Application of Fluorine-containing Solvents to LiCoO2 Cathode in High Voltage Operation

We applied fluorine-containing solvents (FCSs) to an electrolyte for lithium (Li)-ion batteries with a cobalt oxide (LiCoO2) cathode to enhance the upper voltage limit and investigated its electrochemical properties in a proposed FCS-based electrolyte. FCSs were expected to have high oxidation resistance by introducing electron withdrawing fluorine atoms. A test cell containing a FCS-based electrolyte exhibited high and stable discharge capacity in 30 cycles even with a high upper cutoff voltage of 4.5 V when compared with a cell containing a conventional electrolyte. This improvement in the cycle performance was confirmed by an electrochemical impedance measurement. We found that the FCS-based electrolyte provides a favorable solid electrolyte interface (SEI) at the LiCoO2 cathode, leading to reversible charge-discharge behavior of the cathode.