Check out what Scientific American has to say about these gizmos called “ultracapacitors” that could soon fuel cars without gasoline… and without chemical batteries:
Ultracapacitors store electricity by physically separating positive and negative charges. Batteries store energy using toxic chemicals and their effectiveness fades over time. In addition, recycling the heavy metals in batteries is a difficult task. Capacitors, on the other hand, are constructed of much smaller fine carbon nanotubes, Mak says.
A major advantage of ultracapacitors is their ability to efficiently capture electricity from regenerative braking systems and provide that electricity to power a car’s acceleration. Ultracapacitors not only charge more quickly than batteries, they also release energy more quickly, Mak says.
(and for more, there’s AP coverage of EEStor, a company putting ’em in electric cars. Charge for five minutes, drive for 500 miles.)