Preparation method of lithium bis (trifluoromethylsulfonyl) imide

Abstract

The invention discloses a preparation method of lithium bis (trifluoromethylsulfonyl) imide, and aims to solve the problems that the prepared lithium bis (trifluoromethylsulfonyl) imide becomes yellow, is not a white crystal and is low in purity due to the fact that lithium hydroxide is too strong in alkalinity and generates other byproducts. The pH value of the reaction system is reduced from 13-14 to 8-9, and the obtained lithium bis (trifluoromethylsulfonyl) imide is a white crystal and is relatively high in purity; in the process of preparing the lithium bis (trifluoromethylsulfonyl) imide, the synthesis of trifluoromethyl sulfonamide is carried out by adopting a gas-gas in-phase reaction, specifically, liquid trifluoromethylsulfonyl chloride is heated to be converted into trifluoromethylsulfonyl chloride gas with a certain pressure, then the trifluoromethylsulfonyl chloride gas reacts with high-purity ammonia gas with a certain pressure, the reaction rate is high, and the reaction time is short. The product obtained through the reaction is high in purity, no solvent is used, no waste liquid is generated, pollution to the environment is reduced, the waste liquid treatment cost is saved, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery electrolyte preparation, and specifically is a method for preparing lithium bis(trifluoromethylsulfonyl)imide. Background Art

[0002] Lithium-ion batteries have the advantages of high specific energy, long cycle life, no memory effect, and green environmental protection. They are widely used in 3C digital, power tools, energy storage, power vehicles and other equipment. With the continuous development of the lithium-ion battery industry, higher requirements are placed on the safety performance and specific energy of lithium-ion batteries, especially the requirements for the safety of electrolytes. Lithium-ion battery electrolytes are composed of lithium salts, organic solvents and various additives, which have an important impact on the battery's capacity, internal resistance, specific power, operating temperature limit, storage life and safety performance.

[0004] Lithium bis(trifluoromethanesulfonyl imide) salt (LiN(CF3SO2)2) is an organic electrolyte lithium salt with good stability and is also one of the most widely used electrolytes for lithium-ion secondary batteries.

[0005] It starts to decompose only when heated to 360°C, has good thermal stability, and has high electrochemical stability. However, the methods for preparing bis(trifluoromethanesulfonyl)imide lithium salt in the prior art usually have the problems of low purity and yield, and long reaction cycle. Based on this, the applicant has developed a new method for preparing bis(trifluoromethanesulfonyl)imide lithium, that is, first preparing trifluoromethanesulfonamide, then using trifluoromethanesulfonamide with anhydrous triethylamine (acid binding agent) and trifluoromethanesulfonyl chloride to react in an organic solvent to prepare bis(trifluoromethanesulfonyl)imide, and finally reacting bis(trifluoromethanesulfonyl)imide with a lithium source to obtain the target product, bis(trifluoromethanesulfonyl)imide lithium. When the lithium source is lithium carbonate, although the obtained product is white, which is consistent with the color of the target product, the solubility of the solvent in the reaction system for Li2CO3 and bis(trifluoromethanesulfonyl)imide is not enough, resulting in the reaction system being very viscous and difficult to stir. At the same time, there is also a situation where the product wraps lithium carbonate, thereby affecting the quality of the product bis(trifluoromethanesulfonyl)imide lithium salt. Therefore, the applicant adopts lithium hydroxide as a lithium source, but the prepared bis(trifluoromethylsulfonyl)imide lithium is brown, not the target product white crystal, indicating that the product purity is not high. Subsequent methods such as ether extraction, hydrogen peroxide, perchloric acid, activated carbon adsorption are used for decolorization and purity improvement, but still cannot be decolorized completely, and the reason is that lithium hydroxide alkalinity is too strong. In addition, the existing trifluoromethylsulfonamide synthesis method adopts gas-liquid reaction or liquid-solid reaction, and a large amount of waste liquid is produced after the reaction is completed, which is unfavorable for environmental protection. If the waste liquid is processed, there is a problem of increased production cost. Summary of the invention

[0006] Based on the above, the object of the present invention is to provide a method for preparing lithium bis(trifluoromethylsulfonyl)imide with low cost, high yield and high product purity.

