Development, Performance, and Vehicle Applications of High Energy Density Electrochemical Capacitors

This paper is concerned with the development and performance of high-energy density electrochemical supercapacitors (ECCs) and their application in HEVs, PHEVs, and HFCVs. Detailed test data are shown for the Skeleton Technology 5000 F carbon/carbon EDLC device and the Aowei 9000 F hybrid (4 V) supercapacitor (HSC). The EDLC device had an energy density of 8.4 Wh/kg and the hybrid SC had an energy density between 30 and 65, depending on its rated voltage and the power of the discharge. These energy densities are significantly higher than previous ECCs tested. They indicate that good progress is being made in increasing the energy density of commercial ECCs. Vehicle applications of the advanced ECCs were evaluated based on Advisor simulations on city and highway driving cycles. Simulations were made for six vehicle types ranging from compact passenger cars to Class 8 long haul trucks. The fuel economy was calculated for each vehicle type using a lithium battery, the EDLC Skeleton Technology capacitor and the two Aowei hybrid capacitors as energy storage in the powertrain. The 4.1 V hybrid capacitor in all cases was lighter and smaller than the lithium battery. The fuel economies of the HEVs on the FUDS cycle were significantly higher (30–50%) than that of the corresponding ICE vehicle, except for the long haul truck, for which the fuel economy improvement was 20%. In almost all cases, the fuel economy improvement was highest when using the 4.1 V hybrid capacitor. Simulations were also run for fuel cell-powered vehicles. For the fuel cell vehicles, the fuel economies using the three energy storage technologies varied only slightly. For all the fuel cell vehicles simulated, the 4.1 V hybrid capacitor was the lightest and smallest of the energy storage options, and produced the best fuel economy. As in the case of HEVs, the hybrid capacitors appeared to be the best option for energy storage in fuel cell vehicle applications.