Purification method of lithium bis (fluorosulfonyl) imide

Abstract

The invention provides a purification method of lithium bis (fluorosulfonyl) imide, which comprises the following steps: dissolving a lithium bis (fluorosulfonyl) imide crude product in a solvent to obtain a lithium bis (fluorosulfonyl) imide crude product solution; performing reverse osmosis on the lithium bis (fluorosulfonyl) imide crude product solution through a reverse osmosis assembly to obtain a reverse osmosis concentrated solution and a penetrating fluid; adding a solvent into the obtained reverse osmosis concentrated solution for dilution, and then purifying through reverse osmosis of a reverse osmosis assembly to obtain pure product concentrated solution and penetrating fluid of lithium bis (fluorosulfonyl) imide; and carrying out reduced pressure evaporation on the obtained pure lithium bis (fluorosulfonyl) imide concentrated solution to remove the solvent, thereby obtaining the high-purity lithium bis (fluorosulfonyl) imide. The invention provides a purification method of lithium bis (fluorosulfonyl) imide. The preparation method is simple, efficient and environment-friendly, and the lithium bis (fluorosulfonyl) imide is high in yield, green, environment-friendly and low in production cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of preparation of lithium bisfluorosulfonimide, and relates to a purification method of lithium bisfluorosulfonimide. BACKGROUND

[0002] Lithium bisfluorosulfonimide is also known as LiFSI. Because lithium bisfluorosulfonimide has excellent low-temperature performance and high-voltage compatibility, excellent thermal stability and safety, it can be used as a next-generation lithium ion battery electrolyte lithium salt to replace lithium hexafluorophosphate. At present, lithium bisfluorosulfonimide is usually mixed with lithium hexafluorophosphate as a lithium ion battery electrolyte additive and is applied to the electrolyte of a rechargeable lithium battery to improve the capacity of the battery and the electrochemical performance of the battery. In addition, lithium bisfluorosulfonimide also has important industrial applications as a polymerization catalyst and an industrial antistatic agent. The lithium bisfluorosulfonimide added to the electrolyte requires that the purity, moisture, acidity, chloride ions and residual solvents meet certain technical indexes. At present, the preparation of lithium bisfluorosulfonimide mainly includes three steps of chlorination, fluorination and salt formation: synthesis of bischlorosulfonimide, synthesis of bisfluorosulfonimide and synthesis of lithium bisfluorosulfonimide. The synthesis process involves many raw materials and equipment, and a large amount of heat is generated during the reaction, so that the lithium bisfluorosulfonimide synthesized at one time is a crude salt with high water, acid, chloride ion and residual solvents. Therefore, the lithium bisfluorosulfonimide needs to be purified to obtain a salt with qualified indexes.

[0003] At present, high-purity lithium bisfluorosulfonimide is usually prepared by solution crystallization or a combination of synthesis and reduced pressure distillation and crystallization. However, the process is complex, time-consuming, and introduces organic solvents, which seriously pollutes the environment. Subsequent solvent recovery and treatment problems lead to high cost and energy consumption.

[0004] Therefore, it is necessary to provide a new technical solution. SUMMARY

[0005] In order to solve the above technical problems and overcome the deficiencies in the prior art, the application provides a purification method of lithium bisfluorosulfonimide, which has a simple and efficient preparation method, high yield of lithium bisfluorosulfonimide, green environmental protection and low production cost.

[0006] In order to achieve the above purpose, the following technical solutions are adopted:

[0007] The application provides a purification method of lithium bisfluorosulfonimide, which includes the following steps:

[0008] S1, dissolving lithium bisfluorosulfonimide crude product in a solvent to obtain a lithium bisfluorosulfonimide crude product solution;

[0009] S2, subjecting the lithium bisfluorosulfonimide crude product solution to reverse osmosis through a reverse osmosis assembly to obtain a reverse osmosis concentrate and a permeate.

[0010] S3, adding solvent to the reverse osmosis concentrate obtained in step S2 to dilute, and then purifying by reverse osmosis component to obtain pure bisfluorosulfonylimide lithium concentrate and permeate;

[0011] S4, removing the solvent from the pure bisfluorosulfonylimide lithium concentrate obtained in step S3 by vacuum evaporation to obtain high-purity bisfluorosulfonylimide lithium.

[0012] Further, the solvent in steps S1 and S3 is one or a combination of methanol, ethanol and water.

[0013] Further, in step 1, the molar ratio of bisfluorosulfonylimide lithium crude product to solvent is 1:8-20, the dissolution temperature is 20-30℃, and the dissolution time is 0.5-1h.

