An ultracapacitor, also called a supercapacitor, is an electrical double-layer capacitor (EDLC) with very high capacitance. Compared to common capacitors, ultracapacitors have much higher energy density and can store and release large amounts of energy very quickly. Ultracapacitors are used in applications where conventional capacitors would not be able to meet the demands, such as in electric vehicles and wind turbines.
Ultracapacitors are made up of two plates separated by an electrolyte. When a voltage is applied to the plates, ions from the electrolyte are attracted to one of the plates, forming an electrical double layer. This double layer stores charge like a conventional capacitor, but because of the small distance between the plates (on the order of nanometers), the amount of charge that can be stored per unit area is orders of magnitude greater than for a conventional capacitor. This gives ultracapacitors their very high capacitance.
The first commercially available ultracapacitor was developed by General Electric in 1957. Since then, there have been many advances in materials and manufacturing techniques, resulting in significant increases in performance. Today’s ultracapacitors have specific capacitances up to 60 times greater than early models, and energy densities up to 10 times greater than lead-acid batteries.
Ultracapacitors find many uses where extremely high power densities are required for short periods of time. One example is regenerative braking in hybrid electric vehicles or all-electric vehicles: when braking, the vehicle’s kinetic energy is converted into electricity which is stored in the ultracapcitor. The stored energy can then be reused when accelerating again, providing a significant boost to efficiency. Ultrcapactiors are also used as backup power supplies in cell phone towers and other critical infrastructure; if grid power is lost for even a brief period of time, the backup system can provide enough power to keep things running until grid power is restored.