A supercapacitor with graphene-based electrodes was found to exhibit a specific energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C (all based on the total electrode weight), measured at a current density of 1 A/g. These energy density values are comparable to that of the Ni metal hydride battery, but the supercapacitor can be charged or discharged in seconds or minutes. The key to success was the ability to make full utilization of the highest intrinsic surface capacitance and specific surface area of single-layer graphene by preparing curved graphene sheets that will not restack face-to-face. The curved morphology enables the formation of mesopores accessible to and wettable by environmentally benign ionic liquids capable of operating at a voltage over 4 Volts.
Technologically, the nano graphene-based, ionic liquid-enabled supercapacitor provides a specific energy density of 85.6 Wh/kg (based on the total electrode weight) at room temperature and 136 Wh/kg at 80°C, both measured at a current density of 1 A/g (corresponding to a high charge/discharge rate).
a) These are the highest energy density values ever reported for nano carbon material-based supercapaitors dominated by the electric double layer (EDL) mechanism, with minimal contribution from any redox-type pseudocapacitance mechanism.
b) These energy density values are comparable to that of the Ni metal hydride battery. This new technology provides an energy storage device that stores nearly as much energy as in a battery, but can be recharged in seconds or minutes. We believe that this is truly a breakthrough in energy technology.
The theoretical capacitance of graphene is 550 F/g (Farads per gram).