A method for preparing lithium bisfluorosulfonimide

Abstract

In order to overcome the problem of high-temperature decomposition in the existing extraction of lithium bisfluorosulfonylimide from an aqueous solvent system, the present application provides a preparation method of lithium bisfluorosulfonylimide, comprising the following operation steps: providing an aqueous solution of lithium bisfluorosulfonylimide containing an alkaline lithium salt; distilling and concentrating the aqueous solution of lithium bisfluorosulfonylimide to obtain an aqueous concentrated solution of lithium bisfluorosulfonylimide; adding a non-aqueous organic solvent to the aqueous concentrated solution of lithium bisfluorosulfonylimide, distilling water to obtain an organic solution of lithium bisfluorosulfonylimide. In the preparation method of lithium bisfluorosulfonylimide provided by the present application, the addition of an alkaline lithium salt to the aqueous solution of lithium bisfluorosulfonylimide can effectively inhibit the decomposition of lithium bisfluorosulfonylimide during the concentration process, thereby improving the yield and purity of lithium bisfluorosulfonylimide.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte salt materials technology, specifically relating to a method for preparing lithium bis(fluorosulfonyl)imide. Background Technology

[0002] With increasing attention paid to the green and low-carbon economy, rechargeable batteries have attracted much attention. As one of the core materials of rechargeable batteries, electrolyte salts have a significant impact on the cycle life, high and low temperature performance, and safety performance of the battery. As a new type of electrolyte salt, compared with lithium hexafluorophosphate (which has poor thermal stability and is easily hydrolyzed), lithium difluorosulfinylimide (LiFSI) not only has higher conductivity, thermal stability (does not decompose below 200℃) and good hydrolytic stability, but also has advantages such as suppressing battery gas expansion (J. Power Sources, 2022, 535, 231481).

[0003] Currently, there are several main methods for preparing LiFSI: One is to fluorinate bis(chlorosulfonyl)imide (HClSI) to obtain bis(fluorosulfonyl)imide (HFSI), which is then reacted with lithium salt to obtain LiFSI (CN 104925765 A, CN 106044728A); the other is to prepare LiFSI by reacting HClSI with lithium fluoride (CN 113247871 A). The former requires the use of corrosive and toxic hydrogen fluoride (HF), and often involves the addition of thionyl chloride for water removal, resulting in a high chloride ion content in the product and a decline in product quality; the latter generates a large amount of HF, and the residual HF in the product reduces the performance of LiFSI and increases the cost of exhaust gas treatment.

[0004] The above preparation methods mostly use hydrogen fluoride or organic solvents as solvents in the reaction system, which poses high risks, difficulties in waste liquid treatment, and environmental pollution problems. Even though US 8377406 uses water as the reaction solvent because lithium carbonate is insoluble in organic solvents, the reaction requires the use of HFSI to react with lithium carbonate to prepare LiFSI. However, HFSI releases heat when dissolved in water, which will cause it to decompose. Therefore, the patent requires the preparation of HFSI aqueous solution at ultra-low temperature (-78°C), which increases energy consumption.

[0005] Because lithium difluorosulfinylimide readily reacts with water and decomposes at high temperatures, using water as the solvent in the reaction system for the preparation of lithium difluorosulfinylimide presents significant challenges and requires relatively low temperatures. Furthermore, the subsequent extraction of lithium difluorosulfinylimide from the aqueous solvent system inevitably involves high-temperature conditions, posing a considerable risk of affecting the purity of lithium difluorosulfinylimide due to its reaction with water. This hinders the development of a process route for preparing lithium fluorosulfinylimide via an aqueous solvent system. Summary of the Invention

[0006] To address the problem of high-temperature decomposition during the extraction of lithium difluorosulfinylimide from aqueous solvent systems, this invention provides a method for preparing lithium difluorosulfinylimide.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] This invention provides a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0009] An aqueous solution of lithium bis(fluorosulfonyl)imide is provided, wherein the aqueous solution of lithium bis(fluorosulfonyl)imide contains an alkaline lithium salt;

[0010] An aqueous solution of lithium bis(fluorosulfonyl)imide was concentrated by distillation to obtain a concentrated aqueous solution of lithium bis(fluorosulfonyl)imide.

[0011] A non-aqueous organic solvent was added to the lithium bis(fluorosulfonyl)imide aqueous concentrate, and the mixture was then distilled to remove water, yielding an organic solution of lithium bis(fluorosulfonyl)imide.

[0012] Optionally, the alkaline lithium salt includes one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium methoxide, lithium ethanol, lithium hydride, lithium nitride, lithium monomethyl carbonate, and lithium monoethyl carbonate.

[0013] Optionally, the alkaline lithium salt is selected from alkaline lithium salts that are poorly soluble in organic solvents.

[0014] Optionally, the aqueous solution of the lithium bis(fluorosulfonyl)imide contains 0.0001% to 10% by mass of alkaline lithium salt.

