A method for purifying lithium bisfluorosulfonimide

Abstract

The application provides a purification method of lithium bisfluorosulfonimide, which comprises the following steps: dissolving the lithium bisfluorosulfonimide crude product in a solvent to obtain a lithium bisfluorosulfonimide crude product solution; subjecting the lithium bisfluorosulfonimide crude product solution to reverse osmosis through a reverse osmosis assembly to obtain a reverse osmosis concentrate and a permeate; diluting the obtained reverse osmosis concentrate by adding a solvent, and then subjecting the dilution to reverse osmosis through the reverse osmosis assembly to obtain a lithium bisfluorosulfonimide pure product concentrate and a permeate; and removing the solvent from the obtained lithium bisfluorosulfonimide pure product concentrate through vacuum evaporation to obtain high-purity lithium bisfluorosulfonimide. The application provides a purification method of lithium bisfluorosulfonimide, which is simple, efficient, environmentally friendly, has a high yield of lithium bisfluorosulfonimide, is green and environmentally friendly, and has a low production cost.

Description

[Technical Field]

[0001] This invention belongs to the field of preparation of lithium bisfluorosulfonylimide, and relates to a purification method for lithium bisfluorosulfonylimide. [Background Technology]

[0002] Lithium bisfluorosulfonylimide (LiFSI) is a next-generation lithium salt for rechargeable lithium-ion batteries due to its excellent low-temperature performance, high voltage compatibility, superior thermal stability, and safety. It is often used in combination with lithium hexafluorophosphate as an electrolyte additive in rechargeable lithium batteries to improve battery capacity and electrochemical performance. Additionally, LiFSI has important industrial applications as a polymerization catalyst and an antistatic agent. The purity, moisture content, acidity, chloride ion content, and residual solvent content of the bisfluorosulfonylimide salt added to the electrolyte must meet specific technical requirements. The preparation of lithium bis(fluorosulfonyl)imide mainly involves three steps: chlorination, fluorination, and salt formation. These steps include the synthesis of bis(chlorosulfonyl)imide, the synthesis of bis(fluorosulfonyl)imide, and the synthesis of lithium bis(fluorosulfonyl)imide. The synthesis process involves many raw materials and equipment, and there is a lot of exothermic reaction. As a result, the lithium bis(fluorosulfonyl)imide synthesized in one step is a crude salt with high levels of water, acid, chloride ions, and residual solvent. It needs to be purified to obtain a salt that meets all the required standards.

[0003] Currently, high-purity lithium difluorosulfonylimide is often prepared by solution crystallization or a combination of synthesis and vacuum distillation and crystallization. However, these processes are complex and time-consuming, and they introduce organic solvents, which cause serious environmental pollution. The subsequent solvent recovery and treatment issues need to be considered, resulting in high costs and energy consumption.

[0004] Therefore, it is necessary to provide a new technical solution. [Summary of the Invention]

[0005] In order to solve the above-mentioned technical problems and overcome the shortcomings of the prior art, the present invention provides a method for purifying lithium bisfluorosulfonylimide. The preparation method is simple, efficient and environmentally friendly, with a high yield of lithium bisfluorosulfonylimide, and is green and environmentally friendly with low production cost.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] This invention provides a method for purifying lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0008] S1. Dissolve crude lithium difluorosulfonylimide in a solvent to obtain a crude lithium difluorosulfonylimide solution;

[0009] S2. The crude lithium difluorosulfonylimide solution is subjected to reverse osmosis through a reverse osmosis unit to obtain reverse osmosis concentrate and permeate;

[0010] S3. After diluting the reverse osmosis concentrate obtained in step S2 with solvent, it is purified again by reverse osmosis through the reverse osmosis module to obtain lithium difluorosulfonylimide pure concentrate and permeate.

[0011] S4. The solvent in the pure lithium difluorosulfonylimide concentrate obtained in step S3 is removed by vacuum evaporation to obtain high-purity lithium difluorosulfonylimide.

[0012] Furthermore, the solvents in steps S1 and S3 are one or more combinations of methanol, ethanol, and water.

