Preparation method of high-purity bis (fluorosulfonyl) imide alkali metal salt

Abstract

The invention discloses a preparation method of high-purity bis (fluorosulfonyl) imide alkali metal salt. The method comprises the following steps: (1) synthesizing bis (chlorosulfonic acid) imide by taking sulfamic acid, chlorosulfonic acid, thionyl chloride and chlorosulfonic acid isocyanate as raw materials; (2) fluorinating the bis (chlorosulfonic acid) imide by ammonium fluoride to obtain bis (fluorosulfonyl) imide ammonium salt; (3) treating the imidodisulfuryl fluoride ammonium salt solution with a strong acid ion exchange column and concentrating under reduced pressure to obtain imidodisulfuryl fluoride; (4) reacting the alkali metal salt with bis (fluorosulfonyl) imide to obtain bis (fluorosulfonyl) imide alkali metal salt; and (5) carrying out a series of purification processes on the bis (fluorosulfonyl) imide alkali metal salt to obtain the high-purity bis (fluorosulfonyl) imide alkali metal salt. The preparation method has the advantages of mild reaction conditions, low danger coefficient in the technological process, easiness in control, no use and generation of corrosive acid, greenness and environmental protection, and high yield and high purity of the bis (fluorosulfonyl) imide alkali metal salt, and is suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention relates to the field of alkali metal salt technology for new energy battery electrolytes, specifically a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt. Background Technology

[0002] Alkali metal salts are key components in the electrolytes of new energy batteries, and their properties significantly influence the properties of the electrolyte and are closely related to battery performance. Difluorosulfonylimide alkali metal salt, as a new generation electrolyte salt, is favored for its high thermal stability (decomposition temperature >200℃), high ionic conductivity (more than 30% higher than LiPF6), and wide electrochemical window (>4.5V vs. Li). + Its properties, such as those of Li, are considered key components for overcoming the bottleneck of high-voltage cathode materials. Furthermore, due to its high thermal stability, it is often regarded as one of the preferred electrolyte salts for wide-temperature-range battery designs.

[0003] Currently, the production of bis(fluorosulfonyl)imide alkali metal salts still faces challenges such as high synthesis costs, complex processes, low yields, difficult purification, and significant safety hazards. In recent years, a two-step method has gradually become industrialized, offering lower costs and a shorter reaction path. For example, patents CN114348978A and CN115818591A applied for by Times Sicon use sulfuryl fluoride / fluorine chloride, ammonia source, and organic base as raw materials to synthesize bis(fluorosulfonyl)imide alkali metal salts. Subsequent reactions with a suitable alkali metal source yield the bis(fluorosulfonyl)imide alkali metal salt. However, due to the weak nucleophilicity of fluorine in sulfuryl fluoride, the reaction requires high pressure / Lewis acid catalysts, introducing additional impurities. Furthermore, the multiple reaction sites result in the generation of many intermediates, raising issues of product purity and thermal runaway risks. These problems prevent the synthesis from meeting the purity, safety, and cost requirements of bis(fluorosulfonyl)imide alkali metal salts for power batteries.

[0004] Currently, the mainstream industrial approach uses a three-step process: chlorination-fluorination-lithiation. For example, Shenzhen Xinzhoubang's patent CN103935970A uses aminosulfonic acid, chlorosulfonic acid, and thionyl chloride as raw materials to synthesize bischlorosulfonylimide, then fluorinates it with hydrogen fluoride to obtain bisfluorosulfonylimide, and finally reacts it with lithium fluoride to obtain the alkali metal salt of bisfluorosulfonylimide. However, this three-step method inevitably suffers from high costs. Furthermore, it requires sophisticated fluorination equipment, generates significant amounts of waste gas, increases post-treatment costs, and results in lower product purity.

