The butylmethylpyrrolidinium bis(trifluoromethylsulfony)imide (BMP-NTf2) ionic liquid was found to have a very wide potential window of 4.5 V, making it capable of being a medium for electrodepositing metallic Mn thin film. By using an electrochemical process, block manganese counter electrode was dissolved in the ionic liquid to generate divalent Mn, which was subsequently cathodically deposited on the nickel substrate. The current efficiency of this process was confirmed to be extremely high (close to 100%). The Mn thin film can be oxidized to manganese oxide by cyclic voltammetry in Na2SO4 electrolyte. The obtained manganese oxide exhibited an excellent pseudo-capacitive performance and possessed a satisfactory specific capacitance of 265 F/g at a moderate cyclic voltammetric sweep rate of 25 mV/s. (c) 2006 The Electrochemical Society.