[0014] In step S3, the volume ratio of reverse osmosis concentrate to solvent is 1:1.5-3.3.

[0015] Further, in step S3, the volume ratio of reverse osmosis concentrate to solvent is 1:2.

[0016] The volume of the pure bisfluorosulfonylimide lithium concentrate obtained in step S3 is the same as the volume of the reverse osmosis concentrate obtained in step S2.

[0017] Further, step S3 is repeated at least once, wherein the reverse osmosis concentrate used in each repetition of step S3 is the reverse osmosis concentrate prepared in the previous step S3.

[0018] Further, step S3 is repeated 3-10 times.

[0019] Further, step S3 is repeated 5-7 times.

[0020] Further, in steps S2 and S3, the operating pressure of the reverse osmosis component is 15-50 bar, the recovery rate is 50%-70%, and the operating temperature is 22-25℃.

[0021] Further, the reverse osmosis component comprises a reverse osmosis membrane, the reverse osmosis is an organic solvent-resistant reverse osmosis membrane, and the desalination rate of the reverse osmosis membrane is 98.9%-99.2%.

[0022] In step S4, the temperature for vacuum evaporation is 10-60℃, the vacuum degree is 100-600Pa, and the time is 30-50℃.

[0023] Further, it further comprises a solvent recovery step, specifically:

[0024] The permeate obtained from step S2 and step S3 is purified through a secondary reverse osmosis assembly, wherein the operating pressure of the secondary reverse osmosis assembly is 10-25 bar, the recovery rate is 60%-80%, the operating temperature is 22-25 DEG C, and the reverse osmosis membrane of the secondary reverse osmosis assembly is an organic solvent-resistant reverse osmosis membrane.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] (1) The purification method of lithium bisfluorosulfonylimide of the present application can purify lithium bisfluorosulfonylimide through reverse osmosis concentration, and obtain high-purity lithium bisfluorosulfonylimide, which is simple, efficient and more economical compared with the multi-step removal method in the prior art.

[0027] (2) The purification method of lithium bisfluorosulfonylimide of the present application has high yield of lithium bisfluorosulfonylimide, and can greatly reduce the solvent to be evaporated in the final evaporation treatment step, improve the evaporation efficiency, reduce the energy consumption, and reduce the production cost.

[0028] (3) The purification method of lithium bisfluorosulfonylimide of the present application can realize the recycling of waste organic solvents, which is helpful for environmental protection and cost reduction.

DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0030] Figure 1 The structure block diagram of the purification system of lithium bisfluorosulfonylimide of the present application;

[0031] Figure 2 The process flow diagram of the purification system of lithium bisfluorosulfonylimide of the present application.

[0032] Wherein, 1-dissolution module, 2-concentration module, 3-reuse module, 4-evaporation crystallization module, 21-first conveying device, 22-reverse osmosis assembly, 31-liquid storage tank, 32-second conveying device, 33-secondary reverse osmosis assembly, 34-reuse tank, 35-reflux device.

DETAILED DESCRIPTION

[0033] To further help understand the technical solutions of the present application, below, through providing several specific implementation examples, the technical solutions of the present application are described more specifically, all the described examples are only part of the embodiments of the present application, rather than all; the following specific examples can be combined with each other, and the same or similar concepts or processes in some examples can not be described again.

[0034] The purification method of lithium bisfluorosulfonylimide of the present application adopts the following test method:

[0035] The content of lithium bisfluorosulfonylimide obtained in each example is tested by anion chromatography with internal standard method.

[0036] The test method of desalination rate of reverse osmosis membrane in the reverse osmosis assembly in each example adopts salinity meter method: the test solution is 2000 ppm sodium chloride, the pressure is 1.55 Mpa, the temperature is 25℃, and the membrane surface flow rate is ≥0.45 m / s.

[0037] Example 1

[0038] 1 kg of lithium bisfluorosulfonylimide crude product (purity of 92.1 wt%) is added to 3 L of methanol solution, the temperature is kept at 25±5℃, and the solution is fully stirred and dissolved for 30 min to obtain a lithium bisfluorosulfonylimide crude product solution. The lithium bisfluorosulfonylimide crude product solution is passed into a reverse osmosis assembly by a high-pressure pump, the operating pressure of the reverse osmosis assembly is 45 bar, and the temperature is 22-25℃; when the operating recovery rate is 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate are obtained. The obtained 1 L of reverse osmosis concentrate is diluted with 1 L of methanol and then passed into the reverse osmosis assembly by a high-pressure pump for concentration, the operating pressure of the reverse osmosis assembly is 45 bar, and the temperature is 22-25℃; when the operating recovery rate is 50%, 1 L of reverse osmosis concentrate and 1 L of permeate are obtained; the obtained 1 L of reverse osmosis concentrate is diluted with 1 L of methanol and then passed into the reverse osmosis assembly for concentration, and the dilution and concentration steps are repeated for a total of 5 times to obtain a lithium bisfluorosulfonylimide pure product concentrate. The obtained lithium bisfluorosulfonylimide pure product concentrate is subjected to vacuum evaporation at a temperature of 30℃ and a vacuum degree of 200 Pa to obtain high-purity lithium bisfluorosulfonylimide, and the product indexes are shown in Table 1.