[0005] Therefore, it is necessary to design a production process that features mild reaction conditions, easy process control, low risk, no use or generation of corrosive acids, is environmentally friendly, and has a high yield and purity of bis(fluorosulfonyl)imide alkali metal salt, suitable for large-scale industrial application. Summary of the Invention

[0006] To address the problems of complex and hazardous processes and low product purity in existing bis(fluorosulfonyl)imide alkali metal salt production, this invention is based on a three-step process route of "chlorination-fluorination-lithiation". It utilizes ammonium fluoride as a fluorinating agent, which has high safety, mild reaction conditions, and does not require special reaction equipment. Combined with subsequent steps to remove a series of impurities from the crude product, this invention achieves the preparation of high-purity bis(fluorosulfonyl)imide alkali metal salt.

[0007] The purpose of this invention is to provide a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salts, thereby solving the problems existing in the prior art. In particular, these problems include harsh production conditions, high equipment requirements, significant safety hazards, and low product purity.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a high-purity alkali metal salt of bis(fluorosulfonyl)imide specifically includes the following steps:

[0010] (1) Dichlorosulfonic acid imine was synthesized from aminosulfonic acid, chlorosulfonic acid, thionyl chloride, and chlorosulfonic acid isocyanate; the reaction equation is as follows:

[0011]

[0012] (2) Ammonium fluoride fluorinates dichlorosulfonate imide to give difluorosulfonylimide ammonium salt; the reaction equation is as follows:

[0013]

[0014] (3) The difluorosulfonylimide ammonium salt solution was subjected to a strongly acidic ion exchange column and concentrated under reduced pressure to obtain difluorosulfonylimide; the reaction equation is as follows:

[0015]

[0016] (4) Alkali metal salts react with bis(fluorosulfonyl)imide to obtain bis(fluorosulfonyl)imide alkali metal salts;

[0017] (5) The alkali metal salt of bis(fluorosulfonyl)imide was purified through a series of purification processes to obtain high-purity bis(fluorosulfonyl)imide alkali metal salt: the crude bis(fluorosulfonyl)imide alkali metal salt was fully dissolved in the first solvent, filtered to remove insoluble matter, and then the corresponding basic alkali metal source was added to the filtrate for preliminary deacidification, and filtered; the filtrate was added to the reagent for dehydration and deacidification, filtered, concentrated under reduced pressure to obtain bis(fluorosulfonyl)imide alkali metal salt concentrate; the bis(fluorosulfonyl)imide alkali metal salt concentrate was slowly added dropwise to the second solvent for back precipitation, allowed to stand to precipitate, and then separated and vacuum dried to obtain high-purity bis(fluorosulfonyl)imide alkali metal salt.

[0018] In one specific embodiment of the present invention, the molar ratio between aminosulfonic acid, chlorosulfonic acid, thionyl chloride and chlorosulfonic acid isocyanate in step (1) is 1:(1~1.2):(2.5~3):(0~0.2).

[0019] Furthermore, the reaction temperature in step (1) is 110–130°C, and the reaction time is 10–24 h.

[0020] In one specific embodiment of the present invention, the amount of ammonium fluoride added in step (2) is based on a molar ratio of 1:(0.1-2) of dichlorosulfonamide.

[0021] Furthermore, the reaction temperature in step (2) is 20–100°C, and the reaction time is 4–12 h.

[0022] Furthermore, the solvent used in step (2) is an aprotic polar organic solvent, including but not limited to at least one of acetonitrile, propionitrile, isopropionitrile, butyronitrile, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0023] Further, the amount of solvent added in step (2) is based on a mass ratio of ammonium fluoride of 1:(0.1~1).

[0024] In one specific embodiment of the present invention, the flow rate of the solution passing through the ion exchange column in step (3) is selected to be 10-30 mL / min.

[0025] Furthermore, the ion exchange column reaction described in step (3) is marked as ending when the pH of the effluent is >6.

[0026] Furthermore, the temperature for vacuum concentration in step (3) is selected as 60-80°C, and the pressure is selected as 5-20 kPa.

[0027] In one specific embodiment of the present invention, the cation of the alkali metal salt in step (4) is one of lithium, sodium, and potassium.

[0028] Further, the anion of the alkali metal salt mentioned in step (4) is one of fluoride anion, chloride anion, bromide anion, iodide anion, perchlorate anion, carbonate anion, tetrafluoroborate anion, and p-toluenesulfonate anion.

