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

Abstract

To further the energy transition in the transportation sector beyond passenger cars, electrification of trucks is necessary. In these vehicles, commonly employed prismatic battery cells are generally organized as modules, with heat-insulating thermal pads between the cells. Understanding the influence of such thermal pads on thermal runaway propagation is required for developing safer large-scale batteries. In this study, thermal runaway propagation testing was employed at module level to explore the heat flow in the system using various thermal pads. The results show that this mapping, illustrated in Sankey diagrams, is a feasible method to evaluate the heat flow through different heat paths in a module during thermal runaway propagation. The mapping shows that heat paths, including conduction through thermal pads and busbars, heat dissipation into the ambient environment, and heat transfer through venting gas, can be quantitatively analyzed using empirical data. It was also found that heat transfer through the thermal pad is the main contributor to thermal runaway propagation. Low thermal conductivity of the thermal pad thereby significantly prolonged the thermal runaway propagation, from 66 s to 1185 s. This gives guidelines for the cooling system to prevent thermal runaway propagation, where the cooling power should ideally match the heat conduction through the thermal pad.

Keywords: Li-ion batteries, Thermal runaway, Heat flow, Thermal pad