State-of-Charge-Resolved Correlation of Interfacial Impedance and Apparent Lithium Transport in All-Solid-State Batteries

Abstract All-solid-state batteries incorporating layered oxide cathodes suffer from complex interfacial degradation and transport limitations that are poorly captured by conventional electrochemical diagnostics. In particular, the relationship between apparent lithium transport and resistance growth in composite solid-state cathodes remains poorly defined, complicating mechanistic interpretation. Here, we present a correlative electrochemical framework that combines the galvanostatic intermittent titration technique with state-of-charge (SOC)-resolved in situ electrochemical impedance spectroscopy and distribution of relaxation times analysis to examine interfacial and transport phenomena in composite cathodes. By varying the Ni content in the layered oxide cathode and the conductive additive chemistry, this approach enables the separation of cycle-dependent interfacial degradation from SOC-dependent kinetic constraints that emerge during operation. The framework clarifies how transport-related parameters derived from transient electrochemical measurements are influenced by evolving interfacial accessibility rather than by intrinsic bulk diffusion alone, particularly at low SOCs. More broadly, this study highlights the importance of SOC-resolved, correlative diagnostics for physically meaningful interpretation of transport behavior in all-solid-state batteries and provides general insights into the role of interfacial design in mitigating performance decay.