[0007] To achieve its purpose, the present invention adopts the following technical solution: The present invention provides a method for preparing lithium bis(trifluoromethylsulfonyl)imide, which is achieved by a reaction system, wherein the reaction system comprises a first reactor and a second reactor arranged side by side, a third reactor is arranged between the first reactor and the second reactor, the gas outlets of the first reactor and the second reactor are both connected to the gas inlet of the third reactor, and the third reactor is provided with a water cooling and heating system; The preparation method comprises the following steps: (1) Preparation of trifluoromethylsulfonamide Place trifluoromethylsulfonyl chloride in the first reaction kettle, raise the temperature to raise the pressure in the kettle to 0.05Mpa≤P≤0.1Mpa; introduce high-purity ammonia gas into the second reaction kettle to raise the pressure in the kettle to 0.06Mpa≤P≤0.11Mpa; The water cooling and heating system is turned on to raise the temperature of the third reactor and maintain it at 45-55° C. The air outlets of the first reactor and the second reactor and the air inlet of the third reactor are opened to allow trifluoromethylsulfonyl chloride in the first reactor and ammonia in the second reactor to enter the third reactor, and the pressure in the third reactor is maintained at P<0.03Mpa; the reaction is terminated when the pressure in the third reactor is P≤0.01Mpa to obtain a reaction product; the reaction product is dissolved in acetonitrile, filtered, distilled, and dried under reduced pressure, ether is added to the dried product and concentrated sulfuric acid is added to acidify it, the pH is adjusted to 1-2, the dried product is dissolved in the ether phase, and then the ether phase is washed with ultrapure water, and anhydrous magnesium sulfate is added to dry overnight, filtered, reduced pressure, and distilled to obtain trifluoromethylsulfonamide as a white solid; (2) Preparation of bis(trifluoromethylsulfonyl)imide: Add trifluoromethylsulfonamide in step (1) into a three-necked flask at room temperature, add anhydrous triethylamine and acetonitrile, place at -10-10°C, add trifluoromethylsulfonyl chloride at a constant rate, raise the temperature to 80-90°C, and reflux for 24 hours; remove the solvent and cool to room temperature to obtain a brown-yellow solid, add sulfuric acid to adjust the pH to 1-2, then add dichloromethane, dissolve, wash, dry, filter, and remove dichloromethane under reduced pressure to obtain bistrifluoromethylsulfonyl imide; (3) Preparation of lithium bis(trifluoromethanesulfonyl)imide: Dissolve battery-grade lithium hydroxide monohydrate in water and filter accurately to obtain a purified lithium hydroxide solution; continuously introduce CO2 into the purified solution to adjust the pH to 8-9, add the bis(trifluoromethylsulfonyl)imide in step (2), and react at room temperature with stirring for 12-14 hours; then heat to 90-95°C and reflux for 20-40 minutes, filter, and distill the filtrate under reduced pressure and dry in vacuum to obtain white lithium bis(trifluoromethylsulfonyl)imide.

[0008] As a further preferred embodiment of the technical solution of the present invention, in step (1), the heating temperature of the first reactor is 45°C.

[0009] Furthermore, in step (1), the air intake rate of trifluoromethylsulfonyl chloride is 1.5 g / min, and the air intake rate of ammonia is 0.275-0.325 g / min.

[0010] Furthermore, in step (1), the temperature of the reduced pressure drying is 50°C.

[0011] Furthermore, in step (2), the mass ratio of trifluoromethylsulfonamide to anhydrous triethylamine is 0.7-0.8:1, the mass ratio of acetonitrile to trifluoromethylsulfonamide is 11-11.5:1, and the mass ratio of trifluoromethylsulfonamide to trifluoromethylsulfonyl chloride is 0.73-0.77:1.

[0012] Furthermore, in step (2), the trifluoromethylsulfonyl chloride is added dropwise over 30 minutes.

[0013] Furthermore, in step (3), the mass ratio of the battery-grade lithium hydroxide monohydrate to bis(trifluoromethylsulfonyl)imide triethylamine salt is 6.4-7:1.

[0014] Furthermore, in step (3), the reflux time is 20-40 min.

[0015] Furthermore, in step (3), the vacuum drying temperature is 100°C.

[0016] Furthermore, the first reactor, the second reactor and the third reactor are all high-pressure reactors.

