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 promising lithium salt for the usage in lithium-ion battery electrolytes, because it does not&nbsp“;“cause corrosion of the aluminum current collector below 5.0 V vs. Li/Li+ [1]. LiCTFSI can be synthesized in three steps, including Kolbe electrolysis, using 2,2-difluoro-2-(fluorosulfonyl)acetic acid as raw material. Kolbe electrolysis of 2,2-difluoro-2-(fluorosulfonyl)acetic acid can shorten a complicated purification process because this reaction is a supporting electrolyte-free reaction and easy to obtain 1,1,2,2-tetrafluoro-1,2-ethanedisulfonyl difluoride after reaction by layer separation. As a result, we found the conditions to reduce unfavorable by-products and to synthesize the target product in high purity (≥ 99.9%).

Furthermore, NCM111||graphite cells using the as-synthesized LiCTFSI added to an acetonitrile-containing electrolyte resulted in high initial Columbic efficiency and cycle performance by suppressing the aluminum corrosion. LiCTFSI does not cause aluminum corrosion like LiTFSI, lithium bis(trifluoromethanesulfonyl)imide, at the operating voltage of more than 4 V. In addition, the sulfonamide impurity, lithium 1,1-difluoromethanesulfonamide,
contained in LiCTFSI synthesized in this route were found to be corrosive to aluminum. This indicates that by reducing impurities in LiCTFSI synthesis, eliminating the source of aluminum corrosion, capacity losses can be reduced significantly, and short-circuiting can be prevented [2].

The use of acetonitrile as solvent, which has an excellent balance between viscosity and relative permittivity, in combination with LiCTFSI will enable the development of electrolytes with improved ionic conductivity. A lithium-ion batteries that combine high C-rate performance based on&nbsp“;“high ionic conductivity [3]&nbsp“;“with non-corrosive properties&nbsp“;“using LiCTFSI may lead to&nbsp“;“the next generation of&nbsp“;“batteries for a sustainable society.

References

[1] M. Iwaya, K. Ohharu, H. Okamoto, W.O. 2006/106960 A1 (2006).
[2] M. Ito, K. Hori, K. Maeda, K. Yakigaya, N. Uematsu, N. Matsuoka, J. Fluorine Chem. 257-258 (2022) 109975.
[3] N. Matsuoka, H. Kamine, Y. Natsume, A. Yoshino, ChemElectroChem 8 (2021) 2095-3104.