Supercapacitors are energy storage devices with very fast charge-discharge capability, high cyclic stability, high power density (measure of power output per unit volume). Supercapacitor can be classified into two based on the mechanism of charge storage as Electrochemical Double Layer Capacitor (EDLC) and Pseudocapacitor. EDLC store energy via adsorption of ions in the surface of electrode reversibly forming a double layer in the electrode-electrolyte interface. Since there is no chemical reaction is involved in the energy storage mechanism of EDLC, their kinetic is very fast and has longer cycle life and a higher power density but has a lower energy density. On the other hand, pseudocapacitor stores energy via reversible Faradaic reactions occurring in the bulk of the material. Pseudocapacitor has less power density and cyclic life since the energy is stored via chemical reaction and also has the advantage of high energy density than EDLC.

Capacitance (SI unit is F) of a supercapacitor is the ability to store energy as electrical charge and the capacitance can be expressed in terms of mass (specific capacitance), area (Areal capacitance) and volume (Volummetric capacitance).