A method using ferrocene to characterize the solid-electrolyte-interphase in lithium-ion batteries is expanded from steady-state analysis to consider electrochemical impedance spectroscopy and transients in the open-circuit potential. Although surface films formed on glassy carbon differ quantitively among different electrodes, results from impedance are consistent with steady-state findings, that increasing formation time decreases film porosity. Evolution of open-circuit potential shows a qualitative trend consistent with other methods, but does not yield reasonable estimates of film thickness or porosity. Impedance results are less effective at extracting unique characterization parameters than steady-state methods but have major experimental advantages over rotating-disk electrode measurements. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.073203jes] All rights reserved.