There is a continuous need to increase the energy density of battery cells. The most efficient way is the application of high energy materials. This requires an accurate assessment and a holistic understanding of the underlying electro- and thermochemical processes during a potential thermal event of the battery cell to remain today’s battery pack safety level. Nowadays, the safety of battery cells is experimentally investigated, which is confined by the available setups and measurable metrics. At the same time the capabilities of complicated simulation-based assessments are improving, which allow a more detailed look into the battery cell and a quantitative evaluation of physical phenomena. This holds especially true for the challenging physical behavior during a thermal event. Compared to elaborate testing, which cause high costs and waste production, simulation allows an eco-friendly approach with a high flexibility in the investigated setups and a deeper look into the system.

In this work, a three-dimensional numerical model is developed to investigate and describe internal processes in the battery cell during a thermal event. The model is focused on describing the thermochemical degradation and the resulting porous gas flow in a pouch cell. The chemical conversion rate was modelled by Arrhenius equations using power-law kinetics. The fluid flow is governed by Navier-Stokes equations using a k-ϵ turbulence closure. Computational requirements were minimized by using a reduced multi-step reaction mechanism which was developed for a battery cell at 100% state-of-charge and NMC 622/graphite electrodes. First, initial kinetic parameters were identified based on literature values. Then these parameters were optimized with a pseudo 0D approach, including heat conduction and dissipation, and experimental data of an accelerated rate calorimetry. The model was extended to a three-dimensional model of a nail penetration. Here, equations of state for the gas inside the jellyroll were used to allow a pressure evolution resulting in a porous flow in the electrodes. This is the first time a detailed reaction mechanism paired with a fluid flow inside the porous structure of a battery cell was used to simulate a thermal event.