Improving the rate performance and stability of LiNi0.6Co0.2Mn0.2O2 in high voltage lithium-ion battery by using fluoroethylene carbonate as electrolyte additive

Fluoroethylene carbonate (FEC) is investigated as the electrolyte additive to improve the electrochemical performance of high voltage LiNi0.6Co0.2Mn0.2O2 cathode material. Compared to LiNi0.6Co0.2Mn0.2O2/Li cells in blank electrolyte, the capacity retention of the cells with 5wt% FEC in electrolytes after 80 times charge-discharge cycle between 3.0 and 4.5V significantly improve from 82.0 to 89.7%. Besides, the capacity of LiNi0.6Co0.2Mn0.2O2/Li only obtains 12.6mAhg(-1) at 5C in base electrolyte, while the 5wt% FEC in electrolyte can reach a high capacity of 71.3mAhg(-1) at the same rate. The oxidative stability of the electrolyte with 5wt% FEC is evaluated by linear sweep voltammetry and potentiostatic data. The LSV results show that the oxidation potential of the electrolytes with FEC is higher than 4.5V vs. Li/Li+, while the oxidation peaks begin to appear near 4.3V in the electrolyte without FEC. In addition, the effect of FEC on surface of LiNi0.6Co0.2Mn0.2O2 is elucidated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The analysis result indicates that FEC facilitates the formation of a more stable surface film on the LiNi0.6Co0.2Mn0.2O2 cathode. The electrochemical impedance spectroscopy (EIS) result evidences that the stable surface film could improve cathode electrolyte interfacial resistance. These results demonstrate that the FEC can apply as an additive for 4.5V high voltage electrolyte system in LiNi0.6Co0.2Mn0.2O2/Li cells.