A method for synthesizing high-purity lithium bisfluorosulfonylimide in a step-by-step manner

Abstract

The application discloses a method for synthesizing high-purity lithium bisfluorosulfonimide by a step-by-step method. The method adopts a step-by-step reaction idea, slowly introduces sulfuric fluoride under the action of triethylamine in an ammonia gas filled environment, generates fluorosulfonamide triethylamine salt, replaces the fluorosulfonamide with a strong acid to obtain fluorosulfonamide as an intermediate, and then continues to react with sulfuric fluoride to obtain bisfluorosulfonimide triethylamine salt. In the lithiumation process, potassium carbonate is used to replace triethylamine to obtain KFSI, and then LiBF4 is used to react with KFSI to obtain LiFSI, so that the introduction of anion impurities is avoided, and the synthesis of high-purity lithium bisfluorosulfonimide is provided with conditions. The method has the following advantages: 1. The method avoids the use of strong corrosive fluorosulfonic acid as a raw material, and the raw material is cheap and easy to obtain; 2. The method does not need a fluorination process; and 3. The step-by-step method can control the reaction, and high yield (96.97%) and high purity (≥99%) of the product can be realized.

Description

Technical Field

[0001] This invention relates to the field of lithium salt technology for lithium-ion battery electrolytes, specifically a stepwise method for synthesizing high-purity lithium bis(fluorosulfonyl)imide. Background Technology

[0002] Since the commercialization of lithium-ion batteries (LIBs), their high energy density, long cycle life, small memory effect, high operating voltage, wide operating temperature range, and good stability have made LIB research a hot topic in recent years, attracting widespread attention from industries such as electric vehicles, electronic devices, and grid energy storage systems.

[0003] Electrolytes are generally composed of organic solvents, lithium salts, and additives mixed in specific proportions under certain conditions. Lithium salts, as the providers of lithium ions in the electrolyte, are the most important component, largely determining the electrolyte's physical and chemical properties. Therefore, selecting or developing a good lithium salt is of great significance for the rate performance, capacity, cycle life, and safety of lithium batteries.

[0004] Pure lithium bisfluorosulfonylimide (LiFSI) appears as a white solid powder. Due to its unique molecular structure, it possesses high ionic conductivity and thermal stability, effectively improving the low-temperature discharge performance and safety of lithium batteries. Furthermore, it exhibits good compatibility with both the positive and negative electrodes in batteries, making it one of the most promising lithium salts for applications.

[0005] Currently, publicly reported technologies for preparing lithium bis(fluorosulfonyl)imide can be divided into two categories based on the raw materials used: The first is the fluorine / chlorosulfonic acid route, which was the earliest and most mature process, but the raw materials are relatively expensive, the process is complex, and the amount of raw materials required places a burden on the impurity removal process. The second is the sulfuryl fluoride / chlorine route, which was discovered later, but has the significant advantage of inexpensive and readily available raw materials, and ammonia sources are also widely available. However, the three hydrogen reaction sites on ammonia and the two SF reaction sites on sulfuryl fluoride result in complex reaction products and numerous byproducts. Significant breakthroughs in product selectivity and yield represent a major future direction for lithium salt production.

[0006] Therefore, based on the above background, a method for preparing lithium bis(fluorosulfonyl)imide is proposed to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a stepwise method for synthesizing high-purity lithium bis(fluorosulfonyl)imide, in order to solve the problems existing in the prior art, including low product yield, high production cost and high impurity content.

[0008] This invention uses fluorosulfonamide as an intermediate product in the preparation process, and the specific synthetic method is as follows:

[0009] (1) First, ammonia gas is introduced into the first organic solvent, and then an organic base reagent is slowly added dropwise. At this time, the solution is filled with an ammonia source environment. At the same time, a certain amount of sulfuryl fluoride is continuously introduced, and the reaction yields triethylamine fluorosulfonamide. Then, the fluorosulfonamide is replaced with a strong acid, and then filtered, washed and dried to obtain solid fluorosulfonamide.

[0010] (2) The fluorosulfonamide solid obtained in step (1) is further treated in an environment of organic solvent and organic base, and sulfur fluoride is further introduced into the heterogeneous system to react and obtain difluorosulfonamide triethylamine salt.

[0011] (3) Add K2CO3 to the reaction system of step (2) to replace the organic base by the principle of strong base replacing weak base and obtain potassium difluorosulfonyl imide KFSI; at this time, first add anhydrous ethanol to the heterogeneous system, then add LiBF4 solid to obtain sparingly soluble solid KBF4; filter to obtain crude extract containing lithium difluorosulfonyl imide.

