Methanesulfonyl chloride (MSC) forms a room temperature ionic liquid with AlCl3. The electrochemical properties of vanadium pentoxide (V2O5) films prepared by the sol-gel route were studied in this electrolyte. As a potential cathode, sodium is reversibly intercalated into the V2O5 film up to. a stoichiometry of 1.6 mole Na/mole V2O5 (-1 V versus Al(III)/Al < 1.5 V) after the first discharge. The diffusion coefficient (DNa+) in the V2O5 Min was determined to be between 5E- 14 and 9E- 12 cm(2)/s using the potentiostatic intermittent-titration technique.