Present and future applications of supercapacitors in electric and hybrid vehicles

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 and fuel cell vehicles. The first section of the paper presents recent test data for advanced proto-type devices. The data for the new carbon/carbon device from Skeleton Technologies showed 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 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 and fuel cell 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 cost of supercapacitors compared to lithium batteries was discussed briefly. It was shown that when one recognizes that the energy stored in the capacitors is less than 1/10 that in the batteries for hybrid applications, the price of supercapacitors needs to decrease to about .5–1 cent Farad for capacitors to be cost competitive with high power batteries at $500–700/kWh. In addition, there is a good possibility that the life of the capacitors would be equal to that of the hybrid vehicles.