Electric double-layer capacitors (EDLC) using activated carbon as electrodes are practical electric energy storage devices for high power application. However, the common EDLC is limited by the low energy density (less than 4 Wh/kg). Here, we introduce a capacitor with much higher energy density (over 20 Wh/kg), in which graphitic carbon was chosen as the cathode instead of activated carbon. The cost of electrode material for capacitor can be reduced remarkably. The storage mechanism of anions at the graphitic carbon cathode is ascribed to a specific interaction between the anions and graphitic carbon. (c) 2006 The Electrochemical Society.