[0015] Optionally, the aqueous solution of lithium bis(fluorosulfonyl)imide is prepared by the following operation:

[0016] A cation exchange resin column is provided, wherein the cation exchange resin column is filled with a strong acid type cation exchange resin, and the strong acid type cation exchange resin adsorbs lithium ions.

[0017] Ion exchange: An aqueous solution of an alkali metal salt XFSI is provided, wherein X represents sodium ions and / or potassium ions. The aqueous solution of the alkali metal salt XFSI is passed through a cation exchange resin column for ion exchange, and the X ions on the alkali metal salt XFSI are replaced with lithium ions to obtain an aqueous solution of lithium bis(fluorosulfonyl)imide.

[0018] Optionally, the alkaline lithium salt is added to the aqueous solution of the alkali metal salt XFSI prior to the "ion exchange" operation;

[0019] And / or, the basic lithium salt is added to the aqueous solution of the lithium bis(fluorosulfonyl)imide after the “ion exchange” operation.

[0020] Optionally, in the "distillation and concentration" operation, vacuum distillation is used, with a temperature of 5℃ to 80℃ and a pressure of 0 to 30 kPa.

[0021] Optionally, in the operation of "adding a non-aqueous organic solvent to a concentrated aqueous solution of lithium bisfluorosulfonylimide, mixing, and distilling to remove water to obtain an organic solution of lithium bisfluorosulfonylimide", the non-aqueous organic solvent is selected from organic solvents that can form an azeotrope with water but are insoluble in water. Distillation is performed, and water and non-aqueous organic solvents separate into layers in the distillate. The water is removed, and the second non-aqueous organic solvent is returned to the distillate. The solution is distilled until the water content is <200 ppm based on the mass of LiFSI to obtain an organic solution of lithium bisfluorosulfonylimide.

[0022] Optionally, the mass concentration of the bis(fluorosulfonyl)imide lithium aqueous solution is 30%-85%;

[0023] The distillation is carried out under reduced pressure, with a temperature of 5℃ to 80℃ and a pressure of 0 to 30 kPa.

[0024] The distillation process maintains a solution concentration of 2-60%;

[0025] The organic solution of the lithium bis(fluorosulfonyl)imide has a mass concentration of 10% to 80%.

[0026] Optionally, the non-aqueous organic solvent is selected from organic solvents containing at least one functional group selected from ester, cyano, and ether bonds.

[0027] According to the method for preparing lithium bis(fluorosulfonyl)imide provided by the present invention, a method for obtaining lithium bis(fluorosulfonyl)imide from an aqueous solution of lithium bis(fluorosulfonyl)imide is provided. The aqueous solution of lithium bis(fluorosulfonyl)imide is concentrated by distillation, and then a non-aqueous organic solvent is added to the concentrated lithium bis(fluorosulfonyl)imide aqueous solution for distillation displacement to remove water, thereby avoiding the decomposition of lithium bis(fluorosulfonyl)imide at the end of distillation and minimizing the generation of by-products. At the same time, in order to avoid the decomposition of lithium bis(fluorosulfonyl)imide by reacting with water at high temperature during the distillation and concentration process of the aqueous solution of lithium bis(fluorosulfonyl)imide, the inventors found that adding an alkaline lithium salt to the aqueous solution of lithium bis(fluorosulfonyl)imide can effectively suppress the decomposition problem of lithium bis(fluorosulfonyl)imide during the concentration process, thereby improving the yield and purity of lithium bis(fluorosulfonyl)imide. Detailed Implementation

[0028] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] This invention provides a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0030] An aqueous solution of lithium bis(fluorosulfonyl)imide is provided, wherein the aqueous solution of lithium bis(fluorosulfonyl)imide contains an alkaline lithium salt;

[0031] An aqueous solution of lithium bis(fluorosulfonyl)imide was concentrated by distillation to obtain a concentrated aqueous solution of lithium bis(fluorosulfonyl)imide.

[0032] An organic solvent was added to the lithium difluorosulfonylimide aqueous concentrate, and the water was removed by distillation to obtain lithium difluorosulfonylimide solid.

[0033] A method for obtaining lithium difluorosulfonylimide from an aqueous solution of lithium difluorosulfonylimide is provided. The method involves concentrating the aqueous solution of lithium difluorosulfonylimide by distillation, followed by adding a non-aqueous organic solvent to the concentrated lithium difluorosulfonylimide solution for distillation displacement to remove water. This avoids the decomposition of lithium difluorosulfonylimide at the end of distillation, significantly reducing the generation of byproducts. Furthermore, to prevent the decomposition of lithium difluorosulfonylimide by water at high temperatures during the distillation and concentration process, the inventors discovered that adding an alkaline lithium salt to the aqueous solution of lithium difluorosulfonylimide effectively suppresses the decomposition problem during concentration, thereby improving the yield and purity of lithium difluorosulfonylimide.