[0017] The beneficial effects of the present invention are: (1) When synthesizing lithium bis(trifluoromethylsulfonyl)imide according to the present invention, in order to solve the problem that the alkalinity of lithium hydroxide is too strong and other byproducts are produced, resulting in the obtained lithium bis(trifluoromethylsulfonyl)imide being yellow, not white crystals and having low purity, high-purity carbon dioxide is used as a pH regulator to reduce the pH of the reaction system from 13-14 to 8-9. The obtained lithium bis(trifluoromethylsulfonyl)imide is white crystals with high purity. The reaction formula is as follows: CF3SO2Cl+2NH3→CF3SO2NH2+NH4Cl CF3SO2NH2+CF3SO2Cl→CF3SO2NHSO2CF3 CF3SO2NHSO2CF3+LiOH→CF3SO2NSO2CF3Li (2) The existing trifluoromethylsulfonamide synthesis method adopts gas-liquid reaction or liquid-solid reaction. In the process of preparing lithium bis(trifluoromethylsulfonyl)imide of the present invention, the synthesis of trifluoromethylsulfonamide is carried out by gas-gas homogeneous reaction, specifically: liquid trifluoromethylsulfonyl chloride is heated to convert it into trifluoromethylsulfonyl chloride gas with a certain pressure, and then reacted with high-purity ammonia gas with a certain pressure. The reaction rate is fast, the product obtained by the reaction is high in purity, and since no solvent is used, no waste liquid is generated, thereby reducing pollution to the environment. DETAILED DESCRIPTION

[0018] The preparation process of the present invention is described in detail below through specific examples.

[0019] The reaction system of the present invention comprises a first reactor and a second reactor arranged side by side, a third reactor is arranged between the first reactor and the second reactor, the gas outlets of the first reactor and the second reactor are both connected to the gas inlet of the third reactor, and the third reactor is provided with a water cooling and heating system.

[0020] The reactors used are all conventional 1L high-pressure reactors, which are commercially available. The water cooling and heating systems of the third reactor are also conventional systems in the prior art. In the initial stage, the heating system makes the reactor temperature reach 45°C. During the continuous reaction, the reaction water exothermic water cooling system maintains the temperature at 45°C.

[0021] The battery-grade lithium hydroxide monohydrate has a purity of 99.5%.

[0022] Example 1 (1) Place trifluoromethylsulfonyl chloride in the first reactor, raise the reactor temperature to 45°C, and make the pressure in the reactor 0.08Mpa; introduce high-purity nitrogen into the second reactor, and make the pressure in the reactor 0.09Mpa; start the water cooling and heating system, and keep the temperature of the third reactor at 45°C. At the same time, open the gas outlets of the first reactor and the second reactor, and the gas inlet of the third reactor, so that the trifluoromethylsulfonyl chloride in the first reactor and the ammonia in the second reactor enter the third reactor, the trifluoromethylsulfonyl chloride intake rate is 1.5g / min, the ammonia intake rate is 0.3g / min, and the pressure in the third reactor is kept less than 0.03Mpa. When the pressure in the third reactor drops to 0.01Mpa, the reaction is finished; after the reaction, 350ml of acetonitrile is added to the product to dissolve, and the residue is the insoluble byproduct ammonium chloride. The filtrate is distilled under reduced pressure to remove the solvent, and dried under reduced pressure at 50°C to obtain a white solid; 500mL of ether is added to the white solid and concentrated sulfuric acid is added to acidify it. When the pH value is adjusted to 1, the white solid is dissolved in the ether phase. Then, the ether phase is washed with ultrapure water 3 times, and dried overnight with anhydrous magnesium sulfate, filtered, decompressed, and distilled to remove the solvent to obtain a white solid of trifluoromethylsulfonamide; (2) Add 15g of the above trifluoromethylsulfonamide to a 1000ml three-necked flask at room temperature, and add 19.2g of anhydrous triethylamine and 400ml of acetonitrile. Place the three-necked flask at 0°C and drip 20g of distilled and purified trifluoromethylsulfonyl chloride at a constant rate over 30 minutes. Heat to 80°C and reflux for 24 hours. Remove the solvent under reduced pressure with an oil pump to obtain a brown-yellow viscous liquid. Cool to room temperature to obtain 25.3g of a brown-yellow solid. Add sulfuric acid to adjust the pH to 1, then add 400mL of dichloromethane. After dissolving, wash three times with distilled water, dry over anhydrous magnesium sulfate overnight, filter and remove the dichloromethane solvent under reduced pressure to obtain bistrifluoromethylsulfonyl imide. (3) 4.8 g of battery-grade lithium hydroxide monohydrate was dissolved in 100 mL of water, stirred to completely dissolve, and finely filtered using a 0.5 μm filter membrane to obtain a purified lithium hydroxide solution; carbon dioxide was continuously introduced into the purified solution to adjust the pH to 8.5, and then 32.17 g of bis(trifluoromethylsulfonyl)imide in step (2) was slowly added thereto, and stirred for reaction at room temperature for 12 h; then the temperature was raised to 90° C. and refluxed for 20 min, filtered, and the filtrate was decompressed and distilled to remove the solvent to obtain a wet material of lithium bis(trifluoromethylsulfonyl)imide; finally, the wet material was vacuum dried at 100° C. to obtain lithium bis(trifluoromethylsulfonyl)imide, which was white in color. The lithium content thereof was measured by atomic absorption and was 2.42%, which was close to the theoretical value of 2.43%, and the purity was 99.59%.

