In-Situ Spectro–electrochemical Insight Revealing Distinctive Silicon Anode Solid Electrolyte Interphase Formation in a Lithium–ion Battery

The formation and evolution of solid electrolyte interphase (SEI) layer on a silicon electrode in 1 m LiPF₆ in EC/DMC electrolyte is investigated by in-situ FTIR spectroscopy. The results point that lithium alkyl carbonates formation is initiated during a lithiation process via a one-electron reduction of EC/DMC, followed by a free radical reaction. Interesting enough, the studies indicate that most of the SEI material is actually formed in the delithiation process. Carbon dioxide (CO₂) generated at low potentials during the shallow lithiation process is consumed during a deeper lithiation process and also during subsequent delithiation processes, resulting in the formation of lithium carbonate.