How operando analysis enables quantitative understanding of dense lithium metal deposition

Abstract

Achieving dense and uniform lithium (Li) deposition is essential for the practical use of Li metal anodes, yet dendritic growth and unstable interfaces remain major challenges. In this study, we introduce a simple and scalable surface modification strategy that simultaneously functionalizes the surface and bulk of Li metal anodes via conversion reactions with ceramic nanoparticles (SiO2 or Si3N4). Upon thermal treatment, these nanoparticles react with Li to form composite interphases composed of a Li-Si alloy beneath ion-conductive Li2O or Li3N-rich surface layers. To directly observe the impact of these engineered interphases, we employed operando optical microscopy, which enabled real-time visualization of Li plating morphology and volume evolution. The surfacemodified electrodes exhibited highly uniform and dense Li deposition with minimal volume fluctuation, in contrast to bare Li. Electrochemical testing further confirmed enhanced cycling stability and reduced overpotential in both symmetric and full-cell configurations. Kinetic analysis via Tafel and Arrhenius plots revealed improved charge-transfer behavior and reduced activation energy for functionalized interfaces. This work demonstrates that interfacial design through phase-guided conversion reactions, combined with operando visualization, offers a viable route toward high-performance Li metal anodes for next-generation rechargeable batteries.