CN-117699749-B - Purification method of lithium bis (fluorosulfonyl) imide and lithium ion battery

Abstract

The application relates to a purification method of lithium difluorosulfimide salt, which comprises the following steps of modifying a polytetrafluoroethylene membrane by utilizing plasmas and formic acid, immersing the polytetrafluoroethylene membrane into difluorosulfimide acid after modification, heating and drying to obtain a modified polytetrafluoroethylene membrane, dispersing lithium carbonate into dimethyl carbonate, adding difluorosulfimide acid, obtaining a reaction solution after reaction, filtering the reaction solution to obtain a filtrate, concentrating the filtrate for one time to obtain a lithium difluorosulfimide electrodialysis stock solution, carrying out electrodialysis purification on the lithium difluorosulfimide electrodialysis stock solution by utilizing the modified polytetrafluoroethylene membrane, and concentrating and crystallizing the obtained electrodialysis solution to obtain battery-grade lithium difluorosulfimide. The method provided by the application can reduce the purity requirement of the raw material lithium carbonate from the battery level to the industrial level, and is beneficial to industrial production.

Inventors

• WANG JIE
• LIU CHANG
• CHEN XIANWANG
• Kuang Shengjian
• ZHANG XIANGFEI
• QIN YUN
• YUE JINYU
• ZHENG LEI

Assignees

• 宜都兴发化工有限公司

Dates

Publication Date

20260508

Application Date

20231116

Claims (7)

1. 1. The method for purifying lithium bis (fluorosulfonyl) imide is characterized by comprising the following steps: S101, modifying a polytetrafluoroethylene film by utilizing plasma and formic acid, immersing the polytetrafluoroethylene film into difluoro sulfonyl imide acid after modification, heating and drying to obtain a modified polytetrafluoroethylene film, and modifying the polytetrafluoroethylene film by utilizing the plasma for 5-10 min at a heating temperature of 110-130 ℃, wherein the drying temperature is 180-220 ℃; S102, dispersing lithium carbonate in dimethyl carbonate, then adding difluoro sulfonimide acid, obtaining a reaction solution after the reaction is finished, filtering the reaction solution to obtain a filtrate, and concentrating the filtrate once to obtain difluoro sulfonimide lithium electrodialysis stock solution; And S103, carrying out electrodialysis purification on the lithium bis (fluorosulfonyl) imide electrodialysis stock solution by utilizing a modified polytetrafluoroethylene membrane, and concentrating and crystallizing the obtained electrodialysis solution to obtain the battery-grade lithium bis (fluorosulfonyl) imide.
2. 2. The method for purifying lithium difluorosulfimide as claimed in claim 1, wherein the modification of the polytetrafluoroethylene film by plasma and formic acid is carried out by immersing the polytetrafluoroethylene film in formic acid, and generating plasma above the polytetrafluoroethylene film by carbon dioxide and air.
3. 3. The purification method of lithium bis (fluorosulfonyl) imide according to claim 2, wherein the volume ratio of carbon dioxide to air is 7:1 to 10:1.
4. 4. The method for purifying lithium difluorosulfimide according to claim 1, wherein the electrodialysis purification process of the lithium difluorosulfimide electrodialysis stock solution by using the modified polytetrafluoroethylene membrane is that a plurality of modified polytetrafluoroethylene membranes are placed in a polytetrafluoroethylene electrolytic tank, the modified polytetrafluoroethylene membranes divide the polytetrafluoroethylene electrolytic tank into a plurality of electrolytic areas, the lithium difluorosulfimide electrodialysis stock solution is added into the electrolytic area positioned in the middle, anhydrous dimethyl carbonate is added into the rest of the electrolytic areas, and the electrodialysis is performed by electrifying.
5. 5. The method for purifying lithium bis (fluorosulfonyl) imide according to claim 4, wherein the voltage for electrodialysis by energizing is 10-20V for 10-20 min.
6. 6. The method for purifying lithium bis (fluorosulfonyl) imide according to claim 1, wherein in step S102, lithium carbonate is dispersed in dimethyl carbonate, and bis (fluorosulfonyl) imide acid is added after the temperature is reduced to 0 to 5 ℃.
7. 7. The method for purifying lithium bis (fluorosulfonyl) imide according to claim 1, wherein in step S103, the electrodialysis purification temperature is 10 to 15 ℃.

