This paper is concerned with supercapacitors (electrochemical capacitors) and their applications in electric drive vehicles in place of or in combination with batteries. The electric drive vehicles considered are hybrid vehicles. Data are presented for the new carbon/carbon device from Skeleton Technologies showing an energy density of 9 Wh/kg and 95% efficient power capability of 1730 W/kg. Both of these characteristics are significantly better than those of commercially available devices. Test data are also shown for a hybrid supercapacitor from Yunasko that has an energy density greater than 30 Wh/kg and a 95% efficient power capability of 3120 W/kg. This device has the best performance of any supercapacitor device tested at UC Davis to date. Various vehicle applications of supercapacitors have been reviewed in detail. Simulation results are presented for light duty vehicles using supercapacitors in place of lithium batteries in hybrid vehicles. It was found in all cases that the vehicles using the supercapacitors had the same as or better performance than those using batteries and in general were more efficient.

The application of batteries and ultracapacitors in electric energy storage units for battery powered (EV) and charge sustaining and plug-in hybrid-electric (HEV and PHEV) vehicles have been studied in detail. The use of IC engines and hydrogen fuel cells as the primary energy converters for the hybrid vehicles was considered. The study focused on the use of lithium-ion batteries and carbon/carbon ultracapacitors as the energy storage technologies most likely to be used in future vehicles. The key findings of the study are as follows. 1) The energy density and power density characteristics of both battery and ultracapacitor technologies are sufficient for the design of attractive EVs, HEVs, and PHEVs. 2) Charge sustaining, engine powered hybrid-electric vehicles (HEVs) can be designed using either batteries or ultracapacitors with fuel economy improvements of 50% and greater. 3) Plug-in hybrids (PHEVs) can be designed with effective all-electric ranges of 30-60 km using lithium-ion batteries that are relatively small. The effective fuel economy of the PHEVs can be very high (greater than 100 mpg) for long daily driving ranges (80-150 km) resulting in a large fraction (greater than 75%) of the energy to power the vehicle being grid electricity. 4) Mild hybrid-electric vehicles (MHEVs) can be designed using ultracapacitors having an energy storage capacity of 75-150 Wh. The fuel economy improvement with the ultracapacitors is 10%-15% higher than with the same weight of batteries due to the higher efficiency of the ultracapacitors and more efficient engine operation. 5) Hybrid-electric vehicles powered by hydrogen fuel cells can use either batteries or ultracapacitors for energy storage. Simulation results indicate the equivalent fuel economy of the fuel cell powered vehicles is 2-3 times higher than that of a gasoline fueled IC vehicle of the same weight and road load. Compared to an engine-powered HEV, the equivalent fuel economy of the hydrogen fuel cell vehicle would be 1.66-2.0 times higher