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 Cu 6Sn 5-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.