[0034] In some embodiments, the alkaline lithium salt includes one or more of lithium carbonate, lithium bicarbonate, lithium hydroxide, lithium methoxide, lithium ethanol, lithium hydride, lithium nitride, lithium monomethyl carbonate, and lithium monoethyl carbonate.

[0035] In a preferred embodiment, the alkaline lithium salt is selected from alkaline lithium salts that are poorly soluble in organic solvents.

[0036] In a more preferred embodiment, the alkaline lithium salt is selected from lithium carbonate and / or lithium bicarbonate.

[0037] Compared to other basic lithium salts, lithium carbonate and lithium bicarbonate have lower solubility in organic solvents. Therefore, during the subsequent distillation process to remove water by adding organic solvent, as the water content in the solvent system decreases, the basic lithium salts, such as lithium carbonate and / or lithium bicarbonate, can be directly precipitated from the system in a solid state. They can then be removed from the system through solid-liquid separation, effectively avoiding the impact of the added basic lithium salts on the purity of the final lithium bis(fluorosulfonyl)imide.

[0038] In some embodiments, the aqueous solution of the lithium bis(fluorosulfonyl)imide contains 0.0001% to 10% by mass of the alkaline lithium salt.

[0039] Specifically, in the aqueous solution of lithium bis(fluorosulfonyl)imide, the mass content of the alkaline lithium salt can be 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0040] In a preferred embodiment, the aqueous solution of the lithium bis(fluorosulfonyl)imide contains 0.001% to 0.2% by mass of the alkaline lithium salt.

[0041] If the mass content of alkaline lithium salt in the aqueous solution of lithium bisfluorosulfonylimide is too low, it will be difficult to inhibit the decomposition of lithium bisfluorosulfonylimide; if the mass content of alkaline lithium salt in the aqueous solution of lithium bisfluorosulfonylimide is too high, compared with the low content, the inhibitory effect on the decomposition of lithium bisfluorosulfonylimide is not significantly improved, and the risk of introducing impurities and the preparation cost are increased.

[0042] In some embodiments, the aqueous solution of lithium bis(fluorosulfonyl)imide is prepared by the following operation:

[0043] A cation exchange resin column is provided, wherein the cation exchange resin column is filled with a strong acid type cation exchange resin, and the strong acid type cation exchange resin adsorbs lithium ions.

[0044] Ion exchange: An aqueous solution of an alkali metal salt XFSI is provided, wherein X represents sodium ions and / or potassium ions. The aqueous solution of the alkali metal salt XFSI is passed through a cation exchange resin column for ion exchange, and the X ions on the alkali metal salt XFSI are replaced with lithium ions to obtain an aqueous solution of lithium bis(fluorosulfonyl)imide.

[0045] In alkali metal salts of bis(fluorosulfonyl)imide, under solution conditions, due to stronger Coulombic interactions, alkali metal ions with smaller ionic radii and higher charge densities are more prone to causing FSI (freeze-in-place). - The decomposition of [the product] (Electrochimica Acta, 2019, 321, 134644). Compared to lithium bisfluorosulfonylimide, sodium bisfluorosulfonylimide and potassium bisfluorosulfonylimide are more stable, easier to prepare, and easier to purify to obtain high-purity products. Compared to existing methods for preparing lithium bisfluorosulfonylimide via chemical reaction using potassium bisfluorosulfonylimide, this preparation method uses a cation exchange resin column adsorbed with lithium ions to treat an aqueous solution of potassium bisfluorosulfonylimide and / or sodium bisfluorosulfonylimide, preparing an aqueous solution of lithium bisfluorosulfonylimide by ion exchange. This method is simple to operate, has lower environmental requirements, the cation exchange resin and solvent are regenerable and reusable, ensuring high safety, and the resulting aqueous solution of lithium bisfluorosulfonylimide has high purity.

[0046] It should be noted that the addition of the alkaline lithium salt does not interfere with the "ion exchange" operation. Therefore, there are no particular restrictions on the timing of the addition of the alkaline lithium salt. In some embodiments, the alkaline lithium salt is added to the aqueous solution of the alkali metal salt XFSI before the "ion exchange" operation. In other embodiments, the alkaline lithium salt is added to the aqueous solution of the lithium bis(fluorosulfonyl)imide after the "ion exchange" operation. In still other embodiments, a portion of the alkaline lithium salt is added to the aqueous solution of the alkali metal salt XFSI before the "ion exchange" operation, and the remaining alkaline lithium salt is added to the aqueous solution of the lithium bis(fluorosulfonyl)imide after the "ion exchange" operation.

[0047] In some embodiments, the "distillation concentration" operation is carried out under reduced pressure distillation at a temperature of 5°C to 80°C and a pressure of 0 to 30 kPa.

[0048] In a preferred embodiment, the vacuum distillation temperature is 30°C to 70°C.

