The surface film on lithium in LiAlCl4/SO2Cl2 electrolyte, LiAlCl4:3SO2 solvate, and mixture of these two electrolytes has been studied using ac impedance and scanning electron microscopy coupled to energy dispersive x-ray analysis. The film was found to be essentially LiCl in the case of LiAlCl4/SO2Cl2 and the mixture of LiAlCl4:3SO2 solvate and LiAlCl4/SO2Cl2 electrolyte, Differences in the film morphology were observed according to the nature of the electrolyte. Electrochemical results implied that the passivating layer behaved as a two-layer film, a primary thin and compact film and a secondary porous film which progressively covered the inner layer. The nature of the electrolyte and especially the presence of SO2 at the interface, was found to influence the growth of the film. A model of formation and growth of the passivating film is proposed to describe the behavior of the lithium in these electrolytes.