Electrochemical Modeling of Hierarchically Structured Lithium‐Ion Battery Electrodes

Abstract

Hierarchically structured active materials in lithium‐ion battery (LIB) electrodes with porous secondary particles are promising candidates to increase the gravimetric energy density and rate performance of the cell. However, there are still aspects to this technology which are not fully understood. Herein, a mathematical model for half cells with hierarchically structured electrodes aiming at delivering a better insight and obtaining a deeper knowledge to this matter is presented. First, the classical half‐cell model originating back to Newman and coworkers is revisited and the basic assumptions for the electrochemically based equations are presented. As a next step, the mathematical framework of the volume averaging method is used to consistently extend the classical to the hierarchically structured half‐cell model. For both models, the full set of boundary conditions for the half‐cell setup is presented. Finally, the hierarchically structured half‐cell model is validated by experiments taken from literature and parametric studies are conducted. The results suggest that, while the rate‐limiting factor for the classical half‐cells is the diffusion coefficient of the active material, in case of the hierarchically structured half‐cells, it is the combination of electronic conductivity and inner morphology of the secondary particles.