A one-step method for preparing lithium bis(trifluoromethanesulfonyl)imide

Abstract

The present invention provides a method for preparing bis(trifluoromethanesulfonyl)imide lithium by a one-step method, belonging to the field of fine chemicals. Trifluoromethanesulfonyl chloride and lithium amide are reacted in an organic solvent under the action of an alkaline catalyst, reaction temperature 5-25 DEG C, reaction time 20-60min, bis(trifluoromethanesulfonyl)imide lithium crude product can be obtained by filtration, after purification by recrystallization and drying, bis(trifluoromethanesulfonyl)imide lithium purity is more than 99%, and yield is more than 96%. The present invention can prepare bis(trifluoromethanesulfonyl)imide lithium through one-step reaction, and reaction temperature is relatively low, catalyst raw material is cheap and easy to obtain, process route is simple, by-products are few, and yield is high; the bis(trifluoromethanesulfonyl)imide lithium obtained has high purity and meets battery-grade requirements; when the bis(trifluoromethanesulfonyl)imide lithium of the present invention is used as a lithium battery electrolyte solute, performance is better than commonly used lithium hexafluorophosphate, and has broad industrialization and application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery electrolyte solutes, and in particular to a one-step method for preparing lithium bis(trifluoromethanesulfonyl)imide. Background Art

[0002] Lithium-ion battery electrolytes primarily consist of solutes, solvents, and additives. Currently, lithium hexafluorophosphate (LiPF6) is a commonly used solute in electrolytes. LiPF6 offers high conductivity and strong electrochemical stability. It can also form a suitable SEI film on the carbon anode and effectively passivate the aluminum foil of the cathode. However, LiPF6 suffers from disadvantages such as its tendency to crystallize at low temperatures, resulting in decreased conductivity, and poor thermal stability, leading to its easy decomposition at high temperatures. Compared to lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) offers higher conductivity, a higher ion mobility coefficient, and improved stability. As an electrolyte solute, it offers improved low-temperature discharge and high-temperature performance retention, a longer cycle life, and enhanced safety. Therefore, it holds promise as a future replacement for LiPF6.

[0003] Chinese invention patent publication number CN109369474A discloses a method for producing lithium bis(trifluoromethanesulfonyl)imide. The first step requires the introduction of trifluoromethane gas, a difficult-to-obtain raw material. The second step uses lithium bis(trifluoromethanesulfonyl)imide as a raw material, which is both expensive and difficult to obtain. This method is costly and lacks industrial applicability.

[0004] Chinese invention patent publication number CN115232033A discloses a method for preparing lithium bis(trifluoromethanesulfonyl)imide. The method involves chlorinating, aminating, acidifying, and lithiating sodium trifluoromethanesulfonate to obtain lithium bis(trifluoromethanesulfonyl)imide. This method involves complex steps, and the raw material, sodium trifluoromethanesulfonate, is not readily available.

[0005] Chinese invention patent publication number CN112142628A discloses a method for preparing lithium bis(trifluoromethanesulfonyl)imide. The method involves first preparing lithium trifluoromethanesulfonamide, which is then reacted with trifluoromethanesulfonyl chloride to produce lithium bis(trifluoromethanesulfonyl)imide. However, this method requires pretreatment of the trifluoromethanesulfonyl chloride, which is cumbersome and increases costs.

[0006] Chinese invention patent publication number CN105949093A discloses a method for preparing lithium bis(trifluoromethanesulfonyl)imide. The method involves synthesizing benzylbis(trifluoromethanesulfonyl)amide, then bis(trifluoromethanesulfonyl)imide, and finally lithium bis(trifluoromethanesulfonyl)imide. This method is complex, requiring three steps and the use of concentrated sulfuric acid and expensive lithium resin. Summary of the Invention

[0007] The present invention provides a method for preparing lithium bis(trifluoromethanesulfonyl imide). This method has a simple process, can be completed in one step, and produces a high yield and high purity product. The present invention also evaluates lithium bis(trifluoromethanesulfonyl imide as a lithium salt for lithium battery electrolytes and compares it with lithium hexafluorophosphate. The results demonstrate that the lithium bis(trifluoromethanesulfonyl imide synthesized by the present invention has superior performance.

