A method for preparing lithium bis(fluorosulfonyl)imide

Abstract

This invention relates to a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps: reacting bis(fluorosulfonyl)imide and phenolic lithium in an organic solvent to obtain a reaction solution containing lithium bis(fluorosulfonyl)imide, followed by post-treatment to obtain lithium bis(fluorosulfonyl)imide. This invention selects phenolic lithium as the lithium source, reacting it with bis(fluorosulfonyl)imide in an organic solvent. The phenol generated in the reaction is soluble in the organic solvent, while the lithium bis(fluorosulfonyl)imide is insoluble in the selected organic solvent. This solves the problem of synthesizing lithium bis(fluorosulfonyl)imide in aqueous or relatively hazardous systems. The prepared lithium bis(fluorosulfonyl)imide has a purity of over 98.7% and a yield of over 86%. The preparation method of this invention is simple to operate, and subsequent purification is convenient, featuring environmental friendliness and high efficiency, meeting the needs of industrialization.

Description

Technical Field

[0001] This invention relates to a method for preparing lithium bis(fluorosulfonyl)imide, belonging to the field of lithium-ion battery electrolyte technology. Background Technology

[0002] Because the fluoride ions in lithium bisfluorosulfonylimide have strong electron-withdrawing properties, the coordination between cations and anions in the lithium salt is weakened, increasing the mobility of lithium ions. Therefore, lithium bisfluorosulfonylimide exhibits good conductivity. Furthermore, due to its high intrinsic and electrochemical stability, it is considered the most promising novel electrolyte to replace lithium hexafluorophosphate and has received widespread reporting and attention.

[0003] Lithium bis(fluorosulfonyl)imide, as an important electrolyte component in lithium-ion secondary batteries, needs to meet stringent requirements such as high purity and anhydrousness. In particular, once moisture is introduced, adverse side reactions that may occur in the electrolyte system are difficult to remove by heating, drying, or decomposition.

[0004] US Patent 20180141901A1 reports a method involving mixing bis(fluorosulfonyl)imide, water, and triethylamine, adjusting the pH, extracting with valerate, washing the organic phase with water, adjusting the pH with ammonia, collecting the organic phase, and finally reacting it with an aqueous solution of lithium hydroxide, using triethylamine as an acid-binding agent to obtain a mixed salt solution. This solution is then purified by vacuum drying to obtain the product. However, this method involves a reaction in the presence of water, resulting in excessive waste, a lengthy reaction process, and difficulties in industrial-scale production.

[0005] Chinese patent application CN106044728A discloses a method for reacting bis(fluorosulfonyl)imide with lithium metal, lithium hydride, or lithium ammonia hydride in a non-aqueous polar solvent to produce lithium bis(fluorosulfonyl)imide and hydrogen or ammonia gas, followed by direct drying to obtain the product. While this method avoids the influence of water, it presents significant safety hazards due to the fact that lithium metal, lithium hydride, and lithium ammonia hydride are all reactive metal compounds, and the generated hydrogen gas is flammable and explosive.

[0006] Chinese patent application CN116374964A discloses a method for preparing high-purity lithium bis(fluorosulfonyl)imide. The method involves adding a solvent and bis(fluorosulfonyl)imide to a reaction vessel; the mass ratio of bis(fluorosulfonyl)imide to solvent is 1:1 to 5; controlling the reaction temperature, alkyl lithium is added dropwise to obtain lithium bis(fluorosulfonyl)imide and alkanes; the molar ratio of bis(fluorosulfonyl)imide to alkyl lithium is 1:1 to 5; the reaction solution is cooled to separate the alkanes from the reaction solution, thus obtaining the lithium bis(fluorosulfonyl)imide product. This preparation method is quick and produces lithium bis(fluorosulfonyl)imide with high purity and yield. However, the alkyl lithium involved in the reaction is a highly flammable substance that can spontaneously combust in air. The reaction must be strictly controlled in a closed, oxygen-free environment, and the reaction temperature must be precisely controlled. Moreover, because the reaction between alkyl lithium and bis(fluorosulfonyl)imide is violent, the alkyl lithium needs to be added slowly and for a long time, and the temperature must be strictly controlled during the addition process. This poses a huge safety hazard to production and places high demands on reaction equipment and conditions, which is not conducive to large-scale industrial production. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing lithium bisfluorosulfonylimide, in order to solve the problems in the prior art where the preparation of lithium bisfluorosulfonylimide is carried out in an aqueous system or a relatively dangerous system, which poses significant safety risks, high production costs, and complex subsequent processing that affects purity and yield.