[0049] Reduced pressure distillation can effectively lower the distillation temperature, thus reducing the probability of lithium difluorosulfonylimide decomposing at high temperatures or undergoing side reactions with water.

[0050] In some embodiments, the mass concentration of the aqueous solution of the alkali metal salt XFSI is 1% to 50%.

[0051] Specifically, the mass concentration of the aqueous solution of the alkali metal salt XFSI can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 27%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 37%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 47%, 49%, or 50%.

[0052] In a preferred embodiment, the mass concentration of the aqueous solution of the alkali metal salt XFSI is 5% to 25%.

[0053] In some embodiments, the cation exchange resin column is prepared by the following method:

[0054] After packing the strongly acidic cation exchange resin column, the column is sequentially rinsed with water, acid solution, water, lithium hydroxide or alkaline salt solution, and water.

[0055] In the above operation process, the first water rinsing is used to remove soluble impurities from the strongly acidic cation exchange resin; the acid solution rinsing is used to elute the impurity ions adsorbed in the strongly acidic cation exchange resin. At this time, the H+ in the acid solution... + Ions can intercalate into strongly acidic cation exchange resins to replace other impurity ions, such as Ca2+. 2+ Ions, Mg 2+ Ions, Na + Ions, K + The position of ions is determined to restore the ion exchange capacity of the strongly acidic cation exchange resin; a second water rinsing operation is used to remove residual acid from the strongly acidic cation exchange resin; and a rinsing operation with lithium hydroxide or alkaline salt solution is used to allow lithium ions to replace H+ ions in the strongly acidic cation exchange resin. + The position of the ions forms a strongly acidic cation exchange resin adsorbed with lithium ions, which is used for ion exchange with potassium bis(fluorosulfonyl)imide or sodium bis(fluorosulfonyl)imide; a third water rinsing operation is used to remove residual alkali from the strongly acidic cation exchange resin.

[0056] In some embodiments, when rinsing the cation exchange resin with water, the end of rinsing is indicated by an effluent conductivity of <200 μS / cm.

[0057] In a preferred embodiment, when rinsing the cation exchange resin with water, the end of rinsing is indicated by an effluent conductivity of <100 μS / cm.

[0058] In a more preferred embodiment, when rinsing the cation exchange resin with water, the end of rinsing is indicated by an effluent conductivity of <50 μS / cm.

[0059] In some embodiments, when rinsing the cation exchange resin with an acid solution, the rinsing is considered complete when the metal cation concentration in the effluent is less than 100 ppm.

[0060] In a preferred embodiment, when rinsing the cation exchange resin with an acid solution, the rinsing is considered complete when the metal cation concentration in the effluent is less than 50 ppm.

[0061] In some embodiments, when rinsing the cation exchange resin with lithium hydroxide or alkaline salt solution, the pH of the effluent > 8 is used as the end of rinsing.

[0062] In some embodiments, the acid solution includes one or more of hydrochloric acid and sulfuric acid, and the acid concentration of the acid solution is 1% to 50%.

[0063] In some embodiments, when the acid solution is hydrochloric acid, the acid concentration of the acid solution is 1% to 30%.

[0064] In some embodiments, when the acid solution is sulfuric acid, the acid concentration of the acid solution is 1% to 50%.

[0065] In some embodiments, when the acid solution is hydrochloric acid, the second water rinsing operation is performed with an effluent conductivity <200 μS / cm and Cl... - <5ppm is used as the end of rinsing, with Cl being the preferred value. - <2ppm.

[0066] In some embodiments, when the acid solution is sulfuric acid, the second water rinsing operation is performed with an effluent conductivity <200 μS / cm and SO42-. 2- <5ppm is used as the end mark for rinsing, SO4 is preferred. 2- <2ppm.

[0067] In some embodiments, the lithium hydroxide or alkaline salt solution is selected from LiOH, Li₂CO₃, LiHCO₃, C. n H 2n+1 One or more of the OLi solutions, wherein n is 1 or 2; the mass concentration of the hydroxide or alkaline salt in the lithium hydroxide or alkaline salt solution is 0.1% to 50%.

[0068] In a preferred embodiment, when the hydroxide in the lithium hydroxide or alkaline salt solution is lithium hydroxide, the mass concentration of lithium hydroxide in the lithium hydroxide solution is 0.1% to 11%, and more preferably, the mass concentration of lithium hydroxide in the lithium hydroxide solution is 3% to 10%.

[0069] In some embodiments, when the lithium ion concentration in the effluent is <1000 ppm during ion exchange, the cation exchange resin column is regenerated in the same manner as the preparation method of the cation exchange resin column.

[0070] The adsorbed potassium or sodium ions in the cation exchange resin column are washed away by rinsing with an acid solution, and then the lithium ion loading in the strongly acidic cation exchange resin is restored by rinsing with a lithium hydroxide or alkaline salt solution, so as to ensure the regeneration and reuse of the cation exchange resin column.

