The performance of an electrochemical double layer capacitor composed of activated carbon electrodes and 1-ethyl-3-methylimidazolium thiocyanate ([EMIm]SCN) as the electrolyte possessing extremely high conductivity and low viscosity, was investigated by cyclic voltammetry and galvanostatic charging/discharging. The effect of various factors governing the extraordinary performance of this capacitor in terms of its specific capacitance, current density, voltage and cycle-life, was examined in detail. (c) 2006 Elsevier B.V. All rights reserved.