Tracing Lithophilic Sites: <i>In Situ</i> Nanovisualization of Their Migration and Degradation in All-Solid-State Lithium Batteries

The location of lithium (Li) deposition sites and the subsequent dynamic evolution at the solid-state electrolyte (SSE)-Li anode interface critically influence the performance of all-solid-state batteries. Nevertheless, the nanoscale mechanisms governing these processes remain poorly understood, primarily due to the challenges involved in real-time nanoscale observation of buried interfaces. Here, we employ <i>in situ</i> electrochemical atomic force microscopy to directly visualize the interfacial evolution mediated by lithiophilic layers, revealing two distinct degradation pathways associated with on-site formed solid electrolyte interphase (SEI). <i>In situ</i> images show that the Au layer forms Li-Au intermetallic alloy during plating, guiding spherical Li deposition atop it and minimizing Li-SSE contact. This slows SSE decomposition, resulting in an inert, Li₂S/Li₂O-rich SEI that induces Li redeposition onto SEI-free regions during subsequent cycles; The Ag layer forms Li-Ag solid solution that maintains direct contact with SSE during plating, which promotes SSE decomposition and leads to the formation of lithiophilic, Ag₂S-dominated SEI. Interfacial pore formation during stripping causes Li redeposition to be preferentially localized within SEI-rich, pore-free regions. Both lithiophilic evolution pathways cause progressive SEI accumulation and loss of interfacial lithiophilicity during cycling. Inserting an Au interlayer between Ag and SSE can mitigate SSE decomposition, prevent lithiophilic sites migration, thus improving cycling performance. This study reveals the fundamental interfacial degradation mechanisms and offers design strategies for stable Li metal anodes in solid-state batteries.