Pore-scale prediction of transport properties in lithium-ion battery cathodes during calendering using DEM and CFD simulations

Calendering is a crucial step in the production of lithium-ion batteries (LIBs), due to its significant effect on key parameters of porous electrode structure and resultant performance. This study investigates the influence of calendering degree (compression) on porosity, tortuosity and permeability for different particle configurations. With this motivation, the mechanical behaviour of electrode structures was conducted with Discrete Element Method (DEM), and the electrolyte flow as a continuous phase was described using pore-scale computational fluid dynamics (CFD) simulations. Three different electrode microstructures were generated comprising mono- disperse and polydisperse spherical particles, as well as mono-disperse ellipsoidal particles. The predicted pore-scale properties are used in validated electrochemical-thermal models to correlate calendering process to the overall LIB performance. The results revealed that using the ellipsoidal particles, an anisotropy in tortuosity and permeability appeared with the beginning of the compression process. As the compression degree increased to 30%, the level of anisotropy decreased, and as a consequence, the discrepancy of diagonal components of tortuosity and permeability decreased. The electrochemical-thermal models show that it is best to keep the calendering rate around 20% with smaller particle sizes (for both spherical and ellipsoidal cases).