[0039] The reverse osmosis permeate obtained in all the above steps is passed into a secondary reverse osmosis assembly by a high-pressure pump, the operating pressure of the secondary reverse osmosis assembly is 20 bar, and the operating temperature is 22-25℃; when the operating recovery rate is 70%, a secondary reverse osmosis concentrate and a secondary reverse osmosis permeate are obtained; the secondary reverse osmosis concentrate is an impurity-enriched methanol solution, the secondary reverse osmosis permeate is a purified methanol solution, and the secondary reverse osmosis permeate can be reused in the lithium bisfluorosulfonylimide crude product dissolution step.

[0040] The reverse osmosis membrane in the reverse osmosis assembly of the embodiment is an organic solvent-resistant reverse osmosis membrane, and the desalination rate thereof is 99.2%. The reverse osmosis membrane in the secondary reverse osmosis assembly is an organic solvent-resistant reverse osmosis membrane, and the desalination rate thereof is 99.6%.

[0041] Example 2

[0042] The 1 kg of crude lithium bisfluorosulfonylimide (with a purity of 92.1 wt%) was added to 3 L of water solution, and the temperature was kept at 25±5°C. The crude lithium bisfluorosulfonylimide was dissolved by stirring for 30 min. The crude lithium bisfluorosulfonylimide solution was introduced into the reverse osmosis assembly by using a high-pressure pump. The operating pressure of the reverse osmosis assembly was 20 bar, and the temperature was 22-25°C. When the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted with 1 L of water, and then introduced into the reverse osmosis assembly by using a high-pressure pump for concentration. The operating pressure of the reverse osmosis assembly was 20 bar, and the temperature was 22-25°C. When the operating recovery rate was 50%, 1 L of reverse osmosis concentrate and 1 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted with 1 L of water, and then introduced into the reverse osmosis assembly for concentration. The dilution and concentration steps were repeated for 5 times. The pure lithium bisfluorosulfonylimide concentrate was obtained. The pure lithium bisfluorosulfonylimide concentrate was subjected to vacuum evaporation at a temperature of 50°C and a vacuum degree of 300 Pa to obtain high-purity lithium bisfluorosulfonylimide. The product indexes are shown in Table 1. The reverse osmosis membrane in the reverse osmosis assembly is an organic solvent-resistant reverse osmosis membrane, and the desalination rate thereof is 99.2%.

[0043] Example 3

[0044] The 1 kg of crude lithium bisfluorosulfonimide (92.1 wt% purity) was added into 3 L of ethanol solution, the temperature was kept at 25±5℃, and the solution was dissolved for 30 min under sufficient stirring to obtain a crude lithium bisfluorosulfonimide solution. The crude lithium bisfluorosulfonimide solution was passed into a reverse osmosis assembly by using a high-pressure pump, the operating pressure of the reverse osmosis assembly was 50 bar, and the temperature was 22-25℃, when the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted with 1 L of ethanol and then passed into the reverse osmosis assembly by using a high-pressure pump for concentration, the operating pressure of the reverse osmosis assembly was 50 bar, and the temperature was 22-25℃, when the operating recovery rate was 50%, 1 L of reverse osmosis concentrate and 1 L of permeate were obtained, and the 1 L of reverse osmosis concentrate was diluted with 1 L of ethanol and then passed into the reverse osmosis assembly for concentration, and the dilution and reverse osmosis concentration steps were repeated for 5 times to obtain a pure lithium bisfluorosulfonimide concentrate. The pure lithium bisfluorosulfonimide concentrate was subjected to vacuum evaporation at a temperature of 35℃ and a vacuum degree of 200 Pa to obtain high-purity lithium bisfluorosulfonimide, and the product indexes are shown in Table 1. The permeate obtained in the above steps was passed into a secondary reverse osmosis assembly by using a high-pressure pump, the operating pressure of the secondary reverse osmosis assembly was 20 bar, and the operating temperature was 22-25℃, when the operating recovery rate was 70%, a secondary reverse osmosis concentrate and a secondary reverse osmosis permeate were obtained. The secondary reverse osmosis concentrate was an impurity-enriched ethanol solution, and the secondary reverse osmosis permeate was a purified ethanol solution, and the secondary reverse osmosis permeate could be reused in the crude lithium bisfluorosulfonimide dissolution step. The reverse osmosis membrane in the reverse osmosis assembly was an organic solvent-resistant reverse osmosis membrane, and the desalination rate was 99.2%, and the reverse osmosis membrane in the secondary reverse osmosis assembly was an organic solvent-resistant reverse osmosis membrane, and the desalination rate was 99.6%.

