Influence of the Arrangement of the Cells/Modules of a Traction Battery on the Spread of Fire in Case of Thermal Runaway

When designing the battery of an electric vehicle, different parameters must be considered to obtain the safest arrangement of the battery/modules/cells from the mechanical and thermal points of view. In this study, the thermal runaway propagation mechanism of lithium-ion cells is analyzed as a function of their arrangement within a battery pack in case of a fire propagation of a battery pack in which a thermal runaway has occurred. The objective is to identify which cell/module arrangement is most critical within the battery pack, using microscopic analysis of the structure and chemical composition of the most damaged cells, both horizontally and vertically, of a battery belonging to a burnt vehicle. And their final condition was compared with the condition of new cells of the same type. In this way, the structure and chemical composition of the cathode, anode, and separator after thermal runaway were compared. This research was carried out to obtain information to understand the mechanical properties of lithium-ion cells and their behavior after thermal runaway heating leading to the propagation of a fire. Through the analysis carried out, it is concluded that cells placed in a vertical arrangement have worse behavior than cells in a horizontal arrangement. Regarding the safety of the battery, the results of this study will allow us to determine which arrangement and structure of the cells in the battery pack is safer against thermal runaway due to thermal failure.