A New Fluorinated Sultone as Multifunctional Electrolyte Additive for High-Performance LiCoO2/Graphite Cell

The energy density of lithium cobalt oxide (LiCoO2)-based cells can be increased by charging at voltages above 4.2 V. However, the poor interface stability of the cathode/electrolyte deriving from the continuous severe decomposition of the electrolyte on the cathode/electrolyte surface and the instability of the structure of the cathode at high-voltage operation limits their wider commercial application. Herein, a new fluoro-functionalized electrolyte additive, tetrafluoroethane beta-sultone (TFBS), is used for promoting the electrochemical performance of LiCoO2-based cells. Upon cycling between 3.0 and 4.5 V (vs. Li/Li+) with 0.5 C (1 C=274.4 mAh/g), it is shown that the capacity retention of the LiCoO2/graphite pouch-cell with TFBS-controlled electrolyte reaches 96.8 % (183.9 mAh g(-1)), yet it is 66.5 % (126.3 mAh g(-1)) for the pouch-cell without TFBS in baseline electrolyte at the 100(th) cycle. All the results indicate that TFBS can be decomposed prior to the solvents in the electrolyte and can then form low-resistance, high-conductivity interface layers on the surfaces of the cathode-electrolyte and the anode-electrolyte, respectively, thus improving the cycling stability of the cells at a high charging cutoff voltage (4.5 V).