Effect of fluoroethylene carbonate additive on the low–temperature performance of lithium–ion batteries

Abstract

• FEC increased the ionic conductivity and electrochemical stability of electrolyte. • The inclusion of FEC enables Li||LCO cell to work efficiently at −40 °C. • The production of a highly fluorinated interfacial coating can be aided by the FEC. • FEC shows the advantage of high rate discharge at low temperature. The operation of lithium–ion batteries (LIBs) at low temperature is hampered by decreased electrical conductivity and delayed electrode reaction kinetics. Due to its positive solid electrolyte interphase (SEI) formation properties, fluoroethylene carbonate (FEC) is one of the most widely researched additives for LIBs. Herein, charge–discharge tests, electrochemical impedance spectroscopy scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X–ray photoelectron spectroscopy (XPS) were used to investigate the effect of FEC on LCO/Li cells. According to SEM, TEM and XPS results, the addition of FEC results in the formation of a thin and stable cathode–electrolyte interface (CEI) film on the surface of the LCO electrode. Charge–discharge curves show that adding FEC to the electrolyte reduces polarization while increasing the discharge capacity. At −40 °C, the discharge capacity in electrolyte with 10 wt% FEC is 75.3 % that at room temperature and only 46.8 % without FEC at 1C. LiF is the main component of the FEC electrochemistry that forms a CEI, which has a low interfacial resistance and improves the ionic conductivity of the electrolyte, thus facilitating the performance of the battery at low temperature.