Double-layer carbon supercapacitors (electrochemicaldouble-layer capacitor (EDLCs)) based on two carbonelectrodes of high surface area separated by an electrolyteare the most popular electrochemical supercapacitors. Thecharge process is electrostatic with charge separation atthe two electrode–electrolyte interfaces. The EDLCs canthus be modeled with two capacitances in series with whatis called equivalent series resistance (ESR). Given that theelectrode capacitance depends on the reciprocal of thedouble-layer thickness, which is on the order of 1010m,and that it is directly related to the carbon surface area,typically of several hundred square meters per gram ofcarbon, the capacitance of EDLCs is significantly higherthan that of the dielectric and electrolytic capacitors. Thestored energy of EDLCs is also higher than that of thedielectric and electrolytic capacitors, but it is lower thanthat of batteries. Indeed, the faradic charge processes inbatteries involve all the bulk electrode...