[0071] In a preferred embodiment, when the lithium ion concentration in the effluent is <500 ppm, the cation exchange resin column is regenerated.

[0072] In a more preferred embodiment, when the lithium ion concentration in the effluent is <200 ppm, the cation exchange resin column is regenerated.

[0073] In some embodiments, the completion of the ion exchange operation is indicated by a concentration of potassium or sodium ions in the effluent below 6 ppm.

[0074] In a preferred embodiment, the completion of the ion exchange operation is indicated by a potassium or sodium ion concentration in the effluent being below 3 ppm.

[0075] In a more preferred embodiment, the completion of the ion exchange operation is indicated by the concentration of potassium or sodium ions in the effluent being less than 1 ppm.

[0076] In some embodiments, during the ion exchange operation, an aqueous solution of alkali metal salt XFSI can be passed through the cation exchange resin column once for ion exchange. If the effluent after the aqueous solution of alkali metal salt XFSI passes through the cation exchange resin column once cannot reach the mark of completing the ion exchange operation (the concentration of potassium ions or sodium ions is less than 6 ppm), the aqueous solution of alkali metal salt XFSI can be circulated through the cation exchange resin column multiple times for ion exchange, or multiple cation exchange resin columns can be connected in series to perform multiple ion exchange operations on the aqueous solution of alkali metal salt XFSI.

[0077] In some embodiments, the strongly acidic cation exchange resin is selected from sulfonic acid type cation exchange resins.

[0078] In some embodiments, in the operation of "adding a non-aqueous organic solvent to a concentrated aqueous solution of lithium bisfluorosulfonylimide, mixing, and distilling to remove water to obtain an organic solution of lithium bisfluorosulfonylimide", the non-aqueous organic solvent is selected from organic solvents that can form an azeotrope with water but are insoluble in water. Distillation is performed, and water and non-aqueous organic solvents separate into layers in the distillate. The water is removed, and the second non-aqueous organic solvent is returned to the distillate. The solution is distilled to a water content of <200 ppm based on the mass of LiFSI to obtain an organic solution of lithium bisfluorosulfonylimide.

[0079] By selecting the non-aqueous organic solvent as an organic solvent that can form an azeotrope with water but is insoluble in water, it is beneficial to remove water in the form of an azeotrope during the distillation process. At the same time, during the distillation process, the azeotrope formed by water and the non-aqueous organic solvent is removed from the system. After condensation, since water and non-aqueous organic solvents are immiscible, the non-aqueous organic solvent can be separated by layering and then returned to the distillation system, thereby ensuring the recycling of the non-aqueous organic solvent and continuously reducing the water content in the distillation system.

[0080] The organic solution of lithium difluorosulfonylimide prepared by the above method has the advantages of low impurities and high purity. Compared with distilling the organic solution of lithium difluorosulfonylimide until lithium difluorosulfonylimide solid precipitates, the preparation of the organic solution of lithium difluorosulfonylimide consumes less energy. Since existing lithium-ion battery non-aqueous electrolytes also use lithium salt organic solvents, the prepared organic solution of lithium difluorosulfonylimide can be directly used in the electrolyte, realizing the co-production of lithium difluorosulfonylimide organic solution and electrolyte. This can effectively avoid the mixing of water or decomposition of lithium difluorosulfonylimide during the crystallization and drying process, shortening the process flow while ensuring the quality of the electrolyte.

[0081] In some embodiments, the mass concentration of the bis(fluorosulfonyl)imide lithium aqueous concentrate is 30%-85%.

[0082] In a preferred embodiment, the mass concentration of the lithium difluorosulfonylimide aqueous concentrate is 50%-75%.

[0083] In some embodiments, the distillation is performed under reduced pressure, with a temperature of 5°C to 80°C and a pressure of 0 to 30 kPa.

[0084] In a preferred embodiment, the distillation temperature is 30–70°C.

[0085] In some embodiments, the solution concentration is maintained at 2-60% during distillation.

[0086] In a preferred embodiment, the solution concentration is maintained at 30-40% during distillation.

[0087] In some embodiments, the mass concentration of the organic solution of lithium bis(fluorosulfonyl)imide is 10% to 80%.

[0088] In some embodiments, the non-aqueous organic solvent is selected from organic solvents containing at least one functional group selected from ester, cyano, and ether groups.

[0089] In a preferred embodiment, the second non-aqueous organic solvent is selected from carbonate solvents.

[0090] In some embodiments, the water content in the organic solution of the lithium bis(fluorosulfonyl)imide is <200 ppm (based on the mass of LiFSI);

[0091] In a preferred embodiment, the water content in the organic solution of lithium bis(fluorosulfonyl)imide is <100 ppm (based on the mass of LiFSI);

[0092] In a more preferred embodiment, the water content in the organic solution of lithium bis(fluorosulfonyl)imide is <50 ppm (based on the mass of LiFSI).

