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.