Predicting the evolution of flammable gases during Li-ion battery thermal runaway using micro-kinetic modelling

Li-ion batteries are a widely used electrochemical energy storage device. But, catastrophic failure via thermal runaway leads to great flammability and toxicity hazards. As such, there is a need to better understand the thermal runaway process. In doing so, reducing its occurrence and improving predictions of its hazards. To achieve this, we aim to develop a more detailed model of thermal runaway. This is based on fundamental reaction theory. Micro-kinetic modelling techniques are applied to predict the kinetic evolution of the reacting systems on a mechanistic level, based on a detailed analysis of the elementary reaction steps. Using this methodology, we simulate the thermal decomposition of dimethyl carbonate, as a model electrolyte solvent, and predict the product species present in the off-gas. We also investigate the impact of the temperature on the composition of the off-gas and the lower flammability limit. This demonstrates a method for predictive hazard assessments of Li-ion battery failure. For the DMC case study, we show that the LFL increases with increasing the operating temperature due to the large proportion of CO2 generated. This effectively makes the off-gas safer in terms of explosion hazards. Further work will extend this methodology to construct the reaction systems for a complete Li-ion cell.