Preparation method of liquid lithium bis (fluorosulfonyl) imide
By employing a liquid preparation method, organic solvents and porous polymer COFs are used to adsorb HF and HCl impurities. Combined with solvent concentration and lithium molecular sieve purification, the problems of high cost and low yield in traditional solid-state preparation methods are solved, and high-purity and high-yield liquid lithium bisfluorosulfonylimide is prepared.
Patent Information
- Application Number
- CN202511209300.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-27
- Publication Date
- 2026-01-02
AI Technical Summary
In the existing technology, the preparation process involves adding solid bis(fluorosulfonyl)imide lithium produced by the chlorosulfonic acid solid salt method to the electrolyte of a power battery. However, the existing technology suffers from problems such as high production cost and low product yield.
A liquid preparation method was adopted, in which organic solvent and high-purity lithium carbonate were added to the reaction vessel, the temperature and pH were controlled, porous polymer COFs were used to adsorb HF and HCl impurities, and solvent concentration and lithium molecular sieve purification were combined to prepare high-purity liquid lithium bisfluorosulfonamide.
The preparation of high-purity (over 99.9%) and high-yield (over 90%) liquid lithium bisfluorosulfonylimide has been achieved, reducing production costs, improving product purity and yield, and reducing impurity content.
Smart Images
Figure CN121247740A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium batteries, and in particular to the synthesis of lithium bisfluorosulfonylimide lithium electrolyte. Background Technology
[0002] Lithium difluorosulfonylimide has significant advantages over lithium salts such as lithium hexafluorophosphate due to its good electrical conductivity, thermal stability, and chemical stability. As the requirements for battery safety in new energy vehicles become increasingly stringent, the proportion of lithium difluorosulfonylimide added to power battery electrolytes is increasing.
[0003] Most lithium difluorosulfonylimide manufacturers use the traditional chlorosulfonic acid solid salt method to produce lithium difluorosulfonylimide. The main preparation process of the traditional chlorosulfonic acid solid salt method is to mix chlorosulfonic acid, aminosulfonic acid, and sulfonium chloride to prepare dichlorosulfonylimide acid, then react dichlorosulfonylimide acid with hydrogen fluoride to prepare difluorosulfonylimide acid, and then obtain lithium difluorosulfonylimide crystals through lithiation reaction, primary crystallization, and secondary crystallization. After secondary crystallization, a large amount of lithium difluorosulfonylimide still exists in the crystallization mother liquor, which needs to be crystallized again to recover some of the lithium difluorosulfonylimide. However, the presence of lithium difluorosulfonylimide in the mother liquor makes it difficult to effectively and completely crystallize and separate it, resulting in some yield loss. At the same time, multiple crystallizations increase energy consumption, making the process uneconomical. Solid lithium bis(fluorosulfonyl)imide produced by the chlorosulfonic acid solid salt method suffers from high production costs and low product yields, typically ranging from 70-80%. This keeps the overall production cost of lithium bis(fluorosulfonyl)imide high, hindering its large-scale application. To address these issues, this invention proposes a method for preparing liquid lithium bis(fluorosulfonyl)imide. This method not only produces qualified lithium bis(fluorosulfonyl)imide products but also achieves higher yields and significantly lower production costs compared to the traditional chlorosulfonic acid solid salt method. Summary of the Invention
[0004] To address the problems of low yield and high production cost in the traditional chlorosulfonic acid solid salt method for preparing liquid lithium bis(fluorosulfonyl)imide, this invention proposes a low-cost, high-yield method for preparing liquid lithium bis(fluorosulfonyl)imide. The preparation process is as follows: (1) Add an organic solvent to the reactor, then slowly inject difluorosulfonylimide acid into the organic solvent while stirring, and control the reactor temperature to maintain a low temperature of 0-20℃. Then add high-purity lithium carbonate with a purity of 99.9% or higher to the reactor in 3-10 batches, controlling the reactor temperature to not exceed 20℃. The mass ratio of organic solvent to difluorosulfonylimide acid is 1-5:1, and the molar ratio of high-purity lithium carbonate to difluorosulfonylimide acid is 1:2. After adding high-purity lithium carbonate, react for 2-5 hours, then add a small amount of high-purity lithium carbonate to adjust the pH of the solution to 4-8. Add a poor solvent, with a mass ratio of poor solvent to organic solvent of 1-5:1, and then continue stirring at a low temperature for 30-60 minutes. Filter to separate the residue, and the filtrate is the crude difluorosulfonylimide lithium solution. The crude lithium difluorosulfonylimide solution is then transferred to a distillation vessel and concentrated under negative pressure at a temperature of 30-80°C and a pressure of 300-1000 Pa. The total mass of the concentrated liquid is approximately 1.1-1.5 times the lithium difluorosulfonylimide content. The concentration should be carefully controlled to prevent lithium difluorosulfonylimide precipitation. The concentrated solution is then transferred to a glove box, and an organic solvent is added to adjust the lithium difluorosulfonylimide solution concentration to approximately 30 wt%. After adding the organic solvent, the solution is stirred until homogeneous. The organic solvent used here is the same as that used in the previous steps.
