A method for preparing lithium bistrifluoromethylsulfonimide
By using sodium intermediates for directional synthesis and composite catalysts, combined with in-situ lithium exchange, the problems of low purity and yield in existing LiTFSI preparations have been solved, achieving the preparation of high-purity, high-yield LiTFSI, which is suitable for industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- DO FLUORIDE CHEM CO LTD
- Filing Date
- 2026-03-30
- Publication Date
- 2026-05-29
AI Technical Summary
Existing methods for preparing LiTFSI suffer from problems such as high equipment requirements, numerous side reactions, difficulty in controlling fluoride ions and amine residues, and insufficient process integration, making it difficult to achieve continuous production with high purity and high yield.
By employing a method of directional synthesis of sodium intermediates, composite catalysts, and in-situ lithium exchange, and carrying out sodium formation, acylation, solid-liquid separation, concentration, and in-situ lithium exchange under inert gas protection, the method avoids the involvement of ammonia and highly corrosive reagents in traditional routes, achieving continuous production with high purity and high yield.
The preparation of LiTFSI with high purity (≥99.9%) and high yield (over 94.8%) has been achieved, meeting the requirements of battery-grade electrolyte materials, reducing moisture, fluoride ions and sodium residues, and making it suitable for industrial applications.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium salt preparation technology for lithium-ion battery electrolytes, specifically relating to a method for preparing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) that is ammonia-free, low-corrosion, high-purity, and high-yield. Background Technology
[0002] Traditional methods for preparing LiTFSI are mainly divided into two-step and three-step methods. The two-step method uses trifluoromethanesulfonyl chloride and lithium amino group as raw materials, which undergo a condensation reaction under the action of an alkaline catalyst (such as triethylamine) to generate bis(trifluoromethanesulfonyl)imine, followed by lithiation to obtain LiTFSI. This route requires strict control of reaction temperature and catalyst dosage, has high equipment requirements, produces many side reactions, and is difficult to control for fluoride ions and amine residues. The three-step method involves the introduction and removal of the benzyl protecting group, such as preparing bis(trifluoromethanesulfonyl)imine through the sulfonation reaction of benzyl bis(trifluoromethanesulfonamide), followed by lithiation to obtain LiTFSI. This type of method requires the use of highly corrosive reagents such as concentrated sulfuric acid and easily generates byproducts, increasing post-processing costs.
[0003] To overcome the above-mentioned shortcomings, patent CN102020615B reported an improved method using trifluoromethanesulfonyl fluoride as a raw material, but it still involves the processing of intermediates. Patent CN116283671A reduces the water content to below 100 ppm through organic solvent complexation and semi-permeable membrane separation technology, but it requires additional complexation and membrane separation steps, resulting in insufficient process integration.
[0004] Therefore, developing a simple, high-purity, safe, environmentally friendly, and industrially suitable method for preparing LiTFSI is of great significance. Based on this, this application was developed. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing lithium bis(trifluoromethanesulfonyl)imide that is ammonia-free, low-corrosion, high-purity, and high-yield. This method, through directional synthesis of sodium intermediates, composite catalysis, and in-situ lithium exchange, completely bypasses traditional routes, achieving continuous production with high purity and high yield. It provides an innovative solution for overcoming existing technological bottlenecks and promoting the large-scale industrial application of LiTFSI.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing high-purity lithium bis(trifluoromethanesulfonyl)imide, which is carried out entirely under the protection of an inert gas (such as nitrogen or argon), includes the following steps: 1) Preparation of sodium-based reaction solution: Add the first polar aprotic solvent, nitrogen source and sodium source to the reaction vessel, and stir at 20-40℃ until completely dissolved to obtain a homogeneous and transparent sodium-based reaction solution. 