A method for reducing residual solvents of lithium bisfluorosulfonylimide salt

Abstract

The application provides a method for reducing residual solvent of lithium bisfluorosulfonylimide, to solve the technical problems of poor removal effect of residual ester reagent in lithium bisfluorosulfonylimide and low yield in the prior art. The method comprises the following steps: (1) dissolving lithium bisfluorosulfonylimide with residual solvent in a good solvent to prepare a solution; (2) adding a first poor solvent to the solution to prepare a mixed solution; (3) evaporating the good solvent from the mixed solution under negative pressure to obtain a dispersion; (4) filtering the dispersion to remove the poor solvent and obtain a primary product; (5) washing the primary product with a second poor solvent, and filtering the second poor solvent to obtain a secondary product; and (6) performing negative pressure drying treatment on the secondary product. The method can remove the residual ester solvent in lithium salt, realizes the effect of reducing residual solvent, and has high lithium salt yield and is simple and easy to implement.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrolyte materials, and particularly relates to a method for reducing solvent residue of lithium bisfluorosulfonylimide salt. BACKGROUND

[0002] With the rise of the new energy field, lithium batteries for power and energy storage have developed rapidly. In order to better meet the market demand, the preparation of lithium batteries with superior performance has always been in the core channel of the new energy field. As a synthetic body of different materials, the performance of lithium batteries is greatly related to their components. The electrolyte lithium salt, as the soul of the electrolyte, has a great influence on the performance of the entire lithium battery. At present, the electrolyte lithium salt is mainly lithium hexafluorophosphate. Although lithium hexafluorophosphate has superior comprehensive performance, it is also very sensitive and has problems such as poor thermal stability and easy hydrolysis. These defects also promote the development of a new generation of lithium salts. Lithium bisfluorosulfonylimide (LiFSI) as a new generation of lithium salt has excellent high and low temperature performance and high conductivity, and has great potential to replace lithium hexafluorophosphate as the main lithium salt of the electrolyte. The preparation of high-quality lithium bisfluorosulfonylimide salt is the first step to achieve replacement.

[0003] The electrolyte lithium salt, including lithium bisfluorosulfonylimide, has a high requirement for the solvent residue index. The solvent residue of lithium bisfluorosulfonylimide mainly comes from the residue of ester reagents used in the preparation of refined salt by recrystallization. The current methods for solving solvent residue mainly include negative pressure removal of lithium salt at a certain temperature, beating with a poor solvent, and evaporation removal with a good solvent. The above methods can solve the problem of solvent residue of lithium salt to some extent, but also have certain limitations. The negative pressure heating removal method is difficult to reduce the wrapped solvent residue to the qualified index with the help of negative pressure. At the same time, lithium salt may decompose under heating conditions. The beating method uses a poor solvent system of lithium salt, which is difficult to completely remove the residual solvent wrapped in the lithium salt particles. The good solvent dissolution and evaporation method can better remove the residual solvent in lithium salt, but it is difficult to completely evaporate the good solvent because the good solvent and lithium salt are well combined, which leads to the agglomeration of lithium salt and the need for further post-processing, and there is also a possibility of residual good solvent.

[0004] Therefore, it is necessary to further improve the above common solvent residue removal methods so that the solvent residue index of lithium salt meets the standard requirements and the method is simple and easy to operate. SUMMARY

[0005] The purpose of the present application is to provide a method for reducing the solvent residue of lithium bisfluorosulfonylimide salt, which is used to remove the residue of ester reagents. The method has the characteristics of good solvent residue removal effect, high lithium salt yield, and simple and easy-to-operate method.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0007] A method for reducing solvent residue of lithium bisfluorosulfonylimide salt, comprising the following steps:

[0008] (1) dissolving lithium bisfluorosulfonylimide salt with solvent residue in a good solvent with boiling point of 50-80℃ to prepare a lithium bisfluorosulfonylimide solution;

[0009] (2) adding a first poor solvent with boiling point of 90-150℃ to the solution to prepare a mixed solution;

[0010] (3) evaporating the mixed solution under negative pressure to remove the good solvent and obtain a lithium bisfluorosulfonylimide salt dispersion;

[0011] (4) filtering the dispersion to remove the first poor solvent and obtain a lithium bisfluorosulfonylimide salt primary product;

[0012] (5) washing the primary product with a second poor solvent with boiling point of 35-60℃ and filtering the second poor solvent to obtain a lithium bisfluorosulfonylimide salt secondary product.

[0013] (6) drying the secondary product under negative pressure to obtain a lithium bisfluorosulfonylimide salt target product after removing solvent residue.

[0014] Preferably, in step (1), the good solvent is at least one of acetonitrile, ethyl acetate, and acetone.

[0015] Preferably, the mass ratio of lithium bisfluorosulfonylimide salt to good solvent is 1:1-3, and the dissolving temperature is 15-25℃.

[0016] Preferably, in step (2), the first poor solvent is at least one of heptane, octane, and nonane.

