In the communication, the use of photoelectron spectroscopy in evaluating the electrochemical potentials for intercalation phase (Li/V2O5 system) is presented. Two contributions, i.e. Fermi level shift and formation of surface dipole, are the main factors in the change of battery voltage during the Li intercalation. It was found that the formation of surface dipole plays more important role in the decrease of the battery voltage due to the adsorption of Li on the surface. (c) 2006 Elsevier B.V. All rights reserved.