[0093] The present invention will be further illustrated by the following examples.

[0094] Preparation Example 1, Lithium Resin A: The preparation method is as follows:

[0095] Approximately 300 mL of sulfonic acid-type strong acid cation exchange resin was added to a 500 mL chromatography column. After rinsing with 250 mL of ultrapure water, the conductivity of the effluent was 40 μS / cm. Then, 250 mL of 16% hydrochloric acid solution was added. The K+ concentration in the effluent was... + =0ppm, Na + =0ppm, Li + =0ppm; then add 1250mL of ultrapure water to rinse the resin column, the effluent conductivity is 150μS / cm, Cl - =1.42ppm, add 500mL of 6% LiOH solution, the pH of the effluent is 14, and finally add 2000mL of ultrapure water to rinse the resin column. The conductivity of the effluent is 173μS / cm.

[0096] Preparation Example 2, Lithium Resin B: The preparation method is as follows:

[0097] Approximately 300 mL of sulfonic acid-type strong acid cation exchange resin was added to a 500 mL chromatography column, followed by rinsing with 250 mL of ultrapure water. The conductivity of the effluent was 43 μS / cm. Then, 250 mL of 35% sulfuric acid solution was added, and the K+ concentration in the effluent was [not specified]. + =0ppm, Na + =0.33ppm, Li + =0ppm; then add 1250mL of ultrapure water to rinse the resin column, the effluent conductivity is 195μS / cm, SO42- 2- =0.17ppm; then add 3900mL of 1.2% Li2CO3 solution, the pH of the effluent is 10.5; finally add 2000mL of ultrapure water to rinse the resin column, the conductivity of the effluent is 139μS / cm.

[0098] Example 1

[0099] This embodiment illustrates the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, including the following operations:

[0100] Prepare 1456g of a 7.5% KFSI aqueous solution, add 0.0291g of lithium carbonate, mix thoroughly, and then add to a chromatography column containing lithium resin A. Control the eluent flow rate at 40–90 mL / h to obtain a total eluent of 1435g (K). +=0.20ppm). The eluent was added to a flask and distilled under reduced pressure at 40°C to concentrate to 122g. 244g of dimethyl carbonate was added, and the solution was distilled under reduced pressure at 40-60°C until the solution weight was 243g. The dimethyl carbonate component in the distillate was refluxed into the flask, and the above reduced pressure distillation-reflux operation was repeated until the water content in the solution was 96ppm. After filtration, the solution was further distilled and concentrated to 208.05g (0.4450mol) to obtain a 40% liquid LiFSI product with a yield of 89.25% (based on KFSI mass), a water content of 105ppm (based on LiFSI mass), and a main content of 99.97%.

[0101] Example 2

[0102] This embodiment illustrates the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, including the following steps:

[0103] 778g of a 10% NaFSI aqueous solution was prepared and added to a chromatography column containing lithium resin A. The flow rate of the eluent was controlled at 40–90 mL / h, yielding a total of 760g of eluent (Na). + =0.33ppm). The eluent was added to a flask, and 0.0304g of lithium carbonate was added. After mixing thoroughly, the mixture was distilled under reduced pressure at 55°C and concentrated to 83g. 166g of methyl ethyl carbonate was added, and the mixture was distilled under reduced pressure at 40-60°C until the solution weight was 155g. The methyl ethyl carbonate component in the distillate was refluxed into the flask, and the above reduced pressure distillation-reflux operation was repeated until the water content in the solution was 50ppm. After filtration, the solution was further distilled and concentrated until the solution weight was 124.14g (0.3319mol), yielding a 50% liquid LiFSI product with a yield of 86.60% (based on NaFSI mass), a water content of 45ppm (based on LiFSI mass), and a main content of 99.96%.

[0104] Example 3

[0105] This embodiment illustrates the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, including the following steps:

[0106] 4576 g of a 7.5% KFSI aqueous solution was prepared and added to a chromatography column containing lithium resin A. The flow rate of the eluent was controlled at 40–90 mL / h. The final eluent contained Li. +=170ppm, lithium was consumed in the resin column; 1000mL ultrapure water, 5500mL 16% hydrochloric acid solution, 2000mL ultrapure water, 1250mL 6% LiOH solution, and 2250mL ultrapure water were added sequentially to the resin column for rinsing to regenerate the resin column; the above effluent was added to the resin column, and 1560g of 7.5% KFSI aqueous solution was added again, controlling the effluent flow rate at 40-90mL / h; when the Li in the effluent... + When the concentration of K0.01 = 126 ppm, the resin column regeneration operation described above is performed again; all the above effluent is added to the resin column, and the effluent flow rate is controlled at 40–90 mL / h, yielding a total of 6063 g (K0.01) of effluent. + =0.25ppm). The eluent was added to a flask, and 0.1213g of lithium carbonate was added. After mixing thoroughly, the mixture was distilled under reduced pressure at 40–60°C until the solution weight was 522g. 1044g of methyl ethyl carbonate was added, and the mixture was distilled under reduced pressure at 40–65°C until the solution weight was 1306g. The methyl ethyl carbonate component in the distillate was refluxed into the flask, and the above reduced pressure distillation-reflux operation was repeated until the water content in the solution was 95ppm. After filtration, the solution was further distilled and concentrated until the solution weight was 783.34g (2.0945mol), yielding a 50% liquid LiFSI product with a yield of 99.67% (based on KFSI mass), a water content of 41ppm (based on LiFSI mass), and a main content of 99.97%.

