In-situ thermography revealing the evolution of internal short circuit of lithium-ion batteries

The demand for lithium-ion batteries is ever increasing while its safety is arousing great public concerns. The feature of a defective cell that may evolve to catastrophic failure is difficult to characterize, given the observation of the cell's internal structure is hard to make. Herein, this paper proposes a new method using thermography to characterize the evolution process from internal short circuit to thermal runaway inside a lithium-ion cell. The spatial and temporal temperature variation around the initiation point of the internal short circuit as well as the voltage and surface temperature are recorded in high frequency. The internal short circuit is triggered by the magnet and wax. The results show that the aluminum-anode-type internal short circuit can lead to thermal runaway by a sequence of the hot spot, gas generation, and combustion. Inadequate internal short circuit heat generation contributes to a temporary hot spot that gradually cools down to ambient temperature. Thermal runaway tends to occur when the hot spot above 150 °C reaches the area of 50 mm² and the majority of the exothermic side reaction heat in the hot spot area is released within ca. 2s. These results are expected to guide the design of safer lithium-ion batteries.