Implications of Lithium-Ion Cell Variations on Multi-Cell Battery Pack Thermal Runaway

Lithium-ion battery packs are often made of multiple groups of parallel cells connected in series. This article addresses how the inherent variability in lithium-ion cell properties due to manufacturing inconsistencies may cause un-even current sharing between them when used in modules. Non uniform current sharing may cause some cells to overheat, that could lead to a thermal runaway. Results show that the intrinsic variability of cells creates large differences in currents and temperature, suggesting that designs could wrongfully be considered safe if the variability of the properties of the cells happens to be neglected. These differences in temperature and current are also shown to increase as the power demand increases, confirming that the parallel interaction of cells must be considered for the performance calculation for high discharge rate applications.