[0023] Embodiment 2-6 The other steps of Example 2-6 are the same as those of Example 1, except that the pressures of the first reactor and the second reactor in step (1) are changed. The conversion rate of the product trifluoromethylsulfonamide is shown in Table 1.

[0024] From the above examples, it can be seen that when the reaction pressure of the first reactor is 0.05-0.1Mpa and the reaction pressure of the second reactor is 0.06-0.11Mpa, the difference in product conversion rate is not large. Therefore, the reaction can be carried out when the reaction pressure of the first reactor is 0.05-0.1Mpa and the reaction pressure of the second reactor is 0.06-0.11Mpa.

[0025] Examples 7-12 The other steps of Examples 7-12 are the same as those of Example 1, except that the heating temperature of the third reactor in step (1) is changed. When the reaction temperature in the third reactor is other values, the conversion rate of the product is shown in Table 2.

[0026] From the above examples, it can be seen that when the temperature of the third reactor is 45-55°C, the conversion rate of the product is not much different. Considering the energy consumption cost, the reaction temperature of 45°C is preferably selected. In addition, when the reaction temperature is in the range of 45-55°C, it is also ensured that trifluoromethylsulfonyl chloride reacts in the form of gas.

[0027] Examples 13-18 Examples 13-18 are the same as Example 1 in other steps, except that the pressure value in the third reactor at the end of the reaction in step (1) is changed. The conversion rates of the products are shown in Table 3.

[0028] From the above embodiment, it can be seen that when the pressure value in the third reactor at the end of the reaction in step (1) is less than or equal to 0.01 MPa, the conversion rate of the product is not much different. Therefore, it is only necessary to control the pressure after the reaction to be less than or equal to 0.01 MPa.

[0029] Examples 19-23 Examples 19-23 are the same as Example 1 in other steps, except that the pH value after acidification with concentrated sulfuric acid in step (1) is changed. The purity of the product trifluoromethylsulfonamide is shown in Table 4.

[0030] From the above examples, it can be seen that when the pH is adjusted to 1-2, the purity of the product trifluoromethylsulfonamide is not much different. Therefore, it is only necessary to control the pH value to 1-2.

[0031] Examples 24-29 Examples 24-29 are the same as Example 1 in other steps, except that the gas feed rate of ammonia in step (1) is changed. The purity of the product trifluoromethylsulfonamide is shown in Table 5.

[0032] It can be seen from the above examples that when the intake rate of ammonia is 0.275-0.325 g / min, the purity of the product trifluoromethylsulfonamide is relatively high, and the preferred intake rate is 0.30-0.325 g / min.

[0033] Examples 30-39 Examples 30-39 are the same as Example 1 in other steps, except that the temperature of the reaction system after adding anhydrous triethylamine and acetonitrile in step (2) is changed. The conversion rate of the product bistrifluoromethylsulfonyl imide is shown in Table 6.