[0045] Example 4

[0046] The 1 kg of crude lithium bisfluorosulfonimide (with a purity of 90.1 wt%) was added into 3 L of methanol solution, and the temperature was kept at 25±5 °C, and the solution was dissolved for 30 min under sufficient stirring to obtain a crude lithium bisfluorosulfonimide solution. The crude lithium bisfluorosulfonimide solution was passed into a reverse osmosis assembly by using a high-pressure pump, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25 °C, and when the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted with 1 L of methanol and then passed into the reverse osmosis assembly by using a high-pressure pump for concentration, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25 °C, and when the operating recovery rate was 50%, 1 L of reverse osmosis concentrate and 1 L of permeate were obtained, and the 1 L of reverse osmosis concentrate was diluted with 1 L of methanol and then passed into the reverse osmosis assembly for concentration, and the dilution and reverse osmosis concentration steps were repeated for 7 times to obtain a pure lithium bisfluorosulfonimide concentrate. The pure lithium bisfluorosulfonimide concentrate was subjected to vacuum evaporation at a temperature of 30 °C and a vacuum degree of 200 Pa to obtain high-purity lithium bisfluorosulfonimide, and the product indexes are shown in Table 1. The permeate of the reverse osmosis obtained in the above steps was passed into a secondary reverse osmosis assembly by using a high-pressure pump, and the operating pressure of the secondary reverse osmosis assembly was 20 bar, and the operating temperature was 22-25 °C, and when the operating recovery rate was 70%, a secondary reverse osmosis concentrate and a secondary reverse osmosis permeate were obtained. The secondary reverse osmosis concentrate was an impurity-enriched methanol solution, and the secondary reverse osmosis permeate was a purified methanol solution, and the secondary reverse osmosis permeate could be reused in the crude lithium bisfluorosulfonimide dissolution step. The reverse osmosis membrane in the reverse osmosis assembly was an organic solvent-resistant reverse osmosis membrane, and the desalination rate was 99.2%. The reverse osmosis membrane in the secondary reverse osmosis assembly was an organic solvent-resistant reverse osmosis membrane, and the desalination rate was 99.6%.

[0047] Example 5

[0048] The 1 kg of crude lithium bisfluorosulfonimide (92.1 wt% purity) was added into 3 L of methanol solution, and the temperature was kept at 25 ± 5 °C, and the solution was dissolved by stirring for 30 min to obtain a crude lithium bisfluorosulfonimide solution. The crude lithium bisfluorosulfonimide solution was passed into a reverse osmosis assembly by using a high-pressure pump, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25 °C, and when the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted by adding 2 L of methanol and then passed into the reverse osmosis assembly by using a high-pressure pump for concentration, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25 °C, and when the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted by adding 2 L of methanol and then passed into the reverse osmosis assembly for concentration, and the concentration was repeated for 5 times, and a pure lithium bisfluorosulfonimide concentrate was obtained. The pure lithium bisfluorosulfonimide concentrate was subjected to vacuum evaporation at a temperature of 30 °C and a vacuum degree of 200 Pa to obtain high-purity lithium bisfluorosulfonimide, and the product indexes are shown in Table 1. The permeate obtained in the above steps was passed into a secondary reverse osmosis assembly by using a high-pressure pump, and the operating pressure of the secondary reverse osmosis assembly was 20 bar, and the operating temperature was 22-25 °C, and when the operating recovery rate was 70%, a secondary reverse osmosis concentrate and a secondary reverse osmosis permeate were obtained. The secondary reverse osmosis concentrate was an impurity-enriched methanol solution, and the secondary reverse osmosis permeate was a purified methanol solution, and the secondary reverse osmosis permeate could be reused in the crude lithium bisfluorosulfonimide dissolving step. The reverse osmosis membrane in the reverse osmosis assembly was an organic solvent-resistant reverse osmosis membrane, and the desalination rate was 99.2%. The reverse osmosis membrane in the secondary reverse osmosis assembly was an organic solvent-resistant reverse osmosis membrane, and the desalination rate was 99.6%.

