a double-fluorosulfonylimide alkali liquid salt is prepared by using positive pressure filtration. The moisture content of the liquid salt is within 15 ppm, the acidity is within 20 ppm, the chloride ion content is within 2 ppm, the sulfate ion content is within 5 ppm, the sulfamate ion is within 50 ppm, the fluoride ion content is within 12 ppm, and the purity of the liquid salt is above 99.6%. The preparation method of the liquid salt in the application is simple, has low energy consumption and high purity, is suitable for large-scale production, and can be adjusted according to the solvent type of the electrolyte, and is simple and efficient.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a method for preparing a liquid alkali metal salt of bis(fluorosulfonyl)imide. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage equipment, and other fields, the demand for high-performance ion batteries is increasing daily. As a key component of ion batteries, the electrolyte's performance directly affects the battery's energy density, cycle life, and safety performance. Difluorosulfonyl imide alkali metal salts, as novel electrolyte salts, exhibit broad application prospects in the high-end ion battery field due to their advantages such as high ionic conductivity, good thermal stability, and chemical stability.

[0003] Difluorosulfonylimide acid (HFSI) is an important precursor for the preparation of alkali metal bisfluorosulfonylimide salts. However, in actual production processes, due to factors such as raw material purity and reaction condition control, the obtained HFSI often contains various impurities, such as unreacted raw materials, byproducts, and metal ions. The presence of these impurities can seriously affect the purity and performance of the subsequently prepared alkali metal bisfluorosulfonylimide salt, thereby reducing the overall performance of the ion battery.

[0004] Patent document CN113912028A discloses a purification method for bis(fluorosulfonyl)imide, comprising the following steps: Step (1): Under inert gas protection, a certain amount of inorganic acids such as concentrated sulfuric acid, fuming sulfuric acid, aminosulfonic acid, chlorosulfonic acid, and fluorosulfonic acid, or organic acids such as oxalic acid, citric acid, tartaric acid, ascorbic acid, benzoic acid, and salicylic acid, or salts such as oxalate alkali metal salts, citrate alkali metal salts, tartrate alkali metal salts, ascorbate alkali metal salts, benzoate alkali metal salts, and salicylic acid alkali metal salts are added to crude bis(fluorosulfonyl)imide and heated under stirring; Step (2): Distillation / rectification under reduced pressure yields bis(fluorosulfonyl)imide with low chloride content. This document demonstrates that a single distillation or rectification can reduce the chloride content in bis(fluorosulfonyl)imide to below 10 ppm, solving the previous problem of chloride sublimation residue and improving the quality of bis(fluorosulfonyl)imide.

[0005] Patent document CN117534042A discloses a method for removing impurities from bis(fluorosulfonyl)imide. The crude bis(fluorosulfonyl)imide after fluorination is first purified by one-step distillation at a temperature of 100-150℃, a pressure of 0.5-50 hPa, and a reflux ratio of 2-10:1. After reaching the impurity removal temperature, impurity removal agents such as lithium acetylene, lithium tetracarbide, or lithium tricarbide are added to carry out the impurity removal reaction. Finally, the product is filtered through a tetrafluoroethylene membrane with a pore size of 100-200 nm to remove fluorosulfonic acid, sulfur-containing, oxygen-containing, and other acidic group impurities, yielding high-purity bis(fluorosulfonyl)imide. This impurity removal method does not introduce foreign ions and has a significant impurity removal effect.

[0006] Patent document CN118083926A discloses a method for preparing high-purity bis(fluorosulfonyl)imide, comprising the following steps: A1, under inert gas protection, dissolving crude bis(fluorosulfonyl)imide in an organic solvent such as an alkane, olefin, or halogenated hydrocarbon, and maintaining the temperature at -50~17℃ for 1~5h; A2, adding inorganic ammonium salts such as ammonium aminosulfonate, ammonium molybdate, ammonium tungstate, ammonium phosphate, or ammonium polyphosphate, or organic ammonium salts such as carbamate, ammonium oxalate, ammonium citrate, ammonium malate, ammonium tartrate, ammonium benzoate, ammonium salicylate, ammonium succinate, ammonium glycinate, or ammonium ethylenediaminetetraacetate to the reaction system described in A1, reacting for 0.5~5h, then raising the temperature to 17~80℃ and reacting for another 0.5~5h to obtain the reaction product; the reaction product includes insoluble chloride salts and fluorosulfonates; A3, obtaining high-purity bis(fluorosulfonyl)imide by vacuum distillation.

