Preparation method of lithium bis (fluorosulfonyl) imide

Abstract

The invention provides a method for preparing lithium bis (fluorosulfonyl) imide, which comprises the following steps of: reacting lithium fluoride and lithium carbonate serving as a mixed lithium source with the lithium bis (fluorosulfonyl) imide in a polar solvent, and adding the lithium carbonate twice at the same time, so as to finally obtain the lithium bis (fluorosulfonyl) imide with high purity and high yield. The yield of the prepared lithium bis (fluorosulfonyl) imide is 90% or above, the purity is 99.9% or above, the free acid value and the water content are both 30 PPM or below, and the actual use standards are both met. The method provided by the invention has the advantages of low cost and high yield, and is beneficial to industrial production.

Description

Technical field:

[0001] The invention relates to the technical field of battery electrolyte materials, and more specifically to a method for preparing lithium bis(fluorosulfonyl)imide. Background technology:

[0002] As people pay more and more attention to the green and low-carbon economy, lithium batteries are widely used in emerging fields such as new energy vehicles and digital products. Compared with traditional chemical batteries, lithium batteries have obvious advantages such as high operating voltage, high energy density, long life and no memory effect. Lithium batteries are composed of four parts: positive electrode, negative electrode, diaphragm and electrolyte. Among them, the electrolyte has a significant impact on the battery's cycle life, high and low temperature performance and safety performance.

[0003] Currently, lithium hexafluorophosphate is the most successful electrolyte lithium salt in commercial use, but its poor thermal and chemical stability hinders its application in high-power and high-energy storage batteries. Compared with lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide has the advantages of high stability, excellent low-temperature performance, good hydrolysis stability and more environmental friendliness. It can be used as a next-generation secondary lithium-ion battery electrolyte lithium salt to replace lithium hexafluorophosphate.

[0004] Patent CN116621130B discloses a method for preparing lithium bis(fluorosulfonyl)imide, wherein bis(fluorosulfonyl)imide and lithium carbonate are reacted in a mixed organic solvent, and bis(fluorosulfonyl)imide lithium salt is obtained by post-treatment, and each single solvent in the mixed organic solvent has different polarities, so that the reaction process is controlled to lithium bicarbonate, and almost no water is generated. Even if the lithium bicarbonate byproduct generated during the reaction can eventually be converted into lithium carbonate by heating and other methods, and then continue to be put into production, it actually leads to a decrease in the utilization rate of lithium carbonate.

[0005] Patent CN113800485B discloses a method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps: reacting bis(fluorosulfonyl)imide with lithium phosphate in a non-aqueous solvent to obtain a reaction solution containing lithium bis(fluorosulfonyl)imide, and post-treating to obtain lithium bis(fluorosulfonyl)imide. It can be seen from the embodiments of the invention that the purity of the lithium bis(fluorosulfonyl)imide prepared by the invention is not stable enough. In addition, the byproduct generated in the reaction process of the invention is lithium dihydrogen phosphate, which also leads to a decrease in the utilization rate of raw materials.

[0006] CN106430257B discloses a method for preparing porous high-activity lithium fluoride, which can be conveniently used for the preparation of lithium bis(fluorosulfonyl)imide to improve the purity and yield of the lithium bis(fluorosulfonyl)imide product; however, it is necessary to first prepare porous high-activity lithium fluoride, the overall process is relatively complicated, and the production cost is relatively high.

[0007] Therefore, there is an urgent need for a method for preparing lithium bis(fluorosulfonyl)imide with simple operating steps, low production cost, high purity and high yield. Summary of the invention:

[0008] The present invention intends to provide a method for preparing lithium bis(fluorosulfonyl)imide, so as to overcome the technical problems of low raw material utilization and high production cost in the prior art.

[0009] To achieve the above purpose, the technical ideas adopted by the present invention are as follows:

[0010] Lithium fluoride and lithium carbonate are used as mixed lithium sources and bis(fluorosulfonyl)imide are reacted in a polar solvent, and lithium carbonate is added twice in sequence, so as to finally obtain lithium bis(fluorosulfonyl)imide with high purity and high yield.

[0011] The technical solution of the present invention comprises the following steps:

[0012] (1) lithium fluoride, lithium carbonate and bis(fluorosulfonyl)imide are mixed and dissolved in a polar solvent in a molar ratio of 1:(0.1-0.2):(1.4-1.6), and a lithium-based desiccant is added, and the mixture is reacted at 25-40° C. for 2-3 hours; a certain amount of lithium carbonate is added again, and the reaction is continued for 1-2 hours;

[0013] (2) filtering the reaction system after the reaction, removing the desiccant and the generated by-products to obtain a filtrate; continuing to add a lithium-based desiccant to the filtrate, stirring the reaction for 1-2 hours, filtering again, washing, concentrating under reduced pressure, and drying to obtain lithium bis(fluorosulfonyl)imide.

[0014] Preferably, the molar amount of lithium carbonate added again in step (1) is 5-10% of the molar amount of lithium fluoride.