[0005] Preferably, the temperature of the above-mentioned reactor is controlled at 5-10℃.
[0006] Preferably, the pH of the solution is adjusted to 5-6 by adding high-purity lithium carbonate.
[0007] Preferably, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and ethyl acetate. More preferably, the organic solvent is selected from one of the commonly used electrolyte solvents, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.
[0008] Preferably, the undesirable solvent is selected from toluene, xylene, chlorobenzene, chloroform, dichloromethane, dichloroethane, carbon tetrachloride, cyclohexane, n-hexane, etc. More preferably, the undesirable solvent is selected from one of dichloromethane, cyclohexane, and n-hexane.
[0009] Preferably, the mass ratio of the aforementioned undesirable solvent to the organic solvent is 2-3:1.
[0010] Preferably, the concentration temperature is 35-50°C.
[0011] Preferably, the total mass of the concentrated liquid is 1.1-1.3 times the mass of lithium bis(fluorosulfonyl)imide.
[0012] (2) The prepared lithium bis(fluorosulfonyl)imide solution was passed into a packed tower 1 filled with porous polymer COFs, which has a good adsorption effect on acidic molecules such as HF and HCl. The adsorption rate was controlled at 3-5 BV / h. Then, a small amount of organic solvent was used for rinsing to remove the lithium bis(fluorosulfonyl)imide adsorbed on the surface.
[0013] Preferably, the porous polymer is selected from a Schiff base and is polymerized from amine monomers and aldehyde monomers. The amine monomer is selected from 2,5-diaminopyridine, p-phenylenediamine, 1,3,5-triaminobenzene, and benzyldiamine, and the aldehyde monomer is selected from 1,3,5-triformylbenzene and terephthalaldehyde. The polymer is prepared at a reaction temperature of 120°C, using mesitylene as the solvent and 0.1 mol / L trifluoroacetic acid as the catalyst, and reacted for 72 h. The molar ratio of amine monomer to aldehyde monomer is 1:1, and the volume ratio of solvent to raw material is 2:1. The polymer is then filtered, washed with tetrahydrofuran, and vacuum dried to obtain the final product. The entire reaction is carried out under argon protection.
[0014] More preferably, the COFs porous polymer used in this invention is polymerized from 2,5-diaminopyridine and 1,3,5-triformylbenzene. Specifically, the COFs polymer is prepared by reacting 2,5-diaminopyridine and 1,3,5-triformylbenzene at a reaction temperature of 120°C, using mesitylene as the solvent, 0.1 mol / L trifluoroacetic acid as the catalyst, and for 72 h. The molar ratio of 2,5-diaminopyridine to 1,3,5-triformylbenzene is 1:1, and the volume ratio of solvent to raw material is 2:1. The mixture is then filtered, washed with tetrahydrofuran, and vacuum dried to obtain the final product. The entire reaction is carried out under argon protection.
[0015] The packed tower 1 is a stainless steel packing column with an inner diameter of 20 cm and a length-to-diameter ratio of 8, coated with polytetrafluoroethylene. It has a spray head at the top and is filled with a porous polymer to two-thirds of its volume. Lithium difluorosulfonylimide solution is fed from the top of the packed tower 1 and then discharged from the bottom.
