Discrete modeling of the calendering process for positive electrodes of Li-ion batteries

The electronic properties of Li-ion batteries crucially depend on the microstructure of their electrodes. One step of the manufacturing process, called 'calendering', consists in compressing the electrodes between two counterrotating cylinders to increase their density. Through a new simulation model, we investigate the effect of calendering on microstructural and electronic properties of the electrodes. Our model takes into account the real geometry of the rotating cylinder and a new contact law involving the elastic behavior of the active material and the cohesive-plastic behavior of the binder layer. Our results align well with experimental data for porosity, final thickness, and elongation. We show that the bonding structure induced by calendering involves mostly vertical tensile contacts and horizontal compressive contacts. This unexpected observation highlights the importance of shear deformation induced by rolling and thickness reduction. Using the FFT method, we also investigate the ionic and electronic conductivities of the numerically calendered electrodes.