Discharge behavior and operational limits of second-and third-life lithium-ion batteries under different current rates

Abstract The growing volume of retired batteries has created a new market for low-power applications with minimal requirements. This market enables the use of Second-life Batteries (SLB) with a remaining capacity below 80% and Third-life batteries (TLB) with a remaining capacity below 60%. However, the challenge lies in repurposing the pack, particularly in selecting the cells to compose the new pack. It happens because retired batteries have distinct characteristics that differ from one another, and this distinction cannot be observed in simple capacity experiments. Therefore, it is essential to understand battery characteristics during operation to classify their lifetime accurately. Therefore, this work reports 81 experiments on nine batteries, segmented by degradation stage (from first to third life). Each battery was discharged at constant current levels ranging from 0.45C A to 2.05C, with increments of 0.23C. The results indicated that, although the batteries are in the same group, they present different characteristics, especially when discharged at low or high current rates. Although capacity is commonly used as the primary parameter for grouping a new pack, this study demonstrates that cells with similar capacities exhibit distinct behaviors during discharge. Additionally, the operation of retired batteries should be optimized to avoid unnecessary capacity loss. When a battery with low remaining capacity is discharged at high current rates, the voltage discharge profile is influenced by polarization and internal resistance effects, and, as a result, the voltage cut-off reaches the standard 2.5V earlier, reducing the battery’s discharge time. Finally, the study presents a reclassification of the batteries based on empirical insights from the experiments conducted in this work.