Single cell analysis of lithium-ion e-bike batteries aged under various conditions

In most cases, batteries consist of multiple cells with different interconnections in which the weakest cells determine the usable capacity, performance and lifetime. Since data on initial production-related cell to cell parameter variance is well known, only little data on variance change over lifetime is available. This work investigates how variance spreads with age. Twenty differently aged electric bike (pedelec) batteries are disassembled and the state of health, as well as the internal resistance, are measured cell by cell for each of these batteries. The results show the development of cell to cell variation of aged batteries. Gathered data is also used to calculate capacity limitations through progressed variation. The methodology of the investigation can be used to analyse potential use cases for active balancing systems.