Reduced-Order Thermal Modelling of Battery Modules Under Passive Air Cooling

Lithium-ion cells are highly sensitive to temperature fluctuations, which accelerate ageing and degrade performance, making effective thermal management critical for safety and longevity. In large-scale battery packs, maintaining uniform cell temperatures is essential to extend pack life, especially in light electric vehicles where passive air cooling is a common thermal management system. Understanding cell module behaviour under such conditions is key to designing advanced cooling strategies and predictive control systems. Lumped thermal models are computationally efficient for real-time control but often overlook inter-cell heat flows and ambient effects. In contrast, finite element method (FEM) models provide detailed thermal insights but are too computationally intensive for onboard applications. This study introduces a reduced-order thermal model for battery modules under passive cooling, parameterized using FEM simulations. Low errors are observed when the model is compared to new FEM simulation cases. The model is then used to compute module-level temperature profiles under vehicle drive cycles. Significant temperature differences of 3° C and 4° C are observed by the end of US06 and WMTC cycles, respectively. This study enables the development of a real-time controller for a differential cooling enabled battery thermal management system.