Prospects for ultracapacitors in electric and hybrid vehicles

The prospects for ultracapacitors for use in electric and hybrid vehicles in the near-term (within five years) are discussed based on the present status of the technology world-wide and the characteristics of devices that are available for purchase or in an advanced state-of-development and thus nearly ready to be marketed. The energy density (Wh/kg) of the devices presently available for purchase are too low (2.2 Wh/kg) for most vehicle applications and their price ($100-$300) is too high for even applications requiring only a small energy storage capacity (50-100 Wh). Prototype devices having an energy density of 5-8 Wh/kg are almost ready for marketing from several capacitor/battery companies. The higher energy density capacitors are carbon-based and use an organic electrolyte. They are fabricated using existing production equipment, so their price can be expected to be much lower when they are manufactured in high quantities and there are multiple sources for purchasing them. Projections of the future performance of ultracapacitors were made indicating energy densities of 10-20 Wh/kg are achievable in the relatively near-term using carbon electrode materials having specific capacitances of 150-200 F/gm