Preparation method of bis (fluorosulfonyl) imide salt solution

Abstract

The invention relates to a preparation method of a bis (fluorosulfonyl) imide salt solution. The preparation method comprises the following steps: S1, mixing a certain A salt and a polar non-aqueous solvent, and dropwise adding bis (fluorosulfonyl) imide for reaction; and S2, after the reaction is completed, adding a salt B into the reaction liquid to remove impurities. Water is not generated in the reaction process, and the imidodisulfuryl fluoride cannot be decomposed to generate corrosive substances; the hydrogenation form of the byproduct salt is insoluble in the non-aqueous solvent and can be recycled through reaction; by adding the salt A and the salt B, trace unfavorable impurities are removed at a time, the requirement for the purity of the raw material imidodisulfuryl fluoride is low, subsequent complex purification processes such as crystallization and drying do not exist, the product can be directly used for preparation of a battery electrolyte after concentration adjustment, large-scale production of the product is facilitated, and the product has good storage stability.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of difluoromethanesulfonimide salts, and particularly relates to a method for preparing a high-purity difluoromethanesulfonimide salt solution. Background Art

[0002] Difluoromethanesulfonimide salts are widely used in the field of battery electrolytes. For example, potassium difluoromethanesulfonimide is used as an additive for supercapacitors; lithium difluoromethanesulfonimide is used as an additive for lithium battery electrolytes. As a new type of electrolyte, it has various advantages that the most commonly used electrolyte lithium hexafluorophosphate does not have. As described in US Patent US5916475A, lithium difluoromethanesulfonimide (LiFSI) has better thermal stability and better conductivity than lithium hexafluorophosphate, and related products have been industrially produced by Nippon Shokubai in 2013. LiFSI is considered a new type of lithium salt that can replace lithium hexafluorophosphate as the main salt.

[0003] Currently, the most common preparation process of difluoromethanesulfonimide salts is to react difluoromethanesulfonimide or its variants with salts in a non-aqueous solvent, and then purify the product by means of filtration, recrystallization, drying, etc. to prepare high-purity difluoromethanesulfonimide salts. The main disadvantages of this method are complex process, high energy consumption, and the reaction often generates water, which will cause the decomposition of difluoromethanesulfonimide, and the product is prone to thermal decomposition to produce impurities during the subsequent drying process, resulting in a decline in product quality.

[0004] CN116514077A discloses a method in which difluoromethanesulfonimide reacts with salts in a poor solvent, and then the crude difluoromethanesulfonimide salt is purified by means of filtration, washing, drying, etc. This method reduces the energy consumption to a certain extent compared with the above recrystallization purification scheme, but the anionic acid corresponding to the raw material salt generated by the reaction is likely to remain, and it is difficult to recover and recycle, and at the same time, the drying process will also cause partial decomposition of the prepared difluoromethanesulfonimide salt, resulting in a decline in product quality.

[0005] Existing technologies basically need to prepare crude difluoromethanesulfonimide salts through reactions and prepare high-purity difluoromethanesulfonimide solids by means of filtration, washing, drying or recrystallization, filtration, washing, drying, etc. The introduction of the drying process will inevitably lead to the decomposition and deterioration of the product, resulting in an increase in the content of ionic impurities in the product, thus affecting its performance and further affecting its large-scale use. At present, electrolyte manufacturers basically use the electrolyte in a formulated solution system for formula development. In addition, the presence of trace impurities and acidic substances will greatly reduce the storage stability of the product solution.

[0006] In view of the above technical problems in the preparation process of traditional bis(fluorosulfonyl)imide salts and the current usage status of each electrolyte by electrolyte manufacturers, there is an urgent need in the art for a new preparation process for bis(fluorosulfonyl)imide salt solutions. Summary of the Invention

[0007] The purpose of the present invention is to provide a preparation method for bis(fluorosulfonyl)imide salt solutions. Compared with the traditional solid salt process, it omits complex purification processes such as deacidification, recrystallization, and dehydration drying, and the obtained bis(fluorosulfonyl)imide salt solution has high purity, high yield, and strong storage stability.

[0008] To achieve the above purpose, the technical solution of the present invention is:

[0009] A preparation method for bis(fluorosulfonyl)imide salt solutions, comprising the following steps:

[0010] S1. Bis(fluorosulfonyl)imide reacts with salt A (represented by M 2 + X 2- ) in a polar aprotic solvent to undergo a heterogeneous reaction to form bis(fluorosulfonyl)imide salt (MFSI) and MHX, where neither M 2 + X 2- nor MHX is soluble in the reaction solvent;

[0011] S2. Add salt B to the solution obtained in step S1 for impurity removal, and filter to obtain a high-purity solution of bis(fluorosulfonyl)imide salt.

