Unlike batteries, ultra-capacitors can absorb electricity as quickly as an outlet can dispense it and discharge it just as fast.Right now, the best ultracapacitors hold only about 5 percent as much energy as a comparably sized lithium-ion battery—not enough to power an electric car, but enough to work in a supporting role. Carmakers such as Peugeot are already experimenting with ultracapacitors for regenerative braking and start-stop systems, which save fuel by cutting the engine at red lights before starting up again as soon as the driver touches the gas pedal. The next logical step is to add ultracapacitors to electric cars to handle the tasks that put excessive strain on batteries. Joel Schindall, a professor of electrical engineering at MIT, is researching ways to use nanotubes to improve ultracapacitors. "The best solution," he says, "is a hybrid where the battery is optimized for total energy storage, while the ultracapacitor satisfies the peak power demands during acceleration." Schindall and other scientists are working to create ultracapacitors that can store more energy by improving electrode materials on the molecular level. If they succeed—if ultracapacitors can one day approach the charge-carrying capacity of lithium-ion batteries—they could solve one of the more vexing problems facing electric vehicles: slow recharge times. The fastest fast-charge station takes 30 minutes to recharge an empty battery. (Any more current begins to damage the electrodes.) Ultracapacitors, by contrast, could soak up a full charge in a matter of minutes.