Preparation method of bis (fluorosulfonyl) imide salt solution

Abstract

The invention relates to a preparation method of a bis (fluorosulfonyl) imide salt solution, which comprises the following steps: S1, mixing an alkali metal or alkaline earth metal compound with a non-aqueous polar solvent, then adding bis (fluorosulfonyl) imide and a substitute thereof for salt forming reaction, and filtering to obtain a crude product mixed solution; s2, metal salt is added into the crude product mixed solution in the step S1, stirring reaction is carried out for preliminary water removal, filtering is carried out, and a mixed solution is obtained; and S3, adding a metal oxide and / or a metal sulfide into the mixed solution obtained in the step S2, carrying out a stirring reaction, carrying out deep water removal, and filtering to obtain a bis (fluorosulfonyl) imide salt solution. Compared with a traditional water removal process, the method has the advantages that complex and high-cost purification processes such as recrystallization, high-temperature drying or solvent water carrying, molecular sieve adsorption water removal and the like are omitted, the quality of the obtained product is greatly improved, the water content can be reduced to 20 ppm or below, and the preparation process is short in flow, high in yield and free of three wastes.

Description

Technical Field

[0001] The invention belongs to the field of preparation of bisfluorosulfonyl imide salts, and particularly relates to a method for preparing a bisfluorosulfonyl imide salt solution. Background Art

[0002] Bis(fluorosulfonyl)imide salts are widely used in the field of battery electrolytes. For example, potassium bis(fluorosulfonyl)imide is used as an additive in supercapacitors. Lithium bis(fluorosulfonyl)imide is used as an additive in lithium battery electrolytes. As a new type of lithium-ion battery additive, lithium bis(fluorosulfonyl)imide has advantages that are unmatched by the current mainstream electrolyte lithium hexafluorophosphate. U.S. Patent US5916475A points out that the conductivity and thermal stability of lithium bis(fluorosulfonyl)imide are better than those of lithium hexafluorophosphate. Nippon Catalyst achieved industrial production of lithium bis(fluorosulfonyl)imide products as early as 2013. It can be foreseen that lithium bis(fluorosulfonyl)imide has the potential to replace lithium hexafluorophosphate as the main additive for electrolytes.

[0003] At present, there are two mainstream processes for preparing bisfluorosulfonyl imide salts. One is to react bisfluorosulfonyl imide with salt in a non-aqueous poor solvent system, and then obtain a high-purity bisfluorosulfonyl imide salt solid product through filtration, recrystallization, drying and other processes. This process is extremely costly, and the high temperature conditions during the drying process will cause the product to decompose and produce impurities, resulting in reduced product quality. In addition, the bisfluorosulfonyl imide salt itself has extremely strong water absorption, resulting in high drying requirements and difficulty in achieving low water content requirements. The second process is to react bisfluorosulfonyl imide and its substituents with salt in a good solvent of bisfluorosulfonyl imide salt. This reaction is essentially an acid-base neutralization reaction, often accompanied by the generation of water. The final product is then obtained by means of solvent evaporation with water and molecular sieve dehydration. This process has problems such as high temperature conditions with solvent carrying water leading to product decomposition and molecular sieve dehydration leading to excessive metal ions. For bis(fluorosulfonyl)imide salts used as battery dielectrics, excessive water content will cause the salt to decompose, generating a variety of impurities that affect battery performance. Second, excessive water content will promote the decomposition of the electrolyte to generate gases such as hydrogen fluoride, leading to safety accidents. Currently, the above two water removal solutions in the industry are difficult to achieve the water content below 50ppm required by downstream customers.

[0004] For example, as mentioned in CN116514077A, bisfluorosulfonyl imide reacts with a salt in a poor solvent, and then is washed and dried to obtain a purified bisfluorosulfonyl imide salt product. This method may result in an excessive content of impurity anions, leading to a decrease in product quality.

