A method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazole

Abstract

This invention discloses a method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium. Using trifluoroacetic acid, dicyclohexylcarboimide, and diaminocis-butene dinitrile as raw materials, a reflux reaction is carried out in an organic solvent system at a controlled temperature of 100℃–110℃ to prepare the intermediate 4,5-dicyano-2-trifluoromethylimidazolium. The organic solvent system is a mixture of acetonitrile and 1,4-dioxane in a volume ratio of 1:2–3. The intermediate 4,5-dicyano-2-trifluoromethylimidazolium is then reacted with lithium carbonate to prepare lithium 4,5-dicyano-2-trifluoromethylimidazolium. This invention avoids the inconvenience of directly using trifluoroacetic anhydride, improving the safety and operability of the reaction. Furthermore, this invention optimizes and improves the reaction system, reducing the solubility of the reaction byproduct dicyclohexylurea, allowing the byproduct and excess dicyclohexylcarboimide to be removed by filtration. This facilitates operation and prevents its introduction into the final product, thereby improving the purity of the product.

Description

Technical Field

[0001] This invention relates to the field of battery electrolyte technology, and to a method for preparing lithium salts for electrolytes, particularly a method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that primarily function by the movement of lithium ions between the positive and negative electrodes. In recent years, with the widespread use of portable electronic devices such as power banks, mobile phones, and tablets, as well as the rapid development of electric vehicles and new energy vehicles, people's demand and requirements for lithium-ion batteries have gradually increased.

[0003] Currently, lithium hexafluorophosphate (LiPF6) is the most widely used electrolyte lithium salt. However, LiPF6 has revealed problems such as easy hydrolysis and rapid decomposition at high temperatures, which not only pose safety hazards but also significantly reduce battery life. Although many other types of lithium salts have been researched in an attempt to replace LiPF6, it has so far maintained its dominant position in commercial lithium-ion batteries.

[0004] Among them, lithium 4,5-dicyano-2-trifluoromethylimidazolium exhibits excellent conductivity due to its lower fluorine content and stronger carbon-fluorine bonds compared to the phosphorus-fluorine bonds in LiPF6. Furthermore, this lithium salt demonstrates excellent dissociation between the imidazole anion and lithium cation, exhibiting a high thermal decomposition temperature exceeding 250°C, a high electrochemical oxidation voltage, and a relatively high corrosion potential against the current collector aluminum foil. In addition, this lithium salt possesses a high lithium-ion mobility number, meeting the requirements for cathode materials in practical applications. Therefore, lithium 4,5-dicyano-2-trifluoromethylimidazolium is a preferred electrolyte lithium salt.

[0005] Regarding the preparation method of lithium 4,5-dicyano-2-trifluoromethylimidazolium, Chinese invention patent application No. 201610412624.3 discloses a method involving the aminolysis of diaminobutenidine with trifluoroacetate to obtain an amide, followed by intramolecular dehydration to obtain crude 4,5-dicyano-2-trifluoromethylimidazolium. After purification, a high-purity dihydrate of 4,5-dicyano-2-trifluoromethylimidazolium is obtained, which is then mixed and reacted with an aqueous suspension of a metal element salt. Subsequent filtration and purification processes yield a high-purity 4,5-dicyano-2-trifluoromethylimidazolium salt. However, in this method, lower-grade trifluoroacetate has a low boiling point, making it difficult to measure and is flammable, while higher-grade trifluoroacetate has low atom utilization and poor economic efficiency. Chinese invention patent application No. 202010425492.4 further explores this approach, disclosing a method of first adding triphenylphosphine and iodine to an organic solvent and stirring at room temperature, then sequentially adding trifluoroacetate and diaminocis-butenedionitrile, stirring at room temperature first, then refluxing to obtain a reaction solution containing the product, which is then purified to obtain the product 4,5-dicyano-2-trifluoromethylimidazolium salt. Although this method has mild reaction conditions and a relatively simple reaction process and post-processing, the triphenylphosphine used in the reaction is expensive, costing hundreds of yuan for just a few grams, resulting in excessively high raw material production costs and an excessively long reaction time, requiring more than ten hours to complete the entire reaction. Overall, it is not suitable for large-scale industrial production.

