Modeling of Supercapacitors

Supercapacitors, also called electrical double-layer capacitors (EDLCs) or ultracapacitors, have attracted significant attention in recent years as a new class of electrical energy storage devices. Supercapacitors have much higher energy density than conventional capacitors and much higher power density than most batteries. As such, they complement these energy storage devices in many applications. Typically, a supercapacitor consists of electrodes, electrolytes, a membrane separator, and current collectors. When an electrical potential is applied between the two electrodes of a supercapacitor, cations (anions) will migrate into the negatively (positively) charged electrode, and an electrical double-layers (EDLs) forms at the electrode/electrolyte interface. As an analogy to conventional capacitors, in each EDL, the electrode serves as one conductor surface and the counterions adsorbed on the electrode serve as the other conductor surface. Since the separation between the electrode and counterions adsorbed on it is quite small (on the order of 1 nm), the electrical fields within EDLs are very strong, and hence, a large amount of energy can be stored for each unit electrode surface area. By adopting porous electrodes featuring fine pores, the surface area of electrodes can be very high, thus further enhancing supercapacitor’s capacitance. The charge storage capability (i.e., capacitance) of a supercapacitor depends primarily on the choice of electrolyte and electrode materials. Three types of electrolytes have been widely used in supercapacitors. Aqueous electrolytes such as sulfuric acid and KOH solutions are most widely used due to their good electrical conductivity and low cost, but these electrolytes suffer from low decomposition voltage (<1.2 V) and corrosion issues. As an alternative, two types of nonaqueous electrolytes are increasingly being used due to