X-ray photoelectron spectroscopy (XPS) was collected with PHI VersaProbe 3 XPS with an Al K-alpha source (1486 eV). The LLZO sample was transferred from the Ar-filled glovebox to the XPS in a vacuum transfer vessel to prevent air exposure. The depth profiles were collected using Ar + sputtering (1 kV, 0.7 μA, 2 x 2 mm). Both electron and ion neutralization sources were used in data collection. In the energy calibration process, we used the initial scan's metallic state of Ag 3d5/2 at 368.3 eV as the reference point for calibrating all the peaks of Ag 3d, Zr 3d, and La 3d.