[0006] Therefore, further research is needed on the preparation method of lithium 4,5-dicyano-2-trifluoromethylimidazolium to develop a method more suitable for industrial production and promotion. Summary of the Invention

[0007] The purpose of this invention is to reduce the production cost of lithium 4,5-dicyano-2-trifluoromethylimidazolium and to develop a simple and industrially applicable method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium.

[0008] The technical solution adopted in this invention is a method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium. The key lies in using trifluoroacetic acid, dicyclohexylcarboimide, and diaminocis-butenedionitrile as raw materials, and carrying out a reflux reaction in an organic solvent system at a controlled temperature of 100℃~110℃ to prepare the intermediate 4,5-dicyano-2-trifluoromethylimidazolium. The organic solvent system mentioned above is a mixed solvent of acetonitrile and 1,4-dioxane in a volume ratio of 1:2~3. Then, the intermediate 4,5-dicyano-2-trifluoromethylimidazolium is reacted with lithium carbonate to prepare lithium 4,5-dicyano-2-trifluoromethylimidazolium.

[0009] Furthermore, the molar ratio of the above-mentioned dicyclohexylcarboimide, trifluoroacetic acid and diaminocis-butadiene dionitrile is 1:2 to 2.4:0.8 to 1.0; the molar ratio of the above-mentioned 4,5-dicyano-2-trifluoromethylimidazolium and lithium carbonate is 1.4 to 1.8:1.

[0010] Preferably, the reflux reaction time is 50 min to 70 min.

[0011] Specifically, the specific steps for preparing the intermediate 4,5-dicyano-2-trifluoromethylimidazole are as follows:

[0012] Add 1,4-dioxane and acetonitrile to a four-necked flask, then add dicyclohexylcarboimide solid and stir. Add trifluoroacetic acid to the system, keeping the temperature no higher than 35°C and stirring for 15-20 minutes. Then, add diaminocis-butenedionitrile. After the addition is complete, raise the temperature to 100-110°C and reflux for 50-70 minutes. After the reaction is complete, rotary evaporate and filter the insoluble matter. Continue to rotary evaporate the filtrate until the solvent is removed to obtain a brown oily substance. Wash with water and toluene in sequence, filter and dry to obtain the intermediate 4,5-dicyano-2-trifluoromethylimidazolium.

[0013] Optimal, the reflux reaction temperature is 105℃ and the reflux reaction time is 60 min.

[0014] Specifically, the specific steps for the reaction of the aforementioned intermediate 4,5-dicyano-2-trifluoromethylimidazolium with lithium carbonate are as follows:

[0015] 4,5-Dicyano-2-trifluoromethylimidazolium was dissolved in acetonitrile, and lithium carbonate aqueous suspension was added dropwise until the pH of the system was neutral. The reaction temperature was controlled at 20℃~38℃ and maintained for 50min~70min. The insoluble matter was removed by filtration, and the filtrate was vacuum-evaporated and dehydrated by rotary evaporation. The filtrate was then filtered to obtain lithium 4,5-dicyano-2-trifluoromethylimidazolium.

[0016] Furthermore, the temperature for vacuuming and rotary evaporation of the filtrate was controlled at 110°C; the temperature for maintaining the reaction was 25°C for 60 minutes.

[0017] Furthermore, the method also includes recrystallizing the obtained 4,5-dicyano-2-trifluoromethylimidazolium lithium to obtain purified 4,5-dicyano-2-trifluoromethylimidazolium lithium.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention uses trifluoroacetic acid, dicyclohexylcarboimide and diaminocis-butenedionitrile as raw materials to synthesize the intermediate 4,5-dicyano-2-trifluoromethylimidazolium, and then reacts the intermediate with lithium carbonate to prepare lithium 4,5-dicyano-2-trifluoromethylimidazolium.