[0008] The technical solution of the present invention is a one-step method for preparing lithium bis(trifluoromethanesulfonyl)imide, comprising the following steps:

[0009] Trifluoromethanesulfonyl chloride and lithium amide are reacted in an organic solvent under the action of an alkaline catalyst at a reaction temperature of -10-25°C for a reaction time of 20-60 minutes. The reaction solution is filtered to obtain a crude lithium bistrifluoromethanesulfonyl imide product, which is then purified to obtain a lithium bistrifluoromethanesulfonyl imide product. The molar ratio of the trifluoromethanesulfonyl chloride to the lithium amide is 1.8-2.2:1, and the molar ratio of the trifluoromethanesulfonyl chloride to the catalyst is 1:0.01-0.03.

[0010] The reaction equation is as follows:

[0011]

[0012] Preferably, the reaction temperature is -5-25°C, and the reaction time is 20-60 min.

[0013] Preferably, the catalyst is one of LiOH, Li2CO3, NaOH, Na2CO3, NaHCO3, KOH, K2CO3, and KHCO3.

[0014] Preferably, the organic solvent is one of anhydrous acetonitrile, tetrahydrofuran, chloroform, neopentane, cyclobutane, and ethyl acetate.

[0015] Preferably, the ratio of trifluoromethanesulfonyl chloride to the organic solvent is 1 mol: 150-300 ml.

[0016] Preferably, the purification method of the crude lithium bis(trifluoromethanesulfonyl imide) is recrystallization, wherein the crude lithium bis(trifluoromethanesulfonyl imide) is dissolved in a polar organic solvent, and subjected to reduced pressure distillation and drying to obtain white granular lithium bis(trifluoromethanesulfonyl imide) crystals with a purity of ≥99% and a yield greater than 96%.

[0017] More preferably, the polar organic solvent is one of methanol, ethanol, isopropanol, acetonitrile, ethyl acetate, chloroform, dichloromethane, toluene, xylene, and isopropyl ether. The ratio of crude lithium bis(trifluoromethanesulfonyl)imide to polar organic solvent is 1g:3-5ml, the temperature for vacuum distillation is 40-60°C, and the drying step is vacuum drying at 30-50°C for 12-18 hours.

[0018] The prepared lithium bis(trifluoromethanesulfonyl imide) was evaluated as a lithium battery electrolyte solute in a 4.3V lithium iron phosphate / artificial graphite soft-pack battery system. Tests were conducted on 1C gram capacity, high-temperature cycle life, and low-temperature cycle life to measure the battery's capacity and high- and low-temperature performance. The results were also compared with lithium batteries using lithium hexafluorophosphate as the solute.

[0019] The present invention provides a one-step method for preparing lithium bis(trifluoromethanesulfonyl imide) with a simple and environmentally friendly synthesis process. Crude lithium bis(trifluoromethanesulfonyl imide can be synthesized in one step. The reaction temperature is relatively low, saving energy. The catalyst used is an alkali metal salt, which is inexpensive and readily available. The reaction produces few byproducts, facilitating the separation and purification of the crude product. The resulting lithium bis(trifluoromethanesulfonyl imide has high purity (over 99%), high yield (over 96%), and low impurity content (chloride ions less than 8 ppm, water less than 20 ppm, and free acid less than 10 ppm), meeting the requirements of battery-grade products.

[0020] Moreover, after evaluation in a 4.3V lithium iron phosphate / artificial graphite soft-pack battery system, the battery system with lithium bis(trifluoromethanesulfonyl)imide as the solute is superior to lithium hexafluorophosphate in terms of battery capacity and high and low temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a comparison of the positive electrode gram capacity of LiTFSI in Example 1 of the present invention and commercially available LiPF6 at 1C.

