Thermal runaway in a prismatic lithium ion cell triggered by a short circuit

Abstract

Thermal runaway response due to a short circuit in a prismatic lithium iron phosphate battery (LiFePO4) is investigated. The decomposition of both positive and negative electrodes is simulated, representing all the reported exothermic reactions during thermal runaway using lumped and segregated models. It is shown that the reaction kinetics for similar chemistries reported in literature exhibit vastly different decomposition behavior, and that experimental rate kinetics reported in literature do not match decomposition behavior. A short circuit produces thermal runaway reactions that expand initially lengthways along the electrodes and then radially until reaching the wall of the cell; once thermal runaway has reached the cell edges, it rapidly propagates along the length of the cell. Using a reduced accuracy lumped model under predicts the time to reach thermal runaway as well as the average and maximum temperatures reached inside the battery. The magnitude of the short circuit plays a critical role in determining whether thermal runaway will occur throughout a battery. Inaccurate battery material properties are shown to play only a small part in the predicted thermal runaway behavior while initial temperature of simulation, applied heat transfer coefficient and electrode void fraction have a large effect on the thermal runaway response.