[0020] This invention utilizes the dehydrating properties of dicyclohexylcarboimide to prepare trifluoroacetic anhydride from trifluoroacetic acid at low temperatures, avoiding the inconvenience of directly using trifluoroacetic anhydride and improving the safety and operability of the reaction. Although trifluoroacetic acid is a strong acid and easily corrodes production equipment, this invention uses a fed-batch method to minimize the damage of trifluoroacetic acid to the reaction equipment.

[0021] Meanwhile, the present invention optimizes and improves the reaction system by using a mixed solvent of acetonitrile and 1,4-dioxane as the reaction system, which reduces the solubility of the reaction byproduct dicyclohexylurea, so that the byproduct and excess dicyclohexylcarboimide can be removed by filtration. This is convenient to operate and will not be carried into the final product, thereby improving the purity of the product.

[0022] Because the product prepared by this invention has higher purity, it has a more significant effect on improving the electrical performance of the battery. When used in combination with lithium salt and electrolyte additive, it can further improve the high-temperature storage performance and electric cycle performance of the battery, especially the high-voltage electric cycle performance of the battery, which has a greater improvement and more obvious effect. Attached Figure Description

[0023] Figure 1 This is the 1H NMR spectrum of the sample from this invention.

[0024] Figure 2 This is the NMR fluorine spectrum of the sample from this invention.

[0025] Figure 3 This is a high-performance liquid chromatography-mass spectrum of the sample of this invention.

[0026] Figure 4 This is a high-performance liquid chromatography (HPLC) spectrum of the sample from this invention (diode array detector).

[0027] Figure 5 This is the ion chromatogram (conductivity detector) of the sample of this invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified in the examples, the procedures can be followed according to conventional conditions; unless the manufacturers of the reagents or instruments used are specified, they are all conventional products that can be purchased commercially.

[0030] Example 1

[0031] S1. Add 24.3 mL of acetonitrile and 60.7 mL of 1,4-dioxane mixed solvent to a four-necked flask, then add 20.0 g of dicyclohexylcarbonimide solid. Start stirring. Dicyclohexylcarbonimide cannot be completely dissolved in the system and forms a suspension. Add 24.3 g of trifluoroacetic acid to the four-necked flask. The molar ratio of dicyclohexylcarbonimide to trifluoroacetic acid is approximately 1:2.2. Maintain the temperature at 30°C and stir for 18 min.

[0032] S2. Add 9.4 g of diaminobutenidine to a four-necked flask. The molar ratio of dicyclohexylcarboimide to diaminobutenidine is 1:0.9. After the addition is complete, heat the flask and reflux at 105 °C for 60 min.

[0033] S3. After the reaction is complete, the insoluble matter in the system is removed by rotary evaporation and filtration. Then, the solvent is removed by rotary evaporation to obtain a brown oily substance. After washing with water and toluene in sequence, the substance is filtered and dried to obtain intermediate 4,5-dicyano-2-trifluoromethylimidazolium, which is denoted as intermediate 1.

[0034] S4. Weigh 14.4g of the prepared intermediate and dissolve it in 80mL of acetonitrile. Weigh 3.5g of lithium carbonate and place it in 15mL of water and stir to obtain a lithium carbonate aqueous suspension. The molar ratio of the intermediate to lithium carbonate is approximately 1.6:1. Under stirring conditions, add the lithium carbonate aqueous suspension dropwise to the above acetonitrile solution at a uniform rate until the pH of the system reaches 7.

[0035] S5. Control the reaction temperature at 25℃ and the reaction time at 60min. After the reaction is completed, filter to remove insoluble matter. Remove water from the filtrate by vacuum rotary evaporation at 110℃. Filter to obtain crude sample 1 of 4,5-dicyano-2-trifluoromethylimidazolium. Recrystallize the crude product to obtain sample 1 of 4,5-dicyano-2-trifluoromethylimidazolium.

[0036] Example 2

[0037] S1. Add 30.0 mL of acetonitrile and 60.0 mL of 1,4-dioxane mixed solvent to a four-necked flask, then add 20.0 g of dicyclohexylcarboimide solid, start stirring to form a suspension, and add 26.5 g of trifluoroacetic acid to the four-necked flask. The molar ratio of dicyclohexylcarboimide to trifluoroacetic acid is approximately 1:2.4. Maintain the temperature at 35°C and stir for 15 min.