[0015] Preferably, the amount of the polar solvent used in step (1) is 2-4 times the mass of the bis(fluorosulfonyl)imide.

[0016] Preferably, the polar solvent in step (1) is a carbonate solvent or a carboxylate solvent. Further, the polar solvent is preferably one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, and ethyl propionate.

[0017] Preferably, the lithium-based desiccant in step (1) and step (2) is one or more of butyl lithium, lithium hydride, and lithium sulfate. The amount of the lithium-based desiccant in step (1) is 3-5% of the mass of the bis(fluorosulfonyl)imide; the amount of the lithium-based desiccant in step (2) is 0.1-1% of the mass of the bis(fluorosulfonyl)imide.

[0018] Preferably, the washing solvent in step (2) is carbon tetrachloride, the conditions for reduced pressure concentration are reduced pressure concentration at a temperature of 40-50°C and a pressure of -0.090 to -0.098 MPa, and the conditions for drying are drying to constant weight at 90-120°C in a nitrogen atmosphere.

[0019] The unreacted bis(fluorosulfonyl)imide in the system can be removed by washing with carbon tetrachloride, and the carbon tetrachloride and bis(fluorosulfonyl)imide can be recovered by vacuum distillation, respectively, and the corresponding substances can be recycled.

[0020] After testing, the yield of lithium bis(fluorosulfonyl)imide prepared by the present invention is above 90%, the purity is above 99.9%, and the free acid value and water content are both below 30PPM, which meet the actual use standards. The method of the present invention has the advantages of low cost and high yield, and is conducive to industrial production.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. Compared with lithium fluoride, the present invention uses lithium carbonate as a lithium source to react with bis(fluorosulfonyl)imide faster, so that the lithium ions in the reaction system are in an active state faster, thereby improving the reaction efficiency and the product yield.

[0023] 2. The overall amount of lithium carbonate used in the present invention is relatively small, and a lithium-based desiccant is added during the reaction, which can absorb the byproduct water in the reaction without affecting the reaction progress, promote the reaction to proceed in the forward direction, and reduce the water content in the product.

[0024] 3. The present invention adds lithium carbonate in two steps, and the purposes are different: the first step of adding lithium carbonate is to improve the reaction efficiency, and the second step of adding lithium carbonate is to consume the unreacted bis(fluorosulfonyl)imide and the generated hydrogen fluoride by-product; thereby greatly improving the utilization rate of the raw materials and the yield of the product. Specific implementation method:

[0025] In order to make the purpose, technical scheme and advantages of the present invention more clear, the technical scheme of the present invention is further described below through specific implementation methods. Those skilled in the art should know that the embodiments are only to help understand the technical content and technical effects of the present invention and should not be regarded as limiting the present invention.

[0026] Example 1

[0027] (1) 130 g (5 mol) of lithium fluoride, 37 g (0.5 mol) of lithium carbonate and 1267 g (7 mol) of bis(fluorosulfonyl)imide were mixed and dissolved in 2600 g of dimethyl carbonate (water content below 50 ppm), and 60 g of lithium hydride was added at the same time, and the mixture was reacted at 25° C. for 3 h; 37 g (0.5 mol) of lithium carbonate was added again, and the reaction was continued for 1.5 h;

[0028] (2) filtering the reaction system after the reaction, removing lithium hydride and generated by-products to obtain a filtrate; adding 12 g of lithium hydride to the filtrate, stirring and reacting for 1 hour, filtering again, adding 1600 g of carbon tetrachloride for washing, concentrating under reduced pressure at 40° C. and −0.095 MPa for crystallization, and drying at 100° C. under a nitrogen atmosphere to obtain lithium bis(fluorosulfonyl)imide.

[0029] Example 2

[0030] (1) 130 g (5 mol) of lithium fluoride, 74 g (1 mol) of lithium carbonate and 1448 g (8 mol) of bis(fluorosulfonyl)imide were mixed and dissolved in 3000 g of methyl acetate (water content below 50 ppm), and 70 g of butyl lithium was added at the same time, and the mixture was reacted at 35° C. for 2 h; 37 g (0.5 mol) of lithium carbonate was added again, and the reaction was continued for 1.5 h;

[0031] (2) Filter the reaction system after the reaction to remove butyl lithium and generated by-products to obtain a filtrate; continue to add 14 g of butyl lithium to the filtrate, stir and react for 1 hour, filter again, add 1600 g of carbon tetrachloride for washing, concentrate and crystallize under reduced pressure at 40° C. and −0.095 MPa, and dry at 100° C. under a nitrogen atmosphere to obtain lithium bis(fluorosulfonyl)imide.

