Scientists of the Gwangju Institute of Science and Technology in South Korea developed a graphene supercapacitor that stores as much energy per kilogram as a lithium-ion battery and can be recharged in under four minutes.
The supercapacitor was created in two stages. First, the scientists exposed powdered graphite to oxygen in a controlled manner to produce graphite oxide, then continues to heat the graphite oxide to 160°C in a vessel which had an internal pressure of a tenth of an atmosphere. The chemical reactions that followed produced carbon dioxide and steam. The increased internal pressure these gases created, pushing against the reduced external pressure in the vessel, broke the graphite into its constituent sheets. Those, after a bit of further treatment to remove surplus oxygen, were then suitable for incorporation into a supercapacitor.
The result worked well, storing as much energy per kilogram as a lithium-ion battery and could be recharged in under four minutes. Scaled up to the size needed for a car, the current required to recharge it quickly would require a robust delivery system.