Purification process of lithium bis (fluorosulfonyl) imide

Abstract

The invention relates to the technical field of chemical purification, in particular to a purification process of lithium bis (fluorosulfonyl) imide. Comprising the following steps: mixing a crude product lithium bis (fluorosulfonyl) imide with a good solvent, dissolving, and cooling to obtain a lithium bis (fluorosulfonyl) imide solution; and carrying out gradient cooling crystallization on the obtained lithium bis (fluorosulfonyl) imide solution, adding a poor solvent before recrystallization to promote precipitation to obtain lithium bis (fluorosulfonyl) imide crystals, and carrying out drying treatment to obtain pure lithium bis (fluorosulfonyl) imide. According to the method, lithium bis (fluorosulfonyl) imide is dissolved by using a single solvent, recrystallization is performed by adopting a gradient cooling mode, and a poor solvent is added before recrystallization is finished to promote crystallization, so that the recrystallization yield is effectively improved, the recrystallization time is shortened, the energy consumption is reduced, and the method has very good green and environment-friendly advantages. And the product is high in purity, stable in quality and simple to operate. All solvents can be recycled and reused.

Description

Technical Field

[0001] This invention relates to the field of chemical purification technology, specifically to a purification process for lithium bis(fluorosulfonyl)imide. Background Technology

[0002] Lithium bisfluorosulfonyl imide (LiFSI), as a high-performance electrolyte salt in the lithium-ion battery field, has become a core material for next-generation power battery electrolytes due to its high ionic conductivity, wide electrochemical window, and excellent low-temperature performance. However, the LiFSI molecule contains strongly polar groups, making it prone to adsorbing moisture and metal ion impurities during production. Even after purification, it remains hygroscopic, making it difficult to maintain stable purity control. This directly affects battery cycle life and safety performance. Therefore, efficient purification technology is a key bottleneck for the industrialization of LiFSI. Currently, LiFSI purification mainly revolves around dissolution, impurity removal, and crystallization, but all methods have significant limitations.

[0003] Chinese invention patent application CN109923063A utilizes an organic solvent to form an azeotrope with LiFSI aqueous solution, followed by two dehydration processes and evaporation concentration to obtain crystals. While this achieves the target purity, the need for multiple evaporation operations results in significantly high energy consumption, hindering large-scale, low-cost production. Chinese invention patent CN113582145B employs a mixed system of inert solvent and crude product, adding a good solvent at 0-20℃ to promote dissolution, followed by filtration and distillation purification. Although this scheme achieves the required purity, it relies on a dual-solvent system, increasing solvent procurement and recycling costs and leading to low product yields due to solvent compatibility issues. Chinese invention patent application CN115367718A achieves a purity of over 99.95% and a moisture content of <20ppm through gentle dehydration of bismuth trichloride / antimony trichloride at 20-40℃, combined with evaporation concentration and recrystallization. While this optimizes dehydration efficiency, it requires the additional introduction of a metal halide dehydrating agent, posing a risk of residual trace metal impurities. Summary of the Invention

[0004] This invention provides a purification process for lithium difluorosulfonylimide, comprising the following steps: dissolving crude lithium difluorosulfonylimide in a good solvent, cooling to obtain a lithium difluorosulfonylimide solution; subjecting the obtained lithium difluorosulfonylimide solution to gradient cooling crystallization, and adding a poor solvent before the recrystallization is completed to obtain lithium difluorosulfonylimide crystals, which are then dried to obtain pure lithium difluorosulfonylimide.

[0005] The purity of the crude lithium difluorosulfonylimide is 70-95% (mass purity).

[0006] Optionally, the purity of the crude lithium difluorosulfonylimide is 80-95%.

[0007] The good solvent includes one of ethyl acetate, ethanol, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl formate, acetonitrile, and methyl butyl ether.

[0008] Optionally, the good solvent includes one of ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, and acetonitrile.

[0009] The undesirable solvents include one of the following: n-hexane, cyclohexane, dichloromethane, dichloroethane, and tetrachloroethane.

[0010] Optionally, the undesirable solvent includes one of n-hexane, cyclohexane, dichloromethane, and tetrachloroethane.

[0011] The weight ratio of the good solvent to the bad solvent is 1:(1-5).

[0012] Optionally, the weight ratio of the good solvent to the poor solvent is 1:(1-2).

[0013] The dissolution temperature is 0-65℃.

[0014] Optionally, the dissolution temperature is 0-50°C.

[0015] The mass ratio of the crude lithium difluorosulfonylimide to the good solvent is (50-200):100.

[0016] Optionally, the crude lithium difluorosulfonylimide is mixed with a good solvent at a mass ratio of 1:(1-2).

[0017] The filter paper used for filtration has a pore size of 0.5-1.5 micrometers.

[0018] Optionally, the filter paper used for filtration has a pore size of 0.8-1.2 micrometers.

[0019] The gradient cooling crystallization includes the following parameters: cooling to -20 to 0℃ at a rate of 1-15℃ / h, and crystallizing for 1-15h.

