Abstract: The solid electrolyte interface and its formed-behavior on silicon anode, which mainly occur during the first lithium ion insertion, were detected and analyzed by EIS, EDS and XPS. The results show that the SEI film on silicon electrode surface forms under a low lithium-inserting voltage. The thickness of SEI film increases with the
depth of the state of discharge. The depth XPS analysis of the electrode surface demonstrates the inhomogeneous characteristic of SEI film. LiF and Li₂CO₃ are the major lithiated components including in SEI film, whereas Li₂CO₃ more approaches to the surface exposed to the electrolyte and LiF is more close to the side of silicon electrode. Some trace of
silicon-containing compound, which might be the reacting product of electrolyte and silicon electrode, exists in SEI film.

Key words: lithium ion batteries, silicon anode, solid electrolyte interface film