Research into new negative electrode materials as an alternative to carbonaceous materials brings new questions about electrode/electrolyte interface mechanisms. For graphite, these mechanisms have great importance on the ageing phenomena. What about intermetallic alloys, such as Cu-Sn systems? The nature of the electrode and its potential of lithium ions uptake (different from graphite) may have a great influence on the passivation film formed at the surface of the electrode. In this paper, we report on the XPS study of the electrode/electrolyte interface of a Cu6Sn5-based electrode. The main difference with graphite is not the nature and composition of the passivation layer, but its poor dependence on the electrochemical reaction during cycling. (c) 2007 Elsevier B.V. All rights reserved.