Graphite/electrolyte interface formed in LiBOB-based electrolytes - I. Differentiating the roles of EC and LiBOB in SEI formation

The surface chemistry of graphitic anodes cycled in various lithium bis(oxalato)borate (LiBOB)-based electrolytes was studied by X-ray photoelectron spectroscopy, and a correlation was established between the C 1s spectra and the participation of the BOB- anion. Through continuous removal of the semicarbonate species by Ar+ bombardment, it was found that the main solid-electrolyte interface (SEI) ingredients come from two competing sources: the reduction products of cyclic carbonate and those of BOB- anion. Ethylene carbonate (EC) in electrolyte should control the initial surface chemistry owing to its higher reduction potential, while in EC-free solutions, BOB- anion is the main source of reduction products. The performances at elevated temperatures seem to require the coexistence of LiBOB and EC in electrolyte. (C) 2004 The Electrochemical Society.