[0017] Preferably, the mass ratio of lithium bisfluorosulfonylimide salt to the first poor solvent is 1:4-10.

[0018] Preferably, in step (3), the negative pressure evaporation temperature is 30-50℃, and the evaporation endpoint is when the system mass decreases by 90-100% of the mass of the good solvent.

[0019] Preferably, in step (4), the operation is performed under the protection of inert gas nitrogen.

[0020] Preferably, in step (5), the second poor solvent is at least one of dichloromethane, pentane, and chloroform.

[0021] Preferably, the mass ratio of lithium bisfluorosulfonylimide salt to the second poor solvent is 1:1-4.

[0022] Preferably, in step (6), the negative pressure drying temperature is 30-50℃, and the drying time is 2-5h.

[0023] Advantages:

[0024] The application discloses a method for reducing residual solvent of lithium bisfluorosulfonylimide, and through continuous evaporation of a low-boiling-point good solvent, the lithium salt reaches a sustained saturation-precipitation process, the whole process has a relatively slow crystallization rate, and the method avoids the problem that the solvent is wrapped in the lithium salt due to rapid crystallization. Meanwhile, the good solvent well removes the residual ester solvent in the lithium salt in the evaporation process, the effect of reducing the residual solvent is achieved, and in the evaporation process, a large amount of the good solvent is evaporated, and a large amount of high-boiling-point poor solvent is retained, so that the dissolved lithium salt is precipitated in a large amount, and the yield of the lithium salt is high. Overall, the method has the advantages of simplicity and practicability. Finally, the residual ester solvent is less than or equal to 100 ppm, the low-boiling-point good solvent is less than or equal to 150 ppm, the high-boiling-point poor solvent is less than or equal to 250 ppm, and the low-boiling-point poor solvent is less than or equal to 100 ppm. DETAILED DESCRIPTION

[0025] In order to better illustrate the purposes, technical solutions and advantages of the present application, the present application will be further described below in combination with specific examples. It should be noted that the following implementation of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0026] Example 1

[0027] (1) nearly 100g of lithium bisfluorosulfonylimide containing about 10% of DMC (dimethyl carbonate) solvent residue is added into a 1000ml single-neck flask, then 100g of acetonitrile solvent with the same mass ratio is added, the lithium salt is completely dissolved at 25℃ by using magnetic stirring, then high-boiling-point octane poor solvent is added in a mass ratio of 4 times the mass of the lithium salt, and the solvents in the system are completely mixed by stirring, at this time, the lithium salt is not precipitated.

[0028] (2) the above mixture is connected to a negative pressure rotary evaporation device, the temperature of the rotary evaporator is controlled to 40℃, and the negative pressure is about 5000Pa, and the evaporation and crystallization process is carried out, as the acetonitrile evaporates, the lithium salt is precipitated, and when the condensation rate of the acetonitrile evaporation condensate is obviously reduced, the mass of the system is weighed in real time after this time period, and when the mass reduction of the whole system is 90% of the mass of the added acetonitrile, the evaporation and crystallization process is stopped.

[0029] (3) under the condition of nitrogen protection, the evaporation and crystallization liquid is filtered by using a positive pressure filter, the residual high-boiling-point poor solvent in the system is filtered out, then the lithium salt is taken out, reloaded into a single-neck flask, washed by stirring with 2 times DCM (dichloromethane), then the washed lithium salt is filtered again by using a positive pressure filter, the lithium salt is taken out again, and loaded into a 500ml single-neck flask.

[0030] (4) The filtered lithium salt is dried using a negative pressure rotary evaporation device, the drying temperature is set to 45°C, the negative pressure is about 1000 Pa, the whole drying process is maintained for 2 h, then the lithium salt is collected, weighed, and subjected to gas phase detection, the results are shown in Table 1

[0031] Table 1 Comparison of reducing solvent residue of lithium bisfluorosulfonylimide in Example 1

[0032]

[0033]

[0034] Example 2

[0035] (1) About 200 g of lithium bisfluorosulfonylimide containing about 10% DMC (dimethyl carbonate) solvent residue is added into a 2000 mL single-neck flask, then 200 g of ethyl acetate solvent with the same mass ratio is added, the lithium salt is completely dissolved at 25°C using magnetic stirring, then a high-boiling non-solvent n-alkane is added at 4 times the mass ratio of the lithium salt, the solvent in the system is completely mixed by stirring, and no lithium salt is precipitated at this time.

[0036] (2) The above mixture is connected to a negative pressure rotary evaporation device, the rotary evaporator temperature is controlled to 40°C, and the negative pressure is about 5000 Pa, and the evaporation and crystallization process is carried out, as the ethyl acetate evaporates, the lithium salt is precipitated, and when the condensation rate of the ethyl acetate evaporation condensate decreases significantly, the mass of the system is weighed in real time after this time period, and the evaporation and crystallization process is stopped when the total mass of the system is reduced to 90% of the mass of the added ethyl acetate.

