Introduction of bis(fluorosulfonyl)imide (FSI) as an anion to an ambient-temperature ionic liquid electrolyte based on 1-ethyl-3-methylimidazolium (EMI) as well as lithium (Li) cations can provide a reversible Li intercalation into a graphitized electrode. while such intercalation is completely irreversible without FSI. The surface-layer components on the graphitized electrodes, cycled in the ionic liquid electrolytes with and without FSI, were found to be chemically similar based on X-ray photoelectron spectroscopy. Ac impedance spectroscopy revealed that the resistance of the electrode charged with FSI was Much lower even than that charged in a solvent electrolyte system containing ethylene carbonate (EC) and dimethyl carbonate (DMC). On the basis of these physicochemical analyses, the origins of cycleability in the presence of FSI are discussed. (C) 2008 Elsevier B.V. All rights reserved.