An ultracapacitor, also called a supercapacitor, is an electrochemical capacitor with a higher energy density than normal capacitors, which potentially makes them a better fit for hybrid vehicles.
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.

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