[0012] (4) The crude extract containing lithium difluorosulfonylimide was first concentrated, then recrystallized in a second organic solvent, filtered, and dried to obtain pure lithium difluorosulfonylimide.

[0013] Preferably, the first organic solvent in step (1) is selected from acetonitrile, diethyl ether, acetone, dimethyl carbonate, or any two or more of them; more preferably, the first organic solvent is acetonitrile.

[0014] Preferably, the organic base in step (1) is selected from triethylamine, pyridine, etc., and more preferably, the organic base is triethylamine.

[0015] Preferably, the molar ratio of ammonia:thiocyanate:triethylamine in step (1) is (1-1.5):1:(1-3); more preferably, the molar ratio of ammonia:thiocyanate:triethylamine is (1-1.1):1:(2-3).

[0016] Preferably, the time for introducing thioyl fluoride in step (1) is 1.5 to 5 hours; more preferably, it is 1.5 to 3 hours.

[0017] Preferably, the reaction temperature in step (1) is 0 to 20°C, more preferably 3 to 10°C; and the reaction pressure is 0.01 to 0.2 MPa.

[0018] Preferably, the concentration of concentrated sulfuric acid in step (2) is 98%.

[0019] Preferably, in step (2), the organic base (triethylamine) and organic solvent (acetonitrile) are obtained by vacuum distillation of the filtrate after filtration in step (1), and the amount of organic base added must meet the following requirements: the molar ratio of fluorosulfonamide to organic base is 1:(1~1.5); in addition, the amount of thiosulfonyl fluoride is the same as the amount introduced in step (1).

[0020] Preferably, the reaction temperature in step (2) is -5 to 0°C.

[0021] Preferably, the amounts of organic base (triethylamine) and organic solvent (acetonitrile) in step (3) are the same as in step (1);

[0022] Preferably, the amounts of potassium carbonate and lithium tetrafluoroborate used in the reaction in step (3) are as follows: ammonia: K2CO3: LiBF4 = 1: (0.5~1): (2~3); wherein the reaction temperature of potassium carbonate and triethylamine difluorosulfonylimide is room temperature.

[0023] This invention utilizes the difference in solubility of LiBF4 and KBF4 in ethanol to synthesize high-purity lithium bisfluorosulfonylimide via a metathesis reaction, avoiding the introduction of other impurities.

[0024] Preferably, the second organic solvent in step (3) includes acetone, ethyl acetate, dimethyl carbonate, N,N-dimethylformamide, dichloromethane, or any two or more of them.

[0025] Preferably, in step (4), the recrystallization temperature is -5 to 10°C, the drying temperature is 60 to 100°C, and the drying time is 5 to 8 hours. More preferably, the recrystallization temperature is 0°C, the drying temperature is 80°C, and the drying time is 6 hours.

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

[0027] From a reaction kinetics perspective, this invention differs from the conventional method of using excess sulfuryl fluoride followed by slow introduction of ammonia. Instead, ammonia is first dissolved in an organic solvent to achieve an excess of ammonia. Then, sulfuryl fluoride is slowly introduced into the ammonia-rich organic solvent. The sulfuryl fluoride reacts with the ammonia in the organic solvent via ammonolysis, generating a large amount of fluorosulfonamide. Its advantages are: For subsequent partial synthesis using fluorosulfonamide, this method of splitting the synthesis of the bis(fluorosulfonyl)imide structure into two parts effectively increases the yield of the bis(fluorosulfonyl)imide salt, resulting in a better final product yield of 96.97%. Furthermore, this stepwise method, employing intermediate extraction, makes the reaction more controllable and effectively improves the purity of the product (>99%). Attached Figure Description

[0028] Figure 1 This is a diagram of the chemical equations for this invention;

[0029] Figure 2 This is a flowchart of the present invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention have been clearly and completely described, but the implementation of the present invention is not limited thereto. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0031] Unless otherwise specified, the experimental methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the general equipment, raw materials, reagents, etc. used are all commercially available products.

