The cycle life of lithium-ion batteries is influenced by a variety of degradation processes which depend on the composition, structural design and operating conditions of the respective battery cell. One of these degradation processes is the growth of the Solid Electrolyte Interphase (SEI), a thin passivating layer which forms on top of the anode active particles, significantly contributing to capacity fade in the battery. In order to improve cycle life as well as sustainability of lithium-ion batteries, it is crucial to minimize SEI growth.

However, experimental investigations of this degradation mechanism are limited, due to in-operando measurements being only available for specific cell setups and post-mortem analysis being susceptible to distorted results caused by contamination of the sample upon opening the cell.
To compensate for these limitations and gain a deeper insight into the degradation process, experiments can be supplemented by numerical simulations utilizing a combination of detailed physical models and efficient numerical solution strategies. 

In our work, we consider a thermodynamic consistent continuum-scale model spatially resolving the active particle structures of anode and cathode to describe the electrochemical behaviour of the battery cell. Additionally, the model includes the carbon-binder-domain, accounting for the conductivity of the carbon additive as well as the electrolyte transport limitations resulting from the porosity of the binder. The cell model is coupled with an SEI degradation model which simulates the local SEI thickness, such that inhomogenous SEI growth across the graphite anode microstructure can be captured by the simulations. Due to numerical instabilities encountered with a full-implicit approach, we deploy a semi-implicit solver separating the degradation from the electrochemical system of the basic cell model, which is implemented in our Battery and Electrochemistry Simulation Tool (BEST).

The resulting solver enables 3D full cell simulations of the spatially resolved electrode microstructures, allowing to investigate SEI degradation during cycling and storage of the battery. Utilizing these simulations, different cell setups can be compared and evaluated in terms of the observed SEI growth.