The Active Interface of Ta-Doped Li₇La₃Zr₂O₁₂ for Li Plating/Stripping Revealed by Acid Aqueous Etching

All-solid-state lithium batteries incorporating oxide-based solid electrolytes have attracted much attention as a promising battery system for enabling highly reversible Li metal anodes. However, the cycling stability of Li plating/stripping reactions at higher charging/discharging rates on garnet-type solid-state electrolytes must be improved to realize a practical Li metal anode for solid-state batteries. Here, we report that a short acid etching procedure performed in ambient air significantly activates the Ta-doped Li7La3Zr2O12 (LLZT) surface compared to polishing under inert gas atmosphere such as dry Ar. It has been believed that Li7La3Zr2O12 (LLZ) and related doped LLZ solid electrolyte surfaces need to be mechanically polished in dry Ar before the cell fabrication to remove Li2CO3 and LiOH that are present on the surface. However, a commonly used mechanical polishing procedure is found to form a thin electrochemically inactive layer on the LLZT surface, whereas a short acid etching procedure (e.g., HCl) removes the inactive layer, and the acid-etched LLZT exhibits excellent cycling stability.