[0032] like Figure 1 and 2 As shown, the method of this invention uses sulfuryl fluoride, commonly used in agricultural fumigants for insecticidal purposes, as a raw material, ammonia as the ammonia source, and triethylamine as the acid-binding agent to prepare triethylamine bis(fluorosulfonyl)imide. Unlike conventional one-step synthesis, this invention employs a stepwise reaction approach. In an ammonia-filled environment, sulfuryl fluoride is slowly introduced under the action of triethylamine to generate triethylamine fluorosulfonamide. This triethylamine is then replaced with a strong acid to obtain fluorosulfonamide as an intermediate, which continues to react with sulfuryl fluoride to obtain triethylamine bis(fluorosulfonyl)imide. In the lithiation process, potassium carbonate is first used to replace triethylamine to obtain KFSI, and then LiBF4 is used to react with KFSI via metathesis to obtain LiFSI. This avoids the introduction of anionic impurities and provides conditions for the synthesis of high-purity lithium bis(fluorosulfonyl)imide. This method avoids the conventional use of highly corrosive fluorosulfonic acid as a raw material, and the raw material used is inexpensive and readily available; secondly, it eliminates the need for a fluorination process; and thirdly, the stepwise method allows for controllable reaction, enabling high product yield (96.97%) and high purity (≥99%).

[0033] Example 1

[0034] Add 4.35 mL of acetonitrile to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. Slowly introduce 1.103 L of ammonia gas into the acetonitrile solvent at a set flow rate. Simultaneously, slowly add 10.45 mL of triethylamine dropwise into the flask using a constant-pressure dropping funnel. After the triethylamine addition is complete, place the flask in a 5°C water bath. Once the temperature stabilizes and the ammonia gas introduction is finished, begin introducing 1.371 L of thiosulfonyl fluoride into the flask at a flow rate of 15 mL / min. React for approximately one and a half hours. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine is 1:1:1.5. After the raw material gas has been completely introduced, add concentrated sulfuric acid through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0035] The mixture was filtered, and the filtrate was distilled under reduced pressure to recover acetonitrile and unreacted triethylamine. The solid product was weighed to be 4.52 g and placed in a new three-necked flask. Acetonitrile and triethylamine were added, and after the solid was completely dissolved, an equal amount of sulfuryl fluoride gas was passed through to generate difluorosulfonylimide triethylamine salt.

[0036] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0037] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 7.86 g of lithium bisfluorosulfonylimide with a purity of 99.3%, and the yield was 84%.

[0038] Example 2

[0039] Add 4.35 mL of acetonitrile to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. Slowly introduce 1.16 L of ammonia gas into the acetonitrile solvent at a set flow rate. Simultaneously, slowly add 10.45 mL of triethylamine dropwise into the flask using a constant-pressure dropping funnel. After the triethylamine has finished dropping, place the flask in an 8°C water bath. Once the temperature has stabilized and the ammonia gas has finished being introduced, begin introducing 1.371 L of thiosulfonyl fluoride into the flask at a flow rate of 15 mL / min for approximately one and a half hours. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine is 1.05:1:2. After the raw gas has been completely introduced, add concentrated sulfuric acid through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0040] The product was filtered, and the solid product weighed 4.75 g. It was then placed in a new three-necked flask, and acetonitrile and triethylamine were added. After the solid had completely dissolved, an equal amount of sulfuryl fluoride gas was passed through it to generate difluorosulfonylimide triethylamine salt.

[0041] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0042] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 8.83 g of lithium bisfluorosulfonylimide with a purity of 99.4%, and the yield was 94.4%.

[0043] Example 3

[0044] Add 4.35 mL of acetonitrile to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. Slowly introduce 1.215 L of ammonia gas into the acetonitrile solvent at a set flow rate. Simultaneously, slowly add 10.45 mL of triethylamine dropwise into the flask using a constant-pressure dropping funnel. After the triethylamine has finished dropping, place the flask in a 10 °C water bath. Once the temperature has stabilized and the ammonia gas has finished being introduced, begin introducing 1.371 L of thiosulfonyl fluoride into the flask at a flow rate of 15 mL / min. React for approximately one and a half hours. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine is 1.1:1:1.5. After the raw material gas has been completely introduced, add concentrated sulfuric acid through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0045] After filtration, the solid product was placed back into a new three-necked flask, and acetonitrile and triethylamine were added. Once the solid had completely dissolved, an equal amount of sulfuryl fluoride gas was passed through again to generate difluorosulfonylimide triethylamine salt.

[0046] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0047] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 8.63 g of lithium bisfluorosulfonylimide with a purity of 99.2%, and the yield was 92.3%.

