Kinetic Modeling and Adaptive Time Stepping for Battery Thermal Runaway Propagation

<div>0D, quasi-3D, and 3D chemistry solvers with varying degrees of complexity are developed to predict the thermal runaway propagation in battery cells. The 0D solver assumes the system as homogeneous and closed. The quasi-3D solver assumes the system as homogeneous on the selection level and the 3D solver accounts all spatial inhomogeneities in the temperature and composition. Both the quasi-3D and 3D solvers are fully integrated into a computational fluid dynamic (CFD) solver and capable of predicting thermal runaway in multiple battery cells with cell-specific kinetic reaction model. As the modeling complexity increases with each solver, respectively, the accuracy and the simulation time increases. With the large amount of heat and rapid transitions from the onset of thermal runaway, the CFD solvers usually encounter difficulties in predicting the solution accurately and in extreme heat release cases the solver may diverge. A chemical time scale based adaptive time stepping is developed in this work to address the accuracy, convergence, and stability issues of the CFD solver. The proposed timescale contains in the definition the reaction rate, reaction enthalpy, and total enthalpy content of the system. As the thermal runaway progresses, the CFD solver time step is obtained dynamically from the defined timescale. The developed solvers and the adaptive time-stepping method were quite intensively tested and analyzed by using different reaction mechanisms representing different battery cells and test conditions. The analysis of the timescales and the adaptive time stepping proved quite efficient for solution accuracy, simulation time, and solver stability.</div>