[0020] Optionally, the gradient cooling crystallization includes the following parameters: cooling to -20 to 0°C at a rate of 6-15°C / h, and crystallizing for 2-8 hours.

[0021] Optionally, the gradient cooling crystallization includes the following parameters: cooling to -20 to 0°C at a rate of 6-12°C / h, and crystallizing for 2-5 hours.

[0022] This study found that by adding a poor solvent before the end of recrystallization and limiting the gradient cooling crystallization process to include the following parameters: cooling at 1-15℃ / h to -20-0℃, crystallizing for 1-15h, the recrystallization time can be reduced while effectively promoting the precipitation of the purified product. This also increases the yield of lithium difluorosulfonylimide by >95% while reducing the recrystallization time. Lithium difluorosulfonylimide, due to the presence of strongly polar groups in its molecule, easily forms a stable solvation system in good solvents. While simple cooling can reduce its solubility, the solute precipitation rate is slow, and the yield is easily limited due to excessively low supersaturation. Adding a poor solvent before the end of recrystallization can precisely increase the supersaturation of the system by reducing the overall polarity of the system and weakening the solvation effect between the good solvent and lithium difluorosulfonylimide. This rapidly disrupts the dissolution equilibrium of lithium difluorosulfonylimide, shortens the nucleation induction period, and promotes the faster precipitation of lithium difluorosulfonylimide from the solution, thus effectively reducing the recrystallization time. A specific gradient cooling program can achieve a kinetic balance between nucleation and crystal growth. This avoids the formation of a large number of small nuclei due to excessively rapid cooling, while also preventing excessively slow cooling from leading to a prolonged crystallization cycle and uneven solute diffusion. At the same time, a specific temperature reduces the solubility of lithium difluorosulfonylimide in the mixed solvent system, maximizing the reduction of unprecipitated solute in the solution. This provides a sufficient growth window for lithium difluorosulfonylimide crystals, ensuring complete crystal development and minimizing losses due to the dissolution-recrystallization cycle. The synergistic effect of the two not only accelerates the precipitation process of lithium bisfluorosulfonylimide, but also reduces solute residue and impurity interference by regulating the crystal growth process, ultimately achieving the dual effect of shortening the recrystallization time and achieving a lithium bisfluorosulfonylimide yield of >95%.

[0023] The drying temperature is 30-70℃, and the time is 2-18 hours.

[0024] Optionally, the drying temperature is 40-50℃ and the time is 4-8 hours.

[0025] Beneficial effects 1. The yield of lithium bis(fluorosulfonyl)imide obtained by the purification process of the present invention can be >90%.

[0026] 2. The purity of lithium bis(fluorosulfonyl)imide obtained by the purification process of this invention can be ≥99.9%.

[0027] 3. The lithium difluorosulfonylimide obtained by the purification process of this invention has sodium ion ≤5ppm, potassium ion ≤5ppm, chloride ion ≤10ppm, fluoride ion ≤10ppm, sulfate ion ≤15ppm, and water ≤25ppm.

[0028] 4. By adding a poor solvent before the end of recrystallization, the precipitation of lithium bisfluorosulfonylimide can be effectively promoted, and the recrystallization time can be reduced.

[0029] 5. The present invention defines gradient cooling crystallization with the following parameters: cooling to -20-0℃ at a rate of 1-15℃ / h, crystallizing for 1-15h, thereby reducing recrystallization time and increasing the yield of lithium difluorosulfonylimide by >95%. Detailed Implementation

[0030] Example 1 A purification process for lithium difluorosulfonylimide comprises the following steps: 300g of crude lithium difluorosulfonylimide is mixed with 300g of a good solvent (ethyl acetate) for dissolution, with the dissolution temperature controlled not exceeding 40℃. After cooling to room temperature, the solution is filtered through a 0.8-micron filter membrane to remove insoluble matter and cooled to obtain a lithium difluorosulfonylimide solution. The obtained lithium difluorosulfonylimide solution is cooled to -10℃ at a rate of 6℃ / h, and 400g of a poor solvent (tetrachloroethane) is added. The solution is then recrystallized at -10℃ for 5h to obtain lithium difluorosulfonylimide crystals. After drying (40℃, negative pressure 150Pa, 6h), pure lithium difluorosulfonylimide is obtained.

[0031] The physical properties of the crude and pure lithium difluorosulfonylimide are shown in Table 1.

[0032] Example 2 A purification process for lithium difluorosulfonylimide comprises the following steps: 500g of crude lithium difluorosulfonylimide is mixed with 800g of a good solvent (dimethyl carbonate) for dissolution, with the dissolution temperature controlled not exceeding 40℃. After cooling to room temperature, it is filtered through a 0.8-micron filter membrane to remove insoluble matter and cooled to obtain a lithium difluorosulfonylimide solution. The obtained lithium difluorosulfonylimide solution is cooled to -8℃ at a rate of 12℃ / h, and 1000g of a poor solvent (cyclohexane) is added. Recrystallization is carried out at -8℃ for 2h to obtain lithium difluorosulfonylimide crystals. After drying (drying at 50℃ and negative pressure 150Pa for 8h), pure lithium difluorosulfonylimide is obtained.