[0049] Comparative Example 1

[0050] The 1 kg of crude lithium bisfluorosulfonimide (92.1 wt% purity) was added into 3 L of methanol solution, and the temperature was kept at 25 ± 5 °C, and the solution was dissolved by stirring for 30 min to obtain a crude lithium bisfluorosulfonimide solution. The crude lithium bisfluorosulfonimide solution was passed into a reverse osmosis assembly by using a high-pressure pump, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25 °C, and when the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The reverse osmosis concentrate was subjected to vacuum evaporation at a temperature of 30 °C and a vacuum degree of 200 Pa to obtain lithium bisfluorosulfonimide, and the product indexes are shown in Table 1. The reverse osmosis membrane in the reverse osmosis assembly was an organic solvent-resistant reverse osmosis membrane, and the desalination rate was 99.2%.

[0051] Comparative Example 2

[0052] 2 kg of crude lithium difluorosulfonylimide (purity 92.1 wt%) was added to 6 L of methanol solution, and the temperature was maintained at 25 ± 5 °C. The solution was stirred thoroughly for 30 min to obtain a crude lithium difluorosulfonylimide solution. The crude lithium difluorosulfonylimide solution was then passed through a reverse osmosis (RO) module using a high-pressure pump. The RO module operated at a pressure of 45 bar and a temperature of 22-25 °C. When the recovery rate reached 66.7%, 2 L of RO concentrate and 4 L of permeate were obtained. The 2 L of RO concentrate was then passed through the RO module again using a high-pressure pump for further concentration. The RO module operated at a pressure of 45 bar and a temperature of 22-25 °C. When the recovery rate reached 50%, 1 L of RO concentrate and 1 L of permeate were obtained. The 1 L of RO concentrate was then subjected to reduced pressure evaporation at 30 °C and a vacuum of 200 Pa to obtain lithium difluorosulfonylimide. The product specifications are shown in Table 1. The reverse osmosis membrane in the reverse osmosis module is an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.2%.

[0053] Comparative Example 3

[0054] 1 kg of crude lithium difluorosulfonylimide (92.1 wt% purity) was added to 3 L of methanol solution. The temperature was maintained at 25 ± 5 °C, and the solution was stirred thoroughly for 30 min to obtain a crude lithium difluorosulfonylimide solution. The crude lithium difluorosulfonylimide solution was then passed through a reverse osmosis (RO) module using a high-pressure pump. The RO module operated at 45 bar and a temperature of 22-25 °C. When the recovery rate reached 66.7%, 1 L of RO concentrate and 2 L of permeate were obtained. 1 L of methanol was added to the 1 L of RO concentrate for dilution, and the solution was then passed through the RO module again using a high-pressure pump for concentration. The RO module operated at 45 bar and a temperature of 22-25 °C. When the recovery rate reached 50%, 1 L of RO concentrate and 1 L of permeate were obtained. 1 L of the RO concentrate was then diluted with 1 L of methanol and concentrated again using the RO module. This dilution and RO concentration process was repeated 5 times to obtain a concentrated lithium difluorosulfonylimide solution. The lithium difluorosulfonylimide concentrate was subjected to reduced pressure evaporation at 30°C and a vacuum of 200 Pa to obtain lithium difluorosulfonylimide. The product specifications are shown in Table 1. The reverse osmosis membrane in the reverse osmosis module is an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.6%.

[0055] Comparative Example 4

[0056] The 1 kg crude lithium bisfluorosulfonimide (92.1 wt% purity) was added to 3 L of methanol solution, and the temperature was kept at 25±5°C, and the solution was dissolved by stirring for 30 min to obtain a crude lithium bisfluorosulfonimide solution. The crude lithium bisfluorosulfonimide solution was passed into a reverse osmosis assembly by using a high-pressure pump, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25°C, and when the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted with 1 L of methanol and then passed into the reverse osmosis assembly by using a high-pressure pump for concentration, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25°C, and when the operating recovery rate was 50%, 1 L of reverse osmosis concentrate and 1 L of permeate were obtained, and the 1 L of reverse osmosis concentrate was diluted with 1 L of methanol and then passed into the reverse osmosis assembly for concentration, and the dilution and concentration steps were repeated for a total of 5 times to obtain a lithium bisfluorosulfonimide concentrate. The lithium bisfluorosulfonimide concentrate was subjected to vacuum evaporation at a temperature of 30°C and a vacuum degree of 200 Pa to obtain lithium bisfluorosulfonimide, and the product indexes are shown in Table 1. The reverse osmosis membrane in the reverse osmosis assembly is an organic solvent-resistant reverse osmosis membrane, and the desalination rate is 98.3%.

