Suggested Citation:
Burke, Andrew and Jingyuan Zhao (2017) Cycle Life of Lithium-ion Batteries in Combination with Supercapacitors: The Effect of Load-Leveling. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-17-48

Current thinking is that reducing the high current pulses experienced by the batteries in both charge and discharge will reduce the stress on the batteries and thus increase cycle life. This can be done by combining the batteries with supercapacitors. In the present study, modules of LiNiCoAl cells and LiFePO4 cells were cycled at constant current and on a dynamic pulse discharge/charge profile. Each module consisted of three 18650 cells. The average current for both discharge profiles was C/2. The degradation of the modules was tracked in terms of their Ah capacity and resistance as the cycling proceeded. The modules were cycled for about 700 cycles over a period of about six months. The cycling results of the present study were unexpected. For both lithium chemistries, the present data indicated that the modules degraded more rapidly with constant current cycling than using the dynamic pulse profile. One of the difficulties in comparing the data from different studies is that the test conditions, charging algorithms, and discharge profiles are quite different. It is not possible at the present time to identify the reasons for the inconsistencies between the various studies.

Keywords: Cycle life, degradation, dynamic pulse discharge, constant current discharge, LiNiCoAl, LiFePO4