Mapping Heat Flow in Prismatic Battery Modules During Thermal Runaway Propagation Using Empirical Data

To advance the electrification of the transport sector beyond passenger cars, electrifying heavy‐duty trucks is essential. These vehicles typically use prismatic lithium‐ion cells arranged in modules, separated by heat‐insulating thermal pads that enhance safety during thermal runaway (TR). In this study, we developed and applied a method to map heat flow through various paths during TR propagation across three test cases with different thermal pads. The results were quantitatively evaluated using Sankey diagrams, a novel approach in this context. Using this method, we measured in situ thermal conductivity and found significant differences from standard reference values. As expected, lower in situ thermal conductivity increased the delay in thermal propagation. However, the method revealed that while the thermal pad remains the primary heat flow path during TR propagation, other contributors become significant if the pad has sufficiently low thermal conductivity. This finding is noteworthy, as the pad with the lowest conductivity nearly stops the propagation altogether, and attention to the other paths could be the key to achieving a full stop. We conclude that by investigating thermal pads under operational conditions, this study provides valuable insights into critical heat transfer paths and failure mechanisms, offering guidance on optimizing battery safety and lifespan.