[0029] Further, the amount of alkali metal salt added in step (4) is based on a molar ratio of bis(fluorosulfonyl)imide of (1-5):1.

[0030] Further, the solvent used in step (4) is selected from at least one of benzene, toluene, xylene, chlorobenzene, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, n-hexane, and cyclohexane.

[0031] Further, the amount of solvent added in step (4) is based on a mass ratio of 1:(0.05~1) of difluorosulfonyl imide.

[0032] Furthermore, the reaction temperature in step (4) is 0–60°C and the reaction time is 0.1–5 h.

[0033] In one specific embodiment of the present invention, in step (5), the first solvent is selected from at least one of acetonitrile, propionitrile, isopropionitrile, diethyl ether, propyl ether, methyl tert-butyl ether, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, dimethyl sulfoxide, toluene, acetone, butanone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0034] Further, in step (5), the amount of the first solvent added is 1:(0.05~10) according to the mass ratio of crude difluorosulfonyl imide alkali metal salt.

[0035] Furthermore, the filter membrane material used in step (5) is at least one of PTFE, PES, Nylon 6, Nylon 66, glass fiber, PVDF, MCE, and PP.

[0036] Furthermore, the pore size of the filter membrane in step (5) is 0.1 to 1 μm.

[0037] Furthermore, the anion of the alkaline alkali metal source mentioned in step (5) is one of hydroxide anion, carbonate anion, bicarbonate anion, and tetrafluoroborate anion.

[0038] Further, the amount of alkaline alkali metal source added in step (5) is (0.05~1):1 according to the mass ratio of crude difluorosulfonyl imide alkali metal salt.

[0039] Furthermore, the dehydration and deacidification reagent in step (5) is selected from at least one of hexamethyldisilazane, cyclodisilazane, cyclotrisilazane, cyclotetrasilazane, trimethyl orthoformate, thionyl chloride, trifluoroacetic anhydride, acetyl chloride, etc.

[0040] Further, the amount of dehydration and deacidification reagent added in step (5) is (0.01~0.1):1 according to the mass ratio of crude difluorosulfonyl imide alkali metal salt.

[0041] Further, in step (5), the second solvent is selected from at least one of n-hexane, cyclohexane, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, benzene, toluene, xylene, petroleum ether, chlorobenzene, and dichlorobenzene.

[0042] Further, in step (5), the amount of the second solvent added is 1:(0.01~0.1) based on the mass ratio of crude difluorosulfonyl imide alkali metal salt.

[0043] A method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salts, wherein the yield of each step of the reaction using this method is ≥97%, the purity is ≥99.9%, and the free acid content is ≤30ppm, the moisture content is ≤50ppm, the chloride ion content is ≤10ppm, the fluoride ion content is ≤20ppm, the sulfate ion content is ≤10ppm, the content of each impurity metal ion is ≤5ppm, and the DMC insoluble matter content is ≤30ppm.

[0044] As can be seen from the above technical solution, the beneficial effects of the preparation method of high-purity bis(fluorosulfonyl)imide alkali metal salt of the present invention are as follows: the process prepares high-purity bis(fluorosulfonyl)imide alkali metal salt through multi-step reaction, which can control the reaction step by step, gradually optimize the reaction conditions, reduce the risk of side reactions, and is conducive to improving the yield; combined with multi-step purification process steps, the purity of the product is significantly improved, and high-yield and high-purity preparation of bis(fluorosulfonyl)imide alkali metal salt can be achieved.

[0045] Compared with existing technologies, this invention has the following advantages: The classic three-step reaction method for preparing bis(fluorosulfonyl)imide alkali metal salts, using ammonium fluoride for fluorination under mild conditions, not only allows for controllable reaction conditions and low equipment requirements, but also avoids the generation of waste and achieves high reaction yield. Combined with multi-step processes for removing water, acid, insoluble substances, and byproduct impurities, high-purity bis(fluorosulfonyl)imide alkali metal salts can be prepared. Therefore, the method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salts of this invention has high industrial application value. Attached Figure Description

[0046] Figure 1 A schematic diagram of a strongly acidic ion exchange column device and the exchange process in an embodiment of the present invention. Detailed Implementation

[0047] The following embodiments clearly and completely illustrate the specific content of the present invention, but the implementation of the present invention is not limited thereto and should not be construed as a limitation on the scope of protection of the present invention. Improvements and adjustments made by those skilled in the art based on this patent without inventive effort are all within the scope of protection of the present invention.

