Solid-state cathode heterogeneity impact on utilization and fracture dynamics

Structural heterogeneity in solid-state batteries can impact material utilization and fracture mechanisms. Dense crystallographically oriented lithium cobalt oxide cathodes serve as a model electrode system for exploring how density variability contributes to stress relief and build up during cycling. Real- and reciprocal-space operando and ex-situ synchrotron based experiments are utilized to understand structural changes across multiple length scales contribute to stress generation and fracture. Nanotomography uncovers a depth-dependent porosity variation in the pristine electrode and highlights preferential fracture in regions of lower porosity during delithiation. Energy-dispersive X-ray diffraction and 3D X-ray absorption near-edge spectroscopy (XANES) reveal the underutilization of cathode material in these regions. 3D XANES also confirms preferential delithiation near the subgrain boundaries. Chemo-mechanical modeling coupled with site-specific mechanical characterization demonstrate how stress accumulation in dense regions of the electrode leads to fracture and underutilization of active material. Our findings reveal the importance of materials design to alleviate stress in small-volume changing cathodes.