[0057] Comparative Example 5

[0058] The 1 kg crude lithium bisfluorosulfonimide (92.1 wt% purity) was added to 3 L of methanol solution, and the temperature was kept at 25±5°C, and the solution was dissolved by stirring for 30 min to obtain a crude lithium bisfluorosulfonimide solution. The crude lithium bisfluorosulfonimide solution was passed into a reverse osmosis assembly by using a high-pressure pump, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25°C, and when the operating recovery rate was 66.7%, 1 L of reverse osmosis concentrate and 2 L of permeate were obtained. The 1 L of reverse osmosis concentrate was diluted with 1 L of methanol and then passed into the reverse osmosis assembly by using a high-pressure pump for concentration, and the operating pressure of the reverse osmosis assembly was 45 bar, and the temperature was 22-25°C, and when the operating recovery rate was 50%, 1 L of reverse osmosis concentrate and 1 L of permeate were obtained, and the 1 L of reverse osmosis concentrate was diluted with 1 L of methanol and then passed into the reverse osmosis assembly for concentration, and the dilution and concentration steps were repeated for a total of 5 times to obtain a lithium bisfluorosulfonimide concentrate. The lithium bisfluorosulfonimide concentrate was subjected to vacuum evaporation at a temperature of 30°C and a vacuum degree of 200 Pa to obtain lithium bisfluorosulfonimide, and the product indexes are shown in Table 1. The reverse osmosis membrane in the reverse osmosis assembly is an organic solvent-resistant reverse osmosis membrane, and the desalination rate is 98.3%.

[0059] Table 1

[0060]

[0061] As can be seen from Table 1, the solvents used in Examples 1-3 are methanol, water and ethanol respectively, and the purity and yield of the products obtained are relatively high. Compared with Example 1, the number of repetitions of the dilution and re-concentration in Example 4 is adjusted. Compared with Example 1, the dilution multiple in Example 5 is adjusted. As shown in Table 1, the purity and yield of the products obtained in the above examples are relatively high.

[0062] Compared with Examples 1-5 of the present application, Comparative Example 1 and Comparative Example 2 do not perform the dilution and reverse osmosis concentration step of step 3, and the purity of the products obtained is very low, indicating that reverse osmosis concentration alone cannot achieve good purification effect of the product. By repeatedly diluting and concentrating in step 3, and using the reverse osmosis concentrated solution prepared in the previous step S3 each time, high-purity lithium bisfluorosulfonylimide can be obtained, which is simpler, more efficient and more economical than the multi-step removal method in the prior art.

[0063] Comparative Example 3 and Comparative Example 4 show that the desalination rate of the reverse osmosis membrane in the reverse osmosis assembly has a great influence on the purity and yield of the product. Comparative Example 3 shows that when the desalination rate of the reverse osmosis membrane is high, the reverse osmosis assembly has a high retention rate of impurities, so that the impurities are retained together with the product in the concentrated solution, and a good purification effect cannot be achieved. When the desalination rate of the reverse osmosis membrane is low, as in Comparative Example 4, the retention rate of the product and impurities by the reverse osmosis assembly will decrease, so that a large amount of product and impurities will permeate into the reverse osmosis permeate, and the concentration of the product in the reverse osmosis concentrated solution will decrease significantly, resulting in a product with high purity but low yield. The desalination rate of the reverse osmosis membrane in the reverse osmosis assembly of the present application is 98.9%-99.2%, which can obtain a product with high purity and high yield.

[0064] Comparative Example 5 is to replace the reverse osmosis assembly in Example 1 with a nanofiltration assembly. Since the desalination rate of the nanofiltration assembly is lower than that of the reverse osmosis assembly, the retention rate of the product is low, and a large amount of product will permeate into the permeate, resulting in a low yield of the product. The present application uses a reverse osmosis assembly for concentration, which not only purifies lithium bisfluorosulfonylimide to obtain high-purity lithium bisfluorosulfonylimide, but also has a high product yield.

[0065] In summary, the purification method of lithium bisfluorosulfonylimide of the present application can purify lithium bisfluorosulfonylimide by reverse osmosis concentration, obtain high-purity lithium bisfluorosulfonylimide with a purity of up to 99.98%, and is simpler, more efficient and more economical than the multi-step removal method in the prior art.

