Modeling Effective Ionic Conductivity and Binder Influence in Composite Cathodes for All-Solid-State Batteries

In the pursuit for future mobility, solid-state batteries open a wide field of promising battery concepts with a variety of advantages, ranging from energy density to power capability. However, trade-offs need to be addressed, especially for large-scale, cost-effective processing, which implies the use of a polymeric binder in the composite electrodes. Here, we investigate three-dimensional microstructure models of the active material, solid electrolyte, and binder to link cathode design and binder content with electrode performance. Focusing on lithium-ion transport, we evaluate the effective ionic conductivity and tortuosity in a flux-based simulation. Therein, we address the influence of electrode composition and active material particle size as well as the process-controlled design parameters of the void space and binder content. Even though added in small amounts, the latter has a strong negative influence on the ion transport paths and the active surface area. The simulation of ion transport within four-phase composites is supplemented by an estimation of the limiting current densities, illustrating that application-driven cell design starts at the microstructure level.