[0005] In view of the problems of product decomposition, high energy consumption and high cost caused by the above-mentioned traditional bisfluorosulfonyl imide salt preparation and dehydration process, the art is in urgent need of a new bisfluorosulfonyl imide salt preparation and dehydration process. Summary of the invention

[0006] In view of the above problems existing in the prior art, the present invention aims to provide a method for preparing a bis(fluorosulfonyl)imide salt solution. Compared with the traditional water removal process, the method omits the complex and high-cost purification processes such as recrystallization, high-temperature drying or solvent water, molecular sieve adsorption and water removal, and the quality of the obtained product is also greatly improved, the water content can be reduced to below 20ppm, the preparation process is short, the yield is high, and no three wastes are generated.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] A method for preparing a bisfluorosulfonyl imide salt solution comprises the following steps:

[0009] S1: mixing an alkali metal or alkaline earth metal compound with a non-aqueous polar solvent, then adding bis(fluorosulfonyl)imide and its substituent to carry out a salt-forming reaction, filtering, and obtaining a crude product mixture;

[0010] S2: adding metal salt to the crude product mixed solution of step S1, stirring the reaction to perform preliminary water removal, filtering, and obtaining a mixed solution;

[0011] S3: Add metal oxide and / or metal sulfide to the mixed solution of step S2, stir the reaction to remove water deeply, filter, and obtain a bis(fluorosulfonyl)imide salt solution.

[0012] In the present invention, the alkali metal or alkaline earth metal compound in step S1 is one or more of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, and alkaline earth metal carbonates, preferably one or more of lithium hydroxide and sodium hydroxide.

[0013] In the present invention, the purity of the bis(fluorosulfonyl)imide and its substitutes in step S1 is >99%, and the rest is water and impure acid (including: hydrogen fluoride, hydrogen chloride, sulfuric acid, aminosulfonic acid, etc.);

[0014] Preferably, the bisfluorosulfonyl imide and its substituents are one of bisfluorosulfonyl imide, bisfluorosulfonyl imide organic amine salt, bisfluorosulfonyl imide pyridine and its hydrocarbon substituted derivative salt, bisfluorosulfonyl imide pyrrole and its hydrocarbon derivative salt, and bisfluorosulfonyl imide alkyl substituents, preferably one or more of bisfluorosulfonyl imide and bisfluorosulfonyl imide triethylamine salt.

[0015] In the present invention, the non-aqueous polar solvent in step S1 is selected from one or more of alcohols, ethers, amines, halogenated hydrocarbons, aromatics, carbonates, hydrocarbons, and esters, preferably one or more of ethyl methyl carbonate and dimethyl carbonate;

[0016] Preferably, the water content in the non-aqueous polar solvent is controlled to be less than 30 ppm, for example, 29 ppm, 25 ppm, 20 ppm, 15 ppm, etc.

[0017] In the present invention, the molar ratio of the bis(fluorosulfonyl)imide and its substitute to the alkali metal or alkaline earth metal compound in step S1 is 1:(1-10), such as 1:1, 1:3, 1:5, 1:7, 1:9, etc., preferably 1:(1.2-2.5);

[0018] The mass ratio of the bisfluorosulfonyl imide and its substitute to the non-aqueous polar solvent is 1:(1-10), such as 1:1, 1:3, 1:5, 1:7, 1:9, etc., preferably 1:(2.5-8).

[0019] In the present invention, the salt-forming reaction in step S1 has a reaction temperature of -25°C to 80°C, for example, -25°C, -15°C, -5°C, 0°C, 10°C, 20°C, 40°C, 60°C, 80°C, etc., and a reaction time of 0.5 to 24h, for example, 0.5h, 3h, 5h, 7h, 10h, 13h, 15h, 18h, 20h, 24h, etc. Preferably, the reaction temperature is -5°C to 40°C, and the reaction time is 1 to 10h.

[0020] In the present invention, the metal salt in step S2, wherein the cation is one or more of alkali metal and / or alkaline earth metal cations, and the anion is one or more of halide ion, sulfate ion, hydrogen sulfate ion, carbonate ion, hydrogen carbonate ion, nitrate ion, phosphate ion, monohydrogen phosphate ion, dihydrogen phosphate ion;

[0021] Preferably, the metal salt is one or more of lithium chloride, sodium chloride and sodium phosphate.

[0022] In the present invention, the molar ratio of the metal salt in step S2 to the bis(fluorosulfonyl)imide and its substituent in step S1 is (0.2-2):1, for example, 0.2:1, 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, etc., preferably (0.5-1.2):1.

[0023] In the present invention, step S2 is for preliminary removal of water from the reaction, the reaction temperature is -35°C to 40°C, for example, -35°C, -25°C, -15°C, -5°C, 0°C, 10°C, 20°C, 40°C, etc., the reaction time is 0.5 to 24h, for example, 0.5h, 3h, 5h, 7h, 10h, 13h, 15h, 18h, 20h, 24h, etc.; preferably, the reaction temperature is -20°C to 20°C, and the reaction time is 6 to 12h.