[0007] In summary, existing purification methods often involve high energy consumption, complex raw materials, and cumbersome processes, and also cause some degree of environmental pollution, which is inconsistent with the development concept of green chemistry. Therefore, developing an efficient, environmentally friendly, and low-energy-consumption method for purifying HFSI to prepare high-purity electrolyte liquid salts has become a key problem that urgently needs to be solved in the field of ion batteries. Summary of the Invention

[0008] Based on this, the purpose of this invention is to provide a method for preparing liquid bis(fluorosulfonyl)imide alkali metal salts. The method utilizes low-temperature melt crystallization technology to purify crude bis(fluorosulfonyl)imide acid, and then reacts it with an alkali metal salt in a good solvent to prepare liquid bis(fluorosulfonyl)imide alkali metal salts. This method solves the technical problems of high anion index and low purity in the preparation of existing liquid bis(fluorosulfonyl)imide alkali metal salts.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a liquid alkali metal salt of bis(fluorosulfonyl)imide, comprising the following steps: S1, firstly, difluorosulfonylimide acid seed crystals are added to crude difluorosulfonylimide acid, and then the temperature is controlled to crystallize, sweat and melt to obtain purified difluorosulfonylimide acid; S2, the purified bisfluorosulfonylimide acid described in S1 is reacted with an alkali metal salt in a good solvent, and the bisfluorosulfonylimide alkali metal liquid salt is prepared by positive pressure filtration after the reaction is completed.

[0010] Further, the mass of the bis(fluorosulfonyl)imide acid seed crystals added in S1 is 0.1‰ to 0.5‰ of the mass of the crude bis(fluorosulfonyl)imide acid, and the crude bis(fluorosulfonyl)imide acid contains F - ≤2500ppm, NH2SO3 - ≤20000ppm, SO4 2-≤1300ppm, Cl - The purity of the bis(fluorosulfonyl)imide seed crystals is ≥99%, with a purity of ≤50ppm.

[0011] Furthermore, the crystallization process described in S1 is low-temperature crystallization, wherein the temperature of the low-temperature crystallization is 5~18℃, the holding time is 2~6h, and the residual mother liquor is removed.

[0012] Furthermore, the sweating process described in S1 is isothermal sweating, wherein the temperature of isothermal sweating is 10~20℃, the isothermal interval is 1~3℃, the sweating duration is 30min~1h, and the sweating products are removed.

[0013] Furthermore, the residual mother liquor and the sweating product are collected to obtain difluorosulfonylimide acid recycling material, which is then used to replace the crude difluorosulfonylimide acid in S1 for recycling.

[0014] Furthermore, the melting process described in S1 involves heating to 30±1℃ to completely melt the crystals.

[0015] Furthermore, the molar ratio of the purified difluorosulfonyl imide acid to the alkali metal salt in S2 is 0.85~0.99:1, preferably 0.9~0.95:1; the alkali metal salt includes lithium chloride, sodium chloride or potassium chloride.

[0016] Furthermore, the good solvent mentioned in S2 includes ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, or ethylene carbonate.

[0017] Furthermore, the reaction temperature in S2 is -5 to 10°C, and the reaction time is 2 to 8 hours.

[0018] The beneficial effects of this invention are: 1. The method for preparing bis(fluorosulfonyl)imide alkali metal liquid salt provided by this invention utilizes low-temperature melt crystallization technology to purify crude bis(fluorosulfonyl)imide acid. The purified bis(fluorosulfonyl)imide acid can be used to directly prepare high-purity electrolyte liquid salts with satisfactory anion content. The residual mother liquor and sweating products from the purification process, after recrystallization and purification, yield bis(fluorosulfonyl)imide acid that, when used as a raw material, still exhibits good anion content and main component content in the prepared bis(fluorosulfonyl)imide alkali metal liquid salt.