[0032] Comparative Example 1

[0033] (1) 130 g (5 mol) of lithium fluoride and 1267 g (7 mol) of bis(fluorosulfonyl)imide were mixed and dissolved in 2600 g of dimethyl carbonate (water content below 50 ppm), and reacted at 25° C. for 3 h; then 74 g (1 mol) of lithium carbonate was added, and the reaction was continued for 1.5 h;

[0034] (2) Filter the reaction system after the reaction, remove the generated by-products, and obtain a filtrate; add 12 g of lithium hydride to the filtrate, stir and react for 1 hour, filter again, add 1600 g of carbon tetrachloride for washing, concentrate and crystallize under reduced pressure at 40° C. and −0.095 MPa, and dry at 100° C. under a nitrogen atmosphere to obtain lithium bis(fluorosulfonyl)imide.

[0035] Comparative Example 2

[0036] (1) 130 g (5 mol) of lithium fluoride, 74 g (1 mol) of lithium carbonate and 1267 g (7 mol) of bis(fluorosulfonyl)imide were mixed and dissolved in 2600 g of dimethyl carbonate (water content below 50 ppm), and 60 g of lithium hydride was added at the same time, and the mixture was reacted at 25° C. for 3 h;

[0037] (2) filtering the reaction system after the reaction, removing lithium hydride and generated by-products to obtain a filtrate; adding 12 g of lithium hydride to the filtrate, stirring and reacting for 1 hour, filtering again, adding 1600 g of carbon tetrachloride for washing, concentrating under reduced pressure at 40° C. and −0.095 MPa for crystallization, and drying at 100° C. under a nitrogen atmosphere to obtain lithium bis(fluorosulfonyl)imide.

[0038] The lithium bis(fluorosulfonyl)imide prepared in the above examples and comparative examples was weighed, its actual yield was calculated, and the purity test and the moisture content and impurity content test were performed. The test results are shown in the table.

[0039] Table. Actual yield and purity test results of samples in Examples and Comparative Examples

[0040] Actual yield (%) purity(%) <![CDATA[H2O / ppm]]> Free acid / ppm Example 1 95.28 99.96 29 23 Example 2 94.67 99.95 27 26 Comparative Example 1 85.49 99.82 47 21 Comparative Example 2 87.35 99.91 34 106

[0041] It can be seen from the table that the purity of the lithium bis(fluorosulfonyl)imide crystals obtained in the present invention reaches more than 99.9%, which meets the requirements of battery-grade lithium bis(fluorosulfonyl)imide, and the actual yield reaches more than 90%, which greatly saves costs.

[0042] From the comparison between the embodiment and comparative example 1, since lithium carbonate is added in the late stage of the reaction and no lithium-based desiccant is added, the reaction efficiency of lithium fluoride and bis(fluorosulfonyl)imide is not high enough, the yield of the final product is reduced, and its purity is also affected to a certain extent.

[0043] From the examples and comparative example 2, since lithium carbonate is added in the early stage, this will result in the inability to effectively remove the unreacted hydrogen fluoride dissolved in the solvent in the later stage, and the unreacted bis(fluorosulfonyl)imide cannot be effectively consumed, resulting in a decrease in the actual yield and an increase in the free acid contained therein, affecting the overall effect.

[0044] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing lithium bis(fluorosulfonyl)imide, characterized in that: The steps include: (1) lithium fluoride, lithium carbonate and bis(fluorosulfonyl)imide are mixed and dissolved in a polar solvent in a molar ratio of 1:(0.1-0.2):(1.4-1.6), and a lithium-based desiccant is added, and the mixture is reacted at 25-40° C. for 2-3 hours; a certain amount of lithium carbonate is added again, and the reaction is continued for 1-2 hours; (2) filtering the reaction system after the reaction, removing the lithium-based desiccant and the generated by-products, and obtaining a filtrate; continuing to add the desiccant to the filtrate, stirring the reaction for 1-2 hours, filtering again, washing, concentrating under reduced pressure, and drying to obtain lithium bis(fluorosulfonyl)imide.

2. The method according to claim 1, characterized in that The molar amount of lithium carbonate added again in step (1) is 5-10% of the molar amount of lithium fluoride.

3. The method according to claim 1, characterized in that The amount of the polar solvent used in step (1) is 2-4 times the mass of the bis(fluorosulfonyl)imide.

4. The method according to claim 1, characterized in that The polar solvent in step (1) is a carbonate solvent or a carboxylate solvent.

5. The method according to claim 4, characterized in that The polar solvent is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate and ethyl propionate.

6. The method according to claim 1, characterized in that The lithium-based desiccant in step (1) and step (2) is one or more of butyl lithium, lithium hydride, and lithium sulfate.

7. The method according to claim 1, characterized in that The amount of the lithium-based desiccant used in step (1) is 3-5% of the mass of the bisfluorosulfonyl imide; and the amount of the lithium-based desiccant used in step (2) is 0.1-1% of the mass of the bisfluorosulfonyl imide.

8. The method according to claim 1, characterized in that The washing solvent in step (2) is carbon tetrachloride, the conditions for reduced pressure concentration are reduced pressure concentration at a temperature of 40-50° C. and a pressure of -0.090 to -0.098 MPa, and the conditions for drying are drying to constant weight at 90-120° C. in a nitrogen atmosphere.