[0008] To achieve the above objectives, the technical solution of the preparation method of lithium bis(fluorosulfonyl)imide in this invention is as follows:

[0009] A method for preparing lithium bisfluorosulfonylimide includes the following steps: reacting bisfluorosulfonylimide and phenolic lithium in an organic solvent to obtain a reaction solution containing lithium bisfluorosulfonylimide, and then performing post-treatment to obtain lithium bisfluorosulfonylimide.

[0010] The beneficial effects of the above technical solution are as follows: The preparation method of lithium bis(fluorosulfonyl)imide of the present invention involves reacting bis(fluorosulfonyl)imide and phenolic lithium in an organic solvent without introducing water during the reaction. The generated lithium bis(fluorosulfonyl)imide precipitates out in solid form, while the phenol dissolves in the organic solvent. The lithium bis(fluorosulfonyl)imide can be separated by solid-liquid separation, washing and drying. The operation is simple and the reaction conditions are easy to control. The prepared lithium bis(fluorosulfonyl)imide has high purity and high yield, and is suitable for large-scale industrial production.

[0011] Specifically, the phenolic lithium contains less than 30 ppm of water and has a particle size of less than 120 nm. The preparation method of the present invention is carried out in a non-aqueous system, and strict control of the water content of the raw materials can avoid introducing excessive water; while controlling the particle size of the reaction raw materials can effectively improve the reaction efficiency and further improve the purity and yield of lithium bis(fluorosulfonyl)imide.

[0012] As a further improvement, the structure of the phenolic lithium is as follows: As shown, the R1 and R2 groups are each independently selected from H, C1-C3 alkyl, nitro, alkoxy or vinyl-substituted C1-C3 alkyl groups.

[0013] The vinyl-substituted C1-C3 alkyl group is one in which the hydrogen on the C1-C3 alkyl group is replaced by a vinyl group; preferably, the hydrogen at the upper end of the C1-C3 alkyl group is replaced by a vinyl group.

[0014] As a further improvement, the phenolic lithium is any one of lithium phenolate, lithium 2-naphthol, lithium p-methylphenolate, lithium p-nitrophenolate, and lithium eugenol.

[0015] To further increase the purity of lithium bis(fluorosulfonyl)imide, reduce impurities, shorten reaction time, and improve reaction efficiency, the phenolic lithium is one of lithium phenolate or lithium 2-naphthol.

[0016] As a further improvement, the molar ratio of the bis(fluorosulfonyl)imide to lithium phenol is 1:(0.9 to 1.2).

[0017] As a further improvement, the reaction temperature is 30–40°C.

[0018] The beneficial effects of the above technical solution are: controlling the reaction temperature between 30 and 40°C is conducive to the rapid progress of the reaction and the improvement of reaction efficiency, and can effectively prevent the deterioration of the generated lithium bis(fluorosulfonyl)imide.

[0019] As a further improvement, the reaction time is 9 to 60 hours.

[0020] As a further improvement, the organic solvent is a poor solvent that dissolves the phenols generated in the reaction but not lithium difluorosulfonylimide.

[0021] The beneficial effects of the above technical solution are as follows: using a poor solvent that dissolves phenol but not lithium bisfluorosulfonylimide helps to simplify the separation and purification steps of lithium bisfluorosulfonylimide and shorten the overall reaction time.

[0022] As a further improvement, the unsuitable solvent is one of dichloromethane or dichloroethane.

[0023] The beneficial effects of the above technical solution are as follows: by selecting dichloromethane or dichloroethane as the reaction solvent, the generated lithium bisfluorosulfonylimide is insoluble in the reaction solvent, while the generated phenol is readily soluble in the reaction solvent, which facilitates the subsequent separation of lithium bisfluorosulfonylimide.

