The dream for an energy storage device is have an high energy density together with an high power density. The capacitors and the batteries try to improve at the maximum one of these two quality, but the trade-off can be find thanks to the supercapacitors. These new devices are similar to a capacitors, but instead to have a dielectric between the two electrodes they have an electrolyte: the charge’s storage is possible thanks two different phenomena, the electrical double layer and the pseudo-capacitance. The field of application is increasing: they could be use as capacitors when an high power density is needed, however having an high capacitance they could be also integrated with other devices similarly to batteries.