Suggested Citation:
Burke, Andrew, Marshall Miller, Hengbing Zhao (2012) Ultracapacitors in Hybrid Vehicle Applications: Testing of New High Power Devices and Prospects for Increased Energy Density. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-12-06

This paper is concerned with testing several of the new ultracapacitors being developed –both carbon/carbon and hybrid devices – and the application of those devices in micro- and charge sustaining hybrid vehicles. The carbon/carbon devices had energy densities up to 6.9 Wh/kg, 10 Wh/L and power capabilities up to 8.8 kW/kg for a 95% efficient pulse. This performance is significantly better than that of commercially available carbon/carbon devices.

Two new hybrid ultracapacitors were tested – a 1100F device from JM energy and a 5000F device from Yunasko. The 1100F device, packaged in a laminated pouch, had energy densities of 10 Wh/kg and 19 Wh/L and a power density of 2.4 kW/kg. The 5000F hybrid device utilized carbon and a metal oxide in both electrodes. The voltage range of the device is quite narrow being between 2.7 and 2.0V. The energy density is 30 Wh/kg for constant power discharges up to 2kW/kg and a power density of 3.4 kW/kg, 6.1 kW/L for 95% efficient pulses.

Simulations of mid-size passenger cars using the advanced ultracapacitors in micro-hybrid and charge sustaining hybrid powertrains were performed using the Advisor vehicle simulation program modified with special routines at UC Davis. The influence of the ultracap technology and the size (Wh) of the energy storage unit on the fuel economy improvement was of particular interest. The results for the micro-hybrids indicated that a 10-25% improvement in fuel economy can be achieved using a small electric motor (4 kW) and small ultracapacitor units (5-10 kg of cells). The fuel economy improvements for the mild-HEV ranged from 70% on the FUDS to 22% on the US06 driving cycles. In both micro- and mild-HEVs, the differences in the fuel economies projected using the various ultracapacitor technologies were very small.

Keywords: ultracapacitor, hybrid electric vehicle, simulation