Surface film formation on a graphite electrode in Li-ion batteries:: AFM and XPS study

The formation of a passivation film (solid electrolyte interphase, SEI) at the surface of the negative electrode of full LiCoO2/graphite lithium-ion cells using LiPF6 (1M) in carbonate solvents as electrolyte was investigated by means of x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The analyses were carried out at different potentials of the first and the fifth cycles, showing the potential-dependent character of the surface-film species formation. These species were mainly identified as Li2CO3 up to 3.8 V and LiF up to 4.2 V. This study shows the formation of the SEI during charging and its partial dissolution during discharge. Copyright (c) 2005 John Wiley & Sons, Ltd.