Researchers from Korea's Gwangju Institute of Science and Technology in Korea developed high-performance supercapacitors based on graphene. They say these capacitors can store almost as much energy as a Li-Ion battery and can charge/discharge in seconds. They also last for many tens of thousands of charging cycles.
The researchers use a highly porous graphene that has a huge internal surface area. To fabricate this material they reduced graphene oxide with hydrazine in water agitated with ultrasound. This results in a graphene powder that they then packed into a cell shaped like a cell and dried it at 140 degrees Celsius under pressure for five hour. The material was used as an electrode.
The porous material has a huge surface area - a single gram has a surface area that is bigger than a basketball court. This allows the electrode to accommodate much more electrolyte and ultimately determines the amount of charge the supercapacitor can hold. The researcher report that their supercapacitors can store over 60 Watts Hour per kg (at density of 5 Amps per gram) and has a specific capacitance of over 150 Farrads per gram. Just to compare, Li-Io batteries have an energy density of between 100 and 200 Watt hours per kilogram. The supercapacitor though can fully charge in 16 seconds.