[0033] The physical properties of the crude and pure lithium difluorosulfonylimide are shown in Table 1.

[0034] Example 3 A purification process for lithium difluorosulfonylimide comprises the following steps: 500g of crude lithium difluorosulfonylimide is mixed with 700g of a good solvent (acetonitrile) for dissolution, with the dissolution temperature controlled not exceeding 40℃. After cooling to room temperature, it is filtered through a 0.8-micron filter membrane to remove insoluble matter and cooled to obtain a lithium difluorosulfonylimide solution. The obtained lithium difluorosulfonylimide solution is cooled to -20℃ at a rate of 10℃ / h, and 1400g of a poor solvent (n-hexane) is added. Recrystallization is carried out at -20℃ for 3h to obtain lithium difluorosulfonylimide crystals. After drying (drying at 45℃ and negative pressure 150Pa for 4h), pure lithium difluorosulfonylimide is obtained.

[0035] The physical properties of the crude and pure lithium difluorosulfonylimide are shown in Table 1.

[0036] Example 4 A purification process for lithium difluorosulfonylimide comprises the following steps: 1000g of crude lithium difluorosulfonylimide is mixed with 1000g of a good solvent (ethyl methyl carbonate) for dissolution, with the dissolution temperature controlled not exceeding 50℃. After cooling to room temperature, it is filtered through a 0.8-micron filter membrane to remove insoluble matter and cooled to obtain a lithium difluorosulfonylimide solution. The obtained lithium difluorosulfonylimide solution is cooled to -15℃ at a rate of 10℃ / h, and 1800g of a poor solvent (dichloromethane) is added. Recrystallization is carried out at -15℃ for 2h to obtain lithium difluorosulfonylimide crystals. After drying (drying at 50℃ and negative pressure 130Pa for 5h), pure lithium difluorosulfonylimide is obtained.

[0037] The physical properties of the crude and pure lithium difluorosulfonylimide are shown in Table 1.

[0038] Comparative Example 1 The specific implementation method is the same as in Example 1; the difference is that no undesirable solvent is added before the recrystallization is completed in Comparative Example 1.

[0039] Comparative Example 2 The specific implementation method is the same as in Example 2; the difference is that no undesirable solvent is added before the recrystallization is completed in Comparative Example 2, and the crystallization time is extended to 18 hours.

[0040] Comparative Example 3 The specific implementation method is the same as in Example 3; the difference is that no undesirable solvent is added before the recrystallization is completed in Comparative Example 3, and the crystallization time is extended to 36 hours.

[0041] Performance testing methods The physical properties of lithium difluorosulfonylimide before and after purification in the examples and comparative examples were analyzed and tested. The test data are listed in Table 1, where "-" indicates that it was not detected.

[0042] Performance test data Table 1

Claims

1. A purification process for lithium bis(fluorosulfonyl)imide, characterized in that, Includes the following steps: Crude lithium difluorosulfonyl imide was dissolved in a good solvent, cooled, and filtered to obtain a lithium difluorosulfonyl imide solution. The obtained lithium difluorosulfonylimide solution was subjected to gradient cooling recrystallization, and a poor solvent was added before the recrystallization was completed to obtain lithium difluorosulfonylimide crystals. After drying, pure lithium difluorosulfonylimide was obtained.

2. The purification process for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The purity of the crude lithium difluorosulfonylimide is 70-95 wt%.

3. The purification process for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The good solvent includes one of ethyl acetate, ethanol, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl formate, acetonitrile, and methyl butyl ether.

4. The purification process for lithium bis(fluorosulfonyl)imide according to claim 3, characterized in that, The undesirable solvents include one of the following: n-hexane, cyclohexane, dichloromethane, dichloroethane, and tetrachloroethane.

5. The purification process for lithium bis(fluorosulfonyl)imide according to claim 4, characterized in that, The weight ratio of the good solvent to the bad solvent is 1:(1-5).

6. The purification process for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The dissolution temperature is 0-65℃.

7. The purification process for lithium bis(fluorosulfonyl)imide according to claim 5 or 6, characterized in that, The mass ratio of the crude lithium difluorosulfonylimide to the good solvent is (50-200):

100.

8. The purification process for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The filter paper used for filtration has a pore size of 0.5-1.5 micrometers.

9. The purification process for lithium bis(fluorosulfonyl)imide according to any one of claims 1-6, characterized in that, The gradient cooling recrystallization includes the following parameters: cooling to -20 to 0°C at a rate of 1-15°C / h, and crystallizing for 1-15 hours.

10. The purification process for lithium bis(fluorosulfonyl)imide according to claim 9, characterized in that, The drying temperature is 30-70℃, and the time is 2-18 hours.

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