Li Penetration in Ceramic Solid Electrolytes: Operando Microscopy Analysis of Morphology, Propagation, and Reversibility

Solid-state electrolytes (SSEs) have attracted substantial attention for next-generation Li-metal batteries, but Li-filament propagation at high current densities remains a significant challenge. This study probes the coupled electrochemical-morphological-mechanical evolution of Li-metal-Li7La3Zr2O12 interfaces. Quantitative analysis of synchronized electrochemistry with operando video microscopy reveals new insights into the nature of Li propagation in SSEs. Several different filament morphologies are identified, demonstrating that a singular mechanism is insufficient to describe the complexity of Li propagation pathways. The dynamic evolution of the structures is characterized, which demonstrates the relationships between current density and propagation velocity, as well as reversibility of plated Li before short-circuit occurs. Under deep discharge, void formation and dewetting are directly observed, which are directly related to evolving overpotentials during stripping. Finally, similar Li penetration behavior is observed in glassy Li3PS4, demonstrating the relevance of the new insights to SSEs more generally. [Display omitted] •Multiple morphologies of Li penetration are possible in ceramic solid electrolytes•The Li within these structures can be reversibly cycled•The most common Li filaments propagate by a mechanical crack-opening mechanism•The dynamic evolution of filament morphology can be correlated to voltage signatures A key challenge for commercialization of solid-state batteries with Li-metal anodes is the propagation of Li filaments at high current densities. This work utilizes operando video microscopy to study the dynamic evolution of Li penetration within ceramic solid electrolytes. Four morphology types are identified and studied under a range of battery-relevant conditions. Morphology evolution is linked to electrochemical signatures by synchronizing video microscopy with the voltage response of the cells, providing an avenue for on-board diagnostics. A key observation is the reversible plating and stripping of Li filaments before short-circuiting occurs, indicating that if Li propagation is identified through voltage analysis, catastrophic failure modes could be avoided. These findings represent an important step toward understanding and overcoming the challenge of Li penetration and enabling high-rate-capability Li-metal solid-state batteries for applications such as electric vehicles. The dynamic evolution of Li penetration within cer