Lithium doped WO3 electrochromic films have been deposited by thermal reactive evaporation of LiClO4 and WO3 ultra-pure powder mixture for different concentrations of the former from a Joule effect source, using an oxygen partial pressure of 5 x 10(-2) Pa. The substrate was a transparent conducting (20-25 Ohm/square), ITO film previously deposited on standard glass in the same run as the WO3 deposition, and it was kept at 200 degrees C of temperature during the WO3 evaporation. Secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) analysis revealed intercalation of Li+ and Cl- ions on the WO3 layer. Chrono-amperometric measurements with simultaneous optical transmittance analysis were performed in order to evaluate the electrochromic colouring efficiency and also the role played by the Li+ cations and the Cl- anions in the electrochromic structures.