Quantitative Evaluation of LiFePO4 Battery Cycle Life Improvement Using Ultracapacitors

This letter develops a systematic approach to quantitatively evaluate and compare LiFePO4 battery cycle life improvement using ultracapacitors (UCs). The impact of UC sizing on temperature rise, capacity loss, and power fade under a real dynamic load profile is included for a comprehensive discussion and evaluation. It is found that the cycle-related battery capacity losses are reduced by 28.6% (C/3) and 29.0% (1C) using the optimized number of UCs, while the reductions are 36.3% (C/3) and 39.3% (1C) assuming an infinite number of UCs. The reductions on the power fade are 23.6% and 57.3% for the cases with optimized and infinite numbers of UCs, respectively. The reductions on temperature rise, 1.38 degrees C and 1.93 degrees C, in the two cases are also observed when discharging from 80% to 30% state of charge in one test cycle. The developed approach in the letter could serve as a general procedure to evaluate the cycle life improvement for other types of batteries when combined with UCs.