[0012] In the present invention, the principle of the heterogeneous reaction in step S1 is: M 2 + X 2- +HFSI = MHX + MFSI;

[0013] The cation in salt A is selected from monovalent cations of alkali metals such as lithium, cesium, sodium, and potassium; the anion in salt A is selected from one of polyacid anions such as sulfate, carbonate, phosphate, oxalate, EDTA divalent acid root, succinate, adipate, azelate, terephthalate, phthalate, p-hydroxybenzoate, o-hydroxybenzoate, 2,3-thiophenedicarboxylate, 3,4-thiophenedicarboxylate, 2,3-dihydroxybenzothiophene root, maleate, biphenol root, cannabinol root, metasilicate root, etc.

[0014] In the present invention, the purity of bis(fluorosulfonyl)imide in step S1 > 99 wt%, and the remaining are various impurity acids such as sulfuric acid, hydrogen chloride, hydrogen fluoride, sulfamic acid, etc., all less than 3000 ppm.

[0015] Preferably, the molar ratio of the A salt to the bis(fluorosulfonyl)imide is (1 to 10):1, more preferably (1.5 to 3):1; preferably, the reaction temperature in step S1 is -25°C to 40°C, and the reaction time is 1 to 20 h; more preferably, the reaction temperature is -10°C to 20°C, and the reaction time is 2 to 8 h.

[0016] Preferably, the polar aprotic solvent in step S1 is selected from one or more of methyl formate, ethyl formate, propyl formate, isopropyl formate, ethyl acetoacetate, n-butyl acetate, isobutyl acetate, isoamyl acetate, methyl lactate, ethyl acetate, methyl acetate, methyl tert-butyl ether, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl salicylate, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-hexanol, cyclohexanol, n-octanol, isooctanol, glycerol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, dioxolane, propylene oxide, diethoxymethane, anisole;

[0017] Preferably, the mass ratio of the polar aprotic solvent to the bis(fluorosulfonyl)imide is (1 to 10):1, more preferably (2.5 to 9):1.

[0018] In the present invention, in step S2, the anion of the B salt is selected from halogen anions such as F - , Cl - , Br - and the cation is selected from monovalent cations of alkali metals such as lithium, cesium, sodium, potassium.

[0019] Preferably, the molar ratio of the B salt to the bis(fluorosulfonyl)imide is (0.1 to 0.9):1, more preferably (0.3 to 0.6):1.

[0020] In the present invention, the temperature of the impurity removal reaction in step S2 is -25°C to 40°C, preferably -10°C to 20°C, and the reaction time is 1 to 2 h.

[0021] In step S1, the water content of the polar aprotic solvent, the A salt, and the B salt is less than 50 ppm, more preferably less than 10 ppm. The low water content can ensure that M 2 + X 2- has low solubility in the reaction solution with MHX, and the bis(fluorosulfonyl)imide and the bis(fluorosulfonyl)imide salt have less deterioration.

[0022] In step S2 of the present invention, after the impurity removal reaction is completed, the reaction mixture is filtered to obtain a bis(fluorosulfonyl)imide salt solution and a filter residue. The filtration uses a hydrophobic filter membrane with a pore size of 0.1 to 20 μm, preferably 0.2 to 5 μm, and the filtration operation is carried out under a nitrogen atmosphere.

[0023] The filter residue obtained by filtration is mainly excessive A salt and MHX generated by the reaction. The filter residue reacts with an aqueous solution of a fluoride salt, a chloride salt, a hydroxide salt or a carbonate salt to obtain an aqueous solution of A salt. It is preferred to use a hydroxide salt, which does not generate other gas impurities. The aqueous solution of A salt can be recycled after drying.

