The long-term formation kinetics of the solid electrolyte interphase (SEI) was studied on graphite electrodes in 1M LiClO4/PC with 5% acrylonitrile (AN) as electrolyte additive by electrochemical impedance spectroscopy at 1.0 and 0.5V versus Li/Li+, i.e. mainly outside the graphite intercalation region. To support the interpretation of the results, comparative experiments with Ni and Pt electrodes were performed at the same potentials. The resistance of the SEI on graphite and nickel shows similar time dependence. Whereas, R SEI of both electrodes exhibits a linear increase after 5–10h at 1.0V, a parabolic behavior could be observed at 0.5V (and even more expressed for Ni at 0.05V) typical of diffusion controlled growth kinetics. Temperature dependent measurements yielded activation energies for the ionic conduction of the SEI between 0.61 and 0.66eV. The results were the same for graphite at 0.5V and nickel at 1.0, 0.5 and 0.05V.