Ionic liquid electrolytes containing a certain amount of bis(fluorosulfonyl)imide (FSI) anion can provide reversible capacity for a graphitized negative electrode without any additives such as a solvent. Cyclic voltammetry for a graphitized negative electrode in ionic liquid electrolytes containing FSI with other anions suggests that the reversibility of Li intercalation correlates with the relative quantity (or concentration) of FSI in the electrolytes, and that the correlative tendency depends on the other kind of anion. On the basis of the present results, we discuss the effect of FSI in the ionic systems on a graphitized electrode interface. (C) 2008 Elsevier B.V. All rights reserved.