[0019] 2. The preparation method of bis(fluorosulfonyl)imide alkali metal liquid salt provided by the present invention is simple, suitable for large-scale production, and can be adjusted according to the solvent type of the electrolyte, which is simple and efficient.

[0020] 3. The liquid salt prepared by the method for preparing bis(fluorosulfonyl)imide alkali metal liquid salt provided by the present invention has a water content of less than 15 ppm, an acidity of less than 20 ppm, a chloride ion content of less than 2 ppm, a sulfate ion content of less than 5 ppm, an aminosulfonate ion content of less than 50 ppm, a fluoride ion content of less than 12 ppm, and a purity of more than 99.6%. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. All mentioned embodiments are implemented based on the technical solutions of the present invention, and detailed implementation processes are given. However, it should be stated that the scope of protection of the present invention is not limited to the following embodiments.

[0022] The following embodiments provide detailed implementation procedures for the technical solutions of the present invention. Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0023] Example 1

[0024] (1) Slowly add 5 kg of crude difluorosulfonylimide acid to a low-temperature melting crystallizer and add 1.5 g of high-purity difluorosulfonylimide acid seed crystals. Use a constant temperature freezing bath to maintain the temperature at 6℃ for 3 h. Collect 360 g of residual mother liquor. Gradually and slowly raise the temperature to 20℃, with an interval of 2℃ and a time of 40 min (i.e., the isothermal sweating process is: 8℃ 40 min, 10℃ 40 min, 12℃ 40 min, 14℃ 40 min, 16℃ 40 min, 18℃ 40 min, 20℃ 40 min). Collect the sweating product before each temperature increase. Continue to raise the temperature to 30℃. After all the crystals have melted, collect 3478 g of purified difluorosulfonylimide acid. The yield is 69.56%.

[0025] (2) Take 204.3g of dimethyl carbonate into a 500mL flask and place it in a 12℃ constant temperature freezer. Add 21.15g of lithium chloride and stir evenly. Then, slowly add 85.98g of the purified difluorosulfonyl imide acid from step (1). After the addition is complete, continue the reaction for 2 hours. Use positive pressure filtration to obtain the liquid difluorosulfonyl imide lithium product.

[0026] Example 2

[0027] (1) 5 kg of crude difluorosulfonyl imide acid was slowly added to a low-temperature melting crystallizer, along with 2.5 g of high-purity difluorosulfonyl imide acid seed crystals. The temperature was maintained at 8°C for 4 hours using a constant-temperature freezing bath. 385 g of residual mother liquor was collected. The temperature was gradually and slowly increased to 20°C at intervals of 2°C for 45 min (i.e., the isothermal sweating process was: 10°C for 45 min, 12°C for 45 min, 14°C for 45 min, 16°C for 45 min, 18°C ​​for 45 min, and 20°C for 45 min). The sweating product from the previous sweating was collected before each temperature increase. The temperature was increased to 30°C. After all the crystals had melted, 3661 g of purified difluorosulfonyl imide acid was collected, with a yield of 73.22%.

[0028] (2) Take 210.1g of diethyl carbonate into a 500mL flask and place it in a 5℃ constant temperature freezer. Add 29.22g of sodium chloride and stir evenly. Then, slowly add 81.45g of the purified difluorosulfonyl imide acid from step 1). After the addition is complete, continue the reaction for 4h. Use positive pressure filtration to obtain the liquid difluorosulfonyl imide sodium product.

[0029] Example 3

[0030] (1) Slowly add 5 kg of crude difluorosulfonylimide acid to a low-temperature melting crystallizer and add 1.5 g of high-purity difluorosulfonylimide acid seed crystals. Use a constant temperature freeze bath to maintain the temperature at 12℃ for 6 hours. Collect 385 g of residual mother liquor. Gradually and slowly raise the temperature to 20℃ at intervals of 2℃ for 30 min (i.e., the isothermal sweating process is: 14℃ for 30 min, 16℃ for 30 min, 18℃ for 30 min, and 20℃ for 30 min). Collect the sweating product before each temperature increase. After the crystals are completely melted at 30℃, collect 3635 g of purified difluorosulfonylimide acid, with a yield of 73.06%.