[0013] Further, in step 1, the molar ratio of crude lithium difluorosulfonylimide 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] Furthermore, in step S3, the volume ratio of reverse osmosis concentrate to solvent is 1:2;

[0016] The volume of the lithium bis(fluorosulfonyl)imide pure concentrate obtained in step S3 is the same as the volume of the reverse osmosis concentrate obtained in step S2.

[0017] Furthermore, 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, repeat step S3 3-10 times.

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

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

[0021] Furthermore, the reverse osmosis module includes a reverse osmosis membrane, which is an organic solvent-resistant reverse osmosis membrane with a desalination rate of 98.9%-99.2%.

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

[0023] Furthermore, it also includes a solvent recovery step, specifically:

[0024] The permeate obtained in steps S2 and S3 is purified by a two-stage reverse osmosis module to obtain a pure solvent. The operating pressure of the two-stage reverse osmosis module is 10-25 bar, the recovery rate is 60%-80%, the operating temperature is 22-25℃, and the reverse osmosis membrane of the two-stage reverse osmosis module is an organic solvent resistant reverse osmosis membrane.

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

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

[0027] (2) The purification method of lithium bisfluorosulfonylimide of the present invention has a high yield of lithium bisfluorosulfonylimide and can greatly reduce the solvent that needs to be evaporated in the final evaporation process, improve evaporation efficiency, reduce energy consumption and reduce production costs.

[0028] (3) The purification method of lithium bisfluorosulfonylimide of the present invention can realize the recycling and reuse of waste organic solvents, which helps to protect the environment and reduce costs. [Attached Image Description]

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a structural block diagram of the purification system for lithium bisfluorosulfonylimide of the present invention;

[0031] Figure 2 This is a process flow diagram of the purification system for lithium bis(fluorosulfonyl)imide of the present invention.

[0032] Among them, 1-dissolving module, 2-concentration module, 3-reuse module, 4-evaporation and crystallization module, 21-first conveying device, 22-reverse osmosis component, 31-storage tank, 32-second conveying device, 33-secondary reverse osmosis component, 34-reuse tank, 35-reflux device.

Detailed Implementation Methods

[0033] To further aid in understanding the technical solution of the present invention, several specific implementation examples are provided below to describe the technical solution of the present invention in more detail. All of these described embodiments are only some embodiments of the present invention, and not all of them. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0034] The purification method for lithium bis(fluorosulfonyl)imide of the present invention employs the following testing methods:

[0035] The content of lithium bis(fluorosulfonyl)imide obtained in each embodiment was tested by anion chromatography using the internal standard method.

[0036] In each embodiment, the desalination rate of the reverse osmosis membrane in the reverse osmosis module was tested using the salinity meter method: the test solution was 2000 ppm sodium chloride, the pressure was 1.55 MPa, the temperature was 25°C, and the membrane surface flow rate was ≥0.45 m / s.

[0037] Example 1

[0038] 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 a pressure of 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 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 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 pure lithium difluorosulfonylimide concentrate. The obtained lithium difluorosulfonylimide pure concentrate was subjected to vacuum evaporation at a temperature of 30℃ and a vacuum degree of 200Pa to obtain high-purity lithium difluorosulfonylimide. The product indicators are shown in Table 1.

[0039] The reverse osmosis permeate obtained from all the above steps is fed into the secondary reverse osmosis module through a high-pressure pump. The operating pressure of the secondary reverse osmosis module is 20 bar, and the operating temperature is 22-25℃. When the recovery rate is 70%, secondary reverse osmosis concentrate and secondary reverse osmosis permeate are obtained. The secondary reverse osmosis concentrate is a methanol solution enriched with impurities, and the secondary reverse osmosis permeate is a purified methanol solution. The secondary reverse osmosis permeate can be reused in the crude lithium difluorosulfonylimide dissolution step.

[0040] In this embodiment, the reverse osmosis membrane in the reverse osmosis module is an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.2%. The reverse osmosis membrane in the secondary reverse osmosis module is also an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.6%.

