Thermal Runaway Reactions Modeling in Lithium-Ion Batteries

Lithium-ion batteries are ubiquitously used as power source in a variety of applications due to their superior performance and reliability. However, thermal runaway of Li-ion batteries is a serious concern due to risks associated with such catastrophic event, and hence elucidating the different chemical reactions involved in the thermal runaway phenomenon is a highly active area of research. It is both cost and time prohibitive to experimentally assess the different battery pack designs for the possibility of thermal runaway event, and hence mathematical models play critical role in the battery safety research. Thermal runaway of battery pack is usually initiated by one or a small group of cells which are affected by abuse conditions such as internal short circuit, nail penetration, overcharging, etc., and then depending on the battery pack design and thermal management, thermal runaway can propagate to neighboring cells resulting in fires that can sustain for long time. Since understanding chemistry leading to thermal runaway at cell level is crucial, many studies, both experimental and modeling, have focused on this topic. Some of the important reactions involved in the onset of thermal runaway are primary SEI decomposition, secondary SEI formation due to reaction between electrolyte and intercalated lithium ions, electrolyte decomposition, separator melting, and cathode decomposition. Since it is difficult to directly measure the different species involved in these reactions, calorimetric based approaches are used to determine the reaction parameters; DSC and ARC are widely used for this purpose. The model consists of system of differential equations which can be solved as a function of time for species fractions and cell temperature. In this work, we have developed flexible and easy to use framework for solving thermal runaway model equations. Both the electrochemical reactions and thermal runaway reactions are solved together with the aim of tighter two-way coupling between these two different processes. Using this model, we analyze the different reaction mechanisms proposed in the literature. We discuss the models for pressure build up in the cell, venting, and combustion of the vented gases.