[0024] Specifically, the mass ratio of the bis(fluorosulfonyl)imide to dichloromethane or dichloroethane is 1:(1.0 to 6.0), more preferably 1:3.0.

[0025] As a further improvement, the reaction includes preparing a mixture by mixing phenolic lithium and an organic solvent, and then adding difluorosulfonylimide dropwise to the mixture.

[0026] The beneficial effects of the above technical solution are as follows: after preparing a mixture by mixing phenolic lithium and organic solvent, adding bis(fluorosulfonyl)imide dropwise is beneficial to improving the utilization rate of reactants, thereby improving the purity and yield of lithium bis(fluorosulfonyl)imide.

[0027] In the preparation method of lithium bis(fluorosulfonyl)imide of the present invention, the reaction between bis(fluorosulfonyl)imide and phenolic lithium is an exothermic reaction. If the addition is too fast or too slow, the temperature will rise too high. Lithium bis(fluorosulfonyl)imide is a heat-sensitive substance, and it will deteriorate if the temperature is too high.

[0028] Specifically, the time for adding difluorosulfonamide is at least 10% of the reaction time, and the time for adding the bis(fluorosulfonamide) is not included in the reaction time.

[0029] As a further improvement, the phenolic lithium is prepared by the following steps: adding phenol to an aqueous solution of lithium hydroxide, reacting, separating the solid and liquid, and drying to obtain phenolic lithium.

[0030] The beneficial effects of the above technical solution are as follows: by using the above method to prepare phenolic lithium, on the one hand, it can avoid the impact of different batches or quality differences of purchased phenolic lithium, which would affect the purity and yield of the final generated bisfluorosulfonylimide lithium; on the other hand, it does not require a large amount of raw material storage and reduces production costs.

[0031] Specifically, the mass ratio of lithium hydroxide to pure water is preferably 1:(3.0 to 10.0), more preferably 1:5.0; the molar ratio of lithium hydroxide to phenol is 1:(1.0 to 0.5), more preferably 1:0.95.

[0032] As a further improvement, the post-processing includes filtration, washing to remove impurities, and drying to obtain lithium difluorosulfonylimide product.

[0033] To further optimize the purity and yield of lithium bis(fluorosulfonyl)imide, the drying is performed under negative pressure, with a vacuum of -0.05 to -0.095 kPa, more preferably -0.08 to -0.09 kPa; the drying temperature is -20 to 40°C, more preferably 10 to 20°C.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The method for preparing lithium bis(fluorosulfonyl)imide of this invention uses phenolic lithium as the lithium source, which is less prone to deterioration under high-temperature drying conditions. Furthermore, removing moisture from the lithium source beforehand ensures that the subsequent lithium bis(fluorosulfonyl)imide production is carried out under low-water conditions, which is beneficial for improving the purity of the lithium bis(fluorosulfonyl)imide. Moreover, using dichloromethane or dichloroethane as the reaction solvent, the phenol generated in the reaction is readily soluble in the solvent, while the lithium bis(fluorosulfonyl)imide generated is insoluble in the solvent, facilitating separation. The separated filtrate can be directly reused after distillation to recover the reaction solvent, which is environmentally friendly and reduces production costs. Furthermore, the method for preparing lithium bis(fluorosulfonyl)imide of this invention has a simple production process, easily controllable reaction conditions, and low safety risks, making it suitable for industrial production and widespread application. Detailed Implementation

[0036] The present invention provides a method for preparing lithium bisfluorosulfonylimide, wherein bisfluorosulfonylimide and phenolic lithium are reacted in an organic solvent to obtain a reaction solution containing lithium bisfluorosulfonylimide, and then post-processed to obtain lithium bisfluorosulfonylimide.

[0037] Preferably, the structure of the phenolic lithium is as follows: As shown, the R1 and R2 groups are each independently selected from H, C1-C3 alkyl, nitro, alkoxy or alkoxy or vinyl-substituted C1-C3 alkyl groups.