[0022] Figure 2 The figure shows the capacity retention of LiTFSI in Example 1 of the present invention and commercially available LiPF6 after 1000 cycles at 50°C.

[0023] Figure 3 The figure shows the capacity retention of LiTFSI in Example 1 of the present invention and commercially available LiPF6 after 500 cycles at -20°C. DETAILED DESCRIPTION

[0024] The technical solutions of the present invention will be described clearly and completely below in conjunction with the accompanying drawings and embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention. Example 1

[0025] Preparation method of crude lithium bis(trifluoromethanesulfonyl imide): Add 0.5 mol of lithium amide, 0.02 mol of NaOH, and 240 ml of anhydrous acetonitrile to a 500 ml reaction flask, add 1 mol of trifluoromethanesulfonyl chloride in 4 batches over 4 minutes at 20°C, control the reaction temperature at 10°C and react for 40 minutes, filter the reaction solution after completion, and obtain crude lithium bis(trifluoromethanesulfonyl imide.

[0026] The crude lithium bis(trifluoromethanesulfonyl imide) was purified by dissolving 100.5 g of the crude lithium bis(trifluoromethanesulfonyl imide) in 390.5 ml of ethyl acetate. The mixture was subjected to reduced pressure distillation at 50°C for 12 hours, followed by vacuum drying at 40°C for 15 hours. The resulting lithium bis(trifluoromethanesulfonyl imide had a purity of 99.6% and a yield of 97.5%.

[0027] The lithium bis(trifluoromethanesulfonyl)imide was used as lithium salt in 4.3V lithium iron phosphate / artificial graphite soft pack battery system to conduct 1C capacity, 50℃ cycle 1000 cycle capacity retention, -20 ℃ Capacity retention after 500 cycles was evaluated and compared with lithium hexafluorophosphate on the market. Example 2

[0028] Preparation method of crude lithium bis(trifluoromethanesulfonyl)imide: add 0.5 mol of lithium amide, 0.009 molg of LiOH, and 260 ml of tetrahydrofuran to a 500 ml reaction bottle, add 0.9 mol of trifluoromethanesulfonyl chloride in three batches at 20°C within 3 minutes, control the reaction temperature at 15°C and react for 50 minutes, filter the reaction solution after completion, and obtain crude lithium bis(trifluoromethanesulfonyl)imide. The crude product yield is 1.3%.

[0029] The crude lithium bis(trifluoromethanesulfonyl imide) was purified by dissolving 95.2 g of the crude lithium bis(trifluoromethanesulfonyl imide) in 285.6 ml of acetonitrile, distilling under reduced pressure at 60°C for 12 hours, and then drying under vacuum at 50°C for 13 hours to obtain the lithium bis(trifluoromethanesulfonyl imide). The purity was 99.5%, and the yield was 97.2%. Example 3

[0030] Preparation method of crude lithium bis(trifluoromethanesulfonyl imide): Add 0.3 mol of lithium amide, 0.0198 mol of KOH, and 198 ml of chloroform to a 500 ml reaction flask; add 0.66 mol of trifluoromethanesulfonyl chloride in three batches over 2 minutes at 20°C; control the reaction temperature at -10°C and react for 30 minutes; filter the reaction solution after completion to obtain crude lithium bis(trifluoromethanesulfonyl imide).

