A preparation method of lithium bis(fluorosulfonyl)imide

Abstract

The present invention provides a method for producing lithium bis(fluorosulfonyl)imide. Lithium fluoride and lithium carbonate are reacted as mixed lithium sources with bis(fluorosulfonyl)imide in a polar solvent, and the lithium carbonate is added twice, one after the other, to ultimately produce high-purity and high-yield lithium bis(fluorosulfonyl)imide. The lithium bis(fluorosulfonyl)imide prepared by the present invention has a yield exceeding 90%, a purity exceeding 99.9%, and a free acid value and water content below 30 parts per million (PPM), both meeting practical usage standards. The method of the present invention has the advantages of low cost and high yield, making it suitable for industrial production.

Description

Technical field:

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

[0002] With growing interest in a green, low-carbon economy, lithium batteries are widely used in emerging sectors such as new energy vehicles and digital products. Compared to traditional chemical batteries, lithium batteries offer significant advantages such as high operating voltage, high energy density, long life, and no memory effect. Lithium batteries consist of four components: a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte significantly influences the battery's cycle life, high- and low-temperature performance, and safety.

[0003] Currently, lithium hexafluorophosphate is the most successful commercial electrolyte lithium salt, but its poor thermal and chemical stability hinders its application in high-power and high-energy storage batteries. Compared to lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide (LiFPS) offers advantages such as high stability, excellent low-temperature performance, good hydrolysis stability, and a more environmentally friendly design. It is a promising alternative to lithium hexafluorophosphate as a next-generation electrolyte salt for secondary lithium-ion batteries.

[0004] Patent CN116621130B discloses a method for preparing lithium bis(fluorosulfonyl)imide. Bis(fluorosulfonyl)imide reacts with lithium carbonate in a mixed organic solvent, followed by post-treatment to produce a lithium bis(fluorosulfonyl)imide salt. The polarity of each solvent in the mixed organic solvent differs, thereby limiting the reaction to lithium bicarbonate and virtually eliminating the production of water. Even if the lithium bicarbonate byproduct produced during this reaction can ultimately be converted to lithium carbonate through heating or other methods, allowing for continued production, this effectively reduces the utilization rate of the 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, followed by post-treatment to obtain the lithium bis(fluorosulfonyl)imide. The examples of this invention demonstrate that the purity of the lithium bis(fluorosulfonyl)imide prepared is not stable enough. Furthermore, the reaction process generates lithium dihydrogen phosphate as a byproduct, which also reduces raw material utilization.

[0006] CN106430257B discloses a method for preparing porous, highly active lithium fluoride, which can be conveniently used in the preparation of lithium bis(fluorosulfonyl)imide, thereby improving the purity and yield of the lithium bis(fluorosulfonyl)imide product. However, the method requires the preparation of porous, highly active lithium fluoride first, resulting in a relatively complex overall process and high production costs.

[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 provides 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 react with bis(fluorosulfonyl)imide in a polar solvent, and lithium carbonate is added twice in sequence 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 at 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; adding a lithium-based desiccant to the filtrate, stirring and reacting 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 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 separately by distillation under reduced pressure, and the corresponding substances can be recycled.

[0020] Testing has shown that the yield of the lithium bis(fluorosulfonyl)imide prepared by the present invention is greater than 90%, the purity is greater than 99.9%, and the free acid value and water content are both below 30 ppm, both meeting practical usage 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 the addition of a lithium-based desiccant during the reaction process can absorb the by-product water in the reaction without affecting the reaction progress, thereby promoting the reaction to proceed in the forward direction and reducing the water content in the product.

[0024] 3. The present invention adds lithium carbonate in two steps, with different purposes: 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 solutions and advantages of the present invention more clear, the technical solutions of the present invention are further described below through specific embodiments. Those skilled in the art should know that the embodiments are only for helping to 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. 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 to remove 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. 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) The reaction system after the reaction is filtered to remove butyl lithium and generated by-products to obtain a filtrate; 14 g of butyl lithium is further added to the filtrate, and the mixture is stirred for reaction for 1 hour, filtered again, and 1600 g of carbon tetrachloride is added for washing. The mixture is concentrated under reduced pressure at 40° C. and −0.095 MPa for crystallization, and dried 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 the mixture was 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) The reaction system after the reaction is filtered to remove the generated by-products to obtain a filtrate; 12 g of lithium hydride is added to the filtrate, and the mixture is stirred for reaction for 1 hour, filtered again, and 1600 g of carbon tetrachloride is added for washing. The mixture is concentrated under reduced pressure at 40° C. and −0.095 MPa for crystallization, and dried 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. The mixture was reacted at 25°C for 3 h.

[0037] (2) Filtering the reaction system after the reaction to remove 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, moisture content, and impurity content were tested. The test results are shown in the table.

[0039] Table. Actual yield and purity test results of 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] As can be seen from the table, the purity of the lithium bis(fluorosulfonyl)imide crystals obtained in the present invention reaches above 99.9%, which meets the requirements of battery-grade lithium bis(fluorosulfonyl)imide, and the actual yield reaches above 90%, which greatly saves costs.

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

[0043] From the examples and comparative example 2, since lithium carbonate is added in the early stage, it 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 lower 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 merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine 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 at a molar ratio of 1:(0.1-0.2):(1.4-1.6), and a lithium-based desiccant is added. The mixture is reacted at 25-40°C for 2-3 hours. Lithium carbonate is added again at a molar amount of 5-10% of the lithium fluoride, and the reaction is continued for 1-2 hours. (2) Filter the reaction system after the reaction, remove the lithium-based desiccant and the generated by-products, and obtain a filtrate; continue to add the desiccant to the filtrate, stir and react for 1-2 hours, filter again, wash, concentrate under reduced pressure, and dry to obtain lithium bis(fluorosulfonyl)imide.

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

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

4. The method according to claim 3, 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.

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

6. 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 bis(fluorosulfonyl)imide; and the amount of the lithium-based desiccant used in step (2) is 0.1-1% of the mass of the bis(fluorosulfonyl)imide.

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