[0024] In the present invention, to improve the product purity and the reaction yield, the following operation mode is preferably adopted: First, A salt is added to a measured polar non-aqueous solvent to prepare a mixed solution thereof, and the mixed solution is adjusted to the reaction temperature (-25°C to 40°C, preferably -10°C to 20°C), and maintained for 0.5 to 5 hours, preferably 1 to 1.5 hours. Then, bis(fluorosulfonyl)imide is slowly added dropwise to the mixed solution, and the dropping time is controlled to be 10% to 50% of the reaction time, preferably 15% to 25%, and the reaction time does not include the dropping time of bis(fluorosulfonyl)imide. If the reaction temperature is too high, bis(fluorosulfonyl)imide and bis(fluorosulfonyl)imide salt will decompose and deteriorate. If the temperature is too low, the reaction activity will be greatly reduced and the product yield will be low. By adopting the above reaction temperature and premixing method, it is more beneficial to obtain a bis(fluorosulfonyl)imide salt solution product with high purity and high yield.

[0025] The reaction time with A salt is determined by the acidity of the filtrate of the reaction mixture. During the reaction process, the acidity of the filtrate of the reaction mixture is continuously detected. When the acidity is stable, it is the end point of the reaction. At this time, the measured B salt is added to the reaction mixture, and the same reaction temperature as that of A salt is maintained for 1 to 2 hours for impurity removal reaction to remove impurities in the reaction mixture that do not react with A salt or whose reaction products are in a dissolved state, and to remove trace moisture in the reaction solution through the crystallization adsorption ability of B salt.

[0026] The beneficial effects of the present invention are as follows:

[0027] The preparation method of the bis(fluorosulfonyl)imide salt solution provided by the present invention has a simple process, a high reaction rate, no adverse side reactions, and omits complex purification processes such as deacidification, recrystallization, and dehydration drying in the traditional solid salt process. The obtained product has high purity and high yield, and the used A salt can be recycled after treatment. In addition, by optimizing the reaction conditions and the introduction of B salt, impurities in the product mixture after the reaction can be precipitated, reducing the risk of product out-of-control and the requirement for the purity of raw materials, and the deep removal of trace impurities greatly improves the storage stability of the product. Specific Embodiments

[0028] Description of raw material sources and stability tests:

[0029] Bis(fluorosulfonyl)imide: The reaction rectification and purification process of bis(chlorosulfonyl)imide and hydrogen fluoride by Wanhua Chemical;

[0030] Other raw materials appearing in this article are all conventional commercially available raw materials.

[0031] The storage stability was verified by storing each of the prepared product solutions at -10°C, 25°C, and 40°C for 30 days respectively, and then performing ion chromatography and acidity tests.

[0032] The specific test methods involved in the present invention are as follows:

[0033] (1) Sulfate, chloride, fluoride, amidosulfonate, and the anions of the salts used were all tested by anion chromatography, and the quantitative standard was the internal standard method.

[0034] Test instrument: Thermo Fisher ion chromatograph;

[0035] Chromatographic column: Thermo Fisher AS22 (4mm * 250mm) and Thermo Fisher AG22 (4mm * 50mm);

[0036] Detection cell: Conductivity detection cell, temperature 45°C;

[0037] Suppressor: Continuous automatic electrolytic regeneration membrane anion suppressor;

[0038] Injection volume: 25 μl;

[0039] Mobile phase: Sodium carbonate - sodium bicarbonate aqueous solution.

[0040] (2) The liquid phase acidity was determined by aqueous phase titration:

[0041] Test instrument: Micro burette;

[0042] Indicator: Bromothymol blue;

[0043] Titrant: 0.02 mol / L NaOH standard aqueous solution;

[0044] Test standard: Weigh 1 g of the sample to be tested, dissolve it in 10 g of ultrapure water, titrate it with 0.02 mol / L NaOH standard aqueous solution to the end point, and then calculate the sample acidity in terms of HF.

[0045] (3) The trace metal ions in the product solution were tested according to the standard of GB / T 19282 - 2014, and the instrument used was Thermo Fisher iCAP TM 7400 ICP - OES.

[0046] (4) The purity of the bis(fluorosulfonyl)imide salt was tested by nuclear magnetic resonance fluorine spectrum:

[0047] Test instrument: Bruker AVANCE III HD 400;

[0048] Internal standard: Trifluoroacetic acid;

[0049] Deuterated reagent: Deuterated DMSO.