[0038] Preferably, the phenolic lithium is any one of lithium phenolate, lithium 2-naphthol, lithium p-methylphenolate, lithium p-nitrophenolate, and lithium eugenol.

[0039] Preferably, the molar ratio of the bis(fluorosulfonyl)imide to phenolic lithium is 1:(0.9-1.2).

[0040] Preferably, the reaction temperature is 30–40°C.

[0041] Preferably, the reaction time is 9-60 hours.

[0042] Preferably, the organic solvent is a poor solvent that dissolves the phenols generated in the reaction but not lithium difluorosulfonylimide.

[0043] Preferably, the undesirable solvent is one of dichloromethane or dichloroethane.

[0044] Preferably, the reaction comprises preparing a mixture by mixing phenolic lithium and an organic solvent, and then adding difluorosulfonylimide dropwise to the mixture.

[0045] Preferably, the phenolic lithium is prepared by the following steps: adding phenol to an aqueous lithium hydroxide solution to react, followed by solid-liquid separation and drying to obtain phenolic lithium.

[0046] Preferably, the post-processing includes filtration, washing to remove impurities, and drying to obtain lithium difluorosulfonylimide product.

[0047] Specifically, the preparation method includes the following steps:

[0048] (1) Add lithium hydroxide and pure water to a flask, heat to 40-60°C, slowly add phenol, stir to adjust pH to 6-7, filter, concentrate the filtrate, filter, dry to obtain phenolic lithium;

[0049] (2) Phenolic lithium and dichloromethane or dichloroethane are reacted by slowly adding difluorosulfonylimide at 30-40°C, and the pH is adjusted to 6-7 by stirring.

[0050] (3) Cool down to about 20°C, filter, wash with dichloromethane or dichloroethane, dry the filter residue to obtain high-purity lithium difluorosulfonylimide.

[0051] The present invention will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used are all commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0052] I. Specific Examples of a Method for Preparing Lithium Difluorosulfonylimide

[0053] Example 1

[0054] The preparation method of lithium bis(fluorosulfonyl)imide in this embodiment adopts the following steps:

[0055] 1. Preparation of lithium phenolate

[0056] 240g of lithium hydroxide and 720g of pure water were added to a PTFE reactor equipped with a thermometer, stirrer, and heating device. The mixture was heated to 60°C, and 847g of phenol was slowly added. After the reaction was complete (the pH or acidity of the reaction solution was tested; the pH was 6-7, or the acidity was below 150ppm), the reaction system was filtered (to remove unreacted phenol and other water-insoluble impurities). The filtered liquid was then concentrated and filtered again. The filter cake obtained from the second filtration was dried until the moisture content was less than 30ppm. Finally, the dried solid was pulverized to a particle size of less than 120nm, yielding lithium phenolate powder. A total of 866g of lithium phenolate was obtained, with a moisture content of 27ppm, a particle size of 120nm, and a yield of 86%.

[0057] 2. Preparation of lithium bis(fluorosulfonyl)imide

[0058] 492.5g of lithium phenolate prepared in step 1 and 2720g of dichloromethane were added to a tetrafluoromethane reactor equipped with a thermometer, stirrer, and heating device and stirred until evenly dispersed. The reactor was then heated to 30°C, and 905g of bis(fluorosulfonyl)imide was slowly added dropwise (the addition of bis(fluorosulfonyl)imide took about 1 hour). The reaction was then carried out for another 10 hours. After the reaction was completed (the acidity was measured to be 81ppm (acidity was tested by sampling; the reaction ended when the acidity was less than 100ppm)), the reaction system was filtered. The filter residue was washed with dichloromethane and dried under vacuum at -0.085KPa and 20°C to obtain 923.8g of lithium(bis(fluorosulfonyl)imide), with a yield of 98.8%.