[0034] From the above examples, it can be seen that when the reaction temperature is between -10 and 10°C, the conversion rate of the product bistrifluoromethylsulfonyl imide is not much different. Therefore, it is only necessary to control the reaction temperature between -10 and 10°C.

[0035] Examples 40-43 Examples 40-43 are the same as Example 1 in other steps, except that the reflux temperature in step (2) is changed. The conversion rates of the products are shown in Table 7.

[0036] From the above examples, it can be seen that when the reflux temperature is between 80°C and 90°C, the conversion rate of the product bistrifluoromethylsulfonyl imide is not much different. Considering the energy consumption problem, 80°C is preferred.

[0037] Examples 44-53 Examples 44-53 are the same as Example 1 in other steps, except that the mass ratio of trifluoromethylsulfonamide to anhydrous triethylamine in step (2) is changed. The conversion rates of the products are shown in Table 8.

[0038] It can be seen from the above examples that when the mass ratio of trifluoromethylsulfonamide to anhydrous triethylamine is 0.7-0.8:1, the conversion rate of the product is relatively high, preferably 0.76-0.8:1.

[0039] Examples 54-57 Examples 54-57 are the same as Example 1 in other steps, except that the mass ratio of trifluoromethylsulfonamide to trifluoromethylsulfonyl chloride in step (2) is changed. The conversion rate of the product bistrifluoromethylsulfonyl imide is shown in Table 9.

[0040] From the above examples, it can be seen that when the mass ratio of trifluoromethylsulfonamide to trifluoromethylsulfonyl chloride is 0.73-0.77:1, the conversion rate of the product is not much different. Therefore, it is only necessary to control the mass ratio of trifluoromethylsulfonamide to trifluoromethylsulfonyl chloride to be 0.73-0.77:1.

[0041] Examples 58-62 Examples 58-62 are the same as Example 1 in other steps, except that the mass ratio of acetonitrile to trifluoromethylsulfonamide in step (2) is changed. The conversion rate of the product bistrifluoromethylsulfonyl imide is shown in Table 10.

[0042] From the above examples, it can be seen that when the mass ratio of acetonitrile to trifluoromethylsulfonamide is 11-11.5:1, the conversion rate of the product is not much different. Therefore, it is only necessary to control the mass ratio of acetonitrile to trifluoromethylsulfonamide to be 11-11.5:1.

[0043] Examples 63-69 Examples 63-69 are the same as Example 1 in other steps, except that the pH value adjusted by carbon dioxide in step (3) is changed. The purity of the product lithium bis(trifluoromethylsulfonyl)imide is shown in Table 11.

[0044] From the above examples, it can be seen that when the pH is adjusted to 8-9, the purity of the product lithium bis(trifluoromethylsulfonyl)imide is the highest. Therefore, it is only necessary to control the reaction pH to 8-9.

[0045] Examples 70-75 Examples 70-75 are the same as Example 1 in other steps, except that the stirring reaction time in step (3) is changed. The purity of the product lithium bis(trifluoromethylsulfonyl)imide is shown in Table 12.

[0046] It can be seen from the above examples that when the reaction time is 12-14 hours, the purity of the product is relatively high, and the preferred reaction time is 12 hours.

[0047] Examples 76-79 Examples 76-79 are the same as Example 1 in other steps, except that the reflux temperature in step (3) is changed. The purity of the product lithium bis(trifluoromethylsulfonyl)imide is shown in Table 13.

[0048] From the above examples, it can be seen that when the reflux temperature is between 90 and 95° C., the conversion rate of the product is not much different. Considering the energy consumption problem, the preferred reaction temperature is 90° C.

[0049] Examples 80-85 Examples 80-85 are the same as Example 1 in other steps, except that the mass ratio of bis(trifluoromethylsulfonyl)imide to battery-grade lithium hydroxide monohydrate in step (3) is changed. The purity of the product lithium bis(trifluoromethylsulfonyl)imide is shown in Table 14.

[0050] It can be seen from the above examples that when the mass ratio of bistrifluoromethylsulfonimide to battery-grade lithium hydroxide monohydrate is 6.4-7:1, the purity of the product is relatively high, and the preferred mass ratio is 6.7:1.

