A New Insight into the Content Effect of Fluoroethylene Carbonate as a Film Forming Additive for Lithium-Ion Batteries

摘要

The impact of various concentrations of fluoroethylene carbonate (FEC) on the electrochemicalperformance of mesophase-pitch-based carbon fibers (MCF) in ethylene carbonate (EC)-basedelectrolyte for lithium-ion batteries is investigated using cyclic voltammetry (CV) and charge- discharge test. As expected, adding increased concentrations of FEC (up to 1 vol%) to the controlelectrolyte resulted in better electrolyte conductivity, cycling performance and reversible capacity.However, high concentrations of FEC lead to the deterioration of electrochemical performance.Electrochemical impedance spectroscopy (EIS) combining with Scanning electron microscopy (SEM),Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectroscopy are usedin order to better understand the failure mechanisms of graphite electrode in electrolytes with highconcentrations of FEC. The results reveal that the deterioration of electrochemical performance ismainly due to the poor cohesion and flexibility of the solid electrolyte interphase (SEI) film formed onthe graphite electrode which leads to larger charge transfer resistance as well as the SEI filmresistance. Understanding how varying amounts of FEC impact cell lifetime and impedance allows foroptimized electrolyte formulations to be found for different applications that may balance lifetime andpower demands.