Electric double layer capacitor (EDLC) is an electric energy storage device, which operates through charging and discharging dielectric layer (electric double layer) formed on interface between nanoporous carbon electrode and<br />
electrolyte. The EDLC has excellent power density and cyclability, but the energy density is smaller than rechargeable battery. The energy density of the EDLC is proportional to capacitance and square of maximum charge voltage. This review addresses the basic concept to design the nanostructure of porous carbon electrode to improve the energy<br />
density.