Spectroscopic Characterization of Surface Films Formed on Edge Plane Graphite in Ethylene Carbonate-Based Electrolytes Containing Film-Forming Additives

Surface films formed on edge plane pyrolytic graphite electrodes were characterized by attenuated total reflection (ATR)-Fourier transform infrared spectroscopy (FTIR). FTIR-ATR spectra revealed that the surface films consisted mainly of LiOCO 2 R (R = alkyl or lithium alkyl carbonate), Li 2 CO 3 and (CH 2 CH 2 O) n on both the edge and basal planes, while the formation reactions at the edge plane proceeded more rapidly than those at the basal plane. The major constituents of the surface films formed at 0.1 and 0.8 V were LiOCO 2 R and Li 2 CO 3 , respectively. We discuss this difference based on the results in the literature. In addition, surface films derived from film-forming additives, such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), were investigated by ATR-FTIR and X-ray photoelectron spectroscopy (XPS), and the formation mechanisms are discussed by considering the reactivity of intermediate radical compounds.