[0048] In the following examples, the structure of bis(chlorosulfonyl)imide was characterized by 1H NMR spectroscopy, and the structure of bis(fluorosulfonyl)imide and its alkali metal salt was characterized by fluorine NMR spectroscopy. The impurity metal ions, anions, and moisture content in the bis(fluorosulfonyl)imide alkali metal salt were detected by ICP-MS, IC, and Karl Fischer moisture analyzer, respectively. The free acid and DMC insoluble content in the bis(fluorosulfonyl)imide alkali metal salt were determined by self-testing according to the method specified in GB / T19282-2014.

[0049] Example 1

[0050] like Figure 1 As shown, this embodiment provides a method for preparing a high-purity alkali metal salt of bis(fluorosulfonyl)imide, comprising the following steps:

[0051] (1) Dichlorosulfonic acid imine was synthesized from aminosulfonic acid, chlorosulfonic acid, thionyl chloride and chlorosulfonic acid isocyanate. The molar ratio between aminosulfonic acid, chlorosulfonic acid, thionyl chloride and chlorosulfonic acid isocyanate was 1:1.1:3:0.1. The reaction temperature was 122℃ and the reaction time was 18h.

[0052] (2) Ammonium fluoride fluorinates dichlorosulfonamide to obtain dichlorosulfonamide ammonium salt. The amount of ammonium fluoride added is 1:0.4 molar ratio of dichlorosulfonamide to imide. The reaction temperature is 35℃ and the reaction time is 6h. The solvent used is acetonitrile. The amount of acetonitrile added is 1:0.5 mass ratio of ammonium fluoride to acetonitrile.

[0053] (3) Difluorosulfonyl imide ammonium salt solution was passed through a strong acid ion exchange column and concentrated under reduced pressure to obtain difluorosulfonyl imide. The flow rate of the solution in the ion exchange column was controlled at 15 mL / min. The exchange ended when the pH of the effluent from the ion exchange column was ≈7. The temperature for reduced pressure concentration was 68℃ and the pressure was 10 kPa.

[0054] (4) The alkali metal salt reacts with bis(fluorosulfonyl)imide to obtain bis(fluorosulfonyl)imide alkali metal salt. The alkali metal salt is lithium carbonate, and the amount added is based on a molar ratio of 2.5:1 for bis(fluorosulfonyl)imide. The solvent used is toluene, and the amount added is based on a mass ratio of 1:0.5 for bis(fluorosulfonyl)imide. The reaction temperature is 5℃ and the time is 3h.

[0055] (5) After a series of purification processes, high-purity difluorosulfonylimide alkali metal salt was obtained: the first solvent was diethyl ether, and the amount added was 1:0.5 according to the mass ratio of crude difluorosulfonylimide alkali metal salt; 0.25μm PTFE filter membrane was used for filtration; lithium hydroxide was used as the alkaline metal source, and the amount added was 0.05:1 according to the mass ratio of crude difluorosulfonylimide alkali metal salt; hexamethyldisilazane, trimethyl orthoformate, and thionyl chloride were selected as dehydration and deacidification reagents, and the amount added of each dehydration and deacidification reagent was 0.02:1 according to the mass ratio of crude difluorosulfonylimide alkali metal salt; the second solvent was dichloromethane and carbon tetrachloride, and the amount added of each second solvent was 1:0.03 according to the mass ratio of crude difluorosulfonylimide alkali metal salt.

[0056] Example 2

[0057] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (1), the molar ratio between aminosulfonic acid, chlorosulfonic acid, thionyl chloride and chlorosulfonic acid isocyanate is 1:1.1:3:0.15.

