Multi-Mode Heat Transfer Simulations of the Onset and Propagation of Thermal Runaway in a Pack of Cylindrical Li-Ion Cells

Strategies to prevent or minimize propagation of thermal runaway in a pack of Li-ion cells are critically needed to ensure safe operation, storage and transportation. While significant literature already exists on thermal runaway simulations, several key questions of practical relevance have remained unaddressed. This work presents multi-mode heat transfer simulations to predict the onset and propagation of thermal runaway in a pack of cylindrical Li-ion cells. The impact of inter-cell gap and thermal properties of the interstitial material on onset and propagation of thermal runaway is studied. It is shown that high interstitial thermal conductivity promotes thermal runaway propagation. However, too low a thermal conductivity results in heat localization in the trigger cell, also leading to thermal runaway. An optimum range of interstitial material thermal conductivity is thus identified. The impact of trigger cell position on propagation is investigated. It is shown that, depending on external conditions, either the center or the corner position may be more susceptible to propagation. Finally, it is shown that radiation and natural convection play a key role in thermal runaway propagation. It is expected that the trade-offs identified here will help minimize the onset and propagation of thermal runaway in Li-ion battery packs.