Suggested Citation:
Burke, Andrew, Marshall Miller, Hengbing Zhao (2010) Lithium Batteries and Ultracapacitors Alone and in Combination in Hybrid Vehicles: Fuel Economy and Battery Stress Reduction Advantages. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-10-34

Most vehicles presently use batteries for energy storage, but there are vehicle designs in which ultracapacitors alone or in combination with batteries can increase the efficiency of the vehicle and in addition lead to significantly longer battery cycle life. Ultracapacitors can be used alone in charge sustaining hybrid vehicles (HEVs) if the energy storage requirement is less than 150Wh. Simulations show that when ultracapacitors are used alone in HEVs, the roundtrip efficiency of the energy storage is 95-98% and the engine efficiency in on/off operation can be maintained near the peak efficiency value. Vehicle simulations were also run for plug-in hybrid vehicles (PHEVs) using advanced batteries with high energy density (>300 Wh/kg). The simulations were run with the batteries alone and in combination with ultracapacitors. Simulation results for the electric useage (Wh/mi) and all-electric range and fuel economy (mpg) for the PHEVs using batteries in combination with ultracapacitors and batteries alone are presented. In all cases, the vehicles operate in a more ideal manner using batteries in combination with ultracapacitors than with the batteries alone. In addition, the dynamic stress on the batteries due to high current pulses are greatly reduced using the ultracapacitors.