[0066] The purification method of lithium bisfluorosulfonylimide of the present application has a high yield of lithium bisfluorosulfonylimide, with a yield of up to 98.6%, which is significantly improved compared with the comparative examples. The present application can greatly reduce the amount of solvent to be evaporated in the final evaporation treatment step, improve the evaporation efficiency, reduce energy consumption and production cost.

[0067] The purification method of the lithium bisfluorosulfonylimide of the present application can realize the recycling of waste organic solvents, which is helpful for environmental protection and cost reduction.

[0068] Please refer to Figure 1 and Figure 2 In another embodiment, the present application also provides a purification system of lithium bisfluorosulfonylimide, which is used for purifying lithium bisfluorosulfonylimide.

[0069] The purification system of lithium bisfluorosulfonylimide of the present application comprises a dissolving module 1, a concentration module 2 and an evaporation crystallization module 4.

[0070] The dissolving module 1 has an inlet end of the dissolving module and an outlet end of the dissolving module, the lithium bisfluorosulfonylimide crude product enters the dissolving module 1 through the inlet end of the dissolving module, and the lithium bisfluorosulfonylimide crude product is dissolved in the organic solvent in the dissolving module 1 to form a lithium bisfluorosulfonylimide crude product solution.

[0071] The concentration module 2 comprises a reverse osmosis assembly 22 and a first conveying device 21. The outlet end of the reverse osmosis assembly comprises a first outlet end of the reverse osmosis assembly and a second outlet end of the reverse osmosis assembly. The first conveying device 21 is arranged between the dissolving module 1 and the reverse osmosis assembly 22, the outlet end of the dissolving module 1 is connected with the inlet end of the first conveying device 21, the outlet end of the first conveying device 21 is connected with the inlet end of the reverse osmosis assembly 22, and the first outlet end of the reverse osmosis assembly 22 is connected with the inlet end of the evaporation crystallization module 4. The first conveying device 21 is a high-pressure pump. The first conveying device 21 is used for conveying the mixed solution formed by the dissolving module 1 to the reverse osmosis assembly 22, and the reverse osmosis membrane of the reverse osmosis assembly 22 purifies and concentrates the mixed solution to obtain a concentrated solution and a permeate.

[0072] The inlet end of the evaporation crystallization module is connected with the first outlet end of the reverse osmosis assembly, the concentrated solution obtained by the reverse osmosis assembly 22 enters the evaporation crystallization module 4 from the inlet end of the evaporation crystallization module through the first outlet end of the reverse osmosis assembly, and the evaporation crystallization module 4 performs evaporation crystallization treatment on the concentrated solution obtained by the reverse osmosis assembly 22 to obtain lithium bisfluorosulfonylimide pure product.

[0073] Please continue to refer to Figure 2 In one embodiment, the purification system further comprises a recycling module 3. The recycling module 3 performs secondary reverse osmosis purification on the permeate obtained by the reverse osmosis assembly 22 to obtain pure organic solvent, which can be reused in the dissolving module 1, so as to realize resource utilization through circulation.

[0074] Specifically, the reuse module 3 comprises a secondary reverse osmosis assembly 33, a reuse tank 34 and a reflux device 35. The inlet end of the secondary reverse osmosis assembly 33 is connected with the second outlet end of the reverse osmosis assembly 22, the first outlet end of the secondary reverse osmosis assembly 33 is connected with the inlet end of the reuse tank 34, the outlet end of the reuse tank 34 is connected with the inlet end of the reflux device 35, and the outlet end of the reflux device 35 is connected with the inlet end of the dissolving module 1. The secondary reverse osmosis assembly 33 is used for purifying the permeate obtained by the reverse osmosis assembly 22 to obtain secondary reverse osmosis permeate and secondary reverse osmosis concentrate; the reuse tank 34 is used for storing the secondary reverse osmosis permeate purified by the secondary reverse osmosis assembly; and the reflux device 35 is used for refluxing the stored secondary reverse osmosis permeate to the dissolving module 1. The secondary reverse osmosis concentrate obtained by the secondary reverse osmosis assembly is discharged through the second outlet end of the secondary reverse osmosis assembly 33. The reuse module of the present application is used for secondary reverse osmosis of the permeate obtained by the reverse osmosis assembly, to obtain pure organic solvent (secondary reverse osmosis permeate) and reflux to the dissolving module, so that the permeate can be reused, and resource utilization is achieved. Preferably, the reflux device is a circulating pump.