[0016] (3) Pass the lithium difluorosulfonamide solution that has passed through packed tower 1 into packed tower 2 containing lithium molecular sieves, controlling the column flow rate at 3-6 BV / h. Commercially available lithium molecular sieves require pretreatment; the pretreatment method is as follows: Soak the molecular sieve in a solution of lithium hydroxide, lithium sulfate, or lithium nitrate at a concentration of 3-5%, then stir at 50-80°C for 1-3 hours. Filter the solution and repeat the above steps 2-4 times. Finally, wash the solution multiple times with ultrapure water until the pH of the rinsing solution is neutral.
[0017] The solution is then transferred to an oven and dried at 300-350℃ for 8-12 hours to complete the sodium ion removal process. The desodium-ion-removed lithium molecular sieve is then packed into packed tower 2. The lithium bisfluorosulfonylimide solution, after passing through the porous polymer, is injected into packed tower 2 from top to bottom. A small amount of organic reagent is then injected into packed tower 2 for rinsing. A small amount of organic solvent is added to the resulting lithium bisfluorosulfonylimide solution to adjust the concentration to 30wt%, and this organic solvent is consistent with the one described above. Finally, a lithium bisfluorosulfonylimide solution with a purity of over 99.9%, a content of 30wt%±0.5%, and a product yield of over 90% is obtained.
[0018] The packed tower 2 is a stainless steel packing column with an inner diameter of 20 cm and a length-to-diameter ratio of 6, coated with polytetrafluoroethylene. The interior is filled with 95% volume of 4A lithium molecular sieve. The lithium difluorosulfonylimide solution is fed from the top of the packed tower 2 and then discharged from the bottom.
[0019] The present invention also provides a liquid lithium bis(fluorosulfonyl)imide prepared by the method, wherein the liquid lithium bis(fluorosulfonyl)imide has a purity greater than 99.9%, and the liquid lithium bis(fluorosulfonyl)imide contains less than 10 ppm chloride ions, less than 10 ppm fluoride ions, less than 10 ppm free acid, less than 10 ppm sodium ions, and less than 20 ppm moisture.
[0020] Preferably, the liquid bis(fluorosulfonyl)imide lithium contains less than 5 ppm chloride ions, less than 5 ppm fluoride ions, less than 5 ppm free acid, less than 5 ppm sodium ions, and less than 10 ppm moisture.
[0021] Preferably, the liquid bis(fluorosulfonyl)imide lithium contains less than 1 ppm of chloride ions, less than 1 ppm of fluoride ions, less than 1 ppm of free acid, less than 1 ppm of sodium ions, and less than 5 ppm of moisture.
[0022] The present invention provides a method for preparing liquid lithium bis(fluorosulfonyl)imide, which has the following significant advantages compared with the prior art: 1. This invention uses porous polymer COFs to adsorb HF and HCl impurities in lithium salt solution without affecting the yield of lithium bisfluorosulfonylimide, thereby reducing chloride and fluoride ion impurities in lithium bisfluorosulfonylimide to below 3 ppm, or even below 1 ppm.
[0023] 2. This invention employs a dehydration method that combines solvent concentration for preliminary dehydration with molecular sieve refining dehydration, reducing the solution moisture content to 20 ppm or even below 5 ppm. Furthermore, it pre-treats commercially available molecular sieves, ensuring that no sodium ions are introduced during use. The resulting lithium difluorosulfonamide solution contains less than 10 ppm of sodium ions, or even below 1 ppm. Attached Figure Description
[0024] Figure 1 This is a graph showing the IC detection results of Example 1.
[0025] Figure 2 This is a graph showing the IC detection results of Example 2.
[0026] Figure 3 This is a graph showing the IC detection results of Example 3.
[0027] Figure 4 This is a graph showing the IC detection results of Example 4.
[0028] Figure 5 This is a graph showing the IC test results for Comparative Example 1.
[0029] The IC detection method is used to detect the purity of lithium difluorosulfonylimide as a main component and anionic impurities such as fluoride and chloride ions. Detailed Implementation
[0030] To better understand the present invention, the following description, in conjunction with embodiments and related drawings, further illustrates the content of the present invention, but the content of the present invention is not limited to the following embodiments.