2) Catalytic acylation reaction: The obtained sodium-based reaction solution is cooled to -10~10℃, and trifluoromethanesulfonyl chloride is slowly added dropwise while a composite catalyst is added simultaneously. After the addition is complete, the temperature is slowly raised to 30~60℃ and maintained for 3~8 h to directionally generate the intermediate sodium bis(trifluoromethanesulfonyl)imide (NaTFSI). Reaction characteristics: No ammonia gas is involved, and no ammonium salt byproducts are produced; the composite catalyst significantly reduces side reactions and improves the purity of the intermediate; the sodium intermediate is stable, facilitating subsequent purification and lithium exchange. 3) Solid-liquid separation and concentration: After the reaction is completed, cool to room temperature and separate the solid and liquid (e.g., filter to remove insoluble sodium salt byproducts). Transfer the filtrate to a vacuum concentration device for vacuum concentration to remove some of the solvent to a certain solid content and obtain NaTFSI concentrate. 4) In-situ lithium exchange reaction: Add lithium source to concentrate and react with metathesis at 40-80℃ for 2-5 h to produce crude lithium bis(trifluoromethanesulfonylimide). 5) Purification and drying: The crude lithium bis(trifluoromethanesulfonylimide) product is extracted, washed with water to remove inorganic impurities, decolorized with activated carbon, removed most of the solvent by vacuum distillation, recrystallized, and dried under vacuum to obtain battery-grade white crystalline powder LiTFSI with a purity ≥99.9%.
[0007] Specifically, in step 1), the first polar aprotic solvent is selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), acetonitrile, acetone, dichloromethane, tetrahydrofuran, etc. 400–600 mL of solvent is added for every 0.5 mol of trifluoromethanesulfonamide.
[0008] Further, in step 1), the nitrogen source can be trifluoromethanesulfonamide; the sodium source can be one or more of sodium amide, sodium methoxide, sodium ethoxide, sodium tert-butoxide, etc. More preferably, the molar ratio of nitrogen source to sodium source is controlled to be 1: (1.0~1.3).
[0009] Specifically, in step 2), the composite catalyst can be a mixture of triethylamine and a quaternary phosphonium salt or an ionic liquid, wherein the quaternary phosphonium salt includes at least one of tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, etc., and the ionic liquid includes 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, etc.; the molar ratio of triethylamine to the quaternary phosphonium salt or ionic liquid is (3-8):1.
[0010] Furthermore, in step 2), the amount of the composite catalyst added is 5 to 15 mol of the nitrogen source trifluoromethanesulfonamide; the molar ratio of the trifluoromethanesulfonyl chloride to the sodium source is 1: (1.0 to 1.1).
[0011] Specifically, in step 3), the concentration temperature is 40–70°C and the pressure is -0.08–-0.095 MPa; the solid content of the NaTFSI concentrate is 30–60%.
[0012] Specifically, in step 4), the lithium source can be at least one of lithium fluoride, lithium carbonate, lithium hydroxide, lithium chloride, etc.; the molar ratio of NaTFSI to the lithium source is 1: (1.0 to 1.2).
[0013] Specifically, in step 5), the solvent used for extraction can be at least one of ethyl acetate, dichloromethane, methyl tert-butyl ether, etc.; the washing is performed with deionized water 1 to 3 times. Further, the decolorization involves adding 0.5 to 2 wt% activated carbon to the system and stirring at room temperature; the recrystallization is performed at low temperature using a mixed ester / ether solvent; the vacuum drying conditions are: temperature 70–110℃, pressure ≤ -0.095 MPa, and drying time 8–24 h.
[0014] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: This invention provides a method for preparing lithium bis(trifluoromethanesulfonyl)imide that is ammonia-free, low-corrosion, high-purity, and high-yield. This method, through directional synthesis of a sodium intermediate, composite catalysis, and in-situ lithium exchange, completely bypasses traditional routes, achieving continuous production with high purity and high yield. It meets the requirements of battery-grade electrolyte materials and provides an innovative solution for overcoming existing technological bottlenecks and promoting the large-scale industrial application of LiTFSI. The lithium bis(trifluoromethanesulfonyl)imide product prepared using this method has a yield of over 94.8%, a purity of over 99.91%, a moisture content of no more than 32 ppm, a fluoride ion content of no more than 7 ppm, and sodium residue of less than 38 ppm, fully meeting the requirements of battery-grade electrolyte materials. Detailed Implementation
[0015] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.