[0048] Example 4

[0049] Add 4.35 mL of acetonitrile to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. Slowly introduce 1.16 L of ammonia gas into the acetonitrile solvent at a set flow rate. Simultaneously, slowly add 10.45 mL of triethylamine dropwise into the flask using a constant-pressure dropping funnel. After the triethylamine has finished dropping, place the flask in an ice-water bath at 0 °C. Once the temperature has stabilized and the ammonia gas has finished being introduced, begin introducing 1.371 L of thiosulfonyl fluoride into the flask at a flow rate of 15 mL / min for approximately one and a half hours. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine is 1.05:1:1. After the raw gas has been completely introduced, add concentrated sulfuric acid through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0050] The product was filtered, and the solid product weighed 4.69 g. It was then placed in a new three-necked flask, and acetonitrile and triethylamine were added. After the solid had completely dissolved, an equal amount of sulfuryl fluoride gas was passed through it to generate difluorosulfonylimide triethylamine salt.

[0051] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0052] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 8.69 g of lithium bisfluorosulfonylimide with a purity of 99.3%, and the yield was 92.9%.

[0053] Example 5

[0054] Add 4.35 mL of acetonitrile to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. Slowly introduce 1.16 L of ammonia gas into the acetonitrile solvent at a set flow rate. Simultaneously, slowly add 10.45 mL of triethylamine dropwise into the flask using a constant-pressure dropping funnel. After the triethylamine has finished dropping, place the flask in a 20°C cold water bath. Once the temperature has stabilized and the ammonia gas has finished being introduced, begin introducing 1.371 L of thiosulfonyl fluoride into the flask at a flow rate of 15 mL / min for approximately one and a half hours. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine is 1.5:1:3. After the raw gas has been completely introduced, add concentrated sulfuric acid through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0055] The product was filtered, and the solid product weighed 4.61 g. It was then placed in a new three-necked flask, and acetonitrile and triethylamine were added. After the solid had completely dissolved, an equal amount of sulfuryl fluoride gas was passed through it to generate difluorosulfonylimide triethylamine salt.

[0056] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0057] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 8.54 g of lithium bisfluorosulfonylimide with a purity of 99.4%, and the yield was 91.3%.

[0058] Example 6

[0059] Add 4.35 mL of acetonitrile to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. Slowly introduce 1.16 L of ammonia gas into the acetonitrile solvent at a set flow rate. Simultaneously, slowly add 10.45 mL of triethylamine dropwise into the flask using a constant-pressure dropping funnel. After the triethylamine has finished dropping, place the flask in a 20°C constant-temperature water bath. Once the temperature has stabilized and the ammonia gas has finished being introduced, begin introducing 1.371 L of thiosulfonyl fluoride into the flask at a flow rate of 15 mL / min for approximately one and a half hours. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine is 1.5:1:1. After the raw gas has been completely introduced, add concentrated sulfuric acid through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0060] The product was filtered, and the solid product weighed 4.53 g. It was then placed in a new three-necked flask, and acetonitrile and triethylamine were added. After the solid had completely dissolved, an equal amount of sulfuryl fluoride gas was passed through it to generate difluorosulfonylimide triethylamine salt.

[0061] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0062] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 8.41 g of lithium bisfluorosulfonylimide with a purity of 99.4%, and the yield was 89.92%.

[0063] Example 7

[0064] Add 4.35 mL of acetonitrile to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. Slowly introduce 1.16 L of ammonia gas into the acetonitrile solvent at a set flow rate. Simultaneously, slowly add 10.45 mL of triethylamine dropwise into the flask using a constant-pressure dropping funnel. After the triethylamine has finished dropping, place the flask in a 5°C water bath. Once the temperature has stabilized and the ammonia gas has finished being introduced, begin introducing 1.371 L of thiosulfonyl fluoride into the flask at a flow rate of 10 mL / min for approximately two hours. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine is 1.05:1:1.6. After the raw gas has been completely introduced, add concentrated sulfuric acid through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0065] The product was filtered, and the solid product weighed 4.9 g. It was then placed in a new three-necked flask, and acetonitrile and triethylamine were added. After the solid had completely dissolved, an equal amount of sulfuryl fluoride gas was passed through it to generate difluorosulfonylimide triethylamine salt.

[0066] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0067] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 9.07 g of lithium bisfluorosulfonylimide with a purity of 99.3% and a yield of 96.97%.

