We employ a thin film as the metallic silver source to dope the surface of LLZO. To generate a clean and well-defined interface between metallic Ag and LLZO, we cleaved dense LLZO (> 99% of theoretical density) and employed an air-free transfer workflow (Figure ), rather than the conventional polishing approach. First, LLZO was cleaved in an Ar-filled glovebox (H2O < 0.5ppm, O2 < 0.5 ppm). Then, without air exposure, 1 to 50 nm-thick metallic silver coating was sputtered on the LLZO surface at room temperature (RT) and subsequently annealed between 100 and 400 ºC for 1 h (Figure and Figure ). Cryogenic electron microscopy (Cryo-EM) images validate the pristine interface between metallic Ag and the cleaved LLZO. In contrast, the conventional polishing approach leads to a 10-50 nm-thick contamination layer (Figure ).