[0059] Example 2

[0060] The preparation method of lithium bis(fluorosulfonyl)imide in this embodiment adopts the following steps:

[0061] 1. Preparation of lithium phenolate

[0062] 240g of lithium hydroxide and 1200g of pure water were added to a PTFE reactor equipped with a thermometer, stirrer, and heating device. The mixture was heated to 40°C, and 840g of phenol was slowly added. After the reaction was complete (the pH or acidity of the reaction solution was tested; the pH was 6-7, or the acidity was below 150ppm), the reaction system was filtered. The filtered liquid was then concentrated and filtered again. The filter cake obtained from the second filtration was dried until the moisture content was less than 30ppm. Finally, the dried solid was pulverized to a particle size of less than 120nm, and the resulting solid powder was lithium phenolate. A total of 853.9g of lithium phenolate was obtained, with a moisture content of 24ppm, a particle size of 103nm, and a yield of 84.8%.

[0063] 2. Preparation of lithium bis(fluorosulfonyl)imide

[0064] 494.9 g of lithium phenolate prepared in step 1 and 4525 g of dichloroethane were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device and stirred until evenly dispersed. The reactor was then heated to 40 °C, and 905 g of bis(fluorosulfonyl)imide was slowly added dropwise (the addition of bis(fluorosulfonyl)imide took about 1 hour). The reaction was then carried out for another 9 hours. After the reaction was completed (the acidity was measured to be 75 ppm), the reaction system was filtered, and the filter residue was washed with dichloroethane and dried under vacuum of -0.09 kPa and temperature of 10 °C to obtain 927.5 g of lithium(bis(fluorosulfonyl)imide), with a yield of 99.2%.

[0065] Example 3

[0066] The preparation method of lithium bis(fluorosulfonyl)imide in this embodiment adopts the following steps:

[0067] 1. Preparation of lithium phenolate

[0068] 240g of lithium hydroxide and 2400g of pure water were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device. The mixture was heated to 50°C, and 850g of phenol was slowly added. After the reaction was complete (the pH or acidity of the reaction solution was tested; the pH was 6-7, or the acidity was below 150ppm), the reaction system was filtered. The filtered liquid was then concentrated and filtered again. The filter cake obtained from the second filtration was dried until the moisture content was less than 30ppm. Finally, the dried solid was pulverized to a particle size of less than 120nm, and the resulting solid powder was lithium phenolate. A total of 873g of lithium phenolate was obtained, with a moisture content of 28ppm, a particle size of 93nm, and a yield of 87.1%.

[0069] 2. Preparation of lithium bis(fluorosulfonyl)imide

[0070] 479.5 g of lithium phenolate prepared in step 1 and 5430 g of dichloromethane were added to a tetrafluoromethane reactor equipped with a thermometer, stirrer, and heating device and stirred until evenly dispersed. The reactor was then heated to 30 °C, and 905 g of bis(fluorosulfonyl)imide was slowly added dropwise (the addition of bis(fluorosulfonyl)imide took about 1 hour). The reaction was then carried out for 11 hours. After the reaction was completed (the acidity was measured to be 90 ppm), the reaction system was filtered, and the filter residue was washed with dichloromethane and dried under vacuum of -0.05 kPa and temperature of -10 °C to obtain 886.4 g of lithium(bis(fluorosulfonyl)imide), with a yield of 94.86%.

[0071] Example 4

[0072] The preparation method of lithium bis(fluorosulfonyl)imide in this embodiment adopts the following steps:

[0073] Preparation of 1,2-naphthol lithium

[0074] 240g of lithium hydroxide and 2400g of pure water were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device. The mixture was heated to 50°C, and 1375g of 2-naphthol was slowly added. After the reaction was complete (the pH or acidity of the reaction solution was tested; the pH was 6-7, or the acidity was below 150ppm), the reaction system was filtered. The filtered liquid was then concentrated and filtered again. The filter cake obtained from the second filtration was dried until the moisture content was less than 30ppm. Finally, the dried solid was pulverized to a particle size of less than 120nm, and the resulting solid powder was lithium 2-naphthol. A total of 1212.5g of lithium 2-naphthol was obtained, with a moisture content of 24ppm, a particle size of 75nm, and a yield of 80.3%.