[0107] Example 4

[0108] This embodiment illustrates the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, including the following steps:

[0109] Prepare 643g of a 12.5% ​​KFSI aqueous solution and add it to a chromatography column containing lithium resin A. Control the eluent flow rate at 40–90 mL / h to obtain a total of 623g of eluent (K). + =0.36ppm). The eluent was added to a flask, and 0.02492g of lithium bicarbonate was added to dissolve it. The solution was then distilled under reduced pressure at 55°C and concentrated to 76g. 190g of dimethyl carbonate was added, and the solution was concentrated under reduced pressure at 35-60°C to 142g. The water content in the solution was 76104ppm. Then, 1330g of dimethyl carbonate was added in several batches, and the solution was concentrated under reduced pressure at 35-60°C to 142g. The water content in the solution was 93ppm. After filtration, the solution was further concentrated by distillation to 113.52g (0.3035mol) to obtain a 50% liquid LiFSI product with a yield of 82.70% (based on KFSI mass), a water content of 85ppm (based on LiFSI mass), and a main content of 99.96%.

[0110] Comparative Example 1

[0111] This comparative example is used to illustrate the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, which includes the following operations:

[0112] 1456 g of a 7.5% KFSI aqueous solution was prepared and added to a chromatography column containing lithium resin A. The flow rate of the eluent was controlled at 40–90 mL / h, yielding a total of 1435 g of eluent (K). + =0.20ppm). The eluent was added to a flask and distilled under reduced pressure at 40°C to concentrate to 122g. 244g of dimethyl carbonate was added, and the mixture was distilled under reduced pressure at 40-60°C. The dimethyl carbonate component in the distillate was refluxed into the flask. The above reduced pressure distillation-reflux operation was repeated until the water content in the solution was 106ppm. After filtration, the solution was further distilled and concentrated to a weight of 207.71g (0.4443mol), yielding a 40% liquid LiFSI product with a yield of 89.11% (based on KFSI mass), a water content of 110ppm (based on LiFSI mass), and a main content of 99.84%.

[0113] Comparative Example 2

[0114] This comparative example is used to illustrate the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, which includes the following steps:

[0115] 778g of a 10% NaFSI aqueous solution was prepared and added to a chromatography column containing lithium resin A. The flow rate of the eluent was controlled at 40–90 mL / h, yielding a total of 760g of eluent (Na). + =0.33ppm). The eluent was added to a flask and distilled under reduced pressure at 55°C to concentrate to 83g. 166g of methyl ethyl carbonate was added, and the solution was distilled under reduced pressure at 35-60°C until the solution weight was 155g. The methyl ethyl carbonate component in the distillate was refluxed into the flask, and the above reduced pressure distillation-reflux operation was repeated until the water content in the solution was 72ppm. After filtration, the solution was further distilled and concentrated to 123.57g (0.3304mol) to obtain a 50% liquid LiFSI product with a yield of 86.20% (based on NaFSI mass), a water content of 75ppm (based on LiFSI mass), and a main content of 99.85%.

[0116] Comparative Example 3

[0117] This comparative example is used to illustrate the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, which includes the following steps:

[0118] 4576 g of a 7.5% KFSI aqueous solution was prepared and added to a chromatography column containing lithium resin A. The flow rate of the eluent was controlled at 40–90 mL / h. The final eluent contained Li. +=188ppm, lithium was consumed in the resin column; 1000mL ultrapure water, 5500mL 16% hydrochloric acid solution, 2000mL ultrapure water, 1250mL 6% LiOH solution, and 2250mL ultrapure water were added sequentially to the resin column for rinsing to regenerate the resin column; the above effluent was added to the resin column, and 1560g of 7.5% KFSI aqueous solution was added again, controlling the effluent flow rate at 40-90mL / h; when the Li in the effluent... + When the concentration of K0.01 is 162 ppm, the resin column regeneration operation described above is performed again; all the above effluent is added to the resin column, and the effluent flow rate is controlled at 40–90 mL / h, yielding a total of 6063 g (K0.01) of effluent. + =0.28ppm). The eluent was added to a flask, mixed thoroughly, and then distilled under reduced pressure at 60°C to concentrate to 522g. 1044g of methyl ethyl carbonate was added, and the mixture was distilled under reduced pressure at 40-65°C until the solution weight was 1305g. The methyl ethyl carbonate component in the distillate was refluxed into the flask, and the above reduced pressure distillation-reflux operation was repeated until the water content in the solution was 88ppm. After filtration, the solution was further distilled and concentrated to 781.99g (2.0909mol) to obtain a 50% liquid LiFSI product with a yield of 99.50% (based on KFSI mass), a water content of 65ppm (based on LiFSI mass), and a main content of 99.86%.

