Various ionic liquids based on 1-ethyl-3-methylimidazolium cation and tetrafluoroborate, tetracyanoborate, tris(pentafluoroethyl) trisfluorophosphate, bis(trifluoromethylsulfonyl) imide, bis(fluorosulfonyl) imide, and thiocyanate anions have been studied as electrolytes in two electrode supercapacitor test cells based on carbon cloth electrodes. Three electrode test cells were also completed and studied to analyze the processes taking place on electrodelelectrolyte interface at different electrode potentials. Electrical double layer formation and adsorption kinetics of ions onto electrode surface and mass-transfer processes in porous electrode and separator matrix, dependent on the conductivity, viscosity and melting temperature of ionic liquids, have been analyzed using impedance and cyclic voltammetry data. Electrical charge delocalization has been calculated and discussed to point out and explain differences in the behavior of ionic liquids as supercapacitor electrolyte at different electrode potentials. Suitability of 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium tetracyanoborate ionic liquids as electrolytes for supercapacitors has been demonstrated. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.022207jes] All rights reserved.