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 LiNi 0.4 Mn 0.4 Co 0.2 O 2 /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.