Description

Purification method of lithium bis (fluorosulfonyl) imide and lithium ion battery Technical Field The application relates to the technical field of electrolytes, in particular to a method for purifying lithium bis (fluorosulfonyl) imide and a lithium ion battery. Background Lithium bis (fluorosulfonyl) imide is named LiFSI, and the chemical formula is F 2NO4S2 Li. The lithium bis (fluorosulfonyl) imide has the performance characteristics of good high temperature resistance (stable temperature can be kept below 200 ℃), good low-temperature performance, difficult hydrolysis, more environmental protection and the like, and can be used as the electrolyte lithium salt of the next-generation secondary lithium ion battery for replacing lithium hexafluorophosphate. At present, lithium bis (fluorosulfonyl imide) is used as an electrolyte additive of a lithium ion battery, is usually mixed with lithium hexafluorophosphate and is applied to an electrolyte of a rechargeable lithium battery so as to improve the battery capacity and the electrochemical performance of the battery. In addition, lithium bis (fluorosulfonyl imide) has important industrial applications as a polymerization catalyst and an industrial antistatic agent. The synthesis of lithium bis (fluorosulfonyl imide) is generally prepared from a battery-grade alkaline lithium source and bis (fluorosulfonyl imide) acid by acid-base neutralization, and then concentrated, crystallized and purified. The neutralization of acid and alkali is an exothermic process, and water is generated by using alkaline lithium sources such as lithium carbonate, lithium hydroxide and the like, and because LiFSI forms solvates with water to form oil-like crystals which are difficult to crystallize, the crystallization and purification can be carried out only after the water removal agent is added in advance. Patent CN115367718A discloses a purification method of lithium difluorosulfimide, specifically discloses a method for adding a water removing agent bismuth trichloride or antimony trichloride into pretreatment liquid containing a crude lithium difluorosulfimide, carrying out dehydration reaction at 20-40 ℃, reacting for 1-6 hours after no acid gas escapes from a reaction system, filtering to obtain a filtrate, evaporating, concentrating and recrystallizing the filtrate to obtain high-purity lithium difluorosulfimide. According to the method, most of water is removed through the reaction of adding the water scavenger antimony trifluoride, the hydrolysis degree is reduced, the generation of LiFSI decomposed impurity sulfate radical is reduced, the crystallization and purification burden can be lightened, however, the chlorine ion impurity is easily introduced by adding the water scavenger antimony trifluoride, and the recrystallization is needed for further purification. Patent CN104925765A discloses a preparation method of difluoro sulfonimide lithium salt, which adopts thionyl chloride to remove water and separate LiFSI crystal, SO 2 and HCl gas are generated by reaction, a large amount of inert solvent is needed for pulping and cleaning after the post-treatment, and acid waste is high. Patent CN108002355A discloses a preparation method of difluoro sulfonimide lithium salt, which adopts a water remover thionyl chloride, concentrated sulfuric acid or anhydride to remove water, and then obtains a LiFSI crude product, and the LiFSI crude product also needs recrystallization and purification. Based on the analysis, the purification method of the lithium bis (fluorosulfonyl) imide, which does not need to additionally add a water scavenger, is simple and convenient to crystallize and has easily qualified anion content, is necessary. Disclosure of Invention The embodiment of the application provides a purification method of lithium bis (fluorosulfonyl) imide, which aims to solve the problems that the anion content is not easy to be qualified in the purification process of preparing battery-grade lithium bis (fluorosulfonyl) imide in the related art, and a water scavenger is needed to be added before crystallization and purification. In a first aspect, the application provides a method for purifying lithium bis (fluorosulfonyl) imide, comprising the steps of: s101, modifying a polytetrafluoroethylene film by utilizing plasma and formic acid, immersing the polytetrafluoroethylene film into difluoro sulfimide acid after modification, heating and drying to obtain a modified polytetrafluoroethylene film; S102, dispersing lithium carbonate in dimethyl carbonate, then adding difluoro sulfonimide acid, obtaining a reaction liquid after the reaction is finished, filtering the reaction liquid to obtain a filtrate, and concentrating the filtrate once to obtain difluoro sulfonimide lithium electrodialysis stock solution; And S103, carrying out electrodialysis purification on the lithium bis (fluorosulfonyl) imide electrodialysis stock solution by utilizing a modified polytetrafluoroethylene membr