Vinyl ethylene carbonate as an electrolyte additive for high-voltage LiNi0.4Mn0.4Co0.2O2/graphite Li-ion batteries

Vinyl ethylene carbonate (VEC) is investigated as an electrolyte additive to improve the electrochemical performance of LiNi0.4Mn0.4Co0.2O2/graphite lithium-ion battery at higher voltage operation (3.0-4.5 V) than the conventional voltage (3.0-4.25 V). In the voltage range of 3.0-4.5 V, it is shown that the performances of the cells with VEC-containing electrolyte are greatly improved than the cells without additive. With 2.0 wt.% VEC addition in the electrolyte, the capacity retention of the cell is increased from 62.5 to 74.5 % after 300 cycles. The effects of VEC on the cell performance are investigated by cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), x-ray powder diffraction (XRD), energy dispersive x-ray spectrometry (EDS), scanning electron microscopy (SEM), and attenuated total reflectance-Fourier transform infrared (ATR-FTIR). The results show that the films electrochemically formed on both anode and cathode, derived from the in situ decomposition of VEC at the initial charge-discharge cycles, are the main reasons for the improved cell performance.