Modeling 3D Microstructure and Ion Transport in Porous Li-Ion Battery Electrodes

Abstract

This work combines experiments and computer models in order to understand the relationships between electrode microstructure and ionic transport resistances so that one may predict cell performance from fundamental principles. A scanning electron microscope (SEM) with focused ion beam (FIB) was used to image sections of commercially made porous electrodes utilizing LiCoO2 active material. The images reveal the existence of discrete porous carbon domains in the microstructure. Further experiments indicated that these carbon domains are highly tortuous and restrict to a large degree the overall ion transport in the cathode. Two types of 3D models for correlating and predicting the electrode microstructure were explored. The first, known as the dynamic particle packing (DPP) model, is based on aggregates of spheres that move collectively in response to interparticle forces. The second is a stochastic grid (SG) model closely related to Monte Carlo techniques used in statistical physics to study cooperative and competitive phase behavior. The models use a small set of fundamental interdomain and bulk interaction parameters to generate structures from a given electrode mass composition and porosity. Both models were able to semi-quantitatively reproduce experimental tortuosity measurements of cathodes at different porosity values.