Visualizing Electron Transport and Interface Evolution of Li₃InCl₆-Based Composite Cathode for All-Solid-State Batteries

All-solid-state batteries (ASSBs) promise higher energy density and improved safety, but stable solid electrolyte-electrode interfaces remain a key challenge. Mixed ionic-electronic conducting interphases cause degradation, limiting the cathode lifetime. Here, we employ operando electrochemical atomic force microscopy based on modified Kelvin probe force microscopy to visualize nanoscale electron transport and dynamic evolution of the composite cathode interface. By analyzing the contact current (Ic) distribution, we distinguish the interfacial stability of Li3InCl6 (LIC)-based cathodes with LiNi0.8Mn0.1Co0.1O2, both coated and uncoated with LiNbO3, and conductive carbon additives. Operando studies, combined with interfacial mechanical property mapping, reveal that the Ic heterogeneity and magnitude critically influence degradation. In LIC-based cathodes, decomposed organic interphases enhance electron transport, driving the formation of high-modulus inorganic species that accelerate LIC breakdown. These findings link microscopic electron transport and interface evolution to electrochemical performance, offering insights for designing stable interphases to advance ASSB technology.