[0075] As shown in Figure 2 Further, the reuse module further comprises a liquid storage tank 31 and a second conveying device 32. The second conveying device 32 is arranged between the liquid storage tank 31 and the secondary reverse osmosis assembly 33. The liquid storage tank 31 is used for storing the permeate obtained by the reverse osmosis assembly 22. The inlet end of the liquid storage tank 31 is connected with the second outlet end of the reverse osmosis assembly 22, the outlet end of the liquid storage tank 31 is connected with the inlet end of the second conveying device 32, and the outlet end of the second conveying device 32 is connected with the inlet end of the secondary reverse osmosis assembly 33. Preferably, the second conveying device is a high-pressure pump.

[0076] The purification system of lithium bisfluorosulfonylimide of the present application can efficiently remove impurities in lithium bisfluorosulfonylimide, produce high-purity lithium bisfluorosulfonylimide, concentrate the lithium bisfluorosulfonylimide solution to be purified, improve the concentration of the concentrated lithium bisfluorosulfonylimide, and reduce the amount of organic solvent delivered to the evaporation crystallization module, thereby reducing the investment cost of the evaporation crystallization module. The purification system of lithium bisfluorosulfonylimide of the present application can realize recycling and reuse of waste organic solvent, which is helpful for environmental protection and cost reduction.

[0077] It should be noted that any modification made by those skilled in the art to the specific embodiments of the present application does not deviate from the scope of the claims of the present application. Accordingly, the scope of the claims of the present application is not limited to the foregoing specific embodiments.

Claims

1. A purification method of lithium bisfluorosulfonylimide, characterized by, It comprises the following steps: S1, dissolving the lithium bisfluorosulfonylimide crude product in a solvent to obtain a lithium bisfluorosulfonylimide crude solution; S2, reverse osmosis of the lithium bisfluorosulfonylimide crude solution through a reverse osmosis assembly to obtain a reverse osmosis concentrate and a permeate; S3, dilution of the reverse osmosis concentrate obtained in step S2 by adding a solvent, and then reverse osmosis through a reverse osmosis assembly for purification to obtain a lithium bisfluorosulfonylimide pure concentrate and a permeate; S4, removing the solvent from the lithium bisfluorosulfonylimide pure concentrate obtained in step S3 by vacuum evaporation to obtain high-purity lithium bisfluorosulfonylimide.

2. The purification method of lithium bisfluorosulfonimide according to claim 1, characterized by, The solvent in steps S1 and S3 is one or a combination of methanol, ethanol and water.

3. The purification method of lithium bisfluorosulfonylimide according to claim 1, wherein, In step 1, the molar ratio of lithium bisfluorosulfonylimide crude product to solvent is 1:8-20, the dissolution temperature is 20-30℃, and the dissolution time is 0.5-1h; In step S3, the volume ratio of reverse osmosis concentrate to solvent is 1:

2.

4. The purification method of lithium bisfluorosulfonimide according to claim 3, characterized by, In step S3, the volume ratio of reverse osmosis concentrate to solvent is 1:

2. The volume of the lithium bisfluorosulfonylimide pure concentrate obtained in step S3 is the same as the volume of the reverse osmosis concentrate obtained in step S2.

5. The purification method of lithium bisfluorosulfonimide according to claim 1, characterized by, Repeat step S3 at least once, wherein the reverse osmosis concentrate used in each repetition of step S3 is the reverse osmosis concentrate prepared in the previous step S3.

6. The purification method of lithium bisfluorosulfonimide according to claim 5, characterized by, Repeat step S3 3-10 times.

7. The purification method of lithium bisfluorosulfonimide according to claim 6, characterized by, Repeat step S3 5-7 times.

8. The purification method of lithium bisfluorosulfonimide according to claim 1, characterized by, In steps S2 and S3, the operating pressure of the reverse osmosis assembly is 15-50 bar, the recovery rate is 50%-70%, and the operating temperature is 22-25℃.

9. The purification method of lithium bisfluorosulfonimide according to claim 1, characterized by, The reverse osmosis assembly comprises a reverse osmosis membrane, the reverse osmosis is an organic solvent-resistant reverse osmosis membrane, and the desalination rate of the reverse osmosis membrane is 98.9%-99.2%; In step S4, the temperature of vacuum evaporation is 10℃-60℃, the vacuum degree is 100Pa-600Pa, and the time is 30-50℃.

10. The purification method of lithium bisfluorosulfonimide according to claim 1, characterized by, It also includes a solvent recovery step, specifically: The permeate obtained in steps S2 and S3 is purified through a secondary reverse osmosis assembly to obtain pure solvent, wherein the operating pressure of the secondary reverse osmosis assembly is 10-25 bar, the recovery rate is 60%-80%, the operating temperature is 22-25℃, and the reverse osmosis membrane of the secondary reverse osmosis assembly is an organic solvent-resistant reverse osmosis membrane.

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