Effects of vinyl ethylene carbonate additive on elevated-temperature performance of cathode material in lithium ion batteries

The addition of 2% vinyl ethylene carbonate (VEC) into LiPF6/EC + DMC electrolyte can significantly improve the cyclic performance of a LiNi0.8Co0.2O2/Li cell at elevated temperatures such as 50 degrees C. In situ electrochemical mass spectrometry (EMS) was used to investigate the gas evolution spectroscopy in the cell during a charge/discharge process with and without VEC additive. Fourier transform infrared (FTIR), ultraviolet-visible (UV-vis), and liquid nuclear magnetic resonance (NMR) spectroscopies were also carried out to investigate the reactions between various electrolyte components and VEC without the electrochemical reaction. We propose the possible polymerized products based on the spectroscopy and the acting mechanism of the VEC additives.