[0075] 2. Preparation of lithium bis(fluorosulfonyl)imide

[0076] 863.5 g of lithium 2-naphthol prepared in step 1 and 5430 g of dichloroethane were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device and stirred until evenly dispersed. The reactor was then heated to 40 °C, and 905 g of bis(fluorosulfonyl)imide was slowly added dropwise (the addition of bis(fluorosulfonyl)imide took about 1 hour). The reaction was then carried out for 11 hours. After the reaction was completed (the acidity was measured to be 95 ppm), the reaction system was filtered, and the filter residue was washed with dichloroethane and dried under vacuum of -0.05 kPa and temperature of -10 °C to obtain 856.5 g of lithium bis(fluorosulfonyl)imide, with a yield of 91.6%.

[0077] Example 5

[0078] The preparation method of lithium bis(fluorosulfonyl)imide in this embodiment adopts the following steps:

[0079] 1. Preparation of lithium p-methylphenol

[0080] 240g of lithium hydroxide and 2400g of pure water were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device. The mixture was heated to 50°C, and 1138g of p-methylphenol was slowly added (to test the pH or acidity of the reaction solution; the pH should be 6-7, or the acidity below 150ppm). After the reaction was complete, the system was filtered, and the resulting liquid was concentrated and filtered again. The filter cake was then dried until the moisture content was less than 30ppm. Finally, the dried solid was pulverized to a particle size of less than 90nm, yielding lithium p-methylphenol powder. A total of 896.4g of lithium p-methylphenol was obtained, with a moisture content of 19ppm, a particle size of 83nm, and a yield of 78.6%.

[0081] 2. Preparation of lithium bis(fluorosulfonyl)imide

[0082] 599.1 g of lithium p-methylphenol prepared in step 1 and 5430 g of dichloroethane were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device and stirred until uniformly dispersed. The reactor was then heated to 40°C, and 905 g of bis(fluorosulfonyl)imide was slowly added dropwise (the addition of bis(fluorosulfonyl)imide took approximately 1 hour). The reaction was then carried out for 21 hours. After the reaction was complete (the acidity was measured to be 92 ppm), the reaction mixture was filtered. The filter residue was washed with dichloroethane and dried under vacuum at -0.05 kPa and -10°C to obtain 806.7 g of lithium bis(fluorosulfonyl)imide, with a yield of 86.2%. The low yield was attributed to the fact that p-methylphenol is readily soluble in dichloroethane, and lithium p-methylphenol has a certain solubility in a dichloroethane solution of p-methylphenol.

[0083] Example 6

[0084] The preparation method of lithium bis(fluorosulfonyl)imide in this embodiment adopts the following steps:

[0085] 1. Preparation of lithium p-nitrophenol

[0086] 240g of lithium hydroxide and 2400g of pure water were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device. The mixture was heated to 50°C, and 1464g of p-nitrophenol was slowly added (the pH or acidity of the reaction solution was tested; the pH was 6-7, or the acidity was below 150ppm). After the reaction was complete, the system was filtered, and the resulting liquid was concentrated and filtered again. The filter cake was then dried until the moisture content was less than 30ppm. Finally, the dried solid was pulverized to a particle size of less than 20nm, yielding lithium p-nitrophenolate powder. A total of 1157g of lithium p-nitrophenolate was obtained, with a moisture content of 20ppm and a particle size of 11nm, resulting in a yield of 79.8%.

[0087] 2. Preparation of lithium bis(fluorosulfonyl)imide

[0088] 761.3 g of lithium p-nitrophenol prepared in step 1 and 5430 g of dichloroethane were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device and stirred until uniformly dispersed. The reactor was then heated to 40°C, and 905 g of bis(fluorosulfonyl)imide was slowly added dropwise (the addition of bis(fluorosulfonyl)imide took approximately 1 hour). The reaction was then carried out for 56 hours. After the reaction was complete (the acidity was measured to be 103 ppm), the reaction system was filtered, and the filter residue was washed with dichloroethane and dried under vacuum at -0.05 kPa and -10°C to obtain 854.1 g of lithium bis(fluorosulfonyl)imide, with a yield of 91.34%. If the particle size of lithium p-nitrophenol is greater than 30 nm, it basically does not react. Therefore, the particle size of lithium p-nitrophenol is very small, increasing the specific surface area and thus increasing the reaction rate. The para-nitro group increases the difficulty of the reaction. While p-nitrophenol is soluble in dichloroethane, lithium p-nitrophenol has a certain solubility in p-nitrophenol.