[0031] (2) Take 231.7g of methyl ethyl carbonate into a 500mL flask and place it in a -5℃ constant temperature freezer. Add 37.28g of potassium chloride and stir evenly. Then, slowly add 83.26g of the purified difluorosulfonyl imide acid from step 1). After the addition is complete, continue the reaction for 8 hours. Use positive pressure filtration to obtain liquid difluorosulfonyl imide potassium product.

[0032] Example 4

[0033] Collect 4.1 kg of residual mother liquor and sweating product from Examples 1, 2, and 3, and slowly add them to a low-temperature melting crystallizer. Add 1 g of high-purity difluorosulfonylimide acid seed crystals. Maintain the temperature at 8°C using a constant-temperature freezing bath for 4.5 h. Collect 301 g of residual mother liquor. Gradually and slowly raise the temperature to 20°C at 2°C intervals for 35 min (i.e., the isothermal sweating process is: 10°C for 35 min, 12°C for 35 min, 14°C for 35 min, 16°C for 35 min, 18°C ​​for 35 min, and 20°C for 35 min). Collect the sweating product from the previous sweating process before each temperature increase. Raise the temperature to 30°C. After all the crystals have melted, collect 3081 g of purified difluorosulfonylimide acid, with a yield of 75.15%.

[0034] Add 204.3g of ethylene carbonate to a 500mL flask and place it in a 0℃ constant temperature freezer. Add 21.15g of lithium chloride and stir until homogeneous. Then, slowly add 85.98g of purified difluorosulfonylimide acid from step 1). After the addition is complete, continue the reaction for 6 hours. Filter under positive pressure to obtain the liquid difluorosulfonylimide lithium product.

[0035] Comparative Example 1 204.3g of dimethyl carbonate was added to a 500mL flask and placed in a 12℃ constant temperature freezer. 21.15g of lithium chloride was added and stirred until homogeneous. Then, 85.98g of untreated crude difluorosulfonylimide acid from Example 1 was slowly added dropwise. After the addition was completed, the reaction was continued for 2 hours. Liquid lithium difluorosulfonylimide was obtained by positive pressure filtration. The aminosulfonate content was 434.87ppm and the water content was 24ppm.

[0036] Comparative Example 2 210.1g of diethyl carbonate was added to a 500mL flask and placed in a 5℃ constant temperature freezer. 29.22g of sodium chloride was added and stirred evenly. 81.45g of untreated crude difluorosulfonyl imide acid from Example 2 was slowly added dropwise. After the addition was completed, the reaction continued for 4 hours. Liquid sodium difluorosulfonyl imide product was obtained by positive pressure filtration.

[0037] Comparative Example 3 231.7g of methyl ethyl carbonate was added to a 500mL flask and placed in a -5℃ constant temperature freezer. 37.28g of potassium chloride was added and stirred evenly. 83.26g of untreated crude difluorosulfonyl imide acid from Example 3 was slowly added dropwise. After the addition was completed, the reaction continued for 8 hours. Liquid difluorosulfonyl imide potassium product was obtained by positive pressure filtration.

[0038] Implementation effect analysis

[0039] The anionic properties of crude difluorosulfonylimide acid in step (1) of Examples 1-4 are shown in Table 1 below, and the yield and anionic properties of purified difluorosulfonylimide acid are shown in Table 2 below.

[0040] Table 1. Crude difluorosulfonylimide acid anion indexes of Examples 1-4

[0041] Table 2 Yield and anion index of difluorosulfonyl imide acid after purification in Examples 1-4

[0042] Combining the data in Tables 1 and 2, it can be seen that, using the low-temperature melt crystallization process in Examples 1-3, the raw material used for purification was crude difluorosulfonyl imide acid. The content of each anion in the raw material was relatively high, and the yield after purification was above 69%. The anion indicators were significantly reduced after purification, with Cl... - The content of NH2SO3 was reduced to below 7 ppm. - The content of SO4 was reduced to below 900 ppm. 2- The content of F was reduced to below 200 ppm. - The content of SO3F decreased to below 310 ppm. - The content was reduced to below 40 ppm, and even to 0 ppm. In Example 4, the raw materials for purification were the residual mother liquor and sweating products generated in Examples 1-3. The content of each anion in the raw materials was slightly higher than that in the crude difluorosulfonyl imide in Examples 1-3, but the yield after purification was above 75%, and the content of each anion after purification was only slightly higher than that in Examples 1-3.

