Influence of the Layout of Cells in a Traction Battery on the Evolution of a Fire in the Event of a Failure

Research on the safety and impact of lithium-ion battery failure has focused on individual cells as lithium-ion batteries began to be used in small devices. However, large and complex battery packs need to be considered, and how the failure of a single cell can affect the system needs to be analyzed. This initial failure at the level of a single cell can lead to thermal runaway of other cells within the pack, resulting in increased risk. This article focuses on tests of mechanical abuse (perforation of cylindrical cells), overcharge (pouch cells), and heating (cylindrical cells with different arrangements and types of connection) to analyse how various parameters influence the mechanism of thermal runaway (TR) propagation. Parameters such as SoC (State of Charge), environment, arrangement, and type of connection are thoroughly evaluated. The tests also analyse the final state of the post-mortem cells and measure the internal resistance of the cells before and after testing. The novelty of this study lies in its analysis of the behavior of different types of cells at room temperature, since the behavior of lithium-ion batteries under adverse circumstances has been extensively studied and is well understood, failures can also occur under normal operating conditions. This study concludes that temperature is a crucial parameter, as overheating of the battery can cause an exothermic reaction and destroy the battery completely. Also, overcharging the cell can compromise its internal structure, which underlines the importance of a well-functioning battery management system (BMS).