Initiation of thermal runaway in Lithium-ion cells by inductive heating

An alternative thermal runaway initiation method for Li-ion cells has been developed based on the principles of inductive heating. Thermal runaway has been successfully triggered for different battery types, such as 3.1 Ah 18650 cylindrical cells, 39 Ah pouch and 94 Ah hard casing prismatic cells. A short burst of heat (few seconds) corresponding to only 1% of the electric energy of the cell is injected into the cell. The alternating electric field induces eddy current which heats up locally the conductive parts of the cell. Then through heat transfer the separator melts which results in internal short circuit. The initial short circuit develops to a hard internal short which triggers thermal runaway 10–20 s after the heater is switched off. The propagation of the initial internal short to thermal runaway can be observed visually by sparks and as open circuit voltage fluctuations. This newly discovered internal propagation may provide further insights into the failure mechanism of a single cell upon internal short and hence allow the development of new concepts to mitigate thermal propagation.