[0043] (2) Preparation of alkali metal liquid salts The purity and anion index of the alkali metal liquid salts prepared in Examples 1-4 and Comparative Examples 1-3 are shown in Table 3 below.

[0044] Table 3. Indicators for the preparation of liquid salts before and after purification of difluorosulfonylimide acid

[0045] The data in Table 3 show that the bis(fluorosulfonyl)imide alkali metal liquid salt prepared using the method provided by this invention has high purity and meets the requirements for anions and other indicators. Compared with the comparative example of liquid salt prepared using unpurified crude bis(fluorosulfonyl)imide acid as raw material, the bis(fluorosulfonyl)imide acid in this example is first purified by low-temperature melt crystallization, and then the purified bis(fluorosulfonyl)imide acid is used as raw material to prepare bis(fluorosulfonyl)imide alkali metal liquid salt with a main content of over 99.6%, a chloride ion content of less than 2 ppm, an aminosulfonate content of less than 50 ppm, a sulfate content of less than 5 ppm, a fluoride ion content of less than 12 ppm, a fluorosulfonate content of less than 2 ppm, a moisture content of less than 15 ppm, and an acidity of less than 20 ppm, all of which meet the requirements for liquid salt. The yield of bis(fluorosulfonyl)imide acid obtained by recrystallization and purification of residual mother liquor and part of sweating products in this invention is also over 70%, and the anion indicators and main content of bis(fluorosulfonyl)imide alkali metal liquid salt prepared using it as raw material are still good (Example 4).

[0046] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a liquid alkali metal salt of bis(fluorosulfonyl)imide, characterized in that, Includes the following steps: S1, firstly, difluorosulfonylimide acid seed crystals are added to crude difluorosulfonylimide acid, and then the temperature is controlled to crystallize, sweat and melt to obtain purified difluorosulfonylimide acid; S2, the purified bisfluorosulfonylimide acid described in S1 is reacted with an alkali metal salt in a good solvent, and the alkali metal liquid salt of bisfluorosulfonylimide is prepared by positive pressure filtration after the reaction is completed.

2. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 1, characterized in that, The mass of the bis(fluorosulfonyl)imide acid seed crystals added in S1 is 0.1‰ to 0.5‰ of the mass of the crude bis(fluorosulfonyl)imide acid, and the crude bis(fluorosulfonyl)imide acid contains F. - ≤2500ppm, NH2SO3 - ≤20000ppm, SO4 2- ≤1300ppm, Cl - The purity of the bis(fluorosulfonyl)imide seed crystals is ≥99%, with a purity of ≤50ppm.

3. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 1, characterized in that, The crystallization process described in S1 is low-temperature crystallization, with a temperature of 5~18℃ and a holding time of 2~6h, and residual mother liquor is removed.

4. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 3, characterized in that, The sweating process described in S1 is isothermal sweating, wherein the temperature of isothermal sweating is 10~20℃, the isothermal interval is 1~3℃, the sweating duration is 30min~1h, and the sweating products are removed.

5. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 4, characterized in that, The residual mother liquor and the sweating product are collected to obtain difluorosulfonylimide acid recycling material. The difluorosulfonylimide acid recycling material is used to replace the crude difluorosulfonylimide acid in S1 to achieve recycling.

6. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 1, characterized in that, The melting process described in S1 involves heating the temperature to 30±1℃ to completely melt the crystals.

7. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 1, characterized in that, The molar ratio of the purified difluorosulfonyl imide acid to the alkali metal salt in S2 is 0.85~0.99:1; the alkali metal salt includes lithium chloride, sodium chloride or potassium chloride.

8. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 1, characterized in that, The good solvents mentioned in S2 include methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, or ethylene carbonate.

9. The method for preparing the alkali metal liquid salt of bis(fluorosulfonyl)imide according to claim 1, characterized in that, The reaction temperature described in S2 is -5~10℃, and the reaction time is 2~8h.

10. The method for preparing bis(fluorosulfonyl)imide alkali metal liquid salt according to claim 1, wherein the filtration is a nitrogen-purged positive pressure filtration.

Images