Elucidating the effect of electrode calendering on electrochemical performance by using 3D image-based modelling

Abstract

Calendering is the last step in manufacturing of electrodes to achieve optimal performance due to its effects on electrode microstructure. However, the microstructural evolution during the compression process over a relatively large range of calendering degrees (up to 45 %) and the effects on properties are less understood. Herein, we develop a 3D image-based and physics-resolved finite element model using X-ray computed tomography and scanning electron microscope images of real pristine lithium nickel manganese cobalt oxide (NMC) cathodes to predict the evolution of electrode microstructure and mechanical behaviour during calendering, and the resulting porosity, pore tortuosity, and electrochemical performance relating to the varied calendering degrees. Our mechanical model illustrates the movement and deformation of active material particles to represent the microstructure changes more realistically. The results show lithium ion diffusion inside the pore phase starts to limit the overall ion diffusion at higher C rates (>2C) and state of lithiation (SOL). We also show the optimal calendering degree and porosity and carbon binder domain (CBD) volumes that achieved both high gravimetric and volumetric capacities for NMC cathodes at increasing (dis)charging C rates up to 5C, and their effects when electrode thickness is doubled.