With the growth of the electric vehicle market, the demand for smaller and lighter batteries with greater capacity has never been higher. However, a key issue limit in Li-ion battery (LIB) applications is the potential safety. Thermal abuse, which is induced by either poor manufacturing quality control or poor thermal management design in nominal and off-nominal conditions, is the most dangerous scenario among various safety risks. Due to the complexity of the electrochemical/thermal system, LIB safety testing cannot provide sufficient information to show the mechanism of thermal runaway propagation during internal shorting. Therefore, a robust numerical model is the key to understanding the thermal runaway propagation and identifying the dominant parameters to mitigate thermal runaway in a battery module or pack. In Ansys Fluent, a comprehensive three-dimensional safety model for a Li-ion cell, which is based on a multiscale, multidimensional (MSMD) battery modeling methodology, has been developed. This safety model provides a unique capability to investigate the effects of an internal short circuit on thermal runaway propagation in a Li-ion battery. In this webinar, a three-dimensional thermo-electro-chemical model will be introduced. The model will be validated by comparing with the testing data. Moreover, a demo case will be shown to provide further insights into a passive heat sink design for Li-ion battery packs, which can be used to propose a configuration of a battery thermal management system to mitigate thermal runaway.