Solid-state batteries (SSBs) are a promising choice for next-generation energy storage systems due to their high intrinsic energy and power densities, while simultaneously enhancing safety. The electrochemical performance of SSBs is a strong function of the physicochemical interactions occurring inside composite cathode microstructure. The composition and spatial arrangement of constituent phases (e.g., active material, binder, conductive diluent, solid electrolyte) dictate the ionic/electronic percolation pathways and internal resistive signatures. Moreover, the underlying heterogeneity in cathode microstructure can result in non-uniform kinetic and transport processes leading to current focusing and thermal hot spots. Thus, understanding the influence of cathode microstructural heterogeneity on spatiotemporal dynamics of SSBs becomes important. In this work, the mesoscale underpinnings of microstructural heterogeneity in composite cathode and its mechanistic implications on the electrochemical response of SSBs will be examined.