[0041] Example 2

[0042] 1 kg of crude lithium difluorosulfonylimide (92.1 wt% purity) was added to 3 L of aqueous 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 a pressure of 20 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 water 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 a pressure of 20 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 diluted with 1 L of water and concentrated again using the RO module. This dilution and RO concentration process was repeated 5 times to obtain a pure lithium difluorosulfonylimide concentrate. The concentrated lithium difluorosulfonylimide solution was subjected to reduced pressure evaporation at 50°C and a vacuum of 300 Pa to obtain high-purity 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%.

[0043] Example 3

[0044] 1 kg of crude lithium difluorosulfonylimide (92.1 wt% purity) was added to 3 L of ethanol 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 50 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 ethanol 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 50 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 ethanol and concentrated again using the RO module. This dilution and RO concentration process was repeated 5 times to obtain a pure lithium difluorosulfonylimide concentrate. The concentrated lithium difluorosulfonylimide solution was subjected to reduced pressure evaporation at 35°C and a vacuum of 200 Pa to obtain high-purity lithium difluorosulfonylimide. The product specifications are shown in Table 1. The reverse osmosis permeate obtained from all the above steps was passed through a high-pressure pump into a secondary reverse osmosis module. The operating pressure of the secondary reverse osmosis module was 20 bar, and the operating temperature was 22-25°C. When the recovery rate was 70%, secondary reverse osmosis concentrate and secondary reverse osmosis permeate were obtained. The secondary reverse osmosis concentrate is an ethanol solution enriched with impurities, and the secondary reverse osmosis permeate is a purified ethanol solution. The secondary reverse osmosis permeate can be reused in the crude lithium difluorosulfonylimide dissolution step. The reverse osmosis membrane in the reverse osmosis module is an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.2%, and the reverse osmosis membrane in the secondary reverse osmosis module is also an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.6%.

[0045] Example 4

[0046] 1 kg of crude lithium difluorosulfonylimide (90.1 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 7 times to obtain a pure lithium difluorosulfonylimide concentrate. The concentrated lithium difluorosulfonylimide solution was subjected to reduced pressure evaporation at 30°C and a vacuum of 200 Pa to obtain high-purity lithium difluorosulfonylimide. The product specifications are shown in Table 1. The reverse osmosis permeate obtained from all the above steps was passed through a high-pressure pump into a secondary reverse osmosis module. The operating pressure of the secondary reverse osmosis module was 20 bar, and the operating temperature was 22-25°C. When the recovery rate was 70%, secondary reverse osmosis concentrate and secondary reverse osmosis permeate were obtained. The secondary reverse osmosis concentrate was a methanol solution enriched with impurities, and the secondary reverse osmosis permeate was a purified methanol solution. The secondary reverse osmosis permeate could be reused in the crude lithium difluorosulfonylimide dissolution step. The reverse osmosis membrane in the reverse osmosis module was an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.2%. The reverse osmosis membrane in the secondary reverse osmosis module was also an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.6%.

[0047] Example 5

[0048] 1 kg of crude lithium difluorosulfonylimide (purity 92.1 wt%) 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 a pressure of 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. 2 L of methanol was added to the 1 L of RO concentrate for dilution, and the solution was again passed through the RO module using a high-pressure pump for concentration. The RO module operated at a pressure of 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 the RO concentrate was then added to 2 L of methanol for dilution and concentration again. This process of dilution and RO concentration was repeated 5 times to obtain a pure lithium difluorosulfonylimide concentrate. The concentrated lithium difluorosulfonylimide solution was subjected to reduced pressure evaporation at 30°C and a vacuum of 200 Pa to obtain high-purity lithium difluorosulfonylimide. The product specifications are shown in Table 1. The reverse osmosis permeate obtained from all the above steps was passed through a high-pressure pump into a secondary reverse osmosis module. The operating pressure of the secondary reverse osmosis module was 20 bar, and the operating temperature was 22-25°C. When the recovery rate was 70%, secondary reverse osmosis concentrate and secondary reverse osmosis permeate were obtained. The secondary reverse osmosis concentrate was a methanol solution enriched with impurities, and the secondary reverse osmosis permeate was a purified methanol solution. The secondary reverse osmosis permeate could be reused in the crude lithium difluorosulfonylimide dissolution step. The reverse osmosis membrane in the reverse osmosis module was an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.2%. The reverse osmosis membrane in the secondary reverse osmosis module was also an organic solvent-resistant reverse osmosis membrane with a desalination rate of 99.6%.