[0024] In the present invention, the metal oxide and / or metal sulfide in step S3 is one or more oxides and / or sulfides of alkali metals or alkaline earth metals, preferably one or more of lithium oxide, sodium oxide, and sodium peroxide.

[0025] In the present invention, the molar ratio of the metal oxide and / or metal sulfide in step S3 to the bis(fluorosulfonyl)imide and its substituents in step S1 is (0.001-0.025):1, for example, 0.001:1, 0.003:1, 0.005:1, 0.008:1, 0.01:1, 0.012:1, 0.015:1, 0.018:1, 0.02:1, 0.025:1, etc., preferably (0.003-0.015):1.

[0026] In the present invention, the reaction of deep water removal in step S3 has a reaction temperature of -15°C to 40°C, for example, -15°C, -5°C, 0°C, 10°C, 20°C, 30°C, 40°C, etc., and a reaction time of 0.5 to 6h, for example, 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, etc.; preferably, the reaction temperature is -10°C to 10°C, and the reaction time is 1 to 3h.

[0027] In the present invention, the filtration in step S1, step S2 and step S3 uses a filter membrane with a pore size of 0.1 to 20 μm, such as 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, etc., preferably a hydrophobic filter membrane with a pore size of 0.2 to 5 μm. It is mainly used to remove excess alkali metal or alkaline earth metal compounds in step S1, metal salts with crystal water produced in step S2, and hydroxides corresponding to cations in metal oxides and / or metal sulfides produced in step S3, and trace insoluble impurities, the insoluble impurities mainly including lithium sulfamate, lithium sulfate, lithium fluoride, lithium chloride, sulfonamide, ammonium sulfate, ammonium fluoride, etc.

[0028] In the present invention, the metal salt with crystal water produced in step S2 is filtered and recovered, and can be applied after drying. Preferably, the drying temperature is 80-250° C. and the drying time is 5-48 hours; more preferably, the drying temperature is 120-180° C. and the drying time is 8-12 hours.

[0029] In the present invention, in order to improve the yield of each step of the reaction, the water removal efficiency and the purity of the final product, the following operation process is preferably adopted: First, in step S1, the alkali metal or alkaline earth metal compound is mixed with a non-aqueous solvent with accurate measurement, and the temperature of the mixed solution is adjusted to the target reaction temperature (-25°C to 80°C, preferably -5°C to 40°C), and maintained for 0.5 to 3 hours, preferably 1 to 1.5 hours. Then slowly add bisfluorosulfonyl imide or its substituent to the above-mentioned mixed solution, and the dropwise addition time is 5% to 30% of the overall reaction time, preferably 10% to 20%, and the dropwise addition time is included in the overall reaction time. The chemical reaction principle involved in step S1 of the present invention is: XOH + ZFSI = XFSI + ZOH or X2CO3 + 2ZFSI = 2XFSI + Z2CO3, because this reaction contains water, the reaction temperature is too high, and bisfluorosulfonyl imide or its substituent will decompose to produce impurities; too low a temperature will prolong the reaction time and reduce the product yield. The present invention adopts the method of premixing the alkali metal or alkaline earth metal compound with the solvent and strictly controls the temperature range of the salt-forming reaction, which is more conducive to obtaining high-quality bisfluorosulfonyl imide salt products.

