NaI/I-2 mediators and activated carbon were added into poly(ethylene oxide) (PEO)/lithium aluminate (LiAlO2) electrolyte to fabricate composite electrodes. All solid-state supercapacitors were fabricated using the as prepared composite electrodes and a Nafion 117 membrane as a separator. Cyclic voltam-metry, electrochemical impedance spectroscopy. and galvanostatic charge/discharge measurements were conducted to evaluate the electrochemical properties of the supercapacitors. With the addition of NaI/I-2 mediators, the specific capacitance increased by 27 folds up to 150 Fg(-1). The specific capacitance increased with increases in the concentration of mediators in the electrodes. The addition of mediators also reduced the electrode resistance and rendered a higher electron transfer rate between mediator and mediator. The stability of the all-solid-state supercapacitor was tested over 2000 charge/discharge cycles. (C) 2011 Elsevier B.V. All rights reserved.