[0049] Comparative Example 1

[0050] 1 kg of crude lithium difluorosulfonylimide (purity 92.1 wt%) was added to 3 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%, 1 L of RO concentrate and 2 L of permeate were obtained. The 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 RO membrane in the RO module was an organic solvent-resistant RO membrane with a desalination rate of 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] 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 98.3%.

[0057] Comparative Example 5

[0058] 1 kg of crude lithium difluorosulfonylimide (purity 92.1 wt%) 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 nanofiltration module using a high-pressure pump. The operating pressure of the nanofiltration module was 45 bar, and the temperature was 22-25 °C. When the recovery rate reached 66.7%, 1 L of nanofiltration concentrate and 2 L of permeate were obtained. 1 L of methanol was added to the 1 L of nanofiltration concentrate for dilution, and the solution was then passed through the nanofiltration module again using a high-pressure pump for concentration. The operating pressure of the nanofiltration module was 45 bar, and the temperature was 22-25 °C. When the recovery rate reached 50%, 1 L of nanofiltration concentrate and 1 L of permeate were obtained. 1 L of the nanofiltration concentrate was then added to 1 L of methanol for dilution and concentration again. This process of dilution and nanofiltration concentration 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 nanofiltration membrane in the nanofiltration module is an organic solvent-resistant nanofiltration membrane with a desalination rate of 97.3%.

[0059] Table 1

[0060]

[0061] As shown in Table 1, the solvents used in Examples 1-3 were methanol, water, and ethanol, respectively, resulting in products with high purity and yield. Compared to Example 1, Example 4 adjusted the number of dilution-concentration repetitions. Compared to Example 1, Example 5 adjusted the dilution factor. As shown in Table 1, the products obtained in the above examples all had high purity and yield.

[0062] Compared to Examples 1-5 of this application, Comparative Examples 1 and 2 did not perform the dilution and subsequent reverse osmosis concentration step 3, resulting in very low product purity. This indicates that reverse osmosis concentration alone cannot achieve a good product purification effect. In contrast, this invention uses multiple dilutions and concentrations in step 3, with the reverse osmosis concentrate used in each repetition of step S3 being the same concentrate prepared in the previous step S3. This allows for the acquisition of high-purity lithium bis(fluorosulfonyl)imide. Compared to the multi-step removal methods in the prior art, this invention is simpler, more efficient, and more economical.

[0063] Comparative Examples 3 and 4 both demonstrate that the desalination rate of the reverse osmosis membrane in the reverse osmosis module has a significant impact 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 module has a high rejection rate for impurities, causing impurities to be retained in the concentrate along with the product, resulting in poor purification. Conversely, when the desalination rate of the reverse osmosis membrane is low, as in Comparative Example 4, the rejection rate of both product and impurities decreases, allowing a large amount of both to permeate into the reverse osmosis permeate. This significantly reduces the product concentration in the reverse osmosis concentrate, resulting in a high-purity but low-yield final product. In contrast, the reverse osmosis module of this invention has a desalination rate of 98.9%-99.2% for the reverse osmosis membrane, achieving both high product purity and high yield.

[0064] Comparative Example 5 replaced the reverse osmosis module in Example 1 with a nanofiltration module. Since the desalination rate of the nanofiltration module is lower than that of the reverse osmosis module, its product rejection rate is also lower, resulting in a large amount of product permeating into the permeate and thus a lower product yield. In contrast, this application uses a reverse osmosis module for concentration, which not only purifies lithium bis(fluorosulfonyl)imide to obtain high-purity lithium bis(fluorosulfonyl)imide, but also achieves a high product yield.

