Numerical modeling of thermal runaway in high-energy lithium-ion battery packs induced by multipoint heating

Thermal runaway in lithium-ion batteries is a primary safety concern in electric vehicles (EVs). Herein, a numerical thermal abuse model is proposed that integrates ordinary differential equations (ODEs), heat-transfer partial differential equations (PDEs), natural convection in computational fluid dynamics (CFD), and thermal radiation to investigate thermal propagation in a battery pack. A three-dimensional geometric model of a high-energy lithium-ion battery pack comprising 18,650 format cells was constructed to analyze the thermal characteristics using the finite element method (FEM). A thermal abuse test was conducted to simulate the spread of thermal runaway in cells owing to multipoint heating. The maximum differences in the peak temperature between the proposed model and the model without convection were -150 K and 52.0 s, respectively, while the differences between the proposed model and the model without radiation were -52.4 K and -125.0 s, respectively. Furthermore, four additional models with different cell-to-cell gaps were constructed to study the thermal propagation characteristics, showing that the presence of a cell-to-cell gap accelerated heat transfer but compromised energy density for the battery pack. Ultimately, the coupling model at the pack level proposed in this study can improve the design of battery thermal management systems.