Simulative Investigation of Measures to Prevent Thermal Runaway Propagation in Li-Ion-Battery Modules

Li-Ion batteries can reach safety-critical states due to wrong operation conditions, faulty battery management systems or late effects of manufacturing defects. In the worst-case scenario, a thermal runaway can occur. During the thermal runaway, the cell releases within seconds a high heat and gas amount leading to sudden temperature and pressure increase within a battery module. If there are no mitigation strategies considered, this likely leads to a propagation of the thermal runaway to neighboring cells. This work focuses on the investigation of measures to prevent propagation by thermal insulation, distribution and buffering of the released heat of a cylindrical 21700 cell. For this purpose, an FEM simulation model of a module including one cell running into thermal runaway is developed with COMSOL Multiphysics. The module consists of seven parallel arranged cells (see Figure 1). The heat release of the thermal runaway is modelled by decomposition reactions based on Arrhenius formulations. On the outer surfaces of the module, heat transport by convection and radiation is considered. The emitted gases are not considered. The heat amount and kinetical reaction parameters are derived from accelerated rate calorimetry (ARC) measurements. Therefore, a cell is heated stepwise under adiabatic conditions until a self-heating of the cell is detected or the thermal runaway occurs. A simulation study is performed to investigate the different mitigation strategies within a battery module. The cells are surrounded by a material whose properties are modified. For insulation and distribution, low or high thermal conductivities are considered. For heat buffering melting enthalpy and melting temperature of phase change materials (PCM) are investigated. Moreover, the cell distance is changed. The results show the possible combinations of material properties and cell distances. Limits for the different mitigation strategies can be derived.