[0068] Comparative Example 1

[0069] 4.35 mL of acetonitrile was added to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. 2.742 L of thioyl fluoride was then introduced into the flask at a flow rate of 15 mL / min, and the reaction was allowed to proceed for approximately 3 hours. Simultaneously, 10.45 mL of triethylamine was slowly added dropwise to the flask via a constant-pressure dropping funnel, and 1.103 L of ammonia gas was slowly introduced into the acetonitrile solvent at the set flow rate. The molar ratio of ammonia:thioyl fluoride:triethylamine was 1:1:1.5. After the triethylamine addition was complete, the flask was placed in a 5 °C water bath. After the temperature stabilized and the ammonia gas introduction was finished, the reaction was continued for 2 hours. This yielded triethylamine bis(fluorosulfonyl)imide.

[0070] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0071] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 7.36 g of lithium bisfluorosulfonylimide with a purity of 98.9% and a yield of 78.69%.

[0072] Comparative Example 2

[0073] 4.35 mL of acetonitrile was added to a 50 mL three-necked flask equipped with a stirrer, gas inlet, and constant-pressure dropping funnel. 1.371 L of thiosulfonyl fluoride was then introduced into the flask at a flow rate of 15 mL / min, and the reaction was allowed to proceed for approximately one and a half hours. Simultaneously, 10.45 mL of triethylamine was slowly added dropwise to the flask via a constant-pressure dropping funnel, and 1.103 L of ammonia gas was slowly introduced into the acetonitrile solvent at the set flow rate. The molar ratio of ammonia:thiosulfonyl fluoride:triethylamine was 1:1:1.5. After the triethylamine addition was complete, the flask was placed in a 5°C water bath. After the temperature stabilized and the ammonia gas introduction was finished, the reaction was continued for 2 hours. Concentrated sulfuric acid was then added through the constant-pressure dropping funnel to displace the insoluble fluorosulfonamide solid.

[0074] After filtration, the solid product is placed back into a new three-necked flask, and acetonitrile and triethylamine are added. 5g of liquid fluorosulfonic acid is slowly added, which will generate difluorosulfonylimide ammonium salt.

[0075] K2CO3 was added to the flask that produced triethylamine bis(fluorosulfonyl)imide to obtain a heterogeneous system containing KFSI. After filtration, the system was concentrated under reduced pressure to remove a large amount of organic solvent. Then, 10 mL of anhydrous ethanol was added. LiBF4 was then added to displace LiFSI. Finally, KBF4 was filtered off to obtain a lithium bis(fluorosulfonyl)imide solution.

[0076] The lithium bisfluorosulfonylimide solution was concentrated, then a certain amount of dichloromethane was added and the solution was cooled and crystallized at 0°C. After filtration, the solution was dried in an oven at 80°C for 6 hours to obtain 7.59 g of lithium bisfluorosulfonylimide with a purity of 99.1%, and the yield was 81.15%.

[0077] In summary, Table 1 presents the experimental results of Examples 1-7 and Comparative Examples 1 and 2 of this invention. Table 1 shows that this invention differs from the conventional method of using excess sulfuryl fluoride and slowly introducing ammonia. Instead, ammonia is first dissolved in an organic solvent to achieve an excess of ammonia, and then sulfuryl fluoride is slowly introduced into the ammonia-rich organic solvent. The sulfuryl fluoride reacts with ammonia in the organic solvent to undergo ammonolysis, generating a large amount of fluorosulfonamide. Furthermore, the molar ratio of ammonia:sulfyl fluoride:triethylamine has a significant impact on the final yield.

[0078] Table 1. Yield determination results of related products obtained in Examples 1-7 and Comparative Examples 1-2.

[0079] Purity of bis(fluorosulfonyl)imide Difluorosulfonyl imide mass VC yield / % Example 1 99.3％ 7.86g 84％。 Example 2 99.4％ 8.83g 94.4％ Example 3 99.2％ 8.63g 92.3％ Example 4 99.3％ 8.69g 92.9％ Example 5 99.4％ 8.54g 91.3％ Example 6 99.4％ 8.41g 89.92％ Example 7 99.3％ 9.07g 96.97％ Comparative Example 1 98.9％ 7.36g 78.69％ Comparative Example 2 99.1％ 7.59g 81.15％

[0080] Furthermore, as shown in Table 1, the actual data results demonstrate that the purity and VC yield of the bis(fluorosulfonyl)imide obtained by the method of this invention are significantly improved compared to existing methods. The subsequent partial synthesis using fluorosulfonamides, which separates the synthesis of the bis(fluorosulfonyl)imide structure into two parts, effectively increases the yield of the bis(fluorosulfonyl)imide salt, resulting in a better final product yield of 96.97%. In addition, this stepwise method, employing intermediate extraction, makes the reaction more controllable and effectively improves the purity of the product (>99%).

