Understanding the Spontaneous Reactions between Oxide-Free Silicon and Lithium-Battery Electrolytes

Here, we studied for the first time the kinetics of the chemical reactions between oxide-free silicon and electrolytes and the composition and morphology of the surface film formed during these reactions. We found that the kinetics of these reactions is swift; a few nm passivating film is formed during a few milliseconds and a complete passivation takes place in about 30 seconds. XPS study show a passivating film consisting of large organic molecules or polymers containing C-O, C=O, C-Fx and O-C-F moieties, SiFx, SiOxFy, some SiO2 and small amounts of LiF. Containing only traces of Li, it cannot serve as an SEI and may lead to lesser uniformity of the SEI formed on top of it.