Uncovering Ionic Transport Paths within Hierarchically Structured Battery Electrodes

Calendering battery electrodes improves electronic transport and energy density while increasing the ionic resistance in the pore space. In hierarchically structured electrodes, the open porosity of the active material particles offers additional ionic transport paths. However, there is a lack of knowledge about the interaction between these pores and the porosity surrounding the particles. Considering both inter- and intragranular pore space, we combine a Doyle–Fuller–Newman cell model with experimental discharge curves to show that ionic transport paths in hierarchically structured electrodes change with compaction and the discharge rate. If the intergranular porosity is high, it carries most of the ionic current from the separator to the current collector. The intragranular porosity ensures ionic transport into the porous particles. High compaction of a hierarchically structured electrode leads to an increasing contribution of the intragranular pores to ionic transport across the electrode with a rising discharge rate. This study offers a modeling approach to explore the optimum calendering process for different types of hierarchically structured electrode materials.