[0016] In the following examples, all raw materials used are common commercially available products that can be purchased directly, or can be prepared using conventional techniques in the art.
[0017] Room temperature refers to 25±5℃. Example 1
[0018] A method for preparing high-purity lithium bis(trifluoromethanesulfonyl)imide includes the following steps: 1) Under nitrogen protection, 500 mL of acetonitrile, 0.5 mol of trifluoromethanesulfonamide and 0.52 mol of sodium amino were added to the reaction vessel in sequence and stirred at room temperature until completely dissolved to obtain the sodium reaction solution; 2) Cool the system to 0℃ and begin adding 0.52 mol of trifluoromethanesulfonyl chloride dropwise, while simultaneously adding the composite catalyst: 0.04 mol of triethylamine + 0.01 mol of tetrabutylphosphonium bromide. After the addition is complete, slowly raise the temperature to 45℃ and maintain the reaction for 5 h to generate the intermediate sodium bis(trifluoromethanesulfonyl)imide. 3) After the reaction is complete, cool to room temperature, filter to remove by-product salts, and concentrate the filtrate under reduced pressure (concentration temperature is 55℃, pressure is -0.09 MPa) to a solid content of about 50% to obtain NaTFSI concentrate. 4) Add 0.563 mol of lithium chloride to the concentrate, heat to 60℃, stir for 3 h to complete lithium exchange, and generate crude lithium bis(trifluoromethanesulfonylimide). 5) The reaction solution was extracted with ethyl acetate, washed twice with water, and decolorized with activated carbon (the decolorization was performed by adding 1 wt% activated carbon to the system and stirring at room temperature for 0.5 h). Most of the solvent was removed by vacuum distillation, and then recrystallized with a mixed solvent of ethyl acetate / methyl tert-butyl ether (the volume ratio of ethyl acetate to methyl tert-butyl ether was 1:3). The product was then dried under vacuum at 95 °C for 12 h to obtain a white lithium bis(trifluoromethanesulfonyl)imide product. The performance indicators are shown in Table 1. Example 2
[0019] A method for preparing high-purity lithium bis(trifluoromethanesulfonyl)imide includes the following steps: 1) Under nitrogen protection, 500 mL of dimethyl carbonate, 0.5 mol of trifluoromethanesulfonamide, and 0.55 mol of sodium methoxide were added sequentially to the reaction vessel and stirred at room temperature until completely dissolved to obtain the sodium reaction solution; 2) Cool to -5℃ and begin adding 0.55 mol of trifluoromethanesulfonyl chloride dropwise, simultaneously adding a composite catalyst: 0.035 mol of triethylamine + 0.007 mol of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. After the addition is complete, slowly raise the temperature to 50℃ and maintain the reaction temperature for 4 h to generate sodium bis(trifluoromethanesulfonyl)imide intermediate; 3) Refer to Example 1; 4) Add 0.57 mol of lithium hydroxide to the concentrate, heat to 65℃, stir for 2.5 h to complete lithium exchange, and generate crude lithium bis(trifluoromethanesulfonylimide). 5) Referring to Example 1, a battery-grade white lithium bis(trifluoromethanesulfonyl)imide product was obtained. Performance indicators are shown in Table 1. Example 3
[0020] A method for preparing high-purity lithium bis(trifluoromethanesulfonyl)imide includes the following steps: 1) Under nitrogen protection, 500 mL of tetrahydrofuran, 0.5 mol of trifluoromethanesulfonamide, and 0.53 mol of sodium tert-butoxide were added sequentially to the reaction vessel and stirred at room temperature until completely dissolved to obtain the sodium-containing reaction solution; 2) Cool to 5℃ and begin adding 0.53 mol of trifluoromethanesulfonyl chloride dropwise, simultaneously adding a composite catalyst: 0.045 mol of triethylamine + 0.009 mol of tetrabutylphosphonium bromide. After the addition is complete, slowly raise the temperature to 55℃ and maintain the reaction for 6 h to generate sodium bis(trifluoromethanesulfonyl)imide intermediate; 3) Refer to Example 1; 4) Add 0.545 mol of lithium fluoride to the concentrate, heat to 70℃, stir for 3 h to complete lithium exchange, and generate crude lithium bis(trifluoromethanesulfonylimide). 5) Referring to Example 1, a battery-grade white lithium bis(trifluoromethanesulfonyl)imide product was obtained. Performance indicators are shown in Table 1.
