Optimized synthesis of cyclic fluorinated sulfonylimide lithium salts to suppress aluminum corrosion in lithium-ion batteries

LiCTFSI, lithium 4,4,5,5-tetrafluoro-1,3,2-dithiazolidine-1,1,3,3-tetraoxide, is a new promising lithium salt for usage in lithium-ion battery electrolytes, because it doesn't cause corrosion of the aluminum current collector below 5.0 V vs. Li+/Li. LiCTFSI can be synthesized in three steps, including Kolbe electrolysis, using 2,2-difluoro-2-(fluorosulfonyl)acetic acid as raw material. In this study, the synthesis route of LiCTFSI, hereby especially the Kolbe electrolysis, was optimized to achieve high purity (99.9%). Furthermore, performance of 4.2 V batteries using the as-synthesized LiCTFSI as lithium salt in acetonitrile-containing electrolytes showed that LiCTFSI is less corrosive towards aluminum than LiTFSI and reducing the sulfonamide impurity in LiCTFSI synthesis can further reduce aluminum corrosion.