[0050] Example 1

[0051] Take 28.4 g of anhydrous sodium sulfate and add it to 45 g of ethyl methyl carbonate solvent (water content 12 ppm). Cool the mixture of the two to -10 °C and maintain it at a low temperature for 30 minutes. Then, slowly add 18.1 g of bis(fluorosulfonyl)imide dropwise under stirring. The total dropping time is about 1 hour. After the dropping is completed, continue the reaction for 5 hours. After the reaction is completed, add 1.75 g of anhydrous sodium chloride to the reaction mixture and continue the reaction for 1 hour. Then, filter it through a 0.22-μm hydrophobic filter membrane at a low temperature to obtain a high-purity solution of sodium bis(fluorosulfonyl)imide in ethyl methyl carbonate. Through nuclear magnetic resonance fluorine spectrum test, the mass concentration of sodium bis(fluorosulfonyl)imide in the obtained product is 30.8%. Ion chromatography shows that the sulfate ion in the obtained solution is 7.3 ppm, the fluoride ion is 32 ppm, the chloride ion is 12 ppm, and the aminosulfonate ion is 45 ppm. Through ICP detection, K is 1.2 ppm, and other ions (such as Fe / Ca / Cu / Pb / Mo / Ni, etc.) are all less than 1.0 ppm, the water content is 16 ppm, and the acidity is 28 ppm.

[0052] Example 2

[0053] Take 53.1 g of cesium oxalate and add it to 75 g of methyl tert-butyl ether solvent (water content 7 ppm). Cool the mixture of the two to -25 °C and maintain it at a low temperature for 30 minutes. Then, slowly add 18.1 g of bis(fluorosulfonyl)imide dropwise under stirring. The total dropping time is about 2 hours. After the dropping is completed, continue the reaction for 8 hours. When the reaction reaches the end point, add 3.04 g of cesium fluoride to the reaction mixture and continue the reaction for 2 hours. Then, filter it through a 0.45-μm hydrophobic filter membrane at a low temperature to obtain a high-purity solution of cesium bis(fluorosulfonyl)imide in methyl tert-butyl ether. Through nuclear magnetic resonance fluorine spectrum test, the mass concentration of cesium bis(fluorosulfonyl)imide in the obtained product is 29.4%. Ion chromatography shows that the oxalate ion in the obtained solution is 12 ppm, the sulfate ion is 5.7 ppm, the fluoride ion is 26 ppm, the chloride ion is 8 ppm, and the aminosulfonate ion is 36 ppm. Through ICP detection, K is 1.2 ppm, Na is 2.2 ppm, and other ions (such as Fe / Ca / Cu / Pb / Mo / Ni, etc.) are all less than 1.0 ppm, the water content is 7.6 ppm, and the acidity is 32 ppm.

[0054] Example 3

[0055] Take 45 g of dipotassium azelate and add it to 50 g of ethylene glycol dimethyl ether solvent (water content 13 ppm). Keep the mixture of the two at 40 °C and maintain for 30 minutes. Then, slowly add 18.1 g of bis(fluorosulfonyl)imide dropwise under stirring. The total dropping time is about 1 hour. After the dropping is completed, continue the reaction for 6 hours. After the reaction reaches the end point, add 5.95 g of potassium bromide to the reaction mixture and continue the reaction for 1.5 hours. Then, filter with a 0.22 μm hydrophobic filter membrane to obtain a high-purity ethylene glycol dimethyl ether solution of potassium bis(fluorosulfonyl)imide. After testing by nuclear magnetic resonance fluorine spectrum, the mass concentration of potassium bis(fluorosulfonyl)imide in the obtained product is 28.2%. Ion chromatography shows that in the obtained solution, the azelate is 21 ppm, sulfate is 6.9 ppm, fluoride ion is 28 ppm, chloride ion is 6 ppm, bromide ion is 13 ppm, and amidosulfonate is 68 ppm. After ICP detection, Na is 1.4 ppm, K ion is 3.9 ppm, and other ions (Fe / Ca / Cu / Pb / Mo / Ni, etc.) are all less than 1.0 ppm. The water content is 23 ppm, and the acidity is 19 ppm.

[0056] Example 4

[0057] Take 36.5 g of dilithium ethylenediaminetetraacetate and add it to 45 g of tetrahydrofuran solvent (water content 6 ppm). Cool the mixture of the two to -10 °C and maintain at low temperature for 30 minutes. Then, slowly add 18.1 g of bis(fluorosulfonyl)imide dropwise under stirring. The total dropping time is about 1 hour. After the dropping is completed, continue the reaction for 5 hours. After the reaction reaches the end point, add 2.52 g of lithium chloride to the reaction mixture and continue the reaction for 1 hour. Then, filter at low temperature with a 0.22 μm hydrophobic filter membrane to obtain a high-purity tetrahydrofuran solution of lithium bis(fluorosulfonyl)imide. After testing by nuclear magnetic resonance fluorine spectrum, the mass concentration of lithium bis(fluorosulfonyl)imide in the obtained product is 28.9%. Ion chromatography shows that in the obtained solution, the ethylenediaminetetraacetate is 18 ppm, sulfate is 9.4 ppm, fluoride ion is 22 ppm, chloride ion is 4 ppm, and amidosulfonate is 32 ppm. After ICP detection, Na is 1.4 ppm, and other ions (K / Fe / Ca / Cu / Pb / Mo / Ni, etc.) are all less than 1.0 ppm. The water content is 12 ppm, and the acidity is 22 ppm.