[0021] Comparative Example 1 Traditional process: no composite catalyst, single alkali, no directional lithium exchange.
[0022] Under nitrogen protection, 500 mL of acetonitrile, 0.5 mol of trifluoromethanesulfonamide, and 0.6 mol of liquid ammonia (traditional alkali source) were added sequentially to the reactor, and stirred at room temperature until completely dissolved. The mixture was cooled to 0°C, and 0.52 mol of trifluoromethanesulfonyl chloride was added dropwise, along with 0.05 mol of triethylamine catalyst. After the addition was complete, the temperature was raised to 45°C and maintained for 5 h. After the reaction was complete, the mixture was cooled to room temperature, filtered to remove byproduct salts, and the filtrate was concentrated under reduced pressure (concentration temperature 55°C, pressure -0.09 MPa) to a solid content of approximately 50%, yielding a concentrated NaTFSI solution. 0.563 mol of lithium chloride was added directly to the concentrated solution, and the temperature was raised to 60°C, stirred for 3 h. The reaction solution was extracted with ethyl acetate, washed twice with water, decolorized with activated carbon (refer to Example 1), most of the solvent was removed by reduced pressure distillation, recrystallized (refer to Example 1), and vacuum dried (refer to Example 1) to obtain the lithium bis(trifluoromethanesulfonyl)imide product. Performance indicators are shown in Table 1.
[0023] Comparative Example 2 Single alkali, no composite catalyst.
[0024] Under nitrogen protection, 500 mL of acetonitrile, 0.5 mol of trifluoromethanesulfonamide, and 0.55 mol of sodium hydroxide were added sequentially to the reactor and stirred at room temperature until completely dissolved. The mixture was cooled to 0°C, and 0.52 mol of trifluoromethanesulfonyl chloride was added dropwise, along with 0.05 mol of triethylamine catalyst. After the addition was complete, the temperature was raised to 45°C and maintained for 5 h. After the reaction was complete, the mixture was cooled to room temperature, filtered to remove byproduct salts, and the filtrate was concentrated under reduced pressure (concentration temperature 55°C, pressure -0.09 MPa) to a solid content of approximately 50%, yielding a concentrated NaTFSI solution. 0.563 mol of lithium chloride was added directly to the concentrated solution, and the temperature was raised to 60°C and stirred for 3 h. The reaction solution was extracted with ethyl acetate, washed twice with water, decolorized with activated carbon (refer to Example 1), most of the solvent was removed by reduced pressure distillation, recrystallized (refer to Example 1), and vacuum dried (refer to Example 1) to obtain the lithium bis(trifluoromethanesulfonyl)imide product. Performance indicators are shown in Table 1.
[0025] Table 1 Performance indicators of the products of Examples 1-3 and Comparative Examples 1-2
[0026] Table 1 shows that, compared with the embodiments of the present invention, Comparative Example 1, using a traditional liquid ammonia process, resulted in incomplete reaction, numerous byproducts, and a yield far lower than that of the embodiments of the present invention. Comparative Example 1 did not use a composite catalytic system, and its product purity was only 99.21%, far lower than the ≥99.9% battery-grade purity of the present invention. The water, fluoride ion, and metal ion residues in the product of Comparative Example 1 were significantly higher, making it unsuitable for direct use in lithium-ion battery electrolytes. Comparative Example 2, using a single inorganic alkali, a single catalytic system, and a conventional lithiation process, exhibited poor reaction selectivity, numerous side reactions, and high salt residues. Its yield, purity, and impurity levels were far inferior to those of Examples 1-3 of the present invention, failing to meet the requirements for battery-grade electrolyte materials.
