Pyrolysis-based modelling of 18650-type lithium-ion battery fires in thermal runaway with LCO, LFP and NMC cathodes

Abstract

This study presents a modelling approach for simulating fires in thermal runaway and here, it is applied to 18650-type batteries with LCO, NMC, and LFP cathodes at 100% SOC. The model assumes a single-step pyrolysis, where a solid lumped substance, representing the battery components, degrades into volatiles which are vent gases here. Coupling an in-house MATLAB code and FDS solver, a parameter estimation using Bayesian optimization was performed to fit the simulated mass loss and heat release rate to the experimental measurements. One-step kinetics are used for vent gas combustion, with CO yield obtained from literature and soot yield determined via 1-D diffusion flame simulations with CRECK kinetic mechanism in Cantera solver. 3-D simulations using the obtained models yielded maximum values of flame temperature, CO2 and H2O mole fractions, velocity, radiative heat flux, and flame height as 2520 K, 0.47, 0.15, 10.08 m/s, 13.29 kW/m2, and 0.62 m, respectively. The novelties associated with this approach are that, unlike the past studies, there is no need to model the thermal runaway process prior to flaming and, the resulting heat release rate is experimentally verified which makes further analyses, such as flame temperature, height and heat emissions possible.