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

[0066] The purification method for lithium bisfluorosulfonylimide of the present invention has a high yield of lithium bisfluorosulfonylimide, up to 98.6%, which is a significant improvement over the comparative example. Furthermore, the present invention can greatly reduce the amount of solvent to be evaporated in the final evaporation process, improve evaporation efficiency, reduce energy consumption, and lower production costs.

[0067] The purification method for lithium bisfluorosulfonylimide of the present invention enables the recycling and reuse of waste organic solvents, which helps to protect the environment and reduce costs.

[0068] Please see Figure 1 and Figure 2 In another embodiment, the present invention also provides a purification system for lithium bisfluorosulfonylimide, which is used to purify lithium bisfluorosulfonylimide.

[0069] The purification system for lithium bis(fluorosulfonyl)imide of the present invention includes a dissolution module 1, a concentration module 2, and an evaporation and crystallization module 4.

[0070] The dissolution module 1 has an inlet end and an outlet end. Crude lithium difluorosulfonylimide enters the dissolution module 1 through the inlet end and is dissolved in the dissolution module 1 by an organic solvent to form a crude lithium difluorosulfonylimide solution.

[0071] The concentration module 2 includes a reverse osmosis component 22 and a first conveying device 21. The outlet of the reverse osmosis component includes a first outlet and a second outlet. The first conveying device 21 is disposed between the dissolution module 1 and the reverse osmosis component 22. The outlet of the dissolution module 1 is connected to the inlet of the first conveying device 21, and the outlet of the first conveying device 21 is connected to the inlet of the reverse osmosis component 22. The first outlet of the reverse osmosis component 22 is connected to the inlet of the evaporation and crystallization module 4. The first conveying device 21 is a high-pressure pump. The first conveying device 21 is used to convey the mixed solution formed in the dissolution module 1 to the reverse osmosis component 22. The reverse osmosis membrane of the reverse osmosis component 22 purifies and concentrates the mixed solution to obtain a concentrate and a permeate.

[0072] The inlet of the evaporation crystallization module is connected to the first outlet of the reverse osmosis component. The concentrate obtained by the reverse osmosis component 22 enters the evaporation crystallization module 4 from the inlet of the evaporation crystallization module through the first outlet of the reverse osmosis component. The evaporation crystallization module 4 performs evaporation crystallization treatment on the concentrate obtained by the reverse osmosis component 22 to obtain pure lithium difluorosulfonylimide.

[0073] Please continue reading. Figure 2 In one embodiment, the purification system further includes a reuse module 3. The reuse module 3 performs secondary reverse osmosis purification on the permeate obtained from the reverse osmosis component 22 to obtain a pure organic solvent, which can be reused in the dissolution module 1, thus achieving resource utilization.

[0074] Specifically, the reuse module 3 includes a secondary reverse osmosis component 33, a reuse tank 34, and a reflux device 35. The inlet end of the secondary reverse osmosis component 33 is connected to the second outlet end of the reverse osmosis component 22, the first outlet end of the secondary reverse osmosis component 33 is connected to the inlet end of the reuse tank 34, the outlet end of the reuse tank 34 is connected to the inlet end of the reflux device 35, and the outlet end of the reflux device 35 is connected to the inlet end of the dissolution module 1. The secondary reverse osmosis component 33 is used to purify the permeate obtained from the reverse osmosis component 22 to obtain secondary reverse osmosis permeate and secondary reverse osmosis concentrate; the reuse tank 34 is used to store the secondary reverse osmosis permeate purified by the secondary reverse osmosis component; the reflux device 35 is used to return the stored secondary reverse osmosis permeate to the dissolution module 1; and the secondary reverse osmosis concentrate obtained by the secondary reverse osmosis component 33 is discharged through the second outlet end of the secondary reverse osmosis component 33. The recycling module of this invention is used to perform secondary reverse osmosis on the permeate obtained from the reverse osmosis module to obtain pure organic solvent (secondary reverse osmosis permeate), which is then returned to the dissolving module, allowing the permeate to be reused and realizing resource utilization. Preferably, the return device is a circulation pump.

