Method for removing fluorine ions in lithium bis (fluorosulfonyl) imide

Abstract

The invention relates to the technical field of organic synthesis, in particular to a method for removing fluorine ions in lithium bis (fluorosulfonyl) imide, which comprises the following steps: after the reaction of lithium bis (fluorosulfonyl) imide is finished, filtering the reaction material, removing the solvent, adding 1, 1, 1-trifluoro-2-chloroethane into the removed solid, stirring for a period of time while keeping the temperature at 0-5 DEG C, heating to normal temperature, evaporating to remove 1, 1, 1-trifluoro-2-chloroethane, and removing the fluorine ions in the lithium bis (fluorosulfonyl) imide. The method comprises the following steps: washing 1, 1, 1-trifluoro-2-chloroethane by using dichloromethane, removing 1, 1, 1-trifluoro-2-chloroethane, repeating the washing and distilling process of 1, 1, 1-trifluoro-2-chloroethane once, rinsing the solid with 1, 1, 1-trifluoro-2-chloroethane removed by using dichloromethane, carrying out vacuum drying on the rinsed solid to obtain a bis (fluorosulfonyl) lithium imide crude product, and carrying out all the operations under the protection of pure nitrogen. The 1, 1, 1-trifluoro-2-chloroethane is used for removing fluorine ions in the bis (fluorosulfonyl) lithium imide, deep impurity removal can be achieved, no new impurities are introduced, and the process compatibility is high. The boiling point of the 1, 1, 1-trifluoro-2-chloroethane is low, the 1, 1, 1-trifluoro-2-chloroethane can be separated from the LiFSI at normal temperature, high-temperature heating is not needed, and hydrolysis or decomposition of the LiFSI can be avoided.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of organic synthesis, and in particular to a method for removing fluorine ions in lithium bis(fluorosulfonyl)imide. BACKGROUND

[0002] Fluoride ions (F-) are typical harmful impurities in LiFSI production, and their residues can have negative effects on battery performance, product stability, and production compliance, as follows: 1. Damaging key components of lithium batteries, leading to performance degradation LiFSI is mainly used in lithium battery electrolytes. Fluoride ions can react with the positive electrode current collector (aluminum foil) to form an aluminum fluoride (AlF3) insulating layer, increasing the internal resistance of the battery. At the same time, they can erode the SEI film (solid electrolyte interface film) on the surface of the electrode, leading to SEI film rupture, continuous decomposition of the electrolyte, and ultimately causing battery capacity to decrease (capacity retention rate may decrease from 90% to below 70% after 500 cycles) and fast charging performance to degrade.

[0003] 2. Accelerating the hydrolysis of LiFSI itself, reducing product stability Fluoride ions have strong electronegativity and can catalyze the hydrolysis reaction of LiFSI (FSI- + H2O -> F- + HSO3F + NH2SO2F), forming a vicious cycle - the fluoride ions generated by hydrolysis further exacerbate hydrolysis, leading to a decrease in the main content of LiFSI (e.g., purity decreases from 99.5% to below 98% after 3 months of storage), and the generation of new acidic impurities such as fluorosulfonic acid (HSO3F), affecting the stability of the electrolyte formulation.

[0004] The removal of fluoride ions is a key step for LiFSI to achieve battery-level applications. Existing methods for removing fluoride ions can be divided into four categories: chemical precipitation, supercritical fluid extraction, solvent extraction-crystallization, and reaction process fluorine control. Although these methods can meet the basic standards (≤200 ppm), they still have shortcomings in terms of deep impurity removal (≤50 ppm), high yield (≥98%), low energy consumption, and simultaneous treatment of multiple impurities. SUMMARY

[0005] The purpose of the present application is to provide a method for removing fluoride ions in lithium bis(fluorosulfonyl)imide, which can solve at least one of the above technical problems.

[0006] To achieve the above purpose, the technical solution adopted by the present application is as follows: The method for removing fluoride ions in lithium bis(fluorosulfonyl)imide comprises the following steps: After the reaction of lithium bis(fluorosulfonyl)imide is completed, the reaction material is filtered, the solvent is removed, 1,1,1-trifluoro-2-chloroethane is added to the removed solid, stirring is maintained at 0-5 DEG C for a period of time, 1,1,1-trifluoro-2-chloroethane is distilled off at room temperature, and the process of washing and distilling 1,1,1-trifluoro-2-chloroethane is repeated once again, the solid removed from 1,1,1-trifluoro-2-chloroethane is rinsed with dichloromethane, the rinsed solid is vacuum dried, and lithium bis(fluorosulfonyl)imide crude product is obtained, and all the above operations are carried out under the protection of pure nitrogen.