[0038] S2. Add 10.5g of diaminobutenonitrile to a four-necked flask. The molar ratio of dicyclohexylcarboimide to diaminobutenonitrile is 1:1. After the addition is complete, heat the flask and reflux at 100℃ for 70min.

[0039] S3. Same as in Example 1, intermediate 2 is prepared;

[0040] S4. Weigh 15.7g of the prepared intermediate 2 and dissolve it in 85mL of acetonitrile. Weigh 3.4g of lithium carbonate and place it in 12mL of water and stir to obtain a lithium carbonate aqueous suspension. The molar ratio of the intermediate to lithium carbonate is approximately 1.8:1. Under stirring conditions, add the lithium carbonate aqueous suspension dropwise to the above acetonitrile solution at a uniform rate until the pH of the system reaches 7 and then stop the dropwise addition.

[0041] S5. Heat the above solution and maintain the temperature at 38°C for 50 minutes. After the reaction, the treatment method is the same as in Example 1. The crude 4,5-dicyano-2-trifluoromethylimidazolium lithium sample 2 can be recrystallized to obtain 4,5-dicyano-2-trifluoromethylimidazolium lithium sample 2.

[0042] Example 3

[0043] S1. Add 20.0 mL of acetonitrile and 60.0 mL of 1,4-dioxane mixed solvent to a four-necked flask, then add 20.0 g of dicyclohexylcarbonimide solid, start stirring, and add 22.1 g of trifluoroacetic acid to the four-necked flask. The molar ratio of dicyclohexylcarbonimide to trifluoroacetic acid is approximately 1:2.0. Maintain the temperature at 20°C and stir for 20 min.

[0044] S2. Add 8.4 g of diaminobutenonitrile to a four-necked flask. The molar ratio of dicyclohexylcarboimide to diaminobutenonitrile is 1:0.8. After the addition is complete, heat the flask and reflux at 110 °C for 50 min.

[0045] S3. Same as in Example 1, intermediate 3 was prepared;

[0046] S4. Weigh 12.6 g of the prepared intermediate and dissolve it in 80 mL of acetonitrile. Weigh 3.5 g of lithium carbonate and place it in 15 mL of water and stir to obtain a lithium carbonate aqueous suspension. The molar ratio of the intermediate to lithium carbonate is approximately 1.4:1. Under stirring conditions, add the lithium carbonate aqueous suspension dropwise to the above acetonitrile solution at a uniform rate until the pH of the system reaches 7.

[0047] S5. Control the reaction temperature at 20℃ and the reaction time at 70 min. After the reaction, the treatment method is the same as in Example 1. The crude sample 3 of 4,5-dicyano-2-trifluoromethylimidazolium lithium can be recrystallized to obtain sample 3 of 4,5-dicyano-2-trifluoromethylimidazolium lithium.

[0048] Example 4

[0049] S1. Add 25.7 mL of acetonitrile and 64.3 mL of 1,4-dioxane mixed solvent to a four-necked flask, then add 20.0 g of dicyclohexylcarboimide solid, start stirring to form a suspension, and add 25.4 g of trifluoroacetic acid to the four-necked flask. The molar ratio of dicyclohexylcarboimide to trifluoroacetic acid is approximately 1:2.3. Maintain the temperature at 25°C and stir for 20 min.

[0050] S2. Add 9.4 g of diaminobutenidine to a four-necked flask. The molar ratio of dicyclohexylcarboimide to diaminobutenidine is 1:0.9. After the addition is complete, heat the flask and reflux at 108 °C for 55 min.

[0051] S3. Same as in Example 1, intermediate 4 was prepared;

[0052] S4. Weigh 14.4 g of the prepared intermediate and dissolve it in 80 mL of acetonitrile. Weigh 3.1 g of lithium carbonate and place it in 10 mL of water and stir to obtain a lithium carbonate aqueous suspension. The molar ratio of the intermediate to lithium carbonate is approximately 1.8:1. Under stirring conditions, add the lithium carbonate aqueous suspension dropwise to the above acetonitrile solution at a uniform rate until the pH of the system reaches 7.