[0119] Comparative Example 4

[0120] This comparative example is used to illustrate the preparation method of lithium bis(fluorosulfonyl)imide disclosed in this invention, which includes the following steps:

[0121] Prepare 643g of a 12.5% ​​KFSI aqueous solution and add it to a chromatography column containing lithium resin A. Control the eluent flow rate at 40–90 mL / h to obtain a total of 623g of eluent (K). + =0.36ppm). The eluent was added to a flask and distilled under reduced pressure at 55°C to concentrate to 76g. 190g of dimethyl carbonate was added, and the solution was concentrated under reduced pressure at 35-60°C to 142g, with a water content of 69521ppm. Then, 1330g of dimethyl carbonate was added in multiple batches, and the concentration was repeated at 35-60°C to 142g, with a water content of 110ppm. After filtration, the solution was further concentrated by distillation to 113.14g (0.3025mol) to obtain a 50% liquid LiFSI product with a yield of 82.43% (based on KFSI mass), a water content of 100ppm (based on LiFSI mass), and a main content of 99.85%.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing lithium bis(fluorosulfonyl)imide, characterized in that, The following steps are included: An aqueous solution of lithium bis(fluorosulfonyl)imide is provided, wherein the aqueous solution of lithium bis(fluorosulfonyl)imide contains an alkaline lithium salt, wherein the alkaline lithium salt is selected from one or more of lithium carbonate and lithium bicarbonate, and the mass content of the alkaline lithium salt in the aqueous solution of lithium bis(fluorosulfonyl)imide is 0.0001% to 10%. An aqueous solution of lithium bis(fluorosulfonyl)imide was concentrated by distillation to obtain a concentrated aqueous solution of lithium bis(fluorosulfonyl)imide. A non-aqueous organic solvent is added to a lithium bisfluorosulfonylimide aqueous concentrate and mixed. The non-aqueous organic solvent is selected from organic solvents that can form an azeotrope with water but are insoluble in water. The non-aqueous organic solvent is selected from organic solvents containing at least one functional group selected from ester, cyano, and ether bonds. The water is removed by distillation to obtain an organic solution of lithium bisfluorosulfonylimide.

2. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, The aqueous solution of lithium bis(fluorosulfonyl)imide was prepared by the following operation: A cation exchange resin column is provided, wherein the cation exchange resin column is filled with a strong acid type cation exchange resin, and the strong acid type cation exchange resin adsorbs lithium ions. Ion exchange: An aqueous solution of an alkali metal salt XFSI is provided, wherein X represents sodium ions and / or potassium ions. The aqueous solution of the alkali metal salt XFSI is passed through a cation exchange resin column for ion exchange, and the X ions on the alkali metal salt XFSI are replaced with lithium ions to obtain an aqueous solution of lithium bis(fluorosulfonyl)imide.

3. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 2, characterized in that, The alkaline lithium salt is added to the aqueous solution of the alkali metal salt XFSI prior to the "ion exchange" operation; And / or, the basic lithium salt is added to the aqueous solution of the lithium bis(fluorosulfonyl)imide after the "ion exchange" operation.

4. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, In the "distillation and concentration" operation, vacuum distillation is used, with a temperature of 5℃~80℃ and a pressure of 0~30 KPa.

5. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that, In the operation of "adding a non-aqueous organic solvent to a concentrated aqueous solution of lithium bis(fluorosulfonyl)imide, mixing, and distilling to remove water to obtain an organic solution of lithium bis(fluorosulfonyl)imide", distillation is performed, and water and non-aqueous organic solvents separate into layers in the distillate. The water is removed, and the second non-aqueous organic solvent is returned to the distillate. The solution is distilled until the water content is <200 ppm based on the mass of LiFSI to obtain an organic solution of lithium bis(fluorosulfonyl)imide.

6. The method for preparing lithium bis(fluorosulfonyl)imide according to claim 5, characterized in that, The mass concentration of the lithium difluorosulfonylimide aqueous concentrate is 30%-85%; The distillation is carried out under reduced pressure, with a temperature of 5℃~80℃ and a pressure of 0~30 kPa. The distillation process maintains a solution concentration of 2-60%; The organic solution of the lithium bis(fluorosulfonyl)imide has a mass concentration of 10% to 80%.