[0037] (3) The above evaporation and crystallization liquid is filtered using a positive pressure filter under nitrogen protection conditions, the residual high-boiling non-solvent in the system is filtered out, then the lithium salt is taken out, reloaded into a single-neck flask, 2 times of chloroform is added, the lithium salt is stirred and washed, then the washed lithium salt is again filtered using a positive pressure filter, the lithium salt is taken out again, and loaded into a 500 ml single-neck flask.

[0038] (4) The filtered lithium salt is dried using a negative pressure rotary evaporation device, the drying temperature is set to 45°C, the negative pressure is about 1000 Pa, the whole drying process is maintained for 2 h, then the lithium salt is collected, weighed, and subjected to gas phase detection, the results are shown in Table 2

[0039] Table 2 Comparison of reducing solvent residue of lithium bisfluorosulfonylimide in Example 2

[0040]

[0041] Example 3

[0042] (1) Put nearly 200 g of lithium bisfluorosulfonylimide containing about 6% DEC (diethyl carbonate) solvent residue into a 2000 mL single-neck flask, then add 200 g of ethyl acetate solvent with the same mass ratio, completely dissolve the lithium salt at 25°C using magnetic stirring, then add 5 times the mass of the lithium salt of high-boiling non-solvent n-nonane, and completely mix the solvents in the system by stirring. At this time, the lithium salt does not precipitate.

[0043] (2) Connect the above mixture to a negative pressure rotary evaporation device, control the rotary evaporator temperature to 40°C, and control the negative pressure to about 5000 Pa. Perform the evaporation and crystallization process. As the ethyl acetate evaporates, the lithium salt precipitates. When the condensation rate of the ethyl acetate evaporation condensate significantly decreases, the mass of the system is weighed in real time after this time period. When the overall mass of the system is reduced to 90% of the mass of the added ethyl acetate, stop the evaporation and crystallization process.

[0044] (3) Under nitrogen protection, filter the above evaporation and crystallization liquid using a positive pressure filter to filter out the residual high-boiling non-solvent in the system, then take out the lithium salt and re-charge it into a single-neck flask, add 2 times DCM (dichloroethane) to stir and wash the lithium salt, then re-filter the washed lithium salt using a positive pressure filter, take out the lithium salt again, and charge it into a 500 ml single-neck flask.

[0045] (4) Dry the filtered lithium salt using a negative pressure rotary evaporation device, set the drying temperature to 45°C, and control the negative pressure to about 1000 Pa. Maintain the entire drying process for 2 h, then collect the lithium salt, weigh the mass, and perform gas phase detection. The results are shown in Table 3.

[0046] Table 3 Comparison of reducing solvent residue of lithium bisfluorosulfonylimide in Example 3

[0047]

[0048] The applicant declares that the present application is not limited to the above examples, and it does not mean that the present application must rely on the above examples to be implemented. Those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present application all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for reducing residual solvents of lithium bisfluorosulfonylimide salt, characterized by, The method comprises the following steps: (1) dissolving the lithium bistrifluorosulfonimide with solvent residues in a good solvent with a boiling point of 50-80℃ to prepare a lithium bistrifluorosulfonimide solution; (2) adding a first poor solvent with a boiling point of 90-150℃ to the solution to prepare a mixed solution, and the mass ratio of the good solvent to the first poor solvent is (1-3):(4-10); (3) evaporating the mixed solution under negative pressure to remove the good solvent, and obtaining a lithium bistrifluorosulfonimide dispersion; (4) filtering the dispersion to remove the first poor solvent, and obtaining a lithium bistrifluorosulfonimide primary product; (5) washing the primary product with a second poor solvent with a boiling point of 35-60℃, and filtering the second poor solvent to obtain a lithium bistrifluorosulfonimide secondary product; (6) performing negative pressure drying treatment on the secondary product to obtain a lithium bistrifluorosulfonimide target product with solvent residues removed.

2. The method of claim 1, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. In step (1), the good solvent is at least one of acetonitrile, ethyl acetate, and acetone.

3. The method of claim 2, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. The mass ratio of lithium bistrifluorosulfonimide to the good solvent is 1:1-3, and the dissolution temperature is 15-25℃.

4. The method of claim 1, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. In step (2), the first poor solvent is at least one of heptane, octane, and nonane.

5. The method of claim 4, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. The mass ratio of lithium bistrifluorosulfonimide to the first poor solvent is 1:4-10.

6. The method of claim 1, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. In step (3), the negative pressure evaporation temperature is 30-50℃, and the evaporation endpoint is when the mass of the system is reduced by 90-100% of the mass of the good solvent.

7. The method of claim 1, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. In step (4), the operation is performed under the protection of inert gas nitrogen.

8. The method of claim 1, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. In step (5), the second poor solvent is at least one of dichloromethane, pentane, and chloroform.

9. The method of claim 8, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. The mass ratio of lithium bistrifluorosulfonimide to the second poor solvent is 1:1-4.

10. The method of claim 1, wherein the solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and mixtures thereof. In step (6), the negative pressure drying temperature is 30-50℃, and the drying time is 2-5h.

Images