[0053] S5. Heat the above solution and maintain the temperature at 30°C for 55 minutes. After the reaction, the treatment method is the same as in Example 1. The crude 4,5-dicyano-2-trifluoromethylimidazolium lithium sample 4 can be recrystallized to obtain 4,5-dicyano-2-trifluoromethylimidazolium lithium sample 4.

[0054] Comparative Example 1

[0055] The implementation method is the same as in Example 2, except that step "S1" is omitted. The specific operation steps of step "S2" are as follows:

[0056] Add 9.4 g of diaminocis-butene dionitrile to a dry four-necked flask, add 85 mL of 1,4-dioxane, and add 21.0 g of trifluoroacetic anhydride dropwise while maintaining the temperature at 20 °C. After the addition is complete, raise the temperature to 105 °C and reflux for 60 min.

[0057] The subsequent process is the same as in Example 1, to prepare intermediate reference standard 1, and then to prepare crude reference standard 1 and sample reference standard 1.

[0058] During the above process, it is essential to ensure that the reagents and instruments used are dry, as trifluoroacetic anhydride is volatile, highly irritating, and can cause tears; therefore, proper personal protective measures are necessary.

[0059] Comparative Example 2

[0060] The implementation method is the same as in Example 1, except that in "S1, Step", the solvent used is an 85mL pure acetonitrile system.

[0061] The subsequent process is the same as in Example 1, to prepare intermediate reference standard 2, and then to prepare crude reference standard 2 and sample reference standard 2.

[0062] Comparative Example 3

[0063] The implementation method is the same as in Example 1, except that in "S4, Step", 12.9g of the prepared intermediate is weighed and dissolved in 70mL of acetonitrile, and 2.5g of lithium carbonate is weighed into 10mL of water and stirred to obtain a lithium carbonate aqueous suspension. The molar ratio of the intermediate to lithium carbonate is approximately 2:1.

[0064] The subsequent process is the same as in Example 1, to prepare intermediate reference standard 3, and then to prepare crude reference standard 3 and sample reference standard 3.

[0065] Analysis and Testing

[0066] Analysis of the sample in the examples using 1H NMR, fluorine spectroscopy, and mass spectrometry revealed that the structure of the sample conformed to the characteristics of lithium 4,5-dicyano-2-trifluoromethylimidazolium. The results are shown in the appendix. Figure 1 ~Attached Figure 3 .

[0067] The yields of the samples and reference standards were calculated, and the purity of the test samples was detected using high-performance liquid chromatography (HPLC). The results are shown in Table 1, and the test chromatogram for sample 1 is shown in the appendix. Figure 4 .

[0068] The conductivity of the test samples and reference standards was detected by ion chromatography using a conductivity detector at a flow rate of 0.900 mL / min and a mobile phase of 30% acetonitrile. The results are shown in the appendix. Figure 5 The ion peaks of the target product appear near 5.83 min and 23.95 min in the figure, respectively.

[0069] Yield calculation formula:

[0070] In step S3, the intermediate yield = actual weight (g) of the obtained intermediate or intermediate reference standard / theoretical yield (g) calculated based on the amount of diaminobutyronitrile used × 100%;

[0071] In step S5, the crude product yield = actual weight (g) of the crude product or crude product reference standard / theoretical yield (g) calculated based on the amount of 4,5-dicyano-2-trifluoromethylimidazole used × 100%; the sample yield = actual weight (g) of the sample or sample reference standard obtained / theoretical yield (g) calculated based on the amount of 4,5-dicyano-2-trifluoromethylimidazole used × 100%.

[0072] Overall yield = (intermediate yield / 100%) × (sample yield / 100%) × 100%.