Claims

1. A method for preparing lithium bis(trifluoromethanesulfonyl)imide, characterized in that: The preparation method is implemented by a reaction system, which comprises a first reactor and a second reactor arranged side by side, a third reactor is arranged between the first reactor and the second reactor, the gas outlets of the first reactor and the second reactor are both connected to the gas inlet of the third reactor, and the third reactor is provided with a water cooling and heating system; The preparation method comprises the following steps: (1) Preparation of trifluoromethylsulfonamide Place trifluoromethylsulfonyl chloride in the first reaction kettle, raise the temperature to raise the pressure in the kettle to 0.05Mpa≤P≤0.1Mpa; introduce high-purity ammonia gas into the second reaction kettle to raise the pressure in the kettle to 0.06Mpa≤P≤0.11Mpa; The water cooling and heating system is turned on to raise the temperature of the third reactor and maintain it at 45-55° C. The air outlets of the first reactor and the second reactor and the air inlet of the third reactor are opened to allow trifluoromethylsulfonyl chloride in the first reactor and ammonia in the second reactor to enter the third reactor, and the pressure in the third reactor is maintained at P<0.03Mpa; the reaction is terminated when the pressure in the third reactor is P≤0.01Mpa to obtain a reaction product; the reaction product is dissolved in acetonitrile, filtered, distilled, and dried under reduced pressure, ether is added to the dried product and concentrated sulfuric acid is added to acidify it, the pH is adjusted to 1-2, the dried product is dissolved in the ether phase, and then the ether phase is washed with ultrapure water, and anhydrous magnesium sulfate is added to dry overnight, filtered, reduced pressure, and distilled to obtain trifluoromethylsulfonamide as a white solid; (2) Preparation of bis(trifluoromethanesulfonyl)imide: Add trifluoromethylsulfonamide in step (1) into a three-necked flask at room temperature, add anhydrous triethylamine and acetonitrile, place at -10-10°C, add trifluoromethylsulfonyl chloride at a constant rate, raise the temperature to 80-90°C, and reflux for 24 hours; remove the solvent and cool to room temperature to obtain a brown-yellow solid, add sulfuric acid to adjust the pH to 1-2, then add dichloromethane, dissolve, wash, dry, filter, and remove dichloromethane under reduced pressure to obtain bistrifluoromethylsulfonyl imide; (3) Preparation of lithium bis(trifluoromethanesulfonyl)imide: Dissolve battery-grade lithium hydroxide monohydrate in water and filter accurately to obtain a purified lithium hydroxide solution; continuously introduce CO2 into the purified solution to adjust the pH to 8-9, add the bis(trifluoromethylsulfonyl)imide in step (2), and react at room temperature with stirring for 12-14 hours; then heat to 90-95°C, reflux, filter, and distill the filtrate under reduced pressure and dry in vacuum to obtain white lithium bis(trifluoromethylsulfonyl)imide.

2. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 1, characterized in that: In step (1), the first reactor is heated to 45°C.

3. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 2, characterized in that: In step (1), the air intake rate of trifluoromethylsulfonyl chloride is 1.5 g / min, and the air intake rate of ammonia is 0.275-0.325 g / min.

4. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 3, characterized in that: In step (1), the temperature of the reduced pressure drying is 50°C.

5. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 1, characterized in that: In step (2), the mass ratio of trifluoromethylsulfonamide to anhydrous triethylamine is 0.7-0.8:1, the mass ratio of acetonitrile to trifluoromethylsulfonamide is 11-11.5:1, and the mass ratio of trifluoromethylsulfonamide to trifluoromethylsulfonyl chloride is 0.73-0.77:

1.

6. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 5, characterized in that: In step (2), the trifluoromethylsulfonyl chloride is added dropwise over 30 minutes.

7. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 1, characterized in that: In step (3), the mass ratio of the bistrifluoromethylsulfonyl imide to battery-grade lithium hydroxide monohydrate is 6.4-7:

1.

8. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 7, characterized in that: In step (3), the reflux time is 20-40 min.

9. The method for preparing lithium bis(trifluoromethylsulfonyl)imide according to claim 8, characterized in that: In step (3), the vacuum drying temperature is 100°C.

10. A method for preparing lithium bis(trifluoromethylsulfonyl)imide according to any one of claims 1 to 9, characterized in that: The first reactor, the second reactor and the third reactor are all high-pressure reactors.

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