[0031] Crude lithium bis(trifluoromethanesulfonyl imide) was purified by dissolving 82.5 g of crude lithium bis(trifluoromethanesulfonyl imide) in 412.5 ml of ethanol, distilling under reduced pressure at 40°C for 12 hours, and then drying under vacuum at 30°C for 18 hours to obtain lithium bis(trifluoromethanesulfonyl imide). The purity was 99.2%, and the yield was 96.4%. Example 4

[0032] Preparation method of crude lithium bis(trifluoromethanesulfonyl imide): Add 0.47 mol of lithium amide, 0.012 mol of NaHCO3, and 180 ml of neopentane to a 500 ml reaction flask; add 0.9 mol of trifluoromethanesulfonyl chloride in 5 batches over 5 minutes at 20°C; control the reaction temperature at -5°C and react for 60 minutes; filter the reaction solution to obtain crude lithium bis(trifluoromethanesulfonyl imide.

[0033] Crude lithium bis(trifluoromethanesulfonyl imide) was purified by dissolving 112.6 g of crude lithium bis(trifluoromethanesulfonyl imide) in 450.4 ml of isopropanol, distilling under reduced pressure at 60°C for 12 hours, and then drying under vacuum at 50°C for 12 hours to obtain lithium bis(trifluoromethanesulfonyl imide). The purity was 99.1%, and the yield was 96.3%. Example 5

[0034] Preparation method of crude lithium bis(trifluoromethanesulfonyl imide): Add 0.57 mol of lithium amide, 0.016 mol of KHCO3, and 260 ml of cyclobutane to a 500 ml reaction flask, add 1.2 mol of trifluoromethanesulfonyl chloride in 5 batches over 5 minutes at 20°C, control the reaction temperature at 25°C, react for 20 minutes, and filter the reaction solution to obtain crude lithium bis(trifluoromethanesulfonyl imide.

[0035] Crude lithium bis(trifluoromethanesulfonyl imide) was purified by dissolving 96.5 g of crude lithium bis(trifluoromethanesulfonyl imide) in 308.8 ml of methanol, distilling under reduced pressure at 40°C for 12 hours, and then drying under vacuum at 40°C for 15 hours to obtain lithium bis(trifluoromethanesulfonyl imide). The purity was 99.0%, and the yield was 96.8%. Example 6

[0036] Preparation method of crude lithium bis(trifluoromethanesulfonyl imide): add 0.75 mol of lithium amide, 0.022 mol of K2CO3, and 225 ml of ethyl acetate to a 500 ml reaction flask, add 1.5 mol of trifluoromethanesulfonyl chloride in 6 batches over 5 minutes at 20°C, control the reaction temperature at 20°C and react for 40 minutes, filter the reaction solution to obtain crude lithium bis(trifluoromethanesulfonyl imide).

[0037] The crude lithium bis(trifluoromethanesulfonyl imide) was purified by dissolving 94.5 g of the crude lithium bis(trifluoromethanesulfonyl imide) in 378 ml of toluene, distilling under reduced pressure at 50°C for 12 hours, and then drying under vacuum at 50°C for 16 hours to obtain the lithium bis(trifluoromethanesulfonyl imide.) The purity was 99.3%, and the yield was 96.1%.

[0038] In the above embodiments, the alkaline catalysts include LiOH, NaOH, NaHCO3, KOH, K2CO3, and KHCO3; in other embodiments not listed in the present invention, the alkaline catalyst may also be Li2CO3 or Na2CO3, which can also achieve the purpose of the invention. Comparative Example 1

[0039] The lithium hexafluorophosphate used in this comparative example was purchased commercially from McLean, with the brand name 21324-40-3 and a purity of 98%. Similarly, 1C capacity, 1000-cycle capacity retention at 50°C, and 500-cycle capacity retention at -20°C were evaluated in a 4.3V lithium iron phosphate / artificial graphite soft-pack battery system. The tests were performed using a CT-4008-5A6V battery test system.

[0040] Table 1 shows the performance indicators of lithium bis(trifluoromethanesulfonyl)imide of each example and lithium hexafluorophosphate of the comparative example, including purity, free acid content, moisture content, and chloride ion content.