[0058] Example 3

[0059] This embodiment provides a method for preparing a high-purity alkali metal salt of bis(fluorosulfonyl)imide, which is basically the same as that in Example 1, except that in step (2), the amount of ammonium fluoride added is based on a molar ratio of bis(fluorosulfonyl)imide of 1:0.2.

[0060] Example 4

[0061] This embodiment provides a method for preparing a high-purity alkali metal salt of dichlorosulfonyl imide, which is basically the same as that in Example 1, except that in step (2), the amount of ammonium fluoride added is based on a molar ratio of 1:0.6 for dichlorosulfonyl imide.

[0062] Example 5

[0063] This embodiment provides a method for preparing a high-purity alkali metal salt of bis(fluorosulfonyl)imide, which is basically the same as that in Example 1, except that in step (2), the amount of ammonium fluoride added is based on a molar ratio of bis(fluorosulfonyl)imide of 1:0.8.

[0064] Example 6

[0065] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that the reaction temperature in step (2) is 10°C.

[0066] Example 7

[0067] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that the reaction temperature in step (2) is 25°C.

[0068] Example 8

[0069] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that the reaction temperature in step (2) is 50°C.

[0070] Example 9

[0071] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that the reaction time in step (2) is 3 hours.

[0072] Example 10

[0073] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that the reaction time in step (2) is 9 hours.

[0074] Example 11

[0075] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (2), the solvent used is toluene.

[0076] Example 12

[0077] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (2), the solvent used is dichloromethane.

[0078] Example 13

[0079] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (2), the amount of acetonitrile added is 1:0.2 according to the mass ratio of ammonium fluoride.

[0080] Example 14

[0081] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (2), the amount of acetonitrile added is 1:1 according to the mass ratio of ammonium fluoride.

[0082] Example 15

[0083] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (3), the exchange ends when the pH of the effluent from the ion exchange column is approximately 6.5.

[0084] Example 16

[0085] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (3), the exchange ends when the pH of the effluent from the ion exchange column is approximately 7.5.

[0086] Example 17

[0087] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (4), the amount of lithium carbonate added is based on a molar ratio of bis(fluorosulfonyl)imide of 4:1.

[0088] Example 18

[0089] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that: in step (4), the alkali metal salt used is sodium carbonate, and in step (5), the alkaline alkali metal source used is sodium hydroxide.

[0090] Example 19

[0091] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that: in step (4), the alkali metal salt used is potassium carbonate, and in step (5), the alkaline alkali metal source used is potassium hydroxide.

[0092] Example 20

[0093] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of the first solvent added is 1:0.1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0094] Example 21

[0095] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of the first solvent added is 1:0.3 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0096] Example 22

[0097] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of the first solvent added is 1:0.8 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0098] Example 23

[0099] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of the first solvent added is 1:1.5 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0100] Example 24

[0101] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), a 0.45 μm PTFE filter membrane is used for filtration.

[0102] Example 25

[0103] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of alkaline alkali metal source lithium hydroxide added is 0.1:1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0104] Example 26

[0105] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of alkaline alkali metal source lithium hydroxide added is 0.5:1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0106] Example 27

[0107] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the dehydration and deacidification reagents are selected from hexamethyldisilazane, trimethyl orthoformate, and trifluoroacetic anhydride.

[0108] Example 28

[0109] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the dehydration and deacidification reagents are selected from hexamethyldisilazane, trimethyl orthoformate, and acetyl chloride.

[0110] Example 29

[0111] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of each dehydration and deacidification reagent added is 0.05:1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0112] Example 30

[0113] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of each dehydration and deacidification reagent added is 0.08:1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0114] Example 31

[0115] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of each dehydration and deacidification reagent added is 0.1:1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0116] Example 32

[0117] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the second solvent is dichloromethane and n-hexane.

[0118] Example 33

[0119] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the second solvent is dichloromethane and chloroform.

[0120] Example 34

[0121] This embodiment provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the second solvent is dichloromethane and petroleum ether.

[0122] Example 35

[0123] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of each second solvent added is 1:0.01 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0124] Example 36

[0125] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of each second solvent added is 1:0.06 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0126] Example 37

[0127] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of each second solvent added is 1:0.1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0128] Comparative Example 1

[0129] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that chlorosulfonic acid isocyanate is not added in step (1).