[0073] Table 1: Summary of Sample Yield and Purity Test Results

[0074]

[0075] As shown in Table 1, the preparation method of this invention has a high yield, with the total yield after recrystallization still reaching over 82%, and even exceeding 85%. The product prepared by this invention has high purity, reaching up to 99.7%. In Comparative Example 1, the product was prepared directly using trifluoroacetic anhydride, and the difference in total yield and purity compared to this invention was not significant. However, due to the low boiling point and volatility of trifluoroacetic anhydride, it decomposes in water to produce toxic and harmful gases, making direct addition difficult to control. In Comparative Example 2, the reaction system of this invention was modified, resulting in a significant decrease in the yield of the first step reaction and affecting the product purity. This indicates that the reaction system of this invention is more conducive to the separation of the target intermediate and reaction byproducts in the first step reaction, effectively reducing process impurities. In Comparative Example 3, the ratio of intermediate to lithium carbonate was changed, leading to varying degrees of decrease in both crude product yield and product purity, indicating that the material ratio selected in this invention is more scientific.

[0076] Application testing

[0077] The components of the lithium battery electrolyte used include lithium salts, additives, and organic solvents.

[0078] The organic solvents are all composed of ethylene carbonate and ethyl acetate in a mass ratio of 7:3.

[0079] The first test group consists of application samples without additives. The lithium salt concentration in the electrolyte is 1.0 mol / L. The lithium salts used are sample 1 prepared in this invention, reference standard 2 prepared in Comparative Example 2, and lithium hexafluorophosphate (purity ≥99.0%). Lithium batteries with a capacity of 1000 mAh were made using the above electrolytes and are referred to as application samples 1, 2, and 3.

[0080] The second test group consisted of application samples with 0.2% vinylene carbonate added. The lithium salt concentration in the electrolyte was 1.0 mol / L. The lithium salts used were Sample 1 prepared in this invention, Control 2 prepared in Comparative Example 2, and Lithium hexafluorophosphate (purity ≥99.0%). Lithium batteries with a capacity of 1000 mAh were made using the above electrolytes and were designated as application samples 4, 5, and 6.

[0081] Battery performance was tested using the above-mentioned application samples.

[0082] 1. High-temperature external short-circuit test

[0083] After fully charging the battery, place it in an environment of 55℃±5℃. After the battery surface temperature reaches 55℃±5℃, leave it for another 30 minutes. Then connect the positive and negative terminals of the battery with wires and ensure that the total external resistance is 80mΩ±20mΩ. Monitor the battery temperature change during the test. The battery should not catch fire or explode. The maximum temperature should not exceed 150℃. Record the test phenomena. The test results are shown in Table 2.

[0084] 2. High-temperature storage test

[0085] The battery was subjected to three charge-discharge cycles at a charge-discharge rate of 0.5C at room temperature. Then, it was charged to full capacity at a constant current of 0.5C with a cutoff current of 0.025C. The highest discharge capacity Q and battery thickness T of the first three 0.5C cycles were recorded.

[0086] A fully charged battery was stored at 85°C for 6 hours. The battery thickness T0 and 0.5C discharge capacity Q2 after 6 hours were recorded. Then, the battery was charged and discharged three times at a rate of 0.5C at room temperature. The highest discharge capacity Q3 after three cycles was recorded. The capacity was then calculated using the formula:

[0087] Thickness change rate (%) = (T0-T) / T × 100%;

[0088] Capacity retention rate (%) = Q2 / Q × 100%;

[0089] Capacity recovery rate (%) = Q3 / Q × 100%;

[0090] The thickness change rate, capacity retention rate, and capacity recovery rate of the battery during high-temperature storage were calculated, and the experimental results are shown in Table 2.

[0091] 3. Electrical Cyclic Performance Test

[0092] The test environment temperature was 25℃±2℃. The battery was charged at a constant current of 1C to 4.35V, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 3.0V. This was the first cycle.

[0093] Under the above cycling conditions, perform 100, 300, and 500 charge / discharge cycles respectively, and calculate the capacity retention rate after 100, 300, and 500 cycles respectively. The capacity retention rate after cycling is calculated using the following formula:

[0094] The capacity retention rate after cycling is calculated as (discharge capacity after the corresponding number of cycles / discharge capacity of the first cycle) × 100%, and the results are shown in Table 2.

