Reaction mechanism study and modeling of thermal runaway inside a high nickel-based lithium-ion battery through component combination analysis

To diagnose and elucidate thermal runaway accompanying gas evolution of a lithium-ion battery, it is essential to understand the thermal side reactions that lead to thermal runaway inside a lithium-ion battery. It is very useful to make a reliable model that represents these reactions to analyze thermal runaway processes in order to secure battery safety and overcome high costs of large-scale experiments. This study proposes the reaction mechanism and the reaction model through the design of experiments with the combination of battery components such as a cathode, an anode, an electrolyte, and a separator. To develop the reaction mechanism, the peak temperature and calorific value of each reaction are obtained by using a differential scanning calorimeter. The change of mass and produced gas from each reaction are identified by using an online thermogravimetry-mass spectrometer. Based on these measurements, the reaction model is developed by estimating kinetic parameters obtained from the Kissinger analysis. The reaction model exhibits root-mean-square-error of 1.91 mW, 21.79 mW, and 4.53 mW in the electrolyte, the cathode and the anode, respectively, as compared to differential scanning calorimeter results, confirming its high fidelity. The proposed model illustrates the variation of volume fractions of each phase inside a lithium-ion battery to simulate electrochemical performance degradation during thermal runaway stage. The change in internal pressure is also evaluated by using the change in mass and volume of each phase. Based on the mechanism and model derived from this study, it is possible to pinpoint the electrochemical performance degradation and heat generation characteristics during thermal runaway.