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been shown above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A stepwise method for synthesizing high-purity lithium difluorosulfonylimide, characterized in that... Includes the following steps: (1) First, ammonia gas is introduced into an organic solvent, and then an organic base reagent is slowly added dropwise. At this time, the solution is filled with an ammonia source environment. At the same time, a certain amount of sulfuryl fluoride is continuously introduced to react and obtain fluorosulfonamide triethylamine salt. Then, fluorosulfonamide is replaced with a strong acid, and then filtered, washed and dried to obtain fluorosulfonamide solid. (2) The fluorosulfonamide solid obtained in step (1) is further treated in an environment of organic solvent and organic base, and sulfur fluoride is further introduced into the heterogeneous system to react and obtain difluorosulfonamide triethylamine salt. (3) Add K2CO3 to the reaction system of step (2) to replace the organic base by the principle of strong base replacing weak base and obtain potassium difluorosulfonyl imide KFSI; at this time, first add anhydrous ethanol to the heterogeneous system, then add LiBF4 solid to obtain sparingly soluble solid KBF4; filter to obtain crude extract containing lithium difluorosulfonyl imide. (4) The crude extract containing lithium difluorosulfonylimide was first concentrated, then recrystallized in a second organic solvent, filtered, and dried to obtain pure lithium difluorosulfonylimide.

2. The method for synthesizing high-purity lithium difluorosulfonylimide by stepwise method according to claim 1, characterized in that: The key to this method is that the fluorosulfonamide in step (1) is an intermediate product in the preparation process.

3. The method for stepwise synthesis of high-purity lithium bis(fluorosulfonyl)imide according to claim 1 or 2, characterized in that: The first organic solvent in step (1) is selected from acetonitrile, diethyl ether, acetone, dimethyl carbonate or any two or more of them; the organic base is triethylamine.

4. The method for stepwise synthesis of high-purity lithium difluorosulfonylimide according to claim 3, characterized in that: In step (1), the molar ratio of ammonia:thiocyanate:organic base is (1-1.5):1:(1-3), and the introduction time of thiocyanate is 1.5-5h, the reaction temperature is 0-20℃, and the reaction pressure is 0.01-0.2MPa.

5. The method for stepwise synthesis of high-purity lithium difluorosulfonylimide according to claim 3, characterized in that: In step (1), the molar ratio of ammonia:thioyl fluoride:triethylamine is (1-1.1):1:(2-3), and the introduction time of thioyl fluoride is 1.5-3h, the reaction temperature is 3-10℃, and the reaction pressure is 0.01-0.2MPa.

6. The method for stepwise synthesis of high-purity lithium difluorosulfonylimide according to claim 4 or 5, characterized in that... In step (1), the strong acid is concentrated sulfuric acid with a concentration of 98%.

7. The method for synthesizing high-purity lithium bis(fluorosulfonyl)imide by stepwise method according to claim 6, characterized in that: In step (2), the organic base and organic solvent are obtained by vacuum distillation of the filtrate after filtration in step (1). At the same time, organic base needs to be added to satisfy the following: the molar ratio of fluorosulfonamide to organic base is 1:(1~1.5); and the amount of thiosulfonyl fluoride is the same as the amount introduced in step (1).

8. The method for stepwise synthesis of high-purity lithium bis(fluorosulfonyl)imide according to claim 7, characterized in that: The reaction temperature in step (2) is -5 to 0℃.

9. The method for stepwise synthesis of high-purity lithium bis(fluorosulfonyl)imide according to claim 7, characterized in that: The amounts of organic base and organic solvent in step (3) are the same as in step (1); the amounts of potassium carbonate and lithium tetrafluoroborate are as follows: ammonia: K2CO3: LiBF4 = 1: (0.5~1): (2~3).

10. The method for stepwise synthesis of high-purity lithium bis(fluorosulfonyl)imide according to claim 7, characterized in that: The second organic solvent in step (4) includes acetone, ethyl acetate, dimethyl carbonate, N,N-dimethylformamide, dichloromethane, or any two or more of them.

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