Li Plating/Stripping Efficiency in Ether-based Dilute Electrolyte for Anode-free Lithium-metal Batteries: Effect of Operating Potential Range on Subsequent SEI Layer Structure

Anode-free lithium-metal batteries (AFLMBs) are regarded as a promising candidate for next-generation batteries due to a great enhancement of energy density over lithium-metal anode batteries. However, unstable solid-electrolyte interface (SEI) formation accompanied by lithium dendrite growth and electrolyte decomposition causes low Coulombic efficiencies. This study explores the effect of different operating potential ranges on SEI layer structure and further on Li plating/stripping efficiency in the dilute LiTFSI/TEGDME electrolyte in an AFLMB anode half-cell configuration. Cyclic voltammetry analyses reveal the existence of an "oxidative subsequent SEI" formation process (named as OSS) and the improved Li plating/stripping efficiency by blocking reaction OSS, which is further verified by quartz crystal microbalance analysis regarding the insight of such an improvement. XPS depth-profile analysis confirms the formation of the Li2O- and lithium-sulfur compounds-based subsequent SEI layers when the OSS process is blocked, which guarantees the improved stability of Li plating/stripping. A hypothesis is proposed to discuss possible electrochemical reactions via OSS process by combining in situ surface-enhanced Raman spectroscopy analysis. These results together suggested the importance of adjusting operating potential range in a proper manner to achieve a better performance in Li plating/stripping in AFLMB configuration. SEI layer structure: Except native-SEI and pre-SEI during the first cycle, the formation of Li2O- and lithium-sulfur compounds-based subsequent-SEI in the first and subsequent cycles improves Li plating/stripping stability, while the OSS (oxidative subsequent SEI) formation process oxidizes these components to form an unstable subsequent-SEI.image