Nascent SEI-Surface Films on Single Crystalline Silicon Investigated by Scanning Electrochemical Microscopy

Silicon is a promising high-capacity host material for negative electrodes in lithium-ion batteries with low potential for the lithiation/delithiation reaction that is outside the stability window of organic carbonate electrolytes. Thus, the use of such electrodes critically depends on the formation of a protective solid electrolyte interphase (SEI) from the decomposition products of electrolyte components. Due to the large volume change upon charging, exposure of the electrode material to the electrolyte must be expected, and facile reformation of SEI is a scope for improving the stabilities of such electrodes. Here, we report the formation of incipient SEI layers on monocrystalline silicon by in situ imaging of their passivating properties using scanning electrochemical microscopy after potentiodynamic charging to different final potentials. The images show a local initiation of the SEI growth at potentials of around 1.0 V vs Li/Li⁺ in 1 M LiClO₄ in propylene carbonate.