Thermal runaway and jet fire features of battery modules endured high-rate cycling in confined space: mechanism investigation and safety assessment

Lithium-ion batteries (LIBs) are known to be susceptible to thermal runaway (TR) under abusive conditions. Through heat conduction and other effects, thermal runaway propagation (TRP) can occur within a battery module, potentially leading to a much larger disaster. Most current research focuses on the TRP behavior of batteries arranged in specific physical configurations, with limited studies addressing the hazards posed by TR in real-world vehicle scenarios. The novelty of this study lies in using an actual vehicle frame as a confined space to create an experimental platform within a standard combustion chamber. Ten 40 Ah NCM batteries are assembled into a 2S5P module, and thermal abuse is applied to induce TR in one of the modules. The TRP characteristics and their impact on both the vehicle and the environment are systematically investigated. The experiment uses multiple instruments, including thermocouples, heat flux meters, and Fourier-transform infrared gas analyzers, to simultaneously monitor parameters such as temperature, voltage, heat flux density, and gas composition. A safety evaluation system is developed based on six key parameters—propagation time, propagation speed, peak temperature, heat flux density, smoke production rate, and heat release rate—to assess the safety of parallel modules from the perspective of TRP risk and hazard. The results show that the charge transfer effect caused by series–parallel configurations leads to a peak temperature difference of up to 200 °C within the module. The module voltage follows a fluctuation pattern, initially dropping, then rising, before gradually declining to 0 V. The horizontal heat flux density decreases as spacing increases, while the total longitudinal heat release (13.291 MJ) is significantly higher than the transverse release (2.5121 MJ). The concentrations of ten major components in the released smoke exceed the PC-STEL standard. In the parallel-connected module, Cell #6 presents the highest TRP risk, while Cell #8 poses the greatest TRP hazard. By simulating real-world scenarios and quantifying multiple hazard parameters, this study provides both experimental and theoretical support for the development of safety protection technologies for batteries in electric vehicles. © 2025 Elsevier Ltd.