State-of-Charge Implications of Thermal Runaway in Li-ion Cells and Modules

The thermal safety of lithium-ion (Li-ion) batteries for electric vehicles continues to remain a major concern. A comprehensive understanding of the thermal runaway (TR) mechanisms in Li-ion cells and modules due to intrinsic factors such as state-of-charge (SOC) and cell-to-cell arrangement under abuse scenarios such as external heating is critical toward the development of advanced battery thermal management systems. This study presents a hierarchical TR modeling framework to examine the TR behavior of Li-ion cells at various SOCs and probe its implications on the thermal runaway propagation (TRP) in a battery module. We perform accelerating rate calorimetry (ARC) experiments with 3.25 Ah cylindrical Li-ion cells at different SOCs and demonstrate the strong SOC dependence of TR characteristics such as the onset temperature, maximum cell temperature, and self-heating rate. The thermo-kinetic parameters extracted from the ARC experiments are used to develop a TR model that captures the SOC-induced TR response in Li-ion cells. The mechanistic information from the cell-level model is used to examine the pathways for TRP in a battery module consisting of cells with uniform and imbalanced SOCs, thereby demonstrating the underlying role of SOC variability on the resulting TRP under abuse conditions.