[0130] Comparative Example 2

[0131] This comparative example provides a method for preparing a high-purity alkali metal salt of bis(fluorosulfonyl)imide, which is basically the same as that in Example 1, except that in step (2), the amount of ammonium fluoride added is 1:1 according to the molar ratio of bis(fluorosulfonyl)imide.

[0132] Comparative Example 3

[0133] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), a filter membrane is not used for filtration.

[0134] Comparative Example 4

[0135] This embodiment provides a method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the amount of alkaline alkali metal source lithium hydroxide added is 0.01:1 according to the mass ratio of crude bis(fluorosulfonyl)imide alkali metal salt.

[0136] Comparative Example 5

[0137] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the dehydration and deacidification reagent is hexamethyldisilazane.

[0138] Comparative Example 6

[0139] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the dehydration and deacidification reagents are hexamethyldisilazane and trimethyl orthoformate.

[0140] Comparative Example 7

[0141] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the dehydration and deacidification reagents are hexamethyldisilazane and thionyl chloride.

[0142] Comparative Example 8

[0143] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), no dehydration and deacidification reagent is added.

[0144] Comparative Example 9

[0145] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the second solvent is dichloromethane.

[0146] Comparative Example 10

[0147] This comparative example provides a method for preparing a high-purity bis(fluorosulfonyl)imide alkali metal salt, which is basically the same as that in Example 1, except that in step (5), the second solvent is carbon tetrachloride.

[0148] Table 1. Total yield and main salt content of bis(fluorosulfonyl)imide alkali metal salts in Examples 1-37 and Comparative Examples 1-10

[0149]

[0150]

[0151] As shown in Table 1, the total yield of alkali metal salts in Examples 1-37 was ≥90%. Among these, after optimizing the amount of ammonium fluoride added, reaction time, and the purification process by optimizing the first solvent, alkali metal type, alkali metal addition amount, and the ratio of dehydration and deacidification reagents, the total yield was ≥97%, and the main salt content was ≥99.9%. In contrast, the total yield of alkali metal salts in Comparative Examples 1, 2, 4, 6, and 7 was below 90%, and the main salt content was at a low level. In Comparative Examples 3, 5, and 8-10, changing the purification conditions resulted in a total yield above 90%, but the main salt content was very low, indicating a high impurity content in the alkali metal salts.

[0152] Table 1. Impurity content (ppm) in bis(fluorosulfonyl)imide alkali metal salts of Examples 1-37 and Comparative Examples 1-10

[0153]

[0154]

[0155] As shown in Table 2, in Examples 1-23 and 25-37, the free acid content of all alkali metal salt products was ≤30 ppm, the moisture content was ≤50 ppm, the chloride ion content was ≤10 ppm, the fluoride ion content was ≤20 ppm, the sulfate ion content was ≤10 ppm, the content of each impurity metal ion was ≤5 ppm, and the DMC insoluble matter content was ≤30 ppm. In contrast, in Example 24 and all comparative examples, a significant increase in impurities was observed after changing the synthesis and purification conditions.

[0156] Therefore, by changing the synthesis and purification conditions, the yield, main salt content, and purity of the alkali metal salt can be significantly improved. Furthermore, this process route offers mild conditions, easy reaction control, low risk, no use or generation of corrosive acids, and is environmentally friendly. It also produces high yields and high purity of bis(fluorosulfonyl)imide alkali metal salts, meeting the market demand for high-purity bis(fluorosulfonyl)imide alkali metal salts.

