Thermal runaway assessment in automotive battery development is still largely driven by single-point abuse tests, while design decisions often require a quantitative understanding of how cell geometry, material thresholds, and thermal boundary conditions influence TR onset and severity. This paper presents a systematic parameter study using a coupled electrochemical–thermal model (SPMe combined with a lumped thermal model) augmented by Arrhenius-type decomposition reactions to represent the key exothermic pathways leading to Thermal Runaway. Two trigger modes are considered: (i) a nail-induced internal short circuit and (ii) an external heat-trigger scenario.
Four parameter groups are investigated: cell length scaling, separator decomposition temperature, external trigger power, and convective heat transfer coefficient to the environment. For the nail-triggered internal short circuit, larger cells exhibit lower peak temperatures but longer times to reach the maximum, highlighting a geometry-driven shift from “fast and hot” to “slower and moderated” escalation. In the external heat-trigger case, increasing cell size significantly delays Thermal Runaway onset, while peak temperature shows a non-linear trend and tends toward saturation rather than scaling inversely with size.
Varying the separator decomposition temperature reveals a similar saturation effect: above a reference range, the Thermal Runaway onset changes only marginally because alternative reactions can become the dominant trigger, and the causal order between short-circuit formation and chemical acceleration may reverse. For external heating power, a threshold behavior is observed: below a certain level, convective losses can balance input power and establish a quasi-steady temperature, preventing runaway. Even when external heating is stopped at an intermediate temperature, higher preheating power can still lead to higher peak temperatures due to increased remaining reactive inventory at the moment the internal short circuit occurs. Finally, improved heat rejection (higher heat transfer coefficient) consistently delays Thermal Runaway, reduces peak temperature, and markedly accelerates cool-down.
Overall, the study provides practical sensitivity trends and design-relevant “levers,” showing that thermal boundary management is often more effective for TR robustness than isolated material threshold shifts without system-level optimization.