[0031] Example 1 Weigh 5 kg of 99% pure dimethyl carbonate organic reagent and add it to the reaction vessel. Then weigh 2266 g of difluorosulfonyl imide acid and slowly add it to the reaction vessel while stirring, controlling the temperature inside the vessel at 5℃. Next, weigh 492 g of lithium carbonate with a purity of 99.9% or higher and add it to the reaction vessel in 6 batches. React at 5℃ for 3 hours, then take a sample to measure the pH inside the vessel. The pH shows 3-4. Then add 100 g of lithium carbonate to adjust the pH to 6 and continue the reaction for 30 minutes.
[0032] Then, 10 kg of dichloromethane was weighed and added to the reactor. The reaction was carried out at a low temperature for 30 min. After filtration, the clear filtrate was concentrated under reduced pressure at 50°C and 800 Pa until the total mass of the concentrated liquid was 1.2 times the theoretical mass of lithium difluorosulfonylimide. Concentration was then stopped.
[0033] Add 4.5 kg of dimethyl carbonate solvent (99% purity, water content <50 ppm) to the concentrate and stir until homogeneous. Then, pump the adjusted lithium bisfluorosulfonyl imide solution into packed column 1 filled with COFs porous polymer, controlling the flow rate at 3 BV / h. The COFs polymer used in this example is formed by the polymerization reaction of 2,5-diaminopyridine and 1,3,5-triformylbenzene. Unless otherwise specified, the COFs polymers used in other examples are the same as those in this example. Rinse column 1 twice with a small amount of dimethyl carbonate. The material from the bottom of column 1 is then pumped into packed column 2 filled with 4A lithium molecular sieve, controlling the flow rate at 5 BV / h. The 4A lithium molecular sieve underwent sodium removal pretreatment before being packed into the column. Then, column 2 is rinsed with a small amount of dimethyl carbonate (99% purity, water content <50 ppm) to finally obtain liquid lithium bisfluorosulfonyl imide product. The test results are shown in Table 1.
[0034] Example 2 Unlike Example 1, diethyl carbonate was used as the good solvent. The test results are shown in Table 1 below.
[0035] Example 3 Unlike Example 1, the unsuitable solvent used was dichloroethane. The test results are shown in Table 1 below.
[0036] Example 4 Unlike Example 1, another type of COF was used, which was polymerized from monomers 1,3,5-tricarboxymethylbenzene and benzidine under the same reaction conditions. The test results are shown in Table 1 below.
[0037] Comparative Example 1 Unlike Example 1, the concentrated lithium difluorosulfonyl imide, after being adjusted, did not pass through the packed tower 1 filled with COFs polymer, but directly entered the packed tower 2 filled with 4A molecular sieve that had undergone sodium removal pretreatment, and finally obtained the liquid lithium difluorosulfonyl imide product. The test results are shown in Table 1.
[0038] Comparative Example 2 Unlike Example 1, the lithium difluorosulfonamide solution passed through packed tower 1 filled with COFs polymer, but did not pass through packed tower 2 filled with 4A molecular sieve that had undergone desodiumization pretreatment. The test results are shown in Table 1 below.
[0039] Comparative Example 3: Unlike Example 1, the 4A lithium molecular sieve packed in the packed tower 2 was not subjected to sodium removal pretreatment. The test results are shown in Table 1 below.
[0040] Table 1 Detection results of liquid bis(fluorosulfonyl)imide lithium
[0041] The test results from the above embodiments show that the method provided by this invention can prepare high-quality liquid lithium difluorosulfonyl imide with a purity of over 99.5%, fluoride and chloride ion impurities of less than 10 ppm, free acid content < 50 ppm, moisture content < 30 ppm, and sodium ion content of less than 10 ppm, with a yield > 90%, which is superior to the yield of general solid salt processes. Furthermore, the COFs polymer, synthesized from 2,5-diaminopyridine and 1,3,5-triformylbenzene monomers, exhibits better adsorption and removal effects for chloride and fluoride ions. In Comparative Example 1, the product did not pass through packed tower 1 filled with COFs polymer, resulting in insufficient removal of HCl and HF impurities, leading to severe exceedances of chloride and fluoride ions. In Comparative Example 2, the product did not pass through packed tower 2 filled with 4A lithium molecular sieves, resulting in ineffective moisture adsorption, excessive moisture content, and further partial decomposition of lithium difluorosulfonyl imide in an aqueous environment, causing a certain degree of exceedance of fluoride ions and free acid. In Comparative Example 3, the 4A lithium molecular sieve in packed tower 2 was not pretreated for sodium removal, resulting in a serious excess of sodium ions in the liquid bis(fluorosulfonyl)imide lithium product, demonstrating the necessity of sodium removal in the method of this patent invention.
