Abstract

With the high industrial acceptance of lithium-ion batteries as an electric vehicle (EV) energy source, it is necessary to examine these batteries for critical safety issues. The contribution of this research is to investigate the state of charge (SOC) dependent thermal runaway detection of 18650 lithium-ion batteries due to mechanical abuse conditions. To achieve accurate results, an experimental setup was designed to capture temperature variations and deformation of the battery due to loading conditions, where four test protocols were used which were rod, circular punch, three-point bend and flat plate. The numerical simulation model was used for the battery layered model where the concentric layered formation was used for the single battery model. The proposed numerical simulation model integrates both temperature and structural changes.
To ensure accuracy, validation of the numerical simulation model was achieved by comparing these results with experimental results. The validation analysis of battery behaviour shows that the compared results are in good correlation with experimental work and the numerical simulation model can be used for the single battery layered model. Furthermore, numerical simulation analysis of impact load is conducted where results, using quasi-static and impact load, are compared to understand sequential failures and short circuit leading to thermal runaway.
Deformation of cells mimics thermal runaway where various thermal runaway detection strategies are employed in this work, including; force-displacement, voltage-temperature, stress-strain, SOC dependency and separator failure. Results show that a cell can undergo severe conditions even with no fracture or
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rupture, which may be slow to develop but they can lead to catastrophic failures. Short circuit displacement was used as an indication of initial failure for all test conditions and mean short circuit displacement was 6.94mm for all test protocols. Numerical simulation results show that with the moderate number of elements where element size is 1mm for active materials and current collectors, better results can be achieved.