Coupled Electrochemical-Thermal Runaway Model of Lithium-Ion Cells Operating Under High Ambient Temperatures

The risk of thermal runaway (TR) in high energy density Lithium-ion batteries (LIBs), which may initiate at around 90 °C, is a critical safety concern, particularly in regions where summer temperatures can reach nearly 50 °C. While multiple exothermic reactions that cause TR and modeled using Arrhenius equations lead to good predictions in controlled oven tests, their use in practical applications is questionable as these do not consider internal electrochemical processes that cause temperature rise and trigger exothermic reactions. Further, limited literature focuses on coupling electrochemical thermal models with exothermic reactions. This study demonstrates a method to couple the electrochemical and thermal runaway models for a commercial cylindrical Lithium-ion cell. The proposed model averages pseudo-2D electrochemical heat and couples it to a two-dimensional, axisymmetric heat transfer model of 18650-type Lithium-ion cell. The jellyroll structure is approximated as a homogeneous and anisotropic domain for electrochemical and exothermic heating. Simulations are performed through several, uninterrupted charge-discharge cycles at different ambient temperatures and C-rates. We show that while cycling rate is critical in instigating and accelerating TR, parameters like ambient temperature, particle radii and initial electrolyte concentration also play a role in determining the core temperature and its rate of growth in the cell.