Preventing Cell-to-Cell Propagation of Thermal Runaway in Lithium-Ion Batteries

It is presumed that heat generated from a trigger cell under thermal runaway (TR) in multi-cell Li-ion batteries is transferred to adjacent cells mostly by convection of ejected hot matter (and to a lesser degree by direct contact and radiative heat transfer). Therefore, venting the energized materials (ejecta) from the battery compartment should prevent cell-to-cell TR propagation. However, engineering solutions to vent ejecta from TR of an individual cell fail to prevent TR propagation, subsequently causing battery fires. Real-time in situ FTIR spectroscopy of ejecta from a cell driven into TR demonstrates that large amounts of carbonate esters are already vented from the cell before it goes into TR. The vented hot gases cool down and condense on top of adjacent cells. Subsequently, when the trigger cell reaches TR, this condensate ignites, transferring heat and potentially driving the receiving cells into TR. Computational fluid dynamics and thermal simulations of this pathway support the experimental findings. Numerical results indicate that a fraction of the solvent vented from the trigger cell is sufficient for efficient TR propagation. Our results shed new light on thermal propagation in multi-cell Li-ion batteries and suggest novel methods to prevent TR propagation.