[0030] In step S1, the reaction time of bisfluorosulfonyl imide and its substituents with alkali metal or alkaline earth metal compounds is determined by the moisture content and acidity of the reaction mixture. When the acidity and water content values ​​are stable, the reaction is judged to have reached the end point. At this time, the unreacted alkali metal or alkaline earth metal compound is filtered out to obtain a crude product mixture. After the crude product mixture is adjusted to the target preliminary dehydration reaction temperature of step S2 (-35°C to 40°C, preferably -20°C to 20°C), a measured metal salt is added to the crude product mixture, and the moisture content in the liquid is sampled and tested every 1h. After the water content is stable, it is judged that step S2 has reached the end point of the preliminary dehydration reaction. At this time, the metal salt containing crystal water generated by the reaction is filtered out to obtain a mixed solution. After the mixed solution is adjusted to the target reaction temperature of deep water removal in step S3 (-15°C to 40°C, preferably -10°C to 10°C), a measured amount of metal oxide and / or metal sulfide is added to the mixed solution. During this period, the water content is tested as a basis for judging the end point of the deep water removal reaction. After the water content is reduced to the national standard requirement for the electrolyte (50ppm), the hydroxide corresponding to the cation in the metal oxide and / or metal sulfide generated by the reaction and trace insoluble impurities are removed by filtration. The obtained filtrate is a high-purity liquid product of bis(fluorosulfonyl)imide salt.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The preparation process of the bis(fluorosulfonyl)imide salt solution provided by the present invention is simple to operate and has mild dehydration conditions. It does not have the complex recrystallization and high-temperature drying processes of the traditional solid salt dehydration process, nor does it have the high-temperature solvent with water and molecular sieve dehydration processes in the traditional liquid salt dehydration process. The obtained product has higher quality. No additional three wastes are generated during the dehydration process. The metal salt used as the dehydration reagent can be recycled after the crystallization water is removed. The dehydration byproducts of the metal oxide and / or metal sulfide can be used in the salt-forming stage of step S1, which has higher economic value. DETAILED DESCRIPTION

[0033] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0034] In the embodiments and comparative examples of the present invention, the sources of the main raw materials used are as follows. Unless otherwise specified, other raw materials and reagents were purchased from commercial sources:

[0035] Bis(fluorosulfonyl)imide or its substitute: Wanhua Chemical's bis(fluorosulfonyl)imide synthesis and derivatization process (specific process reference patent CN112978689A);

[0036] Hydrophobic filter membrane: Merck FGLP01300 filter membrane;

[0037] Other raw materials mentioned in this article are all conventional commercially available raw materials.

[0038] The specific testing method involved in the present invention is:

[0039] (1) SO4 2- , Cl - 、F - 、NH2SO3 - All the tests were performed using anion chromatography with the internal standard method.

[0040] Testing instrument: Thermo Fisher ion chromatograph;

[0041] Chromatographic columns: Thermo Fisher AS22 (4mm*250mm) and Thermo Fisher AG22 (4mm*50mm);

[0042] Mobile phase: acetonitrile-water solution.

[0043] Buffer system: sodium carbonate-sodium bicarbonate.

[0044] (2) Coulometric method to test the water content of liquid:

[0045] Testing instrument: Karl Fischer moisture tester.

[0046] (3) The metal ions in the final product bis(fluorosulfonyl)imide salt solution were analyzed by Thermo Fisher iCAPTM 7400ICP-OES is tested according to GB / T 19282-2014.

[0047] Example 1

[0048] 13.5 g (0.3214 mol) of lithium hydroxide monohydrate was added to 70.0 g of dimethyl carbonate (water content: 23 ppm), the temperature of the mixed solution was adjusted to 15°C, and after stirring for 1 hour, 29.0 g (0.1602 mol) of bis(fluorosulfonyl)imide (purity > 99%) was slowly added dropwise. After reacting for 5 hours, the mixture was filtered through a 0.22 μm hydrophobic filter membrane to terminate the reaction and obtain 101.5 g of filtrate. At this time, the water content of the filtrate sampled and tested was 27993.8 ppm.

[0049] The filtrate was adjusted to 20°C, and then 4.8 g (0.1131 mol) of anhydrous lithium chloride was added. The reaction was stirred for 8 hours, and filtered through a 0.22 μm hydrophobic filter membrane to terminate the reaction to obtain 98.6 g of filtrate. At this time, the water content of the filtrate was sampled and tested to be 273.6 ppm.

[0050] The filtrate was adjusted to 10°C, and then 0.12 g (0.0040 mol) of anhydrous lithium oxide was added. The reaction was stirred for 1.5 hours, and filtered through a 0.22 μm hydrophobic filter membrane to terminate the reaction to obtain 97.9 g of product liquid. At this time, the water content of the product liquid was sampled and tested to be 12 ppm.

[0051] Ion chromatography showed that the solution contained 6.9 ppm sulfate, 28 ppm fluoride, 3.6 ppm chloride, and 26 ppm sulfamate. ICP detection showed that K / Na / Fe / Ca / Cu / Pb / Mo / Ni ions were all less than 1.0 ppm.