[0058] Example 5

[0059] 23.2 g of lithium malonate was added to 45 g of ethyl methyl carbonate solvent (water content 12 ppm). The mixture of the two was kept at 10 °C for 30 minutes and then 18.1 g of bis(fluorosulfonyl)imide was slowly added dropwise with stirring over a total addition time of about 1 hour. After the addition was complete, the reaction was continued for 6 hours. After the reaction reached the end point, 2.52 g of lithium chloride was added to the reaction mixture and the reaction was continued for 2 hours. After the reaction was completed, the reaction solution was filtered through a 0.22 μm hydrophobic filter membrane. By nuclear magnetic resonance fluorine spectrum test, the mass concentration of lithium bis(fluorosulfonyl)imide in the obtained product was 29.3%. Ion chromatography of the test filtrate showed that the content of malonate was ND, sulfate was 9.7 ppm, fluoride ion was 18 ppm, chloride ion was 3 ppm, and aminosulfonate was 25 ppm. By ICP detection, K was 2.2 ppm, Na was 3.2 ppm, and the other ions (Fe / Ca / Cu / Pb / Mo / Ni, etc.) were all less than 1.0 ppm, the water content was 28 ppm, and the acidity was 18 ppm.

[0060] Comparative Example 1

[0061] 28.4 g of anhydrous sodium sulfate was added to 45 g of ethyl methyl carbonate solvent (water content 12 ppm). The mixture of the two was cooled to -10 °C and kept at low temperature for 30 minutes, and then 18.1 g of bis(fluorosulfonyl)imide was slowly added dropwise with stirring over a total addition time of about 1 hour. After the addition was complete, the reaction was continued for 5 hours. After the reaction reached the end point, it was directly filtered through a 0.22 μm hydrophobic filter membrane at low temperature to obtain a solution of sodium bis(fluorosulfonyl)imide in ethyl methyl carbonate. By nuclear magnetic resonance fluorine spectrum test, the mass concentration of sodium bis(fluorosulfonyl)imide in the obtained product was 29.8%. Ion chromatography showed that the sulfate in the obtained solution was 97.3 ppm, fluoride ion was 232 ppm, chloride ion was 112 ppm, and aminosulfonate was 245 ppm. By ICP detection, K was 21.2 ppm, and the other ions (Fe / Ca / Cu / Pb / Mo / Ni, etc.) were all less than 1.0 ppm, the water content was 1298 ppm, and the acidity was 506 ppm.

[0062] Comparative Example 2

[0063] Take 5.09g lithium chloride and add it to 45g dimethyl carbonate solvent (water content 22ppm), cool the mixed solution of the two to 10 DEG C and maintain at low temperature for 30 minutes, then slowly drip 18.1g bisfluorosulfonyl imide under stirring, drip for a total of about 1 hour, and continue to react for 5 hours after the addition is completed. After the reaction reaches the end point, the reaction solution is filtered, and the mass concentration of bisfluorosulfonyl imide lithium in the obtained product is 29.4% through the nuclear magnetic resonance fluorine spectrum test, and the ion chromatography of the test filtrate shows sulfate 29.7ppm, fluoride ion 19ppm, chloride ion 3183ppm, and aminosulfonate 425ppm. According to ICP detection, K is 12.2ppm, Na is 13.2ppm, and other ions (Fe / Ca / Cu / Pb / Mo / Ni, etc.) are all less than 1.0ppm, and the moisture content is 328ppm, and the acidity is 1897ppm.