[0089] Example 7

[0090] The preparation method of lithium bis(fluorosulfonyl)imide in this embodiment adopts the following steps:

[0091] 1. Preparation of lithium eugenol

[0092] 240g of lithium hydroxide and 2400g of pure water were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device. The mixture was heated to 50°C, and 1609g of eugenol was slowly added (to test the pH or acidity of the reaction solution; the pH should be 6-7, or the acidity below 150ppm). After the reaction was complete, the system was filtered, and the resulting liquid was concentrated and filtered again. The filter cake was then dried until the moisture content was less than 30ppm. Finally, the dried solid was pulverized to a particle size of less than 120nm, yielding lithium eugenol powder. A total of 1399.1g of lithium eugenol was obtained, with a moisture content of 21ppm, a particle size of 80nm, and a yield of 82.3%.

[0093] 2. Preparation of lithium bis(fluorosulfonyl)imide

[0094] 892.5 g of lithium eugenol prepared in step 1 and 5430 g of dichloroethane were added to a tetrafluoroethylene reactor equipped with a thermometer, stirrer, and heating device and stirred until evenly dispersed. The reactor was then heated to 40 °C, and 905 g of bis(fluorosulfonyl)imide was slowly added dropwise (the addition of bis(fluorosulfonyl)imide took about 1 hour). The reaction was then carried out for 36 hours. After the reaction was completed (the acidity was measured to be 98 ppm), the reaction system was filtered, and the filter residue was washed with dichloroethane and dried under vacuum of -0.05 kPa and temperature of -10 °C to obtain 887.89 g of lithium bis(fluorosulfonyl)imide, with a yield of 94.96%.

[0095] III. Experimental Examples and Tests

[0096] This experiment tested the lithium difluorosulfonylimide products prepared in Examples 1-7. The test results for each example are shown in Table 1. The testing was conducted according to the industry standard YS / T 1302-2019, "Lithium Difluorosulfonylimide Salt for Power Battery Electrolytes".

[0097] Table 1. Test results of lithium bis(fluorosulfonylimide) products prepared in Examples 1-7

[0098]

[0099] In summary, the lithium bis(fluorosulfonyl)imide products prepared using Examples 1-4 have high purity and low impurity content, which can meet the requirements for use as electrolyte salts in lithium-ion batteries and are suitable for widespread application.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the content of the present invention's specification shall also be included within the scope of protection of the present invention.

Claims

1. A method for preparing lithium bis(fluorosulfonyl)imide, characterized in that: Includes the following steps: Difluorosulfonylimide and phenolic lithium are reacted in an organic solvent to obtain a reaction solution containing lithium difluorosulfonylimide, which is then post-treated to obtain lithium difluorosulfonylimide; the organic solvent is one of dichloromethane or dichloroethane; the phenolic lithium is any one of lithium phenolate, lithium 2-naphthol, lithium p-nitrophenolate, and lithium eugenol.

2. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The molar ratio of the difluorosulfonyl imide to phenolic lithium is 1:(0.9~1.2).

3. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1 or 2, characterized in that: The reaction temperature is 30~40℃.

4. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 3, characterized in that: The reaction time is 9 to 60 hours.

5. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The mass ratio of the difluorosulfonyl imide to the organic solvent is 1:(1.0~6.0).

6. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The post-processing includes filtration, washing to remove impurities, and drying to obtain lithium difluorosulfonylimide product.

7. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The reaction involves preparing a mixture by mixing phenolic lithium and an organic solvent, and then adding difluorosulfonylimide dropwise to the mixture.

8. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The phenolic lithium is prepared by the following steps: phenol is added to an aqueous solution of lithium hydroxide to react, and after solid-liquid separation and drying, phenolic lithium is obtained.

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