[0052] Example 2

[0053] Take 12.9g (0.3225mol) of sodium hydroxide and add it to 70.2g of ethyl methyl carbonate (water content: 13ppm), adjust the temperature of the mixed solution to 20°C, stir for 1.5h, then slowly add 45.2g (0.1603mol) of bis(fluorosulfonyl)imide triethylamine salt (purity>99%), react for 6h, filter through a 0.22μm hydrophobic filter membrane, terminate the reaction, and obtain 128.1g of filtrate. At this time, the water content of the filtrate sampled and tested was 22522.3ppm.

[0054] The filtrate was adjusted to 20°C, and then 6.4 g (0.1095 mol) of anhydrous sodium chloride was added. The reaction was stirred for 7 hours, and filtered through a 0.22 μm hydrophobic filter membrane to terminate the reaction to obtain 125.2 g of filtrate. At this time, the water content of the filtrate was sampled and tested to be 236.8 ppm.

[0055] The filtrate was adjusted to -15°C, and then 0.19 g (0.0031 mol) of anhydrous sodium hydroxide was added. The reaction was stirred for 6 hours, and filtered through a 0.22 μm hydrophobic filter membrane to terminate the reaction to obtain 125.4 g of product liquid. At this time, the water content of the product liquid was sampled and tested to be 14 ppm.

[0056] Ion chromatography showed that the solution contained 3.9 ppm sulfate, 22 ppm fluoride, 2.6 ppm chloride, and 18 ppm aminosulfonate. ICP detection showed that K / Na / Fe / Ca / Cu / Pb / Mo / Ni ions were all less than 1.0 ppm.

[0057] Example 3

[0058] Take 25.5g (0.2406mol) of sodium carbonate and add it to 140.6g of ethyl acetate (water content: 19ppm), adjust the temperature of the mixed solution to -5°C, stir for 1.5h, then slowly add 50.1g (0.1926mol) of bis(fluorosulfonyl)imide pyridinium salt (purity>99%), react for 10h, filter through a 0.22μm hydrophobic filter membrane, terminate the reaction, and obtain 214.8g of filtrate. At this time, the water content of the filtrate sampled and tested was 8073.7ppm.

[0059] The filtrate was adjusted to -20°C, and then 5.6 g (0.0394 mol) of anhydrous sodium sulfate was added. The reaction was stirred for 12 hours, and filtered through a 0.22 μm hydrophobic filter membrane to terminate the reaction to obtain 212.7 g of filtrate. At this time, the water content of the filtrate was sampled and tested to be 198.9 ppm.

[0060] The filtrate was adjusted to 5°C, and then 0.12 g (0.0015 mol) of anhydrous sodium peroxide was added. The mixture was stirred for 6 hours and filtered through a 0.22 μm hydrophobic filter membrane to terminate the reaction to obtain 211.8 g of product liquid. At this time, the water content of the product liquid was sampled and tested to be 17 ppm.

[0061] Ion chromatography showed that the solution contained 7.3ppm sulfate, 18ppm fluoride, 3.4ppm chloride, and 23ppm aminosulfonate. ICP detection showed that K / Na / Fe / Ca / Cu / Pb / Mo / Ni ions were all less than 1.0ppm.

[0062] Comparative Example 1

[0063] Refer to the method of Example 1, except that no anhydrous lithium chloride is added for preliminary water removal, and other operations and conditions remain unchanged.

[0064] The water content of the sampled product was 27843.5ppm. Ion chromatography showed that the solution contained 24.9ppm sulfate, 48ppm fluoride, 3.6ppm chloride, and 128ppm aminosulfonate. ICP testing showed that the ion content of K / Na / Fe / Ca / Cu / Pb / Mo / Ni was less than 1ppm.

[0065] Comparative Example 2

[0066] The method of Example 1 is referred to, except that anhydrous lithium oxide is not added for deep water removal, and other operations and conditions remain unchanged.

[0067] The water content of the sampled product was 272.8ppm. Ion chromatography showed that the solution contained 7.2ppm sulfate, 32ppm fluoride, 3.2ppm chloride, and 31ppm aminosulfonate. ICP testing showed that the ion content of K / Na / Fe / Ca / Cu / Pb / Mo / Ni was less than 1ppm.

[0068] The embodiments described in the content of the present invention are only for illustrating the specific operation methods and related features of the present invention, and the attached claims are intended to require all conceivable and widest possible ranges. The specific embodiments provided herein are only a few simple examples of all the combinations of embodiments. Therefore, the applicant intends that the attached claims cannot be limited by the embodiments shown in the examples of the present invention. The numerical ranges described in the claims also include their sub-ranges. In addition, any embodiment that can be obtained by simple reasoning of the present invention should also be within the scope of the claims.