[0027] In summary, this invention achieves high yield, high purity, and low impurities through composite catalysts, directional sodium formation, and in-situ lithium exchange. The process is safer, more environmentally friendly, and suitable for industrial production.
Claims
1. A method for preparing lithium bis(trifluoromethanesulfonylimide), characterized in that, The entire process is carried out under inert gas protection and includes the following steps: 1) Preparation of sodium-based reaction solution: Add the first polar aprotic solvent, nitrogen source and sodium source to the reaction vessel, and stir at 20-40℃ until completely dissolved to obtain a homogeneous and transparent sodium-based reaction solution. 2) Catalytic acylation reaction: The obtained sodium reaction solution is cooled to -10~10℃, trifluoromethanesulfonyl chloride is added dropwise, and a composite catalyst is added at the same time. After the addition is complete, the temperature is raised to 30~60℃ and kept at the temperature for 3~8 h to directionally generate the intermediate sodium bis(trifluoromethanesulfonyl)imide (NaTFSI). 3) Solid-liquid separation and concentration: After the reaction is completed, the mixture is cooled to room temperature, the solid and liquid are separated, and the mixture is concentrated under reduced pressure to obtain a concentrated NaTFSI solution; 4) In-situ lithium exchange reaction: Add lithium source to concentrate and react with metathesis at 40-80℃ for 2-5 h to produce crude lithium bis(trifluoromethanesulfonylimide). 5) Purification and drying: The crude lithium bis(trifluoromethanesulfonylimide) product is extracted, washed with water, decolorized, distilled under reduced pressure, recrystallized, and dried under vacuum to obtain the final product.
2. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 1), the first polar aprotic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, acetonitrile, acetone, dichloromethane, and tetrahydrofuran.
3. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 1), the nitrogen source is trifluoromethanesulfonamide; the sodium source is one or more of sodium amino, sodium methoxide, sodium ethoxide, and sodium tert-butoxide.
4. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 3, characterized in that, The molar ratio of nitrogen source to sodium source is controlled to be 1: (1.0~1.3).
5. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 2), the composite catalyst is a mixture of triethylamine and a quaternary phosphonium salt or an ionic liquid, wherein the quaternary phosphonium salt includes at least one of tetrabutylphosphonium bromide and tetrabutylphosphonium chloride, and the ionic liquid includes 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt; the molar ratio of triethylamine to the quaternary phosphonium salt or the ionic liquid is (3-8):
1.
6. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 2), the amount of the composite catalyst added is 5 to 15 mol of the nitrogen source; the molar ratio of trifluoromethanesulfonyl chloride to sodium source is 1: (1.0 to 1.1).
7. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 3), the concentration temperature is 40–70°C and the pressure is -0.08–-0.095 MPa; the solid content of the NaTFSI concentrate is 30–60%.
8. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 4), the lithium source is at least one of lithium fluoride, lithium carbonate, lithium hydroxide, and lithium chloride; the molar ratio of NaTFSI to the lithium source is 1:(1.0 to 1.2).
9. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 5), the solvent used for extraction is at least one of ethyl acetate, dichloromethane, and methyl tert-butyl ether; the water washing is performed with deionized water 1 to 3 times.
10. The method for preparing lithium bis(trifluoromethanesulfonyl)imide as described in claim 1, characterized in that, In step 5), the decolorization is achieved by adding 0.5–2 wt% activated carbon to the system and stirring at room temperature; the vacuum drying conditions are: temperature 70–110℃, pressure ≤ -0.095 MPa, and drying time 8–24 h.