Modeling thermal runaway of lithium-ion batteries with a venting process

Abstract

Thermal runaway poses a critical challenge for the safety of electric vehicles powered by lithium-ion batteries. A series of drastic exothermic reactions take place with gas generation during thermal runaway, making it challenging to accurately model the process. In this work, we present a reliable lumped thermal runaway model by incorporating heat transfer and gas generation reactions based on an experimentally kinetic analysis. The proportions of reactants in 18,650 lithium-ion batteries are determined by disassembling the batteries and weighing the components, while the reaction frequencies and activation energies of gas generation reactions are identified through the thermal gravity analysis tests on the anode and cathode components using Kissinger’s method. The reaction kinetic equations are then combined with energy and mass conservation equations to form the thermal runaway model, which is validated against accelerating rate calorimeter tests. Simulation results show that it is the pressure rather than temperature that triggers the ejection. Therefore, gas generation that can depict the internal gas change should be included in the model to accurately predict the time of the battery venting. Moreover, it is revealed that when the safety pressure increases from 1600 to 2400 kPa, although the venting moment delays from 4294 to 4465 s, the thermal runaway takes place 54 s earlier. Hence, an appropriate safety pressure design range is suggested to be 1800–2200 kPa. This work develops a robust thermal runaway model and offers new insights into the mechanisms of thermal runaway, which provides valuable guidance for the thermal safety design of lithium-ion batteries.