Claims

1. A method for preparing a bis(fluorosulfonyl)imide salt solution, characterized in that: The following steps are involved: S1: mixing an alkali metal or alkaline earth metal compound with a non-aqueous polar solvent, then adding bis(fluorosulfonyl)imide and its substituent to carry out a salt-forming reaction, filtering, and obtaining a crude product mixture; S2: adding metal salt to the crude product mixed solution of step S1, stirring the reaction to perform preliminary water removal, filtering, and obtaining a mixed solution; S3: Add metal oxide and / or metal sulfide to the mixed solution of step S2, stir the reaction to remove water deeply, filter, and obtain a bis(fluorosulfonyl)imide salt solution.

2. The preparation method according to claim 1, characterized in that: The alkali metal or alkaline earth metal compound in step S1 is one or more of alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal carbonate, alkaline earth metal carbonate, preferably one or more of lithium hydroxide and sodium hydroxide; and / or The purity of the bis(fluorosulfonyl)imide and its substitutes in step S1 is > 99%; Preferably, the bisfluorosulfonyl imide and its substituents are one of bisfluorosulfonyl imide, bisfluorosulfonyl imide organic amine salt, bisfluorosulfonyl imide pyridine and its hydrocarbon substituted derivative salt, bisfluorosulfonyl imide pyrrole and its hydrocarbon derivative salt, bisfluorosulfonyl imide alkyl substituent, preferably one or more of bisfluorosulfonyl imide and bisfluorosulfonyl imide triethylamine salt; and / or The non-aqueous polar solvent in step S1 is selected from one or more of alcohols, ethers, amines, halogenated hydrocarbons, aromatics, carbonates, hydrocarbons, and esters, preferably one or more of ethyl methyl carbonate and dimethyl carbonate; Preferably, the water content in the non-aqueous polar solvent is controlled to be less than 30 ppm.

3. The preparation method according to claim 1, characterized in that: In step S1, the molar ratio of the bis(fluorosulfonyl)imide and its substitute to the alkali metal or alkaline earth metal compound is 1:(1-10), preferably 1:(1.2-2.5); and / or The mass ratio of the bisfluorosulfonyl imide and its substitute to the non-aqueous polar solvent is 1:(1-10), preferably 1:(2.5-8).

4. The preparation method according to claim 1, characterized in that: The salt-forming reaction in step S1 has a reaction temperature of -25°C to 80°C, preferably -5°C to 40°C, and a reaction time of 0.5 to 24 hours, preferably 1 to 10 hours.

5. The preparation method according to claim 1, characterized in that: The metal salt of step S2, wherein the cation is one or more of alkali metal and / or alkaline earth metal cations, and the anion is one or more of halide ion, sulfate ion, bisulfate ion, carbonate ion, bicarbonate ion, nitrate ion, phosphate ion, monohydrogen phosphate ion, and dihydrogen phosphate ion; Preferably, the metal salt is one or more of lithium chloride, sodium chloride and sodium phosphate.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the metal salt in step S2 to the bis(fluorosulfonyl)imide and its substitute in step S1 is (0.2-2):1, preferably (0.5-1.2):

1.

7. The preparation method according to claim 1, characterized in that: The reaction in step S2 has a reaction temperature of -35°C to 40°C, preferably -20°C to 20°C, and a reaction time of 0.5 to 24 hours, preferably 6 to 12 hours.

8. The preparation method according to claim 1, characterized in that: The metal oxide and / or metal sulfide in step S3 is one or more oxides and / or sulfides of alkali metals or alkaline earth metals, preferably one or more of lithium oxide, sodium oxide, and sodium peroxide; and / or The molar ratio of the metal oxide and / or metal sulfide in step S3 to the bis(fluorosulfonyl)imide and its substitute in step S1 is (0.001-0.025):1, preferably (0.003-0.015):

1.

9. The preparation method according to claim 1, characterized in that: The reaction in step S3 has a reaction temperature of -15°C to 40°C, preferably -10°C to 10°C, and a reaction time of 0.5 to 6 hours, preferably 1 to 3 hours.

10. The preparation method according to claim 1, characterized in that: In the filtration described in step S1, step S2 and step S3, the filter membrane used is a hydrophobic filter membrane with a pore size of 0.1 to 20 μm, preferably 0.2 to 5 μm.