Coupled thermal runaway and combustion modeling for NMC811 Li-ion batteries safety: development and validation

Industrial lithium-ion battery deployment poses significant process safety risks due to thermal runaway events causing catastrophic fires and toxic gas releases. Accurate combustion modeling is essential for quantitative risk assessment and safety system design. This work presents a validated framework for process safety engineering applications. Accelerating rate calorimetry experiments were conducted on cylindrical cells of 18,650 format and NMC811 chemistry under inert and reactive atmospheres, capturing temperature profiles, pressure evolution, and gas compositions. Significant differences in vented gas mixtures were observed, with CO2, CO, and H₂ as dominant species. These results evaluated five combustion mechanisms: one for battery gas combustion, GRI-Mech 3.0, ANSYS Model Fuel Library and two-step global models. Homogeneous reactors and laminar flame speed simulations were used for evaluation. Detailed mechanisms produced consistent ignition delay and flame propagation results, while simplified models showed deviations. A mechanism reduction is presented, downscaling to 128 species and 794 reactions (80 % reduction) without compromising accuracy. This reduced mechanism was integrated into a 2D axisymmetric CFD model incorporating TR, gas venting, and combustion processes. The model accurately reproduced temperature rise, pressure development, and venting dynamics. The work provides a validated reduced kinetic mechanism for battery gas combustion that can be used to enhance safety of battery module during design processes.