Ultracapacitors, energy-storage devices that absorb and release charge in minutes, could be a rapid-charging, cheaper, and safer alternative to batteries for electric cars. But commercial ultracapacitors can hold just 5 percent of the energy of lithium-ion batteries, providing short power bursts that limit them to uses such as acceleration in hybrid buses. Researchers at Nanotek Instruments in Dayton, Ohio, have now made graphene electrodes that could lead to ultracapacitors with more than five times the energy density of commercial devices.