Fluoroethylene carbonate as electrolyte additive to improve low temperature performance of LiFePO4 electrode

Fluoroethylene carbonate (FEC) was studied as electrolyte additive to improve the low-temperature performance of LiFePO4 electrode in lithium ion battery (LIB). The effects of the FEC on the LiFePO4 electrode were investigated by electrochemical impedance spectroscopy (EIS), galvanostatic charge/discharge tests, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). It was found that the LiFePO4 electrode, which was cycled in electrolyte containing 2 vol.% FEC, exhibited higher discharge capacity and better rate performance at low temperature than that without FEC. SEM and XPS results showed the morphology change and the formation of solid electrolyte interface (SEI). EIS results indicated that the interfacial impedances of the Li/LiFePO4 batteries with FEC additive were far smaller than those without FEC additive, especially at low temperature. The improved performances were ascribed to the enhancement of ion conductivity of SEI film and the decrease of polarization of LiFePO4 electrode.