Investigation of the Solid Electrolyte Interphase Formed by Fluoroethylene Carbonate on Si Electrodes

The solid electrolyte interphase (SEI) formed by a fluoroethylene carbonate (FEC)-based electrolyte on a Si electrode was investigated using X-ray photoelectron spectroscopy (XPS) and time of flight–secondary ion mass spectrometry (ToF-SIMS). The FEC-derived SEI consists of lithium fluoride and a polyene-compound, which are originated from free fluoride and the acetylene unit due to the preferential reaction of FEC, and is very thin. Oxidation of the Si electrode of the EC-based cell was confirmed, although it did not proceed to a significant extent. The FEC-derived SEI protects against not only the decomposition of the FEC-based electrolyte, but also oxidation of the Si electrode. The FEC-derived SEI acts as a passivation film for the Si electrode, which results in the improvement of the cycling performance.