[0007] Further, the condition for removing the solvent is that the temperature is not higher than 55 DEG C under vacuum.

[0008] Further, the temperature is maintained at 0-5 DEG C for 1 hour.

[0009] Further, the amount of 1,1,1-trifluoro-2-chloroethane added is 2-4 times the mass of the removed solid.

[0010] Further, the temperature for vacuum drying is not higher than 55 DEG C, and the drying time is 1-1.5 hours.

[0011] Further, the amount of dichloromethane added is (1-3):1 relative to the mass of the solid.

[0012] Further, the content of fluoride ions in the lithium bis(fluorosulfonyl)imide crude product is less than 30 ppm.

[0013] The beneficial effects of the technical scheme of the present application are: In the present application, 1,1,1-trifluoro-2-chloroethane is used to remove fluoride ions in lithium bis(fluorosulfonyl)imide, which can deeply remove impurities and does not introduce new impurities, and has strong process compatibility. The molecule of 1,1,1-trifluoro-2-chloroethane contains strong electronegative C-F bonds and polar C-Cl bonds, and the whole is weakly polar, which can form "dipole-dipole interaction and weak hydrogen bond" with fluoride ions. This specific interaction can make fluoride ions preferentially dissolve in 1,1,1-trifluoro-2-chloroethane phase, while LiFSI is almost insoluble in the solvent, so that selective extraction of fluoride ions can be realized. Compared with traditional solvents (such as dichloromethane), the solubility selectivity of 1,1,1-trifluoro-2-chloroethane for fluoride ions is increased by 3-5 times, which can reduce the content of fluoride ions in LiFSI from 200 ppm to less than 30 ppm, meeting the strict requirement of ≤50 ppm for high-end power batteries (traditional methods can only reduce to about 100 ppm). The solubility of 1,1,1-trifluoro-2-chloroethane in water is only 9200 mg / L and it is not miscible with water, so during the extraction process, the re-dissolution of fluoride ions into the LiFSI system due to water carried by the solvent can be avoided, thereby avoiding the secondary residue of fluoride ions. 1,1,1-trifluoro-2-chloroethane has a low boiling point, and can be separated from LiFSI at room temperature without the need for high-temperature heating, which can avoid the hydrolysis or decomposition of LiFSI. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0015] Example 1 After the reaction of lithium bis(fluorosulfonyl)imide was completed, the reaction material was filtered, the filtrate was transferred into a rotary evaporator, and the solvent was removed under vacuum at no more than 55°C. 1,1,1-Trifluoro-2-chloroethane was added to the removed solid material in an amount of 2 times the mass of lithium bis(fluorosulfonyl)imide, and the temperature was maintained at 0°C for 1 hour. 1,1,1-Trifluoro-2-chloroethane was distilled out at room temperature. The solid material from which 1,1,1-trifluoro-2-chloroethane was removed was rinsed once with dichloromethane in an amount of 1 times the mass. The rinsed solid material was dried under vacuum at no more than 55°C for 1 hour to obtain crude lithium bis(fluorosulfonyl)imide, wherein the content of fluoride ions was 28 ppm. All operations were performed under pure nitrogen protection.

[0016] Example 2 After the reaction of lithium bis(fluorosulfonyl)imide was completed, the reaction material was filtered, the filtrate was transferred into a rotary evaporator, and the solvent was removed under vacuum at no more than 55°C. 1,1,1-Trifluoro-2-chloroethane was added to the removed solid material in an amount of 3 times the mass of lithium bis(fluorosulfonyl)imide, and the temperature was maintained at 0°C for 1 hour. 1,1,1-Trifluoro-2-chloroethane was distilled out at room temperature. The solid material from which 1,1,1-trifluoro-2-chloroethane was removed was rinsed once with dichloromethane in an amount of 1 times the mass. The rinsed solid material was dried under vacuum at no more than 55°C for 1 hour to obtain crude lithium bis(fluorosulfonyl)imide, wherein the content of fluoride ions was 26 ppm. All operations were performed under pure nitrogen protection.