[0041]

[0042] like Figure 1 As shown, in a 4.3V lithium iron phosphate / artificial graphite soft-pack battery system, using the lithium bis(trifluoromethanesulfonyl imide) of Example 1 of the present invention as the lithium salt, the positive electrode gram capacity at 1C reached 162.5 mAh / g, while using commercially available LiPF6 as the lithium salt, the positive electrode gram capacity at 1C was 132.4 mAh / g. This shows that the lithium bis(trifluoromethanesulfonyl imide) of the present invention can improve the capacity of lithium batteries.

[0043] like Figure 2 As shown, in a 4.3V lithium iron phosphate / artificial graphite soft-pack battery system, using the lithium bis(trifluoromethanesulfonyl imide) of Example 1 of the present invention as the lithium salt, the capacity retention rate after 1000 cycles at 50°C was 92.7%, while using commercially available LiPF6 as the lithium salt, the capacity retention rate after 1000 cycles at 50°C was 65.4%. This shows that the lithium bis(trifluoromethanesulfonyl imide) of the present invention can better improve the high-temperature performance of lithium batteries.

[0044] like Figure 3As shown, in a 4.3V lithium iron phosphate / artificial graphite soft-pack battery system, using the bis(trifluoromethanesulfonyl imide) lithium salt of Example 1 of the present invention as the lithium salt, the capacity retention rate after 500 cycles at -20°C was 86.5%, while using commercially available LiPF6 as the lithium salt, the capacity retention rate after 500 cycles at -20°C was 68.4%. This shows that the bis(trifluoromethanesulfonyl imide) lithium salt of the present invention can better improve the low-temperature performance of lithium batteries.

Claims

1. A one-step method for preparing lithium bis(trifluoromethanesulfonyl)imide, characterized in that: The following steps are involved: Trifluoromethanesulfonyl chloride and lithium amide are reacted in an organic solvent under the action of an alkaline catalyst at a reaction temperature of -10-25°C for a reaction time of 20-60 minutes. The reaction solution is filtered to obtain a crude lithium bistrifluoromethanesulfonyl imide product, which is purified to obtain a lithium bistrifluoromethanesulfonyl imide product. The molar ratio of trifluoromethanesulfonyl chloride to lithium amide is 1.8-2.2:1; and the molar ratio of trifluoromethanesulfonyl chloride to catalyst is 1:0.01-0.

03. The alkaline catalyst is one of LiOH, Li2CO3, NaOH, Na2CO3, NaHCO3, KOH, K2CO3, and KHCO3; the organic solvent is one of anhydrous acetonitrile, tetrahydrofuran, chloroform, neopentane, cyclobutane, and ethyl acetate; and the ratio of trifluoromethanesulfonyl chloride to the organic solvent is 1 mol:150-300 ml.

2. The method for preparing lithium bis(trifluoromethanesulfonyl)imide by one-step method according to claim 1, characterized in that: The reaction temperature is -5-25°C, and the reaction time is 20-60 minutes.

3. The method for preparing lithium bis(trifluoromethanesulfonyl imide) by a one-step method according to claim 1 or 2, characterized in that: The purification method of the crude lithium bis(trifluoromethanesulfonyl imide) is recrystallization, wherein the crude lithium bis(trifluoromethanesulfonyl imide) is dissolved in a polar organic solvent, and subjected to reduced pressure distillation and drying to obtain white granular lithium bis(trifluoromethanesulfonyl imide) crystals with a purity of ≥99%.

4. The method for preparing lithium bis(trifluoromethanesulfonyl imide) by a one-step method according to claim 3, characterized in that: The polar organic solvent is one of methanol, ethanol, isopropanol, acetonitrile, ethyl acetate, chloroform, dichloromethane, toluene, xylene, and isopropyl ether; the ratio of crude lithium bistrifluoromethanesulfonyl imide to the polar organic solvent is 1g:3-5ml, the temperature of the reduced pressure distillation is 40-60°C, and the drying is vacuum drying at 30-50°C for 12-18h.

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