[0042] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations; therefore, any obvious variations or modifications derived therefrom remain within the scope of protection of this invention.
Claims
1. A method for preparing liquid lithium bis(fluorosulfonyl)imide, characterized in that, Includes the following steps: (1) Difluorosulfonylimide acid is dissolved in an organic solvent, lithium carbonate is added, and the pH is adjusted to obtain a crude solution of lithium difluorosulfonylimide. (2) Add a certain amount of unsuitable solvent to the pH-adjusted solution, continue stirring at low temperature for 30-60 min, and filter to obtain crude lithium difluorosulfonylimide filtrate; (3) The crude filtrate is concentrated, degassed, and desolventized. After vacuum concentration, organic solvent is added to obtain lithium difluorosulfonylimide organic solution. (4) Then the above organic solution is passed into a packed tower 1 filled with porous polymer COFs material to fully adsorb the HCl and HF impurities contained in the lithium difluorosulfonylimide solution; (5) The adsorbed lithium difluorosulfonylimide solution is passed into a packed tower filled with 4A lithium molecular sieve to prepare lithium difluorosulfonylimide solution.
2. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 1, characterized in that, In step (1), the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and ethyl acetate.
3. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 1, characterized in that, The undesirable solvent in step (2) is selected from one or more of toluene, xylene, chlorobenzene, chloroform, dichloromethane, dichloroethane, carbon tetrachloride, cyclohexane, and n-hexane.
4. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 1, characterized in that, In step (3), the concentration temperature range is 30-80℃ and the concentration vacuum range is 300-1000Pa; the mass of the concentrated liquid is 1.1-1.5 times the content of lithium difluorosulfonylimide in the liquid.
5. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 1, characterized in that, In step (3), the mass concentration of the lithium difluorosulfonylimide organic solution is 25-40%.
6. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 1, characterized in that, In step (4), the porous polymer COFs is a type of Schiff base.
7. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 6, characterized in that, After adsorbing HCl and HF impurities in the lithium difluorosulfonylimide solution, the content of HCl and HF impurities in the lithium difluorosulfonylimide solution is reduced to less than 3 ppm, more preferably less than 1 ppm, more preferably less than 0.1 ppm, and more preferably less than 0.01 ppm.
8. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 1, characterized in that, In step (5), the pore size of the 4A lithium molecular sieve is 0.2-0.4 nm. Before use, the 4A lithium molecular sieve is soaked in one or more of lithium hydroxide solution, lithium sulfate solution or lithium nitrate solution, and then stirred, filtered and washed at 50-80℃ until neutral. After drying at 300-350℃, the sodium-free 4A lithium molecular sieve is obtained.
9. The method for preparing liquid bis(fluorosulfonyl)imide lithium according to claim 8, characterized in that, In step (5), the 4A lithium molecular sieve after sodium ion removal is filled into the packed tower, and the lithium difluorosulfonamide solution is injected into the packed tower from top to bottom. The column flow rate is controlled at 3-6 BV / h, and the lithium difluorosulfonamide solution is collected.
10. The liquid lithium difluorosulfonylimide prepared by the method according to any one of claims 1-9, characterized in that, The purity of liquid lithium difluorosulfonylimide is greater than 99.9%, and the chloride ion content, fluoride ion content, free acid content, sodium ion content and moisture content in liquid lithium difluorosulfonylimide are less than 10 ppm, less than 10 ppm, less than 10 ppm, less than 10 ppm, and less than 20 ppm. Preferably, the liquid lithium bis(fluorosulfonyl)imide contains less than 5 ppm chloride ions, less than 5 ppm fluoride ions, less than 5 ppm free acid, less than 5 ppm sodium ions, and less than 10 ppm moisture. Preferably, the liquid bis(fluorosulfonyl)imide lithium contains less than 1 ppm of chloride ions, less than 1 ppm of fluoride ions, less than 1 ppm of free acid, less than 1 ppm of sodium ions, and less than 5 ppm of moisture.