[0095] 4. High-voltage electric cycling performance test

[0096] The test environment temperature was 25℃±2℃. The battery was charged to 4.6V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.6V, and then discharged to 3.0V with a constant current of 1C. This was the first cycle.

[0097] The battery was charged / discharged for 100, 300, and 500 cycles under the conditions described above. The capacity retention rate after 100, 300, and 500 cycles was calculated, and the results are shown in Table 2.

[0098] Table 2: Summary of Battery Performance Test Results

[0099]

[0100] As can be seen from the data in Table 2, using lithium 4,5-dicyano-2-trifluoromethylimidazolium as the lithium salt to prepare the battery electrolyte is more beneficial to improving the high-temperature electrochemical performance of the battery compared with lithium hexafluorophosphate, and it performs better in high-temperature storage test and electric cycle performance test.

[0101] The samples prepared by this invention have higher purity, resulting in a more significant improvement in the electrical performance of the battery. Furthermore, when used in conjunction with electrolyte additives, the samples of this invention can further enhance the battery's high-temperature storage performance and cycle performance, particularly for high-voltage cycle performance, where the lithium salt in this invention shows a greater improvement.

Claims

1. A method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium, characterized in that, Using trifluoroacetic acid, dicyclohexylcarboimide, and diaminocis-butenedionitrile as raw materials, an intermediate 4,5-dicyano-2-trifluoromethylimidazolium was prepared by reflux reaction in an organic solvent system at a controlled temperature of 100 ℃~110 ℃. The organic solvent system was a mixed solvent of acetonitrile and 1,4-dioxane in a volume ratio of 1:2~3. The intermediate 4,5-dicyano-2-trifluoromethylimidazolium was then reacted with lithium carbonate to prepare lithium 4,5-dicyano-2-trifluoromethylimidazolium. The molar ratio of dicyclohexylcarboimide, trifluoroacetic acid, and diaminocis-butenedionitrile is 1:2–2.4:0.8–1.0; the molar ratio of 4,5-dicyano-2-trifluoromethylimidazolium and lithium carbonate is 1.4–1.8:

1. The specific steps for preparing the intermediate 4,5-dicyano-2-trifluoromethylimidazolium are as follows: Add 1,4-dioxane and acetonitrile to a four-necked flask, then add dicyclohexylcarboimide solid and stir. Add trifluoroacetic acid to the system, keeping the temperature below 35°C and stirring for 15-20 minutes. Then, add diaminocis-butenedionitrile. After the addition is complete, reflux the mixture at 100-110°C for 50-70 minutes. After the reaction is complete, rotary evaporate and filter the insoluble matter. Continue to rotary evaporate the filtrate until the solvent is removed to obtain a brown oily substance. Wash the substance with water and toluene in sequence, filter and dry to obtain the intermediate 4,5-dicyano-2-trifluoromethylimidazolium.

2. The method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium according to claim 1, characterized in that, The reflux reaction temperature is 105 °C and the reflux reaction time is 60 min.

3. The method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium according to claim 1, characterized in that, The specific steps for the reaction of the intermediate 4,5-dicyano-2-trifluoromethylimidazol with lithium carbonate are as follows: 4,5-Dicyano-2-trifluoromethylimidazolium was dissolved in acetonitrile, and lithium carbonate aqueous suspension was added dropwise until the pH of the system was neutral. The reaction temperature was controlled at 20℃~38℃ and maintained for 50 min~70 min. The insoluble matter was removed by filtration, and the filtrate was vacuum-evaporated and dehydrated by rotary evaporation. The filtrate was then filtered to obtain lithium 4,5-dicyano-2-trifluoromethylimidazolium.

4. The method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium according to claim 3, characterized in that, The temperature of the filtrate being vacuumed and dehydrated by rotary evaporation is controlled at 110 ℃; the temperature of the reaction is maintained at 25 ℃ for 60 min.

5. The method for preparing lithium 4,5-dicyano-2-trifluoromethylimidazolium according to claim 3, characterized in that, It also includes further recrystallizing the obtained 4,5-dicyano-2-trifluoromethylimidazolium lithium to obtain purified 4,5-dicyano-2-trifluoromethylimidazolium lithium.

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