The effect of fluoroethylene carbonate additive content on the formation of the solid-electrolyte interphase and capacity fade of Li-ion full-cell employing nano Si–graphene composite anodes

When fluoroethylene carbonate (FEC) is added to the ethylene carbonate (EC)–diethyl carbonate (DEC) electrolyte, the capacity and cyclability of full-cells employing Si–graphene anode and lithium nickel cobalt aluminum oxide cathode (NCA) cathode are improved due to formation of a thin (30–50 nm) SEI layer with low ionic resistance (∼2 ohm cm2) on the surface of Si–graphene anode. These properties are confirmed with electrochemical impedance spectroscopy and a cross-sectional image analysis using Focused Ion Beam (FIB)-SEM. Approximately 5 wt.% FEC in EC:DEC (1:1 wt.%) shows the highest capacity and most stability. This high capacity and low capacity fade is attributed to a more stable SEI layer containing less CH2OCO2Li, Li2CO3 and LiF compounds, which consume cyclable Li. Additionally, a greater amount of polycarbonate (PC), which is known to form a more robust passivation layer, thus reducing further reduction of electrolyte, is confirmed with X-ray photoelectron spectroscopy (XPS). •Li ion full cells employing Si–graphene anodes were used in this study.•FEC additive improves cyclability of the full-cell by formation of good SEI.•5 wt.% FEC is optimum with high capacity and low capacity fade.•5 wt.% FEC forms less amount of SEI compounds consuming Li+.