Effect of ultracapacitor-modified PHEV protocol on performance degradation in lithium-ion cells

The cycle life of lithium-ion batteries was investigated using a modified USABC electric vehicle testing protocol designed to simulate the effect of a hybrid energy-storage system (ultracapacitor and battery) in a plug-in hybrid electric vehicle. A side-by-side comparison of battery capacity and impedance changes with and without the effect of the ultracapacitor was performed. Calendar-life degradation effects were corrected for using control cells. The battery’s rate of cycle-related capacity degradation decreased by a factor of 2 and rate of cycle-related impedance degradation, by a factor of 5.9 when exposed to the ultracapacitor-modified profile. The modified profile avoids exposure to regeneration energy and reduces maximum voltage of the battery.

► An ultracapacitor in parallel with a battery was modeled and tested experimentally. ► The ultracapacitor lowered the energy throughput of the battery. ► Batteries coupled with an ultracapacitor showed less capacity loss. ► Batteries coupled with an ultracapacitor showed less resistance growth.