[0064] Comparative Example 3

[0065] Take 3.90g lithium fluoride and add it to 45g ethyl methyl carbonate solvent (water content 22ppm), the mixed solution of the two is cooled to -10 DEG C and maintained at low temperature for 30 minutes, then slowly drip 18.1g bisfluorosulfonyl imide under stirring, the dripping time is about 1.5 hours in total, and the reaction is continued for 7 hours after the dropwise addition is completed. After the reaction reaches the end point, the reaction solution is filtered at low temperature, and the mass concentration of bisfluorosulfonyl imide lithium in the obtained product is 29.9% through the nuclear magnetic resonance fluorine spectrum test, and the ion chromatography of the test filtrate shows sulfate 19.7ppm, fluoride ion 30919ppm, chloride ion 83ppm, and aminosulfonate 225ppm. Through ICP detection, K is 22.2ppm, Na is 9.2ppm, and other ions (Fe / Ca / Cu / Pb / Mo / Ni, etc.) are all less than 1.0ppm, and the moisture content is 1028ppm, and the acidity is 32987ppm.

[0066] In addition, the above embodiments and comparative examples were tested for storage stability at -10°C, 25°C and 40°C, and the key index results are as follows:

[0067]

[0068] It can be seen that the bis(fluorosulfonyl)imide salt solution prepared by the process scheme of the present invention has F - 、SO 4 2- Lower content and better storage stability.

[0069] The embodiments described in the present invention content are only for illustrating the specific operation methods and their related features of the present invention. The appended claims are intended to claim the broadest possible scope that can be conceived. Moreover, the specific embodiments provided herein are only several simple examples of the permutations and combinations of all embodiments. Therefore, the applicant's intention is that the appended 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, embodiments that can be obtained by simple reasoning from 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, it comprises the following steps: S1: Bis(fluorosulfonyl)imide reacts with salt A in a polar aprotic solvent to form a bis(fluorosulfonyl)imide salt; S2: Salt B is added to the solution obtained in step S1 for impurity removal, and then filtered to obtain a bis(fluorosulfonyl)imide salt solution.

2. The preparation method according to claim 1, characterized in that, the cation in salt A is selected from monovalent cations of lithium, cesium, sodium, and potassium; the anion is selected from one of sulfate, carbonate, phosphate, oxalate, EDTA divalent acid radical, succinate, adipate, azelate, terephthalate, phthalate, p-hydroxybenzoate, o-hydroxybenzoate, 2,3-thiophene dicarboxylate, 3,4-thiophene dicarboxylate, 2,3-dihydroxybenzothiophene radical, maleate, biphenol radical, cannabinol radical, metasilicate radical.

3. The preparation method according to claim 1 or 2, characterized in that, the molar ratio of the feed of salt A to bis(fluorosulfonyl)imide is (1 - 10):1, preferably (1.5 - 3):

1.

4. The preparation method according to claim 1, characterized in that, The anion of salt B is selected from F - , Cl - , Br - , and the cation is selected from monovalent cations of lithium, cesium, sodium, and potassium.

5. The preparation method according to claim 1 or 4, characterized in that, the molar ratio of the feed of salt B to bis(fluorosulfonyl)imide is (0.1 - 0.9):1, preferably (0.3 - 0.6):

1.

6. The preparation method according to any one of claims 1 - 5, characterized in that, the polar aprotic solvent is selected from one or more of methyl formate, ethyl formate, propyl formate, isopropyl formate, ethyl acetoacetate, n-butyl acetate, isobutyl acetate, isoamyl acetate, methyl lactate, ethyl acetate, methyl acetate, methyl tert-butyl ether, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl salicylate, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-hexanol, cyclohexanol, n-octanol, isooctanol, glycerol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, dioxolane, propylene oxide, diethoxymethane, anisole.

7. The preparation method according to claim 1, characterized in that, the reaction temperature in step S1 is -25°C to 40°C, and the reaction time is 1 - 20 h; preferably the reaction temperature is -10°C to 20°C, and the reaction time is 2 - 8 h.

8. The preparation method according to claim 1, characterized in that, the reaction temperature in step S2 is -25°C to 40°C, and the reaction time is 1 - 2 h.

9. The preparation method according to claim 1, characterized in that, the pore size of the filter membrane used for filtration in step S2 is 0.1 - 20 μm, preferably 0.2 - 5 μm.

10. The preparation method according to any one of claims 1 - 9, characterized in that, it comprises: Adding salt A to the measured polar aprotic solvent to prepare a mixed solution thereof, adjusting the mixed solution to the reaction temperature, maintaining for 0.5 - 5 hours, and then slowly dropping bis(fluorosulfonyl)imide into the mixed solution, controlling the dropping time to be 10% - 50% of the reaction duration, and the reaction duration does not include the dropping time of bis(fluorosulfonyl)imide.

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