Claims

1. A method for preparing a high-purity alkali metal salt of bis(fluorosulfonyl)imide, characterized in that, Includes the following steps: Step (1) uses aminosulfonic acid, chlorosulfonic acid, thionyl chloride, and chlorosulfonic acid isocyanate as raw materials to synthesize dichlorosulfonic acid imine; Step (2) Fluoride dichlorosulfonate imide with ammonium fluoride to obtain difluorosulfonylimide ammonium salt; Step (3) The difluorosulfonylimide ammonium salt solution was concentrated under reduced pressure using a strongly acidic ion exchange column to obtain difluorosulfonylimide; Step (4) The alkali metal salt reacts with bis(fluorosulfonyl)imide to obtain the bis(fluorosulfonyl)imide alkali metal salt; Step (5) The alkali metal salt of bis(fluorosulfonyl)imide is purified through a series of processes to obtain high-purity bis(fluorosulfonyl)imide alkali metal salt: The crude bis(fluorosulfonyl)imide alkali metal salt is fully dissolved in the first solvent, filtered to remove insoluble matter, and then the corresponding alkaline alkali metal source is added to the filtrate for preliminary deacidification, and filtered; the filtrate is added to the reagent for dehydration and deacidification, filtered, concentrated under reduced pressure to obtain bis(fluorosulfonyl)imide alkali metal salt concentrate; the bis(fluorosulfonyl)imide alkali metal salt concentrate is slowly added dropwise to the second solvent for back precipitation, allowed to stand to precipitate, separated, and vacuum dried to obtain high-purity bis(fluorosulfonyl)imide alkali metal salt.

2. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 1, characterized in that: In step (2), the amount of ammonium fluoride is 1:(2-5) according to the molar ratio of dichlorosulfonylimide, the reaction temperature is 20-100℃, and the reaction time is 4-12h.

3. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 1, characterized in that: The solvent used in step (2) is at least one of the following aprotic polar organic solvents: acetonitrile, propionitrile, isopropionitrile, butyronitrile, N,N-dimethylformamide, and N,N-dimethylacetamide.

4. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 3, characterized in that: The amount of solvent added in step (2) is based on a mass ratio of ammonium fluoride of 1:(0.1~1).

5. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 4, characterized in that: The first solvent in step (5) is selected from at least one of acetonitrile, propionitrile, isopropionitrile, diethyl ether, propyl ether, methyl tert-butyl ether, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, dimethyl sulfoxide, toluene, acetone, butanone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. The amount of the first solvent added is 1:(0.05-10) based on the mass ratio of crude difluorosulfonyl imide alkali metal salt.

6. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 5, characterized in that: In step (5), the filter membrane material used for filtration is at least one of PTFE, PES, Nylon 6, Nylon 66, glass fiber, PVDF, MCE, and PP, and the pore size of the filter membrane is 0.1 to 1 μm.

7. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 5, characterized in that: In step (5), the anion of the alkaline alkali metal source is one of hydroxide anion, carbonate anion, bicarbonate anion, and tetrafluoroborate anion, and the amount of alkaline alkali metal source added is (0.05~1):1 according to the mass ratio of crude difluorosulfonyl imide alkali metal salt.

8. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 5, characterized in that: In step (5), the dehydration and deacidification reagent is selected from at least one of hexamethyldisilazane, cyclodisilazane, cyclotrisilazane, cyclotetrasilazane, trimethyl orthoformate, thionyl chloride, trifluoroacetic anhydride, acetyl chloride, etc., and the amount of the dehydration and deacidification reagent added is (0.01~0.1):1 according to the mass ratio of crude difluorosulfonylimide alkali metal salt.

9. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 5, characterized in that: In step (5), the second solvent is selected from at least one of n-hexane, cyclohexane, dichloromethane, dichloroethane, chloroform, carbon tetrachloride, benzene, toluene, xylene, petroleum ether, chlorobenzene, and dichlorobenzene. The amount of the second solvent added is 1:(0.01~0.1) based on the mass ratio of crude difluorosulfonyl imide alkali metal salt.

10. The method for preparing high-purity bis(fluorosulfonyl)imide alkali metal salt as described in claim 5, characterized in that: The high-purity bis(fluorosulfonyl)imide alkali metal salt has a yield of ≥97% and a purity of ≥99.9% per step of the reaction, wherein the free acid content is ≤30ppm, the moisture content is ≤50ppm, the chloride ion content is ≤10ppm, the fluoride ion content is ≤20ppm, the sulfate ion content is ≤10ppm, the content of each impurity metal ion is ≤5ppm, and the content of DMC insoluble matter is ≤30ppm.

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