[0075] like Figure 2 As shown, the reuse module further includes a storage tank 31 and a second conveying device 32. The second conveying device 32 is disposed between the storage tank 31 and the secondary reverse osmosis assembly 33. The storage tank 31 is used to store the permeate obtained from the reverse osmosis assembly 22. The inlet end of the storage tank 31 is connected to the second outlet end of the reverse osmosis assembly 22, the outlet end of the storage tank 31 is connected to the inlet end of the second conveying device 32, and the outlet end of the second conveying device 32 is connected to the inlet end of the secondary reverse osmosis assembly 33. Preferably, the second conveying device is a high-pressure pump 32.

[0076] The lithium bis(fluorosulfonyl)imide purification system of the present invention can efficiently remove impurities from lithium bis(fluorosulfonyl)imide to produce high-purity lithium bis(fluorosulfonyl)imide. Furthermore, by using a concentration system to concentrate the lithium bis(fluorosulfonyl)imide solution to be purified, the system can increase the concentration of the concentrated lithium bis(fluorosulfonyl)imide and reduce the amount of organic solvent transported to the evaporation and crystallization module, thereby reducing the investment cost of the evaporation and crystallization module. The lithium bis(fluorosulfonyl)imide purification system of the present invention, by incorporating a recycling module, can realize the recovery and reuse of waste organic solvents, which helps to protect the environment and reduce costs.

[0077] It should be noted that any modifications made by those skilled in the art to the specific embodiments of the present invention do not depart from the scope of the claims. Accordingly, the scope of the claims is not limited to the foregoing specific embodiments.

Claims

1. A method for purifying lithium difluorosulfonylimide, characterized in that, It includes the following steps: S1. Dissolve crude lithium difluorosulfonylimide in a solvent to obtain a crude lithium difluorosulfonylimide solution, wherein the molar ratio of crude lithium difluorosulfonylimide to solvent is 1:8-20, the dissolution temperature is 20-30℃, and the dissolution time is 0.5-1h. S2. The crude lithium difluorosulfonylimide solution is subjected to reverse osmosis through a reverse osmosis module to obtain a reverse osmosis concentrate and a permeate. The reverse osmosis module includes a reverse osmosis membrane, which is an organic solvent-resistant reverse osmosis membrane. S3. After diluting the reverse osmosis concentrate obtained in step S2 with solvent, it is purified again by reverse osmosis through a reverse osmosis module to obtain lithium difluorosulfonylimide pure concentrate and permeate, wherein the volume ratio of reverse osmosis concentrate to solvent is 1:1.5-3.

3. S4. The solvent in the pure lithium difluorosulfonylimide concentrate obtained in step S3 is removed by vacuum evaporation to obtain high-purity lithium difluorosulfonylimide. In steps S1 and S3, the solvents are methanol, ethanol, and water, or one or a combination thereof; in steps S2 and S3, the operating pressure of the reverse osmosis module is 15-50 bar, the recovery rate is 50%-70%, and the operating temperature is 22-25℃; the desalination rate of the reverse osmosis membrane is 98.9%-99.2%.

2. The purification method for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, In step S3, the volume ratio of reverse osmosis concentrate to solvent is 1:2; The volume of the lithium bis(fluorosulfonyl)imide pure concentrate obtained in step S3 is the same as the volume of the reverse osmosis concentrate obtained in step S2.

3. The purification method for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, 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.

4. The purification method for lithium bis(fluorosulfonyl)imide according to claim 3, characterized in that, Repeat step S3 3-10 times.

5. The purification method for lithium bis(fluorosulfonyl)imide according to claim 4, characterized in that, Repeat step S3 5-7 times.

6. The purification method for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, In step S4, the temperature for vacuum evaporation is 10℃~60℃, and the vacuum degree is 100Pa~600Pa.

7. The purification method for lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, It also includes a solvent recovery step, specifically: The permeate obtained in steps S2 and S3 is purified by a two-stage reverse osmosis module to obtain a pure solvent. The operating pressure of the two-stage reverse osmosis module is 10-25 bar, the recovery rate is 60%-80%, the operating temperature is 22-25℃, and the reverse osmosis membrane of the two-stage reverse osmosis module is an organic solvent resistant reverse osmosis membrane.

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