[0017] Example 3 After the reaction of lithium bis(fluorosulfonyl)imide is completed, the reaction material is filtered, the filtrate is transferred into a rotary evaporator, the solvent is removed under vacuum at no more than 55°C, 1,1,1-trifluoro-2-chloroethane is added to the removed solid material in an amount of 3 times the mass of lithium bis(fluorosulfonyl)imide, stirring is maintained at 0°C for 1 hour, 1,1,1-trifluoro-2-chloroethane is distilled off at room temperature; the washing and distillation process of 1,1,1-trifluoro-2-chloroethane is repeated once again, the solid material from which 1,1,1-trifluoro-2-chloroethane is removed is rinsed once with dichloromethane in an amount of 2 times the mass, the rinsed solid material is dried under vacuum at no more than 55°C for 1 hour to obtain lithium bis(fluorosulfonyl)imide crude product, wherein the content of fluoride ions is 25PPm. All operations are carried out under pure nitrogen protection.

[0018] Example 4 After the reaction of lithium bis(fluorosulfonyl)imide is completed, the reaction material is filtered, the filtrate is transferred into a rotary evaporator, the solvent is removed under vacuum at no more than 55°C, 1,1,1-trifluoro-2-chloroethane is added to the removed solid material in an amount of 4 times the mass of lithium bis(fluorosulfonyl)imide, stirring is maintained at 0°C for 1 hour, 1,1,1-trifluoro-2-chloroethane is distilled off at room temperature; the washing and distillation process of 1,1,1-trifluoro-2-chloroethane is repeated once again, the solid material from which 1,1,1-trifluoro-2-chloroethane is removed is rinsed once with dichloromethane in an amount of 2 times the mass, the rinsed solid material is dried under vacuum at no more than 55°C for 1 hour to obtain lithium bis(fluorosulfonyl)imide crude product, wherein the content of fluoride ions is 25PPm. All operations are carried out under pure nitrogen protection.

[0019] Example 5 After the reaction of lithium bis(fluorosulfonyl)imide is completed, the reaction material is filtered, the filtrate is transferred into a rotary evaporator, the solvent is removed under vacuum at no more than 55°C, 1,1,1-trifluoro-2-chloroethane is added to the removed solid material in an amount of 4 times the mass of lithium bis(fluorosulfonyl)imide, stirring is maintained at 0°C for 1 hour, 1,1,1-trifluoro-2-chloroethane is distilled off at room temperature; the washing and distillation process of 1,1,1-trifluoro-2-chloroethane is repeated once again, the solid material from which 1,1,1-trifluoro-2-chloroethane is removed is rinsed once with dichloromethane in an amount of 2 times the mass, the rinsed solid material is dried under vacuum at no more than 55°C for 1 hour to obtain lithium bis(fluorosulfonyl)imide crude product, wherein the content of fluoride ions is 25PPm. All operations are carried out under pure nitrogen protection.

[0020] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment need necessarily contain every independent aspect described in the specification, and descriptions of a particular embodiment herein in terms of a particular independent aspect should be considered in the context of the specification as a whole and in the context of other embodiments described herein.

Claims

1. A method for removing fluoride ions from lithium bis(fluorosulfonyl)imide, characterized in that, The removal method includes the following steps: After the reaction of lithium bis(fluorosulfonyl)imide is completed, the reaction material is filtered to remove the solvent. 1,1,1-trifluoro-2-chloroethane is added to the solid obtained, and the temperature is maintained at 0~5℃ and stirred for a period of time. The temperature is raised to room temperature to remove 1,1,1-trifluoro-2-chloroethane. The washing and distillation process of 1,1,1-trifluoro-2-chloroethane is repeated once. The solid obtained after removing 1,1,1-trifluoro-2-chloroethane is washed with dichloromethane. The washed solid is dried under vacuum to obtain crude lithium bis(fluorosulfonyl)imide. All the above operations are carried out under pure nitrogen protection.

2. The method for removing fluoride ions from lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The solvent removal conditions are no more than 55°C under vacuum.

3. The method for removing fluoride ions from lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, Maintain the temperature at 0~5℃ and stir for 1 hour.

4. The method for removing fluoride ions from lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The amount of 1,1,1-trifluoro-2-chloroethane added is 2 to 4 times the amount of solid material removed.

5. The method for removing fluoride ions from lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The vacuum drying temperature shall not exceed 55℃, and the drying time shall be 1 to 1.5 hours.

6. The method for removing fluoride ions from lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The mass ratio of the amount of dichloromethane added to the mass of the solid is (1~3):

1.

7. The method for removing fluoride ions from lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The crude bis(fluorosulfonyl)imide lithium contains less than 30 ppm of fluoride ions.